c^S f.■'/■'. ::>:<■ I, A% -/v.-.v,v ;. f. I ''^:::x:>;^:-::::;::v^^S; :,rv-Y:';sX':-:'>:-:-;«:«:v:jt^ffi tp-.Mi;i;i;:ii.^ 4 ;? • • ■«- * ;• - ? ■; » ' : ' • S:f k ;- '' '-.'■. ■ ft r!l! ...I ■\W' A NATIONAL LIBRARY OF MEDICINE Bethesda, Maryland ELEMENTARY CHEMISTRY. QD 30 Fy, 18&0 n? foj&lA* MANUAL ELEMENTARY CHEMISTRY, THEORETICAL AND PBAfTrffjAT. £cXjfc GEORGE POWJES, F.R.S., -ATE PROFESSOR OF PRACTICAL CHEMISTRY IN UNIVERSITY COLLEGE, LONDON. KSOJI THE SEVENTH REVISED AND CORRECTED LONDON EDITION EDITED BY ROBERT BRIDGES, M.D., PROFESSOR OF CHEMISTRY IN THE PHILADELPHIA OOLLEdE OF PHARMACY, ETC. WITH ONE HUNDRED AND NINETY-SEVEN ILLUSTRATIONS. PHILADELPHIA: BLAN/CHARD AND LEA. 1860. av ._____M_____ Entered, according to Act of Congress, in the year 1859, by BLANCHARD AND LEA, in the Clerk's Office of the District Court of the United States for the Eastern District of Pennsylvania. « AMERICAN PUBLISHERS' ADVERTISEMENT. TriE very recent and thorough revision which this work" has received at the hands of the English Editors, has rendered unneces- sary a portion of the notes added to the former American edition, and has left little to be done in revising it for this country. Such additions, however, as could be made without interfering with the design of the volume as a condensed Manual, have been inserted by the American Editor, who has introduced a number of illustrations, and who has carefully superintended its passage through the press, so as to secure the accuracy so essential in a treatise of this nature. The formulae have claimed especial care, and in the collation of them the opportunity has been found of correcting various errors. It is therefore hoped that the work will merit a continuance of the very great favor which it has hitherto enjoyed as a guide for the 6tudent in acquiring a knowledge of Chemical Science. Philadelphia, March, 1859. 1* (v) ADVERTISEMENT TO THE SEVENTH LONDON EDITION. Two years only have elapsed since the previous edition of this Manual was published. The progress of Organic Chemistry has rendered many changes requisite. The most important addition will be found in the theory of the Polyacid Alcohols. Throughout all the Organic Chemistry improvements have been made, and many subjects have been re-arranged. Still the Editors have endeavored to preserve the original plan of the work, and as yet they have thought it most desirable to retain the equivalent numbers which have so long been used in this country. The advance of knowledge will probably lead to changes both in formulae and in nomenclature) but the Editors do not consider that at the present time the Manual should in these respects be altered. The whole work has been corrected and revised throughout. H. Bence Jones. A. W. Hoffman. London, August 20, 1858. (vii) ADVERTISEMENT TO THE THIRD LONDON EDITION. The correction of this Edition for the press was the daily occupa- tion of Professor Fownes, until a few hours previous to his death in January, 1849. His wish and his endeavor, as seen in his manuscript, were to render it as perfect and as minutely accurate as possible. When he had finished the most important part of the Organic Chemistry, where the most additions were required, he told me he should " do no more," — he had "finished his work." At his request I have corrected the press throughout, and made a few alterations that appeared desirable in the only part which he had left unaltered, the Animal Chemistry. The index and the press have also been corrected throughout by his friend, Mr. Robert Murray. H. Bence Jones, M. D. 30 Grosvenor Street, Jan., 1850. (viii) PREFACE. The design of the present volume is to offer to the student com- mencing the subject of Chemistry, in a compact and inexpensive form, an outline of the general principles of that science, and a history of the more important among the very numerous bodies which Chemical Investigations have made known to us. The work has no pretensions to be considered a complete treatise on the subject, but is intended to serve as an introduction to the larger and more compre- hensive systematic works in our own language and in those of the Continent; and especially to prepare the student for the perusal of original memoirs, which, in conjunction with practical instruction in the laboratory, can alone afford a real acquaintance with the spirit of research and the resources of Chemical Science. It has been my aim throughout to render the book as practical as possible, by detailing, at as great length as the general plan per- mitted, many of the working processes of the scientific laboratory, and by exhibiting, by the aid of numerous wood-engravings, the most useful forms of apparatus, with their adjustments and methods of use. As one principal object was the production of a convenient and useful class-book for pupils attending my own lectures, I have been induced to adopt in the book the plan of arrangement followed in the lectures themselves, and to describe the non-metallic elements and some of their most important compounds before discussing the sub- ject of the general philosophy of Chemical Science, and even before (ix) X P-UEFACE. describing the principle of the equivalent quantities, or explaining the use of the written symbolical language now universal among Chemists. For the benefit of those to whom these matters are already familiar, and to render the history of the compound bodies described in the earlier part of the work more complete, I have added in foot-notes the view adopted of their Chemical constitution ex- pressed in symbols. I have devoted as much space as could be afforded to the very important subject of Organic Chemistry; and it will, I believe, be found that there are but few substances of any general interest which have been altogether omitted, although the very great number of bodies to be described in a limited number of pages rendered it necessary to use as much brevity as possible. GEO. FOWNES. University College, London, October 5, 1847. TABLE OF CONTENTS. PAQB Introduction....................37 PART I. PHYSICS. Of density and specific gravity.............39 Methods of determining the specific gravities of fluids and solids . . 39 Construction and application of the hydrometer........44 Of the physical constitution of the atmosphere, and of gases in GENERAL....................46 Elasticity of gases. — Construction and use of the air-pump .... 46 Weight and pressure of the air. — Barometer........49 Law of Mariotte: relations of density and elastic force: corrections of volumes of gases for pressure.............50 Heat......................53 Expansion. — Thermometers..............53 Different rates of expansion among metals; compensation-pendulum. 56 Dauiell's pyrometer.................57 Expansion of liquids and gases. — Ventilation. — Movements of the atmosphere...................59 Conduction of heat.................64 Change of state. — Latent heat.............65 Ebullition ; steam..................66 Distillation....................70 Evaporation at low temperatures.............71 Vapor of the atmosphere; hygrometry..........73 Liquefaction of permanent gases.............75 (xi) Xii CONTENTS. 77 Production of cold by evaporation............ Capacity for heat. — Specific heat . •...........'° Sources of heat.................. Light......................^ Reflection, refraction, and polarization of light........85 Chemical rays.................."0 Radiation, reflection, absorption, and transmission of heat .... 95 Magnetism....................102 Magnetic polarity ; natural and artificial magnets.......103 Terrestrial magnetism................104 Electricity....................108 Electrical excitation; machines.............110 Principle of induction; accumulation of electricity.......112 Voltaic electricity.................113 Thermo-electricity.—Animal..............115 Electro-magnetism; magneto-electricity.........115, 119 Electricity of steam.................120 PART II. CHEMISTRY OF THE ELEMENTARY BODIES. Non-metallic elements................121 Oxygen.....................121 Hydrogen; water; binoxide of hydrogen..........127 Nitrogen; atmospheric air; compounds of nitrogen and oxygen . 137, 143 Carbon; carbonic oxide; carbonic acid..........144 Sulphur; compounds of sulphur and oxygen........148 Selenium....................154 Phosphorus; compounds of phosphorus and oxygen......155 Chlorine; hydrochloric acid.—Compounds of chlorine and oxygen . . 157 Bromine....................104 Iodine.....................165 Fluorine....................j 57 Silicium.....................jgg Boron.....................170 CONTENTS. xiii Compounds formed by the union of the non-metallic elements among themselves................172 Compounds of carbon and hydrogen. — Light carbonetted hydrogen; olefiaut gas ; coal and oil-gases. — Combustion, and the structure of flame...................172, 180 Nitrogen and hydrogen ; ammonia............181 Nitrogen and boron.................182 Sulphur, selenium, and phosphorus, with hydrogen......183 Nitrogen, with chlorine and iodine; chloride of nitrogen.....186 Other compounds of non-metallic elements.........187 Chlorine, with sulphur and phosphorus..........187 0_- the general principles of chemical philosophy,.....190 Nomenclature...................190 Laws of combination by weight.............192 By volume....................197 Chemical symbols.................199 The atomic theory.................202 Chemical affinity..................203 Electro-chemical decomposition; chemistry of the voltaic pile . . . 207 Metals.....................217 General properties of the metals.............217 Constitution of salts................219 Crystallography..................222 Isomorphism.......•...........229 Polybasic acids..................231 Binary theory of the constitution of salts.........233 Potassium....................235 Sodium.....................242 Ammonium....................251 Lithium....................2£4 Barium.....................255 Strontium....................257 Calcium.....................257 Magnesium...................263 Aluminium....................266 Beryllium (glucinum).—Yttrium............269 Cerium, lanthanium, and didymium............269 Zirconium. — Thorium................270 Manufacture of glass, porcelain, and earthenware.......270 Manganese...................274 2 xiv CONTENTS. Iron......................277 n\ ... 284 Chromium.................... Nickel......................287 Cobalt.....................288 Zinc......................2™ Cadmium....................~v* Bismuth.....................292 Uranium....................293 Copper.....................-t,r* Lead.....................29(3 Tiu......................300 Tungsten....................302 Molybdenum...................303 Vanadium....................303 Tantalum (columbium)................304 Niobium and Pelopiuin...............304 Titanium....................305 Antimony.................... 306 Tellurium...........■.........308 Arsenic....................309 Silver.....................314 Gold......................317 Mercury.....................319 Platinum....................324 Palladium....................328 Rhodium....................329 Iridium.....................330 Ruthenium...................332 Osmium.....................332 PART III. ORGANIC CHEMISTRY. Introduction....................334 Law of substitution................ 335 The ultimate analysis of organic bodies.........338 Empirical and rational formulae............347 Determination of the density of the vapor* of volatile liquids 348 Saccharine and amylaceous substances, and the products of their alteration................... 351 CONTENTS. XV Cane and grape-sugars; sugar from ergot of rye; Bugar of diabetes in- sipidus ; liquorice sugar ; milk-sugar; mannite.......351 Starch ; dextrin; starch from Iceland-moss; inulin; gum; pectin; lignin ....................356 Oxalic and saccharic acid..............360, 3G2 Xyloidin; pyroxylin; mucic acid ; suberic acid........363 Mellitic, rhodizonic, and croconic acids..........363 Fermentation of sugar. — Alcohol............364 Lactic acid...................368 Ether, and ethyl-compounds......*........370 Sulphovinic, phosphovinic, and oxalovinic acids.......375 Heavy oil of wine.................3/J Olefiaut gas ; Dutch liquid ; chlorides of carbon.......379 Ethionic and isethionic acids..............382 Chloral, &c....................383 Mercaptan ; xanthic acid...............384 Zinc ethyl; stannethyl................385 Aldehyde; aldchydic acid; acetal............388 Acetic acid...................390 Trichloracetic acid.................395 Acetone....................396 Glycol.....................397 Substances more or less allied to alcohol........400 Wood-spirit; methyl-compounds............400 Sulphomothylic acid . . .............4i'3 Formic acid; chloroform...............404 Formomethylal; methyl-mercaptan............406 Kakodyl....................407 Propylic alcohol..................410 Ally 1 scries . . . '................411 Acrolein and acrylic acid...............412 Butylic alcohol..................414 Potato-oil and its derivatives..............415 Sulphamylic acid.................417 Valeric acid ; trichlorovaleric and quadrichlorovaleric acids .... 418 Fusel-oil from grain-spirit..............420 Homologous series.................421 Oils and fats...................423 Margarin, stearin, and olein; saponification, and its products; gly- cerin .....................424 Palm and cocoa oils.—Elaidin and elaidic acid........ 427 Pni'liu'ts of the action of acids on fats...........428 Wax ; spermaceti; chulcsteriu ; cautharidin........ . 429 Xvi CONTENTS. Castor-oil; caprylic alcohol.............. Suberic, succinic, and sebacic acids...........431 Bitter-almond oil and its products ; benzoyl-compounds.....432 Benzoic acid ; sulphobenzoic acid ; benzone and benzol.....433 Sulphobenzide and hyposulphobenzic acid.......... 435 Nitrobenzol, azobenzol, &c...............436 Formobenzoic acid; hydrobenzamide; benzoin; benzile; benzilic acid; benzimide, &c...................438 Hippuric acid...................439 Homologues of benzoyl-series..............441 Salicin ; salicyl and its compounds............442 Chlorosamide.—Phloridzin.—Cumarin..........443 Cinnamyl and its compounds; cinnamic acid; chloro-cinnose . . . 445 Vegetable acids..................448 Tartaric acid...................448 Racemic acid...................451 Citric acid.........'...........451 Aconitic or equisetic acid...............452 Malic acid....................453 Fumaric and maleic acids...............454 . Meconic acid.................. . 454 Kinic acid ; Kinone and hydrokinone...........455 Tannic and gallic acids...............456 AZOTIZED ORGANIC PRINCIPLES OF SIMPLE CONSTITUTION......460 Cyanogen ; paracyanogen ; hydrocyanic acid........460 Amygdalin; amygdalic acid..............463 Metallic cyanides.................464 Cyanic, cyanuric, and fulminic acids...........466 Chlorides, &c, of cyanogen.............' . 470 Ferro- and ferricyanogen, and their compounds ; Prussian blue. . . 470 Cobalticyanogen..................474 Sulphocyanogen, and its compounds; selenocyanogen; melam; mela- mine ; ammeline ; ammelide.............474 Urea, and uric acid. •...........''.....477 Allantoin; alloxan; alloxanic acid ; mesoxalic acid; mykomelinic acid • parabanic acid; oxaluric acid ; thionuric acid; uramile ; alloxatin ■ murexide; murexan................479 Xanthic and cystic oxides............ 434 The vegeto-alkalis, and allied bodies....... > 4gg Morphine, and its salts............ 4g^ Narco^ine ; opianic and hemipinic acids; cotarnine . . . . 4gg Codeine: thebainc ; pseudo-morphine ; narceine ; meconinc .... 487 CONTENTS. XVU Cinchonine and quinine ; quinoidine...........487 Strychnine and brucine; veratrine ; conicine; nicotine; sparteine; har- maline....................489 Harmine ; caffeine or theine; theobromine ; berberine; piperiue ; hyoscyamine ; atropine ; solanine; aconitine; delphinine ; emetine; curarine....................490 Gentianin ; populin; daphnin; hesperidin ; elaterin; antiarin ; picro- toxin ; asparagin ; santonin.............491 Organic bases of artificial origin...........492 Bases of the ethyl-series.—Ethylamine; biethylamine; triethylamine; oxide of tetrethyl-ammonium.............494 Bases of the methyl-series.—Methylamine; bimethylamine; trimethy- lamine; oxide of tetramethyl-ammonium.........497 Bases of the amyl-series. — Amylamine ; biamylamine ; triamylamine ; oxide of tetramyl-ammonium.............498 Bases of the phenyl-series. — Aniline ; chloraniline ; nitraniline ; cy- aniline; melaniline ................498 Bases homologous to aniline. — Toluidine; xylidine ; cumidine. Naph- thalidine....................502 Mixed bases.—Ethylaniline; biethylaniline; oxide of triethylamyl-am- monium; biethylamylamine; oxide of mcthylobiethylamyl-ammo- nium ; mcthylcthylamylamine; ethylamylaniline; oxide of methyl- etliyl-amylo-phenyl-ammonium............503 Methylated and ethylatcd derivatives of natural bases......504 Basi:s of uncertain constitution............506 Chinoline; kyanol; leucol; picoliue............506 Petinine....................507 Furfurine ; fucusine........... .....507 Amarine; thiosinnamine...............508 Thialdiue; alanine.................508 Phosphorus-bases.................509 Antimony-bases...................510 Arsenic-bases............, ..... . 510 Organic coloring'trincitles..............513 Iudigo; white indigo ; sulphiudylic acid..........513 Isatin; anilic and picric acids ; chrysanilic and anthranilic acids . . 515 Lichens, litmus; lccauorin; orcin; orcein, &c.........517 Cochineal, madder, dye-woods, &c.............520 Chrysammic, chrysolepic, and styphnic acids........522 Volatile oils.—Oils of turpcntin, lemons, aniseed, cumin, cedar, Gaul- theria, valerian, peppermint, lavender, rosemary, orange-flowers, ro 120 Structure of flame...................177 121 Mouth blowpipe . . .*.................177 122 Structure of blowpipe flame................178 123 Argand spirit-lamp...................178 124 Common " ...................178 125 Mitchell's " ...................179 126 Gas lamp......................179 127 Davy's §afe lamp....................180 128 Hemming's safety-jet..................180 129 Effect of metallic coil..................180 130 Apparatus for sulphuretted hydrogen.............I83 131 Multiple proportions ................. ^ 201 132 Water in its usual state............. 209 133 " undergoing electrolysis........... 209 134 Voltameter.................... ^ 210 135 Decomposition without contact of metals........ a\\ 136 Wollaston's voltaic battery............. 213 137 Daniell's constant ".............. 213 138 Grove's " " ................214 139 Bunsen's carbon cylinder............. 215 140 Electrotype....................215 141 Lead-tree................... 216 142 Wire-drawing.................. ^ 21g 143 Wollaston's goniometer............... 223 144 Reflecting " .................224 145 " " principles of.............224 116 Crystals, regular system.................225 \ LIST OF ILLUSTRATIONS. xxiii 147 Crystals, square prismatic system........... 226 148 149 150 151 152 153 right prismatic system..............226 oblique prismatic system..............226 doubly oblique prismatic system...........227 rhombohedral system........... _ 228 passage of cube to octahedron............228 " octahedron to tetrahedron.........229 154 Alkaliraeter........... ... *>-l5 100 .....................246 156 Gay-Lussac's.............. _ 246 15? " "................. 246 158 « Mohr's...................246 159 " clamp, Mohr's............ 247 160 Apparatus for determining carbonic acid......... # 247 161 " " "...... . '. '. '. '. '. 248 162 Iron manufacture. Blast-furnace........ 2S2 163 Crystals of arsenious acid........... 311 164 Subliming tube for arsenic.......... 312 165 Marsh's apparatus.............. 3J3 166 Weighing tube, for organic analysis.............338 167 Combustion " " ...... ->og 168 Chauffer " " ...... 339 169 Water-tube " " ........ 340 170 Carbonic acid bulbs " " ........ 34q 171 Apparatus complete " " ....... o,q 172 Gas apparatus " " ......... 3H 173 " section of five rows........., .341 174 " "* three rows........... 341 175 Bulb for liquids, for organic analysis........... .312 176 Comparative determination of nitrogen.......... , 343 177 Pipette.......................343 178 Absolute estimation of nitrogen............ # 344 179 Varentrap's and Will's method...............345 180 Determination of the density of vapors............348 181 Starch granules....................357 182 Preparation of ether..................378 183 " defiant gas................380 184 " Dutch liquid................380 1S5 Catalysis.......................339 186 Preparation of kakodyle.................408 XXIV LIST OF ILLUSTRATIONS. 187 Preparation of benzoic acid................4^3 188 " tannioacid................456 189 Uric acid crystals....................*79 190 Blood globules....................552 191 Trommer's test.....................560 192 Uric acid calculus...................561 193 Urate of ammonia calculus................562 194 Fusible calculus....................562 195 Mulberry calculus...................562 196 Pus globules.....................567 197 Milk "......................568 A MANUAL OF CHEMISTRY. INTRODUCTION. The Science of Chemistry has for its object the study of the nature and properties of all the materials which enter into the composition or structure of the earth, the sea, and the air, and of the various organized or living "beings which inhabit these latter. Every object accessible to man, or which may be handled and examined, is thus embraced by the wide circle of Chemical Science. The highest efforts of Chemistry are constantly directed to the discovery of the general laws or rules which regulate the formation of chemical com- pounds, and determine the action of one substance upon another. These laws are deduced from careful observation and comparison of the properties and relations of vast numbers of-individual substances; — and by this method alone. The science is entirely experimental, and all its conclusions the results of skilful and systematic experimental investigation. The applications of the discoveries of Chemistry to the arts of life, and to the relief of human suffering in disease, are, in the present state of the science, both very numerous and very important, and encourage the hope of still greater benefits from more extended knowledge than that now enjoyed. In ordinary scientific speech the term chemical is applied to changes which permanently affect the properties or characters of bodies, in opposition to effects termed physical, which are not attended by such consequences. Changes of decomposition or combination are thus easily distinguished from those temporarily brought about by heat, electricity, magnetism, and the at- tractive forces, whose laws and effects lie within the province of Physics or Natural Philosophy. Nearly all the objects presented by the visible world are of a compound nature, being chemical compounds, or variously-disposed mixtures of chemical compounds, capable of being resolved into simpler forms of matter. Thus, a piece of limestone or marble by the application of a red-heat is decomposed 4 (37) 38 INTRODUCTION. into quicklime and a gaseous body, carbonic acid. Both lime and carbomo acid are in their turn susceptible of decomposition, the former into a metal, calcium, and oxygen, and the latter into carbon and oxygen. For this pur- pose, however, simple heat does not suffice, the resolution of these substances into their components demanding the exertion of a high degree of chemical energy. Beyond this second step of decomposition the efforts of Chemistry have hitherto been found to fail; and the three bodies, calcium, carbon, and oxygen, having resisted all attempts to resolve them into simpler forms of matter, are accordingly admitted into the list of elements; — not from any belief in their real oneness of nature, but from the absence of any evidence that they contain more than one description of matter. The partial study of certain branches of Physical Science, as the physical constitution of gases, the chief phenomena of heat and electricity, and a few other subjects, forms such an indispensable introduction to Chemistry itself that it is rarely omitted in the usual courses of oral instruction. A sketch of these subjects is, in accordance with these views, placed at the commence ment of the present volume. • PART I.—PHYSICS. OF DENSITY AND SPECIFIC GRAVITY. It is of great importance in the outset to understand clearly what is meant by the term density and specific gravity. By the density of a body is meant its mass, or quantity of matter, compared with the mass or quantity of matter of an equal volume of some standard body, arbitrarily chosen. Specific gravity denotes the weight of a body, as compared with the weight of an equal bulk, or volume of the standard body, which is reckoned as unity.1 In all cases of solids and liquids this standard of unity is pure water at the temperature of G0° Fahr. (15°-5C). Anything else might have been chosen; there is nothing in water to render its adoption for the purpose mentioned indispen- sable ; it is simply taken for the sake of convenience, being always at hand, and easily obtained in a state of perfect purity. An ordinary expression of specific weight, therefore, is a number explaining tow many times the weight of an equal bulk of water is contained in the weight of the substance spoken of. If, for example, we say, that concentrated oil of vitriol has a specific gravity equal to 1-85, or that perfectly pure alcohol has a density of 0-794 at 60° F., we mean that equal bulks of these two liquids and of distilled water possess weights in the proportion of the numbers 1-85, 0-794, and 1; or 1850, 704, and 1000. It is necessary to be particular about the temperature, for, as will be hereafter shown, liquids are extremely expansible by heat; other- wise a constant bulk of the same liquid will not retain a constant weight. It will be proper to begin with the description of the mode in which the specific gravity of liquids is de- Fig. 1. termined: this is the simplest case, and the one which ^_____y best illustrates the general principle. \ / In order to obtain at pleasure the specific gravity of any particular liquid compared with that of water, it is only requisite to weigh equal bulks at the standard temperature, and then divide the weight of the liquid by the weight of the water; the quotient will of course be greater or less than unity, as the liquid experimented on is heavier or lighter than water. Now, to weigh equal bulks, of two fluids, the simplest and best method is clearly to weigh them in succession in the same vessel, taking care that it is equally full on both occasions, a condition very easy of fulfilment. A thin glass bottle, or flask, with a narrow neck, is procured, of the figure represented in the mar- gin (fig. 1), and of such capacity as to contain, when filled to about half-way up the neck, exactly 1000 grains of distilled water at 60° (15°-5C). Such a flask is readily pro- 1 In other words, density means comparative mass, and specific gravity comparative weight. These expressions, although really relating to distinct things, are often used quite indiffe- rently in chemical writings, and without practical inconvenience, since mass and weight are directly proportional to each, other. (39) 40 DENSITY AND SPECIFIC GRAVITY. cured from any one of the Italian artificers, to be found in every large town, who manufacture cheap thermometers for sale. A counterpoise of the exact weight of the empty bottle is made from a bit of brass, an old weight, or something of the kind, and carefully adjusted by filing; an easy task. The bottle is then graduated, by introducing water at 60°, until it exactly balances the 1000-grain weight and counterpoise in the opposite scale ; the height at which the water stands in the neck is marked by a scratch, and the instru- ment is complete for use. The liquid to be examined is brought to the tem- perature 60°, and with it the bottle is filled up to the mark before mentioned; it is then weighed, the counterpoise being used as before, and the specific gravity directly ascertained. A watery liquid in a narrow glass tube always presents a curved surface, from the molecular action of the glass, the concavity being upwards. It is better, on this account, in graduating the bottle, to make two scratches as represented in the drawing, one at the top and the other at the bottom of the curve: this prevents any future mistake. The marks are easily made by a fine, sharp, triangular file, the hard point of which, also, it may be observed, answers perfectly well for writing upon glass, in the absence of a proper diamond-pencil. It will be quite obvious that the adoption of a flask holding exactly 1000 grains of water has no other object than to save the trouble of a very trifling calculation; any other quantity would answer just as well, and, in fact, the experimental chemist is often compelled to use a bottle of much smaller dimensions, from scarcity of the liquid to be examined. When the specific gravity of a liquid is to be determined with great accuracy, a case which frequently occurs in chemical inquiries, a little glass bottle is used, which is illustrated by fig. 2. This bottle is provided with a perforated conical glass stopper, most accurately fitted by grinding. By completely filling the little bottle with liquid, and by carefully removing the portion of liquid which is displaced when the stopper is inserted, an unalterable measure is obtained. The least possible quantity of grease applied to the stopper greatly promotes the exact fitting. When the chemist has only a very small quantity of a fluid at his dis- posal, and wishes not to lose it, the little glass vessel (fig. 3) is particularly useful. It is formed by blowing a bubble on a glass tube. On that por- tion of the tube which is narrowed by drawing the 'tube out over a lamp, a fine scratch is made with a diamond. The bubble is filled up to this mark with the fluid whilst it stands in water, the temperature of which is exactly known. A very fine funnel is used for filling the bubble, the stem of the funnel being drawn out so as to enter the tube, and the upper opening of the funnel being small enough to be closed by the finger. The glass stopper is only wanted as a guard, and does not require to fit perfectly. The determination of the specific gravity of a solid body is made according to the same principles, and may be performed with the specific. Fig. 3. DENSITY AND SPECIFIC GRAVITY. 41 gravity bottle (fig. 2). The little bottle is first weighed full of water, the solid is then placed in the same pan of the balance, and its weight-determined; finally, the solid is put into the bottle, displacing an equal bulk of water, the weight of which is determined by the loss on again weighing. Thus the weights of the solid and that of an equal bulk of water are obtained. The former divided by the latter gives the specific gravity. For example, the weight of a small piece of Silver wire was found to be . Glass bottle filled with water . After an equal volume of water was displaced by the silver, the weight was..... 98-18 grains. 294-69 " 392-87 383-54 Hence the displaced water weighed From this, the specific gravity of the) 98-18 9-33 silver wire / 9-33 = 10-502 " Another highly ingenious, but less exact method of determining the specific- gravity of solids, is based on the well-known theorem of Archimedes. This theorem may be thus expressed: — When a solid is immersed in a fluid, it loses a portion of its weight; and this portion is equal to the weight of the fluid which it displaces ; that is, to the weight of its own bulk of that fluid. Fig. 4. It is easy to give experimental proof of this very important proposition, as well as to establish it by reasoning. The drawing, fig. 4, represents a little apparatus for the former purpose. This consists of a thin cylindrical vessel of brass, into the interior of which fits very accurately a solid cylinder of the same metal, thus exactly filling it. When the cylin- der is suspended beneath the bucket, as seen in the sketch, the whole hung from the arm of a balance, and counterpoised, and then the cylinder itself immersed in water, it will be found to have lost a certain weight; and that this loss is precisely equal to the weight of an equal bulk of water, may then be proved by filling the bucket to the brim, whereupon the equilibrium will be restored. The consideration of the great hydrostatic law of fluid pressure easily proves the truth of the principle laid down. Let the reader figure to himself a vessel of water, having immersed in it a solid cy- lindrical or rectangular body, and so adjusted with respect to density, that it shall float indifferently in any part beneath the surface (fig. 5)- Now the law of fluid pressure is to this effect: — The pi-essure ex- erted by a fluid upon the contain- ing vessel, or upon anything plunged beneath its sur- face, depends, first, upon the density of that fluid, and, secondly, upon the perpendicular height of the column. It is independent of the form and late- 4* Fig. 5. 42 DENSITY AND SPECIFIC GRAVITY. ral dimensions of the vessel or immersed body. Moreover, owing to the peculiar physical constitution of fluids, this pressure is exerted equally in every direction, upwards, downwards, and laterally, with equal foroe. The floating body is in a state of equilibrium; therefore the pressure down- wards caused by its gravitation must be exactly compensated by the upward transmitted pressure of the column of water, a, b. But this pressure downwards is obviously equal to the weight of an equal quantity of water, since the body of necessity displaces its own bulk. Hence, the weight lost or supported by the water, is the weight of a volume of water equal to that of the body immersed. Whatever be the density of the substance, it will be buoyed up to this amount; in the case supposed, the buoyancy is equal to the whole weight of the body, which is thus, while in the water, reduced to nothing. A little reflection will show that the same reasoning may be applied to a body of irregular form; besides, a solid of any figure may be divided by the imagination into a multitude of little perpendicular prisms or cylin- ders, to each of which the argument may be applied. What is true of each individually must necessarily be true of the whole together. This is the fundamental principle; its application is made in the following manner: — Let it be required, for example, to know the specific gravity of a body of ex- tremely irregular form, as a small group of rock crystals; the first part of the operation consists in determining its absolute weight, or, more correctly speaking, its weight in air; it is next suspended from the "balance- pan by a fine horse-hair, immersed completely in pure water at 60° (15°-5C), and again weighed. It now weighs less, the difference being the weight of the water it displaces, that is, the weight of an equal bulk. This being known, nothing more is required than to find, by division, how many times the latter number is contained in the former; the quotient will be the density, water being taken = 1. For example: — The quartz-crystals weigh in air When immersed in water, they weij 293-7 grains. 180-1 " Difference, being the weight of an equal volume of water.........113-6 " 293-7 - = 2-58, the specific gravity required. • 1 lo*o The arbitrary rule is generally thus written: "Divide the weight in air by the loss of weight in water, and the quotient will be the specific gravity." In reality it is not the weight in air which is required, but the weight the body would have in empty space: the error introduced, namely, the weight of an equal bulk of air, is so trifling that it is usually neglected. Sometimes the body to be examined is lighter than water, and floats. In this case, it is first weighed, and afterwards attached to a piece of metal, heavy enough to sink it, and suspended from the balance. The whole is then exactly weighed, immersed in water, and again weighed. The differ- ence between the two weighings gives the weight of a quantity of water equal in. bulk to both together. The light substance DENSITY AND SPECIFIC GRAVITY. 43 183-7 38-8 << 144-9 << 50-0 44-4 5-6 (< 144-9 5-6 u is then detached, and the same operation of weighing in air, and again in water, repeated on the piece of metal. These data give the means of finding the specific gravity, as will be at once seen by the following example: — Light substance (a piece of wax) weighs in air . . 133-7 grains. Attached to a piece of brass, the whole now weighs Immersed in water, the system weighs Weight of water, equal in bulk to brass and wax Weight of brass in air...... Weight of brass in water..... Weight of equal bulk of water . Bulk of water equal to wax and brass Bulk of water equal to brass alone .... Bulk of water equal to wax alone . . . .139-3 In all such experiments, it is necessary to pay attention to the temperature and purity of the water, and to remove with great care all adhering air- bubbles ; otherwise a false result will be obtained. Other cases require mention in which these operations must be modified to meet particular difficulties. One of these happens when the substance is dis- solved or acted upon by water. This difficulty is easily overcome by substi- tuting some other liquid of known density which experience shows is without action. Alcohol or oil of turpentine may generally be used when water is inadmissible. Suppose, for instance, the specific gravity of crystallized sugar is required, we proceed in the following way:—The specific gravity of the oil of turpentine is first carefully determined; let it be 0-87 ; the sugar is next weighed in the air, then suspended by a horse hair, and weighed in the oil; the difference is the weight of an equal bulk of the latter; a simple calculation gives the weight of a corresponding volume of water: — Weight of sugar in air ...... 400 grains. Weight of sugar in oil of turpentine . . . . 182-5 " Weight of equal bulk of oil of turpentine . . 217-5 " 87: 100 = 217-5: 250, the weight of an equal bulk of water; hence the specific gravity of the sugar,— 2o0 If the substance to be examined consists of small pieces, or of powder, then the method first described, namely, that of the specific-gravity bottle, can alone be used. By this method the specific gravities of metals in powder, metallic oxides, and other compounds, and salts of all descriptions, may be determined with great ease. Oil of turpentine may be used with most soluble salts. The crystals should be crushed or roughly powdered to avoid errors arising from cavities in their substance. The theorem of Archimedes affords the key to the general doctrine of the 44 DENSITY AND SPECIFIC GRAVITY. Fig. 8. equilibrium of floating bodies, of which an application is made in the common hydrometer, — an instrument for finding the specific gravities of liquids in a very easy and expeditious manner. When a solid body is placed upon the surface of a fluid specifically heavier than itself, it sinks down until it displaces a quantity of fluid equal to its own weight, at which point it floats. Thus, in the case of a sub- stance floating in water, whose specific weight is one-half that of the fluid, the position of equilibrium will involve the immer- sion of exactly one-half of the body, inasmuch as its whole weight is counterpoised by a quantity of water equal to half its volume. If the same body were put into a fluid of one-half the specific gravity of water, if such could be found, then it would sink beneath the surface, and remain indifferently in any part. A floating body of known specific gravity may thus be used as an indicator of the specific gravity of a fluid. In this manner little glass beads (fig. 8) of known specific gravities are some- times employed in the arts to ascertain in a rude manner the specific gravity of liquids; the one that floats indifferently beneath the surface, without either sinking or rising, has of course the same specific Fig.9. gravity as the liquid itself; this is pointed out by the number marked upon the bead. The hydrometer (fig. 9) in general use consists of a floating vessel of thin metal or glass, having a weight beneath to maintain it in an upright position, and a stem above bearing a divided scale. The use of the instrument is very simple. The liquid to be tried is put into a small narrow jar, and the instrument floated in it. It is obvious that the denser the liquid, the higher will the hydrometer float, because a smaller displacement of fluid will counterbalance its weight. For the same reason, iu a liquid of less density it sinks deeper. The hydrometer comes to rest almost immediately, and then the mark on the stem at the fluid-level may be read off. Very extensive use is made of instruments of this kind in the arts: they sometimes bear different names, according to the kind of liquid for which they are intended; but the principal is the same in all. The graduation is very commonly arbi- trary, two or three different scales being unfortunately used. These may be sometimes reduced, however, to the true numbers expressing the specific gravity by the aid of tables of comparison drawn up for the purpose. The division of the instrument from below, upwards into 100 parts is much to be preferred to these arbitrary scales. Half of these divisions must be made upon the stem. The 100th division indicates the point of immersion in distilled water at 60° Fahr. (15°-5C.) If in another fluid the instrument sinks less deeply, for example to 60 then 60 volumes of this fluid weigh as much as 100 volumes of water. Hence the weight of 100 volumes, that is, the specific gravity, is ig°ff0 = l-67. By this arrangement of the scale it is evident that the reduction of the specific gravity is so simple that no tables are required. A very convenient and useful instrument in the shape of a small hydrometer for taking the specific gravity of urine, has lately been put DENSITY AND SPECIFIC GRAVITY. 45 Into the hands of the physician;1 it may be packed into a pocket-case, with a little jar and a thermometer, and is always ready for use.2 The determination of the specific gravity of gases and vapors of volatile liquids is a problem of very great practical importance to the chemist: the theory of the operation is as simple as when liquids themselves are concerned, but the processes are much more delicate, and involve besides certain correc- tions for differences of temperature and pressure, founded on principles yet to be discussed. It will be proper to defer the consideration of these matters for the present. The method of determining the specific gravity of a gas will be found described under the head of "Oxygen," and that of the vapor of a volatile liquid in the Introduction to Organic Chemistry.3 1 This and other instruments described or figured in the course of the work, may be had of Messrs. Murray and Heath, 43 Piccadilly, upon the excellence of whose workmanship reliance may be placed. 