ARMY MEDICAL LIBRARY

        WASHINGTON

           Founded 1836
 JNNEX
Section.
Number
1.3A.^M
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 (Revised Juno 13, 1936) 
 
« 
ELEMENTS


             OP
     CHEMISTRY,




                         INCLUDING THE

  MOST RECENT DISCOVERIES AND APPLICATIONS OF THE SCIENCE TO
           MEDICINE AND ITIARMAC Y, AND TO THE ARTS.




          BY  ROBERT KANE, M.D., M.R.I.A.,

      PROFESSOR OF NATURAL PHILOSOPHY TO THE ROYAL DUBLIN SOCIETY J
PROFESSOR OF CHEMISTRY TO THE APOTHECARIES' HALL OF IRELAND ; MEMBER OF THB
     SOCIETY OF PHARMACY OF PARIS, AND OF THE GERMAN PHARMACEUTICAL
                       SOCIETY, ETC., ETC., ETC.



               AN  AMERICAN EDITION,

 WITH  ADDITIONS  AND CORRECTIONS, AND ARRANGED FOR THE USE OF

       THE UNIVERSITIES, COLLEGES, ACADEMIES, AND  MEDICAL

                 SCHOOLS OF THE UNITED  STATES,



           BY JOHN WILLIAM  DRAPER, M.D

     PROFESSOR OF CHEMISTRY IN THE UNIVERSITY OF NEW-YORK, FORMERL7
  PROFESSOR OF PHYSICAL SCIENCE AND PHYSIOLOGY IN HAMPDEN  SIDNEY COLLEGE,
    VIRGINIA; MEMBER OF THE LYCEUM OF NATURAL HISTORY OF NEW-YORK,
                           &C, &C, &C.
                  NEW-YORK:

Published  by Harper &  Brothers,
              No. 8-2 Cliff-Street.
184 8 
■50
Entered, according to Act of Congress, in the year 1842, by
               Harper & Brothers,
Bn the Clerk's Office of the Southern District of New-York. 
PREFACE  TO THE AMERICAN  EDITION.
  In preparing the work of Dr. Kane for the use of Amer-
ican students, I have preserved the original entire, and have
only made those alterations in it which the system of instruc-
tion pursued  in the United States seems to require.
  This work, which, as a text-book, is undoubtedly the best
extant in the English language, representing the present con-
dition of chemical science, necessarily contains much detail.
To  give it completeness, it was  needful  to include the de-
scription of many bodies of little  technical importance, to
describe experimental processes, and sometimes to dwell on
facts of minor value.
  The period of instruction in the  schools of this country is
short, so that many  standard books  are  unavailable from
their extent.   From an experience of several years in public
teaching, I have perceived the importance of separating, for
the student,  the leading principles from  the accompanying
detail.   This will, perhaps, to a certain  extent, be accom«
plished by the mechanical contrivance of printing such works
with different types, the important matter being in the larger
letters.
  The magnitude  of the original prevented  me from making
additions to any great extent; what has been introduced in
this way will be readily distinguished, from being inserted
between brackets.
  From  its having been repeatedly and carefully  read, and
the  errors and misprints revised, this will probably  be found
more correct  than  the foreign edition.
                               John William Draper.
  University of New-York, June 1st, 1842. 
 
PREFACE.
  My object in the following pages is to present to the stu-
dent an account of the general principles and facts of Chem-
istry, and of its applications to Pharmacy, to Medicine, and
to the Useful Arts.
  In the arrangement of a work like the present, if the gen-
eral principles of the science are first described, it is impos-
sible to avoid the difficulty of introducing the names of many
substances with whose history the reader cannot be supposed
conversant; and by entering, in the  commencement, on the
description of individual substances,  reference to the princi-
ples of affinity and the laws of constitution is continually ne-
cessary, in  order  that the reactions  of these bodies may be
understood.  In both cases the student is liable to some em-
barrassment, but I believe it to be greater in the latter, and
hence  I have  adopted the plan of fully describing  all the
general principles and laws of chemical action, before enter-
ing on the  description of the chemical substances in detail.
  Chemistry being itself but a department of Natural Philos-
ophy, although the most extensive in  its objects and the most
important in its uses, it is connected so intimately with the
other branches of Physics, that a knowledge of at least their
general principles is necessary  for the proper understanding
of the  nature of chemical phenomena.  I have consequent-
ly embraced within the design of the  present work a de-
scription of the physical properties of bodies,  so far  as they
serve to complete their chemical  history, or influence their
chemical relations ;  and thus, upon the one hand, supply
characters by which chemical substances may be recognised,
and, upon the other,  modify the affinities by which  the ac-
tion  of chemical substances upon each other is determined.
With this twofold  object,  the chapters on Cohesion, Light,
Heat, and Electricity have been drawn up.
  The portion of the work which  treats of the general laws
of chemical combination, is followed by an account of the
mode of preparation and properties of all inorganic substan-
ces of interest to Science,  to Medicine, or to the Arts.   But
in this part I will pass  over very  briefly the history of nu-
merous bodies which, from  their rarity, are objects only of 
VI
PREFACE.
scientific curiosity, referring those who would wish to study
their history more closely to the extended works of Thomp-
son, of Graham, of Dumas, or of Berzelius.
  In the department of Organic Chemistry my object will be
fully to  discuss the history of all such bodies as are of im-
portance, from  their bearing upon general principles or ex-
isting theories, from their use in medicine or pharmacy, their
employment in the arts or in ordinary life.  The  numerous
series of bodies which  are every day discovered in Organic
Chemistry, but which do not come under  any of  the above
heads, shall be dismissed with  only a notice of their exist-
ence.
  The relations of chemical action to the functions of organ-
ized matter, the applications of Chemistry to Physiology and
to Pathology, will be treated of so far as our accurate  knowl-
edge extends ; and, finally, a succinct description of the mode
of analysis of organic and inorganic bodies will be given.
  As  this work is not intended  to be a complete  system of
Chemistry, nor to satisfy the wants of those who wish to make
Chemistry  their special  study,  I  have in  almost all cases
avoided  references or quotations, which would needlessly
occupy much space ; for, in the larger works already men-
tioned, the original authorities on all  subjects will be found.
  The object  of  a work like the present being to represent
faithfully the general aspect and extent of science at the time
of publication, its details must be in great part founded on
the results  of others.   Hence originality cannot in any great
degree be  either  expected or desired ; but I have not hesi-
tated, in many instances, where  the best consideration  I
could give the subject induced me  to dissent from  views
generally hold, to make  this work the vehicle, in  a popular
form, of such suggestions as I thought deserved to be adopted.
  The processes  given for the preparation  of the various
substances described are,  with  very few exceptions, those
followed either in my private laboratory or in  the manufac-
turing laboratory of the Apothecaries' Hall of Ireland ; and
the  apparatus  figured in the woodcuts are  generally  similar
to those which I employ in  experiments of research or at
lecture. 
CONTENTS.
         INTRODUCTION.
Origin and Objects of Chemistry   .    9

            CHAPTER  I.
OF GRAVITY  AND  COHESIVE FORCES,  AS
  CHARACTERIZING  CHEMICAL   SUBSTAN-
  CES.
Specific Gravities of Bodies	. 11
Constitution of Matter	. 17
Capillarity and Elasticity	. 19
Phenomena of Solution .	. 22
Crystallization	. 23
Systems of Crystallization	. 26
            CHAPTER II.
OF THE PROPERTIES OP  LIGHT AS CHAR-
   ACTERIZING CHEMICAL SUBSTANCES.
Reflection and Refraction of Light .   32
Double Refraction  .     .     .    .34
Polarization of Light     .     .    .38
Circular Polarization    .     .    .41
Wave Theory of Light  .     .    .42

            CHAPTER III.
OP HEAT  CONSIDERED AS CHARACTERIZING
         CHEMICAL SUBSTANCES.
Section  I.
  Of Expansion    .     .     ,    .46
  Nature of Temperature     .    .   49
  Thermometers   .     .     .    .50
  Pyrometers     .     .     .    .54
  Expansion of Air and Gases    .   56
  -----------Liquids  .     .    .58
  -----------Solids   ...   60
Section II.
  Specific Heat     .     .     .    .63
  Connexion of Specific Heat and
    the Chemical  Constitution    .   66
  Specific Heats of Gases     .    .   69
Section III.
  Of Liquefaction   .     .     .    .70
  Latent  Heat of Liquids     .    .   71
  Freezing Mixtures     .     .    .73
Section IV.
  Of Vaporization   .     .     .    .75
  Latent  Heat of Vapours    .    .   76
  Elasticities of Vapours     .    .   78
  Nature of the Boiling Point      .   83
  Spontaneous Evaporation  .    .   87
  Of Steam as a Moving Power   .   89
Section V.
  Of the Transmission of Heat through
    Bodies.....91
  Conduction of Heat   .    .    .92
                                  *«5«
   Radiation of Heat    .     .    .94
   Absorption and Reflection of Heat  96
   Researches of Melloni and Forbes  98
   Polarization of Heat  .     .    . .'01
   Relations of Heat to Light  .    . 102
 Section VI.
   Of the Cooling of Bodies    .    .103
   Theory of Dew and Frost  .    . 104
   Central Heat of the Earth  .    .105
            CHAPTER IV.
 OF ELECTRICITY CONSIDERED AS CHA-
   RACTERIZING CHEMICAL  SUBSTAN-
   CES    ......106
 Section I.
   Of Statical Electricity .     .    . 107
   Distribution of Electricity  .    .110
   Electrical Attractions and Repul-
     sions     .....112
   Theories of Electricity     .    .114
   Electrical Induction   .     .    .118
   Theory of the Leyden Jar  .    . 120
,,  Nature of Induction   .     .    . 122
   Atmospheric Electricity    .    . 125
 Section II.
   Of Dynnmical Electricity    .    . 126
   Simple Galvanic Circles    .    . 128
   Of Electrotype  Copying     .    . 130
   Theory of the Galvanic Battery . 131
   Volta's Theory of Contact  .    . 133
   Construction of Galvanic Batteries 134
   Constant Batteries    .     .    . 136
   Thermo-electric Currents  .    . 139
   Magnetism .    .    .   *•.    .  143
   Electro-magnetic Phenomena   . 145
   Of the Galvanometer .     .    . 147

            CHAPTER V.
     OF  CHEMICAL NOMENCLATURE . 149
 Names of the Simple Bodies  .    . 150
 ----------Primary Compounds .  152
 ----------Secondary Compounds 154
 Symbolical Nomenclature    .    .  156

           CHAPTER VI.
 OP CHEMICAL  AFFINITY, AND  ITS  RELA-
  TIONS TO HEAT, TO LIGHT, AND TO CO-
  HESION.
 Elective Decomposition .    .    .  157
 Order of Affinity not Constant     .'  159
 Relation of Affinity to Cohesion   .163
 Influence of Elasticity on Affinity  .  168
 Influence of Light on Affinity .    .172
Influence of the  Chemical Rays of
  L'ght......173 
vm
CONTENTS.
                                  Pago
Photography   and  Daguerreotype
  Drawing.....175

           CHAPTER VII.
OF THE HEAT AND LIGHT DISENGAGED
  DURING  CHEMICAL COMBINATION  .  178
Products of Slow Combustion     .  179
Constitution of Flame   .    .     .  181
Of the Safety Lamp    .    .     .183
Theories of Combustion .    .     .  185

           CHAPTER VIII.
OF THE INFLUENCE OF ELECTRICITY
      ON CHEMICAL AFFINITY .     .  187
Electro-chemical Classification     .  189
Electro-chemical Theories    .     .  190
Electrolysis and  Electrolytes .     .  194
Origin of the Galvanic Current     .  197
Synthetic Action of Electricity     .  199
Relations of Electricity to Affinity .  201

           CHAPTER IX.
  OF THE  LAWS  OF COMBINATION  .  202
Scales of Chemical Equivalents    .  205
Law of Multiple Proportions  .     .  207
Definiteness of Composition  .     .210
Theory of Volumes     .     .     .  213

           CHAPTER X.
OF THE RELATIONS OF  CHEMICAL CONSTI-
  TUTION TO THE MOLECULAR STRUCTURE
  OF BODIES.
Section I.
  Of the Atomic Theory .    .     .217
  Physical and Chemical Atoms   .  218
Section II.
  Of Isomorphism.  .    .    .     .221
  Isomorphous Groups  .    .     .  223
  Relation of Form to Constitution  226
Section III.
  Of Dimorphism and Isomerism,, and
    of the  Theory of Types    .     .  227
  Approximate Dimorphism  .     .  230
  Principle of Isomerism     .     .  231
  ---------Compound Radicals .  233
  Theory of Organic Types  .     .  234
Section IV.
  Of Catalysis     ....  235
  Communication of Motion .     .  237

           CHAPTER XI.
OF THE CLASSIFICATION OF  THE  EL-
        EMENTARY BODIES   .     .  238

           CHAPTER XII.
OF  THE SIMPLE  NON-METALLIC  BODIES,
  AND OF  THEIR COMPOUNDS WITH EACH
  OTHER.
1. Of Oxygen: Its Preparation and
     Properties     ....  241
2. Of Hydrogen: Its Preparation  .  246
  The Hydro oxygen Blowpipe    .  251
  Of Water:  its Composition     .  253
  Peroxide of Hydrogen     .     .  258
3.  Of Nitrogen     ....
  Of the Atmosphere
  Nitrous Oxide   ....
  Nitric Oxide     .     .    .    ■
  Hyponitrous Acid, Nitrous Acid .
  Nitric Acid.....
4.  Of Sulphur      ....
  Sulphurous Acid ....
  Sulphuric Acid   ....
  Hyposulphurous and Hyposulphu-
    ric Acids .....
  Sulphuret of Hydrogen
5.  Of Selenium    ....
  Its Compounds with Oxygen, Hy-
    drogen, and Sulphur
6.  Of Phosphorus   ....
  Oxide  of" Phosphorus, Phosphor-
    ous Acid.....
  Phosphoric Acid ....
  Phosphuret of Hydrogen
7.  Of Chlorine     ....
  Hypochlorous and Chloric Acids .
  Chlorous Acid   ....
  Hydrochloric or Muriatic Acid
  Chlorides of Sulphur and Phospho-
    rus  ......
8.  Of Iodine.....
  Iodic and Periodic Acids
  Hydriodic Acid   ....
  Iodine with Phosphorus, Sulphur,
    &c.......
  Hydriodate of Phosphuretted Hy-
    drogen   .....
9.  Of Bromine     ....
  Bromic and Hydrobromic Acids .
  Other Compounds of Bromine
10.  Of Fluorine
  Hydrofluoric Acid
11.  Of Silicon
  Silicic Acid or Silica  .
  Chloride of Silicon
  Fluoride of Silicon
12.  Of Boron .
  Boracic Acid
  Chloride and  Fluoride of Boron  .
13.  Carbon   referred  to Organic
    Chemistry     ....

          CHAPTER XII.*
OF  THE GENERAL  CHARACTERS  OP  THE
  METALS, AND  OF  THEIR  COMPOUNDS
  WITH  THE  NON-METALLIC BODIES.
Classification of the  Metals; their
  State in Nature; the Mode of Re-
  duction of their  Ores  .    .    . 327

          CHAPTER XIII.
OP THE INDIVIDUAL METALS, AND OP THEIR
  COMPOUNDS  WITH  OXYGEN,  SULPHUR,
  SELENIUM,  AND  PHOSPHORUS :  THEIR
  ALLOYS.
Section I. Metals of the First Class.
  Potassium :  its  Preparation     . 336
  Potash, Peroxide of Potassium  . 337
 P»ga
2C0
262
272
273
275
277
282
284
286

290
292
294

294
295

296
297
299
300
304
305
307

310
311
313
315

316

316
317
318
318
319
320
321
322
323
324
325
326
326

327 
CONTENTS.
IX
                                  Page
  Sulphurets of Potassium   .     .  339
  Sodium and Soda     .    .     .340
  Sulphurets of Sodium .    .     .342
  Litbium: its Oxide and Sulphuret  342
  Barium:  its Preparation   .     .  342
  Barytes, Hydrate of Barytes     .  342
  Sulphuret of Barium   .    .     .344
  Strontium : its Oxide and Sulphu-
    ret  ......344
  Calcium: its State in Nature    .  345
  Preparation and Properties of Lime  346
  Sulphurets of Calcium     .    .347
  Magnesium, Magnesia, &c.     .  348
 Section II. Metals of the Second Class.
t Aluminum :  its State in Nature  .  349
  Alumina, Sulphuret, &c.   .    .  350
  Glucinum and its Compounds    .  351
  Vttrium, Thorium, Zirconium   .  351
  Cerium, Lanthanum   .    .    .  351
  Of Manganese   ....  352
  Oxides of Manganese  .    .    .  353
  Technical Valuation of Manganese
    Ore......355
  Manganic and  Permanganic Acids  356
  Other Compounds of Manganese .  357
 Section  III. Metals of the Third Class.
  Of Iron : its State in Nature    .  357
  Manufacture of Cast and Soft Iron 359
  Manufacture of Steel  .   .    .360
  Passive Condition of Iron .    .  361
  Oxides of Iron  ....  362
  Sulphurets of Iron    .    .    .  363
  Of Nickel and its Compounds   .365
  Of Cobalt and its Compounds    . 366
  Of Zinc and its Compounds     .  367
  Ol Cadmium.   Of Tin      .    .  369
  Oxides and  Sulphurets of Tin   .  370
  Of Chrome : its Oxide.   Chromic
    Acid.....371
  Of Vanadium    .    .    .    .373
 Section  IV. Metals of the Fourth Class.
  Tungsten and Molybdenum     .  373
  Osmium and its Compounds    . 374
  Columbium and Titanium  .    .  375
  Of Arsenic.....376
  Arsonious Acid, Arsenic Acid   .  377
  Arseniuret of Hydrogen    .    . 378
  Sulphuret of Arsenic  .    .    . 379
  Detection of Arsenic  .    .    . 380
  Of Antimony    .    .    .    .384
  Compounds of Antimony with Ox-
    ygen     .....  385
  Sulphurets of Antimony    .    .386
  Antiinoniuret of Hydrogen  .    .  388
  Of Tellurium  and  its Compounds 389
  Of Uranium and its Compounds .  390
 Section  V. Metals of the Fifth Class.
  Of Copper,  Reduction from  its
    Ores.....390
  Oxides of Copper     .    .    .392
  Sulphurets of Copper  .    .    .  393
  Brass, Bronze, Gun Metal, Specu-
    lum  M< tal     .     .   .    .393
  Of Lead: its Oxides  .    .    .394
                                  Paga
  Sulphurets and Alloys of Lead   . 395
  Bismuth and its Compounds     . 397
 ection VI. Metals of the Sixth Class.
  Of Silver, its Natural State and
    Properties    .... 399
  Oxides and Sulphurets of Silver  . 401
  Of Mercury :  its Preparation and
    Properties    .    .     .    .402
  Oxides and Sulphurets of Mercury 403
  Of Gold: its  Oxides and Sulphu-
    rets  ......405
  Of Palladium and its Compounds 406
  Of Platinum : its Oxides and Sul-
    phurets  .....407
  Of Iridium and Rhodium   .    . 409
          CHAPTER XIV.
OF THE  GENERAL PROPERTIES AND CON-
         STITUTION  OF SALTS.
Neutral, Acid, and Basic Salts ; Dou-
  ble  Salts; Sulphur Salts;  Theo-
  ries of the intimate Constitution of
  Acids  and Salts;  Binary Theory
  of Salts.....410

           CHAPTER XV.
SPECIAL HISTORY OF THE MOST IMPORTANT
  SALTS  OF THE  INORGANIC  ACIDS AND
  BASES.
Of the Salts of Potash.—Chloride, Io
  dide, Bromide, and Fluoride of Po-
  tassium ; Fluosilicate of Potash ;
  Sulphates of Potash; Nitrate of
  Potash ;  Manufacture of Gunpow-
  der ; Hypochlorite and Chlorate of
  Potash;  Perchlorale, Iodate, and
  Silicate of Potash    .    .    .421
Of the Salts of Sodium.—Chloride of
  Sodium ; of Sea-water, Bromide
  and Iodide of Sodium ; Sulphate,
  Nitrate, Hypochlorite, and  Hypo-
  nitrite of Soda;  Various   Phos-
  phates of Soda; Borate and Sili-
  cate of Soda     .... 426
Of the Salts of Lithium—Salts of Ba-
  rium.—Chloride of Barium ; Sul-
  phate and Nitrate of Barytes. Sails
  of Strontium.—Chloride of Stron-
  tium;  Sulphate and  Nitrate of
  Strontian.....429
Of the Salts of Calcium.—Chloride,
  Bromide, Iodide, and Fluoride of
  Calcium ; Sulphate and Nitrate of
  Lime ; Phosphate  of Lime;  Hypo-
  chlorite of Lime;  Manufacture of
  Bleaching Salt; Chlorometry    . 430
Salts of Magnesia.—Epsom Salts   . 434
Salts of Aluminum.—Manufacture of
    Alum.....435
  Constitution of  Glass and Porce-
    lain ; Manufacture  of  Glass;
    Manufacture of  Earthenware  . 437
  Of the Salts of Manganese  .    .  443
Of the Salts of Iron.—Chlorides of 
X
C ON T
E N T S.
     Iron; Manufacture of Copperas;
     Nitrates of Iron    .    .    .  444
   Salts of Nickel and Cobalt .    .  446
   Salts of Zinc and Cadmium     .  447
   Salts of Tin     ....  448
   Salts of Chrome and Vanadium;
     Chromates    ....  449
   Salts of Tungsten,  Molybdenum,
     Osmium, and Columbium     .  451
   Salts of Arsenic, Arsenites, Ar-
     senates  .....452
   Salts of Antimony,  Antimoniates  453
   Salts of Titanium, Tellurium, and
     Uranium.....454
 Salts of Copper.—Manufacture  of
     Blue Vitriol;  Scheele's Green ;
    Emerald Green    .    .     .  455
   Salts of Lead ;  Chrome Yellow;
     Chrome Red   .    .    .     .  457
   Salts of Bismuth     .    .     .  458
   Salts of Silver, Lunar Caustic   .  459
 Salts of Mercury.—Corrosive Subli-
    mate,  Calomel,  Iodides,  Sul-
    phates, and Nitrates of Mercury  461
   Salts of Gold     .    .    .     .465
   Salts of Palladium and  Platinum  466
   Salts of Iridium and Rhodium    .  466

          CHAPTER XVI.
 OF THE GENERAL PRINCIPLES OF THE CON-
     STITUTION OF ORGANIC BODIES.
 Elements of Organic Bodies ; Rela-
   tion  of Vital Force to  Affinity;
   Compound  Radicals;  Theory  of
   Organic Acids ;  Theory of Types ;
   Decomposition of Organic Bodies  467

          CHAPTER XVII.

 OF CARBON AND ITS COMPOUNDS WITH  OX-
    YGEN, SULPHUR, AND CHLORINE.

 Forms  of Carbon ;  Organic Analysis 476
 Carbonic Acid ; Carbonates of Pot-
  ash  and  Soda;  Manufacture  of
  Potashes and Soda-ash ;  Alkalim-
  etry ; Earthy Carbonates; Car-
  bonates  of Iron, Copper, Lead,
  &c. ;  of Carburets    .     .     . 485
Carbonic Oxide, Oxalic Acid, and the
  Oxalates ;  Chlorocarbonic Acid ;
  Oxycarburet of  Potassium ; Rho-
  dizonic,  Croconic, and   Mellitic
  Acids; Sulphuret of Carbon; Chlo-
  rides of Carbon   .... 492

         CHAPTER  XVIII.

OP THE  COMPOUNDS OF NITROGEN 1ND HY-
  DROGEN.  OF AMMONIA, ITS DERIVATIVES
  AND  COMPOUNDS.

 Ammonia; Amidogene ; Iodide and
  Chloride of Azote ; Ammoniurets,
  Amidides ; Azoturets ;  Ammonia-
  Salts of Zinc, Copper, Nickel, Co-
   balt, Silver, Palladium, Platinum,
   and Mercury; White Precipitate 498
Ammonia  and  Anhydrous  Acids;
   Common Ammoniacal Salts; The-
   ory of Ammonium ; Sal Ammoni-
   ac, Sulphates, Phosphates, Oxal-
   ates, &c,  of Ammonia;  Double
   Chlorides of Ammonium    .     . 507

          CHAPTER XIX.

OF CYANOGEN AND  ITS COMPOUNDS, AND
    OF  THE BODIES DERIVED FROM  IT.

Cyanogen.  Cyanic, Fulminic,  and
   Cyanuric  Acids.   Prussic  Acid:
   its  Preparation   and  Detection;
   Valuation of its Strength.   Chlo-
   rides and Iodides  of Cyanogen   . 513
Of the Metallic Cyanides, Potassium,
   Mercury, Iron.   Complex  Cyan-
   ides ; Prussian Blue;  Yellow and
   Red Ferroprussiates of Potash;
   Theory  of the Complex Cyanides 520
Of Sulphocyanogen and  its  Com-
   pounds ; of Mellon, Melam, Mela-
   mine, and their Derivatives     . 525

           CHAPTER XX.
OF  STARCH,  LIGNINE,  GUM,  AND SUGAR,
   WITH THE PRODUCTS OF THEIR DECOM-
   POSITION BY ACIDS AND ALKALIES.
Varieties of Starch ; Lignine  ; Vari-
   eties of  Gum ; Varieties of Sugar;
   Action of Acids on Sugar; Saccha
   rine Fermentation ; Lactine ; Mu-
   cic Acid ; Mannite ; Lactic Acid;
   Glycyrrhizine    .... 527

          CHAPTER XXI.

OF THE ALCOHOLIC AND ACETIC FERMENT-
   ATIONS.   OF ALCOHOL ; THE ETHERS ;
  ALDEHYD ;  ACETIC ACID,  AND OTHER
  BODIES DERIVED FROM  IT.

Vegeto-animal Bodies; Yeast; Man-
  ufacture of  Spirit; Preparation of
  Ether;  Theory of the Process;
  Nature of Ether; its Compounds
  with Acids ;  Sulphovinic  Acid ;
  Oil of Wine ; Compound Ethers ;
  of defiant  Gas and the  derived
  Compounds      .... 537
Oxidation of Alcohol; Aldehyd; Ace-
  tous Fermentation ;  Acetic Acid,
  Acetates of Potash, Lime, &e, Su-
  gar  of Lead, Verdigris, other Ace-
  tates ; of Acetone; Compounds of
  Kacodyl; of Marsh Gas   .    . 553
Action of  Chlorine on Alcohol,  and
  the  Bodies  derived from it; The-
  ory  of the Ethers     .         . 564
Secondary Products  of the Alcoholic
  Fermentation :  CEnanthic  Acid ;
  Amilic Alcohol; Corn Oil  .    . 567 
CONTENT
XI
CHAPTER  XXII.
Page
OP THE ESSENTIAL  OILS, CAMPHORS, AND
               RESINS.
Of the Oils forming Acids, not exist-
  ing in  the  Plants;  Oil of Bitter
  Almonds ;  Amygdaline ; Benzoic
  Acid ; Benzyl; Oils and Acids of
  Cinnamon,  cloves, Mustard, and
  Spirea      .              .     . 569
Oils  pre-existing in the Plant, Prop-
  erties not Acid   .... 574
Camphors or Stearoptens of the Oils
  of Resins.....576
Amber, Succinic Acid, Succinates;
  Caoutchouc     .... 579

         CHAPTER XXIII.
 OF  THE  SAP0NIFIABLE  FATS  AND OILS.

Glycerine, Stearine, Ole'ine, Marga-
  rine ;  Products of the Action  of
  Acids on Fatty  Bodies;  Vegeta-
  ble Fats and Oils; Fish Oils ; Man-
  ufacture of Soaps and  Plasters   . 581
Spermaceti, Ethal,  and the derived
  Bodies.  Wax   .    .    .     .591

         CHAPTER XXIV.
OF  THE ORGANIC  ACIDS WHICH  DO NOT
  PRE-EXIST  IN  PLANTS,  AND  DO  NOT BE-
  LONG TO ANY ESTABLISHED SERIES.

Tartaric Acid ;  Tartrates of Potash,
  Soda, Iron, Antimony, &c. .     .  592
Action of Heat  on Tartaric Acid;
  Raccmio Acid   ....  595
Citric Acid ;  Citrates; its Decompo-
  sition by Heat   ....  597
Malic, Maleic, and  Fumaric Acids .  598
Meconic, Komenic, and Pyromecon-
  ic Acids.....599
Tannic Acid; Valuation of Tannin;
  Tannates.....600
Gallic Acid ;   the Products of its De-
  composition     ....  601
Tannic Acid from Catechu, Cincho-
  na, and Kino     ....  603
Other Vegetable Acids   .    .     .  604

          CHAPTER  XXV.
OF THE  NEUTRAL  ORGANIC  SUBSTANCES,
  AM) OF THE PRODUCTS OF  THEIR  DE-
  COMPOSITION.
Pectine; Salicene;  Phloridzine; As-
  paragine;   Caffeine;   Piperine;
  ('antharadine; Anemonine;  Ce-
  trarine; Picrotoxine; Columbine;
  Cusparine;  Elaterine; Meconine;
  Petidecanine ;  /Esculine ;  Popu-
  lirie ; Qiutssine ; Santonine ; Sapo-
  nine ; Scillitine ;  Sonegine; Smi-
  lacine; Absinthiine ; Lactucine . 605
Of Extractive .Matter; Apotheme ;
  Extracts.....612
CHAPTER XXVI.
Page
     OF THE COLOURING MATTERS.
Of Madder; Anchusa ; Carthamine;
  Carmine;  Logwood ;  Persian Ber-
  ries ; Anotta ;  other  Yellow Bod-
  ies ;  Indigo, and the Substances
  derived  from it;  Lichen Colours ;
  Archil  and  Litmus,  Colours  of
  Leaves  and Flowers ; Theory of
  Dyeing.....613

         CHAPTER XXVII.
OF  THE VEGETABLE  ALKALIES  AND  OP
             THEIR SALTS.
Quinine; Cinchonine; Aricine; Mor-
  phia ; Narcotine  ; Codeine ;  The-
  baine;   Narceine;  Pseudomor-
  phine ; Strychnine ; Brucine; Del-
  phinine  ; Veratrine ;  Sabadilline ;
  Jervine  ;  Colchicine  ;  Emetine ;
  Solanine;   Chelerythrine ;   Cheli-
  donine;  Aconitine; Atropine; Bel-
  ladonine;   Daturine;  Hyoscya-
  mine; Cone'ine; Nicotine; Men-
  ispermine ;  Cissampeline ;  Glau-
  cine; of the Constitution of the
  Vegetable Alkalies    .     .    .623

        CHAPTER XXVIII.
OF THE PRODUCTS OF  THE DECOMPOSITION
   OF WOOD AND THE ALLIED BODIES.
Section I.
   Of the slow Decomposition of Wood.
     Constitution of Ulmine.  Of Turf
    and Coal  ...         .637
Section II.
   Of the  Products  of the destructive
    Distillation  of Wood, Coal, and
    Resin    ..... 646
  Pyroxylic Spirit;  Compounds of
    Methyl;  Formic  Acid ;  Coal
    Gas;  Napthaline; Kreosote, &c. 647

          CHAPTER  XXIX.
OF THE CHEMICAL  PHENOMENA OF VEGE-
                TATION.
Germination,  Assimilation  of the
  Food of Plants ; Sources of Car-
  bon and  Nitrogen; Ashes of Plants;
  Composition of Soils and Manures;
  Rotation of Crops ;  Action of Light
  on Plants.....650
          CHAPTER  XXX.
        OF ANIMAL CHEMISTRY.
Section I.
  Of the  Composition of the Animal
    Tissues.
  Of the Albuminous Constituents ;
    Albumen ;  Fibrine ; Proteine ;
    Gelatine ; Chondrine ;  Fats of
    the Brain ;  Ozmazome; Zomi-
    dine ......  663
  Skin, Epidermis,  Hair,   Horn, 
Xll
CONTENTS.
                                  rago
    Feathers; Cellular and Serous
    Tissues;  Tendons;  Muscular
    Tissue; Brain; Composition of
    Bones,  Teeth, and  Enamel;
    Shells.....670
Section II.
  Of the Composition of the Blood, and
    the Phenomena of Respiration.
  Blood Globules and Serum;  Clot;
    Hematosine.  Blood in Disease;
    Respiration;  Modes  of Action
    of the Air; Animal Heat      .  673
Section III.
  Composition of the Digestive  Or-
    gans, and of their Secretions;
    Chemical Phenomena of Diges-
    tion.
  Mucus; Gastric Juice; Pepsine;
    Analyses  of  the  Bile;  Bilin;
    Taurine;  Cholic  and   other
                                   ftp
    Acids;  Bilifulvine; Chyle  and
    Lymph, Saliva and Pancreatic
    Juice.....679
Section IV.
  Constitution of the Urine in Health
    and in Disease.
  Urea; Uric Acid; Allantoine, Al-
    loxan, Alloxantine,  and other
    Products of the Decomposition
    of Uric Acid; Hippuric  Acid;
    Urinary Deposites and Calculi;
    Mode of recognising  Calculi;
    Urine  in  Diabetes and  other
    Diseases.....683
Section V.
  Of  various Natural and  Morbid
    Products.
  Milk; Caseine; Eggs; Amnios;
    Tissues of the Eye;  Earwax;
    Pus;  Ambergris    .     .    • 8W 
ELEMENTS  OF  CHEMISTRY.
  The science of chemistry has its origin in the principle, that the
bodies which constitute the  external world are  composed of a va-
riety of elements, united according to certain laws.  If we could
conceive a universe consisting only of iron, or quicksilver, or  sul-
phur, the objects of the astronomer might still remain as extensive
and as sublime as they are in the actual state  of things ; for, in
tracing the constitution of  planetary and  satellitic systems, or re-
ducing to precise laws the forces by which the motions of the
heavenly bodies might be produced, all the resources of his science
would  still be brought  into play.   In like manner, the physical sci
ences could attain perfection, for the relations of these bodies to
heat, to light, to electricity, the various problems and laws of stat-
ical and dynamical forces,  could  have been known, and thus all
that is  essential  to  the science  of natural  philosophy might be
attained.  But not even an idea  of chemistry could  have  been
formed.   The duty of chemistry  is to  find the constituent  ele-
mentary substances, which, by uniting, form the various compound
bodies which we  observe ;  to ascertain the nature of the forces by
which they  unite, and the laws by which their union or separation
may be  regulated ; to trace the effects  of their mutual action in
the properties of the new substances formed  by their combination,
and in the phenomena, independent of composition, which accom-
pany the exertion of chemical force.
  This object of chemistry has been at all periods fully recognised ;
for the earliest philosophers, even before the science had received
a name, considered its objects as  well defined  in the arrangement
of the elements of fire, air, earth, and water.   When the methods
of chemistry, and the reasonings to which they led,  acquired a
better form, these elements, which had been assumed from specu-
lations in natural history and metaphysics, gave way to others, as
sulphur,  spirit, salt, oil, and earth, equally incorrect, but still those
which, in the rough trials of the period,  were obtained by decom-
posing compound bodies.   As more accurate ideas and better pro-
cesses were acquired, these elementary principles changed again
their character, until,  finally, the  philosophical idea  of chemistry
was clearly  stated and  established  by Lavoisier: 1st, that we study
to resolve the various compound bodies found in nature  into others
which resist our power, and which we term undecompounded or sim-
ple substances,  without  pretending  that they are  elements; for the
advance  of  science enables us to decompose, in each generation,
bodies which to our own predecessors had appeared simple ; 2d,
that we study to  effect the  recombination  of those simple bodies, 
If*         ORIGIN  AND  USES  OF  CHEMISTRY.
either  in the same proportions, and thus regenerate the natural
compound bodies, or in new proportions, and thus add to the cata-
 jgUe of ^bodies which may exist in nature.
  "jLthesfr t^o*r\eratlpiis. tke*fjr^t,^r,^eparation of a compound
    f into Hie simple substances which constitute it, is termed anal-
ysis.  The second, or combination of simple-*to form a compound
substance, is called synthesis.  All chemical processes are conducted
upon the principle of one or other of these two, and occasionally
they are both, successively or synchronously, accomplished.
  The  objects of  chemistry cannot, however,  be considered as
limited to the mere abstract study  of the laws  of elementary com-
position ; to it also belongs the improvement  of processes in the
useful arts by the more accurate knowledge of their  theory which
chemistry confers, and the invention of new processes or of new
arts, by the application or discovery of substances previously neg
lected  or  unknown; the  alleviation  of disease,  by new  remedies
which may be placed at the command of the physician, or by more
correct ideas of  the origin and results of morbid action, to which
the attentive study of the chemical processes  of the great labora-
tory of the  human frame may ultimately lead, ranks also among
the most important of its applications:  and, although an abstract
science, which reveals some of  the most beautiful of nature's laws,
deserves our best  attention, yet it  becomes  invested with more
general interest, and commands more universal homage, when, as
with chemistry, it appears to be the basis of those practical arts on
which so much of health, of national prosperity, and of civilization
may depend.
  The  origin or derivation  of  the word chemistry is  unknown.  It
was first found as %7/jueto, indicating the art of making gold and
silver among the Egyptians and Greeks of the  Empire, at the com-
mencement  of that extraordinary  perversion  of the idea of  ele-
mentary constitution which fascinated mankind for nearly five hun-
dred years.   From the Greeks it was naturally adopted, with the
vain pursuit which it denoted, by  the Arabians, and, passing with
the Arabic prefix into the languages of modern Europe, became
alchemy.  When  the just objects and powers  of the  science were
finally recognised,  it was termed chemia  or chemistry.
  In studying those properties  of the different kinds of matter by
which they are recognised to be distinct and independent chemical
substances, it is unavoidable to include those qualities which  al-
though common  to all forms of matter, yet differ in degree among
the different kinds, and thus serve  as distinguishing characteristics
of them.  The physical properties of various  bodies are hence in
common use among chemists, as serving to perfect their description •
and, indeed, the limit between properly physical and properly chem-
ical properties of  substances is not always capable  of being dis-
tinctly drawn. 
SPECIFIC  GRAVITY  OF  GASEB.          11
                          CHAPTER L

 OF GRAVITY AND  COHESIVE  FORCES  AS CHARACTERIZING CHEMICAL SUB
                            STANCES.

   The physical forces which are  of most importance in determin-
 ing the characteristic  properties of bodies are gravity and cohesion.
 These  differ, however,  remarkably in principle from  each other,
 and are applied  to  quite  independent purposes.  Gravity is com-
 mon to all forms of matter, and is totally independent of its nature.
 It is  exerted at all,  even the greatest conceivable distances, and is
 the invisible  yet insuperable tie, which,  connecting together  the
 satellites and planets of our system with the central sun, assigns to
 each of the tenants of our boundless skies its place and motions.
 Acting thus only on the mass, gravity is a measure  of the quantity
 of matter present in a body ; and what we term weight  is only  the
 gravitating force exerted  by the  substance which we weigh.   By
 no natural operation can the smallest particle of matter be annihi-
 lated or destroyed ; throughout the most complicated processes  the
 quantity of matter remains constant, and  hence we are  enabled to
 verify the accuracy of  our chemical operations, by proving  the
 weight of the bodies  ultimately formed to be  equal to  the weight
 of the substances by whose action they have been produced.
   Under the same volume different bodies  have  very different
 weights, and hence contain different quantities of matter.  Bodies
 are said to be more or less dense, according as  in a given bulk they
 contain a greater or less quantity  of  gravitating matter; and when
 a certain body is taken as  a standard, and their density  reduced to
 numbers, there is obtained the specific gravityof each body,  or  the
 comparative quantity of matter it contains in a given bulk, which,
 being almost always the same for the same body, is an important
 element in its history,  and may often serve for its recognition.
  The determination of  specific gravities is easily performed where
 the volume  of the substance can  be  exactly measured.  Thus,  for
 liquids, as water, oil  of vitriol, or  alcohol:  if a small bottle  be
 taken containing an ounce of water, or 480 grains, it will contain
 343 grains of sulphuric ether, or 885 grains of sulphuric acid.   Now
 the densities will be as these numbers; or water being taken as the
 standard, and its specific gravity  being assumed as 1000, the spe-
 cific gravities of the others become  proportional to  it;  as,

                  Water  ...  480 :  1000
                  Ether   ...   343 :  715
                  Sulphuric acid   885 :  1845

To  save  this little calculation, the bottle in use is generally made
to hold 1000 grains of  pure water, and then, filling it with the fluid
to be  tried, the weight  gives directly  the specific gravity.
  Where the  substance exists naturally in the  state of gas, a pre-
cisely similar process may be had recourse to ;  in place of a bottle 
12         SPECIFIC  GRAVITY OF  GASES.
 with a ground glass stopper, there is used a globe, g, with a stop
 cock, capable of holding  from twenty to thirty cubic inches.  A
                         quantity of  air  having  been  removed
                         from the globe, the gas, which must pre-
                         viously be  either perfectly dried or per-
                         fectly saturated with  moisture, is admit-
                         ted to supply its place ; and as the volume
                         of o-as which passes in is exactly equal to
                         the volume  of air which had been  taken
                         out,  the relative weights give their den-
                         sities, and hence the  specific gravity of
                         the gas.  For, suppose that the globe full
                         of air weighed 656 grains ; that, having
                         been exhausted of air, it weighed 647-5,
 and then, having received 28 cubic inches of carbonic acid gas, it
 weighed 660*3 grains.   We thus know that the 28 cubic inches of
 air had weighed 8-5 grains, and that 28 cubic inches of the gas had
 weighed 12-8 ; hence the densities are as 8-5 to 12*8, and the specific
                                          .  12-8
 gravity of the gas, air being taken as 1000, is -?,-£-x 1000 = l-o06.

   This brief description being  intended only to explain the princi-
 ple which the words " specific  gravity" involve, it has been consid-
 ered as not liable to alteration ;  but, in reality, the volumes of bodies,
 particularly of gases, are constantly in a state of change.   Accord-
 ing as the air is  warmer or  colder; according  as the  pressure to
 which it  is subjected, as indicated by the barometer, diminishes or
 augments, the volume which a certain weight occupies is altered,
 and the specific gravity is changed.  Hence, when we take air as a
 standard of specific gravities for gases, we do so only with refer-
 ence to a certain standard of temperature and pressure, as at 32 on
 the scale of Fahrenheit's thermometer, and at 30 inches of mercury
 in the barometer tube.   It is only by accident that  an experiment
 might happen to be made at this standard temperature and pressure,
 and hence it is necessary to reduce the observed result to what the
result should have been at the standard points.  If the gas be damp,
it  is necessary also to  correct for the presence of the watery va-
pour, and hence the determination of the specific gravity of  a gas,
although so simple in theory, is in practice a  most delicate opera-
tion.   Under the proper heads of the constitution of gases and
vapours,  with regard to heat and pressure,  the mode of  makino
these corrections will be described.
  The determination of  the specific gravity of a solid body involves
in practice some principles in addition to those above stated.   We
cannot regulate the bulk of a solid body as we wish, and hence the
volume must be determined indirectly.  This is done by finding how
much water it displaces.  Thus, if the solid be in many small frag-
ments, weighing altogether, for example, 357 grains, they may be
introduced into a specific gravity bottle containing 1000 grains of
water. A quantity of water overflows exactly in bulk to the solid
which is introduced.  The  bottle being full,  the  solid body and the
remaining water are then found to weigh 1285 grains.   Now  if no
water had been expelled, the  water and solid  body should  have 
            SPECIFIC  GRAVITY  OF  SOLIDS.          13

weighed 1357 grains.   The difference 72 is the weight of the water
expelled;  and, consequently, the weights of equal volumes, or the
densities of the water and of the solid, are as  72 and 357; or, the
specific gravity of the water being taken as 1000, that of the solid

is 3j>7 X 1000, or 4958.  If the solid be unsuited for that method, its
   72
volume is  next determined by the  principle that  a  solid body im-
mersed in a fluid is partly supported by the upward pressure of the
liquid which it displaces.   The solid, in order  to sink in the liquid,
has to  displace and push  upward a quantity of it  equal to its own
bulk, and to resist  its weight or tendency to sink down again;  for
this purpose a portion of the weight of the solid must be employed,
and it is  only the overplus that  is counterpoised by the weights
when we  proceed  to weigh the solid  body immersed in any fluid.
A solid weighs, therefore, less when immersed in  a fluid than when
weighed in the  ordinary  manner,  the  difference being  the portion
of the weight of the solid which is employed to sink it, or to resist
the force of the  liquid which tends to float it up, and this is equal
to the weight of the liquid which the  solid pushes out  of its place,
and which is of the same volume as the solid.   To effect this op-
eration,  a balance, as  in
the figure, is taken, gen-
erally with one scale dish.
 The solid is hung to the
 other  extremity of the
 beam  by  a fine  hair  or
 thread of cocoon-silk, b,
 and is thus weighed  as
 usual; let us suppose that
 it  weighed 295  grains.
 A vessel of pure water is  then so arranged that the solid shall be
 immersed as nearly as possible in the centre  of it (as a in figure),
 and it, being then again weighed, is found to be lighter than before ;
 let us suppose that it shall weigh 243 grains.   This is the overplus
 of its weight after having neutralized the tendency of the water to
 float it  up.   The  difference of the two  weighings 295—243=52
 grains is therefore the  amount of the upward pressure,  or the
 weight  of the water  which the  solid displaced.   Equal volumes
 thus of  the solid and of  the water are found to weigh respectively
 295 and 52 grains, and  the comparison of these  numbers, water
 being taken as  1000, gives the specific gravity of the solid, which

 is  ~X 1000=5673.
    52
    A variety of other instruments are made use of for measuring
 the specific gravities of solids and of fluids, as areometers, hydrom-
 eters, ccc;  but as here it is rather the general principles than the
 practical details of such operations that are of importance, I shall
 not enter into their description.
   The specific gravity of compound gases is found to have a highly important rela-
 tion to their ultimate  constitution, and throws great light upon some of the most
 general laws of chemistry; but as yet, notwithstanding some interesting specula
 lions of Perzoz and of Boullav which I shall hereafter notice, no  connexion he
                                 13
 
14          SPECIFIC  GRAVITY   OF  VAPOURS.
tween  the chemical properties or  composition of liquid or solid bodies and their
specific gravities has been discovered.  The physical constitution of vapours and
gases being, however, identical, those bodies which, being volatile, are capable ot
assuming the form of vapour, may render, by the examination of the specific grav-
ities of their  vapours, most interesting indications of the manner m which their
elements are combined, and methods of performing this operation have been con-
trived by some of the most illustrious of chemists, as by Dumas and by Gay Lussac.
  The  method of Gay Lussac is the simpler of the two, and, for substances which
           are volatilized at  moderate temperatures, easily applied.   A basin, c, is
           taken, which rests upon a little furnace,  and contains mercury.  In
           this basin the graduated bell glass, a, is inverted full of mercury.  Let
           us suppose we wish to determine the specific gravity of vapour of wa-
           ter.   One or two  little bulbs are taken and filled with water as follows :
           the bulb is warmed with a lamp, and allowed to cool with the point
           dipped into the water ; in this  manner a little water gets admission ;
           this is then boiled in the bulb until  all air has been expelled, and the
           bulb is filled with pure steam; the point being then dipped under the
           surface of the water, as the steam condenses, the water rushes up to
           supply its  place, and the whole becomes  full;  the point being then
           touched to the flame of a  lamp, it is melted, and the orifice is closed.
           A small quantity, three or four grains, of water being thus enclosed,
           the little bulbs are passed under the  edge of the jar, a, and rise to the
           top, where they  float upon the mercury;  a glass cylinder, b, open at
           both ends, is now placed round the jar,  resting on and secured to the
dish, c, and into it is poured  so much colourless oil as shall completely cover the
jar, a,  but allow of the graduation being distinctly seen ; the furnace is then light-
ed, and as the temperature of the oil and mercury rises, the water in the little bulbs
forms steam, which at last bursts the bulbs, and the level of the quicksilver  in the
jar immediately falls, the steam occupying the space above it.   When the mercury
ceases to  descend, it is known that all  liquid has been converted into vapour; the
temperature of the oil, which is necessarily the same as that of the vapour inside,
is ascertained, and by the graduation on the jar the volume occupied by the vapour
is accurately  read off;  the weight of the vapour is known, for  it is the weight  of
the water in the  bulbs, and its volume at this high  temperature is thus found.
Knowing thus the volume of a few grains of steam at 250°, the  volume at 32° may
be calculated; and as the volume of so many grains  of  air at 32° is already known,
the specific gravity of the vapour of water is obtained.  The temperature of the
oil must be at least thirty or forty degrees above  the boiling point of the liquid, and
hence  it is likely to become coloured,  to fume, or even to risk taking fire, unless
great caution is employed.
   The method invented by Dumas has the advantage of being applicable to all tem-
peratures  below the melting point of glass, and it is consequently by its application
that the greatest benefit has been conferred on science.  It is, however, more com-
plex in principle, though not less delicate in practice.  A globe holding from ten to fif-
teen cubic inches, and drawn out at its beak to a capillary orifice, is carefully weigh-
ed, containing, as usual,  atmospheric  air.   It is  then warmed,  and its beak being
dipped into the fluid to be tried, it is allowed to cool, until by the contraction  of the
                                               air a sufficient quantity of the
                                               fluid has made its way in.  The
                                               globe is then fitted in  a sort of
                                               cage, by which it is securely held
                                               in the centre of the liquid bath,
                                               by which the  heat is to be appli-
                                               ed, and which may be water or
                                               oil, a solution of chloride of zinc,
                                               or, best of all, the fusible alloy
                                               of bismuth, tin,  and lead.  The
                                               capillary beak of  the tube just
                                               projects over the surface  of the
                                               bath, as in the figure.  When the
                                               globe becomes sufficiently heat-
                                               ed, the liquid boils, and its va-
                                               pour, in passing away, carries off
                                               the air which had previously fill-
 
DIVISIBILITY  OF  MATTER.
15
ed the globe.  The liquid should be present in such quantity that its vapour, after
carrying off all air, should occupy the interior of the globe completely pure.  The
excess df vapour is known to have passed away when there is no longer a jet pro-
ceeding from the capillary beak, and then by means of a blowpipe the orifice is
closed, and the temperature of the bath being taken at the same moment, the globe
is removed from the bath, perfectly cleaned and weighed.  The liquid condensing
as soon as the globe grows cold, leaves its interior practically empty, and, on break-
ing off the capillary beak under the surface of quicksilver, this last enters into the
vessel, and, if the operation had been well managed, fills it completely.  The globe,
full of quicksilver, is then emptied into a graduated jar, by which the quantity of
the quicksilver being measured, the volume of the globe is known ; when this has
been done, all requisites for calculating the specific gravity of the vapour have been
obtained.  For, knowing the volume of the globe, the weight of the air it contained
is known, and, subtracting that from the first weighing of the globe, the weight of
the globe when empty is obtained.  Subtracting this from the second weighing of
the globe, the weight of the vapour is obtained ; and as the air and vapour occupied
the same volume, the densities should be  as these weights, if they had been at the
same temperature ; but, as this was not the case, a farther calculation is required
to reduce thein to the standard, and obtain the numerical specific gravities.
  No process has been more fruitful in important results than this mode of detei-
mining the specific gravity of vapqurs, for it is only in this way that such substances
as sulphur, arsenic, phosphorus, and mercury, as well as numerous compound bodies
vviili high boiling points, could have been tried.
  The force of gravity is thus  of importance in chemistry, by giv-
ing a measure  of the quantity of matter upon which we experiment,
and  by affording characteristics  of  individual  substances, by the
comparison  of the quantity of  matter they  possess in a  standard
volume.  The force of cohesion, although not so  universally exist-
ant as that of gravity, is  of equal interest, from the numerous pecu-
liarities  in its  activity which  almost everybody  is  capable of pre-
senting, and  by which  bodies   are remarkably distinguished from
each other.   To understand, however, the nature of cohesive forces,
and the  causes of  the variation of their energy, it is necessary to
notice those ideas of the peculiar constitution of matter  on which
philosophers have  generally agreed, and which result from, while
they best serve to explain, those remarkable phenomena.
   From  the earliest period in science, discussions have arisen as to
whether the  masses  of matter which we  ordinarily  employ should
be considered capable of infinite division, or  whether, by continuing
to divide, a term should ultimately be found at which no farther sub-
division could be made ; that thus the ultimate constituent and indi-
visible particles, or atom.-., which, by their aggregation, form sensible
masses, should be discovered.   By no appeal to experiment can this
question  lie resolved; when we call in the assistance of our most
powerful means of mechanical division, we attain only to producing
powders, of which the finest particle is, in  miniature, all that  the
mass from which it had  been formed was  upon a larger scale, and
capable  evidently of just as much  subdivision, if our mechanical
processes were perfect enough to enable us to proceed.
  That this divisibility may actually occur to an  almost incredible
degree, may be easily demonstrated by experiment.  In gilding sil-
ver wire, a grain of gold is spread over a surface  of 1400 square
inches;  and as, when examined in a microscope, the gold upon the
thousandth of a linear inch, or one  millionth of  a  square inch, is
distinctly visible, it is proved that gold may be divided into particles
of at least t-4<to-ooo-ooo  °f a square inch  in  size, and yet possess 
16            DIVISIBILITY OF  MATTER.
the colour and all other characters of the largest mass.   If a grain
of copper be dissolved in nitric acid, and then in water of ammonia,
it will give a decided violet colour to 392 cubic inches of water.
Even supposing that each portion of the liquor of the size of a grain
of sand, and of which there are a million in a cubic inch, contains
only one particle of copper, the grain  must have divided itself into
392 million parts.   A single drop of  a strong solution of indigo,
wherein at least 500-000 distinctly visible portions can be shown,
colours 1000 cubic inches of water ; and as this mass of water con-
tains certainly 500-000 times the bulk of the drop of indigo solution,
the particles of the indigo must be smaller than 25 ott-ooo-oTo-ooT tne
twenty-five hundred millionth of a cubic inch.  A  rather more dis
tinct experiment is the following: if we dissolve a fragment of sil-
ver, of 0-01 of a cubic line  in size, in nitric acid, it will  render dis-
tinctly milky 500 cubic  inches of a clear solution  of common salt.
Hence the magnitude of each particle of silver cannot exceed, but
must rather fall far short of, a billionth of a cubic line.  To render
the idea of this degree of division more distinct than the mere men-
tion of so imperfectly conceivable a number as a billion could effect,
it may be added, that a  man, to reckon Avith a watch, counting day
and night, a single billion of seconds, would require 31-675 years.
  In the organized kingdoms of nature even this excessive tenuity
of matter is far surpassed.   An Irish girl has  spun linen  yarn of
which a pound was 1432 English miles in length, and of which, con-
sequently, 17 lbs. 13 oz. would have girt the globe ; a distinctly visible
portion of such thread could not have weighed more than T2T0 jo or <r
of a grain.  Cotton  has been  spun so that a pound of thread was
203-000 yards in length, and wool 168-000 yards.   And yet these,
so far from being ultimate particles of matter, must have contained
more than one vegetable or animal fibre;  that fibre being itself of
complex organization, and  built up of an indefinitely great number
of more simple forms of matter.
  The microscope has, however, revealed to us still greater wonders
as to the degree  of minuteness which even complex bodies are ca-
pable of possessing.  Each new improvement in  our instruments
displays to us  new races of animals, too minute  to be observed be-
fore, and of which it would  require the heaping together of millions
upon  millions  to be visible to the naked eye.  And yet these ani-
mals live and feed, and have their organs for locomotion and prehen-
sion, their appetites to gratify, their dangers to avoid.   They possess
circulating systems often highly complex, and blood, with globules
bearing to them, by analogy, the same proportion in size that our
blood globules do to us; and yet these globules, themselves organ-
ized, possessed of definite structure, lead us merely to a point where
all power of  distinct conception  ceases; where we discover that
nothing is great  or small but by comparison, and that presented by
Nature on the one hand with magnitudes infinitely great, and on the
other with as inconceivable  minuteness, it only remains to bow down
before the omnipotence of  Nature's Lord, and own our  inability to
understand Him.
  These proofs of great divisibility, however, leave the question of
infinite divisibility quite untouched.   There are, however, many and 
MOLECULAR CONSTITUTION.
17
powerful reasons which have decided almost all modern philosophers
to consider the possible division as being finite.   On the other view
the mind has no resting-place,  until, by the total disappearance ol
material conceptions, the constitution of bodies resolves itself into
a collection of mathematical points, from which, as centres, certain
forces are exerted; but with such abstract speculation  chemistry
lias no connexion.   Its fundamental condition, that there exist many
kinds of elementary matter, of which the quantity is measured by
their weight, is totally independent of our abstract idea of what mat
ter is, or how its properties have their source.
  In proof of the division of  matter having a limit,  experiments
made principally by Faraday and Wollastoh have been quoted.  Thus,
it is ascertained that our atmosphere does not extend into space,
but is confined within comparatively a trifling distance from the
earth, about 45 miles.  Wollaston, considering the particles  of  air
as being balanced between their mutual repulsion and the  general at-
traction towards the earth, suggested that, if these particles could be
divided  to  an infinite degree, there should be an infinite source of
repulsive power, and hence, at a certain distance, this repulsion over-
coming  the gravitating force,  the atmosphere should spread into
space, and, being attracted to the other planets in proportion to their
masses, should form round the  larger, as Jupiter, and especially the
Sun, vast  and dense  atmospheres, the  existence  of which should
easily be  recognised.  No such atmospheres exist, and hence, as
was argued by  Wollaston, the force of repulsion must have a finite
limit, and the number of repelling particles cannot be infinite.  In
like manner, Faraday found that bodies, in evaporating, form atmo-
spheres of certain definite depths above the surface of the body, and
drew from hence the same conclusion.  This argument cannot, how-
ever, be considered as decisive. It is not at all  certain that, because
the elasticity of air is thus found to have a limit, the  number of
particles of air, in  a given space, might not be  infinite.
  I shall consider the masses of matter, whose properties we pur-
pose to examine, as being made up of a great number of lesser masses,
to which the name of molecules or particles may be  assigned.  It
is totally indifferent whether these molecules may be  infinitelv  di-
visible or not j there is no fact  in either chemistry or physics which
requires the positive adoption of either one side or the other.  These
molecules are subjected to the influence of two forces, which oppose
each other, and by the relative balancing or preponderance of which,
all the forms and physical properties of ordinary substances are pro-
duced.  One of these forces is  attractive ; it  is the attraction of ag-
gregation, as it has been termed, or cohesion.  If it acted unimpeded,
the molecules of every portion of matter would cohere with insuper-
able power; unconquerable solidity, hardness,  and tenacity would
alone characterize external nature.  The other force is one of repul-
sion, which, from a variety of evidence, is assumed as identical with
the cause  of heat.  If it alone  prevailed, no  other form of matter
could exist but that of gas ;  the  solid globe, the liquid waters, would
change to  atmospheres of vapours, and the beneficent uses to which
our earth is now adapted  could  not exist.
  Such is, perhaps, approximatively what occurs in those extreme
                              C 
18
STATES OF  AGGREGATION.
members of our planetary system, Herschel and Mercury.  The for-
mer receiving from the Sun but j^ part of the heat which our earth
derives, must be reduced to the temperature of empty space ; and,
with few exceptions, the bodies which on this earth are gaseous or
liquid, if they exist, are there as  rocky masses.  The latter must at
certain periods be so hot, that quicksilver would naturally be a gas
upon its surface, and those metals which here constitute our examples
of solidity, should there form liquid oceans.  On this earth, however,
according as the forces of heat and cohesion vary in different bodies,
they pass through different states of aggregation.  Those bodies in
which cohesion prevails are solid, and by their tenacity and resist-
ance to breakage or change of form, display the force which binds
their molecules together.  Where cohesion has been suppressed, and
the repulsive agency of heat acts uncontrolled,  the body becomes
gaseous, and its particles, devoid of the least trace of cohesive power,
repel each other.  In intermediate cases, where  the two forces ap-
pear balanced, the particles do not cohere, and hence may move
upon and separate from each other without any external force ; but
they do not repel, and thus remain  in contact if no external force
tends to disturb them.  This  is  the liquid condition;  it is that  of
water, of alcohol, of oil, while air and steam are  gaseous, and iron,
wood, and stone are instances of the solid form.
  The peculiar nature of each body determines whether, under com-
mon circumstances, it shall have one  or the other of these forms;
but there are few bodies which are not capable of assuming all the
three.  This is artificially effected by diminishing or increasing the
degree of heat, and  thus by cooling a liquid, it may, by the cohesion
becoming greater, be converted into a solid;  or by increasing the
heat to which a solid is subjected,  it may be  converted into  a  li-
quid, and  from thence into a gas.   One liquid, pure alcohol, has not
yet been frozen ; some solids, as charcoal, have not yet been melted :
organized bodies are generally decomposed too  easily to allow of
a change of state ; but, with these exceptions, the principle of the
change of form, artificially caused by the increase or diminution  of
the quantity of heat, is universal.  These forms  of matter, consid-
ered  as effects of heat, will require  and obtain hereafter  a more
extended notice.
  This force of molecular cohesion acts only at distances so minute
as to escape the most delicate examination.   The fragments of a
piece of glass or metal which has been just broken, when laid ever
so closely together, have  no tendency to unite  again  ; but, if the
surfaces be  pressed together, union  may take place, though only
in a few points, and imperfectly.  Yet, when  pieces of plate glass,
laid flat on each other, and subjected  to considerable  pressure, are
allowed so to remain for a  certain time, they  are found to grow to-
gether so  completely, that  thick  masses may often be ground as if
they had always formed a single  piece.   If two surfaces of lead  be
cut quite clean and  brigfit,  and forcibly pressed together, they unite
also, and  may require a force  of eighty or one hundred pounds to
effect their  separation.  In fluids, although the  force of cohesion
is very nearly absent,  yet it is not  entirely so ; the viscidity  of
fluids depending upon  the traces of  it which remain.   The ©lobular
form of a rain drop, or of a drop of any fluid allowed to fall from 
C 0 H E S I 0 N.--C APILLARITY.
19
n. point, arises also from the cohesive attraction of its particles, and
different fluids differ remarkably in their relations to heat, from the
various degrees of force with which this residue of cohesion is ex-
erted.   The particles of a fluid cohere not only to  each other, but
even more powerfully to solid bodies in many cases.   It is thus
that solid  bodies are wetted by fluids.   If  the finger be dipped into
water,  the particles of the water in contact with the finger adhere
to it more powerfully than they do to  the other  particles of the
fluid, and  when the  finger is removed, they accompany it, and thus
it becomes wet.   Mercury does not wet the finger,  for its particles
cohere too powerfully to each other ; but mercury adheres  to, or
wets a piece of gold, as water wets the  finger.  From this cohe-
sion of fluids to  solids,  all the phenomena of capillary attraction
result,  as  the filtering of liquids in pharmacy and chemistry, to sep-
arate solids which  had been mixed with  them; the absorption of
liquids by porous solid bodies, and many  others.
  The  existence of this form of cohesion may be very simply shown
by an experiment, such
as is illustrated in the
figure.   A disk of any
substance which may
be wetted by water is
to be hung evenly from
the extremity  of the
beam of  the balance,
and brought exactly
into contact with the
water  in  the cup  be-
low.  It will be found necessary to augment considerably the weights
in the scale dish opposite, to separate them ; and, when the disk has
been torn away from the surface of the water, the  force overcome
will be found to have been, not that of the solid to the liquid, which
was still more intense, but the cohesion of the liquid particles to each
other;  for the solid  is found to be  wetted by a layer of liquid par-
ticles which it had torn from the general mass of liquid underneath.
If the experiment be tried with a disk of polished iron, and mercury
as the fluid, there is no  wetting, and the force measured is really
the cohesion of the solid to the fluid.
  [Clairaut found, as the result of his mathematical investigations,
that all the phenomena of capillary tubes depend upon the relation
of two forces : 1st, The cohesion of the particles  of the fluid for
each other ; and, 2d, The attraction of the particles of the solid for
those of the fluid.   When a  glass tube is dipped into different
liquids: if the force of attraction of the  glass is less than half the
force of cohesion of the fluid, the  fluid will be
depressed, and not rise to its  hydrostatic level;
if it be equal to half, the fluid will come  pre-
cisely to its level ;  and if it be more than half,
the fluid will  rise in the tube.
  Connected  with these  conditions is the figure
of the  boundary surface of the fluid.   If three
glass tubes, b c, de,fg, be placed in fluids  which
respectively are depressed, at the true level, or at
JL 
20
COMPRESSIBILITY.
 an elevation, it will be seen that in b c the surface a a of the fluid
 is convex, in d e it is plane, and  in fg it is concave.]
   The particles of a body being  held at certain distances from each
 other by the balance of their attraction and repulsion : if,  by the ap-
 plication of an external force, as pressure, they be brought nearer,
 so as to occupy a smaller volume, the body is said to be compress-
 ible.   If, when the external force is removed, the body, by the mutual
 repulsion of its particles, regain  its  original volume, it is  said to be
 elastic ; if,  on the  contrary, it remains as when compressed, it is
 called inelastic.   In nature there are  few bodies perfectly elastic,  and
 none which can be said to  be perfectly inelastic.   In solid bodies,
 when pressure produces a change of volume, some traces of  it are
 permanent; but in  liquids and in gases, the restoration to  the  origi-
 nal bulk appears to be complete.
   The amount to which solid and liquid bodies may be compressed
 is very small, so much so that very delicate methods are necessary
 to determine it.  Thus it requires a pressure of about 400 lbs. upon
 each square inch of the surface  of water to diminish its volume by
 the T oVo part.  In gases, however, the repulsive force acting without
 interference, and the particles being at much greater distances from
 one another than in the liquid  or solid form, the amount of com-
 pressibility becomes very much  increased, and the law by which it
 is regulated extremely simple, being, that the volume of any  gas
 varies inversely as the  pressure upon it ; that it is doubled if  the
 pressure be diminished to one half, and reduced to one half if  the
 pressure  upon its  surface be  doubled.   Thus, supposing a gas to
 measure 100 volumes under the  pressure of 20 lbs.,

     Then with pressures of 80  . 40   .  20  .   10  .   5  lbs.
     The volume becomes  25  . 50   .  100  . 200  . 400.

   The gases which are used in chemical operations  are liable to
 constant changes of volume, from the alterations in the weight of
 the surrounding atmosphere, by which they are always pressed  ; and
 hence, before we can tell how much of a gas we really have obtained
 by any process, it  is necessary  to ascertain  the  amount  of atmo-
 spheric pressure, and to allow for it.   The pressure which the air
 exercises is measured by the barometer, in which a column of quick-
 silver balances the pressure of the air, and varies in height according
 as this changes; the height of this mercurial column being accurately
 measured by a scale applied to the tube of the barometer.   In  these
 countries, the height of the barometric column fluctuates between
 28 and 31 inches, but the average height of a year is about 29-8
 inches.   For simplicity, a number very near this, 30 inches, is taken
as the standard pressure; and whenever the specific gravity, or  the
volume  of a gas is given, without particular  remark, this standard
height of the barometer is understood to be the pressure.
  If, therefore, we have a gas at a different pressure, it is usual, and often  neces-
 sary, to reduce its volume to what it should have been under the standard pressure,
 or, as it is generally termed, to correct  for pressure : to do this, we use the  rule
 given above for the change of volume with the pressure.  Thus, if, in an analysis
 of morphia, we obtain 4 54 cubic inches of nitrogen gas when the barometer is at
 28 5 inches, we say that, expressing the volume at 30 inches by V,
              V : 285 : : 454 : 30, or V=—X 4-54=4 313. 
LIQUEFACTION  OF GASES.
21
  Knowing, then, the weight of 100 cubu inches of nitrogen gas at 30 inches, the
weight of 4 313 is easily obtained.
  In this manner, the corrections for pressure, alluded to in the description of the
modes of taking the specific gravities of gases and of vapours, are introduced.
Thus, in taking the  specific gravity of steam by Gay Lussac's process (page 14),
the vapour occupying but a portion of the tube, there remains a column of mercury,
suppose 5 inches high : the pressure on the vapour is therefore only the difference
between that and the external pressure, and if this be 30 inches, is (30—5)=25.
Then the measured  volume of the steam is to what it should be at the standard
pressure, as 30 to 25.
  In certain  cases, of which atmospheric air may be  taken  as an
example, this rule, of the volume being inversely  as the pressure,
holds exactly ; but there are many other gases,  in which, when the
compression  is very great, the particles appear to be brought within
the sphere of their respective cohesive forces,  and the volume di-
minishes more rapidly than  it ought by the rule.  Thus, if a tube
full of air and a  tube full of sulphurous acid gas be exposed to ex-
actly the same pressure, the volumes will not diminish m the same
degree when the pressure becomes  high, but as follows:

     The air as  .  .  .  1000   .   853   .   559    .   314.
     Sulphurous acid as  1000   .   851    .   554    .   301

In some other gases the same variation has been observed.
  If such a gas be still more violently compressed, its particles may
be brought so completely within  the sphere of cohesive action, that
this  force comes into active play, and the body changes from the
gaseous to the liquid form.   Thus many gases have been liquefied
by a  degree  of  pressure which  differs  for each gas, and is at 3?°
Fahrenheit as follows:
! of gal.
Nitrous Oxide   .  .  .
Carbonic Acid   .  .  .
Muriatic Acid   .  .  .
Sulphuretted Hydrogen
Ammonia.....
Cyanogen .....
Sulphurous Acid .  .  .
	Pounds u
	Hie Inch
44	660
36	540
21	360
15	225
5	75
3	45
2	30
  Other gases, such as oxygen, hydrogen, and nitrogen, have been
subjected to a pressure of 800 atmospheres, not only without becom-
i*ig liquid, but without even deviating from the rule which implies
perfect elasticity, and hence  without even approximating  to  the
term  at which they should abandon the  gaseous state.  Notwith-
standing this, we cannot consider that there is any physical differ-
ence  of constitution between  those liquefiable and non-liquefiable
gases, and hence the conclusion  is, that,  by a suitable increase of
pr< t-sure, the molecules  of all gases might be so brought into cohe-
rent approximation, and  converted into liquids.
  With regard to the means of applying such pressure, and actually
obtaining those gases in the liquid form, it is necessary to consider
the  manner in which such gases are generated, and such methods
will consequently be  described in the history of those bodies.
  Cohesion is thus antagonistic to the force of heat, which tends to
render the molecules o(  a body repulsive to each other, and to sep-
arate  them to greater distances from each other than they had been 
22
PHENOMENA  OF SOLUTION.
 before.  Cohesion is  therefore diminished, and even annulled, by
 applying heat.
    When the cohesion between the particles of a solid and those of
 a fluid is more powerful than between the particles of the solid it-
 self, the latter is not merely moistened by the fluid, but it abandons
 altogether the solid form, and, becoming liquid, mixes uniformly with
 the fluid, and is said to  have been dissolved by  it.  By this  peculi-
 arity of cohesion, bodies are divided into the soluble and the insoluble.
 Thus common salt and  Glauber's  salt are soluble, while  chalk and
 white lead are insoluble, in water.  These classes are, however, con-
 nected  by  a  series of  intermediate  degrees of  sparingly  soluble
 bodies,  such as cream of tartar and plaster of Paris.   Bodies which
 are insoluble  in water may be  yet easily dissolved by other  fluids;
 thus, resinous  bodies, which do not dissolve  in water, dissolve in al-
 cohol.  A  great deal of  the success of vegetable proximate analysis
 depends on the skill with which the solvent powers of various fluids
 may be successively applied.
  From the tendency of heat to diminish the force of cohesion, it naturally results
 that the solubility of most bodies is increased by heat; thus,  100 parts of water, at
 60° F., dissolve 11 of sulphate of potash, and at 212 dissolve 25.  At 60°,  32 parts
 of dry sulphate of magnesia are dissolved by 100 of water, but 74 at 212°.  This,
 however, is not always the case ; some bodies, as common  salt, are exactly equally
 soluble in water at all temperatures, while in other cases the solubility is greater at
 particular temperatures than either above or below them.   Of this peculiarity, the
 sulphate and nitrate of soda  are examples.  Thus, 100 parts of water dissolve of
 dry sulphate of soda, at 32°, 502 ; at  52°, 1022 ; at 76°, 28 ; at 93°, 53;  at 122°,
 47; and at 212°, 42: the solubility increasing up to 93°, and from thence dimin-
 ishing.  100 parts of water dissolve of nitrate of soda, at 21°, 63 ; at 32°, 80 ; at
 50°, 23 ; 60°, 55 ; and at 246°, 218 parts.  Here the peculiarity is of the  opposite
 kind to what occurs with sulphate of soda : the  solubility diminishing up to 50°,
 and from thence progressively increasing.
  The solubility of bodies  in water may be strikingly represented to  the eye by
means of a kind of map, such as is given in the figure.  The horizontal lines rep-
resent the quantities of the salt dissolved by 100 parts of water, while the  vertical
lines represent the temperatures.  Thus the line  of sulphate of soda commences
32°  52°  72°   92°  112°  132°  152u  172°  192°  212r'  2220 
FORMATION  OF CRYSTALS.
23
at the temperature of 32° at the horizontal line 5, and. rising rapidly, cuts the hori-
zontal line 10 at 52°, cuts the line of 40 at 88'', and attains its highest point of 53
at 93°;  from thence  it commences to redcscend, until at 232° there are only 42
parts dissolved.  The line of chloride of sodium is horizontal, showing that it is
equally soluble  at all  temperatures, and in the other cases the construction of the
scale is  easily seen on inspection.
  In general, when solid bodies dissolve in a fluid, there is cold produced, but oc-
casionally the solution is accompanied with a remarkable evolution of heat; this
last occurs when bodies which naturally contain water, chemically combined, are
deprived of it by heat, and when thus dried, dissolved ;  in such cases, it is probable
that the one portion of water is taken by the salt into a state of intimate chemical
combination, and thus more heat produced than counteracts the cold which should
arise from the inert; solution of the hydrated salt thus formed.  Such examples may
be found in dry chloride of calcium, the dry sulphates of copper, or of zinc and iron.
   Solution is very much promoted by agitation, by  the minute di-
vision of the solid, and  generally by all causes which tend to facil-
itate the contact  of the solid and liquid particles.   When the liquid
has dissolved as much of the solid as possible, it is said to be satu-
rated.   The  cohesion of the liquid to the solid having been reduced
to an equality with that of the particles of the  solid for each other,
it can  dissolve no more.
   If a  saturated  solution be so circumstanced  as to diminish the
cohesion of the  particles of the solid to  each other, a portion  of
the solid separates, the  amount of which depends on the new con-
ditions under which the liquid is placed.  Thus, if to a solution  of
nitre in water there be added spirits of wine, the water mixes with
the spirits of wine and abandons  the nitre, which is precipitated
If strong muriatic acid be added to a solution of chloride of barium
in water, the water is taken by the acid, and the salt falls down as a
white  powder.   But the most  usual case  is where  the  separation
of the  solid is produced by the cohesion of its  own particles, which,
slowly abandoning the  liquid, dispose themselves according to cer-
tain laws, and,  assuming regular  geometrical  forms, are termed
crystals.  Solid bodies, in separating slowly from liquids  in which
they had been dissolved, in general thus crystallize, and the figures
of these crystals being,  to  a great extent, characteristic  of the
bodies, deserve minute attention.
   To  obtain substances regularly crystallized, several processes
may be followed, according to  the  nature of the body.  Where the
substance is soluble, and more soluble in a hot than in a cold liquid,
a  saturated boiling solution may be  made and allowed to cool.   The
excess of the solid body crystallizes out on cooling.   Thus, if 151
parts of sulphate of magnesia  in crystals be dissolved in 100 parts
of boiling water, and allowed to cool to 60°, a quantity of crystals
will be obtained weighing 86 parts; for at 60' the 100 of water can
only dissolve 65, and  the difference  between that  and  the  151,
which  had been  dissolved by the  boiling water, must crystallize.
If the  body be,  like common salt, equally soluble in water  at  all
temperatures, the above process cannot be applied,  and a quantity
of the  liquid must be removed by evaporation;  the  portion of salt
corresponding to the quantity of  water which has passed away, is
thus obtained solid.   If the  evaporation be slowly carried on,  so
that the formation of the crystals  is not disturbed by the  boiling of
the liquid, they form regularly, and may attain to considerable size.
   In  many cases the bodies which it  is necessary to obtain crys- 
24
CRYSTALLIZATION.
tallized are not soluble, or it may be wished to obtain crystals oth-
erwise than by solution.   By melting a solid substance, its particles
are allowed liberty of motion ;  and when it again commences to
solidify,  they may arrange themselves  regularly, and crystallize.
Almost all bodies, when melted, and then allowed to solidify, do
thus crystallize;  but  the spaces left between the crystals  which
first form being completely filled up by the portions which solidify
afterward, there remains only a general crystalline structure, visi-
ble in the fracture of the body.  Thus cast iron, sulphur,  zinc, &c,
have  crystalline  fractures.  The  beautiful feathered appearance
given to  sheet tin by washing with dilute acid, and which was so
popular some years ago  under the  name of moiree metallique, was
simply this crystalline structure, displayed by removing the thin
layer of metal on  the outside, which had  solidified  too  rapidly to
have acquired any trace of crystallization.  To  obtain, therefore,
the metals crystallized by fusion, the excess of liquid metal must
be removed  from around the crystals  that are first formed.  A
quantity  of the metal or of sulphur, having been melted in  a cup,
is  to be allowed to cool until a solid crust has formed  upon the
surface  and at  the sides to a certain  depth; two apertures must
  Bodies  may also be crystallized by sublimation.   When a  sub-
stance has been converted into  vapour, and that, in condensing, it
assumes at once the solid form,  its particles arrange themselves so
as to form crystals.  Thus are obtained in  fine crystals, arsenic,
arsenious  acid, corrosive sublimate, benzoic acid, &c.
  It frequently happens that the same body may be obtained crys-
tallized by more than one of these processes.   Thus, corrosive  sub-
limate may be crystallized by solution or by sublimation ; sulphur
may be crystallized  either by fusion or by solution.  It is remark-
able that, when  this occurs, the crystals obtained  by the two  pro-
cesses are never of the same shape ;  they have not even any simple
relation of figure to one  another, but indicate  a  totally different
mode of  arrangement  of particles, induced  probably, at  least in
part, by the different temperatures at which the  change of state of
aggregation may have occurred.  A  body which crystallizes thus
in two ways is  said to be dimorphous, and this character will be
found  hereafter of the highest importance  in  the theory of the
atomic constitution of  compound bodies.
  The more  slowly  the change  of state  occurs, the more regular,
and the larger, are the crystals that are formed.   Hence, in practice'
solutions are  left to cool very slowly, or to evaporate spontaneously •
and sublimation is effected by the most gentle heat that can be ad-
vantageously applied.   To favour the deposition  of the  particles
a variety  of artificial acids may be applied.  Thus, crystallization
takes place better in a pan with some little roughness at  the sides 
CRYSTALLIZATION.                  25
than when it is quite smooth, and threads are hung in sirup to pro
mote the crystallization of the sugar-candy;  a little  crystal of the
same kind of salt is often introduced, to serve  as a nucleus round
which the  new crystals may gather; and, in  a solution containing
many salts, the  nature  of the salt which  shall  crystallize may be
determined by the nature  of the little crystal introduced : thus, if
equal parts of nitre and of Glauber's salt be mixed  and dissolved
in five parts of water, and the solution divided between two similar
dishes ; on a crystal of nitre being laid in one dish and a crystal
of Glauber's  salt being laid in the other, a crystallization of pure
nitre will occur in the former, while nothing but Glauber's salt will
crystallize in the latter  dish.   Salts which are  mixed together in
solution may also be separated from one another by their respective
solubilities:  thus, if sea-water  be evaporated, common salt alone
will be deposited according as the liquor boils away; when it  has
been removed from the fire no more  common salt  separates, but
Epsom salt will crystallize, and, after it has been removed, the liquor
will be found to  contain chloride and iodide  of magnesium.   The
liquor from which  crystals have  separated is  called the Mother
liquor.
   Crystals occasionally  form in a body,  although it may remain
completely solid.  Thus, when  copper wire  has been kept some
time in the laboratory, it becomes  a  mass of cubical  crystals, and
its tenacity is almost completely lost.  When sugar  is melted and
allowed to cool,  it forms a perfectly transparent  hard mass, desti-
tute of any trace of crystalline arrangement, but after  some months
it becomes opaque and white, having changed into ordinary crystal-
lized sugar.  In cases, also, where bodies are  dimorphous,  one
form is generally unstable, and the body, when crystallized in  it,
changes after sometime into  the other form.  This takes place re-
markably with sulphur, and will hereafter be again referred to.
  A solution of  a  salt, saturated at a high temperature,  is found
occasionally to remain without  crystallizing, although cooled to a
very low degree.  In such  case, on introducing a little crystal,  or
agitating the liquor, it suddenly crystallizes, and  frequently solidi-
fies into one mass.   Sulphate of soda is remarkable for its tenden-
cy to assume  this indifference to crystallization.   If two  parts of
crystallized sulphate of soda  be dissolved in  one  part of water, at
93 ,  and the solution be laid aside to cool, without being disturbed,
it remains quite clear and liquid ; but, on producing crystallization
by any of the means just stated, the whole becomes solid.
  In all cases of  crystallization  there is heat evolved, consequent
on the general law of heat being given out when a  liquid or  va-
pour becomes solid.  There is sometimes a remarkable evolution
of light,  to which  I  shall  refer  again.  Indeed,  crystallization is
sensibly affected  by the presence or absence of light.  If a dish,
half  covered by paper, be set aside with a solution to crystallize,
but few crystals will  form  in  the dark, although  there may be an
abundant crop on the illuminated portion of the vessel.
  It  has been noticed, that  when a body has  been obtained, crys-
tallized at  different temperatures, as #by solution and fusion,  the
crystalline  form is generally different, and the body  is said to be 
26     PRIMARY  AND  SECONDARY  CRYSTALS.

dimorphous.  In  this case, the two  forms are totally  different in
their geometrical character.  But independent of this, a body may,
even simply by  solution, be obtained, crystallized in a great variety
of forms.   In a crop of crystals of sulphate of iron or of alum, obtain-
ed by cooling from a hot solution, a great many different figures  may
be observed, which, however, are, on examination, all referrible to
one  more regular and fundamental form.   Each substance has  thus
a characteristic  form of crystal, which is termed its primary form;
and  it may assume a great variety of figures, produced by modifi-
cations of this  form: these  are termed  secondary forms.   Thus,
carbonate  of lime has  been found  crystallized in more than six
hundred different  secondary forms, all derivable, however, from the
one  original primary figure, the rhombohedron.  The  growth  of a
crystal depending on  the deposition  of  new layers of particles
over its external  surface, any change in the quantity deposited  on
each side  will naturally produce a  change  of form.   It is there-
fore necessary, when crystals  are  left long in a  solution,  to  turn
them, and change their position frequently, as otherwise the  growth
would take place on some  sides rather than others, and secondary
forms would be produced, by which the characteristic figure of the
crystal would be injured.
  The most ordinary source of change of figure consists in the replacement  of an
edge  or of an angle by a plane.  Thus one of the simplest figures of crystals is
the cube a; it has eight edges and  eight solid angles.  The effect of substituting
plane surfaces for the edges is to produce the secondary form b, and by replacing
the solid angles by planes, the form c; when these replacements occur  together,
the more complex figure d is produced.  If the edges of the cube be replaced until
all traces of the original planes disappear, the figure e, the rhombic dodecahedron,
is produced ; and if the replacement of the solid angles by planes be carried on to
tne same extent, there is formed a regular octohedron/.  These last are again sim-
ple and primary forms, for by a similar move of replacement they may be reduced
to each other or to the cube.
  When a crystal augments in size by the deposition of layers of
fresh material upon its faces, the molecular cohesion in each new
layer is greater than its cohesion to the layer underneath, and hence
by skilful splitting, a  crystal may be separated into a number of
plates, exhibiting  the order of  its formation.  The direction in
which a crystal may be split is termed its cleavage, and it is of great
importance in the determination  of the  primary form of the crys- 
REGULAR  SYSTEM.
27
 tal, for it  often occurs that the same secondary  form may be  pro-
 duced by  two different primary forms,  and  in such case, the cleav-
 age being simply related to  the surfaces of  the true  primary form,
 determines which it is.
   Notwithstanding the immense variety of forms of crystals which exist, they may
 yet be reduced to a very few classes, by conceiving them to  be formed by their par-
 ticles being  built up around certain axes, which pass through the centre of the crys-
 tal, and the relative position and magnitude of which determine the manner in which
 the particles are arranged.
   In this way there may be formed six systems  of crystallization, characterized aa
 follows:
   1st System.   The  Regular System. The three  axes are all equal in length, and
 are at right  angles to each other.
   2d  System.  The  Rhombohedral  System has three  axes equal  in  length,  which
 are placed, however, at  equal angles (60°) with  each other,  and are all in the same
 plane, while a fourth and unequal axis is at right angles to that plane.
   3d System.  The Square Prismatic System has  the three  axes  at right angles to
 each other, but there are only two of them equal; the third is either longer or shorter
 than the other two.
   4th System.   The Right  Prismatic System has the  three  axes at  right angles to
 each other, but there are no two of them of the same length.
   5th System.  The Oblique Prismatic System has two of the axes making an acute
 angle with each  other, while the third is placed at right angles to  both.   The three
 axes are all  unequal  in length.
   6th System.  The Doubly Oblique Prismatic System has all  the axes  unequal in
 length,  and making acute angles with one another.
   The various actual forms of crystals, both primary and secondary, are derivable
 from the manner in which the plane surfaces of  the crystals may  be applied around
 these axes.   In order to conceive the application  of the planes,  the axes shall be
 considered as placed with one in a vertical position, and it is called the principal
 axis.   The  nature of the system determines which axis should be selected.
   In the  Regular System, the axes being all equal, it  is a matter  of indifference
 which is chosen as the  principal axis, and their perfect symmetry is also a reason
 that the portions of the  crystal around each axis must be completely simdar.  The
 number of forms belonging to this  system is consequently not  very large, and they
 are remarkable for their simplicity.   Thus, when each plane cuts  the axes at equal
 distances from the centre, the form is the octohedron,  and  as the planes must be
 equally  inclined to all the axes, it is the regular  octohedron /, of which each plane
 is an equilateral triangle.  When each face of the  crystal cuts one axis at right an-
 gles, and is hence parallel to the other two, the form is the cube a. When each
 face cuts two  axes at equal distances from the  centre,  and is  parallel to the third,
 the figure which  results is the rhombic dodecahedron e.   By  the combined positions
 of sets of planes, other and more complicated (secondary) b, c, d, forms are produced,
 arising from  the partial coexistence of the conditions of the  formation of two sim-
 ple forms.
  The crystals belonging to this system are generally very well defined and easily
 recognised:  a  great number of important bodies crystallize    ,-
in the forms belonging to it:  thus  common salt, fluor spar, /j
galena, and iron pyrites, are found in cubes ; alum in octohe- v   ■
drons; the garnet is found  in dodecahedrons.   When pure
metallic substances are  found crystallized, it is always in
forms belonging  to this  system; thus, bismuth, copper, sil-
ver, gold, crystallize in cubes, and lead in octohedrons.
  A peculiarity of crystals, belonging particularly to this sys-
tem and to the next, is, that every alternate face shall become
developed  to  such a degree  as to obliterate the  intervening
planes, and thus to generate a new  form, having one half of
the number of planes.  Thus a crystal of alum is very sel-
dom truly octohedral; it has usually the  figure  of g where
four of the 6ides  of the octohedron  have  become very large,
while the other four remain  very small.   When the oblitera-
tion becomes complete, there is produced the tetrahedron, or
three-sided pyramid of fig. h, which is hence properly called
 
28     RH0MB0HEDRAL  AND  SQUARE  SYSTE
the hemioctohedron.  Such crystals are called hemihedral, from their contaimng
half the proper number of sides.   Certain bodies  have a natural ^l^^'
hedral  crystallization, and are but very rarely found with the proper ™mber  of
planes.  The diamond is a remarkable instance of this.  Its proper form is the leg-
ular octohedron,  but its crystals are universally hemihedral
  In the Rhombohedral system, the supplementary  or fourth axis, is taken as the
                     principal axis, and the crystals are foimed
                     by the planes  being applied to these axes,
                     as in the  former system.   If  the  planes
                     be all inclined at the same angles  to the
                     three horizontal  axes, and cut the verti-
                     cal axis, there is formed  a double six-
                     sided pyramid (i); and  when  the  planes
                     are perpendicular to  the horizontal axes,
                     and parallel to the vertical axis, the six-
                     sided prism (k) is produced.  These forms
                     generally coexist in quartz, as in the figure
i.   By the replacement of the edges in these forms there may
be produced others with twelve sides in  place of six; as a twelve-
sided prism and  a twelve-sided  pyramid, of which quartz also
affords examples.
  This system is more remarkable for its modified forms than for those simple fig-
                 ures  above described, although  the  six-sided prism  and six-
                 sided pyramid are characteristic of very many substances.   If
                 we suppose, in the terminal six-sided pyramid, every  alternate
                 side, above and below,  to grow at the expense of those next
                 it at each side, I will be formed.   Ultimately the  sides of the
                 prism disappear,  and there will remain
                 a figure of six planes, of which all the
                 sides shall be equal and  similar rhombs,
                 the  rhombohedron, m, which  gives its
                 name to this system, although it be but
                 a hemihedral modification  of the true
                 typical form.  The principal axis of the
                 rhombohedron is the vertical axis of the
pyramid, and the horizontal axes are found by joining the
solid angles to the centres of the opposite faces, where ori-
ginally the lateral angles of the pyramid had been.
  The  carbonates of lime, of iron, and magnesia are remarkable for  crystallizing
with this hemihedral figure.  Even in the six-sided prism  of carbonate of  lime, the
rhombohedral tendency  is evident by the crystal  being terminated, not by the six-
sided prism, as in quartz, but by its three hemihedral replacing planes.
  3. Tlie Square Prismatic System.—The crystals of this  class differ from those of
                     the regular system in the vertical axis not being necessarily
                     equal to the other two ;  but, on the contrary, being  in almost
                     all cases either longer or  shorter.   Where there is formed
                     an octohedron, n, it  differs from the regular octohedron  in
                     the terminal angle of each plane being not 60°, but more or
                     less.  Its basis is, however, a square ;  and
                     to distinguish it from the octohedron of the
following system, it is termed the octohedron with the  square base.
By the application of planes perpendicular to the horizontal axes, a
four-sided  pyramid with a square base is formed,  o, and by the re-
placement of the terminal edges of this  prism, four-sided pyramids
may be formed on its base and summit.  By this property the square
prisms and octohedrons are distinguished from all modifications of
the cube and octohedron of the regular system.  When the edge
of a cube  is replaced, the plane substituted  for it gains equally on
the two surfaces, and hence, when one is effaced, the other must
be so also.  But in the square prisms the replacement may efface the terminal plane,
giving a four-sided pyramid, and yet the lateral planes be but little encroached upon.
The sides  of the crystal in this system  are thus independent of the top or bottom,
and may be modified, while the top and bottom remain unaltered ;  this never takes
place in the regular  system, where,  there being  no one side particularly  upper or
 ower,  all  modifications must affect all sides alike.
 
PRISMATIC  SYSTEMS.
29
/ \\
/ \ \ / /'""'■-■A
  4.  The right Prismatic System.—In  this system the three axes
being all unequal, the length, breadth, and thickness  of the crys-
tal may be different from each other.  Thus, in the octohedron./?,
formed by the application of planes, each connecting the extremi-
ties of the three axes,  the  three dimensions of the crystal, as in
the figure, which is the primitive form  of sulphur, are unequal;
the octohedron  has a rhombic base; and by planes which are in-
clined to the horizontal axes, and parallel to the vertical axis, a
prism with a rhombic base may be produced.   This also,  by com-
bination of the  two forms, may obtain pyramidal terminations, as
in some forms of native sulphur.
  An important character of this system, which arises from there
               being no necessary connexion between  the two
               horizontal axes, is, that the lateral edges may be
               alternately modified in a different manner ; or, in other words, that,
               looking at the crystal, its back and front may be differently affected
               from its sides.  Of this an  example may be found in a common
               1 modification of the sulphur octohedron given in figure q.
                  5. The oblique Prismatic System.—From the manner  in which
               the crystals belonging to this system  form, one of the oblique axes
               is generally by much  the most developed, and is taken as the prin-
               cipal axis.   The remaining axes, which are at right angles to each
other, are taken as horizontal, the principal axis making with them the acute angle,
which belongs to the peculiar body.
  By means of planes which are inclined to all the axes, there is formed the ob-
                       lique rhombic octohedron, such  as characterizes gypsum
                       (sulphate  of lime), as  in figure r; and by means  of planes
                       which are inclined to two axes, but parallel
                       to the third, an oblique rhombic prism may
                       be  formed,  s.   A remarkable character of
these crystals is, that from  the crossing  of the  axes and their inde-
pendence of each other, the front and back of the crystal may be
quite different  in relation to the sides.   The crystals of sulphate
of soda, of carbonate of soda, of borax, of sulphate of iron, and of
feldspar, may be taken as examples of the numerous  forms deriva-
ble from  this system.
  6. The doubly oblique  Prismatic  System.—The  axes are all  une-
qual, and all form acute angles with each other, and it is hence in-
different  which is taken as  the principal  axis of the crystal.   The
consequence is complete absence  of  symmetry  between any two surfaces of the
crystal, except such as, being at the ends of the same axis, are parallel to each other.
                       The complexity of crystals of this system is hence usually
                       very great.  The simplest forms are the oblique rhombic
                       octohedron, /, and the oblique rhombic prism, formed  by
                       planes inclined  to all the axes, or to two, and parallel to the
                       third, respectively.  The soda feldspar (albit) and sulphur
                       of copper are examples of this system; the octohedron of
this system  is figured in the margin.
  It  might  be at first supposed that the assumption  of these axes, or lines round
which we have supposed the crystalline particles to be regularly arranged, was
merely a geometrical fiction, by which  the form of the crystal might be more easily
represented to the mind ; but such is not the case.  Evidence derived from a vari-
ety of sources agrees  in demonstrating that this diversity of crystalline systems
arises from  fundamental differences in  the laws of molecular cohesion, by which
the formation of the crystal is regulated, and that these axes, which have been  so
much alluded to, are real centres, the  proportion and position of which determine
all the physical  properties of the body.  It is peculiarly from the action  of crystal-
lized bodies  upon light  that accurate  and extraordinary information has  been ob-
tained of their internal  structure, and  the discoveries that have been made in this
department were the means of advancing the physical theory of light to its present
almost perfect state.
  Substances may assume crystalline forms which do not properly belong to  them
in many ways.  Thus, a group of crystals being  imbedded in a rock, they may, by
the nitration of the water of springs across the  rock, be dissolved out, leaving a hoi-
 
30    FORMS  MODIFIED  BY  FOREIGN  BODIES.
low mould of their form ; and, subsequently, substances of another kind may be in-
troduced into this cavity, and, solidifying there, may simulate the  external form of
the original inhabitant.  But these are no more real crystals than a mass of plaster
of Paris, which has solidified in a hollow mould, and comes out as an Apollo's head,
can be said to have so crystallized.  By cleavage, and by the operation of polarized
light, the unsuited internal structure is recognised, and the crystal is stated to have
been merely pseudomorphous.  Another mode in which a body may come to have  a
form not its own, is by remaining behind after the  decomposition  of the substance
which had really  crystallized.  Thus, when hydrated chloride of copper, which
crystallizes in fine green prisms, is carefully heated, the water is expelled, and the
chloride of copper remains dry,  and of a fine yellowish-brown colour, in the original
crystalline form, and with the  surfaces quite bright.  The red iodide of mercury
combines with ammonia to form a  substance which crystallizes in long prisms of  a
snow-white colour; these, when  exposed  to the  air, lose all  ammonia, and  the
iodide of mercury remains behind, pure, and of a brilliant red, but with the perfect
figure, and bright, smooth surfaces and sharp angles of the body originally crys-
tallized.                                            .
  It has been thought that the presence of foreign  bodies in a solution, even where
they did not enter into combination with the substances which crystallized from it,
might modify their form.  Thus, when common salt  crystallizes in a solution of
urea, it is deposited in octohedrons, and by  dissolving alum in a solution of urea, it
may be obtained crystallized in cubes.   But in this case, the substances which crys-
tallize are no longer common salt nor alum, but the one, a combination of urea with
common salt, and  the other, a basic alum  produced by the mutual  decomposition
of the urea and the alum.  The presence of a trace of lead or tin in a large quanti-
ty of iodide of potassium, has been supposed to modify its form ; but it is more likely
that the mechanical presence of an impurity of the kind may be supposed to produce
a tendency to macled  crystals, and  thus the external form be somewhat altered, al-
though the true constitution of the crystal may remain the same.
   Certain bodies, when  they exist together in solution, may  re-
markably modify  each  other's form, by crystallizing together  so
completely that every individual crystal  shall contain a quantity of
each.   Yet  these  bodies  will  not have combined chemically with
each other, for the quantity  of each present  in  each crystal is quite
indefinite ; they are mixed  together mechanically in the  crystals,
and  hence the  form of the  actual  crystal is intermediate between
those  which the  separate bodies  should have  had  if  they were
pure.  In order that  bodies  may so crystallize  together,  it is not
only necessary that they should be of the same crystalline  system,
but the crystalline forms  must resemble  one another very closely
in all their angles and sides.   Thus, not  only will iodide of potas-
sium and sulphate of soda,  which belong  to different  systems of
crystallization, not crystallize together,  but Glauber salt a:id car-
bonate of soda, which do  belong to the  same system,  will not crys-
tallize together, because the relations of  their angles and sides be-
ing completely different, they cannot mix together so as to form a
uniform solid.  But sulphate of  zinc and sulphate of magnesia be-
long  not merely to the same  crystalline system, but  they are  al-
most identical in their figures ; the eye cannot make any distinction
between their crystals; and  hence,  when a crystal is  being formed
in a  solution containing these  two bodies, the  molecular a°nd crys-
talline forces being the same for both, they  concur  in the building
of the crystal without interfering with each other.  Hence, as there
is a  very small  difference between the angles of the rhombic prisms
of the two salts, the one being 90  30', and the other  91 8', if they
be mixed in equal proportions in the crystal, its angle must be 90°
49'.   Carbonate of  lime  and carbonate  of  magnesia are, like  the 
ISOMORPHISM.
31
sulphates of zinc and magnesia, almost identical in crystalline form,
and they  exist in nature mixed  together, forming the dolomite or
magnesian limestone.   The quantity of carbonate of lime  is to the
quantity of carbonate of magnesia as 50*6 to 42*8 ; and as the angle
of the rhomb  of carbonate  of lime is 105° 4', and that  of carbonate
of magnesia is  107D 40', the angle of the mixed crystal  is found
by multiplying the angle of each constituent by its quantity, adding
these products together, and dividing by the quantity of the  mixture,
and the result is 106°  15', the angle of the rhombic crystal of mag-
nesian limestone.
  The peculiarity of crystallization which such bodies  possess  may
be illustrated  in another manner.   Ordinary alum is a sulphate of
alumina and potash; but there are  a great variety of other double
sulphates which crystallize in the same form, and which constitute
a well-defined crystalline genus.  If an octohedral crystal of com-
mon alum be  placed in a solution of the  sulphate of  alumina and
ammonia, the crystal augments in size by the addition of layers of
it.  If it be then  removed  to a solution of sulphate of potash and
peroxide  of iron, it acquires another layer; by a solution of sul-
phate of ammonia and peroxide of iron another still; and by means
of solutions of the alums, which consist of oxide of chrome united
to potash or ammonia, with sulphuric acid, the crystal  may grow to
a still greater size.  The chemical  constituents of the crystal  may
thus  vary, but it  retains its form ; the number of equivalents of
chemical substances contained in it  remains also the same, although
they  may not remain identical in nature.  The potash and the am-
monia on the one hand, the oxide of iron, the alumina, and the ox-
ide of chrome  on the other,  agree in producing the same crys-
talline arrangement of  particles ;  in impressing  upon their com-
pounds, with  the  same bodies, the  same crystalline  form.   Bodies
so related are called isomorphous.   Oxide  of  zinc and magnesia are
isomorphous ; while lime is a  dimorphous body, being in one form
isomorphous  with magnesia,  and in the other with oxide  of lead.
Isomorphous bodies are remarkably similar in their chemical prop-
erties ; they follow generally the same laws of combination,  and
hence, as shall be farther shown  in the chapter on chemical affinity,
the principle  of isomorphism  has been of the  highest importance
in developing the true  relations of chemical  substances  to each
other, and the intimate connexion of the forces which produce the
chemical  combination, and  those which  direct  the  crystalline ar-
rangement of  the  particles  of bodies.
  It was, some time ago, considered an important question, whether  the ultimate
particles of bodies had the same figure as their primary crystalline form, or wheth-
er they were globular or ellipsoidal.  The law of isomorphism was considered, at
one time, to result from the ultimate particles of those bodies, being themselves
isomorphous ;  and hence, when entering into similar combinations, giving to them
also the same form.  It was at another  time referred to the principle that, in any
chemical combination, the crystalline form was determined by the number of mole-
cules or atoms present, and was independent of their nature.  Neither of these
ideas has been found sufficient; but the complete discussion of the relations of the
isomorphous bodies will be found in a future chapter.
  The angular dimensions  of crystals being  thus the measures by
which they  are recognised and  compared with one another,  the
instruments by means of which  their measurement  is effected re- 
32
GONIOMETER S.---L I G II T.
quire a few words' notice.  They are called goniometers (yovtoc, an
angle ; uerpo), I measure).   The simplest form consists of a semicir-
cular scale of degrees attached to a pair of blades, which, crossing
each other at the centre, allow of the crystal being adjusted exactly
to their edges,  and then show the value of the angle by the  number
of degrees intercepted  on the  scale between the blades.   For all
purposes requiring accuracy,  the goniometer of Wollaston must be
applied.  In it.  the angle of the  crystal is determined by measuring
the number of  degrees  through which it is necessary to turn  the
crystal in order that two rays of light, reflected successively from
the two surfaces, including the angle, may be in exactly the same
direction.  To  the adoption  of this principle  of measurement we
owe almost all  the great advance that has been lately made in  the
relations of the crystalline forms of bodies to  their chemical and
molecular constitution.
  In all that has formed the subject of the chapter which has now
closed, the forces brought into play, and the effects which were pro-
duced  by means  of their action, were not such as  to  involve  the
principle upon which all purely  chemical phenomena are based,  the
existence of a variety of elements.   The laws of cohesion, from its
simplest  action in a liquid  to its most complex manifestation in a
double oblique  crystal,  might have existed in  nature, and, being
studied, make a part of  science, independent of any consideration
of true chemical force, although serving most usefully for the iden-
tification of chemical substances, and capable of modifying  the cir-
cumstances of their mutual action in an eminent degree.
                        CHAPTER  II.

OF THE PROPERTIES OF LIGHT AS CHARACTERIZING CHEMICAL SUBSTANCES

  I shall not attempt to enter into the details of the history of the
mechanical properties of light, as they constitute one of the most
purely mathematical of the physical sciences, and have but indirectly
a relation to chemical phenomena : a short notice of these properties
is, however, necessary, in order that the means of recognising chem-
ical substances may be fully given.
  Light, emanating from any luminous body, moves in straight lines ;
the smallest portion of it which can be admitted through an aperture
being termed a ray.  When a ray of light falls upon the surface of
a body,  it is either bent back again,  or it passes into the substance
of the body; the bending back is termed reflection, and is regulated
by the law, that  the angles of incidence upon the surface, and of
reflection from it, are  always equal.   It is  thus that  the images are
formed  in a looking-glass ; for we see objects in the direction in
which the ray of light arrives  at the eye,  and hence we judge the
image to be as much behind the mirror as  the object is before it.
  When the ray  of light has passed into the substance of the body, 
PROPERTIES  OF  LIGHT.
33
it may be absorbed, in which case the substance, not sending any light
to the eye, appears completely black, or is, rather, totally invisible,
except by contrast with some other body placed behind it; or the
light may be transmitted, in which case the body is said to be trans-
parent, as the light  may arrive at the eye after passing through the
substance.  Bodies which do not transmit light are said to be opaque ;
but there are two kinds of opacity, that of blackness, where the light
which falls upon the object is totally lost by being absorbed, and that
of whiteness, where the light is reflected, and we can see the object
itself, though we cannot  see anything through it.   Where, in  an
opaque  body, the light is partly reflected to the eye and partly ab-
sorbed, there arises the  diversity of colours which opaque bodies
may possess.
   When the ray of light  is neither totally reflected from the surface
nor lost within the substance of the body, but passes through it, it
is refracted ; that is, its direction  is changed ; and if its path be rep-
resented by a  line, it is broken at the surface of the medium, and
hence the name.   It is thus that an oar, partly immersed  in water,
appears broken at the surface.  Any substance through which light
is moving is termed a medium, and the refraction occurs at the lim-
iting surface of the two media, as air and water, air and glass, though
not to the  same degree as if the light had passed into the most re-
fractive  medium directly  from an empty  space.   This refractive
power is of importance as a characteristic property of bodies, but
to the chemist it is specially of use in the study of crystallized bodies;
and it is hence with reference to  the  principles of the molecular
structure of those  substances  already noticed,  that the refraction
of white light shall be examined.
   This reflection, absorption, or transmission of the luminous rays
which fall upon the surface of a body is, however, in no case abso-
lute and simple.  All bodies reflect some light,  and there  are  none
which allow light to pass through them without its undergoing some
absorption.  In general, light incident upon  a body is divided into
three unequal parts, of which one is reflected, another absorbed, and
the third transmitted, and the nature of the body determines which
action shall be most powerful.
  In uncrystallized bodies, a ray of light, in passing from a  rarer
to a denser medium, is generally bent towards a line perpendicular
to the surface of the medium, and in passing from a denser to a  rarer
medium, the refraction is from the perpendicular.  In this case, the
law of refraction is such that the sines of the angles of incidence
and refraction are to each other in a constant proportion, no matter
how the direction of the incident ray may change, and the number
which expresses this ratio is called the index of refraction.
  The velocity with which  light is transmitted is exceedingly great;
the light of the sun arrives at the earth in eight minutes, being at
the rate of 195,000 miles in a second.  This, however, is but the
mean  velocity of the coloured lights which a solar  ray contains, for
these differ in velocity, those which are least refrangible being trans-
mitted with the greatest quickness.  The velocity of light is changed
when it passes from one substance to another, and it is this change
in which originates refraction.  In general, the denser the medium
                             E 
34
REFRACTION.
the more is the velocity diminished ; and it was by the experimental
proof of this that one of the most triumphant testimonies in favour
of the modulatory theory of light was found.
  The refractive power of a body is not connected with its chemical
constitution in any  positive manner ; but inflammable substances
are o-enerally possessed of high  refractive  powers.  It  was this
which led  Newton to the celebrated  prophecy  that the diamond
should be combustible, and that water should possess an inflammable
constituent; but many bodies of high  refracting  powers are not at
all combustible.
  The refracting power, as measured by the refractive index,
the more remarkable bodies in the following table :
                                   Garnet
                                   Oil of cassia
                                   Plate glass
                                   Oil of turpentine
                                   Water
                                   Chlorine  .
                                   Air  .
                                   Vacuum  .
Realgar .	. 2-549
Octohedrite	. 2 500
Diamond	. 2 439
Nitrate of lead	. 2 322
Phosphorus	. 2 224
Sulphur .	. 2-148
Flint glass, from	. 2 028
to	. 1 830
s given for some of

    . 1 815
    . 1 614
    . 1542
    . 1475
    . 1 336
    . 1-000772
    . 1 000294
    . 1-000000
  In uncrystallized bodies, the molecular arrangement being irreg-
ular and indefinite, the action upon light is the same in every direc-
tion, and hence a ray of light undergoes, when passing from air into
water or glass, simple ordinary refraction ; it is bent out of its path
by an angle which depends upon the angle of incidence, by the law
of the proportionality  of their sines.  In bodies which crystallize
in the regular system, where there are three precisely similar axes,
the molecular constitution, although subjected to definite laws, must
be the same in all directions, and hence a ray of light will be  acted
upon, in such a crystal, in the  same manner, no matter in what di-
rection it may go.  Hence, in crystals of the  regular system,  there
is only ordinary refraction and a single image.
  When a ray of light passes, however, into a crystal of the rhom-
bohedral system,  it is differently acted upon, according to the part
of the crystal it passes through.  If it pass along the principal axis,
it is equally related on all sides to  the crystalline forces, and hence,
as in the crystals  of the regular system, there is only  a  single re-
fracted ray.   But if the light pass  in any other direction, it is divi-
ded into two portions, one of which  is refracted  according to the
ordinary law of the sines, while the other, following a  totally new
law, is termed the extraordinary ray.   The angle which these two
rays make with each other increases  according  as the  path of the
incident ray is farther from the principal axis ; and when the lio-ht
falls perpendicular to the sides of the prism, and hence  to the prin-
cipal axis, the divergence of the two refracted rays is the greatest
possible.  In the square prismatic  system, the same peculiar action
upon light  exists ; when a ray of  light passes along the principal
axis of the crystal, it undergoes simple refraction according to the
ordinary law, but in any other direction the ray is subdivided into
two, of which one is refracted in  the ordinary way, and the  other
follows a new and peculiar law.
  The existence of double refraction, and the change in its amount
according to the  direction in which  the  light passes through the 
DECOMPOSITION  OF  LIGHT.
35
crystal, may easily be observed.   If a  round  dot be  marked with
ink on a sheet of paper, and  a rhomb of calc-spar be laid upon it,
the dot will appear double, and  on moving the  crystal round, one
image will be seen to revolve round the other.  By changing  the
position of the eye, the distance between the two images of the dots
will be found to change ; it will be greatest when the eye is in a line
connecting a solid angle and the centre of the opposite plane;  but
to efface the double image and obtain single refraction, new sur-
faces would require to be cut perpendicular to the principal axis.   In
a natural crystal there are, therefore, always two  images of an object
seen through it.
  In the  remaining three classes of crystals, where  the rhombic octohedron,
whether right or oblique, gives the predominant character to the  forms, the exist-
ence of a molecular constitution, regulated by the same cause as the  external fig-
ure, is displayed in a peculiarly striking manner.  There is no longer  a single line
in the crystal, in which ordinary refraction alone occurs,  but there are two such
lines, or  axes of simple refraction.  These axes, however, do not now coincide
with the principal crystalline axis, as was the case when  there was only one, but
their position is so dependant on  that of the crystalline axes as to show that they
are the resultants of the forces  which emanate from them, and which govern all
the molecular actions of the crystal.  If the ray of light does not pass exactly along
one of these axes, but at some distance from it, it is divided into two rays;  and
of these rays, both follow new and peculiar laws of refraction, the proportionality of
the sines being totally abandoned.  The real distinction of  the crystalline systems
is thus completely proved by the existence of these remarkable optical properties
by which they are characterized ; and so perfect is this distinction, that in cases
where the external  form  and cleavage would lead  us  totally astray, the optical
properties of the body may show us its true crystalline position.  Thus the mineral
boracite (borate of magnesia) crystallizes in cubes, which are remarkable, how-
ever, for an  anomalous replacement of the  opposite solid angles by triangular planes.
When, however, boracite was optically examined, it  was found to possess double
refraction, and to appear cubical  only from the accidental circumstances of its rec-
tangular axes being exactly equal to each  other.
   When a ray of white light, S, P, admitted into  a darkened room
                       .x-;:'--                    is parallel  to  its ori-
                    .<.'.'-•'''                       ginal course, and the
               ../;>/                           ray  continues white ;
              ^'i?                              but  if the surfaces of
the refracting medium be not parallel, if it be a prism, A, B, C, the
ray of white light is  separated into a number  of  rays of light, of
different  colours and  of different refrangibilities,  as atg-; and if  it
has been  derived from the sun, in place of  a round white image, P,
there is formed  a series of solar images of different colours, which,
overlapping each other, produce a  long band, which is termed the
prismatic spectrum, or image of the sun.  The order of colours, the
same as that seen in the rainbow, is, commencing with the rays of
greatest refrangibility, violet,  indigo,  blue, green, yellow, orange,
and  red ; the  length of the  spectrum, and the space  occupied by
each  colour, varying  with the  nature  of  the refracting  body, ac-
cording to what is termed its  dispersive power.  White light is,
therefore, not a  simple, but a highly  complex phenomenon,  cou- 
36                PRISMATIC  COLOURS.

sisting of impressions made  simultaneously  on the  eye by  the
lights of these various colours.   This may be verified by experi-
ments  of very simple performance: if a circular  disk be painted
with the  colours of the spectrum, in segments proportional to the
spaces which each colour occupies in the length of the  spectrum,
and then be made to revolve rapidly on a central axis, the eye loses
the sensation  of the  individual colours, and a uniform grayish-
white tinge is  produced: if we had colours as perfect as those of
pure solar light, their reunion would form pure white, and this ac-
tually may be  produced  by receiving the spectrum on  a lens, by
which all the coloured rays are brought to bear upon a  single point,
the focus, where reproduction of the original white light takes place.
  Herschel  has recently discovered that there exists  in the spec-
trum, beyond  the  limits of the violet rays, other rays of a still
higher refrangibility,  and of a colour which he proposes to term
lavender.  This lavender light cannot be merely a weaker form of
violet light; for, on concentrating it by means of a lens, it remains
still unaltered, and appears to have no tendency to assume a violet
tinge when it becomes more intense.  If this  proposal be adopted,
there are then eight prismatic colours; and although some peculi-
arity of vision, with regard to colours, may cause a difference of
opinion,  yet the evidence  obtained by Herschel of the real exist-
ence of simple lavender-coloured light appears to be  satisfactory.
  Of the seven prismatic colours, there  are four which cannot be
considered as  simple lights, but as being formed by the mixing of
rays of two different colours having the same  refrangibility: these
are orange, green,  indigo,- and violet; the first being  the mixture
of the superposing extremes of the red and yellow, the  second of
the yellow and blue, and the third and fourth  of blue  with red re-
maining  in excess.  There are, in fact, blue, red, and yellow lights
spread over every  portion of the spectrum ; and if they were so in
equal quantities, the  spectrum would be white, and we could not
have any decomposition of light by refraction  ; but, although there
are blue  rays of every degree of refrangibility, yet the larger pro-
portion of them have a refrangibility greater than those of  any
other colour, and they are hence collected nearer the upper extrem-
ity of the spectrum.  A portion of red light is spread also over the
whole surface, but the majority of the red rays, having low refran-
              gibility, are thrown to the opposite  extremity, while
              the great proportion of the yellow rays, having a mean
              refrangibility, occupy the centre.  In every portion of
              the  spectrum there is therefore  mixed, blue, red, yel-
              low, and hence white light ;  but where these simple
              lights prevail, the colours  of  the spectrum  are pro-
              duced,  and where two are present in excess over the
              quantities  which form white light, the secondary col-
              ours, orange, green, indigo, and violet, are formed.
              The intensity of these spectra of simple light in  each
              portion of the prismatic spectrum is represented in
              the figure by the distance of the curved lines, R, Y, B,
              from the ground, M, N.  Where the red rises beyond
the yellow and blue,  the red  space of the  spectrum is produced;
where the  curve of the yellow light prevails, the space is coloured
 
ABSORPTIO N.--N ATURAL  COLOURS OF  BODIES. 37
yellow, and similarly in the  blue ;  at the point where the curves
of the red and yellow meet, the tint is orange ; where the yellow and
blue are equal, the colour produced is green ; and where the red and
blue are both in excess over the intermediate yellow, there  is violet.
  This view of the constitution of  the  solar spectrum, leading to
the remarkable and unexpected consequence that there may be
white light unalterable by the prism, its coloured rays having all the
same degree of refrangibility, was obtained by Brewster, by means
of the absorbing power of coloured  bodies.  If a ray of white light
be incident upon a glass coloured red by suboxide of copper, it is
decomposed in passing through it, the yellow and blue lights being
intercepted or absorbed, and the red rays alone being transmitted.
A glass does not possess this property of absorbing certain kinds
of light,  because  it is  coloured; but it appears  coloured to our vi-
sion, because it acts so upon white light.  The colours so given to
glass are of great importance, from the use which is made of them
for ornamental purposes in the arts; but they  afford also to the
chemist one of the most delicate and most certain means of detect-
ing many metallic substances, thus:

         Cobalt is known by colouring glass blue.
         Nickel     "      "       "       orange.
         Chrome and vanadium     "       green.
         Copper    "      "       "       green or red.
         Iron      "      "       "       yellow or green.
         Manganese        "       "       purple.
         Silver     "      "       "       yellow or orange.
         Gold      "      "       '-'       crimson.

And these are not the only cases in which colours are produced.
   The colours of chemical compounds are  so  varied, that  there
cannot he laid down any principle by which they could be arranged:
thus, lead  forms with other  simple  bodies  compounds which are
brown, or  red, or  yellow, or white; mercury has a still greater
range.  There are, however, certain general facts worth bearino- in
mind, in  which classes of bodies, to a certain extent, are character-
ized by colour :  thus, the ordinary  compounds  of copper  are usu-
ally green  or blue ; those of nickel, green; those of cobalt, T.ul£
or blue ; those of chrome, green or purple.  A singular  property
of certain bodies consists in what is termed dichroism, that is, when
seen by light which has passed in different directions, they appear
of different colours, which are often complementary, or  such  as,
when mixed together, would form white light.  This dichroism oc-
curs only in crystals which refract doubly, and in which the absorp-
tion takes place unequally along the  two refracted rays.
  The colours of natural bodies, seen by transmitted light, depend
thus upon the analysis which they effect of the light incident upon
them, and of which they absorb one portion and transmit  another.
Where the object is seen by reflected light, its colour is generally
different  from that given by transmitted light, for it frequently re-
flects, in considerable quantity, the light which it does not transmit.
Thus, solution of litmus,  when  seen by transmitted light, is of a
rich reddish purple, but, seen by reflected light, of a fine, pure blue.
In general, a portion of the light is  reflected from the second sur- 
38
POLARIZATION OF  LIGHT.
face, tinged like the transmitted  portion, which, mixing with that
properly reflected  at  the  first  surface, modifies its  colour,   lhe
transmitted and reflected lights are sometimes truly complementa-
ry;  thus, sea-water, seen  by reflection, is  of  a fine green, but the
light which it transmits is pink.
   When a ray of light is reflected from any surface at a particular
angle,  which is  for°glass 56- 45',  and for water 535 11',  it acquires
peculiar properties which it had  not previously possessed, and is
said to be  polarized.  If the ray  be then made to fall upon a sec-
ond reflecting surface, the effect  varies according to  the position
of the plane °of  the second  reflected ray.  The reflection, if it be
in the  same plane as the first, is complete ; but if it be at right an-
gles to the first, there is no light reflected : in intermediate positions,
the quantity of light reflected varies according to the angle which
the second makes with the original plane.  Light is thus said to be
polarized by reflection.  In all cases of reflection there  is some of
the light thus modified ; for, although the angles above  mentioned
are those at which alone  the polarization is complete, at  all  other
angles the  light, reflected is partially polarized in a degree, accord-
ing to  its deviation on either side  from the proper angles.
  Polarization may be effected by various other  means, as by re-
fraction  or absorption.  Even in  ordinary refraction  some of the
light transmitted is polarized, but it is mixed with so much ordina-
ry  light that  its properties are  obscured : however, if the  same
quantity of light be refracted often, it may be polarized completely ;
and hence, transmitting a  ray of  ordinary light, at a certain angle,
through  a  pile of parallel glass plates, is  a usual mode of polari-
zing it.  In double refraction, the  polarization  of the refracted light
is perfect, and the two emergent  rays are found to be polarized in
planes  at right angles to each other.   If these proceed together to
the eye, they mix  again, and thus recompose the original ray of
common light; but by contrivances, such as in Nichol's  prism, one
may be turned aside or absorbed, and then the other used. In po-
larizing light  by absorption, the  mineral tourmaline  is generally
used ;  this is  a  doubly refracting  substance, of such a nature that
it absorbs completely one refracted ray and transmits the other.  It
therefore gives  only a  single image of any object, but  this image
is formed by light completely polarized.  If two pieces  of tourma-
line be laid together, and the  direction of their crystalline  axes
be the  same in both, they act similarly upon the light, and, the same
polarized ray being transmitted by both, the brightness  of the im-
age is  almost the same with the two as with only  one ;  but if they
be placed with their crystalline axes at right  angles to  each other,
the ray that is transmitted by the first  is absorbed by the second,
and no light can pass.  If  a ray of light be polarized by reflection
or refraction,  it is  known  that the polarization has been .complete
when the ray  is totally absorbed by a tourmaline, the axis of which
is perpendicular to the plane of polarization of the ray.
  When a ray of light so polarized passes through a doubly refracting substance, it
undergoes double refraction like a beam  of ordinary light, being divided into two
rays, polarized in two new planes at right angles to each other; and when these
two rays are received upon another polarizing instrument, they are each  divided
into two portions, again at right angles, which unite, as  the planes of polarization
coincide two and two, and by their union  produce some of the most  beautiful phe- 
POLARIZED  LIGHT.
39
nomcna in optics ; for as, in the doubly refracting substance through which the ray
has passed, the two portions move with different velocities according to the refract-
ive indices of the body, one issues in advance of the other by a certain distance,
and according to this distance, which depends on the difference between the two
refractive indices  of the body, a series of colours  is produced the most gorgeous
that can be imagined, for every little difference of thickness a different colour is
shown ; with the same thickness the colour passes through all the prismatic tints,
according as the plane of polarization of the ray of light is altered, and thus the ac-
tion  exercised  upon the ray by the doubly refracting substance, shows itself in a
manner equally beautiful and strange.
  The apparatus used, in so employing polarized light to exhibit these properties of
bodies, consists in, first, a means of polarizing the ray, which may be any of those
before described, but which is generally a flat plate of obsidian or blackened glass,
by which a polarized reflected ray is given.   The substance to be examined is sup-
ported upon a frame, in a plane perpendicular to the direction of the ray ; or, if it be
fluid, a glass tube is filled with it, and, being closed by plates of glass with parallel
surfaces, it is so placed that the ray shall pass along the axis of the tube.  The ray,
after emergence, is examined in order to detect the modifications which it has un-
dergone, by an apparatus termed the analyzing piece, which may be, where two
images  are required, a  doubly refracting prism,  or, where  only one, the Nichol's
prism, a doubly refracting prism in which one image is  destroyed ;  a tourmaline
might also he used, but the brown or olive colour which tourmalines possess would
deprive the phenomenon to be observed of much of the interest it derives from the
beautiful display of colours.
   In nothing is the action of polarized light so  interesting as in the evidence which
                                 it  gives of the internal constitution of crystals
                                 of the different systems  that have been descri-
                                 bed ; for the  real difference of molecular ar-
                                 rangement  in crystals  belonging to these various
                                 systems, is rendered still more remarkably dis-
                                  tinct by  the action which they exercise  upon
                                  light in this peculiar state of plane polarization.
                                  If a ray of polarized light pass along the princi-
                                  pal axis  of a crystal  belonging to the rhombo-
                                  hedral or to the  square  prismatic system, and
                                  on issuing be examined  by means of an analy-
                                  zing plate,  the axis of the crystal is seen to be
                                  surrounded by a  series  of beautifully rainbow-
                                 coloured rings, the centre being occupied either
                                 by a cross which  is alternately black and white,
                                 according as  the analyzing plate  revolves, as
with calc spar, fig. a, or a circular space which is occupied successively by a series
of colours similar to those which form the rings, as in quartz.
   If the crystal belong  to any of the more complex systems, and its optical axes
                               be not much inclined  to one another, there will
                               be seen, on transmitting a  ray of polarized  light
                               along the   crystalline
                               axis intermediate to the    r   ^7°^,
                               two,  a double system      j£~—'-^-----^s.
                               of rings, which, uniting,    & => _.__L_lfe"%.
                               form  a  very beautiful   if  i?----HL ^%-  %
                               curved figure,  such as  ff ff ff ."_     ^\ \\
                               is represented  in figure  ff g ff        ^ ~%_ \ \
                               b, which is the phenom- ff if ff ff ^^ vs % \\  U
                             ■ enon as seen  with  ni- 3 ff  // s eft H !i \\  a
                              tre.    The  curves  are jj f| if jf ff |  g §  ||  II |
                              crossed by  two bands,
                              black or white, accord-
                              ing  as the  analyzing
                              plate   revolves,   but
                              which, when the crys-
                              tal is turned round  on
                              its principal  axis, open
                              out,  revolving each on
                              its axis, A or B, and
.:=■


^ ^
�79850635�7322 
40       OPTICAL  PROPERTIES  OF CRYSTALS.
1.  Regular system.
2.  Rhombohedral system
3.  Square prismatic system
4.  Right prismatic system
5.  Oblique prismatic system  .    .  >
6.  Doubly oblique prismatic system j
 bend with the convexity towards the centre of the figure.   In substances, as topaa
 and carbonate  of soda, where the axes make a  large angle with each other, the
 complete  system  of rings cannot be at once seen,  and only one half, or the portion
 round one axis,  as in the case of topaz in figure c, is visible  in one  direction.
 The angle of the axes in topaz is 18° 30', but in other cases it may be much greater;
 thus with green sulphate of iron they are at right  angles with each other.
  The physical production of these beautiful phenomena involves optical principles
 too recondite to be here introduced.   It is, for the purposes of the chemist, sufficient
 to say that they arise  from  the mutual action of the two rays, which are  produced
 by the double refraction of the crystal;  and hence, if there be not double refraction,
 there can be no colours produced. With crystals of the regular system there  ia
 consequently no such  result, and hence such crystals are recognised by the com
 plete  absence of coloured rings.
  The optical properties of the different  systems of crystallization may be thus
 summed up.
                                  Single refraction.  No rings by polarized light
                                 ) Double refraction ( Simple system of rings b)
                                 >    with one axis.  \   polarized light.

                                 f Double refraction j Double system of rings by
                                     with two axes, J   polarized light.

  When crystals form in a crowded or confused manner, it frequently happens that
 not merely are their surfaces modified in a complicated way, but  that several crys-
 tals become soldered  together so completely as to simulate a single form which
 does not belong to the substance of which  the crystal is composed.  These crystals
 are called macles,  or twin or hemitrope crystals.  Some bodies have  a remarkable
 tendency to crystallize in this way ; thus,  sulphate of potash had been long consid-
 ered as crystallizing in six-sided prisms, terminated by six-sided pyramids; and
 such crystals of it occur with almost exactly the proportions of the rhombohedral
system ; but by optical examination, this figure was found to be composed of three
or six of  the true crystals,  which are right  rhombic  prisms of the fourth system.
These being laid together, form, by their angles exactly joining, a six-sided prism;
                          but when tested by polarized light, they show, in place
                          of the system of rings which a true crystal should pro-
                          duce, the tesselated structure of the figure.   In many
                          cases, the agglutination of the crystals is less complete,
                          and irregular figures,  with the sides channelled by the
                          imperfect joints, are  found.   A substance which  il-
                          lustrates remarkably this  tendency to the macled form
                          is the mineral analcime, which is termed also  cubizite,
                          from its forms belonging most perfectly, so far as  ex-
                          ternal characters go, to  the regular system.  It  has,
                          however,  no  distinct cleavage  planes, and  refracts
        When examined by a ray of polarized light, the cube of analcime gives a
                              most beautiful appearance.   The diagonals of each
                              surface become occupied by lines, which are alter-
                              nately black and white, according as  the analyzer
                              is made to revolve, and in  the intervening triangu-
                              lar spaces the richest colours of the  rainbow suc-
                              ceed  one  another, according to  the  optical laws.
                              This crystal  is therefore made up of a great number
                              of other  crystals  belonging to some one of  the
                              more complex systems ; but its structure is so ex-
                              traordinary, that the determination of the  form  of
                              its real  crystal  has been  as yet impossible    In
                              this instance, and in that of boracite alrea .y  no-
                              ticed, the optical properties have  been the means
 of showing the true nature of bodies which, from their  external form  should oth
 erwise have been  ranked among those which crystallize in the forms of the res-ular
 system.                                                                 s
  It has been noticed  as a  general character of the crystals of the rhombohedral
 and square  prismatic  systems, that by  the  analysis of a beam of polarized liffht
 transmitted along the principal axis, there is  seen a system of coloured rinsis trav
 ersed by a cross,  alternately black and white, as the  analyzing plate  revolves  but
doubly.
 
ROTATIVE  POWER   OF  LIQUIDS.            41
farther, that in the case of quartz the cross is not produced, the central space being
occupied in succession by all the prismatic  colours.   Even in quartz there have
been found two modifications of this property; with one, the analyzing plate must
be turned from right to left, to obtain  the  spectral colours from red to violet:  but
with the other, the rotation must be in the opposite direction, to show them  in  the
same order.  The molecules of the quartz cause these colours to  appear along the
axis by turning the plane of polarization of each colour round in a different degree,
and thus opening out into a Ian shape those combined lights, which had previously
affected the eye only as white or  black.  This faculty does not depend  upon  the
manner of arrangement of the particles of the quartz ;' it involves  the chemical na
tare of the molecules;  and, although some observations appeared to connect it with
the crystalline structure, it is now fully established to be independent of it.  In
fact, this property of circular polarization, as it is termed, belongs to certain bodies,
independent of their arrangement, and even in many cases accompanies them when
they enter into combination.  It is even found in liquids, particularly the volatile
oils; and when oil of  turpentine is converted into vapour, its  molecules  preserve
unaffected their rotative power.  Its existence  is, however, subjected to remarka-
ble anomalies ;  thus, when oil of turpentine combines with muriatic acid and forms
artificial camphor, it retains its power of rotation ; but when the artificial  camphor
is  decomposed and the oil of turpentine got back again, its power of changing the
plane of polarization of the ray of light has totally disappeared.
   [These phenomena  of  circular polarization may be  readily  traced.  If from a
crystal of quartz a disk is cut transversely, a  system  of rings will be seen enclosing
a circular coloured space.  If the disk be turned round, no change takes place ;  but
if the analyzing plate turns, the colour passes through a series of tints, which, after
100° of rotation, may end in a sombre violet.   If, now, we cut from the same crys-
tal another disk twice the thickness of the former, and make use of it, we shall find
the tint different from  what it last  was; but, by turning the analyzing plate 100°,
we may bring it back again  to  the same sombre violet: with a plate three times
as thick, we should have to turn 100° still farther to produce the same tint, and for
each additional thickness  an additional 100°.   We therefore infer that, when polar-
ized light passes along the axis of  a crystal of quartz, its planes of polarization ro-
tate circularly, or, rather, spirally, in the crystal; and this takes place in some spe-
cimens from right to left, and in others from left to right.   Under these circum-
stances,  light is said to undergo  circular polarization.]
   In cases, therefore, where bodies exhibit this  action  upon light, their power of
rotation becomes an important numerical fact in their descriptions, and it may be
measured by the angle through which a certain thickness of the body is capable of
moving the plane of polarization of a  ray of homogeneous light,  such as  the pure
red given by glass coloured  by sub-oxide of copper.   It may also be  expressed,
when white light is used, by the  angle at which  the pure violet is produced, and the
direction of rotation is  expressed by an arrow turned either to the right or left, ac-
cording as it is necessary to make the analyzing crystal revolve to the one or  the
other side.  Thus, the rotative power of oil  of turpentine, contained in a tube six
inches  long, is for red light 45°<—«s, and  of oil of lemons,  in  the same length,
8-1° ata—>-.  The rotative power of quartz is  about 085 times greater than that of
oil of turpentine.   This property is  beautifully applied  to trace the changes which
occur during the saccharine  fermentation: a solution  of starch  possesses a  high
a»—> power; but it gradually changes into the sugar of grapes, the rotative power
of which is -*.—■*.   Hence the  action of the starch, when fermentation has com-
menced, rapidly diminishes, until there is so much sugar formed that the s=&—> and
<—«& exactly balance, and the  solution is totally without action upon a polarized
ray ; after that, the quantity of sugar  still increasing, the rotation becomes <—eg,
and  increases until all the starch  has been  decomposed.   With such a  solution,
knowing the total quantity of starch originally dissolved, the measure of its rotative
power enables the quantity of sugar present to be at once calculated.  The juices of
plants which contain sugar, as the beet-root, the maple,  the sugar-cane, may be ex-
mtl\ valued by a simple determination of  their rotative power compared with their
specific gravities.   This property of the circular polarization of a ray of light, which
at  I he  first aspect might appear  so  far  removed from proper chemical inquiry
or useful application, becomes thus an  instrument from which the distiller or sugar-
boiler may every day derive advantage; and when we come to discuss the means
by which  we endeavour to learn the  internal constitution of bodies produced by
chemical affinity, we shall find that the  light which ordinary polarization throws upon 
*2
WAVE  THEORY  OF  LIGHT.
the internal mechanical structure of the crystal is not more brilliant than^that which
we obtain of the arrangement of the chemical constituents by their circularly po-

^Som^s^clmens of quartz appear destitute of this rotativ*, power■: thf.purple
auart? an ethvst is severally so, and gives with polarized light the ordinary black
SS2 ' BufE JSSSw of quartz" are related to their crystalline arrangement.
Thus, in those specimens which possess rotative power, the solid ang es of he pyr-
amid (A, page 28) are generally replaced by planes which are unequally inclined to
the axes ;  and where these planes are present, the direction of the rota ion can be
foretold, it being to the  right or to the left,  according as these asymmetrical faces
are inclined.  Such crystals are termed plagihedral; as in the cases where no such
faces can be traced, the rotative power is generally absent, and this arises, as is re-
markably evident in amethyst, from the crystal being formed of separate crystals
rolled up together; and as these may possess opposite rotations, and so neutralize
each other, the action on light should be like that of calcareous spar,  which has no
rotative power.  Such crystals are truly macles; and hence the circular polarization
may show a still more intimate crystalline  arrangement than could be detected by
light in its ordinary polarized condition.
  With such an example, it was not difficult to conclude that the power of rotation
depended on the crystalline arrangement, particularly as quartz, in all its uncrys-
tallized conditions, is devoid of all rotative power; and, accordingly, until the dis-
covery of the power of rotation  in liquids, and that this property was found to ac-
company the molecules of the body through all states  of aggregation, it was con-
sidered to have its origin in the mechanical  structure of the body ; but we must now
invert the argument, and infer that the difference  of rotative power in right-handed
and left-handed quartz does not result from  the difference of crystalline arrangement,
but that this last is caused by actual difference of properties in the molecules them-
selves, of which the most remarkable is detected by the opposite actions upon light.
   The impression of light was at one time considered to be produ-
ced by a series of  exceedingly  minute particles, of a peculiar sub-
stance, emanating from the sun and  from burning or luminous bodies,
and which strike upon the  eye.   This idea has  been, however, now
almost totally abandoned, and all the phenomena are considered to
arise  from the  vibrations  of an exceedingly attenuated  medium,
thrown into waves by luminous bodies of every kind, and which, fill-
ing all space, and being diffused through the substance  of the most
solid bodies, and occupying the spaces between their more  substan-
tial molecules, transmits and modifies these  vibrations, and confers
upon substances transparency or opacity,  colour, and all other proper-
ties of acting upon light which they may possess.
   This medium, or luminiferous ether, as it is termed, is supposed
capable  of vibrating in waves of  different lengths, and from  this
difference in length of wave arises the  difference in colour of the
light produced.  The shortest wave produces  violet, the most re-
frangible light; the longest wave, red, the least refrangible light:
the length of the wave being in all cases inversely proportional to
the refrangibility of the light.   The impression of the different col-
ours arises, therefore, precisely as the impression of different sounds
is produced,  by a difference in the length of the waves in the vibra-
ting air; the shortest wave, in  sound,  giving the highest note  and
in light giving the  violet colour   The actual length of these waves
of light is extremely small:  for violet light there are 57-490 in an
inch;  for red, 39-180; the average  of the different colours  being
50-000; and hence, in white light, there acts upon the eve  in  every
gecond 610-000000-000000 luminiferous vibrations.
   In the case of doubly refracting crystals  with one axis  that is
those belonging to the rhombohedral and the square prismatic sys« 
WAVE  THEORY  OF LIGHT.
43
tern, the  elasticity of the ether is supposed to be  so far modified
by the arrangement of the molecules of  the body, that the velocity
of propagation of the waves is more rapid in one direction than  in
another at right angles to it, and hence there are two refracted rays.
In the three systems, the crystals of which have double refraction
with two axes, the elasticity of the ether is supposed to be differ-
ent in each of three perpendicular  directions, and hence  neither
refracted ray can follow the  ordinary law.  It is thus, as has been
already stated, that the  classification  of all crystallized bodies  in
these systems is  shown, not to be an arbitrary assumption, but a
principle based upon  our most decisive  evidence of molecular ar
rangement.
  The rays  of light derive some of  their most remarkable proper
ties from  the principle that  the  vibrations are accomplished  in a
direction perpendicular to the direction  of the rays.  Thus, if we
conceive a  ray of light  moving  from north to south, the little vi-
brations which constitute it are effected in a direction east or west,
and in every other direction  equally perpendicular  to its path; and
ordinary light is  characterized by the fact that  its vibrations are
accomplished in  every imaginable plane.  If we reduce these vi-
bratory movements to a single plane,  the light becomes polarized,
and is then  in the condition  for dissecting the interior  of crystal-
lized  bodies, and exhibiting the beautiful  illustrations of their struc-
ture that have been already noticed.   But it would lead us too far
away from our proper subject to enter into the description of polar-
izing apparatus, or even  of its principles, in detail, as the indication
just given of its nature is sufficient.
   Perhaps the most remarkable and the most important principle
of the theory of waves  is, that two  portions of light  may act on
each  other so as  to  interfere and produce darkness, though at an-
other point they may form  light of double brilliancy.   To effect
this, it is only necessary they should be  in opposite states of vibra-
tion, that is, while the waves of  one ray should be rising up, those
of the other should be falling down: these motions then compen-
sate each other, and the  result is the same as if no vibratory mo-
tion had existed, that is, as if no light had arrived at the points
where the rays met.  It is only, however, when  one of the simple
coloured lights is employed, that actual blackness occurs by the
mutual destruction of the rays : if white  light be used, there is pro-
duced a  brilliant  series  of prismatic  colours; for  at the moment
when the red light is destroyed, the remaining blue  and yellow form
a bright green ; when the yellow is destroyed, the red and blue pro-
duce  a purple.  Cases of this  kind  of interference are extremely
common: it is thus that the coloured  rings of crystals, and the
colours of the soap-bubble or oil-film are produced.   The brilliancy
of the plumage of birds,  the lustre of many minerals, as  of labrado-
rite, arise from the interference of the portions of light which after
reflection thus act on each other.
   Under ordinary circumstances, l'ght  is always  associated with
heat; the sun, the source of warmth to the surface of  our globe,
being also the natural origin of light: and in most cases where light
is artificially produced, it is associated with heat, which is also ca- 
44
PHOSPHORESCENCE.
pable of being transmitted in a radiant form.  It was, indeed, once
considered,  that  at  certain temperatures heat became  converted
into light, and that the colour of the light depended on the degree
of heat; a body, when first  rendered luminous by being heated,
emitting a dull red light, which gradually becomes brighter as the
temperature rises, until at  the  highest  degree of heat the light
emitted is pure white,  and similar  in  constitution  to the solar ray.
The powers of emitting heat and  o( emitting  light are, however,
although so frequently associated,  quite  independent and distinct;
and the rays of heat and those of light may be perfectly separated
from each other.  It would anticipate too much the account of radi-
ant heat to describe  the means of  separating the heating from the
luminous qualities of ordinary light; but elsewhere they will  be
described in full.  A body may become  luminous  when very mod-
erately  heated, as is the case with many minerals, as fluor spar
Light may be produced also by the friction of bodies, as by rubbing
two  pieces of sugar briskly together, or by striking together two
pieces of quartz; and in these cases it is difficult to assign its true
origin, as, possibly, a minute trace of the substance may be very
intensely heated.  There  are also many bodies which, when  ex-
posed to the light of the sun after having been made  red hot, ap-
pear to absorb a portion of it, and become  capable of emitting it
slowly,  giving a pale bluish light for some time  afterward in the
dark.  This occurs particularly with chloride of barium, native sul-
phate of barytes, carbonate of lime, and a great number of other
bodies.   Such substances are said to be phosphorescent.  Thus fluor
spar is rendered  so by heat, sugar and quartz become so by friction,
and the electric  spark is capable of conferring the phosphorescent
property on a great variety of bodies.
  Organized substances become phosphorescent in the first  stages
of their decay;  thus, rotten wood, and fish  before actual putrefac-
tion  has commenced.  The light emitted is, in such cases, the re-
sult of an exceedingly  slow but distinct process of combustion ; it
requires the presence of atmospheric air, or oxygen,  although  an
exceedingly small quantity may  suffice, and it is extinguished and
revived by all such means as facilitate or retard the chemical ac-
tion of the air upon organic bodies.  The light emitted by the glow-
worm and the fireflies, as well as by the great variety of marine
zoophytes, appears also to be not merely an evolution  of light as a
product of vital  action, but to arise similarly from the secretion of
a substance, which, slowly combining with  the oxyo-en  of the  at
mosphere, produces the light  as  a consequence of  combustion
Animal  phosphorescence is, therefore, to be ascribed to chemical
action.
  The white light, derived from different sources,  does not always
possess the  same physical constitution.  If  the coloured spectrum
produced by the solar ray be closely examined,  it will be  found
crossed by a multitude of black  lines, indicating the total absence
in the sun's light of rays of certain refrangibilities.   That this is
inherent in  the  light is shown  by the fact, that when we chano-e
the nature of the prism, the position  of  the space in  which these
black lines occur may alter, but the lines preserve  all their relative 
         CHEMICAL  RAYS  IN  THE  SPECTRLM.       45

 distances from each other totally unchanged.  Hence,  in place of
 referring to the colours of the spectrum in order to characterize its
 properties, those lines, of which the most remarkable is a double line
 situated in the yellow  space, are  used as marks.  The light of the
 sun, of the  moon  and planets, as well as white light produced by
 our  processes of combustion, all consist of the same elements of
 yellow, red, and blue, and all are distinguished by the same set of
 lines.  In the light of some of the fixed stars the  same lines are
 found, as is the case with Pollux; but in the spectrum formed by
 rays from Sirius  or from Castor, this double line does  not occur,
 but is replaced by one broad line in  the yellow space, and two re
 markable dark lines in the blue.   It  is very curious, that if we ex-
 amine  the spectrum through certain coloured media, as the vapours
 of iodine or bromine,  we find additional black lines, and  by using
 gaseous nitrous acid  these  become almost  innumerable,  and in-
 crease so much when the  gas is heated that the spectrum  is oblit-
 erated  and the gas becomes  opaque.   It  is  possible that  such
 takes place at the  origin of the light of the heavenly bodies, and
 that the sun and the fixed  stars are involved  in absorbing atmo-
 spheres, which allow only certain rays to pass, and that hence there
 may exist in nature kinds of light from which the eye of man is
 screened forever by means of such an impervious veil.
  Some  classes of chemical  substances are,  to  a certain extent,
 characterized by the facility with  which they are decomposed when
 under the influence of  light.  The salts of silver, of gold, of plati-
 na, and, in some instances, of mercury, are subject to this influence.
 A great variety of vegetable and  animal bodies undergo important
 changes in their constitution by the action of the  solar rays, the
 development of certain colours requiring the agency of light, and
 the majority of colours being destroyed when its action is too great:
 hence the fading of dyes arises.  The power of light thus to mod-
 ify the  affinity by  which chemical combination  is produced, has
 been found to be exercised  specially by the violet or more refran-
 gible extremity of the  spectrum,  and even with great intensity by
 invisible rays quite outside  of the luminous  space, and extending
beyond the lavender-coloured prismatic space of Herschel.  It has
been also considered that the rays of the red extremity of the spec-
trum possessed chemical properties of an inverse kind, and that the
 decomposition produced by violet light might be counteracted, and
the  elements brought to recombine  by the red rays.  This is not
certain.  All that has been established is, that there exist in solar
light, and probably in all light derived from sources of combustion,
three distinct sets of rays, the one of proper light, which produces
only luminous effects,  the second of radiant  heat, the nature of
which will be specially examined  in the  following chapter, and the
third of rays which, though neither luminous nor heating, exercise
an influence on chemical affinity, and the nature of which will be
 discussed with more detail when the subject of chemical  affinity
 and its relations to the  other physical forces has been described. 
46
EFFECTS OF HEAT.
                        CHAPTER III.

   OF HEAT CONSIDERED AS CHARACTERIZING CHEMICAL SUBSTANCES.

  At almost  every step of chemical inquiry it is  necessary to in-
troduce the action of heat, either  as modifying the  results of the
chemical action of bodies upon each other, or as affording charac-
ters by which the substances we operate upon may be distinguished.
The  doctrine of heat and the history of its effects have consequent-
ly, at all periods, formed an important portion of the studies of the
chemist; and it is, indeed, only lately, since the brilliant course ot
discoveries that was opened, and so  successfully prosecuted by
Melloni and by Forbes, has identified the theories of heat and light,
that  this subject has been contemplated in its proper aspect as  a
physical science, and its application and influence in chemistry have
ceased to be considered as making up the science, properly so call-
ed, of heat.
  Of all the physical sciences, however, that of Heat, or Thermotic.3,
as it is now termed, is the  most important to the chemist  in guiding
him in his operations, and in the accurate description of their results
On this account it will be necessary to describe the properties of heal
more in detail than those  of any other of the physical agents, ami
to illustrate these properties by more numerous references  to cases
in which their utility in chemistry is apparent.
  The effects of heat, by  which, according to their degrees, bodies
may  be characterized, are,
   1st. Change of volume  for a given change of temperature.  Es*
pansion.
  2d. Quantity of heat required to produce a given change of tem-
perature.  Specific heat.
  3d. Temperature necessary for liquefaction.   Melting points.
  4th. Temperature  necessary for giving a certain elasticity to *
vapour.  Boiling points.
  5th. Quantity of heat required to produce a given change of ag-
gregation.  Latent heat of liquids and vapours.
  6th. Manner and rapidity of communicating or receiving  he<3i.
Conduction and radiation of heat.
  The subject  of  heat  will therefore  be studied specially under
these heads; and  it will be necessary to introduce  an account of
our  mode of measuring heat and  temperature by  the thermometer
and pyrometer, and to add some observations on the  physical rela-
tions of heat and light,  and on the physical theory of heat.

                          SECTION I.

                         OF EXPANSION.

   When describing the effects of  cohesion, I have already noticed
 that the molecular constitution  of all bodies might be considered 
REPULSIVE  POWER  OF  HEAT.
47
to depend on the relative power of the attractive force, cohesion,
and the repulsive  force of heat, upon their particles.   That where
the attraction was in excess, the molecules were knitted  firmly to-
gether to form a solid body; but that where repulsion was most pow-
erful, all cohesion was lost, and the body assumed the form of a va-
pour or a gas.   In the intermediate  condition, where the forces ap-
peared to  be nearly in  equilibrium, the liquid state was produced,
in which the molecules of the body appeared still to unite by a trace
of remaining  cohesion, but that  they  moved  among  one  another
with perfect ease, and the  slightest external force might disarrange
them entirely.   Now the change from one to the other of any two
of these conditions is not quite  abrupt.  If a cold  body be gradu-
ally heated until it shall begin to liquefy, its particles do not remawi
in the same condition up  to the moment when they separate so far
as to change their state of aggregation; on the contrary, from the
instant that the substance becomes warm, the change begins; the
molecules of the  body gradually separate, occupy  more space than
before, and from  the very commencement of the increase of heat,
the body, though it may  remain  solid, yet expands.   In  the same
manner, if a liquid be  heated, the change of  aggregation does not
commence until the  increase  of heat has reached a certain degree ;
but from the beginning a change of volume occurs, the increase of
which marks the  gradual diminution of cohesion.   In  gases there
can  take place no farther change of form,  and the only effect which
heat can produce  upon them is expansion.
  This power of repulsion which we suppose heat to exercise, in causing the tran-
sition from one state of aggregation to another,  as well as the  expansion which oc-
curs without change  of form, may become directly evident to the senses, at least
in a partial way, in many cases.  Thus, many powders, if sprinkled on a  warm
capsule, or, still better, on a silver plate, are thrown into violent motion, and dissi-
pated by the mutual repulsion of their particles, independent of any currents of air
which might affect them.  When  liquids,  particularly alcohol and the oils,  are
brought to boil, the drops which are mechanically thrown up out of the liquid do
not mix with it on falling back, but roll about on the surface, and appear to repel
each  other, and to he repelled  by the hot glass of the vessel  in a  remarkable  de-
gree.  If a brass poker, strongly heated, he allowed to rest against a cold iron bar,
or, still better, if a rounded bar of brass be made very hot and laid upon a flat block
of lead, the surface of the cold  metal becoming heated, repels the warmer brass,
which instantly falls down again, by its weight overcoming the repulsion, when the
metal cools.  When the brass again touches the metal or lead, the latter is again
heated at  the point of contact, and  again there is  repulsion succeeded by a new
contact, and these repeated motions throw the bar of brass into a state of tremulous
agitation, which being conveyed to the ear by the intervening air, gives a remark-
ably distinct and agreeable musical tone.  The  better conductor, the heated body,
and the worse conductor (provided both are metals), the cold body can be, the more
successful is the result.
  This force of repulsion is made still more distinct, and even measurable,  by an
experiment devised by Powell.   When a flat and a convex glass plate are strongly
pressed together, they still do not touch, but are separated by an exceedingly thin
space, by the action of light on which there are produced coloured rings, like those
seen on the surface of a soap-bubble, or in a film of oil floating upon water.  Each
colour belongs to a distinct and measurable thickness of this space ;  and when such
an apparatus  is gradually heated, the rings  close in towards  the centre, showing
that the glass plates recede from one another, and the degree  of repulsion may ba
determined from the narrowing which occurs in  the breadth of any particular col-
oured ring, according as the temperature rises.
  In gases,  the expanding effect of heat is unaffected by any dis-
turbing cause ; there is no cohesion remaining to impede  its oper- 
48
MEASURE  OF  HEAT.
ation;  hence a certain increase of heat affects all gases alike; and
no matter how hot or how cold a gas may be, a certain increase of
heat produces the same increase of volume in every case.  In sol-
ids and in liquids, however, it is different;  the expansion which  oc-
curs is but the result  of the opposing forces of cohesion and of
heat, and hence the amount of expansion  depends not  only on the
quantity of heat which is  applied, but also on the power of cohe-
sion  by which it is resisted, and which depends upon the  nature of
the body.  Consequently,  every fluid and every solid expands in a
degree which is peculiar to it.  There is yet another consequence
of °the  influence of cohesion upon the expansion of solids and of
liquids.  Let us represent the cohesive force of a certain substance,
for example, copper, by 10, and let us suppose that we apply to it a
quantity of heat which will expand it through a space which  we
will  call  1, and will diminish its  cohesion from 10 to 9.   If, then,
we apply another quantity of heat  exactly equal to the former, it
will  not have to contend  against a cohesion of 10, but  of 9, and
will, consequently, be able to produce an  expansion of more than
1, say  U, and it will reduce the cohesion more  than it did before,
as from 9 to 7£.   If, then, another equal quantity of heat be added,
it having still less opposing force to overcome, will act still more
powerfully, reducing, for example, the  cohesion from 7|  to 5, and
the increase of volume becoming, in place of 1\, 2.  In solids and
liquids, the rate of expansion increases thus, with the temperature,
from the diminution of cohesion; but in gases, where the cohesion
remains the same, or, rather, is completely absent, the expansion is
proportional to the additional quantity of heat, no matter how much
may  have been sensibly present in the gas before.
  I shall now proceed to consider in detail the rates of expansion
of various bodies, commencing with those of gases, for which the
simplest results have been obtained.  Before doing so, however, it
is necessary to study the means by which we ascertain the quanti-
ties  of heat which we add or subtract from bodies to effect their
expansion or contraction; to investigate,  in fact, the principle on
which  the thermometer and pyrometer are founded, and such  de-
tails  of their construction as shall hereafter be  found necessary to
be known.
  Let abbe a glass bulb with a long and narrow neck, which is divided
^H
i  i  IT i 1 M  I  I  I
by a scale, as in the figure, of which each division is a certain part, as
ToVt of the volume of the bulb.  Let us suppose the bulb a to be fill-
ed with pure dry air, at the same degree of heat as that at which ice
melts, and separated completely from the external air by  means of
a globule of mercury,  c, which is exactly settled at the commence.
ment of the scale.  If, now, the instrument be warmed, the  air in
the bulb expands, and, according as it increases in volume, pushes
before it into the tube the  globule of mercury.  This last serves
therefore, as an index  of the increase of volume which the air gains
as it is heated, and by its position we can read off the exact propor- 
              NATURE  OF  TEMPERATURE.            49

 lion.  If the source of heat be water boiling, under ordinary cir-
 cumstances, at Dublin, at  the level of the sea, as soon as the air
 has been heated to exactly the same degree as the water, the glob-
 ule will be found to have arrived at the 365th division on the scale.
 Therefore, 1000 measures of air, on being heated from the  degree
 of melting ice to that of boiling water, become 1365.   Now as, from
 the  constitution of air and gases, the  effect of each increase of
 heat is the same, we may consider the whole quantity of heat which
 it received from the boiling water to be divided into 365 parts or
 degrees, and  each of  these parts beipg applied separately to the
 bulb, should have increased the volume of air by TJ„ 7  Part> or should
 have converted the 1000 volumes into 1001.   There  is thus  obtain-
 ed a scale of expansion which  is quite artificial and arbitrary cer-
 tainly, but which,  having been once contrived, may be with perfect
 accuracy applied to measure different quantities of heat.  Thus, if
 we warm water to blood heat, and immerse in it the  air bulb as de-
 scribed, the expansion of the air will move the globule of mercury
 to the  degree  122, which is almost exactly the one third part of
 the  365, and hence the water, in being heated from the degree of
 melting ice to that of blood heat, received almost exactly one third
 of the quantity of  heat which should have made it boil, and its tem-
 perature is one third as high.
   I  have  here spoken of measuring  the  successive quantities of
 heat which the air received, and in this case the manner of expres-
 sion is sufficiently accurate, as well as the most simple.  But it is
 necessary to explain the true meaning of the words quantity of heat
 and temperature.   The amount of expansion which a hot body is
 capable of producing  in the air or mercury  of the  thermometer,
 measures truly what is called its temperature.   The temperature has
 nothing whatsoever to do with the quantity of heat which the body
 may contain, it refers  only to its  expanding power.   If a quantity
 of water,  of oil, of ether, of mercury,  or  of iron produce all the
 same amount of expansion in the air or mercury of the thermometer,
 we say they have the same temperature, without pretending to know
 anything of the  quantity of heat which they may actually possess.
 The thermometer  and pyrometer are  therefore  instruments  for
 measuring, not heat, but temperature, and we denote by degrees of tem-
 perature the amount of expansion produced, marked off on any arbi-
 trary scale which we may think  proper to  adopt.
   Cases expanding more than any other bodies, the  air thermom-
 eter is the most sensible that can be  made, and in  the form  just
 described  it is an exact measure of heat,  subject only to  one  cor-
 rection, which is, that  although  the air, in being heated from the
 degree of melting ice  to that of  boiling  water, actually  expands
 .jPjsj_ of its volume,  yet that expansion is not all visible, for the glass
 bulb expands also on being heated, although in a very small propor-
tion, and holds — „■$ more than it did when cold ; the  visible expan-
 sion on the scale is therefore only 363 degrees, and this  must be
allowed for to have complete accuracy.  The form of the  air ther-
mometer which has been just described is, however, quite  unfit for
ordinary use ; the  adjustment of the index globule,  the necessity
that the instrument should be perfectly horizontal, which is quite
                              G 
50                AIR  THERMOMETER.
therefore  be  accurately

confined, the simple rule
impossible in the majority  of practical cases, renders this kind of
an air thermometer too unmanageable ; and since the air changes its
volume very much for  every change of pressure, and our atmo-
sphere varies in its weight almost every hour, an air thermometer
left open, as at the orifice b, would change continually without ref-
erence to the degrees of heat at all, and would thus give false in-
dications.  The  °end of  the  tube must
closed.
  When, however, the air  inside is thus
of the dilatation being proportional to  the increase of heat, ceas-
es completely.   For if  the point b be closed, and the bulb a be
heated, the  globule of mercury,  in moving along the  scale, con-
denses the air  before it, and thus generates an elastic force, by
which the expansion is resisted and diminished in amount; the de-
grees  would therefore be no longer equal, but rapidly diminish in
size, so that on the upper parts of the scale they could not be dis-
tinguished from  one another, and would hence be useless.  But by
having a second bulb, in the  next figures, the elasticity of the air
 •ompressed in the cold bulb increases  much less  rapidly, and the
scale to be applied to the stem connecting the bulbs is easily con-
structed.  As the stems of these air thermometers are generally
upright, mercury would be too heavy a fluid to introduce in a column,
and the mere globule which we supposed in the example first taken
would not answer, from the facility with which it might be broken
or displaced: to any watery or spirituous fluid there is also an ob-
jection, that the amount of expansion would be  increased  to an
uncertain degree by the portion of fluid converted into vapour.  To
avoid these errors, oil of vitriol  may best be employed, and it is
generally coloured,  red to  render  the motion of the fluid column
more easily visible.
  An air thermometer, closed perfectly, indicates a change of tem-
uerature only by the difference between the elasticity of the air in
                the two bulbs.   No matter how high or how low
                the temperature may be, if it affects both bulbs to
                the same  degree, the air in  each bulb presses on
                the liquid  column with  the same force, and exactly
                balances  the  other.   The
                instrument indicates, there-
                fore, such  temperatures only
                as  affect  one bulb and not
                the other; the difference, in
                fact, between the tempera-
                tures of the two  bulbs, and
                hence is properly called the
                differential thermometer.   In
fig. A the one bulb is much above the other.
In fig. B the stem which terminates above in
a bulb is open  below, and plunges into the
fluid which the  inferior bulb contains.   This
lower bulb is soldered or cemented at its or-
ifice round the  tube, so  as perfectly to pre-
vent the action of the air.  Fig  C represents
 
MERCURIAL  THERMOMETER.
51
the most ordinary form ; the bulbs are on a level, and are connected
by a U-shaped stem.
  The air thermometer is thus, in all its forms, liable to so many in-
conveniences from the limited range of its scale, if it be not open
to the air, and from the complex  form which the scale assumes if
the external air be  prevented from communication, that  it is never
made use  of in practice  except  in  some particular  cases,  which
shall  hereafter be specially noticed.   We  are therefore  obliged to
have  recourse,  for  our accurate measures  of temperature, to other
bodies, which, though not so sensible as air, offer more practical
advantages.
  The liquids which are generally used to measure, by their expan-
sion,  change of temperature, are alcohol and mercury.   The former,
in being raised from the melting point of ice to that at which itself
boils, expands rflTl, whereas air within the same limits would have
expanded ^/y, being about three and a half times as much as alco-
hol:  and mercury, in having its temperature raised from the melt-
ing point  of ice to the  boiling point of  water, expands T^f „, or
about 2V °f the quantity of air.   Hence these liquids  are much  less
sensible, as thermometers, than air; but their other advantages are
decidedly in their favour.  Alcohol  is  only employed  where  the
object is to measure very great degrees  of cold; and for this pur-
pose  it is admirably fitted, as it is the only liquid that  has not  yet
been frozen.   Mercury, on the other  hand, may be  applied to an
extensive range of temperatures, as it freezes only by the applica-
tion of an  intense cold ;  and it does not boil  until it  arrives nearly
at a red heat.  It has  the largest interval between its freezing  and
boiling points of any liquid that is known.  Mercury is also admi-
rably suited to be a measure of heat, by the accidental circumstance
that  its expansion, when contained in a glass  bulb,  is  accurately
proportional to the temperature, and its  indications therefore abso-
lutely true.
  This is occasioned by the circumstance that, as in all liquids and solids the ex-
pansion increases with the temperature, the rate of increase of the capacity of the
glass bulb exactly corresponds to the increase of the rate of expansion of the  mer-
cury, and absorbs it; so that the visible expansion of the mercury is uniform, and a
degree in every  part of the scale is of the same length.  For instance, if mercury
and air be together heated from the freezing to  the boiling point of water, 1000
measures  of air become 1 365, and 10 000 measures of mercury become 10180.
If, then, they be both heated as much more, the  air, expanding at the same  rate,
becomes 1730; but  the mercury, expanding more  rapidly, becomes 10 363: and
hence, if a scale was so applied, there would be shown 180 degrees  in the lower,
and 183 degrees in the upper part of the scale, to the same  quantity of heat.   This
is corrected by the expansion of the glass bulb which holds the mercury.  At the
temperature of melting ice, the bulb holds,  for example, 10 000 measures  of  mer-
cury ;  but, on being heated to that of boiling water, it holds  10026.  The mercury,
however, having become 10 180, the  difference, (10 180—10 026)=154 measures,
passes into the stem, and makes the  rise of temperature upon the scale.  When,
now, the second portion of heat is applied, the mercury becomes  10 363; and the
glass bulb, expanding at the same time, becomes  able to hold 10055: and hence
the difference, (10363—10 055)=308 measures, passes into the  stem and moves
along the scale.  Thus the visible portion of the expansion is rendered exactly pro-
portional to the  increase of heat; and the  mercurial thermometer becomes, not
merely the most convenient, but the most accurate measure of heat  which we
possess.
  In constructing a thermometer, the first requisite is, that the bore of the  tube
shall be perfectly uniform, for otherwise the result  above described, which gives all 
52            OP   THE  STANDARD  INTERVAL.
 its real value  to the quicksilver thermometer, would be completely inapplicable rfl
 practice.  This is ascertained by finding that a small quantity of mercury, moved up
 and down the  tube, occupies exactly the same length in every part.  A proper tube
 having  been thus  obtained, one extremity is closed, and a bulb is blown upon  it;
 another is formed  near the open end, leaving a space between the two bulbs some-
 what longer than the thermometer is intended to be.  The tube and bulbs having
 been heated, are allowed to cool, with the open end immersed in pure and recently-
 boiled mercury.  By the contraction of the internal, and the pressure of the exter-
 nal air, a quantity  of mercury is forced into  the first bulb, and ultimately the bulh
 at the closed end is filled completely by a repetition of the process.  When the in-
 troduction of  the mercury has been completed, the open end of the tube is  closed
 by a little sealing-wax, to prevent the admission of air or dust, and the tube is al-
 lowed  to cool  with the terminal bulb down.   When it has cooled completely, it is
 again heated to the highest degree it is intended to indicate ; and the fine flame of
 a blowpipe being directed upon  the point which is to be the extremity of the tube,
 it  is melted, and the orifice completely closed.  When the instrument then cools,
 there remains  over the mercury in the stem a perfectly empty space.
   It remains, then,  to attach the scale.  When describing the general principle of
 the thermometer, in the example of dry air, pushing, by its  expansion, an index
 globule of mercury along the stem, the  scale which included the interval from the
 freezing to the boiling points of water was supposed to be divided into 365 parts.
 This was, however, merely because the  1000 measures  of air,  in  being heated
 through that interval, expand in that proportion.  The scales that are actually used
 are different, although quite as  arbitrary.  The simplest scale is  that in which the
 interval between the freezing and boiling points of water, which is universally ta-
ken as the standard, is divided into  100 parts ; it is termed the centigrade scale,
 and is employed in France, and  generally in Germany and the north of Europe.  In
 it ice is said to melt at 0°,  and water to boil at 100°.  On the scale generally used
in  this country and Great Britain, the standard interval is divided into  180 degrees,
but the melting point of ice is not taken as 0°, but as 32°, from a very absurd idea of
 Fahrenheit, who was the inventor of this scale.  He mixed together snow and salt,
and having thus produced a more intense cold than anybody before him had done,
he imagined that he had attained  a point at which the bodies had no heat  at all,
that he had arrived at what was afterward called the absolute zero, and he called
that point 0° ; the  melting point of ice was then 32°, and water boiling  at 180°
higher, its temperature was marked 212°.  There is another scale, sometimes, but
not often  used; that of Reaumur, in which  the melting point of ice is the com-
mencement or 0°. and the boiling point  of water is marked 80°.  The first step in
the graduation is to mark the extreme points of the standard interval : the  melting
point of ice, and the boiling point of water.  To do this correctly, some precautions
must be taken.  I have frequently spoken of the melting point of ice and the freez-
ing point of water as meaning  the same temperature, and under ordinary  circum-
stances they do  so ; but they do not so necessarily.  The freezing of water is a
crystallization, and, like all other cases of crystallization, mavtake place with  great-
er or less facility.  If water be  agitated, or if it be contained in rough  vessels af-
fording prominences to which the crystals of ice may attach themselves it freezes
exactly at 32°  on Fahrenheit's scale ; hut if the water be kept carefully at rest and
be contained in smooth glass vessels, free from dust, it maybe easily cooled to25°
 and has been cooled even to 15°. without becoming solid.   Hence  if we wished to
determine the  zero by means of freezing water, an error might easily be committed
 Ice, however, under all circumstances, melts at 32°; and hence, by plunein* the hulh
 of the thermometer into a mixture of ice and water, and marking on the~stem  thp
point at which the  level of the mercury settles, the first fixed point upon the scale is
had. To determine the second point, that at which water boils, it is necessarv to at
tend to the condition of the barometer.  It will be hereafter described how the boil"
 mg point  of every liquid  varies with the atmospheric pressure; it is here  rnniUh
 to notice, that either the boiling point must be determined when the harnmPtPr
 stands at 29 8  inches, or a correction, which will be hereafter given  aoolied ft r »™
 difference of height which  may  exist.  The water must boil alsoin ametalhc ves
 sel for water  m a glass or porcelain vessel has its boiling point somewhat raised"
 and as the thermometer is  to be used  for chemical purposes, the bulb !„HnnfS,
 small portion of the stem should be immersed in the boiling water   Thp ITi A
 points having  been thus obtained, the interval is to be divided into 180 tnZ\ ™rtl
 or degrees for the ordinary  scale of Fahrenheit, and then 32 of theT,Lavlll
 counted downward from the point of melting ice to obtain the zero • for the zero 
THERMOMETRIC  SCALES.
53
 Crt..in he truly got in the manner in which Fahrenheit is supposed originally to
 have invented it, for a mixture of snow and salt is found to produce always a cold
 of about 2°  below zero, or —2°.  As our range of temperature passes far below
 the zero of the scale, we  count downward precisely as we count  upward, only
 prefixing in the former case the — minus sign, whereas,  in the degrees above zero,
 the -j- plus sign is usually omitted.  Thus, -j-50°, or simply 50°, is fifty degrees
 above zero, but —50° is  the same  number below zero.   To construct the centi
 grade scale, the method  is precisely the same, except that we make the point of
 melting ice 0°, and that  of boiling water 100°, and a degree being the -Ag of the
 interval, we count up and down from zero, precisely as in the other case.
  It is generally proper to lay a thermometer aside for a few weeks after having
 filled it before proceeding to apply the scale.  For it is found that as there is a vac-
 uum in the instrument above the mercury, the external pressure acting on the thin
 glass of the bulb gradually changes its form a little, and would move up the fixed
 points, sometimes through one or two degrees, if they had been marked before the
 change.
  The centigrade scale is of such extensive use in the works of most distinguished
 chemists, that it  is well to  show more closely its relation to the ordinary scale of
 Fahrenheit, and the means of reducing one to the other.  The standard interval is
 divided into 180° Fahrenheit, and into 100 centigrade degrees, and hence a degree
 of the former is equal  to }g£, or gths of a centigrade degree.  To reduce any inter-
 val in centigrade degrees to Fahrenheit's, it is therefore to  be multiplied by 9 and
 divided by 5 ; and for the reduction from Fahrenheit to  centigrade, the number is
 to be multiplied by 5  and divided by 9 : but as the degrees  do not in number start
 from the same point, the  Fahrenheit scale  being already 32° when the centigrade
 begins, it is necessary to add 32° to the number of Fahrenheit degrees which have
 been attained by calculation from the centigrade, and to subtract 32° from the num-
 ber of degrees on Fahrenheit, which are to be converted  into degrees  upon the oth-
 er scale.
  Thus, to reduce 167° of Fahrenheit, we proceed :
                        167—32=135. and 135 X £=75°,
 -liu find it to correspond to 75° centigrade.  And to reduce  65° centigrade to Fah-
 renheit's scale, we say,
                     65 X £=117, and 117+32=149°,
 sorrcsponding, therefore,  to 149° of Fahrenheit.
  Reaumur's scale being to the centigrade scale as 4 to 5, similar reductions are
 made to and from it, by using £ in place of £, as has been employed in the example.
   The range  of temperatures observable with a mercurial thermom-
 eter on Fahrenheit's scale  is from —39^ to +630'.   The mercury
 freezes a little below—40° ; and though it does not boil  until  it ar-
 rives at 660\  yet  the quantity of vapour  which it forms  when very
 near its boiling point,  prevents its  indications from being quite ex-
 act between that point and 630°.
  Our means  of estimating  temperatures above the boiling point
 of  mercury are  not  at all  so perfect  as those that have been de-
 scribed for the lower degrees of heat.   Mercury,  when  boiling, is
 not in the  slightest degree luminous, but the temperature at which
 a heated body becomes visible in the  dark, by emitting a dull red
 light,  is not much higher.  Numerous instruments have been in-
 vented  for  the purpose   of determining  the  higher temperatures,
 particularly of furnaces,  and  hence  they have been called pyrome-
 ters.   Of these,  the only one  which appears  to  give  accurate re-
 sults, and hence  deserves description, is that of  Daniell.
  In this pyrometer, the change of temperature is shown by the excess of the ex-
pansion of an iron bar over the expansion of a black-lead case in which it  is en-
closed.   The iron rod a is somewhat shoiler than the black-lead-ware case, and a
plug of earthenware, l>, which fits tight in the case, abuts against the iron rod in-
side, and projects as at c in the  figure.   Let us suppose the length of the case to be
6 inches, that of the iron rod 4J- inches, and that of the earthenware  plug to be 1
inch.  If the whole be heated until the case shall have expanded by  12 parts, the
iron rod will have increased in length by 44, and the earthenware piece by 7, which, 
54
DANIEL L'S  PYROMETER.
added to 44, makes 51.  If the black-lead case did not increase m size, all these
51 parts should project; but as there is additional room made for 12, the project-
ing portion is only 39.  If the parts of the apparatus were all free to move, eacn
contracting again on cooling, the result would be that all would be restored to their
original position ;  but this is not the case.  The bar of iron, in  expanding, pushes
out before it the plug of earthenware, which, however, is held so tight  in the case
that it cannot go back again when the apparatus has become cold.   The protrusion
of the earthenware plug is therefore a permanent index of the greatest amount of
expansion that had been produced while the instrument was exposed to heat.  1 his
expansion is, however, very small. The three pieces being, as stated, 5, 41,  and 1
inch, the expansion, when  heated from 32° to 212°, is  only T^ of an inch; and as
this indicates  180 degrees, the expansion for  a  degree is only about TCT o  °f j"1
inch.  It is therefore necessary to magnify this expansion, in order that the indi:
cation maybe read off;  and this is done by means of a graduated circular arch, d e
f, with a movable index, kept by means of a spring constantly at 0° when undis-
turbed.  On fitting this scale to the pyrometric  black-lead case, after it has been
in the fire, the projection of the earthenware plug, c, catches in the prolonged heel
of the index, e, and moving it round, the point of the index travels over a portion
of the graduated scale, and  indicates the  number of degrees through  which  the
temperature had  been raised.  This  instrument is not  always made of the same
size, and hence the absolute amount of expansion may vary, which, however, is re-
duced to the same proportion on the scale, by which, also, the increase in the rat«
of expansion of the metallic bar at very high  temperatures must be allowed  for.
By means of this very ingenious and useful instrument, Professor  Daniell has de-
termined the melting point of most of the important metals, and also several other
temperatui es at which remarkable phenomena occur.
   The p  rometers of Wedgewood, of Guyton,  and  many  others
that have been proposed, must be  considered as now  totally aban-
doned, and  do not require notice.
   The most delicate, and perhaps the most important, measure of
heat that  has been contrived, is  one totally independent of  expan-
sion, and  founded on the measurement of an electric current which
a change of temperature produces under certain circumstances.   It
is the Thermo-multiplier invented  by Nobili.   The principle which
the instrument involves in its construction  and its form will be  de-
scribed under the  head of electricity,  and the remarkable  results
obtained  by means of  it,  and which  have completely remodelled 
TABLE  OF  TEMPERATURES.
55
our ideas of the physical  constitution of heat,  will be noticed in
another place.
  It may be of interest to subjoin the temperatures on Fahrenheit's
scale  at which some of the most remarkable effects of heat  are
produced
             The greatest cold that has been produced.
             The solid compound of  alcohol and carbonic acid
                 melts.
             Greatest cold by ordinary freezing  mixtures.
             Temperature of the planetary spaces.
             Greatest cold observed in the arctic regions,
             Sulphuric ether congeals.
             Nitric acid congeals.
             Mercury congeals.
             Oil of vitriol  freezes.
        14°.  Oil of turpentine freezes.
        20°.  Wine freezes.
             Blood  freezes.
             Ice melts.
             Olive oil freezes.
             Heat of human blood.
             Phosphorus melts.
             Alcohol boils.
             Rose's metal melts.
             Newton's metal melts.
             Water boils.
             Sulphur melts.
       662°.  Mercury boils.
       810\  Antimony melts.
       980°.  Red heat.
      114-1°.  Heat of a common fire.
      1869°.  Brass melts.
      18733.  Silver  melts.
      1996°.  Copper melts.
             Gold melts.
             Cast iron melts.
  The details which have been given, regarding the construction of the air ther-
n> »meter, will show sufficiently the principle upon which the determination of the
n«.e of expansion of gaseous bodies has been effected.  The exact amount of dileu
U ion was first ascertained by Dalton and Gay Lussac nearly at the same time.
TJ.e apparatus of Gay Lussac consisted of a tin vessel, A, having five apertures.
                           v
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
135°.
121°.

 91°.
 58°.
 60°.
 473.
 45°.
 39°.
  1°.
 25°
 32°
 36°
 98°
108^
174°
201°
211°
2l2n
218°
2200°.
2786°.
Dy means of the aperture in the side, o', there is introduced the tube with the bulb, 
56
EXPANSION   OF  AIR.
g g>, containing air dried by the tube h h', and arranged with the ^uated scale and
index globule of mercury m, as described in page 48  By the opposite oritice ,, is
fixed a thermometer, h s, the bulb b of which is on the  »mp^J^i0;
the air tube.  By means of the central orifice in the top, a ^"i;^™^^*'
is introduced, the bulb of which is situated exactly in.the centre of' thebo*  The
other orifices in the top are for the free escape of steam. ^Jhe apparatus so being
arranged, water, rendered ice-cold by some snow or ice floating on it^.s introduced
until the thermometers and the  air bulbs are covered to he depth of a couple of
inches, and the index globule of mercury is thus brought to the ze ro  fthe scale.
The box is then placed on a furnace, B, and gradually heated   the i isc of  temper-
ature is indicated by the thermometer, /, the expansion by the motion of the index
globule! and at each degree the  thermometer and air bulb may be compared to-
gether until the water is brought  to boil.
  By substituting other substances for water, such as oil, or a bath of fusible metal,
the rate of expansion may  be determined for still higher temperatures, and has been
thus ascertained by Dulong and Petit up to the boiling point of mercury.
  From such experiments, conducted by Dalton, Gay Lussac, and Dulong, it result-
ed  that 1000 volumes of air, when heated from 32° to 212°, became 1375, and that
the change was in proportion for  higher or lower temperatures.   The numbers ac-
tually obtained may be stated as in the following table :
Temperature on a Mercurial Ther-mometer by Fah-renheit's Scale.	10000 Volumes of Air at U" become	Expansion for one Dep-ee on F. Scale in Farts of the Vol-ume at 32°.
— 33 -r- 32 212 300 387 473 559 660	8650 10000 13750 15576 17389 19189 20976 23125	2077 20 83 2070 2082 2084 2083 20 90
  The mean of these results gives the expansion for one degree at 2081, or almost
exactly Tfg- of the volume at 32°, which result had been adopted universally, with-
out any suspicion of its being imperfect.  Circumstances having, however, induced
Rudberg to submit the subject to an accurate reinvestigation,  conducted with ex-
ceeding care and attention, particularly to the state of dryness of the air employed,
he has found that the amount of expansion assigned by Gay Lussac and Dalton ia
somewhat too great, and  that a volume of air,  in being heated from 32° to 212°,
expands from 1000 volumes to 1365.
  The method which he employed was almost exactly the inverse of that of Gay
Lussac.   Having dried with great care the air  in a glass bulb,  the tube of which
was drawn to a fine point, like that described, page 14, for taking the specific gravity
of vapours, he heated it for a long time in a vessel of boiling water, taking care
that all parts of the bulb and tube were equally heated, and then, being completely
certain that  all the  air had attained  the maximum temperature, he sealed, by the
blowpipe, the minute orifice, and thus had the bulb  containing air in the expanded
state.  The vessel being then removed  to a trough of mercury, the orifice of the
tube  was placed deep below the surface, and carefully opened ; a quantity of ice
was  then  laid upon  the globe, and being supplied as fast as it melted, the whole
was  thus left for some hours until the  temperature was well established at 32°,
and all the mercury which would rise into the globe by the  contraction of the air
by cooling, had entered.   The height of the mercury was  then noticed, and the
height of the barometer, and the corrections  necessary for its  positive amount  or
for any change which occurred during the experiment, allowed for, as already 'de-
scribed.   The volume of the  mercury which  had entered into the globe was then
ascertained, and the volume of the globe itself also determined ;  and by a compar-
ison of these, corrected for the expansion of the glass, and for any variation in the
boiling point  from 212°, the rate of expansion and its amount were calculated
   From very numerous experiments,  Rudberg inferred that, in beimr
heated from 32°  to 212°, 1000 volumes  of air became between  1364
and  1366-4 j  we  may consider  1365, which  is between  the two as 
CORRECTION  FOR CHANGE  OP  TEMPERATURE.  57
being- absolutely the  most  correct, and hence that for  each degree
1000 volumes expand ff|=2-028, or ^£3  of its volume at 32 .
  In all operations upon gaseous mixtures, the  rate of expansion
of air comes into play ; for  as all gases expand alike, and the vapours,
even of these bodies which are  least volatile, as camphor and cor-
rosive  sublimate,  expand,  while in  the  elastic form,  precisely as
gases do, their volumes are corrected for temperature and pressure
in the  same manner.  In determining the  specific gravity of a va-
pour, it is also usual to reduce it to the same standard as  those of
gases, that is, air  at  32°, even where the substance is of such a na-
ture as  that at 32° it may not produce any  sensible vapour at all.
In doing so, it is assumed that the vapour should, in  cooling to 32°,
follow the same law as common air ; and hence an error, even though
very slight, in the rate  of  expansion of air, might  lead to incorrect
results in  many cases.
  The application of such corrections follows very simply from what has been de-
scribed.  If there be a certain quantity, as 155 cubic inches of hydrogen gas at 142°
Fahrenheit,  and we wish to know the volume there should be when cooled to 32°,
we say that, as 142° is 110° above 32°, the 155 cubic inches  are equal to the vol-
ume at 32°, and in addition to ]^| of it;  that being the quantity by which it is ex-
panded from 32° to 142°. Therefore, denoting the volume at 32J by the letter V,
there is the  equation :
                    .__   v .  v110   Tr  493X155  loftc
                    155=V4-V A—, or V=----,--- =129 5 :
                          ^ 493      493-4-110
129 5 cubic  inches are therefore  the volume at 32°.
  If, on the other hand, we  have a gas at a low temperature, and we wish to as-
certain what its volume should  be at 32°, it is evident that the  mode is the same,
except  that, in place of subtracting the amount of expansion, we add it to the origi-
nal volume.  Thus, if the 155 cubic inches of hydrogen had been at 6° Fahrenheit,
then the equation should have been 32°—6° being 26.
           26        155 X 493
155=V—V-~-, or V=-—|-—--  = 168-3 cubic inches in exact numbers.
          493       493—26
  It frequently happens that it is necessary to reduce a gas at one temperature to
Its volume at another,  neither of which being 32'', it would require two different sums
to be worked by the above process.   But it may be effected as follows by a single
calculation.
  The volumes at the two temperatures are to one another in the  same propor-
tion as  the standard volume, 493, increased by the amount of expansion proper to
the temperatures.  Thus, at  the  temperatures of 75° and 42°, the standard volume,
which is 493°, at 32° becomes respectively 536 and  503.  Now  any volume of
gas, when heated from 42° to 75°, or cooled from 75° to 42°, changes its volume
in these proportions ;  and hence, if we have, for example, 127 cubic inches of a gas
at 75°,  and we wish to calculate its  volume when at the temperature of 42°, we
Kay, calling the unknown volume V :

               V : 127 : : 503 : 536, and V=127X—=119-2.
                                           536
  The formulae for these  corrections  may be very simply written in a general form.
thus, to reduce a volume to 32°, denoting the temperature on Fahrenheit's scale
by t; by V, the volume of gas which we have  measured at that  temperature ; and
by V'i, the volume at :32°, the formula is :
                          y______493. V
                            I~493±"<7:=32°)'
And to  reduce, without reference to 32° ; denoting the known  volume by V, and
the unknown by Vi; the temperature  of V by t, and that of V, by tu  there is found :
               V,=493± (f,-32)       _y493± (7,-32)
               V   493 ±. (*—32)'     '   493 q= (t—32)'
  Air  which  has been heated  becomes, from  its great increase in
volume, specifically much  lighter  than cold air,  in which  it there-
fore ascends with  a  velocity due  to  the difference  between their
                                  11 
58
EXPANSION  OF  LIQUIDS.
  specific gravities.  It is thus that over  every lamp or candle there
  may be felt a current of  heated air ascending from the flame 5 that
  the heavy dark smoke rises in its heated form from the chimneys of
  our houses ; and that, in crowded apartments or theatres, the upper
  portion of the space will be occupied by oppressively hot air, while
  that near the floor will be quite cool.  By the ascent of the heated
  air from our furnaces and fireplaces, there is generated the draught
  which gives the supply of air necessary for continued burning ; and
  as the intensity of the combustion  and consequent  heat produced
  depends on the  rapidity of draught, the hot  air is kept from being
  cooled by mixing with the cold external  air, by being collected  in
 the chimney, where it obtains an ascensional power corresponding
 to its height, and by which we are  enabled to regulate with accu-
 racy the temperature which shall be produced.   On this ascensional
 power of heated air is founded also the construction of the fire or
 Montgolfier balloon, a bag of hot air, rising in the surrounding colder
 atmosphere, precisely  as  a light flask, filled with oil  or alcohol,
 would  ascend if let loose at the bottom of a vessel full of water.
   It  has been already noticed that  liquids do not, in expanding,
 follow any simple proportion, such as that which exists for gaseous
 bodies, but that  each fluid has a peculiar dilatability of its own, and
 that the rate of expansion varies with the temperature, being greater
 in the  higher portion of the thermometric scale than in the lower.
 Liquids expand much  less than gases, but much more than solids j
 for, as is particularly instanced in the thermometer, the visible ex-
 pansion of a fluid is, in most cases, only the excess of its expansion
 over the expansion of the solid vessel in which it may be contained.
  To measure the amount of expansion  in liquids, they may be introduced into
 graduated thermometer tubes ; and then, when exposed to the same degree of heat
 they will indicate temperatures proportional to their expansibilities.  Thus alcohol
 rising more into the stem than water, and water more than mercury, will stand at
 different marks on the stem, although the temperature be really the same.  It may
 however, be more easily and more accurately done by means of the apparatus in
  r     ----------Tf--------s.  the figures,  a d b is a glass tube, the neck of
 ff b ^                     '**  which is very narrow, and bent as in either fig-
                              ure.   This tube is to be filled completelv at th«
 lowest temperature, with the liquid, whose expansion is to be examined and then
  ^—I^----"-----.-.-.-.:; c  weighed, the weight  of the tube itself being  previously
 ^LLO^i   r—±s ^nown, and the quantity of liquid which it contains is thus
 filr^^Pl   K^lii determmed-  The tube is to be then placed upright in a
    '    ill !il   1 frlf ^linder of water or oil *. ^ which  heat may be applied
    ■    i I  I    PsJ   7 a furnace below 5 and lhe liquid  expanding according
 1  -a  i ! ill   \W  aS ltS temPerature >s raised, the  excess of volume flows
 IM   ! Ill H    I'W   Put at the caPlllai7 teak c, and may be collected as in d or
 i  i   inilUH    W   'et to waste.  When the apparatus has been brought to the
 IP i   !       II rl   g  f ten?Pfature required, and all farther expansion has
    !   i        J °  ceased, as is known by no more liquid passing out at c, the
 1IU—-j- JI f^t Vp*, tube is to be removed from the bath, carefully cleaned and
 .miL — JH1^^> when again cool, accurately weighed.  The loss of Weight
       a  -.k .u    v. . 1S    q,uantlty of lim,id that had been expelled, and this
compared with the whole original quantity of liquid,  gives the  proportion of eW
sion.  In this manner, however, the result appears to be less than it real v STl
the expansion of the glass tube itself diminishes the quantity of liquid exielleH
Such results require, therefore, to be corrected for the expansion of the ilasT whS
is, however, so small, that in the more dilatable  liquids it may be ne&  ?
mercury, however, it affects the apparent expansion very much  : mercury eZ,li„!
in glass through 180°, augments in volume only A, while its real expans'ont "g
heJ is" SfounS to r^11 °f difftrent ***** *" PM8ing thr0Ugh 18»° of Fahren! 
EXPANSION   OF  LIQUIDS.
59
Alcohol   .  .  .
Nitric acid  .  .
Fixed oils   .   .
Sulphuric ether .
Oil of turpentine
Sulphuric acid  .
Water  .  .  .  .
Mercury  .  .  .
14
 1
T7
 1
2?

53
  The actual amount of expansion, independent of the expansion of the containing
vessel, is best observed by the apparatus used by Dulong and Petit.  It consists of
                                     a glass tube a b c, bent in the form of a
                                     U, of which the horizontal portion c is nar-
                                     row, but the  vertical legs pretty  wide.
                                     When mercury is poured into the tube, it
                                     stands  at the  same height  in both legs if
                                     the  temperature be the same ; but one leg
                                     being immersed in a vessel of oil or water
                               -,w   '.by which heat can  be applied to it, and
                               ') \   thereby the mercury in it caused to expand,
                                   "' the  height of the  liquid column  must in-
crease in order to balance the colder column of mercury in the proportion of the
augmented volume.   The difference between the heights being read off, by means of
an accurate scale, with a telescope o, the amount of absolute expansion may be ea-
sily calculated from it.
  By means of this instrument Dulong and Petit determined the rate at which the
expansion of mercury increases with the temperature, as has been noticed generally
in the description of the thermometer.  Their result was, that between 32  and 212°,
measured on the air thermometer, the expansion is j^.^. From 212° to 392°, it is
yj.Lj ; and from  392° to 572°, it is ^.th,-. The consequence is, that, measured by
its bwn  expansion, mercury boils at 680° Fahrenheit; but  from the expansion of
the glass of an ordinary thermometer  bulb,  it boils at 660° on the visible scale,
which coincides almost exactly with 662°, the  temperature given by the dilatation
of air.   The apparent expansion of mercury in glass  is therefore  taken  as being
uniform for 180°. ^, of its volume.
  Considerable simplicity is given to the laws of dilatation of liquids by an observa-
tion of (Jay Lussac, that, in order to obtain any common rule  for them, such as ia
found for gaseous bodies, we must examine them when in the same molecular con-
dition ; that is to say, the cohesive powers of the liquids we employ must be brought
into the same state.   This is most  nearly done by taking these liquids when heat-
ed to their boiling points, for then the cohesion of each  liquid is about to cease alto-
gether.  Thus alcohol boils at 173°, water at 212°, sulphuret of carbon at 134°, and
sulphuric ether at 96 3° ; and, taking 1000 volumes of each at  their boiling  points,
and allowing them to cool,  they contract as follows :
By cooling through	Water conlracti	Alcohol cod tracts	Sulphuret of Carbon contracts	Eiher contracts
18°	661	1143	1201	16 17
36°	13 15	24 34	23-80	31 83
54°	18-85	3474	35 06	46 42
72°	24 10	4568	45-77	58 77
90°	28 56	56 02	5628	7201
108°	32-42	6596	6621	
  We by this means find a very interesting relation between  alcohol and  sul-
phuret of carbon, two fluids remarkably different in their specific  gravities, and in
their chemical constitution and properties.  It appears that their molecular force
must increase at the same rate; for in cooling the same number of degrees below
their boiling points, they contract to exactly the same amount: and a still farther
connexion is exhibited between their molecular  conditions by the remarkable fact
that, in being converted into vapour, the  augmentation of volume which they un-
dergo is the same.
  Many liquids possess the  property of  contracting,  by  reduction
of temperature, only  to a certain  point;  below which, if the  cool-
ing be  continued, they expand.   As the volume at this temperature
is the  least possible,  it  is  called the point of maximum density.
This peculiarity was first recognised in water; but it has since been 
60
EXPANSION  OF  SOLIDS.
found in many other fluids, even in a still more remarkable degree
It is, however, in water that the phenomenon is of most importance.
in consequence of the extensive  agency of that fluid in natural °P"
erations.  The point of maximum density of water has been deter-
mined by the experiments of very many persons to be 39.5^ of 1-ah-
renheit.  When  water below  that temperature  is heated, it  con-
tracts 3 when heated above it, it expands:  when cooled from above
it, it contracts;  when cooled below it, it  expands : and when the
experiment is made in glass vessels, the contraction of the glass has
 ne effect of rendering  the expansion  of cooling below, or  of heat-
ing above, through the same number of degrees, exactly equal.  Thus
100-000 volumes of water become 100-012 equally by being cooled
from 39-5 to 32°, or by being heated from 39-5 to 4GJ, and the spe-
cific gravity of water at 46J and  at 32" is consequently the same.
  A great deal of the permanence of the  existing order of nature
depends  upon this property of water: it is by means of it that the
great mass of water in our lakes and rivers is preserved from being
converted into  solid ice.  When, by the  cooling process of the
winds,  the water has been all reduced to the temperature of 39-5°,
the surface acts as a screen to prevent the farther loss of heat, and
thus retains the  deeper portions at a temperature sufficiently high
for the existence of its organized inhabitants ; for, by the continued
action  of the cold wind, the superficial water being cooled below
39-5°, it  becomes lighter, and floats upon the heavier and  warmer
water underneath ; and from the  bad conducting power which water
will be hereafter demonstrated to possess, the loss of heat is effect-
ually prevented.   If it were not for this property of water, all large
collections of it in lakes and rivers  would, with few exceptions,
be permanently frozen.
  The  dilatation  of solids is much  inferior in  amount to  that of
liquids, and as with these, the  rate of dilatation is not uniform, but
increases with the temperature.   The increase  is, however, so ex-
ceedingly minute, that in almost all  cases it may be neglected, and
hence need not occupy much attention.  The dilatation of solids,
although so small,  may yet be demonstrated to be  real by many
simple experiments.  Thus, if an iron rod be made to fit, when cold,
in length and breadth, an exact scale, it will be found, when  heated,
to be too large to enter  it.  An iron ring, which is, when cold, too
small to pass over a cylinder,  becomes  sufficiently large on being
heated; and if the cylinder could have passed through when  cold,
its diameter becomes too great to allow its passage when  its tem-
perature  is raised.   In the arts, the expansion of solids, particularly
of the metals, in this way becomes the source of numerous incon-
veniences, and of many useful applications.  Thus, the iron rim of
a carriage wheel is secured by the power of its own contraction,
it having been slipped upon the wooden frame while in a hot and ex-
panded state.  The force of contraction of iron bars in cooling has
been applied successfully to restore to the proper position buildings
which had been about to fall, and the rate of expansion has  also, as
in the pyrometers  of Daniell and others, served as a  useful meas-
ure of high temperatures;  on  the other hand, by the  alternate ex-
pansions and contractions, under the  successive influence  of win- 
EXPANSION  OF  SOLIDS.
61
ters and summers, of the metallic bars which had imprudently been
laid in the  masonry of some important public buildings, with the
idea of giving additional security, the courses of stone or brick
have been loosened from one another, and reconstruction rendered
necessary, in order to prevent their being gradually pulled to pieces.
  In estimating the amount of expansion of a solid body, the great*
difficulty is the  accurate  measurement of the small  increase  in
length which takes place.  For this purpose, a great variety of me-
chanical arrangements have been constructed.  As they are all in
principle the  same, and the detailed description of any exact form
would occupy too  much space, it will be sufficient to notice one,
which, though not that  by which very accurate  numbers may be
obtained, is calculated to give a very  satisfactory idea of their gen-
                                            eral construction: a
                                            b is the bar of which
                                            the expansion is  to
                                            be determined;  it is
                                            fastened securely at
                                            the extremity a, and
                                            rests at 6 in a groove
                                            along which it is free
                                            to  move, as in the
                                            figure.   This end of
                                            the bar  at b presses
                                            against a rod c, which
                                            is a lever of the sec-
                                            ond order, very near
                                            the fulcrum, and this
                                            transfers its  motion
                                            to the end of the lev-
er, increased in the proportion of the  distance.   This lever acts on
another similar one, d, the extremity of  which serves  as an index
on the graduated circular arc e, by which the amount of expansion
is red off.  Thus, if the acting lengths  of the arms of the levers
are respectively  1  and 20,  and the end  of  the  bar o  at i moves
ToVo °f an  inch,  the end of the index d will move on  the scale e
        20 x 20   4
through -"i"nnA-==in °f an inch, a space capable of being divided

by a microscope  and vernier into 200 measurable spaces, so that an
expansion of the  two hundred thousandth of an inch can be accu-
rately determined.   For  a popular illustration, the source of heat
may be lamps,  as in the figure; but for accurate experiments, the
bar is completely immersed in a bath of oil or water, and the tem-
perature ascertained by a suitable arrangement of thermometers.
  The most important results thus obtained are the following. The temperature
being raised from 32° to 212°,  the increase in length of a bar of
   Glass varies from . .  . -p^r        Steel.......-A^
             to .--  -  -jVrnr        Gold.....
   Copper......5yj        Silver.....
   Brass.......5^       Lead.....
   Soft iron......?-J-5       Tin......
  The increase in length is called the linear dilatation of a sub-
 r



T^2 
62  EXPANSION  INCREASES  WITH TEMPERATURE.
 stance, tut its increase  of volume is  called the  cubical dilatation,
 and is three times the former.  Thus the cubical dilatation of glass
 is T_3_T, or TJT.   Hence a glass ball which holds 428  measures at
 32°,"becomes capable of holding 429 at 212J; or if it hold 10-000 at
 32J, it holds 10-023 at 212°.  In this manner the correction for the
 expansion of glass is in  all cases made.   But it is necessary to ap-
 ply  the amount of expansion belonging to the  particular  sort of
 glass; thus, in the  account  of the thermometer in page 51,  the
 cubic dilatation of glass was taken, not as 10-023, but  10-026.
  [The reason that the cubic  dilatation may be taken as  equal to three times the
 linear, without sensible error, is due to the circumstance that the linear dilatation
 is always" a  small fraction of the primitive length.  If 1-f-/ represent the dilated
 length, (l-f-0% or 1-f 3 i-f-3 l2-\-ls will be the true  volume ; but as / is a small
 fraction, its triple square and cube may be neglected.]
  Although it is abundantly proved that solid bodies expand more  rapidly at high
 than at low temperatures, yet, except in the case of some particular substances, as
glass, iron, and platinum, whose utility as measurers of heat rendered a knowledge
of the law of their expansion necessary, the subject has been little examined ; the
degree to which the rate of expansion is affected by temperature will be sufficiently
shown in the table which follows.  At the temperature of 212° Fahrenheit, as given
by an air thermometer, the dilatation for one degree is thus, for
Glass.	Platinum.	Iron. | Copper. |
	1	111
a • 0 6 0	5 7 8 6 0	5 « 1 6 0|3 4 120|
while at 572° of Fahrenheit it becomes, for
Glass. 1 S 9 2 2 0	riatinum.	Iron. 1 CVpper 1
	1 6 5 3 4 0	ill 40'6 78i3I860l
and the temperature deducible from the expansion of a thermometer made of each
of these substances should be, in passing from 212° to 572°, as compared with air,
Air.	Glass.	Pl.viimni. 1 Iron.	Coppt r. 623°
572°	667°	592° J 702°	
Platinum expands thus the most regularly of those bodies, and should, therefore, be
best fitted for a metallic thermometer.
   It is remarkable that the rate of expansion is not increased by
rise  of temperature for all solid bodies,  but,  on the  contrary  in
some cases  there exists, for solids as for liquids, a point of maxi-
mum density,  so that the body shall expand whether  it be cooled
or heated from that degree.  This  is peculiarly the case in Rose's
fusible metal, which has been so often mentioned as a means of ap-
plying a steady heat.   When heated from 32  to 111 , this metallic
alloy increases in volume from 100-000 to 100-830 parts, but there
the expansion stops, and when farther heated it contracts until
when at 156', the  volume  is only  99-291, beino;  less than  at  32°!
By a farther rise of temperature it  again expands, and  at 178  is at
its original volume  of 100-000, and continues expanding until bein<r
100-862 at 201 , almost exactly what it had been at  UV  it beo-inl
to melt.  It is curious that it  has no  point of maximum density
when in the  liquid state.                                          J
  The different rates of expansion of different solid bodies are  sub-
servient to  some very important uses in the arts and  in scientific
research.  Thus, the difference between the expansibilities  of plati-
num and brass, or any other two metals which  differ much  mav be
used as a very delicate  thermometric means.   If we take a flat  rule 
   EXPANSION  OF  COMPOUND METALLIC  BARS.  63

of platinum exactly ten inches long  at 32°, and lay it on a similar
rule of brass, to which it is firmly screwed at  one extremity, and
on which, at the free  end, there is engraved  a  scale of parts of an
inch for a small space, the compound rule will serve as a thermom-
eter.  For the two rules being exactly of the  same length at 32°, if
we place  them, fastened together, in boiling water, the brass rule
will be elongated by 0-019, while the platina  rule will expand only
through 0-009 ; hence the end of the brass rule will project beyond
the platina rule by 0-010 of an inch ; and as the expansion is uniform
for these moderate temperatures, each degree of Fahrenheit's scale
will be  indicated  on  the scale  of the brass rule by °7^=7^o6 °^
an inch.   In this form the spaces would be too  minute to be easily
determined ; but by modifying the form, and connecting the rules
through their whole length, the beautiful metallic thermometer of
Breguet has been invented.   Its principle is as follows: if the two
rules be soldered completely together, as in a, in place of being con-
nected only at a single point, the result of the unequal expansion is
to bend the bar, as in b, until, the most expansible metpd being on
             ..............  —— the outside, it forms an arch longer than that
                      formed by the inside rule, by the difference
  ^^g^iiiiiHiiiiiiimiiiii^^^ 0f their expansions.  If the compound bar be
 O                    already bent into a circle, the ends of which
are not opposed, the effect of the expansion is to  make these edges
project, and to diminish the  diameter of the  circle ;  by having  a
number of such circles, the expansion of all  being added together,
a considerable circular  motion is produced  in the extremity.   In
                   the thermometer  of Breguet there  is  such  a
                   compound spiral b, b, fastened at the upper end,
                   and having attached to its lower extremity an
                   index, c, which  moves round a dial, d, d, and
                   indicates  the temperature of the instrument.
                   On this relative expansion is also founded the
                   construction of the  compound  pendulum.  A
                   metallic bar, when used, as  in  an ordinary clock,
                   to  measure time by its vibrations, being con-
                   stantly changing in length according as  the ex-
                   ternal temperature varies, affects the rate of the
                   clock, making it go too fast or too slow by its
shortening or elongation.  This is corrected by having two or more
bars, by the expansion of one of which the vibrating length of the
pendulum is increased,  while by the expansion  of the other it is
just as much shortened ; the  consequence of this opposing action
is, that the pendulum  remains indifferent to all changes of temper-
ature, and the clock becomes an exact measure of time at all sea-
sons.

                          SECTION II.
                        OF SPECIFIC  HEAT.

  It is now necessary to examine into the quantity of heat which
each substance  requires to raise its  temperature  a certain number
of degrees; for, although it be quite impossible to assign the absolute
 
64
METHOD OF  MIXTURES.
proportion, yet, by obtaining the relative proportions, we may arrive
at results which may serve to characterize  those  substances and
may, as shall be hereafter shown, lead us to important views of the
relations between their physical and chemical constitution.  The rel-
ative quantity of heat necessary to raise  the temperature of any
body through a certain number of degrees, as ten,  for example, is
termed its specific heat.
  If we take a  pint of water at 150% and  another pint of  water at
b0J and  mix them well  in  a very thin vessel, the temperature  of
the'mixture is  found to be, if we allow for some sources of er-
ror to which this process is exposed, exactly 100°.   Thus the one
part of the  water has transferred to the other a quantity of heat
sufficient to raise its temperature 50^; and whether this addition was
from 50  to 100 , or from 100  to 150% the result was the same.   In
water,  therefore,  the specific heat does not change within  these
limits ; but it will be found that in high temperatures a trifling in-
crease does occur ; for the present purpose, however, it may be neg-
lected.   If, now, a pint of water be taken  at  150° as before, and a
pint of meicury at 50% and they be well and rapidly mixed together
until both have attained the same temperature, this will be found  to
be  118°.   The  mercury here rises from 50" to 118% through 68°,
while the water cools only through 32', or not quite half as much,
so that the same quantity of heat can raise the temperature of mer-
cury through twice  as many degrees as that of water.
  Taking thus equal volumes, the specific heats  of water and mer-
cury are as  68 : 32; or water being  adopted as the  standard for
liquid and solid bodies, and its specific  heat taken as 1, the specific
heat of mercury is 0-47 nearly.  Such bodies are, however, gener-
ally taken, not  in equal  volumes, but  in equal weights, and hence
it is necessary to divide the 0-47 by 13-5, the specific gravity of mer-
cury, and thus there is obtained 0-035, its  specific heat.
  The process now given is known as the  method of mixtures, and
has been selected for example, as that by which the meaning of the
term specific heat is best explained ;  but it is not the only one, nor
even, perhaps, the best,  by which  specific heat may be  determined.
The sources of error are, that a certain quantity of heat is  absorbed
by the vessel in which the mixture is made, and that, as the mixture
requires  some time to make, a certain loss  occurs by the cooling
power of the air.  But it is, however, in skilful hands, capable of ex-
ceeding accuracy ; and, with the recent improvements that have been
made in its details by Regnault, it has yielded results of the highest
value to  science.  The various forms of apparatus used in such ex-
periments need not be described.  For the  use  of the method  of
mixtures, it is not necessary that the  two bodies should be liquid.
Thus, if a pound of pure copper in a bar be heated in an oil bath to
300 , and be then immersed in a pound of water at 50  , the copper
will give out its excess of heat to the water, and both will arrive at
a temperature of 72 .  The copper has therefore lost 228  , and the
water has gained 22 \ and the specific heats being inversely as these
numbers, that of copper is found thus to be ■£.??—0-096, water being
 1-000.
   One process employed by Dulong and Petit consisted in heating 
THE  CALORIMETER.
65
to the same degree the bodies to be tried, and allowing them to cool
exactly under the same circumstances.  It is evident that, if we know
exactly the rate at which a body cools, and the time which it takes to
cool, we  can calculate  exactly how much heat  it parts with.   Thus,
if we have two bodies heated to 300 ,  and circumstanced in all re-
spects alike, one requires 15 minutes to cool to 50% and the other
25, the latter will have parted with more heat,  in the proportion of
25 to 15, and the specific heat is expressed by  the quantity  of heat
the body gives out in cooling.   Hence  those substances which have
high specific heats require more time to heat or cool, through a cer-
tain number of degrees, than those bodies whose specific heat is less.
   It was by a process of this kind that  the relative specific heats of
bodies was first discovered.   Boerhaave having remarked that, when
two thin glass vessels, containing,  one a pound  of water and  the
other a pound  of mercury, were equally exposed to the heat at the
front of  a  strong fire,  the temperature of the  mercury rose much
more rapidly than that of the  water, and that it attained its greatest
degree in one  half of the time which the water required; and also,
when both, equally hot,  were removed from the  fire, the mercury
cooled twice as fast.  For accurate purposes, however, there  are
many precautions necessary in order to place  the substances under
the same conditions, so as to render the rapidity of cooling depend-
ant only on their different  specific  heats ; thus,  equal weights of
the different bodies are placed in the same thin polished silver ves-
sel, so that their external surface may be the same in extent and na-
ture, and this  vessel cools  in an exhausted receiver in  order that
there may  be  no loss of heat from  contact with the  external  air.
The internal surface of the  receiver must  also be always in the same
state, that the  heat given out may pass off in all cases with equal
facility.
  An extensive series of researches on the specific heats of bodies, conducted by
the illustrious associates Lavoisier  and Laplace, has been found on repetition to
have been rendered useless by the imperfections of the apparatus they employed:
it was termed the  Calorimeter, and consisted of a vessel containing ice, in the centre
of which  the heated body was placed, and the quantity of heat this gave out in
cooling was measured by the quantity of ice which was melted into water. Outside
there was another case of ice to defend the instrument from  the action of the air.
It was found in practice impossible to collect all the water.  A quantity  remained
infiltrated  among the ice, some solidified in one  part of the vessel after having been
melted in another, and, consequently, the numbers given by two of the greatest men
that have ever been attached to science must be considered as quite without au-
thority.  In cases, however, where  the quantity of heat was very large, as when
the Calorimeter was employed to  determine the quantity  of heat produced in com-
bustion, these sources of error became less influential, and such results will be util-
ized in a future chapter.
   The specific heats of  a number of the  most important solid and
liquid bodies, determined by such methods, are given in the follow-
ing table:
Water......=1000
Ether......=0 520
Alcohol.....=0 660
Sulphuric acid  .  .  . =0 333
Nitric acid   .... =0442
Sulphur.....=0-202
Carbon.....=0241
Mercury.....=0 033
Iron.......=0114
Copper......=0 095
Lead......=0 031
Gold......=0032
Antimony.....=0 051
Tin.......=0 056
Iodine......=0 054
Phosphorus  .... =0188 
66   SPECIFIC HEAT.—CHEMICAL  CONSTIT
Arsenic
Platinum
Silver  .
Zinc
Tellurium
Nickel
Cobalt
=0081
=0032
=0057
=0095
=0051
=0109
=0107
Glass......=0J77
Calomel.....=0 041
Common salt   .  •   • — 0'22o
Nitrate of soda  .  .   • =0 240
Lime......=0-205
Magnesia.....—0-276
  Th? numbers given are generally those lately obtained by Reg-

^The specific  heats of bodies are not the same at all temperatures ;
thus Dulong and Petit have found that the specific heats calculated
from the change of temperature from 32J to 212J, and from 32J to
572', differ, as  in the following table:
Mercury
Zinc  .
Antimony
Silver
Copper
Platinum
Glass
Iron  .
Sp. Ilea' Iron
 i'Q 10 212°.
 0 0330
 00927
 00507
 0 0557
 00949
 0 0355
 0 1770
 0 1098
00350
0 1015
0 0549
00611
0-1013
00397
0 1900
0 1218
  The specific heat increases, therefore, with the temperature, and
Nauman and Regnault have found that this holds, even with water ;
for, according to their experiments, the specific heat of water at 32°
being 1-000, that water at 212J is  1-010, consequently the equal dis-
tribution of heat between warm and cold water, which was described
at the commencement of this  section,  does not  exactly hold ; the
temperature of the mixture should be a very little above the mean.
This was, however, omitted, in order not to complicate the account
of that manner of finding the specific heats.
  The specific heats  of bodies are connected very intimately with
their  chemical and molecular constitution, although we are not yet
able to trace the exact cause of this connexion in all its forms.  The
discovery of such connexion was the most remarkable  result of the
experiments of Dulong, and it  may be expressed as follows.  If we
take the specific heats of any of the bodies given in the table, and
divide by each of them the number 3-1, we obtain a  series of num-
bers which  are found to be either those which shall  be hereafter
described as the chemical equivalents of the bodies, or to stand in
some remarkably simple relation to those equivalents,  thus:
Substance.	Sp. Heal. 0031 0056 0 095	31	True Equivalent.
		Sp. Heat.	
Tin..... Zinc.....		100 0 554 32 6	1036 579 323
Bismuth ....	0 030	100 7 12 9	71 0 6T
Carbon ....	0-24		
Iodine .... Phosphorus . . Silver ....	0054 0188 0057	574 165 544	1263 314 108-
  In the first division of this table, the quotient is so close to the
true equivalent as sufficiently to show that, were it not for the un- 
SPECIFIC  HEATS  OF  ATOMS.
67
avoidable errors of experiment, they would coincide.  In bismuth
the result  is 1£ times the true equivalent.  In carbon  it is double
the true equivalent.  In  iodine, in phosphorus, and  in silver, it is
one half.   Each of these illustrations might be much extended, their
numbers being only intended as examples of the fact.
  The above are all simple bodies ; but Nauman and Avogadro have
shown, that  also in compound bodies this connexion between the
equivalent number and the specific heat exists, although the connect-
ing dividend is  no longer 3-1, but  is a different number for each
class of bodies.
  Thus, for the following carbonates, the specific heats being made
the divisors of the number 10-4, there is—
Substances.	Sp. Heat.	10-4 Sp. Heat.	True Equivalent*
Carbonate of lime . . Carbonate of iron . . Carbonate of zinc . . Magnesian limestone .	02044 01819 01712 0-2161	509 572 607 481	506 581 624 467
For certain sulphates the number is 12-4  Thus :
Substances.	Sp. Heat.	124	Equivalent.
		Sp. Heat.	
Sulphate of barytes Sulphate of strontia . Sulphate of lime . .	01068 01300 01854	116 1 954 668	116-1 91 9 686
  For a number of metallic oxides, the constant appears to be 5'4<
Thus:
Substances.	Sp. Heat. 0276 0 049 0132 0 137	*-4 Sp. Kent.	Equivalent.
Magnesia .... Red oxide of mercury Oxide of zinc . . . Oxide of copper . .		19.6 110 2 40.9 39-4	20 7 1094 403 396
  The relation between the specific heats of bodies and their chem-
ical equivalents  is thus remarkably shown to extend not merely to
the simple substances, but even to saline bodies, and indicates a con-
nexion between  the chemical equivalents and the molecules upon
which the heat exerts its action, of an intimate description.  In fact,
the specific heat of a certain weight of any body is thus shown to be
proportional to the number of chemically equivalent masses contain-
ed in that weight;  and the constant numbers, which were divided
by the  specific heats, are the specific heats of the ultimate chemi-
cally equivalent particles.  Thus, the specific heat of chemical mole-
cules of zinc, of lead, and tin, is  3-1; that of the oxides  of zinc,  of
copper, and of mercury, 5-4 ; the specific heat of the chemical atom
or ultimate particle of carbonate of lime or of zinc, 10-4 ;  and that of
the sulphates of barytes, strontia, and lime, 12-4 Attempts have been
made to connect these  constants together, but without good found-
ation ;  for 5-4  and  12-4, although nearly the  double and quadruple
of 3-1, are yet too far  removed to show  any necessary connexion,
and 10-4 is completely out of  the  series  of 3-1,  though  nearly the
double of 5-4.
  I shall have occasion to discuss this remarkable relation between the physical and 
63       HEAT BY  CHEMICAL  COMBINATION.
chemical characters of these bodies when I come to examine the subjectorthe laws
of chemical combination in their full extent.  For the present, the details now given
are sufficient.                              .        .c  ,  ,  „<• j-r
  It is not likely that any law connecting the specific heats of dif-
ferent bodies can be  obtained perfectly consistent, for the various
bodies necessary cannot be examined exactly  in the same  state.
Reo-nault has well observed, that the  quantity of heat which we
measure as specific heat consists of several different portions: 1st,
the true specific heat j  2d, the heat which produces dilatation; 3d,
the heat  which causes the rise  of temperature ;  and, 4th, when a
solid is near its fusing point, the quantity employed in giving the
softness and ductility, which most bodies at certain temperatures ac-
quire.  These last three portions being very small, do not conceal
the law by which the true specific heat is regulated ; but they influ-
ence it so far as to prevent the  law from being verified in its nu-
merical results with the accuracy which otherwise might have been
obtained.
  When bodies combine chemically, there is generally found to  be
a diminution of specific heat; and it has been attempted to account
thereby for the rise of temperature, by which combination is in most
cases accompanied.  Thus, the  specific  heat of sulphuric acid is
0-33 j and when mixed with an equal weight of water, the specific
heat  of the mixtures should be, were  there no action, ^=0,665;
but the true specific  heat of the combined acid and water  is found
to be only 0-587.  The excess, therefore, 0-665—0-587 = 0-078, be-
comes free, and shows itself by raising the temperature of the mix-
ture ; and, accordingly, on mixing together sulphuric acid and water,
it is well known that a temperature higher than that of boiling water
may  be  produced.  It  was even supposed at one time, when heat
was looked upon as being a positive substance which combined with
bodies in different proportions,  that the absolute quantity of heat
which a body contained might be determined  by such an experi-
ment, thus: if the rise of temperature produced by  0.078 of heat
becoming free is expressed by 180° above 32°, then the quantity of
heat which stays behind must be greater than that in the proportion
of 587 to 78 ; and hence is equivalent to ~ 180= 1335J: and thus, at
the temperature of —1303° of Fahrenheit's scale, a body should con-
tain  no heat at all  ; it should be the absolute zero.  But no two such
experiments, with different bodies, ever gave the same result: and
it is evident, from the fact of the specific heat diminishing as the
temperature sinks, that the term at which the two quantities should
vanish must be infinitely remote, and that there is no  such thing as
an absolute zero at all.  In fact, the physical existence of an abso
lute  zero is inconsistent with the more accurate ideas of the nature
of heat, which modern investigation has suggested.
   The development  of heat, in  chemical combination, is also only
in some  cases accompanied by a diminution of specific heat; in at
least as many it is, on the contrary, remarkably augmented.
   The specific heat  of gases and vapours has obtained considerable
 attention; and yet, from the extreme delicacy of the processes neces-
 sary, and the small quantity of material which can be operated  on,
 the  results hitherto  obtained have not  acquired that degree of posi- 
SPECIFIC  HEAT8  OF  GASES.
69
 tive accordance which should render repetition unnecessary.   The
 principal experimenters in this department have beenDelaroche and
 Berard, Delarive and Marcet, Haycraft, Dulong, and, latterly, Apjohn
 and Suerman.
   The method  adopted by Haycraft, and by Delaroche and Berard,
 consisted in heating a quantity of gas to a certain temperature, and
 then, by passing it through a tube in a vessel of water, determining
 how much  it raised the  temperature of the water in being cooled
 through a certain  number of degrees.   In principle, this mode  is
 perfect;  but the extreme accuracy necessary in the management  of
 the apparatus does not appear to have been attained by Haycraft:
 and Delaroche  and Berard  deprived their results of most  of their
 value by the oversight of using the gases in a damp state.  The pro-
 cess of Delarive and  Marcet was not such as could lead to results
 worthy of much confidence.   A glass  globe full of gas, to  which
 was attached a thermometer, with the bulb exactly in the centre,
 was plunged into a vessel of hot water, in the expectation that the
 time occupied by each gas, in having its temperature raised  a cer-
 tain number of degrees,  would be proportional to the specific heat
 under a  constant  volume.   But  the communication  of the heat
 would be so much  and so variously affected by currents, according
 to the density of the gas and the quantity of heat absorbed by the
 gas, so trifling in  comparison  to that which would be required to
 heat the globe, that the amount of liability to error was very  great.
   The process  employed by Dulong was very beautiful in principle,
 and calculated  to give experimental results of great accuracy.   It
 consisted in determining the velocity  of sound in each gas,  which
 was measured by finding the note the  same organ-pipe  gave with
 each: from  this,  by very  ingenious  methods, which, however,
 need not  here be introduced, farther than that the gases with higher
 specific heats give more acute tones, he calculated the specific  heats.
 The calculations were, however,  based  on  certain other principles,
 which are not necessarily true.
  The method contrived  by Apjohn is that which appears to be the
 best calculated to give accurate results, and those which he obtained
 have been verified by the experiments of Suerman.
  Apjohn's method cannot be completely described until we come to speak of the
latent heat of vapours and their relation to space; but the general principle  of it is,
that if several gases be employed to convert a certain quantity of water into vapour,
the gases will be cooled thereby in  inverse proportion to their specific heats.  Thus,
if one gas have double the specific heat of another, it will saturate itself with va-
pour by cooling through only half the number of degrees necessary for that with
the less specific heat; and thus, by measuring simply the cooling power of each
gas, the specific heat may be calculated.
  The  numbers obtained by Delaroche and Berard,  by Dulong and by Apjohn, for
the specific heats of the  gases in equal volumes, are given in the following table:
Gases. jApjohn.	Delaroche. Dulong.
Air......11000 Nitrogen ..... 1048 Oxygen.....-808 Hydrogen .... Il 459 Carbonic acid . . . jl 195 Carbonic oxide... 996 Nitrous oxide . . . !ll93|	1000 1 000 1 006 11 000 ■976 jl 000 ■900 |l 300 1258 1172 1 034 jl 000 1 350 11159 —-----
 
70
LIQUEFACTION.
  These numbers show the diversity which exists among even the best expert-

m^sSfi^at0 ^^X^^^^^P^,
mg tneir specinc neai*.  nit, P>"^ h         soecific heat, is thus shown, by the
that n equal volumes all gases have the same spec f"- "e*
combined4 evidence of all the best results, to be totally «°f^ed
  it is sometimes  necessary to compare the specific heats ol gase
with that of water;  this  being 1-000, that of air is 0-267 for  equal
weio-hts, and so on for the other gases in proportion.
  We do not know  the specific heats of many bodies  in the state
of vapour.  For watery vapour, however it is found to  be  0-847,
water being  1-000,  or 3-172,  air  being  1-000, for  equal  weights.
Water is thus the only substance  of which we know the specific
heat in the three states of aggregation, that of ice being -900, water
1-000, and steam -847, for equal weights.
  When the volume of a gas  or of a vapour increases, its specific
heat increases also, and  vice  versa.  Hence, when air  is suddenly
condensed, so much heat is  evolved that tinder may be  lighted, and
the barrel of a condensing syringe may become too hot  to hold;
thus also, in some kinds  of machinery where air suddenly expands,
so great  a degree of cold is produced that water may be frozen.
  The exact degree of connexion between the amount of expansion
of the o-as and the increase, or of condensation and the diminution
of specific heat,  has not been  ascertained.   They are  not propor-
tional ; that is to say, when  the volume of a gas is doubled, its spe-
cific heat is not doubled, and  vice versa ; and  yet it would appear
that it does not fall much below that ratio.

                         SECTION III.

                        OF  LIQUEFACTION.

  It has  already been frequently explained, that by  the application
of heat  to a  solid body, it  commences,  when its  temperature has
risen to a certain degree, to become liquid,  and that this point, the
melting point of such solid  body, is one  of the most  determinate
and characteristic of its physical properties.  Accordingly, the
melting point is  often used as a means of distinguishing and  recog-
nising substances  otherwise very similar in properties; as, for ex-
ample, the numerous fatty acids  can scarcely  be  otherwise  distin-
guished  from each other, exclusive of analysis, than by  the  tem-
peratures at which they melt.  There has been already given a list
of the melting points of  a number of solid  bodies, and, in the his-
tory of each individual substance, its fusibility will be described.
  The change from the  solid to  the liquid state is accompanied,
however, by a phenomenon differing from  any yet described, and
deserving of great attention  from the important consequences which
flow from it.  It is, that at the moment of liquefaction  a very large
quantity of  heat is absorbed,  combining, as it were, with the  solid
to form the liquid body,  and after combination being insensible to
the thermometer, and having thence obtained the name of latent heat.
A pound of water at  32 and a pound  of  ice at 32'  give on the
thermometer precisely the same degree, and yet, independent of all
considerations  of specific heat discussed in the  last  section, and
•which we now lay aside, the water contains, in a state of intimate 
  ABSORPTION OF HEAT  DURING LIQUEFACTION.  71

 combination, a great quantity of heat, by virtue of which it is liquid
 water, and by losing which it would be reduced to the state of solid
 ice.  In melting, therefore, every body renders latent a quantity of
 heat.
   This principle may be demonstrated by experiments of a very sim-
 ple kind.  Thus, if a pound of ice be taken at 32', and added to a
 pound of water at 172J, the ice dissolves immediately, but the tem-
 perature  of the resulting two pounds of water is found to be 32J
 There has thus disappeared a quantity of heat, which had previous-
 ly raised the temperature of the  water to 172 % or through  140°.
 This heat has been absorbed by the ice in becoming liquid, and ren-
 dered latent ;  and it is therefore said that the latent heat of liquid
 water  is 140°.   If a vessel of water, at the temperature of 52% be
 exposed freely to air below  the freezing point, it will rapidly cool
 until it arrives at 32% but there the lowering of the temperature
 ceases ;  it begins to freeze, and, until the entire mass is reduced to
 solid ice, no loss of heat  sensible  to the thermometer is observed:
 yet it must still be giving out heat precisely as it was when it cool-
 ed from  523 to 32% this heat being, however,  that which gave to it
 the form of liquid water,  and which had been perfectly insensible,
 or latent, until the formation of ice commenced.   If the water had
 taken ten minutes to cool  from 52° to 32°, it will be found to require
 one  hour and ten minutes to  become completely frozen ; and hence,
 as in the same time it loses the same quantity of heat, the external
 air remaining equally cold, the latent heat is 20° X 7= 140 % as in the
 former experiment.   Another mode of verifying the result consists
 in exposing a pound of ice at 32',  and a pound of water at the same
 temperature, to the same  source of heat, as on a steady fire,  and it
 will be found that, by the time the ice  has completely melted, the
 temperature of the water  will have risen to 172 .
   Water is, of all liquids, that which contains the greatest quantity
 of latent heat, and hence that which changes from the liquid to the
 solid state most  slowly;  and inversely, ice is the solid which ab-
 sorbs most heat, and  requires most time to liquefy.   This property
 of water  is of  the highest importance  in the economy of nature,
 for by means  of  it the  change of seasons is  rendered  much less
 sudden than could otherwise occur.  If water passed from 32J to
 31% and  became solid by  losing only the same quantity of heat  as
 it  gives out in cooling from 33  to  32', the change of seasons would
 be so rapid and so uncertain as to interrupt almost entirely the
 proper cultivation of the soil, and, by the vicissitudes of heat and
 cold, become injurious to  the health.   But, as these properties of
 water are now arranged, each  particle, in freezing, becomes a source
 of warmth to all  around,  and mitigates the severity of the cold;
there can be but a comparatively small quantity of water rendered
 solid ; and when, on the return of a warmer season, a sudden lique-
fnotion might prove equally injurious, ice and snow, in melting, ab-
sorb all excess of  heat, and render  the change  gradual, and suitable
to ihe functions of those plants and animals to which a sudden tran-
sition might prove fatal.
  We do not know the latent heat  of many liquid bodies, but those
given in  the following table  will  suffice to show the remarkable 
72      HEAT  EVOLVED  IN  SOLIDIFICATION.
 pre-eminence of water in that respect.  The numbers are  given in
 two columns;  the  first  showing the interval  through which  the
 body itself, in its liquid form, would be heated by the heat it absorbs
 in melting,  and the second showing the  interval through  which
 that heat would elevate the temperature of an equal weight of water.
 Thus:
       Latent Heat of            Mealed by ibelf.              Mea,ured by Water
        Water......140........   140
        Sulphur......144........    2714
        Lead.......370........    HO
        Zinc.......493........    48 3
        Bismuth......550........    23 25
   In every case a solid body begins to melt at the same temperature
 Thus, ice never begins to melt until  it arrives at 32°, and can never
 be raised above 32J without melting ;  consequently, the fixed point
 is the melting point of ice, and not the freezing point  of water ;  for,
 if water be cooled carefully without agitation, its temperature may
 be lowered easily to 25% and has been reduced to 15J without so-
 lidifying.  This is a phenomenon like that which has been (page 25)
 noticed in the crystallization of sulphate of soda, where the solution
 may remain perfectly liquid  until agitated, and then suddenly crys-
 tallizes with the evolution of considerable heat.  If water, so cooled
 below 32%  be agitated,  it freezes suddenly, and the temperature
 rises to 32° ; the latent heat of that portion which freezes becoming
 sensible, and thus warming the entire mass.
   Substances which crystallize easily generally expand in solidify-
 ing, and in doing  so  exert great force.  Thus water is capable of
 bursting the strongest vessels if they be filled  completely  with it,
 and tightly closed so as to prevent expansion otherwise.   It is by
 the agency of this force that the gradual deterioration of the sur-
 face of rocks, and the formation of the soil  on  the lower grounds,
 depends; the rain-water  being  absorbed into the pores and  small
 cavities which even  the hardest rocks contain, and beino- there, in
 winter, frozen, breaks open the substance  of the rock, and causes
 it gradually to fall to powder, thus generating the  soft and porous
 soil fitted for the reception and sustenance of the seeds and  roots
 of plants.  It is also by the action of this force of expansion, exert-
 ed  by many bodies when they crystallize, that  we are enabled to
take accurate copies  of the moulds into  which such substances in
the liquid state,  are poured.  Cast iron, antimony, and the alloy of
antimony used for  printers'  types, the alloy used for stereotype
plates, brass, bronze, and all such bodies, are  capable of making
good castings  by virtue  of  this expanding  power;  while  bodies
which do not distinctly crystallize, as gold, silver, and copper are
not capable of giving accurate castings,  and hence the coinage of
these metals  is made by stamping the necessary marks upon  them
by means of a violent blow.
  By the  addition of small quantities  of salts or vegetable acids
the freezing point of water may be considerably lowered : thus sea-
water does not easily freeze.  When such a  solution  is brought to
solidify, it is pure ice which first crystallizes out.  Thus,  from a
strong solution of potash, ice has been obtained in large s'ix-sided
prisms; and the ice mountains which form in the  Polar  Seas are 
COLD  BY LIQUEFACTION.
73
 found to be almost completely fresh.  This principle has been ap-
 plied also to the concentration of vinegar and lemon-juice by freez-
 ing, a large quantity of mere ice being formed round the sides of
 the vessel, and a  central cavity remaining filled with concentrated
 acid.
   The principle of latent heat  has been applied to  the  production
 of artificial cold.   For if a solid body suddenly  liquefies withoui
 the application of external heat, it must abstract from the surround
 ing bodies the heat necessary  to its liquefaction, and thus reduce
 their temperature and its own.  Hence, when salts are dissolved iit
 water without any chemical  combination, there is  cold  produced.
 Thus, by mixing nitrate of ammonia with an equal weight of water,
 the  thermometer sinks 46° ;  and carbonate and sulphate of soda,
 dissolved in three times  their weight of water, reduce the temper-
 ature, the first 16% and the second 12°.
   In  many cases where,  by  double decomposition, those soluble
 substances may be formed, more powerful effects are produced by
 mixing two salts together than by either separately. Thus neither
 nitre nor sal  ammoniac produce much cold,, but when mixed they
 generate  nitrate  of ammonia, which is very powerful,  and hence
 cause a  reduction of 40%  In other cases the  cold results from a
 quantity of water of  crystallization being set free and suddenly
 liquefying.   Thus, when crystallized sulphate of  soda is dissolved
 in muriatic acid, there are formed  bisulphate of soda and chloride
 of sodium, with which but i of the quantity of water remains ; and
 the  remaining f  being disengaged, and abstracting from the sur-
 rounding bodies the heat necessary for their liquefaction, depress
 the temperature through 50°.
   By using snow or pounded ice,  freezing mixtures of still greater
 power may be produced.   The cold is the greatest when a substance
 is employed  which contains itself a large quantity of water in a
 combined  from.   Thus crystallized chloride  of calcium contains
 half its weight of water, and, when mixed with an equal weight  of
 snow, the whole becomes liquid, and the quantity of heat absorbed
 is proportionally large.   By combining such freezing mixtures in-
 tense degrees of cold have been produced;  Mr. Walker, to whom
 the invention  of most  of them is due, having obtained a  depression
 of temperature to —91° of Fahrenheit.
  The following table contains  the proportions for some of the most useful freezing
 mixtures, and the degree of cold which can be obtained by means of them.  It is to
 be remarked, that in using freezing mixtures a great deal of the success depends on
 the rapidity with  which the liquefaction is produced ; the thinnest possible vessels,
 and a tolerably large quantity of materials should be used.  For producing a great
 degree of cold, it  is also necessary to cool the materials previously as much as pos-
sible ;  thus, to produce the intense cold of —91°, Mr. Walker had cooled the sub-
stances to be mixed down to —68° by means of other freezing mixtures.
                               K 
74  ARTIFICIAL  COLD  BY  FRIGORIFIC  MIXTURES.
FRIGORIFIC MIXTURES WITHOUT ICE.					
Mixtures.			Parts. ~t~ i T 5 16 ~r 2 ~6~ 4 2 4	Thermometer sinks	Degree of cold. 46° 40° 53°
Nitrate of ammonia Water.....				} from -4-50° to -4-4°	
.Muriate of ammonia Nitrate of potash . Water.....				I from 4-50° to +10°	
Sulphate of soda . Diluted nitric acid .				J from -f50° to —3°	
Sulphate of soda . Muriate of ammonia Nitrate of potash . Diluted nitric acid .				I from +50° to —10°	60° 64°
Sulphate of soda . Nitrate of ammonia Diluted nitric acid .			6 5 4	( from 50° to —14°	
Sulphate of soda . Muriatic acid . .			8 5	| from -4-50° to 0°	60° 34°
Phosphate of soda . Nitrate of ammonia Diluted nitric acid .			5 3 4	{ from 0° to —34°	
FRIGORIFIC MIXTURES WITH ICE.
Mixiures.			Parts.	Thermometer sinks		Degree of cold. * * * * 60°
Snow or pounded ice Common salt . .			2 1	> 3 83 0> a. S 03 >-. C 83 E p c;	to —5°	
Snow or pounded ice Common salt . . Sal ammoniac . .			5 2 1 24~ 10 5 5 12" 5 5 ~T 4		to —12°	
Snow or pounded ice Common salt . . Sal ammoniac . . Nitrate of potash .					> to —18°	
Snow or pounded ice Common salt . . Nitrate of ammonia					to —25°	
				| from -L32° to —30°		
Diluted nitric acid .						
Snow.....			2 3	> from -f32° to —50°		82°
Crys. muriate of lime						
Snow.....			3 4	^ from+32° to—51°		83° 46°
						
						
Snow.....			3 2	I from 0° to —46°		
Diluted nitric acid .						
Snow.....			1 2	I from 0° to —66°		66° 25°
Crys. muriate of lime						
Snow.....			8 10	) ,.		
Diluted sulphuric acid				\f	■ora —66° to—91°	
  In the ordinary experiment of freezing mercury by a mixture of snow and crys-
tallized chloride of calcium, success is seldom obtained unless by having two por-
tions of the mixture, and either cooling the materials for the second by means of the
first, or plunging the tube of mercury, when it has exhausted the cooling powers of
the first, into the second and freshly-mixed portion of materials.
   There are many cases in which heat is evolved from solid bodies
without our being able positively to ascertain its source, and where, 
   NATURE OF SPECIAL HEA T.--V A P O R I Z A T I O N.   75

consequently, it may be considered as having previously been latent.
Thus, by the friction of two different bodies together, as when the
axle of a carriage becomes hot, or when, as among savage nations,
fire is obtained by rubbing two pieces of wood together.  But it is
rather a misuse of words to say that the heat evolved had previously
been latent, for the latent  heat of a body should properly be consid-
ered as that by which the fluid condition  is conferred upon it, and
hence a  solid body cannot be said to have  such  latent heat at all.
It is most likely that, as a diminution of specific  heat accompanies
the increase of density which occurs when oil of vitriol and water
are mixed together, so where, by compression,  the density of a solid
body is  increased, its specific heat may be  diminished, and hence
sensible  heat evolved.   Although our knowledge of  this subject is
not at all as satisfactory as its importance merits, it has been ascer-
tained that, when iron is violently compressed, as in  boring cannon
or by repeated hammering, its specific heat becomes much less, and
the heat evolved is so considerable that the  metal  may easily  be
made red hot.  It would  be well to  distinguish between heat, cer-
tainly before latent, which may thus be rendered sensible, and the
true latent heat which is  absorbed during liquefaction, and which
can be only given out again by the reassumption  of the solid form;
and this might be done, perhaps, and its connexion with specific heat
made evident, by adopting the word special heat, or heat peculiar to
the body.  Thus liquids and vapours only can contain latent heat;
but every body contains a quantity of special heat, equally insensible
to the thermometer, but becoming manifest when the  specific heat
is diminished.  The special heat is thus the heat which gives to the
body the temperature which it possesses, and the quantity of  special
heat necessary to produce a rise  of temperature measures the spe-
cific heat.
  Many  bodies undergo, before liquefaction, remarkable changes in
their molecular constitution: thus  iron,  wax, and  glass become
soft and  pasty, so that different pieces may be perfectly united into
one ; and it is, indeed, on this property that the most useful appli-
cations  of glass and iron in ordinary life depend.   This has been
referred  to a certain quantity  of latent heat having already entered
into the  body, and giving an intermediate condition, that of semiflu-
idity.  There is no proof either for or against this view, as no exact
experiments  have been made upon  such  bodies.  In  other cases,
where semifluidity is produced, as in lard, tallow, &c, it is plainly
seen to arise from the substance being a mixture  of two bodies,  of
which one melts easily, and, being then liquid,  forms with the other,
which remains still solid,  a kind of pulp, which gradually becomes
less thick, according as the  temperature rises, until all is liquefied

                          SECTION IV.
                       OF  VAPORIZATION.

  By the application of a  higher  temperature  than that which was
necessary for liquefaction, the generality of fusible bodies are capable
of being converted into vapour.  In this form they resemble, in mole-
cular constitution, the most permanent of the gases, and are subjected 
76
LATENT HEAT  OF  VAPOURS.
 to precisely the same laws of change of volume, for any alteration
 of temperature or pressure, as atmospheric air, as long as the clastic
 form is preserved.  This passage from the  solid  or liquid to the
 gaseous state of aggregation, may occur either slowly and silently,
 or with violence and rapidity ;  the body may either evaporate or
 boil.   The evaporation  may  go  on at any temperature,  even at the
 lowest  ; but boiling commences  only at a certain temperature, which
 depends on the nature of the body, and upon  the pressure to which
 it is subjected.   Each of these modes of generating vapour will re-
 quire to be specially examined ; but it is necessary  to attend, in the
 first place, to the phenomenon which accompanies and may be sup-
 posed to produce the change of form, the absorption of the heat of
 vaporization ; for precisely as a solid absorbs heat in becoming liquid,
 so does a liquid, in assuming the vaporous condition, render heat la-
 tent, and even in still greater quantity.
   If we place upon a steady  fire or over a lamp a cup of water, we
 shall  observe that  its temperature rises  until it begins to boil, but
 then  remains perfectly  stationary until  the last drop of the water
 6hall have  been boiled away.  If we remark the time, we shall find
 it to be in the following proportion.  Let us suppose  the temperature
 of the water to  have been originally 62°, and that at the end of six
 minutes it began to boil, having attained the temperature  of  212°.
 In each minute, therefore, there entered into the water  a  quantity
 of heat  sufficient  to  raise its temperature ^=^=25°.   Now,  the
 source  of heat remaining perfectly steady, it will  be found neces-
 sary to apply it during 40 minutes to boil away all  the water  ; and
 as in each  minute there  enters heat enough to raise  the temperature
 of the same weight of water 25% the total quantity of heat absorbed
by the water in being converted into steam would  have raised its
temperature, had it remained liquid, 25x40=1000% or just to red-
ness.   And yet this becomes perfectly latent, the temperature of the
vapour formed, that is, of the steam, being exactly 212% that of the
water it is  formed from.
  By the inverse process a corresponding observation may be made.  Thus, water
                                         being boiled in a vessel, as in
                                         the figure,  the steam may be
                                         conducted by a tube into a glass
                                         containing a weighed quantity
                                         of cold water, the  temperature
                                         of which is accurately marked.
                                         The  steam,  by condensing in
                                         the cold water, raises its tem-
                                         perature ; and when a  suffi-
                                         cient rise has been  produced,
                                         the steam may be shut off, and
                                         the glass with the warm water
                                         weighed again.  It is found to
                                         be heavier  than  before,  from
                                         the quantity of water added to
                                         it by the condensation of the
                                         steam; and the quantity of heat
                                         given out by the steam in so
                                         condensing may easily be cal-
culated.  Thus : let us suppose that there were eight ounces of water, at 60°, ori-
ginally used, and that, at the termination of the experiment, there were nine ounces
at the temperature of 188°.  It is then evident that one  ounce of steam, in conden-
i,* IncAti 
     INCREASE  OF  VOLUME  IN VAPORIZATION.    7'"'

sing, had raised the temperature of the eight ounces 128°.  The temperature of one
ounce might  have been, therefore, raised 128x8=1024°: but this was not all la
tent heat; for the steam, by merely condensing, should have formed liquid water at
212°, whereas it cooled to 188°.  The difference, =24°, must be subtracted  from
the 1024° ;  and thus the latent heat of steam determined to be 1000% as it had been
found by the previous process.
  The great  quantity of heat thus contained in an insensible form in
steam is  very generally  made use  of for  warming  apartments  and
for chemical operations,  in which exposure to the direct action  of a
fire, or even to a sand bath, might be injurious.   By means of a
series of pipes, steam from a boiler, placed at a  distance, is brought
to circulate through every part of the most extensive buildings, and
condensing gradually as it passes  along  the cooling surfaces, the
liquid water  is conducted back again to the boiler, there to be recon-
verted into steam.  In large manufacturing laboratories, such as those
of the Apothecaries' Halls of Dublin and of London, there are  steam
ranges, or series of evaporating pans and stills, set in cast-iron cases,
within which steam is introduced, and thus  the  most delicate vege-
table preparations, such as extracts and inspissated juices, prepared
at temperatures which, being  completely  under the control of the
operator, allows all the freshness and active properties of the  plants
to be perfectly preserved.
  By means  of apparatus similar in principle to that in the last figure, the latent
heats of the vapours of many fluids have been determined.  It has been found that
the latent heat of equal weights of the vapours of the following bodies would  have
raised the temperature of an equal weight of water in condensing :

               Water...........1000°
               Alcohol...........376°
               Ether    ...........163=
               Oil of turpentine........138°
               Nitric acid..........335°

The latent  heats of bodies, such as vinegar and water of ammonia, which have no
definite chemical constitution, but contain mixed water, do not possess any value
or importance.
  In  changing from the liquid to the gaseous  state, the volume is
increased in  a very great degree ; the amount of increase,  in some
instances, which may be taken as examples, is given in the following
table.
Subitance.	Spe. Gr». Water = 1000.	Boiling Point.	Volume of Vapour at boiling Point.	Volume of Vapour at 212".	Specific Gravity of Vapour.
	1000	212°	1696	1696	620
Alchol ....	907	172°	488	519	1601 \
Ether ....	715	97°	240	289	2583
Oil of turpentine.	867	315°	221	192	4763
Mercury . . .	13500	660°	3395	1938	6969
  In the first column  are the names of the bodies ; in the second, then specific
gravities, water being 1000;  in the third, their boiling points; in the fourth, the
number of volumes of vapour furnished by one volume of each fluid at its boiling
point; in the fifth, the number of volumes of vapour reduced to a standard temper-
ature, 212°, which one volume of fluid may produce; and in the sixth, the specific
gravity of the vapour, air being 1000.
  It has been imagined that  there should exist some physical connexion between
the increase of volume produced by the change from the liquid to the gaseous
Btate, and the quantity of heat rendered latent during  the change; and it is, in
fact, generally true, that those bodies which have small latent heat expand least, aa
oil of turpentine and ether.  But, as yet, from the few experiments that have been 
78  DETERMINATION OF ELASTICITIES OF VAPOURS.
 made upon latent heats, with substances sufficiently pure to be taken as the basis
 of calculation, nothing positive can be considered to be known.
   The passage from  the liquid  condition to the  state of vapour is
 distinguished from the change  of a solid to a fluid,  by the impor-
 tant fact that, while liquefaction is definitely produced at  one tem-
 perature, and at that alone,  vaporization occurs at all  tempera-
 tures; and it is only  from the influence of external  circumstances
 that the  change is accompanied, at a particular temperature, by the
 phenomenon of boiling.  The coldest water is capable  of forming
 vapour ;  even ice evaporates ;  and, in order to do so, it is not neces-
 sary that it shall previously melt; it is thus that snow will gradually
 disappear from the ground, even when shaded  from the sun's rays,
 and though the  air shall have continued below the melting point.
 Other solid bodies also evaporate without previous melting, as cam-
 phor ; and arsenic cannot be melted ;  for, when heated, it is convert-
 ed at once from the solid to the vaporous condition.  The particles
 of volatile bodies appear thus,  at all temperatures,  to  repel each
 other to  a certain  degree, and to spread  abroad, in the form of va-
pour, until they occupy completely the space in which the body is
contained, and exercise  a pressure which is equal to the force  of
their mutual  repulsion, and which is termed the elasticity of the va-
pour.
  The amount of elasticity, or, as it is often called, tension of a va-
pour, is determined by very simple methods.  Thus, for elasticities
                below that of atmospheric air, a series of barom-
                eter  tubes arranged in a stand, P P  a a, are  to be
                carefully filled and inverted in a basin of mercury,
                c c, as in the  figure.   One such tube, d d, is  to be
                kept  untouched, to measure the elasticity of the ex-
                ternal air.  If a little water be allowed  to pass up
                into the next  tube, and there float upon  the surface
                of the mercury, it immediately forms vapour, which
                spreads  through all the empty space, and, pressing
                against the upper surface of the mercurial column,
                counteracts a portion of the pressure of the exter-
                nal air.  The remaining pressure of the air is able
                to support, therefore, only a shorter column of mer-
                cury, and  the height of the mercury in  the tube
                diminishes.  If into another tube some alcohol be
                introduced, there is a similar, but still greater de-
                pression of the  mercurial column caused, and with
                ether the height of the  mercurial column is still
               more diminished.  The  atmospheric pressure  in
               these cases balances  the shortened column of mer-
                cury  added to the elasticity of the vapour, and this
               last is consequently measured by the heio-ht of the
column of mercury which it is capable of replacing, that Is bv the
space through which the mercury has been depressed which  is
read oft by the rule and  index, rvr.  Thus, if the barometer be at
30 inches and the temperature 80°, the  mercury  will stand in the
tube with watery vapour at 29 inches, in that with alcohol at <>8-l
and in that of ether at 10 inches.  The elasticities of these vapours
are therefore at the temperature of 80°.
 
 DETERMINATION OF ELASTICITIES OF VAPOURS. 79

       Vapour of water.............10 inch.
         "   of alcohol.............19
         '    of ether ■.............20 0

  In order to ascertain how the elasticity of a vapour changes with
the temperature, it is only necessary to enclose the upper part of the
tube in a cylindrical case containing water  or oil  heated to the
necessary degree.  As the heat increases the height of the mercu-
rial column will diminish, and at each temperature the elasticity is
so determined.   The apparatus may be modified by  bending the
tube so as to immerse the bent portion containing the vapour  into
a globe of water or oil to which heat may be  applied, but the prin-
ciple remains the same.   In this  way a table of the elasticity  of a
vapour at all temperatures below their boiling points may be form-
ed ;  and as there will be frequent reference hereafter to the tension
of the vapour of water,  the following table is introduced for use
and as an example :
Temperature.	Elasticity.	Temperature.	El i« icity.
32°	0 200 j; 0263 g	90°	136 ^
40°		100°	1-86 g
50°	0 375 jj	120°	3 '33 Z
55°	0 443 ~	140°	574 *
60°	0 524 %	160°	9-46 °
65°	0 616 M	180°	1515 M
70°	0 721 .5	200°	2364 1
80°	1 000 .2	212°	30 00 .5
  When a liquid, in such an apparatus, is heated until the vapour
formed  occupies all the tube and expels the mercury, the elastici-
ty of the vapour is equal to that of the air, and the liquid exposed
to the air boils ;  the  phenomenon of boiling  arising simply from
the fact that  the  elasticity  of  the  vapour balances the pressure
of the air while  the bubble is passing through the fluid:  thus,
suppose  a vessel of water exposed  to the air at 200% and a bub
ble of steam to form  in it; the  pressure exercised by that bubble
being equal to its tension, is equivalent to a column of 23-64> inches
of mercury; but  the  external pressure being 30 inches, the  bub-
ble is crushed in by  a force equal to the difference (6-36 inches
of mercury), and, consequently, dispersed.  If the water, however,
be heated to 212 , the elasticity becomes  equal to 30 inches, and
then the external  and internal  pressures being  equal, the bubble
rises in the liquid without injury, and maintains itself at the surface
until its investing film of water  is ruptured by other causes,  when
the vapour mixes  uniformly with the air.
  It is the bursting of the steam bubbles that are first  formed in
this manner that constitutes the  simmering of a boiler or the sino--
ing of a kettle  on the fire.   The bottom of the vessel heats  more
strongly the layer of water in contact with it, so that the steam has
there a high degree of elasticity, and forms a multitude  of minute
bubbles; when  these separate from the hot metal, they are immedi-
ately  burst in  by the greater external pressure,  and  the mass  of
water is thus thrown into a state of exceedingly rapid and uniform
vibration, which fall upon the ear so regularly, in  many cases, as to
produce a musical and  often agreeable tone, which may become 
80 DETERMINATION OF ELASTICITIES OF VAPOURS.

graver or more acute, according as the bubbles burst more or less



                  212 "he elasticity is doubled.   For high tern-
                  neratures the rate of increase is still more rapid.
                  To  determine the  elasticity at temperatures
                  above  the ordinary boiling point, an apparatus
                  completely cut off from the external air is made
                  use of.   In the figure there is a  globular vessel
                  of strong metal, a, into which is introduced by
                  the stopcock d, the fluid to be experimented on,
                  as, for example, water.   In the aperture c  is
                  fitted  a thermometer, the bulb  of which  dips
                  into the fluid near the centre, and shows its tem-
                  perature.  A quantity of mercury being in the
                  bottom of the vessel, the tube b dips under its
                  surface, and, rising to the necessary height, has
                  attached to it the scale divided  into inches and
                  their parts.  When the apparatus is heated,  as
                  the vapour produced cannot escape, all  junc-
                  tures being perfectly steam-tight,  the tempera-
                  ture rises "continuously  in place of stopping at
                  the boiling point, and the vapour formed press-
                  ing on the surface of the remaining liquid, and
                  by  it  on the mercury underneath,  forces the
                  mercury up the  tube b until the mercurial col-
umn shall have attained such a height as to counterbalance by its
weight the  elasticity of the  vapour.   In these  cases the elasticity
is generally reckoned by atmospheres, each atmosphere being equiv-
alent to a mercurial  column thirty inches high.  In this manner the
vapour of water has been found to exert a pressure  of
 1 atmosphere at 212°
 2 atmospheres at 250°
 3    »   "    275°
 4    «   «    294s
 6    "   "    320°
 8    "   "    342°
12    "   "    374°
16 atmospheres at 398°
20   "    "    418°
25   "    "    439°
30   "   ' "    457°
40   "    "    486°
50   "    "    510°
  It  is necessary, in order to understand such tables, to observe
that this great increase of the elasticity of steam, as the tempera-
ture rises, results not from the expansion of steam already formed,
but from the constant addition of new quantities of steam for every
variation of temperature.  If a  globe full of  steam at 212°, but
containing no  liquid water, were heated to  294°,  it  would tend to
expand precisely as air or any other gas, and the  increase of elas-
ticity would be  only from 30 to 34< inches, or from  1 atmosphere
to l1; but if the globe contain liquid water,  there is such an addi-
tional  quantity of vapour formed and  compressed  into  the same
space, that the elasticity becomes  equal to four atmospheres, or to
120 inches of  the mercurial  column.  Also,  when the pressure on
a vapour is made to vary, the  result deviates from the rule laid down 
        RELATIONS  OF VAPOURS  TO  PRESSURE.     8J

 in page 20, for the action  of pressure upon gases ;  for the elasticity
 of a vapour cannot be really  increased by any increase of pressure :
 it remains the  same, but a quantity of the vapour becomes liquid,
 and  there continues  in the state of vapour only as much as occupies
 with the same  elasticity the  diminished  volume which the column
 of mercury leaves.   Thus, if  we consider the bent      j,
 tube a b, of  which the  extremity at a is closed,
 and  the leg  a  occupied from the dotted  line c d
 by vapour  of ether  at  its boiling point, and bal-
 ancing in the leg  b  a column of mercury thirty
 inches high.   If, now, without allowing the  tern-  :
 perature to change,  mercury be poured in at the  i
 orifice of b until it shall rise  in a up to the line/"  !
g, and occupy exactly one  half of that leg, the va-  j
 pour will not be compressed  into half its volume,  j
 and, acquiring  a  double  elasticity,  support  60  :
 inches of mercury as a gas  should  do, but one i
 half of the ether will assume  the liquid form, and ;
 the"  remainder,  occupying the remaining half  of j
 the original volume, will balance 30 inches of  mer- j
 cury precisely as it  did before,  and the pressing j
 column, counting from the hnefg, will terminate c
 at h.
   If, however, in place of attempting to increase the pressure on a
 vapour, we diminish it, then  the vapour  preserves its elastic form,
 and  its elasticity diminishes in all respects as if it were a gas.
  The  specific gravity of a vapour,  formed at any certain temperature, should be
 proportioned simply to the elasticity, if the volume  were not altered by the change
 of temperature, and it should be inversely as the volume if it could all remain un-
 condensed; but, in reality, the relation is  more complex, and may be calculated
 upon the following principles. Thus, if we wish to know the specific gravity of va-
pour  of water having an elasticity expressed by 7 42 inches of mercury, and the
temperature 150°, we proceed as follows : the specific gravity of steam at 30 inches
and 212° is 6202 ;  and hence, if the volume did not change, the specific gravity of
the vapour at 150°  should be 620-2 x^fVi)=153 39 '> Dut m cooling from 212° to
150°, the portion of steam which retains its elastic form is compressed within a
smaller volume, and hence has  its specific gravity increased in  proportion to the
change, and therefore the 15339 obtained above must  be increased in the propor-
tion of the volume at 150° to the  volume at 212 \ or as 611 : 673, and thus becomes
169 24.   The subjoined table contains specific gravities for some  temperatures cal-
culated  in that way, and accompanied by the temperatures, the elasticities, and the
weight in grains of  100 cubic inches of the vapour.
Temperature.	Elasticity in Inches of Mercury.	Specific Gravity. Air=l000.	Weight of 100 cubic Inches.
32°	0200	568	0 1361
50°	0375	1017	02474
60°	0 524	1406	0 3387
100°	1-860	46 36	11028
150°	7420	16924	4 0543
212°	30-000	620 20	149600
  There is some reason to suspect, however, that vapours do not follow exactly the
theoretic rules upon which such tables are constructed, and which, in reality, apply
only to gaseous bodies.   Thus, Despretz has found the specific gravity of the va-
pour of water to he at 67° 772, while by this calculation it should be 17 26, air at
212° being 1000 ; his results cannot be considered as  decisive, although they show
the necessity for an accurate re-examination of the subject.   At very high tempera-
 
  82     PROPERTIES  OF COMPRESSED  VAPOURS.

  tures, the elasticity does certainly not increase with the specific gravity when the
  volume remains constant.  Ether is found to become gaseous, and to occupy only
  twice the volume it had when  liquid, at the temperature of 320", and its elasticity
  in that state equals 38 atmospheres, whereas, by calculation, its elastic force should
  be 168 atmospheres.  Alcohol, enclosed in tubes hermetically sealed, is totally con-
  verted into vapour, occupying only three times the volume of the liquid at 404°, and
  then  exerts a pressure only of 129 atmospheres, while by theory the pressure should
  equal 221.  Water, also, was  obtained by Cagniard de la Tour gaseous in foui
  times its liquid volume at 773°, and should then, by theory, have an elasticity ol
  780 atmospheres, a force far above what the glass tube employed could possibly
  have-resisted.   It would appear, therefore, that vapours, so far as the relation be-
 tween their specific gravity and their elasticity is concerned, do not follow exactly
 the same law as gases except within certain  limits;  but that, when the elasticity is
 much smaller or much greater than the atmospheric pressure, variations which are
 very remarkable, though not as yet well understood, present themselves.
   When a vapour, as, for example, steam, which has been generated
 in close vessels, and attained a great elasticity, is suddenly  allowed
 to escape  into the air, its temperature is suddenly reduced  in a re-
 markable degree,  even independent of condensation.   If the steam
 had been formed under a pressure of four  atmospheres,  its  volume
 is but one fourth  of what it  should become when  free, and hence,
 on escaping, it  expands in that proportion ;  under that pressure
 its temperature had been 294% but by  the increase of latent heat
 it falls immediately to 212J; there, however, the expansion does
 not stop ;  the impulse  of  the particles of vapour carries them much
 farther ; and  as the specific heat increases so as nearly to be doubled
 when the volume  becomes doubled, a considerable  reduction of the
 temperature below 212° occurs, which is still farther  increased by
 admixture of cold air which presses into the  rarefied space left by
 the expansion of  the steam.  Hence  it is that steam escaping  into
 the air from under considerable pressure possesses much less heat-
 ing power than steam arising from water boiling  in an open vessel:
 it is much less liable to scald.
   The principle  of the  conversion of a solid  or liquid body into a
 vapour at  all ordinary temperatures is  true, even  where the body
 may be very little  volatile.  Thus the space over the mercury in the
 best barometers is not truly empty, but  contains a quantity  of mer-
 curial vapour, exercising a certain elasticity, and, by depressing the
 liquid column, making the pressure of the external air appear small-
 er than it really is.  It would appear, however, that there are,  for
 some bodies  at least, temperatures below  which evaporation does
 not go on ; thus no mercurial vapour can  be detected unless  the
 temperature be above 40% and oil of vitriol  requires to be heated to
 120J before any vapour forms from it: it is probable, however, that
even  in these cases the  general principle holds good, and that it is
only from the minute quantity of vapour eluding our means of  re-
search that the existence  of a limit to evaporation was believed.
  The boiling point of a liquid  being that at which its vapour  can
 support the external pressure, it is liable to constant fluctuation as
the pressure  changes, and hence the  fixing of the temperature of
boiling water  upon the thermometer requires the care and attention
already noticed.   If the barometer stood at 23-64, water would boil
at 200J in place of  212° ; and so close is the connexion between the
pressure and boiling point,  that the height  of any place above  the
level  of the sea may be determined  by the temperature at which 
NATURE  OF  THE  BOILING  POINT.        83
water boils there.   Thus, if, on heating some water on the  summit
of a mountain, it be found to boil at 203% we  find, by reference to a
table, that the elasticity of its vapour is then 25-1 inches, and hence
that  in the same place, at the same moment, the column of mercury
in a barometer should have been at that height.  Then, by the or-
dinary calculation, the height  of the mountain may be found with
as much accuracy as if the barometer itself had been carried up.   On
the summit of Mount Blanc, the highest point of Europe, water has
been found to boil at  184°.
  By reducing, artificially, the amount of pressure upon a fluid, as
by placing the vessel containing it under the receiver of an air-pump
and exhausting the air, the boiling point is lowered in a remarkable
degree.  If the vacuum were perfect, a fluid would  boil even at the
lowest possible temperature ;  but this is not  practicable, as the va-
pour formed  cannot be  so perfectly removed but that it will exer-
cise  some pressure ;  but, with a good air-pump, fluids may be got
to boil  145J  below their ordinary boiling points;  thus  water  will
boil at 67 , alcohol at 32% ether at a temperature at which quicksil-
ver would freeze.   If, at the moment that  such a fluid is in violent
ebullition, the working of the pump be stopped, the vapour accumu-
lates, and, exercising on the surface of the fluid an amount of press-
ure corresponding to its elasticity at the existing temperature, rais-
es the boiling point, and thus  stops the ebullition.  This fact may
be shown in a very simple and singular manner,  by half filling a
flask, B, with water, and boiling the water until all the air in the
                   flask  shall  have been expelled, and then care-
                   fully closing the mouth of the flask, b, by an air-
                   tight cork.  On  removing  the  source of heat,
                   the upper part of  the  flask, B, when inverted
                   as in the figure, remains  full of vapour, which,
                   pressing upon the liquid water, arrests the ebul-
                   lition.  If, then, a jet of cold water, p, be allowed
                   to play upon the flask, the vapour is condensed,
                   and,  a vacuum being thus produced, the water
                   begins to boil; if a jet of  warm water be  em-
                  ployed, the vapour retains its elastic form,  and
                  the ebullition ceases, so  that in this apparatus
                  the application of cold may appear to cause,
                  and that  of heat to  prevent,  the  water's boiling.
  The temperature at which a liquid boils is  thus totally dependant
on the amount of pressure to which it is subjected.  But the limits
within which that pressure varies near the  level of the sea, in ordi-
nary cases, are so  small,  that the boiling point may be looked upon
as one of the most important characteristic properties of a volatile
substance; and from the  facility with which it  may be  determined,
it is almost universally capable of being applied.  Hence, in descri-
bing such bodies, the  boiling point will be in all cases given; but,
for illustrating the present subject, a table  of the boiling points of
some of the most remarkable liquids is subjoined:
 
84       ANOMALOUS  PROPERTY OF  LIQUIDS.
Muriatic ether . . .	52°
Sulphuric ether . .	. 96°
Sulphuret of carbon .	. 116°
Pyroacetic spirit . .	132°
Water of ammonia	. 140°
Pyroxylic spirit . .	. 151°
                                   Water......212
                                   Nitric acid.....*4»o
                                   Oil of turpentine  .  •  •   315^
                                   Phosphorus   ....   554°
                                   Sulphur......601°
                                   Sulphuric acid ....   630°
    Alcohol  . *.....173°       Mercury......660c
  The boiling point is influenced by some other circumstances than
the atmospheric pressure j  the nature of the vessel  may alter it sev-
eral degrees.   Thus, in  a  glass or glazed porcelain vessel,  water
boils, under a pressure of  30 inches, not at 212°, but 214° j and in
graduating a thermometer, it is hence  necessary to use a metallic
vessel.  This latter appears to favour ebullition by the minute irreg-
ularities on its surface, affording a nucleus for the steam to form, as
a crystal dropped into a saline solution facilitates the crystallization ;
and if the smooth surface in the glass vessel be removed in  a single
point by a scratch with a diamond, the bubbles of steam will be seen
to form there before the general mass of liquid comes to boil.   The
influence of roughened or angular  surfaces in thus favouring the
escape of steam, may be shown very well by heating water in a glass
flask to boiling, and then alloAving it to cool a little, so that the boil-
ing shall completely cease ;  if, then, a  little filings of copper, or a
platina wire, be dipped into the liquid,  if the cooling had not gone
too far, the boiling will immediately recommence, the steam forming
at the edges and angles of  the rough substances introduced.
  The temperature of the  steam produced  is not affected by the
boiling point of the liquid.   Thus, although by dissolving salts, such
as chloride of calcium, in water, its boiling point may be raised to
264% the temperature of the vapour immediately over the solution
is found to be but 212J; for, though the temperature of a steam bub-
ble  which rises up through  such a solution must be 264% yet, as its
elasticity and latent heat are proportional to that temperature, it ex-
pands on mixing with the less elastic atmospheric air, and is cooled
down instantly to the ordinary boiling point.  The  heat of a water-
bath may thus be increased by the addition of saline  bodies ; but
the temperature of a steam-bath depends only on  the elasticity of
the steam.
  A curious, though only apparent, anomaly in the relations of liquids
to their boiling points consists in the possibility of the vessel con-
taining the liquid being heated  even to redness without the  liquid
boiling, though exposed  only to the ordinary pressure.  This may
easily be shown by heating a platina crucible to redness, and drop-
ping into it a small quantity of water ; the water remains on the red-
hot metal without disturbance, and appears  scarcely to evaporate;
but if another crucible be heated to 300% and the  water be poured
out of the first into the second, it  instantly boils, and is dissipated
in a gush of vapour.  The  reason is, that in the red-hot crucible the
water is not really  in contact with  the metal, and hence  the heat
passes to it with  extreme slowness; but the water wets the colder
crucible, and, absorbing from it all the necessary heat, is instantly
converted into steam.  The cohesive force of the metal  to the water
being diminished considerably, this lies in  a red-hot crucible as a
clean steel needle floats on water, or a globule of mercury moves 
        ARTIFICIAL  COLD BY  EVAPORATION.      85

upon glass, and is not affected by the heat until it wets the vessel,
just as the needle does not sink in the water until it is wretted by it.
At certain temperatures all liquids manifest the same peculiarity.
  When a liquid evaporates at a temperature below its boiling point,
it still  absorbs  and renders latent a great quantity of heat, and, in-
deed, more heat than it would render latent when converted into va-
pour by ordinary boiling.  It has been found, by accurate experi-
ments  with water, and there  is good reason for supposing it to hold
also with  liquids  in general, that no  matter at what  temperature a
liquid vaporizes, it absorbs the same total  quantity  of heat.   The
more of this that becomes sensible, the less is the portion which re-
mains latent, the sum of the  latent and sensible heats of the vapour
being at all temperatures the same.  Thus, with water evaporating at
               32°, the latent heat is 1180.  the sum being 1212
             100°,     "   "    1112,    "    "   1212
             212°,     "    "    1000,    "    "   1212
             300°,     "    "     912,    "    "   1212
  There is, therefore, no economy in evaporating or distilling at one
temperature rather than another, as the  same absolute quantity of
heat is necessary for the formation of the steam ;  but, for  other
reasons, the formation of vapours at low temperatures affords to  the
chemist processes of the greatest value.   Many vegetable substances
undergo important alterations in their chemical constitution and me-
dicinal properties if they be  exposed  for a long time  even to a heat
of 212J ;  and hence, in the preparation of extracts and inspissated
juices of plants, in pharmacy, forms of apparatus are sometimes
employed, in which the evaporation  is carried on in close vessels
connected with an air-pump, and in which a partial vacuum, meas-
ured by a barometer gauge, may be established.  In the manufacture
of sugar, this principle of evaporation at low temperatures,  by re-
moval of the atmospheric pressure, was the source of great improve-
ment,  as the true crystallizable sugar is converted  into the uncrys-
tallizable  sugar (treacle)  with  great rapidity at the temperature of
boiling sirup, and was hence, to a great extent, lost to the manu-
facturer.  By later improvements in the mode of applying heat, the
necessity of evaporating the  sirup in vacuo has been, however,
completely obviated.
  The absorption of heat in the conversion of a liquid into a vapour
at ordinary temperatures, may become the  source of considerable
cold ;  and it is, indeed, in this way that the greatest cold yet gener-
ated has been produced.  The cold which is felt when a little  ether
or spirits  of wine is dropped  on the hand, arises from this fact  ; and
by surrounding the bulb of a mercurial thermometer with some loose
cotton, and moistening it with liquid sulphurous acid, the quicksilver
in the  bulb may easily be frozen.   By placing some ether in a shal-
low, thin  metallic cup, which rests in a glass vessel containing a
small quantity  of water, and producing,  by the air-pump, the  rapid
vaporization of the ether, the water may be so frozen that the two
cups shall adhere firmly together by the intervening  sheet of ice.
   \\ ater  may be even frozen by its own evaporation, as in the cry-
ophorus, which consists of a long tube terminating in  bulbs which
contain some water, and from  which  the  air had been carefully ex- 
86  SYNCHRONOUS  FREEZING AND  EVAPORATION
pelled by boiling before the apparatus was completely closed.  The
                                            space above the wa-
                                            ter remains then oc-
                                            cupied only by wa-
                                            tery  vapour.   If  all
                                            the water be brought
                                            into  one  bulb,  and
                                            the other bulb be im-
                                            mersed in a freezing
                                            mixture, the vapour
                                            will condense there,
                                            and new vapour be-
                                            ing formed, a  distil-
lation will be produced from the one to the other bulb.  The vapour
which forms in the warm bulb must derive its latent heat from the
water which remains behind, and this is gradually cooled to the
freezing point, and ultimately  completely frozen ;  the latent heat
of about eight parts of water being given up to form the latent heat
of one part of vapour at 32°.  Even without the  application of arti-
               ficial cold, water  may  be frozen by its own evapo-
               ration.  Thus, if under the receiver of an air-pump
               we arrange  two flat dishes, the upper containing
               water,  the lower containing oil of vitriol, and then,
               having removed the air, we  leave the apparatus for
               a short time to act, we shall find the water in the
               upper vessel converted into ice.  Accordingly, as
               any portion  of  vapour forms, it  is immediately ab-
               sorbed by the sulphuric acid, which has a great af-
               finity for water; and the vapour being thus prevented
               from collecting, the loss of heat by evaporation pro-
               ceeds unceasingly, until so much heat has been re-
moved that the residual water is converted into  ice.
   In fluids more volatile than water, this synchronous freezing and
evaporation  may occur still  more simply.  Thus, if strong prussic
acid be allowed to form a pendant drop from  a glass rod, the drop
will become solid by the evaporation of one portion of it, and the
cooling of what remains.  The remarkable  phenomenon of the so-
lidification of carbonic acid  arises from the same principle.  A jet
of liquid carbonic acid being allowed  to  escape into  the air, one
portion instantly flashes into the state  of gas,  and absorbs so much
heat that the  portion which  remains is converted  into a compact
solid mass.
   In warm climates,  the evaporation of water is commonly employ-
ed to moderate the sultriness of the air, by the agreeable cold and
freshness it  produces.   The Spanish alcarrazas are  earthen vessels,
so porous that any  liquid which is put in  them  gradually  filters
through, and, evaporating from  the outer surface, cools the interior
mass.  In chemical operations, the same mode of refrigeration is in
constant use ;  and when describing these operations, "the action of
this principle, in the construction of the apparatus used,  will be re-
ferred to.
   The conversion of a liquid into vapour at ordinary temperatures
 
SPONTANEOUS  EVAPORATION.
87
is often called spontaneous evaporation;  and in the case of water,
from the great extent to which it becomes subservient to the econ-
omy of nature, this process is one of high importance.   It was for-
merly supposed that the atmosphere was necessary to evaporation;
and this idea was strengthened by the fact, that by a current of air
the evaporation is much assisted; but it is now established that the
pressure of air  is really an obstacle to evaporation, and that  a cur-
rent is useful, not by supplying new quantities of air, but by re-
moving the vapour according as it  is formed, and leaving  fresh
spaces into which it  may expand.   When a  liquid forms vapour,
the quantity formed is determined only by the space  into  which
the vapour may spread, and by the  temperature.   It is no matter
whether the  space be occupied before by other vapours or by air,
or whether it be a vacuum ; the quantity of vapour which can form in
it  is in all these cases the  same.
   Dalton was the  first who clearly showed that different gases and
vapours offer no resistance to each other's elasticity : thus, that the
particles of watery vapour in the air are not subjected to the press-
ure  of the atmosphere, but only influenced by the pressure  of the
particles of the same kind ; and hence, that at 32% when the elas-
ticity  of vapour  is only 0-200 inch, it retains perfectly its  elastic
constitution, though diffused through an atmosphere, the elasticity
of which may equal thirty inches.  If we moisten the interior of  a
bell glass, filled by air, with ether, alcohol, sulphuret of carbon, and
water, all  mixed together, there will be formed in the bell as much
 of the vapour of each substance as if the bell had been completely
 empty of the others; each vapour will exercise a pressure propor-
 tional to its elasticity, and by the  sum of all these pressures, the
 pressure of the external air will be equilibrated.  It is,  consequent-
 ly, possible to produce the rapid evaporation of one fluid, while an-
 other beside it, or even mixed with it, shall not evaporate at all;  it
being only necessary to remove the  vapour of the one as rapidly as
 it is formed, while the portion of the vapour of the second produ-
 ced in the first instance shall remain, and prevent its farther change.
 Thus, by placing  a shallow dish of dilute alcohol under the receiv-
 er of an air-pump, with a  quantity of quicklime, the latter combines
 with and absorbs the watery vapour as fast as formed; and there
 is, hence,  a continual evaporation of the water, while  the alcohol,
 after generating as much  vapour as once  fills  the receiver, is press-
 ed upon by it, and cannot  form any more.  In this manner, alcohol,
 almost quite pure, though much the  more volatile, in  the  ordinary
 sense, may be obtained by the evaporation of its solution in water,
 as it were to dryness.
   If the liquid be in excess, the  vapour possesses the elasticity
 belonging to its temperature ; but if there be not liquid enough to
 form so much vapour, the vapour formed  then expands, so as to oc-
 cupy the entire space, and its elasticity diminishes in proportion to
 the increase of volume ; vapours being regulated by the same law
 of pressure which holds with gases.
   If, thus, a bell glass of atmospheric air be confined over water at the tempera-
 ture of 80°, a quantity of vapour diffuses itself through the air, and, as there  is
 water in excess, the elasticity of that vapour will be 1 00 inch.  Now if we suppose
 the elasticity of the air to have been previously 30 inches, it will become, by the 
88
MOIST-BULB  HYGROMETER.
 addition of the vapour, 29, for the vapour counteracts one inch of the external at-
 mospheric pressure ; the air in the bell glass will then expand in the proportion of
 30 to 29 ; or, what is the same in practice, the volume of the damp air is the same
 as the volume which the vapour should occupy, if condensed in the proportion of its
 own elasticity to the atmospheric pressure, added to the volume  occupied by the
 air when dry.  It is thus that the volumes of gases collected over water are cor-
 rected for the watery vapour that is mixed with them.  Thus, in the analysis of a
 substance containing nitrogen, let us suppose that 8 54 cubic inches  of nitrogen have
 been collected over water at the temperature of 63°, and the barometric pressure
 being 29 35 inches ; at that temperature the elasticity of vapour is  058, and hence
 that of the dry air is 29 35—0-58=28-77.  The  volumes which they occupy are as
 these numbers, and hence the 8 54 of damp gas consists of ^^7X8 54=0 17 of
 watery vapour, and ff^x 8-54=8 37 of dry nitrogen.
   This volume should still be corrected for temperature and pressure before the
 quantity of nitrogen by weight could be obtained from it.
   Where the  air is not completely saturated with the watery va-
 pour, it is not so easy  to  determine  the  exact quantity of vapour
 which it contains.  One of the best methods consists  in cooling it
 until its volume is so much diminished  that the quantity of vapour
 is sufficient to saturate it, and  from the temperature at which this
 occurs the quantity of vapour may be calculated.   This temperature
 is termed the dew point of the  air or gas, because,  if cooled in the
 least below that point, a quantity of liquid water is deposited in the
 form of dew upon the neighbouring cold bodies.  This may be ea-
 sily  done by taking a tumbler  of wrater somewhat too warm, and
 cooling it gradually by dissolving in it  a little mixed nitre and sal
 ammoniac, until a slight deposition  of dew is perceptible on the ex-
 terior of the glass ; the water is then at the  temperature of the dew
 point.  Another method consists in observing the rapidity of evap-
 oration from  the surface of the bulb of  a  thermometer which  is
 covered with muslin kept wet by water.  The thermometer so  ar-
 ranged  is always at a lower temperature than an ordinary thermom-
 eter,  from the quantity of heat carried away by evaporation, and
 the temperature will be  lower in proportion to the amount of evapo-
 ration.   In  dry air, evaporation is quickest;  in air saturated with
 moisture  evaporation ceases, and in all intermediate degrees there is
 a connexion between the quantity of moisture already present in the
 air and the depression of temperature, which  accompanies the forma-
 tion  of as much more  as will saturate it.  This method  is peculiarly
 of interest from the means which it afforded  to Apjohn of ascertain-
 ing the specific heats of the gases already  noticed, and it  is easy
now  to  understand  the  general principle  upon which  his process
was established.   If we consider a certain space which may be fill-
ed by the different gases in succession,  and  these gases beino- dry
they are made to saturate  themselves with  watery vapour,  for the
formation of which they themselves supply  the heat, it will be ea-
sily seen, that  as the quantity of heat to be given out  is the  same
for all, their temperatures  will be reduced in a degree inverse to
their specific heats.  Hydrogen with a high specific heat will only
require  to cool about one third the number of degrees necessary for
 air or other gases.  The numerical results obtained by this process
 have been already given.
  Instruments for the purpose of determining the quantity of the  watery vapour
 which the atmosphere contains are termed hygrometers, and that of Daniell is one
of the most elegant and most useful.   It is a cryophorus, a b c, which in place  of 
STEAM AS  AMOVING  POWER.             89
                                 water  contains ether, and in,one bulb of
                                 which, b d, is fixed a very delicate thermom-
                                 eter.   This bulb is made of blackened glass,
                                 and the other bulb, a, is covered with a little
                                 bag of muslin. All the ether having been
                                 made to pass into the black glass bulb, a little
                                 ether is poured on the muslin envelope of the
                                 other.   This, by condensing the vapour inside,
                                 causes the ether to distil from the blackened
                                 bulb, and thus cools it and the air in contact
                                 with it, untd it arrives at the point of satura-
                                 tion, when a dew of liquid water begins to be
                                 deposited, which is at once observed upon the
                                 , blackened glass.   The internal thermometer
                                 I shows the temperature of the  bulb, which is
                                 the dew point, and a thermometer which is
                                 attached to the support of the  instrument
                                 shows the temperature of the external air.
                                   When the dew point has been thus deter-
                                 mined, the  subsequent  calculation  is very
                                 simple.  Thus, if there  be air at 72°,  of
which the dew point is 45°, the barometric  pressure being 30 inches, the elasticity
of steam at 45° is 0 316 ; and as the elasticity diminishes according  as the volume
increases from 45'' to 72°, the elasticity of the vapour in the  air at 72° isO 30; and
the  atmospheric pressure of 30  inches is produced by  the dry atmosphere, which
balances 2970, and the watery vapour which balances 0 30; and the respective
volumes are as these pressures.
  Gay Lussac has sought to establish a close relation between the manner in which
solid bodies dissolve in liquids, and that in which vapours diffuse themselves through
space.  Thus, if a solid body dissolved only because the liquid diminished the co-
hesion of its particles, the diminution of that cohesion  in another way should in-
crease the solubility very much: this, however, does not occur.  When paraffine
dissolves in alcohol, the solubility increases steadily with the temperature, and does
not  change more rapidly at the temperature when the paraffine melts than at any
other.  'I'his is the case also with many other easily fusible bodies.  Hence he com-
pares the diffusion of particles of the solid through the liquid to the diffusion of par-
ticles of vapour of water through the air, which is not affected by the solid or liquid
form of the water, but  depends only on the  temperature;  and certainly this view,
though not applicable to all, or even  the majority of cases of solution,  is of much in-
terest, as pointing out a similarity between solution and  vaporization  previously un-
noticed, and which may be applied to the explanation of many anomalous facts.
  The  employment of steam  as a moving power is of so much im-
portance to  science  and to the arts, that  it would be improper to
terminate a  discussion  of the  properties  of vapours without any
allusion to the manner in which it is utilized.   The little steam cyl-
               inder of Wollaston figured in the margin  contains all
               that is essential to the application of steam, in princi-
               ple, to produce motion.  A glass tube, terminating be-
               low in a bulb, is fitted  with a little  steam-tight piston,
               which slides  up  and down, the rod passing through the
               brass cap at  top.   If,  now, a little water be  placed in
               the bulb and  boiled, its steam, pressing on  the bottom
              of the piston, forces it  up ; and when at top, if the bulb
              be  dipped  into cold water,  the steam condenses, and
              the pressure of the extern il air forces the piston down
              again.   This may be  repeated  any number  of times,
              and is the essential element of the atmospheric steam
              engine of Newcomen.   It was in this  form  when Watt
              commenced his  improvements on it;  and by applying
all the resources of the exact  knowledge of the properties of heat
                                  M
 
90    BOILING  POINTS  OF  CONDENSED  GASES.
then first  obtained by himself and his  illustrious associate Black,
he  converted it, though  still without  changing its fundamental prin-
ciple, from the  machine of Newcomen, which had  been  rejected
from practice for its  inefficiency and expense, into the instrument
which, after the  art of  printing, must be  considered as  the  most
powerful material agent  of human improvement and civilization of
which mankind has ever obtained possession.
  The similarity of constitution of gases and  vapours has been already pointed out
on many occasions, and particularly, in page 21, the conversion of gases into liquids
by the application of great pressure  has been detailed.  A  liquefied gas so con-
tained in a close vessel is precisely in the condition of water heated in a digester,
as in the apparatus figured in page 80,  far above its boiling point, and generating
steam possessed of considerable tension. On this analogy has been founded an in-
teresting speculation concerning the temperatures at which the gases would, at or-
dinary pressures, assume their liquid form, that is, their boiling points when  liquid,
thus:
         At 44-5° the tension of liquid  nitrous oxide is 50 atmospheres.
         At 320°         "         "         "      44
        For 125° an increase of tension of

Steam exerts a pressure of 50 atmospheres at
                  and of 44      "      "
For six atmospheres the difference is   ....
Liquid carbonic acid exerts a pressure of 25 atmos.  at
                               and of 20  "
The tension of steam is 25 atmospheres at   .   .  .
                      20      "      "...
Muriatic acid exerts, when liquid, a tension of 25 atmos.
                                  and of 20   "
Steam balances 25 atmospheres at......
              20      "     "......
Ammonia liquefies and exerts a pressure of 65 atmos.  at
                               and of 5
Steam exerts a pressure of 6 5 atmospheres  at
                        50     "       "  .
6 atmospheres.

511-5°
497-5°
 140°, or just the same.
   ^o \ Difference, 20°

418-5° \ Difference, 21°
                                                 *f   23° [ Difference, 22°

                                                   4185° S Difference, 21°

                                                      3„0 I Difference, 18°
                                                   326°  )
                                                   307 5° S Difference> 18 5°

  It is hence evident that, in every case, the rate of increase of elasticity of these
gases with the temperature follows the same law as that of steam ;  and there is,
therefore, good reason to believe that, if the elasticity were diminished to one  at-
mosphere, the reduction of temperature necessary to effect it  should be regulated
by the same  law as that of watery vapour ; the gases should then, under the ordi-
nary pressure of 30 inches, become liquid,  and when liquid, their boiling points
should be:

    Nitrous  oxide...........— _ 2524° Fahrenheit.
    Carbonic acid...........— __ 2308°      "
    Muriatic acid...........=  __ 202  0°      "
    Ammonia.............=  __  63 4°      "

  The great  increase of elasticity which these liquefied gases acquire by a change
of temperature, limited to a very few degrees, has led  to sanguine opinions of their
advantages as a  source of power in machines.  No experiments at all sufficiently
satisfactory to be decisive upon the question have as yet been made.
  There are  some other properties of gases which, although closely connected with
the subject now discussed. I shall postpone,  in order to introduce them where they
are found to be  of the most practical  importance.  Thus, the manner in  which
gases spread through each other, in virtue of their diffusive power, will be descri-
bed under the  head of Atmospheric Air, to the proper constitution of which this
law is indispensable.  The relation of  gases to water, their solubility in that  and
other liquids, and the various modes of  depriving them of moisture for the purpose
of chemical  experiments, shall enter into the history of the physical and chemical
properties of water. 
CONDUCTION  OF HEAT.
91
                          SECTION V.

         OF THE  TRANSMISSION OF HEAT THROUGH BODIES.

  It is a matter of every-day experience, that heat may be propagated
from one part of a body to another, and also that this propagation
takes place in unequal degrees with different bodies.  Thus, if one
extremity of a poker be heated to bright redness, the other will be-
come so  hot as to be intolerable to  the hand;  while, if a stick of
the same length be inserted in the fire, the heated extremity may be
completely burned off, without the farther extremity having its tem-
perature raised in any remarkable degree.   The extremity of a glass
rod may  be melted by  the flame of a blowpipe, though held in the
fingers scarcely an inch from the flame : but we shall find it difficult
to melt the extremity of a silver wire, from the heat  spreading it-
self generally through its mass,  and  elevating the temperature of
its entire length almost to the same degree.   Bodies which act like
silver are  said to conduct heat well, and are termed conductors.
Bodies which intercept it, like wood or glass, are termed non-con-
ductors.  It is only  a difference of  degree, for there is no body
which prevents totally the  passage of heat across its mass.
  The propagation of heat  through a body, in virtue of its conduct-
ing power, is supposed to take place from particle to  particle,  pre-
cisely as, when we apply a heated to a cold ball of iron, the latter
becomes warmed at  its point of contact.  If, in place of using balls
of iron, cubical masses were employed, touching by their surfaces,
the  communication  of heat would be  much more rapid, from the
greater number of points at which transmission could take place.
In the interior of a body we should expect, therefore, to find the
degree of approximation of the particles to have some influence on
the rapidity of transmission, that is, on the conducting power, or, in
other words, that the power of conducting heat should have some
relation to the density and the cohesion of each body.
  Many series of experiments have been made to determine the con-
ducting power of different bodies.  Such experiments may be  ar-
ranged in a variety of ways.  Thus, if a number of similar rods, of
different  substances, be coated to a  certain distance from one ex-
tremity with wax, and then heat be applied to the other extremity,
the wax  will melt according as the temperature of each rod rises,
from the transmission of the heat along  it; and the length of the
coating melted at the end of a certain time will be  a measure of its
conducting power.   Another mode  consists in forming the sub-
stances to be tried into disks, and, having placed a small morsel of
phosphorus upon each, warming all  equally by laying them  on a
heated surface.   The phosphorus inflames first upon the disk which
transmits most readily the heat, and on the other disks in the order
of the conducting power of their  substance.  But such experiments
are  only  useful in giving the order of conducting power in a gen-
eral way, and are inapplicable to exact purposes.
  The best results are those which have been obtained by Despretz,
whose method was the following.  All the bars  used in his  experi-
ments were square prisms, and were all covered with the same black 
92 RELATIVE  CONDUCTING  POWER  OF  SOLIDS.
 varnish, in order that the loss of heat from their surface might be
 exactly similar.   At every four inches of their length was a hole
 bored to half the depth of the bar, which was  filled with oil or mer-
 cury, into which the bulb of a  delicate thermometer dipped, so as
 at every instant to show the temperature  of the bar at this series of
 points.  By means of a lamp applied to one  extremity of  the bar,
 it was strongly heated, and the steadiness of the  heat secured by
 finding-  the temperature of the thermometer nearest the lamp to be
 stationary for six hours,  the usual time  of  an experiment.  The
 temperature of the air of the  room, which should scarcely at  all
 vary during that time, is  known by a thermometer.
   After the bar has been heated for two or three hours, each ther-
 mometer arrives at a temperature which thenceforth continues the
 same as long as  the source  of heat  is kept up.  This temperature
 depends on the difference  between the quantity of heat that  is prop-,
 agated along the bar from the lamp, and the quantity which is lost
 by cooling.  The excess  of  the temperatures of the thermometers
 attached to the bar above  the temperature of the room, forms, there-
 fore, a series, the ratio of which depends upon the conducting pow-
 er of the bar in  a manner which, though not  simply proportional,
 is easily deduced from it by calculation.   By these principles,  of
which the theory was given by the celebrated Fourier, Despretz has
deduced, from his experiments, the following conducting powers,
gold being assumed as the standard for comparison.
Tin ... .	. . 304
	. . 180
	. . 236
	. . 122
	. . 11-4
    Gold.......1000
    Silver.......973
    Copper......898
    Platinum .-.....381
    Iron.......374
    Zinc.......363
Although this series presents, when compared with  the  specific
gravities, or other physical properties of these bodies, very great
diversity, yet it  is remarkable that the more expansible and more
fusible metals, tin, lead, and zinc, are those which conduct  heat
worst.  The position of platina is, however, quite anomalous, and
must prevent any attempt  at generalization.
  The difference of the conducting power of solid bodies is  of daily
utility in ordinary life, as well as in chemical operations.  It is thus
that substances of exactly the same temperature may produce quite
opposite  sensations to the hand.   If we grasp in one hand  a piece
of metal, and in  the other a piece  of wood,  both at 180% the hand
will be reddened and blistered by the former, but the latter will feel
only moderately warm.  If the metal and  wood be both cooled to
32% the former will feel  intensely cold, but the latter scarcely at all
so.  In the first case, the metal gives out its heat to the hand, and
in the second, abstracts  it from the hand so rapidly that the nerves
and circulation become acutely  sensible of the  change; but with
the  wood, from its low  conducting power, the  flow of  heat takes
place  so  gradually in each direction as almost to escape  notice.
The brickwork of a fireplace or of a furnace is for the purpose of
keeping the heat generated by combustion f.-om spreading to the
surrounding bodies, and so being lost.  It woi Id be difficuU  to light 
CONDUCTING POWER OF  LIQUIDS.        93
a fire in a massive metallic grate, for the heat would be so rapidly
carried off by its conducting power, that the fuel, if not well lighted
before being introduced, would be cooled down and extinguished.
  Liquids conduct heat but very slowly ; so slowly, that they were
long considered to be true non-conductors.   It is now satisfactorily
proved,  however, that they do conduct; and although no accurate
numbers have been obtained, their power appears to be generally as
their density ; mercury being the best conductor,  and alcohol and
ether being the worst.  This low conducting power may  easily  be
demonstrated by experiment.  Thus, if in ajar of water an air ther
mometer be inverted, so that its bulb shall be very   ^-^
near the surface, and the cup containing ether be laid   (?f?)\
floating on the water, as in the figure, the ether may
be set on fire, and allowed to burn for a considerable ;
time before any action on the thermometer becomes ||
sensible, and  even then the  heat  appears  to  havejj'1
travelled rather by the solid material  of the glass j!
than by the water.   If a little water be frozen in the |
bottom of a narrow tube, and a solid adherent piece!'
of ice being so obtained, if more  water be poured  in j
so as to cover the ice to the depth of a few inches,
on  inclining  the  tube, and applying the flame of a
lamp to the water near the  surface, it may be kept  boiling violently,
and for  a long time, before the ice begins to liquefy, and even then
it is by  the glass material of the tube that the heat is  conveyed.
  Notwithstanding such facts, it  is still well known that heat may
be  communicated through large quantities of fluid, so  that the mass
shall be rapidly and uniformly heated.   It occurs,  then, not by con-
duction, but by diffusion ; and the source of heat cannot be applied
indifferently to any surface of the fluid, as it might  be  to a solid
body, but must  be applied underneath.   When any  portion of a
liquid is heated, it expands, and,  becoming  specifically lighter,  as-
cends in the mass,  and is replaced by the  colder  and heavier por-
tions, which, being  in their turn  heated, ascend also,  and
thus generate a circulating current of ascending warm,
and descending  cold liquid,  as in the figure, by which
every particle of the  liquid is brought in succession into
contact  with  the  source of heat, and the resulting  tem-
perature quickly and uniformly gained.
  In the case of water, and such liquids as have  a point
of maximum density, this communication of heat, by as-
cending and descending currents,  occurs in the inverse
order below that point.  Thus, to warm water  which is
below 39-5°, the  heat should be applied above, or to cool
it farther the heat should be abstracted below.  On this
property depends the preservation of the lakes and rivers
of these countries  from total and  eternal congelation.
When the mass of water becomes cooled to  39-5%  the su-  ¥   I |.|lljf j
perficial layer becoming lighter as it cools more, prevents, \l  f  k\■■%
by  its non-conducting power, the  farther abstraction of  v I ty/
heat from the deeper portions; but when the warm air of  N*4i!C^
spring plays on it, the heat is rapidly diffused from  above down-
ward, until the temperature of the entire mass is raised to 39-5°. 
94   COMMUNICATION  OF  HEAT BY  RADIATION.
   In  their mode of communicating heat, gases resemble  liquids.
 Their true conducting power is quite insensible, but by the currents
 which are produced by the ascent of warm and the descent of cold
 particles, they abstract and communicate heat with great rapidity.
 The difference is easily felt by holding the hand  first at the side
 and then over the flame  of a candle, the distance being the same.
 In the latter case the great increase  of heat arises from the ascend-
 ing current of heated  air,which does  not affect  the hand when at
 the side.
   The non-conducting power of gases is practically of great impor-
 tance.  The different kinds of clothing owe their warmth to the fact
 that they prevent the heat of the body  from escaping ; this they ef-
 fect not  so much by the  power of their proper  solid substance, as
 by being of a loose and spongy texture, they imprison in their pores
 a quantity of air, which, not being able to form those continual cur-
 rents, acts as  a non-conductor.  The more loose and spongy, there-
 fore, the tissue of a cloth may be, the  more air does it confine and
 the warmer it is.  This  is fully supported by the  experiments of
 Rumford, who, having heated to  the same degree  a thermometer
 imbedded in  the  materials of which  clothing is generally made,
found that it cooled through 135J with
Air in 576"	Raw silk in 1284
Fine lint " 1032"	Beaver's fur " 1296'
Cotton wool " 1046"	Eider down " 1305'
Sheep's wool " 1118"	Hare's fur " 1315'
  When these bodies are tightly compressed, so as to diminish the
quantity of air confined within their tissue, the power of retaining
warmth diminishes in the same degree.
  On standing before a fire, the influence  of the heat is felt even
at a considerable distance, although the air is, as has been just stated,
so bad  a conductor  that the warmth cannot be ascribed to  direct
transmission through its mass ;  and  since a current of air is passing
to the fire in order to supply its conduction  and produce the draught
of the chimney, no heat can arrive at the body by the current from
the  fire. Also, if a  heated iron  ball be suspended in a room,  it
propagates heat in all directions, although the current of air which,
so far as has been yet described, alone can convey any great quan-
tity of heat, is directed only upward.  Heat is therefore propao-ated
by a third mode, distinct from diffusion and from combustion * and
the  heated body being supposed to emit actual quantities of heat in
straight lines or rays from  every point of its surface, this mode is
termed radiation.
  Radiation is remarkably distinct from conduction and diffusion
m not  requiring for  its existence any material  medium.  On the
contrary the existence of  any coherent substance  in their path is
an obstacle to the transmission of  the  rays of heat, and hence in
most solids and liquids there is little heat transmitted by radiation,
unless we look upon conduction as a kind of radiation from particle
to particle m the interior of the mass, and it is only with  o-ases that
radiation is equal to what  takes place in empty space.   A heated
body throws off rays of heat  precisely as a luminous body throws
off  rays of light; and in every detail of physical constitution that 
PROPERTIES  OF  RADIANT  HEAT.         95
has yet been discussed,  there exists a perfect similarity between
heat and light in these radiant forms.
  Different bodies radiate heat with different powers, which appear
to depend more upon the mechanical nature of the surface  than
upon the internal constitution of the body.   When any substance is
interposed in the path of the rays of  heat, these are either reflected,
or are absorbed,  or they pass through the body without loss.  In
general, all these effects are in part  produced ; that  is to say, one
portion of the incident rays will be transmitted, another portion re-
flected, and  a third will  disappear by being absorbed.  There are
thus in relation to radiant heat four qualities, which various sub-
stances possess in different degrees, the radiating, the absorbing, the
reflecting, and the transmitting power.
  The rays of heat may, like those of light, be concentrated by re-
flection or refraction.  By the former mode, that originally used by
Prevost and  by Leslie, the properties of radiant heat  may be de-
monstrated in a simple manner.
  The form of apparatus generally employed for demonstrative ex-
  Eeriments on radiant
  eat  consists  of re-
flecting mirrors of pol-
ished silvered copper,
of a paraboloid form,
A B ;  the property of
this figure being that
rays  emanating from
the focus of one mir-
ror are reflected  from
it in parallel directions, and falling thus parallel upon the other, are
brought to convergence in its focus.  In this manner the  heat ra-
diating from a body may be  concentrated upon a single point, and
all its properties determined with great precision.  Thus, a hot iron
ball may be placed at a  distance of  a few feet from a bit of phos-
phorus for any length of time without affecting it; but if the hot
ball be placed in the focus of one mirror, C, and the phosphorus in
the focus of the other, D, this immediately begins to  melt, and after
a moment bursts  into flame.  If the  hand be
held in the focus, it feels  hot; but, on moving
it much nearer to the  source of heat, the  iron
ball, it feels cooled.   It is thus not by the di-
rect conduction of the air, or by diffusion of
warm  currents, that the effects are caused,
but from the radiation  of heat in a form which,
like light, admits of being reflected from pol-
ished surfaces, and concentrated upon a focus,
and which will be found to follow the  analogy
of light through all its branches.
  If a thermometer be placed in the  focus of
the  mirror opposite the heated ball, it imme-
diately indicates the rise  of temperature, and ,-
may serve to measure it.  But it is only the
air thermometer which is delicate enough for
 
96          OF  THE  RADIATING,  ABSORBING,
such experiments, and it  is specially for this use that the differen.
tial air thermometer is constructed.  One bulb being placed in the
focus, the difference  of temperature between the two  bulbs is in-
stantly shown;  and it is thus also proved that the rise of tempera-
ture is local, that it is confined to the point  where the rays of heat
are brought to meet, for the instrument is insensible to every gen-
eral change of temperature, no matter how extensive.
  By means of  this apparatus, the radiating  and absorbing, as well
as the reflecting and transmitting powers of bodies may be exam-
ined.  The radiating power may be conveniently exhibited by filling
                                     0  a  tin  cube,  a, with boiling
                                         water, and applying to the
                                         surfaces of the cube the bod-
                                         ies which  are to be exam-
                                         ined.   Thus, one side being
                                         left   brightly polished, an-
                                         other dimmed by being rub-
                                         bed with sand paper, a third
                                         covered by  paper, and the
                                         fourth being blacked by the
                                         smoke from  a candle,  each
side, on being turned towards the mirror c, gives out a quantity of
heat  proportional  to  its radiating  power, and this  being reflected
and brought to bear upon the thermometer in the focus, is measured
by  its  indication.   Leslie thus found the radiating power of the
following surfaces to be relatively,
Lampblack......100
Writing paper.....98
Crown glass.....90
Ice........85
Red lead......80
                                       Plumbago......75
                                       Tarnished lead  ....  45
                                       Clean lead......19
                                       Polished iron.....15
                                       Other bright metals ...  12

  It is here evident that the radiating power is quite independent of the colour of
the body, and that, in all cases, those bodies with bright metallic surfaces radiate
least, the radiating power of lead being doubled by simply tarnishing its  surface.
It  has been rendered probable, however, by recent observation,  that  it is not  the
degree of polishing of the surface which influences the radiating power, so much as
the closeness and density of the exceedingly thin surface layer, on which the quan-
tity of radiant heat depends.  In the process of polishing, the surface of a  metallic
plate, particularly if it be rolled, is very  much compressed, and in  this state radiates
in  the lowest possible degree ;  but if, by rubbing with sand-paper, that dense film of
compressed metal be removed, the softer material underneath radiates with nearly
double the power.  If a plate of silver be cast without being subjected to any press-
ure, the surface, although perfectly bright, radiates with a power  of 22 ;  but if it be
dimmed by rubbing with sand-paper, the compression, even though  so slight, di-
minishes the radiating power to 12.   Substances which  are highly elastic, as ivory,
or very hard, as agate, radiate in the  same degree, no matter  what may be  the
rough or smooth condition of the surface.
   That the texture of the surface should influence  the radiating power  is easily
comprehended,  when we know that it is not from the external surface, but from a
little depth below it, that radiation actually takes place.  If radiation  were truly
from the surface, every point of it emitting rays in all directions equally intense,
there should occur inequalities in the temperature of the surrounding bodies of the
most remarkable and intolerable kind   Thus,  let us suppose two surfaces at right
angles radiating heat, as, for instance, two surfaces of a red-hot poker.  A body A,
at a certain  distance from the angle, should have  its temperature  raised much
more than a body, B or C, directly opposite either side, for it should receive the  rays
A M and A M'  equally intense, while the bodies B and C should receive  from the 
       AND  REFLECTING  POWERS  OF  BODIES.     97

■ame points only the rays B  M or C M'.  But the rays
emanating not from the surface at M or M', but from N' and  A^>^
N, at some depth below, the oblique ray N A has to pass    \0'~-
through so much a thicker stratum of solid matter from N     \\
to P than the direct ray from N to M, that the conjoint     \ \
action of the two  does  no more  than  enable the sur-      \
rounding bodies  to attain an equable temperature.   Bodies       \
obliquely exposed to a fiat radiating surface receive less c    jj
heat; not that a  smaller number of rays impinge upon them,
but that  a greater proportion  of heat  is lost in escaping
from below the surface of the body.
   The radiating powers  of bodies are the foundation of numerous
applications in the  arts.   Those bodies  which radiate least  cool
slowest; and hence, if it be required to keep any material hot  for a
considerable  time, it should  be enclosed in a vessel with a bright
metallic surface, that being the  kind Avhich retards  most the escape
of heat.  If, on the  contrary,  the  object be to diffuse heat, the best
radiating surface should be made  use of.   It is thus that the tubes
by which heated air, or water, or steam is supplied to buildings, for
the purposes  of warmth, should be  bright and polished until  they
arrive at the  precise locality where the heat is to be given out, but
should there  be painted with whitelead or lampblack, the surfaces by
which the heat is  most rapidly given out.
   If two tin vessels, precisely similar in form, but one being painted
and the other polished, be filled with warm water and placed in a cold
room, that  which is painted will cool more rapidly than the other, in
consequence of its greater power of radiation.   If the two vessels,
when cold, be placed opposite a steady fire,  the temperature of the
water in that which is painted will be observed to rise more rapidly
than that of the other ; it will absorb the heat of the fire, precisely
as it had given out the heat of the water,  with most rapidity.  The
bodies, therefore, that radiate best, absorb heat, likewise, with greater
power, and those which, when hot, cool most slowly, are those also
which have least tendency to receive radiant heat.
  The absorbing and  radiating power  may even be proved to be exactly propor-
tioned to one another  by the following experiment.  A large differential thermom-
eter is arranged, whose bulbs are chambers  of considerable size, presenting large
and equal plane  surfaces on the sides that are towards each other.  Of these, one
is polished and  the other coated.  Midway between them is placed a canister hav-
ing equal plane surfaces, facing each of the former respectively, and one polished,
the other coated with the same pigment as before.   This canister is filled with hot
water, and is  capable of turning on a vertical axis; thus the coated surface of the
canister can be turned to the coated bulb or to the polished; in the  former case, a
great effect is produced upon the  coated bulb, and a very small effect upon the
plain ; in the second case, the better radiating surface is directed  to the worse ab-
sorbing one, and  the worse radiating to the best absorbing, and the liquid in  the tube
remains perfectly stationary, establishing thereby the exact equality of the absorb-
ing and radiating powers.
   Although colour is without influence on the radiating power, it yet
appears  to  influence  the  absorbing power in a remarkable degree.
If pieces of cloth of various colours  be laid upon snow, and exposed
to the direct  solar rays, that which is black will, by absorbing more
heat, melt the snow away from under it,  and sink deepest.   White
will sink least, and the others in the order of their depth of colour.
It is, therefore, with  reason that dark-coloured cloths are preferred
for winter use, and light colours for summer.   It is, however, to be
 
98
TRANSMISSION  OF  HEAT.
noticed, that it is only upon the absorption  of those rays of  heat
which accompany rays of light that colour has this power.
  The great difference of absorbing power of a blackened and of a
metallic surface may easily be shown by coating one bulb of a dif-
ferential thermometer with  silver leaf and  blackening  the  other.
When, with the same source of heat, the rays are received upon the
silvered bulb, scarcely any rise of temperature can be observed ; but
wh-n the blackened bulb is placed in the focus, the rise is much
more than would have occurred with the thermometer in its ordinary
condition of the bulb with  a glass surface.
  The mirrors which are used in those experiments do not become
sensibly heated until after a long  time ; they absorb but very little
heat: but if the surface of the mirror be smeared with glue, it loses
to a great degree its power of reflecting;  and having thus obtained
an absorbing and radiating power, it very soon becomes warm.  If
it be coated with lampblack, its reflecting power vanishes, and its
surface becomes highly absorbent.  The reflecting property is there-
fore possessed by the surfaces of bodies in the inverse degree to the
absorbing and radiating powers, and hence the best  absorbers are
those which reflect least.
  The heat which is naturally associated with light in the sun's rays
is capable of being so concentrated  by reflection, that in the focus
of a burning mirror, results equal to those of the most intense arti-
ficial heat may be produced.   The heat of the sun's rays may also be
concentrated by refraction, the heat accompanying the rays of  light
in their passage across lenses ;  hence  the use  of the burning glass.
But when we thus come to discuss the property possessed by bodies
of transmitting heat through their substance, it becomes necessary
to look farther to the source and intimate structure of the heat.  For
the results  which have as yet been  described, we are indebted al-
most exclusively to Leslie, but the power of transmitting heat could
only  have  led to the important consequences  deduced  from it by
Forbes and Melloni more recently, when  the advance of other sci-
ences had placed at the disposal  of the experimenter measures of
temperature infinitely more sensible than any form  of thermometer
formerly in use.
  It is by means of the thermo-multiplier and galvanometer that the  effects  of the
transmission of heat require to be observed.
  The apparatus employed by Melloni was, in its general arrangement, such as is
represented in the subjoined figure.
  On a steady table there rests a frame M M, along the middle of which a slip R R
Is cut, by which the various stands and supports may be moved back and forward,
so as to vary their distances from each other.  On the stand S is  placed the source
of heat; in the figure it is a coil of platina wire ignited by a spirit lamp; but the
flame may be surrounded by a cylinder of blackened copper, or it may be a vessel
of boiling water, or an argand or Locatelli lamp.  The rays proceeding from it are
received by the thermo-multiplier P, from which the wires F F convey the electri-
city generated to the galvanometer G,  which for steadiness is placed at a distance,
and on brackets secured against a wall  These parts, P and G, will be represented
in full in the chapter on electricity. If it be required to study the action of a plate
of any substance upon the rays of heat, the screen E is interposed, having an aper-
ture 0, somewhat smaller than the plate to be employed.  This last is then sup-
 ported immediately behind the aperture by means of the little frame S', so that no
 heat can reach the thermo-multiplier unless after having passed  through it.  As it
 is of great importance to have the end of  P farthest from the lamp uninfluenced by
 any disturbing causes, the screen E" is placed immediately behind it, to  protect it 
TRANSMISSION  OF  HEAT.
99
from irregular radiation and from currents;  and as the action of the heat upon the
pile must be limited to the actual time of the experiment, the double screen E' is
interposed immediately next the lamp, and, being provided with a hinge, is raised
or lowered  at the moment when the rays of heat are to be allowed to pass or are
to be intercepted.
  The, oniii-e of the thermo-multiplier is occasionally fitted with a conical  tube of
plated brass, for the purpose of collecting the rays  of heat in greater number ; but
that is not often wanted.
  The reflecting power  of bodies has been exactly determined by
Buff to be as follows.  Of 100 rays incident at an angle of 60° from
the perpendicular, there  are  reflected, by

        Polished gold................76
           "   silver...............62
           "   brass...............62
       Brass without polish.............52
       Polished brass varnished............41
       Glass plate blackened on back..........12
       I.ooking-glass................20
       Metal plate blackened.............6

  The power of a  body  to transmit heat is termed transcalescence,
and of intercepting heat  intranscalescence.   These properties  are to-
tally independent  of the power of transmitting  light, as will be at
once seen from the following table.   Of  100 rays proceeding from
the flame of an argand lamp, there are transmitted by
Rock salt ....	colourless	92	Glass coloured		yellow	22
Calc spar ....	do.	62	Do. . . .		blue	21
Smoke topaz . . .	brown	57	Sulphuric ether .		colourless	21
Plate glass ....	colourless	40	Gypsum . . .		do.	20
White agate . . .	do.	35	Tourmaline		green	18
Glass coloured . . .	violet	34	Opaque glass		black	16
Do......	red	33	Citric acid .		colourless	15
Chromate of potash .	orange	33	Alcohol . .		do.	15
Borax......	colourless	28	Alum . .		do.	12
Glass coloured . . .	green	231	Water . .		do.	U
Rock salt is thus the most transcalescent substance that has been 
 100      PERMEABILITY OF  BODIES  TO  HEAT.

 found.  Glass arrests more than one half of all the heat which it re-
 ceives, while colourless and transparent alum,  and the most limpid
 water, arrest more of the heat which they receive than the deepest
 coloured  glasses, or topaz,  or  quartz, so  brown  as to be  quite
 opaque.
  But not merely do different bodies  act differently on rays pro-
 ceeding from the same source,  but  the same body  may allow the
 heat from  one source to pass freely through its substance, and inter-
 cept partially or completely the heat radiating from another.   Thus
 using, in his experiments, the heat  emanating from five kinds of
 source, first, the argand lamp ; second, the lamp of Locatelli, which
 is remarkable for the steadiness  of its flame ; third, a red-hot spiral
 of platina wire; fourth, a blackened copper plate heated to 734° ;
 and, fifth, a blackened copper plate heated to 212J by boiling water,
 Melloni found the heat arising from  these sources to be transmitted
m the following proportion per cent. ; the results with the argand
lamp, having been given in the last table, are here omitted.
Substance.	Locatelli Lamp.	Ignited Pbtina.	Copper at 734".	Copper at 212".
Free radiation .	100	100	100	100
Rock salt .	92	92	92	92
Fluor spar . .	78	69	42	33
Calc spar . . .	39	28	6	0
Plate glass . .	39	24	6	0
Agate ....	23	11	2	0
Gypsum . . .	14	5	0	0
Alum ....	9	2	0	0
Ice.....	6	0	0	0
  Eock salt is thus not only the most transcalescent body, but it is
that which alone is  equally transcalescent to heat of all tempera-
tures.   The rays of heat evidently acquire a greater power of trans-
missibility as  the temperature of the  source increases, and hence
glass arrests scarcely any portion  of  the  direct solar heat, while
from the argand lamp it intercepts 47; from Locatelli's lamp, 61;
from ignited platina,  72; from copper at 734 \ 94 ; and from cop-
per at  212°, 100 per cent. The  action of these media upon radi-
ant heat consists not merely in stopping a certain portion of it, but
in separating it into two  portions, physically distinct, of which one
is capable of transmission, while the other is absorbed.  Hence a
second plate, of the same kind of substance, exerts but a very slight
.action  upon the  heat which has already passed  through the first.
Thus, though a plate of alum allows only 9 in 100 of the direct rays
of the  lamp to pass, yet  it admits of the passage of  90 in 100 of
rays which have already passed  through a plate of the same sub-
stance ; and calc spar, which transmits only T3A of the direct heat
transmits  91 of that which had passed through alum, and 89 of that
which  had passed through gypsum.  On the other hand,  a green
tourmaline, which transmitted  18 out of 100 rays directly  incident
upon it, intercepts T\\ of  those which had previously passed through
alum, but gives passage to T\\ of  radiant  heat which had passed
through black glass.
  The nature  of the  physical  distinction between the intercepted
and the transmitted portions of the heat is to be found  in the differ- 
      ANALOGY  OF  HEAT  TO COLOURED  LIGHT.  10]

 ent refrangibility of the  rays of heat emanating from sources of va
 rious temperatures.   If the rays of heat emanating from a lamp be
 incident upon a rock-salt prism, they will undergo refraction, sub-
 ject to the same law of the sines  as in the case of ordinary  light,
 and  there will be obtained a  band or  spectrum of rays from  the
 lamp; the most refrangible will coincide with about the middle of
 the luminous spectrum,  while the least refrangible will extend far
 beyond the limits of the least  refrangible rays of light.   The  mean
 refrangibility of heat is therefore less than that of white light, and
 the  length of its undulation,  if that theory be adopted, longer in
 proportion.
   If, now, the heat spectrum so obtained be examined by means of
 the media which have been already noticed, the explanation of the
 peculiarities in their action will be at once observed.  Rock salt al-
 lows the rays  of all degrees of refrangibility to permeate its mass;
 it is to heat what perfectly colourless glass is to white light;  it acts
 equally on all portions of it.   Alum stops all but the very least re-
 frangible rays ;  it is to  heat what  ruby-coloured glass is  to  light,
 which allows only the rays of the  least refrangible extremity of the
 spectrum to pass through.  Glass, gypsum, and such bodies as give
 passage  to the rays of  least and  of mean refrangibility, resemble
 those  orange-coloured glasses which exclude the blue and violet
 rays of light,  but admit  the others.
   After  long search, Melloni at last found that by coating with soot
 the surface of a plate of rock salt,  it became to heat what blue glass
 is to light; it excluded the rays of inferior refrangibility ; and when
 a plate so  prepared was combined with a plate  of alum, all heat was
 intercepted, precisely  as when, by  laying a plate of blue and a plate
 of orange glass together, perfect  opacity is produced,  the one ab-
 sorbing  the portion of  light which alone the other is  capable of
 transmitting.
   The rays of heat derived from sources of different temperatures
 are thus analogous to the rays of  light  of different colours.   The
 higher the temperature of the source, the more does it resemble  red
 light;  the lower its temperature, the greater is its  analogy with the
 violet  rays.   Hence alum absorbs all the heat from boiling water,
 but gives passage to that from the argand lamp; but alum  is like a
 glass so  deeply coloured red  that  it is almost opaque, and trans-
 mits only a small portion even of  its own coloured light that may
 fall upon it.
  When a ray of heat is incident upon a doubly-refracting substance, it follows
precisely the same law as  light, and is refracted doubly. In this case, also, the
rays after  emergence are found to be  polarized in planes perpendicular to each
other; and all those consequences of the mutual action of polarized rays which give
rise to such magnificent  phenomena of colours in the case of light, must occur with
heat, and be  made sensible if our organs  or our instruments were of a construc-
tion suitable for their appreciation.  As yet, however, the fact which  alone remains
wanting towards a physical theory of heat has not been observed—that of interfe-
rence ; up to the present time, the actual production of cold by  the combined action
of two rays of heat has not been seen ; but the closeness of the analogy, which in
this ease alone requires additional observation between light and heat, is so remark-
able, that we can have little hesitation in referring these agents, in their radiant
i'onn, to the same kind of physical arrangement.
  There is no difficulty in conceiving radiant heat to consist in vibr' linn* *»f the
same ethereal medium which produces light, and in considering that th', d J>vence 
 102   RELATIONS  BETWEEN  HEAT  AND  LIGHT.

 between heat and light should be in the magnitude of the vibrations, and the conse-
 quent refrangibility of their rays.  On the contrary, it is not reasonable to sup-
 pose, that while we are conscious  of the waves in air, although they may vary in
 length  from 32 feet to 3V of an inch, the limits of our sensibility to  the ethereal
 waves should be so narrow that the shortest (violet) is to the longest (red) as 60 to
 38;  it is more  consonant to our idea  of the various and beautiful uses to which
 every object of creation is made subservient, to believe that, while the waves with-
 in these limits produce upon the eye the sensation of coloured light, another  range
 of lengths, greater than those of light, should give to our organs the sensation of ra-
 diant heat; and that  a third  order of vibration, still shorter, and more refrangible
 even than violet light, is capable of acting upon the elementary constituents of bod-
ies, and  constitute the chemical rays.   The coexistence of these three  kinds of rays
in solar  light is  an argument remarkably in favour of this view ;  for we can well
imagine that, by whatever means  the sun communicates to the etlrereal expanse
the vibrations of various lengths which constitute the rays of light, that vibrations
of other magnitudes, greater or less, should be at the  same time produced ;  and
thus  the light, which exhibits to us the beauty of the external world,  be accompa-
nied  by the heating power which animates all  living nature, and without which the
universe would be a tenantless and barren void.
  These arguments,  however natural,  and  in appearance sound, are  met by facts
 which,  if  not positive against light and  heat differing only in the length of the
waves by which they are produced, are at least of so much importance as to de-
 serve attentive study. If it were  so, then the heating rays of the spectrum should
 be thrown always below the coloured space, being less refrangible ; and it is  found
 thai, with a flint glass prism, the greatest heat is produced outside the visible con-
fines of the spectrum  at the limit of the red light.  This is, however, only accident-
 al, from the nature of the prism;  for if a prism of crown glass be employed, the
 rays  of heat are collected in the middle of the  red space : with a prism of sulphuric
 acid, in  the orange ; and by a prism of  oil of turpentine or water, they may be col-
 lected into the centre of the yellow light.
  The  rays of  heat,  therefore, although  generally less refrangible than those of
 light, are still not necessarily, or even always so.   There is distributed over the en-
tire visible spectrum  a heating spectrum, which has its peculiar point of greatest
 energy,  and which may be refracted more or less  quite independently of  the lumi-
 nous space, and may  be brought to overlap it at either end, or to lie evenly upon it.
 The ethereal medium, if it be the means  of transmitting radiant heat, must be ca-
 pable of two distinct methods of vihration, by which rays of equal refrangibilities,
 but totally different properties, may be produced.
   The physical independence of solar light and heat was beautiful-
 ly shown by  Melloni, who, using  quartz and black mica, perfectly
 opaque, upon the  one hand, and  rock  salt made perfectly  opaque by
 soot upon the other, obtained radiant heat of all  refrangibilities to-
tally free from light; and on the other hand, by combining a  plate of
 alum with a glass  coloured green by oxide of copper, he  obtained a
brilliant beam of light, which, when concentrated by a lens upon the
most delicate thermoscope he could apply, exhibited no trace of any
 heating power whatsoever.
  An interesting property of radiant heat, and one which shows the remarkable
distinction  between it and light in a very evident manner, is, that the heat may
change  its degree of refrangibility; and  hence, if  it be vibrations, one wave may
break it up into several, or several smaller waves may unite  to form one.   The
light  of the nun, deprived of all the more refrangible rays by passage through a
plate of alum, msy be received on  a blackened surface, the temperature  of wh ch
 will  be thus elevated, and which,  in turn, will  become a source of radiant heat.
 But the  heat so radiated is found to have totally changed its properties ;  it can no
 longer pass through alum ; it has passed from the state of heat of the lowest to the
 staU; of heat of the highest refrangibility.  In like manner, if the most refrangible
 rays  emanating from a source at  212°  be concentrated by a rock-salt lens, and
 brought to act on a small surface,  they may raise the temperature of this surface
 above 212°, and radiate  from thence in a less refrangible  condition  than before.
 The  parallel case to  this has never been found with light.  Red light has  never
 changed into blue, nor violet into orange ; and there must be in the physical theory 
EQUILIBRIUM  OF TEMPERATURE.        103
  of radiant heat some general principle of so high an order, that the physical optica
  of the present day is but a particular case of it.
   This change of radiant heat from one degree of refrangibility to another occurs
  in nature very often, and is the source of some remarkable phenomena.   Thus the
  heat of the sun's rays, being of low refrangibility from their intensely-heated source,
  is transmitted easily by ice or snow, and hence a layer of snow upon a field, ex-
  posed even to the powerful action of the sun, is but slowly melted; if, however, a
  dark-coloured object, as a branch of a tree,  be laid upon the surface, it absorbs the
  solar heat, and becoming a source of radiation of heat  of great refrangibility, which
  the snow absorbs  completely, this is  melted under  the stick, which  sinks and
  gradually disappears beneath the surface.  The earlier melting of snow upon the
  branches and round the stems of plants, which was supposed to demonstrate a
  kind of natural warmth belonging to the living vegetable, arises from this merely
  physical conversion
   From this results also the influence of colour on the power of bodies to absiorb
  the heat of the sun or of a fire ; the strips of coloured cloth (page 97) melted the
 bhow beneath them, not merely because they absorbed more heat in proportion to
 the depth of colour, but  because they in that proportion  possessed the property of
 changing the heat, which would be transmitted  into the heat which would be ab-
 sorbed by the snow on which they rested.
   The construction of a theory of heat  would be, even were an undulatory hypoth-
 esis adopted  for  its radiant form, involved in difficulties which may require many
 years of research to render them even  clearly understood.  The relation between
 radiation and conduction; the connexion  between specific and latent  heat; the
 laws of cohesive force against which heat acts in causing the expansion of a body,
 will all require to be comprehended within the folds of whatever principle  shall
 hereafter be made the basis of thermotics.  But it is no disrespect to the illustrious
 names that have been connected with speculations on this subject, to conclude, that
 none of the views brought forward appear positive or clear enough to be described
 in a work of an elementary nature like the present.

                              SECTION VI.

                      OF THE COOLING OF BODIES.

   Bodies at an elevated temperature  are  capable of giving  out  the
 heat which they contain by every method by  which, when cold, they
 become  heated at the expense of the  surrounding warmer  bodies.
 Cooling may occur, therefore, by contact or by radiation.   The rapid-
 ity of cooling by the immediate contact  of the hotter with the colder
 body  depends  on the degree of intimacy of the contact, and on the
 conducting powers of the bodies.  Thus solids, which merely touch
 at a few points,  communicate their relative  temperatures but very
 slowly,  while with liquids or gases which  may mix completely with
 each other, the establishment of a  uniform  temperature is  almost
 instantaneous.   The colder body becomes  heated to  the  original
 temperature of the hotter only when there is a continual supply of
 heat to maintain  that temperature, as in a furnace; in  other cases
 the hotter body cools in proportion as the colder becomes warm, and
 the resulting temperature  depends on the specific heat of each, as has
 been described, page  b'2.   In determining, therefore, the temperature
 of a body by a thermometer, it must not be forgotten that the ther- *
 mometer, in becoming hot, cools  the body, so that, unless there be a
 continuous source of heat, the true temperature of a body is never
given  by the instrument.   "Where the substances,  being solid, can
 only come into external contact, the  rapidity with which heat passes
from one to the other depends upon  their conducting power ; thus,
a cold brick  may be laid upon a heated brick for a considerable time
without much heat changing place, but a plate of red-hot iron laid 
    104         THEORY  OF DEW AND  FROST.

    upon a plate of cold iron,  abandons its excess  of temperature so
    rapidly, that a mean temperature is attained by both in a very short
    time.
     The cooling of bodies by radiation is governed by the  principle
    that all bodies in nature are in a continual state  of  interchange of
   heat; no matter how hot or how cold a body may be, it is constantly
   giving out radiant heat to other bodies, and receiving in exchange,
   and absorbing the heat which radiates from them.  The quantity of
   heat thus  radiated depends on  the temperature of the body; the
   higher this is, the greater quantity of heat is thrown off; the lower
   the  temperature, the less heat does a body radiate in a certain time.
   Hence, if we conceive a ball heated to redness, and suspended in the
   centre of a number of similar but colder balls, each will radiate and
   absorb, but the hotter ball will give out more than it can gain in re-
   turn, and will hence cool, while the surrounding  colder  bodies, ab-
   sorbing more of the radiant heat than they return, will have their
   temperature raised.  Everybody in nature, therefore, no matter how
   its temperature may, by peculiar or  local means,  be elevated or de-
   pressed, tends ultimately to an equilibrium with all the neighbouring
   bodies ; and  hence, the instant we remove a substance from our fur-
   naces or freezing mixtures,  it begins to cool or to become less cold.
   This principle explains, in a very perfect manner, a singular but in-
   structive experiment which may be  made with the concave mirror
   apparatus described, page 95.  In the ordinary form, the thermom-
   eter and the heated ball tend, by  radiation, to assume a common
   temperature, and the thermometer, being the colder body, becomes
   heated ; but if, in place of the  heated iron ball, a mass of ice be sub-
   stituted, the temperature of the thermometer in the focus of the op-
   posite mirror immediately sinks below that of the surrounding air.
   The  explanation consists simply in the fact that  the  thermometer
   is now the hotter body, and  hence, giving out to the ice  more heat
   than the ice gives  back, has its temperature reduced.   At first this
   effect appeared to  demonstrate the existence of rays  of cold, which
  were reflected, radiated, and absorbed like rays of heat.
    In this principle of the uniformity of temperature being sustained
  by the equivalent radiation and absorption of the bodies°at the sur-
  face  of the earth, we find the  solution of many interesting natural
  phenomena.   The  production  of dew and frost are to be thus ac-
  counted for.  In the absence of the sun, the surface of the earth
  losing by radiation a great quantity of heat, would have its temper-
  ature  considerably lowered,  were it not that  the canopy of clouds
  which generally lies above it radiate in return, and thus maintains the
  temperature almost the same.  If, then, the clouds be absent, all the
  heat radiated by the  earth is lost in  the planetary spaces, and the
, temperature of its surface brought many degrees below that of the
  atmosphere.   The  stratum of air which lies  in contact with the sur-
  face of the ground is then cooled by contact, and a portion of the
  watery vapour which it had possessed in its elastic form is depos-
  ited as liquid  water.  If the  temperature of the air be  itself low
  and the night very clear, the cooling may proceed so far that the
  drops of dew at the moment  of their deposition shall be frozen and
  thus form frost.  The truth  of  this  explanation is  demonstrated by 
CENTRAL  HEAT  OF  THE  EARTH.         105
the fact that it is only on the surface of good radiators, and during
clear starlit nights, that  dew or frost is found.  If a plate of pol-
ished metal be laid on the centre of a rough board, and exposed to
the air of a frosty night, the  rough surface will be  found in  the
morning covered with copious frost, but on the bright metal no trace
will be deposited.   It  is thus that, by lightly covering a thin layer of
water with straw to increase the radiating power, a sheet of ice may
be obtained in a single night between the tropics, where the actual
temperature of  the air may  have continued far above  the  freezing
point.   That  the cooling effect is produced by the  loss of heat in
its radiant form, and not by the contact or diffusion  of the particles
of the  air, may  be  proved by the interposition of a screen of any
substance which i^ercepts the passage of radiant heat, when the de-
position of dew or frost instantly ceases, and the surface  cools no
more.   Thus plants are protected by mats from the frost of spring
and autumn, and thus the screen of snow, which covers the surface
in the  depth of winter, prevents the loss of heat from the soil below,
and favours the vegetation of the seed.
  The rapidity  of cooling depends upon the difference of tempera-
ture of the radiating bodies, but it is not proportional to this differ-
ence except within a very narrow range of temperature.  Newton
having experimented  only within that limit, announced that law as
general; but the establishment of the true law is due to Petit and
Dulong.   It is, that the rapidity with which a body cools, for a con-
stant, excess of  temperature, increases in a  geometrical proportion,
of  which the ratio  is 1*161, whejL the temperatures increase  in an
arithmetical proportion.   Bodies at moderately high  temperatures
cool,  therefore, much more rapidly than they should do  by  New-
ton's law.
  The  haat, by means of which we produce a rise of temperature, or any other of
the effects which have been described, may be derived from any one of a variety of
sources.  To the earth at large the sun is the source of warmth ;  and by his vary-  j
ing position in the heavens, by which his rays strike upon  the surface with different  I
inclinations, and, passing through the different thicknesses of atmosphere, undergo  I
absorption to a variable amount, the change  of seasons as  to temperature  is  pro-  j
duced ;  and the alternation of vital activity and torpor which characterizes the ve-  J
getable  world, and a great portion of the animal creation, is occasioned.   Although /
at the surface the temperature of the earth is solely dependant upon the radiating 1
power of the sun, yet it is found that it contains within itself a source of Seat, which,
in ages  excessively remote, must have retained the general mass of all constituents
of the mineral globe in igneous liquefaction.   In fact, if we dig below the surface
of the earth, we arrive, at a depth of about forty feet, at a layer of which the tem-
perature is in winter and in summer exactly the same.  It is termed the stratum of
invariable temperature, and is in general of the mean temperature of the place;  that
is, the temperature  of the surface falls in winter as much  below that of the  invari-
able stratum, as in summer it is raised above it by the excessive action of the solar
rays.  The heat of the sun, falling upon the surface, is transmitted inward in virtue
of the conducting power of the ground ; and thus, each summer, a thin layer of ele-«  ■
vated temperature  moves inward, those of successive summers being separateoajp
from each other by the intervening colder shell, which marks the period of  dimin-
ished heat in winter, until they mix and confound themselves in the layer of con-
stant temperature, below which the influence of the sun  is felt no more. But, on
descending beyond this depth, the temperature steadily  increases, and, altiough.
siWiect  tO( irregularities consequent on the different conducting powers of therocksV
* 
106          PROPERTIES  OF  ELECTRICITY.
V
be subjected : at four miles' depth tin and bismuth would naturally be liquid ; and
at five miles, lead.  At a depth of thirty miles the temperature would be so high as
to melt iron ; and still more easily, almost without exception, the rocks, which con-
stitute the solid earth which we inhabit.  The central heat, therefore, although in-
sensible at the surface, is still, there is every reason to believe, in violent activity
at a small depth below : we live upon a pellicle of solid crystalline rocks, with which
the melted mass has become skinned over, and which extends but to Tiff of the
distance to the centre.  Hence we can well  imagine, that  in many places where
orifices or cracks in this solid crust might form, violent manifestations of the  inter-
nal fire  should be  produced, and the magnificent phenomena of  volcanoes and
earthquakes should  thus arise.
  For artificial purposes, the source of heat is generally chemical combination.
The details of this mode of generating heat will require to be carefully and minutely
considered hereafter, under the heads of Combustion, and the Relations of Heat to
Chemical Affinity.  By mechanical causes, as  percussion^nd friction,.heat may
also be set free; but such cases arise  from  a  change in tie specific heat of the
bodies before and after the mechanical action ; and hence, although once considered
as influencing'our ideas of the nature of heat,  do not now require speciaI*"notice.  A
very interesting source of heat consists in the respiration of certain kinds of animals,
and constitutes an  important branch of chemical physiology, which shall %e dis-
cussed in its proper place : and, finally, one of the most remarkable sources of heat
is to be found in the properties of electricity, in its various  forms ;  and to the de
scription of this interesting and important agent we shall now proceed.
                               CHAPTER IV.


   OF ELECTRICITY CONSIDERED AS  CHARACTERIZING CHEMICAL SUBSTANCBg.


     Among the various forces which concur to the production of nat-
   ural phenomena, there are few whose agencies are more remarkable
   or more general than those of electricity;  and  so intitnafely does it
   appear to  be connected with chemical action, becoming  sensible in
   all cases of union or decomposition, and  being even developed in
   a degree proportional to  their amount, that the most eminent phi-
   losophers  have not  hesitated to consider  electrical and chemical
   agencies as being, if not identical, at least intimately connected with
   each other.
     It is not the object of this work to enter into the minute description of electrical
.   phenomena,  nor to attempt the detailed discussion of their causes ; as for a complete
   examination of the subject, it. must be considered as one, and certainly not one of
   the least extensive branches of natural philosophy ; it is only with regard to the in-
   fluence which electricity exercises in the operations and the theor.vof chemistry
   and the means which the electrical properties of bodies afford for their recognition'
   that it requires notice here ;  and hence, although it is necessary to describe the pe-
   culiar origin  and characters of  each form which electricity assumes yet that shall
   be accomplished within the shortest limits  that are consistent with the importance
»<>f this branch of science.  In the present chapter the subject will be  studied in its
   general history, and considered  as affording useful characteristics of substances the
   properties of which we have to learn ; and in a future place the influence which it
   exercises upon chemical affinity, and the opinions which have been advanced con-
   cerning its relation to purely chemical forces, shall be carefully discussed-     - • :
 /  Of the  true nature of  electricity  nothing is positively kno\rf.:
f  whether it be a mere property of matter like attraction or c&iesio|§%
I  mere force acting independently of  all interposed material, Or wheth-
\ er, like light, it consists in the undulations of an etjiereaimedium fill-
r 
NATURE  OF  ELECTRICITY.
107
 in or space,, canpot be determined.  Indeed, the ordinary views of its
 nature consist in supposing the existence of one or of two fluids of
 electricity, of exceeding tenuity and of perfect elasticity ; and that,
 according as ordinary bodies were supposed to contain more or less
 of these fluids of electricity, they acquired or lost the properties of
-electrical excitation.y Of these opinions it is  exceedingly  difficult
 to say which is the more reasonable or more  consonant to experi-
 mental truth, so far as the explanation of phenomena is concerned ;
 but no positive evidence has ever been obtained of the existence of
 such an electric fluid : it has never been found capable of being sep-
 arated from the  ordinary particles  of matter, of which it  appears
 always  as an»additional property assumed under peculiar circumstan-
 ces, anchkot as a s^eradded constituent.  I consequently incline to
 the  ideaiynat, in the phenomena of electricity, we have exhibited
 only the Results of new mechanical conditions of the ordinary par-
 ticles of matter, produced by the action of forces which may be called
 into.ptay in a variety of ways, and which may be either totally new
 forces which are first generated at the time, or modifications of the
 forces of gravity and cohesion which  exist already.  But, although
 such may be the true condition of the electric properties of bodies,
 yet such views are far too abstract and indefinite to be as yet carried
 out  into the detailed explanation of experiments; and hence, in the
 present chapter,  I shall adopt the language of that view, which has
 been so long in use as to have become incorporated with  science,
 and speak of an  electric fluid uniting  with or separating from ordi-
 nary bodies, without being considered as at all believing in its actual
 existence.
   This electric fluid, whether it be looked upon as of one or of two
 kinfls, may, like air or water, be examined in a state of rest or in    •* ■
 motion; and the science of electricity  may be  thus divided into
 electrodynamics and electrostatics.   The electricity generated  by
 friction, or by  change of state of aggregation, is ranked under the
 latter head; while the effects  of electricity in  motion are found to
 include the phenomena of magnetism, of galvanism, and their rela-
 tions to each other, electro-magnetism and magneto-electricity, and
 also those of the electricity produced  by a change of temperature in
 bodies.  Under these heads, therefore, the subject will be tseated of
 at present.

                           SECTION  I.
                     OF  STATICAL ELECTRICITY.
                                                        *
   Electricity, in  its statical condition,  may be evolved in various   *•/
 ways, of which one of the most remarkable, and that most commonly  f*
 employed, is friction.  If a piece of silk, or a handkerchief, warm #
 and  dry, be rubbed briskly against the surface of a dry'glass rod, a
 peculiar odour will become manifest ; and in the dark,  the surface
 of the glass rod will appear covered with a peculiar phosphores-
 cent glow.  If  the rod be brought near the cheek, a sensation #is if
 a spider's web had been  drawn across the face will be felt;  and on
 approaching to the  rod, as in the figure, any very light bodies, as a
 silk  thread, a feather, balls of elder pith, or little bits of paper, they
^       * 
108   ELECTRICITY PRODUCED  BY FRICTION.
      -                will suddenly spring towards the rod, and be-
      [          j\\     come  attached to  it  for  a moment ;  after
                / \    which they will spring from  it, and fall away
                /  \   with equal power, assuming  the  positions of
               /   \   the dotted lines.   The rod which has acquired
          ^\  /    \  these properties is said to have been electri-
            \v( J   V, fied by friction with the silk  handkerchief; it
             yV      has become excited, and the phenomena pro-
             V\      duced are known ;  the phosphorescent appear-
    f\         V     ance, as  the electrical  light; the motion to
  _,•-*—*-■%.             and from the rod by the light bodies, as elec-
  trical attraction and repulsion ; in which also, acting on the  minute
  down of the cheek, the sensation above described has.i££ source.
  It is not alone by rubbing together silk and glass that these^bhenom-
  ena  may be produced;  two pieces of silk, by their mutual friction,
  become  electric also, particularly if they be of different cqjpurs;
  thus, on laying flat together slips of black and of white riband, and
  drawing them smartly through the fingers, each will attract the
  feathers or pith balls;  and being both  light bodies, they will also
  attract each other.  A  piece of sealing-wax, or  any other resinous
  body, when rubbed with flannel or a woollen cloth,  becomes similar-
  ly excited.  Sulphur and amber, in which last, indeed, the property
  was first discovered, and from the Greek name of which, rfktKrpov,
  the science electricity has its name, assume this excited state with
  remarkable facility and power.
    It is not  every  substance which may be thus electrified by fric-
  tion, and even the same  substance  may often become incapable pf
  being excited; thus, if the  silk or flannel be not completely dry,
  if the glass rod be  damp, no electric properties can  be conferted
  upon them.   But  it matters not how much care we use in drying a
  metallic surface which  rests upon the ground, or which we support
  by the hand, it cannot be electrically excited by any amount of fric-
  tion.  Such a body is  termed a  non-electric ; dry glass, resin, sul-
  phur, silk, &c, being called electrics.  Excitation may therefore be
  produced by  rubbing together two  electrics, but by the friction of
  non-electrics no electrical effects can be observed.  This distinction
  is, however, not real; it arises from the construction of the appara-
  tus ; for if, in place of resting the metallic rod or plate upon the
  ground,  or  grasping it in the hand, we support it on a piece of seal-
  ing-wax, or hold it by a glass or resinous handle, it becomes, when
  rubbed  with the silk, as  highly electrified as any  of the electrics;
  and in this way, by suitable arrangement of supports, all bodies in
  nature may be made to assume electric properties by friction.
    To account for  this diversity of character, bodies are  supposed to
JWretain the  electric fluid upon their surface with different degrees of
'"power,  according to their nature.  When by friction electricity has
  been accumulated upon the surface of a glass rod, it being a highly
  elastic fluid, its particles repel each other, and tend, consequently,
  to efcape from the limited space  which  it occupies, precisely as air
  tends to escape from  a  vessel into which it has been powerfully
  condensed.   Glass, resin, sulphur, amber, silk, flannel, and  such
  bodies, do not allow of  such escape of the electricity, and it is hence 
RELATIVE  CONDUCTING  POWERS.        109
retained in its elastic form upon their surface, and produces all the
effects of excitation.  They are electrics because they are non-con-
ductors of electricity.  But such is the molecular constitution of the
metals, that they allow  of the  escape  of all that is set free upon
their surface, unless its passage away to other bodies is intercepted
by the interposition of  some non-conducting substance.   A metal
is  thus a  non-electric because  it is a conductor of electricity; and
when, by supporting it upon  a non-conductor, we  oblige it to retain
its charge of electricity, it is said to be insulated.  Ice is a non-con-
ductor of electricity, and by rubbing a  stick of ice  it becomes ex-
cited ;  but it must not melt  upon  the surface,  for liquid water, al-
though inferior to the metals in conducting power, is yet so excel-
lent a conductor, that  it  allows the electricity which we might de-
velop to  pass totally away.   Hence the necessity of  drying care-
fully the  substances which  are, by their friction,  to produce  the
electricity, and also the  reason  that insulating bodies must be kept
free from damp;  for if the thinnest layer of moisture  be deposited
upon their surface, the electricity will  instantly escape by the path
so opened for it.
  The conducting powers of bodies have as yet been scarcely as-
certained with accuracy enough to justify their being expressed in
numbers, at least for the non-metallic bodies.  The general order
appears to be, commencing  with the best insulators or worst con-
ductors :
Dry air.
Shell-lac.
Resins.
Oil of turpentine.
Sulphur.
Glass.
Spermaceti.
Damp organic bodies.
Damp air.
Water.
Strong acids.
Fused saline bodies.
Charcoal.
Metals.
  The worst metallic conductor is many thousand times better than
water, and by the following method an  idea of their relative power
may be formed.  A wire, across which an electric discharge is passed,
becomes heated in proportion to the resistance offered to the motion
of the  electricity, and therefore the rise of temperature is inversely
proportional to the conducting power.   By such experiments Harris
found that, with
                              The Heat              The conduct-
                              evolved.              log Power.
           Silver.......6.......120
           Copper......6.......120
           Gold.......9.......80
           Zinc.......18.......40
           Platinum.....30.......24
           Iron.......30.......24
           Tin.......36.......20
           Lead.......72.......12

  These  numbers are merely comparative, and can only be looked
upon as approximations.
  The  difference of the conducting power  explains the fact that,
when we excite by friction the surface of a glass plate or rod, it is
only at the points actually rubbed that  electricity at first appears,
and it requires considerable time to creep over the other portions;
but  on  exciting an insulated metallic rod or plate, no matter how ex- 
 110       DISTRIBUTION  OF  ELECTRICITY.

 tensive or how long, the electricity,  when evolved by  friction at a
 single spot, appears uniformly distributed over the entire.  Hence,
 also, a spark may be obtained by electricity passing instantly along
 a great extent of metal surface, but is interrupted by a narrow inter-
 val filled by any non-conducting matter.
   The rapidity with  which the electric impulse is propagated has
 been examined by Wheatstone in a very ingenious manner, the de-
 tails of which could not  be well introduced here, but which enabled
 him to determine  an interval of the TJgVo o °f a second ; he found
 that the impulse of the shock of a Leyden jar is transmitted from
 each end of an interposed wire, and arrives latest at the centre,  so
 far appearing favourable to the idea  of the existence of two fluids
 rather than of only one, and that the velocity of transmission of this
 impulse is greater than  that with which  light passes through the
 planetary space, that is, at the rate  of more than 195,000 miles in a
 second of time.
  The electricity, when thus evolved, accumulates upon the surface
 of the body, not penetrating to any  appreciable depth, but formino-a
 layer of fluid, which by  its elasticity, and hence expansive power,
 tends constantly  to  break away and pass to  other  bodies which
 are not excited.  It thus passing through air produces  the electric
 spark, and is accompanied by a snapping report.   The tendency  to
 escape under the form of the spark depends upon the thickness of
the layer of electricity, and is accurately proportional to its square;
 so that if we excite  a brass ball with double or treble the  quantity
of electricity, the force of the electricity to pass away will be quad-
rupled, or increased  ninefold.   Hence it requires exceedingly good
insulation to retain electricity of great intensity.
    These principles may be easily demonstrated by means of the appa-
  ratus in the figure.   A is a hollow sphere of some conducting  sub-
  stance, and B B are hemispheres of gilt paper or thin metallic  foil,
  which, when closed upon the globe,  cover its surface accurately.
  They are provided with insulating handles, C C.  The hemispheres
  being placed on the globe, if the whole be excited by friction or  by a
  spark from the machine, the electricity will be found uniformly diffu-
  sed over the whole external surface ; and if the hemispheres be  sud-
  denly removed by means of the handles, the globe A will remain total-
* ly deprived of its electricity, which will be found all collected on the
  surf ces of B and B ; but it will be no longer uniformly spread ; its
  intensity will be found much greater  on and near the edges of the
  hemispheres, and towards the centres of the surfaces the signs of
  excitation will be extremely feeble.
    The form of a body has a remarkable influence upon  the manner
  in which the electricity is distributed upon its surface.   In a sphere
  the layer is everywhere of equal thickness, but in an elono-ated body 
      OPPOSITE  CONDITIONS  OF  EXCITATION.   Ill

it accumulates more at the extremities of the longest axis.  Hence
on a wire or a needle, the electricity is accumulated almost exclu-
sively on the ends ; and even though the total quantity of electricity
may not be large, it is there so thickly heaped that it breaks off and
rapidly escapes.   Hence electrical apparatus should be completely
smooth except where a point or projection is intentionally attached,
and  many remarkable experiments are founded upon the escape of
electricity from  points.  Electricity is not merely  prevented from
accumulating upon a pointed body itself, but it  cannot collect upon
any  surface near it, the point  abstracting the electricity.  Thus,  a
point held near to the excited glass tube used in the experiments
first described may prevent the attraction  of the light bodies, which
demonstrates its excited state, by concentrating all the action upon
itself.   The detailed theory of this power of points to dissipate their
own electricity and to absorb that of other bodies, will be hereafter
fully noticed  ; at present it is sufficient to refer it  to the thickness
and high elasticity of  the layer of electric  fluid which forms upon
them.
   It has been already  stated that, when two slips of silk riband are
excited by rubbing against each other, the electricity appeared to be
equally evolved  upon each.  This occurs in all cases of excitation
by means of friction.  Thus, when silk and glass are rubbed together,
the  silk acquires as much  electricity as  the glass, but by  the  silk
 being held in the hand, the electricity escapes by the dampness which
 is always present, and is lost.  If, however, the silk be insulated;
 if a disk  of dry wood covered with some  folds of  silk be held  upon
 an  insulating handle, and rubbed against a similar disk of glass, then
 the same phenomena are produced in an equal degree by both.  The
 attraction and repulsion of light bodies, the odour and the phospho-
 rescence belong to both, and thus in every case where bodies are
 rubbed together, the  excitation  is completely mutual.  There is,
 however, a profound and curious  difference between the two condi-
 tions : separately they attract and repel  other bodies exactly in the
 same  way; together they produce neither attraction nor repulsion:
 separately they  may manifest  the most remarkable evidence of ten-
 sion, giving sparks and shocks; but when combined, all signs of free
 electricity are lost, and the body on which they  are collected appears
 as destitute of excitation as if the power had never been called into
 existence.   The states  of the two bodies are therefore so far op-
 posed that they may interfere ; and as from the action of two lights
 there may be produced total darkness, so from the coalition of the
 excitation of the two bodies which had been rubbed together,  abso-
 lute indifference may  result.
   This neutralizing power of the excitation of each body  for that of the other may
 be shown by very simple means.  If a feather be suspended by a silken string, and
 upon the one side there be presented to it the disk of glass, and upon the other the
 disk of silk, which had been rubbed together, it may be brought to remain, by man-
 aging the distance, perfectly at rest.  If there be the glass  alone, it instantly at-
 tracts the feather; the silk alone acts in  the sune way;  but no matter how strong
 the  power of each may be, when at equal distances the feather remains indifferent
 to both.  In order, however, to obtain perfect demonstration of this principle, it is
 useful to examine it by means of more exact  instruments than the feather or other
 light bodies, which hitherto have been sufficient, and for this purpose the gold-leaf
 electroscope is best  adapted : deferring the description of its  principle to another 
112   ELECTRICAL  ATTRACTIONS  AND  REPULSIONS.
place, I shall here only notice its construction and the indications which it gives
                  A glass jar, A, is closed at the top by a metallic (brass) plate,
                  B, to which are attached below, by a wire, two slips of gold leaf.
                  lying, when unexcited, flat on one another, and reaching below
                  the middle of the jar.   The jar rests on a wooden or metal foot,
                  with which are connected two slips of tin foil, applied to the in-
                  side of the glass, and rising so far that the gold leaves,on open-
                  ing out, may come into contact with them.   When this occurs
                 . there is evidently a free conducting medium from the upper me-
               0 tallic plate to the ground ; but, except when the gold leaves touch
               — the slips of tin foil, the cap and leaves are perfectly insulated,
if the instrument be  kept dry.   When this electroscope is brought near to an exci-
ted body, the gold leaves diverge,  and  remain so, in the position  of the figure, as
long as the  excited body be kept near.   But if the instrument be not touched, the
leaves collapse on its removal, and all remains indifferent, as it had been before.
By the divergence of the gold leaves, therefore, the existence of free electricity act-
ing on the electroscope is made known.
  No matter what may be the nature of the excited body acting on this instrument,
it gives the same indication of its presence, but when exposed to the action of the
two bodies which had been rubbed together, the gold leaves remain quiescent.  If
they be made to separate by the influence of the glass, and the excited silk be then
slowly approximated, the divergence gradually diminishes, until at last the leaves
lie close together.  If the silk be then brought still nearer, there is a new divergence,
but it is due to the excess of power of the silk after the neutralization of the glass.
On removing either of the excited bodies when the instrument is in the neutralized
condition, the leaves diverge, from that remaining being free to act.  Not merely
is the excitation assumed by the two bodies immediately rubbed together, of these
opposite kinds, but it may be shown that this  peculiar power may exist in the con-
ditions of  two bodies rubbed by a third, as if a glass be rubbed with silk, and an in-
sulated  metal rod be  likewise excited by rubbing with silk, the glass and metal rod
assume electricities which destroy  each other, or the silk is related to the metal as
the glass had been to the silk.  Bodies rubbed by different other substances are also
so circumstanced ; if a stick of sealing-wax be rubbed by flannel, it will assume op-
posite excitation to that of glass when rubbed with silk, and would counteract its
influence ; and, consequently, the condition of the flannel in the one case, and the
silk in the other, would be opposite also.  This assumption of opposite states of ex-
citation may be caused by trifling mechanical conditions :  thus, if smooth glass and
muffed glass be both  rubbed with silk, they become oppositely electrified ; and two
pieces of silk, which differ markedly in colour, neutralize each other when electrified
by their mutual friction.   The peculiar characters of these two forms of excitation
extend, however, much farther than the principle of mutual destruction.   If we hang
by a dry silk thread, varnished with shell-lac in order to render it a better insulator,
a little cylinder of gilt, paper, and bring near it an excited body,  the cylinder is at-
tracted, and  moves towards the body until it touches, when it is  immediately and
forcibly repelled.  It  has by contact participated  in the state of excitation of the
body, and, when that is so, they mutually repel  each other.  In  all  cases, bodies
which are in the same electrical condition repel each other ; and it is thus that the
gold  leaves of the electroscope  become an index of any electricity which may be
present; for as both slips of leaf are necessarily excited in the same way, they repel
each other, and, consequently, they diverge.
  If, now, the insulated gilt paper  cylinder which has been, as above described, re-
pelled by the glass rod, after having shared its electricity, be brought near  the silk
against  which the glass rod had been rubbed,  or to any body which is in the same
state  of excitation as the silk, attraction will ensue, and this will he found more
powerful than if the body had previously been neutral.   If two such gilt paper cyl-
inders be touched, both with the glass rod or both with the silken disk, they will
repel each other; but if one be touched with the glass and the other by the silk,
they will attract each other, and move  until they touch, when the states of excita-
tion neutralize each other, and they become inactive.
   When bodies are rubbed  together, therefore, they become elec-
tric, and with  such properties, that while each when separate gives
signs  of powerful excitation,  together  they destroy each  other's
power.  Bodies when thus oppositely electrified attract each other j 
LAW  OF  ELECTRICAL  ATTRACTIONS.      113
 bodies which are  excited  in the  same manner repel each other ;
 and  these attractions and  repulsions  arise from the  exertion of a
 force which,  like  that  of  gravitation,  diminishes in  intensity ac-
 cording as the square of the distance between the bodies becomes
 greater.
   This law, which is of the greatest importance for the theory of electricity, was
 discovered by Coulomb by means of the torsion electrometer.  The gold-leaf appara-
 tus, though exceedingly sensible  as a test of the presence of  free electricity, is yet
 not susceptible of being used to measure  its amount.  It is an electroscope, but not
 an electrometer.   The torsion  balance of Coulomb consists of a
 glass drum, a, on the centre of which rises a glass tube, b, to  the
 heigbt of one or two feet.  From the top  of this tube is hung, by
 a fine thread of glass or of cocoon silk, a very light wooden beam,
 c, to which is attached at one end a ball of dry elder pith, and at
 the other a piece of gilt paper, which serves  as a counterpoise,
 and by its surface prevents irregular motions of the beam.  The
 pith  ball is usually gilt, to  give it  a  more uniform  surface.  In ^<
 the top of the drum there  is an aperture, by means of which a
 second gilt pith ball, d, may be  introduced, and made to  touch
 that  of the balance ; and around the  centre of the drum is fixed
 a scale of degrees, by which the angular distance to which  the
 balls  separate after repulsion may be measured.   Now let us
 suppose that, by touching the  second, or,  as it is called, the car-
 rying ball, to an  excited body, we charge it with electricity, and,
 having inserted it in the aperture, it touches the ball of the bal- spC
 ance, which is immediately repelled :  in moving away, this twists
 the thread by which it is suspended,  and  the amount of the  twisting which is ne-
 cessary in the opposite direction to bring it back again, and maintain it at a certain
 distance, measures the force of repulsion the  balls then exercise.  This  measure-
 ment is effected  by the glass or silken thread being attached, not to the tube, but to
 a stem  carrying an  index, which shows, on a graduated circle, the number of de-
 grees through which the thread is twisted ; and as the thread is  exceedingly long
 in proportion to its thickness, and its elasticity almost exact, the force of torsion is
 taken as proportional to the angle through which the index moves.
   By this instrument, into the detail of experiments with which it would be improper,
 here to enter, Coulomb established  the fundamental law of electrical attraction and
 repulsion ;  and it has been found, that from this law all the results of the distribu-
 tion of electricity on bodies, its accumulation on and escape from points, that have
 been noticed, might be deduced.
  The fundamental principles of electrical excitation, the distribution of electricity
 on bodies, and the manner in which the electric states of the excited bodies are re-
 lated to each other, having been thus described, I shall pass to the explanation of
 the general principles under which those phenomena and laws have been arranged,
 and a knowledge of which we shall find necessary to our future progress.  I shall
 lay aside  all consideration of the  more abstract theories  of electricity, which refer
 it to  mere  molecular disturbance or  to vibrations, and consider only those views
 which suppose the existence,  in the one case, of two electric fluids, the theory of
 Dufay, and, on the other, that of a single fluid,  the theory of Franklin.
   Theory of two< Fluids.—It is  assumed that there exist  in nature two
 kinds of electricity, each a highly elastic fluid, whose particles  repel
 each other according to the law of the inverse  square, while they
attract  the particles of matter, and also attract each other, accord-
ing to  the same  law:  that every  body in nature  contains usually
an exactly equal quantity of each fluid  ; that bodies then are in their
ordinary state; and hence, manifesting no  unusual properties,  we
look upon them as  being quiescent:  but  if a  body contains more
of one  fluid than of another, it comes into an extraordinary state
and,  acquiring new properties,  we  say that it has become excited. '
  I'pon this view, the phenomena of electricity are capable  of very
simple explanation.   When two bodies are rubbed  together  the re- 
114          THEORIES  OF  ELECTRICITY.
suit is, that one electric fluid accumulates in excess upon the one,
and the other upon the other body.  They  are thus  both  brought
into a state of excitation ; and as'the excess of the one fluid musi
be exactly equal to that of the other, the excitation of both  is equal,
and,  being  opposite, must neutralize  each other when  they are
brought to  reunite.  Of these  electricities, that which passes to
glass" when it  is rubbed with silk is termed, in  the language of Du-
fay, vitreous electricity, and that which accumulates on resin when
rubbed with flannel is called resinous.  There are few bodies which
ma\  not assume vitreous or resinous excitation, according to the
substance by which the friction is produced, and hence these names
are liable  to some objection, and are not much employed.
  Since the electric fluids and matter attract each other, the bodies
upon which the electricities become free  appear to attract  or repel
each other according as they are invested by the same or opposite
fluids, in consequence of the  necessity  of accompanying these flu-
ids in their action on each other.  Hence the electric attractions
and repulsions which manifest themselves in all cases of excitation,
and hence the bodies return to  their indifferent condition as soon
as the excess  of electricity they contain is neutralized.  It was for
a long time supposed that the atmosphere, by its mechanical press-
ure, assisted in retaining the  free electricities upon the surface of
the excited bodies ;  but this is not the  case.   The air acts as an in-
sulator of the  excited body, without which no  accumulation of free
electricity could occur ; but the mechanical  pressure of the air may
be removed without affecting the electrical conditions.
  Theory of one Fluids—In  the hypothesis of Franklin  there is as-
sumed to  exist but one electric fluid, of which, in its ordinary state,
every substance contains a certain quantity.   This  fluid is  consid-'
e'red to be highly elastic, to  repel  its  own  particles with a force
varying as the inverse square  of the distance, and to attract the par-
ticles of matter according to the same law.  A substance  with its
proper share of electricity is therefore in its indifferent condition,
possessing no properties beyond what we ordinarily attribute to it.
But when two such bodies are rubbed together, a quantity of elec-
tricity abandons one and collects upon the other, and  thus both are
brought into an abnormal state,  and assume  the unusual properties
which constitute excitation.   The excitation is equal, for  the one
has gained  precisely what  the  other lost;  and by recombination
they destroy each other's action, for they are  brought to their ori-
ginal ordinary state.  The excitation being produced, according to
this view, by  one body having electricity in excess, while  that of
the other is deficient, one is  said  to be  plus  and the other minus
electrified; or, more generally, the one  to  be positively, tho other
negatively excited, and the  signs -f and — are often used as abbre-
viations for these words.
   The particles of the electric fluid being mutually repulsive, and at-
tracting those of matter, it is natural that two bodies having elec-
tricity in excess shall mutually  repel,  and that a body ha vino- an
excess of electricity shall attract one having an excess of matter
Bodies both + therefore repel, a + and a— body attract each other'
But, to explain the mutual repulsion of bodies both in the neo-ative 
ELECTRICAL  MACHINES.
115
condition, an assumption is required  which at first sight appears to
militate considerably against our reason ; for as it is matter  which
is  in excess in that condition,  we must consider that the particles
of matter mutually repel each other, according to precisely the same
law, as it is demonstrated by the whole construction of the universe,
that the particles of matter mutually attract  each other.   There is
not, however, any real contradiction  in  these principles ;  the  law of
gravitation applies to matter in its ordinary  state, in which it con-
tains its natural  quantity of electricity; and it affords no grounds
for supposing that, if matter were deprived  of that  natural electri-
city,  it  would continue to attract.  There is, consequently, nothing
illegitimate in that assumption ; and the theory of a single fluid may
be as easily and  successfully applied to the explanation of phenom-
ena as that of the two fluids before described.
  Already, indeed, considerable progress has been made towards a theory of elec-
tricity upon this idea.  In order to account for the ordinary molecular constitution
of matter, it is necessary to  suppose that the forces which act upon its particles
may change from attractive to repulsive, and again from repulsive to attractive, ac-
cording  as the distance between the particles is made to vary;  and Mosotti has
shown that it is only necessary to  assume  that the  mutual repulsion of matter,
when destitute of electricity, is inferior to its attraction for electricity, and to the
mutual repulsion of the electricity itself, and the law of gravitation becomes a neces-
sary consequence of the conditions under which  alone electrical equilibrium can be
established.
   Such are the theories of electricity that have hitherto met with most general ac-
ceptation.   In the succeeding portions of this work, I shall adopt the language of
the theory of the two fluids, except that I shall use the words positive and negative
flunls in place of vitreous and resinous; but  I do so merely from convenience, and
seek not to connect the idea of a fluid in any way more intimately with the true
causes of the electrical properties of bodies.
   Before  passing to the description of the phenomena, and the dis-
cussion of the principles of electricity which yet remain, it is  ne-
cessary to notice the construction of some electrical apparatus, which
is employed in all ca-
 
116
electri;al  machines.
inder, A, or of a plate.   There are hence the cylinder and the plate
machines.  To produce the friction, an elastic rubber, B, is covered
with silk, and made to press against the  surface of the glass accord-
ing as the plate or cylinder is turned  round by means of the handle.
The rubber being generally insulated, the electricity evolved upon
it is at once collected, and may be transferred along conductors, or
drawn as sparks from the knob of brass attached to it at the back.
The electricity which is diffused upon the glass passes from its sur-
                                    face to that of a brass  cylin-
                                    der, termed  the  prime con-
                                    ductor, C, being collected by
                                    means of a series of pointed
                                    wires, which graze the sur-
                                    face of  the cylinder accord-
                                    ing as it is turned round. The
                                    prime conductor is also insu-
                                    lated ; and in the case of a
                                    cylinder machine, the  glass
                                    itself is often supported upon
                                    insulating pillars, by which
                                    the loss of electricity is pre-
                                    vented.   To increase the en-
                                    ergy of the machine, the silk
                                    of  the  rubber  is generally
                                    smeared over with a mixture
                                    of grease and an amalgam of
                                    tin  and zinc, and  a silken
apron extends from the rubber half over  the cylinder or plate to con-
duct the electricity to the points, and prevent its being carried away
by the air.
  Although I shall have occasion, when we have examined the rel-
ative action of excited bodies and conductors somewhat better, to
notice the true theory of the prime conductor, yet for the present it
maybe considered as simply, from its proximity, collecting the free
electricity on its points from the surface of the glass cylinder or plate,
and by thus accumulating it upon a confined surface, enabling the
experimenter to apply it or carry it to other bodies at his  pleasure.
When the machine is worked, the two portions of electricity become
developed, as in the rubbing of the tube  and handkerchief,  upon the
silk and glass; and if all be insulated, they attract each other  so in-
tensely that they break through the intervening air, and recombine
across the surface of the cylinder, or round the edges of the  plate,
presenting the appearance of a brilliant  spark,  and accompanied by
a snapping noise and a peculiar phosphorescent  odour.   To prevent
this recombination, which would, of course, render accumulation up-
on the prime conductor impossible, the rubber, when the machine is
required  for active work, is connected  with the ground by a wire
or chain, through which the  electricity  which forms upon the silk
makes its escape ; and as new quantities are then liberated at each
moment, those passing  from the glass to the  prime conductor, by
the projecting points with which  it is always furnished, collect upon
it, and, acquiring a high degree of tension, pass under the form of
sparks to any  conducting body which may be brought near.
 
  PHENOMENA  OF  THE  ELECTRICAL  MACHINE. 117

  By means of a machine of such construction, the opposing prop-
erties of the electricities of the bodies rubbed together may be sim-
ply  and completely shown.
  The  degree of excitation of the prime conductor  is generally,
though  not very accurately, shown by means of the  quad-
rant electrometer.   This consists of a stem of brass, which
rests in a socket in the prime conductor, or, when not in
use, in  a wooden foot, as in the figure.  To this is attached
an ivory semicircular scale, of which a portion is graduated,
from whence  the name ;  on an axis at the  centre of  the
ivory scale there is hung, by a light  arm of whalebone, a
pith ball,  which,  when  the apparatus is unexcited, lies in
contact with the brass stem, and thus assumes the same elec-
trical condition with it when the instrument is placed on the      1
prime conductor and the machine worked.  The stem and the pith
ball then repel each other, and the ball being consequently set in mo-
tion by the united  repulsion, its radius moves through  an  angular
6pacc on the graduated scale, which serves in rough experiments as
an index of the intensity of the excitation.  Now if, when this instru-
ment is fixed on the prime conductor, the latter be connected with
the insulated rubber by a  chain or wire, no matter how vigorously
the machine may be worked, no signs of excitation can be produced ;
the electricity collected  from the glass  by the prime conductor
passing along the  chain or wire to unite with that which is devel-
oped on the rubber, and the two being evolved in equal quantities,
complete neutralization is produced.  That bodies similarly electri-
fied repel each other, is shown by the principle of this  instrument,
as its indications of free electricity depend upon the  stem and ball
being both excited in  the same way, and the repulsion being  the
6aine, whether it be fixed  upon the rubber or the prime  conductor.
  To prove on a large scale, by means of the machine, that the op-
posite  electricities  attract each other, it is only necessary to place
in connexion with the conductor on each side a metallic wire, tc
which  is hung, by a wetted thread, a ball of pith, or a cylinder of
gilt paper.   When  the machine is turned, the balls attract each oth
er across  the cylinder, and touching, interchange the electricities
by  which  they are  excited, and thus the fluids, separated  by  the
friction, are  continually reconiposed, being  brought together by
their mutual attractions.  If to each wire there be hung two such
balls, those of each side  will be seen  to repel each other, while
they move towards  those  oppositely excited.  Numerous experi-
ments of an amusing kind, which it would be foreign to my purpose
to introduce,  are founded  on these principles.
  There have  been  now noticed four methods by which bodies may
be electrically excited.  1st, by friction, which is,  indeed, the only
true direct  excitation.   2d,  by contact ; as when  an insulated
brass disk excited by friction is touched to another, also insulated
and neutral, a spark passes between them at the moment previous
to actual contact, and the first is found to have divided  its  electri-
city with the  second in proportion to its surface.   In  this case the
two bodies, after contact,  are in the same  state of excitation.  3d.
as where the  prime conductor, which  is neither itself rubbed, nor
 
118          EXCITATION  BY INDUCTION.
 does it touch the cylinder of the machine, yet gathers from it the
 electricity which is evolved thereon, and allows it to be transferred,
 under  the form of the spark, to other bodies ; and, finally, all the
 attractions and repulsions which have been observed indicate a pow-
 er of action  and excitation even at considerable distances ;  and this
 mode,  which results from the attraction and repulsion of the elec-
 tric fluids for each other, is, when examined, found  really to com-
 prehend the second and third modes of excitation, by contact and
 by gathering with points.  There  are, therefore, truly, only two
 means  of excitation, this at a distance, which is termed induction,
 and that by friction.
   It is  not difficult to understand how bodies come to be excited by
 induction.  Let us consider the insulated  cylinders, B C, as  being
                                             neutral, and having
                                             their natural electri-
                                             cities combined, and
                                             distributed  uniform-
                                             ly over their surface.
                                             If  a globe, A, exci-
                                             ted,  say with  posi-
 tive electricity,  be brought near, it will attract the opposite electri-
 city of  B to  the end which is nearest it, and repel the electricity
 of the  same  name  to the farthest extremity ;  both electricities of
 B will thus become free, and B  will  be  excited by the influence of
 the electricity of the body, A, at a distance ; and the condition of
 B is characterized by its two extremities being in opposite states,
 and hence, at a  certain point between  them, perfect neutrality re-
 maining.   The positively excited end of B influencing C in a cor-
 responding way, brings it also into an excited state, and this com-
 munication of action would go  on through any number of bodies,
 the force set free being regulated by the law of the inverse square
 of the distance from  the original disturbing  cause at A.  As long
 as A remains  in  its place, the state of electrical excitation  is kept
 up; if A be totally removed, the natural electricities of each body
 recombine, and all become  neutral;  if A be  brought very close to
 B, or B  to C, the attractions between the opposite electricities be-
 come so great that they unite across the intervening space of air,
 and a spark passes.  The bodies are then found to be in the  same
 state, and the communication by contact, or  the  excitation which
 occurs,  is shown to be only the termination of the inductive action.
 For suppose that A had 10  parts of  -\-  electricity, and that, by in-
 duction, it  set free 5 of the — and 5 of the + fluid on the  surface
 of the body B ; then, when the spark had passed, the —5 destroy-
 ing -f-5 of the body A, the two bodies should remain each with
 + 5, and thus the results of contact described already should be
produced.
  The distance at which the combination of the electricities of the
inducing and  the induced body may occur, depends upon the inten-
 sity of the fluids collected on the parts  of the surface  nearest to
each other; and hence, when there is on the body a point on which
the great proportion of the liberated fluid, as has  been already de-
scribed, becomes accumulated, the fluid  escapes from thence before 
THEORY  OF  THE  GOLD  LEAF  ELECTROSCOPE.  119

it is in sufficient mass to break its way under the form of a spark,
and thus the permanent and similar excitation of the body  silently
occurs.  This is the true theory of what has  hitherto  been  de-
scribed as the power of points to gather and to  disperse the elec-
tric fluid.  If a pointed body be excited by friction, it  induces  an
opposite state  in the  particles of air by which it is surrounded, and
communicates to them, with great rapidity, the  charge which it had
received.  The prime conductor of the machine, being insulated,
has its electricities separated  by the inductive action of the  excited
glass cylinder or plate ; the  negative  electricity collected  on  the
points  turned  towards  the glass  escapes  from  thence, and unites
with the  positive  fluid which had been set loose  by friction, and
proportional quantities of the positive fluid of the prime conductor
being left  free upon its surface, it  serves the same purpose as a
source of electricity as  if it had  come directly from the glass.   A
point placed on the prime conductor prevents the accumulation  of
the electricity, because it gives the -+■  to the air as fast as the oth-
er  points give  the — to the glass ; a point held near the prime con-
ductor also prevents  its excitation, by giving to  it  by induction  —
electricity as fast as it obtains -f- electricity from the  glass of the
machine.
   In all these  cases of induction where the electricities attract and
repel each other, the  bodies on which the electricities are collected
will accompany them in their motions if  they be  not too heavy.
Hence all the singular  motions of bodies, w7hen excited,  are  ex-
plained upon this principle.   The variety  of  dancing figures, ring-
ing bells, revolving wheels, affrighted heads, and  so  on, that are ex-
hibited in popular  lectures on this subject, will serve to practise the
ingenuity of the student in tracing  out their theory in the detail,
with which it would  be quite  improper to occupy this work.
  The theory of the Beunet's gold leaf electrometer, with which some of the most
important principles of statical electricity are demonstrated,  must not,'however, be
omitted.  When an excited rod is brought over the electroscope, it separates  the
electricities of the metallic portions of the instrument, attracting the opposite to  the
upper surface of the cap, and repelling that of the same name into the gold leaves,
which, being thus excited with the  same electricity, repel each other, and hence
diverge.  It the exciting body be -f-, it is the -|- fluid by which the instrument ap-
pears affected ; if it be—, the leaves diverge from the presence of— electricity.
Hence if, when it is under the influence of a glass rod rubbed with silk, a stick of
sealing-wax which had been rubbed  with flannel be  brought near,  the divergence
diminishes, until at last the leaves collapse completely, the resin having driven down
as much negative electricity as there had been positive brought into action by  the
glass, and hence the gold leaves coming into their natural and indifferent condition.
That it is by this inductive process that the gold leaves act, may  be thus shown.  If
the cap of the electroscope  be rubbed with a dry silk handkerchief,  it becomes excited,
and the  leaves  diverge with negative electricity , if then  an excited glass rod be
brought near, the divergence is neutralized, showing that positive electricity had been
sent down by the glass ; but if an excited resinous body be approached, the diver-
gence increases, indicating the superaddition of electricity of the same name from
the inducing power of the resin.
  If, as in the figure (page 118), the cylinder 0 be connected with the ground by
means of a wire or a welted thread, D, the positive electricity passes from that body
through the wire into the earth, where, from the enormous surface of the globe, it
may he looked upon as lost, and the surface of C is altogether in  a state of negative
excitation.   If, now, the exciting body A be taken away, the quantity of positive fluid
returns along the wire, and brings the body C into its neutral state ; but if before the
body A be taken away, the conducting communication with the ground be cut off by 
120     CONSTRUCTION  OF  THE  LEYDEN  JAR.
the removal of the wire or thread, the body C cannot get its posit, vc electnc y bac^
and hence remains in a state of negative excitation  In tl%™"™r * ^'JJ^
may, by induction, be made to receive a permanent charge,  rins s often useful n
experiments with the electroscope, and the manipulation  ^^v^lSSnZZSi
as follows : If it be desired to charge it positively, an excited stick of resin is held
near, and the cap of the electroscope is touched with  he finger   ^J^e^
tricity then escapes by the hand into the ground, and the P™tive electric  y, accu-
mulating over the cap and leaves, these last diverge. On then removing the finger
the leaves are insulated ;  and when the stick of resin is taken away the permanent
charge remains.  To charge with negative electricity, an excited glass rod is to be
used • and it will be recollected, that where the charge of the leaves is temporary,
its electricity is the same as that of the exciting body ; but where the charge is per-
manent, the electricity is of an opposite kind.
  After the excitino-body, in the latter instance, has been withdrawn, the divergence
of the gold leaves becomes much greater than it had been before.  This arises from
the charge being increased by its action on the surrounding bodies, particularly on
the glass by which the leaves are enclosed.   By taking  advantage of the increase
of charge, by secondary inductive action, various forms of the electroscope have been
contrived for rendering it more sensible, and are described in special treatises on
electricity under the name of Doubters and Condensers. As they do not add anything
to our knowledge of principles, and have no peculiar chemical  relations, I shall not
enter on their farther consideration.
  One  of the most  interesting  instruments  in statical  electricity,
founded on the principle of induction, is  the  Leyden Jar, so called
            from  the city where its  construction  was  discovered.
            It consists of a glass bottle, which is coated inside and
            outside,  to a  small distance from  the top, with tin foil,
            and has  fitted to the orifice a wooden  or cork stopper,
            through  which passes a stout wire, touching at the bot-
            tom the  internal coating, and  terminated outside  by a
            metallic  knob.   When this jar is insulated, and the knob
         J^is touched to the prime  conductor of the machine, and
         -=*- the handle turned, the positive electricity passes to  the
internal coating of the jar, and excites it to an equally powerful  de-
gree.   This, then, reacting by induction upon  the electricities of the
external coating, separates them, attracting the negative to the side
next the glass, repelling the positive to the outer  side.   The  posi-
tion becomes, therefore, -f- — + ;  and  when the  +  fluid inside
makes  up by its  greater  quantity  for the  thickness of the glass by
which it is separated from the — fluid, no more can enter into  the
jar.  In this  case the  inside of the jar may be considered as being
merely an extension of the prime conductor; and the  electricities
of  the  external  coating, although separated  from  each other,  are
only in the quantities which had  been always present.   But if  the
external coating be connected with  the ground, the -f-  fluid, being
repelled by that inside, passes away, and  another quantity, entering
from the prime conductor  into the jar, decomposes a new quantity
of the natural fluids of the external  coating,  of which also the posi-
tive escapes and the negative remains behind, held by the attraction
across  the glass to the positive fluid  inside.   New quantities of pos-
itive electricity  entering continually from the machine, the accu-
mulation of negative electricity on the outer coating proceeds, un-
til the tendency of the  two to combine is  so intense  as to break
 their way across the glass, cracking the jar, or to creep over the
mouth from  the  edge of one coating to  that  of the  other, and thus
 the jar discharges  itself.   To discharge  a jar  in which  the  elec-
 
ELECTROPHORUS  OF  VOLT A.           121
 tricities are  so accumulated, it is only necessary to connect by a
 wire  the internal and oxternal coatings ;  when  the  extremities of
 the wire, which are generally terminated  by brass balls, approach,
 a large brilliant spark passes, accompanied by a loud report, and the
 jar returns to its original neutral state.
   By thus collecting ?ronl quantities of electricity in large jars or
 in sets of jars (electrical batteries), the most beautiful and remark-
 able phenomena of electrical force may be exhibited.
   The  principle of the construction of the Leyden jar may be ex-
 perimentally demonstrated as follows: First, it has been already
 explained that the jar, when insulated, is incapable of receiving any
 other charge from the machine than what its internal coating obtains
 by forming part of the surface of the prime conductor ; the principle
 of induction requiring, in order that one  electricity may accumu-
 late upon its outer surface, the other shall be dissipated on the ground.
 Second, a light body placed  between two balls, connected, one with
 the internal, and one wilh the external coating, is alternately attract-
 ed  and  repelled by  each, and thus the accumulation on the two
 coatings is shown to be of opposite kinds.   Third, the  quantity of
 electricity which passes from the  external coating  may be  shown
 to be equal to that which passes into the internal coating from the
 machine, by  insulating the jar, and applying the knob of a second
 jar which is not insulated  to its outer surface; this second jar will
 be found charged to the same degree as the first, and the inner and
 outer coatings will be respectively in the same state.
   Statical electricity, thus accumulated in the Leyden jar, is capa-
 ble of giving violent shocks to the animal frame, of evolving light
 and heat, and producing- also powerful mechanical effects.
  An instrument founded on the principle of  induction,  and which
 is of frequent use in chemical experiments,  when an electric  spark
 of moderate power is required, is the electrophorus of Volta.  It con-
 sist s of a flat cake of resin, b, which is generally spread  on a circu-
 lar  board of  eight or ten  inches  diameter.   There is laid on this
 another circular plate, a, somewhat smaller, and which may be either
 of brass or tinned iron, with the edges turned  up over a  thick wire,
 so as to round it, or a board covered with tin foil.  To  this upper
 plate is attached an insulating handle of glass, c, and from its edge
 projects a wire terminated by a knob.  The resin-
 ous plate, being warmed, is  to  be strongly  excited
 by  friction with a warm  flannel cloth or  a  cat's
 skin, and then the upper plate is to be laid  on it, and
 is touched with the finger.   The negative electricity
 of this passes,  then, into the ground, and the positive
 accumulates on the surface next the resin,  of which
 it, by induction, increases the negative charge.  This new portion
 of negative fluid decomposes a new quantity of the electricities of
the upper plate, which again reacts, and thus the plates are mutually
brought into a state of very intense excitement.   If, then,  the finder
be removed, the upper plate is insulated, and its charge of positive
electricity retained upon it;  and on applying the knob of the wire
to any conductor or  to the knuckle, a strong spark may be obtain-
ed from it; the instrument may be repeatedly charged and dischar-
 
122         TRANSMISSION  BY  INDUCTION.
 ged in a few minutes, and retains its charge better than the electrify-
 ing machine.                             ,,     _             ,
   This inductive action  of electricity would  at first appear to be
 exercised  at a distance,  altogether independent of the  interposed
 substances, and  to produce the motions to which  it  gives rise, as
 gravity causes the revolutions of the planets and their  satellites,
 without the existence of any interposed medium;  but a more exact
 examination shows that this is not the case.  The substances inter
 posed in the path of the inductive action are necessary to its trans-
 mission, and modify, by their nature, its direction and amount; and
 it is, indeed, only from molecule to molecule of  any substance, gas-
 eous or solid, that the decomposition of the natural electricities can
 take place.
   This may be beautifully shown by plunging in a vessel of oil of
 turpentine, which is an excellent fluid insulator,  two brass balls, of
 which one is in  connexion  with the  electrical machine, and the
 other with the  ground.  On turning the machine, the latter be-
 comes excited by induction.   If, now, a number of short shreds of
 sewing silk be mixed with the oil of turpentine,  the mechanism of
 the  inductive action  is shown by each little bit of silk acting like
 the  bodies B and C in the figure (p. 118) ; and attaching themselves
 mutually by  their extremities, they transmit the electricity of the
 machine, by a  series of decompositions, to the  ball which is  con-
 nected with the ground.  If the excitation be  very violent, the at-
 tractions and repulsions become too strong to be  regularly trans-
 mitted ; and this  induction is accompanied by a powerful current
 of the particles  of the  oil from the first ball to  the second.  The
 particles immediately in contact with the directly  excited ball ac-
 quire its state, and, being repelled, immediately pass off to that which
 has obtained, by induction, the opposite condition, and there become
 neutralized.  Now what here occurs with the oil of turpentine takes
 place in ordinary induction with the air ; every molecule of it inter-
 posed between the solid bodies becomes itself subjected to the in-
 ductive action, and forms a chain of alternate positive and negative
 poles, by which the effect may be transmitted to any  distance.  If
 the excitation be very great, the neutralization may occur with vi-
 olence and rapidity, and generate currents, as  in the oil of turpen-
 tine.  It is these currents which, being produced by the repulsion
 of the particles of air from excited  points, are rendered  sensible in
the effect termed  the electrical aura, and are shown by the experi-
ments of revolving flies.  A still more violent and rapid recomposi-
tion  of the electricities of the  air molecules, which had  been  sep-
arated by induction, gives the  electric  spark in  its various forms,
such as the star, the brush, &c, according to the manner in which
it is  received and generated.
  That the excitation by induction  of a body at a distance is effect-
ed in this manner, from particle to particle of  the interposed  sub-
 stance, is beautifully shown in the results obtained by  Faraday con-
cerning the influence of the nature of the medium on the amount
of inductive  charge  transmitted.   The instrument, which he has
termed an  inductometer, consists of a hollow sphere of brass, a a b,
and a sphere of smaller size, h, also of brass, which is placed exact- 
SPECIFIC  INDUCTIVE  CAPACITY.        123
ly  concentric  with it.   The  interval between
these, o o, may be occupied by any substance,
as  air, or glass, or sulphur ; and then the central
sphere being insulated  from the outer by the
shell-lac column b, and having been excited from
the machine through the ball and  wire  B, the
outer one is uninsulated, and the whole becomes
a Leyden jar, in which the material may be va-
ried at the will of the experimenter.  By means
of the tube and stopcock f d, the air in o o may
be removed, and any other gas substituted for it. a
The outer  sphere opens at b  in  two, so  that
melted sulphur or shell-lac may  be  poured in to
form the inductive medium.
   When the internal sphere is  excited always
to the  same degree,  the  charge of the external
coating should  be  the  same,  no matter what
might be the nature of the intervening substance,
if  the action took place simply at a distance, after
the manner of gravitation.  But this  is not the
case.   With the same internal charge, the exci-
tation of the external sphere was found to be,
that with air being 100, with shell-lac 150, with
flint glass  17G, and  with sulphur  22-k   In these cases, therefore,
the molecular excitation was transmitted in proportion to  these
numbers, which express, therefore, the degree of excitation that a
common amount of inductive influence is able to produce in masses
of these bodies.  All gases, no matter how different in chemical
properties and constitution, even though the temperature and press-
ure do not  remain the same, possessed the same  specific inductive
capacity as air.
   This  principle is farther shown in an interesting manner by the
fact that the induction is not exercised only in
the straight line connecting the solid inducing
and induced bodies, but that at every intervening
point there  is  a lateral  action exercised by the
interposed molecules of air, which may be them- h\
selves  considered centres  of  inductive force.
Thus, if a cylinder, a, of shell-lac be excited  by
friction, and a brass hemisphere, h, placed on top
of it, the intensity of the  induced electricity will
be found to depend not merely  on  the distance  &
from the excited source and the nature of the
interposed  material,  but  to  be  more  energetic
in  certain positions in the air, as when the car-
rier ball of  Coulomb's torsion electrometer was
placed at o, than when it  was lower or higher at
n or p.
  Faraday has been  led  by his  experiments to  conclude that  the
difference between conducting  and non-conducting bodies is, that
the former assume \$ith  exceeding rapidity, under an  inductive in-
fluence, this condition of molecular excitation, and hence appear to
 
124 OTHER  CAUSES OF  STATICAL EXCITATION.

allow the electricity to pass  actually and instantly through their
substance, whereas, in reality,  it is only that the separation and re-
composition of the electricities of the chain of molecules has been
so accomplished.  They lose also this condition as soon as the ex-
citing cause has been removed, whereas non-conductors, when their
particles have acquired electrical excitation, remain in that state of
tension for a certain time.  Thus, if the internal and external coat-
ings of a Leyden jar were connected by a metallic wire, the induct-
ive action would be  propagated immediately across it; but the in-
stant that the  source of the excitation was removed, the electrici-
ties  of the two coatings would recombine, from the  facility with
which the molecules  of the wire can assume the inverse condition.
But with an interposed plate of glass the result is different; the in-
ductive action is propagated equally, but more slowly; and that it
is the particles of  the glass that really produce the charge by their
excitation, is demonstrated by the fact that the metallic  coatings
may be removed,  and yet the accumulated electricities be not dis-
turbed ; the tin foil serving only to  discharge  at the same moment
every particle of the  glass, as if a wire had been individually applied
to each.  That the  induction  has acted on  the substance  of  the
glass explains also the peculiarity of what  is called the secondary
or residual charge.   When the particles at the surface have been
discharged, they are  acted on  by the deeper  molecules which  are
still excited, and hence acquire a second inductive charge ;  and with
thick glass, and particularly with bodies which do not  insulate quite
so well as glass, there may be even a third or a fourth charge of
this kind.
  Conduction is therefore only the highest, most intense, and most
rapid form of induction; and it appears from  Faraday's investiga-
tions that the  permanent  excitation of an  electrified body has its
origin  also in the  inductive influence of the bodies that are around.
  The source of the  electricity evolved by the  electrical  machine
cannot  be considered as being positively  known.   Wollaston in-
stituted a series of experiments, by  which it appeared to be demon-
strated that there was no electricity evolved except where chemical
combination  took  place, and the superior power given to the ma-
chine by the amalgam of tin and zinc being spread upon the rubber
was supposed to verify this idea.  These experiments of Wollaston
have been latterly repeated  with great care  by Peltier,  and with
different results;  he found that the  electricity evolved was propor-
tional  only to the  amount of friction, and was the  same  under va
rious circumstances  of liability to the presence or absence of chem
ical action of the  materials rubbed.   It is  therefore  likely that, at
least, the electricity of the machine may be generated by the sim-
ple molecular derangement and vibration which friction necessarily
produces; and this view is very much supported by the undeniable
fact, that by other agencies purely molecular, where no trace  of
chemical action can  be pretended,  the same  form  of statical elec-
tricity may be produced.
  In almost all cases  where the particles of bodies are suddenly and violently dis-
arranged, the separated surfaces are found to be electrically excited; for instance,
if a piece of mica be torn into thin leaves, these are powerfully electric.  In many
mineral substances a  change of temperature causes a manifestation of electrical 
ATMOSPHERIC  ELECTRICITY.             125
polarity in a very remarkable degree ; thus, if a long prism of tourmaline be heated,
one extremity becomes positive and the other negative ; when the temperature at-
tains its highest point and becomes stationary, all symptoms of electricity disappear,
but on cooling they return ; in the inverse order, however, the end which had
been positive becoming negative, and so on.  In this case it appears as if the par-
tides, in  the internal motion which the expanding force of heat produces in them,
acquired  the  same  condition of polarity as they would have done by an  external
friction.  If the  expansive effect  of heat  and  the  consequent change of position
among the  particles of the  tourmaline had  been the same throughout, there would
have been no reason for  electrical  disturbance; but this mineral, and some  others
wlrch likewise become electric on being heated, as  boracite, are exceptions  to the
general law of crystalline symmetry, and in other respects, as with regard to light,
indicate a kind of structure which  is very complex and peculiar.   In such cases, an
internal friction by the action of expansion on the unsymmetrically situated mole
cules of the crystal is  the origin of the electrical excitation.
  The source of statical electricity, which is of the greatest importance in  nature
from the universality of its action, is that of change of state of aggregation.   When
any body passes from the liquid to the solid, or from the liquid to the vaporous con
dition,  or in the reverse order, from being solid or being gaseous becomes liquid, dis-
turbance of the previous  electrical equilibrium results.   Thus, if a little melted sul-
phur be poured into a glass, or if melted  tallow  or resin be poured out on  a me-
tallic plate, the bodies after solidification will be found excited.   If a  cup of watei
be placed on  the plate of the  electroscope, and a red-hot ball of metal, or even a
red hot cinder, be dropped into it, the gold  leaves immediately diverge by the influ-
ence of the negative excitement which is assumed  by the water which  remains,
and which  communicates itself to the metallic cup and to  the instrument; if the
gush of vapour had been allowed to impinge on the plate of another instrument, it
would  have shown excitation by positive electricity.   This last is one of the nost
abundant sources of electricity; for  as at all ordinary temperatures evaporahon
takes place from the surface of all the water of the  globe, and the vapour produced,
carrying with it the prodigious quantity of positive electricity which is thus set free,
mixes with the air, our atmosphere is almost continually in an electrical condition,
generally positive, but at some times, from interfering causes, negative.  The great
body of  vapour, when condensed  by the more elevated and colder regions of the
air, collects  into the  peculiar condition which constitutes a mass of cloud, and
therein is thus concentrated all the electricity evolved by evaporation at the sur-
face.   The clouds are, therefore, intensely electric  ; and when attracted by induc-
tion to each other, or  to some prominent object on the earth, as  a mountain-peak
or an elevated building,  the discharge and neutralization of the electricities take
place with  the brilliancy and destructive agency of the lightning, while the  report,
re-echoed from the surfaces of the remaining clouds, or by the sides of the adja-
cent mountains, produces the effect upon  the ear  of the continuous rattle  of the
thunder.
  There  is no doubt,  however, but that in many  cases  of chemical combination
and decomposition  electricity in its statical form  may be  evolved;  thus Pouillet
proved decisively, that when charcoal is burned, the carbonic acid which passes off
is in a  state of positive excitement, and the residual mass of charcoal  becomes neg-
atively charged.   When hydrogen burns in air, the vapour of water carries  off the
positive electricity, while the  negative  fluid distributes itself on the hydrogen re-
maining, and the vessel  from which it issues.  There is thus, in the combustion
of our ordinary fuel, a vast source of the electricity of our atmosphere, in addition
to that evolved by water in evaporating ; and it has been found that the evaporation
of a saline solution, as sea-water, produces a much greater degree  of excitement
than when  the water is completely pure, owing, perhaps, to the destruction  of the
condition in which the salt  and water had  been united.  The evolution of statical
electricity occurs, also, when the chemical action is of a much more  complex and
obscure kind; thus, in the  growth of a seedling  plant, the carbonic  acid which it
evolves is in a positively  excited state, and the substance in which the seed is im-
bedded becomes negative.   It would appear, however, that frequently electricity
that had been imagined to arise from  the chemical relation of the bodies brought
into contact, arose from  their merely mechanical  action  on each other;  thus the
electricities produced by sifting  lime and oxalic acid together on the plate  of the
electrometer are produced.
  The  mere contact of bodies has been supposed sufficient to evolve electricity upon 
126            DYNAMICAL  ELECTRICITY.
 their surface.  The trace of excitation in such experiments is so small, and dimin-
 ishes so much in proportion as care is taken  to avoid friction and other causes,
 that we may consider contact as being in itself without power.
  The  remarkable characteristic of statical electricity developed by any of these
 methods, is the amazing energy of its action on bad conductors, and on  the best
 conductors if their substance be not of sufficient mass to give it free passage from
 one point to  another ;  while it is only with difficulty that we can  obtain, by means
 of il, the slightest chemical decomposition.  In the language of the  theory of elec-
 trical fluids,  the electricity is developed in exceedingly small quantities by friction
 or change of aggregation, and hence can perform but feebly such offices as chemi-
 cal decomposition, which depend on the quantity that passes in a given time; but
 this small quantity is gifted with immense tension; the few molecules which be-
 come polarized are so to an intense degree, and the attractive and repulsive forces
 which they exert are then sufficient to cause the greatest mechanical effects

                            SECTION II.
                     OF DYNAMICAL ELECTRICITY.

   The  sources  from which  electricity is derived  in  a  continually
 circulating form, so that its properties shall result from its uninter-
 rupted motion, must  necessarily consist in arrangements from which
 all insulating substances are to be carefully excluded.   In statical
 electricity, the connexion, by a conducting medium, of the opposite
 extremities of an inductively excited body, caused all electrical in-
 dications instantly to disappear, while that kind of connexion is ab-
 solutely necessary to the continuous flowing of the electricity which
 constitutes its dynamical condition ;  and when the conducting circle
 is broken by the intervention of the smallest portion of insulatino-
matter, either all electrical  excitation ceases, or at  most a feeble
trace of it  remains, with the properties which characterize its stat-
ical condition.
   1st.  Electricity  thus circulating  through  conductors is  found
naturally existing  in those substances  which thereby possess mag-
netic properties.   There is every reason to believe that the  native
loadstone,  as well  as all our artificial  steel and iron magnets, are
 closed  circles  of  dynamical  electricity,  set  in motion by  forces
which  depend on the chemical and mechanical constitution of these
bodies.  2d. When any closed conducting circuit is at the same
time unequal in mechanical constitution and in temperature, so that
the current may pass more easily through one  point than another,
 such a current is generated, flowing from the portion where the ob-
 stacle  is greatest  to  that  part  where  it is least.   3d.  When  sub-
 stances capable of mutual chemical combination or  decomposition
act on one another, there is  a  current  of electricity produced.  In
 the case of simple union or  double decomposition, the  circle is in-
ternally closed, like that of a steel magnet ; but where there  is sim-
ple decomposition  or replacement,  the current may be  directed
 through any kind of  circuit; and thus  constituting the most  impor-
tant branch of dynamical electricity, is called Galvanism or Voltaism
 from the names of its most illustrious investigators.
   4th.  By  means of organized  structures, of which'it is only lately
 by the researches  of Matteucci, that the true nature  and functions
 have become known, certain fishes possess the power of transmit-
 ting a current of electricity  across even imperfect conductors and
 employ, instinctively,  the effect  of  this  current  upon the  living
 frame  of smaller animals  in order to  obtain them for  food.  The 
GALVANIC  ELECTRICITY.
127
identity of the electricity from this animal origin, with the fluid of
the other dynamic sources, has been completely proved, particular
ly  by Faraday ; and as the question of the anatomical structure of
the electric organ, and of the peculiar part of the brain from which
the electric nerves arise, interests the physiologist rather than the
chemist, I shall merely state that the current so obtained possesses
all the  properties that will be described as characterizing galvanic
electricity of very high tension, and allude no farther to it.
  To the chemist, the electricity of the Galvanic or Voltaic battery
is  the most interesting of all the forms which this agent may as-
sume, from the intimate relation which exists  between it and the
force by which the elements of bodies are bound together in chem-
ical combination.  To it, therefore, I  shall especially direct  atten-
tion, and consider the remaining sources only  so far as the electri-
city which they yield may differ from  it.  I shall endeavour, also,
to consider it only as characterizing bodies by their properties of
exciting the  current, or of conducting it when excited,  deferring
the important topic  of the  action  of  the current upon compound
bodies until the nature of chemical affinities has been  described.
   Galvanic FJectrkity.—The  manner  in which  this form of excita-
tion occurs may be very simply shown.   If a slip of perfectly pure
zinc be partly immersed in a cup of dilute muriatic acid,
this last remains  totally without action on it, and there
is  no appearance  of electrical  disturbance ; but if a slip
of copper be introduced, which touches the zinc at  C,
out of the liquid, active decomposition of the  muriatic
acid begins, the chlorine combining with, and dissolving
the metallic zinc, and the hydrogen making its appearance under the
form of minute bubbles on the surface of the copper.   At the same
moment a remarkable state of electrical excitation is produced, in
which  the zinc resembles a body to which negative electricity, in a
state of exceedingly low tension, is uninterruptedly supplied, while
an equal quantity of  the positive fluid flows along the copper, and
these, uniting at the point of contact, produce the effects which are
spoken of as  those of the electric current, the passage of which may
be rendered evident in a great variety of ways.
   The precise  manner in which the  electrical excitement is here
produced, may be explained sufficiently well without  involving any
consideration of  the  theory of chemical decomposition,  which at
the present moment would require a knowledge of principles that
have not been as yet described.   We may suppose, simply, that the
chemical relations of  the zinc and muriatic acid are such, that when
placed in contact  they mutually induce on each  other a development
of electricity  : that part of the zinc which is immersed becoming -f-,
and that out of the acid —, while the molecules of the  acid near the
zinc become—, and the general mass of the fluid obtains -f- excita-
tion ; the + electricity of the zinc being, however, balanced between
the fluids of  its own  mass and of the acid, and the — fluid of the
acid being in equilibrium  between the  + fluids of the zinc and of
its own particles,  it results that this condition of induced excitation
may remain for any length of time without increasing or diminishinc'
in  intensity, the apparatus being in  the condition of a very feebly
charged Leyden jar:  and  on applying  the slip  of copper by which
z \ \c 
128          SIMPLE  GALVANIC  CIRCLES.
 the excited surfaces, the zinc and acid, are placed in communication,
 the negative electricity of the zinc unites with the positive of the
 copper, whether by direct translation or by inductive action, and the
 positive electricity of the  liquid unites with the negative of the cop-
 per to produce neutralization ; at the same time the + of the zinc
 and the —of the acid combine.  As,  on the theory of Franklin, the
               single electric fluid is  supposed to pass from  the
               body which is positively to the body which is neg
               atively excited, it is usual to imagine this exchange
               of electricities to take place by a current, which in
               this case, as shown by the arrows in the figure, is
               from the copper to the zinc at the superior junction,
               but from the zinc to the copper in the acid under-
               neath. At every moment, according as the neutral
               ization of the electricities is effected, the system is
               competent to generate new quantities, and hence the
 analogy of the weakly-charged Leyden jar, noticed above, does not
 completely hold ; for, to be  accurate, it would require the jar to pos-
 sess a power of charging itself as rapidly as it could be discharged
  The passage of the current is accompanied by the solution of the
 zinc and the  liberation of the hydrogen.  This hydrogen accompa
 nies the positively electrified molecules of the acid across the fluid,
 and is discharged under  the form of gas upon the surface of the
 copper plate.
  The essential elements  of an arrangement by which  a current of
 electricity  may be  produced are, therefore, first,  two  bodies, one
 simple and one compound, which act  chemically upon one another
in such a way as  that the  simple element shall be  substituted  for a
constituent of the  other,  which shall be expelled ; and, second, a
conducting substance, which is indifferent in a chemical point of
              view, and  only  furnishes a route for the fluids of the
              actual elements to recombine continually with each
              other.  In  the example given just now, this conduct-
              or was a slip of copper ; but it may be of any form, or
              almost any substance; thus, as in the figure, a wire
              may be soldered to the end of each slip, and on bring-
              ing these wires into contact at X, the current passes
              precisely as if the contact of Z with C had been direct.
              Such an arrangement is termed a simple circle.
  It is not even necessary  that  the conductor should be solid or me-
tallic ; it is, indeed, only for convenience that the ordinary conduct-
           ing  plates and wires are metallic.   Thus, in the figure,
           A Z W, a plate of zinc is in contact on the one side witfe
           muriatic acid, A, and on the other with water,  W, to
           which a better conducting power has been given by dis-
           solving in it a little common salt.  The current is then es-
           tablished, being from the conductor to the zinc, and from
           the zinc to the acid, precisely as in the former instances.
  The passage of the current under  these various circumstances
 may be shown, and also  that,  for its  origin and transfer, metallic
 communication between the plates Z  and C is not necessary  by
 a very simple experiment.  If  the slip of zinc be bent,  as in B, and
r	n	^
		
A.		
		
 
GALVANIC  AND  CHEMICAL  ACTION.      129
i
f^i*
M
a bit of paper moistened with iodide of potassium be laid
upon it, and the wire from A be then brought to touch the
upper surface of the moistened paper, the current passes in
the direction of the arrow, and iodine is evolved at the
point of contact of the wire.   If the surface of the paper
next the zinc plate, B, be examined, it will be found to be
alkaline, from free potash.   Thus the  chemical action of
the current, which will hereafter assume so  important a
position, may here  be simply used as  a test of its having
passed.
  The direction of the current depends upon the nature of the chem-
ical action which is produced at  the  period  of its passage, and on
this principle  is founded one of the most cogent and reasonable ar-
guments in favour  of the idea that the current is produced by the
chemical  decomposition, and not by the  contact of the metals, as
has been maintained.   Thus, if a slip of iron and a plate of copper
be immersed in muriatic acid, the action is altogether on the iron,
and the current passes from the copper to the iron  at the point of
contact.   But if the metals be immersed in a strong solution of am-
monia, which acts upon the copper, but not upon the iron, the cur-
rent is produced in the  reverse direction.  If persulphuret  of lime,
dissolved in water, be used as the exciting fluid with iron and cop-
per, the  current  is from the copper to the iron through the fluid;
but on using zinc and copper with the same fluid, the  direction of
the current is reversed; in the first case the  copper, and in the last
the zinc,  is acted on :  with  acid solutions the  copper would have es-
caped action, and the current would be in both cases from the iron
or zinc to it, through the liquid.
   It thus  appears  that  the relation  between the  current  and the
chemical action is of the most intimate nature possible ; the one, as
Faraday and others have decisively shown, cannot exist in such ar-
rangements without the other, and the nature and tendencies of one
determine the power and the direction of the other ; for the quantity
of electricity which is set in motion in such an arrangement depends
strictly on the amount of chemical decomposition which occurs in
the liquid clement, and  is simply  proportional to it.
  It is usual to arrange the various bodies in a list with relation to a fluid, in which,
if they be immersed and brought to touch outside, a current is generated  from that
of the two metals which stands highest in the scale to that which is below; the
current through the fluid is, of course, in the  opposite  direction.  The metals ar-
range themselves, however, very  differently with different fluids, according to their
liability to chemical action from them, as may be seen in the following table •
Dilute Nitric j Strong Nitric		Mu ' r A	S>lu ion of	Yellow Hvdrosul-
Acid. Acid.			Caustic Potash-	phuret of Potassium.
Platinum. Platinum.		Platinum.	Platinum.	Platinum.
Silver. Nickel.		Antimony.	Silver.	Iron.
Copper.	Silver.	Silver.	Nickel.	Nickel.
Antimony.	Antimony.	Nickel.	Copper.	Bismuth.
Bismuth.	Copper.	Bismuth.	Iron.	Antimony.
Nickel.	Bismuth.	Copper.	Bismuth.	Lead.
Iron.	Iron.	Iron.	Lead.	Silver.
Tin.	Tin.	Lead.	Antimony.	Tin.
Lead.	Lead.	Tin.	Cadmium.	Cadmium.
Cadmium.	Zinc.	Cadmium.	Tin.	Copper.
Zinc.	Cadmium.	Zinc.	Zinc.	Zinc.
R 
130    PRINCIPLE  OF  ELECTROTYPE  COPYING.

  At the head of each column is placed the name of the exciting fluid ; on taking
any two of the metals of the  list beneath, and making them the solid elements of
the circle, the current is, at the point of contact, from the upper to the lower, and
is more powerful in proportion as the metals are farther separated from one another
in  the  list; thus, with dilute, nitric acid  and with solution of caustic potash, the
most powerful current is, after platinum, by silver and zinc ;  with muriatic acid by
antimony and zinc, and with  persulphuret of potassium with iron and zinc.
  If  the  metals in  contact with the exciting liquid be such as that one is totally
without chemical action on it, it serves only as a means of mechanically transmit-
ting the inductive force, and  the current  is simply due and is proportional to the
electricity evolved by the action of the acid on the  other.  But if  both metals be
such that either would act upon the acid if by itself, and thus produce excitation,
as  when zinc and copper are placed in dilute nitric acid, then the molecules of acid
are submitted to two polarizing forces in opposite directions, which, if equal, would
exactly neutralize ; but in practice they are not equal, and a current is produced
proportional to their difference.  Hence, the more nearly the metals resemble each
other in their chemical relations to  a given liquid, the weaker  is the current they
produce ; but,  though acting similarly to one liquid, they may be oppositely related
to  another, with  which,  therefore,  they become a source of powerful excitation.
Thus  copper  and zinc, being both  acted on violently by sulphuret of potassium,
generate  but a feeble current, while with  dilute acids, which  act very differently
on each, the current is very powerful;  and thus platinum, which is inattackable by
almost all liquids, forms the best possible element in every instance.
  The metal which is used as the conducting medium conducts by having its natu-
ral polarity inverted ; and hence, in place of a disposition to combine with the oxy-
gen or chlorine of the liquid, it would, if already combined, abandon it; hence this
metal remains clean and bright.  On this principle was founded the mode of protect-
ing the copper sheathing of ships, by attaching small portions of iron of about -^
of the  surface; the chlorine of the salt in  the sea-water being thus transferred to
the iron, and  the copper, in  place  of becoming covered with the green rust of
oxychloride of copper, remaining completely  bright.  This  process succeeded in
practice  somewhat too well; for  the  negative  elements of the  sea-water  being
transferred to the iron, the positive  bases present, lime and  magnesia, were depos-
ited upon the copper, and thus affording points of adhesion for marine plants and
shell-fish, caused the bottoms of the vessels to become so foul as materially to in-
jure their sailing powers.  The process at present so extensively employed,  of fix-
ing a  layer of zinc upon iron surfaces, acts  in protecting them from rust in the
same manner.
  This transfer of the elements of the exciting liquids has become recently, in the
hands  of Spencer, the basis of one of the  most beautiful and important of the ap-
plications of science to the arts.  If one of the exciting liquids be a solution of sul-
phate of copper, as in Daniell's battery (page  136), the metallic copper which sep-
arates is deposited upon the surface of the plate to which the current passes in the
liquid,  and there is formed a  layer of metal, which may be  obtained, by  slow and
long-continued action, as dense and homogeneous as the best hammered copper.
Any prominences or depressions, even a scratch of a pin, drawn on the plate on
which the deposite forms, are accurately represented on its internal surface :  and it
is  only necessary to use as the negative metallic element a  medal in relievo  or in-
taglio, to  reproduce, with  an  accuracy equalling the powers of the most finished
hand or machine, the finest works of art.  This principle has been shown  by Mr.
Spencer  to be  applicable to the copying of all varieties of designs, and may  be looked
upon as the most important means of facilitating the possession of works  of art,
and thus elevating public taste, that has been made since the discovery of the method
of transferring engravings to any number of steel plates.
   The  electricity which is evolved by the chemical action  of such
simple  circles  is  remarkably different  in  its  characters from that
form which has been described as  its statical condition.  Although
present in  much  greater quantity than can be developed by  friction
with  the most powerful machines,  yet, from its state  of  continued
recombination, it  cannot acquire  intensity; it  hence  can pass only
through good conductors ;  pure water, which, from the facility with
 which  it allows of the  passage of machine electricity  proves the 
COMPOUND  VOLTAIC  CIRCLES.         131
great  source  of failure  and uncertainty in our experiments, inter-
cepts  almost  completely the current from a simple circle, and the
wires which are used to effect communication may be touched with
the fingers without any tendency to lateral shock becoming  evi-
dent ; and yet the disproportion in quantity between the fluid, which
bursts through the strongest insulating bonds of our  apparatus, or
breaks from  the  clouds, devastating forests, as the lightning, and
that which passes silently across the wires of the voltaic circle, is
such as almost to surpass  belief.  By  actual experiment, the im-
mersion  of two wires,  one of  platina  and the other  of zinc, each
0*06 inch in  thickness,  to a depth of five eighths of an inch, in di-
lute sulphuric acid for  three seconds, gave as much electricity as
could be generated by  thirty turns of the most  powerful machine
of the Royal Institution.   Indeed, Faraday has shown that,  in the
current which passes  during the decomposition of a grain of water,
there  is  contained more  electricity than in the brightest flash  of
lightning.
   If the  metallic elements of a simple  circle  be  connected, not di-
rectly by metallic contact or by a wire, but by means of one or more
other similar simple circles, interposed in the course of the current of
its electricity, it is not at all interfered with, but the quantity of elec-
tricity which circulates is precisely equal to  what is generated by
the chemical action which takes place in each celli  For, consider-
ing the circle of  four cells, represented in the figure, consisting of
copper and zinc plates, acted  upon by muriatic acid, the copper of
each cell discharges its positive electricity upon the negative  fluid
of the zinc in the adjoining cell, and hence there is neutralization
of effect at the points a, b, and c, and it is  only the amount of elec-
tricity liberated upon  the copper and zinc plates in the  terminal
cells that passes along the wires, and, recombining at d, produces
the phenomenon of the current ;  but  this is the same quantity as
should be evolved  by  any one of these  simple cells by itself, and
hence the remarkable result, which has been fully demonstrated by
experiment, that no matter how we may increase the number of the
elements of a galvanic circle,  the quantity of electricity passing in
the current is equal only to that evolved by a single cell.  If the
chemical action be not of the same energy in all the cells, there
passes little more electricity than  what is generated where the de-
composition is least active ; for, as the excess would have to pen-
etrate through the liquid conductor in  all the cells, the obstacle af-
forded to its progress is so great that it is almost totally absorbed.
  Although the increase in number of the elements of the  galvanie 
132 RELATION  OF  INTENSITY  AND  QUANTITY.


circuit is inefficient towards augmenting the quantity of electricity
which passes, yet it changes the  character of the current m a  very
remarkable deo-ree, and confers upon the fluid an intensity  which,
in a simple circle no matter of what magnitude, it never can possess.
It has been seen, that by the state of mutual excitation into which the
zinc and acid are thrown before the circuit is completed, the inten-
            sity  of  the evolved  fluids  is  limited to that which will
            not suffice to enable the excited particles of acid to dis-
            charge  themselves upon the oppositely excited particles
            of zfnc ; for if this discharge occurred, all  should  be
            brought back to the neutral condition.   Now, if there be
            interposed a second cell, containing an equal quantity of
the  same liquid as the first, its particles must be  brought  into  an
equally excited  state before discharge can occur;  and as the  elec-
tricity has  then to pass  through  a bad conductor of double the
length, it will require much greater intensity to penetrate it.  The
process, in virtue of which, therefore, the electric  equilibrium is in
the first instance disturbed,  continues, even before  contact is made,
until the intensity accumulated  is  sufficient to propel the  current
across the  interposed retarding liquid, and is  hence  proportional
to the  number of cells, or, as it is usually stated, to the  number of
pairs of plates.   The peculiar character of intensity may be suppo-
sed to arise, also, from the electricity  generated by the  outside
plates  obtaining additional velocity, in passing across the  intermedi-
ate cells, in each of which it meets an equal quantity of fluid moving
in the  same direction, and whose motion it absorbs, restoring  them
to rest, and being  thereby hurried itself onward in proportion.
   The intensity of the electricity which is  thus excited is very slight, even where
the number of combinations is considerable;  thus, it requires a series of at least
200 pairs of plates, four inches square, immersed in dilute sulphuric acid, to cause a
sensible divergence of the gold leaves of the most delicate electroscope.   It  is only
where the arrangement involves some tlwusands of couples that  electricity is
evolved of sufficient tension to produce a spark across a non-conductor, such  as that
given by the electrical machine, or to cause any of those attractive and  repulsive
motions by which  the  feeblest form of statical electricity is recognised ;  to obtain
these effects also, the circuit must be broken, for even with the most powerful com-
binations the current of electricity is without any action of intensity.   Where, how-
ever, by means of a sufficient number  of elements, intensity has been  given, the
quantity of electricity  which accumulates, and the quantity of chemical action from
which it has its origin, are exceedingly minute.  This is exemplified in the dry piles
of Zamboni, tlie form in which electricity may be considered as connecting its purely
dynamical and properly statical conditions.  The pile of Zamboni contains no ap-
parent liquid element; it consists of disks of gilt paper, and of exceedingly thin zinc
foil, laid alternately over one another, to  the number of from five to twenty thousand,
                                 care being taken to turn all the gilt surfaces
                                 the same way.  These are enclosed in  a glass
                                 tube, and terminated at  each end by a brass
                                 cap with a pressure screw.   The paper con-
                                 taining in its pores, when not artificially dried,
                                 a small  quantity of water, this gradually acta
                                 upon the zinc, and electricity is evolved, which
                                 from the great obstacle presented to its  recom
                                 bination through the disks internally,  and by
                                 the atmospheric air outside, attains a  degree
                                 of intensity so high that it acts decidedly upon
                                 the electroscope, as shown in the figure, and
                                 is amusingly applied to produce various  at-
                                 tractive aad repulsive motions, such as  ringing
m
 
             volta's theory  of  contact.         133

 belh, etc ;  for there being a continual source  of electricity in the action of the
 moisture of the paper on the zinc, these phenomena may continue manifested for
 years without diminution.
   Such a dry pile, when insulated, shows opposite electrical excitation at the two
 extremities, these being, however, of equal force, and  hence producing neutrality
 when combined.  If, therefore, the two ends of a dry pile be connected by a wire,
 the electricities which had accumulated recombine, and the pile becomes inert, and
 requires a certain time before it can recover a charge equal to that which it had
 lost.  When the pile is examined at a distance from its ends, the excitation is found
 to be less powerful, until at the centre it is exactly neutral.  This arises from the
 action at each point being the resultant of the opposing actions of the two extrem-
 ities, and vanishing  at the centre where  these last are equal, precisely as there ex-
 ists  a neutral place upon the surface of any body inductively excited by ordinary
 electricity.  If the pile be held in the hand by one extremity, the electricity of that
 end  is dissipated, and the other end becomes  capable of acting more powerfully
 upon the electroscope, from the opposing influence being removed.
   No principle has ever been discovered in science more rich in consequences than
 this  of the increase of tension  given  to electricity in motion by the connexion of a
 number of simple galvanic circles.   Hence, deservedly, the instrument so formed
 has  obtained the name of the Voltaic pile.  It has enriched chemistry with a crowd
 of important substances discovered by its means, and has led,  by its results, to the
 suggestion of the most plausible theory of chemical combination that has been as yet
 proposed.  In physical science it became the origin of all subsequent improvement
 in the domain of  electricity, for without  its agency it is hard to see how the steps
 which followed could have been made.
   The form in which the Voltaic  pile was first constructed was sim-
 ilar to that of the dry pile noticed above.  The disks were of zinc
 and silver  or  copper.  The fluid conductor,  which  was rendered
 more capable  of acting on the zinc by the addition  to it of some
 acid or of common salt, was  imbibed in disks of common cloth,
 which were interposed between every pair of metallic disks.   There
 were thus,  copper-zinc, acid, copper-zinc, acid, copper-zinc,  and so
 on  to  an  indefinite extent.  It is a peculiarity of this  instrument,
 which, as it extends to many forms of it even  now in use, and  affects
 our chemical nomenclature  remarkably,  it is necessary to notice,
 that the current in the connecting wires appears to  be in a direction
 opposite to  that described in  the battery of cells of page 131;  for
 the  outer  copper plate at the  one  end, and the outer zinc plate at
 the  other, having no  communication with the  exciting  acid, trans-
 mit  the current merely as portions of the  attached wires, and hence
 the  direction of the current is in  appearance from  the  zinc  to the
 copper end, while it is properly the  copper from which the positive
 fluid emanates, and it is the  negative which arises from the zinc.
 This diversity  had its origin in the circumstance that  the theory of
 the  pile maintained by Volta, and even at the present moment sup-
 ported by some illustrious men, ascribed the  origin of the electri-
 city not to the  action of the acid  upon  the zinc, but to the contact
 of the zinc  with  the copper ;  the  point where the  metals touched
 being  supposed to be a continual  source of positive  electricity  to
 the copper.   It was even attempted to prove  this by  solderino-  to-
 gether plates of zinc and copper, and testing their electrical condi-
 tion  by the gold-leaf condenser, which  was supposed to indicate a
permanent state of excitation, independent of all fluid or chemically
acting media.  It  has been  fully  proved, however, that, according
as such contact experiments are made  with increased care the re-
sults become less  evident in favour of that theory.   Such trials tend
to show the  evolution  of minute traces of statical electricity, where- 
134  VARIOUS FORMS OF  GALVANIC  BATTERIES.
 as the simple galvanic circle is characterized by the great quantity
 of electricity it may yield, and by its total want of statical intensity.
 Even, therefore, if it were proved, which it is not, that the mere
 contact of bodies evolved  electricity affecting the gold-leaf electro.
 scope, it would be as far  from accounting for the totally different
 kind of electrical excitement by which the galvanic  battery is cre-
 ated, as it would be from giving a true or  satisfactory theory of the
 cause of magnetism.
   But the pretended excitation by contact, or  the electromotor force,
 as it was termed by Volta, must be carefully distinguished from the
 capability of inductive excitement, which bodies capable of chemi-
 cal action, as a slip of zinc and muriatic acid, mutually confer upon
 each other.
   This last arises from the possible substitution  of the zinc for the
 hydrogen of the  acid, which does occur as soon  as the interchange
 of the electricities allows of the transfer  of elements; for  on  the
 first immersion of the zinc, the equilibrium of the chlorine and hy-
 drogen, which had previously been totally  engaged with each other,
 is interrupted, and that of the particles of the zinc, which had be-
 fore been all circumstanced alike, is disturbed by some  of them be-
 ing nearer the acting muriatic acid than the others, and thus the in-
 duced condition  of both arises.  On  this positive  and necessary
 principle,  the theory of the simple and compound  circles already
 described has been given; and although it will require  to be again
 noticed in describing the  phenomena of decomposition which ac-
 company the passage of the current, yet, for the only purpose which
 we here require, of studying the manner  in which the current of
 electricity of the battery has its rise, the peculiar and important in-
 fluence exercised by the chemical reaction among the elements of
 which it consists has been  sufficiently described.
   It is now necessary to notice more in detail the construction of
                                 some of the more usual forms of
                                 the Voltaic or Galvanic battery.
                                 The first improvement on the pile
                                 of Volta consisted in placing it
                                 horizontally in a wooden trough,
                                 and replacing by cells containing
dilute acid the moistened  disks of cloth employed  by the orio-inal
inventor.   It being  difficult to cleanse the surfaces of the  plates,
                                   which in  that form were per-
                                   manently cemented  into the
                                   trough,  this was made of delft-
                                   ware divided into cells, and the
                                   plates, being soldered together
                                   by projecting bands at the top,
                                   were hung upon a rod, as in the
                                   figure, so that,  when wanted,
                                   they  may be  immersed with
                                   great rapidity,  and withdrawn
                                   as easily from the liquid when
                                   the battery is not wanted.  The
                                   power of such  troughs is in-
 
     INTERFERING  ACTION  OF  COMMON  ZINC.   135

creased by one half when the copper slip is doubled over so as to
oppose both surfaces of the zinc.  Batteries intended rather for in-
tensity than for quantity, and which  consequently consist of a great
number of plates of moderate dimensions,  are generally employed
on this last construction : each delftware trough holding ten pairs of
plates, and any number of troughs that may be required being rap-
idly and easily arranged together.   When a current of electricity
of great quantity, but not of intensity, is required, it is usual to em-
ploy a few, or even only one pair of plates of considerable size. Thus,
a sheet of copper and a sheet of zinc, each of from 80 to 120 square
feet of surface, being kept separated by ropes of horsehair, have
been rolled up together and immersed into a large tub of acid, form-
ing thus a simple circle, giving a current so feeble in intensity as to
pass with difficulty through a short column  of distilled water, and to
be quite insensible to the feeling, but which fused down into globules
the most  refractory metals, and gave with charcoal points a light of
brilliancy insupportable to the eye.   The copper plate may be very
conveniently made  to act as the cell containing the acid: cylindrical
batteries of moderate size  are very  frequently so constructed.
  I have  supposed, in the  description of the nature of simple and
compound Voltaic  circles, that the  zinc employed was completely
pure, in which state, when first immersed in the acid, there is no chem-
ical action, but only  the preparatory inductive state produced,  the
decomposition of the acid by the  zinc commencing only when  the
circuit is completed.  But such pure zinc is too expensive for ordinary
use, and the commercial zinc contains always traces of impurities,
particularly iron, from which it acquires a power of  generating  a
multitude of little secondary currents across the fluid, and thus pre-
venting to a great extent the  formation of the proper current.  For
suppose that there is on the centre of a plate of zinc a little piece of
iron or of copper, this serves to return to the zinc from the acid  the
positive electricity, which had passed away from it precisely as if
it had been a copper wire, which touched the acid with the one end,
and the zinc plate with the other.   Such a plate is therefore  occu-
pied almost solely with its  own self-contained currents, and scarcely
assists in generating the electricity which is brought into play in the
battery at large.  To this cause must be assigned the property which
ordinary zinc possesses of dissolving readily in an acid, and of evolv-
ing hydrogen  upon its own surface.   It evolves the hydrogen upon
those points of its surface on which  foreign metals being deposited,
serve to complete its circuits.  This injurious property of ordinary
zinc is remedied by coating the surface of the plate with mercury,
or, as it is termed, amalgamating it.   By this means the whole sur-
face of the metal is brought into the same state, and must hence  act
in  the  same manner  on the acid.   Any  secondary current which
might arise could therefore find no means of discharge, and such
zinc is not acted on until the circuit is completed, and then all hy-
drogen is carried by the excited  molecules of acid to the copper
plate, and there evolved as gas.
  To amalgamate the zinc plates of a battery, a quantity of mercury
is to be laid in a flat dish, sufficient  to cover the bottom ; moderately
dilute nitric acid, to which a  small  quantity of nitrate  of mercury 
136       FORMS  OF  CONSTANT BATTERIES.
 has been added, is to be then poured on the mercury, so deep that
 the zinc plate, when floating on  the mercury, shall be covered by
 the acid.  Before immersing the  zinc plate, it should be, if not new,
 cleaned  as well as possible with sand-paper from adhering dirt, and
 then it combines with the mercury very rapidly, so as to form a sur-
 face which, by rubbing with a little flannel, may be rendered com-
 pletely uniform.   The zinc  should not be too  highly mercurialized,
 for then  it becomes extremely brittle, and requires considerable care
 in  using it.  The power  of a battery  may often be quadrupled by
 this method.  A source of great inconvenience in the ordinary bat-
 teries  arises from the hydrogen acting on the oxide of zinc which
 is dissolved, and reducing it to the metallic state, when it is carried,
 with the  remaining hydrogen, to .the copper plate, and deposited upon
 it.   In this way there is gradually  formed a second  zinc surface
 opposite to the proper zinc  plate, and  which,  tending to transmit a
 current in the reversed direction, neutralizes a certain proportion of
 the power of the circle, and  may even destroy  it altogether.   Hence
 an  ordinary battery is most active when first brought into play, and
 diminishes very rapidly in power until, after the lapse of some hours,
 even though the acid be not saturated, its action ceases.
  This disadvantage has been beautifully removed  by  the principle
 of absorbing the hydrogen  by means of a solution of sulphate of
 copper, which it decomposes, and precipitates upon the surface of
 the copper plate a layer of clean, new, metallic copper, in the best
 possible  condition for supporting the  action  of the battery. The
 simplest  arrangement of this kind is that of Mullins; the mechani-
 cal  construction is most perfect in Daniell's constant battery.  Mul-
               lins' battery consists  of a  delftware trough, D, in
               which the cylindrical  zinc  plate B, of nearly the
               same diameter, is placed, and inside  of which, again,
               is the  copper cylinder A, which  is close, and acts
               only by its external surface ; round the upper edge
               of the copper cylinder C is tied a bladder, into which
               fluid may be introduced by means  of a row of ap-
               ertures in the rim to which the bladder is attached.
               A solution of sulphate  of copper is  poured into the
               bladder, and its state of concentration is kept up by
heaping  some coarsely-pounded crystals on the top of the copper
                  cylinder.   Into the trough in contact with the
                   zinc is then poured dilute sulphuric acid.   When
                   the action commences, the hydrogen is transfer-
                   red through the membrane, and, meeting there
                   the solution of sulphate of copper, is absorbed
                   in the  production of metallic copper.   The cop-
                   per cylinder never wears nor dirties.   The metal
                   is all  recovered  from the sulphate of copper,
                   and the  only thing necessary is that the plates
                   of zinc  shall  be  renewed from time  to time.
                   Daniell's battery has the advantage that the cop-
                   per is outside, and hence  is  capable, with ex-
                i;||| posure of the same surface of zinc, of producing
                   a much more  powerful current.   The cell con-
 
CONSTANT BATTERIES.
137
sists of a copper cylinder, a, c, near the top  of which is attached
a perforated plate, P, on which, when the cell has been filled  with
the solution of sulphate of copper, a quantity of  crystals are  laid,
to be dissolved according as they are required.   A solid zinc rod,
m, supported at the top  of the copper cylinder by a wooden cross-
piece, is contained in a membranous bag, formed of the gullet of an
ox, g, h, and into this is poured the dilute acid, which consists of
one part of  oil of vitriol and eight parts of water.  Any number of
these cells may be arranged together so as to give a battery, which,
if all the coppers be connected upon the one  hand, and all the zinc
rods upon the other, will evolve  large  quantities of  electricity of
low tension ; but when the copper and zinc elements are alternately
connected with each other, the tension of the electricity  evolved is
much increased, though at the expense of the quantity generated.
   The great advantage of such batteries is the perfect uniformity
of their action, by which they deserve fully the  name applied by
Daniell to his construction, of the constant battery;  with such an
instrument,  the conditions of the current may remain  for days per-
fectly unaltered ; and thus the laws of action of  the  current  have
been determined, particularly  in its chemical relations, with com-
plete success, and views of the analogies between affinity and elec-
tricity, equally novel and important, which will be discussed in an-
other place, have been arrived at by its means.
   Latterly,  the membranous bags, originally used by Daniell  and
others as the diaphragm between the  acid solution and that of the
sulphate of copper, have been with great advantage replaced by
porous cells of biscuit-ware, such as is represented in the figure by
g, n.
   Some forms of battery have recently been proposed, in which,
under a small compass, very great power is obtained, by, 1st, bring-
ing the plates very near  each  other;  2d, selecting solid elements,
which differ as much as possible in their chemical relations;  and,
'id, using  as the  exciting fluids those of the most  intense action,
and  of the highest conducting power.  In this way, the most pow-
erful Voltaic  combination that has  been  yet made is that of Mr.
Groves.   Plates of zinc and platina are separated  by diaphragms of
porous earthenware, the zinc being acted upon by dilute sulphuric
acid mixed  with some nitric acid, and the platina being in contact
with tolerably strong nitric acid."" The  hydrogen evolved by the
zinc  is completely absorbed by  the  nitric acid  on which it acts,
forming nitrous acid which remains dissolved ;  and the  metals, beino-
those most opposite in their electrical  relations, give the most pow-
erful  current possible.
  The conducting powers of various bodies for this form  of electri-
city has been determined with great care by Pouillet, whose results
are, that the relative conducting  powers of the various metals are
expressed by the  following numbers :
Palladium   .   .  .  5791
Silver.....5152
Gold.....397.1
Copper   ....  3838
Platina   ....   855
Bismuth  ....   384
Brass from.  .
     to  .  .
Cast steel from
     to  .  .
Iron ....
Mercury   .  .
900
200
800
500
600
100 
138       RELATIVE  CONDUCTING  POWERS.
   He ascertained, also, the relative conducting powers of the saline
 solutions usually contained in the  cells of the Galvanic  battery ;
 and it appears that  the conducting power of platina is two million
 and a half times that of a saturated solution of sulphate of copper,
 and hence that of copper is  sixteen million times as great.   The
 conducting power of the saturated solution  of the sulphate of  cop-
 per being'taken as 10-000, he found that of
       a saturated solution of sulphate of zinc to be .  4-170
       distilled water...........0-025
       distilled water with ^o^o of nitric acid   .  .  0-150

 The great retardation which  occurs when the current has  to pass
 through any  considerable length of liquid, will now be easily under-
 stood.   Pure water  may be considered, with  feeble circles, as an
 absolute non-conductor ; and even with the most  powerful combi-
 nations that  have  been yet made, the current is unable to force its
 way through the smallest measurable interval of air.  It was not
 long ago believed that, even with simple  circles, a spark indicating
 the passage  of a  current was seen  on making contact,  and hence
 that the electricity had passed before the metals had touched, and,
 consequently, that the chemical action should be alone considered
 as the source of the  electricity.   It is, however, now acknowledged,
 that no  spark can pass until the Avires have  touched and are again
 separated, and  the passage  of the electricity is then accomplished,
 not by the action of  the excited molecules of air, as occurs with the
 machine, but  by the  violent inductive polarization of the particles of
the terminal  conductors, which are torn off and pass from one pole
 to the other.
  When the  current of electricity is retarded by means of an in-
sufficient conducting medium, the centre of the conductor becomes
hot, and thus the most brilliant effects of heat and light may be pro-
duced ;  even  the most refractory metals, as gold and platina, being,
when in thin  foil or  wire, dissipated  actually in smoke.   By termi-
nal points of well-burned charcoal, this phenomenon is beautifully
produced, the ignition being totally independent of combustion, for
it takes place in vacuo or in carbonic acid gas; and when the points
are separated from  one another  to a certain distance, the  interval
becomes occupied by a splendid arch of light, formed by the induc-
tively excited particles of charcoal, which, in a state of intense ig-
nition, abandon the  positive to  attach themselves  to the negative
extremity of  the conductor.
  The action of galvanic electricity upon the animal frame does not
properly fall  within the scope of the  present work, but in termina-
                         ting the subject,  the mode in which the
                         first view of this important  science was
                         obtained may with propriety be noticed.
                         Galvani was professor of anatomy at  Bo-
                         logna, and, while preparing  frogs  for
                         some physiological experiments, he hap-
                         pened  to touch,  by one extremity of a
                         metallic wire, the lumbar nerves which
                         still remained attached to the spine, while
 
        G A L V A N I S M.--T HER MO-ELECTRICITY.     139

the other extremity of the wire was in contact with the muscles of
the leg ; these last were instantly thrown into strong convulsions.
To perform this  experiment Avith success, the legs of the frog are
to be left attached to the spine by the crural nerves alone, and then
a copper wire and a zinc  wire being either twisted or soldered to-
gether at one  end, the  nerves are to be touched with one wire,
while the other is to be applied to the muscles of the  leg.
   Galvani erred in the explanation of this remarkable effect; he look-
ed upon the body as being in  the  state of a charged Leyden jar, of
which the nerves and muscles were the external and internal coat-
ings, and that, on connecting these by the conducting wire, the elec-
tricities  recombined, and the  passage renewed for the  instant the
phenomena  of life.  Volta  pointed out, however,  that, in order to
produce full effect, the presence of two metals in the conductor was
required, and he ascribed  the origin of the electricity not to the
body, but to the  contact of the two metals, and  supposed the con-
vulsive motions  to be merely the indication of the passage of the
current across the  body of the frog.  This view has also been since
modified by ascribing the  electricity  to minute  traces of chemical
action on the wires; but  it was so fruitful in results, of which the
construction of the Voltaic pile is the most remarkable, that Volta
is, with justice, looked upon as the true originator of this branch of
electricity as a science, although  it was Galvani who  observed the
first fact belonging to it.
   The frog so prepared is a most delicate test of the passage of a
Galvanic current;  it is truly  a galvanoscope, corresponding to the
gold-leaf electroscope for ordinary electricity ; but it does not meas-
ure  the  quantity or  intensity of the electricity which passes.  As
3ret we have no exact measure of the intensity  of Galvanic electri-
city ; but that its quantity may be  exactly determined, two of its
properties  may be applied: the first consists in  determining  the
quantity of a given chemical substance, as water, which  the current
can  decompose in a certain time, for the quantity decomposed is
proportional to the quantity of electricity which passes ;  the second
consists in observing the degree to which the current  is able to de-
flect the magnetic needle from  its natural position  of north and
south, for the angle of deflection is connected with the quantity of
electricity in the  current by a very simple law; we are not yet in  a
position  to understand fully the theory either  of the chemical or
the magnetic  galvanometer, and hence  I merely indicate, for the
present, their existence and their names.
  Thermo-electricity.—If heat be applied to  a wire, uniform in tex-
ture and thickness, bent into a ring, there is no disturbance of elec-
trical equilibrium ;  but if any obstacle to the transmission of the
heat, such as a knot or a coil  in the wire, exist, a cur-
rent  will be established, of which  the direction will be
from the point of  the circuit to which the heat is applied
towards the point where the retarding cause exists.  If
in  place  of merely causing an artificial  obstacle on a
uniform wire, two metals, a b,  be selected, which differ
in conducting power, and the point at which they  touch
one another, c, be kept at a different temperature from  ■*»=—=~-
the rest, a current  is also produced from the latter point towards
 
140         THERMO-ELECTRIC  CURRENTS.
the metal which is the worst conductor.  The more unlike the met-
als are in molecular constitution, and the greater the difference be-
tween their conducting powers,  the more energetic is the current.
The best combinations are  therefore  of a crystalline and  a non-
crystalline metal, or of two metals which crystallize in different sys-
tems.  Bismuth and antimony, which are the worst conductors  of
the metals, are also amonsr the most crystalline ; and while bismuth
crystallizes in cubes, the form of antimony is a rhombohedron ; these
metals, therefore, combine all the essential qualities for generating
a current when unequally heated,  and they are, consequently, the
most powerful sources of thermo-electricity that have been found.
The results obtained with other metals will be understood by wri-
ting them down  in the following order, any two of them  being
capable of forming a current when  their junctions  are unequally
heated, the current being from the metal highest to that which is
lowest in the list, and the power  of the current  being greater in
proportion to the  distance between the metals in the following or-
der : bismuth, platinum, lead, tin, copper or silver, zinc, iron, anti-
mony.   The molecular texture would appear from this list to have
more influence  on the production of the current than the mere dif-
ference of conducting power.
   The intensity of the thermo-electric current so excited is exceed-
ingly small; it is only capable of  passing through very good con-
ductors,  and it requires the combination of a number of exciting
couples to give sufficient tension to enable it to produce a spark, or
to show  any signs of chemical influence.  It then, however, agrees
in all respects with the electricity  of the Galvanic battery when in
an excessively feeble state of tension, and it resembles remarkably
the hydro-electric current, in being able to reproduce at a distance
the circumstances in which it originates; for precisely as a current
passes through a  combination of  antimony and  bismuth when  its
junctions are at unequal temperatures, so, when a similar current
from any other source is passed through the metallic couple, a change
of temperature is produced at the place where the two  unite; if the
current pass from the bismuth to the antimony, the junction becomes
heated; but if the electricity pass in the opposite direction, the junc-
tion is cooled  to  a  remarkable degree,  so that,  if a little  hole be
bored where the metals touch, and a drop of water be laid therein,
it is frozen after a few moments.  This result, which was first ob-
tained by Peltier, and has been confirmed by Bottger,  is one of the
most remarkable proofs of connexion between the physical sources
of temperature and electrical equilibrium that has been as yet dis-
covered, and may influence our theories  of the nature  of heat in no
inconsiderable  degree.
   The principle  of strengthening  the thermo-electric current, by
                            combining  together the action of  a
                             number of metallic couples, is due to
                             Nobili.  If we consider  a number of
                             bars of  antimony and bismuth, a b,
                             soldered together alternately at their
                             ends, so that every alternate soldering
                             shall be in the  same  plane,  and  the
                             extremities of the  terminal  bars be
 
      CONSTRUCTION OF  THE  THERMOSCOPE.   141

connected by a wire, on applying heat to the alternate solderings,
a current is generated at each, which, being all in the same direc-
tion, travel together through the system, and thus increase its en-
ergy in proportion to the number of combinations.  The important
distinction  between  this  and  the combination of elements in the
Voltaic pile is, that in the latter the increase of number affects only
the tension of the current, but leaves the quantity the same as the
single couple ; but in the thermo-electric pile, although the intensity
is increased, yet  the quantity which passes in the current is aug-
mented also.
   It is this principle which has been applied by Nobili to the con-
struction of the thermo-multiplier or thermo-electroscope used by
Melloni  and Forbes in their researches on radiant heat, of which a
sketch has  been given in the last chapter.  The  thermoscope con-
sists of fifty small bars of bismuth and antimony, placed parallel  be-
side one another, and forming a single prismatic bundle, F, F', about
1^ inch  long and  f inch square in section.  The two terminal  faces
are blackened.  The bars of bismuth, which are arranged alternately
with those  of antimony, are soldered at their extremities, and sep-
arated all through their length by an insulating substance.  To  the
first and last bars are attached copper wires, which terminate in the
pins C C,  of the same metal, passing across a piece of ivory fixed
on the ring A A.  The space between the interior of this ring and
the elements of the pile is filled by insulating material.  The free ex-
tremities of the two wires are  put  in communication with the ter-
minal wires of a magnetic galvanometer,  the needle of which indi-
cates  by its motions when the temperature of the anterior surface
of the thermo-electric pile is raised or lowered, in comparison to that
of the posterior surface.  (See P in figure, page 99.)
  By means of a jointed support, the axis of the pile may be turned
in any direction that may be wished ; and  to protect its surface from
lateral radiation, the metallic tubes B B, brilliant externally and black
ened on the inside, are attached to the extremities of the ring A A.
  If by changing through one  degree the temperature of a sino-L;
soldering, a current of a certain  power be  obtained, there should be
with fifty  solderings  a current  fifty times as strong,  or an equal
current when the temperature of the solderings varies  through one
fiftieth of  a degree.   It has been ascertained that instruments of
this kind may be made to indicate a variation of temperature of 5~?
of a degree on Fahrenheit's  scale.
  The electricity which is thus evolved by change of  temperature
in conducting  bodies, although  so feeble  in quantity and intensity
as to be utterly devoid  of those brilliant qualities which attach much
popularity to the phenomena of Galvanism and of machine electri-
city, has thus  been found the means of assigning the true laws of
some of the most interesting and important branches of the physical
sciences ; and it will be hereafter seen that thermo-electric currents, 
142  RELATIONS  OF  THERMO-ELECTRIC  CURRENTS.


excited in the superficial stratum  of the globe by the inequality of
temperature which arises from the action of the sun,  may generate
not  only the magnetic properties on which are  founded  the com-
mercial intercourse of civilized nations, but, by influencing the affin-
itary powers of the elementary constituents of our planet, may have
been the agent in silently, but effectively,  regulating the constitution
of inorganic nature.
  [From the extensive employment of thermo-electric currents as measures of tem-
perature, it is desirable to understand their habitudes.  Dr. Draper has shown that
equal quantities of heat do not set in motion equal quantities of electricity ;  with
certain combinations of metals the proportion increases, and with  others decreases.
For this reason, temperatures  estimated in  this way must  always undergo correc-
tion, as the following table shows :
		Waer boils	Mercury boils.
i<- Mercurial thermometer .		212	662
«.3	r Copper and iron . . .	202	257
8 o.	Silver and palladium	235	880
s-3'	Iron and palladium . .	211	539
	Platina and copper . .	244	1030
	Iron and silver . . . ^Iron and platina . . .	170	279
&s		212	829
We therefore infer, that in these six systems of metals, the developments of electn.
city do not increase proportionally with the temperatures, but in some with greater
rapidity, and in others with less.
  The tension of these currents undergoes a slight increase with  increase of tem-
perature :  a phenomenon due to the  increased resistance to conduction of metals
when their temperature rises.   In hydro-electric pairs, the quantity of electricity
evolved depends on the surface of the plates; but in thermo-electric arrangements,
the quantity of electricity is independent of  the amount of  heated surface, a mere
point being just as  efficacious as an  indefinitely extended surface.  And in a com-
pound series of many pairs, the quantity of electricity evolved is directly proportional
to the number of pairs.
  Thermo-electric currents traverse metallic masses only on account of differences
of temperature existing at different points.  When a current flowing from the poles
of a battery is made to traverse a wide metallic sheet, the whole of it does not
                                    pass  in a straight  line from one pole to
                                    the other,  but diffuses itself through the
                                    metal, diverging  from  one pole and con-
                                    verging to  the other.   For these reasons,
                                    there  are  certain forms  of  construction
                                    which give thermo-electric arrangements
                                    peculiar advantages. For example, the sur-
                3                  faces united by soldering must not  be too
                                    massive.  Let a, fig. I, be a  bar of anti-
                                    mony, and  b a bar of bismuth ;  let them be
                                    soldered  together along the line c d, and at
                                    the point d let the temperature be raised,
                                    a current is immediately excited , but this
does not pass round the bars a b, inasmuch as it finds a shorter and readier chan-
nel through the metals between c and d, circulating, therefore,  as  indicated  by the
arrows.  Nor will the whole current pass round the bars until the temperature of
the soldered surface has become uniform.
  An obvious improvement on such  a combination is shown in fig. 2, which con-
sists of the former arrangement cut out along the dotted lines ;  here the whole cur-
rent, as soon as it exists, is forced  to pass along the bars.  And because the mass
of metal has been diminished along the line of junction, such a pair will change its
temperature very quickly.
   One of the very best forms for a thermo-electric couple is given  in fig. 3, where  a
is a semi-cylindrical bar of antimony, b one of bismuth, united together by the oppo-
site  corners of a lozenge-shaped piece of copper, c.  From its exposing so much
surface, the copper becomes hot and  cold with the greatest promptitude ; and from
its good conducting power, it may be made very thin without injury to the current.]
■<v				*wv	£*	
	C		b			
	m					
 
MAGNETIC  PROPERTIES  OF  IRON  AND STEEL. 143
  Magnetic Electricity.—The properties which are now known as
magnetic were  first recognised in a peculiar ore of iron, found in
the vicinity of  the town Magnesia, in Asia Minor, from which the
names of the  substance  and of the science have been derived.  The
native magnetic ore or loadstone consists of iron and oxygen.   This
mineral, although quite  inert with regard to all other bodies, attracts
iron and steel with great power; and the pieces  of  iron and steel,
while in contact with the loadstone, participate in its powers, and
are capable of attracting other pieces to themselves.  Iron and steel,
though both  attracted by the magnet, differ remarkably in the fact
that iron, although magnetic while  in contact with  the loadstone,
loses all its properties when it is removed; while steel, which is at
first attracted with inferior power, when it has become magnetic by
contact with  that mineral, retains  that condition after separation,
and thus becomes a permanent  artificial  magnet.  A steel magnet
thus formed may in its turn be used in place  of a loadstone to form
others ; and almost all the  magnets we employ in experiments have
thus obtained their power, as native loadstone is not found in suf-
ficient quantity, or sufficiently intense in action, for our purposes.
The steel bars which are magnetized are generally straight, but often
also bent in the centre, so that  the halves are nearly parallel, and
are then called horseshoe magnets.
   When a magnetic bar is dusted  over with iron filings, it will be
found that the filings attach themselves to ,,,-;t'p'^-^^^^^^^j^
the extremities of the bar, and scarcely at 'T*t**'p'          fWjM
all to the  centre ; the magnetic  power is *%rW<'*'*^wV|l,l|l'l"'M^'WP!i
thus seen to  exist only  near the  ends of the bar.  Each filing being
itself for the time a magnet, attracts others, so that they form strings,
which arrange themselves, according to  definite laws, in an order
which is termed  the  magnetic curves, and from  the disposition of
these curves it is evident  that the action of the magnet emanates
from a single point, P, near each
extremity ; these points being the
centres of action of the magnet,
are termed its poles.  Thus, in the
figure, the bar being a magnet, the , :~~ --;. Jz^i'?]^'*"""^
points P and P are the poles, and      -  "7*  a/" v"" r-^v-j- %
the directions of attractive force \-:.:}S^-i^^70}i^!-^^--#i$%^;X^';£
are indicated by the diverging! .   '   \'t%   ; ~~ ' , ~}^\-\"   y
lines, which, uniting on the inner L_.-. ;".'■'•  '  - ■  ' "    '   .    '
side, form the magnetic curves.  ' ■—■ -—'---■---     '-----     —
  The utility of the magnet in navigation is well  known ;  it  arises
from the poles of the magnet being attracted by the earth in such a
way, that,  when free to move, the magnet rests in a direction nearly
north and south ;  the pole of the magnet which  is turned to the
north is termed the north pole, the other the south pole.  If two
magnets be brought into the neighbourhood  of one another, they do
not attract indifferently, as either would attract a mass  of iron ; but
the north  pole of one magnet attracts the south pole of the  other,
and is attracted by it, while the north  poles of the two,  or the south
poles, if brought near each other, repel as powerfully.   In magnets,
therefore,  poles of the same name repel, and poles of opposite names
 
144     INTIMATE  STRUCTURE  OF  MAGNETS.
  attract, a condition precisely similar to that which holds between the
  electricities evolved by friction.  In magnetism, also, the attractions
  and repulsions follow the law of the inverse square of the distance,
  and thus complete the superficial  analogy which led astray for so
  many years the investigators of this branch of science.
   The action of the earth upon magnets  at its surface can only be explained by
? supposing the earth itself to possess magnetic properties. The northern portions
  of the earth attract the north pole of a magnet, and must therefore possess south
  ern polarity; the southern portions of the earth attracting the  south  pole of the
  magnet, must possess  northern polarity.   The action of the earth  cannot be ex-
  plained, however, by supposing it to be a  simple magnet with a pole at each ex-
  tremity.   It possesses at least two centres of force or  poles in the north, one in
  Siberia and one in North  America, while the exact distribution of the centres of
  magnetic force in the southern hemisphere has not been yet made out.  These cen-
  tres themselves are, however, not fixed;  the needle is continually changing in di-
  rection ; at present it points to 24p west of north;  but in the year 1664 it pointed
  to the north, and it had previously pointed in an easterly direction, towards which
  it is now returning.
    Prior to the discovery, by Ampere, of the true nature of magnetic
  phenomena, a  theory  similar for the  most part to that  of the two
  electrical fluids was maintained; two  magnetisms were supposed to
  exist, the particles of the same fluid  repelling  each other,  but the
  particles of one fluid attracting those of the other.   The assumption
  of magnetic properties by a piece of iron  or steel in  contact with a
  magnet  became, therefore, a phenomenon of  induction similar to
  that described under the head of statical electricity, the constitution
  of iron being such that the fluids recombined on the disturbing cause
  being removed; the constitution of steel,  on the contrary, prevent-
  ing their reunion.   There existed, however,  one great difference
  between a magnetic bar and a body excited by induction  with ma-
    p._______^_______?    chine electricity.   If the bar A, C, B,  excited
    L_______1________J   by induction, and of which the portion A is
   /\      J\     J\   positive, and B negative, the middle C being
                        neutral,  be  cut in  two at C, the portions A
    r~------]  i------\   and B retain their  peculiar states,  one posi-
    f\~            j\~   tive and the other negative.   But if the mag-
                  _°°   netic bar A, C, B  be broken across at  the
  j-" '"A____C   ::>$&:■  neutral portion C,  then each  half becomes
  7.iv:Ct^,_______—4r'Jl   a Pei'fect magnet of half the  strength of the
   ' ■: •         '"';W.'  entire; the  points  C   and C",  which had
   < fA- ..^ :-.;.c, :'<f:;, .:.;-.b;.:;.   been neutral, acquire magnetic power; and
   ^jp^-ii^- : Ipt^J:   if these portions be again broken, each frag-
                        ment  is  a perfect  magnet.   Magnetism be-
 longs, in this  way, to  the inmost particles  of  the body, and in  the
 general mass  each magnetic molecule is still  active  and independ-
 ent; a magnet resembles, therefore, an exceedingly bad conductor,
 which has been inductively excited by common electricity, and the
 particles  of which  retain for an indefinite length of time their state
  of polar excitation.
   In  order to  understand the real nature of  magnetic action, we
  must free ourselves, however, from all these analogies to machine
  electricity, no matter how well grounded they may appear to be
  when superficially examined.   The electricity of the  magnet is
  constantly circulating, and it possesses so  little  tension °that it 
Magnetic  qualities  of  galvanic  current.  145
[■11;. 2.
/<[m0
 never leaves the magnetic element, or molecule of iron or steel, in
 which it has its origin ;  in fact, every current of electricity possess-
 es magnetic properties, and simulates the action of a magnet situ-
 ated transversely to it.  Thus, if a needle be held transversely on a
 wire carrying an electric  current,  it becomes magnetic precisely as
 if it had been laid parallel to a magnet; and by bending the wire
 round so as to form a coil, the magnetism  which it confers being
 increased in proportion to the number of turns, may be rendered so
 intense as to  surpass that of the  most
  fowerful steel magnets that are made.
  n fig. 1 a small coil is  represented, by
 which magnetism  is conferred upon the
              bar of steel inside.  And
              in  fig. 2, a large horse-
              shoe of soft iron, by being covered by a helix of many
              hundred turns, may become able to  raise a weight of
              some  hundreds of  pounds by the magnetism it ac-
              quires.
                The  coil of wire carrying the  current may be
              shown, also, to possess magnetic properties by its
              attractive and repulsive action on a magnet.  A coil
              as in fig. 3, suspended so as       Fi„ 3
              to be able to move freely,  is
              attracted and repelled by the
              poles of a magnet precisely
              as if it also had  a magnetic
 pole at each end.  A flat coil,  as  in fig.  4,
 is also found to be magnetic, the poles be-
 ing indefinitely near each other at the cen-
 tre of the coil.  A beautiful form of the cx-
          Fig. 5.          periment   consists
           "^         in  a  long  wire,
                      which is made into a close coil, and connect-
                      ed at the ends with a pair  of little plates of
                      zinc and copper, as in fig. 5.  On placing this
                      system, buoyed by a piece  of cork, in a dish
        IplfiT"    m °^ adulated water,  it settles itself at right
              ---■■HI angles to the direction of the magnetic nee-
              WHjj die, and behaves in all respects like a mac
               "  HKf net situated in the centre of the coil, and
                    ™ perpendicular to its plane.
                        It  is now necessary to examine into the
                      relation which the direction of the current
bears to the poles of the magnets  which it forms, or which  mio-ht
represent  its action.   If A B be a  wire in which a current
is descending, as marked by the arrow, and a needle, N S,   f A
is placed transverse to it,  the right-hand  end of the needle
■].:
  ,;" .*:   becomes the north, and left-hand end of the nee- S   N
 ex   j_i  die the south pole ; if the direction of the current   'B
 S \* ^ Dc reversed, the  north pole is formed at the left.  In a
   E     circular current, the position of the  pole may be, conse-
quently, easily  seen;  the current A  B, which descends  in  front
                              T 
146  magnetic action of a  galvanic current.

of, and ascends behind the needle,  produces in the bar, N fe,  a
northern polarity to the right, and a southern to the lelt; the ac-
tion  of mao-netic currents  upon each other supplies the explana-
tion of thes°e phenomena.   If two wires carrying Galvanic currents
be brought near each other, there is attraction or repulsion  accord-
in cr to  the direction of the currents; if the two currents be  in the
same direction, the wires attract ; if in opposite directions, the wires
       w   repel each other.  The cause  is evident on  inspecting
       J   the  figure: the upper wires  being arrows which carry
     g-R- currents in the  same direction, they act on each  other,
   '    »   as should a pair of magnets  placed  transverse  to  their
           direction; the ends of the magnets which are juxtaposed
   I    \   have opposite polarities, and  attract; while in the lower
         s arrows,  where  the currents are in opposite directions,
   V    I   the  effect is the same as would result from the magnets
of which the contiguous poles are of the same name, and hence re-
pulsion.
  A wire carrying an electric current being thus a magnet, it acts
upon permanent magnets, attracting or  repelling, according to its
position, and generally, from the combination  of the two forces,
generating very complex  and  singular  motions.   These actions
have been so minutely and so extensively studied as to constitute
a distinct branch of this department, termed electro-magnetism ; but
being  unimportant in detail except in  physical relations, I shall
only notice the experiments by which  CErsted first  created this
branch of science, and which have ultimately led to one  of the best
treasures of electricity, the multiplying galvanometer.
   If a Galvanic current be passed over a magnet in the direction of
                               the arrow in  the  figure,  and the
                        "^"     needle  be movable on  its centre,
                            \i it endeavours to assume a position
                            i)\ such as will bring it parallel, and
                               with opposite poles presented to
                               the magnet which the wire repre-
                               sents ;  and hence, in the figure, the
                -«—'           motion would be to bring the south
pole above the plane of the  paper,  and  to depress the  north pole
below it, until  the needle had assumed  a position perpendicular  to
the  conducting wire.  If the current had been in the opposite di-
rection, the action would have  been reversed, and the  north pole
would have been turned up  from the paper; but if the  current be
reversed at the same time that it is brought under the needle, as in
the figure, it causes a deflection similar to that of the superior por-
tion, and hence the angle through which the needle moves is much
 increased.  If the needle  wTere affected only by the current passing
 over or under  it, its ultimate position would be, in all cases, at right
 angles to the current; but as the magnetic action of the  earth tends
 constantly to bring it back to its direction of north and south, the
 position which it  ultimately assumes is the  resultant  of the two
 forces.
   The deflection of the needle being thus an indication of the pas-
 eage of an electric current through the wire, it is desirable in prac
 
ASTATIC  COMBINATIONS  OF  MAGNETS.    147
tice to give the  power of the current as much effect as possible,
and at the same time to diminish as much as can be done the action
of the terrestrial magnetism.   The first is effected easily by increas-
ing to the desired degree the number of turns which the wire makes
round the needle ; for the total effect, as will easily be understood
from the description of the figure above, is proportional to the num-
ber of coils ; but the diminution of the effect of the earth upon the
needle requires some more care.   If the  needle be made but feebly
magnetic, the power of the  current  to turn it diminishes just as
much as the power  of the earth to prevent its turning, and there is
hence nothing gained ; but the object is effected by using a combi-
nation of two, three,  or four powerful needles,  so arranged that
with regard to the earth they are made to represent one very feeble
needle.   Thus, in the figure, the three  magnets N  and S,  being
suspended  with their opposite poles next one
another, act on each other so powerfully that.
Di
the remote and weaker opposing action of the   N-c
earth becomes almost  insensible.  A  current
I
C =
3N
=>S
>
=N
 assing in the direction of the arrows, C, E,   gc__
 ), will tend to depress the north poles of the
upper and lower, and the south pole of the middle needle below the
plane of the paper ; and when it passes under the middle needle,
its action upon it will be  the  same, since its direction is reversed.
The amount of deflection of such  a system  of needles will still be
regulated by residual terrestrial influence ; but as this may be ren-
dered as small as may be wished, the  delicacy of the apparatus may
be increased without  limit.  It is  not desirable that the system of
needles should be completely astatic, that is, indifferent to the earth,
for then the degree of  deflection  by  a given  current would be af-
fected by trivial and accidental causes; but  by leaving a small resi-
due of terrestrial magnetic effect,  the current  acts against this, and
thus produces a deflection subject to  an assignable law, by which
the strength of the  current may be determined.   Within a certain
limit, about 30', the angle of deflection is proportional to the quan-
tity of electricity flowing along the wire, but beyond that it follows
a more complicated law, which, as involving  mathematical relations,
I shall not admit here.   To obtain a greater degree of delicacy and
uniformity of action, the system of needles is in all good instruments
hung by a thread of glass or  of silk,  like the beam of Coulomb's
balance (page 113).  The deflecting force then acts against the force
of torsion, and the resistance to be overcome is reduced to its sim-
plest possible conditions.
  The galvanometer, such as,  with the thermo-pile, constitutes the
thermo-multiplier, is represented in section and  in perspective in
the following figures ;  the same letters apply to both.  A, B, C is the
frame around which the copper wire is coiled, the ends T of which
terminate in the metallic tubes  F, F\   This frame is fixed on a hor-
izontal plate D,  E, which can turn  in its own plane  around its  cen-
tre by means of a toothed wheel and  endless screw, which are put
in motion by the button G.  Q, M, N is the support of the astatic
system of two magnetic needles, suspended to a  thread of cocoon
silk V, L.  K, S is the glass cylinder, secured by brass rings P, S, 
148   CONSTRUCTION OF  THE  GALVANOMETER.
Y, Z, which covers the  apparatus, and rests on the base K, I.  A
graduated semicircle, accurately divided, is drawn upon the card,
and by means of the supporting screws, and the movement of the
frame A, B, C, the upper needle is brought  to be exactly parallel to
the coils, and to point  to  the  commencement of the scale, being
regulated in its height  by  means  of the screw X, with which the
silk thread is in connexion.
  Where the current to be measured by the galvanometer is deri-
ved  from a thermo-electric combination, it is necessary that the
wire should be much thicker than for a similar current from a hydro-
electric source,  as the low intensity of the fluid thrown into motion
by heat might cause false indications of its quantity, unless an am-
ple path were opened through the best conductors for it; the num-
ber of coils for a thermo-electric galvanometer should also, for the
same reason, be as few as possible.  It is,  therefore, not usual to
employ the same instrument  for these two  kinds of researches.
The position of the galvanometer  in employing the thermo-electric
pile in the researches on radiant heat, has been described, page 98,
and its use in measuring the  quantity of  electricity flowing from
galvanic sources, which has been already partly noticed, will be far-
ther described in a future place.
   The passage of an electric current in the  vicinity of any substance
capable of assuming magnetic properties is thus, by what has pass-
ed, shown to be sufficient  for their excitation, and conversely if a
magnet, whether permanent or temporarily produced, be brought
near a substance through which  an electric current may circulate,
a current is immediately formed,  the direction of which is always
the same as that of a pre-existing current,  which would have  con-
ferred on the magnet the properties which  it actually has.  In like
manner, one current may  generate another in a closed conductor
near it, precisely as one magnet  may produce  another, or that a
body statically excited may induce the electric  condition on the 
 EARTH'S  ROTATION A  SOURCE  OF  CURRENTS. 149


bodies in its neighbourhood; but  such  peculiar influences are too
removed from the proper domain of chemistry to justify any detail-
ed description of them.
  In  concluding this section of the  subject of electricity, it is, however, important
to prevent its being supposed that, by the omission of such considerations, they are
to he considered as of inferior interest in the phenomena of nature.  It is so much
the reverse, that perhaps one of the most active sources of the electricity which
we shall find to play a most important part in chemical combination, is derived from
the induction  of the magnetic influence of the earth itself: for the earth being ren-
dered magnetic by means of the thermo-electric currents which circulate  around
it spirally from the equator  to the poles, it is sufficient to bend a bit of copper wire
into  a ring, and whirl it round the  finger in the  plane of the magnetic equator, to
obtain a current through the wire.   A disk of copper revolving in this plane is a
source of electricity derived from the inductive influence of the earth, differing, in-
deed, amazingly from  the brilliant excitation  of  the thunder-cloud, but surpassing
it far in real power of effect, and in  the quantity of the electric fluid actually brought
into  play.   We arrive here, indeed, at the extreme modification of this active and
omnipresent force : we found it in the commencement, though existing in exceed-
ingly small quantity, preservable only by the very best insulating means, and mani-
festing its tendency to escape  by the attractions, the flashes, the  mechanical vio-
lence which characterize machine electricity: while, in the form of magnetism, or
of a  magneto-electric current, though present in  a quantity many millions of times
greater, it flows uniformly, and  almost  insensibly, along the perfect  conductors
through which alone it is competent to pass, and it requires particular care to suc-
ceed in demonstrating its heating, its luminous,  or its mechanical effects ;  but we
recognise in it, nevertheless, the untiring agent by which the inorganic  superstruc-
ture  of the habitable globe has been produced, by which the depositories of the most
important metals in  the  clefts of rocks have been  accumulated, and which being
thus the safeguard of navigation, the source of all metallurgic industry, becomes not
less  important to the civilization of  mankind at large, than it  is found, from its par-
amount influence on chemical  affinity, its power to separate those elements most
intimately joined, and to  effect the union  of those which appear most adverse to
mutual combination, as well as the  facility with which its principles may be applied
to the explanation of the laws of chemical phenomena, to be  available in the hands
of the philosopher for  the advancement of science.
  To the  chemist, therefore, the most useful property of electricity is the power
which it possesses of modifying, annulling, or superseding chemical affinity.  I have
hitherto avoided as much as possible involving any ideas of chemical decomposition
in the account of electricity just  given, restricting myself to narrate such circum-
stances as  might serve for the recognition of bodies by means of their electrical
properties,  independent of their chemical  constitution.   But the question whether
electrical influence and affinity are identical, or what are their exact relations,
and the discussion of the theory of  electro-chemical combination, still remain, and
will  be examined when, first, the nature of affinity and the distinction between it
and the action of cohesive force have been described, and the general system of nom
enclature by which chemical substances are designated has been briefly noticed
                             CHAPTER V.

                      OF  CHEMICAL  NOMENCLATURE.

   The general properties and laws of the physical agents, cohesion,
light,  heat, and electricity, having been now described so far as was
necessary, that we may avail ourselves of those properties in char-
acterizing the substances, elementary or compound, whose more pe-
culiarly chemical relations we shall now proceed to study, it  is ne- 
150        PRINCIPLES  OF  NOMENCLATURE.
cessarv to prefix to the description of the forces by which chemical
union is effected, and of the laws by which it is controlled  a short
statement of the principles upon which the names of the substances
to which there will be frequent occasion to  refer have been con-
structcd
  There' are at present known fifty-five substances which the chemist
has not been as yet able to separate into other elements.  These are
distinguished by the following names:
Oxygen,	0.	Potassium,	K.	Arsenic,	As.
Hydrogen,	H.	Sodium,	Na.	Antimony,	Sb.
Nitrogen,	N.	Lithium,	Li.	Tungsten,	W.
Carbon,	C.	Barium,	Ba.	Molybdenum,	Mo.
Boron,	B.	Strontium,	Sr.	Tantalum,	Ta.
Silicon,	Si.	Calcium,	Ca.	Chromium,	Cr.
Sulphur,	S.	Magnesium,	Mg.	Vanadium,	V.
Selenium,	Se.	Aluminum,	Al.	Uranium,	U.
Phosphorus,	P.	Glucinum,	G.	3old,	Au.
Chlorine,	CI.	Zirconium,	Zr.	Iridium,	Ir.
Iodine,	I.	Thorium,	Th.	Osmium,	Os.
Bromine,	Br.	Yttrium,	Y.	Platinum,	PI.
Fluorine,	F.	Cerium,	Ce.	Tin,	Sn.
Tellurium,	Te.	Lanthanum,	Ln.	Lead,	Pb.
Mercury,	Hg-	Manganese,	Mn.	Bismuth,	Bi.
Zinc,	Zn.	Iron,	Fe.	Silver,	Ag.
Cadmium,	Cd.	Copper,	Cu.	Palladium,	Pd.
Cobalt,	Co.	Titanium,	Ti.	Rhodium,	R.
Nickel,	Ni.				
  By the combination of these bodies among each other, the various
substances which exist in nature are produced.
  These simple bodies have been divided, from the earliest days of
accurate chemistry, into two,classes, the metallic and the non-me-
tallic elements.  The first thirteen in the list are non-metallic; the
remaining bodies are metallic.  It is found, however, that this di-
vision is only popularly correct; no  matter how wo may define a
metal, we cannot avoid breaking through connexions of the most in-
timate and important kind if  we endeavour to retain the class of
metals as one founded on really existing chemical principles.  Thus,
in density and lustre, arsenic and tellurium are indubitably metals;
and yet, if we class these bodies with copper or lead, we break through
all laws of chemical analogy,  for in their combinations they  assim
ilate themselves most perfectly,  one to sulphur,  and the other to
phosphorus.  In selenium, also, the metallic characters are so feebly
marked, that even did we not know that by its properties it must be
classed  w7ith sulphur, we could not place it as a metal without great
doubt.
   In describing the simple bodies, I shall retain  as  a division the
chemistry of the metals, for the classification, like all those which
have been long in extensive use,  has in some  respects much utility
and truth; but in cases where the study of certain bodies will be fa-
cilitated by departing from it, I shall not hesitate to do so.  In order
to avoid confusion subsequently, I shall here describe, as  succinctly
as possible, the nomenclature which has been adopted in  chemistry ;
for in a science where  the multiplicity of objects to be  noticed  is
so great, it is of the highest importance that the principles  upon 
 NOMENCLATURE  OF  LAVOISIER  AND  GUYTON. 151

which the names of these  objects are founded should be  clearly
understood.
  In all conditions of science, the nomenclature has been regulated
by the prevalent  theoretical ideas of the time, and it is probably vain
to look for a system of names which shall tell what the bodies really
are, and not pretend to tell more ; for that would suppose that we
knew what the bodies are, whereas,  in the most  perfect state of
science, we only know what we believe them to be.  Thus, at a time
when, by a mal-application to chemistry of the analogy of the human
body and its soul, all bodies were looked upon as  having a volatile
and a fixed, an active and an inert element, the names of spirit of
wine, spirit of hartshorn, and spirit of salt were invented; at a later
period, when the theory of phlogiston prevailed  in the minds of
chemists, the spirit  of salt became  dephlogisticated marine acid;
when the important functions of oxygen were pointed out by Lavoi-
sier, the name was in his  theory changed to oxymuriatic acid ; and,
finally, when the present view  was introduced by Davy, the name
hydrochloric acid became the most correct.  The cause of this is,
that in a good system of chemical nomenclature, we require two con-
ditions which it  is very difficult to successfully combine;  that the
name shall not only tell us that the substance is an independent sub-
stance, but that it shall give to us an idea of its most important chem-
ical character, its composition ; thus the name prussic acid is less
strictly scientific than that of hydrocyanic acid, which shows us that
its elements arc  hydrogen and  cyanogen ; and iron pyrites  gives a
less perfect picture of the body it describes than the words bisulphuret
of iron.  The necessity  for indicating by the chemical name of a
body its  chemical composition,  is thus what renders chemical nom-
enclature at once so  variable and so complex, but it is also that which
alone enables us to connect distinct ideas with our words.
   The benefit conferred upon chemistry by the nomenclature intro-
duced by Lavoisier and Guyton was  scarcely inferior in its impor-
tance to the accurate ideas of combination in which it had its orio-in.
The removal of  the  unconnected  and unfounded names, which had
been invented by the older chemists, and the invention of the idea
that every name  of a compound body should express its composition,
involved the increase of accuracy in the minds of those chemists by
whom science was subsequently  to  be prosecuted, which  may be
looked upon as the most fertile source of the  discoveries made up
to the present day.
   The names  most employed in  chemistry are acid, base, and salt.
The word acid signifying originally sour, was applied  to all bodies
which  tasted like vinegar.   The word base  signifies any substance
which, uniting with an acid, forms a compound, of which it is the
basis or foundation ;  and the compound formed by their union, beino1
generally similar to common salt in superficial characters, is termed
a salt.  Thus, oil of vitriol tasting, when mixed with water, sour, is
an acid;  soda is a base, and, when combined, they form the well-
known salt called after Glauber, who discovered it.  Such  are the
names of those classes of bodies, the  discovery of  which dates from
n remote period.
   Acting on the principle that,  in naming a simple substance, the 
 152  SIMPLE  BODIES AND PRIMARY  COMPOUNDS.

 name should be derived from its most characteristic property, La-
 voisier formed the word "oxygen" from  ofvc, acid, and ytvvao), I
 generate, to signify the important substance, the functions of which
 he was the first to show, and which he imagined to have the peculiar
 property of forming acids.  In like manner, he constructed the word
 "hydroo-en" from vdcop, water, and yevvau), to express its most im-
 portant property, of bein<r an  element of water.  This principle can,
 however, seldom be rigidly  acted on ;  for  example, oxygen is as
 much a water former as hydrogen ; and the name of oxygen itself is
 not without objection, as  the pre-eminence as acid former, which
 Lavoisier imagined it to possess, has been latterly overthrown.   In
 the case of simple bodies, names derived from quite arbitrary sources,
 as tellurium from tellus, the earth ; selenium from OTjXrjyn, the moon ;
 vanadium and thorium from  Vanadis  and Thor, deities of Scandi-
 navian mythology ; chlorine  from ^/Lwpoc, yellowish green (its col-
 our) ; and similarly iodine from  toeidnc (like a violet), have a great
 superiority over those which, by attempting to teach more when
 first invented,  have the disadvantage of teaching falsely at a future
 period.
  The simple  bodies, combining with each  other, form compound
 bodies of the first order, or binary compounds.  The names of those
 binary compounds which contain oxygen are of two kinds, according
 as the compound possesses acid  properties or not; if it  be an acid,
 the word acid  is added to that of the  other  body to which the ter-
 mination ic is joined.  Thus the acid  compound of sulphur and
 oxygen is sulphuric acid ; the acid compound of phosphorus and
 oxygen  is phosphoric acid.   It  frequently happens that the same
 body forms with oxygen two acids, in which case, that containing
 most oxygen retains the terminal ic,  while  that in which there is
 least oxygen ends in ous.   Thus there is sulphurous acid, and phos-
phorous  acid, consisting of sulphur united with less  oxygen than
 could form the sulphuric or the phosphoric acids.  Many bodies form,
 however,  with oxygen more than two  acids, and in  this case a
 new principle of  nomenclature  has  been introduced:  the words
 vno, hypo, and vitep, hyper, under and over, are prefixed to the de-
 grees terminating as before  stated.  Thus there is an acid of sul-
 phur containing less oxygen than the sulphurous acid, and it is call-
 ed hypo-sulphurous acid ; and also an acid containing more oxygen
 than the  sulphurous, but less than the  sulphuric acid : this might be
 called either hyper-sulphurous  or hypo-sulphuric acid ; the latter name
 has been universally  adopted.   Chlorine forms, with  oxygen, four
 acids, which are the  hypo-chlorous acid, chlorous acid, chloric acid,
 and hyper-chloric acid, or, as it is  often called, substituting the short-
 er Latin per for the Greek vnep, perchloric acid.
  In cases where the compound  formed with oxygen is not an acid
 it is termed an oxide of the substance with which the oxyoen is uni-
 ted.  Thus oxide of  lead, oxide of iron,  oxide  of copper, are re-
 spectively the compounds of  oxygen with lead, with iron, and with
 copper.   In many cases, where oxygen  unites with bodies in more
 than one proportion, one compound may be an acid, and the other
 not.  Thus manganese, uniting with oxygen,gives manganic acid and
 permanganic acid, but in a lower degree of oxidation it forms several 
VARIOUS  CLASSES  OF PRIMARY  COMPOUNDS.  153
oxides of manganese.  For as a substance uniting with oxygen may
form  many acids, so  may  it form many oxides also ; and  in  such
cases it becomes necessary to distinguish them from one another.
This is done  by the adoption of the Greek words 7rporoc, devrtpoc.,
rpiror (first, second, third), prefixed  to  the word  oxide.  Thus we
say protoxide of lead, deutoxide of lead, tritoxide of iron ;  the ox-
ide which contains most oxygen is often called the peroxide, and that
which contains least the suboxide, as peroxide of manganese, suboxide of
copper.  The  word sesqui (one and a  half) is also used for oxides in-
termediate between protoxides and deutoxides, but the nomenclature
then involves numerical proportions, which will  require to be de-
scribed herafter.
  .Some other simple non-metallic bodies, in combining with the met-
als, form compounds, of which the names are constructed on the same
plan as those of the metallic oxides.   Thus,
Chlorine forms Chlorides.
Iodine     "   Iodides.
Bromine forms Bromides.
Fluorine   "  Fluorides.
  The compounds of sulphur with the metals having been popularly
named before Lavoisier's time, and it being desirable to retain, as
much as possible, the names  already in common use,  a different
form  of termination is adopted for  that body and some others.
Thus,
Sulphur  gives Sulphurets.
Selenium   "   Seleniurets.
Tellurium  "   Tellurets.
Carbon     "   Carburets.
Nitrogen  gives Nitrurets.
Phosphorus   "  Phosphurets
Arsenic      "  Arseniurets.
   To distinguish between the different sulphurets or chlorides, &c,
 of the same metal, the Greek prefixes are adopted, as in the case of
 oxides.  We  have  thus proto chloride  and deuto-chloride  of manga-
 nese ;  also pcrchlorides and subchlorides.  The Latin bis  is  often
 substituted for the Greek deuto, as the bichloride of tin in place of
 the  deuto-chloriclc.   Among Continental  chemists,  names which
 should be  translated  chloruret in place of chloride, and sulphide in
 place of sulphuret, are frequently employed ; but as these are found-
 ed on certain theoretical ideas that have not yet been discussed, the
 propriety  of adopting such  additional  terminations cannot be con-
 sidered until we have proceeded farther.
   Where  two  non-metallic bodies are  united, it is a  question how
 the name of the compound should be formed.  Thus, in a compound
 of chlorine and phosphorus, should  it be  called chloride of phos-
 phorus or  phosphuret of chlorine \  This is decided by referring to
 the classification of the  simple bodies which will be hereafter given,
 and which  is founded on a view of all their chemical properties taken
 together.   Whichever  element stands highest in the scale gives
the characteristic name to the compound body.  Thus chlorine is
above phosphorus, and we say chloride of phosphorus.   Iodine is also
above phosphorus, and we say iodide of phosphorus ;  but iodine is
below chlorine, and we  hence call the compound which  they  form
chloride of iodine.
  The  combination of the metals with  each other, except in some
                               U 
 154     NAMES  OF  SECONDARY  COMPOUNDS.

 peculiar instances, are termed alloys.   Thus we say brass is an alloy
 of copper  and zinc ; fusible  metal is an alloy of bismuth, tin, and
 lead.  Where one metal is mercury, the alloy is  termed an amalgam
 of the other metal; thus, an amalgam of silver is an alloy of mercury
 and  silver ; an amalgam of tin is an alloy of mercury and tin.   Arse-
 nic and  tellurium  are  so  far removed from  the metals by their
 chemical characters, that their compounds with the proper metals
 have the peculiar termination in *uret.
  By the union of two primary  compounds there is formed a sec-
 ondary compound.  These secondary compounds are generally termed
 salts.  The word salt is, however, applied to numerous classes of
 primary compounds.  Thus, the metallic iodides, chlorides, bromides,
 and fluorides are recognised as salts.  It is now also a debated ques-
 tion  whether the bodies formed by the direct union of an acid and
 an oxide are  really primary or secondary compounds; but  I shall
 now describe  only the ordinary nomenclature of  those bodies, post-
 poning the discussion of their intimate constitution to another place.
 When°an acid and a metallic oxide, both primary compounds, com-
 bine to form a secondary compound or a salt, the specific name of
 the salt is that of the base, without any change ;  we thus say a salt
 of soda, a salt of oxide of copper ; the generic name is taken from the
 acid, the word acid being omitted, and the final ic being changed into
 ate, or the  final ous into ite.   There is  thus formed  from sulphuric
 acid and soda sulphate of soda. From  nitric acid and oxide of lead,
 nitrate of oxide of lead.   From sulphurous acid and potash, sulphite
 of potash.  From hypochlorous acid and lime, hypochlorite of lime.
 Where the salt contains an oxide of one of the common metals, it
 is usual to  suppress the words of oxide in its name, and thus  to say
 sulphate of copper  in place  of sulphate of oxide of copper; nitrate
 of lead in place of nitrate of oxide of lead.  The strict correctness
 of language is thus  sacrificed ; but if the idea of the  composition of
 the salt be held clearly in the mind, the abbreviation is not  injuri-
 ous ;  this mode of naming salts is so universal, that breaking in on
 it might be productive of more injury than allowing it to remain ; I
 shall therefore say,  for example, nitrate of lead, understanding, how-
 ever, that the  nitric acid is combined not with lead, but with  oxide
 of lead.
  It  frequently happens that a metal forming with oxygen two ox-
 ides,  will form with acids a class of salts  for each oxide. In this
 case the  words proto, deuto, sesqui, or per, by which the oxides are
 distinguished  from  each other, are prefixed to the generic name of
the salt.  We  thus  say  proto-sulphate  of iron, persulphate of iron ;
 indicating that there is  in one salt the  protoxide, and in the  other
the peroxide of iron.  We have sesqui-sulphate of manganese, and
 deuto-sulphate of platinum.   The relative quantity of acid and base
 being liable to variation, there are acid salts with an excess of acid,
 and basic salts with  an excess  of base.   In such case, the proportion
 of acid is marked by the Latin bi, ter, &c, as bisulphate of potash, and
 the proportion of base where  it is in excess by the Greek Sic, rptc,
 &c,  as di-sulphate  of zinc, tri-sulphate of mercury ;  or still better
 by the words bi-basic, tri-basic, &c, to indicate the quantity of base;
 there is thus tribasic-sulphate  of mercury, quadribasic-sulphate of
 copper, and so on. 
     TERNARY  AND  QUATERNARY  COMPOUNDS.  155

   There are many other kinds of secondary compounds than the salts
just noticed.  Thus water enters into numerous compounds, which
are called hydrates.  This water may act in very many different ca-
pacities, and its nomenclature must be varied accordingly,  as will
be seen under its  proper head; but where we wish to indicate that
a body contains water, without determining more nearly the specific
function of the water, we describe the body as being hydrated.
   Oxides  and chlorides combine together to form  secondary  com-
pounds, which are called oxychlorides, as the oxychlorides of mercury,
the oxychloride of lead.  Oxides and sulphurets combining form oxy
sulphurets, as oxysulphuret of antimony.  Chlorides and sulphurets
form by their union chloro-sulphurets, as chloro-sulphuret of mercury.
   When two chlorides combine, the compound is termed a double
chloride, or a chloride of the metals ;  as  the chloride of gold and sodi-
um, the chloride of copper and potassium.  In the same way there are
double  iodides and  double bromides.  But where two sulphurets unite,
the nomenclature has received an important  change.
   Berzelius has proved that,  in very numerous cases, where  a  body
forms  an  acid with oxygen, which acid uniting with a metallic oxide
forms  a salt, that body, uniting also with sulphur, gives a sulphur
acid, which, uniting with a  sulphuret of a basic  metal (a sulphur
base),  forms what he terms a sulphur salt.   Thus  double sulphurets
are salts,  consisting of a sulphur  acid united to a sulphur  base.
Hence, as arsenic combining with oxygen forms arsenious acid, so,
uniting with sulphur, it produces sulpho-arsenious acid, which,  uniting
with sulphuret of lead, forms sulpharsenite of lead, precisely as the
oxygen acid, uniting with  oxide of lead, produces what should be
called oxyarse?iite of lead.  The prefix  oxy is, however, not used;
the ordinary salts are supposed to contain the oxygen acid, and  it
is only where a salt does not contain an oxygen acid that an  addi-
tional  word is necessary to point out what sort of acid it does con-
tain.   Tellurium and selenium act like sulphur ; there are tellurium
acids and tellurium bases, selenium acids and selenium bases, and  hence,
in place of calling the compound of seleniuret of  antimony and se-
leniuret of sodium a double  seleniuret, it  is called the selenio-sti-
biate of sodium.
  An attempt was made to assimilate the nomenclature of the chlorine and  iodine
bodies to that of the oxygen and sulphur compounds ; thus, to call chloride of mer-
cury a chlorine acid, and chloride of sodium a chlorine  base, and the compound
which they form a chlorine salt, chlorohy drargyrate of sodium.  This idea, howev-
er, has not  been received into  science; for, indeed, now the direction of the ideas
most popular among chemists points precisely contrary, and in place of assimilating
the double chlorides to ordinary oxygen salts, there is  a general tendency to class
tht ordinary salts along with the simple chlorides.
   Ternary compounds are formed by the union  of two secondary com-
pounds.   Thus dry alum is a compound of sulphate of potash and sul-
phate of alumina.  Compounds  of this order seldom  exist in more
than one proportion.  Alum  combining with water to  produce the
crystallized alum,  generates a  quaternary compound; and even more
complicated stages may be attained ; but they are so rare, and of so
little scientific importance,  that they do not require notice here.
   In organic chemistry, the principles of nomenclature are  for the
most part identical with those now stated ; where deviations occur,
they will be noticed under their proper heads.   The progress of sci 
156         SYMBOLICAL  NOMENCLATURE.
ence has, however, introduced remarkable changes in the mode of
representing the constitution of bodies, particularly by means of the
symbolical nomenclature now universally adopted after Berzehus.
  In the list  of the simple bodies in  page 150, the  name of each
substance  is accompanied by its symbol, which  is generally the in-
itial letter of its Latin name ;  and in cases where the  name of more
than one body begins with the same letter, they are distinguished
by adding to the symbols of all the bodies but  one a second letter
in smaller  type, which may be the second letter of the word, or
whatever letter will best  serve to  characterize the name.
  If there be but one non-metallic substance in the group, it is gen-
erally selected to be denoted by the single letter, as C. and P. for
carbon and phosphorus, while the metals whose symbols have the
same letter are denoted by Ca., Co., Cd., Ce., and PL, Pb., Pd.  Where
there are more than one non-metallic body commencing with the
same letter, it is a  matter of indifference which is designated by
the one or by the two, but the single letter is generally attached to
the body  which is  of most  importance in  chemical phenomena.
Thus S. is  sulphur,  while Si. and Se. denote  silicon and selenium
respectively.
  The  symbols of compound bodies are constructed by grouping to-
gether the symbols of their constituents; thus Pb.O. represents a
compound  of oxygen and lead; C.H.N.O. a compound  of carbon,
hydrogen, nitrogen, and oxygen.  The algebraic sign of addition is
frequently used to connect symbols, as CI.+ 8., chloride of sulphur;
I +K., iodide of potassium.  But  I shall use that sign only where I
wish to express that the bodies so connected are united by an infe-
rior degree of affinity; thus Cl.Ca. is chloride  of calcium dry, but
when crystallized it becomes  Cl.Ca.-f-6H.O., in which the -f sign is
used to show that the water is united with the  Ca. CI. by a power
distinct from, and inferior to, that which retains Ca. and CI. in com-
bination.  Water thus combined is often represented by the symbol
Aq., for water  is capable  of acting in a variety of ways in combina-
tion, and, as will be shown when we come to speak of the chemical
relations of water, it requires to be expressed sometimes as H.O. and
sometimes  as Aq.
  But that  which requires special notice in speaking of symbolical
nomenclature  is, that it involves  essentially the idea of numerical
relations.   Thus the symbols Pb.  or Cu. do not  call up to the mind
of the chemist the simple ideas of lead or copper, but of a quantity
of lead and of a quantity of copper, in the proportion of 103-6 and
31-7, which is  termed an  equivalent of each.   Thus, also, the sym-
bol Pb.O. signifies not merely a compound of lead and oxygen, but
specially a compound of an  equivalent of lead and  an equivalent
of oxygen, in the proportion by weight of 103-6 of lead and  8-0 of
oxygen.  It is thus  that the symbol Pb.02, or Pb.-f 20., which rep-
resents also a compound  of lead with oxygen, shows to the chemist
that this second body contains to the  same 103-6 of lead twice as
much,  or 16-0 of oxygen, as  had existed  in the former.  Pb.O. is
therefore protoxide, and Pb.O, is the peroxide of lead..
   The details  of the application of those symbols involve thus the
numerical laws of constitution, which have yet to be described ; and 
NATURE  OF  CHEMICAL AFFINITY.
157
hence it is unnecessary to develop their arrangement farther at
present.  It was necessary to allude so far to them when speaking
of nomenclature, as I may have occasion to introduce some of them
in a general way in the  next chapter.
                        CHAPTER VI.

OF CHEMICAL AFFINITY, AND ITS RELATIONS TO HEAT, TO LIGHT, AND TO
                           COHESION.

  The peculiar power by which we suppose chemical phenomena to
be produced, is specially distinguished  from cohesion, and from all
other forces in nature, by exerting in the different kinds of element-
ary or compound substances various degrees of energy ; and by its
capability of acting upon certain bodies exclusively, and in prefer-
ence to acting upon others, which, so far as physical circumstances
go, appear equally exposed to its effects.  Thus, if to some liquid
muriatic  acid there be added a mixture of lime  and magnesia, the
lime will all dissolve  in the  acid before any trace of the magnesia
will be taken up.  If a slip of iron  be placed in a cup of nitric acid,
a large quantity of deep red fumes is immediately  expelled from
the acid, with an appearance of boiling or effervescence; and the
iron disappears, being taken up by the liquid in place of the  sub-
stances which had been expelled.  If a slip of copper be dipped in
the acid, the same effect is produced;  but if the  iron and copper be
left together in the acid, no action takes place upon the copper until
the iron shall have been totally dissolved.  The muriatic acid, there-
fore, presented equally to lime and magnesia,   combines with the
lime in preference, and the nitric acid takes up  copper, givino- off,
to make room for  it, a quantity of gaseous elements (nitrous  acid
fumes) it had previously contained ; but it will take iron in prefer-
ence to copper, if the two be  presented to it   at the same time.
Chemical affinity is therefore elective;  it chooses among a variety
of bodies which it  will act upon, and is  thus different from cohesion
or gravity, which will act upon all bodies equally exposed to their
influence at the same time.
  In the  example  of the metal and nitric acid,  there is involved a
second phenomenon, which, equally with elective affinity, is char-
acteristic of chemical force.   It is  decomposition.  The  copper  can-
not dissolve in the nitric acid without the expulsion of another  sub-
stance.  By a simpler example, the decomposition may be rendered
more evident.   Sulphuret of hydrogen consists  of sulphur and hy-
drogen ; if it be brought into contact with iodine, the iodine expels
the sulphur and takes the hydrogen ; the  sulphuret  of hydroo-en is
decomposed, and a new body, iodide of hydrogen, is  formed.  Here
the hydrogen chose between iodine and sulphur, and preferred the
former :  the greater affinity for the iodine caused the decomposition.
Hydrogen has, however, a still more decided tendency to combine 
158 PRINCIPLES  OF  ELECTIVE  DECOMPOSITION.

with chlorine; and if chlorine be brought into contact with iodide
of hydrogen, the iodine is in its turn expelled, and chloride of hy-
drogen formed.  Here is a series of decompositions depending on
the relative power of the affinities  of chlorine, iodine, and sulphur
for the one body,  hydrogen.  Thus, by the elective affinity of an
uncombined body,  choosing among a variety of other  bodies  all
equally uncombined, there is produced a new combination, contain-
ing that for which its affinity was strongest.   But when an uncom-
bined body is put in contact with two substances already united, it
tends to separate them, to  combine with one  and to  set  the other
free.
  If we could combine any one body, as  hydrogen, for example,
with every other of the simple substances, we might, by such ex-
periments as those described with the sulphuret of hydrogen, iodine,
and chlorine, obtain an idea of the exact order of intensity of the
affinity of each of them for  hydrogen, and could  easily  represent,
under a tabular form, such an idea.   This has accordingly been tried,
and was, indeed, the result of the first sound ideas of the nature of
chemical affinity which were obtained.   It was not done completely
in any case, for even at present our knowledge is not sufficient to
enable us  to form a series, including all the simple bodies.  It was
particularly in the chemistry of the salts  that the benefit of this
principle was found, and it  was to explain and predict  the result of
the decomposition of salts that tables of the elective affinity were
constructed.
  It has been stated that, if lime and magnesia be placed together
in contact with muriatic acid, the acid will dissolve all the lime be-
fore it acts upon the magnesia ; the affinity of lime for muriatic acid
is therefore greater than that of magnesia for the same  acid, and
hence, if to a solution of magnesia there be lime added, the mag-
nesia will be expelled and the lime will take its  place.   If to the
lime solution of soda be added, the  lime will separate, and soda may
be in turn expelled by potash.  On the other hand, there  are many
metallic oxides which enjoy a still more feeble affinity than magne-
sia ; thus, if to a  solution containing oxide of iron,  magnesia  be
added, the oxide of iron is thrown down and the magnesia taken in
its place.  In this manner may be arranged a series of compounds,
consisting of different bases, in union with the same acid ; and by
observing the order of decomposition by each other, a view of the
relative  affinities which they exercise  may be fovnied.  If, also, a
series of acids be  combined with the same base, a similar view of
their relative affinities may be drawn up.  Thus, when a solution
of potash  is exposed to the air, it absorbs carbonic acid, for which,
therefore, the potash has an affinity of a certain energy ;  on adding
acetic acid, the carbonic  acid is expelled, and acetate of potash
formed;  on adding nitric acid, the acetic acid is  expelled from it,
and nitrate of potash formed ; and from this, by means of sulphuric
acid, the nitric acid may be  recovered, the  potash remaining in the
state of sulphate.
   The results so described may be  exhibited as follows, by writing
in a column the names of the different acids, in the order of their
affinities for a certain base (soda), which is placed at top.   Similarly 
ORDER OF  ELECTIVE DECOMPOSITION.
159
in a column, at the top of which is placed the name of a given acid,
the  various  bases  in the order of their affinities may  be written.
Thus:
    Soda.
Sulphuric acid.
Nitric acid.
Muriatic acid.
Acetic acid.
Carbonic acid.
Muriatic Acid.
Potash.
Soda.
Lime.
Magnesia.
Oxide  of iron.
  For the simple bodies similar lists might be constructed : thus, in
the same way as the series of affinities for hydrogen already noticed,
a table of affinites of the different metals for oxygen may be  drawn
up from observation.  If to a solution of nitrate of silver, in which
the silver is combined with oxygen, a globule of mercury be placed,
it dissolves, and the silver  is set free.  By dipping into the solution
of nitrate of mercury a slip of copper, the mercury is thrown down,
and the  copper takes its  place.  From  the nitrate of copper the
metal may be thrown down by lead, and the lead again precipitated
by a plate of zinc.   The affinities of the simple bodies for each other
may be therefore  expressed, taking hydrogen and oxygen as illus
trations,  by the following columns:
Hi/drogcn.
Chlorine.
Iodine.
Sulphur.
 Oxygen.
Zinc.
Lead.
Copper.
Mercury.
Silver.
in which any one body in the list may expel all below it from com-
bination, and will itself be expelled by every body below which it
stands.
  Such  is simple elective affinity; but it often manifests itself in a
more complex form, as when it acts  among a greater number of
bodies than three; and by the mutual action of two compound bod-
ies, two new ones may be formed.  Thus,  when nitrate of lime  is
decomposed by potash, there is simple decomposition, and the lime
is set free ; but if, in place of pure potash, we employ carbonate of
potash, the result is the formation of  carbonate of lime ; for when
the potash leaves the carbonic  acid to go to  the nitric  ncid, and
the nitric acid leaves the lime to go  to the potash, the carbonic
acid and the lime, finding themselves in presence of one  another,
unite, and precipitate as carbonate of lime.   The nature of the de-
composition may be more clearly shown from the figure:
                ( Nitric acid.  Potash.
                ( Lime.       Carbonic acid.

The bodies existing before mixture being composed of those writ-
ten above one another, and those formed by decomposition consist-
ing of those which are in the same horizontal line.
  This action is  termed  double  decomposition.  In the example just
stated, the difference between  it and  simple decomposition  may 
160
DOUBLE DECOMPOSITION.
appear to have been accidental, the potash acting precisely as if it
had been free, and the lime and carbonic acid uniting only because
they came  into  contact, without  any other ties and hence  com-
bined together; but the peculiarity of double  decomposition ,s,
that  by  means  of it reactions may occur  which  could  not  have
been produced  by simple affinity, and which,  on the contrary, ap-
pear to have  been produced in opposition to  it.  Thus,  ammonia
cannot decompose nitrate of lime ; on the contrary, lime will take
nitric acid from ammonia; and yet,  if we mix a solution of nitrate
of  lime  and carbonate  of ammonia, they decompose each other,
and, by double elective affinity, there are formed nitrate of ammo-
nia 'and  carbonate of lime.   As  in  the  former diagram, the com-
pounds,  before  and after mixture, are found arranged in the hori-
zontal and vertical lines  of the diagram :
                 ( Nitric acid.  Ammonia.
                 ( Lime.       Carbonic acid.

In fact, in order to understand the cause of  such double decompo-
sition, we must  take  into account  not  merely  the  affinity of the
ammonia for the nitric acid, but that of the lime for the carbonic
acid.  Thus, if  the affinity of lime for nitric  acid  be represented
by  80, and that  of ammonia for nitric acid  be represented by 70,
the lime will be the stronger, and  can, when by itself, expel ammo-
nia ;  but if the carbonic  acid intervene, and  the  affinity of lime for
carbonic acid be 50, and of ammonia for the same acid be 30, then
decomposition must occur ;  for the forces preventing decomposi-
tion are the affinities of nitric acid for lime, and of carbonic acid
for ammonia; that is, 80 + 30 = 110; while those tending to cause
decomposition are the affinities of nitric acid for ammonia, and of
carbonic  acid for  lime,  =70-1-50 = 120; the  latter are the more
powerful, and the constituents of the two  salts consequently ex-
change places.   The former  affinities  are termed the quiescent, the
latter the divellent affinities; and  whenever  the  sum of the divel-
lent is greater than that  of the quiescent affinities, decomposition
must occur.
  Thus the simple affinity of hydrogen for sulphur is much greater than that of
mercury for sulphur, and the affinity of mercury for chlorine is much greater than
its affinity for sulphur; and yet, on bringing chloride of mercury into contact with
sulphuret of hydrogen, complete decomposition ensues, chloride of hydrogen and
sulphuret of mercury being produced.  In this case, the affinity of mercury for
chlorine being 20, and for sulphur being 10; the affinity of hydrogen being for sul-
phur 15, and for chlorine 30, the result may be shown as follows :
                              30

                   „n ( Chlorine.    Hydrogen. > , _
                   "" I Mercury.    Sulphur.  J 10

                               10
the  force producing decomposition being 30-f-10=40, and greater than those,
20+15=35, which tend to keep the elements as they were.
  Such are the results of chemical affinity manifesting itself in its
simple and in its  more  complex form; hence  there would appear
to be nothing more easy than to  determine  the  scale of affinities,
and to construct a series of tables in which all existing substances 
CAUSES  WHICH  INFLUENCE  AFFINITY.    161
should find their place, and all possible cases of chemical decompo
sition might be foretold with the same accuracy as the law of grav-
itation allows the disturbing effects of a new planet to be calculated ;
but, unfortunately for the simplicity of expression which the laws of
chemical affinity  would thus assume, new and  unexpected compli-
cations arise, and embarrass all our explanations ; thus, if wre take
muriatic  acid, and form a  table of the  affinities of bases for it,  we
shall find that it is as given in No. 1,  and constructing for sulphuric
acid an independent column, we shall find it to  be as in No. 2.
                                       No. 2—Sulphuric Acid.
                                        Barytes.
                                        Strontia.
                                        Potash.
                                        Soda.
                                        Lime.
No. 1.—Muriatic Acid.
 Oxide  of silver.
 Potash.
 Soda.
 Barytes.
 Strontia.
 Lime.
 Magnesia.
Magnesia.
Oxide of silver.
   Here the order is quite reversed, for oxide of silver, the strong-
 est base in one column, is  the weakest in the  other ; and barytes
 and strontia,  which manifest the  most intense affinity for sulphuric
 acid, are found but midway among the bases arranged in order of
 strength for muriatic acid.  Which column must be taken as repre-
 senting  the true  order of affinities'?  What principle is there by
 which these conflicting testimonies of experiments may be brought
 to correspond 1   The answer is, that neither table is  exclusively
 correct; that these lists, although showing the order of decomposi-
 tion, and thus exhibiting to the eye, most usefully, the result of a
 great number of experiments, must not be supposed as strictly show-
 ing to us the order of the affinities of these bodies, unless wre apply
 thereto a number of corrections, arising from those numerous and
 important  causes which influence and disturb the simple action of
 affinity, and frequently invert altogether the results, which, if unim-
 peded, it would have produced.
   For the chemical action of two bodies does not arise simply from
 their chemical affinities, but  results from the combined influences of
 heat, electricity, cohesion, and other physical agencies, which  fre-
 quently modify the chemical forces to a remarkable  extent.   By a
 change of temperature, an affinity originally weak may be made to
 preponderate  over  one previously much  stronger; by electrical
 conditions, the strongest and most direct chemical affinities may be
 overcome; according  as the cohesion of the  acting bodies may pre-
 vail, decompositions, simple or compound,  may be produced in op-
 posite ways;  and  thus a chemical result is  not the  simple conse-
 quence of affinity directly acting, but is  the resultant of a number
 of forces acting in different directions, and  with variable intensities,
 of which affinity is but one, although that one which, for our  ob-
ject, is the most important.
  It is indeed fortunate lor the intellectual progress of mankind that it is so ; for on
the variability of the intensity with which chemical affinity may be exerted depends
the existence of the infinite variety of organized and inorganic beings which people
and beautify this earth.  Had  mere affinity been omnipotent;  had those bodies
which attract each other most  powerfully been in all cases able to combine •  and
                               X 
 162    CAUSES WHICH  INFLUENCE  AFFINITY.

 had there been no means of dissolving their connexion when once formed, immedi-
 ately on the origin of our globe, those bodies which have the most powerful affinities
 would have satisfied them by entering into eternal union ;  those next in power would
 subsequently have satisfied their tendency to combine, and long-since all nature would
 have been arranged into some few chemical combinations, the breaking up of which
 could not be  accomplished by any existing force.  The complex changes of animal
 and vegetable digestion and respiration could not go on ; the working of the metals,
 the chemical arts of civilized life, could not have been invented ; and the planet which
 we inhabit would have revolved in space a barren and uninhabitable ball.
   The action of these modifying causes may be easily exhibited by one or two ex-
 amples.   It has been already described how a solution of muriate of lime is decom-
 posed by carbonate of ammonia ; carbonate of lime being precipitated, and muriate
 of ammonia remaining in  the liquor; but if, in place of  bringing these substances
 into contact in solution, they be brought to act on each other at a high temperature,
 the result is exactly the reverse.  If muriate of ammonia and carbonate of lime be
 heated together without water,  carbonate of ammonia is  found to be sublimed, and
 muriate of lime remains behind.  If watery vapour be brought into contact with me-
 tallic iron heated to bright redness, it is decomposed, one of its constituents, oxygen,
 combining with the iron, the other, hydrogen,  being set free ; here evidently the af-
 finity of iron  for oxygen is greater than that of hydrogen.  But if oxide of iron be
 heated to redness also, and hydrogen gas be passed over it, the oxygen is totally re-
 moved by the hydrogen in the state of water, and metallic iron is set free ; here the
 order of affinity is exactly  the reverse, and we shall soon discover the cause to
 which it must be attributed.
   The  philosopher who first declared that the order of decomposi-
 tion was not the order of affinity, and  pointed out the importance
 of attending to  the other forces that modify it, was led by his ob-
 servations  to assert that  the power to which we have attached so
 much importance,  elective affinity, had no real existence;  he said
 that chemical union differed from mechanical cohesion  only in beinor
 exerted between the particles of different substances, and that in all
 cases where  certain bodies combined in  preference to others, the
 source was to be found in  the accidental and external circumstances.
 On his  ideas, the force by which the particles  of a fragment of sul-
 phate of soda are united, differs from the force  by which the  sulphu-
 ric acid is  united to  the  soda only  in  the fact that the  cohesion
 unites particles of the same kind, while affinity unites particles of
 different kinds.  A salt dissolved in  water is thus held in  solution
 by chemical attraction.  Two pieces of lead which adhere together
 are retained by mechanical cohesion ; but if a piece of lead adhere
 to a piece of tin, or a  drop of water to a surface of glass or metal,
 the union should be attributed to chemical affinity.   It will be seen
 hereafter that a great  deal of this peculiarity of view arose from the
 principle of indefinite chemical combination,  which, although sup-
ported by the amazing talents of Berthollet, has been finally  and to-
tally given  up.   We do not now consider such phenomena as solu-
 tion to be produced by chemical affinity, for we require that a chem-
ical compound should  have parted with the properties of its constit-
uents, and acquired peculiar properties of  its own, in order to prove
its title to the name.
   But  it  is still by no means  easy to fix  upon the limits beyond
which the change of properties must pass.   A change of state of ag-
 gregation is one of the most common  evidences ofDchemical combi-
nation, as where muriatic acid and ammonia, both gases, become sol-
id ; oxygen and hydrogen, both gases, become liquid;  water and
bichloride of tin, both  liquid, become solid, and innumerable other 
AFFINITY AND COHESION.
163
cases.  The production of heat, and often light, is one of the most
universal attributes of chemical action ;  and hence for many ages
the explanation of the phenomena of combustion included all that
was of importance in the philosophy of  chemistry.  A change of
volume is also very frequent, though not.  so universal; and conse-
quent on this change of volume, a change, generally an increase,  of
the specific gravity of the body from the mean specific gravity of its
constituents ; thus, when oxygen and nitrogen unite to form nitrous
oxide, the volume of  the compound is but f of that of the mixed
constituents ; when nitrogen and hydrogen unite to form ammonia,
the resulting volume is but £ of that of the gases mixed before com-
bining ; if 100 volumes of alcohol  be mixed with 100  volumes of
water,  the  mixture will  occupy  but 196 volumes; and on mixing
similar quantities of water and oil of vitriol, the resulting volume is
but 185.   Change of colour  also frequently occurs; but in all these
cases, although such marked results indicate an intimacy of union
that can  scarcely be explained by mere cohesion, yet other physical
forces may  intervene, and in addition to the evidence  of chemical
action already stated, the most important and necessary still remains,
change of chemical properties.
   I have on several occasions  mentioned change of properties' as
characteristic of  chemical combination, but it may be  proper here
to enter  into a few detailed examples of its nature and its source
Chemical affinity is not  a single force, giving  to all bodies within
its influence the same properties, though it may be in  different de-
grees.  On the contrary, the power which confers upon bodies their
chemical properties is of two kinds, antagonistic to each other,'and
such that, by acting with equal energies, their effects are mutually
destroyed.  Gravity,  in acting  upon bodies, acts upon  all bodies in
the same manner; the molecular forces^.which  determine the hard-
ness, the ductility, the solid, or liquid condition of bodies, may make
one body more or less hard or ductile than  another, or they may
render one body solid and another gaseous; but it is not in the na-
ture of cohesive forces to render the hardness of one body opposite
to the hardness of another, so that together they shall produce soft-
ness.   Yet such is the nature of the sources of chemical activity;
thus sulphuric acid and soda are actuated by affinities for each oth-
er ; the same force which gives to them their tendency to combine,
gives to  one the properties  of an intense, acid, and to the other the
character of a powerful  alkali ; yet these forces are so peculiarly
related to each other, that,  when the bodies have combined, the
acid and  the alkaline properties disappear, and  there results a sub-
stance, formed by their union (Glauber's salt),  innocent, inactive,
with little tendency to combine, destitute of chemical  affinity for
other  bodies, yet containing in itself constituents which may be
again  set free, and exhibited writh all their active properties.
   The force of cheTnical affinity is therefore exerted only between
bodies posscssihg'Sippo'site qualities, and by their union  a substance
is  produced  possessing quaHtieys which are not  the mixed qualities
of its  components.  The forces which produce  cohesion and  solu-
tion are  found most active  where  the resemblance between the
bodies is most complete.  Thus metals adhere  most  powerfully to 
164
AFFINITY AND  COHESION.
 other metals,  and for their solution, mercury, a liquid  metal, can
 alone be used  ; salts dissolve in water always most easily when they
 show their resemblance to it by already containing water of crystal-
 lization in their mass; inflammable bodies, as sulphur and phospho-
 rus, do not dissolve in water, nor in acids, but in liquids, themselves
 inflammable, as ether, sulphuret of carbon, and the oils; camphor,
 the resins, the fatty matters, require also, for their solution, fluid
 menstrua of analogous,  oily, and spirituous natures.  It is the con-
 trary with chemical combination ; the more complete the  opposition
 of properties may be, the more intense is the affinity by virtue of
 which combination is effected: a  metal combines with  oxygen or
 chlorine : ether, or a metallic oxide, combines with the acids to form
 salts.  In all these cases the  opposition of properties is the cause
 of the chemical affinity, and the neutralization or change of proper-
 ties  is its effect.   Thus the gases, ammonia, and muriatic acid, a
 caustic  alkali, and an intense acid, form the  solid sal ammoniac, a
 neutral  salt, destitute of the active  properties of its constituents:
 thus carbon, hydrogen, and nitrogen, elements of our daily  food,
 combine to generate the most active poison that has been found,
 the prussic acid ;  and this prussic  acid, by farther combination with
 oxide of iron  and with  potash, may generate a yellow salt, which
 is perfectly without action on the  living body, and which, under the
 name of ferro-prussiate  of potash,  is of daily extensive employment
 in the arts.
  The elements which,  mixed together, constitute our atmospheric
air, combined  in one proportion, form a gas which, when breathed,
produces agreeable intoxication (nitrous oxide) ; in other propor-
tions, a  deep orange-coloured gas  (nitrous acid), which,  by intense
cold, may be obtained liquid; and in an intermediate form, a gas
 colourless and transparent (nitric  oxide), which, when mixed with
 air, produces,  by  combining with  its  oxygen, the nitrous acid.  In
 all these cases new properties are assumed, the characters of the
 constituent elements furnishing no means of predicting the proper-
 ties of the compound.
  This clear distinction between chemical affinity and cohesion was
 not perceived  by  Berthollet; and hence, misled by the supposed
 existence of compounds which connected together the extremes of
 chemical and  mechanical force, he advanced the principle that the
 differences observed between them arose solely from  external cir-
 cumstances.   This principle has been rejected; but the  discussion
 to which it was subjected showed the importance  of attending to
 the influence which external circumstances really do exercise, and
 which is frequently, in practice, more  powerful than the force of af-
 finity itself.  It is therefore necessary to study in detail the  influ-
 ence of the  external physical agents upon chemical affinity.
   1st.  Influence  of Cohesion.—A  diminution  of cohesive power
 among the particles of  one  body,  allows those of another to come
 into closer approximation to them, and favours the chemical action
 of the two bodies.  Thus the ancient chemists expressed the  influ-
 ence of cohesion  by the Latin proverb: Corpora non agunt nisi sint
 soluta;  bodies do not  act  unless they  be  dissolved.  And of all
 forms of matter, liquidity is that in which  chemical action is most
 rapid and most energetic. 
                INFLUENCE  OF  COHESION.           165

  There are many instances of bodies acting on each other, although
in the solid form.   Thus, when chlorate of potash and sulphur, or
chlorate of potash and sulphuret of antimony, are rubbed together,
the mixture explodes from the  rapid decomposition which ensues.
When fulminate of silver, or iodide of amidogen, is even  slightly
touched, detonation follows.  In these cases, the original arrange-
ment of particles must have been so instable,  that the imperfect ap-
proach produced by mechanical mixture, or the slight change of po-
sition arising from a sudden shock, was sufficient to cause a new
mode of combination.   But, if such cases as these be considered as
exceptions, we may look upon solid bodies in general as being with-
out chemical action on one another.
   In the gaseous form  of matter, chemical affinity appears to be
controlled and weakened by the mutual mechanical repulsion of the
gaseous particles.  Thus,  oxygen  and hydrogen, bodies whose af-
finities are so strong,  may remain  in contact as gases, for an indefi-
nite period.   Nitrogen and hydrogen have no apparent tendency to
unite when mixed.  Hydrogen, in  the form of a gas, is without ac-
tion on carbon, or arsenic, or phosphorus, although under other
 circumstances it  unites with them, forming characteristic bodies.
 In order to  obtain the full  chemical action of gaseous bodies, they
 must be brought into play at the moment  of their being  set free or
 formed ; in their nascent state, as it is termed.   It may well be, that,
 when water  is decomposed and hydrogen is  liberated, there  is a
 moment before the hydrogen actually assumes the permanently  elas-
 tic form ; and being then, perhaps,  liquid, and in a highly concentra-
  ted condition, its affinities are manifested with  extraordinary force.
  It is the  same with  other gases;  they act always with  their full
  power only in their nascent state.
    The  influence of cohesion in  determining  chemical action is,
  however, of much greater  importance in  another way,  as serving,
  upon the principles of Berthollet, to explain the anomalous discord-
  ance between those experiments upon which the tables of the affin-
  ities of bodies for each other had been constructed.   Thus it has
  been shown, that in a table of affinities of the bases, oxide of silver
  would appear to be the strongest base if we  used muriatic acid:
  barytes should be looked  upon as the most powerful if  sulphuric
  acid had been employed ;  while, if the relation  of the bases to nitric
  acid were taken as the standard, potash would be found to excel the
  others.  In such cases, the diversity is to be ascribed to the  influ-
  ence of cohesion; and in all cases of the mutual action of various
  bodies in solution, the result is found to  be the formation of such
  compounds as are least soluble.
    Let us imagine a quantity of sulphate of soda and nitrate of potash
  to  be dissolved in water.   Each acid is attracted at  the  same mo-
  ment by both bases, and each base by both acids, so  that there oc-
  curs a division  of each acid between  the two bases, and of each
  base between the two acids.  There are  thus in solution sulphate
  of soda and sulphate of potash, nitrate of soda and nitrate of potash ;
  and while the solution is dilute, all remain  so; but if the liquor be
  very much  concentrated,  the sulphate of potash, being a sparingly
  soluble salt, is deposited  in crystals, and a new distribution  takes 
166    ARRANGEMENT  OF ACIDS  AND  BASES.
the acids, and a new portion of sulphate of potash is formed, which,
by a new crystallization, may be separated.  In this way, according
as the evaporation is continued, new quantities of sulphate of potash
are consecutively formed, until there  remains m solution neither
potash nor sulphuric acid, but  only soda in combination with nitric
acid.   Here, then, supposing the  chemical affinities of  potash and
soda  of  sulphuric and of nitric acids, to be exactly equal, the de-
composition which actually occurs, and the manner  in which it real-
ly takes  place, are explained perfectly  by the  greater  cohesion of
the sulphate of potash, and its consequent  sparing solubility.
  In like manner, ordinary hard water contains soda, muriatic acid,
lime,  and sulphuric acid.  The soda is  certainly  the stronger base,
and the  sulphuric the stronger acid ; and  yet,  on evaporating such
water, the salt which first crystallizes  is sulphate  of lime; and on
continuing the evaporation,  all sulphuric acid  may be  removed in
combination with the lime.  But the acids and bases being divided
among one another in solution, there coexist sulphate of lime, sul-
phate of soda, muriate of lime, and muriate of soda.  But when the
liquor is concentrated, the sulphate of lime is first  deposited, and a
new quantity being formed, all its constituents  are eliminated in
combination, precisely as the  sulphate  of potash was separated in
the former case.
  In these instances the separation of the least soluble ingredients
took place by degrees, and, as it were, artificially ; but if any one
of the substances produced be perfectly insoluble, it is  at once and
in full quantity expelled.  Thus, when we  mix  together solutions of
nitrate of barytes and sulphate  of soda,  there is instant formation of
sulphate of barytes, and the solution contains only nitrate of  soda.
But even here, although the formation of the sulphate of barytes ap-
pears instantaneous to the senses, it yet may, in point of fact, be
just as gradual as in other cases.  Thus there may have been a mo-
ment after mixing the solutions when there were present, dissolved
together, nitrate  of barytes, nitrate of  soda, sulphate of soda, and
sulphate of barytes ; in the next moment the latter precipitates, and
the barytes in solution, still dividing itself between the two acids,
another quantity  is formed.  This then  precipitates, and thus, in a
space of time that  is too small to be detected, the  quantity of ba-
rytes in the solution is reduced to  the mere trace of sulphate which
the quantity of water can dissolve, and  which is too small  to be de-
tected by our ordinary tests.
  The nature of double decomposition depends thus on the relative
solubility of the compounds formed.   In whatever way the most in-
soluble bodies may be generated,  the decomposition occurs.   It is
thus that, on mixing solutions of carbonate of ammonia and of nitrate
of lime, there are formed carbonate of lime and nitrate of ammonia ;
not merely that the divellent affinities were more powerful than the
quiescent forces, but that the  insolubility  of the  carbonate of lime
produced its separation from the liquid, and hence the union of the
substances which compose it 
DISTRIBUTION NOT  INVARIABLE.        167
  The  inversion of affinity which is produced  by the influence of
cohesion is not limited to cases of double decomposition.  There
is no doubt but that acetic acid is a stronger acid than carbonic acid ;
and on adding acetic acid to a solution of carbonate of potash in
water, the carbonic acid is  expelled, and acetate of potash formed.
Yet, if a stream of carbonic  acid gas be passed into a solution of
acetate of potash in alcohol, the salt is decomposed, acetic acid be-
ing set free, and carbonate of potash formed.  The cause  of this is
the insolubility of the carbonate  of potash in alcohol; for, on the
first action of the  carbonic acid, the potash divides itself between
the two acids, and there is formed some carbonate, which is thrown
down ; then another quantity, which also separates, until ultimately
all is precipitated,  and thus one of the feeblest acids may overcome
the affinities of another which is  much stronger.
  By this principle of distribution of acids and bases, we  are thus
enabled to account for a variety  of facts, which appear totally op-
posed to affinity, if it were not subject  to such modifications; but,
although it is so convenient for explanation, it should not be ad-
mitted as a principle in science if there could  not be adduced evi-
dence of its actual and independent truth.  That it does occur in
many cases cannot well be doubted ; thus the solution of  sulphate
of  copper in water  is of a rich blue  colour, and that of muriate
(chloride) of  copper of an emerald green.  Now, on mixing mu-
riatic acid with a  solution of sulphate of copper, the blue solution
is immediately changed to green, showing that the weaker acid has
divided  the  oxide of copper with  the stronger, although, so far
from precipitation occurring, the new compound is the more  solu-
ble of the two.  Also, on mixing a solution of sulphate of iron with
sulpho-cyanic acid, the liquor becomes intensely blood-red colour-
ed, showing that a  quantity of  sulpho-cyanide  of iron  has  been
formed, although  the sulpho-cyanic acid is much weaker  than the
sulphuric, and no  precipitation occurs to favour its production.
   These, and many other  such examples which  might be brought
forward, show that  the opinion of Berthollet, that the acids and
bases, when mixed together in solution, arrange themselves so that
each base shall be divided among all the acids, and each acid among
all the bases, is in a  great many cases true, and that it is one of the
most fruitful sources of the decompositions which occur in our ex-
periments ; but it remains to be decided whether it  is universally
true,  and whether, if all acids and  bases act  thus equally on one
another, we  should  abandon the idea  of chemical  affinity being-
elective.
   The answer to this question has been long since received in sci-
ence.   The principle of Berthollet  does not hold always, for nu-
merous instances  may be produced where this partition of acids or
of  bases does  not take place.   Thus  boracic acid and  sulphuric
acid both redden  litmus, but the former colours it of a port-wine
colour, while the latter tinges it  of the red of  an onion-skin.  If a
quantify of borax  (borate of soda) be dissolved in water coloured
blue by litmus, and some sulphuric acid added thereto, the liquor
becomes coloured wine-red from free boracic  acid ;  but, although
the slightest  trace of sulphuric acid in  excess would show itself by 
   168  INFLUENCE OF ELASTICITY ON  AFFINITY.

   changing the red to that of the onion-skin, no  sign of it  is found
   until all the boracic acid has been expelled.   Here, therefore, there
   is no partition of the base between two acids ; all the sulphuric acid
   which is added unites with the soda, and all the boracic acid is ex
   pelled.   If a solution  of  carbonate  of soda be  coloured  blue  by
   litmus, and sulphuric acid added, it may also be shown, by the ab-
   sence of the peculiar red which free sulphuric acid gives, that there
   is no division of base between the two.   The carbonic acid is to-
   tally expelled, and the sulphuric acid combines exclusively with the
   soda.   If the solution be dilute, the carbonic acid remains dissolved
   in the  liquor;  if it be concentrated, it is evolved in  the  gaseous
   form ; that makes no difference.
    Affinities are not, therefore, as Berthollet considered, all the same
   in power.  The framers of the tables of  affinity were right as to
   the general principle, that different  bodies  have different degrees
   of affinity for each  other; but they  erred in supposing that they
   could construct a table for the absolute order of affinities.
    To  sum  up the details that  have been given of the  influence  of
   cohesion on the affinities of bodies acting on each other in solution,
   it may be said that,  1st, In almost all cases of precipitation, the na-
  ture of the  double decomposition is determined much more by the
  fact of one of the bodies formed being insoluble, than by the result-
  ant of the united affinities of the bodies  which are  engaged.  2d,
  That where there is no separation of an insoluble or of a sparingly
  soluble compound, the acids and bases, if they differ very  much in
  energy,  are exclusively united, the strongest acid with the strong-
  est  base, and the weakest  acid with the weakest base ; and if there
  be not base sufficient to neutralize all of the acids, a corresponding
  quantity  of the  weakest acid being  left out of combination alto-
  gether ; but, 3d, That if the  acids and bases be not very different
  in energy of affinity, they arrange themselves  in such a manner
  that each base shall be divided between all the acids, and each acid
  divided  between all the bases, in  proportions which depend upon
  the quantities of each acid and of each base that may be  present,
  and on its  affinitary force.  Thus, if there be two acids  and two
  bases present, there will  be four  salts ;  if three acids and three
  bases, nine  different  salts ; and  generally,  the number  of com-
  pounds in solution will be  equal to the whole number of acids mul-
  tiplied by the whole number of bases present.
    2d.  The Influence of Elasticity.—The  absence of cohesion, or, still
  more, the substitution for  cohesion of  its  antagonist  power  repul-
  sion, as  shown by the property of elasticity  in the form of gas or
  vapour, modifies chemical affinity in  a perfectly analogous manner
  to that which has  been already described ; for, precisely as  the
, formation of an insoluble  substance  in a liquid will  enable  lower
  degrees of  affinity to preponderate by removing the  body which is
  formed by its insolubility, so  will repulsion or elasticity determine
  the production of such substances as by their volatility  may  be
  driven off, even though the affinities of their elements may  be much
  feebler than  those  of other bodies.   In all  such cases the same
  principle of distribution, so fully described already,  may be suppo-
  sed to  hold: thus a solution of sulphate of magnesia is perfectly 
    INFLUENCE OF COHESION  AND  ELASTICITY.  169

 decomposed by ammonia, the magnesia being precipitated ;  but, on
 mixing sulphate of ammonia with dry magnesia, and applying heat,
 the ammonia  is expelled, and  the  sulphuric acid  remains, united
 exclusively with the  magnesia.  Supposing that there is little dif
 ference between the affinities of these two bases for sulphuric acid,
 the acid in the mixture  may be divided between the two ; in each
 case there is free magnesia and free ammonia, for the acid  is only
 able to saturate a part of each.  In the solution  the excess of mag-
 nesia is insoluble, and it is expelled ; in the dry'way the excess ot
 ammonia is gaseous, and it is driven off; and thus, with the same
 substances  and the same affinities, precisely opposite decomposi-
 tions are produced by the  influence  of cohesion and  elasticity.
 The decomposition of muriate of lime by carbonate  of ammonia
 in  solution has been  already noticed, where carbonate  of lime is
 formed in consequence of  its insolubility.   If the carbonate of
 lime and the muriate of ammonia so produced be dried and heated,
 the precisely reversed decomposition will take place ; there are at
 first, produced muriate and carbonate of lime, muriate and carbonate
 of ammonia ; and this latter, being volatile at the high temperature
 which is used, is driven off,  and new portions formed  until  the in-
 terchange of elements is complete.
  The boracic acid has been already noticed, as being one so  fee-
 ble in its affinities  that the law of the division  of acids and bases
 does not hold with it, but that sulphuric acid can deprive it of every
 particle of base.  This is quite  true as long as these acids are in the
 liquid form, but at a high  temperature the reaction  is reversed.
 If a mixture of sulphate of soda and boracic acid be heated to redness
 in a crucible, the sulphuric acid will be driven off in consequence of
 its volatility, while  the fixed boracic acid will remain combined with
 the whole quantity of base.   The white, inert, earthy substance,-sil-
 ica  (powdered flints), the  acid properties of which are so  feeble
 that it is only  from analogy that it is recognised by chemists to be
 an acid, may, at a high temperature, expel the most powerful acids
 from  their combinations ; thus the  commonest sort of  pottery is
 glazed by throwing over it, when at a bright red heat, handfuls of
 common salt; this is instantly decomposed ; the silica of the earthy
 material of the  vessels combines with the soda of the common salt,
 and the muriatic acid is driven  off in white clouds of elastic vapour.
 Here the acid, which is the feeblest when dissolved in water, may
 expel the strongest  when the temperature is raised; and admitting
 that in the commencement a  partition of the base between the  two
 took place, even to a very small extent, the final and complete ex-
 pulsion of the more volatile must result.
  From the  great variety of compounds into which water enters, it
 is easily expelled,  not that it is inferior in affinity to most other
 bodies, but from its greater volatility.   We shall hereafter see reason
for  looking upon water as being a base of considerable force,  and
 entering into combination in  forms which should possess consider-
able stability ;  but when a compound of water is subjected to heat,
the  elasticity of the water diminishes its affinity so far that it may
easily be expelled.
  The  elasticity which certain elements possess  when free, may be
                              Y 
 170  INFLUENCE  OF VARIOUS MODIFYING  CAUSES.

 a cause why the compounds which they form are easily decomposed
 by heat, if their actual affinity to one another be not considerable.
 Thus the nitrate of barytes, which contains nitrogen and oxygen  in
 combination with barytes, gives, when heated, a mixture of nitrogen
 and oxygen gases : nitrate of lead gives, when heated, pure oxygen
 and nitrous acid fumes.  Chlorate of potash, by a high temperature,
 abandons all its oxygen gas; and the  remaining elements, having a
 powerful affinity for each other, resist the increase of heat, and re-
 main as  chloride of potassium.
   When the decomposition of a body by heat is thus  determined
 by the elasticity of one of its constituents, it is necessary, for the
 success of the process, that this constituent should be allowed freely
 to escape.  If it be forced to remain enveloping the residual sub-
 stance, the decomposition ceases.  Thus, by heating carbonate of
 lime to redness, it is resolved into lime and carbonic acid; but if the
 carbonic acid be not removed, the decomposition would immediately
 cease, and the carbonate of lime might be melted without being de-
 composed.  The removal of the carbonic acid is accomplished, in
 burning lime on the large scale, by the limestone being  heated in  a
 kiln, through which there is a continuous draught, by which the car-
 bonic acid is carried off  according as it is formed.  The necessity
 for the removal of the carbonic acid may be shown by placing bits
 of white  marble in a porcelain tube, heated to redness in a furnace,
 connected with a pneumatic trough, and fitted to a retort at the other
 end, by which steam may be passed into the tube ; at first scarcely
 any carbonic acid is set free ; but, by keeping up a supply of steam,
 the gas is rapidly produced, and the lime becomes very soon com-
 pletely caustic.
  It is in this way, also, that we may explain the contrary order of
 decomposition that may be produced by oxygen, hydrogen, and iron.
 If metallic iron be in the tube, and the latter be kept full of steam,
 every particle of hydrogen which is formed is carried off; and there
 being then a space provided into which the hydrogen can easily
 spread itself, the steam will be decomposed, and the iron converted
 into oxide.  If, on the contrary, the tube contain oxide of iron, and
 be kept  full by a current of hydrogen  gas, there is presented to
 every molecule of steam produced room for  its escape ; and the
 formation of steam  being thus  favoured  by its elasticity being al-
 lowed full play, the  reduction of the metal is  completed.
  Independent of its  influence  on cohesion,  a change  of tempera-
ture is capable of modifying the affinities of bodies in a remarkable
 degree.   Thus charcoal is not capable of being melted or vaporized,
and yet,  although at  ordinary temperatures quite inert,  few bodies
can resist its deoxidizing action  at a red  heat.  Bodies which take
fire when heated do so in consequence of their affinity for oxygen
being augmented by the increase of temperature.   The action of the
electric spark in producing the explosion of gaseous mixtures, de-
pends on its heating very much the few particles of gas which lie
immediately in its path, and the combustion being communicated
by them to the general mass.  The affinities of bodies for each other
appear to be thus exalted by the agency of heat in many cases, but
the exaltation does not appear to be the same for all.  Heat appears 
BERTHOLLET's  THEORY OF  AFFINITY.    171
often to diminish the affinity of bodies; thus the explosion  of de-
tonating compounds was so explained; but this appears to arise
from the heat really exalting the affinity of the more powerful con-
stituents, so that new and more permanent bodies may be formed:
thus fulminating silver explodes, not that its elements may separate,
but that bodies of a more permanent constitution may be formed
The iodide and chloride  of azote were looked upon  as being exam-
ples of mere separation of elements on the application of heat;  but
Marchand and 1 have found that these bodies contain hydrogen,  and
that they are decomposed in consequence of the formation of hy-
drochloric or hydriodic acid.   To produce many bodies of instable
nature, it is necessary to  avoid the use of heat; not that heat dimin-
ishes the affinities  of  their elements  in general, but  that the heat
enables those elements to satisfy their affinities better, by combining
in a more stable form.
   It has been mentioned that Berthollet  considered affinity as be-
ing  not elective, but that the combination of one body to another
was determined by the circumstances under which they were placed;
and that, in cases where many bodies of equal solubilities existed
together, they were divided among one another in proportion to
their masses ; but he in this case introduces a term which has caused
great difficulty in the discussion of the doctrines which he advanced.
He says that the bodies mixed together  combine, not only in pro-
portion to their masses, but of their affinities ;  and hence might ap-
pear to admit that bodies had different degrees of affinity, and that
this might, therefore,  be elective ;  but, if I conceive his opinions
rightly, the  affinity of which he  spoke was not the force to which
we assign the power of choice of one body over another, but he  car-
ried on the analogy to cohesion, and considered that the affinity of
one body, A, to another,  B, might be greater than to a third, C, not
so as to make A unite with B in preference to C, but that,  when it
had been united with B,  it would hold it  more firmly than it could
retain C.  This is  like what  is  found with  cohesion ;  if several
bodies be placed beside each other, they show no power of elective
cohesion ; but if they be brought into actual close contact, the degree
of cohesion may be different for  each. It is  in  this way that Ber-
thollet recognises a difference  of  affinity, and hence the obscurity
that is often ascribed to his statement of his views,  from the sense
which he attached to the word  affinity being mistaken.
  We owe to this philosopher an attempt at measuring this power of affinity,
which, though incorrect, yet, as being one of the first steps made towards numeri-
cal laws in chemistry, deserves notice.  He looked upon the neutralizing power of
a body as being the measure of its affinity for another, and considered that the de-
viations from this rule arose from the  influence of cohesion or  of elasticity: thus
the same quantity of potash is saturated by
    Sulphuric acid  ...  40 parts.  I   Muriatic acid .  .  .  365 parts.
    Nitric acid  ....  54   "       Acetic acic   ...  51    "
    Carbonic acid  ...  22   "    ]   Oxalic acid   ...  36   "
Hence, if mere affinity was allowed to act, carbonic acid should be the strongest,
and nitric acid the weakest in the list; in like  manner, the same quantity of sul-
phuric acid neutralizes
Potash.....48 parts.
Soda......32   "
Ammonia.....17   "
Lime .......28 parts.
Barytes......76   "
Magnesia.....18   " 
172     INFLUENCE  OF  LIGHT ON  AFFINITY.

and ammonia and magnesia should be the strongest of all bases, were it not for
the insolubility of the one and the volatility of the other body.
  These numbers, which are now known as expressing the quantities of substan-
ces that are equivalent to each other in combination, are fully recognised as totally
independent of the force of affinity exercised by each body. As yet we have no
other measure of affinity than the order of decomposition, controlled by the  esti-
mate of the influence  which  cohesion and elasticity may exercise.  From the
electrical relations of bodies, attempts have been made  to estimate the relative
affinities of chemical substances, the results  of which will be described in their
proper place.
   Of the  Influence of Light on Chemical Jljfinity.—Although attention
has latterly been very much directed to the influence of light on
chemical affinity, from the accidental discovery of some very re-
markable circumstances connected Avith it, yet  there have not been
discovered as yet any general principles to which those results can be
reduced; and the greater number of the investigations that have been
made are occupied by experiments of detail, which, from their want
of connexion and their multiplicity, cannot be successfully contem-
plated from any general point of view at the present moment.  So
far, however,  as  positive facts have been discovered, and as even
plausible explanations of those facts have been suggested, I shall en-
deavour  to represent, briefly, the actual condition of our knowledge
of this department.
   In many cases, bodies which in obscurity remain totally without
action on one another, are brought into combination by exposure to
light, and the rapidity of their reaction is proportional to the brilliancy
of the light.   Thus chlorine and hydrogen mixed remain unaltered
for any period in the dark; if exposed to the diffuse daylight, they
silently combine, but explode suddenly if a direct  ray of sunshine
fall upon the mixture.  Chlorine dissolved in water, if kept in  the
dark, remains a long time unaltered, but if exposed to sunshine, is
rapidly converted into chloride of hydrogen, water being decompo-
sed, and oxygen eliminated in a gaseous form.   Chlorine unites with
carbonic oxide only under the influence of light, whence the name
Phosgene, a light-formed gas, was given to the compound by its  dis-
coverer,  Dr. Davy.   Chlorine and  sulphurous acid unite also only
when exposed to brilliant sunshine ;  so much so, that in Dublin but
few days in summer  are found bright enough to form it.  The de-
composing action of chlorine,  iodine, and bromine upon organic
bodies, which consists  in the separation of hydrogen, and the as-
sumption generally of a corresponding quantity of chlorine, &c, in
its place, is regulated also in a remarkable degree by the brilliancy
of the light under which this operation is carried on.  Thus, even
in summer, in Dublin, I  never could deprive acetone of more than
one third of its hydrogen, forming  from C3 H3 O., the bodyC3H2Cl.
0.; but  in Paris, in summer, the chlorine removed another equiva-
lent of hydrogen, and Dumas and I  succeeded in obtaining the body
C3 H. Cl2 O.  In like  manner, in bright sunshine, the°action  of
chlorine  on pyroxylic spirit is so violent, that unless the vessel be
carefully shaded, the decomposition proceeds by a series of explo-
sions, while I  have  found it exceedingly difficult in  gloomy weather
to produce any action whatsoever.   Instances of this kind might be
very much multiplied, but those described are sufficient to point out
the general manner in which light  is found to act. 
PHOTOGRAPHIC  DRAWING.
173
  The action  of li^ht appears occasionally  limited to the simple
separation of bodies previously combined.  Thus colourless nitric
acid, when exposed to sunshine, evolves oxygen gas, and becomes
coloured yellow from  nitrous acid which remains.  The fading of
Prussian-blue patterns on cotton, which Chevreul found to  depend
on the escape of cyanogen,  and the conversion  of the blue into a
white compound, containing less cyanogen, is also an example of this
principle.
  Setting aside, for the  present, the influence of light on the pro-
duction of colouring matters in organic bodies, which will be de-
scribed as a portion of the chemical history of the individual sub-
stances, I shall now only  advert to the action of light upon the com-
pounds of the easily-reducible metals, particularly silver, by the study
of which such remarkable results have latterly been obtained.
  Scanlan first showed that,  when nitrate  of  silver blackens under
the influence  of light, its decomposition  is  produced by organic
matter, as by contact with paper, or by the organic substance, which
even distilled  water contains in small quantity.  Chloride of silver
also  is affected by light only when  in contact with organic matter or
with water, and in the latter case, also, most probably from acting on
the organic matter  which the water  held in solution.   When oil of
vitriol is poured over  chloride of silver, this is not altered by the
light, the sulphuric acid  combining with the water, and probably de-
stroying the organic matter therein dissolved.   I apprehend that in
most, if not all cases of the decomposition of a metallic salt and the
reduction of the metal under the influence of light, a substance con-
taining hydrogen, exclusive of the water of solution, must come into
play.
  The decomposition  of the  salts of silver in contact with paper
under  the influence of light, has become of interest to the arts as a
process of obtaining accurate outlines, and is called photography, or
photographic drawing.   If a sheet of paper be washed with a very di-
lute  solution of chloride, iodide, or,  better, bromide  of  potassium,
and then with  a solution  of nitrate of silver, there is  formed in the
substance of the paper chloride iodide, or bromide of silver, which,
being in  contact with abundance of organic matter, is blackened by
a very short exposure  even to moderate light.  If an opaque body
be laid between  a sheet of such paper and the light, the portions to
which  the light arrives become dark, while that under the object re-
mains white, and thus the most delicate and complicated outlines of
foliage or fibres  may, by  a few minutes' exposure to the  solar rays,
be fixed upon the paper with  a degree of accuracy inimitable by the
hand.  To render such a drawing  permanent, it is necessary to re-
move the silver compound under the pattern ; for if it  remained, the
blackness would gradually become uniform over the entire surface,
and the picture would be effaced.  This is effected by washing the
paper, after the image has been completely formed, by a solution of
some substance capable of dissolving out all of the undecomposed
salt of silver ; for this purpose, ammonia, hypo-sulphite of soda, and
strong solution of common salt are those generally employed.
  The  most remarkable features connected  with the chemical agen-
cies of light result from the recent experiments of Herschel.   He 
174  COLOURING EFFECTS OF THE CHEMICAL RAYS.

has shown, as was slightly noticed when describing the general char-
acters of light, that the chemical effects are not regulated by, nor
limited to the luminous spectrum, but by totally distinct rays, which,
according to the substance employed to show their decomposing ac-
tion, may extend far beyond  the visible limits on either side, or may
stop short in the middle of the coloured space ; and that the greatest
effect, which generally occurs at the violet extremity of the spectrum,
may be produced  at other and widely-distant points.
  A singular, and at present unaccountable,  consequence of the ac-
tion of the  prismatic spectrum on paper impregnated with chloride
of silver is, that the spaces on which the coloured rays fall become
coloured, acquiring a tint corresponding to that of the light incident
upon them, so that the spectrum fixes its own image on the paper.
Thus  the colours  impressed were in one experiment:
Spectrum Colours.	Colours formed on the Paper.
Extreme red.	None.
Mean red.	None.
Orange.	Faint brick red.
Orange yellow.	Brick red, pretty strong.
Yellow.	Red, passing into green.
Yellow green.	Dull bottle green.
Green.	Do., passing into bluish.
Blue green.	Very sombre blue.
Blue.	Black, passing into metallic yellow.
Violet.	Do. Do.
Beyond the violet.	Violet, or purplish black.
  It is in the lavender-coloured space that the chemical effects are
generally most intense ; when the light of it had been  concentrated
by a lens, and received  on a piece of prepared paper, the blacken-
ing was instantaneous, precisely as if a red-hot body had been ap-
plied behind, or  a smoky flame directed on the paper over all the
space illuminated, and accurately marking its outline.
  In the table of impressed colours just given, the red rays appear
to have produced no effect; but they are by no means destitute of
action.  When a quantity of diffused light is allowed to fall  upon
the paper,  in addition to the more  brilliant spectral colours, the
chemical image  is found to acquire  a pure white prolongation be-
yond the red space, in  which the darkening action of the diffuse
light appears to have been suspended.  The  opposite extremities of
the spectrum appear, therefore, to have  different powers, the  dark-
ening quality of  white light being due to the difference between the
two in favour of  the violet end ; and it is probable that by a balance
of action, a sensitive paper might be exposed to the action of united
beams of brilliant violet  and red light, and remain perfectly unalter-
ed in its colour.   Herschel did not, however, succeed so far :  paper
blackened by violet light has that blackness  removed by the action
of red light upon it; but it was found impossible to catch the  point
where the paper  should be white ; for, according as the black of the
violet  end  passed off, the red impression was substituted for it.
When, however, the different coloured  rays were made to fall si-
multaneously on the paper, the neutralizing power  of the opposite
ends of the spectrum was beautifully shown.  The blackening pow-
er of the more refrangible rays was suspended over  all the  space 
    DAGUERRE's  PROCESS  OF  TAKING  IMAGES.   17-5

upon which the less  refrangible rays fell, and the  shades of green
and  sombre blue, which the latter would have impressed  upon  a
white  paper, were  produced on that portion which, but  for their
action, would have been merely blackened.
  The  paper with  which  those results were obtained derived its
sensibility to light from chloride of silver; but the action of other
salts of silver gives  such anomalous  and variable effects, that no
general principle whatsoever  can be  deduced from them ;  thus,
with bromide of silver, the blackening  proceeds uniformly over the
whole of the visible spectrum, and the whitening effect is produced
beyond it to a considerable distance.   The subject has been shown
by Herschel to be one of considerable importance and great extent;
and  from the popular interest it excites, some clew to a more  gen-
eral knowledge of its principles will probably be soon obtained.
  The  process lately discovered by Daguerre, of fixing the  images
of external objects upon a prepared metallic plate, is one which also
deserves attention, as being founded upon the chemical agencies of
light, although hitherto there has been but little success in the at-
tempts made to assign a theory of it.   It is not complicated in de-
tail.  A plate of silvered copper is cleaned  with dilute  nitric acid,
so that the surface of silver may be absolutely pure, and is then ex-
posed to the vapour of iodine until a gold-coloured pellicle of iodine
of excessive tenuity is deposited upon it.   In this state it  is  very
sensible to light.  The  plate so prepared is placed in a camera-ob-
scura, and the image of the object required is allowed to remain on
it for a space of time, which varies with the brightness of the light.
When  it has been  sufficiently exposed, it is removed, and  submit-
ted  to the action of the vapour of mercury, by which the picture is
rendered visible.  As there still remains, however, a general sensi-
bility to the farther influence of light, this is removed by dissolving
away all the iodine  and iodide  of silver by a solution of hyposul-
phite of soda.  The shadows remain then marked by smooth amal-
gamated surfaces, and the lights, by the corresponding portions be-
ing  of a dull  gray colour, possessing only a power of diffuse reflec-
tion.
  The explanation of this  process, which, from my own observations, I am disposed
to suggest, is, that the iodine combines with the silver, and forms iodide of Silver,
which is spread in an amorphous state, forming an excessively thin layer, like var-
nish,  over the surface of the plate. Under the influence of the light, I consider that this
crystallizes as melted sugar does, but so minutely as to be invisible to the eye, and
the closeness and completeness of the crystalline structure being proportional to the
duration and intensity of tin1 light to which it had been exposed. When,  then, the
vapour of mercury attacks the plate, the  iodide of silver in both conditions is de-
composed, and the iodine being replaced by mercury, an amalgam of silver is form-
ed, uniform in surface, and perfectly metallic in its lustre, over the shaded portions;
but the crystalline iodide, in being decomposed, gives a crystalline amalgam, which,
from  the minuteness of its particles, presents only a grayish tint, and, being mixed
with  interspersed points of bright, smooth amalgam where the light had been less
powerful, shades off proportionally all the intermediate effects.
  The application of the mercurial fumes cannot be pushed far enough to decom-
pose all the iodide of silver, for it would injure the picture by depositing itself irreg-
ularly and in excess.  It is therefore necessary,  as soon as enough has been acted
on by the mercury to bring out the picture in a  distinct manner, to remove the re-
mainder by the washing which has been described.
  The influence of colour  on the production of  pictures by  Da-
guerre's process is  very marked ;  the images of green objects are
scarcely at  all defined, so that the method is scarcely applicable to 
 175      PROCESS  FOR  TAKING  PORTRAITS.

 taking landscapes.  Red and orange are also very feeble in their ef-
 fect ; but blue, even so intense as to be not at all bright, is more
 powerful than a brilliant white light.  In order, therefore, to produce
 good effects, objects should be selected either white, or of colours
 from which red and orange should be absent.   The fixation of col-
 ours in a manner similar to that discovered by Herschel, and already
 noticed, has been remarked  in Daguerre's process, although so ir-
 regularly that no advantage has as yet been taken of it for technical
 uses; but I have myself seen, on more than one occasion, where a
 deep blue  sky was interspersed by patches  of bright  white clouds,
 a perfect picture of the sky in its natural colours to be formed upon
 the plate.  Time-worn stains, and marks upon the surface of stone
 buildings, are also occasionally represented in their natural colours.
 In the majority of cases, however, where colours are produced upon
,the plate, they do  not correspond in position or tint to those  of the
 natural objects whose image  had  been obtained.
   [Since the  preceding paragraphs  were written by Dr. Kane, nu-
 merous improvements have  been made  in  this beautiful chemical
 art in America  and elsewhere : the theory of the process is also
 much better understood.  The most important of these improve-
 ments is the application of Daguerre's  process to taking portraits
 from the  life.   This is due  to Dr. Draper,  who succeeded with it
 soon after the French process was known in this country.  At first
 the direct or reflected rays of the sun were required; but modes of
 preparation, giving the plate more sensitiveness, have been since dis-
 covered, so that the ordinary diffused light of day  is now sufficient.
  The best process for  obtaining portraits is as follows: The plate,
 having been carefully cleaned, is iodized to a pale lemon colour ; it
 is then exposed to the  vapour of  bromine for  a sufficient length of
 time to bring  it  to a golden yellow.  It is a great advantage to keep
 it in total  darkness for three or  four hours before using it.  The
 person whose portrait is to be taken, having been seated in a suita-
 ble chair, with a support to keep the head perfectly steady, before a
 window, so that the light shall illuminate all those portions seen in
 the camera with proper strength, the plate is  to be exposed to the
 focal image for a time, which may be determined by previous trials.
  Much of the beauty  of the picture depends on the object glass of
 the  camera; very good  proofs may be had by  an arrangement of
 uncompensated  convex lenses four inches  in diameter and eight
 inches in focus; but the most finished  pictures are obtained by the
 use  of achromatics, which ought always to be  preferred.
  The process of exposing the proof to the mercurial vapour  is one
 of great delicacy ; sometimes the object is suddenly evolved, some-
 times it requires the mercury to be  maintained at 175  Fahrenheit
 for a long time.  Experience alone can determine when the full ef-
 fect has been obtained.
  After the picture has been  brought out, and  the coating of iodide
 of silver removed, it remains  only to effect the gilding.  ^This is ac-
 complished by pouring all over the  silver surface a very weak solu-
 tion of the chloride of gold in hyposulphite of potash, and warming
 it gently with the flame of a  spirit-lamp.  At a particular tempera-
 ture, the shadows increase in depth  and the lights in brillancy ; the
 plate is then to be thoroughly washed. The gilding serves to render 
      THEORY  OF THE PROCESS  OF  DAGUERRE.   177

the picture immovable  by ordinary exposure  or accident, and im-
parts to it a beautiful satiny lustre, and chatoyant play of colour.
   The great difficulty in the management of the  Daguerreotype lies
in the circumstance that the iodide of silver is  not affected corre-
spondingly  by lights that are of different degrees of brilliancy, if
they should be of different colours.  And it  is only under particular
circumstances, not easy to reproduce, that lights of the same colour,
but of different strengths, produce a corresponding degree of white-
ness on the plate.   Often, when the light is too active, the proof
takes on an unpleasant slate-blue colour, from the exterior portions
of the iodide assuming a state of solarization  before those beneath
have had time to undergo change; a phenomenon resembling  what
takes place when a sheet of paper is held before a very bright fire,
the exposed surface  becoming scorched, while the back has scarce-
ly had time to become warm.
   As respects the theory of this process, I do  not coincide with the
views  expressed by Dr.  Kane.  In the  shadows  no mercury exists;
the lights are an  amalgam.  When a Daguerreotype is exposed to
the vupour of mercury to bring out its picture, a decomposition  of
all  those  portions of the iodide  which have  been exposed to the
light ensues ; an amalgam is formed, and the iodine expelled unites
with the metallic silver behind, effecting, therefore, a corrosion  of
the plate ; no iodine is  evolved, and for obvious reasons such  an
event  is impossible.   The light therefore imparts to those portions
of iodide on which it has impinged, the quality of being decomposed
at a lower temperature  by the vapour of mercury than the temper-
ature at which an unexposed iodide can be  decomposed; an amal-
gam therefore forms on  such positions when the temperature  does
not rise beyond 175^ F.,  though the whole surface might be decom-
posed  and  whitened  if the temperature were carried high enough.
  The chemical  rays which affect the iodide of silver are chiefly
those of high refrangibility, and these rays manifest many habitudes
resembling those of radiant heat.  They are absorbed  and lost  in
effecting the change, so that a ray of light which has  once fallen
on a Daguerreotype plate, and is reflected by it, has lost  all its activ-
ity.  Whatever, therefore, will interfere with the absorption, will in-
terfere with the sensitiveness of different compounds.   Thus it has
long been known that there is a proper colour to which the plate
may be brought when it  possesses the  maximum of sensitiveness:
this is the  golden yellow ; when it is  red, or green, or blue,  it  is
much less sensitive ; and when of a lavender colour, hardly sensitive
at all.  This arises from  the circumstance that under these condi-
tions the optical character of the  plate is such  that it reflects the
active rays in part or altogether.
  I have already  remarked that  lights which vary in intensity do
not affect these plates in a corresponding way ; this arises from the
circumstance that, as the iodide of silver is  undergoing change, a
large quantity of light becomes latent, precisely as a piece of ice in
the act of melting absorbs a large quantity of heat, not discoverable
by the  thermometer ; this phenomenon accompanies the  blueness
which the compound assumes as it changes into  the condition  of a
•ubiodide.] 
178
NATURE  OF COMBUSTION.
                        CHAPTER VII.

 OF THE LIGHT AND HEAT  DISENGAGED  DURING CHEMICAL COMBINATION.

  It has been already noticed that the union of substances having
chemical affinity for each other is accompanied by increase of tem-
perature ; and in cases where the affinity is powerful, the effect may
be so great that the bodies shall become luminous : in such instances
the chemical action is said to be accompanied by combustion.  In con-
sidering the relations of this  phenomenon to affinity, it will be ne-
cessary to notice, first, the general circumstances of combustion;
secondly, the relation between the amount of affinity and the quan-
tity of heat evolved; and, finally, the explanations that have been
offered  of the origin of the light and  heat.
  In ordinary language, a body is said to burn when its elements
unite with the oxygen of the  air, and form new products.  The ac-
companying phenomena are in general those on which popular at-
tention  becomes fixed, and for which the process is generally car-
ried on  ; and hence, to the world  at large, combustion is of impor-
tance only as a source of heat and light.  One of the bodies, as hy-
drogen  or sulphur, is termed  the burning or combustible body, and
the oxygen is said to be the supporter of combustion ; but this lan-
guage, although  convenient for common use, is incorrect as a scien-
tific expression ; for oxygen may be burned in a vessel of hydrogen,
as well  as hydrogen may be burned  in a vessel of oxygen gas, the
one and the other being equally active in the process, and being re-
lated to each other in every way alike.  In combustion, as, indeed,
in all cases of combination, no particle of matter becomes lost or
annihilated ; it assumes new forms, in general gaseous and invisible
to the  eye of popular  observation, but easily collected, weighed,
and analyzed by the means  that  chemistry possesses.  The solid
coal  or wood which burns to  ashes, changes but its external aspect;
mixing with the general  mass of air under the form of carbonic acid
gas and watery vapour, its elements become the food of living plants,
which in their turn, cut down or fossilized, form to succeeding ages
the stores of light and warmth such as we now enjoy.
  There are but few bodies endowed with so  great an affinity for
oxygen as to enter into  combustion at ordinary temperatures by
contact with it.  If they  do combine at ordinary temperatures
with oxygen, the products are not those which combustion would
tend to generate, but a  distinct class of substances, containing  a
smaller proportion  of oxygen combined.  Thus nitric oxide gas
combines with oxygen, even when quite cold, forming  red  fumes
of nitrous acid  gas,  which  is an  inferior degree of  oxidation.
Phosphorus,  when burning at  common temperatures,  emits but
little light, and forms phosphorous acid ; if it be heated, it bursts
into brilliant flame,  and  forms phosphoric acid, which contains 
PRODUCTS  OF  SLOW  COMBUSTION.      179
 |ths more oxygen.  Potassium combines at common temperature
 with oxygen, forming potash ; but when heated it burns with flame,
 and combines with three times as much oxygen.  In the complete
 combustion of organic  matters, the products are always water and
 carbonic acid.   Thus, woody fibre, which is C.H.O., combines with
 20. to form C02 and H.O.; and alcohol, which is CzU,0., combines
 with GO.  to form 2(C.O,) and  3(H.O.).  But at  common tempera-
 tures the slow oxidizement of woody fibre produces the black ve-
 getable mould, a form of ulmine, the C.H.O. taking 0. to form C.H.02.
 At eummon temperatures alcohol becomes acetic acid, the C2H30.
 combining with  20. to form C,H20, and H.O.   The pyroxylic spirit
 at common temperatures becomes, by slow combustion, formic acid,
 C,H,02 taking (), to form C,H<04  and 2(H.O.).
   This slow combustion produces heat, although so much less than
 is evolved by the more rapid  process that it may easily be over-
 looked.   But  if a number of sticks of phosphorus be laid together
 and allowed to  oxidize, they will warm each other so much as to
 melt and  burst into vivid flame.  The oils and tallow, if there be a
 large surface exposed to the air,  as when cotton or linen rags im
 bibed  in oil lie  in  a heap, combine  so rapidly with oxygen°as to
 form a sort of resin, that by the  heat evolved the mass  will be set
 on fire ; and hence the  origin of those spontaneous fires, so called,
 which consumed the naval arsenal at St. Petersburgh, and, in many
 cases,  cotton-mills in England.  To this cause also may be ascribed
 the light  which  issues from points in the surface of a marsh or bog,
 and the luminous appearance which fish assumes when decomposi-
 tion has  just commenced.   The energy of this slow combustion
 may be much  increased by heat applied below the point which pro-
 duces  rapid action : thus tallow, when heated below redness, burns
 with a pale lambent flame, invisible in daylight, but still  so marked
 that, if it be plunged into a vessel of oxyjren, the whole mass bursts
 into brilliant combustion, forming then the ultimate products, wa-
 ter and carbonic acid.
   On  this fact of the increased energy in the process of slow com-
 bustion produced  by a  heat  below  that at which the body is in-
 flamed, is founded the construction of the  lamp without flame, or
 the aphlogistic lamp.  If a wine-glass be taken,  and rinsed inside
 with strong alcohol or ether, and then a coil of fine platina wire,
 or a ball of spongy platina heated to redness, be suspended in the
 middle of the glass, it will remain red until  all the alcohol or ether
 has been exhausted.  The glass becomes filled with a mixture of
 air ind  inflammable vapour,  which, by the influence of the heated
 plutma, is enabled to combine, and form acetic  and formic acids.
 By this combination heat is evolved, which prevents the cooling of
 the wire or ball,  and thus, as long as any combustible  material re-
 mains,  the platina is kept  ignited.  The platina  ball or wire  may
 also be  (and in  practice generally is) fixed over the wick of a spirit-
lamp, and  the lamp having been ignited, is blown out as soon as the
platina  has become red, which then continues to glow until the lamp
has been emptied of the spirit, the latter ascending through the
capillary wick, and  forming  over  its top a little explosive atmo-
 sphere, in which the ball of platina is  immersed and works. 
 ISO  CONSTRUCTION OF THE  PLATINA GAS LAMP.

   This property of platina appears to depend  on the  power which
 it possesses of attracting to its surface in a condensed form a layer
 of particles of whatever gaseous mixture it is immersed in.  Hence,
 if its surface is in the slightest degree soiled, it ceases to exert this
 action ;  and by increasing the surface, its energy may be augmented
 in a remarkable degree.   The form in which it is most powerful is
 that of the slightly coherent spongy mass, obtained by reducing at
 a full  red heat the ammonia chloride of platinum; if a ball of the
 metal so prepared  be plunged into a vessel of oxygen and hydrogen,
 mixed in suitable proportions to form water, the  gases instantly ex-
plode ; for the oxygen and hydrogen, being absorbed by the spongy
platina, are brought into intimate contact upon its surface, and unite,
evolving so much  heat as  to raise  the temperature of the platina
ball to redness, and thereby inflame the remaining gas.  The action
 of the spongy platina may be weakened by mixing it with some pipe-
 clay, or using, as in  the aphlogistic lamp, the platina in  the form of
 plate  or wire.   In  this way all combustible gases may be caused to
 combine gradually with oxygen, but they  require different temper-
 atures, and the action is  modified by the  presence of other gases
 in a manner which is often taken advantage of in gaseous analysis.
   The most remarkable  application  of this property  is to procure
             instantaneous light by means of  the hydrogen gas
             lamp.  A vessel,/, contains dilute  sulphuric acid, into
             which  the tube of the vessel g h dips nearly to the bot-
             tom, having attached a piece of ordinary zinc, e.   The
              vessels being ground air-tight where  they fit to one
              another, when the stopcock b is closed, and the  acid
            a acts on the zinc, the hydrogen evolved cannot escape,
              and, pressing on the  liquid  in f, forces it up into A,
             until the acid falling below the level of the  zinc, the
             action  ceases.   To the stopcock b is  attached a jet,
             c, in front of which is fixed a ball of spongy platina, a,
which, being in the air, has always condensed in its pores a quantity
of oxygen gas; on opening the stop-cock, the  hydrogen, issuing
from the jet, strikes  upon the platinum, and combining with the ox-
ygen, heats the ball  so highly that  it inflames the jet of  gas, and
thus affords a  flame at which any other substance may be lighted.
This lamp has assumed a variety of forms, of which  the  above is
that which best shows  its  principle.  All bodies  possess this prop-
erty to a slight extent, particularly when hot;  but in none is it ac-
tive enough to be usefully applied, except in platinum.
  The temperatures  at which bodies enter into  rapid combustion
are very various;  thus phosphorus  inflames  at  a temperature of
 120° F., and sulphur at 30(P  F.   Phosphuretted hydrogen gas in-
flames at all ordinary temperatures, while hydrogen requires a  dull
red, and  carburetted hydrogen a bright red heat before they  will
take fire.  The inflammability of phosphorus  has been shown by
Graham to be affected by the presence of small quantities of various
 substances in a very curious manner ; thus phosphorus may be  sub-
 limed in  air saturated with vapour of oil of turpentine, without any
 tendency to combustion, or combination with oxygen, being evinced.
  Combustion occurs only at the point where the two substances
 
CONSTITUTION  OF  FLAME.
181
which enter into union are in contact.  Thus, in an ordinary flame,
the true combustion is limited to a thin sheet, the inside of which
is  totally dark, and occupied by the combustible material of the
burning body  in a  state  of  gas.  This is easily shown by holding
over the flame of a candle or a spirit-lamp a piece of wire  gauze:
the burning  sheet is marked by a ring of light, but the interior is
dark, although full of inflammable vapour, which passes through un-
inflamed, and may be ignited on the opposite side of the gauze.  In
the flame of an ordinary candle, a, four distinct portions may be ob-
served, having  totally distinct constitutions;  at the base    A
of the flame, i i, a pale, blue-coloured light is emitted, for   /ink
there the air is in excess, and the combustion is at once e§kV^
complete ; higher up, from i i to c, the combustible material  If Am
is in excess, and the most brilliant light is produced by the  II B II
active combination ; this portion is surrounded by a sheet  j^3M[
of much paler  and yellower light, e e, which is observable  f ■ "^
particularly at the sides of the flame, while the inside of  fllffM
the flame, b, remains completely black, and is occupied only  I  |§[jH
by vapour incapable of burning from having no access to  ||HH
the external air.   The light emitted arises also from the   ^HHv
circumstances of the combination; the temperature of  flame is in
all  cases exceedingly high,  although often but little luminous, for
it  is found that a current of air hot  enough to brilliantly ignite a
solid  body,  is  itself not at  all incandescent.   Hence, in all cases
where bright light is produced in combustion, one of the bodies en-
gaged must be solid, and the light is really derived from its becom-
ing ignited.   Thus hydrogen and sulphur give, in burning, very little
light, because the one is a gas,  and the  other,  when burning,  is in
the state of vapour, and the products of combustion are, when form-
ed, in both cases gaseous.   Phosphorus,  when it, in burning, forms
a volatile body, gives but little light, but when it forms a fixed prod-
uct, is one of the most brilliant instances of combustion.  Iron and
zinc, which form solid oxides, burn with great light, and carbon, al-
though forming a gas, being  itself solid, produces light also.  In the
case of a candle,  the source  of light is to be found in the decompo-
sition which the inflammable vapour inside of the flame undergoes
from the high  temperature to which it is subjected;  one half of its
carbon is deposited in the solid form, forming smoke, and it is this
smoke which, becoming ignited,  constitutes the great source of
light.  A body which could not form smoke,  could  not give out
much light in burning.  The separation of this  carbon (soot) in the
flame may easily be shown by placing over the  flame of the candle
a sheet of wire gauze: below the middle  of the luminous space the
flame becomes  dull, and the  carbon, which in burning should have
rendered it brilliant, passes  as smoke through the gauze, and  may
be inflamed above ;  when the supply of air is insufficient, this smoke
is  not completely burned, and a  corresponding  quantity of heating
and lighting material is lost; and as it carries off with it  a great
quantity  of the heat  already formed, it  actually  cools the flame.
When, therefore, a high temperature, or a clear flame without smoke
is  required, all the carbon must be consumed.   This is effected by
a variety of contrivances : in the burner of the Argand lamp or gas 
182          HEATING  EFFECTS OF  FLAME.
 jet, a current of air is established  through the centre of the flame,
 and thus the combustion of the  inflammable vapour much accelera-
 ted ; in the flame of  the  blowpipe the same  effect is  produced  by
 the current of  air from the bellows  or the mouth ; and on a large
 scale  by the numerous ways of  burning smoke, so necessary in fac-
 tories situated  in large cities.   In the employment of the blowpipe,
 the constitution of the flame is  of  great importance ;  for according
                   as the body to be heated is placed at b, where the
                   oxygen of the  air preponderates, or between a and
                   b, where it is immersed in an atmosphere of inflam-
                   mable material, the  most opposite effects of violent
                   oxidation, and  of reduction from the state of oxide
                   may be  produced.   Thus  a glass  of  copper be-
                   comes green at b, and red from a to b ;  a glass of
 manganese is rendered purple  at b,  but  colourless from a to b ; there
 being few bodies whose relations to the blowpipe can be  completely
 known without a comparison of the  effect of the oxidizing and re-
 ducing flames.
  During combustion, the  heat evolved is at first absorbed by the body which is
 then produced; but it is afterward distributed through the mass of all neighbour-
 ing bodies in proportion to their conducting powers.  It is easy to  calculate the
 temperature  to which the  product of the  combustion is in the first place raised.
 Thus eight parts of oxygen unite with one  part  of hydrogen by weight to form nine
 of water.   If watery vapour had the same capacity for heat as water, the tempera-
 ture of the vapour produced should be,  since  one part of oxygen heats twenty-nine
 parts of water, 180 degrees =$ (29 x 180)^:4640 above the freezing point; but the
 capacity of watery vapour in equal weight is only 0 847, and therefore it is more ea-
 sily heated in that  proportion than liquid water; hence the temperature really pro-
 duced is =4640x0 847, or 5478 above the  freezing point of water.  If, however, in
 place of pure oxygen, atmospheric air had been made  use  of, then 23 1 parts of
 oxygen are mixed  therein with 76 9 parts of nitrogen, which must be  heated to the
 same temperature with the watery vapour,  and,  of course, at its expense.  The ca-
 pacity of nitrogen  gas for  heat is 0 2865, one third that  of watery vapour; but  in
 the  air which is necessary to form nine parts of water,  there are  26 8, or almost
 exactly three times as much nitrogen, so that precisely one half of the quantity of
 heat produced is absorbed by the nitrogen, and the temperature of the  mixture rises
 only to 2739° above the freezing point.
  Such being the temperatures produced by hydrogen gas in burning in oxygen and
 in atmospheric air, it is easy to understand why we  can by its power fuse those
 substances which resist almost every other means.   The melting point of cast iron
is 2786°, that is, almost exactly the same as that produced by hydrogen burning  in
the  open air;  but the temperature of  5478°, given by hydrogen burning in oxygen,
 is very nearly double that,  and  passes,  therefore, far  beyond the melting point of
platinum, and exceeds the heat of all our other artificial fires ;  it is only in the dis-
charge of the galvanic battery, or in the solar rays concentrated by a lens, that the
heating effects of burning hydrogen and oxygen can  be equalled.   If the nitrogen
had been present in a quantity ten times as great, it would have absorbed M of the
amount of heat evolved, and hence the resulting temperature should be onlv about
500°.  Such a mixture, therefore, could  not explode at all, for the first little "portion
which might be burned could not produce the  necessary temperature for communi-
cating the combustion to the mass.  In this manner, the combustibility of gaseous
mixtures may be destroyed by mixing them with other gases in such quantities as
may cool them below the temperatures at  which explosion  can take place. One
                                           - iight volumes of hydrogen, or
five volumes of nitrogen, explosion may occur.
  The greater density of solid bodie^ and the greater rapidity with
which they are capable of conducting away the heat which they re- 
CONSTRUCTION OF  THE  SAFETY-LAMP.    183

ceive, enables them, in a still more remarkable degree, to reduce the
temperature of flame, and, consequently, to extinguish it.   Thus, if
a piece of metallic gauze be held over a jet of ig-   .>^
nited coal gas, the flame will be arrested at the low-   |«Vix
er surface of the  gauze; and although the gas and   Y^\^\^
air may pass through, forming an explosive mixture, WbI^^'I^
yet no inflammation can be propagated;  and if the   \^^
mixture of air  and gas be allowed to pass through
the metallic gauze, and  then  ignited at its upper
surface, it will burn there; but, although the space
between  the jet and gauze be  occupied by  inflam-
mable material, the flame cannot pass down, the me-
tallic tissue  conducting away the heat so rapidly as  to prevent the
temperature from rising to the necessary degree.  Another and a
very striking form of this experiment is  to  lay on the metallic
gauze a piece of camphor, and to hold it over a lamp; the camphor
will melt and vaporize, but as  it melts it will  in part filter through
the gauze ; this portion takes fire, and a sheet of smoky flame cov-
ers the lower  surface ; but above,  the camphor in vapour mixes
with the  air without inflaming.
  The application of this principle to the construction of the safety-
lamp for mines, constitutes one of the most beautiful instances  of
the advantages which may practically flow from what, superficially
considered, might appear a mere abstract principle in science.   The
fire-damp, or light carburetted hydrogen, which, issuing  from the
minute fissures in the excavations of  a coal-mine, is diffused through
the air introduced for the purposes  of ventilation,  often forms  an
explosive mixture, which,  being  set on  fire by accident  or negli-
gence, detonates  with awful violence, and destroys all living beings
which  may at the time be in the mine.  This gas is one of the  least
easily  inflammable, and hence, most fortunately for  humanity, one
to which the principle of cooling orifices may  be most  successfully
applied.   The  candle  or lamp,  b,  by
which  light  is to be obtained for work-
ing in the mine, is surrounded by a cyl-
inder of wire gauze, of about 1500 ori-
fices in the square inch.  Inside of this
the inflammable  mixture may explode,
but the flame cannot pass out; the com-
bustion cannot be communicated to the
general mass of external air, and thus
the miner, guided by  the never-failing
indications of his safety-lamp, passes
along through  galleries  under ground,
where  the emission of a spark would
cause destruction, and measures, by the
appearance of the lamp, the actual con-
dition  of the air he breathes, the phe-
nomena of the  flame indicating also its
fitness  for respiration.'  If the air  t.e
pure, the lamp  burns clear, as in t!'e
upper air; if some fire-damp be present,
 
 184 QUANTITY OF  HEAT  EVOLVED  IN  COMBUSTION.

 the lamp shows much less light, the flame becomes red and smoky,
 if the noxious impregnation be still increased, the flame of the lamp
 itself becomes extinguished, and the cylinder of metallic gauze is
 filled by a sheet of lurid flame ;  the miner being then enveloped by
 an atmosphere fully  explosive,  and even fatal to life  if it  be  long
 respired.  If he proceed still farther, all flame is lost;  for, as the
 fire-damp then predominates, there is produced, from  deficiency of
 oxygen, only  a slow  invisible combustion ; but even this is made,
 by the sublime genius of its inventor, Davy,  to give the  miner the
 last warning to return to safer regions : a sheet of thin platina, being
 coiled up and  hung over the wick of the lamp, becomes ignited, as
 in the aphlogistic lamp,  and continues to  emit a faint, but  most use
 ful beacon glow, until an atmosphere  is obtained where there is ox-
 ygen  enough  to  support a rapid combustion,  or until a place is
 reached so destitute of oxygen that no combustion whatsoever can
 take place.
   The determination of the quantity of heat produced during the
 combustion of a given quantity of combustible substance  is a prob-
 lem of great importance in  the arts, as on it depends the  economic
 value  of all varieties of fuel.   The plan  generally followed has been
 to burn the substances  by  means  of the  smallest quantity of air
 which is sufficient, in a  vessel surrounded, as far as possible, with
 water.   If it be found that the burning of  a  pound of wood heats
 37 pounds of water from 32° to 212°, no idea can be thereby formed
 of the quantity of heat evolved ; but if, in another trial, it be found
 that the burning of a pound of charcoal raises the temperature of
 74 pounds of water through the same range, it follows that the char-
 coal had double the  calorific power of the wood.  True relative
 numbers can thus be obtained, although they have independently no
 positive signification.   The results obtained in this manner have
 been exceedingly discordant; but,  by the late  researches of Des
 pretz and of Bull, which appear to have been conducted with more
 attention to accuracy than former ones, a very interesting rule has
 been obtained: it is, that in  all cases of combustion the quantity of
 heat evolved is proportional to the quantity of oxygen which enters
 into combination.  Thus Despretz found
 1 lb. of oxygen, uniting with hydrogen, heats from 32° to 212°, 29^ lbs. of water,
    "     "     "      charcoal,       "       "      29      "
    "     "     "      alcohol,       "       "      28      "
    "     "     ••      ether,        "       "      28£    "
  This rule, however, must be liable to some very curious changes ; for one pound
of oxygen, in combining with iron, could heat, by Despretz's experiments, 53 pounds
of water, or almost exactly twice  as much as in the former list, and with tin and
zinc the same  double  proportion held.  With phosphorus a singular peculiarity
was observed, which, when the subject comes to be more fully studied, may throw
some light upon the former differences.  When phosphorus burns slowly, so  as to
form phosphorous  acid, it heats, in combining with  a pound of oxygen, 28 pounds
of water ; but when it burns brilliantly and forms phosphoric acid, the heat evolved
is doubled, and becomes the same as that produced with iron, tin,  or zinc.   As a
 suggestion, I would remark, that in the cases where the  smaller proportion of heat
 is evolved, the products of combustion are all volatile, and where the larger propor-
 tion is produced, the products are  fixed and solid ; even  in the case of phosphorus,
 when it combines, producing least heat, it forms a volatile product, but one which
 resists a full red heat in the case where the combination has been complete.
  Hess has lately pointed  out a relation between the amount of chemical action 
         Lavoisier's   theory  of   combustion.    185

  and  the quantity of heat evolved, which may, when examined in a greater number
  of cases, lead to very important conclusions.  He has  found  that sulphuric acid, in
  combining with any base, generates in all cases the same quantity of heat;  the rise
  of temperature is, of course, greatest when the acid and base are both in an un-
  combined condition, as where vapour of anhydrous  sulphuric  acid produces, by con-
  tact  with dry barytes, brilliant ignition -, but, although the barytes generates, by con-
  tact  with dilute sulphuric acid, much  less heat, yet, if the two quantities evolved,
  first  by mixing the strong acid with water, and then the dilute acid  with the base,
  be added  together, the sum appears, from  a great number  of experiments, to be
  constant; thus, diluting oil of vitriol with  water,  and neutralizing it, so  diluted,
  with ammonia, Hess found the heat in each case to be,
                                With Ammonia.  With Water.        Sum.
              Oil of vitriol   .   .  . 595 8......  .   . 595 8
              First dilution .   .  . 5189  . .  778  .  .   . 5967
              Second dilution  .  .480 5  .  .  1167  .  .   . 597.2

  Connecting these  results with those of Despretz, just given, for the bodies which
  unite with oxygen, it would appear likely that the quantity of  heat evolved in chem-
  ical combination may be connected with  the equivalent  number  and the electrical
  condition of the substances by a definite law, which farther investigation may dis-
  nlose.
   At all periods in the history of chemistry, the explanation  of the phenomena of
  combustion was that for which  the general theory of the science  was constructed;
  and,  accordingly,  we find that  every period of its progress has been marked by the
  views  adopted to account for the heat and light so evolved.   The coarse and un-
  philosophical  ideas of the existence of inflammability which prevailed before Lavoi-
  Bier's time, do not require notice; but the theory which he proposed, although not
  now  received, is yet, like all his works, of so much interest and importance, that
  it would  be improper to pass it over.
   When Lavoisier lived,  the minds  of philosophers were  fixed in  the  opinion
  that  heat  and light were positively existing substances, which  might enter into
  combination,  or be disengaged from combinations in  which they had previously
  been engaged, just as lead,  or oxygen, or any other of the ordinary bodies we oper-
  ate upon in our experiments.  Gases  were believed to be compounds  of the true
 solid body with light  and heat; and hence, when oxygen gas combined with iron
 or with phosphorus, and assumed the solid form, the light and heat with which the
 real oxygen  had previously united were set free.   Hydrogen  and oxygen gases, in
 combining to  form liquid water, underwent the greatest condensation, and by their
 union, therefore, the greatest heat was evolved ; and in all such cases where a gas
 became a  liquid or a solid, this theory was fully competent  to explain the facts.
 However, in very many cases  it failed completely; thus, by the union of carbon
 with oxygen, so far from a gas becoming  solid and  so  evolving a heat, a solid be-
 comes  a gas, and should produce an  equivalent degree of cold.  Lavoisier here
 brought in to his aid the relative specific heats of the gases before and after  union ;
 thus,  if the carbonic acid formed by burning carbon in oxygen gas had a much less
 specific heat than  oxygen, there might be evolved a quantity of heat in the same
 way as  it occurs with water and sulphuric acid; but this is  not the fact;  on the
 contrary, the carbonic acid has a specific heat greater than that of the  oxygen gas
 it was  formed from, in the proportion  of 1195 to 808 ; and hence, on  Lavoisier's
 views, an intense degree of cold  should be produced in the combustion of charcoal,
 as well  by the  latent heat which the solid should absorb in becoming gaseous, as by
 the increased  specific heat  of the gas so formed.  This example is sufficient to
 show  the  way in  which Lavoisier's theory became inapplicable to the wants of
 science.
  Pr.  Thompson has recently endeavoured to account for the heat evolved in chem-
 ical combination by an application of the law of Dulong regarding specific heats
 (described page 66).  Every  molecule  of a  simple body  being supposed provided
 with the same quantity of heat, he suggests that, when a number of them combine
 together, the heat of one or more is expelled, and thus produces  the rise of tem-
 perature.  Thus, considering oil of vitriol to contain seven combining equivalents,
 two of hydrogen, four  of oxygen, and one  of sulphur, and that the specific heat of
all of  these is the same, 31,  as results  from Dulong's law if it be supposed rigidly
                                                 31  X 7
exact, the specific  heat of oil of vitriol should be  -j—=0 442, 49 1 being the

                                   Ai 
 186  HEAT  OF  COMBINATION,   WHENCE  DERIVED.

 equivalent number of oil of vitriol; but the specific heat found by experiment la
 only 0 352; so that exactly one fifth of the total quantity of heat has been  lost by
 the act of combination, and may hence be supposed to have caused the phenomena
 of combustion.                                    ,    _  _,
   In the extension of this principle  a little farther than Dr. Thompson appears to
 have contemplated its application, some coincidences, with results already known,
 are found, which  give  it an aspect of considerable theoretic interest.  Thus we
 may consider certain metallic oxides as consisting of an equivalent of each constit-
 uent, and hence their proper specific heat should be, if none were lost by combina-
 tion,^ 1 x2=6 2 ; but the specific heat of the compound molecule is experimentally
 found  to be 5 4, and thus that 0 8 of heat had been lost, producing the phenomena
 of combustion in  combination.  In this  manner we can understand why Desprptz
 found  that a certain quantity of oxygen evolves the same quantity of heat in com-
 bining with very many bodies.   If we  examine the sulphates noticed, p. 67, in re-
 lation  to the same principle, we find that as there are in each six molecules, the
 specific heat should be 18 6=31 x6 ;  but it is found to be but two thirds of that,
 124.  Now if here, as in the oxides, the combustible material retains its heat, and
 it is from  the oxygen that  the  portion set free is taken, the experimental  result
 arises  from the heat of each oxygen molecule being reduced by 16, and hence that
 when oxygen forms a salt with  sulphur and a metal, the heat evolved is double that
 produced  in simple oxidation   The  fact of the same quantity of oxygen giving
 double the amount of heat when it converts phosphorus into phosphoric acid, com-
 pared with what is evolved when it forms only phosphorous  acid, may have its ori-
 gin in  an analogous condition.
  In the case of the carbonates, another form of the principle becomes manifest;
 but on this view it is necessary  to consider carbonic acid as containing five mole-
 cules, one  of carbon and four of oxygen, and as uniting with  two  molecules of a
 metallic oxide.   The carbon and metal burn each in halt  of the quantity of oxygen
 with which they ultimately unite, and, like  phosphorus, separate from that oxygen
 only the smaller quantity which it can lose when entering  into combination; the
 carbonic acid  and suboxide then  unite with the  residue of oxygen, and from it
 separate the  larger portion  of heat as occurs when phosphoric acid  is produced.
 The resulting  specific heat for a carbonate is therefore 9 3-^-6 9-|-5=20 7;  or, re-
 duced  to the equivalent number  used in p. 67, it is 10 35, the experimental number
 being 10-4.
  The results  in these three cases may be shown in the form of the following table,
 in which the first column contains the equivalent molecule of the body, M. denoting
 the equivalent of a  metal; the second column contains the specific heats calculated
on the  supposition  that there is  none lost in combining; the third, the calculation
by which the fourth column of  true calculated specific heats is obtained; and the
fifth, the specific heats that have been found by experiment.
1.	2.	3.	4.	5. ~54 ~12A
M. O.	62	3 1-1-2 3	54 LT2	
M 04s.	18 6	(2X3 l)-L(4xl-5)		
M206C.	27 9(3x31)-f-(3x2 3)-f3xl 5)		20.7	208
  The coincidences refer  only to  the bodies  already  selected,  p. 67, as exam-
ples of simplicity in the relation of their specific heats, and certainly do not exist in
a great number of other cases in  which I have sought for them ; they may there-
fore be accidental;  but there is yet so much likelihood of some physical law of the
kind being to be discovered, that  everything that may assist in its detection is of
importance.
  Laying aside altogether the attempt at deducing the phenomena of combustion
from any change in  the amount of latent  or of specific heat in the bodies which
enter into combination, it remains  only to be admitted as a general and independent
principle that chemical combination  is a source of heat and light.  It is, however,
impossible to arrest inquiry at that point, and, accordingly, the  speculations of phi-
losophers have been directed in seeking a cause  for the phenomena of combus-
tion to the disengagement of electricity, which accompanies all manifestations  of
chemical action, and have  endeavoured to identify the light and heat emanating
from a burning body with that which is produced by the separation or combination
of the electric fluids.  The evidence in favour of this view will be best described
among the relations of electricity to  affinity. 
INFLUENCE  OF  ELECTRICITY  ON  AFFINITY.  18*7
                       CHAPTER VIII.

     OF THE INFLUENCE OF  ELECTRICITY ON CHEMICAL AFFINITY.