1 [The graduation of the urinometer is such that each degree represents 1-1000, thus giving the actual specific gravity without calculation, for the number of degrees on the scale cut by the surface of the liquid when this instrument is at rest, added to 1000 will represent the density of the liquid. If, for example, the surface of the liquid coincide with 23 on the scale, the specific gravity will be 1023, about the average density of healthy urine. — K. B.] I3 The mode of determining the specific-gravity of a liquid by means of a solid Fig. 11. has been omitted in the text. It results from the theorem of Archimedes, that if any solid be immersed in water and then in any other liquid, the loss of weight sustained in each case will give the relative weights of equal bulks of the liquids, and on dividing the weight of the liquid by the weight of the water, the quotient will be the specific-gravity of the liquid experimented on. For in- stance, let a piece of glass rod be suspended from the balance-pan and exactly counterpoised, then immerse it in water and restore the equipoise by weights added to the pan to which the glass is suspended, the amount will give the loss of weight by immersion or the weight of a bulk of water equal to that of the rod. Now wipe the glass dry, and having removed the additional weights, im- merse it in the other.liquid, and restore the equipoise as before; this latter weight is the weight of a bulk of the liquid equal to that of the water. The latter divided by the former gives the specific-gravity. For example : — The glass rod loses by immersion in water..................... Tho glass rod loses by immersion in alcohol...................., — =z -836 the specific-gravity required. — R. B.J 171 grains. 143 46 PHYSICAL CONSTITUTION OF THE PHYSICAL CONSTITUTION OF THE ATMOSPHERE AND OF GASES IN GENERAL. Fig. 12. It requires some little abstraction of mind to realize completely the singu- lar condition in which all things at the surface of the earth exist. We live at the bottom of an immense ocean of gaseous matter, which envelopes everything, and presses upon everything with a force which appears, at first sight, perfectly incredible, but whose actual amount admits of easy proof. Gravity being, so far as is known, common to all matter, it is natural to expect that gases, being material substances, should be acted upon by the earth's attraction, as well as solids and liquids. This is really the case, and the result is the weight or pressure of the atmosphere, which is nothing more than the effect of the attraction of the earth on the particles of air. Before describing the leading phenomena of the atmospheric pressure, it is necessary to notice one very remarkable feature in the physical constitution of gases, upon which depends the principle of an extremely valuable instru- ment, the air-pump. Gases are in the highest degree elastic; the volume or space.which a gas occupies depends upon the pressure exerted upon it. Let the reader imagine a cylinder, a, closed at the bottom, in which moves a piston, air-tight, so that no air can escape between the piston and the cylinder. Suppose now the piston be pressed downwards with a certain force; the air beneath it will be compressed into a smaller bulk, the amount of this compression depending on the force applied; if the power be sufficient, the bulk of the gas may be thus diminished to the one hundredth part or less. When the pressure is removed, the elasticity or tension, as it is called, of the included air or gas, will immediately force up the piston until it arrives at its first position. Again, take fig. b, and suppose the piston to stand about the middle of the cylinder, having air beneath in its usual state. If the piston be now drawn upwards, the air below will expand, so as to fill completely the increased space, and this to an apparently unlimited extent. A volume of air, which under ordinary circum- stances occupies the bulk of a cubic inch, might, by the removal of the pres- sure upon it, be made to expand to the capacity of a whole room while a re- newal of the former pressure would be attended by a shrinking down of the air to its former bulk. The smallest portion of gas introduced into a laro-e exhausted vessel becomes at once diffused through the whole space, an equal quantity being present in every part; the vessel is full although the gas is in a state of extreme tenuity. This power of expansion which air possesses may have, and probably has, jn reality, a limit; but the limit is never reached in practice. We are quite safe in the assumption, that for all purposes of experiment, however refined, air is perfectly elastic. OF THE ATMOSPHERE. 47 It is usual to assign a reason for this indefinite expansibility by ascribing to the particles of material bodies, when in a gaseous state, a self-repulsive agency. This statement is commonly made somewhat in this manner: matter is under the influence of two opposite forces, one of which tends to draw the particles together, the other to separate them. By the preponderance of one or other of these forces, we have the three states called solid, liquid, and gaseous. When the particles of matter, in consequence of the direction and strength of their mutual attractions, possess only a very slight power of motion, a solid substance results; when the forces are nearly balanced, we have a liquid, the particles of which in the interior of the mass are free to move, but yet to a certain extent are held together; and, lastly, when the at- tractive power seems to be completely overcome by its antagonist, we have a gas or vapor. Various names are applied to these forces, and various ideas entertained concerning them: the attractive forces bear the name of cohesion when they are exerted between particles of matter separated by an immeasurably small interval, and gravitation when the distance is great. The repulsive principle is often thought to be identical with the principle of heat. The ordinary air-pump, shown in section in fig. 13, consists essentially of a metallic cylinder, in which moves a tightly-fitting piston, by the aid of its Fig. 13. 1/ IF rod. The bottom of the cylinder communicates with the vessel to be ex- hausted, and is furnished with a valve opening upwards. A similar valve, also opening upwards, is fitted to the piston; these valves are made with slips of oiled silk. When the piston is raised from the bottom of the cylinder, the space left beneath it must be void of air; since the piston-valve opens only in one direction; the air within the receiver, having on that side nothing to oppose its elastic power but the weight of the little valve, lifts the latter, and escapes into the cylinder. So soon as the piston begins to descend, the lower valve closes, by its own weight, or by the transmitted pressure from above, and communication with the receiver is cut off. As the descent of the piston continues, the air included within the cylinder becomes compressed, its elas- ticity is increased, and at length it forces open the upper valve, and escapes into the atmosphere. In-this manner, a cylinder full of air is at every stroke f the pump removed from the receiver. During the descent of the piston, 48 PHYSICAL CONSTITUTION the upper valve remains open, and the lower closed, and the reverse during the opposite movement. In practice, it is very convenient to have two such barrels or cylinders, ar- Fig. 14. ranged side by side, the piston-rod3 of which are formed into racks, having a pinion, or small-toothed wheel, between them, moved by a winch. By this contrivance the operation of exhaustion is much facilitated Fig. 15. and the labor lessened. The arrangement is shown in fig. 14. A simpler form of air-pump is thus constructed: the cylinder, which may be of large dimensions, is furnished with an accurately-fitted solid piston, the rod of which moves, air-tight, through a contrivance called a stuffing- b'ox, at the top of the cylinder, where also the only valve essential to the apparatus is to be found: the latter is a solid conical plug of metal, shown at a in the figure, kept tight by the oil contained in the chamber into which it opens. The communication with the vessel to be exhausted, is made by a tube which enters the cylinder a little above the bottom. The action is the following: let the piston be supposed in the act of rising from the bottom of the cylin- der ; as soon as it passes the mouth of the tube t, all com- munication is stopped between the air above the piston and the vessel to be exhausted; the enclosed air suffers com- pression, until it acquires sufficient elasticity to lift the metal valve and escape by bubbling through the oil. When ^t the piston makes its descent, and this valve closes a vacuum is left in the upper part of the cylinder, into which the air of the receiver rushes so soon as the piston has passed below the orifice of the connecting tube. In the silk-valved air-pump, exhaustion ceases when the elasticity of the air in the receiver becomes too.feeble to raise the valve: in that last de- OF THE ATMOSPHERE. 49 scribed, the exhaustion may, on the contrary, be carried to an indefinite extent, without, however, under the most favorable circumstances, becoming complete. The conical valve is made to project a little below the cover of the cylinder, so as to be forced up by the piston when the latter reaches the top of Fig. 16. the cylinder; the oil then enters and dis- plao.-s any air that may be lurking in the cavity. It is a great improvement to the machine to supply the piston with a relief-valve opening upwards; this may also be of metal, and contained within the body of the piston. Its use is to avoid the momentary condensation of the air in the receiver when the piston descends. The pump is worked by a lever in the manner represented in fig. 16. The air-pump may be used for condens- ing instead of for rarefying the air. If the cylinder (fig. 15) is filled with air from the opening (t), by the rise of the piston it may be compressed as it passes through the valve (a), into a communica- ting chamber, and this operation may be frequently repeated. To return to the atmosphere. Air pos- sesses weight: a light flask or globe of glass, furnished with a stop-cock and ex- hausted by the air-pump, weighs con- siderably less than when full of air. If the capacity of the vessel be equal to 100 cubic inches, this difference may amount to nearly 30 grains. The mere fact of the pressure of the atmosphere may be demonstrated by se- curely tying a piece of bladder over the mouth of an open glass receiver, and then exhausting the air from beneath it; the bladder will become more and more concave, until it suddenly breaks. A thin square glass bottle, or a large air- tight tin box, may be crushed by with- drawing the support of the air in the in- side. Steam-boilers have been often de- stroyed in this manner by collapse, in consequence of the accidental formation of a partial vacuum within. After what has been said on the subject of fluid pressure, it will scarcely bo necessary to observe that the law of equality of pressure in all directions also holds good in the case of the atmosphere. The perfect mobility of the particles of air permits the transmission of the force generated by their gravity. The sides and bottom of an exhausted vessel are pressed upon with as much force as the top. If a glass tube of considerable length could be perfectly exhausted of air, and then held in an upright position, with one of its ends dipping into a vessel of liquid, the latter, on being allowed access to the tube, would rise in its inte- rior until the weight of the column balanced the pressure of the air upon the 6 bO PHYSICAL CONSTITUTION surface of the liquid. Now, if the density of this liquid wore known, and the height and area of the column measured, means would be furnished for exactly estimating the amount of pressure exerted by the atmosphere. Fig. 17. Such an instrument is the barometer: a straight glass tube is n taken, about 36 inches in length, and sealed by the blowpipe flame at one extremity ; it is then filled with clean, dry mercury, care being taken to displace all air-bubbles, the open end stopped with a finger, and the tube inverted in a basin of mercury. On _ removing the finger, the fluid sinks away from the top of the | tube, until it stands at the height of about 30 inches above the level of that in the basin. Here it remains supported by, and I balancing the atmospheric pressure, the space above the mer- cury in the tube being of necessity empty. The pressure of the atmosphere is thus seen to be capable of sustaining a column of mercury 30 inches in height, or there- abouts : now such a column, having an area of one inch, weighs between 14 and 15 pounds, consequently such must be the amount of the pressure exerted upon every square inch of the surface of the earth, and of the objects situated thereon, at least near the level of the sea. This enormous force is borne without inconvenience by the animal frame, by reason of its perfect uni- formity in every direction, and it may be doubled, or even tripled without injury. A barometer may be constructed with other liquids besides mercury; but, as the height of the column must always bear an inverse proportion to the density of the liquid, the length of tube required will be often considerable; in the case of water it will exceed 33 feet. It is seldom that any other liquid than mer- cury is employed in the construction of this instrument. The Royal Society of London possessed a water-barometer at their apartments at Somerset House. Its construction was attended with great difficulties, and it was found impossible to keep it in repair. It will now be necessary to consider a most important law which connects the volume occupied by a gas with the pressure made upon it, and which is thus expressed :— The volume of a gas is inversely as the pressure; the density and elastic force are directly as the pressure, and inversely as the volume. For instance, 100 cubic inches of gas under a pressure of 30 inches of mer- cury would expand to 200 cubic inches were the pressure reduced to one-half, and shrink, on the contrary, to 50 cubic inches if the original pressure were doubled. The change of density must necessarily be in the inverse propor- tion to that of the volume, and the clastic force follows the same rule. This, which is usually called the law of Mariotte, though really discovered by Boyle (1661), is easily demonstrable by direct experiment. A glass tube, about 7 feet in length, is closed at one end, and bent into the form represented in fig. 18, the open limb of the syphon being the longer. It is next attached to a board furnished with a movable scale of inches, and enough mercury is introduced to fill the bend, the level being evenly adjusted, and marked upon the board. Mercury is now poured into the tube until it is found that the enclosed air has been reduced to one-half of its former volume ; and on apply- ing the scale, it will be found that the level of the mercury in the open part of the tube stands very nearly 30 inches above that in the closed portion. The pressure of an additional "atmosphere" has consequently reduced the bulk of the contained air to one-half. If the experiment be still continued until OF THE ATMOSPHERE. 51 Height above the sea. in miles. 0 ............. Vol lime of air. . 1 ............ . 4 ............ Hei ;ht of barometer, in inches. .... 30 2-705 ............. .... 15 6-41 ............. .... 7-5 §•115 ............. , 8 ............ .... 3-75 13-525 ............ . 16 ............ . 32 ............ .... 0-9375 1623 ............. the volume of air is reduced to a third, it will be found that the'column mea- sures 60 inches, and so in like proportion as far as the experiment is carried. The above instrument is better adapted for illustra- tion of the principle than for furnishing rigorous proof Fig. 18. of the law; this has, however, been done. MM. Arago and Dulong published, in the year 1830, an account of certain experiments made by them in Paris, in which the law in question had been verified to the extent of 27 atmospheres. And with rarefied air, of whatever degree of rarefaction, the law has been found true. All gases are alike subject to this law, and all vapors of volatile liquids, when remote from their points of liquefaction.1 It is a matter of the greatest importance in practical chemistry, since it gives the means of making corrections for pressure, or determining by cal- culation the change of volume which a gas would suffer by any given change of external pressure. Let it be required, for example, to solve the following problem:—We have 100 cubic inches of gas in a gradu- ated jar, the barometer standing at 29 inches; how many cubic inches will it occupy when the column rises to 30 inches ?—Now the volume must be inversely as the pres- sure ; consequently a change of pressure in the propor- tion of 29 to 30 must be accompanied by a change of volume in the proportion of 30 to 29; 30 cubic inches of gas contracting to 29 cubic inches under the conditions imagined. Hence the answer:— 80 : 29 = 100 : 96-67 cubic inches. The reverse of the operation will be obvious. The prac- tical pupil will do well to familiarize himself with these simple calculations of correction for pressure. From what has been said respecting the easy com- pressibility of gases, it will be at once seen that the atmosphere cannot have the same density, and cannot exert equal pressures at different elevations above the sea-level, but that, on the contrary, these must diminish with the altitude, and very rapidly. The lower strata of air have to bear the weight of those above them; they become, in consequence, denser and more compressed than the upper portions. The following table, which is taken from Prof. Graham's work, shows in a very simple manner the rule followed in this respect:— o-l---1 The numbers in the first column form an arithmetical series, by the constant addition of 2-70-"); those in the second column an increasing geometrical, series, each being double its predecessor; and those in the third, a decreasing geo- metrical series, in which each number is the half of that standing above it. 1 When near the liquefying point the law no longer holds; the volume diminishes more rapidly than the theory indicates, a smaller-amount of pressure being then sufficient. 52 PHYSICAL CONSTITUTION OP THE ATMOSPHERE. In ascending into the air in a balloon, these effects are well observed; the expansion of the gas within the machine, and the fall of the mercury in the barometer, soon indicate to the voyager the fact of his having Fig. 19. left below him a considerable part of the whole atmosphere. The invention of the barometer, which took place in the year 1643, by Torricelli, a pupil of the celebrated Galileo, speedily led to the observation that*the atmospheric pressure at the same level is not constant, but possesses, on the contrary, a small range of variation, seldom exceeding in Europe 2 or 2-5 inches, and within the tropics usually confined within much narrower limits. Two kinds of variations are distinguished; regular or horary, and irregular or accidental. It has been observed, that in Europe the height of the barometer is greatest at two periods in the twenty-four hours, depending upon the season. In win- ter, the first maximum takes place about 9 a.m., the first mini- mum at 3 p.m., after which the mercury again rises and attains its greatest elevation at 9 in the evening: in summer these hours of the aerial tides are somewhat altered. The accidental varia- tions are much greater in amount, and render it extremely diffi- cult to trace the regular changes above mentioned. The barometer is applied with great advantage to the mea- surement of accessible heights, and it is also in daily use for foretelling the state of the weather; its indications are in this respect extremely deceptive, except in the case of sudden and violent storms, which are almost always preceded by a rapid fall in the mercurial column. It is often extremely useful in this respect at sea. To the practical chemist, a moderately-good barometer is an indispensable article, since in all experiments in which volumes of gases are to be estimated, an account must be taken of the state of the pressure of the atmosphere. The marginal drawing represents a very convenient and economical siphon-barometer for this purpose. A piece of new and stout tube, of about one- third of an inch in internal diameter, is procured at the glass- house, sealed at one extremity, and bent into the syphon-form, as represented. Pure and warm mercury is next introduced by successive portions until the tube is completely filled, and the latter being held in an upright position, the level of the metal in the lower and open limb is conveniently adjusted by dis- placing a portion by a stick or glass rod. The barometer is, lastly, attached to a board, and furnished with a long scale, made to slide, which may be of boxwood, with a slip of ivory at each end. When an observation is to be taken, the lower extremity or zero of the scale is placed exactly even with the mercury in the short limb, and then the height of the column at once read off. HEAT. 53 HEAT. It will be convenient to consider the subject of Heat under several sections, and in the following order:— 1. Expansion of bodies, or effects of variations of temperature in altering their dimensions. 2. Conduction, or transmission of heat. 3. Change of state. 4. Capacity of bodies for heat. The phenomena of radiation must be deferred until a sketch has been given of the science of light. EXPANSION. If a bar of metal be taken, of such magnitude as to fit accurately to a guage when cold, heated considerably, and again applied to the guage, it will be found to have become enlarged in all its dimensions. When cold, it will once more enter the guage. Again, if a quantity of liquid contained in a glass bulb, furnished with a narrow neck, be plunged into hot water, or exposed to any other source of Fig. 20. Fig. 21. Fig. 22. heat, the liquid will mount in the stem, showing that its volume has been increased. Or, if a portion of air be confined in any vessel, the application of a slight degree of heat will suffice to make it occupy a space sensibly larger. This most general of all the effects of heat furnishes in the outset a prin- ciple, by the aid of which an instrument can be constructed capable of taking cognizance of changes of temperature in a manner equally accurate and con- venient: such an instrument is the thermometer. A capillary glass tube is chosen, of uniform diameter: one extremity is closed and expanded into a bulb, by the aid of the blowpipe flame, and the 6* 54 HEAT. Fig. 26. other somewhat drawn out, and left open. The bulb is v™**™*^** by a spirit-lamp, and the open extremity plunged into a vessel of mercuiy, a portion of which rises into the bulb when the attcr ^^"f^I Which had been expanded and driven out by the heat. By agam applyng "he flame, and causing this mercury to boil, 'K^^^L tl e cond" ^D expelled/and the whole space filled with mercurial vapor, on the condensation of which the metal is forced into the instrument by the pressure of the air until it becomes completely filled. The thermometer thus filled is now to bo heated until so much mercury has been driven out by the expansion ot the remainder, that its level in the tube shall stand at common temperatures at the point required. This being satisfactorily adjusted the heat is once more applied, until the column rises quite to the top; and then the extremity of the tube is hermetically sealed by the blowpipe The retraction of the mercury on cooling now leaves an empty space m the upper part of the tube, which is essential to the perfection of the instrument. ..... .. The thermometer has yet to be graduated; and to make its indications comparable with those of other instruments, a scale, having certain fixed points, at the least two in number, must be adapted to it. . . . It has been observed, that the temperature of melting ice,- that is to say, of a mixture of ice and water, is always constant; a thermometer, already graduated, plunged into such a mixture, always marks the same degree of temperature, and a simple tube filled in the manner described and so treated, exhibits the same effect in the unchanged height of the little mercurial column, when tried from day to day. The freezing-point of water, or melting-point of ice. consti- tutes then one of the invariable temperatures demanded. Another is to be found in the boiling-point of water, or, more accurately, in the temperature of steam which rises from boiling water. In order to give this tem- perature, which remains perfectly constant whilst the barometric pressure is constant, to the mercury of the thermometer, distilled water is made to boil in a glass vessel with a long neck, when the pressure is at 30 inches (fig. 23). The thermometer is then so placed that all the mercury is surrounded with steam.' It quickly rises to a fixed point, and there it remains as long as the water boils, and the height of the barometer is unchanged. The tube having been carefully marked with a file at these two points, it remains to divide the interval into degrees: this division is entirely arbitrary; in the greater part of Europe, the scale called Centigrade is employed' the space in question being divided into 100 parts, the zero being placed at the freezing-point of water. The'scale is continued above and below these points, numbers below 0 being distinguished by the negative sign. In England the very inconvenient division of Fahrenheit is still in use: the above-mentioned space is divided into 180 degrees, but the zero, instead of starting from the freezing-point of water, is placed 32 degrees below it, so that the temperature of ebullition is expressed by the number of 212°. The plan of Reaumur is nearly confined to a few places in the north of Germany and to Russia: in this scale the freezing-point of water is made 0°, and the boiling-point 80°. It is unfortunate that an uniform system has not been generally adopted in graduating thermometers: this would render unnecessary the labor which now so frequently has to be performed of translating the language of one scale into that of another. To effect this, presents, however, no great difficulty. Let it be required, for example, to know the degree of Fahrenheit's scale which corresponds to 60° Centigrade. HEAT. 55 Consequently, 100° C = 180° F, or 5° C = 9° F. 5 : 9 = 60 : 108. But, then, as Fahrenheit's scale commences with 32° instead of 0°, that number must be added to the result, making 60° C = 140° F. The rule then will be the following:—To convert Centigrade degrees into Fahrenheit degrees, multiply by 9, divide the product by 5, and add 32; to convert Fahrenheit degrees into Centigrade degrees, subtract 32, multiply by 5, and divide by 9. The reduction of negative degrees, or those below zero of one scale into those of another scale, is effected in the same way. For example, to convert — 15 C into degrees of Fahrenheit — Wo have — 15 X | + 82 = — 27 + 32 = + 5 F. o Mercury is usually chosen for making thermometers, on account of its regularity of expansion within certain limits, and because it is easy to have the scale of great extent, from the large interval between the freezing and boiling points of the metal. Other substances are sometimes used; alcohol is employed for estimating very low temperatures. Air-thermometers are also used for some few particular purposes; indeed, the first thermometer ever made was of this kind. There are two modifications of this instrument: in the first, the liquid into which the tube dips is open to the air; and in the second, shown below, the atmosphere is completely excluded. The effects of expansion are in the one case complicated with those arising Fig. 24. Fig. 25. from changes of pressure, and in the other cease to be visible at all when the whole instrument is subjected to alterations of temperature, because the air in the upper and lower reservoir, being equally affected by such changes, no alteration in the height of the fluid column can occur. Accordingly, such instruments are called differential thermometers, since they serve to measure differences of temperatures between the two portions of air, while changes effecting both alike are not indicated. Fig. 25 shows another form of the same instrument. 56 HEAT. The air-thermometer may be employed for measuring all temperatures from the lowest to the highest; M. Pouillet has described one by which the heat of an air-furnace could be measured. The reservoir of this instrument is of platinum, and it is connected with a piece of apparatus by which the increase of volume experienced by the included air is determined. An excellent air-thermometer has been constructed and used by Rudberg, and more recently by Magnus and Regnault, for measuring the expansion of the air. Its construction depends on the law, that when air is heated and hindered from expanding, its tension increases in the same proportion in which it would have increased in volume if permitted to expand. All bodies are enlarged in their dimensions by the application of heat, and reduced by its abstraction, or, in other words, contract on being artificially cooled: this effect takes place to a comparatively small extent with solids, to a larger amount in liquids, and most of all in the case of gases. Each solid and liquid has a rate of expansion peculiar to itself; gases, tm the contrary, expand nearly alike for the same increase of heat. The difference of expansibility among solids is very easily illustrated by the following arrangement: a thin straight bar of iron is firmly fixed, by nume- rous rivets, to a similar bar of brass: so long as the temperature at which the two metals were united remains unchanged, the compound bar preserves its straight figure; but any alteration of temperature gives rise to a corres- ponding curvature. Brass is more dilatable than iron ; if the bar be heated, therefore, the former expands more than the latter, and forces the straight bar into a curve, whose convex side is the brass; if it be artificially cooled, the brass contracts more than the iron, and the reverse of this effect is produced. Fig. 26. This fact has received a most valuable application. It is not necessary to insist on the importance of possessing instruments for the accurate mea- surement of time; such are absolutely indispensable to the successful cultiva- tion of astronomical science, and not less useful to the navigator, from the assistance they give him in finding the longitude at sea. For a long time, notwithstanding the perfection of finish and adjustment bestowed upon clocks and watches, an apparently insurmountable obstacle presented itself to their uniform and regular movement: this obstacle was the change of dimensions to which the regulating parts of the machine were subject by alterations of temperature. A clock may be defined as an instrument for registering the number of beats made by a pendulum: now the time of oscilla- tion of a pendulum depends principally upon its length; any alteration in this condition will seriously affect the rate of the clock. The material of which the rod of the pendulum is composed is subject to expansion and con- traction by changes of temperature; so that a pendulum adjusted to vibrate seconds at 60° (15°-5C) would go too slow if the temperature rise to 70° (21°-1C), from its elongation, and too fast if the temperature fall to 50° flO°C), from the opposite cause. HEAT. 57 Fig. 28. This great difficulty has been overcome: by making the rod of a number of bars of iron and brass, or iron and zinc, metals whose rates of expansion are different, and arranging these bars in such a manner that the expansion in one direction of the iron shall be exactly compensated by that in the opposite direction of the brass or zinc, it is possible to maintain under all circumstances of temperature an invariable distance between the points of suspension and of oscillation. This is often called the gridiron pendulum; fig. 27 will ck-arly illustrate its principle; the shaded bars are sup- posed to be iron and the others zinc. A still simpler compensation-pendulum is thus con- structed. The weight or bob, instead of being made of a disc of metal, consists of a cylindrical glass jar con- taining mercury, which is held by a stirrup at the ex- tremity of the steel pendulum-rod, fig. 28. The same increase of temperature which lengthens this rod, causes the volume of the mercury to enlarge, and its level to rise in"the jar: the centre of gravity is thus elevated, and byjjroperly adjusting the quantity of mercury in the glass, the virtual length of the pendulum may be made constant. In watches, the governing power is a horizontal weighted wheel, set in motion in one direction by the machine itself, and in the other by a fine spiral spring. The rate of going depends greatly on the diameter of this wheel, and the diameter is of necessity subject to variation by change of temperature. To remedy the evil thus involved, the circumference of the balance-wheel is made of two metals having different rates of expansion, firmly soldered together, the more expansible being on the outside. The compound rim is also cut Fiir. 29. through in two places, as represented in the drawing. When the watch is exposed to a high temperature, and the diameter of the wheel becomes enlarged by ex- pansion, each segment is made, by the same agency, to assume a sharper curve, whereby its centre of gra- vity is thrown inwards, and the expansive effect com- pletely compensated. Many other beautiful applica- tions of the same principle might be pointed out; the me- tallic thermometer of M. Brdguet is one of these. Mr. Daniell very skilfully applied the ex- pansion of a rod of metal to the measure- ment of temperatures above those capable of being indicated by the thermometer. A rod of iron or platinum, about five inches long, is dropped into a tube of black-lead earthenware ; a little cylinder of baked por- celain is put over it, and secured in its place by a platinum strap and a wedge of porce- lain. When the whole is exposed to heat, the expansion of the bar drives forward the cylinder, which moves with a certain degree of friction, and shows, by the extent of its displacement, the lengthening which the bar has undergone. It remains, therefore, to measure the amount Fig. 30. 58 HEAT. 2*W Tempered steel 8 07 ttVt T"iV* air, which, becoming expanded, rises, and gives place to another, and in this manner an ascending current is established, —the colder and heavier air streaming in laterally from the more temperate regions, north and south, to supply the partial vacuum thus occasioned. A circulation so commenced will be completed in obedience to the laws of hydrostatics, by the establishment of counter-currents in the higher parts of the atmosphere, having direc- tions the reverse of those on the surface. Such is the effect produced by the unequal heating of the equatorial parts, or, more correctly, such would be the effect were it not greatly modified by the earth's movement of rotation. As the circumference of the earth is, in round numbers, about 24,000 miles, and since it rotates on its axis, from west to east, once in 24 hours, the equa- torial parts must have a motion of 1000 miles per hour; this velocity diminishes rapidly towards each pole, where it is reduced to nothing. The earth in its rotation carries with it the atmosphere, whose velocity of movement corresponds, in the absence of disturbing causes, with that part of the surface immediately below it. The air which rushes towards the equator, to supply the place of that raised aloft by its diminished density, brings with it the degree of momentum belonging to that portion of the earth's surface from which it set out, and as this momentum is less than that of the earth, under its new position, the earth itself travels faster than the air immediately over it, thus producing the effect of a wind blowing in a contrary direction to that of its own motion. The original north and south winds are thus deviated from their primitive directions, and made to blow more or less from the eastward, so that the combined effects of the unequal heating and of the movement of rotation is to generate in the northern hemisphere a HEAT. 63 constant north-east wind, and in the southern hemisphere an equally constant south-east wind. In the same manner the upper or return riS- s3> current is subject to a change of direction in the reverse order; the rapidly-moving wind of the tropics, transferred laterally towards the poles, is soon found to travel faster than the earth beneath it, producing the effect of a westerly wind, which modifies the primary current. The regularity of the trade-winds is much interfered with by the neighborhood of large continents, which produce local effects upon a scale sufficiently great to modify deeply the direction and force of the wind. This is the case in the Indian Ocean. They usually extend from about the 28th degree of latitude in both hemispheres to within 8° of the equator, but are subject to some variations in this respect. Between them, and also beyond their boundaries, lie belts of calms and light variable winds; and beyond these latter, extending into higher latitudes in both hemispheres, westerly winds usually prevail. The general direction of the trade-wind of the Northern Hemisphere is E.N.E., and that of the Southern hemisphere E.S.E. The trade-winds, it may be remarked, furnish an admirable physical proof of the reality of the earth's movement of rotation. The theory of the action of chimneys, and of natural and artificial ventilation, belongs to the same subject. Let the reader turn to the demonstration given of the Archimedean hydro- static theorem: let him once more imagine a body immersed in water, and having a density equal to that of the water; it will remain in equilibrio in any part beneath the surface, and for these reasons: — The force which presses it downwards is the weight of the body added to the weight of the column of water above it; the force which presses it upwards is the weight of a column of water equal to the height of both conjoined; —the density of the body is that of water, that is, it weighs as much as an equal bulk of that liquid; consequently, the downward and upward forces are equally balanced, and the body remains at rest. Next, let the circumstances be altered: let the body be lighter than an equal bulk of water; the pressure upwards of the column of water a c, is no longer compensated by the downward pressure of the corresponding column of solid Fig. 34. and water above it; the former force prepon- I __ __„ derates, and the body is driven upwards. If, on the contrary, the body be specifically heavier than water, then the latter force has the ascend- ency, and the body sinks. All things so described exist in a common chim- ney; the solid body, of the same density as that of the fluid in which it floats, is represented by the air in the chimney-funnel; the space a b rep- resents the whole atmosphere above it. When the air inside and outside the chimney is at the same temperature, equilibrium takes place, because the downward tendency of the air within is counteracted by the upward pressure of that without. Now, let the chimney be heated ; the air suffers expansion, and a portion is expelled; the chimney therefore contains a smaller weight of air than it did before; the external and internal columns no longer balance each other, and 64 nE AT. the warmer and lighter air is forced upwards from below, and its place sup- plied by cold air. If the brick-work, or other material of which the chimney is constructed, retain its temperature, this second portion of air is disposed of like the first, and the ascending current continues, so long as the sides ot the chimney are hotter than the surrounding air. Sometimes, owing to sudden changes of temperature in the atmosphere, the chimney may happen to be colder than the air about it. The column within forthwith suffers contraction of volume; the deficiency is filled up from with- out, and the column becomes heavier than one of similar height on the out- side ; the result is, that it falls out of the chimney, just as the heavy body sinks in the water, and has its place occupied by air from above. A descend- ing current is thus produced, which may be often noticed in the summer-time by the smoke from neighboring chimneys finding its way into rooms, which have been for a considerable period without fire. The ventilation of mines has long been conducted upon the same principle, and more recently it has been applied to dwelling-houses and assembly-rooms. The mine is furnished with two shafts, or with one shaft, divided throughout by a diaphragm of boards; and these are so arranged, that air forced down the one shall traverse the whole extent of the workings before it escapes by the other. A fire kept up in one of these shafts, by rarefying the air within, and causing an ascending current, occasions fresh air to traverse every part of the mine, and sweep before it the noxious gases, but too frequently present. CONDUCTION OF HEAT. Different bodies possess very different conducting powers with respect to heat; if two similar rods, the one of iron the other of glass, be held in the flame of a spirit-lamp, the iron will soon become too hot to be touched, while the glass may be grasped with impunity within an inch of the red-hot portion. Experiments made by analogous, but more accurate methods, have estab- lished a numerical comparison of the conducting powers of many bodies ; the following may be taken as a specimen:— Gold . Silver Copper Iron Zinc As a class the metals are by very far the best conductors, although much difference exists between them ; stones, dense woods, and charcoal, follow next in order; then liquids in general and gases, whose conducting power is almost inappreciable. Under favorable circumstances, nevertheless, both liquids and gases may become rapidly heated: heat applied to the bottom of the containing vessel is very speedily communicated to its contents: this, however, is not so much by conduction as by convection, or carrying. A complete circulation is set up; the portions in contact with the bottom of the vessel get heated, become lighter, and rise to the surface, and in this way the heat becomes communi- cated to the whole. If these movements be prevented by dividing the vessel into a great number of compartments, the really low-conducting power of the substance is made evident; and this is the reason why certain organic fabrics, as wool, silk, feathers, and porous bodies in general, the cavities of which are full of air, exhibit such feeble powers of conduction. The circulation of heated water through pipes is now extensively applied to the warming of buildings and conservatories, and in chemical works a ser- pentine metal tube containing hot oil is often used for heating stills and eva- porating pans; the two extremities of the tube are connected with the ends 1000 Tin . 304 973 Lead . 179 898 Marble . 23-6 374 Porcelain . 12-2 363 Fire-clay . 11-4 nE AT. 65 of another spiral built into a small furnace at a lower level, and an uninter- mitting circulation of the liquid takes place as long as heat is applied. CHANGE OF STATE. If equal weights of water at 32° (0°C) and water at 174° (78°-8C) be mixed, the temperature of the mixture will be the mean of the two temperatures, or 1U:!° (3U°-4C). If the same experiment be repeated with snow or finely-pow- dered ice, at 32° (0°C) and water at 174° (78°-8C), the temperature of the whole will be only 3^° (0°C), but the ice will have been melted. 