  It has been already shown, that in  the production of galvanic or
hydro-electric currents, there always occurs between the  liquid and
solid elements of the circle a degree of chemical action, to which
the quantity of electricity generated  is  exactly proportional in
amount, and that no current, such as was there described, can be gen-
erated  without, by the  chemical action of the more oxidizable met-
al, the  liquid being  decomposed, and some one element of it expell-
ed, in place of which a corresponding quantity of zinc may be sub-
stituted.   I did not then attempt to discuss the question of whether
the chemical action in  the  battery  be  the cause or the effect of the
current of electricity which arises, as that can be best done when
the action  of the current, no matter from what source it may have
been derived, upon chemical substances, similar to  those that are
used as exciting liquids in the galvanic battery, has been described.
   If the wires belonging to the plates Z C, of the simple circuit in
the figure, be brought into communication by means
of a cup of water, the current passes, and it is found
that at the terminations of the wires  bubbles of gas
form in considerable number, which, when collected,
are found to be, from the wire in connexion with the
copper plate, oxygen  gas, and hydrogen  gas from
the wire which  is attached to the plate of zinc.   If
the conducting liquid had been muriatic acid, hydro-
gen would have been evolved as gas at the zinc extremity, and chlo-
rine liberated upon the wire  of the copper plate, though from its
solubility in the liquid  it would not be disengaged as gas.
   If a  solution of  iodide of potassium had been  employed, iodine
would  appear upon the copper side,  and potassium  should be set
free upon the zinc  wire; but  by the action of the water,  the metal
is instantly converted into potash, and hydrogen set free.
   It is not necessary that such bodies should be in solution, for this
only serves to give to their particles the freedom  of motion, which
may allow their  elements to separate.   If chloride of lead melted in
a cup  be  used to complete the voltaic circuit, chlorine  is evolved
upon the +, and  lead upon the — wire ; with oxide of lead (litharge),
the evolution of lead at the —, and of oxygen upon  the  -f- extrem-
ity of  the wires, occurs  similarly  ; protochloride of tin, iodide of
lead, chloride of silver, all act in the  same way.
   In place of bodies consisting of two elements, such as those above
described, we may employ  in solution, or in a fused state, secondary
compounds, consisting of an acid and a base.  If the current of elec-
tricity  pass through a solution of sulphate of  soda, the sulphuric
acid appears upon the  +,  and the alkali  upon  the — wire.   With
sulphate of magnesia, the earth passes to the negative, and the acid
to the  positive extremity of the liquid circuit; in these cases water
 
188 CHEMICAL AFFINITY ELECTRICAL ATTRACTION.

is also decomposed, of which the hydrogen accompanies the base,
and the oxygen the  acid; but, on using a salt  of lead, of silver, or
of copper, the metallic oxide is reduced by the action of the nascent
hydrogen, or, at least, it may be so expressed,  and the metal is de-
posited in crystals upon the — wire, while the  acid and the oxygen
are evolved together upon the extremity of the positive conductor.
   The affinity which held together these bodies in combination is
superseded during the passage of the electric current.  The elements
previously united appear to  repel each other, and to be at the same
time attracted by the excited terminations of the metallic wires, by
which  the battery is placed in connexion with the substance to be
decomposed.
   The simplest mode of accounting for these phenomena is to say
that water is  decomposed, because  the  oxygen  is  attracted more
powerfully by the positive pole of the galvanic battery than by the
hydrogen with which it had  previously been associated,  while this
last is more powerfully attracted by the negative pole than by the ox-
ygen.   The elementary bodies separate, therefore, from each other;
but, not being capable of entering into combination with the substance
of the poles, they are evolved as gas.  This explanation may be ap-
plied to all such cases.   Oxygen, chlorine,  iodine, sulphur, as well
as the various acids, are attracted  by the positively electric pole,
while hydrogen, potassium,  sodium, copper, silver, lead, and the
various bases, are attracted to the negative pole of the battery.  But
one force cannot completely supersede another, as electricity here
supersedes affinity, unless it be of the same kind, or, at least, closely
resembling  it in nature.  What, then, is the relation between the
chemical force which had kept the elements united, and the elec-
trical force which makes them separate 1  The cause  was easily
found :  they are identical.  The oxygen  and  hydrogen  united ori-
ginally from being in opposite electrical states, and they are forced
to separate from being subjected to the action of still more power-
ful attractions; the  decomposition of water by the voltaic current
becoming thus a case of double decomposition, in which the original
electricities of the two  simple bodies were the quiescent, and the
excitation of the opposite poles of the battery were the  divellent
forces.
   Chemical substances were thus considered to have affinities for
each other, from being in opposite electric  states, and the peculiar
play of affinity of each  body depended on which electricity it was
naturally excited by when in combination ;  those bodies which are
attracted by the positive pole of the battery being necessarily in  the
negative condition, and vice  versa.  Thus, all substances  may be di-
vided into two classes ,  those being termed electro-negative which
are evolved at the copper pole of a simple,  or at the zinc pole of a
compound circle, and those which appear at  the opposite pole being
termed electro-positive.   The simple bodies thus classified are ran-
ged as in the following list: 
ELECTRO-CHEMICAL  CLASSIFICATION.     189
Electronegative.		---N	Electro-positive.
Oxygen	Mercury.	Palladium.	Potassium.
i Fluorine.	Chrome.	A Silver.	Sodium.
T Chlorine.	Vanadium.	1 Copper	I Lithium.
| Bromine.	| Iridium.	1 Lead.	f Barium.
Iodine.	Rhodium.	Tin.	T Strontium.
Sulphur.	y Cranium.	Bismuth.	Calcium.
Selenium.	Osmium.	Cobalt.	Magnesium.
i Tellurium.	Platinum.	Nickel.	Glucinum.
T Nitrogen.	Titanium.	.Iron.	Yttrium.
% Phosphorus.	1 Gold.	T Manganese.	| Thorium.
Arsenic.	T Molybdenum.	1 Cadmium.	T Aluminum.
Antimony.	* Tungsten.	*Zinc.	"V Zirconium.
Silicon.	Columbium.	Hydrogen.	Lanthanum.
Boron.		Carbon.	Cerium.
  Th( most powerfully negative  bodies are placed in the first, and
those most  powerfully  positive in the fourth column, these being
connected by the intermediate  columns in the order marked by the
brackets and arrows.  Any substance in the  list is positive with re-
gard to any other towards which the arrow points, and negative in
relation  to  any from which the arrow is directed.   Thus hydrogen
is negative to all in the fourth, but positive to all  in the three  pre-
ceding  columns, and so on.   These positions should also indicate
the relative affinities of the simple bodies towards  each other ;  but,
in interpreting such arrangements, it must be recollected that the
order of affinities may  be totally changed by heat or by cohesion,
and that the electrical order maybe completely different, according
to the nature of the exciting liquid, as in  the table, p. 129.
  Two bodies in combination are therefore like two pith balls which
mutually adhere, but of which the attraction is permanent from their
electricities not  being discharged.   How do these bodies acquire
those oppositely excited states 1  and why, if their condition resem-
bles that of ordinary electricity, do they remain combined, when
their opposite fluids might unite,  and neutralization being produced,
all combination cease 1
  These two questions have not yet been answered.  Several times their explana-
tion has been attempted ; and thus the electro-chemical theories of Davy, Ampere,
and  Berzelius  have  been proposed.   I shall briefly notice the leading features of
these before proceeding to discuss the remarkable advance recently made in our
ideas of the electro-chemical relations of bodies by  Faraday and Graham.
  The theory of Davy was based upon the principle that bodies in their ordinary
uncombined condition do not contain free electricity, but that by contact they be-
come excited.  Thus a disk of sulphur touched to a disk of copper becomes nega-
tive, and the copper positive; its charge increases in intensity on  applying  heat,
until, at a certain temperature, the tension of the electricities becomes so great that
they suddenly lecombine, carrying with them the molecules of the sulphur and cop-
per which thus enter into union, and producing the evolution  of light and heat hy
which the chemical action is accompanied.  The sulphuret of copper, when formed,
Is no longer electric; it remains permanent in virtue of a force which Davy does
not  strictly define, but which he appears to have considered an intimate cohesion
between the particles which had been closely approximated by their electrical at-
tractions ;  and when, by an electric current, the molecules of copper and sulphur are
brought into the reverse state to that which favoured their combination, they sep-
arate.  This view supposes, therefore, the electrical excitation to be only moment-
ary, during the act of combination and during the moment of disunion ; before and
after, all is neutral.  To all phenomena  of decomposition, this theory suffices but
it is vitally deficient  in the principle upon which it is based.  It has been since 
 190 THEORIES  OF  DAVY,  AMPERE,  AND  BERZELIUS.

 completely proved  that  it is  not  the  contact which  evolves electricity,  but  the
 chemical  action ; and also, on Davy's views, the electrical disturbance only suffi-
 ces to account for the  secondary phenomena of union, the light and heat, leaving
 the act of combination to be ascribed to a different and independent force of affin-
 ity or cohesion.
   A more complete theory was proposed by Ampere, whose philosophical views in
 magnetism and  other sciences have been found so singularly in accordance with
 experiment.   He proposed to consider that  each substance in  nature is endowed
 with a definite amount of one or of the other electricity, and is  thus naturally and
 invariably electro-positive or  electro-negative, and  stands higher or lower in  the
 list  of bodies, according to the intensity of the charge.   Such  an excited body he
 considered to attract round its mass an atmosphere of electricity of the opposite
 kind, and corresponding  in intensity.   Now, on bringing into contact an electro-
 positive and an electro-negative body, their atmospheres unite, and produce the heat
 and light  resulting from their chemical action on each  other;  but the bodies them-
 selves must  remain permanently  combined, as each retains  its own  excitement,
 and they  hence attract without cessation.   When one body is exactly as negative
 as the other is positive, the resulting compound cannot manifest any signs of elec-
 tro-chemical activity ; but if the charge of the negative body be more powerful than
 that of the positive element, the resulting compound will be negatively excited to
 the amount of the difference  between the two ;  if the  proportions be reversed, the
 new body formed will be positive in the same degree ;  and such compound electro-
 negative and electro-positive  bodies, being acids and bases, attract each other, and
 unite to form neutral salts.
   All that was difficult to  comprehend upon  the theory of Davy is here beautifully
 explained. The  light and heat of combination are produced by  the atmospheres
 of electricity; the permanence of combination by the invariable excitation  of the
 molecules.  The  gradually diminishing intensity of charge, according as the bodies
 formed  become more complex, necessarily  follows; but the assumption that any
 one body  is naturally  and invariably  positive or negative, is contradicted by the
 liistory of almost all the simple substances.
  Thus, if sulphur or arsenic be heated in oxygen gas, they burn, and the combina-
 tion is effected with all the phenomena  of intense action, the resulting compounds
 being acid and electro-negative.  The  sulphur and  arsenic are thus shown to have
 been feebly positive bodies.  But if sulphur  or  arsenic be heated with potassium,
 there is similarly  combustion, showing that chemical combination has taken place ;
and  as potassium is the  most positive body in the  series, the sulphur and arsenic
 must be the negative elements of the compounds.  Sulphur and arsenic are there-
 fore at one time positive, and at another negative.   There is, indeed, no substance
 known which can be said to  be  invariably  negative or positive.  Nor can  the
 amount of negative or positive excitement be in any case looked upon as constant,
 for oxygen is  often found to be less negative than chlorine, and potassium to  be
less positive than iron or than carbon ;  and hence, if electrical forces be considered
 as representing affinitary power, they must be capable of the  same fluctuations in
intensity.
  It was  for the purpose of bringing  Ampere's  theory into harmony  with  the
changes of chemical decomposition, that Berzelius  proposed the modification of it
which  now remains to  be described.   He  suggested that each  body  should  be
looked upon as containing the two electricities, but that the  one might be more
powerfully developed than the other, as in a magnet one pole may be stronger than
the other ; also, from the analogy of certain  bodies, which were  supposed to admit
the passage of one electricity rather than  the other, he imagined that a body thus
excited with the two fluids might discharge the one and yet retain the other.   Thus
oxygen possesses high negative and feeble positive excitation ;  hydrogen an intense.
positive, hut a feeble negative  charge.  When these bodies combine, the phenomena
of combustion follow from the union of the positive fluid of the oxygen with  the
negative of the hydrogen, and the more intense and more permanent charges retain
 the bodies in combination.  To account in this way for certain bodies being at one
 time electro-negative and at another electro-positive, Berzelius considers that, when
 potassium is brought into  contact with sulphur, the naturally feeble negativity of
 the latter  is heightened by induction, while, if the sulphur be acted on by "oxygen, it
 is its positive charge that is increased ; and thus any substance near the middle of
 the electro-chemical series may become positive  or negative, according as it com-
 bines with a body situated nearer to the negative or positive extremity 
 DISENGAGEMENT  OCCURS  AT  LIMITING SURFACES. 191

   This view might explain most chemical phenomena ; but it is, like Davy's theory,
 founded on physical principles which cannot be considered sound.  Thus, although
 the effect of one pole of a magnet may be weaker than another, that only happens
 where the  action is complicated by the existence of more poles than two ;  and in all
 cases the amount of north and south magnetism present is exactly equal.   Also, the
 fact of the  existence of bodies which conduct the one better than the other electricity,
 is now abandoned by all sound reasoners, and cannot be looked upon as even in any
 degree probable in theory.  Indeed, all views like those of Berzelius and Ampere,
 which are  founded on the existence of different degrees of electrical excitement,
 winch represent the different powers of affinity by which chemical substances com-
 bine, must  be now abandoned ; tor it has been proved by Faraday that a molecule of
 oxygen,  in uniting with hydrogen to form water, or with zinc to form its oxide, a
 molecule of iodine or chlorine uniting with lead, with tin, with silver, or with potas-
 sium, bodies so far separated in the electro-chemical scale founded on their reactions,
 evolve in uniting the same  quantity of electricity, and require for their separation,
 when combined, the same amount of current derived from another source.
   Before more definite and correct  ideas  of the electrical relations
 of chemical substances can  be obtained, it is  necessary to study
 somewhat more  in detail  the chemical phenomena which occur in
 the galvanic battery, which,  for simplicity, shall be considered as a
 simple circle, and  in the  liquid through which the circuit is com-
 pleted  ; the former is generally termed the generating, and the latter
 the decomposing cell.
   The  decompositions hitherto  described have been considered as
 resulting from the attractive and repulsive forces of the extremities
 of the  wires, on which  the  charge of the battery was supposed to be
 collected.   Hut, when  the  circuit is completed, no such accumula-
 tion  can exist;  once the  current passes, it is everywhere present
 in equal  quantity and of uniform tension ;  and such forces of attrac-
 tion  and  repulsion, acting upon molecules already electrically exci-
 ted,  were only imagined for the foundation of the imperfect theories
 already noticed,  and, when impartially  examined, are found to have
 no real existence.  It is also  fatal to the idea of attractive forces ex-
 ercised by the poles, that the substances evolved upon their surface
 do not  necessarily combine with them ;  thus, if one platina pole have
 such attraction for oxygen as to separate from  the hydrogen  it had
 been united with, it is unreasonable that it should lose, suddenly and
 completely,  this power, and allow the oxygen totally to escape ; the
 other platina pole behaving similarly to the hydrogen.
   Faraday has definitely shown that the disengagement of the sub-
 stances, which are  separated from each other by the  current, takes
 place in all cases at the bounding surfaces of the body decomposed;
 and that where they are evolved on the metallic
 conducting wires, it is  only because those are the
 limits of  the decomposing fluid.   The proofs of
 this principle are numerous and simple : thus, in
 a glass basin, a partition of mica, a, is cemented so
 as to  be completely water tight, and extending half
 way to  the bottom ; a strong  solution of sulphate
 of magnesia is poured in until  it rises a little above
 the edge of the  partition, and then distilled water  -—...______jj  I
 poured  in on the side c, d,  with such precaution      ^^_\    j
 that it shall not mix with  the  saline solution, but L   Cj^J^~\,
shall  float on it, the surface  separating the two  ^—
liquids remaining perfect at c.  The solution of sulphate of magne
 
192     ELEMENTS  NOT  EVOLVED  ON  POLES.
	X		a ~b			
A	N		■<r-<m		p	B
			c		u	
 sia is now to be connected with the negative pole of a battery by
 means of the platina plate b, and the water with the  other pole of
 the  battery by the plate e, which  dips  slightly inclined  below the
 surface.  When the circuit is completed, the sulphate of magnesia
 and the water are simultaneously decomposed, the oxygen appears
 upon the  plate b, the hydrogen gas upon the plate  e ;  but, although
 the sulphuric acid is liberated freely upon the plate b, no magnesia
 travels farther than the limiting surface of the saline liquor c.  Here
 the metal e serves as a pole to the hydrogen, but not to the magne-
 sia ;  and the water on which the magnesia has evolved has no power
 to prevent the farther passage of the hydrogen.
   If A, C, B be filled with solution of sulphate of soda, and by means
                     of the plates P and N, a current from a battery
                     be passed through it, the acid will collect upon
                     the one and the alkali upon  the other plate:
                     but if, by means of pieces of bladder, a and b,
                     the vessel be divided into three compartments
                     A, C, and B, and the  central one being filled
 with  a solution of sulphate  of  soda, dilute  nitric acid  is poured
 into those at the side in order to afford  a conducting  medium,
 the acid and alkali do not appear at the metallic poles when the cur-
 rent passes, but are evolved upon the inner surfaces of the partitions
 a and b: it is only when, by mechanical filtration, some of the liquor
 of C  passes into A and B, that the slightest trace of sulphuric acid
 or of soda can be found upon the metallic plates.
  By the  electricity of the machine the same principle can be de-
 monstrated : if a slip of paper moistened with solution of iodide of
 potassium be held near the insulated prime conductor of the elec-
 trical machine while in action, and the rubber be connected with the
 ground so as to ensure a continuous discharge of positive electricity
 into the air, iodine will be evolved in quantity upon the point of the
 paper nearest tne prime conductor, while hydrogen and potash may
 be traced  as lar  as. any  liquid conductor  admitting  of  tin ir passage
 goes,   ilere mere is nothing that can be termed a pole ; the iodine
 is discharged upon the  limiting surface, which is here that of the
 atmospheric air.
  Hence the idea of poles which  produce attractions and repulsions
 in a closed circuit must be abandoned, and  some other way of ex-
plaining the decomposition of the liquid elements of the circuit must
be obtained.  The word poles must first be laid aside, and the ex-
pressions proposed by Faraday in their place  deserve universal adop-
tion.   The surfaces, whether of metal, of water, of acid, or of air,
by which the current passes from one kind of conductor to another,
he terms electrodes (rj'eiirpov, 080c), they being the routes through
which the electricity  makes its way.  I  shall therefore, in future,
speak of the positive and negative electrodes in relation to the sur-
faces, generally of metal, by which the battery is brought to act upon
the substance which is to be decomposed.
  Since there are thus no attractive forces by which the chemical
affinities of the substances in the decomposing cell can be overcome,
to  what mechanism can we  attribute the separation  of elements
which occurs 1  Concerning this, as yet, there is only speculation to 
ELECTRO-CHEMICAL  DECOMPOSITION.     193
be presented.  The decomposition is certainly  propagated from
particle to particle, that is to say, at the moment that the molecule
of water loses oxygen at the positive electrode,  a different mole-
cule  gives  off its  hydrogen upon the negative electrode ; neither
the hydrogen  of the former nor the oxygen of the  latter  become
free, but the decomposition is transferred from one particle to an-
other along the line, all particles of oxygen advancing a step against
the current, and the molecules of hydrogen moving in a correspond-
ing manner in the direction  of it.   Thus, if a line  of particles of
water in a decomposing cell be represented       ^  >
before  the  current passes, the electrodes be- -J-O.H. O.H. O.H.—
ing represented by the plus and minus signs,
on the current passing, a molecule of oxygen       ^  q
will be evolved upon the positive, and one of —H. ' tt' ' u' ' 0.+
hydrogen upon  the  negative side,  as  in  the
second line ; and as this motion is participated
in by every molecule of oxygen and hydrogen
in the circuit, they will come into the final po-
sition of the third line.  The current still pass-
ing,  another  molecule of each will be evolv-     "• ' jj_ ' "•  i
ed, as  in the  fourth; and,  ultimately,  all the
intervening water may be  decomposed ;  the       t n u*
separation of the elements  being thus accom-       '  '  '
panied  by  a  continual rotation on  each other of the intermediate
molecules, each molecule of oxygen being successively united with
every  mohcule of hydrogen in the  series, and each molecule of hy-
drogen combining in turn with every particle of oxygen as it passes
along.   In Faraday's words, the current is an axis of power, equal,
and  exerted in opposite directions, by which, in every case  of a
true binary compound, the  molecules of one element are carried in
one  direction, while those of the other constituent move in the re-
verse course.
   From this idea, the  evolution of the iodine, the soda, the magne-
sia on surfaces of air,  of bladder, or of water, is easily understood.
The sulphates of magnesia  and soda are decomposed, because there
exists  in the solution a chain of particles  of sulphuric acid capable
of conveying their bases along, and these are evolved where  that
chain of acid particles is broken, although there may be other con-
ductors to complete the circuit.   The iodine is evolved where the
air touches the  surface of the paper, because the air has no potas-
sium by which it could be carried farther.   The decomposition ap-
pears thus to be  effected,  not by annulling chemical affinity, but
with its assistance, for it is exactly with  those conducting bodies
whose elements have the strongest affinities for each other that de-
composition is most easily  effected.  Thus  iodide of potassium is
decomposed much more easily than iodide of lead, yet the affinity
of potassium for iodine is certainly greater than that of lead for the
same element.
  It is in this manner that arise the remarkable phenomena of transfer observed first
by Humphrey Davy.
  If a solution of sulphate of soda be placed in the glass a, dilute sulphuric acid in
the glass b, and water in the glass c, and they be connected together with slips of
amianthus, moistened to allow the passage of the current, and the positive electrode
                              Bb 
 194     ELECTROLYSIS  AND ELECTROLYTES.

       >^?^^k    ^^^*.        °f a Dattery De immersed in a, and the ncga-
 Jj^c—^;^—7!^^  tive in c, the sulphate of soda will be decom-
  pFElH   (BXil   BwSl   posed, and its alkali will appear  in c, although
  Hr WSr   W^uB   w^W   the acid  in b, through  which  it  must have
   ^ajr^   ^^Mr     ^&t^   passed, retains all its power.  Here, then, was
   QjlL—    Qj\g^--   ^pi^m^  the affinity of the acid in b for soda complete-
   C S^^   ^—s^-   ---     ly annulled by the superior attraction of the
negatively electric pole in c, and this was considered  to be  farther proved by the
acfd preventing the passage of barytes, for which its affinity was so much stronger;
when a contained nitrate of barytes, the earth, on entering into b, combined with
the sulphuric acid, and went no farther.  But in these experiments,  considered at
the time so decidedly in favour of Davy's theory, that which was believed to be the
obstacle «o the passage of the soda is in reality the cause of it.  Had  there been no
acid in b. no alkali could have passed across it, and the barytes remained combined
only because, becoming insoluble, it  no longer formed  any portion of the liquid-con-
ducting medium.
  It has been,  indeed, found, that although a feeble current may
be transmitted through liquid conductors without any  sign  of de-
composition, yet, in general,  the passage of a  more powerful cur-
rent can only be accomplished by means of bodies which are at the
same time  decomposed by its  influence.  Faraday proposes to term
the decomposition  by the current electrolysis [rjXeKrpov, Xvuf\, and
such bodies as undergo  electrolysis  electrolytes.  It is, therefore,
only electrolytes that are capable of conducting,  and they do so  by
the opposite  directions  in which the chains of liberated  particles
move.   That electrolysis may occur, it is necessary that the sub-
stance be in the liquid state, and hence all conducting power is lost
when the body becomes solid ; ice is a non-conductor, and it is only
by being melted that the chlorides and iodides of lead  and silver,
and such bodies, become capable of conduction, and of being hence
decomposed.   But there  are many bodies which insulate when cold,
and yet, when heated, allow the current to pass  even before they
fuse, its passage being unattended by any electrolysis, even though
the current  be very powerful.   Sulphuret of silver, iodide and chlo-
ride of  mercury, and  fluoride of lead, are remarkable examples  of
this anomaly.
  Faraday, considering that the words electro-positive and electro-
negative involve too much those ideas of attractive and repulsive
forces emanating from the poles, which have been proved  to be  in-
correct, proposed  some  changes of nomenclature, which, if not
adopted, deserve to be at least described.  If we  consider  a voltaic
battery lying on the ground, with the  positive end to the east, and
the wire connecting the ends bent into  an arch,  similar to that
which the sun describes  in his daily rotation, the current  will flow
up from  the point of the sun's  rising, and pass down into  the battery
opposite the point at which he sets.   If the wire be now interrupt-
ed by a decomposing cell, the surface at which the current enters
the liquid may be termed the anode (ava, upward), and the other the
cathode  (tcard, downward) ; oxygen, chlorine, and such  bodies  are
evolved  upon the surface of the anode, while from the cathode hy-
drogen  and the  metals are liberated.  The elements which, by their
combination, form electrolytes, Faraday proposes  to term ions, ln\ii,
and  to  distinguish them  into  anions which  pass  to the  anode, and
cations  which  pass to the cathode.   Electro-negative  bodies'  are
therefore anions, and electro-positive substances are cations  in Far- 
THE CHEMICAL VOLTAMETER.         195
 aday's nomenclature.   These  names are shorter, and involve less
 theory than the older terms, and hence deserve adoption.
  The most  important principle that has  been as yet discovered,
 connecting the agencies of electricity and affinity, is the law of def-
 inite electro-chemical decomposition.   If the same current of elec-
 tricity pass  through a  series of electrolytes,  it will decompose  a
 quantity of each which is proportional to  its chemical equivalent.
 Thus, at the  same time and by the same force, there are obtained
  8   grains of Oxygen and   1 of Hydrogen from  9  parts of water.
 35 4   "   Chlorine and   1  " Hydrogen  "   36 4   "  muriatic acid.
 35 4   "   Chlorine and 108 "Silver     "  1434   "  chloride of silvei.
 126-3   "    Iodine and  103 6  " Lead      "  229 9   "  iodide of lead.
  The principle of definite electro-chemical action may be applied
 to measure the quantity of  electricity which is circulating in the
 current, for by collecting the substances evolved in the decomposing
 cell, we may obtain a standard to which all other effects may be re-
 duced.   In such case the decomposing  cell becomes a voltameter, or
 measurer of voltaic electricity.   One    jj
 of its most convenient forms consists
 in a conical vessel, A, terminated by a    i
 tube, B,  in the neck of which are sol-   f
 dered the platina electrodes in connex-   h~
 ion with  the battery ; the vessel and   p
 tube being filled with  water, which is A/V
 rendered easily  decomposible by the ^•'^7.
 addition of sulphuric acid, the circuit  ^~~"J-
 is completed ; a quantity of oxygen and hydrogen,  proportional to
 the amount of electricity which passes, is evolved, and, issuing from
 the aperture  at  C, may be collected in  an  inverted glass and  meas-
 ured.  A variety of other forms, not differing in principle, have been
 proposed and are in use.
  If the absolute identity of electrical  and chemical agency be in-
 sisted on, then, in all electrolytes, the elements must be held togeth-
 er by the same  force, since they require the same amount of elec-
 tricity to  produce decomposition; and we  should return nearly to
 the  principles of Berthollet, that chemical affinity was equally pow-
 erful for  all bodies, and merely appeared  to vary from external in-
 fluences;  but this would be a rash and unphilosophical conclusion;
 the  electrolytes are but one class of chemical bodies, those which
 are  primary compounds, of an equivalent of each element;  the cur-
 rent does not act upon  deutoxides or  bichlorides, and on double
 salts its agency is exceedingly complicated.   AH that  can  be infer-
 red  from this very beautiful result is, that the elements of bodies
 combine, in separating from each other under the influence  of a cur-
rent, all with  the same quantity of electricity, and that, as the spe-
 cific heats of the ultimate particles of bodies  have  been already
found to bear a simple  relation to each other, the specific electrici-
ties may follow an equally, or still more simple law.
  Having  thus examined the important phenomena produced in the
decomposing  cell, the current being considered as  originating in
any  sufficient source, we  shall  pass to the discussion of what oc-
curs in the generating cell, where the current which passes through
 
196     ACTION  IN  THE  GENERATING  CELL.
 the other is evolved by the mutual  action of the  liquid and solid
 elements of the voltaic battery.
   For the generation of the current, it has been already shown to
 be necessary that the liquid excitant should be an electrolyte, and
 that the solid elements should  occupy positions in the electro-
 chemical scale as remote as possible from each other m relation to
 the liquid which  is employed.  That the solid elements also should
 be conductors, by which the selection is limited to the metals and
 to some forms of carbon.  Now, when a slip of zinc is immersed in
 an electrolyte, which we shall, for simplicity, consider for the future
           to be muriatic acid, the particles of the acid are brought
           into a state of excitation, the molecules of hydrogen  be-
           coming positively excited, and those of chlorine becom-
           ing negative.  This condition has been already described
           (page 132) as being that of the acid particles; but it is
           now necessary to indicate more nearly the  immediate
 manner in which it  is produced.  The mass of zinc  itself,  which
 we before considered as having, like a magnet, its positive excita-
 tion referrible to one, and its negative to the other extremity, must
 also, like the magnet, be looked upon as consisting of a great num-
 ber of excited  elements, each  of  which has its positive and nega-
 tive  extremities ; or, for greater definiteness, they may  be consid-
 ered as grouped  in pairs, of which  one molecule is positively and
 the other negatively excited.   The condition of the slip of zinc of
 the last figure may therefore be represented as in the figure at the
               A             side, the particles of zinc  being con-
    rY.V ifj.^rOi/^r^/^l  tained in the  shaded bar, and those
 ^J^J^^J^^^^^^^zy  of  the liquid, consisting of chlorine
  Zn. Zn. Zn. Zn. CI. H. CI.  H.  and hydrogen, represented outside
 of it.  The terminal particle of zinc becoming positive, and the
nearest particle of chlorine becoming negative, there would result
immediate  union if no other action  interfered ; but the chlorine is
held back by the positive  molecule of hydrogen with which it is
united, and so the action continues balanced, no matter how far the
series may extend on either side.   If, now, the plate of copper be
introduced so «■   . cmplete the circuit, and to allow the  passage of
the galvar'   urrent, it is easy to see how the decomposition of the
 exciting nuid follows; for although, in the arrangement above de-
 scribed, the inductive excitement is most active at A, and diminish
 es from thence as it  extends along the zinc upon the one hand, and
                through the fluid upon the other,  yet when, as in
                the figure, the circuit is completed, the action be-
                comes equally powerful all through ; the particles
                of copper  assume a condition similar to those of
                the  zinc, but in the reverse order, the molecule
                next the acid  being negative, and that becoming
                positive which is in contact with the zinc, and hence
                a complete chain  of inductively polarized particles
                being established, precisely such as are represented
                by cuttings of silk thread which convey a current
 from an electric machine through  oil of turpentine ; the molecular
 arrangement being represented in the following  figure.   Such  be-
 
ORIGIN  OF  THE  GALVANIC CURRENT.     197
 ing the position  of the mutually-excited
 molecules, the electricities of the particles
 of  zinc and chlorine nearest to each other
 combine, and their neutralization is follow- Zn
 ed  by that of the entire chain; the adjacent
                    particles of zinc  and
        ^^Jk     chlorine  then  unite, ^^CY^/CV+^
 ZincX*#  \\^Cop. and the hydrogen, dis-     V>'\_>/VVV_y
                    engaged,  is   thrown         Acid-
                    upon  the second  particle  of chlorine,  its hy-
                    drogen upon the  third chlorine  molecule,  by
                    which the  hydrogen it had previously been
                    united with, being thrown off", is emitted under
                    the form of gas.
  The three distinct stages in this reaction  are, therefore, 1st, The
 mutual excitation, by inductive polarization of the zinc and muriatic
 acid.  This is the fundamental fact due to the chemical relations of
 these bodies.   2d, The completion of the chain of inductively polar-
 ized particles, by the intervention of the copper plate and connect-
 ing wire.  3d, The  passage of the current,  and the consequent de-
 composition of the liquid electrolyte in the  cell, the chlorine being
 evolved upon the zinc, with which  it enters into combination, and
 the hydrogen being eliminated upon the surface of the copper plate.
  The  source of the current is therefore not to be found in  the de-
 composition of the acid, for it precedes  it; but the quantity of chem-
 ical action in the generating cell is proportional to  the quantity of
 electricity which passes, for  it is produced  entirely by its agency.
 There is, therefore, no difference in reality between the generating
 and the decomposing  cell  ; the action  in each is equally produced
 by  the  passage of the electric current  ; but  in the generating celh
 one element at least, the chlorine, is absorbed by the electrode (the
 zinc) on which it is evolved, and the amount of obstacle presented
 to the passage of the current  is proportionally less.
  Such is the theory of galvanism which I believe to  be most con-
 sistent with all the results hitherto  obtained.  The  current  cannot
 have its origin in the contact of solid bodies, for it remains the same,
 no  matter how much the circumstances of contact maybe changed;
 and by every alteration of the conditions of chemical  action, it va-
 ries in direction and in power, although the relations of the solid
 bodies which are in contact are not affected.   Neither  does the cur-
 rent arise from the transfer of elements which occurs  in the  gener-
 ating cell, for,  on the contrary, the transfer of elements results from
 the  passage of the current, indicating its direction and measuring
 its amount;  but the current arises from the continuous restoration
 through the copper, or positive element, of the excitation produced
 by the tendency of the zinc to  combine with the chlorine of the mu-
 riatic acid.  In fact, although I have hitherto considered the zinc as
 only influencing the acid by means of a disposition to unite with one
of its constituents, yet such expressions, being rather abstract and
 indefinite, may  in the present case be  laid aside.  The zinc does,
on immersion, decompose a certain  quantity of acid, of which the
hydrogen is evolved  in the form  of gas, constituting upon the sur- 
 198 COMPOUND  BODIES  FORMED BY  THE  CURRENT.


 face of the zinc  an exceedingly thin layer.   The chlorine is then in
 a state  of combination, which is not without analogy in other cases ;
 that is,  in presence of two substances for which its affinity is equal-
 ly intense, it is disposed  to unite with either, according as external
 forces intervene, and is determined  to the zinc  by the establishment
 of the current.
   The  proofs that hydrogen must be thus nascently liberated upon
 the surface of the zinc are to be found  in  a phenomenon already
 noticed under the head of affinity—the  precipitation  of one metal
 from its salts by means of another having a  greater affinity for ox-
 ygen than  it.   If we immerse in a solution of sulphate of copper a
 slip of pure zinc, there is instantly a deposition of copper,  which
 we must ascribe to the superior affinity of zinc  for  oxygen and sul-
 phuric acid ; but when the zinc has  become thus sheathed in  metal-
 lic copper, the decomposition would cease, by the access of the acid
 being prevented, were it  not that the copper deposited  acts  as the
 copper element  of a galvanic circuit, and the subsequent decompo-
 sition proceeds,  each new portion of copper being deposited on the
 outside, farthest from the zinc,  the  action of which becomes  thus
 at every moment more intense.  If hydrogen had a physical consti-
 tution,  such as would enable it to act as the positive  element of a
 simple galvanic circle, then, no doubt, the  purest zinc would decom-
 pose the muriatic acid, the circuit being completed by the hydrogen
 evolved; but such is not the case, owing to its gaseous form;  but it
 being that  alone  which is the obstacle, the previous step, which de-
 pends simply on  the chemical affinity of hydrogen and chlorine, may
 reasonably be considered  to have occurred.
  The action of electricity in separating the elements of bodies is scarcely of greater
 interest or importance from the ideas it suggests of the nature of chemical affinity,
 than it becomes as a means of presenting to each other, under the most favourable
 circumstances for union,  the different elements  of the voltaic circuit, and thus
 causing the formation of bodies for whose construction the ordinary processes of
 the laboratory are much too violent and abrupt.  In this way some of the most re-
markable  substances of the mineral kingdom may be artificially produced, the se-
cretion of the metalliferous ores into the veins and cavities of rocks accurately rep-
resented, and bodies, whose affinities for each other rank as the most intense, com-
pletely, though silently and gradually, separated from each  other.  It is to Becque-
rel that we owe almost all our knowledge of this important function of electricity;
from him we  have also received the important lesson, that it is not in the brilliant
effects of the  great batteries of Davy or of Daniell that we  must seek a clew to the
history of the electrical processes of chemical affinity,  but in the slow but uninter-
mitting action of currents of such low intensity that a drop of pure water would be
an insuperable obstacle in their path.  The electricity to be employed in the artifi-
cial formation of compound bodies must be  such as is generated by a single pair,
and these generally of metals whose similarity prevents that current from being of
great amount.
  These phenomena, into the examination of which I cannot enter with much de-
tail, are best observed by means of a tube bent into a  U shape, and at the bottom
               of  which is interposed a  porous partition of clay  or  plaster of
               Paris ; the liquids, whose mutual reaction is to generate the new
               substance, are placed in the legs of the tube, one at each side of
               the partition, through the pores of which  they gradually mix with
               each other.  The voltaic current is then supplied either  by con-
               necting the liquids with the poles of a feeble battery, or by im-
               mersing in one leg a zinc, and in the other  a copper  or platina
               plate, connected by a wire with each  other.   If a solution of car-
               bonate of soda and of sulphate of copper be thus brought to act
               on one another,  a double carbonate of copper and soda  crys-
               tallizes on the plate immersed in the copper liquor; and if then
 
         SYNTHETIC  ACTION  OF  ELECTRICITY.     199

the solution of soda be replaced by ordinary water, a new current is generated
which decomposes the first product, and forms a new crystallization of carbonate of
copper.   If the zinc leg be filled with  a solution of oxide of zinc  in potash water,
and a solution of nitrate of copper be placed on  the copper side, a crystallization of
oxide of zinc is produced upon the  zinc plate, and a deposition of crystallized cop-
per upon  the metallic surface in the other tube.
  By using two  liquids  which  have unequal chemical  actions  on a
strip of metal, this  may be made to precipitate  itself, being reduced at
one extremity according as it is dissolved at the other.   Thus, if the
glass A be filled with solution  of nitrate of copper to a, and then water,
rendered slightly acid  by nitric  acid, be gently added, up to the level
of B, a slip of copper, introduced so as to present equal surfaces to
the two liquids, generates a current which passes up through its mass,
and down from the lighter to the  denser fluid :  the copper  dissolves,
therefore, above, and the salt formed being electrolyzed by the current,
its metal is deposited on the lowest surface under the form of crystals,
and  this  is continued until the free acid,  and hence the  electromotive
force in the liquid, becomes equal, when, of course,  no current passes.
  Dr. Bird, who has extended considerably the results obtained by Becquerel, has
constructed an apparatus for such reactions, with which  he has obtained, in an iso-
lated form, those  simple bodies,  as boron, silicon, potassium, &c, whose compounds
resist ordinary means most obstinately.  It consists of a  generating and of a decom-
posing cell.   This last is a glass cylin-
der, a, within another glass cylinder,
b.  The  inner one, a, is four  inches
long, and an  inch and a half in diame-
ter,  and  is closed at the lower end by
a plug of plaster of Paris, 0 7 inch in
thickness.   This cylinder is supported
within the other, b, which is an ordi-
nary jar, about eight inches deep and
two  inches  diameter, by  means  of
wedges of cork.  A piece of sheet cop-
per, c, four inches long and three inch-
es  wide, having a  copper conducting
wire soldered to  it, is loosely coiled up
and placed in the inner cylinder, while
a piece of  sheet zinc, of equal size, is  also coiled up and laid on the bottom of the
outer cylinder, it being also furnished with a conducting wire.  The  outer cylinder
is then to be  nearly filled with a weak brine, and the smaller with a saturated so-
lution  of sulphate of copper; the two fluids being prevented from  mixing by the
plaster of Paris diaphragm.   After  it has been in action  for some weeks, chloride of
zinc is found in the external cylinder, and beautiful crystals of metallic copper, fre-
quently mixed with  the ruby protoxide (closely resembling the native ruby copper
ore), and large crystals of sulphate of soda, are found adhering to the copper plate
in the smaller cylinder, especially on that part where it touches the plaster diaphragm.
The apparatus is completed by the decomposing cell, which is, in fact, a counterpart
of the battery itself, consisting,  like it, of two glass cylinders, one within the other,
the  smaller one  having a bottom or  floor of  plaster of Paris fixed into  it; this
smaller tube may be about half an  inch wide and three  inches in length, and is in-
tended to hold the metallic solution submitted to experiment, the external tube, b,
into which it is immersed being filled with a weak solution  of common salt.   Into
the latter solution, a slip of amalgamated zinc (for the positive electrode),  soldered
to the wire coming from the copper plate  of the battery,  is immersed, while for the
negative electrode,  a slip of platina foil, fixed to the wire from the zinc plate of the
battery, passes through a cork,  c, fixed in the mouth of the smaller  tube, and  dips
into the metallic solution it contains.
  The influence which electricity thus exercises upon affinity, and the modifications
in its results  producible by its means, although proving a most intimate connexion,
do not go, as  I believe, so far as to demonstrate a complete identity of cause.   It
is possible  that, hereafter, some sublime  generalization  may embrace the phenom-
ena of heat, of light, and of electricity, of cohesion and gravity, as well as of chem-
ical affinity, within one law, and indicate  how,  by varied manifestations of a single
agent, their separate peculiarities may arise ; but, though we may look forward to
 
200    E L E C T R O-C II EM ICAL  THEORY   PROPOSED.

such a state of science, we dare not rashly seek to anticipate its approach ;  and I
look upon  electricity  as producing and being produced  by  chemical phenomena,
precisely as we find heat to influence as well as to be evolved by chemical combi-
nation.
  Where  electricity  is  brought into play so  powerfully by the action of a simple
body upon  a compound  fluid, it is.  I consider, unreasonable to imagine that,  in the
combination of simple bodies, or of compound  bodies with each other, no electricity
should be set  free, particularly when it is proved that in such cases some electri-
city does appear, although in quantity bearing no proportion to that of the feeblest
galvanic battery.  If  I were to suggest an electro-chemical theory, such as  might
agree with the facts that have hitherto been discovered, I should  consider that bod-
ies  in their free state  are  perfectly destitute  of excitation ; hat that chemical
union, or the degree  of intimate approximation which  precedes union, may be a
source of  electrical disturbance, and is that which, in all ordinary cases, gives ori-
gin to the electricity employed in our experiments.  When united, bodies are like-
wise destitute of electrical properties; in iodide of potassium, the bond is the affin-
ity of iodine and potassium for each other, and  not that the iodine is in a perma-
nent state of negative excitation while the potassium remains positive.
  If hydrogen gas be burned in oxygen, there is evolution of electricity, of  which
only a trace escapes immediate recombination under the form of light and heat, but
the existence  of which, in a  highly intense form, has been demonstrated by  Pouil-
let.  The  oxygen and the vapour of water produced assume the positive  condition ;
the residual hydrogen becomes negative.  If carbon be burned in oxygen, there ia
likewise combustion and evolution of electricity, of which the positive  passes  off
with the carbonic acid,  and the negative rests upon the carbon.   The evolution of
heat may be in these cases an independent  effect of combination, but I would look
upon it as being more probably the result of the union of the electricities  evolved.
If the bodies which act upon each other are dissolved in water, there is no combus-
tion, but heat  is still evolved, and  the electricities unite with  one another without
the necessity  for any intermediate circuit.   It is only where the replacement of
one body by another occurs, that the establishment of the chain  of inductively  po-
larized molecules becomes necessary ; for the particles of zinc and hydrogen, which
become oppositely  united, have no  power to combine, and hence cannot be restored
to neutrality unless by the medium of a third  body, to which both may impart their
excitations.  That the zinc and hydrogen  upon the one hand, and the copper and
hydrogen  upon the other, do  not unite, is, I  conceive, fatal to those views  which
assume the identity of chemical and  electrical, or, as they call it, current or  induc-
tive affinity ;  for if a molecule of copper in the acid stood in the place of, and acted
as a molecule  of chlorine, it should unite with the hydrogen in place of allowing it
to pass off free.
  The act of chemical union being  such as to  produce electrical excitation and dis-
charge before it is completed, and  the permanent combination of the elements
being the  result of the  return to  the neutral state, it is easy to understand that
when these conditions are reversed, the chemical affinity should be superseded, and
the bodies brought into the state in which they had been at the moment of excita-
tion, and while their  elements, oppositely  excited, were yet separate  from each
other.   A  compound body is therefore, as I apprehend, decomposed by  the bat-
tery, from having this electrical state given to it by the current; and the transfer
of its elements across the liquid is accomplished by a series of neutralizations and
excitations, accompanying the unions and decompositions by which they pass to the
electrodes, on  which  they yield up their ultimate excitation, and appear isolated
and completely  neutral. The  quantity of electricity necessary to decompose a
body  is therefore  the  same as it had evolved when  its elements  entered into
union, and it  should  hence  follow that the current of electricity  evolved  in  the
union of chemical  equivalents of the simple  bodies with each other should he  the
same.   That this actually occurs  appears probable from the  analogy of heat;  an
equivalent of oxygen, in combining with various metals, evolves the same quantity
of heat, and if the heat be a consequence of the neutralization of electricity, the quan-
tity of this evolved should be the same also.   It appears, likewise, that an equiva^
lent of sulphuric acid, in combining with different bases, evolves the same quantity
of heat, and to decompose  the various salts thus formed, the  same  quantity of
electricity should be required ; and  hence, that the two actions, so completely equiv-
alent to each other, may satisfactorily be referred to the same source.
  Such is the interpretation I put upon the phenomena of electro-chemical decom 
    becquerel's  ELECTR O-C h e m I c a l  theory.  201

 position, and the relations of electrical forces to affinity.  In the molecular condition
 of polar  excitation which accompanies the passage of a  current, I adopt fully the
 peculiarly explicit mode of representing  he actions of the  bodies on each  other
 proposed by Graham, but I consider it too hypothetical to assume  that such mole-
 cular state naturally exists in bodies ; it may or it may not; but in the absence of
 evidence that it does, I am not inclined to presuppose it unnecessarily.  I look upon
 the current as being produced by the union of opposite polarities, which are them-
 gelvcs not the cause, but the consequence, of the  chemical  affinities of bodies.
 Graham is not disposed to admit that the union of simple bodies may be accom-
 panied by an  electrical phenomena, and to exclude also from the application of an
 electro-chemical theory the combination of acids and of bases with each other, as
 not capable  of generating currents ;  but the reason of this is, as I imagine, that the
 currents so  generated are necessarily closed.
   In  concluding the admirable  treatise on electricity with which he has enriched
 scientific literature, M. Becquerel details the views which  he  has adopted regarding
 the electro-chemical relations of bodies ; and although they are not expressed with
 the definiteness which  might be wished  from so admirable a  philosopher, I shall
 endeavour, in concluding this section, to  give a short description of them.  In the
 main, they do not differ much from the principles of electro-chemical combination
 which I  have long since adopted, and which have been already noticed.
   M. Becquerel considers that in all bodies there  is  distributed a quantity of elec-
 tricity indefinitely great, which is so intimately connected with  their  molecular
 constitution, that it is disturbed, and excitation produced in  all cases where mole-
 cular disarrangement is produced ;  hence pressure, friction, an unequal distribution
 of heat,  <Stc, are sources of electricity.
   Chemical affinity is also a source  of electrical disturbance.  When an  acid com-
 bines with an alkali, the first sets free positive electricity, and the  second an equal
 quantity of negative electricity ; these two combine immediately in  the liquor, form-
 ing neutral  fluid, and produce as many currents as there had been particles in ac-
 tion , now this  multitude of little currents ought to determine the production of a
 quantity of heat, depending on the energy with which the affinity was manifested,
 and tin;  conducting power of the  liquid.   In decompositions, the  electrical effects
 are  inverse, that is, the  acid takes the negative, and the  alkali  the positive electri-
 city ; hence it may be  concluded, as M. Becquerel had already stated with regard
 to aggregation, that if electricity does not constitute  affinity, it  is at least indispen-
 sable to  its manifestation, since it is always subjected to the same  laws every time
 that simple  or compound atoms unite or separate.  From all considerations, it ap-
 pears that the electricity produced  by chemical action is only an effect resulting
 from  the action of the affinities brought into play ; and this effect being brought into
 inverse action in decomposition, announces  at the same time  a molecular electric
 state, indispensable to the permanent union of the elements of compound bodies.
  To explain  decomposition by a current of electricity, M. Becquerel adopts Am-
 pere's idea of electrical atmospheres, although he  denies that any  bodies are natu-
 rally or permanently in  a positive or negative condition;  but he supposes that the
 neutral condition of a body consists  in the molecule  being either positive or nega-
 tive, and being surrounded  by an atmosphere in an opposite state.  When bodies
 unite, the union of their atmospheres produces light and heat, and the molecules re-
 main  excited while in union, although the union  is the  cause of the electrical dis-
 turbance, ami not its effect.   Now, when zinc is put in contact with water, this last
 is decomposed, and there is hence a disturbance of electricity;  the particle of zinc
 abandons its negative atmosphere, and unites in a positive condition with the neg-
 ative and nascent oxygen ; the hydrogen is liberated  nascent also,  and highly pos-
 itive ; in this state the oxygen would be balanced between the two  equally positive
 particles  of zinc and hydrogen, and the decomposition could not proceed; but, if a
 slip of copper be introduced, this supplies a  negative atmosphere to the hydrogen,
 which, becoming neutral, is evolved  as gas, and, transferring its positive electricity
 to the point of contact with the zinc, neutralizes its excess of negative excitement,
 and generates the current.   M. Becquerel  refers the chemical action of the current
in the decomposing cell to each electricity setting the same electricity of the com-
pound in motion in the same direction with which  the particles are transferred by
a series of combinations and decompositions, as has been already described,  until
tin- limits of the substance are attained, and then the elements are evolved in the
neutral state.
  M. Becquerel has endeavoured to apply the agency of electricitv to determine the
                                      Cc 
202
LAWS  OF  COMBINATION.
relative affinities which bodies have for each other.   His principle is as follows : it
nitrate of copper and nitrate of silver be dissolved together in equal quantities, and
decomposed by a galvanic current, the nitrate of silver alone is at first affected, be-
cause the affinity of the  silver for the oxygen and acid is so much less than that
of the copper for the same.  But, when the quantity of nitrate of copper is gradually
increased, a term is arrived at when the electric current is exactly equally divided
between the two metals, the greater quantity of copper making up for the greater
resistance it offers to the decomposing power.  His results are, that when the solu-
tion contains twenty parts of copper  to one of silver, the current acts equally on
both; when the copper is 25 to 1, the current acts  as if it divided itself g to the
copper and -J- to the silver; and when the quantity of copper is thirty times that
of the silver, there  are three equivalents of the copper salt decomposed for one of
the salt of silver.  M. E. Becquerel has essayed the same important problem in a
different way, by testing the power of  solutions of chlorine, iodine, and bromine, to
absorb nascent hydrogen and nascent oxygen, evolved in their mass by means of a
galvanic current.  His results appear  to show that the affinities are expressed by
the numbers; for
         Hydrogen.
For Chlorine.....922
    Bromine.....712
    Iodine......212
          Oxygen.
For Chlorine.....169
    Bromine.....380
    Iodine......469
  These two series are, however, independent of each other, and afford no mutual
term of comparison whatsoever.
  It is to be trusted that such investigations, conducted with the ingenuity and ac-
curacy which the  Becquerels can so well apply, may lead to results of the highest
interest to science. The reduction to numerical laws of the influence of quantity
on affinity, and the determination in numbers of the tendencies of the simple bodies
to unite, would certainly advance the  condition of chemistry, as an exact science,
in a remarkable degree.
CHAPTER  IX.
ON  THE LAWS OF COMBINATION.
  The general nature of affinity, and the modifications which it un-
dergoes from the influence of the physical agents, having been now
stated, I shall proceed to discuss the numerical laws to which its re-
sults are subjected, the discovery of which was the first step in con-
ferring upon chemistry the character of an exact science.
  It is characteristic of chemical  affinity, that the  proportions in
which bodies are  brought to  unite  by its agency are limited  upon
both sides, whereas, in those cases where molecular forces alone
prevail, the proportions, although perhaps limited  in one direction,
are  indefinite in the other.   Thus  a saturated solution of  chloride
of sodium cannot take up any more salt, but it may be mixed with any
quantity of water, whereas the chloride and the  sodium, which con-
stitute the salt, form it  only in certain proportions which are inva-
riable, 100 parts containing always 39-66  of  sodium and 60-34  of
chlorine.  If it were not for this constancy of proportion, the science
of chemistry could never have advanced beyond its merest elements;
for, had chlorine and sodium  been capable of combining in all inde-
terminate proportions, or had the properties which we recognise in
chloride of sodium been ascribable  to compounds of those elements 
CHEMICAL  EQUIVALENTS.
203
in every possible proportion, no accurate ideas regarding the con-
stitution or properties of bodies could have been acquired, and none
of the benefits derivable from experience or experiment could have
been attained.   The first law of constitution is, therefore, that the
composition and properties of any given substance are always the
Bame.
  When, by the intervention of superior affinities or by double de-
composition, a compound body is decomposed and a new compound
formed, the proportions by weight of the various substances brought
into action have a constant relation to one another, and, as they rep-
resent the quantities of  the bodies which exercise equal, or, at least,
equivalent  combining powers,  they are termed, when reduced to
numbers, the combining proportions or equivalents of these bodies.
Thus, if 100 parts of oxide of copper be heated in a current of hy-
drogen gas, it is reduced, and the hydrogen, uniting with the  oxygen
which it contained, forms water.  In the 100 of oxide there were 79*83
of metallic copper and 20-17 of oxygen, which last, taking  2*52 of
hydrogen, forms 22-69  of water. Now, in this case, the 2*52 of hy
drogen produce the same result of satisfying the combining power of
the 20*17 of oxygen as the 79-83 of copper ; and hence these quanti-
ties of hydrogen and copper are equivalent to each other.  This ex-
ample may be, however, brought much farther.  If, in place of treat-
ing the oxide of copper by hydrogen gas, it had been acted on by
chloride of hydrogen, the oxygen should have been carried off by the
hydrogen,  which would abandon its chlorine  for that purpose ; but
the chlorine should not be set free;  it, on the contrary, would unite
with the copper from which the oxygen had been taken, and the re-
action would be so proportioned that the quantity of copper reduced
by the hydrogen of the chloride of hydrogen would be exactly suf-
ficient to unite with all  the chlorine which was therein contained, and
form with it chloride of copper.  In this case the 100 parts of oxide
of copper would require for its decomposition 91*73 of chloride of
hydrogen,  and there would be formed 169*04 of chloride of copper
and 22-69 of water.  Here, as before, the 20*17 of oxygen  uniting
with 79*83 of copper and 2*52 of hydrogen, show their  equivalency ;
but we learn in addition, that 79*83 of copper and 2*52 of hydrogen
unite equally with 89*21 of chlorine, and hence that that quantity of
chlorine corresponds, and is equivalent in combination, to 20*17 of
oxygen.
  Starting  from  this point, we may proceed to a still more  extend-
ed range of instances.  If we treat sulphuretted hydrogen gas with
iodine, we find that it is totally decomposed, sulphur being pre-
cipitated, and iodide of hydrogen being formed.  Now, taking the
quantity of the sulphuret of hydrogen, containing the weight obtain-
ed in the former example, 2*52 of hydrogen, we find it to  be 43*09,
and hence to contain 40*57 of sulphur, which separates by the action
of the iodine, of which  318*28 parts, uniting with the 2-52 of hydro-
gen, form 320-79 of iodide of hydrogen.  If this iodide of hydrogen
be next treated with chlorine, it abandons its iodine, and forms 91*73
of chloride of hydrogen.
  Setting  out, therefore, from 100 parts  of  oxide of copper, and
tracing its  elements throus"h a variety of decompositions, in all of 
 204    SCALES  OF  CHEMICAL EQUIVALENT".

 which the quantities engaged effect the same purpose of satisfying the
 tendency to combine, we found for the numbers which  express the
 equivalent quantities of the simple bodies employed the following:
    Copper......79-8;?         Chlorine.....89-21
    Hvdrogen.....252         Sulphur.....40 57
    Oxygen......20 17         Iodine......318 28
 and as the compound bodies formed are also equivalent, from their
 being produced by the  same,  or  equivalent combining  actions, we
 may express also in numbers their combining proportions thus:
    Oxide of copper  .  .  .  10000         Sulphuret of hydrogen .  43 09
    Oxide of hydrogen  .  .  22 69         Iod ide of hydrogen .  .  32079
    Chloride of hydrogen  .  9173         Chloride of copper .  .  169 04
  It is evident that if, in place of oxide of copper, any other metal-
 lic  oxide reducible  by hydrogen had been employed, its  equiv-
 alent should have been obtained,  and in this way the equivalents of
 the majority of metals have been  determined.
  These numbers are quite arbitrary; and  any other  body in  the
 list might as well have been taken for the origin as oxide of copper.
 In practice such numbers are reduced to a standard, which is taken
 as 1 or 100, and  for this purpose, oxygen or  hydrogen, the most
 important bodies, are selected.
  Any number experimentally obtained,  as  the above,  may be re-
 duced to the standard scale by the rule of simple proportions : thus,
 the equivalent of copper being 79*83, oxygen being 20*17, and  hy-
 drogen 2*52, it is
            20*17 : 79*83 :  : 100=395*7  Oxygen  =100
         and 2*52 : 79*83 :  :    1 = 31*71  Hydrogen =1

  It is difficult to decide which of the two scales thus  formed  de-
 serves preference :  the  hydrogen scale has been, by the authority
 of Davy, so long prevalent in these countries,  that  it is difficult to
 supersede it; and it possesses the advantage that  hydrogen has the
 smallest equivalent of all bodies.  The standard of oxygen is, how-
 ever, for use, the  more convenient,  as, in consequence of the great
preponderance of bodies in which oxygen exists, the calculations
are much simplified by its number being 100; and there are  but
two or three bodies which, on that scale, require to be expressed
in a fractional  form.
  When the study of these equivalent proportions first occupied the
minds of chemists, Doctors Prout  and  Thompson  were led, from
 speculations regarding the physical  constitution of gaseous bodies,
to suggest that the  equivalent  numbers of all substances were sim-
ple multiples of that of hydrogen;  and as, representing hydrogen
by 1, the other numbers therefore became all whole numbers, "the
 scale acquired thereby considerable simplicity.   The researches of
Berzelius appeared, however, to controvert that hypothesis ;  and in
his numbers, which are,  for the most part, those given in the follow-
 ing list, no trace  of such  a law can be detected: later  researches
 have also, in the hands of Turner and of Penny, afforded additional
 support to  this oninion ; but Phillips has lately reopened the dis-
 cussion, and uumas is inclined to  consider the original views of
 Prout as being probably correct.   In any case, the numbers given 
SCALES  OF CHEMICAL  EQUIVALENTS.    205
in the list must be looked upon as being, in a slight  degree, still
open to revision.
  In the following table, the equivalents of all the  simple bodies are
expressed on each of these scales ; and throughout this work the
two equivalent numbers will be given for each compound body, ex
cept where it is otherwise remarked.
Nimei of Elements.	Equ.valen...					Equivalents	
	U.— 100 17L2	u=i				O. = l00 | H.= l	
Aluminum . . .		13 7 !'Mercury . . . .				1265 8	101 43
Antimony . . .	16129	129 2 'iMolybdenum				5985	4796
Arsenic ....	940 1	75 34	Nickel . .			3697	2962
Barium ....	856 9	68 66	Nitrogen			1750	1400
Bismuth . . .	886 9	71 10	Osmium			12445	99-72
Boron ....	1362	1091	Oxygen .			1000	801
Bromine . . .	978 3	7839	Palladium			6659	53 36
Cadmium . . .	696 8	5583	Phosphorus			3923	31 44
Calcium ....	2560	20 52	Platinum			12335	98 84
Carbon ....	760	608	Potassium			4899	39 26
Cerium ....	574 7	46 05	Rhodium			6514	52 2
Chlorine . . .	442 6	3547	Selenium			494 6	39 63
Chromium . . .	351 8	2819	Silicon .			2773	2222
Cobalt ....	3690	29 57	Silver			1351 6	1083
Colutnbium. . .	2307 4	184 90	Sodium .			290 9	2331
Copper ....	395 7	3171	Strontium			5473	43 85
Fluorine ....	233 8	1874	Sulphur .			201 17	IP 12
Glncinum . . .	331 3	26 54	Tellurium			801 76	6425
Gold.....	24860	199 21	Thorium			7449	59-83
Hydrogen . . .	12 5	1 00	Tin . .			735 29	58-92
	15795	1266	Titanium			303 66	24 33
Iridium ....	1233 5	98 81	Tungsten			1183 0	94 80
	3392	27 18	Vanadium			8569	68 66
Lanthanum . .			Uranium			2711 4	21726
Lead.....	12945	103-73	Yttrium .			402 5	3225
Lithium ....	80 3	641	Zinc . .			4032	3231
.Magnesium . .	158 3	12 69	Zirconium			4202	33 67
.Manganese .	345 9						
  The determination of the equivalents of compound bodies is an
equally remarkable application of the principles that have been laid
down.   The equivalent number  of a compound is the sum of the
equivalent numbers of its constituents, as has been already seen in
the numbers obtained for the oxides and chlorides of copper and of
hydrogen.  In this way may be constructed lists of the equivalents
of compound  bodies;  thus, reducing the  substances already noti-
ced to the scales, there are:
Oxide of copper
Oxide of hydrogen
Chloride of hydrogen
Kqu
= 11*11 H.= l
Substances.
195 7|3!)-?2' Chloride of copper
112 5 9 01 j, Iodide of hydrogen
445T36 47iiSulpliuret of hvdrogen
Equivalents.
(>.=I00  H.= l
 838-3 6718
15920J127-57
 2137 1712
  It is in relation, however, to the mutualdecomposition of saline
bodies that the principle of equivalent proportion becomes of most
interest, and by which it is best illustrated.   If to a solution of ni-
trate of barytes we add a solution of sulphate of soda, there is im-
mediate decomposition, by the mutual interchange of acids and ba
»es, and the neutrality of the solution remains completely undisturb
ed; the salts which exist after mixture are equally neutral with 
206    EQUIVALENTS  OF  COMPOUND  BODIES.
those which had existed previously, and the quantities of acids and
bases which  are  involved in the decomposition are hence  equiva-
lent  to each  other.  Thus, if we take  130-7 parts of nitrate of ba-
rytes, we find that they require for their decomposition exactly 71*3
parts of dry sulphate of soda, and that there are formed  1167 parts
of sulphate of barytes  and 85*3 parts of nitrate of soda.   The com-
position of these four  salts is:
   Sulphate of Barytes.
Sulphuric acid  .  .   40
Barytes  ....   76-7
                 TT6-T
   Nitrate of Barytes.
Nitric acid  ...   54
Barytes  ....   767
                 130-7
    Nitrate of Soda.
Nitric acid  .  .
Soda.....
    Sulphate of Soda.
Sulphuric acid   .  .
Soda......
54
31-3
"85~3

40
31 3
71~3
All four are neutral ; the acids and bases are in all equally neutral-
ized, and  hence the 40 of sulphuric acid and 54 of nitric acid, being
capable of saturating the same quantity of base, whether it be soda
or barytes, are equivalent quantities,  and represent the combining
proportions of these acids; and the 76*7 of barytes and the 31 3 of
soda being likewise shown to  possess equal powers of neutralizing
the acid, whether nitric or sulphuric, are the numerical equivalents of
those bases.   If there  had been a larger quantity of either salt pres-
ent, it would have remained unaffected, the interchange of elements
taking place only in equivalent  proportions. Had nitrate of lead been
employed in place of  nitrate of barytes,  the proportion necessary
would have been different, and a different quantity of sulphate of lead
would have been produced from the same sulphate of soda.  Thus,
to the 71*3 of sulphate of soda, there  should be,
       Nitric acid  .  .   54 0, producing Sulphuric acid   . .    401
       Oxide of lead  .   1117,    "    Oxide of lead .  .  .   Ill 7
       Nitrate of lead    165 7         Sulphate of lead      1518
   If, in place of sulphate of soda, we  take oxalate of soda, we shall
find that 67-3 of it will exactly fulfil the functions of 71*3 of sulphate
of soda, and  these, consisting of 31*3 of soda and 36 0 of oxalic acid,
will, by decomposing  I3(k7 of nitrate of barytes or 165*7 of nitrate
of lead, produce 147-7 oVoxalate of lead or 112-7  of  oxalate of ba-
rytes.  36 of oxalic acid are therefore equivalent to 40*1 of sulphuric
acid and 54-0 of nitric acid.
   A table of equivalents of acids and bases might thus be drawn up:
there should be,
Substances.	Kquiv.	ems.	Substances.	(■ quiva en's.	
	11 = 100.	H.= l 540 40 1 360		O = .'0.	H.--I 31-3 76 7 111-7
Nitric acid . . Sulphuric acid . Oxalic acid	577 0 501-1 1529		Soda .... Barytes . . . Oxide of lead	390 1 9569 13945	
  It was in this form that the equivalency of different quantities of
chemical substances was first recognised, and numbers assigned with
extraordinary skill, by Wenzel, whose labours, although overlooked
at the time, must be considered as the first and greatest step towards
assigning the numerical conditions of chemical action. 
LAW  OF  MULTIPLE  PROPORTIONS.       207
  The mode of determining the equivalent number  of a  new sub-
stance can now be easily  understood.  If it be an acid, it is to be
combined with some base  of which the equivalent is known ; if it be
a base, it must be united with  an acid.  If it be a metal, it may be
united with chlorine or oxygen.  If it be a simple non-metallic body,
it may be united with a metal.  In  any case, a well-defined com-
pound of the new body with one whose equivalent number is already
known must be obtained and accurately analyzed.   The equivalent
numbers of the two  bodies are proportional to the quantities in
which they were combined, provided we have reason to consider
that  the compound  examined contained an equivalent  of each.
Thus, if the  new body form  with sulphuric acid a perfectly neu-
tral and soluble salt, and,  on analysis, this yields 37*3 of  sulphuric
acid  and 62*7 of the new base  in 100, the  equivalent  is found by the
proportion, as, 37*3 : 62*7 : :  40*1 :  x = 67*4, which is the equiva-
lent  of the body, 40*1 being that of sulphuric acid, and  hydrogen
being = 1.
  A  calculation of this kind requires, however, to be checked by a
knowledge of the next law of combination, that of multiple propor-
tions ; for, as has been stated, we presume, in the example, the salt
analyzed to be composed  of an equivalent of each constituent.  It
may  be, however, that it contained two equivalents of acid to one
of base, in which case the number for  the latter  would become
134*8 ; or two equivalents of base to  one of acid, which would make
the number 33*7.  The proportions  might be even still more com-
plex ; and hence, before attempting to decide on the equivalent num-
ber of a body, its general  history must be studied.
  The third law of combination is, that where one body unites with
another in  more proportions than one, there exists a simple relation
between the quantities of the  second, which, in the different com-
pounds, unite with the same quantity of the first.  Thus, taking man-
ganese and nitrogen,  which are remarkable for the number of com-
pounds which  they form with oxygen, there are,
   315 9 of manganese unite with 100 of oxygen, forming protoxide.
   345 9         "          150       "       sesquioxide.
   345 9         "          200       "       peroxide.
   315 9         "          250      "       manganous  acid.
   315 9         "          300      "       manganic acid.
   315 9         "          350      "       permanganic acid.
And  with nitrogen,
     175 of nitrogen unite with 100 of oxygen, forming nitrous oxide.
     175         "         200       •'        nitric oxide.
      175         "         300       •'        hyponitrous acid.
      175         "         400       "        nitrous acid.
      175         "         500       "        nitric acid.
Here the successive  quantities of oxygen taken by the  manganese
are as the numbers 2, 3, 4, 5, 6, 7, and those which combine with the
nitrogen  are as 1, 2, 3, 4, 5.   In the last case  they are all simple
multiples of the first proportion, but  in the case of manganese they
are multiples of one half of the quantity  contained in the protoxide.
The  analogy of some other similar bodies, however, renders it ex-
tremely  probable that, though  it has not been yet discovered, there 
208      LAW  OF  MULTIPLE  PROPORTIONS.
 exists a compound of 348*9 of manganese with 50  of  oxygen, and
 this should then be the first term of the series.
    This law of multiple proportions holds not only with regard to the
 simple bodies already stated, but also with compound bodies of every
 class.   Thus  chromic acid combines with potash in three different
, *oroportions,  forming by
          52 2 chromic acid-f-47.3 potash, neutral chromate of potash.
         104 4     "     -4-47 3   "   bichromate of potash.
         256-6     "     -j-47 3   "   terchromate of potash.

 Sulphuric  acid combines with potash in two proportions,
              40 1 sulphuric acid -4-47 3 potash, neutral sulphate.
              80-2       "      -j"47'3  "   bisulphate.
 It was, indeed, by the verification of it in the carbonates and ox-
 alates of  potash  by Wollaston, that this law obtained in the  first
 instance general acceptation.
         22 of carbonic acid -f-47 3 potash, form carbonate of potash.
         44      "       -4-47-3      "    bicarbonate of potash.
         36 of oxalic acid  -4-47-3 potash, form oxalate of potash.
         72      "       -4-47 3      "    binoxalate of potash.
         144      "       -{-47 3      "    quadroxalate  of potash.

 In  salts with  excess  of base, the  same principle holds.  Thus, in
 the sulphates of copper, I have shown  that
        39-7 oxide of copper -4-40 1 sulphuric acid, form neutral sulphate.
        79-4      •'      -f 40-1        "        bibasic sulphate.
       158 8      "      -f-40 1        "        quadribasic sulphate.
       317 6      "      -j-401        "        octobasic sulphate.

 In other cases the series, though not so complete, evidently follows
 the same  law.
    The great use  of the symbolical nomenclature, noticed already in
 page 156,  consists in its  supplying an  exact expression of this law
 of multiple proportions.  The ordinary symbol of a  simple body in-
 dicating an equivalent of it, the  number by which  that symbol is
 multiplied, in the formula of each compound body, represents the
 number of equivalents therein contained.  Thus, for manganese and
 nitrogen, already used as instances, the symbolical expression of the
 law is edven in
N.O.  Nitrous oxide.
N.O.,  Nitric oxide.
N.03  Hyponitrous acid.
N O,  Nitrous acid.
N.O,  Nitric acid.
Mn.O. Protoxide of manganese.
Mn,03 Scsquioxide.
Mn.O, Peroxide.
Mn.03 Manganic acid.
Mn207 Permanganic  acid.
  The numerical  coefficient  is sometimes  placed,  as  here, below
and to the right of the letter symbol;  by other chemists it is placed
to the left and on the same line, as Pb. + 20. Cr.-f 30., and sometimes
to the right and above the letter, as  Pb.O2  Cr.O3.   This makes no
difference in  chemistry; but the  student must be careful not to
confound chemical with mathematical symbols, in which  the  posi-
tion of the number might alter its power and meaning altogether.
It must be noticed, however, that numbers written as the above af-
fect only the immediate symbol to which  they are attached; but 
RESEARCHES  OF  PROUST.              209
(toinetimes a number affects a group of symbols: thus,  3Mn.O. is
three equivalents of protoxide of  manganese =Mn3Oj: thus, also,
S.Oj K.O. + AI.O,. 3S.Oj, the formula of dry alum, contains four fig-
ures of 3, of which  the  first, second, and fourth only affect the O.,
to which they are subjoined, but  the third affects the S.Oj, to which
it is prefixed.  A little  practice  will enable the student to become
quite familiar with the arrangement of the  symbols, or formulae, as
they are  termed, of bodies,  even of the most complicated nature.
  This is the principle of multiple proportions: that the successive
quantities in which one  body may unite with another are multiples
of the first by a whole  number; and  the cause of this is at once
seen, and a simple  and  positive  meaning given to this  law, by say-
ing that the first body contains an equivalent of each element;  the
second,  one equivalent of one and two  equivalents of the other, and
60 on ; the successive  steps being formed  by the number of com-
bining proportions  of the second body which unite with one com-
bining proportion of the first.
  This principle, which establishes a remarkable distinction  between the action of
chemical affinity and of cohesion, was,  at the moment of its first being  traced, at-
tacked by  Berthollet, to whose exclusive doctrines it was quite fatal.   Berthollet,
in fact, considered that  the affinity of bodies should make them unite in all possible
proportions, and thai it  was only by the  influence of cohesion and elasticity that the
formation of the bodies  actually produced resulted.   Thus he asserted that sulphu-
ric acid and barytes actually  unite in all proportions ; but those of 40 1 of acid to
76 7 of base forming the body of the least solubility, the whole quantity of acid it
determined to  unite with  the barytes  in those proportions, and in none others
Thus he imagined, also, that mercury and oxygen should unite in  all proportions
and that it was only by the intervention of external causes that their union was de-
termined  in preference to occur in the proportions of 1014 of mercury to 4 of oxy-
gen, and  101 1 of metal to eight of oxygen.  We owe to Proust the complete  refu-
tation of Berthollet's views in this respect; he cleared away a heap of incorrect
ideas which had prevailed regarding compound bodies, showing that numerous de-
grees of oxidation, which had been looked upon as  intermediate, and connecting
the extreme limits, as Berthollet thought they ought to be connected, were impure
and badly prepared mixtures  of the true compounds,  and that, when pure, the tran-
sition from one state to the other is sudden and definite, as  has been shown to be
the consequence of the  law of multiple proportion.  It is interesting to notice, how-
ever, as an example of how easily a great discovery in science may be lost, that, al-
though Proust had in his hand all materials necessary for establishing the laws of
combination, such as they have been described, they escaped his notice, from hia
having contemplated his results only in one point of view;  thus he found that in
100 parts,
1st Oxide of copper contained
    Oxygen.....11 22
    Copper......88-78
1st Oxide of mercury
    Oxygen.....380
    Mercury.....96 20
1st Sulphuret of iron
    Sulphur.....37 23
    Iron......62 77
2d Oxide of copper contained
    Oxygen.....20 17
    Copper    .....79 83
2d Oxide of mercury-
    Oxygen    .....7-32
    Mercury.....92-68
2d Sulphuret of iron
    Sulphur.....54-26
    Iron.......45 74
  He proved that no indefinite intermediate degree of combination could be traced,
md that the influence of cohesion could not be supposed to be the only cause of the
detinitcness o/ constitution ; but, had he made a tntting change in his way of calcu-
lation ; had he taken a certain weight of one element as the standard, and not 100
parts of the compound body, his numbers would have become,

  1st Oxide of copper                 I   2d Oxide of copper
     Oxygen.....1000          Oxygen.....2000
     Copper.....7914    |      Copper.....791-4
                                 Do 
210       METHODS  OF  DETERMINING THE
  1st Oxide of mercury                 3d Oxide of mercury
      Oxygen.....100-0         Oxygen.....2000
      Mercury   .... 2531 6         Mercury.....2531 b
  1st Sulphuret of iron                 2d Sulphuret of iron
      Sulphur.....2012         Sulphur.....402*4
      Iron......339 2         Iron......339 2
  And thus the fact of the quantity of oxygen or sulphur in the second range of
compounds bein<* exactly double that in each of the first, would have been evident,
and the law of multiple proportions  been discovered twenty years before its exist-
ence was suspected.                      .         .
  We are now in a condition to examine more in detail the method
of determining the equivalent number  of a body, which, as was be-
fore noticed, i°s rendered difficult, sometimes, when the substances
in question  unite in more proportions than  one.   Thus it  is evident
that the manganese series might be represented as
        100 of oxygen -f 345 9 of manganese, forming protoxide.
        100     "     2305      "       "      sesquioxide.
        100     "     1729      "       "      peroxide.
        100     "     138 3      "       "      manganous acid.
        100     "     115 3      "       "      manganic acid
        100     "      98 8      "       "      permanganic acid.
And the metallic oxides and  sulphurets above described might be
written, and express  still the  law of multiple proportion ; as,
                                   2d Oxide of copper
                                      Oxygen.....1000
                                      Copper.....3957
1st Oxide of copper
   Oxygen.....100 0
   Copper.....791-4
1st Oxide of mercury
   Oxygen.....100 0
   Mercury.....2531-6
1st Sulphuret of iron
   Sulphur.....2013
   Iron......3392
2d Oxide of mercury
    Oxygen.....1000
    Mercury   .... 12658
2d Sulphuret of iron
    Sulphur.....2012
    Iron......1696
  There might thus be deduced from each kind of compound a dif-
ferent  equivalent for each simple body, and it is therefore neces-
sary to lay down sornq general principles  by which one must be
guided in their choice.
  First. Whenever  there exists  but one  proportion in which  two
bodies are capable of combining, it may be concluded, unless there
are good  reasons to the contrary, derived from other sources, that
the proportion is one  equivalent of each element.   Thus  lime  and
magnesia are the only compounds formed  by the metals  calcium
and  magnesium uniting with oxygen, and are hence looked upon
as protoxides.
  Second. Whenever  one body combines with another in two pro
portions,  as a metal with oxygen, and  the quantities of oxygen are
as 2 :  1, it may be concluded, unless there are other reasons for an
opposite decision, that the  bodies consist either of one equivalent
of metal united respectively with  one and two of oxygen, or of one
equivalent of oxygen united respectively with one and two of metal.
To decide between  these views, it  must be considered, that as the
tendency of the metal and of oxygen to unite is pretty well satiated
by the combination of an equivalent  of  each, if the protoxide so
formed unite with another equivalent of either metal or of oxygen,
this will be retained with inferior  power, and when the substance
so produced is exposed to decomposing agencies, it may be resolved 
      EQUIVALENT CONSTITUTION  OF  BODIES.  211

into protoxide and metal  in the one case, and  protoxide  and free
oxygen in the other.  Thus  copper, lead, and mercury unite each
with oxygen in  two proportions; and if black  oxide  of  mercury
be  heated, it resolves  itself easily  into metallic mercury and  red
oxide,  while the red oxide undergoes no change except  total  de-
composition into mercury and free oxygen.  Red oxide of copper
decomposes itself easily  into metallic copper and  black  oxide of
copper ; but this last does not admit of any decomposition which
is not total.   If  we take yellow oxide of lead, we cannot change it
by  the application of heat;  but if we heat brown  oxide of lead, it
gives off one half of its  oxygen, and yellow oxide remains; similarly,
when peroxide of manganese is heated  by deoxidizing agents, it
abandons one half of its oxygen, but the oxide so formed cannot be
farther reduced.  In this way, therefore, we conclude that

         Red oxide of copper is suboxide.  Cu20.
         Black oxide of copper  is protoxide.   Cu.O.
         Black oxide of mercury is suboxide.   Hg20.
         Red oxide of mercury is protoxide.   Hg.O.
         Yellow oxide of  lead is protoxide.  Pb.O.
         Brown oxide  of lead is deutoxide.  Pb.O,,.
         Olive oxide of manganese is protoxide.  Mn.O.
         Black oxide of manganese is deutoxide.  Mn.Or

Thus, also, hydrogen and oxygen unite in two proportions, to form, in
one, water, a body remarkably neutral in properties and permanent in
constitution, and in the other oxygenated water, of which half of
the oxygen is so loosely combined that its  decomposition  is provo-
ked by the slightest causes, and is explosively violent.  It is hence
concluded that

             Water is protoxide of hydrogen.   H.O.
             Oxygenated water is deutoxide.  H.02.

If there be  still more  degrees  of combination  of the two bodies,
these principles apply still more determinately to their characteristic
properties.
  Third. The constitution of an acid may be frequently determin-
ed  by  the consideration  that an equivalent of it is  the  quantity
which neutralizes an equivalent  of a well-characterized base.   Thus
the equivalent number  of potash on the hydrogen scale is  47*3, and
this combining with 40*1 of sulphuric acid to form neutral sulphate
of potash, this number is determined to be the equivalent of  the
acid; and as it is made up of 16*1 of sulphur and 24- of oxygen,  the
acid is considered to  be  composed of one equivalent  of sulphur
16*1, and three  equivalents of  oxygen 8x3 — 24.  Its formula is
therefore S.O.,.  In the same way, on analyzing hyposulphate of
potash, it is found to consist of 47*3 of potash, united to 72*2 of the
acid, which is, therefore, its equivalent number.  But this number
is made up of 32*2, or  two equivalents of sulphur, and 40, or five
equivalents of oxygen, and the formula expressing its constitution
is SO,.
  Where an acid forms several classes of salts, it is difficult to de-
termine which is that containing an equivalent of each element, and 
212       METHODS  OF DETERMINING  THE

hence this mode of ascertaining the constitution of the acid may be
occasionally at fault.  This  happens particularly with  the acids of
phosphorus and arsenic ;  and in these cases it is necessary to recur
to considerations regarding the constitution of their  salts, which
will be described when we come to speak of salts in general.
  Fourth. In cases where the ratio between the quantities in which
the bodies combine does not follow the simple proportion of 1 : 2 : 3,
&c, but  assumes the more  complex form of 2 : 3,  or  3:4, or
3 : 5 : 7, it is necessary to seek for analogies between the members
of the series and certain other bodies with regard to which there is
not the  same uncertainty.   Thus  there are  two oxides of  iron
which may be looked upon as consisting, either

              the 1st of 27*9 of iron  + 8 oxygen.
              the 2d     27 9   "    +12   "
           or the 2d     18*6   "    +8   "
              the 1st    27*9   "    +8   "

In the first mode of view the oxygen varies as 2 : 3, but in the sec-
ond it is the metal which changes in proportion.  Here we obtain a
guide in the study of the salts formed by these bodies.   It is found
that the oxide which contains 27*9 of iron to 8 of oxygen agrees in
its laws and properties with magnesia, with black oxide of copper,
and with olive oxide of manganese, which are all protoxides, and
that it differs totally in  its relations from such bodies  as  are very
fully known to be suboxides.   This oxide of iron contains, therefore,
an equivalent of each element, and its formula is Fe.O.  The per-
oxide of iron then becomes Fe.O 1£ ; but as the equivalent of oxygen
cannot be considered to  be divided, we look upon  it as  being rather
Fe^03, and having its equivalent number twice as large.  This view
is confirmed by finding that when sulphate of peroxide of iron unites
with sulphate of potash to form iron alum, it does  so in the propor-
tion of Fe^03, dry iron alum being S.03, K.O. + Fe,,03, 3S.03;  and as
this is the only proportion in which these two salts unite,  it  is rea-
sonable to suppose that it contains an atom of each element.
  This mode of controlling  the equivalent numbers is beautifully
shown in the instance of the compounds of chrome with oxygen.
There are two ;  the

  Green oxide of chrome consists  of 18*79 chrome +  8 oxygen.
  Chromic acid          "          18*79   "    +16   "

Here the quantity of oxygen is doubled in the second compound;
and as this yields half of its oxygen readily, either by heat, or to any
substance having an affinity for it, it would appear highly probable
that the 18*79 is the equivalent of  chrome, and that the  oxide of
chrome should be looked upon as a protoxide ;  but such is not the
case.   Sulphate of chrome combines with sulphate of potash to form
a chrome alum, resembling in all characters and constitution the iron
alum  already noticed, and hence oxide of chrome corresponds to
peroxide of iron, and its formula  is Cr203-  This  is farther proved
by the relations of chromic acid to  bases.  The chromates resemble
perfectly the  sulphates  with which they are isomorphous, and to
saturate 47-3 of potash 52*2 of chromic acid are  required, consisting 
     EQUIVALENT  CONSTITUTION OF  BODIES.   213

 of 28*2 of chrome  and 24 of oxygen ; and hence the  formula  of
 chromic acid is Cr.03,  resembling that of sulphuric acid S.03.
   Fifth. In cases where there is only one compound of a body with
 oxygen, we may be induced to consider it not to be composed of an
 equivalent of each element from analogical grounds, such as those
 now described.   Thus aluminum and oxygen form only one com-
 pound,  alumina;  but this  resembles, in all its laws of combination
 and  crystalline form, oxide of chrome and peroxide of iron, and
 hence it is considered to be a compound of two equivalents of metal
 and  three of oxygen, and  its formula to be A1203.
   Sixth. When bodies are found combined in proportions expressed
 by high numbers, they are generally looked upon as secondary com-
 pounds, formed by the reunion of others, the ratio of whose elements
 are simple.  Thus lead forms with oxygen compounds intermediate
 to the two true oxides already described, the one containing three
 equivalents of lead and four of oxygen, the other four of lead and
 five  of  oxygen ; these consist really of the protoxide and peroxide
 united in  the proportions shown by the equations:
        Pb405=3Pb.O. + Pb.02, and Pb304=2Pb.O.+Pb.02.

 In like  manner, between the two proper oxides of iron there inter-
 vene the two magnetic oxides, the formulae of which are Fe405 and
 Fe304, being compounds of protoxide and peroxide, as,

        FeA=2Fe.O.+Fe203, and Fe304=-Fe.O.+Fe203.
 By this means the constitution of an extensive class of complex bod-
 ies is reduced to very simple forms.
   If we take  oxygen, hydrogen, chlorine, and nitrogen  in the pro-
 portions by weight which  correspond to their equivalent numbers,
 and  measure  the volumes  which, as gases, they occupy, an exceed-
 ingly striking relation will be found between them, the volume  of
 oxygen being exactly one  half that of each of the other gases.  If,
 also, we heat  iodine and bromine in quantities proportional to their
 equivalents by weight, we shall find that, when converted into va-
 Sour, they occupy precisely the same volume as the  equivalent  of
 ydrogen gas at the same  temperature and pressure.  On convert-
 ing into gas equivalent weights of arsenic and phosphorus, they oc-
 cupy precisely the same volume, which is equal to that of the equiv-
 alent of oxygen gas ; and by similarly treating an equivalent  of sul-
 phur, its volume becomes one third that  of the oxygen.  Finally,
 when a  quantity of mercury, representing its equivalent number, is
 converted into vapour, its volume, reduced to the same standard of
 temperature and pressure,  is four times that of oxygen, and double
 that of hydrogen or chlorine  gases.  It hence results, that although
 the equivalent weights  of the simple bodies may be totally uncon-
 nected, and may range within very extensive limits, yet the volumes
 which these equivalent quantities occupy when in the state of gas
 or vapour, have a very simple relation to one another; thus, taking
 the equivalent weight of oxygen as 100, and its equivalent volume
as 1,  the proportion  of the other bodies mentioned are: 
214 EQUIVALENT VOLUMES OF  COMPOUND BODIES.
Name of Sub-tance.	Equivalent Weight.	Equivalent Volume.	Sp. Gr. of Vapour. Air = l000.
Oxygen . •	1000	1	1102 6
Hydrogen . •	125	2	68 8
Chlorine . •	442 6	2	24700
Iodine . . •	15795	2	8701-0
Bromine . •	978 3	2	53930
Nitrogen . .	175 0	2	976 0
Sulphur . •	2012	l 3	66480
Phosphorus .	3923	1	43270
Arsenic . .	940 1	1	103620
Mercury . .	12658	4	6969 0
			
   Not merely does this simple proportion of equivah.it volumes
hold among the simple bodies, but it determines in the compounds
which they form an equally regular constitution.
   The volumes of the gases which unite are necessari'y in simple
equivalent proportion to each other, and when the same gases unite
in more than one proportion, the second is a multiple of the first.  In
all cases, also, where, after union, a condensation of volume occurB,
the resulting  volume is simply related to  the volumes which the
constituents had occupied before combination.  Thus, in the forma-
tion of water, one volume of oxygen unites with exactly two of hy-
drogen, and the volume of watery vapour which is formed is equal
to that of the  hydrogen  employed.  To form ammonia, one volume
of nitrogen unites with three of hydrogen, and the four volumes are
condensed into two by the combination.  There may, therefore, be
arranged for the various bodies which assume the gdVjous form, a
series of equivalents in volume, which will not be totally unconnect-
ed numbers, like those of the equivalents by weight, but are found
to be, as the weights should become if the suggestion of Proust were
verified,  simple multiples of the equivalent of some standard body
which may be selected, as oxygen in the table.
Name of the Compound Vapour.
Water.....
Nitrous oxide .  .   .
Nitric oxide   .  .   .
Sulphurous acid  .   .
Sulphuric acid .  .   .
Sulphuretted hydrogen
Muriatic acid  .  .   .
Hydriodic acid .  .   .
Hydrobromic acid
Ammonia   ....
Arseniuretted hydrogen
Terchloride of arsenic
Calomel.....
Corrosive sublimate  .
Arsenious acid   .   .
Sulphuret of mercury
Chloride of sulphur  .
Protochloride of phosphorus
Perchloride of phosphorus .
Formula.
H.O.
N.O.
N.Oj
S02
S.03
S.H.
01.H.
I.H.
Br.H.
N.H3
As.H3
As.CI3
Hg2Cl
HgCl.
As.03
Hg.S.
S2C1.
P.C13
PC15
Wei?ht.
 112 5
 275 0
 3750
 401 2
 501 2
 2137
 455 1
15920
 990 8
 2145
 952 6
2268 0
2974-3
1708 5
12401
14670
 845 0
17201
25053
 Kqiivalem
 Volume of
Cons iuents,
 3
 3
 4
 7
10
 7
 4
 4
 4
 4
 7
 7
 6
 8
 4
 7
 4
 7
11
Volume of
Compound
 >p Gr. of
ihe Vapnur.
4ir=1000 0
  6202
  15273
  10393
 2210 6
 2761 9
  11770
  12695
 4385 0
 27310
  591-5
 26940
 62950
 8204 0
 94390
136700
 5384-0
 46860
 474M
 4788-1
  The simplicity thus shown to exist between  the  volumes of the
constituent and compound vapour enables us very often to calculate
beforehand what the specific gravity of a vapour should be, and thus 
 SPECIFIC GRAVITIES  OF COMPOUND VAPOURS. 215

to ascertain how closely the numbers found experimentally by the
methods  described in the first chapter may approach to absolute
correctness.   Thus, to calculate the specific gravity of ammonia:
it is formed by the union of three volumes of hydrogen and one of
nitrogen, and the weights of these volumes being as their specific
gravities, the weight of the ammonia formed should be 976+(3x
69)— 1183 if the four volumes  of constituents were condensed into
one; but as the condensation  is  into two, the specific gravity of
the  ammonia is 1183-7-2 = 591*5, as given in  the  table.  Sulphur
and hydrogen unite in the proportion  of one volume of sulphur to
six of hydrogen, and hence, if  there were but one volume  of result-
ing gas, the specific gravity should be 6648+(6 x 69) = 7062 ;  but as
there are six volumes of gas formed, the true specific gravity of sul-
phuretted hydrogen is 7062 — 6 = 1177.   The general rule being to
multiply  the  specific gravities of the simple gases or vapours re-
spectively by the  volumes in  which they combine, to  add those
products together, and then to divide the sum by the number of vol-
umes of  the compound gas produced.
  By the application  of this principle, we may often decide with
great probability on the specific gravity which certain bodies should
have in the state of vapour, although it has not  been as yet pos-
sible to weigh their vapours experimentally.  Thus the temperature
at which antimony is volatile is so high that the specific gravity of
its vapour may possibly never be determined by experiment; but
the chloride  of antimony resembles, in all its chemical  relations,
chloride  of arsenic, and  there  is the  greatest  probability that the
constitution of the two are alike  in the state of vapour.  Now we
know that chloride of arsenic consists of six  volumes of chlorine
and one  volume  of arsenic vapour condensed into four  volumes;
and hence, if we multiply the specific gravity of the vapour of chlo-
ride of antimony, which is  8106*5, by  four, we  obtain 32426 0, and
subtracting from  it the weight of six volumes  of chlorine =14820,
there remains 17606, which, if the analogy between  the arsenic and
antimony be correct, must  be the specific  gravity of the vapour of
antimony reduced to the standard of air = 1000.
  Similar principles have been applied to  the determination  of the
specific gravity which  carbon  should  possess  if it were converted
into vapour.  This number would be of great importance  in all cal-
culations of the specific gravities  of the vapours of organic bodies,
most of which contain carbon as  an  element; but, unfortunately,
there is no volatile body so similar to carbon  as that its  analogies
can be taken as a  guide, and hence  the bases of the calculated
density of gaseous carbon are  purely hypothetical.  Indeed, chem-
ists are not agreed upon the precise number, some making it the
double  of what it  is estimated  at by others.  If we look upon car-
bonic acid as consisting of equal volumes  of vapour of carbon and
oxyg-en, the two condensed into one, the specific gravity of carbon
is 1524*1—1102*6--421*5 ; but if the carbonic acid consist of two
volumes of oxygen and one of  carbon, the three volumes condensed
into two, the calculated specific  gravity  of  the  latter  vapour is
304S-2-2205 2 = 843*0.  On the first idea, the  carbonic oxide con-
sists of two volumes of carbon  vapour and one of oxygen, the three 
216  CHEMICAL AND  MOLECULAR  CONSTITUTION.

condensed to two (2x421*5+ 1102*6)-^2=972*8 ; and on the latter,
of equal volumes united without condensation (S43-0+ 1102*6)-2=
972*8.  It is this latter view which I adopt, and in any calculations
that may  occur hereafter, I shall consider the specific gravrty of
gaseous carbon as 843. It does not at all necessarily follow that
the true specific gravity is either of these numbers,  as it may be
that the relations by volume of carbonic acid  and carbonic oxide
are much more complex.   Before the specific gravity of the vapour
of sulphur had been experimentally determined, it was considered,
from similar theoretic  grounds, to be 2216, but it is actually three
times as great, 6648, and we must hence not  reckon too implicitly
on the  relations by volume at present  given  for the gaseous com-
pounds of carbon.
  In the combination by volume, the same laws of multiple propor-
tion hold as in combination by equivalents; thus the compounds of
chlorine and oxygen, which are by weight CI. O., C1.04, CI. 0„ and
CI. 07,  are by volume two of chlorine to one, to four, to five, and to
seven volumes of oxygen respectively, and so  in all other instan-
ces ; and,  consequently, all remarks  that have  been made regard-
ing the law of multiple proportions in equivalents by weight, apply
to combinations of equivalents by volume also.
                        CHAPTER  X.

OF  THE RELATIONS  OF  CHEMICAL  CONSTITUTION  TO  THE  MOLECULAR
                     STRUCTURE  OF BODIES.

  It has been abundantly shown, throughout the preceding portions
of this  work, that even the most purely physical properties of a
body are closely connected with its chemical constitution ; and that
thus the density, the crystalline structure, or the electrical relations
of a substance, or the manner in which it is acted on by heat, may,
by affording distinctive characters, or by influencing its affinities,
become necessary to its chemical history.  The numerical laws of
constitution last described yield additional evidence of the intimate
relation of chemical to molecular constitution; and in the present
chapter I purpose to conclude  the description of the general histo-
ry of chemical  action, by an  account of such principles as have
been advanced, and such facts as  have been discovered  illustrative
of this connexion.   They are as follow :
   1st.  The connexion between the molecular constitution and the
equivalent numbers of bodies.  The atomic theory.
  2d. The connexion between the crystalline form and the  chemical
equivalency of bodies.   Isomorphism.
   3d. The relation of constitution to composition.   Of Dimorphism
and Isomerism.  The theory of types.
   4th. Of chemical action independent of affinity.   Catalysis. 
THE  ATOMIC  THEORY.
217
                           SECTION I.

                     OF THE ATOMIC THEORY.

  It was natural that, as soon as the remarkable laws of combination
 discussed in  the  last chapter had been  discovered, philosophers
 •mould be anxious to  ascend to the causes in which they had their
 rise, and to trace, in  the  operation of some one general principle,
 the three determinate numerical  conditions to  which experiment
 proved chemical action to be subjected ; accordingly, such theoreti-
 cal  views were promulgated even before the  laws of combination
 were fully understood ; and it has been since one of the most difficult
 tasks of the philosophic chemist to disentangle the real and practi
 cal  from the merely speculative portions of atomic chemistry.
  For Dalton, in promulgating the law of multiple combination, the
 most beautiful, as well as the most extensive principle that had been
 conferred on chemistry since the epoch of Lavoisier, announced it
 as the result of speculations which, though in their general nature
 true, and constituting still the essential basis of all theories of chem-
 ical action, were yet overlaid by a tissue of hypotheses so irregular
 and so unnecessary, that for a  long time the real dignity and excel-
 lence of the experimental laws  were underrated and misunderstood.
 Those accessory speculations have now, however, passed away, and
 the theory of combination laid  down by Dalton may, in all its essen-
 tial conditions, be very briefly  expressed as follows :
  All substances are  supposed to be constituted  of  particles per-
 fectly indivisible, and hence truly atoms.   In different kinds of mat-
 ter, these atoms are of different weights,  and  probably of different
 magnitudes; but this latter quality is of no material interest.  When
 bodies combine chemically, their combination must be so  effected
 that one atom of one unites with one atom of another ; or one of the
 first with two, or three, or four of the second;  or two of  the first
 with three, or five, or  seven of  the second ; but no intermediate de-
 grees can possibly occur,  for the atom being absolutely indivisible,
 no  intermediate degree of  union can take  place.   The  relative
 weights of these atoms are the equivalent numbers  of the bodies
 combined; eight parts of oxygen unite with one part of hydrogren,
 by weight, to form water, because the simplest  proportions in which
 they can unite are one atom of each, and the atom  of oxygen is
 eight times as heavv as the atom of hydrogen ; eight parts of oxygen
 are  equivalent to 35*4 parts of  chlorine, because, when an atom of
 hydrogen leaves the atom of oxygen, it combines  with an atom of
 chlorine in its place,  which is  heavier than that of oxygen in the
 proportion of 35*4 to  8, and the quantity  must be  consequently so
 determined.  When a second atom of oxygen combines with hy-
 drogen,  it being equally heavy  with the first,  doubles the quantity
 of oxygen which the equivalent of hydrogen has taken up, and, as
 might be illustrated by any series of examples, introduces as a ne-
cessary consequence the law of multiple combination.
  Such is the atomic theory of Dalton.  It expresses  faithfully the
laws of combination ;  1st, the law  of definite constitution ;  2d, the
principle of equivalent proportion ;  and, 3d, the  law of multiple com-
                            £ E 
 218       PHYSICAL  AND  CHEMICAL ATOMS.

 bination.   It is therefore, even in this form, the most embracing and
 perfect generalization that has ever been proposed in chemistry ; but,
 before committing ourselves implicitly  to its adoption,  it is neces-
 sary to examine into its bases with some detail.
   Dalton  assumes that matter is constituted  of indefinitely  small
 particles,  atoms, but he advances no proof that it is so; he adopts,
 unreservedly, that side of the discussion which, from  the earliest
 ages, has  divided the opinions  of philosophers,  and shows that on
 that hypothesis all the most remarkable phenomena of chemistry can
 be explained.   But I have already, in the first  chapter of this work,
 pointed out, that the question of the ultimate constitution of matter
 is now no nearer its solution than it was twenty centuries ago ; and
 I will now proceed to show, that for the explanation of the laws of
 combination, the atomic theory of Dalton is unnecessary, or, at least,
 that it becomes only one  out of a variety of molecular conditions
 which matter may assume.   In  the first  place,  it  is necessary to as-
 certain in what manner the relative weights of the atoms of bodies,
 if they really exist, are to be determined.
  I pointed out in  the last chapter the number of circumstances
 which should be taken into account  for the determination of the
 equivalent number of a body ;  it is by such considerations that in
 similar cases the atomic weight of a body is determined ; and where
 the idea of the existence of such ultimate combining molecules is
 adopted, the atom is the equivalent, and the number is  its weight.
 If, therefore, the theory of molecular constitution involved chemical
 results alone, no difficulty would occur ;  but when we consider these
 atoms as building up the mass, and conferring upon it its physical
 properties at the same time that they produce its chemical consti-
 tution, inconsistencies  are  found which must prevent our coming
 too hastily to a conclusion.
  When Gay Lussac first determined the existence  of those simple
 relations which have been described as existing between the volumes
 of gases  which combine together, it was considered certain that
 all gases contained in the same  volume the  same number of atoms.
 The gases are remarkable for all possessing the same physical con-
 stitution.   Their relations to pressure and to heat are governed by
 the same law in all cases, which can be best explained by supposing
that in the same space  they contain the same number of ponderable
atoms, set at equal distances from  each other, and whose material
repulsion  is expressed by the same law.  Hence, when one volume
 of chlorine unites with one of hydrogen, an equal number of atoms
 of each element come into play, and an atom of the  compound con-
 sists of an atom of each constituent.   But  here a difficulty  occurs;
the chloride of hydrogen which results  occupies two volumes, and
yet it is in physical properties identical with the  hydrogen or chlo-
rine ;  all physical evidence would lead us to believe that  muriatic
 acid gas contained in the same volume the same number of atoms
 as its constituents, but the  most positive chemical  evidence shows
 that it contains but  half  so  many.   In like manner, on physical
 grounds, there  should  be the same number of atoms in the  same
 volume of oxygen and hydrogen ; and as water is formed by the
 union of  one volume  of oxygen with two  of hydrogen, it should 
          PHYSICAL AND CHEMICAL  ATOMS.       219

consist of one atom of oxygen and two atoms of hydrogen ; but the
most  perfect chemical evidence we possess proves  that water  is
composed of an equivalent of each element.  The number of chem-
ical molecules in gases is different, therefore, for each gas; it is the
combining or  equivalent volume which  contains equal numbers of
chemically equivalent molecules or atoms, and, as has been shown
in the tables  in the last chapter, those volumes differ remarkably from
one gas to another.
  Another physical condition, which  is  intimately connected with
the molecular constitution and the chemical relations of bodies,  is
their specific heats, on the remarkable law of which,  regarding the
simple bodies, as discovered  by Dulong  and Petit, and extended to
many compound bodies by Nauman and Avogadro, I have already
fixed attention (page 67).  If we look upon the specific heats of all
the ultimate particles of simple bodies as being the same, we should
at once have a mode of determining their atomic weights, and these
should coincide with the equivalents deduced from chemical consid-
erations.
  In the great majority of cases, the atomic weights of the solid sim-
ple bodies, deduced from their specific  heats, coincide with those
adopted from chemical considerations;  and in some  of  the excep-
tional  instances,  as bismuth and  silver, there  is doubt as to the
true number, which may be  fairly interpreted as so  far remaining
neutral.   But in other cases we find that it completely fails ;  thus,
the atomic weight of iodine, deduced from its specific heat, is 63*1,
while there  is  no  doubt but  that its  chemical  equivalent is 126*3,
twice as much.  Also, the history of arsenic  and phosphorus is so
complete, that there is no doubt that their equivalents are 75*4 and
31*4; but when we calculate the atomic  weights  from their specific
heats, we find as  the result  for  arsenic 37*7,  and for phosphorus
157, that is, in each case but the half of the real number.  In the
gases, also, there is complete discordance between the specific heats
and the chemical equivalents, no matter  whether we consider their
purely molecular constitution, by  which  they should have an equal
number of atoms  and equal specific heats in  equal volumes, or
whether we  compare their  combining volumes with  their specific
heats.   The  specific heats of equal volumes (p. 69) of oxygen and
of hydrogen  have  been proved by Apjohn to  be as  808 to 1459,
while on chemical grounds that of oxygen  should be double, and
on molecular considerations the same as that of the hydrogen.
  It follows, from  what has been  said, that it is totally  impossible
to adopt completely the opinion of Dalton, that bodies  are composed
of ultimate and indivisible particles,  which, aggregating together,
give origin to sensible masses of the same nature when similar par-
ticles unite,  and to the phenomena of chemical  combination when
the union  is  between particles of different kinds; I adopt fully the
idea of Dumas, that it is possible,  and, indeed,  more consonant to
experiment,  to explain all the laws of chemical  combination quite
independent  of all  considerations  as to  whether the masses which
combine are indivisible or the  reverse.  The word atom, if interpret
ed in its strict and proper sense, is unnecessary, and may  be  inju
rious if employed with any vague  or undefined meaning. 
220  VARIOUS  ORDERS  OF  MOLECULAR GROUPS.

  I consider, as I have already stated (page 17), that sensible masses
of matter are constituted of a number of lesser masses, which again
may be made up of similar  constituent groups, proceeding down-
ward to any extent, but still without involving the question of a limit
to the  degree of possible division.  One class  of these groups of
particles I consider to be represented by the equivalent numbers;
and it  is possible that these  numbers may indicate the manner in
which the chemically combining groups may be supposed to subdi-
vide themselves, in order to  generate a set of groups of an inferior
class.  The specific heats of bodies may be considered to have ref-
erence to an  order of groups of particles often, but not necessarily,
coincident  with  those  which combine to produce chemical  com-
pounds ; and the third, probably the most remote, engaged in the or-
dinary properties of matter, may be such as, being uniformly distrib-
uted in the gaseous form, confers upon those bodies the properties
which characterize mechanically that condition, and are independent
alike of the chemical properties and specific heats which appertain
to, and are exhibited by, groups of a  more complex structure and
superior order.
  From this  point of view I contemplate the atomic  theory;  for
these groups, engaged in  chemical combination, and indivisible by
chemical means, are, in all chemical relations, atoms.  Their relative
weights are our equivalent numbers.   From their union the laws of
definite and multiple combination  directly follow.  But, when  we
remove them from their proper sphere, when we  subject  them to
physical forces, we may dissect them,  and separate them into other
groups; or we may unite many of them together  to form a larger
group, characterized by the relations  to heat and  to pressure that
have been already stated,  but no longer the group or atom  engaged
in chemical operations.  Thus  the group which is acted on by the
heat when a  gas expands, occupies only half the space  in  muriatic
acid that the chemical group takes up ; but  in gaseous sulphur it
occupies three times the space of the chemical atom.   In gaseous
oxygen, arsenic,  and  phosphorus,  the mechanical atom is of the
same volume, but the  chemical atom  only of half the volume that
they respectively occupy in hydrogen, chlorine,  and  iodine.  In
most of the simple bodies the same groups produce chemical com-
bination, and determine the specific heat;  but in iodine, in arsenic,
and in phosphorus, the group which enters into chemical combina-
tion contains two of  the groups which are  pointed out from the
specific heats of these bodies.
  I shall frequently employ the word atom in the course of the fol-
lowing page., but I  do so only as an abbreviation for the terms
equivalent quantity or combining masses.   Of the ultimate particles of
matter, or true atoms,  we know nothing; and all of the  discussions
that have taken place, from the earliest and vaguest speculations of
Democritus or Leucippus, to the modern experiments  of Wollaston
and Faraday, must be  considered as absolutely without  influence on
the positive decision of the question. 
RELATION  OF  CONSTITUTION TO  FORM.   221
                          SECTION II.

                        OF  ISOMORPHISM.

   The general principles of the isomorphism of crystallized sub-
 stances have been already noticed, with relation to the fact of their
 substitution for each other (page 31), and of the advantage with
 which this property may be  applied to determine equivalent num-
 bers (page 212) ; it now remains to study this character, as indica-
 tive of the molecular constitution of the body.
   It must, in the first place,  be carefully observed, that identity of
 crystalline form does not imply similar chemical constitution,  un-
 less under limiting circumstances, which require to be studied with
 great care.  The  principle upon which all  subsequent  reasoning
 must rest is, that in proportion as the structure of the crystal  be-
 comes more  complex, and  the conditions  necessary  for  its forma-
 tion, consequently, more varied, the  greater probability  is  there
 that two bodies shall not assume exactly the same form, unless their
 chemical constitution and the molecular arrangement belonging to
 it be the same, or, at least, similar in both. Hence, in the regular sys-
 tem, there can be no inference whatsoever  drawn with  regard to
 constitution from the crystalline form alone.  Bodies the  most con-
 trasted  possible in their properties and composition have identical
 external figures, as fluor spar, bismuth, alum, sulphuret of  lead, com-
 mon salt.  The conditions  of molecular arrangement for the  forms
 belonging  to this system being the easiest  possible to  fulfil,  the
 greatest variety in the number and grouping of the chemical con-
 stituents is allowable.
   In the other  systems  of crystallization, where the double refrac-
tion and the rings produced by polarized  light, transmitted  along
their principal  axis, indicate  a  much greater complexity of  struc
ture, it becomes highly  improbable that the molecules of two bod-
 ies shall be so similar to  each other as to produce identity  of crystal-
 line form, unless there is, if the body be compound, a similarity of
 composition, or, if the body be  simple,  such similarity of  properties
 as brings  the two into  the same group in  a natural classification.
 This probability increases with the complexity of molecular  struc-
 ture of the crystals.
   The isomorphism of compound bodies has been explained upon
 the supposition that,  in  such cases, the replacing elements were
 themselves isomorphous, and hence  might change places  without
 disturbing the mechanical arrangement of the other components of
 the crystal.   Thus, in the sulphuric, chromic, selenic, telluric, and
 manganic acids, which contain  each three equivalents of oxygen,
 the molecules of sulphur, chrome, tellurium, selenium, and manga-
nese have all the same form.   The perfect  determination of wheth-
er those elements are really thus isomorphous, is very difficult, from
the fact of comparatively very few being crystallizable.  Thus  tel-
lurium and sulphur are those  of which, alone, we know the crystal-
line form, for the only crystals  of selenium that have been observ-
ed are microscopic and  imperfect, and  neither chrome nor manga-
nese can be had crystallized at all.  We must, therefore,  be guided 
 222     ISOMORPHISM OF  COMPOUND BODIES.

 by analogy in such cases ; and if we examine another group of com-
 pounds into  which chrome and manganese enter,  we find that Crg
 03 and Mn,03 are isomorphous with FeA> and Mn.O. and Fe 0. are
 isomorphous with Cu.O.  Now we here arrive, by a chain of iso-
 morphous conditions, at a metal which may be obtained crystallized,
 but the crystalline form of copper is always one of the regular sys-
 tem, as the cube, octohedron, rhombohedron, dodecahedron, &c.;
 while sulphur, with which it should be isomorphous, if this princi-
 ple were absolutely true, crystallizes in two forms, of which one be-
 longs to  the oblique  prismatic, and the other to the right prismatic
 system ;  while tellurium belongs  to the rhombohedral system, af-
 fecting a totally different form altogether.   Numerous other instan-
 ces might be taken ; thus the periodic, perchloric, and permanga-
 nic acids are isomorphous (1.07,  CI 0T, and Mn20;), while the ele-
 ments themselves are certainly  not necessarily  isomorphous, as
 iodine belongs to the right prismatic system.   Also the isomorph-
 ism of the phosphoric  and  arsenic  acids (P.05 and As.05) is one
 of the best examples  that has been found ; but phosphorus and arse-
 nic are so far from being isomorphous, that phosphorus crystallizes
 in the regular, and arsenic in the rhombohedral system.   The prin-
 ciple that compound bodies  are  isomorphous, because their repla-
 cing elements  have  necessarily  the  same figure, is therefore one
 which cannot be received in science.
  Another idea suggested for the explanation of the phenomena of
 isomorphism is, that the crystalline  form of a body is completely
 independent of its chemical composition, and is produced only by
 the number of ultimate  particles or atoms by which it is made up.
 Thus alum has the same form, whether it contains aluminum or iron,
 or manganese or chrome, not because their particles have the same
 figure, but because, in all these cases, the molecule of alum is made
 up of the same number (71) of simple atoms.  This idea is, however,
 even less tenable  than the former; for it supposes that we have ar-
 rived at the ultimately simple bodies, the true  elements, which is a
very unphilosophical  assumption; and according to  it, bodies could
 replace each other only when they were all simple or all of the same
 degree of composition, which is not the case ; and also among the
 simple bodies, that the replacement should be always by an equal
number of ultimate molecules, which is also  negatived by experi-
ment.  Thus we find that an equivalent of a simple  body, K., is re-
placed by a group of five equivalents, N.H4, and that the simple atom,
CI., is replaced by the two atoms Mn2.  This suggestion cannot, there-
fore, be considered as satisfactory, and we "must examine farther
 into the conditions of isomorphous replacement before we attempt
the farther discussion of the source from whence it  has its rise.
  It is necessary first to study the crystalline relations of the unde
 composed bodies, both so far as they have been really observed, and
 as they generate similar compounds which are isomorphous.  The
 simple bodies which are known to crystallize are: 
ISOMORPHOUS  GROUPS.
223
Regular System.
 Carbon.
 Phosphorus.
 Selenium.
 Copper.
 Silver.
 Gold.
 Platinum.
 Mercury.
 Bismuth.
 Titanium.
 Lead.
Rhombohedral.
   Carbon.
   Tellurium.
   Arsenic.
   Antimony.

Right Prismatic.
   Sulphur.
   Iodine.

 Oblique Prismatic.
   Sulphur.
  It is thus seen that, of the simple bodies which may be obtained
crystallized, two thirds crystallize in the regular system, which, as
already noticed, prevents our resting upon their forms any chemical
reasoning; and the bodies whose isomorphous equivalency is  best
established, are not found to  belong even to the same system.   Car-
bon and sulphur are known also to have  each two forms of different
systems, and to be thus dimorphous.  It  must be observed, however,
that tlie assumption of the  forms of the  regular system by so many
of the  simple  bodies, particularly among the metals, may arise from
circumstances such as confer the external cubical figure on analcime
or boracite, and that their internal structure may  be, in reality, more
complex, and their arrangement different; for the metals do not reflect
light as other bodies of the regular system do; they change it into
the state of elliptical polarization ; and in the only case  where light
can  be examined, after, having been refracted through a metal, that
of gold leaf, it is found to be elliptically polarized also.  The dia-
mond  resembles the metals in this property, and  is found sometimes
to possess double refraction,  which should belong also to the metals,
probably, if their  nature allowed it to be tried.  The cubic crystals
of gold, copper, and bismuth, the octohedrons of lead, silver, and
zinc, may therefore belong to the square or right prismatic systems,
the three axes being equal among each other, and  hence the iso-
morphism of the simple bodies be rendered still less probable.
  The examples of isomorphism in compound bodies, which are most deserving of
attention, are the following:
Sulphuric acid......S.O
Telluric acid.......Te.O
Selenic acid.......Se.O. S
  These acids, the composition of which
is similar in all, form salts, which, when
they  contain  the same  base, and the
Chromic acid '                Cr o' fsame ProPortion of base and of water of
Manganic acid'  .'  .'  ."  .'  '.  '. Mn!o| J crystallization, have the same crystalline
Magnesia.....
Protoxide of iron   .   .
Protoxide of manganese
Oxide of copper  .  .   .
Protoxide of cobalt .   .
Protoxide of nickel .   .
Oxide of zinc ....
Oxide of cadmium  .   .
  GROUP II
Mg.O.
Fe.O.
Mn.O.
Cu.O.
Co.O.
Ni.O.
Zn.O.
OilO J
   These protoxides combine with acids
 and form salts, which, when in the same
 degree of saturation with base and water
>o( crystallization, have the same form.
 The sulphates of these oxides combine
 with sulphate of potash to form isomorph-
 ous double salts. 
224
ISOMORPHOUS GROUPS.
                                GROUP III.
 Sesquioxide of iion   .... Fe^"}   These  sesquioxidcs, combined  with
 Sesquioxide of manganese  .   . Mn2Oj I sulphuric acid, with sulphate of potash,
 Oxide of chrome......Cr2G-3 [and with water, form the different spe-
 Alumina........A1203 J cies of alum, which have all the octolie-
 dral form.  They are themselves also isomorphous.
                                GROUP IV.
 Potash........     K.O. A   These fixed alkalies may be substitu-
 Soda........    Na.O. I ted for each other  in the different spe-
 Hydrated ammonia .... N.H3H.O. [cies of alum.   The hydrated ammonia,
 Hydrate of lime.....Ca O.H. O.J H.O. N.H3 (often called oxide of ammoni-
 um, N.H40.), is truly isomorphous with potash in all its compounds; but it is only
 rarely that the compounds containing soda appear to have the  same form.  In min
 erals, and in some forms of alums, potash is replaced by an atom of any oxide in
 Group II., united with  an  atom of water, as hydrate of lime, or by two atoms of
 such compound without water.

                                group v.
 Phosphoric acid......P.O5 )   These  acids combine  with bases in
 Arsenic  acid.......As.05 \ different proportions to form each  three
 classes of salts, between which  respectively the isomorphism  is complete.  It was
 by the study of the forms of the  corresponding arseniates and  phosphates that Mit-
 scherlich first established the principle of isomorphism,  although the true laws of
 their constitution escaped his notice, and were only brought into view by the later
 excellent researches of Graham. Even now there is no example of isomorphism
 between two complete  series of compounds so well established as that of the ar-
 seniates and phosphates.

                               GROUP VI.
 Perchloric acid......Cl.O?^   The corresponding salts of these  acids
 Permanganic acid.....Mn207 > are truly isomorphous, and this group af-
 Periodic acid.......1.07) fords  an example of a form to which I
 shall recur, that of one  equivalent of one body being replaced by two of another as
 CI. by Mn2.

                               GROUP  VII.
 Sulphuret of antimony  .... Sb.S^   These bodies, which are found crystal-
 Sulphuret of arsenic.....As.S3 >lized  in nature, have  the same form.
 Sulphuret of bismuth   .... Bi2S3/The oxide of antimony and the arsenioua
 acid, Sb.03 and As 03, though they are not found crystallized in the same form, ap-
 pear to replace each other in some  salts without changing  its figure, and  may,
 therefore, be sometimes isomorphous.

                               GROUP VIII.
 Stannic acid.......Sn.02 >   These are found native crystallized in
 Titanic acid.......Ti.02 Sthe same form.
  There are many other cases in which similarity of crystalline form has been ob-
served between bodies of more or less analogous constitution  ; but as here I  wish
to bring forward only a  sufficient number of the  most  remarkable examples of the
principle,  I shall postpone for the present the consideration of the remainder.
  The  principle of isomorphism, as  thus described, has been  sup-
  osed to require that the angles of the  crystals of  the isomorphous
  odies should be truly equal, which they are not found really to be,
for even in the best  examples taken slight differences appear.  Thus,
in the carbonates of lime  and  magnesia, the angles of the rhombs
 differ by 2° 36';  in the sulphates of  zinc and  magnesia they differ
by  38 ;  in the sulphates of barytes and  strontia the difference is 2°
 48'.  To express this, the  word plesiomorphism, indicating that such
 crystals are  not  exactly,  but  nearly, of  the same form,  has been
proposed ; but it is  totally  useless, as absolutely isomorphous forms
would then be extremely rare.   It is easy to understand that slioht
 
   ISOMORPHISM IMPORTANT  TO THE  CHEMIST.  225

changes in external circumstances might prevent the absolute iso-
morphism of two bodies, particularly as it is found that  the value
of the angles in different specimens of even  the same substance is
liable to fluctuation even to nearly a degree.  I apprehend that we
must seek the cause of these plesiomorphic differences in the pecu-
liar  circumstances under which the body forms,  particularly with
regard to temperature ; for when a crystallized body, not of the reg-
ular system, is heated or cooled, it expands in different degrees,ac-
cording to the direction  of its axis, and may even contract in one
direction while  it is expanding in another; thus, when carbonate of
lime is heated from 32' to 212 , the linear expansion in the direction
of the principal axis is 0*001961, while in the direction of each hor-
izontal axis a contraction of 0*00056 occurs ;  in consequence of this,
the obtuse angle of the rhomb, which at 50' Fah. is equal to 105°
4, becomes more acute by 8J-', and the acute angles,  which are 74°
54  15 ', become more obtuse  in a corresponding degree.   Hence, if
we heated or cooled, through a certain range of temperature, the
various crystallized bodies of that group, they might be brought to
coincide absolutely in  form,  and possibly, when at first generated,
they were  thus  coincident; but by change of figure,  when brought
to ordinary temperatures, the small plesiomorphic differences may
have occurred.
   Isomorphism, considered as thus sketched, affords to the chemist
the most valuable criterion at present at his disposal for  determin-
ing  those  substances which replace each other most truly in com-
bination ; and where a number of bodies are so connected by exter-
nal form, very important conclusions may be obtained as to the in-
ternal arrangement of their constituents.   In this manner it has
been satisfactorily established, that bodies may replace each other
in proportions quite different from  their ordinary equivalents, and
thus pass,  as it were, by  a  doubling or trebling of their atomic
weights, into a  different  natural group; and that even two bodies,
combined in an equivalent of each, may form a complex group, ca-
pable of being substituted  for one of simpler structure.  Thus an
equivalent of chlorine is replaced by two equivalents of manganese ;
an equivalent of silver is  replaced by two equivalents of copper ; an
equivalent  of soda or of  potash is replaced  by two equivalents of
lime, or of one of lime  and one of water, or by one of lfme and one
of oxide of manganese  or of iron, or by ammonia  and water united
to each other, or to an equivalent of a protoxide of the magnesian
group.  By such observations we obtain the foundations of a philo-
sophical classification of bodies, with which the  analogies drawn
Croin  purely chemical characters are found remarkably  to corre-
spond.
  But it is important to ascertain whether the isomorphism of various bodies es-
tablishes necessarily, or even probably, in the absence of other reasons,  grounds for
assimilating the formulae of the bodies, or imagining that their chemical constitu-
ents are equivalent  and are arranged in the same way.   This is a point which has
been, as I consider,  much misunderstood, and has led to some error and confusion.
Thus anhvdrous sulphate of soda crystallizes in the same form as perchlorate of
barytes and permanganate of barytes; and if it be necessary, as a consequence of
isomorphism, that these bodies  should have similar constitutions, we must change
the formula, S.Oj . Na.O. into S207 . Na^O.. in order to make it resembie Mn207.
Ba.O.  This requires us to compare the sulphates whose elements are most pow- 
 226  PRINCIPLES  OF ISOMORPHOUS REPLACEMENT.

 erfully united, with some of the most easily decomposed salts that we know ; it re-
 quires us to consider the alkalies as  being  suboxides, which is opposed by every
 circumstance in their history; and it requires us to consider two equivalents of so-
 dium as being equivalent to one of barium, for which no other evidence can be had
 from other examples.  But, again, the anhydrous sulphate of soda  is isomorphous
 with sulphate of silver, and hence the formula of this last should be S207 . Ag20.,
 which is so totally unsupported by other evidence that it has been proposed to sub-
 divide the atomic weight of silver and sodium, for the purpose of explaining the iso-
 morphism of Cu2 and Ag.   These examples are sufficient to show how unphilosoph-
 ical is the attempt at rashlv inverting the principle of isomorphism, and seeking to
 deduce, as  a necessary consequence  of the  mere similarity of form, similarity of
 chemical constitution.  Bodies of similar chemical constitution affect the same
 crystalline form ; but bodies  of the most diverse natures may have the same crjs-
 talline form also.  Even without speaking of the regular system, where fluor spar
 and alum, Ca.F. and K.O.  . S.03+A1203 . 3S.03+24H.O., have the same form,  we
 find numerous examples of this fact;  nitrate of soda and carbonate of lime are iso-
 morphous in the rhombohedral system, and nitrate of potash and carbonate of lead
 in the right prismatic system; the chemical constitution of the formulae N.05. Na.O.,
 and C02 . Ca.O., and that  of the  formulae N.03  . K.O.,  and C02 . Pb.O., are
 widely different, but the forces by which the assumption of crystalline form is gov-
 erned  are alike.  Even in these instances the attempts at generalizing the chemical
formulae have been tried, and the nitrates of soda  and  potash have been written
 N.06 K. and N.06. Na., with which the formulae of the carbonates, when doubled,
 C206Ca2 and C206Ba2, have been compared.  In this way one equivalent of soda is
made  isomorphous with two  of barytes, while by a former and similar reasoning,
one of barytes was made  isomorphous with two of soda.  Bisulphate of potash,
 K.O. . S.03-r-H.O. . S.O3,  crystallizes in two forms,  one of which is  that of sul-
phur, a simple body, and the  other of which is that of feldspar, K.O. . S3-f-Al203.
3So3.  Here, in neither case  is there the slightest similarity of constitution.
   The circumstances  of isomorphous replacement may be reduced
 to the  following  simple  propositions, with which I shall  terminate
 the subject:
   1st.  Similarity of  crystalline  form  requires  that the molecular
 structure of the bodies shall be alike, but has no necessary reference
to the chemical nature or composition of  these molecules.  Exam-
ples.—Nitrate of soda and  carbonate of lime, sulphate of soda and
 perchlorate  of barytes, bisulphate of potash and sulphur.
   2d. When the physical molecules consist of chemical elements
which follow the same  laws of combination,  and  which belong  to
 the same chemical family, the similarity of molecular  structure is
most  completely and  most easily  produced, and such crystals are
isomorphous.  Examples.—Sulphate of zinc and sulphate of magnesia,
carbonate of lime and carbonate of zinc, sulphate of barytes and sul-
phate of strontia.
   3d. But identity  of molecular structure may  result from  the ag-
gregation of substances the most different in their chemical relations,
and hence isomorphous bodies are not necessarily  of similar chem-
ical constitutions.
   4th.  As the influence  of the chemical constitution does not extend
 to the  absolute determination of the molecular structure, a  body,
 chemically  the same, may  assume incompatible crystalline  forms,
 and so become dimorphous ; but as the chemical structure influences
 the molecular  arrangement in some  degree,  dimorphous  bodies,
 which are isomorphous  in one form, are generally so in the  other,
 they  are isodimorphous.   Examples.—Sulphur, bisulphate of potash,
 nitrate of potash and  carbonate of lime, garnet and  idocrase,  arse-
 nious acid and oxide of antimony.
   5th. We cannot assert that the similarity of form of truly isomorph- 
OF DIMORPHISM AND ISOMERISM.       227
ous bodies results from the isomorphism of their elements ;  for,
so far as our observation goes, their simple constituents are not
necessarily, or even usually isomorphous.   Examples.—Arseniates
and phosphates, sulphates and seleniates.
  6th. We cannot assert that isomorphism  results from the aggre-
gation of the same number of simple molecules ; for we  do not
know what bodies are truly simple, nor do we know, without doubt,
that we  can value the relative number of atoms present; but, even
in the existing state of our knowledge,  we have numerous exam-
ples  of  bodies truly isomorphous which contain an unlike number
of atoms according to our present ideas.  Examples.—Potash and
ammonia, natrolite and mesotype, sulphur, feldspar, and bisulphate
of potash.
  Finally. Isomorphism does result from the aggregation, according
to the same laws, of similar molecular groups, which are most gen-
erally formed by the reunion of similar chemical substances in the
same state of combination.

                         SECTION III.
   OF DIMORPHISM AND ISOMERISM, AND  OF THE THEORY OF TYPES.

  The fact of the same body being capable of crystallizing in forms
belonging to two different systems has been already frequently re-
ferred to,  but, for convenience of reference, a more detailed list of
such cases is here inserted, taken from Professor Johnston's excel-
lent report on the subject made to the British Association. 
228
LIST  OF  DIMORPHOUS  BODIES.
I. Elementary bodies:
  Sulphur.....A
  ------.....B
  Carbon.....A
i\
II. Bi-elementary Compounds :
   Dioxide of Copper  . A i

   -------------   . B\
   Disulphur. of Copper A )
Sulphuret of Silver
Sulph. of Manganese A
------------------B
Bisulphuret of Iron
on .  A >
    Biniodide of Mercury A

    Bichlor. of Mercury  . A )

    Arsenious acid   .   . A )
    ------------.   . B i
    Oxide of Antimony  . A (
    -------------—  . B i
III.  Compounds of 3 Elements ■'
    Carbonate of Lime  . A \
    ---------. b(
    Carbon, of Magnesia A i
    ------------------B f
Carbonate of Iron

Carbonate of Lead
Nitrate of Potash

Chromate of Lead
AbS

bS
M
B J
M
B i
IV.  Compounds of 4 or more
      Elements:
    Sulphate of Nickel  . A
    ----------------. B
    Seleniate of Zinc   . A
                       B
Bisulphate of Potash A (

-----------------B

Biphosphate of Soda A

------------------B
Garnet.....A


Idocrase.....B
Baryto-Calcite
Sulphato- Tricarbon-
  ate of Lead
■:.\
     Symbol or Form._______


         s.

         C.


       Cu,0.


   Cu.S. orCu2S.

   Ag.S.or AgjS.

       Mn.S.

       Fe.S2.

       Hg.Ij.

      Hg.Cl2.

      AsjOj.

       Sb,03.


    Ca.O.+C.Oa.

    Mg.O.-+-C02.

    Fe.O.+C.Oj.

    Pb.O.+C.Oj.

 *   K.O.+N.Os.

    Pb.O.+Cr.O,.



 Ni.O.+S.03+7H.O.

Zn.O.+Se.O,+7H.O.
K.O.+S.03+H.O.+S.03.


  Na.O.+P205+4H.O.

    or Na.H2P.+2H.

            AlV
Ca3Si.+-
Fe
Si.
Ca.O.)po   Ba.O.)rn
Sr.0.fLO»+Sr.O.,CO*

      Pb.S.+3Pb.C.
 _______________Crytallmc Fnrni.

  Rt. Rh. Pr, M. on M. 101-59, Haid.
  Oblique Rh. Pr. of 90° 32', M.
  Reg. Octohedron.
  Rhombohedral.

  Cube.
  Rh.  of 99° 15', 6 sid. Pr. Rhomb.
   cleav., Sk.
I Do., Primary a Rhomb., P. on P'
^  =71° 3C.
( Reg. Octohedrons.
( Cube in Silver glance.
I Rhomboid.
j Cubes.
( Rhomboid.
i Cubes.
  Rt. Kh R., M. on M'. 106° 2'.
i Octohed. with square base.
\ Rt. Rh. Pr., M.M.= II4°.
I Rt. Rh. Pr., M.M.=71-55.
( Octohed. with rect. base.
i Reg. Octohedrons.
) Rt. Rh. Pr.
I Do., M. on M'. 136° 58'.
( Reg. Octohedrons.

t Rhomb, of 105° 4', M.
1 Rt. Rh. Pr. of 116° 16', A*
) Rhomb, of 106° 15'.
} Rt. Rh. Pr.
j Rhomb, of 1070.
{ Rt. Rh. Pr., 108° 2fi', 118° 0'?
J Rhomboid, 104° 53£' ?
\ Rt. Rh. Pr. of 117° \4',Ku.
j Rt. Rh. Pr., M.on  M'.=118052',Iu,
\ Rhomboid of 106-36, Fm.
i Ob. Rh Pr.
\ Square Prism.
i Rt. Rh. Pr., M. on M'. 91" 10', Bk.
( Square Prism.
i Rt. Rh Pr.
( Square Prism.
i Rhombic Octohed. (form of sulphur)
<  M.
( Ob. Rh. Pr. (form of feldspar), M.

  Rt. Rh. Pr. of M. on M'.93° 54'.

  Do.        of         78° 30'.
  Reg. Dodecahedron.
 Square prism.
i Oblique Rh. Prism.
< Right Rh. Prism (form of arrago-
f   nite).
< Acute rhomboid of 72° 30'.
( Rt. Khomb. Prism,*  M.on.M=120.
  * Haidinger says an oblique rhombic prism, which, according to the subsequent measurement of Brooke, iii»
correct. Bk., Brooke ; Ku., Kupfer; Lv.,hevy; M., MitscherUcli;  Sic, Suckow. 
VARIOUS STRUCTURE  OF DIMORPHOUS B O D I E S.  229

  The molecular arrangements which produce this diversity of form
are not in general of equal stability; on the contrary, one figure ap-
pears to be in general forced upon the body, and is abandoned by
it upon very slight disturbance.  Thus, when  a prism of arragonite
is heated in the flame of a spirit-lamp, it breaks up into a congeries
of little rhombs  of common calc spar at a temperature far  below
that at  which the carbonate of lime commences to be decomposed*
but no  alterntion of temperature can convert calc spar back again
into arragonite.  Indeed, arragonite appears to be formed only be
tween very narrow limits of temperature.   When chalk is melted,
it forms, on  cooling, marble, whose fracture  shows it to have the
rhombohedral structure ;  and when carbonate of lime is precipitated
at ordinary  temperatures, the  microscopic  crystals  produced are
rhombohedrons ; but when it is precipitated from a boiling solution,
it deposites minute crystals of arragonite, which a hi  her or a lower
temperature would have prevented.
  When sulphur has been crystallized by fusion in oblique rhombic
prisms, these lose their transparency after  a day or two, and change
into a mass of very minute right rhombic  octohedrons.  When the
arsenious acid is crystallized in rhombic  prisms, it alters slowly,
and eventually becomes a dull white  mass, which is a congeries of
regular octohedrons ; but if the rhombic form of the acid be dissolved
in muriatic acid, and the solution set to crystallize, it is deposited
in the octohedral form, and the formation of each crystal is accom-
panied by a brilliant flash of light, indicating probably the moment
of the  change of molecular condition.   One form is therefore the
stable condition of arrangement, the other being produced by the
sudden fixation of the  molecules in a form which is  naturally  only
transitive, and from which they free  themselves  as soon  as the ex-
ternal  circumstances admit of their suitable motion among each
other.
  Independent of  the change in external figure,  dimorphous bodies
present remarkable differences in physical properties * thus the den-
sity is  generally different *  in one form the substance is more solu-
ble than  in the other; they differ also in  hardness, and, generally
speaking, in all characters  derived from the physical arrangement
of molecules.
  A body in its dimorphous conditions presents frequently a differ-
ence of chemical  properties deserving of particular  notice.   The
bisulphuret of iron, in its cubical form, is remarkably permanent,
not being acted on either by air or water * but in its right rhombic
form, when  exposed to  moist air, it absorbs oxygen with avidity,
and is converted into a crystalline mass of copperas.   On this prin-
ciple depends, most probably,  the change of molecular condition
which takes place in oxide of chrome, peroxide of tin, zirconia, and
alumina, when exposed to a temperature just below redness.  These
substances, which  had been  easily soluble in acids, become almost
totally  insoluble, except in  boiling oil of vitriol,  and this change is
generally  accompanied by  the  spontaneous ignition  of  the body,
which  the temperature applied would  be quite insufficient to  pro-
duce.
  Independent of crystalline form, we must refer to circumstances 
230    CHANGES APPROACHING  DIMORPHISM.

similar to those which produce dimorphism, a variety of differences
in physical constitution observable in certain  bodies;  thus melted
sulphur is, at 230D F., perfectly liquid* on being heated to 430J it
becomes thick, and so tenacious that the vessel containing it may
be inverted without it running out ;  when heated farther to 480 , it
becomes again liquid, and continues so till it begins to boil.  When
the red oxide of  mercury is heated  nearly  to redness, it becomes
almost quite black.  If the red iodide of mercury, formed by pre-
cipitation, be sublimed, it becomes yellow ; but if the sublimed mass
be scratched with a pin, the edges of the scratch turn  red, and the
redness spreads from thence until the whole mass  is converted into
its original condition.  Even in liquids and gases,  this difference in
molecular condition, whether produced by temperature or by other
causes, appears frequently to  occur.  Thus the  liquid hyponitrous
acid (N.03)  is deep green at 60\  but at 4° it is quite  colourless;
and the deep red  gas of nitrous acid (N.04) becomes, when heated
to 212 , absolutely black and opaque.  The compound of starch and
iodine, so beautifully blue-coloured  at ordinary temperatures, be-
comes colourless  when heated to 200', but acquires its original  tint
in proportion as it again cools.  In all such  cases, there is scarcely
room to doubt but that, if we had as perfect methods of determining
the molecular structure as is afforded by the measure of the angles
and the optical properties of the bodies when crystallized, we should
find these phenomena to  depend upon causes of the  same kind.
  In solid bodies, a difference of molecular structure, fully equiva-
lent to that to which dimorphism may be referred, is capable of being
produced by very  simple means. Thus, when a plate of glass is com-
pressed by means  of a screw, it assumes a doubly refracting structure,
and gives with polarized  light a cross and rings, variously disposed
according to the direction of the pressure.   In this case, the change
of structure arises necessarily from an  increase  of density in  the
compressed  portions; but the  same effect may be produced by the
converse process  ; a plate of glass which has been suddenly cooled
from  having been red-hot, assumes a similar doubly refracting  and
polarizing structure, although here the density is diminished in place
of being  increased.  I have  found  the  sp. gr. of  glass suddenly
chilled to be  about  r^  less than that  of glass of the  same  kind
which had cooled slowly, indicating that the volume was the same
that it had occupied at a dull  red heat, and  that hence the internal
molecules were arranged so as to occupy a greater space than in the
usual condition.
   The differences of chemical properties may, however, proceed
much farther, so that in place of considering that there is one chem-
ical substance which may exist in two molecular conditions, we are
obliged to consider that  the individuality of the  body is lost, and
that in  its two forms it  constitutes two  distinct  and  independent
chemical substances.   Thus, by the  action of sulphuric acid on al-
cohol, we obtain  a gas consisting of carbon and  hydrogen, in the
proportion of an equivalent of each.  In the destructive distillation ol
wood, a solid substance is obtained, fusible like wax, and volatile  only
at a high temperature ; this consists also of carbon and hydrogen,
and in the same proportions.  These elements, so combined, present, 
PRINCIPLE  OF  ISOMERISM.
231
therefore, a difference in molecular arrangement still greater than
those which have been observed among merely dimorphous bodies,
and when we examine their chemical relations, the diversity becomes
still more marked.  The gas (olefiant gas) is remarkable for the num-
ber of compounds to which it gives rise, and has been, from the va-
riety  of its reactions, of great influence on the existing theories of
organic chemistry.  The solid is inattackable even by the strongest
agents, and, from its total indifference to combination, has been called
paraffine (parum affinis.)  In this case, the difference of properties
indicates a difference of structure  much more profound than that by
which change of density,  colour,  or even crystalline arrangement
could have its source ;  it is not merely that the molecules are dif-
ferently placed, but that the molecules are different; the carbon and
hydrogen which unite to constitute the chemical equivalent of the
body  are themselves differently arranged, and thus give rise to dif-
ference of properties; and the physical molecules formed  by their
reunion being again grouped according to dissimilar laws,  produce
the diversity of  physical properties and states of aggregation; the
bodies being thus in every property unlike, are to be looked upon
as independent substances; they are said to be isomeric (from tooe;
fjppoc) because they have the  same ultimate composition, but in all
their  chemical relations  they may differ as widely as bodies which
have  no  element in common.
   When, therefore, the groups of chemical molecules are differently
arranged, the various differences in colour, density, solubility, and
figure which belong to dimorphous bodies are produced ; but when
the difference of arrangement extends to the chemical constituents
of these molecular groups,  independent, but isomeric bodies are
produced.
   It is generally found that this difference in the constitution of the
chemical molecule has the effect of changing, in a simple  manner,
the equivalent number of the body.  Thus oil of turpentine and  oil
of citron are isomeric, each having the composition C,H4; but when
we combine these  oils with muriatic  acid, we find that the  equiv-
alent  group of oil  of turpentine  contains C20H,6, while that  of oil of
citron is only C,0H.,; it  is  remarkable that,  though  the  chemical
group of oil of citron is only one  half the weight of that  of oil of
turpentine, it exercises the same power of circular polarization, but
in the opposite direction.   Another example  of this simplicity of
proportion  in weight between the equivalents of isomeric bodies, is
met with in common alcohol and methylic ether, that of the former
being t\H„02, that of the latter being C\H30.
  The difference of the chemical constitution  in isomeric bodies is
not limited to  magnitude, as determined by the weight  of their
e juivaleut, but extends to internal structure.  Thus alcohol is com-
posed of ether and water, C.H ,0.-f H.O., while methylic ether cannot
be resolved into those substances.  Formiate of methylene and o-lacial
acetic acid  are each C4H404, not differing even in the weight of their
equivalent; but all the properties of these bodies show that glacial
acetic acid is C4H3Oj+H.O., while formiate of methylene is C2H.03 +
C.H.,0   Instances  of this kind might  be multiplied to any extent,
'rut these will be sufficient to illustrate the principle. 
232 CONNEXION OF DIMORPHISM AND ISOMERISM.

  It is necessary, however, in studying such cases of isomerism, to
bear in mind what has been so beautifully shown by Graham, that
the presence of foreign bodies, in quantities so small as to be total-
ly unappreciable, except in the most rigidly accurate analysis, may
change so completely the properties of bodies that they will sim-
ulate isomerism.   Thus phosphuretted hydrogen may exist in two
conditions, in one of which it is spontaneously inflammable, and in
the other not.   They both give,  on  analysis,  the  same formula,
P.H3 • but the first may be changed into the second  by mere admix-
ture with a very small quantity of the vapour of ether, and the sec-
ond may be converted into the first by the most minute bubble of
nitrous acid gas.   Such bodies, therefore, which owe their diversity
of  properties to  accidental circumstances, are not isomeric, and
must be carefully distinguished from those before described.
  As we have thus traced a gradual transition from the feeblest in-
dications of dimorphism, to the complete difference  of structure and
properties constituting isomerism, it  becomes  an interesting ques-
tion whether we  may not have occasion to retrace our steps, and
to seek in those  bodies which we have hitherto considered as only
differino- in physical properties, for evidence of difference in chem-
ical arrangement.  May not a simple substance, as  sulphur or anti-
mony, enter into  combination with equivalents  of different weights,
and so resemble  oil  of turpentine and oil of citron; and may not
this difference in equivalents be the source of diversity in forml
When sulphur crystallizes in the form of bisulphate of potash, may
we  not  reasonably suppose  that its  molecules are  grouped into a
complex figure, like  that of the compound salt, and that its equiv.
alent is, in proportion, greater than when it crystallizes as a simple
body 1  We  say that two ordinary equivalents of manganese replace
one of chlorine,  but  is it not really that when  manganese replaces
chlorine, its equivalent is double what it is when it replaces hydro-
gen or copper'(   Manganese  replacing chlorine, is to manganese re-
placing copper, what oil of turpentine is to oil of citron ; and hence
it may be isomeric with  itself, for the functions it performs in  its
two modes of combination are the most widely different possible.
The bisulphuret of iron, in its cubical form, is Fe.S2, and, like Mn.02,
is decomposed only by a red  heat, when it parts with one third of
its volatile constituent;  but in its rhombic form, may not its equiv-
alent be Fe2S4, resembling C1.04, and, like it, be decomposed by the
slightest causes'?
  The circumstance that isomeric bodies are almost  universally con-
nected by simple relations between  their atomic weights, coupled
with the idea that even among the simple bodies a  kind of isomer-
ism may be the cause of their dimorphous conditions, acquires  re-
markable interest from the fact that the equivalent numbers of many
of the simple bodies are closely related to one another, as is shown
in the following  table : 
NATURE OF  COMPOUND RADICALS.      233
1^ equivalent of bismuth
= 106 6511  equivalent of zinc
2 " palladium. .	. 10672	1	" yttrium
2 equivalent of osmium . .	. 199 72	i	" antimony .
1 " gold . . .	. 19921	i	" tellurium .
1 equivalent of platina . . .	. 9884	2	" sulphur
1 " iridium . .	. 9884	1	equivalent of cobalt . .
1 equivalent of molybdenum .	. 4796	1	" nickel . .
4 " tungsten . .	. 4740	h	" tm . . .
                                                        :  3231
                                                        .  3225
                                                        .  32 40
                                                        .  32 13
                                                        .  3224
                                                        .  29 57
                                                        .  2962
                                                        .  29-46

  May it not be possible that science shall hereafter find the metals
so connected to be truly isomeric 1   In no case are their properties
more  different; and  we find in  the racemic and tartaric  acids an
example of the general similarity of  properties in the compounds
of isomeric bodies, which is so remarkable in the combinations of
sulphur and tellurium, or of cobalt and  nickel, among the simple
substances.
  Considerable probability is given to the idea of the compound na-
ture of bodies at present considered  simple,  by the  existence of
certain  compound bodies which simulate the properties of, and
enter into combination subject to the same  laws as the undecom-
pounded substances.   Thus carbon  and hydrogen unite to form a
gas, cyanogen, which combines  with  the metals, with oxygen, with
hydrogen, &c., precisely as chlorine does ;  it is the origin or root
of a series of cyanides, as chlorine is of a series of chlorides, and
it is hence called a compound radical.  The discovery of  this prin-
ciple by (!ay Lussac was the foundation of all that is exact and
philosophical in our  views of organic  chemistry.  Bodies  which
contain the same ultimate elements may be different, because they
contain different  radicals, precisely as the  salts of niekel and the
salts of cobalt will remain quite  distinct, even should nickel and co-
balt be  hereafter  shown  to  be isomeric bodies. This principle of
compound radicals is so  beautiful and  so easily applied that its use
has  been, as I  conceive,  somewhat  too  extensively adopted; and
hence, wherever simplicity  of expression was  sought  for, or a dif-
ference of properties was to be  explained, the formulae of organic
bodies were  perhaps too hastily grouped, by  the assumption of a
hypothetic radical, of which the different bodies of the series were
supposed to be combinations.  It is certain that, in many cases, this
plan has been of great use to science, as in the benzyle theory  of
Liebig,  and in the ether and  ammonia  theories proposed by Ber-
zelius and myself; but I consider the degree to which it has latterly
been extended, by which the existence of a great variety  of bodies
lias been assumed, for which there is scarcely any reason, except
some additional simplicity of formula;, which often served to con-
ceal the truth, to have been productive of much disadvantage  to
true >eience and a misdirection  of thought, which we should seek
as much as possible to avoid.
  In all that has been described  of the arrangement of the elements
of compound bodies, their union has been considered as  resulting
from  their antagonistic and mutually neutralizing  properties, and
the  successive stages of composition  being  effected  in binary
groups: thus crystallized alum  is a compound of water and dry
alum ; this last, a compound of sulphate  of potash and sulphate of
                             Gg 
234    CONSTITUTION OF  ORGANIC  BODIES.
alumina; these respectively, compounds of sulphuric acid and a base
which consists of oxygen united to a metal; the sulphuric acid it
self being formed by the union of oxygen and sulphur.  This view
results necessarily from what has been said of the nature of chem-
ical affinity, and expresses faithfully the principle upon which the
electro-chemical theory has been formed ;  there is no doubt but that
the constitution of inorganic bodies is regulated in this way, but we
meet  with considerable  difficulty in applying its principles to or-
ganic chemistry.   Thus  I  myself suggested a few years ago, that
the formic and acetic acids should be looked upon as oxides of com-
pound radicals, formyle and  acetyle, C2H.03 = Fo.03 and C4Ha03=
Ac.03, by which means a variety of bodies of analogous constitution
were  simply connected together, as the formyle  or  acetyle, which
combine with  oxygen to  form those vegetable acids, combine with
iodine, chlorine, sulphur, and cyanogen to form binary compounds,
precisely as manganese (a simple radical) combines with oxygen to
form manganic acid, and with chlorine, &c, to form an analogous
series of bodies.  I am far from  abandoning this view : the question
of its full applicability will be discussed among the general laws of
organic chemistry, but at present we will attend to only one circum-
stance connected with it.   Hydrated acetic  acid is formed from al-
cohol, by the latter losing two equivalents of hydrogen, and gaining
two of oxygen in their place; and in like manner, hydrated formic
acid is produced from pyroxylic spirit, by losing H2 and gaining 02,
thus:
Alcohol.....C4H6C-2
    gives by  .   .  —Hj-f-Q2
Hydrated acetic acid .  C4II4O4.
Pyroxylic spirit  .  .  C2H40-2
   gives by  .  .  —H,-f02
                                    Hydrated acetic acid .   C2H2O4.

  Now, if acetic acid contains acetyle, does it exist in alcohol; or
must  we consider that,  by the  gradual process of oxidation, the
molecular structure of the alcohol is totally broken up, and that the
acetic acid formed has no natural or necessary connexion with itl
  We owe to Dumas the introduction of a principle  into organic
chemistry, which, applied to changes such as those described above,
promises to shed considerable light  upon the  reactions and consti-
tution of organic bodies; but  it yet involves conditions so opposed
to our present ideas of chemical affinity, that we can only look on
it as a proposition which merits profound attention.  He considers
that the elements of organic bodies are not united by affinity arising
from opposition of properties, but that  they  represent a group of
molecules  connected by a  single force, precisely as the  planetary
masses are by gravitation,  and just as any of the planets might be
replaced in the solar system by a ball of  matter of totally different
chemical  properties,  provided its gravitating mass remained the
same, without disturbing in the  least the conditions of mechanical
equilibrium ;  so, in an organic substance, elements of the most di-
verse characters may be substituted  for each  other, and yet the
molecular group remain  unaltered in  structure and  physical consti-
tution.  Thus the  molecular  group  of  alcohol (C4H60,) contains
twelve chemical atoms. When  it is changed into acetic acid (C4H4O4),
the number of chemical atoms is the same ; the mechanical type of 
OF ACTIONS  BY  CONTACT.
■)'>*"■
 the body is unaltered, although its chemical properties are complete-
 ly changed and a new substance formed.  Bodies, therefore, are
 classified by Dumas according to certain types or models.  When
 the number of molecules in the equivalents of the bodes remains
 the same while the nature of the elements changes, the bodies have
 the same mechanical type ;  but if the substitution of elements is ac-
 companied by a change of properties, the chemical type of the ori-
 ginal body is destroyed.   Thtis alcohol and acetic acid have not the
 same chemical type.
   When acetic acid is treated with  chlorine, it loses three equiva-
 lents of hydrogen and gains three of chlorine (C4H404—H3+C13=
 (',('l.;H.Oj), forming chloroacetic acid.  The sum of the molecules
 is here twelve, and this substance has the same mechanical type as
 alcohol and common acetic acid ; but in changing to this body, com-
 mon acetic acid scarcely changes its properties, and hence is said
 to retain its chemical  type.  When ether (C4H,0.) is treated with
 chlorine, its hydrogen is totally replaced by chlorine, and the body
 (C4C1,0.), chlorine ether, is produced  ; the number of molecules being
 the same, the mechanical type is preserved ; but more, the chlorine
 ether combines with acids forming salts like those of common ether,
 which it resembles in all essential chemical characters, and hence,
 in this case, the chemic il type is undisturbed, notwithstanding the
 total substitution of chlorine for hydrogen, a body differing from it
 so much in general characters.
   The question how far this theory of types should be adopted, and
 how far the law of substitution  on which it rests is verified by ex-
 periment, will be hereafter examined.  The theory is here only no-
 ticed as involving important relations between the mechanical struc-
 ture and the chemical constitution of organic  bodies.

                          SECTION IV.
                       OF  CATALYSIS.

   The decomposition of compound bodies is frequently effected by
 the intervention of causes which cannot be referred to ordinary af-
 finity ; and in many cases, bodies which have  but little tendency to
 unite, enter into combination when brought into contact with a sub-
 stance for  which neither has affinity, and which remains, after the
 action is completed, perfectly unaltered.  Thus, when hydrogen and
 oxygen, mixed together in a gaseous form, are brought into contact
 with a clean slip of platinum, they  gradually unite, and so  much
 heat may be evolved by their rapid combination as to  ignite the
 platinum, and explode the remainder of the gas.   In this case we
 seek to explain the phenomenon by supposing  that the platinum
 condenses  powerfully on its surface  a layer of mixed gaseous par-
ticles, and thus brings them within the sphere of their mutual attrac-
tion.  But  this explanation  does not apply  to other cases.   If we
boil starch (C^H, 0m) with diluted sulphuric acid, it is converted suc-
cessively into dextrine, gum, starch-sugar, and,  finally, crystallizable
grape-sugar (C H,,0 ), having associated to itself the constituents
of two equivalents of water.   At  the  termination of the process, the
sulphuric acid is found unaltered in  properties and in quantity, so 
236           ANALYSIS  AND  CATALYSIS.
that the smallest  portion of sulphuric acid is sufficient to convert
into sugar an  indefinitely great quantity of starch.  If oxamide
(CAN-H.) be diffused through water, in contact with the smallest
possible quantity  of oxalic acid, it gradually disappears, and, appro-
priatincr to itself the elements of an equivalent of water is converted
into ne°utral oxalate of ammonia, (CA+N.H3), the small quantity of
oxalic acid originally  added remaining unaltered and in excess.
  Amono- instances of decomposition by forces of this kind, the ox-
ygenated water (H.O,) may be taken as an example.  This substance,
when pure, separates spontaneously, after some time, into water and
oxygen  gas, but its decomposition may be rendered violent and in-
stantaneous by putting  it into  contact with finely-divided metallic
platinum,  or metallic silver, or black oxide of manganese, or fibrine,
or a variety of other bodies.  In all these cases, the body added re-
mains quite unaltered ; no affinity can be traced between it and the
oxygenated water, the mere presence of the foreign body appearing
to cause the decomposition.
  Berzelius, who  first directed general attention to these phenomena,
proposed  to attribute them to a peculiar  force, differing  from ordi-
nary affinity.  When one body is decomposed by another, in virtue
of a superior affinitary power, the decomposing body combines with
one element of the body which is decomposed, and the other is then
expelled.   It is in this way that we obtain the constituents of bodies
by  ordinary analysis ; and for distinction, he proposes  to term such
decompositions as those just described, operations of  catalysis, and
to name the power which these bodies have of acting by mere con-
tact, a catalytic force.
   It is evident, certainly, that by giving a name to this class of phe-
nomena, we are enabled usefully to  contemplate them as a group,
and to  examine more easily their relations  to each  other and to
ordinary action ;  yet  the word  catalysis really teaches us nothing of
the  phenomena, and it is, indeed, improbable  that such varied cases
of union and separation should be derivable from one single force.  It
is hence necessary, before concluding on the nature  of this action,
to trace it through a greater variety of cases, and to revert  briefly
to  the conditions of affinity by which the elements  of compound
bodies are held together.
   The elements  of a compound substance are retained together in
a certain molecular arrangement, because the affinities are then sat-
isfied ;  but it is natural to suppose that,  while the elements remain
the same, their affinities for each other might be just as  completely
 satisfied by a different molecular arrangement.   The  original body
 might therefore be changed into another, by a change in the action
 of its own particles, independent of any substance acting chemically
 on it from without;  and hence the principle of catalytic decompo-
 sition resolves itself  into a means of disturbing the molecular equi-
 librium of a compound body, so that it can  be  only restored when
 the particles are  differently arranged.  Catalysis may, therefore, be
 produced not  merely by the presence of various bodies, but stin
 more  remarkably by the action of  physical agents, among which
 heat is the most powerful ; thus, when acetate of lime (C4Ha04Ca*)
 is strongly heated, the equilibrium  of its  molecular  group is over 
COMMUNICATION  OF  MOTION.          237
turned, and when the affinities again satisfy themselves, two new
bodies result, acetone and carbonate of lime (C3H30. and C.OaCa.).
Destructive distillation is therefore a catalytic process, and the or-
igin of all pyrogenic products is to be traced to the new conditions
under which the affinities are satisfied, which had originally united
the elements of the body exposed to heat.  The sudden decomposi-
tion  of  explosive bodies by an elevation of temperature or by  a
slight blow, is traceable to the same disturbance of the old equilib-
rium, and establishment  of the new.  A  most important means of
thus setting into motion  the particles of  bodies, and enabling them
to rearrange themselves under new forms, consists in bringing them
into contact with a substance already in a state of decomposition;
thus, if oxygenated water be brought into contact with oxide of sil-
ver, the  decomposition is propagated to the latter, which is com-
pletely resolved into oxygen and metallic silver ; if peroxide of lead
be used, it is converted into protoxide by the escape of half its ox-
ygen, and even the black oxide of manganese may be  reduced to
the state of protoxide if the solution contain an acid; in all these
cases, the decomposition, which commenced with the oxygenated
water, extends to  the metallic oxide, in  virtue of the motion com-
municated to  their particles, enabling the new arrangement to be
effected.  In some  instances, in  organic chemistry, this principle is
still more beautifully shown.  If a solution of  sugar (Cl2HuO,,) be
brought into contact with a little decomposing gluten or yeast,  it
unites with the elements of an equivalent of water, and divides it-
self into two equivalents of alcohol, 2 (C,H„02),  and four of carbonic
acid, 4  (C02).  If  a solution of urea (C.O.N.H2) be put in contact
with  yeast, it  unites also with an atom of water, and is then decom-
posed into an equivalent of ammonia (N.H3) and one of carbonic
acid.   The conversion of starch into sugar in the processes of ger-
mination and of malting, is effected by a  substance which accompa-
nies the starch in the grain.  This substance is called diastase, and
is analogous in  most  of its properties to vegetable  gluten.  The
slow decomposition of the diastase communicates to the molecules
of many thousand  times  its  weight of starch the degree of motion
necessary for  their rearrangement,  and  the appropriation of the
elements of water  requisite for the formation of starch-sugar.
  If platinum, which is, by itself, totally unacted on by nitric acid,
be alloyed with silver, the alloy dissolves in dilute nitric acid with-
out leaving any residue.   Pure  copper is not acted upon  by dilute
sulphuric acid ; but when it is alloyed with  nickel and zinc, as in
the argentine, or German silver of  commerce, it dissolves complete-
.y.  In these cases, the molecular action which produces the com-
bination  with the acid was not possessed by the platina or copper
when alone, but is acquired by them, being transmitted from  the
other metals with which  they are alloyed.
  It may not be easy to  reduce to the action  of  this principle all
phenomena of catalysis; for, in the imperfect light  by which we
contemplate them,  it is possible that we may rank together circum-
stances  whose real  nature is very different;  but, at all  events, we
must recognise in this  principle, the definite introduction of which
into  science is due to  Liebig, a cause of chemical decomposition 
238          CLASSIFICATION  OF  BODIES.
peculiarly important in explaining the complex reactions of organic
bodies.  It is remarkable, also, that this law, of which the simplest
expression is, that where two chemical substances are in contact,
any motion occurring among the particles of the  one may be com-
municated to the particles of the other, is of a more purely mechan-
ical nature than any other principle as yet received in chemistry ■
and when more  definitely  established by succeeding research, it
may be the basis of a  dynamical theory in chemistry, as the law of
equivalents and of multiple combination expresses the statical con-
dition of bodies which unite by chemical force.
  We must, at least, look upon these actions of catalysis, the con-
ditions of molecular arrangement which give  rise to isomerism and
dimorphism, and the introduction of the principle of types in oppo-
sition to that of  mere binary combination, as tending towards a
change in our ideas of the  nature  of  chemical affinity, which may,
before long, remodel the whole constitution of the science.
                         CHAPTER  XI.

         ON THE CLASSIFICATION OF THE ELEMENTARY BODIES.

   The principal classifications of the simple bodies that have been
 proposed are those of Berzelius, founded on their electro-chemical
 relations, and of Thompson, who divided them into supporters and
 ton-supporters of combustion.   It has, however, been fully shown,
 that in combustion each body  is mutually a supporter and a com-
 bustible : oxygen burns in hydrogen or in the vapour of sulphur, just
 as much as hydrogen or sulphur burn  in oxygen ; Thompson's prin-
 ciple is therefore radically defective;  and the electro-chemical the-
 ory, although far  superior as a principle, is liable to weighty objec-
 tions of a somewhat similar kind.   These have been  already, how-
 ever, so far noticed, and the arrangement of the simple bodies in that
 series  so fully given, p. 188, that it is unnecessary to recur farther
 to the  subject.
   The kind of classification that is suited to the present wants of
 chemistry must be founded upon the  general analogy of properties
 between substances belonging  to the same class, and on their iso-
 morphous replacement of one another.  This last character is not
 absolute ; for, from the dimorphism of many of the simple bodies,
 it is often difficult to assign their true crystalline relations to each
 other,  and in many cases we do not possess any positive information
 of their forms.
,   Graham has recently proposed a classification which expresses,
 more completely than any other, the natural relations of the simple
 bodies.  The first class consists of oxygen,  sulphur,  selenium, and
 tellurium.   The parallelism in  properties of the last three is com-
 plete, and their compounds are strictly isomorphous; their similar-
 ity to oxygen is not so perfect, but they resemble it in their method
 of combination and in  the characters  of the substances which they
 form in uniting with hydrogen and the metals. 
CLASSIFICATION  OF  ELEMENTS.       239
  The second class comprises magnesium, calcium, manganese, iron,
cobalt,  nickel, zinc, cadmium,  copper, hydrogen, bismuth,  chromi-
um, aluminum, glucinum, vanadium, zirconium,  yttrium, thorium.
The similar salts of the protoxides of this class are isomorphous ;
and, as has been already shown under the head of Isomorphism, two
equivalents of a protoxide of this class replace one equivalent of an
alkali.   Chromium,  aluminum, glucinum, vanadium, and zirconium
do not form protoxides, but sesquioxides, the salts of which are iso-
morphous with those of the sesquioxides of iron and manganese.  A
remarkable connexion is established between this class and the prece-
ding by the ismorphism  of the  manganic acid (Mn.03) and chromic
acid (Cr.03) with sulphuric acid (S.03), indicating that under cer-
tain circumstances these metals may change from one natural fam-
ily to another.
  The  third class contains barium, strontium, and lead.  Their salts
are strictly isomorphous, and they are connected together by great
similarity of chemical properties.  Thus the sulphates of the metals
of the second class  are soluble in water, while  the sulphates of this
class are almost insoluble.  Calcium approximates to this condition
by the  sparing solubility of sulphate of lime ; and the connexion be-
tween the two families is still more fully shown by the dimorphism
of carbonate  of lime, it having  in one form the figure of the  carbon-
ates of magnesia and of iron, and in the other that of the carbonates
of barytes and  of lead.
  The fourth class consists of potassium, sodium, and silver.  The
similarity of  chemical properties of potassium and sodium is suffi-
ciently evident; and although their  compounds are not frequently
isomorphous, yet there  is good reason for attributing that to the di-
morphism of each.   Silver differs remarkably  in its chemical rela-
tions from potassium and sodium, and the only grounds for inserting
it in this class  is the isomorphism of sulphate  of silver with anhy-
drous sulphate of soda.
  The salts of potash  are perfectly isomorphous with the salts of
ammonia which contain an atom  of  water ;  and  hence, if  the base
of the  ammoniacal  salts (N.H3-r-H.O.)  be written N.H4. 0., it may
be considered as an oxide of a compound radical which is isomorph-
ous with potassium, and would rank, did we not know its  compo-
sition,  in the present group.   This  view of the composition of the
ammoniacal salts was suggested by Berzelius, who gave to that com-
pound  radical the name ammonium ; but I have since shown that
the replacement is  really by two equivalents of a hydrogen com-
pound, as already noticed in speaking of the second class.
  Fifth class, chlorine,  iodine, bromine, and fluorine.   This group
is best characterized by similarity of chemical properties;  and, so
far as  observation extends, their isomorphism appears to be com-
plete.   It is connected with the  first and second classes by means
of manganese, of which two equivalents replace, in truly isomorph-
ous compounds, one of chlorine.
  Sixth class, nitrogen, phosphorus, arsenic, and antimony.   In their
chemical history these compounds exhibit considerable, the ugh not
complete similarity.  The corresponding compounds of arsenic, an-
timony, and phosphorus are generally isomorphous, but in no case 
240        CLASSIFICATION  OF  ELEMENTS.
  has isomorphism been observed between their compounds and those
  of nitrogen.  A certain analogy appears to exist between nitrogen
  and the substances of the fifth class, as the nitric acid corresponds
  remarkably in properties to the chloric and iodic acids, with which,
  however, it is not  isomorphous.  Nitrogen appears also to replace
  oxygen in many cases in the proportion of one third of its equiva-
  lent weight.
    Seventh class, tin and titanium, connected by the isomorphism of
  titanic  acid and peroxide of tin.
    Eighth class,  silver and gold, from their isomorphism in the me-
  tallic state.
    Ninth class, platinum, palladium, iridium, and osmium, from the
  isomorphism of their double chlorides, by which also Graham con-
  siaers this class to be connected with the seventh.
    Tenth class, tungsten and molybdenum ; the tungstates and mo-
  lybdates being isomorphous.   These metals will probably be found
  to be of the same family with chrome, as chromate of lead has been
  found crystallized in the same form as the molybdate.
    Eleventh class, carbon, boron, and silicon: of these  substances
  no isomorphous'relations are known; they are brought together by
  a general, though imperfect analogy of properties.
    Graham makes no attempt at classifying mercury, cerium, colum-
  bium, lithium, rhodium, or uranium.
    I agree completely with the general principles of this  classifica-
  tion, but, in a few cases, researches made since it was drawn  up by
  Graham render some alterations necessary ; thus the similarity of
  constitution between the compounds of  bismuth and copper, which
  had induced him to insert bismuth in the second class, has no real
  existence, and I would transfer it to the same class with antimony;
  their sulphurets being isomorphous, and their chemical properties
  being, generally speaking, very similar.  Indeed, it is almost certain
  that the oxide of bismuth is not a protoxide, but a sesquioxide, and
  hence corresponds to the oxide of antimony.
    I do  not consider the isomorphism of sulphate of soda  and sul-
  phate of silver as being a sufficient ground for ranking the  latter
  metal in the fourth class.  We have already seen numerous examples
  of isomorphism among substances of totally different chemical con-
  stitution, and the properties of the compounds of silver resemble so
  completely those of'lead,-'as  to demonstrate positively that  it be-
  longs to the same natural group.   When copper enters into combi-
  nation in a double equivalent Cu2, it becomes likewise a member of
  the lead and barytes group, as is shown by the sparing solubility of
  its sulphate and chloride ; and its being isomorphous with'silver fur-
  nishes additional evidence of its true position.
    Silver and gold  being isomorphous only in the regular system,
  and their compounds being  totally dissimilar in constitution, I do
  not retain the eighth class of Graham.
    I have satisfied myself of the perfect analogy of palladium with
  copper; it therefore must be separated from platinum, and removed
  to the second class.  When mercury enters into combination with
  Jthe equivalent  101,4 (Hg.), it  coincides in the nature of  its  com-
**-'pounds with palladium and copper, and attaches itself to the second 
NON-MKTALLIC BODIE S.--O X Y G E N .        241
class; but when its equivalent is 202,8 (Hg2), its compounds resem-
ble those of lead and silver, and, like copper, it then becomes a mem-
ber  of the third class.
  A classification such as this, although necessary for the philosoph-
ical study of the relations  of the simple bodies, could not, without
considerable inconvenience, be strictly  adhered to in an elementary
work like this ; I shall, therefore, having thus laid down these gen-
eral principles, place it for a time  aside, and commence  the  study
of the non-metallic bodies, and  their compounds with each other,
without reference to any arrangement, except  that of treating first
those subjects that may be  useful towards understanding or illustra-
ting those that follow.
                         CHAPTER XII.

 OF THE SIMPLE NON-METALLIC BODIES, AND THEIR COMPOUNDS WITH EACIT
                              OTHER.

                            Of Oxygen.
   From the great quantity in  which it exists in nature, the numer-
 ous processes into which it enters as an agent, and the influence
 which  its discovery exercised  upon the progress of chemical theory,
 oxygen may  be  looked upon  as the most important of the  simple
 bodies. It constitutes more than a fifth of the atmosphere by which
 our planet is  invested, eight ninths of the whole quantity  of water
 which  exists  upon its surface,  and, besides existing in great quanti-
 ty  in most animal and  vegetable bodies, it forms at least a third of
 the total weight  of the mineral crust of the  globe.  On it the pro-
 cesses  of combustion  and of respiration are  dependant,  and the
 functions of organized existence, in both its forms, are  essentially
 connected and sustained through its agency.
   Oxygen  exists only under the form of gas ; it is  colourless  and
 transparent; its specific gravity is  1102*6 ;  100 cubic inches of it
 weigh 31-2 grains; its  refractive  index is 0*8616, that of air beino-
 1*0000.  It  is  very spa-
 ringly dissolved  by wa-
 ter, i00 cubic inches of
 water taking up only be-
 tween three and four of
 the  gas. -It is,  conse-
 quently, in most  cases,
 collected over water, by
 forms of apparatus that
 shall be now described.
  For the collection and pres-
ervation of gases, such as ox-
ygen, the instruments gener-
ally  employed are the pneu-
matic trough and the gasom-
eter  The former is any ves-
                               He
 
?42 GASOMETERS.--PREPARATION  OF  OXYGEN.
sel, g, containing water, for such gases as are not absorbed by it, in which is
inverted a glass vessel full of water, which is sustained in it by the pressure of the
external air, as is the mercury in the tube of the barometer.  The orifice of the
tube c, from which the gas issues, being brought under the edge  of the jar, which
is generally sustained  upon  a  shelf, the water descends according as the  bubbles
of gas ascend;  and when the jar in the water has been all replaced by the  gas, the
jar may  be removed on a tray, containing as much water as serves  to prevent all
communication from the interior with the external air.
                      The gasometer, or gas-holder, consists of a cylindrical
                     copper vessel, on which another is secured by five  props of
                     copper, of which two are hollow tubes, in connexion with
                     the cylinder below.   The tube m passes down nearly to the
                     bottom of the cylinder, but the other, n, only extends to
                     the  upper surface;  both are provided with stopcocks, so
                     that the communication between the  cylinder and the
                     upper vessel  may be opened or cut off at pleasure. At I
                     there is also a small tube with a stopcock, and below there
                     is a large orifice at i, which can be tightly closed by means
                     of a screw-plug.
                       To  fill the cylinder with water, the orifice i is to be
                     3losed, and all the  stopcocks, m, n, I, left  open.   Water
                     being then  poured into the upper vessel, it flows in  through
                     the  tubes m and n, while the air issues at I.   When water
                     begins to flow out at  I, that stopcock is  to be closed, and
                     then the air which still remains escapes by the tube n, bub-
                     bling through the water in  the upper vessel.  When this
                     also ceases, the stopcocks m  and n are to be closed, and
the orifice i being then opened, the cylinder remains full of water by the external
pressure.  The tube from which the  gas issues is inserted at i, and a quantity of
water escapes by that aperture equal in volume to the gas which  passes in.
   A great variety of processes may be put in practice for the pur-
pose of obtaining  oxygen gas ; one, which is very simple in theory,
and of great interest in history, from being that by which the  impor-
tant agencies of  oxygen  in chemistry were  first  recognised, al-
though it is not at present practicably useful, is the  following:
   Some  red oxide of  mercury (Hg.O.) is to be  introduced  into a
retort, a, of hard glass, to which is then attached a receiver,  b, with
a tube, c, passing to the pneumatic trough.  On applying the heat of
the argand spirit-lamp to the  oxide of mercury,  it is decomposed;
the oxygen is given off in the state of gas, and may be collected in
the bell  glass  e, and  the  mercury distils over, and,  condensing in
the neck of the retort,  collects in drops which flow into the receiv-
er.  The substance used is thus resolved into mercury and oxygen;
from 109*4 grains, there would have  been  obtained 101*4 grains of
metallic  mercury, and 8  grains of oxygen  gas,  occupying  at the
Btandard temperature and pressure 23*4 cubic inches.   It was by an 
PREPARATION OF  OXYGEN.
243
experiment of this kind that Lavoisier demonstrated the true  con-
stitution of the metallic oxides.
  Although there are few metallic oxides which, as that of mercury,
admit of being resolved by heat completely into free metal and ox-
ygen, yet  many, when heated, give off a portion of their oxygen,
the metal  remaining in a lower degree of oxidation.  Of this  kind
are the peroxides of lead and of manganese; and it is generally from
the latter that oxygen is obtained  for experimental purposes, when
it is not required to be absolutely pure.  The peroxide  of manga-
nese (Mn.02) abandons, when at a red heat, one  third of its oxygen,
and a complex oxide, Mn304, remains, analogous to the black mag-
netic oxide of iron,  and formed by the union of equivalents of pro
toxide and of sesquioxide (Mn.O. + Mn^Oa).   For this purpose tne
manganese is introduced in an iron bottle, a, to the neck of which
is attached a piece of gun-barrel, b, and this connected by a cork, c,
with a smaller tube, d.  For sake of freedom of motion, the tube/",
which passes to the pneumatic trough or the  gasometer, is attached
to d by  a caoutchouc connector, e.  The bottle  having been filled
nbout two thirds with oxide of manganese, may be placed either in
a common fire or in a furnace, its parts being all arranged as in the
figure.  When first heated some water passes off, and frequently,
from the occurrence of carbonate of lime and of ammonia in the
substance, the first portions of gas are mixed ivith carbonic acid or
with nitrogen ; these should be allowed to pass away, and the oxy-
gen collected only when a small tube full of it is capable of relight-
ing a taper four or five times.  The pure  dry oxide of manganese
consists of 27*7 of manganese, united to sixteen of oxygen, of which
5*3 are given  off, and hence 1 lb. troy of it is capable of furnishino-
about 700 grains, or nearly 2000 cubic inches, equal to seven irnpe- 
244           PREPARATION  OF  OXYGEN.
rial gallons of gas.  The oxide of manganese found in commerce is,
however, not pure ; in general it does not contain more than 65 per
cent, of pure oxide, and hence the quantity of oxygen furnished by
a pound of it is about two thirds only of that just stated.
  Peroxide of manganese yields more of its oxygen when treated
with oil  of vitriol than when  simply ignited, one half becoming
free, while the manganese,  with the remainder, forms protoxide,
which combines with the sulphuric acid thus : H.O. . S.03-t-Mn.O,=
H.O. . S.03 . Mn.O. + O.                                .
  This operation is conducted by placing the manganese in a flask,
                                        a, supported in a little
                                        cup of sand, b, over a
                                        lamp, and mixing it with
                                        twice its weight of oil of
                                        vitriol; a tube, c, bent, as
                                        in  the  figure, passes to
                                        the pneumatic  trough,
                                        and dips under the edge
                                        of  the  jar in which  the
                                        gas is  to be  collected.
                                        When the flask is heat-
                                        ed, oxygen  gas is rapid-
                                        ly  disengaged, but care
                                        must be taken that, to-
                                        wards the close, the  wa-
ter  of the trough may not pass back into the  flask, where, mixing
with the hot oil of vitriol, it  might produce an  unpleasant explosion.
  The decomposition*which here occurs has been supposed to con-
sist simply in the expulsion of the second atom of oxygen by  the
sulphuric acid which takes its place.  This, however, is not the case.
By  a very gentle heat, the sulphuric acid decomposes the peroxide,
Mn.O^, into protoxide, Mn.O., and permanganic acid, Mn.O, (5Mn.0a
= 3Mn.O.-(-Mn207).  This last is decomposed, when the temperature
rises, into  2(Mn.03),manganic acid, giving out one equivalent of ox-
ygen ; but the temperature  must be raised very much to complete
the separation of the Mn.03  into 02 and Mn.O.  Hence, in this pro-
cess, as ordinarily conducted, the residue  in the flask is found to be
green, from manganic acid ; and, although in  theory a more  abun-
dant source of oxygen than that by simple  ignition, in the propor-
tion of 3 to 2, it is not so useful in practice.
  When oxygen is required completely pure, it is generally prepared
  gygEg^-. <zWte\     by heating  in a glass  tube or  flask, to  which a
              II    bent  tube is attached, as in the figure, a small
              Il    quantity of chlorate of  potash.  This salt con-
              1     sists of chloric acid united to potash Cl.Oi+K.O.,
              I    and  when heated somewhat above its melting
              11    point, it is  decomposed, all the oxygen it con-
              I    tains being evolved in the state of gas, and the
              P|   other elements remaining  combined as chloride
                   of potassium.  The constituents of this salt are
               I   by weight 35*4 chlorine, 39*7 potassium, and 48
               I   of oxygen.  Hence 100 parts of it give 39 of
               %b» oxygen  by weight, or an ounce troy, 187 grains,
 
PROPERTIES  OF  OXYGEN.
245
 or 543 cubic inches.   An ounce of it is therefore equivalent in ef-
 fect to six ounces of ordinary peroxide of manganese.
  The most remarkable property of oxygen is the energy with which
 it supports combustion.   If a lighted taper be  blown out, so that a
 point of the wick shall continue red, it will be brilliantly relighted
 on  being plunged into a vessel  of oxygen gas, and this may be re-
 peated  several times in succession.   A bit  of charcoal, heated to
 redness at  a single point, burns, when  immersed  in  oxygen, with
 rapid scintillations of exceeding brilliancy; and when phosphorus
 is inflamed inVxxygen, the splendour of the combustion is insupport-
 able to  the eye.  Even bodies which are not combustible under or-
 dinary circumstances, may be made to burn in  oxygen.  Thus, if an
 iron wire be tipped at its extremity with sulphur, or have attached
 to it a small bit of waxed cotton wick, on lighting this, and plunging
 the whole into the gas, the combustion extends from the sulphur or
 wick to the iron, which is converted into oxide, with the disengage-
 ment of most  brilliant light.   The  heat evolved by the combination
 of the oxygen and iron is so great, that the oxide formed is melted,
 and flows down  in drops from  the extremity  of the burning wire,
 which, even after having passed through a layer of water, fuse them-
 selves into the substance of the  earthenware plate, upon which the
 gas jar  generally stands.  If, at the moment when a drop of oxide
 is about to fall, it be projected by a little jerk against the side of the
 glass, it will melt its way into  its substance,  or even, if it be not
 thick, pass completely through.
  The heat evolved  when the body burns in pure oxygen may be readily shown bv
 ■simple methods   If a jet, m, be attached to the lat-
 eral stopcock, I, of the gasometer, and the flame of a
 spirit-lamp, h, be urged by the issuing stream of gas,
 as by a  blowpipe, the most  refractory substances
 may be fused by it.   If the tube be curved down-
 ward, the jet may be brought to bear on a  little cup
 of red-hot charcoal,  in which the body to be fused
 may be laid, and thus, upon a small scale, the con-
 struction  and effect of the most powerful wind fur-
 naces may be imitated.
  Oxygen gas  is necessary to the support
 of animal life.   It is the oxygen which ex-
 ists in the  atmospheric air that  fits it for
 its  uses in  the economy of nature.  The
 blood which returns dark and venous into the lungs is there changed
 into the bright  arterial state, by  absorbing oxygen and evolving car-
 bonic acid, in a manner of which the  exact details will be hereafter
 studied.  This change occurs even with blood which has been re-
 moved from the body.  If a quantity of dark blood, drawn from a
 vein, be agitated in a vessel of oxygen gas, it is immediately changed
 into the  vermilion-coloured arterial  blood.  An animal can live long-
 er in a vessel of pure oxygen than in the  same  volume of atmosphe-
ric air;  but still, pure oxygen is  not fitted for the support of life.  It
is too stimulating ; the animal lives too fast, and ultimately dies with
 symptoms of general inflammatory fever, even though there  may re-
 main still a  quantity of oxygen gas  capable of supporting the life of
another  animal  for a considerable time.
  The name of oxygen was given to this body from the idea of its
 
246          PREPARATION  OF  HYDROGEN.
     peculiar power of conferring acid properties on its compounds; and,
     in reality, most of the bodies recognised by chemists among the
     class of acids contain oxygen.  But  this is not  invariable ;  other
     simple bodies possess the same power, as has been already noticed
     on more than one occasion, and I shall have opportunities of recur-
     ring to it when describing the properties of those bodies.

                              Of Hydrogen.
       Hydrogen exists abundantly in nature as a constittijfit of animal
     and vegetable substances, and is particularly of inter/st by forming
     a constituent of water.  From this fact it derives  its name, vdwp
     yevvao) (I form water), and it is by the decomposition of water that
     hydrogen is almost always obtained for experimental purposes.
       If a small quantity of the metal potassium be placed  in contact
     with water, it immediately abstracts the oxygen, forming potash,
     which is an oxide of potassium.   The hydrogen is set free, and ap-
     pears as a gas.   If the experiment be performed under a  bell glass,
     inverted in a basin of mercury or water, the gas may be collected;
     but if the decomposition takes place in contact with the atmospheric
     air, so  much  heat is evolved by the rapidity and intensity of the
     action, that the  hydrogen takes fire,  and burns according as  it  is
     produced.  This is the simplest form  under which  the decomposi-
     tion of water can be  exhibited, the reaction being K.+H.O.=K.O.
     +H.
       If the circuit of the electrical current from a voltaic  battery be
     completed  through  water, which has been rendered a  good  con-
     ductor by the addition of sulphuric acid, or common  or Glauber salt,
     the two constituents of the water are evolved at the opposite elec-
     trodes, or terminating surfaces of the liquid, and the two gases may
     be collected either separately or mixed together, and will be then
     found to have been evolved in such proportions that the hydrogen
     will be double the volume of the oxygen.  The theory of this mode
     of obtaining hydrogen has been described, so far  as we are compe-
^    tent to explain it, in a former chapter.
       These methods, although the  simplest, are yet not applicable  to
     ordinary purposes, from their expense; those usually employed are
     the following.  There are  many metals which, although having a
     powerful affinity for oxygen, are yet not able to abstract  it from hy-
     drogen, and so  to decompose water at ordinary temperatures; but
     at a red heat the decomposition  rapidly takes place.  For this pur-
     pose iron is generally employed.  A gun-barrel, or an iron tube, c c,
     is taken, and the interior having been loosely filled with iron turn-
     ings or coils of iron wire, it is placed horizontally in a furnace,  by
     means of which it can be brought to a full red heat.  To one extrem
     ity of the tube is connected a small glass retort, a,  containing water;
     to the other, a flexible metal tube,/, which passes  under the shelf of
     the pneumatic trough.  The iron tube being red hot, the water in
     the retort  is  made  to boil ;  the  vapour passes into the tube, and
     comes  into contact  with the red-hot iron ;  decomposition immedi-
     ately occurs, and the iron is oxidized, while the hydrogen gas is
     disengaged in large quantity.  The state of combination Into which
     the iron is found to have passed is that of the black oxide, such as the 
PREPARATION OF  HYDROGEN.          247
scales that are formed at the smith's forge by the action of the at-
mospheric air on iron, and which is also formed when iron is burn-
ed in oxygen gas.  The action may, however, be simply represent-
ed as follows:
          Fe.4- H.O.= H.+Fe.O. Protoxide of iron.
          2Fe. + 3H.O. = 3H.-f Fe2Q3 Peroxide of iron.
          3Fe. + 4lIX).=4H.**r-FeA~Black oxide of iron.

   The action of the iron in thus decomposing water might appear
paradoxical, as it will be seen hereafter that by means of a current of
hydrogen gas, acting at a red heat, oxide of iron may be decomposed,
the iron separating in the metallic state, and water being produced ;
and thus, at the same temperature, two decompositions, precisely the
reverse of each other, may go on.  It would appear that this is one
of those cases in which affinities, nearly equal otherwise, are direct-
ed to one or the other  object, according as  one or the other  sub-
stance  is in excess.  When  the iron is kept in a stream of watery
vapour, this latter  is decomposed, and the hydrogen being carried
away, according as it is formed, by the current, it cannot interfere
by its presence in any opposing manner.  On the other hand, when
oxide of iron is heated in a stream of hydrogen gas, it is decompo-
sed, and the water being removed as rapidly  as it is produced, the
tendency to  reaction is prevented.
  By the agency of a dilute acid we may also increase the tenden-
cy of a metal to combine
with water, so that  the de-
composition  of water can
be effected rapidly even at
common temperatures.  If
n few slips of zinc  or iron
be placed in a  flask,  to
which  a  bent  tube, /, is
adapted, as in the appara-
tus represented in the fig-
ure, and then oil of vitri-
 
 248  PREPARATION  AND PROPERTIES  OF HYDROGEN,

 ol, diluted with eight times its weight of water, be poured upon it
 through the funnel, an abundant  effervescence occurs, arising from
 the escape of hydrogen  gas, and the zinc or iron rapidly dissolves.
 The action continues until the acid has been all  neutralized by the
 zinc, or the zinc all dissolved by the acid;  or, finally, until so much
 of the compound formed during the reaction has been  produced,
 that the water present cannot dissolve any more.  This compound
 consists of oxide of zinc or of iron united to the  sulphuric acid, the
 oxygen of the decomposed water uniting with the metal, while the
 hydrogen is set free.  The process may be thus represented, zinc
 being used, Zn.+S.03+H.O.=H.+(S.OJ+Zn.O.)
   To  account for the circumstances  of this reaction, a peculiar
 power was at  one time supposed to exist, termed disposing affinity;
 and it was said that the presence of the sulphuric acid disposed the
 zinc to decompose the water, because the oxide of zinc, when formed
 by the decomposition, might unite with the  acid.  This theory is
 quite futile.   There can be no oxide of zinc  to  influence the acid
 until  the water has been decomposed, and the effect,  the  source of
 which was to  be sought for, had consequently passed  away.  It ap
 pears to me that  the explanation  is of a much simpler form.   Zinc
 and iron decompose water at ordinary temperatures, even without
 the presence of any acid, but with excessive  slowness, so that the
 effect is almost imperceptible.  In fact,  the first  minute trace of ox-
 ide which is formed, being insoluble in water, coats over the metallic
 surface with a varnish impermeable  to the fluid,  and  thus prevents
 its farther action.  This coating of metallic oxide is soluble in acids;
 and thus, by the presence of an acid, a fresh surface of bright metal
 is kept constantly exposed, and the decomposing action  is allowed
 to proceed without hinderance.   It is possible,  however, that this
 simple view may require some alteration, and  that this mode of ob-
 taining hydrogen gas may be found to involve  voltaic conditions
 which at present are not well understood.  Pure zinc is but  very
 feebly acted on even by a diluted acid;  and the rapid action which
 occurs with commercial  zinc or iron may be referred to decompo-
 sition by the electric currents which circulate from one portion of
 the impure metal to the other, through the liquid.  See page 135.
   Hydrogen gas, when it  has been prepared by  any of these process-
 es, is seldom pure.   The iron and zinc of commerce contain  gen-
 erally traces of carbon, of sulphur, and sometimes of arsenic, which,
 combining Avith some hydrogen, form gaseous or volatile  products,
which give to  the hydrogen, a peculiar disagreeable odour, and col-
our its flame.  Occasionally, also, traces of potassium and zinc, in
very minute division, are carried  up  with the hydrogen by the me-
chanical force  of the effervescence, but by repose  these latter impu-
rities  are found completely to separate.  To get rid of the former
class  of impurities, the gas may  be made to bubble  very slowly
through solutions of potash and of corrosive  sublimate, by which
the arsenic and  sulphur  would be absorbed, and through alcohol,
which would for the most part dissolve the carburetted^hydrogen.
It  is, however, better, when pure  hydrogen is required, to prepare
it by acting upon water with metallic sodium mixed with quicksilver,
so as to moderate the rapidity of  the decomposition.   Zinc, which 
PROPERTIES  OF  HYDROGEN.
249
 ha^ been refined by distillation, gives also, with sulphuric acid and
 water, a gas almost completely pure.
   When free from foreign matters, hydrogen gas burns with a very
' pale white flame, almost invisible in bright day.   In burning, it com-
 bines with the  oxygen of the air, and forms water.   If a jar of hy-
 drogen gas be suddenly turned with the  orifice upward, and infla-
 med, the whole mass of gas rushes out, and gives a sheet  ol pale
 white or yellowish flame.   If it be  mixed with  air previous to being
 set  on fire, the combustion of the mixture is instantaneous,  and  ac-
 companied with an explosive report.  The proper proportions  are two
 volumes of hydrogen gas to five of air.   If a lightedtaper be plunged
 into a jar of  hydrogen,  it  is  immediately  extinguished, the  gas not
 being able to support combustion.
   H , drogen gas is colourless and transparent;  it is absorbed by wa-
 ter  in very small  quantity, and hence, for  ordinary purposes, is al-
 ways collected over that liquid.   It refracts light strongly, its  re-
 fractive  index being 6*61,  air being 1*00.   In its capacity for heat
 it exceeds all  other gases, being 21*9 by Apjohn's experiments, air
 being 1*00 for  equal weights, or 1*46 for  equal volumes.  It is the
 lightest  substance known, being only one  fifteenth  of the   specific
 gravity of air; or, more accurately, its  specific gravity is 68*8, air
 being 1000*0.
   It is hence used for filling balloons; as the balloon full of hydrogen weighs less
 than  the same volume of air, it ascends with  a  force equal  to the difference of
 weight.  For the purpose  of  illustrating.this property of hydrogen, a small balloon
 made of gold-beater's skin, or of the serous membrane of the turkey's craw, may
 be made use of.   On this minute scale, however, the gas should be used dry, as,
 when prepared and collected over water, its specific gravity may be so much in-
 creased by the watery vapour  it may contain, that, although good enough for  a
 larger balloon, it could  not carry up a small one,  the small balloon being really
 much heavier in proportion to the quantity of gas  it can contain ; consequently, the
 hydrogen should be dried, which may be effected  by causing il to stream  from the
 gasometer through a tube filled with fragments of fused chloride  of calcium, which
 absorbs water with great avidity, and from thence  to enter the balloon.  At present,
 hydrogen gas is but seldom employed, it being found cheaper to make the balloon
 very large, and to use coal gas, which, although much  heavier than hydrogen, is
 considerably lighter than atmospheric air under the same volume.
   By the same experiment, the three most remarkable properties of hydrogen may
 be exhibited in an  interesting  form.  If a jar of hydrogen be held vertically, with
 the orifice downward and open,  it will remain filled by the hydrogen  for a certain
 time, as the air, being so much heavier, mixes itself with  the  lighter gas  but very
 slowly.  If a lighted  taper be now  applied, the  gas will  inflame at  the surface
 where it is in contact with the atmosphere, hut, on plunging the  taper upward into
 the pure gas, it will be extinguished; being then lowered, it can be relighted at the
 sheet of flame which marks the  surface of contact of the gas and the atmosphere,
 and when again raised into the pure gas, it will again be extinguished ; this can be
 repeated very often: the horizontal sheet of flame  having been gradually rising into
 the jar according as the hydrogen consumed, if  then the jar be suddenly turned
 with  the orifice directed upward,  the residual gas will at once rush out, and, niixiiif
 with  the air, will burn explosively with a single flash.
  The same experiments on the combustion of hydrogen may be made with pure
oxygen gas in place of atmospheric air, but  then the results are at least five times
more brilliant.  The proportions for  burning hydrogen with  oxygen  gas  are two
volumes ol hydrogen and one of oxygen ; then, if  the gases were pure, nothing but
pure  water should remain.
  If  a bladder be filled with the two gases mixed in these proportions, and being
punctured,  the flame of a taper be applied to the orifice, the whole explodes with a
flash  of brilliant Iiirht and deafening explosion, the strongest bladder being torn to
ehreds by the expansive force of the ignited gases.  In this experiment the bladder
                                  I I 
250           PROPERTIES  OF HYDROGEN.
IK
must, of course, be secured, which is easily done by tying the stopcock by which
the gas has been passed into the bladder between two nails, with some stout cord
or copper wire.                         ,        , ,  . ,          r ,,   .
  A mixture of hydrogen and oxygen may also be exploded by means of the elec-
tric  spark; for this purpose a strong tube, closed at the  top, and graduated into
parts of a cubic inch, is taken, and two brass or platina wires  are inserted through
the opposite sides near the top, their extremities being kept about one eighth ol an
                            inch asunder.  This tube is termed a eudiometer,
                            as it is frequently used to measure the quantity of
                            oxygen in the atmosphere, and generally for the
                            analysis of gaseous mixtures.   The oxygen and
                            hydrogen gases being confined  in this  tube over
                            water or mercury, an electric spark  is  passed
                            through the mixture by means of the wires; the
                            gases explode, and, if the proportions  had  been
                            accurately observed, no residue is found; if one
                            or the other gas had been in excess, the excess
                            remains behind, one third of the volume which
                            disappears being oxygen, and the other two thirds
                            being hydrogen   In order to  explode  a bladder
                            full of the mixed gases by means of electricity, a
                            very simple plan is to fasten the bladder upon a
                            large cork, having  in the centre an opening, into
                            which a stopcock  is screwed for the passage of
                            the gas, and through which,  near the edges, pass
                            two stout brass wires,  terminating  inside the
                            bladder in small knobs ; these ends being brought
near each  other, and the external ends being connected by long wires with the
coatings of a charged Leyden jar, the spark passes  between the terminal knobs in
the bladder, and the explosion immediately occurs.
  Hydrogen and oxygen are capable  of entering into combination,
and forming water  without any explosion or  visible combustion.
If the mixed gases be transmitted through a tube heated to scarcely
visible  redness, they quietly  combine, and this effect occurs  at  a
still lower  temperature,  if the  tube  contains  coarsely-powdered
glass or sand.   Slips of gold and silver are still  more favourable;
but the most rapid union is effected, even at ordinary temperatures,
by platinum.  This  effect appears to be due to  the metallic surface
retainino- a thin layer of gas by so strong a force as by condensation
to bring the  molecules within the  sphere  of their mutual chemical
attraction ; they, combining, form water, and a new quantity of the
gaseous mixture  comes into contact with the platinum, and follows
the same course.  If the platinum be in the form of a  sponge, in
which the acting surfaces  are very great,  the union  takes  place so
rapidly, that  the heat evolved raises the temperature  of the platinum
ball  to bright redness, and then the remaining  gas explodes.   Pla-
tinum in  form of sponge always contains a quantity of air in this con-
densed condition, and hence, when  a jet of hydrogen gas is caused
to play upon a morsel of spongy platina, it is absorbed, and water be-
ing formed, the ball of platinum becomes red hot, and inflames the
jet  of gas.   This constitutes a sort  of lamp for instantaneous light,
equally pretty and ingenious, the jet  of hydrogen in its turn being
contrived to  fall upon and  light a little lamp.  See p. 179 and 235.
  Spongy platinum  introduced into a mixture of oxygen and hydro-
gen explodes them  instantly, but  it  can be  usefully diluted,  as it
were, by being  made into balls with a little pipe-clay,  and then it
can only  produce their union in the slow and silent  way.  This mode
is accordingly often used  in the analysis of mixtures of gases, and 
HYDRO-OXYGEN  BLOWPIPE.
251
tne energy of the platinum balls can be graduated by the proportions
of metal and of pipe-clay which are employed.  Hydrogen and oxy-
gen, however, are not the only gases which can be made to unite by
the agency of platinum surfaces, as will be elsewhere shown.
  The heat produced by the combustion of oxygen and hydrogen
gases is the  most intense that  can  be obtained by any artificial
means.  It is hence, at present, much used in an instrument termed
the hydro-oxygen blowpipe.  The apparatus employed must be of
euch a nature as to prevent any risk of injury from explosion, which,
with any large  quantity of the  gases, might produce most serious
accidents.  The safest form  for experiment  on a large  scale con-
sists in having the gases separate, in two gasometers connected by
tubes, and  of such  a size  and  pressure  as  that  in  the same  time
there will  be delivered two volumes of hydrogen to one of oxygen
gas.   The hydrogen gas tube terminates in a hollow cylindrical jet,
inside  of which passes the jet of oxygen gas; the flame  thus pro-
duced resembling that of a candle, into the interior  of which is in-
jected a stream of air by the blowpipe in common use.  Another form
consists of a metallic box, made so  exceedingly  strong that,  even
were the gases to explode within it, there could be no danger of its
being burst.  The gases, previously mixed  in a bladder, are forced,
by means of a condensing  syringe, into the box, and a sufficient
quantity having been introduced, the condensing syringe is removed,
and a stopcock connected with a jet  opened.  The  pressure of the
condensed gas  inside forces out  a stream, which  is  ignited, and, if
the flame  be not allowed to burn too long,  the rapidity of the cur-
rent is sufficient to prevent the passage backward of the flame.
This form  is now, however, almost totally  superseded by the very
ingenious safety cylinder and jet of Mr. Hemming.   It consists of
a brass cylinder of about  five or six inches long, by three fourths
of an inch  in diameter, which is filled as closely as possible by a
bundle of fine brass wires, into the centre of which a wedge-shaped
brass rod  is  introduced and driven very hard, so as to pack the
wires closely.   The interstices between the wires form thus a col-
lection of exceedingly minute tubes, through which the  gas  must
pass.   To one end of this cylinder is connected a bladder contain-
ing the mixed gases; the other end terminates in a  jet from which
the gas issues ; the  flame, in passing  backward from the jet, must,
in its way to the bladder, stream through the metallic cylinder, and
then  comes into contact with so great a surface, and so large a  mass
of material which conducts heat  rapidly,  that the gases are cooled
far below the temperature at which their union can occur, and  their
farther combustion is, of course, prevented.
  For experiments upon a small scale, this little apparatus combines
the highest qualifications of convenience, security, and simplicity.
  In the flame of the hydro-oxygen blowpipe, the most infusible sub-
stances are melted ; flint, pipe-clay, the most refractory metals, as
platinum, not merely fuse, but even appear  to evaporate : a rod of
iron  takes fire,  and  burns with a brilliancy surpassing that of its
combustion in oxygen gas.   Some of the earths alone, are capable
of resisting its highest power.  These, as lime and  magnesia, par-
ticularly the former, become, in  the  flame of the mixed gases, so 
252     CHEMICAL  RELATIONS  OF  HYDROGEN.

brightly luminous as  to rival  in  intensity  the noonday  sun, and
hence furnish one of the most important uses  of  the  blowpipe,  by
serving for optical purposes as a substitute for the solar ray, which,
in our climate, is so uncertain in its supply.   The  solar microscope
fitted up with a ball of lime, ignited by a jet of the mixed gases in
place of the  solar rays, constitutes the hydro-oxygen microscope,
now a common exhibition in our large towns ;  and the same light has
been proposed for use in lighthouses, and has been actually employ-
ed for signals in connecting the trigonometrical surveys of the Brit-
ish islands.   In one case the light  emitted  by the ball of  lime was
distinctly visible at a distance of seventy miles.
  A singular phenomenon, which is best produced by the flame of hydrogen, al-
though not peculiar to it, is the production of musical sounds, if an open tube be
held over the flame.  The flame, in fact, although uniform to the eye, consists of a
succession of little explosions of mixed  air and gas, which recur too rapidly to be
individually distinguishable.  If the tube be now held over the flame, it will be seen
to flicker, and after a few irregular, interrupted, explosive sounds, a distinct musi-
cal note is heard.  The explosions set the air in the tube to vibrate, at first irregu-
larly, but at last with such  a velocity of vibration as corresponds to the length of
the tube, and to the rapidity with which the explosive mixtures of air and gas can
be formed ;  and  thus, by any of the known methods of determining the number of
vibrations corresponding to a given note, the frequency of the little explosions may
be found. Occasionally, also, a distinct beat, or alternations of sound and silence,
may be heard, as in two organs, which being nearly, but not completely in unison,
sound together; this arises from a current of hot air ascending in the centre of the
tube, while a current of cold air is formed next the side. These do not, for a time,
vibrate completely as one mass ; and hence, at certain periods, alternately  redouble
and destroy the sounds which they produce.
   In its relation to other bodies, hydrogen plays a very remarkable
and peculiar  part.  It was at one fime supposed that it shared with
oxygen the power of generating acids; and as sulphur, chlorine, cy-
anogen, iodine, &c, form one class of acids  by combining with ox-
ygen, so they formed a second class, called  hydracids, by entering
into union with hydrogen ;  and hydrogen was believed to be related
to hydrochloric acid, as oxygen was to  the sulphuric or the phospho-
ric acids.  In the year 1832,1 proved that this view was totally incor-
rect, and that all the properties of the compounds of hydrogen com-
bined to show that it was an eminently electro-positive body ;  that it
took a place along with iron, manganese, and zinc ; and that the com-
pounds of hydrogen with chlorine, oxygen, iodine, and sulphur were
almost universally electro-positive in combination, and possessed ba-
sic characters derived from the pre-eminent positive energies of the
hydrogen itself.   These views have, since that period, been still far-
ther corroborated  by the researches of Graham, and by additional
investigations of my own ; and although the old familiar nomencla-
ture will still retain  its place to a great extent, yet there rests now
no doubt upon the minds of philosophical chemists, that hydrogen
is most closely allied to the metals, particularly to zinc and copper;
that  the chlorides, iodides, and fluorides of hydrogen, although they
simulate some of the characters which we assign to acids, resemble,
in all important points, the chlorides, iodides, &c, of  the  metals
above mentioned ; that, in fact, hydrogen  is a metal enormously
volatile, standing  probably in the  same  relation  to  mercury that
mercury does to platinum in that respect, but still possessed of  all
truly chemical peculiarities of the  metallic state, and no more de- 
CONSTITUTION  OF  WATER.           2-33
 pnvcd of the commonplace qualities of lustre, hardness, or brillian-
 cy, than is the mercurial atmosphere which fills the apparently empty
 top of the tube of a barometer, or the salivating atmosphere of a
 quicksilver mine or of a gilder's workshop.

                  Of  Water—Oxide of Hydrogen.
                              H.O.
   It  has been already shown that  water consists of hydrogen and
 oxygen combined, in the proportions of two volumes of the former
 gas to one volume of the  latter, and by weight of one  part of hy-
 drogen united to eight of oxygen, or of  11*1 hydrogen and 88*9 of
 oxygen in 100 parts.
   The exact determination of the composition of water is one of the
 most important investigations in the  domain of chemistry, as from
 the great range of affinities which  oxygen and hydrogen  exercise,
 and the variety of compounds into which they respectively enter,
 the numbers adopted  for the combining proportions of almost all
 other bodies hinge upon those  which are employed for the constit-
 uents of water.  It has, consequently, attracted the attention of many
 distinguished chemists.  But, although the determination of the re-
 spective volumes in which the oxygen and hydrogen unite, as de-
 termined by  Gay Lussac, gave  a very accurate result, yet  the most
 positive determination was obtained by Berzelius, with the method
 now to be  described.
   A known weight  of black oxide  of copper is  introduced into a
 glass tube, on which a bulb is blown,  and to the extremity of which
 a  flask, containing the materials for generating pure hydrogen gas,
 is connected.  As, however, the hydrogen gas passes off in a damp
 condition, and thus introducing water might falsify the result, there
 is interposed a tube  containing fragments of fused chloride of cal-
 cium,  by which the  hydrogen  gas is completely  dried  before it
 conies into contact with the oxide of copper.  When the apparatus
 has been filled with  pure dry hydrogen, heat is applied  to the  bulb
 containing the black oxide of copper, and, as soon as its temperature
 has been raised to dull redness,  decomposition  commences.   The
 oxide of copper becomes glowing red, and then, even if  the heat of
 the lamp be much reduced, the  reaction still goes on; the glowing
 gradually pervades the whole mass,  water is formed and condensed
 on the colder parts of  the tube  in considerable quantity, and when
 the reaction is completed, there remains  in the bulb a porous mass
 of pure metallic copper.  It is  necessary, however, to determine
 exactly the quantity of water formed :  for this purpose, a small tube
 filled with fragments of fused chloride of calcium is attached to the
 bulb tube by  means of a caoutchouc connector,  and the stream of
 hydrogen gas is allowed to continue through the apparatus until
 the residual copper has become quite  cold, and all traces of water
 have been carried into the chloride of calcium tube, where it is com-
 pletely absorbed and retained.  The oxide of copper tube havinc
 been weighed before  and after the experiment, the loss found is the
oxygen which has  been carried off: the  chloride of calcium tube
having been also weighed before and after, the gain gives the weight
of  water formed, and hence the composition of water may easily
be  calculated, thus: 
254          CONSTITUTION  OF  WATER.
             100 parts of black oxide of copper give
              79*85 of metallic copper, and lose
              20 15 of oxygen, which form
              22*67 of water;

consequently, 22*67 of water consist of
              20.15 of oxygen,
               2*52 of hydrogen;

or in 100 parts,
              88*9 of oxygen,
              11*1 of hydrogen.

  To determine  the combining equivalents of these substances, or,
in theoretical language, their atomic weights, it is first necessary to
ascertain what grounds there are for deciding on the atomic consti-
tution of water.
  It has been already mentioned that at one time equal volumes of
all  gases were considered to contain the same  number of atoms;
and hence, as water is formed by the  union of one  volume of oxy-
gen and two of  hydrogen, it was considered by some chemists to
consist of one atom of oxygen united to two of hydrogen ; there-
fore, if we take oxygen as the standard of atomic weights, and call its
equivalent number 100, the result  would be that 88*9 : 11*1 :: 100 :
12*48 =  weight of two atoms of hydrogen ; and hence the atomic
weight of hydrogen should be 6*24.  To the adoption of this number
there are very many objections : 1st, The ground upon which it was
first adopted has been proved to be false, as the same volumes of all
gases certainly do not contain the  same number of chemical atoms;
and, although hydrogen enters  so much into combination, it is but
very rarely that it does so in the proportion of 6*24.  Likewise wa-
ter, in all the modes in which it is capable of combining, does so in
a quantity containing  12*48 and not  6*24 ; and, finally, water in com-
bination allies itself to a variety  of metallic oxides, all  of which
there is the strongest reason for supposing to  be composed of one
equivalent or atom of the metal united with one of oxygen.
  Water is therefore  assumed to  be composed of an equivalent of
each of its constituents;  and according as the standard of oxygen or
of hydrogen is taken, its  atomic weight is

      One atom of oxygen    .....100*00      8
      One atom of hydrogen       .  .   .    12*24      1
                                          112*24      "9
  Water is colourless, transparent, destitute of taste and smell. If
agitated, it solidifies at a temperature of 32° F. (0 Centigrade), but
if preserved quiescent, it may be cooled  much lower without freez-
ing; if it be then touched or shaken, a portion is immediately  con-
verted into ice, and the temperature of the whole is raised to 32°.
In freezing, water  expands very much, and exerts therein so great
a force as to burst the strongest  vessels in which  it is contained.
It is thus that the surfaces of the hardest rocks are gradually crum-
bled into soil fit  for the support of vegetable life; the water perco- 
SOLUTION  OF  GASES  IN  WATER.        255
lating into minute crevices and fissures during the warmer months,
and,  when  frozen  in winter, breaking down,  by repeated and in-
creasing expansive  efforts during successive  years, the  substance
of masses which would appear, from compactness and hardness, fit-
ted to withstand the severest effects of time and climate.
  The specific gravity of  steam, such as it would be at the standard
temperature and pressure, is found to be 620*1, atmospheric air be-
ing 1000*0.  Two  volumes of steam contain two of hydrogen and
one of oxygen ;  hence there is a condensation of three volumes to
two produced by the union of the gases.   The calculated result is
thus  found:
         Two volumes of hydrogen  .   68*8x2= 137*6
         One volume of  oxygen.....=1102*6
         give two  volumes of vapour of water  =1240*2
         hence  one volume of vapour of water  = 620*1

  In  forming steam at 212 , and a pressure of 30 inches  mercury,
water expands to 1696 times its volume according to the determina-
tion of Gay Lussac, which gives almost exactly the proportion of a
cubic inch  of water forming a cubic foot of steam, which contains
1728 cubic  inches.
  The solution of  gases  in water appears  to  be governed by prin
ciples similar to those  which regulate the solvent action of water
upon  solid  bodies.   In  some instances there  certainly takes place
chemical union, as  in the case of muriatic acid gas and ammonia; and
in these cases the condensation of the gases by the water is accom-
panied by the evolution of considerable  heat.  But in other cases,
particularly where  the quantity  of gas is small, the result appears
to be merely a mechanical distribution of the molecules of  the gas
throughout the mass of the liquid.  The following is a table of the
quantity of these gases  absorbed  by water  without combination
  100 volumes of water at 6J° Fahr. and 30 inches bar. absorb of
       Sulphuretted hydrogen.........253 volumes
       Sulphurous acid...........438   "
       Chlorine..............206
       Carbonic acid............100   "
       Nitrous oxide............76   "
       Oleliant gas.............125  "
       Oxygen..............    37  "
       Nitrogen  )                                 16  "
       Hydrogen S.........
  The mixture of  nitrogen and oxygen, which constitutes the air
we breathe, is absorbed  by water, and it is to the air thus  dissolved
that  water, in great part, owes its refreshing taste.  If  water be
boiled this  air is expelled, and this should be done  if it be  wished
to saturate  the water with any other gas, as the power of water to
absorb any  other gas is remarkably diminished by the presence of
even a small quantity of air.  If water already saturated  with one
gas be exposed to  the action of a second, it  lets a portion of the
first  escape, and absorbs  a corresponding  quantity of the second.
In this way, a very small  quantity of a sparingly soluble gas  may
expel a large quantity of one much more soluble.  A  familiar exam-
ple of this fact consists in taking a glass half full of Champagne, and 
256      CHEMICAL RELATIONS  OF  WATER.
having formed the palm of the hand into a hollow cup, to strike the
top of the glass, closing the glass and flattening the hand at ihe same
time ; the air above the wine is thus forcibly compressed, and a por-
tion is then absorbed, under pressure, by the fluid,  from which a
quantity of carbonic acid is expelled, greater than that of air absorb-
ed in the proportion of 1060 to 16, and thus the effervescent char-
acter of the wine restored.
  Notwithstanding this character of neutrality, which renders wa-
ter  so useful as a vehicle or solvent for more  energetic bodies, wa-
ter  is actively engaged in a great variety of chemical reactions, in
which its elements, separating from one another, appear in an iso-
lated state, or, by combining with other  substances which  may be
present, generate new compounds.  Even, however, independent of
decomposition, water plays a most important part in chemical theory,
from the numerous classes of compounds of which it forms a con-
stituent.   The generality of saline bodies, in crystallizing, retain a
quantity  of water, often  more than  one half  their weight; this is
termed water of crystallization.   On the  application  of a moderate
heat this water  separates, and frequently the salt dissolves in its
own water of crystallization on being heated, undergoing what is
termed watery fusion.
  Salts  containing water of crystallization  often attract  still more
if surrounded by damp  air, and fall into a liquid  state: such are
termed deliquescent salts;  others, on the contrary,  give off their
water of crystallization even at ordinary temperatures, if the air be
moderately dry; some, such as the carbonate  and sulphate of soda,
losing all;  others, as the phosphate of soda, only a portion of that
constituent: these are termed efflorescent salts ; when the efflores-
cence is complete, they  lose their crystalline  arrangement and fall
to powder.
  Graham  has shown, that in many classes of salts, particularly in
the   sulphates, one  portion  of the water  is much more intimately
united  than the remainder; that, in fact, in addition to the  mere
water of crystallization, which may be removed without injury, there
is water  essential to the constitution of  the  salt, and replaced by
other bodies when the salt enters into  combination.   Thus, in the
common crystallized sulphate of copper there are five atoms of wa-
ter, of which four are removable by a temperature of 150 ;, but the
fifth withstands a temperature of 300\   The formula of this salt is,
therefore, not Cu.O.. So3  + 5H.O., but Cu.O.. S.03 H.O. -f 4H.O., the
four atoms being water of crystallization; now if this salt be com-
bined with sulphate of potash, this fifth atom of water  disappears,
and the double salt is (Cu.O. . S.03) (K.O.. S.Os)  + 4H.O.; the K.O.
S.03 having entered into the place of the water which had been ex-
pelled ; water thus circumstanced is termed  constitutional water,
as being necessary to the complete constitution of the substance.
  Water, in combination with the stronger acids, is capable of act-
ing as a base, and, indeed, we know of the existence  of many acids
only in the form of their compounds with water.   Thus the nitric,
the chloric, the oxalic, the acetic acids, have never been obtained
in a separate form; what we  generally term  those acids beingi in
reality, compounds of these acids with  water—salts of water.   Oil 
         WATER  IN  CHEMICAL  COMBINATION.     257

 of vitriol is a compound of sulphuric acid and water, sulphate of
 water, and it  combines with more water, producing great heat, to
 form a sulphate of water  with  excess of base, precisely as the sul-
 phate of copper combines with more oxide of copper to produce a
 corresponding basic salt.   The salts of water possess the most com-
 plete similarity  with those of  zinc and copper, and  it is from their
 comparative study that the evidence in favour of the view inculca-
 ted already, of hydrogen being a volatile metal, has been in greatest
 part derived.
   Water combines also with bases : the majority of metallic  oxides
 combine with water, often with the evolution of considerable heat.
 The slacking of lime, which is the act of combination of dry lime
 with water, produces  so  much heat as  to  ignite gunpowder,  and,
 when in  large quantity, to become red hot.  Ships  laden with lime
 have often  been burned  at sea, from water getting into the  hold
 among the lime, and so much  heat being evolved as to set the ship
 on fire.  Barytes  and  strontia produce, in slacking,  still more heat.
 Potash retains water so strongly that it can only be obtained free
 from it by the  direct  combustion of the  metal, potassium,  in dry
 oxygen gas or air.  In relation to these powerful bases, water ap-
 pears, therefore, to act the part of a feeble  acid.
   The compounds of water have been generally termed by chemists
 hydrates ; thus, hydrate of lime, hydrated oxide of copper, hydrated
 sulphuric acid, hydrated sulphate of zinc.   The very different func-
 tions performed by water, in  the various modes of combination it
 nffects, render it necessary to  adopt a definite principle of nomen-
 clature in this respect.   In the subsequent pages I shall employ the
 word hydrate only  where  the water is combined with a base, such
 as a metallic oxide ; thus, hydrate of lime, hydrate of potash, hy-
 drated oxide of lead.  Where the water is united to an acid,  I shall,
 in all  cases in  which  the true chemical nature of the compound
 comes into  play, term  it  a salt ;  as sulphate of water, oxalate of
 water, &c.; but where no strict theoretical  explanation is involved,
 I shall continue to use  the common name,  as oil of vitriol,  strong
 sulphuric acid, oxalic acid, aquafortis, &c.   There is no name pecu-
 liarly applicable to the form of compounds which contains constitu-
 tional water, but it will serve as well to characterize the absence or
 deprivation  of this water by  the word anhydrous, the ordinary
 name of the substance  being supposed to include the combined wa-
 ter ;  thus, common sulphate of zinc, freed from water of crystalliza-
 tion, is Zn.O.. S.O.j. H.O.; anhydrous sulphate of zinc is Zn.O.. S.03.
   When there exists water of crystallization in a salt, it is of course
 included  when the  salt is  spoken of as  crystallized.  In formulae,
 for the purpose  of  distinguishing between water of crystallization
 and water more  closely united, the latter will always be marked by
 the symbols of its constituents, the former by the two initial  letters
 of the Latin word aqua, aq.;  thus the crystallized oxalic acid  is
 CO,. H.O. + 2Aq.   The phosphate of soda is P,05+2Na.O.. H.O.+
 ii.'Yq.
  Water  does not exist  in nature in a perfectly pure condition.  It
 contains dissolved a small portion of atmospheric air and of carbonic
acid, and also certain quantities of solid impurities,  of which com
                              K K 
 258 MINERAL  WATERS.—PEROXIDE  OF  HYDROGEN.

 mon salt, sulphates and carbonates of lime, and chloride of magne-
 sium, are the most important.   In particular localities, the water is-
 suing from the earth contains iron, and often sulphuretted hydrogen ;
 also traces of iodine and bromine ; and occasionally the quantity of
 these foreign matters present is so great as to confer upon the wa-
 ter medicinal properties, and to make such springs, under the name
 of mineral springs, spas, be resorted to for the purpose of preserving
 or  recovering health.  These impurities arise from  the water, in
 percolating through the porous rocky strata, of which the  mount-
 ains and general crust of the earth are composed, dissolving in small
 quantity almost  all the  substances it meets.  Hence  rain-water or
 snow-water, collected at a distance from houses, is the purest water
 which can be obtained  in nature.   It contains only some carbonic
 acid and air dissolved.   The  sea  being the  general reservoir into
 which all the rivers  of the earth discharge their waters, contains
 in a concentrated form  all  the materials which the river waters had
 carried down.  Although not of absolutely the same constitution all
 over the globe, yet it varies so  little that the deviation  may be  ex-
 plained by local circumstances.  It  is in many countries the source
 from  which  common salt and  sulphate of magnesia are derived.
 When sea-water freezes, the ice contains scarcely a trace of saline
 matter, so that,  when  melted,  it  forms a sweet,  drinkable water.
 Hence, in voyages in the Northern Seas, supplies of fresh water are
 obtained by chopping blocks  of ice from the frozen surface of  the
 ocean.   To obtain water pure for chemical purposes, it is necessary
 to distil it.  The saline  and fixed impurities remain behind, the pure
 water passes over.  Its purity may be ascertained by means of  the
 reagents fitted to detect the most important impurities.  Thus, if
 free from common salt, it will give no precipitate with a solution of
 nitrate  of silver; if free from lime, it will not be affected by oxalic
 acid ; and if it be not rendered  turbid by nitrate of barytes, it can
 not contain sulphuric acid.
  From the inactivity of water, and  the facility with  which it may
 be obtained pure, as well as the  important part which it plays in  the
 economy of nature, it is taken as the standard with which the prop-
 erties of other bodies, when numerically determined, are compared.
 Thus the specific heats  of solids and  liquids are reduced to a scale,
water being taken as 1*000.  The specific gravities of liquids and
 solids are also taken in numbers, that of water being  the standard.
If, however, the  specific gravities, and heals  of gases and vapours
were reduced to the standard of water, the fractions by which they
 should be expressed would be inconveniently small; and hence, for
this class of bodies, a better suited  standard substance  is found ia
ntmospheric air.

           Of Oxygenated Water.  Peroxide of Hydrogen.
                       H.O. + O.,  or H.O,.
  This  singular  substance  was first discovered  by  Thenard; its
 preparation is somewhat circuitous and indirect, oxygen and hydro-
 gen not combining with  each other directly in any other proportions
 but those which form water.
  For its preparation, peroxide of barium must be first procured; this is prepared 
  PEROXIDE  OF  HYDROGEN,  PREPARATION, ETC. 259

by placing pure barytes (oxide of barium) in a porcelain tube, which  is heated to
redness in a charcoal furnace,  and then a stream of pure oxygen gas passed over it
as long as it is absorbed, the barytes absorbs as much more oxygen as it already
contained, and from Ba.O. becomes  Ba.02
  This substance may be still more easily  prepared  by mixing pure barytes with
its weight of chlorate of potash, and heating it nearly to redness;  when the disen-
gagement of oxygen from the chlorate  of potash has  set in, the mass becomes
glowing red at one point, and this appearance spreads over the whole mass like tinder.
The barytes burns, as it were, in the atmosphere of oxygen, and forms the deutox-
ide of barium.  If, then, the residual mass  be washed with water, the chloride of
potassium, which remains from the chlorate of potash, is dissolved, and the deutox-
ide of barium, combining with  an equivalent of water to form a bulky, white, insol-
uble hydrate, remains behind, and may be collected on a filter.
  The  best mode of obtaining peroxide of hydrogen from this substance is that pro-
posed by Pelouzc.   To dilute hydrofluoric acid (fluoride of hydrogen), the peroxide
of barium is added until the acidity of the liquor is completely neutralized.  The
reaction is very simple ;  the fluorine combines with the barium, while all the oxy-
gen  is  transferred to  the hydrogen,  which  the  fluoric  acid  abandons; thus,
H.F.+Ba.0«=Ba.F.-L-H.O2.
  The  fluoride of barium is insoluble, and  may be collected on a filter along with
the excess of peroxide of barium; the liquor contains only pure oxygenated water.
Fluosilicic acid, which is cheaper, and more convenient than the  fluoric acid, may
also be used in this decomposition.   The fluosilicate of barium separates as an in-
soluble white powder, and the peroxide of hydrogen remains dissolved.
  Thenard's plan consisted in dissolving the peroxide of barium  in  dilute muriatic
acid, and  then precipitating the barytes by sulphuric acid.  The muriatic  acid
which became free was then neutralized  by another portion of peroxide of barium,
and this again precipitated by sulphuric acid.   When the liquor had become strong
enough, the free muriatic acid was removed by the cautious addition of sulphate of
silver,  and the sulphuric acid then evolved was precipitated by the addition of pure
barytes, carefully avoiding an  excess.
  The weak  solution of peroxide of hydrogen thus obtained must be placed, along
with a capsule of sulphuric  acid, under the exhausted receiver  of the air-pump.
The  water being more volatile, evaporates first, and the liquor gradually becomes
more concentrated, until, finally, the peroxide of hydrogen remains pure behind.  If
left too long in the exhausted  vessel, it evaporates itself without alteration.
  Peroxide of hydrogen  is a  thick, colourless liquid.   Its specific gravity is L452.
It has a nauseous taste, and irritates the  skin.   It bleaches and destroys all vegeta-
ble colours.  Its  reactions are generally so violent  that it must  be  diluted with
many times its volume of water before they can be accurately observed.
  Its most curious property is, that  by being put in contact with any one of a great
number of solid substances, it is decomposed with great rapidity,  being resolved
into oxygen and water.   Black oxide of manganese is one of the most  active.   If a
little of this substance, in  powder, be introduced into strong peroxide of hydrogen, in
a graduated tube, over mercury, the latter is decomposed almost explosively, disen-
gaging 475 times its volume of oxygen, the oxide of manganese remaining perfectly
unaltered.  Platinum, gold, silver, quicksilver, particularly if  the  metal be in  the
form of leaf or sponge, produce the same effect; and if the peroxide  of hydrogen
be put into contact with an oxide of these metals, as oxide of silver, it is not mere-
ly decomposed itself, but the oxide is also decomposed, the  oxysren and metal both
becoming free.  In the dark, and with strong peroxide of hydrogen, a flash of light is
seen  to accompany its decomposition, and the tube becomes red hot.  The decompo-
sition of the oxide of silver cannot, however, be referred to the great heat produced,
as, even if the peroxide of hydrogen be diluted with fifty times its volume of water,
oxide of silver produces complete decomposition, evolution  of oxygen, and separa-
tion of metallic silver; yet the effervescence is not very energetic, and the liquor
does not  become sensibly warm to the hand.
  With other metals, the oxygen, in place of becoming free, enters into combinatipn,
forming an oxide of a higher degree ; thus, with the oxides of lead  and  bismuth
there are formed peroxides  of  those metals;  with arsenic there  is formed arsenic
acid.  The animal substances fibrine and albumen,  which  are so similar in most
respects,  are distinguished from each other by their action on  this body, fibrine de-
composing it with rapidity, while albumen is without effect.   It is highly probable,
that in  the decomposition of water by the voltaic pile, some of this compound may 
260       PREPARATION  OF  NITROGEN  GAS.

be formed, as the quantity of oxygen collected is frequently smaller than it should
be; and a portion of the process of bleaching, by exposing the wetted cloth to the
action of light and air, may possibly be carried on by the formation and subsequent
decomposition of this substance.
  Peroxide of hydrogen, when kept for any length of time, even in a dilute condi-
tion, gradually decomposes, oxygen being given off, and water remaining behind.
The presence of an acid in the liquor retards this action very much, while the pres-
ence of an alkali accelerates it.  It was  in great part from the remarkable charac-
ters of this body that Berzelius derived his evidence in favour of the existence of a
catalytic force influencing chemical action,  which has been described already.

                           Of Nitrogen.
                               N.
   It  has been already noticed, that the substance by which the ox-
ygen is diluted in atmospheric air,  so as to render it suitable to the
respiration of animals, is called  nitrogen, from its being the basis
of nitric acid and nitre (the nitre  former).  It is also called by some
chemists azote, from its incapability  of  supporting life; but, as a
great number of gases resemble it in that respect,  the former name
is the more characteristic, and it alone will be  hereafter used.
   As nitrogen exists in great quantity in the air we breathe, it  is
                        most easily obtained by acting upon a con-
                        fined portion of the air so as to abstract the
                        oxygen, when the residual gas is found to
                        be nitrogen almost completely pure.  Thus,
                        if a small piece of phosphorus, laid in a cup
                        d, floating on water, be set on fire, and a bell
                        glass, a, be inverted over it, the phosphorus,
                        in  burning, unites with the oxygen of the
                        air, and  forms white fumes of phosphoric
                        acid.  At first, from the great expansion of
the air caused by the high temperature  of the  flame,  some bubbles
escape from  under the edge of the  glass ; but soon, even before the
phosphorus has ceased to burn, the water begins to rise  in the bell,
and, finally, the clouds of phosphoric acid gradually dissolving in the
water, the  residual gas will be found to  occupy about four fifths of
the original  volume of the air, and to be colourless as the air had
been before.   Any other burning body would answer the same pur-
pose, although not so perfectly as the phosphorus.  Thus, if spirit
of wine, or pyroxylic spirit, or ether, which burn without smoke, be
placed in the little cup, and  set  on fire under  the bell glass, as  in
the former instance,  the inflammable constituents, carbon and hy-
drogen, combine with the oxygen of the air,  forming carbonic oxide
and water, the nitrogen remaining  behind.  The gas thus obtained
must be washed well with water, or, better,  a little solution of pot-
ash,  to remove the carbonic  acid, and even  then the  nitrogen con-
tains some oxygen unconsumed ; for in  every case where carbonic
acid is formed by a burning body, the combustion  ceases before all
the oxygen present has been consumed, the carbonic acid exercising
on combustion a positively impeding  power,  similar to  that which it
has on respiration.   The purest  nitrogen is consequently obtained
by means of phosphorus.
   Independent of this source of nitrogen in atmospheric air, it may
£
 
          PREPARATION OF  NITROGEN GAS.       261

be obtained indirectly from  a great number of substances.  Thus
most animal substances contain nitrogen in large quantity, united to
carbon, hydrogen, and oxygen. If, therefore, some pieces of muscle,
or albumen, or gelatine, be boiled in a retort with some nitric acid,
the oxygen of the nitric acid combines with the carbon and hydrogen
of the animal substance, forming different compounds according to
the temperature  and the proportions, while the nitrogen of both is
disengaged.
  If  a gas, termed nitrous oxide, which will be described in a sub-
sequent section,  be put into contact with a slip of metallic zinc, at
the moment of its formation the zinc deprives it of its oxygen, form-
ing oxide of zinc, and the nitrogen is set free.   The apparatus used
for this purpose  consists of  a tubulated retort, into which is intro-
duced the salt (nitrate of ammonia), which, when heated, yields ni-
trous oxide.  Into the tubulure is fitted a cork, through which passes
a copper wire, to the end of which a slip of zinc is fastened.  To
the neck of the  retort a bent tube is adapted, passing to the pneu-
matic trough.  Heat being applied to the retort by means of a lamp,
the salt melts, and  then begins to emit gas.   At this moment the
copper wire is depressed, so that the slip of zinc may touch the sur-
face  of the melted mass.  The effervescence immediately becomes
much more violent, white clouds of oxide of zinc  are formed, and
the gas, which passes over,  is nitrogen quite pure.   The theory of
the formation of the nitrous oxide will be noticed under the proper
head.  Its decomposition by the zinc is simple: nitrous oxide is N.
0., and acted on by Zn. their products are N. and Zn.O.
   If ammonia dissolved in water be exposed to the  action  of a cur-
rent  of chlorine, it  is decomposed, sal ammoniac is formed, and ni-
trogen gas is disengaged.   The solu-   -^
tion  of ammonia may be contained in  owf
a bottle with a wide neck, g, to which
a cork is fitted, perforated  to admit
two  tubes, the one, /, conveying the
chlorine from the vessel a,  in which
it is  disengaged, and opening under
the surface of the liquid near the bot-
tom, the  other  projecting  but little
under  the cork, and leading to  the
pneumatic trough.  The action of the
chlorine upon the ammonia is accompanied by the formation of white
fumes and the evolution of much heat.  If the solution be  strong, a
flash of light is seen at the  entrance of each bubble of chlorine gas;
but these  are not attended  with any danger.  The  ammonia, how-
ever, must, all through the  process, be kept in excess, as, were the
chlorine in excess,  it might produce a body, chloride of amidogene,
possessed of the most eminently dangerous explosive properties.
   The reaction which here takes place may be  simply shown.  Am-
monia consists of one equivalent of nitrogen and three of hydrogen ;
by the  action of three equivalents of chlorine there are formed three
of chloride of hydrogen (muriatic acid), which unite then with three
equivalents of ammonia to form three of sal ammoniac (muriate of
ammonia).  Thus (N.+3H.) and 3C1. give N. and (3C1.H.), which
 
262 PROPERTIES OF NITROGEN.--ATMOSPHERIC AIR.

eombine with 3N.IL, to form  3(C1.H. . N.H3), one equivalent of ni-
trogen becoming free.
  Nitrogen, when  obtained by any of these processes, is a perma-
nent gas, colourless and transparent;  it is absorbed by water only
in very small quantity.  It is lighter than atmospheric air, its specific
gravity being 976,  air being 1000.  It is characterized by. the com-
plete  absence of the positive properties which distinguish other
gases.  Thus, it does not support combustion or respiration ; it ex-
tino-uishes a taper, and animals  are suffocated  in it ; but these ef-
fects appear to be  due only to the absence of oxygen.
  Although nitrogen is thus incapable of combining directly with
oxygen, yet by indirect methods they may be  made to unite, and
the compounds formed of these  elements  are surpassed in number
and importance by few series of binary combinations.   When oxy-
gen and  nitrogen  combine, their result is almost  universally that
which contains most oxygen, nitric acid ; their union may be effect-
ed by the electric  spark, provided water,  or a solution of an alkali
be present; hence  rain-water often contains traces of nitric acid,
particularly if its  deposition has been preceded by discharges of
lightning between  the clouds; and lime or potash contained in old
walls are found, after a certain time, to be neutralized by nitric acid.
A mixture of ammonia and  oxygen may be converted into nitric
acid and water, likewise, by spongy platinum at a temperature of
572\
  The combining proportion of  nitrogen is, on  the  hydrogen scale,
14*0, and on the oxygen scale, 175.  In a great number of instances,
however, it appears to enter into combination with one third of its
ordinary equivalent, and I have  found this peculiarity to extend to
arsenic and phosphorus, which are  so closely assimilated to it
throughout their chemical relations.
  Before  entering upon  the history of the compounds of nitrogen
with oxygen, I shall describe more particularly the properties and
composition of atmospheric air, which, being of so much importance
in the majority of  chemical reactions which occur on a large scale,
and being assumed as the standard of properties for  gaseous and
vaporous bodies, deserves minute attention.

                       Of the Atmosphere.
  The analysis of  atmospheric air was the first important problem
in the chemistry of gaseous  bodies with which chemists occupied
themselves, and hence the names of instruments originally devised
for examining atmospheric  air  became generally used to  indicate
those employed in the analysis of gaseous mixtures or compounds
of any kind.  The word eudiometer signifies a measurer of the good-
ness of the air ; and from the interest which the problem presented,
numerous methods were  early invented, although it is only recently
that very great precision  has been obtained.  It was at first believed
that the relative salubrities of districts, and even of different local-
ities in the  same neighbourhood, could be determined by the pro-
portions of oxygen and nitrogen  whicn the air of these places might
contain; and that the admixture of pernicious substances, exhaling
from a marsh, or generated within the ill-ventilated apartments of 
ANALYSIS OF  AIR.
263
an hospital or of a jail, might be recognised,  and means discov-
ered of removing them, or of destroying their activity, when their
nature had become  determined by the analysis of the air in which
they had been contained.   The differences between the results of
various  chemists, on which these expectations had been  founded,
have gradually disappeared by the use of better  methods, and the
constitution of atmospheric air is now recognised as being almost
absolutely the same throughout  its entire  mass; but from  other
sources,  the  very results which  had been  originally sought after
now appear to form a legitimate and promising subject of inquiry.
  In addition to oxygen and nitrogen, its principal constituents, at-
mospheric air contains some carbonic acid and watery vapour; the
quantity  of the  latter  is  determined by methods almost  entirely
physical, and  forms  a practical department in the theory of vapours,
termed hygrometry.  I shall, therefore, not touch upon it here, refer-
ring to  what has been already noticed of it in the  sections upon
water and upon heat.
  The determination of the quantity of carbonic acid present in at-
mospheric  air has  been  made accurately by Saussure,  who  found
that, in general, 10,000 volumes of air contain 4*15 of carbonic acid ;
the maximum of carbonic acid he  found to be 5*74, and the minimum
3*15. Over the surface of lakes,  as that of Geneva, the  quantity of
carbonic acid is smaller, but in cities greater, amounting to 4*46 in
the average : the quantity is somewhat greater by night than by day,
and  in the higher regions of the  air than on the surface of the low
ground  ; it is diminished also during and for some time after rain.
To determine the quantity of the carbonic  acid, a  large globe  or
bottle containing air is taken, and  a solution of barytes is introduced,
until, after having  been well  agitated with  the air,  it is found,  by
browning turmeric  paper, to  be  present in  excess.   The carbonic
acid combines with baryte.-: to form a white powder, carbonate  of
barytes,  which, being collected on a filter and weighed, gives, by a
6imple calculation,  the volume of the carbonic  acid in the air.
  The experiments of Saussure and of Boussingault have made it
probable that carbon combined with hydrogen  (probably as the gas
of marshes) exists in very small quantity in atmospheric air.  Thus,
when Saussure, after having removed all carbonic acid  by barytes,
detonated the residual air with pure hydrogen, he obtained a quan-
tity of carbonic acid equal to nearly one part in 2000 of the air em-
ployed ;  and, although employing other methods, the results of Bous-
singault strongly corroborate the same idea:  he found sulphuric acid
to be blackened when exposed to air, although  all access of dust or
accidental  impurities was removed, and that when  air, previously
freed from carbonic acid,  was passed over red-hot oxide of copper,
a perceptible  quantity of water and of carbonic acid was produced.
  But the most important portion of the analysis of atmospheric air
is to ascertain the proportions of the oxygen and nitrogen.  To ef-
fect this, any one of a great variety of bodies which  are capable  of
uniting  with  oxygen may be used; thus, if  a solution of sulphuret
of potassium be exposed  to air,  it absorbs  oxygen, and gradually
passes to the state of hyposulphite of potash, and by the amount of
absorption the quantity of oxygen may be ascertained.  This is the 
264     COMPOSITION  OF  THE ATMOSPHERE.

method of Scheele.   One proposed by Sir Humphrey Davy consisted
in agitating the  deep olive  liquor formed by passing  nitric  oxide
gas into a solution of green sulphate of iron, with a measured quan-
tity of atmospheric  air; but it  is now abandoned.   An excellent
mode of using these bodies as eudiometers is to fill with the  liquid
a small caoutchouc  bottle, holding about two fluid ounces, and then
tie it securely on the tube of air which passes pretty closely in at
the neck ; the mass of air and fluid can thus be brought extensively
into contact, and the absorption  is shown by the gradual rise  of the
liquid in the tube, the soft parietes of the bottle yielding to the  press-
ure of the external air.
  Nitric  oxide gas possesses the property of combining with the
oxygen of the air, and forming deep red fumes of nitrous acid, which
dissolve  in water.   By this means, using an excess of the nitric ox-
ide, all oxygen  may easily  be removed from atmospheric  air, but
the composition of  the nitrous acid fumes is  not always the  same,
and hence  the quantity of oxygen which the air contained  is liable
to be mistaken.   This mode, therefore, from the great precaution
necessary in its  use, has been quite laid aside.
  The use of the hydrogen gas eudiometer, whether the combination
of that substance with the oxygen be accomplished  by the agency
of the electric spark, or by means of spongy platina, has been already
noticed.  It is one of the most accurate and easy methods  that can
be used, and. hence has been most  generally  employed.  The risk
of accident from the violence of the explosion by the electric spark
is much  diminished by using the form proposed by Ure.  The tube,
which need not  be  at all so stout as  in the  common form,  is taken
about twice as long, and bent into the form of a U.  Having been
filled with  mercury, the mixture of air and hydrogen is transferred
to the sealed leg, and then, the open  leg being about half occupied
by air, it is to be firmly closed by the thumb  or by a cork.   When
the explosion follows, the air in the open leg yields to the  pressure
and graduates the shock; no portion of the exploded mixture can
be projected.
  Slips of copper foil, moistened with muriatic acid, absorb oxygen
with great  avidity, and have been proposed by Gay Lussac for the
analysis of atmospheric air.  Saussure has used in his accurate re-
searches thin filings or turnings of lead, which combine with oxygen
very rapidly, and remove it totally from the air.
  Phosphorus, which burns in oxygen and  in air  so brightly, may
also be employed to form a eudiometer.   It may be used either by
slow or by rapid combustion.  In the former mode, a stick of  moist-
ened phosphorus, placed in a graduated tube of air, deprives it com-
pletely of its oxygen in about twenty hours ; the residue  is nitro-
gen, which has the  smell  of phosphorus, and  requires a  correction
for a small quantity of vapour  of that substance which  is  diffused
through it.   The rapid combustion of  phosphorus is too violent, and
exposes the vessels  to too much risk  of breaking, to be made use of
for accurate experiment.
  All of these methods are, however, liable  to error to the amount
of nearly 1 per cent., which is to be in great part attributed  to the
small quantity of air which the apparatus allows to  be experimented 
       CONSTITUENTS  OF ATMOSPHERIC  AIR.   265

on.   This disadvantage has been obviated by the mode proposed  by
Brunner, and used by him in some determinations lately made, in
which the liability to error has been reduced to 0*20 per cent.   In
the  figure, a, b, c is a tube, consisting of a wide por-
tion, b, and a narrower, c ;  the wider part  being
drawn in a to a capillary opening.  Into it is intro-
duced a quantity of loose cotton and some bits of
phosphorus,  and being then  warmed, the melted
phosphorus is allowed to spread over the fibres of
the  cotton so as to expose  a very great surface.
The tube at c fits air-tight to the orifice of the ves-
sel d, which  is graduated  and filled with mercury;
a cock at e allows the mercury to flow out on oc-
casion.  To  use this apparatus, the tube a,  b, c  is
weighed, and then attached to the vessel d; the
cock e is then slightly opened ;  the mercury issues
out  in a properly graduated stream, and its place  is supplied by air,
which, entering  at the capillary  orifice a, streams over the surface
of the phosphorus, by which  all its oxygen is removed,  and the  re-
sidual nitrogen passing into the graduated vessel, its volume can be
easily read off;  or the mercury which flows off  being  caught in a
graduated glass, its volume is equal to that  of the nitrogen which
has  passed  in.   Besides  extending the surface of the phosphorus,
and thus quickening the absorption of the oxygen, the mass of cot-
ton  serves as a filter to collect  the white fumes  or flakes  of phos-
phorous acid formed.  When a sufficient quantity of air has passed
through the  apparatus, the tube a, b, c is  to be weighed again ; the
increase of weight is the  quantity of oxygen absorbed,  from which
the  volume may be known, and the mercury measured is the volume
of the  nitrogen, from whence its weight may be calculated.  The
air must be of course dry.  This is effected by securing to  the tube
a, b, c. by means of a caoutchouc connector, a small tube  contain-
ing  fragments of fused chloride of calcium, through which the  air
streaming deposites the moisture it may contain.
  The result of all these methods indicates that atmospheric air con-
tains from 20*79  to 21*08  of oxygen gas in 100 volumes ; and from
experiments  of  Gay Lussac  on air brought down by him from a
height  of 21,735 feet,  to which he had ascended in a balloon, and
those  of Brunner for the  air on  the summit  of the Faulhorn, 8020
feet above the level of the sea, the constitution appears to  be iden-
tical at all heights.  By weight, the constituents of the atmospheric
air in 100 parts are, omitting carbonic acid and water,

             Oxygen gas.....=23*04
             Nitrogen gas.....=76*96
                                          To^oo

  This permanency of constitution of atmospheric  air, together
with many other circumstances which I shall briefly notice, led to
the  opinion  among many chemists of its being a compound, and not
a mere mixture of its constituents.  The analysis not being then  so
accurately made, it was supposed to consist of one volume of oxy-
gen united to four volumes of nitrogen, a simplicity of proportion
 
266     VELOCITY  OF DIFFUSION  OF  GASES.
which characterizes chemical  union among gases.  It Avas also re-
marked, that if the nitrogen and oxygen were merely mixed, their
different densities should cause them to separate ; the heavier oxy-
gen accumulating near the earth, while the lighter nitrogen should
occupy the higher regions of the air.  The former ground has been
completely disproved by later research, and the  elements of air are
separated  from one another by such feeble means, thus, by nitric
oxide, by  metallic lead, by agitation with  water, &c, as would be
unexampled in chemistry  among substances of a constitution such
as it, if a  true compound, should  be supposed  to have.  Besides,
its density, its refractive  power,  its specific heat, are the mean
qualities of the oxygen and nitrogen which form it; circumstances
which necessarily occur if it  be a mixture, but  which do not take
place in any case of chemical combination.  An artificial mixture,
also, of oxygen and nitrogen  possesses all the properties of atmo-
spheric air.
  It is also not the fact that gases of different densities tend, when
        mixed  together,  to separate, and form  different layers, in
        accordance with their specific gravities.  On the contrary,
        if two bottles, containing, the one, a, a lighter, and the other,
        e,  a heavier gas, be connected by stopcocks, b, c, d, and al-
        lowed to  stand for a  few  hours, the bottle containing the
        heavy gas being lowest, they will be found to mix, the light-
        er gas finding its way to  the lower bottle, and the  heavy
        gas ascending to the bottle which is above.   In this process
        the gases evince  a positively active power of penetrating
        into  the  spaces occupied  by each other; and this occurs
a
mre
        even when they are separated by membranes, or by masses
        of porous earthy substances.  This peculiar  property of
        gases was first recognised by Dobereiner, and then studied
by Mitchell, but finally examined, and its laws accurately assigned,
by Graham.  When gases of unequal densities are placed in con-
tact  with each other, they tend to  mix ultimately in  a uniform
manner; but the rapidity with which they penetrate each other's
volume, or, as it is  termed by Graham, the velocity of diffusion of
the gases, is  unequal, and depends upon their densities; the lighter
gases diffusing themselves most rapidly, the heavier more slowly.
Thus, if a tube be closed at the  top  by a plug of plaster of Paris,
which, when dry, is very porous, and filled with  hydrogen gas, the
plug being kept dry, the hydrogen and the external air tend to mix
across the porous plug ; but the hydrogen comes out more rapidly
than  the air gets in, and hence the water rises considerably in the
tube.  In a similar way,  if a glass be  filled with hydrogen gas, and,
the top being closed by a sheet of India rubber,  a bell glass of air
be inverted over it, the hydrogen passing out of the glass more rap-
idly  than air enters to supply its place, the  sheet  of India rubber
is gradually bent into the glass, and ultimately burst by the external
pressure.  On the contrary, if the  small glass contain air and the
bell glass hydrogen, the  membranous cover is gradually forced up-
ward by means of the excess of hydrogen  which  passes  in, and
which finally breaks through it by the elasticity  thus produced in-
side. 
LAW  OF  DIFFUSION  OF  GASES.          267
  The exact law of the diffusion of gases is, that the velocity of diffusion is inverse-
ly proportional to the square roots of the specific gravities of the gases.  This is ex-
hibited in the following table.
	Specific Graiitia.	Square Roots of S. 6.	Diffusion Vol
Hydrogen . .	. . 0 0688 . .	. . 0 2623 .	. . 457
Ammonia . .	. . 0 5898 . .	. . 07681 .	. . 130
Air ... .	10000 . .	. . 10000 .	. . 100
Carbonic acid .	. . 15239 . .	. 1-2345 .	. . 81
Chlorine . .	. . 2 4700 . .	. . 15716 .	. . 64
  By this table it  will be seen, that in the same time in which 100 volumes of at-
mospheric air escape from a vessel through a membranous  or  porous  plug, 457
volumes of hydrogen pass in; and if the vessel were previously  full of hydrogen,
157 volumes will escape from it during the entrance of 100 volumes of atmospheric
air.  If the vessel contained carbonic acid, the result would be the passage of 81
volumes in the same time, and so of the other gases.
  [This law is,  however, entirely departed  from when the  gases are  separated
from one another by a plug or barrier which exerts upon them a condensing action,
and the diffusion volumes are found to be other than those indicated in the forego-
ing table.  A plug of stucco exerts but little condensing effect upon the gases, and
hence their diffusion takes place into one another with a velocity inversely propor-
tional to the square roots of their  densities ;  but a thin lamina of India rubber, ef-
fcctmsi a powerful condensation, presents the two gases to each  other with densi-
ties that are abnormal, and hence disturbs their rate  of diffusion.
  Phenomena of this kind may be very beautifully  shown by means of  soap-bub-
bles.  If a vial that has had a film of soap-water spread over its mouth be exposed
under a jar to an atmosphere of ammonia or protoxide of nitrogen, its horizontally
is instantly disturbed, and it begins to assume a spherical convexity, and  continues
expanding until, after passing through a series  of brilliant colours, it may become
bo thin as to be almost invisible.  To show the great rapidity with which a gas or
vapour will pass through such barriers, if a soap-bubble be expanded in a vial con-
taining a little aqua  ammonia', and the air from its interior be immediately with-
drawn into the mouth, the strong caustic taste  of the ammonia will be immediately
perceived.
  Through thin  pieces  of India rubber gases  will diffuse  into each other, though
resisted by any given pressure.  I have found that sulphuretted hydrogen will thus
pass into atmospheric air against a pressure of  more than fifty atmospheres.]
  This law  of the passage of gases through each other is the same as that for the
passage of a gas into a perfectly empty space.  If the different gases be allowed to
strain through a  porous plug  into a vessel from which the air has been removed by
the air-pump,  they will enter with different velocities, regulated by  their specific
gravities, precisely as in the former instance;  and hence  it is experimentally de-
monstrated that different gases are ultimately permeable to each other, precisely as
the spaces they  occupy would  be  if  entirely empty; that the gases, in  fact, form
vacua  to each other, but that so far as the law of mixture and the final effect are
concerned, the mixture taking place more slowly, in consequence of the mechani-
cal obstruction.
  This general principle had, however, been laid  hold of by the keen intellect of
Dalton, and  announced long before its truth had been accurately proved in the man-
ner that has been now described ;  to him we are indebted for the  first philosophical
view of the molecular constitution of the atmosphere ;  he proposed to consider the
different gases which exist in the  atmosphere as being in all points independent of
each other, mixed uniformly in  virtue of the diffusive power which he  had  been
the first to recognise, and exercising pressures  upon the surface of the  earth pro-
portional to their quantities.   Thus, if we suppose 100 parts of atmospheric  air to
consist by weight of,

                Nitrogen gas  .  .        ... 75-88
                Oxygen gas   .          ... 2304
                Watery vapour           ...   1 03
                Carbonic acid .        ....    05

the pressure of  the  air being taken at thirty  inches of mercury, the respective
pressures of the  independent atmospheres will  be as follows:
100 00 
268  CONSTITUTION OF THE  ATMOSPHERE PERMANENT.

                                             22764 inches
                                              6912   "
                                              0309   "
                                              0015   "
                                             30 000

  The different constituents of air are thus in the state best suited
to the  purposes for which the atmosphere is destined ;  no one gas
can interfere with, or retard the others' action; there are no affini-
ties to be overcome, or existing combinations to be broken up, before
the ao-ency of watery vapour, of carbonic acid, and  of oxygen can
be brought into the extended alternations on which the continu-
ed and bappy existence of animal and vegetable life  depends, from
which arises the diversity  of aspect of our ever varying sky, and
the gradual detrition of the  solid rocky materials of the earth's sur-
face giving a fruitful soil.
  By the processes of combustion and of respiration which are in ac-
tion on the  surface of the earth,  the oxygen of the  atmosphere is
continually removed, and an equal volume of carbonic acid gener-
ally  substituted for it.  This carbonic acid is absolutely a narcotic
poison, and  the air becomes unfitted for the  support of life  before
one  half of the quantity of  oxygen it contains has been consumed.
A healthy man spoils in twenty-four hours, by respiration, 720 cubjc
feet of atmospheric air, that is, a mass of air eleven feet square and
six feet thick.  The burning of three ounces of charcoal produces
the same effect.  In many factories there  are burned daily ten tons
of coal, which deteriorate at least as much air as the same weight
of charcoal, and hence each day, by such a factory, there is render-
ed unfit for respiration 3,185,760  cubic yards of air, which would
cover  to the depth of six feet a space a quarter of  a mile square.
Nevertheless, it has been already  mentioned, that even in cities, the
relative proportions of oxygen, nitrogen,  and carbonic  acid in the
air are but little altered, and it becomes an object of great interest
to ascertain in what manner that permanency, on which the stabili-
ty, in truth, of all organized nature seems  ultimately  to depend, has
been secured.
   In the first place, from the frequent occurrence of storms and vio-
lent currents, which agitate vast tracts of  air, accumulation of nox-
ious oases or corrupted portions cannot take place, except in some
rare and limited localities, which  do not affect the condition of the
atmosphere even  near at hand ; and  although  the numbers which
have been shown as indicating the amount of air destroyed become
enormous when multiplied  by the number of breathing beings and
the quantity of fuel burned  on the earth's  surface, they yet bear but
a trifling proportion to the  immensity of the  aerial ocean in which
we live.  The atmosphere may be considered as being, if brought"
throughout  to its usual density at the surface of the earth, about
five  miles deep; and Prevost  has  calculated that the loss of all the
oxygen employed in respiration and  combustion for 100 years could
not  diminish its quantity by ^-^ part, a quantity too trifling to be
detected by our  methods, even had the exact sciences flourished
for such a period as to allow a comparison to be made.
   But, independent of this negative proof 6f permanence of corn-
Pressure of the nitrogen gas .   .
     "      oxygen gas .   .
   '  <•      watery vapour  .
     "      carbonic acid gas 
ATMOSPHERIC  PRESSURE.
269
position, science  has pointed out, in  the peculiar relations of the
functions of vegetable and animal beings, a provision of adaptation
to each other's wants, which retains the atmosphere in a condition
practically of eternal identity of constitution.   A healthy growing
plant, exposed to sunlight,  is found to absorb carbonic acid, and to
emit oxygen from the surfaces of its green leaves.  In the dark, an
inverse effect takes  place,  oxygen being absorbed, and  carbonic
acid formed.  The coloured parts of plants, as flowers and fruits,
absorb likewise oxygen, and emit carbonic acid; but as the green
surfaces preponderate so much throughout the vegetable world, and
the stimulus of light is active throughout the greater portion of the
twenty-four hours, the ultimate effect  is, that an action the opposite
of that which animals exercise upon  the atmosphere is constantly
going on.   That which the plant rejects is to the animal the source
of energy and of all vital powers, while the same element which the
plant absorbs, and from  which it forms its tissues, has been thrown
out as useless by the animal, and would, if not removed, accumulate
in the end, and destroy  all animal existence.
  The  most accurate experiments have determined that 100 cubic
inches  of atmospheric air, freed from  moisture and carbonic acid,
weigh  31,0117 grains; the  barometer being at 30 inches, and the
thermometer at 60J.  Its specific gravity is taken as the  standard
for gases and vapours,  and  is hence  1000.  It is about 780 times
lighter than  water at 40*5° Fahrenheit, when water is at its greatest
density, and is then also 10,600 times lighter than quicksilver.
  The  weight of the atmosphere pressing upon the surface of the
earth is equivalent to about  fifteen pounds on  each square inch of
surface.  The existence of this pressure may be shown  in many
ways :  a bladder or a thin plate of glass may be  burst if the pressure
of the  air be removed from  one side by the  air-pump  while it is al-
lowed  to act against the other; a pair of brass hemispheres, which
are easily separated while filled by  air, are pressed most firmly to-
gether  if the air be removed from their interior.  This pressure is
equivalent to that exercised  by a column of mercury in a tube about
thirty inches high, and,  accordingly, an instrument, the common ba-
rometer, or pressure measurer, is thus constructed, to register, at ev-
ery moment, the pressure which the atmosphere exercises.   A tube
closed  at one end, and about thirty-two inches long, is to be care-
fully filled with pure mercury; it is then inverted in a  basin of mer-
cury, and being placed in a vertical position, the column of mercury
sinks to a certain height in the tube, generally between twenty-nine
and thirty inches, leaving above it a space which is, at low temper-
atures,  the  most perfectly empty that can be  experimentally pro-
cured.   From the name of the inventor of this instrument, it is called
the Torricellian vacuum. If the external pressure varies, the height
of the column of mercury alters likewise, rising when the  pressure
increases, descending when  it is  diminished;  and as considerable
chamrcs in the amount of pressure generally depend on violent mo-
tions in the  air, which  produce changes in  the weather also,  the
barometer is popularly regarded as a weather-glass, although no ac-
curate  indications of approaching changes can be at all  reckoned on
from its use. 
270 PRESSURE  AND  EXTENT  OF  THE  ATMOSPHERE.

  If the atmosphere preserved throughout its entire mass the same
density and elasticity which it possesses at the surface of the earth,
its  height  would be about five miles.  But such  is not the case;
the low°er portions of the air, which press upon the earth, are pressed
upon by  the portions next over them, these  again  by those still
higher up,  so  that  the  amount of pressure, and, consequently, the
density of  the air,  decreases  continually as we ascend through its
mass.  The rate of diminution is even very rapid, forming a  geo-
metrical  proportion when the heights  are taken in  an arithmetic
series * and on this principle  is founded  one  of the  most accurate
modes of  estimating heights that  has been yet discovered.  If a
barometer  be  carried to the  summit  of a mountain, the column of
quicksilver will be observed to be shorter than it had been upon the
plain, and the difference being marked, the height corresponding to
it is determined, from a knowledge of the law just stated.  In prac-
tice there  are corrections depending on temperatures and other
causes, to which it is not necessary to allude.   So rapid is this dimi-
nution of density, that one half of the whole mass of the atmosphere
lies within  three  miles of the  surface of the earth, and four fifths of
it withira eight miles.  Hence, in those elevated regions, the lungs
receive, even in a deep inspiration, but little oxygen, and the blood
not  being  well arterialized,  causes the  headaches,  lassitude, and
faintness which those who ascend high mountains or in balloons feel
so severely.  The lakes in the mountainous valleys of Switzerland
and  the Andes are, for the like reason, destitute of fish;  the water
holds no air dissolved to fit it for their respiration,  precisely as
one  may kill a fish in water  by placing it under the receiver of an
air-pump and abstracting  the atmospheric air.
  The question of how far the atmosphere really extends in space,
possesses,  in relation to the views of the ultimate constitution of
matter, already noticed, considerable interest.  If the particles of
atmospheric air were capable of division  to an infinite degree,  then
the attenuation which occurs in the higher regions of the air should
have no limit, and we should look upon all space as occupied by the
elements which form our atmosphere, rarefied to an inconceivably
great degree, and our earth as having provided itself, in its course
through space, with as much of this circumambient matter as,  from
its attractive power, it was able to  keep round it.  If, on the other
hand, the oxygen and nitrogen of the air consist of molecules of defi-
nite form and size, these, being in the gaseous form, are subjected to
the simultaneous action of two forces :  one,  the mutual repulsion
which characterizes the gaseous condition, and which causes  their
elasticity, but which,  diminishing with this elasticity, must become
very small in the upper strata of our atmosphere ;  the  other, the
general attraction of the earth, which, though  much  inferior at the
surface, must, since it diminishes but very little in ascending so far,
at a certain point become equal to  the former, and then all farther
expanding  tendency being overcome, the  atmosphere should be ter-
minated by a definite surface, similar in form to that of the solid earth,
having its  tides  and  currents like those  of our great oceans, and
from these various fluctuations  in its  depth, produce the regular
variations  in the height of the barometer, which,  though involved
by the irregular motions of much larger amount, have been detected. 
          POISSON'S  ATMOSPHERIC   THEORY.        271


  The amount  of refraction  proves  that the  sensible atmosphere
does not  extend beyond 45 miles;  at least, if it exist higher up, it
must  be so rare as to have no  effect in  deflecting  a ray  of light.
But other considerations prove  that the air does not  extend through
space.  If we had obtained our atmosphere by gathering up, in vir-
tue of our attracting force, the thin air which pervades all space, the
other bodies of our system should  also possess atmospheres whose
densities should  represent the masses  of the bodies they include.
However, exact observation has shown that even the largest bodies
of our system possess no  atmospheres.   A  ray of  light suffers no
bending in its course, although it  passes by the  edge of Jupiter;
yet, from the immense size of  that planet, it should have collected
round it an atmosphere so  dense, that by its refraction  a star should
become visible  to us upon one  side of it before it had disappeared
at the other.   The sun, likewise, the gravitating centre of our sys-
tem,  does not possess a trace  of atmosphere sufficient to cause a
sensible refraction.
  Poisson  has recently suggested a view of the constitution  of our atmosphere,
upon grounds, however, so little connected with experiment that  il would  not be
a subject for  notice here, had  it not been introduced  to the  notice of chemists
under the sanction  of Dumas's eloquent discourses.   I will, therefore, briefly describe
the theory he has  put forward.
  The  atmosphere, as we ascend, grows colder.   The  source  from which the at-
mosphere derives its heat is not the sun, but  the solid earth ;  the solar rays passing
through the air as  they pass through glass and all transparent bodies, without com-
municating much of their heat.   These  heating rays are absorbed  by the dark and
rugged surface of the earth.  From this the layer of air next to it derives its warmth,
and hence, the farther from the  earth the  air is taken, the colder it is found to be.
Hence, even under the glare of a tropical sun, there exists an elevation where the
temperature never rises above 32°, the melting point of ice ; above that height all is
eternal snow   Farthest from the level of  the sea at the equator, being 15,000 feet,
this line of perpetual congelation gradually descends, until at the poles it sinks below
the surface of the  earth.  In these countries we have no mountains with perpetual
snow, the line of congelation being 6000 feet above the surface.
  From this source,  also, are derived  the various phenomena of fog and cloud, the
production of snow, of hail and  rain.  The vapour forming at the surface of a pond
is generated with  an elasticity proportional to its temperature; and when the air,
thus mixed with vapour, rises to a  higher and colder stratum,  the elasticity of the
vapour is diminished, and a portion  separates either as cloud or rain.  Thus, if air
becomes loaded with vapour at the surface  having a temperature of 60°, and, on
ascending, it becomes cooled to  40°, the quantity of water separated is thus found-

                The elasticity at 60° is 0 521 inch of mercury.
                               40° is 0 263       "
                the difference  is  .  . 0.261       "

But 521 : 261  : : 100 : 49 8, or nearly  50, and hence almost exactly one half of the
quantity of vapour carried up is deposited  under the form  of cloud ; in addition to
this, another portion of vapour is deposited as liquid water, from the circumstance
of the diminution in volume of the mixture of gas and vapour produced by the low-
ering of its temperature;  this is equal to about four per cent., so that there remains
as invisible vapour only about forty-six, while fifty-four per cent, are engaged in the
production of the  cloudy masses.  The farther properties of  clouds, the circum-
stances which determine  the production  of rain, snow, or hail, are of so little refer-
ence to chemistry  that I shall pass from them without remark.
  Reasoning from the principle that  all gases may, by suitable reduction of their
temperature, be  reduced to the  solid form, Poisson proposes to consider the atmo-
sphere as being extended above  the earth, gradually becoming more attenuated and
more cold, until it arrives at a point  at which it freezes;  there then should be  a
Bhell of transparent  colourless air-ice, lined  on  its concave  surface with a sea of 
272
NITROUS OXIDE,
Nitrous oxide
Nitric oxide  .   .
Hyponitrous acid
Nitrous acid  .   .
Nitric acid  .  .   .
Nitrous Oxide.
liquid oxvffen and nitrogen mixed or combined together  From such assumption
liquid oxygen ana niuogt  "UA      , astronomjcal refractions more definite and
SSZTB  oStrbS"/ Ss can scarce,, ,e *~d ««*.
» justify the adopt,™ of J-«-»ifflS 'S^JS.^X'^tl
eral evidence can be found, the fundamental va<mi" -J       f „  ^  .    f     •
for it results from Fourier's researches on the-distribution of, «^lv thf l|'c ttm"
Derature of the olanetary spaces cannot be below —57  ol 1 ahrenneit, a degree of
£ which  is met with in Melville Island during winter  and which has been far
exceededI by artificial means.  At this temperature air shows no sign of even be-
comTng liqSd?far less solid; and hence the supposition of such a hollow sphere
of frozen air cannot be granted.                                        ■-•

               Compounds  of Nitrogen and  Oxygen.
                              N. = 14*0+  0.= 8=N.O=22-0
                              N. = 14-0 f-2O.= 16=N.O2=30*0
                              N. = 14*0+3O. = 24=N.O3-38*0
                              N. = 14*0+4O.=32-N.O4=46*0
                              N =^14*0+50.=40=N.O5=54*0

                               Protoxide of Nitrogen.  ;

   This substance, which exists, under ordinary pressure, ini the gav
 eous form, is best and most easily prepared by heating to about 350
 Fah. the crystallized nitrate of ammonia.   This salt melts at  300
 Fah. into a  colourless liquid, without  being^at all  decomposed or
 losing  water;  but when the temperature  is raised to  350  , a lively
 effervescence occurs, and the salt is totally  resolved into vapour of
 water and nitrous oxide gas, an  equivalent of nitrate of ammonia
 producing two equivalents of the  gas and four of  water, thus:
                 N.03+N.H40.=2(N.O.)+4(H.O.)

   The nitrate of ammonia may be placed in the  flask a,  imbedded
                                           in the little cup of sand.
                                           A bent tube conducts the
                                           gas evolved to the pneu-
                                           matic  trough,  as in the
                                            figure, or to the gasom-
                                            eter, if  the  quantity be
                                            large.   In  this  process
                                            the  temperature should
                                            not be allowed to rise be-
                                            yond  the point at which
                                            the effervescence is mod-
                                            erately brisk ;  for  when
                                            the salt becomes much
                                            hotter,  the decomposi-
                                            tion is tumultously rap-
  id, and the gas obtained may not be at all pure.
    The nitrous  oxide  gas  so  obtained is perfectly colourless and
  transparent; it is absorbed by water in moderate quantity, and hence
  the water over which it is collected should always be heated to about
  90° in order to diminish the loss  of gas thus suffered.   It is heavier
  than air, its specific gravity being 1*527.
    A lighted taper burns with increased brilliancy  in this gas j  and if
 
,         ITS  PROPERTIES  AND  COMPOSITION.     273

blown out, may be relighted, provided a pretty large portion of the
wick remains  bright red.  If the gas be mixed with its own volume
of hydrogen, it may be inflamed by a taper or by an electric spark,
and then bi rns with a loud explosion.   If phosphorus be heated in
this gas, it inflames and burns with almost as much brilliancy as in
pure oxygen.
   In none  of these instances does the nitrous oxide enter into com
bination.   It is decomposed by the high temperature of the burning
body  and the  affinity of this last for oxygen, and the  combustion is
maintained by means of the oxygen which is thus disengaged.  After
the process is completed, the nitrogen of the nitrous oxide remains
free.
  In this manner nitrous oxide may be analyzed. If a little bit of potassium or of
phosphorus be heated in a measured quantity of the gas until the decomposition is
complete, and then the apparatus-be cooled to its original temperature, it will be
found that a quantity of nitrogen  remains exactly equal in volume to  the nitrous
oxide used, and  the  quantity of oxygen absorbed is such, that in its gaseous form
it had exactly half that volume. The nitrous oxide consists, therefore,  of two vol-
umes of nitrogen and one of oxygen condensed to two volumes, and hence its spe-
cific gravity may be calculated thus :
                Two volumes of nitrogen 976x2=1952 0
                One volume of oxygen  .    .  . 1102 6
                give two volumes of nitrous oxide 3054 6
                and one volume weighs, therefore 1527.3
   By weight,  the composition of  nitrous oxide and  its equivalent
number on each scale are expressed as follows:
         Nitrogen, 63*9      One equivalent,  14 0 or 175
         Oxygen,  36*1              "         8*0 "  100
                  100*0                       22*0    275
and its formula is N.O.
   The most singular  property of this  gas  is, that when  breathed
pure for  a  few minutes it produces a lively  and agreeable  intoxica-
tion, which does not leave any lassitude or disagreeable  sensation
when it goes off.  To prepare gas for being breathed, it is necessa-
ry to  attend to the purity of the nitrate of ammonia used, as very
frequently  the salt found  in commerce contains muriate of ammo-
nia, in which  case the gas obtained may be contaminated by nitrous
acid and chlorine, and  prove very irritating to the lungs.  To ob-
tain the full effects of the gas upon the system, four or five quarts
must  be introduced into an air-tight bag or  bladder, and  inspired
throurrb a pretty  wide glass tube.   About two ounces of nitrate of
ammonia yield sufficient gas to intoxicate one  person.

              Nitric Oxide.  Deutoxide of Nitrogen.
   This substance exists naturally  under the form  of a gas, which
chemists have not, as yet, been able to reduce to the liquid form.  It
is very  easily prepared, being almost always the principal product
of the decomposition of nitric acid by  the metals.
   If a small quantity of quicksilver, or of copper cut into small bits,
be placed in the gas bottle in the figure, and diluted nitric acid, pre-
pared by mixing equal volumes of the aquafortis of commerce and of
water, be poured in by the funnel a, effervescence is immediately pro-
                              Mm 
274   PREPARATION,  ETC, OF  NITRIC  OXIDE.
                                       duced, even without  the
                                       application  of heat, and
                                       the metal dissolves in  the
                                       acid,  which becomes pale
                                       green-coloured if quicksil-
                                       ver  had been  employed,
                                       but of a rich blue if cop-
                                       per had been used.  From
                                       greater economy, the lat-
                                       ter metal is almost always
                                       that employed.  For some
time after  the action commences, the space in the bottle over the
liquid is occupied by reddish fumes ; but these gradually pass  away,
and the o-as may be collected when the upper part of the generating
flask is occupied by it completely colourless.
  The theory of this  process is very simple: a quantity of nitric
acid gives off three fifths of  its oxygen to the copper, and the ni-
troo-en  is evolved in  combination with the  remaining two  fifths,
formino- nitric oxide.   The copper, being thus oxidized, combines
with another portion of nitric acid to form a fine blue  salt, nitrate
of copper, which exists in the blue liquor, and may be obtained crys-
tallized.  For complete decomposition, four  equivalents of nitric
acid and three of copper are required, and the action may be then
expressed as follows:  4N.03  and  3Cu. give 3(N.O,. Cu.O.)  and
(N.O,).
   By the action of organic substances, such as starch or sugar, upon
nitric acid, nitric oxide may  also be formed in abundance, but it is
not then so uniformly pure as when  obtained by means of mercury
or copper.                                 t
   This gas is colourless and transparent;  it is scarcely absorbed by
water, and may hence be, on all occasions, collected over it.  It is
a little heavier than air, its sp.  gr. being 1039 ; its refractive index
is 0*8761.  A lighted taper plunged into this gas is extinguished, and
a red-hot wire maybe applied to phosphorus in it without inflaming
it; but if the phosphorus be already set on fire, it not only continues
to burn when plunged into the  nitric oxide gas, but the combustion
is almost as brilliant as in pure oxygen.  In this case, it is indeed in
oxyo-en, and not in nitric oxide, that the combustion actually occurs;
for the gas is decomposed by the high temperature of the burning
phosphorus, and, being resolved into its constituents, the oxygen is
the body with which the phosphorus combines, and the nitrogen re-
mains untouched.
   In this way nitric oxide may be analyzed, and is found to consist of equal vol-
 umes of nitrogen and oxygen united without any condensation.  From this its spe-
cific gravity may be calculated :
                One volume of nitrogen  .  .  . = 976 0
                One volume of oxygen   .  .  . =1102 6
                give two volumes of nitric oxide   2078 6
                of which one is found to weigh  .   1039 3
   Its equivalent volume is therefore 4, and its composition by weight
 and its equivalent number on each scale are  as follows: 
HYPONITROUS  ACID.
275
        Nitrogen, 46*95     One equivalent,   =175 or 14*0
        Oxygen,  53*05     Two equivalents,  =200 or 16*0
                 100*00                         375    3CHT
 and its formula is N.O,.
   Nitric oxide may be deprived of one half of its oxygen, and so be
 reduced to the state of nitrous oxide, by remaining in contact for
 some days with moist iron or zinc filings; in  this case  its volume
 is reduced to  one half.
   The  most remarkable property of nitric oxide is its tendency to
 unite with oxygen  when this last  is uncombined.  Nitric   oxide
 cannot take oxygen from any other substance ;  but when  it is mixed
 with air, or with any mixture of gases, of which oxygen is  one, it
 unites with this,  forming deep red fumes.  It is this which  causes
 the red fumes in the flask in which the  nitric oxide is  generated.
 The oxygen,  in combining with the nitric oxide,  may form  either
 hyponitrous acid (N.03)  or nitrous acid (N.O.,), and they  are  both
 generally  formed in uncertain  proportions.  Hence we cannot ex-
 actly calculate the quantity of oxygen that had been present;  and
 this process  does not answer well for  gaseous analysis, but it is
 useful for  removing oxygen from a gaseous mixture, which it  effects
 completely if the nitric oxide be added  in excess.   The red fumes
 so  formed are soluble  in water, and, by washing  the mixed gases
 with water, may  therefore be completely removed.
   Nitric oxide combines with a great number of salts and with some
 acids to form compounds, which in some respects possess consid-
 erable  interest: these shall be  noticed under those heads to  which
 their history more particularly belongs.

                         Hyponitrous Acid.
   The  red fumes which are formed when nitric oxide is mixed with
 atmospheric air or oxygen, consist in great part of hyponitrous acid,
 particularly when the nitric oxide  is in excess.   To  obtain it pure,
 four volumes  of nitric oxide  should be mixed with one volume of
 oxygen, and the vessel containing the hyponitrous acid vapour form-
 ed, exposed to a cold of about 40 degrees below the freezing point
 of  water.  The  acid then  condenses  into a deep green-coloured
 liquid, which is excessively volatile.
  When  hyponitrous acid, either in the state of liquid or of vapour, is brought into
 contact with water, it is in great part decomposed, being resolved into nitric oxide
 and nitric acid, three equivalents of hyponitrous acid (3N.03) giving 2(N.02) and
 N.Oj.  The  same occurs when it is  acted on by bases dissolved in water, and
 hence the salts of this acid can only be prepared by indirect means.
  When  nitre has been kept melted for some time, so as to have parted with a portion
 of its oxygen, it is reduced to the state of hyponitrite of potash, N05. K.O. giving off
 20 , and leaving N.03 . K.O.  This  is known by the hyponitrite being decomposed
 by acetic  acid, and giving off copious red fumes, while the nitrate of potash is unal-
 terable by acetic acid.  The hyponitrite of potash cannot be crystallized so as to
 free it from the excess of unaltered nitre, but it may be converted into sparingly
soluble salts, as those of  silver and of lead, and so pure salts  of hyponitrous acid
formed.
  The specific gravity of the vapour of this acid has not been experimentally deter-
mined   It consists of two volumes of nitrogen united to three of oxygen, but of
their condensation we know nothing.
  Its composition by weight and its equivalent constitution are, 
276   PREPARATION,  ETC.,  OF  NITROUS  ACID.

       Nitrogen, 37*11     One equivalent,    =175 or 14*0
       Oxygen,  62*89     Three equivalents, =300 or 24*0
                100-00                           475    38*0

                Nitrous Acid.  Nitroso-nitric Acid.
  This substance presents itself, like the last, under the form of deep
red fumes, and is produced when the  oxygen is in excess with regard
to the nitric oxide.  By a cold of about 0^ on Fahrenheit's scale, it
may be rendered liquid.   To form it directly, four volumes of nitric
oxide are to be mixed with two volumes of oxygen, and the mixture
exposed to a great cold; but it is more conveniently prepared by
means of the decomposition of nitrate of lead by heat.
  A quantity of finely-powdered and dry nitrate of lead is to be pla-
ced in an earthenware or hard glass retort, and heated to full red-
ness.  The red vapours that are produced  are to be conducted into
a receiver,  carefully cooled by a mixture  of snow and salt.   They
then condense into a liquid, while a quantity of oxvgen gas escapes,
and oxide of lead remains behind in the retort.  The nitric acid of
the nitrate of lead is decomposed into nitrous acid and oxygen, aa
follows :  N.05. Pb.O. gives Pb.O., free N.04 and O.
  The liquid nitrous acid is  nearly colourless  at zero, at 60° it is
orange yellow, and  at  —40J it  solidifies  into  a white crystalline
mass.   It boils at 82°,  and its vapour, which is  ruddy red at that
temperature, is almost  perfectly black at 212 \  In  these various
coloured states,  it exercises remarkable absorbing power on light.
The specific gravity of  the liquid acid is; 1*451.
   Nitrous acid is  the most stable  compound of nitrogen and oxy-
gen ; it is not decomposed by a red heat; it is decomposed in great
part by water, nitric  acid being formed, and nitric oxide being given
off as gas.   Thus, 3(N.04) give N.O, and 2(N.0o).  The nitric acid
formed always protects a portion of the nitrous acid from this reac-
tion.
  When the nitrous acid is formed by the direct union of nitric oxide and oxygen,
it is found that the six  volumes of gas are condensed by combination into two;
hence the specific gravity of nitrous acid vapour should be 31812 ; thus,
               One volume of nitrogen   .           976 0
               Two volumes of oxygen  ...'.. 22052
               One volume of nitrous acid  ....  3181 2

   Its composition by weight and the constitution of its  equivalent
are as follows:

       Nitrogen, =30*33     One equivalent,  =175 or 14*0
       Oxygen,   =^69^7     Four equivalents, =400 or 32*0
                   100*00                        575     4~6:6
  Considerable doubt has been thrown upon the nature of this substance, for many
chemists regard it as  incapable of uniting with  bases, and hence look upon it as a
kind of acid  salt, consisting of nitric and hyponitrous acids combined together;
2fN.04)=N.05-|-N.03.  But late researches have shown that it does produce true
salts, and that even many saline compounds which had been supposed to be salts
of hyponitrous acid really contain this substance ; thus, the yellow basic salt, formed
by boiling a solution of nitrate of lead on metallic lead, is a true nitrite.   I retain,
therefore, for this body the old name of nitrous acid, the more as that of peroxide
of nitrogen, proposed for it by Graham, is frequently applied to nitric oxide 
NITRIC  ACID.
277
                         Nitric Acid.
                             N.O,.
  It is found that when nitric  oxide is brought into contact with a
great  excess of oxygen over water, they combine in the proportion
of four volumes of the  first to three of the second; and when the
red fumes which are produced have dissolved in the water, that is
found to be a solution of pure nitric acid.   Looking to the compo-
sition of nitric oxide,  we find in this manner that the nitric acid
consists of two volumes of nitrogen gas united with five volumes
of oxygen.
  Although nitrogen and oxygen do not unite at once when directly
brought into contact with each other, yet they are capable of com-
bining under certain  circumstances ;  and there is no doubt but that
the great, if not the only source of nitric acid in nature, is the union
of the nitrogen and oxygen of the atmosphere.   Although nitrogen
is not strictly inflammable, yet, if some of it be mixed with  hydro-
gen, and this  mixture  be set on fire, the flame  is coloured  green,
and the water formed is found to contain nitric acid; if a series of
electric sparks be passed through a quantity of  air confined over a
strong solution of potash, this gradually loses its alkaline reaction,
and after a time crystals of saltpetre (nitrate of potash) form in it.
This  may be shown, also, by  simply moistening some litmus paper
with  a solution of an alkali, and taking, by  means of it, a succession
of sparks from a strong electrical machine ; at the point where the
spark passes,  the paper becomes reddened, and that nitric acid has
been  formed is shown by its burning like touch paper when dried
and set  on fire.   Rain-water, particularly that  which falls after a
thunder  storm, contains a certain quantity of nitrate of ammonia;
the lightning forming,  as the  electric spark does, nitric acid  in pass-
ing through the air, and this uniting with the ammonia which is al-
ways present  in our atmosphere from decomposing animal remains.
   In  warm climates, where the abundance of organic matter and its
rapid decomposition pour into the atmosphere a copious supply of
ammonia, the formation of nitric  acid proceeds with extraordinary
energy, and the nitrate of ammonia being washed down by the rains
into the porous limestone soils, the ammonia is again given off, while
 the ground becomes coated with an efflorescence  of earthy  nitrates
 when it dries on the cessation of the rain ; a small quantity of ni-
 trate  of potash is also  thus formed, but the nitrate of lime, of which
 the crude produce  of  nitre principally consists, is converted  into
 saltpetre  by  means  of carbonate  of potash.  In  this way there is
 formed in the East Indies a quantity of nitrate of potash sufficient
 to  supply the wants of Europe.   On the Continent, this process is
 imitated in artificial nitre-beds, and large  quantities of home-made
 saltpetre are used in France  and  Germany for the manufacture of
 gunpowder.   In South America, particularly in Chili and Peru, there
 are found immense deposites of nitrate of soda upon the surface of
 the soil, and it is now extensively imported  into these  countries;
 the source of the nitric acid is, in this case also, the union of the
 elements of the atmosphere, although the circumstances which sup-
 plied the alkali cannot be distinctly seen. 
278        PREPARATION  OF  NITRIC  ACID.
  It is from the nitrates  of soda or potash so produced that  the
nitric acid is always obtained.  True nitric acid has never been  iso-
lated ; that substance which is generally spoken  of as nitric acid,
and which I shall, unless  especially remarked otherwise, be under-
stood to mean in the following account of its properties and prepar-
ation, is a compound of it  with water;  it is a nitrate of water, or, as
it is popularly termed, liquid nitric acid, or aquafortis.
  To prepare liquid nitric acid from nitrate of potash, equal weights
                                       of this salt and of oil of vit-
                                       riol are mixed in a glass re-
                                       tort, A, which is placed in
                                       a furnace, supported  in a
                                       sand bath, as in the figure.
                                       The oil of vitriol consists
                                       of sulphuric acid and  wa-
                                       ter,  and  by the reaction
                                       which ensues, the sulphu-
                                       ric acid combines with the
                                       potash of the nitre, while
                                       the water of the oil of vit-
                                       riol uniting with the nitric
acid, forms the liquid nitric acid, which distils over, and is conden-
sed in the receiver, B.   To render the condensation more complete,
this is surrounded by a net, and placed in a trough, c c ; a stream of
cold water flows continually on it  from the  pipe  i, and  being  dis-
tributed  evenly over the  surface by the network, flows out by the
exit pipe of the trough, /, and escapes into d e.  Using the propor-
tions just noticed  (equal weights), the quantity  of sulphuric  acid
present is double that  necessary to neutralize the potash of the ni-
tre, and completely expel the nitric acid;  for
  The nitre consists of          Oil of vitriol consists of
    One  atom nitric acid, 54*0     One atom sulph.  acid,  40*1
    One  atom potash  .    47*3     One atom water     .   9*0
                        ToT3                           4JH

These, reacting upon each other, should produce,

                                   Liquid  nitric acid formed of
                                     One atom nitric acid, 54*0
                                     One atom water    .  9*0
Sulphate of potash consisting of
  One atom sulph. acid, 40*1
  One atom potash   .  47*3
87*4
63*0
And hence nitre might be decomposed by half its weight of oil of
vitriol;  but the following reasons prevent those proportions being
employed in practice.
  When oil of vitriol acts upon nitre, there is at first but one half of
the sulphuric acid taken by the potash, and  the sulphate of potash
so produced  unites  with the remaining oil  of vitriol (sulphate of
water) to form bisulphate of potash, thus,  2(S.03. H.O.) and K.O..
N.03 give
             (S.03. H.O.+K.O.. S.03) and H.O. N.03.

  If there be  oil of vitriol enough, the nitre is thus perfectly decom- 
             PREPARATION  OF  NITRIC  ACID.         279

posed at a temperature not exceeding 260° F., and the bisulphate of
potash  which  remains is very easily soluble and fusible,  and  may
hence  be  removed from the  retort without inconvenience.   But if
the nitre  and  oil of vitriol be used in the proportion of an equiva-
lent of  each, or by  weight in round numbers of two parts of nitre
to one  of  oil of vitriol,  then one  half of the nitre remains at first
totally  unacted on, and the retort contains, when the process  is half
finished, a pasty mass of bisulphate  of potash and of nitre,  which
do  not  fully act on  each other until the temperature rises to 400°.
The nitre  is then decomposed ; the  nitric  acid distils  over, and
there remains in  the  retort  a mass of  neutral sulphate of potash,
which can seldom be removed from glass vessels with success.  The
high temperature necessary  also  increases  very much the risk of
the apparatus  breaking.
  The scientific chemist and the apothecary, however, do not prepare nitric acid; it
is made on the large scale for the purposes of the arts, and the processes of purify-
ing  the acid of commerce is so simple that no other  source is required.  On the
great scale,  the nitric acid is prepared, not in glass retorts, but in iron cylinders,
connected with condensers, as represented in the figures, one being a section per-
pendicular to the axes of the cylinders, and the other a section parallel to the axes:
the  same letters apply to both.
  a is the grate, and d the ashpit of the furnace, b.  In each furnace two cast iron
cylinders, c, c. are set, of such capacity that about It cwt. of the nitrate used may
he decomposed at once.   The ends of the cylinders are closed by covers, e, e, in
one of which is fixed a tube,/, for introducing the oil of vitriol, and to the other is
adapted a tube of glazed earthenware, g, h, by which the vapours of the nitric acid
are conducted to the range of condensing jars of earthenware, fitted with safety
tubes, of which the first is seen in the figure, as h, I, k. The flues, m, m, m, pass
from the furnaces to the chimney, n.   As in this apparatus the temperature can be
raised to dull redness without injury, and as the residuum can be removed in the
solid form, a smaller quantity of oil of vitriol may suffice, and  is generally used.
  Since the introduction of nitrate of soda into commerce, it has almost completely
superseded nitrate of potash for making nitric acid.   It is much cheaper, and it
yields a larger product.   It does not require, either, so much sulphuric acid nor so
high a temperature.   The nitrate of soda consists of
             One equivalent of nitric acid......54 0
             One equivalent of soda........31 3
                                                      853
and hence 100 parts of it yield about 74 parts of liquid nitric acid, while 100 parts
of nitrate of potash yield but 62.
   In making nitric acid, there always occurs at the commencement
of the process a disengagement of red fumes, which dissolve in the
liquid acid which comes next, and tinge it yellow.  This arises from
the oil of vitriol  in excess  abstracting the water from some of the
nitric acid, which then is decomposed into nitrous acid, and some
oxygen becomes free.   At the termination of the  process, if the tem- 
 280  PROPERTIES,  ETC.,  OF  LIQUID  NITRIC  ACID.

 perature  pass much beyond 300°, there is a new evolution of red
 fumes, for the nitric acid is then similarly decomposed into  N.04
 andO.
  The strongest nitric acid that can be thus made is of specific gravity \ 521, and
 consists of N.Oji-r-H.O.
         One equivalent of nitric acid .   .  . 54 0 or per cent. 8571
         One equivalent of water   .... JH>     "     1429
                                       630         10000
  It boils at 187° F., but cannot be distilled withoutrpartial decomposition.  The
 acid is very seldom obtained of this strength.  In general, the specific gravity of
 the strong liquid acid is 1500, and it consists of 2N.05-f-3H.O.
         Two equivalents of nitric acid  .  . 108 0 or per cent. 80 00
         Three equivalents of water .  .  . 270     "     20 00
                                       135 0          100 00
  When the nitric acid  is gradually mixed with water, the boiling point rises until
 when  the specific gravity is 1420, it boils at 248°.  If it be farther  diluted, the
 boiling point is again lowered.  At this point the acid has  a definite chemical con-
 stitution ; it consists of N.Os-f 4H O.
         One equivalent of nitric acid .  .  . 54 0 or per cent. 60 22
         Four equivalents of water  .... 36 0     "     39 78
                                       90 0          100 00
   The liquid nitric acid is, when pure, completely colourless; it
 fumes when exposed to the air, and if exposed to the direct  solar
 light, very  soon becomes deep yellow, while oxygen gas is disen-
 gaged ; the same decomposition into nitrous acid and oxygen gas
 may be instantly effected by passing the vapours of the acid through
 a  red-hot porcelain tube.   In  a great variety of processes where
 substances  are to be oxidized, nitric acid is employed.  It  acts with
 remarkable rapidity on the  generality of the metals and of organic
 bodies, supplying oxygen for the constitution of a variety  of new
 compounds, and being itself reduced to the state of nitric or nitrous
 oxide, or even pure nitrogen.
   If the organic body  do not contain nitrogen, it is generally ulti-
 mately converted into the oxalic  and carbonic acids;  with animal
 substances, new bodies are formed of a deep yellow colour, and
 hence the stains produced  upon the nails  and fingers where nitric
 acid touches, and it is  hence used for stamping the yellow patterns
 on woollen  table covers.   The decomposition of the acid  is gener-
 ally accompanied by the  production of red fumes.
   In its action on the metals, nitric acid  presents some remarkable
 anomalies;  when of the specific gravity of 1*48, it may be put into
contact with tin or iron  without acting on those metals,  although,
 if a little  stronger or weaker, its action is very great; and  this inac-
tive acid may be brought into activity by various means, as  by touch-
 ing the immersed metal with another different one.  These phenom-
 ena appear  to involve conditions probably electrical, which are not,
 as yet, completely understood.
   The nitric acid prepared by  decomposing nitre by half its weight
 of oil of vitriol, is always of a  deep red or orange colour,  owing to
 a  quantity of the acid having  been decomposed into nitrous  acid,
 which remains dissolved.   This deep-coloured acid is frequently 
DETECTION  OF  NITRIC  ACID.          281
useful, as it gives off oxygen still more  easily than the pure acid,
and is hence sometimes applicable as an  oxidixing agent where the
colourless acid fails.  A deep red fuming acid may be prepared by
passing a-stream of nitric oxide gas through the colourless acid ; it
is absorbed in great quantity, and the liquor assumes successively
various shades of yellow, green,  and red, according to its state of
dilution.  The nitric oxide (N.O,,) decomposes the nitric acid (N.O,),
and forms nitrous acid (N.04), which dissolves in the excess of liquid
acid.   If it be required to obtain a colourless acid,  it is sufficient
that the coloured acid should be boiled  for a few minutes; all the
nitrous acid fumes  pass off, and the nitric acid  remains colourless,
though somewhat weaker.
  I  have mentioned that the nitric acid is not prepared on the small
scale, as the commercial aquafortis is easily  purified.   The impuri-
ties of it are, generally, chlorine, arising from  the nitre employed
having contained common salt; sulphuric acid, from some having
been distilled over  by too great heat; and some iron, arising from
the  cylinders or stoneware bottles in which the acid is preserved.
These may be easily detected ; on mixing a  few drops of the com-
mercial acid with half an ounce of distilled water, a drop of solution
of nitrate of barytes will give a precipitate if  sulphuric acid be pres-
ent ; nitrate of silver will  indicate, by a precipitate, the presence of
chlorine ; while a little solution of yellow prussiate  of potash will
form Prussian blue  if the acid contained  any  iron.  From these im-
purities the acid may be freed by being redistilled; the chlorine
passes off'  along with the portions which first  come over, and  by
thus testing from  time to time the acid which is thus obtained, it
will be found no longer to precipitate the nitrate of silver, and may
then be considered  pure ;  the iron and sulphuric acid remain behind
in the retort, provided the distillation be  not pushed too far.  I have
found that  from twelve pounds of commercial aquafortis there can
be obtained eight quite pure, three being allowed to come over first
to carry off the chlorine, and one being left in  the  retort with  the
fixed impurities.
  The detection of nitric acid is not difficult;  it cannot be recog-
nised by forming precipitates, as all its neutral salts  are soluble, but
its properties  are very marked.  1st, The production of red fumes
by nitric oxide when it is brought into contact with a metal, is char-
acteristic of it.  2d, When a drop of nitric  acid is  added to water
tinged blue by  sulphate of  indigo, and  the  mixture  boiled, it is
bleached by the oxidizement of the indigo by the acid.  3d, When
a small crystal of protosulphate of iron is placed in contact with
water  containing nitric acid, a ring of  deep olive-coloured liquid
forms round it, according as it dissolves ; from one portion of the
protosulphate  reducing the acid to the state of nitric oxide, which
then combines with the remaining protosulphate.  4th, Nitric acid
confers upon muriatic acid the power of dissolving gold leaf, but
this test is not of  such distinctness  as  the  others, from the same
effect being produced  by the chloric and some other acids.  5th,
Nitric  acid may also be distinguished by the  deep red colour it pro-
duces with a crystal of morphia.
  For the  detection of a small quantity of nitric acid, the best plan
                              Nn 
282          SOURCES,  PROPERTIES,  AND
is to neutralize the liquor, if it be acid, by a solution of potash, and
to evaporate to dryness.  The salt so obtained crystallizes m sharp
needles, and deflagrates when placed on ignited charcoal; heated with
a little bisulphate of potash and some copper filings, it evolves copious
red fumes, and with a drop of sulphuric acid and a crystal of pro-
tosulphate of iron, produces the olive-coloured liquor already noticed.
AJ1  solid compounds of nitric acid, such as the basic nitrates, may
be recognised in this way.
  The nitric acid not being isolable, we do not know the state of
condensation of its elements, which  are united in the proportion of
two  volumes of nitrogen to five  of oxygen.   Its composition by
weight and its  equivalent numbers are as follows:

       Nitrogen, 26*15       One equivalent,   =175 or 14*0
       Oxygen,  73*85       Five equivalents, =500 or 40 0
                100*06                          675    54*0
  The specific gravity of the vapour of the liquid nitric acid, H.O.. N.O*, is not known;
but Bineau has found the sp. gr. of the vapour of the liquid acid, which boils at 248°,
H.O. . N.Oo-(-3H.O., to be 1243, which  might result from
       Two volumes of nitrogen.......976x2=19520
       Five volumes of oxygen.......1102 6x5=55130
       Eight volumes of watery vapour ....   620 1X8=49608
    condensed into ten volumes...........12425 8
    of which one, therefore, should weigh........1242 6
This result requires confirmation.

                             Sulphur.

   This substance exists in large quantity in nature in combination.
The most important ores of copper, lead, silver, mercury, antimony,
and many other metals, are their sulphurets; and a great quantity
of the sulphur at present used in commerce is derived from the iron
pyrites,  bisulphuret of  iron.   Sulphur is exhaled  in large quantity
also from volcanoes, partly uncombined, partly in the state of sul-
phuret of hydrogen, arising probably from the decomposition of me-
tallic sulphurets by the high temperature in the interior of the earth.
The native sulphur so produced, condensing in fissures, constitutes
the  great deposites of volcanic  sulphur  of Sicily and other places,
which supply a large proportion of that employed in commerce.  It
exists also native, combined with oxygen and various metallic oxides,
forming native sulphates, of whirh those of lime and of barytes are
the  most abundant.  In many organic bodies, also, sulphur exists as
a constituent, as in the  white, and particularly the yolk of egg, the
hair, the horns, and hoofs of animals, and in the black mustard-seed
it exists in considerable quantity.
   At ordinary temperatures  suiphur exists generally as an opaque
solid, sp.  gr.  1*98.   When heated, it melts  at 226  into an amber-
coloured thin  liquid ; if the temperature be  then raised to about
400 , it  becomes dark brown, opaque, and so thick  that the vessel
 containing it may be inverted without its pouring out; but when heat-
 ed farther it becomes thinner, until  at 601 \ its boiling point, it is as
 thin and limpid as when first it began to  melt.   If the'sulphur, when
 just  melted, be allowed to cool slowly,  and the internal liquid be 
PREPARATION  OF  SULPHUR.
283
poured out when the outer crust has solidified, the
interior will  be found lined with crystals, as  in the
figure, which have the form of the oblique rhombic
prism, of which a common modification with second-
ary faces, and the surfaces of the octohedron, which
                          determines  the height of
                          the  principal  axis of the
                          crystal, is given.  These crystals,  when
                          first obtained, are transparent and amber-
                          coloured, but  after a few days  they be-
                          come opaque, sulphur yellow, and friable,
                          being then  changed into the  dimorphous
                          state.
   If the thick tenacious sulphur at 400J be suddenly cooled by im-
mersion  in a large quantity of water,  it  forms a soft and transparent
mass of considerable  elasticity, and  may be drawn out  into long
threads like  India rubber ; after some  time, however, it changes
into the ordinary state.
   Sulphur is  used in pharmacy under two forms, that of roll  and
flowers ; the former is made by melting the  rough native sulphur,
and  pouring  it into slightly conical moulds,  in which it  solidifies.
The flowers  of sulphur are formed by  the condensation of the va-
pour of sulphur so rapidly that the molecules have not time to form
crystals of any perceptible size, so that the condensed sulphur, al-
though really crystalline, appears to  the  sight and  touch as an im-
palpable  soft powder.
  For the manufacture of (lowers of  sulphur,  the apparatus is arranged as in
the * unjoined figures, in which A is a vertical and B a horizontal section, to which
the same letters refer.   In an apartment and shed, M, M, a chamber, A. is con
structed. which must have at least 2000 cubic feet capacity.  Outside of this cham-
ber is an iron pan, r, in which, by a fire at o, the sulphur is kept gently boiling.  The
boiler and fireplace must be completely surrounded by brickwork, so that as little
heat as possible may be communicated  to the vaulted chamber, A ; the draught
from the fire passes to the chimney,^,- the pan  is supplied with  sulphur by the
door, n, which can be closed air-tight;  the vapour of sulphur mixes with the air in
the wide space, d, over  the boiler, and, passing through the aperture b, rises into
the chamber, where, mixing with the  large mass of cold air, the sulphur  is con-
densed, and falls like a fine snow shower upon the floor underneath.  When a suf-
ficient quantity of the flowers of sulphur have been thus formed, they are removed
by the door at p.  If, at the commencement of the process, the mixture of sulphur-
vapour and air should inflame, the explosion opens the valve at e, the gases escape
at /. and all danger is avoided.
  The form of crystal of sublimed sulphur is the right rhombic oc-
tohedron, of which  a common modification is represented  in the 
284    RELATIONS  OF  SULPHUR  TO  OXYGEN.
              margin.  Sulphur is found crystallized in this form on
              the edges of the craters of  most volcanoes,  the crys-
              tals being transparent, and sometimes of considerable
              size.  When sulphur  is deposited from its solution in
              chloride of sulphur or in sulphuret of carbon, it is in
              this form also that its particles arrange themselves.
                Sulphur  may be  obtained, however, in a  state of
              much more minute  division, and destitute of all crys-
talline structure, by precipitation from solution.   Thus, if the per-
sulphuret of potassium, K.S0, be decomposed by muriatic acid, four
equivalents of  sulphur are set free, and  separate as a milk-white
powder.  This constitutes the Sulphur Precipitatum of pharmacy.
In all cases where sulphur is precipitated from a cold solution, it is
pure white.
  Sulphur is  not soluble  in water or in alcohol;  it dissolves in the
oils, still more in those liquids mentioned above.  It dissolves in
alkaline solutions, or  in milk of lime ;  but there then occur complei
reactions, which will be studied hereafter.
  When sulphur is boiled it forms a deep yellow vapour, the specific
gravity  of which is 6648.  Sulphur evaporates,  however, very rap-
idly long before it boils, and  even forms some vapour below its
melting point.   At a temperature of about  300' it takes fire, burning
with a bluish violet flame, and  forming sulphurous acid (S.02).
  The resemblance of sulphur to oxygen in its chemical relations is very striking,
by combining with the same bodies, according to the same proportions, they gener-
ate  completely parallel classes of acids, bases, and salts.   Thus, with carbon and
potassium, there are formed
                                     C.S2 Sulpho-carbonic acid.
                                     K.S. Sulphuret of potassium.
                                     K.S.. C.S2 Sulpho-carbonate of potas-
                                              sium.

                                     As.S5 Sulpharsenic acid.
                                     K.S.  Sulphuret of potassium.
                                     K.S. . As.S5 Sulpharseniate of potav
                                              sium.
  In like manner, the similar compounds  Fe304 and Fe3S4  are not altered by heat,
but are magnetic, while Fe.S2 and Mn.02 give out oxygen and sulphur, and are re-
duced to Fe3S4 and Mn304.  I shall have frequent occasion to revert to these con-
siderations, which have already been noticed under another point of view (p. 238).
  The equivalent number of  sulphur is 16*1 or 201*2, and its com-
bining volume one third that  of oxyo-en.
  Sulphur combines with oxygen, forming
       Sulphurous acid......S.02.
       Sulphuric acid......S.03,
       Hyposulphurous acid  ....  S202,
       Hyposulphuric acid    ....  S205,

                         Sulphurous Acid.
  Sulphurous acid exists at  ordinary  temperature  and  pressure in
the gaseous form ; it is one,  however, of the most easily  liquefied
gases.   It is produced always when sulphur burns either  in air or
in pure oxygen,  sulphur not being  capable of passing directly to a
  COs Carbonic acid.
  K.O. Oxide of potassium.
  K.O. . 0.02 Carbonate of potassium.

and with arsenic and potassium,
  As.Os Arsenic acid.
  K.O. Oxide of potassium.
  K.O. . As.Oj Arseniate of potassium.
or	S.O,	.0.
or	s.o?	.s.
or	2S.02	0.
 