1 lb. of water at 32° (0°C) ) 2 ft at 103o (39o.4C) 1 lb. of water at 1<4° (<8°-8C) / 1 lb of ice at 32° (0°C) |=2 lb_ ^ at 32o (&oC) 1 lb. of water at 1/4° (<8°-8C) j v ' In the last experiment, therefore, as much heat has been apparently lost as would have raised a quantity of water equal to that of the ice through a range of 142° (78°-8C). The heat, thus become insensible to the thermometer in affecting the lique- faction of the ice, is called latent heat, or better, heat of fluidity. Again, let a perfectly uniform source of heat be imagined, of such intensity that a pound of water placed over it would have its temperature raised 10° (5°-5C) per minute. Starting with water at 32° (0°C), in rather more than 14 minutes its temperature would have risen 142° (78°-8C); but the same quantity of ice at 32° (0°C), exposed for the same interval of time, would not have its temperature raised a single degree. But, then, it would have become water; the heat received would have been exclusively employed in effecting the change of state. This heat is not lost, for when the water freezes it is again evolved. If a tall jar of water, covered to exclude dust, be placed in a situation where it shall be quite undisturbed, and at the same time exposed to great cold, the temperature of the water may be reduced 10° or more below its freezing-point without the formation of ice ; but then, if a little agitation be communicated to the jar, or a grain of sand dropped into the water, a portion instantly solidifies, and the temperature of the whole rises to 32° (0°C); the heat dis- engaged by the freezing of a small portion of the water will have been suffi- cient to raise the whole contents of the jar 10° (5°-5C). This curious condition of instable equilibrium shown by the very cold water in the preceding experiment, may be reproduced with a variety of solutions which tend to crystallize or solidify, but in which, that change is for a while suspended. Thus, a solution of crystallized sulphate of soda in its own weight of warm water, left to cool in an open vessel, deposits a large quantity of the salt in crystals. If the warm solution, however, be filtered into a clean flask, which when full is securely corked and set aside to cool undisturbed, no crys- tals will be deposited, eveu after many days, until the cork is withdrawn and the contents of the flask violently shaken. Crystallization then rapidly takes place in a very beautiful manner, and the whole becomes perceptibly warm. The law thus illustrated in the case of water is perfectly general. When- ever a solid becomes a liquid, a certain fixed and definite amount of heat dis- appears, or becomes latent; and conversely, whenever a liquid becomes a solid, heat to a corresponding extent is given out. The amount of latent heat varies much with different substances, as will be seen by the table: Water i . 142° (78°-8C) i Zinc . . 493° (273°-8C) Sulphur . 145 (80 -5C) Tin . . 500 (277 -7C) Lead . . 102 (90 -5C) | Bismuth . 550 (305 -5C) 1 MM. De la Trovostaye and Regnault. Ann. Chim. et I'hys., 3d series, viii. 1. 6* 66 HEAT. When a solid substance can be made to liquefy by a weak chemical attrac- tion, cold results, from sensible heat becoming latent. This is the principle of the many frigorific mixtures to be found described in some cf the older chemical treatises. When snow or pounded ice is mixed with common salt, and a thermometer plunged into the mass, the mercury sinks to 0° (-17°-7C), while the whole after a short period becomes fluid by the attraction between the water and the salt: such a mixture is very often used in chemical experi- ments to cool receivers and condense the vapors of volatile liquids. Pow- dered crystallized chloride of calcium and snow produce cold enough to freeze mercury. Even powdered nitrate of potassa, or sal-ammoniac, dissolved in water, occasions a very notable depression of temperature: in every case, in short, in which solution is unaccompanied by energetic chemical action, cold is produced. No relation is to be traced between the actual melting-point of a substance, and its latent heat when in a fused state. A law of exactly the same kind as that described affects universally the gaseous condition; change of state from solid or liquid to gas is accompanied by absorption of sensible heat, and the reverse by its disengagement. The latent heat of steam and other vapors may be ascertained by a similar mode of investigation to that employed in the case of water. When water at 32° (0°C) is mixed with an equal weight of water at 212° (100°C), the whole is found to possess the mean of the two temperatures, or 122° (50°C); on the other hand, 1 part by weight of steam at 212° (100°C), when condensed in cold water, is found to be capable of raising 5-4 parts of the latter from the freezing to the boiling-point, or through a range of 180° (100°C). Now 180 X 5-4 = 972; that is to say, steam at 212° (100°C), in becoming water at 212°, parts with enough heat to raise a weight of water equal to its own (if it were possible) 972° (540°C), of the thermometer. When water passes into steam, the same quantity of sensible heat becomes latent. The vapors of other liquids seem to have less latent heat than that of water. The following table is by Dr. Ure, and serves well to illustrate this point:— . 967° (537°-2C) . 442 (246 -6C) . 302 (167 -7C) . 178 (98 -8C) . 178 (98 -8C) . 532 (295 -5C) . 837 (145 -0C) . 875 (486 -1C) Ebullition is occasioned by the formation of bubbles of vapor within the body of the evaporating liquid, which rise to the surface like bubbles of per- manent gas. This occurs in different liquids at very different temperatures. Under the same circumstances, the boiling-point is quite constant, and often becomes a physical character of great importance in distinguishing liquids which much resemble each other. A few cases may be cited in illustration:__ Vapor of water alcohol ether petroleum oil of turpentine nitric acid liquor ammonise vinegar . Substance. Aldehyde . Ether Bisulphide of carbon Alcohol Water. Nitric acid, strong Oil of turpentine Sulphuric acid . Mercury Boiling-point. 69°--4 (20°-8C) (34 -9C) (46 -1C) (78 -4C) (100 C) (120 C) (155 -5C) (326 -2C) (350 C) 94 115 173 212 248 312 620 662 HEAT. 6'j For ebullition to take place, it is necessary that the elasticity of the vapor should be able to overcome the cohesion of the liquid and the pressure upon its surface; hence the extent to which the boiling-point may be modified. Water, under the usual pressure of the atmosphere, boils at 212° (100°C): in a partially-exhausted receiver or on a mountain-top it boils at a much lower temperature: and in the best vacuum of an excellent air-pump, over oil of vitriol, which absorbs the vapor, it will often enter into violent ebulli- tion while ice is in the act of forming upon the surface. On the other hand, water confined in a very strong metallic vessel may be restrained from boiling by the pressure of its own vapor to an almost un- limited extent; a temperature of 350° (177°C) or 400° (204°C) is very easily obtained; and, in fact, it is said that it may be made red-hot, and yet retain its fluidity. There is a very simple and beautiful experiment illustrative of the effect of diminished pressure in depressing the boiling-point of a liquid. A little water is made to boil for a few minutes in a flask or retort placed over a lamp, until the air has been chased out, and the steam issues freely from the neck. A tightly-fitting cork is then inserted, and the lamp at the same moment withdrawn. AVhen the ebullition ceases, it may be renewed at pleasure for a considerable time by the affusion of cold water, which, by condensing the vapor within, occasions a partial vacuum. The nature of the vessel, or, rather, the state of its surface, exercises an influence upon the boiling-point, and this to a much greater extent than was formerly supposed. It has long been noticed that in a metallic vessel water boils, under the same circumstances of pressure, at a temperature one or two degrees below that at which ebullition takes place in glass; but it has lately been shown1 that by particular management a much greater difference can be observed. If two similar glass flasks be taken, the one coated in the inside with a film of shellac, and the other completely cleansed by hot sulphuric acid, water heated over a lamp in the first will boil at 211° (99°-4C), while in the second it will often rise to 221^ (105°C) or even higher; a momentary burst of vapor then ensues, and the thermometer sinks a few degrees, after which it rises again. In this state, the introduction of a few metallic filings, or angu- lar fragments of any kind, occasions a lively disengagement of vapor, while the temperature sinks to 212° (100°C), and there remains stationary. 'These remarkable effects must be attributed to an attraction between the surface of the vessel and the liquid.2 * Marcct, Ann. Chim. et Phys.. 3d series, v. 449. a [A remarkable modification of the relation between the temperature of liquids and the vessel containing them, results where the repulsive action predominates. When a small quantity of water is thrown into a red-hot platinum crucible, it assumes a spheroidal form, pren-sts no appearance of ebullition, but only a rotary motion, and evaporates very slowly; but when the temperature falls to 300°, this spheroidal condition is lost, the liquid boils and is soon dissipated. In the spheroidal state there is no contact between the water and metal, in consequence of the high tension of the small quantity of vapor which is formed and surrounds the globule, but on the fall in temperature, the tension lessens and with it the re- pulsive action, contact takes place and the heat is rapidly communicated to the liquid, which at once is converted into steam. So slight is the influence of the caloric of the vessel on the contained liquid in this condition, that if liquid sulphurous acid be poured on the globule, the water is by the sudden evaporation of the acid converted into ice at the bottom of the red-hot crucible. When a liquid which boils at a low temperature, is thrown on another heated nearly to ebullition, and whose boiling-point is high, the spheroidal state is likewise assumed, as water on oil, spirits of turpentine, sulphuric acid, &c, and ether on water, &c. As connected with this phenomenon, it has been observed that perfect immunity from the caloric of highly heated liquids may be obtained by previously moistening the part to which the application is made with some fluid which evaporates at a low temperature. Thus the hand, while moistened with ether, may be plunged into boiling water without even the sensa- tion of heat. When wet with water it may be dipped into melted lead without injury or 68 HEAT. A cubic inch of water in becoming steam under the ordinary pressure of the atmosphere expands into 1696 cubic inches, or nearly a cubic foot. Steam, not in contact with water, is affected by heat in precisely the same manner as the permanent gases; its rate of expansion and increase of elastic force are the same. When water is present, the rise of temperature increases the quantity and density of the steam, and hence the elastic force increases in a far more rapid proportion. This elastic force of steam in contact with water, at different temperatures, uas been very carefully determined by MM. Arago and Dulong, and lately by M. Regnault. The force is expressed in atmospheres : the absolute pressure upon any given surface can be easily calculated, allowing 14-6 lb. per square inch to each atmosphere. The experiments were carried to twenty-five atmos- pheres ; at which point the difficulties and danger became so great as to put a stop to the inquiry: the rest of the table is the result of calculations founded on the data so obtained. Vrcssure of steam Corresponding Pressure of steam Corresponding in atmospheres. temperature. in atmospheres. temperature. F. C. F. ' C. 1 . . 212° 100° 13 . . 381° 155°-1 1-5. . 230 112 -2 14 . . 387 157 .7 2 . . 251 121 -2 15 . . 393 200 -5 2-5 . . 264 128 -8 16 . . 398 203 -1 3 . . 275 125 17 . . 404 206 -2 3-5. . 285 140 -5 18 . . 409 209 -4 4 . . 294 145 -5 19 . . 414 212 -2 4-5. . 300 148 -8 20 . . 418 214 -4 5 . . 308 153 -1 21 . . 423 217 -2 5-5 . . 314 156 -2 22 . . 427 219 -4 6 . . 320 160 23 . . 431 221 -2 6-5 . . 326 163 -1 24 . . 436 224 -4 7 . . 332 166 -2 25 . . 439 226 -1 7-5 . . 337 169 -4 30 . . 457 236 -1 8 . . 342 172 -2 35 . . 473 245 -1 9 . . 351 177 -2 40 . . 487 252 -7 10 . . 359 181 -2 ■45 . . 491 255 11 . . 367 186 -1 50 . . 511 266 -1 12 . . 374 190 It is a very remarkable fact, that the latent heat of steam diminishes as the temperature of .the steam rises, so that equal weights of steam thrown into cold water exhibit nearly the same heating power, although the actual temperature of the one portion may be 212° (100°C), and that of the other 350° (176°-2C) or 400° (204°-4C). This also appears true with temperatures below the boiling-point; so that, it seems, to evaporate a given quantity of water the same absolute amount of heat is required, whether it be performed slowly at the temperature of the air in a manner presently to be noticed or whether it be boiled off under the pressure of twenty atmospheres. It is'for this reason that the process of distillation in vacuo at a temperature which the hand can bear, so advantageous in other respects, can effect no direct saving in fuel.1 strong sensation of heat, and still less is perceived if alcohol or ether be used. A similar ex- periment has been performed with melted castnron as it runs from the furnace and the drv parts subjected to the radiant caloric have been found more affected than that exDOsed to th« melted metal. v The immunity in the case of using water as the moistening agent arises from the fact that the temperature of the globule in the spheroidal state is much below the boiling-point of the * The proposition in the text, of the sum of the latent and sensible heats of steam beino- n constant quantity, is known by the name of Wall's law, having been deduced by that illus- nEAT. Fig. 37. The economical applications of steam are numerous and extremely valuable ; they may be divided into two classes: those in which the heating power is employed, and those in which its elastic force is brought into use. The value of steam as a source of heat depends upon the facility with which it may be conveyed to distant points, and upon the large amount of latent heat it contains, which is Fig. 36. disengaged in the act of condensation. An invariable temperature of 212° (100°C), or higher, may be kept up in the pipes or other vessels in which the steam is contained by the expenditure of a very small quan- tity of the latter. Steam-baths of various forms are used in the arts with great convenience, and also by the scientific chemist for drying filters and other objects where excessive heat would be hurtful; a very good instrument of the kind was contrived by Mr. Evcritt. It is merely a small kettle, surmounted by a double box or jacket, into which the substance to be dried is put, and loosely covered by a card. The ap- paratus is placed over a lamp, and may be left with- out attention for many hours. A little hole in the side of the jacket gives vent to the excess of steam. The principle of the steam-engine may be described in a few words: its mechanical details do not belong to the design of the present volume. The machine consists essentially of a cylinder of metal a, in which a closely-fitting solid piston works, the rod of which passes, air-tight, through a stuffing- box at the top of the cylinder, and is con- nected with the machinery to be put in motion, directly, or by the intervention of an oscillating beam. A pipe communicates with the interior of the cylinder, and also with.a vessel sur- rounded with cold water, called the conden- ser, marked b in the sketch, and into which a jet of cold water can at pleasure be intro- duced. A sliding-valve arrangement, shown at c, serves to open a communication between the boiler and the cylinder, and the cylinder and the condenser, in such a manner that while the steam is allowed to press with all its force upon one side of the piston, the other, open to the condenser, is necessarily vacuous. The valve is shifted by the engine itself at the proper moment, so that the pis- ton is alternately driven by the steam up and down against a vacuum. A large air-pump, not shown in the engraving, is connected with the condenser, and serves to remove any air that may enter the cylinder, and also the water produced by condensation, together with that which may have been injected. Such is the vacuum or condensing steam- trious man from experiments of his own. It has always agreed well with the rough practical results obtained by engineers, but has lately been proved by Kegnault's most perfect experi- ments to be only approximately true. According to Regnault, the vapor of water at the tem- perature of melting ice contains lOUl/^of latent heat, and the total heat that vapor contains at temperatures above this may be expressed by the formula T = 1091-7 -f- 0305 (t__32). Hence it increases appreciably with the temperature, and at 212° amounts to as much as 1146°-6. 70 HEAT. engine. In what is called the high-pressure engine the condenser and air- punm are suppressed, and the steam is allowed to escape at once from the cylinder into the atmosphere. It is obvious that in this arrangement the steam has to overcome the whole pressure of the air, and a much greater elastic force is required to produce the same, effect; but this is to a very great extent compensated by the absence of the air-pump and the increased sim- plicity of the whole machine. Large engines, both on shore and in steam- ships, are usually constructed on the condensing principle, the pressure sel- dom exceeding six or seven pounds per square inch above that of the atmos- phere ; for small engines the high-pressure plan is, perhaps, preferable. Loco- motive engines are of this kind. A peculiar modification of the steam-engine, employed in Cornwall, for draining the deep mines of that county, is now getting into use elsewhere for other purposes. In this machine economy of fuel is carried to a most extra- ordinary extent, engines having been known to perform the duty of raising more than 100,000,000 lb. of water one foot high by the consumption of a single bushel of coals. The engines are single acting, the down-s'troke, which is made against a vacuum, being the effective one, and employed to lift the enormous weight of the pump-rods in the shaft of the mine. When the piston reaches the bottom, the communication both with the boiler and the condenser is cut off, while an equilibrium-valve is opened connecting the upper and lower extremities of the cylinder, whereupon the weight of the pump-rods draws the piston to the top and makes the up-stroke. The engine is worked expansively, as it is termed, steam of high tension being employed, which is cut off at one-eighth or even one-tenth of the stroke. The process of distillation, which may now be noticed, is very simple: its object is either to separate substances which rise in vapor at different tempe- ratures, or to part a volatile liquid from a substance incapable of volatilization. The same process applied to bodies which pass directly from the solid to the gaseous condition, and the reverse, is called sublimation. Every distillatory apparatus consists essentially of a boiler, in which the vapor is raised, and of a condenser, in which it returns to the liquid or solid condition. In the still employed for manufacturing purposes, the latter is usually a spiral metal tube immersed in a tub of water. The common retort and receiver constitute the simplest and most generally useful arrangement for distillation on the small scale; the retort is heated by a lamp or a charcoal fire, and the receiver is kept cool, if necessary, by a wet cloth, or it may be surrounded with ice. (Fig. 38.) HEAT. 7J- The condenser of Baron Liebig is a very valuable instrument in the labora- tory ; it consists of a glass tube tapering from end to end, fixed by perforated Fig. 39. corks in the centre of a metal pipe, provided with tubes so arranged that a current of cold water may circulate through the apparatus. By putting a few pieces of ice into the little cistern, the temperature Fig. 40. of this water may be kept at 32° (0°C), and extremely volatile liquids condensed. Liquids evaporate at temperatures below their boiling-points: in this case the evaporation takes place solely from the surface. Water, or alcohol, exposed in an open vessel at the temperature of the air, gradually dries up and disappears; the more rapidly, tlie warmer and drier the air above it. This fact was formerly explained by supposing that air and gases in general had the power of dissolving and holding in solu- tion certain quantities of liquids, and that this power increased with the temperature: such an idea is incorrect. If a barometer-tube be carefully filled with mercury and in- verted in the usual manner, and then a few drops of water passed up the tube into the vacuum above, a very remarkable effect will be observed;—the mercury will bo depressed to a small extent, and this depression will increase with increase of temperature. Now, as the space above the mercury is void of air, and the weight of the few drops of water quite inadequate to account for this depression, it must of necessity be imputed to the vapor which instantaneously rises from the water into the vacuum ; and that this effect is really due to the elasticity or tension of the aqueous vapor, is easily proved by exposing the barometer to a heat of 212° (l()!i°C), when the depression of the mercury will be com- plete, and it will stand at the same level within and without the tube; indicating that at that temperature the%elasticity of the va- por is equal to that of the atmosphere—a fact which the pheno- menon of ebullition has already shown. By placing over the barometer a wide open tube clipping into the mercury below, and then filling this tube with water at differ- ent temperatures, the tension of the aqueous vapor for each degree of the thermometer may be accurately determined by its ♦72 HEAT. depressing effect upon the mercurial column ; the same power which forces the latter down one inch against the pressure of the atmosphere, would of course elevate a column of mercury to the same height against a vacuum, and in this way the tension may be very conveniently expressed. The following table was drawn up by Dr. Dalton, to whom we owe the method of investi- gation :— Temperature. Tension in inches Temperature. Tension in inches F. c. of mercury. F. c. of mercury. 32° 0° 0-200 130 . 54-4 4-34 40 4-4 0-263 140 . 60 5-74 50 10 0-375 150 . 65-5 7-42 60 15-5 0-524 160 . 71-1 9-46 70 21-1 0-721 170 . 766 1213 80 26-6 1-000 180 . 82-2 15 15 90 32-2 1 -360 190 . 87-7 19-00 100 37-7 1-860 200 . 93-3 23-C4 110 43 3 2-530 212 . 100 30 00 120 48-8 3-330 Fig. 41. Other liquids tried in this manner are found to emit vapors of greater or less tension, for the same temperature, according to their different degrees of volatility: thus, a little ether introduced into the tube depresses the mercury 10 inches or more at the ordinary temperature of the air; oil of vitriol, on the other hand, does not emit any sensible quantity of vapor until a much greater heat is applied ; and that given off by mercury itself in warm summer weather, although it may by very delicate means be detected, is far too little to exercise any effect upon the barometer. In the case of water, the evaporation is quite distinct and per- ceptible at the lowest temperatures, when frozen to solid ice in the barometer-tube: snow on the ground, or on a house-top, may often be noticed to vanish, from the same cause, day by day in the depth of winter, when melting is impossible. There exists for each vapor a state of density which it cannot pass without losing its gaseous condition, and be- coming liquid; this point is called the condition of maxi- mum density. When a volatile liquid is introduced in suf- ficient quantity into a vacuum, this condition is always reached, arid then evaporation ceases. Any attempt to increase the density of this vapor by compressing it into a smaller space will be attended by the liquefaction of a por- T/n M eUu ty- °f the remaincler being unchanged. If a lit le ether be introduced into a barometer, and the latter flnn/tHV ,° a ,ei'y,d?CP Cistern of mercury, it will be Zt h" -h!u1Glght °f the COlnmn of mercury in the tube above that in the cistern remains unaltered until the upper meS K t-,e1baromet5r1aPP/oaclies the surface of the £ Si I k colTVnd,a11 the ether has become liquid. It will be observed also, that, as the tube sinks the little Stratum of hquid ether increases in thickness, bu! no i£ sity a-e always., under ordinary!*£„J^T.TuS" directly proportionate to each other in the same vapor ' The point of maximum density of vnnnv* ;<, j \ * HEAT. 7* ture rises. This is well shown in the case of water. Thus, taking the spe- cific gravity of atmospheric air at 212° (100°C) = 1000, that of aqueous vapor in its greatest possible state of compression for the temperature will be as follows: — Temperature Specific Gravity. Weight of 100 cubic inches. F. C. 32° 0° . . . 5-690 . . 0-136 grains. 50 10 60 15-5 100 37-7 150 65-5 212 100 10-293 . . 0-247 14108 . . 0-338 46-500 . . 1-113 170-293 . . 4-076 625000 . . 14-962 The last number was experimentally found by M. Gay Lussac; the others are calculated from that by the aid of Dr. Dalton's table of tensions, on the assumption that steam, not in a state of saturation, that is, below the point of greatest density, obeys the law of Mariotte, (which is, however, only ap- proximately true,) and that when it is cooled it contracts like the permanent gases. Thus, there are two distinct methods by which a vapor may be reduced to the liquid form—pressure, by causing increase of density until the point of maximum density for the particular temperature is reached; and cold, by which the point of maximum density is itself lowered. The most powerful effects are of course produced when both are conjoined. For example, if 100 cubic inches of perfectly transparent and gaseous vapor of water at 100° (37°-7C), in the state above described, had its tem- peratures reduced to 50° (10°C), not less than 0.891 grain of fluid water would necessarily separate, or very nearly eight-tenths of the whole. Evaporation into a space filled with air or gas follows the same law as eva- poration into a vacuum ; as much vapor rises, and the condition of maximum density is assumed in the same manner, as if the space were perfectly empty; the sole difference lies in the length of time required. When a liquid evapo- rates into a vacuum, the point, of greatest density is attained at once, while in the other case some time elapses before this happens; the particles of air appear to oppose a sort of mechanical resistance to the rise of the vapor. The ultimate effect is, however, precisely the same. When to a quantity of perfectly dry gas confined in a vessel closed by mer- cury, a little water is added, the latter immediately begins to evaporate, and after some time as much vapor will be found to have risen from it as if no gas had been present, the quantity depending entirely on the temperature to which the whole is subjected. The tension of this vapor will add itself to that of the gas, and produce an expansion of volume, which will be indicated by an alteration of level in the mercury. Vapor of water exists in the atmosphere at all times, and in all situations, and there plays a most important part in the economy of nature. The pro- portion of aqueous vapor present in the air is subject to great variation, and it often becomes exceedingly important to determine its quantity. This is easily done by the aid of the foregoing principles. If the aqueous vapor be in its condition of greatest possible density for the temperature, or, as it is frequently, but most incorrectly expressed, the air be saturated with vapor of water, the slightest reduction of temperature will cause the deposition of a portion in the liquid form. If, on the contrary, as is almost always in reality the case, the vapor of water be below its state of maximum density, that is, in an expanded condition, it is clear that a con- 1100 cubic inches aqueous vapors at 100° (-37°-7C), weighing 1-113 grain, would at 50° (10°C) become reduced to 91'07 cubic inches, weighing 0'225 grain. 7 •T4 HEAT. siderable fall of temperature may occur before liquefaction commences. The degree at which this takes place is called the dew-point, and it is determined with great facility by a very simple method. A little cup of thin tin-plate or silver, well polished, is filled with water at the temperature of the air, and a delicate thermometer inserted. The water is then cooled by dropping in fragments of ice, or dissolving in it powdered sal-ammoniac, until a deposition of moisture begins to make its appearance on the outside, dimming the bright metallic surface. The temperature of the dew-point is then read off upon the thermometer, and compared with that of the air. Suppose, by way of example, that the latter were 70° (21°-1C), and the dew-point 50° (10°C); the elasticity of the watery vapor present would cor- respond to a maximum density proper to 50° (10°C), and would support a column of mercury 0-375 inch high. If the barometer on the spot stood at 30 inches, therefore, 29-625 inches would be supported by the pressure of the dry air, and the remaining 0-375 inch by the vapor. Now a cubic foot of such a mixture must be looked upon as made up of a cubic foot of dry air, and a cubic foot of watery vapor, occupying the same space, and having tensions indicated by the numbers just mentioned. A cubic foot, or 1728 cubic inches of vapor at 70° (21°-1C), would become reduced by contraction, according to the usual law, to 1662-8 cubic inches at 50° (10°C); this vapor would be at its maximum density, having the specific gravity pointed out in the table; hence 1662-8 cubic inches would weigh 4-11 grains. The weight of the aqueous vapor contained in a cubic foot of air will thus be ascertained. In this country the difference between the temperature of the air and the dew-point seldom reaches 30° (16°-6C); but in the Deccan, with a tempera- ture of 90° (32-2C), the dew-point has been seen as low as 29° (-1-6°C) making the degree of dryness 61 (33°-8°C).1 Another method of finding the proportion of moisture present in the air is to observe the rapidity with which evaporation takes place, and which is always in some relation to the degree of dryness. The bulb of a thermometer is covered with muslin, and kept wet with water; evaporation produces cold, as will presently be seen, and accordingly the thermometer soon sinks below the actual temperature of the air. When it comes to rest, the degree is noticed, and from a comparison of the two tempera- tures an approximation to the dew-point can be obtained by the aid of a mathematical formula contrived for the purpose This is called the wet-bulb hygrometer; it is often made in the manner shown in fig. 42, where one thermometer serves to in- dicate the temperature of the air, and the other to show the rate of evaporation, being kept wet by the thread in connexion with the little water reservoir. The perfect resemblance in every respect which vapors bear to permanent gases, led very naturally, to the idea that the ,«ZTt rby-?e aPPlication of citable means, be made to assume the liquid condition, and this surmise was, n the hands of Mr. Faraday to a great extent verified. Out of the small number of such substances tried, not less than eight Tave way; and it is quite fair to infer, that, had means of fuffident power been at hand, the rest would have shared the same fate and proved to be nothing more than the vapors of volatS liquids in a state very far removed from thnt Ir tv. ■ v°latlle density, The subjoined table represents the resuRof mJ F^SJ^Z vestigations, with the pressure in atmospheres, and the rprnt!™ - 7 I- C the condensation took place." temperature at which »Phil^ Fig. 42. HEAT. 75i Atmospheres. Temperatures F. C. Sulphurous acid 2 . 45° 7°-2 Sulphuretted hydrogen . . 17 . 50 10 Carbonic acid. . 36 . 32 0 Chlorine. . 4 . 60 15 -5 Nitrous oxide. . 50 .45 7-2 Cyanogen . 3-6 . .45 7-2 Ammonia . 6-5 . . 50 10 Hydrochloric acid . . 40 . 59 10 The method of proceeding was very simple: the materials were sealed up in a strong narrow tube, together with a little pressure-gauge, consisting of a slender tube closed at one end, and having within it, near the open ex- Fig. 43. tremity, a globule of mercury. The gas being disengaged by the application of heat or otherwise, accumulated in the tube, and by its own pressure brought about condensation. The force required for this purpose was judged of by the diminution of volume of the air in the gauge. Mr. Faraday has since resumed, with the happiest results, the subject of the liquefaction of the permanent gases. By using narrow green glass tubes of great strength, powerfully-condensing syringes, and an extremely low tem- perature, produced by means to be presently described, defiant gas, hydriodic and hydrobromic acids, phosphoretted hydrogen, and the gaseous fluorides of silicon and boron, were successively liquefied. Oxygen, hydrogen, nitro- gen, nitric oxide, carbonic oxide, and coal-gas, refused to liquefy at the tem- perature of—166° (— 74°-4C) while subjected to pressures varying in the different cases from 27 to 58 atmospheres.1 Sir Isambard Brunei, and, more recently, M. Thilorier, of Paris, succeeded in obtaining liq uid carbonic acid in great abundance. The apparatus of M. Thilorier (fig. 44) consists of a pair of extremely strong metallic vessels, one of which is destined to serve the purpose of a retort, and the other that of a receiver. They are made either of thick cast-iron or gun-metal, or, still better, of the best and heaviest boiler-plate, and are furnished with stop-cocks of a peculiar kind, the workmanship of which must be excellent. The generating vessel or retort has a pair of trunnions upon which it swings in an iron frame. The joints are secured by collars of lead, and every precaution taken to prevent leakage under the enormous pressure the vessel has to bear. The receiver resembles the retort in every respect; it has a similar stop-cock, and is con- nected with the retort by a strong copper tube and a pair of union screw- joints ; a tube passes from the stop-cock downwards, and terminates near the bottom of the vessel. The operation is thus conducted: 2£ lb. of bicarbonate of soda, and 6} lb. of water at 100° (37°-7C), are introduced into the generator; oil of vitriol to the amount of 1J lb. is poured into a copper cylindrical vessel, which is lowered down into the mixture, and set upright; the stop-cock is then screwed 1 Phil. Trans, for 1845, p. 155. M. Natterer, in Vienna, has since succeeded, by means of a condensing pump, which can be worked without any risk, in directly condensing nitrous-oxide giui, without the use of strong frigorific mixtures. 3Q HEAT. into its place, and forced home by a spanner and mallet. The machine is next tilted up on its trunnions, that the acid may run out of the cylinder Fig. 44. and mix with the other contents of the generator: and this mixture is favored by swinging the whole backwards and forwards for a few minutes, after which it may be suffered to remain a little time at rest. The receiver surrounded with ice, is next connected with the generator, and both cocks opened; the liquefied carbonic acid distils over into the colder vessel, and there again in part condenses. The cocks are now closed, the vessels disconnected, the cock of the generator opened to allow the contained gas to escape; and, lastly, when the issue of gas has quite ceased, the stop- cock itself is unscrewed, and the sulphate of soda turned out. This operation must be repeated five or six times before any very considerable quantity of liquefied acid will have accumulated in the receiver. When the receiver thus charged has its stop-cock opened, a stream of the liquid is forcibly driven up the tube by the elasticity of the gas contained in the upper part of the vessel. It will be quite proper to point out to the experimenter the great personal danger he incurs in using this apparatus, unless the utmost care be taken in its management. A dreadful accident has already occurred in Paris by the bursting of one of the iron vessels. The cold produced by evaporation has been already adverted to- it is simply an effect arising from the conversion of sensible heat into latent bv the rising vapor, and it may be illustrated in a variety of ways A little ether dropped on the hand thus produces the sensation of great'cold • and water contained in a thin glass tube, surrounded by a bit of ra«- is srjeed'lv frozen when the rag is kept wetted with ether. °' i>*™>v HEAT. 77 When a little water is put into a watch-glass, supported by a triangle of wire over a shallow glass dish of sulphuric acid placed on the plate of a good air-pump, the Fig. 45. whole covered with a low receiver, and the air withdrawn as perfectly as possible, the water is in a few minutes converted into a solid mass of ice. The absence of the impediment of the air, and the rapid absorption of watery vapor by the oil of vitriol, induce such quick evapo- ration that the water has its temperature almost immediately reduced to the freezing-point. The same fact is shown by a beautiful instrument contrived by Dr. Wollas- ton, called a cryophorus, or frost-carrier. It is made of glass, of the figure represented below, and contains a small quantity of water, the rest of the Fig. 46. Fig. 47. space being vacuous. When all the water is turned into the bulb, and the empty extremity plunged into a mixture of ice and salt, the solidification of the vapor gives rise to such a quick evaporation from the surface of the water, that the latter freezes. All means of producing artificial cold yield to that derived from the evapo- ration of the liquefied carbonic acid, just mentioned. When a jet of that liquid is allowed to issue into the air from a narrow aperture, such an intense degree of cold is produced by the evaporization of a part, that the remainder freezes to a solid, and falls in a shower of snow. By suffering this jet of liquid to flow into a metal box provided for the purpose, shown in the draw- ing of the apparatus, a large quantity of the solid acid may be obtained; it closely resembles snow in appearance, and when held in the hand occa- sions a painful sensation of cold, while it gradually disappears. Mixed with a little ether, and poured upon a mass of mercury, the latter is almost instantly frozen, and in this way pounds of the solidified metal may be obtained. The addition of the ether facilitates the contact of the carbonic acid with tho mercury. The temperature of a mixture of solid car- bonic acid and ether in the air, measured by a spirit-thermometer, was found to be — 106° (— 76°.6C); when the same mixture was placed beneath the receiver of an air-pump, and exhaus- tion rapidly made, the temperature sank to —166° (— 110°C). This was tho method of obtaining extreme cold employed by Mr. Faraday in his last experiments on the liquefaction of gases. Under such circumstances the liquefied hydriodic, hydrobromic, and sulphurous acid gases, carbonic acid, nitrous oxide, sulphuretted hydrogen, cyanogen, and ammonia, froze to colorless transparent solids, and alcohol became thick and oily. ^ 78 HEAT. The principle of the cryophorus has been very happily applied by Mr. Daniell to the construction of a dew-point hygrometer, fig. 47. It consists of a bent glass tube terminated by two bulbs, one of which is half filled with ether, the whole being vacuous as respects atmospheric air. A delicate thermometer is contained in the longer limb, the bulb of which dips into the ether; a second thermometer on the stand serves to show the actual tempera- ture of the air. The upper bulb is covered with a bit of muslin. When an observation is to be made the liquid is all transferred to the lower bulb, and ether dropped upon the upper one, until by the cooling effect of evaporation a distillation of the contained liquid takes place from one part of the apparatus to the other, by which such a reduction of temperature of the ether is brought about, that dew is deposited on the outside of the bulb, which is made of black glass in order that it may more easily be seen. The difference of temperature indicated by the two thermometers is then read off. CAPACITY FOR HEAT ; SPECIFIC HEAT. It is a very remarkable fact that equal weights of different substances having the same temperature require different amounts of heat to raise them to a given degree of temperature. If 1 lb. of water, at 100° (37°-7C), be mixed with 1 lb. at 40° (4°-4C), as is well known, a mean temperature of ---i— _ 700 (21°-1C) is obtained. In the same way the mean tempera- ture is found when warm and cold oil, or warm and cold mercury, &c, are mixed together. But if 1 lb. of water at 100° be mixed with 1 lb. of olive- oil at 40°, or with 1 lb. of mercury at 40°, instead of the mean temperature of 70°, in the one case 80° (26°-6C), in the other case 98° (36°-7C), will be obtained: 20 degrees of heat, which the water (by cooling from 100° to 80°) gave to the same weight of oil, were sufficient to raise the oil 40°, that is, from 40° to 80°, and 2° which the water lost by cooling from 100° to 98°, sufficed to heat an equal quantity of mercury 58°, namely, from 40° to 98°. It is evident from these experiments, that the quantities of heat which equal weights of water, olive oil, and mercury, require to raise their tempera- ture to the same height, are unequal, and that they are in the proportion of the numbers 1 : f g : -£$. That quantity of heat which is necessary to raise the unit of weight of any substance one degree is called the capacity for heat; and those numbers which express the relation of the different capacities for heat of different bodies are called the specific heat. Thus the specific heat of oil is |£ =- ■£, when that of water = 1. The specific heat of mercury is about -^ — J^'that of water. There are three distinct methods by which the specific heat of various sub- stances may be estimated. The first of these is by observing the quantity of ice melted by a given weight of the substance heated to a particular tempera- ture ; the second is by noting the time which the heated body requires to cool down through a certain number of degrees; and the third is the method of mixture, on the principle illustrated; this latter method is preferred as the most accurate. The determination of the specific heat of different substances, has occupied the attention of many experimenters; among these MM. Dulong and Petit, and recently M. Regnault, deserve especial mention. From the observations of these and other physicists, it follows that each body has its peculiar capacity for heat, and that it increases with the increase of temperature. If, for example, the heat which the unit of water loses by cooling from 50° (10°C), to 32° (0°C), be marked at 18, then the loss by cooling from 122° (50°C), to 32° will be not 90, corresponding to the differ- ence of temperature, but 90-16. By cooling from 212° (100°C) to 32° it is 180-90, and rises to 365-76, when the water is heated under great pressure to H EAT. 79 392° (200°C), and afterwards cooled to 32°. Similar and even more striking differences have been found with other substances. It has also been proved that the capacity for heat of any substance is greater in its liquid than in its Bolid state. For example, the specific heat of ice is 0-504, that is, not more than half as great as that of liquid water. It is remarkable that the capacity for heat of water is greater than that of all other solid and liquid substances, and is only exceeded by that of hydro- gen. The capacity for heat of the solid parts of the crust of the globe is on an average J, and that of the atmosphere is a little more than £ that of water. If the specific heat of any body within certain degrees of temperature be accurately known, then from the quantity of heat which this body gives out, when quickly dipped into cold water, the temperature to which the body was heated may be determined. Pouillet has founded on this fact a method of measuring high temperature, and for this purpose, with the help of the air- thermometer, he has determined the specific heat of platinum up to 2912° (1600°C). The determination of the specific heat of gases is attended with peculiar difficulties on account of the comparatively large volume of small weights of gases. Satisfactory results have, however, been obtained by the method of mixing for the following gases. SPECIFIC HEAT. Equal volume. Equal weights. The volume The pressure Air = 1. Water = 1. constant. constant. Atmospheric air 1 1 0-2669 Oxygen 1 0-9045 0-2414 Hydrogen 1 14-4510 3-8569 Nitrogen 1 1-0295 0-2748 Carbonic oxide 1 1-0337 0-2759 Protoxide of nitrogen 1-227 1-160 0-7607 0-2030 Carbonic acid 1-249 1-175 0-7685 0-2051 Olefiant gas . 