    PREPARATION,  ETC., OF  SULPHUROUS  ACID. 285

higher degree of oxidation.  In the burning of sulphur, the volume
of sulphurous acid gas formed is exactly equal to that of the oxygen
consumed.
  When required pure, it is prepared generally by decomposing
Bulphuric acid by means of a metal not very easily  oxidized,  as
mercury or copper.   The metal combines with one atom of the ox-
ygen of the sulphuric acid, and the sulphur, with the remaining two
atoms of oxygen, pass off as sulphurous acid gas ; the oxide formed
unites with the remaining sulphuric acid to form a salt.   Thus, if
mercury be used, S.O.s and Hg. give S.02 and Hg.O., and Hg.O. unites
with S.03 to form sulphate of mercury.  If the heat be  not raised
beyond 200° in this process, it is black oxide of mercury which is
produced (Hg^O.j, but above that degree the red oxide (Hg.O.) alone
is formed.
  Sulphurous acid gas may also be very simply prepared by heating
three parts of flowers of sulphur  with  four of peroxide  of manga-
nese.   The reaction is very simple;  one part of the sulphur uniting
with the metal, and another with the oxygen, form sulphuret of man-
ganese  and sulphurous acid ; thus, Mn.02 and 2S. give  Mn.S. and
S.O,.  The apparatus used in these processes may be that figured
under the heads of oxygen (p.  244) or nitrous oxide (p. 272).
  Sulphurous acid  gas is absorbed by  water; and hence, in  order
to examine its  properties in that  state, it must be collected over
mercury.   It is colourless and transparent, possessing  an odour pe-
culiarly irritating (the smell of burning  sulphur),  and  cannot  be
breathed.   It is not combustible,  nor does it support combustion.
It bleaches a variety of vegetable and  animal bodies,  and is  hence
used in the arts to whiten  straw  bonnets, corn, silk,  sponges, and
other substances.  The bleaching is  produced by the sulphurous
acid combining with the coloured substance, and forming a white
compound, from which the gas gradually escapes on exposure to
air, and hence such bleaching is  not permanent.   The sulphurous
acid may be expelled, also, from this kind of compound  by a stronger
acid, and the colour generally restored ;  thus, if a red rose be ex-
posed to the fumes of burning sulphur, it becomes completely white;
but if washed in dilute sulphuric acid, its red colour is perfectly
renewed.
  The  specific  gravity of sulphurous  acid gas is 2210*6, and it is
formed by
      One volume of sulphur-vapour.....6648*0
      Six volumes of oxygen........6615*6
     the seven volumes condensed to six, give .   . 13263.6
      Weight of one volume of S.02.....2210*6

  When this gas is exposed to a  cold of 0° F., it  condenses  into
liquid heavier than water, which  boils  at  14", and produces  by  its
evaporation a very intense cold;  it
is easily obtained in the liquid  form
by putting a quantity of mercury and
oil of vitriol into a tube, and  sealing
up the ends, as in the figure ; on applying heat to the extremity o,
 
286  PROPERTIES,  ETC.,  OF  SULPHUROUS ACID.
containing those materials, and cooling the other end by means of
ether, the°gas evolved is liquefied by its own pressure, and collects

in quantity at b.                         .,,.,,-.      .
  When a lar«*-e quantity of sulphurous acid is required dissolved in water, or when
                                      it is to be employed to form com-
                                      pounds with bases, it may be pro-
                                      duced in a much cheaper way than
                                      those described above.   Into a mat-
                                      rass, a,  placed in a furnace, is in-
                                      troduced a quantity of well-burned
                                      charcoal, in bits about the  size of a
                                      hazel-nut, and by means of the safe-
                                      ty-funnel I, as much oil of vitriol is
                                      poured in as that the mixture shall
                                      half fill the vessel; a tube passes to
                                      a bottle, i, containing some water to
                                      wash the gas from any adhering sul-
                                      phuric acid, and it is then  conduct-
                                      ed  by the tube /, which passes to
                                      the bottom of the vessel h, contain-
                                      ing the liquor in which the gas is to
                                      be dissolved.   On applying heat, the
                                      carbon  of the charcoal  abstracts
from the sulphuric acid one third of its oxygen, so that with C. and 2S.03 there are
formed C02 and 2S.02 ; there is produced a mixture of two volumes of sulphur-
ous acid and one of carbonic acid, which last cannot  enter into combination, and
passes off from the apparatus without change.
   Water dissolves about thirty-seven times its volume of sulphurous
acid ;  the solution possesses the properties of the gas in a very high
degree, and bleaches vegetable  colours with  great power; when
kept for some time, it gradually absorbs oxygen, and the sulphurous
becomes changed into sulphuric acid.
   The  sulphurous acid is one of "the feeblest acids, and is expelled
from its combinations by almost  all but the carbonic acid.  Of its
salts, those  which are soluble, all possess alkaline reaction.
   The  sulphurous  acid passes  into the state of sulphuric  acid by
absorbing oxygen from many bodies ; thus, when it is heated with a
solution°of  gold or silver, or of mercury, these metals are reduced
to the metallic state; others yield but a part of their oxygen; thus
the  peroxide of iron abandons a third, and th^black oxide of copper
one half of that constituent.
   The salts of sulphurous acid possess the same deoxidizing power.
   The composition and equivalent of sulphurous acid are as follows:

        Sulphur, 50*14
        Oxygen, ^9*86

                100*00
One equivalent,
Two equivalents,
=201*2 or 16*1
= 200 0 or 16*0
  4uT~2    32*1
                          Sulphuric Acid.

                                S.03.
  Sulphuric acid, one of the most important compound bodies, from
the energy of its action, and the variety of combinations which it
forms, is not  produced  by the direct union of oxygen and sulphur
in any case, but arises from the combination of sulphurous acid with
another quantity of oxygen.   Thus, by the action of sulphurous acid
on the easily  reducible  metallic  oxides, sulphuric acid is produced.
This principle is beautifully  shown by passing  a mixture of sulphur- 
PREPARATION  OF  SULPHURIC  ACID.      287
 ous acid gas and air through  a tube filled with spongy platinum,
 and heated to dull redness, when there issues from the extremity a
 mixture of vapour of sulphuric acid, mixed with the residual nitro-
 gen of the air;  by such  processes, however, it could not be formed
 in quantities suited to the purposes of commerce.
   The preparation of sulphuric acid is effected upon the large scale
 by bringing  sulphurous  acid, produced by the burning of sulphur,
 into contact with watery vapour and nitrous acid fumes ;  these unite
 to form  a  white crystalline solid, which appears to be a compound
 of sulphurous acid and nitrous acid (S.O^ + N.O,), united with a quan-
 tity of sulphuric acid and water which is not constant.  The forma-
 tion of this substance may be  shown by the arrangement in the
 figure.  The central  vessel, the  inner surface  of  which is slightly
 moistened, contains  atmospheric
 air ; by  means of the tubes, sul-
 phurous acid gas generated in the
 flask a, and nitric oxide  formed  in
 b, are  introduced, to  the latter  of
 which the oxygen  is supplied  by
 the air to form nitrous acid fumes ;
 the interior of the vessel becomes
 gradually covered with a deposite
 like hoar-frost, consisting of this
 substance; and, in order that  its A
 production may  proceed without
 interruption,  the vessel may be filled with fresh atmospheric air by
 blowing through  one of the tubes c, d, while  the residual gases are
 expelled through the other.
  This crystalline substance is decomposed by a larger quantity of
 water; hence, if the bottom of the central vessel be covered by a layer
 of water, the crystalline substance  falling into it according as it is
 generated, is resolved into sulphuric  and hyponitric acids; thus S.
 02t"N.O, gives  S.O., and N.03, which last is  decomposed by the
 water  into nitric acid and nitric oxide,  3N.03 giving  N.O; and  2
 N.O,,;  the  nitric acid remains combined with  the water along with
 the sulphuric acid, while  the nitric oxide escaping with effervescence,
 generates,  on arriving at the air, a new quantity of red fumes, and
 oxidizes a  new quantity  of sulphurous acid.
  It was supposed that a certain quantity of water was necessary to the existence
 of this solid body, although a larger quantity decomposed it; but it has been found
 that a similar substance may be formed which contains no water.  Sulphurous and
 nitrous acids do not act on each other when in the gaseous form, unless water be
 present; but they combine if placed  in contact under  considerable pressure, and
 liquid, even when completely dry.  A portion of the nitrous acid converts an equiv-
 alent of the sulphurous acid into sulphuric acid, it being itself reduced to the state
 of hyponitrous acid, while another quantity of nitrous  and sulphurous acid unites
 directly ; there are thus  formed from  2S.02  and 2X 04 a white crystall.ne solid
 SO, . N.04-j-S.03, and  a quantity of N.O-, which is given off on the tube in
 which the combination is produced being opened.
  It may be questioned, however, whether this substance, for the discovery and
 analysis of which we are indebted to M. de Prevostaye,  interferes in the formation
 of sulphuric acid on the large scale, where the nitrous and sulphurous acids act on
one another in the gaseous forms.
  In the manufacture of sulphuric acid, the apparatus  consists of a long  leaden
chamber consisting of two portions;  the lower a tray  of about 1$  feet deep, the 
288      MANUFACTURE  OF   OIL   OF  VITRIOL.
other a quadrangular bell, which,  being suspended on  a wooden framework, b, b,
rests with its  edges immersed in the liquid, with which the tray is filled, like the
cylinder of a bell gasometer.   The bottom of the chamber, which is supported at a
certain distance from the ground on pillars, a, a, a, slants from  before, so that the
liquid which occupies  it increases in  depth towards the end.  Under the front is
placed a furnace, d, on the floor of which, e, the sulphur is burned, and the sulphur-
ous acid passes into the chamber by the chimney/; the heat necessary is supplied
by the fireplace under e ; the nitrous  acid is obtained by placing  over the burning
sulphur in e a pan containing a quantity of nitrate of soda and oil of vitriol, the ni-
tric acid evolved from which directly  oxidizes a portion of sulphurous acid, and
then, being brought to  the state of N.04, acts on the mass of sulphurous acid as has
been just described : g is a boiler, by which steam is driven into the chamber at A,
and thus, in the interior, are provided  the conditions for the reunion  of steam, sul-
phurous acid gas and nitrous acid fumes, which produce, as in the apparatus figured
already, the white crystalline solid, by which,  when decomposed by the water  at
the bottom of the chamber, the sulphurous acid is produced, and nitric oxide gas
evolved.  This nitric  oxide, mixing  with  the atmospheric air,  which is always
present in large excess in the interior  of the chamber, is reconverted into nitrous
acid, which  combines with a new quantity  of sulphurous acid, generating another
proportion of the solid body, from whose decomposition by the water the nitric oxide
is again evolved with little loss ;  and thus the oxygen of the air is gradually trans-
ferred to the sulphurous acid by the intermediate agency of the nitrous acid fumes.
Were there  no  nitric acid formed, the same quantity of nitric oxide might convert
an infinite quantity of sulphurous acid into  sulphuric acid ;  but as the oil of vitriol
produced always retains a certain proportion of the nitric acid, it is necessary  to
supply its loss, and to send into the chamber a continued current of nitrous acid fumes.
This is secured by the construction already described, about one part of nitrate of soda
being decomposed for every eight or nine parts of sulphur burned  in the furnace d,
e.  The draught is regulated by the  chimney c, which is fitted with a valve, by the
position of which a current of air is  established through the chamber sufficient  to
bring the  gases into complete  mixture  inside, and  in due  proportions, but which
does not carry them away until their action  is completed.
  The inclination given to the bottom of the chamber is for the purpose  of allow-
ing the water,  which,  having dissolved most  of the  sulphuric acid, and become
heavy, to flow down to the farthest end ; and thus there is, on the surface has next
the front, a  layer of the weakest  acid, ready to  absorb  and decompose  the great 
MANUFACTURE  OF  OIL  OF  VITRIOL.      289
 ra.inuty of the  crystalline body formed when the mixed sulphurous and nitrous
 acid gases meet the damp atmosphere of the chamber.
  The water in  the chamber is allowed to remain unchanged until it has attained
 a specific gravity of about 1 600 ; it is then removed  by leaden pipes, and concen-
 trated by evaporation in leaden cisterns, until  its specific gravity is increased to
 about 1 76.  At this strength it begins to act upon the lead, and must be transferred
 to vessels of glass, or, still better, of  platinum, in which the concentration may be
 finished.  In the strongest form in which it can be so obtained, its specific gravity
 is 1 si?, and it contains 81 51 of real  acid in 100.
  Thus is the oil of vitriol of commerce manufactured. At present, a modification
 of the process has been introduced, in consequence of the extensive use of the iron
 pyrites (bisulphuret of iron,  Fe.S2) in place of sulphur, as the source of the sul-
 phurous acid.   Instead of the furnace r, f there is built in front of the chamber a
 kiln, somewhat  like  a  limekiln, except that it is  narrowed at top into a chimney
 pas>ing  into the chamber.  At the bottom of the kiln is placed a layer of coal or
 wood, on it the  pyrites in small pieces.   The fire is lighted, and the ignition being
 communicated to the pyrites, the sulphur burns, forming sulphurous acid, which is
 conducted into the chamber, while the iron remains behind as peroxide.  The  pan
 with nitre and oil of vitriol is supported in the kiln at such a height above the mass
 of burning pyrites as that the temperature may not be too great.  As the combus-
 tion proceeds, new quantities of pyrites are introduced by apertures high up in the
 kiln, while the residue of adherent rock and oxide of iron is raked out from the
 ashpits at the bottom.
   A  form of sulphuric  acid is  prepared upon  the  Continent,  and
 known as German  oil of vitriol,  or fuming  sulphuric acid, which is
 much stronger than  can be made by the combustion of  sulphur, as
 has been  described.
  It is obtained by exposing sulphate of iron to a red heat, in earthen  retorts.  If
 the sulphate of  iron, perfectly dry, be strongly heated, the sulphuric acid is driven
 off, and oxide of iron remains behind; but the acid is mostly  resolved into sulphur-
 ous acid and oxygen, and consequently lost.   But if the sulphate of  iron  be not
 completely dried, the sulphuric, acid combines with the water, and, distilling over in
 combination with it, forms a dark-coloured liquid of a thick, oily consistence, spe-
 cific- gravity about 19, and consisting generally of about 90 of real acid and 10 of
 water in 100, approaching closely to the formula 'iS.O.j-'-II.O.  At the same time,
 a quantity (one half) of the acid is  decomposed, the iron becoming peroxidized,
 and sulphurous acid gas being evolved.  Thus  4(S.03-j-Fe.O.) and H.O.  give
 •JS.Oa-j-lI.O. and 2S.O2, leaving behind 2Fe203, known in commerce as colcothar
 of vitriol.
  This process  is carried on in a long  furnace, in  which are  ranged about  120
 earthen re:oris, as I, in rows of 20, containing the
 partially-dried  sulphate of iron.  They are gradu-
ally heated until the fumes of sulphuric acid begin
 to appear, and the receiver A is then attached, in which the acid is condensed by
 means of cold  applied externally.
   When this  fuming sulphuric  acid is heated, it is  resolved into  or-
 dinary oil of  vitriol and real sulphuric  acid.  This last,  being very
 volatile, distils  over  in  colourless vapours,  which, on  coming into
 contact  with  moist air,  form dense white fumes of liquid  acid.   If
the colourless vapour be received  in a dry vessel, cooled by a freez-
 ing mixture,  it  condenses  in  beautiful white satiny fibres,  consti-
tuting the dry  sulphuric acid.  This acid  melts  at 77 , and very
little  above  that temperature it boils.   The specific gravity of  its
vapour is  2762, formed  by

       One volume of vapour of sulphur.......= 6648 0
       Nine volumes of oxygen.......11026x9= 9923 4
       The ten  volumes forming six.........=16571 4
       Of which one wciglis, therefore........     2761 9

   When this  dry sulphuric acid  in vapour is brought into contact
                                  O o 
 290  SULPHURIC  ACID.--HYPOSULPHUROUS  AI'IU.

 with dry barytes, lime, or magnesia, they combine with  brilliant
 combustion, forming  sulphates of those  earths.   When a  mass of
 the crystals is thrown into water, it hisses as on  the immersion of
 red hot iron, and ordinary liquid  sulphuric acid is produced.
   There  exist several  definite compounds  of sulphuric acid with
 water, of which the most remarkable are two :  the  first is the strong-
 est oil of vitriol made  in this country, and contains an  equivalent
 of acid united to one  of water ; its formula is S.03-f H.O. ;  its most
 important properties  have been already described.  The other con-
 tains twice as much water ; its formula being S.03-r-2H 0.;  its spe
 cific gravity is 1780.   When  exposed to the temperature of melting
 ice,  this acid forms large and regular crystals, while the stronger
 or weaker acids  require very  intense cold to solidify them.   When
 oil of vitriol is mixed with water, the great heat which is produced
 results from the  formation of definite compounds; and  it has been
 already shown (page  185) that, no matter what combination a cer-
 tain  quantity of  sulphuric acid forms,  it evolves the same quantity
 of heat on entering into union.
   Sulphuric acid, formed by the combustion of sulphur, as described,
 in leaden chambers, is liable to be contaminated by the presence of
 some nitric acid and lead ; from these it may  freed by redistilla-
 tion, which should, however,  be conducted  with great care, as the •
 vapour of the acid forms interruptedly and by sudden bursts, which
 might endanger the apparatus.   On diluting common oil of vitriol,
 a white powder is generally seen to form, which is sulphate of lead,
 that had been held in solution by the  strong acid,  but which precip-
 itates from the diluted  acid.   The  acid now formed from the iron
 pyrites  is found to contain frequently arsenic and  selenium: the
 presence  of the former  may become of great importance in  medico-
 legal investigations, and the detection of it will be fully described
 in its proper place.
   Sulphuric acid is very easily detected by means of a solution of
 nitrate  of barytes. If  the  smallest quantity  of sulphuric  acid be
 present, a white precipitate is  formed, which is insoluble in muriatic
 acid, even when  boiled.
   Sulphuric acid appears to dissolve  certain bodies in small quantity,
 which are  not  soluble  without  alteration  in  any  other medium.
 These are sulphur, carbon, tellurium,  and selenium.  These  solu-
 tions are not, however,  of any independent interest.

                      Hyposulphurous Acid.
                         S202, or  S.024-S.
  When a stream of sulphurous acid gas (S.02) is passed into a solution of sul-
phuret of calcium, it is absorbed, a quantity of sulphur is precipitated, and the liquor,
when filtered, is found to be a solution of hyposulphite of lime.   The reaction
which occurs is simple. Half of the oxygen of the sulphurous acid  passes to the
calcium to form lime, reducing the sulphurous to the state of  hyposulphurous acid,
 and, at the same time, the sulphur which had been combined with the calcium js
 set free, 2Ca.S. and 2S.02  giving 2Ca.O.-f S202, while 2S. is  precipitated.
  This acid "is also formed when sulphur is  boiled with an alkaline liquor or with
milk of lime.  Thus,  when soda and sulphur are boiled in water, the liquor contains
 hyposulphite of soda and sulphuret. of sodium, produced by 3Na.O. and 4S. giving
 Na.O.-r-SjO, and 2Na.S.
  This acid itself is very  easily decomposed; it may, however, be obtained, at 
HYPOSULPHURIC  ACID.
291
least for a time, in a free state, by adding to any of its salts a stronger acid, or, bet-
ter, by bringing sulphurous acid and sulphuretted hydrogen gas to meet in water;
the reaction which occurs is  that 4S02 and 2S.H. give 3S202  and 20.H.   The
water gradually becomes intensely sour, but after some time this acid resolves itself
into sulphur and sulphurous acid.
  The most remarkable character which the compounds of hyposulphurous  acid
possess  is, that they dissolve those compounds of silver which are insoluble  in
water, as the chloride and iodide, and form a solution possessing an intensely sweet
taste ; upon this property is founded their use in Daguerreotype and photogenic draw-
ing.   This acid is also recognised by its silver salt being decomposed, when boiled,
into black sulphuret of silver and free sulphuric acid, S202-^-Ag.O. giving S 03 and
Ag.S.  It is an important fact, also, in the history of the hyposulphuric acid, that
its salts do not always contain metallic oxides, but that it may form salts with me-
tallic sulphurets;  thus there are  two hyposulphites of sodium, of which one con-
tains  oxide of sodium (soda), the other sulphuret  of sodium.  Their formulae are
S202-|-Na.O., and S2Oa-|-Na.S   Each of these, in crystallizing, combines with ten
atoms of water, like common sulphate of soda ; they possess, like it, a point of max-
imum solubility, and the crystals of all  three appear to be isomorphous.  There
are, therefore, three salts,

                         S.02  . S.-j-Na.S.+lOH.O.,
                         S.02  . S.+Na.O.+10H.O.,
                         S.02  . O.-j-Na O.-f-ioH.O.,

the similar constitution of which evidences the relation of sulphur and oxygen in a
remarkable degree, and will furnish the ground of speculations of great interest,  to
which I shall again recur.

                         Hyposulphuric Acid.

                           S20„ or  S204-|-0.
  When sulphurous acid gas is passed through water in which pure peroxide  of
manganese  is diffused, this dissolves, and the solution contains neutral  hyposul-
phate of manganese.  The reaction by which it is produced  is simply that the sec-
ond atom of oxygen of the  peroxide of manganese converts two equivalents of sul-
phurous acid into hyposulphuric acid, which is exactly neutralized by the protoxide
of manganese that is evolved, Mn.02 and 2S02 giving Mn.0.4-S205.
  When a salt bf hyposulphuric acid is heated, it is resolved into sulphurous acid,
winch passes off as gas, and a neutral sulphate which remains  behind, S*205-r-RO.
giving S.Oj and S.03-|-R.O.  The acid may  be obtained free by decomposing its
barytes salt by sulphuric acid, but it cannot be kept long.  When heated, it  gives
off sulphurous acid, and sulphuric acid remains; and even when cold it rapidly
forms sulphuric acid by absorbing oxygen.

Remarks on the  Constitution of the Compounds of Oxygen and Sulphur.

   The  progress of science has gradually brought into view a num-
ber of  facts, by which it is now very nparly fully established, that
of the bodies just now described, we must look upon the sulphurous
acid  as the  only direct compound of sulphur and oxygen, and that
in the others, sulphurous acid must be  considered as pre-existing.
The  reasons for this  are very numerous.   By  the direct union of
sulphur and oxygen we can never obtain any other compound than
sulphurous acid; the others being always formed from it, prepared
either perfectly distinctly, or at the moment of  the reaction, and
then  presented to other elements with which it may unite.
  On this view the necessity of the indirect process of manufacture
of sulphuric acid becomes evident.   The sulphur,  when it forms sul-
phurous acid, is fully  saturated with  oxygen, and  cannot combine
with  any more ; but the sulphurous acid (S.O,) aets as a compound
radical, like cyanogen, as described in p. 233, and  may unite with 
292       PREPARATION  AND  PROPERTIES
 any of the simple and compound bodies.  It does not unite directly
 with oxygen, but it does so with nitrous acid, and the body so form-
 ed  is decomposed by water, producing sulphuric acid, as has been
 fully described.  In like manner, to form hyposulphurous acid, the
 radical, sulphurous acid, combines with sulphur ; the compound is
 a sulphur acid, S.O, + S., and combines with sulphur bases to form a
 distinct class of salts.   The hyposulphuric  acid contains also sul-
 phurous acid as its basis; but there are two equivalents of the rad-
 ical to one of oxygen : it is  2S.02-f-0.  This hypothesis is render-
 ed  still stronger by the fact that sulphurous acid combines with
 chlorine and with iodine to  form the chloro-sulphurous acid S.Oj
 -{-CI.,  and  the iodo-sulphurous acid S.O,-f I.   It combines also
 with  nitric oxide to form  the nitro-sulphurous acid  S.02 + N.02.
 The chloro-sulphurous acid  is  produced by the direct  combination
 of  chlorine and sulphurous acid, when exposed  to strong sunlight.
 The iodo-sulphurous acid is  formed by passing sulphurous acid gas
 through a solution of  iodine in pyroxylic  spirit, and the nitro-sul-
 phuric acid, which exists only  combined with bases, by placing a
 solution of sulphite of potash in contact with nitric oxide, which it
 gradually absorbs.  The sulphurous acid forms, therefore, an exten-
 sive range of combinations, in which it serves as a compound radi-
 cal, and of which the formulae are as follows:
        Sulphuric acid...........S.02+0.
        Hyposulphuric acid.........2S 02-j-0.
        Hyposulphurous acid .   ........S.02-j-S.
        Chloro-sulphurous acid........S.02-fCl.
        Iodo-sulphurous acid.........S.02-j-I.
        Nitro-sulphurous acid.........S.Oa-J-N.Oj.

  The ordinary salts of sulphurous acid, the Sulphites, I rank  along
 with the compounds of chlorine with the  metallic oxides and with
 peroxide, of hydrogen, which bodies they  resemble also in their
 bleaching powers.

               Compounds of Sulphur and Hydrogen.
  Sulphur unites with  hydrogen in two proportions, forming a gas,
Sulphuretted Hydrogen, by an equivalent of each element, and a heavy
liquid when in the  proportion of one equivalent of hydrogen to two
of sulphur.
  To prepare  sulphuretted hydrogen, the  protosulphuret of iron
(Fe.S.) is acted on by dilute sulphuric acid, in the apparatus figured
in" p. 247.  A lively effervescence  occurs from the escape of sul-
phuretted hydrogen gas, and the solution contains sulphate of pro-
toxide of iron ; a gentle heat may be applied to favour  the reaction
of the materials.  In this process water is decomposed, its oxygen
being transferred to the iron, and its  hydrogen to the sulphur;  the
result may be  expressed as follows: Fe.S. and S.O3+H.O.  give
H.S. and S.03-4-Fe.O.  This  gas may also be obtained by acting on
sulphuret of potassium by dilute sulphuric or muriatic acid, in which
case the theory is the same  as that already given.  Sulphuret of
antimony and liquid muriatic acid produce, when heated, very pure
sulphuretted hydrogen, the  reaction being that Sb2S3 and 3(H.C1.)
give Sb2Cl3 and 3(H.S.). 
OF  SULPHURETTED  HYDROGEN.         293
  The sulphuretted hydrogen gas, being absorbed by water, cannot
be well collected over it, except it be saturated with common salt,
or be heated to above  90°, in which case its solvent power is very
much diminished.   It cannot be kept long over the mercurial pneu-
matic trough, for the lead and tin always present in the mercury of
commerce gradually decompose it, combining with the  sulphur, and
leaving the hydrogen free ;  the volume  of the gas remains the same
during this decomposition.
  This gas is colourless and transparent: it is characterized by its
fetid odour, that of rotten eggs, which, indeed, owe their peculiar
odour to the formation  of this gas during  their putrefaction.   Its
specific gravity is 1177.  It consists, therefore, of
         One volume  of vapour of sulphur.......6648 0
         Six volumes of hydrogen......688x6=  4128
       the seven volumes are condensed to six......7060 8
       of which one weighs, therefore.........11768
  The sulphuretted hydrogen gas dissolves in  water, forming a so-
lution which is extensively used as  a reagent  for the  metals, from
the solutions of most of which it precipitates metallic  sulphurets of
various colours, by which many metals may be recognised.  Thus
antimony gives an orange, manganese a flesh red, arsenic and cad-
mium a canary yellow, and several,  as lead, mercury,  and bismuth,
black or brown precipitates.
  Sulphuretted hydrogen is highly inflammable ; if burned in a lim-
ited quantity of air, the hydrogen is consumed, while most of the
sulphur is deposited.   By means of nitric acid  or chlorine it may be
completely decomposed ; hence chlorine acts as a disinfectant and
purifier of sewers or rooms impregnated with  the odour of sulphu-
retted  hydrogen.  This gas is very poisonous; air being capable of
producing death to large animals, if respired, though  it  may not con-
tain more than ^ Jff  of this gas.  Many of the metals  decompose sul-
phuretted hydrogen, particularly when heated in this gas, combining
with the sulphur, and setting the hydrogen free.  This occurs slow-
ly, even  at common temperatures ;  and hence metals, as gold and
silver, which are not oxidized by the air, are gradually tarnished by
the sulphuretted hydrogen, which, exhaled from decomposing animal
matter,  is always present in  the atmosphere.   This  gas, evolved
probably by the action of water on  the native sulphurets of iron, at
high temperatures, is a frequent constituent of  mineral springs, and
forms the class of spas termed sulphureous, such as those of Har-
row-gate, Lucan, and Golden-bridge.  They are easily recognised
by the fetid odour, by blackening a silver spoon, or by giving a black
or brown precipitate with a solution of acetate  of lead.
  In its chemical relations,  sulphuretted hydrogen assimilates it-
self closely to water;  its composition and  equivalent  numbers are
as follows:
      Sulphur,  94*18     One equivalent, =201*2 or 16*1
      Hydrogen, 5-S2     One equivalent, = 12*5 or  1*0
                100*00                       213*7    17*1
  Bisulphuret of Hydrogen.—To prepare this substance,  bisulphuret of potassium
is to be dissolved iii water, and the solution gently poured into dilute muriatic acid; 
294  SELENIUM, ITS COMPOUNDS WITH OXYGEN, ETC.

the potassium combines with the chlorine, and the  hydrogen unites with the sul-
phur,  K.S2 and H.Gl. giving K.C1. and  H.S2; the latter sinks to the bottom  of the
vessel as a heavy yellow liquid, insoluble in water, but decomposed rapidly by con-
tact with it, unless free acid be present.  It is not easily obtained pure, as the sul-.
phuret of potassium, formed by melting  salt of tartar and sulphur together, or by
dissolving sulphur in a solution of caustic potash, always contains an excess  of sul-
phur beyond two atoms, which, precipitating along  with  this true compound, dis-
solves in it, and modifies its properties  and composition.
  This oily liquid is characterized by separating, with great ease, into sulphuretted
hydrogen gas and solid sulphur; indeed, the best way of obtaining sulphuretted hy-
drogen condensed into a liquid, is to seal up, in a strong tube, a quantity of this bi-
sulphuretted hydrogen, which, after a short time, is decomposed ;  the gas, not being
able to escape, is liquefied  by the pressure it exercises, while the sulphur separates
in octohedral crystals.
  This body is decomposed by all substances which decompose deutoxide of hydro-
gen.  Black oxide of manganese, or oxide of silver put in contact with it, evolve
sulphuretted hydrogen gas, and often  with the appearance of light  and heat; it
corrodes the skin, and appears to possess bleaching properties.
   Sulphurets of Nitrogen have been discovered and described ; they are solid and
crystallizable, but are of no importance.

                              Of Selenium.

   Selenium was discovered by Berzelius, and accompanies, although
in exceedingly small quantity, the native metalli-c sulphurets, existing
as seleniurets of the same metals.  It remains  even still a very rare
substance : it has not been introduced into  the arts or into medicine,
and it will hence be necessary  to touch upon  its  history  but  very
slightly.
   When extracted from its native combinations, selenium is a  solid
of a  dark brown colour, and when smooth,  with metallic lustre.  Its
density  is 4*32; its fracture  is  crystalline; it melts  a little above
the boiling point of water, and boils at 650  ;  its vapour is of a deep
yellow colour, like that of sulphur.   In its manner of combination
it resembles, almost completely, sulphur.
   In one respect, however, they differ; when selenium is  burned in air, it combines
with but one equivalent of oxygen, forming oxide of selenium (Se.O.), a colourless
gas, which is remarkable  for  its pungent odour of horseradish.  By this  means
selenium  may be recognised, even when  present in exceedingly small quantity.
Sulphur does not appear to form a similar compound.
   When selenium  is boiled with nitric acid, it unites with two equivalents of oxy-
gen, and forms selenious acid, Se.02   This may be also produced by burning se-
lenium in oxygen gas  at a high temperature.   It is solid, white, volatile, and may
be  obtained crystallized by  sublimation, or from its watery  solution.   Selenious
acid may be deprived  of its  oxygen by contact with zinc or iron  filings, or by sul-
phurous acid : selenium is set free as a crimson precipitate.  When selenite  of am-
monia is heated, it gives water, nitrogen, and free selenium.
   If a current of chlorine gas be passed  through a solution of selenious acid, or if
selenium be melted with nitre, the selenic acid is formed (Se.03), which has the
most remarkable analogy with sulphuric acid   All their similar salts are isomorph-
ous, and almost identical in properties.   Indeed, to distinguish them, it is necessary
to boil the salt with muriatic acid, which has  no action on the sulphate, but gives
with the seleniate, chlorine, and selenious acid.
   Seleniurctted Hydrogen is formed by the action of acids  upon metallic seleniurets,
in precisely the  same manner as that described under the head of sulphuretted hy-
drogen.  It is a colourless gas, of an extremely fetid odour, irrespirable, soluble
in water, and precipitating, from the solutions of many of the metals, metallic sel-
eniurets ;  these are generally black  or  brown ;  but the seleniuret of manganese is,
like the sulphuret, flesh-red, and that of zinc is white.
   When sulphuret of hydrogen is passed  into a solution of selenious acid, water is
formed, and a sulphuret of selenium is produced analogous  to selenious acid, its
formula being Se.+S2.  It is a canary  yellow powder, insoluble in water. 
        PHOSPHORUS,  ITS  PREPARATION,  ETC.    295


                           Of Phosphorus.

  Phosphorus exists in nature, principally in the animal kingdom,
in the bones of the vertebrated animals, in the fluids of the body,
and also in the pulpy material  of the brain and nerves.  It is found
in small quantity in many vegetables, and is a constituent of some
minerals.   It is prepared as an article of manufacture in large quan-
tity in  London and Paris.   In the latter city it  is computed that
about 200,000  lbs.  of phosphorus are annually obtained.
  The principal source of phosphorus is the earthy material of bones (phosphate of
lime).  The bones are first burned until  they become completely white, and then
ground to powder.  To three parts of this powder are added thirty parts of water
and two  of oil of vitriol. The sulphuric  acid unites with a portion of the lime of
the bone ashes, while the remainder  forms, with the whole of the phosphoric acid,
a soluble salt, which is obtained in the liquor, when the insoluble sulphate of lime is
separated by straining through a cloth.  The
liquor  is evaporated to the consistence of a sirup,
and gradually mixed with a quantity of powdered
charcoal, about one fourth the weight of the
bones  that had been used, and the whole com-
pletely dried at a temperature just below redness.
The mass is  introduced, in powder, into an
earthen  retort, a, which is placed in a furnace,
as in the figure.  To the neck of the  retort is
adapted  a copper tube, 6, the other extremity of
which dips a little into the water in the bottle
■which serves  as  a receiver.  The retort being
gradually heated, the excess  of the  phosphoric
acid is decomposed by the charcoal,  the carbon
of which combines with the oxygen to form car-
bonic  acid, while  the phosphorus becomes free ;
this being volatilized  by the  high temperature,
passes in the state of vapour  into  the  copper
tube, where it is  condensed, and, flowing down
in the liquid form into the bottle, collects under the surface of the  water.   The  cop
per tube must dip so little under the water, that by no condensation could this be
forced back into the retort.
   The phosphorus so obtained is again  melted under  the surface of the  water,
and poured into glass tubes, where it is allowed to solidify.   It thus gets the cylin-
drical form in which it is found in commerce.
   Phosphorus, when  pure, is transparent  and  colourless;  but,  as
generally found, it is of a pale, yellow, or  even  of a reddish col-
our.  At ordinary temperatures it is soft, so that it may  be bent or
cut with a knife ;  but at 32  it becomes quite brittle and crystalline
in its fracture.  It is insoluble in  water, but it dissolves in the vol-
atile  oils, in ether, and  in sulphuret of carbon, from which last it
may  be obtained in crystals of considerable size,
which are regular dodecahedrons, as in the figure.
It has  also  been obtained  crystallized by fusion,
under  the form of octohedrons.  At  108   phos-
phorus melts  into a colourless liquid, and at 550°
it boils, forming* a  colourless vapour, the sp. gr.
of which is 4327.   Phosphorus appears to assume
an anomalous condition like that of sulphur ; when
strons-ly heated and  suddenly cooled,  it  becomes  jet  black and
opaque, but gradually returns to its ordinary aspect.
   Phosphorus is exceedingly  inflammable.  Even  at ordinary tem-
peratures, when exposed to the air, it burns slowly,  forming phos-
 
   296  COMPOUNDS   OF   PHOSPHORUS  AND  OXYGEN.


   phorous acid, and emitting light visible in  the dark, from whence
   its name (0wc (pepco, I bring light).  It,  at  the same  time, emits a
   remarkable and penetrating garlic  smell.  It is hence that phospho-
   rus is used to analyze atmospheric air,  and that it must always be
   preserved under  water.   When heated  to  120  phosphorus  bursts
   into brilliant flame, and unites with oxygen to form phosphoric acid.
   The combustibility of phosphorus  is influenced by the presence of
   various  gaseous  bodies in a  very remarkable degree.   Thus, in
   pure  oxygen, phosphorus does not burn  nor give any light until the
   temperature  is raised to  80';  and if the  oxygen  or air be  mixed
   with  small quantities of olefiant gas, or  the vapours of ether or of
   oil of turpentine,  its  slow combustion  may  be totally prevented.
   This  influence even  extends,  under some  circumstances, to much
   higher temperatures.
      The atomic weight of phosphorus  had  been formerly taken as
   15*7 (H. = l) in  consequence of some views of the constitution of
   its compounds, which are now generally abandoned, and I consider
   the true equivalent number to be 31*4, double the former.
     Phosphorus  combines with oxygen  in four proportions, forming an oxide and
   three acid compounds, the constitution of which  follows :

            Oxide of phosphorus   .  .  .  =2P.-l-0.=62 8+ 8 0=70 8
            Hypophosphorous acid .  .  .  = P.4-0.=31-4-f- 8 0=39 4
            Phosphorous acid   .  .  .   .  = P.-j-03=31 4-f24 0=55 4
            Phosphoric acid .....  = P.-f05=31-4+40-0=71-4

     Oxide of Phosphorus.—When phosphorus is exposed to light, in water containing
   air dissolved, it gradually becomes covered with  a white powder, which is a com-
   pound  of phosphorus with water; but there forms, at the same time, a reddish sub-
   stance, which is oxide of phosphorus.  It  is generated, also, whenever phosphorus
   is incompletely burned, and may be formed in  large quantity by melting phosphorus
 /  under  water, and bringing a stream of oxygen gas to act upon it by means of a tube
/  passing to the bottom of the vessel;  the phosphorus burns brilliantly, but, being
/   present in great excess, it passes principally only to the lowest degree of combina-
l   tion that it can form.   It may be obtained purer by other processes, which are, how-
\ ever, too complicated to be introduced  in this place.
   ■  The oxide of phosphorus so formed is a red or yellow powder, insoluble in water;
   it is exceedingly inflammable in some  forms, but  in others does not  take fire until
   heated to near  the boiling point of mercury.  It  is not probable that the red and
   yellow substances which are called oxide of phosphorus are really identical, as they
   differ in their most striking characters besides in  colour.  The formula P20. is that
   obtained from the yellow  matter; Pelouze considers the reddish matter to be ex-
   pressed by P302.
     Hypophosphorous  Acid.—This acid is very little known ; it is formed when phos
   phorus is heated in a solution of an alkali or earth : water is decomposed; one por-
   tion of phosphorus combining  with the hydrogen, and another with the oxygen,
   produce phosphuretted hydrogen  gas, which passes off, and hypophosphorous acid,
   which  remains combined with the alkali or earth employed;  the reaction  may be
   shown thus with phosphorus and  solution of barytes : 4P., 3H O . and 3Ba  O . give
   3(P.O.-|-Ba.O.)andP.H3.                                             5
     The hypophosphite of barytes, so obtained, may  be decomposed by sulphuric acid,
   and the sulphate of barytes being removed by filtration, the hypophosphorous acid
   remains uncombined; its solution may be evaporated to the consistence of a sirup,
   but it  cannot be obtained solid; it  is decomposed, by continuing the heat, into
   phosphuretted hydrogen, phosphoric acid, and some phosphorus is set free.
     Its salts are all soluble in water, and most of them crystallize and contain water
   of crystallization ; when heated strongly, they give phosphuretted hydrogen and a
   phosphate of the base.
     Phosphorous Acid.—This acid is the principal product of the slow combustion of
   phosphorus, but, to obtain it pure, it is necessary to avoid carefully an excess of
   oxygen ; for this purpose, a glass tube of ten inches long and half an inch bore is 
    PHOSPHORIC  ACID, ITS  PREPARATION,  ETC.  297

drawn out at one end to a point, with an aperture large enough to admit a pin, and
bent at an obtuse angle about two inches from the point; at the bend is laid a piece
of phosphorus, which is heated until it takes fire, but the temperature must not rise
bo high as to sublime any of it.  As there is a great excess of phosphorus present,
the principal product, of the combustion is phosphorous acid, which, being formed in
exceedingly light flakes, is carried by the current of air to the upper part  of the
tube, where it is deposited.  These flakes are volatile, and may be sublimed from
one  part of the tube to another;  they attract water so powerfully, that the heat
evolved is sometimes great enough to inflame the phosphorous acid, which then
combines with more oxygen, and forms phosphoric acid.
  Phosphorous acid is more easily prepared in the liquid form; for this purpose,  a
quantity of phosphorus is placed in a thin glass vessel, covered with water  to the
depth of some  inches ;  a current  of chlorine is then  conducted by a tube  to the
phosphorus, which inflames and forms  protochloride of phosphorus ; this substance
is immediately decomposed by tin? water, phosphorous acid and muriatic acid being
produced; the PC13 and 3H.O. giving I\03 and 3H.C1 ; both acids dissolve in the
water, but by evaporating the  solution to the consistence of a sirup, the muriatic
acid passes off as gas, and the hydrate of phosphorous acid, P.03-{-3H.O., remains
behind.   This hydrated acid cannot be freed from water by farther heat, it being
then decomposed into phosphoric acid, and the  variety of phosphuretted hydrogen
which is not spontaneously inflammable. Thus4(P.03-r-3H.O.)give3P.05-j-3H.O.)
and P.H3.
  The solution of phosphorous acid absorbs oxygen rapidly from the air, and, with
the assistance of heat, reduces to  the metallic  state  the salts of mercury, silver,
gold, and platina.  It is hence  occasionally used as a deoxidizing agent.
                          Phosphoric Acid.
  When this acid is required in large quantity,  it  is  generally pre-
pared from the earth of bones, which are acted on by  sulphuric acid,
as was  described for the preparation of phosphorus.   The  acid so-
lution of superphosphate of lime is decomposed by carbonate of am-
monia,  by which the lime is thrown  down in combination with car-
bonic acid, and the phosphoric acid remains in solution as phosphate
of  ammonia.  This salt  may be crystallized,  but  it is generally
evaporated to dryness, and ignited ; the ammonia passes off, and
the phosphoric acid remains behind melted,  and solidifies  on cool-
ing into a colourless glass,  the glacial phosphoric  acid.
  It may also be obtained by acting on phosphorus with dilute nitric
acid.  This  supplies oxygen to the phosphorus, and  nitric  oxide is
evolved.   When the  action has terminated, the  solution  is  to be
evaporated to dryness, and  the residual phosphoric acid ignited, to
expel all  traces of nitric  acid.  This process is somewhat danger-
ous, as sometimes fragments  of phosphorus are  projected by the
effervescence out  of the  liquid,  and burning in the nitric oxide gas,
may burst the retort.   The phosphoric acid may also be prepared
very simply,  and  in  a pure  and dry state,  by  setting  fire to  some
phosphorus in a little  cup,  and covering it  with a large bell  glass.
The oxygen  of the contained air forms phosphoric  acid, which is
deposited in  white flakes  on the inside  of the glass and  on the sup-
porting plate.  In all these cases,  the acid so obtained  is destitute
of water ; it  is anhydrous.
  The  phosphoric  acid has  a great affinity for water, combining
with it almost explosively-   It may form three distinct compounds,
phosphates of water, the constitution  of which is as follows:
        .'Monobasic, phosphate of water   .  .  P.O,4- H.O.
        Bibasic phosphate of water   .   .  .  P.O,+2H O.
        Tribasic phosphate  of wat^r  .   .  .  P.05-f-3H O.
                                 V P 
298
PHOSPHATES OF  WATER.
  This relation was first established by the researches of Graham,
whose admirable memoir on the arseniates and phosphates formed
an important epoch in science.   The phosphoric acid combines not
only with water in these three  proportions, but each of them is a
type of a series  of  salts which  the phosphoric acid is capable of
forming.  Thus there is a class of monobasic phosphates,  another
class of bibasic phosphates, and a third, which is the most common, of
tribasic phosphates ; the water contained in the phosphates of water
being  replaced to a greater or  less extent by means of equivalent
proportions of ammonia or metallic oxides.
  A solution of phosphoric acid in water may contain any one  of
the three  phosphates of water that have been described, and, when
neutralized  by bases, may hence produce  totally different salts.
The properties of a solution  of phosphoric acid may therefore  be
totally different, according to the manner in which it had been pre-
pared, and hence this acid was at one time ranked as a remarkable
instance of isomerism ; but Graham has beautifully shown that the
difference of properties is only the result of the existence of the
different states of combination in which the phosphoric acid actually
exists.  It will consequently  be  necessary to  study  separately the
properties of the three compounds of phosphoric acid with water.
  Monobasic Phosphate of Water.—A solution of this body reacts pow-
erfully acid  ; it precipitates albumen (white of egg) in white curds;
when neutralized by a base,  it  gives  salts which  contain  but one
atom of base, their formula being P.O,+ R.O., and a soluble salt of it
produces, in solutions of silver, a white, soft precipitate, P.O,-f-
Ag.O.   This is the least stable of the phosphates of water; it grad-
ually passes into the other  forms, particularly when its solution is
boiled.
  Bibasic Phosphate of Water.-—This form of the acid may be pre-
pared  by decomposing bibasic  phosphate of lead by sulphuretted
hydrogen,  It is characterized by combining always with two equiv-
alents  of  base, forming salts, whose  formula is  P.O, + 2R.0.; its
salts give, with nitrate of silver, a white precipitate,  P.03 + 2Ag.O.,
which  is not pasty like the monobasic phosphate.   The salts of this
acid may  contain only one equivalent  of fixed base, the other being
water,  and may hence, at first sight, appear to be constituted like
the monobasic salts ;  the basic water is, however, easily known to  be
present, by its not being expelled by a moderate heat with the water
of crystallization, but requiring  a temperature approaching to igni-
tion for its expulsion.
  Tribasic Phosphate of Water. — This is the form of phosphoric acid
which  represents  the class of salts most generally known;  it  is
characterized by not  precipitating albumen, and by combining with
three equivalents of base when  fully neutralized.  In the majority
of cases, of the three equivalents of base, one is water ; thus the com-
mon phosphate of soda is a tribasic phosphate, its  formula being
(P.O, + 2Na O.H.O.)f2+Aq.;  when moderately heated, or  even  by
loner exposure  to dry air, it loses  the 24Aq., but it requires to  be
melted at  a  red heat in order to  drive off the twenty-fifth atom  of
water ; and, if this be done, on redissolving the fused  mass in water,
it crystallizes in a totally diflerent form, and is found to have been 
PHOSPHURETTED  HYDROGEN.          299
changed  into bibasic phosphate of soda, the formula of which is
(P.05 , 2i\a.O.)-r-lOAq.   The difference is remarkably  shown  by
the action of these salts on solution of silver; common  phosphate
of soda precipitates nitrate of silver of a canary yellow, and the so-
lution becomes acid; one  equivalent of tribasic phosphate of soda
decomposing three equivalents of nitrate of silver, producing one
equivalent of tribasic phosphate of silver, two of nitrate of soda,
and one of nitrate of water; this  last being liquid nitric acid,  of
course, renders the liquor acid.  The reaction may be simply ex-
tJrGSSGCl •
          P.03+2Na.O.H.O. and  3(N.O,-*-Ag.O.)
      give P.03 + 3Ag.O... 2(N.03+Na.O.) and N.03+H.O.
If, on the other hand, bibasic phosphate of soda be used, the liquor
remains neutral, for PO, + 2Na O.  and 2VN.03 +Ag.O.) give P.05 +
2Ag.O. and 2(N.03 + Na.O.).
   In the tribasic phosphates it frequently occurs that there is but
one equivalent of fixed base, the other two being water; such salts
have frequently an acid  reaction, and were formerly termed biphos-
phates.  Thus one tribasic phosphate of soda  is P.03 + Na.O.. 2H.
0.; the biphosphate of  ammonia is tribasic, its formula being P.0S
+ NH40. .'2H.0.
   These salts  of phosphoric acid were originally designated  by
Graham metaphosphates, pyrophosphates, and  common phosphates,
but the systematic names which he has  since proposed should be
universally adopted.
   In the general  remarks on the constitution of salts, and on some
other occasions, I shall  have opportunities to return to the  consid-
eration of this subject.

             Compounds of Phosphorus and Hydrogen.
  Although  it is probable  that there exist at least two compounds
of phosphorus and hydrogen, yet I shall describe only that which
is gaseous (P.H,), as of  it alone do  we possess  accurate knowledge.
   The modes of preparing this  gas have  been  already noticed.  It
may be formed, 1st, when  phosphorus is heated  in  a solution  of
potash or barytes, or with milk of lime ; the  water being  decom-
posed, gives its oxygen to  one portion of the phosphorus to form
hypophosphorous acid, and its hydrogen to another, forming phos-
phuretted hydrogen gas: 2d, when the hydrated phosphorous acid
is heated, the water is decomposed, and phosphoric acid and phos-
phuretted hydrogen are produced.  The gas, prepared in these ways,
possesses  very different properties; I shall term  that obtained  by
the first process the
A, and  that by the
second the B variety.
If the A gas, evolved
from  the  retort a,
be allowed  to  bub-
ble through  the wa-
ter of the pneumatic
trough, each bubble
of gas, as it bursts in
 
300           PHOSPHURETTED  HYDROGEN.
the air, takes fire spontaneously, and, burning with a beautiful white
flame,  forms a ring of phosphoric  acid smoke, which, widening as
it rises, may ascend to a considerable height, if the air of the apart-
ment be still, without its form being broken up.  The structure of
this ring is  exceedingly curious and pretty ;  it consists  of an ama-
zino- number of small rings, which revolve with great rapidity on
their axis, and whose plane is perpendicular to that of the general
rino- which they produce.   This is spontaneously inflammable phos-
phuretted hydrogen : if the gas bubbles be received in a jar of pure
oxygen, the combustion is excessively brilliant and explosive.  The
B variety of the gas is not spontaneously inflammable, but if set on
fire it  burns with the same appearance as the other.
  On analysis, the two varieties give exactly the same result; they
are colourless and transparent, and of a very disagreeable garlic
smell; but slightly absorbed by water, and precipitating the generali-
ty of metallic salts, giving insoluble phosphurets.  The specific grav-
ity is the same for both, being 1185, which arises from
       One volume of phosphorus-vapour.......-=43270
       and six volumes of hydrogen   .  .  .  .  .  .68-8x6=412-8
     being condensed to four............4739 8
     of which one weighs, therefore..........1184-9
Their  constituents by weight, and equivalent numbers, are as fol-
lows :
    Phosphorus, =91*29     One  equivalent,    =392*3 or 31*4
    Hydrogen,      8*71     Three equivalents, = 37*5 or 3*0
                 100*00                          429*8    "344

   These two varieties were naturally looked upon as isomeric, but
Graham  has shown that the difference of properties may arise from
the presence of a small quantity of foreign substance, as such may
change the one  variety into the other.  Thus a very small quantity
of the vapour of ether removes altogether the power of spontaneous
inflammability from the A variety ; the vapour of the essential oils,
and even carbon, phosphoric acid, and potassium, produce the same
effect.  On the other hand, an exceedingly small quantity of vapour
of nitrous acid  or nitric  oxide converts the variety B into A, and
makes it spontaneously inflammable.  Graham  considers that, in
obtaining the gas from phosphorus and milk of lime, &c, it is accom-
panied by a very minute trace  of some compound of phosphorus and
oxygen, probably the same as is formed by nitrous acid with the B
variety, which is really spontaneously inflammable, and, acting as a
match, inflames the general mass of gas (see p. 296.)
  Phosphuret of Nitrogen.— This compound has been discovered and described by
Rose, but possesses no important properties.
  Sulphuret of Phosphorus is formed by melting together sulphur and phosphorus in
equivalent weights.  It appears  that these elements unite in more proportions than
one.  The compound is much more inflammable than phosphorus, and is the mate-
rial used in the phosphorus match-boxes.

                           Of Chlorine.
   Chlorine  exists in large quantity in nature, principally combined
with sodium, forming immense deposites of rock-salt (chloride of 
CHLORINE,  ITS PREPARATION.          301
sodium) in England,  in  Poland, and elsewhere ; and in the  same
state it communicates the saltness, and constitutes  the chief ingre-
dient of sea-water.  It is found also combined with calcium, mercury,
leal, silver, and some other metals ;  but these compounds are rare,
and  exist  only  in  small  quantity.   The only source of chlorine
practically useful in chemistry and in the arts is from common salt,
  To obtain chlorine in large quantity, the common salt is mixed with peroxide of
maiijiaiicse, and then decomposed by sulphuric acid ;  the half of the oxygen of th<
peroxide of manganese passes to the sodium, the chlorine being  expelled, and the
soda and protoxide of manganese both unite with the sulphuric acid.  Thus Mn.O,
and Na.Cl., treated with 2S.03, produce S.03 .  NaO.-f-S.O3  . Mn.O., and CI. is
evolved.  By weight, about six parts of oxide of man-
ganese and eight of chloride of sodium are employed
with  thirteen of oil of vitriol;  and as the manufactu-
rers of chloride of lime arc generally makers of oil of
vitriol also, a proportionate quantity of acid of 1600
from the chamber (p. 289) is generally used in place
of strong oil of vitriol, the  expense of concentration
being thus saved.  Into  a leaden still, h, h, such as is
represented in the figure, the mixed salt and manga-
nese  are introduced at the aperture i, which is then
tightly closed; the sulphuric acid enters by the bent
funnel b, and these materials are well mixed by means
of the agitator, turned by the cross handle n; the gas
evolved escapes by the tube a, which conducts it to its
destination.  At first the operation does not require
heat, but the still sits in  an iron jacket, e, e, into which steam  is  conducted by the
tube I, and thus the heat necessary for the decomposition is kept up ; a waste-pipe,
g, serves for running out the residue of one  process, in order  to clear the still for
another.
   When chlorine is required in small quantity in the laboratory, it
may be more conveniently prepared  from the muriatic acid of com-
merce, which is a solution of chloride  of  hydrogen  gas in water.
This is completely decomposed by peroxide of manganese  at very
moderate temperatures, the hydrogen'of the muriatic acid combining
with the oxygen of the peroxide of manganese to  form a deuto-
chloride of  manganese,  which  is completely  resolved by  a very
moderate heat into  protochloride and free chlorine.  Thus,  at first,
Mn.O, and 2C1.H. give Mn.Cl2 and   2H.O., and  then Mn.Cl2 sep-
arates into Mn.CI. and CI., which is  evolved as gas.   For this it is
only necessary to introduce about one part  of peroxide and three  of
muriatic acid into an apparatus, such as those already often figured,
and  the gas  may be  obtained.
The collection of the  chlorine
requires some remark.  It is ab-
sorbed rapidly by  cold water,
and it cannot be collected over
mercury, as  it combines  rapid-
ly with it, forming calomel; wa-
ter heated to above  90J should
therefore be used ; but it is still
better to take  advantage  of the
great density  of chlorine for its
collection.
  If  the  tube  conducting the
chlorine from  the  flask a, in
 
302      BLEACHING  POWER  OF CHLORINE.

which it is generated, be brought to the bottom of a dry glass, c, the
chlorine issues there, and, being much heavier than the air, pushes
the air up out of its way, and gradually fills the jar completely, pre-
cisely as, by conducting a stream of water to the bottom of a vessel
containing oil, this might be perfectly expelled, and the vessel filled
with water.   The colour of the chlorine allows the gradual filling of
the bottle to  be seen, and by  stopping its aperture with a greased
stopple, the gas may be preserved unaltered for  a long time.
  The  chlorine,  when  thus prepared, is  a greenish yellow gas,
whence its name (^/.wpoc); of an extremely suffocating odour, ir-
ritating the air passages when respired, even very much diluted, in
an intolerable degree.   Its specific gravity is 2470.   On plunging
a lighted taper into chlorine, it burns for a moment with a red, smoky
flame, but is soon extinguished.   Many bodies burn, however, more
readily  in chlorine than in air, or even in oxygen gas.  If some
powdered antimony  or arsenic be thrown into a bottle of chlorine,
they take fire, with bright scintillations.  Tin  or brass foil bums
spontaneously, as also phosphorus,  although with little light.  A
paper dipped in oil of turpentine takes fire spontaneously,  the hy-
drogen  burning, and the  carbon being deposited as  a thick black
smoke.   The  affinity of chlorine for hydrogen is very great: when
mixed, these  gases gradually  unite, even at common  temperatures,
and  suddenly, with  explosion if set  on fire  by a  taper or by the
electric spark.  In consequence of this affinity for  hydrogen, chlo-
rine decomposes most organic substances, one half of the  chlorine
removing an  equivalent  quantity of hydrogen,  and the  other half
going in its place ;  thus ether and chlorine give chloride of hydro*
gen and chlorine ether, C4H,0. and 10C1. giving C„C130. and 5H.C1.
Very often, however, the action of chlorine is much more complex.
  Perhaps the most important character of chlorine, and certainly
that upon which its value in  the arts depends, is its power of re-
moving the colour of organic  substances ; its bleaching properties.
Formerly it was considered that water was necessary for this bleach-
ing, and that  the chlorine combined with the hydrogen, while the
oxygen of the water, being thus thrown upon the organic substance,
oxidized it, and formed a new body, which was  colourless.  I have
shown, however, that this is not the case, but that the chlorine enters
into the constitution of the new substance formed, sometimes repla-
cing hydrogen, at others simply combining with  the coloured body,
and in some, the reaction being so complex that its immediate stages
cannot be completely traced.  I shall notice this agency of chlorine
again when describing the chloride of lime, and also  when discuss-
ing its  relations to organic chemistry.
  From this action on organic bodies, chlorine  is extensively em-
ployed as a disinfectant, to remove the miasmata and  infectious im-
purities by which the atmosphere of an hospital may be contaminated.
For this purpose, it is desirable to evolve the gas slowly,  but con-
tinuously ;  in order to do so, some chloride of lime, diffused through
water,  may be placed in a capsule or  teacup, and by a funnel, the
throat of which is partly stopped, dilute sulphuric acid be allowed
to drop down on it.   The acid takes the lime, and the chlorine is
set free. 
          OXIDIZING  POWER OF  CHLORINE.       303

  When chlorine is brought into  contact with water at 32°, they
combine, forming a hydrate which  crystallizes in plates, and which,
when heated to about 45 , is decomposed.   If a quantity of these
crystals be sealed up in a strong glass tube, the chlorine, when  lib-
erated, exercises so much pressure as to condense itself into a liquid.
This was the first  instance in which the liquefaction of the gases
was successful.  Water holding chlorine in solution possesses  the
colour, odour, taste, and bleaching properties  of the gas itself, and
may hence be used for  the purposes of the arts, although not  so
manageable  or convenient as many other forms.   When chlorine
water is exposed to the light, it is gradually decomposed, chloride
of hydrogen being formed, and oxygen set free ;  the  solution  be-
comes  colourless, loses its bleaching powers,  and  acquires an acid
reaction.  In contact with other bodies, chlorine may decompose
water much  more  rapidly,  and is hence frequently employed as an
oxidizing agent, substances being  frequently  oxidized by chlorine
to a higher degree than by nitric acid.   This results, probably, from
the chlorine first combining with the body, and the compound then
decomposing water ;  thus, when chlorine converts selenious  acid
into selenic acid, it is probable that it is not that the chlorine decom-
poses water, but that it unites with the  selenious acid, forming chlo-
ro-selenious acid, Se.02 . CI., which, in contact with water, is resolv-
ed  into Se.02 . O. and Cl.H.   Very frequently chlorine oxidizes a
metal to a higher degree by combining with  one portion of it,  and
hence  throwing all of the  oxygen upon the remainder ; thus pro-
toxide of iron is converted into peroxide by chlorine, because GFe.
0., acted on by 3C1., produce Fe2Cl3 and 2Fe203.  The direct decom-
position of water by chlorine I consider to occur very  seldom.
  The combinations of chlorine form, perhaps, next to those of ox-
ygen, the  most complete  series which exists in chemistry.  Its af-
finities are so varied that it unites with almost all the simple bodies,
metallic and non-metallic, and in most cases it forms more than  one
compound with the other body.  Its metallic compounds are gener-
ally constituted like the oxides of the same  metals, but in its union
with the non-metallic bodies it does not appear to follow so closely
the analogies of oxygen.
  Chlorine possesses also the property of combining with metallic
oxides, apparently without decomposition in many cases, and form-
ing compounds resembling peroxides, in which a portion of the ox-
ygen is replaced by chlorine.   Thus, with lime it  forms Ca.O. . CI.,
with protoxide of lead Pb.O. . CI., with barytes Ba.O.. CI., which  cor-
respond probably to Pb.02 and Ba.02.   In the hydrate of chlorine,
which  is Cl.-f 10H.O., it is likely that a compound corresponding to
peroxide of hydrogen may exist, and  that the  constitution of the
crystals may be H.O. . C1. + 9H.O., and that bleaching compounds in
general may have  that type.
  Chlorine is easily recognised, when free, by its peculiar odour, by
its bleaching powers, and by  producing with a solution of nitrate of
silver a white curdy precipitate, which is insoluble in  acids, soluble
in water of ammonia, and is rapidly blackened by exposure to the sun's
rays.   When  in combination with a  metal,  its solution  gives the
same kind of precipitate of chloride of silver, but the bleaching prop-
erties and smell are absent. 
 304    HYPOCIILOROUS  ACI D.--C 11 L O R I C  ACID.


               Compounds of Chlorine  with  Oxygen.
  These are four, constituted as follows :
         Hypochlorous acid  ....  =Cl.-f- 0.=35 4+8
         Chlorous acid......=Cl.+40.=35 4+32
         Chloric acid......= Cl.+5O.=35-4+40
         Percliloric acid.....=Cl.+70.=35 4+56

                       Hypochlorous Acid.
  If red oxide of mercury, diffused through a small quantity of wa-
 ter,  be introduced into bottles  containing chlorine, and the whole
 be agitated, the gas is rapidly absorbed, and, combining with both
 constituents of the oxide, forms chloride of mercury and hypochlo-
 rous acid.   Thus  Hg.O. and 2C1. give Hg.Cl. and Cl.O.  As there is
 always an excess of oxide of mercury employed,  the  chloride of
 mercury combines with it, forming the insoluble brown  oxychloride
 of mercury Hg.Cl.+ 3Hg.O., which separates, and the  hypochlorous
 acid remains nearly pure in solution in the water.   By a very mod-
 erate heat it may  be distilled in a dilute form, and so obtained quite
 pure  from sublimate, but at  212  the  acid  is rapidly decomposed
 into chlorine  and  oxygen.
  A solution of hypochlorous acid is yellow ; its odour is like that
 of chlorine ; it bleaches powerfully ; it decomposes spontaneously
 even in the cold, forming chlorine  and chloric acid ;  it  oxidizes most
 bodies with extreme energy.  To obtain it in the gaseous form, it
 is sufficient to introduce a small quantity of the solution into a tube
 over mercury, and to add pieces of dry nitrate of lime ;  the water is
 absorbed by this deliquescent salt, and  the acid remains as a green-
 ish yellow gas,  very similar to chlorine in all  respects; water ab-
 sorbs 100 volumes of it;  by raising its  temperature  even slightly, it
 explodes, and its volume is increased by one half:  100  volumes of
 it produce 100 of  chlorine and fifty of oxygen.   Its specific gravity
 is by theory 3021*3, and  its equivalent numbers 542*6 or 43.4: its
 formula is Cl.O.
  The hypochlorous acid combines with bases to form  salts, hypo-
 chlorites, which possess the bleaching properties of  the acid in a
 great degree ; but their nature  is involved so much in  the general
 history of the bleaching compounds of chlorine,  that I shall not enter
 upon any notice of them here.

                         Chloric  Acid.
  When chlorine  is brought into  contact with an alkaline solution,
it is absorbed with great avidity,  and  the  liquor acquires powerful
bleaching properties.  Concerning the nature of the  reaction, the
opinions of chemists are not completely  settled ;  it  may be sup-
posed, on the one hand, that  the  chlorine unites directly with the
alkali,  forming simply, if potash be employed,  chloride of potassa,
K.O. . CI.  But, on the  other hand, it is possible that  a  quantity of
alkali may be decomposed,  as certainly occurs  with oxide of  mer-
 cury, and that chloride of potassium and hypochlorite of potash may
 coexist in the liquor ; thus, that 2K.O. and 2C1. should  produce K.
 CI. and Cl.O.+K.O.  The majority of chemists incline to the latter
view, but the  subject will hereafter receive detailed consideration.
=434
=674
= 75 4
=91-4 
           CHLORIC  ACID.--CHLOROUS  ACID.       305

In any case, this bleaching alkaline liquor is completely decomposed
by boiling, particularly if it be very concentrated.   Oxygen is then
evolved in considerable quantity, while chloride of potassium  and
chlorate of potash are produced: thus 9(K.O. f Cl.O) evolve 1"20.,
and form 8K.C1.  and K.O. +C1.0,.  It is in this way that the chlorate
of potash of commerce is obtained, and from it the chemist prepares
chloric acid.
  A solution of  this acid is readily prepared by decomposing a so
lution of chlorate of barytes by sulphuric acid.  It cannot be obtained
solid, as, when a concentrated solution of it is heated, it is resolved
into chlorine, oxygen, and perchloric acid.  It does not bleach ; it does
not precipitate a solution of nitrate of silver:  when in its strongest
form, of a thick, oily consistence, it sets fire to many organic bodies,
and is a powerful oxidizing agent.
  The compounds of chloric acid are easily recognised, by yielding,
when heated, oxygen and a metallic  chloride ; thus the chlorate of
potash is  used in the preparation of oxygen (p. 244), CI 0,-l-K.O.
giving Cl.K. and 60.  When mixed with sulphur and rubbed in a
warm mortar, they explode, and if thrown upon an ignited  coal, they
deflagrate with violence.
  The chlorate  of potash is of very great commercial importance,
from its utility in making matches, and is the source from whence
the chemist obtains the remaining compounds of  chlorine and ox-

  The constitution and equivalent numbers of  chloric acid are as
follows :  by weight,

       Chlorine, 46*95     One equivalent,  =442*6 or 35*4
       Oxygen,  53*05     Five equivalents, =500*0 or 40*0
                i0(HXF                      942*6   7;V4

  Its formula is  Cl.O , and, like the nitric acid, which it resembles m
so many other properties, it consists of five volumes of oxyoen uni-
ted to two of the other element.
  Chlorous .hid. — When chlorate of  potash in fine powder is decom-
posed by moderately strong sulphuric acid, the  chloric acid, at the
moment of being set free, breaks up  into two other compounds, one
containing more, and the  other less oxygen,  the former  being the
chlorous,  and the latter the perchloric  acid, 3C1.0,  givino- 2(C1.
04) and C1.07.  This process must be  conducted very cautiously, and
the retort  warmed very gently in a water bath.  The  chlorous acid
may be collected over mercury, or, from its great density, like chlo-
rine, in a  dry jar ; there remains in the retort  a mixture of bisul-
phate  and  of perchlorate of potash.
  This acid gas  is of a rich yellowish-green colour, and an aromatic
odour ; it  is rapidly absorbed by  water ; it bleaches strongly, and is
a powerful oxidizing agent, its elements separating from the slightest
causes,  if it be  heated above 212 , it explodes with a flash of light;
phosphorus immersed in it takes fire  spontaneously, and burns brill-
iantly in the mixture of chlorine and  oxygen which results from its
decomposition.   This may be very  well  shown by placing some\
crystals of chlorate of  potash  and  some phosphorus together, at
                             Q Q. 
306
PERCHLORIC  ACID.
the bottom of a tall glass  filled with water, and conducting to the
mixture, by means of a long glass funnel, some oil of  vitriol; the
phosphorus burns in each bubble of chlorous acid gas which forms,
and a brilliant combustion  under water results.
   When this gas is decomposed, 100 volumes produce 150, of which
50 are chlorine and 100 oxygen: its specific gravity may therefore
be calculated to be 2337-T).
   The chlorous acid combines with  bases to form salts, chlorites,
which possess bleaching properties, but are not of much importance,
as they do not enter into practical use.
  Perchloric Acid.  This acid is formed in the process for obtaining
chlorous acid, as already described, and is obtained by washing the
saline residue with cold water.  The bisulphate of potash readily
dissolves, leaving behind the perchlorate of potash, which is but
sparingly soluble  therein;  this may then be  dissolved in boiling
water, from which it crystallizes as the solution cools.   When the
object is only the preparation of perchloric acid, and not  of chlorous
acid, the process becomes easier by heating  chlorate of potash with
dilute nitric acid ; the elements of the chlorous acid are then sep-
arated, merely mixed together, and the  explosions and  sputtering
which occur with sulphuric acid are avoided.
  In the process of obtaining oxygen from chlorate of potash, there
occurs a period  at which it is necessary to elevate the temperature
very much in order to  keep up the  evolution  of  gas ; this arises
from the  salt being at first decomposed  into  oxygen, chloride of
potassium, and perchlorate of potash, 3(K.O.C1.0,) giving 2(C1.K.)
and K.O.C1.07, while 80. are evolved as  gas.   This is exactly half
of the oxygen which the salt contains.  If the saline mass then re-
maining be washed with a small quantity of water, the chloride of
potassium dissolves, and the perchlorate of potash  remains behind.
  Perchloric acid may be prepared from  this potash salt by mixing
it in a retort with half its  weight of oil of vitriol, and as much wa-
ter, and  distilling ; the  acid passes over with the water.  If it be
distilled with an  excess of oil of vitriol, it  may be obtained free from
water, and is then a white crystalline mass, very deliquescent, and
evolving great heat when mixed with water.  In this process, how-
ever, a great part  of the acid is decomposed.
  The perchloric  acid is the most stable  compound of chlorine and
oxygen.   It is not decomposed by muriatic acid, by which the chlo-
ric acid is immediately decomposed, a mixture of chlorous acid and
chlorine being evolved ; Cl.O, and Cl.H. giving H.O. and a  mixture
of C1.04 with CI., which was described by Sir Humphrey Davy as a
peculiar  gas, Euchlorine.  By this means the salts of perchloric and
of chloric acid may be distinguished.   It is not decomposed by al-
cohol, nor has it any spontaneous action on organic bodies.   It is
well characterized by the very sparing solubility of its potash salt,
whence it has been employed as a reagent to detect that alkali.
  The constitution and equivalent numbers of perchloric acid areas
follows:

      Chlorine,  38*74     One equivalent,   =442*6 or 35*4
      Oxygen,   61*26     Seven equivalents, =700*0 or 56*0
              100*00                       -u^Tq    9171 
CHLORIDE  OF  HYDROGEN.
307
               Compound of Chlorine and Hydrogen.
   This compound  exists naturally as a  gas, of which a solution in
 water has been known since a very early period in chemistry under
 the names of spirit of salt, marine acid,  muriatic acid, hydrochloric
 acid, and, more properly,  chloride of hydrogen.  In speaking of it
 under ordinary circumstances, I shall use the common names of li-
 quid or gaseous muriatic  acid, according as it is  free or combined
 with water; but in cases where its functions in combination are dis-
 cussed, 1 shall term it chloride of hydrogen.
   To prepare the gaseous muriatic acid, a small quantity of the com
 mercial  spirit of salt may be placed in  a flask  or retort  connected
 with the  mercurial pneumatic trough, and the gas, which passes off
 on the application of heat, collected.  It may also be prepared by
 the action of oil of vitriol on common salt; water being decomposed,
 its oxygen unites with the sodium, forming soda, which combines
 with the  sulphuric acid, while its hydrogen, uniting with the chlo
 rine, produces the chloride of hydrogen, which is given off as a gas;
 the reaction may be thus expressed: S.03H.O. and Na.Cl.  give  S.
 03Na.O. and H.C1.
   This gas may also be formed by putting together chlorine and hy-
 drogen  in equal  volumes.  Even  in diffuse  light  they combine
 completely  in some hours, but in the  direct  sunshine  the union
 is instant  and explosive.   The mixture may also be fired by the ta-
 per or by the electric spark ; the  colour of the chlorine disappears,
 and the resulting  muriatic acid gas occupies  the  same volume  as
 its ingredients.  In almost all  cases of the action of chlorine on or-
 ganic matters, this substance is also formed; indeed, the agency of
 chlorine in bleaching, and in decomposing  organic compounds,  ap-
 pears generally to result  from its disposition  to unite with hydro-
 gen.
   The chloride of hydrogen is a colourless and invisible gas.  When
 completely dry it  has no action on vegetable colours, but if a trace
 of moisture be present it  reddens litmus  paper, and restores the
 colour of turmeric paper that has been browned by an alkali ; hence
 it is generally  looked upon as a powerful acid.   When mixed with
 damp air it forms heavy white  fumes by uniting with  the wa-
 tery vapour, and condensing in minute drops of liquid acid.  It may
 be liquefied by great pressure.  It cannot be breathed, but does not
 produce anything  like the  suffocating effects of chlorine.
   When muriatic  acid gas is put  in contact with a metallic oxide,
 both are decomposed, a metallic chloride and water being produced;
 thus Cu.O. and H.C1. give Cu.Cl. and H.O.  If any of the  more oxi-
 dable metals, as iron, zinc, or potassium, be heated in a current of
 the pas, it is decomposed, a metallic chloride being formed  and hy-
 drogen gas evolved.  This occurs, also, when these metals  are im-
mersed in the liquid acid ; a copious effervescence is produced  by
the escape of hydrogen, and the water holds a chloride of the metal
in solution.  In this way muriatic acid may be proved to  consist of
equal volumes of hydrogen and chlorine united without condensa-
tion.   Its specific gravity is, by theory, 
308      PREPARATION  AND  PROPERTIES  OF
            One volume of chlorine.......=24700
            One volume of hydrogen  .......=  68 8
            give two volumes of muriatic acid  ....   =2538 8
            of which one weighs, therefore......1269 4

Its constitution and equivalent numbers are therefore,

        Chlorine,   97*26    One equivalent,   =442*6 or 35*4
        Hydrogen,   2*74    One equivalent,   =  12 5 or   1*0
                   100*00                          455*1    3bH

   This gas is distinguished  by its great affinity  for water.   If a jar
of it be opened under water, this fluid rushes in, as if it were into a
vacuum.   If a fragment of ice be introduced into a bell glass of the
gas, over  mercury,  the ice  instantly melts, and the  mercury rises
in the  tube, the  gas being  totally absorbed.   The solution  of  the
gas in water is  one of the most valuable  agents in  chemical  re-
search.
  To prepare liquid muriatic acid in the  laboratory, chloride of sodium is to be in-
troduced into a glass globe, placed  in a sand-bath on the furnace, and then an equal
weight of sulphuric acid and water, mixed together, are to be introduced by the  fun-
nel : the decomposition proceeds as already explained, and the gas evolved passes
»y the tube into the first of a range of three-necked bottles, as in the figure.  Eai*..
bottle is about half full of water.   When that in the first has become completely sat-
urated with the gas, this passes into  the second, and when  it has been saturated,
into the third.  The vertical tube in the central neck of each  bottle is a safety-tube,
the action of which is as follows.   If a sudden  condensation occurred in the first
bottle, the acid in the second might, by  the  greater pressure on its surface, be
forced back into it; but, before it can rise so high as to pass through the connecting
tube, the external air enters by the safety-tube, being driven  in by the difference of
pressure inside and outside, and thus restores the equilibrium.  Pure muriatic acid
may be much more conveniently prepared for laboratory use  by rectifying the spir-
its of salt of commerce.  When this is placed in  a distilling apparatus, arranged as
that figured in p. 278, and  about one  fourth as much water  is introduced into the
receiver to condense the quantity of gas which  is first expelled, the distillation may
be carried on until the retort is nearly empty,  and an acid so obtained completely
pure, and of a very convenient strength for the general range of applications.
  The manufacture of this acid is carried on on  a very large scale more generally
with a view to the extraction of the alkali from the residual sulphate of soda than for
the sake of the muriatic acid, the great difficulty  in  a soda factory being how to get rid
of the muriatic acid which is produced.  When  the object is. however, to prepare the 
MURIATIC  ACID.
309
liquid acid, precisely the same apparatus is employed as for the manufacture of nitric
acid, which has been already  figured and described (p. 278), the cylinders being
somewhat larger, as from four  to five cwts. of common  salt are  generally decom-
posed in each cylinder at a charge ; the upper part of the cylinder  is generally, both
in  this operation and in the making of nitric acid, protected from  the too corrosive
action of the  acid vapours by being lined  internally with thin fire-tiles, and the
heads e e in the figure are very frequently constructed, not of metal, but of  free-
stone or of granite.   In the decomposition of the salt upon this large scale,  the oil
of  vitriol is employed of the strength to which it is brought in the chambers, without
concentration, and in such  quantity that for each equivalent  of chloride of sodium
an equivalent  of real sulphuric acid is employed.   The strongest liquid muriatic
acid, thus prepared, possesses a specific gravity of 1-211.  In order to obtain water
fully saturated with the gas, it must be kept near the freezing  point  by artificial
cold ; it then absorbs 480 times its volume, and increases in bulk by about one fifth.
Its constitution is quite definite, for in this state it consists of H.CI.-J-6H.O., or in
numbers,

          Muriatic acid  . 40 27     One equivalent  .  =4551 or 364
          Water   .  .  .59 73     Six equivalents  .  =675 0 or 54 0
                        10000                       1130 1   Wi

  When this concentrated acid is heated, it evolves  a large quantity of gas, and
the boiling point gradually rises to  230°, at which temperature  the residual acid
distils over unchanged;  it  then has  a specific gravity of 1.094, and  consists  of
H.Cl.-j-lOH.O.. or in numbers,

     Muriatic acid  .  20 13   One equivalent   .   .  . = 4551 or  36 4
     Water   .   .  .  79 87   Sixteen equivalents  .  . =1800 0 or  144 0
                    100 00                             2255 1    1804

  Graham has found that the strong acid, when evaporated in the open air, aban-
dons a quantity of gas, while the remaining liquid becomes 1I.C1-|-12H.O.
  The metallic character of hydrogen, and the analogy  of its combinations with
those of zinc,  are completely shown by comparing the formulae of the compounds
of  oxide and chloride of hydrogen with the compounds  of oxide and chloride of zinc,
and their combinations with water.  Thus I have shown that the hydrates of oxy-
chloride of zinc are as follows :
                           Zn.Cl.+6Zn.O.
                           Zn.('l.-j-6Zn.O.-f 6Aq.
                           Zn.CI.-j-GZn.O.-j-lOAq.

and the definite states of liquid muriatic acid are

                           II.C1.+6H.O.
                           H C1.+6H.O.+ 6Aq.
                           H.Cl.-j-6H.O.-j-10Aq.

  As we proceed, other similar proofs of the electro-positive and metallic character
of  hvdrogen will be found.
  The other degrees of strength of the lquid muriatic acid are solutions in water
of  one or other of these definite compounds ; a table of them will be found in the
■ lppelldiX.
   The muriatic acid of commerce frequently contains sulphuric acid,
and  always a  trace of iron, derived from the  metal cylinders in
which it is fabricated.   Occasionally, sulphurous  acid is formed in
it  in small quantity.    These impurities are detected thus: by dilu-
ting the  muriatic acid with  water, and  adding nitrate of barytes, a
white  precipitate is  formed if sulphuric  acid  be present;  yellow
ferroprussiate  of potash indicates the existence of iron ;  while solu-
tion of protochloride of tin produces a brown precipitate of  sulphuret
of tin if sulphurous acid had been present.
   .Muriatic acid is easily recognised, as a gas, by its action on moist
litmus paper, its fuming in the air, its forming with  ammonia dense 
310
NITRO-MURIATIC  ACID.
 white clouds of sal ammoniac, and in solution, by giving with nitrate
 of silver a curdy white precipitate,  which blackens on exposure to
 light, is totally insoluble in nitric acid, but dissolves easily in water
 of ammonia.
    Nitromuriatic Acid.  Aqua Regia.—When  nitric  and muriatic
 acids,  both  colourless, are  mixed together, the  mixture becomes
 deep yellow, and exhales a strong smell of chlorine and  of nitrous
 acid, H.C1. and  N.05 giving CI. and N.04, with formation of H.O.
 This decomposition, however, proceeds only so far as to saturate
 the liquid with chlorine; but  if a metal  be placed in the liquid it
 unites  with the  chlorine, and new quantities of the acid are decom-
 posed.  Thus the  nitromuriatic acid  is a  source of chlorine in a
 very concentrated  state, and  is hence employed to  dissolve gold
 and platina, which are not soluble in nitric acid, and to oxidize some
 bodies (metallic  sulphurets) which  resist the action of nitric acid.
 The name aqua regia was given to  it  from its  power of  dissolving
 gold, the ancient rex rnetallorum.
   Chloride of Sulphur.—In order to obtain this body, a quantity of sulphur is placed
 in a tubulated retort, into which a current of chlorine gas is conducted by means
                                           of the bent tube e, in the figure.
                                           The chlorine and sulphur unite to
                                           form a volatile reddish yellow li-
                                           quid, which distils over, and con-
                                           denses in the receiver /,  which
                                           must be kept very cool; anyuncon-
                                           densed gas is conducted away by
                                           the  tube /.  The chloride of sul-
                                           phur, thus obtained, has  always
                                           an excess of sulphur dissolved in
                                           it, from which it may be freed by
                                           a second distillation.  Its specific
 gravity is 1 -687.  When exposed to the air  it gives off very acrid fumes;  it boils
 at 280° ; the specific gravity of its vapour is 4686.  It consists of  one equivalent of
 chlorine united to two of sulphur, S2C1., and in contact with water, muriatic acid,
 sulphur, and hyposulphurous acid  are formed by mutual decomposition.
  It is probable that there is another chloride of sulphur consisting of one equiva-
lent of each, S.C1.
  Chlorides  of Phosphorus.—Chlorine unites with phosphorus in  two  proportions,
forming a liquid protochloride, P.C1?, and a solid perchloride, P.C15.   These may
be prepared in a simple apparatus, like that used for chloride of sulphur; but as a
more complex arrangement is necessary for examining the action of chlorine upon
many substances that will be described hereafter, I will introduce the description
 
        CHLORIDES  OF  PHOSPHORUS.--IODINE.    311

 of it here.   The chlorine is generated by liquid muriatic acid and peroxide of man-
 ganese, in  the flask a, supported on a sand-bath over the lamp; from it a bent tube
 passes to the receiver b, in which  a  quantity of watery vapour  is condensed, and
 Berves to absorb any muriatic acid gas that might escape decomposition.  The pure
 chlorine passes then through the  tube c, which is filled with fragments of fused
 chloride of calcium, which, from its great affinity for water, dries the gas completely.
 In the bulb e is contained the  substance to be acted on by the chlorine, and the
 product of  the reaction, if volatile, distils over into the receiver k, in which it conden-
 Bes ; the excess of chlorine escapes  by the tube I, and a stream of water from the
 reservoir i h retains the receiver A  at the tempeiature proper for condensation.
  The phosphorus being placed m the bulb e, takes fire on the arrival of the chlorine
 gas, and continues burning until it is all converted into  the liquid chloride which
 collects in  k.  While there is an excess of phosphorus, the protochloride is princi-
 pally formed; but after all the phosphorus has  been consumed, if the current of
 chlorine be continued, it is absorbed by  the liquid in k, which changes into the solid
 perchloridc.
  The Protochloride of Phosphorus  is obtained pure by stopping  the process before
 all the phosphorus has been consumed, and rectifying the colourless liquid  by dis-
 tilling il in a retort containing some bits of phosphorus, which bring back any per-
 chloride it might  contain  dissolved, to the state of protochloride.  This  body  is
 heavier than water, by which it is  completely decomposed, P.C13 and  3H.O. giving
 P.Oa and  3H.CI.  It is thus that  the  liquid phosphorous acid is obtained, as de-
 scribed in  p. 297.
  The Pcrchloride of Phosphorus is a white solid, volatile under 212°, and conden-
 sing in a crystalline  form.  In contact with water, it is decomposed with the evo-
 lution of great  heat, producing  phosphoric acid and muriatic acid, P.CI5 and 5H.O.
 giving P.05 and 511.0.  ; the sp. gr. of its vapour is 4788, consisting of ten volumes
 of chlorine and one of vapour of phosphorus, the eleven being condensed to six.
  There is a  Chloride  of Selenium analogous in general  properties to the chlorida
 of sulphur.

                                 Iodine.

   Iodine is found principally in sea-water, associated w.th chlorine,
 combined with sodium and magnesium.   It has beei. also discover-
 ed in the mineral kingdom, united with silver.   For the purposes of
 commerce it is always  extracted  from kelp, which  is a  semifused
 mass of saline ashes remaining after the burning of various species
 of fun (sea-weed).
   For this purpose,  the  powdered  kelp  is lixiviated in water,  to
 which it  yields about half its weight of salts.   The solution is evap-
 orated down  in an  open pan,  and when  concentrated to  a certain
 point, begins to deposite  its soda-salts, namely, common salt, car-
 bonate and sulphate of soda, which  are removed from the boiling
 liquid by means  of a shovel  pierced with holes like a  colander.
 The liquid  is  afterward run into a shallow pan to cool, in  which
 ft deposites a crop  of  crystals of chloride of potassium ;  the  same
 operations are repeated  on the mother-ley of these crystals until it
 is exhausted.  A  dense, dark-coloured liquid remains, which  con-
 tains the  iodine, in  the form, it is believed, of iodide of sodium, but
 mixed with  a  large quantity of  other  salts, and  this  is  called the
 iodine ley.
  To this ley, sulphuric acid  is  gradually added  in such quantity
as to leave the liquid very sour,  which  causes  an evolution of car-
bonic acid, sulphuretted hydrogen, and sulphurous acid gases,  with
a considerable deposition  of  sulphur.  After standing for a day or
two, the ley so  prepared is heated with peroxide of  manganese, to
separate the iodine.  This operation is conducted in a leaden retort, 
312
PREPARATION  OF  IODINE.
                                         a, of a cylindrical form,
                                         supported in a sand-bath,
                                         which  is heated  by a
                                         small  fire  below.   The
                                         retort has a large  open-
                                         ing, to which a capital,
                                         b, c, resembling the head
                                         of an  alembic,  is adapt-
                                         ed, and luted with pipe-
                                         clay.  In the capital it-
                                         self there are two  open-
                                         ings, a larger and a small-
                                         er, at b and c, closed by
                                         leaden  stoppers.  A se-
                                         ries of bottles, d, having
                                         each two openings, con-
                                         nected  together, as rep-
                                         resented  in the figure,
and with their joinings luted, are used as condensers.  The prepa-
red ley being heated to about 140° in the  retort, the manganese is
then introduced, and b c luted to a.  Iodine immediately begins to
come off, and proceeds on to the condensers, in which it is collect-
ed ; the progress  of its evolution  is watched by occasionally re-
moving the stopper at c ; and additions of sulphuric acid or man-
ganese  are made by b, if  deemed necessary.  This description of
the manufacture of iodine upon the large  scale at Glasgow is due
to Professor  Graham.
  In this operation, the peroxide of manganese will be in contact
at once with hydriodic, hydrochloric, and  sulphuric acids; but for
success, the quantity of sulphuric acid must be sufficient only to de-
compose the iodides, but  not  the chlorides.  If both were decom-
posed, the  chlorine and iodine simultaneously evolved would  unite
to form chloride of iodine, by which the iodire would be lost; but
as the chlorine  remains combined, the action becomes simoly, that
the metal of  the iodide present is oxidized by the oxide of manga-
nese, and the iodine set free ; thus, with iodide of sodium, S.03-f-
Mn.02 and Na.I. give Mn.O. . S.O?. Na.O. and I.
  Another mode of preparing iodine consists in adding to the solu-
tion containing iodide of  sodium, a solution of sulphate of copper.
in which the  copper is reduced to the state of sub-oxide  (Cu.,0.) bv
means of protosulphate of iron dissolved along with  it.   By the in-
terchange of elements, sulphate of soda is formed, and a sub-iodid*
         of copper of a very pale yellow colour, and quite insoluble
         in water, is produced, S.03+Cu20. and Na.I. giving S.O3 +
         Na.O. and Cu2I.  This last is then  decomposed by peroxide
         of manganese and sulphuric acid, as in the former process *
         in this way the  various crystallizations  described above
         may be avoided.
           Iodine exists generally in crystalline  sca.es of a bluish
         black colour and metallic lustre.  It may also be  obtained
         from solution,  in the form of oblique octohedrons with a
rhomboidal base, as in  the  figure, or in prisms.  The  density oi
 
       PROPERTIES  OF IODINE.--IODIC  ACID.    313

iodine is 4 94S ; it fuses at 225°, and boils at 347° ; but it evaporates
at the usual temperature, and more rapidly when damp than when
dry, diffusing an odour having considerable resemblance to chlorine,
but easily distinguished from it.  Iodine stains the skin of a yellow
colour, which, however, disappears in a few hours.  Its vapour is of
a splendid violet colour, which  is seen to great advantage when a
scruple or two of iodine is thrown at once upon a hot brick.   Hence
its name,  from loudnc, violet-coloured.   The vapour of iodine is
one of the heaviest  of gaseous bodies, its  density being 8707*7, ac-
cording to calculation from  its atomic weight.
  Pure water dissolves about l-7000th of its weight of iodine, and
acquires a brown colour.   In general, iodine comports  itself like
chlorine, but its affinities are much less powerful.  Iodine is soluble
in alcohol and ether, with which it forms dark reddish-brown liquors ;
solutions of iodides, too, all dissolve much iodine.
  A solution of starch forms an insoluble  compound with iodine, of
a deep blue  colour,  the production of which is an exceedingly deli-
cate test of iodine.   If the  iodine be free, starch produces at once
the blue precipitate ; but if it be in combination as a soluble iodide,
no change takes place till chlorine is added to liberate the iodine.
If more chlorine, however, be added than is necessary for that pur-
pose,  the  iodine is  withdrawn  from the starch, chloride of iodine
formed, and the blue compound destroyed.   The iodide of starch, in
water, becomes colourless when heated, but recovers its blue colour
if immediately cooled.  The soluble iodides give, with nitrate of
silver, an insoluble  iodide of silver, of a pale yellow colour, insoluble
in ammonia; with  salts of lead, an  iodide of a rich yellow  colour;
and with corrosive  sublimate, a fine scarlet iodide of mercury.
  Iodine combines  with most of the  non-metallic bodies, and with
all the metals, forming compounds which possess the closest sim-
ilarity to the analogous compounds of chlorine.  It is employed in
the laboratory for many chemical preparations, and as a test of starch
and for  several metals.

                Compounds of Iodine and Oxygen.
  Iodine appears to  combine with oxygen in three proportions, form
ing the iodous acid,  the iodic acid, and the periodic acid.   Of the con-
stitution of  the first there is nothing positively known; it  has not
been isolated, and the substances that have been supposed to contain
it may also be considered as compounds of an iodide with an iodate.
The description  of  these compounds will be  found in the  chapter
on the salts; and I  shall, therefore,  at present, only notice the other
two acids.
  Iodic  Acid.—1h\» acid  may  be very easily prepared  by boiling
iodine in fuming nitric acid  until it is all dissolved, and then distil
linir off the excess of acid;  the  iodic acid remains as a white crys
talline mass, which  deliquesces in the air.  If the quantity of iodine
be laro-e, this process would occupy a very long time ; and  a much
shorte°r, though more complex method is the following:  The iodine
being  diffused through water, a  current of chlorine is passed through
it until all iodine is dissolved ;  the  acid liquor so obtained  is to be
neutralized by carbonate of soda, by which a quantity of iodine is 
 314  PROPERTIES  OF  IODIC  ACID.---P ERIODIC  ACID.

 precipitated ;  the chlorine is then passed through until this iodine
 disappears, and then more carbonate of soda added, and this alter-
 nation continued  until the addition of the carbonate of soda produces
 no deposite of iodine; the solution contains then iodate of soda and
 chloride of sodium, generated by the decomposition of the soda by
 the chloride of iodine first formed.  Thus 5C1. and I. produce I.C15,
 which, with GNa.O., give 5Na.Cl. and Na.O.+I.03.   This solution is
 then mixed with a solution of a salt of barytes, and iodate of barytes
 precipitates, which may be decomposed by boiling it for some time
 with one fourth its weight of oil of  vitriol and  \\  times its weight
 of water ;  the  sulphate of barytes may be then separated by the fil-
 ter, and the solution of iodic acid  evaporated gently to dryness.
   Iodic acid is very soluble in water; from a  strong solution it crys
 tallizes in  rhombic plates and octohedrons.   When  heated strongly,
 it separates into  iodine and  oxygen.  It first  reddens, and then
 bleaches litmus paper.   It acts as powerfully as nitric acid in oxi-
 dizing the metals.  When mixed with solution  of  sulphurous acid,
 water and sulphuric acid  are  formed, and iodine is  set free ; with
 sulphuretted hydrogen it gives water and iodide of sulphur.   By an
 excess of these agents, the iodine is  finally converted into iodide of
 hydrogen.  By these means the iodic  acid may be recognised, and
 also by its peculiar action  upon  morphia,  which  it  decomposes, io-
 dine beino* set free.   This is more valuable as a character of mor-
 phia than of iodic acid.
  The salts of iodic acid resemble the chlorates in most  respects,
 and, like them, when heated, separate  into  oxygen  and a metallic
 iodide.   One mode of preparing the iodide  of  potassium  of com-
 merce is founded  on this property.   Iodine is dissolved in a solution
 of potash,  and, when dried down, gives a mixture of 5K.I. and 1.05.
 K.O.   When this mass is fused, oxygen is given off in abundance,
 and ultimately pure K.I. remains.   The commercial salt prepared in
 this way has been shown by Mr. Scanlan frequently to contain iodate
 of potash, either  fradulently or accidentally, left undecomposed.
  The composition >nd equivalent numbers of the iodic acid are as
 follows,  its formula being 1.03:

     Iodine,   75*96       One equivalent,  =1579*5 or 126*6
     Oxygen,  24*04       Five equivalents, — 500-0 or  40*0
               100*00                          2079*5   1661
  Its elements are united in  the  proportion, by volume, of two vol-
umes of vapour of iodine to  five  volumes of oxygen.
  Periodic Acid, I 07— If a solution of iodate of soda be mixed with a great excess
of caustic soda, and acted upon by  a current of chlorine, a quantity of the soda is
decomposed ; its sodium combining with the chlorine, while its oxygen, being added
to the iodic acid, converts it into the periodic acid, which combines with two equiv-
alents of soda.  Thus, 2C1. acting on 3Na O. and I 05-|-Na.O., produce 2Xa.Cl. and
I.07-(-2Na.O.  On adding to the solution of this salt nitrate of silver, a basic peri-
odate of silver is produced, which, beinjr dissolved in nitric acid, gives yellow crys-
tals of neutral penodate of silver   When put in contact with water, these crystals
are decomposed, half  of the periodic acid precipitating with the whole of the oxide
of silver as the insoluble salt, I.07+2Ag.O., while the other half of the acid remains
in solution quite pure, and by evaporation may be obtained as a white crystallized
mass.
  This acid is more  stable than the iodic acid; it resists a  higher temperature 
         II YURI O DIC  ACID, ITS  PREPARATION.     3i0

 without decomposition.  All its  important characters may be inferred from the
 method of preparation.
  Its composition and equivalent numbers  are,
        Iodine,  69 31        One equivalent,   =1579 5 or 126 6
        Oxygen, 30 69        Seven  equivalents, = 7000 or 56 0
               100 00                        "22795   182~6

        Compound of Iodine and Hydrogen.  Hydriodic Acid.
   There is but one compound of iodine with hydrogen :  this exists
 under ordinary temperatures and pressure as a colourless  gas, which
 may be best generated in the  following manner: Some iodine and
 small fragments of phosphorus are to be put together at the bottom
 of a glass tube, then covered with pounded glass, and gently heated,
 so as to produce combination.  Iodide of phosphorus is thus formed.
 If a little  water be now poured on the pounded gjy^
 glass, it filters through to the bottom, and there,
 acting violently on the iodide of phosphorus, is
 decomposed; from P.i. and H.O. there are pro-
 duced P.O. and H.I.   To the mouth of the tube
 may be adapted, by a cork, a smaller tube, bent
 as in the figure, and the hydriodic  acid gas issu-
 ing from it may be collected.   This gas is obtain-
 ed by the  method of displacement, as  has been
 described for chlorine (p. 302) ; and as it  fumes
 like muriatic acid in  contact with the  air, it can
 easily be recognised when the bottle is full.

  The specific gravity of this gas is 4385, produced by
          One volume of vapour of iodine.....=8701 0
          One volume of hydrogen........=  68 8
        united without condensation........8761 8
        and one volume weighing, therefore.....4384 9
  To obtain hydriodic acid dissolved in water, the simplest process
 is to act on iodine, diffused through water, by sulphuretted hydrogen
 gas.   The  iodine  combines with the hydrogen, and the  sulphur is
 set free.  When the iodine  has all  disappeared, the  liquor should be
 well boiled, to drive  off the excess of sulphuretted hydrogen, and
 then filtered ; the  liquid hydriodic  acid may be evaporated to a sp.
 gr. of 1*700 :  it is then in its strongest form, and may be distilled
 unaltered.   Liquid hydriodic acid  reddens litmus  paper  strongly;
 it  dissolves iodine in large quantity;  it is decomposed  by all the
 oxidable metals, and even by mercury ; and hence the gaseous acid
 cannot be collected  over mercury. Exposed to the  air,  it rapidhr
 absorbs oxygen, water being formed, and iodine being set free.  It is
 decomposed by sulphuric acid, sulphurous acid and iodine beino-pro-
 duced ; also by nitric acid and by chlorine.
  Hydriodic acid may also be obtained by acting on iodide of barium
with dilute sulphuric acid.
  Its composition  and equivalent numbers are as follows  :

     Iodine,    99*22      One equivalent, = 1579*5 or  126-6
     Hydrogen,  0*78      One equivalent, =  12*5 or    1*0
               100*00                        1592*0   127*6
 
316         IODO-PH O S PH URE T   OF  HYDROGEN.
    A solution of hydriodic acid or of a metal produces,  with nitrate
 of silver, a curdy pale yellow precipitate, which is  insoluble in acids
 and in water of ammonia;  by this character the iodides are  distin-
 guished  from the  chlorides, even without the  action of  starch upon
 the iodine when set free.
   Iodine  and sulphur may be melted  together in equivalent proportions, and, on
 cooling, form a steel-gray crystalline mass, iodide  of sulphur, which  is decomposed
 giadually by exposure to the air, and appears to  be rather a  mixture than a true
 compound of its elements.
   When iodine and  phosphorus  are warmed together very gently,  they combine,
 evolving considerable heat, and forming iodides of phosphorus, the constitution of
 which depends on the proportions used;  there appears to be at least three: the
 first fuses  at 212°, is orange coloured, and gives,  when  decomposed by water, hy-
 driodic  and hypophosphorous acids ; its composition is therefore P I. : the second is
 gray ; it fuses at 84°, and gives, with water, hydriodic and phosphorous acids; its
 formula is hence P.I3.   The third, which produces, when decomposed by water,
 hydriodic acid and phosphoric acid, consists of P.I5, is  black, and melts at 114°.
   Hydriodic acid combines with  phosphuretted hydrogen, forming  a  white  solid
 compound, the  constitution of which is of considerable interest.  It  cannot be pre-
 pared directly, as the gases are without  action on  each other except when in their
 nascent form.   It is best prepared by introducing eight parts of iodine, two of phos-
 phorus,  and one of water, into a retort, mixed with some coarsely-powdered glass;
 to the neck of the retort is adapted a wide glass tube with a cork, through which a
 small tube passes and dips into some  water.   On applying heat, the phosphorus
 and iodine unite, and the iodide of phosphorus being  instantly decomposed by the
 water,  hydriodic acid and  hypophosphorous acid  are  produced, which last is re-
 solved,  by contact with the water at that  temperature, into phosphorous acid and
 phosphuretted hydrogen.  This last immediately unites with the hydriodic acid, and
 the compound formed condenses in the neck of the retort in well shaped crystals,
 which, by a proper management of the heat, may be driven into the wide glass tube
 to be preserved.  The excess of  hydriodic acid gas is conducted off by the small
 tube, and condensed in the  water.
   This  body was supposed to crystallize in cubes, and to be isomorphous with hy-
 driodate of ammonia, to which this formula, in  one way, might  assimilate it,
 H.I.-fP.Hs corresponding to H.I.+N.H3, the difference being  only that phosphorus
 replaced nitrogen.  It will, however, be shown fully, in the division on organic
 chemistry,  that ammonia is not mere nitruret of hydrogen, N.H3, but  that it con-
 tains amidogene (N H2), being amidide of hydrogen, Ad.H.  It has been also shown
 that the crystals of the body H.I.-j-P.H3 are not  cubes, but belong to a rhombic
 system.  When I come to describe the compounds of mercury, I shall show that
 there exist similar bodies containing phosphuret of mercury and nitruret of mercury,
 and  that the constitution of phosphuretted hydrogen  may, with great reason, he
 supposed to be, not P.H3, but that a quantity of phosphorus equal to one third of
 its ordinary atomic weight unites with an equivalent of hydrogen, its formula being
 j.H , and the commonly  received equivalent of phosphuretted hydrogen being in
 reality three equivalents, =3 j.H.   I therefore consider the compound which I have
just described as having for its true constitution H.I.+3J.H., as there will be here-

 after described the bodies Hg.Ol.-f 3.?.,Hg,  and  2Hg.Cl.+3.£.Hg. :  the equiva-
 lent of nitrogen being capable of the same subdivision by three  3
   This  Hydrwdate of Phosphuretted Hydrogen  is decomposed by  water, hydriodic
 acid and phosphuretted hydrogen being given off, the last in the  B variety.  But if
 m 2l1n°fl      h.  "^ .- sPrinTk,ed on the  salt> the gas is evolved in its spontane-
 ously inflammable condition.  It burns when heated in air, but, in a dry tube con-
 taming  no oxygen  it may be sublimed from place to place  unaltered.
   Chlorides of Iodint—l have  shown that chlorine and  iodine unite in three pro-
 portions, forming bodies  having the  formulae I.-fCl,  I.+3C1   and I 4-5C1   By
 Z^t ZTLa\ I hSt  3nd STmd are decomposed, prodTcing muriatic and  iodic
 acids, and iodine becoming free.  The  third, which was lonf ago discovered by
Humphrey  Davy, gives muriatic  and iodic acids without Reparation of iodine

SS^bs1ire\dy "OS1"8 °* " ^ empl0yed t0 °btai» the iodlc and Periodic 
PROPERTIES  OF BROMINE.
317
                          Of Bromine.
  This subst ance, which is intermediate in almost all chemical prop-
erties to chlorine and iodine, exists associated with those bodies in
sea-water, in many varieties of sea-weeds, and in some of the brine-
springs belonging to the deposites of rock-salt in the earth.   In these
cases it is generally combined  with sodium  or with  magnesium,
forming very soluble salts, which remain behind when the common
salt crystallizes  out  by evaporation from sea-water.  When a cur-
rent  of chlorine gas is passed through the mother liquor so obtained,
which is called bittern, the  bromine is set free, and tinges the solution
yellow.   On agitating this liquor with some ether, the bromine  is
completely taken up by it, and an ethereal solution of bromine, of a
fine hyacinth-red colour, is produced ;  when this is acted on by pot-
ash, there is formed a mixture of bromide of potassium andbromate
of potash, which by fusion gives off oxygen,  and pure bromide of
potassium remains;  this is mixed with peroxide of manganese and
sulphuric acid, and precisely as  in the preparation of chlorine or of
iodine, the bromine is set free and may be distilled over.  It is ne-
cessary to condense the bromine with great care, and to receive it
in water, to the  bottom of which it sinks ; the reaction that occurs
is that 2S.03, Mn.02, and  K.Br,  produce (S.03. Mn.O-r-K.O. . S.03)
and  Br.
   Bromine  is a  liquid at  ordinary temperatures, but at 4°  it solidi-
fies ; it is deep red by transmitted, but black by reflected light; it is
much heavier than water, its specific gravity being 2*97; its odour
is like that of  chlorine, but much more disagreeable, whence its
name (from Ilpw/^oc).  It  is very volatile, boiling at 116  ;  but even
at common temperatures it forms copious fumes, which  have the
same orange-red colour as those of nitrous acid ;  the specific grav
ity of its vapour is 5*393; it does not conduct  electricity; it must
be preserved under  water, as otherwise the quantity  of vapour it
would  form might burst the vessel containing it.   It dissolves spa-
ringly  in water, but copiously in alcohol and ether.  A taper  is ex-
tinguished by its vapour, but not immediately, burning for a moment
with a green flame and much smoke.  Some of the metals in fine
powder or leaf burn spontaneously in its vapour, as in chlorine;  a
drop of liquid bromine, put in contact with a globule of potassium,
unites  with it  explosively and with brilliant ignition.  It  bleaches
vegetable colours, but leaves itself a yellowish stain,  less intense
than that of iodine ; it is  poisonous.
   Bromine unites  with water, forming a crystalline hydrate like that
of chlorine.
   With starch, bromine produces a fine yellow colour, which is not
intense if the solution be  very much diluted.
   Bromine  is easily recognised by the peculiar  colour and odour
of its vapour, which can  only be confounded with that of nitrous
and  hyponitrous acid, from which its other characters completely
separate  it. A solution containing bromine or  a metallic bromide
gives, with nitrate of silver, a white, curdy precipitate, insoluble in
nitric acid, but  dissolved by ammonia.  This precipitate  is distin-
guished  from the  chloride of silver by giving vapours of bromine
when heated with a little chlorine water 
318     B R O M 1 C  A C I D.--H YDROBROMIC  ACID.
    The  equivalent  numbers of bromine are  978*2 on the  oxygen
 scale, and 78*4, hydrogen being unity.
    Bromic Acid.—There is known only  one compound of bromine
 and oxygen, the bromic acid, the history of which is still ve,y im-
 perfect.   When bromine is dissolved in a solution of potash, bro-
 mide  of potassium and  bromate of  potash are formed,  6Br.  and
 6K.O. giving 5K.Br. and Br.Oj-f-K.O.  On adding  a  solution of a
 salt of barytes to the liquor so  obtained, bromate of barytes is pre-
 cipitated, and  this may be  decomposed by sulphuric acid, which
 forms sulphate of barytes, leaving the bromic acid in  solution.
    The bromic acid has not been obtained solid ;  it  is still more
 easily decomposed  by deoxidizing agents than the chloric acid ; thus
 the sulphurous acid and the phosphorous acid liberate bromine.  The
 same effect is  produced by sulphuretted hydrogen.   Its salts have
 not been much examined,  but appear to resemble the  chlorates and
 iodates.
    Its  formula  is Br.03, its composition by weight and equivalent
 numbers being,

       Bromine, 66*18      One equivalent,  =978*2 or 78*40
       Oxygen,  33*82      Five equivalents, =500*0 or 40*00
                100*00                         1478*2  T18-40
   These elements  are  united by volume in the ratio of two vol-
 umes of bromine vapour to five  volumes of oxygen.
   Hydrobromic Acid.—The processes for obtaining the bromide of
 hydrogen are precisely the  same as those described  for preparing
 hydriodic acid in the liquid or in the gaseous form, to  which I shall
 therefore  refer (p.  315), bromine being substituted  for iodine in
 every case.   This gas is colourless; it  is rapidly absorbed by wa
 ter, the  solution reacting  acid ; it is  not decomposed by oxygen,
 nor does bromine decompose water, so that  it stands between iodine
 and chlorine  in that respect.  It resembles muriatic acid in almost
 all its reactions, but is at once distinguished  from it by  evolving
 bromine on contact with chlorine  or nitric  acid.  If bromide of po-
 tassium  be acted on by oil of vitriol, the result is partly as occurs
 with a chloride, water being decomposed  and hydrobromic acid
 evolved, and partly  as occurs with an iodide, bromine  and  sulphur-
 ous acid being  evolved together ; hence  hydrobromic acid cannot
 be  prepared pure in that way.
  The sp.  gr. of hydrobromic acid gas is 2731, being produced by
               One volume of bromine-vapour  .  . . 53930
               One volume of hydrogen.....68 8
             united without condensation  .... 5461 8
             and hence one volume weighs .... 2730 9

ab^S Br°m?ie °f SulPhur is a heavy reddish liquid, like chloride of sulphur, prob-
  There are two Bromides of Phosphorus, one liquid, P.Br3, and the other solid,
P.Brs, which present complete analogy with the chlorides of  phosphorus. Neither
of these bodies presents  particular interest
nJhA bTidf °i hfydro*^n unites with phosphuretted hydrogen, forming a com-
pound similar to that already noticed, containing hydriodic acid   It is sufficient to
mix the two gases together over mercury • a dense white cloud forms, which con-
denses on the sides of the glass in small crystals, which appear to be cubes, but are 
OF  FLUORINE.
319
not so really.  This substance can also be formed in the indirect manner described
for the iodine compound.  It consists of an equivalent of each element, its for-
mula being Il.Br.-j-P II3, or, as I prefer to write it, for the reasons already stated,
H Br+3 J II.
  This body is volatile, and may be sublimed, provided neither oxygen  nor water
be present;  heated in oxygen, it takes fire, and with water it is instantly decom-
posed.
  The  Chloride of Bromine and the Bromides of Iodine resemble in general charac-
ters the compounds of chlorine and iodine.  The first, when decomposed by water,
produces hydrochloric and bromic acids; the latter, on the contrary, gives hydro-
bromic and iodic acids.  These bodies are not otherwise of interest

                          Of Fluorine.

  Although the existence of this body is rendered exceedingly prob-
able  by analogical reasoning, and recent experiments have  gone
very  far in establishing its  distinctive characters, yet it cannot
be prepared in an  isolated  form,  or  exhibited like  all the simple
bodies as yet described; for such  is the intensity and variety  of its
affinities, that no sooner is it liberated from combination with one
substance, than it enters into union with some other, attacking the
materials  of which the apparatus used  may be constructed.  The
most  successful  experiments made for examining it in its isolated
form  are due to two talented Irish chemists, the ^Messrs. Knox.
  The only substances on which fluorine is incapable of acting be-
ing such as already are fully  saturated  with  it, .Messrs. Knox had
vessels constructed of fluor spar  (fluoride of calcium), which were
filled  with pure dry chlorine gas.   Into these vessels was then in-
troduced fluoride of mercury, and the whole carefully warmed.  The
chlorine decomposed the  fluoride of mercury, forming chloride  of
mercury,  and  the fluorine  was disengag-ed, Hp-.F.  and CI. ffivinor
Hg.Cl. and F.   There was  in  this way obtained a colourless gas,
which acted with violence on the fragments of metallic foils, that
by means  of a very ingenious arrangement were submitted  to its
action.  The small quantity of material on which the experiments
were  conducted  did not allow of the metallic compounds so formed
being analyzed ; and  the only doubt that can  exist of the  isolation
of fluorine in this process is that,  as it was liberated, it might have
combined with the excess of chlorine  present, and that the colour-
less gas may have been chloride of fluorine, and not the mere fluo
rine itself.
   The specific gravity of  gaseous fluorine,  calculated from the
analogy of its compounds to those of chlorine, is 1289 ; its equivalent
number is  233*8, or 18.7.
   Fluorine does not combine with oxygen.
  The most important compound of fluorine  that is known is the
Fluoride of Hydrogen, or  Hydrofluoric Acid.  To prepare it, pure
fluor  spar, which consists of fluorine  and calcium, is reduced  to
powder, and distilled in a leaden retort with twice its weight of the
strongest  oil of vitriol.  The receiver must also be of lead, and be
kept cool  by ice.  An acid liquor distils over, of an excessively suf-
focating odour, and so intensely corrosive, that a drop let  fall upon
the hand produces a sore very difficult  to heal.   This liquid is hy-
drolluoric  acid, the reaction be ?ig that H.O.. S03 and  Ca.F. give
Ca.O.. -S.Oj and H.F.   Sulphate  f lime  remains in the retort. 
320
HYDROFLUORIC  ACID.
  The hydrofluoric acid, which is thus  obtained  in an  anhydrous
form, is very volatile, boiling at 60 \  It  is heavier than  water, and
becomes still more so when diluted to a certain degree.   It dissolves
the more oxidable metals rapidly with the escape  of hydrogen gas,
and the formation of a metallic fluoride.   The only metals which it
does not act upon are gold, platina, silver, and lead.  There must
be no solder about the leaden vessels in which the acid  is kept, as
it is acted on very violently.  It is dangerous to  have much to do
with the anhydrous acid, from its corrosive power; and as a dilute
acid answers for all practical purposes, a  quantity of water is gener-
ally put into the receiver, into which  the acid is distilled.
  The most remarkable property of hydrofluoric  acid is its action
upon  glass,  which it  corrodes and dissolves.   The glass contains
silica, which the hydrofluoric decomposes, Si.03 and 3H.F. producing
3H.O'. and Si.F3.   This fluoride of silicon is a gas, decomposed by
water in a way that will  be soon described.  Patterns  or designs
may therefore'be  etched upon glass by  means of this hydrofluoric
acid.   There are two modes in which this  operation  may be  con-
ducted:  1st, by the liquid acid ; 2d, by the acid in vapour.  For the
first, the glass  plate being covered with a  uniform coating of wax,
the design is traced on it with the point of a needle or graving tool,
taking care  that the surface of the glass  shall be laid bare through-
out the whole extent  of each line ; a rim of wax being then formed
round the edge of the plate, the liquid acid, the strength of which
must be regulated by the depth of engraving required, is poured on
the plate to the depth of two  or three lines, and left for a time de-
pendant on  the judgment of the operator.  When it has remained
long enough, the remaining acid is poured off, and the wax cleared
away.  The etched portions  of  the  glass are equally transparent
with the others, and the design is therefore indistinct except in cer-
tain incidences of the light.  A glass plate so prepared may be used
as a copper plate to print from, but the risk of breaking is too great
to allow of  its  introduction into practice.
   To etch by the second mode, the plate of glass is prepared exactly
as described for the first, except that there need  not be any raised
edge.   A flat leaden basin, of the size of the plate, is used to hold
the mixture of powdered fluor spar and  oil  of vitriol,  and the glass
plate is laid upon it,  with  the waxed side  down; the  basin  is then
heated =o gently as not to melt  the wax or injure the accuracy of
the design ;  the hydrofluoric  acid, which rises in vapour, acts upon
the  surface of glass  exposed,  and  decomposes the silica, forming
fluoride of silicon; but a sufficient quantity of watery vapour rises
to decompose  this substance, and a quantity of silica is regenerated
and deposited upon the corroded surface, giving it  a rough and white
appearance, so as to be easily visible in every direction.   When the
action has continued long enough, the  plate is removed from the
basin, and the wax cleared offby means of some spirits  of turpentine.
Other uses of the hydrofluoric acid, such as in mineral analysis, will
be described hereafter.
   The composition and equivalent numbers of the hydrofluoric acid
tire as follows: 
OF  SILICON.
321
      Fluorine,   94*93     One equivalent,  =233*8 or 18*7
      Hydrogen,   5*07     One equivalent,  =  12*5 or   1*0
                TOO-OO                      246*3    19*7
  There arc no other combinations known of fluorine with any of the simple bodies
as yet described, except sulphur and phosphorus: these are dense volatile liquids.
The Fluoride of J'/msphoras, when decomposed by water, produces hydrofluoric acid
and phosphorous acid ;  it is, therefore, P.l-Y When heated in the air, it burns, but
the product of the combustion has not been examined.

                            Of Silicon.

  This substance  is one of the most extensively distributed of the
undecomposed bodies, constitutinir, probably, a sixth of the  total
weight of the mineral crust  of the  globe.  It never exists free, but
always in nature combined with oxygen, forming silicic acid, or, as
it is termed in popular language, the earth  silica.  Quartz, in the
state of rock and  crystallized, flints, agate,  sand, and  many other
mineral substances, are silica completely or  nearly pure, and when
combined with various metallic oxides,  it forms the great family of
silicates, which includes the majority of earthy minerals.
  It is exceedingly difficult  to deprive  silicic acid  of its oxygen ;
even by ignition with potassium it  is but imperfectly decomposed.
To  prepare silicon, therefore, a somewhat complex body is selected
to be acted on, the double fluoride  of silicon and potassium  (2Si.F3
-f-3K.F.), which is a white powder like starch, very sparingly  soluble
in water ; a quantity of this substance  is to  be mixed with nearly
its own weight  of potassium, cut into little bits,
and placed in an iron cylinder, or  in a tube  of
hard glass, which may be held, as in the figure,
over the flame  of  a spirit-lamp.  As soon as  the
bottom of the tube has been heated to  redness,
vivid ignition occurs by the decomposition, which
spreads, with little need of external heat,  through-
out the entire  mass;  when cool,  the  residual
brown  matter is to be washed carefully  with wa-
ter : fluoride of potassium dissolves, and the silicon remains behind ;
the  l2Si.F3-r- 3K.F., acted on by 6K., give  9K.F. and 2Si.   To have the
silicon quite pure, numerous precautions are  necessary, which  need
not be  detailed here.
  The  silicon so  obtained is a dull brown  powder, which, when
heated in air or in oxygen, takes  fire  and  burns, formino- silicic
acid.   If it be ignited in a closely covered vessel, it shrinks in vol-
ume, increases  very  much  in density, and  becomes insoluble in
acids or alkalies, which, in  its original  form, it would  dissolve in
with evolution of hydrogen  gas ;  it then also  cannot be made to
burn in oxygen gas ;  it burns in the vapour of sulphur and in chlo-
rine, combining with these bodies.   When  ignited with  carbonate
of putash, the silicon burns brilliantly, setting carbon free,  and form-
ing, with the oxygen  of the  carbonic acid, silicic acid, which com-
bines with the potash.   The equivalent  number  of silicon is  277*31
or 22*22, according as the oxygen or the hydrogen standard may be
adopted.
                               S s
 
322
SILICIC  ACID.
  Silicic Acid.  Silica.—This, the only  compound of  silicon  and
oxva-en,  exists in  nature completely pure, in masses constituting
quartz rock, and in crystals which belong to the rhombohedral  sys-
              tern * their ordinary form is  represented  in the mar-
              gin.  It is exceedingly hard, and,  in order to be re-
              duced to powder,  requires to be heated  first to  red-
              ness and then thrown into  a large mass of cold water.
              The piece of quartz cracks in every direction by be-
              ino- so suddenly cooled, and is then easily reduced
              to°powder in  aii agate  mortar,   it may  be obtained
              in a state  of much more minute division, by melting,
              in a platinum  crucible, a mixture of equal weights of
              carbonate of potash and of carbonate of soda, and ad-
              dino- thereto powdered flint, by small quantities  at a
time ; the silica dfssolv. s in the melted alkali, while  carbonic  acid
gas is given off.  When the alkaline silicates, so formed, are  dis-
solved m water, and  a stronger acid added, the  silicic  acid is  pre-
cipitated as  a gelatinous hydrate, which,  when completely dried,
forms a white powder, still somewhat gritty to the feel.  When the
gaseous fluoride of silicon comes into contact with water, a portion
of it  is  decomposed, fluoride of hydrogen and  silicic acid being
produced ; this last separates in the gelatinous form, but, on drying,
becomes an exceedingly fine light powder.
   Silica, even when prepared by precipitation,  feels gritty between
the teeth ; when in mass, it is exceedingly hard, scratching glass
and the  generality of minerals.   Its specific gravity is 2*66 ;  it is
fusible o'nly  by the oxyhydrogen blowpipe, in the flame of which
it melts into a colourless glass ; when once  dried it is totally in-
soluble in water, but in its gelatinous form  it is soluble to a small ex-
tent ; hence many mineral waters contain silica,  which, being grad-
ually precipitated in  the substance of  decomposed organic matter,
produces the silicious petrifactions in which the most delicate vege-
table tissues are so beautifully preserved.   The differences between
silica in its dry and in its hydrated condition are so  great, that we
can scarcely suppose them to be satisfactorily accounted for by the
presence of a substance for  which the  silica appears to have so lit-
tle affinity.  When a dilute  alkaline solution of silica is decomposed
by an acid, there is no precipitation, the  silica remaining dissolved;
but on evaporating the  liquor to dryness, the silica assumes the in-
 soluble  condition, and remains behind when the saline constituent
is dissolved.   On the other hand, by the presence of an alkali, the
 insoluble silica is made  to assume the soluble state.
   There is some difference of opinion  as to whether the compounds
 of silica and water are truly definite, but I look  upon the existence
 of at least one, having the formula 2Si.03 + H.O., as  being certain;
 I have found the light spongy masses of silica deposited from vol-
 canic springs, and on the edges of volcanic craters from Iceland and
 Teneriffe, to have accurately that constitution.
   It  is probable that a great deal of the  silica which exists in nature
 has been originally deposited in the soluble condition.  The struc
 ture  of the agates,  chalcedony, and  many other minerals, proves
 that  they were  formed by a solution of  silica having penetrated 
CHLORIDE  OF  SILICON.
323
into a cavity in  the surrounding rock, and having then gradually
dried down or  crystallized.   It is even pretty certain that the crys-
tallized quartz  is also of this aqueous origin.
   In the arts, silica is of exceeding importance, being an essential
constituent of glass, porcelain, and every kind of delft and earthen-
ware.   For purely  chemical purposes, it  is only  of  interest from
the compound  which silicon forms with fluorine;  the hydrofluoric
acid being the  only acid capable of dissolving silica.
   The composition of silica and  its equivalent numbers  are as  fol-
lows, its formula being Si.03.

      Silicon,  48*04     One equivalent,     =277*3 or 22*22
      Oxygen,  51*96_     Three equivalents,  =300*0 or 24*00
              100*00                           5773    46~22

   Silicon does  not combine with  hydrogen nor with nitrogen : there
exists a sulphuret of silicon, which is probably  Si.S3, as when acted
on by  water it  produces soluble  silica and sulphuretted hydrogen.
  Chloride of Silicon.—This substance,  although not  itself important, is  yet inter-
esting from the fact that the method of preparing it is one by which a number of
remarkable compounds of chlorine have been discovered, and  hence it deserves to
be described.  Chlorine has no  action on silica at any temperature; but if finely-
divided silica be mixed with powdered charcoal, and  heated  to redness in a porcelain
tube, a, c, inserted in the furnace, as in the figure, and by means of a glass tube at
£»=
tached at b, a current of dry chlorine be made to stream over the ignited mixture,
decomposition ensues, the oxygen of the silica combining with the carbon to form
carbonic oxide gas, while the chlorine and silicon unite, producing the chloride of
silicon, which, being a very volatile liquid, requires to be carefully condensed ; for
this purpose, the tube cf is wrapped up in a cloth, or a paper kept constantly wetted
by a stream  of water from the reservoir e, and the  liquid produced then collects
                                            in the bottle /, while the oxide
                                            of carbon and  the excess of
                                            chlorine pass off by the tube
                                            m.   In this process the reac-
                                            tion is such, that  3C1. acting
                                            on  si.Os  and 3C,  give rise to
                                            3C.O. and Si.Cl3.
                                               The stream of dry chlorine
                                            may be very conveniently ob-
                                            tained  by the apparatus  here
                                            figured; the muriatic acid and
                                            peroxide  of manganese are
                                            placed  in the flask a, ard the
                                            gas evolved, depositing the ac-
                                            companying liquid  in  the re-
                                            ceiver  b,  passes through the
                                            tube c, which, being filled with
 
324
FLUORIDE  OF  SILICON.
fragments of recently-fused chloride of calcium, absorbs all the watery vapoui
The gas issues dry from the extremity, where it is connected with the end b of the
porcelain tube in the preceding figure.
  The chloride of silicon is a colourless liquid, denser than water; it boils at 124°;
in contact with water, it is resolved into silica and hydrochloric acid, from whence
its formula must be Si.Cl3.
  Fluoride of Silicon.—This is the most remarkable compound of
silicon after  silicic acid ; it  is a gas colourless and transparent; to
prepare it, fluor spar and sand, or glass in powder, are mixed together,
and heated in contact with oil  of  vitriol ; the mass  swells up very
much, so that a  large vessel must be  employed.  In this reaction
we  may  look upon water as being decomposed  or not, as the results
maybe explained in either way.  Thus the oxygen of the silica may
combine with the calcium, forming lime, and this with the sulphuric
acid, while the silicon unites with the fluorine of the fluor spar.  Or,
water being decomposed,  hydrofluoric acid and lime may be first
produced, and the former, reacting on the silica, may reproduce wa-
ter, and  form fluoride of  silicon.   I prefer to omit  here, as I did
when describing the  formation of chlorine, all the unnecessary the-
oretic agency of the water, and to express the decomposition as
3(S.03. H.O.) with  Si.03 and 3(Ca.F.) give 3(S.03. Ca.O.. H.O.) and
Si.F3.
  This  gas must be  collected over mercury, and in vessels dried
with  the greatest care.  When it mixes with air,  it forms dense
white fumes, which arise from the formation of silica by the watery
vapour present being decomposed.
  It is colourless and transparent ;  its  specific  gravity is 3600.  Its
composition and equivalent numbers are as follows, its formula being
Si.F3.
      Silicon,  28*32      One equivalent,    =277*3 or 22*22
      Fluorine, 71*68      Three equivalents, =701*4 or 56*22
              10(MJ0                          978*7    7844
  The hydrofluosilicic acid, or the double fluoride of hydrogen and
silicon, cannot be  obtained  free from  water, but its solution is of
considerable importance as a chemical reagent, and hence its prep-
aration requires to be described.
  The mixture  of powdered fluor spar and sand is introduced into
                          the matrass a, which  is imbedded in a sand-
                          bath,  as in the figure.  By means of the
                          siphon  funnel /, the oil of vitriol is then
                          poured in, and the gas evolved is conduct-
                          ed by the tube  to the water in  the ves-
                          sel d e.   If the tube opened into the wa-
                          ter directly, so much silica would be de-
                          posited at its orifice  as to  stop it up every
                          moment; and hence a quantity of mer-
                          cury, e,  is placed at the bottom, and the
                          end of the tube dips into it.  The gas bub-
                          ble, therefore, does  not  touch the water
                          until completely separated from the tube:
                          it escapes from the surface of the mercu-
                          ry, and then it becomes invested with a
 
OF  BORON.
325
coating of silica, like a bag of tissue paper, of which many preserve
their form for a certain time.  The passage of the gas is to be con-
tinued until the water becomes thick from the quantity of silica sep-
arated ; it is then to be poured on a fine linen cloth, and the silica
removed  by straining and pressure.  In this process, one third of
the fluoride of silicon  is  decomposed by the water forming silica
and hydrofluoric acid, which last  unites with the remaining fluoride
of silicon to form the hydrofluosilicic acid, the formula of which is
2(Si.F3)+3H.F.
  When a solution of this acid is heated, fluoride of silicon is given
off, and hydrofluoric acid remains.  Hence, although the hydrofluo-
Bilicic acid is without action upon glass, glass vessels in which it is
evaporated are corroded.
  The property of this acid which is of most interest to the chemist
is, that it forms, by acting  on the salts of potassium and barium,
compounds, fluosilicates, or  double fluorides of those metals  which
are very  sparingly soluble in water; and hence  it is used to detect
the presence of these  substances in solution.   The  precipitate  so
obtained  is remarkable for being  at first so gelatinous and transpa-
rent that it can be recognised in the liquor only by the play of colours
in the light reflected from its  upper surface.  When collected on a
filter and dried, these compounds  appear like powdered starch.  The
constitution of the  salts of the hydrofluosilicic acid resembles that
of the acid itself, the  hydrogen being  replaced by  a  metal; thus
the fliiosilicate of potassium, already described as used for preparing
silicon, is expressed by the formula 2Si.F34-3K.F.
  The composition  of hydrofluosilicic acid is easily known from that
of the  hydrofluoric  acid and fluoride of silicon.   Its equivalent num-
ber is 2696*4 or 216*2.

                           Of Boron.
  The history of this substance presents a very close analogy with
that of silicon.  It was first obtained by decomposing boracic acid by
galvanism,  but is best prepared by acting on the fluoborate of pot-
ash by metallic potassium, exactly as has been described under  the
head of silicon.   That salt  consists of fluoride  of  boron united to
fluoride of potassium ;  by the reaction, all the fluorine passes to  the
potassium, and the boron is  set free.
  Boron  is a dark olive substance, which does not  conduct electri-
city.   It  is insoluble in water and  all other neutral fluids.   When
heated to 600 in the air or oxygen, it takes fire, and burning, forms
boracic acid ; the same effect is produced by boiling with nitric acid,
or by ignition with  nitrate or with carbonate of potash.
  This element is not  extensively distributed in nature, and only
found combined with oxygen, forming boracic acid.   This exists in
certain springs in India, combined with soda, and, being crystallized
in an imperfect way, was brought  into commerce under the name
of tinkal, or crude borax.  The boracic acid is also found, and in
much larger quantity, free, or combined only with a small quantity
of ammonia, in the  small volcanic lakes-or lagoons  of Tuscany.   It
accompanies the watery vapour which gushes out of fissures in  the
earth, and which contains also muriatic  acid.  The water of these 
326    BORACIC  ACI D.--C HLORIDE  OF  BORON.

lakes is evaporated, and the  boracic acid being crystallized, is im-
ported into these countries for the manufacture of borax (borate of
soda) and  other  salts.
  The boracic acid is the  only  compound of boron and  oxygen;  it
may be obtained quite pure from  the  native  acid by boiling  this
with eight parts  of water  and a little white of egg, and filtering the
solution.   On cooling  slowly,  the boracic acid crystallizes in large
brilliant  plates, soft  and  unctuous to the feel, and  of an irregular
crystalline form.  It may be also produced from borax by dissolving
it in four times  its weight of  boiling water, and  adding sulphuric
acid until  the  liquor becomes sour to  the  taste.   On cooling, the
boracic acid crystallizes ; but as it retains a little sulphuric acid  and
sulphate of soda, a second solution and crystallization is necessary
to have it  pure.
  The crystals of boracic acid, so prepared, contain water, the oxy-
gen of which is  equal to the  oxygen of  the acid; when heated, this
water passes off,  and the acid  melts ; on cooling, it forms a colourless
glass; when completely dry it is fixed, but in the presence of wa-
ter it is  carried  oft' by the vapour in great quantity.  The glacial
acid, when exposed  to the air, absorbs  water,  swells, and becomes
opaque.   The boracic  acid is much more soluble in hot than in cold
water, the crystals requiring twenty-six parts  of water  at 60', and
only three at 212J for their solution.   Alcohol dissolves boracic acid
copiously  ; and  the solution, when  set on fire, burns with a beauti-
ful green flame,  by which this body may easily be recognised.  The
boracic acid possesses but very feeble acid properties ; many of its
soluble salts possess alkaline reaction,  and all are decomposed by
the weakest acids.   It does  not  redden litmus, but gives it a port-
wine colour, and a strong solution of it browns turmeric paper like
an alkali.  At high temperatures, however, boracic acid may decom-
pose the salts of the nitric, or  even of the sulphuric acids, from the
principles  that have been already explained in the chapter on Affin-
ity (p. 169).
  The composition and equivalent numbers of boracic  acid are as
follows, its formula being B.03:

       Boron,   31*22     One  equivalent,    =136*2 or  10*9
       Oxygen,  6878     Three  equivalents, =300*0 or  24*0
               lOO-Ob                          436*2    34*9

  Boron does not combine  with hydrogen or nitrogen; its com-
pounds with sulphur and selenium are not important.
  Chloride of Boron—Boron burns  spontaneously in chlorine gas, but the best way
to prepare the compound of chlorine and boron is to  proceed as described for ma-
king chloride of silicon, substituting boracic acid for the silica.  The product is a gas,
colourless and transparent, but producing dense  white fumes in contact with damp
air, owing to its decomposition, and  the formation of boracic and hydrochloric acids.
The presence of this last in the volcanic lagoons would render it probable that by
some subterraneous  action chloride of boron is generated, and is decomposed when
mixed with the watery vapour simultaneously exhaled.  The chloride of boron  ia
rapidly absorbed and decomposed by water; its specific gravity is 4079 ; it contains
l£ times its volume  of chlorine -, its formula is B.C13.
  Fluoride of Boron.—This  substance  is prepared in exactly the
same way  as fluoride of  silicon, substituting the  boracic acid for
the silicic  acid.   It is a gas, rapidly absorbed and  decomposed by 
      GENERAL  CHARACTERS  OF  THE  METALS.  327

wnier, and generating hydrofluoboric acid, which is perfectly anal-
ogous to  the hydrofluosilicic  acid.  It hence forms dense  white
fumes when  mixed with damp air.   Its specific gravity is 2362.
  The hydrofluoboric acid is obtained by  precisely the same plan
as that described for the hydrofluosilicic acid.  The boracic acid is
deposited in crystals according as  the gas is absorbed.  If the li-
quor be evaporated without the acid deposited being removed, it is
all again  taken up and carried off as  gaseous fluoride  of boron.
The  liquid hydrofluoboric acid resembles, in the  combinations that
it forms, the hydrofluosilicic acid, and is similar to it also in con-
stitution,  its formula being 2(B.F3)-f-3H.F.
  No other compound of boron of any interest is known.

  The history of carbon involves so many considerations regarding the constitution
and properties of organic substances, that I shall postpone entering upon it until
after  the description of the metals and their salts, and other compounds with the
non-metallic bodies.  I will then commence the study of the chemistry of organic
substances  with that of their most constant ingredient, carbon.
  The compound of nitrogen with hydrogen (ammonia) has not been introduced
among those of the non-metallic bodies with each other, because all the details of
its history attach it to organic chemistry, under which head it will consequently be
found.  The hypothetical compounds of nitrogen and hydrogen (amidogene and am-
monium) will be associated with it.
  The substances hitherto described as chloride and iodide of nitrogen having been
found  to contain hydrogen, and to range themselves in an  important series of or-
ganic combinations, have not been noticed in the chapter now closed, but will be
found  in their true position hereafter.
                         CHAPTER  XII.*

OF THE GENERAL CHARACTERS OF THE METALS, AND OF THEIR COMPOUNDS
                  WITH THE NON-METALLIC BODIES.

  Although, as has been already noticed, the metals cannot be con-
sidered as forming a class of bodies, united by  such analogies of
chemical properties and laws  of  combination as would constitute a
natural family, yet in their  physical characters, and the  most prom-
inent facts of their technical history, they have so much in common
as to render a notice of the conditions in which they exist in na-
ture, the methods by which they are extracted upon the  large scale,
and the physical and chemical properties by which they are distin-
guished as a great division of the elementary bodies, necessary, be
fore proceeding to the detailed history of the individual metals.
  The metals are forty-two in number ;  their names have been al-
ready given in more than one  place (p. 150 and 189).  They reflect
lio-ht powerfully, and  hence possess what is termed metallic lustre.
If the  incident  light be plane polarized, it undergoes a  remarkable
chiinrre, produced  only by the metals and by diamond, becoming
elliptically polarized  on reflection.  The metals are characterized
very completely by their power  of conducting heat and  electricity,
in which, although they  differ  among each other, yet the worst
excels all non-metallic bodies.   Lists of their relative  conducting 
 328   GENERAL  CHARACTERS  OF  THE  METALS.

 powers in these respects have been already given (p. 92, 109,  and
 137).  By the combination of these characters, the lustre and con-
 ducting power, the metallic or non-metallic nature of a body is al-
 ways determined.
  In the other properties of the metals there is found  remarkable
 diversity ; thus in colour, although silver is purely  white, the major-
 ity of the metals are of  various shades  of bluish-white  or gray,
 while copper and titanium are reddish coloured, and gold is yellow.
 In specific gravity,  the  metals  include some of the lightest along
 with the heaviest solids that we know ;  the density of platinum beinw
 21 times, of gold 19 times, and of potassium only -^ that of water.°
  Some of the most important applications of the metals in the arts
 depend on their malleability and ductility.  Those metals are malle-
 able which admit of being rolled  or beaten out into thin leaves*
 those  being  ductile which can be drawn into wire.  Gold is  the
 most malleable of metals; gold leaf may be obtained of__J-__ of
 an inch in thickness, and is hence the only metal in which any trace
 of transparency has been found; silver, copper,  tin, rank next in
 malleability.   The most  malleable metals  are  not at all the most
 ductile ;  platinum, and even iron, can be obtained in finer wire than
 gold ; platinum wire was made  by Wollaston of 3^^^ inch  diame-
 ter ; but a metal which is not malleable  cannot be  ductile, and vice
 versa ; thus antimony, arsenic, and bismuth, the brittle metals, may
 be powdered in a mortar, but  give neither leaves nor wire. The
 texture of the metals which produces the malleable and ductile con-
 ditions, depends closely upon temperature.  Thus  zinc is malleable
 and ductile at 300'; it loses this power, but remains tough,  at 60°,
 while at 600° it becomes so brittle  that it powders as easily  as bis-
 muth. In the drawing of lead pipe, and in making most of the me-
 tallic wires, there is a peculiar  temperature required for the most
 perfect execution, by which is regulated the rapidity with which  the
 process is carried on.
  In strength and tenacity the metals differ also ; iron is the strong-
 est metal ; an iron wire of a given thickness will support a greater
 weight than a similar wire of any other metal * copoer is next to iron,
 but only about  one half so strong;  then platinum,  silver, and gold;
 tin and lead are the  weakest of  the metals.  The tenacity depends
 also  on the molecular  structure ; if the wires had been annealed, so
 as to allow of an approach to internal crystallization, the tenacity
 is often found to be  reduced to one half.
  In their relations to heat the  metals exhibit remarkable variety:
but one metal is liquid at ordinary temperatures.   All  the  metaU
are fusible, but they require for their liquefaction the greatest ranoe
of temperature which can be produced; thus mercury melts at —39°.
potassium and  sodium below the heat of  boiling water ; tin, lead.
zinc,  antimony, and  tellurium below a red  heat, and manv metals
as platinum, are infusible in the most intense heat of a blast furnace"
and yield  only to the flame of the  oxyhydrogen blowpipe,  in  the
history of each individual metal, its point of fusion  will be given, so
far as it is known.
  The majority of the metals are fixed at  the greatest heat of  our
furnaces; but mercury, zinc, cadmium, arsenic, tellurium, potassium,
and sodium may be volatilized. 
CLASSIFICATION  OF  THE  METALS.       329
  The generality of metals, when  exposed  to  the air, particularly
when damp, absorb  oxygen and form oxides; some becoming mere-
ly tarnished upon the surface, others becoming thoroughly oxidized.
Some  metals, however, as  gold, silver, platinum, palladium, and
mercury, are  not liable to this action.   Those metals which oxidize
when exposed to air, unite with oxygen at a  higher  temperature
with great rapidity,  many with actual combustion.   Thus zinc, when
heated to full redness, takes fire  and burns brilliantly with a white
flame, and the combustion of iron wire in oxygen is one of the pret-
tiest lecture  experiments.   ..Mercury also, which  does not tarnish
when exposed to oxygen at common temperatures, becomes oxi-
dized when  heated to near its boiling point,  but the oxide is resolv-
ed again at  a  red bent into oxygen and metallic mercury.
  It is owing to  their affinity for oxygen that many of the metals
decompose  water, and  one  of the  most convenient  classifications
that have been proposed for ordinary use is founded on  the fact of
the different degrees of facility with which  this decomposition pro-
ceeds.   Thus,
Potassium,
Sodium,
Lithium,
Barium,
Strontium,
Calcium,
Magnesium,
Aluminum,
Glucinum,
Thorium,
Yttrium,
Zirconium,
Lanthanum,
Cerium,
Manganese,
Iron,
Nickel,
Cobalt,
Zinc,
Cadmium,
Tin,
Chromium,
Vanadium,
Tungsten,
Molybdenum,
Osmium,
Columbium,
Titanium,
Arsenic,
Antimony,
Tellurium,
Uranium,
Copper,
Lead,
Bismuth,
Silver,
Mercury,
Cold,
Palladium,
Platinum,
Rhodium,
Iridium,
  The first class consists of metals which decompose water with
lively effervescence, even at 32°.
   The second class consists of metals which do not decompose watei
>with lively effervescence, except at about 212°, but very far below a
 red heat.
   The third class consists of metals which do not decompose water
> except at a red heat, or at common temperatures  in contact with
 strong; acids.
   The fourth class consists of metals which decompose vapour of
> water energetically at a red heat, but which do not decompose it at
 common temperature, even in contact with strong acids.
"\   The fifth class consists of metals which decompose water at a red
 >heat but very feebly, but whose oxides are not reducible to the me-
J tallic state by heat alone.


    The sixth class consists of metals whose oxides are  decomposeu
 >alone at a high temperature, and which do  not decompose water
  under any circumstances.
Tt 
 330      CLASSIFICATION  OF THE  METALS.

   This kind of classification was first proposed by Thenard, and has
 been adopted by Graham in a form differing very slightly from that
 now given.
   The following classification, although old, and founded solely on
 popular considerations,  is yet so far consonant with the simplest
 characters of the metals as to be  frequently referred to, and hence
 to be worthy of notice.
   Those metals which  do not tarnish on exposure to the  air, and
 the oxides of which  are reduced by heat alone,  were termed  the
 noble or perfect metals ; at the head of this list  stood gold, and at the
 bottom mercury.
   All the other metals  known to the older chemists were termed
 ordinary or imperfect metals.   Of the metals of the first and second
 class, none had been then discovered ; and  of their oxides, only
 potash, soda, barytes, lime, magnesia, and alumina were  known.
 From the old name of potash, Kali, with the Arabic prefix al, potash
 and  soda, at one time confounded together, were termed alkalies,
 and ammonia, resembling them very much when dissolved in water
 or combined with acids, was  also called an alkali ;  it was the vol-
 atile alkali, potash and soda being fixed alkalies ; it was also termed
 the animal alkali,  while  soda was the mineral alkali, being derived
 from rock-salt  or from the ocean ; and potash received the name of
 the vegetable alkali, from its source being the ashes of plants grow-
 ing upon land.   The alkalies are characterized by being very soluble
 in water, and by neutralizing  the strongest  acids.   They  hence  re-
 store the blue colour of reddened  litmus  paper, and  change the
 vegetable colours in general: the yellows to brown, the reds and
 blues to green.
   Paper tinged yellow by turmeric is a delicate test of the presence
 of an alkali, by which it is browned.
   Magnesia and alumina were  termed earths, and silica was classed
 with them ; these bodies, the earths proper, are  insoluble  in water,
 and have no action on turmeric paper.
  Barytes, lime, and strontia were termed alkaline earths ; they are
 soluble  in water, but much less so than the alkalies; these solutions
 brown turmeric paper, and neutralize acids ; but they are complete-
 ly distinguished from the alkalies by their  combinations  with car-
 bonic acid, which are insoluble in  water, while the alkaline  carbon-
 ates are very soluble in that liquid.   These phrases of alkalies and
 earths are of constant recurrence in descriptions of chemical pro-
cesses and results, and are thus seen to be founded on, and express-
 ive of, some of the most important characters in those bodies.
  Most  of the metals combine with  oxygen in more than one pro-
portion, and the characters of the  oxides are found to be  regulated
in a great degree by their composition.  All protoxides (R.O.) (R.
representing an equivalent of any metal) appear capable of combi-
ning with acids to form neutral salts ; they constitute, properly, the
 metallic basis, but in many cases  suboxides, (R/3.), such as those
 of copper and mercury,  form well-characterized salts, and  sesqui-
 oxides, (R,03), as those of iron, manganese, aluminum, and chrome,
produce well-defined classes of salts'also, which, however, in solu-
 tion always possess an acid reaction.  Peroxides, (R.O,), as those 
    AFFINITY OF  METALS  FOR  CHLORINE,  ETC. 331

of manganese, tin, titanium, and lead, are either indifferent or feebly
acid, and the higher degrees of oxidation lose all  basic character,
and become true acids, as the manganic acid, Mn.03, and the chro-
mic acid (Cr.03).
  The different oxides of the same metal frequently unite with each
other,  producing compounds which have great similarity to salts.
Examples of this will be found under the heads of manganese, of
iron, and of lead.
  The affinity of the  metals  for  chlorine is, in many cases, even
more remarkable than that which they  manifest for  oxygen ; thus
gold and platinum,  which resist even  nitric  acid, at  once combine
with chlorine ;  and tin, copper,  mercury, antimony, arsenic, and
bismuth, which require  a  high temperature to effect  their rapid
combination with oxygen, burn spontaneously when introduced into
chlorine gas  in a state of minute division.   Most metallic  oxides
are decomposed by chlorine also  at a high temperature ; thus, if a
stream of chlorine  gas be passed  over lime  heated to redness in a
porcelain  tube, oxygen  gas is  expelled, and the calcium remains
combined with chlorine.  On this account, the chlorides are gener-
ally, after the  oxides, the most   important  metallic  compounds.
Towards iodine, bromine, and  fluorine, the metals are related near-
ly as to chlorine, the affinities being, however, much weaker towards
bromine, and  still more  so  towards iodine:  of fluorine we do not
as yet  possess much positive knowledge, but its affinities appear to
be at least as  intense of those of chlorine.
  The compounds of sulphur with the metals constitute a very  ex-
tensive and important series, which, as has been more fully noticed
in p. 284, resembles in a very striking manner the series of oxides
ol the  same metal.   Many metals, at a high temperature, combine
with sulphur with brilliant combustion ; and even at  common tem-
peratures, if iron filings and sulphur be mixed together with a little
water,  they will, in uniting, produce so much heat as to burst into
flame,  if the mass be  moderately  large.  The metallic  sulphurets,
like the metallic oxides,  are some  acids and some bases, and these,
by uniting, form the extensive classes of sulphur-salts.   The metals
combine with  selenium and with phosphorus, subject to nearly the
some conditions as  in  forming sulphurets, but the  history of those
compounds is not nearly so complete.   As yet but very little has
been done towards the history  of the compounds of the metals with
nitrogen, silicium, or boron.
  Some of the metals, tellurium,  arsenic, and  antimony, combine
with hydrogen, forming  gaseous compounds, which resemble very
closely the sulphurets and phosphurets  of hydrogen in properties
and constitution. In these bodies the hydrogen is  the positive ele-
ment, the metal playing the part of the sulphur or of  oxygen.
  The  circumstances under which the metals are  found in nature
are  exceedingly diverse.  Some are found  native, or only  alloyed
with other metals, as gold, silver, tellurium, bismuth, and some oth-
ers.  Many exist combined  with arsenic, the sources of cobalt and
nickel being almost  exclusively their native arseniurets.  Some me-
tallic chlorides and iodides exist also native, but the most abundant
forms in which the  metals are to  be found  are combinations with 
332         GENERAL PRINCIPLES  OF  THE
oxygen and sulphur.   There are few of the metals that do not exist
naturally in the state of oxides, which are either free or else com-
bined with acids, forming salts.  Thus lead, copper, iron, zinc, tin,
manganese, antimony, are all  found in abundance as native oxides,
or as native sulphates, carbonates, arseniates, phosphates, silicates,
&c.   The majority of the metals exist also in nature combined with
sulphur.  The sulphurets of  lead, of zinc, and of  copper are  the
sources from whence the supplies of those metals are obtained;  and
the sulphuret of iron exists in great abundance, and, although  not
used for the extraction of the metal,  is of great importance  in the
manufacture of green vitriol, of alum, and of sulphuric acid.  These
native compounds of the metals are termed ores ; and the metal is
said to be mineralized by the substance with which it is united.
  The processes followed in the extraction of the metals must be, of
course, regulated by the composition of the ores in which it is con-
tained ; and as it will save the necessity of frequent  repetition here-
after, I  shall describe the general manner of treating each kind of
ore, so far as  may serve the purpose of an elementary work like the
present, in which the introduction of minute and technical details
would be  useless and improper.   In cases where  the plan followed
for any particular metal deviates essentially from that now  about
to be described, I shall notice  the circumstance in its special history.
  Where the  metal exists in a simply oxidized  condition, it is only
necessary to heat the ore strongly in contact with the fuel, by which
carbon is supplied in abundance for its reduction.  The carbon com-
bines with the oxygen, and the metal is set free.   It is not often that
the ores have this simple constitution, but in many cases the  metal
exists as a carbonate, and then the carbonic acid being expelled by
the first application of the heat, the oxide which remains is reduced
by the deoxidizing action of the ignited fuel.  Thus the native car-
bonates of lead, of copper, of zinc, and especially of iron, are simply
reduced in this way:  the last mentioned is the ore which consti-
tutes the great iron deposite of the neighbourhood of Glasgow.
  If the mineralizing substance, however, be any other than oxygen,
carbon, no matter how intensely heated, cannot produce any  effect
upon the ore.   Thus the native sulphurets and  arseniurets are  not
acted upon by^carbon.  Nor  can the  metals be obtained in a pure
form from any of their salts, except the carbonates, by means of car-
bon, for the oxygen of the  acid and base being simultaneously re-
moved by its agency, the radical of the acid remains  united with  the
metal, which is  thus only changed into a new kind  of ore.   Thus,
if sulphate  of  lead be heated with any of the forms  of carbon, it is
converted into sulphuret of lead, S.03 4-Pb O. and 4C. giving S. 1-Pb
and 4C.O.  And if arseniate of iron be ignited  with carbon, all the
oxygen is removed, and the arsenic and iron remain in combination.
In  such cases, it is necessary to adopt somewhat more  circuitous
methods, suited to the constitution of the individual  ores.
  In the case of certain metallic sulphurets, the metal may be very
simply separated by melting the ore with a proportional quantity of
a metal having a greater affinity for sulphur.   Thus metallic anti-
mony is very generally obtained by the fusion of the native sulphu-
ret with iron; Sb,S3 and 3Fe.  giving 3Fe.S.  and Sb...   On the lar<re 
REDUCTION  OF THE  METALS.
333
scale, however, this method would  not be  economically available.
In order to extract the metal from its sulphuret, as in the generality
of the ores of lead, of copper, and of zinc, the ore, first reduced to
fine powder, is healed to redness in  a current  of air, by the oxygen
of which the sulphur is converted into sulphurous and sulphuric acid,
while the metal is  oxidized.  This process is termed calcination.  A
great part of the sulphuric acid  formed is carried off with the cur-
rent  of air, and the remaining product is a sulphate of the  metal,
with excess of base.   When  the  salt so formed is deoxidized  by
contact with the ignited fuel, the excess of oxide abandoning  its  ox
ygen, yields an equivalent quantity of metal, which, however, would
be impure and of inferior quality, by having dissolved a portion of
the sulphuret reproduced by the reduction of the sulphur from  the
sulphuric acid.   It is  therefore necessary to get rid of that residual
portion  of  the sulphuric acid before the  deoxidizing process com-
mences, and this  is effected by mixing up a proper quantity of lime
with the calcined mass.   The lime decomposes the metallic sulphate,
combines with the sulphuric acid, and sets the  oxide free ; and when
the deoxidizing flames of the furnace pass  over the calcined mass,
the metallic oxide being reduced, yields a pure metal, while the  sul-
phate of lime, by losing  its oxygen, is brought  to the state  of  sul-
phuret of calcium, and remains  as  glassy scoria upon the surface
without injury.  This kind of operation is generally carried on in  a
sort  of furnace termed reverberatory,  from its office of beating down
the flames from the fireplace upon the materials  strewed upon itf*
hearth.   The adjoining figures  will
give an idea of its construction. The
upper is a  vertical, and the lower a
horizontal section, to which the same
letters apply,  a is the fireplace, and
b the ash-pit; at r a low wall is rais-
ed, termed the bridge, and the flames
and  heated air ascending from  the
fire are reflected  downward by the
low, vaulted roof, and, impinging up-
on the hearth, or sole  of the furnace,
d, produce the greatest  heating ef-
fect  upon the materials laid thereon.
The openings i and g serve for the   %,"■. -^ /^^^r-r^^h—^ JL
introduction of the materials, and for   ^    a    °     u
giving them the  arrangement, agitation, and mixture most cono<»-
cive  to  the success of the operation.   The damper, p, in the flue,
regulates the draught, and hence the intensity of the fire.
  In  this furnace, the  calcining  or oxidizing, and  the reducing or
deoxidizing effect is produced, according as the supply of fuel and
of air is regulated ; and thus the two stages just described, in the
extraction of a metal from its native sulphuret, are carried on.  The
hearth, d, is generally dished or concave towards the centre, so that
the reduced metal,  in its melted condition, may flow there, and be
run out  by an aperture in the side of the furnace when  the opera-
tion is concluded.
  In  the case of sulphuret of lead, a very simple  and beautiful pro
15 
334        GENERAL  PRINCIPLES OF  THE
cess of reduction consists in roasting the ore at a moderate temper-
ature, so that about one half of it shall be converted into sulphate
of lead by oxidizement, without any of the sulphuric acid being driv-
en off; and then, having mixed this up well with  the unaltered por-
tion of the ore, increasing the temperature very rapidly, so that the
two shall be fluxed together.  The result is the complete conversion
of the mixture into sulphurous acid gas, which passes off, and pure
metallic lead, which remains, the  sulphur of the unaltered ore com-
bining  with the sulphur and oxygen of that portion which had been
oxidized.  Thus S.03 + Pb.O. and S. -(-Pb. produce exactly 2S.O, and
2Pb.
  One of the most interesting processes of reduction is that by which
iron is obtained from its most abundant ore, the clay iron  stone.
This substance consists of oxide of iron of greater or less purity,
combined with alumina and silica.  Now, as carbon cannot deprive
silica of oxygen except under very peculiar circumstances, such as
those described in page 323, so the  metal cannot be obtained by
mere deoxidation; and even if the oxygen were removed, the result
would not be pure iron, but a compound of silicon and iron, which,
indeed, is formed  in small quantity, and is found generally in cast
iron.  It is necessary, therefore,  to decompose the silicate of iron
of which the ore is constituted, and this is effected by means of lime.
The coal  or coke and the ore are introduced into the furnace,  mixed
with a proportion  of  limestone, which, being calcined by the heat,
yields lime, which seizes upon the silicic acid, and the oxide of iron
being set free, is immediately reduced by the carbon of the fuel with
which  it is in contact, and produces  metallic  iron.  The limej the
silica, and the alumina  being melted  together, form a substance of
a nature somewhat between glass and porcelain, which floats upon
the mass  of melted metal, and constitutes the slags or scoriae of the
iron furnaces.
  In the case of ores containing arsenic, of which only the arseniu-
rets of cobalt and nickel are of  technical importance, the method
followed is to roast the ore in a furnace so constructed that a pow-
erful oxidizing action shall be produced by a current of air stream-
ing over the ignited ore ; both metals being thus oxidized, arsenious
acid, and oxide of cobalt  or of nickel are produced;  the greater
part of the former is  expelled by the  heat, and, being carried off by
the draught, is conducted into large chambers, where it is gradually
deposited under the form of a fine white powder  upon the walls and
floor.  The metal with which  the  arsenic had been combined re-
mains in the state of oxide united with a  little arsenious acid, and
is subsequently extracted or employed in other processes.
  The reduction of a  metal from the state of sulphuret is frequently
effected upon the  small scale by  fusion with a mixture of lime and
charcoal,  or of carbonate of potash and charcoal,  which last is fa-
miliarly termed black flux.  The  theory of this process is very sim-
ple. Thus, if sulphuret of antimony, lime, and charcoal be  melted
together, the sulphur combines with the calcium  of the lime, the
oxygen of which unites with the  antimony, Sb2S3 and 3Ca.O. giving
3Ca.S. and Sb203.   This last is then  decomposed by the charcoal,
the oxygen combining with the carbon, and the  metallic antimony
separates. 
REDUCTION  OF  THE  METALS.          335
  The black flux used in such operations is prepared by deflagrating
to"t iln-r equal parts of  nitre and cream of tartar; the nitrogen and
oxygen of  the former unite with the carbon and hydrogen  of the
latter,  forming  carbonic acid, nitrogen, and water: the  potash of
both remains behind as carbonate, mixed with the excess of carbon
which  had  escaped  combustion.   If two parts of nitre be used with
one of cream of tartar, there remains after  deflagration a white
mass of carbonate of potash, which is known as white flux, and used  in
processes where the deoxidizing effect of the carbon is not required.
Thus, for the reduction of chloride of silver, it is sufficient to fuse
it with half its weight of white flux ; the chlorine combines with the
potassium,  and the  silver, which at a lower temperature would have
united with the  oxygen and carbonic acid, is  separated, those two
bodies escaping in  the  gaseous form ;  the formula  of the reaction
being that  K.O.  . C02 and Cl.Ag. give K.C1. and  free Ag., while O.
and CO are driven off.
  Hydrogen, although  inapplicable to the reduction of  the  metals
upon the large scale, and  for the purposes of the arts, is yet to the
chemist a most valuable agent for this office, as it acts upon all va-
rieties of metallic combinations, whether oxides, chlorides,  or sul-
phurets ; and that the results it gives are  so accurate as  to serve as
bases for some of the most fundamental propositions of the science.
Thus we have already  seen that the composition of water  is  best
determined by the  action of  hydrogen gas upon oxide  of  copper,
and in analytical investigations, the isolation of a metal, by decom-
posing  its  chloride  or  sulphuret in  a  stream of  hydrogen gas,  is
frequently  employed.   The deoxidizing action  of hydrogen is oc-
casionally  used  in  an  indirect  manner.  Thus a very convenient
mode  of obtaining  silver from  the chloride  consists in fusing  it
with some common resin:  this consists  of carbon, hydrogen, and
oxygen, of which only  the  hydrogen is active ;  it combining with
the chlorine carries it off as muriatic acid gas,  while the metallic
silver is separated.   If the  chloride of silver be diffused through
water rendered  slightly acid,  and a  slip of zinc  be introduced, an
evolution of hydrogen commences, and the silver separates as a fine
metallic powder as  the  zinc dissolves.   But the action is here more
properly galvanic ;  an equivalent (32*3) of zinc combining with the
chlorine in place of each equivalent  (108) of silver which is set
free.   The precipitation of copper from the water of copper  mines,
which holds sulphate of copper dissolved, by dipping therein pieces
of iron, and, indeed, all cases of the precipitation of one metal by
another, are referrible to the same souice.
  The physical agent, electricity, which has been already found to
influence chemical action  to so remarkable a degree, has been  em-
ployed with considerable  success in the  reduction of certain met-
als.  It was first applied by  Davy, who  thereby made his wonderful
discoveries of the composition of the  alkalies and  earths.   It has
been totally superseded in that point of view by simpler processes,
but has recently been applied by Becquerel, upon  the large scale, to
the extraction of the precious metals from their ores.
  There are  many  other methods of reduction,  which, however,
being limited in their application to individual  metals,  will form
more properly a part of their special history. 
336
POTASSIUM.
                        CHAPTER XIII.

OF THE INDIVIDUAL METALS, AND  OF  THEIR COMPOUNDS  WITH OXYGEN,
               SULPHUR., SELENIUM,  AND PHOSPHORUS.

                           SECTION I.
                    METALS OF THE  FIRST CLASS.

                          Of Potassium.

  Potassium is the metallic basis of the alkali potash.  It was origi-
nally discovered  by Sir Humphrey Davy, who  obtained it by  sub-
mitting a piece of caustic potash, slightly moistened, so as to  be a
conductor of  electricity, to the action of a  powerful galvanic bat-
tery ; the water and the potash were simultaneously decomposed,
oxygen being  evolved at the positive electrode, while hydrogen and
potassium were separated at the  negative  wire.   From  the  heat
generated by  the intense power used, the metallic globules gener-
ally burned  as soon as they came  into contact  with  the air, and it
was with difficulty that a  quantity was obtained  sufficient for the
important researches  in which  it  was employed  by its illustrious
discoverer.   By using  mercury as  the negative electrode, the de-
composition   can be effected by a much weaker force, and  even
with a single  pair of plates, as in the  arrangement of Dr. Bird, de-
scribed in p.  199.
  The decomposition  of potash by truly chemical means is due to
Gay Lussac, but it is  by the  process  of Brunner that the metal is
now universally obtained.  As it is carried on only, however, in the
most extensive and best-appointed  laboratories, a very short sketch
of it will suffice here.
  Cream of tartar, which consists of tartaric acid united to potash,
is to be ignited in a covered crucible,  until there remains a mass of
carbonate of  potash mixed with carbon in  a state of very  minute
division, and  this  mass is to be intimately  mixed, while  still hot,
with a quantity of coarsely-powdered wood  charcoal, which serves
to  render the whole porous, so as to allow of the escape of the
gases generated in  its  interior without its swelling up.  The mate-
rial so prepared is  introduced into an iron bottle, such  as those in
which quicksilver is imported ;  to  the mouth of the bottle, which is
laid horizontally in  a  wind furnace, is adapted a  short iron  tube,
passing to a  copper condenser partly filled  with rectified naptha,
and so constructed with partitions as to exclude the air, while there
passes through it a stout iron  wire,  terminated  by a screw,  with
which the iron tube can be cleared of any solid material that might
be  deposited  in it.   The apparatus being so arranged, and  the re-
ceiver surrounded by ice, a fire  is lighted in the furnace, and when
the  iron bottle has become  white hot, the  decomposition of the
potash begins, the metal distils  over, and condenses in the receiver 
PREPARATION  AND  PROPERTIES  OF  POTASSIU.t. 337

in globules, which are protected by the naptha, in which they sink
while the oxygen of the potash and of the carbonic acid combines
with carbon, forming carbonic  acid, which, escaping under the par-
titions in the  receiver, passes away ; K 0. + C.0.. and 2C. producing
K. and 3C.O.   The great difficulty and loss in this process  arise,
however, from a cause which  is  not  at first apparent; it  is, that
carbonic  oxide  and potassium unite  to form a  dark  gray  mass,
which sublimes, and, condensing in the short iron tube, renders the
screw necessary to keep the passage  clear, and frequently caeses
the failure  of the  process.   Even in  the  most  successful  results,
one half of the metal  actually reduced is lost by combining with
the carbonic oxide.
  The potassium thus obtained is very impure, containing  much
carbon, and a quantity  of that  compound of carbonic  oxide which
passes over into the receiver.  To purify it, it is redistilled in cast
iron retorts, from which  the air has been  previously excluded by
vapour of naptha, and  it is  thus obtained in globules like peas, in
which  state  it  may be preserved under naptha perfectly free from
oxygen.
  At common temperatures, potassium is soft,  and may be moulded
in the  fingers  like wax.  At 32 it is quite brittle, and crystallizes
in cubes; at 70  it is pasty,  and at  150  perfectly liquid.  At a dull
red heat it boils, forming a green vapour, and  may,  as described
above, be easily distilled.   It is specifically lighter than water, its
specific gravity being 0*865.
  The colour  of potassium  is of a bluish white,  but its surface in
stunt ly becomes gray when  exposed to the air,  owing to the absorp-
tion of oxygen and the formation of a crust  of potash.  If it be
heated, it  bums with a vivid violet flame.  So great is its affinity
for oxygen that it decomposes water,  and  even ice, with great vio-
lence, so much heat being evolved that, if the  experiment be  made
in the air, the hydrogen gas evolved  and  the metal  both inflame
and burn with a fine violet  colour.  When  the metal  has been all
consumed, a globule of fused dry  potash remains, which, when it
has cooled to a certain degree, combines with water with a loud re-
port, and instantly then dissolves.
  Potassium is remarkably characterized by its great affinity for ox-
ye.en, which it  abstracts from almost all bodies ;  thus its use in the
preparation of boron and silicon has been already noticed ;  and al-
though, at very high temperatures,  iron and carbon take oxygen from
potassium, yet at a lower degree of heal, oxide of iron and carbonic
acid are both  decomposed  by  potassium,  carbon being  deposited
from the one, and metallic iron separated from the other.
  The symbol of potassium is  K., the initial of  the word Kalium,
6y which the  metal is designated by most of the Continental chem-
ists; the old name kali being still retained in preference to the word
potash, which has been adopted only in Great Britain and in France.
liie equivalent  is 490 or 39*3, according to the scale.
  Oxides of Potassium.—Potassium combines with oxygen  in two
proportions, forming a  protoxide K.O., and a peroxide  K 03.
  The protoxide of potassium constitutes the important alkali pot-
ask ; it can only be  obtained free from water by exposing potassium
                            U u 
338 PREPARATION  AND  PROPERTIES  OF  POTASH.

to the action of dry air, when it  is converted into a  white powder,
whicfc is fusible at a red, and volatile at a  white heat; if this sub-
stance be once  united  with  water, it cannot be  separated from it
except by  combination  with an  acid.   The potash  of commerce,
and that used in  the laboratory, is, therefore,  always hydrate of
potash;  the  dry potash, in  uniting  with water, becomes ignited.
Before the discovery of carbonic acid, the alkalies and their carbon-
ates were  distinguished from  each other  by the epithets of mild
and caustic, and  hence for medicinal purposes,  and  in  some phar
macopceias, the hydrate of potash is still termed caustic potash.
  To prepare a solution of potash, the carbonate of potash of com-
merce, derived from the sources to be detailed in its description, is
to be dissolved in ten parts of water, and the  solution being made
to boil smartly,  is to be decomposed by one part of slacked lime in
fine powder, which is to be gradually added, the boiling being briskly
kept up; the lime abstracts the carbonic acid from the potash, and
carbonate of lime is formed, which at that temperature, constituting
minute crystals of  arragonite, is rapidly and completely deposited.
The clear liquor is to be tested  occasionally by adding  to a small
quantity of it an excess of muriatic acid ; as soon as the absence of
effervescence shows that all the alkaline carbonate has  been decom-
posed, the pan is to be  removed, and being laid aside, carefully cov-
ered, until the carbonate of lime has been well settled, the clear li-
quor  may be siphoned off.  The decomposition  of the  carbonate of
potash by the lime would  take place also at ordinary temperatures,
but the precipitate would  be in  the  rhombohedral form, and being
specifically lighter and more  finely divided,  would occupy  much
more room,  and would  not separate so well.  If the carbonate  of
potash be dissolved in less than six parts of water, it is not decom-
posed by lime ;  on ihe  contrary, when a strong  solution of caustic
potash is boiled with carbonate of lime, carbonate of potash is pro-
duced, and lime set free.
   When the solution of caustic potash is  evaporated  in a basin of
iron, or silver, or  platina, there remains a liquid which solidifies on
cooling into  the hydrate of potash, K.O. . H.O.  This liquid is gener-
ally run into cylindrical moulds, in which  form the caustic potash
or fused potash of the  shops is generally found.  In this state it is,
however, impure, and it requires to be freed from the  admixed sul-
phate and  carbonate of potash, chloride and peroxide of potassium,
and oxide  of iron, which  it generally contains,  by being dissolved
in absolute alcohol, the solution evaporated to dryness, and the re-
maining potash fused a second time.
   Hydrate of potash is a pure white solid,  of a crystalline fracture;
it fuses  below redness. In the fingers  it has a  peculiar soapy feel,
owing to its dissolving the  cuticle,  with whicji it forms a kind of
soap ; it acts powerfully on all organic tissues, dissolving and decom-
posing them, and hence its use in surgery, and  its name of caustic
potash.  It dissolves in water, with the evolution of considerable
heat; a concentrated  solution of it crystallizes when exposed to
 cold, in rhombic octohedrons, whose composition is K.O. + 5H.0.
   The solution of potash is pre-eminently alkaline ; it neutralizes the
 strongest acids, browns turmeric paper, and restores the blue colour 
SULPHURETS OF  POTASSIUM.
339
of litmus paper reddened by an acid.  It absorbs carbonic acid rap-
idly from the air, and must hence be preserved in close vessels.   It
acts rapidly on glass containing much alkali or lead, and hence should
be preserved in bottles of common green glass.
  The uses of potash in chemistry are too numerous to mention ;  it
being the strongest base, is employed  in almost all  cases of  saline
decomposition, and its various compounds are of great importance
in the chemical arts, of which many will be noticed hereafter  in de-
tail.
  Potash is distinguished, when free, first,  by its general alkaline
characters, and by its not being  precipitated by carbonate of soda,
which  separates  it from  everything but soda and ammonia.   From
the  latter it is known by the brown stain produced on turmeric paper
being permanent, whereas the brown colour produced by ammonia
disappears when the paper is warmed;  and from soda it is known
by giving with an excess of the perchloric, tartaric, and hydrofluo-
silicic acids, sparingly soluble salts, whereas the soda salts of these
acids are all easily soluble.   A solution of potash, if neutralized by
muriatic acid,  gives, on the addition of chloride of platinum,  a  fine
yellow precipitate, whereas, with a solution of  soda, no precipitation
occurs.
  The salts of potash -act in all  respects similarly,  except that, as
there is  no alkali in excess, the  action  on vegetable colours  is not
that of an alkali.  The salts of ammonia resemble precisely the salts
of potash in their action  on  those precipitants  described above, but
they are at once distinguished by the application of heat.   The salts
of ammonia are all volatilized, either with or without decomposition,
by a red heat, while those of potash are fixed,  and give to the flame
of the  blowpipe a distinct and characteristic violet tinge.
  Potash consisting of an equivalent of each element, its formula  is
K.O., and its composition,
        Potassium, 83*05      One equivalent =490 or 39*3
        Oxygen,   16*95      One equivalent =100  or  8*0
                  JOO-00                      "590    ^f3

  Peroxide of Potassium.  K03.—This substance, which is of very little importance,
is formed by burning potassium in an excess of oxygen gas ; it  is a yellow powder,
decomposed by water, potash dissolving, and oxygen  being given off.  When hy-
drate of potash is heated to redness in  air, some peroxide is always formed, and
hence the fused potash of the Ihops generally gives off minute bubbles of  oxygen
gas when dissolved in water.
  Sulphurets of Pot&e$ium.—When  potassium is gently  heated in
contact with  sulphur,  they unite  with brilliant  combustion, and, ac-
cording to the proportions in which they are employed, form  the
sulphurets of potassium, of which there are altogether four.  These
bodies are, howover^always prepared in practice by more econom-
ical processes.
  Il  sulphate of potash be ignited in a glass tube, and a current of dry hydrogen gaa
be V.issed over it, all the oxygen, both of acid and base, is removed in the state of
water, and protosulphurct of potassium remains.  Thus K.O. S03 and 4H. produce
411.0. and K.S.  The same result follows from  igniting strongly, in a crucible, a
mixture of charcoal and sulphate of potash ; all the oxygen is removed as carbonic
oxide, and the sulphur and the potassium remain in combination, K.O.. S.03 and 40.
giving 40.f). aud X.S. 
340    SULPHURETS  OF  POTASSIUM.--SODIUM.

  This protosulphuret is of a brown colour, fusible below a red heat, easily solu-
ble, and its solution is yellow, and reacts highly alkaline and caustic.  When ex-
posed to the air, it absorbs oxygen rapidly ; and in preparing it from sulphate of pot-
ash, by carbon, if lampblack be used, so that the product shall be in a state rf very
minute division, it  takes fire spontaneously on coming into contact  with  ihe air,
constituting a pyrophorus.   If the protosulphuret of potassium be acted upon  by
acids, water is decomposed, K.S.  and  H.O. giving K.O. and U.S. ; the potash  re-
mains united with the acid, and the sulphuret of hydrogen is given off.   No solid
sulphur is deposited, and the liquor remains clear.
  A solution  of the protosulphuret dissolves  sulphur  in large quantity, the Higher
sulphurets being formed.   It absorbs sulphuretted hydrogen in such proportion that
a compound  is produced, K.S.-J-H.S., exactly similar to the  hydrate of potash,
K.O.-r-H.O.
  The tersulphuret of potassium corresponds to the peroxide, its formula being K.S3.
It constitutes the mass of the hepar sulphuris, liver of sulphur, of the pharmaco-
poeias.  It  may be  prepared by fusing, at a low red heat, one part of sulphur and
two of carbonate of potash, the mass being kept liquid as long as it effervesces, from
carbonic acid gas being evolved.  In this reaction, a quantity of oxygen from the
potash combines with one portion of the sulphur, forming hyposulphurous or sul-
phuric acid, according to the temperature, while the remainder of the sulphur com-
bines with the potassium, producing a sulphuret, the composition of which is de-
termined by the quantity of sulphur present.  With the above proportions the reac-
tion may be considered thus : 4(K O.-f-C 02) and 10S. give 3K.S3 and K.O. . S.03l
which constitute the fused mass, while 4C02 is driven off with effervescence.  If,
however, equal weights of carbonate of potash and  of sulphur be employed, the
sulphuret formed contains  five equivalents of sulphur : it is the pentasulphuret.
  These sulphurets resemble each other completely in external appearance; they
are liver-brown ; they deliquesce in the air, and absorb oxygen rapidly.  Their solu-
tions, which  are at first deep yellow,  become colourless  by  uniting with  oxygen,
hyposulphite  of potash being formed, and sulphur precipitated.   If a solution of the
tersulphuret or pentasulphuret be treated with an acid, water is decomposed, and
potash being formed, sulphuret of hydrogen is produced; the remaining sulphur
then separates in a  state of very minute division, and of a milk-white colour, con-
stituting the lac sulphuris,  or the sulphur precipitatum of pharmacy.  If the acid em-
ployed be strong and in great excess, a quantity of bisulphuret of hydrogen is form-
ed, as explained in  page 293.
  Rose is of opinion that the whiteness of precipitated sulphur depends not merely
upon its minute division, but that it is owing to the  presence  of a trace of bisul-
phuret of hydrogen.  When the hepar sulphuris is decomposed  by an acid, it is not
merely that the excess of sulphur is set free, but in addition, as there is always hy-
posulphurous acid present; this, when evolved, acts on the sulphuretted hydrogen,
and the sulphur of both is precipitated, water being formed; S.O2 and 2H.S. giving
2H.O. and 2S.
  The Pentasulphuret of Potassium is prepared perfectly pure by decomposing sul-
phate of potash by sulphuret of hydrogen, at a red heat.  Thus K.O. . S.03 and
4H.S. give K.S5 and 4H.O.  This reaction supports very much the view that this
pentasulphuret is really sulphate of potash, in which  the oxygen, both  of acid and
base, is replaced by sulphur, for K.S5 may be constituted of K.S. and S.S3.
  The seleniurets of potassium are similar in constitution  to the sulphurets.  They
evolve seleniuret of hydrogen when treated  ^y acids, with  precipitation of seleni-
um when it is present in greater proportion than one  equivalent.

                                Of Sodium.
    Sodium  exists  in  great  quantities in  the  mineral kingdom, es-
pecially combined with chlorine, as  common  salt, of  which enor-
mous deposites are found inEngland, Poland, and elsewhere, besides
forming the leading saline ingredient of the waters  of salt lakes and
 of  the ocean.   It is found in  many minerals, and  is  remarkably
 prevalent in the animal  fluids,  all of  which  contain common salt.
 It  is, indeed, from the chloride of sodium  that we  derive, whether
 directly or indirectly, all the supplies of the various compounds  of
 this metal. 
SODIUM AND  SODA.                 341
   The discovery of sodium was made in the same manner, and im-
 mediately  subsequent  to  that  of  potassium,  by Humphrey  Davy,
 and it is now prepared in exactly the same manner as that  metal.
 It is, however, much more easily prepared ; its reduction does not
 require so  high a temperature, and it does not unite with carbonic
 oxide, so that the formation of the black sublimate, which  is the
 principal source of loss and failure in preparing potassium, does not
 occur.
   Sodium  is lighter than water, its sp. gr. being 0*972 ;  it conse-
 quently floats upon that liquid ; and when a globule of the metal is
 thrown into a basin of water, this is decomposed with great rapidity,
 hydrogen being evolved ;  but the action is not so energetic as with
 potassium ; the gas does  not  take  fire spontaneously.  But  if the
 globule be  prevented from moving about, the water becomes heat-
 ed, and the action increases so much as to set fire to the  gas;  this
 occurs when there is so little water that the globule does not swim,
 or when it  is fastened to the edge of the vessel,  or if the water be
 thickened by gum or starch.  If some oil of vitriol be added  to the
 water, the  action is so  much more active, that combustion occurs
 even when the metallic globule moves rapidly about.
   The symbol of sodium is Na., derived from  the word Natrium, as
 soda still retains  in many countries the name  Natron.   Its equiva-
 lent numbers are 291 or 23*3.
   Sodium  unites with oxygen in two proportions, forming the  pro-
 toxide,  or  soda, Na.O.,  and the peroxide, of which the constitution
 is not exactly known.   This last is prepared just as the peroxide of
 potassium, which it resembles completely in  its properties.   The
 former only requires detailed notice.
  The preparation of  dry soda is  effected like  that of potash, by
 heating the metal in  dry air or oxygen.   It is grayish white,  and
 absorbs water with excessive  power. From  the hydrate of soda
 the water can be expelled  only by  an acid.   The caustic soda is,
 therefore, always like caustic potash, a hydrate of the alkali.   For
 the preparation of caustic soda, the same process is to be followed
 as for that of potash.  The carbonate of soda of commerce, dissolv-
 ed in boiling water, is decomposed by slacked  lime, it being neces-
 sary, however, to use one third more lime, from the smaller equiv-
 alent number of soda.    The solution of caustic soda resembles that
 of caustic potash  in all  its alkaline characters, but its action is  not
 so intense.  It is a weaker alkali, its salts being decomposed in
 all cases by potash.
  The soda consists of  an equivalent of each  element ; its formula
 is Na.O., and its composition,
         Sodium, 74*42    One equivalent =291 or 23*3
         Oxygen, 25*58    One equivalent =100 or  8.0
                 100-00                     391   3T3
  The detection of soda is very simple.  On adding to a solution of
the substance to be examined a solution of carbonate of soda, if there
be no precipitate produced, the base of the salt present must  be an
alkali.   On then applying  the various tests for potash and for am-
monia detailed in the last  section, if no evidence  of their presence 
342
L I T H I U M.--B A R I U M.
 be obtained, the alkali  must be  soda ;  and even  where potash also
 is present, a small quantity of soda may be  recognised, by its tin-
 ging the flame of the blowpipe of a fine yellow colour.
   The compounds of soda are very  numerous and  important, and
 will be described in  their proper place, among the salts.
   The sulphurets of sodium resemble so completely the sulphurets of potassium as
 not to require more than a reference to their description.  To  the seleniurets of
 sodium the same remark applies.

                               Lithium.
   This metal is found only in a few  minerals, of which one of the
 most  common, spodumene, occurs at Killiney, near  Dublin.  This
 mineral is a double silicate of the alkali lithia (oxide  of lithium) and
 alumina.  The metal has  been obtained by  voltaic decomposition,
 but only in  very small  quantity.   It  is white, like sodium, and be-
 comes oxidized immediately  on  exposure to  the  air.   Its symbol is
 L., and its equivalent number 80*3 or 6*4.
  To obtain lithia, the simplest  process is to  mix the mineral containing it (gener-
 ally lepidolite or spodumene), previously reduced to very fine powder, with fluor
 spar, and digest the mass with oil of vitriol, until it is completely decomposed; the
 silica is carried off by the hydrofluoric acid (see page 324), and the lime, the alumina,
 and the lithia remain combined with the sulphuric acid.  By the  action of a small
 quantity of water, the sulphates  of lithia and alumina are dissolved out, and the last
 then precipitated by ammonia.   The sulphates of lithia  and ammonia being then ig-
 nited, the sulphate of ammonia  is decomposed, and the sulphate of lithia obtained
 pure.   This is but a general outline of the process, which requires manv additional
 operations  for a fully successful result.
   Lithia is distinguished from the other alkalies  by the sparing sol-
 ubility of its carbonate, in which  character it approximates to the
 property of the earths,  thus connecting the two  classes of metals.
 Being so rarely found, and of no application  in the arts, its history
 is not of much importance.
   Lithia  is recognised by the  sparing  solubility of its  carbonate, and
 by tinging the flame  of the blowpipe of a brilliant red colour.  This
 last character easily  distinguishes it from soda.   Lithia is a protox-
 ide, its formula being L.O. ;  its equivalents 180*3 or  14*4.
   The sulphurets and seleniurets of lithium do not possess any in-
 terest.

  The  alkali ammonia might, on one hypothesis of its nature, be  described  here.
 When combined with hydrogen, it is considered by Berzelius  and  many other chem-
 ists to form a  remarkable compound metal, ammonium, N.H4, whose relations to
 potassium are  of an exceedingly intimate kind ; and the salts of ammonia, which
 contain ammonia and water, N.H3+H.O.. are  looked upon as consisting of an oxide
 of that metal, N.H4. O. in combination with an acid.  I prefer, however, to study the
 history of ammonia, and all the classes of compounds into which it enters, among
 the bodies of organic origin.

                               Barium.
  Barium is found exclusively in  the mineral kingdom, where its
 oxide, barytes, is the basis of several minerals, as the sulphate and
 carbonate, which are the usual  sources from which  it  is obtained
 for use.
  The metal barium was discovered by Sir Humphrey  Davy imme-
diately after the discovery of the basis of the alkalies.   It may be
prepared by voltaic action, as described under  the head of potassium, 
PREPARATION  OF  BARYTES.
343
 or  much  better by passing the vapour of potassium over barytes
 heated  to redness;  the potassium takes the oxygen of the barytes,
 and the barium is set free.   By washing the residue with mercury,
 the  metallic barium  is dissolved out, and  the mercury being then
 distilled off in  a retort of hard glass, the barium remains behind *  it
 is a white metal like silver; it  fuses below a red heat; it is denser
 than oil of vitriol: it decomposes water with  great  rapidity, evolv-
 ing  hydrogen gas and forming  barytes (oxide of barium).
  The  name barium is derived from fiapvg, heavy ; the native sul-
 phate of barytes having been called formerly terra ponderosa, or heavy
 spar.  Its symbol  is Ba.; its equivalent numbers 856*9 or 68*7.
  Barium combines with oxygen in two proportions, forming a pro-
 toxide,  which is the earth  barytes, Ba.O., and a deutoxide, Ba.02.
 The preparation of this last has been described so fully when ex-
 plaining its only important use, the  formation of deutoxide of hy-
 drogen  (p.  258), that it  need  not be farther noticed here.  The
 protoxide, barytes, is, however, one  of the most important earths.
  To procure pure  barytes, the nitrate of barytes is to  be gently
 heated  to redness  in a porcelain crucible.  It fuses at a  dull red,
 and  boils briskly from the  rapid escape of oxygen; when this has
 terminated, there  remains  a gray loosely  coherent  powder, which
 is barytes.  The melted salt is  in this process very  apt to froth up,
 so much as to overflow, unless the vessel be  of  considerable size ;
 this is very simply avoided  by mixing the nitrate of barytes, before-
 hand, with  twice its weight of  sulphate of barytes  in fine  powder.
 When the  nitrate  melts, the sulphate gives  the mass a degree of
 consistence which prevents its  frothing up, and  on  boiling  the re-
 sidual mass with water, all  the  pure  barytes dissolves, the sulphate
 remaining totally unacted on.
  If the native carbonate of barytes, Ba.O.. C02. be strongly heated with carbon, the
 carbonic  acid  is converted into carbonic oxide, which passes off, and pure barytes
 remains behind, Ba.O.. C02 and  C. giving Ba.O. and 2C.O. ; the former process is,
 however, so much easier, that it alone  is now usually employed.  Graham has sug-
 gested the employment of iodate of barytes  as a substitute for the nitrate .- other
 processes will  be described under the head of sulphuret of barium.
  Pure  barytes is  a heavy gray powder ; when  exposed to the air,
 it absorbs water rapidly, giving out much heat, and falling into a fine
 white powder, hydrate of barytes,  Ba.O. + H.O.   Another hydrate may
 be obtained  crystallized, by  dissolving barytes  in three parts of boil-
 ing water, and allowing the  solution to cool slowly;  it contains nine
 equivalents  of  water.  The solution  of barytes is very caustic and
 alkaline ; exposed to the  air, it absorbs carbonic acid,  and a white
 precipitate of carbonate of barytes is formed; it is hence  used to
 determine the quantity of carbonic acid present in the air (p. 263),
 and  in some other cases.          *»
  The detection of  barytes is very simple; its soluble compounds
 give white precipitates with carbonate of soda, with  sulphuric acid,
 and with hydrofluosilicic acid, and none of these are affected  by a
solution of  sulphuretted hydrogen gas in water.  The  sulphate of
barytes  is not merely insoluble  in water, but  also in nitric and mu-
riatic acids,  which is a farther characteristic of this  earth.
  The formula of barytes is Ba.O., and its composition, 
344    SULPHURET  OF  BARIUM.--STRONTIUM.


        Barium,  89*55     One equivalent =856*9 or 68*7
        Oxygen,  10*45     One equivalent =100*0 or  8*0
                100-00                      956:9   7*67

   The soluble compounds of barytes are all poisonous, and the car-
bonate, although  insoluble in water, is yet dissolved by the free
acids of the stomach, and becomes poisonous.  The antidote to all
barytic preparations is sulphate of soda,  or sulphate of magnesia,
administered in excess;  the sulphate of barytes then produced is
absolutely inert.
   Sulphuret of Barium.  Ba.S.—This body is of considerable inter-
est, as the source  of barytes and of most of its ordinary compounds ;
to prepare it, sulphate of barytes in fine powder is to be mixed with
one fourth of its weight of lampblack, and exposed to a very strong
heat for two hours; the  carbon removes all the oxygen from the
salt;  carbonic oxide is evolved, and sulphuret  of barium remains;
Ba.O. . S.03 and 4C. giving 4C.O. and Ba.S.   The  mass thus ob-
tained is to be boiled in water; a deep yellow solution is then pro-
duced, from which the sulphuret of barium crystallizes on cooling;
it is then a hydrate, but its water of crystallization may be removed
by a moderate heat.  The  sulphuret of barium  is decomposed by
acids, sulphuret of hydrogen being  evolved, and a salt  of barytes
formed : it is thus that the  salts of barytes are  obtained for labora-
tory use.
   A simple mode of obtaining caustic barytes directly from the sul-
phuret of barium has been  recently given by Mohr.  It consists in
adding to a boiling solution of the sulphuret, black oxide of copper,
until the whole of  the sulphuret of barium is decomposed, as is easily
ascertained, by adding a drop of the solution to a solution of acetate
of lead ; the copper combines with the sulphur, while the barium
and the oxygen unite, Ba.S. and Cu.O. producing Ba.O. and Cu.S.
This is probably the simplest and cheapest means of obtaining pure
barytes.
                         Of Strontium.
   This metal  is the basis of the earth strontia, protoxide of stron-
tium,  which exists native combined with sulphuric and carbonic
acids.  The native carbonate of strontia was first found at Strontian
in Scotland, and proved to  contain an earth different from barytes
by Dr. Hope.  The similarity of these two earths is very great, so
lhat the general  outline of the history of strontia is the same as that
of barytes.
  The metal strontium is  obtained precisely as  barium, with which
it perfectly agrees in character so far as its properties have been
ascertained.  Its symbol is  Sr., and its equivalent number 547*3 or
43*8.  To obtain strontia, the same processes may be employed which
were described for the preparation of barytes, substituting the native
carbonate or sulphate of strontia for the compounds of barytes.  The
strontia is gray, slacks on exposure to the air, forming  a hydrate,
Sr.O. . H.O., and by crystallization from its watery solution, another
hydrate, Sr.O. + 9H.O.   Strontia is less soluble than barytes, its taste
is not so caustic, nor is it so poisonous 
COMPOUNDS  OF  CALCIUM.
345
   Strontia is distinguished from barytes by tinging the flame of the
blowpipe  a rich crimson.  The red lights  used in fireworks  owe
their colour to nitrate of strontia, which is used in the preparation.
Like barytes, the  soluble salts of  strontia are precipitated by sul-
phuric acid, but the sulphate of strontia is not so very insoluble as
sulphate of barytes ;  a solution of strontia is also precipitated by
carbonate of soda.  The  hydrofluosilicic and the  hyposulphurous
acids, which precipitate barytes, do not precipitate strontia, and thus
these earths may be distinguished and separated from each other;
the chromic acid acts in a similar manner.
   The sulphuret and seleniuret of strontium resemble perfectly those
of barium, and are prepared in  the same  way.

                          Of  Calcium.
   The existence of this metal was first recognised by Sir Humphrey
Davy, it being obtained from lime by the same method as that de-
scribed under the head of barium ; it is while like silver ; it sinks in
water, which it decomposes rapidly, evolving hydrogen,and uniting
with oxygen,  forms lime  (protoxide of calcium).   The symbol of
calcium is Ca., and its equivalent number 256  or 20*5.
   Calcium combines with oxygen  only in one proportion, forming
lime, the most important of the earths.  It is found very extensively
distributed in the  mineral kingdom, principally combined with  sul-
phuric and carbonic acids, foiming sulphate of lime (gypsum, plas-
ter of Paris) and carbonate of lime (marble, limestone, chalk).  These
substances exist as rocks or crystallized, the last  constituting the
mineral species, arragonite and calc spar, often referred  to  under
the heads of  crystalline  systems,  isomorphism, and  dimorphism.
Lime is found also combined with phosphoric and arsenic acids in
several minerals, and the native fluoride of calcium  is the fluor spar,
used  for the  preparation  of the hydrofluoric  acid  and other com-
pounds of fluorine.
   Notwithstanding the immense quantities of carbonate of lime
which are  found constituting a great portion of the surface of  the
globe, as,  for instance, the whole centre of Ireland is one vast plain
of limestone, and in that as well as other forms, chalk,  marble, &c,
it  is equally extensive in most other countries, it is questionable
whether lime  should not be looked  upon as  rather  a characteristic
of the animal than  of the mineral kingdom of nature.  The bony or
testaceous skeleton, by which the softer portions of the animal frame
are attached, is always  found to consist of lime united either with
carbonic or phosphoric acids, and the diversity of chemical compo-
sition in this respect  is found to coincide in a remarkable degree
with the most  natural physiological classification.  The skeletons of
the vertebrated animals consist principally  of phosphate of lime,
while in the shells  of the invertebrate animals, the carbonate of lime
is  the prevalent  component.  The teeth  also consist of phosphate
of lime ; in all these cases, the phosphate  of lime is associated with
fluoride of calcium, just as occurs in the native phosphate, the min-
eral apatite.
  Now  it is  remarkable that all the great  geological formations
which contain carbonate of lime are found to  consist of the aggre-
                               Xx 
346
PROPERTIES  OF  LIME.
gated skeletons (shells) of myriads of the tribes of invertebrated an-
imals, which had existed in  some  former period of the world's his-
tory.  From the densest and hardest limestone to the softest chalk,
the entire mass resolves itself ultimately into a congeries of animal
remains, and hence the great  supply of lime in the mineral state
arises from the destruction of its animal sources.  Even  those crys-
talline marbles in which no organic remains can be traced, appear
destitute of them only from having been subjected, by volcanic heat
or otherwise, to the influence of causes which have gradually render-
ed the texture of the mass completely uniform.  The lime which
exists in nature must therefore be looked upon as being continually
in a  state of  passage between the  organized  and the inorganic king-
doms.   The  plants which grow upon  the soil take up, by dissolution
in their juices, salts of lime, which pass into the substance of the
animal which feeds upon them, and, accumulating in its  system, af-
ford materials for the  proper development of the  skeleton.  When
the animal dies, the materials of its tissues either serve for the nu-
trition of some other animal, or, being totally decomposed, its ele-
ments return to the mineral kingdom, to be, in after ages, the sub-
ject  of similar alternations.
  Lime is always obtained, for the purposes of chemistry and of
the arts, by the decomposition of  the native carbonate.  To obtain
lime perfectly pure, crystals of calc spar or  pieces of Carrara mar-
ble should be strongly heated in a crucible loosely covered, so that
the carbonic acid can  readily escape.  In the presence of carbonic
acid carbonate of lime is not decomposed by heat, as was explained
already in p. 170.  On the large scale, lime  is obtained by burning  «
the ordinary limestone in kilns.  At the bottom is a grate on which
fuel  is laid, and the kiln then filled with limestone and fuel (culm or
small coal), mixed in suitable proportions ;  when the fire is lighted
on the grate, the combustion extends throughout the mass, and as
the perfectly burned lime is extracted at the bottom by the orifice
of the grate, new quantities of fuel and limestone  are  introduced
above, so that the combustion is continuous;  the carbonic  acid
evolved is completely removed by the rapid draught through the
fire.
  Lime is a pure white earth.  When exposed to the air, it rapidly
absorbs water, and  falls into a  white powder (slacked lime), which
is a hydrate,Ca.O. . H.O.  If a little water be poured on a piece of
well-burned lime, it is absorbed instantly, and the lime appears quite
dry,  but after a few moments cracks, and falls  into the powder of
hydrate, evolving so much heat as to  char wood  and  inflame gun-
powder when in large  quantities.  It is thus  that vessels laden with
lime have been  burned at sea, by water penetrating to the hold.
Lime is soluble in water, though but sparingly, and still less soluble
in boiling than in cold water; one part of lime requiring 778 of wa-
ter at 60 , and 1270 at 212 for its  solution ; hence, when lime-water
is boiled, it becomes turbid.  The solution of lime has an acrid, slight-
ly caustic taste; it reacts alkaline; exposed to the air, it absorbs
carbonic acid, becoming covered with a crystalline pellicle of car-
bonate of lime.  On breathing into lime-water through a  glass tube,
it is  immediately rendered turbid by the carbonate of lime produced 
SULPHURETS OF  CALCIUM.
347
 by respiration; an excess of the carbonic  acid, however,  dissolves
 the precipitate.  It is in this way that carbonate of lime is held dis-
 solved in almost all  ordinary spring and river waters.  If lime be
 perfectly dry,  it has little or no tendency to absorb  carbonic acid;
 it requires to  be first slacked, and then the  hydrate is  decomposed,
 the water being expelled  by the carbonic acid;  the absorption  is
 very rapid until the  lime becomes  one half saturated, a compound
 of Ca.O.. C.02-r-Ca.O.. H.O. being  probably formed, but after that
 point it advances very slowly.
   Lime being  a protoxide, its formula is Ca.O., and its composition
 and equivalent numbers are  as follows:
        Calcium, 71*91        One equivalent =256*0 or 20*5
        Oxygen,  28*09        One equivalent = 100*0 or  8*0
                 100*00                          356*0    28*5

   Lime is easily distinguished by its dilute solutions not being pre-
 cipitated  by sulphuric acid or sulphate of soda, but  giving a white
 precipitate of oxalate of lime on the addition of a  solution of oxalic
 acid; an excess of oxalic acid does not redissolve this precipitate.
 The  nitrate of lime is deliquescent  and soluble in  alcohol, in which
 it also differs from the preceding earths.  The compounds of lime,
 when ignited  before the blowpipe, tinge the flame  of a brick-red
 colour.
   Lime is of great importance in the arts,  from its  use in making
 mortar, and in agriculture from its  application as a  manure.   The
 lime  in  mortar is not as  carbonate, and its coherent property  ap-
 pears to  depend only on the gradual drying of the  hydrate by which
 the stones are  retained together, as  boards are by the drying of the
 glue  between  their  surfaces.  The  use  of lime as a  manure arises
 from its  decomposing the  insoluble organic matters of the soil,
 woody fibres, ulinine, &c, and producing other products more read-
 ily taken up by the  radicles  of the  growing plants.   It is hence on
 such  soils as  possess a  large quantity of organic matter, but are
 still barren from its not being in the suitable  condition, that the ben-
 eficial effects of lime are peculiarly  marked.
  There is a deutoxide of calcium. Ga.02, prepared by adding a  solution of deutoxidt
 of hydrogen to lime-water; it resembles deutoxide of barium, but is of no impor
 tanee.
  There are three compounds of sulphur and calcium known , the first, or proto-
 sulphuret of calcium, Ca.S., may be prepared by heating sulphate of lime to rednesa
 in a stream of hydrogen gas, or, more simply, by igniting sulphate of lime with one
 third of its weight of lampblack; all the oxygen of the salt is carried off as watei
 in the one, or as carbonic  oxide in  the other case, and the sulphur and calcium re-
 main united.  It is a white powder, but very sparingly soluble in water.  It playa
 an important part in the manufacture of carbonate of soda, as  will be hereafter ex-
 plained.  When flowers of sulphur and slacked lime are boiled together in water, a
 deep yellow solution is obtained, which is said to be a sulphuret of lime, but which
 really consists of a mixture of hyposulphite of lime and bisulphuret of calcium, 6S.
 and 30a.O. producing SoOa-l-Oa.6. and 2Ca.S2. If the solution  be concentrated, this
 last separates in yellow prisms with water of crystallization   It is from this yellow
liquor that the precipitate d sulphur is prepared ; lor, on adding to it an acid, sulphu-
ret of  hydrogen is  evolved from the  sulphuret of calcium in such proportion a.; to
decompose the livdrosulphurous acid, and all the sulphur is precipitated, while the
lime remain* in combination  with the acid which is employed.  If the sulphur be
in great excess in proportion to the lime, a pentasulphuret of calcium may be formed.
  The seleniuret of calcium is not important. If phosphorus  in vapour be passed 
348         PREPARATION  OF  MAGNESIUM.
through a red-hot tube loosely filled with lime, a brown substance is produced, pop-
ularly termed phosphuret of lime, but which is a mixture of phosphate of lime and
phosphuret of calcium; the  temperature must not be raised too high, or else the
phosphorus may be expelled again.   When this phosphuret of calcium is brought
into centact with water, it is decomposed, phosphite  of lime and phosphuretted hy-
drogen being  produced ; this last being evolved in its spontaneously inflammable
condition, it is an interesting experiment to throw a fragment of the brown sub-
stance into a glass ot water; numerous gas bubbles are immediately formed, which
explode when they reach the air, as described in p. 300.
                          Of Magnesium.
   This metal, like  the bases of the other earths, was first recog-
nised by Humphrey Davy, but the process  by which it is best pre-
pared is that given  by  Bussy.   A few pieces of potassium are to be
placed at the bottom of a tube of hard glass, and then a quantity of
anhydrous chloride of magnesium  in small fragments to be laid upon
them ; the  part of the tube containing  the  earthy chloride is  to be
heated to near its point of fusion, and the metal converted into va-
pour by the  application of the lamp, as in the figure,  p. 321; as
soon as the vapour of the potassium comes into contact with the
heated  salt, vivid ignition ensues, and chloride of potassium being
formed,  the magnesium is liberated in the metallic state, Mg.Cl.
and  K. giving K.C1. and Mg.   When the action has  ceased and the
tube is completely  cool, the mass is to be washed with warm wa-
ter; the chloride  of potassium dissolves, and leaves the magnesium,
with perfect metallic properties, behind.   It is white like silver, mal-
leable and  fusible at a red heat;  it  is not  changed by dry air, and
but  slowly  oxidized by damp air ;  it may be boiled in water without
this being decomposed.   If magnesium be  heated to  redness in air
or oxygen, it  burns with  brilliancy, forming  magnesia,  and it in-
flames spontaneously  in  chlorine ; it dissolves in dilute  acids with
the  evolution of hydrogen gas, and  the formation of a salt of mag-
nesia.   The symbol of magnesium is Mg., and its equivalent number
is 158*3  or  12-7 according to the standard.
  Magnesia, the  only known compound of  magnesium and oxygen,
is a  protoxide.  It exists  in considerable quantity in nature, being
a constituent of a great variety of minerals ; it is found as hydrate,
as carbonate, sulphate, and silicate, but its  most abundant source is
the magnesian limestone,  common both  in  Ireland and in England,
which consists of an equivalent of each carbonate, its formula being
Ca.O.. C.02 + Mg.O. . C02.  The pure magnesia is always prepared
by exposing the carbonate of magnesia of commerce, the preparation
of which will be described among the salts, to a full red heat; the
carbonicacid is expelled, and the earth remains pure.  Magnesia is
a very light white powder, without taste or smell ; it is almost per-
fectly infusible; but it  and lime are remarkable for becoming beau-
tifully  phosphorescent  when  strongly heated,  and it is hence that
lime is used as a source of the most  brilliant light when it is heated
in the jet of the  oxyhydrogen blowpipe.  It is very sparingly solu-
ble in water, and  still less so in hot than in  cold water ; its solution
browns turmeric  paper very slightly.  It is remarkably inferior to
lime in basic power, but still neutralizes the strongest acids perfect-
ly, forming  excellently characterized classes of salts.
  The formula of magnesia is  Mg.O., and its composition and equiv-
alent numbers  are, 
             PREPARATION OF  ALUMINUM.         349

       Magnesium,  61*29    One equivalent —158*3 or 12*7
       Oxygen,     38*81    One equivalent = 100*0 or  8*0
                 100-00                      258-3     20-7
  Magnesia is recognised by its sulphate being very soluble in wa-
ter, and a solution containing it being precipitated by the alkalies
and their  carbonates.  The precipitate so obtained is  redissolved
on adding to the liquor a strong solution  of sal ammoniac.   The
most delicate test for magnesia consists in rendering the  liquor sus-
pected to contain it alkaline  by ammonia, and then adding a solution
of phosphate  of  soda; after  a short time the  phosphate of ammonia
and magnesia crystallizes on the side of the glass, particularly if it
be scratched  by  a glass rod: this double salt is almost completely
insoluble in an alkaline liquor.   A solid substance containing  mag-
nesia possesses the property, that, if it be moistened by a very  small
quantity of nitrate of cobalt, and ignited strongly by  the blowpipe,
it becomes a fine pink or rose colour:  the presence of other bodies
may, however, interfere with this result.
  The sulphurets and seleniurets of magnesium are of no impor-
tance  ; they resemble, almost perfectly, those of calcium already
noticed.

                          SECTION II.
                  METALS OF THE SECOND CLASS.
                         Of Aluminum.
  This metal is  prepared by the action of potassium upon its  chlo-
ride, exactly as described for magnesium in the last  division, but the
operation  must  be performed in vessels of platinum  or porcelain,
as the heat spontaneously evolved during the reaction is so intense
as to  fuse the  most refractory glass; the quantity operated on
should likewise be small.  A gray melted mass of chloride of potas-
sium and metallic  aluminum remains, which is to be washed  with
cold water, and  the  metal is thus obtained in minute but brilliant
scales.
  Aluminum  docs not decompose water at  ordinary temperatures,
and only slowly  even at  a boiling heat, but it  dissolves  rapidly in
dilute acids, and also in solutions of the caustic alkalies, with the
evolution of hydrogen gas, from the water being decomposed.   The.
syirhol of aluminum  is Ah, and its equivalent numbers are 171*2 or
13*7,according to the scale.
  There is but one compound known of aluminum  and  oxygen:  it
is alumina.  This earth exists in very large quantity in nature, being
even still more abundant than lime ; it is a principal ingredient of
almost all rocks,  except the purest kinds of limestone ;  it constitutes
the great mass of the ordinary clays and soils, these deposites being
produced by the gradual decomposition and detrition of variouskinds
of rocks.  In all these forms the alumina is generally combined with
silica, and sometimes with sulphuric or phosphoric acids; it is also
met with pure, or at least contaminated by the presence of only a
trace of foreign  matter; thus the ruby and the  sapphire,  two of the
most highly prized precious stones, are alumina, combined with  small 
350  PREPARATION AND PROPERTIES OF  ALUMINA.

quantities of colouring  matter.  The importance of alumina in the
arts is very great; it is a necessary ingredient in the formation of all
kinds of earthenware, from tiles or bricks to the finest kinds of por-
celain and is extensively used as the basis or mordant for some of
the most brilliant and durable colours that can be fixed upon cotton
or woollen cloth.  The alumina derives its name from the salt which
it forms with potash and sulphuric acid, the alum of commerce, from
which it is always prepared for the purposes of the chemist.
  To prepare pure  alumina, a solution  of alum is  to  be decom-
posed by carbonate of potash, and the precipitate separated by  the
filter.  This  precipitate is alumina,  the sulphuric acid being  taken
by  the potash, and the  carbonic  acid, which cannot  combine with
the alumina, being evolved as gas.   The  alumina thus produced is,
however, not quite pure;  it always carries down with it  a little sul-
phate of potash, from which it must be separated by being dissolved
in dilute muriatic acid, and again precipitated by carbonate of am-
monia ;  being then well washed, until the water passes from the fil-
ter completely  free  from  sal  ammoniac,  it  may be looked  upon as
pure.  The alumina so obtained, when dried at  common tempera-
tures, constitutes a bulky gummy  mass, which is a hydrate, the earth
and the water containing equal quantities of oxygen.  To expel this
water completely, it must be exposed  to a white heat ; in drying it
contracts  very much.   It was on the measurement of this contrac-
tion that Wedgewood founded his pyrometer, now gone  out of use,
and to allow for it, all  vessels of earthenware and china are made
much larger than they are intended  to be when completely  baked.
  In consequence of the great power with which alumina  absorbs
and retains moisture, it adheres strongly to the tongue, producing a
very peculiar sensation when applied to it.  The more or less reten-
tive quality of soils results from the  same property, and is generally
proportional to the quantity of pure  clay  which they contain.
  Alumina is white ; if dried at moderate temperatures, it dissolves
freely in acids and in solutions of the fixed caustic alkalies, but if
it be very strongly heated, particularly if fused  by the oxyhydrogen
blowpipe, it dissolves much more slowly.  It is particularly remark-
able for its tendency to unite with  organic matters.  If a cotton cloth
be immersed in  a solution of  acetate of alumina, the earth will de-
posite itself completely on the fibres of the cotton, and leave the acetic
acid free.   The  most important processes in calico printing repose
upon this principle.
  Although alumina is the only compound of aluminum and oxygen,
it  is yet not  to  be considered as a protoxide.   I have already de-
scribed, pages 213 and 223, the isomorphous and other relations which
establish its constitution to be similar to that of peroxide  of iron.
It is hence a sesquioxide, and its  formula is A1203.  Its composition
and equivalent numbers are,

      Alumina,  53*3    Two equivalents,   =342*4  or 27*4
      Oxygen,  46*7    Three equivalents, =300*0  or 24*0
               1000                        "642*4   "51*4

  Alumina is easily recognised.  Its solution is precipitated by the
alkaline carbonates, and the precipitate is dissolved by the caustic 
          GLUCINUM,  YTTRIUM,  THORIUM,  ETC.      351


fixed alkalies, but not by ammonia.   It is also precipitated white by
hydrosulphuret of ammonia.   If a solid substance containing alumina
be moistened with a trace of nitrate of cobalt, and ignited by the
blowpipe,  it becomes of a beautiful blue colour.
   If aluminum be heated in the vapour of sulphur,  it takes fire, and forms a gray
mass of sulphuret of aluminum.  This is decomposed by water, producing alumina
an J sulphuretted hydrogen, showing that its formula was AI2S3, which with 3H.O.
g; v AI2O3 and 311 S.  This sulphuret, therefore, cannot be formed in solution ; and
when a solution of alumina is precipitated by hydrosulphuret of ammonia, as already
noticed, the  precipitate is pure alumina, and the liquor contains  sulphuret of hy-
dio^'ii.
   The seleniuret and phosphuret of aluminum are known, but are of no importance.

                               Of Glucinum.

   The earth of which this metal is the basis has been found but in a few rare min-
erals, and as it exercises  no influence on science from the nature of its compounds,
and is of no  application in medicine or in the arts, a  very brief notice of it will suf-
fice.  It exists in the emerald, beryl, and  euclase.   To  obtain it from beivl,  the
mineral is fused with carbonate of potash, the mass treated  with dilute muriatic
acid, and evaporated to dryness to separate the silica.  The portion which dissolves
then in water is to be decomposed  by ammonia, which precipitates the alumina and
glucina together, and the  moist precipitate  digested in a strong cold solution of car-
bonate of ammonia, in which the glucina dissolves.  On boiling the filtered liquor
so obtained,  the glucina separates in combination with carbonic acid, from which it
is freed by ignition,  and so obtained pure.
  This earth is tasteless and inodorous : it is insoluble in water, and has no action
on vegetable colours.  Its salts taste remarkably sweet, whence its name (ylvavc).
ft is easily recognised by  its relation to pure and carbonated ammonia, described in
the details of its preparation.   The metal  glucinum is prepared from its chloride
precisely as  aluminum and magnesium, which  it resembles very  closely in all its
properties.   Its symbol is G., and its e< uivalent numbers are 331 4 or 26 5
  (ilucina is considered  to be, like alumina, a sesquioxide, and its  formula being
G2O3, its composition and equivalents may easily be  calculated.

                 Of Yttrium, Thorium, and Zirconium.

  These  metals  are the bases of earths, concerning which, from  the rarity of the
sources from which  they have hitherto been derived, but little is known, and from
their being destitute of scientific importance as well as of practical application, short
notice of their characters  only need be given.
   Yttrium.—The earth yttria, oxide of yttrium, exists in  some rare  Swedish min-
erals, which  were its only sources until the very remarkable discovery, by Apjohn,
of its presence in the ordinary Bohemian garnet or pyrope. The method of its ex-
traction is too complicated for description here.  It is insoluble in the fixed caustic
alkalies, and is precipitated by the yellow prussiate of potash,  by which it is com-
pletely distinguished from  the  other earths.  It  is a  protoxide.   Its formula  is
hence Y.O.
   Thorium.—The earth thoria, oxide of thorium, Th.O., has been found but in two
very rare minerals.   It is the heaviest  of all the earths, its sp. gr. being 9 4.  It re-
sembles yttria closely in its properties.
   Zirconium.—The  earth zirconia, sesquioxide of zirconium, Zr203, is found in two
rare minerals, the hyacinth and zircon.   It resembles alumina very closely in all its
properties, and in some respects assimilates itself to silica, and appears to form the
link by which the metallic and  non-metallic  bodies are connected in  this direction.
Thus the double fluoride ol zirconium and potassium  is a sparingly  soluble salt, like
the fluoride of  silicon and  potassium, and it is from this double fluoride  that zirco-
nium is obtained, by a process identical with that which is described in page 321,
for the preparation of silicon.

                          Cerium.    Lanthanum.

  These  metals are found in a few rather rare minerals, and have  been but very
recently distinguished from one another.  They are always associated together id 
352    MANGANESE,  ITS  PREPARATION, ETC.
nature  Their history does not possess any particular interest, and need hence be
noticed but very briefly.                          ,,  .,   .         . ,
  The metallic cerium is obtained by igniting the protochloride of cerium with po-
tassium, as has been already described for other metals    It is a slightly coherent
brown powder which decomposes water slowly, evolving hydrogen, particularly if
the water be hot, and forming oxide of cerium.  It combines with oxygen in two
proportions forming a protoxide and a sesquioxide, Ce.O. and U\>()3.   but all the
results obtained with it  now require revision, as the discovery of lanthanum has
thrown much  doubt on the purity of the substances that have been hitherto analyzed
as compounds of cerium, and on its received atomic weight.  The protoxide of
cerium is ol a pale fawn  colour.  If it be heated in the open air, it absorbs oxygen,
and  changes into the dark brown  peroxide ; and if  this be reduced by hydrogen
gas, at a red heat, it forms a yellow complex oxide, probably Ce304.
  Lanthanum.—It was found by iMosander, that by calcining protoxide of cerium
so as to convert it into peroxide, only a portion of it  became insoluble in dilute ni-
tric acid, and  that which dissolved was found, on accurate examination, to be really
an oxide  of a new metal, which, not terming an  insoluble peroxide, may be ihus
separated from oxide of cerium.  From its having been so  long hidden in the oxide
of cerium usually made, he named it lanthanum (kavOavu), but its detailed his-
tory remains yet undeveloped.
                           Of Manganese.
  This  metal exists very extensively diffused  through nature, al-
though not in very great quantity.   Traces of it are found in the an-
imal and veo-etable kingdoms, but its great sources are the numerous
combinations which it forms with oxygen,  and which  are employed
for the purposes of  the arts  and of research.  Its name is a modifi-
cation of magnesia,  for the native peroxide was once termed magne-
sia nigra ; but when the peculiar metal which it contained was recog-
nised, the present appellation was given to it.
  Manganese is one of the metals most difficult to reduce, from its
great affinity for  oxygen, and the high temperature  necessary for
its  fusion.   To obtain it, the oxide must be taken in a state of  very
fine division, and for that object it is best to use an oxide artificially
prepared, as described farther on.   This  is  to be mixed with an
equal weight of lampblack, and made  into a dough with oil, and this
mass fixed into a crucible, previously coated with a mixture of clay
and charcoal powder.  The  crucible, so  filled,  being  covered,  is to
be  exposed to  the most violent heat of a smith's forge for a couple
of  hours.  On then examining it, a button of  metallic manganese
will be  found occupying its  lowest portion.
   The metallic manganese  is grayish white,  granular, and brittle;
its sp. gr. 8*013.   It is exceedingly infusible.  It very  soon tarnishes
in  the  air,  absorbing oxygen, and falling into a black powder  after
some time.  It decomposes pure water, but very slowly ; but rapidly
 dissolves in  dilute  sulphuric acid, with the evolution of hydrogen
gas, sulphate of the protoxide of manganese being formed.
   The symbol of manganese is Mm, and  its atomic weight is 346 or
27*7, according to the standard.
   It is remarkable for the number of compounds which it forms with
 oxygen, which are  as follows :
            Protoxide of manganese   ....  Mn.O.
            Sesquioxide of manganese   .   .   .  Mn2Os.
            Peroxide of manganese    ....  Mn.02.
            Manganic acid.......Mn.03.
            Permanganic acid......Mn207. 
OXIDES  OF  MANGANESE.
353
  In addition, there are two complex oxides:

      The red  oxide  ....   MnA, or Mn.O. + Mn203.
      Varvicite......Mn407, or Mn203-f-2Mn.02.
  The metallic  manganese being  of such difficult  preparation, the
various compounds of it are usually obtained from its most abundant
source, the native  peroxide, which is sent into commerce  in large
quantities, to be employed in the arts  for the fabrication of chlorine,
and in  chemistry to prepare  oxygen, and  many  other purposes.
The simplest way of preparing the salts of manganese from this na-
tive peroxide, which is usually associated with a large quantity of
oxide of iron, consists in dissolving it in an excess  of muriatic acid,
and evaporating the liquor  so obtained to dryness.  The resulting
mass consists of chloride of manganese mixed with perchloride of
iron.  When this mass is heated to redness, the perchloride of iron
is  partly  decomposed and partly  volatilized, and  on digesting the
residual mass in water,  oxide of iron  remains undissolved, and a
colourless or faintly amethystine  solution of protochloride  of man-
ganese  is obtained.  From this the various other preparations may
be easily  formed.
  Protoxide of JManganese—Mn.O.; equivalent 446 or 35*7—may
be prepared in  many ways.   If to a solution  of  protochloride of
manganese an excess of a caustic alkali be added, a bulky white
precipitate is produced, which is hydrated protoxide of manganese.
In this state it rapidly absorbs oxygen from the air, becoming reddish
brown, being converted into red oxide, which is the most permanent
of the oxygen compounds of manganese.  If any of the higher ox-
ides of manganese, in a state of fine division, such  as the red oxide
or peroxide artificially prepared,  be heated to redness in a tube of
hard glass, in a stream of hydrogen gas, oxygen is  removed in such
proportion as to leave protoxide of manganese  behind.  The oxide
so obtained is of a greenish gray colour ; it does not absorb oxygen
at all so rapidly as the hydrated oxide  ; but  if it be exposed to the
air while hot, it rapidly becomes  brown, or even  burns.  But it is
best obtained by mixing together  chloride of manganese, carbonate
of soda, and sal ammoniac, and exposing them in a  kind of platinum
crucible to a full red heat.   The  chloride of manganese is decom-
posed by the carbonate of soda, chloride of sodium and  carbonate
of manganese  being formed ; Mn.Cl. and Na.O. .  C02  giving  Na.
CI. and Mn.O.. C02.  The carbonic acid is,  however, driven off by
the high temperature, and the protoxide of manganese set free, being
evolved in presence of the sal ammoniac, which readily yields hy-
drogen, is prevented from passing to a higher degree of oxidation.
The oxide obtained at this high  temperature  has no  tendency to
combine  farther with oxygen under  ordinary  circumstances,  and
may hence be easily preserved.
   The oxide is  of various shades  of grayish green, according to the
method of preparation.   It is without action on vegetable  colours,
but it combines with all the acids, evolving in some cases, as with
oil of vitriol, intense heat, and forms salts remarkable for their def-
initeness  and  neutrality.   These salts are generally colourless, but
often of a peculiar rose colour, which is not due to the presence of 
354  SESQUIOXIDE  AND  PEROXIDE  OF  MANGANESh.

any higher degree of oxidation, but  to a  peculiar (isomeric) con-
dition of the salt itself.
  Sesquioxide of Manganese.—Mn2Os.  Equivalent 992 or 79*4.   This
oxide is found in nature in considerable quantity,  either pure, as in
the mineral braunite, or combined with water, as in the mineral man-
ganite.  It maybe prepared artificially by exposing the peroxide for
a short time to a dull red heat, but it is difficult to manage the de-
composition of that substance so that it shall not proceed  too  far.
The sesquioxide is of a dirk brown colour;  exposed to a strong
heat it is  partly decomposed, evolving  oxygen, and being reduced
to the state of red  oxide.  It combines  with acids, forming salts
which are  of a  deep red  colour, and which are isomorphous with
those of alumina.  Its salts are immediately decolorized by sulphur-
ous acid  and by sulphuretted hydrogen.   This oxide possesses  the
property of staining glass purple  or violet, and by this character an
exceedingly small trace of manganese can be detected by fusing the
substance with borax in the oxidating flame of the blowpipe.
  Peroxide of Manganese, or Black Oxide.— Mn.02.  Equivalent 54G
or 43.7.   This substance,  which is the most  abundant source of
manganese, and that from which all  its technical applications  are
derived, exists in nature in a variety of forms.  Crystallized and  pure,
it forms the mineralpyrolusite ;  combined with water, 2Mn.0i-f-H.
O.,  it constitutes the mineral Wadd, which,in an impure form, con-
taminated with variable quantities of peroxide of iron, carbonate of
lime,  and carbonate of barytes, forms the earthy varieties, which  are
those usually found in commerce.  This oxide may be prepared ar-
tificially by decomposing the protochloride of manganese by a solu-
tion of chloride  of lime, Mn.Cl.  and 2Ca.O. + Cl. producing 2Ca.Cl.
and Mn.02.  It is also produced when permanganate of potash is de-
composed by any organic  substance.  In these cases it is precipita-
ted in combination with one equivalent of water, Mn.02-4-H.O., from
which it may be freed by a temperature below redness.
  This peroxide of manganese is black ;  exposed to heat, it abandons
oxygen, being reduced first to the state of sesquioxide, and finally
to that of red oxide.  It does not unite with either acids or alkalies ;
but, when heated with strong sulphuric acid, it is decomposed in  the
manner fully described under the head of oxygen, in page 244.   Its
use in the preparation of chlorine has been also noticed, page 301.
An  important object to which it is applied  is to peroxidize the iron
contained in the ordinary materials used in the manufacture of glass.
If the iron were as protoxide, it would colour the glass green ; but the
red oxide produces only  a very  faint yellowish tinge ; and as  the
protoxide of manganese is itself destitute of colouring power, by the
action of Mn.02  on 2Fe.O. there  are formed Mn.O. and Fe,03, two
substances which have no  injurious effect  upon the glass; if, how-
ever, the peroxide of manganese be added  in excess, a purple colour
is produced.
  Of  the complex oxides, the red oxide is alone of  interest.  It is
the most stable of the compounds of manganese ; and whenever the
quantity of this metal present in  a substance is to be determined by
analysis, it is always as the red oxide that it is obtained.   A solution
of any salt of manganese, being precipitated by an  excess of a  caus- 
      ANALYSIS  OF  PEROXIDE  OF  MANGANESE.   355


tic alkali, the precipitate, cautiously washed and ignited in an  open
crucible, gives the quantity of red oxide corresponding  to the quan-
tity of manganese present.  The varvacite, the other complex oxide,
is a mineral of  rare occurrence, and  only of interest as it  may be
mistaken for the peroxide, to which it is inferior in technical value.
  The peroxide of manganese found in commerce is never quite pure ; and  as its
use in the arts, and, consequently, its price, are, generally speaking, due exclusivt ly
to the quantity of oxygen it is capable of yielding, a ready mode of effecting its anal-
ysis becomes of great importance.  There are two modes in which this may  be ac-
complished upon very simple principles, and in a short time, with sufficient  accu-
racy for all practical purposes.   The first consists  in converting oxalic  acid into
carbonic acid, by means of the second atom of oxygen which the peroxide of man-
ganese contains ; for Mn.02 and C203 produce Mn.O. and 2C02.   For this purpose
100 grains of the manganese are to be introduced into a weighed flask, and  150
grains of oxalic acid, dissolved in 500 grains of water, are to be then poured upon
it; to this 350 grains of oil of vitriol  are to be added, and the orifice of the flask
closed by a cork, through which passes a tube containing fragments of recently-fused
chloride of calcium.  The weight of this cork and tube are to be included in the tare
of the flask.  On the addition of the oil of vitriol, a brisk effervescence takes  place,
owing to  the escape of carbonic acid gas, which, passing over the fragments of
chloride of calcium in the tube, are dried, so that the gas alone passes off.   When
the action slackens, a  gentle heat may be applied until all the oxide of manganese
has dissolved ;  a small quantity of a light brownish sediment, which generally forms,
is easily distinguished from the particles of black oxide : as  soon as the action is
quite over, the  liask is suffered to cool, and as  it contains still a quantity of carbonic
acid gas, this is removed  by taking out the cork, and blowing  air into  the flask
gently by a glass tube ; the cork is then to be replaced, and the flask, with its con-
tents, weighed.  It  is found  to  be  lighter than it and  the  materials together had
been, and the loss is the carbonic acid.  The quantity of carbonic  acid formed is
thus found, and the quantity  of oxygen it contained calculated ;  one fourth of
this had been derived from the peroxide of manganese by its conversion into pro-
toxide, which remains combined with sulphuric acid in the liquor, and the quantity
of peroxide in the 100 grains  of the ore is thus directly found.  Thus, taking as
an example an actual  determination, the flask and  materials weighed altogether
1876 grains ;  after the action  had  terminated it weighed 18165 grains ; the loss
was, therefore, 59 5.   This consisted of 16 3 of carbon and 43 2 of oxygen.   The
oxygen derived from  the  mineral  was, therefore,  —=108,  which represent 59
grains of pure peroxide of manganese in the 100 of the substance used.
  The second mode of analysis consists in treating a certain quantity of the native
oxide with an excess of muriatic acid, and passing the chlorine so evolved through
water in which lime is diffused ; chloride of lime is formed.   A certain quantity of
protosulphate of iron (green copperas) is to be dissolved in water, and the solution
of chloride of lime added thereto, until the iron liquor ceases to strike a blue colour
with a drop of solution of red prussiate of potash ; then comparing the quantity of
the solution of chloride of lime required with the quantity that was produced, the
total quantity of chlorine generated, and, hence, the total quantity of oxygen availa-
ble in the mineral, are known.  The theory of the process may be still more simply
expressed by the formulae  of the bodies engaged, as follows : Mn.02 and 2H.CL,
acting together, produce Mn.Cl. and 211.0., while CI. is given off as gas; this combines
with Ca.O. When the compound Ca.O.CI. is brought  in contact with 2(Fe.O.. S.03),
the oxygen passing from the lime to the iron, we have Ca.Cl. and Fc203. 2S.O, pro-
duced.   As long as any protosulphate of iron exists, the solution gives  Prussian
blue with the red prussiate of potash ; but when all the iron is changed to peroxide,
the blue colour is no longer produced.  The following example of an actual opera-
tion will complete this explanation.   100 grains of commercial oxide of manganese
were placed in a flask with about one ounce of strong spirits  of salt, and  the chlo-
rine evolved was conducted by a bent tube to the bottom of a  deep  jar containing
1000 grains of  water with  100  grains of slacked lime ; when the  oxide of manga-
nese had  been completely decomposed by the  muriatic acid, and all evolution of
chlorine had ceased, a quantity of the solution of chloride of lime was filtered for
use ; this being very strong, 500 grains of it were diluted with 1000  of water.  On
the other  hand, 100 of crystallized  protosulphate of iron were dissolved in 1000
grains of water, and the dilute solution of chloride of lime added thereto by  drono 
356
MANGANIC  AND  PERMANGANIC  ACIDS.
from an accurately graduated tube, until, by the test of red prussiate of potash, a»,<
the iron was peroxidized.  It required 1300 grains of the dilute solution, and hence
433 of the strong solution.  Now,  as  100  grains of the mineral had given 1600
grains of this strong solution, the 433 grains corresponded to 27 grains ; the avail-
able  oxygen of which was exactly equivalent to transfer the iron of the  protosul-
phate to the state of peroxide.  Now the 100 grains contain 45-6 of water, 289 of
acid, and 255 of protoxide of iron, consisting of 19 7 of iron and 5 8 of oxygen, and
it requires one half more,  that is, 29, to form peroxide.  The result is, that in the
27 grains of commercial oxide of manganese, the available oxygen is 2 9, and the
quantity of  pure peroxide  consequently 158 grains, or 587 per cent.  This whole
process, although, when thus described in detail,  it may appear complex, is exceed-
ingly simple in execution,  and does  not occupy much time.  In accuracy, the two
methods are about equal, giving results which may be depended  on to one  percent.
  A  mode has been recommended, which consists in simply adding the green sul-
phate of iron directly to the muriatic acid and oxide of manganese in the flask, until
the salt is found to be slightly in excess by the filtered liquor giving Prussian blue
with red prussiate of potash ;  the quantity of green copperas added  is known  by
having previously weighed out  a quantity, and  then weighing  what may remain
after the process has been completed.  If no chlorine could escape the action of the
iron salt, this method would  be much the shortest and simplest that could be em-
ployed ; but it is exceedingly difficult so to  manage  the decomposition as  to avoid
its partial loss.  On this account, I look upon this method as inferior  in accuracy,
and really not much simpler of execution, than those previously described.
  The composition of the  commercial oxide is very  variable, but the general limits
may  be considered as being  between 60 and 70 per  cent, of pure peroxide in 100.
Frequently,  the commercial substance contains sesquioxide, or one of the complex
oxides ; but in all these cases, the methods given, as they determine the quantity of
available oxygen, show the true value of the specimen, no matter what the state of
combination of the metal may be.
   Manganic  Acid.—Mn.03.  Equivalent 646  or 517.  If peroxide
of manganese be  mixed with  caustic potash, or carbonate or nitrate
of potash, in a crucible, and ignited strongly,  a green fused  mass is
obtained,  which dissolves  in a  small quantity  of water with a fine
grass-green colour.   After some time, particularly if  the solution
be diluted, it  gradually changes colour, a  brown precipitate separ-
ates, and  the  liquor becomes of a  splendid red colour.  This  sub-
stance first got the name  of  mineral chameleon from these changes,
but  their  production  is now known to  depend  on the formation  of
two distinct acids of manganese.   The peroxide  of manganese  in
these  cases combines with another atom  of  oxygen to  form man-
ganic  acid, which unites with the potash.  If potash, caustic or car-
bonated, be used, the oxygen is derived from the air ;  if nitre, it sup-
plies oxygen ; but the best source  consists in  mixing four parts  of
peroxide of manganese in  fine powder with 3£  parts of chlorate  of
potash, and adding thereto five parts of caustic  potash dissolved in
a small quantity of Avater.   This mixture is to be evaporated  to dry-
ness, powdered, and afterward ignited in a platinum crucible,  at a
low  red heat insufficient for fusion.  By digestion  of this mass  in
cold water, a deep green solution is obtained, from which, by evap-
oration in vacuo, the manganate of potash is obtained in crystals.
The salts  of this acid are  isomorphous  with those of the sulphuric
and  chromic acids.  They are decomposed very easily, particularly
if organic matter be present,  and the acid itself is hence incapable
of being exhibited in  an isolated form.
  Permanganic Acid.—Mn20-,.  Equivalent 1392 or 111*4. When a
solution of manganate of potash is  diluted  with boiling water, a co-
pious  precipitate of hydrated peroxide  of  manganese forms, and a 
          DETECTION  OF  MANGANES E.--1 RON.       357

fine  crimson  solution of  permanganate  of  potash  is  obtained.
3Mn.O:i  produces Mn.02 and  Mn207.  By rapidly  evaporating this
solution until a pellicle forms, an abundant crop of crystals of per-
manganate of potash is obtained on cooling: these are  isomorphous
with the perchlorate  of potash, and are almost completely black,
but with a very peculiar bronze lustre.   The  salts of  this acid are
very stable,  and by  treating  the permanganate of barytes with a
proper quantity of dilute sulphuric acid, a deep crimson solution  of
permanganic acid  is obtained.  This acid  cannot  be had solid, ac-
cording to Mitscherlich, its solution when  heated  to 100° F.  being
decomposed into peroxide of  manganese  and oxygen gas.   It  is
very probable that the solid substance  described  as  dry perman-
ganic acid by some chemists contained some other matter combined
with it.
   The formation  of these acids by the action of sulphuric acid on
peroxide  of  manganese has  been  already noticed, and  the  most
delicate test of the presence  of manganese in minerals consists in
fusing a fragment of the substance with a little carbonate of soda
on a slip of  platina foil, by means of the oxidizing flame of the blow-
pipe.  The mass, on cooling, becomes apple-green, from the forma-
tion of  manganate of soda, if there be the  smallest trace of manga-
nese in the  substance used.
   There is but one sulphuret of manganese.   It is found as a min-
eral, and  formed also by heating oxide of manganese  and  sulphur
(page 285).   It is precipitated in a hydrated state,  when a solution
of manganese is  decomposed by hydrosulphuret of ammonia. Its
colour is then flesh red.   Its formula is Mn.S.
   The  detection of manganese is very  simple.  When in a  solid
form, its compounds are recognised by giving  before the blowpipe a
purple glass with borax, and  a green bead  with carbonate of  soda.
In solution,  if the manganese be as protoxide, the solution is col-
ourless, and yields with the caustic alkalies a white precipitate  (Mn.
0.), rapidly becoming brown (Mn304) : with the alkaline carbonates,
a white precipitate, Mn.O. . C.02; and with hydrosulphuret of am-
monia, a flesh red hydrated sulphuret.  The yellow prussiate of pot-
ash precipitates the salts of manganese pure white, if there be no
trace of iron present.  When the manganese  is not in the state of
protoxide, the solution is always coloured red  or green.  These so-
lutions are decolorized by sulphurous acid and by sulphuretted hy-
drogen, which absorbs oxygen from all the  higher degrees of oxida-
tion, and a colourless solution of protoxide is  then  obtained, which
gives the reactions already described.

                         SECTION III.
                  METALS OF  THE THIRD CLASS.
                           Of Iron.
   This is the most extensively distributed, and also the  most im-
portant  of the metals ; it may, indeed, be considered as being,  after
those elements necessary to the functions of animal existence, that
which is most indispensable to man for the wants of ordinary life.
")n its employment  and applications is founded  every important 
358
STATE  OF  IRON  IN  NATURE.
step which marks the gradual progress of the human race from bar-
barism to civilization.   The difficulties which its reduction from the
state of ore present, the variety of conditions necessary for its being
successfully wrought into useful forms, and  the pre-eminent advan-
tage it possesses over every other metal for the construction equally
of the  simplest tool and the  most complex machine, for the imple-
ments  of war as well as peace, all combine  to excite the energies
of a people to its  acquisition, whether  by their own labour or  by
commerce ; and thus impel them to mental activity  and civilization,
either  of native and independent growth, or borrowed  from more
advanced neighbours.  As gold and jewels hence become the type
of ignorant and barbaric pomp, so iron may be regarded as the great-
est material source of national intelligence and industry.
  Iron exists in nature under a variety of forms ; it  is found native;
for, in  addition to  loose blocks of metallic iron found on the surface
in various countries, and to which a different nature may be assigned,
it is found in veins, in mines,  in  Russia and America.  Its most
abundant form is  that  of  oxide, either  pure,  forming the various
black and magnetic oxides, the haematite, or  red oxide, &c, or com-
bined with carbonic acid, constituting the clay iron stone from which
the iron of commerce  is principally extracted.  Its sulphurets are
also found in abundance, and native arseniates, phosphates, sulphates,
and other salts have been found.
  A most remarkable source of iron is one not truly terrestrial, but
that, occasionally, masses appear in our atmosphere at great heights
above  the surface,  and  presenting all the appearances of vivid igni-
tion and combustion ; they move generally  with great velocity ob-
liquely towards  the ground, and generally, before touching, or at the
moment of contact with the surface, burst with an  explosion, scat-
tering  their fragments to considerable distances.  These masses are
termed wrolithes ;  they consist,  in general, of an alloy of iron, with
some nickel and chrome, with traces of other metals, and are generally
invested with a vitreous glaze of earthy matter, which is constituted
of minerals (olivine and pyroxene) found native in volcanic rocks.
The only theory which can  explain the  origin of these meteors  is,
that they are expelled violently from the active volcanoes which
telescopic research has proved to exist in great numbers on the sur-
face of the  moon,  and that, passing beyond the limits of the attrac-
tion of our  satellite, they come under the influence of this earth, and
fall towards its  surface.  No such  substances are  ever found pro-
jected  from terrestrial volcanoes.
  The general principles  of the smelting  of the  clay iron stone
have been already noticed (p. 334), both considering  it as a mere car-
bonate of iron, and where  it contains clay,  silica,  and  alumina,  so
as to render lime necessary as a flux. It is, however, a remarkable
property of iron-one on which rests, perhaps, its most useful appli-
cations—that the metal so obtained is  not  pure.   The iron, when
reduced, combines with a  quantity  of carbon, generally about five
per cent., approximating to the  formula C. + 4Fe., and forming cast
iron, which is easily fusible, while  the pure metal  is almost quite
infusible.  The cast iron is,  however, not by any means a pure car-
buret of iron ; it contains small quantities of  silicon and phosphorus, 
        PREPARATION  OF MALLEABLE  IRON.     359

according to the proportions of which it varies in properties, so as
to constitute a number of varieties, known in the arts by their col-
our and texture, but of which it would be superfluous to speak here.
When cast iron remains under water for a considerable time, it be-
comes  gradually  oxidized, magnetic oxide  of iron being  formed,
and the carbon  remaining under the form  of a spongy mass, pre-
serving, even in minute details, the figure of the original mass.
  Cast iron has a great tendency to  crystallize in becoming solid,
and then expands powerfully ;  hence its property of filling up the
most minute  crevices  of moulds into which it is poured in the li-
quid state, and its multifarious uses  for  making  castings, from
whence it derives its name.
  Pure or malleable iron is made from cast iron by taking advantage
of the fact that, though iron and carbon are both combustible, yet
carbon is the more so of the two.  Hence, if cast iron be melted in
a reverberatory furnace (see p. 333), and exposed to a current  of
air, the  carbon is gradually burned out, the  metal becomes less and
less fusible, and ultimately breaks up into  an incoherent granular
mass like sand ; by then increasing the heat, these grains  aggluti-
nate, and  are worked up into a ball about the size of a large loaf,
which  is  taken  out of the furnace on  a shovel, and subjected  to
great pressure by machinery.  The soft, pasty particles  of malleable
iron are thus welded to each other, and any portions of liquid, un-
altered  cast  iron  that might remain  are   squirted out, as  water
would  be by pressure from the pores of a sponge ;  this lump of
malleable iron is then passed through a succession of rollers, driven
by powerful steam engines ;  each pair of rollers having a smaller  in-
terval than the preceding, the  mass, is  gradually elongated into a
bar, and finally  is delivered,  at the end farthest from the furnace, in
the form of the soft bar  iron of commerce.  The heat evolved  by
the enormous pressure to which the metal is subjected  in this pro-
cess is so great, that the bar remains  soft  enough to  be moulded
by the rollers all through its passage.
  This process by the reverberatory  furnace is termed pudling, and
has been very much improved lately by burning out the carbon  by
means of a certain quantity of oxide of iron  or oxide of manganese.
Thus, by heating together two parts of cast iron  and one of scales
of black oxide of iron from a forge, all the carbon and oxygen pass
off as  carbonic acid, and the iron of both remains pure.  Fe304 and
Fe C. produce FeM and C204.
  The bar iron  thus obtained differs remarkably from the cast iron
in all characters: it is soft, flexible, ductile,  and malleable, none  of
which properties cast  iron  possesses.  It  fuses  only  at the very
highest  temperatures, and then  becomes only semifluid.  It is, con-
sequently, quite  impossible  to  run  it into  moulds.  It possesses,
however, the important character of welding at a white heat; that
is to say, it assumes a doughy consistence, so that several pieces
of it, laid  together, may be kneaded into one by blows of a hammer
or by  pressure  between  rollers, so  as  to form a single mass, the
points of junction being  totally undistinguishable.  It is thus that
soft iron is always worked at a white heat.   Its  strength is  much
increased by several pieces being thus welded together, and hence 
360
MANUFACTURE  OF  STEEL.
all parts which require to possess peculiar tenacity, such as anchors,
&c, are always made, not in a single piece, but by thus welding to
gether a bundle of  small bars.
   A third and equally important form in which iron exists in  the
arts, is that of steel.  Steel is intermediate to cast iron and bar iron
in constitution,  containing generally about 1*5 per cent, of carbon.
Steel may be formed directly from the ore or from cast iron by pro-
portioning the action of the fuel and of the air in the furnaces so as
to leave combined with the iron as much carbon as constitutes steel.
But the most important and curious mode of making steel is by what
is termed cementation.   Bars of iron are laid in boxes, imbedded in
powdered charcoal, and exposed for some hours to a full red heat;
the carbon gradually penetrates through the whole substance of the
iron, changing it into a  bar of steel  of pretty  uniform structure.
The bar becomes frequently blistered  from gas bubbles forming in
its substance.   This process can be effected even though the car-
bon may not directly touch the iron, provided oxygen be present;
carbonic oxide being formed, which is decomposed by the iron, half
the carbon being absorbed, and carbonic acid given off".   It is the es-
cape of this last gas under the form  of bubbles that produces  the
blistering of steel.   The decomposition of the carbonic oxide takes
place at the surface of the bar  in great part, but the carbon is trans-
ferred from particle to particle of the  iron until the entire mass as-
sumes the same constitution.  Steel is harder and more fusible than
pure iron, but its peculiar hardness is given to it only when it has
been heated to redness and suddenly cooled ; it is then exceedingly
brittle, hard, and elastic, and is thus fitted for its  extensive use in
cutting  instruments, pivots, files, &c.  The steel, when it has cooled
slowly,  is so soft that it  is easily engraved upon,  cut, and may be
welded  with soft iron; the instrument being so constructed, it is
heated to  redness and suddenly cooled; it is thus hardened, but is
still unfit for being employed until it  is tempered to the particular
use for which it is  destined by being heated in oil to a certain  de-
gree,  and  then allowed  to cool slowly.  By this means the excess
of hardness is got rid of, and  the  steel remains of the quality  re-
quired.
  The peculiar  property of iron and  steel of  becoming magnetic,
has been  described in  page  143.  Not only  is  iron  in the pure
state, and when combined  with carbon, attracted by the magnet,
but several of its oxides  and sulphurets possess the same charac-
ter ;  of these,  one constitutes, indeed, the natural magnet, the native
loadstone.
  Pure  iron is bluish white, exceedingly brilliant, very malleable
and ductile ; it is the strongest of all the metals.  Its specific grav-
ity is 7*8.   It  becomes pasty when  intensely heated, whence its re-
markable power of welding, which belongs, besides, to platinum and
sodium.
  When iron in  mass is exposed to dry air,  it does not become  ox,
idized;  but  when in a state  of very minute division, it takes  fire
when gently warmed, and burns, forming peroxide of iron; when
strongly heated  in oxygen gas, as by attaching a little sulphur or a
bit of taper wick to a wire, and plunging it into a vessel of oxygen, 
             PASSIVE CONDITION  OF IRON.         361

it bums with exceeding brilliancy, and  forms globules of black ox-
ide of iron, Fe..04.   The true product of the combustion is peroxide,
Fe^0„ but this loses one ninth of its oxygen by the intense tempera-
ture, and forms the black magnetic oxide.  It is hence that, when
iron is burned in oxygen gas,  the oxide, which is thrown  off in mi-
nute grains, collects on the inside of the jar as peroxide, but the lar-
ger globules, which are  intensely heated for some time  before  they
melt off the wire, are reduced  to the state of  black oxide.   It is not
quite certain whether iron  decomposes water in the absence of an
acid, but the presence of a small quantity even of carbonic acid  pro-
duces decided action, and hence the rapid corrosion of iron in damp
air, forming carbonate of iron (rust).   In  dilute  sulphuric acid  iron
dissolves with great rapidity,  evolving  hydrogen,  which,  however,
is  very impure, for even the softest iron contains traces of carbon,
which combines with some  of the  hydrogen, forming compounds,
which give the gas a peculiar odour, and colour its  flame yellow.
At a red heat water is decomposed rapidly by iron, as fully descri-
bed in p. 246.  If iron be  immersed in  water holding potash, lime,
or soda in solution, or if the  iron be covered up  in  quicklime, all
rusting is prevented, probably  from any  carbonic acid present being
totally  taken up by the base.
  A remarkable property of iron, though  not absolutely peculiar to
it alone, is, that when placed in contact with the hydrated nitric acid,
sp. gr. 1 35,  it may remain unacted on, becoming passive;  although,
under ordinary circumstances, it is rapidly dissolved by that  acid
with evolution of nitric oxide.  This passive  condition may be  pro-
duced in many ways.   1st.  It one end of a long iron wire be igni-
ted, and then, when cool, the  wire be immersed in the acid, the ig-
nited end  being dipped  first, it remains unaltered.  2d. If a piece
of platina wire  be fastened to  a piece  of iron wire, and then immer-
sed in the acid, the platina  first.  3d. By placing a platina wire in
the acid, then immersing an iron wire in contact with it, the platina
wire maybe withdrawn, and the iron wire  remain passive.   4th. By
making the iron wire the positive pole  of a galvanic battery.   5th.
By  contact with a wire already passive ;  thus, an iron wire being
immersed  in the acid, as in No. 3, another wire may be put in  con-
tact with it, and the first then withdrawn, and so on for an  unlimited
succession of wires.   These are not the only methods,  but merely
the most remarkable.
  The properties of iron thus rendered passive are curious.  It ap-
pears to have lost  all  tendency to unite with oxygen;  it  does not
dissolve in acids; it does not precipitate copper from its solutions;
and when used as a positive electrode for a voltaic battery, oxygen
is evolved from it precisely as if the  electrode had been  platinum.
We do not as yet know the true theory of these effects.   The most
available explanation is, that the iron, by an alteration of molecular
structure, assumes a condition by which  it becomes  similar in its
electrical relations  to  the  noble metals.   It  is possible  that  this
property may be connected with the equivalency of two  equivalents
of the iron and manganese  group of metals to one  of  chlorine,  and
that when, by a change  of molecular arrangement, like  isomerism^ 
362            VARIOUS  OXIDES  OF  IRON.
the particle becomes Fe2 in place of Fe., it is incapable of acting as
the positive element in galvanic or chemical combinations.
  The equivalent of iron is not so accurately known as those of
rnetals much less important and less common.  The best determi-
nations make it about 339 upon the oxygen, and 27*2  upon  the hy-
drogen scale.  Its symbol is  Fe., from its Latin name.
  0"xides of Iron.—Iron combines with  oxygen in two proportions,
forming a protoxide and a sesquioxide, and these, again, unite to form
complex oxides, the black or magnetic  oxides of iron.
  Protoxide of Iron.—Fe.O.  Equivalent 439  or 35*2.  This oxide
cannot be obtained pure in a dry state, from the rapidity with which
it absorbs oxygen.  It exists as the basis of a very extensive class
of salts, the green or protosalts of iron.  From their solutions, it is
precipitated by an alkali as a white hydrate, which rapidly becomes
green, and finally brown-red, from absorption of oxygen.  If we at-
tempt  to form the protoxide by processes similar to those described
for obtaining protoxide of manganese,  the  iron is reduced either to
black oxide or to the metallic state. This oxide exists native, com-
bined with carbonic acid, in the  common carbonate of iron, and is the
form in which the metal exists, dissolved in all chalybeate springs.
  Peroxide of Iron.—Fe203.   Equivalent 978 or 78*4.  This substance
exists  in very great abundance in nature, crystallized in rhombohe-
drons, being isomorphous with the crystallized alumina, corundum.
This, the ologist iron, constitutes the celebrated Elba  iron ore.  It
forms, in a more or less hydrated condition, the hematite, of various
shades of red and brown, from which a great deal of  the best iron
and steel is made.  It exists in a variety of minerals, and forms the
red or yellow colouring matter of clay  and of the different kinds of
ochres.  I have noticed that when  iron is burned in a  full supply of
oxygen, ihis red oxide is formed, and it is produced also when iron
rusts, for the protocarbonate which first forms is gradually  decom-
posed, abandoning its acid, and absorbing  oxygen.  It is thus that
the margins of chalybeate springs become coated with an  ochrey
deposite ; the carbonate of iron originally dissolved being gradually
converted into red oxide, while the carbonic acid passes off.
  The peroxide of iron may be artificially prepared by precipitating
a solution  of any of its salts with  an alkali caustic or carbonated.
In the  latter case, the carbonic acid is given off, as the peroxide of
iron does not combine  with it.  The  hydrated peroxide which is
precipitated is of a light reddish-brown colour, but when dried it
becomes dark brown.  Strongly  ignited, it becomes nearly  black;
and, indeed, by an intense heat  it loses  some of its oxygen,  3;Fe203)
giving 2(Fe304), and 0. escaping, being decomposed just as  the ses-
quioxide of manganese, but requiring much greater heat.  The per-
oxide of iron combines with acids to form  salts, which are all acid,
and  easily decomposed.  They  will  be  described  hereafter.   Its
chemical combinations resemble those  of alumina and sesquioxide
of manganese, with which they are isomorphous.
  When a solution of a protosalt  of iron  is exposed  to the air, it
gradually absorbs oxygen until two thirds of the i on become per-
oxidized, and then the decomposition ceases.  The liquor then con-
tains a compound oxide, Fe.O. -j-FeA, and  on the addition of a caus- 
SULPHURETS  OF  IRON.
363
tic alkali this is precipitated as a black powder, which, when dry, is
powerfully attracted by the magnet.   This is the artificial magnetic
oxide of iron.  It may be  prepared at will by taking three equal
portions of protosulphate of iron, and peroxidizing two of them by
means of a little boiling nitric acid, then mixing the solutions, and
precipitating the whole by water of caustic ammonia.  The precip-
itate is a hydrate, but may be  deprived of the water without altera-
tion.
  This magnetic oxide of iron exists  native in great abundance ; it
constitutes the common loadstone, and is that produced when  iron
is oxidized at high temperatures.  It  thus constitutes the scales  of
iron which form  in smithies and forges during the successive heat-
inors and hammerings to which the metal is subjected.   These scales
of iron are, however, not uniform in constitution, and are hence in-
ferior as a steady medicinal agent to  the oxide artificially prepared
by precipitation.
  Sulphurets of Iron.—Sulphur combines with iron in three propor-
tions, forming the protosulphuret, the sesquisulphuret, and the bi-
sulphuret.   These again combine, so  as to produce complex (mag-
netic) sulphurets.  Other degrees (subsulphurets) are problematical.
  Protosulphuret of Iron.—Fe.S.  Equivalent 540*4 or 43*3.  The af-
finity of iron for sulphur is very remarkable.  If a rod  of iron be
heated to whiteness, and then touched to a  stick of sulphur, they
combine with  energy, and the sulphuret of iron flows down in copi-
ous drops.  If vapour of sulphur be made to gush from a jet, and
an iron  wire heated to bright redness be  placed in it, it takes  fire,
and burns with scintillations as brilliantly as if it had been immersed
in  oxygen gas.  In  these cases, where the iron is in excess, the  pro-
tosulphuret  is  formed.  It is most conveniently prepared by heating
together to  bright redness, in a crucible, three parts of iron filings
or turnings, and two of sulphur ; at a high temperature the resulting
mass may be fused.  This compound is black, its fracture yellowish.
It dissolves in dilute acids, evolving sulphuret of hydrogen, and form-
ing a salt of protoxide of iron.  This is almost its only use in the
laboratory.  The manner of obtaining sulphuret of hydrogen from
it has been described in page 292.   This protosulphuret  of iron ex-
ists sometimes, though rarely, in nature, and is dangerous, particu-
larly in coal mines, from the avidity with which, when moist, it ab-
sorbs oxygen,  forming protosulphate  of iron,  Fe.S. and 40. giving
Fe.O. . S.O,; during which process it occasionally becomes so heat-
ed as to set  fire to the beds of coal near it, and thus cause consid-
erable loss.
  This sulphuret may  be prepared in  the  moist way by adding hy-
drosulphuret of  ammonia to a protosalt of iron.   Thus  Fe.CI. and
S.H. + N.II, produce Fe.S. and Cl.H +N.H3.   It is a jet black pow-
der,  which dissolves readily in acids, and when  exposed moist  to
the nir, rapidly absorbs oxygen, forming green copperas.
  Sesquisulphuret of Iron.—Fe.S.,.  Equivalent 1282 or  102-7.   This
compound, which corresponds to the peroxide, is very  instable  in
constitution.  It may be prepared in  the moist way by adding  to a
persalt of iron in solution,  hydrosulphuret  of ammonia.  A black
precipitate forms, which may be dried in vacuo.  It  may be  also 
364
SULPHURETS OF  IRON.
produced by heating peroxide of iron in a current of sulphuretted
hydrogen gas, water being formed.  It is not attracted by the mag-
net.   It dissolves in acids, but one third of the  sulphur is precipita-
ted, two thirds only combining with hydrogen, and the iron existing
in solution as a protosalt.  Thus Fe2S3 and 2H.C1. give 2(Fe.CI.)
and 2H.S. with deposition of S.  This arises from the circumstance
that "peroxide  of iron is reduced by sulphuretted hydrogen to pro-
toxide, water being formed, and sulphur set free.
  Bisulphuret ofIron. — ¥e.S2.  Equivalent 741*5  or 59*4.  This
substance is met with in very large quantity in nature, constituting
the iron pyrites used in the manufacture of sulphuric acid and of
copperas.  It  is dimorphous (pages 229-232), and in its two forms
possesses very different properties.   It may be prepared artificially
by heating  together the protosulphuret in a state  of minute division,
with halMts weight of sulphur.  When the excess of sulphur has
been  distilled off, there remains a voluminous yellow powder, not
acted on by the magnet,  and insoluble  in acids,  which is the bisul-
phuret of iron.  This bisulphuret of iron  is found  in  a variety of
forms, which belong properly to the different kinds of native oxides
of iron, which being probably  acted  on by vapour of sulphur from
volcanic sources, have lost their oxygen, and, without being melted,
have  changed into  bisulphuret.  It is also found  simulating the fig-
ures of a variety of organic remains, as nautili,  &c, where, proba-
bly, the animal having perished in water holding traces of sulphate
of iron in solution, the hydrogen compounds evolved by its decom-
position  have reacted on the sulphate of iron, abstracting its oxygen
and producing a deposite of pyrites.
   Magnetic Sulphurets of Iron.—Of these the most remarkable is that
which corresponds to the magnetic  oxide, having the formula Fe3
04=Fe.S.-f-Fe2S3.  It  is found native at Barege,  and may be formed
by exposing to a red heat, in close vessels, the bisulphuret or sesqui-
sulphuret: "the pyrites 3(Fe.S2) producing Fe3S4 and  S2, precisely
as peroxide  of manganese 3(Mn 02) produces  02 and Mn304. If,
however, the heat be raised too high, more sulphur is expelled, and
another kind  of magnetic sulphuret, Fe7S8=5Fe.S.-f Fe2S3, formed,
which is also found native, and  which  corresponds  to the black
scales of oxide of iron, which are 5Fe.0.4-Fe203.   This compound
is always formed in making the protosulphuret, if there be an excess
of sulphur above the proper proportion used.
   The seleniuret and phosphurets of iron resemble very closely the
sulphurets.  Phosphuret  of iron exists generally  in cast iron in small
quantity.
   The detection  of iron is very simple.  It may exist in solution in
the state either of protoxide, black oxide, or peroxide;  and as the
application of reagents becomes much simpler in the last case, it  is
best, when the object is  only to ascertain the presence or absence
of iron, to  boil the  solution with a few drops of nitric acid, by which
any iron that may  be present is peroxidized.
   A solution  containing  peroxide of iron produces with water of
 ammonia a reddish-brown  precipitate  of hydrated peroxide ; with
 yellow prussiate  of potash, a fine Prussian blue ; with sulphocyan-
 ide of potassium, a deep  blood-red colour, but no precipitate j with 
PREPARATION  OF  NICKEL.
365
a solution of tannin or tincture of  galls, a deep violet  or black.
With sulphuret of hydrogen there is no effect except the separation
of a  deposite of pure sulphur, but with hydrosulphuret of ammonia
a black precipitate of sesquisulphuret of iron.
  If  the solution contain the iron only as protoxide, ammonia pro.
duces  a precipitate, at first whitish,  but  rapidly  becoming bluish-
green.  The yellow prussiate of potash, a precipitate, at first white,
but rapidly  becoming blue.  The sulphocyanide of potassium, the.
tannin, and the sulphuret of hydrogen are without  effect, but the hy-
drosulphuret of ammonia forms the black protosulphuret.  The char-
acteristic reagent for protoxide of iron is the red prussiate of pot-
ash,  which gives Prussian  blue, but does not act upon the solution
of peroxide.
  If  the solution contain at the  same  time both oxides, the precipi-
tate  by ammonia is, from the commencement, green or blajck, and
all the other reagents concur in the demonstration of the presence
of the  two states of oxidation of the metal.
                            Of  Nickel.
  An ore which, from  its external  characters, was supposed by the
German miners to  contain copper, but resisted all  endeavours to
extract that metal from it, received the name of kupfer-nickel, or de-
ceitful copper.  Subsequently it was  found  to consist of a peculiar
metal united to arsenic, and this metal retained the name  nickel,  its
meaning  being forgotten  or lost sight of.   A  substance found in
commerce,  termed speiss, a residue from the manufacture of smalts,
is also an arseniuret of nickel, and from either of these sources the
metal  is generally extracted.
  The mass containing nickel and arsenic is dissolved by a mixture of nitric acid
and sulphuric acid, diluted with water.  By this means the nickel is converted into
sulphate of its oxide, and the arsenic into arsenious acid.   On concentrating the li-
quor,  most of the latter is got rid of by crystallization.  Carbonate of potash is then
to be  added to the liquor, until the green precipitate which first forms ceases to be
redissolvcd.  On then evaporating and cooling, a double sulphate of nickel and pot-
ash is obtained, which, by two or three ree.rystallizations, is freed from all traces
of arsenic  This double salt may, however, be contaminated by iron and copper;
from  the first it is separated by sulphuretted hydrogen, and from  the last by  the
solubility of the oxide of nickel in water of ammonia.  From the ammoniacal  so-
lution, the oxide of nickel may be precipitated by oxalic acid, as an insoluble  ox-
alate, which, when dried and heated, gives off carbonic acid, and  leaves metallic
nickel, Ni.0.4-Co03, producing 20.02 and Ni.  The  metallic nickel is then in the
form of a very light sponge.
  It  is  somewhat more fusible  than  cast iron; of a  silvery white
colour.  It  does not rust  when  exposed even to damp air.  Its  sp.
gr. is about 85. It is nearly as magnetic as iron, and retains its mag-
netism, resembling  in that respect steel rather  than pure iron.   In
its permanency of lustre, nickel resembles the precious metals, and
its alloys are of singular brilliancy and whiteness.  It is hence that,
added  to brass in the proportion of one to five, it is employed as a
substitute for silver, constituting the German silver,  nickel silver,
argentine, and  British  plate of commerce, as well as the packfong
long used in China.
  the symbol  of nickel is Ni.;  its equivalent 369*7 or 29*6.
  Oxides of Nickel.—This  metal combines with oxygen in two pro-
portions,  forming a protoxide and a sesqjioxide. 
366             COBALT  AND  ITS OXIDES.
  The protoxide, Ni.O., is prepared by precipitating a salt of nickel by caustic potasii;
agrass-green hydrated oxide of nickel separates, Ni.O.-{-H.O., which, when dry, gives
the pure ash-gray oxide. •' This is the only oxide of nickel which forms salts.  It is
not, by itself, soluble in water of ammonia; but if a salt of nickel be decomposed
by ammonia, the precipitate which first forms is dissolved on adding an excess of
the alkali, forming a blue solution, in a great degree characteristic of this metal.
  The Peroxide of Nickel, Ni2Oa, is a  black  powder, prepared by boiling the pro-
toxide in a solution of chloride of lime ;  the oxygen of the lime changes the pro-
toxide into peroxide, SJNi.O. and Ca.O.CI. producing Ni2.03 and Oa.Cl.  When  igni-
ted, this oxide gives oxygen and protoxide; with muriatic acid it forms  protochloride
and chlorine.  It does not form any true salts.
   Nickel  is easily recognised by its solutions giving with ammonia
a green precipitate, which dissolves  in  an  excess, forming  a blue
solution,  and by  giving with yellow prussiate  of potash a  white
precipitate.  The  solutions  of  nickel are not precipitated by  sul-
phuretted hydrogen, but give a  black sulphuret  of nickel with  hy-
drosulphuret of ammonia.
   The sulphuret,  seleniuret, and phosphuret of nickel do not present
any point of interest.

                              Of  Cobalt.
   The name of this metal  has its origin in  a still more singular  cir-
cumstance than that of the preceding; from the  bright metallic ap-
pearance of its ores, the miners  of the Middle Ages were led to  ex-
pect  an abundant  produce, but the modes of reduction then  in  use
were  employed without avail ;  it  was hence imagined  that  these
ores  were especially protected by the guardian spirits  of the mines,
or  Kobolds, and these minerals  were termed Die  Kobold's e.rze, the
Kobold's ores.  At  a later period a peculiar metal was extracted from
them, and as the older name had been corrupted into kobalt ore, the
metal was called cobalt.
   Cobalt exists  in nature, combined with arsenic and with sulphur;
it is universally associated  with nickel, which it resembles so closely
in  its properties that  the perfect separation of these two metals is
one of the most difficult operations in analysis.
  To obtain the cobalt, the  native arseniuret is roasted in a current of air, so as to
oxidize both rnetals, as described, p. 334.  The residual impure oxide of cobalt is
sold in commerce under the name of Zaffre.  This zafTre is dissolved in muriatic
acid, and treated with sulphuretted hydrogen,  by which the copper and arsenic are
separated.   From the filtered liquor, the cobalt is thrown  down  by Carbonate of
potash, and then, to free it  from oxide of iron, it is digested with oxalic acid, which
dissolves the peroxide of iron, and leaves an insoluble oxalate of cobalt; this  may
still be contaminated with nickel, but for the details of the separation of these met-
als, I must refer to more extended works.
  The oxalate of cobalt,  when  ignited,  yields  carbonic acid  and
metallic cobalt in  a  spongy form.  Cobalt melts into a button more
easily than cast iron ;  it is reddish-gray ;  specific gravity  8*5 ;  when
perfectly pure, it is  not susceptible of becoming  magnetic.  It acts
upon water and acids  more rapidly  than nickel, but much less ac-
tively than iron  or zinc.  The symbol of cobalt is Co., and its equiv-
alent 369 or 29*6.
   Oxides of Cobalt.—Cobalt combines with oxygen to form two well-
defined oxides, a protoxide and sesquioxide; there are also a com-
plex  oxide, and a compound of  which the constitution is not well
known, but which is probably a deutoxide.
  Protoxide of Cobalt,  Co.O., is prepared by adding caustic potash to a solution of a 
        USES  OF  COBALT IN  THE  ARTS.--ZINC.    367

salt of cobalt;  a fine blue powder falls, which is a hydrate, Co.O. . H.O.; when de-
prived of its water, it becomes ash-gray : it is the only oxide of cobalt which lorms
sails with acids.
  Sesquioxide of Cobalt, C02O3, is prepared as the sesquioxide of nickel; it is a black
powder, which, with hydrochloric acid, gives chlorine and protochloride:  it does
not form salts.
  Tie complex oxide is Co304-.= Co.O.-p-CoaOa, similar to the magnetic oxide of
iron and red oxide of manganese.
  Cobalt is  recognised in  solution by producing with water of am-
monia  a blue precipitate, which redissolves in  an  excess of the  al-
kali, forming a  liquor which  is of a fine  rose  colour if the  cobalt
be pure, but brownish red if nickel be present;  it is not precipitated
by sulphuretted hydrogen, but is thrown  down black by hydrosul-
phuret  of ammonia   The  most remarkable test for cobalt  is  its
power of colouring glass blue.  The most  minute trace of this metal
may be thus recognised before the blowpipe.   It is, indeed, on this
character that  is founded  the most  important uses of cobalt  in the
arts; glass coloured deep blue by  cobalt, and  ground to an  impal-
pable powder,  constitutes the smalts used to give to writing  paper
and to linen  a delicate shade of blue.   The blue colours upon por-
celain  and delft  are also  produced by cobalt ; when speakino-  of
magnesia (p. 349) and alumina (p. 351), I have noticed the assistance
given by cobalt in the detection of these earths before the blowpipe ;
alumina, coloured strongly blue by  cobalt, is used in commerce as
a pigment, cobalt blue, in  place of ultramarine.
  The blue colours of cobalt are spoiled if brought into contact with chlorine or ox-
ygen, the black sesquioxide of cobalt being formed.  If paper be blued  by smalts
without the bleaching liquor having been well washed out of  the pulp, it is  injured
by acquiring a  brown tinge ;  and by melting together cobalt glass and black oxide
of manganese, a deep black glass is  formed, 2(Co.O.) and Mn Oi giving Co203 and
Mn.O.
  The sulphuret and seleniuret of cobalt consist of an equivalent of each element,
but do not require notice.

                             Of Zinc.
  This  metal is found in nature in considerable quantity, combined
with sulphur, forming sulphuret of  zinc, zinc blende; also as  oxide
of zinc, which, united with carbonic acid or  with silicic  acid,  forms
the two varieties of calamine.   The reduction of the metal is effected
from these ores respectively on the principles already described in
Chapter XII , but, from the volatility  of the  metallic zinc, the process
is carried on in crucibles or large  earthen retorts in place of the
open reverberatory furnace.   In England  the crucibles are closed
above, but perforated at the bottom, so as to admit an  iron tube to
be fitted in, the top of which rises a little above the surface  of the
materials, and the bottom of which, passing through the floor  of the
furnace, opens just  over the  surface of a  reservoir of water.   The
zinc, when reduced,  is converted into vapour, which escapes  throuo-h
the tube, condensing when  it gets below the  fire into a liquid  metal,
which,  dropping into  the water,  solidifies.   In Silesia very large
earthen retorts are employed, not unlike those  figured  in page 289
for the preparation of German oil of vitriol.
  The zinc  of  commerce, as  thus obtained, is  impure;  it contains
traces of carbon, iron, cadmium, and often  arsenic.   It may be freed
from the fixed  impurities by redistillation  in an iron retort; and  by 
368
OXIDE  OK  ZINC.
rejecting the portions which distil over first, and which contain the
cadmium and arsenic,  it may be obtained quite pure.  It is owing
to the presence of these foreign bodies that ordinary zinc dissolves
so rapidly in dilute sulphuric acid, as explained in page  135.  It is
a brilliant bluish-white metal, of a very crystalline texture;  its sin-
gular variations of tenacity are described  in page  328.   At 773 it
melts, and at a full red  heat is volatilized,  its  vapour burning in air
with a splendid white flame, and forming clouds of oxide  of zinc, so
lio-ht as to have been called by the older chemists lana philosophica
and nihil album.  When exposed to the air, even in presence of wa-
ter, zinc is not continuously oxidized.  It becomes covered with a
varnish of a gray substance, probably a definite suboxide, which is
not farther altered by exposure, and hence this metal is  admirably
fitted for  the various  purposes of  domestic  and  technical use to
which it has recently been applied.  In a galvanic circuit  of two
metals,  zinc is almost  always positive, and hence it preserves the
other metal, even  if it be iron, from oxidation.  The actual corro-
sion is,  however, in this case, not diminished, but rather augmented
in amount;  but, being concentrated solely upon the zinc, it is easy
to arrange it so as to  prevent injury.  If zinc be quite  pure, it is
little acted upon by acids ; all that is known of its relations in this
respect has been already described in pages 198 and 248.
  The symbol for  zinc is  Zn.  Its equivalent number 403*2 or 32*3.
  Oxide of  Zinc. — Zn.O.   Equivalent  503*2 or  403.  Although
there is some  reason to  suppose  the existence of other oxides of
zinc,  yet at  present we  possess accurate  knowledge only of the
protoxide.   This is formed when the metal is burned in air or oxy-
gen.  It is produced, also, when the zinc is oxidized by the decom-
position of water, either  at a red  heat or  assisted by an  acid.  To
form  the oxide by combustion, it is sufficient to project a  small frag-
ment of zinc into  a  crucible heated to bright  redness, and slightly
inclined, so that a current of air may pass through it.   When the
metal takes fire, another crucible  is to be  placed  inverted over the
first, but still allowing  a  certain access of air.  The oxide of zinc
being not really volatile, but only mechanically carried  up by the
current of air,  is deposited on the inside  of the upper crucible as
a loose  cottony mass, which, while very hot, is of a fine canary col-
our, but becomes pure white when completely cold.
  Such is the tendency of oxide of zinc to enter  into combination,
that the precipitates given by the  caustic alkalies in a solution of
a salt of zinc  are basic salts, and not the mere oxide.  To prepare
the oxide, a  solution of sulphate  of zinc  is to be decomposed by
carbonate of soda ;  the precipitate is  carbonate  of zinc ; and by
heating this to redness in a crucible, the  carbonic acid  passes off,
and the oxide of zinc remains pure.   This oxide is a powerful base ;
it neutralizes the strongest acids, and its salts are some of the most
definite and  characteristic  that exist: they are easily recognised.
In their solutions, the caustic alkalies all produce voluminous white
precipitates, which are  redissolved by an excess of the alkali.  An
alkaline carbonate  gives  a  similar precipitate, which, however, is
not redissolved by an  excess, except it be carbonate of ammonia.
Hydrosulphuret of ammonia  produces a white precipitate of hydra 
CADMID M.--T I N.
369
ted sulphuret of zinc, if the solution be not very acid.   Sulphuret-
ted hydrogen does  so only if the  solution  be  completely neutral
A solution of zinc with much free acid is not affected by sulphuret-
ted hydrogen, either free or combined.
  The native Sulphuret of Zinc, Zn.S., is found in crystals of a va-
riety  of colours ; it is a  protosulphuret,  and  may  be artificially
formed by melting zinc and sulphur together.  It is decomposed by
acids, sulphuretted hydrogen being given off, and a salt of zinc pro
duced.

                           Of Cadmium.
   This metal exists but in  small quantities in nature ; the only ore
of it is its sulphuret, a mineral but lately found, and still very rare;
it  accompanies almost universally, though  in small quantities only,
the ores of zinc, and is obtained in the  working of zinc ores by ta
king advantage of its  greater volatility.  The  details of its purifi-
cation need not be inserted.   It is white like tin ; it is more fusible
and more volatile than zinc ;  its specific gravity is 869 ;  it dissolves
very slowly in dilute sulphuric acid, but rapidly in dilute nitric acid;
it  combines with oxygen only in one proportion.  Its  symbol is Cd.,
and its equivalent 696*8 or 55*8.
  The Oxide of Cadmium, Cd.O., equivalent 796 8 or 63 8, is obtained by processes
exactly such as described for oxide of zinc.  When anhydrous, it is an orange pow
der; its salts, which are very stable, resemble  closely those of zinc, from which
they are distinguished by giving with sulphuretted hydrogen a fine yellow precipi-
tate, and with carbonate of ammonia a white precipitate, insoluble in an excess:
its salts, like those of zinc, are all colourless.
  Sulphuret of Cadmium, Cd.O , is found native near Greenock; it is yellow like
orpiiiient, but is not volatile ; it does not dissolve in  water of ammonia nor of pot-
ash.

                               Of Tin.
   This metal, from the ease with  which it is extracted from its ores,
 has been known from the earliest ages, and in all countries,  both of
 the East and West.   Before the working  of iron was  discovered,
 cutting  instruments of all kinds were made of an alloy of  tin and
 copper (bronze), which in  hardness was little inferior to steel ; but,
 from  its incapability of being tempered with  the  same exactness,
 was only an imperfect substitute  for it.  It was from the tin mines
 of Cornwall that England first became known to the then more civ-
 ilized  nation of Phoenicia.  A great quantity of the tin of commerce
 is  still obtained from  that county ; but, in addition,  it is imported
 from  Mexico and the  East Indies.   The tin ore has been found in
 Ireland  (county Wicklow), but not  as  yet sought for with a view
 of extracting the metal from it.
   The usual ore of tin is the  native peroxide, which is found  in
 veins, and also in fragments  in the soil formed  by the disintegration
 of the  rocks.   The  process of reduction  is the  simplest possible,
 the ore being smelted with the fuel, as  described p. 332.  The met-
 al thus obtained is still farther  purified from any admixture  of for-
 eign  metals by the  process  of liquation,  which is founded on the
 easy  fusibility  of  pure tin.   The ingots, or pigs of  tin, are gently
 heated until they begin to melt, and then the heat being prevented 
370                   OXIDES  OF  TIN.
from rising higher, the pure metal melts  completely out, leaving
behind the  impurities combined with  a proportion of tin, forming a
mass of  less commercial value.   The tin  thus purified  is termed
grain tin  ;  the  residual  mass  is  called  block tin.   The former  is
known  by  presenting the appearance of a mass of irregular  col-
umns, like  those formed by starch, or by basalt, as  in the Giant's
Causeway,  and  emitting,  when  bent, a  peculiar creaking  sound.
The block tin possesses these characters in a very small degree, or
not at all.
   Tin,  when pure, is white like  silver, brilliant, and after gold, sil-
ver, and copper, the most malleable of the  metals.   It is very soft,
may be bent easily, and has but little tenacity.   Its specific gravity
is 7-3.  It is one of the  most fusible  of the metals, melting at 442'
Fah.   Tin  oxidizes but  very  slowly in contact with  air and water,
and is hence used to protect  the  surface of the more easily oxida-
ble metals, particularly copper, in household use.  It dissolves but
slowly  in dilute muriatic acid, but rapidly if the acid be strong and
boiling.  Nitric acid acts with great  energy on it when concentra-
ted, forming the peroxide.
   The  symbol  of tin is Sn., derived  from its Latin  name stannum.
Its equivalent numbers are 735*3  or 58*9.
   There  are three  oxides of  tin, of which the  first acts as a base,
the second appears indifferent, and the third possesses acid proper-
ties.
   Protoxide of  Tin.—Sn.O.  Equivalent  835*3 or 66*9.   On adding
water of ammonia  to a solution  of protochloride of tin, a copious
white precipitate is obtained, which does not contain ammonia, but
is the hydrated oxide, Sn.O.  . H.O.   The same precipitate is pro-
duced  by an alkaline carbonate, the  carbonic  acid becoming  free.
When  this white hydrate is  heated in a retort filled with carbonic
acid  gas, it gives  off its Avater,  and  the true  protoxide of tin re-
mains as a dense black powder.
   If the hydrate be heated in the open air, it absorbs oxygen, and becomes perox-
ide ; and if the black protoxide be touched when  cold with a red-hot coal or wire,
it inflames and burns like tinder, forming peroxide  The salts of tin may be formed
by digesting the hydrated oxide in acids.  It also-dissolves in solutions of the caus-
tic fixed alkalies, but after some time metallic tin is deposited, and a compound of
the alkali with peroxide of tin remains dissolved, 2Sn.O.  producing Sn. and Sn.O*.
This protoxide of tin is remarkable for its tendency to  unite with  more oxygen.
Hence, by a solution of a protosalt of tin, the less oxidable metals are reduced from
their solutions.  In this way mercury, silver,  gold, platina, may be thrown down in
the metallic state, and iron and copper reduced from the higher to the lower degrees
of oxidation
   The  Sesquioxide of Tin,  Sn^O:;, is prepared by boiling peroxide of
iron in a neutral solution of protochloride of tin.  The sesquioxide
of tin precipitates,  and protochloride of iron dissolves,  2Sn CI. and
Fe203 producing Sn203 and 2Fc.Cl.   It is a  gray powder ; it absorbs
oxygen readily, and appears to form  salts, which have been, as yet,
little examined.
   Peroxide of Tin.  Stannic Acid.—Sn.02.  Equivalent 935*3 or 74*9.
This substance is  produced  in  all cases where tin is allowed  to
combine  with   oxygen freely.  It exists in nature, constituting the
common ore of tin  (tin stone).  It is most readily prepared artificial-
ly by pouring  the liquid nitric acid, sp. gr. 1*42, on  metallic tin,  in 
               s. C ! L P 11 U R E T S  OF  T 1 N.--C HEOME.           371


  foil or powder ; the  action  is very violent, and  the metal is totally
  converted  into  a white powder, which  is the  hydrated  peroxide.
  By ignition the water is given oft* and the  anhydrous oxide remains
  of a pale yellow colour.
    If the  perchloride of tin be decomposed by an alkali, a white precipitate of hy-
  drated oxide is obtained, in appearance identical with that  prep'ared by nitric  acid,
  but  so diflerent in properties that Berzelius, and after him many  chemists, look
  upon them as isomeric bodies.   He calls that by nitric acid, a peroxide, and thai
  from the  perchloride, (3 peroxide, and their properties may be contrasted as follows
    The a modification is totally insoluble in nitric acid and in sulphuric acid, wlieth
  er strong or dilute.  It is  insoluble in muriatic acid, but is changed by it into an in
  soluble basic salt.
    The ji modification dissolves while yet moist in dilute nitric and sulphuric acids
  very copiously, and the solution is permanent if some salt of ammonia  be added to
  it.   In muriatic acid it dissolves rapidly and copiously
    The two modifications ol oxide of' tin dissolve in solution of caustic potash,  and,
  when again precipitated from it by an acid, retain their original properties.  These
  modifications  arc also capable of being transformed into each other; the a into ji
  by distillation with strong muriatic acid, and the /? into a by boiling with nitric acid.
   The hydrated peroxide of tin reddens litmus, and combines with alkalies to form
  salts, but not with acids, except in the /3 lorm.  It is used in the arts as a polishing
  material under the name of putty, and in glass and enamelling, in order to give the
  milk whiteness used for dials of watches and other purposes.
    There are three sulphurets of tin corresponding  to the  oxides
   The Protosulphuret, Sn.S, is precipitated as a brown powder from a solution of
  protochloride of tin on the addition of sulphuret of hydrogen.   It thus serves for
  the detection of tin in that condition.  The Sesquisulphuret, Sn2S3, is of no impor-
  tance.
   The  Bisulphuret of Tin, Sn.S*, equivalent 11376  or 91 1, may be prepared by
 decomposing a solution of perchloride of tin by sulphuretted  hydrogen, which  it
 precipitates of a golden yellow colour.   This is a strong sulphur acid.   It dissolves
 readily in solutions of the sulphurets of the alkaline metals, forming  sulphur salts.
 If it  be strongly heated, it abandons an atom of sulphur, and is converted into the
 protosulphuret.  It may be also prepared in the dry way, and then possesses con-
 siderable interest as being one of those substances which, being obtained from the
 common metals, and simulating the appearance and some of the properties of gold,
 led the ancient alchemists to the belief of probable  success in their attempts at
 transmutation   The bisulphuret of tin may be prepared in  the dry way according
 to several processes, but to give it the peculiar lustre which obtained for it its name
 of  mosaic gold, the following is the best though not the most simple :  twelve parts
 of pure tin are to be melted with six parts of mercury, and rubbed up  in a glass
 mortar with seven of flowers of sulphur and six of sal ammoniac.   This  mixture is
 to he placed in a glass flask, and heated in a sand-bath until no  more fetid white
 vapours are given off.   The heat  is to be then raised to dull redness, sulphuret of
 mercury and chloride of tin sublime, and the mosaic gold remains in the  bottom of
 the vessel in metallic-looking scales of a brilliant gold colour.  The use of the mer-
 cury in this process is to facilitate the combination of the tin and sulphur, and  the
 sal  ammoniac, seems by its evaporation to prevent the temperature  becoming so
 high as to decompose the bisulphuret.
  The seleniurets and phosphurets of tin are not known.
  Tin  is easily recognised in solution by the action of hydrosulphu-
 ret of ammonia, which  produces  with solutions of  the peroxide a
 golden yellow, and in solutions of the protoxide a brown precipitate.
 These  both dissolve in an excess of the precipitant.  The protoxide
 of tin is also  known by its power of reducing the salts of gold, silver,
and mercury to  the metallic state.

                       Of  Chromium,  or  Chrome.

  This metal derives its name from the variety and brilliancy of the
colours of its compounds (Xpo)//oc).   It exists as chromic acid com-
bined with lead or with copper in some rare  minerals, but abundant- 
372         OXIDE  AND  ACID  OF  CHROME.
 Iy as  chromic  oxide in  the  chrome-iron  ore (Fe.O. + Cr203).  It
 is from this source that  all the preparations of chrome are obtained
 indirectly, but that ore  being treated upon the large scale for the
 manufacture of chromate  of potash, it is this salt, as found in com-
 merce, that may be  looked upon as the source  of chrome for all
 other purposes.  The metal  is obtained by mixing the  oxide  with
 lampblack and oil,  and exposing  it to an intense  heat in a crucible
 lined with charcoal.  It is a grayish-white  metal, very infusible,
 brittle, not magnetic, and sp.  gr. 5*9 or 6*0.  It is not attacked by
 dilute  sulphuric or muriatic acids, but dissolves in hydrofluoric  acid
 with evolution of hydrogen gas.
   Chrome combines with oxygen in two proportions, forming an ox-
 ide and an acid.  Its symbol  is Cr., and its equivalent numbers are
 351*8 or 28*19.
   Oxide of Chrome, Cr203, equivalent 1003*6 or  80*4, may be  ob-
 tained by a great variety of processes.  Thus, if  chromate  of mer-
 cury be heated to redness, the oxide of mercury  and half the oxy-
 gen of the chromic acid  are expelled, and the chromic oxide remains
 of a beautiful green colour.
   If bichromate of potash be mixed with sal ammoniac and heated to redness, chlo-
 ride of potassium, water, nitrogen, and oxide of chrome result, and  the latter is
 obtained pure by washing the residual mass with boiling water.  In this process,
 2Cr.03+K.O. and C1.N.H4 produce K.C1., N., 4H.O., and Cr203.  The oxide so
 obtained is pulverulent, but it  may be obtained crystallized as follows: the vapour
 of a compound which will be hereafter described, chlorochromic acid, is to be pass-
 ed through a tube of* hard glass, kept at a full red heat, oxygen and chlorine gases
 are given off, and oxide of chrome is deposited on the inside of the tube in rhombic
 octohedrons. isomorphous with those found native of alumina (corundum) and per-
 oxide  of iron ; the chlorochromic acid,  2(Cr.02Cl.) giving  off 2C1.  and 0., and
 Cr203 remaining.
   This oxide of chrome  is the basis  of an extensive class  of salts,
 and it may also be  obtained by precipitation from  any solution con-
 taining it.  Its salts are  generally made from the bichromate of pot-
 ash of commerce, by the  addition of some deoxidating agent and the
 necessary acid.   Thus,  to form sulphate of chrome, a solution of
 bichromate of potash is warmed, and treated successively with  sul-
 phuric  acid and alcohol,  until its orange colour is changed into deep
 green.   The liquor then  contains  the double sulphate of chrome and
 potash  (chrome alum), and from it the oxide may be precipitated on
 the addition of an alkali,  as a pale  green hydrate.   In this condition,
 the oxide of chrome dissolves readily in acids, and also in solutions
 of the  fixed caustic alkalies, but  scarcely in  ammonia, resembling
 very  closely, in all these  characters, alumina.   Its solutions  are
 either green or  purple, and it is probable that  this difference is due
 to more  than a mere difference  in the degree  of concentration.
 When the hydrated oxide  is heated nearly  to redness, it suddenly
 begins  to glow like tinder, giving off its water, and losing its solu-
 bility in acids, except they be hot and concentrated.   It is  remark-
 able that sulphate of chrome, made from  the ignited oxide,  will not
 combine with sulphate of potash to form a chrome alum.
  Chromic Acid. -Cr.03.   Equivalent 651*8 or  52*2.  To  prepare
 this acid, a solution of bichromate of potash is to  be treated by hy-
drofluosilicic acid gas, until the potash has been precipitated com-
 pletely.  The resulting liquor is to be cautiously evaporated to dry- 
V A N A D I U M.--T U N G S T E N.
373
ness, and then redissolved in a small quantity of water.   The solu-
tion is of a dark brownish-red, and when evaporated again gives the
dry chromic acid.   It may be obtained in a  beautiful form, though
not in quantity, by decomposing the  vapour of the perfluoride of
chrome  by a moistened  slip  of paper.   Cr.F3 and  3H 0. produce 3
H.F. and Cr.Oj, which last is deposited on the surface of the paper
in crimson scales and needles of great brilliancy.  This acid, when
heated strongly, gives up half its oxygen, being reduced to the state
of oxide.   It combines with bases, forming several important classes
of salts,  in which it is isomorphous with the  sulphuric and manganic
acids.   Its salts are  all coloured, generally yellow, orange, or red.
They will be described in another chapter.
  Chromium is characterized by the remarkable colours of its com-
pounds when  dissolved,  and  by giving, when in the state of oxide,
a green precipitate  with the alkalies.   In the  state of acid, it isknown
by producing, with the salts of lead, a yellow, and with the salts of
the black oxide of mercury,  an orange precipitate.  It  is at once
recognised by the beautiful green colour which it  communicates to
glass.   It  is, on this account,  extensively  used in staining glass  and
painting on porcelain, and a number of its salts are  employed as pig-
ments and  as  dyes.
  By the action of deoxidizing agents, or sulphurous acid or sugar, upon bichromate
of potash, a brown substance is generated, concerning the nature of  which opinion
is very much unsettled.  There  is reason to suspect  the existence  of a peroxide
of chrome, Cr.02, which this matter may possibly be.  When it is washed  with
much water, or digested in alkaline  liquors, chromic acid is dissolved out and oxide
of chrome remains. Cr203-f-Or.03=30r.02.
  The sulphurets, seleniurets, and phosphurets of chrome are not important.

                            Of Vanadium.
  This metal, of recent discovery, derives its name from Vanadis, a deity of Scan-
dinavian  mythology.  It  is found native as vanadic  acid, in  a very rare mineral,
vanadiate of lead, but is of so little importance that a slight  notice  of it will  suf-
fice, although it forms a great variety of combinations,  which resemble very remark-
ably those of manganese and chrome.  The metal itself has been obtained, but of
its properties  nothing positive is known.  Its symbol is V. ; its equivalent numbers
are 856 9 or 68 7.
  The Protoxide of Vanadium, V.O., is a black powder, formed by acting on vanadic
acid at a red heat with  hydrogen gas.  It combines with acids, forming salts which
resemble probably those of the protoxide of manganese.  When heated in the air,
it absorbs oxygen and becomes vanadic oxide, V.O2, which is a  base combining with
acids and forming salts which are generally blue.  It  acts also as an acid, forming
crystal I izable  salts with the fixed alkalies.
  The Vanadic Acid, V.03, resembles very much the chromic  and manganic acids.
It is a red  powder, which may be melted at  a red heat without losing oxygen.  It
is very slightly soluble in water.   It forms various classes of salts, of which some
are whi\e, some yellow, and others orange red.  In these characters it resembles
the chromic acid, but it is distinguished from chrome by producing, when deoxidized,
a blue solution, while that from chrome is green.

                             SECTION IV.

                   METALS OF  THE FOURTH  CLASS.

                     Tungsten and Molybdenum.
  Tungsten.—This metal exists, combined  with oxygen, as tungstic. acid, in the
native tnngstates of lime and iron ;  by boiling the tungstate of lime in strong  mu-
riatic acid, the lime is dissolved out, and tungstic acid  remains as a yellow powder,
which may be farther  purified by solution in water of ammonia, and igniting the 
374       TUNOSTE N.—M OLYBDENU M.—O S a
tungstate of ammonia.   It is a deep yellow powder  which forms w^defined crys.
.oii?™Mo c-oi.    uk (u niiniip*   The symbol of tungsten is VV., from its German
nam^l w": "  1  ^etufvalents^HS or 948.  The  tungstic acid resembles the
chromicacidbeta"  W.O..  When this acid is exposed to a current of  hydrogen
SSiteiramre about dull redness, it loses one third ol its oxygen, and forms
£?«£&-oSTo  of a copper-red colour.  This may be also formed by diffusing
 nmSic ^id through dilute muriatic acid in which  a sip of zinc is immersed; the
nascem hydrogen then effects the dcoxidation   At a  full reel heat, hydrogen reduces
tun-sten to the  metallic state, removing all the oxygen.  The metal is like iron in
appearance, and verv heavy, its sp. gr. being about Iro.
  The most curious "fact in the historv of tungsten is its producing a substance hav-
ing an extraordinary similarity to gold.  It is prepared by adding to fused tungstate
of soda as much tungstic acid as it will dissolve, and exposing the product at a full
red heat to a current of hydrogen gas; the residual  tungstate of soda  is then to be
dissolved out   The new compound, which consists of tungstic oxide united to soda,
Na O -f'2W 62  remains in scales and cubes of a splendid gold colour.  It resists the
action of acids and alkalies, even of aqua regia, in which gold dissolves, and only
yields to strong  hydrofluoric acid.  Had it been discovered at an earlier period in
science it might have lent exceedingly plausible support to the belief in transmuta-
tion  It is the more curious, as it cannot be formed by directly combining soda with
tungstic oxide, which, indeed, appears unable to unite either with alkalies or acids.
  There exist two sulphurets of tungsten, W.S2 and  W.S3) of which the latter is the
most interesting.   It is formed bv dissolving tungstic acid in hydrosulphuret of am-
monia and precipitating by an acid.   It is a blackish-brown powder, and one of the
strongest sulphur acids.  Many of its compounds with the sulphurets of the alka-
line metals may be crystallized.
  Molybdenum—-This metal exists combined with sulphur, and also with oxygen, as
molybdic acid, in some minerals.  It is not of any considerable interest.  When ob-
tained in the metallic state it is white, sp. gr. 8-6. acted on only by  concentrated ni-
tric and sulphuric acids, and by aqua regia.  Its  symbol is Mo.  Its equivalent
598-5 or 479.  It combines with  oxygen in three proportions.
  Molybdic Acid, Mo.Os, is easily  prepared  by roasting  the  native  sulphuret  of
molybdenum; the sulphur burns out as sulphurous  acid gas, and the molybdenum,
absorbing oxygen, remains as molybdic acid.   This may be purified as described for
tungstic acid.   Molybdic acid prepared at a low temperature is white, but becomes
yellow when fused at a red heat.  It is sparingly soluble in  water.  It dissolves m
alkaline liquors, forming salts which are neutral and crystallizable.
  Molybdic Oxide, M0.O2, is best prepared by mixing together molybdate of soda
and sal ammoniac in a crucible, and igniting the mass rapidly.   When the product
is washed with water, a dark brown powder is obtained, which  is molybdic oxide.
This  oxide appears to form salts with both acids or alkalies, of which  some may be
crystallized.  A molvbdate of molybdenum, or, rather, a complex oxide, also exists,
Mo.02-i-2Mo.03-Mo3Os.   It is a blue powder.
  When a solution of molvbdate is decomposed by as much muriatic acid as redis-
solves the molybdic acid, which is at first thrown down, and a slip of zinc is immcr
sed in the liquor, the hydrogen evolved deoxidizes the molybdic acid, and aprecipi
tate is formed upon the "zinc, at first blue, then brown, and finally black; thus passing
through all the intermediate degrees to the last, the MdyMous Oii'le,  Mo.O.  This
is a very feeble base, forming with acids salts which do not crystallize.
  Sulphur combines with molybdenum in three proportions, forming M0.S2, Mo.S3)
and M0.S4.   Of these the bisulphuret, M0.S2, is important, as being the native ore
from  which the metal and its compounds  are generally prepared.  It is a soft gray
substance, so like black lead as to have been mistaken for it until its nature was
pointed out by  Scheele.  All these sulphurets are sulphur acids, and form salts.