1-754 1-531 1-5829 0-4225 For the comparison of the specific heat of atmospheric air with that of water we are indebted to Count Rumford ; for the comparison of the specific heat of the various gases to Delaroche and Berard, Dulong and Regnault.1 * Regnault's recent researches confirm the statement that equal volumes at the same pres- sure of the elementary gases, oxygen, nitrogen, and hydrogen, possess the same specific heat The numbers found for chlorine and bromine, however, show that the law does not hold good for all the elementary gases. The following are Keguault's results:— Specific Heat at Equal Pressure. Specific gravity For equal volumes Atmospheric air Oxygen 1-1056 0-2412 Nitrogen 0-9713 0-2370 llvdnmeii 0-0602 0-2356 Chlorine 2-4400 02962 Bromine vapor 5-39 0-2992 Carbonic oxide 0-9674 0-2399 Carbonic acid 1-5290 03308 Protoxide of nitrogen 1-5250 0-3413 Binoxide of nitrogen . 1-0390 0-2406 Olefiant gas . 0-9672 03277 Marsh gas . 0-5527 0-3572 Aqueous vapor 0-6210 0-2950 Sulphuretted hydrogen 1-1912 0-2886 Sulphurous acid . 2-2470 0-34S9 Bisulphide of carbon . 2-6325 0-4146 Hydrochloric acid Ammonia 1-2474 0-6894 0-2302 0-2994 For equal weights. 0-2377 0-2182 0-2440 3-4046 0-1214 0-0552 0-2479 0-2164 0-2238 0-2315 0-5929 0-3694 0-4750 0-2423 01553 01575 0-1845 05080 80 HEAT. The observations of Delaroche and Berard led to the supposition that tho specific heat of gases increased rapidly when the temperature was increased; and that with any fixed volume of gas it increased in proportion to its density or tension. Regnault has, however, found that the quantity of heat which a given volume of gas requires for heating is independent of the density of the gas, and for each degree of heat between -22° (-30°C) and 437° (225°C) remains constant. Whenever a gas expands, heat becomes thereby latent. Hence the amount of heat required to raise a gas to a certain temperature increases the more we allow it to expand. Dulong has found that if the amount of heat required to raise the temperature of a volume of gas (observed at the melting-point of ice, and at a pressure of 30 inches) to a given height, without its volume under- going any change, be represented by 1, then if the gas be allowed to expand until the pressure is reduced again to 30 inches whilst the high temperature is kept up, the additional amount of heat which is required for this purpose is, for oxygen, hydrogen, or nitrogen 0-421; for carbonic acid 0-423; for bin- oxide of nitrogen 0345 ; and for olefiant gas 0-240. If there be no source of heat from which this additional quantity can be obtained, then the gas is cooled during expansion, a portion of the free heat becoming latent. On the other hand, if a gas be compressed, this latent heat becomes free, and causes an elevation of temperature, which, under favorable circumstances, may be raised to ignition: syringes by which tinder is kindled are constructed on this principle. In the upper regions of the atmosphere the cold is intense; snow covers the highest mountain-tops even within the tropics, and this is due to the increased capacity for heat of the expanded air. # MM. Dulong and Petit observed in the course of their investigation a most remarkable circumstance. If the specific heats of bodies be computed upon equal weights, numbers are obtained all different, and exhibiting no simple relations among themselves; but if, instead of equal weights, quantities be taken in the proportion of the chemical equivalents, an almost perfect coin- cidence in the numbers will be observed, showing that some exceedingly inti- mate connexion must exist between the relations of bodies to heat and their chemical nature; and when the circumstance is taken into view, that relations of even a still closer kind link together chemical and electrical phenomena, it is not too much to expect that ere long some law may be discovered far more general than any with which we are yet acquainted. The following table is extracted from the memoirs of M. Regnault, with whose results most of the experiments of Dulong and Petit closely coincide. Specific heat Substances. of equal weights. Water . . 1-00000 Oil of Turpentine 0-42593 Glass . . 0-19768 Iron . . 0-11379 Zinc . . 009555 Copper . . 0-09515 Lead . . 0-03140 Tin . . 0-05623 Nickel . . 0-10863 Cobalt . . 0-10696 Specific heat of equivalent weights. 3-0928 3-0872 3-0172 3-2581 3-3121 3-2176 3-1628 Substances. Platinum . Sulphur . Mercury . Silver Arsenic . Antimony Gold Iodine Bismuth . Specific heat of equal weights. . 0-03243 . 0-20259 . 0-03332 . 0-05701 . 0-08140 . 0 05077 . 0-03244 0-05412 . 0-03084 Specific heat of equivalent weights. . 3-2054 . 3-2657 . 3-7128 . 6-1742 . 6-1326 . 6-5615 . 6-4623 . 6-8462 . 219171 ' [The equivalent of bismuth being assumed as 71, but adoptinz 208 tho n,.mi,„. • the head of bismuth, the specific heat of an equivalent weight willbe it&m^ JT'S UD^ the five preceding.—R. B.] e e ° iail> or coincide with HEAT. 81 Of the numbers in the second column, the first ten approximate far too closely to each other to be the result of mere accidental coincidence; the five that follow are very nearly twice as great; and the last is one-third less. Independently of experimental errors, there are many circumstances which tend to show, that, if all modifying causes could be compensated, or their effects allowed for, the law might be rigorously true. The observations thus made upon elementary substances have been extended by M. Regnault to a long series of compounds, and the same curious law found, with the above limitations, to prevail throughout, save in a few isolated cases, of which an explanation can perhaps be given. Except in the case of certain metallic alloys, where the specific heats were the mean of those of their constituent metals, no obvious relation can be traced between the specific heat of the compound body and of its components. The most general expression of the facts that can be given is the following:— In bodies of similar chemical constitution, the specific heats are in an inverse ratio to the equivalent weights, or to a multiple or submultiple of the latter.—Simple as well as compound bodies will be comprehended in this law.1 SOURCES OF HEAT. The first and greatest source of heat, compared with which all others are totally insignificant, is the sun. The luminous rays are accompanied by rays of a heating nature, which, striking against the surface of the earth, elevate its temperature ; this heat is communicated to the air by convection, as already described, air and gases in general not being sensibly heated by the passage of the rays. A second source of heat is supposed to exist in the interior of the earth. It has been observed, that in sinking mine-shafts, boring for water, &c, the temperature rises in descending at the rate, it is said, of about 1° (i°C) for every 45 feet, or 117° (65°C) per mile. On the supposition that the rise con- tinues at the same rate, at the depth of less than two miles the earth would have the temperature of boiling water; at nine miles it would be red-hot; and at 30 or 40 miles depth, all known substances would be in a state of fusion.2 According to this idea, the earth must be looked upon as an intensely-heated fluid spheroid, covered with a crust of solid badly-conducting matter, cooled by radiation into space, and bearing somewhat the same proportion in thick- ness to the ignited liquid within that the shell of an egg does to its fluid con- tents. Without venturing to offer any opinion on this theory, it may be suffi- cient to observe that it is not positively at variance with any known fact • that the figure of the earth is really such as would be assumed by a fluid mass; and, lastly, that it offers the best explanation we have of the phenomena of hot springs and volcanic eruptions, and agrees with the chemical nature of their products. The smaller, and what may be called secondary, sources of heat, are very numerous: they may be divided, for the present, into two groups, mechanical motion and chemical combination. To the first must be referred elevation of temperature by friction and blows; and to the second, the effects of combus- tion and animal respiration. With regard to the heat developed by friction, it appears to be indefinite in amount, and principally dependent upon the nature of the rubbing surfaces. An experiment of Count Rumford is on record, in which the heat developed by the boring of a brass cannon was suf- * Ann. Chim. et Phys., lxxiii. 5; and the same, 3d series, i. 129. "The Artesian well at (irenelle, near Paris, has a depth of 1794-5 English feet; it is bored through the Chalk basin to the sand beueath ; the work occupied seven years and two months Tho temperature of the water, which is exceedingly abundant, is V2° ^7°-7C); the mean tem- perature of Paris is 51° (10°-5C); the difference is 31° (17°-2C), which gives a rate of about 1° (*°C) for 68 feet. 82 HEAT. ficient to bring to the boiling-point two and a half gallons of water, while the dust or shavings of metal, cut by the borer, weighed a few ounces only. Sir H. Davy melted two pieces of ice by rubbing them together in vacuo at 32 (0°C); and uncivilized men, in various parts of the world, have long been known to obtain fire by rubbing together two pieces of dry wood. The origin of the heat in these cases is by no means intelligible, although from the inte- resting investigation of Joule on the mechanical equivalent of heat, we know that the quantity of heat evolved by rubbing is proportioned to the amount of mechanical work employed. Malleable metals, as iron and copper, which become heated by hammering or powerful pressure, are found thereby to have their density sensibly increased" and their capacity for heat diminished ; the rise of temperature is thus in some measure explained. A soft iron nail may be made red-hot by a few dexterous blows on an anvil; but the experiment cannot be repeated until the metal has been annealed, and in that manner restored to its original physical state. The disengagement of heat in the act of combination is a phenomenon of the utmost generality. The quantity of heat given out in each particular case is in all probability fixed and definite; its intensity is dependent upon the time over which the action is extended. Science has already been enriched by many admirable, although yet incomplete, researches on this important but most difficult subject. It is not improbable that many of the phenomena of heat, classed at pre- sent under different heads, may hereafter be referred to one common cause, namely, alterations in the capacity for heat of the same body under different physical conditions. For example, the definite absorption and evolution of sensible heat attending change of state may be simply due to the increased capacity for heat, to a fixed and definite amount of the liquid over the solid, and the vapor over the liquid. The experimental proof of the facts is yet generally wanting: in the very important case of water, however, the de- cidedly inferior capacity for heat of ice compared with that of liquid water seems fully proved from experiments on record. The heat of combination might, perhaps, in like manner, be traced to con- densation of volume, and the diminution of capacity for heat which almost invariably attends condensation. The proof of the proposition in numerous cases would be within the reach of comparatively easy experimental inquiry. LIGHT. ^83 LIGHT. The subject of light is so little connected with elementary chemistry, that a very slight notice of some of the most important points will suffice. Two views have been entertained respecting the nature of light. Sir Isaac Newton imagined that luminous bodies emit, or shoot out, infinitely small particles in straight lines, which, by penetrating the transparent part of the eye, and falling upon the nervous tissue, produced vision. Other philosophers drew a parallel between the properties of light and those of sound, and con- sidered that, as sound is certainly the effect of undulations, or little waves, propagated through elastic bodies in all directions, so light might be nothing more than the consequence of similar undulations transmitted with inconceiv- able velocity through a highly-elastic medium, of excessive tenuity, filling all space, and occupying the intervals between the particles of material substan- ces, to which they gave the name of ether. The wave-hypothesis of light is at present more in favor, as it serves to explain certain singular phenomena, discovered since the time of Newton, with greater facility than the other. A ray of light emitted from a luminous body proceeds in a straight line, and with extreme velocity. Certain astronomical observations afford the means of approximating to a knowledge of this velocity. The satellites of Jupiter revolve about the planet in the same manner as the moon about the earth, and the time required by each satellite for the purpose is exactly known from its periodical entry into or exit from the shadow of the planet. The time required by one is only 42 hours. Romer, the astronomer, at Copenhagen, found that this period appeared to be longer when the earth, in its passage round the sun, moved from the planet Jupiter; and, on the con- trary, ho observed that the periodic time appeared to be shorter when the earth moved in the direction towards Jupiter. The difference, though very small for a single revolution of the satellite, by the addition of many so in- creases, during the passage of the earth, from its nearest to its greatest dis- tance from Jupiter, that is, in about half a year, that it amounts to 16 minutes and 16 seconds. Romer concluded from this, that the li°-ht of the sun, reflected from the satellite, required that time to pass through "a distance equal to the diameter of the orbit of the earth; and since this space is little short of 200 millions of miles, the velocity of light cannot be less than 200,000 miles in a second of time. It will be'seen hereafter that this rapidity of transmission is rivalled by that of the electrical agent. When a ray of light falls on a plane surface it may be disposed of in three ways: more or less is absorbed and so disappears, the rest is either wholly or partly reflected, and partly transmitted. Those bodies which absorb nearly all the rays of light falling on them appear black. Those which, like glass or water, allow the greater part to pass through are called transparent. The reflected light may be reflected diffusely or regularly. Those bodies which reflect regularly the greater part of the light possess lustre like polished bodies: the perception of bodies depends on the diffused reflected light. The law of regular reflection is extremely simple. If a line be drawn per- pendicular to the surface upon which the ray falls, and the angle contained 84 LIGHT. Fig. 48. between the ray and the perpendicular measured, it will be found that the ray, after reflection, takes such a course as to make with the perpendicular an equal angle on the opposite side of the latter. A ray of light, r, falling at the point p, will be reflected in the direction pb/, making the angle b/pp/ equal to the angle rpp' ; or a ray from the point r falling upon the same spot will be reflected to r' in virtue of the same law. Farther, it is to be observed, that the incident and reflected rays are always contained in the same ver- tical plane. The same rule holds good if the mirror be curved, as a portion of a sphere, the curve being considered as made up of a multitude of little planes. Parallel rays become permanently altered in direction when reflected from curved sur- faces, becoming divergent or convergent according as the reflecting surface is convex or concave. It has just been stated that light passes in straight lines; but this is only true so long as the medium through which it travels preserves the same den- sity and the same chemical nature; when this ceases to be the case, the ray of light is bent from its course into a new one, or, in optical language, is said to be refracted. Let r be a ray of light falling upon a plate of some transparent substance with parallel sides, such as a piece of thick plate glass; and a its point of contact with the upper surface. The ray, instead of holding a straight course and passing into the glass in the direction a b, will be bent downwards to c; and, on leav- ing the glass, and issuing into the air on the other side, it will again be bent, but in the op- posite direction, so as to make it parallel to the continuation of its former track. The general -When the ray passes from a rare to a denser medium, it is usually refracted towards a line perpendicular to the sur- face of the latter; and conversely, when it leaves a dense medium for a rarer one, it is refracted from a line perpendicular to the surface of the denser substance: in the former case the angle, of incidence is said to be greater than that of refraction; in the latter, it is said to be less. In both cases the direction of the refracted ray is in the plane r a s, which is formed by the falling ray, and by the perpendicular s a drawn from the spot where the ray is refracted: the angle KAs = BAS,is called the angle of in- cidence. The angle c a s is called the angle of refraction. The difference of these two angles, that is, the angle cab, is the refraction. The amount of refraction, for the same me- dium, varies with the obliquity with which the ray strikes the surface. When perpendicular to the latter, it passes without change of direc- tion at all; and in other positions, the refrac- tion increases with the obliquity. Let r represent a ray of light falling upon the surface of a mass of plate glass at the point a. From this point let a perpendicular fall law is thus expressed: Fig. 50. LIGHT. 85 and be continued into the new medium, and around the same point, as a cen- tre, let a circle be drawn. According to the law just stated, the refraction must be towards the perpendicular; in the direction ar' for example. Let the lines a —a, a' — a', at right angles to the perpendicular, be drawn, and their length compared by means of a scale of equal parts, and noted ; their length will be in the case supposed in the proportion of 3 to 2. These lines are termed the sines of the angles of incidence and refraction respectively. Now let another ray be taken, such as r; it is refracted in the same manner to r/, the bending being greater from the increased obliquity of the ray; but, what is very remarkable, if the sines of the two new angles of incidence and refraction be again compared, they will still be found to bear to each other the proportion of 3 to 2. The fact is expressed by saying, that the ratio of the sines of the angles of incidence and refraction is constant for the same medium. Different bodies possess different refractive powers; generally speaking, the densest substances refract most. Combustible bodies have been noticed to po-v-ess greater refractive power than their density would indicate, and from this observation Sir I. Newton predicted the combustible nature of the diamond long before anything was known respecting its chemical nature. The method adopted for describing the comparative refractive powers of different bodies is to state the ratio borne by the sine of the angle of refrac- tion to that of incidence, making the former unity: this is called the index of refraction for the substance. Thus, in the case of glass the index of re- fraction will be 1 -5. When this is once known for any particular transparent body, the effect of the latter upon a ray of light entering it, in any position, :an be calculated by the aid of the law of sines. Substances. Index of Refraction. Substances. Index of Refraction Tabasheer1 . 1-10 Garnet . 1-80 Ice . 1-30 Glass, with much oxide Water . . 1-34 of lead 1-90 Fluor spar . 1 -40 Zircon . 200 Plate glass . - . 1-50 Phosphorus . 2-20 Rock crystal . 1-60 Diamond 2-50 Chrysolite . 1-69 Chromate of lead 3 00 Bisulphide of carbon . 1-70 Fig. 51. When a luminous ray enters a mass of substance differing in refractive power from the air, and whose surfaces are not parallel, it becomes perma- nently deflected from its course and altered in its direction. It is upon this principle that the properties of prisms and lenses depend. To take an example.—Let the sketch represent a triangular prism of glass, upon the side of which the ray of light r may be supposed to fall. This ray will of course be refracted in entering the glass towards a line perpendicular to the first surface, and again, from a line perpen- dicular to the second surface on emerging into the air The result is the deflection acr, which is equal to the sum of the two deflections which the ray undergoes in passing through the prism. A convex lens is thus enabled to converge rays of light falling upon it, and a concave lens to separate them more widely; each separate part of the surface of the lens producing its own independent effect. The light of the sun and celestial bodies in general, as well as that of the electric spark and of all ordinary flames, is of a compound nature. If a ray of light from any of the sources mentioned be admitted into a dark room by 8 * A siliceous deposit in the joints of the bamboo. 86 LIGHT. a small hole in a shutter, or otherwise, and suffered to fall upon a glass prism in the manner described below, it will not only be refracted from its straight Fig. 52. course, but will be decomposed into a number of colored rays, which may be received upon a white screen placed behind the prism. When solar light is employed, the colors are extremely brilliant, and spread into an oblong space of considerable length. The upper part of this image or spectrum will be violet and the lower red, the intermediate portion, commencing from the violet, being indigo, blue, green, yellow, and orange, all graduating imper- ceptibly into each other. This is the celebrated experiment of Sir Isaac Newton ; and from it he drew the inference that white light is composed of seven primitive colors, the rays of which are differently refrangible by the same medium, and hence capable of being thus separated. The violet rays are most refrangible, and the red rays least. Sir D. Brewster is disposed to think, that out of Newton's seven primitive colors four are really compound, and formed by the superposition of the three remaining, namely, blue, yellow, and red, which alone deserve the name of primitive. When these three kinds of rays are mixed, or superimposed, in a certain definite manner, they produce white light, but when one or two of them are in excess, then an effect of color is perceptible, simple in the first case, and compound in the second. There are, according to this hypothesis, by no means universally adopted, rays of all refrangibilities of each color] and consequently white light in every part of the spectrum, but then they are unequally distributed; the blue rays are more numerous near the top, the yellow towards the middle, and the red at the bottom, the excess of each color producing its characteristic effect. In the diagram below, the intensity of each color is represented by the height of a curve, and the effects of mixture will be intelligible by a little consideration. Fig. 53. BLUE, YELLOW. RED. SOLAR SPECTRUM. Bodies of the same mean refractive power do not always equally disperse or spread out the differently-colored rays: because the principal yellow or red rays, for instance, are equally refracted by two prisms of different materials, it does not follow that the blue or the violet shall be similarly affected. Hence, prisms of different varieties of glass, or other transparent C2./.::5�� LIGHT. 87 substances, give, under similar circumstances, very different spectra, both as respects the length of the image, and the relative extent of the colored bands. An examination into a peculiar mode of analysis of light, discovered by Sir John Herschel, in a solution of sulphate of quinine, has within the last few years led to the discovery of a most remarkable fact. Mr. Stokes has observed that light of certain refrangibility and color is capable of experiencing a peculiar influence in being dispersed by certain media, and of undergoing thereby an alteration of its refrangibility and color. This curious change can be produced by a great number of bodies, both liquid and solid, trans- parent and opaque. Frequently the change affects only the extreme limits, at other times larger portions, and in a few cases even the whole, or, at all events, the major part of the spectrum. A dilute solution of sulphate of quinine, for instance, changes the violet and the dark-blue light to sky-blue; by a decoction of madder in a solution of alum all rays of higher refrangibility than yellow are converted into yellow; by an alcoholic solution of the coloring matter of leaves all the rays of the spectrum become red. In all cases in which this peculiar phenomenon presented itself in a greater or less degree, Mr. Stokes observed that it consisted in a diminution of the refrangibility. Thus, rays of so high a degree of refrangibility, that they extend far beyond the extreme limits of the spectrum visible under ordinary circumstances, may be rendered luminous, and converted into blue and even red light. The colors of natural objects are supposed to result from the power which the surfaces of the bodies possess of absorbing some of the colored rays, while they reflect or transmit, as the case may be, the remainder. Thus, an object appears red because it absorbs, or causes to disappear, a portion of the yellow and blue rays composing the white light by which it is illuminated. A ray of common light made to pass through certain crystals of a particular order is found to undergo a very remarkable change. It becomes split or divided into two rays, one of which follows the general law of refraction, and the other takes a new and extraordinary course, dependent on the position of the crystal. This effect, which is called double refraction, is beautifully illustrated in the case of Iceland spar, or crystallized carbonate of lime. On placing a rhomb of this substance on a piece of white paper, on which a mark or line has been made, the object will be seeii double. Again, if a ray of light be suffered to fall on a plate of glass at an angle of 56° 45/, the portion of the ray which suffers reflection will be found to have acquired properties which it did not before possess; for on throwing it, at the same angle, upon a second glass plate, it will be observed that there are two particular positions of the latter, namely, those in which the planes of incidence are at right angles, when the ray of light is no longer reflected but entirely dispersed. Light which has suffered this change is said to be polarized. The light which passes through the first or polarizing plate is, also, to a certain extent, in this peculiar condition, and by employ- ing a series of similar plates, held parallel to the first, this effect may be greatly increased; a bundle of fifteen or twenty such plates may be used with great convenience for the experiment. It is to be remarked, also, that the light polarized by transmission in this manner is in an opposite state to that polarized by reflection; that is, when examined by a second or analyzing plate, held at the angle before mentioned, it will be seen to be reflected when the other is transmitted, and to be dispersed when the first is reflected. It is not every substance which is capable of polarizing light in this manner; glass, water, and certain other bodies bring about the change in question, each having a «■ particular polarizing angle at which the effect is greatest. 88 LIGHT. The metals also can, by reflection, polarize the light, but they do so very imperfectly. The two rays into which a pencil of common light divides itself in passing through a doubly-refracting crystal are found on examination to be polarized in a very complete manner, and also transversely, the one being capable of reflection when the other vanishes or is transmitted. It is said that both rays are polarized in opposite directions. With a rhomb of trans- parent Iceland spar of tolerably large dimensions the two oppositely-polarized rays may be widely separated and examined apart. There is yet another method of polarization, by the employment of plates of the mineral tourmaline cut parallel to the axis of the crystal. This body polarizes by simple transmission, the ray falling perpendicular to its surface; Fig. 55. Fig. 56. a part of the light is absorbed, and the remainder modified in the manner described. When two such plates are held with their axis parallell as in fig. 55, light traverses them both freely; but when one of them is turned round in the manner shown in the second cut, so as to make the axis cross at right angles, the light is almost wholly stopped, if the tourmalines be good. A plate of the mineral thus becomes an excellent test for discriminating between polarized light and that which has not undergone the change. Some of the most splendid phenomena of the science of light are exhibited when thin plates of doubly-refracting substances are interposed between the polarizing arrangement and the analyzer. Instead of the tourmaline plate, which is always colored, frequent use is made of two Nichol's prisms, or conjoined prisms of carbonate of lime, which, in consequence of a peculiar cutting and combination, possess the property of allowing only one of the oppositely-polarized rays to pass. If the two Nichol's prisms are placed one behind the other in precisely similar positions, the light polarized by the one goes through the other unaltered. But when one prism is slightly turned round in its setting, a cloudiness is produced, and by continuing to turn the prism this increases until perfect darkness ensues. This happens, as with the tourmaline plates, when the two prisms cross one another. The phenomenon is the same with colorless as with colored light. Supposing that polarized light, colored, for example, by going through a plate of red glass, passed through the first Nichol's prism, and was altogether obstructed, in consequence of the position of the second prism, then, if between the two prisms a plate of rock-crystal, formed by a section at right angles to the principal axis of the crystal, is interposed, the light polarized by the first prism by passing through the plate of quartz is enabled partially to pass through .the second Nichol's prism. Its passage through the second prism can then again be interrupted by turning the second prism round to a certain extent. The rotation required varies with the thickness of the plate of rock-crystal, and also with the color of the light that is employed. It in- creases from red in the following order—yellow, green, blue, violet. This property of rock-crystal was discovered by Arago. The kind of pola- LIGHT. 89 rization has been called circular polarization. The direction of the rotation is with many plates towards the right hand; in other plates it is towards the left. The one class is said to possess right-handed polarization; the other class left-handed polarization. At present only very few other crystalline compounds are known to possess the property of circular polarization even in a slight degree; among these are chlorate and bromate of soda. Biot observed that many solutions of organic substances exhibit the property of circular polarization, though to a far less extent than rock-crystal. Thus, solutions of cane-sugar, glucose, and tartaric acid, possess right-handed pola- rization ; whilst albumen, uncrystallizable sugar, and oil of turpentine are left-handed. In all these solutions the amount of circular polarization in- creases with the concentration of the fluid and the thickness of the column of liquid through which the light passes. Hence circular polarization is an important auxiliary in chemical analysis. In order to determine the amount of polarization which any fluid exhibits, the liquid is put into a glass tube not less than from ten to twelve inches long, which is closed with glass plates. This is then placed between the two Nichol's prisms, which have previously been so arranged with regard to each other that no light could pass through. An apparatus of this description, the saccharometer, is chiefly used for de- termining the concentration of solutions of cane-sugar. The form of this instrument may be seen in the fig. 57. The two Nichol's prisms are enclosed in the corresponding fastenings a and b. Between the Fig. 57. ;............m^-sam*............i two there is a space to receive the tube which is filled with the solution of sugar. If the prisms are crossed in the way mentioned above before the tube is put in its place, that is, if they are placed so that no light passes 8* 90 LIGHT. them, by the action of the solution of sugar the light is enabled to pass, and the Nichol's prism, for instance, a, must be turned through a certain angle before the light is again perfectly stopped. The magnitude of this angle is observed on the circular disk s s, which is divided into degrees, and upon which, by the turning of the prism, an index z is moved along the division. When the tube is exactly ten inches long, and is closed at both ends by flat glass plates, and when it is filled with solution containing ten per cent, by weight of cane-sugar, and free from any other substance possessing an action on light, the angle of rotation is 13-35. Since the magnitude of this angle stands in direct relation to the length of the column of fluid and also to tho quantity of sugar in solution, it is clear that the quantity of sugar in any given solution, when the length of the column of fluid is I inches, and the angle of rotation is a degrees, can be determined by the equation z = ——. lo'oO This process is not sufficient when the solution contains cane-sugar and un- crystallizable sugar, for the latter rotates the ray to the left; then only-the difference of the two actions is obtained. But if the whole quantity of sugar be changed into uncrystallizable sugar, and the experiment be repeated, from the results of the two observations the quantity of both kinds of sugar can easily be calculated. It is difficult to find exactly that position of the Nichol's prisms in which the greatest darkness prevails. To make the measurements more exact and easy, Soleil has made some additions to the apparatus. At q before the prism b, a plate of rock-crystal cut at right angles to the axis is placed. It is divided in the centre of the field of vision, half consisting of quartz, rotating to the right hand, and half of the variety that rotates to the left; it is 0-148 inch (3-75 millimetre) thick ; this thickness being found by experiment to produce the greatest difference in the color of the two halves, when one prism is slightly rotated. The solution of sugar has precisely the same action as the rotation, since it increases the action of the half which rotates to the left. Hence the two halves will assume a different color when the smallest quantity of sugar is present in the fluid. By slightly turning the Nichol's prism a, this difference can be again removed. Soleil has intro- duced another more delicfjfc means of effecting this at the part /, which he calls the compensator. The most important parts of this are separately re- presented in fig. 57. It/consists of two exactly equal right-angled prisms, of left-handed quartz, whose surfaces, c' and c, are cut perpendicular to the optic axis. These prisms can, by means of the screw v and a rack and pinion, be made to slide on one another, so that, when taken together, they form a plate of varying thickness, bounded by parallel surfaces. One of the frames has a scale I, the other a vernier n. When this points to zero of the scale, the optical action of the two prisms is exactly compensated by a right-handed plate of rock-crystal, so that an effect is obtained as regards circular polari- zation, as if the whole system were not present. As soon, however, as the screw is moved, and thus the thickness of the plate formed by the two prisms is changed, we will suppose it increased, then a left-handed action ensues which must be properly regulated, until it compensates the opposite action of a solution of sugar. Thus a convenient method is obtained of rendering the color of the double plate uniform, when it has ceased to be so in conse- quence of the action of a solution of sugar. Faraday has made the remarkable discovery that if a very strong electric current is passed round a substance which possesses the property of circular polarization, the amount of rotation is altered to a considerable degree. The luminous rays of the sun are accompanied, as already mentioned by others which possess heating powers. If the temperature of the different- colored spaces in the spectrum be tried with a delicate thermometer it will be found to increase from the violet to the red extremity, and when th'e prism is of some particular kinds of glass, the greatest effect will be manifest a little LIG HT. 91 beyond the visible red ray. It is inferred from this that the chief mass of the heating rays of the sun are among the least refrangible components of the solar beam. Again, it has long been known that chemical changes both of combination and of decomposition, but more particularly the latter, could be effected by the action of light. Chlorine and hydrogen combine at common temperatures only under the influence of light, and parallel cases occur in great numbers in organic chemistry: the blackening and decomposition of salts of silver are familiar instances of the chemical powers of the same agent. Now it is not always the luminous part of the ray which effects these changes; they are chiefly produced by certain invisible rays, accompanying the others, and which are found most abundantly beyond the violet part of the spectrum. It is there that certain chemical effects are most marked, although the intensity of the light is exceedingly feeble. From the fact that some salts of silver are less readily decomposed by the luminous—yellow, orange, and red rays—than by certain rays which extend beyond the ordinary visible spectrum, it has been concluded that there exists in the sunbeam, in addition to heat and light, a principle having a distinct action, to which the provisional term acti- nism has been given — from AkAv, a ray. The actinic rays are thus directly opposed to the heating rays in the common spectrum in their degree of re- frangibility, since they exceed all the others in this respect. The luminous rays, too, under peculiar conditions, exert decomposing powers upon salts of silver. The result of the action of any ray depends, moreover, greatly on the physical state of the surface upon which it falls, and on the chemical constitution of the body; indeed, for every kind of rays a substance may be found which under particular circumstances will affect it, and thus it appears that the chemical functions are by no means confined to any set of rays to the exclusion of the rest. Upon the chemical changes produced by light is based the art of photo- graphy. In the year 1802,1 Mr. Thomas Wedgwood purposed a method of copying paintings on glass by placing behind them white paper or leather moistened with a solution of nitrate of silver, which became decomposed and blackened by the transmitted light in proportion to the intensity of the latter; and Davy, in repeating these experiments, found that he could thus obtain tolerably accurate representations of objects of a texture partly opaque and partly transparent, such as leaves and the wings of insects, and even copy with a certain degree of success the images of small objects obtained by the solar microscope. These pictures, however, required to be kept in the dark, and could only be examined by candle-light, otherwise they became obliterated by the blackening of the whole surface from which the salt of silver could not be removed. These attempts at light-painting attracted but little notice till the publication of Mr. Fox Talbot's '* papers, read before the Royal Society, in January and February, 1839, in which he detailed two methods of fixing the pictures produced by the action of light on paper impregnated with chlo- -ride of silver, and at the same time described a plan by which the sensibility of the prepared paper may be increased to the extent required for receiving impressions from the images of the camera obscura. Very shortly afterwards, Sir John Herschel3 proposed to employ solutions of the alkaline hyposulphites for removing the excess of chloride of silver from the paper, and thus preventing the farther action of light; and this plan has been found exceedingly successful. The greatest improvement, however, which the curious art of photogenic drawing has received, is due to Mr. Tal- bot,4 who, in a communication to the Royal Society, described a method by • Journal of the Royal Institution, i. 170. " Phil. Mag., March, 1839. • Phil. Trans, for 1840, p. 1. phl1- Mag., August, 1841. 92 LIGHT. which paper of such sensibility could be prepared as to permit its application to the taking of portraits of living persons by the aid of a good camera obscura— the time required for a perfect impression seldom exceeding a few seconds. The general plan at present in use is the following:— Writing-paper of good quality is washed on one side with a solution of thirty grains of nitrate of silver in an ounce of distilled water, and then left to dry spontaneously in a dark room; when dry, it is immersed for from five to ten minutes in a solution of one ounce of iodide of potassium in twenty ounces of water. The paper is then soaked in water for half an hour, changing the water three or four times to remove the excess of iodide of potassium, and is then dried. These operations should be performed by candle-light. When required for use, the paper, thus coated with yellow iodide of silver, is brushed over with a solution made by adding together one part of a solution of nitrate of silver, fifty grains, to an ounce of water: two parts glacial acetic acid, and three parts of a saturated solution of gallic acid; after a few seconds the excess is removed by blotting-paper. This, which is called Talbotype or Calo' type paper, is now ready for use ; exposure to diffused daylight for one second suffices to make an impression upon it, and even the light of the moon pro- duces the same effect, although a much longer time is required. For land- scapes and fixed objects, and when the paper is required to be prepared long beforehand, the above mixture of " gallo-nitrate" should be diluted with from twenty to fifty volumes of water, since, especially in hot weather, without this precaution the paper blackens spontaneously. The images of the camera obscura are at first invisible, but are made to appear in full intensity, by once more washing the paper with a mixture of one part of the silver solution (fifty grains to an ounce of water) and four parts of the saturated solution of gallic acid. The development of the image soon commences, and should reach its maximum in a few minutes. The picture is of course negative, the lights and shadows being reversed; to obtain positive copies nothing more is necessary than to place a piece of pho- tographic paper prepared with chloride of silver, or a piece of talbotype paper, beneath the negative cover, to press the two papers iu contact by means of a glass, and to expose the whole to the light of the sun for a short time, or longer to diffused daylight. Before this can be done, the negative must, however, be fixed, otherwise it will blacken: this is done temporarily by washing with a solution of bromide of potassium, ten grains in an ounce of water, and then rinsing in common water. The ultimate fixing is effected by immersion in a solution of one part of hyposulphite of soda, in from four to ten parts of water: the weaker solu- tion should be used hot, about 180° (82°-22C), and the immersion continued until the yellow tint arising from the undecomposed iodide disappears: finally, repeatedly washing in hot water, drying, and saturating with white wax termi- nates the process. _ The positives are also fixed by hyposulphite of soda, by cyanide of potas- sium, or by ammonia; all of which act by removing the undecomposed chlo- ride of silver. The conservation of the positive is a point of difficulty. Mr. Malone recommends immersion in a strong solution of caustic potassa, heated to about 180° (82°-22C); a change of tint ensues, and greater permanence is acquired. After removal of the alkali and any sulphur and chlorine com- pounds present, the picture should be sized and hot-pressed, or varnished keeping the finished proof most carefully excluded from sulphuretted vapors! Sir John Herschel has shown that a great number of other substances can be employed in these photographic processes by taking advantage of the sin- gular deoxidizing effects of certain portions of the solar rays. Paper washed with a solution of a salt of sesquioxide of iron becomes capable of receiving impressions of this kind, which may afterwards be made evident by ferricya- LIGHT. 93- nide of potassium, or terchloride of gold. Vegetable colors are also acted upon in a very curious and apparently definite manner by the different parts of the spectrum.1 The daguerreotype, the announcement of which was first made in the sum- mer of 1839, by M. Daguerre, who had been occupied with this subject from 1826, if not earlier, is another remarkable instance of the decomposing effects of the solar rays. A clean and highly-polished plate of silvered copper is ex- posed for a certain period to the vapor of iodine, and then transported to the camera obscura. In the most improved state of the process, a very short time suffices for effecting the necessary change in the film of iodide of silver. The picture, however, only becomes visible by exposing it to the vapor of mercury, which attaches itself, in the form of exceedingly-minute globules, to those parts which have been most acted upon, that is to say, to the lights, the shadows being formed by the dark polish of the metallic plate. Lastly, the drawing is washed with a solution of hyposulphite of soda to remove the undecomposed iodide of silver, and render it permanent. The images of objects thus produced bear the most minute examination with a magnifying-glass, the smallest details being depicted with perfect fidelity. Great improvements have been necessarily made in the application of this beautiful art to taking portraits. By the joint use of bromine and iodine the phtes are rendered far more sensitive, and the time of sitting is shortened to a very few seconds. When the operation is completed, the color of the plate is much improved by the deposition of an exceedingly thin film of gold, which communicates a warm purplish tint, and removes the previous dull leaden-grey hue, to most persons very offensive. The difficulty of obtaining good paper for the talbotype has led to the inven- tion of various substitutes: albumen on glass and collodion are used with suc- cess ; a soluble iodide, or some analogous salt, is mixed with either liquid, and applied to a glass or porcelain plate, dried, and immersed in a solution of nitrate of silver; thus a sensitive coating is formed upon which the images of the camera or microscope are thrown, and developed by subsequent treatment with deoxidizing agents—either pyro-gallic acid, gallic acid, or a salt of prot- oxide of iron may be used. The fixing is accomplished by hyposulphite of soda. The result is either negative or positive at the will of the operator. The proofs on porcelain or glass may be burned in, and perhaps thus rendered indestructible by time. Etching and lithographic processes, by combined chemical and photographic agency, promise to be of considerable utility. The earliest is that of Niepce: he applied a bituminous coating to a metal plate, upon which an engraving was superimposed. The light being thus partially interrupted acted une- qually upon the varnish ; a liquid hydro-carbon petroleum used as a solvent removed the bitumen wherever the light had not acted; an engraving acid could now bite the unprotected metal, which could eventually be printed from in the usual way. Dr. Donne" and Dr. Berres, by submitting the daguerreo- type to the action of nitric acid and its vapor, obtained etchings from which proofs could be taken. Mr. Grove, by using chlorine evolved by voltaic agency, succeeded in obtaining a more manageable process; and very suc- cessful results have been obtained by M. Fizeau: he submits the daguerreo- type to the action of a mixture of dilute nitric acid, common salt and nitrate of potassa, the silver only is attacked, the mercurialized portion of the image resisting the acid, and an etching is obtained following minutely the lights and shadows of the picture. To deepen this etching, the chloride of silver formed is removed by ammonia, the plate is boiled in caustic potassa and again treated with acid, and so on till the etching is of sufficient depth. In extreme 1 Phil. Trans., 1842, p. 1. 94 LIGHT. cases electro-gilding is resorted to, and an engraving acid used to get still more powerful impressions. Among the latest results are those obtained by Mr. Talbot on steel plates: he uses a mixture of bichromate of potassa and gelatine, which hardens by exposure to the light; the parts not affected are removed by washing; bichlo- ride of platinum is used as an etching liquid, it has the advantage of biting with greater regularity than nitric acid. The bitumen process of M. Niepce has been applied to lithographic stone; and positives obtained from negative talbotypes have been printed off by a modification of the ordinary lithographic process. M. Niepce finds that ether dissolves the altered bitumen, while coal-tar naphtha, or benzol, attacks by preference the bitumen in its normal condition. RADIATION OF HEAT. 95 RADIATION, REFLECTION, ABSORPTION, AND TRANSMISSION OP HEAT. RADIATION OF HEAT. If a red-hot ball be placed upon a metallic support, and left to itself, cooling immediately commences, and only stops when the temperature of the ball is reduced to that of the surrounding air. This effect takes place in three ways: heat is conducted away from the ball through the substance of the support; another portion is removed by the convective power of the air; and the residue is thrown off from the heated body in straight lines or rays, which pass through air without interruption, and become absorbed by the surfaces of neighboring objects which happen to be presented to their impact. This radiant or radiated heat- resembles, in very many respects, ordinary light; it suffers reflection from polished surfaces according to the same law; it is by dull and rough surfaces partly reflected, partly absorbed; it moves with extreme velocity; and, finally, it traverses certain transparent media, undergoing refraction at the same time, in obedience to the laws which regulate that phenomenon in optics. The fact of the reflection of heat may be very easily proved. If a person stand before a fire in such a position that his face may be screened by the mantel-shelf, and if he then take a bright piece of metal, as a sheet of tinned plate, and hold it in such a manner that the fire may be seen by reflection, at the same moment a distinct sensation of heat will be felt. The apparatus best fitted for studying these facts consists of a pair of concave metallic mirrors of the form called parabolic. The parabola is a curve possessing very peculiar proper- F'S- 58- ties, one of the most prominent being the following: — A tangent drawn to any part of the curve makes equal angles with two lines, one of which proceeds from the point where the tangent touches the curve in a direction parallel to what is called the axis of the parabola, and the other from the same spot through a point in front of the curve called the focus. It results from this that parallel rays, either of light or heat, falling upon a mirror of this particular curvature in a direction parallel to the axis of the parabola, will be all reflected to a single point at the focus; and rays diverging from this focus, and impinging upon the mirror will, after reflection, become parallel (fig. 58). If two such mirrors be placed opposite to each other at a considerable distance, and so adjusted that their axes shall be coincident, and a hot body placed in the focus of the one. while a thermometer occupies that of the other, the reflection of the rays of heat will become manifest by their effect upon the instrument. In this manner, with a pair of by no means very perfect mirrors, 18 inches in diameter, separated by an interval of 20 96 RADIATION OF HEAT. feet or more, amadou or gunpowder may be readily fired by a red-hot ball in the focus of the opposite mirror (fig. 59). Fig. 59. The power of radiation varies exceedingly with different bodies, as may be easily proved. If two similar vessels of equal capacity be constructed of thin metal, and the surface of one be highly polished, while that of the other is covered with lamp-black, and both filled with hot water of the same tempera- ture, and their rate of cooling observed from time to time with a thermometer, it will be constantly found that the blackened vessel loses heat much faster than the one with bright surfaces; and since both are put on a footing of equality in other respects, this difference, which will often amount to many degrees, must be ascribed to the superior emissive power of the film of soot. By another arrangement, a numerical comparison can be made of these differences. A cubical metallic vessel is prepared, each of whose sides is in a different condition, one being polished, another rough, a third covered with lampblack, &c. The vessel is filled with water, kept constantly at 212° (100CC) by a small steam-pipe. Each of its sides is then presented in succes- sion to a good parabolic mirror, having in its focus one of the bulbs of the differential thermometer before described (fig. 23), the bulb itself being blackened. The effect produced on this instrument is taken as a measure of the comparative radiating powers of the different surfaces. The late Sir John Leslie obtained by this method of experiment the following results: — Emissive power. Emissive power. Lampblack . 100 Tarnished lead . . 45 Writing-paper . . 98 Clean lead . 19i Glass . 90 Polished iron . . 15 Graphite. . 75 Polished silver . . 12 The best reflecting surfaces are always the worst radiators; polished metal reflects nearly all the heat that falls upon it, while its radiating power is the feeblest of any substance tried, and lampblack, which reflects nothing, radiates most perfectly. The power of absorbing heat is in direct proportion to the power of emission. The polished metal mirror, in the experiment with the red-hot ball, remains quite cold, although only a few inches from the latter; or, again, if a piece of gold leaf be laid upon paper, and a heated iron held over it until the paper * The supposed influence of mere difference of surface has been called in question bv M Melloni. who attributes to other causes the effects observed by Sir John Leslie and others among which superficial oxidation and differences of physical condition with respect to hard- ness and density, are among the most important. With metals not subject to tarnish scratching the surface increases the emissive power when the plates have been rolled or ham- mered, i. e , are in a compressed state, and diminishes it, on the contrary, when the metal has been cast and carefully polished without burnishing. In the case of ivory, marble, and jet where compression cannot take place, no difference is perceptible in the radiating Dower of polished and rough surfaces. — Ann. Chim. et Phys., lxx. 435. RADIATION OF HEAT. 97 is completely scorched, it will be found that the film of metal has perfectly defended that portion beneath it. The faculty of absorption seems to be a good deal influenced by color. Dr. Franklin found that when pieces of cloth of various colors were placed on snow exposed to the feeble sunshine of winter, the snow beneath became equally melted, the effect being always in proportion to the depth of the color; and Dr. Stark has since obtained a similar result by a different method of experimenting. According to the late researches of Melloni, this effect depends less on the color than on the nature of the coloring matter, which covers the surface of the cloth. These facts afford an explanation of two very interesting and important natural phenomena, namely, the origin of dew, and the cause of the land and sea breezes of tropical countries. While the sun remains above the horizon, the heat radiated by the surface of the earth into space is compensated by the absorption of the solar beams; "but when the sun sets, and the supply ceases, while the emission of heat goes on as actively as before, the surface becomes cooled until its temperature sinks below that of the air. The air in contact with the earth of course participates in this reduction of temperature; the aqueous vapor present speedily reaches its point of maximum density, and then begins to deposit moisture, whose quantity will depend upon the propor- tion of vapor in the atmosphere, and on the extent to which the cooling process has been carried. It is observed that dew is most abundant in a clear calm night, succeeding a hot day: under these circumstances the quantity of vapor in the air is usually very great, and at the same time radiation proceeds with most facility. At such times a thermometer laid on the ground will, after some time, indicate a temperature of 10° (5°-5C), 15° (8°-3C), or even 20° (11°-1C) below that of the air a few feet higher. Clouds hinder the formation of dew, by reflect- ing back to the earth the heat radiated from its surface, and thus preventing the necessary reduction of temperature; and the same effect is produced by a screen of the thinnest material stretched at a little height above the ground. In this manner gardeners often preserve delicate plants from destruction by the frosts of spring and autumn. The piercing cold felt just before and at sunrise, even in the height of summer, is the consequence of this refrigeration having reached its maximum. Wind also effectually prevents the deposition of dew, by constantly renewing the air lying upon the earth before it has had its temperature sufficiently reduced to cause condensation of moisture. Many curious experiments may be made by exposing on the ground at night bodies which differ jn their powers of radiation. If a piece of black cloth and a plate of bright metal be thus treated, the former will be often found in the morning covered with dew, while the latter remains dry. Land and sea breezes are certain periodical winds common to most sea- coasts within the tropics, but by no means confined to those regions. It is observed, that a few hours after sunrise a breeze springs up at sea, and blows directly on shore, and that its intensity increases as the day advances, and declines and gradually expires near sunset. Shortly afterwards a wind arises in exactly the opposite direction, namely, from the land towards the sea, lasts the whole of the night, and only ceases with the reappearance of the sun. It is easy to give an explanation of these effects. When the sun shines at once upon the surface of the earth and that of the sea, the two become unequally heated, because the water, although it possesses greater power of absorbing heat, yet is more slowly warmed in consequence of its greater capacity for heat, and the greater depth to which the rays of the sun can penetrate. The air over the heated surface of the ground, being expanded by heat, rises, and has its place supplied by colder air flowing from the sea, producing the sea-breeze. Wheu the sun sets, both sea and land begin to D8 TRANSMISSION OF HEAT. cool by radiation: the rate of cooling of the latter will, however, far exceed that of the former, and its temperature will rapidly fall. The air above becoming cooled and condensed, flows outwards in obedience to the laws of fluid pressure, and displaces the warmer air of the ocean. In this manner, by an interchange of air between sea and land, the otherwise oppressive heat is moderated, to the great advantage of those who inhabit such localities. The land and sea-breezes extend to a small distance only from shore, but afford, notwithstanding, essential aid to coasting navigation, since vessels on either tack enjoy a fair wind during the greater part of both day and night. TRANSMISSION OF HEAT ; DIATHERMANCY. Rays of heat, in passing through air, receive no more obstruction than those of light under similar circumstances ; but with other transparent media the case is different. If a parabolic mirror .be taken, and its axis directed towards the sun, the rays both of heat and light will be reflected to the focus, which will exhibit a temperature sufficiently high to fuse a piece of metal, or fire a combustible body. If a plate of glass be now placed between the mir- ror and the sun, the effect will be perceptibly diminished. Now, let the same experiment be made with the heat of a kettle filled with boiling water; the heat will be concentrated by reflection as before, but, on interposing the glass, the heating effect at the focus will be reduced to nothing. Thus, the rays of heat coming from the sun traverse even glass in considerable quantity, but not so easily as air, whilst rays from hot water are entirely stopped by glass. In the year 1833, M. Melloni published the first of a series of exceedingly valuable researches on this subject, which are to be found in detail in various volumes of the Annales de Chemie et de Physique.1 It will be necessary, in the first instance, to describe the method of operation followed by this philosopher. Not long before, two very remarkable facts had been discovered: Oersted in Copenhagen, showed that a current of electricity, however produced, ex- ercises a singular and perfectly-definite action on a magnetic-needle; and Seebeck, in Berlin, found that an electric current may be Fig. 60. generated by the unequal effects of heat on different _____—» ' metals in contact. If a wire conveying an electrical cur- _r rent be brought near a magnetic needle, the latter will immediately alter its position and'assume a new one as nearly perpendicular to the wire as the mode of suspension and the magnetism of the earth will permit. When the wire, for example, is placed ditectly over the needle and parallel to its length, while the current it carries travels from north to south, the needle is deflected from its ordi- nary direction and the north pole driven to the eastward. When the current is reversed, the same pole deviates to an equal amount towards the west. Placing the wire below the needle instead of above produces the same effect as reversing the current. When the needle is subjected to the action of two currents in opposite directions, the one above and the other below, they will obviously concur in their effects. The same thing happens when the wire carrying the current is bent upon itself and the needle placed between the two portions • and since every time the bending is repeated a fresh portion of the current is made to act in the same manner upon the needle, it is easy to see 1 Translated also in Taylor's Scientific Memoirs. Fig. 61. TRANSMISSION OF HEAT. 99 how a current, too feeble to produce any effect when a simple straight wire is employed, may be made by this contrivance to exhibit a powerful action on the magnet. It is on this principle that instruments called galvanometers, galvanoscopes, or multipliers, are constructed; they serve, not only to indicate the existence of electrical currents, but to show by the effect upon the needle the direction in which they are moving. The delicacy of the instrument can be extraordinarily increased by the use of a very long coil of wire and two needles of equal strength, and with opposite poles conjoined (fig. 80). These needles are hung by untwisted silk, so that one is between the coils and the other above them, so that the current acts in the same direction on both. The thickness of the wire has some influence on the delicacy of the instru- ment. For the following experiments it should not be less than Jf of an inch thick. When two pieces of different metals, connected together at each end, have one of their joints more heated than the other, an electric current is immedi- ately set up. Of all the metals tried, bismuth and antimony form the most powerful combination. A single pair of bars, having one of their junctions heated in the manner shown (fig. 62), can develop a current strong enough to deflect a compass-needle placed withm, and, by arranging a number in a series and heating their alternate end3, the intensity of the current may be very much increased. Such an arrangement is called a thermo-electric pile. Fig. 62. M. Melloni constructed a very small thermo-electric pile of this kind con- taining fifty-five slender bars of bismuth and antimony, laid side by side and soldered together at their alternate ends, as shown in fig. 63. He'con- nected this pile with an exceedingly delicate multiplier, and found himself in the possession of an instrument for measuring small variations of temperature far surpassing in delicacy the air-thermometer in its most sensitive form and having great advantages in other respects over that instrument when em- ployed for the purposes to which he devoted it. The substances whose powers of transmission were to be examined were cut into plates of a determinate thickness, and, after bein°- well nnlUliPr) nv ranged in succession in front of the little pile, the extremity of which was blackened to promote the absorption of the rays. A perforated screen the area of whose aperture equalled that of the face of the pile, was placed between the source of heat and the body under trial, while a second screen served to intercept all radiation until the moment of the experiment After much preliminary labor for the purpose of testing the capabilities of the apparatus and the value of its indications, an extended series of researches was undertaken and carried on during a long period with great success • some of the most curious results are given in the annexed table. 100 TRANSMISSION OF HEAT. Four different sources of heat were employed in these experiments, differ- ing in their degrees of intensity; the naked flame of an oil-lamp; a coil of Fig. 64. platinum wire heated to redness; blackened copper at 734° (390°); and the same heated to 212° (100°C). Substances. (Thickness of plate 0-1 inch, nearly.) Rock-salt, transparent and colorless. Fluor-spar, colorless...... Rock-salt, muddy....... Beryl........... Fluor-spar, greenish...... Iceland-spar........ Plate-glass ......... Rock-crystal ........ Rock-crystal, brown...... Tourmaline, dark-green..... Citric-acid, transparent..... Alum, transparent...... Sugar-candy........ Fluor-spar, green, translucent . . Ice, pure and transparent .... Transmission of 100 rays of beat from 92 78 65 54 46 39 39 38 37 18 11 9 92 69 65 23 38 28 24 28 28 16 2 2 0 6 0 92 42 65 13 24 6 6 6 6 3 0 0 0 4 0 92 33 65 0 20 0 0 0 0 0 0 0 0 3 0 On examining this remarkable table, which is an abstract of one much more extensive, the first thing that strikes the eye is the want of connexion between the power of transmitting heat and that of transmitting Heht- taking, for instance the oil-lamp as the source of heat, out of a quantity of heat represented by 100 rays falling upon the pile, the proportion intercepted by similar plates of rock-salt, glass, and alum, may be expressed bv tl numbers, 92, 39, and 8; and yet these bodies are equally transparent with respect to light. Generally speaking, color was found to interfere with th transmissive power, but to a very unequal extent: thus, in fluor-spar col less, greenish, and deep green, the quantities transmitted were 78 46 ' inds" while the difference between colorless and brown rock-crystal was 'on> 1 TRANSMISSION OF HEAT. 101 Bodies absolutely opaque, as wood, metals, and black marble, stopped the rays completely, although it was found that the faculty of transmission was possessed to a certain extent, by some which were nearly in that condition, as thick plates of brown quartz, black mica, and black glass. When rays of heat had once passed through a plate of any substance, the interposition of a second similar plate occasioned much less loss than the first: the same thing happened when a number were interposed; the rays, after traversing one plate, being but little interrupted by others of a similar nature. The next point to be noticed is the great difference in the properties of the rays from different sources. Out of 100 rays from each source which fell on rock-salt, the same proportion was always transmitted whether the rays pro- ceeded from the intensely-heated flame, the red-hot platinum wire, or the copper at 734° (390°C) or 212° (100°C); but this is true of no other sub- stance in the list. In the case of plate-glass, we have the numbers 39, 24, 6, and 0, as representatives of the comparative quantities of heat transmitted through the plate from each source; or in three varieties of fluor-spar, as in the following statement: — Colorless Greenish Flame. . 78 . . 46 . Red heat. . 69 . . 38 . 734° (390°C). . 42 . . 24 . 212° (100°C.) . 33 . 20 Dark green . 8 . 6 . 4 . 3 One substance, beryl, out of 100 rays from an intensely-heated source, suf- fers 54 to pass; and out of the same number (that is, an equal quantity of heat) from metal at 212° (100°C), none at all; whilst another substance, fluor-spar, transmits rays from the two sources mentioned in the proportion of 8 to 3! These, and many other curious phenomena, are fully and completely ex- plained on the supposition, that among the invisible rays of heat differences are to bo found exactly analogous to those differences between rays of light which we are accustomed to call colors. Rock-salt and air are the only sub- stances yet known which are truly diathermanous, or equally transparent to all kinds of heat-rays: it is to the latter What white glass or water is to light; it suffers rays of every description to pass with equal facility. All other bodies act like colored glasses, absorbing certain of the rays more abundantly than the rest, and coloring, as it were, the heat which passes through them. These heat-tints have no direct relation to ordinary colors; their existence is, nevertheless, almost as clearly made out as that of the colored rays of the spectrum. Bodies at a comparatively low temperature emit rays of such a tint only as to be transmissible by a few substances: as the temperature rises rays of other heat-colors begin to make their appearance, and transmission of some portion of these rays takes place through a great number of bodies • while at the temperature of intense ignition we find rays of all colors thrown out, some of which will certainly find their way through a great variety of substances. By cutting rock-salt into prisms and lenses, it is easy to show that radiant heat may be refracted like ordinary light, and its beams made to converge or diverge at pleasure; and, lastly, to complete the analogy, it has been shown to be susceptible of polarization by transmission through plates of double- refiaeting minerals, in the same manner as light itself.1 * Dr. Forbes, Phil. Mag. for 1835; also M. Melloni, Ann. Chim. et Phys. lxv. 5. 9* 102 MAGNETISM. MAGNETISM. A particular species of iron ore has long been remarkable for its property of attracting small pieces of iron, and causing them to adhere to its surface: it is called loadstone, or magnetic iron ore. _ If a piece of this loadstone be carefully examined, it will be found that the attractive force for particles of iron is greatest at certain particular points of its surface, while elsewhere it is much diminished, or even altogether absent. These attractive points are denominated poles, and the loadstone itself is said to be endued with magnetic polarity. If one of the poles of a natural loadstone be rubbed in a particular manner over a bar of steel, its characteristic properties will be communicated to the bar, which will then be found to attract iron-filings like the loadstone itself. Farther, the attractive force will appear to be greatest at two points situated very near the extremities of the bar, and least of all towards the middle. The bar of steel so treated is said to be magnetized, or to constitute an arti- ficial magnet. When a magnetized bar or natural magnet is suspended at its centre in any convenient manner, so as to be free to move in a horizontal plane, it is always found to assume a particular direction with regard to the earth, one end pointing nearly north and the other nearly south. If the bar be moved from this position, it will tend to reassume it, and, after a few oscillations, settle at rest as before. The pole which points towards the astronomical north is usually distinguished as the north pole of the bar, and that which points south- ward, as the south pole. A suspended magnet, either natural or artificial, of symmetrical form, serves to exhibit certain phenomena of attraction and repulsion in the presence of a second magnet, which deserve particular atten- tion. When a north pole is, presented to a south pole, or a sduth pole to a north, attraction ensues between them; the ends of the bars approach each other, and, if permitted, adhere with considerable force: when, on the other hand, a north pole is brought near a second north pole, or a south pole near another south pole, mutual repulsion is observed, and the ends of the bars recede from each other as far as possible. Poles of an opposite name attract, and of a similar name repel, eaeh other. Thus, a small bar or needle of steel, properly magnetized and suspended, and having its poles marked, becomes an instrument fitted not only to discover the existence of magnetic power in other bodies, but to estimate the kind of polarity affected by their different parts. A piece of iron brought into the neighborhood of a magnet acquires itself magnetic properties: the intensity of the power thus conferred depends upon that of the magnet and upon the interval which divides the two, becoming greater as that interval decreases, and greatest of all when in actual contact. The iron, under these circumstances, is said to be magnetized by induction or influence, and the effect, which in an instant reaches its maximum is at once destroyed by removing the magnet. When steel is substituted for iron in this experiment, the inductive action is hardly perceptible at first, and only becomes manifest after the lapse of a certain time: in this condition, when the steel bar is removed from the mag- V MAGNETISM. 103 n net, it retains a portion of the induced polarity. It becomes, indeed, a per- manent magnet, similar to the first, and retains its peculiar properties for an indefinite period. A particular name is given to this resistance which steel always offers in a greater or less degree both to the development of magnetism and its subse- quent destruction; it is called specific coercive power. • The rule which regulates the induction of magnetic polarity in all cases is exceedingly simple, and most important to be remembered. The pole pro- duced is always of the opposite name to that which produced it, a north pole de- Fis- en- veloping south polarity, and a south pole north polarity. The north pole of the magnet figured in the sketch induces south polarity in all the nearer extremi- ties of the pieces of iron or steel which surround it, and a state similar to its own in all the more remote extremities. The iron thus magnetized is capable of ex- , erting a similar inductive action on a J second piece, and that upon a third, and ^ so to a great number, the intensity of the force diminishing as the distance from the permanent magnet increases. It is in this way that a magnet is enabled to hold up a number of small pieces of iron, or a bunch of filings, each separate piece be- coming a magnet for the time by in- duction. Magnetic polarity, similar in degree to that which iron presents, has been found only in some of the compounds of iron, in nickel, and in cobalt. Magnetic attractions and repulsions are not in the slightest degree inter- fered with by the interposition of substances destitute of magnetic properties. Thick plates of glass, shellac, metals, wood, or of any substances except those above mentioned, may be placed between a magnet and a suspended needle, or a piece of iron under its influence, the distance being preserved, without the least perceptible alteration in its attractive power, or.force of induction. One kind of polarity cannot be exhibited without the other. In other words a magnetic pole cannot be insulated. If a magnetized bar of steel be broken at its neutral point, or in the middle, each of the broken ends acquires an op- posite pole, so that both portions of the bar become perfect magnets; and, if the division be carried still farther, if the bar be broken into a hundred pieces, each fragment will be a complete magnet, having its own north and south poles. »* This experiment serves to show very clearly that the apparent polarity of the bar is the consequence of the polarity of each individual particle, the poles of the bar being merely points through which the resultants of all these forces pass; the largest magnet is made up of an immense number of little magnets i nm \zm en nm rm □■ na laanprwiizMizMiZMai VZMEM regularly arranged side by side, all having their north poles looking one way, and their south poles the other. The middle portion of such a system cannot 104 MAGNETISM. possibly exhibit attractive or repulsive effects on an external body, because each pole is in close juxtaposition with one of an opposite name and ot equal power; hence their forces will be exerted in opposite directions and neutralize each other's influence. Such will not be the case at the extremities of the bar; there uncompensated polarity will be found capable of exerting its specific power. . This idea of regular polarization of particles of matter in virtue ot a pair of opposite and equal forces, is not confined to magnetic phenomena; it is the leading principle in electrical science, and is constantly reproduced in some form or other in every discussion involving the consideration of molecular forces. Artificial steel magnets are made in a great variety of forms; such as small light needles, mounted with an agate cap for suspension upon a fine point; straight bars of various kinds; bars curved into the shape of a horse-shoe, &c. All these have regular polarity communicated to them by certain processes of rubbing or touching with another magnet, which require care, but are not otherwise difficult of execution. When great power is wished for, a number of bars may be screwed together, with their similar ends in contact, and in this way it is easy to construct permanent steel magnets capable of sustaining great weights. To prevent the gradual destruction of magnetic force, which would otherwise occur, it is usual to arm each pole with a piece of soft iron or keeper, which, becoming magnetized by induction, serves to sustain the polarity of the bar, and even increases in some cases its energy. The direction spontaneously assumed by a suspended needle indicates that the earth itself has the properties of an enormous magnet, whose south pole is in the northern hemisphere. A line joining the two poles of such a needle or bar indicates the direction of the magnetic meridian of the place, which is a vertical plane coincident with the direction of the needle. The magnetic meridian of a place is not usually coincident with its geographical meridian, but makes with the latter a certain angle called the declination of the needle ; in other words, the magnetic poles, of the earth are not situated within the line of the axis of rotation. The amount of this declination of the needle from the true north and south not only varies at different places, but in the same place is subject to daily, yearly, and secular fluctuations, which are called the variations of declination. Thus, at the commencement of the 17th century, the declination was eastward; in 1660 it was 0; that is, the needle pointed due north and south. After- wards it became westerly, slowly increasing until the year 1818, when it reached 24° 30/, since which time it has been slowly diminishing, and, in the year 1857, in London it had returned to 21° 48/. Of late the march of the daily variations of declination has been carefully compared with the positions of the sun as well as the moon at the correspond- ing period. This inquiry, suggested by General Sabine, and carried on for a number of years in several localities, has led to the remarkable result that these celestial bodies exert a definite influence upon the magnetic needle and must therefore be considered as magnets, like the earth itself. If a steel bar be supported on a horizontal axis passing exactly throuo-h its centre of gravity, it will of course remain equally balanced in any position in which it may happen to be placed; if the bar so adjusted be then magnetized, it will be found to take a permanent direction, the north pole being down- wards, and the bar making an angle of about 68° 5', with a horizontal plane passing through the axis. This is called the dip or inclination of the needle and shows the direction in which the force of terrestrial magnetism is mo«t energetically exerted. The amount of this dip is different in different lati- tudes ; near the equator it is very small, the needle remaining nearly or quite horizontal; as the latitude increases the dip becomes more decided; and over the magnetic pole the bar becomes completely vertical. Such a situation is, MAGNETISM. 105 in fact, to be found in the northern hemisphere, considerably south of the geographical pole on the west coast of Boothia Felix, lat. 70° 5' N. and longitude 96° 46' W. ; the dipping-needle has here been seen to point directly downwards, while the horizontal or compass-needle ceased to traverse. Tho position of the south magnetic pole has lately been determined by the obser- vations of Captain James Ross to be about lat. 73° S. and long. 130° E. By observing a great number of points near the equator in which the dip becomes reduced to nothing, a line may be traced around the earth, called the magnetic equator, and nearly parallel to this, on both sides, a number of smaller circles called lines of equal dip. These lines present great irregu- larities when compared with the equator itself and the parallels of latitude, the magnetic equator deviating from the terrestrial one as much as 12° at its point of greatest divergence. Like the horizontal declination, the dip is also subject to change at the same place. Observations have not yet been made during sufficient time to determine accurately the law and rate of alteration, and great practical difficulties exist also in the construction of the instruments. In the year 1773 it was about 72°; at the present time it is near 68° 32' in London. The inductive power of the magnetism of the earth may be shown by holding in a vertical position a bar of very soft iron; the lower end will be found to possess north polarity, and the upper, the contrary state. On reversing the bar the poles are also reversed. All masses of iron whatever, when examined by a suspended needle, will be found in a state of magnetic polarity by the influence of the earth; iron columns, tools in a smith's shop, fire-irons, and other like objects, are all usually magnetic, and those made of steel perma- nently so. On board ship, the presence of so many large masses of iron — guns, anchors, water-tanks, &c. — thus polarized by the earth, causes a derangement of the compass-needles, to a very dangerous extent: happily, a plan has been devised for determining the amount of this local attraction in different positions of the ship, and making suitable corrections. The mariner's compass, which is nothing more than a suspended needle attached to a circular card marked with the points, was not in general use in Europe before the year 1300, although the Chinese have had it from very early antiquity. Its value to the navigator is now very much increased by correct observations of the exact amount of the declination in various parts of the world. Probably every substance in the world contributes something to the mag- netic action of the earth; for, according to the latest discoveries of Mr. Faraday, magnetism is not peculiar to those substances which have more especially been called magnetic, such as iron, nickel, cobalt, but it is the property of all matter, though to a much smaller degree. Very powerful magnets are required to show this remarkable fact. Large horse-shoe magnets, made by the action of the electric current, are most proper. The magnetic action on different substances which are capable of being easily moved, differs not only according to the size, but also according to the nature of the substance. In consequence of this, Faraday divides all bodies into two classes. He calls the one magnetic, or, better, paramagnetic, and the other diamagnetic. The matter of which a paramagnetic (magnetic) body consists is attracted by both poles of the horse-shoe magnet: on the contrary, the matter of a diamagnetic body is repelled. When a small iron bar is hung by untwisted silk between the poles of the magnet, so that its long diameter can easily move in a horizontal plane, it arranges itself axially, that is, parallel to the straight line which joins the poles, or to the magnetic axis of the poles; assuming at the end which is nearest the north pole, a south pole, and at the end nearest the south pole, a north pole. Whenever the little bar is removed from this position, after a few oscillations, it returns again to its previous position. 