                                 Of Osmium.

  This metal exists in nature alloyed with iridium, and  accompanies the ores of
platinum.  The methods of its extraction from these ores are so complex and circui-
tous that I shall not  introduce them here.  In the  systematic works, a complete ac-
 count of the processes pursued will be found.
   The most interesting property of osmium is its forming a hisrhly volatile oxide of
 an exceedingly penetrating odour, whence the name (nauri).  When this is dissolved
 in muriatic acid, and placed in contact with mercury, the osmium is reduced, and by
 distilling off the mercury it is obtained as a black powder; but by heat and compres-
 sion  it may be rendered coherent, and of a brilliant white colour.  In the state of
 powder, osmium burns when heated to redness in the air, and is oxidized by nitric 
COLUMBIUM  AND  TITANIUM.
375
acid, but loses both these characters when ignited.  The symbol of osmium is Os.
Its equivalent is 1-211-5 or 9'J 7.   It combines with oxygen in three proportions.
  The Osmif. Acid, or  Peroxide of Osmium,  Os.04)  is always formed when osmi-
u n is  burned in air or in oxygen gas.   It condenses in long white needles.   Its
odour is remarkably acid and pungent.  It melts at 212°, and boils at a heat little
higher.  It is soluble in water.   The solution has no action on vegetable colours,
but it combines with the alkalies, forming osmiales.
  The Osmic 0.culc, D'utoxide of Osmium, Os.Oi, is produced by the decomposi-
tion of a solution of osmiate of ammonia, by a temperature of 150°;  nitrogen gas is
given off, and a brown  powder is deposited.
  The Protoxide of Osmium is produced by decomposing a solution of protochloride
of osmium by potash; a deep green, almost black, powder is thrown down, in which
ihe oxide is combined with water and traces of the alkali.
  The sulphurets of osmium are not known.

                        Columbium, or  Tantalum.

  This metal was discovered first in an American mineral, from whence its name,
it was subsequently, but independently, discovered in some very rare Swedish min-
erals, and from the difficulty of its extraction, the name  tantalum was given to it,
which it still bears upon the Continent, and from whence its symbol is  Ta.  The
process required to prepare it need not be described, as it is similar to that for ob-
taining silicon.
  Metallic Columbium, or Tantalum, is  a black powder, which, when burnished,
appears iron gray.   No acid but  the hydrofluoric appears to have  any action on it.
It takes fire when heated in the air, and burns vividly.  Its equivalent numbers are
2307 or 1H5.   It combines with oxygen in two proportions.
  T1i.11/11lir, or Columbia Acid, Ta.63, exists  native  in all the minerals containing
the metal.  To procure it, the mineral is fused with carbonate of potash, and the
tantalate of potash, which is soluble, is to be decomposed by muriatic acid.  The
tantalic acid  precipitates as a white powder, which contains w ter, and reddens lit-
mus paper.   When tantalic acid is heated strongly in a crucible with charcoal, but
a slight film of it is reduced to the metallic state, the great mass being brought only
to the state of tantalic oxide,  Ta.02.  This substance is gray.   It is insoluble in  all
acids.
  The similarity of tantalum to silicon is very great; it resembles it in forming, with
fluorine and potassium,a double fluoride, from which the metal is obtained.

                                  Titanium.

  This metal, although not met with in large quantities, is yet found in a great va-
riety of minerals.  It is not found native in a metallic state," but combined with ox-
ygen, forming titantic acid.  To obtain metallic titanium, the volatile perchloride
is employed.   This body absorbs ammonia,  forming a white substance, Ti.Cl2-f-2
N.H3> which, when heated to redness, gives  metallic titanium, with sal ammoniac
and nitrogen,  the hydrogen carrying off the chlorine.   It is of a bright copper colour,
almost perfectly infusible.   Titanium exists in most  of the  clay iron stone, and
hence, being reduced during  the smelting of the iron, is found in the slags, crystal-
lized in cubes of excessive hardness and brilliancy,  sp. gr. 53.  This metal is not
acted upon by any  acid except a  mixture of nitric acid with hydrofluoric acid, and
is oxidized, but very slowly,  by melted nitre.  It is perfectly unalterable by air or
water.   Its symbol  is Ti. Its equivalent numbers are 3037 or 243, and it com-
bines with oxygen in two proportions.
  Titanic  Aid, Ti.O>, exists native, constituting the  mineral rutile, isomorphous
with tin stone (Sn.Oj), and also in the mineral anatasc.  More abundantly it is found
in the  titanic iron,  ilmenite,  the  formula  of which is Fe.O. . Ti.02,  and,  which is
very remarkable, from having the same crystalline form as peroxide of iron, Fe203|
sN that the titanium would appear to replace the second atom of iron, and the formu-
la to be Fe.Ti.-r-03.  This is merely speculative, however,  as iron is never iso-
morphous with tin, and in no other case with titanium, and I hence consider this
instance as one of the coincidences of form described in pages 221 and 22G.
  Titanic  acid is artificially prepared from the titanate  of iron by igniting it with
sulphur.  The oxide of iron and sulphur form sulphurous acid and "sulphuret of iron,
and when this last is dissolved out by muriatic acid, the titanic acid remains be-
hind.   It requires other processes to render it absolutely pure,which need not be de-
scribed here.   It is a pure white  powder,  resembling silica very remarkably in  iu
propel ties, and, like it, having a soluble and an insoluble modification.  It is iemark- 
376
ARSENIC,  ITS  PREPARATION,  ETC.
 ably characterized by its solution in muriatic acid, giving with tincture of galls
 an orange precipitate, and by the immersion of a slip of zinc a fine purple powder.
 which is Oxide of Titanium, Ti.O.; the second atom of oxygen being removed fro in
 the acid by the nascent hydrogen.   This oxide of titanium may also be procured by
 igniting titanic acid with charcoal; it is then a black powder, insoluble in all acids.
   The Bisulphuret of Titanium, TLS2, is a strong sulphur acid, but not otherwise
 important.

                            Of Arsenic.

   This  metal exists in  nature in a great variety of  forms, and  in
 considerable  quantity.  It is found native, but more generally com-
 bined with other metals, as nickel, cobalt, iron ; beino- considered
 like oxygen and sulphur, as a mineralizer of other metals.   Combined
 with sulphur, it  constitutes the native orpiment and realo-ar; and
 with oxygen, as  arsenic acid, it is united with metallic oxides in the
 native arseniates of lime, of iron, of lead, Ace.   The great proportion
 of the arsenic of commerce  is obtained in the roasting of the cobalt
 and nickel ores, as described in p.  334.   The current  of hot air
 which has passed over the ignited ore carries with it, into a series
 of large chambers,  the  volatile arsenious acid, which is deposited
 under the form  of  a fine grayish  powder  on the walls and floor.
 This is discoloured by some  of the oxide of the fixed  metals, which
 is carried over mechanically by the draught, and  it is, therefore
 resublimed in iron vessels, the covers of which are allowed to be-
 come so hot that the arsenious acid, in condensing, shall aggregate
 itself into a vitreous mass, in which state it is sent into commerce.
   The metallic arsenic may be prepared from the arsenious acid in
 many ways, but best by  mixture with three times its weight of black
 flux  (p. 334)  in a crucible or earthenware retort, which is then to
 be heated to redness.  If a crucible be  used, another  cold crucible,
 somewhat larger, must  be inverted over it, on the inside of which
 the metal condenses, but with a retort it is deposited in the neck as
 an irregular mass of rhombohedrons, variously modified.   It is very
 brittle* its  sp. gr. 5*96.   It  sublimes at  356J F. without  previously
 melting.  The sp. gr. of its  vapour is 10362.   Its vapour, if in con-
 tact  with the air, has a very  characteristic  garlic odour; which,
 however, belongs not to the  pure metal, but to an oxide produced
 by a low degree  of combustion which occurs.   In the air it o-radu-
 ally absorbs oxygen, and falls into gray powder (suboxide, fly powder).
 By nitric acid it  is rapidly  oxidized, and deflagrates violently in
 melted nitre.   In fine powder  it burns  spontaneously in chlorine
 gas,  with a brilliant white flame, and burns similarly  when heated
in oxygen gas.   The symbol of  arsenic is As., and its  equivalent
numbers are 940*1 or 75*34.
   Arsenic  combines with oxygen in  three  proportions,  forming  a
suboxide, of which the composition is not known.  Many chemists
look upon it as a mere mixture of metal and arsenious acid, for
when it is heated it separates into these bodies.   The other decrees
 of oxidation, the arsenious acid and arsenic  acid, are of o-reat im-
portance.
   Jr*munu  Acid  White Arsenic.  Oxide of Arsenic~As.03, equiv-
alent 1240*1  or 99-34-is found  in  commerce in masses, which, if
recently  sublimed, are  perfectly  colourless  and transparent  but 
          ARSENIOUS ACI D.--A RSENIC  ACID.       377

gradually  become milk-white and  opaque.  In general,  the  outer
portions of the commercial masses have thus changed, while the in-
terior retains its original transparency.  This alteration is probably
connected with the dimorphism of arsenious acid (p. 228), for the
acid in these conditions differs in density and in solubility.   The
transparent is sp. gr. 3*74, and 100 parts  of boiling water dissolve
9*68 parts of it;  but the opaque acid is of sp. gr. 3*69, and 11*47 of
it are soluble in  100 parts of boiling water.  A solution of the vit-
reous acid reddens litmus paper, but that of the opaque acid restores,
though feebly, the blue colour of litmus paper  already reddened by
an acid.   The taste of arsenious acid is not marked, but rather
Blightly sweet: it leaves upon the palate, however, an acrid sensa-
tion.
  The arsenious acid sublimes at 380' F. without previously melt-
ing.  Its vapour is  of sp. gr. 13670, being produced by

              One  volume of vapour of arsenic  =103620
              Three volumes of oxygen   .   .  = 3307 8
            the four volumes forming one  .   .  -=13661)-8
If it be very slowly sublimed, it  condenses in  regular octohedrons
of exceeding brilliancy.  It is, however, sometimes found, in the
roasting of its ores, in crystals belonging to a different system (the
rhombohedral).   Arsenious acid  is dissolved by liquid muriatic acid
in large quantity, but crystallizes  from that solution in octohedrons.
If the opaque acid  had  been  employed, the crystallization is not pe-
culiar ; but if it had been the, transparent variety, the deposition of
every crystal is accompanied by  a sudden flash of light,  very brill-
iant in the dark.  The crystals so produced belong to the opaque
kind, so that it would appear as if, at the  moment of deposition, the
particles changed their mode  of arrangement, so as to  pass from
the transparent to the opaque dimorphous form, and that the alter-
ation in molecular constitution  occasioned the  evolution of light,
and probably of heat and electricity.
  The arsenious acid combines with bases to form  salts, which are,
however,  of such  unstable  constitution  that they  are  but little
known.  It is particularly of importance  from  its highly  poisonous
properties, and from its being, more frequently than any  other sub-
stance, administered to  produce  death.   Its recognition  is,  there-
fore, to the medical chemist, one of the  most important problems
in analysis, and will be fully discussed when the other combinations
of arsenic have been described.
  Arsenic Acid.—As.O,.  Equivalent 1440*1 or 115*34.   To obtain
this acid,  eight parts of arsenious acid are to be placed in a  retort
with two  parts of  strong muriatic acid,  and boiled, while twenty-
four parts  of dilute nitric acid, of sp. gr. T25, are  to be  added in
small quantities at  a time.   The mixture is to be distilled in a re-
tort to the consistence of a sirup, and then  transferred to a platina
dish, in which it is  to be evaporated to perfect dryness, and heated
until all traces of nitric acid are expelled.  The residual mass is
milk-white, but  anhydrous arsenic acid.   The heat should not be
raised to near redness, for then the arsenic acid is decomposed into
arsenious acid and  free oxygen.  The mass thus obtained dissolves
                            Bbb 
378          ARSENIURET  OF  HYDROGEN.
but slowly in water, but  ultimately the solution  is complete ; the
arsenic acid  has  even so much affinity for water as to deliquesce
rapidly in vessels which are not kept carefully closed.
   The arsenic acid reddens litmus paper strongly, and forms with
the alkalies perfectly neutral salts.  At a high temperature it is ca-
pable of expelling  all the volatile acids, even  the sulphuric acid,
from their combinations.   In its compounds it resembles very close-
ly the  phosphoric acid ; but it  appears  capable of forming only one
of the  three classes of salts which phosphoric acid produces.  The
arseniates  are all tribasic, but  as  the quantity of fixed base varies,
there are some neutral and others acid arseniates ; the latter were
formerly called binarseniates.  Thus there  are,
  3Na.O.+As.O,-f-24 aq.       called subarseniate of soda,
  2Na.O. . H.O.-f-As.0,-1-14 aq.   "   neutral arseniate of soda,
  Na.O. . 2H.O.-r-As.O, + 2 aq.    "   binarseniate of soda *
but the quantity of base is really constant, being in each three atoms,
made up partly of water and partly of soda.
   The arsenic acid is recognised  by  being  precipitated golden yel-
low by sulphuretted hydrogen.  The precipitate dissolves instantly
in ammonia,  and even in  an excess of sulphuret of hydrogen ; so
that it may not be  visibly produced, if the quantity of arsenic be
small,  until the liquid shall  have  been  well boiled.  A solution of
any arseniate gives with nitrate of silver a  brick-red powder, arse-
niate of  silver, 3Ag.O. -f- As.O,, the formation of which is easily ex-
plained.   An insoluble arseniate heated in  a glass tube with char-
coal powder  gives a sublimate of  metallic arsenic.
  Arseniuret of Hydrogen. - It has been supposed, that when metal-
lic  arsenic is used as the negative electrode  of  a voltaic  battery,
the hydrogen evolved combines with it, and forms a brown powder,
hydruret of arsenic.  The  same body was supposed to  be generated
in other  ways* but it is now known that this substance is  only me-
tallic arsenic finely divided, and that there is but  one compound of
arsenic and hydrogen, the gaseous arseniuret of hydrogen. As.H,.
  This  compound  is  easily obtained whenever  nascent hydrogen
comes into contact with metallic  arsenic :  thus, when  an alloy of
equal parts of zinc and arsenic is dissolved  in dilute sulphuric acid,
the hydrogen evolved combines  with  the  arsenic, 3(S 03 + H.O.)
and Zn3As. producing  3(S.03-(-Zn.O.)  and  H As.  It is still more
easily prepared by adding  muriatic acid to  a solution of arsenious
acid in water, and immersing therein a  piece of zinc ; the hydrogen
first evolved  reduces the arsenious acid, and the metal is then sep-
arated  as a  fine brown  powder, with which the hydrogen next
evolved combines.  This  gas is generally stated to have a very dis-
agreeable odour,  which, however, I have not found it to possess.
It is excessively  poisonous; it burns with  a brilliant  white flame,
water being formed, and arsenious acid or metallic arsenic,  being
deposited according to the  supply of oxygen to the gas; it is not
absorbed by water; its specific gravity is 2694, formed by
             One volume of arsenic vapour  .  .   =10362 0
             Six volumes of hydrogen  68 8x6  .   -=412 8
             The  seven being condensed to four  .   107748"
             Of which one weighs......   3693-7 
SULPHURETS  OF  ARSENIC.
379
  Arseniuret of hydrogen decomposes most metallic solutions, pre-
cipitating metallic arseniurets of corresponding constitution (RsAs.).
If a current of it be passed over chloride of copper, heated to about
4.00 ,  it is decomposed, H3As. and 3Cu.Cl. giving Cu3As. and 3H.C1.
This gas is absorbed by dry sulphate of copper, which  it decompo-
ses, water being evolved, and a blackish compound  of sulphuric
acid and arseniuret of copper being produced.   This property is
made  available  in the medico-legal examination of substances  con-
taining arsenic.  If a  fragment of  chloride of mercury be heated
in this gas,  it is rapidly decomposed, muriatic acid gas and arse-
niuret of mercury being formed.   At a full red heat the gas is de-
composed completely  by  itself, so that if a single point of a tube,
through which  it streams, be ignited, all the arsenic is deposited a
little beyond that point, in the metallic state, and only  pure hydro-
gen passes on.
  Sulphur and arsenic combine in several proportions : the Bisulphu-
ret of  Arsenic, As.S2, exists native, forming the mineral realgar.  It is
prepared by fusing the following sulphuret with metallic arsenic,
and subliming the product.  It is  a ruby-red crystalline mass ; when
it is digested in solution of caustic  potash, a blackish powder re-
mains, which may be  looked  upon as a subsulphuret; its definite
nature is problematical.  The Tersulphuret of  Arsenic, As.S3, yellow
arsenic, orpiment, is found native,  and may be easily prepared by de-
composing a solution of arsenious acid with sulphuret of hydrogen,
As.Oj and 3H.S. giving As.S3 and 3H.O.  It is a rich yellow powder ;
when  heated, it melts ; and  in close vessels sublimes unaltered, but
otherwise it burns,  partly forming arsenious and  sulphurous acids;
it is not quite insoluble in water.  It is insoluble in  acids, and best
precipitated from an acid liquor.   It  is a strong sulphur acid, com-
bining with the sulphur  bases to  form salts, sulpho-arsenites.  It
hence dissolves readily in hydrosulphuret  of ammonia, and also in
the  caustic  alkalies.   In  the last  case there  exists in solution an
ordinary arsenite besides the  sulphur salt ; for, using  potash,  2As.
S3 and 6K.O. produce  (As.S3 + 3K.S.) and (As 03 + 3K.O.).  When
sulphuret of arsenic is ignited with black flux,  metallic arsenic sub-
limes; and the separation of the metal is still more elegantly effect-
ed by  heating the sulphuret, mixed with carbonate of potash, in a
current of dry hydrogen gas.
  The Persulphuret of Arsenic, As.S,, corresponds to the arsenic acid,
and is prepared by decomposing a solution of it, or of any of its salts,
by sulphuretted hydrogen.  It is  yellow, paler than orpiment;  sub-
limes  without alteration in close vessels ; is a strong sulphuric acid,
and hence  dissolves in solutions of  the alkaline  hydrosulphurets,
forming sulpho-arseniates ; the metal may be eliminated from it by
the same means as those described for orpiment.
  A substance sold in this country for killing flies, under the name
of king's yellow, is, or ought to be, orpiment.   The best sort is made
by boilinp; together lime,  sulphur, and white arsenic; but  much of
it* consists merely of white arsenic coloured by some sulphur mixed
with it.   From  the  facility with which it may be obtained, and the
manner in which it  is left exposed, it is very frequently the source
of fatal accidents. 
380
DETECTION  OF  ARSENIC.
  Notwithstanding the scientific importance which arsenic possesses
from the number and variety of its compounds, it is of much higher
interest in consequence of the frequent necessity for the detection
of excessively minute traces of  it in cases of suspected poisoning,
where a responsibility, involving the life of a fellow-creature, rests
on the skill and accuracy of the medical chemist.   The detection
of arsenic under all possible circumstances is an object, therefore,
to which all the powers of analysis should be brought to bear, and
the methods at our disposal appear, if properly applied, to be  satis-
factory and complete.   In a question  so grave as this, no colours
of precipitates, however so marked—no arrangement of mere results
by test, no matter how corroborative, should be considered as by
themselves decisive ; the object of the chemist should be, the iso-
lation and production of the metallic arsenic ; and where this has not
been done, it is certain that either there is  no arsenic present, or
that the skill of the operator cannot be absolutely relied on.
  In poisoning by arsenic, the substance used is almost universally
arsenious acid.  To this, therefore, I  shall confine  my remarks at
present ; I shall afterward notice the peculiarities of its other  prep-
arations.
  The arsenious acid being a very heavy powder, and but sparingly
soluble, it is very rapidly deposited from any liquid  through which
it might  have been diffused, and hence  the  vessels in which  food
had been contained should be carefully examined for any traces of
it which  might remain.  This should  not  be omitted, even though
they might appear to have been  subsequently rinsed.   Any substan-
ces vomited by the person suspected to be  poisoned should be  care-
fully examined for the  same object; and in case of death, the mate-
rials in the stomach and its mucous surface must be similarly search-
ed.  The little grains of arsenious acid adherent to the surface of
the stomach are frequently  tinged yellow at the  surface by sulphu-
retted hydrogen, if the examination be deferred until some time af-
ter death.
  In case of such traces of white powder being found, the examina
tion is very simple.  Their porperties are:
  1st. Heated alone in a glass tube, the powder sublimes and con-
denses in minute brilliant octohedrons.
  2d. Mixed, in a tube closed at one  end, with  a little  black flux,
and ignited, metallic arsenic sublimes, forming a steel-gray crust,
brilliant on the side  next the  tube, but dull  and crystalline on the
inside.  On applying the nose to the  open end of the tube and in-
spiring, a garlic odour is perceived.
  3d. On cutting off the sealed end of the tube, and  then heating
the part containing the metallic crust, the  tube being slightly  incli-
ned,  the metal  disappears, and a crust  of white arsenic condenses a
little higher up.  A current of air passes through the tube, with the
oxygen of  which the metal combines.  In this process the garlic
smell becomes  more marked than in No. 2.
  4th. The white powder dissolves in water.  It yields precipitates
with the  following reagents :
  A.  Sulphuretted Hydrogen.—A rich  yellow: soluble in  ammonia,
and precipitated on the addition of an acid.  This precipitate is or'
piment. 
LIQUID  TESTS FOR  ARSENIC.          381
  B. Ammonia-nitrate of Silver.—A canary yellow ; arsenite of silver.
This reagent  is very delicate,  but the precipitate is  soluble both in
acids and ammonia, so that an excess of either must be avoided.
  C. Ammonia-sulphate of Copper.—A fine apple-green.   This is re-
dissolved also by an excess of acid or of ammonia.
  Each of these liquid reagents is liable to fallacy,  which must be
guarded against.
  A. Sulphuretted Hydrogen gives precipitates more or less  resem-
bling that from arsenic with the following  metals:

             Cadmium.                   Antimony.
             Tin (persalts).               Iron (persalts).

  The  precipitate from cadmium is not soluble in water of ammonia.
  The  precipitate from tin, when dried and ignited with black flux,
gives no sublimate of metal.
  The  precipitate of antimony acts in the  same way as tin, but also
it dissolves in strong muriatic acid, and the solution, diluted with
much water, gives a white precipitate.   The sulphuret of antimony
is much more orange-coloured than that of arsenic.
  The  precipitate from a persalt of iron is pure sulphur; heated, it
melts and burns completely away, without forming any solid pro-
duct.
  B. Ammonia-nitrate of Silver.—Phosphate of soda  produces a yel-
low precipitate of tribasic phosphate of silver, exactly  resembling
the arsenite.   It is, however, much more soluble in ammonia.   They
are at once distinguished by being collected and ignited.   The ar-
senite  gives off oxygen and arsenious acid, while metallic  silver re-
mains ; but the phosphate gives no volatile product.
  C. The Ammonia-sulphate of Copper is uncertain, unless it be dried
and reduced ; for there are numerous basic compounds of copper,
which resemble it very much  in colour.
  None of these liquid reagents are,  therefore, in themselves posi-
tive, unless by extraction of the metal ; and this is the more impor-
tant when the  operator has to work,  not  with  the  clear  solutions
prepared intentionally for illustration, but with the complex and
discoloured liquids  obtained from  the  stomach and  intestines.
  The  process to be then followed maybe either of two kinds; the
first consists  in converting the arsenic into sulphuret, the  second
into arseniuret of hydrogen.   I will describe each in their turn.
  The  contents of the stomach and  small  intestines, or the  matter
ejected by vomiting during life, are to be boiled  in distilled water
for half an hour, and then the  liquor strained through a linen cloth.
If it be too thick or coloured to allow of a small quantity of  precip-
itate being observed and  separated, a current of chlorine  gas is to
be passed through it, by  which most of the animal matter dissolved
is coagulated, and a more convenient solution obtained.  This be-
ing strained or filtered, is to be well boiled to expel the excess of
chlorine, and  then submitted to the action of a current of sulphuret-
ted hydrogen  gas.  The animal matters may also be removed from
the solution  by rendering it acid by nitric  acid, and then adding an
excess  of nitrate of silver.  When the precipitate which forms has
been separated, the excess of silver is to be thrown down by  some 
382          MARSH'S  TEST  FOR  ARSENIC.
common salt, and the liquor being then filtered, is fit for the action
of the sulphuretted hydrogen.
   When the liquor smells strongly of this gas,  there  has been
enough  passed through, and it is then  to be boiled briskly for a few
minutes to expel  the excess, and favour the deposition of the pre-
cipitate  produced.  This is to be then collected on a filter, wasbed
carefully with water acidulated by muriatic acid, and  dried at a
moderate heat.
   When completely dry, it is to be mixed with about twice  its bulk
of black flux, and ignited in a small tube of hard glass closed atone
end.  In introducing the materials, care must be taken not to soil
the sides of the  tube ; metallic arsenic sublimes,  which is recog-
nised by the characters given already  in pages 376, 380.
   The process by arseniuretted  hydrogen was first proposed by Mr
Marsh, and has been found of  surprising  delicacy and exactness;
the liquid having been  freed from animal  matters, and obtained as
thin a fluid as possible by  either of the processes, by chlorine or
nitrate  of silver,  already described, it is rendered moderately acid
by muriatic or sulphuric acid, and introduced into a flask or bottle,
to the neck of which is adapted a narrow tube of hard glass, which,
after passing horizontally  for a few inches, turns  up and forms a
jet; a piece of zinc being introduced into the acid liquor, hydrogen
is evolved,  which combines with any  arsenic that may be present,
and, forming the  gaseous arseniuret of hydrogen, passes off.   When
the gas issuing from the jet is set on fire,  if the hydrogen be pure,
no other product is generated  but water;  but if a  slight  trace of
arsenic  be present, the flame is  whitish, and on holding over the jet
a fragment  of glass or porcelain, or a film of mica, a deposite is pro-
duced, which may be white from arsenious acid, or brown from me-
tallic arsenic, according to the height at  which the plate is held,
and the consequent completeness of the combustion, or the reverse.
If the quantity of arsenic be too small to produce this effect in a cer-
tain time, it may  be better detected by  igniting a portion of the hori-
zontal arm of the tube.   AH the arseniuretted hydrogen, in passing
that point, deposites its arsenic, which is carried a little beyond the
heated  portion by the  current,  and condenses there as a  distinct
metallic film ; as the tube  may be kept thus red-hot for some hours,
the smallest trace of  arsenic may be thus  concentrated on a single
point, and  its properties accurately verified.
   Where the liquor is still thickish from dissolved organic matter,
the gas bubbles would not break rapidly,  but form  a froth,  which,
passing into the tube, would prevent altogether the successful em-
ployment of the  methods just described.   In  this case the liquid
should be made so feebly acid as that the gas shall be generated but
very slowly, and  that there shall be but little  hydrogen in excess.
The tube, in place of terminating  in  a jet, is to be bent down so
that it shall pass  under  the edge of a jar in the pneumatic trough,
and, the apparatus being so left for any  length of  time,  the gas
evolved may be collected and subsequently examined.  Or, what is
perhaps still better, the tube may dip  under the surface of a dilute
solution of nitrate of silver or of sulphate of copper,  and all the ar-
seniuretted hydrogen being then absorbed and decomposed, metallic 
SOURCES OF  ERROR.
383
arseniurets are produced, which easily yield, by the application of
heat, the arsenic in the metallic form.
   In this mode of detecting the presence of arsenic, it is necessary
to avoid some sources of error, into which, without previous knowl-
edge of their existence, an operator might easily fall.  If the  effer-
vescence be rapid, it frequently happens that very minute portions
of zinc, or  of the salt of zinc generated, may be carried up by the
stream  of gas, and, being deposited upon  the  plate,  form a crust,
which might lead to suspicion, or perhaps wrong conclusions.  This
may be avoided by either moderating the effervescence, or by pass-
ino- the gas, before using it, through a tube filled loosely with cotton,
by which it is filtered,  as  it were, and all  mechanically diffused
particles separated.  Much more important sources of error  arise,
however, from the existence of arsenic in most of the zinc and some
of the sulphuric acid of commerce.  The ores of  zinc occasionally
contain orpiment, which being  reduced  along with the other sul-
phuret,  it is necessary to distil the zinc in order to have it  pure,
and to reject it as  long as it contains arsenic.   The iron pyrites
also occasionally contains traces of orpiment,  and this passes into
the oil of vitriol.   In employing this method, it is necessary, there-
fore, to  test the purity of the zinc and sulphuric acid by the method
itself.   A jet of the hydrogen, evolved from  the zinc and dilute
sulphuric acid simply,  should be burned, or the gas passed through
a solution of ammonia-nitrate of silver for a quarter of an hour.  If
no trace of deposition of arsenic occur, the materials may be con-
sidered  as  pure, and  the suspected liquor may then be employed
with confidence in the result.
  A more remarkable  source of error  arises from the fact that the
compounds of antimony yield, under similar circumstances, a pre-
cisely similar gas, antimoniuret of hydrogen.  It  would anticipate too
much the history of that metal to enter into the  details of the means
of distinguishing that gas from the arseniuretted hydrogen, but they
will be fully described  in their  proper place.
  Arsenious acid possesses the power of preventing the putrefac-
tion of animal substances, and hence the bodies of  persons that have
been poisoned by it do not readily putrefy.   The arsenious acid
combines with the fatty and albuminous tissues to form solid  com-
pounds, which are not  susceptible of alteration under ordinary cir-
cumstances.  It hence  has frequently occurred, that the bodies of
persons poisoned by  arsenic  have been  found,  long after death,
scarcely at all decomposed, and even where the general mass of the
body had completely disappeared,  the  stomach and intestines had
remained preserved by the arsenious acid which had combined with
them, and by its detection the crimes committed many years before
were brouo-ht to light and punished. In the cases where the whole
body has been found fresh, it resulted from  the  person having survi-
ved for a length of time sufficient for the complete permeation of the
tissues by the absorption of the poison ;  in the others, death had
occurred while  it was yet only  in the intestinal tube.   The absorp-
tion of the arsenious acid in cases where death has not been rapid,
renders  its  detection possible in all the various organs, particularly
where the poisoning has been produced, not by the administration 
384 ANTIDOTE  TO  ARSENIOUS ACID.--A NTIMONY,

of a single dose, but by frequently repeated doses, each insufficient
to produce rapid poisoning.  The decision in such cases is rendered,
hovvever,  extremely difficult by  the fact, recently established, that
the resemblance of function, so often alluded to, between arsenic
and phosphorus, is  such, that the latter element, which  character-
izes the  animal tissues by  its almost  constant presence, may  be
replaced  as a constituent of  our organs by  arsenic.   Thus,  the
bones may contain arseniate  of lime  as a substitute for some  of
their proper phosphate of lime,  and in  the phosphoric salts, which
are found  in the blood,  a similar replacement may occur.  It is
certain that the quantity of arsenic thus found naturally replacing
phosphorus in  the  body  is  very small, but there is  no  necessary
limit to its extent;  and although, in cases of suspected chronic poi-
soning, the  analysis of the  organs might  lead to useful evidence,
yet the discovery of arsenic out of the alimentary canal should, as
I conceive, not without great caution, be considered as necessarily
involving  its having been administered.
  The sulphuret of arsenic of commerce, king's yellow, when taken
as a poison, is  recognised by its solubility  in ammonia, from which
it is again thrown down by an excess of any acid.   Its reduction to
the metallic state has been already fully described.
  An antidote has been recently discovered to the poisonous effects
of arsenious acid, which  is founded on a very remarkable reaction.
When hydrated peroxide of iron is made into  a thin paste with so-
lution of arsenious  acid, this disappears, being changed into arsenic
acid, and the iron into  protoxide, 2Fe203 and As.03 producing 4Fe.O.
-f-As.05.   This arseniate of iron has no action on the system; and
hence, in cases of poisoning by arsenic, this  hydrated peroxide
should be administered as  largely and as rapidly as possible.  It
may be made in a few  moments  by adding  carbonate of soda to any
salt of red oxide of iron (permuriate, muriate, or acetate tincture).
It need not be  washed, as the liquor contains only a  salt of soda,
which would be, if not beneficial, certainly not injurious.
  The preparations of arsenic are of very extensive use in the arts.
The metal is used to alloy the lead of which shot is made.  White
arsenic is employed in glass-making,  to prevent the deoxidation of
the oxide of lead, and the orpiment is employed to  render indigo
soluble in some processes  of dyeing.   It has many other less exten-
sive uses.

                         Of Antimony.
  This metal was first discovered, and its preparations  introduced
into medicine by Basil Valentine, from the unpleasant  results of
whose experiments upon his fellow monks it got the  name of anti-
moine ; its proper Latin name is stibium, and hence its symbol, Sb.
Antimony exists in nature,  principally as  sulphuret,  sometimes as
oxide, and also these two combined, forming the oxysulphuret, red
antimonial ore.   It is  from the  native sulphuret that the metal is
prepared.  The process  for obtaining it by means of iron  is no-
ticed p. 332, but it  is had purer by fusing  the sulphuret at a bright
red heat  with black flux.  Sulphuret of potassium and oxide of an-
timony are first formed, and this last being decomposed  by the car- 
                 OXIDES  OF  ANTIMONY.              385

bon, carbonic  oxide  is evolved, and metallic  antimony  separates;
this process is farther detailed in p. 334.
  The antimony thus obtained is a brilliant white metal, of a highly
crystalline fracture, and may be obtained crystallized in rhombohe-
drous, like those  of  arsenic, by  fusion, as described in  p. 23 ;  its
specilic  gravity is 6*8; it melts  at about 800  , just below  redness,
and may be volatilized by a white heat.  If heated violently in con-
tact with air, it takes fire, burning with a brilliant white  flame, and
forming antimonious acid, which, though not volatile, is carried up
by the current of air, and is deposited on the neighbouring bodies
as a white powder, flowers of antimony.  Antimony in powder takes
fire  spontaneously in chlorine, burning with a  yellowish flame; the
antimony is not oxidized by exposure to the air nor by water ;  it
is not acted on by sulphuric nor muriatic acids, but is rapidly oxi-
dized by nitric acid.   The symbol of antimony is Sb.; its equiva-
lent numbers are  1613 or 129*2; it combines with oxygen in three
proportions.
  Oxide of Antimony—Sb.Oa; equivalent  1913 or 153*2—may  b«
prepared by adding  to an acid and boiling solution of chloride of
antimony in water, carbonate of soda in excess.  The carbonic acid
does not combine with oxide of antimony, which therefore precip-
itates pure ;  it is  a white powder, not quite insoluble in  water, and
becomes yellowish when heated.  If  metallic antimony  be burned
in a limited  supply of air, this oxide  forms, and has been  obtained
crystallized both  in the prismatic and  octohedral forms of arsenious
acid, with which it is, therefore, isodiinorphous ; both the metal and
this oxide, when ignited in a full supply of air, produce antimonious
acid.
  This oxide of antimony combines with acids to form salts of very
little stability,  but it  produces with the acid potash salts of the veg-
etable acids, double  salts of remarkable constitution ;  of these the
potash tartrate of antimony (tartar emetic) is the most important;  it
also acts as a feeble  acid ;  thus,  if in  its preparation caustic potash
be used  to decompose the chloride, a granular white powder is ob-
tained,  in which the oxide  of antimony is combined with potash;
it is on this account called hypo-antimonious acid by many chemists.
  Oxysulphuret of Antimony. - Sb.03 + 2Sb.S3.  This substance con-
stitutes  the red ore of antimony, and may be  artificially produced
by roasting the native sulphuret in contact with the air; the sulphur
burns out as sulphurous acid, and the antimony becomes oxidized ;
the  product generally contains an excess of  oxide, which may be dis-
solved out by  tartaric acid, and  it is  thus  that the basis for tartar
emetic is sometimes  prepared ; by continued roasting, the whole  of
tie  sulphur may be expelled, and an impure oxide of antimony pro-
duced ;  this, when melted,  constitutes the glass of antimony, and
the  oxysulphuret  is the crocus of antimony of the older pharmaco-
peias.
  Antimonious Acid.   Peroxide  of  Antimony.— Sb.04.   Equivalent
-013 or  161*2.   This is the most stable compound of oxygen and an-
timony ;  it  is formed when antimony is oxidized freely, either  by
combustion or  by  the action of nitric acid, and  igniting the resulting
powder.  It is  a white powder, insoluble in water ; it is not volatile j 
386          SULPHURETS  OF  ANTIMONY.
it combines with alkalies, forming salts insoluble in water, and from
which, by a stronger acid, it is separated as a hydrate, Sb.04-|-H.O.
This hydrate dissolves in strong  muriatic acid.
  Antimonic  Acid.   Sb.03.  Equivalent  2113 or 169*2.   This sub-
stance is first formed when metallic antimony is oxidized by an ex-
cess of nitric acid, and  remains as a pale yellow powder,  which,
when exposed  to a dull  red heat,  abandons one  atom of oxygen,
leaving antimonious acid, as just described ; it is, however, more
stable in combination, and may  hence be  prepared by deflagrating
antimony with  nitre ; when the  resulting  mass  is digested in  cold
water, nitrate and nitrite of potash dissolve out, and leave the anti-
moniate of potash as  a white powder; this is decomposed by boiling
water, which dissolves a  basic salt,  and leaves one with an excess of
acid behind.  In its hydrated condition, this acid dissolves in hy-
drochloric acid.
  Antimony and sulphur combine in three proportions, forming sul-
phurets,  which resemble completely, in constitution,  the oxygen
compounds;  they are sulphur acids, dissolving  in a solution of the
alkaline sulphurets, and forming  sulphur salts.
  Sulphuret of Antimony.— Sb.S3.  Equivalent 2216*6 or 177*5.  This
substance constitutes the common  gray  ore of antimony, and crys-
tallizes in the same form as orpiment, with which it is frequently
contaminated ;  in its native state it  is dark gray,  with highly metallic
lustre, crystalline in  structure, and very easily reduced to powder;
it may be prepared also by precipitation from a  solution of anv salt
of oxide of antimony, as the chloride, or tartar emetic, by sulphu-
retted hydrogen ; it is then an orange powder, which becomes darker
on being dried, and has the  same composition as the native sulphu-
ret, with which it becomes identical in appearance by fusion.  This
sulphuret dissolves  in alkaline solutions, on which circumstance are
founded  the various pharmacopoeial processes for  its formation.  It
has been used in medicine ever since the first discovery of antimony,
and in all countries ;  the methods of preparation, and the purity of
the products obtainable, are, therefore, exceedingly variable.
  When finely powdered sulphuret  of antimony is boiled in a strong
solution  of caustic potash, it dissolves, and the  liquor contains two
salts perfectly similar to one another, but containing, the one sul-
phur and the other oxygen, united to antimony and potassium.  For
one  half of each substance is decomposed, the oxygen passing to
the antimony, and the sulphur to  the potassium,  so that oxide of an-
timony and sulphuret of potassium result, and these respectively
combine with the  quantities of  potash and sulphuret of antimony
that had not been altered;  in this way,

           C Sb.S3    3K.O. i         (   Sb.S3+ 3K.S. )
           <      and      \ produce <      and     }
           ( Sb.S3    3K.O. )         (  Sb.03-f-3K.O. )

  When the solution cools, both  compounds are partly decomposed,
so that a quantity of sulphuret and of oxide of antimony precipitate
mixed together ; and hence an opinion has generally prevailed, and,
indeed, been supported by the high authorities of Leibig and Gay
Lussac, that these  bodies are chemically united in the precipitate 
         PREPARATION  OF  KERMES  MINERAL.     387

 so obtained, and that it is an oxysulphuret, identical in constitution
 with that already described.   It is, however, quite established, par-
 ticularly by the experiments of Berzelius and H. Rose, that the ox-
 ide and the sulphuret are but  mechanically mixed ; under the  mi-
 croscope, the former is seen as brilliant white crystals, mixed with
 the line  amorphous brown powder of the latter; and, besides,  the
 quantity of oxide is completely variable, and in  no case so great as
 the composition of the true oxysulphuret should require.
   The precipitate thus obtained by cooling is  generally of a fine
 orange brown colour, the exact  shade of which varies very  much
 with the temperature, and the degree of concentration of the liquor.
 It is termed in pharmacy kermes mineral, from a very remote analogy
 of its colour to that afforded by the insect  kermes (coccus ilicis),
 which is used as a cheap substitute for cochineal.
   After the separation of the kermes, the liquor, containing still the
 sulphur and oxygen salts above described, but  with a greater pro-
 portion of  base, is  precipitated by adding an acid  in excess.   The
 sulphuret of potassium is decomposed,  and the sulphuret of anti-
 mony, with which  it had been combined, separates; at  the  same
 time, the sulphuretted hydrogen, evolved from the sulphuret of po-
 tassium,  reacts  on  the  oxide of antimony, converting it  into sul-
 phuret.   This precipitate is  much  lighter-coloured generally than
 the kermes, and is sometimes called the golden sulphuret of anti-
 mony, although that name properly belongs to a  different substance,
 to be described farther on.  In many cases, in  place  of collecting
 the kermes and the portion  precipitated by the acid  separately as
 now described, the hot filtered liquor is added  to the acid before
 the kermes has had  time  to  separate, and the  whole being then
 mixed, assumes an intermediate shade of colour, and constitutes  the
 brown sulphuret, or  orange sulphuret of antimony of the  British  phar-
 macoprxias.
  In place  of caustic potash, the native sulphuret of antimony is
 frequently  boiled with carbonate of soda.  In this case the whole
 of the carbonic acid unites with one half of the soda, formino- bicar-
 bonate, and the  other half of  the soda acts with the sulphuret of
 antimony precisely  as if it had been used in the  caustic state.
  An important  mode of preparing these pharmaceutical substances
 consists in fusing the materials together instead of boiling their solu-
 tions.  Thus an excellent  kermes is prepared  by fusing together
 three parts of native sulphuret and one of carbonate of potash.  The
 general reaction is the same as described when  the materials  were
 dissolved ;  the melted mass is boiled in  water, and the solution so
 obtained  treated as already noticed.  Rose has,  however,  directed
 attention to a circumstance which, though occurring in all  cases, is
 more marked in  this process than the others.  It is, that some anti-
 mony separates in the  metallic state,  while another portion  is
 changed into persulphuret; thus 5Sb.S3 produces 3Sb.S5, and 2Sb. is
 set free.   The solution contains, therefore, not  only the ordinary
 sulphuret, but  some persulphuret of antimony, the colour  of which
 is much brighter than that of  the other, and it hence  modifies the
tint of the preparation in a variable manner.  The persulphuret car-
ries down with it also some sulphuret of potassium, and hence the 
 388         ANTIMONIURET  OF  HYDROGEN.

 ordinary kermes mineral appears always to contain traces of potash.
 The quantity of persulphuret of antimony present seldom  exceeds
 two or three per cent.
   Sulpho-antimonious Acid.—Sb.S4.  This substance is  produced as
 a yellow powder when the solution of antimonious acid is decom-
 posed by sulphuretted hydrogen.
   Sulpho-antimonic Acid—Persulphuret of Antimony, Sb.Si—is obtain-
 ed when a  solution of antimonic acid in  muriatic acid  is treated
 with  sulphuretted hydrogen.  It is of a fine golden orange colour.
 Its formation in the process  for kermes mineral has been already
 explained.   This is the true golden sulphuret.   To obtain it  in large
 quantity, as  is given in many pharmacopoeias, three parts of sul-
 phuret of antimony and one of carbonate of potash are to be  fused
 with one half part of sulphur ; this last converts the  antimony into
 the persulphuret.  The fused mass is to be dissolved in water, and
 decomposed by muriatic acid.
   Antimoniuret  of Hydrogen.—Sb.H3.  When hydrogen is  evolved
 in contact with  antimony in a nascent or finely divided state, they
 combine and form a gas, which, in properties and constitution, has
 a remarkable similarity to arseniuret of hydrogen.  The easiest  mode
 of effecting this is to dissolve zinc in dilute sulphuric acid to which
 tartar emetic has been added.   The gas so evolved is colourless, in-
 soluble in water, has neither acid  nor alkaline  reaction.  It precip-
 itates the salts of mercury and most metals, but not copper, by
 which it is  distinguished from the  arseniuret  of hydrogen.  Its
 specific gravity has not been experimentally determined ; but if it be
 composed, like arseniuretted hydrogen,  of  one volume of metallic
 vapour and  six of hydrogen condensed to four, it should be 4504*7.
 When this  gas burns,  water  is formed, and  antimony deposited,
 either as metal or as oxide, according to the supply of  oxygen.  It
 hence superficially resembles  in its combustion the gas containing
 arsenic, but it is distinguished readily by the following  characters.
   1st.  The  antimoniuret of hydrogen,  when  it is decomposed by
 heating a point of the tube  through which  it passes  to redness,
 deposites the metal at  the  heated part, while arsenic  settles at a
 certain distance beyond, where the tube is colder.
  2d. The metallic crust is not volatilized at any temperature which
 can be applied to glass.
  3d. If the metallic scale be deposited on a porcelain plate, and ox-
idized by the outer flame  of the blowpipe, it forms  a powder yel-
low while hot, but white when cold, which  is  not  volatilized by
any farther application of the flame.   Arsenic,  on the contrary, be-
comes oxidized only in the act of being vaporized.
  In certain cases  of compound poisoning,  and where tartar emetic
has been given as  an emetic in cases of poisoning by arsenic, it is
possible  that the two metals may coexist in solution.  In  the.se
cases they  may be separated by converting  both into  the  hydrogen
compounds, and decomposing the  mixed gases by igniting the tube
through which they pass.   The antimony is deposited close to the
heated part, and the arsenic at a little distance.
  The detection of antimony is generally simple ; in  all its combi-
nations it is immediately recognised by the formation  of its  cora> 
TELLURIUM  AND   ITS  COMPOUNDS.         389
pound with hydrogen just  described.   In solution,  in the state of
oxide, it gives with sulphuretted hydrogen the  orange precipitate
of sulphuret.   In  the other states  of oxidation the precipitates by
sulphuret of hydrogen are more yellow, but are all easily distinguish-
ed from orpiment by  not  being volatile, and from the bisulphuret
of tin  by  yielding the  antimoniuret  of hydrogen.   From the  sul-
phuret of cadmium they are known by their solubility in  hydrosul-
phuret of ammonia.


                               Of  Tellurium.

   This is one of the rarest of the metals, and, although classified with them, from its
lustre and power of conducting electricity and heat, in which it is, however, far in-
ferior to the  others, it ranks naturally with sulphur and selenium, to which last it
assimilates completely in its properties.  It exists in nature, native, and combined
with a variety of metals, gold, silver, antimony, lead, &c, forming ores of very in-
definite constitution.   Its extraction, which is still farther complicated by the pres-
ence of sulphur and selenium, would require too detailed description, and is too sel-
dom an object with chemists to require description here.  Its properties and princi-
pal compounds alone deserve attention.
   Pure tellurium is silver white  and very brilliant.  It crystallizes easily in rhom-
boheirons.   it is brittle and easily powdered.   Its sp. gr. is 614.  It is  about as fu-
sible as antimony, and at a very nigh temperature may be volatilized.   Its vapour
smells like selenium;  when heated in the air it burns with a bluish flame, forming
'elluroiis acid.  It is rapidly oxidized by nitric acid.
   Tne analogy of tellurium to sulphur is very close.  When tellurium is boiled in
a strong solution of potash, there is formed tellurite of potash and telluret of potas-
sium; out if this solution be diluted, the potassium reduces  the tellurous acid, and
the metal is precipitated, potash being regenerated.  The symbol of tellurium is Te.
Its equivalent numbers are 8018 and 6T-2.
   Tellurium comuines with oxygen in  two proportions, forming tellurous and tel-
luric acids.  The former, tellurous acid, Te.O.-, is piepared by decomposing the bi-
chloride of tellurium  by water, Te.Cb and  2H.O. producing 2H.C1.  and Te.O*.
This List precipitates as a bulky white powder containing combined water.   In this
state it is  sensibly soluble in water, and reddens litmus.  It dissolves readily both
in acid and  alkaline solutions, forming compounds of a very instable character.
When its solution in water is heated to about 110°, it deposites the  tellurous acid in
an anhydrous form.  The water is also expelled by a moderate heat from the hy-
drated acid in powder.  The anhydrous acid thus obtained differs  essentially from
the hydrated form.  It is insoluole in water, in  acids, and in alkalies,  and has no
acid reaction whatsoever.  No salts of it can be formed in the humid way; but if it
be fuse 1 at a  red heat with carbonate of potash, the carbonic acid is expelled, and
tellurite of potash formed, which dissolves in water;  from this solution the hydra-
ted tellurous acid is thrown down on the addition of an acid.
   Berzelius considers  these remarkable differences of properties as indicating an
isomeric distinction between  the two  acids.  In a subsequent chapter I shall point
out the manner in which I believe such compounds should be viewed.
   TMuric A:id, Te.03. is prepared by deflagrating tellurous acid with nitre; a sol-
uble tellurate of potash  is thus  obtained, which, when mixed with nitrate of ba-
ryti'-, gives an insoluble tellurate of barytes, and this, acted on by sulphuric acid,
yiel Is sulphate of barytes, and in  solution telluric acid, which crystallizes in la-ge
prisms containing three atoms of water.   Of these, two are given off at  212° P.
It  dies not taste acid,  but reddens litmus slightly.  It combines readily with bases,
forming classes of salts containing one, two, and four equivalents of acid.   When
the crystallized telluric acid is heated to redness, all its water passes off, it becomes
orange and undergoes a change of properties like stannic acid.  It becomes insolu-
ble in water, in acids, and alkaline  solutions;  when very strongly heated, it gives
off oxygen, and tellurous acid remains; but if this anhydrous acid be fused with
potash, the telhirate of potash which dissolves contains the acid in its hydrated
state.  These forms are considered as being isomeric, and not identical bodies;
tlr.'ir real  nature will be noticed hereafter.
  Tellurium  and hydrogen combine to form a gas, telluret of hydrogen, H.Te., which
resembles in  its characters sulphuret of hydrogen, particularly in its odour; it  red- 
 390  URANIUM  AND  ITS  COMPOUND S.--C OPPER,

 dens litmus, is soluble in water, decomposes the alkalies and earths, forming soluble
 tellurets, and precipitates insoluble tellurets from solutions of the other metals.
  Tellurium combines with sulphur in two proportions, forming sulphurets, which
 do not require detailed notice.  Its compounds with the metals resemble so com-
 pletely the metallic sulphurets as to render a separate account unnecessary.  Thus,
 in every case where a metallic sulphuret evolves sulphuretted hydrogen gas with an
 acid, the telluret of the metal produces lelluretted hydrogen, and the metallic tellu-
 rets are soluble or insoluble in water, precisely as the sulphurets of the same metals
 are.
                             Of Uranium.

  This metal exists in some rather rare minerals, particularly mpechblemle, combined
 with oxygen; the processes for its extraction  are rendered very complex by the
 presence of a great number of other metals, and I shall refer, therefore, to the sys-
 tematic works for the details of its extraction; the metal itself is easily obtained
 pure by the action of hydrogen gas on either of its oxides at a red heat.  It is of a
 dark gray colour, difficultly fusible, specific gravity 90.  Its symbol is U., its equiv-
 alents are 2711 or 2173, being the largest numbers for any of the simple bodies;  it
 combines with oxygen in two proportions.
  Protoxide of Uranium, U.O., is obtained by decomposing any salt of uranium by
 a caustic  alkali; it  precipitates as a greenish hydrate, which rapidly becomes yel-
 low, forming the peroxide by absorbing oxygen: the protoxide of uranium is dis-
 solved by an excess of ammonia.  Peroxide of uranium, U.03) is lbrmed when the
 protoxide is heated in air; it is yellow, and possesses some of the  characters of an
 acid, uranic acid; it reddens litmus;  it enters into combination as well with alka-
 lies as with acids; the alkaline and earthy uranates are insoluble, yellow or orange
 coloured.   This oxide is used to colour glass of a fine lemon yellow.
  The sulphurets, &c, of uranium are unimportant.

                             SECTION V.

                     METALS OF  THE FIFTH CLASS.

                             Of Copper.

  Copper is one  of  the most important of the metals, and  one, also,
 of the most extensively diffused through nature.  It exists  native in
 veins, and frequently crystallized, in forms belonging to the regular
 system ;  in the state of oxide it is found, both uncombined  and form-
 ing arseniates, phosphates, carbonates, and other salts, but its most
 abundant source is the  native  sulphuret.  The ordinary copper ore,
 copper pyrites, is a double sulphuret of copper and iron, Cu.S.-f Fe2S3,
 and  from this the metal is extracted for  the purposes of commerce.
  The general processes for the reduction of a metallic  sulphuret
have been already described (p. 333),  but, from the composition of
the copper ore, some additional management  is required ;  there are
two  metals present  in the ore, and as neither is volatile, the product
after complete reduction should be, if  the  process was simply man-
aged as  for a simple sulphuret, not pure copper, but an alloy of one
 equivalent  of copper and two  of iron ; this is avoided by arresting
the process of reduction at a certain stage ; the copper, having less
 affinity for oxygen  than the iron, assumes the metallic  state first,
 and, if it were possible  to work so accurately, the whole of the  cop-
 per might be reduced  before any iron, and this last metal left  alto-
 gether in the scoria: as  oxide or silicate ;  but this not being feasible,
 the  copper first  obtained is rendered  impure by the  presence  of  a
 quantity  of iron,  and also of  sulphur ; this  impure copper is  then
 calcined ; the iron and sulphur, being the more combustible bodies,
 are  first  oxidized, and  then again, by  other reductions and calcina-
 tions, the copper is  ultimately brought  to a state of complete purity. 
PROPERTIES  OF  COPPER.             391
The separation of the iron is facilitated by adding a small quantity
of sand  to the calcined mass before the process of reduction ;  the
silicic acid unites exclusively with the oxide of iron, and the silicate
of iron not being reducible under ordinary circumstances, the puri-
fication  of the copper is more rapidly effected.
  Though the copper is thus rendered quite pure from iron, great
care  is  still required in these  operations, in order to secure  the
proper softness, ductility, and tenacity necessary in  the employ-
ment of this metal in the  arts;  thus,  if it has been too  long in con-
tact with the fuel, it combines with a small quantity of carbon ; if, on
the other hand, the deoxidizing action of the fuel be not applied long
enough, some suboxide remains undecomposed, which dissolves in
the metallic copper.   In both these  cases the  metal is brittle  and
of a bad grain, so as to be unfit for many of its  uses.
   Copper is obtained also in the metallic state by precipitation from
the water which collects in the galleries and shafts of copper mines,
and which, from the oxidation  of the sulphuret  of copper, contains
sulphate of copper dissolved.  Fragments of old iron are thrown
into the reservoirs  in which the drainage water of the  mine is  col-
lected,  and by electro-chemical  action, as described  p. 193, 195,
and 335, the iron is dissolved and the copper precipitated in  irreg-
ularly crystallized masses.
   Pure  copper is of a  peculiar well-known  reddish  colour.   It is
very malleable and ductile ; after iron, it is the strongest of the met-
als.  It  crystallizes by fusion in  a form which  is not  the same as
that found native, or produced when  the metal  is precipitated from
its solutions.   Its sp. gr.  is 8*9.   It  is fusible at 1996 .   It  is not
volatile.  In dry air it is not tarnished, but in damp air it gradually
becomes covered with a greenish coating of basic carbonate of cop-
per.   When  heated in contact with  air, copper combines rapidly
with oxygen,  and passes  through a variety of rainbow colours, but
is at last converted into black oxide, which forms as scales upon its
surface.  The  series of colours arises first from the action of light
upon the thin  coating of oxide, as also happens in the  oxidation of
iron.  The generality of acids do not act on  copper at ordinary
temperatures, unless in contact with air, for the copper is incapable
of decomposing water ; but at the point of contact with air, oxygen
is directly  absorbed, and the acid combines with the oxide so gen-
erated.   In this way the feeblest acids may act  upon copper,  as the
acetic acid and the acids  contained in the various fatty bodies, and
the metal be thus introduced into culinary preparations, and so pro-
duce poisonous effects.   The acids which give oft* oxygen directly
dissolve copper, as nitric acid, with evolution of nitric oxide. Strong
oil of vitriol, also, when boiled on copper, gives sulphate of copper
and sulphurous acid gas
   The symbol of copper is Cu., from its Latin name ; its equivalent
395*7 or 31*7.
   Copper combines with oxygen in two proportions, forming  a sub-
oxide and a protoxide.
   Protoxide of Copper.—Cu.O.  Equivalent 495*7 or 39*7.  This ox-
ide is formed  by exposing copper, at a red heat, to a current  of air.
It may  also be obtained by igniting  the nitrate of copper.   It  is a 
392                OXIDES  OF  COPPER.
dull black powder, which, by a very high temperature, muy be melt-
ed, and crystallizes on  cooling.  It dissolves but slowly in acids,
forming the ordinary blue or green  salts of copper.   When heated,
even below redness, in a stream of hydrogen gas, it is perfectly re-
duced, water being formed.   It is thus that, as described in p. 253,
the composition of water is best determined.  At a dull  red heat,
this oxide is reduced  completely by carbon and all  its compounds,
carbonic acid  being  produced.  For this reason it is extensively
employed in the ultimate analysis of organic substances, of which it
converts the carbon into carbonic acid, and the hydrogen into water.
The metallic copper thus obtained by the reduction from the  oxide
is  a fine pinkish-red powder, which has a  remarkable  affinity for
oxygen, and is hence used in the analysis of organic  substances con-
taining nitrogen, to prevent the formation of nitrous  or nitric oxides.
  When a solution of caustic potash is added in excess to a solu-
tion of a salt of copper, the protoxide is thrown down as a hydrate,
Cu.O. .  H.O.  It is a fine blue  powder, which is  decomposed by a
very gentle heat, so  that even if a liquor containing it be boiled, it
becomes brown and anhydrous, though in the midst of water.   It is
hence that, if the solution of copper be added to  a  boiling solution
of potash, the precipitate is the dark brown anhydrous oxide, which,
however, obstinately retains a little potash.
  Suboxide of Copper.—Cu20.  Equivalent891*4 or 7T4.   Thisbody
exists native, constituting the ruby copper ore, and may be prepared
artificially by igniting a mixture of five parts of black oxide of cop-
per and four of copper filings;  half of the oxygen of  the former
passes to the latter,  and the whole  becomes suboxide.   It is  like-
wise made by fusing together three parts of subchloride of copper
and two of dry carbonate of soda; chloride of sodium and suboxide
of copper result, Cu2Cl. and  Na.O. giving Cu20.  and Na.Cl.,  while
the carbonic acid  is  given  off.   This suboxide of copper is a red-
dish-brown powder, which is much less acted on by moist air than
pure copper ; and hence, under ordinary circumstances, when cop-
per becomes brown  by  being  coated with this  oxide, the action
ceases.   Articles  of copper are thus coated  intentionally, for the
purpose  of preserving their  surface, by covering them with a paste
of red oxide of iron, which, when  heated,  is thus  reduced to the
state  of protoxide, 2Cu. and Fe203  giving Cu20. and 2Fe.O.;  this
last, is then removed  by digestion  in a boiling solution of acetate
of copper.
  The generality of acids decompose the  suboxide of  copper into
metallic copper, and  the black oxide with which the acid combines;
but, besides the subchloride of copper, several of  its salts may be
formed  by the action of deoxidizing agents on the salts of the black
oxide ;  thus sulphurous acid converts the hydrate of the black oxide
into  sulphate  of  the  suboxide, S.02 and 2Cu.O.  producing S.03 +
Cu20.   From the  solution of this salt, a fine orange hydrate of the
red oxide is thrown down by the  caustic alkalies.  Protochloride
of tin and protosulphate of  iron also reduce the salts of copper to
this state of oxidation.
   Sulphur combines with copper in two  proportions, forming sul-
phurets equivalent to the oxides just described; they are both found 
DETECTION  OF COPPER.             393
native, and constitute, particularly the subsulphuret, important ores
of copper.   They may be prepared  artificially by f'usino* too-ether
sulphur and metallic copper ;  the union takes place with brilliant
combustion.  If some sulphur be placed in a flask, and heat be appli-
ed so as to  fill  the flask with the vapour of sulphur,','a thin copper
wire dipped in it burns, as iron does  in oxygen, forming the subsul-
phuret ; these bodies are not of importance, except as the great
sources of metallic copper.
  The sulphurets of copper may also be formed by precipitating the
salts of copper with sulphuretted hydrogen ; a deep brown powder is
produced, which is Cu2S. or Cu.S., according as the solution contain-
ed the suboxide or the protoxide of the metal.
  The detection of copper in  solution  is very simple ; the salts of
the black oxide are generally green or blue ; on the addition of am-
monia, a precipitate is produced, bluish or green, according to the
acid with which the oxide had been combined, but in all cases pro-
ducing with an  excess of the ammonia a deep violet-coloured solu-
tion.  The  only metal which  resembles copper in this  respect is
nickel, and  from it, it  is  distinguished by all its other properties,
particularly  by the yellow prussiate of potash,  which produces a fine
chocolate brown precipitate of ferrocyanide of copper.  With sul-
phuret of hydrogen, the salts of copper give a dark brown sulphuret,
insoluble in  hydrosulphuret of ammonia; and when  a slip of clean
iron or zinc is introduced into a liquor containing copper, this is re-
duced, and deposited upon the surface of the zinc or iron as a bright
coating  of metallic copper.
  When the copper exists as suboxide, its reactions are very differ-
ent; it gives, with ammonia, a white precipitate, which redissolves
in an excess, forming a colourless liquor ; if there be no excess of
acid, chloride of sodium gives a white precipitate of subchloride of
copper.   But in practice it is never necessary  to look for copper by
these reactions, the salts  of the suboxide absorbing oxygen  with
such avidity, that by a few minutes'  exposure to  the  air their con-
stitution changes.  The colourless solution of suboxide of copper in
ammonia becomes violet blue in the act of pouring it from one bot-
tle  to another; and hence, for the mere  detection of copper, the
properties of the protoxide alone need be taken into account.
  Like the oxides of cobalt and nickel, the oxides of copper are not,
by themselves, soluble in water of ammonia.  The solutions of these
metallic compounds in water of ammonia are basic salts, to the con-
stitution of which the acid, with which the metallic oxide had been
originally combined, is  necessary.   The  detailed nature of these
bodies will be noticed among the compounds of ammonia.
  The detection of copper by  the blowpipe is very  simple and  dis-
tinct.  Fused with borax, a substance  containing the most minute
trace  of copper gives a glass,  which, when heated in  the  oxidizing
flame, becomes green, being coloured by the protoxide ; but when
ignited  in the reducing flame  and  suddenly cooled, is deep  ruby
red, generally opaque.  This change of colour arises from the cop-
per bein<T reduced to the  state of suboxide   The colour given to
glass by this suboxide is a pure prismatic red,  so homogeneous that
red light may be obtained for  optical experiments by transmitting
                             D D D 
394     USEFUL  ALLOYS  OF  COPPE R.--L E A D.

white light through this coloured glass, and the tint is so fine that
this ruby glass is the most valuable that can be used for ornamental
purposes.
  The salts of copper  generally  tinge  the  flame  of the blowpipe
blue or green, according to the  other bodies that may be present.
  Independent of the direct employment of copper in  the arts, for
which its properties eminently qualify it, it  enters into the compo-
sition of a great number of alloys of great importance.  Thus bronze,
formerly used as a substitute for  steel, and still employed in  the
casting of statues and monuments, from the accuracy with which it
adapts itself to the mould, and its durability, consists of ninety parts
of copper and ten of tin in  100.   It  is curious, that from the very
earliest ages, this, which is still the best proportion,  should have been
employed; the bronze  swords from ancient Egypt, from Scandina-
via, and those found in Ireland, having all this constitution.  Gun
metal, or that of which cannons are cast, is an inferior kind of bronze,
containing somewhat less tin.
  The elasticity and sonorousness of these alloys are very remark-
able.   That used for bells, bell metal, consists of 80 parts of copper
and 20 of tin.   The Indian gongs  have  this composition, but com-
mon bells contain less  tin, and, in place of it,  some lead and zinc.
In the proportion of two  parts of copper  to  one of tin, or, more
accurately,  of four  atoms of copper to one of tin, 127 to  59, an
alloy is formed of exceeding brittleness and hardness, and so brill-
iant, when truly polished, as to be used for the mirror surface in
reflecting telescopes ; it is hence called speculum metal.  The quality
of this alloy is remarkably deteriorated by a slight deviation to ei-
ther side of the true atomic proportions.
  The alloys of zinc and copper are very numerous and  important,
constituting the different varieties of brass.   The best brass consists
of four atoms of copper to one of zinc; but,  by changing the pro-
portions of the metals, a variety of  shades of gold lustre, used in
counterfeit jewelry, are obtained.  In the proportion of equal parts
of copper and zinc, hard solder  is produced; this is used in solder-
ing together surfaces of brass and copper.

                             Of Lead.
  This metal exists in nature,  very extensively diffused, and in  a
great  variety of forms.  The sulphate, phosphate, arseniate, car-
bonate, and chloride of lead are found native;  but it is exclusively
from  the sulphuret of lead,  galena, that the metal is  extracted for
the purposes  of commerce. The methods used in its reduction
have been very fully described in the preceding chapter, p. 334.
  Lead is one of the softest and least tenacious of the metals ; it is
bluish white, and very brilliant, but rapidly tarnishes in the air, be-
coming covered with a grayish coating, beyond which  the  action
does not appear to  extend;  its specific gravity is 11*44 ; it melts at
612 , and in solidifying diminishes in volume,  so that it is unfit for
accurate castings ;  it may, however,  be obtained, by fusion, crystal-
lized in octohedrons ; it is not  volatile ; it  is not sensibly acted on
by  muriatic nor sulphuric  acids, except at  very high temperatures,
but by nitric acid it is rapidly oxidized  and dissolved. 
OXIDES OF  LEAD.
395
   When lead is exposed at the same time to air and moisture  its
oxidation proceeds with great rapidity, so as to be used to analyze
atmospheric air (p. 264).   The oxide so formed is not quite insolu-
ble, so  that when pure water, rain, or even common soft water is
preserved in leaden cisterns, an impregnation with lead may occur
in such amount as to  produce dangerous consequences, if employed
habitually as a drink.  Fortunately, this is obviated, in general,  by
the small quantities of saline matters, particularly sulphates, which
all ordinary spring and river waters contain.  These react on the
oxide of lead, and, forming compounds totally insoluble in water, re-
move all traces of it from solution.   A whitish crust gradually forms
on the interior of the cistern, and assists, subsequently, in protecting
it from the  oxidizing action of the  air; no danger is  therefore to
be apprehended from  the supply of water to a city being conveyed
through leaden pipes,  and preserved in leaden cisterns; for all water
of mineral origin dissolves, in filtering through the layers of rocks
in its passage to the surface, a sufficiency of saline matters to serve
for its protection.
   The symbol of lead is Pb., from its Latin name ; its equivalent is
1294*5 or  103*7.  It  combines  with oxygen in  two proportions,
forming oxides, which, again uniting, form an intermediate complex
oxide.
   Protoxide of Lead.—Pb.O.  Equivalent 13945  or  111*7.  This
may be prepared  by exposing metallic lead at  a red heat to a cur-
rent of air ; the lead  rapidly combines with oxygen, and the oxide
so produced fuses.  It  forms, on  cooling, crystalline  masses of a
greenish-yellow colour; this constitutes the litharge of commerce,
which  is generally obtained in the cupellation of lead  for the pur-
pose of extracting from  it the small quantity of silver which its ores
generally contain.  When  the litharge is  kept for some time, the
masses of it break up into a brick-red crystalline powder,  evolving
heat.   This change is technically termed slacking, but it is not due,
like the slacking of lime, to combination with water, but to a change
of the crystalline form  of the litharge.  The yellow form appears
to be more permanent if the lead be oxidized at a lower temperature,
and, when powdered, was once used as a yellow pigment under the
name of massicot.   This may be produced of the richest colour by
decomposing the  subnitrate of lead at a temperature insufficient for
the fusion of the  oxide.
  This oxide may also be prepared  by decomposing a soluble salt
of lead by caustic potash ;  a white  precipitate is produced, which is
a hydrate of the oxide, 2Pb. -f- H.O.; by a great excess of caustic pot-
ash the precipitate may be redissolved.  The oxide of lead appears
to have the  power of uniting with most of the alkalies and earths
to form compounds more or less soluble.   A body of this kind, form-
ed by boiling lime and litharge together, is capable of crystallizing,
and is used to dye the hair black.   The hair contains sulphur, and
a  black sulphuret of lead forms in  its substance, and is not liable to
change.  The protoxide of lead requires  12,000 parts  of water  to
dissolve it ;  the solution reacts feebly alkaline ; it is a strong base,
and the only oxide of lead  which combines with acids.
  Peroxide of Lead, Pb.02, is obtained by digesting the protoxide 
396      OXIDES AND SULPHURET OF  LEAD.

in chlorine water, or in a solution of chloride of lime.  In the first
case, 2Pb.O. and CI. produce  Pb.02 and Pb.Cl.  In the second case,
Pb.O. and Ca.O.Cl. produce Pb.O, and Ca.Cl. ;  another simple plan
consists in heating red lead,  which is a compound of the  protoxide
and the peroxiderwith dilute nitric acid, until all the protoxide is
dissolved out, washing the residue well, and drying it at a moderate
heat.   The peroxide  so obtained is of a dull  dark  brown colour;
when heated  it gives off half its oxygen, leaving litharge.   With
muriatic  acid it produces chlorine  and protochloride of lead, and
with sulphurous acid,  which it  rapidly absorbs,  neutral white sul-
phate of lead, Pb.02 and S.02 producing Pb.O.-(-S.03.  This  oxide
of lead does not form salts.
  The Red Lead,  or Minium, Pb304= 2Pb.O. + Pb.O,, is  produced
when lead is  oxidized, so that the oxide formed shall not be fused,
and when the metal is all converted into the yellow powder, increas-
ing the heat to incipient redness.  Oxygen continues to be absorbed
until one third of the metal  is converted  into peroxide, giving the
constitution above expressed.  This is the pure red lead, the colour
of which  is exceedingly  brilliant; but the generality  of red lead
found in  commerce contains  an  excess  of protoxide, which may be
removed by boiling in a solution of neutral  acetate of lead.
  When red  lead  is ignited, it gives off oxygen and becomes pro-
toxide ; with muriatic acid it forms protochloride and chlorine.  It
does not form any proper salts,  but  it dissolves in acetic acid com-
pletely, giving a colourless  liquor, from which,  after a little  time,
peroxide of lead separates.
  It is probable that there exist  other oxides of lead ; thus the gray
coating which forms on  lead exposed to the air  is looked upon by
many chemists as a suboxide  ; and on heating oxalate of lead to low
redness,  a gray powder is obtained  of a similar nature, and yields,
on analysis, the formula Pb20.   In general, these bodies have been
considered as mixtures of the metal in powder  with the real pro-
toxide; but I think the evidence of their definite constitution very
strong.
  From the similarity of the  formula of red lead, Pb3Oj, to those of
the black oxide of iron, Fe304, and of the red oxide of manganese,
Mn.jOj, it has been suggested  that it may contain sesquioxide of lead,
Pb,03, similar to Fe203 and Mn203.   The formula of red lead should
then become Pb.O.+Pb203; but this idea, though interesting, is only
hypothetical.
  Sulphuret of Lead.—There is  but  one compound  of  sulphur and
lead,  the protosulphuret,  Pb.S.   It  constitutes the  abundant lead
ore, galena, and may be formed artificially, either by fusing together
lead and  sulphur, or by decomposing a  solution of a salt of lead by
sulphuretted  hydrogen  gas or hydrosulphuret of ammonia,  it  is
then a black powder, insoluble in water, and in alkalies, and  dilute
acids.  It is  rapidly oxidized by nitric acid, being  converted into
sulphate of lead.   From the perfect  insolubility and  marked colour
of this sulphuret, a salt of lead  and sulphuretted hydrogen are re-
spectively the most delicate  reagents for each  other.
  There  are  some indications of the existence of other sulphurets
of lead, which, however, do not  require special notice.   If a salt of 
    DETECTION  AND  USES  OF  LEA D.--B I S M U T II. 397

lead be decomposed by bisulphuret of calcium, a red precipitate ap-
pears, possibly a bisulphuret of lead, analogous to  the deutoxide, and
galena may be fused with metallic lead, forming a homogeneous
mass, in which, probably, subsulphurets  are contained.
  The detection of lead  is simplified very much  by its forming but
one series of salts, those of the protoxide.  Its solutions are recog-
nised  by giving, with caustic potash, a white  precipitate, soluble in
excess ; with carbonate of potash, one also white, but insoluble in
excess; with  sulphuretted  hydrogen, one dark brown or  black,
whose characters are described above;  with a solution of  bichro-
mate of potash, the salts of lead produce a fine yellow  precipitate,
chrome yelloiv ; and  with iodide  of potassium, the iodide of lead, in
brilliant yellow scales, like fragments of gold leaf.   Yellow prussiate
of potash gives a white precipitate, and sulphate of soda a white
sulphate of lead, insoluble in water, but not insoluble in acids.  If
the solution contain much lead, any soluble chloride  throws down
sparingly soluble chloride of lead, which, however, remains dissolv-
ed, if the solution be dilute.
  Lead and its preparations are of  the most extensive use in the arts.
In making  pipes and cisterns, sulphuric  acid chambers,  bullets, and
a variety of other purposes,  the metal is employed unaltered; and
its alloys are also of important application. Thus the metal of which
printing types are  made consists of three parts of lead to  one  of
antimony.   The inferior sorts of  pewter are alloys of lead and tin,
but the fine kinds should be tin  with very little lead, and some anti-
mony and bismuth.   The solder used for soldering surfaces  of lead,
or of tinned iron, to each other, consists of lead and tin, the  propor-
tions of which vary from two parts of tin and one of lead, to three
parts of lead and one of tin, according to the  object.   The more  tin
the alloy contains, the more  fusible it is.  Fine solder fuses at 3603,
coarse solder at 500 '.

                          Of Bismuth.
  Bismuth is not a  common  metal.   It is found but in a few places,
and only in the  metallic state in quantity, for the  sulphuret of bis-
muth  is too rare  to be  of technical interest.  It is extracted from
the rocks through  which it  is  disseminated  by reducing them  to
coarse powder, and igniting this in  a kind of kiln ;  the bismuth, being
very fusible, melts  out, and collects at the bottom in a trough pla-
ced to receive it.
  It is a white metal, with a peculiar reddish shade, and  remarkably
crystalline structure.  It may be  obtained in separate  crystals  of
considerable size, which are cubes,  generally hollow at the sides.
To obtain good  crystals, the metal should be perfectly pure ; this
is effected  by deflagrating some nitre on the  surface of the  melted
metal; the impurities are more easily oxidized than the bismuth, and
hence pass into the scoriae which form  on the surface.   The crys-
tals so obtained have frequently beautiful rainbow tints on  their sur-
face, from an exceedingly thin layer of  oxide of bismuth  by which
they become coated.
  Bismuth is very brittle and easily oxidized.  It is  scarcely acted
on by sulphuric  or  muriatic acid,  but it decomposes nitric acid vio- 
 398         BISMUTH AND  ITS  COMPOUNDS.

 lently, evolving nitric  oxide,  and forming oxide  of bismuth, with
 which the nitric acid combines.  It fuses at 497% is volatile at a white
 heat,  and then burns with a bluish-white flame.  Its sp. gr. is 9*9.
   The symbol of bismuth is Bi.  Concerning its equivalent, there is
 some  doubt at present as  to  whether it should be 886*9, or three
 times so  much, 2660*7, on the oxygen scale, and hence 71*1, or
 213*3, on the hydrogen scale.
  The  first number assumed would make the oxide of bismuth a protoxide, Bi.O.,
 the last a teroxide, Bi.03.  The ground upon which the  former view stands is the
 supposed similarity of some salts of bismuth to those of magnesia and the protoxide
 of copper,  but recent examination has gone to show that this analogy is not at all
 so strong as had been supposed, and  that their difference is more remarkable  than
 their resemblance. On the other hand, the sulphuret of bismuth is isomorphous
 with the sulphurets of antimony  and arsenic, and the equivalent deduced from the
 specific heat of bismuth agrees with those for arsenic and antimony, and assigns
 the same constitution to the compounds of the three.  The salts of the oxide of bis-
 muth are exceedingly instable, and, like those of antimony, are decomposed by wa-
 ter, so that, while it allies itself to that metal in every important point of physical
 and chemical characters, it recedes in all the important facts*of its nistory from cop-
 per, iron, zinc, and the other metals of the magnesian class.  I therefore think
 these are sufficient grounds for abandoning the numbers 8869 and 71-1, given in the
 table, p. 205, and to assume 26607 and 2133, as the equivalents of bismuth on the
 oxygen and hydrogen scales respectively.
   Oxide  of Bismuth—Bi.03; equivalent 2960*7 or 237*3—may  be
 prepared by the combustion of bismuth at a high temperature, or by
 the ignition of the subnitrate of bismuth.   It is a buff-coloured pow-
 der, which may be melted.   It combines with acids to form well-
 characterized  salts.
   The Superoxide of Bismuth, Bi.O^, is prepared by boiling finely-
 levigated oxide of bismuth in a solution of chloride of soda.  A fine
 brown powder is produced, which  is freed with great difficulty from
 admixed unaltered oxide.   When heated to dull redness it is decom-
 posed into oxygen and oxide of bismuth ; with muriatic acid it gives
 chlorine  and ordinary chloride  of bismuth.   Its  composition was
 supposed to corroborate the idea that the  yellow  oxide was a pro-
 toxide, for on  that idea this would be  a sesquioxide, Bi203, like the
 sesquioxides of cobalt  and  nickel,  which  it resembles  so  much  in
 properties; but the formula, Bi.05, agrees as well with the analyti-
 cal results, and I look upon it  as corresponding to antimonic acid.
  Sulphuret of Bismuth, Bi.S3, exists native, in crystals isomorphous
 with the  sulphurets  of  antimony and arsenic.   It may be prepared
 by fusing bismuth  and  sulphur together, or by adding sulphuretted
 hydrogen to a solution of a salt  of bismuth: it then precipitates as
 a brown  powder.   It is insoluble  in water and in hydrosulphuret
 of ammonia.
  Bismuth is easily known by its solutions being precipitated brown
by sulphuretted hydrogen and by  iodide of potassium, and yellow
by chromate of potash. The  caustic  and  carbonated alkalies pro-
 duce a white precipitate of  hydrated oxide of bismuth, which is in-
 soluble in excess.   A strong solution of a salt of bismuth is decom-
posed  by the addition of water,  whereby a white basic salt is pre-
cipitated, and the liquor contains free  acid.
  Bismuth is extensively employed  for some  purposes  in  the arts.
The  alloy used for casting  stereotype plates  consists of tin, lead,
and bismuth j and by increasing the quantity of bismuth, the fusibil- 
     EXTRACTION  OF   SILVER  FROM  ITS  ORE.    399

ity of this alloy becomes so great, that a compound of two parts of
bismuth, one of tin, and one  of lead, fuses at 201 \   This is the fu-
sible metal used for the bath in taking  the specific gravities of va-
pours,  as described  p.  14, and for supplying a steady  source of
heat for other purposes.

                          SECTION VI.

                   METALS OF THE SIXTH  CLASS.

                           Of Silver.
  This metal exists native, and in the state of sulphuret, in a great
variety of places; and from  the facility with which  it may be ex-
tracted, and  the permanence of its lustre, it became known at a very
early period.  The principal sources of silver  are the  mines of
South America; in Europe, those  of Saxony are the  most remark-
able.  A great deal of silver  is also obtained  from the ores of lead,
the sulphuret of lead  being generally accompanied by the sulphuret
of silver  in small quantity.
  The native silver of America exists, generally speaking, too fine-
ly disseminated to  be  simply  melted out.  It is washed out by mer-
cury, this fluid  metal  dissolving the  silver, and being then distilled
off, leaves the precious  metal behind.   A very remarkable process
is used to extract the silver from the sulphuret.   This ore is roast-
ed in a reverberatory furnace with  chloride  of sodium, by which
chloride  of  silver  and sulphuret of sodium are formed, Ag.S. and
Na.Cl. giving Ag.Cl. and Na.S.  This last is  washed  out, and then
the chloride of silver being put into barrels with some water, pieces
of iron, and mercury, the iron decomposes the chloride of silver,
forming chloride of iron  and setting the silver free, and this  dis-
solves in the mercury, forming a fluid  amalgam ;  this  is strained
through leather bags, by which a great part of the  mercury passes
off, and a pulpy mass of amalgam of silver  is obtained, which is then
submitted to distillation, by which the mercury is separated, and the
silver remains pure.
  The method of extraction  of the  silver which accompanies the
lead, in galena, is founded on the greater rapidity with which lead
combines with oxygen.  In the smelting of the ore, the silver is re-
duced with the lead, and the  resulting impure metal is melted  in a
shallow porous dish made of bone ashes, and when at a full red heat
a current of air is urged across it from powerful bellows.   The lead
becomes  converted into  litharge, as described in p. 395, and new
coatings  of  oxide  of  lead succeed  one another upon the surface,
until the  whole quantity of that metal has been removed.  When
the  silver remains pure, the surface becomes suddenly brilliant, and
the  completion of the work is known by the metal thus flashing or
lightening, as it is technically termed.   This is the process of cupel-
lation.  The porous bone earth capsule,  or cupel, absorbs a great
deal of the litharge, and the  rest is blown away from the surface,
as it forms, by the blast  of air, and is collected  in the front of the
furnace.
  This process has been remarkably shortened by the  discovery 
400
PROPERTIES  OF  SILVER.
that the quantity of silver  may be concentrated in a comparatively
small  quantity of lead,by crystallization.  The silver is not diffused
uniformly through all the lead, but combined in atomic proportions
with a certain quantity of it, forming an alloy, which is then mixed
with the excess of lead.   This alloy is more fusible than lead, so
that when a large basin of lead, containing a small quantity of sil-
ver, is melted, and allowed to cool very slowly, so as to crystallize,
the portions which first solidify are pure lead, and these  being re-
moved with iron colanders, all the silver remains in the mother li-
quor.   The process must  be stopped, however, before this begins
to congeal.  By a succession of crystallization of  this sort the great
excess of lead is gradually got rid of, and  the quantity to be oxi-
dized at the cupel diminished in a corresponding  degree.
  The silver of commerce is never pure, and hence, for  chemical
purposes, must be freed from the metals, generally copper, associa-
ted with it.  For this purpose it is dissolved in nitric acid, and  its
solution precipitated  by common salt.   Chloride of silver separates,
which is then reduced by  any of  the methods described in p. 332,
333.   The method of assaying may also  be used  to obtain pure sil-
ver.  The impure silver is melted with from four to eight times  its
weight of lead, and this alloy cupelled as already  detailed ; the lead
is not only itself oxidized, but the other metals present, which would
not otherwise  separate,  are  converted  into oxides, which pass off
with  the  oxide  of lead.   It  is in  this way  that the standard alloys
of  silver, for coinage and plate, are verified at the mint and other
offices.
   Silver, when  completely pure, is very brilliant; it  is the whitest
of  the metals, and takes a fine polish.  It is very ductile and malle-
able.   Its sp. gr. is 10 5;  it fuses at 1873°.  It is not altered by air
or  water, but when kept melted for a considerable time, it absorbs
oxygen, which  it appears  to hold rather dissolved than combined,
for on solidifying it discharges this oxygen, by which the  surface is
thrown into irregular granulations.  The quantify of oxygen may
be so great as twenty times the volume of the metal.
   Silver is very soft.  It is hence necessary, in coin, and in articles
for domestic use, to  add  a certain quantity of copper, to render it
less liable to deterioration from use or in being cleaned.
   When silver is exposed to the air, it gradually  tarnishes, which is
due, not to the  formation  of oxide, but of sulphuret, the air always
containing traces of sulphuretted  hydrogen, derived from organic
bodies.   It is not acted on by sulphuric or muriatic acid, but is rap-
idly dissolved  by nitric acid, with  evolution of nitric oxide gas.
   Silver combines with  oxygen  in three proportions, forming ox-
ides,  of which only one, the protoxide, is well known.  The equiv-
alent  of silver  is 1351*6 or 108*3, and its  symbol is Ag.,  from  the
Latin name.
   Protoxide  of Silver—Ag.O. ; equivalent  1451*6 or  116*3—may
be prepared by adding caustic potash, or lime water, to  a solution
 of nitrate of silver.   A brown powder is thrown down, which may be
 dried at a gentle heat without alteration.   It then  becomes very
 dark.  When  heated strongly, it is decomposed into oxygen and
 metallic silver, and this takes place even at ordinary temperatures, 
SULPHURET  OF  SILVER.              4QJ
 if it be in contact with organic matter.  It neutralizes the strongest
 acids, as the sulphuric and nitric, and forms well-characterized salts.
 It is not acted on by the fixed  alkalies, but with ammonia it gives
 fulminating silver, one of a series of bodies to be hereafter examined.
 When citrate of silver is heated to  212   in a current of hydroo-en
 gas, the metal is not reduced, as should have occurred with the pure
 oxide, but one half of the oxygen is removed,  and the citric ,.cid
 remains combined with  the suboxide  of silver, Ag^O.  This  salt dis-
 solves in water, the solution  being brown, and giving a brown pre-
 cipitate of suboxide with potash.  When a solution of this salt is
 heated, it becomes colourless, contains a salt of the  peroxide,  and
 metallic silver separates.  Some other silver salts of organic acids
 give the same result with hydrogen gas.  When a solution  of ni-
 trate of silver is decomposed by the battery, a substance is deposited
 upon the positive electrode in needles, sometimes half an inch long.
 These are resolved by  sulphuric acid into  protoxide of silver and
 oxygen, and give, with  muriatic acid, chloride of silver and free
 chlorine.   They  are, therefore, crystals of peroxide of silver, proba-
 bly Ag.O,.
   Although silver does not combine with oxygen directly, yet when
 it is heated in contact with glass, it  stains this of a deep yellow or
 orange colour, being converted into  oxide.
   Sulphuret of  Silver, equivalent 1552*8 or 121*4, exists native
 pure, and also  in  combination with  other metallic  sulphurets, par-
 ticularly those of lead, antimony, copper, and arsenic, formino- a va-
 riety of minerals.  It is the  most common ore of silver.  It may
 be formed artificially by fusing  together sulphur and silver, the ex-
 cess of sulphur being expelled  by the  heat.   Silver has, indeed, a
 remarkable affinity for sulphur,  so that it even decomposes sulphu-
 retted hydrogen, and hence arises the tarnishing of silver when ex-
 posed to the atmosphere.  An exceedingly delicate test for sulphur
 in a solid body consists in igniting a  minute  fragment of it on char-
 coal, in the reducing flame of the blowpipe ;  the fused globule is to
 be then laid on a bright  surface of silver, as  on a clean shilling, and
 moistened; if there  be a trace of sulphur in the substance,  a  black
 or olive spot will form on the silver where it is moistened.
  The  sulphuret  of silver may be formed also in the wet way, by
 adding sulphuretted hydrogen or hydrosulphuret of ammonia to a
 solution of a salt of silver.  It  forms as  a black powder, which is
 not soluble  in  an excess of the precipitant.  This sulphuret is a
 powerful sulphur base, and in its native forms  is generally associa-
 ted with negative metallic sulphurets.
  The  detection of silver is very easy ;  from the facility with which
 its oxide is reduced  to the metallic state,  its solutions are precipi-
 tated by the sulphites, by protosulphate of iron, and by  protochlo-
 ride of tin, the silver being reduced. A solution of  common salt
 or muriatic acid gives a  white curdy precipitate of chloride of sil-
 ver, which is insoluble in water  and in acids, but dissolves in water
of ammonia ; when exposed to light in contact with organic matter,
the chloride of silver becomes tinged violet or black, owing to the
formation  of a subchloride;  on  this  is founded its application in
photography, described p. 173.   The solutions of silver  give,  with
                             E E E 
402 MERCURY,  ITS  EXTRACTION  FROM  ITS ORE.

iodide of potassium, a canary-yellow precipitate, insoluble in ammo-
nia,  and with sulphuretted  hydrogen  a  deep brown  sulphuret of
silver.
  The uses of silver are well known ;  its advantages as a  medium
of exchange depend on the steadiness of the quantity of it  brought
into commerce,  which prevents great changes in its value, and on
its not being corroded  or worn down by ordinary agents.  In a pure
state it would, however, be too soft to be used as coin, and  is hence
hardened by being alloyed, in the proportions of 222 parts  to IS of
copper; this is the standard silver of the mint; the silver  used for
the purposes of luxury contain a greater, but a variable quantity nf
copper.             •
                  Of Mercury, or Quicksilver.
  From the remarkable properties of this metal, and its occurring in
the metallic state in nature, it has attracted  much attention  from
the earliest ages, and  formed  the object of the most  elaborate in-
quiries of the older chemists   Its volatility and the variety of its
compounds made it enter into the theories of that period as an im-
portant  element, and hence  there is, perhaps, no metal concerning
which so much valuable knowledge was obtained in the infancy of
chemistry.
  Mercury is found native, and also combined with gold and silver,
but its most abundant ore is the native  sulphuret, cinnabar;  from
this it is extracted by one or other of two processes.  The first con-
sists in distilling the ore with lime, or with iron in small pieces;  in
the first case, Hg.S. and Ca.O. produce Ca.S., while Hg. and 0. pass
off, the temperature being too high to allow of the formation of ox-
ide of mercury; in the second case, Hg.S. and Fe. produce Fe.S.
and Ho-.;  this process is carried on in long furnaces,  in which are
arranged numbers of earthen or iron.retorts, to which are  adapted
receivers,  in which  the mercurial vapours condense.   The other
plan, which is that now adopted in the  best  arranged works, con-
sists of a kiln, like that in which the pyrites is roasted for the  man-
ufacture' of oil of vitriol': below, there  is a grate on which is lighted
a fire of brushwood ; over this is a light arch  of fire-brick,  with nu
merous perforations, and on this is arranged the cinnabar, the poor-
est kinds being  placed  below, until the  kiln is filled  nearly to the
orifice of the chimney, which passes off at the side ; the fire  com-
municating to the ore, the sulphur contained  in it burns, and the
mercury is set free, Hg.S. and  20. producing S.02 and Hg.  The
kiln is so hot that the metal is completely volatilized, and the mixed
vapour of mercury  and  sulphurous acid  gas are carried by the
draught into the chimney, which leads into a wide chamber  of brick-
work, the  sides  of which are hung with leather ; on these  the mer-
cury condenses in drops, which gradually flow down and collect on
the floor,  while the sulphurous acid  gas passes away by a  small
chimney at the farther end, by means of which the continuous com-
bustion of the ore is sustained; at certain periods, an aperture in
the side of this chamber is opened, and the mercury which  had col-
lected is withdrawn.
   The mercury is sent into commerce in iron bottles, but generally 
OXIDES  OF  MERCURY.               403
in a very impure state, it being intentionally adulterated with  the
alloy  of tin, lead, and bismuth, already noticed p. 398, of which it
can dissolve large quantities.  It may be purified by distillation, or
by being left for some time in contact with dilute nitric acid.  The
mercury, having less affinity for oxygen than any of the other metals
present, is the last to dissolve, and as soon as the liquor is found to
contain mercury, the metal remaining may be looked upon as pure.
  Mercury is distinguished by  being liquid  at ordinary tempera-
tures  ; this, together with its resemblance to  silver in brilliancy, is
the origin of its various names, hydrargyrum (vdoip apyvpeog), quick-
silver, argentum vivum.  If pure, it is not tarnished by  exposure to
the air, but in damp  air its impurities become oxidized very rapidly,
in consequence  of a complete  galvanic  circuit being formed with
the mercury and the other metals present.  At 39" it becomes solid,
and crystallizes in octohedrons; it then contracts very much; its
sp. gr. being 135 when  liquid, and  14*0  when solid.   At 662° it
boils, and forms a colourless vapour, the sp.  gr. of which  is 6978.
At and just  below its boiling point it absorbs oxygen from the air,
forming oxide, which at a red heat is again decomposed.
  Mercury is not acted on at common temperatures by sulphuric or
muriatic acid;  nitric acid oxidizes it  rapidly, the nature of the pro-
duct varying with the circumstances.  Boiling oil of vitriol is de-
composed by mercury, sulphurous acid being evolved, and oxide of
mercury produced.   There are two oxides of mercury, a suboxide
and a protoxide. The  symbol of mercury is Hg., from its Latin
name, and its equivalent is 1265*8 or 10T4.
  Suboxide of Mercury.—Hg20.   Equivalent 2631*6 or 210*8.  This
oxide is the basis of many important  preparations, and is best pre-
pared by decomposing calomel (subchloride of mercury) by a solu-
tion of potash.  The calomel being insoluble, the  action  must be
favoured by mixing  the two together  well by agitation in a mortar ;
a black powder  is produced, which must  be  dried in the dark, and
by a very gentle heat.  In this process, Hg2Cl. and  K.O. produce
K.Cl.  and Hg20.  Lime water may  be  used in place  of  potash.
When this suboxide, or, as it is often called, black oxide  of mercury,
is heated,  it is  resolved into metallic  mercury  and the protoxide,
and this change occurs slowly at ordinary temperatures if it be ex-
posed to the light.  This oxide combines with acids and forms well-
characterized salts.
  Protoxide of Mercury—Hg.O.; equivalent 1365*8 or  109*4—may
be prepared  in a variety of ways: 1st. By exposing mercury for a
long time to  the action of the air, at a temperature just below its
boiling point, it is gradually converted into small deep red crystals
of this oxide;  in this  state it was the red precipitate per se of the
older chemists.  2d.  By heating crystals of nitrate of mercury until
all the water and nitric  acid have been expelled, the oxide remain-
ing is  a crystalline powder of an orange-red colour, the red precipi-
tate by nitric acid.  3d. When a solution of chloride of mercury (cor-
rosive sublimate) is  decomposed by caustic  potash or  lime water,
Hg.Cl. and K.O. produce K.Cl. and Hg.O.  It is thus  obtained as a
canary-yellow hydrate, which, however, when dried, becomes deeper
coloured.  The red precipitate also, when finely divided, assumes the
same yellow tint. 
404           SULPHURETS  OF MERCURY.

  This oxide of mercury is slightly soluble in water.  The solution
browns turmeric paper slightly, and restores the blue colour of red-
dened litmus.   It combines with acids, forming a numerous and im-
portant class of salts.  At a full red heat it is totally resolved into
mercury  and oxygen, as described fully in page 242.  It changes
its colour remarkably with the temperature, becoming nearly black
when very hot.
  Subsulphuret of Mercury, Hg^S., may be prepared by decomposing
any salt  of the suboxide  by hydrosulphuret of ammonia.  It is a
black powder,  which,  on the application  of heat, is decomposed
into the protosulphuret and metallic mercury.
  Protosulphuret of Mercury—Hg.S.; equivalent 1467 or 117*5—con
stitutes the native cinnabar, the usual ore of quicksilver.  It may
be prepared artificially by fusing sulphur in a crucible, and adding
thereto six times  its weight of mercury; they combine with the
evolution of considerable heat.   The mass  must be stirred frequent-
ly to favour their  union, and covered in order to prevent the sul-
phur from burning away.   In this state it is black, but  when sub-
limed at  a red heat in glass vessels, it becomes deep red, constitu-
ting factitious cinnabar, and this, when levigated, and  exposed  to
strong light, in flat dishes covered with a thin layer of water, grad-
ually assumes a very brilliant colour, and forms the pigment vermil-
ion.  This sulphuret may also be prepared by adding to a solution
of corrosive sublimate an excess of hydrosulphuret of ammonia or
sulphuret of hydrogen • it is then a dense black powder.  It may,
however, be obtained red, but not so bright as vermilion, in the wet
way, by  digesting white precipitate (chloramide of mercury) with
hydrosulphuret of ammonia, to which an excess of sulphur has been
added.   The  sulphuret of mercury forms at first black, but after
some time becomes red, which colour may be brightened by the
action of a warm solution of caustic potash.
  The phosphurets and seleniurets of mercury are of no importance.
  The presence of mercury in solution is very easily ascertained.
By the immersion of a clean slip of copper, the mercury is precipi-
tated in the metallic state, as a  gray powder on the surface  of the
copper.  With a magnifying-glass, this  is found to consist  of mi-
nute but  brilliant globules, and the surface becomes brilliant when
rubbed.  Protochloride of tin and phosphorous acid also precipitate
the mercury in the metallic state, which, by boiling, aggregates into
larger globules, easily collected and recognised.   Any  solid body
containing mercury gives, when ignited in  a tube of hard glass, par-
ticularly on the addition of a little carbonate of potash, a sublimate
of metallic mercury, which, if in very small quantity, appears only
as a ring of gray powder, but is found to consist of brilliant glob-
ules when inspected with a lens.
   The two  classes of salts which quicksilver forms are very dis-
tinctly characterized by their behaviour to reagents.  The salts of
the suboxide  give with the caustic alkalies black or gray precipi-
tates.  Sulphuretted hydrogen  produces  the  black subsulphuret.
Solution of chloride of sodium  gives a white precipitate, which is
calomel, and the bichromate of potash produces an orange chromate
of the suboxide. 
     EXTRACTION  AND PROPERTIES  OF GOLD.  405

  The salts of the red oxide are precipitated, yellowish by an excess
of caustic potash, and white by ammonia; with sulphuretted hydro-
gen in excess, a black precipitate of protosulphuret; and with iodide
of no/assium, a red precipitate, which is redissolved in an excess.
  In many cases, the appearance of these precipitates varies with
the  nature of the acid with which the oxide of mercury had been
combined ; but in all cases ammonia gives a black precipitate with
the  salts of the suboxide, and a white precipitate with those of the
red  oxide, in the cold.
  There is a class of pharmaceutical preparations obtained by trit-
urating mercury with other inactive substances.  In these the mer-
cury is only reduced to a  state of very minute division;  it  is not
oxidized.  By triturating mercury with sulphur, however, a certain
quantity of sulphuret is formed, although the great mass of the met-
al and of the sulphur remains uncombined.

                           Of Gold.
  This valuable metal is found only  in the metallic  state,  either
pure or alloyed with other metals, particularly  silver, tellurium, and
mercury ;  the rocks in which it is found distributed are generally
those of igneous origin, but the greater part of the gold  of com-
merce is obtained by washing the sands of the  rivers which have
their source in such mountains, the particles of metal being carried
down with the detritus of the rock, and, from their  greater density,
being deposited first when  the sand is washed ; any fragments large
enough to be visible are separated by the hand, but the remainder
is dissolved  out by  a process of amalgamation, similar to that de-
scribed, p. 399, for the extraction  of native  silver.   When  the gold
is alloyed with silver,  they are  separated by means of nitric acid,
which dissolves the latter metal; but if the quantity present be small,
the  gold protects it from the action of the acid, and a process term-
ed quartation is employed;  this  consists in alloying the gold with
three times its weight  of silver, and then acting on the mass with
nitric acid; when the solution of the silver has once commenced, it
does not cease until  the entire quantity present has been removed.
  Pure gold  is yellow, very malleable and ductile, and nearly as
soft as lead ;  hence,  for the purposes  of commerce  and of the coin-
age, it is alloyed with a quantity of copper, amounting to 83 in 1000.
Instances of the exceeding degree of division to which this metal
may be reduced, have been given, p. 15.  Gold has  no tendency to
combine with  oxygen or sulphur, and hence retains its brilliancy  in
the open air for any  length  of time.   It melts at 2016°;  its density
is 19*5 ; it is not acted on by any single acid, but is dissolved by ni-
tromuriatic  acid, and by a mixture of nitric and hydrofluoric acids.
  The  symbol  of gold is An., from its Latin name, and its equiva-
lent numbers are 2486 or 199*2.
  There are two oxides of gold, obtained by the decomposition of
the corresponding  chlorides, which will be  hereafter described.
The deutoxide of gold, Au.O,, is  a green powder, which does not
combine with  acids, but dissolves in solution of caustic potash, and
soon separates into the higher oxide and metallic gold.   The perox-
ide  of gold, auric acid,  Au.03, is  best prepared by decomposing per 
406     PROPERTIES  OF  G O L D.--P A L L A D I U M.

chloride of gold by an excess of magnesia ; chloride of magnesium
dissolves, and an insoluble aurate of magnesia remains; this is to
be then digested in cold dilute  nitric acid,  which  dissolves out the
magnesia with a little auric  acid, but  leaves  the greater p^-£ of
this last behind as a reddish hydrate, which, when dried in the air,
becomes brown,  and at 212J gives off water, and remains black.
This substance does not combine with  any acid ;  by muriatic acid
it is decomposed, perchloride of gold being formed ; it  combines
with alkalies strongly, so that the precipitate given by a solution of
gold with a caustic alkali is always a compound of auric acid with
the base ; there are  soluble and insoluble aurates, but their atomic
constitution has not been studied.   Solutions of auric acid, and even
that body in powder, are decomposed rapidly  on  exposure  to the
light, metallic gold being separated.
  Gold is deposited from its  solutions by means of any of the de-
oxidizing agents noticed under  silver and mercury.   Protosulphate
of iron gives a brown powder, which, under the burnisher, assumes
the colour and brilliancy of the metal;  protochloride of tin produ-
ces a fine purple  precipitate, the purple of Cassius, which is not me-
tallic gold, but it appears to be a compound of oxide of tin and a
suboxide of  gold, for  it is  perfectly soluble in water of ammonia,
and mercury digested  on it does not dissolve out any metallic gold.
Various  processes are  given for this preparation, which it  is not
easy to obtain of the proper depth and  purity of colour;  when ex-
posed to a red heat, it is changed into a mixture of peroxide of tin
and metallic gold, but its purple  colour remains ; it is hence employ-
ed for painting on glass and porcelain.  When metallic gold is heat-
ed  on the surface of glass, it appears to become  oxidized, and in
that state to combine with the glass, staining it a rich purple col-
our.
  Sulphur and gold combine to  form sulphurets similar in constitu-
tion to the oxides; they are produced  by decomposing the corre-
sponding chlorides by sulphuretted hydrogen ; they are brown pow-
ders, which are strong  sulphur acids, and dissolve in hydrosulphu-
ret  of ammonia.
  The uses of gold are well known.  The commercial value of  its
alloys is ascertained, either by cupellation,  p. 399, by quartation, p.
405, or by the touchstone, which is a variety of flinty slate (Lydian
stone) or basalt, of a uniform black colour.  A streak is drawn  on
the surface of the stone with the piece of gold  to  be tried, and this
is compared with those given  by a series of alloys, the composition
of which is known, until one is found  identical  in aspect with it,
which must result from the two being of the same  degree of purity.
In these trials it is necessary, however, to know beforehand wheth-
er the alloy  is silver or copper, or whether, as frequently occurs,
both be present.

                         Of Palladium.
  This metal is found  associated with platinum, but seldom consti-
tutes more than one per cent, of the ore.  After  the platinum has
been precipitated from  the solution in aqua regia, by means of sal
ammoniac, cyanide of mercury is added, by which all the palladium 
       COMPOUNDS  OF  PALLADIUM.--PLATINUM.  407

is thrown down as  cyanide;  this, when ignited, is totally decom-
posed, and metallic palladium  remains.
  The general characters of palladium are very similar to those of
platinum ; it is white, almost infusible, but admits of being welded;
it is malleable  and  ductile ;  specific gravity  1T5.   When  heated
below  ignition,  its surface  becomes blue and green, from the forma-
tion of a  thin layer of suboxide ; but by a stronger  heat this is  re-
duced, and  the  metal  becomes bright.  Palladium  is not sensibly
acted on  by muriatic  or sulphuric acid, but it dissolves  in nitric
acid with facility.   The symbol of palladium is Pd., and its  atomic
weight 665*9 or 53*4.
  There are three  oxides of palladium, of which only one, the protoxide—Pd.O.;
equivalent 7659 or 61 4—has been as yet studied with much care; this oxide is form-
ed when palladium dissolves in nitric acid, and is obtained as a black powder when
the nitrate is decomposed at a temperature below redness;  by the addition of potash
to a salt of palladium, this oxide is  thrown down, hydrated, as a brown powder.
If the protoxide of palladium be exposed to a dull red heat, it parts with half its
oxygen, and a suboxide, Pd20.,is produced, which gives a series of salts,  resembling
in general characters those of the suboxide of copper.
  By decomposing the bichloride of palladium with carbonate of potash, the deutox-
ide, 1M.02) is obtained as a yellowish brown powder; it appears to combine both with
acids and alkalies,  but of its properties very little is known.
  There are sulphurets of Palladium, which correspond to the oxides, but farther than
that they are brown powders, generated by the action of sulphuret of hydrogen on
the respective chlorides, they have not been much examined.
  Palladium in solution  is at once recognised by giving with ammonia a flesh-red
precipitate, which redissolves in an excess, giving a colourless solution; with cya-
nide of  mercury it produces a whitish precipitate, and with iodide of potassium, a
black powder.
                            Of Platinum.
  Platinum was originally  discovered in the sands  of  some South
American rivers, and from its similarity to silver (plata),  obtained
the name of platina (little silver).  It has since been found more
abundantly  in the mountains of the Oural, which separate European
from Asiatic Russia.   The supply of  platinum has increased  so
much  lately, that  a  coinage of it, issued some years ago  by the
Russian government, was  obliged to be recalled,  from  the rapid
diminution in value which it underwent.
  The platinum exists native, but is associated  with  a great number
of metals, particularly  four, remarkable for not being found  except
along with it.   The  grains of metal  are disseminated in  rocks  of
igneous origin (granite, syenite),  and in the  sands of rivers which
flow over them.  The processes for the extraction of platinum from
the crude ore are very complex,  and as the working of it has be-
come a branch of manufacture, the chemist always obtains the pure
metal in commerce, and its details need  not be  inserted.
  Pure platinum is white like silver, but not so brilliant.   It is the
densest of all  bodies,  its  sp.  gr. being  21*5.   It is very malleable
and ductile.  It is infusible except by the hydro-oxygen blowpipe, but
at a high temperature  may be welded like iron, and thus worked
into the" various forms in which it  is employed in the chemical arts.
Platinum  may also exist in a state of minute division,  and thereby
becomes useful  in  many operations, particularly those of slow com-
bustion, as noticed in p. 180, 250, 2S7.  The finely-divided  platinum
is of two kinds, spongy platinum and platinum-black.   The former is 
408
COMPOUNDS OF  PLATINUM.
prepared by dissolving chloride  of platinum and sal ammoniac sep-
arately in alcohol, and mixing the solutions; the double chloride of
platinum and ammonium is thus produced as a fine yellow powder,
which, while yet moist, is to be made into balls like peas, and heat-
ed to full redness.   The chlorine is  all carried off by the  hydrogen
of the ammonia, and the platinum remains as a light gray sponge,
in the  form  of the little  balls;  it is this kind  of platinum that is
used in the aphlogistic  lamp, in the  eudiometer, and for other pur-
poses already noticed.   The platinum-black may be obtained either
by precipitating a solution of bichloride of platinum with zinc, and
boiling the precipitate in muriatic acid for a few  minutes; or, bet-
ter,  by dissolving protochloride of platinum in a boiling solution of
potash, and adding thereto alcohol, in small  quantities at a time,
until all effervescence  ceases ;  a jet-black  precipitate  is produced,
whieh is to be boiled successively with alcohol, muriatic acid, and
potash,  and,  finally,  four or  five times in water.  The substance
thus obtained is pure metallic platinum, but it is a dull black pow-
der.  It absorbs oxygen in considerable quantity, and hence,  when
brought into an atmosphere of any inflammable vapour, it facilitates
the  combination of the  two with remarkable energy.   Dmbereiner
terms it an oxyphorus from this  property.  Many interesting reac-
tions in organic chemistry succeed only by the aid of this  platinum-
black.
  Platinum  has no tendency to combine with  the oxygen  of the
air,  but it is oxidized slightly when nitre  or even potash is fused in
contact with it.  It resists the action of  all acids except the nitro-
muriatic  acid and the nitro-hydrofluoric  acids, and  in  these  it dis-
solves more slowly than gold.
  The  symbol of platinum is PI.  Its equivalent  is 1233*5 or 98*8.
By the  decomposition of the chlorides of platinum, two oxides of it
are obtained.
  Protoxide of Platinum—Pt.O.; equivalent 13335 or 1068—is produced by digest-
ing the protochloride with as much potash as exactly suffices  for its decomposition.
An excess of potash dissolves it, forming a dark olive liquor.  When pure it is a
black powder, easily decomposed by heat into platinum and oxygen.  It combines
with acids, forming salts, which have been as yet but little studied.
  Deutoxide of Platinum.—Pt.02.  Equivalent 14335 or 1148.  This substance has
a remarkable tendency to combine with bases, and hence cannot be obtained pure
by the direct decomposition of the chloride, as it  carries down with it, always, a
quantity of the alkali employed, if this  be in excess; and if it be not, then  only a
basic chloride is obtained.  The  nitrate of platinum, however, when decomposed
by soda, yields one half of the oxide of platinum, pure, but hydrated, forming a
brown powder like the peroxide of iron; when anhydrous, it is black; by heat it is
resolved into oxygen and platinum.  This oxide appears to form two kinds of salts,
one with acids, in which it is the base, and the  other with alkalies and earths, in
which it is the acid.  In another place I shall notice them farther.
  There are two sulphurets of Platinum corresponding to the two oxides. The first,
Pt.S., is produced by digesting the protochloride with sulphuret of hydrogen. It is
a deep brown powder, decomposed by a red heat, but not otherwise interesting. The
bisulphuret, Pt.S2, is produced in a similar way by adding sulphuret of hydrogen to
a solution of bichloride of platinum.  It is a brown powder, which absorbs oxygen
rapidly even in drying, and becomes acid.  By nitric acid it is converted with in-
tense action into sulphate of platinum.
  Phosphurets and seleniurets of platinum have been formed, but they are not im-
portant.
  The  detection of platinum  is effected easily by precipitating its
solution by a  slip of zinc,  when a black  powder separates, soluble 
IRIDIUM  AND  RHODIUM.
409
 only in aqua regia, and then giving with reagents the folio win 0* re-
 sults.  A solution  of sal  ammoniac in  alcohol gives  a fine yellow
 crystalline precipitate;  a solution of iodide  of potassium a black
 precipitate, which dissolves in an  excess, producing a  rich crimson
 solution ; with sulphuret of hydrogen, the brown bisulphuret of pla-
 tinum ; and with protochloride of tin, a chocolate precipitate or a
 deep reddish solution, according to the quantity  present.
   The action of this last reagent is founded on the reduction of the
 bichloride of platinum to  the state of protochloride by the  first por-
 tion  of protochloride of tin employed.   This  test acts, therefore,
 also with solutions of the protoxide of platinum, and the metal may
 be also known to  be in  the state  of protoxide, when,  on the appli-
 cation of iodide of potassium  in excess, the liquor is  not  coloured
 red, but becomes so on the  addition of a drop of nitric acid or chlo-
 rine water.
   The great use of  platinum  is for  the  manufacture  of the large
 boilers used in the concentration of oil of vitriol; it  is also univer-
 sally employed as the material for the crucibles used in  the more
 delicate operations of mineral  analysis.  Indeed, the accuracy now
 attained  in that department of research is in a  great part due to the
 introduction of platinum vessels into  the laboratory;  it is  also ac-
 casionally used in enamelling on glass and porcelain.


                       Of Iridium and Rhodium.

  These metals are, like palladium and iridium, found only associated with plati-
 num, and are extracted from the crude ore already noticed; the iridium and osmium
 are, however, united, forming an alloy, the crystalline grains of which  are merely
 mixed with the particles of the platinum  ore in which the rhodium and palladium
 are contained; when the platina ore is dissolved in aqua regia, the  iridium  and os-
 mium ore  remains undissolved, and requires to be treated  by fusion with  caustic
 potash; the iridium then becomes oxidized, and combines with the alkali.  The pro-
 cesses of purification need not be inserted.
  Metallic iridium resembles platinum, but is still more infusible; when fused  by
 the voltaic  battery, it is white and very brilliant;  specific gravity 1868; after being
 strongly heated, il is insoluble in acids, but when obtained in the spongy form  by
 the reduction of its oxides by hydrogen at a red heat, it becomess lightly oxidized,
 and is soluble in aqua regia.
  Iridium combines with oxygen in four proportions; its symbol is Ir.; and its equiv-
 alent 1*233-5 or 1)8-8, the same as that of platinum.
  Protoxide of Iridium, Ir.O., is obtained by decomposing the protochloride  by car-
 bonate of potash;  it appears as  a greenish-gray hydrate; this oxide combines with
 acids.  The szsquioxide, Ir.-03, is that formed when the metal is ignited with potash;
 it is a bluish-black powder, and is the most permanent of the oxides; it is not decom-
 posed except at a heat above the  melting point of silver, whereas  the higher and
 lower degrees pass into it on the application of heat.  This oxide unites with acids,
 giving dark blood-red coloured salts.   The deutoxide of Iridium, lr.02, exists com-
 bined with  acids, but has not been isolated. The peroxide, lr.03, is formed in small
 quantity when iridium is ignited with nitre, but is best prepared by the decomposi-
 tion of the perchloride.  Solutions containing salts of the protoxide and of the per-
 oxide together, present a great variety of shades of purple and blue,  and hence gave
 origin to the name of the metal (Iris).
  Rhodium.—This metal remains dissolved in the nitromuriatic solution of the pla-
 tinum ore after the platinum and palladium have been separated from it; for the
 mode of eliminating it from the many metals which still remain, I refer  to the sys-
 tematic works.
  Metallic  rhodium is obtained by the decomposition of its chloride at a red  heathy
 hydrogen gas; when rendered coherent by pressure,it is white, but very brittle and
hard; sp. gr. about 11-0.  If completely pure, it is not acted on even by aqua regia,
but it illustrates remarkably the principle of communicated affinity, described p.
                                  Fff 
410      GENERAL  CHARACTERS  OF  SALTS.

237; for, when alloyed with copper, lead, or platina, it dissolves along with the other
metal in aqua re<na.  Rhodium derives its name from the beautiful rose (podog) col-
our of its solutions; it combines with oxygen in two proportions; its symbol is It.,
and its equivalent 6614 or 5*2.2.
  Of the protoxide of Rhodium, it is only known that it exists in certain salts that
have been but little examined; the sesquioxide, R^Os, is the basis of the most impor-
tant compounds of this metal.  It is prepared by igniting metallic rhodium with a
mixture of caustic potash and nitre; a brown mass is formed, which, when decom-
posed by muriatic acid, yields the oxide as a gray hydrate, insoluble in acids. Ber-
zelius is of opinion that there are two isomeric forms of this oxide, the salts of one
being yellow in solution, and those of the other being rose-coloured.  There are sup-
posed to exist, also, complex oxides of rhodium, resembling, probably,  the complex
oxides of iron and manganese.  The equivalent of rhodium is so nearly equal to
that of palladium, that some relations might be expected in the constitution of their
combinations, which, as yet, does not appear to have been experimentally investi-
gated.
                         CHAPTER XIV.

      ON THE  GENERAL PROPERTIES AND CONSTITUTION OF SALTb.

  The bodies included under the name of salts may be arranged in
two classes, characterized by a remarkable  difference of chemical
constitution ;  the first comprehends such as are formed by the union
of a simple body of the chlorine family with  a metal;  thus chloride
of sodium, iodide of potassium, bromide of iron, fluoride of calcium,
are of this kind.  The  salts of the second  class, on  the contrary,
are formed by the union of substances already compound,  and pos-
sessed of those opposite properties by which one is determined to
be an acid  and the other a base.  The general characters of acids
and  bases, and  of the salts formed  by their  union,  have been suffi-
ciently  described  in  many places already  (p.  151, 154,  157), and
need not be here repeated.   In general, the acids and bases so en-
gaged contain oxygen as their electro-negative ingredient; but there
are classes of salts formed by the  union of sulphur acids and sul-
phur bases, and, as noticed in p. 238 and 294, selenium and tellurium
resemble oxygen and sulphur in this respect.   The history of the   *
metallic compounds in the  last chapter affords many cases of the
existence of such  salts, and  in the detailed history of the more im-
portant salts which will follow, others will be described ; but there
are some points of more  genera]  interest, touching the salts as  a
class, the laws of formation to which they are subjected, and the
relations between their several subdivisions, which I shall now pro-
ceed to notice as briefly as the subject will admit.
  I have frequently adverted to the  circumstance  that  the bodies
termed hydracids were in  reality not  acids,  but compounds of hy-
drogen, in which that element acted as a positive metallic constitu-
ent ; and that, when they act  on a metallic oxide, double decomposi-
tion generally  occurs, precisely as  when a chloride or  iodide  of
zinc or  copper is decomposed'by potash or by soda.  Thus Cl.H.
and K.O. produce Cl.K. and H.O., precisely as when Cl.Cu. and K.O. 
           GENERAL  CHARACTERS  OF  SALTS.       4H

 produce Cl.K. and Cu.O.   The chlorides and iodides of hydrogen
 although popularly called acids (muriatic and hydriodic acids), are
 thus really salts, and in all  their reactions display that constitu-
 tion.  Also, when a hydracid is put in contact  with  a metal, the
 solution of it is determined altogether by its power.of expelling the
 hydrogen  and of taking its  place.  From Cl.H.  and Zn. there are
 produced Cl.Zn., and H. becomes free, precisely as chloride of cop-
 per, Cu.Cl., is decomposed by zinc, copper being precipitated.   The
 hydracids, therefore, do not unite with metallic oxides to form  salts,
 but they decompose them, water being  evolved.
   The hydracids are capable  of forming what are termed acid-salts ;
 thus the fluoride of potassium combines with hydrofluoric  acid to
 form an acid compound;  the chloride of hydrogen combines with
 chloride of gold :  but these  bodies  are really double  salts.   The
 compounds of hydrogen, in such combinations, resembling the cor-
 responding compounds of zinc,  copper, &c, which, under the  same
 circumstances, all form corresponding double salts.
   I have already described the  functions of water in the hydrates
 of the ordinary oxygen  acids:  these are salts  of water, subject to
 the same rules of composition  as the  ordinary salts of the  same
 acid.  When such an acid, as, for example, oil of vitriol, S.03-f-H.O.,
 acts upon a metallic oxide, the water is displaced, and a salt of the
 metallic oxide formed.   When such  a hydrated acid acts on a  met-
 al, this may be dissolved either by substitution for, and displacement
 of the hydrogen, as in the ordinary  cases of obtaining that gas, or
 by the direct decomposition of a part of the  acid, as in the process-
 es for obtaining sulphurous acid  and  nitric oxide (p. 285, 274).
   Salts may be either neutral, acid, or basic.   A salt is neutral which
 does  not manifest, in its action  on vegetable colours, acid  or  alka-
 line properties, and consists generally of one equivalent of  acid
 united to one equivalent of base, this last containing one equivalent
 of oxygen.  The true neutral  salts have, therefore, for bases, either
 suboxides or protoxides.   The salts of sesquioxides and  deutoxides
 generally react like acids,  except where there is an excess  of base.
 The quantity of acid with which metallic oxides  are disposed to
 unite in their most neutral salts,  is subject to a remarkable propor-
 tion, being one equivalent for each atom of oxygen which the  base
 contains.   Thus a protoxide or suboxide combines with one equiv-
 alent of acid.  The sulphate of zinc is Zn.O.. S 03;  sulphate o;  cop
 per Cu.O.. S.03; the subnitrate of mercury, Hg,0. . N.03.   A sesqui-
 oxide unites with three equivalents of acid, as sulphate of alumina,
 Al,03+3S.Oa.   Salts in which this law is observed to hold are  gen-
 erally described as neutral, even though their action on vegetable
 colours may indicate a preponderance of acid ; and understanding
 by the word, not the absence  or  presence of the property of chan-
 ging turmeric or litmus, but the  state in which the characteristic
 properties of acid and base are  most neutralized,  the definition of
 a neutral salt may best be  that  in which the number of atoms of
 acid is equal to the number of atoms  of oxygen  in the base
   There are two kinds of acid salts:  1st, those in which  the excess
 of acid is present in its hydrated form; and,  2d, those in which
the dry acid is in excess.   These differ remarkably in nature, those 
 412       GENERAL  CHARACTERS  OF  SALTS.

 of the first class being not really acid salts, but double salts, of which
 one base is water.  Thus the common bisulphate of potash, of which
 the formula is K.O.. S.03 + H.O. . S.03, is one of a family of double
 salts, in which sulphate  of potash is united to a sulphate of a pro-
 toxide, as sulphate of copper, of zinc, of iron, or of magnesia.  There
 is thus really no excess of acid.  In  like manner, the bicarbonate
 of potash is a double  carbonate  of potash and water, K.O.. C.02+
 H.O. . C02, to which similar analogies exist.  These  salts resemble
 completely the acid salts of the hydracids, described in the begin-
 nino- of this chapter; K.O. . S.03-(-H.O. . S.03 corresponding exact-
 ly to K.F.+H.F.
   It is only the salts which do not contain water that can be looked
 upon as having a true excess of acid.   Of these, the chromates of
 potash afford  the best examples, in which an atom of potash is com-
 bined  with one, two, or three equivalents of acid, forming K.O.-f-
 Cr.03, K.O.+2Cr.03, and K.O.+ 3Cr.03.    There exists a similar
 compound of sulphuric acid and potash, which is easily decomposed
 by water, being changed into the ordinary bisulphate.
   Basic salts  are those  in which there is  present more than one
 equivalent of base for each equivalent of acid ; thus, in turbeth min-
 eral there is 3Hg.O. + S.03;  in basic nitrate of copper, 3Cu.0. + N.
 05. H.O.; in basic sulphate of copper, 4Cu.O.-f-S.03+4H.O.  It has
 been thought  that the proportion of base in basic salts bore a sim-
 ple relation to the  quantity of oxygen  in the acid, being generally
 equal to it.   This idea was founded on the circumstance  that the
 early analyses of many basic  sulphates gave the proportion of three
 atoms of base to one  of  acid ;  but the  basic sulphate  of mercury is
 the only example I have found really to exist of that constitution,
 the other sulphates containing always a quantity of metallic oxide,
 amounting to  two, or four, or six equivalents.
   The first and most  remarkable insight into  the constitution of
 basic  salts which we obtained was the  principle laid  down by Gra-
 ham, that all salts are really neutral in constitution.  The analogies
 of hydrogen to the  magnesian family of metals, and hence  of water
 to the  oxides  of that  class, suggested  the idea that the excess of
 base should not be  considered as actually combined with the acid,
 but that it replaced the  water  of crystallization which the  neutral
 salt contains.   This view was remarkably supported by  the evi-
 dence  of the  basic  nitrates  adduced by Graham, and has been ex-
 tended to the chlorides and  sulphates by my own investigations.
 Thus  nitrate of copper, in its crystallized and neutral condition, is
Cu.O.. N.03 + 3H.O., and the basic nitrate is formed by H.O.. N.0S
 -f 3Cu.O.  Comparing these two with  the hydrated nitric acid, sp.
gr. T42, the formula3

          Nitrate of water,       =H.O.. N.O,+ 3H.O.
          Nitrate of copper,      =Cu.O..  N.05-|-3H.O.
          Basic nitrate of copper, =H.O.. N.06+3Cu.O.

 evidently correspond,  the only difference  being  that, in place  of
 oxide  of hydrogen, there is oxide of copper substituted, in  a pro-
portion continually  increasing.  From  these conditions it follows,
 that with the same acid and base there may be formed a great va- 
SALTS  OF  POLYBASIC ACIDS.          413
nety of basic salts; for the neutral salt may crystallize with many
different proportions of water, and from each there may  be one or
more basic salts derived, by substitution of metallic oxide.  Thus
the sulphate of zinc generally contains eight atoms of base to one
of acid ; and in its common crystallized form, these consist of one of
oxide of zinc and seven of water; but in becoming basic, the quan-
tity of oxide of zinc gradually increases, and a series of basic salts
is formed, as
         S.03+Zn.0.4-7H.O.,    S.03-r-6Zn.O. + 2H.O.,
         S.03 + 4Zn.O.-r-4H.O.,   S.03+8Zn.O.
  The  salts, consisting of a simple body of the chlorine family uni-
ted with a metal, as chloride of sodium, iodide of potassium, &c,
and which, from the analogy of common salt, are termed haloid salts
(ale and etdoc), combine frequently with the oxide  of  the metal
which they contain, and form basic haloid salts.  Thus we have  Cu.
Cl.-f-3Cu.O., basic chloride  of copper; Hg.01.-f-3Hg.O., basic chlo-
ride of mercury ;  Pb.I. + 2Pb.O., basic iodide of lead.  Such com-
pounds are, however, generally termed oxychlorides, oxyiodides, &c.;
they are subjected to precisely the same laws of derivation and con-
stitution as the basic salts of the same metals with ordinary acids.
  From what  has been said above, it  might be concluded that a
neutral salt consisted in all cases  of  one equivalent of base united
to one of acid, and that, wherever the base was  present in larger
quantity, the salt  should  necessarily be termed basic ; but an  im-
portant distinction requires to be here laid down.   There are  three
phosphates of silver, which  contain respectively one, two, and three
atoms of oxide of silver united to one atom of acid; but we do not
consider the first as being neutral, and the others  as containing  an
excess of base, for we find  them to arise from the state of the phos-
phoric  acid, which, according as  it  has been combined with  more
or less basic water, gives origin  to classes of salts containing  one,
two, or three equivalents of oxide.   The peculiar relations of  the
phosphoric  acid, and of arsenic  acid also, to water, and  the effect
of it on the composition of these salts, have  been noticed  already in
p. 297  and  377.  In  addition, therefore, to ordinary neutral  salts,
which are monobasic, or contain  an equivalent of base and  one  of
acid, there are bibasic and tribasic salts, containing respectively two
and three equivalents of base to  one of acid, and yet being neutral;
by which is meant, not that they are without  action on test paper,
since one tribasic salt may redden litmus, while another may brown
turmeric paper, but that they are  derived from a definite combination
of the acid  with basic water, and not by the replacement of the wa-
ter  of crystallization by metallic oxide, as in the case  of  real basic
salts.
  A simple distinction between bibasic and tribasic salts on  the one
hand, and  ordinary basic  salts on the other, is, that in the former
the different atoms of base  may be of different  kinds, while in the
latter the metallic  oxide replacing the water is all  of the  same sort.
Thus, there is basic sulphate of zinc and basic sulphate  of  copper,
but there could not be a basic sulphate partly of zinc and partly  of
copper, the sulphuric  acid being monobasic.   But there is a  tribasic 
414                  DOUBLE  SALTS.
phosphate of soda, ammonia, and water ; another of magnesia, am-
monia, and water; others of potash and water.  The presence of
two or more bases of diflerent kinds thus distinguishing completely
the salts of the bibasic and tribasic acids from  the  ordinary basic
salts.
  These principles,  which are now of the highest  importance  in
philosophical chemistry,  were first  applied by Graham to the  salts
of the phosphoric and arsenic acids, but they  have  been found  to
throw light upon some of the most difficult questions in the history
of the organic acids, of which a great number have been shown by
Liebig to be similarly circumstanced.
  Double salts are formed by the union of two simple salts.  In gen-
eral, both salts contain the  same acid, but different  bases, and the
two bases belong to  different natural groups;  as when sulphate of
potash combines with the sulphates of the protoxides of the metals
of the second isomorphous group, replacing therein the atom of
constitutional water which they all contain.   Thus ordinary sul-
phate of zinc, Zn.O.  . S.03. H.O.+6Aq., gives with K.O. . S.03 the
double salt (Zn.O.  . S.03+K.O. . S.03)-f6Aq.; and sulphate of cop-
per, Cu.O. .  S.03 . H.O. +4Aq., gives (Cu.O. . S.03---K.O. . S.03)-f-
4Aq.  The sulphate of potash  combines also with the sesquioxides
of the third  isomorphous group, such as alumina, and gives origin
to the various kinds  of alums.  Similar classes of salts are formed
by the union of the  other alkaline  sulphates with the sulphates of
the second and third isomorphous groups.  The salts of isomorphous
bases with the same  acid do not appear capable of combining so as
to produce double salts,  but in crystallizing are mechanically  mix-
ed (p. 31).  This  rule, however, is not without exception, as the
constant composition of the magnesian limestone, Ca.O. . C.02-r-Mg.
O. . C.02, indicates that its elements are chemically united.
  Salts of different acids with the same base may combine to form
double salts,  as the oxalate  and  nitrate of  lead ; and there are ex-
amples, though few,  of a double salt containing two  acids and two
bases.
   The relations of salts  to  water have  been fully discussed under
the heads of solution and crystallization (p. 22, et seq.), and of the
chemical properties  of water (p. 253), to which it is sufficient to
refer.
  The haloid salts combine together to form  double salts, as the
double chloride of gold and sodium, the double  chloride of copper
and potassium, and conform therein to the same general principles
that have been just described for the oxygen salts.
  It has been always mentioned, that when  muriatic acid acts on a
metallic oxide, water is formed,  and a chloride of the metal produ-
ced.  The question  of whether  this always occurs  is not without
interest, and  has been  often agitated.   There is no  doubt but that
it is the general rule, but I am inclined  to think it may not be with-
out exception.  The difference  of properties  of the chlorides of
magnesium and of aluminum in the  anhydrous state and when  crys-
tallized with  water, is  so great  as  to give reason to suppose that
these chlorides decompose water, and that the crystallized hydrated
salts are not Al2Cl3-r-3H.O. and Mg.Cl. + H.O., but Ala03+3H.C1. and 
        CONSTITUTION OF  ACIDS  AND  SALTS.     415

 Mg.O.-f-HCl.  Hence it  is probable  that  magnesia and alumina
 combine with hydracids without decomposition.
  The sulphur salts consist of a sulphur acid, which is generally a
 sulphuret of an electro-negative metal  or of carbon, combined with
 a sulphur base, which  is a sulphuret of an electro-positive metal.
 In their constitution  they resemble the analogous oxygen salts.
 Many of their characters have  been described already (p. 282, 386).
  The positive metallic sulphurets combine frequently with the ha-
 loid, or oxygen salts of the same metal,  to form basic salts; this is
 the case particularly with mercury.  Thus there is Hg.O. . S.03 +
 2Hg.S., similar to Hg.O. .  S.03-|-2Hg.O., ordinary  turbeth mineral.
  It had been long remarked as curious, that bodies so totally dif-
 ferent in composition as the compound of chlorine with a metal on
 the one hand, and of an oxygen acid with the oxide of the metal on
 the other,  should be so similar in properties, that both must be
 classed together as salts, and should give origin  to series of basic
 and  acid compounds  for the most  part  completely parallel.  This
 difficulty has been so much felt by  the most enlightened  chemists,
 that doubts have been raised as to whether the acid and base, which
 are placed in contact to form by their union an oxygen salt, really
 exist in it when  formed; and it has been suggested that at the  mo-
 ment of union a  new arrangement of elements takes place, by which
 the structure of the resulting salt is assimilated to that of a com-
 pound  of chlorine or  of iodine with a metal.   This view, at  first
 sight so  far fetched, which considers that in Glauber's salt there is
 neither sulphuric acid nor soda, but sulphur, oxygen,  and sodium,
 in some other and simpler  mode of combination, is now very exten-
 sively received by chemists; and I shall proceed, therefore, to de-
 scribe, with some detail, the form which  it has assumed, and the ev-
 idence by which it is supported.
  The greater number of  those bodies which  are  termed oxygen
 acids have  not been in reality insulated, and what are popularly so
 called are merely supposed to contain  the dry acid combined with
 water.   Thus  the  nearest  approach we  can make  to nitric acid is
 the  liquid N.O0H. ; to acetic acid, the crystalline body C4H404;  and
 to oxalic acid, the sublimed crystals C204H.; we  look upon these
 bodies  as being  combinations of the dry acid with water, and we
 write their formulae N.05+H.O., and C4H303-f-H.O., and C203+H.O.;
 but  that these  dry acids exist at all  is a mere assumption.   Hence,
 with regard to these instances, and they embrace the  majority of
 all known acids,  the idea that the acid and base really exist in the
 salt formed by the action of hydrated acids on a base is purely the-
 oretical.
  When we compare the constitution of a neutral salt with that of
 the  hydrated acid by which it is formed, we find the positive result
 to be the substitution of a metal for the hydrogen of the latter ; thus
 S.O.,4-H.O. gives with zinc  S.03-f-Zn.O. ;  and where  a metal is
 acted on by a hydrated acid, the hydrogen is thus evolved either
 directly as  gas, or it reacts on  the elements of the acid, and gives
 rise to secondary products which are  evolved, such as sulphurous
acid, nitric oxide, cVc.  In  all cases we may consider the action of
a metal on a  hydrated acid to be primarily the elimination of hy- 
416     THEORY  RESPECTING  THE INTIMATE

drogen and the formation of a neutral salt.  But in this respect the
action becomes completely analogous to that of the metal on a hy-
dracid, except that in the latter case  a haloid salt is formed ; and
hence we assimilate the two classes in constitution by a very sim-
ple arrangement of their formula?.
  There are, however, a number of acids which may be obtained
in a dry and isolated form, as the sulphuric, the silicic, the telluric,
the stannic, the arsenic, the phosphoric, &c.; and when they com-
bine with bases, it is most natural to consider the  union as beino-
direct, and that the salt contains acid and base really as such.  This
is, accordingly, the  strongest point of the ordinary theory.   But
other  and  important circumstances intervene.   These  acids, al-
though they may be obtained free from water, yet in that  state they
combine with bases but very feebly, and require a high temperature
in order to bring  their affinities into play.   On the other hand, in
all cases where these bodies manifest their acid  characters in the
highest degree, they are combined with water, as in oil of vitriol
and  phosphoric acid, and when expelled from combination with a
base, they immediately enter  into combination with water in an
equivalent proportion.  Thus, where phosphate  of lime  is decom-
posed by oil of vitriol, it is not  phosphoric  acid (P-05) which is
found  in the liquor, but its terhydrate (P.054-3H.O.), as is shown
by its forming with oxide of silver the yellow  phosphate, P.Oi-f-
3Ag.O.  In the case of telluric  acid, its hydrate (Te.03-r-3H.O ) is
very soluble in water ;  it crystallizes in large prisms ; by 212  two
atoms of water are given off, but its nature is not changed; the
body which remains (Te.03 + H.O.) is still  acid and soluble in wa-
ter, perfectly neutralizing the alkalies; but by a  red heat this last
atom of water is driven off, and then the whole nature of the  body
changes; it is insoluble in water, and even in the strongest alkaline
solutions, and can only be brought back to its former state by be-
ing fused with potash at a red heat.  Here it  is evident that the
acid properties and the water go  together ; and we may conclude
that, in order to manifest strong acid properties, the  acid must be in
its hydrated form.   But in that hydrated form, if the water acted
as a base simply,  the tendency of the acid to combine with other
bases would be inferior to that of the dry acid  ; for if we place
oil of vitriol and barytes together, the water must be first expelled
before the  barytes and  sulphuric acid can  unite, and hence an im-
pediment would exist to  their union which would not occur with
cold barytes and dry sulphuric acid in vapour, and yet cold barytes
and  oil of vitriol will combine with such  intensity  as to produce
ignition, while the barytes must be heated before it  begins to  com-
bine with the dry sulphuric acid.  The water, therefore, is essential
to the manifestation of strong acid properties, and it does not exist
in combination with the acid merely as a base.  What, then, is the
constitution of a hydrated oxygen acid 1
  When muriatic  acid  (H.Cl.) acts on zinc, the metal is taken up,
forming Zn.Cl., and hydrogen is expelled;  and  if, in place of zinc,
oxide  of zinc  be taken, the effect is the same, except that the hy-
drogen combining with the oxygen of the oxide forms water,  H.Cl.
and  Zn.O. giving  Zn.Cl. and H.O.  Now we have in oil of vitriol 
       CONSTITUTION OF  ACIDS  AND  SALTS.     417

the elements S.O,H. combined together; when put in contact with
zinc, II. is expelled, and S.04Zn. is formed ;  and with Zn.O. and
S.O,H., there  are produced S.04Zn., and H.O. is set free.   In both
cases, of which the former  may be taken as the type of all the ha-
loid salts, and the latter of all salts formed by oxygen acids, there is
H. as the element, which is removable by a metal, precisely as one
metal  is replaceable  by another, as, indeed, from the real metallic
character  of hydrogen,  may be considered to occur in this  case.
Every acid may  therefore  be considered to  consist  of hydrogen
combined  with  an electro-negative  element ;  which may be simple,
as chlorine, iodine, fluorine ; or may be compound, as cyanogen,
N.C,, and  yet capable of being isolated; or, as occurs  in the  great
majority of cases, its elements may be such as can only remain to-
gether when in combination.  Thus'oil of  vitriol does not  contain
S.O, and H.O., but consists of hydrogen united to a compound rad-
ical S.04.   Liquid nitric acid does not contain N.O, and H.O., but
consists of hydrogen united to a compound radical  N.Ob,  and the
acetic acid is  written  C4H304-r-H., the oxalic acid C204-f H., and
so on.
   The elegance and simplicity with which  the laws of saline com-
bination may be deduced from these principles is really remarkable.
Thus  it  has been remarked as a  fact substantiated by experiment,
that in neutral salts the  number of equivalents of acid was  propor-
tional to the number of equivalents of oxygen in the base,  but the
ordinary theory gave  no indication of why this should occur.  It
follows necessarily from the principles of the  newer theory.   Thus,
if a protoxide be  acted on by an acid, M. denoting the metal of the
oxide, and R. the radical of the acid, the resulting action is,
        M. + O. and H. + R. produce H. + O. and M. + R. ;

and in the neutral salt, there is an equivalent of each.   Now in the
case of a sesquioxide, in order that water  shall be formed, and so
neither acid nor base in excess, the reaction is that
      M,-f-03 and 3(H.-f-R.) produce 3(H. + 0.) and M24-R3,
a sesqui-compound being for;ned perfectly analogous to a sesqui
oxide, and the number of atoms of  acid, 3(H. + R.), is equal to the
number of atoms  of oxygen in the base (M203), because that  number
of atoms of hydrogen is required  for the decomposition of the base.
In like manner, for a deutoxide, there is
      M. + O, and 2(H. + R.) producing 2(H.O.) and M. + R2.

The power of salts to replace water in the  magnesian sulphates, so
as to form double salts, becomes much more intelligible when we
compare II. + 0.  with  K. + S.04,  than where H.O. was contrasted
with the complex formula K.O.-j-S.03.
   The circumstance that on the new theory (or, as it is now often
called, the Binary theory of salts) it is necessary to  admit  the ex-
istence of a great number of bodies (these salt-radicals) which have
never been isolated, and in favour  of whose  existence there  is no
other proof than their utility in supporting this view, becomes more
powerful as an objection when we proceed to apply its principles 
418           BINARY  THEORY  OF  SALTS.
to the salts  of phosphoric acid.   For it has been already described
that this acid forms three  distinct classes of salts, all neutral, and
which have  their origin in the three hydrated states of the phos-
phoric acid.  These states are written on the two views as follows:
                           Old Theory.           New Theory.
         Monobasic acid,  P.O.H-H.O.   .  .  . P.O. + H.
         Bibasic acid,     P.O,-r-2H.O.  .  .  . P.07-f-H2.
         Tribasic acid,    P.0. + 3H.0.  .  .  . P.Oa+H3.

  Now  it appears very useless, where the older view accounts so
simply for the properties and constitution  of these salts, to adopt
so violent an idea  as that there  are three distinct compounds of
phosphorus  and oxygen, whic.h no chemist has ever been able to
detect.   But here, again, other circumstances must be studied ; first,
the difference of properties of phosphoric acid, in  its three states,
is totally inexplicable, on the idea of their being merely three de-
grees of hydration.  Nitric  acid forms  three  hydrates,  but when
neutralized by potash, it always gives the same saltpetre; sulphuric
acid forms two perfectly definite  hydrates, but with soda forms al-
ways the same Glauber's salt; while phosphoric acid, when neutral-
ized by  soda, gives a different kind of salt according to the state it
may be  in.  Also, the permanence of these conditions of phospho-
ric  acid  is a powerful proof that they do  not consist in the adhesion
of mere water.   The idea that the phosphoric acid is a different hy-
dracid in each of its three conditions, on the other hand, not mere-
ly explains the fact  of these differences of properties, but it renders
the formation of bibasic and tribasic salts, which is such an anoma-
ly on the old theory, a necessary consequence of the new; for the
phosphoric salt radicals, P.06, P.0T, and P.O., differ not merely in
the quantity of oxygen they contain, but are combined with differ-
ent quantities of hydrogen, and hence, in acting on metallic oxides
(bases), there is a  different number of atoms required for each to
replace  the hydrogen ?nd form water.   Thus,
P.OJL and Na.O. give H 0.  and  P.06Na., monobasic phosphate of
      soda;
P.07H2 and 2Na.O.  give 2H.O. and TO:Na2, bibasic phosphate ;
P.OBH3 and 3Na.O.  give 3H.0. and F.03Na3, tribasic phosphate.
A circumstance which gives additional reason to infer that the wa
ter  is not merely as base  in  triphosphoric acid, is the following:
if it were so, then  it should be  most comoletely  expelled by the
strongest bases, and the bibasic and tribasic phosphates of the alka-
lies  should be those least  likely  to reta«n any portion  of the basic
water; but the reverse is  the fact;  while  oxide  of  silver, a very
weak base, is that which most easily and totally replaces the water.
On the  idea, however, of hydracids, this is easUy understood, for
the  oxide of silver is  one most  easily reduced by hydrogen, and,
consequently, one on which the action of a hydrogen acid, as P.Oa
-)-H3, or P.07-r-H2,  would be most completely exercised.
  A remarkable verification of this theory has been recently found
in the decomposition of solutions  of the oxysalts in water by voltaic
electricity.  It has  been already explained (p. 187, et seq.) that it re- 
EVIDENCE  IN  FAVOUR  OF  THE  NEW  THEORY.  419

quires the same quantity of electricity to decompose an equivalent
of any binary compound, such as iodide of lead, chloride of silver
muriatic acid, or  water.  Now,  if we dissolve  sulphate of soda in
water, and pass a current of voltaic electricity through that solution,
we have water decomposed, and also  the  Glauber's  salt; oxygen
and sulphuric  acid being evolved at one pole, and soda and hydro-
gen at the other.   Here, on the old view, the electricity performs
two decomposing actions at the same time, and, as it thus divides
itself, its action on each must be lessened, and the quantity of each
decomposed be diminished, so that the  sum should represent the
proper energy of the current.  On measuring these quantities, how-
ever, the result is totally different;  the quantity of sulphate of soda
decomposed is found to be  equal to the full duty of the current, and
an equivalent of water appears to be decomposed in addition.  It is
quite unphilosophic to imagine that the strength of a current should
be thus suddenly doubled, and a simple and sufficient explanation of
it is found in the new theory of salts.   The sulphate of soda in so-
lution having the formula Na.S.04, is resolved by the current into its
elements Na. and S.04, as  chloride of sodium  would also  be ;  the
sodium, on emerging at the negative  electrode from  the influence
of the current, instantly decomposes water, and  soda and hydrogen,
of each an equivalent, are evolved ; at the positive electrode, the
compound radical S.04 also decomposes water, and produces H.S.04
and 0.  The appearance of the oxygen  and hydrogen is thus but
secondary, and the  body really decomposed by the current is only
Na.S.O.,.
  In the case of the salts of such metals as do not decompose water,
the phenomena are much more simple.  Thus, a solution of sulphate
of copper, when decomposed by the battery, yields metallic copper
at  the negative, and sulphuric acid and oxygen at  the positive elec-
trode, and the quantity of copper  separated represents exactly the
energy of the current which has passed ;  for the salt being Cu.S.04,
is simply resolved into its elements, but S.04 reacting  on the water,
produces H.S.04, and 0. at the positive electrode.   On the old view
it was supposed  that water and sulphate  of copper were  both de-
composed, oxygen and acid being evolved at one side, and  oxide of
copper and hydrogen being  separated at the other;  which reacting,
produced water and the metal.  Such  an explanation, however, is
directly opposed to  the law of the definite action of electricity, and
cannot be received.
  In the case of solutions of chlorides or iodides,  where there can
be no doubt  of the relations of the elements, the  results of voltaic
decomposition are precisely similar.  Chloride of copper gives sim-
ply chlorine  and copper, no water being decomposed.   Chloride of
sodium or iodide  of* potassium give chlorineor iodine at the one
electrode, and alkali and hydrogen at the other ; the evolution of
these last being caused by  the action of the  metallic  basis on the
water of the solution.
  Professor Daniell, to whom these important electro-chemical re-
searches are  due, considers the truth of the  binary theory of salts
to be fully established by them.
  If this theory be adopted, a profound change in our nomenclature
of  salts  will  become  necessary.  Graham has proposed  that the 
420      VIEWS  RESPECTING DOUBLE SALTS.

name of the salt-radical should be formed by prefixing to the wovd
oxygen, the first word of the ordinary name of the class of salts, and
that  the salts  be termed by changing oxygen into oxides.  Thus g-5.
04, sulphatoxygen, gives sulphatoxides ;  the sulphates, N.Oc, nitrat-
oxygen, gives nitratoxides, the nitrates, and so on ; but I consider
that  the form of nomenclature proposed by Daniell deserves the
preference.  It has been described (p. 194) that Faraday proposed
to term the elements which pass to the electrodes of the battery,
ions ; acting on this, Daniell proposes to  term  the electro-negative
element of the sulphates, oxysulphion ; that of the nitrates, oxynitri-
on, and  so on, and the salts may be termed oxysulphion of copper,
oxynitrion of sodium,  &c.  It would be  desirable, however, for a
long time, to introduce these names only  where theoretical consid-
erations rendered their employment decidedly useful, and hence, in
all future  description of the salts, I shall make use of the language
of our ordinary views, and treat  of their preparation and composi-
tion  without any reference to  the discussion in which we have been
engaged.
  The general adoption of the binary theory of salts has deprived
of much of its interest and importance a question which some years
since was very ingeniously discussed, viz., whether, in  the forma-
tion  of  double salts, the salts which unite had  the same relation to
each other that the acid and base were then thought to have. Thus
it was supposed that the electro-negative qualities of sulphuric acid
being less controlled by oxide of copper than  by potash, the alka-
line  sulphate  acted as  a base  to the sulphate of copper when these
two  salts  combined to form the double sulphate of potash and cop-
per,  and so on in other instances; but, in addition to the circum-
stance that all we have said as to the constitution of the salts mili-
tates against  this view, Ave have the positive  evidence that, first,
these double  salts  are formed, not by  combination merely, but by
replacement of the  constitutional water of the sulphates of the cop-
per  or magnesian class, which water nobody would contend to act
in them as a base ; and, second, that when a solution of such a dou-
ble salt is decomposed by the battery, the two  salts are  not separa-
ted as if they  were  acid and base, but are  decomposed independent-
ly in the proportions of an equivalent of each,  making together the
sum of the chemical energy of the current.
   A similar idea was advocated by Bonsdorff regarding the doubie
chlorides, iodides, &c.  He proposed to  consider the chlorides of
gold, platina,  mercury, &c, as chlorine acids,  and those of potassi-
um, &c,  as chlorine  bases, and so with the iodides.   This  view,
however,  although  at first very extensively adopted, has given way
to the gradual growth of knowledge.  There is no analogy between
a dry oxygen acid  and a chloride ; but  the chlorides are in perfect
analogy with  the neutral salts. Thus Cu.Cl. does not resemble S.03,
but  Cu.S.O, and Cu.Cl. + K.Cl. are analogous, not to S.03.K.O., but
to the double salt,  Cu.S.04+K.S.04.  Bonsdorff's idea was exactly
counter to the direction of truth ; he sought to bring all salts under
the  one head, by extending to all the constitution of oxygen acids
and oxygen bases, while  the  progress  of science has led us to the
opposite  generalization  of reducing all salts  to the simple haloid
type. 
SALTS  OF POTASH.
421
                       CHAPTER  XV.

6PECIAL HISTORY OF THE MOST IMPORTANT SALTS OF THE INCRGANIC ACIDS
                          AND BASES.

  The  multitude of salts known to chemists is so very great, that
it is only possible  to  detail the  history of the most important of
each class.   They  are arranged according to their bases, except in
some few cases, where a metal is also the radical of their acid ele-
ment.   In that case, the salts of the acids of the metal are described
after those  formed by its oxides with other acids.  This plan has
been adopted in order to give as much unity as possible to the his-
tory of each metal, and influences only  the compounds of chrome
and arsenic to any degree.

                     Of the Salts  of Potash.
  Chloride of Potassium.—K.Cl.  Eq. 932 6 or 74*7.  This salt may
be artificially produced  by neutralizing potash  with hydrochloric
acid.   It exists abundantly  in the water  of many brine springs, and
in the  ashes of  plants.   It is  very soluble in water, producing  so
much cold as to  be employed as a  freezing mixture ; it crystallizes
in cubes, which are anhydrous; its principal use is in the manufac-
ture of alum.
  Iodide of Potassium.—K.l.   Eq. 2069*4  or 165*8.   A variety  of
processes may be  employed to prepare  this salt.  One of the sim-
plest consists in  dissolving  iodine  in solution of potash until this is
completely neutralized.  The  potash being decomposed, there is
formed from 61.  and 6K.O., 5K.I.  and K.O. . 1.03.  The solution is
evaporated to dryness, and the  mass being heated to redness, is
kept fused as long as bubbles of oxygen gas are given off: the re-
sidual salt,  which is pure iodide of potassium, is,  when cold, to  be
dissolved in its weight of boiling water, and allowed to crystallize
very slowly.  A  certain loss may  occur in  this process if the heat
applied be too high, and if the temperature be not high enough, io-
date of potash  may remain undecomposed ; this  last effect  being
advantageous to the  manufacturer by increasing the quantity  of
product, is more liable to occur, and may be detected by means  of
tartaric acid, as very ingeniously proposed by Mr. Maurice Scanlan.
This acid is without  action on pure iodide of potassium, farther
than to liberate hydriodic acid, which remains for a certain  time
unaltered ;  but if a trace of iodate of potash be  present, the iodic
acid which  is set  free immediately  reacts on the hydriodic  acid,
water being formed and iodine liberated, which may be recognised
by means of starch.
  Another  process, adopted by the London and Edinburgh  Phar-
macopoeias, consists in  putting together iodine, metallic iron, and
carbonate of potash ; the iron and iodine  unite directly to form a
soluble iodide of  iron, which  is decomposed as rapidly  as formed 
422 IODIDE,  BROMIDE,  AND  SULPHATE  OF POTASH.

by the carbonate of potash.  Iodide of potassium is produced with
oxide of iron and carbonic acid ; a quantity of the latter combines
with the oxide of iron, but as this is not pure protoxide,  most of
the carbonic acid is evolved as gas.  The reaction consists in Fe.I.
and K.O. . CO,, giving rise to  K.I. and Fe.O. . CO..  The liquor be-
ing; filtered and evaporated to a pellicle, the iodide of potassium is
obtained crystallized.   This salt crystallizes in  cubes; sometimes
in square prisms, which are  macles.   It is not  deliquescent when
pure, and is without action on turmeric paper; by this means it is
known to be free from carbonate of potash.  It is sometimes adul-
terated by chloride of potassium, which may be detected  by decom-
posing its solution by nitrate of silver, washing the precipitate with
water,  digesting it in strong water of ammonia, and filtering; if the
solution, when rendered slightly acid with nitric acid, give a white
precipitate of chloride of silver, chloride  of potassium was present,
and its amount may be  thus determined.
  The iodide of potassium is extensively used in medicine, by the
chemist as a reagent, and  for the preparation of other metallic io-
dides.
  A solution of  iodide of potassium dissolves  iodine in large quan-
tity, forming a brown liquor used in medicine.   It is not certain,
however, that in this case  any definite compound (as a  biniodide)
is formed.
  Bromide of  Potassium.—K.Br.  Eq.  1468*3  or 117*6.  This salt
may be prepared exactly as the iodide of potassium, which it re-
sembles  in  most of its  physical characters.  It is recognised by
giving, with oil of vitriol, orange-red fumes of bromine.  The com-
mercial article is frequently adulterated with chloride of potassium,
the presence of  which may  be  detected as follows : dissolve 100
grains  of the salt in four ounces of water, and decompose it by an
excess of nitrate of silver ; collect the precipitate, wash it carefully,
and dry it in a capsule  till it ceases to lose weight ;  then weigh it.
If it were perfectly pure, the  bromide of silver should weigh 158*8
grains; but the  presence of chloride of potassium would have the
effect (from the  smaller equivalent of chlorine) of increasing the
weight;  therefore, if the precipitate, when quite dry, weighs more
than 158*8 grains, the sample  is impure, and the quantity of chloride
present may be calculated from the overplus weight,  for  100 grains
of pure chloride of  potassium should give 192*6 grains  of precipi-
tate.  Thus, if there were  10 per cent, of impurity, the precipitate
would  weigh  162 grains;  if 20 per cent., it would  weigh  165*4.
Thus the precipitate  increases in weight about 3*3 for each  10 per
cent, of chloride of potassium present.
  The properties of the Fluoride and of the Silico-fluoride of Potas-
sium are not of importance beyond what has  been already said in
p. 321, 323, and 324.
  Sulphate of Potash.—K.O. .  S.03  Eq. 1091*1 or 87*43.   This salt
is produced upon the large scale in the manufacture  of the sulphu-
ric and nitric acids, where  nitrate of potash is  employed.  It may be
prepared by the direct union of its constituents,  and, being but spa-
ringly  soluble, it precipitates as a fine crystalline powder when oil
of vitriol is mixed with a strong solution of potash.  It is more sob 
SULPHATE  AND  NITRATE  OF POTASH.     423
uble in boiling water, and crystallizes, on cooling, in right rhombic
prisms, or  in six-sided prisms  terminated by pyramids, which are
macles, being formed by the union of three simple crystals, as de-
scribed in p. 28.  In the figures, A represents the manner in which
the three rhombic prisms  adhere together, the letters  jh-,/
marking  the  corresponding planes in each original, and  A.L
B the form which results when all traces of the junctions
have disappeared.  This salt does not contain water; its
crystals decrepitate violently when heated, but are not decomposed.
100 parts of water dissolve 8*3 of the salt at 32 , and
25 parts at 212°.  This salt combines with dry sul-
phuric acid to form a  bisulphate of potash, K.O.-|-
2S 03, which may be prepared by exposing the neu-
tral salt to the vapour of dry sulphuric  acid, or by
dissolving  it with U equivalents of oil of vitriol in
the  smallest  possible  quantity  of distilled  water.
This  bisulphate of potash crystallizes in  small  prisms, which are
gradually  decomposed  by  water, the following salt being formed.
  Common Bisulphate of Potash.   Double Sulphate of Water and Pot-
ash.-K.O. .S.03-fH.O. .S.03.  Eq. 1704*7 or  136*6.  This salt  is
produced  when nitrate of potash is decomposed by two atoms of
oil  of vitriol, and is formed when neutral sulphate of potash is gen-
tly  heated with half its weight  of  oil of vitriol to just below red-
ness.  It  may be obtained crystallized  from a  strong  solution  in
ri"-ht rhombic prisms.   It is  decomposed  into neutral sulphate and
oil of vitriol by a large quantity of water.   When heated to full
redness, it fuses, and may be obtained, on  cooling, in oblique rhom-
bic crystals; it is thus dimorphous (see p.  227; ; at a higher tem-
perature  it abandons its  excess of acid,  and neutral  sulphate  re-
mains.
  There exists also a hydrated sesquisulphate of potash, 2(K.O.. S.U3)
 -f H.O.. S.O,,  which  crystallizes in  fine  needles.  Similar  com-
 pounds of sulphate of potash with hydrated nitric and phosphoric
 acids have also been described.
   Nitrate of Potash.   Saltpetre.  Nitre.—K.O.. N.05. Eq. 1266*9 or
 101*5.  The  general  principles of the formation of nitric acid  by
 the conjoined action  of decomposing animal matter and of  earthy
 bases on  atmospheric  air, have  been described already.   By lixivi-
 ating the  materials thus  obtained, whether naturally or from arti-
 ficial nitre  beds, with water,  a solution  is obtained,  containing,
 among other  saline matters, a  considerable quantity of nitrate  of
 lime ;&this is then decomposed by an impure carbonate of potash,
 and  carbonate of lime being precipitated, a solution of nitrate of
 potash is  obtained, from  which the salt is procured by  evaporation
 and crystallization.  Its form is that of a six-sided prism with dihe-
 dral summits, derived from the  right rhombic  system.   It is anhy-
 drous ; 100 pnrts of water dissolve 13*3 parts at 32 , and 240 parts
 at  *212° •  when heated to redness, it melts and evolves oxygen, at
 first^ pure, but subsequently mixed with nitrogen gas.
   As nitrate of potash contains oxygen in large quantity and gives it out readily to
 combustible bodies, it is much employed for the preparation of firework, and espe-
 cially of gunpowder.  The action of gunpowder depends upon «s generating.hen
 decomposed/a lanre quantity of gases, which occupy more than 1000 times its vol. 
424         MANUFACTURE  OF  GUNPOWDER.
urne.  If this took place instantaneously  all bodies near which could not resist
this force, would be burst or broken; as takes place with chloride of azote which, if
placed in a gun, would burst it, but have no power to propel a ball; the decomposi-
tion of gunpowder  however, occupying a certain time, the disengagement ol gas is
prog?esfiverand the ball is forced through the barrel with the velocity due to the ul-
 imate effect of the whole quantity of gas produced.  When gunpowder is comp etely
decomposed  the products are found to be sulphuret of potassium, nitrogen, and car-
bonic acid gas, and from  these the proportions by weight of its constituents may be
calculated, for S, K.O. . N.O5, and 3C, produce K.S., N., and 3C.02.  The parts by
weight are, therefore,
                 Theory.
         S — 161 — 11*8
       3C.= 18-3— 13-5
K.O. . N.O5-=101-5 — 7-1-7
             135-9   1000
The proportions employed in the government factories of the most important coun-
tries are given also above.  The Prussian mixture agrees best with theory.   For the
coarse blasting powder, there are employed sixty-five parts of saltpetre, twenty of
sulphur, and fifteen of charcoal.  The excess of sulphur renders the explosion more
intense,  but would corrode firearms too much.  A mixture of three parts of salt-
petre, four of carbonate of potash, and one of sulphur, is decomposed instantaneously
when fused, and with an explosion so violent, that, if it be placed on a thin iron plate,
it may be perforated.  If three parts of nitre be mixed with one of finely-powdered
charcoal, a mass is obtained which, when touched with an ignited coal, burns nearly
as fast as loose gunpowder, but totally without explosion.  It  is  therefore the sul-
phur which determines the violence and rapidity of the deflagration of gunpowder,
while the charcoal produces the great volume of gas on which its mechanical effect
depends.
  The preparation of the  materials for making gunpowder requires great  care.
Most of the success depends on the preparation  of the  charcoal.  This should be
made from a light wood containing little ashes, such as birch, and carbonized in cyl-
inders, very slowly, and at the lowest possible heat.  When reduced to impalpable
powder, this charcoal is so inflammable as sometimes to take fire at ordinary tem-
peratures.  The purification of the saltpetre is performed by successive recrystalli-
zations,  and by washing the crystals with water already saturated with saltpetre,
which dissolves out any common salt that may be present, but does not act on the
crystals of saltpetre.  The description of the mechanical operations of the manufac-
ture would be out of place here.
  Hupochlorite of Potash.—-When gaseous chlorine is passed into a solution of carbon-
ate of potash, it is abundantly absorbed, but no carbonic acid is disengaged until
the liquor contains an atom of chlorine  for every two atoms of alkaline carbonate.
On examination, it is then found to contain hypochlorite of potash, chloride of potas-
sium, and bicarbonate of potash, which are mixed in solution, and may be partially
separated by crystallization.   The reaction has been such that 2C1. and 4K.O.. C.
02give  K.CL, K.O.. Cl.O., and 2(K.O.-r-C.02+H.O.. C02).   If the stream of chlo-
rine  be  continued, carbonic acid is copiously evolved, and as much more chlorine is
absorbed, giving ultimately a mixture of K.Cl. and K.O.. Cl.O.  The liquor becomes
deep yellow, owing to the  liberation of a quantity of hypochlorous acid by the free
carbonic acid, and hence the quantity of chlorine absorbed amounts to much more
than the exact atomic proportion.
  Farther details  of the theory of these bleaching compounds are given under the
head of chloride of lime.
   Chlorate of Potash.—K.O. . C1.03.   Eq. 1532*6 or 122*81.   When
chlorine gas is passed into a strong solution of potash, it is absorbed
rapidly until the alkali is  completely neutralized,  and chloride of
potassium and hypochlorite of potash are formed  ; 2K.O. and  2C1.
giving K.Cl. and K.O.  . Cl.O.   If, then, this liquor be boiled for some
time,  oxygen gas is given off, the hypochlorite being decomposed,
and chloride  of potassium and  chlorate  of potash  being formed ;
9(K.O. . Cl.O.) producing 120. with 8K.C1. and K.O. .  Cl.O,.   If car-
bonate of potash has been employed, the absorption of the chlorine
is rapid until half of the  salt has been decomposed, and the remain- 
CHLORATE  OF  POTASH.
425
der converted into bicarbonate, from combining with the evolved
carbonic acid, as described under the preceding head ; but a hio-h
temperature and a great excess of chlorine being necessary to com-
plete the reaction, render the operations tedious and  very trouble-
some ; and  as, owing to the large quantity of oxygen evolved, there
is but one  equivalent of chlorate of potash obtained  by the action
of eighteen equivalents of chlorine  on eighteen of potash, the pro-
cess is one  of considerable expense.
  We owe  to Graham a method which is free from these  disadvan-
tages.  If an  equivalent  of carbonate of potash be mixed with one
of hydrate of lime (by weight about 2 of K.O. . CO to 1  of Ca.O. .
H.O.), and exposed to a current of chlorine, the gas is absorbed with
avidity, and the solid mass becomes very hot, while water is given
off abundantly.  When saturated, it may be  gently heated to com-
plete the decomposition.  No oxygen is given off, the reaction being
that 6(K.O. .  CO,) and 6(Ca.O. . H.O.), acted on  by  6C1., produce
5K.C1.,  6Ca.O.  . C02, and K.O. . Cl.O,, while 6H.O.  are evolved.
By  digesting  the mass in water, the potash salts are dissolved out,
carbonate of  lime remaining,  and  the chlorate  of potash may  be
separated from the chloride of potassium by crystallization.  By this
means three times as much product  may be obtained from  the same
materials as by the older process.
  This salt crystallizes in rhomboidal tables of a  pearly lustre : it is
anhydrous : 100 parts of water dissolve but 3-5 parts at 32", and 60
parts at 219\   It tastes sharp and cooling, like nitre ;  when heated,
it melts and evolves oxygen gas, being decomposed into chloride of
potassium and hyperchlorate of potash ; on increasing the  heat, this
also is decomposed, and  chloride of potassium  remains pure.   Its
uses in preparing oxygen, and the compounds of chlorine and oxy-
gen, have been already noticed.   From its supplying oxygen still
more readily  than nitre, it is the basis of a variety of deflagrating
mixtures.   When  rubbed in  a mortar with sulphur or with sulphu-
ret  of antimony, it explodes  violently.   Placed  in contact  with a
minute bit of phosphorus on  an  anvii, and struck  by  a hammer, it
gives a dangerous detonation.  The ordinary lucifer matches are
formed by mixtures of chlorate of potash with sulphur  and  charcoal,
or sulphuret  of antimony  or  of  cinnabar,  made  into  a paste with
gumarabic, and applied to the extremity of a bit of stick, previously
smeared with sulphur.   Students should be very cautious how they
employ this salt in such experiments as those now noticed.
  Perchlorate of  Potash—K.O..CUV. Eq. 173*2-6 or 1388—is of  importance only
from being one of the least soluble salts of potash, and, consequently, that the per-
chloric acid may be used as a  test for the presence of potash in solution, it giving
a granular crystalline precipitate if that alkali be present.  Its preparation is suf-
ficiently noticed  in page 300.
  The Silicate of Potash is of considerable importance as a constituent of glass, and
will  be noticed as such hereafter.
  Iodate of Potash.—K.O.. I.O-,.  This salt, which is but sparingly soluble in water,
may be obtained by neutralizing the  perchloride of iodine with caustic potash ; I.
Cl;, and 6K.O. produce 5K.C1. and K.O. .1.05.   This last separates in crystalline
grains.  It may also be obtained by adding iodide of potassium to fused chlorate of
potash; the mass froths up, the oxygen passing to the iodine, and there is obtained a
mixture of chloride of potassium and iodate of potash, which may be separated by
crystallization.  This salt has a remarkable tendency to form acid and double salts,
of which, however, none are specially interests g.
                               H H H 
426
CHLORIDE  OF  SODIUM.
                        Salts of Sodium.
  Chloride of Sodium.  Common Salt.  Sea Sa/f—Na.Cl.; Eq. 733*6
or 58-8—exists  in great abundance in nature ; solid, as rock salt,
and in solution in the water of the ocean, and of many inland seas
and lakes.   The deposites of rock salt occur only among the more
recent (secondary) geological formations, lying above the coal, and
in connexion with the new red sandstone, as in Cheshire.  The beds
of salt are sometimes of great magnitude; thus, at Northwich, the
bed now worked is supposed to be not less than 60 feet thick, a mile
and a half long, and 1300 yards wide ; and the deposites  at Wie-
liczka, in Poland, appear  to be still larger.  The origin of these de-
posites of salt is probably to be found  in the gradual drying up, by
evaporation, of salt lakes, to which fresh quantities of salt were con-
tinually supplied by the surrounding springs.  Owing to admixture
of earthy matters, the rock salt, as quarried, is generally brownish-
coloured, and  hence  requires to be dissolved  in water and crystal-
lized for use.  The expense of extracting the salt may be in many
cases lessened, by simply boring down  to the bed with a pipe a few
inches in diameter, and letting thereby water  run in upon the salt;
a strong solution of salt  is thus produced, which is pumped up and
evaporated.   The expense of sinking a shaft and quarrying out the
solid salt is thus avoided.
  In warm countries, as on the coasts of Portugal and of the south of
France, salt  is obtained by  the spontaneous evaporation of sea-wa-
ter, which is allowed, on the rise of the tide, to flow into shallow
basins, being passed from one to another, according as it becomes
more concentrated, and,  finally, the  evaporation being finished by
means of artificial heat.  The sea-water is not evaporated to dry-
ness, as its  other saline  ingredients would in that case be mixed
with the common salt.  The sea-water is generally composed of
          Chloride of sodium  .   .  .  2*50'
          Chloride of magnesium  .  .  0*35
          Sulphate of magnesia  .  .  0*58
          Carbonate of  lime and  )      . ft   J, 100*00,
          Carbonate of  magnesia $   '
          Sulphate  of lime  ....  0*01
          Water.......96-54,

with generally some traces of iodide and bromide of magnesium.
According as the evaporation proceeds, the common  salt fs depos-
ited in crystals, and the mother liquor, or bittern, being rich in salts
of magnesia, is preserved for the manufacture of Epsom salts.
  In addition to these sources, chloride of sodium may be obtained
by the direct combination of its elements, or by decomposing car-
bonate of soda by muriatic acid.  In practice, however, this is never
done.
  Chloride of sodium crystallizes in cubes.   Its taste is purely sa-
line.  It is equally soluble in water at  all temperatures, 100 of wa-
ter  dissolving 36*5 ; by  a very  strong heat it may be volatilized.
Its  crystals  are  anhydrous, but are generally fissured, containing
water, which,  when heated, bursts  the crystal, producing loud de- 
MANUFACTURE  OF GLAUBER'S  SALT.      427
crepitation.  A strong solution of salt does not freeze at 0°, but de-
posites crystals in rhombic plates, which are a hydrated chloride
of sodium.   If these crystals be heated beyond 15J they give out
water, and are changed into minute cubes.
  The uses of chloride of sodium are very numerous and important.
Besides being employed in seasoning food, it is now universally the
source from  whence  the  other compounds  of sodium,  such as the
carbonate and sulphate, are obtained.  It is employed also in the
manufacture  of glass and  of porcelain, and as a manure.
  The bromide and iodide of Sodium resemble, in properties and mode
of preparation, the corresponding compounds of potassium, and do
not require special notice.
  Sulphate of Soda.  Glauber's Salt.—Na.O.. S.03-f-10 Aq.  Eq. 892*1
+ 1125 or 71*48-f-90.   So named after its discoverer:  exists in some
mineral waters, and may  be prepared by neutralizing carbonate of
soda by dilute sulphuric acid.   For the purposes of commerce, it is
manufactured in  great quantities from common salt, as described
under the head of muriatic acid (p. 307).
  As it is not the object of the process to economize the muriatic
acid gas, the  decomposition is carried on in a  reverberatory furnace
similar to that figured in p. 333.  Three or four hundred weight of,
salt being spread  over the floor of the furnace, forming a layer three
or four inches deep,  the  equivalent quantity  (an equal weight) of
sulphuric acid, of the strength 1*600, as taken from the chambers, is
poured in through an aperture in the dome, and a moderate fire kept
up until the materials begin to dry ;  the fire is then increased grad-
ually until all the muriatic acid gas has  been expelled, and the resid-
ual  sulphate  of soda  begins to fuse.  The  acid gas passes up the
chimney, and is either allowed to pass  away into the air, or is con-
densed by  meeting with a stream of water, and the weak liquid acid
thus formed  is suffered to run to waste.  The  greater part of the
sulphate of soda  thus produced is  immediately used to make car-
bonate of soda; but to form Glauber's  salt, it is only necessary to
dissolve it  in warm water, and let it crystallize by cooling.
  The sulphate of soda crystallizes in six-sided prisms, as in  the
figure, very much channelled at the sides.  It is
easily soluble in water, having a point of maxi-
mum solubility at  93 , as figured in page 22.  Its
ordinary crystals  contain 56 per cent, of water;
by exposure to the air it  loses all its water by
efflorescence, and falls into a white powder ; from
a hot saturated solution opaque rhombic octohe-
dral crystals are deposited, which are anhydrous.
The isomorphism of these crystals with  permanganate of barytes,
and the speculations founded  on it, have been  noticed p. 224.  A
bisulphate  and a sesquisulphate of  Soda may be formed by adding
oil of vitriol  to a  solution of the  neutral salt, and crystallizing by
evaporation.  They are much less determinate than the acid sul-
phates of potash.
  Nitrate of Soda.   Cubic Nitre.—Na.O.. N.O,. Eq. 1067 5 or 85*57.
The spontaneous formation of this salt by the atmospheric influence,
probably on a soil containing chloride of sodium, has been  noticed
 
428
PHOSPHATES  OF  SODA.
p. 277.  It may also be obtained by means of nitric acid and carbon-
ate of soda.   It crystallizes in rhombs, isomorphous with calc spar
(p. 224).  It is very soluble in water, and is slightly deliquescent;
hence it cannot be employed in the manufacture of gunpowder.   It
is used for the manufacture of nitric and sulphuric acids,  and as a
manure.
  Hyposulphite of Soda.—Na O. .  S20,+ 10 Aq.  This salt,  which
nas become  of some practical interest, from its  use in  dissolving
off the sensitive silver compounds in making photogenic drawings,
may  be made  by boiling together  three parts of dry carbonate  of
soda with one of sulphur until this last is dissolved, and then pass-
ing a stream of sulphurous acid gas through the liquor until it smells
strongly of it.   Na.O. . G02, with  S. and S.02, produce Na.O. . S202,
while C02 is  evolved.  If  the three parts of carbonate of soda be
boiled with two  of  sulphur, and  the deep yellow  liquor be exposed
to the air until it yields a colourless liquor  on filtration, the salt is
more simply produced, the necessary quantity  of oxygen being  ab-
sorbed from the air.   The hyposulphite of soda thus formed is easily
soluble in water.  Its  resemblance  to Glauber's salt in form, and its
other properties, are noticed in p.  291.
  Hypochlorite of Soda.  Chloride  of Soda.  Disinfecting Liquor of
Labaraque—Is  produced by treating a solution of carbonate of soda
with chlorine as  long  as  this  is absorbed, but no  carbonic acid
evolved.   For  farther  observations, see the hypochlorites of potash
and of lime.
  A. Tribasic Phosphate of  Soda.—The common phosphate of soda
of the  shops is a tribasic salt, containing (P.O- + 2Na.O.-fH.O.) +
24 Aq.  It is prepared by decomposing the solution of acid tribasic
phosphate of lime obtained from bones (as described in p. 295)  by
means  of carbonate of soda.  Carbonate of lime is thrown down,
and phosphate of soda  formed.   It is easily soluble in  water, and
              crystallizes in oblique rhombic  prisms, as in the fig-
              ure,  which  react alkaline.   When  exposed to  the
              air, it loses  some of its water  by efflorescence (ten
              atoms 1), but the  crystals retain their form.   If this
              salt be  mixed with an  excess of caustic  soda,  the
              atom of basic water  is  displaced, and  the  subphos-
              phate of soda (P.O. +3Na.O + 24 Aq.) crystallizes in
              long prisms  ; and by  the addition  of hydrated phos-
              phoric  acid to its solution, and cautious evaporation,
the  acid tribasic phosphate  (P.05+Na.O.+2H.O.)+2 Aq., which
crystallizes in  oblique rhombic prisms, is formed : it is dimorphous.
  The  characteristic of these three salts is to give with nitrate of
silver a yellow precipitate  of tribasic phosphate of silver.
  B. Bibasic Phosphate of Soda.—Of these salts, that termed the Py-
rophosphate of  Soda,(P.O,-\- 2Na.O.) -f 10 Aq., is of interest, as its dis-
covery led the way to the true history of these bodies.  It is form-
ed by fusing the  common phosphate of soda, (P.054-2Na.O. + H.O.)
■+24 Aq., at a red heat.  All the  water of crystallization is given
off at a very moderate heat; but  by a red heat the twenty-lifth or
basic atom  is expelled, and, when the salt  is then redissolved,  the
phosphoric acid does not recombine with basic water, but remains
 
BORATES  OF  SODA.--SALTS  OF  B A R I h M.   429
united only  with the soda.  It is recognised by giving a white pre-
cipitate with nitrate of silver.
  C. The Monobasic Phosphate of Soda, P.03 + Na.O., is obtained by
heating the  acid tribasic  or bibasic phosphates of soda to redness.
All the volatile  base being thus expelled, the phosphoric acid re-
mains combined with one equivalent of soda.  This salt fuses into
a transparent glass ; is deliquescent ;  its solution does not crystal-
lize.  It is easily recognised  by throwing down from solutions of
lead and silver,  precipitates, which are not powders, but soft, tena-
cious pastes.
  Borates of Soda.—Boracic acid combines with soda in many pro-
portions, forming salts, of which the most important is the biborate,
the borax of commerce (Na.O. + 2B.O:i) +10 Aq.   It exists in the
water of several lakes in Thibet  and China, also  in Hungary, and
was imported thence in small  crystals, smeared with a fatty matter,
under the name  of tinkal.  The borax  of commerce is now obtained
by treating the native  boracic acid obtained  from  Tuscany, p. 326,
by carbonate of soda.   On the application of heat, the acid dissolves
with the evolution of carbonic acid and ammonia;  the liquor is run
into large vats lined with lead, where it cools very slowly, and the
borax gradually crystallizes in oblique rhombic prisms, as i, u, m,
in the figure.  If a strong solution of borax be kept at
33J, the salt crystallizes  in  regular octohedrons with
only five atoms  of water.  Although this salt contains
two equivalents  of acid, it has an alkaline  reaction :
when heated, it froths up very much, abandoning  its
water.  The dry salt melts at a red heat into a colour-
less glass, which  dissolves most metallic oxides very readily, and
hence is serviceable in experiments with the blowpipe, as enabling
the metals to produce the coloured glasses by which they are rec-
ognised ;  under  the head  of  glass and porcelain,  its use  in  these
branches of art will be again  noticed.
  The remaining compounds  of boracic acid with soda, as the neu-
tral borate, Na.O.. B.03 + 8 Aq., and acid salts, as Na.O. + 4B.03 and
Na.O. + 6'B.03, are not important.
  Silicate of Soda will be described under the head of glass.
  Salts of Lithium.—From the rarity of this body, its salts require no farther notice
than that its carbonate is but very sparingly soluble in water, yet its solution pos-
sesses an alkaline reaction.  It thus serves to connect the alkaline with the earthy
bases.

                        Salts of Barium.
  Chloride of Barium.—Ba.Cl. + 2 Aq.  Eq. 1299*6^-225 or  104*8 +
18.  This salt may be prepared by decomposing the native carbon
ate of barytes with dilute muriatic acid, or, more economically, by
decomposing the sulphuret of barium, the preparation of which is
described in p.  342, by dilute muriatic  acid.  In the former case,
carbonic acid, in the  latter,  sulphuretted hydrogen, is  given off.
The chloride of barium  crystallizes from a  hot solution in rhom-
boidal tables which contain 14*7 of water.
  Sulphate of Bartjtes.—Ba.O.. S.03.   Eq. 1458 or 119*5.   This salt
exists native, in great abundance,  being the  most common source
of barytes.   It is very generally associated with sulphuret of lead,
f\ ' h		
\	i m.	k y
		
 
430  SALTS  OF  BARIUM, STRONTIUM, AND CALCIUM.

and serves as an indication  of the  probable proximity of that ore.
It is  totally insoluble in  water.   Its crystalline form  is an  oblique
                      rhombic prism, generally very flat, as in the
                      fio-ure ; derived from an octohedron of which
                      i and e are planes; the secondary planes, p
                      and u, belong to  the prism.   It is  one of the
                      heaviest of saline bodies, its specific  gravity
beino- 4-3* hence its name of heavy spar  and terra ponderosa.   When
ground to fine powder, it is used as a  cheap  substitute for white
lead in  painting, for which large quantities of it are employed; but
its crystalline texture prevents it having the opacity or body neces-
sary in a good pigment.  It may be prepared artificially  by adding
sulphuric acid to any solution containing barytes ; it falls as a heavy
white crystalline powder. Its total insolubility renders its constit-
uents excellent reagents for  each other.
   Nitrate of Barytes—Ba.O  +N.05; Eq.  1633*9 or 130*9—may be
produced by acting on carbonate of barytes with dilute nitric acid,
or, more cheaply, by mixing strong hot solutions of sulphuret of ba-
rium and nitrate of soda.  The sparingly  soluble nitrate of barytes
crystallizes as the  mixed liquors cool, but the sulphuret of  sodium
remains dissolved.   In this process, from Ba.S. and  Na 0. . N.05 we
obtain  Ba.O. . N.05 and  Na.S.   This  salt  requires  twelve parts of
cold water for solution,  but dissolves in four of boiling water, from
which it crystallizes on cooling in octohedrons.  These crystals are
anhydrous.   When heated, they yield pure barytes.
   The other salts of barytes do not require notice.

                        Salts of Strontium.
   Chloride of Strontium.—Sr.CI. + 6 Aq.  Eq. 989*9 or 79*3:2.   This
salt is obtained from the native  carbonate or sulphate of strontia,
exactly as chloride of barium is obtained from the native salts of
barytes.  It crystallizes  in long needles  which deliquesce.   It is
very soluble in water.
   Sulphate of Strontia.—Sr.O.. S.03.  Eq.  1148-4 or 91*9.  This, the
most abundant source of strontia, is found native  crystallized, iso-
morphous with sulphate  of barytes.  It  may be produced artificial-
ly as a white powder, by adding sulphuric  acid to any solution con-
taining  strontia.  It is dissolved by 3600 parts of boiling water, and
remains dissolved after cooling.   It is fused by a strong heat;  with
charcoal it gives sulphuret of strontium.
   Nitrate of Strontia—Sr.O. . N.O-—crystallizes  in octohedrons,
which dissolve in five parts of cold, and  one half part of boiling
water.  Mr. Scanlan  has observed, that during  the crystallization
of this salt bright flashes of light are emitted.  It is anhydrous, but
decrepitates when  heated, owing to mechanically  included water.
On the  application  of heat, these crystals  evolve oxygen and nitro-
gen, and leave pure strontia.

                         Salts  of Calcium.
   Chloride of  Calcium—Ca.Cl. + 6 Aq.;  Eq. 698*7+675 or 55-98+
54—is obtained by decomposing carbonate of lime with muriatic
acid.  In the laboratory it is  abundantly  procured as the residue of
 
 FLUORIDE  OF  CALCIU .M.--S (ILPHATE  OF  LIME. 431

the preparation of carbonic acid, ammonia, &c.  It is very soluble
in  water ; its  solution, evaporated to the consistence of a sirup,
gives, by cooling,  long, striated, rhombic prisms, which deliquesce
with great rapidity, and when  heated undergo watery fusion, soon
after which  it abandons two thirds of its water of crystallization,
and a powder is obtained, Ca.Cl+2 Aq., in  which form  it is  best
adapted for freezing mixtures.  Heated still farther, it becomes an-
hydrous, and at a red heat fuses.  In this  state it is phosphorescent
in  tbe  dark, forming Homberg's pyrophorus.   It has a very great
affinity for water, combining with two atoms of it, with the evolu-
tion of much heat, and is hence employed to dry gases for experi-
mental purposes, and to remove water from liquids, as in the recti-
fication of alcohol.
   This salt  combines with lime, forming an  oxychloride of calci-
um, Ca.Cl. l-3Ca.O., which is obtained by boiling a solution of it
with an excess of lime, and  filtering.  The new substance crystal-
lizes, on cooling, in small flat rhombs, which contain  forty-nine  per
cent., or fifteen atoms of water.
   The  bromide or iodide of Calcium do  not present any interest.
   Fluoride of Calcium, Ca.F., is an abundant mineral known as fluor
spar, found crystallized in cubes  and octohedrons, but principally
massive.  When first extracted  from the  earth  it  is moderately
tough and soft, and is cut into ornaments,which present a beautiful
variety  of colours.  Its crystals become  strongly phosphorescent
by heat or by electricity.  It is insoluble in water ; from it all  the
other preparations of fluorine are derived, as noticed  in p. 319, 324,
and 327.  It appears as a gelatinous  precipitate when hydrofluoric
acid is added to any  soluble salt of lime.   When heated in contact
with silicious or aluminous minerals, it  forms easily fusible com-
pounds, and being thus of use as a flux in the smelting of metallic
ores, its name of fluor spar was thence derived.
  Sulphate of Lime—Ca.O. . S.03 + 2 Aq. ;  Eq. 857*2 + 225 or 68*69 +
18—may be prepared artificially, by mixing a solution of any solu-
ble salt of lime with sulphuric acid.  It forms a crystalline powder,
nearly  equally soluble in hot and cold water, requiring 461 times its
weight for its solution.  It occurs  in nature abundantly, and in vari-
ous forms: 1st, in  distinct colourless  crystals; 2d, in semi-transpa-
rent masses of crystalline structure, constituting alabaster,  and in
amorphous masses, forming extensive  rocky strata, in many places,
in  which state it is called common gypsum.   From thisplaster of Paris
is  prepared, by calcining the gypsum, broken into  small  pieces, in
ovens at a temperature below 300 \ until  its water of  crystallization
is  expelled.   In this operation it falls to powder, and is to be put up
in  tight vessels so  as to exclude the air.   When mixed with water
it rapidly recombines with the two atoms, evolving heat and expand-
ing in  becoming  solid, so as to fill up all interstices of the mould
into which it may  be poured.  On this property is founded the art
of  easting in plaster and the formation of the various kinds of stucco,
or  artificial stone, in which a solution of glue, or of various earthy salts,
may be substituted for pure water.  If the gypsum be heated, in ba-
king, above  300;, it is changed in nature, and no longer combines
with water so as to set ; it is then converted into a form which exists
in  nature crystallized, and which is termed anhydrite. 
432    MANUFACTURE  OF  CHLORIDE OF  LIME.
  A double salt of sulphate of lime and sulphate of soda is found
native, and termed Glauberite.  It  is insoluble in water,  by which
it is also decomposed.  It cannot be formed artificially.
  The Hyposulphite of Lime is  a soluble salt, the mode of  preparing
which is described p. 291.
  The Nitrate of Lime is very deliquescent, and is decomposed by
a moderate heat.
  Phosphoric  acid combines with  lime  in  several proportions, of
which the most important is the Basic tribasic Phosphate of Lime, or
Earth of Bones.   This salt,  which constitutes the inorganic portion
of the skeletons of the mammalia, mixed only with small  quantities
of carbonate and sulphate of lime, and of fluoride of calcium, has the
formula  8Ca.O.+ 3P.O;.   It may be  obtained  precipitated by dis-
solving bone earth in muriatic acid, and exactly neutralizing the so-
lution by caustic ammonia.   It falls as a gelatinous powder contain-
ing four atoms of water.  As the phosphoric acid of bones is in its
tribasic condition, Graham  considers it to be a combination of two
phosphates, thus,  2(3Ca.O. . P.O, + Aq.) + (H.O. . 2Ca.O. . P.O +
Aq.).  Each of these tribasic  phosphates of lime may be obtained
separate, by decomposing solutions of chloride of calcium by solu-
tion of the ordinary phosphate, or of the subphosphate of soda.
  Hypochlorite of Lime.   Chloride of Lime.    Bleaching Salt.—When
speaking of the oxygen  compounds of chlorine, and of the chlorate
and hypochlorite  of potash, I have had occasion to notice  the diver-
sity of  opinion regarding the nature of the bleaching substances
formed by the action of chlorine on the alkalies and  on lime.   Of
these the chloride of lime is by far  the  most important in the arts.
  It is prepared by generating chlorine in a large still, a, b. h,f as described p. 301,
the materials being kept constantly mixed by means of an agitator moved round by
the  handle d.  The gas is conducted by the tube e e to the upper part of a wood-
en reservoir or apartment, as in the figure, made  very tight, i, i, on the floor
of which pure hydrate of lime is exposed to the action of the gas.  The lime is
introduced by the door k, k, and the surface is changed occasionally by stirring
with rakes by means of the apertures I, I, I.- the absorption should take place so slow-
ly as no' to evolve any sensible heat. In this way 100 parts of slacked lime combine
generally with from fifty to sixty of chlorine.  If the process be carried on too rap-
idly, a quantity of lime is decomposed, chlorate of lime and chloride of calcium be-
ing  formed, which may be recognised  by the product getting  damp when exposed
to the air
999999 
VALUATION  OF   CHLORIDE  OF   LIME.      433
  The best bleaching powder thus prepared by the dry way does not contain  more
lhan forty per cent, of chlorine; this does not correspond to any exact atomic con-
stitution; but if lime be diffused through waler so as to form a thin cream, it then
absorbs more than its  own weight of gas, and  is  totally dissolved.  It is probably
the mechanical disadvantages of the dry way which prevents the absorption of  the
gas reaching this limit, and the best bleaching powder may be looked upon as a mix-
lure of true chloride of lime,  with about eighteen per cent, of hydrate of lime in  ex-
cess.  Accordingly, when ordinary bleaching powder is treated with water, the true
atomic compound is dissolved out, and the excess of  lime remains.  The composi-
tion of the tticoretical and best practical substances may, therefore, be expressed as
follows:
               Theoretical.                                Best practical.
    1 atom chlorine, 3547     48G3           Chlorine.....4032
    1  "   lime,     28-57     3904           Lime......4540
    I  "   water,     'J 00   _L233_           Water......1428
                    731)4   TOO-OO                                  10000

 But the generality of good samples in  commerce will be found not to exceed thirty
 per cent, of chlorine.
  The solution of this chloride of lime has a marked alkaline reaction; it is without
 any bleaching powerexcept an acid be present, which liberates chlorine, and enables
 it to destroy the colouring matter.  It is thus that the colour can be removed from
 certain points without injuring others, which is of very great importance in calico
 printing; thus a piece of cloth being dyed uniformly  with madder (as Turkey red),
 the pattern is printed on with tartaric acid thickened with gum, and the whole being
 immersed in a bath of chloride of lime, the chlorine is liberated by the acid at every
 point of the pattern, and the  cloth is there bleached, giving a white ground, on which
 other colours may be applied, while the general surface remains deep red.  A solu-
 tion of bleaching powder in  water exhales a sensible odour of chlorine, owing to the
 absorption of carbonic acid  from the air, and obtains thereby weak bleaching prop-
 erties.
  As the technical value of bleaching powder depends on the total quantity of chlo-
 rine which it contains, this  may be determined without reference to its  theoretical
 constitution.  For this purpose a variety of methods have been proposed,  and the
 process is termed  Chloromctry.   The  earliest method employed consisted in prepa-
 ring a standard solution of sulphate of indigo, which, being of a deep blue colour, was
 bleached by the chlorine expelled from the lime by the sulphuric acid, and evidently,
 the richer the bleaching powder was in chlorine, the more solution of indigo a certain
 weight of it could bleach.   The action  of chlorine on indigo is, however, so com-
 plex, that this method was found exposed to numerous fallacies, and may be con-
 sidered as now obsolete.  Latterly, (Jay Lussac has  proposed to substitute for  this
 the more definite action of chlorine in "acidifying arsenic.   He prepares a solution
 of arsenious acid in murLtic acid, and dilutes this with water.  On adding thereto
 a solution of chloride of lime, the muriatic acid takes the lime, and the chlorine, de-
 composing water, converts the arsenious acid into arsenic acid, and itself forms hy-
 drochloric acid; As.Os with 201.  and 2H.O. producing As.05 and  2H.C1.  The
 proportions which I employ in this reaction are as follows:  100 grains of arsenious
 acid are to be dissolved in 2000 grains of strong spirits of salt, and this liquor diluted
 with distilled water till it occupies the volume of 7000 grains of water.  This is the
 standard test liquor; to employ it,  100 grains of the  bleaching powder to be  tested
 arc to be diffused  through  1000 grains of  water, and the test liquor to be gently
 poured from a graduated glass on it, in a deep jar, continually stirring the mixture.
 A drop of weak solution of sulphate of indigo is to be occasionally applied, by means
 of a glass rod, to the surface of the liquor;  as long as any chlorine remains unalter-
 ed, the blue colour of the drop is instantly destroyed, and the addition of the arsenic
 liquor is to be continued until the blue drop remains unaltered.  Then the quantity
 of chlorine present in the 100 grains of bleaching powder is represented byyi^thof
 the quantity  of the test liquor employed;  thus, if there were 2565 grains of the test
 liquor necessary to destroy the bleaching power of the 100 grains of chloride of lime,
 the quantity of chlorine would be 25 05.  This is not absolutely correct; for in theo-
 ry, the true quantity of chlorine indicated would be 2G08; but as a few drops of the
 solution arc always employed, more  than what should by theory be necessary, the
 practical proportion of T *^th comes very close to the truth.  Even one half part per
 cent., which is the limit of error, is quite unimportant in practice.
   Another method which  is simple  and  rapid in execution, is  nearly the same as
  that described in p. 355 for determining the technical value of black oxide of man-
                                      I I 1 
 434 CONSTITUTION  OF  THE  BLEACHING  SALTS.

 ganese by means of copperas (green sulphate of iron).  The proportion and meth-
 od ol testing which I employ are as follows: 390 grains of clean and dry crystals of
 green sulphate of iron are to be dissolved in as much water as will bring ihe solu-
 tion to the volume of 5000 grains  of water.  On the other hand, 100  grains of the
 chloride of lime a*-e to be diffused  through 1010 grains of water, and the solution of
 copperas is to Le added thereto, until the presence of a trace of the protosulphate of
 iron in excess is indicated, by the mixed  liquor striking a full blue colour when a
 drop of it is placed on a slip of paper, imbibed with red prussiate of potash.  The
 quantity of chlorine present in the 100  grains of the bleaching powder is ,/Tr,thoi' the
 quantity of the standard copperas liquor employed; thus, if 27t-3 grains measure of
 the volume of the solution be found necessary, the sample contains 27 Ki of chlorine
 per cent.  For the 2783 of liquor  contains 217 grains of sulphate of iron, which is
 peroxiciized by the action of 27*6 grains of chlorine; here, also, the limit of error need
 not exceed one half per cent. Other processes have been proposed, founded, some
 on the change of yellow prussiate into red prussiate of potash, by means of the chlo-
 rine of the bleaching powder; and others,  by decomposing the bleaching powder by
 means of an excess of water of ammonia,  and measuring the nitrogen gas evolved;
 but these are  more troublesome  and less exact than the processes already detailed
 which are those most worthy of confidence from the manufacturer.
   As to the theoretical nature of bleaching powder, chemists are
 not as  yet  able to decide  positively.   The original and simple idea
 of a direct  combination between the chlorine and  the lime  has been
 revived by  Millon, who advanced that, by decomposing the salts of
 lead, iron,  and copper by solution of chloride of lime, precipitates
 were obtained, which were compounds of the protoxide of the metal
 united  with as much chlorine  as  was equivalent to the  oxygen ne-
 cessary to  form peroxide. Thus, that with lead, a chloroxide Pb.O.
 CI.; that with  iron, a  chloroxide  Fe202Cl.   The  chloride  of  lime,
 Ca.O CI., would thus be equivalent to deutoxide of calcium, Ca.0.0.
 It has  been found, however, that the evidence is not yet satisfac-
 tory.   The peroxide of potassium is  K 03, while chloride of potash
 is not K.O.CL, but K.O.C1.  The composition  of all these bleaching
 compounds appears to be  an atom of chlorine united to an atom of
 a protoxide, and this may  be explained by supposing a hypochlorite
 and a metallic chloride to  be  formed ; thus  2Ca.O. and  2C1. may
 give Ca.O. + Cl.O. and Ca.Cl.   But, if this happens, the chloride of
 calcium certainly remains  combined,  forming  a double salt; for the
 bleaching powder, if properly  prepared, has  no tendency to  deli-
 quesce, and only  becomes damp when long kept * and  then  chlorate
 of lime and free chloride of calcium are formed, and all its bleach-
 ing  qualities  are lost.   There  are thus two views equally  tenable:
 first, that  the bleaching compounds  are chlorides of oxides, corre-
 sponding to peroxides; and, second,  that they are double salts of a
hypochlorite with a chloride ;  but there is no  reason to consider
that the chlorous acid, C1.04, comes into play in their manufacture,
although the salts of that acid, when otherwise prepared, do possess
bleaching properties.

                        Salts of Magnesium.
  Chloride of Magnesium—Mg.Cl.; Eq. 600 9 or 48.16—may be ob-
tained in  solution by acting  on  the carbonate of magnesia with mu-
 riatic acid ; by evaporation, it may be  obtained  in prisms with 6
 Aq., which  are very deliquescent.  These  crystals cannot be de-
 prived  of water without total decomposition,  the chlorine passing
 off as muriatic acid, and magnesia remaining behind.  The chloride
 may, however, be obtained anhydrous, by previously mixing its so- 
SALTS  OF  MAGNESIUM  AND  ALUMINUM.    435
  lution with sal ammoniac, with which it forms an anhydrous double
  salt, which, when heated to  redness, gives  off sal  ammoniac, and
  the pure chloride of magnesium remains melted, and forms a 'clear
  crystalline mass when cold.   The chloride of magnesium  exists in
  sea-water.
    Sulphate of Magnesia.—Mg.O. . S.03.  Eq. 759*4 or 50*8.  This salt
  exists abundantly in saline mineral springs, as those  of Seidlitz, Sel-
  ters, and Epsom, from whence it derives its common name of Epsom
  salt.  It is  extracted  principally from  the  magnesian limestone,
  wbich is calcined, and the mixed  lime and  magnesia treated  with
  dilute sulphuric acid ; the sulphate of lime, being°very sparingly sol-
  uble,  is easily separated  from  the sulphate of magnesia by washing
  with water; the  latter is dissolved out, and the liquor  evaporated
  and crystallized. A great deal is also made from the mother liquor
  of sea-water, or bittern (p. 426).  This is decomposed by sulphuric
  acid,  and the salt formed separated by crystallization.
    The sulphate  of magnesia crystallizes  in  eight rhombic prisms,
  as in  the figure, containing  seven atoms of water,
  of which one is constitutional, and the other  six
  crystalline ;  its formula is therefore Mg.O. . S.03.
  H.O. + 6 Aq.; when heated to  212'  it easily aban-
  dons the 6 Aq., but retains the seventh atom of wa-
 ter even at 400'.  It combines with  the sulphate
 of potash to form a double  salt, (Mg.O. . S.03 + K.
 0.. S.Oa) -(- 6 Aq., the atom of constitutional water
 being replaced by the alkaline sulphate.  The sul-
 phates of soda and of ammonia act in the same way.
  Nitrate of Magnesia. AI-.O.. N.05) is very soluble and deliquescent.  It cannot be
 obtained dry, as it crystallizes with six equivalents of water, of which five are ex-
 pelled by a moderate heat, and by a higher temperature the nitric acid itself passes
 off and magnesia remains behind; Mg.O.. N.05. H.O. producing Mg.O. and H.O..

  The Borate of Magnesia constitutes the mineral boracite. whose electrical and
 crystalline properties have been already noticed.
  Then- exists a great number of combinations of silicic acid with magnesia, con-
 stituting the steatite, or soapstone; the meerschaum, of which pipe-bowls are cut; oli-
 vine and serpentine., which exist abundantly in the green marble of Galway:  these
 are simple  silicates of magnesia;  others, as amphibole and pyroxene, are double sili-
 cates of magnesia and lime, more or less replaced by protoxide of iron.

                         Salts of Aluminum.
  Chloride of Aluminum.—A12C13.  Eq. 1670*3  or 133-84.  In a hydrated form this
 salt may be prepared by dissolving alumina in muriatic acid, a solution  being ob-
 tained, which, when evaporated, yields very deliquescent crystals, containing twelve
 atoms of water  On applying  heat to this, the salt itself is decomposed, muriatic
 acid is  given off, and pure alumina remains.  The dry chloride of aluminum is
 lonned only by a process analogous to that described for chloride of silicon p  323.
 Pure alumina is mixed with lampblack and  ignited in a porcelain tube  while a
 stream of dry chlorine is passed over it: the oxygen of the alumina combines  with
 the carbon, and forms carbonic oxide, and the chlorine combines with the aluminum.
 The resulting chloride, being volatile, sublimes, and is condense^ in the cool portion
 ol the tube, which is allowed to project some distance beyond the furnace for that
 purpose, or a wide glass tube is adapted to receive the salt.
  The chloride of aluminum thus formed is a pale-green crrstalline mass.   Exposed
 to the air, it fumes and deliquesces.  Once combined wim"water, it cannot be freed
 from it.   It is used m obtain metallic aluminum, as described p. 349.
  The Fluoride of A: minvm is  found in the mineral kingdom.  The beautiful gem,
the topaz, is a double fluoride and silicate of alumina.
 
436
MANUFACTURE  OF  ALUM.
  Sulphate of Alumina (A1203 + 3S.03) + 18 Aq. —This salt is obtain-
ed by dissolving alumina in dilute sulphuric acid ; it has a sweetish
styptic taste, is°very soluble in water, and crystallizes in thin flexi-
ble plates; when  heated, it abandons its  water, and  at a red heat
its  sulphuric acid, alumina remaining pure.   The  sulphuric acid
unites with alumina in many other proportions, of which that con-
stituting the mineral aluminite is the most important; its formula is
Al20j + S.03 + 3 Aq., the base, acid, and water each containing the
same quantity of oxygen.   This salt is produced, also, by adding
an excess  of caustic ammonia to a solution of alum ;  hence caustic
ammonia cannot be used to prepare pure alumina (p.  351).
  The  sulphate of alumina combines with the alkaline sulphates to
form the  remarkable double salts, the common alums.   The most
ordinary kind is the double sulphate of alumina  and potash, the for-
mula of which  is (K.O.. S.03+Al203 + 3S.03) + 24 Aq.
  From the large quantities of this salt employed in the processes of dyeing, its man-
ufacture is conducted upon the great scale.  In the coal districts, and underlying
the beds of good coal, strata of clay-slate are generally found, containing a  certain
quantity of coally material, and, through which abundance  of bisulphuret of iron is
disseminated in the instable rhombic form  (see p. 332 and 358).  When this alum
slate is exposed to the air, the sulphuret of iron rapidly absorbs oxygen and forms
copperas, with an excess of sulphuric acid, which reacts on  the clays, with the
alumina of which it combines.  This effect is accelerated by the application of heat,
which is applied  by building up  the mineral into pyramidal heaps, with some fuel
underneath,  and channels through the interior, by which a draught may be establish-
ed ; the fuel below being set on fire, the slate contains coal enough to maintain its
own combustion, and the mass changes in colour as it burns, becoming brick red;
according as the process is carried through, successive quantities of mineral are ad-
ded to the burning heap, until it often acquires a height of sixty or eighty feet.  When
the mass thus calcined has become quite cold, it is powdered and lixiviated with
water; a large quantity of sulphate of alumina and sulphate of iron dissolve out,
and the liquor is brought by evaporation to a certain degree of strength.  A solution
of some salt of potash is then added, generally the waste chloride of potassium from
soap-boilers, and the sulphate of iron being decomposed, forms sulphate of potash,
which unites with the sulphate of alumina, and crystallizes out as alum, while the
iron remains as chloride in the liquor.
  In some volcanic countries, as Italy, a mineral is found already containing potash
and sulphuric acid united to alumina, from which is obtained a very pure alum,
rock-alum, which is valued very much by dyers, on account of its total freedom from
sulphate of iron, of which  English alum generally contains a small trace, which in-
jures the colours of the dyes.
  Alum crystallizes  in regular octohedrons, the solid angles  being
often replaced by the surfaces of a cube.  When heated, the  water
is first expelled, and at a red heat it  parts with most of its sulphuric
acid, sulphate of potash and pure alumina remaining.  The taste of
alum is sweet  and astringent; it  reacts acid, and is soluble in 18*4
parts of cold, and in 0-75 parts of boiling  water.  A remarkable py-
rophorus,  that of Homberg, is prepared from  alum ; three parts of
dried alum and one of lampblack well mixed are  to be placed  in a
stout glass bottle, and, being bedded with sand  in a crucible,  are to
be  carefully  heated to redness, until  a blue flame appears  at the
mouth of  the bottle;  when this has lasted a few minutes, the bottle
is to be stoppered with a bit  of chalk,  and the whole cautiously
cooled.  The  bottle  contains a black powder, a  mixture  of lamp-
black,  alumina, and  sulphuret of potassium, which last, being in  a
state of exceedingly  minute division, takes fire when a little of the
product is shaken out of tbe bottle, and emits considerable light.
   Basic Alum.  Cubical Alum.—A1203 . 2S.03+K.O. . S.03.  Thia 
GLASS  AND  PORCELAIN.
437
gubstance, which is preferred as a mordant to ordinary alum, is pre-
pared by adding carbonate of potash to a solution of alum,  as long
as the precipitate which first forms is  redissolved by agitation.   It
crystallizes in cubes which have no acid reaction.
  The sulphate of soda combining with sulphate  of alumina, forms
the soda alum, which is not much used.   The ammonia alum will be
hereafter noticed.
  The Phosphate of Alumina constitutes a remarkable mineral found in Cork and
Tipperary, the wavellilc.
  The simple and double silicates of alumina constitute probably the majority of all
known minerals; such of  them as possess technical or pharmaceutic value are
noticed under the heads of the uses to which they are applied. For a description of
the others, I refer to the ordinary works on mineralogy.
  One substance, however, of which the constitution is very  curious, may, from its
technical importance, here be noticed, the Uipis-lazuli, ultramarine.   It  is found in
veins in igneous rocks in Siberia, but particularly in China.  It is of a rich  blue
colour, not crystalline, and being powdered, serves in painting as the  richest and
most permanent blue ; its composition has been found to be, in 100 parts, silica, 358;
alumina,  318; soda, 232;  sulphur,  31; carbonate of lime, 3-1: it is difficult to de-
duce a formula from these, numbers, and the state  of combination of the sulphur is
not well understood.  Attempts  at imitating the composition of this body have been
partially  successful, and  a  large quantity of artificial ultramarine is now made for
painters' use  by the following process: freshly precipitated silicic acid and alumina
are mixed with sulphur in  a solution of caustic soda, all in  the proportions above
given, and the mixture dried down;  the resulting mass is placed in a covered cruci-
ble and exposed to a white  heat; it  gives a dark and pure blue mass, to which, for
the perfect bringing out of the colour, the air must have had partial  access during
its ignition.  The product  is reduced to impalpable  powder by the same process
adopted for the native substance.
                Constitution of Glass and Porcelain.
  I deferred  the description of  the silicates  of  potash, soda,  and
lime, because they stand so closely allied with the silicate of alumi-
na,  in relation to the  important  manufactures of glass and earthen-
ware, that  their  properties  could only  be well  understood when
studied in  connexion with it.
  Silicic acid combines with the alkalies  in  many proportions, of
which those that contain  a considerable  excess of base  are  soluble
in water.   Thus is prepared the liquor of flints, by melting together
one part of powdered  quartz  and  two  of carbonate of potash ;  the
carbonic acid is expelled,  and a glassy mass is obtained, which  de-
liquesces in the air, and is  very soluble  in water.   It reacts strongly
alkaline, and  gives, with acids, a precipitate of silica in its  soluble
form, as described p. 321.   In this preparation, soda may be substi-
tuted for potash  in a  proportion one third less,  and  a  mixture of
seventy parts of carbonate of potash, fifty-four of dry carbonate of
soda, and 152 of fine quartz sand, gives a still more fusible and sol-
uble product.  This  substance, under the  name of soluble glass,
has been employed to render wood incombustible, several coats of
a strong solution  of it  being applied under the paint.
  When the quantity' of  silicic acid is greater, the resulting alkaline
silicate  is insoluble in  water,  and possesses  the qualities which give
to glass its peculiar value. These are, first, to solidify,  after bein»
melted, very  gradually,  and  to pass through a condition  of pasti-
ness, which admits of its being blown out, cut, and fashioned in  ev-
ery way ; and, second, to  remain, when solid, quite transparent, and
destitute of any tendency  to  crystalline structure.   Its composition 
438
MANUFACTURE  OF   GLASS.
 should  also be such as to  resist completely the  action  of air and
 water.
   The materials  used  in  the manufacture of glass are,  1st, quartz
 sand, as free as possible from iron ;  2d, lime, used sometimes pure,
 sometimes slacked ;  occasionally chalk is employed in place of lime ;
 3d, carbonate of potash (pearl ashes of commerce) ; 4th, carbonate
 of  soda, or a salt of soda,  as Glauber's salt  or common salt ;  5th,
 old  broken glass, technically termed  cullet; 6th, red lead, which
must be extremely pure ;  and for corrective purposes, arsenious acid
sometimes, but more frequently  black oxide of manganese.
  These materials are by no means all employed together;  the composition of va-
rious kinds of glass differing very much, as is shown  in the following table of th«
best analvses of glass.
	Hard wlu.e 1 CrovrnGlia Bottle GIiss.						Lrjs-		
Constituents.							No. 7. 59 2		
	No 1.	No. 2.j No. a.		No 4. No 5. 69*2 60-4		No. b 53-5		No. 8. 51 9	No. 9.
Silicic Acid . . .	71 7	692	62-8						42 5
	12 7	15-8	221	8-0 3-2		5-5	90	13-8	11 7
	2 5	30		30 . .					
	10-3	7*6	12-5	130 20-7		29-2			0-5
Alumina ....	0-4	1-2	)	3-610-4		60			1-8
		20	V2G	06	0-6				
Oxide of Iron . . .	03	0-5	s	16	3-8	5-8	0-4		
Oxide of Manganese	0-2						10		
							28-2	333	43-5
	98-1	99 3	1000	990	991	1000	978	99 0	1000
  Although in some of these analyses a slight loss occurred, yet they are sufficiently
 accurate lor  all purposes.  No. i is  the hard Bohemian glass, so valuable to the
 chemist, from the high temperature it bears without softening.  No. 2, also a Bohe-
 mian glass, is much more  fusible, and is  that in  ordinary use.   No. 3 is English
 plate, and No. 4 German plate glass.  Nos. 5 and  6 are both French.  Nos. 7 and
 8 are English glass for table use and chemical apparatus ;  and No. 9 is the glass so
 celebrated for optical purposes, made by Guinaud.
  It is difficult to trace any definite relation between the  acid and bases in  these
 glasses;  indeed, we cannot look upon the different silicates  as being really combined
 with each other; they are rather in a state  of intimate mechanical mixture; hence,
 if the glass be kept soft, but not liquid, for a considerable time, the silicates gradu-
 ally separate; the less fusible crystallizing, and rendering the glass opaque white.
 This takes place most easily with such glass as contains  much silicate of lime oi
 alumina.  In this form, the  mass is so hard as to strike fire with steel, and becomes
 almost infusible. From the name of its discoverer, it is termed Ren lemur's Porcelain.
  The arrangement of the furnaces for the manufacture of glass varies according to
 the materials and the kind of product. The materials, reduced to the state of very
fine powder, are intimately mixed, and fused  in crucibles of very refractory clay.
 The silica decomposes the carbonates of lime and potash or soda, and, expelling the
carbonic acid, combines with the alkali  and earth.  If sulphate of soda had been
used, a certain quantity of carbon is added, by which the sulphuric acid is decom-
posed, sulphurous and carbonic acids being evolved (p. 292), otherwise the silica
 could not completely expel the sulphuric  acid.  From the presence of minute quan-
tities of protoxide of iron in the materials, the glass  has. at first, a pale-greenish tint,
which is counteracted by the addition of a little nitre or arsenious acid, these agents
giving oxygen to the iron, which does not colour when peroxidized; with the latter
body the metallic arsenic is evolved in vapour, the  bad effects of which should pre-
vent its employment.  More generally peroxide of mangtincx: is used, which, acting
on protoxide of iron, produces peroxide of iron and pmtoxiflc of manganese, neither
of which bodies  gives any sensible tint to glass.   ]f then-  be too much manganese
employed, the glass acquires a violet tint.   There  is  reason to suspect that soda
glass is greenish even when absolutely free  from iron.
  The general arrangement of a glass furnace may be illustrated by reference to the
figures, which  represent the essential parts of one of the most perfect forms employ-
ed in the manufacture of the  fine crown glass of  Germany.  In the oval furnace
A. which is covered by a dome, the crucibles are arranged  "in two rows, on banks, 
MANUFACTURE   OF  GLASS.
439
of which one is represented in the sectional figure.  These crucibles are left open,
but  if employed for a glass
containing lead, they should
be covered by  a hood, pre-
senting only an aperture ex-
ternal to  the   furnace  for
the  workman,  as the glass
would require to be thus pro-
tected from the smoke and
combustible gases of the fur-
nace,  which would  reduce
the lead  to the metallic state.
Heiween the banks is a rec-
tangular space for the fire,
resting on the  gratings b b,
which are separated  by the
partition wall  F, and have
apertures at the sides for the
introduction of the fuel.  By
means of the passage D, there is access beneath the grate for the purpose of clearing
it, and the draught is regulated  by the opening  or closing of the  doors e c.   The
flame of the fuel, which should  be either wood  or a very bituminous  coal, issues
partly through  the apertures in front of the crucibles o o, and partly  passes by g into
the  wings  and  chimney; by means of the wings, a great quantity of the heat is
economized for preparatory operations.  Next the furnace are placed the fresh cru-
 cibles e e, which, being always made in the glass-house, are there dried, baked, and
 ultimately brought to a full red heat, so as to be fit for introduction into the furnace
 with a charge of glass.   The draught passing in the direction of the arrows over
 the low partition, the flame and hot air acts on the space k, on the floor of which are
 spread the materials for the next charge of glass, well mixed, and introduced by the
 apertures 11; these being brought to a dull red heat, undergo a commencement of
 vitrefaction, and are thus fritted, or prepared for the perfect combination  by fusion
 in the  crucibles.   This operation  of fritting was formerly  performed in a separate
 reverberatory furnace.   The draught escapes partly from the small chimney x; but
 a portion of the hot air, having passed over  the partition m, is conducted into the
 chamber w, which  is filled with wood supported on the grating; the hot air, in  pass-
 ing off, carries  away the moisture of the wood, which is thus brought to a state of
 perfect desiccation, so as to give the greatest  possible effect in the furnace.
  For  the perfect  combination of the materials, and  obtaining  a mass  free  from
 streaks and air-bubbles, it is essential that the glass should be  brought into a state
 of perfect  liquidity, so as to allow the gases to pass off freely,  and then be suffered
 to cool until it acquires the pasty consistence which fits it for being worked into the
 necessary forms.   In  thus cooling  down, however,  those glasses which contain
 oxide of'lead frequently separate into two or more layers of glass of different den-
 sities, which, when stirred up by the tools of the workman, give by their  imperfect
 mixture a clouded  and streaked appearance to the articles made from such  glass.
 This impcfeciion is peculiarly fatal to glass for optical purposes, as each layer may
 have a different refractive power, and thus give distorted images.
  The (jreat use of glass in the arts and in ordinary life depends  upon its  plasticity
at a red heat, which renders it capable of being moulded into every form; its insol- 
440
COMPOSITION  OF  CLAY.
 ability in water; its resisting the action of acids and the generality of chemical re-
 agents under all ordinary circumstances; its transparency and lustre, and the rela-
 tions to heat, to light; and to electricity, which have been already fully noticed, from
 the low conducting power of glass lor heat, thick portions of it are liable to bieak
 when suddenly warmed, the part to which the heat is diiectly applied expanding, and
 thereby.separating from that -which^remains cold.  When a lump of glass is sudden-
 ly cooled, as by being laid, while soft, on a plate of cold iron, or being dropped into
 water, the internal portions being prevented from contracting, remain in a stale of in-
 stable arrangement, on which depends its double refracting and polarizing propeities
 (p. 230).  When the molecules of such a piece of chilled glass are made to vibiate, by
 being scratched, or a little fragment being broken off; they change totally their dis-
 position, and, flying asunder, the mass crumbles into powder with an  explosion.
 Prince Rupcn's arops, with which this property of glass may be exemplified, aie pre-
 pared by taking up on an iron rod a little melted glass, and allowing the drops of it
 to fall into a vessel of cold water; when one is held in the hand, and the long pro-
 jecting tail broken off, a smart blow is felt with a dull noise, and the drop is found
 to be reduced  to fine powder.  As this excessive frangibility would render glass un-
 fit for most household and chemical purposes, it is necessary to lessen it as much as
 possible, which is done by allowing  it  to cool very slowly.   For this purpose, th«
 vessels, when formed, are placed in the annealing furnace, or leer, which is a long gal
 lery containing a number of iron trays moveable along it by means of an endless
 chain ; the hot glass articles  are placed in the trays at one end, where a strong fire
 is made, the flame of which sweeps to a certain distance into the gallery.  Accord-
 ing as new trays come up, those already full are  drawn down into the cooler part
 of the gallery by the chain, and finally issue at the other end quite cold.  Ihe pas-
 sage down occupying from twenty-four to forty-eight hours, the particles of the glass,
 in cooling, have time to assume their most stable arrangement, and may then be ex-
 posed, if not  very thick, to changes of temperature, provided they be not very
 sudden.
   The specific  gravity of glass varies with its composition from 2*4
 to 3*6, the latter being that of flint glass, containing 40 per  cent, of
 oxide of  lead.   The lighter glasses  are  generally those which are
 hardest,  and  resist the  action  of water and of reagents best.  The
 oxide of lead in flint glass is acted  on by a variety of chemical sub-
 stances, which unfits it for many  laboratory  uses.  Where  alkali
 predominates, the  glass is rapidly acted on  by  the  air, attracting
 moisture, and  thus frequently  embarrassing electrical experiments.
 Bottle glass which contains much alumina is so rapidly corroded
 by the cream  of tartar in wine, as sometimes to become  opaque,
 and spoil  the  wine  in the  course  of a few clays.
  I have had frequent occasion to notice the various coloured glasses produced by
 the addition of metallic oxides  (see p. 37); on this principle is founded the art of
painting on, or staining glass, and also the manufacture of artificial gems.  These
arts I shall have to notice farther on, and any detail of their methods would be foreign
to a work like the present.
   The manufacture  of porcelain and earthenware depends on two
principles, first, that of the plasticity and fusibility of clay, and, sec-
ondly, the fusibility of a glass by which the  substance of the porous
clay  may  be imbibed, and thus  rendered water-tight.   Clay, when
perfectly pure,  is a neutral  silicate of alumina, Al203-|-3Si.03; but
as the great deposites of clay used  for the purposes of the  arts are
produced  by the weathering (decomposition) of a variety of rocks,
a number of foreign ingredients are intermixed  in  smail quantity,
and produce varieties which influence very much  the proportions
used  in the  manufacture.   The purest porcelain clay  is formed by
the decomposition of the feldspar contained  in  granitic  and  syenitic
rocks. The feldspar  has the formula K.O..  Si.O...-HAlA+3'Si 0,) i
by the action of water, the silicate of potash is dissolved out as sol-
 able  glass (p. 437), and the  silicate  of alumina remains  as a  fine 
MANUFACTURE  OF  EARTHENWARE.       441
powder, perfectly white, impalpable,  forming with water a  paste
capable of being moulded into any form, and, when heated, abandon-
ing the water and  contracting  in  volume, but  retaining the form
which had  been  given to it.   The pure porcelain clay is seldom
found, and hence is used only for the  finest objects; other clays of
greater or less purity are therefore  used, either alone, or mixed with
porcelain clay, for such objects as stone-china and delft; and clays
in which a quantity of alumina is replaced by  iron, and which, con-
sequently, when burned, assume a red or yellow colour, are em-
ployed for common earthenware.   In  the clays  which contain very
little  iron, and hence burn white, there are present, almost univer-
sally, certain quantities of alkali, remaining from  the decomposed
feldspar;  this  is  generally  potash,  but may be soda when the clay
is formed from albite (Na.O.. Si.O +3Ali03-f-3Si.03) ; and when  the
source of the clay is not a pure granitic rock,  the associated miner-
als generally yield a  certain quantity  of lime  which mixes with it.
Hence the composition of the following clays,  from various  coun-
tries,  used in the manufacture of porcelain, can easily be account-
ed for:
Clay from	Mnrl. 7142"	Schnee-berg.	Limogrs.
Silica ....		436	46-8
Alumina . . .	26 07	37 7	373
Lime ....	0 13		
Potash ....	045		25
Water ....		120	130
Oxide of Iron . .	1 93	1*5	
   If  clay alone were  used in the  fabrication  of earthenware, al-
 though, from  its plasticity, it would assume perfectly the required
 form, yet, from  its infusibility, it would, when baked, have so little
 coherence, and, from its  great contraction, be  so  liable to crack,
 that in  practice it could  not be beneficially employed.   The paste
 of which the china and delft articles are made, consists, therefore,
 of clay, to which is added silica, lime, and potash—in other words,
 the constituents of crown glass— which, being fusible at a hio-h tem-
 perature, cement together the particles of clay, and enable the dif-
 ferent portions  of the  vessel  to  hold together during  the bakings.
 Thus, to form the body of ironstone chinaware, forty parts of Dev-
 onshire  clay are mixed with  from  forty to sixty of feldspar, and
 generally about  five parts of flint glass and ten of quartz.
  It would not be within the  object of the present work to detail the mechanical pro-
 cess of fashioning articles of earthenware.  When formed, they are first dried in the
 air, and then heated moderately, to expel as  much water as will fit them for the re-
 ception of the glaze.  This consists in covering them perfectly with a sheet of easily-
 fusible glass, which, by entering into all their pores, and varnishing their surface,
 renders the vessels impervious to water;  the glassy constituents of the paste having,
 in quantity and fusibility, only sufficient.power to cement the particles of the clay
 together,  without  depriving, the mass of its porosity.  The composition of the glaze
 may vary much in different  establishments; an ordinary onej for ironstone china,
 consists of feldspar 36, quartz 20, white lead 40, flint glass 8. These materials are
 flitted  together, and then, being reduced to impalpable powder, are diffused through
 water,  into which  the vessel to be glazed is dipped, and is then taken out again.  The
 clayey substance  of the vessel rapidly imbibes the water, and the fine powder of the
glaze remains uniformly spread upon the surface.  The articles so prepared are ar-
ranged in capsules of a very  refractory ware, and placed in the kiln or furnace to be
baked.  The construction of the porcelain kiln is represented in the figure.  It is a 
442 BAKING  AND GLAZING  OF  EARTHENWARE.
vaulted building, generally of three stories, provided with five fireplaces, from which
                                              the flames pass into the
                                              kiln by the passages b, m,
                                              a,  p, marked with the ar-
                                              rows ; from the third story
                                              the chimney  issues.   The
                                              highest floor  is reserved
                                              for drying the capsules in
                                              which the articles to be
                                              baked are arranged; on the
                                              floor of the second, the ar-
                                              ticles are dried to the de-
                                              gree which fits them for the
                                              reception of the glaze; and
                                              in  the lowest chamber, by
                                              the full action of the fire,
                                              the final baking is perform-
                                              ed. The  operation  com-
                                              mences, first, with a moder-
                                              ate fire, the fuel being in-
                                              troduced into the cavity A,
                                              and supplied with air by
                                              the apertures  e s; the heat
                                              being allowed to rise grad-
                                              ually for six or eight hours,
                                              the space becomes full of
                                              ignited fuel, and a strong
draught is established.  The apertures are then closed, fuel (and for this, as for
glass-making, wood answers best) is heaped on the rest b, and the air admitted to
the kiln only after having passed through h.  The temperature is thus kept uniform-
ly intense for seventeen or eighteen hours, and then, the kiln being allowed to cool
slowly for three or four days, the articles are extracted in their finished state.
  The  glaze on earthenware  being a transparent glass, it may be
coloured by various metallic oxides, and thus the patterns produced
which give  to the finer kinds of ware so  much popularity.  The
coloured glass, being reduced to fine  powder, is mixed up with oil
of spike, and  either laid on with a  brush,  as in ordinary painting,
or printed, in  a very ingenious manner,  by having the  pattern  en-
graved on copper, and printing it with the  glaze made with oil into
a very thin ink on damp tissue paper.   The paper with the figure
thus formed is laid  evenly on the vessel, which, from its porosity,
immediately absorbs the liquid materials of the ink, and leaves the
powder  of the glaze on  the surface in all the fine tracings of the de-
sign.  The paper  is then  cautiously rubbed off by  the  finger in a
vessel of cold water, and the  uniform glazing  applied  over all, as
before described.   The blue patterns  are produced by cobalt;  the
black by a mixture  of oxides  of iron  and manganese; the crimson
by  gold;  and gold and platina are applied also in their metallic
state, by dissolving their chlorides in oil of turpentine,  and apply-
ing this varnish with a  pencil, then burning, and burnishing the me-
tallic surface.
  A coarse kind of glazing,  given to the common articles of earth-
enware, is produced by  throwing into the kiln,  when  intensely hot,
a few handfuls of common salt; by  means of the watery vapour
produced by the combustion of the fuel, the silicic acid on the sur-
face of the earthenware  decomposes the common salt, which is con-
verted into vapour by the  heat; Si.03 with  Na.Cl. and H.O., produ-
cing Na.O. .  Si.03, which forms a transparent glassy varnish on their
surface, while H.Cl. passes  off with the  excess of watery vapour,
forming copious white  fumes. 
SALTS OF  MANGANESE.
443
   The general characters of the salts of glucinum, thorium, yttrium, zirconium, lan-
 thanum, and cerium have been noticed under the heads of these respective metals
 (p. 351, et seq.), and do not require farther detail.

                        Salts of Manganese.

   Manganese may give  origin  to  four  classes of salts, in  two of
 which it  constitutes  the base, and in the others forms an element
 of the acid ;  these last, the manganates and permanganates, have been
 noticed in p. 356, and it remains only to describe the former.
   Protochloride of Manganese.—Mn.Cl.-(-4 Aq.  Eq. 788*5+ 450 or
 63* 19 -f- 3(i.  This salt maybe obtained by digesting the commercial
 black oxide in muriatic acid until all the excess  of  chlorine has
 been expelled, then evaporating to dryness, and fusing the mass, at
 a bright red heat, in a crucible.   The chloride of iron, which is form-
 ed by the impurities of the ore, is decomposed by  the  last portions
 of water, and muriatic acid being given off,  oxide  of iron remains.
 Hence, on digesting the melted mass in water, protochloride of
 manganese dissolves, and all  the iron remains insoluble.  The solu-
 tion, which is of a pale pinkish tint, is to be evaporated, and the salt
 crystallized.  The crystals  are  rhombic  tables, rose coloured; by
 heat they lose their water of crystallization, but are not otherwise
 altered.   It is known to  be free from iron when its solution gives,
 with yellow prussiate of  potash, a pure white precipitate.
   Perchloride of  Manganese, Mn.Cl2, appears to be formed when
 strong muriatic acid is digested on peroxide of manganese without
 heat.  A  gentle heat resolves it into protochloride and free chlorine.
   Protosulphate of Jlanganese.—Mn.O. . S.03-|-7 Aq.  This salt may
 be obtained pure  from the commercial oxide by mixing this  into a
 thick  cream  with oil of vitriol,  and heating it in  a  shallow dish
 until it becomes quite dry, oxygen  being given off.   The dry mass
 which contains the mixed sulphates of iron and manganese is to be
 then placed in a crucible, and heated to bright redness ;  the sulphate
 of iron is decomposed, its sulphuric acid being expelled by the heat;
 but the sulphate of manganese  is not altered, and on digesting the
 resulting  mass  in water,  dissolves, and is obtained crystallized by
 evaporation and cooling.   This salt crystallizes in oblique rhombic
 prisms with 7 Aq., but is  also found with 5 Aq. and with 4 Aq., its
 form changing in each case.   In all, one equivalent  of water is con-
 stitutional, and may be replaced  by an alkaline sulphate, with which
 the sulphate of manganese forms double salts, like those of sulphate
 of magnesia.                                                 s
  Sesquisulphate of .Manganese,  Mn,03-f 3S.03 may  be obtained by
 dissolving  the sesquioxide in sulphuric acid.  The solution is of a
 rich crimson colour : when  heated, it  becomes colourless,  giving
 off oxygen, and it is instantly bleached by sulphurous  acid or any
 deoxidizing agent.  Its most  important property is  that of forming
with the sulphate of potash or of  ammonia double salts, crystallizing
in  octohedrons,  which are manganese alums, similar  in constitution
to  the  ordinary alum,  but with A1203 replaced by Mn203.
  No other salt of manganese requires special notice. 
444
SALTS  OF  IRON.
                           Salts of Iron.
   There are  two series of iron salts, corresponding to the two ox-
 ides, proto-sults and sesqui-salts.
   Protochloride of Iron.—Fe.Cl.-J-4H.O.   This salt is formed when
 metallic iron  is dissolved in muriatic acid, hydrogen being evolved;
 the solution, which is of a pale bluish-green colour, yields, on evap-
 oration, rhombic crystals of the hydrated chloride, which are slightly
 deliquescent.   This solution absorbs oxygen from the air with great
 avidity, and becomes dark-green coloured.   When these  crystals
 are heated they lose  water, and, if the air have not access, a white
 mass of dry protochloride of iron is obtained, but  otherwise per-.
 chloride  is formed and the  whole decomposed.   The  anhydrous
 protochloride is very elegantly prepared by passing a stream of dry
 chloride of hydrogen over fine iron wire, coiled up in a tube of hard
 Bohemian glass,  and heated to  bright redness:  hydrogen  gas  is
 evolved, and protochloride of iron formed, which sublimes into the
 cold part of the tube as brilliant  white spangles.   By the action of
 the air it is rapidly decomposed.
   Sesquichloride of Iron.—Fe2Cl3.  This salt is formed when iron is
 dissolved in aqua regia; a deep brown solution is obtained, which,
 when evaporated to the consistence of a sirup, gives large red crys-
 tals of hydrated chloride, which  are very deliquescent.   On the ap-
 plication of heat, this salt is totally decomposed ; muriatic acid  is
 given off, and the red oxide of iron remains behind, with some un-
 altered chloride, as a basic salt.   To  obtain the anhydrous sesqui-
 chloride, a stream of dry chlorine gas is to be  passed over iron wire
 heated  to redness in  a tube of Bohemian glass.  The iron  burns in
 the chlorine, and the  salt  sublimes into the cool portion of the tube,
 where it forms a dark olive crystalline mass, which rapidly attracts
 moisture from the air.  This salt is very soluble in alcohol.
   The sesquichloride of iron, when dissolved  along with  sal ammo
 niac,  may form a  true double salt, containing an equivalent of each
 salt ;  but the  crystals which are generally thus obtained, although
 deeply-coloured red,  contain but  two or three  per cent, of the chlo-
 ride of iron.
   Protoiodide of Iron, Fe.I., is formed by digesting iodine in wa
ter on an excess of iron filings.  Considerable heat is evolved, and
a colourless solution  is obtained, which, when evaporated, yields a
crystalline mass containing water of  crystallization, and which  is
decomposed by a farther  action of the heat, iodine being evolved.
It  absorbs oxygen very rapidly.  A solution of protoiodide of iron
dissolves iodine abundantly, becoming brown,  and possibly contain-
ing the  sesqui-iodide, FeJ3; but it is more likely that the iodine  is
not combined, as it is sensible to the test of starch.
   The bromides of Iron resemble perfectly  the  iodides.
   Protosulphate of Iron.  Green Copperas.—Fe.O. . S.03 + 7 Aq.  The
manufacture of this salt is conducted on the large scale for the pur-
poses of the arts, by exposing to  the action of air and moisture the
nodules of bisulphuret of iron, which  are found abundantly in the
strata of alum-slate-clay (p. 436).   Oxygen is rapidly absorbed both
by the iron and the sulphur, sulphuric acid and oxide of iron being 
SALTS  OF  IRON.
445
formed, and the liquor which, holding these in solution, drains from
the beds of decomposing pyrites, is run into tanks,  where it is put
in contact with pieces of old iron, which serve to neutralize the ex-
cess of acid produced from the  pyrites, being  a bisulphuret, and
also, by means of the hydrogen evolved, to retain all the iron in the
state of protoxide; after  proper  evaporation, the salt is  obtained
crystallized from these solutions.   On the small scale, it may be
prepared by dissolving iron wire  in  dilute sulphuric acid,  as in the
process for preparing hydrogen gas (page 247).   The protosulphate
of iron generally crystallizes with seven  atoms  of water,  of which
one is  constitutional, and may be replaced by an alkaline  sulphate,
forming double  salts.  The form of its  crystal is a short oblique
rhombic prism, i, u, u, with numerous secondary faces, as (3,  c, in
the fig.  Its taste is styptic and metallic; it dissolves
in 1 64 parts of water at 50\ and  in 0*30 parts at 212\
Like the other protosalts  of iron, it is  but very spa-
ringly soluble in alcohol.   When heated, it abandons
first its water, and at full red heat  its sulphuric acid,
of which a portion is decomposed into sulphurous acid and oxygen,
by which the iron becomes peroxidized.   The peroxide of iron  thus
formed is used in the arts, under the names of  rouge and  colcothar,
as a polishing material.  On these properties is founded the manu-
facture of fuming oil  of vitriol, described in page 247.  The proto-
sulphate of iron absorbs oxygen rapidly even when dry, and becomes
covered with a reddish crust of basic persulphate, whence its com-
mercial name.  In  solution, the absorption  of. oxygen  proceeds
quickly, until two thirds of the iron are peroxidized and a reddish
solution obtained, from which alkalies throw down  the black mag-
netic oxide (see page 363).  This solution does not crystallize.
  Sesquisulphate of Iron. — Fe,03+-3S.03.  Eq. 2481*9 or 198 9.  This
salt is found native  in large quantities  in Chili, combined with 9 Aq.
It may be prepared  artificially by pouring oil of  vitriol on red oxide
of iron, stirring the mass well, and applying a moderate heat to ex-
pel the excess of acid.  The salt may then  be  dissolved in water,
forming a red solution, and giving, when evaporated, a deliquescent
mass scarcely crystallized.  In this  way it retains an excess of acid,
which may be driven off by a heat just below redness.  The persul-
phate then appears as a white powder, which  dissolves  but very
slowly  in water.  By a strong heat  this salt is totally decomposed.
The protosulphate may be  converted into persulphate  by adding to
a boiling solution nitric acid in small quantities, as long as any ni-
tric oxide  gas is given off.  There are several basic  persulphates
of iron, of which the most important is the  rust-coloured powder,
which  precipitates from a  solution  of protosulphate of iron when
oxidized by exposure  to the air ; its formula is 2Fe203-{-S.03-r-3 Aq.
  The  persulphate of iron  combines with the alkaline sulphates to
form a class of alums, which contain Fe203 in place of Al ,03. These
iron alums are generally pale red in colour, but  have the form, sol-
ubility, and nearly the taste of common alum.
  Protonitrate of Iron may be formed by dissolving sulphuret of iron
in cold dilute nitric acid.; it  crystallizes  in pale-green  rhombs,
which,  when heated,  evolve nitric  oxide gas, and form a  basic ni-
 
 446     SALTS  OF  IRON,  NICKEL,  AND  COBALT.

 trate of the peroxide.  Metallic iron dissolves in dilute nitric acid
 without the evolution  of any  gas, water and  nitric acid being si-
 multaneously decomposed, and oxide of iron and ammonia produced.
 Thus N.O, with 3H.O.  and 6Fe., give  6Fe.O. and N.ll3.
   Pernitrate of Iron is produced when  iron  is dissolved in hot nitric
 acid ;  the solution is reddish  brown, and  gives,  by drying,  a deli-
 quescent mass easily decomposed by heat.  When a  solution  of
 this salt is  decomposed by carbonate of potash added in excess, the
 oxide of iron,  which first precipitates,  is redissolved, and a deep red
 liquor  obtained,  which is sometimes used in medicine under the
 name of StahVs alkaline tincture of Iron.
   Protophosphate  of  Iron, Tribasic—H.O. . 2Fe.O.-f-P.O—may  be
 formed by decomposing a solution of protosulphate  of iron with tri-
 basic phosphate  of soda.  It is a white powder,  which rapidly be-
 comes  blue by exposure  to the air,  a  portion of the iron  becoming
 peroxidized.  This  blue phosphate  of  iron is a double salt, which
 exists  in nature,  forming the bog iron  ore, and may  be produced ar-
 tificially by adding solution of phosphate of soda to the solution of
 mixed  sulphate of iron,  from which alkalies precipitate  the  black
 oxide (p. 363).   The precipitate which forms is of a rich blue col-
 our, and is not changed by exposure to the air.   Its formula is (H.
 0.. 2Fe.O. -f P.03) -f-(2Fe203. P.05).   It is used in medicine.
   Sesquiphosphate of Iron, 2Fe203-f-P.05, is  obtained by decompo-
 sing a  solution of sesquisulphate  of iron by phosphate of soda.  It
 is a white powder, insoluble  in water.   It is used in medicine.
   The  salts of the protoxide of iron  are remarkable for absorbing
 nitric oxide in considerable quantity, and forming therewith a deep
 olive-coloured liquor, which  rapidly attracts oxygen from the air.
 The quantity  of  gas absorbed  is  one  atom for two atoms of  salt,
 and the nitric  oxide may be considered as  replacing the third atom
 of oxygen, which forms the  sesquioxide.   Thus the protochloride
 gives Fe2 + Cl2. N.02, and the  protosulphate (Fe2-f-0,. N.02)+ 2S.03,
 analogous  to  Fe2-j-Cl.3 and (Fe2 +03) + 2S.03.   The utility of this
 olive liquor as a test for nitric acid  and in eudiometry, has been
 noticed in p. 264 and 281.

                     Salts of Nickel and Cobalt.
  Chloride of Nickel, Ni.Cl., may be obtained by dissolving oxide of nickel in dilute
muriatic acid, or by acting on the metal with the hot concentrated acid. It crystal-
lizes in emerald green rhombs.  When heated, it loses its water of crystallization,
and gives a yellow powder,  which by a red  heat sublimes in crystals, resembling
Mosaic gold.
  Sulphate of Nickel—Ni.O.  . S.03.  This salt  is obtained by dissolving the oxide
in dilute  sulphuric acid, or by acting on the metal with a mixture of nitric and sul-
phuric acids diluted with water; the nitric acid then supplies oxygen. This solu-
tion gives fine emerald green crystals,  which vary in form according to the quanti-
ty of water they contain.  When they form below 60°, they are long rhombic prisms,
cpntaining 7 Aq., and isomorphous  with the sulphates of zinc and magnesia; but
when formed at any temperature above 60°, the quantity of water is six atoms, and
the form  is an octohedron with a square base.  If a prismatic crystal be exposed to
a moderate heat or to sunshine, it gives off an atom of water, arid becomes oqaque
by breaking up into a number of very minute crystals of the octohedral form.  In
sulphate  of nickel one atom  of water being constitutional, may be replaced by the
alkaline  sulphates, and double salts formed, of which some are very beautiful.
   Chloride of Cobalt,  Co.CI,, is formed  by  dissolving  oxide of co-
balt, or the zaffre of commerce, in muriatic acid.  The solution is 
SALTS  OF  COBALT  AND  ZINC.           447
pinkish, and gives, on  evaporation,  rose-red crystals  of hydrated
chloride ;  if the evaporation be pushed very far, the liquor becomes
blue, and  dark blue crystals  of anhydrous  chloride are  deposited.
If the solution contains nickel, which is always the case when pre-
pared from  zaffre, the colour  becomes green,  and  it  is thus that
sympathetic  inks of cobalt  are produced, and  summer and  winter
scenes in  landscapes  alternated ;  the surface of a drawing washed
with a very  dilute  solution  of  chloride of cobalt being white until
dried before  the  fire, but then becoming grass green.
  S'dp/iale of Cobalt,  Co.* ).+S.03, is obtained by treating zaffre with sulphuric acid.
In its general characters it resembles the chloride;  when heated strongly, it gives
off sulphuric acid, and oxide of cobalt remains; it contains six atoms of water of
crystallization, and gives a double salt with sulphate of potash.
  "T/m-ip/ii/li:  of Cobnll, H.O.. 2C0.O.+P.O5, is precipitated in dark violet flocks when
solution of sulphate of cobalt and phosphate of soda are mixed together.  This sub-
stance is the basis of a very beautiful pigment, T/ix/u/ra's Blue, which is prepared by
mixing intimately one part of phosphate of cobalt  with two or three of alumina,
and exposing the mixture to an intense white heat  in a wind furnace.  The  blue
tint thus given to alumina serves as a test for that earth, particularly to distinguish
it from magnesia by the blowpipe.  (See p. 349 and  351).
   Silicate  of Cobalt constitutes the  blue smalts employed  to tinge
paper and to  colour glass ;  the finest kind is known in  commerce
as azure.  Its manufacture is conducted on the great scale in Sax-
ony and Sweden, and is the process in which most of the arsenic
of commerce is obtained,  that  being expelled in the roasting of the
cobalt ores  (p. 366, 376).   From the  zaffre  a sulphate of cobalt is
prepared,  and on the  other hand a silicate  of potash, by melting to-
gether fine  sand and carbonate of potash ;  these  solutions being
mixed, silicate of cobalt is precipitated, while sulphate of  potash
remains dissolved.  This  precipitate is the best material for colour
ing porcelain and glass;  but the ordinary smalts are formed by melt-
ing  impure  carbonate of cobalt with potash  and quartz into  a blue
glass, which is then reduced to impalpable powder, and sorted ac-
cording to the quality, for commerce.

                     Salts of  Zinc and Cadmium.

  Chloride of Zinc—Zn.Cl.; Eq.  8159  or 67 78—may be prepared by burning metal-
lic zinc in chlorine,  or by dissolving the metal in muriatic acid.  The solution is
colourless; when evaporated, it  yields rhombic crystals, which contain water, and
deliquesce with extreme rapidity.  The dry salt is white, and melts a little above
212°, so that a solution, when evaporated, never becomes solid.  It  is hence some-
times applied as a bath in place of oil or fusible metal, in taking the specific gravity
of vapours (p.  14).   From its fusibility and softness, it had formerly the name of
Batter of Zinc.   From its affinity for water, it acts powerfully as a caustic on the liv-
ing tissues, and is employed in medicine as such.
  Chloride of zinc combines with oxide of zinc in many proportions, forming oxy-
chlorides, of which there are three worthy of notice : the first, which  is long  known,
is formed by decomposing chloride of zinc by a small quantity of ammonia; its for-
mula is Zn.Cl.+3Zn.O.+1 Aq.   The second results from the  action of water on
the ammoniacal chloride of zinc; its formula is Zn.Cl.+6Zn.O.+10 Aq., and is that
whose analogies to the liquid muriatic acid have been pointed out in p. 309.  The
third is formed by acting on chloride of zinc with an excess of potash; its formula
isZn.Cl.+9Zn.O. + ll Aq.
  The bromide and iodide of Zinc resemble completely the chloride in general char-
acters : a solution of iodide of zinc is <■ ■■ n;i' >le of dissolving a large quantity of iodine.
  Sulphate of Zinc, Zn.O. .  S.0, + 7 Aq., may be  produced by dis
solving the metal in dilute sulphuric acid.  For the purposes  of the
arts, it is made upon the  great scale  by roasting, in a current  of hot
air in a reverberatory furnace,  the native sulphuret of  zinc, blende. 
448
SALTS  OF  TIN.
 The metal and sulphur both combining with oxygen, a neutral sul-
 phate  of the oxide is formed, which being then dissolved  out by
 water, the solution is evaporated to a pellicle, and allowed to crys-
 tallize.  Sometimes the blende, in place of being roasted, is exposed
 on sloping beds to the action of the air and moisture, when it grad-
 ually attracts oxygen, and is treated as  has been described under
 the  head of sulphate  of iron.   The crystals which first form are
 heated until they undergo watery fusion, and are then  poured into
 conical moulds, where they  solidify, and the salt is thus sent into
                 commerce in  masses like sugar-loaves:  its com-
                 mercial name is white vitriol.   The crystals of sul-
                 phate of  zinc  are  eight  rhombic prisms, as in the
                 figure, containing 43*9 per cent, of water, and are
                 soluble in two and a half times their weight of cold
                 water.  It is permanent  in  the  air.  It  combines
                 with the  alkaline sulphates, which  replace its con-
                 stitutional water, forming double salts, and with ox-
 ide of zinc  to  form basic salts,  of which several are  known, and
 which agree in constitution  with the oxychlorides  of zinc.  Their
 composition has been already noticed in p. 368.
  Nitrate of Zinc, Zn.O.. N.O5, is obtained by dissolving the metal in dilute nitric
 acid ; it crystallizes in flat four-sided prisms.  It is deliquescent, and soluble in al-
 cohol.
  No other salt of zinc is of importance.
  Chloride of Cadmium, Cd.Cl.. crystallizes in large four-sided prisms;  it is not de-
 liquescent.  The  other salts of cadmium resemble completely the corresponding
 salts of zinc, and do not require notice.

                           Salts of Tin.

  Protochloride of Tin.—Sn.Cl. + 3 Aq. Eq. 1177*9 + 337*5 or 94*39
 +27.   This salt is obtained  anhydrous by heating tin in  a current
 of muriatic acid gas, hydrogen being evolved ; or by distilling  a
 mixture of equal parts of tin and corrosive sublimate in a glass re-
 tort, the metallic  mercury first passes over, and,  finally, the proto-
 chloride of tin  sublimes at a strong red heat.   It forms a gray glassy
 mass.   In combination with water, it may be obtained by dissolving
tin in strong muriatic acid until it is saturated, and  on evaporation
 the salt crystallizes in long prisms, which contain three atoms of
water.   When these  crystals are heated, they first  lose water, but
 afterward muriatic acid passes off, and a  basic  salt remains.   This
 crystallized protochloride, under  the name of salt of tin, is used ex-
 tensively in  dyeing as a  mordant;  in its preparation on a large
 scale, copper vessels  may be employed, because, as long  as  any
metallic  tin is present, the copper  is electrically protected by it,
and is not acted on by the  acid.   This salt is very soluble in water,
but is decomposed by  a large quantity, a basic salt, Sn.Cl-f Sn.O.,
being thrown down ; hence, in order to have a dilute  solution clear,
 it requires the addition of a few drops of muriatic acid.  Protochlo-
ride of tin is remarkable for its affinity for oxygen and for chlorine;
it reduces the  salts of  silver, quicksilver, and°gold to the metallic
 state, and the salts of  copper, iron, and manganese  to the lowest
state of oxidation.  It  acts similarly on many organic  substances,
as indigo, litmine, orceine ; forming colourless compounds, which
 have some important applications in the art of dyeing.
 
    SALTS  OF  TIN, CHROMIUM, AND  VANADIUM.  449


   The protochloride of tin combines with chloride of potassium and
 with  sal ammoniac to  form  double salts, which were analyzed by
 Apjohn.
   Perchloride of Tin, Sn.Cl2,  is  prepared  anhydrous by  distilling a
 mixture  of four parts of  corrosive sublimate and  one  of metallic
 tin ; at a very moderate heat, a  colourless liquid distils over, which
 forms dense white fumes where it comes  into  contact with the air:
 this is the bichloride of tin, the fuming liquor of Libavius.  Metallic
 mercury remains  in  the retort.   This singular  compound boils at
 248 Fah.; the  specific  gravity of its  vapour is 9*12.   When mixed
 with one third of its weight of water, it solidifies  into a crystalline
 mass,  and it is  hence that it  forms such dense  fumes by  exposure
 to  damp air.  It may be prepared in  this crystallized  form  by  dis-
 solving  tin in  nitromuriatic  acid and  evaporating the  solution, or
 by passing chlorine into a solution of protochloride as long as it is
 absorbed.  If the  crystals  be heated,  they are  decomposed,  muriat-
 ic acid being given off, and peroxide  of tin  remaining.
  Protoiodide of Tin, Sn.L, may be formed by heating together tin and iodine, or by
 mixing solutions of iodide of potassium with a slight excess of protochloride of tin.
 It is a brownish red mass, soluble in water, and crystallizing from the  solution in
 long prisms of a bright orange colour.  It is decomposed  by a large quantity of wa-
 ter. It combines with the iodide of potassium  to form  a soluble double iodide.   The
 biniodide of tin crystallizes in yellow needles, which are decomposed by much water.
  The bromides of Tin are not important.
  Prolosulphate of Tin, Sn.O.. S.O3, is  formed when tin  is  dissolved  in strong sul-
 phuric acid.  A saline mass is obtained,  which dissolves in water, giving a brown
 solution, from which the salt crystallizes  in small needles.  Bancroft's mordant, for
 dyers, is prepared by digesting two parts of tin with three of strong muriatic acid for
 an hour, ancl then adding one and a  half parts  of oil of vitriol very cautiously.   The
 mass becomes hot, and the tin is rapidly dissolved.  The heat is to be kept up on the
 sand-bath as long as hydrogen is evolved.  The solution, on cooling, forms a crys-
 talline mass, which is to be dissolved in  water, so that eight parts of the solution
 shall contain one of tin.
  The sulphuric and nitric acids may be neutralized by freshly-precipitated  peroxide
 of tin; but these salts possess very little  stability, and are of no technical or scientific
 interest.  The peroxide of tin itself acts as an acid, and its relations -o the alkalies
 have been described in p. 371.
  The sulphurets of tin act as sulphur acids, combining with the sulphurets of the
 alkaline metals. The bisulphuret forms with sulphuret of sodium  a crystallizable
 salt, 2Na.S.+Sn.S2-f-12 Aq., sidpliostannate of Sodium.

                  Salts of Chromium and Vanadium.
  There are two kinds of salts of chrome, one  in which the  oxide of chrome is the
 base, and the other in which the chromic acid is combined with bases.
  A. Salts of Oxide of Chrome.
  Chloride of Chrome.—CviCXs.  Eq. 2031-6 or 162-8.  When oxide of chrome is mix-
 ed with lampblack, and treated  by  a current of dry chlorine at a red heat, as de-
 scribed for the preparation of the chlorides of silicon and aluminum, the  chloride is
 obtained sublimed in the cold part of the tube  in peach-blossom-coloured scales of
 exceeding beauty.  It may also be obtained by dissolving  oxide of chrome in muri-
 atic acid, and evaporating the solution; it remains as  a green mass, in which it is
 combined with 311.0.  When heated to 450°, it froths up  very much, gives off that
 n-ater, and forms a rose-coloured mass not so beautiful as that obtained by the pro-
 cess first described.
  Cihror/irimiic. Acid.—Cr.Cl3+2Cr.03.   This   singular compound  is obtained by
 in'. inng together in a crucible ten parts of  common salt and seventeen of bichromate
of potash;  the melted mass is poured out on a slab, and broken into small pieces,
 with which a tubulated retort may be filled, and after a receiver and  condensing ap-
paratus  have been attached, forty parts of oil of vitriol are  to be poured on the mass.
The decomposition occurs so violently, that in a few minutes all the product distils
 •Ver, without the application of external  heat.   This  substance is  a thin bl od-red 
450
CHROMATES OF  POTASH.
liquid, appearing black by reflected light; it fumes much by exposure to the air; its
vapour is red like nitrous acid.  When its vapour is heated to redness, it is decom
poseci, r-s descriled in p. 373.  It is decomposed by water.  Alcohol placed in con-
tact with it takes fire, burning with a bright flame; phosphorus  acts  in the  same
way   This substance may either be looked upon as a compound of perchloride of
chrome with chromic acicl, Cr.Cl3+2Cr.03) or as a compound of chlorine with a
deutoxide of chrome, Cr.02Cl.  The analogy of the sulphuric to the chromic acid
is supposed to favour this latter view, as also the sp. gr. of its vapour,  which is 59.
  S.dphate of Chrome, Cr203+3S.03, may be formed by dissolving oxide of chrome
in dilute sulphuric acid, but does not crystallize. Its only important  character is,
that it combines with the sulphates of potash or of ammonia to form  double  salts,
the c/iron.e alums, which  crystallize in dark purple octohedrons, and which contain
the same proportion of acid, alkali, and water ;;s common alum, but oxide of chrome
in place  of alumina.  The solution of chrome alum in cold water is purple, but
when heated it becomes green, and the elements of the salt are then found to Ie no
longer united, as by evaporation they may be separated. It  would appear, indeed,
that almost every salt of chrome may exist in either a green or a red condition, and
that in the former they do not crystallize.  The chrome alum is obtained abundant-
ly by setting aside for a few days the residue of the process for making aldehyd, as
described farther on.
  The Peifluoride of Chrome, Cr.F3, is formed by acting with  oil of vitriol on a mix-
ture of powdered fluor spar and bichromate of potash in a platinum retort. It is a
gas of a rich crimson colour, which can only be collected in a platinum crucible in-
verted in the quicksilver trough.  Its decomposition by water, and the consequent
formation of chromic acid, has been already noticed, p.  373.

                     B. Salts of  Chromic Acid.

  Chromates of Potash.—The manufacture of  the bichromate of  pot-
ash, K.O.-}-2Cr.03,  is carried on extensively, as it is from that  salt
that all the compounds of the metal used in chemistry or  in the  arts
are prepared.  It  is made from  the only abundant ore of chrome;
the chrome-iron, Fe.O.-r-Cr203, by the following process.   Two parts
of the ore, ground to a fine powder, are intimately mixed with  one
part of saltpetre,  or four parts of ore are used with two parts of
pearl ashes and one of saltpetre, and the mixture exposed for  sev-
eral  hours on the floor of a reverberatory furnace to a violent heat.
Under the influence of the potash, the oxide  of chrome absorbs the
oxygen from the air, and  forms chromic* acid.  The  calcined mass
is lixiviated with water, and a  deep yellow liquor is produced,  which
contains  neutral chromate of potash, which may be obtained crys-
tallized by evaporation; but as this salt is not well  suited for the
purposes  of commerce, it is generally  changed into the bichromate
by adding to the liquor a quantity of sulphuric acid, which takes one
half of the potash, and  the bichromate is then obtained by crystalli-
zation in  tanks lined with lead.
  Bichromate of Potash crystallizes in large four-sided prisms  and
square tables of a rich orange-red colour.  It melts,easily,  and in
cooling crystallizes in  another form.   It is soluble in ten parts of
cold water.   It  is not  decomposed except by a white  heat,  which
expels oxygen, and leaves a mixture of oxide of chrome and neutral
chromate of potash.
  The neutral Chromate of Potash, K.O. . Cr.O,, maybe  prepared by
t adding  to a solution  of bichromate of potash as much
           more alkali as it already contained.  It is soluble in twice
           its weight of cold water.   Its solution is intense  golden
           yellow  ; it crystallizes in rhombic prisms, isomorphous
           with those of sulphate of potash, as in the figure, of which
n, n and u, u are primary, and i, m are secondary planes. 
       SALTS  OF  TUNGSTEN,  MOLYBDENUM,  ETC.   45l


    If bichromate of  potash be dissolved in hot dilute nitric  acid  a
  terchromate of potash, K.O. . +3Cr.03, crystallizes when the solution
  cools.
    When  bichromate of potash is dissolved in rather more than its
  own weight  of strong muriatic acid, with a very gentle heat, so  that
  no clilorine   shall  be evolved, and  the liquor shall retain its clear
  orange colour, a salt crystallizes on  cooling in fine four-sided prisms,
  which is  very  remarkable in  constitution,  consisting of an  equiva-
  lent of chloride  of potassium united to two  of chromic acid, K.Cl.
  -f-2Cr.03.
    None other of the  chromates of the  metals that have been as yet
  described possess  interest.
    Vanadium is the  basis of several classes of salts, which,  however, from the ex-
  ceeding rarity of the metal, have been but little  studied.   The salts containing the
  vanadic oxide are generally splendid  blue; those containing the vanadic acid as basis
  are red or yellow, while those which contain vanadic acid as acid are colourless, or
  coloured according to the nature of the base with which it may be combined.

        Salts of Tungsten, Molybdenum, Osmium, and Columbium.

   Tungsten combines directly with chlorine in two proportions, forming the bichlo-
  ride and perchloride, according as the metal or the gas is in  excess.  Both  are vol-
  atile, and condense in red needles. They are decomposed by water, giving muriatic
  acid and tungstic oxide, W.O2, or tungstic acid, W.O3. A chlorotungstic acid exists,
  W.O2CI., analogous to the chlorochromic acid.
   None of the compounds of tungsten with oxygen act as bases.  The nature of the
 salts of tungstic acid has been sufficiently explained already  in p. 374.
   Molybdenum takes fire when heated in a stream of chlorine gas, and forms the ter-
 chloiide, M0.CI3, which crystallizes in the cold part of  the  tube in brilliant black
 scales, like  iodine.   Its vapour is dark red.  Two other chlorides of this metal, Mo.
 CI. and M0.CI2, are known to exist.
   The protoxide of molybdenum forms salts with the oxygen acids, which are pur-
 ple or black coloured, and are very easily decomposed by heat.  Thus the sulphate
 i> resolved into sulphurous acid gas and molybdic oxide.  The molybdic oxide also
 forms a series of salts, generally red coloured, which do not possess any special in-
 terest.  The molybdic acid forms two series of salts, in one of which it acts as base,
 and in the other as an acid.
   Osmium is the basis of several salts which are as yet  very little known.  When
 metallic osmium is heated in a stream of dry chlorine, in a long glass tube, a volatile
 mixture of  protochloride and perchloride of osmium is produced.   The former,
 which is the less volatile, condenses near the heat in long needles of a fine green
 colour;  while the latter, being carried much  farther by the current of gas, is depos-
 ited as a red powder destitute of any crystalline texture.  Both these salts combine
 with the alkaline chlorides, forming double salts.  All three oxides of osmium com-
 bine with the oxygen acids to form salts  which do not crystallize, and have been
 very little studied.
   Columbium forms a volatile chloride.   Its  oxide, Ta.02, does not combine with
 acids, and the columbic acid forms salts which are not of practical importance.

                            Salts of Arsenic.

   Chloride of Arsviic—\s.C\3; Eq. 22G8 0 or 181-74—is formed when the metal bums
 spontaneously in chlorine;  it is a volatile  liquid,  which forms dense white fumes on
 exposure to the  air.   It may be obtained,  also, by mixing intimately one part of ai»
 senious acid  and three of common salt; putting  them into a retort to which a con
 denser is attached, and adding four parts  of oil of vitriol.  By a moderate heat the
 chloride of arsenic distils over as a dense  liquid.   By much water it is resolved Into
 arsenious and muriatic acids.  The sp. gr. of its  vapour is 6295.
  Iodide of A-smic,  As.I3,  is best prepared by digesting one part of arsenic with.
 five of iodine and fifty of water,  until the  iodine disappears;  on  cooling, theioaide
separates in orange-red crystals.   It is decomposed by water into hydriodic and ar-
senious acids.  The bromide of arsenic may be similarly  formed.
  Arsenic does not form any compound with  chlorine, bromine, or iodine analogous
to arsenic acid. 
452
SALTS  OF  ARSENIC.
  Neither compound of arsenic with oxygen is capable of acting as a base, and
hence the only classes of salts of arsenious or arsenic acids, are those in which
they constitute the electro-negative element.
  Arsenious Acid is dissolved in large  quantities by the caustic and
carbonated alkalies, but the salts thus  formed cannot be obtained
crystallized, and appear to be very indefinite in constitution.  The
combinations  of arsenious acid with the earths are white powders,
of which the only one of interest is arsenite of Lime, H.O. . 2Ca.O.-j-
As.03, which  precipitates when arsenious acid is mixed with lime-
water, or arsenite of potash with a salt of lime.   It  is redissolved by
an excess of any acid.
  Arsenious acid is decomposed by peroxide of iron, an arseniate
of the  protoxide being produced ; on this is founded the efficacy of
the peroxide of iron as an antidote to the poisonous effects of ar-
senious acid (see p. 384).
  The arsenite of Cobalt is found native, as  a rose-red powder, and
the arsenite of Nickel exists as a mineral of a pale-green colour ; both
contain combined water.   The arsenites of copper and silver will be
described under the heads  of these metals,  and have been  already
noticed in p. 381, et seq.
  The constitution of  the  salts of arsenic  acid has been  already
mentioned in p. 377.   They are all tribasic, and are isomorphous
with the corresponding tribasic phosphates.  Some of them are of
technical and medicinal importance.  The neutral  arseniate of pot-
ash, H.O. . 2K.O.-|-As.05, forms a  deliquescent saline mass. The
binarseniate of Potash, 2H.O. . K.O.-f As.05, is formed by adding to
the former as much arsenic acid as it  already contained, or by ig-
niting  in a crucible equal weights of arsenious acid and nitrate of
potash ; red fumes  are given off, and on dissolving the residual mass
in boiling water, the salt is obtained  in large  crystals, which are
modifications of the square octohedron.
  There are three arseniates of Soda, which resemble the three triba-
sic phosphates of soda.  The first, (3Na.O.-f As.05)-}-24 Aq., is ob-
tained by igniting arsenic acid with an excess of carbonate of soda.
When a solution of arsenic  acid is neutralized by carbonate of soda,
the salt H.O.. 2Na.O.-*-As.05 is obtained, which may be had either
with 24 Aq. or 14  Aq.,  according to the temperature  at which it
crystallizes.  The binarseniate of Soda, 2H.O.. Na.O.-f As.Od, resem-
bles the corresponding  salt of phosphoric acid.
  The arseniates of the earths are white  powders, insoluble in wa-
ter, but soluble  in an excess of any  acid.
  Arseniates of Iron. -That of the protoxide, H.O.  . 2Fe.-fAs.05, is
a white powder, which, by exposure to the air, gradually becomes
green by absorbing oxygen, thereby approaching to the constitution
of the  native  arseniate  of iron, in which the iron is in the state of
black magnetic  oxide.  This salt corresponds to the blue phosphate
of iron, its formula being (2Fe.O.. H.O. -j- As.05) -f 2Fe203. As.05-f
12 Aq.
  The perarseniate  of Iron  is a white powder, which, when heated,
gives off 12 Aq. and becomes red ;  it has the singular property of
dissolving totally in water of ammonia.
  Arseniate of Nickel is a pale green powder. Arseniate of Cobalt is a rose-red pow-
der, and mav be used in place of phosphate of  cobalt in preparing Thenard's blue 
CHLORIDE  OF  ANTIMONY.
453
(p. 447).  It is prepared on the large scale by roasting the native arseniuret of co-
balt, Co3As.
  The sulphur salts of arsenic are some of the best characterized among that class
(p. 379).  There are three sulphoarseniates of Potassium, having respectively the for-
mula; (3K.S.+As.S5), (2K.S.+As.S5), and (K.S.+As.S5).  They are all deliques-
cent, and crystallize with water.  It would be very interesting to find whether the
second and third salts contain basic water, such as would keep up the tribasic char-
acter of the first. The sulplwa.rse males of Soaium resemble those of potassium.  The
basic salt (3Na.S.-j-As..S5-t-15  Aq.) crystallizes in large colourless rhomboidal ta-
bles.  When orpiment is dissolved in solution of sulphuret of potassium, sulplwarse-
n/teof pot.i^sium is obtained, K.S. t-As.S3, which, when evaporated, is decomposed,
and deposites a brown powder, which consists of K.As.S3, and appears to contain a
bisulphuret of arsenic, As.s2, combined with K.S., which is decomposed when sep-
arated from the state of combination.

                        Salts of Antimony.
  Sesquichloride  of  Antimony.—Sb.Cl3.  Eq. 3383*5  or  271*1.  To
obtain this salt completely pure, sulphuret of antimony in fine pow-
der is to be  mixed with its own weight of corrosive sublimate, and
distilled in a hard glass  retort.  The chloride of antimony  distils
over with a gentle heat as an oily liquid, which gradually solidifies
into a white  crystalline mass. It is very  deliquescent, and becomes
soft  on  exposure to the air, whence its old  name  of Butter of Anti-
mony ;  it may be obtained  more cheaply for surgical  use, but not
quite dry,  by mixing  together two  parts of fine  common salt and
one of crocus of antimony (oxysulphuret, see p. 385), and distilling
them in a retort  with one part of strong oil  of vitriol.   Chloride of
antimony distils  over, and there remains behind  sulphate of soda
mixed with  sulphuret  of antimony.   In  this operation, the crocus
antimonii being 2Sb.S3-f-Sb.03, the former remains passive ; but the
latter, acting on  3Na.CI.  and 3S.03, produces Sb.Cl3 and 3Na.O.. S.
03.   As there is, however, some water supplied by  the oil of vitri-
ol, the  product  is not solid.  It is, however, quite  strong enough
for  its  successful application as  a caustic.
  When chloride of antimony is put in contact with  much  water,
both are decomposed,  and a white  oxychloride is  precipitated, call-
ed Powder  of Algarotti, from the name of its discoverer.  If the wa-
ter be hot, the precipitate is distinctly crystallized. In  it one  fourth
of the metal is combined with chlorine, and three  fourths with oxy-
gen ; it contains also water, its  formula being, according to Berze-
lius, Sb.Cl3 + 3Sb.03 + 3 Aq.   The  formula  given  by Malaguti and
Johnstone  is 2Sb.CI3-f-9Sb.03, and  it is possible that there are two
oxychlorides, which may be produced separately or mixed, accord-
ing to the  circumstances of the  precipitation.  This oxychloride is
employed to furnish oxide of antimony in the preparation of tartar
emetic, and of some other salts of antimony.
  The  terchloride of antimony  combines with the chlorides  of the
alkaline metals, forming double  salts, consisting of an equivalent of
each constituent.
  Perchloride of Antimony, Sb.Cl-, is formed when  metallic anti-
mony is burned in chlorine gas.   It is a heavy liquid,  which fumes
in the air,  and  has a very bad smell ; with  a small quantity  of wa-
ter  it forms  crystals (hydrate) ; with a  large quantity of water it
gives antimonic  and muriatic acids:  it is formed, also, by heating
sulphuret of antimony  in chlorine gas. 
 454    SALTS  OF  TITANIUM,  TELLURIUM,  ETC.

  The bromide and iodide of Antimony are prepared by the direct combination of their
 elements; the operation does not require external heat; the former is colourless,
 the latter orange-red.  They are both easily fusible, volatile, and decomposed by
 water.
  The sulphurets  of antimony act  as sulphur acids (p. 387, 3S8), combining with
 the sulphurets of the alkaline metals to form double salts, of which several may be
 crystallized in large rhomboidal tables, perfectly colourless.  The basic hyposulplw-
 anlinwnile of Potassium which remains in solution after the precipitation of Kermes
 by cooling, crystallizes on evaporation in colourless deliquescent plates.
  The sesquioxide of antimony combines with oxygen acids to form salts, which
 possess but little interest.  Metallic antimony decomposes hot oil of vitriol, evolv-
 ing sulphurous acid gas, and forming the sulphate of Antimony, a white salt, which is
 decomposed by water.
   Antimonial Powder.  James's Powder.—This  preparation, to  which,
 at  one  time,  the  highest  medicinal virtues were  attached, is pre-
 pared by mixing together  equal parts of sulphuret of antimony and
 hartshorn shavings, and calcining them together in an iron pot, at a
 dull red heat, until  the mass  becomes ash-gray; this is to be  then
 placed in  a loosely-covered  crucible,  and  exposed to a white  heat
 for two hours,  or until the mass  becomes quite white ; it is then to
 be  reduced to a fine powder.   In this process the sulphur, and the
 carbon and hydrogen of the hartshorn, are burned away, and the an-
 timony  is converted into antimonious acid, of which a small quan-
 tity unites with the  lime that had been as carbonate in the  bone ;
 the  rest of the lime  remains as phosphate, mixed  with the antimo-
 nite of lime and the  antimonious acid.  Its composition  varies  very
 much; it seldom contains  more  than one per cent, of antimonite of
 lime, which is  its only soluble and  active principle ; and where it
 has been washed, as is sometimes done, even this is removed.  It
 is also a mere mechanical mixture of its ingredients.
   Tartar emetic  will be described under  the head  of tartaric  acid
 and its salts.

             Salts  of Titanium, Tellurium, and Uranium.

  Chloride of Titanium, TLCI2, is best prepared by treating a mixture of titanic acid
 and lampblack by  chlorine, as for the preparation of chloride of silicon.  It is a col-
 ourless liquid, very volatile, fuming in the air, resembling closely bichloride of tin;
it combines with water so violently as to produce  explosion, and is decomposed by
a large quantity.
  There are no oxygen salts of titanium of any interest.
  Bichloride of Tellurium, Te.Cl2, is produced by heating tellurium in a current of
dry chlorine; a thick liquid is produced, at first dark red, but becoming yellow as it
 cools, and at last solidifying into a  snow-white crystalline mass.  This  salt is de-
composed by water into tellurous and muriatic acids, and combines with the alka-
 line chlorides to  form double salts.  The protochloride is prepared by melting togeth-
er equal weights of the bichloride and cf tellurium, and distilling; it condenses as
a deep yellow liquid, which solidifies, but does not  appear crystalline.   It forms
double salts.
  The tellurous acid appears to possess feeble basic properties, as it unites  with the
strong acids to form compounds which are not important.  The relations  of tellu-
 rous and telluric acids to bases have been already noticed at sufficient length  (p. 389).
  The chlorides of Uranium, U.C1. and  U2CI3, give yellowish green solutions, but
 do not crystallize.   With the alkaline chlorides they unite, forming crystallizable
 double salts.
  Protosulphate of Uranium crystallizes in green prisms.
  Sesquisulphate of Uranium, U2O3+3S.O3, is not itself crystallizable, but combines
 -vith sulphate of potash in several proportions to form double salts of very complex
 constitution.
  The Sesquinitrale of Uranium,  U2O3+3N.O5, crystallizes in large tabular crystals
 «tf a bright yellow  colour.  This salt is remarkable as the most definite nitrate of  a
 tesquioxide that is known to chemists.
  All these salts are prepared by dissolving the oxides of uranium in the dilute acids. 
SALTS OF  COPPER.
455
                         Salts  of Copper.
   Copper forms two series of  salts, one corresponding to the sub-
oxide, and the other to the black oxide.  The former are generally
white, and the latter blue or green.
   Chloride of Copper, Cu.Cl.,  is  produced  by dissolving copper in
aqua regia, or oxide of copper in muriatic acid.  Its solution is green,
and it gives, on evaporation, the hydrated salt in long, slender green
prisms, Cu.Cl.-|-2Aq., which are slightly deliquescent, and are solu-
ble in alcohol.   When heated  they give off water, and the dry chlo-
ride remains as a brown powder, which recombines with water, with
the evolution of much heat.  Strongly heated, it fuses, gives off half
its chlorine,  and the subchloride remains, melted into a brown resin-
ous-looking mass, whence its  name of resina cupri.   By the action
of an alkali on a solution of chloride of copper, an oxychloride may
be formed, which precipitates as a  fine green powder,  having the
formula Cu.Cl.-f-3Cu.O.-f-Aq., and which  is used as a pigment by
the name of  Brunswick Green.  There exist two other oxychlorides
of copper, which have the formulae Cu.Cl.-|-2Cu.O. + 3 Aq.,  and Cu.
Cl.-|-4Cu.O.-{-6H.O., prepared by the decomposition of the ammo-
niacal chlorides of copper.
   The Subchloride of Copper, Cu2Cl.,  may be prepared either by heat-
ing the chloride as above, or by digesting the clippings of thin cop-
per in a strong solution of chloride  of copper, to  which some muri-
atic acid had been added.  The  liquor gradually  acquires an olive
colour, and the subchloride is deposited in the form of a white pow-
der.  In this case the Cu.Cl. combines with a second equivalent of
copper, forming Cu2Cl.   It also precipitates when  chloride of copper
is acted on  by protochloride  of tin, 2Cu.Cl. and Sn.Cl. producing
Cu_,Cl. and Sn.Cl2.   This  subchloride  is insoluble in water  ; it  dis-
solves in muriatic acid, which lets it fall by dilution with water.  It
absorbs oxygen rapidly from the  air, and becomes green.  It forms
with water of ammonia a  colourless solution, which rapidly becomes
blue on exposure to  the air.
   Both chlorides of copper combine with the chlorides of the alka-
line metals to form double salts.
  The Bromide and Subbromidc of Copper, Cu.Br. and Cu2Br., resemble in every re-
spect the chlorides just described.
  The Iodide, of Coppzr, Cu.I., does not appear to exist except in combination.  If so-
lutions of iodide of potassium and chloride of copper be mixed, the subiodide is pre-
cipitated, while half the iodine is set free, 2Cu.Cl. and 2K.I. producing 2K.CJ. and
Cu2l., with free  I.  But if an excess of iodide of potassium be added, these elements
recombine, and a double salt,  Cu.I.-f-K.l., may be obtained. The preparation of
the subiodide of copper just given involves the loss of an atom of iodine, which is
avoided by previously mixing the liquor with an excess of solution of protosulphate
of iron, by which the copper salt is reduced to the state of suboxide, and all the io-
dine then precipitated as  subiodide.  Thus made, it is a pale yellow powder, unal-
tered by the air.
   Sulphate of Copper.—Cu.O. . S.03. H.O.+ 4 Aq.   Eq. 996*9 + 562*5
or 79*9  f 45.   For the purposes of the arts, in which this salt is ex-
tensively employed,  it is prepared by  treating the native sulphuret
of copper in  the manner described under the head of the sulphates
of iron  and zinc.  It may also be obtained by boiling oil of vitriol
on metallic copper,  when sulphurous  acid  gas is given off, or by
acting on the metal with  dilute sulphuric acid, to which some nitric 
456 scheele's green  and emerald green.
acid  had been added.   It  crystallizes in large  doubly-oblique
rhombs, of a fine blue colour, whence its name, Blue Vitriol.  In the
                    fiffure, the primary rhomb and the most usual
                    secondary form are given, i,u, v marking the
                    primary  planes in  each.   These crystals dis-
                    solve in  four parts of cold and two of boiling
                    water.   Of the five atoms of water which it
                    contains, one is constitutional, and may be re-
                    placed by the  alkaline  sulphates, to form a
                    class of  double salts of great beauty.  By the
                    action of a small quantity  of ammonia, a basic
sulphate is obtained, of which the formula is Cu.O,. S.03-f-3Cu.O.-(-
4 Aq.; and another, containing Cu.O, . S.03-|-7Cu.O.-4-12 Aq., is oc-
casionally observed to form.
  Nitrate of Copper.—Cu.O.. N..05'4- 3 Aq.   This  salt  is  obtained
when copper is dissolved  in dilute nitric acid; it crystallizes in ob-
lique  rhombs of a  rich blue colour, and sometimes in  paler rhom-
boidal plates, which contain 6 Aq.  This salt .deflagrates  violently
when thrown  on burning coals, or when struck on an  anvil  with a
little  phosphorus.   If some of it be wrapped up tight in tin  foil, it
becomes very hot, swells  up, fumes, and oxidizes the tin so rapidly,
that in some points brilliant sparks  are thrown  out.  When heated
above 200°, it  loses acid, and a basic  nitrate remains, which may
also be formed by adding  a small quantity of ammonia to a solution
of the neutral salt.  The  formula of the basic salt is H.O.. N.05-f-
3Cu.O.
  Phosphate of Copper, H.O.. 2Cu.O. +P.05, and  the arseniate of Cop-
per, H.O.  2Cu.O.-f-As.05,,are pale green powders, obtained by dou-
ble decomposition.
  Arsenite of Copper, H.O.. 2Cu.0-J-As.03, is obtained by the de-
composition of arsenite of potash  and  sulphate of copper:  it  is a
fine apple-green powder, the importance of which, as a test for ar-
senic, has been already discussed (p. 381).  It  is employed  in the
arts, under the name of Scheele's Green, as a pigment, and is  prepared
on the large scale by dissolving two pounds of pure sulphate of cop-
per in twelve quarts of water,  previously heated  in a copper pan.
In another pan two pounds of pure calcined pearlash are dissolved,
with eleven  ounces of arsenious acid, in four quarts of pure water.
Both  liquors are strained  through linen, and then the arsenical so-
lution is gradually added  to the solution of copper.  The precipi-
tate  is collected on a cloth  and  carefully dried.  The produce
should be 1  lb.  6i oz.  A  still more beautiful pigment, which  may
be best described here, is prepared  under the name of Schweinfurt
Green, or Emerald Green ;  itjs  a compound of acetate of copper and
arsenite of copper,  Cu.O.. a-(-3(H.O. . 2Cu.O. + As.03).   It  is pre-
pared by mixing up ten parts of pure  verdigris with as much hot
water as will make it into a  thin pulp, and straining it through a
sieve  to separate the impurities : nine or ten parts of arsenious acid
are to be then dissolved  in 100 parts  of boiling  water, and while
boiling, the  verdigris pulp is  to be gradually added thereto,  con-
tinually stirring.   At first a mere arsenite  of copper falls, and  all
the acetic acid remains in the  liquor ,*  it being only after much agi-
 
SALTS OF  LEAD.                   457
tation that the double salt is produced, which is known by the li^ht
flocculent precipitate changing into a heavy granular powder of a
brilliant green colour.
  The salts  of the suboxide of copper with the oxygen acids pos
sess no practical interest.

                         Salts of Lead.
  Chloride of Lead,  Pb.CL, may be  produced  by boiling lead in
strong muriatic acid, or by acting on oxide of lead with the  same
acid ; but more simply by adding to any soluble salt of lead  a so-
lution of chloride of sodium.  A curdy white precipitate  falls, which
dissolves in boiling  water, and, on cooling, crystallizes in  opaque
plates  of a  pearly lustre, which do not contain  water.   This salt
requires  135 parts of cold  water  to  dissolve it, but is  much  more
soluble in boiling water.  It is easily  fused, and,  on cooling, forms
a semi-transparent mass like horn, whence the old name, plumbum
corneum.   By  the action of ammonia on chloride of lead,  several
oxychlorides  may be formed, of which none  are now of interest.
  Bromide of Lead resembles perfectly the chloride..
  Iodide of Lead,  Pb.I.,  is formed  by adding iodide of potassium to
a solution of nitrate  of lead ; a bright lemon-yellow precipitate falls,
which  requires 1235 parts of  cold, and but 194 of boiling water to
dissolve it.   The solution is colourless, and, on cooling, deposites
the iodide of lead in splendid  gold-coloured six-sitied plates, which
maintain their metallic lustre perfectly in  drying.  The iodide of
lead  forms  double  salts with  the alkaline  iodides, and  gives, with
ammonia, oxyiodides when the alkali is not in exfcess.
  Sulphate of Lead.—Pb.O.  . S.03. This salt is fojind in  the mineral
kino-dom in large transparent rhombs, isomorphous with sulphate
of barytes, and of which the  octohedron i, y, in  the  figure, is the
primary form.  It may be also formed by  adding to
any solution containing lead sulphuric acid or a sul-
phate.   It falls down as a white powder, which, from
its insolubility, furnishes a good test for lead.  When
strongly ignited, it melts without  decomposition,  but
with  charcoal it is reduced to sulphuret of lead.   The sulphate of
lead is soluble in strong acids; and hence  the oil of vitriol, manu-
factured in leaden chambers, generally contains a  small quantity of
it dissolved, which is precipitated on the addition of water.
  Nitrate of Lead, Pb.O.. N.05, is obtained by dissolving lead in di-
lute nitric acid, and evaporating.  It crystallizes in regular octohe-
drons,  often modified, which are generally  opaque ; it is soluble in
seven and a  half parts  of cold, and much less of boiling water.  It
is not soluble  in nitric acid.  When heated, it gives out a mixture
of oxygen and nitrous acid gases (p.  276), and leaves melted pro-
toxide of lead.  By the action of ammonia, a series of basic salts are
obtained  which contain two,  three, and six atoms of oxide  of lead
united to one  of nitric acid.
  When  a solution of nitrate of lead is boiled  on finely-divided
metallic lead, this dissolves, and on cooling, brilliant yellow plates
are deposited, which are basic nitrite of Lead, 2Pb.O. + N04.  By
addino* sulphuric acid to a  solution of this salt, a neutral nitrite is
                             jl m m
 
458 CHRO MATES OF  LEA D.--S ALTS OF  BISMUTH.

obtained, Pb.O. . N.04+H.O., which crystallizes in  yellow octohe-
drons.  If  an excess of lead be  used in the preparation of the ni-
trite, the acid is still farther deoxidized, and a hyponitrite of Lead,
3Pb.O.-f N.03+3 Aq., is  produced, which crystallizes in rose-red
scales.   These salts are of interest, as it was doubted whether the
nitrous acid (N.04) could  combine with bases, and  it is  only  in
these cases that we have obtained positive evidence  of its doing so,
which we owe to Peligot.
  Phosphate of Lead, H O.. 2Pb.O. + P.Oj, is formed by the action
of common tribasic phosphate of  soda on a solution of nitrate of
lead ;  t is  a white powder, which is changed by ammonia into  3Pb.
0.+P.06.
  Silicate of Lead has been noticed  in relation to crystal and to flint
glass.
   Chromate of Lead—Pb.O. . Cr.03.—Chrome Yellow is formed by
mixing together solutions of nitrate of lead and bichromate of pot-
ash.  It  precipitates as  a fine lemon-yellow powder, insoluble in
water.  It  occurs  native  in ruby-red crystals, constituting  the red
lead ore.  This salt is manufactured largely for a pigment, which is
found  of various shades of yellow and orange in the market, being
mixtures of the true neutral chromate,  prepared as above, with the
basic chromate of Lead, 2Pb.O.-(- Cr.03, which is of a bright vermilion
colour, and is termed Chrome Red.  This may be prepared by adding
potash to a solution of chromate  of potash until  this reacts strongly
alkaline, and then mixing it with  nitrate of lead, or by digesting
the  neutral chromate of  lead in  a  warm solution of potash, which
removes half the acid.   These give products, however, inferior in
brilliancy of tint to the following.   Saltpetre is to  be melted  in a
crucible at  a dull red heat, and chrome yellow gradually added there-
to, as long as effervescence, with escape of red fumes, occurs.   The
potash abandons the nitric acid and takes half the chromic acid, and
basic chromate of  lead is  formed.  The mass becomes black, and is
then to be allowed to settle, and the melted salt poured off from the
heavy powder at the bottom ; this, when cold, becomes of a splendid
vermilion red, and is to be taken out and washed with the smallest
possible quantity of water.

                       Salts of Bismuth.
  Chloride  of Bismuth, Bi,Cl3, is  formed by  dissolving bismuth in
hot strong  muriatic acid;  by evaporation it forms a crystalline mass
which  is very deliquescent, volatile, and fusible.   By water it is
decomposed, giving  the  oxychloride of bismuth, a  white powder,
having the composition Bi2CI3-f2Bi203 + 3H.O.  In the arts this pow-
der is sometimes employed under the name of Spanish White or Pearl
White.
  The chloride of bismuth combines with the chlorides of the alka
line, metals, forming double salts, in which the  chlorine combined
with the bismuth is to that  combined with the other metal as three
to two.  In the double salts formed by  protochlorides, this relation
is never observed, and hence it furnishes additional proof that the
chloride of bismuth is a sesquichloride, on which idea the formula!
wecome 2K.Cl.+Bi-iCl3 + 2 Aq. and 2Na.Cl. + Bi,Cl3 + 3 Aq. 
SALTS  OF  SILVER.
459
  Sulphate of Bismuth, Bi.,03-f3S.03,  is formed by dissolving bis-
muth in hot sulphuric acid.   It forms a deliquescent mass of acicu-
lar crystals, which are decomposed by water, giving  a white  pow-
der, the basic sulphate of Bismuth, Bi203-f-S.03.
  The Nitrate of Bismuth, Bi203+3N.O,-|-9 Aq., is formed  by dis-
solving the metal in dilute nitric acid  ; by evaporation and cooling
rhomboidal crystals are obtained,  which easily deliquesce; when
heated, they lose water and  nitric  acid, and form a basic salt, and
finally oxide of  bismuth remains behind.   Like the other salts of
bismuth, this is decomposed by water, and may produce one or other
of two basic salts, according  to circumstances.  When the crystals,
without any excess of acid,  are decomposed by water, the precipi-
tate has the  composition 4Bi203-f 3N.05+9H.O. ; while, if an acid
liquor be decomposed by  water, the precipitate has the formula Bi.
03 + N.05.   Both of these salts yield very nearly the same quantity
of oxide of bismuth on analysis, and were  hence long confounded
together.   Many reasons for  considering the oxide of  bismuth to be
a sesquioxide have been given (p.  398).  These subnitrates of bis-
muth are  used indiscriminately in  medicine,  but the  latter form is
more generally  found in  the shops.   The names Pearl White, &c,
are also applied to these bodies.

                         Salts of  Silver.
  Chloride of Silver—Ag.Cl.  ; Eq. 1794*3 or 143*8—exists native as
an ore of silver, horn silver,  and may  be  formed by mixing  a  solu-
tion of common salt with  a soluble salt of silver.  It forms a curdy
white precipitate, perfectly insoluble in water and in acids, but  easi-
ly soluble in water of ammonia.   When heated, it fuses below red-
ness, and  on cooling,  congeals  into a semitransparent mass  of a
horny aspect, whence its old name.  When freshly precipitated, it
is exceedingly sensible to the action of light, becoming pink, violet,
and ultimately black by exposure to the sun's rays ; but for this re-
action, it is necessary that organic  matter or water should be pres-
ent, with the hydrogen  of which the chlorine may combine, and that
thus a thin layer of subchloride or of metal may be produced.  The
relations of chloride of silver to light are of the highest importance
in photography,  and in examining the structure of the  solar rays, as
noticed in p. 173, et seq.  The processes for the reduction of chlo-
ride of silver to the metallic state have been described  in p.  399,
400.
  Iodide of Silver, Ag.L, is obtained by decomposing a soluble salt
of silver by  iodide  of potassium ; a  primrose-yellow precipitate
falls, which is insoluble  in water and in ammonia ; at least it requires
2500 parts of strong water of ammonia to dissolve one of iodide of
silver.  It  is easily  fusible,  and  becomes opaque  on  cooling.  In
certain forms it  is still more  sensible to light than the  chloride, and
is hence the basis of the impression in the photographic process of
Daguerre (see p. 175).   It is reduced to  the  metallic  state  by the
same  means as the chloride.
  Bromide  of Silver, Ag Br., resembles the chloride  in  every par-
ticular respect.
  Sulphate of Silver, Ag.O..  S.03, is formed by boiling metallic sil 
460
SALTS  OF  SILVER.
 ver in oil of vitriol;  sulphurous gas is given off, and a white saline
 mass formed, which, when more strongly heated, is totally decom-
 posed, leaving metallic silver.   This salt dissolves  in  eighty-eight
 parts of boiling water, and crystallizes, on cooling, in small needles.
   Hyposulphite  of Silver.—2Ag.O. + S202.   The relations of hypo
 sulphurous acid to oxide  of silver are  very curious.  On adding a
 neutral solution of nitrate of silver to a solution of hyposulphite of
 soda, a  white precipitate appears, which  at first redissolves,  but
 subsequently becomes  permanent.   It soon loses its pure colour,
 especially if heated,  and at last becomes black  from sulphuret  of
 silver, while the liquor contains sulphate of silver;  thus 2Ag.O.-f.
 S202 produce Ag.S. and Ag.O. . S.03.  The solution  of this salt is
 extremely sweet.   So great is  the affinity of hyposulphurous acid
 to oxide of silver, that a solution of it dissolves chloride of silver,
 forming an intensely sweet liquor ;  and the solutions of the alkaline
 and earthy hyposulphites dissolve all the salts of silver insoluble in
 water, except the arseniate  and the iodide,  and form  double salts
 of  exceedingly sweet  taste.   The double  hyposulphites  contain
 generally  one equivalent  of hyposulphite  of silver to  two  of the
 other salt, but our knowledge of these salts is  not, as yet, by any
 means complete.
  Nitrate of Silver.—Ag.O.. N.05.   Eq. 2128*5  or 170*57.  This is
 the most important salt of silver ; it is manufactured on a very laro-e
 scale in  the Apothecaries' Hall of Ireland for medicinal use.
  It is prepared by dissolving granulated silver in dilute nitric acid,
 which at first occurs without the disengagement of any gas, as the
 nitric acid dissolves  the nitric oxide formed, but towards the end
 copious  red fumes are evolved.   By evaporation and  cooling, the
 salt is obtained in colourless rhomboidal  plates, as  in the figure,
                       often four inches across, which are anhy-
                       drous.   It is soluble in its own weight  of
                       cold water.  When  heated  to  about 430°.
                       it  melts into a colourless liquid, which  is
                       poured  into cylindrical  silver moulds, and
                       congealing, forms the sticks of lunar caus-
                       tic used in surgery.   This fused salt should
be snow-white ; it is  not affected by light unless organic matter be
present, as has been fully shown by Scanlan ; but with organic mat-
ter  it  soon becomes quite black, silver being reduced.   It is hence
used as marking ink, and for staining hair black.  When  strongly
heated, nitrate of  silver is totally decomposed.   It yields its oxy-
gen readily to combustible bodies ;  thus, if a few grains of it be laid
on an anvil with a little bit of phosphorus, and  struck with a ham-
mer, it explodes violently.   Its solution is reduced to the metallic
state by all deoxidating agents.
  Hyponitrite of Silver, Ag.O.. N.03, is  obtained in  granular crys-
tals by adding the soda salt prepared by melting nitrate of soda (p.
428) to  a  boiling solution  of nitrate of silver,  and filtering while
very hot.
  Tribasic Phosphate of Silver, 3Ag.O. + P.O„ is the canary-yellow
precipitate, produced by adding a tribasic  phosphate of socm to a
solution  of nitrate of silver.  Its relations  to the other  phosphates
 
SALTS  OF  MERCURY.
461
of silver, and to the silver test for arsenic, have been noticed in n
298 and 381.                                                  P*
  Arseniate of Silver, 3Ag.0. + As.0f), is precipitated as a reddish-
brown powder on adding any  solution of an arseniate to a solution
of nitrate of silver.   Its formation is one of the most characteristic
properties of arsenic acid.
  Arsenite of Silver, H.O. . 2Ag.O. 4-As.03, is produced, as has been
noted in p. 401, by adding a solution of arsenious acid to the am-
moniacal nitrate of silver, or of arsenite of potash to nitrate of sil-
ver.   It is a canary-yellow powder, soluble in ammonia and in ni-
tric acid.  When heated,  it first yields water and becomes brown;
then it gives oxygen, arsenious acid,  and leaves metallic silver.