106 MAGNETISM. The whole class of paramagnetic bodies behave in a precisely similar way under similar circumstances; only in the intensity of the effects great diffei*Gnc6S occur On the contrary, diamagnetic bodies have their long diameters placed equatorially, that is, at right angles to the magnetie axis. Ihey behaye, as if at the end opposite to each pole of the magnet, the same kind of polarity existed In the first class of substances, besides iron, which is the best representative of the class, we have nickel, cobalt, manganese, chromium, cerium, titanium, palladium, platinum, osmium, aluminium, oxygen, and also most of the compounds of these bodies ; most of them, even when in solution. According to Faraday, the following substances are also feebly paramagnetic (magnetic): paper, sealing-wax, Indian-ink, porcelain, asbestos, fluorspar, minium, cin- nabar, binoxide of lead, sulphate of zinc, tourmaline, graphite, and charcoal. In the second class are placed bismuth, antimony, zinc, tin, cadmium, sodium, mercury, lead, silver, copper, gold, arsenic, uranium, rhodium, iridium, tungsten, phosphorus, iodine, sulphur, chlorine, hydrogen, and many of their compounds. Also, glass free from iron, water, alcohol, ether, nitric acid, hydrochloric acid, resin, wax, olive oil, oil of turpentine, caoutchouc, sugar, starch, gum, and wood. These are diamagnetic. If diamagnetic and paramagnetic bodies are combined, their peculiar properties are destroyed. In most of these compounds, occasionally, in consequence of the presence of the smallest quantity of iron, the peculiar magnetic power remains more or less in excess. Thus green bottle-glass and many varieties of crown glass, are magnetic in consequence of the iron they contain. In order to examine the magnetic properties of fluids they are placed in very thin glass tubes, the ends of which are then closed by melting; they are are then hung horizontally between the poles of the magnet. Under the influence of poles sufficiently powerful, they begin to swing, and according as the fluid contents are paramagnetic (magnetic), or diamagnetic, they assume an axial or equatorial position. Under certain circumstances substances which belong to the paramagnetic class behave as if they were diamagnetic. This happens in consequence of a differential action. Thus, for example, when a glass tube full of a dilute solution of sulphate of iron is allowed to swing in a concentrated solution of sulphate of iron, instead of in the air, it assumes an equatorial position. The air, in consequence of the oxygen in it, is itself paramagnetic (magnetic). Hence, such bodies as appear to possess feeble diamagnetic properties, can only show their true properties when hung in a vacuum. Faraday has tried the magnetic condition of gases in different ways. One way consisted in making soap bubbles with the gas which he wished to investigate, and bringing these near the poles. Soap and water alone is feebly diamagnetic. A bubble filled with oxygen was strongly attracted by the magnet. All other gases in the air are diamagnetic; that is, they are repelled. But, as Faraday has shown, in a different way, this partly arises from the paramagnetic (magnetic), property of the air. Thus he found that nitrogen when this differential action was eliminated, was perfectly indifferent, whether it was condensed or rarefied, whether cooled or heated. When the temperature is raised, the diamagnetic property of gases in the air is increased. Hence the flame of a candle or of hydrogen is strongly repelled by the' magnet. Even warm air is diamagnetic in cold air. b For some time it had been believed that bodies in a crystalline form had a special and peculiar behavior when placed between the poles of a magnet It appeared as though the magnetic directing power of the crystalhad some peculiar relation to the position of its optic axis; so that, independently of the magnetic property of the substance of the crystal, if the crystal was MAGNETISM. 107 positively optical, it possessed the power of placing its optic axis parallel with the line which joined the poles of the magnet, while optically negative fystals tried to arrange their axis at right angles to this line. This suppo- 'tion is disproved by the excellent investigation of Tyndall and Knoblauch, who showed that exceptions to the above law were furnished by all classes of crystals, and proved that the action, instead of being independent of the magnetic nature of the mass, was completely reversed where, in isomorphous crystals, a magnetic constituent was substituted ' for a diamagnetic one. Rejecting the various new forces assumed, Tyndall and Knoblauch referred the observed phenomena to the modification of the magnetic force by struc- ture, and they imitated the effects exactly, by means of substances whose structure had been modified by compression. In a later investigation Tyndall demonstrated the fundamental principle on which these phenomena depend, showing that the entire mass of a magnetic body is most strongly attracted when the attracting force acts parallel to the line of compression; and that a diamagnetic substance is most strongly repelled when the repulsion acts along the same line. Hence when such a body is freely suspended in the magnetic field, the line of compression must set axial or equatorial, according as the mass is magnetic or diamagnetic. Faraday was the first to establish a differ- ential action of this kind, in the case of bismuth; Tyndall extended it to several magnetic and diamagnetic crystals, and showed that it was not confined to them, but wns a general property of matter. It was also proved that for a fixed distance the attraction of a magnetic sphere, and the repulsion of a diamagnetic sphere, followed precisely the same law, both being exactly proportioned to the square of the exciting current. 108 ELECTRICITY. ELECTRICITY. It glass, amber, or sealing-wax be rubbed with a dry cloth, it acquires the power of attracting light bodies, as feathers, dust, or bits of paper: this is the result of a new and peculiar condition of the body rubbed, called electri- cal excitation. If a light downy feather be suspended by a thread of white silk, and a dry glass tube, excited by rubbing, be presented to it, the feather will be strongly attracted to the tube, adhere to its surface for a few seconds, and then fall off. If the tube be now excited anew, and presented to the feather, the latter will be strongly repelled. The same experiment may be repeated with shellac or resin ; the feather in its ordinary state will be drawn towards the excited body, and after touching, again driven from it with a certain degree of force. Now, let the feather be brought into contact with the excited glass, so as to be repelled by that substance, and let a piece of excited sealing-wax be pre- sented to it, a degree of attraction will be observed far exceeding that ex- hibited when the feather is in its ordinary state. Or, again, let the feather be made repulsive for sealing-wax, and then the excited glass be presented, strong attraction will ensue. The reader will at once see the perfect parallelism between the effects de- scribed and some of the phenomena of magnetism; the electrical excitement having a twofold nature, like the opposite polarities of the magnet. A body to which one kind of excitement has been communicated is attracted by another body in the opposite state, and repelled by one in the same state. The excited glass and resin being to each other as the north and south poles of a pair of magnetized bars. To distinguish these two different forms of excitement, terms are employed, which, although originating in some measure in theoretical views of the nature of the electrical disturbance, may be understood by the student as purely ar- bitrary and distinctive : it is customary to call the electricity manifested by glass rubbed with silk positive or vitreous, and that developed in the case of shellac, and bodies of the same class rubbed with flannel, negative or resinous. The kind of electricity depends in some measure upon the nature of the sur- face and the quality of the rubber; smooth glass rubbed with silk becomes ordinarily positive, but when ground or roughened by sand or emery, it ac- quires, under the same circumstances, a negative charge. Glass dried by heat and rubbed with wood is generally also negative. The repulsion shown by bodies in the same electrical state is taken advan- tage of to construct instruments for indicating electrical excitement and pointing out its kind. Two balls of alder-pith, hung by threads or very fine metal wires, serve this purpose in many cases: they open out when excited m virtue of their mutual repulsion, and show by the degree of divergence the extent to which the excitement has been carried. A pair of gold leaves suspended to a metal rod having a brass plate on its upper end constitute a wthS?, ™ aJTS^lnt' and °ne °f great value in a11 electrical in- h must b?f T C ™Jshould be covered ™th a thick coating of shellac, and it must be fastened by means of a cork, air-tight, into a |lass flask The flask must have been perfectly dried previously by warming it These in- ELECTRICITY. 109 Btrument= are called electroscopes or electrometers: when excited by the com- munication of a known kind of electricity, they show, by an increased or Fig. 68. diminished divergence, the state of an electrified body brought into their neighborhood. One kind of electricity can no more be developed without the other than one kind of magnetism: the rubber and the body rubbed always assume op- posite states, and the positive condition on the surface of a mass of matter is invariably accompanied by a negative state in all surrounding bodies. The induction of magnetism in soft iron has its exact counterpart in elec- tricity : a body already electrified disturbs or polarizes the particles of all Burrounding substances in the same manner and according to the same law, inducing a state opposite to its own in the nearer portions, and Fi„ 69 a similar state in the more re- mote parts. A series of globes suspended by silk threads, in the manner represented, will each become electric by induction when a charged body is brought near the end of the series, like so many pieces of iron in the vicinity of a magnet, the positive half of each globe looking in one and the same direction, and the negative half in the opposite one. The posi- tive and negative signs are intended to represent the states. The intensity of the induced electrical disturbance diminishes with the distance from the charged body; if this be removed or discharged, ail the effects cease at once. So far, the greatest resemblance may be traced between these two sets of phenomena; but here it seems in great measure to cease. The magnetic polarity of a piece of steel can awaken polarity in a second piece in contact with it by the act of induction, and in so doing loses nothing whatever of its power: this is an effect completely different from the apparent transfer or discharge of electricity constantly witnessed, which in the air and in liquids often gives rise to the appearance of a bright spark of fire. Indeed, ordinary magnetic effects comprise two groups of phenomena only, those, namely, of attraction and repulsion, and those of induction. But in electricity, in addi- tion to phenomena very closely resembling these, we have the effects of dis- charge, to which there is nothing analogous in magnetism, and which takes place in an instant when any electrified body is put in communication with 10 110 ELECTRICITY. the earth by any one of the class of substances called conductors of electri- city; all signs of electrical disturbance then ceasing. These conductors of electricity, which thus permit discharge to take place through their mass, are contrasted with another class of substances called non-conductors or insulators. The difference, however, is only one of degree, not of kind; the very best conductors offer a certain resistance to the electri- cal discharge, and the most perfect insulators permit it to a smallextent. The metals are by far the best conductors; glass, silk, shellac, and ary gas, or vapor of any sort, the very worst; and between these there are bodies of all degrees of conducting power. . Electrical discharges take place silently and without disturbance in good conductors of sufficient size. But if the charge be very intense, and the con- ductor very small or imperfect from its nature, it is often destroyed with violence. When a break is made in a conductor employed in effecting the discharge of a highly-excited body, disruptive or spark-discharge, so well known, takes place across the intervening air, provided the ends of the conductor be not too distant. The electrical spark itself presents many points of interest in the modifications to which it is liable. The time of transit of the electrical wave through a chain of good con- ducting bodies of great length is so minute as to be altogether inappreciable to ordinary means of observation. Professor AVheatstone's very ingenious experiments on the subject give, in the instance of motion through a copper wire, a velocity surpassing that of light. Electrical excitation is apparent only upon the surfaces of bodies, or those portions directed towards other objects capable of assuming the opposite state. An insulated ball charged with positive electricity, and placed in the centre of the room, is maintained in that state by the inductive action of the walls of the apartment, which, immediately become negatively electrified; in the interior of the ball there is absolutely no electricity to be found, although it may be constructed of open metal gauze, with meshes half an inch wide. Even on the surface the distribution of electrical force will not always be the same : it will depend upon the figure of the body itself, and its position with regard to surrounding objects. The polarity will always be highest in the projecting extremities of the same conducting mass, and greatest of all when these are attenuated to points ; in which case the inequality becomes so great that discharge takes place to the air, and the excited condition cannot be maintained. The construction and use of the common electrical machine, and other pieces of apparatus of great practical utility, will, by the aid of these prin- ciples, become intelligible. A glass cylinder (fig. 70) is mounted with its axis in a horizontal position, and provided with a handle or winch by which it may be turned. A leather cushion is made to press by a spring against one side of the cylinder, while a large metal conducting body, armed with a number of points next the glass, occu- pies the other: both cushion and conductor are insulated by glass supports, and to the upper edge of the former a piece of silk is attached long enough to reach half round the cylinder. Upon the cushion is spread a quantity of a soft amalgam of tin, zinc, and mercury,1 mixed up with a little grease: this substance is found by experience to excite glass most powerfully. The cylin- der as it turns thus becomes charged by friction against the rubber and as quickly discharged by the row of points attached to the great conductor- and as the latter is also completely insulated, its surface speedily acquires a charge of positive electricity, which may be communicated by contact to other • ' wP-arLt,i?' * -inC' 1?Kd 6 merCUry# Ao,^S3? °f Permanent softness and great efficacv to °leathef mmDg mercury, 2-1 tin, and 11 zinc. It is better applied to silk than ELECTRICITY. Ill insulated bodies. The maximum effect is produced when the rubber is con- nected by a chain or wire with the earth. If negative electricity be wanted, the rubber must be insulated and the conductor discharged. Another form of the electrical machine consists of a circular plate of glass moving upon an axis, and provided with two pairs of cushions or rubbers, attached to the upper and lower parts of the wooden frame, covered with Fte. 71. 112 ELECTRICITY. amalgam, between which the plate moves with considerable friction An in- sulated conductor, armed as before with points, discharges the plate as it turns, the rubbers being at the same time connected with the ground by he wood-work of the machine, or by a strip of metal. The modification of the apparatus is preferred in all cases where considerable power is wanted. In the practical management of electrical apparatus, great care must be taken to prevent deposition of moisture from the air upon the surface of the glass supports, which should always be varnished with fine lac dissolved in alcohol; the slightest film of water is sufficient to destroy the power of insula- tion. The rubbers also must be carefully dried before use, and the amalgam renewed if needful: in damp weather much trouble is often experienced in bringing the machine into powerful action. _ _ When the conductor of the machine is charged with electricity, it acts indi- rectly on, and accumulates the contrary electricity to its own, at the surface of all the surrounding conductors. It produces the greatest effect on the con- ductor that is nearest to it, and which is in the best connexion with the ground, whereby the electricity of the same kind as that of the machine may pass to the earth. As the inducing electricity attracts the induced electricity of an opposite kind; so, on the other hand, is the former attracted by the lat- ter. Hence, the fluid which the conductor receives from the machine must especially accumulate at that spot to which another good conductor of elec- tricity is opposed. If a metal disc is in connexion with the conductor of a machine, and if another similar disc, which is in good connexion with the earth, is placed opposite to it, we have an arrangement by which tolerably large and good conducting surfaces can be brought close to one another: thus the positive condition of the first disc, as well as the negative condition of the other, must be increased to a very considerable degree: the limit is in this case, however, soon reached, because the intervening air easily permits spark- discharge to take place through its substance. With a solid insulating body, as glass or lac, this happens with much greater difficulty, even when the plate of insulating matter is very thin. It is on this principle that instruments for the accumulation of electricity depend, among which the Leyden jar is the most important. A thin glass jar is coated on both sides with tinfoil, care being taken to leave several inches of the upper part unco- vered; a wire, terminating in a metallic knob, communicates with the interna] coating. When the outside of the jar is connected with the earth, and the knob put in contact with the conductor of the machine, the inner and outer surfaces of the glass become respectively positive and negative, until a very great degree of intensity has been attained. On com- pleting the connexion between the two coatings by a metallic wire or rod, discharge occurs in the form of an exceedingly bright spark, accompanied by a loud snap; and if the body be interposed in the circuit, the peculiar and disagreeable sensation of the electric shock is felt at the moment of its completion. By enlarging the dimensions of the jar, or by connecting together a number in such a manner that all may be charged and discharged simultaneously, the power of the apparatus may be greatly augmented. Thin wires of metal may be fused and dissipated; pieces of wood may be shattered, many combustible substances set on fire and all the well known effects of lightning exhibited upon a small scale. The electric spark is often very conveniently employed in chemical inquiries for firing gaseous mixtures in close vessels. A small Leyden iar charged bv the machine is the most effective contrivance for this purpose ; but, not*unfre- quently, a method may be resorted to which involves less preparation. This Fig. 72. ELECTRICITY. 113 is by the use of the electrophorus. A round tray or dish of tinned plate is prepared, having a stout wire round its upper edge; the width may be about twelve inches, and the depth half an inch. This tray is filled with melted shellac, and the surface rendered as even as possible. A brass disc, with rounded edge, of about nine inches dia- meter, is also provided, and fitted with an Fie. 73. insulating handle. When a spark is wanted, the resinous plate is excited by striking with a dry, warm piece of fur, or a silk hand- kerchief; the cover is placed upon it, and touched by the finger. When the cover is raised, it is found so strongly charged by induction with positive electricity, as to give a bright spark; and, as the resin, is not dischaged by the cover, which merely touches it at a few points, sparks may be drawn as often as may be wished. It is not known to what cause the disturbance of the electrical equilibrium of the, atmosphere is due; experiment has shown that the higher regions of the air are usually in a positive state, the intensity of which reaches a maxi- mum at a particular period of the day. In cloudy and stormy weather the distribution of the atmospheric electricity become much deranged, clouds near the surface of the earth often appearing in a negative state. The circumstances of a thunderstorm exactly resemble those of the charge and discharge of a coated plate or jar; the cloud and the earth represent the two coatings, and the intervening air, the bad conducting body, or dielectric. The polarities of the opposed surface and of the insulating medium between them become raised by mutual induction, until violent disruptive discharge takes place through the air itself, or through any other bodies which may happen to be in the interval. When these are capable of conducting freely, the discharge is silent and harmless; but in other cases it often proves highly destructive. These dangerous effects are now in a great measure obviated by the use of lightning-rods attached to buildings, the erection of which, however, demands a number of precautions not. always understood or attended to. The masts of ships may be guarded in like manner by metal conductors: Sir W. Snow Harris has devised a most ingenious plan for the purpose, which is now adopted, with the most complete success, in the Royal Navy. ELECTRIC CURRENT ; ELECTRIC BATTERY. When two solid conducting bodies are plunged into a liquid which acts upon them unequally, the electric equilibrium is also disturbed, the one acquiring the positive condition, and the other the negative. Thus, pieces of zinc,.z, and plati- Iig.74. num. c, put into dilute sulphuric acid, constitute an arrangement capable of generating electri- cal force: the zinc being the metal attacked, becomes negative; and the platinum remain- ing unaltered, assumes the positive condition; K and on making a metallic communication in 1 any way between the two plates, discharge | ensues, as when the two surfaces of a coated and charged jar. are put into connexion. No sooner, however, has this occurred, than the disturbance is repeated; and as these suc- cessive charges and discharges take place through the fluid and metals with inconceivable 10* 114 ELECTRICITY. Fig. 75. rapidity, the result is an apparently continuous action, to which the term elec- tl'icul CMTTCYlt is fflVGIl It is necessary to guard against the idea, which the term naturally suggests, of an actual bodily transfer of something through the substance of the con. ductors, like water through a pipe: the real nature of all these phenomena is entirely unknown, and may perhaps remain so; the expression is convenient not- withstanding, and consecrated by long use; and with this caution, the very dan- gerous error of applying figurative language to describe an effect, and then seek- ing the nature of the effect from the common meaning of words, may be avoided. The intonsity of the electrical excitement developed by a single pair of metals and a liquid is too feeble to affect the most delicate gold-leaf electro- scope ; but, by arranging a number of such alternations in a connected series, in such a manner that the direction of the current shall be the same in each, the intensity may be very greatly exalted. The two instruments invented by Volta, called the pile and crown of cups, depend upon this principle. Upon a plate of zinc is laid a piece of cloth, rather smaller than itself, steeped in dilute acid, or any liquid capable of exerting chemical action upon the zinc; upon this is placed a plate of copper, silver, or platinum ; then a second piece of zinc, another cloth, and a plate of inactive metal, until a pile of about twenty alternations has been built up. If the two terminal plates be now touched with wet hands, the sensation of the electric shock will be expe- rienced ; but, unlike the momentary effect produced by the discharge of ajar, the sensation can be repeated at will by repeating the contact, and with a pile of one hundred such pairs, excited by dilute acid, it will be nearly insupportable. When such a pile is insulated, the two extremities exhibit strong positive and negative states; and when connexion is made between them by wires armed with points of hard charcoal or plumbago, the discharge takes place in the form of a bright enduring spark or stream of fire. The second form of apparatus, or crown of cups, is precisely the same in principle, although different in appearance. A number of cups or glasses are Fig. 76. arranged in a row or circle, each containing a piece of active and a piece of inactive metal, and a portion of exciting liquid; zinc, copper, and dilute sulphuric acid, for example. The copper of the first cup is connected with the zinc of the second, the copper of the second with the zinc of the third, and so to the end of the series. On establishing a communication between the first and last plates by means of a wire, or otherwise, discharge takes place as before. When any such electrical arrangement consists merely of a single pair of conductors and an interposed liquid, it is called a simple circuit ■ when two or more alternations are concerned, the term "compound circuit" is applied • they are called also, indifferently, voltaic batteries. In every form of «uch apparatus, however complex it may appear, the direction of the current may be easily understood and remembered. The polarity or disturbance may be considered to commence at the surface of the metal attacked, and to be pro- pagated through the liquid to the inactive conductor, and thence back again by the connecting wire ; these extremities of the battery being always respect- ELECTRICITY. 115 ively negative and positive when the apparatus is insulated. In common par- lance, it is said that the current in every battery in an active state starts f'rona the metal attacked, passes through the liquid to the second metal or conduct- ing body, and returns by the wire or other channel of communication ; hence, in the pile and crown of cups just described, the current in the battery is always from the zinc to the copper; and out of the battery, from the copper to the zinc, as shown by the arrows. In the modification of Volta's original pile, made by Mr. Cruikshank, the zinc and copper plates are soldered together and cemented water-tight into a mahogany trough, which thus be- Via. r7 liii^sMs comes divided into a series of cells or compartments capable of receiv ing the exciting liquid. This appa- ratus is well fi tted to exhibit effects of tension, to act upon the electroscope and give shocks ; hence its advan- tageous employment in the application of electricity to medicine, as a very few minutes suffices to prepare it for use. The crown of cups was also put into a much more manageable form by Dr. Babington, and still farther im- proved, as will hereafter be seen, by Dr. Wollaston. Subsequently, various alterations have been made by different experimenters with a view of obvi- ating certain defects in the common batteries, of which a description will be found towards the middle of the volume. The term "galvanism," sometimes applied to this branch of electrical sci- ence, is used in honor of Professor Galvani, of Bologna, who, in 1790, made the very curious observation that convulsions could be produced in the limbs of a dead frog when certain metals were made to touch the nerve and muscle at the same moment. It was Volta, however, who pointed out the elec- trical origin of these motions; and although the explanation he offered of the source of the electrical disturbance is no longer generally adopted, his name is very properly associated with the invaluable instrument his genius gave to science. In the year 1822, Professor Seebeck, of Berlin, discovered another source of electri- city, to which allusion has already been made, namely, inequality of temper- ature and conducting power in different metals placed in contact, or in the same metal in different states of compression and density. Even with a great number of alternations, the current produced is exceedingly feeble compared with that generated by the voltaic pile. Some animals of the class of fishes, as the torpedo or electric ray, and the . electric eel of South America, are furnished with a special organ or apparatus for developing electrical force, which is employed in defence, or in the pursuit of prey. Electricity is here seen to be closely connected with nervous power; the shock is given at the will of the animal, and great exhaustion follows repeated exertion of the power. ELECTRO-MAGNETISM. Although the fact that electricity is capable, under certain circumstances, both of inducing and destroying magnetism, has long beeh known from the effects of lightning on the compass-needle and upon small steel articles, as knives and forks, to which polarity has suddenly been given by the stroke it was not until 1819 that the laws of these phenomena were discovered by Professor Oersted, of Copenhagen, and shortly afterwards fully developed by M. Ampere. 116 ELECTRICITY. Fig. 79. A The action which a current of electricity, proceeding from any source, exerts upon a magnetized needle is quite peculiar. The poles or centres ol magnetic force are neither attracted nor repelled by the wire carrying the Current, but made to move around the latter, by a force which may be termed tangential, and which is exerted in a direction perpendicular at once to that of the current, and to the line joining the pole and the wire. Both poles of the magnet being thus acted upon at the same time, and in contrary direc- tions, the needle is forced to arrange itself across the current, so that its axis, or the line joining the poles, maybe perpendicular to the wire; and this is always the position which the needle will assume when the influence of ter- restrial magnetism is in any way removed. This curious angular motion may even be shown by suspending a magnet in such a way that only one of its poles shall be subjected to the current; a permanent movement of rotation will continue as long as the current is kept up, its direction being changed by altering the pole or reversing the current. The movable connections are made by mercury, into which the points of the conducting-wires dip. It is often of great practical consequence to be able to predict the direction in which a particular pole shall move by a given current, because in all galvano- scopes, and other instruments involving these principles, the movement of the needle is taken as an indication of the direction of the circulating current. And this is easily done by a simple mechanical aid to the memory: —Let the current be supposed to pass through a watch from the face to the back; the motion of the north pole will be in the direction of the hands. Or a little piece of apparatus may be used if reference is often required: this is a piece of pasteboard, or other suitable material, cut into the form of an arrow for indicating the current, crossed by a magnet having its poles marked, and arranged in the true po- sition with respect to the current. The direction of the latter in the wire of the galvanoscope can at once be known by placing the representative magnet in the direction assumed by the needle itself. The common galvanoscope, consisting of a coil of wire having a compass-needle suspended on a point within it, is greatly improved by the addition of a second needle, as already in part de- scribed, and by a better mode of suspension, a long fibre of silk being used for the purpose. The two needles are of equal size, and magnetized as nearly as possible to the same extent: they are then immovably fixed to- gether parallel, and with their poles opposed, and hung with the lower nee- dle in the coil and the upper one above it. The advantage gained is two- fold : the system is asta- tic, unaffected, or nearly so, by the magnetism of the earth; and the nee- dles being both acted up- on in the same manner With much greater force than one alone would be - alHhracUonsTf evSy I :d [£: jrjj Fig. 80. ELECTRO-MAGNETISM. 117 Fig. 81. part of the coil being strictly concurrent. A divided circle is placed below the upper needle, by which the angular motion can be measured; and the whole is enclosed in glass, to shield the needles from the agitation of the air. The whole is shown in fig. 80. , The action between the pole and the wire is mutual, as may be shown Dy rendering the wire itself movable, and placing a magnet in its vicinity: on completing the circuit the wire will be put in motion, and, if the arrangement permits, rotate around the magnetic pole. A little consideration will show, that, from the peculiar nature of the electro-dynamic force, a wire carrying a current, bent into a spiral or helix, must possess the properties of an ordinary magnetized bar, its extremities being attracted and repelled by the poles of a magnet. Such is really found to be the case, as may be proved by a variety of arrangements, among which it will be sufficient to cite the beautiful little apparatus of Professor de la Rive. —A short wide glass tube is fixed into a cork ring of considerable size ; a little voltaic battery, consisting of a single pair of copper and zinc plates, is fitted to the tube, and to these the ends of the spiral are soldered. On filling the tube with dilute acid, and floating the whole in a large basin of water, the helix will be observed to arrange itself in the magnetic meridian, and on trial it will be found to obey a magnet held near it in the most perfect manner, as long as the current circulates. When an electric current is passed at right angles to a piece of iron or steel, the latter acquires magnetic polarity, either temporary or permanent as the case may be, the direction of the current determining the position of the poles. This effect is pro- digiously increased by causing the current to circulate a number of times round the bar, which then acquires extraordinary magnetic power. A piece of soft iron, worked into the form of a horse-shoe, and surrounded by a coil of copper wire covered with silk or cotton for the purpose of insulation, furnishes an excellent illustration of the inductive energy of the current in this respect; when the ends of the wire are put into communication with a small voltaic battery of a single pair of plates, the iron instantly becomes so highly magnetic as to be capable of sustaining a very heavy weight. M. Ampere discovered in the course of his investiga- tions a number of extremely interesting phenomena resulting from the action of electrical currents on each other, which become evident when arrangements are made for giving mobility to the conducting-wires. He found, that when two currents, flowing in the same direction, were made to approach each other, strong attraction took place between them, and, when in opposite directions, an equally strong repulsion. These effects, which are not difficult to demonstrate, have absolutely no relation that can be traced to ordinary electrical attractions and repulsions, from which they must be carefully distinguished; they are purely dynamic, having to do with electricity in motion. M. Ampere founded upon this discovery a most beautiful and ingenious hypothesis of magnetic actions in general, which explains verv clearly the influence of the current upon the needle. Fig. 82. 118 MAGNETO-ELECTRICITY. MAGNETO-ELECTRICITY. A current of electricity can thus develop magnetism in a transverse direction to its own; in the same manner", magnetism can Fig. 83. call into activity electric currents. If the two extremities of the coil of the electro-magnet c, above described, be connected with a galvanoscope, and the iron magnetized by the application of a permanent steel horse-shoe magnet, a, b, to the ends of the bar, a momentary current will be developed in the wire, and pointed out by the movement of the needle. It lasts but a single instant, the needle returning after a few oscilla- tions to a state of rest. On removing the magnet, whereby the polarity of the iron is at once de- stroyed, a second current or wave will become apparent, but in the opposite direction to that of the first. By employing a very powerful steel magnet, surrounding its iron keeper or armature with a very long coil of wire, and then making the armature itself rotate in front of the faces of the magnet, so that its induced polarity shall be rapidly reversed, magneto-electric currents may be produced, of such intensity as to give bright sparks and most powerful shocks, and exhibit all the phenomena of voltaic electricity. Fig. 84 represents a very powerful arrangement of this kind. Fig. 84. When two covered wires are twisted together or laid side by side for some distance, and a current transmitted through the one, a momentary electrical wave will be induced in the other in the reverse direction, and on breaking connexion with the battery, a second single wave will become evident by the rud of the galvanoscope, in the same direction as that of the primary current In the same way when a current of electricity passes through one turn in a coil ot wire, it induces two secondary currents in all the other turns of the coil; when the circuit is closed, the first is moving in the opposite direction MAGNETO-ELECTRICITY. 119 to the primary current; the second, when the circuit is broken, has a motion in the same direction as the primary current. The effect of the latter is added to that of the primary current. Hence, if a wire coil be made part of the conducting wire of a weak electric pile, and if the primary current, by means of an appropriate arrangement, be made and broken in rapid succes- sion, we can increase in a remarkable manner the effects which are produced at the moment of breaking the circuit either at the place of interruption — Buch as the spark-discharges — or, in secondary closing conductors, such as the action on the nerves or the decomposition of water. If two copper wires, the one above the other, be twisted round the same hollow cylinder, and one of these wires—for instance, the inner one—be made part of a galvanic circuit, a current of short duration is induced in the outer wire, both by making and by breaking contact. . The strength of this current can be very appreciably increased by filling the hollow cylinder with a bundle of thin iron rods, when magnetic and electrical induction are made to co- operate. The more frequently contact is alternately made and broken, the greater is the number of induced currents that follow each other, and the more powerful, within certain limits, is the action. Dr. Neef has constructed an ingenious contrivance, in which contact is made and broken by the current itself, whereby his induction apparatus actually becomes an electrical machine. Fig. 85 exhibits the original apparatus slightly modified. The arrangement Fig. 85. essentially consists in an elastic copper stripe a a', which is fixed at af, and carrying at b a small plate of soft iron. The latter hangs over the iron rods of the induction coil, which are somewhat raised in this particular point, but without touching them. The end, a, of the copper stripe is covered with a little plate of platinum, which presses against a platinum point of the screw, c. The current, having traversed the inner coil, passes from the point, c, to the plate, a, in order to return through the copper stripe, a a', and the wire s/. By the passage of the current the iron rods have become magnetic and attract the iron plate, b, whereby the end, a, of the copper stripe is removed from the platinum point, and contact is broken. But as soon as the current ceases, the iron rods lose their magnetism, the elastic copper stripe returns to its former position, and establishes again the current for a short period. By the screws, c and d, the position of the spring is regulated, and the time of its oscillations, the velocity of which may be estimated by the pitch of the notes produced. This apparatus, which was first made by Dr. Neef, in 1830, has 120 ELECTRICITY OF VAPOR. been considerably improved within the last few years. M. Rhumkorff, espe- cially, by a more perfect isolation of the wire coils, has to a much greater extent succeeded in preserving the electrical induction. He has thus obtained a state of electrical tension which resembles that produced by fnctional electricity ; the spark is capable of crossing the air in measurable distances, not in isolated discharges, but in streams of brilliant light, The shocks of this apparatus resemble those of a moderate Leyden jar, but differ from the latter by the rapidity with which they may be repeated at pleasure. By means of Ruhmkorff's coil, Grove has lately effected decomposition in water and other bad-conducting liquids, which resCnible those obtained many years ago by Wollaston by means of the electrical machine. Those phenomena of decomposition which in water, for instance, furnish oxygen and hydrogen at the same pole, must be distinguished from true electrical decompositions; they are, in fact, effects of heat, as Grove has pointed out. ELECTEICITY OF VAPOR. The electricity exhibited under certain peculiar circumstances by a jet of steam, first observed by mere accident, but since closely investigated by Mr. Armstrong, and also by Mr. Faraday, is now referred to the friction, not of the pure steam itself, but of particles of condensed water, against the interior of the exit tube. It has been proved with certainty in the last few years that evaporation alone is not capable of disturbing the electrical equilibrium, and the hope first entertained, that these phenomena would throw light upon the cause of electrical excitement in the atmosphere, is now abandoned. The steam is usually positive, if the jet-pipe be constructed of wood or clean metal, but the introduction of the smallest trace of oily matter causes a change of sign. The intensity of the change is, cceleris paribus, increased with the elastic force of the steam. By this means effects have been obtained very far surpassing those of the most powerful plate electrical machines ever constructed. Although no electricity can be directly evolved by evaporation, yet vapor possesses in a high degree the property of discharging into the atmosphere that electricity which often accumulates in those bodies from which it arises. The fresh branches and leaves of trees do this to the greatest extent. When ^ moistened with rain or dew their surfaces become positively electrical, whilst the internal parts, even to the roots, become negatively electrical. PART II. CHEMISTRY OF ELEMENTARY BODIES. The term element or elementary substance is applied in chemistry to those forms or modifications of matter which have hitherto resisted all attempts to decompose them. Nothing is ever meant to be affirmed concerning their real nature; they are simply elements to us at the present time; hereafter, by new methods of research, or by new combinations of those already posssesed by science, many of the substances which now figure as elements may possibly be shown to be compounds: this has already happened, and may again take place. The elementary bodies, at present recognized, amount to sixty-two in number; of these, about forty-seven belong to the class of metals. Several of these are of recent discovery and as yet very imperfectly known. The distinction between metals and non-metallic substances, although very con- venient for purposes of description, is entirely arbitrary, since the two classes graduate into each other in the most complete manner. It will be proper to commence with the latter, and less numerous division. The elements are named as in the subjoined table, which, however, does not indicate the order in which they will be discussed. Non-metallic Elements. Metals. Oxygen Antimony Gold Barium Hydrogen Chromium Aluminium Strontium Nitrogen Vanadium Beryllium Calcium Chlorine Tungsten (or Glucinum) Magnesium Iodine (or Wolfram Zirconium Zinc Bromine Molybdenum Norium Cadmium Fluorine Tantalum Thorium Nickel Carbon (or Columbium) Yt trium Cobalt Silicon Niobium Cerium Copper Boron Pelopium Erbium Iron Sulphur Titanium Terbium Manganese Selenium Uranium Lantanum Lithium Phosphorus Platinum Didymium Sodium ___ Palladium Bismuth Potassium Dements of interme- Rhodium Tin diate characters. Iridium Mercury Arsenic Ruthenium Silver Tellurium Osmium Lead OXYGEN. Whatever plan of classification, founded on the natural relations of the elements, be adopted, in the practical study of chemistry, it will always be found most advantageous to commence with the consideration of the great constituents of the ocean and the atmosphere. 11 " (121) 122 OXYGEN. Fig. 86. Oxygen was discovered in the year 1774, by Scheele, in Sweden, and Dr Priestley, in England, independently of each other, and described under the terms empyreal air and dephlogisticated air. The name oxygen1 was given to it by Lavoisier some time afterwards. Oxygen exists in a free and uncombined state in the atmosphere, mingled with another gaseous body, nitrogen: no very good direct means exist, however, for separating it from the latter, and, accordingly, it is always obtained for purposes of experiment by decomposing certain of its compounds, which are very numerous. The red oxide of mercury, or red precipitate of the old writers, may be em- ployed with this view. In this substance the attraction which holds together the mercury and the oxygen is so feeble, that simple exposure to heat suffices to bring about decomposition. The red precipitate is placed in a short tube of hard glass, to which is fitted a perforated cork, furnished with a piece of narrow glass tube, bent as in the figure. The heat of a spirit-lamp being applied to the substance, decomposition speedily commences, globules of metallic mercury collect in the cool part of the wide tube, which answers the purpose of a retort, while gas issues in considerable quantity from the appa- ratus.2 This gas is collected and examined by the aid of the pneumatic trough, which consists of a vessel of water provided with a shelf, upon which stands the jars or bottles destined to receive the gas filled with water and in- verted. By keeping the level of the liquid above the mouth of the jar, the water is retained in the latter by the pressure of the atmosphere, and en- trance of air is prevented. When brought over the extremity of the gas-de- livering tube, the bubbles of gas rising through the water collect in the upper part of the jar and displace the liquid. As soon as one jar is filled, it may be removed, still keeping its mouth below the water- level, and another substi- tuted. The whole arrange- ment is shown in fig. 8(5. The experiment describ- ed is more instructive as an excellent case of the re- solution by simple means of a compound body into its constituents, than valu- able as a source of oxygen gas. A better and more economical method is to expose to heat in a retort, or flask, furnished with a bent tube, a portion of the salt called chlorate of potassa. A common Florence flask serves perfectly well, the heat of a spirit- 1 From o|wf, acid, and ytvvdu, I give rise to. 2 Chemists are in the habit of representing the elements by symbols, and their compounds by formula-. The same symbolical language, winch is fully explained in a subsequent section of the work (General Principles of Chemical Philosophy), is used for representing the changes which the chemical compounds undergo. For the benefit of the advanced stuUent the for- mulas expressing the more important decompositions are now given in foot-notes if,'0 Hon™, position of oxide of mercury is thus represented:— uecom- HgO Hg + Oxide of mercury. Mercury. Oxygen. OXYGEN. 123 lamp being sufficient. The salt melts and decomposes with ebullition, yielding a very large quantity of oxygen gas, which may be collected in the way-above described. The first portion of the gas often contains a little chlorine. The white saline residue in the flask is chloride of potassium. This plan, which is very easy of execution, is always adopted when very pure gas is required for analytical purposes.1 A third method, very good when perfect purity is not demanded, is to heat to redness, in an iron retort or gun-barrd, the black oxide of manganese of commerce, which under these circumstances suffers decomposition, although not to the extent manifest in the red precipitate.3 If a little of the black oxide of manganese be finely powdered and mixed with chlorate of potassa, and this mixture heated in a flask or retort by a lamp, oxygen will be disengaged with the utmost facility, and at a far lower temperature than when the chlorate alone is used. All the oxygen comes from the chlorate, the manganese remaining quite unaltered. The materials should be well dried in a capsule before their introductien into the flask.3 A similar disengagement of oxygen takes place if a solution of chloride of lime (bleaching powder) bo gently warmed with a small quantity cf hydrated prot- oxide of cobalt. In this reaction the whole amount of oxygen contained in the chloride of lime is given off, the protoxide of cobalt remaining unaltered. These experiments afford an instance of an effect by no means rare, in which a body seems to act by its mere presence, without taking any obvious part in the change brought about. Whatever method be chosen—and the same remark applies to the collection of all other gases by similar means—the first portions of gas must be suffered to escape, or be received apart, as they are contaminated by the atmospheric air of the apparatus. The practical management of gases is a point of great importance to the chemical stu- dent, and one with which he must Fig. 87. endeavor to familiarize himself. The water-trough just described is one of the most indispensable ar- ticles of the laboratory, and by its aid all experiments on gases are carried on when tho gases them- selves are not sensibly acted upon by water. The trough is best con- structed of japanned copper, the form and dimensions being regu- lated by the magnitude of the jars. It should have a firm shelf, so arranged as to be always about an inch below the level of the water, and in the shelf a groove should be made about half an inch in width, and the same in depth, to admit the extremity of the delivery-tube beneath the jar, which stands securely upon the shelf. When the pneumatic trough is required of tolerably large dimensions, it may with great advantage have the form and disppsition represented in the cut (fig. 87), and the end of the groove spoken of, which crosses the shelf or shallow portion, is shown at a. Chlorate of potassa. 3Mn02 Binoxido of manganese. KC1. Chloride of potassium. MnO, Mn203 Oxygen. Proto-sesquioxide of manganese. • [It is important that the oxide of manganese should be of ftiir quality, at any rate to con- tain no combustible substance. Explosions have resulted from want of precaution in this respect. A preliminiary trial of a small quantity of the mixture by heating it in an iron capsule should always be mado when the slightest doubt exists.—R. B.] 121 OXYGEN. Gases are transferred from jar to jar with the utmost facility, by first fil g the vessel into which the gas is to be passed with water, inverting it, caretu y retaining its mouth below the water-level, and then bringing beneath it the aperture of the jar containing the gas. On gently inclining the latter the gas passes by a kind of inverted decantation into the second vessel, When the latter is narrow, a funnel may be placed loosely in its neck, by which loss of gas will be found to be prevented. . Ajar wholly or partially filled with gas at the pneumatic trough may be removed by placing beneath it a shallow basin, or even a common plate, so as to carry away enough water to cover the edge of the jar; and many gases, especially oxygen, may be so pre- ^ served for many hours without material in-'^ jury- Gas-jars are often capped at the top, and fitted with a stop-cock for transferring gas to bladders or caoutchouc bags. When such a vessel is to be filled with water, it may be slowly sunk in an upright position in the well of the pneumatic trough, the stop-cock being open to allow the air to escape, until the water reaches the brass cap. The cock is then to be turned, and the jar lifted upon the shelf, and filled with gas in the usual way. If the trough be not deep enough for this method of pro- ceeding, the mouth may be applied to the Btop-cock, and the vessel filled by sucking out the air until the water rises to the cap. In all cases it is proper to avoid as much as possible wetting the stop^cocks and other brass apparatus. Mr. Pepys contrived many years ago an admirable piece of apparatus for storing and retaining large quanti- Fig. 89. ties of gas. It consists of a drum or reservoir of sheet-copper, a, sur- mounted by a shallow trough or cis- tern, d, the communication between the two being made by a couple of tubes, b c, furnished with stop-cocks, one of which, c, passes nearly to the bottom of the drum, as shown in the sectional sketch. A short, wide, open tube, e, is inserted obliquely near the bottom of the vessel, into which a plug may be tightly screwed. A stop-cock, b, near the top, serves to transfer gas to a bladder or tube apparatus. A glass water-gauge, /, affixed to the side of the drum, and communicating with both top and bottom, indicates the level of the liquid within. To use the gas-holder, the plug is first to be screwed into the lower opening, and the drum completely filled with water. All three stop-cocks are then to be closed, and the plug removed. The pressure of the atmosphere retains the water in the gas- holder, and if no air-leakage occur, the escape of water is inconsiderable. The extremity of the delivery-tube is now to be well pushed through the open OXYGEN. 125 aperture into the drum, so that the bubbles of gas may rise without hindrance to the upper part, displacing the water, which flows out in the same propor- tion into avesssl placed for its reception. When the drum is filled, or enough gas has been collected, the tube is withdrawn and the plug screwed into its place. When a portion of the gas is to be transferred to a jar, the latter is to be filled with water at the pneumatic trough, carried by the help of a basin or plate to the cistern of the gas-holder, and placed over the shorter tube. On opening the cock of the neighboring tube, the hydrostatic pressure of the column of water will cause compression of the gas, and increase its elastic force, so that on gently turning the cock beneath the jar, it will ascend into the latter in a rapid stream of bubbles. The jar, when filled, may again have the plate slipped beneath it, and be removed without difficulty. Oxygen, when free or uncombined, is only known in the gaseous state; all attempts to reduce it to the liquid or solid condition by cold and pressure having completely failed. It is, when pure, colorless, tasteless, and inodorous, the sustaining principle of animal life, and of all the ordinary phenomena of combustion. Bodies which burn in the air, burn with great increased splendor in oxygen gas. If a taper be blown out, and then introduced while the wick remains red-hot, it is instantly rekindled: a slip of wood or a match is relighted in the same manner. This effect is highly characteristic of oxygen, there being but one other gas which possesses the same property; and this is easily dis- tinguished by other means. The experiment with the match is also constantly used as a rude test of the purity of the gas when it is about to be collected from the retort, or when it has stood some time in contact with water exposed to air. When a bit of charcoal is affixed to a wire, and plunged with a single point red hot into a jar of oxygen, it burns with great brilliancy, throwing off beau- tiful scintillations, until, if the oxygen be in excess, it is completely consumed. An iron wire, or, still better, a steel watch-spring, armed at its extremity with a bit pf lighted amadou, and introduced into a vessel of oxygen gas, exhibits a most beautiful appearance of combustion. If the experiment be made in a jar standing on a plate, the fused globules of black oxide of iron fix themselves in the glaze of the latter, after falling through a stratum of water half an inch in depth. Kindled sulphur burns with great beauty in oxygen, and phosphorus, under similar circumstances, exhibits a splendor which the eye is unable to support. In these and many other similar cases which might be mentioned, the same ultimate effect is produced as in atmospheric air; the action is, however, more energetic, from the absence of the gas which in the air dilutes the oxygen, and enfeebles its chemical powers. The process of respiration in animals is an effect of the same nature as common combustion. The blood contains substances which slowly burn by the aid of the oxygen thus introduced into the system. When this action ceases, life becomes extinct. Oxygen is bulk for bulk a little heavier than atmospheric air, which is usually taken as the standard of unity for the specific gravity of gases. Its specific gravity is expressed by the number 1-1057 ;l 100 cubic inches at 60° (15°-5C), and under the mean pressure of the atmosphere, that is, 30 inches of mercury, weigh 34-29 grains. It has been already remarked, that to determine with the utmost degree of accuracy the specific gravity of a gas is an operation of very great practical difficulty, but at the same time of very great importance. There are several methods which may be adopted for this purpose : the one below described appears, on the whole, to be the simplest and best. It requires, however, 1 Dumas, Ann. Chim. et Phys., 3d series, iii. 275. 11* 126 OXYGEN. the most scrupulous care, and the observance of a number of minute precau- tions, which are absolutely indispensable to success. The plan of the operation is as follows: —A large glass globe is to be filled with the gas to be examined, in a perfectly pure and dry state, having a known temperature, and an elastic force equal to that of the atmosphere at the time of the experiment. The globe so filled is to be weighed. It is then to be exhausted at the air-pump as far as convenient, and again weighed. Lastly, it is to be filled with dry air, the temperature and pressure of which are known, and its weight once more determined. On the supposition that the temperature and elasticity are the same in both cases, the specific gravity is at once obtained by dividing the weight of the gas by that of the air. The globe or flask must be made very thin, and fitted with a brass cap, surmounted by a small but excellent stop-cock. A delicate thermometer should be placed in the inside of the globe secured to the cap. The gas must be generated at the moment, and conducted at once into the previously- exhausted vessel, through a long tube filled with fragments of pumice moistened with oil of vitriol, or some other extremely-hygroscopic substance, by which it is freed from all moisture. As the gas is necessarily generated under some pressure, the elasticity of that contained in the filled globe will slightly exceed the pressure of the atmosphere; and this is an advantage, since by opening the stop-cock for a single instant when the globe has attained an equilibrium of temperature, the tension becomes exactly that of the air, so that all barometrical correction is avoided, unless the pressure of the atmos- phere should sensibly vary during the time occupied by the experiment. It is hardly necessary to remark, that the greatest care must also be taken to purify and dry the air used as the standard of comparison,.and to bring both gas and air as nearly as possible to the same temperature, to obviate the necessity of a correction, or at least to diminish almost to nothing the errors involved by such a process. The compounds formed by the direct union of oxygen with other bodies, bear the general name of oxides: these are very numerous and important. They are conveniently divided into three principal groups or classes. The first division contains all those oxides which resemble in their chemical rela- tions potassa, soda, or the oxide of silver or of lead: these are denominated alkaline or basic oxides, or sometimes salifiable bases. The oxides of the second group have properties exactly opposed to those of the bodies mentioned; oil of vitriol and phosphoric acid may be taken as the typical representatives of the class: they are called acids, and they tend strongly to unite with the basic oxides. When this happens, what is called a salt is generated, as sulphate of potassa, or phosphate of silver, each of these substances being compounded of a pair of oxides, one of which is highly basic and the other highly acid. Then there remains a third group of what may be termed neutral oxides, from their slight disposition to enter into combination. The black oxide of manganese, already mentioned, is an excellent example. It very frequently happens that a body is capable of uniting with oxygen in several proportions, forming a series of oxides, to which it is necessary to give distinguishing names. The rule in such cases is very simple, at least when the oxides of the metals are concerned. In such a series it is always found that one out of the number has a strongly-marked basic character; to this the term protoxide is generally given. The compounds next succeed'ino- receive the names of binoxide or deuloxide, teroxide or tritoxide, &c, from the Latin and Greek numerals, the different grades of oxidation being thus indicated If there be a compound between the protoxide and binoxide, the name s'esaui oxide is usually applied. So it is usual to call the highest oxide not having distinctly acid characters, peroxide, from the Latin prefix, signifying excess Any compound containing less oxygen than the protoxide, is called a suboxide Superoxide or hyperoxide is a word sometimes tued instead of peroxide HYDROGEN. 127 Ozone.—It has long been known that dry oxygen, or atmospheric air, when exposed to the passage of a series of electric sparks, emits a peculiar and some- what metallic odor. The same odor may be imparted to moist oxygen, by allowing phosphorus to remain for some time in it, and by several other pro- cesses. A more accurate examination of this odorous air has shown that, in addition to the smell, it assumes several properties not exhibited by pure oxygen. One of its most curious effects is the liberation of iodine from iodide of potassium. This odorous principle has been the subject of many researches lately — particularly by Prof. Schoenbein, of Basle, who proposed the name of ozone1 for it. Ozone, as produced by electrical processes, and according to the late researches of Dr. Andrews from every source, is a peculiar modifica- tion of oxygen, in which tho affinities of this element are enhanced in a remarkable manner.u (See also teroxide of hydrogen, p. 136.) JIl'DKOGEN. Hydrogen is always obtained for experimental purposes by deoxidizing water, of which it forms a characteristic component.3 If a tube of iron or porcelain, containing a quantity of filings, or turnings of iron, be fixed across a furnace, and its middle portion be made red-hot, and then the vapor of water transmitted over the heated metal, a large quan- tity of permanent gas will be disengaged from the tube, and the iron will be converted into oxide, and acquire an increase in weight. The gas is hydro- gen : it may be collected over water and examined. When zinc is put into water, chemical action of the liquid upon the metal is imperceptible ; but if a little sulphuric acid be added, decomposition of the water ensues, the oxygen unites with the zinc, forming oxide of zinc, which is instantly dissolved by the acid, while the hydrogen, previously in union with that oxygen, is disengaged in the gaseous form. The reaction is repre- sented in the subjoined diagram.4 Water \ Hydr0SeQ —----------------------------Free ( Oxygen------------- Zinc--------------^^ ------—oxide of zinc 1 Sulphate of Sulphuric acid__________________________________) oxide of zinc. The simplest method of preparing the gas is the following:—A wide-necked bottle (fig. 90) is chosen, and fitted with a sound cork, perforated by two holes foi the reception of a small tube-funnel reaching nearly to the bottom of the bottle and a piece of bent glass tube to convey away the disengaged gas. Granu- lated zinc, or scraps of the malleable metal, are put into the bottle, together with a little water, and sulphuric acid slowly added by the funnel, the°point of which should dip into the liquid. The evolution of gas is easily regulated by the supply of acid; and when enough has been discharged to expel the air of the vessel, it may be collected over water in ajar, or passed into agas> 1 From 8£oi, I smell. 4 [A. Housuau has procured oxygen from the deutoxide of barium by sulphuric acid, in the modified form of ozone. It is a colorless gas, with a strong odor, which is not at first repulsive, but by repetition becomes unbearable and produces nausea. It loses its active properties by heat; 167° F. is sufficient. At ordinary temperatures it oxidizes most metals, even silver, and raises some oxides to a higher state of oxidation, as arsenious into arsenic acid. It decomposes hydrochloric acid, uniting with the hydrogen and setting free the chlorine. On iodide of potas- sium it acts even more rapidly, iodine being evolved. Solutions of litmus, logwood, indigo, &c. are decolorized even more rapidly than by chlorine. The density of ozone is estimated by Tho^ mas Andrews to be four times that of ordinary oxygen.—R. B.] * Hence the name, from HSwp, water, and ytvvdui. I give rise to. 4 IIO,SOa -f Zn = Zn 0, SOs + H Hydrated sulphuric add. Zinc. Sulphate of zinc. Hydrogen. 128 HYDROGEN. holder. In the absence of zinc, filings of iron or small nails may be used, but with less advantage. Fig. 90. A little practice will soon enable the £_. pupil to construct and arrange a variety VT/ of useful forms of apparatus, in which \) bottles, and other articles always at hand, are made to supersede more costly instruments. Glass tube, purchased by weight of the maker, may be cut by scratching with a file, and then applying a little force with both hands. It may be softened and bent, when of small di- mensions, by the flame of a spirit-lamp. or even a candle or gas jet. Corks may be perforated by a heated wire, and the hole rendered smooth and cylindrical bj a round file; or the ingenious cork-bore* of Dr. Mohr, now to be had of most in- strument-makers, may be used instead. Lastly, in the event of bad fitting, or un- soundness in the cork itself, a little yel- low wax melted over the surface, or even a little grease applied with the finger, renders it sound and air-tight, when not exposed to heat. Hydrogen is colorless, tasteless, and inodorous when quite pure. To obtain it in this condition, it must be prepared from the purest zinc that can be ob- tained, and passed in succession through solutions of potassa and nitrate of silver. When prepared from commercial zinc it has a slight smell, which is due to impurity, and when iron has been used, the odor becomes very strong and disagreeable. It is inflammable, burning, when kindled, with a pale-yel- lowish flame, and evolving much heat, but very little light. The result of the combustion is water. It is even less soluble in water than oxygen, and has never been liquefied. Although destitute of poisonous properties, it is inca- pable of sustaining life. In point of specific gravity hydrogen is the lightest substance known; Du- mas and_ Boussingault place its density between 0-0691 and 0-0G95:1 hence 100 cubic inches will weigh, under ordinary circumstances of pressure and temperature, 2-14 grains. When a gas is much lighter or much heavier than atmospheric air, it may often be collected and examined without the aid of the pneumatic trough. A bottle or narrow jar may be filled with hydrogen without much admixture of air, by inverting it over the extremity of an upright tube delivering the gas. In a short time, if the supply be copious, the air will be wholly displaced, and the vessel filled. It may now be removed, the vertical position being carefully retained, and closed by a stopper or glass plate. If the mouth of the jar be wide, it must be partially closed by a piece of cardboard during the operation. This method of collecting gases by displacement is often extremely useful. Hydrogen was formerly used for filling air-balloons, being made for the purpose on the spot from zinc or iron and dilute sulphuric acid. Its use is superseded by that of coal-gas, which may be made very lio-ht by employing a high temperature in the manufacture. Although far inferior to pure hydrogen in buoyant power, it is found in practice to possess advantages over that substance, while its greater density is easily compensated by increasing the magnitude of the balloon. 1 Ann. Chim. et Phys., 3d series, viii. 201. Fig. 91. HYDROGEN. 129 There is a very remarkable property enjoyed by gases and vapors in gene- ral, which is seen in a high degree of intensity in the case of hydrogen : this is what i3 called diffusive power. If two bottles containing gases, which do not act chemically upon each other at common temperatures, be connected by a narrow tube and left for some time, these will be found at the expiration of a certain period, depending much upon the narrowness of the tube and its length, uniformly mixed, even though the gases differ greatly in density, and the system has been arranged in a vertical position, with the heavier gas downwards. Oxygen and hydrogen can thus be made to mix, in a few hours, against the action of gravity, through a tube a yard in length, and not more than one quarter of an inch in diameter; and the fact is true of all other gases which are destitute of direct action upon each other. If a vessel be divided into two portions by a diaphragm or partition of porous earthenware or dry plaster of Paris, and each half filled with a differ- ent gas, diffusion- will immediately commence through the pores of the dividing substance, and will continue until perfect mixture has taken place. All gases, however, do not permeate the same porous body, or, in other words, do not pass through narrow orifices with the same degree of facility. Profes- sor Graham, to whom we are indebted for a very valuable investigation of this interesting subject, has established the existence of a very simple relation between the rapidity of diffusion and the density of the gas, which is expressed by saying that the diffusive power varies inversely as the square root of the density of the gas itself. Thus, in the experiment supposed, if one half of the vessel be filled with hydrogen and the other half with oxygen, the two gases will penetrate the diaphragm at very different rates; four cubic inches of hydrogen will pass into the oxygen side, while one cubic inch of oxygen travels in the opposite direction. The densities of the two gases are to each other in the proportion of 1 to 16; their relative rates of diffusion will be inversely as the square roots of these numbers, i. e., as 4 to 1. _ By making the diaphragm of some flexible material, as a Fig. 92. piece of membrane, the accumulation of the lighter gas on the side of the heavier may be rendered evident by the bulging of the membrane. The simplest and most striking method of making the experiment is by the use of Professor Graham's diffusion-tube. This is merely a piece of wide glass tube ten or twelve inches in length, having one of its extre- mities closed by a plate of plaster of Paris about half an inch thick, and well dried. When the tube is filled by displace- ment with hydrogen, and then set upright in a glass of water, the level of the liquid rises in the tube so rapidly, that its movement is apparent to the eye, and speedily attains a height of several inches above the water in the glass. The gas is actually rarefied by its superior diffusive power over that of the external air.1 It is impossible to over-estimate the importance in the economy of Nature of this very curious law affecting the con- stitution of gaseous bodies: it is the principal means by which the atmosphere is preserved in an uniform state, and the accumulation of poisonous gases and exhalations in towns and other confined localities prevented. A distinction must be carefully drawn between real diffusion through small apertures, and the apparently similar passage of gas through wet or moist membranes and other substances, which is really due to temporary liquefac- tion or solution of the gas, and is an effect completely different from diffusion 1 Professor Graham has since published a very extensive series of researches on the passage which will be found in detail in the Philosophical Transactions i niiL'wur urr;iu;un lias since puuil.' of t'ast's through narrow tubes, which for lvlfl, p. 572. 130 11 Y D It O G E N . properly so called. For example, the diffusive power of carbonic acid into atmospheric air is very small, but it passes into the latter through a wet bladder with the utmost ease, in virtue of its solubility in the water with which the membrane is moistened. It is by such a process that the function of respiration is performed ; the aeration of the blood in the lungs, and the disengagement of the carbonic acid, are effected through wet membranes; the blood is never brought into actual contact with the air, but receives its supply of oxygen, and disembarrasses itself of carbonic acid by this kind of spurious diffusion. The high diffusive power of hydrogen against air renders it impossible to retain that gas for any length of time in a bladder or caoutchouc bag: it is even unsafe to keep it long in a gas-holder, lest it should become mixed with air by slight accidental leakage, and rendered explosive. It has been stated that, although the light emitted by the flame of pure hydrogen is exceedingly feeble, yet the temperature of the flame is very high. This temperature may be still farther exalted by previously mixing the hydro- gen with as much oxygen as it requires for combination, that is, as will pre- sently be seen, exactly half its volume. Such a mixture burns like "-un- powder, independently of the external air. When raised to the requisite temperature for combination, the two gases unite with explosive violence. If a strong bottle, holding not more than half-a-pint, be filled with such a mixture, the introduction of a lighted match or red-hot wire determines in a moment the union of the gases. By certain precautions, a mixture of oxygen and hydrogen can be burned at a jet without communication of fire to" the contents of the vessel; the flame is in this case solid. A little consideration will show, that all ordinary flames burning in the air or in pure oxygen are, of necessity, hollow. The act of combustion is nothing more than the energetic union of the substance burned with the surrounding oxygen; and this union can only take place at the surface of the burning body. Such is not the case, however, with the flame now under considera- tion, the combustible and the oxygen are already mixed, and only require to have their temperature a little raised to cause them to combine in every part. The flame so produced is very different in physical characters from that of a simple jet of hydrogen or any other combustible gas; it is long and pointed, and very re- markable in appearance. The safety-jet of Mr. Hemming, the construction of which involves a principle not yet discussed, may be adapted to a common bladder containing the mixture, and held under the arm, and the gas forced through the jet by a little pressure. Although the jet, properly constructed, is believed to be safe it is best to use nothing stronger than a bladder, for fear of injury in the event of an explosion. The gases are often con- tained in separate reservoirs, a pair of large gas-holders for example, and only suffered to mix in the jet itself as in' the contrivance of Professor Daniel]: in this way all danger is avoided. The eye speedily becomes accustomed to the pecu- uar appearance of the true hydro-oxygen flame, so as to-per- mit the supply of each gas to be exactly regulated by suitable stop-cocks attached to the jet (fig. 93). *^f eJ°f thick Platinum wire introduced into the flame ot the hydro-oxygen blowpipe melts with the greatest a watch-spring or small steel file burns with the utmo- hancy throwing off showers of beautiful sparks • an incom- bustible oxidized body, as magnesia or lime, becomes so in- tensely ign.ted as to glow with a light insupportable to *L eye, and to be susceptible of employment as a most powerful niuminator a Fig. 93. ease; st bril- nYDROGES. 131 8. substitute for the sun's rays in the solar microscope, and for night-signals iu trigonometrical surveys. If a long glass tube, open at both ends, be held over a jet of Fig. 94- hydrogen (fig. 94), a series of musical sounds are sometimes pro- duced by the partial extinction and rekindling of the flame by the ascending current of air. These little explosions succeed each other at regular intervals, and so rapidly as to give rise to a musical note, the pitch depending chiefly upon the length and diameter of the tube. Although oxygen and hydrogen may be kept mixed at common temperatures for any length of time without combination taking place, yet, under particular circumstances, they unite quietly and without ex- plosion. Some years ago Professor Dobcreiner, of Jena, made the curious observation, that finely-divided platinum possessed the power of determining the union of the gases ; and, more recently, Mr. Fara- day has shown that the state of minute division is by no means in- dispensable, since rolled plates of the metal have the same property, provided their surfaces are absolutely clean. Neither is the effect strictly confined to platinum; other metals, as palladium and gold, and even stones and glass, enjoy the same property, although to a far inferior degree, since they often require to be aided by a little heat. When a piece of platinum-foil, which has been cleaned by hot oil of vitriol and thorough washing with distilled water, is thrust into a jar containing a mixture of oxygen and hydrogen, standing over water, combination of the two gases immediately begins, and the level of the water rapidly rises, whilst the platinum becomes so hot that drops of water accidently falling upon it enter into ebullition. If the metal be very thin and exceedingly clean, and the gases very pure, then its temperature rises after a time to actual redness, and the residue of the mixture explodes. But this is an effect altogether accidental, and dependent upon the high temperature of the platinum, which high temperature has been produced by the preceding quiet combi- nation of the two bodies. When the platinum is reduced to a state of minute division, and its surface thereby much extended, it becomes immedi- ately red hot in a mixture of hydrogen and oxygen, or hydrogen and air; a jet of hydrogen thrown upon a little of the spongy metal, contained in a glass or capsule, becomes at once kindled, and on this principle machines for the production of instantaneous light have been constructed. These, how- ever, only act well when constantly used; the spongy platinum is apt to become damp by absorption of moisture from the air, and its power is then for the time lost. The best explanation that can be given of these curious effects is to suppose that solid bodies in general have, to a greater or less extent, the property of condensing gases upon their surfaces, and that this faculty is enjoyed pre- eminently by certain of the non-oxidizable metals, as platinum and gold. Oxygen and hydrogen may thus, under these circumstances, be brought, as it were, within the sphere of their mutual attractions by a temporary increase of density, whereupon combination ensues. Coal-gas and ether or alcohol vapor maybe made to exhibit the phenomenon of quiet oxidation under the influence of this remarkable surface-action. A close spiral of slender platinum wire, a roll of thin foil or even a common platinum crucible, heated to dull redness, and then held in a jet of coal-gas, becomes strongly ignited, and remains in that state as long as the supply of mixed" gas and air is kept up, the temperature being maintained by the heat disengaged in the act of union. Sometimes the metal becomes white hot and then the gas take fire. A very pleasing experiment may be made by attaching such a coil of wire to a card, and suspending it in a glass containing a few drops of ether 132 HYDROGEN. Fig. 95. having previously made it red hot in the flame of a spirit-lamp. The wne continues to glow until the oxygen of the air is exhausted, giving rise to the production of an irritating vapor, which attacks the eyes. The combustion of the ether is in this case but partialI; a portion of its hydrogen is alone removed, and the whole of the carbon left untouched. A coil of thin platinum wire may be placed over the wick of a spirit-lamp, or a ball of spongy platinum sus- tained just above the cotton: on lighting the lamp, and then blowing it out as soon as the metal appears red hot, slow combustion of the spirit drawn up by the capillarity of the wick will take place, accompanied by the pungent vapors just mentioned, which may be modified, and even rendered agreeable, by dissolving in the liquid some sweet- smelling essential oil or resin. Hydrogen forms numerous compounds with other bodies, although it is greatly surpassed in this respect not only by oxygen, but by many of the other elements. The chemical relations of hydro- gen tend to place it among the metals. The great discrepancy in physical properties is perhaps more apparent than real. Hydrogen is yet unknown in the solid condition, while, on the other hand, the vapor of the metal mercury is as transparent and colorless as hydrogen itself. This vapor is only about seven times heavier than atmospheric air, so that the difference in this respect is not nearly so great as that in the other direction between air and hydrogen. There are two oxides of hydrogen, namely, water, and a very peculiar substance, discovered in the year 1818 by M. Thenard, called binoxide of hydrogen. It appears that the composition of water was first demonstrated in the year 1781 by Mr. Cavendish ;1 but the discovery of the exact proportions in which oxygen and hydrogen unite in generating that most important compound has from time to time to the present day occupied the attention of some of the most distinguished cultivators of chemical science. There are two distinct methods of research in chemistry, the analytical, or that in which the com- pound is resolved into its elements, and the synthetical, in which the elements are made to unite and produce the compound, The first method is of much more general application than the second; but in this particular instance both may be employed, although the results of the synthesis are the more valuable. The most elegant example of analysis of water would probably be found in its decomposition by voltaic elec- tricity. When water is acidulated so as to render it a conductor, and a portion interposed between a pair of platinum plates connected with the extremities of a voltaic apparatus of moderate power, decomposition of the liquid takes place in a very interesting manner; oxygen, in a state of perfect purity is evolved from the water in con- tact with the plate belonging to the copper end of the battery, and hydrogen, equally pure, is disengaged at the plate, connected with the zinc extremity, the middle por- tions of liquid remaining apparently unaltered. By placing small graduated jars over the platinum plates, the gases can be collected, and their quantities determined. Figure 96 will show at a glance l A claim to the discovery of the composition of water, on behalf of Mr Jithps w,» i,„. been very strongly urged, and supported by such evidence that the reader of'thecolwj^ may be led to the conclusion that the discovery was made bv both ^rtirTw^Sl «• c°ntrover,sy and unknown to each other. y y l Paities, nearly simultaneously, HYDROGEN. 133 Fig. 97. the whole arrangement; the conducting wires pass through the bottom of the glass cup, and away to the battery. When this experiment has been continued a sufficient time, it will be found that the volume of the hydrogen is a very little above twice that of the oxygen: were it not for the accidental circumstance of oxygen being sensibly more soluble in water than hydrogen, the proportion of two to one by measure would come out exactly. Water, as Mr. Grove has shown, is likewise decomposed into its constituents by heat. The effect is produced by introducing platinum balls, ignited by electricity or other means, into water or steam. The two gases are obtained in very small quantities at a time. When oxygen and hydrogen, both as pure as possible, are mixed in the proportions mentioned, passed into a strong glass tube filled with mercury, and exploded by the electric spark, the mixture disappears, and the mercury is forced up into the tube, filling it completely. The same experiment may be made with the explosion-vessel or eudiometer of Mr. Cavendish (fig. 97). The instrument is exhausted at the air-pump, and then filled from a cap jar with the mixed gases ; on passing an electric spark by the wires shown at a, explosion ensues, and the glass becomes bedewed with moisture, and if the stop-cock be then opened under water, the latter will rush in and fill the vessel, leaving merely a bubble of air, the result of imperfect exhaustion. The process upon which most reliance is placed is that in which pure oxide of copper is reduced at a red heat by hydrogen, and the water so formed, collected and weighed. This oxide suffers no change by heat alone, but the momentary contact of hydrogen, or any common combustible matter, at a high temperature, suffices to reduce a corresponding portion to the metallic state. Fig. 98 will serve to convey some idea of the arrangement adopted in researches of this kind. A copious supply of hydrogen is procured by the action of dilute sulphuric acid upon the purest zinc that can be obtained; the gas is made to pass in succession through solutions of silver and strong caustic potassa, by which its purification is completed. After this, it is conducted through a tube three or Fig. 98. MM HH^ four inches in length, filled with fragments of pumice-stone steeped in con- centrated oil of vitriol, or with anhydrous phosphoric acid. These substances have such an extraordinary attraction for aqueous vapor, that they dry the gas completely during its transit. The extremity of this tube is shown at a. The dry hydrogen thus arrives at the part of the apparatus containing the oxide of copper, represented at 6 ; this consists of a two-necked flask of verv 12 J 134 HYDROGEN. hard white glass, maintained at a red heat by a spirit-lamp placed beneath. As the decomposition proceeds, the water produced by the reduction of the oxide begins to condense in the second neck of the flask, whence it drops into the receiver c, provided for the purpose. A second desiccating tube prevents the loss of aqueous vapor by the current of gas which passes in excess. Before the experiment can be commenced, the oxide of copper, the purity of which is well ascertained, must be heated to redness for some time in a current of dry air; it is then suffered to cool, and very carefully weighed with the flask. The empty receiver and second drying tube are also weighed, the disengagement of gas set up, and when the air has been displaced, heat slowly applied to the oxide. The action is at first very energetic; the oxide often exhibits the appearance of ignition; as the decomposition proceeds, it becomes more sluggish, and requires the application of a considerable heat to effect its completion. When the process is at an end, and the apparatus perfectly cool, the stream of gas is discontinued, dry air is drawn through the whole arrangement, and, lastly, the parts are disconnected and reweighed. The loss of the oxide of copper gives the oxygen ; the gain of the receiver and its drying tube indicates the water, and the difference between the two the hydrogen. A set of experiments, made in Paris in the year 1820,l by MM. Dulong and Berzelius, gave as a mean result for the composition of water by weight, 8-009 parts oxygen to 1 part hydrogen ; numbers so nearly-in the proportion of 8 to 1, that the latter have usually been assumed to be true. Quite recently the subject has been reinvestigated by M. Dumas,2 with the most scrupulous precision, and the above supposition fully confirmed. The composition of water may therefore be considered as established ; it contains by weight 8 parts oxygen to 1 part hydrogen, and by measure, 1 volume oxygen to 2 volumes hydrogen. The densities of the gases, as already mentioned, correspond very closely with these results. The physical properties of water are too well known to need lengthened description: it is, when pure, colorless, and transparent, destitute of taste and odor, and an exceedingly bad conductor of electricity of low tension. It attains its greatest density towards 40° (4°-5C), freezes at 32° (0°C), and boils under the pressure of the atmosphere at or near 212° (100°C)'. It evaporates at all temperatures. One cubic inch at 02° (16°-7C) weighs 252-45 grains. It is 815 "times heavier than air; an imperial gallon weighs 70,000 grains or 10 lbs. avoirdupois. To all ordinary observation, water is incompressible; very accurate experiments have nevertheless shown that it does yield to a small extent when the power employed is very great; the diminution of volume for each atmosphere of pressure being about 51-millionths of the whole. Clear water, although colorless in small bulk, is blue like the atmosphere when viewed in mass. This is seen in the deep ultramarine tint of the ocean and perhaps in a still more beautiful manner in the lakes of Switzerland and other Alpine countries, and in the rivers which issue from them ; the slightest admixture of mud or suspended impurity destroying the effect. The same magnificent color is visible in the fissures and caverns found in the ice of the glaciers, which is usually extremely pure and transparent within although foul upon the surface. ' ° Steam, or vapor of water, in its state of greatest density at 212° (100°C)" compared with air at the same temperature, and possessing an equal elastic force, has a specific gravity expressed by the fraction 0-G25. In this condition it may be represented as containing, in every two volumes, two volumes of hydrogen, and one volume of oxygen. Water seldom or never occurs in nature in a state of perfect purity • even the 1 Ann. Chim. et Phys., xv. 386. 