                       Salts of Mercury.
  Chloride of Mercury.  Corrosive Sublimate—Ug.C].; Eq. 1708*5 or
136*9—may  be  prepared by dissolving red  oxide of mercury in mu-
riatic acid, and evaporating.  It crystallizes in long right-rhombic
prisms,  generally opaque.   It may also  be very economically pre-
pared by dissolving  the basic sulphate (turpeth mineral) in  strong
muriatic acid, and crystallizing ; the sulphate of mercury remains in
the mother liquor, and may be again converted into basic sulphate
by the action of water.  The  corrosive sublimate is, however, gen-
erally prepared, for pharmaceutic purposes, by the dry way, as fol-
lows: sulphate of mercury, Hg.O. . S.03, is to be well mixed with
its own  weight of common salt, Na.Cl., and the mixture introduced
into a wide-necked  glass retort, or, on the  large scale, into a stone-
ware pot,  to  which a globular glass head is attached.   The  retort
or pot, being bedded in sand, is gradually heated to redness; decom-
position occurs, the chlorine of the common salt combining with the
mercury, while  the  sodium takes the oxygen and acid ; we  have
therefore formed Hg.Cl., which sublimes into the head, formino* a
mass of prismatic crystals, which, being partly fused by the heat, co-
here  strongly together, and sulphate of soda, which remains behind',
Hg.O. .  S.03 and Na.Cl. giving Hg.Cl.  and  Na.O. . S.03.
  The sublimed chloride of mercury crystallizes in a right-rhombio
prism, as represented in the figure.   Its specific gravity is 5*4; it
melts at  509% and boils at 563 \  The specific gravity   /r-~-
of its vapour is  9420.   It dissolves  in two parts of |\    "^""N^
boiling and in twenty of cold water ; the hot solution   [  "---...-'""
crystallizes,  on  cooling, in prisms  of a different form   ;       I
from that of the sublimed salt;  it is therefore dimorph-   i
ous; it  is soluble in  2.',-  parts of cold alcohol, and in  i^^-^j
three  parts of cold  ether ;  it dissolves  much more \|       i\
readily in muriatic acid and in solutions of the alka-  ^^--^i/^
line chlorides than in pure water, as it forms with these bodies
double salts, which  are  very soluble ; of these, the double chloride
of mercury and ammonium, sal alembroth, is employed in pharmacy.
It will be  specially  described  hereafter.  A solution  of corrosive
sublimate yields ail the reactions of a salt of the red oxide of mer-
cury, described in p. 403.    \\ hen  a  small quantity of potash is ad-
ded to a solution of sublimate, a brown precipitate falls, which by
boiling becomes black and crystalline j the same substance may be 
462           PREPARATION  OF  CALOMEL.

formed by boiling red oxide of mercury in a solution of sublimate j
it is an oxychloride of mercury, whose formula is Hg.Cl.+ 3Hg.O.
  If a solution of sublimate be treated by a small quantity of sulphu-
ret of hydrogen, a  precipitate forms, at first brownish, but which ul-
timately becomes quite white, provided there be sublimate in excess;
it is a ddorosulphuret, of which the formula is Hg.Cl.+ 2H-T.S.
  Subchloride of Mercury.  Calomel.—Hg2Cl.  Eq. 2974-3 or  238*3
This important medicinal agent may be prepared either by precipi-
tation or by sublimation.  For the former object, nine parts of mer-
cury are to be digested in eight  parts of nitric acid, sp. gr. 1*25,
without heat, until no  more  mercury appears to dissolve, and the
liquor begins to assume a yellow colour; eight parts of common
salt are next to be dissolved in 250 parts of boiling water, to  which
a little muriatic acid may be  added: these solutions being mixed,
the calomel immediately precipitates, and thus prepared, it is abso-
lutely pure.  The mercury dissolving in the nitric acid, forms nitrate
of the suboxide, and by the chloride of sodium, nitrate of soda and
subchloride of mercury are formed ; Hg20. . N.O^and Na.Cl.  giving
Hg.Cl. and Na.O. . N.05.
  To obtain calomel by sublimation, four parts of corrosive  subli-
mate  may be rubbed up with  three parts  of mercury, so intimately
that no trace of metal shall be visible ; and the mixture being intro-
duced into  an  earthen  pot to which a glass head is fitted, heat is
to be gradually applied until the  materials have all sublimed.  In
this operation, Hg.Cl.  combining directly with Hg., gives Hg^Cl.
The union  is never perfected  by the first  sublimation, and the prod-
uct is to be again powdered, well mixed, and again sublimed.   The
process followed by the British pharmacopoeias is different,  and is
best carried on  in the following proportions :  Thirty-one parts of
dry sulphate of the  red oxide of mercury (persulphate) are to be in-
timately mixed with twenty and one third parts  of metallic mercury
and twenty parts of fused common salt,  and  the whole rubbed to-
gether until the mercurial globules totally disappear.  This method
is the same as  the  former in principle, except that the corrosive
sublimate is generated  only when  required to combine with the ad-
ditional quantity of mercury to form calomel.  The sublimation is
carried on  as described above.  The sublimed  mass is always con-
taminated with some undecomposed sublimate.  Hence it must be
carefully levigated,  and washed with boiling water as long  as the
washings give any milkiness  on the addition of a few drops of wa-
ter of ammonia.
                   The precipitated calomel is a pure white  pow-
                 der.   When sublimed, it forms a crystalline mass,
                 whose primitive form, as in the figure, is a square
                 prism.   It  is insoluble in  water; and the mi-
                 nute  division of  the  sublimed  calomel may be
                 elegantly secured by conducting its vapour into
                 a vessel containing boiling water, by the  vapour
                 of which  it is suddenly condensed,  and falls as
                 an excessively fine powder.   Its  specific  gravi-
                 ty is  6*5.   The presence  of sublimate in the cal-
                 omel  of the shops is detected by boiling for a few
                 minutes in alcohol, and adding to the alcoholic li-
 
IODIDES  OF  MERCURY.
463
quor some water of ammonia, which gives a white precipitate  if
corrosive  sublimate  be present.  By boiling with muriatic acid  or
with solution of common salt or sal  ammoniac, calomel is gradually
decomposed into  sublimate, which dissolves, and metallic mercury,
which remains behind.
  The Bromide and Subbromide of Mrrcury, Hg.Br. and HgzBr., may be prepared,
the first by acting directly on mercury wita  bromine, when a colourless solution is
obtained, which gives prismatic crystals by evaporation;  the second, by decompo-
sing nitrate of the suboxide by bromide of potassium. These bodies resemble com-
pletely sublimate and calomel in their properties.
  Iodide of Mercury.  Red Iodide—Hg.I.;  Eq. 2845*0  or 228*0—may
be formed by the direct combination of its elements, even without
heat, by trituration together with a few drops of alcohol.  It is  then
dark red,  but  may be obtained of a  brilliant red colour by precipi-
tating a solution of corrosive sublimate with an equivalent of iodide
of potassium.  An excess of the latter redissolves the  precipitate,
as it forms a double salt (K I.-fHg.I.), soluble in water, and crystal
lizable in  octohedrons.  The iodide of mercury is insoluble  in wa-
ter; when heated, it fuses and  sublimes, condensing  in a crystalline
mass, formed  of rhomboidal plates,  which, when broken  or scratch-
ed, gradually become  red, breaking up  into a number of minute
crystals of a different form.  It is somewhat soluble  in alcohol, and
abundantly in aqueous hydriodic acid.   A hot solution of iodide  of
potassium dissolves  much  more than the atomic proportion of it;
the excess crystallizes in long, red,  square prisms, according as the
solution  cools.   It dissolves also in a  strong solution of corrosive
sublimate, with which  it combines  in two proportions.   It forms a
class of double salts, equally extensive  with that produced by cor-
rosive sublimate.
  Subiodide of .Mercury, Hg.I., may  be  formed by triturating iodine
with mercury, or by precipitating a solution of iodide of potassium
by a slight excess of nitrate of the suboxide of mercury.   It is  an
olive-green powder, which  is resolved  by heat  into metallic mercu-
ry and iodide, and is similarly decomposed by a solution of iodide
of potassium, with which the iodide of mercury formed combines.
  Sesquiodide  of Mercury, or Yellow Iodide.— HgJ3 or 2Hg.I. + Hg,I.
To obtain this substance, a solution  of iodide of potassium, to which
half as much  iodine as it already contained has been added, is to  be
decomposed by a slight excess of a solution  of the subnitrate  of
mercury.   The bright yellow powder  which  precipitates must  be
dried cautiously  with little  exposure to light.   By means of a solu-
tion of iodide of potassium, it is resolved into red  iodide and me-
tallic mercury.   The reaction by which  it is formed is that, of the
subiodide first produced, by the K.I. and Hg.O. . N.O,,  one half is
converted into red iodide by the additional atom of iodine which
is supplied ; 2(K.I.)+I. and 2(Hg20. . N.O,) giving 2(K.O. . N 0,)
and  Hg2I.-|-2Hg.I.   This preparation is employed in pharmacy.
  A preparation  which has been proposed by  Donovan, under the
name of Iodo-hydrargyrate of Arsenic, is prepared by rubbing togeth-
er 6*08 grs. arsenic, 15*38 grs. of mercury, and 50 grs.  iodine, with
a few drops of alcohol, until they combine, and then adding eight
ounces of water  with a few drops of hydriodic acid ; a  solution  is
obtained, at first  colourless, but soon becoming yellowish-brown  by 
  464         OXYGEN  SALTS  OF  MERCURY.

  light, from iodine being set free.  This preparation is not a cnem-
  ical compound ; but the iodide of arsenic being decomposed by the
  water, the iodide of mercury  is dissolved by the  hydriodic acid
  formed, while arsenious acid exists free in the solution.
   Sulphate of Mercury—Hg.O.  . S.03;  Eq. 1867 or 149*6—is produ-
  ced by boiling oil of vitriol on  mercury,  until it is converted into a
  white saline mass, which requires to be finally heated nearly to red-
  ness to expel the excess of  acid.  Sulphurous acid is evolved, Hg.
 and 2S.03 giving Hg.O. . S.03  and  S.02; but this may be avoided
 by adding from time to time a small quantity of nitric acid, by which
 oxygen will be supplied.   This salt forms a white powder, not crys-
 talline ;  at  a  full red heat it is resolved into mercury, sulphurous
 acid, and oxygen.  Its use  is  extensive  in preparing calomel and
 sublimate.  By a large quantity of water  it is decomposed into free
 acid  and basic sulphate, turpeth mineral,  3Hg.O. + S.03,  which is a
 bright yellow powder, which, jfrhen  heated with muriatic acid, gives
 neutral sulphate  and corrosive sublimate, 2H.CI. and (3Hg.O.-f-S.
 03) producing 2Hg.Cl. and  Hg.O.. S.03, water being formed (see
 p. 461).
   Subsulphate of Mercury—Hg20.. S.03—Sulphate of the Black Ox-
 ide may be formed by heating metallic mercury with oil of  vitriol,
 provided  the  heat do not pass  beyond 212° ; or by mixing  strong
 solutions of nitrate of the black oxide and of sulphate of soda.  It
 is a white powder, very sparingly soluble in water, by  which it is
 not decomposed,  and is thereby  distinguished from the preceding
 salt.
   Nitrate of Mercury. Nitrate of the Red Oxide.—2Hg.O. . N.05-f-
 2 Aq.   This salt is formed when  mercury is dissolved in an  excess
 of nitric acid with heat.   It crystallizes in rhomboidal plates, which
 are deliquescent, and  soluble in a small quantity of water.   Its so-
 lution is decomposed when diluted, a basic nitrate of the Red Oxide
 being  precipitated of a bright canary colour, and having the formu-
 la H 0. . N.O, -|- 3Hg.O.  If this  powder be boiled with much  water,
 a still more basic salt is formed, which has the formula N.0,-f-6Hg.
 0.  Both this salt and the sulphate, when heated by sulphuretted
 hydrogen not  in excess, give white basic  compounds, like the chlo-
 rosulphuret (p. 464), having the formula} Hp-.O. . N.0, + 2Ho*.S. and
 Hg.O..S.03 + 2Hg.S.
  Subnitrate of Mercury.   Nitrate of the Black Oxide.—When mercu-
 ry is dissolved in dilute nitric acid, without any heat, or with only
 as much as  sustains a  very moderate action, the black oxide  forms,
 and may unite with the nitric acid in various proportions.   1st. If
 there  be nitric acid in  excess, the solution gives by cautious  evapo-
 ration  clear transparent rhombs  of neutral subnitrate,  having the for-
 mula Hg20. . N.03+2H.O.  2d. If there  be an excess of mercury,
 large opaque white rhombic prisms sometimes form,  which have the
 composition (3Hg20. + 2N.05+3H.O.).  3d. By letting this solution
 stand,  these crystals  gradually  disappear, and very  small canary-
 yellow crystals, nearly spherical, with numerous brilliant facets, are
 produced: this is a basic salt, the  formula being H.O. . N.05+2Hg.
 O.  This salt may also be formed by the  action of water on either
the first or second ; both being decomposed into free acid, and the 
             SALTS  OF  GOLD  AND  PALLADIUM.        4(J5

 basic salt, which is not farther altered even by boiling water.  The
 second salt may be looked upon as a compound of the first and third
 since (311-0. I-2N.O, f 3II.O.) = (IIg.O. .N.OJ+2H.O.) + (H.O. .N
 0*4-211* A).
   S,ibthromate of M rcury, Ilg20.+Cr.03, produced by mixing solutions of chro-
 mate of potash and subnitrate of mercury, is a bright orange powder, insoluble in
 water; when heated to  redness, it gives oil'mercury and oxygen, and chromic oxide
 of a fine green colour remains (p. 372).
   Red nitrate of mercury combines with iodide of mercury to form a double salt,
 which is formed by half precipitating a solution of the mercuric salt by iodide of po-
 tassium, and boiling until the precipitate redissolves; on cooling, the new salt is de-
 posited in brilliant red crystalline scales, which are decomposed by much water.
                             Salts of Gold.
   Perchloride of Gold.—Au.Cl3.  When  gold  is  dissolved in  nitro-
 muriatic acid,  and  the solution evaporated  very cautiously to dry-
 ness, this salt remains as a ruby-red crystalline mass, which dissolves
 with a yellowish-red  colour in water.   Its  solution is  acid,  and  is
 decomposed by the light, and by all deoxidizingagents.  It combines
 with  muriatic  acid,  and forms a  deep  yellow  liquor,  from  which
 the acid chloride of Gold crystallizes in long yellow needles.   It  is
 soluble in alcohol and in ether, from which last solution it is  depos-
 ited in the metallic state on evaporation, the chlorine combining with
 the ether.   In this way some  forms  of  gilding are  effected,  as  on
 steel.  The chloride of gold combines with many other  chlorides,
 forming double salts.   The chloride  of gold  and potassium, Au.Cl.,4-
 K.CI.4-5 Aq., crystallizes in orange-red striated rectangular prisms.
 It effloresces in the air, and may  be obtained  anhydrous; it is then
 ruby-red.   Chloride  of gold and  sodium (Na.CI.-f Au.Cl3+4  Aq.)
 forms crystals  of the same  form  and colour, but which  do not ef-
 floresce :  when heated,  they fuse in their  water of crystallization.
   Subchloride of Gold, Au.Cl , is produced  by heating the chloride to
 about 450' in  a porcelain  dish, stirring it  very carefully until no
 more  chlorine  is given off.   It is a yellowish-white mass, insoluble
 in water,  by which it is  gradually  decomposed  into chloride and
 metallic gold.   It is in this way only that a solution of chloride of
 gold perfectly  free  from an excess of acid can be obtained.
  1 > tides of G Id.—When solutions of chloride of gold and iodide of potassium are
 mixed, a greenish  precipitate occurs of subiodide of Gold, Au.I., while two thirds of
 the iodine become free.  If the iodide of potassium be  in great excess, however, the
 iodine and subiodide are both redissolved, and a double salt obtained, which crystal-
 lizes, and which-contains iodide of Go! / • its formula is K.f+Au.I3; by  the cautious
 addition of chloride of gold to a solution of this salt, a greenish precipitate may be
 obtained without any liberation of iodine, and which hence must be the  iodide.
  The oxides of gold do not act as bases, and the general nature of the salts which
 they form, as acids, has  been noticed in p. 406.
                          Salts of Palladium.
  Chloride of Palladium, Pd.Cl., is formed by dissolving palladium in nitromuriatic
 acid.  Its solution is deep brown, and  it forms, by evaporation, a crystallihe mass;
 by the action of a small quantity of caustic  alkali, a basic salt, or oxychloride of Pal-
 ladium., Pd.Cl.+3Pd.f>. [ 1 Aq., is produced ;  it is a brown powder, insoluble in wa-
 ter.  The chloride of palladium combines with other chlorides to form double salts:
 when heated to about (500°, it abandons half its chlorine, and subchloride of Palladi-
 um remains, an olive-brown powder insoluble in water.  By a strong red heat this
 is totally decomposed.
  D^dochlor'ule of Palladium, Pd.d2, is formed when the -chloride of palladium is
gently heated with aqua regia; it forms a  dark brown liquor, which gives, with a
                                N N N 
406 SALTS  OF  PLATINUM,  IRIDIUM,  AND  RHODIUM.

solution of chloride of potassium, a sparingly soluble double salt,  K.n.+Pd.CU.
This deutochloride cannct be obtained solid, its solution giving ofl chlorine, and
chloride remaining.                 ,     ,     ,.,.■•,,,.
  lo.tiue of Pattauium, Pd.L, is a black powder, obtained by double  decomposition.
It forms double salts with other iodides.  By heat  it is decomposed, without form-
ing any subiodide.                       ,     ,,,.,.   ,
  Silphate of Palladium, Pd.O.. S.O3, is produced by dissolving the metal in a mix-
ture of nitric and  sulphuric acids.  By evaporation, a saline mass is obtained,
which is decomposed by water.
  NL'1 ate of Palladium, Pd.O.. N.Os, is obtained by acting on the metal with nitric
acid.  At first it dissolves without any evolution of gas, forming a deep olive liquor;
but when heated, it gives off N.O2, and becomes brown.   The nitrate of palladium
is decomposed by water, giving basic salts.

                          Salts of  Platinum.

   Protochloride of Platinum, Pt.Cl., is formed  by exposing  the bi-
chloride, in fine powder, to a temperature of about 500  in a  porce-
lain dish,  and frequently stirring; one half of the  chlorine  being
evolved, a greenish olive powder is  produced, which  is  the  proto-
chloride.   It is insoluble  in water ; by a red heat it is resolved into
chlorine and metallic platinum.  If the bichloride be exposed only
to a temperature of about 400  , water dissolves from out of the re-
sulting mass,  a  substance  which colours it intensely brown, and
which is, probably,  a sesquichloride, rt3Cl3.
   Bichloride  of Platinum.—Pt.Cl2.   This salt  is produced by dis-
solving platinum  in nitromuriatic acid.   The  solution, when free
from  excess of acid, is intensely yellow : on evaporation, it gives a
crystalline deliquescent mass.   This salt  is very soluble in alcohol,
and is  so  used  for the detection of potash (p.  339).   It combines
with  other chlorides, forming double salts, of which some possess
considerable interest.  Those with  chloride  of potassium, K.Cl.4
Pt.Cl2) and with  sal  ammoniac, N.H^Cl. + Pt.CL,  are precipitated as
yellow powders  from strong solutions, or as minute octohedral or-
ange-red  crystals  from  dilute solutions   of those alkalies, and are
hence used for their detection.   These  salts are insoluble in alco-
hol.   The sodium double  salt (Na.Cl.-j-Pt.Cl,) is,  on the contrary,
 easily soluble both  in  alcohol and water.
   The Iodides of Platinum are black powders, insoluble in water, formed by the
double decomposition of iodide of potassium  with the respective  chlorides.  The
 biniodide combines with iodide of potassium  to form a double salt K.I.+Pt.l2, which
 dissolves in water, giving a solution so deeply claret-coloured  that it may seive to
 detect a very minute trace of platinum in solution.
   Although many oxygen salts of platinum  are described  in the systematic books
 (Milphate, nitrate, &c), I consider that we possess no accurate knowledge whatever
 of that class of combinations.

                      Salts of Iridium and Rhodium.

   There are four chlorides of iridium.  The protochloride, Ir.Cl., is  prepared  by
 heating metallic iridium to redness in chlorine; it is an olive-green body, which is
 insoluble in water, but combines with other chlorides to form double salts. Th?
 sesquichloride, lr2C\s, is formed by dissolving the sesquioxide in muriatic acid. It ij
 a brown crystalline substance, volatile, and forming double salts.  The bichloride,
 Ir.Cl2, is produced when a concentrated solution of the former is treated with aqua
 regia.  It forms a dark brown solution,  giving, when dried, a black mass.   It gives
 •with chloride of potassium a sparingly soluble double salt in black octohedral crvs-
 tals.  The perchloride, I.C13, is not known except in the state of a double salt, K.Cl.
 4-I.CI3, which is produced by processes, for which I refer to the larger systematic
 works.
   The protoxide, sesquioxide, and deutoxide of iridium  form salts with the oxygen 
ELEMENTS OF  ORGANIC  BODIES.        467
acids;  the solutions of the first class being green or purple, thosp of the second class
bloOii-red, and those of the third orange, produce the variety ot tints whhh gives the
name Iridium to the metal; they are not otherwise important.
  Ss/ui'hloridc of Rhodium, IhCh, is prepared by decomposing the double chloride
of rhodium and potassium by Hydrofluosilicic acid.  The filtered liquor gives, when
evaporated, a brown-red mass, destitute of crystalline stmcture; by heat it is com-
pletely  decomposed.  It combines with other chlorides to form well-defined double
salts, such as that 2K.Cl.+R2Cl3+2 Aq. formed by acting on metallic rhodium and
ch.oride of pota.ssium by aqua regia.  When metallic rhodium alone is treated by
chlorine, a rose-red powder is obtained, insoluble in water and acids, which is a sim-
ilar  compound of protochloride  and sesquichloride  of  rhodium,  R4013—2R.C1.4-
R2Cla.
  By igniting metallic rhodium with bisulphate of potash, a double salt is obtained,
which does not crystallize.   The  nitrate of rhodium is a dark red deliquescent salt,
whicli gives with nitrate of soda a double salt in dark red crystals.
CHAPTER XVI.
  ON THE GENERAL PRINCIPLES OF THE CONSTITUTION OF ORGANIC BODIES.

   Organic bodies are  distinguished generally by a much greater
 complexity of composition than occurs in substances of mineral or-
 igin.  Except in the case  of carbonic oxide, there is no example of
 an atom of an organic compound containing but two simple atoms;
 and carbonic acid and cyanogen are  the only examples of an organ-
 ic atom being formed by three elementary atoms.   On the contrary,
 the number of simple atoms entering into the composition of an or-
 ganic body is sometimes very great:  thus an equivalent of oleic acid
 contains 270 simple atoms ;  an atom of albumen is  formed of 883
 simple  atoms; an atom of spermaceti includes 468  simple  atoms;
 numbers to which we  find no form of combination approaching  in
 inorganic compounds.
   Besides this greater complexity of constitution, organic bodies
 are distinguished by the nature of their elements.   I have had oc-
 casion already to describe as inorganic fifty-four undecompounded
 bodies,  which, by their reunion in various proportions, generate the
 compound  substances  which  constitute  the mineral  crust  of the
 globe ;  but among organic bodies we meet  with few of these.  Al-
 though  equalling in number and surpassing  in variety of properties
 the mineral species, the products of the animal and vegetable king-
 dom may be  looked upon as consisting  almost  exclusively of six
 elements, of which two, sulphur and phospaorus, are met with but
 seldom  ; nitrogen is much more extensively found, especially in
 animal substances; oxygen and hydrogen exist in almost all; but
 the element which is peculiarly organic,  and which, with the  one
 exception of ammonia,  exists in all bodies derived from  an animal
 or vegetable source, is Carbon.  It is hencu that I have deferred the
 description of carbon and its compounds until I could pass directly
 from it  to  the great variety of organic bodies of which it is the ba-
 sis.  With the constituents of inorganic bodies it has but an acci-
dental connexion ; for, as I  shall hereafter show, there is no form of 
468         CLASSES OF  ORGANIC  BODIES.
carbon which has not at some time made part of an organized being.
Besides these six elements of organic bodies, there are many which
enter into the structure of animals and plants, and are subservient
in an important degree to  the  proper performance  of their func-
tions, without being really constituents of their organic tissues or
secretory products.  Thus iodine and bromine exist in many ma-
rine  plants and sponges;  common  salt and oxygen salts of potash,
soda, lime, and magnesia exist in most animal  and vegetable juices;
phosphate of lime  constitutes the bony skeleton of one, and carbo-
nate of lime  the testaceous covering of another tribe of animals,
while silica forms  the solid basis of some of the lower tribes of zo-
ophytes. In the red colouring matter of the blood, iron is an essen-
tial element,  and the same metal has  been found in minute quantity
in other parts of animals; indications of fluorine and of silica have
been found in the bones  and  teeth ;  but in all these instances, ex-
cept the one fact of the iron  element of red blood, we find these
saline substances  to be  contained  in fluids in a condition of mere
physical solution, or to be deposited as solids in the bones or teeth
in a purely inorganic  form, clearly  to be  distinguished from the
proper  state  of organic  combination, in which the  carbon, hydro-
gen, oxygen, and nitrogen of the tissues and secretory products are
united.
  Among organic  bodies, it is necessary to distinguish three class-
es, which differ no less  in complexity of composition than in the
circumstances under which they are formed, and their relation to
organic bodies.  These are, first, those bodies which are directly
elements of an organized and living being, and which, while in con-
nexion with  it,  appear to possess the power of elaborating, from
certain nutritious  juices,  additional material similar  to themselves.
Such are the organic constituents of the animal and vegetable tis-
sues  and  of  the blood, which, while in connexion with, and form-
ing portions  of  the animal or plant, participate to a certain degree
in its vitality, and do not obey  the laws of ordinary affinity, unless
by being,  in the first instance, killed ; these bodies  should be more
properly called organized  than merely organic ; their chemical rela-
tions commence only  when they have been deprived of their moot
essential character, life.   They  are organs; their constitution can-
not be expressed in formulae,  nor their properties accounted for by
analysis.  After their death we  may obtain from them, by chemical
treatment, a variety of organic bodies ; but that they were composed
of these bodies, and that  their properties resulted from the combi-
nation of  such elements as we extract from them, it would be false
philosophy to imagine.   The fibrine  and albumen of the blood, the
muscles, and the cellular tissues, the fatty matter of the brain, per-
form their functions in virtue of vital power, and not of any chem-
ical properties they possess.  The albumen of the egg is not a chem-
ical substance,  but a  delicately-constructed  mass, "destined to  be
transmuted into the organs of the chick, and  by participating in  its
life, protected from putrefaction.  But when albumen is precipitated
by corrosive sublimate, it is killed, and the product of its decompo-
 sition combines with the oxide  of mercury.
   This class of bodies have their origin, therefore, in actions purely 
  RELATION  OF ORGANIC  FORCE  TO  AFFINITY.  469

 vital.  They have a structure  organic-molecular, totally different
 from crystallization, and for the most part  consisting*  of  minute
 cells.  When dead, these tissues undergo spontaneous decomposi-
 tion, with more or less rapidity, according as their composition is
 more complex ; but for this water must be present.   Some forms
 of animal tissue, which appear to lose the organized  structure and
 vitality with which they  were at first formed,  are capable  still of
 remaining in connexion with the living system, and, although dead,
 have no tendency to  putrefy, probably from not being in any de-
 gree soluble  in water.   The formation and growth  of nails  and
 hoofs, hair and horns, are  examples  of the important uses of  this
 property.
   It is by virtue of the vital forces of the bodies of this first class,
 not  individually, but united together so as to  constitute the tissues,
 glands, &c, of plants  and animals, that the  organic bodies of the
 second class have their origin.  These are substances produced (se-
 creted) from the elements by which organized bodies are nourished,
 probably by the union, under peculiar conditions, of such portions
 of the constituents of the food as were not proper or proportioned
 to be assimilated to the organized tissues of the living being itself.
 It is thus that, by a plant  which uses water,  carbonic acid, and at-
 mospheric air as nutriment, after the assimilation of a certain quan-
 tity  of their constituents to its proper tissues, sugar, starch, and al-
 bumen, adapted for the nutrition of its young, may be formed as
 secreted products, and oils, resins, colouring  matters, &c, rejected
 as useless  or injurious.
  The third class  of organic bodies contains those which are evolv-
 ed by the  chemical decompositions, whether spontaneous or arti-
 ficial, to  which substances of the first  and second class are subject-
 ed.  Thus sugar, by fermentation, yields alcohol and carbonic acid;
 alcohol, by oxidation,  yields acetic  acid, or  aldehyd ; acetic acid,
 variously treated, produces acetone,  or alkarsin; while lio-neous
 fibre gives origin, when heated, to a crowd of organic products, of
 which pyroxylic spirit is an example.
  It  is very interesting to contrast these classes of bodies with each
 other, in relation to the forces by which their constitution is regu-
 lated, as  compared with the simpler forms of affinity by which  the
 actions of inorganic elements are controlled.   In the  first there is
 found nothing referrible to  chemical attraction ; all  affinity is  an-
 nulled by the supremacy of life and organization.  Hence it is only
 when dead that such bodies can be analyzed, and by treatment with
 reagents  a crowd of products belonging to the third class be obtain-
 ed from  their more or less evident  decomposition.   No  matter,
 therefore, how perfect our mediate or  immediate analyses of such
 substances may be, the synthesis of such bodies, or their production
 by the union of their elements, is strictly impossible to the chemist.
 The  formation  of a molecule of albumen would not be a case  of
 chemical combination, but of the formation of a portion of an  or-
 ganized cell ; it would  require not merely the  combination of its el-
 ements, but also that the compound should have life imparted to it.
  In  relation, however, to the second and third classes, the circum-
stances are quite  diflerent;  although  we cannot trace, precisely, 
 470       THEORY  OF  COMPOUND  RADICALS.

 the force by which the organized tissues act in eliminating from a
 liquid of uniform composition, such as the blood or sap, the various
 secretions which constitute  the  second class, yet the circumstan-
 ces of their  formation  admit of being examined, and  already some
 insight has been obtained as to the way in which organic bodies
 may separate, or be converted intoothers, without reference to the
 mere affinities of their  elements, by means of the influence that has
 been  already described as catalytic (p. 236, et seq.) ; in this way the
 functions of  organized tissues may be  imitated, and a true synthesis
 of organic bodies of the second class may be effected.   With the
 bodies  of the  third class we find, also, that the circumstances of
 their  formation are either purely artificial, or capable of being easi-
 ly imitated, and the reactions by which they are evolved, although
 often catalytic, fall, in the majority of cases, under the rules of or-
 dinary  affinity. In structure, also, the bodies of the second and
 third  class range  themselves with inorganic  compounds; those
 which are solid may, for the most part, be obtained crystallized, and
 the liquid substances possess definite freezing and  boijing points.
  Between such organic bodies and mineral  substances we find  the
 greatest similarity,  not  merely in their physical relations, but in
 chemical properties also.  The great classes of acids and bases  ex-
 ist, well marked, among organic bodies, and in their  combinations
 with  each other, the same  principles of multiple and equivalent
 combination  are followed as hold  for inorganic compounds.   So
 perfect is the analogy of general characters, that  it has  long been
 an object with chemists to unite, under one principle, the laws of
 composition of organic and inorganic bodies ; and as the character-
 istic distinction of mineral substances  is to consist of  a series of el-
 ements which are respectively combined, two and two, in virtue of
their  opposite  affinities, attempts  have been made to reduce the
complex constitution of organic bodies to the same principle of bi-
nary union, by supposing that certain  of the elements are, in the
 first instance, grouped  together  so as to form a single  molecule,
and that this, acting as a simple body, combines with the element
which remains.  It is from the discovery of  cyanogen, and the dis-
 cussions as to the nature of the ethers and of the ammoniacal salts,
that we must date the positive introduction of this theory of com-
pound radicals into chemistry.   Its utility has not been  limited to
the explanation of the constitution of organic bodies; on the con-
trary, it has been applied successfully to explain the phenomena pre-
 sented by numerous classes  of inorganic compounds, such as  the
compounds of sulphur  and oxygen, noticed p. 292, and  especially
to the foundation of the binary theory of salts, as described in  the
fifteenth chapter.
  Were we, however, to apply the theory of compound radicals in-
 discriminately  to explain the constitution  of organic bodies,  we
 should be liable to fall into continual error.   The criterion which  I
would assume as decisive of the constitution of an  organic body is,
whether certain of its elements may be exchanged for others, in ac-
 cordance with the ordinary laws of substitution of inorganic bodies,
and thus a series of compounds be produced, through°which some
 elements of  the original substance shall have p:\ssed untouched, 
          THEORY  OF COMPOUND RADICALS.      471

and from which again, by suitable reactions, the original substance
can be obtained unaltered.   In  such case I would consider those
elements which remain unaffected as being strictly united with each
other, and constituting a compound radical, which, combining with
other bodies, gives origin to  a series of compounds  more or less ex-
tensive.  Thus, if we treat oil of bitter almonds, C,4H„0,;, by chlorine,
we obtain a compound Cl4H,O^Cl., which gives, with  iodide or sul-
phuret of potassium, bodies whose formulae arc respectively CuH.O^
I. and CI4H,0,S.  Again  acted  on by oxygen, it gives crystallized
benzoic acid, CuH„0„ or, rather, C,4H,03-|-Aq.   Now  it will be seen
that, throughout this whole series, the element C|4H,02 has remained
unaltered.  In the oil it was combined with hydrogen ; in benzoic acid
it unites with oxygen ; in the other bodies it is united  with chlorine,
iodine, &c, and from these  the  oil may  be recovered by  processes
by no  means indirect.   Now when we state that in these compounds
the elements C,4HJ02 are  united, first with each other, by an affin-
ity which ordinary reagents cannot overcome,  and that this com-
pound group unites with the simple bodies, hydrogen, oxygen, &c,
by an affinity so much weaker that they can be readily substituted
for each  other, we state  only an established fact, and in denomina-
ting the  group, Cl4H,0_,,  the  root or radical of the  series of  bodies
thus produced, we  involve no hypothetical idea.   For  brevity,  we
express that compound radical by the symbol Bz., and we  term it
Benzyle ;  we write the formula of its combinations, respectively, Bz.
H., Bz.Cl., Bz.I., and Bz.0.4-Aq.
  But we must not  be induced, by the  brilliancy  shed  on  certain
branches of organic chemistry through the application of this prin-
ciple,  to  transgress the boundaries of sound induction.   There are
numerous org-anic  compounds in which I believe that  no  binary
structure exists, and,  consequently, to which the theory of organic
radicals should not be applied.  It is the class of bodies character-
ized by a remarkable  indifference to combination, and which, when
decomposed by the influence of reagents, lose not  merely one con-
stituent and gain  another in  its place, but are totally transformed
into new compounds, into which all of  their original components
enter, and towards which the reagent that had been applied fre-
quently appears indifferent, so that the action  appears to have more
the character of catalysis than of true chemical affinity.   Such bod-
ies are gum, sugar, starch, some of the oily and colouring matters,
urea, and many others: treat these bodies as you will, there  are no
phenomena of  true replacement;  they may be decomposed, but bod-
ies of a totally different type are  formed,  and the original substances
cannot be regenerated.
  The organic  radical which is  thus assumed as the  basis of a se-
ries of compounds,  acts as a simple  body, but it does so only in re-
lation  to  the nature and  intensity of the  forces that act upon it ; it
mav  be decomposed, and frequently it  cannot be separated from
combination without total  decomposition; hence few  compound
radicals can be isolated.   But they can be decomposed, even while
still in combination, by the  intervention  of powerful  affinities; and
this decomposition may be  either  total, so as to leave  no trace of
the  original constitution  of  the  substance, or by giving  origin to 
472           ITS  APPLICATION  LIMITED.
another series of combinations, may indicate a still more intimate
constitution, and unveil an organic radical of a simpler structure
acting as the basis of the first.
   Thus we  have seen what positive grounds there are for admit-
ting benzyle, Cl4HO,, to be the radical of the oil of bitter almonds
and  of benzoic acid ;  but if we digest oil of bitter  almonds with
ammonia, all oxygen is removed, and we obtain a compound of ni-
trogen with the body,  C H„  which may also be obtained in other
forms  of combination.   Now this organic substance, CI4H„ acts as
the basis of benzyle, for the oil of bitter almonds can be reproduced
from it; and we thus obtain evidence of three stages of constitution
in benzoic acid, whose formula should be written, therefore, as (C,4
H--f-02) 1-0.  The  considerations  described in p. 291 point out a
perfect analogy to this in the constitution of sulphuric acid.  Re-
duced to its  ultimate elements, its formula is S.03; but powerful evi-
dence  shows that its real basis is sulphurous acid, and not sulphur,
its rational formula being S.024-0.  Now here the primary radical,
C14H-, corresponds to sulphur, and  benzyle to sulphurous acid ; the
total quantity of oxygen in such acids being divided into  two por-
tions, differing in order and intensity of combination with the ulti-
mate radical.   If we  add to these considerations the view of salt-
radicals, and consider the salts of benzoic acid as expressed by the
formula Bz.02+M, as that of the  sulphates has been shown to be
S.O,. 024-M., we observe even a fourth degree to which the mole-
cular structure of the complex organic radical may be traced.
   It is, indeed, when  applied to explain the constitution of the or-
ganic acids, that the theory of compound radicals, as employed in
the new views of the  constitution of oxygen salts, appears most in-
teresting, as the anomalies of properties and composition presented
by the  salts  of the organic acids were more numerous and  more ex-
traordinary  than any which the mineral acids presented, and were,
indeed, totally unintelligible, until  illustrated by the conjoined in-
vestigations of Dumas and of Liebig. An example of this may easi-
ly be selected.  Of the organic acids, the majority are  monobasic,
but there  are also many bibasic and tribasic ; thus the citric acid,
whose formula is C|2H,0,,, combines with three atoms of base; the
meconic acid, C,4H.OM, is also tribasic; the tartaric acid, CSH40IO,
and  the mucic acid, C,,H80M, are bibasic.  In these instances, the
quality of combining with many atoms  of base, which is so anoma-
lous on the  older view, necessarily follows from  the formulae of the
hydrated acids, which become  respectively, for citric acid, Cl2H,0,4
+ H3; for meconic acid, CNH.0,44-H3; for tartaric acid, C.H4Ol24-H2;
and for mucic acid, Cl2H,Ol64-H2.   By its means many  other singu-
lar properties of organic acids are explained:  thus there appear to
exist three acids, having  absolutely the same composition of C2N.
O., viz., the cyanic, the fulminic, and the cyanuric acids; they are
isomeric ; they  possess excessively different  properties.  Whence
has that difference its rise '( If we say that the cyanic acid contains
cyanogen ready formed, and that the others do not, it still remains
to explain the isomerism of the others; and we find that the cyanic
and cyanuric acids are  transformed into each other by the slightest
causes.  We  obtain, however, at  once the key  to this isomerism, 
       CONSTITUTION  OF  COMPOUND RADICALS.  473

 when we  study the salts formed by these acids.   The  cyanic  acid
 is monobasic ; its hydrate is C2N.O.-f H.O.: the fulminic acid is bi-
 basic; its hydrate is C^iVO, r2H.O.: the cyanuric acid is tribasic;
 its formula is CoNj03-j- 31I.O.   These acids  are thus found to have
 different atomic weights; their molecular groups are ascertained to
 contain different numbers of  molecules,  and hence to admit of to-
 tally distinct internal structure.  When expressed in formulae on
 the binary theory, we have C2N.024-H. for  the cyanic,  C4N2044-H2
 for the fulminic, and C„N30o4-H3 for  the cyanuric  acid; and not
 merely the difference in nature of the acids, but also the distinctive
 characters of their salts necessarily result.
   Although chemistsare unanimous in regardingthe principle of com-
 pound  radicals as the basis of the philosophy of organic chemistry,
 yet science has  not yet arrived at the point when the  principle is
 adopted by all  in the same form of detailed  application.  On the
 contrary, there  are few  specific examples of that principle that are
 not still open to  discussion.   The views of Berzelius on  this subject
 are specially of importance.  He considers that the compound rad-
 icals of organic bodies consist only of carbon  and  hydrogen, or of
 carbon and nitrogen : that  they never  contain  oxygen.   Hence he
 does not admit  the  existence  of benzyle in  benzoic acid or in oil
 of bitter almonds ; he considers the only radical to be the  carbo-
 hydrogen, C,4II, and  benzoic acid  to  be directly C^Hj-f 03.  He
 looks upon the  oil  of bitter  almonds  as containing ready-formed
 benzoic acid, combined  with  the true hydruret of  the radical, as 3
 (C..1Hu02)^2(C,1H-)-|-03)4(C14H-)4-Hl).   The chloride of benzyle he
 looks upon as an oxychloride, 3(C,4Hj. 02C1.) being equal to 2(C,4H5
 -f-OJ -f-(C,4Hi-L-CI3).   This is evidently the same difference of view
 that exists as to the nature of  the sulphurous  acid compounds, which
 Berzelius also regards as more complex.  Thus the chlorosulphu-
 rous  acid is, according to  him, a compound  of sulphuric acid with
 a  terchloride of sulphur, 3(S.02C1.)=2S.03  + S.C13;  and so  in all
 other bodies similarly circumstanced.
   The opinions  of a man to whose extraordinary industry and  ge-
 nius we owe  some of the most important additions, both theoretical
 und practical, that science has  received since  the epoch of Lavoisier,
 should not be rejected without much consideration;  but on  apply-
 ing those ideas to express  the constitution of the crowd of bodies,
 containing four or five elements, which have recently been discov-
 ered, we are led to suppositions destitute of experimental proof, and
 yet which, assuming the existence of numerous hypothetic bodies
 of anomalous constitution,  and  combined in  very unusual  ways,
 would require for their  legitimate admission into  science a very
 strong body of experimental evidence.  It would be impossible here
 to  discuss the principles  of  his opinion in detail; I am led to con-
 clude, from the consideration of the whole body of facts which bear
 upon it, that it is inferior in power, and simplicity of explanation of
 known facts, and as an instrument of discovery, to the simpler view
of  the constitution of organic bodies which has been described ; and
being thus deficient in all the  important duties  of a sound theory, I
do  not hesitate to reject  it.
 The proposition of the theory of types by Dumas (see p. 234)
                             O o o 
 474         THEORY  OF  CHEMICAL  TYPES.

 will probably constitute an epoch in science, by fixing attention on
 the  permanent equivalency of an  organic atom, notwithstanding
 complete alteration in the nature of its elements.   This did not fol-
 low necessarily from the theory of compound radicals, nor does the
 conservation of the type  require that the radical be preserved  unal-
 tered,  but  only  the  type of the radical.  Thus, when aldehyd is
 changed into chloral (C4H,0, into C4H.. C1,02), the type is preserved,
 since° the hydrogen is replaced by an equivalent  of  chlorine  ; the
radical is altered, since acetyl, C4H3, is changed into  C,C13, but the
new radical is still  constructed on  the type  of the original.  The
theory of types, so far from being  inconsistent with the theory of
compound radicals, is in perfect harmony with it, at  least as I un-
derstand it, and as I believe it to have been proposed by Dumas.
The bases upon which it  rests  may be announced as follows:
  1st.  That the  hydrogen of a compound  radical  may be replaced
by chlorine or by oxygen, &c , equivalent for equivalent, and a new
radical thus produced, which,  being constructed on the same  type
as the original, will have  the same general laws of combination, and
will  hence  form compounds of the same type  as  those containing
the original radical.  Thus, from C4H3 may be formed C4CL, and
these, combining with oxygen and water,  form C4H30.-f Aq. or C4
H303-f-Aq,  and C4C130 -fAq.  or  C4C13034-Aq.:  also, by uniting
with chlorine, they produce C4H,C1. and C4C13C1.
  2d. That when bodies of the same type, and containing radicals
of the same type, are subjected to the action of strong affinities, by
which  their constitution is  broken up, the resulting  products are
constituted also upon the same plan, although differing in  composi-
tion ; thus  C4H404, when heated with potash, gives 2C.02 and C.H4;
and  C4H. . C1,,04, similarly treated, gives 2C02 and  C2H.C13; the
types of C2H.H3 and C,H.C13 being the same, and containing equiv-
alent radicals.
  3d. When bodies of the  same chemical,  though of different me-
chanical  types, or, as 1 would term them, bodies of the same natural
families, as the alcohols, are submitted to the action of affinities of
equal power, the bodies generated have the same relation to one
another as  the original bodies had ;  and  the radicals are either un-
changed, or all changed in a similar degree.  Thus from wine alco-
hol  (C4H002),  methylic alcohol (C2H40,),  essential  oil of  potato
spirit, C,,Hl202, and ethal, C3,H3102, there are produced by the ac-
tion of potash  a series of acids, each having  the same  type and
containing  the same radical as its alcohol ; thus the acetic acid (C,
H404),  the formic acicl (C2tL04), the valerianic  acid (C10HltO4), and
the ethalic  acid, C32H3_,0,.
  Considered in this way, the theory of types is an important ad-
dition to our ideas on the constitution of organic bodies.  It serves
to attach, under a few very  simple principles, numerous classes of
compounds, whose composition would otherwise nppear very com-
plex and anomalous, and will  probably, when applied  to the sfcudy
of such bodies as, not containing compound radicals, give only  their
molecular group as a muss to our examination, become a source of
still more important additions  to our knowledge.
  Although each organic substance gives, when  acted on  by re« 
        PRINCIPLE  OF ACTION  OF  REAGENTS.    475

 agents, products which are characteristic of, and often peculiar to
 itself,  yet there are some  general rules which, being now noticed
 will obviate the necessity  of much detail hereafter.
   When an organic substance  is treated with dry chlorine, it either
 combines directly with the gas, or, as more frequently happens, hy-
 drogen is removed to an amount equivalent  to that  of the chlorine
 absorbed.  Even in the first case, the direct union  is often  but ap-
 parent, and arises from the  muriatic acid formed  combining with
 the true product.   Thus olefiant gas, C4H4, gives the oily liquid C4
 H,C12;  but this, in place of being a direct combination, consists  of
 C,H3C1., which  is the true product  formed  by  substitution of CI.
 for II., but is united with  the H.Cl. thus generated.
   If water be present, it influences  the reaction very much, being
 generally decomposed.  In some cases, all the chlorine unites  with
 its hydrogen, while the  oxygen  combines  with the organic  sub-
 stance ;  but,  generally, the chlorine  unites with both elements  of
 the water, forming muriatic acid, which remains free, and hypochlo-
 rous or chlorous acids, which enter into the  composition  of  the or-
 ganic product.  In other  cases, again,  the presence of water  does
 not appear to exercise any influence.
   When an organic substance is treated with nitric acid, it is  always
 raised to a higher degree of oxidation.   Very rarely does the action
 stop there.   Hydrogen is  usually separated, and oxygen put in  its
 place ;  while the new products formed contain usually  a smaller
 number  of molecules  than the original organic substance.   Thus
 gum (Cl2H„,O,0), when acted on by nitric acid, gives, first, by  sim-
 ple oxidation, mucic acid  (Cl2Hl0O|6) ; but, if the  action of the  acid
 be more violent, all hydrogen is removed, and two atoms  of oxygen
 substituted, thus producing C12013, the elements of six atoms of ox-
 alic acid.
  In many cases, the action of nitric acid is  not limited to the oxi-
 dation,  whether direct or indirect, of the organic substances ; but,
 by the  removal of some hydrogen from  it, in combination with some
 of the oxygen of the nitric acid, water is formed, and the nitrogen,
 or nitric oxide, or nitrous  acid, combines with the remaining organ-
 ic elements, and forms new products.  Thus, from  napthaline and
 benzine, numerous  substances containing  nitrogen  are derived.
 This fixation  of nitrogen may occur even with bodies which already
 contain it; thus  indigo, treated with nitric acid, produces bodies,
 the indigotic  and the picric acids, which contain a larger proportion
 of nitrogen than the indigo itself.
  The  peroxides of manganese and lead often serve to oxidize or-
 ganic, bodies  in a more regulated manner than nitric acid, the  new
 substance combining with the protoxide of the metal ; thus,  by Pb.
 02, uric acid  is decomposed into allantoin, urea, and oxalic acid.
  By  fusion  with hydrate of potash, the oxidizement of organic
 substances is very powerfully  effected  ; water being decomposed,
its hydrogen evolved, and the oxygen uniting with the organic body
to form an acid, which remains combined with the  potash.  Thus
alcohol, C4HcA a^ 2H.0 , produce acetic acid, C,H404, and  H4 be-
comes  free.   Often the organic substance is merely  broken up  into
other bodies of simpler constitution, as  when tartaric acid, C>H4O10j 
476         ORGANIC ORIGIN  OF  CARBON.

by fusion with  potash, is decomposed into acetic acid, C4H404, and
oxalic acid, 2(C203).   In every case, if the  temperature be much
raised, carbonic acid is one of the products;  thus acetic acid (C4H4
0,) separates into C4H4 and 2C.02.
  The action of sulphuric acid on organic bodies may be very dif-
ferent, according to circumstances; thus from  starch we  may ob-
tain, by a merely catalytic  influence, gum,  grape-sugar, and ulti-
mately sacchulmine.   In  these  cases,  the sulphuric acid  remains
totally unchanged and  free, but generally it enters into combination
with the organic  body, either without decomposition, as in the sul-
phovinic and sulphomethylic acids, or  else water is formed by its
reaction  on the organic  body, which, thus deprived of an  atom of
hydrogen, combines with hyposulphuric acid, S205.  It is thus that
the sulphurous  element exists in the sulphobenzoic acid, the isethi-
onic acids, &c.
  If an organic substance containing nitrogen be acted on by these
reagents at a high  temperature, this is generally separated  under
the form of ammonia ; water being decomposed, and its hydrogen
so applied, while its oxygen forms the ordinary oxidized organic
products.   If potash be the reagent, the ammonia is  expelled, and a
salt of potash with the new organic acid remains;  if sulphuric acid
be the reagent, the organic acid is set  free, and a sulphate of am-
monia remains.
  By the action of heat upon fixed organic compounds, a variety of
products are formed, which may generally be described  as formed
by the abstraction of a portion of carbon and oxygen, as carbonic
acid, and of hydrogen and oxygen, as water.  Hence such pyrogen-
ic products are  always richer in hydrogen and carbon than the bod-
ies they are formed from, and of less acid characters.   This kind
of decomposition will, hovvever, require to  be  described in a dis-
tinct chapter.
                       CHAPTER  XVII.

OF CARBON, AND ITS COMPOUNDS WITH OXYGEN, SULPHUR, AND CHLORINE.

  Carbon exists in large quantities, and very extensively distributed
in nature, as a constituent of all vegetable and animal bodies.  It is
found, also, in the mineral kingdom, under forms, however, which
may be shown to have originally been derived from organic bodies.
Thus the different varieties of coal have been produced by the ag-
gregation of great quantities of wood, the materials of primeval for-
ests, which, being submerged in water, and covered by  the gradual-
ly-deposited layers of sand and mud,  have been elevated, in connex-
ion with the strata of clay and sandstone  so produced, to their  pres-
ent situations.  The wood thus circumstanced has undergone a kind
of decomposition,  which shall be  hereafter fully  noticed, and the
mixture of fixed and volatile organic  products, which constitute our 
      NATURE  OF  LIMESTONE  ROCK.--DIAMOND.  477

 coal, has thus its origin.   This formation of coal, as well as the
 formation of peat and  turf at the present day, almost at the surface
 is accompanied by a disengagement of carbonic acid in large quan-
 tity, and hence the probable source, in the air and in mineral wa-
 ters, of that substance, of which, also, much may be  derived  from
 the respiration of animals.
   A more strictly mineral form of carbon is  that of carbonic acid
 united to lime, and to  other metallic oxides, forming the numerous
 class of native carbonates.  Of these the most abundant is the car-
 bonate of lime, which, under the form of chalk, oolite,  coral, mount-
 ain limestone, &c, constitutes a large  proportion of the geological
 formations of our globe.   In all these cases, the rock is formed  of
 shells of animals, aggregated together  in great masses; these geo-
 logical formations, resulting from the collection, at the bottom of a
 sea or lake,  of the spoils of myriads of generations of those animals,
 which, by superincumbent  pressure, may be  more or less densely
 aggregated ; or by proximity of igneous  rocks, may be partially or
 completely fused, and their organic characters obliterated to a great-
 er or less degree.   In this way the crystalline marbles are formed,
 in which few or no traces of organic origin remain.  The compara-
 tively small  quantity of carbonate of lime, which is found separately
 and distinctly crystalline, either as arragonite or calc  spar, may  be
 traced to the solvent action of water impregnated with carbonic  acid,
 filtering through strata containing shells, and then gradually depos-
 iting, in  favourable situations, the matter it had thus  taken up, in
 crystals, the form of which depends upon the temperature at which
 they are produced (page  225).   The  other  native carbonates,  of
 which the quantity is very small in comparison with that of the car-
 bonate of lime, may have been produced by  double decomposition.
 Thus a water, holding carbonate of lime in solution, filtering across
 a stratum containing  oxidized  iron or copper pyrites, would  give
 origin on the spot to a crystalline deposite of sulphate of lime, and,
 at a certain  distance, carbonate of iron or of copper would be sep-
 arated.  Those instances suffice to point out the reasons for consid-
 ering carbon as truly the organic element, and that its appearance
 in a mineralized condition  arises from secondary actions.
  Carbon presents  itself in a  great variety  of forms.  Absolutely
 pure, it constitutes the  diamond, which,  from its exceeding hardness,
 brilliancy, and  rarity,  ranks as  the first of gems.  It  is found dis-
 seminated in alluvial strata in Golconda, Brazil, &c, and is separa-
 ted from  the sand and mud  by processes of washing.  No deposition
 of diamond  in rocks  has ever  yet been  found.   It crystallizes in
 forms of the regular system,  generally having a great number of
 sides, bounded by  curved  edges, in  virtue of which it s*plits  glass
 like a wedge, in place of  scratching it as a file.  Its crystals are
 generally hemihedral,  and  frequently rough and discoloured at the
 surface.  These crystals all cleave parallel to  the faces of a regular
 octohedron (fig. /, p. 26), but the properties of the diamond separate
 it completely from  the  proper mineral crystals  of the regular system.
 Thus it possesses double refraction in some cases ; it polarizes light
elliptically;  its structure has been found by Brewster  to consist  in
layers, sometimes containing cavities, indicating that the crystal had 
478     ORIGIN  AND  NATURE OF  PLUMBAGO.

been originally soft, and only concreted by degrees ; and in the re-
cent researches of Dumas on the atomic weight  of carbon, it was
found that, when burned, diamonds generally leave behind a minute
skeleton of inorganic matter.  These considerations fully show that
the diamond denves its origin from  the decomposition of organic
matter.   The diamond  is  the hardest body known; it cuts every
other, and can be ground only by means of its own powder.  It is
usually  colourless, but  sometimes brown  or rose-coloured ; its re-
fractive  power is very  great (2-439), whence its  great  brilliancy.
It  conducts  heat and electricity very badly; it resists most chemi-
cal agents, but burns in melted  nitre brilliantly, forming carbonate
of potash ;  it burns, also, when heated to redness in oxygen gas, and
evolves sufficient heat to maintain the continuance of the combus-
tion;  its specific gravity is about 3*5.
   Another very remarkable form of carbon is that of plumbago or
graphite.  This is found in  many localities,  but sufficiently pure for
the purposes  of the arts only in Borrodale, in Cumberland,  it is
perfectly opaque, crystallized in  rhombohedrons, or six-sided ta-
bles;  but its usual appearance is in brilliant leaves or spangles; it
is  soft and unctuous to  the touch, and gives, on paper, a continuous
gray streak, whence its name of blacklead, and its use in making pen-
cils.  Its formation appears to be connected with the action of iron,
and with a high temperature : it  is found only in igneous rocks, as
granite  and  mica slate, and contains almost always a large quantity
of iron  intermixed in the  metallic state, so that  it was  once sup-
posed to be a carburet of iron.  Graphite may be formed artificial-
ly  by adding  charcoal to melted cast iron ; the  charcoal dissolves
largely,  but  on cooling is found to separate  in  brilliant flexible
plates, more or less  regularly six-sided.   Graphite is lighter than
diamond, its  specific gravity being 2*5, and  it conducts heat and
electricity much better.  It is very hard to  set on fire, and does not
continue to  burn unless heat be applied from without.
   Carbon, in a form  more or less mixed  with foreign matters, is
obtained by the application  of a very high temperature  to animal
or vegetable substances in  close vessels.   The kinds of carbon thus
produced still differ very much.  Thus coke is obtained by heating
coal in  iron retorts until  all the volatile  products are  driven off,
and the  excess of carbon  remains mixed  with the earthy matter
which all coal contains.   The properties of coke approximate more
or less to those of graphite, according to the temperature at which
it  has been  produced.  By the proximity of igneous rocks to coal
under the earth, a similar expulsion of its  volatile matters may be
effected, and a form of carbon nearly pure, anthracite, results.  These
fuels are difficult to light,  but, when once  ignited, give  out an in-
tense  heat by  their combustion.
   If an  organic  substance,  which contains hydrogen and  carbon, be
set on fire, and there be a copious supply  of air, it is  totally con-
verted into  water and carbonic acid ; but if the  supply of air be
limited, the affinity of the  hydrogen for the oxygen preponderates,
and no carbon is consumed until all hydrogen is converted into wa-
ter.  By this method of imperfect combustion, several forms of car-
bon are  prepared,  such as wood-charcoal  and lampblack.  If we 
•
CHARCOAL  AND LAMPBLACK.
479
take a splinter of wood and  set it on fire, we observe that at first
only the volatile products of the  wood burn with flame, and that a
ni• i--> of charcoal forms inside, and remains unaltered as long as, be-
ino* surrounded by flame, it is protected from the air ; but when the
end  projects beyond the flame, it ignites and burns away,  leaving
only a trifling ash.   If, however, a tube be taken, and, as in  the  fig-
ure, as the combustion advances along the stick b, the burn-
ed portion a be  gradually plunged into a narrow tube, this J
becomes  filled with carbonic  acid, which does  not  support  ft
combustion,  and the cylinder of charcoal formed may thus
be permanently preserved ; on this principle wood-charcoal is
prepared.  Billets  of wood are heaped together regularly, so
as to form a  hemispherical mass of about forty feet diameter  ;
in the centre a hole reaches from the top to the bottom, form-
ing a chimney.   The  outside  is then coated with sods, so as
to render it  impervious to air except at  the bottom, where
some apertures are left.  Burning charcoal is then thrown into  the
chimney, and the fire  communicating to the  billets, these burn with
a supply  of  air so limited  that the charcoal remains unconsumed,
the combustion commencing at the top and proceeding down.  The
outside of the  heap is then covered with denser sods, so  as to  cut
off the supply  of air as the  combustion proceeds.  When the car-
bonization has been completed, the whole mass is covered  up and
allowed  to cool perfectly before  being opened.  In  this country,
most of the charcoal used is  obtained in the preparation of vinegar
by the destructive  distillation of wood, as will be hereafter noticed.
The quantity of charcoal produced  from wood varies very much
with  the  rapidity  of the process ; the generality of fresh   woods
yielding but  thirteen or  fourteen per cent, by a rapid decomposition,
while, when  slowly charred, they may yield  twenty-five or twenty-
six.   The mode of conducting the process, therefore, must be chan-
ged according  as the residual charcoal, or the volatile materials, are
the  most valuable products.   The charcoal preserves, in a remark-
able manner, the structure of the wood from which it is produced,
so that by the microscope some of the most delicate forms of vege-
table  organization  may be traced  in charcoal that has been slowly
prepared.
 Limpblack is formed by a still more direct application of the principle of imper-
fect combustion.  In the apparatus represented in the  figure, a is a pot placed in a
furnace which is vaulted over, so that all vapour from it
m:iy pass into the chamber b, c, while by some apertures
a small quantity of air is allowed to sweep over its sur-
f*H*;';  the sides of the round chamber are lined with leath-
er, and above is a  conical  cover  of coarse  linen, d,
through which the draught from the furnace passes, and
which may be lowered or raised by the cord and pulley.
A quantity of pitch or tar is placed in the pot and made
to boil; it takes fire, and, as  the quantity of air which
has access to it is very small, the hydrogen alone burns,
and the carbon, being carried up by the current in a  very
finely-divided state, is deposited- on the sides and cover
as an impalpable powder.
  Animal charcoal is produced by the decom-
position  of  animal  matters  in close  vessels.-
From its properties, which I shall just  now notice, it is manufactured
 
•
480
PROPERTIES  OF  ANIMAL  CHARCOAL.
 in large quantities for the arts, especially from bones, and is hence
 called Ivory-black or Bone-black.   The bones are placed  in  iron cyl-
 inders, which are arranged, vertically or horizontally, in a furnace,
 in connexion with a series of condensing vessels containing water;
 the  volatile constituents of the  animal matter 'being expelled prin-
 cipally as carbonate of ammonia, of which  a large quantity is thus
 made, the excess of carbon remains in a state of very minute divis-
 ion, mixed  with  the earth of bones (phosphate of lime).
  Some of the most important uses of carbon are founded  on prop-
 erties which the  various forms  of it possess in different  degrees.
 Its  inflammability varies with its density and closeness of aggrega-
 tion ; being least in  graphite, and becoming so great when wood
 charcoal, prepared at a low temperature, has been reduced to pow-
 der for the preparation of gunpowder, as to inflame  sometimes spon-
 taneously, and give rise to destructive accidents.   Carbon possesses
 a remarkable tendency to unite with colouring and odorous  substan-
 ces.  This property is specially  possessed by ivory-black, in conse-
 quence of the extreme degree of division of its particles.   When a
 purely organic body yields carbon, the molecules  of the latter ag-
 gregate themselves to a degree which depends on the temperature;
 and if, as in wood, there be a fusible ash present, this acts as a ce-
 ment, and diminishes the porosity very much.   If the organic sub-
 stance be fusible, as starch or sugar, the closeness  of texture of the
 charcoal becomes still greater, and its utility less ;  but in bones, the
 molecules of  organic  matter are separated by  an  infusible earthy
 salt, and when carbonized, the charcoal is  obtained in the  greatest
 possible state of comminution.   A  still more  efficient charcoal is
formed by calcining dried blood, hoofs, or horns, with carbonate of
potash, which prevents the aggregation of  the particles of carbon,
which, the alkaline salt being washed out with water, is left in  the
most active condition possible.   In the arts, this property is applied
to the purification of sugar ;  to clearing solutions of many  organic
 substances; and barrels in which water is to be kept are charred on
 the  insides,  in order to remove any organic matter described in the
 water, which might be liable  to putrefy.
  The following  table contains some numerical results of the rela-
 tive  decolorizing power  of  equal quantities of  carbon  in various
 forms; the first column containing the number  expressing the pow-
 er of removing the colour  of a  solution of indigo, and the second
column that of a solution  of coarse sugar.  The power  of ivory-
black is taken as  the standard :
Common ivory-black.......*  ~  j   \
Well ignited lampblack...........
Lampblack ignited with pot ashes.......
Charcoal from the decomposition of acetate of potash .
Starch ignited with pot ashes.........
Blond ignited with phosphate of lime  ......
Ivory-black digested in muriatic acid......
Ivory-black digested in muriatic acid, and afterward
  ignited with pot ashes
Blood ignited with pot ashes
lndi,f>
T~
 4
17
 56
119
119
 1*9

45 3
50
%uz
 1

10
 44
 89
10
 17

20
20 
ATOMIC  WEIGHT  OF  CARBON.
481
  The decolorizing power is thus not the same for all bodies.  If
charcoal that had once been used be  again  ignited, it does not re-
cover its activity, as the colouring matter fuses before charrino*, and
thereby lessens its porosity.  Charcoal possesses also a remarkable
power of absorbing gases,  if a fragment of wood charcoal, which
had been strongly heated, and allowed  to cool without  access of
air, be  introduced into a tube containing ammoniacal gas, in the
mercurial pneumatic trough, an  immediate absorption  occurs, to
the amount of ninety times  the volume of the charcoal,   in other
cases the absorption  is not so great; a cubic inch of boxwood char
coal, which is the most active, absorbing
90 cubic inches of ammonia.
8")  "    "     muriatic acid.
65  "    "     sulphurous acid.
55  "    "     sulphuretted hydro-
35  "    "     oleliant gas.  [gen.
40 cubic inches of nitrous oxide
35  "     "     carbonic acid.
 9 25     "     oxygen.
 7 5      "     nitrogen.
 1 75     "     hydrogen.
   These gases in this absorption undergo no chemical change, but
 appear to be retained on the surface of the pores of the charcoal by
 powerful  cohesion,  and probably in the liquid form, as it is such
 gases as  may be  rendered liquid by pressure that are absorbed in
 larger quantity.
   The number  expressing the atomic weight of carbon is not at
 present exactly  known.  By Drs. Prout and Thompson it was fixed
 at seventy-five upon the oxygen, and six upon the hydrogen scale;
 but the investigations of Berzelius and Dulong induced the majority
 of chemists  to  adopt  a higher number, 76*4 or 6*13.   The  latest
 experiments of Dumas and Stass directed to the determination  of
 this  point, induce those eminent  chemists to recur to  the  original
 number, 7.") ;  while  Liebig and Redtenbachar have deduced from
 their researches the numbers 75*8.  Dr. Clarke, from a re-exami-
 nation of Berzelius's results, finds that they  give,  when  corrected
 for some minute sources of error, 75*6; and, until opinion becomes
 more unanimous upon  this important point,  I shall assume as the
 number expressing the equivalent of carbon, 75*6 upon the oxygen,
 and 6*05 upon the  hydrogen scale.
  If we admitted  the truth of Dulong and Petit's law (p. 66, 219),
 connecting the specific heat with the atomic weights of bodies, we
 should consider the equivalent of carbon to  be double that above
 given, as Regnault has  found the specific heat to be 0*241.  This
 idea  appears favoured by the fact, that it is doubtful whether  there
 really exists a combination of carbon containing an odd number of
 equivalents, taking the number as 6*05.  But the force of this result
 is totally obviated  by the fact that the specific heat of carbon varies
 with  its state of aggregation so much, that for poplar charcoal it  is
 0*29b, and for diamond  but 0*147; hence we cannot connect these
 numbers with the chemical equivalent of the body.
  Notwithstanding that carbon is absolutely infusible and fixed, yet,
 from  the variety of gaseous and volatile compounds into which  it
 enters, and whose  constitution is remarkably illustrated by the ap-
plication of the theory of volumes, carbon vapour is  frequently spo-
ken of by chemists, although its existence is purely hypothetical.
I have mentioned (p. 21j) the difference of opinion as to its specific
                             P p p 
482          ANALYSIS  OF  ORGANIC   BODIES.
 gravity, which I assume at 843.   The new results  would appear to
 show  that it is  really but  836*8 upon  the  one, or 418*4  upon the
 other view.

                 General Principles of Organic Analysis.

  Substances which contain much carbon are, in general, easily recognised, by their
being more  or  less combustible, and forming carbonic acid when burned, besides
often leaving a carbonaceous residue.   Even where  ihe bodies  are not inflammable
simply, they deflagrate more or less violently when heated with nitre, and form car-
bonate of potash.
  Although  it is not within the scope of the present work to embrace the details of
chemical analysis,  it would yet be improper  to  omit  a general description of the
methods adopted for the determination of the quantities of carbon, hydrogen, and ni-
trogen, which enter into the constitution of organic bodies.  The general principle
upon which  this process is carried out, consists in supplying oxygen so abundantly
to the organic substance, as that all its carbon shall be converted into carbonic acid
and all its hydrogen into water,  and yet the supply of oxygen shall be so graduated^
and the decomposition  so regularly progressive,  as to admit of the products bein»
collected with accuracy.  The  nitrogen  is  always determined by an independent
operation, in which the other elements are neglected; and, although prpcesses have
been proposed which provided  for a direct valuation of the oxygen, it is found in
practice better to obtain its value by subtracting the weight of all the other  constit-
uents from that of the substance employed.   For the  analysis of an organic sub-
stance, there are, therefore, two processes; the first, to determine the carbon  and hy-
drogen, and  the second  to determine the amount of nitrogen.
  The substance generally used to supply oxygen is the black oxide of copper, pre-
pared by gently igniting the nitrate.  Sometimes chromate of lead is employed, par-
ticularly for bodies rich in chlorine.  Where the substance to be analyzed burns
with difficulty, it is  often necessary, in order to be certain of the complete combus-
tion of the carbon, to pass a stream of oxygen  gas over it at the termination of the
process.
  A  straight tube of hard Bohemian glass, of about sixteen inches long, and from
                                                     one third to half an inch
                                                     in diameter, is to be drawn
                                                     out at one end  to a point,
                                                     which is  to be  sealed and
                                                     turned up,  as in the fig-
ure.  Some  oxide of copper (or chromate of lead, as the case may be) is to be then
poured in so as to occupy about two inches of the tube next the bottom   As much
axide of copper as will  occupy about six inches of the tube is to be then  intimately
mixed with the substance to be analyzed, if it be solid, by rabbin<* in a mortar and
this mixture then introduced.  The mortar is next to be rinsed out with as much ox-
ide of copper as will fill two or three inches; and, finally, pure  oxide of copper is to
be placed for about three inches in front of all.   The "whole materials'thus intro-
duced will occupy about fourteen inches of the tube, when it is shaken down by tap-
ping it, nearly horizontally on the edge  of a table, so as to leave, as in the figure
where the dotted lines mark the spaces of the several portions, a free passage above
the materials from end  to end of the tube.  In these operations the greatest eare
must be taken to avoid  all  access of moisture; the tube, the mortar, and the sutv
stance must be made absolutely dry, and the oxide of copper, being powerfully hy-
groscopic should be ignited before each operation, and allowed to cool under a bell
glass with a capsule of oil of vitriol, or by being placed while very hot in a long dry
tube, which  is then to be corked completely tight.  After the substance and oxide of
copper have been placed in the tube, it is generally necessary to remove even the tra-
ces of damp which might have been absorbed by exposure to the air during the mix-
ing in the mortar.  This is done by means of a small exhausting  syringe, which is
attached to the combustion tube by a cork, a mbe containing fused chloride of ca.-
cium being-interposed    The combustion mbe is  bedded in warm sand, and by
means of the syringe the damp air it contains is withdrawn,  and replaced by a:r,
which, passing over the chloride of calcium, becomes completely dry  After a lew
repetitions of this process, all  moisture is removed,  and the combastion tube is
ready to be  attached to the other parts of the apparatus.

 'i_3     ' ^^^^^^-^^lyLU^^.   These are> lst. a tube of the form repre-
         ^^s*>—     Si^:^  sented in the figure, into which  a little cot-
            a                 o     ton wool is dropped at a, and it is then filled 
ANALYSIS  OF  ORGANIC  BODIES.
483
•with recently-fused chloride of calcium in fragments of the size of a split pea.  \tba.
little cotton wool is also placed, and a sm.ll  tube is connected with it by a cork
To its smaller end a cork is adapted, which accurately fits the end of the combus-
tion tube, and which has been carefully dried.  This apparatus (but without the last
cork) is carefully weighed before the operation.
  The second apparatus is the potash bulb-tube, the invention of which by Liebig was
the great cause of the rapid progress of organic chemistry within the
last few  years, as it facilitated the analysis of organic bodies in a re-
markable degree.  It consists of a tube on which  are blown five-
bulbs; the three  interior  communicating by jnniy wide openings,
but each outer bulb  separated from the  otln is»liV a couple of inches
of tube.   The proportions of the respective bulbs may be collected
from the figure, which represents also the form into which the tube
is bent.  The three central bulbs are to be nearly filled with a strong
solution  of caustic potash (sp. gr.  125), and the apparatus  attached  to the small
tube, b, of the voter tube by a caoutchouc connector tied very carefully on.  It is to
be allowed to incline, at the angle represented in the next figure, so that the carbonic
acid gas, when passing through it, shall bubble from bulb to bulb, without any dan-
ger of expelling any portion of the liquor.
  The combustion tube is to be placed in a sheet iron furnace, the form and size of
which may be collected from the figure,  its open end so far projecting (1£ inches) as

                          m
 that the cork by which the water tube is attached shall not be in any danger of be-
 ing charred, but yet shall be so hot that no water can condense upon it.  The joint-
 ings being found to be  completely tight, and the water  tube and potash bulbs being
 attached, and arranged as in the figure, the analysis may be proceeded with.  Some
 ignited  charcoal  is  to be placed round  the first  three  inches of the tube,  and
 when the pure oxide of copper is completely red-hot, the next portion, which, having
 rinsed out the mortar, contains some traces of the organic substance, is  to be simi-
 larly ignited.  The hydrogen of the substance reduces the oxide of copper, and forms
 water, which is collected by the chloride of calcium in the water tube, and the car-
 bon, also reducing the oxide of copper, is converted into carbonic acid, which, being
 dried in passing over the chloride of calcium, is totally absorbed by the potash in the
 bulbs.   By the addition of burning charcoal,  the combustion of the organic matter
 is made to progress down the tube, the operator being directed in his proceedings by
 the rate at which the evolution of carbonic acid and its  absorption  proceed, until he
 arrives within two inches of the end of the tube.  He then stops until he has made
 the point and the pure oxide of copper near it red-hot, and then closes in the char-
 Coal on  the remaining space.
  The combustion being thus completed, the  tube remains, however, occupied by a
 mixture of watery vapour and carbonic acid, which must not be lost; for this the
 point of the tube  serves.  It is broken with a nippers, and then a current  of air is
 gently sucked, by means of a tube  fitted to the potash bulb-tube, through the whole
 apparatus;  this carries the water vapour to the water tube,  and the carbonic acid to
 the potash, so that all the products  of the combustion are obtained.   The apparatus
 is then taken asunder, and the  potash tube and water tube weighed; the increase of
 weight gives, of course, the  quantities of carbonic acid and of water collected,  and
 hence, by simple calculation, the proportions of carbon and hydrogen contained in
 the quantity of substance that had been operated on.
  If the  substance had been one very difficult  to burn, and  hence requiring oxygen
 to finish its  combustion, the tube is  not drawn out at the end, but widened a little, so
 as to form a small bulb, in which some chlorate of potash is placed.  At  the end of
 the process, this being heated evolves oxygen, which not only burns any traces of car-
 bon that might remain, but serves also to carry the carbonic  acid and vapour fully
 into the  water tube and bulbs.                                             _
  There are a variety of circumstances to be attended to in this operation,  in order to
obtain the hi"h degree of accuracy which alone confers value on numerical results.
These can be3learned only in the laboratory, and not even from the most detailed de- 
484          DETERMINATION  OF  NITROGEN.
scription.   My object is merely to afford an idea of the  general principles of the

mettxod-                        If the substance to be analyzed be liquid and vol-
                             atile, it is introduced into small  bulbs of the size of
                             the figure, by the method  given in page 11.  There
                             are generally two of  these bulbs, one placed  aboul
two and the other about six inches from the sealed end of the tube  as shown in ihe
                                                 figure; the little stem  is broken
                                                 across in the act of inlroducinj
o
        ^^-,-----—-----———i—-^------ ^r—z^J  them, so  that the liquid may
■^•■--^Sg^^^x^****^^   easily  flow out) when,  by  the
approach of a piece of red-hot charcoal, it is gently heated, so as to form a vapour.
The peculiar precautions necessary in the  management of the analysis ol such bod-
ies  and the methods  adopted for non-volatile liquids and other bodies of peculiar
properties, can only be learned by experience, and do not fall within my purpose to

  To determine the nitrogen of an organic substance,  a long combustion tube is
taken (2 or 2*5 feet), sealed at one end, but not drawn out, as in the figure.  Next


        f___________j______J_________________J__________1 ' '  j"./~r-<>--.r,',ruV \

the sealed end is placed carbonate  of copper for a space of six or eight, inches, and
then the pure oxide of copper, the mixture, the rinsing of the mortar, and again
pure oxide, occupying fourteen or fifteen inches, exactly as in  the former case; in
front of all, five or six inches are occupied by clean metallic copper in a  finely-di-
vided state, either as reduced by hydrogen from  the oxide, or as very thin turnings.
These divisions and the general form of the tube  are given by the figure.  To  the
combustion tube there is fitted by a tight cork a quill tube, which is in connexion
on  the one hand with  an exhausting syringe, and then, by a vertical tube more than
thirty inches long, passes to the mercurial pneumatic trough.  All the joinings being
found tight, and the combustion tube arranged in the furnace, red-hot charcoal is ap-
plied to the closed end of the tube, where it disengages carbonic acid from the carbon-
ate of copper, which, sweeping through the apparatus,  expels the atmospheric  air.
To render this the more effectual, the whole apparatus is exhausted by the syringe,
and again filled with  carbonic acid, and this is  continued until the bubbles  of  gas
which come over are  perfectly absorbed by solution of potash.   In this expulsion of
the air of the apparatus, not more than one half of the carbonate of copper  should
have been rsed.
   The fire is now to  be withdrawn  from the closed end of the  tube, and applied to
the part occupied by  the metallic copper.   When this is red hot, the combustion is
carried backward, just as in the former example;  and  when  all the substance  has
been burned, the  coals are applied to the remaining carbonate of copper, which,
evolving carbonic acid, clears out all the  nitrogen of the apparatus, just as it had in
the commencement cleared out all the atmospheric air.   The mixed gases that are
produced in this operation are received in a bell-glass  which contains some strong
solution of potash, by which the carbonic acid is absorbed, and the nitrogen remain-
 ing may then be measured.  The volume of gas is next to be corrected for temper-
 ature and pressure, as directed in p. 57 and 20, and its weight then calculated.
   The use of the metallic copper in the front of the mixture requires notice; when
 nitrogen passes over  red-hot oxide of copper, there is always some nitric oxide form-
 ed, which would falsify the result, as its volume is double that of the nitrogen it con-
 tains ;  but nitric oxide is  completely decomposed by red-hot metallic copper, pure
 nitrogen being evolved, and hence  the purity of the resulting gas is secured by this
 arrangement.   Indeed, in all combustions of an azotized body, the mixture should
 have some bright metallic copper in front of it.
   The direct valuation of nitrogen is thus a very delicate operation, and occupies
 several hours.   If the substance  contain a large quantity of nitrogen, its amount
 may be indirectly ascsrtained in a much simpler way.  The quantity of carbon in
 the substance is first learned by an ordinary analysis, then another combustion lube
 is arranged  with very clean copper in front; but, "in place of adapting the water tube
 and bulbs, the water is taken no count of, and the gases evolved are collected in
 narrow graduated tubes, over mercury.   In order to clear out the air from the  tube,
 some of the mixture next the sealed end is first ignited, and the gas allowed  to es-
 cape, the tubes being filled from the products of the subsequent periods of combus-
 tion.   In this case no weights need be attended to, as it is  only the analysis of the
 gas in the t bes that is required for the result.  The volume of gas in a  tube being 
       CARBONIC  ACID,  ITS  PREPARATION,  ETC. 485

 marked, some solution  of potash is introduced and agitated in it.  The carbonic
 acid is absorbed, and the nitrogen remains, the volume of which is read off, taking
 care  that  the level of  the mercury is the same inside as  outside the tube.  The
 relative volumes of the  carbonic acid and nitrogen gases are thus found; and as an
 equal volume represents an atom for each, the relative number of atoms of carbon
 and nitrogen is thus determined; and as  the total quantity of carbon is known by a
 previous experiment, the total quantity of nitrogen may be  calculated.  When the
 relation of the number of atoms of carbon to those of nitrogen is simple, as occurs
 in cyanogen and oxamide, C2N., mellon, C3NZ, caffeine and taurine, C4N., this method
 gives very accurate results.
  Where  the organic substance contains chlorine, sulphur, arsenic, &c, it is to he
 destroyed  by nitric acid, or by ignition with potash or lime, and the inorganic con-
 stituents then determined in the ordinary way.  In organic salts the metallic basis
 is determined by igniting the substance, burning away the organic element, and de-
 termining the quantity of inorganic base by whatever method  is best suited to its
 individual nature.

   Carbon combines with oxygen in several proportions, of which
 three, those in which  it forms the carbonic oxide, and the carbonic
 and  oxalic acids,  are the most important, and deserve  the most de-
 tailed  description.

              Of  Carbonic Acid.   Eq. 275*6 or 22*05.

   Carbonic acid  exists in the atmosphere as  a product of combus-
 tion  and of the  respiration of animals.   Combined with metallic
 oxides, it forms  the numerous class  of native  earthy and metallic
 carbonates, of which the carbonate of lime is much the most impor-
 tant.   It is a result, also, of the  slow decomposition of most vege-
 table substances,  and is evolved in great quantity from the ground
 in volcanic countries.  In the fermentation of sugar it is produced
 in abundance along with alcohol.   For the purposes of the chemist,
 it is generally  prepared  by decomposing  marble or calc spar  by
 means of any stronger acid ;  from its cheapness, and the solubility
 of the residual salt, muriatic  is  generally  employed.   Some frag-
 ments  of white marble being placed in a  wide-necked bottle, the
 acid, diluted with  its own volume of water, is poured in by a funnel
 tube, as  in the figure, p. 247, and the gas which is  evolved is con-
 ducted by  the bent tube, to be made use  of as  required.  The re-
 action consists in  H.Cl. and Ca.O. . C02 producing H.O. and Ca.Cl.,
 which  remains in  the bottle, while C02 is driven off.   Carbonic acid
 being dissolved by water, and  it being generally required in  larger
 quantity  than it is convenient to  collect over mercury, we take ad-
 vantage  of the density of the gas  to  collect it  in  dry jars,  as de-
 scribed and figured for chlorine in p. 301.   The  jar is known to  be
 full when a lighted taper, applied near the  mouth,  is instantly ex-
 tinguished.
  The properties  of carbonic  acid  are very remarkable ; it is per-
 fectly colourless and invisible ; it is irrespirable, producing, when
 an attempt is made to breathe it,  violent spasms of the  glottis.   If
 it be inspired, mixed with  air, even in the proportion of 1 to  10, it
 gradually produces stupor and death, acting as  a narcotic poison.
 Its specific gravity is 1*521.   It  hence, when  disengaged in  large
 quantities,  whether by natural operations or in processes of manu-
 facture, accumulates in all  cavities within its reach, and may cause
fatal  accidents  to  animals who enter unadvisedly.   Thus workmen 
 486      LIQUID  AND  SOLID  CARBONIC  ACID.

 engaged in cleaning out dry wells or vaults, or the large vats from
 which  fermenting liquors have  been run off, should carefully ob-
 serve whether a candle can  remain for some time burning brightly
 at the bottom.  In volcanic countries, caverns are frequently occu-
 pied to the level of  their surface by this  gas, exhaled from the
 ground ; and an experiment  often tried, to amuse the traveller, con-
 sists in walking into such a  cavern with a dog, which, holding the
 head near  the floor, is almost instantly asphixiated by the layer  of
 carbonic acid, while  the  men, whose heads are  above its level,
 breathe pure air ;  the dog, on  being thrown immediately into  a
 neighbouring pond, recovers from his stupor.  Carbonic acid does
 not support combustion.   A taper plunged into a jar full of the gas
 is instantly extinguished,  and the high specific gravity of the gas
 may be well shown by placing a lighted taper at the bottom of a jar
 containing air, and taking in the  hand another jar containing car-
 bonic acid ; on inclining this jar, the heavy gas pours over the edge,
 nearly as water would do, into that in which the taper is placed,
 and, falling to the bottom, extinguishes it.
   Water dissolves its own volume of carbonic acid  gas, forming a
 solution of an agreeably acidulous taste, which sparkles when agi-
 tated ; it colours blue litmus  paper of a wine-red, which  disappears
 on exposure to the air or by heat.   By means  of pressure, water
 can be made to absorb a large quantity of carbonic acid, which es-
 capes with effervescence when the pressure  is removed, and  is thus
 the basis of a variety of agreeable effervescing beverages.  Solution
 of carbonic acid in water precipitates solutions of lime and barytes
 white, forming carbonates, which redissolve in an excess  of the car-
 bonic acid.
  Under a pressure of thirty-six atmospheres, carbonic acid may
 be liquefied.   It then forms a colourless, exceedingly mobile  liquid,
 of specific gravity 0*83 at 32 , which is  remarkable for  its  exces-
 sive expansibility by heat, it having four times that of air, or nearly
 one per cent, for each degree  of Fahrenheit. When the pressure
 is suddenly removed from  this liquid acid, it gasefies with such ra-
pidity that, one portion absorbing heat from the  other, this latter is
rendered solid (see page 86).  Solid carbonic acid can thus be ob-
tained  in large  quantity by thp apparatus contrived by Thilorier.
It is a white body, in filamentous masses, like  asbestus ; it evaporates
but slowly  ; it is very soluble in alcohol and  ether ; the ethereal so-
lution produces by its  evaporation the most intense cold known, es-
timated at  —180 degrees of  Fahrenheit.
             The composition of carbonic acid may be determined
           by very simple experiments.  If into a bottle of pure ox-
           ygen gas we insert a little bit of charcoal, ignited at one
           point, at the end of the wire a, as in the figure, it burns
           with vivid scintillations, and the oxygen is all converted
           into carbonic acid.  The  stopper  of the bottle, through
           which the wire passes, being perfectly tight, it  will be
           found that  the volume of  the gas, when cold, has not
           sensibly altered, and thus that carbonic acid contains its
           own volume of oxygen.  It consists, therefore, of
 
            MANUFACTURE  OF  POTASHES.           487

             Two volumes of oxygen  .  1102 6x2 — 2*20o 2
             One volume of carbon vapour  ....  SliiO
           Forming two volumes of carbonic acid  2-*-30482
           Of which one volume weighs, therefore,  = 1524 1
  The  corrected specific gravity of carbonic acid, 1*521, indicates
that the theoretical density of carbon vapour should rather be taken
as S'-{(j  than 843.
  To demonstrate the existence of carbon in carbonic acid gas, it
is sufficient to heat to dull redness, in a current of the gas, a small
alobule of potassium.  The metal takes fire, burning with a brilliant
violet flame, and forms potash, while carbon is abundantly deposit-
ed as a brilliant jet-black film on the interior of the tube.
  Carbonic acid combines  with the bases, forming a very important
class of salts, the carbonates.   It forms neutral, basic, and acid salts,
which  last are really double salts, containing  carbonate of water,
which, however, exists only in  combination, as the carbonic  acid
does not combine  with water directly in definite proportions.  All
salts of carbonic acid are known, by yielding, when acted on by
muriatic  acid in the cold, the gas  possessing the properties  now
described.
  Carbonate of Potash.—K.O. . C02.  Eq. 866*3 or 69*4.  This  salt,
which  is  the  great source of all other combinations of this  alkali, is
obtained  for  the purposes of commerce from  the ashes  of plants
growing  at a distance from the sea.  The vegetable  juices contain
potash, combined  with various acids, as the nitric, oxalic, acetic,
malic,  &c, which, by the burning of the wood, are  converted  into
carbonates.   The  produce differs according to the  kind  of wood,
and with the season.  The softer and more juicy the plants are, the
more potash  they  yield.   Plants of  the natural families compositae
and cruciferm are the richest;  the  grasses rank next; and among
the woods, the leaves yield more than the small branches, and these,
again,  more  than  the stems.  In countries where there are large
forests, as America  and Russia, the small wood is burned,  and the
ashes collected ; these are boiled with water in large  iron pans  or
pots, from  whence the name potash is derived.  By this means, a
lara*e quantity of insoluble salts is separated, and the carbonate  of
potash, which dissolves,  is obtained in  a purer  form  by evaporation
to dryness.   It then constitutes the pearlashes, or refined potashes
of commerce. Even these still retain much silica, sulphate of potash,
and chloride  of potassium, so that the best American  pearlashes sel-
dom contain more than eighty-five  per  cent., and Russian potash
often not sixty per cent, of true carbonate of potash.
  The purification of  pearlashes being difficult, carbon-     -p.
ate of potash is  best  prepared for chemical purposes by    // j\
calcining cream of tartar ;  the tartaric acid which it con-   / jd\ A
tains is^decomposed, and  carbonic  acid formed, which  //f*~-*-l...\
combines with  the  potash ;  the mass  is digested with y\   \ "~j
water,  filtered to separate the  excess  of charcoal, and  \1~~~4y
evaporated to dryness in a  clean iron  vessel.  A white  \  \£'J
granular  mass is obtained, the salt of tartar of the older   \\JJ
pharmacopoeias.   It is very deliquescent, soluble in half    Kp
its weight of water, and crystallizes with  two atoms of  water  in 
488
CARBONATE  OF  SODA.
oblique rhombic octohedrons, a, a, a", a"', as  in the figure (K.O.
CO -j-2 Aq.).  It reacts strongly alkaline.  It is almost insoluble in
alcohol and when added to w°eak spirit,  combines with the excess
of water, forming a heavy fluid, which remains separated from the
lighter and stronger alcohol above.
  As it is only the carbonate of potash that constitutes the value of
pearlashes  in the manufactures to which it is applied, it is important
to be able to determine, by a single and simple operation, the relative
worth of commercial samples.  This process is termed alkalimetry.
The best method of performing it will be described under the head
of " Carbonate of Soda."
  Bicarbonate of Potash, K.O.. C02 -f H.O. .CO,, is formed by passing
                 a current of carbonic acid gas through a  saturated
                 solution of the neutral carbonate, the temperature
                 of which should not be above 100\   On cooling,
                 it crystallizes in right  rhombic  prisms of eight
                 sides, as in the figure.   It dissolves in  four parts
                 of cold water, and in much less when hot.  If its
                 solution be boiled, it abandons its second atom of
                 carbonic acid, and becomes neutral carbonate.  Its
                 reaction on vegetable colours is feebly alkaline.
  Carbonate of  Soda—Na.O. . C.02+10  Aq. ; Eq.  667*3 + 1125 or
53-474- 90 — is manufactured upon a very large scale, for the purposes
of commerce, from common salt, which must first be converted into
sulphate of soda in the manner described in page 427.
  The  dry  sulphate of soda is to be mixed with its own weight of'
limestone or chalk, and half its weight of small coal, and the mix-
ture being  reduced to fine powder, is introduced into a reverbera-
tory furnace, such as is figured in page  333, in charges of about 2 cwt.
each.   After  being exposed to a full red  heat for about an hour, on
the floor of the furnace, the mass fuses, and being well stirred for a
few minutes,  is raked off through the opening in the side, and re
ceived in metal  boxes.   It forms a black mass, which is known in
commerce as black-ash, or British barilla.  The theory of this process
is very remarkable ; the sulphate of  soda being melted in contact
with the coally matter, is deoxidized, its oxygen being carried off by
the carbon, and sulphuret of sodium remaining.  This is immediately
decomposed  by the carbonate of lime,  sulphuret  of calcium  and
carbonate  of  soda being  produced.  S.03 . Na.O.  and  2C. form
2C.02and Na.S., which,  with Ca.O. . C02, gives Ca.S. and Na.O.. C.
02.  As, however, much of the carbonic acid of the chalk is expelled
by the heat, a certain quantity of the soda remains caustic in the
produce, and also some sulphuret of sodium undecomposed.  This
black-ash generally contains about 22 per cent, of real alkali.  To
obtain the  soda under a purer form, the masses of  black-ash are
broken up, and  digested in warm water until all soluble matter is
extracted.  The  residue consists of sulphuret of calcium and the
excess of coally matter.   The liquor  is then evaporated to dryness,
and the saline mass obtained is calcined in a reverberatory furnace
with one fourth  of its weight of sawdust, in order to  convert all of
the alkali into carbonate, and to burn out some traces of sulphur
which still remain ; on being then redissolved in water, and the clear 
METHOD  OF  ALKALIMETRY.
489
solution dried down, it constitutes white-ash, or soda-ash of the best
quality,  containing from 45 to 50  per cent,  of real alkali.
  I'm  the preparation of the crystallized carbonate, the soda-ash is
dissolved in boiling water, and the  solution being  evaporated to a
pellicle, is  left to  crystallize  for  some days.   The mother  liquor,
when drained  off the crystals, yields, when dried down, an inferior
soda-ash, which is, however, applied to many manufacturing uses.
The pure carbonate of soda crystallizes in  flat, oblique  rhomboidal
prisms, as in the  figure,  which contain
ten atoms of water, Na.  . C.0,-4-10 Aq.
In a dry atmosphere, they lose by efflo-
rescence all their water, and fall into a
white powder.  It dissolves in five parts
of cold, and in less than one ol boiling water.  By a  gentle heat,
the  salt undergoes aqueous fusion,  and when dried, gives a white
powder, soda siccata.  By a strong  heat, the  carbonate of soda melts,
but is  not otherwise affected.
  Prior  to  the invention of  the soda process described above, the
carbonate of soda was  obtained from  the ashes of marine  plants, as
the salsola,  and various fuci, which  were burned in large quantities
on the west coast  of Ireland, in the  Orkneys, and on the  coasts of
France and Spain.   The saline products thus obtained  were  known
in commerce as kelp, barilla, varec ;  but these sources of alkali may
now be  considered as extinct.  Graham  states, on  the authority of
Mr.  Muspratt, that in 1838 there were manufactured from common
salt  50,000 tons of soda-ash and 20,000 tons of crystallized carbon-
ate,  and the manufacture is continually on  the  increase.
  To the practical chemist and the manufacturer, it is important to be able  to deter-
mine, by a rapid  and easily executed process, the real quantity of alkali present in
any sample of pearlashes or  soda-ash that may be in the market.  All such pro-
cesses depend on measuring the quantity  of sulphuric acid necessary to produce a
neutral salt with  a certain weight of the sample; but  in the management of the de-
tails considerable difference may exist.  A mode which I have found to be  very ac-
curate, and easily executed  even by ordinary persons, consists  in preparing before-
hand a stock of a dilute sulphuric acid, of sp. gr. 1068 at a temperature of 60°.  This
acid may be formed  by mixing one ounce of the strongest oil of vitriol with nine
ounces of water;  but its sp. gr. should be verified by trial before being used.
  One hundred grains of the sample to be tried are then to be powdered and stirred
up in a capsule with an ounce of water.  A glass jar  about a foot high  and an inch
wide, provided with a  lip to pour from and a steady foot, and graduated  into 400
parts, of which each part indicates five grains of the standard acid, is  to  be filled
with  the acid up to the 400th mark, and then, by pouring very cautiously  from the
lip a few drops at a time, the alkaline liquor in the capsule is to be exactly neutral-
ized. A little bit of litmus paper may be left in it, and stirred about well after each
addition of a few drops of acid.  A drop of  acid in excess reddens the litmus paper
permanently; and as this does not injure the result sensibly, it may be done in order
to secure  complete neutralization.  The graduations of the  glass being numbered
from above downward, simple inspection shows how much acid has been employed;
and it is only necessary to multiply the number of divisions by thirty-one  if the al-
kali be soda, or forty-seven  if the alkali be potash, and divide in each  case by 100,
to obtain the quantity of real alkali present in the 100 grains examined.
  The principle of this method is, that 100 grains of the standard acid contain eight
grains of  dry sulphuric acid,  and hence 100 measures contain forty grains, which
number being  that of the equivalent of the acid, neutralizes almost exactly thirty-
one Tains of soda or forty-seven grains of potash, which are the equivalent weights
also." To find, therefore, the quantity of either alkali in  a sample neutrahzed by,
for example, 137 measures of acid, we say,
               For potash,   100 : 47 : : 137 : -*- J-^x-17--  CM ;
               And for soda, 100 : 31 : : 137 : .r= "J x31=42*5."
                                 Qqq
 
490
CARBONATE  OF  LIME.
  A table may easily be constructed beforehand on those principles, so as to save
even this little calculation.  The greatest amount of error at all likely to occur in
this process is one division of acid in excess.  The difference made by this, however,
does not influence the result for commercial purposes ; thus, in the examples above
taken, if the quantity of acid had been measured wrongly at 138,  the indications
would be, for potash,'61*9, and for soda, 42*8; the error in no case exceeding half a
part per cent., and being exactly counterbalanced by taking  the numbers 31 and 47
instead of the correct equivalents,  31*3 and 47*3.
  Bicarbonate of Soda, H.O.  . C.02 + Na.O. . C02,  is formed by pass-
ino* a current of carbonic acid gas through a cold solution of carbon-
ate ;  the new salt precipitates in  small opaque crystals, having the
appearance of starch.  It requires fifteen parts of cold water for its
solution; it  has  an alkaline reaction, but is not disagreeable to the
taste.
  Sesquicarbonate of Soda occurs native on the banks of certain lakes
in northern Africa, whence  it is exported under the  name of trona.
Its  formula is  2Na.O. . C.02 + 3C024-4H.O.  It  cannot be formed
at will.
  Carbonate of Barytes.—Ba.O. . C02.   This salt exists native, crys-
tallized in oblique rhombic prisms; it is insoluble in pure water, but
dissolves in water containing  carbonic acid.   It is very poisonous.
It may be prepared  artificially  by mixing  solutions of chloride of
barium and carbonate of ammonia; a white precipitate falls, which,
being well washed and  dried, is pure carbonate  of barytes.   It is
used  in the  analysis of minerals containing alkali, and for the prep-
aration of various salts of barytes.  It has been used in the manu
facture of glass.
  Carbonate of Strontia resembles perfectly the former.
  Carbonate of Lime.—Ca.O. . CO,.  Eq. 632*5 or 50*7.   The cir-
cumstances and  forms under  which this salt exists in nature have
been  so  frequently noticed (p. 477, 225), and the molecular consti-
tution and peculiar relations to light of its crystals so fully described,
that it is not necessary to enter upon its history here  farther.   It
may be prepared pure by decomposing chloride of calcium by means
of carbonate of ammonia ; it forms then a white powder insoluble in
pure water, but dissolving in water containing carbonic  acid.  This
is not due to the formation  of a bicarbonate of lime, but owing to a
specific  solvent power which  a  solution  of carbonic acid  in water
has on many bodies,  as silica,  phosphate  of lime,  &c, which are in-
soluble in pure water.  It is thus that carbonate of lime is held dis-
solved in most waters, and  is deposited  as a crust on  the interior
of any vessels in which such water may be boiled.   By the gradual
dissipation of the carbonic acid on exposure to  the air, the carbonate
of lime may be  slowly deposited,  and then crystallizes ; thus are
formed the remarkable stalactites, &c, of limestone caverns.
  Carbonate of Magnesia.—Mg.O. . CO,.   This salt exists anhydrous
             in nature, crystallized in rhombohedrons like calc spar.
             By dissolving magnesia  in water by  a stream of car-
             bonic acid, it may be formed, and is  gradually deposit-
             ed in rhomboidal  prisms of six or eight  sides, as m, u,
             a, in the figure, which contain three atoms of water.   It
             is this salt, Mg.O. . C.0, + 3 Aq., which exists in Mur-
             ray's solution of magnesia.   When acted on by pure hot
             water, this salt  is decomposed, carbonic acid escaping,
 
CARBONATE  OF  IRON,  ETC.
491
and basic carbonate of magnesia being produced.  It is this basic car-
bonate which constitutes the magnesia alba, or common carbonate of
magnesia of the shops.   It is prepared by mixing boiling solutions
of sulphate of magnesia and carbonate of soda, leaving the former
slightly in excess.  The  precipitate is very light  and  bulky, and al-
most totally insoluble in  water.  One fourth of the carbonic acid is
given off in this reaction, and the precipitate is found to be a com-
pound  of carbonate and  of hydrate  of magnesia, Mg.O. . H.O.-(-3
(Mg.O. . CO,. H.O.), or  4Mg.O. + 3C02 + 4 Aq.
  The nature of dolomite or magnesian limestone has been already
sufficiently noticed (p. 348).
  Carbonate of Manganese, Mn.O. . C02,  is a white powder formed
by double decomposition, and decomposed by a red heat.
  Protocarbonate of Iron, Fe.O. . C02, exists native in rhombs iso-
morphous with  calc  spar.  It  may be prepared by  decomposing
protosulphate  of iron by carbonate of soda ; it forms a white pre-
cipitate, which,  by exposure to the air, rapidly absorbs oxygen and
gives out carbonic acid, becoming green, and ultimately red, being
then mere peroxide of iron.  The carbonate of iron  can therefore
scarcely be obtained  pure ;  but by mixing the fresh precipitate with
sugar, and evaporating to dryness with constant agitation, a quantity
of the  carbonate remains undecomposed,  being protected from the
air  by  a varnish of sugar on its particles, and thus constitutes the
carbonas ferri cum saccharo of pharmacy.   The  carbonate of iron is
soluble in water containing carbonic acid, and exists thus dissolved
in chalybeate spas.
  When solutions of sulphate  of zinc and carbonate of soda are
mixed together, a basic carbonate of Zinc is formed, consisting of 2
(Zn.O. . CO,)-f-3Zn.O. . H.O. if the solutions were warm, but of Zn.
O.. CO?-r-2Zn.O.. H.O. if cold; carbonic acid gas is given off in
both cases.
  There are two carbonates of Copper, both basic ;  the green carbon-
ate  exists native (malachite), and is used as a pigment.   It may be
formed by mixing solutions of a salt of copper and an alkaline car-
bonate ; the precipitate is at first flocculent, and of a fine pale blue,
but when boiled it becomes dense, granular, and  bright green: its
formula is 2Cu.O.-4-C.02-|-H.O.   The blue  carbonate  exists  also
native  (Copper-azure), but cannot be prepared artificially so as to be
permanent:  its formula is 3Cu.O. + 2C.02-(-H.O.
  Carbonate of  Lead, Pb.O. . CO,,  exists  native, crystallized in
forms isomorphous with those of the carbonate of barytes, and may
be formed as a finely-crystalline powder  by  decomposing solution
of nitrate  of lead by carbonate  of soda.  There are several basic
carbonates of lead, which, in a  greater or less degree  of mixture,
constitute the White Lead, or Ceruse of commerce, so much used in
painting.  The composition of white lead generally  falls between
those given by the formulae 3Pb.O.+ 2C02+H.O. and 4Pb.O + 3C
02 + H.O.
  For  the manufacture of white lead, very thin sheets of the metal
are  exposed to the fumes arising from vessels containing weak vin-
egar, which are kept moderately  warm by being imbedded in fer-
menting tan ;  the lead, absorbing oxygen from  the air, combines 
492
CARBONIC  OXIDE.
with the acetic  acid, forming a basic acetate of lead, which is de-
composed by the carbonic acid of the surrounding air, basic carbon-
ate of lead being produced, and neutral acetate of lead remaining;
this, under the Action of the air, takes up a new quantity of lead,
and the same decomposition is renewed, a minute quantity of acet-
ic acid  thus serving to  produce a very large quantity of ceruse.
This process has lately been much improved by exposing litharge,
finely ground and  mixed with one per cent, of acetate of lead, to a
stream of carbonic acid,  generally derived from the fermenting vats
of a brewery ; the  one portion of neutral acetate successively unites
with all the litharge to form basic acetate, the successive portions
of which  are decomposed by the carbonic acid, white lead beino*
formed, and the original quantity of neutral acetate remaining un-
combined at the end.
  The carbonates of the  other metals are unimportant.
  Carbon combines with the metals to form carburets,  of which the
best known are  those of iron and silver; the former has been fully
noticed  in the description of cast-iron and steel (p.  360), and the
carburet of silver  is  a gray powder, which  remains when certain
silver salts of organic acids, as the citrate and tartrate, are imper-
fectly burned away.

          Carbonic Oxide.—CO.  Atomic Weight 14*051
  If carbonic acid gas be passed through a tube containing red-hot
charcoal, it takes up as much more carbon as it already contained,
and forms carbonic oxide ; its volume being thereby doubled.  The
gas may also be prepared by heating to redness, in an iron retort,
a mixture  of charcoal and chalk, when the carbonic  acid evolved
from the latter combines with the excess of carbon, and forms car-
bonic oxide ; in  place of charcoal, iron filings or zinc may be used;
the metal, in this case, takes half of the  oxygen from the carbonic
acid, C02 and Zn. giving Zn.O. and CO.
  A very  simple and elegant way of obtaining this gas consists in
warming strong  oil of vitriol with crystals of oxalic acid, in a flask,
a b, from which  a tube,/, passes to a bottle containing solution of
                            caustic  potash, a, as  in the  figure;
                            from this another tube conducts to
                            the  pneumatic  trough.   The  oxalic
                            acid, C203-f H.O., yields  up  its basic
                            water to the  sulphuric acid, and, as
                            the  oxalic  acid cannot  exist except
                            in combination with  some base, it is
                            resolved in carbonic oxide  and  car-
                            bonic acid (C203- CO. + C.OJ, which
                            are evolved as gases, mixed in equal
                            volumes ; in  bubbling  through  the
bottle containing potash, the carbonic acid is completely absorbed,
and the  pure carbonic oxide may be collected over  water.
  It is a colourless, inodorous gas, and has no  action on vegetable
colours; it extinguishes a taper, but is combustible, and, burning
with a pale blue flame, forms  carbonic acid.   It is this gas which
produces, on the top of  a clear coke fire, a blue flame, which ap-
 
MANUFACTURE  OF  OXALIC  ACID.       493
pears purple when seen with  the  red background  of the glowing
cinders.  It contains half its volume of oxygen ;  its specific gravity
is 972*8.   Carbonic oxide appears  to enter into  union with a great
variety of bodies, and  to act  in such  compounds as a compound
radical.

      Oxalic Acid.—C203 or 2(CO.) + 0.  Eq. 451*2 or 36*1.
  Oxalic acid  is one of the most  important organic bodies.  It is
found combined with potash, forming the Salt of Sorrel, in several
plants of the genera oxalis and rumex, and  combined with lime in
the roots of rhubarb, and in a variety of lichens.  It was formerly
extracted  principally from the oxalis  acetosella, from  whence its
name is derived, but is now manufactured in larger quantities arti-
ficially.   It is  generally a product of the oxidation of vegetable sub-
stances  by nitric acid, on which  fact its mode of preparation is
founded.  The substances employed are usually starch or sugar, a
quantity of which is placed in an earthen pipkin, of which a great
number are arranged in a shallow vessel containing warm  water;
about four  parts of nitric acid, specific  gravity 1*42, are poured into
each pipkin.   The starch is rapidly oxidized, and nitrous fumes giv-
en off abundantly ; when the action has become slow, one part more
of acid is to be added,  and the heat increased.   The liquors so ob-
tained, are mixed,  evaporated  to a pellicle, and set aside to crystal-
lize, and the crystals are purified by re-solution  and crystallization.
From the  mother liquors new quantities of  oxalic acid  may be ob-
tained by heating with more nitric acid.
  If we consider the sugar in  its dryest form as being C,2H909, the
action of the nitric acid  should  consist in first  removing the  nine
equivalents of hydrogen, and substituting for them nine  equivalents
of oxygen; thus Cl2Il9Ou and 6N.O3 should give  6(0,0,) with 9H.0.
and 6N.02.  But the action is not  so simple, as  other products, es-
pecially the Saccharic Acid, are at the same time formed.   By means
of permanganate of potash, however, the carbon of sugar may be
very elegantly and  directly changed into oxalic acid, CJH^O,, and
6(Mn20;+K.O.) producing 12(Mn.02)  with 9H.0. and  6(C203+K.
0.), the oxalic acid formed exactly neutralizing the potash of  the
manganic  salt  employed.
  The oxalic acid crystallizes from its  solution in oblique rhombic
prisms, of which those planes marked i c are prima-  «----:—
ry, and af secondary :  the summit is often dihedral,  /h"
in which case  the plane a, and that vertically oppo-  kK\ c
site to it, are absent.   These crystals contain three ct\-\-—
atoms of water, of which one is basic: COj + H.O.   \^—2
-f-2 Aq.  When warmed, they give off 2 Aq., and  the hydrate of
oxalic  acid remains as a white  powder, which  melts at 350 , and
when heated farther sublimes, a portion  being, however, decompo-
sed ; the products of the reaction of oil  of vitriol  on oxalic acid have
been already noticed (p. 492).  Oxalic acid is converted into car-
bonic acid  by  contact with many peroxides,  as the peroxide of man-
ganese, by which means the technical value of manganese ores may
be determined (see p. 355).   By contact with a great excess of hot
nitric acid or  of chlorine, it is also converted into carbonic acid. 
494
OXALATES OF  POTASH.
   The acidity of oxalic acid  is very great; a grain of it dissolved
in 30,000 grains of water will still affect litmus paper.  It neutrali-
zes the alkalies perfectly, and forms with them two series of acid
salts.  In the neutral oxalates, the oxygen of the acid to that of the
base is 3 : 1.   By heat, those of the metals proper are generally con-
verted into carbonic acid and metal, C203+M.O. giving C204 and M.
Those of the earths and alkalies evolve carbonic oxide, and produce
a carbonate,  CA+M.O. giving CO. and C02+M.O.   The former
action is  usefully applied to obtain cobalt and nickel in the metal-
lic state.
  Oxalic  acid  is detected easily  by its strong acidity, and its not
leaving a carbonaceous residue when heated.  Its solution gives,
with lime-water, a precipitate  which is insoluble in an excess of ox-
alic acid, or of any  organic  acid.  It precipitates, also, the  solu-
tions of barytes and lead.  It acts  violently on animals as a poison;
for an antidote magnesia is the best, but chalk or whiting is the most
readily procured.
  Several of the oxalates deserve special  notice.   There are three
oxalates of Potash, remarkable  as being the bodies by which Wollas-
ton satisfied himself of the truth of the law of multiple combination,
p. 208, their proportions of acid being as 1 : 2 : 4.
  The neutral  Oxalate  of Potash,  K.O. . C203 + Aq., may be formed
by acting on sugar by  permanganate  of potash, or by heating any
fixed organic matter, as sawdust or paper, with an excess of potash,
below redness.  It is more simply produced by neutralizing oxalic
acid, or the following salt, with carbonate of potash;  it crystallizes
in rhombic prisms, of  a bitter taste, which dissolve in three parts
of water, and are insoluble in alcohol.
  Binoxalate  of Potash, K.O.. C03+H.O. . C203 + 2 Aq., exists  nat-
urally in the  various  kinds of sorrel,  from whence it was originally
extracted under the  name of Salt of Sorrel, but is now artificially
made.   One  part of  oxalic acid is exactly neutralized by potash,
and then exactly as much more oxalic  acid is added to the solution,
from which, by evaporation and cooling, the salt crystallizes in ob-
lique  rhombic  prisms, which  are soluble in forty parts of cold  and
in six parts of boiling water.   Its taste  is strongly  acid and saline,
and it is poisonous, though  less so than  the  acid uncombined.
When  heated,  the  salt is decomposed, evolving carbonic acid  and
carbonic oxide, and leaving a  residue of carbonate of potash, which
should be scarcely coloured if the salt were pure.
  Quadroxalate of Potash, K.O. . C203+3H.O. . C203-f 4 Aq., is form-
ed by neutralizing one  part of oxalic acid by potash, and adding to
the solution three times as much oxalic acid more.  It may also be
prepared by dissolving  the binoxalate  in muriatic acid, which takes
half of the alkali, and the quadroxalate crystallizes out.   This and
the last  ealt  are indiscriminately  sold in commerce as salt of  sor-
rel, and also  often as Salt of Lemons, for removing iron moulds and
stains of ink, vyhich they do by  forming, with the peroxide of iron,
a soluble double salt.
  There is but one oxalate of Soda ; it is not important.
  Oxalate of Lime, Ca.O.. C203-f2 Aq., exists abundantly in nature,
forming the hard earthy basis of many lichens, and may be prepared 
         DOUBLE  OXALATES  OF  POTASH,  ETC.     495

by mixing  solutions  of oxalate of ammonia and of any soluble salt
ol lime.  It forms  a  white flocciilent precipitate, which, by boilino-
becomes heavy and granular.  It is totally insoluble in water, and
is hence used as a means of removing lime from solutions, and de-
termining its quantity.  It dissolves in the mineral acids, but is in-
soluble in all organic acids, even the acetic.  When heated, it leaves
a perfectly white residue  of carbonate of lime.
   The remaining simple oxalates are  not important,  except the ox-
alate of Silver, which is a white powder, prepared by double decom-
position, and remarkable for being decomposed by a moderate heat,
with a slight explosion, into  carbonic  acid and metallic silver.
   There are several double oxalates of interest.
  Oxalate of Potash and  Peroxide of Iron, (Fe203-t-3C203)+3K.O. . C2O3+6 Aq.,
is prepared by dissolving peroxide of iron in  solution of binoxalate of potash; it
crystallizes in fine grass-green tables, which are permanent in the air.  There exists
a similar salt containing soda.
  Oxalate of Potash and Chrome, (Cr203-|-3C203)-|-3K.O. . C203+6Aq., is prepared
by dissolving together  in hot water one part of bichromate of potash, two  of crys-
tallized oxalic acid, and two of binoxalate of potash.  A copious evolution of car-
bonic acid occurs, the chromic  acid being deprived of half its oxygen by a part of
the oxalic acid, with the remainder of which the oxide of chrome unites.  The li-
quor assumes a fine purple colour, and on cooling, yields prisms of a splendid blue
colour, so deep as to be perfectly opaque, unless the crystals be very thin.
  Oxalate of Copper and Potash, K.O. . C203+Cu.O. . C2O3+2 Aq., is formed by di-
gesting a solution of binoxalate of potash on oxide of copper. It crystallizes in fine
Blue prisms.  It may be obtained with 4 Aq.
   Chloro-carbonic  Acid. — C.O. + C1.   Eq.  619*1  or 49*5.   When
equal volumes  of carbonic oxide  and chlorine are exposed for some
hours to the light, they gradually combine, forming a colourless gas,
wbich was termed by  J. Davy,  its discoverer, Phosgene  Gas.  Its
odour is very irritating ;  the volume  being diminished to one half,
its density is 3412.  It is decomposed by water, carbonic and mu-
riatic acids being formed.  It is decomposed by most metals, which
unite with the chlorine and liberate  carbonic  acid.  Its action on
ammonia and on alcohol will be hereafter noticed.

  Combination of Carbonic Oxide and  Potassium,  and the Products
                        of its Decomposition.
   If potassium be  heated in a current of carbonic oxide, the gas is
rapidly absorbed, but no charcoal is  separated, as occurs with car-
bonic acid gas.  The metal is converted into a  blackish-green po-
rous mass.  If the air  be admitted to this while hot, it  inflames ;
when brought into  contact with water,  it is immediately decomposed,
a peculiar gas being  given off, and a  rhodizonate of potash formed.
This oxycarburet of potassium is obtained in quantity in the process
by which potassium  is procured, and  constitutes the great obstacle
to obtaining that metal, as described in page 337.  It is also formed,
but very impure, by merely brightly, igniting cream of tartar in a
covered crucible for an hour.  The composition of this body is not
yet known, and hence the mode of its decomposition cannot  be ex-
pressed in  formulae.   The gas which it evolves by solution in water
has been examined by Air. Davy.   It is colourless and  inflammable,
and burns  more brightly than olefiant gas.   Its characteristic prop-
erty is to detonate with a brilliant flash, and deposite  charcoal when
mixed with chlorine, even in the dark.  He assigns to it the formula
C8H- 
496         ISOMERIC OXIDES  OF  CARBON.
   Rhodizonic Acid.—This is formed when the oxycarburet of potas-
sium is  dissolved in cold water.  It is, when dry, isomeric  with
carbonic oxide, C707, but it appears  to be a tribasic hydracid, and
its formula C7O,0-f H3.   Its salts are of a  fine scarlet red colour,
whence its name.
   Croconic Acid, 0,04, is formed when a  solution of rhodizonate of
potash is boiled ; an atom of potash becomes free, and  croconate
and oxalate of potash are produced; C707 + 3K.O. giving K.O. and
C03-f-K.O., with C,04-|-K.O.   The salts  of croconic acid are bright
yellow coloured, but do not require other notice.
   Mellitic Acid, C03,  when  dry, is found only native,  combined
with alumina, in a very rare mineral, mellite or honeystone.  It crys-
tallizes with water, COj + H.O., and  from its characters, especially
the properties  of the mellate of  silver, it appears to be properly a
hydrogen acid, having carbonic oxide as  its radical, and its formula
to be C404-|-H.   When its ammonia salt is decomposed by heat, it
is resolved into two very singular bodies, paraban and euchroic acid:
whose history, however, is not important here.
  In concluding this account of the oxygen compounds of carbon, it
is proper to notice  the  peculiar function  which the carbonic oxide
appears to play.  From  the composition of its chlorine compound,
it is certain that the equivalent of the gas  is CO., and, combining
with oxygen, it forms carbonic acid, C02.   But I consider that we
cannot look upon oxalic acid  as being a  lower degree of oxidation
of the same radical as carbonic  acid.  On the contrary, the  body
C202, which is the basis of it, enters into a completely distinct series
of compounds, such as  oxamide, and is  probably merely  isomeric
with carbonic oxide, into which it may be changed by a variety of
reactions.  Still less is carbonic oxide the basis of the rhodizonates,
C 07, or of the  croconates or mellates ; but  the gas is changed into
these more complex bodies by an  isomeric action, which appears to
occur at the moment that it combines with the potassium.  I look
upon the carbonic oxide.gas, therefore, as  being the basis only of
carbonic acid and phosgene gas, and that the radicals of the oxalic
acid and the bodies of  its series, as  well as of the rhodizonic and
other acids, are compounds of carbon and oxygen, isomeric  with
carbonic oxide, but not yet  isolated.
              ♦
        Of Sulphuret of Carbon.—CS2.  Eq. 478*7 or 38*3.
  This remarkable substance is  formed  whenever sulphur comes
into contact with red-hot charcoal.  It may be prepared  by means
of the apparatus figured in page 323; the tube a, c being filled with
pieces of charcoal  about the size of almonds, and bits of sulphur
introduced from time to time at  h, which is to be then tightly clo-
sed with a cork.  The sulphuu fuses, and the tube being a little in-
clined, runs down upon the ignited charcoal, combines  with it, and
the product passing as vapour into the long glass tube e, f is con-
densed, and collected as a liquid in the bottle.
1  In large quantity, it is more conveniently prepared by fixing, air tight, into an iron
cylinder about a foot high (such as a quicksilver bottle), two iron tubes, one long, b,
reaching nearly to the bottom, and projecting a foot  above the top, and the other
short, c, and bent at a right angle, serving to convey the product to the condensing
apparatus.  By means of the tube c, the bottle may be filled with small fragments 
SULPHURET  OF  CARBON.
497
  of charcoal, and then, being placed in a furnace, the^wide glass tube c, and the nar-
  rower/, are to be attached by corks,  from the cock d a stream of water flows,
  which, guided by the tin-plate gutter o, cools the tube/, and .is conducted by the
  thread h to the basin x.  When the bottle is bright red, small pieces of sulphur are
  to be dropped in by the long tube, the end of which is to be then carefully closed up
  by a cork.   The sulphur, being vaporized, acts on the charcoal, and the sulphuret of
  carbon formed being condensed in the narrow tube cf, collects in the bottle n, which
  is half filled with ice in order more perfectly to preserve it.  Any incondensible gas-
  es that may be formed escape by the tube m.  The process might be continued until
  all the charcoal in the bottle had been converted into sulphuret; but if sulphur were
  allowed to be present to excess, it would melt the bottom of the bottle.  The process,
  therefore, should not be pushed so far.
   The sulphuret of carbon thus  obtained contains an excess of sul-
  phur dissolved in it, and must  be purified by redistillation at a very
  moderate  heat (in a water  bath); when  about nine tenths have dis
 tilled  over, by allowing the residue to evaporate spontaneously in a
 capsule, very fine right rhombic  crystals of sulphur may be obtain-
 ed (p. 284).
   The sulphuret of carbon is a colourless liquid, of a very disagree-
 able garlic smell.  It  does not mix with water, but dissolves in al
 cohol and ether.   It   dissolves  sulphur and  phosphorus  in large
 quantity.  Its specific  gravity is  1*272.   It boils at 1083  Fah., and
 forms a colourless vapour,  whose specific gravity is 2*621.  From
 its volatility, it obtained the name of Alcohol of Sulphur.  In evap-
 orating it  produces great cold ; mercury may be frozen by suspend-
 ing under  a bell-glass  a thermometer, the bulb of which is envel-
 oped by cotton moistened by this fluid, and rapidly exhausting the
 air. It is very inflammable, burning with a blue flame, and producing
 carbonic and sulphurous acids.   If a few drops of it be let fall into
 a strong bottle containing  oxygen, so much of it evaporates as to
 form an explosive  mixture with the gas, which then detonates when
 touched with a lighted taper, like a mixture of oxygen and hydro-
 gen.  When the  sulphuret of carbon  is heated in contact  with a
 metal, carbon is separated, and a metallic sulphuret produced.  It is
 thus found to consist of one  atom of carbon united to two  of  sul-
 phur, and its formula to be  C82.
  It is a powerful sulphur acid, combining with the sulphurets of
 the alk*ine metals and forming  sulphur salts, which are  crystalli-
gable ; with the sulphurets  of lead, silver,  copper, &c,  it forms in-
                              R R B 
498       CHLORIDES  OF  CARBO N.--A M M O N I A.


soluble compounds, which correspond closely in composition, to the
ordinary carbonates.  This substance is, in fact, exactly equivalent
to carbonic acid, CO., the sulphur being  replaced by oxygen, with
which its analogies have been already  noticed in p. 291.   The sul-
phuret of carbon is hence often called  Sulphocarbonic Acid.
  Moist chlorine converts this body into a crystalline  substance vike
camphor; but this, as well as the products of the action of nitric
acid and of strono- alkalies, have not yet been accurately examined

                         Chlorides of Carbon.

  Subchloride of Carbon, C2C1., is formed by passing the vapour of the protochloride
many times through an ignited glass tube; chlorine  is given off, and the subchlo-
ride deposited in silky crystals, which are fusible, and sublime at  about 300° un-
changed.
  Protochloride of Carbon, C2CI2, is also formed from the sesquichloride of carbon
by heating its vapour to redness, when chlorine is given off; or better by distilling
the sesquichloride with an alcoholic solution of sulphuret of potassium, which re-
moves one third of the chlorine.  It is a limpid fluid, boiling at 160°; the sp. gr. of
its vapour is 286*2.  By a strong heat it gives subchloride and free chlorine.
  Sesquichloride of Carbon, C2CI3, is produced by the action of a great excess of chlo-
rine in bright sunshine on olefiant gas or on muriatic ether; all the hydrogen of
these bodies is removed, and  the carbon remains united with chlorine.  It forms a
white crystalline mass like camphor, which is insoluble in water,  but soluble in. al-
cohol and ether.  It melts at 320°, and sublimes at 360° unchanged;  at a red heat it
abandons chlorine, and forms the bodies last described.
  Bichloride of Carbon, C2CI4, is formed by  exposing a  body termed chloroform,
whose formula is C2H.Cl3) or  marsh gas, C2H4, to an excess of chlorine in bright sun-
light.  The hydrogen is gradually removed and replaced by chlorine.  It is liquid;
its sp. gr. is 1*6; it boils at 192°.  The sp. gr. of its vapour is 5302.
                         CHAPTER XVIII.

OF THE COMPOUNDS OF NITROGEN AND HYDROGEN.  AMMONIA, ITS DERIV-
                       ATIVES  AND  COMPOUNDS.

  Although there  is very perfect evidence that hydrogen and ni-
trogen unite in two, perhaps  in three  proportions, we as yet know
but one of these in an isolated form, which is  the  volatile alkali,
Ammonia.  This was  known  to the earliest chemists, but the im-
portance of its history to the progress of chemical philosophy has
been but lately felt to its just extent.
  Ammonia is produced in almost all reactions where nitrogen and
hydrogen are brought together, one or both being nascent.  Thus,
when  an electric spark  is passed  through  damp air, nitric acid and
ammonia are both formed, and hence the rain which falls after thun-
der-storms contains nitrate  of ammonia.   It  is  evolved  in large
quantities in the putrefaction  of  organic substances containing ni-
trogen, and is formed  also by their distillation at high temperatures,
whence the greater supply of ammonia used in the  arts is derived.
When any oxide of nitrogen  is mixed with hydrogen,  and passed
through  a tube containing red-hot spongy platinum,  ammonia is
formed ; and, lastly, it  is produced abundantly when iron or tin is 
PREPARATION'  OF  AMMONIA.
499
oxidized violently by nitric acid, the oxygen being taken both from
the acid and water, the nascent hydrogen and nitrogen unite. Am-
monia  is also  a  product  of organization,  being  contained  in the
sweat of animals, and being exhaled by the flowers of many  plants
and by the  leaves,  also, of the cruciferse.
  For  the  purposes of the chemist, ammonia is obtained from the
muriate of ammonia, or  sal ammoniac, which  is manufactured  in
large  quantities  for commerce, by processes to be hereafter de-
scribed.  Equal parts of the sal ammoniac, in powder, and slacked
lime are to be intimately mixed and heated in  a flask, from which
a bent  tube passes; the gas which issues is to be conducted through
a tube, as in the figure (p. 310), containing dry lime  or fused pot-
ash, by which  adhering moisture is removed,  and it  may then  be
collected over  mercury. It is colourless and transparent.  Its odour
is strong, pungent, and irritating, well known as the smell of harts-
horn.   When perfectly dry, it has  no action on vegetable colours;
but if damp, it  reacts powerfully alkaline.  The  brown colour which
it produces on turmeric disappears when heat is applied, by which
it is distinguished from the browning by the fixed alkalies or  earths.
By a pressure of 6| atmospheres, or at a temperature of —61°, gas
eous ammonia is liquefied.  When inspired pure, it proves excess
ively caustic and poisonous.
  Ammonia is slightly combustible.  It does not support combus-
tion.   When a series of electric sparks is passed through a quan-
tity of the  gas confined over  mercury, its volume enlarges, and ul-
timately becomes  double.  It is then totally decomposed, and the
resulting gas consists of three volumes of hydrogen and one of rii-
trogen: the specific gravity of ammonia is therefore 591*5, as de-
duced  in p. 215,  and its formula N.H3.   If a current of ammoniacal
gas be passed  through a  red-hot tube filled with iron wire, it is de-
composed  in  the same way as by  electricity.   If the tube contain
red-hot charcoal, carbon is taken up, and prussiate of ammonia and
carburet of hydrogen produced.
  Ammoniacal gas is rapidly absorbed by water, which takes  up
780 times its volume at  32°.  Great heat is thereby  evolved, and
the solution, which augments two  thirds in volume,  has a specific
gravity of 0*872, and boils  at 120°.   It contains then about 32 per
cent, of ammonia,  and approximates to the formula N.H34-4 Aq.
This solution is  termed Water of Ammonia, or,  improperly, Liquid
Ammonia.   To prepare it upon a larger scale,  the matrass and se-
ries of three-necked bottles,  described and figured in p. 308, may
be employed.  Five parts of lime, slacked, and mixed with as much
water as will convert it into a thin  paste, are to  be introduced, with
four parts  of powdered sal ammoniac, into  the matrass, which  is
then to be placed upon the  sand-bath, and connected with the range
of bottles.  The  first bottle is left empty, in order to catch any wa-
ter  or  mixture that may be carried over, and it should be allowed
to grow warm, in order that it may retain no gas; in the other bot-
tled water  is placed, by which the gas is absorbed,  and they are
kept cool by damp  cloths applied to their  surface.   For ordinary
purposes water  of ammonia  need not contain more  than  18 per
cent, of gas; it then has a specific gravity of 0*930. 
500          CONSTITUTION  OF  A M*M O N I A.
  The watery solution of ammonia possesses all the characters of
the gas in a strong degree.  It neutralizes the strongest acids, and
acts in all respects as a strong base, ranking next to lime.  It forms
many classes of combinations, in some of which it exists unaltered,
but in others it first undergoes peculiar decomposition. Its action
on chlorine  is very violent, and accompanied by flame; sal  ammo-
niac is formed and nitrogen set free, as  described in p. 261.
  Ammonia is very easily recognised: its odour, the brown colour
given to turmeric paper, which is removed by a gentle  heat,  and its
forming dense white fumes on the approach of a glass rod  moisten-
ed with strong muriatic  acid, characterize it when free; all  sub-
stances which contain ammonia are either  volatilized by heat, or
decomposed, the  ammonia being generally liberated;  in all cases,
by heating the body with moist caustic potash, ammonia is evolved
as gas, and may be known by the properties now described.
  The real  nature of ammonia  has recently been  the subject of
much inquiry ; its equivalent is  satisfactorily  determined to be
17*1, and hence its formula is N.H3, and its equivalent volume 4. It
may enter into combination directly with dry oxygen  acids, but it
does not then form the proper ammoniacal salts, which all contain
an atom of water  essential to their constitution.  It combines with
a great number of saline bodies, and then resembles, in its functions,
their water of crystallization.  Its  most remarkable property, how-
ever,  is, that, in acting on  metallic compounds, and on certain or-
ganic acids, it abandons an atom of hydrogen, and the remaining
N.H2 combines with the metal, or with the radical of the acid.  Thus,
with Hg.Cl.  and N.H3 there result Hg.N.H2 and H.Cl.; with Pt.Cl2
and 2N.H3 there are formed Pt. + 2N.H2 and 2H.C1.;  from Hg.. N.06
and N.H3 are produced Hg.N.H, and H.N.OG.  Of organic bodies,
oxalate of ammonia gives, when heated, C202-r-N.H2, and benzoate
of ammonia produces  similarly CuH502-fN.H2.   It is hence evident
that the third atom of hydrogen is  not so  intimately combined with
the nitrogen as the remaining two ; it may be eliminated  by the
simplest reactions, but the N. and H2 remain  much  more  firmly
united, and  separate only when the constitution of the ammonia is
totally broken up. I hence concluded that the N.IL should be con-
sidered as  the radical of ammonia, and proposed to term it Amido-
gene,  and its symbol Ad.   The ammonia is then Amidide of Hydro-
gen, and its rational formula  N.H2H. or Ad.H.  Ammonia  is  thus
assimilated  to water,  and to  chloride of hydrogen  in  constitution,
the radical  amidogene having the closest analogy to  oxygen and
chlorine.   These conclusions have been almost unanimously adopt-
ed by chemists.
   These views are remarkably illustrated by the action of ammonia
on potassium; when this metal is  heated in the dry aas, hydrogen
is disengaged, and a fusible olive-green substance is obtained.  The
quantity of hydrogen evolved is the same as that  which the metal
 should evolve from water, that is, one atom, and the olive body con-
 sists of K.JN.H2.  It is Amidide of Potassium.  When put into water,
 potash and ammonia are produced, K.Ad. and H.O. giving K.O. and
 H.Ad.  When this olive substance is heated nearly to  redness, am-
 monia is expelled and Nitruret of Potassium remains, 3K.. N.Hj giv- 
COMPOUNDS  OF  AMIDOGENE.
501
ing 2N.H, and K3N.  The  phenomena are exactly  the  same with
sodium, an amidide  and a nitruret of sodium being thus formed.
  In describing the  compounds of ammonia, it is necessary to dis-
tinguish those in which ammonia acts simply as amidide of hydro-
gen, resembling in its functions the  oxide or chloride of hydrogen,
from the class of bodies in which the ammonia  is associated with
water, the proper salts of ammonia, which, as already noticed, are
isomorphous with those of potash.   I shall have occasion to discuss
the theory of these  bodies farther, but shall first describe the most
important members  of the former class.
  Ammonia and Chlorine.—If a bottle full  of chlorine gas be  in-
verted in a cup containing a solution of sulphate or  muriate of am-
monia,  it is gradually absorbed, and a heavy yellow liquid collects
in globules in the bottom of the cup.  This substance  must be treated
with the utmost caution ; if strongly rubbed or struck, or if it be
touched with  any greasy body, or with phosphorus, it explodes with
intense violence ;  a globule as large as a pin-head, on being exploded
in a teacup, shatters it to pieces.   Almost every chemist who has
examined it has  been severely hurt, and hence  its  composition is
not yet well known.   Sir Humphrey Davy found  that, when decom-
posed over mercury, it gives nitrogen and chlorine in the propor-
tions by volume of  1:3, and hence it was concluded to be Chloride
of Azote, N.C13, under which name it  is described  in most books.   It
has been observed, however, that traces of sal ammoniac are formed
when it  is decomposed ; it consequently  must  contain hydrogen,
and it may probably be bichloride of  Amidogene, Ad.Cl2, which,  when
decomposed,  should produce N. and Cl3, besides Ad.H.. H.Cl.
  Iodine and Ammonia.—When the  semi-fluid compound of iodine
and ammonia  is put into water, it is  decomposed into  hydriodate
of ammonia, and a brown powder which is  usually described as Io-
dide of Azote, N I3.  This substance may also be prepared by digest-
ing iodine in water of ammonia, the  iodine  gradually changing into
the brown substance, and the solution containing hydriodate of am-
monia : this body must be collected on filters in very small quantity,
and dried merely  by exposure to  the air;  if it be rubbed, even un-
der water, it explodes with a violent  detonation, though not so pow-
erfully as the  previous body.  The cloud of hydriodate of ammonia,
formed by its decomposition, is very evident; it  therefore contains
hydrogen, and i look upon it as a biniodide of Amidogene, Ad.I2.
  A corresponding compound containing bromine has been formed.
  By the action of  ammonia on metallic oxides, a numerous class
of bodies may be formed, which all possess more  or less violent
detonating properties ; they all contain combined water.   It is im-
possible to say, positively, whether  the  ammonia exists undecom-
posed in these bodies ;  I  rather  think it  does,  and I shall hence
term them ammoniurcts.
  Ammoniuret of Silver.—This is the most violent of all these com-
pounds:  it is  prepared by digesting recently-prepared oxide of sil-
ver in water of ammonia, or by dissolving nitrate of  silver in an ex-
cess of water of ammonia, and precipitating the solution by caustic
potash.   It is a brown powder, which detonates violently by the
slightest shock or friction ; when exploded, it is said to produce 
502         NITRURETS  AND  AMMONIURETS.
               water, azote, and metallic silver, which should give for its formula
               N.H3-(-3Ag.O.-(-Aq.  But the facility of  its decomposition,  which
               has been the cause of many  serious accidents, has prevented it be-
               ing accurately  analyzed.
                 Ammoniuret  of Gold, Au.03-f 2Ad.H., is produced by the  action
               of water  of ammonia  on peroxide  of gold.  It is a brown  powder,
               nearly as explosive as the former body, but it has been accurately
               analyzed  by Dumas.  These  bodies are known as Fulminating Gold
               or Silver.
                 The Ammoniuret of  Platinum is formed  by digesting hydrated
               oxide of platinum in water of ammonia.  It is a light-brown  powder,
               not yet  analyzed,  and  quite  different from the  impure  substance
               described in books as Davy's fulminating  platinum.
                 I have examined the ammoniurets of Copper and Mrcunj formed by digesting the
               oxides of these metals in water of  ammonia:  the first is blue, the second yellow;
               their formulae are  3Cu.O.+2Ad.H.+6 Aq., arm 3Hg.O+Ad.H.+2 Aq.  They de-
               tonate feebly when heated.  There exist, also, compounds of ammonia with the ox-
               ides of uranium, of iron, and of osmium, which have not been accurately examined.
                By the action of heat on some metallic compounds of ammonia, true nitrurets of
               the metals have been obtained, of which the most remarkable are those of copper
               and mercury.  The nitruret of Copper was formed by passing ammonia over anhy-
               drous oxide of copper at a temperature of 480° Fah.;  water is evolved, and the
               nitrogen and copper unite, forming a black powder, which, at the temperature of
               540°, is decomposed, with the evolution of a red light, into its elements.  Its formula
               appears to be CugN., which corresponds to the suboxide  CU2O., as when replacing
               oxygen ^ is equivalent to O. (see p. 262) and Cu6N.=3(Cu2+^).  Schraeter, to whom
               the discovery of the above compound is due, formed  also a nitruret of Chrome, whose
               formula is not quite ascertained.
                Ammonia is absorbed in large quantities hy the chlorides of phosphorus and of
               sulphur, and substances produced which possess singular properties.
                Ammoniacal Protochloride of Phosphorus, P.Cls+5Ad.H., is obtained by exposing the
               liquid chloride of phosphorus to  a current of dry ammonia.  It forms a white pow-
               der, which, when put in contact with water, produces sal ammoniac, and an insol-
              uble white  substance that has not  been analyzed; the  reaction is  probably that
               3(C1.H.. Ad.H.) and P.N2H3 result.  If the ammoniacal protochloride of phosphorus
               be calcined without access of air, a very remarkable body, phosphuret of Azote, the
               formula of which is P.N2, is produced, while phosphorus, hydrogen, ammonia, and
               sal ammoniac are  expelled.   The phosphuret of azote is insoluble in  water,  and re-
               sists the action of  the most powerful acids  and alkalies.  The composition of the
              ammoniacal perchlorides of Phosphorus is not  quite certain, as these bodies  appear to
              decompose each other.  The formula is P.Cl5+2Ad.H.   When calcined they yield
              phosphuret  of azote.
                Gaseous ammonia and chloride of sulphur combine in two proportions, according
               as each ingredient  is in excess.  The formulae cf these bodies are S.Cl.+Ad.H. and
               S.Cl.+2Ad.H.  The former is a brown powder, soluble  in alcohol and ether; the
              latter is a citron-yellow powder.  They are remarkable for delivering as a product
               of their decomposition, by water or by heat,  the sulphuret of Azote (S3N.), which is a
¥             volatile yellow powder, decomposed by the prolonged action of water into ammonia
               and hyposulphurous acid, 2(S3N.) and 6H.O. giving 3S2Oj and 2Ad.H.
                When chloride of sulphur is digested with water of ammonia, a brown  substance
               is formed, whose composition is C1.S4. N3H6.   It is  probablyformed of chloride and
               amidide of sulphur, S.Cl.+3(S.Ad.)
                Ammoniacal gas is absorbed in great quantity by the volatile chlorides of boron,
               arsenic, tin, and titanium.  The compounds formed  are white and crystalline; they
               are decomposed by water, and the solution  contains sal  ammoniac,  and the metal
               or the boron, in combination with oxygen.
                 There are few metallic salts which do not absorb ammonia when exposed to  a
               current of the dry gas; but certain metals are specially distinguished  by the charac-
               ter that ammonia added to their solutions produces precipitates which either contain
               ammonia or amidogene, as is the case with mercury, palladium and  platinum, or
               by an excess of the ammonia the precipitate is redissolved, and soluble compounds
               containing  ammonia are produced,  as occurs with zinc, copper,, nickel, cobalt and
               also palladium and platinum.  The number of combinations thus formed is so very 
AMMONIA-SALTS  OF  ZINC,  COPPER,  ETC.   503
great that it would be tedious to describe all, and I shall hence notice only such as
possess scientific or pharmaceutical importance.

                       1. Ammonia-Salts of Zinc.

  Dry sulphate of zinc exposed to a current of dry ammonia absorbs it, producing a
white powder, 2(Zn.O. . S.U3)+5Ad.H., which dissolves perfectly in water.
  If water of ammonia be added to a solution of chloride of zinc, a basic chic ride is
precipitated, which being redissolved by an excess  of ammonia, a colourless solu-
tion is obtained, which crystallizes on cooling.  According to the proportion of am-
monia in excess, I have found that one or other of two compounds may be formed,
one in long and  brilliant prisms, the other in fine pearly tables.  The latter salt con-
sists of Zn.Cl.+2Ad.H.+H.O., the former of 2(Zn.Cl.)+2Ad.H.+H.O. In  these
salts as in all such  as are produced by the action of an excess of ammonia on a
metallic salt, I consider that the acid exists combined with ammonia, and not with
the metallic oxide, in which they differ essentially from those produced by the di-
rect absorption of ammonia by a salt, in which I conceive the union of the acid and
oxide not to be disturbed.   Hence I write the formula of the tabular ammonia-chloride
of Zinc as  Ad.H. . H.Cl.+Ad.H. . Zn.O.  When heated it gives off ammonia and
water, and a white powder, Ad.H. . Zn.Cl., remains.
  By the action of an excess of ammonia on a solution of sulphate of zinc, the am-
monia sulphate of Zi nc is formed: its formula is Ad.H. . H.O. . S.Os+Ad.H. . Zn.O.
It crystallizes in short prisms; when heated  it evolves Ad.H. . HO., and a  white
powder, Ad.H.  . Zn.O. . S.O3 remains.   In crystals it contains  3 Aq., of which it
loses two by efflorescence,  and the third by a moderate heat.

                      2. Ammonia-Salts of Copper.

  Chloride of copper absorbs dry ammonia, forming a blue compound, Cu.Cl.-j-3Ad.
II., soluble in water.
  When ammonia is added to a strong and hot  solution of  chloride of copper, until
the precipitate  which first forms  is perfectly redissolved,  a deep purple liquor is
produced,  from which octohedral crystals are deposited on cooling.  Their for-
mula is Ad.H.  . H.Cl. + Ad.H. . Cu.O.   When heated, these crystals evolve am-
monia and water, and a blue  powder, Ad.H.. H.Cl., remains, which is totally decom-
posed by a strong heat.
  Dry sulphate of copper exposed to a current of dry ammonia  forms a fine purple
powdl-r, whose  formula is 2(Cu.O. . S.03)+5Ad.H.
  An excess of ammonia gives, with a strong solution of  sulphate of
copper, a rich purple liquor, from which the ammoniacal, sulphate of Cop-
per  crystallizes  on cooling in hrge  right rhombic prisms, u, u', with
dihedral summits, i, /, as in  the figure, m being a secondary  plane.  I
consider these crystals, however, to be macles.  The formula of this
salt is Ad.H. . H.O. . S.03+Ad.H . Cu.O.  When heated, it gives off
ammonia and water, and a  green powder, Ad.H.. Cu.O.. S.O3, remains.
  Under the name of cuprum  ammoniatum, the ammoniacal sulphate of copper is em-
ployed in medicine.   It is then prepared by rubbing together sulphate  of copper and
carbonate of ammonia in a mortar.  The "mass becomes pasty, owing to the  water
of crystallization of the sulphate of copper becoming free, and carbonic acid  is giv-
en off.   The purple mass which results is soluble in water, and generally contains
carbonate of ammonia in excess.
  When a hot and strong solution of nitrate of copper is decomposed by an excess
of ammonia and allowed  to cool, the  ammoniacal  nitrate of Copper crystallizes in
rhombic octohedrons of a  fine purple  colour: its formula  is Ad.H. .  H.O. .N.O5+
Cu. Ad.  In this body there is no doubt of the metal being combined with amiduecne,
and not the oxide with ammonia; hence probably arises its remarkable character
of deflagrating violently when heated until it  begins to melt.
  The  iodide and fluoride of copper produce compounds  resembling those  of the
chloride.

               3. Ammonia-Salts of Nickel and of Cobalt.

  These resemble the corresponding salts of copper so perfectly, that it is sufficient
to refer to the foregoing for their properties;  and their composition is obtained by-
substituting Ni. or Co. for  Co. in the formulae.
 
504   AMMONIA-SALTS  OF  SILVER,  PALLADIUM,  ETC.
                       4. Ammonia-Salts of Silver.

  The chloride of silver is soluble in water of ammonia. The solution gives opaque
white rhombic crystals, which exhale ammonia when exposed to the air, and leave
chloride of silver.
  When the sulphate or the nitrate of silver is treated with an excess of water of
ammonia, colourless solutions are obtained, which yield by evaporation double salts,
in rhombic prisms, having the formulae Ad.H.. H.O.. S.Os+Ag.Ad. and Ad.H. .H.
O.. N.05+Ag.Ad.  in both salts the silver is combined with amidogene.  Chromate
of silver and ammonia gives a similar salt. The ammonia-nitrate of silver is employ-
ed in testing for arsenic and in preparing fulminating silver.  A remarkable prop-
erty of it is, that when fused it evolves ammonia and nitrogen, and metallic silver
remains mixed with ordinary nitrate of ammonia, and coats the sides of the glass
containing it with a brilliant mirror surface.   By a higher temperature the nitrate
of ammonia is decomposed, and nitrous oxide evolved.

                    5.  Ammonia-Salts of Palladium.

  This metal is remarkable for giving with ammonia  two  series of salts, of which
one is soluble and the other insoluble in water.
  When ammonia is added to a solution of protochloride of palladium, a flesh-col-
oured precipitate is produced, having the formula Pd.Cl.. Ad.H.  When more am-
monia is added, it dissolves, and from the solution the second salt crystallizes in
long rectangular prisms, having the  formula Ad.H.. H.Cl.+Pd.O.. H.Ad. By a
gentle heat, an atom of water is given off, and the metal exists then in the salt as
amidide.   If, in a solution of this salt, the excess of ammonia be neutralized by mu-
riatic acid, a yellow crystalline precipitate forms, which has the same formula as the
first salt,  Pd.Cl.+H.Ad.
  With solution of sulphate of palladium and water of ammonia, a precisely similar
series of salts is formed; the first being flesh-red, Pd.O.. S.03-|-H.Ad.; the second
salt in colourless prisms, Ad.H.. H.O.. S.03+Pd.O.. H.Ad., and, when dried,  the
last member becoming Pd.Ad.; and by  a small quantity of an acid, a crystalline
precipitate, which consists also of Pd.O.. S.03+H.Ad.
  The iodide of palladium gives similar salts.  With the  nitrate no other than the
colourless crystalline salt can be obtained, whose form is thin rhombic plates, Ad.
H..H.O..N.Os+Pd.Ad.  When heated, it deflagrates like loose  gunpowder,  and
leaves behind metallic palladium as a black powder.
  In the red and yellow insoluble ammonia-salts of palladium, although the experi-
mental composition is the same, I consider that an important difference of constitu-
tion exists.  The red salts are formed by adding ammonia to a simple salt of the
metal;  direct union then occurs, and we have, for example, Pd.Cl.+H.Ad.   But
when we form the yellow salt by adding an acid to a solution of the soluble ammo-
nia-salt, I conceive that the acid unites directly with the amidide of the metal,  and
thus forms, for example, Pd.Ad.+H.Cl.  Th* yellow ammonia-iodide, Pd.Ad.+H.I.,
gradually changes itself back into the red substance, Pd.I.+H.Ad.

                     6. Ammonia-Salts of Mercury.

  From the great influence these bodies have had on  the  theory of ammonia, and
their importance in pharmacy,  the mercurial compounds containing ammonia  de-
serve more detailed notice than those of any other metal.

       A.  Action of Ammonia on the  Haloid Salts of Mercury.

  When-corrosive sublimate is heated in a current of dry ammoniacal gas, it unites
therewith, forming a white compound, fusible and volatile, having the composition
21Ig.Cl.+H.Ad.  By contact with water, this body is decomposed into sal alem-
bioth and white precipitate; the former, a compound  of sublimate and sal ammo-
niac, dissolving, and the latter, whose composition will be next studied, separating
as a whue powder.
  If we add to a cold solution of corrosive sublimate a very slight excess of ammo-
nia, a copious white precipitate is produced, and the liquor is found to contain exact-
ly half the chlorine of the sublimate combined with hydrogen and  ammonia as sal
ammoniac; the white powder, which had been known to the early chemists as White
Precipitate of Mercury, contains all the mercury and the remaining half of the chlo-
rine of the sublimate.  It was supposed to contain, also, ammonia and oxygen but I
have proved that it contains only the elements of amidogene and no oxygen; that its 
PRECIPITATES  OF  MERCURY.            505
formula is ITg.Cl.+IIg.Ad., it being a true chloro-amidide of mercury.  The theory
of its formation is very  simple, 2Iig.Cl. and 2H.Ad. producing, by interchange of
the elements of one equivalent of each body, Ilg.Cl. + Hg.Ad., which precipitates,
and H.Cl.+H.Ad., which remains dissolved.  Tins was the first instance in which
amidogene was discovered to be combined with a metal, and from its establishment,
the true constitution of ammonia was first recognised.
  Wiute Precipitate is insoluble in cold water.  It is decomposed by boiling water,
two atoms of which, reacting on two of white precipitate, produce sal ammoniac,
which dissolves, and a heavy yellow powder, which is insoluble in water, and has
the formula  Hg.Cl.+2IIg.O.+Hg.Ad.  This body  is completely analogous to the
oxychloride of mercury, llg.01.+3Hg.O., from which it may be  prepared by the ac-
tion of ammoniacal gas, the third atom of Hg.O. and H.Ad. giving Hg.Ad. and
II.O., which is expelled.   When white precipitate is heated suddenly, it is totally
converted into calomel, nitrogen, and ammonia, but by careful management of the
heat, sublimate and ammonia are given off, and a red powder remains, which is a
compound of chloride and nitruret of mercury, Hg.Cl.+Hg3N.; or, rather, as the ni-
trogni here  replaces  oxygen, and has hence the  one third atomic weight, Hg.Cl.+
Sll^.j, exactly analogous to the oxychloride; by careful management, all the subli-
mate may be expelled, and the azoturet of Mercury, Hg.g, is obtained as a brown pow-
der, which detonates with  great violence when struck.
  The white precipitate which has been now described must be distinguished from
another body which  has been confounded  with  it in the pharmacopoeias, until the
difference was shown by Woehler's observations and my analysis.  This second or
beta-white precipitate is prepared by adding caustic potash to  a  cold solution of the
double salt formed by corrosive sublimate and sal ammoniac.  It may also be form-
ed by boiling alpha-white precipitate in a solution of sal ammoniac.  It has a crys-
talline aspect, and is not decomposed by boiling water; when heated, it fuses,and
gives off ammonia and azote, while a mixture of calomel, sublimate, and sal ammo-
niac sublimes.  Its formula is very simple,  1 I^.Cl.+H.Ad.;  but it may also be look-
ed upon as  a compound of alpha-white precipitate and sal ammoniac,  (Hg.Cl.-t-
HgA<l.)+(H.Cl.+H.Ad.)=2(Hg.Cl.+ H.Ad.).
  When calomel  absorbs dry ammonia, it forms a dark gray powder, which is 2
Hg-Cl.+lI.Ad.;  by  a gentle heat all ammonia may be expelled, and the  calomel
remains quite white.
  If the calomel be, however, digested in water of ammonia, one half of its chlorine
is converted into sal ammoniac, and a dark gray powder results, which is a com-
pound of subchloride and subamidide of  mercury, Hg.-Cl.+HgaAd.  This  body,
which I have termed Black Precipitate, is formed by a similar  reaction to that by
which alpha-white precipitate is  produced, 2Hg2Cl. and 2H.Ad. giving l.lg:Cl.+
Hi,-jAd. and H.Cl.+H.Ad.  By several chemists, the action of water of ammonia
on calomel  is given as a means of preparing black oxide of mercury, which is quite
incorrect.   The compound formed  contains no oxygen.
  The action of the bromides of mercury with ammonia has  not been so minutely
studied as that of the chlorides;  it is known, however, that bromide of mercury gives
with water of ammonia a white precipitate, consisting of bromide and amadide, Hg.
Br. + Hg.Ad., and analogous to the alpha-white precipitate.  The subbromide of
mercury produces with water of ammonia  a black powder, consisting of Hg2Br.+
Hg,Ad.
  Iodide of mercury dissolves plentifully in hot water of ammonia, and the solution
deposites, on cooling, long prisms of a snow-white colour,  which, however, rapidly
exhale ammonia when exposed to the air, and leave red iodide of mercury in pseu-
domorphous crystals.  This white body has the formula 2Hg.I.-j-H.Ad.        _^
  There is no iodine compound analogous to alpha-white precipitate; but when fUrT^**
substance is warmed in a solution of iodide of potassium, ammonia is evolved and^t*^^
brown powder is  formed, having the formula Hg.I.+2Hg.O.+Hg.Ad.         W

       B.  Action of Ammonia on the Oxygen Salts of Mercury.

  When sulphate of mercury is digested in water of ammonia, it is converted into a
white substance,  to which I have given the name of ammonia-turprth.   It is not act-
ed on by water nor by alkalies.   Its formula is 3Hg.O.+S.03+Hg.Ad.  It is  there-
fore ordinary turpeth mineral combined with amadide of mercury.
  When water of ammonia is added to a solution of nitrate of mercui yjHing cold
and not in  excess, a white precipitate is formed, a basic ammonia-nib^, which is
found to consist of H.Ad. . N.O,+ 3Hg.O.   It is therefore a basic nitrate of mercu-
ry, analogous to  the ordinary basic nitrate, H.O. .  N.05+3Hg.O., except that am.
                                    S s s 
506          AMMONIA-SALTS   OF  PLATINUM.
   monia (amidide of hydrogen) is substituted for water (oxide of hydrogen).  If an ex-
   cess of ammonia be'added, and the mixture boiled, the white precipitate becomes
   heavier and granular, and is then found to consist of Hg.Ad. . N.05+3Hg.O.   This
   substance, the (i basic ammonia-nitrate, is evidently analogous to the former, the hy-
   drogen being replaced by mercury, and it corresponds accurately in constitution also
   to the ammonia-turpeth.
     If either of these basic ammonia-nitrates be boiled in water containing  much
   nitrate of ammonia, they dissolve and form double salts;  that usually formed is in
   short opaque white prisms, having the very simple composition 4Hg.O.+3(H.Ad..
   HO   N Os)* but as  it is decomposed by water into the (i basic  ammonia-nitrate,
   its formuia must be (Hg.Ad. . N.05+3Hg.O.)+2(H.Ad. . N.05+3H.O.).  The dou-
   ble salt which forms less frequently, is in yellow plates, and has the formula (Hg.
   Ad. . N.05+3Hg.O.)+(H.Ad. . N.05. H.O.).
    These double salts may also be generated by boiling oxide of mercury in solution
   of nitrate of ammonia.   If the common basic nitrate of mercury be boiled in a solu-
   tion of nitrate of ammonia, this  is decomposed; the ammonia being employed in
   forming  amidide of mercury,  and the nitric acid being set free, as may be recog-
   nised by litmus.
    The subsulphate of mercury, Hg20. . S.O3, acted on by water of ammonia, pro-
   duces a black powder, the formula of which is Hg20. . S.03+Hg2Ad.: it is easily
   decomposed.
    By acting on a solution of subnitrate of mercury in water with ammonia added
   dilute, and in such quantities as to leave a portion of the mercurial salt undecompo-
   sed, a fine velvet black precipitate is obtained, known in pharmacy as Hahnemann's
   soluble Mercury.  It is very easily decomposed by heat or by an excess of ammonia.
   In order  to obtain it pure, the solution should be quite free" from red oxide, and not
   more than three fourths of the whole quantity of mercury should be precipitated.
   When quite pure, I have found  its formula to be H.Ad. . N.Os+2Hg20., it  being
   perfectly analogous  to the common basic subnitrate H.O. . N.Oo+2Hg20., the ox-
   ide of hydrogen being replaced by the amidide.
    The results with the other salts, both of the red and  black oxide of mercury, are
   similar to those above described; but as none of them are specially important, I shall
   not occupy space with their description.

                       7. Ammonia-Salts of Platinum.

    When protochloride of platinum is dissolved in muriatic acid, and an excess ol
   ammonia added, a green precipitate is produced, composed  of Pt.Cl.+H.Ad.  It
   may be prepared in larger quantity by passing a current of sulphurous acid gas
   through a solution of bichloride of platinum until it assumes  a deep brown Colour,
   and then adding ammonia.  By boiling this green substance in strong water of am-
  monia, it forms a white powder, the formula of which is Pt.Cl.+2H.Ad.
    The action of ammonia on a solution of bichloride of platinum is very complex;
   it gives origin to a series of bodies, composed of bichloride, binoxide, and binami-
  dide of platinum, in  proportions which vary with the temperature and proportions
  used.  The ultimate effect is the formation of a colourless solution, when the ammo-
  nia is boiling and in considerable excess, from which a white powder separates by
   cooling, or by the addition of alcohol.  This powder, which consists of (Pt.Cl2+Pt.
  Ad2)+2H.Ad.+2 Aq., combines with acids, and generates a very remarkable series
  of double salts, discovered by Gros, who formed them  differently, having  obtained
  the nitric acid salt by heating the green substance Pt.Cl.+H.Ad. with nitric acid,
  and the other salts by double decomposition.  Liebig proposed to consider, that in «
  these salts there exists a compound radical, Pt.Cl.. N2HR, which combines with chlo-
Mjme and  with oxygen, and the oxide of which  unites with acids.  Thus  the oxa-
^ISTe contains Pt.Cl. . N2H60.+C20.% <fcc.   But as the gradual formation of this sup-
    sed oxide can be traced from the bichloride of platinum,  we must admit it to con-
    n a compound of bichloride and binamidide, similar, in many respects, to white
  precipitate, and we must look upon the salts formed by Gros as consisting of that
  compound united to ordinary ammoniacal  salts,  just as  are the double ammonia-ni-
  trates of mercury.
    The formula; of Gros's salts are upon my view:

            ■^°'»+EtAdI)+2'H.O. . H Ad.), the base of the series.
           •Jn1 ■£ 2i£l MO-f^H CI. . Tf Ad.), the muriatic salt.
          %tSStS-»cHt2fH-°- •N °< * H Ad*)',he "itric salt*
            % nH~5■ *!Kt2(Ha • S °» * H*Ad->' the sulphuric salt.
            (Pt Cl2+Pt.Ad2)-|-2(H O. . C203 . H.Ad.), the oxalic salt.
"■l^Me
 ^^K-*-_s
     t!nr 
AMMONIACAL SALTS.
507
  The action of ammonia on biniodide of platinum is more simple; a deep red pow-
der is formed, which has the formula Pt.l2+Pt.Ad2+4 Aq.
  Our knowledge of the action of ammonia on the oxygen salts of platinum is yet
too inexact to justify me in bringing forward here  the statements that have been
made concerning the results.
  By the action of ammonia on perchloride of gold, an olive-brown powder is pro-
duced which fulminates when rubbed.  It is decomposed by water, and its real for-
mula has not yet been established.

     Products of the  Action of Ammonia on  the Anhydrous Acids.

  When chloro-sulphurous acid, S.O2CL, is exposed to dry ammonia, it is converted
into a white saline mass, which is  a mixture of sal ammoniac and sulph-amiue, S.
O2CI. and 2Ad.H. giving S.O?Ad. and H.Cl.+H.Ad.   The former, which consists
of amidogene united to  sulphurous acid, is soluble  in water, and  may be obtained
crystallized, but when boiled with water  it  is changed into  common  sulphate of
ammonia, 2H.O. and S.O^Ad. giving S.Os+Ad.H. . H.O.
  When dry sulphurous acid and ammonia gases are mixed, they  combine to form
a reddish substance, which is decomposed by water; there appear to be two propor-
tions, giving the bodies  S.02. H.Ad. and 2S.()2 . H.Ad.
  Dry sulphuric acid unites with dry ammonia in two proportions, forming S.Os. H.
Ad. and 2tS.03 . H.Ad.  I consider these compounds as corresponding to the English
and German hydrates of sulphuric acid,  the ammonia playing the part of water.
A solution  of these bodies is not at first precipitated  by barytes, but gradually be-
comes changed into ordinary sulphate of ammonia.
  It was supposed that the chloro-carbonic acid, C.O.CL, combined  directly with
ammonia, but Reguault has found that decomposition occurs, and that sal ammo-
niac and amidide of carbonic oxide result.  This body, which he  terms carb-amide,
CO.Ad., is white, soluble in water, is not deliquescent, and resists the action of al-
kalies and acids, unless they be very concentrated.

                 Of the Common Ammoniacal Salts.

  Prom the great number of classes of compounds described  in the
preceding sections, it is evident that ammonia enters  into  combina-
tion with acids and with bases, with haloid and with oxygen salts,
in such manner as  assimilates  it fully to the oxide and chloride of
hydrogen in its action, but  removes it totally from all analogy with
the alkalies, to which it, in other points  of view, strictly belongs.
For the ordinary salts of ammonia, of  which the description now
comes, are isomorphous writh the corresponding salts  of potash, and
the strong basic characters of the  solution of ammonia had given to
it, from the  earliest times, the name of the  Volatile, or the Animal
Alkali.  The characteristic  distinction is,  that in all cases where it
acts as an alkali, ammonia is associated  with water : it is not Ad.H.,
which is the alkali, but Ad.H. + H.O., or, rather, N.H40., the ele-
ment which replaces potassium in the isomorphous salts being sub-
amidide of Hydrogen, Ad.H2,  or  N.H4.
  At the time when Mitscherlich showed the  isomorphism of the
potash and ammonia  salts, nothing was known of the  true  constitu-
tion of ammonia or of amidogene  ; and, in order to explain the ne-
cessity of the  presence of water,  a very ingenious theory was pro-
posed  by  Berzelius and  Ampere.   It was,  to  consider  that  these
ammoniacal salts do not contain ammonia at all,  but  another com-
pound of nitrogen  and hydrogen, N.H4, which is metallic, and re-
sembles potassium  in all general characters, and for which the name
Ammonium was proposed.   This  view squared accuratelywith ex-
periment, as in every  oxygen salt  of ammonia there is j|j#0 I"u^1
water  as may  form with the ammonia Oxide  of AmmWnim, jN.H4
O.; and in every haloid salt, the electro-negative  body is combined 
508            AMMONIACAL  AMALGAM.

with as much hydrogen as may convert the ammonia into the com-
pound  metal; thus N.H3. H.O. + S.03 and  N.H3 + H.C1. would give
N.H40.^-S.03 and  N.H.C1.  Not  merely  was this theory conso-
nant to numbers, but experiment gave very good reason to believe
in  the  real existence  of this compound metal, by the remarkable
properties of the ammoniacal amalgam.
  When  a o-lobule of mercury, immersed in water of ammonia, is
made the negative pole of a galvanic battery, it increases fifty times
in  volume, becomes semi-fluid and covered with warty excrescen-
ces, and finally  becomes so light as to float on water.  No hydro-
gen is  evolved from its surface, but oxygen is copiously given off
from the positive electrode.  If the current be interrupted, a copi-
ous disengagement  of hydrogen occurs from this metallic sponge,
which  also gives off ammonia, and it soon falls back to its original
appearance.  By cold, this decomposition may be retarded ; the
pasty mass may be removed from the liquor, and  is found to crys-
tallize  in  cubes at a cold of 0° ;  and if decomposed when dry over
mercury, it evolves  ammonia and hydrogen, by volume in  the pro-
portion of 2 : 1.  This indicates that the  mercury is therein com-
bined with a body which consists of N.H4, and as the mercury re-
tains its lustre, the  compound formed is properly  an alloy, and the
body N.H4 is of a metallic nature.  It may  be the metal Ammonium,
almost  perfectly isolated.   All these phenomena may be  observed
by dissolving one grain of potassium in 100 grains of mercury, and
dropping the globule into  a glass containing strong solution of sal
ammoniac.  By the action  of K.Hg. on  N.H4C1., there  are p-**o-
duced K.Cl. and Hg.N.H,; the globule  of mercury swells up rapid-
ly, and  the amalgam is sufficiently permanent to be easily examined.
  I have  no doubt  there  is thus obtained a substance possessing
some metallic characters, and consisting of ammonia and hydrogen *
in fact, subamidide of Hydrogen, Ad.H2; but whether the water which
is found in the common ammoniacal salts exists therein as  such, or
whether these salts contain true oxide of ammonium, is not thus
decided.   In fact, among the metallic compounds of ammonia al-
ready examined, we have  found bodies every way similar to the
ordinary salts of ammonia, except that  a  part of the hydrogen is
replaced by a metal.  Thus, if we compare  sal ammoniac with other
similar bodies, as in the following formulae,
             1. C1.N.H4,             5. Cl.N.. H3Ni.,
             2. Cl.N..H3Cu.,        6. Cl.N..H3Hg.,
             3. Cl.N..H3Zn.,        7. Cl.N..H2Hg2,
            4>. Cl.N..H3Pd.,        8. Cl.N..H2Pt;,
and find them all produced by the action of ammonia on a chloride
of a metal, just as sal ammoniac is formed by the action of am-
monia  on chloride of  hydrogen, we must  admit their similarity of
constitution ; and if we say that in No. 1, N.H4 forms a compound
metal,  we must consider all the  others as chlorides of compound
radicals also.  Still more, the connexion  is so perfect from these
bodies  to  such  as  resemble the  yellow powder, Hg.Cl.+ 2Hff.O.+
Hg.Ad.J^from that to the oxychloride, Hg.Cl. + 3Hg.O., that if
we insis^^ assuming the compound metal ammonium  to  exist
ready formed in the salts of ammonia, we  must lay down as a gen- 
•*■
           MANUFACTURE  OF  SAL  AMMONIAC.      509

 eral  principle that all  basic  salts  are  salts of compound metals,
 which could not be tolerated in an exact science for a moment.  At
 the same  time, therefore, that I consider the ammoniacal amalgam
 to contain ammonium, I believe it  to be formed  only at the time,
 and that the ordinary salts of ammonia contain ammonia and water,
 the latter  being united  as the constitutional water is in the magne-
 sian  sulphates, but more intimately.   Thus, sulphate or ammonia,
 S.O;i-|-Ad.'H.. H.O., I consider to resemble the bihydrated sulphuric
 acid, S 03-(-H.O.. H.O.   In  both cases an atom of  water may be re--
 placed by  an oxide of the magnesian class.
   It will be necessary  only to notice  the more important of the or-
 dinary salts of ammonia.
   Muriate of Ammonia.   Sal Ammoniac.—Cl.H2Ad.  Eq. 666*8 or 53*5.
 This salt, formerly derived from Africa,  is now  manufactured on
 the large scale  from the ammoniacal liquor obtained in the destruc-
 tive distillation of horns, bones, coals, and such other organic mat-
 ters as contain nitrogen.  Those liquors which contain ammonia,
 combined  principally with carbonic acid and sulphuretted hydrogen,
 are decomposed by means of muriatic acid added in slight  excess.
 By evaporation  to a pellicle  and cooling, the sal ammoniac is obtain-
 ed in small crystals, deeply coloured  with tarry matter. They are
 purified  by re-crystallization,  and finally placed in cast iron  pots,
 set in a  furnace, lined with fire-tiles,  and  fitted with leaden heads,
 into which the  sal ammoniac  is sublimed.  The temperature is so
 managed that  the sublimed salt forms a coherent, hemispherical
 mass,  often weighing 100 lbs., and  when  pure should be perfectly
 free from  yellow stains, and nearly transparent.   If muriatic acid
 be dear, the  ammoniacal liquor may be  neutralized by sulphuric
 acid ;  sulphate  of ammonia  is formed, which is decomposed by the
 addition of common salt, and the sulphate of soda and sal ammo-
 niac separated by crystallization.
   Sal ammoniac is very soluble in water; it crystallizes  both by
 sublimation and solution, in cubes  and octohedrons; it is  slightly
 deliquescent, and is soluble in alcohol; it volatilizes below a red
 heat.   When heated with lime or potash, it yields  ammonia, as de-
 scribed in  p. 499.  It consists of an  equivalent of each element, its
 formula beino H.Cl. . H.Ad.   It may be formed  by their direct com-
 bination.   When equal  volumes of dry muriatic acid gas and am-
 monia are  mixed together, the two gases disappear, and a snow-
 white powder  of sal  ammoniac  results.  Hence  arise the white
 fumes when a  rod dipped in water  of ammonia is brought where
 chlorine  or muriatic acid gas  is evolved, or when  a  rod dipped in
 muriatic  acid is brought to where ammonia is escaping.  It  thus
 renders these bodies the means of detecting each other.
  S.i.l ammoniac is remarkable for the number of double salts which it produces,
 and of which some  deserve notice.
  With chloride of magnesium, it forms the anhydrous salt Ad.H2Cl.+Mg.Cl.,
 which is used in preparing metallic magnesium.
  With perchloride of iron, it crystallizes in fine red octohedrons,  Fe2Cl3+3('Ad.Hj
 CI.).  When these are heated, sal  ammoniac sublimes, coloured  by some  chloride
 of iron, and forms thus the Flares Martiales.
  The double salts formed with the chlorides of copper, zinc, and nickel.xrystallize
 in cubes  They are all composed like that of copper, which is Cu.Cl.+Ad.H2Cl.-f-
2 Aq. 
510   HYDROSULPHURET,  ETC.,  OF  AMMONIA.
  Corrosive sublimate unites in two proportions with sal ammoniac. The first salt,
Of which the formula is lig.Cl.+Ad.H2Cl.+Aq., is very soluble in water, and crys-
tallizes in flat rhomboidal tables, which effloresce when exposed to the air.  This is
the Sal Alcmbroth of the older chemists.  The second salt crystallizes in rhomboidal
prisms, which sublime unchanged, and have the formula 2Hg.Cl.+Ad.H2Cl.  It is
by the formation of these salts that corrosive sublimate becomes so easily soluble in
a"solution of sal ammoniac.
  Sal ammoniac and bichloride of platinum form a double salt, whose formula is
Pt.Ch+Ad.H2Cl.  It precipitates as a  bright yellow powder when solutions of its
constituents are mixed, and especially if alcohol be added, in which if is quite in-
soluble.  It is but very sparingly soluble in water, but more so in boiling water, from
which it crystallizes in orange-red octohedrons.  When ignited, it leaves  behind
metallic platinum  in the form of a light sponge.  It is of use in preparing  spongy
platina, and in the detection of ammonia.
  With chloride of gold, sal ammoniac forms a double salt, which crystallizes in
orange-red cubes, having the formula Au.Ci3+Ad.H2Cl.+2 Aq.
  The hydrobromate and  hydriodate of ammonia do not require notice.  They re-
semble the sal ammoniac in all important characters, and combine with the metal-
lic bromides and iodides to form similar double salts.
  Hydrosulphuret of Ammonia.—When sulphuretted  hydrogen and
ammonia gases are mixed in equal volumes, in  a vessel cooled  by
ice,  they combine, forming colourless needles, which evaporate at
ordina v temperatures.   The formula of this compound is S.H. + H.
Ad., or S.N.H4,  analogous to protosulphuret of potassium, S.K.   Like
that, it combines with as much more sulphuret of hydrogen, forming
a volatile crystalline compound, Ad.H2S.-)-H.S.  This bihydrosul-
phuret of Ammonia is formed  also  when  sulphuretted hydrogen is
passed into water of ammonia, as long as it  is absorbed.  For each
atom of ammonia present, two atoms of sulphuretted hydrogen are
taken  up.  By  exposure to the  air, this  solution becomes  yellow,
owing to the absorption of oxygen and the liberation  of sulphur.  It
is capable of dissolving a large  quantity  of sulphur, forming com-
pounds analogous to the higher  sulphurets of potassium.  This hy-
drosulphuret of ammonia is of great importance  in the detection  of
the metals, from  the  formation of metallic  sulphurets  It is  a sul-
phur base, and forms salts with the  sulphur acids, analogous to  those
formed by sulphuret of potassium.
  Sulphate of Ammonia.—Ad.H,. O.S.03 +Aq.   This salt is formed
on the large scale in  the  manufacture of sal ammoniac; it  may  be
prepared pure by neutralizing water of ammonia by sulphuric acid; it
# crystallizes in flat rhomboidal prisms, as in the figure, or in
           macles, isomorphous with the crystals of sulphate of pot-
           ash.   It is very soluble in water, but insoluble in alcohol;
           when heated, it gives off water, ammonia, and azote, and
           sulphite of ammonia sublimes.   It combines with the sul-
phates of copper, zinc,  iron, alumina, &c, forming double salts ex-
actly analogous to those formed by sulphate of potash.  With  oil
of vitriol it unites to form bisulphate of Ammonia, which is deliques-
cent and  soluble in alcohol.
  Nitrate of Ammonia, Ad.H20. . N.05, is formed by neutralizing ni-
tric  acid by ammonia.   It crystallizes in striated hexagonal prisms,
isomorphous with nitre, of a bitter  saline taste ; they°are deliques-
cent and very soluble in water.   When heated, they fuse  at 230°,
and  at about 460J are rapidly decomposed  into nitrous oxide and
water, as described p. 272.  By the presence  of a large excess of
sulphuric acid,  this action takes  place  at much lower temperatures. 
PHOSPHATES  OF  AMMONIA.
511
 When heated with combustible bodies, it deflagrates with extreme
 violence.                                                     £
   Phosphates of Ammonia.—The tribasic phosphoric acid forms with
 ammonia two salts;  the  first, whose formula is (P.O- + Ad.H20.+-
 H.O.) + Aq., is prepared by adding  the acid in  excess  to water of
 ammonia; it crystallizes  in rhombic prisms, which are very soluble
 in water.  Their reaction to test-paper  is strongly acid.  If the am-
 monia be added in excess, a salt crystallizes, possessing nearly the
 same characters, except that its reaction is alkaline, and its formula
 P.0,+2kAd.H2O.)+H.O.  Both  of  these salts  yield, by ignition,
 phosphoric  acid.
   Arnmoniaco-Magncsian Phosphate.—When a solution of a salt of
 magnesia is added to  any  soluble phosphate, and the liquor rendered
 alkaline by ammonia, a crystalline  precipitate is formed, which  is
 soluble in acids,  sparingly soluble in water,  but insoluble in alkaline
 liquors.   Its formula is  P.03-|-(Ad.H,0. + 2Mg.O.) +12 Aq.  Its
 formation is often of use for the detection of  magnesia, and it  is
 occasionally generated in urine by the action of ammonia, produced
 by the spontaneous decomposition of  urea  upon the soluble  phos-
 phates of magnesia which it contains.  It then constitutes a com-
 mon variety of calculus.
   Phosphate of Ammonia and Soda.—This  salt, of which  the formula
 is P.OJ + (Ad.H20. + Na.O.+-H.O.) + 8 Aq., is  easily produced by
 mixing together, in solution, six parts of common phosphate of soda
 and one of sal ammoniac.   On cooling, it crystallizes in large prisms,
 which effloresce in the air.  When heated, it gives monobasic  phos-
 phate of soda and free phosphoric acid, as  a source of which it  is
 much used in blowpipe experiments, under the name  of Microcosmic
 Salt.   It is found in all the animal fluids.
  Carbonates of Ammonia.—The salt which,under this name,is used
 for medicinal purposes, is prepared by mixing together  one  part of
 sal ammoniac with two of powdered chalk, and exposing the mixture
 in an  earthen pot to a heat below redness.   These bodies reacting,
 produce chloride of calcium and carbonate of ammonia, which sub-
 limes, and is condensed as a crystalline semi-transparent mass, in a
 dome-shaped receiver, which is fastened on  the subliming pot.  By
 right, this should be a neutral salt, Ad.H2Cl. and Ca.O.. C.O_, giving
 Ca.Cl. and Ad.H20. . C02; but a quantity of ammonia and water is
 given off, and the sublimed salt was considered to be a sesquicarbon-
 ate, consisting  of 2(Ad.HJ0.)-f-3C02, until Scanlan showed that
 it was a mixture  of two different salts, which may be separated by
 water.  Rose has recently thoroughly examined the  carbonates of
 ammonia, of which there are a great number, but only four sufficient-
 ly important to be noticed here.
  The proper neutral carbonate  of  ammonia, Ad.H>0.. C.Oj,  does
 not exist except  in combination, but its compounds are very nu-
 merous ; it forms,
  1st. With  carbonate of water, the ordinary bicarbonate of Ammonia,
 Ad.H,0. . C.O. + H.O.  . C.0.2.   This is prepared by washing the  com-
 mercial sesquicarbonate with cold water or alcohol, when it remains
 behind as a skeleton  of crystalline grains, which are isomorphous
with bicarbonate  of potash.   It evaporates  spontaneously,  with  a 
 512  CARBONATES  AND  OXALATES  OF AMMONIA.

 weak odour of ammonia.  Its solution reacts  feebly alkaline.  By
 during on the commercial sesquicarbonate as much boiling  water
 as dissolves it, and letting the solution cool in a close bottle, so that
 no carbonic acid can escape, this salt may be obtained in large rhom-
 boidal crystals, which contain one and a half atoms of water.
   2d. The  substance which is dissolved out of the sublimed mass
 of sesquicarbonate by alcohol is identical with that formed by the
 union of dry carbonic acid and ammonia.  Its formula is therefore
 Ad.H. . C02, and the  ordinary sesquicarbonate is a mechanical mix
 ture of  it with the bicarbonate.
   When the sublimed sesquicarbonate is distilled  at  a  moderate
 heat in  a retort, it abandons  carbonic  acid, and two salts,  differing
 in volatility, are condensed in the neck.  The more volatile consists
 of Ad.H20. . C.02-f-H.Ad.. C.02, being a compound of neutral carbo-
 nate with dry carbonate, or a bicarbonate in which the basic oxide of
 hydrogen is replaced  by amidide of hydrogen, the two double  salts,

  Ad.H20.. C.02-}-H.O. . C02, water-bicarbonate of ammonia,
  Ad.H20.. C.02-|-H.Ad.. C02, ammonia-bicarbonate of ammonia,

 being precisely equivalent in composition.   The less volatile product
 is  of very complex composition ; its formula is 4(Ad.H20.)-j-5C02,
 or it consists of an atom of neutral carbonate united to an  atom of
 each of the  different bicarbonates, thus :

     Ad.H20.. C02              )
     Ad.H20.. C.02+H.O. . C02 } =4(Ad.H20.)-f-5C.02.
     Ad.H20.. C.02+H.Ad.Co2   $

  Oxalate of Ammonia, Ad.H20. . C203, may be prepared by neutral-
          izing oxalic acid by water of ammonia; it crystallizes in
 /*/*-?! J*iK right rhombic prisms, as in the figure, where p,  u, u are
          primary, and i, t secondary planes.   These crystals  con-
          tain an  atom of water, which they lose by efflorescence
          in dry air.   When  heated, it is completely decomposed,
          water being evolved, and oxamide subliming, Ad.H20.. C2
 03 producing 2H.O. and Ad.C202.  This neutral oxalate of ammonia
combines with oxalic  acid, forming a binoxalate and a quadroxalate
like those of potash.
  The oxamide may also be prepared by acting on  oxalic ether  with
water of ammonia, or by dissolving oxalic acid in a mixture of equal
volumes of oil of vitriol and alcohol, and adding ammonia in excess.
It is a light white powder, tasteless and insoluble in water ;  it is de-
composed by acids and by strong bases, in contact with water, ox-
alic acid and ammonia being regenerated.   Its discovery by Dumas
laid the  foundation of our present knowledge of the nature of am-
monia, by leading him to the  idea of the probable existence of ami-
 dogene.
 
PREPARATION OF  CYANOGEN.          513
                       CHAPTER XIX.

OF CYANOGEN AND ITS COMPOUNDS, AND OF THE BODIES DERIVED FKOM IT.

  There is no class of organic bodies of which  our knowledge is
more extensive and exact, than those which have  cyanogen as their
basis.  The powerful affinities which this radical exerts, the simpli-
city of its constitution, and, above all, our being  able to prepare it
in an isolated form, and to generate its compounds directly from it,
as we could those of a truly simple body, render its history the most
advanced portion of organic chemistry,  and that to which the anal-
ogy of mineral bodies and the theory  of compound radicals is most
undeniably applicable.
  Cyanogen does not exist in nature ready formed; the kernels of
peaches, plums, bitter almonds, &c, and the leaves of the cherry-
laurel, yield, by simple  distillation,  abundance of prussic acid (cy-
anide of hydrogen), but this is only then produced by the decompo-
sition of other substances containing nitrogen.
  Cyanogen may, however, be formed abundantly, and in a  simple
manner, by bringing its elements together at a high temperature, in
contact  with substances with which  it may unite.   Thus, when any
organic substance containing nitrogen is calcined with potash, the
nascent carbon and nitrogen  unite, and cyanide of  potassium is
formed ; even with pure charcoal this occurs, nitrogen being derived
from the air ; and Mr.  Fownes has shown, that when a mixture of
pure charcoal and  potash is ignited  in a tube, and a current of
pure nitrogen passed through  it, this is absorbed, and carbonic oxide
gas being given off,  cyanide of potassium is produced, 3C. with K.O.
and N. giving CO.  and  C.N.K.  By the  action of ammonia, also, on
ignited  charcoal,  cyanogen is formed in  abundance ;  it combines
with hydrogen and the excess of ammonia, and produces prussiate
of ammonia.  In this case 2C. and 2N.H3 produce C2H. + N.H„ and
H2 become free.   It is by virtue of these processes that cyanogen
is produced for its various applications in the arts ; but, as I shall re-
turn to them in detail,  1 shall now only  consider farther the  mode
of obtaining it free and pure.
  Cyanide of silver, or  cyanide of mercury, of which the prepara-
tion will be described  hereafter, is  to be  introduced  into a  small
glass retort, and heated to just below redness; a gas is given off,
which must be collected over the mercurial trough; the cyanide of
silver separates simply into metal and  cyanogen ; but when cyanide
of mercury is used,  a brown powder appears, the quantity of which
is less as the  temperature of  decomposition  has been lower.   The
gas which comes over is, however, cyanogen completely pure.
  Its properties are very marked.  It is colourless, of a sharp smell,
which irritates the eyes.  Its  sp. gr. is 1S19.  If a quantity of cya-
nide of  silver be sealed up in a strong tube, bent as in the figure,
and then heated at one end, a, the cyanogen is condensed by apress-
                             Ttt 
514
CYANIC  ACID.
                              ure of about four atmospheres, and
                              collects at the other end, b, as a col-
                              ourless liquid.   It  is  combustible,
                              burning with a beautiful rose-colour-
ed flame, and producing two volumes of carbonic acid and  one of
nitrogen.   It is constituted, therefore, of equal  volumes of carbon
vapour and nitrogen, the  two volumes  being  condensed to  one;
hence 843 + 976=°l8l9 is its sp. gr.   It dissolves abundantly in al-
cohol and  water, but these solutions soon undergo very complex
decompositions, the  liquor being found  to  contain  carbonic  acid,
prussic acid, ammonia, urea, and oxalic  acid, besides  a brown in-
soluble matter.  A similar decomposition is produced  much more
rapidly by  contact with water  of ammonia.  The composition of
this brown  matter appears to be C4N2. H.O.  It dissolves in alkalies,
and gives precipitates with  the metallic  salts;  it has been termed
hence Azulmic Acid.   When heated, it gives off water, and leaves a
deep brown powder, of the same composition as cyanogen, and
which has been termed Paracyanogen.  This may be also formed by
heating cyanide of mercury very strongly.  It  dissolves in hot ni-
tric acid, and  the solution gives, with water, a yellow precipitate,
which combines with bases, and has been termed Paracyanic Acid.
By strong ignition, paracyanogen evolves nitrogen, and  a very dense
carbon remains.
  Cyanogen combines directly with hydrogen and with the metals,
but its oxygen combinations require  to be indirectly formed; there
are three compounds of cyanogen and oxygen,  which are all acids,
and are polymeric bodies.  It unites also  with sulphur, and its com-
pounds have a remarkable tendency to form double and triple com-
binations.
  The formula of cyanogen is indifferently written C2N. or Cy.  Its
equivalent  number is 328*6 or 26*05.

                          SECTION I.
              NON-METALLIC COMPOUNDS OF CYANOGEN.
               Compounds of Cyanogen and Oxygen.
  Cyanic Acid— Cy.O.;  Eq. 428*6 or 34*05—is very easily obtained
in combination, by calcining the cyanide of potassium in contact
with the air, at a temperature below redness, in which  case oxygen
is directly absorbed  ; or by heating the cyanide with nitre, or  with
peroxide of manganese, which yield  the oxygen  required. For this
purpose the yellow  prussiate of potash  of commerce  may be em-
ployed, as  the cyanide  of iron which it contains is totally decom-
posed, and the^cyanide of potassium then acts as if it were  com-
pletely pure.  The  cyanic acid cannot,  however, be isolated  from
these salts by a stronger acid, as it th< n  rapidly changes into bicar-
bonate of  ammonia, uniting with the elements  of three atoms of
water; thus C2N.O.  and 3H.O. produce N.H3 and 2C02.
   The cyanic acid can be obtained free only by distilling the cyan-
uric acid,  Cy303+3H.O., which then transforms itself into  the hy-
drated cyanic acid, Cy.O. + HO., and is to be collected in a receiv-
er surrounded with  snow.  It is a colourless liquid, of a very pun- 
             SALTS  OF  CYANIC  ACID,  ETC.          515

gent odour, cauterizes the skin, and, when  mixed  with water,  is
decomposed as above stated.   When pre&erved in its most concen-
trated form, it soon transforms itself into a white mass, like porce-
lain, of the  same composition, C2N.. H.02, which has been termed
Cyunamelide.   This body  is insoluble in water, but by heat is trans-
formed back again  into hydrated cyanic acid, and by strong acids
is resolved into carbonate of ammonia.
  Cyanic acid does not exist in the anhydrous state.
  The cyanic acid forms but one series of salts,  being monobasic;
those of  the alkalies are soluble ;  the  others are white insoluble
powders.
  Cyanate of Potash.—Cy.O. . K.O.  The yellow prussiate of potash
of commerce, being roasted in an earthen dish, absorbs oxygen, and
the  cyanide  of  potassium is converted  into  cyanate  of potash.
When the mass  becomes adhesive  from the fusion of the product,
it is to be digested with alcohol,  from which the pure cyanate crys-
tallizes, on cooling, in rhombic  tables like chlorate  of potash.  In
contact with water this salt is rapidly decomposed, ammonia being
evolved, and carbonate of potash formed.  If dry  cyanate of potash
and dry crystals of oxalic acid be rubbed together in a mortar, ox-
alate of potash is formed, and the cyanic acid changes into cya-
namelide.
  Cyanic  Acid and Ammonia.—If hydrated cyanic acid be placed in
contact with dry ammonia, they combine, and form a white, woolly
mass, which dissolves in  water, and acts as an ordinary cyanate.  It
appears to contain  Cy.O.-fH.O. + 2N.H3.  If it be gently heated it
gives off  ammonia, and is transformed into an important  substance,
Urea, which, though thus  capable  of being artificially produced, will
be specially described as a product of the organization,  in another
chapter.   Whenever we  attempt to form the neutral cyanate of
ammonia, Cy.O. . N.H,. H.O., urea is produced; thus, by acting on
cyanate of silver  with muriate of ammonia,  or by mixing solutions
of sulphate of ammonia and cyanate of potash.  But still  we cannot
consider  urea to be merely cyanate of ammonia,  to  which it bears
the  same  relation that cyanamelide  does to hydrated  cyanic acid.
  Fulminic Acid.—Cy202+2II.O.   This acid, which  has attracted
much attention from the detonating properties of its salts, is  pre-
pared by  the action of nitric acid on alcohol, in presence of oxide
of mercury or silver.  The reaction is very complex; a crowd of
products  of the oxidation of the  alcohol being evolved, as aldehyd,
formic, acetic, and  oxalic acid, &c.  If the  action were  limited to
the  essential conditions,  it would probably consist in two equiva-
lents of alcohol and two of nitric acid, producing one of acetic acid,
one of fulminic acid, and ei»ht of water ; thus 2N.O5.and 2(C4H502)
give C4H404 and C.N Oj, besides  SH.O.
  The fulminic acid cannot be obtained in an isolated form; when
we  attempt  to separate  it  from  bases,  it is  instantly decomposed.
Thus, if  fulminate  of silver be  acted on by dilute  muriatic  acid,
chloride of silver, and a peculiar acid containing chlorine and cyan-
ogen, are produced.  The  fulminic acid is  bibasic, and  forms two
series of  salts, of which the neutral contains two equivalents of fixed
base, the  acid salts containing one  of fixed base and one of water. 
516 FULMINATES  OF  SILVER  AND  MERCURY,  ETC.

  Fulminate of Silver.—Cy202 + 2Ag.O.  It is prepared by dissolv-
ing silver in ten parts of nitric  acid, specific gravity l*3o, and pour-
ing the solution, when cold, into twenty parts of rectified spirits of
wine.   The mixture is to be gently heated till it begins to boil, and
then left  to cool  slowly.  The fulminate of silver is deposited in
fine  silky crystals, snow-white, and equal in weight to the silver
employed.  It is very sparingly soluble in cold water.  It detonates
with the slightest  shock, or by contact with  sulphuric acid.  When
acted on by a caustic alkali, as potash, half of the silver separates
as oxide, and a salt is formed, Cy202 + K O.. Ag.O.  If it be dissolv-
ed in warm dilute  nitric acid, half of the silver is also removed  and
replaced by water, and  on cooling, the acid fulminate of silver, Cy2
02-(-H.O. . Ag.O.,  crystallizes out.  This  explodes  more  readily
than the  first salt, by friction, and by contact with  oil of vitriol or
chlorine gas.
  By digesting  these fulminates of silver  with metallic  zinc or
copper, fulminates of these metals with two  atoms of oxide are ob-
tained ; and by acting on these salts with an alkali or barytes, salts
with two  different bases may be formed. In no case, however,  can
a fulminate containing  two atoms of an alkaline base be produced.
All these  salts possess detonating properties more or less violent.
  Fulminate of the Suboxide of Mercury.—Cy202-|-2Hg20. This, the
most important salt  of fulminic acid, is prepared by dissolving mer-
cury in nitric acid,  and treating it by alcohol, as in  preparing ful-
minate  of silver.   As  the  solution  cools, some metallic mercury
precipitates, and the fulminate of the suboxide is deposited in hard,
opaque, white crystals, generally very minute.   It is to be washed
and redissolved in boiling water, and crystallizes then in fine silky
"needles.  This salt  detonates  violently when struck between  two
hard bodies.   It is extensively used in the manufacture of the per-
cussion caps used for firearms.  As  a  great quantity of alcohol is
wasted in this process, it was proposed to carry on the action in
close vessels, and condense the  spirit, which, however, was found
to be unfit for any but the same  use, from containing a large quan-
tity of prussic acid.

                  Cyanuric Acid.—Cy303+3H.O.

  This acid  is produced under  a variety of circumstances where
the elements of cyanic acid become free.  Thus, if the solid chlo-
ride of cyanogen  be treated with water, Cy.Cl. and  H.O. produce
H.Cl. and Cy.O., but this transforms itself immediately into cyanu-
ric acid.  It is formed abundantly, as a white sublimate, in the dry
distillation of uric acid, and may be very simply produced by heat-
ing urea a little above  its point of fusion in a glass retort; ammo-
nia is  given off, and the urea changes into a dry, gray mass, which
is to be dissolved in strong sulphuric acid, and treated with nitric
acid, added in small quantities, until it  becomes quite colourless.
Being then diluted  with its own weight of water, the liquor yields
crystals of cyanuric acid on cooling.  It is evident that three atoms
bf urea, 3(C2H4. N202), contain the  elements of three atoms of am-
monia and one of cyanuric acid, C6N303+3H.O.
   By means of a  substance which will be hereafter noticed, termed 
PREPARATION  OF  PRUSSIC  ACID.        517
Melam, cyanuric acid may be formed simply and in quantity.  The
details of the process will be given when describing the properties
of that body.
  Cyanuric acid is colourless and nearly tasteless, possessing a very
slight acfd reaction.  It crystallizes in oblique rhombic prisms, which
have the formula Cy303+3H.O. + 4 Aq.   By a moderate heat, the 4
Aq. are expelled, and when more strongly heated, the dry acid chan-
ges into hydrated cyanic acid.  This  acid, being tribasic, forms
three  distinct classes of salts, which differ as the quantity of  fixed
base is one,  or  two, or three atoms.   If any of these salts be acted
on by a stronger acid, the cyanuric acid is completely  liberated.

     Cyanide of Hydrogen.  Hydrocyanic Acid.   Prussic Acid.
  This remarkable substance maybe formed by the direct combina-
tion of hydrogen and cyanogen.  It exists  in  the water  distilled
from bitter almonds, or from the leaves of the cherry-laurel, being
produced by the decomposition of a peculiar  substance, Amygdaline,
which those plants contain.   For  the  purposes of medicine  and
chemistry, it  is  prepared by  indirect  processes of  many kinds.
Thus, if formiate of ammonia  (C2H.03+N.H40.) be passed in va-
pour through a red-hot porcelain tube,  it is  totally converted into
prussic acid and water, C2N.H. and 4H.O.  Also, by passing ammo-
nia over red-hot charcoal, hydrocyanate of ammonia  is formed in
such quantity that prussic acid  may be economically prepared from
it.  If cyanide of silver be decomposed by muriatic acid, chloride
of silver and cyanide of hydrogen are produced (Ag.Cy. and H.Cl.
giving Ag.Cl. and H.Cy.); and by sulphuret of hydrogen, cyanide
of mercury gives sulphuret of mercury and prussic acid.   For its
preparation on  the large scale,  however, the substance used is the
yellow prussiate of potash of commerce.
  This salt, the preparation of which will be hereafter described,
consists of cyanide of iron united to cyanide of potassium ; by the
action of sulphuric acid, three fourths of the latter are  decomposed,
bisulphate of potash being formed, and prussic  acid liberated, 2(S.
03+H O.) and Cy.K. giving (K.O.  . S.03+-H O. . S.03)  and Cy.H.
The cyanide of iron remains still combined with the  other fourth
of the cyanide of potassium, forming a compound first  described by
Mr. Everitt.  The prussic acid thus produced contains, therefore,
one half of the cyanogen which existed  in the salt employed.  The
precise decomposition is, that two equivalents of the yellow ferro-
prussiate of potash, 2(Fe.Cy. + 2K.Cy.), acted on  by six  atoms of oil
of vitriol, 6(S.O, + H O.), produce three  atoms of bisulphate  of pot.
ash, 3(H.O. . S.03+-K.O. . S.03), and three atoms  of prussic acid, 3H.
Cy.; there remains then an atom of Everitt's salt, 2(Fe.Cy.+-K.Cy.),
which, when first formed, is yellow, but by rapidly absorbing oxygen
it becomes greenish, and, abandoning its cyanide of potassium, is
finally converted into basic Prussian blue.
  The mode of conducting the process depends on the degree  of
strength at which the prussic acid is required.   To obtain the an-
hydrous acid, three parts of yellow prussiate of potash, in fine pow-
der, arc to be decomposed by a mixture of two parts of oil  of vit-
riol and  two of water, in a small retort, at a very gentle heat, and 
518         PROPERTIES  OF  PRUSSIC  ACID.
 the product collected in a receiver, surrounded by ice, and contain-
 ing some fragments of recently-fused chloride of calcium, by which
 any traces of water which  come over are absorbed.   The process
 originally employed by Gay Lussac consists in decomposing cyan-
 ide°of mercury by strong  muriatic  acid, and passing tht* vapour
 through a lon^ tube, of which the half next the retort contains small
 fragments of marble, and the other half fragments of recently-fused
 chloride of calcium ; any muriatic acid vapour is arrested by the
 former, and the prussic  acid is rendered anhydrous by the latter;
 the vapour is then condensed in a receiver, surrounded by ice.
  Pure prussic acid is a colourless liquid ; its specific  gravity at
 67  is 0*6969 ;  at 5  Fah. it congeals into a mass of fibrous crystals,
 and at 80' boils.   In consequence of this great volatility, if a drop
 of it be suspended from a glass rod, one part of it will be solidified
 by the cold, produced by the rapid evaporation of another portion.
 The density of its vapour is 943*9, consisting  of equal volumes of
 cyanogen and hydrogen, united without condensation, as (1819*0 +
 68*8)-r-2 =943*9.  It reddens litmus paper feebly, and the tint dis-
 appears by heat.   Its odour is extremely suffocating  and pungent,
 and resembles  that of bitter almonds.   Its taste is bitter and acrid.
 It is  combustible, burning with a bright white flame.  Being a poi-
 son of intense activity, the greatest care should be used in manipu-
 lating with it in this concentrated form.
  Anhydrous prussic acid decomposes rapidly, especially if exposed
 to light.   It forms  ammonia, and a brown substance, probably the
 same  as  that produced from a solution of cyanogen in water, and
termed Azulmic Acid, as noticed p. 514, but of which the composi-
tion is not well known.   By contact with a strong acid, prussic acid
assimilates the elements of  three atoms of water, and produces for-
 mic acid and  ammonia  (Q2N.H.  and 3H.O.  giving  C2H.03 and  N.
 H3).   Hence, in the preparation  of prussic acid, an excess of any
mineral acid should be avoided.  With chlorine, prussic acid forms
muriatic  acid  and chloride  of cyanogen,  and  with iodine it acts
 similarly.
  For medicinal use, the prussic acid is  prepared in a very dilute
 condition.   The directions  sometimes  given in pharmacopoeias to
 distil  over an acid of a  specific strength,  are,  in practice, very dif-
 ficult  to execute, and might give  rise to serious errors.  The prop-
 er method is to prepare an  acid stronger than that required; then,
to ascertain by accurate analysis  its strength, and dilute it with dis-
tilled  water until  it be  brought exactly to the  degree  required.
This process is carried  on in the manufacturing laboratory of the
Apothecaries'  Hall of Ireland as follows: 1 lb. of crystallized yellow
prussiate of potash, in fine powder, is placed in a capacious retort,
and 2 lbs. of water poured  on it ; to this is added a mixture of 12
 ozs. of oil of vitriol and 2 lbs. of water, previously suffered to cool.
 These materials are well agitated,  and allowed to digest  for three
or four hours,  and then  between 2 and 3 lbs.  of dilute acid are dis-
tilled  over into a receiver containing already 1 lb. of distilled water;
there  are obtained thus 3 or 4 lbs. of an acid containing from 6 to
8 per  cent, of  real acid.   200 grs  of this are weighed and decom-
posed by an excess of nitrate of  silver ; the cyanide of silver pre- 
DETECTION OF  PRUSSIC  ACID.         519
cipitated  is  carefully collected, washed,  and  dried.   Being  then
weighed,  the exact per centage of  acid present is  found by calcu-
lation, and the necessary quantity of water is added, so as to bring
it to the  standard strength of the Dublin pharmacopoeia, which is
that of 1*6 per cent,  of real acid, and specific gravity of 0*998.
  As an example of this process, let us suppose that the 200 grs. of distilled acicl gave,
with nitrate of silver, 71 grs. of cyanide; as this contains 1195 of cyanogen, the 200
grs.  contained 1 f>T>3 of real acid, or 7*76 per cent.; now, to reduce this to the Dublin
standard, divide 77ti by  ltj, which gives  i85; indicating that by adding 3«5 lbs.
of distilled water to each pound of acid, the mixture will have accurately the strength
directed by  the pharmacopoeia.  Some of this calculation may be spared by consid-
ering the cyanide of silver to be equivalent to one fifth of its weight of real prussic
acid; the quantity per cent, in the supposed example should then be one tenth of
the weight of cyanide of silver obtained from the 200 grs., that is, 7 4 per cent.; and
the  water necessary to bring  it to the Dublin standard should be 3 G3 times its
weight.  The error introduced by this simplification is not sensible, being hut 0002
per cent.
  The strength  of the prussic acid  directed by the British pharma-
copoeias differs very much : that prescribed by the  London College
contains about  2 per cent, of real acid ;  that of the Edinburgh Col-
lege  contains about 4 per cent. ; while the Dublin strength is but
1*5 or 1*6 of real acid per cent.  This should be carefully attended
to in practice.
  A method has been proposed for determining the value of prussic acid, by digest-
ing  it on a known quantity of red oxide of mercury; when the prussic acid has sat-
urated itself with  the oxide,  what remains is to be washed, dried, and weighed.
Now, as 1164 of oxide of mercury is converted into cyanide by 271 of prussic acid,
which proportion is nearly 4 to 1, the quantity of prussic acid is pretty correctly one
fourth of the weight of the oxide of mercury dissolved.  But as cyanide of mercury
may combine with art excess of oxide, and as the quantity thus liable to be taken
up is not constant, it is dangerous to rely on this method for medicinal or analyti-
cal purposes.
  The detection of  prussic acid  is very simple.   1st. Its  solution
gives, with  nitrate of silver, a white  precipitate, cyanide  of silver,
insoluble in strong nitric acid when cold, but dissolved by boiling;
it is insoluble in ammonia.  If a liquor containing even a  very  small
trace of prussic  acid  be  boiled, the vapour produces a white  cloud
on  a piece of glass moistened with solution of nitrate of silver.  2d.
If a solution of sulphate of iron be added  to prussic acid, there is
no  change;  but on adding some potash liquor, a dirty greenish pre-
cipitate is produced, from which muriatic acid dissolves out the ex-
cess of oxide of iron, and leaves Prussian blue (cyanide of iron) of
a very rich  colour:  it is essential to the proper action of this test,
that both protoxide  and peroxide  of iron be present in  the solution.
3d.  If a solution of sulphate  of copper be  added to the liquor con-
taining prussic  acid, and  then treated successively with potash and
muriatic  acid,  as above, a white precipitate  remains  undissolved,
which  is  cyanide of copper.   The theory of these last  actions is,
that  the  prussic acid is  too weak to  decompose, by  itself, either
metallic  sulphates, but, on the addition  of potash, double decompo-
sition occurs, sulphate of potash and  a metallic cyanide being  form-
ed.   As  the potash is always added  in  excess, a quantity of metal-
lic  oxide  is at the same time precipitated, which masks  the colour
of  the result, but is  removed  by  the  addition of the  muriatic  acid.
4-th.  These  insoluble cyanides may be recognised very elegantly by
beatin^ them with  a little potash  and  sulphur, and dissolving the 
520          CYANIDE  OF  POTASSIUM,  ETC.
fused  mass in water.   The solution gives, with a persalt  of iron, a
fine blood-red  colour.  5th. The cyanide of silver, also, is known
by giving off cyanogen when heated.
  There are two chlorides of Cyanogen of the same composition, and bearing to each
other the same relation as the cyanic and cyanuric acids.   One is gaseous, the other
solid; the first is prepared by acting on moist cyanide of mercury by chlorine, or by
passing chlorine into weak prussic acid, and warming the mixture in which the
chloride of cyanogen dissolves.  This gas, which is very  irritating and poisonous,
may be obtained crystallized in needles by exposure to a very low temperature.  It
combines with ammonia, forming a crystalline substance.
  The solid chloride may be  prepared by acting on anhydrous prussic acid with
chlorine, or by heating sulphocyanide  of potassium in a current of chlorine.  It sub-
limes in white transparent needles.  It dissolves unaltered  in alcohol and ether, and
is decomposed by hot water into hydrochloric and cyanuric acids.
  Iodide of Cyanogen is prepared  by distilling, in a retort, a mixture of iodine, cyan-
ide of mercury, and water.   At a moderate heat, the iodide of cyanogen passes over,
and condenses in the neck of the  retort as a flocculent mass of snow-white needles.
These crystals irritate the  eyes:  they dissolve in  water unaltered, and volatilize at
113°.
                            SECTION II.
                     OF THE METALLIC CYANIDES.
  Cyanide of Potassium, K.Cy., may be  formed by  the direct union
of its elements, or by adding an excess of prussic acid to a solution
of potash, and evaporating rapidly without the  access of air.  It is
produced also whenever carbonaceous matter is calcined in contact
with potash, provided  nitrogen be present.  The best mode of ob-
taining it, however, is to  expose the  yellow prussiate of potash to a
full red heat, in a close iron crucible.   The cyanide of iron is de-
composed, nitrogen being given off,  and carburet of iron remaining
with the unaltered  cyanide of potassium.  The half-melted mass is
to be  coarsely powdered,  and digested in boiling, weak spirit of
wine, from which the  salt  crystallizes in cubes on cooling.  Spirit
of specific gravity 0*900 at 60\ is remarkable for dissolving a large
quantity of cyanide of potassium when boiling, but  depositino*  it
nearly totally when it cools.
  This salt in solution reacts alkaline, and smells of bitter almonds,
and hence probably  decomposes water when dissolved.   Its crystals
deliquesce and  are  decomposed, even in close vessels, after a short
time, by contact  with  water, into ammonia and formiate of potash.
  The  properties of the cyanide of sodium and  of the hydrocyanate
of ammonia are quite  similar.
  The Cyanides of Barium, strontium, calcium, and magnesium are soluble in wa-
ter, and crystallizable.
 _ Cyanide of Zinc is prepared by adding prussic acid to a solution of acetate of
zinc, when it precipitates as a white powder.  Chloride of zinc is not decomposed
by prussic acid. With cyanide of potassium it forms a double salt
  Cyanvkof Copper}s formed as a whitish precipitate when prussic acid and potash
are added to a solution of sulphate of copper.  When boiled it becomes yellow, and
combines with the oxide of copper to form  an oxycyanide of a lively green colour.
It forms double salts with the alkaline cyanides                 * b
  Cyanide of Mercury—Hg.Cy. { Eq. 1594*4 or  127*45—may be pre-
pared by boiling two  parts of Prussian  blue with one of red oxide
of mercury and eight of water, until the residue becomes red-brown.
The filtered  liquor yields  cyanide  of mercury in  crystals,  which,
however,  are not quite free from iron, and  require to be dio-ested
with a little more  oxide of mercury and recrystallized.   The best 
               CYANIDE  OF  MERCURY,  ETC.            521

mode of preparing it is to distil  fifteen parts of yellow prussiate of
potash, with thirteen of oil of vitriol and 100 of water, nearly to dry-
ness, and to digest the prussic acid so obtained with twelve parts
of finely-powdered  oxide of mercury,  until this is completely dis-
solved.  The solution  yields, by evaporation  and cooling, fourteen
parts of pure crystallized cyanide of mercury.   By washing out the
residue in the  retort with water, five parts of pure  Prus-   ^-^^
sian blue may  be obtained.
  Cyanide of mercury  crystallizes in  colourless rectan-
gular prisms, as q q, in the figure, terminated  by numer-
ous  secondary faces, as e e.   These crystals are  anhy-
drous, and occasionally opaque.    When heated, it  is re-
solved  into mercury and cyanogen, of which a portion  is resolved
into the brown powder (paracyanogen).   It is  sparingly soluble  in
alcohol.  It  tastes  as  the other  mercurial  salts.   So great  is the
affinity of mercury to  cyanogen,  that  cyanide  of  potassium, when
boiled with  oxide  of mercury, is decomposed, and caustic potash
liberated.  In  a  solution of cyanide of mercury, no test indicates
the presence of the metal except sulphuretted hydrogen.  It is not
decomposed by oxygen  acids, but muriatic  acid forms  prussic acid
and  chloride of mercury.
  Cyani.de of mercury, when digested with an excess of oxide of mercury, combines
wilh  it in two proportions, forming the oxycyanides of Mercury, Hg.Cy.+f l-^.O. and
Hg.Cy.+3Llg.O.   These bodies are soluble in water, and crystallize in prismatic
needles.
  With iodide of potassium, cyanide of mercury combines, forming a substance, 2
Hg.Cy.+K.I., which is very soluble in boiling water, and crystallizes in brilliant
white micaceous plates on cooling.  This salt is instantly reddened by any mineral
acid which liberates iodide  of mercury.  With sulphocyanide of potassium a simi-
lar compound is formed, 2Hg.Cy.+K.Cy.S2.
  Cyanide of  mercury combines with the  alkaline cyanides, and  with the alka-
line chlorides and bromides, forming double salts possessing no special interest.   It
combines with many oxygen salts also, as the chromate and formiate of potash.
  As prussic acid is now no longer prepared from cyanide of mercury, this body is
not so important as formerly. It is poisonous, and  is occasionally employed in
medicine.
  Cyanide of Silver, Ag.Cy., is a white  powder insoluble in water, which combines
with  other  cyanides to form double salts.  It is soluble in water of ammonia, but
insoluble in nitric acid, except it be strong and boiling.  Heated, it gives cyanogen
and metallic silver.
  Ci/omde of Palladium.—In its affinity for cyanogen, palladium resembles mercury,
Every soluble salt of palladium is decomposed by prussic acid, a pale yellow precip-
itate  being formed.  This cyanide of palladium is insoluble in water, but soluble in
acids and in ammonia.  Heated, it gives cyanogen and  leaves the metal.   It forms
a very extensive class of double salts.
  Cyanide of Gold, Au.Cy3,  is a pale yellow powder, forming double salts with  the
alkaline cyanides.
  Protocyanide of Iron, Fe.Cy., is not known in an isolated form, but it enters into
combination with the other  metallic cyanides, forming double salts, which are some
of the most interesiing of the cyanogen compounds.  The iron in these salts cannot
be separated by an alkali, and "hence may be looked upon as an element of the neg-
ative constituent; they are hence often termed ferrocyanides, or frropruss'uites of
whatever other metal thev may contain.
   Ferrocyanide  of  Hydrogen.   Ferrocrjanic  Acid.—Fe.Cy. -f2H.Cy.
When  the ferrocyanide of lead is decomposed by sulphuret of hy-
drogen, a solution is obtained, which yields,  on evaporation in vacuo,
small  granular crystals, which  have  a well-marked  acid reaction,
and  produce, by acting on metallic  oxides, all the  ordinary ferrocy-
anides.  If  the solut-on be boiled,  it  is resolved into prussic acid,
                                U u  u 
522          FERROCYANIDE  OF POTASSIUM.
and a white precipitate, which becomes blue in the air.   The crys-
tals undergo the same change spontaneously after some time.
  Ferrocyanide of Potassium.—Fe.Cy. + 2K.Cy. + 3 Aq.   Eq.  2656*9
or 212*5.   This compound, of which I have often spoken as Yellow
Prussiate of Potash, is prepared on the large scale for the purposes
of the arts and of pharmacy, by calcining  together some  animal
matters,  as blood,  hoofs, horns,  &c, with  pearl  ashes and  iron
filino-s.  It may be formed even if the organic matter  do  not contain
nitrogen, as that element may be  supplied from the air.  The oper-
ation is conducted in large iron pots arranged in a furnace, so that
the mass can be heated to dull redness, and continually agitated as
it forms a  tenacious paste, the calcining  of which is continued as
long as it burns with a white flame ; it is  then taken out of the pot,
and when cold, boiled in water,  which, by evaporation, yields  the
salt in  crystals.  If it has not dissolved iron enough, some copperas
is added as long as the Prussian blue, which at first forms, is found
to redissolve.  After  what has been said  of the formation of cyan-
ogen (p. 513), the  theory of this  process  may easily be understood.
  The  ferrocyanide of potassium crystallizes in truncated octohe-
A/-3----IZT"--,B _      —   drons with a rectangular base,  e e  e'\
 /X   e   v '.-'/ /^?^xr'^) as *n tne fiDUrei °f which A represents
^  \............Xy Q^^^T^y   ^e  usual simple, and B a  more com-
^^/ e" _i/   \-----C^   plicated form ;  the secondary plane n
often being so large  as to  render the crystal merely tabular.   Its
colour is fine  citron-yellow, but when dried it becomes white.   By
a farther heat in close vessels it  fuses, and when ignited gives  off
nitrogen, and leaves  cyanide of  potassium  and carburet of iron.
Heated in  open vessels, it absorbs oxygen, and forms cyanate of
potash.  Its use in  the preparation of these  bodies and of prussic
acid has been  already detailed.  If it be digested with oxide of mer-
cury, cyanide of mercury is  formed, and  oxide of  iron and  caustic
potash set free.  With sulphate of mercury it gives sulphate of pot-
ash, cyanide of mercury, and Everitt's yellow salt.
  With cyanide of  mercury,  ferrocyanide  of  potassium forms a
double salt, whose formula  I found to be 3Hg.Cy. +(Fe.Cy.+ 2K.
Cy.) + 4 Aq.   It crystallizes in pale yellow rhombic tables.
  In the arts, the ferrocyanide of potassium is of importance  for
dyeing various shades of blue ; to the chemist it is specially of in-
terest,  as from it all the cyanogen compounds are most economi-
cally formed, and from the peculiar precipitates it gives with solu-
tions of most metals, it is  of eminent service in their detection.
Thus, with solutions of silver, mercury, bismuth, tin, lead, nickel, zinc,
manganese, and cerium, it  gives white precipitates; that with  mercu-
ry gradually becomes blueish, and  that of manganese reddish.   With
copper, the  prenpitate is of  a rich chocolate colour; with cobalt,
greenish, changing to red;  with  uranium and molybdenum, brown;
and with chrome, grayish-green.  All these precipitates  contain cy-
anide of iron, united  to  two atoms of cyanide of the other metal,
being true ferrocyamdes.
  It is on solutions of iron that the action  of this reao-ent is the most
remarkable.  With solution of protosulphate of iron" a whitish pre-
cipitate is obtained, which consists of the cyanide.; of iron and pg- 
       PREPARATION  OF  PRUSSIAN  BLUE, ETC.    523

tassium, united in proportions which are not well known.  Exposed
to the air, this body absorbs oxygen and becomes blue.  With a so-
lution of sulphate of iron pure Prussian Blue  is precipitated.  This
substance is insoluble  in water  and in muriatic acid,  and gives with
caustic alkalies oxide of  iron ""and ferrocyanide  of  potassium ; its
formula is Fe Cy,, or  it consists of 3Fe.Cy. + 2Fe2Cy3.   Its forma-
tion involves 3(Fe.Cy.+-2K.Cy.) and 2,Fe203 +3S.03), and there re-
main dissolved six atoms of sulphate of potash.   For the manufac-
ture of Prussian blue for the purposes of the arts, the impure liquor
obtained by digesting  in water  the calcined mass  of  animal matter,
potash and iron, described p. 522, is decomposed by an excess of
sulphate  of iron, and the resulting precipitate digested in  muriatic
acid, and  exposed to the air until it assumes  its proper colour.  It
is then dried carefully at a moderate heat.
   Another kind  of Prussian  blue is  produced when Everitt's salt,
or the white  precipitate produced by protosulphate of iron with yel-
low prussiate of potash, is exposed  moist to the  air.  It is termed
basic Prussian Blue.   As Everitt's salt  consists of 2Fe.Cy.+-K.Cv.,
and this  last dissolves out, there is the same  number of atoms of
cyanogen and iron, and the excess of iron above that necessary to
form  true  Prussian blue combines with the oxygen  of  the  air, the
oxide so formed remaining united with the Prussian blue.   From 9
Fe.Cy. and 30. there is thus formed 3(Fe.Cy.-J-2Fe2Cy3-f-Fe203), the
basic compound.
   The ferrocyanides of Sodium, Barium, &c, possess all  the essential characters of
the potassium salt, and need not be farther noticed.
   The ferrocyanides in many cases combine with each other, forming salts, which
contain three different metals combined with cyanogen.
   Sesqwkyanide of Iron, Fe?Cy3, is not known in an isolated form, but, like the pro-
tocvanide, enters into a number of combinations with the other  metallic cyanides,
which may be called either p:rf;rrocyanides or ferridcyanides, as proposed by Liebig.
   Ferridcyanide of Potassium—Red Prussiate of Potash, Fe2Cy. + 3K.
Cy., is formed by passing chlorine through a solution  of yellow prus-
siate  of  potash until  it ceases to give Prussian blue with solution
of persulphate of iron.  The liquor becomes of a deep green colour,
but on evaporation yields anhydrous fine ruby-red  prismatic crys-
tals, which arc generally macles.  The products  of  its decomposi-
tion by heat  are  the same as those of the yellow salt.  It dissolves
in thirty-eight parts of cold water;  its solution, if pure, is yellow,
but more commonly is green.
   This salt rivals that already described in its utility as a reagent
for the proper metals.   The precipitates it gives with their solutions
are, tin,  white ; mercury, silver, and  zinc, yellow; titanium, nickel,
copper, and bismuth, yellowish brown ; and cobalt, uranium, and man-
ganese, brown.   It is,  however, with the salts  of iron that its reac-
tion is most  remarkable.   With a persalt of  iron  it  merely colours
the liquor green, but  with a  solution of a protosalt  it gives a blue
precipitate, even richer in colour than the proper Prussian blue, and
consisting of Fe Cyc,  or  of Fe,Cy3 + 3Fe.Cy.; thus  contiiining the
same protocyanide with half  as  much sesquicyanide as exists in
common  Prussian blue.    This ferridcyanide  of  Iron  is made for
commerce, and sold as TurnbulPs Prussian Blue.
   Ferridcyanide of Hydrogen.—If we  digest  ferridcyanide  of lead 
524     THEORY  OF  THE  COMPLEX  CYANIDES.
 with  dilute sulphuric acid, a  red liquor is obtained, which yields on
 evaporation a  mass of minute brownish-yellow needles, the formula
 of which is Fe,Cy3+3Cy.H.   This body reddens litmus, and has a
 sour  astringent taste ;  upon another theory it  is  considered to be a
 compound  of  hydrogen with a compound  radical,  (Fe2Cy6), and is
 termed Ferridcyanic Acid.
   In the history of these complex cyanides we meet three facts, on which the  the-
 ories of their constitution must be founded.   1st. The  extraordinary tendency to
 double combination,  which no other body possesses in  the same degree.  2d. In
 almost all cases, the  cyanogen enters into the compound in  the proportion of three,
 six, or nine atoms; and, 3d. One metallic  element, as iron, in each compound, is
 retained with extraordinary force,  not being detected therein by its ordinary re-
 agents.  The original view proposed by Berzelius, of considering these compounds
 as mere double salts, and  upon which the formulae given hitherto have been con-
 structed, does not account sufficiently for these facts, and  I hence consider it as
 less applicable to  them than the theories suggested by Graham and by Liebig.
   The latter  chemist founds his view upon the third fact, and supposes that there
 exists  a series of  compound radicals, consisting of cyanogen united with a metal.
 Thus,  Ferrocyanogen, (Fe.Cy3) orCfy., and Ferridcyanogen, (Fe2Cy6) or Cfy2, these
 two being isomeric ; Cobaltocyanogen, (Co2Cy6) or Cky., and many others; and these
 radicals combine  with hydrogen to form polybasic hydracids, from which, the  hy-
 drogen being replaced by a metal, result the ordinary complex cyanides.  Thus,
 the ferrocyanogen being bibasic, its acid is Cfy.-J-2H. ; its potash  salt,  Cfy.-f-2K.;
 its copper salt, Cfy.-f 2Cu.; and if each atom of hydrogen be replaced by a different
 metal, then the triple salts formed by Mosander are produced : thus, the salt writ-
 ten on Berzelius's view as (Fe.Cy.-+2K.Cy.)-f-(Fe.Cy.-|-2Ca.Cy.) becomes Cfy.-j-
 Ca.K., and similarly there, is Cfy.-f-Ca.K., &c.
  The red prussiate of potash Liebig supposes to contain a radical, (Fe2Cy6) or
 Cfy2, isomeric with, but of double  the atomic weight of ferrocyanogen ; this fer-
 ridcyanogen forms with hydrogen a tribasic acid, Cfy2-|-H3, by replacement of  the
 hydrog*en, in  which, by three atoms of the same or of different metals, the various
 ferridcyanides are produced, as Cfy2-f-K3, Cfy2-4-3Cu., &c.
  The Prussian  blues, on this theory, are considered to be compounds of ferro-
 cyanide with  ferridcyanide of iron ; thus,
            3Cfy.Fe2-J-Cfy2Fe3 expresses common Prussian blue.
            Cfy2Fe3               "     Turnbull's Prussian blue.
            3Cfy.Fe2-j-Cfy2Fe34-Fe203 " basic Prussian blue.

  This theory accounts very strictly for the first and  third of the fundamental
 facts which I have described as characterizing  the cyanogen compounds.  The
 theory  of Graham is specially based upon the tendency of three atoms of cyanogen
 to enter together into combination with other  bodies, as is shown not only in its re-
 lation to metals, but  to oxygen, as in cyanuric acid,  and hence we may assume
 that cyanogen, as Cy3, with three times its ordinary atomic weight, forms a dis-
 tinct radical  (paracyanl), which forms with  oxygen and with hydrogen tribasic
 acids, Cy303  and  Cy3H3.   From the replacement of more or less of this hydrogen
 in the  latter  by equivalents of one or more  metal, the various cyanides may be
 formed.  Thus, for example,

             Cy3-j-Fe.2K. .  . . yellow prussiate of potash.
             Cy3-j-Fe.K.Ca. . . ferroprussiate of lime and  potash.
             Cy3-{-Fe.2H. .  . . ferroprussic acid.

  The  basis of the red prussiate of potash should be, then, another polymeric cyano-
gen, Cy6, which would form, with hydrogen, a pentabasic acid, Cy6+H5, in which
more or less of replacement by metals  should give  the various  ferridcyanides.
Thus ferndprussic ax-id should  be Cy6+-Fe2H3, and red  prussiate  of potash Cy64-
 te2K3, and so on ; Turnbull's Prussian blue becomes, on this theory, simply Cye-4-
 Fe,; the common Prussian blue is  (Cy3-f Fe2)-f Cy6Fe5  ; and, by  the addition of
 Fe203 to that, the  basic Prussian blue is formed.
  I am rather inclined to adopt Graham's view, although, in the present state of
 our knowledge, we have not grounds for positive decision.   He proposes to term
 the radical Cya Prussme, but has not given any name to that whose formula is Cy« 
M K T A LL I C  -s V L P II O C V A X I D E S.
525
     Of Sulphocyanogen, and the Products of its Decomposition.
  If yellow prussiate of potash, well dried, and mixed carefully with
half its weight of sulphur, in fine powder, be heated in an iron ves-
sel to perfect fusion, which takes place  at a dull red heat, the sul-
phur combines with  all the  cyanogen, forming  sulphocyanoo*en
which unites with the potassium, while the iron is converted into
sulphuret.  By digesting the fused mass in water, the former dis-
solves, and is obtaiued, by evaporation and cooling, in long striated
prisms, similar to those of nitre.  If the temperature be not raised
too high,  the  iron forms also sulphocyanide, which  dissolves, and
may  be decomposed by the addition of a slight excess of carbonate
of potash; by this means one half more product may be obtained
than  is yielded if the  sulphocyanide of iron be too violently heated,
and thereby converted into sulphuret.
  Sulphocyanogen is prepared by passing a current of chlorine gas
into  a solution of the salt thus formed, or by heating it in  dilute
nitric acid ;  chloride,  or nitrate of potassium is formed, and a deep
yellow precipitate produced, which contains all the sulphur and cy-
anogen  of the  salt, its formula being Cy.S2.  It is very light, and
insoluble in water.  It combines with all the metals and with hy-
drogen, forming well-defined salts.
  Hydrosulphocyanic  Acid,  Cy.S2 + H., is formed  by decomposing
sulphocyanide of lead by dilute sulphuric acid, or by sulphuret of
hydrogen.  It  is a colourless liquid, which reacts, and tastes acid.
By distillation it is decomposed.
  Sulphocyanide of Potassium.—Cy.S2+K.  This  salt, of which the
mode of preparation  has  been just  described,  forms  anhydrous
prisms, cool and pungent in  taste ; it is abundantly soluble in water
and alcohol, and slightly deliquescent. It is employed in the labor-
atory as a test for peroxide of iron.
  Sulphocyanide of Lead is  a crystalline  powder, prepared by mix-
ing solutions of a salt  of lead and of sulphocyanide of potassium.
  Of the sulphocyanides of Iron, the protosalt, Fe. + Cy.S2, forms a
colourless solution, which becomes red on exposure to the air.  The
sesquisalt, Fe2+-3Cy.S2, forms a deep  blood-red liquor, when a sol-
uble  sulphocyanide is mixed with any salt of the peroxide of iron.
It serves thus as a very delicate test of the presence of iron, and
also for that of cyanogen ; it is so applied to the  detection of prus-
sic acid, as noticed p. 520.
  These  sulphocyanides may be considered either as double sul-
phurets of cyanogen and of a metal, as Cy.S. + S.K., &c, or as salts
of the  compound radical  sulphocyanogen, Cy.S2 + K., &c.  The
latter view has been almost universally adopted by chemists.
  It  appears,  however, from  the researches  of  Parnell,  that  al-
though sulphocyanogen really exists  in  these salts, yet the yellow
substance extracted from them by chlorine or by nitric acid,  as de-
scribed just now under that name, is  only a product  of the decom-
position of the real sulphocyanogen, which has not been  as yet iso-
lated.  The formula of the yellow powder he finds to be S,,CI2N6 .
H30.  When acted on by alkalies or  by  nitric acid, it produces an
acid  which  he terms the Thiocyanic, which is polybasic.   It is a 
526
MELLON,  MELAM,  ETC.
   pale yellow powder, sparingly soluble in water, more so in alcohol.
   Its  formula is  S12CI0N5 . Ub02.  Its  compounds with  the oxides of
   lead, silver, mercury, &c, are insoluble.  This new acid is but one
   of the bodies produced in  this reaction;  the others have not  been
   examined.
     Mellon.—When  sulphocyanogen  is  heated, it is  decomposed,
   yielding sulphur, sulphuret of carbon, and  a yellow powder which
   remains as fixed residue, and  to  which Liebig has given the name
   of Mellon.   This is a compound  radical,  analogous to cyanogen in
   its characters.   It is insoluble in  water, alcohol, or dilute acids.  Its
   formula is C6N4 or Ml., and when  strongly ignited it is decomposed
   into three volumes of cyanogen and one of nitrogen.   Heated  with
   potassium, they unite with combustion  ; and if it be fused with the
   iodide or bromide of potassium, iodine  or bromine is expelled, and
   mellonide of potassium formed.
     Hydromellonic Acid, HMI, is formed by dissolving mellonide of potassium in
   boiling water, and adding a strong acid.   A gelatinous white precipitate forms,
   which dries into a yellowish powder, H.Ml.-j-Aq.
     Mellonide of Potassium, K.M1., is produced  by adding  mellon to sulphocyanide
   of potassium, fused in a porcelain capsule ; sulphur  and sulphuret of carbon are
   evolved.  On dissolving the brown mass thus formed in boiling water, the mellon-
   ide of potassium crystallizes, on cooling,  in fine colourless needles.
     If we take the formula of sulphocyanogen at C2N.S2, the formation of mellon con-
   sists in 4(C2N.S2), producing 2(C.S2) with 4S., and  leaving C6N4;  but, on Mr. Par-
   Hell's view, the decomposition is by no means so simple.
     When mellon is boiled with strong nitric acid, it dissolves, and, on cooling, the
   liquor yields octohedral crystals of Cyanilic Acid.  This substance has the same for-
   mula as cyanuric acid, Cy303-|-3 Aq., but its relations to  bases are not well under-
   stood.  Nitrate of ammonia is formed ;  mellon, C6N4, and three atoms of water,
   giving C6N303 and N.H3.
     Melam.—Ci2H9Nn.  Sulphocyanide of ammonium,  on  being heated, is  decom-
   posed into ammonia, sulphuret of carbon, and sulphuret of hydrogen, which pass off,
   while a grayish-white powder remains, which is Melam.   The same result is ob-
   tained by heating  to fusion  a mixture of sulphocyanide  of potassium and  sal am-
   moniac : in  this case chloride of  potassium also remains behind, but may be
   removed by washing.   Melam is insoluble in water and alcohol.  It is dissolved
   and decomposed by boiling acids and alkaline solutions, giving origin to a series of
   remarkable bodies.
     Melamine, C6C6Ne, is prepared by boiling melam with a dilute solution of caustic
   potash until the liquor becomes quite clear; it is then to be evaporated until it be-
   gins to deposite small crystalline plates, and being then  allowed to cool, the mel-
   lamine crystallizes out in colourless octohedrons,  scarcely soluble in cold water.
   It has no action on vegetable colours, but it combines with dilute acids, acting as
   a  base, and forming well-defined salts, which have an acid reaction, and may be
   obtained crystallized.
     Ammeline.—C6N5 . H502.  After the alkaline solution has deposited the melamine
   by cooling, it  contains ammeline, which precipitates when  acetic acid is added.
(   This is to be purified by solution in dilute nitric acid, and precipitation by carbonate
   of ammonia.  It then forms  fine silky needles, insoluble in water and alcohol.  It
   combines with the dilute acids, forming crystallizable salts.
    The origin  of these bodies consists in the  melam decomposing two atoms of
   water, and then CI2H„ . N„02 producing  C6HGN6 and CGN5 . H502.   By boiling
   melam in dilute muriatic acid, the same decomposition occurs, and the muriates
   of melamine and ammeline crystallize together on cooling.
    If any of the above  three bodies be dissolved in strong sulphuric acid,  and the
   solution be precipitated by alcohol,  a white powder is obtained, insoluble in water
   and alcohol, but soluble in strong acids and  alkalies.  It is nearly  indifferently acid
   or base, as it combines with nitric acid, and also with oxide of silver.   It is termed
   Ammehde.  Its formula is CI2H7. Nfl04-f 2 Aq.  When this body is boiled for a long
   time with dilute sulphuric or nitric  acid, it is resolved into ammonia and Cyanum
   Acid, which last is the ultimite product of the similar treatment of all the bodies of
   this series. 
OF  STARCH,  ETC.
527
  The theoretical constitution of these bodies remains exceedingly obscure.  The
bases, melamine and ammeline, are of great importance, from their close analogy
to the alkaloids, which are found naturally in many plants; but still  we have no
idea of the mode of arrangement of their elements.
  Some other sulphur compounds of cyanogen are known, but do not require much
notice.  Cyanogen and sulphuretted hydrogen combining, form orange crystals, in-
soluble in water.
                       CHAPTER XX.

OF STARCH,  LIGNINE, GUM,  AND SUGAR, WITH THE  PRODUCTS OF THE1B
               DECOMPOSITION BY ACIDS AND ALKALIES.

  The substances now to  be described form a very remarkable class
of organic  bodies.  They are found abundantly  in most plants, but
varying  somewhat in  characters, according to  their  immediate
source,  and are subservient to the most important  offices  of the
vegetable organization, being the materials from  whence the tissues
and secretions of the plant are elaborated.   In a chemical point of
view, they  are distinguished by a remarkable similarity of compo-
sition, all containing the same quantity of carbon (twelve atoms) in
the equivalent, united to  oxygen and hydrogen, which are always
present  in the proportions to form water.  In this may be found the
cause of the extraordinary transmutations of these bodies from  one
to another, by the mere fixation  of the elements of water, effected
by the influence of reagents, or by the organic power of the plant.
In these bodies, also, we  find an  example of the  difficulty of distin-
guishing between a constitution derived from  physical, and that re-
sulting from vital force.  In the  different kinds  of sugar, the crys-
talline condition,  solubility, &c, indicate  that the  elements  are
combined by forces merely  chemical; but in the diflerent varieties
of starch, and especially  in  lignine,  traces  of organized structure
are found, and properties manifested, which attach their history as
closely to the physiology as to the chemistry of  plants.  Under  this
point of view they shall be hereafter  reconsidered.

               Of Starch, its Varieties and Products.
  The most  important variety of this principle is that known as
Common Starch.   It exists in most plants, and in all parts of them.
It is extracted from the seeds of wheat and barley  ; from the tubers
of the potato ; from the root of the jatropha manihot, as Tapioca or
Cassava, and of the maranta arundinacea, as Arrow-root; and from
the stems of palms, as the sagus rumphii, which furnishes the  Sago
of commerce.  The starch  is imbedded in the cellular tissue of the
plant as small white grains,  totally destitute of any crystalline struc-
ture.  They differ in size in almost every plant.   Those of the po-
tato, which are the largest,  do not exceed in  diameter ^.th of an
inch * those of arrow-root,  which are some of the smallest,  do not
exceed -^-th.  In form, these grains vary also, some being globular, 
 528        PREPARATION  OF  STARCH, ETC.

 others ovoidal, and often, eve" in the same plant, irregular.  Each
 grain is formed by a number of concentric layers, which  increase in
 density and consistence from  the centre;  the  most external  beino*
 so  hard  as to resemble a membranous envelope  filled  by  a  softer
 material.
  The grains  of starch are quite insoluble in cold water; in boilincr
 water they dissolve, except the  outer layers, which, floating in the
 liquor, give it a peculiar opalescent aspect.  On cooling, the solu-
 tion gelatinizes.   If the solution of starch be dried at a gentle heat
 and then  digested with cold water, the outer  layers of the o-rains
 may be separated  by filtration, and a colourless transparent solution
 of starch  thus obtained.
  The preparation of starch rests on its insolubility in cold water.
 The texture of the plant is first broken  up by rasping or coarse
 grinding,  and  being then mashed up with  water, the starch grains
 fall out from the ruptured cells, and are carried off by the current
 from- which they  deposite themselves when the liquors  are left at
 rest.  In  obtaining starch from wheat, this liquor is allowed to fer-
 ment and become  sour, by which a quantity of gluten  that would
 otherwise attach itself to the starch is removed. If the moist starch
 grains  be  dried at a temperature of about  140^, they gelatinize to a
 semitransparent mass,  which  remains  so  when  dried, and is not
 granular or mealy.  It is  thus that the peculiar aspect  of  tapioca
 and sago is produced.
  By the  vital action of the seed in germination, the transformation
 of starch into sugar is effected, and constitutes the saccharine fer-
mentation.  It  is artificially induced by malting the grain,  for the
preparation of alcoholic liquors by brewers and distillers.  The cir-
cumstances of this change will be, specially noticed when  describing
 the mode of nutrition and of the growth of plants.
  If starch be heated beyond  240', it softens and becomes brown.
If the  heat be increased until the  mass smokes, it is found to be
 changed  into  a substance totally soluble in cold water, and known
 as British Gum.
  The action  of reagents on starch is very remarkable.   By boiling
 with dilute sulphuric or muriatic  acids, a kind of saccharine ferment-
 ation is induced,  it being changed  successively into gum, sugar,
 and  sacchulmine.   By  boiling with nitric  acid, it  gives  saccharic
and oxalic acids.   These reactions will  be hereafter studied in de-
tail. A solution of it is precipitated by  basic acetate of lead and by
infusion of galls.   With bromine it gives a yellow precipitate, which
is decomposed by heat, the bromine being expelled.   With iodine
it produces a compound of an intense blue colour, which is its most
remarkable property.
  Iodide of Starch  is produced when a solution of free  iodine is add-
 ed to a solution of starch.   Its colour is violet blue or nearly black,
 according to the proportion of starch.  It is very  soluble in water,
 but insoluble in alcohol, and  may be obtained solid by adding alco-
 hol to  a very  strong aqueous  solution,  and collecting the  precipi-
 tate on a  filter.  It is decomposed by alkalies and by chlorine;  in-
 deed, by all bodies which combine with iodine ; and its formation
 serves, therefore,  as a test only for free iodine, as described in p. 
           INULIN, LICHENINE, AND  LIGNINE.       529

 313.   When a  solution  of iodide of starch  is  heated, it  becomes
 quite colourless below 200 , and, if it be not boiled, regains its col-
 our perfectly as it cools.   When the liquor remains colourless after
 cooling, the  blue may be  restored by  oxalic acid or by  chlorine
 which expels the iodine  from the combination it had formed.
   The  composition of starch, no matter what plant it may be deri-
 ved from, is C,,Hl0Ol0,  as confirmed  by a variety of reactions.   Its
 combination with  oxide  of lead, Amylate  of Lead, is C,2H10O0+2
 Pb.O.
   Inulin— This kind of starch is found in the roots of the inula, dahlia, angelica,
 leontodon, and many other plants.  It may be prepared in the same way as common
 starch.  It is a white and very fine powder, almost insoluble in cold water, but easi-
 ly dissolved by boiling water;  forming a liquor which becomes thick, but not gelati-
 nous, when  it cools, and deposites the greater part of the  inulin unchanged.  It is
 transformed by acids, like common starch, but more easily.  It is precipitated, like it,
 by solutions of borax and subacetate of lead, and by infusion of galls.  It is pecu-
 liarly distinguished from it by not giving with iodine any blue colour, being  merely
 tinged yellow.   The structure of the grains of inulin has  not  been accurately  ex-
 amined.  Its formula is Ci2HioOio, like that of common starch,  but in  combining
 with oxide of lead it appears to lose one atom of water, and to become C12H9O9, as
 remarked by Parnell.
   L'cheninr.—This  variety of starch, which is found in many lichens, especially the
 Iceland moss and the carrigeen (sphcerococcus crispus),  is not contained in  the
 plant in grains, but  in a soluble condition.  To obtain it, the lichen is  first digested
 in a cold dilute solution of carbonate of soda, to  dissolve the bitter resinous  princi-
 ple, and this being completely washed away, the lichen is boiled for a long time
 in water; a liquor is obtained, from which, on cooling, the lichenine separates as an
 opaque gray jelly, which, when dried, is black, hard, and glassy.  Its properties are
 very similar to those of inuline.  It gives with iodine a greenish-brown colour.  Its
 composition is expressed by the same formula as the others, Ci2HioOio.

               Of Lignine.   Principle of Woody Fibre.
   When  any kind  of wood is treated  successively and repeatedly
 by dilute acids  and alkalies, by water and by alcohol,  so  that every
 soluble material is  removed  from  it, we find   that the  substance
 which remains is of very constant composition,  being expressed by
 the formula  C,2H.O,.   Of this  substance, Lignine, the proper  wood
 of the plant  is  constituted ;  its molecules being arranged  so  as  to
 form  the tubes  and cells of the vegetable tissues, and cohering  so
 firmly as to produce the fibres of flax, cotton, and hemp, which con-
 stitute the materials of our most important  woven textures, of pa-
 per, 6Yc.   Although  the lignine is thus rather the remains of an or-
 ganized body than a mere chemical substance, it forms some  com-
 binations  which  are of great importance in the arts.   Thus, if linen
 or cotton  cloth  be dipped  in  dilute solution of  acetate of alumina,
 the earth abandons the acid to combine with the lignine, and  thus
 serves as  the means of  fixing on the  cloth the various colouring
 matters used in the processes  of dyeing.   The same occurs with
 oxide of  iron ;  and  other  metallic  oxides have a  similar, though
 weaker affinity  for lignine, and thus serve as mordants for various
 colours.
  Lio-nine, when quite  pure, is white;  the bleaching of linen, cot-
 ton, paper' &c,  being  effected by destroying, by means  of the air
 or of chlorine, the resinous and other matters which are associated
 with the lignine in the fibres  or cells of the plants; the  lignine it-
self resists these agents, unless applied in a very  concentrated form
                                X x x 
530        ARABINE  AND  TRAGACANTHINE.
With cold nitric acid lignine combines directly, forming a very re-
markable  substance, Xyloidine, which may be  produced by immer-
sing for a moment a piece of paper in strong  nitric  acid, and then
washing it well in  pure water.   It assumes  the feel  and toughness
of parchment, and  is so combustible  as to  serve  for tinder.  Hot
nitric acid converts lignine into  oxalic acid ; with sulphuric acid it
is changed into gum, and ultimately into sugar, as will be detailed
farther on.
   If sawdust be heated with  a warm solution of potash for some
hours, the liquor will be found  to  contain a considerable quantity
of common starch, capable of striking a blue colour with iodine;
but by this means  the  ligneous  fibre is dissected, and  not decom-
posed.  The starch may be extracted also  by mechanical means,
and pure lignine does not yield any.  If lignine be strongly heated
with hydrate of potash, hydrogen is evolved, and a mixture of ace-
tate  and oxalate  of potash results;  C12H6Os and 4H.O.  giving 6H.,
with 2(C203) and 2(C4H303).
   In dry air, or immersed under water free from air, lignine remains
for an indefinite length  of time unaltered ; but  if both air and water
have access, oxygen is absorbed, and carbonic  acid and water given
out,  and  a series  of products of decomposition result, which form
the basis of vegetable soil, and  thus serve as the materials for  a new
generation of plants. By the  conjoint action of heat and water, lig-
nine produces  another  class  of products, and a third series  arises
from the  destructive distillation of dry wood.   These subjects will
be examined specially in their proper place.

                 Of the different Varieties of Gum.
   It is necessary to distinguish three varieties  of gum, to  which
the names  of Arabine,  Cerasine, and Dextrine  may be given.   The
first two are natural, the last  is  a product of the transmutation of
starch.
   Arabine is found in the juices of many species  of acacia and pru-
nus ; it exudes from crevices  in the bark, and forms lumps, in  which
state it is found in commerce (Gum Arabic and Gum  Senegal).  The
roots of mallow,  comfrey, and  many other plants contain a great
deal of arabine.  It is never crystalline, and  is colourless and trans-
parent, with a vitreous fracture.   It is  dissolved by water  in  all
proportions, forming a thick, adhesive liquid  (mucilage).  It  is not
dissolved by alcohol, which  precipitates its  watery  solution.  It
combines  with bases, forming well-defined, insoluble  compounds,
and  is not in any way acted on by iodine.   A solution of arabine
exercises sinistral rotatory power on a ray of polarized light (p. 41).
By contact with sulphuric acid,  arabine is gradually converted into
dextrine, and, if the digestion be continued, this then changes into
sugar.  With nitric  acid arabine  gives mucic acid, and afterward
oxalic acid ; another characteristic property of it is, that of giving
a precipitate with solution of silicate of potash  (soluble glass, p.
437).  Its composition is expressed by the formula C.A.O,,.
   Tragacanthine, or Vegetable Mucus, exists in  cherry-tree gum mix-
ed with arabine, but is  purer  in  gum tragacanth,  in flaxseed, and in
quince-seed.  It is extracted by digestion in water, when it gradu- 
DEXTRIN E.--C A N E-S U G A R.
531
ally swells  up and appears rather to imbibe the water than to dis-
solve ; a thick tenacious liquor is obtained, which is precipitated by
alcohol and by solution of basic acetate of lead, but not by silicate
of potash.  With sulphuric and nitric  acid, the same products are
formed as from arabine.
  The Salep of commerce is the tragacanthine extracted from the
roots of various species of orchis, and dried.
  Dextrine.—This variety of gum  is formed from the  starch of the
seed, in  germination, and may be obtained by digesting  starch in
dilute sulphuric acid.  If five parts of starch,  with one of oil of vit-
riol and fifteen of water,  be kept at 200  for  some time, the starch
completely disappears, the solution loses its power of gelatinizing;
it acquires  the characteristic rotatory power of Dextrine, and colours
iodine of a port-wine red, without any tinge  of blue.   If the liquor
be neutralized by carbonate  of barytes, the  whole quantity of sul-
phuric acid separates, and by evaporation, the dextrine is obtained
as a pale yellow mass of a vitreous fracture;  it is not adhesive like
common  gum, nor does it yield any mucic acid when acted on by
nitric acid.
  Dextrine precipitates a solution  of basic acetate of lead, but is not
affected by silicate of potash.  If dextrine be boiled too long with
the sulphuric  acid,  it passes  into a  substance more  analogous to
tragacanthine, which  is also  formed when arabine or lignine is so
treated.   In this state its rotatory power is feeble, and it is not at
all coloured by iodine.   In both  these forms the composition of
dextrine is  C12HI0Oj0.
                Of the  different Varieties of Sugar.
  The species of sugar are  much better distinguished from  each
other, both by properties  and composition, than the various  kinds
of starch, or of gum, have been found to be.   They are all charac-
terized by being capable of undergoing the alcoholic fermentation.
  Cane-sugar.—C12Hl0O10-|-Aq. when crystallized.  This species of
sugar is found abundantly in the juices of many plants.  It is ex-
tracted for  use from the  sugar-cane, the maple, and the  beet-root.
The juice,  when  fresh, runs into fermentation with great quick-
ness, and is therefore clarified by being warmed to 150J, with  a lit-
tle lime, by which the vegetable albumen is coagulated, and the fer-
mentation  checked.   The juice  is then evaporated with as  little
heat as possible, and allowed to cool in vessels, at the bottom of
which a number of small apertures, stopped with plugs, are situated.
The sirup congeals into a granular mass, and when it is quite  cold,
the apertures  below are opened, and the liquid  portion allowed to
run out.    The sugar thus  obtained  in fine  crystalline grains is
brownish-coloured, and is termed Muscovado, or Raw Sugar.  The li-
quid uncrystallizable portion constitutes Molasses, or Treacle.  To ob-
tain the  suo-ar pure, it  is redissolved,  and the liquor having  been
cautiously  evaporated (in some  establishments, in vacuo, see p. 85)
to the necessary degree, is poured into cones  of unglazed earthen-
ware which are placed on their  summits, the orifice in  which is
stopped  by a plug.   When, by cooling, the sirup  has  crystallized,
during which  the mass  is continually  stirred about  to render the 
532       SACCHULMINE.--SACCHARIC  ACID.

crystals very minute and close, the plug below is removed, and the
coloured liquor drains out;  the last portions of it being removed by
laying a sponge, moistened with some spirit  or with a clear sirup,
on the sugar at the base of the cone, and allowing the pure liquid
to filter through.  Thus is obtained refined, or Loaf-sugar.  If a strong
sirup be laid aside in a warm place, it crystallizes in very  beautiful
oblique rhombs, which constitute the Sugar-candy of commerce.
  Cane-sugar is perfectly colourless.   Its sp. gr. is  1*6 ; when heat-
ed,  it fuses at 350^ into a clear yellow liquid, and congeals, on cool-
ing, into a hard brittle mass  (barley-sugar), which, after some weeks,
becomes opaque, white, and crystalline.  If the temperature rises to
630'), water is given off, and the sugar becomes  dark brown, being
changed into Caramel ;  more strongly heated, it is totally decom-
posed.  Sugar dissolves in one third  of its weight of cold, and in all
proportions in boiling water.   A saturated solution becomes quite
solid when it cools.   If a strong solution of sugar be kept for some
time near its boiling point,  it is gradually changed  into uncrystalli-
zable sugar; hence arises the most important source of loss in the
manufacture and refining of sugar.   It is sparingly soluble in abso-
lute  alcohol, and but moderately in weak spirit.
  Sugar combines with some bases and salts, acting as a feeble acid;
the  compound with oxide of lead is  insoluble, and has the formula
C,2H|0Ol0-f 2Pb.O.; that with barytes is crystalline*, its formula is
C,2H,0Oi0-f Ba.O.  With common salt sugar combines, forming crys-
tals, easily soluble in water, and consisting of C|2H10O10-f-Na.Cl.
  The action of acids on cane-sugar  is very remarkable.  When di-
gested with very dilute sulphuric or muriatic acid, it is converted
into  grape-sugar ;  but with stronger acids, it is changed  into two
brown  substances, insoluble in water, one of them soluble, the other
insoluble in alkaline  liquors.   The  former is termed Sacchulmino,
the  latter,  Sacchulmic Acid.  These  bodies are  formed even with
very dilute acids if the digestion be continued for a long time.  Ac-
cording as the reaction proceeds, the sacchulmine separates in mi-
nute brilliant brown  crystalline  plates, mixed with a dull  brown
powder, which  is sacchulmic acid.   They are separated  by water
of ammonia, which dissolves the latter.   The composition of these
bodies is  not quite definitely established, as  it appears to be influ-
enced by the strength of the acid  used and  other circumstances.
The best-grounded idea is,  that they have both the same  composi-
tion, CS0H,3O13, being isomeric with ulmine.  If in  this reaction the
atmospheric air have  access, oxygen  is absorbed, and a large quan-
tity of formic acid generated.
  The preparation of oxalic acid by means of nitric acid  and sugar
has been already described (p. 493).  If dilute acid be used, so that
the oxidation may not be forced so  far, a liquor is obtained  which
gives with carbonate  of lime a neutral solution.   When this is de-
composed by acetate of lead, a white precipitate is thrown down,
which being acted on by sulphuretted hydrogen, the acid is set free,
and  maybe obtained crystallized by evaporating and cooling its so-
lution.  This is termed the Saccharic Acid.   It gives an  extensive
series  of salts, being a pentabasic acid.  Its formula is Cl2H40„-f-5
H.O. when crystallized.  Its potash  salt is C12H6On-f-K.O. . 4H.O. 
GR A PE-SUG A R.
533
 Its lead salt C12H,Oll + 5Pb.O.   The saccharate of lime is sparingly
 soluble in water, but dissolves in a very slight excess of acid, which
 distinguishes it from an oxalate.  An ammoniacal solution of sac-
 charate of  silver  is decomposed by heat; metallic silver being de-
 posited, and forming a mirror-surface on the interior of the vessel.
   The Caramel formed by heating sugar to 650; appears as a porous,
 shining, jet black mass.  It is completely soluble in water, and free
 from any empyreumatic taste.   It is insoluble in alcohol;  it com-
 bines with bases ; its formula is Cl2H909*  The sugar, in forming it,
 therefore, loses the elements of an atom of water, besides its water
 of crystallization.   By heating sugar with lime, a volatile liquid is
 obtained, which has the formula C^O., and is termed Metacetone.
   Grape-sugar.  Glucose.—Cl2H,,On + 3 Aq. when crystallized.  This
 kind of sugar is  still more extensively distributed in nature than
 the former.  It gives the sweet taste to fruits, and forms the solid
 part of honey.  It is produced in the animal body  in certain forms
 of disease, as diabetes, and by  the transformation of starch in ger-
 mination, and by artificial processes.   In consequence of this vari-
 ety of sources, it  is better to term it glucose, as suggested by Du-
 mas, than to use a name indicating any  one special origin.
   Glucose may be  obtained from raisins or honey by digestion,
 first with  cold, strong alcohol, to remove the uncrystallizable sugar,
 and then  expressing the residue, which is to be dissolved in water,
 and neutralized by chalk.   The liquor so obtained may be clarified
 by white  of egg, and evaporated to crystallization.
   From starch, gum, or cane-sugar, it may be prepared by  the  ac-
 tion of sulphuric acid as follows: one part of potato-starch  is to be
 boiled with  four parts of water and ^th of oil of vitriol during 36
 or 40 hours, the water which evaporates being replaced.  The jelly
 does not assume any consistence; the liquor remains clear, and the
 material used  is found completely converted into sugar.  By means
 of chalk, the acid  is removed,  and the  solution being  evaporated,
 the sugar crystallizes.
   If starch  paste  be  moistened with an  infusion of pale malt, it is
 rapidly converted  into dextrine, and thence  into grape-sugar.  This
 occurs from the catalytic influence  of a principle termed Diastase,
 which exists in the malt, and the  formation of which  will be de-
 tailed under the head of germination.
   To convert  lignine into sugar, bits of paper or linen are to be im-
 bibed with their own weight of  oil of vitriol, until they are convert-
 ed  into a  uniform  viscid mass, taking care that it shall not become
 hot; this  is then to be diluted, and the liquor boiled for some time.
 The acid  being then removed by chalk, the sugar is obtained pure,
 by crystallization,  as in the former case.
  Sugar of grapes crystallizes in hard colourless tables or in hemi-
 spherical  grains, consisting  of  minute needles closely  aggregated
 together;  its specific gravity is  1*38 ; it is much sweeter than cane-
 sugar, and less soluble in water.  When  heated to 212°, it gives off
 two atoms of water, which it recovers when redissolved ; but by a
 stronger  heat it is changed into caratnel.   It is soluble in twenty
parts of boiling absolute alcohol, and separates almost  totally  on
coolinnf, in granular crystals, which contain alcohol combined.  It 
 534       CONSTITUTION  OF  GRAPE-SUGAR.

 combines with bases, forming compounds analogous to  those given
 by cane-sugar.
   The composition of crystallized grape-susrar is Cl2Hl40M, or C,2H„
 0,, + 3 Aq.   When fused at  212°, it becomes C12H, Ol2, or 0,^,0,,
 + Aq.   Its compound with chloride of sodium, which  crystallizes
 in fine double six-sided pyramids, consist of 2(Cl2H120,2)4-Na.Cl.-f-
 2 Aq.   With a solution  of  basic acetate of lead  it gives a white
 precipitate, the formula of which is C^HnOn-fSPb.O.,  correspond-
 ing to the crystallized sugar.   The dry grape-sugar has evidently
 the same composition as the crystallized cane-sugar.
   The kinds of sugar (glucose) derived from these different sources
 are not  so  really identical as has been  generally supposed, since
 they are found to act differently upon polarized light.  Grape-sugar
 as  contained in the grape-juice or  in the  juice  of the flowerino*
 grasses, rotates the plane of polarization to the left; but if the juice
 be evaporated and the sugar crystallized, its molecular constitution
 is so totally altered, as that, when redissolved, it gives a rotation to
 the right.  The starch-sugar, as well as cane-sugar, rotates also to
 the right, but in a much  inferior degree  to  the starch-gum, which,
 as already  mentioned,  receives its name  of  dextrine  from  that
 quality.
   As lignine, starch, gum, and cane-sugar all contain the same quan-
 tity of carbon  (C,2), their transformation  into grape-sugar consists
 evidently in  the fixation of the elements of water; thus lio*nine
 C12HbOs takes 4H.0., and 100 parts of  sawdust  have been found to
 give 115 of sugar;  starch (Cl2H10O,0) takes 2H.O., and 100 parts of
 it usually yield  106.  It has been remarked, that a certain quantity
 of Mannite is at the same time produced, besides sacchulmine.
   Grape-sugar yields,  when  treated with dilute sulphuric acid,  the
 same brown substances as cane-sugar; but if the  sulphuric acid be
 concentrated, it forms with  the elements of the  sugar a peculiar
 acid termed the Sulphosaccharic.   Sugar of starch  or grapes is to be
 fused at  a low heat, and  1£ parts of oil of vitriol  then well mixed
with it.  If the sugar be pure and the temperature be kept low, the
product is not coloured.  Its constitution is not rigidly determined,
but its lead salt consists of 2(C,2H110ll) + S.03+4Pb.O.
  In acting on grape-sugar, nitric acid gives rise  to the same pro-
ducts, oxalic and saccharic acids, as cane-sugar ; indeed, it appears
probable, that, like the  other strong acids, this also  first changes  the
cane-sugar into glucose,  and that the  saccharic acid is really  de-
rived from the latter.   On this  view its  formation is more easily
explained ; for as the dry glucose is 0,^,0,,, and the saccharic acid
is CuHjO,,, the oxygen of the nitric acid  simply removes six atoms
 of the hydrogen of the grape-sugar, and the elements of the acid re-
main.
  By contact even with the strongest bases, cane-sugar is but slowly
 altered, and hence lime may be employed to clarify the vegetable jui-
 ces which contain it; but, under the same circumstances, grape-su-
 gar is rapidly decomposed and an acid formed, which is termed Glu-
 cic Acid.  It  is very soluble in water, and  does not crystallize ; with
 lime, barytes, and lead, it forms  neutral soluble salts, but it precip-
 itates a solution of basic  acetate of lead.  Its taste is purely acid, 
L A C T I N E.--M A N N I T E.
535
 and it reddens litmus.   Its composition is C,2Hf,0,, and it is isomeric
 therefore, in its dry state, with lignine.   When a strong solution of
 caustic potash  is added to fused grape-sugar boiled, the glucic acid
 which at  first  forms  is decomposed.   The liquor becomes  deep
 brown, and yields, on the  addition of muriatic acid, a black floccu-
 lent  precipitate of Melassic  Acid.   The  formula C24H12O10 has  been
 assigned to it,  but  its nature is not well  known.
   Lactine, or Sugar of  Milk.—This remarkable substance, which  is found only in
 the milk of the mammalia, is obtained by evaporating whey to a pellicle and setting
 it aside to cool, when  the sugar crystallizes in small square prisms,  white, semi-
 transparent, hard, and gritty under the teeth.  The  taste of the crystals is  but
 Blightly sweet, but that of a strong solution is much more so.  It dissolves very
 slowly in watei;, and is insoluble in alcohol.
   When the crystals of lactine are gradually heated to 270°, they give  off two
 atoms of water; at about 300c they fuse,  and give off three atoms of water more.
 The composition of the dry sugar thus obtained  is C24Hi90i9, and of the crystals
 Cu\l\gO\9-\-5 Aq.  By  mixing solutions of sugar  of milk and of  basic acetate  of
 lead, a white precipitate is produced, the formula of which is C^HigOig-f-SPb.O.
   By digestion with dilute sulphuric acid, sugar of milk is changed  into grape-sugar,
 and then produces the other reactions already described.  With alkalies the decom-
 position is also the same as that of glucose, but the  action of  nitric acid on lactine
 differs from that on any other sugai, as the acid formed is not the saccharic, but
 that already noticed as obtained from native gum, the  Mucic Acid.
   To obtain mucic acid, one part of gum  or lactine is to  be dissolved  in four parts
 of nitric acid, specific gravity 1*42, mixed with one part  of water.  Heat is to  be
 applied until all effervescence has ceased,  and the mucic acid  is deposited on cool-
 ing.   It is a crystalline  powder, gritty under the teeth, and feebly acid.  It dissolves
 in six parts of boiling water, but is insoluble in alcohol.  Its crystals have the form-
 ula Ci2H10Oi6,  being formed from gum by the simple addition of six equivalents  of
 oxygen.  This formula contains, however, 2 Aq., as it is a bibasic acid, and its salts
 consist of C2iH80|4-(-2M.O.  The alkaline mucates are soluble, the earthy and me-
 tallic salts are insoluble in water.
   When mucic acid is long boiled with water, its acid  properties become  much
 stronger, and it becomes more soluble in water and soluble in  alcohol; it gradually
 returns from this state,  to its ordinary condition, even when combined with bases.
 If mucic acid be distilled at a high  temperature, water and carbonic acid are evolv-
 ed, and a sublimate forms in brilliant white plates, which are soluble in alcohol and
 water ;  C|2Hi0Oi6 give 20.02 and 6H O., besides C10H4O6, which is the formula  of
 the hydrated Pyromucic Acid. This substance fuses at 270°, and is volatile at 290°
 without decomposition.   Its salts  contain  one  equivalent of  base ; those of lead,
 barytes, and silver are insoluble ; those of the alkalies are very soluble in water.
   With this acid a certain quantity of chlorine may be combined, forming Chloro-
 pyromucic Acid, Ci0H3. CI4O5, which is prepared by acting with chlorine on Pyro-
 mucic Ether.
   Sugar of Mushrooms  is deposited in rhombic prisms from the watery solution of
 the alcoholic extract of ergot of rye.  They are insoluble in ether ; they give oxalic
 acid  by nitric acid, and  undergo the alcoholic fermentation.  Their  composition
 was found to give the formula Ci2Hi30i3, but little is known accurately of this  va-
 riety of sugar.

                      Of Mannite and  Glycyrrhizine.

  These bodies are connected so closely with the  true sugars, that, although want-
 ing in the characteristic of forming alcohol by fermentation, they  may be best  de-
 scribed here.
  Mannite, CeHvOs, is found in manna, of which it constitutes the  sweet principle.
 It exudes also from the bark of  other trees, and exists in most mushrooms,  ft is
 produced by the decomposition of cane-sugar in certain cases.   To obtain it, manna
 is digested  in boiling alcohol, and the liquor filtered while very hot; on cooling, the
 mannite is deposited almost totally, and may be  purified by  repeated crystalliza-
tions   Its taste  is slightly sweet;  it is very soluble in water, and  it crystallizes in
brilliant white prisms'of silky lustre.  When  heated gently, it fuses without losing 
 536           LACTIC  ACID.--GLYCYRRHIZINE.

 weight.   With nitric acid it gives oxalic and saccharic acids.  It does not appeal
 to combine with bases.
   If the unclarified juice of the beet or carrot root be kept at a temperature of 100°
 for some time, a tumultuous decomposition sets in, which is termed the mucous fer-
 mentation.  All  the sugar disappears, and the liquor is found to contain a large
 quantity of gum and of mannite, with a peculiar acid, which exists naturally in all
 the animal fluids, but especially in milk, and is termed the Lactic Acid.  At the
 same time, carbonic acid gas is evolved, and the liquor contains ammonia.  This
 reaction is too complex to be expressed in formula?, but  it may be noticed that one
 equivalent of dry cane-sugar contains the elements of two equivalents of lactic acid;
 while, by abstracting two atoms of oxygen from an equivalent of crystallized grape-
 sugar, the constituents of two atoms of mannite remain.
  Lactic acid is most easily prepared by means of this mucous  fermentation, but
 may be also obtained  abundantly from sour whey, or the  sour waters obtained in
 making wheaten starch.   The acid liquor is to be neutralized by carbonate of lead,
 and the solution of lactate of lead evaporated until it is tolerably concentrated.  It
 is then to be decomposed by sulphate of zinc, and the precipitated sulphate of lead
 being removed by  the filter, the lactate of zinc may be obtained in large crystals,
 easily rendered  quite pure by re-solution and crystallization.  A solution of pure
 lactate of zinc being decomposed by water of barytes, lactate of barytes is obtained,
 which, with sulphuric acid, gives sulphate of barytes, and the pure  lactic acid dis-
 solves.   The  solution is to be placed in vacuo over sulphuric acid  ; it gives a sirup-
 thick liquor, which has the formula OsH606 or C6H50s-f-Aq., as it contains an  atom
 of basic water ; it  tastes strongly acid.   When heated to 480° it gives off water,
 and a white sublimate forms in brilliant white rhomboidal  plates, which is Paralac-
 tic Acid.  It is purified by solution in boiling alcohol, from which it crystallizes.
 The composition of this body is  C6H404;  it fuses at 225°, and sublimes at 450° ; it
 tastes very slightly acid, and dissolves but very slowly in water; the solution gives,
 when evaporated, only the sirupy liquid  of the hydrated acid, and  does  not crys-
 tallize.
  The lactic acid coagulates albumen ;  it mixes with milk when cold, but coagu-
 lates it when boiled.  It forms monobasic salts, in which its  formula is C6H505.
 They are all soluble in water, and  crystallize but imperfectly, except that of zinc,
 which  forms brilliant white four-sided prisms, containing  three atoms of crystal-
 water.   The Protolactate of Iron, CeHsOs-j-Fe.O.-f^ Aq., may be  obtained crystal-
 lized in small prisms of a greenish-yellow colour.  The Perlactate  of Iron  dries into
 a reddish transparent mass like shell-lac.   These last are used in  medicine.
  The lactic acid will be again noticed as a constituent of the animal system.
  Glycyrrhizine.—This substance, which is found in the liquorice-root, and in some
 other sweet woods, is obtained by boiling the root or liquorice  in water, and,  after
 concentrating the liquor,  adding thereto sulphuric acid.  A white precipitate, con-
 taining  the glycyrrhizine combined with  sulphuric  acid and albumen, is formed.
 This is to be washed with acid water, and then with pure water, and to be dissolv-
 ed in alcohol,  which leaves the albumen.  The alcoholic solution is to be decom-
 posed by carbonate of potash, which throws down  ths sulphuric acid, and by evap-
 orating the filtered  liquor, the sweet principle  remains pure as a yellow transparent
mass.
  Its most remarkable property is that of combining very definitely  with acids and
 bases, and with  several neutral salts.  Almost every acid  precipitates  a compound
from a solution  of glycyrrhizine.  It expels the carbonic acid from the carbonates
of potash, soda,  and barytes, combining with the base, and it precipitates the solu-
 tions of most of the ordinary metallic salts   Neither the pure (substance nor any
of its compounds have been accurately analyzed. 
OLUTEN,  MUCIN, AND  ALBUMEN.         537
                          CHAPTER XXI.

 OF THE ALCOHOLIC AND ACETIC FERMENTATIONS—OF ALCOHOL, THE ETHERS,
      ALDEHYD, ACETIC ACID, AND OTHER BODIES DERIVED FROM IT.

   An aqueous solution of pure sugar may remain perfectly unaltered for
 any length of time, if carefully excluded from the air.  If the air  have
 access, it is gradually decomposed, becoming brown and sour, but no al-
 cohol is generated.  If, however, the  solution of sugar be brought in con-
 tact with any organic substance which is itself in the act of slow decom-
 position, then tbe particles of sugar  participate in  the  change which is
 going forward, and carbonic acid and alcohol result.
   The substance which is specially  active in inducing this kind of fer-
 mentation is an  azotized body termed yeast; but a number of animal
 and vegetable substances can also effect it.   Blood, white of egg, glue,
 flesh, if they  have begun to putrefy,  are capable of  exciting it; but the
 bodies of most practical importance  in that  respect are vegetable albu-
 men and  gluten.  These bodies exist in all fruits and  seeds, in greater
 or less  proportion, but they differ in character, according to the plants
 they are derived  from, nearly in the same way as the varieties of starch.
 I shall here only  notice them as derived from wheat and from beans, as
 I shall have occasion to describe some other forms hereafter.  If wheaten
 flour be washed with water in a linen bag, the  starch  passes off, and a
 tenacious paste  remains, which consists of albumen and gluten  mixed.
 They may be separated by boiling in alcohol, which dissolves the latter,
 and leaves the  former behind.   On mixing the alcoholic liquor  with
 water, the gluten is precipitated, and may be collected and dried.
   Vegetable Gluten so obtained is pale yellow, and forms, when soft, an
 adhesive  mass, very extensive and elastic.   Its solution in  alcohol  is
 thick-fluid when concentrated; insoluble in ether;  it dissolves in acetic
 acid, and  in  alkaline solutions.  It   combines with  the mineral acids,
 forming bodies very sparingly soluble in water, which  are  precipitated
 by adding the acid to the solution of gluten in acetic acid or in potash.
 If these solutions be mixed with  solutions of earthy or metallic  salts,
 precipitates are  formed, which  are compounds of  the  gluten  with  the
 metallic oxide.
   In all these reactions, the gluten is accompanied  by a slimy material,
 termed Mucin, which it is difficult to  remove perfectly from the gluten ;
 it is best effected  by boiling with water, when the mucin  remains dissolv-
 ed.  Its solution  is precipitated by sulphate of iron and  infusion of galls,
 but not by acetate of lead or corrosive sublimate.
   Vegetable Albumen remains behind after the  rough  gluten has been
 boiled in alcohol.  It is destitute of elasticity when softened, and dries to
 a hard white  mass;  it is moderately  soluble in water, and its solution is
 coagulated  by heat; it dissolves in alkaline liquors.  Its solutions  are
 precipitated by acids, except the phosphoric and acetic, and by all earths
and metallic salts ; these precipitates are white or coloured, according to
the nature of the  metallic oxide : with ferro-prussiate of potash and with 
538         LEGUMIN.—- NATURE  OF YEAST.
infusion of galls, the solution of vegetable albumen in acetic acid gives
white precipitates.
  Legumin.— This substance, which exists in pease and beans, possesses
properties  intermediate to those of the  gluten and albumen of wheat.
When powdered pease are diffused through water, the starch settles to
the bottom, but the legumin is dissolved, and separates by evaporation,
on the surface of the liquor, in mucous transparent pellicles. Its solution
is not coagulated by heat; it is  insoluble in alcohol.   It dissolves in so-
lutions of the vegetable acids, and is  precipitated on the addition of a
mineral acid.  It dissolves  in alkalies,  and gives, with the earthy and
metallic salts, compounds insoluble in water.
  All  these  substances differ from most vegetable bodies, in containing
a large quantity of  nitrogen, and, in the latter case,  sulphur, as a con-
stituent.   They leave behind, when burned, an ash consisting of phos-
phates of lime, magnesia,  and iron, similar to the  ash of animal sub-
stances.   Indeed, an almost perfect similarity of properties exists be-
tween these bodies, and fibrine, albumen, and casein among animal prod-
ucts; in the  case of casein and lupuline  probably  amounting to identity.
In contact with  air and water, these bodies  enter  spontaneously into
decomposition,  evolving carbonic acid and ammonia, and  forming new
products; and in this state of decomposition they superinduce the alco-
holic  fermentation on those  particles of sugar which  lie in contact with
them.   Hence, in fruits, the sugar may lie in contact  with these vegeto-
animal substances without  any change occurring, as long as the investing
membrane of the fruit-cells remains perfect; but  if the fruit be crushed,
so that the air have access, then  oxygen is absorbed, the vegeto-animal
body  begins to putrefy, and the sugar is  soon engaged in the decomposi-
tion.   It is remarkable, that the necessity  for oxygen is at  the com-
mencement of the decomposition : when the  putrefaction  of the albu-
men or gluten has  once  begun,  it extends itself throughout  its  whole
mass  without requiring any farther action of the air.
  The principles of the conservation of vegetable juices, by enclosure in
vessels  from which  the air  is excluded, can easily be understood from
this, as well as the utility of such agents as  sulphurous acid or sulphite
of potash, which absorb any traces of oxygen that may be present, and
prevent it from acting on the organic substance.
  The general characters  of these natural ferments being thus sketched,
it is necessary to add the important facts of the history of artificial fer-
ment,  or  yeast.    This  is nothing more  than the decomposing mass of
vegetable gluten or  albumen produced in a previous  fermentation.  If
the yeast be  too old, that is, if all the  vegeto-animal  matters be already
decomposed,  its power of exciting action is destroyed ;  it is also destroyed
by boiling, by alcohol,  by  many salts and  acids, and, generally, by all
those  means which give to the albumen and gluten an insoluble form, and
prevent their farther putrefaction.
  When a solution of pure sugar is fermented  by contact with a certain
quantity of yeast, this last  is found to be very much diminished in quan-
tity, and to have  totally lost its activity.   On the contrary, if, in place of
pure  sugar, grape or currant juice, or an infusion of malt, be used,  the
quantity of ferment is found to be  much  increased, and to preserve all
its power.   In this case the albumen and gluten of the vegetable juices
are themselves brought into the same train of decomposition as the added 
ALCOHOLIC  FERMENTATION.
539
portion of yeast, andthus form a new and larger quantity of active fer-
menting  material.   Thus, in a  brewery, the quantity of yeast  continu-
ally increases.   If yeast be examined with the  microscope, it is found to
contain a vast  number  of minute globular bodies, possibly animalcules,
which  derive their nutriment from it; but recently some very unfounded
attempts have  been  made to connect these globules  essentially with the
process of fermentation, by the idea that, in the process of nutrition, they
absorbed the sugar, and that the products of fermentation were excreted
subsequently by them.  But this  is shown to  be absurd  by the simple
fact that the weight  of the alcohol and carbonic acid is greater than the
weight of the sugar.
   The phenomena of the alcoholic fermentation are best observed on the
clear-expressed grape-juice, kept at a temperature between 70° and 80°,
in a lightly covered vessel.  After a few hours a slight effervescence is
observed, and  the liquor  becomes turbid, as if pipeclay  were diffused
through it.  As the effervescence increases, the liquor becomes  warmer,
and the precipitate forms  flocculi, on  which the gas.bubbles are evolved,
being thereby carried to the surface of the liquor, and falling down again
when the gas-bubbles have broken.  This circulation continues  until the
fermentation has ceased,  when  the precipitate collects  at the bottom.
The liquor no longer tastes sweet; it contains no sugar, but in place of
it an  equivalent quantity of alcohol.  An infusion  of malt  does not so
readily ferment as the grape juice, unless some yeast be first added.  In
its spontaneous fermentation, most of the gum and  sugar which it con
tains  passes  into the mucous fermentation,  while  but little alcohol is
formed.  In the practical  manufacture of malt-drinks and  spirits, there-
fore, the worts  are  always  set  to ferment by the addition of a suitable
quantity of the  yeast formed in a preceding operation.
   Although the essential character of sugar is to be  capable of alcoholic
fermentation, yet the diflerent kinds of sugar enter on that process with
unequal facility.  The sugar  of milk requires the  presence of a  very
active  ferment, and  of an acid,  by the influence of which it is changed
into sugar of grapes.  Thus milk does  not ferment until it has become
clotted and sour ; the casein then  acts as yeast, in superinducing the al-
coholic fermentation. Indeed, no matter  what kind of sugar is employed
in this process, it is changed into grape-sugar before fermenting,  as is
shown by the action of the liquor upon polarized light.  The grape-sugar,
as dried at 212°, contains exactly the elements  of two atoms of alcohol
and four of carbonic  acid,  as 2(C4H602) and 4C02 arise from Ci2H,20,2.
As cane-sugar takes  an atom of water to  form grape-sugar, it follows that
cane-sugar, in fermenting, should yield more than its own weight of car-
bonic acid and alcohol;  and it has been  ascertained  by experiment that
100 parts actually give 104, while by theory 105 should  be produced,
consisting of 51*3 of carbonic acid  and 53*7 of alcohol.   This coinci-
dence of numbers proves  that these bodies are  the only products.   The
influence of the yeast is, therefore, strictly what Berzelius  terms cata-
lytic, but its  action becomes much more  definitely intelligible by consid-
ering it as a case of  the general principle expressed by Liebig, that mo-
tion (decomposition)  may be communicated  from the particles of one
body (yeast) to  those of another (sugar)  by virtue of proximity, as  de-
scribed more fully in p.  235-237.
  As farther details  of  the circumstances of the alcoholic fermentation 
540          CONSTITUTION  OF  ALCOHOL.
would vary with  the  nature of the  liquor to be produced, whether it be
for immediate drinking, as wine, ale, or porter, or lor distillation, and
as these lead to purely technical descriptions of the arts  of brewing,
&c, 1 shall not enter on them.

             Of Alcohol and the Ethers derived from it.
   When any saccharine liquor, which has  undergone the alcoholic fer-
mentation, is distilled at a gentle heat, a very volatile liquid  passes over,
which, by successive rectifications, may be deprived of most  of the water
which had been mixed with it.   In various degrees of strength, and con-
taminated  by  minute traces of essential oils, characteristic of the plants
from  which the saccharine liquor bus been obtained, it  constitutes the
potato-smrit, brandy, malt-whiskey, arrack, rum, &c,  of commerce.  In
a still stronger  form it constitutes the spirit of wine, or  rectified spirit,
the term alcohol being applied to it only  when it is chemically  pure.
By mere distillation alcohol cannot be freed from all the admixed water,
for which it exerts  a strong affinity.   When its specific gravity is redu-
ced to  0*813 at 60°, in which  state it  still contains 8*2  per cent, of
water, or exactly half an equivalent, its boiling point remains constantly
at 172°, and it distils over unchanged.   In the  form of proof spirit of
commerce, its sp. gr. is about 0*920, and it contains 48 per  cent, of ab
solute  alcohol;  the rectified  spirit containing about  83  per cent., and
having  the specific  gravity 0*839 at 60° F.
   To obtain real alcohol, or absolute alcohol, as it is generally termed,
rectified spirit is to be distilled at a moderate heat from some substance
having  a stronger affinity for water;  as  lime, caustic potash, carbonate
of potash, or chloride of calcium.   Of these the last named should  be
preferred.   The water of the spirit combines with the body used, and,
forming a hydrate, the real  alcohol distils over.   The  rectification
should be conducted in  a water-bath.
  A singular  mode of concentrating alcohol is founded on the fact that
alcohol  does not moisten the animal tissues, but corrugates, and rather
abstracts water  from them.   Hence, if a bladder be filled with spirit of
sp. gr.  0*820, containing 90 per cent, of alcohol, and if  it be  left for a
few days in  a warm room, the spirit will  be  found to have its sp. gr.
reduced to 0*800, containing 97 per cent,  of real alcohol.  The water
permeates  the bladder,  and evaporates from the outer side; but, as the
alcohol  does not moisten the  bladder, it cannot get through, and conse-
quently remains behind, freed from water.
  The very ingenious way  of obtaining alcohol, devised by  Graham, by
evaporation in vacuo with quicklime, has been described  in  p.  87.
  Alcohol thus  obtained anhydrous has a  sp.  gr.  of 0*7947 at 60°; it
boils at 168°;  tne  specific  gravity of its vapour is 1601 ;  it  does not
become solid even in the most intense cold; its taste is burning and dry
upon  the tongue, owing to  its abstracting  water from its tissue.  It is
highly inflammaole, and burns with little light.   From  its  volatility, if
some  drops of it are poured into ajar of oxygen gas,  its  vapour forms a
powerfully explosive mixture.   It does not conduet electricity.  It mix-
es with  water in every proportion, contracts in volume, and evolves heat.
The sp. gr. of spirituous liquors is therefore always above the  mean sp.
gr. of the alcohol and water  they contain.   The greatest condensation
occurs with 54 volumes of alcohol and 50 of water;  the mixture  occu- 
USES  OF  ALCOHOL.
541
 pies only 100 volumes, and its sp. gr. is 0*927, being a little denser
 than proof spirit.
  The formula of alcohol is C4Hg02, and its composition is,
              4 equivalents of carbon,   -=242  .  .  .  52 66
              6   "    "     hydrogen, = 60  .  .  .  12 90
              2   '•    "     oxygen,  =160  .  .  .  3444
              The equivalent of alcohol, =46-2  .  .  .  10000
  This is confirmed by the products of its decomposition, and by the specific gravity
 of its vapour; for,
              4 volumes of carbon vapour  . (843x4)—3372 0
              12    "      hydrogen  .  .   (68 8x12)= 8256
              2     "      oxygen    .  .  (1102 6x2)=2205 2
              Give four volumes of alcohol vapour  .    6402*8
              Of which one volume weighs .  .  .  .    1600 7
  It will be Miown, however, that alcohol consists of ether united to water, and that
 its formula is C4H50.-|-Aq.  Its vapour is then formed by the union of
               £ volume of vapour of ether, =1290 6 ) lfi0o.7
               i volume of vapour of water, = 310-1 J
   The  uses of alcohol in chemistry and pharmacy are numerous and
 important.   It dissolves  the caustic alkalies and most deliquescent salts,
 combining  with them to  form alcoales, which resemble very remarkably
 the hydrates.  Thus, if dry chloride of calcium be dissolved in alcohol,
 the alcoate crystallizes by cooling in large transparent plates.   By heat,
 these arc decomposed, and also by contact with water, which expels the
 alcohol, and takes its  place.  The  permanent and efflorescent salts are
 generally insoluble in alcohol, and  may be even precipitated by it from
 their solution in water, the alcohol seizing on the water.
   An important pharmaceutic use  of alcohol is  for the solution of the
 resinous principles of plants, in the preparation of tinctures and alcoholic
 extracts.   The strength  of the alcohol  must in these cases be regulated
 by  the  nature of  the substances to  be  dissolved.   Sometimes rectified
 spirit, at other times proof spirit being more effectual.
  The  manufacture of alcohol is itself one of the most  important  arts;
 it is the basis, also, of the manufacture of vinegar, of the making of res-
 inous varnishes, and various other  processes.   To the chemist it  is
 specially of interest  as the type  of  a very interesting group of organic
 bodies,  and yielding by its decomposition a very numerous  series  of
 products, which are of  great importance in science, in pharmacy, and
 iti the arts.
  When alcohol  is  exposed to the air it  gradually  absorbs  oxygen,
 aldehyd and acetic acid  being formed.   It is  then said  to undergo the
 acetous fermentation.   Under the influence of acids  it loses an atom  of
 water, compounds being  formed which  are termed ethers, into the  com-
 position of which the acid  employed generally enters.

          Of Sulphuric Ether.   Ether.   Oxide of Ethyle.
  This substance may be prepared  by any process which deprives  alco-
 hol of the equivalent of water which  it contains.   Thus,  if potassium  be
placed in contact with absolute alcohol, hydrogen gas is evolved, and a
compound of ether and potash crystallizes, C4H50. + H.O. and K. giving
C4H50.-|-K.O. and free  II.  If a current of gaseous fluoride of boron 
542
PREPARATION  OF  ETHER.
(p. 326) be passed into alcohol, it is absorbed, and boracic acid separates
in crystals, while the liquor contains ether; here, also, the water of the
alcohol  is decomposed, fluoric and boracic acids being produced, and
ether liberated.  By distillation  with chloride of zinc,  also, the water
may be abstracted from alcohol, and  ether  obtained ;  but the affinity of
the other deliquescent salts is not  sufficiently intense to decompose it.
  It is by the action of sulphuric  acid upon alcohol that ether  is, for
practical purposes, always obtained.   Equal weights of rectified spirit
and of oil  of vitriol being well mixed, and avoiding any considerable rise
of temperature, are to be introduced into a glass globe, to which heat
may be applied by a sand-bath, as represented in the figure.  To  this
may be  attached the  form  of  condenser devised  by   Liebig for the
distillation of very  volatile liquids.   It consists  of  a glass  tube three
fourths or one inch wide, and twenty-four or thirty inches long, d d, to
which is attached at one end by a good cork a narrower tube, passing
to the globe, and to the other end is soldered a smaller tube, bent at an
obtuse angle, and conducting to the receiver e.   The tube d d fits water-
tight  by corks into a tinned cylinder c, the proportions of which may  be
judged from the figure ; this is kept full of cold water.  When the distil.
lation commences, the hot vapours entering the condensing tube at d,
give out their latent heat to the surrounding water, and that part  of the
condenser would soon get hot, were not the water constantly changed;
by the funnel /, a stream of cold water flows from the reservoir i into the
lower part of the tube c, and presses up before it the  warm and  lighter
water, until this is  expelled by  the tube h, when it is  collected at b.
The supply  of cold water should be so proportioned to the supply of va-
pour, that,  flowing away  at h,  it  should  not  be sensibly  warm to the
hand.   With this precaution, most  volatile liquids may be perfectly con-
densed even in the midst of summer.   The mixture of acid and spirit in
the globe being brought to a temperature  of about 260° as rapidly as
possible, il begins to  boil, and the ether distilling  over, accompanied by
some water and unaltered  alcohol, collects in the  receiver.
   Since the quantity of sulphuric acid  continually increases in the globe
as the distillation proceeds, its action on the remaining alcohol changes, 
         CONTINUOUS  FORMATION  OF  ETHER.     543

the mixture becomes dark coloured, an oily substance distils over (oil of
wine), and  the quantity of ether formed diminishes rapidly.  Sulphurous
acid and olefiant gases are then evolved, and finally the mixture  becomes
thick and black, and froths up very much.   When the object is only  the
preparation of ether, these reactions may be prevented, and a much lar-
ger product obtained, by  admitting  to the globe,  by means  of  the bent
funnel, a continual  but minute stream of rectified spirit.  The action of
the sulphuric acid is thus exercised  upon successive quantities of spirit,
and the liberation of the ether continues until the  acid becomes so weak
as to be no longer able to decompose the alcohol, which occurs when  the
whole quantity of rectified spirit used is about twice the weight of the oil
of vitriol, which is then reduced to the strength of S.03+4 Aq.
   Although we may represent the results of this reaction by considering
the sulphuric acid to take water directly from the alcohol, and set  the
ether free,  such is by no  means really the case; on the contrary, when
the alcohol acts on the oil of  vitriol, the  water of both is  disengaged,
and the sulphuric acid and ether unite to form Sulphate of Ether, (C4H5
O. + Aq.) and S.03+Aq. giving C4H30. + S.O? and 2 Aq.  This body,
which resembles very much sulphate of ammonia in its tendency to com.
bination, unites with an atom  of oil of vitriol to form Bisulphate of Ether,
or, as it is  generally termed,  Sulphovinic  Acid.   The two atoms of sul-
phuric acid thus engaged  change very much in properties, forming salts
with barytes and  oxide of lead, which are very soluble in water.  The
two equivalents of  water, which, as  above described, are set free, dilute
the remaining sulphuric acid  to such a degree  as  that it cannot decom-
pose more alcohol; hence, if absolute  alcohol be used, 3(C4H50. + Aq.)
with  8(S.03 . H.O.) produce 3(C4H60. . S.03+H.O. .  S.Oa)  and 2(S.
03-p-4 Aq.), one fourth of the sulphuric acid remaining over ; if a weak-
er alcohol be used, the quantity of dilute sulphuric acid formed  becomes
proportionally greater.   An  acid which already contains four atoms of
water, forms no sulphate  of ether when put in contact even with absolute
alcohol, except the temperature be very high.
   The ether obtained by distilling a mixture of alcohol and oil of vitriol
results, therefore, not from the water being seized on by the oil of vitriol,
but from the decomposition of its compound  with sulphuric acid, the sul-
phate of ether; the ether being a base not much superior in energy to
water, is expelled  by it in  turn under  favourable circumstances, especially
when the water is present in excess.   In this respect it  resembles, as
Rose has remarked, the  sesquioxides of iron, antimony, and  bismuth,
which form salts  with sulphuric acid that are totally decomposed by a
large quantity of water, especially if their solutions be boiled ;  the acid
then combines with the water, and the metallic oxide precipitates.  Be-
fore decidino* on this view of the  production of ether, it is necessary to
describe some collateral phenomena.
  If absolute alcohol and strong oil of vitriol  be employed in the prepara-
tion of ether, it is found that the distilled product consists of ether and
water, formino* two distinct  layers  in virtue of their different  specific
gravities, but in quantity identical with those which constitute alcohol;
100 parts of the mixed liquids consisting of  19*5  water and  79*5 ether,
when separated from a quantity of alcohol which had escaped decompo-
sition.  The oil of vitriol remains in  the retort in its original state of
concentration, and hence might be applied to etherify an infinite  quantity 
 544   THEORY  OF THE  FORMATION OF  ETHER.

 of absolute alcohol, introduced in a continuous stream.   To explain this
 very remarkable result, Mitscherlich  advanced that the action of the
 sulphuric acid on the alcohol is merely catalytic; that  it splits it, as it
 were, into ether  and water, and these pieces not being  able to reunite,
 come over in vapour, merely mixed with each other ; this idea is, how-
 ever, quite inadmissible, as the whole  quantity of ether  is proved to be
 united with the sulphuric acid  in the  first place, and to  distil  over only
 after the decomposition of the compound that had been so formed.   The
 observations of Liebig and Rose have removed  the difficulty which this
 simultaneous evolution of water and ether presented to  the adoption of
 the theory which supposes the ether to be expelled from  its combination
 with  the sulphuric acid by the water.    In fact, it is only at a  particular
 temperature  that the ether and water  come over in atomic proportions,
 and this then results from the identity of the boiling points of the solution
 of sulphovinic acid  and of the dilute sulphuric acid.   Thus, when  we
 heat together sulphate of ether, (C4B50 +S.03), and the dilute sulphuric
 acid, S.03+4  Aq.,  the  former is decomposed,  bihydrate  of  sulphuric
 acid, S.034-2 Aq., being formed, and  ether set free ; but at this temper-
 ature the sulphuric  acid begins to abandon its second  atom  of water,
 which then distils over  with  the ether.  If we  conduct the distillation
 very  slowly,  and retain the  temperature  below 212°, the  ether cornea
 over, almost perfectly  free from water; but at a  higher  temperature,
 the ether, when liberated, is immediately converted  into elastic vapour,
 which bubbles through the liquid like a gas, and  the water evaporates in
 the space thus afforded, as it should evaporate in a current of air forced
 to bubble through the liquid in the same way.
   The production of ether depends, therefore, upon the facts, that when
 alcohol and oil of vitriol are  mixed, sulphate of ether is  formed and wa.
 ter is set free ; but on the application of heat, this action  is inverted, and
 the ether is expelled from the acid, with which the water recombines.  If
the distillation be conducted so that the  mixture boils, the  dilute sulphuric
acid  concentrates itself, at the same time, by giving off an atom of water,
which condenses  mixed  with the ether, but had  its origin in a perfectly
independent action.
   If we heat alcohol in contact with glacial phosphoric or arsenic acids,
it is  similarly acted on, and the ether  forms a phosphovinic or arseniovi-
nic acid, which is decomposed by boiling, the ether being set free.  These
acids would be too costly to admit of their employment in the prepara-
 tion  of ether on the great scale, and, besides, they do not act as power-
fully as oil of vitriol.  Although this ether does not contain any sulphuric
acid, it is very generally called Sulphuric Ether, and I shall often use that
name, but the distinction between it and the compound ethers formed by
its union with acids must be carefully  kept in mind.
   The ether formed by the process now described is rendered impure by
admixture with alcohol and water, and sometimes oil of wine and sul-
phurous  acid.  It is freed from these by rectification,  from a water-
bath, over some dry carbonate of potash.  It is then a colourless liquid,
of an agreeable penetrating odour, and a pungent taste.   Its sp. gr. is
0*720 at 60° ; it does not conduct electricity ; at —47° F. it freezes
into  a crystalline mass ; it boils at 96° ; the  sp. gr. of its vapour is
2581*3.   In evaporating it produces great cold,  of which numerous ap.
plications have been noticed under the head of vaporization.  (Sec. IV.,
Chap. III.) 
CONSTITUTION  OF  ETHER.
545
   Ether  is very combustible ;  its vapour, diffused through air or oxygen,
 forms powerfully explosive mixtures.  Exposed to the air, it gradually
 absorbs oxygen, forming acetic acid.  Its fiame is brighter than that of
 alcohol, but it gives no smoke; it dissolves sulphur and pho.spliorus in
 small quantity ;  iodine and bromine are  abundantly dissolved, but they
 soon act  on the ether ; most bodies  that  are soluble in alcohol are dis-
 solved by ether,  except salts, of which only very few, as the perchlorides
 of gold, of platina, and of iron, are taken up by it.   Ether combines with
 almost all acids, forming well-defined neutral salts, the compound ethers,
 which have a remarkable similarity to the ammoniacal salts.  It is. there-
 fore, an organic base ; its composition is expressed in the formula C4H50
 giving the numbers by weight:

            4 equivalents of carbon  .   .  .  24*20   .  .  .  65 31
            5     "     "   hydrogen   .  .   5 00   .  .  .  13*33
            I     "     "   oxygen  .   .  .   8 00   .  .  .  21*36
                                        37*20         100 00
 uid by volume,
               4 volumes of  carbon vapour,    (843x4)=3372 0
              10    "      hydrogen  "   (68*8x10)= 688 0
               1     "    • oxygen   " .  .  .  .  =1102 6
              Produce two volumes  of vapour of ether  .  5162*6
              Of which one weighs, therefore   ....  2581 3

   In chemistry and pharmacy ether is of importance as a vehicle for the
 solution of  many resinous and  other bodies, and from its action on the
 animal economy.  By the  action of reagents it yields a great number
 of derived compounds, of which the  most  important  will be described in
 their proper place.
   The question of the intimate constitution of ether has been very much
 discussed, and opinions have followed precisely the same  course, with
 regard to  the theory of its  compounds, as for that of the combinations
 of ammonia;  thus it has been  looked upon as an oxide  of a compound
 (metallic ?) radical, Ethereum or Ethyle, as  the salts of ammonia were sup-
 posed to contain a compound metal, Ammonium.   The formula of ethyle
 should be  C4H5, and its symbol Ae.    On the other hand, it may be con-
 sidered to consist of defiant gas, C4H4, united  to water,  and the latter
 then takes the  place of the  ammoniacal gas in  the theory of ammonia.
 I shall frequently employ for ether the symbol Ae.O., and speak of it and
 other bodies as compounds of ethyle,  as oxide, chloride, &c, but without
 any other  present object than convenience of language, for it would be
 impossible to discuss the comparative merits of these theories,  without
 knowing the properties of the compound ethers, of  olefiant  gas, of al-
 dehyd, acetic acid, and many other boc-ies, which are involved in the re-
 actions by which  wc may endeavour to test their value, and hence I shall
 postpone all  details of the principles of the ether-theories until the end of
 the present chapter.
               Compounds of Ether with Sulphuric Acid.
  Sulphovinic  Acid.  Bisulphate of Ether, C4HsO.. S.03+H.O.. S.O„ is produced by
mixino- alcohol with oil of vitriol, as described for the preparation of ether, or by
passing vapour of ether into oil of vitriol as long as it is absorbed.  By heat this
Bohuion is decomposed.  The sulphovinic acid cannot be obtained in a solid form*
if ft solution of sulphovinate of lead be decomposed by sulphuret of hydrogen, a col-
                                 Z z z 
546         SULPHOVINATE  OF  POTASH,   ETC.

ourless and very acid liquor is obtained, which, when concentrated, evolves ether,
blackens, and is totally decomposed.  Its salts are all soluble, and  generally deli-
quescent;  when boiled with muriatic acid, alcohol is evolved, and  sulphuric acid
set free.   By a  high temperature  they arc  decomposed, oil of wine, ether, oletiant
gas, and  sulphurous acid being given off, while a metallic sulphate or sulphuret re-
mains behind, mixed  with some charcoal.   By distilling a sulphovinate with a pot-
ash salt of any  volatile acid, a compound  of ether with that acid distils over, and
sulphate  of potash  remains.   By  fusing a sulphovinate with a caustic alkali, water
and oienant gas are expelled, and all the sulphuric acid remains combined with the
alkali.
   Sulphovinate of Potash, Ae.O.. S.03-}-K.O.. S.Oj, crystallizes in colourless rhom-
boidal plates, which are anhydrous ;  it is very soluble in water, but sparingly solu-
ble in alcohol.  Sulphovinate of Barytes, Ae.O. . S.03-j-Ba.O.. S.On-"-2 Aq , crystal-
lizes in oblique rhomboidal prisms unalterable in  the  air ; it tastes strongly acid ;
in vacuo it abandons its water, and is then  not altered by a heat of 212°, but if the
hydrated salt be heated to 212°,  alcohol is given off, and sulphuric acid set free.
Sulphovinate of Lime crystallizes in thin hexagonal plates, which are very deliques-
cent ;  it  is soluble in  less than its own weight of cold  water.   Sulphovinate of Lead
forms large rhombic crystals,  deliquescent; very soluble in water and in alcohol ■
it  is  gradually  decomposed at ordinary  temperatures.   Sulphovinate of Copper,
Ae.O. . S.Oj-f-Cu.O.. S.03-}-4 Aq., forms large  blue  octagonal  plates, permanent
in the air,  and very soluble in alcohol and water ; heated to  212° it is totally de-
composed.
   Ethionic and  Isethionic Acids.—These substances are farmed by acting on alco-
hol or ether with the vapours  of anhydrous sulphuric acid ; the liquor, neutralized
by barytes, gives the insoluble  sulphate and the soluble ethionate of barytes, which
last separates from the concentrated liquor as a crystalline precipitate on the addi-
tion of alcohol.  A solution of this salt, when decomposed by sulphuric acid, gives
free Ethionic Acid, which, by boiling, is decomposed into sulphovinic acid and isethi-
onic acid,  of  which,  indeed, Liebig  considers it  to be, in reality, only a  mixture.
The isethionic acid is formed  more characteristically  by the direct union  of anhy-
drous sulphuric  acid and olefiant  gas, and will be described as a compound of that
body.
   Allhionic and  Methionic Acids.—When the mixture of  alcohol and oil  of vitriol,
for making ether, has been distilled so far as that it has become black and begun to
froth,  it  produces,  when neutralized with bases, a series of salts, which, though
having the same per cent, composition as the sulphovinates, differ very much from
them in properties ; thus the Althionate of Lime does not crystallize ,* the Althionate
of Barytes crystallizes in fine  needles, in place of the large plates of the sulphovi-
nate ;  the  Althionate  of Copper is  still more distinct,  as its crystals are thin, acute
rhombs,  of a pale green dolour.
   If the ether, into which the  vapours  of sulphuric acid are passed, be allowed to
grow hot, it becomes black, sulphurous acid is evolved, and an acid is formed dif-
ferent from any of the preceding ; it is called the Methionic Acid, and is character-
ized by its barytes  salt being  totally insoluble in alcohol,  and  but sparingly soluble
in water.  When its  salts are fused with caustic potash, merely sulphite  of potash
remains ; the formula of the acid  contained in the barytes salt is C2H3 . S207.   It
evidently does not contain any simple combination of alcohol  or ether.
   Heavy Oil of Wine.   Sulphate of Ether and Ethcrol.—C8H90.+2S.03, or Ae.O..
S.03-j-C4H4 ■ S.03.   When one  part of rectified spirit is distilled with two and a
half parts of oil  of vitriol, a little ether passes over, followed by an oily yellow liquid
and water, with much sulphurous acia.  The oil is to be washed with a little water,
and then dried in vacuo under a bell-glass, beside two cups, one of oil of vitriol and
the other of caustic potash ; the first absorbs the water and ether, and the last the
sulphurous acid. This substance is then a thin oil, sometimes green and sometimes
yellow ;  its odour aromatic and pungent;  its specific gravity 1*133; when heaced
it begins to boil, but is rapidly decomposed, blackening  and evolving sulphurous
aeid, and but little  distilling over.  It is scarcely soluble in water, but abundantly
so in  alcohol and  ether.  When  boiled  with water,  or with  an  alkaline solution,
sulphovinic acid is  formed, and Etherol (light oil of wine) set free, which floats upon
the surface.
   The composition of this body is not absolutely constant.   I consider it to be a
mixture, in variable proportions, of true Sulphate of Ether, Ae O.. S.03, with Sulphate
of Etherol, C4H4 . S.03.  I have found that when distilled with oxalate or acetate 
                    COMPOUNDS  OF  ETHER.               ,547

 ot potash, with chloride or sulphuret of potassium, oxalic and acetic ethers, muriat-
 ic ether, &r,., are generated, and, at the same time, etherol remains indifferent to
 these re-agents.
   Another process for obtaining this heavy oil of wine consists in mixing dry sul-
 phovinate of lime with its own weight of quicklime, and distilling at a heat not  ex-
 ceeding 520°.  The oil which comes over mixed  with alcohol is to  be purified aa
 already noticed.
   Etherol and Etherine.—C4H4.  The  oil which  is separated from  the foregoing
 substance by  hot water or by alkalies, divides itself generally, after some time, into
 a liquid and a solid portion ; the first constitutes the light oil of wine, Etherol. ' It is
 pale yellow, and thick, like olive oil;  its odour is  aromatic ; its specific gravity
 =0 921; it boils  at 500° ;  at —35° it freezes.  The Etherine forms hard, brittle, col-
 ourless prisms ;  it is tasteless ;  its specific gravity 0-980 ; it melts  at 230°, and
 boils  at 464° ; it is soluble in alcohol and ether.  The composition  of both these
 bodies is the same, consisting  of equal numbers  of atoms of carbon and hydrogen,
 but their atomic weights are not known.  It is very  probable that the etherol is re-
 allya mixture of two other bodies; for when a saturated solution  of chloride of zinc
 in alcohol is distilled, an oily liquor is obtained, which, by rectification, may be sep-
 arated into two fluids, of which one, boiling at 212°, has the formula  CSH7, and the
 other, which boils only at  570°, has the formula C8H9.   A mixture of equal  quanti-
 ties of the two should have the composition assigned to etherol.
   Liebig and Regnault have found the etherol  obtained by alcohol  and sulphuric
 acid to have the formula C4H3, so that it must be looked upon as an irregular mix-
 ture of several oils, which have not yet been obtained pure.  The etherol, or Ethe-
 real Oil, is employed to prepare Hoffman's Anodyne Liquor, being dissolved in a mix-
 ture of one part of ether and two of spirit of wine.

      Compounds of Ether  with the Phosphoric and Arsenic Acids.

   Phospkovinic Acid. — Ae.O. . P.Os-f 2H.O.  When concentrated tribasic phos-
 phoric acid is dissolved in alcohol, great heat is evolved, and one atom of water re-
 placed by an atom of ether.   The acid salt thus formed may be obtained crystal-
 lized,  but when its solution is heated strongly  it  is decomposed.   It combines with
 two atoms of base to  form the  Plwsphovinates, of which few are as yet well known.
 The barytes salt, P.05+Ae.O. . 2Ba.O.-|-12 Aq., crystallizes in brilliant colourless
 plates, and is remarkable  for being equally soluble in water at 32°  and 212°,  but
 three times more soluble in water at 104°.
   Arseniovinic Acid, As.05-}-Ae.O.-j-2H.O., is formed with arsenic acid and alcohol,
 like the body last described. Its salts have been but very slightly examined.

           Compounds of Ether with the other Mineral Acids.
   Muriatic Ether.   Chloride of Ethyle,  C4H5C1., is prepared by distilling
 a mixture of three  parts of oil of vitriol, four of fused common salt, and
 two of absolute alcohol.  The retort should  be connected with two two-
 necked bottles,  of which the first should be immersed in a  vessel of water
 at 60°, and  the second  be surrounded  by  ice,  or  a freezing mixture.
 Some alcohol and common ether, which pass over, are condensed in the
 first bottle, while the muriatic ether is reduced to the  liquid state  oniy
 in the second.  By digestion with some chloride of calcium it is rendered
 quite  pure.
   It is a colourless liquid, of a pungent garlic odour ; its specific gravity
 =0*874 ; it boils  at 5*2° ; is neutral ;  sparingly soluble  in water ■   it
 burns with a bright flame, green at the edges, and gives off muriatic acid
 gas.  By passion*  through  a  red-hot  tube,  it  affords equal volumes  of
 defiant and  murtatic acfd gases, or by heating with potash, it gives ole-
 fiant <>-as and chloride of potassium.   Heated with alkaline salts, it yields
 compound ethers and alkaline chlorides.   When muriatic ether is heated
 with potassium, Lbwig states that chloride of potassium is formed and a
 !i<»ht oily substance separates, which has  the  formula C4H3.   It should be
Ethyle, but so important an observation has  need of verification.   This 
548           HYDROBROMIC  ETHER,  ETC.
body is often called  light Muriatic Ether, to distinguish it  from heavy
Muriatic Ether, which results from the action of chlorine on weak alco.
hoi.
  Hydrobromic Ether.   Bromide of Ethyle, C4H5Br., is obtained by dis-
tilling together two parts of bromine, one of phosphorus, and six of alco-
hoi.   There is first formed bromide of phosphorus, which instantly de-
composes the water of the alcohol, and the nascent hydrobromic acid
acting on the ether forms the hydrobromic ether.  In properties it per-
fectly resembles the following body :
  Hydriodic  Ether.  Iodide of Ethyle, C4H5I.,  is formed  by distilling
iodine, alcohol, and phosphorus.   It is a colourless liquid, of a pungent
ethereal smell; its specific gravity =1*92 ;  it boils at 161° ; it is abun-
dantly soluble in alcohol.  Heated with potash, it gives pure olefiant gas
and iodide of potassium.   The theory of its formation is the same as in
the former case.
  Hydrosulphuric Ether.   Sulphuret of Ethyle, C4H5S., may be formed
by acting on  muriatic ether with an alcoholic solution of sulphuret of
potassium.  It boils at 187° j it combines with sulphuret of hydrogen to
form  the following very remarkable substance :
   Sulphur-alcohol, or Mercaptan, C4H6S2, or Ae.S. + H.S., which is obtain.
ed directly by distilling in a water-bath concentrated solutions of sulpho-
vinate of lime and of potash saturated with sulphuret of hydrogen, K.S.-f-
H.S. and Ae.O. . S 03+K.O. . S.03 producing 2K.O.. S.Os and Ae.S.
-f-H.S.;  the  mercaptan distils over, and  sulphate of potash remains in
the retort; it is a colourless, thin liquid, of an  insupportable smell of
onions; it boils at 96° ; its specific gravity is 0*84 ; it dissolves in ah
cohol; is perfectly neutral ;  burns with a bright blue flame ;  and by cold,
freezes into a crystalline mass.  In constitution, it is perfectly analogous
to alcohol, the oxygen being replaced  by sulphur.  When placed in con.
tact with metallic oxides, water is formed, and a double sulphuret of ethyle
and the metal produced.  This occurs remarkably with oxide of mercury,
whence the barbarous name given to this body by Zeize, from Mercurium
 Captans, and  to its  compounds of Mercaplides.   That of mercury is a
crystalline solid, fusible at 110°, and soluble in alcohol.
   The properties of this body induced its discoverer, Zeize, to look upon
 it as a compound of hydrogen with a compound radical, which he called
 Mercaptum, which should be really the following compound.  Its formula
 then became  C4H5S2-|-H.   He extended this view also to common alco-
 hoi,  which he considers as C4H502-f-H. ; but his theory  has  met with
 very few supporters.
    Thialol.  Bisulphuret of Ethyle, Ae.S2, is formed by distilling a mix.
 ture of sulphovinate of lime and persulphuret of potassium.  It is a lim-
 pid, oily fluid, with a strong garlic smell;  it boils at 124°.   Its solution
 in alcohol precipitates the salts of lead and mercury.   By the action of
 nitric acid on these sulphurets of ethyle, acids are produced analogous to
 the sulphovinic, but which are not, as yet, accurately known.
    The Seleniuret and Telluret of Ethyle have been formed, but do not re-
 quire description.
    Nitrous Ether.   Hyponitrite of Ethyle.—Ae.O. . N.03.  When alco-
 hol and nitric acid are directly mixed, the action is very violent;  heat
 is evolved, red fumes are copiously given off, and acetic, oxalic, and car-
 bonic acids  formed.  Even when the acid is  dilute, its  action is very 
NITROUS  ETHER,  ETC.
549
complex ;  giving up two atoms of oxygen to one portion of Ihe alcohol,
it produces aldeliyd, and acetic and oxalic acids, and it is only the hypo-
nitrous acid thus produced that acts on the remaining alcohol, and, com-
bining with the ether of it, forms  the  proper nitrous ether.   To avoid
these oxidized products, the best plan is to generate red fumes of hypo-
nitrous acid, by acting on starch by nitric acid in a  retort, and to conduct
these fumes by a bent tube to  the  bottom of a two-necked bottle contain-
ing alcohol.   They are copiously  absorbed, and  combine directly with
the ether.   From the second neck of  the  bottle a  tube  should pass to a
condensing apparatus and receiver ; enough of heat is evolved by the ab-
sorption of the red  fumes to distil over the nitrous ether formed, which
may be thus obtained quite pure.
   Another process, which  may now be considered  as obsolete, consisted
in distilling a mixture of oil  of vitriol,  nitrate of potash, and rectified
spirit, by the heat of a water-bath, into a receiver cooled by snow.  The
nitric  -cid acted very violently on the alcohol, and the product was im-
pure, and small in quantity.
   Nitrous ether is a liquid, colourless or pale yellow, of a pungent odour
of apples ; it usually reacts acid from slight decomposition,  but is  neutral
if quite pure ;  its specific gravity is 0*947 ;  it  boils at 61° Fah.   Exposed
to the air, it absorbs oxygen rapidly, and forms aldehyd, acetic and formic
acids; at the same  time, nitric oxide is given off.   By contact with any
strong base, it is decomposed, alcohol  being  set free, and  a hyponitrite
formed.   A solution of this nitrous ether in  spirit (spiritus nitri dulcis)
is employed in pharmacy.   It is prepared  by distilling a mixture of one
part of nitric  acid and  ten  of rectified spirit,  collecting the first seven
parts which come over, and digesting them on  a little dry  carbonate of
potash, to remove any traces of free acid.  Its specific gravity should be
0*850.   It may be prepared directly by dissolving one part of real nitrous
ether in  eight parts  of spirits of wine.

                    Cyanogen Compounds of Ether.
   Hydrocyanic Ether.   Cyanide of Ethyle, Ae.Cy., is prepared by distil-
ling a mixture of sulphovinate of potash and cyanide of potassium at a
moderate heat.   It  is a colourless  liquid,  of a  strong  garlic odour ;  it
boils at 179°, and is lighter  than waler ; it is very poisonous.
  Cyanuric Ether, 3Ae.0.+*2Cy303+6 Aq., is formed when the vapours of hydrated
cyanic acid are passed into ether, as long as they are  absorbed.  After some time,
the new compound separates in crystals, which are colourless prisms, destitute of
taste and smell, soluble in water, and but sparingly soluble in ether.
  Hudrosulphocyanic Ether appears to be formed by distilling sulphocyanide of potas-
sium with sulphovinate of potash.   It is a liquid heavier than water.
            Compounds of Ether  with the Acids of Carbon.
  Carbonic Ellicr.  Carbonate of Ethyle.—Ae.O.. C.O2.   This ether can onfy he pro-
duced  by an indirect process, the theory of which is  not well  understood.   Metallic
potassium or sodium is added, in  small pieces, to oxalic ether, as long as a disen-
gagement of carbonic oxide gas occurs ; a thick brown mass is formed, which is to
De distilled, the excess of metal being first destroyed by the addition of water; the
carbonic acid distils over.  It  is a colourless liquid, of an aromatic smell, lighter
than water.   It boils at *2G0°; it is insoluble in water,  but dissolves in alcohol; its
alcoholic solution is decomposed by potash,  alcohol and carbonate of potash being

  Carbonate of Ether and Water.   Carbovinu Acid.—Ae.O.. C.O2+H.O.. C02.  At
one time it was considered that anhydrous sugar was actually bicarbonate of ether,
C6H50-=C4H50 +'20.02, and  that the alcoholic fermentation consisted in the sep. 
550                 OXALIC  ETHER,  ETC.
aration of these bodies, the nascent ether combining with water to form alcohol;
but that idea is now inadmissible.  The true carbovinic acid is prepared by dissolv-
ing caustic potash in absolute alcohol, and passing dry carbonic acid gas through
the liquor as long as it is absorbed.  A crystalline mass is formed of carbonate and
Carbovinate of Potash, which last is dissolved out by cold alcohol; and this solution,
being mixed with ether, deposites the salt, whose formula is Ae.O.. C.O2 + K.O.. C.
Oi, in pearly plates, which are immediately decomposed by water into  alcohol and
bicarbonate'of potash.  The carbovinic acid is not known in an isolated form.
  Oxalic Ether.   Oxidate of E/hyle, Ae.O..C Ah, is prepared by distilling one part
of alcohol with one of binoxalate of potash and two of oil of vitrio'..  At first alcohol
and common ether come over, but then a heavy fluid, which sinks to the bottom of
the receiver.   The portions last distilled are  richest  jn product.   It is  rectified by
another distillation from off a little litharge.   It' is a colourless oily liquid, denser
than water, of a heavy but aromatic smell; it boils at 370°.  In contact with water
or bases, it is gradually decomposed into alcohol and oxalic acid.  The sp.gr. of its
vapour is 5077.
  Oxalovinic Acid.—Ae.O.. C2O3+H.O.. C2O3.   This acid  is not known except in
combination.  It is produced  by adding to a solution  of oxalic ether in alcohol half
as much  potash as would suffice to decompose it.  The Oxalovinatc of Potash sep-
arates  as a crystalline powder, being insoluble in alcohol.  By an excess of base it
is decomposed into alcohol and an oxalate.  Its other salts do not require special
notice.
  Oxamellian.—Ae.O.. C2O3+C2O2ACI.  When oxalic ether is acted  on by  water
of ammonia, it is totally decomposed, alcohol  and oxamide being formed, as already
noticed.  If a  solution of ammonia in alcohol  be  used, but one half of the oxahc
ether is decomposed, and the  oxamide produced unites with the other half, forming
a substance  soluble in alcohol and water, and crystallizing in  brilliant  prisms and
plates.  It melts at 212°, and  sublimes unchanged at 430-'.  Its solution in cold wa-
ter does not precipitate lime-water, but if it be boiled  alcohol is expelled, and the
solution contains binoxalate of ammonia.  By water of ammonia it is totally  chan-
ged into oxamide.
  Chloroxytarbonic Ether.—Ae.O.. C.O2+C.O.CI.  This substance is formed by the
action of chlorocarbonic  acid gas on absolute alcohol.  It is a colourless liquid,
perfectly neutral, heavier  than water, and boiling at 201°; sparingly soluble in wa-
ter.  It consists, or, at least, contains the elements,  of an atom of carbonic ether and
an atom of phosgene gas.  When  put in contact with water of ammonia, it is dis-
solved violently, and heat evolved, sal ammoniac and a peculiar substance termed
Ure.than being  formed.  The liquor is to be dried down, and the residue distilled in a
dry retort with an oil-bath.  The urethan passes over, and solidifies in the receiver
to a crystalline mass resembling spermaceti.  In it the chlorine of the preceding
substance is replaced by amidogene, its formula  being Ae.O.. C.02+C.O.Ad.; it
consists thus of carbonic ether and  carbamide in the proportion of one atom of each.
  Sulphocarbohic Ether.   Hydroxanthic Acid, Ae.O. .C.S2+H.O. .C.S2, is prepared
by decomposing the xanthate of potash by dilute sulphuric acid.  A milky liquor is
obtained, from which, after some time, a heavy oil separates; it is to  be lapidly
washed with water, and dried by chloride of calcium.   It is then pale yellow, slight-
ly acid, inflammable, and burns with a blue sulphurous flame; it is decomposed by
warm  water into alcohol and sulphuret of carbon; it decomposes the alkaline car-
bonates,  expelling the carbonic acid.  Of its  salts, that of potash is obtained direct-
ly, and from it the others.  Xanthate of Potash, Ae.O.. C.S2+K.O.. C.S2, is formed
by adding sulphuret of carbon to a warm solution of caustic potash in alcohol. On
cooling the liquor, it deposites the salts in crystals, which are to be collected on a fil-
ter, washed  with ether, and dried  between folds of  bibulous paper.  The salts of
lead, copper, &c, may be prepared by double decomposition; they are. all yellow,
whence me  ordinary name of the acid.
  Mucate of Ether is sqlid and crystalline.  It is formed by dissolving mucic acid in
cil of vitriol, and gradually adding an equal weight of alcohol.  The liquor  vields,
after some time, the mucic ether in crystals, which  are to be dried on a porous'stone,
and recrystaliized from alcohol.
   The remaining compounds of ether with acids will be described along with the
other salts of those acids.

                    Of Olefiant  Gas and  its Compounds.

   This gas has been frequently mentioned as one of the  products of the ac-
tion of sulphuric acid on alcohol  The  usual process to obtain it consists 
PREPARATION  OF  OLEFIANT  GAS.       551
in heating one part of alcohol with six of oil of vitriol in a flask, b, froi..
which a tube passes to the water pneumatic trough, as in the figure ; the
mass  becomes dark ;
ether, water,  and  oil
of wine collect in the
interposed  globe,  a,
and olefiant gas is co-
piously evolved,  mix-
ed with an equal vol-
ume  of  sulphurous
acid, which, however,
being absorbed by  the
water, the  other gas
remains  pure.  To-
wards the end of  the
process the materials
in the flask swell up very much, and  might boil over if not carefully at-
tended to.  The theory of this action  appears, at first sight, very simple;
the alcohol losing  an atom of water, is first converted into ether, which,
by the influence of the excess of sulphuric acid, is deprived of the ele-
ments of another equivalent  of water, and olefiant gas remains, C4H50.
giving C4H4 and H.O. ;  but we cannot by this process generate the ole-
fiant  gas, without,  at the same time, more complex products appearing,
as etherol, sulphurous acid, and the black matter which remains in the
retort.   This  last, which had been considered formerly as charcoal, ap-
pears to consist of C27H804+S.03 ;  it  combines with bases, and is termed
the Thiomelanic Acid  • it evidently results from the sulphuric acid, giving
up oxygen to the hydrogen of a portion of the alcohol.
   Olefiant gas is  generated  on the large scale by the decomposition of
coal, pitch, 1)il, &c, at a red heat, and is employed for the purpose of il-
lumination, being the most valuable constituent of the gas  which is burn-
ed in our streets and shops.   To this source of it 1 shall have occasion
to return.                                              .        .   .
   We may obtain this gas, however, by much more definite and simple
processes.   Thus, if vapour  of muriatic ether be passed through a red-
hot porcelain tube, it is resolved into  equal volumes of olefiant and muri-
atic acid gases; also, if  muriatic ether be heated with ammoniacal gas,
sal ammoniac is formed, and olefiant  gas evolved ; the same decomposu
tion ia caused bv caustic potash.   If vapour of alcohol be  passed into oil
of vitriol so far diluted as to  boil at 320°, and heated to that degree, it is
totally resolved  into water  and  olefiant gas.   In a  theoretical point of
view, these sources of olefiant gas  are peculiarly of interest.
   Olefiant gas, when  pure, is colourless ; its odour is very slightly ethe-
real*  it is sparincrly absorbed by water; it burns with a brilliant white
flame, producing much smoke.   When  mixed with twice its volume of
chlorine, and  set on fire in  a tall  narrow jar, a brilliant flame descends
rapidly, muriatic acid  being formed  and charcoal, smelling strongly of
napthaline, separating in dense floccuh.   Its spec.fic grav.ty is,980 8 as
one  volume of it contains a volume of carbon  vapour and two volumes
hydrogen (843*0 + 137 6 = 980*6).   It consurts  of an equal number of
equivalents of hydrogen and carbon, but chemists are not unanimous as
2 iU real atomic  weight.   Berzelius, who  looks upon it as an organic 
552           COMPOUNDS OF  ETHERENE.
 radical, and the basis of a series  of compounds with  oxygen^ chlorine,
 &c, has proposed for it the name Elayl, and the formula C2H2.  The name
 Olefiant Gas being very inconvenient, I shall, in  speaking of its com-
 pounds, term it, for the present, Ethercne.   The principal support of the
 theory, which considers this gas to be the radical of the ethers and of al-
 cohol,  is derived from the great simplicity of their constitution by volume,
 in the  state of vapour, on that view.   Thus, two volumes of olefiant gas
 combine with two of vapour of water to form alcohol; with one of vapour
 of water to form ether ;  with two  of muriatic or hydriodic acid gases to
 form the hydriodic  or muriatic ethers, and so in similar  simple propor.
 tions of volume in other cases.   But this evidence is very insecure, as
 we might show nearly as simple gaseous relations  upon  other and very
 improbable points of view.   Its combinations are generally formed indi-
 rectly,  as from alcohol or ether, but it combines immediately with iodine,
 chlorine, and sulphuric acid.
   Anhydrous sulphuric acid absorbs etherene in  large  quantity, form-
 ing white crystals, which, when dissolved in water, constitute Isethionic
 Acid, identical  in every respect with that formed as described  p. 546.
 When  dry, its  composition is S206+C4H4; but when in  contact with
 water,  it  combines with two  atoms thereof, and becomes isomeric with
 sulphovinic acid.   That  it differs  from  it essentialily  in constitution is
 shown  by its salts giving a mixture of sulphate and sulphite when fused
 with potash ; the sulphurous element is  therefore as hyposulphuric, and
 not sulphuric acid, and its rational  formula is  S205-|-C4H40.   This ise-
 thionic  acid is much more energetic than the sulphovinic ; it decomposes
 all salts of organic acids ; its own salts are all  soluble and crystallizable,
 and sustain a heat of 450° without  decomposition.
   If a jar of olefiant gas, c, be inverted  in the pneumatic trough, over a
 capsule, b, as in the figure, and bubbles of chlorine be  passed up into it,
                    both gases disappear, and a heavy oily liquid collects
                    in the capsule, the formation of which  gave to the gas
                    its common name of  Olefiant Gas.  In this process
                    a quantity of gas is totally  decomposed,  and muriatic
                    acid is evolved in great quantity, but the oil  results
                    from the direct union of the chlorine and etherene,
                    its  formula being C4H4C12.  I will name it  Chlor-
                    etherene, but it is called the  Oil of the Dutch Chemists,
                    as it was  first formed by the members of a scientific
                    association in Holland.  When quite pure it is col-
ourless, of a sweet ethereal odour.  Its specific gravity =1*25 ;  it boils
at  180°  ;  it burns with a greenish  flame, giving  off muriatic acid; the
specific  gravity of its vapour is 3421.   Exposed to an excess of chlorine,
it  is decomposed, hydrogen being removed, and replaced by chlorine ; a
volatile  oily liquid, C4H2C14, and ultimately sesquichloride of Carbon, C4
Cl6, are  produced.
   The chlor-etherene is not decomposed by a watery solution of potash ;
but if it be dissolved in an alcoholic solution of that alkali, and gently
warmed, chloride of potassium is formed, and a peculiar body produced,
whose composition is expressed by the formula  C4H3C1.   This substance
is  gaseous;  of a garlic odour,  burning with difficulty with a smoky red
flame ; its specific gravity is 2166.  It is evident that the chlor-etherene
may be  considered as a  compound of this gas  with muriatic acid, C4H,
 
PREPARATION  OF  ALDEHYD.
553
CI.-h H.Cl., in which case the action of the potash  is easily explained.
This gas itself is supposed to be a chloride of the same carbohydrogen
as is the basis of acetic acid and aldehyd, (C4H3), or Acetyl; and the ole-
fiant gas, on this view, is Hydruret of Acetyl, C4H3+H., or Ac.H.   The
farther discussion of this opinion will be reserved for another place.   If
the  gas, C4H3CI., be  passed over perchloride  of  antimony, it combines
with more chlorine and forms a  liquid, which boils at 240°, and consists
of C4H3CI3; by an alcoholic solution of potash this  is decomposed into
muriatic acid, and another body, also liquid, but boiling at 86°, and hav-
ing  the  formula C4H2CIZ.   By contact with chlorine, this  produces the
liquid C4H2CI4, noticed in  the preceding paragraph, as  obtained directly
from chlor-etherene, and, as the next stage, the sesquichloride of carbon.
  If a mixture of olefiant gas and vapour of ether be acted  on by chlorine, an oily
liquid is obtained, which boils at 350°, and consists of 04H4. Cl.O.; it is called Chlor-
ethcral, but is properly a compound of aldehyd and the chlor-etherene, C4H4Cl2-{-
C4H402.
  Bromine combines with olefiant gas, with the same phenomena as chlorine, and
gives rise to a similar series of compounds, which it is consequently unnecessary
to detail.
  Iodine absorbs olefiant gas abundantly, and forms a white crystalline substance,
which melts at 180°, and may be sublimed if air be not present.  It is  soluble in
alcohol, insoluble in water; its formula is OjHib, but the products of its decompo-
sition are not similar to those of the chlorine compound.
  When bichloride of platinum is dissolved in alcohol, a very complex reaction oc-
curs, and a substance is produced consisting of Pt.Cl.-j-C2H2. This body combines
with the chlorides of the alkaline metals to form double salts. On Berzelius's view,
the C2H2 being a compound radical (Elayl), may  be supposed simply to replace the
second atom of chlorine, and  thus form an Elayl-chloride of platinum, which has
the same power of forming double salts as the ordinary bichloride.  They are thus
(Pt.-fEl.Cl.H-K.Cl. and (Pt.-{-E].01.)+Na.Cl., &c.

   Of the Products of the.  Oxidation of Alcohol, Aldehyd, Hypoacelous
                      Acid.—Eq. 555*6 or 44*2.
   It  has been mentioned,  in speaking of nitrous  ether, that by the ox-
idation of alcohol we  obtain a crowd of products, as aldehyd and acetic
acid, formic, malic,  and oxalic acids ; these last are secondary products
of the too violent reaction, and the result of the true oxidation of alco-
hoi is found to be aldehyd or acetic acid, according to the point at which
the process stops.   The formation of acetic acid  thus  directly from al-
cohol constitutes the acetic fermentation.
  Although aldehyd is formed when nitric acid  acts on alcohol, yet, from
the other products being difficult to  separate, it  is not so prepared ;  a
large quantity of it is generated in the destructive distillation  of wood,
and it may be obtained in the rectification of the pyroxylic spirit.   The
most  ordinary process is that given by Liebig ; six parts of oil of vitriol
with four of water, four of spirit of wine, and six of black oxide of man-
ganese, are to be distilled with a very gentle heat, and the product col-
lected in  a receiver surrounded with melting ice.   The apparatus de.
scribed for preparing  ether (p. 542) should be employed.   The process
is completed as soon as the materials in the retort cease to froth up.  I
have found a purer product to be obtained  by distilling, at a very gentle
heat, two parts of spirit  of wine with three of bichromate of potash,  three
of oil of vitriol, and six of water ;  the last two being previously mixed
and allowed to cool.  To obtain the aldehyd absolutely pure, it is  to be
combined with ammonia, and  the crystallized aldehyd-ammonia decom.
                                  4 A 
554      PROPERTIES  OF  ALDEHY D.---A C E T A L.

posed by dilute sulphuric acid, distilled in a water-bath at 120° with the
greatest care, and rectified over fused chloride of calcium.
   Aldehyd is a colourless liquid, of an agreeable but suffocating odour;
it  boils at 71° ; it is lighter than water;  it mixes with water, alcohol,
and ether; it is neutral and inflammable, burning with a blue flame ;  in
contact with oxidizing agents, it  is  changed  into acetic  acid, passing
through an intermediate state of Aldehydic Acid.  On this fact is found-
ed its most characteristic property ;  if any liquor containing aldehyd  be
added to a solution of the ammoniacal nitrate of silver, and gently heat-
ed, the silver is deposited as a brilliant metallic film, lining the sides of
the vessel like a mirror, and in the liquor is found aldehydate of silver ;
if to  this potash be added, oxide of silver precipitates, and on boiling for
a moment, it is reduced to  the state of metallic silver, and  acetate  of
potash is formed.  From the composition of aldehyd, these changes are
at  once explained.   It is formed by the abstraction of two atoms of hy.
drogen  from alcohol, which are carried away, as water, by the oxygen
supplied ; its formula is hence C4H402: now, in contact with Ag.O., it
forms, first, aldehydic acid, C4H403, and metallic silver, and then C4H403
with Ag.O. gives hydrated acetic acid, C4H404, and another quantity of
silver.  The formation of acetic acid  from alcohol consists, therefore, in
two stages ;  first, the abstraction of hydrogen, by which aldehyd is form-
ed, and, second, the addition of oxygen, by which acetic acid is produced.
   When aldehyd is heated in a solution of potash, this becomes brown,
and  by  an acid a solid  brown substance separates, which is fusible, and
possesses  many properties  of a resin.  This also  is  a very distinctive
character of aldehyd.
   When long kept,  aldehyd undergoes  an isomeric  change into  two
bodies, one liquid, Elaldehyd, the other solid, Metaldehyd; they have the
same formula as aldehyd, C4H402, but differ in  all their properties.
   The general characters of aldehyd  show that it contains the same rad-
ical  as  acetic acid,  Acetyl, C4H3 or Ac, combined with oxygen;  it is,
therefore, Hydrated Oxide of Acetyl, Ac.O. + Aq.=C4H402; it has been
called, also, Hypoacetous Acid, for it  is capable of perfectly neutralizing
ammonia.  Its compound  with ammonia  is, indeed, very remarkable ;
it  is  best  prepared by dissolving aldehyd in ether, and passing ammo-
niacal  gas  into  the  liquor  ;  the aldehyd-ammonia, being very sparingly
soluble in ether, crystallizes as it forms in large hexagonal plates, which
are very brilliant and colourless.   Their solution in water soon decom.
poses, becoming brown, and exhaling  an animal smell.  The dry crystals
        cz-a        may be  fused and  sublimed without alteration ; their
       rMt       formula is C4H30. + H.O. . N.H3.
     ^  "-^       Aldehyd is formed also by the direct action of the
   /        \.   air on alcohol; this may be facilitated very much by
   /            \  means of spongy platina, which contains much oxy-
        a          gen condensed in its pores, but the process is of more
                  interest in consequence of another body which then
                  forms, and which cannot be otherwise generated ;  it
                  is Acetal.   To prepare it, a large bell-glass  is ta-
                  ken, open above,  and standing in a basin, so sup-
                  ported as to allow the air inside  to be frequently re-
                  newed,  as in the  figure ;  through the top passes the
                  tube of a small funnel, a, under which is a  watch-
 
FORMATION  OF  ACETIC  ACID.          55q
glass, 6, with a layer of platina black (p.  407).   Into the funnel strong
alcohol is poured, so that from time to time a drop falls into the watch°
glass ;  being thus presented  to oxygen in a favourable condition,  it is
decomposed,  and  aldehyd,  acetic acid, and  acetal are formed.   These
liquids are vaporized by the heat evolved,  but  condense on the sides
of the  bell-glass,  and, flowing down,  collect in  the basin  underneath.
By processes detailed  in the systematic  works,  the acetal is  purified.
It is a colourless liquid, boiling at 200° ;  its odour is agreeable ;  its for-
mula is C8H903, and it appears to be a compound of aldehyd and ether,
C4[I402+C4H,0.
   The Aldehydic Acid—Acetous Acid—as already noticed, is formed by
the partial oxidation of aldehyd ;  but it appears to  be produced also under
the circumstances of slow  combustion, described in p.  179, aloncr  with
acetic and formic acids.  It  is obtained  pure by  decomposing its silver
salt by sulphuret  of hydrogen, forming a liquor of an agreeably  acid
taste.

           Of Acetic Acid.   Vinegar.—Eq. 755*6 or 51*2.
   As all alcoholic liquors are liable to undergo spontaneous decomposi.
tion, and form vinegar, this acid has been known from the earliest  ages
as produced by the  acetous fermentation;  its origin was,  however,  long
wrapped in  obscurity, for  the complex constitution  of the fermented
liquors, in which  it was ordinarily produced, prevented the simple na-
ture of the change from being understood.   It is now fully established,
that the change from alcohol  to acetic  acid consists simply in the remo-
val of two atoms of the hydrogen of the alcohol,  and addition of two
atoms of oxygen ; these actions  not being simultaneous, but successive,
and aldehyd being the intermediate product, thus:
       Alcohol, C4H602,            and            Aldehyd, C4H402,
         gives by —H2,                             gives by -f-02,
      Aldehyd, C4H402.               Hydrated Acetic Acid, C4H404.
By means of chromic  and nitric  acids, but  especially by the platinum
black as  described just now, this reaction may be  carried on with perfect
accuracy and distinctness.
   But if we place ourselves in the actual  condition  of practice,  the the-
ory of the acetous fermentation becomes much more difficult; for exactly
as a pure solution of grape-sugar will not break up into alcohol  and  car.
bonic acid, and a cause of  disturbance is necessary in order to enable
the new arrangement of its particles to occur, so do we find it  to be in
changing  alcohol into  acetic acid.  Pure  alcohol, whether weak  or
strong, absorbs  no oxygen by mere exposure to the air, and hence forms
no vinegar*,  it is necessary there should be  another body  more liable to
decomposition (ferment), which,  abstracting oxygen from the air for the
purpose of its own decomposition, may confer upon the molecules of al-
cohol such instability of structure as will admit of, and cause the similar
absorption of oxygen by them.   The ferment, in decomposing, evolves
water and carbonic  acid;  the alcohol  evolves water  only, but  absorbs
the oxyo-en from the air.   The platinum  black, in  the process that has
been described, supplies the place of the  ferment.  In making  vinegar
from malt liquors or from  wine, they are placed  in hogsheads  partially
full and left more or less exposed to the air, according to circumstances.
To' supply oxygen,  the air  must  have  access;  but if the  air were  very 
556            MANUFACTURE  OF  VINEGAR.
rapidly renewed, a large quantity of the volatile aldehyd would be car-
ried off.   These solutions contain abundance of organic matter, proper
for acting as ferment ;  and when the fermentation is complete, the prod-
ucts of their decomposition collect upon  the bottom and  sides of the
vats, in a gelatinous mass, termed mothers.
  The manufacture of wine or malt vinegar by the old process of mere partial ex-
posure  to the air in vats consumed  much time, and is  almost superseded by the
German method, by which excellent  vinegar  may be made in thirty-six hours.   A
                cask is  to be filled, as in  the figure, with wood shavings, and
                closed at the top by a pan, b,  the bottom of which is perforated
                with a number of  small holes, through which short threads are
          ^M( passed, to bring down the liquid more rapidly.  The shavings,
  'KaV H^- ^i,V'M\ before being used,  are well steeped  in vinegar, which is itself
  ky^:'^J.y?l':i'i^j\ one °f Oie most active ferments.  Below, at c c, is a circle  of
  ^^^-^ >"i/'r holes about half an inch in  diameter, by which the air may enter,
                which then escapes above by a  number of tubes, which pass
                through  the pan, and are left white in the figure.  If now we take
                a spirit containing  about one part of proof spirit to four of water,
                and, having mixed with it -roVo'h of honey or yeast, pour  it
                into the pan above, it trickles down  the orifices by the threads,
and, spreading over the shavings, has its surface  enormously extended.  It absorbs
oxygen very rapidly, and, having been warmed to about 75° before being poured in,
its temperature soon rises to 100° ; the interior being so hot, a current of air is es-
tablished through the vessels, by which a constant supply of oxygen is kept up.
According as the liquid passes down, it escapes through the pipe at the bottom, and
is collected in the vessel a; when it has passed  through three or four times, it  is
found to be converted into excellent  vinegar, and the whole time occupied is only
between twenty-four and thirty-six hours.
  The manufacture of vinegar by the distillation of wood will be described in an-
other place.
   The vinegar of commerce has frequently its pungency and acidity in-
creased by the addition of acrid  herbs, as  capsicum, and  by sulphuric
acid.  To obtain it free from these impurities, it  is redistilled.  As, how.
ever, its volatility is about the same as that of water, it cannot be con-
centrated  in that way, and hence the strong acetic acid must be obtained
by the decomposition of its salts  by a stronger acid.   For  this purpose,
one  part of acetate of soda, which has  been dried at  a gentle heat,  is to
be distilled with two parts of oil  of vitriol; so much  heat  is evolved by
the mixture, that a quantity of the acetic acid distils over spontaneously,
and to complete the  decomposition only  a very moderate heat need be ap-
plied.  In this process, S.03+Aq. and Na.O.-f C4H303 give S.03+Na.O.
and  C4H303+Aq.   The acid which passes over generally contains some
sulphurous  acid, arising from  its secondary action on the oil of vitriol;
in order to separate this, it is rectified over some peroxide of lead, with
which  the sulphurous acid forms sulphate of lead.   The liquid acetic
acid which  distils is then to  be exposed to  a cold of about 23°, and the
crystals which form are to be separated from the liquid portion; these
crystals are the Protohydrate of Acetic Acid, and  in its most concentrated
form.
  Acetic acid  may be prepared also by distilling acetate of lead with oil
of vitriol, or by the destructive distillation of acetate of copper : by this
last  method an acid  is obtained (radical  vinegar) of an agreeable aromat.
ic odour, from  an admixture of Acetone.   The acetate of potash is pre-
scribed by the Dublin Pharmacopoeia;  but, as acetate of soda is found
abundant  and cheap in commerce, it is  now exclusively employed.
   The Hydrated Acetic Acid, when free from  any excess of water,  crvs- 
          PROPERTIES  OF  ACETIC  ACID,  ETC.      557

tallizes at 50° in large white  plates, which do not again become liquid
until heated above 60° ; it is hence called Glacial Acetic Acid; its odour
is very characteristic and pungent; its taste caustic; it blisters the skin ;
it mixes with water, alcohol, and ether, and dissolves camphor and essen-
tial oils,  which solution constitutes  the  aromatic vinegar of the  shops.
When liquid, its sp. gr. is 1*063 ;  but its specific gravity does not indi-
cate its strength, as it increases according as water is added until it  be-
comes 1*078, which is that of an acid containing 34 6 per cent., or three
atomsof water;  being a definite compound, C4H303-}-H.O.+ 2 Aq.   On
farther dilution,  the sp. gr. again diminishes, and an acid containing 64
per cent, of water has a sp. gr. of 1*063, the same  as  that of the most
concentrated acid.   The  strength of any acetic acid may, however, be
very simply found by immersing in it a weighed piece  of white marble,
and weighing  it again when the  acid has been completely neutralized;
the loss of weight gives pretty accurately the quantity of acetic acid, as
the atomic weight of Ca.O. .  C02 (50*5) is nearly  the same as that of
C4H303 (51*2);  of course, if  the  acetic  acid  be not pure, this  method
cannot be employed.
   The formula of hypothetic  dry  acetic  acid  is C4H303, and its equiva-
lent =51*2.   The acetate of water, C4H303+Aq., consists of
              4 equivalents of carbon,   -=24 20  .  .  40 20
              4      "      hydrogen, = 4 00  .  .   664
              4      "      oxygen,  =32 00  .  .  53 16
                                       6020      10000
   The hydrated acetic acid boils at 240°.  The specific gravity of ;ta
vapour is 2278,  and is anomalous  as showing that its equivalent volume
is 3, in place of 4 or 2, as occurs with almost all other organic bodies.
   The products  of the decomposition of acetic acid by chlorine and by
bases will be hereafter noticed ; with powerfully oxidizing bodies it yields
formic, oxalic, and carbonic acids.
   Acetic  acid is recognised  by its  peculiar odour  and its volatility; it
reddens litmus powerfully ;  its solutions are precipitated  by the nitrates
of silver and of  black  oxide of mercury, giving white  crystalline salts,
sparingly soluble in cold water.  But  even strong solutions are  not af-
fected by the salts of lead or barytes.  It combines with  all  bases form-
ing salts, of which none are quite insoluble in water, but  generally very
soluble and easily crystallized.  The most  important  of these acetates
will now be described.
   Acetate of Potash, K.O. . C4H303,  is  formed by neutralizing acetic
acid by  means of pure carbonate of  potash.   The solution is generally
evaporated at once  to  dryness, and the salt fused at a dull red  heat, in
order to obtain  it quite white.  It  forms, on cooling, a foliated mass,
greasy to the feel.  From  its  concentrated solution it  may be obtained,
also, in delicate  crystals.  It is very  deliquescent, and dissolves copiously
in alcohol.
   Acetate of Soda, Na.O. .  C4H403-f 6 Aq., may be obtained  in  the
same way as acetate of potash, but is made on the large  scale in purify-
ing the rough wood-vinegar.   The  impure acetate of lime, obtained by
neutralizing the pyroligneous liquors with chalk, is decomposed by 6£
times its weight of crystallized sulphate  of soda.  These are in the pro.
portion of two equivalents of  Glauber's salt, as but one half of the quan-
tity added is decomposed by the acetate of lime.  It answers still better 
558       ACETATE  OF  BARYTES,  LIME,   ETC.
to neutralize the acid liquors by sulphuret of sodium, prepared by roast.
ing Glauber's salt with small coal, as for making soda-ash (p.  488).
                tWhcn purified by successive crystallizations, the acetate
              of soda forms oblique rhombic prisms, as i, u, in  the figure,
              with  many secondary planes, as  a, e, o.   These contain six
              atoms of  water.   It is permanent in  the air;  soluble in
              three parts of cold and  in  one  of boiling  water ; at a red
              heat  it melts.   Its  principal use is in  the  preparation of
              acetic acid.
  Acetate of Barytes, Ba.O. . C4H303, is formed by neutralizing  acetic acid with
carbonate of barytes or sulphuret of barium.  It  crystallizes  in oblique rhombic
prisms ; by heat it is completely decomposed into carbonate of barytes and acetone
(Ba.O. . C.02 and C3H3O.V
  Acetate of Lime is made on the large scale, but  in a very impure form, as one
stage  in the process of purifying  the wood-vinegar.   When pure, it crystallizes in
needles, which do not  deliquesce.  It  is decomposed by heat in the same way as
the preceding salt.
   Acetate of Alumina is of considerable technical importance, from its
use as a mordant in dyeing.   It is formed by mixing solutions of alum
and of  acetate of  lead  when to  be employed in the  arts.    The solution
then  contains much  acetate  of potash.   To  obtain  it pure, the simple
sulphate of alumina should be decomposed by acetate of barytes.   Evap-
orated at a very gentle heat, it dries into a  transparent gummy mass;
but if boiled, acetic acid passes off, and a basic acetate of Alumina is de-
posited as a white powder.   This effect is produced also by contact with
linen or cotton cloth, the acetic acid becoming free.   A piece of calico
is thus mordanted uniformly by immersion in a bath of acetate of alumina,
and then dried at  about 80c, or it is mordanted partially,  so  as subse-
quently to form a coloured  pattern, by b^ing  printed with the solution of
this salt, thickened with gum or starch, in order that it may not spread;
on  being then dried  by passing over warm  cylinders, the acetic  acid
passes off, and the alumina fixes itself upon the tissue.
  Acetate of Zinc, Zn.O. . C4H303-|-3 Aq.  Metallic zinc dissolves in acetic  acid,
                evolving hydrogen; but this salt is generally prepared by mixing
                solutions of acetate of lead and sulphate of zinc, and separating
                the sulphate of lead which  is formed by filtration.  On  evapora-
                ting the solution, the acetate of zinc crystallizes in brilliant, soft,
                hexagonal rhombic tables, as in the figure, of which i, u are pri-
                mary, and m a secondary face.  They are unalterable in the air,
                but very soluble in water.   When boiled with alcohol, a basic
                acetate of Zinc  precipitates, 3Zn.O.-4-C4H303.  A solution of this
salt is completely decomposed by sulphuret of hydrogen.
  Protoacetate of Iron.—Fe.O.  . C4H303. This salt,  which may be prepared by dis-
solving protosulphuret of iron  in acetic acid, forms a  colourless solution, which
yields, when evaporated in vacuo, pale green prisms, which attract oxygen with
great avidity   It cannot be formed by decomposing protosulphate  of iron by ace-
tate of lead, as only a portion of the lead  salt precipitates  until the iron becomes
peroxidized.
   Sesquiacetaie of Iron, Fe203 + 3(C4H303), is  prepared by dissolving red
oxide of iron in acetic acid, or by  decomposing red sulphate of iron with
acetate of barytes.   It  forms a brownish red  solution, which, when boil-
ed, gives off acetic acid, and oxide of iron separates.   By very cautious
evaporation, a dark red gummy mass  may be  obtained, which redissolves
in cold water.   It thus resembles closely acetate of alumina, and, like it,
serves in dyeing as a mordant, to fix  upon the cloth  oxide  of iron, with
which the colouring matters  may  combine;  being roughly prepared by
 
ACETATES  OF  LEAD.
559
digesting old  iron in the impure acetic acid from wood, it is commonly
termed Pyrol.ignile of Iron.
   A  tincture of Acetate  of Iron is  employed  in medicine, which,  as
directed by the Dublin Pliarmacopceia, is formed  by triturating together
protosulphate of iron and  acetate of potash, and digesting in alcohol ;  in
order that the solution shall have the rich wine-red colour which  is re-
quired, the mixture of the  salts should be  left for a little time pasty, so as
to absurd oxygon, and there, should be  present an excess of acetate of
potash.   The iron is present in these tinctures as black oxide.  If too
much sesquioxide be formed, the solution  decomposes very easily, red
oxide of iron separating,  and acetic ether and aldehyd being produced.
If the protoxide be  present  in excess, the colour is a  brownish yellow,
and the preparation is  liable to spoil  when oxygen has subsequently ac-
cess to  it.   Although the acetate of  potash does not form a true double
salt in  this  case, yet it gives much  greater  stability to  the  acetates
of iron.
   Acetates of Lead.—Acetic acid forms, with oxide of lead, four well-
characterized salts.
   Neutral Acetate of Lead.  Sugar of  Lead, Pb.O. . C4H303-f 3  Aq.,
is prepared by  dissolving  litharge, or white lead, in acetic acid,  of which
a slight excess  should be  used.   The liquors yield by evaporation right
                      rhombic prisms with dihedral summits, as in the
                      figure,  which are very  bright and  colourless;
                      their taste is  sweet and astringent;  the  solution
                      in  water  reddens  litmus, but turns  sirup of vio-
                      lets  green.    In  very  dry air they effloresce;
                      when heated  to 136°  they undergo  aqueous fu-
                      sion, but, having  lost  their water  of crystalli-
                      zation, become solid again.  The dry  salt thus
obtained fuses  again at a higher temperature, and without blackening,
is decomposed into  carbonic acid, acetone, and sesquibasic acetate of
lead, which  remains, 3(Pb.O. .  C4H303) giving C02  with  C3H O. and
 3PbO. + 2C4H303.
   This neutral salt dissolves easily in alcohol; it is very pois   .ous ; the
antidote to it is Glauber's or Epsom salt, which forms insolu .e  sulphate
of lead.
   Sesquibasic  Acetate of Lead.—3Pb.O. + 2C4H303.  This salt,  which
is formed as just described, dissolves in water, and the sirupy solution
crystallizes in  pearly hexagonal plates ;  its solution reacts alkaline.
   Tribasic Acetate  of Lead.—3Pb.O.+04H303.  When  ammonia is
added to a solution of neutral acetate of lead, so as to render it  strongly
alkaline, it does  not combine with it as with most other metallic suits,
but acetate of ammonia and tribasic  acetate of lead are formed  ; it may
also be prepared by boiling together six  parts of crystallized  acetate of
lead, seven  of litharge, and thirty of water.   This solution, known in
pharmacy as Exlractum  Saturni, gives,  by evaporation, a  mass of fine
crystalline needles;  it reacts powerfully  alkaline;  it is insoluble  in
alcohol.
   Sexbasic  Acetate  of Lead, 6Pb.0.-j-C4H303, is precipitated when a
solution of neutral acetate is added to a great excess of water of ammo-
nia * it is formed, also, when acetic acid acts on  metallic lead with access
of air and is hence generally present in the Ceruse of commerce.   (See
 
560   ACETATES  OF COPPER,  MERCURY,  ETC.
 p. 491.)  It forms minute feathery crystals when deposited from boiling
 water, in which it is slightly soluble.
   All these basic acetates of lead are  decomposed by  carbonic  acid,
 giving neutral acetate and carbonate of lead.
   Acetates  of  Copper.—The acetate of the suboxide of copper is not
 important;  there  are four acetates of the black oxide.
   Neutral Acetate of Copper.   Distilled Verdigris, Cu.O.. C4H303+ Aq.,
               is prepared by dissolving verdigris in acetic  acid.  It forms
               oblique rhombic prisms, as in the figure, where i, u, u are
               primary, and e, e secondary faces of a fine deep green col-
               our.   It crystallizes in another form  with five atoms of
               water:  these crystals are blue, like  sulphate  of copper,
               and when heated to 86°, give off 4 Aq., and change into
               the common green crystals; it effloresces gradually in
               the air ;  when heated in close vessels, it gives a mixture
 of acetic acid and acetone ; in the air it takes fire, burning with a bright
 green flame.
   If a solution  of this salt be mixed with sugar or honey, and heated, it
 deposites a  green powder of carbonate of copper,  which changes  into
 minute  crystals of  the  orange-red  suboxide : the liquor  contains then
 abundance of formic acid.
   Bibasic Acetute of Copper.   Verdigris. — 2Cu.O. + C4H303+6  Aq.
 This  salt is manufactured in  wine  countries by stratifying plates of
 copper alternately with  the residual stalks and pulp of the  grapes  that
 have  passed into acetous fermentation ; oxygen is absorbed, and the mass
 being occasionally turned over and moistened, to give access to air, the
 plates of copper become covered with a crystalline crust of basic acetate;
 this is scraped off, made into a paste with vinegar, and put into moulds,
where it is  allowed  to dry;  the  mass  so formed contains all the basic
salts mixed  together.   In  this  country it is prepared by stratifying cop-
per plates with cloths steeped  in pyroligneous  acid.   When pure, the
bibasic acetate  is of a fine blue colour; it is  decomposed  by water  into
the insoluble tribasic acetate, and the soluble sesquibasic acetate of cop-
per, which forms a pale  blue solution, whence it may be precipitated in
crystalline scales  by alcohol.
   Tribasic Acetate of Copper, 3Cu.O.-f-C4H303+2  Aq., remains as an
insoluble residue when verdigris is treated with water, or by digesting a
solution of neutral acetate with oxide of copper.   It is a  clear green
powder, which detonates feebly when heated.  For Emerald Green, see
p. 456.
  Acetate of Black  Oxide of Mercury, Hg.02+C4H303, may be formed
 by mixing boiling  solutions of acetate of potash  and subnitrate of mer-
cury, and filtering  rapidly.   On cooling, it is deposited in brilliant white
Crystalline scales, which are very sparingly  soluble in  cold water, and
 insoluble in alcohol.   The Acetate of the Red Oxide is very soluble in wa-
 ter, and does not crystallize.
   Acetate cf Silver,  Ag.O. . C4H303, is formed by mixing boiling solu-
 tions  of nitrate  of silver and acetate of  potash, and  filtering the liquor
 while very  hot.   On cooling, it crystallizes in  pearly white  needles,
 which are but  very sparingly  soluble  in cold water.  These last salts
 serve as tests for the acetic acid in liquids.
   Acetate of Ammonia, N.H40. .  C4H30„ is prepared by passing ammo- 
ACETATE  OF  E T II E R.--A C ETON E.         561
niacal gas  over the crystalline hydrate  of acetic acid, or by  heating
moderately a  mixture  of equal parts  of acetate of potash and of sul
ammoniac.   Tne acetate of ammonia  sublimes mixed with a  little free
acetic acid ; it crystallizes  in needles, which are  very soluble in alcohol
and in water;  by exposure to  the air it loses ammonia, and appears to
form  an acid salt; its solution in water, prepared by neutralizing distilled
vinegar with carbonate of ammonia, i.s  used in  medicine by the name of
Spirit of Mindererus ;  in its original  form, when the carbonate of ammo-
nia, obtained by the distillation  of bones [salt of  hartshorn), and  which
contained cmpyreumatic animal oil, was used, it was  a much more pow.
erful  medicinal agent than when prepared, as  now, with  pure carbonate
of ammonia.
   Acetate  of Ether.   Acetic Ether, C4H30.-f C4H303,  is  prepared by
distilling 16 parts of dry sugar of lead, 4£ of  alcohol, and  6  of oil  of
vitriol ; the  product should be rectified  over  some  lime to  remove free
acetic acid.   This ether is colourless, and very inflammable; it boils at
165°; it is  lighter than water;  it is  remarkable for being isomeric with
aldehyd, their  per  cent, composition  being the same, but the sp. gr. of
the vapour of acetic ether (3063) is double that of aldehyd (1531).

        Products of the Decomposition of Acetic Acid by Heat.
                  A. Of Pyroacctic Spirit.   Acetone.
   When acetate of lime or barytes is heated  to redness, the acetic acid
is completely decomposed, an  earthy  carbonate remaining, and a volatile
inflammable liquid, of  an agreeable  aromatic odour,  distilling  over, C«
H303 separating itself into CO, and  C3H30.  The metallic acetates are
similarly decomposed,  but the products are not so pure.   This liquid,
for which I shall retain the name Acetone, is formed also  abundantly
when the vapour of acetic acid is  passed through  a tube containing
charcoal, at a temperature just below  redness.
   Acetone  is colourless, and lighter than water ; it burns with  a lumin-
ous flame;  it buils at 132°; the specific  gravity  of its vapour is 2022.
When heated with hydrate of potash,  it is totally converted into carbonic
acid and marsh gas,U3H30. and  H.O.  producing C2H4  and C02.  When
treated by oxidizing agents,  as permanganate of potash, or bichromate of
potash and  sulphuric  acid, it is totally converted into acetic  acid.
  With sulphuric acid, acetone yields a series of products closely analogous to those
derived from  alcohol, but still presenting such characteristic differences as induce
me to look upon  them as not simply extracted from acetone, but derived from its
total decomposition   Thus it gives  a hydrocarbon,  Mcsi/ylcne, whose formula is
C6H4  and also an ether,  Mcsitk  Ether, C6H50.  With sulphuric acid, this forms the
Sulp'homcsitic and Pcrsulphomesitic Acids, which  are  remarkable,  as  the sulphuric
acid retains all its power  of saturating bases.  With phosphoric acid, it produces
Phosphomesitic Acid, and with hypophosphorous acid  a  very remarkable compound,
whose barvtes salt has the formula C6H.-,0.-j-2Ba.O.. P.O.  The series of wine-alco-
hol contains no similar body. The mesitic ether combines also with protochloride
of platinum.                     ,,,,.,,          .        .       • _■
  When acetone is treated with chloride of phosphorus, it gives phosphoric acid
and ChloTomcsitic Ether, 06H3C1.; with iodide of phosphorus it produces Iodomesitic
Ether  Cullsl  * and, when acted on by chlorine, it tbrms, first, the Mesitic Chloral, of
which the formula is O3II2 • CIO., and subsequently another body, also a heavy,
oily liquid, C3H. . C120             .,          , .                        , .
  When red  fum< - of hyponitrous acid are passed into acetone, and the vessel 13
kept cool  they are copiously absorbed, and, on  adding water, a dense fluid separ-
ates which is iK'ilrous Mesitic Ether, 06H,0.-fN.03.
  Bv at-tino*  on  mesitylene, Cell* with nitric  acid, a heavy liquid is  produced,
      ■  °                      4. B 
562       BODIES  OF THE  KACODYL  SERIES.

which is termed Mesitic Aldehyd; its formula is C6H30.-f Aq.  Its solution in alka-
line liquors becomes brown after some  time, and precipitates most sails of the
heavy metals.   By chlorine, the mesitylene is converted  into a crystalline body,
soluble in ether, and separating from it in brilliant colourless prisms.  Its formula
is CoHaCI.  I have termed it Chloride of Plclcyl.
  In my original examination  of this series of bodies, I looked upon acetone as an
alcohol {Mesitic Alcohol), C(iHb02=(C6Ii:10.-r-Aq.), Iroru which they wen- all derived;
but I do  not how consider that either mesitylene or mesitic ether pre-exists in ace-
tone.  The intimate nature of that body remains yet to be examined.
                B.  Of the Bodies of the Kacodyl Series.
  When equal weights of acetate of potash  and arsenious  acid are mix.
ed and  distilled  at a  dull red heat, a dense colourless liquid is obtained,
which had been long  known to  chemists  as the Fuming Liquor of Cadet.
The admirable  researches of Bunsen have  shown thai it is an oxide of
a compound  radical,  which he has succeeded in isolating,  and which, in
the variety of its combinations, and  the influence their  discovery will
doubtless exercise on science,  ranks with cyanogen.  Nevertheless, as
they are not  of  practical importance, a short notice of them will suffice.
   The Fuming Liquor of Cadet, or Alkarsine, when pun lied from ace-lone
and other accidental products  of the distillation,  is colourless ;  much
heavier than water.  It freezes at —9°, and boils at 300°.   The specific
gravity of its vapour  is 7180 ;  its odour is excessively disagreeable, pro.
yoking weeping and nausea ;  it is actively  poisonous ; in contact  with
the air it fumes very much, and absorbs oxygen so  rapidly, that if a large
surface be exposed, it takes fire spontaneously, and burns with a large
white flame, throwing off much arsenious acid.   Its composition is ex.
pressed by the formula C4IT6. As.O., and in all the combinations which
it gives, the  oxygen alone is replaced.    Thus, when distilled with strong
muriatic acid, a  dense liquid of an insupportable odour is produced, which
gradually changes  into a crystalline mass,  consisting of C4H6  . As.CI.
By digesting this liquid with zinc and water, in a vessel kept full of pure
carbonic acid, chloride of zinc  is formed, and the radical C4H6As. is set
free ;  this is an oily-looking, heavy liquid, insoluble in water, and taking
fire immediately on  contact with air.   This is the Kacodyl, and as its
symbol 1 shall  adopt that used by Bunsen,  Kd. = C4H6As.  The alkar-
sine is  therefore oxide of kacodyl, Kd.O., and the body formed by mu-
riatic acid is the chloride, Kd.Cl.   The iodide,-bromide, sulphuret, and
cyanide of kacodyl, may be formed by the simple process of distilling al.
karsine with  the corresponding  hydracids, or the chloride of kacodyl with
the iodides, &c, of potassium.
   When alkarsine is distilled with dilute muriatic acid, or when  chloride
of kacodyl is treated with water, this is decomposed, and an oxychloride
obtained, the formula of which  is Kd.O.-f-3Kd.CI.   In a  similar  man.
ner, a  corresponding oxybromide, Kd.O. + 3Kd.Br., may be produced,
and an oxyiodide.
   If alcoholic solutions of oxide of kacodyl and of corrosive sublimate be
mixed, a brilliant white precipitate  is obtained, which is  soluble in wa-
ter, and crystallizes therefrom  in large but  delicate rhombic tables, of a
satiny lustre.   It is  a direct combination,  its formula being  Kd.O.-f
2Hg.Cl.   A precisely similar compound is formed with the bromide of
mercury.
   When alkarsine is exposed to the air, so  that it may absorb oxygen,
but not burst into flame, it is  changed totally into a white  crystalline
mass ;  at the same time, arsenious acid  and some volatile products  are 
SOURCES,  ETC., OF  MARSH  GAS.         563
tormed.  The crystals being dissolved in a small  quantity of water, this
liquor is evaporated to dryness, and the residue dried by blotting paper,
and rocrystullized from alcohol.  The substance thus obtained is termed
Alkargene ;  it forms large oblique prisms, which are inodorous and taste.
less; it deliquesces in moist air;  it combines with alkalies and metallic
oxides, forming very instable compounds; it  melts  at  390J, and is de-
composed  by a stronger heat.   By deoxidizing  agents, as  protochloride
of tin or  phosphorous acid, it is reduced to the state of alkarsine ;  il is
not poisonous.   Its composition is expressed by the formula C4H7. As.
04, or Kd.03+Aq. ; its proper name is therefore Kacodylic Acid.
          C.  Of light Carburetted Hydrogen.  Marsh Gas.
   This gas is formed  by the decomposition of almost every organic sub-
stance  at a high temperature.   Thus it exists always  mixed  with  olefi-
ant gas, in the coal or oil gas used  for  illumination.   It may  be formed
by passing olefiant gas through a red-hot  tube, when half of its carbon is
deposited  and  its volume doubled.   It is produced, also, by passing the
vapours of alcohol, of ether, or of acetic acid through bright red-hot
tubes in a similar manner.
   A very interesting source of this gas is the decomposition of vegetable
matter in contact with water, but excluded  from the air.   By assimila-
ting  the elements of four atoms of water, the lignine breaks up into car-
bonic acid and this gas, CI2H808 with  4H.O. giving 6C02 and 6C.H,.
As the origin of the great deposites of coal is to be found in the slow de-
composition of submerged  forests of high antiquity, this  gas  was  then
generated  in large quantity, and,  being subjected to enormous pressure
under the  mineral strata, which gradually settled on the vegetable mass-
es, it remained infiltrated through the coal,  probably  in a liquid condi-
tion.   During the operations of mining,  when this great pressure is re-
moved, it  reassumes its gaseous  condition, and, mixing with  the air of
the mine, creates the danger of explosion, against which the genius of
Humphrey Davy provided by the construction of his safety-lamp (see p.
183).  Under the name of"Fire-damp, this gas  is known and dreaded
by the  miners, while the carbonic acid, which results  simultaneously from
the decomposition of the wood, and is known, also, from its fatal effects
when breathed, is termed Choke-damp.
   This decomposition of wood goes on in every muddy ditch.  If the
mud be stirred, numerous gas bubbles will be  seen to ascend,  and when
collected will be found to consist of fire-damp  mixed with carbonic acid ;
hence this gas has got the name of Pond or Marsh Gas.  It is obtained,
however, most pure by the  decomposition of acetic  acid by hydrate of
potash.  About equal parts of acetate of potash and caustic potash are
to be well mixed, and heated in a  hard  glass retort  nearly to redness.
The acetic acid and water  are  simultaneously decomposed, C4H303 and
11.0. producing 2C.H2 and 2C.02.  This last  remains combined  with
the potash  while the gas which passes off may  be collected over water.
   It is colourless ancf transparent.  It burns with a yellow flame, pos-
sessing but little illuminating power ; its sp. gr. is 559  ; its formula be-
ing C.Tl2, and consisting of
          One volume of carbon vapour......=843 0
          Four volumes of hydrogen.......=27^2
          Forming two volumes of marsh gas  ....   HIS 2
          Of which one weighs, therefore    .....   5691 
564          CHLORAL.--CHLORO ACETIC  ACID.

Or it may be considered as containing one volume of olefiant gas and two of hydro-
gen, condensed to two, (980 4+137 6)-^-2=559.

  The real  atomic weight of the marsh gas  is difficult  to determine, as
it  does  not  form any well-defined  combinations.    There is reason to
suppose it to be C2H4.    When acted on  by chlorine, it gives  muriatic
acid gas and bichloride of carbon (p.  498), which has been  already no.
deed.

Of the Action of Chlorine on Alcohol, Aldehyd, Acetic Acid, and the va.
                          rious Kinds of Ethers.

  When  chlorine gas  is passed into alcohol not  absolutely anhydrous, a heavy
oily liquid is  obtained, known as heavy  Muriatic Ether or  Chlorine Ether.  It is a
mixture of several substances in indeterminate proportions.
  When the alcohol is anhydrous and the gas quite dry, the action is definite, and
gives rise to a remarkable result.  Five sixths of the hydrogen of the alcohol are
removed, and are replaced by three of chlorine, and,  after the evolution of a large
quantity  of muriatic acid gas, a dense  oily liquid  is obtained, to which the name
of Chloral has been given ;  its formula is C4H. . Cl302.   The first operation of the
chlorine  is to remove two equivalents of hydrogen, and thus to reduce the alcohol
to the state of aldehyd. just as any other  oxidizing agent should have done; but
then it acts on the hydrogen of the radical, acetyl, and, expelling it, takes its place,
generating a new compound radical, Accchloryl, C4CI3.  This is combined with oxy-
gen and water in chloral, as acetyl is in ordinary aldehyd ;  the rational formula of
chloral is therefore C4Cl30.+Aq.
  Chloral combines with water, forming a  crystalline hydrate.  It gradually chan-
ges into  an isomeric porcellaneous-looking  substance.  The equivalent change of
common aldehyd has  been  described (p. 554).  When chloral is acted  on by  a
solution of potash, it yields formic acid and chloroform, C4H. . CI3O2 and H.O. giv-
ing C2H.03 and C2H.C13.
  By the action of chlorine on aldehyd, chloral is directly formed.
  When the crystallized acetic  acid is exposed to the action of chlorine  in bright
sunshine, a substance is formed  which crystallizes  in  brilliant, rhombs,  and pos-
sesses strong acid properties;  its formula is C4H. . C1304.  It is formed  by the
replacement  of the hydrogen of the radical  acetyl by chlorine, forming  thus, the
Chloroacelic Acid, C4Cl303+Aq.   Its salts crystallize with  facility, and have great
similarity to the acetates  When the chloroacetate of potash is heated with an ex-
cess of potash, it is decomposed into carbonic acid and  chloroform;  C4C1303 and
H.O. giving 2C.O2 and C?H.013.   This reaction is exactly similar to that of the
common acetate of potash, the chloroform replacing the pond gas.
  When chlorine acts upon  sulphuric ether,  a remarkable series of bodies  is pro-
duced ; the first  formed is a dense  oily liquor,  having  the formula  C4H3 , C120.,
which, by contact with water  or an alkali, is decomposed into hydrochloric and
acetic acids. 3(C4H3 . CI2O.) and 6H.O. producing CH.C1. and 3(C4H303).  Thia
body is properly, therefore, Oxychloride of Acetyl; it is decomposed by sulphuret of
hydrogen, muriatic acid being given off, and  an Oxysulphuret of Acetyl being formed,
which resembles it in properties.
  In presence of a great excess of chlorine, this oxychloride is totally  decomposed,
the chlorine entering into the place of the hydrogen in the acetyl,  and forming the
same radical as exists in chloral and chloroacetic acid.  The substance  thus pro-
duced is solid and crystalline; it bears a very simple  relation  to sulphuric ether,
as  its formula is COUO., being apparently  ether, in which all hydrogen is replaced
by  chlorine.   It may be termed Chloryl Ether.
  The action of chlorine on the acetic and  oxalic ethers has thrown much light on
the theory of these bodies.
  Acetic ether combines with two atoms of chlorine and loses two atoms of oxy
gen, thus giving from C4H303+C4H50.,the Chloroacetic Ether, CtH303+C4H3. C120.,
an  oxychloride  of acetyl, containing twice as much acetic  acid as that  just now
described, and its rational  formula being, therefore, Ac:Cl3+2Ac.03; with potash
it gives chloride of potassium and acetate of potash.
  By a stream of dry chlorine gas oxalic ether is totally  converted into a mass of
crystalline plates, which are  tasteless and perfectly neutral;  this body contains no
hydrogen, its formula being  CtiCl504=C4ClsO.+C203.  It is, therefore, a combina- 
ACTION  OF  CHLORINE  ON  MURIATIC  ETHE
tion ol oxalic acid with chloryl ether, and is termed Chloroxalic Ether.   With water
of ammonia it gives oxamide ;  by the action of dry ammonia it forms  a substance
also crystalline, which is soluble  in alcohol and  ether, sparingly soluble in water
and the  formula of which is CsH2Cls . N.06; at the same time," chloryl ether and
water are evolved ;  the  rational  formula of this  body, Chloroxamethan, is at once
seen by comparing  it with the oxamethan, formed by  ammonia on oxalic ethpr
(p. 550).   Thus,

   2 atoms of oxalic ether, Ci2Hio08, give an atom of oxamethan, C8H7. N.06.
   1 atom of ammonia, N.II3, gives an atom of alcohol, C4H50.+Aq.

In like manner,

2 atoms  of chloroxalic ether, C|2Cl,0Os, give 1 of chloroxamethan, C8C15H2. N.Oe-
1 atom of ammonia, N.II3, gives  1 of chlorine alcohol, C4Cl50.+Aq.

  The rational formula of the chloroxamethan is therefore C4C150.. C203+C202Ad.
  When  chloroxamethan is dissolved in water of ammonia, and the solution evap-
orated, crystals are obtained, which are Chloroxal.ovinate  of Ammonia, their formula
being C8H4Cl5 . N.Os, or, in  its  rational  form,  C4C150. . C203+C203 . N.H40. ,
identical  in constitution with the  ordinary oxalovinate of ammonia, except that it
contains chloryl ether in  place of common ether;  the Chloroxalovinic Acid itself has
been isolated ; it crystallizes in long needles, which  react acid, and combines with
all bases  to form well-defined salts ;  its formula is C4Cl.-,0. . C203+C203Aq.
  A crystallographic examination has rendered the isomorphism of the ordinary
oxamethan with the chloroxamethan exceedingly probable.
  The results of the action of chlorine on the light muriatic ether have led to re-
markable results.   Regnault considered this body as affording a test experiment
for  the actual presence  of olefiant gas in ether; for if olefiant gas be Ac.H., and
muriatic  ether be Ac.H.  . H.CL, the  result of the action  of chlorine  should be the
same on both bodies, as  the muriatic acid in the latter could not influence such a
reaction   Now,  by  acting on  muriatic ether with chlorine, a series  of bodies is
obtained, isomeric with those arising from olefiant gas, but quite different in prop-
erties.   Thus there is first formed a liquid, C4H4C12; this has the composition of
Dutch oil; next,  a liquid forms whose formula is C4H3CI3; afterward, bodies  con-
sisting of C.1H2CI4 and C4H Cl-„ and ultimately C4C16, Sesquichloride of Carbon.  Now
the bodies C4H4Cl2 and C4H3C13, as derived from olefiant gas, are separated by pot-
ash into C4H3CI. with H.Cl., and into C4H2C12 with H.Cl. ; but the bodies C4H4C12
and C4H3C!3, from muriatic ether, are not decomposed  by that alkali.  I  do  not,
however, believe in .the  indefinite replacement  of  hydrogen  by chlorine, which
Regnault assumes, and look upon  the relation of these series of bodies as being the
following:
            From Olefiant Gas.                      From Muriatic Ether.
    C4H4C12=C4H3C1.+H.C1.          C4H4C12=C4H3C1.+C4H5C1.
    C4H3C13=2(C2H.C1.) and H.Cl.      C4H3C13.
    C4H2C14=2(C2H.C12).               C4H2C14=C4C15C1.+2(C4H3C13).
                                     C-»H. C13=C4H3C13+ 2( C14CUC1.).

  Both these give, finally, sesquichloride of carbon, C-iCIaCI.   The  bodies from
olefiant gas,  which  contain chloride  of hydrogen, are decomposed by an alcoholic
solution  of potash, but thos^  :n  which the chlorine is combined with an  organic
radical are not affected by that reagent.
  By the action of chlorine on mercaptan, a similar series of products is obtained,
of which  the terminal body is C4H. . CUS., consisting of C4H3S3+2(C4C15C1.).

On the Theoretical Constitution of Alcohol, and the Bodies derived from it.

  The  theory of alcohol  and the ethereal  combinations is of the more
impoi lance, as the principles of it regulate our ideas, not merely concern-
iri-r the bodies that have been  now described, but a vast number of others ;
for the ordinary, or wine alcohol, is but one example of a numerous  family
of bodies, which resemble  it  in  all its general laws of reaction,  with, of
course,   peculiarities characteristic of each;  thus  wood-spirit, oil of  po-
tato-spirit,  and  ethal are alcohols.
  The generic properties of an  alcohol are, that its composition may be 
566
THEORY  OF  THE  ETHERS.
represented hy a hydrocarbon isomeric  with  olefiant gas,  united  with
two atoms of water ;  that it gives an ether, which contains an atom of
water less, and acts as a base ; and  that, by combining the hydrocarbon
with four atoms of oxygen, an acid is formed.   Thus we have,
          Wine-Alcohol        Wood-Alcohol.       Oil of Polato-Spirit.         Elhai.
Alcohol,   C4H4+2H.O.    C2H2+2II.O.    C,0Hl0+2H.O.    C32H32+2H.O.
Ether,    C4H4+H.O.     ('-H2+H.O.     C,0H,o+H.O.     C32H32+H.O.
Acid,     C4H40.         C2H2O4         C10H10O.i         C32H3204.

  Such being the connexion of the bodies of this class, the propositions
in which 1 shall now proceed to imbody the principles of the constitution
of the substances derived from wine-alcohol, may be  hereafter immedi-
ately applied to illustrate  the history of the other alcohols.
  1. From the action of sulphuric acid, of chloride of zinc, of fluoride of
boron, of potassium, and of chlorine on alcohol, it results that it contains
an atom of water ready formed, united with sulphuric ether; its formula
is therefore C4H50. + Aq.
  2. The sulphuric ether is a base, neutralizing the strongest acids, and
producing both oxy-salts and haloid  salts, perfectly resembling those of
an alkali.  The oxygen in  ether may be replaced by all other electro-
negative bodies, while the carbohydrogen, C4H5, remains constant.  By
the conditions laid down in p. 467, this, therefore, is a compound radical;
it is called Ethyl, and its  symbol is written Ae.  Ether is oxide of ethyl,
and its symbol is Ae.O.
  3. By the action of oxidizing agents, hydrogen may be  removed from
ethyl, and a new radical, C4[]3, produced, which, by combining  with oxy.
gen, forms aldehyd and acetic  acid, its symbol being Ac.  Aldehyd is
protoxide, Ae.O., and acetic acid, peroxide of  acetyl,  Ac.Os, both being
considered free from waler.
  4. From olefiant gas, by the action of oxidizing agents, we cannot, in
any case, pass to the  series of bodies containing acetyl; nor can we,
by  bringing olefiant gas  in  contact with  water  or acids, produce any
form of alcohol or ether.   On the contrary, the isethionic acid is essen-
tially distinct  from these acids, which  c~r.!ain  ether, and yields none by
any form of decomposition ; olefiant gas, on  the  other hand, gives, by
the action of chlorine, a series of bodies, which are quite different from
those given by muriatic ether, but which indicate that it is itself a radi-
cal,  having laws of combination peculiar to itself, and independent, as
Berzelius had already suggested, both of the  alcohol and acetic  series.
Its formula is therefore C2ff2; its symbol El.;  and the Dutch oil is truly
Chloride of Elayl. The ethyl may change itself readily into elayl by loss
of hydrogen,  since C4H5=2('2H2 and H., and  it is thus broken up when
the hydriodic or muriatic ethers are decomposed by  heat, or  by  potash,
or ammonia; or when sulphuric ether  is acted on by an excess of sul
phuric acid.
   5. Although from  the  decomposition  of ether we obtain olefiant gas,
or light oil of wine, yet as ether  cannot be in  any way regenerated from
these bodies by the influence of water or otherwise, neither can the other
products derived from ether, as acetic acid, be produced from them, we
must abandon the theory which considered ether to be a hydrate of C4H4,'
and consider  it simply as an organic base,  the oxide of ethyl.
   6.  By the  action of chlorine on  the  ethereal compounds and  on ole-
fiant  gas, radicals are  generated, which are  precisely equivalent to the 
THEORY  OF  THE  ETHERS,   ETC.          567
tnree, ethyl, acetyl, and elayl,  but which contain chlorine in place of hy-
drogen.  Their formulae are C4CI3, C14C5, and C2CI2.  This last is the pro-
tochloride  of carbon, already  described;  the  first,  Acechloryl, exists in
chloraldehyd and  in  chloroacetic  acid;  the second,  Ethchloryl, exists
combined with  oxygen in  chloryl ether, which acts  as a base similar to
common ether towards the oxalic and acetic acids.  In  contact with an
excess of chlorine, it breaks up, as ethyl does, into olefiant gas and hy.
drogen, into the protochloride  of carbon and chlorine, and thus the ulti-
mate result is the sesquichloride of carbon, C2CI3.
   7.  The  series of bodies formed by the action of chlorine on elayl  and
on  chloride of ethyl,  are  double combinations of  bodies containing the
hydrogen and chlorine radicals, and hence results their isomerism.  Thus
the body (C4H2CI4), from  elayl, consists of C2H2C1.+C2CI2CI., while the
bidy  (C4fl2Ci4). from  the muriatic  ether, is really  2(C4H3OI3)+C4CI3CI3.
The body. C4H3CI., from  elayl, is 3(C2M2)+C2CI2.
   8.  Tne  relation of acetyl to ethyl is simply that of internal  constitu-
tion, described in p. 467.   For as benzoic acid contains benzoyl, C14H502,
while this, again, contains, as radical, the carbohydrogen, CI4H5, so ethyl,
C4HS, contains within it, ready formed, the  radical  acetyl, and  its formula
niignt be still more correctly written as Ac.H2.   This  is simply shown
by the action of  chlorine  on  ether,  where  C4fl3.  H20.  becomes  first
CJIj. Cl20., and subsequently changes to C4CI3 . CLO.; the intermediate
compound, Ac.CI2, relating itself to  the oxygen, as the sulphurous acid,
S.0_„ or the benzoyl,  CMH,-,02, in the sulphuric and benzoic acids.   Al-
though the connexion of these two  radicals is thus analogous to that of
amidogen, Ad., and ammonium, Ad.FI2=:Am., yet a broad  line of distinc-
tion is drawn between the ammonia and ether theories, by the very defi.
nite character of ether, oxide  of ethyl, as contrasted with the hypothetic
oxide of ammonium; and,  on  the  other hand, there does not appear to
be any acetylide of hydrogen corresponding to ammonia, the  amidide of
hydrogen,  for  the  assumption  of olefiant  gas as being that body is  not
based  upon sufficient  evidence.
           Secondary Products of the Alcoholic Fermentation.
  I have already noticed that, besides the carbonic acid and alcohol which are de-
rived  from the sugar, other bodies are evolved  in minute quantities, and by their
odour and taste characterize the spirit obtained from  particular vegetables.  Thus,
in the fermentation of grape-juice, CEnanthix Ether is produced ; in the  spirit dis-
tilled from potatoes, a peculiar oil is found ; and in the fermentation of malted corn,
both of these  bodies are generated, besides a third,  to which the  name of Oleum
Siticum, or Corn Oil  has been given.
  The CEnanlhic Ether is a thin, colourless liquid, of an almost stupifying odour of
wine, as to it the peculiar bouquet of wine is due ; its specific, gravity is 0 8f>2 -, it
boils at 415° ; when heated with caustic soda, it  evolves alcohol, and forms cenan-
thate of soda, from which the <E'onHilar Add may be separated by muriatic  acid.
This is a white crystalline solid, which  melts at 88 \ and distils over at 560° un-
changed ; its  formula is C|4H|302; it combines  with water,  forming a thick oil,
which solidifies only at 55°, is tastelpss and inodorous, but reddens litmus sensibly.
The formula of the ether is Ae .0.+d4Hi302; it is remarkable as the only ether
that exists as a natural product, but it may also be formed artificially by means of
alcohol and oenanthic acid.
  The Com Oil, of which the  formula is C42H3i04, is lighter than water, of a  very
penetratin"* odour, a biting taste, and cannot be  distilled without partial  decompo-

  The Od of Po'u'o-spint has become of much interest, from the discovery that it
eives rise to a scries of ethereal combinations similar to those of wine alcohol; the
Dime  ofAmilic -leolod mav be applied to it;  it is colourless, oily, its odour at first 
568                  AMILIC  ETHER,  ETC.
pleasant, but subsequently nauseous ; its taste acrid ;  it burns with a blue flame
its sp. gr. is 0 812 ;  it freezes at 4°, and boils at 294° ;  it dissolves  in alcohol and
ether; its formula is C10H12O2.  In this alcohol a compound radical  is assumed to
exist, termed Amilyl, C,oHu  ; its symbol is Ayl., and it is combined with oxygen
and water, Ayl.O.+Aq., as ethyl is in wine-alcohol.
  The Amtlic Ether, Ayl.O., is not known except in combination with  acids ;  its
bisulphate, or Sulph-amilic Acid, is  obtained by acting on amilic alcohol with  oil
of vitriol; its formula is Ayl.O. . S.03+S.03. H.O.; its barytes  salt crystallizes in
pearly  plates, colourless, very soluble in water and alcohol.  This  salt  is decom-
posed when its solution is boiled.   The salts of lead and lime are completely sim-
ilar in properties.
  Chloride of Amilyl, CoHnCl. or Ayl.CI., is prepared hy acting on amilic alcohol
with chloride of phosphorus ;  it is  a colourless oil, which boils at  217°.  By the
action of bromine or iodine  and phosphorus on the amilic alcohol, the bromide and
iodide of Amilyl are prepared ;  they possess properties similar to those of the chlo-
ride.
  Acetate of Amilyl, Ayl.O.+Ac.03, is easily formed by  distilling acetate  of potash,
oil of vitriol, and amilic alcohol; it is a volatile, colourless liquid,  which boils  at
257°.  The Oxalate of Amilyl may  be similarly formed.
  By distilling  amilic alcohol  with glacial phosphoric  acid, a colourless aromatic
liquid is obtained, having the formula C:oHi0.   It is in this series what olefiant gas
is in that of the wine-alcohol; it is termed Amilene; the sp. gr. of its vapour is 4918.
  Valerianic Acid.—C!0Hi0O4.  When the amilic alcohol is exposed to the air, it ab-
sorbs oxygen, but its oxidation is more  rapidly effected by heating it with caustic
potash.   By a loss of hydrogen and absorption of oxygen precisely  similar to  that
by which wine-alcohol forms acetic acid, it produces a volatile, oily acid, remartoble
as naturally existing in the  roots of the Valeriana officinalis, and being  extra%£d
therefrom by distillation ; it  is lighter than water ;  it boils at 347°, and neutralizes
bases, forming soluble sweet-tasted salts ;  it must be  considered as containing a
radical analogous to acetyl, valeryl, =CioH9 or VI, and its formula  becomes VI.O3
+Aq.
  When  valerianate of lime is heated, carbonate of lime is formed, and a volatile
liquid like  acetone  distils over;  it is termed Valeron, Ci0HgO3 giving  C.O2 and
C9H9O.   The roots of the valerian  contain, besides the valerianic acid, another oil
destitute of active properties.
  By cautiously treating amilic alcohol with sulphuric acid and chromate of potash,
an oily liquid is obtained, which is  Valerianic Aldehyd, C10.H10O2 or Al.O.+Aq.  By
an excess of chromate of potash it  is changed into valerianic acid.
  Treated with chlorine, the amilic alcohol, and the various amilic ethers, as well
as the valerianic acid, give new products, which contain chlorine, and arc constitu-
ted according to the same principles as have been fully  described for wine-alcohol.
                            CHAPTER XXII.

            OF  THE  ESSENTIAL  OILS,  CAMPHORS, AND  RESINS.

  The bodies now to be  described constitute three groups, very closely
allied  in composition, in  properties, and in origin.   For the  most part
they exist ready formed in plants, as secreted by their proper organs, or
they are derived, by reactions of a very simple kind, from  substances so
circumstanced.   They are employed  in medicine for their  aromatic and
stimulant properties, and  in the arts for the manufacture of a variety of
perfumes, varnishes, lacquers, &c.

                  A. Of the Essential or Volatile Oils.
  These oils are so named from their solubility in alcohol, such solutions
being called essences, and  from their volatility.   In virtue of this last prop. 
        PREPARATION,  ETC.,  OF  AMYGDALINE.     569

erty, they are generally obtained by the distillation of the plants with water.
If the oil were extracted by the distillation of the dry plant, the heat would
rise so high as to destroy  its odour and alter its composition ; but. by
using a  large quantity of water, the mixed vapours  of the oil and water
pass over at a much lower temperature, as at 212° ;  for, although the
boiling point of the oil may be 400n, yet  it forms a quantity of vapour at
212° proportional to its tension  at  that degree.  (See p. 78.)  To pre-
vent even  the injurious heat which might  arise from the plant  touching
the  sides of the still, when fragrant flowers or leaves are operated on,
they are suspended in a cage in the centre of the still, and allowed  only
to come into contact  with the vapours.   These oils are somewhat solu-
ble  in water,  and, giving  to it  their odour and taste, form the various
medicated waters.   Hence  often the  same quantity of water  must be
distilled  with fresh quantities of the plant before the oil is in such  pro-
portion as to separate.
  Most  essential  oils, as those of turpentine, lemon, peppermint,  &c,
exist actually  in the plant, as  secretions from  peculiar glands; but oth-
ers  are  produced  only at  the  moment  of distillation, by the decompo-
sition of substances  which did  exist in the plant,  and  which  undergo
a kind of fermentation.   This  is  the case  with the oils  of bitter al-
monds, of spirosa, of mustard, and these oils possess much more active
chemical properties  than  those  of the former  class.  Another impor-
tant difference among essential oils is, that some, by absorbing oxygen
directly, produce well-characterized acids, as occurs in the oils of bitter
almonds, of cinnamon, and of cloves ;  while others, as the oils of tur-
pentine, citron, and copaiva, by  a much more indirect action of oxygen,
give origin to  resins.   On  these principles 1 will arrange the oils in two
classes,  for convenience of description.

     1st Class.—Oils forming  Acids not pre-existing in the Plant.
              Of Amygdaline and  Oil of Bitter Almonds.
  All plants which yield prussic acid  on distillation  produce, at  the same
time, a volatile oil, which is known  as the Oil of Bitter Almonds, it being
most abundantly obtained from that fruit.   The leaves of the cherry-lau-
rel, peach-kernels, &c, also yield it.  The oil and the  acid both arise
from the decomposition of another substance, Amygdaline.   This is pre.
pared by bruising bitter almonds, and pressing them strongly  between
plates of hot iron, to  force out the fixed oil;  the residue is  treated by
alcohol of 93 per cent., and the solution evaporated in a water-bath to
the  consistence  of a  sirup;  this is then diluted with water, and  a  little
yeast added,  which,  by inducing fermentation, destroys a quantity of
sugar.  When this is over, the liquor is to  be again evaporated  to  a
sirupy consistence, from  which the amygdaline is precipitated  by the
addition of cold strong alcohol, in which it is scarcely soluble;  being
dissolved in boiling alcohol, it is finally obtained pure by crystallization.
  The formula of amygdaline is C40H27 • N.O„ ; it forms short silky nee-
dles, which arc anhydrous, tasteless, and inodorous; it is very soluble in
water, and  crystallizes therefrom in large colourless prisms, containing
6 Aq.   By contact with nitric acid it  produces ammonia, oil  of bitter
almonds, benzoic and  formic acids, and  by caustic alkalies it is decom-
posed into  ammonia and Amygdalic Acid, C,0H,bOJ4 + Aq.
  When bruised bitter almonds are distilled with water,  all amygdaline
                                1 C 
570
OIL  OF  BITTER  ALMONDS.
disappears, and a number of products, as  prussic acid and volatile oil,
are evolved.   Pure  amygdaline  may, however, be boiled in water with-
out beino* altered.   It is the animo-vegetal principle which constitutes the
mass of°the cotelydou of the almond  that induces the reaction;  it has
been called  Emulsine, and appears very similar  in  properties and con-
stitution to the vegetable albumen or legumine, described  as the active
principle in the alcoholic fermentation.   (See p. 538.)  The emulsine
is soluble in water,  but  insoluble in alcohol.  If solutions often parts of
amygdaline in 100 of water, and 1 of emulsine in 10 of water, be mixed,
immediate decomposition occurs; the liquor becomes milky, smells of
bitter almonds ; it contains sugar, prussic acid, formic acid, and volatile
oil, and the emulsine coagulates.   It is most probable that the emulsine
is itself also decomposed in this reaction, but we may explain the origin
of these bodies from the amygdaline alone  thus:
            1 equivalent of prussic acid, C2H.N.,  *\

            I     ;;     sv±rle011' gBHT4,l=C4°H--No-once(iuiva-
            J            foffiacid, (2h&  f     ^nt of amygdaline.
            7     "     water,      H7O7,    )
   In the cotelydon of the almond, the amygdaline and emulsine are in
distinct cells, and have no means of acting on each other, but when bruis-
ed in water both dissolve, and decomposition immediately occurs.  The
preparation of the oil by distillation can hence be fully understood.
   The  mixture of  amygdaline and  emulsine has  been employed as a
means of producing  a  prussic acid of standard strength for medicinal
purposes.

             Oil of Bitter Almonds.  Hydruret of Benzyl.
   Prepared by distilling bruised  bitter  almonds  with water.   In this
rough  state it contains a  great quantity  of prussic  acid,  from  which
it  is freed  by distillation with some water, chloride of iron, and  lime.
It is then  colourless, of a strong peculiar  smell, sp. gr. 1*043;  it boils
at 356° ;  when exposed to the air it absorbs oxygen, and forms crystals
of benzoic acid ;  when heated with hydrate of potash, hydrogen  is evolv-
ed, and benzoate  of potash formed.   The formula of this oil is CuH^;
but, from the series  of compounds to which it {jives rise, it is believed to
contain an  organic radical. CuH502, termed Benzyl, and its rational for-
mula is therefore Rz.H.  (See p. 471.)
   Chloride of Benzyl, Bz.Cl., is formed by acting on the  hydruret with
chlorine.    It is  a  liquid heavier than  water;  it boils at  383°;  when
heated with water,  it gradually changes into  benzoic and muriatic acids.
By heating chloride of benzyl with iodide of potassium, Iodide of Benzyl
is formed; and by using the bromide, sulphuret, or  cyanide of potassi-
um, compounds of benzyl with  these electro-negative bodies  may be
formed.
   Amidide of Benzyl.   Benzamide,  Bz.Ad., is formed  by acting on
chloride of benzyl  with dry ammonia, 2(H.Ad.) and Bz.Cl.  give Bz.
Ad. and  Ad.H.  . H.Cl. ;  it forms  rhomboidal  prisms,  which melt at
240°, and  may b.: distilled  unaltered; heated with  potash,  it gives am-
monia and  benzoate of potash.
   Oxide of Benzyl.  Benzoic Acid.— Bz.O.+Aq.   This acid is found
 ready formed in  the  resin of benzoin and in dragon's blood; it some- 
COMPLEX  BENZOIC  COMPOUNDS.         571
times appears in the urine  of herbivorous animals, and is formed by the
oxidation of oil  of bitter almonds and of amygdaline.
  The"following process for  obtaining it pure was devised at the same
time by  Mohr and  Hennell:  1  lb. of benzoin  resin, in powder, is to be
spread on the bottom of a metal dish, eight or nine inches diameter, and
two inches deep, which is to  be covered  with  a drum of blotting paper,
pasted to the edge of the dish;  the whole is to be covered with  a cylin-
drical cap of stout packing paper.   To render the heat uniform, the dish
is to be placed on a metal plate, covered with sand, resting on a furnace ;
heat being  cautiously applied  for  three  or four hours, the cap is  found
full of splendid  crystals of benzoic acid  ; the  empyreumatic oil, which
usually contaminates the sublimed product, being arrested by the  drum
of blotting paper, through which the vapour of the acid passes freely.
   It may also be extracted from the resins by boiling these with lime; a
soluble benzoate of  lime is  produced, from which the benzoic acid is pre-
cipitated by the addition of muriatic acid; it is then to be  dissolved in
boiling water, and allowed to crystallize by cooling slowly.
   Benzoic acid  crystallizes in hexagonal needles; when pure, it is ino.
dorous ;  it reddens litmus feebly ;  melts at 248° ; the fused acid boils first
at 462°,  but it sublimes freely at 293° ; it dissolves in 25 parts of boiling
water, but requires  200  parts  of cold water for its solution ;  it is soluble
in twice  its  weight of alcohol or ether;  it forms a very extensive series
of salts, of which few require special notice.
  Benzoate  of Lime, Ca.O. . Bz.O.+Aq., crystallizes in brilliant prisms ;
at a dull  red heat it  is decomposed into carbonate  of  lime and Benzone,
the formula  of which is C13H50.   Another liquid, Benzin, C12H6, is at the
same  time formed by virtue of a much more complex process, nupthaline,
carbonic acid, and carbonic oxide  being evolved.
  Benzoate of Ammonia. Ad.H20.  . Bz.O., crystallizes in brilliant plates.
This salt is  employed in mineral analysis to separate  iron from manga-
nese ; a solution of  peroxide  of iron, not containing any excess of acid,
beino- completely precipitated by neutral benzoate  of ammonia, while the
salts of manganese are not affected hy it.
  Benzoate  of Silver, Ag.O. . Bz.O., is  obtained  by double  decomposi-
tion ; crystallizes from a boiling solution, on cooling, in brilliant colourless
needles.
  Pormobenzoic  Acid.— H.Bz.+Fo 03.  If water, saturated with the  impure oil of
bitter almonds, be  mixed with muriatic acid and evaporated, this substance crystal-
lizes   The prussic. acid is decomposed into formic acid and ammonia (p. 517), and
the nascent formic acid combines with  the hydruret of benzyl; in this body all the
saturating power of the formic  acid is preserved.
  If a current of  chlorine be passed through a solution of impure oil of bitter al-
monds in  water, a similar body is formed, consisting of benzoic acid  and  hydruret

^Suhkobricloic ,h J.-C,4IL03+S203+2 Aq.  This body is formed  hy the action
of dry  sulphuric acid on benzoic acid.  A viscid mass results, which, when neutral-
iyprl hv hni-vtes vields a salt permanent in the air, crystallizing in  rhomboidal
 nsms* and Wing the formula  C14II,03+S,0-+,Ba.0.+3 Aq.   From, tlrj .the
mire acid  mav  be obtained ; it is decomposed if its solution be boiled, but ulien
evaporalcd it. vacuo it crystallizes.  The sulphobenzoate of copper crystallizes in
large rhombs of anchblue colour                                     .g ^
  Bromobenzou W,, CfcH9 .»    ^„jn'   m        , ,,, .        fusrg at 2iao,
composed by  bromine.   It is a   >     ^^  ^/^^ ^      flf „asp
andI sublimes at 4s    iu J      ai3ti„ation of benzoate of lime. Bczone. C-IUO,
does io!  SmaSy compounds *, but Bcnzin. CUH, produces with sulphuric acid, 
572
OIL   OF  CINNAMON.
nitric acid, and chlorine, a series of bodies, of which the formulae alone  need be
here given ;  they are,
        Sulphobenzide,      Ci2II5 - S.O2.       Chlcrbenzin, Called,;. .
        Sulphobenzidic acid, C^Hj.SjO.,.       Chlorbenzid, C2H3CI3.
        Nitrobenzide,        C12II-.-N.O4.       Azobenzid,   C12H5N.
  I shall have occasion to refer to benzin as a product  of the distillation  of resin
and coal.  It is colourless, of an agreeable ethereal odour; it boils  at 187° ;  its
specific gravity is 0 85 ; that of its vapour is 2378 ;  at 32° it freezes into a crystal.
line mass, which melts first at 43°.
  Oil of Bitter Almonds with Ammonia.—By the action of water of ammonia on hy-
druret of benzyl, all oxygen  is removed,  and a crystalline body, Hydrobcnzamide,
produced ; its formula  is C42HisN2-  Jt is soluble in  alcohol, and by boiling the so-
lution is decomposed into ammonia and hydruret of benzyl.   The nitrogen  here en-
ters into the constitution of the radical, replacing the oxygen, and the body is Hy-
druret of Azobenzyl (C]4H5. |N)+H.   This  azohenzyl is itself also formed in  the
6ame process as the former, and also the Azobcnzoilic Acid (Ci4Hs. |N.) + JN., which
is benzoic acid, in which all oxygen  is replaced by  nitrogen.  The origin  of these
bodies is explained by the constitution  of the radical benzyl, as described in p. 471.
  In the impure oil of bitter almonds a substance exists, termed Bcnzoive, which is
isomeric with the oil, its formula being C1.4H6O2 ; it crystallizes in colourless prisms.
By potash it  gives benzoic acid and hydrogen ; by  ammonia it forms a substance
isomeric with Hydrobcnzamide.   By chlorine it gives muriatic acid, and in place of
chloride of benzyl, a crystalline body, which  is isomeric with that  radical, its  form-
ula being O14H5O2; this is termed  Bcnzo'il:  when heated with potash it gives  the
Bcnzoilic Acid,  which has the formula C24HnOr,+Aq.
  By acting on oil of bitter almonds with a solution of  sulphuret  of ammonium in
alcohol, Laurent has obtained a series of bodies, in which the oxygen of the radical
benzyl is replaced by sulphur, and  in  some cases partly by sulphur and partly by
azote ;  there should thus  be  Sulphobenzyl (CMH5S2), corresponding to the  azoben-
zyl.   It is unnecessary, in an elementary work, to enumerate the  individual sub-
stances, but I look upon their  formation  as corroborating very much Berzelius's
idea,  that the true radical of the benzoic series is the carbohydrogen, Ci4H5, and
that the chloride, &c, of benzyl are really oxychlorides, &c.  (See p. 471.)  Cer-
tainly the element which remains truly constant in  those reactions (and hence sat-
isfies the definition of a radical, p. 467) is C1JI5, and not Ci4H502.

               Oil of Cinnamon and the  derived  Compounds.
  This oil is found in the bark and flower-buds of the laurus cinnamomum  and lau-
rus cassia.   It  is heavier than  water, and possesses the odour of the plant in  the
highest degree.   It boils at 428° ; its formula  is C20H11O2, and for  distinction I shall
term  it the a oil.   When exposed to the air it absorbs oxygen, and forms  another
oil, which is  that generally found  in  the shops, the 8 oil, the formula of which is
C|«HS02.  Two resins, a and 3, are at the same time produced.
        3 atoms of a oil, =C60H33O6, -           f * resin' =°3°U15°4'
                 absorbing          I produce J % re]sm> =°,225°-
        6 atoms of oxygen, =06,     )           P °"'   — Li«H«"a;T n
                                               V 5 atoms water, =H505.
  The 8 oil of cinnamon, although thus only a product of the decomposition of the
true oil, is very important,  from the variety of compounds it gives rise to.   It  is
heavier than water;  it dissolves in water of potash or of barytes, a cinnamate of the
base  being formed, and an oil  lighter  than water separating, 2(C,8Hu02) and H.O.
giving OisHkA- and  C,8HT03.  The properties of this oil indicate that it  contains
an  organic  radical, Cinnamyl, C18II702, united to hydrogen.   It is Hydruret of  Cin
namyl, Ci.H., and the oil lighter than water is  Ci.H3.
  Cwnamic  Acid, Ci.O.+Aq., is formed by  exposing the hydruret of cinnamyl  to
the air; it absorbs two atoms of oxygen, and forms crystallized cinnamic  acid.  It
forms colourless groups of plates of an acid  taste ;  it is almost insoluble in  water,
but easily soluble in alcohol and ether.  It melts at 264°, distils  over at  554° un
changed.  Its salts are exceedingly similar to the benzoates.
  Hydruret of cinnamyl combines directly with muriatic  acid, with  nitric acid, and
with ammonia, forming compounds which are solid and crystalline.  Their formulae
are Ci.H. . H.CL,  Ci.H. . H.Ad., and  Ci.H. .  H.O.+N.O5.   By chlorine  one  half
of the hydrogen of this 8 oil is removed, and a white crystalline body formed, Cig
H4. ChOz.  The chlorine here  enters into the constitution of the  radical. 
OIL  OF   CLOVft*  AND   S P I R & A.            573
   Oil of cinnamon combines with iodide, of potassium and  iodine to form a  «n,h.
 stance which crystallizes 1.1 large needles of a brilliant bronze colour  like Derm™
 ganate of potash   Its lormula is Ci.H.l3+K.I.   Once formed, it is decomposed bv
 water.   It was discovered by Moore, of Dublin, and analyzed by Apiolm
   The origin of the Balsams of Peru and Tolu is closely related to the oiiof cinna
 mon.  I hey consist of resinous substances  (the a and 8 cinnamic  resins i) and of
 an oil which may  be obtained pure by distillation.  It is called Cinnameine •' its for-
 mula is  C,AUOi,  being isomeric with  the 8 oil of cinnamon. It is  neutral • but
 when its alcoholic solution is borled with potash, it forms cinnamate of potash'- or
 by simple boiling of its alcoholic solution, Cinnamic Ether is  produced, and another
 oil, Pcruoine, is separated, the  formula  of which is CigHP02   In these cases three
 atoms of cinnameine  and two of water produce two atoms of dry cinnamic  acid
 and one  of peruvine.
   These researches on the nature of the balsams are due to Fremy; but Richter
 has  advanced that the balsam of Peru contains two oils, which  he terms Mono-
 spermine and  Myroxyline, the relation of which  to peruvine and cinnameine is not
 yet established.
   By the action of an excess of nitric acid, both oil of cinnamon and cinnamic  acid
 are converted into oil of bitter  almonds and  benzoic acid.

                      Oil of  Cloves, Eugenic Acid, t\c.
   The oil obtained by  distillation from the undeveloped flower-buds of the eugenia
 caryophyllata is  a  mixture of several bodies.   By the action of potash, it is separa-
 ted  into  a volatile oil which  does not  possess  active properties, is  lighter  than
 water, and  consists  of OioHg, while a eugenate of potash  dissolves. °From  this
 solution the Eugenic yield is precipitated by  any  strong acid.
   Eugenic Acid.   Heavy OilofClooes, C2tH|50.-., is a colourless oil,  sp.  gr. 1079 ;  it
 boils at 470° ; its taste and  smell are those  of cloves.  It forms, with the metallic
 oxides, well-defined salts, most of which are soluble and crystallizable.
   When the common oil of cloves is kept for some time, it deposites  a  crystalline
 substance, Caryophyllme, C2oH|602;  it is soluble in  alcohol,  insoluble in water.  It
 is volatile.   From water distilled with  cloves a  different body separates in pearly
 scales, having the  formula O-oHuOt.  It is called Eugeninc.
   The eugenic acid and eugenine are rendered blood-red by contact with nitric acid.
   The Light Oil of Cloocs has  sp  gr. =0 918 ; it boils at 287°.

             Oil of Spircea  Ulmaria.  Salicide of Hydrogen.
   The oil distilled from the  flowers  of  the meadow-sweet is a mixture of a light
 and  of a heavy oil, with a solid body like camphor.   The  heavy oil is of much in-
 terest, from  the number of compounds which it forms, and from  our being able to
 form it at will, although from a body, salicine, which has not been found to exist in
 the spiraea.   The  impure oil of spiraea is purified by adding potash, by which the
 light oil is separated, and  Salicide  of Potassium formed, which, when  acted on by
 sulphuric acid, yields the Salicide of Hydrogen pure.
   To form it artificially, equal parts ot salicine and bichromate of potash are to be
 distilled with 2£  parts of oil  of  vitriol and 20  of water.  There is heat evolved  and
 much gas disengaged;  on then distilling, the heavy  oil passes over.   Two atoms
 of dry salicine (C42H2AS),  without any oxygen, might yield  three atoms of oil,
 3(Ci4IT604), and six of water;  but the reaction is far more complicated  in reality,
 as four parts of salicine yield but one of oil.
  The properties of this oil  show it to be a compound of a radical  (Ci4Hj04), Sali-
 cyle,  Syl., with hydrogen ;  it  acts as a hydracid in combining with metallic oxides ;
 its specific gravity  is 1*173 ;  it  boils at 330°.   The specific gravity  of its vapour is
 42G0.  In this and in  coaiposition it agrees with crystallized benzoic  acid,  with
 which it is isomeric.  The alkaline Salicidcs are soluble and crystallizable;  those
 of lead, zinc, and mercury are insoluble.  If a solution of any salicide be mixed
 with a solution of  a sesqui-salt of iron, the liquor assumes a fine purple colour, by
 which the oil is well characterized.
  When  salicide of hvdrogen is heated with caustic potash, hydrogen is evolved,
 and Salicylic Acid, Syi.O., formed ; the potash salt  being  dissolved in water,  and
 muriatic acid added, the new acid is precipitated, and is purified  by recrystalliza-
 tion ; it  dissolves  in boiling water;  it  may be  sublimed,  and condenses  in long
 needles  like benzoic  acid;  it  possesses the usual  acid properties ;  its salts  are
generally soluble, and resemble closely  the benzoates. 
574
OIL   OF  MUSTARD,  ETC.
  By the action of chlorine on salicide of hydrogen, Chloride of Salicyle is formed,
Syl.Ul. ;  it crystallizes in  rhomboidal tables, which melt and sublime undecom-
posed ; bromine and iodine give similar compounds ; with nitric acid it  produces
NUrosalicylic  Acid, Syl.N.04, which crystallizes in long prisms, and unites with
bases forming salts.
  The connexion of salicyl with benzyl is very remarkable ; they contain the same
hydrogen and carbon, Culls, but it is combined in salicyl with 4, and in benzyl with
but 2 atoms of oxygen.  By the action of ammonia on the chloride of salicyl and on
the oil, this relation is more clearly shown, for the  oxygen in  the  radical may lie
brought to the composition of benzyl.   Thus the  Chlorosalicamide  is C42H|5Clj.
06N:2, or, properly, 3(C,4H502 . §N.)C1.;  that  is, (Bz.fN.)Cl.  By the direct action
of ammonia on the salicide of hydrogen, the corresponding (Ci4H502 .  |N.)+H.
may be formed.  To  this new radical, which is evidently Nitruret of Benzyl, the
name Azosalicyl might be given (see p. 572).

                        Essential Oil of  Mustard.

  The oil obtained by distilling the seeds of the sinapis nigra with water is remark-
able for  an unusually complex constitution, as it contains five elements; its  for-
mula being C32H;-oN4 . S305.  When pure, it  is colourless; it boils  at 289°;  ita
specific gravity is 1015 ;  that of its vapour is 3370 ; when acted on by nitric acid,
it yields sulphuric acid and an organic product; with caustic potash  it forms sul-
phuret and sulphocyanuret of potassium, and organic products which have not been
examined.  With ammonia it forms a  substance in large white crystals, the for-
mula of which is C32H2oN4 . Si05+4N H3.  Our knowledge of the chemical nature
of this oil is yet imperfect.   It has been  only established that it does not  exist in
the seeds, being,  like oil of bitter almonds, formed at the moment of distillation.
  The seeds of mustard contain two crystalline substances.  Of these, Sulphosin-
episine is obtained by a process similar to that used for preparing amygdaline.   It
is, when  pure, white;  soluble in alcohol and water;  it contains the same  five ele-
ments as the oil,  which is probably formed from it by the action of the emulsin of
the  seed, as is the case with amygdaline.  The principle of the mustard seed to
which  it  appears to owe most of its pungency has been  termed Sinapisine; its
preparation is complex; it does not contain  any sulphur, and hence can act  but
indirectly in the formation of the  essential oil.  Fremy considers the essential oil
to be formed  by the action of the albumen of the seed  on a  peculiar acid body,
which he terms Myronic Acid ,• but this has not been analyzed, and we do not know
its relations to sinapisine, with which  it may  possibly  be identical.   The formula
given above for the oil is that of Dumas ; Lowig has since analyzed it, and denies
that  it contains  oxygen, assigning to it the  formula  N.Cs . H5S2.   Accurate re-
searches on the constitution of these bodies are very much to be desired.

    2d Class.—Oils pre-existing in the Plant.   Properties not Acid.

  These oils are very numerous, and so similar in properties that a spe-
cial  description is quite unnecessary for each.   They are characterized
by not dissolving in solution of potash, by being lighter than water, and
by a less energetic action on  the animal system than the oils of the first
class.   They combine with muriatic acid to form  heavy oily substances,
in some  cases crystalline.   When put in contact with iodine, they fre-
quently combine with it so energetically as to produce a feeble explosion.
By  chlorine, hydrogen is removed, and an oily liquid, heavier than water,
is produced.   The  oil, as yielded by the plant, consists of two  suhstan-
ces, one solid (Slearoplen), the other liquid (Elaopten);  the former gener-
ally crystallizes when the oil  is long kept.    I prefer to term the  liquid
simply the oil, and the solid portion the camphor of the plant.   We some-
times observe these oils forming the camphor artificially, by contact with
water.
  These oils may be very naturally divided into two groups, according
as they contain oxygen or not.  The following table includes all the  im-
portant facts of the history of the oils (elaoptens) containing  oxygen : 
NEUTRAL ESSENTIAL OILS,  ETC.
575
Plant yitliing ihe oil.
(Jajeput .   .
Lavender   .
Ilosemary  .
Pennyroyal
Uamphor-tree
Valerian
Spearmint  .
Marjoram  .
Asarum .   .
Fennel .   .
Anise  .   .
Peppermint
liue  .  .   .
Olibanum   .
Cumin
0 {J-Z'i
0 896
0 897
0 925
0910
0914
0*807
0997
0 902
0837
0866
0 860
:'17J
397c
365^
395°

518-

354c
446c
323c
418-
(J,olf,t>.
C,-,ll140.
C4,H^)2
OioH(,().
02oH,60.
02nH12O.
03.-,il2,O.

016H9O,
CfflH.iO,
C20H12o;
02,11,002
C„H,,03
C3-,HtoO.
02011,20,
7690

5091
  From the recent experiments of Gerhardt and Cahours, it appears that,
by the action of fused  hydrate of potash, most essential oils containing
oxygen  may be separated into an acid,  and an oil destitute of oxygen.
Some of the  results obtained by those chemists are of great interest;
thus, from the oil of valerian, C20Hl2O.,  valerianic acid is obtained, and
an oil which absorbs oxygen with great  rapidity and generates common
camphor.   The oii of chamomile also yields valerianic acid.
  The oil of cumin (cuminum cyminum), of which the characters have
been given in the table, yields, when treated with hydrate of potash, a pe-
culiar acid, Cumenic Acid, whose formula is 0,011,103+ Aq. ; it is per-
fectly white, crystallizes in fine  prismatic  tables, tastes  sour, fuses  at
197°, and may  be distilled unchanged.   If cumenate of barytes be dis-
tilled at  a dull red heat, a colourless liquid oil is obtained, which boils at
292°; it is termed Cymen; its formula is C1SH,2, being  isomeric with
mesitylene ;  with sulphuric acid  cymen unites, forming Cymcnsu/phuric
Acid, C|SHI2. S206, which forms well-characterized soluble  salts.  By the
action of chlorine and  of  bromine on the oil of cumin, heavy oily com-
pounds are obtained, whose formulas are C20llii. 0.2CI., and C20H„ .  02Br.
  It is evident  that in  these compounds  a radical (Cumyl), C20HnO2, ex-
actly analogous to benzyl, may be assumed, and the cyiiien has the place
of benzin.  The carbohydrogen of the oil of cumin is termed by Ca-
hours Cumen ;  its formula isC2tH,4; its specific gravity 0*860; it boils
at 330°  ; it may be prepared artificially also from common  camphor ;
with  sulphuric acid it forms Cumensulphuric Acid, which resembles com-
pletely the other acids  of that class.
  Tiie stearoptens, or  camphors containing oxygen, will be described by.
and-hy.
  The followin"* table  contains a similar view of the most  important oils
not containing oxygen :
i yielding the Oil.
Citron .   .  •
Copaiva   .  .
Parsley   .  .
Juniper   .  .
Savine.   .  .
Cubcbs   .  •
Black Pepper
Bergamotte .
Turpentine.
0*861
Sp. «r. as liquid. 0-84T	Holing Point "3433
0878	473°
	410°
0839	311°
	315°
0 929	
315°
m
S|i. Kr. ,-u
Vapour.
Circular Polarizing
   Pomr   S
+80° 9', right
+34° 3', left.

—3° 5', left.

—40° 1', left.

+29^ 3', 1'ght.
—43° 3', t-'ft. 
576       ISOMERIC  OILS OF  TURPENTINE.
   Although these oils have all the same per cent, composition, they dif.
 fer in the  formula of their atom, that of turpentine  being C20UI6, that
 of cubebs, C15H12, and all the others being C10E18.   Although, even as giv-
 en in the table, they constitute a remarkable group of isomeric  bodies,
 yet each one  is capable of changing its molecular condition in various
 ways, and  thus  generating other  bodies, still more closely  isomeric, as
 they differ only in their action on  polarized light.   Of these changes
 I shall describe only those of oil of turpentine, which will  serve as an
 example.
   By contact with oil of vitriol, oil of turpentine changes into another
 liquid, which has the same specific gravity both in the state of liquid and
 of vapour, the same boiling point, and the same  atomic weight, but is to-
 tally without action on polarized light.   This new liquid is called Tere-
 bene.  If the oil of turpentine be acted on by muriatic acid gas, it com-
 bines therewith, forming a dense liquid, which is muriate of terebene, and
 which has  no action on light; but another portion of the turpentine unites
 with the muriatic  acid  unchanged, and forms a solid,  which crystallizes
 in fine white prisms, and, from its remarkable odour, is called artificial
 Camphor.   In this solid the oil of turpentine preserves all its action upon
 light, and,  for convenience, it may obtain the name  Camphene, and the
 soiid  is then Muriate of Camphene.   Now if this solid be distilled with
 lime, the muriatic acid  is removed  and an oil obtained,, which differs
 from  camphene only in  having no  action on light, while it differs from
 te re bene in forming with muriatic acid a solid  product.   This oil is
 termed Camphilene, and  the Muriate of Camphilene is distinguished from
 the muriate of  camphene in being  quite destitute of rotatory power.
 From  none of these products can the true oil of turpentine, or camphene,
 be  regenerated.   There are  thus three  forms of oil of turpentine, of
 which two give solid  compounds, and the third a liquid, with muriatic
 acid ;  two  are without action  on light, but the camphene rotates power-
 fully to the left:  with chlorine they all give heavy liquids, all of  which
 have the formula C20H,2CI4, but are distinguished from  each other by their
 action upon polarized light;  the  Chlorcamphene  presenting the anom.
 alous character of a rotatory power  to the right.
  When oil of turpentine is mixed with  nitric acid and gently heated, a
thick and heavy oily substance is produced, apparently by  their  direct
 union, and  may be separated by the addition of cold water.   If, however,
 the materials be left to themselves, after some  time,  violent, almost ex.
plosive action sets in, copious red fumes are given off, and a resinous ma.
terial formed,  which, by boiling with  more nitric acid, dissolves, and the
solution, on  cooling, yields crystals of Turpentinic Acid.  Its composition
 was found by Bromeis to be C14H607 + Aq.   The exact theory of its for-
 matioti has not been as yet ascertained.
  The other oils  of  this class are  capable  of  similar metamorphoses,
which  need  not be specially detailed.
  The type C6H4 exists probably in all essential oils, for it will be seen,
by reference to the former table of oils containing oxygen, that their for.
mula consist in multiples of CJT4, combined with oxygen, or with the
elements of water.

            B. Of the Camphors or Stearoptens of the Oils.
  The most remarkable substance of this class is the common camphor, 
CAMPHOR.---CAMPHORIC  ACID.          577
which is extracted from  the wood of the laurus and dryabalanops cam-
phoru by distillation with water.  In the plant it is mixed with the cam-
phor-oil (C2,lIiG0.), from  the gradual oxidation of which it appears to be
produced.
  Camphor forms a white semitransparent mass, crystallized in irregu-
lar octohedrons.   It is very tough and difficult to powder;  its specific
gravity is 0*986 ; its taste is bitter ;  its odour is well known ; it melts at
347°, and boils at 390°, subliming unaltered ; it  is sparingly soluble in
water, but easily so in alcohol and ether; its formula is C20H,GO2.   The
specific gravity of its vapour is 53*17, which might be considered as form-
ed by one volume of vapour of camphene and half a volume of oxygen
(4776 + ">.">l*3).   Hence  camphor and camphor-oil may be looked upon
as oxides of an oil of the turpentine family.
  When camphor is heated  with  lime, water, and an oil,  Camphron
(GjoUhO.), are produced.  With muriatic acid it  unites, forming a col.
ourless liquid, whose formula is C20Hl7 . 02CI.   By boiling with strong
nitric acid, it is completely converted into Camphoric Acid.
  This acid crystallizes in small rhomboidal tables, which taste sour and
bitter ; it  melts at 145°, gives off water, and leaves the anhydrous acid,
which melts at 423°, and distils  over at 518° without  alteration.   The
formula of the anhydrous acid is  C10H7O3;  the crystals contain an atom
of water.   The salts of camphoric acid are not important, and appear to
differ in properties according as the dry or hydrated acid was employed
to form  them.   The Camphorate of Ether is a dense liquid, which, with
camphoric acid, forms the Camphovinic Acid,  a thick, heavy liquid, which
is decomposed by heat, and forms unimportant salts.
  When camphor is distilled with glacial phosphoric acid, water is form-
ed, and a volatile oil pusses over, having the formula C20H14, and identical
in every respect with the Cymen  obtained from oil of  cumin, as descri-
bed in p. 575.
  When camphor in vapour is passed over hydrate of  potash, heated to
about 700°, an acid is formed,  which has the formula C20H,7O3+Aq.
This Camphoric Acid fuses at  176°, and  boils at 482° ; it may be distil-
led unchanged.  It is insoluble in water, but  dissolves  abundantly in al-
cohol and ether, and crystallizes from these solutions on cooling. When
it is heated with phosphoric acid, a volatile oil is produced, Camphol'en,
having the formula ClsHi6>   When campholeate of lime is distilled, an-
other oily fluid is formed, whose formula is C|9H170.
  Of the camphors of the other volatile oils,  only a few require any de-
tailed notice.   The characters of most of them are given in  the follow.
ing table :
Plant giving the Camphor.
Rose (Otto) .
Parsley  .  .
Iris Florentina
Elicampane .
Asarum  .  .
Fennel  .  •
Anise .  .  .
Peppermint .
Cubebs  .  .
Turpentine .
Sp Gr.
s  Liquid,
1014
1057
77°
70°
108°
104°
 68°
 64°
 91°
302°
550°
552°
530°
428^
430°
406°
3llc
X
4D
5680
5455
C.H.
CI2H704
C4H40.
C7H50.
Ci6H,|04
C20H12O2
UaHnOa
C2] H20O2
C|6H|40.
C2nH2o04 
578
RESINS  OF  TURPENTINE.
  On comparing these formulae with those of  the  corresponding oils
(p. 575), it is seen that the camphors arise from various causes ; in some
cases they are isomeric with the oils, in others  oxides of them, and  in
others hydrates ; thus the camphor of turpentine may be formed at will,
by agitating the oil with water, and then exposing it to cold ; the hydrate
crystallizes out in colourless prisms, sometimes of great size.
  The peppermint-camphor has been found to yield,  by the action  of re-
agents, a series of compounds.   Thus, by the action of glacial phosphoric
acid  or of  oil cf vitriol, a light oil  was obtained, having the formula C21
II,8, which  is termed Menthen.   By the action of chlorine,  a thick, heavy
liquid is produced, C21H14. C1602.   By nitric acid, menthen  yields a heavy
oily liquid, C2|H1609, which possesses acid properties ; and  with chlorine,
menthen yields a sirupy yellow liquid, having the formula  C2|H|3CI5.
  The anise-camphor yields with bromine a crystalline substance, C20H9.
Br302, and with sulphuric acid an oily substance, Anisoine, isomeric with
itself.   By nitric acid it  i.s converted into a body which crystallizes in
long needles, Anisic Acid, C16H605+Aq., which "forms salts with metal-
lie oxides, and gives by farther action the Nilranisic Acid, CI6H5. N.03+
Aq.,and Nitranisid, C20Hi0. N2O10.

                         C. Of the Resins.
  The bodies of this class approach closely to the camphors in compo-
sition and  properties, but are distinguished  by not being volatile without
decomposition, and being generally  capable of acting as acids.   The most
important  will  be first specially noticed, and the properties and formula-*
of the remaining expressed in a table.
  Resins of Turpentine.—The ordinary white resin  coexists, in  the dif-
ferent species of pine, with oil of turpentine, and is obtained by makino-
incisions through the  bark, when  the thick, tenacious turpentine  flows
out.   This, when  distilled with water, gives off the  oil, while the  resin
remains, and is called Colophony.   It  is a mixture of two  resins, which,
though having  the same composition, differ in properties, and are termed
the pinic and sylvic acids.
  The  Pinic Acid is  obtained  by digesting  colophony reduced  to fine
powder,  in cold spirit of sp. gr. 0*865, which  does  not dissolve sylvic
acid.  The solution is to be mixed with a spirituous solution of acetate
of copper  as long  as a precipitate forms.   This Pinate of Copper  is
to be dissolved in  strong boiling spirit, decomposed by a little muriatic
acid, and then  mixed with water;  the pinic acid precipitates as a  resin-
ous powder, which may be dried at a moderate heat.
   When quite  pure, pinic acid is colourless ; it melts at 257°, but be-
comes soft at 149° :  its solution in alcohol reacts  acicl.  It expels car-
bonic acid from bases ; its alkaline salts are soluble ;  its earthy and me-
tallic salts insoluble in water, but many of them soluble in  spirit ; its for-
mula is C40H30O4.
   When a solution of pinic acid in alcohol is long exposed to the air, it
absorbs oxygen and forms Oxypinic Acid, the formula of which is  C40HM
08;  it is a stronger acid than the pinic.  When heated with lime, pinic
acid is decomposed, and three different volatile oils obtained, which need
not be specially noticed.
   The Sylvic Acid remains when the  pinic acid is dissolved hy weak  al.
 cohol.   As it  is not pure, the residue is to be dissolved in two parts  of 
COMPOSITION  OF  RESINS.
579
boiling spirit of 0*865 ;  on cooling, the sylvic acid separates.   By a sec-
ond solution, all the traces of pinic acid may be removed.   The pure syl-
vic acid crystallizes from its alcoholic  solution in colourless rhombic
prisms; it melts at 212° ; it is easily soluble in strong alcohol and in
ether, but insoluble in  water ; its formula is dof^O^   Its salts are ex-
actly similar to those of pinic acid.
   When either pinic or sylvic acids are kept melted for some time, they
become brown, and change into  a resin very sparingly soluble in alcohol,
and possessed of stronger acid properties than either ;  it is termed Colo-
phonic Acid;  it exists  in small quantity  in common resin.
   The resin of the spruce fir has been found by Johnstone to be a  mix-
ture of two resins, which are separated by means of alcohol.   The more
soluble, or A resin, has the formula  C40H3,O6;  the less soluble, or B res-
in, that  of C40H39O3; they both possess acid  characters.
   For the manufacture of tar and pitch, the pine wood containing tur-
pentine  is exposed to a kind of destructive distillation,  in kilns hollowed
out in the ground.   Although a large quantity of the resin flows out un-
decomposed (as colopholic acid), yet  the important components of the
tar are  bodies belonging to a different  series, which  will  be described
hereafter.
   A great variety of resins, of important use in medicine and in the  arts,
exude from trees, either pure, or mixed with  oils,  or  with gums (Gum
Resins), sometimes with benzoic or cinnamic acids, constituting Balsams.
Frequently there  are many kinds of resins  mixed together, but they all
possess  the characters  of fusibility, insolubility  in  water, and of being
dissolved by alcohol, ether, essential oils, and alkaline solutions.  Their
composition is given in the following table :
                                    B.  Sandarach   .  .
Anime Resin  .  .  .  . > r* tj* n
Elemi Resin  .  .  .  . \ °*>H»°-
Fossil Copal  ....   C4oH320.
B. Mastic Resin  .  .  .   C4gH3|02
Anliar Resin  ....   CioHix^
B. Copal Resin   .  .  .   C4oH3,03
Birch Resin.....C4oH3j03
A. Mastic Resin  .  .  .\r> ti n
Copaiva Resin   .  .  . \
A. file mi Resin   .  .  . j c40H32O4
B. Olibanum Resin  .  . )
C. Sandarach ....   C40H30O6
Ammoniac Resin .  .  .   C40H2)O9
B. Assafcetida ....   C40H2SOg
Guiacum......CU5H23O10
                 •  •Jc.oHaiOs
A. Euphorbium   .  !  '. \ C«>H«0«
AsP^»tene.....|C«H«06
A. Olibanum  .... 5
Labdanum.....CjsHssOt
Pasto Resin.....CwH^Og
Sagapenum.....CioH^Og
Scammony.....doH^O-jo
Jalap Resin.....C40H3jO20
Galbanum.....C40H27O7
Dragon's Blood   .  .  .   C40H21O3
Gamboge......C^HaOu
A. Assafcetida ....   C^HosOig
Acaroid Resin ....   CotljoOu
Opoponax.....C40H'sOn
B. Benzoin Resin .  .  .   C40H>2O9
A. Benzoin Resin .  .  .   CjoEtaO?
  A. Sandarach .
  In all this series of resins, it is evident that  the carbon remains unal-
tered, and Johnstone has shown that they may all be eoasidered as deri-
ved from oils having the turpentine constitution = C40H32.
  A  substance which is  connected with the preceding in many ways is
Amber.  This body is found in rounded  pieces, mixed with or attached
to fra"-merits of decomposing wood, in the lignite beds of the north of Eu-
rope.0 It is also found, cast on shore by the waves, along the coast of
the Baltic.   It is yellow, transparent, and often contains imbedded in it
insects and parts of plants, so as to  prove  it to have been perfectly liquid
when first  formed.  It is, in fact, the turpentine of unknown  trees, be-
lon^m"* to  a former geological epoch;  its specific gravity is 1*067; 
580           AMBER,  SUCCINIC  ACID,  ETC.

when heated it melts, and is  then totally decomposed ; its  relations  to
electricity have been fully noticed, p. 108.  Amber is found to be a mix.
ture of two resins, which are soluble in alcohol and ether, a bitumen in-
soluble in those  liquids, a volatile oil, and a peculiar  acid, the Succinic
Acid.   It is used very extensively in the arts as a material  for varnish-
es,  but to chemists  its principal interest is its electrical properties, and
as a source of its acid.
  Succinic Acid is  obtained by the destructive  distillation of amber; it
partly sublimes into the neck  of  the  retort, in discoloured crystals, and
partly dissolves  in  the water  which comes over; by solution in  nitric
acid it may  be freed from the  resinous colouring matters.   It may also
be  obtained from  the amber  by digestion with alcohol or  solution of
potash ;  it hence pre-exists in the  amber, and is not produced  by the
heat.  It is  found in small quantity also in colophony, and is abundantly
produced by the action of nitric acid on the fatty acids, as the stearic or
margaric.
            Succinic  acid  crystallizes, from its  solution  in water, in
          colourless right rhombic prisms, as m, t, a in the figure, which
          have the formula C4H203+Aq.;  when heated to 350° it melts,
          abandoning half its water, and at 450° sublimes in an anhy-
          drous state; its solution in water is  markedly  acid; when
          heated with lime, a volatile liquid  is  produced, Succinone, the
          exact formula of which is not established.
           The salts  of succinic acid are mostly soluble and crystalli.
zable.
  The Succinate of Soda, prepared by neutralizing the acid by  carbon-
ate of soda, crystallizes in doubly oblique rhombic prisms, of which i, u,v
            are primary, and z, n secondary faces in the figure ;  it is per-
            manent in the air, and very soluble in water.  The Succinate
            of Ammonia, which is much used in mineral analysis for the
            separation of iron from manganese, crystallizes in nearly the
            same form as the soda-salt figured above.  The succinates
            of barytes, lime,  and lead are white  powders,  insoluble in
water.   The  Succinate of Manganese  forms rose-red, four-sided pris-
matic  crystals, permanent in  the air, and  soluble  in ten parts  of cold
water.   The Succinate of the Peroxide of Iron is precipitated when an
alkaline  succinate is added to any salt of iron  not containing an excess
of acid ; it  forms a pale brownish-red  powder, insoluble in cold water,
but  decomposed by boiling water, which dissolves out  the  acid with a
small quantity of the iron ;  it dissolves readily in acid liquors.
   The Bisuccinate of Ammonia gives off water when heated, and a white
crystalline solid sublimes, which  is termed Succinamid.  Its formula is
CeH5. 04N.
   The  rare mineral, Mellite  (see p. 498), is only found accompanying
amber in the deposites of lignite.
   Caoutchouc.   Indian Rubber.—This substance, now so much used in
the laboratory for connecting  pieces of apparatus, and  so extensively em-
ployed in the arts, possesses much similarity to the resins.    It dissolves
but imperfectly even in ether, its proper solvent being the  volatile oils,
into which it is converted by distillation.   One of these is the lightest
liquid known, its specific gravity being but 0.654 ; it boils at 92° ; it has
been termed  Faradyn.   Another, known as  Caoulchene, has a specific
 
CONSTITUTION  OF FATTY  BODIES.       581
gravity of 0.842 ; it boils at 340°.  The composition of these liquids,
or of caoutchouc itself, is not well known, as they have-not been, as yet,
obtained absolutely pure; but, so far as I can judge, they appear all to
have the same composition as oil of turpentine.
                        CHAPTER XXIII.

                OF THE SAPONIFIABLE FATS AND OILS.

  The substances of this class are found both in the animal and vegeta-
ble kingdoms very extensively distributed.   In animals, the various fats
are deposited in the cavities of the cellular tissue, but  often also diffused
through the mass of the glandular organs.   In plants, the oils or fats are
generally found in the investing membranes of the seed, or in the cellu-
lar texture of the fruit.  The leaves or roots seldom contain any fatty
matter.   The fats and oils, as they exist in nature, are mixtures of a
few simple fatty and oily bodies in variable proportions, their degree of
consistence depending on the relative preponderance  of the solid or li-
quid constituent.  The greater number of fats consist of two simple fats,
Stearine and Margarine, and a simple oil, Ole'in; but these  three bodies,
which may be considered as the bases of all fats and oils, are accompa-
nied generally  by smaller  quantities of solid or  liquid fats, which are
often peculiar to a particular  animal or plant.  These  fatty bodies are
all fixed; that  is, they cannot be  distilled without  decomposition; but
they are  totally converted by heat into volatile  bodies, undergoing, in
some cases, singular metamorphoses, which will be described in the his-
tory of the individual  fats.
   Exposed to the air, the fatty bodies gradually absorb  oxygen,  and
evolve carbonic acid ; they at the same time obtain an acid reaction, and
a  smell well known as rancid.   Most of this change appears  to result
from minute quantities of azotized organic tissues, which remain inter-
spersed through the fats.   A great number of oils, however, absorb ox-
ygen very rapidly, and, evolving carbonic acid, change into a soft resin-
ous body ; they are hence  termed Drying Oils, and are used so in paint-
ing.  This drying quality is increased by combining the oil with a small
quantity of a base, as  oxide of lead.
   The most important fact in the history of the fixed oils and fats is,
that, by the action of alkalies, they are converted into soaps; whence
the name of saponifiable given  to the class.   By means of the alkali, the
fat or oil is decomposed into an acid, which combines with the base, form-
ing a true salt, which is the Soap, and  a substance  soluble in water, of
a sweet taste, which is the same, no  matter what kind  of  fat had been
employed.  This substance, the sweet principle of the  oils,  or Glycerine,
is united in each fat  with a different acid, and hence, as the fats are best
described as salts of glycerine, I shall  first notice the composition  and
properties of the base itself.
  Of Glycerine.—Ceim+kq.   Eq. 1157*4 or 92*3.  To obtain gly-
cerine, any fatty matter is to  be saponified  by a caustic alkali.    Ihe
solution bein»- decomposed by tartaric acid, which precipitates the fatty 
582   GLYCERINE, STEARIN E,  AND  STEARIC  ACID.

acid, is to be evaporated, and the glycerine dissolved out by strong alco-
hol.   It may also be obtained by saponifying the fat  by oxide of lead,
and treating the watery solution with sulphuretted hydrogen to precipi.
tate some oxide of lead, which dissolves ;  the glycerine may then be ob-
tained  by evaporation.
  Glycerine cannot be obtained solid.  When brought  to its greatest
degree of consistence by evaporation in vacuo over sulphuric acid, it  is
a colourless sirup, sp.  gr. =1*26 ;  it dissolves in water and alcohol, but
is  insoluble in ether;  it is  decomposed by heat.  With nitric acid  it
produces oxalic and formic acids.   Boiled with solutions of copper,  it
precipitates metallic copper.   With chlorine it forms a white flocculent
solid, having the formula  C12H,, .  O10CI3, and with bromine  it gives  a
dense oily liquid, whose formula is C^H,, . O10Br3.
  When glycerine is mixed  with oil of vitriol, they unite  without black.
ening,  and  form an acid compound, Sulphoglyceric  Acid, the formula of
which  is C6H705 . 2S.03 . H.O.   With bases  this  acid forms soluble
salts, having considerable analogy to  the sulphovinates.   The Sulpho-
glycerale of Lime crystallizes in long delicate needles, whose formula is
CGH703 . S.03+S.03 . Ca.O.   The  compounds of glycerine  with  the
fatty acids constitute the various kinds of fats and oils.

                    Of Stearine and Stearic Acid.
  Stearine  is the essential constituent of all solid fats, and  preponder-
ates in  proportion to their consistence.  It is best obtained from mutton-
suet, either by washing it with ether, as long as anything is dissolved,
or by mixing up melted suet with six times its volume of ether, and sub-
jecting the  mass, when cold, to strong  pressure.   In both  cases the stea.
rine remains behind;  it is generally crystalline like spermaceti, not at
all greasy between the fingers, and  is easily powdered ; it melts at 143° ;
it is insoluble  in water and in  cold ether;  it dissolves in  boiling alcohol
or ether, and  crystallizes out  as it cools.   The formula of stearine is
CJ42H141017,  consisting  of
            1 atom of glycerine,    =C6H705,   •,
            2 atoms of stearic acid, -=Ci36Hi32Oio, > =Ci42Hi4iOi7.
            2 atoms of water,     =H202,     )
  By the action of strong bases or of strong acids, it is separated into
these constituents.  A similar decomposition is effected by heat.
   Stearic Acid is obtained pure by saponifying stearine by potash, and
decomposing the solution by means of warm dilute muriatic acid.  The
stearic acid which precipitates is to  be washed with water and dissolved
in boiling alcohol, whence the  pure acid crystallizes, on cooling, in brill-
iant white plates.
   When m'jtton-suet is directly saponified, very troublesome operations
are necessary  to free  the stearic acid from the other fatty acids which
accompany it.
   Pure stearic acid  is  tasteless and inodorous.  It does  not melt below
158° ;  the  melted acid forms a crystalline mass on cooling; it is appa-
rently volatile, and may be distilled unaltered in close vessels; it is in-
soluble in water, but dissolves in hot alcohol ;  the solution reddens lit-
mus ; its composition, when crystallized, is C68H660;+2 Aq.  When heat-
ed  in contact  with lime, carbonic acid is formed, and a volatile liquid,
Stearon, whose formula is C^H^O. 
           MARGARINE  AND MARGARIC  ACID.       583

  Stearic acid is but feeble  in  its action: it expels the carbonic acid
from the alkalies only when the solution is boiling.  It  is bibasic, form-
ing two classes of salts, the Bistearates, which contain one atom of water
and one of fixed base, and the Neutral Stearates, which contain two atoms
of fixed base.  The alkaline stearates are the only salts soluble in water *
they dissolve also in alcohol.  If neutral  stearate of potash be  mixed
with a large quantity of boiling water, it is decomposed, one half of the
potash becoming free, and the Bistearate of Potash precipitating in minute
crystalline scales.  A solution of soap precipitates all earthy and metal-
lic salts, producing insoluble stearates.
   The Stearic Ether is exceedingly remarkable, as it corresponds exactly
to stearine in composition, the glycerine being replaced  by ether.  Thus
its formula is
   1 atom of ether,       =CtH50.,    \
   2 atoms of stearic acid, =C136Hi32Oio, >  Ci40Hi39Oi3=l atom  of stearic ether.
   2 atoms of water,     =H202,     )

   Stearic acid is now very extensively  used for making candles.  The
tallow is saponified by boiling with a thin paste of lime.   The glycerine
is washed out, and the soap being decomposed by muriatic acid, the oleic
acid is removed from the stearic acid by violent  pressure  between folds
of cloth.   The pure stearic acid, when solidifying, assumes a crystalline
structure, which would spoil the appearance of the candle, and  this ten.
dency is removed by the very improper  addition of one  part of arsenious
acid to about 2000 of stearic acid.

                  Of Margarine and  Margaric Acid.

   Margarine exists along with stearine  in  most fats, but is most char-
acteristic of human fat.   It is  prepared from the ethereal solution, which
has left the stearine undissolved.   This  liquor is to be evaporated, and
the residue dissolved in  boiling alcohol, from which the  margarine crys-
tallizes as the solution cools ;  it melts at 118°.   In all  other properties
it resembles stearine, but is much  more soluble in ether and alcohol; it
consists of C74H740,2.
    1 atom of glycerine,      -=C6H705,  i
    2 atoms of margaric acid, =C68H6606, > =C74H740i2, 1 atom of margarine.
    1 atom of water,        =H.O.,    j
   By the action of bases it  is separated into glycerine and margaric acid.
   The preparation of Margaric Acid is precisely similar to that of the
stearic acid, which it resembles very  closely, being most different in its
melting  point, which  is 140°.  On  solidifying, it  crystallizes  in white
needles.  When carefully  heated,  it volatilizes without  alteration.  The
formula  of margaric acid is C^I"!^^ Aq.   If it be mixed with  lime and
distilled, carbonic acid  is produced, which  combines with the lime, and
a volatile substance is obtained, which is termed Margaron.  Its formula
is CjnllagO.  It  is a white solid, of a pearly lustre, which melts  at 170°,
and  forms, on coo.ling, a crystalline mass like spermaceti.  By repeated
distillation with lime, all oxygen is removed as carbonic acid, and a vol.
atile oily substance obtained,  having the composition of olefiant gas.
   The experiments of Redtenbachei* have indicated a remarkable source
of margaric acid in the distillation  of stearic acid.  The  distilled  product,
thouo-h^in appearance unchanged stearic  acid, yet does not in reality 
584
OLEIN  AND  OLEIC ACID.
contain any trace of it, being a mixture of margaric acid, of margarone,
and of the volatile oily carbohydrogen.   The reaction being that
                               ( 6 atoms of margaric acid, C2o4I I204O24,
     4 atoms of hydrated 1        I 1 atom of water,         H.O.,
         stearic acid,    \ produce^ 1   "    margarone,     C^H^O.,
         C272H272O2S,    J        U   "   carbonic acid,   C02,
                               vThe oily carbohydrogen,  C34HM.

  Redtenbacber doubts the real existence of stearone, as none of it is
produced in this reaction.
  The salts of margaric acid  resemble perfectly the stearates in their
properties, but the acid being monobasic, there is but one class of marga-
rates.   The pearly lustre of the crystalline  scales of the margarate of
potash gave occasion to  the name of this  acid, from the word jxapyapt-
tt]s, a pearl.
  If we compare the formulae of the bodies now described, we find them
capable of being expressed by a very simple theory : thus, indicating an
hypothetic carbohydrogen, C34H33, by R., the stearic acid becomes R2 +
05, and the margaric acid, R. + 03, being related as hyposulphuric and
sulphuric acids.  Also, as Redtenbacher  has  remarked, all the results
obtained might be accounted for by ascribing  to margarone the formula
C^HjaO., in which case it becomes R. + O., and the volatile oil may be
R. + H.   Farther researches are, however, wanted to give experimental
evidence on these points.

                      Of Olein and Oleic Acid.
   Ole'in exists in small quantity in the  various solid fats, but constitutes
the great mass of the liquid fixed oils which are not drying oils.   It
holds dissolved, more or less, stearine and margarine, of which the great-
est part may be  separated  by exposure to cold, when they crystallize.
Olive oil contains a large quantity of margarine, and hence freezes very
readily.   The expressed oil of sweet almonds is the purest native olein ;
next to it is rape oil.
   To obtain pure olein, almond oil is dissolved in hot ether, and the so-
lution  exposed to great  cold; the traces of  margarine crystallize  out
completely, and by evaporation  the  ether is  removed.  Olein remains
.iqu/d  at 0° Fah.   In constitution it resembles the solid fats, containing
a peculiar acid, Oleic Acid, combined with glycerine and water.
       1 atom of glycerine, C6H705,  )
       2 atoms of oleic acid, C88H7808, I produce  1 atom olein, C-mHotO^.
       2 atoms of water,   H2O2,    )
   Oleic Acid is obtained by saponifying olein with a strong solution of
potash, then decomposing the oleate of potash by muriatic acid, washing
the oil which separates, and drying  it with chloride of  calcium ; when
cooled below 20° F., it congeals as a mass  of needly crystals.   Its  spe-
cific gravity at 60°  is 0*898;  it is tasteless and  inodorous when pure;
it is insoluble in water, but  abundantly  soluble  in  alcohol  and ether;
these solutions react strongly acid ;  its composition has been determin-
ed by Varrentrapp  to be C^O.+Aq.; its alkaline salts are  soluble,
and form soft masses, destitute of tendency  to crystallize ; they are still
more soluble in alcohol.  The earthy and metallic salts are white, plas-
tery substances, insoluble in  water.   The Oleate of Lead is soluble in
ether, by which it may be perfectly separated from the stearate or mar- 
SEBACIC  ACID, ETC.
585
 garate of lead.   The Oleic Ether was formed by Varrentrapp by passing
 muriatic acid ga.s into a solution of oleic acid in alcohol.   It  is a colour
 less liquid, sparingly soluble in alcohol, lighter than water, but heavier
 than alcohol, from which it is deposited  as it  forms;  its  formula  is
 C^HyA+Ae.O.
   When oleic acid is distilled, a portion of it passes over unaltered, but
 the  greater  part is decomposed, and some charcoal remains in the retort.
 The distilled products  are Sebacic Acid  and  a liquid carbohydrogen,
 isomeric with olefiant gas ; sebacic acid is not produced by the distilla-
 tion of any other fatty substance than oleic acid, and hence may be con-
 sidered as characteristic of it.  The decomposition consists in  that

           ........    .,          f 1 atom of sebacic acid,   C0H9O4,
   2  atoms of hydrated oleic acid, >    d   J 3 atoms of carbonic acid, C306,
           UisHboOio,           J v      "S carbohydrogen,          C71H7i,
                                       V residual charcoal,       C4.
   Sebacic Acid had been considered as a product  of the destructive dis-
 tillation of all fatty bodies ;  but it has  been shown  by RedtenbaCher to
 arise only from  oleic acid ;  the distilled product  is to be washed with
 boiling water, which dissolves the sebacic acid ; on the addition of ace-
 tate of lead, a white precipitate is obtained, which, being decomposed  by
 sulphuretted  hydrogen, gives sulphuret  of  lead, while the pure sebacic
 acid dissolves, and may be obtained  crystallized by the evaporation and
 cooling of its solution.
   The crystallized sebacic acid closely resembles the benzoic acid  in
 properties  and  appearance;  its  solution  reddens  litmus; its  alkaline
 salts are very soluble ;  its lead, silver,  and mercury salts are insoluble
 in water ; from a strong solution of an alkaline  sebacate, the acid is pre-
 cipitated in  voluminous crystalline  flocks on  the  addition of  a stronger
 acid.   When completely pure, the sebacic acid is  totally without odour,
 the  strong smell of heated oil being  due to the formation of a totally dif-
 ferent  substance,  Acroleon.   The  dry sebacic acid  has  the   formula
 C10tf 03;  when crystallized it becomes C10HsO3+Aq.

   Of the Action of Nitric Acid on Stearic, Margaric, and Oleic Acids.

  By the gradual oxidation of those fatty acids, a series of  bodies result, which
 have so much connexion with each other as to be most conveniently studied in  re-
 lation to their origin.
  A. If stearic  acid be digested with two or three times its weight of common
 aquafortis at a moderate heat, a very lively action commences  after some time, and
 copious red fumes  are given off.  When the mixture has ceased  to froth up, and
 the action of the acid ceases, the only product forms a colourless layer on the sur-
 face  of the acid liquor, and is found to be pure Margaric Acid.  The change here is
 evidently a simple oxidation, as R2+O5 and 0. give 2(R.+03), as described in p. 584.
  If  the fatty acid be acted  on by successive quantities of the nitric acid until it
 disappears, the watery liquor deposites, on cooling, abundance of crystallized Suc-
 cinic  Acid, and the mother liquor of these crystals  being  evaporated  to  one half,
 forms, on cooling, a thick mass of crystals, which may be washed with cold  water,
 and being purified by recrystallization, are found to be identical with the acid form-
 ed by the action of nitric  acid on the peculiar woody tissue which exists in cork,
 Suberinc, and which will be hereafter described.   This acid is termed the Suberic
Acid; it  is white, inodorous, and of a feebly acid taste ; easily soluble in alcohol
and water ; the crystals melt at 248°, and when heated more strongly, are decom-
posed in great part; it precipitates solution of acetate of lead ;  its alkaline salts are
soluble  and crystallizable ; when crystallized, the formula of the acid  is C.*H603+
Aq.  The Suberic  Ether was prepared as described above for the oleic ether; it
is liquid, and its formula is  C,H603+Ae.O.  By the  distillation of the  suberate of
lime, a  volatile liquid, Suberone, is obtained, whose formula is C7H60.
                                   4E 
586      PIMELIC,   ADIPIC,  LIPIC  ACIDS,   ETC.
  The artificial formation of the succinic  and suberic acids in this way is exceed-
ingly curious ; but Bromeis and Laurent, to whom the observation is due, have not
been able to trace the precise reaction in which they originate.
  B. The action of nitric acid on oleic acid is much more violent than on the stearic
acid.   Among the products of the reaction are found the succinic and suberic acids,
but in addition, four other acid bodies, of which, however, a very slight notice will
suffice.
  The Pimelic Acid forms white crystalline grains, which melt at 273°, and sublime
easily in brilliant needles ;  its alkaline salts  are soluble, but its earthy and metallic
salts insoluble in water ; the formula of the acid is C7H603+Aq.
  Adipic Acid resembles closely the  former; it dissolves  in water, alcohol, and
ether ; melts at 223° ;  it sublimes in very beautiful crystals ; its  formula is CMH9
07+2 Aq., it being a bibasic acid.
  The Lipic  and Azoleic acids are still less  important, and our knowledge of their
constitution very  imperfect.  All these bodies are obtained from the mother liquors,
from which the succinic and suberic acids  have crystallized.
  The most important products of the action of nitric acid on oleic acid, or on olein,
are Elaidine and the Ela'idic Acid; these bodies are of pharmaceutic interest, from
their constituting the  Citrine Ointment, or Unguentum Nitratis Hydrargyri of the
Dublin and London pharmacopoeias.
  Elaidine is prepared by the action of nitric acid, or, still better, of the red fumes
of the  nitrous acid on  ole'in ;  the oil gradually becomes thick, and  finally congeals
into a butyraceous mass of a deep yellow colour.  By  digestion with warm alcohol,
a deep orange-red oil is dissolved  out, and the pure elaidine is obtained  perfectly
white;  it melts at 97°, is  insoluble  m water, and but sparingly  so in alcohol;  it
dissolves readily in ether ;  with caustic alkalies, it saponifies completely, glycerine
being set free.  The whole action of the  nitric acid in this reaction is exerted on
the oleic acid, and the  elaidine is a true  fat, consisting of ela'idic acid  united to
glycerine.
  Elaidic acid may be prepared by saponifying elaidine, and decomposing the alka-
line elaidate by a stronger acid, but it is obtained  in a much purer form by passing
nitrous acid fumes, generated by heating nitrate of lead (p. 276) into pure oleic acid,
prepared from oil of sweet  almonds ;  after some time, the liquid  becomes a nearly
solid mass of crystalline plates, of a fine yellow colour ;  this mass is to be boiled in
water to remove adhering nitric acid  ; then dissolved in boiling alcohol, and allowed
to cool.  The orange-red oil remains in solution, while the  elaidic acid crystallizes
in large, brilliant, white rhombic tables.   This body, when pure,  fuses at 113° ; it
dissolves readily in alcohol and  in ether ;  these solutions  redden litmus ; when
boiled with a solution of carbonate of potash, carbonic acid is expelled, and elaidate
of potash formed;  its earthy  and metallic salts are insoluble in water.   The crys-
tallized elaidic acid has the formula C72II66O5+2 Aq. ;  it is a bibasic acid. The
Elaidate of Silver is hence C72H6603+2Ag.O.;  and the Ela'idic  Ether, which is a
colourless fluid lighter than water, consists of C72H6605+H.O. . Ae.O.
  The orange-red oil, which is formed simultaneously with  the elaidic acid, has not
been, as yet, accurately examined, and hence we cannot explain by precise formulae
the mode in which these  bodies  are generated.  It  is this oil which  gives to the
Citrine Ointment its characteristic colour  and smell; it is  lighter than water, and
dissolves in alkaline liquors, but does  not form true soaps.
  In the formation of citrine ointment, the conversion of the olein into  elaidine is
effected by  the nitrous acid which the solution of the mercurial  salt always con-
tains, it being formed by the deoxidation of the nitric  acid,  and there being no heat
used to expel it.  The  subnitrate of  mercury is then  mechanically mixed with the
elaidine and with the yellow oil.   Some of the mercurial salt is often  decomposed,
however, as metallic mercury may usually  be  detected interspersed through the
ointment.
   Both oleic and elaidic acids  give origin, when heated with fused hydrate of pot-
ash, to  a peculiar fatty  acid, discovered by Varrentrapp ; it is white, solid, and crys-
talline ; melts at 144°,  and has the formula C32H3o03+Aq   There is formed, at the
same time, a large quantity of acetic acid.   Another point  of connexion between
the oleic and elaidic acids  is,  that by distillation both  furnish sebacic acid
   The  Acroleon, to which  is due  the  exceedingly sharp and disagreeable smell of
highly  heated oil or fat, is  generated  by the  decomposition  of the  glycerine and in
 isuch exceedingly small quantity, that its isolation has not yet been successfully at-
 tempted.  According to the observation of Brandes, it is a colourless oil, of sp gr 
ACTIO.N  OF  SULPHURIC ACID  ON  MARGARINH, ETC.  587
0 578, which, when distilled with caustic soda, becomes inodorous, while the soda
combines with a fatty acid ; no analytical investigation of it has been as yet made.

           Action  of Sulphuric Acid on Margarine  and Oleine.

  When olein is mixed with oil  of vitriol, the sulphuric  acid combines with both
the glycerine and the oleic acid, forming sulphoglyceric and sulpholeic acids.  This
last is soluble in  water, but insoluble in dilute sulphuric acid ,  and hence, by adding
water gradually to the mixture of oil of vitriol and oleine, it separates, floating as a
thick sirup  on the surface, while the sulphoglyceric acid and the excess of sulphuric
acid  dissolve.   The sulpholeic acid thus obtained forms, with lime and barytes,
soluble salts, which are analogous to the sulphovinates ; when its  solution in water
is heated, it is decomposed, sulphuric acid becoming free, and the oleic acid being
converted into two acids, which  have been named the Mctaolcic and the  Hydrolc'ic
Acids.
  These acids are both liquid like oleic  acid ;  they are principally distinguished, as
to properties, by the sparing solubility of the former in alcohol, and are thus separa-
ted.  The  constitution of  these  bodies had been examined  by  Fremy at a time
when the true constitution of the oleic acid had not been established, and the formu-
lae he assigned to them are not now admissible. They are isomeric with each other;
when distilled, they produce carbonic acid, and two volatile liquids, Olein and Ela'en,
which are isomeric with olefiant gas.   From the circumstances of the formation of
these acids, the change must consist in the fixation of the elements of water, as no
other body containing carbon is  produced ; but, from his analysis,  the anhydrous
inutaoleic acid has evidently the same composition as the hydrated  oleic  acid, and
its formula is therefore C44H40O5 when in combination, and C44H4i06 when free.  Its
decomposition by heat consists  in the separation of 3C.O2, and  C4iH4i remaining,
which contains the  elements of the two volatile oily  liquids.
  With margarine, oil of vitriol  does not  combine directly ;  but  if margarine and
olein together, as they are in olive oil, be mixed with oil of vitriol, union occurs,
and a sulphomargaric acid is produced, which, being treated similarly to the sulph-
oleic acid, gives two other acids, the Mctumnrguric and Hydromargaric.   These
are soluble in alcohol, from which they crystallize by cold,  so combined as to pro-
duce distinct salts,  and to affect  all the characters of an independent acid, called by
Fremy the Hydromargaritic.
  If the mixed solutions of sulphomargaric and sulpholeic  acids be left to decom-
pose without heat,  in place of being boiled, the metamargaric and metaolei'c acids
separate and float  on the top, but the  hydromargaric and  hydrolc'ic acids remain
dissolved, and separate only by bringing the solution  to boil.   Each of the products
thus obtained is  to  be dissolved in alcohol, and the modified margaric acids crystal-
lize on cooling, while the modified oleic acids remain dissolved.   The metamarga-
ric  acid is polymeric with the margaric  acid ; its formula is C6sH66C»o+2 Aq., but
the hydromargaric acid  contains the elements of four atoms of water more, its
 formula being CGsII7oOio+2 Aq.

                         Olein  of the Drying Oils.

  The oils which possess the property of rapidly absorbing  oxygen and evolving
carbonic acid, thereby being changed into a kind of transparent  resinous varnish,
consist of  glycerine united to a liquid acid, quite distinct  from  the ordinary oleic
acid; treated with nitric  acid, it yields first a resinous substance, and then oxalic
acid.'  The drying properties of these oils is known to be much increased by boiling
on litharge of which  a quantity dissolves ; in this case, however, Liebig has shown
that no saponification occurs ; the litharge serving only to combine  with, and coag-
ulate a quantity  of vegetable mucus, which, being diffused through the oil, prevented
its acting as rapidly on the air as it does when pure.

                   Of Cocoa-tallow and  Cocoa-stearic Acid.

  The albumen of the cocoa-nut contains a  solid fat, which is extracted from it,
and imported largely into these countries, to be used in the manufacture of candles.
It i* a mixture  of ordinary olein with  a stearine, which contains a peculiar acid.
The olein and stearine are separated by pressure or  by ether,  or by solution in boil-
im*  alcohol, from which the stearine  crystallizes on cooling, exactly as described for
ordinary stearine.                                              .         .
  The cocoa-stearine is white and crystalline ; its specific gravity is 0 925 ; msolu- 
588         PALMITINE, PALMITIC  ACID,  ETC.

ble in water; it. dissolves but sparingly in alcohol, except when boiling ;  it is moro
soluble in ether ;  it melts at 77°.  The products of  its decomposition by heat have
not been well examined. ' With caustic  alkalies it  forms soaps, from which, by a
stronger acid, the cocoa-stearic acid is separated.
  This acid, purified by repeated crystallizations from alcohol, is brilliant white ; it
fuses at 95°,  and  cannot be distilled without total decomposition.   Its formula was
found by Bromeis to be C27H2603+Aq.; its alkaline  salts are soluble, but the earthy
and metallic salts are insoluble in water.   By the process described for oleic ether,
the cocoa-stearic  ether was prepared by Bromeis ; it is a clear oil,  lighter than w,*
ter ; its formula is C27H2603+Ae.O.

                       Palm Oil and  Palmitic  Acid.
  This solid oil, which is now extensively employed in the manufacture of yellow
soap, is prepared in Africa, by pressing and boiling the fruits of the  cocos butyracca
or of the avoira elais;  it is of the consistence of butter, reddish-yellow colour, and
an aromatic odour.  When kept, it acquires a  rancid smell,  and becomes white;
the colour results from a small quantity of a substance which may be decomposed,
and the palm oil  bleached  by chlorine or any oxidizing agents.  Besides ordinary
oleine, this oil  contains a  peculiar stearine, Palmiline, which has been accurately
examined by Fremy and Stenhouse.
  Pure Palmitine melts at  118°, and  is crystalline.   It is insoluble in water, very
sparingly soluble even  in boiling absolute alcohol, but abundantly soluble in ether.
It is quite neutral; when saponified by potash, and the soap decomposed by an
acid, palmitic acid is set free.   The palm oil of commerce usually contains a large
quantity of free palmitic acid, and hence is more easily saponified than  any other
fat; it also contains free glycerine, so that the palmitine would appear to undergo
a spontaneous decomposition.
  Palmitic Acid melts at  140° ; it dissolves in hot alcohol, and crystallizes therefrom
by cooling.   Its formula in crystals is C64H6206+2H.O.;  it  is a bibasic acid; its
silver salt is C64H6206+2Ag.O.  The Palmitic Ether, which  may be prepared by
heating palmitic acid with alcohol and oil of vitriol, is solid, and crystallizes in fine
prisms,  which melt at 70°, and have the formula  C&JH6206+2ACO.   By distilla-
tion, the palmitic  acid is not altered ; by the action of chlorine, hydrogen is removed
from it, and an  acid containing chlorine produced, the formula of which appears to
be C64H54 . C1806.
  The constitution of palmitine was found by Stenhouse to be expressed by the
formula C70H66O8, from which should follow, that the substance united with the pal-
mitic acid is  formed of C6H402, and hence differs from common glycerine,  C6H7O5,
in having lost the elements of three atoms of water.  This would be a very impor-
tant fact to reinvestigate.

                     Nutmeg  Butter.    Myristic Acid.
  This substance is a mixture of an aromatic volatile oil, with three fats, of which
two are easily  soluble in alcohol, and are  thus simply separated from the third,
which has been termed by Playfair Myristicine.  Of the fats soluble in alcohol, one
is liquid and the other solid ; but we do not know whether they are peculiar, as the
analyses of Playfair have been confined to the third.
   Pure myristicine is obtained by crystallization from its ethereal solution ; it has
a silky lustre, and melts at 88°.   When  saponified, it yields glycerine and  Myristic
Acid.   This substance is snow-white and crystalline, easily soluble in hot alcohol,
and then  reddening litmus;  it melts at  120°;  its composition is expressed by the
formula C2sH2703+Aq.; its salts are very well characterized and  crystallizable.
The Myristic Ether is analogous in constitution to  the stearic ether (583), consist-
ing of
  Two atoms of myristic acid,  =C56H5406, )
  One atom of ether,          =C4H50.,   } One atom of myristic ether, CeoHeoOg.
  One atom of water,          =H.O.,    )
   The myristicine was found by Playfair to have the  formula C)lsH1I30i5,  consist-
ing of
             Four atoms of myristic acid, =-=C1PHio80i2, )
             One atom of dry glycerine,  =CGH402,    } C„8H1I30,5.
             One atom of water,          =H.O.,      )
   Bv distilling myristicine, much acroleon is generated, but no sebacic acid. 
BUTYRINE,  CAPROINE,   ETC.             £89
          Ordinary  Butler.   Butyric,  Capro'ic, and Capric Acids.
   Jutier is a mixture of six different fats, viz., common stearine, margarine, and
 iteine, with butyrine, caproine, and caprine; by meiting the butter, and keeping it for
 some days at a temperature of 68°, the stearine and  margarine crystallizerwhile
 the others remain liquid.  By means of alcohol, the oleine  is then separated fiom
 the other fats, which are  more easily soluble in that menstruum ;  their farther pu-
 rification depends on  successive solutions  in alcohol, but none of them can be con-
 sidered as having been obtained completely pure.
   Butynnc is a colourless  oil, with the odour of heated butter.  It solidifies at 32° ;
 with  alkalies, it gives a soap, and sets glycerine free.  Its elementary composition
 is not known.
   Caproine and Caprine cannot be obtained sufficiently free from butyrine, or from
 each  other, to be described.
   When butter is saponified,  and the soap decomposed by tartaric acid, stearic,
 margaric, and oleic acids separate, while the other acids remain dissolved. On dis-
 tilling this liquor, the butyric,  capric, and capro'ic  acids pass over along with the
 <vater, and, being neutralized by barytes,  the three barytic  salts are separated  by
 repeated crystallizations.  Of these acids, the history of the Butyric Acid is most
 complete.  It is  a clear, oily liquid, of a penetrating, sour smell of rancid butter ;
 tastes pungent  and  acid, and  leaves a white  mark on the tongue.  Its specific
 gravity is 0 976;  its  boiling point  is above 212° ;  it burns with a brilliant  white
 flame, and  is  abundantly soluble in water, alcohol,  and  ether.   Its  formula is
 C7Hc03+Aq. ;  when  distilled with lime, it gives a neutral volatile  liquid, Butyrone,
 whose formula is C6H60.  The Capro'ic Acid agrees in  properties closely with the
 butyric acid, but  has  a characteristic odour of sweat;  its formula  is Ci2H903—Aq.
 The Capric Acid crystallizes in  fine needles, which melt at 66°, and have the for-
 mula  CisHi403+Aq.

              Of Fish Oils, Delphinine, and Delphinic Acid.
  These oils are generally composed of ordinary margarine, stearine, and oleine;
 but some, as  whale  oil and dolphin oil, contain a peculiar fat, Delphinine, which
 yields Delphinic Acid.   From the fish oil  the delphinine is extracted by cold alcohol,
 which dissolves it more readily  than the other oils; it is liquid, of specific gravity
 0 954; it is not acid, but  becomes so by exposure to the air ; it saponifies readily.
 From the soap, the delphinic acid is separated by tartaric acid, and may be obtained
 pure by distillation.   It is a  thin oil, of  specific gravity 0-932; it boils above 212°,
 and distils unchanged; it has a peculiar aromatic smell; tastes acid, and reddens
 litmus strongly ; it dissolves  in twenty parts of water ; its formula is Ci0H9O3+Aq.,
 and when distilled with lime, it gives a volatile  neutral liquid, Dclphinon, C9H90.
  The delphinic acid  has been found in the berries of the viburnum opulus, and its
 composition being the same,  and its properties very closely resembling those of the
 valerianic acid, I think it very likely that a re-examination of it would demonstrate
 its identity with that remarkable vegetable acid.

                      Of Castor Oil and its Products.
  The oil of the  ricinus communis (castor oil)  is, according to Lecanu and Bussy,
 a mixture of three fats, ricino-stearine, ricino-oleine, and ricine, which are all easily
 soluble in alcohol.  Like the fats of butter, they can be but imperfectly separated ;
 but, when saponified, they yield acids, which can  be more  accurately examined:
 the soap, being decomposed by muriatic acid, yields an oil, from which, by cooling,
 the hicino-stearic Acid crystallizes, and the remaining oil, when distilled, separates
 into the Rkinic Acid,  which passes over, and the Ricin-oleic Acid, which is not vol-
 atile.
  Purified by  recrystallization  from alcohol, the ricino-stearic  acid forms  pearly
 scales, which are  easily soluble in alcohol, redden litmus, and do  not melt below
 266°.   The ricin-oleic acid freezes a  few degrees below 32°.   The ricinic acid  is
 solid and crystalline, melts at 71°, and distils unchanged at a temperature but little
 higher.
  When  castor oil is acted  on by nitrous acid, it  is converted into a solid sub-
stance, termed by Boudet Palmine; it is  white, of a  waxy appearance, and melts at
151°; it  is  easily soluble  in alcohol  and  ether; with  alkalies, it yields glycerine
and Palmic Acid.   We do  not possess any knowledge  of the elementary composi-
tion of these bodies. 
590
MANUFACTURE  OF  SOAP.
   The products of the complete oxidation or castor oil by nitric acid have been ac-
 curately  examined  by Mr. Tilly.  The action is violent, and much nitrous acid
 fumes are  given off.  Besides suberic and lipinic acids, a peculiar fatty acid is
 formed, which is colourless, of an agreeable smell, and a sweet, stimulating taste ;
 it boils at 300°, but cannot  be distilled without being in great part decomposed.
 Its formula was found to be Ci4Hi303+Aq. ; he formed the ether of this acid  in the
 way described for oleic ether, and ascertained its formula to be 0|4Hi303+Ac. 0. This
 body is termed the Pcrcenanthic Acid, as it contains the same carbon and hydrogen
 as the cenanthic acid which exists in wine, as described in page 567, but combined
 with an atom more of oxygen.

              Oil of Tig Hum.   Crotonine.   Cro tonic  Acid.
  The experiments that have been made on this oil have not given very satisfac-
 tory results: by saponification, it  yields an acid which is  exceedingly volatile ; but
 whether the active properties of the oil reside in this crotonic acid is not estab-
 lished, nor have any analytical results been obtained as to its constitution.

               Of the Manufacture of Soaps and Plasters.
   Although the general principles of the  constitution  of soaps have been
 frequently alluded to in the description of individual fatty substances, and
 a detailed account of their manufacture would be out of place in  the pres.
 ent  work, yet it  may not be uninteresting to  notice briefly some cir-
 cumstances of the processes employed, which could not be  deduced from
 the mere theory of their nature, and yet are  essential to practical success.
   There are found in commerce three varieties of soap : 1st, hard while
 soap, which is made from tallow and  caustic soda ; 2d, hard yellow soap,
 which is made'from soda  with tallow, palm oil, and resin ; 3d, soft  soap,
 in winch the alkali is potash, combined with whale or seal oil, and some
 tallow.  The difference of consistence depends principally upon the al-
 kali ;  as the fatty salts of soda unite with water to form true hydrates,
 which are completely solid, while the potash salts absorb water, and form
 a semitransparent gelatinous mass, such as is the ordinary soft soap.
   For the preparation of the hard white soap, a solution of caustic soda
 is prepared, of specific gravity  1*050, by decomposing soda-ash by the
 proper quantity of lime ;  the soda-ley being brought to boil, the tallow
 is added in small portions at a time, until the free alkali has  been all
 combined with fatty acids, and the ley will  saponify  no  more.  The li-
 quor contains then free glycerine, and the fatty salts of soda, all dissolved
 together in the water; and as the soap scarcely crystallizes, a  peculiar
 method is  necessary to separate it from  the solution.  This is founded
 on the fact  that soap is insoluble in a solution of common  salt.   If to a
 solution of  soap in water, as much common salt be  added as the water
 can  dissolve, the  soap is  separated, and floats  on  the surface of the li-
quor completely  deprived  of water.   But this  is not the state in which
the manufacturer  wishes it to be.  Hence the salt is added  but gradually
to the soap-ley, and the water then dividing itself between the  sal*  and
the soap, a  point is obtained at which the soap  is in its proper live!rated
condition, and this being  recognised  by the  appearance of the boil  and
the texture of the layer of soap, the latter is run into wooden boxes, where
it congeals, and is then cut by a  wire  into the forms it has in commerce.
  The hard white soap thus made generally contains from forty to fiftv
per cent, of water.   When very hard it  still  retains above thirty, and
may hold seventy per cent, without being very soft.
  The formation  of the  Yellow, or Resin Soap, depends on  the direct
combination of an acid resin (colophony,  p. 578) with soda.   In  this 
SPERM ACET I.--E T H A L.
591
case no glycerine is set  free, as  there is no proper saponification.   A
mere compound of resin  and soda would be, however, too soft, and also
act too powerfully on clothes ; and hence there is always  a quantity of
fat added, generally  tallow, and  some palm oil, which brightens the col-
our, and musks tbe disagreeable  odour of the resin.   A good soap should
contain two parts of fatty matter to one of resin.
   The Soft Soap is manufactured by heating  the oils  in shallow pans,
and gradually adding a strong solution of caustic potash, boiling and con-
tinually agitating the mass until the  milkiness  produced by the oil van-
islies, tbe  mass  becomes  transparent, and the  froth subsides.   As this
soap cannot be separated  from the liquor by the addition of common salt,
which  would decompose it, forming a soda-soap and chloride of potassi-
um, the liquor is evaporated until the operator  recognises that it has at-
tained  the  proper strength, and  it is-then cooled as  rapidly as  possible.
The glycerine of the oils exists, therefore, mixed through the substance
of the  soap.   To  give it  greater consistence,  some tallow  is generally
employed ; and the stearate of potash crystallizing  gradually, forms the
white points which  are seen in most specimens of soft soap.
   Plasters are metallic soaps.   Of these, the  only one  of pharmaceutic
importance is the Litharge Plaster, prepared  by boiling litharge, olive oil,
and water  together ;  oleate and margarate of  lead are formed, and float
upon the surface ; when  the  mass has obtained the  proper  consistence,
it is removed, and formed  into rolls for use.   The  watery  solution con-
tains glycerine and a large quantity  of oxide of lead dissolved.   If lith-
arge plaster be  digested in ether, oleate of lead dissolves, and  the mar-
garate of  lead is left behind.

             Of Spermaceti, Elhal, and the derived Bodies.
   Spermaceti exists in the cavities of the head of the  physeter macro.
cephalus, and some allied  species of whales, dissolved in the spermaceti
oil, from which  it separates by crystallization  alter the death of the ani-
mal.   To  obtain it pure,  it is to be crystallized repeatedly from its alco-
holic solution by cooling ; it is a remarkably beautiful crystalline fat,
melting at 120°, and  volatilizing at 680° without change, if the  air be
excluded.   By  boiling with very strong  alkaline solutions, it gradually
saponifies,  a margarate and  an  oleate being  formed ;  but. in  place of
glycerine,  a peculiar base, which  is termed Elhal, being set free.  To
obtain  it  pure,  spermaceti  is  saponified by  being fused  with  half its
weio-ht of potash ;  the resulting mass being digested  with water and mu-
riatfc acid, the oily acids and the ethal separate from the liquor and float
upon the surface.   Being then mixed with lime, which combines with the
oily acids,  and boiled in absolute alcohol, the ethal dissolves, and crystal-
lizes out on cooling.
   It is a  solid  crystalline white  substance, destitute of taste or smell;
neutral to  test paper ;  it  melts at 119°, and volatilizes  rapidly at 250° ;
it is insoluble in water ; its formula is C32H3402, or C^I"^©^ Aq.  The
spermaceti itself consists of
       2 atoms of margaric acid, -^sHr-Os, ) c^H.^O,,-, one equivalent
       1 atom of oleic acid,      — Xu  n' (      of spermaceti.
       3 atoms of ethal,         =Ce9tli02O6, )
   The ethal is remarkable for its analogy, in composition and properties.
to the  bodies of the alcohol group ;  like  them, it may be looked upon as 
592 WAX,  CERINE, MYRICINE, AND  TARTARIC ACID.

formed of water united to a carbohydrogen, isomeric with olefiant gas,
and by distilling ethal with glacial phosphoric acid, this  body is actually
obtained, and has been  termed Cetene.   It is an oily liquid, colourless,
soluble in alcohol and ether ; it boils at 527°.   From its reactions and
the specific gravity  of its vapour, 7846, it results that its  formula  is

  If ether be heated with perchloride of  phosphorus, a heavy liquid  is
obtained, having the formula C32H33Cl. ; and by fusing ethal with potassi.
urn, hydrogen is evolved, and a white solid substance formed, consisting
of QbUjbO. + K.O., which, with water, gives hydrate of potash and ethal.
With sulphuric acid  ethal forms sulphoethalic acid, which resembles the
sulphovinic  acid, and   has  the formula  C^H^O. . S.03+S.03 . II.O.
Farther, if the  ethal be heated with potash, hydrogen gas is given off,
and an acid formed,  the formula of which  is C32H3103+Aq.:  it is term-
ed the Ethalic Acid.
  From this analogy of ethal to wine-alcohol, a compound radical, Cetyl,
similar to ethyl, may be assumed to  exist  in these combinations, and its
formula be written C^H^ or Ct.   Ethal is  then Ct.O. + Aq.   (See  p.
566.)
   Wax.—Ordinary beeswax is a mixture of two substances, which are
separated  by boiling alcohol.  Cerine dissolves; it is  quite white; its
specific gravity is 0*969 ; it is less fusible than wax ; it does not combine
with bases ; its formula is C2oH20O2.   The substance insoluble in alcohol
is Myricine, which melts at 95° ; its formula is C20H20O.   In yellow wax a
colouring matter  is present which has not been examined.   When  wax
is bleached by nitric acid, oxygen is absorbed, and a peculiar  substance
formed, Cerate  Acid, which has the formula C20H2o03.   All these bodies
are probably derived from oils, isomeric with otto of roses, which exist
in the flowers of odoriferous plants.
  When cerin is boiled with  solution of  potash, a  soap is formed, and
from this a peculiar waxy substance (Cera'ine) is obtained, as ethal is from
spermaceti:  its properties are but very little known; from an analysis
by Ettling, its formula would appear to be C1SH,907.
                        CHAPTER  XXIV.

OF THE ORGANIC ACIDS "WHICH PRE-EXIST IN PLANTS, AND DO NOT BELONa
                     TO ANY ESTABLISHED SERIES.

                   Tartaric Acid.—C8H4O10+2 Aq.
  This important acid exists in most kinds of fruit, occasionally free, but
more usually combined  with potash, forming cream of tartar, or as tar-
trate of lime.  For the  purposes of commerce, it is almost exclusively
prepared from  the  bitartrate of potash.   This salt exists abundantly in
grape-juice, and being but very slightly soluble in spirituous liquors, it
gradually separates as the alcoholic fermentation proceeds, and collects
in irregularly crystallized layers on the insides of the casks in which the
wine is made.  It is purified, as will be elsewhere described. 
TARTARIC  ACI D.---C REAM  OF  TARTAR.     593
  When one part of carbonate of lime is added to a solution of four parts
of bitartrate of pota.sh, one half of the  tartaric acid  combines with  the
lime, carbonic  acid being expelled  with effervescence.  Tartrate of lime
precipitates as a white powder, and neutral  tartrate  of potash  remains
dissolved.  By the addition of chloride of calcium to the liquor, this por-
tion, also, of tartaric acid is thrown down, and chloride of potassium is
formed.  The whole quantity  of tartrate of lime being then collected and
washed,  it is to  be digested  with  a  quantity of oil  of vitriol, half  the
weight of the cream of tartar employed, and diluted with four parts of
water ; sulphate of lime is formed,  and tartaric acid set free.  The mix-
ture, having been boiled for a short time, is to be strained, and the liquor
evaporated  gently to a pellicle; the  tartaric acid  then crystallizes  on
cooling.
  The tartaric acid forms colourless oblique rhombic prisms, generally
tabular, as in the figure, where i, u, u are  primary, and
a,c,m secondary faces;  it is permanent in the air, and  S  f-\  I
dissolves  readily in half its weight  of water;  it is  also /**^-i
easily  soluble  in  alcohol;  its  taste and reaction are  N*\ M
strongly  acid.   When heated, it  abandons  water, and
forms two acids which will be again noticed.   When a  solution  of it is
long exposed to the  air, it absorbs oxygen, and forms carbonic and acetic
acids.   This effect may be instantly produced  by boiling it with  an ex-
cess of oxide of silver, metallic silver being set free.
  Tartaric acid is known by  its  not being volatile, and  by leaving  a co-
pious coaly residue when heated.   If it be  fused with potash, it is de-
composed, acetic and oxalic acids  being produced (p. 475); with  other
oxidizing agents, as black oxide of manganese and sulphuric acid, it gives
carbonic and formic sfcids. A solution of tartaric acid precipitates lime-
water, but the precipitate is redissolved by an excess of acid or by  so-
lution  of sal ammoniac.   The soluble neutral tartrates give  white pre-
cipitates, which are  not crystalline, with the neutral  salts  of  lead, lime,
and silver, which all redissolve in an  excess of acid.
  The tartaric acid is bibasic, its  formula  being C6H4Ol0+2 Aq. ; sev-
eral  of its salts are of considerable importance.
     Bitartrate of Potash.   Cream of Tartar.—CsH10O4 + K.O.Aq.
  This salt, just now noticed as being deposited from grape-juice, accord-
ing as alcohol  is formed, is sent into commerce under  the name of Argol,
which  is  red or white, according  to  the kind of wine  it was deposited
from.  This is dissolved  in  boiling water, and mixed with some  pipe-
clay,'which, combining with the colouring  matter of the grape, renders it
insoluble * the  clear liquor is  then allowed to cool slowly, and the cream
of tartar is deposited in irregular crystals  on the sides of the vessel, still
containing a small  quantity of tartrate of lime.  It crystallizes m right
rhombic  prisms, as  in the figure, p, u, u being primary,
and a,  a', i. m secondary  planes. It is but very sparingly
soluble in cold water, requiring 80 parts  at 60 , and  7
parts at 212° ; hence an  excess  of tartaric acid produces
a crystalline precipitate in solutions of potash which are
not very dilute.  By calcining cream of tartar either alone or  with  nitre,
the black or white fluxes employed in metallurgy are formed (p. 334).  Its
                                 4 F
 
594
TARTRATES   OF  POTASH,  AMMONIA,  ETC.
p\y.
calcination furnishes also the purest source of carbonate of potash, which
hence derives its name of Salt of Tartar (p. 487).
   Neutral. Tartrate of Potash.   Soluble Tartar.—C8H4O10+K.O. . K.O.
This  salt is  formed  by adding cream of tartar to a hot solution of car.
bonate of potash, until this be  completely neutralized.   It  crystallizes
with  difficulty  in right rhombic  prisms, whieh, when pure, are  not  deli.
quescent.   100  parts  of water dissolve 130 parts of it at 60°,  and 268
parts at 212°.    Any acid added to its solution takes half the potash, and
precipitates cream of tartar.
   The Tartrates of Ammonia resemble closely those  of potash.   The
neutral Tartrate of Soda crystallizes in large rhombic  prisms like nitre;
it  is  very soluble  in  water;  its formula is  C8H4O10+Na.O.  . Na.O.
            + 4Aq.
               Tartrate of Potash and  Soda.  Rorhellc Salt, CsH4Oi0+
             K.O. . Na.O.+ 10 Aq.,  is  prepared by  neutralizing a  hot
             solution of carbonate of soda with cream of tartar :  by evap-
             oration and  cooling it forms large  prismatic crystals,  with
             muny  sides,  of the right  rhombic  -system,  p,  u,  u being
             primary,  and i, i,  t. e, e  being  secondary  faces.    These
             crystals are remarkable for being often but  half formed, so
             as  to present the aspect  represented  in   the lower figure.
             Its taste is mildly saline, and  not very disagreeable, whence
             its popularity as a medicine.  It is permanent in the air ex-
             cept it be very dry, when it  effloresces slightly at  the sur-
             fkco ; it dissolves in two parts of cold  water.
   The Tartrate  of Lime  is very sparingly soluble in water, and is precipitated as a
white powder, when solutions of a neutral tartrate and of a salt of lime are mixed.
It dissolves in an excess of acid ; and if this solution be neutralized, it is deposited
in small octohedral  crystals, which have the formula  C8H4Oio+CaO. . Ca.O.-f 8
Aq.   Nolner has asserted that, when tartrate of lime is mixed with yeast,  a ferment-
ation sets in, by which a new acid, Pseudo-acetic Acid, is produced; this requires,
however, confirmation.
   Prototartrate of Iron, C8H4Oio+2Fe.O., is a white powder, very sparingly solu-
ble in water; it is formed in minute crystals when hot solutions of protosulphate of
iron and of cream of tartar are mixed together.  The Prototartrate of Iron and Pot-
ash, Coll40io+Fe.0  . K.O, is formed by digesting cream of tartar and water with
metallic iron.  Hydrogen gas is evolved, and a white, sparingly soluble salt  is ob-
tained, which, when exposed to the  air, rapidly absorbs oxygen, and becomes green-
ish brown or black.   In  this state it contains magnetic oxide  of iron, and is much
more soluble.  Pertartrate of Iron, formed by dissolving the freshly precipitated red
 oxide of iron in a solution of tartaric acid,  gives hy evaporation a brown jelly   If
the red oxide of iron be boiled with  a solution of cream of tartar, it dissolves abun-
 dantly, giving a fine brown-red liquor, from which, by cautious evaporation, small
 ruby-red crystals  may be obtained;  but it is generally dried down completely, when
 it forms a translucent brown mass,  deliquescent in damp air.  An excess of tartaric
 acid  should be avoided,  as it acts on the peroxide  of iron during the evaporation,
 reducing it to the state of protoxide, and carbonic acid being given off.   Hence the
 pharmacopceias direct perfect neutrality of the liquor to be secured by the addition
 of a  small quantity of ammonia. The formula of this salt is C8H4Oio+K.O.. Fe°03.
 It is  very soluble in water, and its solution is not precipitated by an excess of potash.
   Tartrate of Antimony.—3(C3H4Oio)+Sb.03.  This salt is obtained  by the solution
 of the sesquioxide of antimony in tartaric acid ; it is colourless, and crystallizes in
 short deliquescent prisms.
    Tartrate of Potash and Antimony.   Tartar.Emetic.—C8H4C,o+K.O. .
 Sb.03+2 Aq.   This salt,  a  most  important compound of antimony, is
 prepared  by  boiling  together  in water  equal weights of sesquioxide of
  antimony and  cream of tartar.   In the Dublin and Edinburgh pharma- 
PROPERTIES  OF  TARTAR-EMETIC.        595
copoeias, the Powder of Algarotli (p. 453) is employed as the source: of
oxide of antimony, but by the London college an impure oxide  is pre-
pared,  by gently deflagrating  together sulphuret of antimony and nitre
with a little  muriatic acid, and washing  out the soluble  products.   In
either  case  the  oxide of antimony  replaces the second  atom of base
(water) in  the cream of tartar, and by evaporation and cooling  it may
be obtained  in crystals, which are right rhombic octohedrons, with many
secondary planes, as in the figure.   This suit  dissolves
in fourteen  parts of  cold and in two of  boiling water.
In dry air it effloresces, losing  the 2 Aq.   Its solution is
not affected  by  alkalies;  but  the oxide of antimony is
precipitated by sulphuric or muriatic acids, and by am-
moniu.  In  the  preparation of tartar-emetic, the whole
product, from the materials used, can never be obtained
crystallized ; the mother liquor contains a  substance
which dries  down to a transparent mass, like gum Ara-
bic.   By alcohol it i.s decomposed into tartar-emetic and
free tartaric acid.   According to Knapp's analysis, this
salt i.s  the neutral tartrate  of  potash  and  antimony, having the formula
C4H205. K.O.+(3C4H205+Sb.03)+2 Aq.   It  may be formed by dissolv-
ing tartar-emetic in a strong  solution of tartaric acid,  and then crystal-
lizes in minute  oblique rhombic prisms.    In order to  form this  salt,
however, from  cream of  tartar and oxide  of antimony,  a  quantity of
potash must enter into  some  form of combination, which has not been
explained.
   Owing to the  occasional  presence  of arsenic in the ores of antimony,
the tartar-emetic of commerce is not unfrequently contaminated by its
presence, and should, in  such case,  be  absolutely rejected  from medi-
cinal use.
   If tartar-emetic be exposed to a temperature of 480°, it abandons, be-
sides its crystal.water, two equivalents of water, the elements of which
are abstracted  from  the  constitution of the  tartaric acid as generally
assumed.   In this  dried tartar-emetic, therefore, the organic element is
not CgH.,0,0, but C8H208.    When redissolved  in water, it resumes  the
two atoms of water, forming ordinary tartar-emetic again.   Of the other
salts of tartaric acid, but  one possesses  this property, the borotartrate
of [iotash being also reduced by loss of water at 480° to the formula
CJ !,(.)„+K.O. . B.03.   Chemists are not unanimous in explaining  this
peculiarity.   The  simplest idea is,  that these two atoms  of  water exist
ready formed in these salts, and that tartaric acid is  really quadribasic;
beiix-*  in its crystallized form, C8H2Os+4H.O. ; the  cream of tartar
bei.i- C8H203+K.O.  . 3H.O.; Rochelle salt, C8H2Os+K.O. . Na.O. . 2
II (T • and for tartar-emetic, the oxide of antimony replacing three atoms
of a protoxide, the  formula is C8H208+K.O. . Sb.03+2 Aq.+2 Aq.,and
the two portions of water being retained by very unequal forces, are given
off at very different temperatures.  Berzelius considers that in  this change
the nature of the acid is totally altered ; and as opinion is so much divided
on the subject, I shall not enter farther into its discussion.
  Anion of Heat on Tartaric Acid—When tartaric acid is cautiously heated, it fuses
into a mass  like gum, and gives off water.  In this state it combines with bases,
for nin-r salts quite different from  the tartrates ; it retains its bibasic character, but
k -i omic weight  is increased to one and a half times that of tartaric acid, its for-
mula being C,2H6015+2 Aq.   It thus constitutes Tartralic Acid; it does not crys- 
596          RACE MIC  ACID  AND  ITS  SALTS.

tallize, and in solution gradually passes back into tartaric acid.  If the tartralic acid
be kept long melted at 360°, it abandons still more water, and forms Tartrelic And,
in which  the bibasic character remains,  its formula being  Ci6H802o+2 Aq.  This
acid is characterized by forming insoluble salts with lime and barytes, thereby dif-
fering from the tartralic acid.   If the heat be still longer kept up, a porous white
mass is formed, which is insoluble in water and in alcohol. It is Anhydrous Tar-
taric Acid; its formula is  CsH4Oi0.  If left long in contact with  water, it changes
successively into the tartrelic, tartralic, and common tartaric acid.  This change is
produced more  rapidly by  boiling with a solution of potash : this substance appears
to hold the same relation to tartaric acid  that the white sublimate does to the prop-
er lactic acid (p. 536).
  If tartaric acid be distilled at a  still higher temperature, it abandons water and
carbonic acid,  and forms  Pyrotartaric Acid, CsH4Oi0 giving off 3C 02 and  II.O.,
and C5H303 remaining.  The process succeeds best at about 400°.  This acid  is
white ;  it crystallizes from the distilled liquors in prisms, which are to be purified
from empyreumatic oil by recrystallization and digestion with animal charcoal;  it
reacts very acid; it melts  at 210°, and sublimes at 360° ; is very soluble in  water
and alcohol.  It is a monobasic acid, forming salts which, with few  exceptions, are
soluble and crystallizable.
   Racemic  Acid.—(J8H4O10+2 Aq.   This acid is found in grape-juice,
replacing tartaric acid to  a greater or less extent; its formation appears
to depend  on very peculiar circumstances, as it  has never  been found
except in the  district about the Vosges Mountains, and only in some sea-
sons.  It is combined with potash,  forming a kind of cream of tartar,
which is biracemate  of potash, and from which  it is  prepared by the
same methods as have been described for tartaric acid.
   It crystallizes in colourless oblique rhombic  prisms, which contain
water, of which one half  is lost  by efflorescence  in warm  dry  air; the
remaining hydrate  is identical in composition with crystallized tartaric
acid; it tastes  and reacts as  strongly acid.   In its relation to salts, it
follows exactly the same rules as the tartaric acid,  but their  crystalline
form is completely different;  it. is a bibasic acid, and its formula,  when
crystallized, is  C8H~4O10+2H..O.+2  Aq.   The characters by  which  it
is distinguished  from tartaric  acid  are, first, racemic acid  requires ten
times as much water for  solution, and  they are  hence easily separated
by crystallization.  Second, that the corresponding salts are not of the
same crystalline form.   Third, the  racemate of  potash and soda is un-
crystallizable, giving  merely  a  gummy  mass,  while the  Rochelle salt
forms  very large  crystals.  Fourth, the racemate of lime is insoluble
in a solution of sal ammoniac.  The two acids, however, form a most
perfect example of isomerism,  as not merely their composition, but their
atomic weight is absolutely the same.
   When heated, racemic acid passes through precisely the  same changes
as have  been described for tartaric  acid, abandoning water, and forming
bibasic acids, whose formula? are respectively C12H6015+2H.O. and C,s
H3O20+2H.O.   They  are distinguished  by their salts, which differ  in
characters from each other, and from those of the bodies formed by tar-
taric acid.
   By the destructive distillation of  racemic acid  is generated the  Pyro-
racemic Acid, in which the isomerism with  the  tartaric  acid series is
broken through ; its formula being  C6H305.   It differs totally in proper-
ties from the pyrotartaric acid ; it does not crystallize ; it tastes acid ;  its
salts are all soluble and crystallizable, but pass also into a gummy con-
dition.  If a  little crystal of copperas be laid in a solution of one of these
salts, it becomes coloured bright red. 
CITRIC  ACID  AND  ITS  SALTS.
597
                 Citric Acid.— C12H50„+3H.O.+2 Aq.
  This acid exists in the juices  of fruits, especially the lemon, orange,
currant, and quince.   It is usually prepared from lemon-juice, which is
clarified by rest, then saturated  with chalk, and  the  neutral solution is
boiled until the citrate of lime is  completely deposited ;  this is then wash-
ed and decomposed by a quantity of oil of vitriol, equal in weight to the
chalk employed, and  diluted with six volumes of water.   After the sul-
phate  of lime has been removed by straining, the liquor is evaporated,
and  allowed  to crystallize  by very  slow cooling ;  its form  is  generally
that of a  right rhombic prism,  very much modified,  as in the figure,
where i, u, u are primary, and n', y, r are secondary planes.
In this case its formula  is that given above;  but if its  solu-
tion be evaporated  at 212° to a pellicle, it crystallizes while DO ] ^Lj
hot in  a  totally different form, and  its formula is  then C12l
H,0,,+3H.O.   By exposing the hydrated crystals  in vacuo
to sulphuric acid or to a gentle heat, the 2 Aq. may also be  removed.
   The citric acid possesses an agreeably sour  taste; it dissolves in less
than its own  weight of cold, and in half its weight of boiling water  ; it is
sparingly  soluble in alcohol;  when heated, it fuses, becomes yellow, and
ultimately gives the usual pyrogenic products of organic acids.  It is a
tribasic acid, and gives  rise to three classes of salts ;  and, as these con-
tain different quantities of combined water, their history was very confu-
sed until  Liebig explained  their true  constitution.  Very few of  these
salts  are,  however, of practical or medicinal interest.
  Citrate of Soda crystallizes in efflorescent prisms, having the formula  C|2H50U+
3Na.0.+4  Aq.+7 Aq.  By exposure to a heat of 212° the 7 Aq. are removed, and
at 400°  the remaining 4 Aq. are driven off: Berzelius is of opinion that in this ac-
tion the real constitution of the citric acid is changed, and that it is partly convert-
ed into aconitic acid; but the point is not yet experimentally decided, and Liebig's
views explain the phenomena with such beautiful simplicity, that I have no hesita-
tion in adopting them, at least provisionally.
  The Citrate of Lime is obtained by mixing solutions of a soluble citrate and of a
salt of lime ; it forms a white  powder, sparingly soluble in pure water, but much
more so if the liquor be acid.  Its constitution is Ci2H5On+3Ca.O.+4 Aq.   When
boiled with an excess of lime-water,  citric acid forms a basic Citrate of Lime, which
is less soluble than the neutral salt.
  The Citrates of Lead and of Barytes are white powders, insoluble in water, form-
ed by double decomposition, and  resembling in constitution the citrate of lime;
there are also basic salts, the formation of which, as in that of lime, appears to re-
sult from the crystal-water (2 Aq.) of the acid being more or less replaced by  metal-
lic oxide, in addition to that which fulfils  the proper basic function.
  The citric acid is easily recognised by forming no precipitate with lime-water un-
less the liquor be heated.   Its potash salt is also very soluble, even with an excess
of acid ; it  is thus distinguished from the racemic and tartaric acids.
  When citric acid is heated,  it  fuses, gives off water, and is converted into an
acid, which, from being found in the  aconitum napellus, is called Aconitic Acid, but
it exists also abundantly in various species of equisetum, and is hence often called
Eouisetic icid   To complete the change of the citric acid, it must be distilled un-
til the '^iscs which come over cease  to be inflammable, and oily drops appear in the
receive!- the process is to be then interrupted, the mass remaining in the retort to
be'dissolved in water, the  solution filtered and  evaporated to a pellicle.  On cool-
insr it forms a crystalline  mass, from which ether dissolves out the aconitic acid,
and leaves  unaltered citric acid  behind ; the former may then  be obtained crystal-
lized bv evaporation.                 ,,,    Jit        <•     i   •  r> u r»  i
  Aconitic  acid is soluble  in water,  alcohol, and ether ; its  formula is C,2H309+
3 \q • like citric acid, it is tribasic ; it forms well-characterized salts : the  aconi-
te e of ether had been mistaken for citric ether; for, when citric acid is  put in con-
tact with alcohol and  oil of vitriol, it  changes into aconitic acid. 
598            MALIC  ACID  AND  ITS  SALTS.
   If aconitic acid be heated until it boils, it gives off carbonic acid, and forms Ita-
 home Acid, which distils as an oily liquid, and forms a crystalline mass  as it cools;
 by solution in alcohol and slow evaporation, it may be obtained in long prismatic
 needles * its salts of which there are two classes (it being bibasic), generally crys-
 tallize very well; 'its formula is C10H4O6+2 Aq. ■ formed by the aconitic acid losing
 C204  but  an  atom  of water, previously basic, entering  into  the organic element.
 When the Itakonic Acid  is redistilled, it is converted  into water and a heavy oily
 liquid, Citrakonic Acid, the formula of which is C10H3O5+Aq.   In contact with wa-
 ter, it'forms  a crystalline mass containing 2 Aq.               ..,,..„.
  All these products are simultaneously and successively formed in the distillation
 of common citric acid.  Acetone is also generated, C12H12O12 giving 3(C3H30.), with
 3H.O. and 3(C02).
                     Malic  Acid.— C,H408+2H.O.
   This acid exists in most fruits, associated  with citric and tartaric acids,
 but is found purest and most abundant in the berries of the mountain ash
 and  in  the houseleek.   The best mode of extraction is the  following, de-
 vised by  Liebig.   The juice of the berries  of the mountain ash (sorbus
 aucuparia)  i.s to be nearly, but not completely, neutralized by  lime, and
 the liquor then boiled for some hours, during which the malate of lime
 precipitates as a  sandy white powder ; when no more falls down, the
 neutralization is completed by adding a little more lime, and on cooling,
 the remainder of the salt is obtained.  This malate of lime is to be dis.
 solved  by boiling  in the smallest possible quantity of very dilute nitric
 acid.   On  cooling,  the  acid  malate of  lime crystallizes,  and  is to be
 purified by  recrystallization.   This salt  being then decomposed by ace-
 tate  of lead, malate of lead is formed, which, being acted  on by sulphu-
 retted hydrogen, gives sulphuret of lead and free malic acid ;  by evapo
 ration of the liquor and cooling, a sirup-thick liquid is obtained, which,
 after long repose, forms a white crystalline  mass.
   Malic acid is deliquescent,  and very soluble in water.   It tastes and
 reacts strongly acid ;  its relations to bases are very curious ;  thus  mag-
 nesia is the  only earth by whose carbonate it can be completely neutral-
 ized.   This arises from its tendency to form salts, in which one atom of
 basic water is  preserved, it being a bibasic acid.   Another peculiarity
 pointed out byHagen is, that it forms with many bases two  neutral salts,
 of which one  retains  water with  obstinacy at 212°, at  which  tempera-
 ture the other at once abandons it.  When crystallized it appears to con-
 tain  only basic  water ; its formula is hence C8H408 + 2 Aq.  None  of its
 salts  are of technical or medicinal interest,  and hence require but  brief
notice.
   The  alkaline malates are very soluble in  water, scarcely crystalliza-
ble, sparingly soluble in alcohol.
  The Malate of Lime forms as a granular white precipitate when malic acid is
neutralized by lime.  Its formula is C8H408+2Ca.O. ; it separates in hard, brilliant
crystals, which contain 5 Aq., when the following  salt is neutralized by  an alkaline
carbonate.  Bimalatc of Lime, CsH408+Ca.O. .H.O.+6 Aq., crystallizes in large
right rhombic octohedrons.  Water  dissolves it abundantly when boiling, but very
sparingly when cold.
  The Malate of Lead, C8H,08+2Pb.O., precipitates, on mixing solutions of a solu-
ble malate with acetate of lead, as a white curdy mass, which, after  some time,
changes into  minute but  brilliant  crystalline scales.  By boiling in water, a small
quantity of it  is dissolved, which  separates in  brilliant plates  on cooling.  It fuses
below 212°, and is then nearly insoluble in waler.
  Malic acid  is distinguished both  from tartaric and citric acids by not giving any
precipitate with lime-water either by heat or when cold.
  When malic acid is heated to a temperature of about 400°, it abandons water and 
MECONIC   ACID  AND  ITS  SALTS.          599
gives origin to two acids, of which one is remarkable as being found naturally ex-
isting in several plants.  They are the Maleic Acid and the Fumaric Aeid, the latter
so called from having been first discovered in the  fumaria officinalis.   These acids
arc isomeric, the  reaction being in both cases that CII,08 produces 2H.0.  and
CsH'06-   Both acids may be formed in the same  process ; the maleic acid passes
over with the water, and  crystallizes from the condensed liquor ; the less volatile
fumaric acid constitutes the residue in the retort,  which solidifies into a crystalline
mass as it cools.   From the plants which contain  this acid, it may be obtained by
precipitating the clarified juices by acetate of lead, and decomposing the salt of lead
by sulphuretted hydrogen.   The liquors yield the acid by crystallization when con-
centrated to the necessary degree.
  The Maine And, which had been thought identical with the Aconitic Acid, al-
ready noticed, forms crystals  of a sour, bitter taste, soluble  in water, alcohol, and
ether.   When heated, it abandons water, and the anhydrous acid  remains, which,
if the water  be allowed to flow back, gradually changes into fumaric acid.   This
anhydrous acid melts at 167°, and sublimes at 350°.   Of its salts, that of barytes
alone is remarkable ;  it is a white precipitate, which changes soon into a mass of
brilliant plates.
  The Fumaric Acid, which  exists also in  Iceland  moss, crystallizes in fine long
prisms, which fuse with difficulty, and volatilize  first at 400°.  It requires 200 parts
of water for its solution.  When heated, it is decomposed into water and anhydrous
maleic acid.  The fumarate of silver  is so insoluble, that one  part of the acid, dis-
solved in  200,000 parts of water, is precipitated  by nitrate of silver, but the precipi-
tate dissolves in nitric acid.   The salts, with copper, iron, and lead, are also very
sparingly soluble.
   When muriatic acid gas is passed into a solution of malic acid in absolute alco-
hol, Ilagcn found that the ether formed contains fumaric, and not  malic acid.   It is
a liquid, heavier than water, of an  agreeable  smell.   With potash it gives alcohol
and fumarate of potash.  Its formula is C4H.03+Ae.O.  On adding water of am-
monia to this ether, a  substance is deposited in brilliant white scales, insoluble  in
cold water and in alcohol, but dissolved by boiling water.   It  is Fumaramid, its
formula being C4H. . 02Ad.  By potash, ammonia  is set free, and fumarate of potash
formed.

                 Meconic Acid.—C14H.On+3H.O.+2 Aq.

   This acid is found only in opium ; it is best extracted hy adding chloride of cal-
cium to an infusion of opium in cold water.   A white precipitate of mixed meconate
and sulphate of lime occurs.   This, being washed with hot water and with alcohol,
is to be treated with dilute muriatic acid, heated to about 180°.   The meconate of
lime dissolves,  and,  from the liquor on  cooling,  bimeconate of lime separates  in
brilliant crystalline plates.  On dissolving these in warm, strong  muriatic acid, and
cooling the solution, the pure meconic acid crystallizes.  It may be freed from any
adhering colouring matter by combination with potash, decomposing the crystallized
meconate of potash by muriatic acid, and recrystallization.
   When pure, meconic acid is in brilliant white crystalline scales, containing 2 Aq.,
which they give off at 212° , it is soluble in four parts of boiling water; it is a triba-
sic acid, forming salts, of which those with the earths and heavy metallic oxides
arc generally inso uble in water.  There are  three classes of Meeonates, according
as the quantity of fixed base is one, two. or three  atoms.  Few of them are specifi-
cally of importance.   The most characteristic properties of  this  acid are, 1st, that
it produces with solutions of  the peroxide of iron a blood-red colour, analogous  to
that of the sulphocyanide of iron,  from which it  is distinguished by the fact that,
on  the addition of the acetate of lead, a white precipitate is formed, which, when
heated to full redness with a  little sulphur and potassium, and treated with water,
gives no  red colour with  the  salts ol  iron (sec page 525) ; 2d, that with nitrate of
silver it gives  a white precipitate,  which  is dissolved by dilute nitric acid; the
liquor  however, when boiled, becomes milky, and deposites cyanide of silver.
   If a'strono* solution of meconic acid be boiled for a long time, or if the crystallized
acid be dissolved in Strom.**, boilimr muriatic acid, it is converted into  Komenic Acid,
carbonic acid bun" given off  The crystallized meconic acid undergoes the  same
ch im'e when heated to l'^1-   This acid forms granular crystals, which are soluble
on'lv Tn sixteen parts of boilmg water, and have the formula C2H2O.+2H.O., as the
C  11 O  loses C.()4 and ga ns H.O.   This acid  is bibasic ; the third atom of water,
which was basic'in the nieeonic acid, entering  into the radical  here. It also red- 
600
PREPARATION  OF  TANNIN.
dens the per-salts of iron.   It forms two series of salts, which in properties resem-
ble closely the corresponding meconates.  When it is heated to 500°, it gives off
water and carbonic acid, and forms Pyromekonic Acid, of which the formula is C,«
H305+H.O.  This acid forms crystalline plates, which fuse at 240°, and are vola-
tilized by a heat little higher.  It is very soluble in water, alcohol, and ether; it is
a monobasic acid, forming salts, which, with the exception of that of lead, are all
soluble  in water.  Like the acids from  which it  is derived, it strikes a blood-red
colour with solutions containing peroxide of iron.
             Tannic Acid, or Tannin.—C18H509 + 3II.O.
  This important substance exists in the bark of most exogenous trees,
particularly the oak and horse-chestnut, accumulated principally in the
inner layers of bark.  It is found also in the roots  of the tormentilla and
bistort, in the leaves of roses  and pomegranates ;  but its most  abundant
source is the gall-nut of the oak (quercus infectoria).
  To distinguish this from the other kinds of tannin, of which there is a
great number, it may be suitably termed Gallo-tannic Acid, and I shall
generally, though, perhaps, not uniformly, employ  that name.
  The method given by Pelouze for its extraction, and which serves for
the preparation of a variety of other vegetable principles, is as follows :
           Into a globular funnel, b, which can be  closed at the top by a
           stopper, and  rests in a bottle, a, as in the figure, is to be intro-
           duced a quantity of nut-galls in powder,  moderately compress-
           ed,  after the tube of the funnel has been stopped with  a little
           cotton.  The upper empty part of the  funnel is to be then filled
           with ether, as it is usually in the shops, containing about one
           tenth of water dissolved in it, and the apparatus allowed to stand
           for some days.   The bottle is then found to contain two lay-
           ers of liquid.  The inferior, sirup-thick, is a concentrated so-
           lution  of tannic acid in water,  with very little ether.  The
           upper is  ether, containing but  a trace of tannic and gallic
           acids.  Being separated, the lower layer is to be washed once
           or twice with a little ether, and then evaporated in vacuo with
a capsule of sulphuric acid.    A faintly-yellowish white mass remains, of
a distinctly crystalline  structure, which is  pure gallo-tannic acid.  The
theory of this process is, that  the tannic acid  is so greedy of water as to
withdraw it from  the ether, and to dissolve it to the exclusion  of every
other constituent of the  gall-nut.
  The watery solution of gallo-tannic acid reddens  litmus ; it is probably
insoluble in absolutely anhydrous alcohol and ether ; its  taste is intense-
ly astringent, but not bitter.    The most characteristic property of tannic
acid is, that it combines with the animal substance Gelatine, and  forms a
compound insoluble in water, which is  the basis of most kinds of leather ;
hence  any tissue, as skin, which contains gelatine, removes gallo-tannic
acid from  its watery solution, on which is founded the art of  Tanning.
It is a tribasic acid, and forms three classes of salts, which are of inter-
est from the  colours of precipitates it gives  with  metallic solutions, being
often useful as a test for the presence  of certain metals.  Hence an in.
fusion, or  tincture  of Galls, is always found in the laboratory as a rea-
gent ;  it does not affect the solutions of Zinc or  Cadmium, or the protox-
ides of Iron and  Manganese, nor  any of the alkaline  or earthy salts.
 With the other metals it gives precipitates which, with  Lead and Anli-
mony,  are  white ;  with  Copper, gray ; with Tin, Nickel Cobalt,  Cerium,
 Tellurium, and  Silver, are various shades of yellow ; with Tantalum and
 
PREPARATION  OK  GALLIC  ACID.         601
Bismuth, are orange ;  with Titanium, blood-red ;  with Platinum, green ,
with Chrome, JMolyb'lemii/i, Uranium, and Gold, are brown;  and with Os-
mium and peroxide of Iron, are rich bluish purple.   This last is the most
important of all, from its  great delicacy and distinctness.   If the solu-
tions be very strong, the liquor appears absolutely black, and constitutes
the material of ordinary writing ink.
   The insolubility,  and consequent inactivity of tartrate of antimony, is
taken advantage of in medicine, infusion of oak-bark  or galls  being em.
ployed as an antidote in poisoning by tartar-emetic.   I  shall have occa
sion hereafter to notice its use in the detection  and neutralization  of the
vegetable alkaloids.
   The gallo-tannic  acid is not the only kind  of tanning material employ-
ed in the manufacture of leather ; yet, as the others will hereafter come
und-.-r notice, I shall give Humphrey Davy's  estimate  of the comparative
power of such substances  as  contain true  tannic acid.  He found the
quantity of active material in 100 parts of the following bodies to  be,
Gall-nuts........27 I
Oak bark entire......6*3
Horse-chestnut bark entire .  .  4-3
Elm bark entire......2*7
White inner oak bark  .   .  .  160
White inner horse-chestnut  .  15*2
Sicilian sumach.....16*2
Malaga sumach.....10*4
  These numbers are but approximative, and such as are given by very
rough processes, the true quantity of tannic acid present being much lar-
ger ; thus the gall-nuts  easily yield, by Pelouze's method, forty per cent
of pure product.
  When a solution of tannic acid  is exposed to the air, it is decomposed ,
absorbing oxygen and evolving carbonic acid, the liquor becomes colour
ed, and a large quantity of gallic acid is found to be produced.

                 Gallic Acid.—C7H.03+2H.O.+Aq.
  This remarkable substance does not appear to exist naturally formed
in plants, but is generated  by  the decomposition of gallo-tannic acid.
Powdered galls are to be made into a thin paste with water, and exposed
to the air for  some weeks, at a temperature  of about  80°, water  being
supplied  according as it evaporates away ; the resulting mass is  to  be
boiled with water, and the gallic acid  crystallizes out of the liquor as it
cools.   By digestion with ivory black and recrystallization, it is obtain-
ed completely pure.
  In this process the reaction is very simple, as an atom of tannic acid,
CltIU),2, absorbing from the air eight atoms  of oxygen, produces 4C02
and vi(C7H.03 + 3  Aq.).
  The conversion of gallo-tannic acid into gallic acid may occur, howev.
er, without the access of air, and, indeed, be  effected almost instantane.
ously ; thus, if tannic acid be boiled in a strong solution of potash for a
few minutes, and an excess  of  sulphuric acid be then added, a copious
product of gallic acid is obtained  crystallized on cooling ; or, if sulphu-
ric acid be added  to a strong solution of gallo-tannic acid, and the pre-
cipitate thus formed be washed  with  a small quantity of water, and then
added Gradually to boiling dilute sulphuric acid, it dissolves, and on cool-
in<-* the''-'*allie acid crystallizes.   In these reactions,  which  succeed also
perfectly1 with infusion  of galls, some other substances must  be simulta-
neously'formed, which are as yet not  known.   Gallo-tannic acid contains
exactly  the  constituents of gallic acid and acetic acid, as C1SH309=2(C,
                                 4 G 
602   PYROGALLIC,  MKLANOALLIC  ACIDS,  ETC.
 H.O3)+C4H303; but Liebig has  determined that acetic  acid  is not pro-
 duced.
    This change may occur in the nut-gall itself, which it is very probable
 contains a principle analogous  to yeast, which, under favourable ciicum-
 stances, induces this kind of decomposition in the gallo-tannic acid.  This
 idea,  first suggested by Robiquet, has derived much support from the ex-
 perirnents of Larocque, who found that the matter of the nut-gall which
 remains after  the extraction of the tannin has the power of exciting the
 alcoholic fermentation in solutions of sugar.   As yet, however, we pos.
 sess no accurate knowledge of the theory of this interesting transmuta-
 tion.
    Pure gallic acid  crystallizes in  colourless oblique rhombic  prisms, as
 u, z in the figure, where i is a secondary plane ; it tastes bitter and slightly
             acid, and requires 100 parts of cold, but much less of boiling
             water for its solution ; it is less soluble in alcohol; its crys-
             tals contain three atoms of water, of which one is expelled at a
             temperature of 230°, but the  remaining two are only remov-
             ed when replaced by bases.   It  is a bibasic acid, forming two
             classes  of salts ; those with the alkalies are very soluble ; the
             earthy  and metallic salts are insoluble  in  water.  With a
 per-salt of iron, gallic acid gives  a  blackish-blue precipitate, which dif-
 fers from the tannate of iron in becoming gradually colourless, the acid
 being decomposed,  and the iron reduced to the state of protoxide ; this is
 effected instantly by boiling, carbonic acid gas being evolved.    The gal.
 lie acid is farther distinguished  from  the tannic by not precipitating gela-
 tine nor any of the  vegetable alkalies.

              Products of the Decomposition  of Gallic Acid.
   Pyrogallic Acid.—When gallic acid is carefully heated to about  400°, it is totally
 decomposed into carbonic acid and pyrogallic acid (C7H305=C6H603+C.02), which
 sublimes in brilliant white plates ; it is easily soluble in ether, alcohol, and water ;
 it  reacts feebly acid ; it fuses at 240°, and sublimes at 400°.   If a solution contain-
 ing peroxide  of  iron  be added to a solution of pyrogallic acid, a black colour is
 struck, but the iron is  rapidly reduced to the state of protoxide, and the liquor as-
 sumes  a rich  red tint.   If, however, a salt of pyrogallic acid be used,  the solution
 remains permanently blue.
   Melangallic Acid.—If, in the distillation of pyrogallic acid, the temperature be al-
 lowed to rise  beyond 450°, it is decomposed, water is given off, and a  shining, jet-
 black mass, like coal, remains in the  retort, which  is  this  body ;  its formula is
 C, H303,  being formed from 2(C6H303) by loss of 3H.O.; it  is insoluble in water,
alcohol, and ether; at  a temperature of 500° it is totally decomposed into the ordi-
nary pyrogenic products ;  it dissolves in alkaline solutions, forming salts of a black
colour,  which do not crystallize, these  salts give  black precipitates with solutions
of the earthy and metallic salts.
  If gallo-tannic acid  be heated to about 400°, it is resolved totally into pyrogallic,
melangallic, and carbonic acids and  water.
  Ellagic Acid.—In the formation of gallic acid  by the slow fermentation of tannic
acid, a  certain quantity of ellagic acid  generally,  though  not constantly, appears.
Being insoluble in water, it remains when  the gallic acid has been dissolved out;
and, by digesting the residue with a weak solution of potash, it  is taken  up, and
may then be precipitated by muriatic acid.
  It forms minute crystals, whose formula is C7H 03+H.O.+ Aq.   The Aq. is driven
off by a heat of 212°, and the dry acid is then isomeric with the gallic acid, but it is
monobasic; it is very  feebly acid, not expelling carbonic  acid from its salts; the
earthy  and metallic Ellagatcs are all insoluble, and all white or yellow,
  If gallic acid be heated to 280° with oil of vitriol, it dissolves, and  on  cooling,
brilliant crystals of a dark scarlet colour are deposited, which constitute Parcllasic
 Acid.   This body is isomeric with ellagic. acid ;  it forms with bases salts which are 
CATECHUIC   AND  CATEUHU TANNIC  ACIDS.   603
generally red.  It is worthy of notice,  that ellagic acid  acted on by oil of vitriol
gives no parellagic acid.
   It is here probably best to notice  the formation of what has been termed
Artificial Tannin;  it is produced by mixing  one part of almost any kind
of vegetable substance with live parts of oil of vitriol, letting the mixture
stand for some days, and then heating it as  long as  any sulphurous acid
gas is evolved.   A black  mass remains, from which the remaining acid
is to  be washed with water, and then the tannin dissolved out by alcohol ;
the solution is dark brown, and when evaporated  gives a black extract-
ive matter, which tastes astringent, smells of burned sugar, and dissolves
in water ;  it precipitates  gelatine,  but  does not affect the  salts  of iron
like true  tannin.
   Another and a  very singular manner  of producing artificial  tannin
consists in boiling  pure charcoal  in nitric acid as long as  any reaction
occurs ;  the liquor is then  brown  ;  being evaporated to the consistence
of a sirup and  mixed  with water, a brownish-yellow substance falls, and
the filtered solution gives, by evaporation, a hard  black mass, which red-
dens litmus, tastes astringent, is soluble in water  and alcohol, and copi-
ously precipitates gelatine  ; when heated, it smells  like horn, and contains
nitrogen  ;  it precipitates most metallic salts brown.   The true nature of
these bodies is not well known, as  they have not been much  studied since
the methods of organic chemistry acquired their present exactness ; they
are  probably  mixtures of many bodies, as  ulinine  in  its various  forms
with crenic and  aprocrenic acids.

                  Catechuic Acid and Catechutannic Acid.
   The Catechu, or Terra Japonica, a brown extract prepared from the wood of the
mimosa catechu, appears to contain at  least  four acids, the precise composition and
connexion of which  have not yet been definitely established.  The rough catechu,
as imported, is of extensive use in medicine, and in the arts for tanning and for giv-
ing a rich permanent brown dye.  Davy estimated that 100 parts of Bengal catechu
contain forty-eight, and of Bombay catechu  about fifty-four per cent, of useful tan-
 ning material.                             ,,,.,.,           j    •.  i <■
   If catechu be treated with ether, by the method of displacement as described for
 tannic acid, the  liquor  docs not separate into two layers,  but a strong solution of
 Cutrchutannic Arid in ether  is obtained, which, by evaporation, yields  it as a  pale
yellow  scarcely crystalline mass, in taste and appearance similar  to tannic acid;
its solution in water  precipitates gelatine, but not  tartar-emetic;  with the salts of
 peroxide of iron  it strikes an intensely  olive-green colour, which is best marked with
 the perchloride,  being somewhat purple with the  persulphate ; exposed to the air,
 its solution rapidly absorbs  oxygen, becomes red, and  finally brown, depositing a
 brown insoluble matter.  This change is instantly effected by any oxidizing  agent.
   The  catechutannic acid has been analyzed  by Pelouze, who ascribes to it the
 formula C,sH808+Aq. ; it would thus appear to be formed by the abstraction of four
 atoms of oxygen from tannic  acid.                  ••,,.,             A
   When catechu has been deprived of the catechutannic acid by ether or continued
washings with cold water, the residual  mass is to be boiled in alcohol, and the fil-
 tered liquor evaporated to one third of its volume; on cooling, Cutrchuic And crys-
 tallizes   If coloured it is to be dissolved in boiling water, precipitated by acetate
 of le id' the catechuate of lead diffused through boiling  water, and decomposed by
sulDhui-'etted l>vdro-*cn  ; the liquor being filtered, gives, on cooling, a perfectly white
m, 1 Dureca eclunc°ae.d ; it forms satiny flakes, indistinctly crystallized ;  it is very
little soluble in cold water, but abundantly in boiling water and in alcohol; it is in-
w,We in ether ;  its  solution is not acid ;  it appears to exist ,n very different states
of hv lratio  or on^iblv. different kinds ot catechu contain substances which are
totallv dist,.u-t  for the formula*  assigned to it are quite discordant, and chemists
ar  not •» "reed  quite as to its propert.es   Svanberg, who exam.ned  the catechu
frc inThe murns?" tech... gives as its  formula C,-,Hs05+Aq.  Zwenger, who states
K    He   wked^with to be the  produce of  the nauclea gambir, gives 
604  CINCHONATANN1C  AND  CINCHONIC  ACIDS, ETC.
C2oH908+Aq.;  and Hagen, who used Bengal catechu, found the catechuic acid to
be C14H606+3 Aq., and its lead salt C14H606+2Pb.O.  Additional researches are
required to clear up this confusion.
  When catechuic acid is heated, it fuses, gives off water, and, finally, a white crys-
talline sublimate, Pyrocatechin, which has the formula C6H20.+Aq.,  its character-
istic property is that of forming a bright green solution with alcohol.
  If a solution of cither of the acids now described be exposed to the air, oxygen is
absorbed, and much more rapidly in presence of an alkali.  The  substance formed
is termed Japonic Acid; it makes up the mass of the coloured portion of  catechu ;
it is almost insoluble  in water; soluble in caustic, but  not in carbonated alkalies.
Svanberg gives for it the formula  Ci2H204+Aq.   If catechuic acid be boiled with a
solution of carbonate of potash, Rubinic Acid is formed, whose formula is said to be
Ci<H609.  By farther absorption of oxygen it forms japonic acid.  None of these re-
sults, however, can be considered as definitely established.

                Cinchonatannic Acid  and Cinchonic  Acid.
  These substances exist in the barks of various species of cinchona, combined with
quinia and  cinchonia.  The first is extracted by digestion in dilute muriatic acid and
precipitation with magnesia.   The  precipitate is to  be dissolved in acetic acid and
precipitated with acetate of lead,  which leaves the alkaloids dissolved; the cincho-
natannate  of lead being decomposed by sulphuretted hydrogen,  the  filtered liquor
yields, on evaporation, the Cinchonatannic Acid pure, and of a very pale yellow col-
our, not crystalline.   In  properties  it resembles closely ordinary tannic acid, it
precipitates gelatine and  tartar-emetic.  An infusion of cinchona is  hence recom-
mended as an antidote in cases of poisoning by tartar-emetic.  It colours solutions
of  the per-salts of iron green.  By exposure to the air, it is converted into a rust-
coloured substance termed Cinchona Red.   Nothing is known of  the composition of
these bodies.
   The Cinchonic Acid, which Berzelius believes to exist in the inner bark (albumen)
of fir and of most trees, is obtained by adding lime in small quantity to a  cold infu-
sion of cinchona bark.  The alkaloids being thus  separated,  the liquor  is filtered and
evaporated very carefully to the consistence of a  sirup.  On standing for a  few days,
the cinchonate  of lime crystallizes in needles, which are to be  decomposed by an
exact equivalent of sulphuric acid.  The gypsum being  removed by the filter, the
solution is concentrated, and the cinchonic acid crystallizes.  It forms small acid
needles ;  is very soluble  in water ;  its salts are all soluble in water; it affects nei-
ther gelatine,  tartar-emetic, nor the per-salts  of iron;  its formula  appears  to be
Ci4H808+4 Aq.   When  it is heated, a substance sublimes in brilliant yellow nee-
dles, which is termed Chinoyl, and consists of C3H.O.

                      Kinoic Acid, or  Coccotannic Acid.
   The  substance known in  pharmacy as  Cum Kino, which is an extract  of the
 wood of the coccoloba uvifera, is to be dissolved in cold water, the solution precipi-
 tated by sulphuric acid, the precipitate washed, dissolved in boiling water, and solu-
 tion of barytes added until the sulphuric acid is all removed ; the liquor is then care-
 fully evaporated to dryness.   The kinoic  acid forms a crimson transparent mass,
 soluble in  alcohol and water, but not in ether ; its taste is astringent, but not bitter.
 The salts  of this acid are not known, nor  has its composition been examined.  It
 does not precipitate solution of tartar-emetic.
    Of the following acids we possess little more than a knowledge of their probable
 existence.
    Lactucic Acid is said to exist in the lactuca virosa.  The expressed juice is  pre-
 cipitated by acetate  of lead, and the lactucate of lead decomposed by sulphuretted
 hydrogen.  From the liquor the acid crystallizes by evaporation and cooling, like
 oxalic acid ; it tastes acid, and gives with  protosalts of iron a green, and with salts
 of copper  a brown precipitate.
    Fungic Acid exists in  most mushrooms ; their expressed juice is boiled, and the
 coagulated albumen  removed by filtration ;  the  liquor is  then evaporated to a sirup,
 and treated with alcohol. Fungate of potash remains undissolved, from which the
 acid is obtained by acetate of lead and sulphuretted hydrogen.   The fungic acid is
 colourless, sour, deliquescent, and not crystalline.
    Bolctic Acid is obtained from the boletus ignarius, in the same way as the last acid
  is from other mushrooms.   It crystallizes readily, and sublimes without decompo-
 sition. 
              K RAM ERIC  ACID,  ETC.--PECTIN.          605

  Kramcric Acid exists in rhatany root (krameria triandria).   The watery infusion
is precipitated,  first by gelatine, and then by copperas.  The filtered liquor is con-
centrated, neutralized by lime, precipitated by acetate of lead, and the kramerate of
lead decomposed by sulphuret.of hydrogen ;  it crystallizes irregularly, and tastes
strongly acid and astringent;  its formula is probably Ci0H8O5, by Liebig's analysis.
  Caineic Acid  exists-in the root of the chiococca racemosa. Its mode of extraction
resembles that  of the krameric acid ; it crystallizes in needles ;  is but sparingly sol-
uble in water;  its solution reacts acid ;  it appears to have the same formula as kra
uieric acid, and perhaps they are really identical.
  Vcrdous and  Venlie Acids  exist in a variety of plants of the families dipsaceae,
composita.-, and eupatoriae; it is best prepared from the roots of the scabiosa succi-
sa.  They are to be digested  in alcohol, and the solution mixed with ether.  Impure
verdous acid is thrown down ; it is to be dissolved in water, and the liquor precip-
itated by  acetate of lead ; the verdite of lead being collected and decomposed  by
H.S., gives  the pure Verdous Acid, which remains after evaporation as a clear yel-
low mass, which is not altered by the air ; it reddens litmus strongly.  If it be neu-
tralized by an alkali, it then absorbs oxygen rapidly, and the solution becomes deep
green; from this, acids throw  down a brown-red powder, which is Verdic Acid
Runge, who observed these facts, considers that the two acids are different oxides
of the same radical, but no exact researches have been made about them.
  Other acids,  of which the existence has been only  indicated, will  be noticed in de-
scribing the more important bodies with which they are associated  in the plants.
                           CHAPTER XXV.

 OF  THE  NEUTRAL  ORGANIC SUBSTANCES AND THE PRODUCTS  OF THEIR
                             DECOMPOSITION.

  The bodies to be described in this chapter are  distinguished  by the
absence of distinct acid or  basic characters, and also that they  are at
least so destitute of colour as not to be included in  the list of colouring
matters.   In other respects they possess no direct  connexion with each
other,  and are united only for convenience of arrangement.

                       Pectin, or  Vegetable Jelly.
  This substance,  which  is to be carefully distinguished  from  animal
jelly, or Gelatine, to which  it  by no  means  bears the  relation that the
albumen  of plants  does to  that  of animals, is very extensively diffused,
being  found in almost  every kind of plant, and distributed through  all
their parts.   It is very easily prepared from the  expressed juice of white
beet, celery, parsley,  currants, cherries,  or  plums.    It  is sufficient to
filter the  juice and mix  it  with  alcohol; after  some hours, the pectin
separates  as a consistent jelly, which  is to be collected on a filter, wash-
ed with alcohol, and dried by a very  moderate  heat.   It forms a trans-
parent mass, like isinglass,  and is almost insipid.   When  immersed in
water, it swells up; one part gives a firm jelly with 100 parts of water.
When acted on by nitric acid, it  produces pectic and the mucic acid.   It
precipitates the salts of barytes, lead, copper, and sesquioxide of iron, but
does not  affect  solutions  of silver, of protosulphate  of iron,  of  tartar-
emetic, of tannic acid, or  of silicate of potash.    Its formula, as from the
experiments of Fremy, is  C24Hi:Oj:.   By  long boiling, or by contact with
any  powerful acid or base, it changes into the following substance: 
606  PECTIC  AND  METAPECTIC  ACIDS.---SALICINE.

  Pcctic Acid appears to exist naturally combined with lime in many plants, and ia
precipitated from their juice on the addition of muriatic acid.   The precipitate is to
be boiled with a little lime, and the solution again decomposed by muriatic acid.
The peetic  acid, which then separates pure, is to be washed with distilled water and
dried.  It does not crystallize, but forms white transparent scales, tastes distinctly
acid, and reddens litmus.  It dissolves very sparingly in cold, but more copiously
in boiling water; the solution is colourless, and does not gelatinize  on cooling, but
is coagulated to' a transparent jelly by  acids,  by lime-water, alcohol, and many
salts.   .Sugar gradually converts the solution into a firm jelly, and is thus useful in
the  manufacture of the preserves of juicy fruits.
  The peetic acid is isomeric  with pectin, its formula being C24H1-O22.   It appears
to be  bibasic, the pectate of lead  being C2iHn022+2Pb.O.  Its alkaline  salts  are
soluble in water, but the others are insoluble, and form  transparent jellies while
moist.
  If pectin  or peetic acid be boiled in a solution of potash, the alkali being in  ex-
cess, until the liquor ceases to give any precipitate on the addition of muriatic acid,
Mctapcclic Acid is formed.   On the addition of sugar of lead, metapectate of lead is
thrown down, which, being decomposed by sulphuretted hydrogen, the  metapectic
acid dissolves, and is obtained by  cautious evaporation to dryness.  Its taste and
reaction are strongly acid ;  it deliquesces, and dissolves easily in alcohol and water;
it is not volatile.   When dry, it is isomeric with the preceding bodies, its formula
also being C24H17O22; hut its salts  contain five atoms of base.   Those of the alka-
lies are soluble and uncrystallizable, but those of the earths and heavy metallic  ox-
ides are insoluble in water.

                Of Salicine, and the Bodies derived from it.

  This  substance  exists  in the leaves and bark  of a great variety of
trees, but  is particularly abundant in those species of salix which have a
bitter taste.   The bark is to  be boiled three or four  times with water,
the decoction evaporated till it amounts to but three times  the  weight of
the bark  employed, then  digested for twenty-four  hours with  oxide of
lead,  and the clear liquid evaporated to the consistence of a  sirup.  After
a few days  this becomes a mass  of crystalline fibres, which,  separated
by  pressure from the mother liquor, are to  be  purified by solution, diges-
tion with animal charcoal, and recrystallization.
  When pure, salicine is in the form of small white rectangular crystal-
line plates or prisms; its  taste is very bitter.   It  dissolves in  eighteen
parts of cold  and  in  one of boiling water ; it  is soluble in alcohol, but
not in ether; at 212° it melts, and on cooling solidifies into a crystalline
mass.   The composition of salicine has been  very accurately  determin-
ed ; its formula is,  when crystallized, C2]H)209+2 Aq. ;  it precipitates  the
basic acetate of lead, forming  a white compound, the formula of which is
C2,H,209+3Pb.O.
  The products  of the decomposition  of salicine  are  exceedingly remarkable.
When it is boiled with dilute sulphuric acid, it is decomposed into grape-sugar, and
a resinous substance  termed Saliretine.   Three atoms of salicine, CoH^t, giving
saliretine, C5|H240,5, and sugar, C2H12O12.   When quite pure, this body is white or
pale yellow.  It is insoluble in water, but soluble in alcohol and ether.
  With  sulphuric acid  and  chromate of potash,  salicine gives hydruret of salicyl
(oil  of spiraea), as described page  573.   Although the evolution of formic and car-
bonic  acids, which occur in this reaction, show  that it is in reality complex, yet its
result may  be expressed by the simple abstraction of water from the  salicine. as
2(C2lHl209)-6H.O-3(C14H604).
  When salicine is boiled with nitric acid, it is totally converted into  picric acid.
As this body is, however, more closely connected with indigo,  it will be there fully
described.
  By  the action  of chlorine on salicine  two bodies are produced,  one crystalline,
whose formula is C21H12 C1209, and the other a heavy oil, consisting of C2iH8
C1409.  They are both soluble in alcohol, but sparingly soluble in water.
  If strong oil of vitriol be poured on salicine, it is decomposed into water and a 
PHLORIDZINE  AND   ITS  PRODUCTS.         607
deep olive-green powder, O/ir.in, the formula of which is C2iH906.  This action is
accompanied by the disengagement of much heat.  Olivin is crystalline, insoluble
in waler, alcohol, and ether   If the oil of vitriol be  in great excess, it becomes
red-coloured, and the salic.ne dissolves.  The red substance thus formed is termed
Rnfi.ii; it is obtained more simply from phloridzine.  If a large quantity of salicine
be acted on by sulphuric acid, it forms a tenacious mass, which,  when treated with
water, and  the  liquor neutralized  by lime, gives a brown resinous body, which is
termed Rutdin.  This contains sulphuric acid, its formula being C2sHi204+S.03.

                     Of Phloridzine and its  Products.
  This remarkable substance exists in the bark of the roots of the various  species
of apple, pear, plum, and cherry trees.   It is prepared by infusing the root-bark in
weak spirit for  eight or  ten hours at 120°.   The greater part of the spirit may then
be distilled off, and on cooling, the phloridzine crystallizes from the remaining liquor.
It forms brilliant silky plates and needles, perfectly white when  pure.  It is easily
soluble in alcohol, ether, and in  boiling water, but requires 1000 parts of cold watei
for  its solution.   Its taste is bitter and astringent.  The formula of the crystals is
C2iHnOs+4  Aq.   At 212°  it gives off 2 Aq.; it melts at 226°, and boils at 350°,
but is decomposed, water being evolved, and a new substance produced.   The solu-
tion of phloridzine precipitates some metallic salts.  The persulphate of iron gives
a brown precipitate, but the perchloride of iron produces a blood-red liquor and no
precipitate.
  The decomposition of phloridzine by heat is not complete until the temperature
rises to 450° ;  it then forms a  deep red mass of Rufm, the same substance as is
produced by  the action of oil of vitriol  on salicine; it is very soluble in alcohol, in-
soluble in ether;  boiled in water, it dissolves, but loses its red colour, and the liquor,
on cooling, becomes milky.  It dissolves in water of ammonia or potash with a rich
red colour, and is precipitated on the addition of an acid;  its formula is C14H7O5;
it combines with oil of vitriol, forming Rufin-sulphuric Add, which unites with  the
metallic  oxides, forming red or brown salts, which possess considerable analogy to
the sulphovinales.
  When phloridzine is dissolved in dilute sulphuric  acid,  and tbe liquor boiled, a
white crystalline  substance separates, which is termed Phlorctme; the liquor then
contains "much grape sugar.  The formula of phloretine is Ciil^O,;; its taste is
sweet;  it is  sparingly soluble in water, but very soluble in alcohol; it melts at 300°;
when heated with nitric acid, it forms Phlorctic And, the formula of which is C5|ll24.
N20.-,;  it is a yellow-brown powder, of a velvety aspect, but not crystalline ; insol-
uble in water, and soluble in alcohol.
  The most remarkable action on phloridzine is that  exorcised  by ammonia with
access of air.   Over a capsule containing water of ammonia are arranged several
capsules containing phloridzine in very thin layers, and the whole is  so covered
with a large bell-glass as that the air shall have  free aceess ; after a few days the
contents of  the capsules are changed  into a thick sirupy liquor, nearly black ;  the
excess  of  ammonia being removed by exposure in vacuo  with  sulphuric acid, the
excess  of  phloridzine is dissolved out by alcohol, and the residue then being  dis-
solved in water, gives a magnificent blue liquor, from which the colouring substance,
Phloridzein,  is precipitated by the cautious addition of acetic acid ; it is not crys-
talline "it  forms a transparent resinous mass of a rich crimson colour; its taste is
bitter 'boiling water dissolves enough of it to be  coloured red, but cold water, al-
cohol,'or ethe°r appear scarcely  to act upon it.
  The formula of phloridzein is C2lH14. Ol3V+Aq. ;  it is formed, therefore, by the
combination of phloridzine with five atoms of oxygen and  one  of ammonia;  it is
not  however, a salt of ammonia,  for tin* alkalies dissolve phloridzein without alter-
ation  Ibrmin'**- magnificent blue solutions ; from metallic  solutions  it precipitates
purple or blue lake" the composition of which renders it probable that the equiva-
lent of phloridzein is (\Mx • 020X2+2 Aq. ; then the
               Phloridzelnate of ammonia, =C42H2< ■ XiO:,+ \ H3.
               Phloridzeinate of silver,    -=C4.ll2s  XiOjt+SAg.O.
               Phloridzelnate of lead,     =C42H:s ■ X2026+2Pb.O.

If the blue solution of phloridzelnate of ammonia be put  in  contact with a slip of
zinc  nrotochloride of tin, sulphuretted  hydrogen, or any other deoxidizing agent, it
is deprived of colour, but bv exposure  to the air it rapidly reassumes its tmt; with
chlorine the  colour is instantly and permanently destroyed. 
608   ASPARAGIXE,  CAFFEINE,   AND  PIPERINE.


                       Asparaginc.   Aspartic Acid.

  Asparagine is found  in the young shoots of asparagus and of potatoes, in the
roots of liquorice and marsh-mallow.  From the latter it is easily prepared.  The
decorticated roots are to be digested in cold water for forty-eight hours, and the li-
quor then strained and evaporated to the consistence of a sirup.   By standing foi
some time, the asparagine gradually crystallizes, and  the crystals are to be purified
in the ordinary manner  by animal charcoal.  It forms rectangular octohedrons and
prisms; it is colourless and tasteless; it  requires about sixty parts of cold, but much
less  of'hot water for solution ; it.is insoluble in alcohol;  it contains nitrogen, its
formula being N.O,. H403+Aq.;  the water goes away by a heat of 230°.
  When asparagine is boiled with a strong  solution of barytes, ammonia is  expell-
ed, and aspartate of barytes formed ;  by  cautiously adding sulphuric acid, the bary-
tes may be precipitated, and the liquor yields,  on evaporation and cooling, crystal-
lized aspartic acid.   In  this reaction 2(N.C4 . H403) produces N.H3 and N.C8. H306,
which is the formula of aspartic acid.  This substance is tasteless, sparingly solu-
ble in  cold,  but abundantly in boiling water, and  is  deposited as a white crystal-
line powder  as the solution cools ;  it reddens litmus.   Its salts are generally solu-
ble, except those of lead, silver, and black oxide of mercury.
  It  is not easy to decide whether the ammonia exists ready formed or not in the
asparagine ; if so, the remaining organic  element may be aconitic acid (see p. 597),
and then there should be,

      Asparagine=anhydrous aconitate of ammonia=C4H.03+N.H3.
      Aspartic acid=anhydrous binaconitate of ammonia-=2(C4H.03)+N.H3.

In the case  of the  anhydrous compounds of ammonia with  the mineral acids, it is
retained with the same obstinacy as in asparagine (see p. 508).

                    Caffeine or Theine.   Caffe'ic Acid.

  This  has been found  only in the coffee-berry, the tea-leaf, and the paulinia sor-
balis (guarana).  To prepare it, raw coffee is to be boiled in water, and the  decoc-
tion treated  with subacetate of lead as long as the precipitate which forms  is col-
oured.  The caffeine crystallizes from the filtered liquor by evaporation and cooling;
if it  be coloured, it is to  be boiled with oxide of lead and ivory black, and again
crystallized ; when pure, it forms brilliant long needles of a rich  satiny lustre ; its
taste is purely bitter ; it dissolves in fifty parts of cold, but in much less of  boiling
water ; it is very soluble in proof spirit,  but insoluble in absolute alcohol; its solu-
tions  react neither  acid nor alkaline ; it is not precipitated by any metallic  salt.
Caffeine is remarkable for the large quantity of nitrogen it contains (29 per  cent.),
being more than any other vegetable substance ; its  formula is N2C3. H502+Aq.
When caffeine is boiled with solution of barytes, cyanuric  acid, ammonia, formic,
and carbonic acids are produced.
  The coloured  precipitate produced in  the decoction of raw coffee by acetate of
lead  contains  two peculiar substances, which may be extracted from  it by treat-
ment with a stream of sulphuretted hydrogen gas, evaporation to the consistence of
a sirup, and digestion of the residue in  strong alcohol.   That which dissolves is
Caffetannic Acid; it is dark brown ;  tastes acid and astringent;  colours the per-
salts of iron emerald green ; it precipitates the salts of barytes and lime yellow, of
copper green, but does not affect tartar-emetic.   The  substance insoluble in alcohol
is a white powder,  which, when heated,  evolves the  characteristic aromatic smell
of roasted coffee ; its solution in water reddens litmus ; it is termed Caffeic  Acid.
  These bodies have not been accurately examined.  It is not known if the tannic*
acid  of tea and coffee be the same.

                         Piperine.—N.C^. H1906.

  This substance exists in white, black, and long pepper;  it is prepared from white
pepper by digestion in spirit of wine, and distilling the liquor to the consistence of
an extract, from which, by digestion in a solution of caustic potash, a quantity of
resin is to be removed ;  the residue is then to be dissolved in alcohol, and the  solu-
tion  abandoned to spontaneous evaporation, when the  piperine gradually crystallizes
in transparent rhombic prisms.  It melts  at 212° ;  is tasteless and inodorous ; des-
titute of either  acid or  basic properties; nitric acid  colours it red; when  heated
strongly, it yields ammoniacal products. 
         ONINE,  C E T R A R I N E,  P I C R O T O X I N E,  ETC.  609

   Cantharidine.—C]0H6O4.   This substance is extracted from the blistering fly (va-
 rious species of cantharis and lytta) by digesting  a watery extract of the flies in al-
 cohol,  evaporating the  solution to dryness, and treating the residue with ether
 which dissolves out the cantharidine.   By spontaneous  evaporation  it is obtained
 crystallized ;  it forms  colourless pearly scales,  which fuse* when gently heated,
 and sublime unaltered at a higher temperature ;  it is, when pure, insoluble  in water
 and  in cold alcohol;  it is perfectly neutral, and  has no  affinity either to  acids or
 bases.
                       Anemonine.   Anemonic  Acid.

   This substance exists in various species of anemone ; it is extracted by distilling
 the plant with water ;  it separates,  after some  time, from the distilled water, in
 brilliant white needles ; it melts and volatilizes at a high temperature,  yet not with-
 out partial decomposition ; its formula is C6H304;  when it is dissolved m strong
 muriatic acid, and the liquor evaporated to dryness, Anemonic Acid is formed ;  its
 formula is C6ll405+Aq.   It  is not important.

                         Cetrarine, or Lichen Bitter.

   This substance  is  found in Iceland moss ; to extract it, the lichen,  being well
 crushed, is to be digested in  alcohol as  long as this acquires a bitter  taste  ; the li-
 quor may then be distilled in^reat part off, and the cetrarine is  deposited,  on cool-
 ing,  in granular crystals ; these are to be, while  still moist, washed with ether  and
 cold alcohol, by which  they are rendered white, and then being dissolved in  200
 times their weight of boiling alcohol, the pure cetrarine separates  on cooling as a
 white  powder of a slightly  crystalline aspect.  It  is but sparingly soluble in  any
 menstruum ;  its only remarkable character is, that by digestion  with  muriatic acid
 it lbrms a deep blue mass, but the nature of the  reaction is not known, as  the con-
 stitution of these bodies has  not been accurately  investigated.

                          Picrotoxine, or Cocculine.

   This substance exists in the seeds of the menispermum cocculus (cocculus Indi-
 cus), constituting their  active  ingredient; to prepare it, the  seeds, freed from the
 capsules, are to be digested in alcohol,  and the solution evaporated to an extract;
 this  is to be then treated with water as long as anything is dissolved, and then
 some muriatic acid added to  the liquor; by cooling, the cocculine crystallizes in
 brilliant white  needles.   Its  reaction is neutral; its taste intensely bitter; it dis-
 solves  moderately  in boiling, but sparingly in cold water.   The portion of the alco-
 holic extract which does not dissolve  in water contains another substance. Picro-
 toxic Acid, which is brown, and possesses the properties of a resin ; it dissolves in
 alkaline liquors, from which acids throw it down  unchanged.  The formula  Ci0ll6O4
 lias been assigned to  picrotoxine, and that of C||H604  to picrotoxic acid.
   Columbine.—Found in the roots of the menispennum palmatum.   The coarsely-
 powdered columbo-roots are  to be digested in ether, and  by the  spontaneous evap-
 oration the columbine crystallizes ; or  by digesting  the roots in  alcohol,  and decol-
 orizing the liquors by animal charcoal, it may also be prepared  ; it forms  brilliant
 right rhombic prisms; its taste is intensely bitter ; its reaction neutral; it dissolves
 but sparingly in water, alcohol, or ether ; its solution does not precipitate any me-
 tallic salt; its formula appears to be C^H^Cy
   Cusparinc.—This is the active principle of the true angustura (cusparia  febrifuga).
 The  bark is to be extracted by alcohol,  and the solution concentrated very much by
 spontaneous  evaporation  *, on  cooling then below 32°, granular  crystalline masses
 of cusparine  separate, from  which the liquor is  to  be strained ; by redissolving in
 alcohol, and precipitation  of the colouring matter by acetate of lead, it is  ultimately
 obtained pure.  When crystallized from a solution some degrees below 32°, cuspa-
 rine  forms colourless  but irregular needles ; by a  very gentle heat it melts and gives
 off ;wenty-three per cent, of water of crystallization ; it  dissolves readily in water
 and  alcohol,  but is insoluble in ether ;  by heat it is totally decomposed  ; its solu-
 tions precipitate most metallic salts.   Its composition is not known.
  Elatcrine is the active material of the expressed juice of the momordica elaterium;
 the juice, being evaporated  to the  consistence of an  extract,  is to be digested hi
 (strong alcohol, the solution  thus formed is to be distilled to a small bulk, and then,
on bem"* mixed with water, it deposites the elaterine as a white crystalline powder.
It mehs  at about 320°, but is  totally decomposed by a stronger heat; its  taste is
                                      4 H 
610  MECONINE, PEUDECANINE,  iESCULINE,  ETC.

intensely bitter ; it is almost insoluble in water, but abundantly in alcohol; it pos-
sesses no characteristic chemical property.
  Mecomnc— This substance exists mixed with the more  important ingredients in
opium ;  it is most abundant in the inferior kinds ;  its preparation is very circuitous,
and will be described in the general analysis of opium, under the  head ol narceine.
Meconine crystallizes in white six-sided prisms ; it melts at 194°, and may be sub-
limed unaltered ;  it  dissolves sparingly in  cold, but moderately  in  boiling water,
abundantly in alcohol and ether;  its lormula appears to be C20H9O7+Aq.   By nitric
acid  it is dissolved, and a substance crystallizes from  the  liquor in  long needles,
which is termed Nitromeconic Acid; its formula is N.C20 ■  H9O12; its solution in water
reddens litmus; it volatilizes at  370°, but is partly decomposed.   By contact with
chlorine, meconine is coloured red, and substances formed whose constitution  is not
well known.
  Peudecanine.—This substance is  found in the roots of the  peudecanum officinale,
and is extracted by digestion with alcohol and evaporation ; it crystallizes in deli-
cate white  needles of a slightly aromatic taste ; it  fuses at 140° ;  it is insoluble in
water, and but sparingly in cold alcohol; it dissolves copiously in boiling alcohol,
in ether, and the oils.

                          Msculine, or Polychrome.
  A great number of vegetables give, when treated with  hot water, a solution which
appears yellow by transmitted, but  violet or blue by reflected light.  This phenom-
enon  results from  the presence of a body hence called Polychrome, and also Msculine,
being most abundant in the bark  of the horse-chestnut.  The bark is to be digested
in alcohol,  and the liquor to be concentrated by distillation' to the consistence of a
sirup, in which, when set aside for some weeks, the aesculine crystallizes; by wash-
ing with ice-cold  water it is  freed from the liquid extractive matter ; the impure
crystals are to  be dissolved in a  boiling mixture of five  parts of alcohol with one of
ether, from which, by cooling, the pure substance  separates, perfectly  colourless,
and generally as a light powder,  like  magnesia alba.  It tastes bitter ; it dissolves
in 672 parts of water at 50°, and in thirteen parts at 212° ;  its cold, watery solution
is perfectly colourless by transmitted, but slightly blue by reflected light; if spring-
water be used, the blue becomes much  stronger ;  acids  destroy this property, but it
is restored to the  solution  by the addition of a few drops of any alkali.
  The watery  solution  of aesculine reddens litmus, yet it does not neutralize the al-
kalies, nor precipitate any  of the ordinary metallic salts  ; it dissolves  abundantly in
alkaline liquors, and the solutions give a magnificent play of colours with reflected
light; its formula is C|6H9Oi0.
  Populine exists in the bark and leaves of different species of populus, along with
salicine ; the  latter  is  removed  from the liquors  by precipitation with  acetate of
lead,  and then, by evaporation, the populine is obtained crystallized ; its taste  is bit-
ter-sweet,  like liquorice ; it is very sparingly soluble in  water ;  when heated, it fu-
ses, and is then decomposed ; like salicine,  it gives with nitric acid, picric acid, and
with  sulphuric acid, rutilin ; its composition is not known.
   Quassine constitutes the bitter principle of the quassia amara and excelsa.   The
rasped  wood  is to be  boiled  several times with  water, and the filtered decoction
evaporated down  to three fourths  the weight of the wood  employed.  The  liquid,
when cold, is  to be mixed with slacked lime, and, after twenty-four hours, filtered
and evaporated nearly to dryness ;  the residue is to be treated with alcohol, and the
solution distilled in a water-bath to dryness ; it is  then  impure quassine ; it is to be
washed  with  ether, and then redissolved  in  alcohol, and this treatment repeated
until it becomes completely white.
   Quassine forms small white prisms of an intense but  purely bitter taste ; but spa-
ringly soluble in water or in ether, it dissolves abundantly in alcohol; when heated,
 it fuses like a  resin ; its solution is not  precipitated by any metallic salt, but  abund
 antly by tannic acid ; its formula is C2oHi206.
   Santonine.—This substance exists  in the flowering tops and seeds of a number of
 species  of artemisia, from one of  which (art. santonica) it derives its  name.  To
 prepare it, four parts of the seeds  are to be mixed with one and  a half of dry lime,
 and  boiled in  twenty parts of alcohol three times  ; the united decoctions  are to be
 distilled to fifteen parts ; tbe residue, when cold, is to be filtered, evaporated to one
 half, and,  having been rendered  slightly acid by vinegar,  boiled for some  time ; on
 cooling, the santonine  crystallizes in large  feathery crystats, which are to be puri-
 fied  from  an adhering resinous substance by washing with alcohol.   Being then re- 
SAPONINE,  SCILLITINE,  SENEGINE,  ETC.    611
dissolved, and the solution  slowly cooled, the santonine crystallizes in  colourless
rectangular prisms and plates; it is tasteless; it is very sparingly soluble in  water;
more so in alcohol and ether; at 338° it melts, and by a carefully-applied heat may
be sublimed without decomposition, otherwise it becomes brown, and a yellow crys-
talline substance is formed.  Santonine appears to possess feeble acid properties ;  it
produces with the alkalies soluble, and with the  earths and ordinary metallic oxides
insoluble compounds, but they are of instable constitution.   The  formula of santo-
nine is CioH602-
  By exposure to  light, santonine  undergoes a  change apparently isomeric  ; it be-
comes  gold-coloured, and forms yellow solutions, which,  however,  soon become
colourless.
  Saponine.—This substance  is most, easily extracted from the roots of the sapona-
ria  officinalis by boiling  in  weak  spirit; on cooling, the saponine separates ; it  is
purified by digestion with animal charcoal; it is a white powder, of a sharp,  piquant
taste; very soluble in water, it is sparingly soluble in alcohol, and insoluble in ether;
its  formula appears to be C2UH28016.   By the action of nitric acid, saponine forms
mucic acid and a  resinous  substance ; when dissolved in  solution of caustic pot-
ash, it  forms Saponinic Acid, which is precipitated as a white powder on adding a
stronger acid to the liquor.  The  formula  of saponinic acid is C26H22O12. It is  in-
soluble in cold, but soluble in  boiling water.
  Sallitine is the active  principle of the squill (scilla maritima).  The fresh juice is
evaporated,  and the extract treated with alcohol.   The spirituous solution is to be
dried down, and the residue, being dissolved in water, is to be precipitated with ace-
tate of lead, and filtered ; sulphuretted hydrogen  being passed through the clear li-
quor removes the excess of  lead, and then, by filtration and evaporation, the scillitine
may be crystallized.
  It forms a hard, brittle mass, like resin, of an intensely bitter taste ;  it deliques-
ces and dissolves readily in alcohol and water, but not in ether.
  Senegine.—This substance  is extracted  from the roots of the polygala senega by
boiling with  water, precipitating the concentrated decoction with the acetate  of lead,
filtering and removing the  excess of lead  from the solution by sulphuretted hydro-
gen, and evaporating cautiously to dryness ;  the residue is to be digested in alcohol,
and'this solution being dried down, the product  is to be digested in ether.  The ma-
terial which remains undissolved is then  to be passed through the same series of
operations until it  becomes  a  white pulverulent  mass, which is pure Senegine.  Tt is
sparingly soluble in cold, but abundantly in boiling water ; it is very soluble  in alco-
hol, but insoluble  in ether.   With sulphuric acid it produces a curious play of col
ours becoming first yellow, after some time rose-red, and then dissolving ;  the so-
lution gradually becomes violet, after some time grayish-blue, and finally colourless,
while a gray precipitate falls down.   Senegine appears to possess feeble acid prop-

  Smilacine, or Sarsaparilline.— This  substance is found in the roots of the smilax
sarsaparilla and the bark of the China nova.  It is obtained by boiling with alcohol
and distilling the decoction  to two thirds ;  on cooling, the smilacine crystallizes, and
is purified by animal charcoal and recrystallization.  It is white in very minute nee-
dles ■ its  taste nauseous and slightly bitter; very sparingly solub e  in water, more
an J .,.™-n,u „,„«*. in ether:  with sulphuric acid  it gives colours like those of sen-
so in alcohol, most in ether;  with sulphuric acid it gives

egAbsintiuine —The bitter principle of the wormwood (artemisia absinthiurn)  It is
prepared by a succession of operations almost identical with those described for ob-
Eng senegine ;  it is hence  unnecessary to repeat their descr.p ion.  ^ hen com-
Setely pure, it is white  and crystalline;  its taste is intensely bitter; ,t fuses at a
hgtemprature, and  closely resembles a resin ; its best solvent  is alcohol.   It
nign «  iperdt    ,        f   veak acid, being much more soluble in alkaline liquors
possesses the characte.s 01a   t           »       fa so)utlons on the addition  of

 n" Vi2 PW,thao ^"itriot1 it° iSured first yellow, and then dark reddish purple.
  Lactucine is obtained  by digesting the inspissated juice of the lactuca virosa (lac-
  Lactucine 1. 001       j   *ntanooU8 evap0ration of the solution, it forms a mass
tucarimn   n « uur    y      r   |ouro(1 yellow ■ it has a strong bitter taste, is fusi-
of crysta hne needles sj ^     .^^ m       alcoho]j and ether   It  ig

utc'om^d by^i^i*  ">* *Pl'ears "ot  t0 have any tendenCy t0 f°rm S3ltS- 
612
APOTHEM E.--E XTRACTIVE.
            Of Extractive Matter.  Apotheme.  Extracts.
  If from  any plant, or portion of a plant, the soluble ingredients be
dissolved out by water, a variety of substances exist in the liquor, some
acid, others basic, others indifferent; of these  bodies, the majority pos-
sess the property of absorbing oxygen when the solution is exposed to
the air, and often, also, of evolving carbonic acid, changing thereby into
substances insoluble, or scarcely  soluble in water.   Thus gallo-tannic
acid first forms gallic acid, and is then converted into a brown insoluble
mass; so  gum and sugar ultimately produce certain forms of ulmine;
and there  are few of the neutral principles  described  in the  present
chapter that do not rapidly undergo a similar change.
  During the  evaporation of a vegetable infusion or  decoction, these re-
actions rapidly occur, being promoted by the heat; the liquor, which had
been at first clear, becomes turbid and brown, a deposite forms, and when,
finally, it has  been evaporated to the consistence of a thick sirup, what
remains is  termed an extract; it is a mixture of the constituents of the
plant in great  part decomposed.  If this extract be  treated with water,
and the soluble  portion again evaporated, the same changes occur, so
that, no matter what may have been the original  nature of the vegetable
substances, they are ultimately reduced  to  this insoluble and inert con-
dition.  This  brown substance is termed Apotheme; its true nature is
not known, but it is probable that its composition and properties  vary in
some  degree with the  nature of the substance  it is formed from ; we do
not even know of its relations to the various  kinds  of ulmine;  though,
from its solubility in alkaline liquors, and its precipitating metallic salts,
its being separated from these by acids,  and obstinately retaining a por-
tion of the acid  used  to  precipitate it,  its identity with  ulmic  acid or
humic acid is  not improbable.
   When the conversion of the real  constituents of the plant into apo-
theme is yet incomplete, the  material, which dissolves equally in water
and dilute alcohol, but not in absolute alcohol or  in ether, is  termed
extractive.   Such a mixture can have no distinctive chemical properties;
it is more  or less coloured, and uncrystallizable ; it precipitates  metallic
salts ;  it absorbs oxygen, forming apotheme (oxidized extractive).   The
different classes of plants are considered by pharmaceutic writers to con-
tain different  kinds of  extractive matter; there are thus bitter extractive,
gummy extractive, astringent extractive, and so on ;  but, to the chemist,
these  names  convey  only the idea of  absolute  ignorance of the real
nature of  these bodies; the  chemist  recognises no such substance as
extractive  matter,  or Apotheme;  they are  merely complex products of
decomposition of other bodies, and have not, as yet, been accurately ex-
amined.    In the preparation of an extract of a plant, the ambition of the
operator should be, not to have either extractive or  apotheme produced,
but, by employing the lowest possible temperature, and excluding air as
much  as possible, to obtain the constituents of the plant in a concentrated
form,  but  not destroyed, as  they  too  frequently are, by the operation:
accordingly, in  the manufacturing laboratory  of the Apothecaries' Hall
of Ireland, the greatest precautions are  taken  to ensure  success  in the
preparation of extracts; but details of the  methods belong to pure phar-
macy, and are unfitted for the present work.
   A great number of bodies, that have been from time to time announced as the
active principles of many plants containing them, are really but such extracts, proji- 
COLOURING  MATTERS.                 613
eny prepared, but still not the pure chemical substances.  Thus, from colocynth,
Colocynthine;  from hippo, Emetine; from rhubarb, Rke'ine, &c. It is on this account
that many bodies, to which distinct names have been given by their discoverers as
chemical  species, are not noticed as such by me.
  The latter principle of the Aloes is one of these which have never been obtained
chemically pure, and yet the very remarkable products of the action of nitric acid
on it show that it i3 a truly distinct substance.   When socotrine or hepatic aloes
are digested with hot nitric acid, red fumes are abundantly  evolved, and four dif-
ferent acids produced, for the accurate examination of which we are indebted to
Schunk.  They are, the Alo'etic Acid, the Aloe-resinic Acid,  the Chrysammic Acid,
and the Chrysolepic Acid, and they are generated by successive oxidation of the bit-
ter principle of the aloes, in the order in which their names stand.
  The Alo'etic Acid is a yellow powder, insoluble in water, but forming soluble salts,
of which  that with potash crystallizes in ruby-red needles.  The Aloe-resinic Acid
is soluble in water ;  its potash salt uncrystallizable ; its combinations with the me-
tallic oxides insoluble, and generally  brownish-red.   The  analyses of these bodies
are not yet published.
   The Chrysammic Acid is a greenish-yellow crystalline powder; it is  very  spa-
ringly soluble  in water, yet tinges it purplish-red ; it is more soluble in alcohol, ether,
and acids; when heated, it fuses, and is then decomposed with  a slight explosion,
and a bright but smoky flame ; it contains nitrogen ;  its formula is C15H2 . N2O12+
Aq.  The chrysammate of barytes is a  red  insoluble powder.  The chrysammate
of potash is the most insoluble of all the  salts of potash, requiring 1250 parts of wa-
ter at 60° for  solution, and may hence serve as an excellent reagent for that alkali;
it is a dark red crystalline powder when precipitated, but when  it crystallizes from
a hot dilute solution, it forms gold-coloured plates
  The Chrysolepic Acid is distinguished by its solubility in water; it crystallizes m
beautiful  gold-coloured plates, closely resembling Picric Acid, with which it is isom-
eric, its  formula being Ci2H2 . NsOi3+Aq.   It is distinguished, however, by the
much greater solubility of its potash  salt, and by the action of heat, as it may be
fused and volatilized without decomposition, if cautiously heated.
                          CHAPTER XXVI.

                      OF  THE  COLOURING MATTERS.

  The substances to be now described  may be arranged in two classes,
according  as they pre-exist in the plant, or as they are  merely products
of the decomposition of  other bodies which are not  coloured ; of these
last an example has already been given in the formation of phloridzeine
from  phloridzine.
                               SECTION I.
               OF THE PRE-EXISTING  COLOURING MATTERS.
                    Colouring Principles of Madder.
  The dried roots of the rubia tinctorum constitute the madder of com-
merce,  which,  furnishing  the well-known  Turkey red,  is  perhaps  the
most  important of the dyestuffs.  The constitution  of madder is very
complex;  it contains five different colouring  matters and two colourless
acids, the  general preparation and properties of which  are  as follows:
  Madder Purple, or Purpurine.—Madder roots are to be  well washed
with  water at 80°, then boiled several times in a strong solution of alum,
and  each  liquor filtered while very  hot.   On cooling,  a red-brown  sub-
stance precipitates, which is impure Madder Red; it is to  be separated 
614     COLOURING PRINCIPLES  OF  MADDER.

by the filter.   On adding to the clear red solution  some  sulphuric acid,
the madder purple is thrown down.  To obtain it quite pure,  it is to be
dissolved in boiling alcohol, and the solution allowed to evaporate slowly.
It separates as a fine orange-red  crystalline  powder,  sparingly soluble
in cold, but more easily in boiling water.   The solution is rose-red ; its
solutions in ether and alcohol are bright red.  Acids turn it yellow ■  al-
kalies  dissolve it with a rich red colour.   It  is fusible, and, when  more
strongly heated, a portion sublimes as a red powder, but the greater part
is decomposed.
  Madder Red, or Alizarine, as precipitated in  the preparation of pur-
purine, is to be purified by repeated boiling with solution of alum, and
then crystallized by  solution in  ether and spontaneous evaporation. It is
a browi.ish-yellow crystalline powder.  When heated, it sublimes, form-
ing brilliant orange  needles; it is sparingly soluble in water, more so in
alcohol and ether.   Ammonia dissolves it with a purple red, and potash
or lime with a violet colour.   The formula C^H^O,,, has been  assigned
to this body.
  Madder Orange.—The roots are to be  digested for sixteen  hours in
eight parts of water at 70° ; the infusion is to be filtered  and set aside;
small orange crystals gradually form;  these are to be collected and dis.
solved in boiling alcohol.  On cooling, the madder-orange crystallizes as
a yellow powder.    When heated, it fuses, and is decomposed  in great
part, some of it subliming in yellow fumes;  it is  most easily soluble in
ether; it dissolves in alkaline, forming brown-red liquors.
  Madder Yellow, or Xanthin.—The cold  infusion of madder is  to be
mixed with an equal volume of lime water.   The dark-red precipitate
is to be treated with dilute acetic acid ; the lime and the yellow dissolve;
any traces of the other  colouring matters are removed from the liquor
by a woollen  cloth  mordanted  with alum.   The solution is to be then
evaporated, the residue dissolved in alcohol, and  precipitated by sugar
of lead ; the scarlet precipitate separated, and decomposed by sulphuret-
ted  hydrogen.  The liquor so  obtained gives, on evaporation,  the xan-
thine pure; it is yellow,  uncrystallizable, and  very soluble in alcohol
and water.
  Madder Brown is totally insoluble  both in alcohol and water.  The
acids which exist in madder are but very little known, and do not possess
any interest either technical or scientific.
  Of these colouring matters, the Red, or Alizarine, is the most important,
as it forms with an  alumina mordant the magnificent  Turkey Red.  With
an  iron mordant it gives a permanent black, and with mixed mordants
of the two, various intermediate shades of purple.  The great complexity
of the process for dyeing Turkey red arises from the difficulty of dis-
solving away the other  four  bodies, so that  only pure madder red may
remain.

                    Alkanna Red, or Anchusic Acid.
  This substance exists in the roots of the anchusa tinctoria.  They are to be well
boiled in water, and then digested in a solution of carbonate of potash ; on the ad-
dition of an acid to this liquor, the colouring matter precipitates;  it may also be
obtained by digesting  the roots in alcohol and evaporating ; it is a dark-red resin-
ous body, insoluble in water, soluble  in alcohol, ether, and the  essential oils ,  it
combines with  alkalies, forming blue  solutions, which give  blue or crimson lakes
with metallic salts.  The formula C17H,oO, has been assigned to this body
  Brazihine is the colouring matter of various species of ca*salpina (Brazil wood, 
SAFFLOWER  RED,  ETC.
615
Ifernambouc wood).  The decoction of the wood in water is to be agitated with hy-
drated oxide of lead, then filtered and evaporated to dryness.  The residue is to be
treated  with  alcohol, the solution mixed with water and gelatine,  which  throws
down a quantity of tannic acid, then filtered, again dried, mixed with alcohol, and
filtered to separate the excess of gelatine, then again evaporated, and set aside to
crystallize.
  When pure, braziliine forms orange crystals;  it is soluble in water, alcohol, and
ether; the solutions are reddish-yellow ; alkalies and  most metallic salts give pur-
ple, and alum a red precipitate, with the solution of braziliine
  Santaline exists  in the red sanders wood (pterocarpus santalinus).  Its extraction
and  properties are  exactly  similar  to that  of  the  Alcanna Red.  Its  formula is
Ciolls03.
  Hamaloxylinc.—This substance, the  colouring principle of the  logwood  (haema-
toxylon Campechianum), is frequently met with naturally crystallized  in stellated
groups of prisms, sometimes of considerable size, in clefts of the wood ; it may also
be prepared by a process similar to that described for braziliine; it is slightly  bitter
and  astringent; it is very sparingly soluble in water, but copiously in  alcohol and
ether, forming brownish-red  liquids.   Acids colour  its solutions yellow,  alkalies
purple; with the earths and metallic oxides it forms purple or blue lakes.

                        Safflower Red, or  Carthamine.
  The petals of the safflower (carthamus tinctorius) contain a red and a yellow ma-
terial ; the former alone is of technical importance.  The flowers  are to be  washed
with water acidulated  with  acetic acid until all the Safflower Yellow is removed.
By digestion  then  in a solution of carbonate of soda, the carthamine is dissolved,
and  may be precipitated by any acid, but citric acid answers best; it forms a dark
red powder, insoluble in water and in acids, and  but sparingly soluble in alcohol or
ether; it reddens  litmus, and gives  with  the alkalies yellow solutions; its  com-
pound with soda  crystallizes in silky needles ;  with alumina  it forms a beautiful
red  lake, Rouge, used as a cosmetic and in dyeing.   This substance is much em-
ployed for dyeing silk of various shades of  pink and rose colour.
  I have found in  the petals of the salvia fulgens a colouring matter possessing con-
siderable analogy to carthamine,  and capable of being substituted for it.
  Quercitrine.—This substance is extracted from the bark of the quercus infectoria
by simple decoction in water; after  some days  the  colouring  matter separates in
crystals; or, better, by digesting the  bark in alcohol, precipitating the tannin by gel-
atine and  evaporation: when pure,  it resembles  very  minute  crystals of yellow
prussiate of potash ; it  is easily soluble in water  and  in alcohol, and appears to pos-
sess feeble acid properties.   Its formula, by Bolley's analysis, appears to be C,6H90e
+Aq.  With metallic oxides it gives brilliant yellow lakes.

                     Chrysorhamnine.   Xanthorhamnine.
  I  have found the unripe berries of the rhamnus tinctorius (Persian berries, grains
d'Avignon) to  contain  a substance soluble in alcohol and  ether, and crystallizing
from its ethereal  solution in minute silky needles of a brilliant  yellow colour; it
gives with metallic  oxides yellow lakes.   When cautiously heated  it fuses, but is
not  volatile.   In the ripe berry, this substance, to which  I have given the  name
Chrysorhamnine, is totally replaced by another,  which I  term Xanthorhamnine,
which is of a  much less beautiful yellow,  and does not  crystallize;  this change is
efleeted, also, by boiling the chrysorhamnine for a few  minutes with water,  or by
contact with alkalies.   The xanthorhamnine is totally insoluble in ether, but easily
soluble in alcohol  and water.   It is  formed by the union of the elements of  water
with chrvsorhamnine.   Its silver salt is yellow wben first thrown  down, but rap-
idly becomes black, metallic  silver  separating, and a colourless organic substance
beiii» formed   The Persian berries are much used for dyeing yellow, but, from the
processes employed, the xanthorhamnine alone is actually brought into play.
  Luicoline is  the colouring  principle of the weld (reseda luteola), and probably of
the  elvers' broom  (genista t.nctoria)   Its mode of preparation resembles  that of
quercitrine  It is soluble in  water, alcohol, and  ether; it copnhtnes with both acids
ami  alkalies  form in"* yellow compounds.   With alumina and the oxides of tin and
lead  il -nves brilliant yellow lakes ;  with iron, a dark brown precipitate.
  ' Monnc is the colouring principle of the yellow-wood (morus tinctorius); it is pre-
pared like  quercitrine, with which its properties accurately agree.
  Ordlinc—The seed of the bixa orellana are imbedded in  an orange-red colouring 
616
COCHINEAL  RED,  ETC.
 matter, which is separated by washings and a kind of fermentation ; when deposit-
 ed from the liquors, so as to form a consistent paste, it is sent into commerce under
 the names of Rocou, Orleans, or Anotta.  To obtain the colouring principle pure, the
 orange-red mass is digested in alcohol, and the solution distilled nearly to dryness*;
 the residue is then treated with ether, which dissolves the orelline, and yields it, on
 evaporation, as an orange-red, somewhat crystalline powder; it colours water pale
 yellow; it is more soluble in alcohol, but gives with ether or oils deep red solutions;
 it dissolves in alkalies, and is precipitated  therefrom by acids.  With  alumina, ox-
 ide of tin, and  oxide  of lead, it gives fiery red precipitates.  It is extensively used
 in dyeing, and also to heighten  the colour of cheese and butter.
   Curcumine is found in the roots of the curcuma longa (turmeric), and is obtained
 by treatment with boiling alcohol, evaporation to dryness, and digestion of the resi-
 due in ether, which dissolves the pure colouring matter, and yields it by spontane-
 ous evaporation.   Curcumine melts at 104° ;  it possesses the properties of a resin ;
 alkalies brown it, on which its employment for a test-paper rests ; acids render its
 proper yeilow much paler, except boracic acid, which stains it yellowish-red.
   Berberine exists in the roots of the berberis vulgaris ;  it is prepared by boiling the
 roots in water, and evaporating the decoction to the  consistence of an extract,
 which is to be treated with spirit of wine as long  as this acquires a bitter taste.
 The spirit is to be distilled in great part off, and the residue suffered to stand in a
 cool place for twenty-four hours ; the crystals which form are to be recrystallized,
 first from water, and then from alcohol.  Pure berberine forms a light crystalline yel-
 low powder of a strongly bitter taste ; it is very sparingly soluble in cold, but abun-
 dantly in boiling water and in  alcohol; it is insoluble in ether.  At 268° it melts,
 and, if farther  heated, is  decomposed, giving ammoniacal products;  by chlorine
 it is converted into a brown-red substance ; it combines with bases, acting feebly as
 an acid ; its alkaline  compounds crystallize ; those with the earths and heavy me-
 tallic  oxides  are insoluble, and generally yellow ; a solution of it precipitates the
 iodide, cyanide, ferrocyanide, and sulphocyanide of potassium.  Berberine contains
 nitrogen, its formula being  N.C03 . HibOi2.

                        Cochineal Red, or Carmine.

  This very remarkable substance differs from all of the other colouring matters
here described, in being a  product of the  animal kingdom.  It exists  in many in-
sects of the genus  coccus, as the coccus cacti (the true cochineal), the  coccus ilicis
(kermes), the coccus ficus (lac dye), &c.  For its preparation the cochineal is to be
digested in ether to remove a quantity of fat, and then boiled in alcohol as long as
this is coloured.  The alcoholic liquors, being mixed, are to be concentrated by dis-
tillation, and then  cautiously dried ; the impure  carmine  thus obtained is digested
in alcohol, and the solution mixed with ether, which precipitates the colouring mat
ter quite pure.
  It is a purple  red powder, easily soluble in water and alcohol, insoluble  in ether.
It melts at 122°, but is decomposed  by a high heat; chlorine turns it yellow;  al-
kalies colour cold solution of carmine red, but it becomes yellow by exposure to the
air or by boiling.  With alumina it forms a precipitate,  which is crimson when pre-
pared with a cold, but violet if with a hot  solution.  All metallic salts give lakes
with the alkaline solution of carmine ; that of the protoxide of tin is a rich scarlet.
The carmine of commerce  is  an alumina lake more or less pure ; that called Chi-
nese Carmine is  the compound with oxide of tin.
  The carmine contains nitrogen ; the formula N.C32 . H2602o has been assigned to
it, but cannot be considered as definitely established.

                Of Indigo, and  the Bodies derived from it.

   The blue indigo  of commerce is derived from the leaves of a variety
of plants of different genera.  The genus  indigofera includes a number
of productive species, also the genera nerium and  isatis, marsdenia, as-
clepias, and polygonum, galega, spilanthus, and amorpha.   Of these the
 great majority are  natives of the  tropics ;   but a  few,  as the isatis tincto-
 ria and the polygonum tinctorium, belong to temperate regions, the for-
 mer being  indigenous both to Ireland  and to England.
   The indigo is secreted in the cellular tissue of the leaf, in a form (white 
BLUE  AND  WHITE  INDIGO.
61
indigo) which can also be artificially produced ; it is then colourless
and remains so as long as the tissue of the leaf  is perfect.  When the
leaf begins to wither, oxygen is absorbed, and, the indigo assuming its
colour, the leaves become covered with a number of blue points, the first
appearance of which shows that the period for collecting them  has arri-
ved.   The fresh leaves are thrown into large  vats with some water, and
pressed down by weights.  After some time, a kind of mucous ferment-
ation sets in, carbonic acid, ammonia, and hydrogen gases are evolved,
and a yellow liquor is obtained, which holds  all the  indigo dissolved.
This is separated, mixed with lime-water, and then exposed to the air un-
til the indigo becomes blue and insoluble, and  is completely deposited as
a precipitate.   The theory of this action is, that, by the putrefaction of
the vegeto-animal  matter of the  leaves,  the indigo is  kept in  the same
white, soluble condition in which it exists in the plant, and a clear solu-
tion of it  being thus obtained, it is precipitated, according as it absorbs
oxygen, in a much purer form than otherwise could be effected.
  The putrefying pasty mass of leaves obtained from the isatis tinctoria
constitutes the woad or wad employed in the hot  indigo bath for dyeing
cloth.
  The blue indigo, as thus obtained, is still  a  mixture of several bodies,
as indigo.red, indigo-brown, indigo-gluten, which are removed by repeat-
ed treatment with alcohol and dilute acids and  alkalies.   When pure, the
precipitated indigo is  a rich blue powder, which, when rubbed by a knife,
assumes tho colour of metallic copper ;  it is  perfectly insoluble ; when
cautiously heated.it sublimes in rectangular prisms of a dark purple col-
our and metallic lustre ; its vapour is of a rich purple ; it contains nitro-
gen,  its formula, as fully established by Dumas, being N.C,fa. H502.
   White Indigo.—When indigo is acted upon by deoxidizing agents, as
protochloride of tin, protoxide of iron, or sulphurous acid, it loses its blue
colour, and the white  indigo, which is insoluble in water, but soluble  n
alkaline solutions,  is produced.  Its mode of preparation is simple :  one
and a half parts of commercial indigo, two and  a half parts of slacked
lime, and  two parts of green  copperas, are to be well mixed up with six-
ty parts of water,  in a vessel from which the  air is carefully excluded.
The  protoxide of iron, formed by the action of the lime on the copperas,
peroxidizes itself at the expense  of the indigo and water, and  the white
indi'To thus formed dissolves  in combination with lime.   On adding mu-
riatic acid to the clear solution, the white indigo precipitates,  and may
be obtained dry, as a crystalline powder, by suitable precautions to pre-
vent the access of air.
  The simplest theory of this  process should be, that the oxide of iron
directly abstracted oxygen from the indigo: hence the names of Deoxidized
Indigo and Indigogene were given to the white substance ; but  the anal-
yses of Dumas have  proved  that the white  indigo is a compound of hy.
dragon with the blue  indigo,  its formula being C16H5. N.02 + H.  In its
formation, therefore,  water is decomposed, the elements of it combining
respectively with the  blue indigo  and the deoxidizing body.
  On the properties of this white indigo depend the important application
of indigo as a dyeing  material.   The indigo is rendered soluble  either by
lime and  copperas  (cold indigo  bath), or, being diffused through warm wa-
ter with a quantity of woad,  by the fermentation  of which ammonia and
hvdroo-en are evolved, a soluble compound of ammonia and white indigo
 *   °                            4  1 
618           SULPHATES  OF  INDIGO,  ETC.
is obtained (hot indigo bath) ; the former is employed for cotton, and the
latter for woollen cloth.   The cloth is immersed in the bath until it  has
fully imbibed the solution;  it is then exposed to the air, the  oxygen of
which carries off the hydrogen of the white indigo, and the blue insoluble
indigo attaches itself to the fibres  of the cloth so  firmly at the moment
of its formation, as to constitute the most permanent and the most beau-
tiful of our blue dyes.
   Sulphate of Indigo.—When blue indigo, in very fine powder, is digest-
ed with strong oil of vitriol, for which  purpose the German or fuming  sul.
phuric  acid answers best, it dissolves in great part, and two acids  are
formed,  the  Sulphopurpuric  and Sulphindylic; the former is the  prin-
cipal  product when the indigo is in excess, the latter when the oil of  vit-
riol preponderates ; they are separated  by dilution with water, the sul-
phopurpuric acid being insoluble, while the sulphindylic acid dissolves.
  The  sulphopurpuric acid, though  insoluble in  dilute acids, dissolves
readily in pure water;  it forms, with the alkalies and earths, blue com-
pounds, which are sparingly soluble in water, but soluble in  alcohol.   By
the analysis of Dumas, it  appears to consist of C^H,,,. N204+2S.03, and
in its potash salt to contain one atom of alkali.
  The  sulphindylic acid, C,6H5. N.02 + 2S.03, when dried from its solu-
tion in  water, forms a dark blue mass.   Its salts are of a rich blue col-
our ;  those of the alkalies are soluble, those of the earths and metallic  ox-
ides insoluble in water.  They consist, according to Dumas's analysis, of
an atom of indigo, two of sulphuric acid, and one of base.  The sulpho.
purpuric  and sulphindylic acids thus  contain  the same organic element
(indigo), but in different proportions,  united to sulphuric acid.
  Berzelius considers  that, besides these two, there are generated, by  the
action of sulphuric acid on indigo, several other acids of complex nature ;
but, as we  possess no exact  results  concerning them, and as they  are
of no technical  importance, it is unnecessary to describe them in detail.
  This solution of indigo in oil of vitriol constitutes the Saxon Blue, or
Chemic Blue, used  extensively in dyeing; on  neutralizing the liquor by
an  alkali (carbonate of soda), and immersing the tissue, whether  wool,
Bilk, or cotton,  the  indigo combines with  the  fibre of the cloth, and  the
sulphuric acid remains combined with the  alkali.
  By the gradual oxidation of indigo, a substance is formed which crystallizes in
large red prisms, and is termed by Laurent Isatine;  its formula is Ci6H5. N.O*.  If
the process be more violently carried on, the constitution of the indigo is broken up,
and a new type formed, thus: by the action of an excess of nitric acid on indigo,
two remarkable bodies are formed, the  Anilic and the Picric Acids.  A mixture of
one part of fuming nitric acid and ten of water being brought to boil, indigo is to be
added in fine powder as long  as any effervescence occurs;  the liquor is to be then
filtered while hot.  Both acids crystallize on cooling; the crystals are to  be drain-
ed, redissolved in water, and precipitated by acetate of lead ; picrate  of lead falls;
amlate ot lead remains dissolved, and, being decomposed by sulphuretted hydrogen,
the  Anihc Acid crystallizes in white needles ; its taste is bitter and acid ; it requires
1000 parts of cold and but ten of boiling water; its salts are all soluble; its for-
mula is C|4H4 . N.09+Aq.
  The Picric Acid may be obtained by diffusing the  picrate of lead through  boiling
water, and decomposing it by sulphuretted hydrogen gas;  on filtering and cooling,
the picric acid crystallizes.   It may be obtained, however, much  purer and more
abundantly by digesting salicine in  nitric  acid (p. 606), and directly from the  sub-
stance which exists  in coal gas naptha, termed by  Laurent hydrate  of phenyl; it
forms yellow prisms, sparingly soluble in cold water; when heated, it explodes, as
do also its salts; its potash salt requires  260  parts of cold water for solution, and
it is hence sometimes used as a reagent for that alkali; its formula is C12H3. N3Ou 
ACTION  OF  CHLORINE  ON   INDIGO.        619
  When indigo is mixed with a strong boiling solution of caustic potash, it dissolves
and C/injstJiulie Acid is formed, which may be precipitated by muriatic acid as an
orange-red powder;  it dissolves in alcohol and ether, and crystallizes by the evap-
oration of the solutions ;  its formula appears to be C2SH10 . N.05+Aq.  By exposure
to the air  while hot, or directly by contact with peroxide of manganese, this acid is
converted into  another, Anthranilic Acid, the properties of which are remarkable •
it is soluble, crystallizes, gives very well-marked and  crystallizable salts, fuses at
275°, and sublimes a  little above that temperature unchanged ; if it be strongly
heated, however, it is decomposed, the sole products being carbonic acid and a vol-
atile liquid, Amlene.  The formula of the hydrated anthranilic acid is C14H7 . N.O4,
and it gives 20.02 and  C12H7N.
  This liquid, anilene, is a body closely analogous to the melamine (p. 526); it acta
as a powerful base, combining with the hydracids directly, and with the oxacids by
including  an atom of water;  it thus resembles ammonia.  These important sub-
stances, for whose discovery we are indebted to Fritzche, are still under examina-
tion.
  Action of Chlorine on Indigo.—This subject, so important in relation to the theory
of the bleaching of colouring matters, has been very minutely investigated  by Erd-
man, of whose  numerous and complex results  the elementary nature of this work
will allow but a general notice to be given.  Dry chlorine has no action on indigo,
but  in presence of water it converts it into a yellow mass, from which is separated,
by distillation, a  substance  termed Chlorindoplen, which sublimes in white scales
and needles ; its formula is C16H4 . 02CU; it is sparingly soluble  in water, copiously
in alcohol  and  ether.  This appears to  be a secondary product.   The substance
which remains  behind  in the retort, on being dissolved in boiling alcohol, yields, on
cooling, red prismatic crystals of Chlorisatine: its formula is  C|6H4C1. .  N.03;  it is
hence indigo, in which  an equivalent of hydrogen is replaced by chlorine, and united
to an atom of oxygen ; with an excess of chlorine it gives Bichlorisatine, which con-
sists of C|SH4Cl2. N.03.  If these  bodies be treated with sulphuretted hydrogen,
sulphur is set free, and the hydrogen enters into combination; in contact with pot-
ash, the elements of an atom of water are assimilated, and an  acid formed, which
unites with the potash.   In this  way chlorisatine gives Chlorisalyd, C|6H5C1. . N 03,
and  Chlorisatic Acid,-GwH$Cl. . N 04, and bichlorisatine  gives  two corresponding
bodies.
  If chlorisatyd be heated, it produces water, chlorisatine, and a violet powder, Chlo-
rindine, which has the formula CieHsCl. . N.02,  and is hence a compound of indigo-
blue with  chlorine.   By heating bichlorisatyd, the Bichlonndinc, C|6H5N. . 0SC12, is
similarly formed.
  By passing chlorine  through a solution  of chlorisatine in alcohol, all hydrogen is
removed,  and a substance formed which crystallizes in pale yellow plates, and  has
the  formula C602Cla ;  it is termed Chloranil.  By the secondary reactions of these
bodies, a number of others are generated, which it is not necessary specially to de-
scribe.
  Notwithstanding the attention devoted by the  most distinguished chemists to the
compounds and derivatives of indigo, the theory of that body  remains  very obscure.
The derivation  of picric acid from the  body C,2H50.+Aq. (Hydrate of Phcenyl), dis-
covered as a product of destructive distillation by Laurent, may serve as a connect-
ing  point for many of the bodies derived from indigo, and which otherwise had ap-
peared totally unconnected.   Thus the picric acid  is evidently  formed  by the sub-
stitution of 3N O4 for  3H. in  C12H5O., and the  anilene is probably C12H5+NT.Ha ;
other speculative ideas might be brought forward, but I shall only mention that the
blue indi"o contains  exactly the elements of cyanogen  and benzyl, CoX+CuHjOj,
and that.na.s the cyanogen is converted so easily into oxalic acid and ammonia, the
derived bodies,  which contain Cu, may thus have their origin.

            Of the  Colouring  Matters  derived from the  Lichens.
  Many species of lichen contain substances which, although colourless themselves,
produce by contact with air and ammonia, the  rich purple or blue colouring mat-
ters  constitutin ' the archil and litmus of commerce.   The species of lichen that
hive been in tin's respect most accurately examined are the variolaria dealbata by
Robiquet and D mias, and the rocella tinctona by myself.
  The useful substance in the variolaria is termed Orctne; it is obtained by digest
in ■  the lichen in alcohol, evaporating  to dryness, dissolving  the extract in water,
concentrating the solution to the  thickness of a  sirup, and setting it aside to cm- 
620           ORCEIN E,  ERYTHRYLINE, ETC.
tallize ; it forms, when quite pure, colourless prisms of a nauseous-sweet taste; it
fuses easily, and may be sublimed unaltered ;  its formula is C|8H703+2 Aq. when
sublimed ; when crystallized from its aqueous solution, it contains 5 Aq.
  If orcine be exposed to the combined action of air and ammonia, exactly as de-
scribed for phloridzine (p. 607), it is converted into a crimson powder, Orccine, which
is the most important ingredient in the archil of commerce.  The orce.'i'ne may also
be obtained by digesting dried archil in strong alcohol, evaporating the solution in
a water-bath to dryness, and treating it with ether as long as anything is dissolved ;
it remains as a dark blood-red powder, being sparingly soluble  in water or ether,
but abundantly in alcohol; its formula is Ci8Hi0. N.08.  The orcei'ne in archil is,
hovvever, frequently  found  to contain less oxygen, and to be represented by  the
formula C|SHio. N.05.  I have termed the first kind Alpha-orceine, and  the second
Beta-orccine; in properties they  are identical.
  Orcei'ne dissolves in  alkaline liquors, with a magnificent purple colour ; with me-
tallic oxides it forms lakes,  also, of rich purple, of various shades.  In contact with
deoxidizing agents it combines with hydrogen, as indigo does,  and  forms Leucor-
ce'ine, Ci8H|0 . N.08+H. When  bleached  by chlorine, a yellow substance is formed,
Chlororceine, the formula of which I have found to be C18Hi0.N.O8+Cl., analogous
to the other.
  In the rocella tinctoria there is no orcine ;  the origin of the coloured  substances
is a body which I have termed Erythryline; it is soluble  in ether and alcohol, insol
uble in water, but is  gradually decomposed by it ;  its formula  is C22H16O6.  By the
action of the air it is gradually changed into Erythrine, a substance which dissolves
sparingly in cold, but abundantly in boiling water,  from which  it separates on cool-
ing in brilliant micaceous plates; it is  very soluble in alcohol and ether;  its  formula
is C22H,309.   By prolonged boiling in  water, erythrine is changed into a substance
very soluble in water and in alcohol, Amarythrine, the formula of which is C22H|3014;
and, finally, by the still farther action of the air, Telerylhrine is formed, which crys-
tallizes in small grains, and has the formula C22H90|8.
  If, however, in addition  to the air, ammonia have access  to these  bodies,  the
crimson colour is produced, and the two varieties of orcei'ne are formed.   I conceive
the oxidizing stage to proceed as far as amarythrine, and that, by combination with
ammonia and oxygen,  a substance is  formed, to which I have given the name of
Azoerythrine.  Its formula  is C22H16 . N.O,9+3 Aq.  By  the loss  of  4C02  and
6H.O., it gives alpha-orceine, C,8H|0.NO5, which, absorbing  oxygen, gradually
forms the true or beta-oreei'ne, Ci8Hl0 . N08.
  When an  alkaline solution of orcei'ne is exposed to the air, it absorbs more oxy-
gen, and a substance is produced which  constitutes a great part of the colouring
material of litmus.  I have termed it Azolitmine ; its formula is C|8Hi0 . N.O,0 ;  it is
a dark red powder, which is insoluble in alcohol or ether, and  but sparingly soluble
in water;  it dissolves  better in acid liquors, which render it  a  pale red, and with
alkalies it gives the  rich blue colour of litmus.  With the earths and metallic  ox-
ides it forms purple or blue  lakes ; with deoxidizing agents it  is decolorized, form
ing Leucolitmine, and by chlorine  a yellow substance  is produced, having  the  foi
mulaC,8H,0.N.O,o+Cl.
  Besides the bodies of the erythrine series, the lichen rocella contains a substance,
termed Rocelline, which is white, fusible,  insoluble in water, soluble  in alcohol  and
ether ; its formula is C26H24O6.  By exposure to the air,  it is converted into a fatty
substance of a rich crimson colour, which I have termed Erythrolcic Acid; this body
exists in archil, and  is separated from the orcei'ne by means of its solubility in ether.
Its formula is C2eH2208; it is capable,  under circumstances which are not yet well
understood, of being broken up  into two  substances, which are  both found to exist
inlitmus; they are Erythroleine, which  has the formula C26H2204, and Ervthrolit-
•""".which consists of C26H22012.   The  erythroleine  and erythroleic acid are, like
the alpha and beta orce.'nes, distinguished only by their composition ; they  have the
same colour are sparingly soluble in water, but copiously in alcohol and ether; they

fhf«I?auJSlT ' rlU°rS W1uh  f "Ch  Crimson colour* and  Sive  c"mson lakes with
the meta he salts.   Ihe erythrohtm.ne, on the  other hand, is bright red, verv  spa-

Sff Utnrinn nf m^V^^ S°'Uble in alcoho1*  M^s *rn it bright blue ;

^:^oli!Xo^s^s'but its compound with ammonia is insoiubie:
  The brief history of these substances now given  will render intelligible the nrnoess
of manufacture of archil and litmus, and  the"principled?$ Zefl£? ,n tne ar S
in the laboratory.  The lichens employed are ground up with water  to a uniform 
COLOURING  MATTERS   OF  LEAVES,  ETC.    621
pulp, and this  is then mixed with as much water as makes the whole thick-fluid.
Ammoniacal liquors from the gas or ivory-black works, or even stale urine, are from
time to time added, and the mass frequently stirred, so as  to promote the action of
the air.   The  orcine or erythrine which existed in the lichen absorbs oxygen and
ammonia, and  forms orcei'ne ; the rocelline absorbs  oxygen, and forms erythroleic
acid ; these being kept in solution by the excess of ammonia, the whole liquid is of
an intensely rich purple tint, and constitutes ordinary archil.  If the oxidizing ac-
tion of the air be  allowed to go too far, we have the purple colour replaced by a
shade more or less blue ; the orcei'ne changes to azolitmine, and the erythroleine
gives erythrolitmine ;  a quantity of chalk and plaster of Paris is then added to the
liquor,  so as to form a consistent paste, and this, cut into little cubical masses and
dried, forms the Litmus of  commerce.  From the constitution of archil and litmus,
such must  be  the  general  principles  of the manufacture, although, particularly for
litmus, the details are kept very secret by those engaged in the trade.
  The use of  litmus paper as a test for the presence of a free acid arises from the
blue colour belonging to compounds of the erythrolitmine and azoerythrine with an
alkali, and  as  this is taken by  even the weakest acid, the red  colouring materials
are set free.

             Of the  Colouring Matters of Leaves and Flowers.
   The green  colour of plants is due to the presence of a substance termed Chlor-
ophyll.   Even  deeply-coloured plants contain but very little of it, and it has not, as
yet, been obtained in a state of  such  purity as that any formula can  be assigned to
it.   It  does not contain nitrogen ;  it is insoluble in water, soluble  in alcohol and
ether; it is dissolved by strong acids, and  precipitated  therefrom  by dilution ; it
enters into union with bases, and gives pale green lakes.  With deoxidizing  agents
it shows the same process of decoloration as most other bodies  of this class.
   Berzelius has noticed that there are really three kinds of chlorophyll: the first,
which exists in fresh leaves, dissolves in acetic acid with a rich grass-green col-
our ; the second, formed from the first by drying, gives an indigo-blue solution with
the same acid ; and the solution of the third, which exists principally in the pjrus
aria and other dark-leaved plants, is brownish-green   So excessive is the colouring
power  of this  body, that Berzelius has calculated that the entire mass of leaves of
a large tree seldom contains ten grains of chlorophyll.
   It is known that  in autumn  the leaves of many trees, as the sorbus aucuparia,
cornus sanguinea, &c, assume  a fine red colour, while the foliage of others, partic-
ularly  of forest-trees, becomes bright  yellow.  Berzelius, who has  examined the
nature of this change, found the chlorophyll to be replaced in such leaves by a red
and a  yellow colouring matter, to which he gave respectively the names Erythro-
phyll and Xanthophyll.  The former is an extractive  matter, easily soluble in alcohol
and water; by the air it is gradually changed into a brown insoluble matter; with
alkalies  it  forms rich green solutions, and with metallic oxides, green lakes; by
acids the  red  colour is restored; a green leaf containing chlorophyll is, however,
not reddened  by an acid.   It is remarkable, that all trees in whose  leaves erythro-
phyll forms in autumn bear red  fruit, as the cherry, currant, &c.
   Xanthophyll is a deep yellow, fatty substance, which  melts between  100° and
 120° •  it is insoluble in water, but  dissolves copiously in  alcohol and ether; its so-
lution, exposed to the air and light, is rapidly bleached : alkalies dissolve it sparing-
ly with a yellow colour, which is bleached by light.
   We possess but very little accurate knowledge of the colouring matters of flow-
ers * they constitute a very remarkable  group of bodies, closely related to each
other and  distinct from the colouring matters that have been as yet examined. It
has been stated that the colours of all flowers result from two ; one blue (Anthocy-
an) which is soluble in water  and alcohol, reddened by acids, rendered green by
alkalies  and from these changes producing the  red, and all intermediate shades of
purple and violet • the yellow substance (Anthoxanthine) is likewise easily soluble
in  alcohol  and water, and is coloured  intensely blue by oil of vitriol.  These sub-
stances  possess most analogy  to hematoxylin and to safflower-yellow; but it is
hhrhlv probable that a great number of species of colouring matters exist in flowers
as thev  do in woods.   The quantity present in the flower is generally so  excess-
ively minute,  that the accurate examination of their  properties is exceedingly dif-
ficult 
622           THEORY  OF  DYEING, ETC.
 On some general Characters of Colouring Matters, and on the Principles
                             of Dyeing.

   In addition to the detailed history of the individual colouring matters,
 there are a few remarks belonging to them as a class which deserve
 notice.
   Under the heads of indigo and of orceine, I have described the forma-
 tion of white compounds, by the action of deoxidizing  agents, and that
 in those, which are the only cases that have been  accurately examined,
 it resulted  from the direct combination of hydrogen with the  colouring
 matter.   This character of forming a colourless compound with hydro-
 gen appears to belong to all colouring substances.   If an infusion of log-
 wood, of cochineal, of violets, of immerin, be rendered acid by muriatic
 acid, and a slip of zinc immersed therein, the  liquor becomes  gradually
 colourless, and  on  adding ammonia, a white lake is precipitated, consist.
 ing of the  hydruret of the colouring matter combined with oxide of zinc.
   With oxygen all colouring matters appear also to combine to form bod.
 ies quite or nearly destitute of  colour.  Thus, if the chrysorhamnale of
 silver be boiled in  water, metallic silver separates, and oxidized colour-
 ing matter  dissolves.  This illustrates the manner in which colours fade,
 and they are more or less fugitive, according as their tendency thus to
 combine with oxygen is greater.   On this principle was founded the  old
 process  of  bleaching, by exposing the cloth to  the  conjoined agencies of
 water, air, and  light.  The bodies whose colour injured the whiteness of
 the cloth were gradually changed by oxidation into others, less coloured
 and more easily removable by washing.   In the majority of cases,  how.
ever, the process is not limited  to simple oxidation, but carbonic acid is
evolved, and the colouring  matter is totally broken up in constitution.
   The colour of many substances, as logwood, archil, litmus,  indigo, of
most flowers, &c,  is removed by sulphuretted hydrogen and by sulphur.
ous acid.   In these cases there is direct combination, and the colour is
restored by expelling the  combined gas, by heat,  or by  a  strong  acid.
For commerce, many bodies, particularly those of a yellow colour, are
given  a temporary whiteness  by stoving or smoking with sulphurous
acid, by placing them in a room where sulphur is burned ;  this is  done
with corn,  with straw for hats, with sponges, &c.  The sulphurous acid
gradually goes off afterward, and the yellow colour returns.
   The destruction  of colours by means of chlorine  is the most important
decomposition to which this class of bodies is subject, as on it the modern
 processes  of bleaching  all our woven tissues,  paper,  &c, is  founded.
 Innumerable niceties in the application of coloured patterns  on  cloth
 would be impossible, and the art of the calico printer restrained to very
 narrow limits, were it not for the power which  chlorine gives him  of re-
 moving the original  colour from any chosen space, and  replacing it by
 others of various  tints.   The  theory of this action of chlorine,  which
 had been formerly  thought  to depend  upon a mere oxidation of the  col-
 ouring matter,  water being decomposed, has been shown by my results
 with orceine, and confirmed by  those of Erdman on indigo,  to consist in
 the formation of new substances containing chlorine.   The chlorine in
 some  cases replaces hydrogen ; in others it combines directly with the
 colouring matter;  in others, again, water is decomposed, and the prod-
 uct, besides containing chlorine, is also more highly oxidized.   The 
        FIXING  OF  COLOURS  ON  CLOTH,  ETC.     623

action of chlorine on colouring matter is therefore subjected to the same
laws as when it acts  upon other organic substances, the series of bodies
derived from indigo by chlorine having much analogy  to  the series  of
bodies formed with alcohol or olefiant gas.
  In relation to  the  processes of dyeing, colouring substances are divi-
ded into  two classes, the substantive and adjective.   The substantive
colours  are those which, being very  sparingly soluble in water, and
having a strong  affinity for the fibre of the cloth, combine directly with
it;  such  are carthamine and indigo; the adjective colours  are incapable
of so permanently fixing themselves, and the necessary insolubility and
affinity for the  cloth is given through  the intervention of a base with
which the colouring  substance may combine.   The cloth  is mordanted
with alumina (p. 436), or iron (p.  558), or tin (p.  448), or mixtures  of
these metallic oxides, and as the  lakes so formed are of different  colours,
a great variety of tints may be produced.  The field of application  of
substantive colours,  also, is  greatly enlarged by the use of mordants ;
the simple colouring  matter could, of course, give but its own tints, while
it forms,  with the bases, lakes of various colours.
  The resources of  the dyer are by no means  limited  even by  the vast
number of coloured substances described in the  present chapter.   From
the mineral kingdom, some of the  richest colours are  now procured,  as
has been already noticed in the special history of the salts  of chrome, of
iron, of copper, of lead, of manganese, and of antimony.   It is remarka-
ble, that hitherto no true green colouring matter has been found  capable
of application in the  processes of dyeing, the only greens which  exist in
nature  being the chlorophyll and the  green  of the stems of buck-thorn
(sap-green), neither  of which is  capable of being attached to cloth:  all
greens are, therefore, in practice, formed by the superposition of a blue
(indigo or Prussian blue) and a yellow (chromate of lead or chrysotham-
mine).
  The details of the processes of  dyeing and printing in patterns, al-
though embracing some of the most refined applications of the properties
of the colouring  matters, do  not enter into the plan of an elementary and
general work, such as this should be.
                        CHAPTER XXVII.

                    OF THE VEGETABLE  ALKALIES.

  The substances now to be described constitute a very remarkable
family of bodies.  They exist naturally in the plants from which they
are derived, and confer upon them their most active medicinal prop-
erties ; they act as bases, forming, with few exceptions, well-char-
acterized and neutral salts even with the strongest acids, and they
are distino-uished from most substances of vegetable origin by con
tainino* nitrogen.  The presence of this element, indeed, has been
considered as standing in immediate connexion with the source of
their alkaline power, and has given rise to theories of their intimate 
624
QUININE  AND ITS  SALTS.
   constitution, of which I shall notice  the most important at the con-
   clusion of their special histories.

          Quinine.,-(N.O,,. H.A)  or Qu.   Eq. 163*1 or 2039.
     The bark of the various species of cinchona contains three vege-
   table alkalies, combined  with the  cinchonic and  cinchonatannic
   acids already described.  These are quinine, cinchonine, and ari-
   cine; of these, the quinine is by far the most important, and is gen-
   erally extracted from the yellow bark.  The coarsely-powdered bark
   is to be boiled with eight  or ten parts of water,  to which  two parts
   of muriatic acid have been added.  When  the  liquor will dissolve
   no more, it is to be allowed to cool, and strained; lime is then to
   be added in very fine powder until the  liquor has a marked alkaline
   reaction; the precipitate is to be collected on a  linen cloth, washed
   once or  twice  with water, and then  dried;  from this, boiling alco-
   hol dissolves out quinine and cinchonine; the solution being  mixed
   with water, the alcohol may be distilled off and  saved; the residue
   is to be  then neutralized by dilute sulphuric  acid, and a  slight ex-
.   cess added to form acid  salts.  On evaporating this liquor  to the
   proper point, the sulphate  of quinine crystallizes, while the sulphate
   of cinchonine remains in solution.
     To obtain pure quinine, solution of sulphate of quinine is  to be
   decomposed by caustic potash, and the white curdy precipitate, be-
   ing carefully dried, is to be dissolved in the  smallest possible quan-
   tity of spirit of wine.  By then  allowing it  to evaporate  spontane-
   ously in a warm  place, the pure quinine crystallizes with an atom
   of combined water.
     When heated cautiously, the quinine abandons its crystal-water,
   and then fuses;  its taste  is intensely  bitter; it requires  200 parts
   of boiling water for solution, and is almost insoluble in cold water;
   it dissolves easily in alcohol and ether.
     The salts of quinine  are  generally crystallizable, and soluble in
   alcohol and water; those with the oxygen acids  contain an atom of
   water, in which they agree with  the salts of ammonia, of melamine,
   and of anilene ; it combines directly with the hydracids.
     The Muriate of Quinine, (Qu.-f-H.Cl.), forms  pearly needles. It
   dissolves easily in water ; with corrosive sublimate and with bichlo-
   ride of platinum it forms  double salts, soluble  in water,  and crys-
   tallizable.
     The Basic Sulphate of Quinine is the  most important preparation
   of this base;  its manufacture is conducted on  a very large  scale,
   according to the  process  just now given for  preparing quinine, or
   various analogous methods.   When  crystallized, it contains water,
   its formula being (Qu2+S.03+8 Aq.).  It effloresces when  gently
   heated or in very dry air, giving off six atoms of water and retain-
   ing two, which cannot be expelled without partial decomposition;
   it is but sparingly soluble  in water, requiring  thirty parts  of boiling
   and 740 parts of cold water ;  it  requires  eighty parts of  cold alco-
   hol, but much less of hot; its crystals are small pearly plates or
   needles, which, when heated, phosphoresce strongly  and fuse ; by
   a strong heat it is, of course,  totally decomposed.
     The Neutral Sulphate of Quinine crystallizes in rectangular prisms, 
SALTS  OF  Q U I \ I N E.--C INCHONI N E.       625
which have the formula (Qu. + S.Oj -f 8 Aq.).  They effloresce easily,
dissolve in ten parts of water at 60', and undergo aqueous fusion at
212\   It  is also very  soluble in alcohol; though neutral in consti-
tution, its solution reddens litmus.
  The sulphate  of quinine  of commerce is  sometimes adulterated
with sulphate of lime  and with boracic acid, which are  known by
remaining when the organic substance is burned away, and also
with su-Tar and with margaric acid.   The latter  is detected by its
insolubility in dilute acids;  the former by washing the sample with
a little water, and precipitating the quinine that is dissolved by a
drop of solution of carbonate of soda, when the taste of the sugar
is recognised.
  Phosphate of Quinine crystallizes  in  small but very brilliant nee-
dles, which are soluble in water and alcohol.
  The Tannate of Quinine is formed  by adding solution  of tannic
acid or infusion  of galls to any  salt  of quinine.  A white precipi-
tate appears, which is totally insoluble  in water, but dissolves in
acetic and muriatic acids.
  Ferroprussiate of Quinine is formed by boiling together one part
of sulphate of quinine and  one and a half of yellow prussiate of
potash with seven parts of water.  The newly-formed salt separates
as a oreenish-yellow oily substance.   When the liquor is cold, it is
to  be  poured off, and the  ferroprussiate  of quinine  dissolved in
boilino- alcohol, from which it  crystallizes in greenish-yellow nee-
dles by spontaneous evaporation.
  The action of chlorine on quinine and its salts is very character-
istic.   If  sulphate  of  quinine  be  dissolved  in a  large quantity of
chlorine  water,  and some water  of ammonia added, a deep green
precipitate is formed,  and the liquor becomes also intensely green.
To the body so formed the name Dalleiochin has been given.  If
the green solution be evaporated with contact of air, it becomes
dark-red  coloured, sal ammoniac is  formed, and  two bodies, of
which one  is soluble  in alcohol, and the other not; the former is
called Rusiochin,  and  the latter Mclanochin.  Formula;  have been
proposed  for these bodies, but as  no security for  their accuracy
has been  given, I think it better not to bring them forward.   These
reactions,&combined with the  action  of tannic acid, serve as tests
for quinine.
       Cinchonine.-^.C„ . H120. or Ci.  Eq. lf>5*l or 1939.
   This alkali exists most  abundantly in the gray bark (cinchona
micrantha) from which it may be obtained by the same kind of pro-
cess as the'yell°vv-bark is subjected to for the extraction of quinine;
but it is  usually prepared from the mother liquors which remain
after  the  crystallization  of the sulphate of quinine, as just now de-
scribed *  from its alcoholic solution it crystallizes in thin colourless
prisms;'its taste  is peculiar and bitter; it  requires 2500 parts of
boilincr water for solution,  but dissolves easily  in  alcohol and m
ether ° At 330° it fuses, without  losing weight.  Its salts resemble
verv closely those of  quinine.
  Muriate of Cinchonine, Ci.+H.Cl.,  crystallizes easily in brilliant
                                4 K 
626
A R I C I N E.---M O R F H I A.
interwoven needles ; it forms double salts with the metallic chlo-
rides, similar to those  of quinine.
  Sulphate of Cinchonine.—^he  basic sulphate,  Ci, + S.03+2 Aq.,
crystallizes in rhombic prisms; it requires fifty-four parts of cold
water for solution.  The neutral salt, Ci. ->- S.O;H 8 Aq., is much more
soluble, and crystallizes in large, well-formed rhombic octohedrons.
The Tannate of Cinchonine is a white insoluble powder.
  In contact with chlorine, cinchonine  forms a dark  red  solution,
and  after some time  a brown precipitate appears.  If iodine and
cinchonine be dissolved together in alcohol, and  the  liquor evap-
orated spontaneously,  a compound crystallizes in  saffron-coloured
needles, which is described as Iodide of Cinchonine, which it  cannot
be,  as hydriodic acid is formed.

        Aricine.—N.C20. H1203 or Ar.  Eq. 171*1 or 2139.
  This alkaloid is  found  in the bark known as China de cusco,  or
arica bark, with which the  genuine cinchona bark  is often adulter-
ated; the tree yielding it is not known.   It is obtained by precisely
the same  process as cinchonine and quinine are procured from the
pale and yellow  barks.
  It crystallizes in  brilliant white needles; it is totally insoluble  in
water, but easily dissolves  in alcohol and ether.   These solutions
have an intensely bitter taste ; by nitric acid it is  coloured  green;
its salts have been  but very little examined, but they appear  to cor-
respond very closely in constitution and properties to the salts  of
quinine and cinchonine.

        Morphia.—N.C35. H20O6 or Mr.   Eq. 293*8  or 3673.
  To this body is due, in most part, the medicinal activity of opium,
as a substitute  for which it is prepared upon a very large scale-
The processes adopted in the British pharmacopoeias for this pur-
pose are very simple,  and deliver a  product which, although by  no
means chemically pure, is yet sufficiently so for all medicinal ob-
jects ; as they are, however, more  especially applied to the prep-
aration of the muriate of morphia, I shall describe  them under that
head.
  To obtain pure morphia, the process invented  by Wittstock is
perhaps the best.  One part of opium,  eight of  water, and  two  of
muriatic acid are to be digested together for six hours ; when the
mixture has cooled, the brown solution  is to be poured off, and the
residue treated twice  more with water  and acid.   The liquors so
obtained, being  mixed, are to be saturated with  common  salt, on
which they become milky, and after a few hours, a brown clotty
precipitate forms ;  this being removed by the  filter, ammonia is to
be  added in slight excess, and the whole allowed to stand  for twen-
ty-four hours.   The precipitate which forms in this  time is  to be
collected on a filter, washed with a little water, dried, and digested
in spirit of specific gravity 0*820, which dissolves  out the morphia.
By  distillation,  the greater part of the spirit  is removed, and  the
morphia, being dissolved in a small quantity of boiling alcohol, crys-
tallizes on cooling.   In this process the narcotine is  separated by
 the addition of the common salt, in a solution of which it is insolu- 
PROPERTIES  OF MORPHIA.           627
ble ; the meconic acid, codeine, and thebaine remain dissolved after
the  addition  of  the ammonia in  excess, and  the  other principles
present in the opium remain  in the mother liquor after the morphia
crystallizes.                               .
  The process of Merck is founded on the insolubility ot morphia
in a  solution of sal  ammoniac,  and  its solubility  in  lime-water.
Opium is to be digested in three times its weight of water, then ex-
pressed, and  this repeated three or four times ;  these solutions be-
ino- mixed, are brought to boil, and milk of lime added in slight ex-
cels ; the precipitate  which  forms is to be collected on a strainer
and strongly pressed; the liquor  is then to be evaporated until it is
about twice the  weight of the opium employed, and to be then fil-
tered  brought to boil, and for each pound of opium, one ounce of
sal ammoniac added in powder.  The morphia separates in crystals
and may be purified by boiling with some lime and ivory black, and
precipitation again by sal ammoniac.
  Morphia crystallizes  in right rhombic prisms, as in the figure, z,
 u being  primary,  and m a  secondary plane, containing /-ffvYx
 2 Aq. which they lose  by efflorescence in a gentle heat, pp ,   ^
 and become  opaque ; its taste is strongly and permanent- U \u\ ■».
 ly bitter ; it is  almost  insoluble  in water, requiring 400 Uj^k\J
 parts when boiling, and separating almost comp etely as  >i^
 the liquor cools.  The solution reacts strongly alkaline ; it dissolves
 readily in alcohol, but very  sparingly in ether.  It dissolves in so-
 lutions of the caustic alkalies or  earths.   If morphia  or any of its
 salts  be brought into  contact with nitric acid, they become coloured
 red;  this property belongs  also  to some other vegetable alkalies,^
 and appears not to be possessed by morphia when absolutely pure.
 With chlorine water, morphia is first coloured orange-red, and then
 dissolved.  If iodic acid be  brought into contact with morphia, it is
1 immediately  decomposed, and iodine set free.
'If morphia or any of its salts be added  to a solution of sesquichlo-
 ride  o   on, the  solution assumes a rich blue  colour, which is re-
 moved by an excess  of acid, but  returns on the neutralization of it
Ibv In alkali.  With tannic acid it gives a copious white precipitate.
 By these remarkable reactions, the recognition of morphia is ren-
 dered more simple than that of any other body of its class.
   Sorphia co^letely  neutralizes the strongest acids, forming salts



 moSint compound^^^^^^^ ^
 by the Brtush  pharmacopcems    as io£      ^        ^P ^
 opium having beenved o     y  o       of a gi    and then
 liquors are to be  WX^uantity of feculent matter (apotheme)
 cold -ater added, by^h ch  aj     ^ d       oged .      gH h

 » sePfa^dl'henfCS fLondon) or of chloride  of calcium (Edin,
 cess of chlonde ofJ-dCLon    J   ^ ^              ^

 burgh).  The mecona      of !fme or lead is precipitated, and mu-
 ,ng decomposed, ™ec™aiedissolvcd . the liquor  is to be carefully
 riate of --P^^d"   a pellicle  on cooling, the salt crystalli-
 fesTtlis'is to be pressed  between  folds of cloth, to  remove the 
628
N A R C O T I N E.--C O D E I N E.
dark mother liquor, and then dissolved in boiling water, digested
with ivory black, and recrystallized until the crystals become per-
fectly white.
  The product of this method, although not chemically pure, is suf-
ficiently so for medicinal uses.  It contains codeine, and sometimes
others of the  opium alkaloids.  To obtain  the pure salt, pure mor-
phia should be dissolved in dilute muriatic acid, and the  solution
crystallized.
  Sulphates of Morphia.—The neutral sulphate, which crystallizes in
groups  of soft needles, and dissolves in twice its weight of water,
has the formula Mr.H.O.. S.034-5 Aq.   The Bisulphate of Morphia
does not crystallize.
  Acetate,  of Morphia is formed by dissolving the alkali in acetic
acid, or by decomposing muriate of morphia by acetate of  lead; it
is soluble in water and in alcohol, and, after the muriate, is the most
important salt of morphia.
  Morphia is  precipitated by ammonia and by tannic acid from  so-
lutions  of any of these salts.

        Narcotine.—7$.Ci6. H,20J3 or Nr.  Eq. 5230 or 418.
  This  alkaloid may be obtained at once from opium by digestion
with ether, or when the impure  morphia is  thrown down by ammo-
nia, ether dissolves out the narcotine from it.  It crystallizes in col-
ourless rhombic prisms, which  are generally larger than those of
morphia;  it fuses at 338°, and remains liquid until cooled  to 266°,
when it congeals as a mass of radiated needles.  It is almost insol-
uble in  water, but easily soluble in alcohol and ether; its salts have
but little stability, few of them  crystallize,  and most are decompo-
sed by dilution with much water.  By ammonia and tannic acid they
are precipitated.
  From morphia, narcotine is very easily distinguished by  its solu-
bility in ether, insolubility in caustic alkalies and earths, and its not
giving the reactions characteristic of morphia with nitric  acid or
with sesquichloride  of iron.  But if narcotine be put in contact with
sulphuric  acid, and  oxygen  is  supplied either  by the  air  or by a
trace of nitric acid, it  becomes red.   Under these circumstances,
however, morphia becomes green.

        C0rfeme.-N.C3j. H20O5 or Cdn.   Eq. 3573 or 285*8.
  This  alkali  remains dissolved after  the  morphia, narcotine, and
other substances have been precipitated by ammonia.   The filtered
liquor  is to be  evaporated  to dryness, and digested in  solution of
potash; a substance remains undissolved, which gradually becomes
crystalline.  This is to be Avashed with water, and then dissolved in
boiling  ether,  from which, by spontaneous evaporation, the codeine
separates  in colourless prismatic crystals, which contain  2 Aq.
  Crystallized codeine fuses at 300°, giving off its crystal water. It
dissolves copiously in water ; the solution reacts strongly alkaline;
it  is insoluble in alkaline  liquors, but forms with  acfds perfectly
neutral crystallizable salts.   These are precipitated  copiously by
tannic acid, but not by ammonia; it does  not produce any of the
reactions described as characterizing morphia. As none  of its salts 
        T II E B A I N E.---N A R C E I N E.--S TRYCHNINE.    629

are employed in pharmacy or medicine, they need not be specially
noticed.                                                       •*

        Thebdine.—N.Cx . Hu03 or Tb.  Eq. 2542 or 203*4.
  The watery infusion of opium being treated with milk of lime, so
that the morphia may rest undissolved,  the  precipitate is  to'be
washed with water until it becomes  white, and then dissolved in a
dilute acid.  From this solution thebaine  is precipitated by ammo-
nia.  The  precipitate being  dissolved in ether, and the  solution
evaporated, pure thebaine crystallizes in  colourless short  rhombic
prisms, which taste sharp and  styptic, and  have a  strong  alkaline
reaction.   At 300' it fuses, and solidifies then only when cooled to
230'.   It is scarcely soluble in water, but abundantly so in alcohol
and ether.
  By acids thebaine is decomposed, a resinous substance and a salt
of ammonia being formed.   In  its other characters it completely
resembles narcotine.
  Narceine.—The watery solution of opium  is to be  heated first by
ammonia, which throws  down  morphia,  narcotine, thebaine, and
some other bodies, and these being removed by filtrations, the me-
conic acid and codeine are to be precipitated by an excess of solu-
tion of barytes.   The excess of barytes  being then removed by a
current of  carbonic  acid gas, the filtered  liquor is to be evaporated
to the  consistence of a sirup and set aside ; after some time crys-
tals form, which  are a mixture of meconine (see  p. 610) and narceine.
These  are  separated by ether,  which dissolves  the  meconine, and
the residual narceine being dissolved in alcohol and decolorized by
animal  charcoal, crystallizes, by the  cooling of its solution, in deli-
cate needles.
  It tastes  bitter, fuses at 200°, and forms a crystalline solid  on
cooling ; it dissolves in 230 parts of boiling water ; it is very solu-
ble  in alcohol, but insoluble in ether; its solution does not react  al-
kaline,  and  it is decomposed by strong acids ;  in its constitution,
however, it resembles the true vegetable  alkalies, its formula being
N.C8.H20Oi;.
  Pseudomorphine, N.C54. II,sOl4, occurs but very rarely in opium.
For its  mode of preparation, when present, I shall refer to the lar-
ger systematic  works; in  its reactions it is absolutely identified
with morphia, from  which it is  distinguished, however, by  its com-
position, by crystallizing in plates, and by  not forming any well-
characterized salts, although it dissolves very readily in dilute acids.

        Strychnine—N,CU . Un04 or Stc.   Eq. 4355 or 348.
  This alkaloid exists associated with brucine in several species  of
strychos (nux vomica, ignatia, colubrina, Sec), also in the substance
used by the natives of Borneo for poisoning  their arrows, and term-
ed Upas-tieuta, or Woorara ; it is obtained most easily from the Ig-
natius's beans, which contain but little brucine ; but, as these are not
often  found in commerce, the nux vomica  is most  generally em-
ployed.   The seeds arc to be boiled for some  time  in strong alco-
hol, which dissohes out a quantity of fatty  matter; being then dried
in a stove,  they are easily reduced to powder; this powder  is to  be 
630     STRYCHNINE,  ITS PROPERTIES,  ETC.

then boiled two or three times in  alcohol, and the liquor  distilled
until the greater part of the alcohol has come over.  To the resi-
due, acetate  of  lead is to be added as long as any precipitate oc-
curs ; by this means more fat, colouring matter, and some organic
acids are removed.  The filtered liquor is to be then evaporated so
far, that from sixteen  ounces of nux vomica it  amounts to  six or
eight ounces.  To this quantity two drachms of magnesia are to be
added, and the  whole  allowed  to  stand aside for some days; the
precipitate which  forms is to be collected on linen, pressed,  dried,
and dissolved in alcohol, from which the strychnine crystallizes on
coolino*, while the brucine  remains  in the mother  liquor.  As the
strychnine, however, is not yet pure, it is to be dissolved in dilute
nitric acid, and  the solution evaporated to a pellicle.   On  cooling,
the nitrate of strychnine crystallizes in brilliant white, soft, feathery
prisms, while the  nitrate of brucine separates afterward in  large,
hard, rhombic prisms.   From  sixteen ounces of nux vomica, forty
grains  of nitrate of strychnine and fifty grains of nitrate of brucine
may be obtained ; from the solution of the  pure nitrate in water,
the strychnine may be precipitated by ammonia, and, being dissolv-
ed in spirit of wine, it  crystallizes, by  spontaneous evaporation, in
small white four-sided prisms.
  Strychnine has  an intensely  bitter, somewhat metallic taste ; it
requires  7000 parts of cold  water for solution ; and yet, if one part
of this be  diluted with 100 parts more of water, this liquor  tastes
strongly  bitter;  it is insoluble in absolute alcohol and in ether, but
dissolves  readily  in  spirit of wine.   With acids strychnine unites,
forming well-characterized  and crystallizable salts; it differs from
the other vegetable  alkalies in containing two atoms of nitrogen in
its equivalent.   With chlorine strychnine gives a white precipitate ;
also with tannin ; when completely pure, it is not reddened by nitric
acid, but such as it exists in commerce it generally is so, owing to
the presence of traces of brucine.
  Muriate of Strychnine, Stc. + H.Cl., crystallizes in crowded  rhom
bic needles,  which dissolve readily in water.  With corrosive sub-
limate, with  bichloride of platinum, and with cyanide of mercury,
it gives insoluble  double salts.
  Hydrocyanate of Strychnine is  obtained by dissolving strychnine in
prussic acid ; it  crystallizes in needles, which are decomposed even
by a gentle heat.  If solution of sulphocyanide of potassium  be ad-
ded to  a solution of any salt of strychnine, the liquor, when agitated,
deposites the Sulphocyanate of Strychnine in fine radiated  needles,
which are insoluble in water.  By this means one part of strychnine
may be recognised in  375 of water, and hence Artus has proposed
this reaction as  the best medico-legal test for strychnine.
  Sulphate of Strychnine forms small cubic crystals, which contain
4 Aq.,  and are soluble in ten parts of water.
  The characters  of the Nitrate of  Strychnine have been  described in
the method of preparing the alkaloid.
  Strychnine is, perhaps, after pure prussic acid, the most intense
of  poisons.   It kills  by producing tetanus. 
         B R U C I N E.--D E L P H I N I N E.--V E R A T R I N E.     631


          Brucine.—N2C48. H,<A or Br.  Eq. 408 or 5107.
   This substance is found associated with strychnine, as already de-
 scribed, and also  in the bark of the  false angustura, which is now
 known to be the strychnos nux vomica, though formerly supposed
 to be the brucia  antidysenterica, whence the name of this alkaloid
 is derived.  Its mode of preparation from the nux vomica has been
 sufficiently described in the  preceding article.
   From its solution  in spirit, brucine crystallizes  in  colourless
 rhombs, containing  water, which they abandon on melting at  220°.
 It dissolves in 850 parts of cold and in 500 parts of boiling water;
 these solutions react alkaline, and taste intensely bitter ; it dissolves
 readily in alcohol, but  is insoluble  in ether.
   With nitric acid,  brucine becomes of a rich red colour,  which, on
 the addition of protochloride of tin, changes to  a  fine violet; this
 distinguishes  it  from  the  red of morphia, which is completely
 bleached  by protochloride of tin and  by sulphurous acid.
   With chlorine, brucine gives a yellowish-red, and with iodine a
 chocolate-brown precipitate.
   The salts of brucine have  a bitter  taste, are generally crystalliza-
 ble, and give with tannin and with  ammonia white precipitates.
   The Curara, or Urari poison, used in the Indian Archipelago for
 poisoning arrows, contains  a vegetable alkaloid, Curarine, which
 forms a yellow uncrystallizable mass, which dissolves easily in wa-
 ter and in alcohol, but  is insoluble in ether; it reacts alkaline, and
 combines with acids ;  its salts do not crystallize ;  its solution is pre-
 cipitated by tannic acid.
   The  tree from  which curara is derived is not accurately known,
 but is supposed to be a strychnos.
   Delphinine.—N.C27. Hl902 or De.   Eq. 2659 or  212*4.—This sub-
 stance  is extracted  from the  seeds  of the stavesacre, delphinium
 staphisagria, by digestion in water, to which some  sulphuric acid
 had been  added.   The  acid liquor is to be decomposed by a slight
 excess of magnesia, and the precipitate being washed and dried, is
 to be boiled in alcohol, which dissolves the delphinine.  To obtain
 it quite pure, it is to be redissolved in a dilute acid, boiled with ani-
mal charcoal, filtered, precipitated with ammonia, and the precipitate
dissolved in alcohol, from which the delphinine separates on cooling
as a  white crystalline powder.
  It  is soluble  in ether and alcohol ;  almost insoluble in water; its
solution has an intolerably sharp taste;  it melts  at 250'; chlorine
turns it green ; oil of vitriol colours  it red, and then carbonizes it ;
its salts are very soluble, but crystallize badly ;  Courbe states that
the stavesacre contains also a substance, Stephysaine, (N.Ca2. H^O., 1),
which is  distinguished  by its insolubility in ether; it is a yellow
resinous mass, insoluble in water, but dissolving in dilute acids  with-
 out neutralizing them.
         Ferafr-me.-N.C34. H2lOB or Ve.  Eq. 3647 or 289.
  This alkaloid is found in the roots of the veratrum  album, and in
the seeds of the veratrum sabadilla;  the  best process  for its extrac-
tion  is that given by Vasmer. 
632    SABADILLIN E.--J E R V I N E.--C OLCHICINE.


   The sabadilla seeds are to be infused in water, containing an ounce
of oil of vitriol for each pound of seeds, as long as anything is dis>-
solved.   The filtered liquor is wine-yellow; it is  to be accurately
neutralized by carbonate of soda, and evaporated to the consistence
of an extract.   While yet warm,  alcohol is to be poured on it, and
digested  until everything  soluble is taken  up.   From this  solution
the alcohol is then to be distilled off, the residue digested in dilute
sulphuric  acid, and from this liquor the veratria precipitated by car-
bonate of soda.  The  precipitate must be redissolved  in  a dilute
acid, digested  with ivory black, and again precipitated by a carbon-
ated alkali in order to obtain it pure.
  Pure veratrine appears as a white uncrystallized resinous powder ;
it melts at 230°, reacts alkaline, has no  smell, but  produces violent
sneezing; its taste is exceedingly sharp, but without bitterness ; it
is insoluble in  water, but dissolves readily in alcohol and ether; its
salts are  mostly crystallizable and neutral, but if mixed  with much
water they are decomposed, acid being set free, and a basic  salt pre-
cipitated.   Veratrine itself is actively poisonous, and is much used
in medicine,  but none of its salts  are important.

        Sabadilline.—N.C20. H,305 or Sa.   Eq. 2351 or 188*1.

  This body, which, accompanies veratrine, is separated  from  it by boiling the pre-
cipitate produced by the carbonate of soda with water. From the liquor the sabadil-
line gradually separates  in radiated  crystalline needles, of a pale rose colour, but
when purified it becomes white;  its taste is intolerably sharp; it is sparingly soluble
in water or in ether, but abundantly soluble in alcohol; it reacts strongly alkaline,
and forms crystallizable salts with acids.

           Jervine.—N2Cm . H506 or Je.   Eq. 5952 or 476.

  This alkaloid accompanies veratrine in veratrum album;  it is prepared by a pro-
cess similar to  that for  veratrine, from which it is separated by the facility with
which it crystallizes from its alcoholic solution,  and by the very sparing solubility
of its sulphate.   When pure it is white, easily fusible, totally decomposed at 400°,
nearly insoluble  in water, but copiously soluble in alcohol.   Of its salts, the sul-
phate, nitrate, and muriate are sparingly soluble  in water or in mineral acids; the
acetate dissolves readily.  Muriate of jervine forms, with bichloride of platinum, a
vpry sparingly soluble double salt.  Crystallized  jervine contains 4 Aq.

               Colchicine.—(Formula not established.)

  This alkaloid is obtained from the seeds of the meadow saffron (colchicum autum-
nale) by digestion in a mixture  of weak alcohol and sulphuric acid.  The  excess
of acid in the liquor is to be then neutralized  by lime, and the alcohol distilled off.
The residual liquor is to be decomposed by carbonate of potash in excess, the pre-
cipitate washed, dried, dissolved in absolute alcohol, decolorized by animal chaicoal,
and gently evaporated, a few drops of water being added.  The pure  colchicine
crystallizes  in colourless needles.  Its taste  is intensely bitter, but not biting, like
that of veratrine, nor does it  produce the violent sneezing; it is pretty soluble in wa-
ter, and very soluble in alcohol and ether; its solution reacts feebly alkaline, but
neutralizes acids perfectly.   Tincture of iodine precipitates it of a rich orange col-
our.  Nitric acid colours it dark violet and  blue.  Though most abundant in the
seeds, all parts of the meadow saffron contain colchicine.
   Emetine.—(Formula not established.)  This  substance exists in all
those plants  whose  roots  are sent into commerce under the name
of Ipecacuanha, or Hippo. The roots are to be powdered and digest-
ed in ether, by which a fatty substance is taken up.   They are then
to be boiled  with alcohol, the decoction mixed with water, and the
spirit distilled off.   The residual  liquor is to be  filtered, and then
boiled with magnesia;  the precipitate is to be dried and digested  in 
            S O L A N I N E.---C HELERYTHRINE,  ETC.        633


alcohol, which dissolves the emetine.   This solution is  to be evap-
orated to dryness, the residue dissolved in a dilute acid, the liquor
boiled with ivory black until  completely decolorized, then filtered
and the emetine precipitated by an alkali.
   When completely pure, emetine  is white and nearly tasteless ; it
is very poisonous;  scarcely  soluble  in water  or in  ether,  it  dis-
solves readily in  alcohol; it possesses  strong  alkaline  properties;
its salts are  completely neutral,  but  cannot be crystallized ;  they
dry down  to  gummy masses.   Tannic acid and corrosive  sublimate
produce white precipitates ; iodine, bichloride  of platinum, brown
ish-yellow precipitates with the salts of emetine.

          Solanine.—N.C48 . H7302s or So.   Eq. 7519 or 601.

  This alkaloid is found in the berries of the solanum nigrum ;#in the berries, leaves,
and stems of the solanum dulcamara (bitter-sweet) and tuberosum (potato).
  The powdered stems of bitter-sweet are to be digested with spirit of sp. gr. 0865,
mixed with one third  of sulphuric acid.   The liquid, is to be supersaturated with
milk of lime, the spirit distilled off, the residue washed with water, and what remains
treated with  dilute sulphuric acid. From the solution thus obtained  the solanine is
to be precipitated by an alkali, washed with water, dissolved in alcohol, decolorized
by animal charcoal, and then obtained by evaporation.  It forms a white  brilliant
powder, of a slightly bitter, nauseous taste; it does not brown turmeric,  but restores
the blue colour of reddened litmus; it melts a little above  212° ;  it is  almost insolu-
ble in water, sparingly soluble in ether, but copiously in alcohol.  With  acids it
forms neutral salts, which  do not crystallize, and are strong narcotic poisons.
  The injurious properties  of unripe  potatoes result from the presence of this body.
It exists abundantly in the  early snoots (under ground) and buds  of the tubers.

               Chelerythrine.—(Formula not established.)

  This substance is extracted from the roots of the chelidonium majus by digestion
with dilute sulphuric acid.   The liquor so obtained is to be evaporated and mixed
with ammonia.   The brown precipitate which falls is to be washed, pressed between
folds of paper, and digested in alcohol with some sulphuric acid.   The alcoholic
solution being mixed with water and the  spirit  distilled  off, the residual liquor is
precipitated  by ammonia, and the precipitate being washed and dried by pressure, is
to be digested in ether, and the ethereal solution evaporated to dryness.  The  mass
so obtained is then digested in dilute muriatic acid, which leaves a resinous sub-
stance undissolved.  The  deep red liquor evaporated to  dryness and washed with
ether, leaves a mixture of  muriate of chelerythrine and muriate  of cheledoline, the
former of which is dissolved by washing with a  small quantity of water, while the
latter remains undissolved.
  From the  solution  of the muriate, the chelerythrine is  precipitated by ammonia
as a white curdy powder.  From  its ethereal solution it remains as a  resinous mass,
which remains soft for a long time; it is insoluble in water; its solutions in alcohol
and ether are pale yellow,  A^ilh acids it forms salts of a rich crimson colour,
which generally crystallize.  Tannic acid produces in their solutions a precipitate
soluble in alcohol.
                    Chelidonine.—N3C40. H20O6  or  Ch.

  The preparation of this  substance has been in great part described in the prece-
ding article.  By digesting the sparingly soluble muriate with ammonia, then dis-
solving in sulphuric acid, and precipitating with muriatic acid, it is  freed from all
traces&of chelerythrine, and finally the pure chelidonine,  separated by ammonia, is
dissolved in  boiling alcohol, from which it crystallizes, on cooling, in brilliant col-
ourless tables.   It Is insoluble in  water, soluble in alcohol and ether;  it tastes bitter,
and reacts alkaline • its  salts are colourless, and those with the mineral acids  crys-
tallize ; its solutions' give with tannic acid a precipitate.

                Aconitine.—(Formula not established.)

  The fresh-expressed juice of the monkhood (aconitum napellus) is  to be boiled
and tiltered, and the clear liquor mixed with an excess  of carbonate of potash.  The
                                   4 L 
634     A T R O P I N E.--B ELLADONIN E.--D A T U R I N E.


mixture is to be agitated with ether as long as anything is taken up, and by evapo-
rating this solution the aconitine remains.   From the  dry plant  or from the seeds,
the aconitine may be obtained by processes similar to those described for veratrine
and colchicine.
  Aconitine partly crystallizes from its ethereal or alcoholic  solution in white grains,
but for the most part forms a colourless, vitreous-looking mass;  it tastes sharp and
bitter, and is intensely poisonous: it reacts  strongly alkaline, and neutralizes  the
strongest acids ;  alkalies precipitate its solution white; chloride of gold  and tannic
acid also give white precipitates, and iodine throws it down orange.

                      Atropine.—N.C^ . H^Og or  At.

  This alkaloid exists  in all parts of the atropa belladonna, but most abundantly in
the roots.  To prepare it, the fresh roots are to be powdered  and digested in alcohol,
of specific gravity 0820.  The liquor obtained is to be mixed with lime, in the pro-
portion of one part to twenty-four parts of roots, and laid aside for twenty-four hours
with frequent agitation; the  mixture is to be then filtered,  and the deposite treated
with dilute sulphuri* acid: the filtered solution is distilled, and the spirit being thus
removed, the residual liquor is  concentrated  by evaporation until  it  equals one
twelfth of tne roots employed.  To this liquor, when  cold,  is to be added a strong
solution of carbonate of potash,  until  a dirty brown precipitate occurs, which is to
be removed  by the filter, and then more carbonate of potash added as long as any
precipitate is formed.   This  last, which is impure atropine, is to  be washed witn
water, then  dried, and dissolved  in strong  alcohol, the solution decolorized by boil-
ing with animal charcoal, filtered, and gradually evaporated, whereby the atropine
separates in small white silky prisms.
  The taste of atropine is sharp, bitter,  and metallic.  It dilates the pupil  perma-
nently and strongly; if impure, it is brown, does  not crystallize, and has a horrible
smell, but if quite pure it has no smell; it requires 2000 parts of cold water for so-
lution, but dissolves in thirty-four parts of boiling water, from which some crystalli-
zes by cooling, but  the greater part is decomposed; it dissolves readily in  alcohol
and ether.
  The alkaline properties of atropine are feeble; most of its salts are decomposed
by boiling with water into ammonia and a substance of an excessively disagreeable
smell; this decomposition is instantly effected by the  caustic fixed alkalies.  Most
of the salts  of atropine crystallize; tannic acid precipitates  their  solutions white;
the chlorides of platinum and gold, yellow; and iodine, orange-yellow.
  Belladonine.—(Formula not established.)  The dried  root of belladonna  is to be
mixed with  a strong solution of caustic potash and rapidly  distilled; the distilled
liquor is to be decomposed by bichloride of platinum, and the white precipitate which
forms being washed and dried, is to be mixed  with carbonate of potash rnd gently
heated.   Belladonine sublimes and condenses in colourless  rectangular prisms, with
a penetrating odour like ammonia; it dissolves  in water;  the solution reacts alka-
line;  it is not very poisonous; its salts resemble closely the corresponding  salts of
ammonia.
  It appears to me likely that this substance is  a product  of the decomposition of
the atropine by the caustic potash, and does not exist in  the plant.
  Daturine.—This  substance is  obtained from the seeds of the thorn apple (datura
stramonium), by the same process as has been described  for  the preparation of aconi-
tine.  From its solution in spirit, it crystallizes  in%ery brilliant colourless groups
of needles.  When perfectly pure  it  is inodorous, but when impure  it smells  dis-
gustingly narcotic; its taste is bitter, and like that of tobacco; it dissolves in seven-
ty-two parts of boiling, and in 250 of cold water, in twenty-one of ether,  and in three
of alcohol;  it melts below 212°, and volatilizes unchanged, at a stronger heat in white
clouds.
  A solution of daturine reacts  strongly alkaline, and forms crystallizable neutral
salts, which, like pure daturine, are very poisonous.   Towards reagents it acts likfl
atropine.
   Hyosajamine.—This alkaloid, which is the active principle of the henbane  (hyos-
cyamus niger and albus), is  best prepared from the seeds, in the same way as atro-
pine, except that to the spirit in which the seeds are digested  some sulphuric  acid
should  be added.   It crystallizes in  radiated groups  of silky needles,  but is more
usually obtained as a  transparent vitreous mass.  In  its properties it resembles so
perfectly atropine and daturine, that they need not be specially detailed.  It neutral-
izes acids perfectly; its salts are intensely poisonous;  they are decomposed very
easily, even by boiling with  water. 
C O N E I N E.--N I C O T I N E.
635
           Coneine.—N.CI2 . 014H. or  Cn.   Eq. 1359 or  108*7.

   This remarkable substance is the active principle of the hemlock (conium macu-
 latum), in all parts of which  it exists, but is more easily extracted, from the seeds.
 These are to be bruised, mixed with one fourth of a strong solution of caustic pot-
 ash and eight parts of water, and distilled as  long as  the water which comes over
 has any smell.   This is to be neutralized by dilute sulphuric acid, and  evaporated
 to the consistence of a sirup.   The residue is treated two or three  times with a mix-
 ture of one part of ether and  two  of alcohol, sp. gr. 0820, wherein the sulphate of
 coneine dissolves.  From this solution the ether and spirit are distilled off, then some
 water added, and the liquor  evaporated  to dryness.   The residue is to be mixed
 with half its weight of strong solution of potash, and rapidly distilled  to dryness.
 The  receiver should be carefully cooled.  The oily  coneine should  be separated
 from the watery liquor, and this last distilled again with some lime.  If the coneine
 contain ammonia, it may- be got rid of by exposure for a few hours in vacuo, beside
 a capsule of oil of vitriol.
   Pure coneine is a colourless transparent liquid, of sp. gr. 0*89; its odour is highly
 penetrating and nauseating, partly like that of the plant;  its taste is disgustingly
 sharp; it is extremely poisonous.   100 parts of cold water dissolve one  of coneine,
 and the solution becomes turbid when heated.   Coneine itself dissolves one fourth of
 water, and this  liquor becomes milky even by the heat of the hand; it mixes with
 alcohol, ether, and oils in all proportions; in close vessels it distils unaltered at
 370°, t>ut at a much lower temperature if water be present.  When completely an-
 hydrous,  coneine has no alkaline properties,  but acts very powerfully  if water is
 present; it saturates acids completely, and has the smallest atomic weight of any
 organic alkali known.   Its salts crystallize but imperfectly; they are decomposed
 by much water; they dissolve readily in water, alcohol, or a mixture of alcohol and
 ether, but in pure ether they are  insoluble.  Their watery solution is precipitated
 by iodine, saffron-yellow;  and by  tannic acid, white.  Coneine itself is coloured by
 nitric acid blood-red; by exposure to the air, especially if warm, coneine is decom-
 posed ; it becomes brown,  ammonia is evolved,  and a bitter, inodorous, resinous
 substance is  produced, which has  no poisonous properties.

                  Nicotine.—(Formula not established.)

   This substance is  the characteristic ingredient of  tobacco (nicotiana tabacum,
 and many other species).   For its preparation, precisely the same process is to be
 followed as has been described for coneine, to  which it has a very great similarity.
 When pure,  nicotine is a colourless oily liquid, of a  pungent tobacco smell, and a
 sharp, burning taste; it differs from all other organic bases in mixing with water in
 all proportions;  it  mixes also with alcohol and ether.  When anhydrous,  it gives
 off" white fumes at 212°, and distils at 480° ; but the greater part of it is decomposed.
 If water be present, it distils easily at a much  lower temperature.
   Nicotine possesses a strong alkaline reaction, and neutralizes acids perfectly.   Its
 salts  are generally very soluble, some crystallizable,  inodorous, but with a strong
 tobacco taste.   With alkalies they evolve the  characteristic odour of the plant.
   Menisperniim.—N.Cis. HiiO^.  This substance is found in the capsules of the coc-
 culus Indicus, associated with picrotoxine (page 609).  The alcoholic extract is to be
 boiled with acidulated water,  and  when the  picrotoxine has crystallized from the fil-
 tered  liquor,  an  excess of alkali is to be added. The precipitate is  to be dissolved
 in alcohol, decolorized bv animal charcoal, and evaporated to dryness.  The residue
 is to be digested with ether, which dissolves Alenispermim, and [eaves another body,
 Paramcnisperminc, undissolved.
   From the ethereal solution,  menispermine crystallizes in white square prisms.  It
 is tasteless, and not poisonous ; it  forms neutral crystallizable salts.  The parame-
 nispermine dissolves in acids, but  does not neutralize them.
   Cissampeline exists in the roots of the cissampelos pareira (pareira brava), and is
 prepared by the same kind of process that has been frequently described.   From the
 evaporation of its ethereal solution, it remains  as a yellowish, transparent, vitreous
 mass  which combines with water, forming a white powder like magnesia.  It is very
 easily decomposed; it is a  powerful organic  base; its salts form gummy masses,
 but scarcely crystallize.                                                  .   .
  Glaucinr exists in the glaucium  luteum (horned poppy).   Its preparation is sim-
ilar to that of aconitine;  it crystallizes in pearly scales; it possesses the same range
of properties as the  other vegetable bases, and  forms crystallizable salts.  The
horned poppy contains another crystalline principle (Glauco-picnnc), which appears
also to act as a base. 
 636  CONSTITUTION OF  VEGETABLE  ALKALOIDS.

  A great number of plants are stated to contain organic bases, which, however,
 have been as yet so imperfectly examined and described as to render their intro-
 duction here useless.  Of such substances, the most important are: in the croton
 tiglium, Crotonine, which is crystalline, but is not the active principle; in the a2thusa
 cynapium, Cynapine, crystalline; and in the digitalis purpurea, Digilaline, which ap-
 pears most to resemble coneine.
           Of the Constitution of the Vegetable Alkaloids.
  From the  period  of  the  first discovery of this class of bodies,
 chemists have endeavoured to ascertain on  what depended the ba-
 sic properties by which they are so remarkably characterized.  The
 discovery, by Liebig, that each equivalent of an organic base con-
 tained an equivalent of nitrogen,  suggested  the very plausible idea
 that  they  contained  ammonia ready formed, and that in their salts
the acid was  neutralized by the ammonia, and the organic substance
 remained combined  with the  salt, as it had been with the  ammonia
before.   This idea, however, cannot be sustained, as we cannot ob-
tain  ammonia  from any vegetable  alkaloid, unless by processes
which totally destroy its constitution, and which, indeed, eliminate
ammonia from  any organic  substance  containing  nitrogen.  More-
 over, it is now known that Liebig's rule is not universally true ;  the
equivalents of strychnine and  of brucine contain each two atoms of
nitrogen, and we know of other organic bases, as melanine, amiline,
jervine, and  urea, in which the quantity of nitrogen in the equiva-
lent  goes much  beyond one  atom.   We may hence conclude that
 there is  no  reason to  suppose that the vegetable alkalies contain
ammonia, or  owe their  basic properties to its presence.
  Some remarkably simple  relations  of composition occur among
 certain  bodies  of this  class,  which would at first appear  to  throw
light  upon their constitution.  Thus  morphine  and codeine differ
in composition  only by morphia containing an atom of oxygen
more ; and if we supposed (N.C35. H20O4) to be a compound radical
R., then codeine  should be protoxide, R. + O., and morphia deutox-
ide, R. + 20.   In like manner, if we take the cinchona alkalies, we
find them to  differ only in the quantity of oxygen they contain, and
making (N.C20H 2) a compound radical, cinchonine should  be R.-f-
 0., quinine R. + 20., and aricine,  R. + 30.  These remarkable facts
might lend considerable support to the idea that these alkaloids are
oxygen bases, oxides of compound radicals; but a closer  examina-
tion  of their relations  does away with all probability of its truth.
 Thus, if morphia were  R.+20.,  then  by  muriatic  acid we should
 have  a bichloride formed, R.-f 2CL, and water separated ; in place
 of which, the morphia combines directly with one atom of muriatic
 acid, and so in all other  cases ; we cannot find in the compounds of
these vegetable alkalies any of the laws which govern the formation
 of salts by metallic oxides.   In addition, the salts formed  by these
 alkaloids with the oxygen acids  contain an  atom of water, which
 cannot be expelled without decomposition.   In  this they resemble
 ammonia, and I think that it is the  only analogy which we can estab-
 lish by the facts at present known ; but whether, in these  vegetable
 alkalies,  the  nitrogen makes part  of a  compound radical analogous
 to amidogene, remains  to be decided by future investigations. 
ULMINE  BODIES FROM SUGAR.         637
                      CHAPTER XXVIII.

 OF THE  PRODUCTS  OF  THE DECOMPOSITION  OF  WOOD AND THE ALLIED
                             BODIES.

                          SECTION I.
  OF THE SLOW DECOMPOSITION  OF  WOOD.  CONSTITUTION  OF ULMINE
                       OF TURF  .AND COAL.
  The gradual decomposition of the woody tissues of plants gives
 origin to a class of bodies which had been long confounded under
 the name of Ulmine,  but which are now recognised  to consist of
 several distinct substances, differing in their origin, and still more
 essentially in their properties. From the influence which they ex-
 ercise in agricultural operations, by forming an element of the soil,
 and their importance  as fuel, by constituting the great mass  of turf,
 they deserve a somewhat  detailed notice.  I have already  stated,
 that by the action  of acids upon sugar (p. 532), lignine, starch, and
 similar bodies (page 528), brown  substances are produced, the com-
 position of which was not definitely established.  Mulder has, how-
 ever,  recently reinvestigated the history of this class of bodies, and,
 from  his known accuracy, his results may be looked upon as\atis-
 factory.                                                       .,
  When  sugar is acted upon  by  a very dilute acid, and  the liquor
 not allowed to boil, two brown substances are formed, of which one
 is soluble in solution  of carbonate of soda, but the other not.   For
 these  bodies the names Sacchulmine and Sacchulmic Acid maybe re-
 tained.  From  the alkaline solution the  latter may be precipitated
 by any stronger acid.  These bodies are insoluble in water and in
 alcohol.  The formula of the Sacchulmine  is C40Hlt)Ol4; that of the
 Sacchulmic Acid is C40H14O12.   They differ, therefore,  in the  former
 containing the elements of water, which, however, cannot be expell-
 ed without total decomposition.
  If the sacchulmic acid be dissolved in water of ammonia and pre-
 cipitated  by an acid,  it  retains a  quantity of the alkali; and if the
 nmmoniacal solution be decomposed by a metallic salt, the precipi-
 tate which forms is a double  compound of sacchulmic acid,  ammo-
 nia and the metallic  oxide.   It was the unsuspected existence of
 ammonia in these cases which produced  the discordance of  former
 results.
  If the sugar be acted on by  a stronger acid, and the solution kept
 boiling for a considerable time, the ulmine bodies disappear, and are
 replaced  by two dark brown  or black substances, possessing  very
 analogous properties,  the Saccharo-humine and Saccharo-humic Acid.
 This change takes place more readily if the air have  free access.
Both are  insoluble in  water and alcohol; they are separated by al-
kaline liquors, which  dissolve the acid body.   From this solution it
is thrown down by any stronger acid.  The composition of saccha- 
638          ULMINE  BODIES  FROM  WOOD.
 ro-humine is expressed by the formula C40H,-Ol5; that  of the  sac-
 charo-humic acid by C40H12O12.  Like the former bodies, these differ,
 therefore, in the elements of water.
   Mulder found that access of air was not necessary for the forma-
 tion of sacchulmine or its acid,  but that  without  air no saccharo-
 humine nor its acid could be produced.   In this action, even with-
 out access of air, formic acid appears, although but in small quantity;
 at the same time, glucic acid (p. 534), and  another body first de-
 scribed by Mulder, Apoglucic Acid, are generated.
   When wood remains long in contact with air and moisture, it is
 gradually converted into a mixture of two brown substances, which,
 from their having  been originally found as a product of the decom-
 position of elm, are specially termed Ulmine and Ulmic Acid.  The
 latter is insoluble in alcohol and water, soluble in alkaline solutions;
 in its natural state it contains ammonia, which can only be expelled
 by boiling with caustic potash, by which the greater part of the ul
 mic  acid is itself  decomposed.   Its formula, as derived from  the
 analysis of a specimen furnished  by a  rotten willow, was C4CHl20I2,
 being isomeric with saccharo-humic acid,  but distinguished from it
 by many minor characters, especially that when treated with acids
 it retains twice as  much ammonia as the artificial product.   Mulder
 considers the natural ulmine to contain more hydrogen ;  its formula
 should then be C40H]4O|2, and by  the continued action of the air it
 should change into ulmic acid.  The formation of these bodies from
 the woody fibre  results from the absorption of oxygen and the evo-
 lution of carbonic  acid and water : thus four atoms of lignine, C48
 Hj,032, with fourteen of oxygen, produce 8C02 with 18H.O., and an
 atom of ulmine,  C40H14O,2.
  Another kind  of decomposition to which wood  is subject is  the
 conversion of the ligneous fibre into a white friable  substance, which
 is formed abundantly in the interior of dead trees; its composition
 is found to be expressed by the formula CgHj-O^.  It is evidently
formed  by the  lignine combining with oxygen from the  air and
with the elements  of water, and then  giving off carbonic acid gas,
 C3tH24024 with 30. and  3H.0. forming C33H27024 and 3C02.
  The rotting of wood is, however, by no means necessarily in-
 duced by the mere presence of air and water ; for lignine may be
 exposed to these agents for centuries without being altered in any
 sensible degree. Precisely as in the alcoholic and  acetous ferment-
ations, it is necessary that an azotized  substance should  be present,
which, being first  decomposed, and forming, probably,  crenic  and
apocrenic acids,  communicates the action  to the lignine ; the albu-
minous juices which exist in  the  vessels of the wood act thus as a
ferment, and the decomposition of the wood may  be prevented by
precisely the same methods as counteract the tendency to the  fer-
mentation of sugar or of alcohol ; any deoxidizing substance, as
 sulphurous acid; any metallic salt, as  corrosive sublimate  or blue-
 stone, which may combine with the albumen and  render it insolu-
ble, will thus protect wood from  decomposition, and are at present
extensively used as preservatives  against what is technically termed
the dry rot.
  It  is by a similar decomposition that the roots and other remains 
INE  BODIES FROM THE  SOIL,  ETC.    639
of  plants are converted into a substance which, by virtue of its di-
rect absorption, or  by means of the  products of its farther change
contributes  powerfully to the nutrition of the succeeding race of
plants, and thereby constitutes the essential element of every fertile
soil; but though, like ulmine, derived from the rotting of vegetable
matters, and for the most part of the same composition, the organic
substance of the  soil is by no means identical with it.  It would
even appear, from Mulder's results, that the vegetable constituent
of the  soil  varies in composition according to the nature  of the
crop.  For distinction, I shall apply to the ulmic acid of the soil the
name  of  Geic Acid, proposed by Berzelius.   To extract it, the soil
is  washed with boiling water until this passes away quite clear, and
then boiled  with carbonate of soda ;  the brown  filtered liquor is
precipitated by muriatic acid, and the precipitate boiled with alco-
hol to dissolve out  two organic acids,  which will be shortly descri-
bed.   In  this  state  the substance is really  an  ammoniacal  salt, its
formula being C40H,2Ol2 + N.H1 + 4.H.O., and even by caustic  potash
it cannot be completely deprived of ammonia.   In the geic acid of
a meadow, the same organic element  was found to be united  with
twice  as  much ammonia; and in one case, where the substance had
been obtained from the soil of an  orchard, the geic  acid had the
formula C40H,,O14.  The  geic acid, C40H ,0,,, though isomeric  with
the saccharo-humic and ulmic acids, is proved not to be identical
by numerous minor  characters, which  need not be described here.
  In  that decomposition of vegetable  matter which gives origin to
turf,  water is present in much greater quantity than in any of the
former cases, in many instances the plants  being totally immersed,
and so matted together, from their mode of growth, that the  access
of air must  be very much prevented.  Hence we  no longer  find in
turf the  comparatively simple  decomposition  of the wood  into an
ulmine and  an ulmic acid, but, in addition to these bodies, the turf
allies  itself  to the  varieties of coal, in containing several kinds of
fossil, resinous, and waxy substances, which are produced  by sec-
ondary and more  complicated reactions.  Here  it is necessary, how-
ever, to describe  only such constituents of the turf as are analogous
to those  already noticed, and for distinction I shall  term them Hu-
mous and Humic Acids.  The former  is found principally  in the
light,  pale brown turf, which is not  imbedded  in water ; the latter,
on the contrary, in the heavy black turf, to which water has had
free access.   They  are prepared  precisely as noticed for the geic
acid, the turf containing in abundance the  same organic acids, sol-
uble in alcohol, as does vegetable soil.
   The Humous Acid resembles perfectly in its properties the sac-
chulmic acid, with  which it is isomeric, its formula being C40Hl4Ol2,
but it Das no tendency to retain ammonia when precipitated by an
acid  from its combination  with that  alkali.  The Humic Acid, on
the contrary, combines with ammonia  so intimately that they can-
not be separated  by any reagent ; and  it even absorbs ammonia in
the laboratory, from the small quantity of the gas which may be set
free in other operations.  As extracted from the black turf, its for-
mula is C40H,3O,5 + N.H4O.  It is, therefore, when free from ammo-
nia, isomeric with the saccharo-humine, but differs totally in com- 
640
FORMATION  OF COAL.
position from the saccharo-humic acid, with which it is so identified
in properties.
  The azotized acids which have been noticed as existing in vege-
table  soil and in turf, are termed  the Crenic and Apocrenic Acids;
they derive  their origin from the  rotting of those  elements of the
plant which  contain nitrogen, as albumen, &c, and are formed, also,
in the  decomposition of animal substances  under peculiar circum.
stances;  thus certain soft minerals,  as polishing slate and rotten-
stone,  contain so much organic matter  as  to  be used for food in
time of distress in the north of Europe, and Berzelius found this to
consist of crenic acid, formed  from the  bodies of  the microscopic
animals, whose silicious skeletons  constitute the mineral portion of
the rock.
  These  acids were  first discovered in mineral springs, whence
their  name  (Kprjvrj), and are most easily obtained pure from the
ochery deposites which form  on  the sides  of the spring, and in
which  they are combined  with  oxide  of iron and silica.   They are
separated by means of their copper salts, the white crenate of cop-
per being soluble, while the brown apocrenate of copper is insolu-
ble in  a  liquor containing free acetic acid ; from the copper salts
they may be set free by sulphuretted  hydrogen.
  The Crenic  Acid  is a pale yellow gummy mass, of  an  astringent
taste, very soluble  in alcohol  and water; its formula is N.C,4. H,6
0,2; by exposure to the air it changes  into Apocrenic Acid; this
is brown, of an astringent taste, reddens litmus, and is  much less
soluble in alcohol and water than the crenic  acid; its  formula is
N6C28.H,4Oc.
  The relations of these acids,  and of the several species of ulmine
to the  nutrition of plants, will be hereafter considered.
  The circumstances under which coal is formed have been already
noticed generally in p. 476 and 563, but it remains  to examine spe-
cially the mode of decomposition  to which the wood is subjected
during that change.  The  coal  appears to require for its production
that the  ligneous fibre should  be  in  presence of water, with little
or no access of air, and that in  most cases the  temperature shall be
elevated.  Thus, while  ulmine  is  produced when the woody mate-
rial is  on the  surface, or,  at least,  only immersed in water, the for-
mation of any of the  varieties  of coal requires the conjoined influ-
ence of moisture, of great pressure, arising from the superposition
of beds of rock or soil, of a high  temperature, given by the prox-
imity of volcanic foci, or generated  by  the decomposition  of  the
vyood itself, and, finally, that the access  of  air shall be much more
limited than in the former cases.   Then, according to  the age of
the geological formation, the  nature of  the superincumbent rock,
and the degree to which the temperature is raised, the coaly mate-
rial varies in  composition.  The  more recent species  {Lignite or
Fossil Wood), which  peculiarly belong to  the tertiary formations,
are characterized  by  the perfect preservation  of the  organized
structure of the wood, and a  more  or  lees  deep brown, but  not
black  colour.   Their composition  may generally be  expressed by
formulae which indicate that, without any absorption of oxygen from
an external  source, the wood has given off carbonic acid and water. 
COMPOSITION,  ETC.,  OF  COAL.          641
 In  the  coals of the secondary strata (the proper coal formation)
 great diversity of constitution exists, depending on  local circum-
 stances.  It would appear that, where  the conversion from lignite
 into true coal is perfect, the  proportion  of carbon and hydrogen be-
 comes  uniformly  CSJH12,  these elements  being united with  small
 quantities of oxygen, generally amounting to from  three to five
 atoms.   The cannel coal of  Wigan, the splint coal of Workington,
 and the caking coal of Newcastle, have been ascertained, by John-
 stone, to be so constituted.  Here, also, the change  arises from the
 elimination  of the  elements of water and carbonic  acid from  the
 wood, as C3l)H24024 produces exactly 4C02 and  12H.O., with C32
 H1204.
  When  the mass of decomposing vegetable matter has been sub-
 jected to a very high temperature, as by the direct contact of vol-
 canic rocks, it becomes  almost completely carbonized, and the va-
 riety of coal termed Anthracite is formed.   The  small quantity of
 hydrogen and oxygen which anthracite  contains, can only be refer-
 red to traces of the proper  coal that have escaped  decomposition,
 and if pure, it would be a Mineral Coke, identical in nature with the
 coke artificially prepared.
  The formulae here given as expressing the constitution of the pro-
 ducts of the decomposition  of wood, are to be considered only as
 illustrative  of the  kind of reaction which  goes on between its ele-
 ments ;  for none of these  products are pure chemical substances;
 they form no definite compounds;  they have no precise equivalent
 number, and hence it is  only for illustration that a formula can be
 legitimately employed to express their  composition.
  The following table contains the ordinary composition of the most
important varieties of coal and turf.   The numbers  given were se-
lected from those obtained in the analyses by Richardson  and Reg-
nault.
Kind of Fuel.
Turf.   .  .
Lignite .  .
Splint Coal
Cannel Coal
Cherry Coal
Caking Coal
Anthracite
Carbon.
58 09
7171
8292
83 75
84 84
87 95
91 98
Hydrogen, pf^

       31 37
       21*67
       1086
        8 04
        8*43
        541
        3 16
593
485
649
566
505
521
392
 Ashes.

tut
 177
 0 13
 255
 1 68
 140
 0 94
Economic
 Value of
100 Paris.
_171-
  208
  262
  260
  25S
  271
  273
  At the same time that the great masses of fossil fuel are thus gen
erated by the decomposition of wood, a great number of other pro-
ducts make their appearance, which, although much inferior in quan-
tity  possess, at  least in some cases, considerable interest.  Thus
the'fire-damp of mines (p.  563) consists in most part of marsh gas,
but contains in some cases, also, olefiant gas and free hydrogen.
  Interspersed through the masses of coal are found small quantities of a great va-
riety of bodies, principally carbohydrogens, resembling the oils and stearoptens of
plants closely in properties and constitution  Thus Ozochent or Fossil W ax, is found
in cavities in the rocks lying upon coal; it is brown, of a foliated structure -it fuses
at 143°  Paraffine, which is an important constituent of the tar produced in the
destructive distillation of wood, is also found associated with coal  It is white,
crystallizes in brilliant plates; it fuses at  111*, and may be distilled unaltered; it
dissolves readily in ether and alcohol; it is not acted upon by any reagent, whence
                               •t M 
642        MANUFACTURE  OF  WOOD  VINEGAR.
its name (parumaffinis).  Both these bodies have the same composition as olefiant
gas, consisting of C.H.  Many waxy fossil substances are isomeric with oil of tur-
pentine, and one, which is interesting as being the matrix in which the native cin-
nabar of Idria is imbedded (page 402), has the formula C21H7; it is termed Ilria-

  Others of these products are liquid, and frequently issue forth from the surface of
the ground, constituting springs, which, from theirinflammability, have been invested
in uncivilized countries  with a sacred character.  Such liquids are known as Rock
Oil or Petroleum.  Some specimens  of it that have been accurately examined are,
like paraffine, isomeric with olefiant gas, while others are isomeric with oil of tur-
pentine, and, absorbing  oxygen, are gradually converted into a resinous substance
Asphalt, for which the formula C40H32O-6 has been assigned.

                             SECTION II.

   OF THE PRODUCTS OF  THE DESTRUCTIVE DISTILLATION  OF WOOD, COAL,
                              AND RESIN.

   The  results of the  action  of heat on an  organic  substance  are
strictly analogous to  those of an imperfect combustion.   A quanti-
ty of carbon  is removed,  as carbonic acid, and a quantity of hydro-
gen, as water.   The other products contain, therefore,  relatively
less oxygen.   If the substance upon  which we operate be pure, and
the heat  be carefully managed,  the result is  in  all cases  perfectly
simple and distinct, as where  acetic acid gives acetone and carbon-
ic acid ; malic acid gives water, carbonic acid, and  maleic acid ;  but
if the temperature change, another set of reactions occurs, and  oth-
er products are generated, which arise, properly  speaking, from  the
decomposition of the first.   Thus acetic acid gives marsh gas ; ma-
lic acid gives fumaric acid.   Hence, if substances be  taken, through
which,  either from their mass  or their non-conducting  power, the
heat cannot  be uniformly diffused, a  number of different  reactions
takes place in different portions at the same time, according to their
respective temperatures; the bodies generated  in the interior are
altered  according as  they approach the surface, and  hence a very
high degree  of complexity is  given to the ultimate results.
   When the substances operated on are not pure, but, as common wood, coal, turf,
(fee, contain various organic bodies of different natures mixed together, it becomes
quite impossible to express the precise reactions which occur, and the number ot
bodies generated becomes very great.  It  is  to the classes of bodies thus produced
that I wish to direct attention in the present section, as in all cases where the mode
of origin of a pyrogenic product is accurately known, I have described it in connex-
ion with the body from  whence it is usually derived.
   According as the object of the process is the manufacture of vinegar or of tar, the
distillation of wood is very differently managed.  For the first, a cast iron cylinder,
                                                  a, is built into a furnace.
                                                 of which c is the grate, d
                                                 the fire-door, and e, e, e the
                                                 flue, which winds spiral-
                                                 ly round the cylinder, so
                                                 as to heat it as uniformiy
                                                 as possible.  The wood, in
                                                 pieces which fit accurate-
                                                 ly the interior of the cylin-
                                                 der, is  introduced by  an
                                                 opening in the top, which
                                                 is then closed by the plate
                                                 b.  The volatile and gas-
                                                 eous products of the dis-
                                                 tillation pass off by the
                                                 tube g, which is bent zig-
zag, and is surrounded at i, i by larger tubes, through which a stream of cold water
constantly passes.  This water is supplied from a reservoir, n, by the tube I, and,
 
PYROXYLIC   SPIRIT,   ETC.
643
entering below at m, passes from one jacket to another by the cross pipes o o  and
escapes ultimately above atp;  this cooling arrangement being a form of Lie'bio-'s
condensing tube (p. 512), convoluted, as it were, in order to occupy less room.   The
liquids which are thus condensed collect in the tubs r, and the gases which come
over are allowed by the cock t to issue from the tube s, and, being set on fire, play
on the bottom of the cylinder, and thus economize a certain quantity of fuel.
  The liquid products separate, on standing, into  two  layers, the upper formed of
oily and tarry matters, the lower of water, acetic acid, pyroxylic spirit, &c.  By the
connecting tube, this heavier liquid passes into the second tub, while the tar remains
in the first.   The impure acetous liquor is neutralized by carbonate of lime; the
acetate of lime decomposed by sulphate of soda or sulphuret of sodium;  the acetate
of soda crystallized and fused in order to expel the adhering tar, then dissolved, re-
crystallized, and decomposed  by oil of vitriol.  Pure acetic  acid is thus obtained,
which is then diluted  with water to the various degrees of strength required in com-
merce (p.  557).
  When the acetous liquor has been  neutralized by  the lime,  it is concentrated by
distillation, whereby a spirituous liquid is obtained, which is termed Pyroxylic Spirit,
and has a  close analogy to alcohol in its characters.  In this state it is, however, a
mixture of a variety of bodies ; some of these, as aldehyd and acetone, have been
already noticed,  and the others will now be described. Mr. Scanlan first recognised
the various constituents of the impure pyroxylic spirit, and their history was accu-
rately investigated by Dumas and Peligot, by Lowig and by myself.
  The impure pyroxylic spirit having been deprived of water by repeated rectifica-
tions over  lime, as much chloride of calcium as it can dissolve is to be added to it, and
the mixture allowed to stand for a few days.   Being then distilled in a  water-bath,
the body to which  the name of pyroxylic spirit is specially applied remains in the
retort, combined with the chloride of calcium, while  there distils over a mixture of
two liquids, Xylit and Mesit, which are separated from each other by frequent rectifi-
cation, as  their boiling points differ.  Besides these  three bodies, there exist in the
rough liquor an  oil, Methol, and a solid substance, discovered by Mr. Scanlan, and
termed Eblanine.
  This last body remains behind when the spirit is rectified over lime,  from which
it is separated by adding muriatic acid, and being then dissolved in boiling alcohol, it
crystallizes on cooling; it  forms deep orange-yellow needles;  it fuses at 350°, and
volatilizes in a current of air or of vapour, but is decomposed  if heated  by itself; it
is insoluble in water,  but dissolves in alcohol and volatile oils ; sulphuric acid col-
ours it indigo blue; its formula is C21H9O4.  No combinations of it are known.
  The Methol contains no  oxygen, its formula being C4H3.   It boils at 350°, and
possesses  the general characters of an essential oil.
  Xylit resembles alcohol closely in its properties.   Its  odour is agreeable and ethe-
real;  its specific gravity, 0*816; it boils at 143°; with  acids  it produces ethereal
compounds,  which have not  been  closely examined; its formula appears to te
C12H12O5.
  ATesit can scarcely be considered  as having been as yet  obtained pure;  in its
properties it closely resembles xylit, but has a higher boiling point; its formula has
been stated to be C6H602.  I shall have, on another  occasion, to notice tne probable
constitution of* these bodies.
  The proper Pi/roxylic Spirit is obtained pure from its combination with chloride
of calcium by the addition of water and distillation; by rectification  in a water-
bath  with dry lime  it is freed from water.   When quite pure, it is a colourless
liquid of a peculiar aromatic smell;  it burns with a flame still less luminous than
that of spirit of wine; its specific gravity is 0793;  it boils at 140'; its formula is
CaEUV the specific gravity of its vapour is 1*1105; in its action upon other bodies,
this substance ranges itself completely with wine-alcohol, and it is hence frequently
termed M.thylic  Alcohol, from the Greek words peto,  and vfy.   In the history of its
combinations it will, therefore, be sufficient to fix attention on those points which
are more specially characteristic of it, its series being in many respects more com-
plete  than that of ordinary alcohol.        ,  . ,   1. *  *•            J   •  -1   .
  Pvroxvlic spirit combines with bases and with salts to form compounds similar to
the alcoates   It i«= decomposed by the chlorides of zinc and alcohol, by the fluorides
of silicon and boron;  methylic ether is evolved, the reactions being precisely as in
the case of ordinary alcohol.
  When treated with sulphuric acid, the methylic alcohol produces an ether, an or-
•?-.nic acid  and a heavy oil,  precisely similar to those formed by spirit of wine.
But the reaction is much more distinct; all the products remain properly in the se-
ries of the methylic alcohol, no gas equivalent to olefiant gas being evolved. 
 644    METHYLIC  ETHER  AND   ITS  COMPOUNDS.

   The Methylic Ether is, at ordinary temperatures and pressures, a colourless gas,
 of an ethereal odour; it burns with a blue flame. Water absorbs thirty-seven times
 its volume  of it; its formula is C2H3O.; it hence is  isomeric with  wine-alcohol,
 with the vapour of which it has the same specific gravity, =1601*5, but its atomic
 weight is only one half that of alcohol; it  combines directly with anhydrous sul-
 phuric acid, forming a heavy oily liquid, and with the other acids to form compound
 ethers.   For the same reasons as have been fully discussed under the  head of wine-
 alcohol,  it is assumed to be an oxide of a compound radical, Methyl,  C2H3 or Me.,
 and the formula of tho pyroxylic spirit is therefore Me.O.+Aq.
   The Sulphomethylic  Arid is formed  precisely as the sulphovinic acid, which it
 closely resembles in properties, except that it may be obtained crystallized in white
 needles by cautious evaporation of its solution.   Its formula is Me.O.. tS.O3-fS.O3.
 H.O.; its salts are generally more permanent, and crystallize  more easily than the
 sulphovinates.
   Sulphate of Methyl.—Me.O.+S.03.   This substance passes  over as a heavy oil
 when one part of pyroxylic spirit is distilled with five  or six parts of oil of vitriol,
 and is formed also by the direct union of methylic ether and dry sulphuric acid.   It
 has a strong garlic odour; its specific gravity is  1-324;  it boils  at 370°.  By boiling
 water or strong  bases, it is immediately removed into its constituents.   With dry
 ammonia it  forms a white crystalline mass, Sulphomethylan, which consists of Me.
 O.. S.03+S.02Ad.  *
   Chloride of Methyl, C2H3CI. or Me.Cl., is formed by heating a mixture of common
 salt, pyroxylic spirit, and oil of vitriol.   A permanent gas is evolved, which may be
 collected  over water, which absorbs  but twice  its volume of it; it burns with a
greenish-white flame.
  Iod-ide of Methyl, C2H3I. or Me.I., is prepared by distilling a mixture of phospho-
 rus, iodine, and pyroxylic spirit.   On the addition of water to  the distilled liquor,
 the iodide of methyl separates as a heavy oily  liquid, of sp. gr. 2*237; it boils at
 about 112^.
  Fluoride of Methyl, C2H3F. or Me.F., is formed by heating a mixture of sulphate
 of methyl and fluoride of potassium, and collecting the gas evolved over water.   It
is  colourless, and burns with a whitish flame, evolving  fumes of hydrofluoric acid.
  Methylene-mercaptan.  Sulphuret of Methyl.—These bodies are prepared precisely
as the corresponding substances in the series of ordinary alcohol.
  Nitrate of Methyl, Me.O.. N.O5, is prepared by distilling nitrate of potash, pyrox-
ylic spirit, and oil of vitriol, mixed together in  a capacious retort.  The receivers
are to be carefully cooled, and a gentle heat applied to the retort to commence the
 reaction,  which then continues to the end without any farther  external heat.  The
product, when purified by redistillation over some oxide of lead, is a  colourless li-
 quid, neutral, of an ethereal odour; it burns with a yellow flame; its sp. gr. is 1182;
it boils at 151°.  If a drop of it be heated to 300°, it explodes,  and this takes place
much more easily if there be a quantity; hence its distillation must  be very cau-
 tiously conducted.
   Carbomethylic Acid is formed by passing a stream of dry carbonic acid into a so-
 lution of barytes in pyroxylic spirit.  Carbomethylate of barytes forms in minute
 plates, which are insoluble in spirit, but dissolve easily in water. This salt rapidly
 decomposes  into carbonate of barytes,  free carbonic acid, and methylic alcohol.
 With chlorocarbonic acid and sulphuret of  carbon, the pyroxylic spirit gives com-
 pounds precisely similar to those already described in the series of ordinary alcohol.
   Oxalate of Methyl, Me.O.. C2O3, is best formed by distilling a mixture of equal
 parts of oxalic acid, pyroxylic spirit, and oil  of vitriol.  The product crystallizes in
 large rhombic plates; it fuses at 124°, and boils at 312°; it dissolves easily in water
 and alcohol.   With water of ammonia it produces oxamid and methylic alcohol;
 with dry ammonia it forms a crystalline body, Me.O.. C203+C202Ad., Oxamethylan.
  Acetate of Methyl—Me.O.. Ac.03.  Formed by distilling together oil  of vitriol,
 pyroxylic spirit,  and acetate of soda.   It forms a colourless liquid, which boils at
 136°; its  specific gravity is 0*919.   The substance known as Mcsit may be consid-
 ered as a compound of methylic  alcohol and aldehyd, C2H3O.+C4H3O., and  the
 xyht is probably a mixture of that body with the acetate of methyl.
  The combinations of methylic ether with the other acids  resemble so closely
 those of vinic ether that they need not be specially described.

              Products of the Oxidation of Pyroxylic Spirit.

   If pyroxylic spirit be distilled  with chromate of potash and sulphuric acid, it
 Is  totally converted  into carbonic acid and water.  If black  oxide of manganese
 be used,  and, after the first violent effervescence has ceased,  a gentle heat be ap- 
PREPARATION  OF  FORMIC  ACID,  ETC.     645
plied, a liquid distils over, which, when completely pure, has the formula C&Hs04;
it boils at 104° ; its sp. gr. is 0855; it is termed Methylal.
  If pyroxylic spirit be brought into contact with oxygen by means of spongy plati-
num, as described for ordinary alcohol  in p. 554, hydrogen is removed and oxygen
absorbed in equivalent proportion, and the methylic alcohol is totally converted into
hydrated Formic Acid, C2H4O2 and 20. giving 2H.O.  and C2H2O4.  In this  reac-
tion there does not appear to be any intermediate state equivalent to that of aldehyd,
which body appears  to be without a representative in the pyroxylic series, at least,
except in combination.  For practical purposes, this mode of preparing formic acid
is not had recourse to, as it may be derived more easily from the oxidation of most
organic bodies.
  The formic acid derives its name from existing in a very concentrated form in
the common  ant (formica rufa), and produces the pain of their sting on being in-
jected into the puncture which the animal makes ; it was formerly prepared by dis-
tilling the ants with a little waler; but the process of Dobereiner is now generally
followed.  It consists in mixing one part  of starch, or sugar, or tartaric acid, with
four of black oxide of manganese, four of water, and  four of oil of vitriol.   Con-
siderable effervescence occurs, owing to the escape of carbonic acid.  When this is
over,  the mixture  is to be distilled until four and a half parts have passed over;
this acid liquor is  to be neutralized by carbonate of soda, and the formiate of soda
crystallized by evaporation and cooling.  From this salt the formic acid may be ob-
tained in any required degree of concentration, by distillation with oil of vitriol, in
precisely the manner described for acetic acid (p. 556).
  If sugar, or starch, or barley be simply heated with dilute sulphuric acid until it
becomes brown, a certain quantity of formic acid is produced, along with ulmine and
ulmic acid.   The generation of this acid as a product of the decomposition of prus-
sic acid, of chloral, and of hydrated oxalic acid, has been already noticed.
  Pure hydrated formic acid is a limpid colourless liquid, which fumes slightly in
the air; its odour  is intensely pungent; when cooled  below 32°, it crystallizes in
brilliant plates; it boils at 212°; its specific gravity is 1-235.  In this most concen-
trated form it is an absolute caustic if applied to the  skin, producing a sore very
difficult to heal; its formula is C2H.O3+H.O., and, like acetic acid, it is supposed
to contain a radical, Formyl, C2H. or Fo., and its rational formula to be F0.O3+H.
0.  Combining with water, it forms at least one other definite hydrate, the formula
of which is Fo.03+2H.O.
  The resemblance of formic  acid to acetic acid is very close, but they are at once
distinguished by their behaviour to certain reagents.  When heated with an excess
of oil of vitriol  it is decomposed, with lively effervescence, into water and carbonic
oxide (C2H 03=C202 and H.O.).  If a solution of formiate be mixed with a cold so-
lution of nitrate of silver, a white crystalline precipitate of formiate of silver falls,
which when heated, is totally decomposed into metallic silver, water and carbonic
acid  C2H Os+Ag.O. giving 2O02 with H.O. and Ag.  If formic acid be digested
on red oxide  of mercury, carbonic acid is given off, and a sparingly soluble crysta -
line formiate of the black oxide of mercury is produced : this, when boiled, is  total-
ly decomposed, metallic mercury separating, and carbonic acid and water being

^Thedkaline formiates are  soluble and crystallizable; that of ammonia crystal-
lizes in right rhombic prisms, which melt  at 250°, and sublime without alteration.
If its vaS be passed through a red-hot porcelain tub^ it is totally converted into
Drussilacid  and water, C2H.03+N.H40. giving C2N.H and 4H.0
P F01miateofSoda crystallizes in rhombic prisms, which have the formula  Na.O..
pSJ  When heated, it undergoes aqueous fusion  and  by a higher tempera-
mre fs d^efomposed   A solution of this salt, when boiled with the salts of silver,
mercuryfgold; palladium, or platinum, precipitates the metal, and is hence useful in

a"SL of Barytes.-Bz.O.. F0.O3. It is obtained in large
   tollman, uj "J   ,   fio.ure where u. v are pnmary, and 1 a
rhombic prisms ^J*J^*Wtto  ta^, an/aie no't altered
secondary plane  whicn n            ^ insoluble .Q alcohol

b7,?e  nl ollimlZeSw produced  by neutralizing lime with
   For,mate of Lime is eas■  >v        ^ ^ ^ .q ^ ^

  o tn6! TK  onv  ob amea"cV/stallized by slow evaporation • it
so that it is  °n->       t   ld  water; it is insoluble, in alcohol.
dissolves in  tenjparts °i to ^ ^  Jf formic add fee added (o &       ^u^
   Formiate oj Lean.     ■  • •   gaU  separates after a short time  in stellated groups
ofSant needles, w£ch are anhydrous, and require forty parts of water fer sola-
 
646    PRODUCTS  OF  DISTILLATION  OF  COAL.
tion; it is totally insoluble in alcohol.  By  the formation  of this salt, the formic
acid is readily distinguished from the acetic acid, and the two, if present together,
mav be thus separated.
                Formiate of Copper crystallizes in large rhomboidal prisms, as in
              the  figure, where i, u, u are primary, and m  a secondary plane,
              which are very regular, transparent, and of a fine, clear  blue colour.
              It effloresces in dry air.
                The Formiates of Mercury.—That of the red oxide is very soluble;
              it can only exist at ordinary temperatures; by a very gentle heat it
              changes into the formiate of the black oxide, and this, when boiled,
              gives metallic mercury, as already described among the tests lor
              formic acid.  The formiate of the black oxide may also be prepared
bv mixing solutions of formiate of soda and of subnitrate of mercury; it separates
in small pearly plates of  four and six sides, which may be dried between folds of
blotting paper, and have a fine silky lustre.
  Chlorides and Iodides of Formyl.—When, under the influence of powerful reagents,
the constitution of the compounds of acetyl or elayl is broken up, a series of bodies
is generally produced, which are supposed to contain as their radical formyl.  Thus,
by the action of chlorine on the chloride of elayl,  a heavy oily liquid is formed, C2
H.CI2 or F0.CI2, Bichloride of Formyl; and by acting on chloral by caustic potash,
formic acid is produced, and a heavy oily liquid, which is termed Chloroform, and
consists of C2H.CI3  or Fo.Cl3, being  Perchloride  of Formyl.  This, which is the most
interesting of these  bodies, is easily prepared by distilling alcohol, acetone, or py-
roxylic spirit with chloride of lime ;  it is colourless, of an agreeable ethereal odour;
its specific gravity is 1-480; it boils  at 141°; the specific gravity of its vapour is
4*116; with an excess of chlorine it gives bichloride of carbon.
  Periodide of Formyl.  Iodoform, Fo.I3, is produced by adding  caustic  potash to a
solution of iodine in alcohol until it is completely  decolorized, but avoiding an ex-
cess of alkali; on then evaporating, the iodoform  is deposited in brilliant  gold-col-
oured  plates; it is insoluble in water, but very soluble in alcohol and ether; it vola-
tilizes at 218°; with potash it gives iodide of  potassium and formiate of potash.
There exist also bromides, cyanides, and sulphurets of formyl, which do not require
notice.
  By acting on the methylic ether  and on the chloride of methyl with  chlorine,
Regnault obtained two series of bodies, which follow precisely the same principles
of constitution as have been described fully when speaking of wine-alcohol (p. 565).
Malaguti also obtained, from the oxalate and acetate of methyl, bodies similar to
those generated by  chlorine with the ordinary oxalic and acetic ethers, and hence
it is only necessary to say that all the conclusions there drawn respecting the nature
of these bodies, and the theory of the chlorine  radicals, may be applied to explain
the origin of the bodies derived from the methylic  alcohol also.

                  Products of the Distillation of Coal.

  The  products of the distillation of  coal in close vessels  possess
a remarkable analogy  to  those that  have been now described, and,
indeed, in many instances, are identical  with them.  Thus the gas-
eous  products are marsh gas, olefiant  gas, and carbonic acid.  The
liquid products  consist of various bodies closely analogous to pe-
troleum, and the solids consist of napthaline  and  paraffine.   The
relative  proportions  of these  products vary with the  temperature.
The  lower  the  heat  employed, the  less gas, and the  more  solids
and liquids are produced; the higher  the temperature,  the  greater
is the  quantity  of  carburetted hydrogen ;  but, for  the purposes  to
which  the practical  process  is applied, the temperature  must not
be  raised too high, for then the gas  evolved would be  mostly marsh
gas and  pure hydrogen, which  possess little  illuminating  power,
while a  great  deal of  illuminating power may be derived from  the
vapours  of some  highly  volatile  liquid  products.   In the manufac-
ture  of coal gas for the purpose of illumination, the object is, there-
fore, to maintain a temperature too high  for the production  of much
napthaline or  paraffine, but not high enough to produce  hydrogen 
COMPOUNDS  OF  NAPTHALINE.          647
or marsh  gas, and thus  obtain  the greatest possible quantity of a
gaseous product  of olefiant gas and vapours of  liquid  carbohydro-
gens.
  From the albuminous constituents of the  wood, coal always con-
tains a certain, though small quantity of nitrogen, and hence ammo-
nia is evolved in  its distillation.   The gas liquor  so  obtained is  ex-
tensively  used  in the  manufacture of sal ammoniac.   From the sul-
phates existing in the plants, or in water which has filtered through
the bed of coal,  or from iron pyrites, which is generally associated
abundantly with  the rocks of the coal  formation (p.  363), a small
quantity of sulphur always exists in coal,  which is  evolved during
the  distillation as sulphuretted hydrogen,  and  requires to  be care-
fully separated from  the other gases, which is effected by  washing
them with the milk of  lime, which absorbs also the carbonic acid.
The  apparatus used for making coal gas does not differ in principle,
although  very  much  in  arrangement, from that  figured in p. 642.
The ammoniacal liquor and  the  tar  are collected  in  the tubs,  and
the gas, in place  of being burned at the orifice of the tube s, is con-
ducted to the purifiers, and thence to the gasometers  for use.
   Most of the substances  produced in this process have been already noticed.  It
only remains now to describe, as briefly as possible, the properties of such others as
are important.
   Of Napthaline and Us Derivatives.—This substance is a very usual product ot the
decomposition of organic  substances by heat; it is obtained abundantly by rectifying
coal-gas tar; it crystallizes in white silvery plates;  its specific gravity is 1048; it
melts at 136°, and boils at 413°, but sublimes rapidly at much lower temperatures;
it burns with' a strong smoky flame;  its smell is powerful and very peculiar; it is
insoluble in water, but abundantly soluble in ether, alcohol, and oils; its formula is
 C2oHs* the specific gravity of its vapour is 4488. It is remarkable for the number
 of compounds to which it gives rise.   When digested with nitric acid, it forms two
 combinations;  the  first,  Nitronapthalid, crystallizes in sulphur-yellow prisms; its
 formula is C20H7. N.04;  the second, Nitronaphdehyd, is a white crystalline powder,
 havin<* the formula C10H3. N.04.  Both these bodies are insoluble in water, but dis-
 solve easily in alcohol and ether, from which solutions they crystallize  on cooling.
 When nitronapthalid is  distilled with lime,  a substance  is obtained which resem-
 bles  eblanine (p. 643) in properties,  but consists of C20H7O.  Laurent termed it
 Oxide of Napthalese.                     .,,..,  ,.  , ,   ,,  c    ■ /-. tr
   Chlorine forms with napthaline a heavy oily liquid, which has the formula C2oHa
 Ch   It gradually evolves muriatic acid gas, and deposites a crystalline substance.
 This change is effected immediately by heat or by a base   This solid body is term-
 ed Chlomapthelid; it consists of C*H7C1.  If this be melted and submitted to the
 continued action of chlorine, hydrogen is removed and  a crystalline solid formed,
 Chk>rnapth(khyd,C  H4CI2.  By acting on napthaline with an excess  of chlorine,
 and distillin- the product, a solid substance is obtained, which crystallizes in  large
 prisms  and has the formula C20H6Ci2.  All of these bodies are insoluble in water,
 hut dissolve in alcohol and ether.                  .    .,         c  .
   Whpn these chlorine compounds are boiled  in nitric acid, a series of substances
 a Jobtei. e?containing  chlorine and oxygen.   Thus from CsoHsCl. is  formed C20
 H  O £2  which is a brilliant yellow crystalline  matter  insoluble in water, and
 ™ iHrwrVt' -'DIP   Bv farther treatment with nitric  acid, the Chloronapthalic Acid is
 formed" the formula of which is C2oH3. 06Cl2.   This body is insoluble in water, but
 £S.s  in ether  and crystallizes, on cooling, in short, brilliant yellow prisms; it
 IpI^ n?400- ind mav be sublimed unchanged.  With bases it forms well-charac-
 •SedI s-Ilts which are orange or red-coloured; those of the alkalies and earths are
 soluble and crystallizable; those of the heavy metals are insoluble in water  In
 somoie .uiu *-> j     ^^ formed a substance which does not contain  chlorine; it re-
 sembfos closely benzoic  acid;  it is term.;d Xpthalic And, but its composition  is not
 vPMliridea • another product noticed by Mar.gnac is an acid possessing  the remark-
 yti iicw   , '      fppi ^Oj                                            1
 ^ThTaclioTof sulphuric acid on napthaline varies, as the acid is hydrated or an-
    1 ne -^-"j-.^ the la'tteJ.  casC;  sulphurous acid is evolved and a series  of products 
648         BODIES  OF  THE  PHENYL  SERIES.
formed, which have been described by Berzelius as follows: SulpJumapthahne, Cu
H8. S.O2, crystallizes in white plates, which melt below212° to a colourless liquid;
Sulphonaptlialid, C24H10. S.O2, is  a snow-white  powder,  which  may  be separated
from the former by means of its insolubility in cold alcohol.  In addition to these
bodies there are formed two acids, the Sulphonapthalic and the Sulphonapthic;  they
are isolated by taking advantage of the insolubility of the barytes salt of the latter in
cold alcohol, and then, by decomposing the barytes  salts by dilute sulphuric acid,
these  organic acids may be obtained crystallized.   The Sulphonapthic Acid forms
soft crystalline scales, of a soapy feel, like talc, which taste bitter and sour.  Its for-
mula  is C22H9. S4O12+2 Aq.;  it combines with two atoms of fixed base.  The Sul-
phonaplhalic Acid forms a hard crystalline mass,  which is acid and bitter, inodorous,
fusible below 212°; it is very  deliquescent; its formula is C2oHs. S203.   The salts
of these acids are all soluble in water.  There is still another acid product, termed
by Berzelius Suiphoglucic Acid, the constitution of which  is not known.
 "Notwithstanding that few subjects have been so often investigated as  the history
of napthaline and its derivatives, there are few bodies whose theory is more obscure.
It  would appear that  all  its hydrogen, or at least six atoms of it, is capable of re-
placement by chlorine or nitrous acid, and there  does not exist any distinct charac-
ter by which the existence of a compound  radical, either primitive or  derived, as a
basis  of these combinations, could with reason be  assumed.   The hypothesis of
Marignac is, that napthaline itself is a compound of two carbohydrogens, C16H4+
C4H4, by the diverse action of reagents  upon which the various bodies may be de-
rived; but this idea does not afford sufficient advantages to justify its adoption.
  Paranapthaline.—This substance is associated  with napthaline in the gas-tar, and
is isomeric with it, its  formula being OjoHg; it differs in its fusing and boiling points,
which are very much higher;  it may be  distilled  unaltered; it is  insoluble in water,
very sparingly soluble in alcohol  or ether, but copiously so in oil of turpentine; its
relations to other bodies are not well known;  with nitric acid it produces a colour-
less crystalline body, having the formula C15H4O2.
  The liquid products of the distillation of coal have been  as yet studied only by
Laurent, of the most interesting of whose results, as yet, but the  general nature has
been published.   This liquid, which is properly termed Gas-naptha, contains a crys-
talline solid, which volatilizes without decomposition, and acts  as an  acid;  its for-
mula  is Ci2H50.+Aq.  Its discoverer considers it  as a  hydrated  oxide of a com-
pound radical, which he terms Phenyl; it combines with potash and barytes, forming
crystalline compounds.  With sulphuric acid it  forms Sulphophenic Acid, C12H5O..
S.03+S.03 . H.O., which forms salts resembling the sulphovinates; with chlorine it
forms, first, Chloropfienesic Acid, Ci2H3 . C^O.+Aq., which crystallizes  in rhombo-
hedrons, and possesses a very nauseous odour; and afterward Chlorophenic Acid,
the formula of which  is C12H2. Cl30.+Aq.
  With nitric acid, the hydrated  oxide of phenyl produces,  first, Nitroplvenesic Acid,
Ci2H3(N20s)0.+Aq., and  by  continuing  the action, the Nilrophenic Acid, C12H2
(N30i2)0.+Aq., which is the Picric Acid described p. 618,  as  formed from indigo
and salicine.  This phenyl series appears, therefore, to be the final result of the ox-
idation of a great number of organic bodies.  As yet, our knowledge of the proper-
ties of these  bodies is not sufficiently detailed to justify any discussion  of their na-
ture, but the connexion with the bodies derived from indigo  is exceedingly remark-
able.   If we consider the radical as C12H5, then amilene is Amidide of Phenyl, and
all the characters of its salts are easily explained.  The  substance termed by Lau-
rent Chloraliine, Ci2H6Cl2, is probably C12H5CI.+H.CI.
   In preparing olefiant gas for the purposes of illumination, by  the destructive dis-
lillation of resin, a number of substances, some solid, others liquid,  are produced,
which have been examined by Pelletier and Walter.  Those not already described
are as follows: Retisteren, a white crystalline solid, which melts at 152° and boils at
'■>17°.   In its properties it resembles napthaline; its formula is C32Hu.  Retinal is
a colourless liquid, tasteless and  inodorous; specific gravity =0-9; it boils at 460°;
its formula is C32Hi , being isomeric with benzin ; the specific gravity of its vapour
is 7*25.  Retinaptha is a colourless liquid, of an  agreeable odour; its specific gravi-
ty is 0-86;  it boils at 226°;  its formula is Ci4H8.  Retinyl, also a liquid,  boils at
 300°; it consists ofC!8Hi2, being polymeric with mesitylene.
   When the gas obtained by the destructive distillation of oil is strongly compress-
 ed, a liquid separates, which was found by Faraday to  contain three distinct sub-
 stances.  Of these the most abundant was the benzin described already (page 571),
 as produced in the decomposition of benzoic acid.   Of the others, one" is known as
 Faraday's Quadrwarbwret of Hydrogen; it is also  formed abundantly in  the distillation
 of caoutchouc; its specific gravity is 0-627; it boils below 32°; it combines with 
KREOSOTE,  KAPNOMOR,  ETC.           649
chlorine, forming a heavy oil; it is isomeric with olefiant gas, its formula being C4
H4, and the specific gravity of its vapour is double that of the gas, being 1-96*2. The
third liquid boils at 183°. Its formula is probably C6H4, being isomeric with mesit-
ylene and retinyl.
  During an elaborate examination of the nature of the tar produced
from  the  destructive distillation of wood, Reichenbach described a
number of bodies, of which one, Kreosote, has  become of much in-
terest, from its remarkable properties, but the others are still very
little  known.  For the preparation of kreosote, the tar is rectified  by
successive  distillations, until  the  oil which passes  over becomes
heavier than water, and then  digested with a solution  of caustic
potash, which dissolves the kreosote ; when this liquor is  exposed to
the air,  it becomes brown, and being then  neutralized by  an acid,
the kreosote separates.  This process,  of  solution  in an alkaline
liquor and precipitation by an  acid, is to be repeated until the solu-
tion is no longer browned by  exposure to the air; the kreosote is
then  pure.   It is an oily, colourless liquid, with a penetrating odour
of  smoke; its taste is sharp  and burning; its  specific  gravity is
1037 ; it boils at 400° ; it burns with a strong smoky flame ; with
water it unites in two ways:  100 parts of  Avater dissolve  1*25  of
kreosote, and  100 parts of kreosote  take up ten of water ; the solu-
tion is quite neutral ; kreosote mixes with ether, alcohol, and acetic
acid  in all proportions.  It unites  with  alkalies and  with acids, but
without  appearing to form any definite compounds, and it is not cer-
tain  that it  has ever been  obtained really  pure.  The formula  as-
signed to it is C14H902.                         .   ,   •       i ^
   The most remarkable property  of kreosote is, that it  coagulates
albumen and the colouring matter of the blood, and these bodies are
then no  longer  susceptible of putrefaction.   Fibrine, or muscular
flesh, immersed in a solution of kreosote for some minutes, has no
tendency to putrefy even if exposed to the heat of the sun after-
ward ; from this is its name derived (xpeu?  ooi^).  Kreosote is the
antiseptic principle in pyroligneous  acid, and in turf or wood smoke.
If  placed on the tongue, it makes a white  mark, with violent pain.
Tte neo n« n caustic remedy for toothache is well known.


also liquid, it doiisj»l° ' ..      t 0J1 of vitriol  and kreosote, the former pro-
needles, insoluble^^ all liquids except on             forms & ^ Mue ^
duc.ng a blue, and ^J latter a pu.rpL= solul °      u contains nitrogen; it is in-


SaS^S ^ZoT^^^oZ^^ of thefe bodies has Jt
been examined             the coai.gas naptha, Runge obtained a series of bod-
   By the  action of reagents on        5     ^     .^^ [o gc     . .
ies, a re-examniatioD, ol « men w           properties, and generate salts, which
Kon^EoF a^eTarich Uuecolou, PThPey  belong apparently to the same
class of bodies as anilene
eratea, oi a si*u<*s —- v    f severai bodies, to which he has given names; Dut,
by Unverdorben as a mixu         whatsoever of their properties, I do not think
as we possess Doaccara         ^     ration>
it necessary to give bis actum        t  • 
650
GERMINATIO N.---M A L T I N G.
                         CHAPTER XXIX.

            OF THE  CHEMICAL PHENOMENA OF VEGETATION.

   In the seed of a plant, the germe of the future individual is associated
 with one or more organs, termed cotyledons, which contain,  in general,
 starch and some form of azotized matter, as albumen, gluten, or legu-
 mine, which substances are so disposed in order to supply the nutriment
 necessary for the development of the embryo, until its organs are fitted
 for the collection of nutriment from external sources.
   The  first act  of  growth  in  the seed  is termed germination, and is
 accompanied by a remarkable change in the constitution of  the cotyle-
 donous  mass.   For perfect germination, it is necessary that the seed be
 moderately supplied  with water and with air, and that it be either in the
 dark, or exposed  but to little light; all these circumstances are perfectly
 secured by the ordinary mode of sowing seeds in a moistened  soil, which
 Bhall be so loose as to admit air, and yet exclude the light.
   A seed so circumstanced gradually swells to much beyond its original
 volume, and its temperature rises ; it absorbs "oxygen from the air, and
 evolves water and carbonic acid, and  the starch of the cotyledon gradu-
 ally disappears, being changed into sugar.   From the point of  the seed
 where the embryo is situated, two shoots spring forth, one of which, the
 radical, takes its direction downward into the soil, while the other, the
 plumula, strikes up towards the air, to become the origin of the stem ;
 according as this growth proceeds, the quantity  of sugar in  the seed
 diminishes, and by the time that the radical  is fit for the performance of
 its functions, as root,  in absorbing nutriment from the soil, nothing  re-
 mains of the seed but its ligneous husk, which in some cases  completely
 perishes under ground, but in others rises, and, assuming the functions of
 leaves (seed-leaves), assists in providing nutriment for the young plants,
 until the stem has been furnished with leaves by  which it may act upon
 the surrounding air.
   This  process of germination is artificially produced, for the purposes of
 the arts, by the operation of malting;  the grain is  steeped in water until
 it  has absorbed  the  proper quantity of it; it  is then spread on  the
 floor of the malthouse, and its  temperature prevented from rising  too
 high by the mass being frequently spread  out,  and  new surfaces  ex-
 posed to the  air.  When  the seed contains the  maximum quantity of
 sugar, that is, when  the  conversion of the starch is most complete,
and yet before much sugar has been assimilated  by the germe, which
is  practically found to be  when the radical  has  grown as long as  the
grain, but does not project beyond it, the young plant  is killed by  ex-
posing the malted corn to  a current of hot dry air in the malt-kiln, and
the malt is then employed as a source of sugar in the fermentative pro-
cesses of the brewer  and distiller.
  The saccharine fermentation which thus furnishes nutriment for  the
young plant in the first stage of its existence, resembles the transforma-
tion of starch by means of sulphuric acid, described in p.  528, and is  ex- 
CONSTITUTION  OF  PLANTS.
651
cited by the presence of a peculiar ferment produced by the decomposi-
tion  of the  vegetable albumen  which the seed contains.   This  active
substance is termed Diastase; it does not pre-exist in the seed, but is
itself produced by the action of the air and water upon the albumen ; it
is not identical with the ferment which  induces the alcoholic fermenta-
tion, but they appear to be but successive stages of the decomposition of
the same  substance.   The diastase may be obtained solid by bruising
malt with a small quantity of  water, and  expressing the liquor ; to this
alcohol is to be added, which  precipitates a  quantity of unaltered  albu-
men, and on evaporating the filtered liquor to dryness, the diastase  re-
mains, though by no means pure ; it is a  white  gummy mass ;  it is pre.
cipitated by infusion of galls and most metallic salts; one  part of it rap-
idly and completely converts a solution of 2000 parts of starch in water,
first  into dextrine, and finally into grape-sugar.   It has been suggested
by Saussure that diastase  is identical with the  substance  termed mucin
in p. 537, but this is doubtful;  it contains nitrogen, and is most proba-
bly, as already stated, the  first product of the putrefaction of the gluten
or albumen.
   When  the process of germination is over, the plant is found provided,
by its  roots and leaves, with the means of procuring such nutriment as
its future offices require, from  the atmosphere and the soil.   For  the
constitution of its proper ligneous tissue, carbon, hydrogen, and oxygen
are required, and these serve  also for the formation of the  majority of its
excreted  products, as sugar,  gum, starch, resin, oils, and  acids; but, in
addition,  nitrogen is required ; and although the proportion of nitrogen
in any plant is  small, compared with that of the other elements, yet it
is of great importance as a constituent of the active  principles of most
medicinal plants, as the vegetable alkalies, amygdaline, &c.; and of still
higher interest, as Bousingault has shown the nutritive power of each
plant,  when used as food, to be  proportional to the quantity of nitrogen
which it  contains.   In  every plant  there exists  also  certain  inorganic
elements, acids, and  bases, which, though small in quantity, are yet  es-
sential to its healthy growth.  The examination of the modes, chemical
and  vital, by which these various substances are supplied to  the plant
and  assimilated by its organs, constitutes an important branch of vege-
table physiology, which can here be but superficially sketched ; and, in
its relation to practice, the manner of supplying these materials so as to
favour the growth  of plants, and develop their  most useful principles,
must be the basis of every system of enlightened  agriculture.

               Of the Assimilation of Carbon by  Plants.
   In describing the constitution of the atmosphere (p. 269), I have  had
already occasion to notice the beautiful provision by which the two great
classes of organized beings mutually compensate for the change  which
each produces  in  its nature, and  thus  retain  it  in the condition most
conducive to the healthful existence of both.   That while the animal, in
his respiration,  throws off carbonic acid  and absorbs  oxygen,  the  plant,
from the  surfaces of its green leaves, in  sunlight, absorbs carbonic acid
and  wives out oxygen.   It only remains here to examine the circumstan-
ces of this change with reference to the other functions of the  plant.
   As  water is abundantly absorbed  by plants, both with  the  roots  and
leaves, the assimilation of carbon from the air  should, with it, supply at 
652        FORMATION  OF  WOODY  TISSUE.
once the elements of the woody matter, as well as of those other bodies,
as sugar, starch, and gum, which contain oxygen and  hydrogen in the
proportions to form water.  But this respiratory function of the leaves
does not in reality possess the simplicity and uniformity of effect which
has been just assigned to it.  It is found that the absorption of carbonic
acid and the liberation of oxygen occur only  under the influence of sun-
light, and from the green portions of the plant, while the coloured por-
tions, as the flowers and fruits,  and even  the green leaves during the
night, absorb  oxygen and  give  out carbonic acid,  thus  tending to in-
crease  the vitiation of the atmosphere  produced by animals in place of
counteracting  it.   The existence of these opposing  actions had induced
some physiologists to doubt whether they did not neutralize each other,
and hence to seek for the source of the  carbon of the plant in the action
of the roots upon the organic substances  of the soil.  But the experi-
ments of Daubeny have conclusively established that a healthy plant
evolves  so much more oxygen  in  the  day  than  it  absorbs during the
night, and inversely absorbs so much more carbonic acid during the day
than it evolves at night, as may satisfactorily account for  the growth of
the woody material of the plant, and  compensate for the influence of ani-
mal respiration and combustion upon the air.
   It has been  already shown, that the grains of starch, when elaborated
by the organs  of the plant, possess a structure totally different from that
which characterizes  bodies constituted in virtue of mere  affinity, and
more analogous to certain animal organs, as the crystalline lens of the
eye.  In the different varieties of starch, it  is not difficult  to trace the
gradual transition to  lignine, and, as stated in page  530, ordinary wood
still retains in the tubes and cells formed by the arrangement of the par-
ticles of lignine, a considerable quantity of unaltered  starch.   In the me-
dulla of various trees, the passage  from starch to lignine is still more
evident.   Now for the formation of starch there are required but water
and carbon, its formula being C12H10OI0, and  this I consider as the actual
result of the true respiratory process of the  plant;  carbonic acid being
absorbed, and  an equal volume of oxygen being exhaled, the carbon is
assimilated by the vital  power  of the  plant, and, with the  elements of
water, produces a substance  partially organized in structure, the starch
globule.   The outer  layer of this gradually increasing in  density, and
water being separated from the internal portion, should give  a cell, or, by
the reunion  of many, a continuous fibre or  tube of true  lignine.   The
change  being simply the loss of water, the formula of the lignine becomes
C,2Hg08.  The nature of the starch globule, and, hence, the structure and
physical properties of the ligneous fibre, varies in different plants.   Thus
I consider, in  the adult plant, starch to be the first product of the assimi-
lation of carbon and water, that it is already possessed of a low degree
of organization, and  is, in structure and  composition, adapted for the
change  (growth rather than transformation) into true wood.
   By contact with the albuminous or fermentative principles, the starch,
whether accumulated in the seed or roots, or distributed throughout the
substance of the plant, undergoes changes of an opposite kind.  Its or-
ganized character is  lost; it successively forms gum and  sugar.   We
cannot yet form cane-sugar artificially from  starch,  but we  can have no
doubt that it arises, as grape-sugar does, from  the catalytic metamorphosis
of the starch, arrested, in virtue of the vital power of the plant, at a  point 
SECRETION  OF  PLANTS, ETC.          653
where we cannot seize it in the laboratory.   These are the truly nutri-
tious elements of the plant, whether designed for the support of the adult
individual, or, collected in proper  reservoirs, to serve for the sustenance
of the future individual in the seed.
  In the conversion of the  starch into the numerous secondary products,
as acids, colouring matters, oils, &c, the presence of which characterizes
the  generality of plants, we may  find  the source of that inverse respira-
tory action which  so much masks the real and simple nutritive process.
Of the circumstances of the formation of these bodies, we have an exam-
ple  admirably illustrative of the point, in the  conversion of lignine into
ulmine.  Here, though the change would at first appear to  require only
the loss of the elements of water, we  find it to be much more profound;
the constitution of the lignine is totally broken up; oxygen  is abundant-
ly absorbed from the air; a quantity  of its carbon is carried off as car-
bonic acid, and a quantity of its hydrogen as water.  This action, which
may be looked upon as equivalent to  the various processes  of secretion
performed upon the blood by the  organs  of animals, by which substances
adapted  to the  use or structure  of different parts are  there deposited,
while others unfitted for the purposes  of the organized  being are thrown
off, is carried on by the leaves, probably by all portions of the surface of
the plant, and is the source of the continued exhalation of water and car-
bonic acid which occurs.   During the day, and especially in bright sun-
shine, the assimilating power of  the plant being in full action, carbonic
acid is taken in, and oxygen given out;  during the night, while the plant
is in repose, this nutritive action  ceases.  Through the whole time, how-
ever, the process of the secretion is carried on, water and carbonic acid
given off, though in such proportion only as to  secure at the end of the
twenty-four hours an excess of assimilated carbon sufficient fully to se>
cure and account  for the rapidity of growth.
   The changes of constitution  which accompany the  ripening of fruit
deserve to be considered  more in detail  than  those of which the general
nature  has been just noticed.   If we examine  the composition of a young
apple, we find it to be nearly tasteless, and to consist of a loose ligneous
tissue, in which is imbedded a quantity of ordinary starch ;  as its growth
 proceeds, the starch diminishes in proportional amount, and the fruit be-
 comes intensely sour, from the presence  of tartaric acid ; after some time
 the acidity becomes of a  much  less  disagreeable  kind, and the tartaric
 acid  is found to be replaced by malic acid ;  and in the next and conclu-
 ding stage of maturity, this acid  disappears, its place being taken by pec
 tine'and^by sugar.  During the whole of these actions, oxygen is absorb-
 ed from the air, and water and carbonic acid  given off.  Their theory is
 simply indicated : thus starch, which is Cl2H,oOIO, absorbing 140., pro-
 duces 6 Aq.  and  4C02, with tartaric acid, CsH4Ol0;  and  of this, three
 atoms, absorbing  60., produce 8C.02 and 4 Aq., with two atoms of malic
 acid, 2(C8H4Os)T   The change of tartaric to malic acid may also occur
 without the absorption of oxygen from  the air, as 6(C8H4O10) may pro-
 duce 5(C8H4Os) with 8C.O, and  4 Aq. ;  but as fruits do not  ripen in close
 vessels, unless' when  they absorb oxygen, the former is more probably
 the process which actually takes place.  The formation of the pectine
 and sugar from the malic acid may be produced by the absorption of ox-
 y«ren and the giving off of water  and carbonic acid, as 8(C8H408) with
 9H.0. and 50?, produce pectine, CuH170tt, sugar, 2(C12H„012) with 16C. 
654        SOURCE  OF  CARBON  IN  PLANTS.
02.  That neither pectine nor sugar is derived originally from the starch,
is  evident, as the starch abounds but  in  the very earliest  stage, and
gives place  to  the tartaric acid, while  the increase in quantity  of the
gelatinous and saccharine matter is  proportional to the disappearance
of the acid constituents of the fruit.
   When our knowledge  of the ultimate effect of the complex actions of
plants upon the atmosphere was still uncertain, it was considered, and
upon  very rational grounds, that the plant was indebted for its carbon to
the organic substances of the soil, and the necessity for a continued sup.
ply of animal or vegetable manure to keep up the fertility of the soil, was
thus satisfactorily explained ; it was considered that the roots and  leaves
remaining from the  preceding crop, or intentionally mixed  up with the
soil, were converted, as already  described, into ulmine, which, either by
itself, or in combination  with inorganic bases, was taken up by the ab-
sorbing rootlets of the plant, carried  into its vessels, and assimilated to
the constituents of its tissues ; for, in fact, if we examine, at any moment,
any kind of fertile soil, we find it to contain abundance  of a kind of ul-
mine (geic acid, p. 639); we find this ulmine to be  a product of the de-
composition of the organic substances used as manure ; we find that, in
barren soils, the ulmine is either absent, or it  exists in another isomeric
form  (humine,  &c), and hence the vegetation  appeared distinctly con-
nected with, and attributable to the quantity of geine present.  But, not-
withstanding such plausible evidence, Liebig  has brought forward very
strong proof that the action of the ulmine can be but secondary towards
the nutrition of the  plant.   His arguments are derived from the  facts:
first,  that the plant may fully vegetate, though totally unconnected  with
the ground, as has been proved by experiments upon cellular plants, sus-
pended in the air, and supplied with water; second, that, from the insol-
ubility of every kind of ulmine, either free or when combined with  earthy
bases, which alone are presented in sufficient  quantity in the soil,  it can-
not be directly absorbed by the  rootlets of the plant, which totally reject
every kind of solid matter ; and, third, that if we compare the quantity of
ulmine in a soil before the growth and  after the collection of a crop, we
find the diminution to  be so small when compared with the great quanti-
ty of carbon contained in the mass of vegetable matter that has been ob-
tained, as fully to prove the produce of carbon in the crop to bear but an
indirect, if any, proportion to the quantity of ulmine in the soil.  The true
office of the organic matter in the soil  appears  to be, that, by its gradual
decomposition, a constant supply of carbonic acid is afforded to the plant,
by which, during the first  stages of its development, and while destitute
of the expanse of leaf requisite to collect the necessary quantity of nutri-
ment from the air, a more concentrated, and, as it were, richer  food is
applied to the  absorbing roots,  and  its healthful and rapid  growth thus
provided for ;  it  is not, therefore, the ulmine  of the soil, but the organic
matter generally, in changing into ulmine, that  may supply carbon to the
young  plant, the office of the soil-ulmine (geic acid) being different, as
will be shortly shown ; and, even in this action of the organic matters,
the functions of the plant remain the same, being the absorption  of car-
bonic acid and evolution of oxygen.

                  Assimilation  of Nitrogen by Plants.
   The organic substances which contain nitrogen belong to two classes; 
           SOURCE  OF NITROGEN  IN  PLANTS.        655

those of the first, which constitute the active or characteristic principles
of many plants, although of much interest in relation to medicine and to
abstract science, are of very little importance with reference to the growth
of the plant, and its use as food.  The bodies whose origin and proper-
ties are here of interest, belong to that class  of vegeto-animal substan-
ces, as albumen, gluten, legumine, of whose extraordinary power in in-
ducing catalytic decompositions of  other  bodies I have so often spoken ;
they are found in all parts of  the plant, dissolved or diffused through its
juices, but especially collected where transformations necessary for growth
or germination are to be accomplished.   Although present in but small
quantity, no function of the plant, in any  stage of its existence, could be
accomplished without their aid.   The conversion of starch into sugar for
the nutrition of the germe; of starch or  lignine into the vast variety of
secretory  products in the adult plants ; the elaboration of the fruit, its ri-
pening, and even the ultimate destruction of  the  vegetable tissues, have
their  origin in a series of actions, induced and maintained by communi-
cation from the active fermentation of these azotized materials.
   Not merely does the presence of this class of bodies regulate the prop-
er performance of the functions of the plant, but they play an equally im-
portant part in favouring the  assimilation of vegetable matter when used
as food by animals.  Bousingault has shown by experiments,  to which
I shall have occasion again to refer, that  in herbivorous animals, the to-
tal quantity of nitrogen assimilated for the growth of its muscular and
other tissues is derived from, and equal to that contained in the vegeta-
ble substances used as  food, and that hence, to  ascertain the nutritive
value of any organic substance, it is only necessary to determine the quan-
tity of nitrogen which it contains.  The results so calculated agree with
the  mean experimental results  of the most  enlightened agriculturists,
within limits as narrow as could be expected in experiments of that kind,
and  may, by farther research, be brought to still greater accuracy.
   Like the carbon, the nitrogen of plants is  obtained, in great part, by
absorption from the air, but yet  it is  not  merely gaseous nitrogen which
is assimilated.  The atmosphere always contains a quantity of ammonia,
derived from the putrefaction of organic  bodies.   This is absorbed, and
passes  into the constitution of a new set of plants, and from  them to an-
imals, to be again thrown into the air after their death, and thus circulate
from a«*e to age, entering into the constitution of each successive race of
oro-anized beings.  We  cannot refer, however, the total quantity of ni-
trogen  in plants to this one source ;  for if the produce of one year deri.
ved its  nitrogen only from the decomposition of the plants of the previous
year, the total quantity should be constant; whereas experience teaches
us that, by proper methods, the quantity of vegetables  produced on a soil
may  be continuously increased, and for this the nitrogen must be derived
strictly by absorption from the  air.
   Plants  vary exceedingly in the facility with which they derive nitrogen
from the  air, whether by direct absorption of gas or as ammonia.   Thus
trefoil vegetates and thrives  nearly as well when planted in pure sand,
and  supplied only with water  and air, as when  sown in ordinary soil;
and when fully grown, the quantity of nitrogen is found to be  increased
twenty-six per cent. ; but, on the contrary, wheat grows but slowly un-
der  the same circumstances,  makes no attempt to flower, and, on analy-
sis, the whole plant is found to contain  even a little  less nitrogen than 
 656      ASSIMILATION  OF  HYDROGEN,  ETC.

 had originally existed in the seed.   Wheat has, therefore, no power to
 assimilate nitrogen from the air, while trefoil possesses that character in
 probably its greatest vigour.   Yet  wheat, when fully grown, is rich in
 nitrogen ; its seed is more nutritious than that of any other corn, as it
 contains more gluten; its  nitrogen must, therefore, be derived from  an-
 other source: it is extracted from the organic matters of the soil.
   Without entering here  into  the question of the nature of manures,
 which will require especial consideration, it may be stated that, though
 wheat is thus peculiar in deriving its supply of nitrogen exclusively from
 the soil, yet all plants do so in a greater or less degree.  In the soil, how-
 ever, the nitrogen is not present uncombined.  It is evolved as ammonia
 from the decomposing organic substances of the manures, and hence an-
 imal manures, as producing  more of it, are proportionally richer.   It
 has been already noticed (p. 639) that the ulmine  of the soil is always
 combined with ammonia, which it retains with exceeding force.  But in
 presence of strong bases, such as lime, which all fertile soils contain, the
 ulmine is slowly decomposed, the elements of carbonic acid and of am-
 monia are eliminated from it, and these both being in a state fit for ab-
 sorption by the rootlets of the plant, are assimilated, and  supply carbon,
 nitrogen,  and water.  Independent of the ammonia derived from the or-
 ganic substances  actually  contained  in  the  soil, much of that diffused
 through the atmosphere is  carried to  the  roots of plants  by showers  of
 rain, and by the direct absorption of the gas by the  porous clay.   There
 are few specimens of clay, especially  if they contain iron, which do not
 give out ammonia when heated, and  the absorption occurs with greater
 power when the clay has been strongly dried.   Hence the increased fer-
 tility often given  to a soil by burning the surface to the depth of a few
inches.

                     Assimilation of Hydrogen.
  I have described (p. 653) as  the source of the carbonic acid evolved
by plants during the night, the conversion of the starchy substance, which
I conceive to be that first elaborated by the plant, into the various se-
cretory  products, acids,  colouring  matters,  &c.   But there are many
classes of important vegetable  products  in which  hydrogen so far pre-
dominates, that we must conceive for  their formation water to be decom-
posed, and its oxygen to  be evolved, either free or  in  combination with
carbon.    Of such bodies, glycerine, all of the fixed  and many of the vol-
atile oils, wax, and caoutchouc, are  examples.  The  secretory action
may thus, in place of opposing that of the respiration of the plant, coin.
cide with  it in result, according to the nature of the substances formed,
since, if all the carbon of the starch remains  in the constitution of the
secretion, oxygen is evolved from the water which is decomposed to sup-
ply the necessary quantity  of hydrogen.

               Of the Inorganic Constituents of Plants.
  If we make a plant vegetate in water which holds dissolved small quan-
 tities of inorganic salts, we find that, as  long as the plant  remains in
 health, it exercises upon these salts a  remarkable discretionary power of
 absorption, taking up some and rejecting others, which pass into its sub.
 stance only when, by the death or weakness of the plant, the liquor enters
 the tubes  by merely physical capillarity.   If a plant, whose tissues have 
RELATION  OF  SOIL TO  PLANT.         657
been thus imbibed with saline matters by its own spontaneous power of
absorption, be placed in a vessel of pure water, it will  be  found to yive
out certain of the saline matters it had taken up, but  to  retain others.
In this manner we may recognise the action of inorganic salts upon plants
to be of three kinds :  first, directly poisonous, which are rejected  by the
plant as long as it is in health, and to this class belong most substances
poisonous to  man ;  2d, those to which the plant appears indifferent, which
are taken up by it and given off again, without any apparent influence on
its growth ;  and, 3d, those which, when absorbed by the plant, are  assim-
ilated to its proper tissues, and are not given up by the  plant to water in
which it may be immersed.
   The bodies of this last class are all combinations of alkalies and earths,
and  principally with organic acids ; they form the ashes of the plant
when the organic matter is  burned away, and  then always  possess an al-
kaline reaction  from the formation of carbonates.   As  a general  princi-
pie,  we may say that each plant requires for its healthy growth inorganic
substances in certain quantity and of a certain nature ; but replacement
of one base by another may occur in certain cases, without  positive injury
to the plant.   Thus  the plants which yield soda when grown upon the
seashore (salsola, salicornia),  if transplanted to the interior, gradually
lose the soda, and acquire potash in its place ; so that, after a generation,
no trace of the former alkali remains.  The ashes of oaks or pines grown
upon a granitic or basaltic soil contain abundance of  magnesia  and of
potash, while trees of the same species  will flourish on a limestone soil,
and  in their  ashes lime  will be the predominant ingredient.  But these
cases of substitution of one base for the other in a plant are still but rare
exceptions to the principle, that each kind of plant requires for its vigor-
ous  and healthy growth to be  supplied with inorganic substances of a
specific  nature and in certain  quantity.
   It is this  principle which determines the more successful cultivation of
certain plants in certain soils.  Thus, if we examine the composition of
the  ashes of wheat, we find abundance of silica, phosphoric acid, magne-
sia,  lime, and potash.   If we sow wheat in a soil which contains neither
potash nor phosphoric acid, some of the materials necessary for the per-
fection of the plant being absent, the crop cannot be productive; but if
we  previously manure  the soil with  bonedust, with ashes of weeds, or
other substances which  may  supply  the necessary inorganic  elements,
these will be  absorbed, and the  plants obtain their  full development.
Even when  the quantity of the required inorganic base is but exceeding.
ly minute it will still be collected by the vital action of the plant in the
necessary quantity.   Thus, in most sea-plants, iodide of magnesium ex-
ists  in such proportion as that it affords the universal source of iodine for
all technical and scientific objects; and yet that salt, which is  excess.
ivelv soluble, is removed by the plant  from the  sea-water, which con-
tains but minute traces of  it, and is retained in the vegetable tissue by a
power which prevents its being washed out again.   It is this power of a
plant to search for and remove from the soil all traces of those inorganic
 bases which it  most requires, that renders many sods incapab e of bear-
 ing  successive crops of the same kind, without the intermediate apphca-
 ,iogn of suitable mineral manures.   But if the soil be of such nature as to
 contain itself those  elements, it may become truly inexhaustible  for the
 growth of most species of plant.   It is hence that soils formed by the de- 
658
CONSTITUTION  OF  SOILS.
composition of basaltic rocks or of modern lavas are, for every kind of
crop, some of the most productive ; the facility with which these rocks
are decomposed by the action of air  and water, provides a constant sup.
ply of soil absolutely new, and from the constitution of these rocks, the
great variety of their mineral components renders such soil abundant in
every element that plants in general require.

             Of the  Constitution of Soils and of Manures.
  From what has been already said, it  is easy to judge of the  circum-
stances which render a soil barren or productive, but from the importance
of the subject to vegetable physiology and to agriculture, it requires more
detailed examination.
  The organic elements of the plant being derived for the most part from
the  atmosphere, the office of the soil, so far as they are concerned, is re-
duced to supplying to the roots, during those periods when there is  not
a sufficient expanse of foliage to absorb nutriment from the air,  the car-
bonic acid produced by the gradual  rotting of  the ligneous matter, and
ulmine, and ammonia from the azotized elements of the manure.   For
this purpose the soil is, in respect to its mineral  composition, unimpor-
tant ; it should be porous, in order to admit of the  easy penetration of the
rootlets, and to allow free access of oxygen to the  organic matter to form
carbonic acid;  it should yet be close  enough to  retain moisture in  the
average intervals of rain, in order that the water necessary for vegeta-
tion may not be absent.
  These physical conditions are not, however, combined in any one kind
of mineral material.   If we take a soil  of pure sand  or of pure limestone,
we find them so loose and porous that  the water  filters oft almost imme-
diately after falling, and the plants necessarily  perish.   If a soil consist
of pure clay, its tenacity would  be such  as totally to  prevent the access
of air, and all growth of the absorbing filaments of the roots.  To com-
bine the two proper conditions  of a soil, the clay should be mixed with
the porous  material, in proportions which vary  with the  nature of the
plant to be cultivated ; and thus the simplest  soil, in order to  fulfil its
physical conditions, as supplemental to the atmosphere, should contain two
mineral substances, of which  one should be clay, and the  other lime or
silica ; and as in practice, unless for some special object, the presence of
caustic lime would prove  injurious to  the absorbing rootlets, this should
be present, combined with carbonic acid, as in  any of the usual  varieties
of limestone rocks.
   The proper action of the soil, that which it exercises independently of
its office in replacing the atmosphere, is to supply to the plant,  those in-
organic constituents, the importance of which have been already shown.
For this  purpose, a far greater complexity of constitution is  required.
Thus  there is no plant that does not  contain  both lime and  silica, and
hence, in the simplest soil, both must  be present.   There is scarcely  a
plant whose ashes, do not contain a fixed  alkali, generally potash; and
hence minerals which may yield, by their decomposition, the necessary
quantity of that base, should be present in a fertile soil.   For most plants,
also, magnesia must be supplied ;  and  for many,  and  especially  the vari-
ous kinds of corn, phosphoric acid.   In average soils, most of these bodies
are naturally present in the necessary degree.    When  the soil has origi-
nated in the decomposition of granitic  or of slaty rocks, the silica, the al- 
EXCRETIONS  OF PLANTS,  ETC.          659
umina, and the potash are abundantly supplied from feldspar and from
mica : lime and magnesia also may be derived from associated minerals ;
but, in general, it is necessary to add lime to such soils, in order that the
quantity necessary to full fertility may be present.   In purely limestone
soils, clay and silicious gravel must be added ; and to make up the defi-
ciency in  potash, the ashes of other plants  and cinders of coal.  If the
soil be purely silicious, the addition of clay and lime (marl) may bring it
to the proper composition.
  In these few words are contained the theory of what are termed miner-
al manures, with few exceptions.  In adding lime or marl, bonedust or
cinders, to a soil, we either render its physical condition of porosity  and
tenacity more suitable to the circumstances of the  plant,  or we supply
some ingredient which was either primitively deficient in the soil, or  had
been removed from it by a previous crop of the same kind.   On this  last
condition  is founded  also the necessity, in an economic agriculture, of
alternating crops which  take up from the ground materials of different
kinds.  Thus, if wheat be grown upon a soil, the rocky substance of which
is rich in potash and phosphoric acid, the crops will, after a few years, be
unproductive, and the soil impoverished, because the rock decomposes too
slowly to supply materials for the wheat as fast as they are required;  but
if we take from  that soil a crop  of wheat but once in three years, and in-
terpose some other plant, as trefoil, which  takes up but little potash  and
no phosphoric acid, the soil has  time to recover its constitution, and the
series of crops, thus arranged in  rotatory order, so far from impoverishing
the soil, may bring it to a higher degree of richness, by the additions made
to its azotized organic components by the roots and rejected leaves of the
various crops which are left upon it, and the manure derived from the con-
sumption  of its produce by animals.
   The advantage of a rotation  of crops may be thus deduced from the
necessity  of  the  soil  renewing  its  mineral constituents, by the gradual
decomposition of the subjacent  rocky matter (subsoil).   But the obser-
vations of Macaire  and Decandolle indicate another and not less  im-
portant reason for its use.  These physiologists have found, that from
the rootlets of a plant the same  process of excretion is carried on as by
its  stem  and leaves, and  that  brown-coloured  substances are exuded,
which possess  much analogy with tannin,  and which are poisonous to
plants of the same kind when  dissolved  in the water with which their
roots are supplied.   On the other  hand, the excretory products of one
plant may be  used  without  injury, and even  advantageously, for  the
growth of another plant of a different natural family ; and in this respect
the grasses and the leguminous  plants are most remarkable.  It is hence,
probably, for example, that wheat unfits the soil  for the growth of an-
other crop of wheat,  not merely by removing the potash and phosphoric
acid which is required for the perfection of its parts, but  it also gives out
a substance poisonous to a plant of the same kind, but which acts bene-
ficially upon the rootlets of a  leguminous  plant, favouring its growth,
while the soil has time  to regain from the subsoil the inorganic mate-
rials of which it had been deprived.                   ,    ,.    .   .
   The utility of manures mav now be  easily understood ; their action is
either as bone-earth,  marl, lime, cinders, or silicious gravel, to supply to
the soil some mineral  ingredient  in  which it had been deficient, or to
provide, as by the ordinary vegetable or animal manures, soot, dec, or- 
660         ACTION  OF  ORGANIC  MANURES.

ganic matter, which, by its  decomposition, may give out cniboinc sujd
and ammonia for the nutrition of the young plants,  hi some row -.awes
the action of manures is more indirect; thus  the leguminous plants ([tre-
foil) require but little inorganic matter, but much ammonia,  and yet
there is no manure so efficient in the promotion of their growth as plas-
ter of Paris (sulphate of lime).  The plant, however, contains no sul-
phate of lime ; it is not absorbed.   The action of this manure appears
to be, as was first suggested by Liebig, that, acting on those substances
of the ulmine family which always  retain a large  quantity of ammonia
intimately united in the  soil, it forms, by double decomposition, ulmate
of lime  and  sulphate of ammonia, which last, being soluble, is easily ab-
sorbed by the rootlets of the  plant, and the nitrogen assimilated to its
tissues.
   With regard to organic manures, their great value depends on the pro-
portion of nitrogen  they supply.  In  plants, the great mass of nitrogen is
always  deposited in organs, as the seed, the  tuber, &c, which, for that
very reason, are sought after and  collected by man, either as food, or for
medicinal purposes, from the  active (azotized) principles they contain.
The roots, stems, and leaves of plants, such as  are rejected in  the col-
lection of the crop,  contain little nitrogen, they  being rejected as useless
for that very reason. Hence the residue of a former season may manure
the land abundantly so far as carbon  is concerned, but be quite incapable
of supplying nitrogen,  and in providing materials for a future abundant
crop.  The object of the agriculturist  must be, so far as organic mate-
rial is concerned, to supply nitrogen,  especially for such plants as  the
different species of corn,  which are incapable of deriving that important
element directly from the atmosphere.  The value of an organic manure
may therefore, for practical  purposes,  be considered as being measured
by the quantity of  nitrogen  which it contains, and  the directness or in-
directness of the benefit  derivable from it depends  upon the manner in
which the nitrogen is combined.  If mere ammoniacal salts be used, or
materials, as animal manures, urine, &c, which soon form ammoniacal
salts by their putrefaction, the whole benefit of the manure is given to
the crops immediately succeeding its  application ; but if organic  sub-
stances be employed which resist decomposition, their nitrogen is evolved
but slowly;  and though little immediate amelioration be observed from
their addition to the soil, their influence is gradually  and steadily exerted,
and  becomes ultimately sensible  to  the full degree proportional to the
nitrogen they contain.
   A mode of restoring to the soil the principles it had lost by indiscreet
cultivation,  is that  of fallowing.  It is a method  synonymous  with an
ignorant and improvident agriculture.   The  soil having,  by over  work,
lost, on the  one hand, some  of its essential mineral  ineredients, requires
time to gather, by the decomposition of the underlying subsoil or rock,
a proper quantity of them to supply the elements of  the succeeding crops,
and having  been deprived of its organic elements, especially the nitrogen,
it  must  be allowed to gain from the atmosphere a suitable quantity of am-
monia, or by the gradual rotting of the roots of the preceding crop, a quan-
tity of carbonic acid suitable to the wants of that which is to follow.   But
all of these  effects may be more perfectly and more profitably secured by
the intervention, in a succession suitably arranged, of other crops, which
exercise upon the soil actions alternately opposed.   Thus,  if we arrange 
ACTIVE  PRINCIPLES  OF  PLANTS.        661
that wheat, which probably removes from the soil a greater quantity and
a greater number of elements than any other crop, shall be succeeded by
sown grasses, for forage or hay, which, as they are not allowed to mature
their seeds, exercise but little deteriorating action ; these, again, by oats,
the exhausting power of which is but one sixth that of wheat; then pease
or beans manured ;  that these be followed by barley, the exhausting power
of which is one third, and this by a manured green crop, the soil may be
brought into  a condition superior to that from which  we had set out, and
the series may be recommenced with wheat, the soil  being every season
economized.   This is but one of the many kinds of rotation which have
been found by experienced agriculturists to be as beneficial  in practice as
theory indicates that they ought to  be ; and no other reason can be assign-
ed for allowing a field to lie idle every second or third year, but ignorance
on the part of the farmer of what  could otherwise be  done with it.
   It remains only  to notice, in relation to the theory  of  the growth of
plants, a few additional circumstances connected  with  the formation of
some of their peculiar principles.   It  is not unusual  to hear, from even
intelligent agriculturists, objections to the cultivation of certain plants, on
the grounds of their exhausting the soil too much.  A plant exhausts the
soil only in consequence of its forming in proportional quantity some sub-
stance, the elements of which are derived from the soil, and which con-
stitute in almost every case the valuable portion  of  the plant.   Wheat
exhausts the soil, because it derives therefrom the large quantity of nitro-
gen  which its grain  contains;  but it is precisely that  great quantity of
nitrogen which renders wheat more valuable  in the market than oats or
barley.  Tobacco  exhausts  the soil, because  it takes  up abundance of
nitrogen, with which it forms its nicotine ; the more of the active princi-
ple the plant produces, the more it exhausts the soil; but in the  same
proportion, the  greater value  does it possess when  sold.   To produce
indigo, nitrogen  must be supplied to the plants  by  abundance of rich
manure; no crop is more exhausting ;  but without the nitrogen no col-
ouring matter could be formed, and the plant would be completely worth-
less.   Examples of this kind might be adduced in any number; but these
suffice to place in a distinct,  though popular aspect, the general principle,
that where a plant exhausts the soil, especially as to  its nitrogen, it is for
the  production  of the substance  which gives the plant its commercial
value and  importance, and that hence the quantity of manure necessary
for the production of an abundant crop is fully repaid by the improved
quality of the produce.                          _          .
   Without seeking to enter into  the general  question of the influence ot
 the physical agents on vegetation, which for its discussion would require
 more extended limits, and lead to considerations too  far  removed from
 chemistry to justify its introduction, I shall, in concluding this sketch of
 the  chemistry of vegetation,  notice the peculiar action which light exer-
cises upon plants.   It is not merely that it acts as a general stimulus and
 thus provokes the activity of nutrition, which determines the ultimate re-
 sult of the purification of the atmosphere by plants, and  that its w-ithdraw.
 al is followed, with plants as with  higher beings, by a torpor and tendency
 to rest, which closes their petals,  and  folds their leaves at  nigh .   But in
 the production of the coloured  parts of plants the agency of light is indis.
 nensable   A plant which grows  in darkness, as in the  gallery of a mine,
no matter to what size its form may reach by means of a  copious supply 
662  ACTION  OF  LIGHT.--ANIMAL  CHEMISTRY.

of food, remains soft, its wood unformed, its colour pale ;  the chlorophyll
not being generated, unless under  the influence  of light.   For culinary
purposes, precisely this effect is produced by covering  up the stems of
celery and asparagus, the softness  and whiteness admired upon the table
bein-j the evidence of the sick and  abortive organization of the stem.
   The action of light in favouring the production  of colour in plants  is,
however, accompanied by a more material change.  The petals, and  all
coloured parts of plants, except the leaves, absorb oxygen from  the air.
This is  precisely what we find a number of bodies to effect, when pass-
ing from their colourless condition to that in which their proper colour
is  displayed.  Thus white indigo  becomes  blue by absorbing oxygen.
Thus rocelline,  by absorbing oxygen and giving  off water, forms ery.
throlitmic acid.  It is thus, too, by deoxidizing agents, we may remove the
colour from  logwood, archil,  and the flowers of most plants, and restore
their tints by again admitting it.  Frequently, also, the generation  of the
coloured substance is accompanied not merely by  an absorption of oxy.
gen, but by  an escape of carbonic acid; this, which is shown in the  la-
boratory in forming orcei'ne from erythrine, appears to take place  in the
tissues of most flowers, which rapidly give out carbonic acid for some
time after they have first opened.
   In similar actions, carried  on in the laboratory by means of chlorine,
the influence of light in furthering  the removal of hydrogen, and even  of
carbon, if water be present, is most remarkable, and illustrates the opera-
tion of that physical agent in  producing  the colours of plants in a distinct
and satisfactory way.   This  action has been, however, so fully noticed
in describing the general chemical  agencies of light (p. 172) and the ac-
tion of chlorine on colouring  matters (p. 622), that 1 deem it  necessary
only to  refer to what has been there said upon the subject.
                         CHAPTER XXX.

                       OF ANIMAL CHEMISTRY.

  In describing the various classes of organic bodies which have hitherto
come under our notice, I have made no distinction as to their animal or
vegetable origin, for the point of view under which they were then con-
sidered, and the  properties which they manifested,  were independent of
their source.  It was thus with ethal, the fatty acids, and colouring mat-
ters ; and,  indeed,  in many instances, the same substances were found to
be products of both kingdoms of organized nature.  In the present chap.
ter I purpose to describe, so far as our accurate knowledge  extends, the
chemical history of those bodies which  I characterized in another place
(p. 468) as being rather organized than organic; as  constituting, not
merely a product of the vital operations of the being, but the mechanism
itself by which these vital operations are carried on ; as making part of
the tissues  essential to its proper  organization  and life, and as being,
while in connexion with the animal, and participating in its  life, protect- 
FIBRINE,  ITS PROPERTIES.            663
ed from the truly chemical reactions of their proper elements, which,
after the death of the animal, especially in contact with  air and water,
rapidly assume simpler forms of union, and, breaking up the complex an-
imal tissue into a crowd of binary compounds, induce the change well
known as putrefaction.
   In connexion with these substances, which form the basis of the tissues
and organs of the animal frame, I will bring under survey the processes
by which, from the atmosphere, or from  the materials of our food, the
substance of our organs is continually renewed, their growth provided
for, and the conditions necessary  for the  continuance of  health and life
maintained.   The functions of respiration and of digestion, so far as the
chemical  phenomena which they embrace are known ; the composition of
those secretions  and excretions, whose agency in the furtherance of those
processes has been studied, will here be described ; and, finally, the com-
position of those excretions which have for their office the separation of
elements  unfit for the nutrition of the beings, or which are not intended
for its support.
   In each of these divisions I shall add to the description of the compo-
sition and properties of  these tissues or secretions in the  state of health,
such facts  in  reference  to the modifications introduced by disease, as
have been observed with proper accuracy.

                             SECTION I.
              OF THE COMPOSITION OF THE ANIMAL TISSUES.
            A. Of the Albuminous Materials of the Tissues.
                              Of Fibrine.
   This substance constitutes the basis of the muscular tissue, and forms
 an important constituent of the  blood.   In the latter it  exists dissolved
 during life, but separates after death or extraction  from the body, produ-
 cing with the colouring material, the  phenomenon of coagulation.   In
 the muscles, the fibrine is arranged in a truly organized and living con-
 dition, constituting  the  contractile  fibres, in which it  is so  interwoven
 with nervous and vascular filaments as to render its isolation impossible.
 To obtain pure fibrine, therefore,  we have recourse to blood, which, it im-
 mediately on being drawn it be briskly agitated with a little bundle of twigs,
 does not  coagulate, but the fibrine  is deposited on the twigs in soft tenacious
 masses,  which,  being washed to remove  any adhering colouring matter,
 a:.d  digested in  alcohol  and ether to remove some traces  of fatty substan-
 ces which adhere to it,  constitute pure fibrine, which may be dried by a
 gentle heat, and appears then as  a yellowish opaque mass, hard, tasteless,
 and inodorous :  if it be at all transparent this results from traces of ad-
 hering fat.   It is insoluble in water, alcohol, and ether ;  it absorbs, how-
 ever,°so  much water as  to treble  its weight and thereby recovers the
 volume,  softness, and flexibility it possessed before being dried.  This
 Z 2 e is not  sensible to the hand, but  by strong pressure between folds
 S bibulous paper it may be removed, and the fibrine rendered complete-
 W dryWiI boiled with water for a great length of time, fibrine is de-
 composed and dissolves, but it does not form any kind of gelatine.
    Fibrine  is remarkable for decomposing deutoxide of hydrogen rapidly
 bV catalytic  force (p. 235, 258), evolving oxygen.   Several of he animal
 tissues produce this  effect, though not containing fibrine.  Albumen is,
 however, totally destitute of it. 
664
ALBUMEN.
   Fibrine absorbs cold oil of vitriol, and swells up to a yellow transpa-
rent jelly.   On the addition of water, it shrinks up and becomes hard ;
but if all the excess of acid be washed away, the residual mass, which is
a neutral compound of fibrine and sulphuric acid, dissolves in pure water.
With nitric  acid, fibrine  evolves nitrogen  and  nitric oxide, and forms a
yellow powder, xanthoproteic acid, to which I snail shortly recur.  Tri-
basic phosphoric  acid and acetic acid dissolve  fibrine.   The solution  is
precipitated by the mineral acids  and by  caustic potash, an  excess  of
which last, however, redissolves the precipitate.   The mono,  or bibasic
phosphoric acids, act as sulphuric acid towards fibrine.   If perfectly dry
fibrine be digested in strong muriatic acid, it swells up, and after a few
minutes dissolves into a rich dark blue liquid.   No gas is evolved.   This
blue liquor is precipitated by yellow prussiate of potash.
   Fibrine is dissolved even  by a dilute solution  of caustic potash, and
appears thereby to neutralize the alkali almost completely.   This solu-
tion is coagulated by alcohol and by acids, but not  by heat.  The pre-
cipitates given by acetic and tribasic phosphoric acids are redissolved by
an excess.
   If sulphate of soda or nitrate of potash be added to newly-drawn blood,
its coagulation is prevented ; and if fibrine be digested in a strong solution
of nitre, it dissolves, forming a thick liquid, which is coagulated by heat,
by alcohol, and acids, and is precipitated by  the salts of mercury, lead, and
copper, and  by yellow  prussiate of potash.   This property of fibrine will
again come  under notice.
   The composition of fibrine is expressed by the formula CgooH^. N100
O^Q-f-P.Sjj.   It contains, besides, minute quantities  of lime and magne-
sia, so that, when incinerated, it leaves 0*77 per cent, of sulphates and
phosphates of those bases.

                           Of Albumen.
   This substance is even  more extensively  distributed through the animal
frame than fibrine.   Like fibrine, it exists  in two conditions, one soluble,
and the other insoluble in water; but whereas  the fibrine becomes insol-
uble almost  instantly on  being withdrawn  from the body, albumen may
retain that state for an indefinite time, and its  history is therefore more
complete.   In its soluble  form it exists in the blood, the egg, in the serous
secretions, in the humours of the eye, &c.; in the soluble or  coagulated
form, it constitutes a portion of most of the solid tissues.  Albumen de-
rives its name from its constituting the mass of white of egg.
   Soluble Albumen.—This is obtained in the solid form by evaporating
to dryness, at a temperature which  does not exceed 120°,  the serum of
blood, or white of egg, the membranous investments of the  latter having
been torn up by triturating with some angular fragments of glass.  The
dry mass is yellow, transparent, hard, tough, and contains, besides  the
albumen, the salts and some other constituents of the blood, or white of
egg, in minute quantity.   These are extracted  by digestion  in alcohol
and ether, which leave the albumen  pure.   When thus completely dry,
it may be heated  beyond  212° without passing into the coagulated condi
tion.   If digested in cold water, it gradually swells up, and  finally dis-
solves.  This solution, when heated to a temperature between 140° and
150°, coagulates.  If dilute, the solution  may even be heated to 165°
without coagulating, and when present in  very small quantity, the albu- 
STATES  OF  ALBUME N.--P EOTEINE.       665
men may not separate until the water boils.   When once coagulated in
this manner, albumen is totally insoluble in water; it is changed into its
second form.   The  solution of albumen is precipitated  by alcohol, by
acids, and metallic salts, exactly as  the  solution  of fibrine  in saltpetre.
The only distinction  that can be drawn between the two is, that the saline
solution of fibrine is partially decomposed by the addition of a large quan-
tity of water.
   The precipitates yielded by solution of albumen with metallic salts are
mixtures of two distinct substances,  one  a compound of albumen with the
acid, the other a compound of albumen with the metallic  oxide ; the for-
mer'is generally somewhat soluble, the latter insoluble ; and hence results
the application of albumen as an antidote to mineral poisons, as corrosive
sublimate and bluestone.
   Albumen is also  coagulated by many organic  bodies,  as tannic acid
and kreosote, which last acts catalytically, as a very minute quantity of
it coagulates a large quantity of albumen, without entering into combina-
tion with it.
   Coagulated Albumen is obtained by heating serum of the blood, or white
of eg", to between 140° and 150°, so that they solidify ;  washing the mass
with water, digesting with alcohol and ether until  all soluble is removed,
and then drying with care.  Thus  prepared, it  retains some  inorganic
salts, principally phosphate of lime, from  which it may be obtained free
as follows : The serum of the blood is to be coagulated by muriatic acid ;
 the coagulum washed with  acidulated water, and then so much pure water
 added as may dissolve it.   This solution being then decomposed by car-
 bonate of ammonia, the pure albumen is separated as a flocculent white
 precipitate.                                .         ,   .   .  ,
    When dry, it is yellow  and transparent;  in every chemical character
 except its relation to deutoxide of hydrogen, it identifies itself with  fibrine,
 and it is hence unnecessary to repeat the details of these  reactions; in
 its composition it is very closely related to it; their organic element is
 the same, and they differ only in the quantity of  sulphur, the formula of
   ,.       i  ■  „ n  H    NT0  4-PS.    The auantity of ashes remain-
 albumen being UaoH620 . lN|oo*~'2.io^r**:V    illc H""1"1^
 in*** from albumen is greater than from  fibrine.
    The comparative history of these bodies, as now given, leads  to con-
 siderable doubt as to how  far they are chemically distinct, although their
 physiological characters  are so different.   Mulder,  to  whose accurate
 researches we are  indebted for the greater part of our knowledge of the
 constitution of these bodies, looks  upon both as compounds of the  real
 ominic  substance, which he  terms Proteine, with sulphurets of phos-
 S    In Set, the sulphur and  phosphorus may be removed by very
 simple  methods, and the  body (proteine) which  then remains deserves

 ^When albumen, fibrine, cheese,  or flesh  is freed, by  digestion in wa-
 ter alcohol,  and ether, from all  bodies soluble in these liquids  and  by
 ter, aiconoi,  £»u      '      .     ,  h     b    removed, it is to be dis-
 di ute muriatic acid, all eariuy sctus -.-a*                     whprehv
 solved in a dilute solution of caustic  potash, and  heated to 120 , whereby
   he sulplmr  and phosphorus form  phosphate of  potash and sulphuret of
  ootassium   From the filtered liquor the proteine may  then be  precipi-
  Cly acetic acid, which must be added on y in very  slight excess, as


  0t£o^^ 
666
COMPOUNDS  OF  PROTEINE.
come hard and yellow, and give an amber-coloured powder.  It absorbs
water, swells up, and regains the appearance it had before being dried.
By long boiling with water it is decomposed and dissolved.
   Proteine dissolves in all very dilute acids, forming neutral compounds
which are insoluble in strong acid  liquors, and are  hence precipitated on
the addition of strong acids, except the acetic and tribasic phosphoric
acids.   With oil of vitriol it combines as described under the  head of
fibrine, and forms  Proteosulphuric Acid.   It combines also with earthy
and metallic oxides,  forming insoluble compounds,  which are identical in
characters with those obtained  with albumen.
   The composition of proteine, as found by Mulder, and confirmed by
the analyses of its  acid and basic combinations, is  expressed by the for-
mula C40H32. N5012.   We may evidently consider albumen and fibrine
as compounds of proteine;  for if  we represent proteine by the symbol
Prt., albumen becomes Prt^-f-P.S^ and fibrine is Prtgo-f-P.Sg. I consider,
however, that the state of combination of these bodies requires some far-
ther consideration.
   It is found that proteine constitutes the basis, not merely of the animal
substances now under examination, but that it is obtained also from ve-
getable albumen, gluten, and legumine (p. 538), and constitutes  the pure
caseous matter of milk, and that the similarity of properties and compo-
sition in these bodies is such  as  to justify us in  looking upon them as
identical.   We have seen that, between albumen  and  fibrine,  the dis-
tinctive chemical characters are,  if any, so trivial as to leave no firm
ground for their distinction in that  way; and if we  examine the evidence
of their being compounds of proteine with sulphur and phosphorus, we
shall find them  quite inconclusive.   First, it is not  certain that such sul-
phurets of phosphorus exist as P.S2 and P.S4;  second, the compounds of
sulphur and phosphorus  do not manifest any tendency whatsoever to
combination; and, third, in all the reactions of albumen and fibrine, the
proteine on the one  hand, the sulphur  and phosphorus on the other, act
as if they were totally distinct.   I  look upon albumen and fibrine, while
in connexion with the body, as organized and living substances, in whose
functions the minute quantity of sulphur and phosphorus may act an im-
portant part as a  catalytic  body.   The proteine  I  consider,  not, with
Mulder, as the  basis of our  tissues, but as  the simplest  product of their
decomposition.   It enters in combination with acids and with  bases, as
indigo or  morphia do, which I  look upon as totally foreign to the char-
acter of a body possessed of vital properties.
   Having thus  described what I consider to be the  true place of proteine,
in relation  to albumen and fibrine, I shall briefly notice some of its de-
rived compounds.
   Chloroproteic Acid is formed  by  passing chlorine into a solution of al-
bumen.   It is  a white powder.  Its formula is C40H3I . N5012+C1.04.
By ammonia it is decomposed, nitrogen being evolved, and a white sub-
stance formed,  Oxyproteine, the  formula of which is C40H31 . N6015.
   The formation of  Xanthoproteic  Acid,  by the action of nitric  acid on
fibrine, has been already noticed.   It is an orange-yellow powder ;  when
washed from  adhering acid, tasteless and inodorous,  but reddens  moist
litmus paper.   Insoluble  in water, alcohol, and ether, it unites with acids,
forming compounds which are pale yellow, and insoluble; with  bases it
forms soluble salts, generally deep  red coloured.   Its formula is CjmHjs .
N4O12, 
             SOURCES,  ETC.,  OF  GELATINE.          667


           B.  Of the Gelatinous Constituents of ihe Tissues.
                            Of Gelatine.
  When the skin, cellular or serous tissues, tendons, and some  forms of
cartilage, as that of bones, are boiled in water, they dissolve in great part,
and form a solution which gelatinizes on cooling.   Some of these tissues,
o.s the skin, dissolve easily, and almost completely; others  dissolve but
partly, and  leave behind a quantity of coagulated albumen.  In  most
kinds of cartilage, a very prolonged boiling is  necessary to extract any
sensible quantity of gelatine.   These various tissues are thus found to
consist of albumen and  gelatine, united in various  proportions,  and each
presenting various degrees of condensation of texture, but by boiling they
may be completely  separated from each other.
  The gelatine is known in commerce as the material of isinglass and of
common glue.   When  pure it  is colourless and  transparent, very spa-
ringly soluble  in cold water, by contact with which, however, it swells
up and softens.  In hot water it dissolves readily,  and on cooling, forms
so strong a jelly, that with yfyth part it is a consistent solid.   It is insolu-
ble in alcohol  and ether.   When a solution of  gelatine is long exposed
to the air, or frequently heated and cooled, it undergoes a commencement
of putrefaction, and loses its property of gelatinizing.   The composition
of gelatine, by Mulder's analyses, is  expressed by the  formula C13H10
N205.
   The action  of reagents on gelatine is in some  cases  of high interest.
By digestion with strong sulphuric acid, as with caustic  potash, the same
results  are  obtained.   Ammonia is evolved, a white  crystalline  body
{Leucine) and a sweet substance (Sugar of Gelatine) are formed.   They
are separated from each other, and from some less important  products,
by repeated crystallizations.   From its alcoholic  solution, Leucine sep-
arates in brilliant colourless plates.   It feels greasy, is tasteless and ino-
dorous ; heated to 336°, it sublimes  totally unchanged.  It dissolves in
twenty-eight parts of cold  water, but requires 625  parts of alcohol, and is
insoluble in ether ; its formula  is C,2Hia. N.04.   It combines with nitric
acid to  form Nitroleucic Acid, which crystallizes in brilliant needles, and
forms with bases neutral salts.   Its formula is C12H12. N.04+N.03Aq.
   The  Sugar of Gelatine crystallizes from its solution in alcohol, by spon-
taneous evaporation, in large prisms, which are colourless, taste sweet,
and  feel gritty between the teeth.   It is decomposed by heat.   At 60° it
dissolves in five parts of water, but it is sparingly  soluble in alcohol and
ether.   The crystals consist of C16H15 . N40„ + 3 Aq.  It forms, with
bases, well-characterized compounds, and unites also with nitric acid.
   When acted on by chlorine, gelatine is converted into a  white  floccu-
lent substance, insoluble in water, but dissolved by an excess of gelatine.
Its composition is expressed by the formula C32H40 . N8029 + Cl.04, con-
sisting,  therefore, of four  atoms of unaltered gelatine and one atom of
chlorous acid.   Gelatine is not  precipitated either  by solutions of ordina-
ry or of basic alum ;  but if a solution of common salt be also mixed, the
gelatine falls down, combined with alumina, as  it decomposes the muri.
ate of alumina which is then formed.   On this principle is founded the
manufacture of white leather, by a kind of tanning with alum.
   The  most important compound of gelatine  is that with  tannic  acid,
which constitutes ordinary leather.  This reaction is so distinct, that one 
668 MANUFACTURE  OF  LEATHE R.--C HONDRINE.

part of gelatine in 5000 of water is at once detected by the infusion of
galls.  The constitution of the  precipitate varies according as  one or
other of these materials is employed in  excess, the  tannic acid and ge-
latine being capable of uniting in at  least  three different proportions ;  100
parts of dry gelatine combine with 136 parts of tannic acid, when the
latter is in great excess : this compound contains an atom of each ingre-
dient.
  The technical applications of gelatine are numerous, and, for the most
part, well known.  For glueing together  wood, paper, &c, thickening
colours, filling up the pores  of writing paper, and as isinglass and calves'
feet jelly, an article of food,  it is abundantly employed ; but its most im-
portant use is in the manufacture of leather.  The skins are cleaned by
digestion with lime and scraping with a  knife, from the hair and epider-
mis on the one, and  the loose cellular tissue on the other side, and then
steeped in  pits containing an infusion of oak  bark,  valonia, sumach, or
other of  the substances rich in tannic acid (p. 601).  At  first  the tan-
ning liquor is used very weak, as otherwise the surface of the skin would
become impervious, and the interior could  not afterward be tanned ; but
having passed through a succession  of liquors gradually becoming strong-
er, the skins are in the last pit interstratified with oak bark, and so, for a
considerable time, submitted to the  action of the tannic acid in its high-
est state  of concentration, until  the conversion  into leather is complete
throughout the entire substance.  They are then removed, and subjected
to finishing and cleaning processes, which  I need not notice.
  Many chemists consider  that gelatine is merely a product of  the de-
composition of albumen or  fibrine  by boiling water, and not a true con.
stituent of the tissues.  I  believe this idea  to be incorrect on the follow-
ing grounds:  First, pure  fibrine, or albumen, gives no gelatine by boil.
ing ; second, in the process  of tanning, the  tannic acid combines with ge-
latine in a skin  which  has  never been boiled ; and, third, that we  can
easily understand why some tissues give  gelatine more easily than others
by the different degrees of condensation in their structure ; but I rather
consider that gelatine bears the  same relation to the organized tissue of
the  skin or cellular membrane  that proteine does to the  fibrine of the
blood, being really a product, of its death and decomposition, though the
only representative of it which we can have.
  Chondrine.—Those cartilages in which  bone is not deposited, are re-
solved by boiling into a substance possessing much analogy to gelatine,
but still distinguished from it by the following properties : it precipitates
solutions of alum, sulphate of iron, and acetate of lead, and is precipita-
ted  by acetic acid, none of which bodies  have any action on ordinary ge-
latine, which, however,  chondrine  resembles in  all its other characters ;
in composition, however, it differs, its formula  being, by Mulder's anal.
ysis, C|6H13.  N207;  it, however, contains a trace of sulphur, its complete
formula being C320H260 . N40O140+S.  The physiologist M tiller, to whom
the discovery of chondrine is due, considers that the skeleton of cartila-
ginous fishes yields a third  variety  of gelatine.

              C.  Of the fatly Constituents of the Tissues.
  The fatty  bodies already  described in Chapter XXIII.,  although con-
tributing essentially to the support  of the animal frame, are mere secre-
tions, and  do not form  any portion of its  organized tissues.   The sun- 
 CEREBROTE,  CEREBROL,  CHOLESTERINE, ETC.  669

stances properly included under the present head are the constituents of
the nervous tissue, such as it is  found in the brain, the spinal cord, and
nerves.
   In  the composition of the  brain it is possible to  distinguish  at least
three, perhaps five, distinct substances of a fatty nature ; the most char-
acteristic and important is termed Cerebrote :  its mode of preparation
can easily be gathered from its characters ; it is a white powder, taste-
less and inodorous, feeling not at  all greasy, but like starch ; when heat-
ed, it does not melt until it has become brown, and in great part decom-
posed ;  it is insoluble in water, sparingly soluble in alcohol or ether when
cold, but abundantly when hot; on cooling, it is deposited from its alco-
holic solution as a white powder, not at all  crystalline ; it is not acted
upon by alkalies.   In composition  it resembles albumen, containing  a
large quantity of nitrogen, with sulphur and phosphorus in  minute quan-
tity, but its precise formula cannot be considered as being yet established.
   Cerebral is a liquid reddish oil, having the  odour of fresh brain, and a
disagreeable rancid taste.  It is soluble in all proportions in ether and
in oils, but only moderately so in alcohol.   It contains the same elements
as the cerebrote, and  apparently in nearly, if not exactly, the same pro-
portions ; but the  analyses of Couerbe,  who alone  has examined their
composition, are not authentic enough to be brought  forward.  The cer-
ebrol is not saponifiable, nor is  it in any way altered  by digestion with
caustic alkalies.
   In addition to these two bodies, the brain contains a large quantity of
a substance, which, from having been first discovered as a constituent of
biliary calculi, is termed Cholesterine : it is insoluble in water, but dis-
solves abundantly in boiling alcohol, from which it crystallizes, on cool-
ing, in brilliant plates ;  it melts at 290°, and sublimes  partially by  a
stronger heat; it  dissolves readily in ether ; it is not altered by  caustic
alkalies ;  its formula is C36H30O.  By treatment with  hot  nitric  acid,  it
is converted into  a substance which crystallizes in  yellow needles, and
forms, with bases, yellow salts.   This is  Cholesteric Acid, the formula of
which appears to  be C26H20. N.O,,.
   Couerbe has described as constituents of the  brain two other fatty bod-
ies,  Cephalot and  Stearocenol; they are brown  coloured resinous bodies,
which, I consider, will most probably, on re-examination of the subject,
be found to be impure or decomposed mixtures of cerebrote and cepha-
lol.   I hence only indicate their supposed  existence.  The cholesterine
I look upon as being deposited in the brain as ordinary fat is in the cel-
lular tissue, or in the substance of other organs, and not as  making up an
essential portion of the nervous tissue.  This idea is  strengthened by the
fact that the cholesterine  frequently aggregates in the  brain in masses,
forming one variety of the  fatty tumours of that organ.

      D.  Of the Saline and Extractive Constituents of the Tissues.
   We find in all the animal tissues small quantities of a great variety of
salts, the same as  those  which will be hereafter noticed as existing in the
blood, to the presence of which  in the substance of  the tissues they are
probably due.   In the tissue  of the bones and  teeth, however, these sa-
line matters are deposited in  much  greater quantity, and  in disease and
in old age bony deposites occur  in all those tissues which  yield true ge-
latine on boiling.   The composition of the bones and teeth will be here-
after noticed. 
670
SKI N.---E P I D E R M I S.---II O R N.
   The extractive  matters of the  tissues, like  the extractive matter of
plants (p. 612), do not pre-exist as such, but are formed by the decom-
position,  by protracted boiling in water, of the fibrine, albumen, gelatine,
&c, which they really contain.  Berzelius has pointed out the existence
of a great number of different substances that are  thus generated, of
which two need here  only require notice.  For the first, the name Ozma-
zome may be  retained, and the name Zomidine applied to the second.
Ozmazome is soluble in water, and also in absolute  alcohol;  it cannot
be dried  by heat, but  forms a semifluid of an acid and salty taste, which
evolves  powerfully the odour of concentrated  decomposing urine.   Its
solution in water is yellow ; it is precipitated  by the salts of mercury,
lead, and  tin.
   The zomidine is insoluble in alcohol; it dries down to a brown extract,
of a strong and agreeable  odour of soup.   It dissolves in water in all
proportions.   Its solutions are precipitated by  the salts  of lead and tin,
but not by corrosive  sublimate or tincture of galls.   When  heated it
gives out an odour of roasting meat, the  taste and smell of which are
indeed due to  its formation.   Both ozmazome  and zomidine contain ni-
trogen.

Of the  Composition of the Tissues, and of ihe Secretions in Health  and in
                              Disease.
   Having described thus the  constituents of the tissues individually, I
shall now present such results as  have been hitherto obtained  as  to the
quantitative composition of the organized tissues formed by their reunion,
their secretory products, and morbid  alterations.
   Of ihe Skin, Epidermis, and its  Modifications.—The  skin of animals
is a congeries of  finely-constructed organs, sensitive  and secretory, im-
bedded in a peculiar  tissue, which is one  of those most easily yielding
gelatine, whence the process of tanning skins.  The relative proportions
of solid and liquid matter in a skin freed from adhering fat and cellular
membrane, but soft and imbibed with its natural proportions  of  water,
was found by  Wienhalt to be,
           Proper cutaneous tissues, including blood-) 30.53
            vessels and nerves........$
           Albumen............   154
           Extractive soluble in alcohol.....083
              Do.   soluble only in water ....   760
           Water.............5750^

   On the surface of the  skin there  is  secreted a substance,  which,
though varying in anatomical  structure  and appearance exceedingly, as
it forms  the  fine  epidermis, the  nails,  proper horn, the tortoise-shell,
feathers, hairs, &c, is yet, throughout all their shapes, identical in chem-
ical character, and may  be described as the same substance.  The best
example of horn is that  which covers the process of the frontal bone in
the ox.   It varies in colour, is translucent, tough, and elastic.   When
heated beyond 212°,  it softens without being decomposed, and may then
be bent,  moulded, and soldered, on  which properties many of its uses
depend.   It is scarcely farther acted on by water even after  an ebulli-
tion of several days.   When  treated by strong  acids, horn is softened,
and becomes  soluble  in water.  Heated with solution of caustic  potash,
it evolves ammonia, dissolves, and the liquor contains sulphuret of potas-
> 10000. 
CELLULAR,  SEROUS,  AND MUSCULAR  TISSUES.  671
sium and an organic substance, precipitable by an  acid.   The composi-
tion of these products, or  of horn itself, has not been accurately exam-
ined.
   The principal mass of hair is composed of the same substance as horn,
but the colour is due  to  an oil, which may be extracted by ether.   If,
by virtue of the sulphur contained in hair, a solution  of litharge in lime-
water  blackens the  hair,  nitrate of silver  blackens the  hair also,  but
by the deposition  of the metal.   When horn or  hair is strongly heated,
it  fuses,  gives  off carbonate of  ammonia, and gases of a characteristic
disagreeable smell ;  if air be present, it burns  with a  brilliant  flame.
The perspiration  from the surface of the skin  varies in nature according
to the part of the  body; it is generally acid, contains traces of albumen,
fatty  matter, and the  salts  of the blood.   It  often  contains a  volatile
odorous  principle, characteristic of the animal by which it is secreted.
   Of the Cellular and  Serous Tissues.—These tissues are constituted of
gelatinous material, similar to that in the  skin, and hence dissolve  by
boiling in water, being converted into gelatine.   In the natural condition
of these  membranes their surfaces  are moistened by  a  watery  liquid,
which, accumulating in excessive quantity,  gives rise to  the dropsies of
the cavities or of the cellular tissue.   This  serum of the cavities is clear
and colourless.   It reacts alkaline ; its specific gravity 1*010 to 1*020;
its composition, though liable to fluctuate, is, in  general, as found  by
Berzelius,
Albumen.........1*66"
Substance soluble in alcohol .  .  3*32
Free soda........0*28
Alkaline chlorides.....609
Earthy phosphates.....009
Waterf.........987*56 J
.1000*00 nearly.
  In the serum of dropsical effusions I have found stearine, elaine, and
urea.  This observation has also been made by Marchand.
  The cells of the cellular tissue, in which fat is usually deposited, are
often filled  up  by an albuminous material, having considerable analogy
to caseiim.   It is thus  that the diffused hardening of the cellular tissue
and the local white tumours have their origin.   Tendons, aponeuroses,
and fibrous membranes are similar in their chemical relations to the cel-
lular and serous tissues.
  Of ihe Muscular Tissue.—From what has been already said of fibrine,
it is evidently the essential element of the muscular tissue, and it only re-
mains here to give the numerical results of two analyses of beef muscle,
made by Berzelius and Braconnot.  They found in 100 parts,
         Muscular fibre (with vessels and nerves)  .  15-80)   18.lg
         Cellular tissue giving gelatine.....1*90 5
         Soluble albumen and colouring matter  .  .  2*20 .   1/0
         Alcoholic extract with salts......1 *0 .   1*94
         Watery extract with salts......105 •   0-15
         Phosphate of lime.........J>'0° •   -•
         Water and loss......• •  •  ■  "lt  •  ' •Vd
  Composition  of the Brain.—The most exact analyses of the brain tnat
we possess  are those by Lassaigne.   The differently coloured  portiona
differ essentially in their nature, as he found in 100 parts, 
t>72          COMPOSITION  OF  THE  BONES.
                           Medullary
                           Substance.
Albumen........9*9
Colourless fat.......13*9
Red fat.........0 9
Ozmazome and organic salts  .   1*0
Phosphates.......1*3
Water.........  730
Cortical
Substance
  7-5^1
  10
  3*7
  14
  1*2
 85*2
M 00*00.
  The nerves or spinal marrow have not been specially analyzed.
   Composition of the Bones.—Miiller has found that, prior to ossification,
the cartilage of the bones is in that condition which yields chondrine, al-
though  it is afterward totally changed into  the  gelatine cartilage.  In
the vertebrated animals with osseous skeletons, the earthy material, in
all cases, consists  principally of phosphate of lime with some phosphate
of magnesia, carbonates of lime and soda, and fluoride  of calcium.  By
digesting a bone in dilute  muriatic acid, all of these inorganic salts are
removed, and the cartilage remains, preserving perfectly the form of the
bone.   By burning the bone in a moderate current of air, all animal mat-
ter may be consumed, and the earthy material then remains in the form
of the bone, and perfectly white ;  100 parts of burned bone of the follow-
ing animals  have been found to contain,
                         Human Bone.
Phosphate of lime and fluoride ) QC .
  of calcium.......\86i
Carbonate of lime.....10-3
Carbonate of magnesia  ...   0*3
Carbonate of soda.....30
Beef Bone.
90*70
 216
 110)
 5*74 <
 Lion.
950
 2*5
 2*5
Sheep.
800
19*3
 0*7
But these proportions vary in the bones of different individuals of the
same kind of animal.
  The quantity of animal matter  in the bones varies in different classes
of animals.  In  the  mammalia it  is  generally about  thirty-three per
cent.  Thus human and ox bones, deprived of their marrow and perios-
teum, and dried until they ceased to lose weight, gave Berzelius,
Human Bone.
 32* 17 >
  1*131
Cartilage soluble in water
Vessels.......
Phosphate of lime and fluoride ) co ca
  of calcium.......J53'04
Carbonate of lime.....11*30
Phosphate of magnesia  . .  .   1*16
Soda and a little common salt .   1*20
33 30

57-45
 3-85
 2-85
 3-45
10000.
  The teeth  present, in their constitution, the closest analogy to bohc
The principal and organized substance of the teeth is indeed true bone,
containing, however, less  cartilage (twenty-nine  per cent.)  and more
phosphate of lime (sixty-four per cent.) than  the other bones.  The
enamel, which is an inorganic secretion from the  upper surface of the
bony tooth, is almost destitute of any animal matter, the analyses of Ber-
zelius giving,
_.,   ,     „,,              Human Enamel. Beef Enamel.
Phosphate of lime and fluoride of ) QQ ,    Q, A
  calcium   .  .               > 88'5    85°
Carbonate of lime......    8*0
Phosphate of magnesia .  .    '    1*5
Soda  .  .  ........     «
Animal matter and water '.  '.  '.    2*0
7*1
3*0
1*4
3*5
M 00*00.
  The proportion of fluoride of calcium is greater in enamel than in com-
mon bone, and the animal membrane appears to belong only to the con-
nexion of the enamel with the subjacent bony tissue of the tooth.  The 
                BLOOD --C OAGIJLU M.--S ERU M.           673

 exterior crusta petrosa of the teeth, which exists most developed in her-
 biferous animals, has the same compositlbn as bone.
    In the invertebrate animals, the internal skeleton is replaced by an ex-
 ternal shell, which contains cartilage, with earthy salts, similar to those
 of proper bone, but in different proportions, the carbonate of lime prepon.
 derating.   Thus  the shells of crabs  and lobsters contain from fifty to
 sixty per cent, of carbonate, and but from  three to six of phosphate of
 lime, the rest being animal matter.  Oyster-shells contain but a trace of
 animal matter, being almost pure carbonate of lime; and the substance
 termed cuttle-fish bone has the same composition  nearly as crab-shells.
                             SECTION II.
  OF THE  COMPOSITION OF THE  BLOOD, AND THE PHENOMENA  OF RESPI-
                               RATION.
   Blood is, in the higher classes of animals, an opaque, thick, red  fluid;
 its specific gravity about  1*055 ; it has a salty and nauseous taste, and a
 peculiar smell, resembling that of the animal whence it had been derived.
   When  the blood of any red-blooded animal is allowed to rest, it grad.
 ually forms a soft jelly, from which, after some time, athin yellowish fluid
 (serum) separates, while  the red jelly or coagulum contracts in volume,
 and acquires greater consistence.  If this coagulation of the blood takes
 place slowly, the  upper portion of the coagulum becomes white or pale
 yellow, forming thus the  buffy coat.   There is no doubt  that the  blood,
 while in connexion with the animal, participates in its life, and the phe-
 nomena of coagulation are  to be referred to a new arrangement of its
 materials consequent on  the loss of that vitality.
   The serum of the blood, when coagulation has been perfect, is of a yel.
 lowish, sometimes greenish  colour ; its  taste is dull and  salty; its spe-
 cific gravity about 1*028; it is thick-fluid, like olive oil; when heated to
 140°, it coagulates.
   If we examine under  the microscope the appearance  presented  by
 blood, we find that it consists of a great number of minute red particles
 swimmino*in a nearly colourless liquor.   These red particles are flatten-
 ed  disks,  in  man  and the mammalia  round, in  other animals elliptical.
 Their size is variable, being in man from n'jjth to ?^\\\ of an inch in
 diameter, but larger in most other animals.   In the frog they are about
 T_i__th.   They consist of a central colourless nodule, and an investing
 rino*. which is coloured red  by  a material (Hcmatosine), which may  be
 dissolved out without the  constitution of the  globule being otherwise es-
 sentially altered.
  The blood contains a large quantity of albumen, partly dissolved, and
 remaining in the serum after coagulation, partly in a solid state, forming
 the great"mass of the globules.  In the  living body the blood contains
 also fibrine in solution, but this  separates soon after extraction from the
 body ; it assumes a solid  form, and investing, as a sponge, the red glob-
 ules, forms with them the coagulum.   The fibrine is thus the element
active in the coagulation  of the blood, the globules being but passively
eno-a^ed in it.  In addition to these essential organic elements, the  blood
contains a variety of salts, as common salt, phosphates of magnesia, am-
monia, and lime, lactates  of soda and  magnesia.   The best analyses  of
the  blood are those by Lecanu, and the results for blood and serum are,
that they contain, 
674
S E R O L I N E.--H EMATOSINE.
           Blood globules  .  .  ^ .  •  •
           Fibrine.........
           Albumen........
           Fatty substances.....
           Extractive matters.....
           Alkaline salts......
           Earthy salts.....•  .
           Water...........78-0*3
           Loss.........

  He found these proportions liable to fluctuation, and to vary according
to the sex.   The maxima and minima of each constituent which he found
for the human subject of each sex were,
Bio™! of Man.	Serum of Ma&
1330	
•21	
0*51	8-12
•37	•34
•30	■Hi
•81	•75
•21	09
78*0-3	9010
•2-1	14
10000	100-00
Constituents.	Male. Female.		
	Max.	Mm. I Max.	% j iii.
Water ....	805	732 '8484	7500
Albumen....	6-3	4-85[ 68	500
Globules ....	186	1105 16 71	714
Fibrine ....	•4	*20j 31	•20
   The fatty substance of the blood is a mixture of cholesterine with stearic
and oleic acids, and a peculiar fatty substance, termed Seroline, the history
of which is yet incomplete, and which differs from cholesterine most in
containing nitrogen.   None of the phosphuretted fats of the brain appear
to exist in  blood.
   The chemical history of fibrine and albumen having been already given,
it  remains only to describe the peculiar colouring mutter,  for the most
accurate knowledge  we  possess  concerning which we are indebted to
Lecanu's elaborate researches on the  blood.  His method  of preparing
hematosine is as follows :
   Blood, which has been freed from fibrine by beating with a twig, is to
be mixed, with continual agitation, with sulphuric acid diluted with its
own weight of water, until the  whole mass solidifies  to a brown pulp,
from which the acid  liquor is  to  be then drained off on  filtering paper,
and the last portions  removed  by washing with  alcohol.  The mass thus
obtained, which is  a mixture of sulphates of albumen and of hematosine,
is  to be boiled in successive portions of alcohol as long as  this becomes
brown.   The liquors, being filtered when cold, are to  be neutralized by
ammonia, by which albumen and much sulphate of ammonia are precip-
itated, while a compound of hematosine and  ammonia remains dissolved.
This solution is to be then  evaporated in a water-bath to dryness, and the
residue washed with water, alcohol, and ether, to remove  the salts and
fatty matters  which were contained in it.  Being then redissolved in al-
cohol by means of ammonia, evaporated to dryness, and washed  again
with water, the hematosine remains pure, but in its coagulated form.
   It is a dark brown mass, tasteless and inodorous ; when heated, it does
not melt, but  swells up and evolves ammoniacal products; it is insoluble
in water, alcohol, and ether; it forms with the mineral acids  compounds
which are insoluble in water, but  soluble in alcohol.  Bv  caustic alkalies
it is dissolved with a blood-red  colour, and these combinations are soluble
in water, alcohol, and ether.   Hematosine contains neither  phosphorus
nor sulphur,  but iron in large quantity (6-64 per cent.).   By Mulder's
analysis, the  formula of hematosine is C^H^ . 06Fe.   It hence has no
connexion  with proteine or albumen.  The state in which the iron exists 
HEMATOSINE,  GLOBULIN E,  ETC.          675
in hematosine has been, even  up to the present day, an object of much
discussion among chemists; but with the  knowledge we now  possess of
hematosine in its pure form, we must consider the iron  to be an integral
part of its organic constitution, as sulphur is in albumen, or arsenic in
alkarsine; and the opinion of its being oxidized, and combined with the
true organic element as a kind of salt, can no longer be supported.   If a
solution of hematosine be acted on  by chlorine gas, a white flocculent
precipitate is produced, and the solution contains chloride of iron.
  Although  hematosine is the colouring material of the globules of the
blood,  it is present but in very small  quantity ;  100 parts of dried glob-
ules containing but from four  to five  of pure hematosine.   In the blood
globule, the  hematosine is in its uncoagulated state, and possesses prop-
erties somewhat different from those  of its coagulated form, as prepared
by the process above given.   A solution  of  the coloured blood globules
in water, when exposed to the air, becomes of a brighter red colour, be-
ing thus partially arterialized.   When evaporated  at a temperature of
120°, it gives  a dark red mass, which is completely soluble in cold water.
Its solution coagulates at 155°, leaving the liquor clear yellow.  It is co-
agulated also  by alcohol and by acids.  The hematosine then passes into
the insoluble condition already described.
  I have hitherto  spoken of the colourless ingredient in the blood glob-
ules as being albumen, with which, indeed, it is almost identical in proper-
ties, but  still differs in some points.   It has been termed Globuline.   In
its uncoagulated condition it cannot be separated from hematosine, and
is there  distinguished  from albumen  principally by being insoluble even
in a very dilute saline solution, which dissolves albumen  readily.   It  is
hence  that the globules swim  unaltered in the serum of  the blood, but are
readily dissolved  by pure water.   On this principle is founded a method
of isolating the blood  globules.  If the blood, when extracted from the
vein, be received in a vessel containing a solution of Glauber's salt, coag-
ulation is prevented, as the fibrine remains dissolved, and by filtering the
liquor so obtained, the serum  and water pass  off, and the globules remain
mixed only  with a little of the salt.   The globuline cannot, however, be
separated from the hematosine except by acids, which, as  described in
the preparation of hematosine, then combine with the globuline.   Mulder
found  the organic element in  the sulphate of globuline  to have the com-
position of proteine (see p. 666).
   Alteration of the Blood in Disease.—The  examination of the state of
the blood in disease, although presenting  important relations to patholo-
gy  and to Dractice, has been hitherto conducted in  a manner too discon-
nected and  superficial to afford satisfactory results.   This branch of
chemical pathology has,  however, been taken up by the illustrious  An-
dral, who, in  conjunction with M. Gavaret, has published the results of
the analysis of the blood in 360 cases of disease, in a memoir, from whose
publication may be dated the commencement of a true  pathology of this
fluid.                                                     ,  ,
   In the method  which, by the advice of Dumas, they adopted, the quan-
tity of fibrine, of globules, of the solid materials of the serum (which may
be* considered as albumen), and the quantity of water in each specimen
of blood, were determined.  The pure hematosine was not isolated, and
the salts' were considered as sufficiently  important to  necessitate their
separation only in certain cases.  As a point of comparison, they assume 
 676  ALTERATION  OF  THE  BLOOD  IN  DISEASE.

 as the standard of healthy blood, that 1000 parts contain 790 of water,
 127 of globules, three of fibrine, and eighty of solid constituents of the
 serum, of which eight are inorganic ; which numbers almost coincide with
 Lecanu's analysis, as already  given.   Their researches have enabled
 them to recognise four  classes of diseases in which the  composition of
 the blood is essentially altered, though in different ways.
   The first class presents as a constant alteration an increase in ihe
 quantity of fibrine; it includes diseases  remarkably different in their lo-
 cality  and form,  but all  belonging  to the class of acute inflammations.
 In some cases of  morbid deposition, as in tubercle and cancer, a  similar
 increase in the quantity of.fibrine is found, but it may be doubted wheth-
 er it be due to the abnormal growth, or to the inflammatory action which
 accompanies it.
   In the second  class, the fibrine remains stationary, or even diminishes
 in quantity, while the globules increase in proportion to the fibrine.  The
 diseases which  belong  to this class  are continued fevers without  local
 inflammation, and  some form of cerebral haemorrhages.
   In the third class, the fibrine remaining unchanged, there is a remark-
 able diminution in the quantity of the  globules ; of these diseases chlorosis
 may be taken as  the  example ; and in  the fourth class, it is no longer
 the fibrine or globules which are the subject  of  the  morbid change, but
 the quantity of albumen in the serum is diminished.   Of this class of af-
 fections Brighi's disease  is the type.
   Without entering into the details  of these  researches, which are ex-
cluded by the limited extent of this work, I shall merely present in th'e
 following fable  an example of the constitution of blood  in each of these
 classes of morbid alteration.
Constituents.	Health.	1st Class.	2d Class.	3a Class.	4th Class.
Fibrine ....	3	7	2	3	3
Globules ....	127	125	136	47	82
Albumen . . .	72	78	69	75	58
Salts.....	8	7	7	8	7
Water ....	790	783	786	867	850
  The appearance of albumen in the urine in Bright's disease is evident-
ly connected with its diminution in the serum.  The oily materials which
are usually found in the blood, and the remarkable diminution which oc-
curs, not so much in the globules as in the hematosine, had not attracted
Andral's attention in the memoir now described.   These oily substances
are of the same nature as the proper fatty matters of the blood, but pres-
ent in excessive quantity.
  It has been observed that in  cholera the blood  becomes so thick as to
arrest the circulation, and contains  from thirty to forty-five per cent, of
solid matter ;  it is then, also, less strongly alkaline than healthy blood.
This is connected probably  with the  matters vomited and  evacuated,
which are strongly alkaline, and contain a quantity of albumen.
  The blood has been found occasionally, in cases of diabetes mellilus,
to contain  traces of sugar ; the great discordance of the results obtained
may perhaps result from the sugar being contained in the blood only for
a short time after meals, and then  being  rapidly evacuated by the kid-
neys.   In  jaundice the green colouring  matter of the  bile has been ob-
served in the serum of the blood.  Other observations of morbid constit-
uents of the blood are too  indefinite to justify me in  occupying space 
PHENOMENA  OF  RESPIRATION.         677
with them.   The  observation of Barruel, that, by heating the blood of
any animal with a little oil of vitriol, the odour of the animal is so pow-
erfully evolved as to be easily recognised, appears well founded, and may
be useful  in  medico-legal questions, where, however, it should be em-
ployed with exceeding circumspection.
   Of Respiration.—In the living body, the blood in the veins  and arter-
ies is well known to differ remarkably  in colour, in the former being of
a dark purple red, and in the latter of  a bright vermilion colour.  The
change from the venous to the arterial state is effected during the pas-
sage of the blood through the capillary vessels of the lungs, where it is
exposed to the action of an  extensive surface  of atmospheric air, while
the arterial  blood, in traversing the general capillary system of the body,
assumes the dark red condition in which it is returned to the  heart by
the veins.   Even out  of the body, this change of colour is produced
when venous blood is exposed to the air, especially if agitated therewith,
and  still  more  with  pure oxygen; even the  globules,  when  separated
from  the  serum and dissolved in water, become brighter in colour, and
partially  arterialized  by exposure to  the air.   Yet, although  the vital
properties of the blood depend essentially upon this change of colour, we
are not yet able to connect it with any alteration in the composition of
the constituents of the blood, or even in their  relative  proportions.   Ar-
terial and venous  blood contain  sensibly the same quantity  of water,
fibrine, globules, albumen, and salts ; and, by analysis, the composition of
these bodies is found to be identical, no matter what kind of  blood they
are derived  from.   To trace the difference of  nature between arterial
and venous blood, it is therefore necessary to  study it under other points
of view than its proximate or elementary composition, so far as we have
yet examined it.
   The air which has been  employed in respiration is found to have un-
 dergonc an important change of constitution;  its volume is but slightly,
 if at all, altered ;  but a quantity of oxygen has disappeared, and is re-
 placed by carbonic acid, in  generally an equal volume.  Air which has
 been  once  respired  is found to  contain from  three to four per cent, ot
 carbonic acid ; and if the same quantity of air  be continually breathed,
 the animal dies, with all symptoms of  narcotic poisoning, when the car-
 bonic acid has accumulated  to from eight to ten per cent.  The action of
 the air in expiration is therefore to remove carbon from the blood.  Ihe
 quantity  so  taken from the  system in twenty-four hours is  very large,
 and  makes  up the principal portion  of that  element which we take m
 with our food ; yet such is  the activity with  which its assimilation pro-
 ceeds, that no perceptible change in the solid  elements  of the blood can
 hp dptPCtGG*
   It was at  one time a much disputed point whether the  carbon so separ-
 ated  from  the  system was directly secreted from  the lungs,  and burned
 off  asTwcre, by contact with  the oxygen  of the air  or whether the
 oxiin was first absorbed by the blood, and carried by the circulation to
 ever°v portion  of the  body, where it  combined with the carbon which
 was there  present in excess, and the carbonic acid  so produced, being
 oMssolved by the venous blood, was thrown off, on arriving at the surface
 o the atmosphere, in the lungs.  The progress  of science has, however,
 «  ntSl. d in favour of the  latter view, to which the fullest  confirma-
 [lonhyasbeengi"enby the careful and elaborate experiments of Magnus. 
678
THEORY  OF  RESPIRATION.
He found that both arterial and venous blood hold dissolved quantities
of gases, oxygen, nitrogen, and carbonic acid, which amount to from one
tenth to one twentieth of the volume of the  blood.  The proportions of
these gases to each other are different  in arterial and  venous  blood; the
oxyaen  in arterial blood being about one half of the carbonic  acid, while
in the venous  blood it seldom amounts  to more than one fifth.   The dif-
ference  is greatest in young  animals, and  probably  is proportional  to
their activity  of nutrition.   The quantity of nitrogen appears to  be the
same in both  kinds of blood, making  from  one  fifth to one tenth  of the
gaseous mixture.
   The physico-chemical conditions of respiration are simply explicable
upon these  results.   By the principle of  gaseous diffusion (p. 267), the
fine lining  pulmonary membrane being  permeable to gases when the
venous  blood  arrives at the surface of the  lungs, a portion of the  car-
bonic acid which it contains is evolved, and  a quantity of oxygen gas ab-
sorbed in place of it.  These two quantities are  not necessarily equal  at
each moment, though ultimately they  become so, and hence  the volume
of oxygen absorbed is generally, though not universally, equal to that  of
the  carbonic  acid given out.   There  appears, from  the presence of ni-
trogen in equal quantity in both kinds  of  blood, to be an  absorption and
evolution of that gas, simply from physical laws, and independent of any
direct application of it to the nutrition  of the animal; hence  the volume
of nitrogen in air is sometimes increased,  and at others diminished,  by
respiration, and an animal evolves much nitrogen when respiring an ar-
tificial  atmosphere  of oxygen  and  hydrogen, while Bousingault has
shown the rate of nutrition of an animal to  be proportional to the quan-
tity of  nitrogen  it receives as food, and that none of that principle is
 really assimilated from the air.
   It is  still not by any means easy to decide  upon the cause of the change
 of colour which occurs in the blood during respiration; for this should
 appear connected, not merely with the presence of certain gases in  the
 blood, but upon a true change in the constitution of the hematosine, which
 analysis cannot direct.  Stevens first directed attention  to the  remarka-
 ble influence  which saline bodies have upon the colour of the blood.   If
 dark venous  blood be  put  in contact with a solution  of common salt,
 Glauber's  salt, nitre, or carbonate of  soda, it becomes  as vermilion-col-
 oured as if it had been truly arterialized.   On the contrary, the presence
 of carbonic acid impedes this action, and gives to blood, so reddened by
 a salt not in excess, the dark tint of venous blood.  If we consider, there-
 fore, the arterial tint to be due to the  natural combination of the colour.
 ing matter with the saline constituents of the serum, this will be  darken-
 ed when, by  passing through  the capillary system, the blood takes up an
 excess of carbonic acid ; and again, in the  lungs, when the carbonic acid
 is replaced by oxygen, the vermilion colour is restored, not by  any active
 agency of  the oxygen, but by the natural  tint  of saline hematosine be-
 coming evident.  Although this theory of  the change of colour  is  by no
 means free from objections, it appears to  me to be  better founded than
  any other that has been proposed.
    Animal Heat.—The phenomena of respiration consisting  mainly in
  the conversion of carbon into carbonic  acid by union  with oxygen, the
  heat which is developed in the  body of all  red-blooded  animals has been
  naturally referred  to  that source ;  and as  we know  that the change 
MUCUS.--GASTRIC  JUICE.
679
from  the arterial to the venous condition of the  blood  occurs at every
point  of the system, the almost complete equality of temperature through-
out the  body  in health is explained.   That  the great source  of heat
is  the respiratory process, is abundantly proved by the temperature be-
ing highest in  those  animals, and  in  the same animal at those  periods
when the circulation is most rapid, and the  quantity of air consumed the
greatest; but it has been calculated that the heat evolved  by the combus-
tion of the quantity of carbon thrown off from the  body in twenty-four
hours is  not more than eight tenths of the quantity generated in the body
during that time, and the  origin of the remainder must be found in the
action of the muscles and in the nervous power,  which appears of itself
to be a distinct source of animal  heat.

                            SECTION III.
  COMPOSITION  OF THE DIGESTIVE  ORGANS AND OF THEIR SECRETIONS.
                 CHEMICAL PHENOMENA OF DIGESTION.
   Mucus.—The lining membrane of the alimentary canal is moistened
with a liquid possessing many characters of the vegetable mucus (traga-
canthine, p. 530), but  containing  nitrogen.  It  is a thick  tenacious sub-
stance, which contains, dissolved in the water through which it  is diffused,
the ordinary salts of the serum of the blood ; it swells up with water to
a considerable  mass, but  without dissolving ; it dissolves in  alkaline li-
quors, and is precipitated  therefrom  on the addition of an acid  and  by
tincture of galls ; the  mucus from different parts of the mucous membrane
is, however, by no means identical in properties.
   The liquid secreted by the internal surface of the stomach, the  Gastric
Juice, which exercises an important influence on digestion, differs essen-
tially in  its characters from mucus.   When the stomach is empty and
contracted, it contains only ordinary mucus ; but if even indigestible sub-
stances be introduced, and still more after taking proper food, a liquid is
abundantly poured out, which is colourless or very pale yellow, and con-
tains a very small quantity of solid matter (two per cent.), which consists
principally of  inorganic salts (common salt and  sal ammoniac, with a
trace of  a salt of iron) ; it is specially characterized by the presence of a
notable quantity of free muriatic  acid, the proportions of which appear to
vary  with  the activity of the digestive powers at the time.  This gastric
juice  possesses the  remarkable property of softening down and dissolving
fibrine and albumen,  and  thus converts the  masses of food into the uni-
form  pulp  (Chyme), from which the absorbing vessels of the small intes.
tines  take  up the nutritious elements.
   If we  form an artificial  gastric juice by mixing together the muriatic
acid and salts  in the  proper proportions, it  is found  to be totally  incapa.
ble of dissolving the  materials of the food,  and, indeed, to be  quite inac
tive towards digestion.   The organic material of the gastric juice,  al-
though its  quantity  be so  minute, is therefere essential to  its powers, and
these may be  perfectly conferred upon  the previously  inactive artificial
juice  by the addition of a little of the mucus of the stomach, or by steeping
in the acid liquor, for  a short time, a small portion of a mucous membrane,
and filterinf** the liquor.   For this purpose it is not even necessary to use
the mucous membrane of the stomach, for that of the bladder has been found
to act equally well.   The substance which is dissolved out of the membrane
in these  cases  has been termed Pepsine.   It has not been obtained in a 
680
PEPSINE,  SALIVA, ETC.
truly isolated or pure form, but its properties are very remarkable.  For
its full activity it requires the presence of a free acid, as the artificial gas-
tric juice becomes much less active in dissolving food, when neutralized by
an alkali, though it retains other properties, as that of coagulating milk like
rennet.  If the artificial gastric juice be precipitated by acetate of lead,
the precipitate washed, and then decomposed  by sulphuret of hydrogen,
the solution thus obtained possesses all the digestive powers of the juice.
Hence the pepsine and muriatic acid act together in combining with oxide
of lead.   The process given by Schwann for preparing the best artificial
gastric juice, is  to mix water with 2| per cent, of muriatic acid, of spe-
cific gravity 1*13, and digest therein the mucous membrane of a stomach
for twenty-four hours, then to filter.
  Pepsine appears to be completely decomposed by contact with alcohol,
or by the  heat of boiling water.  Its  powers  are destroyed, also, by de-
oxidizing  substances.   The solution  of albumen  and fibrine in gastric
juice is essentially different from their solution in muriatic acid, as  in the
former case the  quantity of acid is very minute in relation to the quantity
of material dissolved, and after solution the acid still remains  quite un-
combined.
  Fremy  has discovered that the peculiar fermentative  process, which
sometimes spoils the manufacture of sugar, and which I have described
(p. 536) as the mucous fermentation, is capable of being induced by con-
tact  with mucous membrane (by pepsine ?).   He has found that sugar of
milk may thus be converted to an unlimited extent into lactic acid, no
other product appearing.   The vegetable ferments are able  to produce
the same  effect, but  in a different stage of decomposition from that in
which  they induce the saccharine or alcoholic fermentations.
  The action of the stomach in digestion appears, therefore, to be, so far
as our actual knowledge extends, a purely catalytic fermentative action j
one in which the active excitant is an  organic  substance (Pepsine) secre-
ted  by the mucous surface, and whose  properties are developed  by the
presence of muriatic acid, which is secreted at the same time.   The new
products into which the food, fibrine, albumen, gluten, starch, oils, sugar,
&c, are converted, and  which collectively constitute the white uniform
pulp termed by physiologists Chyme, have  not been made the subject of
accurate chemical research.
  In the  mouth the mass of nutritive  material is acted on  by a  liquid
which  is secreted by the salivary glands, the Saliva.   It is alkaline, and
holds in solution not one per cent, of solid matter, which contains  some
carbonate of soda and common salt, admixed mucus, a trace of sulphocy-
anide of potassium, and a peculiar organic body termed  by Tiedemann
and  3melin Salivary Matter.  This last substance is soluble in water;
its solution is not coagulated by heat, nor precipitated by tincture of galls,
corrosive  sublimate, acetate of lead, nor by  acids.  The pancreas, though
so similar  in structure to the salivary glands, has a different secretion ;
it contains no salivary matter, nor any sulphocyanide of potassium, but
albumen and some salts; it is generally slightly acid.
   Composition of the  Bile.—The precise part  which this remarkable se-
cretion performs in the animal  economy is not yet fully known.  It
has  been  the subject of repeated and  accurate chemical examination,
although,  from the facility with which its elements are transformed into
other bodies, by the action of  the  reagents employed, every succeeding 
ANALYSES OF  THE  BILE.
681
analysis has led to different results.   I shall only notice the late researches
of Ginclin, Demarcay, and Berzelius.
   In the elaborate work on digestion, undertaken in  conjunction with
Tiedemann, Gnielin analyzed principally  the bile of the ox, from which,
however, as far as observations have been made,  human bile does  not
appear essentially to differ.  He obtained from it a volatile body having
the odour of musk, cholesterine, margaric and oleic acids, a peculiar acid,
the Cholic  Acid; colouring matters, Biliary Resin, Biliary Sugar, Tau-
rine, a glutinous substance,  caseiim, salivary matter, ozmazome, and a
number of salts of organic and inorganic  acids.  Demarcay looks upon
all of these substances as being produced by the reactions used, and  de-
nies that any of them really  exist in the bile.  He considers the bile to
be a soda-soap of a peculiar fatty acid, the Choleic Acid, that is, a Cho.
leate of Soda.  The choleic  acid is obtained by dissolving one part of the
alcoholic extract of ox-gall in 100 parts of water, and mixing the solution
with two parts of sulphuric acid diluted with ten of water.   By gradual
evaporation of the liquor, oily drops separate.  It is to  be then cooled,
and these drops,  which are common fat, removed.   On then standing for
eight or ten hours, the choleic acid gradually separates, and, being digest.
ed with ether to  remove some adhering fat, is pure.  It is a brittle yel-
low-white  mass,  tastes bitter, softens by a heat  of 250°,  but does  not
really  melt; it is slightly soluble in  water, but abundantly in alcohol and
ether.   It forms, with bases, salts which  do not crystallize;  its formula
was found to be 042^ . N.O,2.
   When the alcoholic extract of the gall  is boiled for a  longtime in con-
tact with an excess of muriatic acid, the choleic acid is  decomposed, and
the most remarkable products are the Taurine of Gmelin, and a new acid,
the Choloidic Acid.  The latter is a fatty acid, not volatile, yellow, of a
bitter taste ; it forms a soft mass with warm water, but without dissolving ;
it dissolves readily in alcohol  and ether, and these solutions redden lit-
mus.  By Dumas's analysis the formula of this body appears to be C^
H3107.   It does  not contain  nitrogen.  The  Taurine, which remains in
the acid liquor from which  the  choloidic acid separates, is obtained  by
evaporation, and mixing with alcohol, from which solution it crystallizes
gradually  in six-sided prisms, which are  perfectly neutral; it fuses and is
decomposed by a strong heat; it dissolves  in twelve and a  half parts of
cold, and in less  of boiling water, but requires  573 parts of spirit of wine
for solution; it is scarcely acted on even by the strongest acids, and ia
not precipitated  by any metallic salt;  its  formula is remarkable, being
C H7. N.O,o, including the elements of binoxalate of ammonia and 2 Aq.
   It' the bile be treated with an excess of a strong alkali, the choleic acid
is totally broken up into ammonia  and the Cholic Acid of Gmelin.   It
crystallizes from its hot aqueous solution in delicate silky needles, of a
brilliant white colour;  its taste is at once  acid and sweet;  by heat it is
melted and decomposed ; it is very slightly soluble in water, but copious.
ly in alcohol;  its solutions redden litmus ; it contains no azote ;  its  for-
mula being, as determined by Dumas, C^H^O,,,.
   Uemarcay's examination  of the bile appears thus quite satisfactory in
show-in*-- that the cholic acid and the taurine are secondary products, and
he considered the other substances found  by Gmelin to be choleic or cho-
loidic acids in an impure form.   But Berzelius, who has been occupied in
the reexamination  of the subject,  has decided that the choleic acid of
                                4 R 
682      COLOURING  MATTER  OF  THE  BILE.

Demarcay is really the body which is impure, being a mixture of the true
biliary substance (Bilin, Gmelin's Biliary Sugar) with  the biliary resins.
He found that when  the alcoholic extract of the bile is mixed  with sul-
phuric acid, no precipitate appears for a considerable time, showing that
the substance, which really exists in the bile combined  with soda, is com-
pletely soluble in water, and it is only by  its gradual change that the pre-
cipitate (choleic acid) occurs.   By digesting this substance  with  ether,
he removed  from it a resin, which, by possessing acid properties, and  by
means of combination with barytes, is shown to  be a mixture of two dis-
tinct acid resins, Fellic Acid and Cholinic  Acid.  The material  insolu-
ble in ether  is the true Bilin; it is  not acid, of  a bitter taste, soluble in
alcohol and  water in all proportions, but  insoluble in ether;  when  heat-
ed, it becomes soft, and burns like a resin ; its watery solution is rapidly
decomposed, especially if warmed ; by contact  with acids or alkalies, it
is  immediately changed in constitution : the substances produced are dif-
ferent, according as  the degree  of alteration is  more or less advanced.
Those more important are the following  :
   The Biliary Matter, which is the  state  in which the greater part of the
bilin exists in ordinary hjle, being the first product of its decomposition,
is  a white, bitter substance, which has a marked acid reaction, and is de-
composed by oxide of lead into  bilin and Bilifellmic Acid, which  is the
choleic acid of Demarcay.   The formation of taurine is accompanied by
that of another body, Dyslysin, which is a colourless resinous substance,
very  sparingly soluble in water.   The  fellinic and cholinic acid  have
been noticed above.
   When  the bile has been  kept, for a long time, it is  decomposed by a
kind of fermentation, and  two  acids formed, termed  the Fellanic and
Cholanic Acids:  they are white  earthy powders sparingly soluble in wa-
ter ; the former melts only far above 212°; the latter is very  easily  fu-
Bible.
   The Colouring Matter of the Bile is present during health in  but  small
quantity,  but in disease it sometimes accumulates so as to produce solid
masses.   When pure, it is a reddish-yellow powder,  which is scarcely
soluble in water or in alcohol, but dissolves easily in solution of caustic
potash.   This solution is of a clear yellow colour, but when exposed to
the air it becomes deep  green,  absorbing  oxygen.  This change is  re-
markably produced by nitric acid, and it is indeed the  reaction  by which
the presence of the bile in the serum of the blood, in the urine, in the skin
and eyes, &c, may  be shown in cases of jaundice.  If too much nitric
acid be not  added at once, the yellow liquor becomes at first green, then
blue, violet,  and finally red, all these changes occurring in a few seconds.
After a moment the  red colour also disappears, the solution becomes yel-
low, and the colouring matter is found to  be totally decomposed.   The
solution of the colouring matter  in potash is precipitated by muriatic acid
in  deep  green  flocculi, which dissolve in  nitric  acid with the  effect al-
ready noticed, and are soluble  in caustic  ammonia and  potash,  with  a
rich emerald-green colour.   These reactions show that, by a  process of
oxidizement from the original yellow substance, green and red materials
may be generated, in which forms  the colouring matter exists naturally
in various animals, according as their bile is yellow, green, or reddish,
and also gives rise to the concretions of  various kinds that are deposited
in disease.   The most common kind of gallstone consists, however, of
cholesterine. 
NATURE  OF  CHYLE AND  LYMPH.         683
  This  yellow material Berzelius names Bilifulvin.   He considers the
green colouring matter present in healthy bile to be identical with chlo-
rophyll (p. 621).
  The bile contains generally about nine percent, of solid matter ; but in
the present state of our knowledge of its constituents,  it is evidently im-
possible to assign the numerical proportions in which they exist.
  The substance found in the bile, and termed Erythrogen  by  Bizio, is
too apocryphal to require any notice.
  The examination of the farther processes of digestion involves consid-
erations too purely  physiological to be entered into.
  Chyle and Lymph.—The nutritive materials extracted from  the food
by the absorbing vessels of the intestine is thrown into the thoracic duct,
where it meets with another fluid, which is transmitted to the same vessel
from all parts of the  body by the colourless veins or lymphatics.  'Ihe
fluid from the intestines is termed Chyle, that from the  body  generally is
termed Lymph.   It is the mixture of these that alone has been examined,
for the vessels which carry either separately  are too minute to  allow of
the extraction of their contents in a pure form.
   When taken  from  the  thoracic duct a few hours after a meal, when,
probably, the chylous element prevails, it is a whitish, opaque liquid like
milk, with generally a reddish shade ;  a short time after separation from
the body it coagulates ; the clot is at first  pale, but it soon becomes light
cinnabar red ;  the milkiness of the serum is due to the presence of oil; it
contains albumen, and coagulates by heat.   Except that it is  more dilute,
and that the hematosine is for the most part absent (not yet formed), the
chyle and lymph have the same composition as the blood.  It appears to
vary, however,  with the nature of the food, as Dr. Prout found the chyle
of dogs fed  on  vegetables to contain a much smaller quantity of  albumen
than when they had had animal food.   Dr. Prout also indicates in chyle the
existence of a substance which he terms Incipient Albumen, which is not
coatrulated  by heat, except after the addition  of acetic acid.   The prop-
erties of this form of albumen, however, are not fully  known.   The re-
suits  of  their analyses of chyle are  here given ;  that  by Berzelius was
the chyle of a horse,  killed some time after having fed abundantly with
oats ; and of those by Dr. Prout, No. 1 was from  a dog supported on
vegetable, and No. 2  of a dog supported on animal food.  100 parts con-
tained,
        Berzelius.
Dry Clot  ....  078
Albumen  ....  449
Fatty matters   .  .  1*67
Extractive matters )  j.4i
  and salts  .   .  )
Water.....9162
      Prout.         No.1.    No. 2.
Fibrine.....0-6     08
Incipient Albumen .   46     4*7
Albumen  ....   0*1     4*6
Oil and Sugar   .  . trace    trace
Salts......0 8     0*7
Water.....93 6    892
                            SECTION IV.
       CONSTITUTION OF THE URINE IN HEALTH AND IN DISEASE.
  The nature of this secretion has at all periods been an object of con-
siderable interest to the physician and to the chemist, from the indica-
tions which changes in its composition give of disease of important or-
gans and from the number and interest of the organic substances it con.
tains'  As in almost all other branches of animal chemistry, Berzelius
first determined accurately its constitution, and lately Lecanu has ascer- 
684        COMPOSITION OF  URINE.--UREA.
10000
tained with great care the limits to which the proportions of its ingredi-
ents may vary in health, and thus established a correct basis of compar
ison for urine in the various conditions of disease.
  The specific gravity of urine varies from  1016 to 1030.   In general,
if the  excretion exceeds in quantity  thirty-two  ounces  in twenty-four
hours, the specific  gravity falls proportionally below 1030; but if the
quantity be under thirty-two ounces, the specific gravity for a man in ac
tive health is generally 1030, but less for women.   The important organ-
ic constituents of the urine are Urea and Uric Acid, which will require
a detailed and special  examination;  the other principles, though numer-
ous, beino* of less moment, need be  only noticed in the  following state-
ment of Berzelius's general analysis of the urine.   He  found 100 parts
to contain,
          Water.............933 00^
          Urea..............3010
          Free lactic acid, lactate of ammonia, and >   \n-i4
           animal extract.........J
          Uric acid............100
          Mucus of the  bladder........0*32
          Sulphates of potash and soda.....6*87
          Phosphates of soda and ammonia ....   4*59
          Common salt...........4*45
          Sal ammoniac...........1*50
          Phosphates of lime and magnesia .   ...   100
          Silica..............003 J
             rjrea._N2C2 . 02H4 or Ur.   Eq. 60 or 750.
  The artificial formation of this  remarkable substance in various ways,
has been noticed  already in  many places (as 511, 515).  It may be ob-
tained  from urine by evaporation to  the consistence of a thick sirup in a
water-bath, and mixing the mass remaining  with three times its volume
of nitric acid, specific gravity about  1*25, which had been perfectly freed
from all traces of nitrous acid which it might contain, as this last instant-
ly decomposes urea.   The liquor forms a  crystalline pulp, which, being
kept carefully cool, may be freed from the  liquor by draining and press-
ure between  folds of paper.  The impure crystallized nitrate of urea thus
obtained is to be  dissolved in  a small  quantity of boiling water, and re-
crystallized by cooling.  These crystals being again dissolved in water,
are to be digested with animal charcoal to remove the colouring matter,
and  then with an excess of carbonate of  lead, until completely neutral.
The solution so obtained, being evaporated very carefully in a water-bath
to dryness, is to be treated with boiling alcohol, and filtered.   The  pure
urea separates from the alcoholic solution, on cooling, in brilliant white
four-sided prisms.
  Urea is much more simply and economically obtained by the transform-
ation of cyanate of ammonia, for which purpose  the process  given by
Liebig answers best.
  An  impure cyanate  of potash is prepared by roasting  yellow  prussiate
of potash (as described p. 515), and this is mixed with a solution of sul-
phate  of ammonia in water, and the whole then boiled with alcohol, which
dissolves  out urea, and leaves the sulphate  of potash undissolved.   On
cooling, the  urea crystallizes, and may be obtained  quite pure by anoth-
er crystallization from alcohol.
  The taste  of urea is fresh like nitre; its reaction is quite  neutral ; it
is inodorous.  When  healed to 220°,  it melts, and at a  higher tempera- 
SALTS  OF UREA.--URIC  ACID.          685
ture is decomposed, giving carbonic and cyanuric acids and ammonia.
It dissolves in less than its own weight of water at 60°, producing great
cold ; it is soluble in much less boiling water.  If the urea be quite pure,
its solution remains for a long time unaltered ;  but if it contains any tra-
ces of an azotized substance which putrefies, this acts as a ferment, and
the decomposition extending to the urea, this assimilates the elements of
water, and is totally converted into carbonate of ammonia, N C2 . 02H4
and  H404  producing  2(C.O +N.H4O.).   It is this  decomposition  that
renders urine alkaline  in a few hours, generally, after it is voided.  Urea
dissolves in five parts  of cold and one of boiling alcohol.  In ether  it  is
almost insoluble.
   In  contact with strong acids, urea is decomposed,  giving off carbonic
acid, and forming an ammoniacal salt.   When the acids are dilute, it unites
with  them, although  without neutralizing  them, and forms crystalline
compounds, of which  but a few have  been accurately examined.   The
oxygen salts of urea resemble  those of the vegetable  alkalies, melamine,
ammonia, &c, in containing an atom of associated water.
   Nitrate of Urea (Ur.H.O. -f-N.05) crystallizes in large brilliant plates
by the cooling of its solution.   It is pleasantly acid, and is soluble in al-
cohol, but much more so in water; if heated rapidly, it explodes.   It  is
sparingly soluble in dilute  nitric acid,  whence the addition of a great ex-
cess of nitric acid serves as a test for the presence of urea, this salt be-
ing precipitated in bright pearly scales.
   Oxalate of  Urea (Ur.H.O.-fC203) crystallizes in  long rhomboidal
tables.  It tastes acid ;  it is copiously soluble in boiling water, but crys-
tallizes almost completely out on cooling, as 100 of water retain but 4 of
the salt.   It is still less soluble in alcohol.
   Lactate of Urea crystallizes in fine  plates and needles; it  is very solu.
 ble.   There  is reason  to consider that the urea is naturally combined
 with lactic acid in the urine.   The other salts of urea are not important.
   The quantity of urea secreted in health  appears pretty regular in the
 same individual, when the diet remains the same, and not to  depend  upon
 the  quantity of liquor excreted.  It varies, however,  very much in differ-
 ent  individuals, and is much more abundant in men in active age than in
 women or in old  men.  Thus Lecanu found the quantity of urea secreted
 in twenty-four hours, by men in the  prime of age, to  vary  from 350 to
 500  grains; in women it varies from  150 to 430 grains; while with
 old  men the limits were 80 and 180 grains.  In children the quantity is
 still smaller, and infants secrete scarcely a trace of urea.

                Uric Acid, and the Bodies derived from it.

   The uric acid exists in the  urine of all carnivorous animals.  In birds,
 reptiles, and many insects, it is voided with the excrements, and the urine
 is in such a state of concentration as to form a white mass, nearly solid,
 which consists almost totally of urate of ammonia.  In the  small islands
 of the South Sea, which are inhabited by great flocks of aquatic birds, it
 accumulates  in such quantity as to  be an article of commerce  being
 brought to South America, and even to Europe, under the name of guano,
 and used  as manure.   In many diseases it is generated  by the system in
 abnormal quantity, and constitutes, free or combined with bases, the gouty
 and arthritic concretions, and many forms of vesical calculus
   For  he purposes of the chemist, the uric acid  is  most easily obtained 
686      URIC  A C I D.--A L L A N T O I N.--A L L O X A N.

from the white solid excrements of the larger serpents  in the menageries.
This is to be boiled in a solution of caustic potash, and the filtered liquor
decomposed by the addition of muriatic acid  in excess.  The precipitate
should be boiled in water for some  time, then well washed and dried.   It
crystallizes in  minute brilliant white scales, which are very slightly solu-
ble in boiling water ; the solution reddens  litmus ;  it is tasteless ;  it dis-
solves  in oil of vitriol, forming a crystallizable compound, which  is de-
composed on the addition of water: the action  of nitric acid is different.
When  heated,  it is decomposed,  giving a great variety of products, urea,
hydrocyanic and cyanuric acids, carbonate of ammonia, &c.  Its formu-
la is N4CI0 . HA; its salts are  not well characterized ;  those of the al-
kalies are very sparingly soluble, and are decomposed  by all acids except
the carbonic acid.   The Urate of Ammonia  is the material of the white
excrement (dry urine) of birds and  serpents.   The Urate of Soda is the
principal material of gouty deposites.  The  uric acid is  specially inter-
estino*  for the number of important  bodies to which it gives origin  by the
action  of reagents, and of which some are  also products of the organiza-
tion ; for our accurate knowledge of these we are indebted  to the recent
investigations of Liebig  and Wohler.
   Allanto'in.—This substance exists in the waters of the  allantois  of the
cow, beino* contained in  the urine of the foetus, from which it may be ex-
tracted by evaporation and crystallization.  It is, however, much more
easily  formed from uric acid.   Freshly-prepared peroxide of lead is to be
added  to uric acid, diffused through  twenty parts of boiling water as long
as its colour is destroyed.  The boiling liquor is to be filtered, evapora-
ted till  crystals begin to form, and  then allowed to cool.   The allanto'in
crystallizes, and  the  mother liquor  contains abundance of urea.   At the
same time, oxalate of the protoxide of lead is  produced,  2(N4C,0. H406)
and 5H.O. with  4Pb.02, producing 4(C203+Pb.O.) ;  with  urea, 2(N2
C2 . H402), and allantoi'n, N4C8 . H505.   On this reaction Liebig founds
a theory of the constitution of uric acid, to  which I shall have occasion
again  to recur.   He considers it to contain urea ready formed, and a hy-
pothetic substance, for which he proposes the names of Uril, or Cyanox-
alic Acid, it being oxalic acid in which oxygen is replaced  by cyanogen,
CA+Cy.   Thus uric acid, N4C10 . H406=N2C2 . H402+2(C202Cy.).
In forming allantoin on this view,  the urea is set  free, and the cyanox-
alic acid, with oxygen and water, gives oxalic acid and allantoin.
   Allantoin forms rhombic prisms, which  contain an  atom of water.   It
is sparingly soluble in water, and perfectly neutral.  By boiling with a
strong alkali, it combines with the elements  of water, giving oxalic acid
and ammonia.  It does not form a definite compound with any base but
oxide  of silver.
   Alloxan.—The products of the  action of nitric acid  on uric acid present consider-
able interest, from their number  and connexion.  On adding one part of uric acid
gradually to four parts of strong nitric acid, it is dissolved with much heat, and co-
pious disengagement of carbonic  acid and nitrogen.  The rise of temperature being
prevented as much as possible, the liquor solidifies on cooling to a mass of granular
crystals, which are to be drained, and then recrystallized from the smallest possible
quantity of boiling  water.   This is Alloxan; its crystals  are short right rhombic
prisms, brilliant and colourless.   In dry air they effloresce, losing 6 Aq.; at a higher
temperature it crystallizes in oblique rhombic prisms which are anhydrous, and have
the formula N2Cs . H4O10;  its solution in water  reddens litmus, and stains the skin
purple; when neutralized by an alkali, it strikes an indigo-blue colour with a proto-
salt of iron; it is decomposed by almost all reagents, producing a series of bodies
 that will be  successively examined; its origin consists, probably, in the uryl being 
ALLOXANIC  AND  MYCOMELINIC  ACIDS,  ETC.  687
oxidized by oxygen from the nitric acid, leaving hyponitrous acid, which, reacting
on the urea, gives the mixture of the carbonic acid and nitrogen gases.  The allox-
an may thus be considered as a hydrated deutoxide ot'uryl.
  Alliuanic Acid is tbrmed  by acting on alloxan with strong alkalies or by barytes-
wIh.-u separated  from its combinations by a stronger acid, it crystallizes in colour-
less needles, which have a strong acid reaction; its alkaline salts are soluble; those
with the earths and  heavy metallic oxides sparingly soluble; it is insoluble in wa-
ter ;  its formula is N2C3. II2O8 when dry, the  alloxan having lost the elements of
two atoms of water.   When a solution of alloxanate of barytes is boiled, or when a
solution of alloxan is gradually added to a boiling solution of sugar of lead,  another
acid is formed, M'so.culic Acid, which in the latter case precipitates an insoluble salt
of lead, and the liquor contains urea; the alloxan breaking up into N2C2. H4O2 and
2C3U4,  which  is the constitution of the mesoxalic acid, which has probably, there-
fore, an isomeric oxide of carbon (C3O3) for its base, and belongs to the same group
as the mellitic and rhodizonic acids (p. 49G).   By oxidizing agents, the inesoxalic
acid is converted into  carbonic acid;  thus, with a solution of nitrate of silver, it
gives a clear yellow precipitate,  which, when boiled, is converted into carbonic
acid and metallic silver.
   Mycomelinic Acid.— If a solution  of alloxan in water of ammonia be heated, a
brownish-yellow precipitate falls, which is mycomelinate of ammonia, by boiling
which, or by washing with dilute sulphuric acid, the ammonia is removed,  and the
mycomelinic  acid remains as a yellow jelly, which dries to a coarse yellow powder.
It is sparingly soluble  in water; its salts are gelatinous, sparingly  soluble flocks;
the formula of the acid is N4C8. H5O5, being isomeric with anhydrous allantoin.
   Para/janic Acid.—If alloxan be  heated with  an excess of nitric acid, it dissolves,
nitrogen gas  is  evolved, and, on cooling, the new  acid separates; it is also easily
procured from uric acid by using an excess of nitric acid; it forms colourless, trans-
parent, six-sided prisms, and tastes like oxalic acid,   ft is partly volatilized and
partly decomposed by heat.  If the crystals he heated to 212J, they assume a reddish
colour; the formula of the crystallized acid is  N_>< 'g04+2 Aq.;  hence  alloxan with
20.  produces 2C.O2, with 4H.O.  and N2C604.   By contact with bases, this acid is
decomposed,  producing the Oxnturic Acid.  This is best prepared  by dissolving pa-
rabanic acid in caustic ammonia,  boiling, and  then letting the liquor cool;  it Ibrms
a mass of small brilliant white crystals of oxalurate of ammonia.  The oxaluric
acid is also a product of other reactions on uric acid, some of which  will be  special-
ly noticed hereafter. It is a strong acid, and is obtained  free by dissolving its am-
monia  salt in boiling water, adding an excess of dilute muriatic acid, and rapidly
cooling, when the oxaluric acid separates as a white or slightly yellow powder;  if
long boiled in water, it is decomposed into oxalic acid and oxalate  of urea, of which
it contains the elements, its formula being N2C6 . H30---*-Aq.
   Taiomiric Aral.—If sulphurous acid gas be passed  through a saturated solution
of alloxan until the  liquor begins to smell strongly of the gas, and  then ammonia be
added  in excess,  after some time brilliant white  rhombic tables form, which are
thionurate  of ammonia.   By recrystallization, this salt generally becomes  pale
rose-red, but  is not altered in constitution.   To obtain the acid free, a solution of
this ammonia salt is to be precipitated by acetate of lead,  and the thionurate of lead
decomposed bv sulphuretted hydrogen.  By evaporation  of the liquor, the  acid re-
mains  as  a white semicrystaliine mass; it is easily soluble in water, reddens lit-
mus strongly; its formula  is N3Cs. H7O14S2:  it contains thus the elements of one
atom of alloxan, one of ammonia, and two of  sulphurous acid; it is a bibasic acid.
If a stron0* solution of thionuric acid be boiled, it becomes turbid, and soon solidifies
to a mass°of brilliant silky crystals, while the liquor contains much sulphuric acid;
the' crvstalline  substance  being drained  and washed with cold water, in which it
scarcely dissolves, is termed Uramil;  it is white, soluble  in dilute alkaline  liquors,
and precipitated therefrom unchanged by the addition of an acid, but by strong al-
kalies  it is decomposed, ammonia being evolved, and urainilic acid formed.   The
formula of uramil is NsCs •  Hs06; the thionuric acid might be considered as bisul-
phate of uramil.  The Uramilic Aid is formed by the action of acids and  alkalies
on'uramil • it crystallizes in colourless needles, which dissolve in acids and alkalies,
formin°* with the latter well-defined salts; its formula is N,( :,6. H,0Ol5.
   ■1 'hvantin" — This substance is  formed as a product ot  the moderate oxidation
of uric acid  or it may be obtained by acting  on alloxan with deoxidizing agents.
Uric acid is'to  be dili'used through boiling  water,  and the dilute nitric acid added
until a perfect solution  is obtained.  On filtering and cooling the  alloxantme grad-
ually crystallizes    The mother liquor contains much urea.  It sulphuretted hydro-
gen "gas has been passed through a solution  of alloxan, sulphur is deposited, and al-
taxaatine formed, and the same effect  is produced by acidulating the solution of at 
688         DIALURIC  ACID,  MUREXID,  ETC.
loxan, and immersing therein a slip of zinc; the alloxan is deoxidized by the nas-
cent hydrogen.  By the galvanic battery alloxan is resolved into oxygen and allox-
antine.   It is sparingly soluble in cold, but much  more in  boiling water, and crys-
tallizes in short oblique rhombic prisms which contain 3 Aq., which they lose only
by  a heat  above 300°.  The solution of alloxantiiie reddens  litmus, but does not
form salts  with  bases, being immediately  decomposed  by  contact with them.  Its
formula is  N2C8. 11,0,0.
  By oxidizing bodies, as nitric acid, chlorine, or  oxide of silver, it is immediately
converted into alloxan.  If treated by an excess of sulphuretted hydrogen, more sul-
phur is set free, and the liquor becomes strongly acid.   The body thus formed, if
mixed with alloxan, regenerates alloxantine from both.  If neutralized by carbonate
of ammonia, a white crystalline precipitate forms, which is a salt of ammonia, of
which the formula is N3C8. H.7Os.   Liebig considers it  to contain a body which he
terms the Dial uric Acid, the formula of which is N2CS04, being isomeric with the
cyanoxalic acid or uryl already noticed.   The Dialurate of Ammonia is therefore
N2C8O4+N.H4O.+3 Aq.   It may be produced  by adding hydrosulphuret of ammo-
nia to a saturated solution of uric acid in dilute nitric acid, or by acting on alloxan
with zinc and muriatic acid in excess.  Though white  when first produced, it be-
comes rose-red by drying,  and at 212° blood-red, and loses ammonia.  It is by no
means established that this body is a true ammoniacal salt as described by Liebig,
or that the  dialuric acid really exists.   Berzelius looks  upon it as a compound of
alloxantine and alloxantine-amide.
  By boiling with sal ammoniac, alloxantine is converted into uramil and alloxan,
while muriatic acid becomes free.   By the action of oxygen upon an ammoniacal
solution of alloxantine, uramil, oxaluric acid, and  mycomelinic acid are generated.
  Murexid.—This remarkable substance may be produced by a variety of reactions,
none of which are, however, quite constant in their result.  On evaporating a solu-
tion of uric acid in very dilute nitric  acid until the liquor becomes flesh-red, and
then adding dilute water of ammonia  in slight excess, and cooling, the murexid
crystallizes.  In this process a very slight  excess or deficiency of any of the ingre-
dients prevents success, and Gregory proposes, as the most certain method,  to dis-
solve four parts  of alloxantine and  seven of hydrated alloxan in  240 parts of boil-
ing water and eighty of solution of carbonate of ammonia, when the murexid crys-
tallizes by gradual cooling.  By the action of uramil and ammonia it may also be
generated, and is the  ordinary source of the purple colours that are produced in
many of the reactions already described.
  The Murexid, the name of which is derived from the murex, the  shell-fish furnish-
ing the Tyrian purple, crystallizes in short rhombic prisms of a garnet-red colour,
and by reflected  light have a green metallic lustre.  It dissolves sparingly in cold,
copiously in boiling water;  it is insoluble in ether and alcohol.  Gregory has found
that it is  sometimes soluble, and at others  insoluble in water of ammonia, whence
he  suggests that two  different bodies have been confounded under this name.  It
dissolves in caustic potash, with an indigo blue colour, which disappears by heat,
ammonia being evolved; it does not appear to  combine with bases; its formula is
N5C12. H608.  By the mineral acids and by sulphuretted hydrogen it is decompo-
sed, ammonia, alloxantine, alloxan, and dialuric  acid being evolved, besides an-
other body  termed Murcxan.  This substance is more abundantly produced by dis-
solving murexid in  a  boiling solution of potash, and when the blue colour has to-
tally disappeared, adding sulphuric  acid in excess.   It precipitates in white silky
crystalline  scales; its  formula is N2C6. H.,05;  it dissolves in caustic alkalies with-
out neutralizing them.  If its solution in ammonia be exposfed to  the air, oxygen is
absorbed and murexid regenerated.
  The murexid was long since described bv Prout under the name of Purmirateof
Ammonia;  and Fritzsche has revived the idea that it is  really an ammoniacal salt
of a distinct acid, Purpuric Acid.  By the  double decomposition of murexid  with
salts ot potash, barytes, lead, and silver, he  has  obtained purpurates of these bases
the formula of which shows the acid to be composed of N5C.6. H4Ok.  The mu-
rexid is,  according to this chemist, composed of N6C,6 . H8On=NoCl6 . ^O.o-l-
JN.H40.  1 he evidence brought forward by Fritzsche against Liebig's view is verv
strong.                                                        °    .       -*
  '? th^rinejlherbiv°r?us animals, and occasionally in children, the uric  acid is
replaced  by a different body, the Hippuric Acid, which exists therein combined with
soda. .The urine of horses and cows is to be evaporated  to one eighth of its volume
and mixed with munatic acid, which produces, after some time, a yellowish ciysl
talhne precipitate   This is to be dissolved by  boiling with some  lime; chloride of
                                                            lime; chloride of

has disappeared; being then digested wiTh ivory blacFSiter^^
v^L^i^tl-l^l^^L™1'}il .is: nearly decolorized, and the smell of urine 
URINE  IN  DISEASE.
689
separated by muriatic acid.  By the cooling of the liquor it crystallizes in delicate
silky needles or rhombic prisms; its taste is very slightly bitter, but it reddens lit-
mus strongly. When heated, it melts, and is then decomposed, giving a crystalline
sublimate of benzoic acid with ammonia and prussic acid.  It is very sparingly
soluble in cold, but copiously in boiling water; very soluble in alcohol.  By nitric
acid and other oxidizing agents, it is decomposed, and  benzoic acid is formed.  Its
salts are all soluble and crystallize; they resemble the  benzoates exactly. The for-
mufa of the  crystallized acid is N.Cis • H80j+Aq.  The constant transformation of
this acid into benzoic acid has given origin to many theories of its constitution.  It
has been supposed by some to contain benzoic acid ready formed, by others benza-
mid, and by others oil of bitter almonds, but none of these views have even much
probability in their favour.
               Of the Urine in Disease.   Urinary Calculi.
   To  the  pathologist  and physician, the indications of disease  of  the
urinary and digestive  organs, furnished by changes in the composition
of the urine, are most  valuable.  The  majority of the substances which
are taken  into  the  circulation, but are incapable of assimilation to our
organs, are thrown  off by this secretion, and hence a variety of medicinal
substances may be traced to it after having been  ingested, sometimes quite
unaltered,  at others modified in their nature.  Thus, if alkaline salts of or-
ganic acids be taken into the stomach,  the organic  material is oxidized,
probably during the action of respiration, while  the alkali passes into the
urine in  the state of carbonate.   If, however, the organic acid be taken
uncombined, it  escapes decomposition,  and, passing into the urine, pro-
duces an abundant  precipitate of salts of lime, in the case of the tartaric
and oxalic acids.
   Iodide of potassium and iodine pass into the urine, the  latter as hy.
driodic acid.   Some organic bodies, as asparagine and oil of turpentine,
are decomposed, and the products which they form are excreted, giving
to the urine peculiar odours, in the latter case like  that of violets.   Ni-
trate of potash, yellow prussiate of potash, and  most other alkaline and
earthy salts, pass into the urine unchanged.   The  majority of colouring
matters are thrown out of the system by means of this secretion, while
others, as  cochineal and litmus, are not so given off.
   The mineral  acids, alcohol, camphor, most metallic salts, do not pass
into the urine in any sensible degree.
   Urine in Diabetes.—The most remarkable change in the nature  of the
urine occurs in diabetes mellitus.   It  is voided in great quantity.   Its
specific gravity is very high, from  1030 to 1050, and it is found to con-
tain a very large  quantity of grape-sugar, and  very little urea.  It was
supposed that, in  this disease, urea ceased to be formed by the system,
and was replaced by sugar ; but I have shown that, although the quantity
of urea is very small  in any one  specimen  of the urine, yet the total
quantity is so  much  increased, that in twenty-four  hours the natural
quantity of urea is secreted ;  the secretion of sugar being an act of faulty
digestion,  and totally unconnected  with the urea.   These  results have
been fully  confirmed by Macgregor.  The diabetic urine sometimes con.
tains albumen, which arises from complication of other forms of disease.
   As the average composition of urine  in diabetes, the following may be
taken, analyzed°by myself.  Its specific gravity was 1*0363 ;  it contained
in 1000 parts, water 913, sugar 60,  urea 6*5, salts, extractive matters,
and uric acid 20*5.   This  patient  made in volume  about four times the
healthy quantity of urine in twenty-four hours.
   Urine  in Dropsies.—In these diseases, particularly where associated
                                 4 S 
 690      URINARY  DEPOSITES  AND  CALCULI.

 with disease of the kidneys, the urine is  not  increased  in quantity ; its
 specific gravity is  very low, 1005 to 1015, and it contains but very little
 urea, but generally albumen, and sometimes casetim.  In these cases, the
 urea, which is deficient in the urine, is found  in the serum of the blood
 and in  the dropsical effusions.  In some  states of the system, which  do
 not appear connected with any distinct disease, milk passes into the urine,
 in which as well the butter as the caseum  may be detected.   Such cases
 have even been met with in males.  In jaundice the colouring material
 of the  bile  passes  abundantly into the urine, and  may  be detected by
 nitric acid.   The natural elements of the urine are, however, not altered
 in quantity.
   Blue and Black  Urine.—The urine has been observed coloured deeply
 blue  by a peculiar  organic  substance, which, however, has not been ac-
 curately examined.  Braconnot found that it contained nitrogen, and was
 reddened by acids,  and  the colour restored by alkalies.   But Sprangen-
 berg  found, in  the  case he observed, that acids  dissolved the blue sub.
 stance without changing its colour.   Moncet observed in the  urine of  a
 child  a  black matter insoluble in water, but soluble in alkalies.   Prout,
 who also observed  this substance, termed it melanic acid.
  In  many  states  of the system, particularly in arthritic rheumatism,
 there is a great tendency to the formation of uric acid, and the urate of
 ammonia is deposited under the  form of  a crystalline  precipitate when
 the urine cools.  It is usually mixed with more or less of a yellowish-red
 body, which is  not  purpurate of ammonia  (murexid), as Prout supposed,
 but a peculiar organic substance, soluble in alcohol, which deserves more
 minute  examination.   The deposition of  this excess of  matter in the
joints and sheaths of the  tendons, produces the gouty concretions, which
 consist, for the most part, of urate of soda.
  In  other conditions of the system, the  formation of phosphatic salts
 predominates, and  precipitates occur in the urine which  are generally
 more crystalline and less highly coloured than those of uric  acid or of
 urates.   As these  different conditions of the  secreting  organs require
 different modes of  treatment, it is necessary to be able simply to distin-
 guish between  these two  kinds of sediment.   It is  sufficient  to remark,
 that the uric acid deposite is soluble in alkalies and insoluble  in  dilute
 acids, while the phosphatic sediments dissolve  in dilute acids, but not in
 alkaline liquors, even though decomposed by them.
  The  uric acid and the inorganic salts  of the urine are afterward de-
 posited  in the bladder, and form urinary calculi.
  The  Uric Acid Calculus is probably the most common.  It is recog-
 nised by being decomposed by heat ;  being soluble in caustic alkalies,
 and  precipitated by acids.   When  dissolved  in nitric acid,  evaporated
 and moistened  with water of ammonia, it gives the rich purple colour of
 murexid.
  The  Urate of Ammonia Calculus, in addition to the characters of uric
 acid,  gives off ammonia when dissolved in  solutions of caustic potash.
  The  Phosphate  of Lime  Calculus fuses with difficulty, or  not at all,
 before the blowpipe.  It is dissolved by muriatic acid, and precipitated
 by caustic ammonia from this solution as a white powder not crystal-
 line.
  The  Ammoniaco-magnesian Phosphate  Calculus is generally crystal-
 line in  structure ;  before the  blowpipe it  gives off ammonia, and ulti- 
CYSTIC  AND XANTHIC  OXIDES, ETC.      691
mately melts, though with ditTiculty.   It  also gives off ammonia when
boiled with caustic potash.  It dissolves in dilute acids, and is precipita-
ted as a crystalline powder on the addition of causiic ammonia.
   The two latter calculi often  form together, and produce the Triple
Phosphate, or Fusible Calculus.   This melts  readily before the blowpipe,
and if dissolved in a  dilute acid,  it gives with oxalic acid a precipitate of
oxalate of lime, and  then, with an alkali, a crystalline deposite of ammo-
niaco-magnesian  phosphate.
   All of these various deposites  may occur in the bladder, either success-
ively, and form the Alternating Calculus, or together, forming the Mixed
Calculus.   The recognition of these species will depend  on the  careful
application of the methods by which each component may be known, as
already described.
   It is not very unfrequent to meet with calculi formed of materials which
do not exist in healthy urine, but are produced by the decomposition of
its natural constituents.   Thus the Mulberry Calculus, so called from its
usual external form, consists of oxalate of lime.   When ignited it leaves
caustic  lime,  which  browns wet turmeric paper strongly, dissolves in
muriatic acid, and is precipitated by adding oxalate of ammonia.  Cal-
culi have  been found also, though rarely,  consisting of carbonate of lime
and of carbonate of magnesia.
   The most remarkable calculi of this class, however, are those formed
of the Cystic  Oxide and Xanlhic Oxide, substances of purely organic na-
ture.  The latter body is yellow, soluble in alkalies, and is precipitated
by the addition of an acid.  It dissolves in nitric and sulphuric  acids, but
not in muriatic or oxalic acids.   Its formula is N4C10 . H404.   It con-
tains, therefore, the same carbon, nitrogen,  and hydrogen as uric  acid,
but less oxygen,  whence  the name Uric Oxide has been proposed for it.
The Cystic Oxide Calculus consists of small yellow crystalline plates,
which dissolve in alkalies, and crystallize  out again on the addition  of an
acid, by an excess  of which the cystic oxide is, however, redissolved.
 When heated  strongly it is decomposed, evolving sulphurous  acid and
ammonia.  It forms definite salts with the nitric and muriatic acids.  Its
formula is N.C6H6 •  04S2.
    When  blood is effused into the bladder, the fibrine is occasionally ag-
gregated  as a calculus, the recognition of which is very simple, from what
has been  said of the properties of fibrine  (p. 663).
    Those who would wish for more detailed information of the properties
 of calculi, and of the composition of the urine in health and  disease,  I
 would refer to the truly classical work of Doctor Prout on the Diseases
 of the Stomach and Urinary Organs.

                             SECTION V.
    OF THE MILK, AND OTHER  NATURAL AND MORBID  PRODUCTS, NOT
                 INCLUDED IN THE PRECEDING SECTIONS.
    Some  of the  most remarkable constituents of milk have been al-
 ready described, as lactic acid (p. 536), the sugar of milk (p.  53a),
 the butter fats  (p. 589).  It only remains to notice the general com-
 position  ofmilked (he properties of the  Co*** or curd   It  is
 well known that, by standing, milk abandons the greater part  of its
 butter which separates, with  other substances, as  Cream.  Berzehu, 
692          COMPOSITION  OF  MILK,  ETC.
found the cream from cows' milk to have specific gravity 1*0244,
and to consist, in 100 parts, of 4*5 of butter, separated by agitation,
3*5 of caseiim, with some butter, separated by coagulation, and 92
of whey.  The skimmed milk had a specific gravity of 1*0348, and
contained in 100 parts :
         Caseous matter with some butter  ....  2*600"|
         Sugar of milk...........  3*500
         Alcoholic extract with lactic acid ....  0 600
         Chloride of potassium........0170
         Alkaline phosphates.........0025
         Earthy phosphates and a trace of iron  .  .  0-230
         Water..............92875,
  The following table presents the best  results that have been as yet
obtained on the average composition of the milk of different animals:
10000.
Specific gravity . Extractive . . Caseine . . . Ashes . . . .	\ \	Human.	Mares. 1 0395	Asses.	Cows.	Sheep. 1 0380	Dogs.
		1 0323		1 0322 90 47 1*95 1*29 629	1 0320		
		88*36 1*24 3*40 2*53 425 0 22	88*68 1*82 0*75 8 75		8591 700 3 93 2*87 029	532 (Cream 115) 15*3 58 42	65*74 290 17*40 1620 (Salts 1 50)
  The butter of human milk is more solid than that of the cow, and appears to con-
tain no butyrine.
  The Caseiim or Caseine is capable of existing in a  soluble and an
insoluble condition, like albumen.  In milk it is principally dissolved,
but a part insoluble, united with the butter, produces the emulsive
appearance of the milk.   On adding sulphuric acid to skimmed milk,
the caseine precipitates, combined with the acid, as a white coagu-
lum, which, being washed with water so as to remove all adhering
milk, and then  digested with carbonate of barytes, the caseine dis-
solves  in the water, and may, by filtration, be freed  from all traces
of the  butter, sulphuric acid, or barytes.  The caseine may also be
precipitated by alcohol, and when the curd is digested with ether
to remove all traces of butter,  it may be looked  upon as pure.
  The solution of caseine in water is thick, like  mucilage ; it smells
as boiled milk, and dries down to an amber-coloured mass, which is
again  soluble  in water.  The  solution  is coagulated by all acids,
even acetic acid, particularly when hot, and by alcohol.  In relation
to acids, caseine is similar to albumen, except that to acetic acid;
the constitution of its precipitates being precisely similar.
  The coagulated condition of caseine is not produced by boiling,
but only by the digestive principle (rennet, pepsine), as already de-
scribed (p. 679).  When thus  coagulated, caseine is absolutely un-
distinguished from coagulated albumen in its properties.  It con-
tains a considerable quantity  of bone-earth  (phosphate  of lime),
amounting to five or  six per cent.,in intimate  combination.  Its or-
ganic  element was found by Mulder to be proteine, of which ten at-
oms are combined with one of sulphur, the formula of caseine being
C4ooH3io- N5o0120 + k.   It  contains  no phosphorus, but to  each atom
so expressed, two atoms of bibasic phosphate of lime.
   When coagulated caseine containing water (cheese) is kept for 
  EGGS,  AMNIOS,  CONTENTS OF  THE  EYE,  ETC.  693

 a long time, it undergoes a remarkable kind of decomposition, and
 a substance, crystallizable and soluble in water, is obtained, termed
 by  Braconnot  Aposepedine.  By Mulder's experiments it appears,
 however,  to be impure leucine (p. 667) ;  and the Caseous Oxide and
 Case'ic Acid of Prout appear also to be  the same bodies as have been
 already noticed as formed from the decomposition of the other pro-
 teine substances.
  By contact with caseine, sugar of milk is rapidly converted into
 lactic acid, which precipitates the caseine, without, however, really
 coagulating it; hence, on  neutralizing the acid, the caseine redis-
 solves, and may react on  a  new quantity of sugar.   In  this manner
 Frep--" nas shown that the Lactic Fermentation may be carried on to
 an  indefinite extent.
  Constitution of Eggs.—The shell of hens' eggs consists of from
 90  to 95 per cent, of carbonate  of lime, one to five of phosphate of
 lime, and two to five  of animal matter.   Internally  it is lined by a
 membrane analogous to epidermis.  The white of egg  is a concen-
 trated solution of albumen, contained in the cells of a delicate mem-
 brane, in the centre of which the yolk  is suspended.   The nutritive
 material of the yolk consists of albumen and an oil  * also a yellow
 colouring matter analogous to that of  bile.  The Oil of Eggs is ob-
 tained by expressing  the egg boiled, and partly torrefied;  it  is red-
 dish-yellow, thick, and solidified by cold; it soon  becomes rancid ;
 the solid  portion of it appears  to be cholesterine ;  the liquid  con-
 tains phosphorus and  nitrogen,  and is  not saponifiable.   When the
 young animal is developed during incubation, the quantity of phos
 phoric acid in its bones is exactly represented by the  quantity of
 fihosphorus in the yolk and white ; but as these bodies contain very
 ittle lime, that earth must be derived from the shell, which becomes
 thin and brittle as the animal advances in growth.
  Liquor of the Amnios.—This fluid, in  which the foetus is immersed
 before birth, appears  to be  identical in constitution with the liquor
 effused from serous surfaces in  dropsy (p. 671).  The Liquor of the
 Allanto'is  of the cow, which is really  the urine of the  foetus, is of
 the same nature, but contains, in addition, a small quantity of allan-
 toin, the artificial formation of which is described  p. 686.
  Black Pigment of the Eye.—This substance is insoluble  in water
 and alcohol. It is decomposed by strong acids and alkalies.  Caus-
 tic  potash dissolves it, forming a yellow liquor, from which  acids
throw down a clear brown powder.   The action  of nitric acid  is
nearly the same.  The Cuttle-fish Ink  has much analogy with the
black matter of the eye, giving, when  dried, a black  powder, insol-
uble in water, alcohol, and ether, which dissolves in  nitric  acid and
potash with a reddish-yellow colour, from which solution a yellow-
ish  powder falls when it is  neutralized.   The true nature  of these
black  colouring matters, and their relation to the melanic acid of
Prout, which sometimes appears in the urine, would deserve atten-
tive study.
  The Humours of the Eye consist of water, holding in  solution al
bumen in  small quantity, with the salts which usually  accompany
it.  The crystalline lens consists of albumen, in a state of beautiful 
694        CERUMEN,  PUS,  AMBERGRIS, ETC.
 and complex organization, amounting to about thirty-eight per cent.
 of the entire mass, which contains about sixty of water.
   Cerumen.  Wax of the Ear.—This substance contains an albumi-
 nous material insoluble in water, a solid and a liquid fat soluble in
 ether, and a deep yellow matter  soluble in alcohol and insoluble in
 ether, to which its colour and very disgusting taste are  due * an-
 other constituent, which appears to be peculiar to this secretion, is
 brown, insoluble in  caustic potash ; it most  resembles horn in its
 properties, but is still quite distinct from that body.
  Pus.—This remarkable morbid secretion has generally a specific
 gravity of 1*030.  It consists of a clear liquor, in which float a great
 number of yellow globules,  of various sizes, the largest *-«f which
 are about twice the size of the  globules of  the blood.  Pus Joses
 by drying 86*1 of water in 100 parts, and hence contains 13*9 of
 solid material, from which alcohol takes 5*9 of fatty and extractive
 matters, and leaves  7*4  per  cent, of a residue, which consists of
 coagulated albumen, the  solid globules,  and a substance peculiar
 to pus.
  The  globules of pus appear to  consist  of coagulated albumen.
 The serum contains two liquids, both coagulable by heat.  One is
 albumen, the other Pyin, which is characterized by being coagula-
ted both by heat, by acetic acid, and by a solution of alum.  Giiter-
bach, who has recently examined pus with great care, finds the only
certain distinction between pus and mucus to be, that the pus glob-
ules sink always in water, while the mucus swims.  If the suspect-
ed liquid be  dried, the  extraction  of the fatty substance by ether
should decide very positively.
  Ambergris.—This substance,  which is generally found floating on
the seacoasts of tropical islands,  is known to be an intestinal con-
cretion of the  spermaceti whale, analogous  to  the  gallstones of
cholesterine in other animals.  Its principal ingredient is the Am-
bre'ine, which is  obtained by solution in  boiling alcohol, whence it
crystallizes, on cooling, in fine needles.   It is white, tasteless, of a
very agreeable odour ; it is not saponifiable * its formula is C^^O.
By boiling with nitric acid it produces ambreic acid, which crystal-
lizes from its solution in alcohol  in small colourless tables;  it red-
dens litmus, but is scarcely soluble in water ; it forms  well-defined
yellow salts with  the alkalies; its  formula appears to be C2tH20.
ri .Ol2.

                         SECTION VI.
   OF THE PRESERVATION  AND PUTREFACTION OF ANIMAL  MATTERS.
  From the  greater complexity of composition of animal substances,
their  decomposition is more  rapid, and its products  more diverse
than in the  case of organic bodies  of vegetable origin ; while the
carbon, hydrogen,  and  oxygen  give origin to the various kinds of
ulmine and other substances of the same class, the nitrogen is gen-
erally evolved as ammonia, and the sulphur as sulphuretted hydro-
gen.  It is the presence of these bodies that give to putrefying sub-
 stances the disagreeable odour  by which that process is distinguish-
 ed from mere mouldering or rotting.                        to 
PUTREFACTION.
695
  Even during life the constituent particles of the body are in a
continual  state of change, being absorbed and  thrown out of the
system, while others are  assimilated in their place.   Any part of
our constituents, liquid or solid, which becomes unfitted for  this
vital function, is thereby  killed, and must, if not got rid of, induce
the death of the individual.  Hence precisely the same means which
give to animal substances the fixity of constitution which belongs
to true chemical compounds,  and thus preserve them from decom-
position by the disturbing action of their own elements (as when
we coagulate albumen by an acid, by corrosive sublimate, or by
sulphate of copper), produce, if  applied to the  living body, the
death  of the part or of the whole being,  by  depriving the blood or
the tissue of the mutability of constitution which is required for the
functions of  the animal frame.
   It is thus that the generality of metallic poisons act  in producing
death. Being absorbed into  the  system, they unite with the albu-
men and fibrine of the blood, and, converting them into the insolu-
ble compounds which we form in the laboratory,  unfit them for the
continual absorptive and secretive offices which, as organs, while
they live they must fulfil   If the injury be local, and limited in ex-
 tent, the  part so coagulated may be thrown  off, and after a certain
 time the functions return to their proper order.   If the mass, or the
 importance  of the affected parts be greater, the system cannot so
 get rid of the portions  which have thus been removed from the
 ao-ency of life to submit  to merely chemical laws; on the contrary,
 the vital powers of the remaining portions of the animal are so much
 weakened in the effort that general death is caused.
   For putrefaction it is thus  necessary, 1st, that the force of vitali-
 ty  which governs  so completely the mere chemical tendencies of
 the elements of our tissues, be removed ; 2d, that there shall not be
 present any powerful chemical reagent with which the organized
 material may enter into  combination, and thus the divellant tenden-
 cies of the affinities of its elements be overcome ; 3d, that water be
 present in  order to  give the necessary  mobility ; 4th, that  oxygen
 be  present,  or at least some  other gas, into the  space occupied by
 which the  o-aseous  products may be diffused; and, lastly  that the
 temperature shall be within moderate limits, putrefaction being im-
 possible below 32° and above 182°.
    The agency of the first of these preventive powers need not  be
  farther noticed.  The second is extensively employed in the prepar-
  ation of bodies for anatomical purposes, by baths, or injections into
  the arteries of solutions of corrosive sublimate, acetate of alumina,
  sulphate of  ron, tannin,  wood vinegar, and kreosote ;  this last body,
  however, does not appear to act by direct combinations, but by  he
  complete (catalytic) coagulation it produces in all the tissues of the
  body hat We proteine  for their base.  The necessity for the pres-
  ence of water is shown by the fact that, by drying the animal sub-
  s ances They are completely preserved.  It is thus that the bodies
  of "hose Sshin--  in the Arabian deserts are  recovered years sab-
  ot those pensni          letel   fresh.  Alcohol and common  salt
  aTfnIS   nimaT'bodie's by their  affinity for water.  If a
  pieceofflesh[ be'covered with salt, the water gradually passes from 
696               MIASM S.--C O N T A G I O N.
the pores of the flesh, and, dissolving the salt, forms a brine, which
does not wet the flesh (p. 540), but trickles off its surface; the wa-
ter necessary for putrefaction  is  thus  removed.  The  mode  of
strengthening alcohol in a bladder  (p. 540) rests on the same prin-
ciple.  Fourth, by excluding oxygen, the putrefactive process is  re-
tarded, precisely as the fermentative action of the gluten in grape-
juice (p.  538) cannot begin until a  small quantity of oxygen  be ab-
sorbed.   It is thus that meat which is sealed  up in  close vessels,
and then boiled  for a moment, is preserved ; the small quantity  of
oxygen of the air remaining then in the vessel is absorbed, and the
product of that minute change being coagulated by the heat, it can-
not proceed farther.  A high temperature stops putrefaction  by co-
agulating the azotized materials; a  temperature below 32J, by freez-
ing the water, acts as if the tissue  had been dried ; in both cases
putrefaction is arrested.
  During putrefaction, at a stage prior to any fetid gas beino* evolv-
ed, a peculiar organic substance is generated, possessed of intensely
poisonous properties, and the blood of persons who have died from
its effects is found to be quite disorganized and irritating when ap-
plied to wounds.  The blood of over-driven cattle is  found to pro-
duce effects similar to those of venomous reptiles, and the wounds
received in dissection are sometimes followed by similar fatal con-
sequences.  The communication of disease in this way has recently
been very ingeniously ascribed by  Liebig to the general  principle
of the communication of decomposition by contact (p. 663).  The
small quantity of diseased organic matter originally introduced into
the system by absorption,  acts as a ferment, and reproduces itself
in the mass of blood until this becomes unfitted for the performance
of its functions, and the animal is killed; the active principle beino*
thus copiously present, is exuded from the skin and lungs, and gives
a contagious character to the disease, or  it  remains only in the
blood, or is secreted in pustules, &c, constituting infection, by which
the disease may be communicated to another person.
  In the decomposition of vegetable matter  in marshes, similar
maleficent products may be evolved, and throwing the blood  of the
animal, by whom they are absorbed, into fermentative  decomposi-
tion, produce the effects  of Malaria and Marsh Miasm. 
INDEX.
Absinthii'ne, 611.
Absorption of Light, 45.
---------of Heat, 96.
Acechloryl, 564.
Acetal, 554.
Acetone, 561.
Acetyl, 554.
Acid, Acetic, 555.
 ---Adipic,  586.
----Aldehydic, 555.
----Althionic, 546.
----Aloetic, 612.
----Anchusic, 614.
----Anilic, 618.
----Antimonious, Antimonic, 385.
----Arsenic, 377.
----Arsenious, 376.
----Auric, 405.
----Azulmic, 518.
----Boletic, 604.
----Boracic, 326.
----Bromic, 318.
----Butyric, 589.
----Carbonic, 485.
----Capric, Capro'ic, 589.
----Catechutannic, Catechuic, 603.
----Caincic, 605.
----Chloric, 304
----Chloroacetic, 564.
----Chlorochromic, 450.
----Chlorous, 305.
----Chromic,  372.
----Chrysammic, 613.
----Chrysolepic, 613.
____Cinchonic, Cinchonatannic, 604.
 ----Cinnamic, 572.
 ----Citric, 597.
----Colophonic, 579.
----Columbic, 375.
.----Crenic, Apocrenic, 640.
----Croconic, 496.
----Crotonic,  590.
____Cumenic, Cumen-sulphuric, 575.
----Cyanic, 514.
----Cyanuric, 516.
----Delphinic, 589.
.----Elaidic, 586.
----Ellagic, 602.
----Ethionic, 546.
.----Eugenic, 573.
----Formic, 645.
----Fulminic, 515.
----Fungic, 604.
----Gallic,  601.
----Glucic, 534.
  Acid, Hippuric, 688.
  ----Humous, Humic, 639.
  ----Hydriodic, 315.
  ----Hydrobromic, 318,
  ----Hydrochloric, 307.
  ----Hydrocyanic, 517.
  ----Hydrofluoboric, 327.
  ----Hydrofluoric, 319.
  ----Hydrofluosilicic, 325.
  ----Hydroxanthic, 550.
  ----Hypoantimonius, 385.
  ----Hypochlorous, 304.
  ----Hyponitrous, 275.
  ----Hypophosphorous, 296.
  ----Hyposulphuric, 291.
  ----Hyposulphurous, 290.
     — Iodic, 313.
     — Isethionic, 546.
     — Kinoic, 604.
     — Kramcric, 605.
     — Lactucic, 604.
  ----Lipic, 586.
  ----Manganic, 356.
  ----Margaric, 583.
  ----Mellitic, 496.
  ----Metaphosphoric, 299.
     — Methionic, 546.
     — Molybdic, 451.
     — Muriatic, 307.
  ----Myristic, 588.
     — Nitric, 277.
     — Nitromuriatic, 310.
     — Nitrous, 276.
     — Oleic, 584.
     — Osmic, 374.
     — Oxalic, 493.
     — Oxalovinic, 550.
     — Palmitic, 588.
  ----Paracyanic, 514.
     — Perchloric, 306.
     — Periodic, 314.
     — Permanganic, 356.
     — Phosphomesitic, 561.
     — Phosphoric, 297.
     — Phosphorous, 296.
     — Picric, 618.
     — Pimelic. 586.
     — Pinic, 578.
     — Purpuric, 688.
     — Racemic, 596.
  ----Rhodizonic, 496.
  ----Saccharic, 532.
  ----Saccharohumic, 637.
  ----Sacchulmic, 532.
     — Sebacic, 585.

4T 
698
INDEX.
  Acid, Selenious, Selenic, 294.
  ----Silicic. 322.
  ----Stannic, 370
  ----Stearic, 582.
  ----Succinic, 580.
  ■----Sulphomesitic, 561.
  ----Sulphuric, 286.
  ----Sulphurous, 284.
  ----Sylvic, 578.
  ----Tannic, 597.
  ----Tantalic, 375.
  ----Tartaric, 592.
  ----Tellurous, Telluric, 389.
  ----Titanic, 375.
  ----Tungstic, 374.
  — Valerianic, 568.
  ----Vanadic, 373.
  ----Verdous and Verdic, 605.
  Acids, Polybasic,  413.
  Acroleon, 585.
  Actions by Contact, 235.
  Adhesion of Solids to Liquids, 19.
 Uroliths, 357.
 Affinity,  Chemical, 157.
 ---------------- Order of, 159.
 -------influenced by Cohesion, 164.
 ------------------Elasticity, 168.
 ------------------Light, 172.
 ■-------Measure of,  202.
 Aggregation, States of, 16.
 Air, Atmospheric, 262.
 --- Expansion  of,  48.
 Alabaster, 431.
 Albumen, Animal, 663.
 Alcohol, Ordinary,  540.
 Alembroth, Salt of, 461.
 Algarotti, Powder of, 453.
 Alkalies,  330.
 Alkalimetry, 489.
 Alkaline Earths, 330.
 Alkarsine, Alkargene, 563.
 Allanto'ine, 686.
 Alloxan, 686.
 Alloxantine, 687.
 Alum, 436.
 Aluminum, Alumina, 349.
 --------- Salts of, 435.
 Amber, 579.
 Ambergris, Ambreine, 694.
 Amidogene, 500. ..
 Amilic Alcohol,  567.
 Ammeline, 526.
 Ammonia, 498.
 ---------Ordinary Salts of, 507.
 Amygdaline, 569.
 Analcime, 40.
 Analysis,  Nature of, 10.
--------Organic, 482.
Anatase, 375.
Anhydrite, 431.
Animal Charcoal, 480.
------ Electricity,  138.
Antimonial Powder, 454.
Antimoniuret of Hydrogen, 388.
  Antimony, 384.
  ---------Detection of, 388.
  ---------Oxide of, 385.
  ---------Salts of, 453.
  ---------Sulphurets of, 386.
  Antimony Crocus,  Glasses of, 385.
  Apotheme, 612.
  Aqua-regia, 310.
  Arabine, 530.
  Aricine, 625.
  Arseniate of Iron, 452.
  -----------Potash, 452.
  -----------Silver, 461.
  Arsenic, 376.
  -------Acids of, 377.
  -------Antidote to, 384.
  -------Detection  of, 381.
  -------Salts of, 451.
  -------Sulphurets of, 379.
  Arsenite of Copper, 456.
  ----------Potash, 452.
 ----------Silver, 461.
 Arseniuret of Hydrogen, 378.
 Atmosphere, 262.
 -----------Composition of, 263.
 -----------Effect   of  Respiration  on,
                268.
 -----------Extent and Form of, 270.
 -----------Pressure of, 269.
 Atmospheric Electricity, 125.
 Atomic Theory, 217.
 Atoms, Physical and Chemical, 219.
 ------Specific Heat of, 66.
 Atropine, 634.
 Aurates, 405.
 Azote, 260.
 Azure Blue, 447.

 Balance, Electrical,  113.
 Barium, 342.
 -------Chloride of, 429.
 -------Sulphuret of, 344.
 Barytes, 342.
 ------- Salts of, 429.
 Batteries, Constant,  136.
 -------- Galvanic,  131.
 Bell Metal, 393.
 Benzyle -Compounds, 570.
 Bile, Constitution of the, 680.
 Bileine, Bilifulvine, 682.
 Bismuth, 397.
 --------Oxides of,  398.
 --------Salts of, 458.
 --------Sulphuret of, 398.
 Blende, 367.
 Blue, Azure, 447.
 ----Thenard's, 447.
 Boiling Points of Liquids, 83.
 Boracic Acid,  Boron, 326.
 Boracite, 435.
 Borax, 428.
 Boron, Fluoride of, 327.
Brass, 394.
Bromates, 318. 
INDEX.                             699
Bromide of Sulphur, 318.
Bromine, 317.
-------Chloride of, 318.
Bronze, 393.
Brucine, 631.

Cadmium and its Compounds, 369.
------- Salts of, 448.
Caffeine, 608.
Calamine, 367.
Calc Spar, 345.
Calcium and its Oxides, 345.
-------Salts of,  430.
------Sulphuret, 347.
Camphene, 576
Cantharidine, 609.
Caoutchouc, Caoutchine,  580.
Capacity of Bodies for Heat, 63.
Caramel, 533.
Carbon, Forms of, 476.
Carbonates, 485.
Carbonic Acid, 485.
-------Oxide, 492.
Carburets, 485.
Carmine, 616.
Carthamine, 615.
Caseiim, Caseine, 691.
Catalysis, 235.
Cementation, 360.
Cerebrot, Cerebrol, 669.
Cerium and its Compounds, 351.
Chalk, 345.
Chameleon Mineral, 356.
Chemical Action  of Galvanism, 129.
-------Affinity, 156.
-------Formulae, 156.
 -------Nomenclature, 149.
-------Rays of Light,  173.
 Chemistry, Origin and Object of, 9.
.--------Derivation of, 10.
 Chloral, 564.
 Chlorate of Potash, 304, 424.
 Chloride of Aluminum, 435.
 ---------Antimony, 453.
 .-----.----Arsenic, 452.
 _________Barium, 429.
 _________ Bismuth, 458.
 _________ Boron, 326.
 _________- Calcium, 430.
 ._________Chrome, 449.
 _________Cobalt, 446.
 _________. Copper, 455.
 ._________Gold, 465.
 .       ___Hydrogen, 307.
 ________- Iodine, 317.
 _________Iron, 444.
 ._________Lead, 457.
 _________. Magnesium, 434,
 _     ----Manganese, 443.
 _________Mercury,  461.
 .______.— Nickel, 446.
 _________Palladium, 466.
 _________Platinum, 466.
 __________Potassium, 421.
Chloride of Rhodium, 466.
---------Selenium, 311.
--------- Silicon, 323.
---------Silver, 459.
--------- Sodium, 426.
---------Strontium,  429.
--------- Sulphur,  310.
---------Tin, 448.
--------- Titanium, 454.
--------- Zinc, 447.
Chlorine, 300.
-------Compounds with Oxygen, 304.
Chlorophyll, 621.
Chondrine, 668.
Chromates of Lead, 458.
----------Mercury,  464.
----------Potash, 449.
Chrome Alum, 449.
------Iron, 371.
Chromium, 371.
---------Oxide, Acid of, 371.
---------Salts of, 449.
Chrysorhamnine, 615.
Chyle and Chyme, 679.
Cinchonine and its Salts, 625.
Cinnabar, 402.
-------Factitious, 403.
Circular Polarization, 41.
Classification of Bodies, 238.
Cobalt, 366.
-----Salts of,  446.
Cocculine, 609.
Cohesion and Affinity,  163.
Columbine, 609.
Columbium, 375.
---------Salts of, 451.
Combination, Laws of,  202.
Combustion, Slow, 173.
---------Theories of, 185.
Communication  of Motion, 235.
Conduction of Heat,  91.
Coneine, 635.
Constant Battery, 136.
Contact, Actions by, 235.
Cooling of Bodies, 103.
Copper, 390.
------Alloys of, 393.
------Oxides  of, 392.
------Pyrites, 390.
 ------Salts of, 453.
 ------Sulphurets of,  393.
 Crystalline Forms, 23.
 Crystals, Dimorphous,  227.
 ------- Isomorphous, 221.
 -------Polarization by, 38.
 -------Systems of, 26.
 Currents, Galvanic,  126, 197.
 Cyanogen, 513.

 Daguerreotype Images, 175.
 Definite Proportions, 202.
 Dew, Nature of, 104.
 Dex rine, 331.
 Diamond, 477. 
700
INDEX.
Diastase, 651.
Differential Thermometer, 50.
Dimorphism, 227.
Distillation, 83.
Divellent Affinities, 157.
Divisibility of Matter, 17.
Double Decomposition,  157.
------Refraction, 34.
Dynamic Electricity, 126.

Ebullition, 83
Elasticity of  Gases, 19.
-----------Vapours, 78.
--------and Affinity, 168.
Elaterine, 609.
Elayl, 552.
Elective Decomposition, 157.
Electrical Attraction, 112.
--------Balance, 113.
--------Battery, 120.
--------Induction, 118.
Electricity, Distribution of, 110.
----------Dynamic, 126.
----------Interference of, 112.
----------Nature of, 106.
----------of the  Air, 125.
■----------Positive and Negative, 114.
----------Statical, 107.
----------Theories of, 113.
Electrics and Non-electrics, 107.
Electro-chemical Theories, 187.
Electro-magnetism, 145.
Electrolysis and Electrodes, 194.
Electrotype, 130.
Elements, Nature  of, 9.
--------- Classification of, 238.
Emetine, 632.
Epsom Salt, 434.
Equivalent Decomposition, 206.
Ethal, 591.
Ether, Luminiferous, 42.
----- Sulphuric, 541.
Etherene, 547.
Ethers,  Theory of the, 544.
Ethyl, 545.
Eudiometer, Use of the, 262.
Evaporation,  77.
-----------Spontaneous, 87.
Excitation, Electrical, 106.
Expansion by Heat, 46.
        — of Gases, 56.
             Liquids, 58.
— Solids, 60.
Fermentation, 539.
Fibrine, 603.
Flame, Constitution of, 181.
Flashing, 399.
Flints, 321.
------Liquor of, 437.
Fluidity, 70.
Fluoborates, 327.
Fluoride of Boron, 327
---------Calcium, 430.
Fluoride of Hydrogen, 320.
        — Phosphorus, 321.
           Silicon. 324.
Fluorine, 319.
Fluor Spar, 430.
Freezing Mixtures, 71.
Frost, Nature of,  104.
Fulminates, 513.
Fusion, Liquefaction, 70.

Galena, 395.
Galvanic Batteries, Common, 134.
                  Constant, 136.
— Circles, 128.
— Electricity, 126.
   Intensity, 131.
Galvanism, Contact Theory of, 133.
Galvanoscope, 147, 195.
Gases, Conduction of Heat by, 92.
------Liquefaction of, 20.
------Specific Gravity of,  11.
              Heat of, 69.
Gelatine, 667.
Glass, Composition of, 437.
      of Antimony, 385.
Glucinum, Glucina, 351.
Glucose, 533.
Glycerine, 581.
Glycyrrhizine, 535.
Gold, 405.
Gravity, Nature of, 11.
Green, Brunswick, 455.
------Emerald, 455.
------Scheele's, 455.
Heat, Central, of the Earth, 104.
-----Conduction of by Solids, 92.
-----Interference of, 101.
-----Latent of Liquids, 70.
               Vapours, 76.
— of Liquefaction, 70.
— Polarization of, 101.
— Radiation of, 94.
- Reflection and Absorption of, 98.
— Relation of to Light, 102.
— Repulsive Power of, 46.
- Sources of, 105.
— Specific of Atoms, 66.
          — Gases, 69.
            Solids, 63.
-----Transmission of, 91.
Heavy Spar, 342.
Hematite, 362.
Hematosine, 674.
Hematoxyline, 615.
Hepar Sulphuris, 339.
Hydriodate of Phosphuretted Hydrogen,
    316.
Hydriodic Acid,  315.
Hydrobromic Acid, 318.
Hydrochloric Acid, 307.
Hydrofluoric Acid, 320.
Hydrofluosilic Acid, 324.
Hydrogen, 246. 
INDEX.
Hydrogen, Antimoniuretted, 388.
--------Arseniuretted, 378.
--------Oxide of, 253.
--------Peroxide of, 258.
--------Phosphuretted, 299.
--------Seleniuretted, 294.
.--------Sulphuretted, 292.
Hydro-oxygen Blowpipe, 251.
Hydruret of Arsenic, 378.

Indigo, Blue,  616.
Inuline, 529.
Iodine, 311.
-----Compounds of, 313.
Iridium, 409.
-------Salts of, 466.
Iron, 357.
----Magnetic Oxide of, 362.
----Malleable, 359.
---- Oxides  of, 362.
----Passitivity of, 361.
----Pyrites, 363.
----Salts of, 444.
---- Smelting of, 359.
---- Sulphurets of, 363.
Isomerism, 231.
Isomorphism, 221.
Isomorphous Groups, 223.

Kacodyl Compounds, 562.
Kalium, 337.
Kermes Mineral, 386.
King's Yellow, 379.
Kupfer Nickel, 365.

Lac-sulphuris, 339.
Lactine, 535.
Lactucine, 611.
Lamp, Aphlogistic, 179.
-----Safety, 183.
 Lampblack, 479
 Lana Philosophica, 367.
 Lanthanum,  351.
 Latent Heat of Liquids, 70.
 _____..------Vapours, 76.
 Laws of Combination, 202.
 Lead, 394.
 Legumine, 538.
 Lichenine, 529.
 Light, Chemical Rays of, 173.
 -----Wave Theory of, 42.
 Lignine, 529.
 Lime, 345.
 -----Salts  of, 430.
 Liquefaction, 70.
 Lithium, 342.
 -------Salts of, 429.
 Lymph, 683.

 Madder, Colouring Bodies of, 613.
 Magnesium, 348.
 -------— Salts of, 434.
 Magnetism,  143.
 Manganese, 352.
Manganese, Salts of, 443.
Mannite, 535.
Marsh Gas, 563.
Meconine, 609.
Melam, 526.
Melamine, 526.
Membrane, Cellular, 671.
Menthene, 578.
Mercury, 402.
-------Salts of, 461.
Mesitic Ether, 561.
Mesitylene, 561.
Metal, Bell, 393.
-----Gun, 393.
      Speculum, 393.
Metals, Properties of, 327.
Methyl, Salts of, 644.
Minium, 395.
Molecular Cohesion, 19.
Molybdates,  373.
Molybdenum, 373.
            Salts of, 451.
Mordants, Action of, 622.
Morine, 615.
Morphia, 627.
Mosaic Gold, 370.
Mucus, 679.
Multiple Proportions, 207.
Murexid, 688.
Muriatic Acid, 307.
Myriospermine, 573.

Napthaline, 647.
Narcotine, 628.
Natrium, Natron, 342.
Nickel, 365.
        Salts of, 446.
Nicotine, 635.
Nitric Oxide, 273.
Nitrogen, 26.
-------Oxides of, 272.
Nitrous Oxide, 272.
Nomenclature, 149.

Oleine,  581.
Olivine, 607.
Ologist Iron, 362.
Orcine,  Orceine, 619.
Organic Analysis, 476.
        Bodies, 467.
Orpiment, 379
Osmium, 374.
-------Oxides of, 374.
         Salts of, 451.
Oxamethane, 350.
Oxides of Aluminum, 349.
-------Antimony, 385.
.-------Arsenic, 377.
-------Barium, 342.
-------Bismuth. 397.
-------Cadmium, 369.
-------Calcium, 346.
------— Cerium, 351.
------- Chlorine, 304. 
702
INDEX.
Oxides of Chrome, 371.
_______Cobalt, 366.
_------Copper, 392.
._______• Glucinum, 351.
.------- Gold, 405.
-------Hydrogen, 253.
-------Iridium,  409.
-------Iron, 362.
------- Lead, 394.
------- Lithium, 342.
_______Magnesium, 348.
_______Manganese, 353.
.-------Mercury, 403.
_______ Molybdenum, 373.
_______Nickel, 365.
-------Nitrogen, 272.
_______Osmium, 374.
------- Palladium, 406.
.-------Phosphorus, 296.
.____--- Platinum, 407.
-------. Potassium, 337.
 .__.____Rhodium, 409.
------- Silver, 401.
-------Sodium, 340.
 -------Strontium, 344.
 .-------Thorium, 351.
-------Tin, 369.
._______Titanium, 375.
 ------- Tungsten, 373.
-------Uranium, 390.
.-------Vanadium, 373.
—------Yttrium, 351.
-------Zinc, 367.
-------Zirconium, 351
 Oxychloride of Antimony, 453
 -----------Bismuth, 458.
 .-----------Calcium, 430.
 .-----------Chrome, 449.
 -----------Copper, 455.
 .-----------Lead, 457.
 .-------— Mercury, 462.
               Palladium, 466.
Oxygen, 241.
------ Preparation of, 241.
Oxyhydrogen Blowpipe, 251.

Palladium, 406.
-------- Compounds of, 406.
Paracyanogen, 514.
Pectine, 605.
Perchlorates,  306.
Periodates, 313.
Permanganates, 357.
Pewter, 397.
Phenyl, Hydrate of, 648.
Phloridzine, 607.
Phosphates of Water, 297.
Phosphites, 297.
Phosphorus, 295.
---------Compounds of, 296.
Photography, 175.
Piperine, 608.
Platinum, 407.
Polarization,  Circular, 41.
Polarization of Heat, 102.
           — Light, 38.
Polychrome, 610.
Populine, 610.
Porcelain, Nature of, 437.
Potash, 337.
Potassium, 336.
--------Oxides of, 337.
--------Salts of, 421.
           Sulphurets of, 339.
Proteine, 665.
Puddling, 359.
Purpurates, 688.
Pus, 694.
Putty, 370.
Pyrites, Copper, 390.
        Iron, 363.
Pyrometer, Daniell's, 54.
Pyrophorus, 339.
Pyroxylic Spirit, 643.

Quartation, 405.
Quartz, 322.
Quassine, 610.
Quicksilver, 402.
Quinine, 624.

Radiation of Heat, 94.
            Light, 32.
Radicals, Compound, 333.
-------Nature of, 233.
Realgar, 379.
Red Lead, 394.
--- Precipitate, 403.
Reflection of Heat, 96.
----------Light, 32.
Refraction of Heat, 100.
--------Double, 34.
          Single, 32.
Regular System, 26.
Respiration of Animals, 677.
Rhodium, 409.
          Salts of, 466.
Rutile, 375.
Rutiline, Rufine, 607.

Safety Lamp, 183.
Salop, 531.
Salicyl Compounds, 573.
Salts, Constitution of, 410.
----Crystallization of, 23.
----Isomorphism of, 221.
----Solubility of, 22.
Salts of Alumina, 435.
----- Antimony, 453,
-----Arsenic, 452.
-----• Barium, 429.
-----Bismuth,'458.
----- Cadmium, 448.
------ Calcium, 430.
----- Chrome, 449.
----- Cobalt, 446.
-----Copper, 455.
----- Gold, 465. 
INDEX.
7Qf!
Salts of Iridium, 466.
------Iron, 444.
------  Lead, 457.
------Magnesium, 434.
—  —  Manganese, 443.
-----  Mercury, 461.
------Molybdenum, 451.
------  Nickel, 446.
------  Osmium, 451.
------  Palladium, 466.
------  Platinum, 466.
------  Potassium. 421.
------  Rhodium, 466.
------  Silver,  459.
■-----  Sodium, 426.
------Strontium, 429.
------Tin, 448.
■-----Zinc, 447.
Santaline, 615.
Santonine, 610.
Saponine, 611.
Scillitine, 611.
Selenium, 294.
------- Compounds  of, 294.
Senegine, 611.
Silica, 322.
Silicate of Alumina, 437.
--------Cobalt, 447.
--------Potash, 426.
--------Soda, 429.
Silicon, 321.
------Chloride of,  323.
------ Fluoride of, 324.
Silver,  399.
-----Oxides of, 401.
-----  Salts of, 459.
-----Sulphurets of, 401.
Simple Bodies, 9.
------------Table of, 149.
Skin, Nature of, 670.
Slacked Lime, 346.
Smalts, 447.
 Smilacine, 611.
 Soap, Manufacture of,  590.
 Soda, 340.
 ----Detection of, 340.
 Sodium, 340.
 ------Salts of, 426.
 Solanine, 633.
 Solder, 396.
 Solids, Conduction of Heat by, 92.
 -----Expansion of, 60.
 -----Specific Gravity of, 11.
 Specific Heat, 63.
 Speculum Metal, 393.
 Speiss. 365.
 Spermaceti, 591.
 Spirit of Salts, 307.
 Starch. 527.
 Steam, Elasticity of, 78.
 ------Latent Heat of, 76.
 -----Motive Force of, 89.
 Stearine, 582.
  Steel, 360.
Stibium, 384.
Strontium, 344.
--------Oxides of, 345.
--------Salts of, 429.
Strychnine, 629.
Sugar of Liquorice, 536.
Sugarcane, 531.
Sulphites, 284.
Sulphocyanogen, 525.
Sulphosinapisine, 574.
Sulphur, 282.
Sulphurets of Aluminum,  350.
---------- Antimony, 386.
----------Arsenic, 379.
----------Barium, 344.
----------Bismuth, 398.
----------Cadmium, 369.
----------Calcium, 347.
----------Chrome,  371.
----------Cobalt. 367.
----------Copper, 393.
 ----------Gold, 405.
----------Hydrogen, 292.
----------Iron, 363.
----------Lead, 395.
---------- Magnesium, 348.
----------Manganese, 357.
----------Mercury, 404
----------Molybdenum, 373.
----------Nickel, 366.
----------Palladium, 407.
----------Platinum, 407.
------:----Phosphorus, 299.
---------- Potassium, 339.
----------Selenium, 295.
----------Silver, 401.
 ----------Sodium, 342
 ----------Strontium,  344.
 __________Tin,  370.
   ________Zinc, 368.
 Synthetic Action of G.ilvanism, 199.
 Systems of Crystallization, 26.

 Tantalum, 375.
 Telluret of Hydrogen,  389.
 ------Salts of, 454.
 Tellurium, 389
 --------Compounds of, 389.
 Temperature, Nature of, 49.
 Thebaine, 629.
 Theory, Atomic, 217.
 ------of Volumes, 213.
 Thermo-electricity, 139.
 Thermometer, Nature of the, 49.
 ■-----------  Kinds of,  50.
 Thermometric Scales, 53.
 Thialol. 54S.
 Thorium, 351.
 Tin, 369.
 ---Grain, 369.
 ---Oxides of, 369.
 Tincal, 4-29.
 Titanium, 375.
 Transcalescence, 98. 
704
INDEX.
Tragacanthine, 530.
Transfer of Elements, 194
Tungsten, 373.
--------Salts of, 451.
Types, Chemical, 234.

Ulmine, from Soil, 637.
Uranium, 390.
--------Salts of, 454.
Urea, 684.
Urine, 689.

Vanadium, 373.
---------Salts of, 451.
Vaporization, 75.
Vapours, Elasticities of, 78.
-------Latent Heat of, 76.
-----— Volumes of, 77.
Veratrine, 631.
Vermilion, 404.
Vitriol, Oil of,  286.
Voltaic Electricity, 126.
 Volta's Theory of Contact,  133.
 Volumes, Theory of, 213.

 Water, Composition of, 253.
 Wave Theory of Light, 42.
 --------------Heat,  102.
 Wax, 592.
 Welding, 359.
 White, Pearl, 458.
 ------Vitriol, 447.

 Xyloidine, 530.

 Yeast, 538.
 Yttrium, 351.
 -------Salts of, 443.

 Zaffre, 366.
 Zinc, 367.
---- Butter of, 447.
Zirconium, 351.
--------- Salts of, 443.
THE  END.