2 Ibid., 3d series, viii. 189. UYDROQEN. 135 rain which falls in the open country contains a trace of ammoniacal salt, while rivers and springs are invariably contaminated to a greater or less extent with soluble matters, saline and organic. Simple filtration through a porous stone or bed of sand will separate suspended impurities, but distillation alone will free the liquid from those that are dissolved. In the preparation of distilled water, which is an article of large consumption in the scientific laboratory, it is proper to reject the first portions which pass over, and to avoid carrying the distillation to dryness. The process may be conducted in a metal still furnished with a worm or condenser of silver or tin; lead must not be used. Tho ocean is the great recipient of the saline matter carried down by the rivers which drain the land; hence the vast accumulation of salts. The fol- lowing table will serve to convey an idea of the ordinary composition of sea- water; the analysis is by Dr. Schweitzer,1 of Brighton, the water being that of the British Channel: — 100 grains contained Water.........904-745 Chloride of sodium...... 27-059 Chloride of potassium ...... 0-7GG Chloride of magnesium......3-6GG Bromide of magnesium......0-029 Sulphate of magnesia ...... 2-29G Sulphate of lime.......1-400 Carbonate of lime ....... 0-333 Traces of iodine and ammoniacal salt 1000-000 Its specific gravity was found to be 1-0274 at 60° (15°-5C). Sea-water is liable to variations of density and composition by the influence of local causes, such as the proximity of large rivers or masses of melting ice, and other circumstances. Natural springs are often impregnated to a great extent with soluble sub- stances derived from the rocks they traverse: such are the various mineral waters scattered over the whole earth, and to which medicinal virtues are attri- buted. Some of these hold protoxide of iron in solution, and are effervescent from carbonic acid gas: others are alkaline, probably from traversing rocks of volcanic origin ; some contain a very notable quantity of iodine or bromine. Their temperatures also are as variable as their chemical nature. A tabular notice of some of the most remarkable of these waters will be found in the Appendix. Water enters into direct combination with other bodies, forming a class of compounds called hydrates; the action is often very energetic, much heat being evolved, as in the case of the slaking of lime, which is really the production of a hydrate of that base. Sometimes the attraction between the water and the second body is so great that the compound is not decomposable by any heat that can be applied; the hydrates of potassa and soda, and of phospho- ric acid, furnish examples. Oil of vitriol is a hydrate of sulphuric acid, from which tho water cannot be thus separated. Water very frequently combines with saline substances in a less intimate manner than that above described, constituting what is called water of crys- tallization, from its connection with the geometrical figure of the salt. In this case it is easily driven off by the application of heat. Lastly, the solvent properties of water far exceed those of any other liquid known. Among salts a very largo proportion are soluble to a greater or less extent, the solubility usually increasing with the temperature, so that a hot 1 Phil. Mag., July, 1S39. 136 HYDROGEN. saturated solution deposits crystals on cooling. There are a few exceptions to'this law, one of the most remarkable of which is common salt, the solu- bility of which is nearly the same at all temperatures; the hydrate and cer- tain organic salts of lime, also, dissolve more freely in cold than in hot water. Water dissolves gases, but in very unequal quantities; some, as hydrogen, oxygen, and atmospheric air, are but little acted upon ; others, as ammonia and hydrochloric acid, are absorbed to an enormous extent; and between these extremes there are various intermediate degrees. Generally, the colder the water, the more gas does it dissolve; a boiling heat disengages the whole, if the gas be not very soluble. When water is heated in a strong vessel to a temperature above that of the ordinary boiling-point, its solvent powers are still farther increased. Dr. Turner enclosed in the upper part of a high-pressure steam-boiler, worked at 300° (149°C), pieces of plate and crown glass. At the expiration of four months the glass was found completely corroded by the action of the water; what remained was a white mass of silica, destitute of alkali, while stalactites of siliceous matter, above an inch in length, depended from the little wire cage which enclosed the glass. This experiment tends to illustrate the changes which may be produced by the action of water at a high temperature in the interior of the earth upon felspathic and other rocks. The phenomenon is manifest in the Geyser springs of Iceland, which deposit siliceous sinter.1 Binoxide of hydrogen, sometimes called oxygenated water, is an exceedingly interesting substance, but unfortunately very difficult of preparation. It is formed by dissolving the binoxide of barium in dilute hydrochloric acid, care- fully cooled by ice, and then precipitating the baryta by sulphuric acid: the excess of oxygen of the binoxide, instead of being disengaged as gas, unites with a portion of the water, and converts it into binoxide of hydrogen. This treatment is repeated with the same solution and fresh portions of the bin- oxide of barium until a considerable quantity of the latter has been consumed, and a corresponding amount of binoxide of hydrogen formed. The liquid yet contains hydrochloric acid, to get rid of which it is treated in succession with sulphate of silver and baryta-water. The whole process requires the utmost care and attention. The binoxide of barium itself is prepared by exposing pure baryta, contained in a red-hot porcelain tube, to a stream of oxygen. The solution of binoxide of hydrogen may be concentrated under the air- pump receiver until it acquires the specific gravity of 1-45. In this state it presents the aspect of a colorless, transparent, inodorous liquid, possessing remarkable bleaching powers. It is very prone to decomposition; the least elevation of temperature causes effervescence, due to the escape of oxygen gas; near 212° (100°C) it is decomposed with explosive violence. Binoxide of hydrogen contains exactly twice as much oxygen as water, or 16 parts to 1 part of hydrogen. A teroxide of hydrogen2 is said to exist, although it has never been obtained in the pure state. Its properties are similar to those of tho binoxide; it is likewise a powerful oxidizing agent. According to the researches of Dr. Baumert, minute quantities of this substance are formed in the decomposition of water by electricity, and impart the odor by which the products of this process are characterized. It has been mentioned that this peculiar odor which is evolved in several processes, such as the oxidation of phosphorus, the passage of the electric spark through gases containing oxygen, is ascribed to the same substance, namely, ozone. Dr. Baumert's experiments appear to show that there are at least two substances which have hitherto been con- 1 Phil. Mag., Oct. 1834. 1 In symbols the composition of water and binoxide of hydrogen is thus exnressed •__ Water......HO ' Binoxide of hydrogen . . . HOa Teroxide of hydrogen . . . HO3 NITROGEN. 137 founded under the term ozone; for the odor produced by the passage of the electric spark through atmospheric air cannot possibly be due to the forma- tion of teroxide of hydrogen. It is not known whether the odorous substance, which is generated during the oxidation of phosphorus, is teroxide of hydro- gen, or identical with the ozone of the electric spark. Dr. Andrews denies the accuracy of Dr. Baumert's experiments, and states that the teroxide of hydrogen is nothing but active oxygen. Fig. 99. Nitrogen1 constitutes about | of the atmosphere, and enters into a great variety of combinations. It may be prepared for the purpose of experiment by several methods. One of the simplest of these is to burn out the oxygen from a confined portion of air by phosphorus, or by a jet of hydrogen. A small porcelain capsule is floated on the water of the pneumatic trough, and a piece of phosphorus is placed in it and set on fire. A bell-jar is then inverted over the whole, and sufl'ered to rise on the shelf of the trough, so as to project a little over its edge. At first the heat causes expansion of the air of the jar, and a few bubbles are expelled, after which the level of the water rises con- siderably. When the phosphorus becomes extinguished by exhaustion of the oxygen, and time'has been given for the subsidence of the cloud of finely-divided snow- like phosphoric acid, which floats in the residual gas, the nitrogen may be transferred into another vessel, and its properties examined. Prepared by the foregoing process, nitrogen is con- taminated by a little vapor of phosphorus, which com- municates its peculiar odor. A preferable method is to fill a, porcelain tube with turnings of copper, or, still better, with the spongy metal obtained by reducing the- oxide by hydrogen; to heat this tube to redness, and then pass through it a slow stream of atmospheric air, the oxygen of which is entirely removed during its progress by the heated copper. If chlorine gas be passed into solution of ammonia, the latter substance, which is a compound of nitrogen with hydrogen, is decomposed; the chlorine combines with the hydrogen, and the nitrogen is set free with effervescence. In this manner very pure nitrogen can be obtained. In making this experi- ment, it is necessary to stop short of saturating or decomposing the whole of the ammonia; otherwise there will be great risk of accident from the forma- tion of an exceedingly dangerous explosive compound formed by the contact of chlorine with an ammoniacal salt. Nitrogen is destitute of color, taste, and smell; it is a little lighter than uir, its density being, according to Dumas, 0-'.>72. 100 cubic inches, at 60° (I5°-.")C|, and 30 inches barometer, will therefore weigh 30-14 grains. Nitro- gen is incapable of sustaining combustion or animal existence, although, like hydrogen, it has no positive poisonous properties; neither is it soluble to any notable extent in water or in caustic alkali; it is, in fact, best characterized by negative properties. The exact composition of the atmosphere has repeatedly been made the subject of experimental research, lie-ides nitrogen and oxygen, the air con- tains a little carbonic acid, a very variable proportion of aqueous vapor, a trace of ammonia, and, perhaps, a little carbonetted hydrogen. The oxygen nud nitrogen are in a state of mixture, not of combination, yet their ratio is ■ T. «. Geucrator of nitre; also called azote, from a, privative, and Cuifi 12* 'pri, life. 138 NITROGEN. always uniform. Air has been brought from lofty Alpine heights, and com- pared with that from the plains of Egypt; it has been brought from an ele- vation of 21,000 feet by the aid of a balloon : it has been collected and ex- amined in London and Paris, and many other places ; still the proportions of oxygen and nitrogen remain unaltered, the diffusive energy of the gases being adequate to maintain this perfect uniformity of mixture. The carbonic acid, on the contrary, being much influenced by local causes, varies considerably. In the following table the proportions of oxygen and nitrogen are given on the authority of M. Dumas, and the carbonic acid on that of De Saussure: the ammonia, the discovery of which in atmospheric air is due to Liebig, is too small in quantity for direct estimation. Composition of the Atmosphere. By weight. By measure. Nitrogen ... 77 parts . . . 79-19 Oxygen .... 23 '< .... 20-81 100 100-00 Carbonic acid, from 3-7 measures to 6-2 measures, in 10,000 measures of air. Aqueous vapor variable, depending much upon the temperature. Ammonia, a trace. 100 cubic inches of pure and dry air weigh, according to Dr. Prout, 31-0117 grains : the temperature being 60° F. (15°-5C) and the barometer stand- ing at 30 inches. The analysis of air is very well effected by passing it over finely-divided copper contained in a tube of hard glass, carefully weighed, and then heated to redness; the nitrogen is suffered to flow into an exhausted glass globe, also previously weighed. The increase of weight after the experiment gives the information sought. An easier, but less accurate method, consists in intro- ducing into a graduated tube, standing over water, a known quantity of the air to be examined, and then passing into the latter a stick of phosphorus affixed to the end of a wire. The whole is left about twenty-four hours, during which the oxygen is slowly but completely absorbed, after which the phosphorus is withdrawn, and the residual gas read off. Professor Liebig has lately proposed to use an alkaline solution of pyrogallic acid (a substance which will be described in the department of organic chemistry) for the absorption of oxygen. The absorptive power of such a solu- tion, which turns deep black on coming in contact with the oxygen, is very considerable. Liebig's method combines great accuracy with unusual rapidity and facility of exe- cution. Another plan is to mix the air with hydrogen and pass an electric spark; after explosion the volume of gas is read off and compared with that of the air. employed. Since the analysis of gaseous bodies by explosion is an operation of great importance in practical chemistry, it may be worth while describing the process in detail, as it is applicable, with certain obvious variations, to a number of analogous cases. A convenient form of apparatus for the purpose is the syphon eudiometer of Dr. Ure; this consists of a stout glass tube, having an internal diameter of NITROGEN. 139 about one-third of an inch, closed at one end, and bent into the form repre- sented in the drawing. (Fig. 101.) Two pieces of platinum wire, melted into the glass near the closed extremity, serve to give passage to the spark. The closed limb is carefully graduated. When required for use, tho instrument is filled with mercury, and in- verted into a vessel of the same fluid. A quantity of the air to be examined is then introduced, the manipu- lation being precisely the same as with experiments over water; the open end is stopped with the thumb, and the air transferred to the closed extremity. The instrument is next held upright, and after the level of the mercury has been made equal on both sides by dis- placing a portion from the open limb by thrusting down a piece of stick, the volume of air is read off. This done, the open part of the tube is again filled up with mercury, closed with the finger inverted into the liquid metal, and a quantity of pure hydrogen introduced, equal, as nearly as can be guessed, to about half the volume of the air. The eudiometer is once more brought into an erect position, the level of the mercury equalized, and the volume again read off; the quantity of hydrogen added is thus .accurately ascertained. All is now ready for the explosion; the instru- ment is held in the way represented, the open end being firmly closed by the thumb, while the knuckle of the forefinger touches the nearer platinum wire; the spark is then passed by the aid of a charged jar or a good electrophorus, and the explosion ensues. The air confined by the thumb in the open part of the tube acts as a spring and moderates the explosive effect. Nothing now remains but to equalize the level of the mercury by pouring a little more into the instrument, and then to read off the volume for the last time. What is required to be known from this experiment is the diminution the mixture suffers by explosion; for since the hydrogen is in excess, and since that body unites with oxygen in the proportion by measure of two to one, one- third part of that diminution must be due to the oxygen contained in the air introduced. As the amount of the latter is known, the proportion of oxygen it contains thus admits of determination. The case supposed will render this clear. Air introduced......100 measures. Air and hydrogen......150 Volume after explosion ..... 87 Diminution ....... 63 ^ = 21; oxygen in the hundred measures. The working pupil will do well to acquire dexterity in the use of this valu- able instrument, by practising the transference of gas or liquid from the one limb to the other, &c. In the analysis of combustible gases by explosion with oxygen, solution of caustic potassa is often required to be introduced into the closed part. Compounds of Nitrogen and Oxygen. There are not less than five distinct compounds of nitrogen and oxygen thus named and constituted:— 140 NITROGEN. Nitrogen. Oxygen 14 8 14 16 14 24 14 32 14 40 Composition by weight. Protoxide of nitrogen1 Binoxide of nitrogen2 . Nitrous acid Hyponitric acid 3 Nitric acid4 Nitric or Azotic Acid.—In certain parts of India, and also in other hot dry climates where rain is rare, the surface of the soil is occasionally covered by a saline efflorescence, like that sometimes apparent on newly-plastered Walls: this substance collected, dissolved in hot water, the solution filtered and made to crystallize, furnishes the highly-important salt known in commerce as nitre or saltpetre: it is a compound of nitric acid and potassa. To obtain liquid nitric acid, equal weights of powdered nitre and oil of vitriol are introduced into a glass retort, and heat applied by means of an Argand gas-lamp or char- coal chauffer. A flask, cooled by a wet cloth, is adapted to the retort to serve for a receiver. No luting of any kind must be used. As the distillation advances, the red fumes which first arise disappear, but towards the end of the process again become manifest. When this happens, and very little liquid passes over, while the greater part of the saline matter of the retort is in a state of tranquil fusion, the operation may be stopped; and when the retort is quite cold, water may be introduced to dissolve out the bisulphate of potassa. The reaction is thus explained.5 Nitre 5 Ni )Pc itric acid __ Potassa Oil of vitriol Water Sulphuric acid Liquid nitric acid. Bisulphate of potassa. In the manufacture of nitric acid on the large scale, the glass retort is replaced by a cast-iron cylinder, and the receiver by a series of earthen con- densing vessels connected by tubes. Nitrate of soda, found native in Peru, is often substituted for nitrate of potassa. Fig. 102. Liquid nitric acid so obtained has a specific gravity of from 1-48 to 1-52 • it has a golden-yellow color, which is due to nitrous or hyponitric acid held' in * Otherwise called nitrous oxide. * Called by Professor Graham peroxide of nitrogen. * In symbols the composition of these substances is thus expressed:— Protoxide of nitrogen Binoxide of nitrogen . Nitrous acid Hyponitrio acid . Nitric acid . Otherwise called nitric oxide. 5 KO, NOs Nitrate of potassa. + 2 (HO, S03) Sulphuric acid. KO, S03; HO, SOa Bisulphate of potassa. NO NOs NOa NO4 NOs + HO, NOa Nitric acid. NITROGEN. 141 solution, and which, when the acid is diluted with water, gives rise by its de- composition to a disengagement of nitric oxide. It is exceedingly corrosive, staining the skin deep yellow, and causing total disorganization. Poured upon red-hot powdered charcoal, it causes brilliant combustion; and when added to warm oil of turpentine, acts upon that substance so energetically as to set it on fire. Pure liquid nitric acid, in its most concentrated form, is obtained by mixing the above with about an equal quantity of oil of vitriol, redistilling, collecting apart the first portion which comes over, and exposing it in a vessel slightly warmed, and sheltered from the light, to a current of dry air, made to bubble through it, which completely removes the nitrous acid. In this state the pro- duct is as colorless as water; it has the sp. gr. 1-517 at 60° (15°-5C), boils at, 184° (84°-5C), and consists of 54 parts real acid, and 9 parts water. Although nitric acid in a more dilute form acts very violently upon many metals, and upon organic substances generally, this is not the case with the compound in question ; even at a boiling heat it refuses to attack iron or tin, and its mode of action on lignin, starch, and similar substances is quite peculiar and very much less energetic than that of an acid containing more water. A second definite compound of real nitric acid and water exists, containing 54 parts of the former to 36 parts of the latter. Its sp. gr. at 60° (15°-C) is 1-421, and it boils at 250° (121°C). An acid weaker than this is concentrated to this point by evaporation; and one stronger, reduced to the same strength by loss of nitric acid and water in the form of the first hydrate.1 Absolute nitric acid, in the separate state, was unknown up to 1849, when M. Deville succeeded in obtaining this remarkable substance by exposing nitrate of silver, which is a combination of nitric acid, silver, and oxygen, to the action of chlorine gas. Chlorine and silver combine, forming chloride of Bilver, which remains in the apparatus, whilst oxygen and anhydrous nitric acid separate. The latter is a colorless substance, crystallizing in six-sided columns, which fuse at 86° (30°C), and boil between 113° and 122° (45° and 50°C), when they commence to be decomposed. Anhydrous nitric acid has been found to explode sometimes spontaneously. It dissolves in water with evolution of much heat, forming hydrated nitric acid. It consists of 14 parts of nitrogen and 40 parts of oxygen. Nitric acid forms with bases a very extensive and important group of salts, the nitrates, which are remarkable for all being soluble in water. The hydrated acid is of great use in the laboratory, and also in many branches of industry. The acid prepared in the way described is apt to contain traces of chlorine from common salt in the nitre, and sometimes of sulphate from accidental splashing of the pasty mass in the retort. To discover these impurities, a portion is diluted with four or five times its bulk of distilled water, and divided between two glasses. Solution of nitrate of silver is dropped into the one, and solution of nitrate of baryta into the other; if no change ensue in either case, the acid is free from the impurities mentioned. Nitric acid has been formed in small quantity by a very curious process, namely, by passing a series of electric sparks through a portion of air; water, or an alkaline solution, being present. The amount of acid so formed after many hours is very minute; still it is not impossible that powerful dis- charges of atmospheric electricity may sometimes occasion a trifling produc- tion of nitric acid in the air. A very minute quantity of nitric acid is also produced by the combustion of hydrogen and other substances in the atmos- phere ; it is also formed by the oxidation of ammonia. Nitric acid is not so easily detected in solution in small quantities as many other acids. Owing to the solubility of all its compounds, no precipitant can be found for this substance. One of the best tests is its power of bleaching « The two hydrates of nitric acid are thus expressed by symbols:—NOs, IIO and NOs, 4HO. No compound containing two equivalents of water appears to exist. 142 NITROGEN. a solution of indigo in sulphuric acid when boiled with that liquid. The absence of chlorine must be insured in this experiment by means which will hereafter be described, otherwise the result is equivocal. Protoxide of Nitrogetf Nitrous Oxide (laughing gas).—When solid nitrate of ammonia is heated in a retort or flask,1 fig. 103, furnished with a perforated cork and bent tube, it is resolved into water and nitrous oxide. The nature of the decomposition will be understood from the subjoined diagram.2 f Nitrogen 14 [ Nitric acid I Oxygen 54 ] Oxygen 8 Nitrate of j { Oxygen 24 Ammonia. \Ammonia J Nitrogen 14 17 I Hydrogen 3 Water 9----------------- Protox. nitrogen. 22 rrotox. nitrogen. Water 27 Fig. 103. No particular precaution is required in the operation, save due regulation of the heat, and the avoidance of tumultuous disen- gagement of the gas. Protoxide of nitrogen is a colorless, transparent, and almost inodorous gas, of distinctly sweet taste. Its specific gravity is 1525; 100 cubic inches weigh 47-29 grains. It supports the combustion of a taper or a piece of phosphorus with almost as much energy as pure oxygen; it is easily distinguished, however, from that gas by its solubility in cold water, which dissolves nearly its own volume; hence it is neces- sary to use tepid water in the pneumatic trough or gas-holder, otherwise great loss of gas will ensue. Nitrous oxide has been liquefied, but with difficulty; it requires, at 45° (7°-2C), a pressure of 50 atmos- pheres: the liquid when exposed tinder the bell- glass of the air-pump is rapidly converted into a snow-like solid. When mixed with an equal volume of hydrogen, and fired by the electric spark in the eudiometer, it explodes with violence, and liberates its own measure of nitrogen. Every two volumes of the gas must consequently contain two volumes of nitrogen and one volume of oxygen, the whole being condensed or contracted one-third; a con- stitution resembling that of vapor of water.3 The most remarkable feature in this gas is its intoxicating power upon the animal system. It may be respired, if quite pure, or merely mixed with at- mospheric air, for a short time, without clanger or inconvenience The effect is very transient, and is not followed by depression. Binoxide of Nitrogen.—Clippings or turnings of copper are put into the apparatus employed for preparing hydrogen,* together with a little water, and nitric acid added by the funnel until brisk effervescence is excited. The gas may be collected over cold Avater, as it is not sensibly soluble. 1 Florence oil-flasks, which may be purchased at a very trifling sum, constitute exceedingly useful vessels for chemical purposes, and often supersede retorts or other expensive apparatus. They are rendered still more valuable by cutting the neck smoothly round with a hot iron, softening it in the flame of a good Avgand gas-lamp, and then turning over the edge so as to form a. lip, or border. The neck will then bear a tigbtly-fitting-cork without risk of splitting. a NII4O.NO5 = 2XO + 4HO Nitrate of ammonia. * See page 134. Protoxide of nitrogen. Water. * See page 128. NITROGEN. 143 The reaction is a simple deoxidation of some of the nitric acid by the copper; the metal is oxidized, and the oxide so formed is dissolved by another portion of the acid. Nitric acid is very prone to act thus upon certain metals.1 The gas obtained in this manner is colorless and transparent; in contact with air or oxygen gas it produces deep-red fumes, which are readily absorbed by water: this character is sufficient to distinguish it from all other gaseous bodies. A light taper plunged into the gas is extinguished; lighted phospho- rus, however, burns in it with great brilliancy. The specific gravity of binoxide of nitrogen is 1039; 100 cubic inches weigh 32-22 grains. It contains equal measures of oxygen and nitrogen gas united without condensation. When this gas is passed into a solution of prot- oxide of iron it is absorbed in large quantity, and a deep-brown or nearly- black liquid produced, which seems to be a definite compound of the two substances. The compound is again decomposed by boiling. Nitrous acid. — Four measures of binoxide of nitrogen are mixed with one measure of oxygen, and the gases, perfectly dry, exposed to a temperature of 0° (— 17°-8C.) They condense to a thin mobile green liquid. Its vapor is orange-red. Nitrous aeid is decomposed by water, being converted into nitric acid and binoxide of nitrogen. For this reason it cannot be made to unite directly with metallic oxides ; nitrite of potassa may, however, be prepared by fusing nitrate of potassa, when part of its oxygen is evolved; and many other salts of nitrous acid may be obtained by indirect means. Hyponitric Acid. — It has been doubted whether the term acid applied to this substance be correct, since it seems to possess the power of forming salts only in a very limited de"gree: the expression has, notwithstanding, been long sanctioned by use. Moreover, a beautiful crystalline lead-salt of this sub- stance has been discovered by M. Peligot. It is formed by digesting nitrate of lead with metallic lead. It is chiefly the vapor of hyponitric acid which forms the deep-red fumes always produced when binoxide of nitrogen escapes into the air. When carefully-dried nitrate of lead is exposed to heat in a retort of hard glass, it is decomposed; protoxide of lead remains behind, while the acid is resolved into a mixture of oxygen and hyponitric acid. By surrounding the receiver with a very powerful freezing mixture, the latter is condensed to the liquid form. It is then nearly colorless, but acquires a yellow and ultimately a red tint, as the temperature rises. At 82° (27°-8C) it boils, giving off its well-known red vapor, the intensity of the color of which is greatly augmented by elevation of temperature. This substance, like the preceding, is decomposed by water, being resolved into binoxide of nitrogen and nitric acid. Its vapor is absorbed by strong nitric acid, which thereby acquires a yellow or red tint, passing into green, then into blue, and afterwards disappearing altogether on the addition of successive portions of water. The deep-red fuming acid of commerce called nitrous acid, is simply nitric acid impregnated with hyponitric acid gas.2 Nitrogen appears to combine, under favorable circumstances, with metals. When iron and copper are heated to redness in an atmosphere of ammonia, 1 4(IIO,NO:,) + 3Cu = NOj + •" CuO.NOo) + 4IIO Nitric'ai-id. Copper. Binoxide of Nitrogen. Nitrate of copper. Water. 1 Much doubt yet hangs over the true nature and relations of these two acids. According to M. 1'eligot, the only product of the union of binoxide of nitrogen and oxygen is hyponitria acid, which, in the total absence of water, is a white solid crystalline body, fusible at 16° (—8°-9C). At common temperatures it is an orange-yellow liquid. The same product is ob- tained by beating perfectly-dry nitrate of lead. From these experiments it would appear that nitrous acid in a separate state is unknown.—Ann. Chim. et. Phys. 3d series, ii. y*. 144 CARBON. they become brittle and crystalline, but without sensible alteration of weight. M. Schrotter has shoAvn that hi the case of copper, at least, this effect is caused by the formation and subsequent destruction of a nitride, that is, a compound of nitrogen with copper. When ammonia is passed over protoxide of copper heated to 570° (298°-9C), water is formed, and a soft brown powder produced, which, when heated farther, evolves nitrogen, and leaves metallic copper. The same effect is produced by the contact of strong acids. A similar compound of chromium with nitrogen appears to exist. CARBON. This substance occurs in a state of purity, and crystallized, in two distinct and very dissimilar forms, namely, as diamond, and as graphite or plumbago. It constitutes a large proportion of all organic structures, animal and vege- table: when these latter are exposed to destructive distillation in close vessels a great part of their carbon remains, obstinately retaining some of the hydro- gen and oxygen, and associated with the earthy and alkaline matter of the tissue, giving rise to the many varieties of charcoal, coke, &c. When per- fectly separated from all foreign matter, this kind constitutes a third variety of carbon. The diamond is one of the most remarkable substances known : long prized on account of its brilliancy as an ornamental gem, the discovery of its curious chemical nature confers upon it a high degree of scientific interest. Several localities in India, the island of Borneo, and more especially Brazil, furnish this beautiful substance. It is always distinctly crystallized, often quite transparent and colorless, but now and then having a shade of yellow, pink, or blue. _ The origin and true geological position of the diamond are un- known; it is always found embedded in gravel and transported materials whose history cannot be traced. The crystalline form of the diamond is that of the regular octahedron or cube, or some figure geometrically connected with these. Many of the octahedral crystals exhibit a very peculiar appear- ance, arising from the faces being curved or rounded, which gives to the crystal an almost spherical figure. Fig. 104. The diamond is infusible and unalterable by a very intense heat, provided air be excluded; but when heated, thus protected, between the poles of a strong galvanic battery, it is converted into coke or graphite • heated to white- ness in a vessel of oxygen, it burns with facility, yielding carbonic acid ga« This is the hardest substance known: it admits of being split or cleaved without difficulty in certain particular directions, but can only be cut or abraded by a second portion of the same material; the powder rubbed off in this process serves for polishing the new faces, and is also highly useful to the lapidary and seal engraver. One very curious and useful application of the diamond is made by the glazier; a fragment of this mineral, like a bit of flint or any other hard substance, scratches the surface of glass; a crystal of dia' mond, having the rounded octahedral figure spoken of, held in one particular position on the glass, namely, with an edge formed by the meetino- of two adjacent faces presented to the surface, and then drawn along with gentle CARBON 145 pressure, causes a deep split or cut, which penetrates to a considerable depth into the glass, and determines its fracture with perfect certainty. Graphite or plumbago appears to consist essentially of pure carbon, although most specimens contain iron, the quantity of which varies from a mere trace up to five per cent. Graphite is a somewhat rare mineral: the finest and most valuable for pencils is brought from Borrowdale, in Cumberland, where a kind of irregular vein is found traversing the ancient slate beds of that district.1 Crystals are not common: when they occur, they have the figure of a short six- sided prism —a form bearing no geometrical relation to that of the diamond. Graphite is often formed artificially in certain metallurgic operations: the brilliant scales which sometimes separate from melted cast-iron on cooling, called by the workmen " kish," consist of graphite. Lampblack, the soot produced by the imperfect combustion of oil or resin, is the best example that can be given of carbon in its uncrystallized or amor- phous state. To the same class belong the different kinds of charcoal. That prepared from wood, either by distillation in a large iron retort, or by the smothered combustion of a pile of fagots partially covered with earth, is the most valuable as fuel. Coke, the charcoal of pit-coal, is much more impure; it contains a large quantity of earthy matter, and very often sulphur; the quality depending very much upon the mode of preparation. Charcoal from bones and animal matters in general is a very valuable substance, on account of the extraordinary power it possesses of removing coloring matters from organic solutions; it is used for this purpose by the sugar-refiners to a very great extent, and also by the manufacturing and scientific chemist.2 The pro- perty in question is possessed by all kinds of charcoal in a small degree. Charcoal made from box, or other dense wood, has the property of con- densing into its pores gases and vapors; of ammoniacal gas it is said to absorb not less than ninety times its volume, while of hydrogen it takes up less than twice its own bulk, the quantity being apparently connected with the property in the gas of suffering liquefaction. This deodorizing effect, as well as the decolorizing power, no doubt depends in some way upon the same peculiar action of surface so remarkable in the case of platinum in a mixture of oxy- gen and hydrogen. The effect of deodorizing is indeed considerably increased by saturating charcoal with solution of platinum, and igniting it subsequently, so as to coat the charcoal with a thin film of platinum. Dr. Stenhouse, who suggested this plan, finds that the gases thus absorbed undergo a kind of oxi- dation within the pores of the charcoal.3 'chlo- -bath dried. Thus prepared, this substance, when heated to a temperature approaclTn^TAd'heat0 swells up to a voluminous mass of finely-divided graphite. ° ' a [It removes from solution in water the vegetable bases, bitter principles, and astringent sub- stances, when employed in excess requiring from twice to twenty times their wei"htfor total precipitation. A solution of iodine in water, or iodide of potassium, is quickly deprived of color. Metallic salts dissolved in water or diluted alcohol are precipitated, though not entirely- requiring about thirty times their weight of animal charcoal. Arsenious acid is totally car- ried out of solution. In these cases it acts in three different ways: the salt is absorbed unal- tered; the oxide in the salt may be reduced; or, the salts precipitated in a basic condition the solution showing an acid reaction as soon as the carbon begins to act. It is in this last'ease especially that traces of the bases can be detected, the acid set free preventing their total preci- pitation. The precipitation may hence be prevented by adding an excess of acid, and the bases after precipitation may be dissolved out by boiling with an acid solution.—Warrington Mem Chim. Soc. 1845; Garrod, Pharm. Journ. 1S44; Wappen, Ann. de Chim. 1845.__U. B~l ' ' [Carbon is a combustible uniting with oxygen and producing carbonic acid. Its different forms exhibit much difference in this respect; in the very porous condition of charcoal it lo 146 CARBON. Compounds of Carbon and Oxygen. There are two direct inorganic compounds of carbon and oxygen, called car- bonic oxide and carbonic acid; their composition may be thus stated; — Composition by weight. Carbon. Oxygen. Carbonic oxide.......6 8 Carbonic acid ....... 6 16 Carbonic Acid is always produced when charcoal burns in air or oxygen gas; it is most conveniently obtained, however, for study, by decomposing a carbonate with one of the stronger acids. For this purpose, the apparatus for generating hydrogen may again be employed; fragments of marble are put into the bottle with enough water to cover the extremity of the funnel- tube, and hydrochloric1 or nitric acid added by the latter, until the gas is freely disengaged. Chalk-powder and dilute sulphuric acid may be used instead. The gas may be collected over water, although with some lo6S; or Fig. 105. ■tt^^sttz£*&*VJiAZaSi&XtsiKl very conveniently by displacement, if it be required dry, as shown in tho figure. The long drying-tube is filled with fragments of chloride of calcium, and the heavy gas is conducted to the bottom of the vessel in which it is to be received, the mouth of the latter being lightly closed.2 Durns readily, while in its most dense form, the diamond, it requires a bright red heat and pure oxygen. In the form of charcoal it conducts heat slowly Fig 106. and electricity readily. Carbon is insoluble in water, and not liable to be affected by air and moisture. It retards putrefac- tion.—R. B.] 'CaO,C02 + HC1 = CaCl + HO + CO.i Carbonate of lime. Hydrochloric acid. Chloride of calcium. Water. Carbonic acid. a In connecting tube-apparatus for conveying gases or cold liquids not corrosive, little tubes of caoutchouc, about an inch long, are in- expressibly useful. These are made by bending a piece of sheet India-rubber loosely round a glass tube or rod, and cutting off the superfluous portion with sharp scissors. The fresh-cut ed^es of the caoutchouc, pressed strongly together, cohere completely? and the tube is perfect, provided they have not been soiled by touching with fingers. The connectors are secured by two or three turns of thin silk cord. Tubes of various sizes made of vulcanized India-rubber are now articles of commerce, and may be conveniently substituted for those made in the laboratory. The glass tubes are sold by wei"ht and are easily bent in the flame of a spirit-lamp, and, when neces' sary, cut by scratching with a file, and broken asunder. CARBON. 147 Carbonic acid gas is colorless; it has an agreeable pungent taste and odor, but cannot be respired for a minute without insensibility following. Its spe- cific gravity is 1-524.1 100 cubic inches weighing 47-26 grains. This gas is very hurtful to animal life, even when largely diluted with air; it acts as a narcotic poison. Hence the danger arising from imperfect venti- lation, the use of fire-places and stoves of all kinds unprovided with proper chimneys, and the crowding together of many individuals in houses and ships without efficient means for renewing the air; for carbonic acid is constantly disengaged during the process of respiration, which, as we have seen (page 125), is nothing but a process of slow combustion. This gas is sometimes emitted in large quantity from the earth in volcanic districts, and it is con- stantly generated where organic matter is in the act of undergoing fermentive decomposition. The fatal " after-damp " of the coal-mines contains a large proportion of carbonic acid. Alighted taper plunged into carbonic acid is instantly extinguished, even to the red-hot snuff. Wheii diluted with three times its volume of air, it still retains the power of extinguishing a light. The gas is easily known from nitrogen, which is also incapable of supporting combustion, by its rapid absorption by caustic alkali, or by lime-water; the turbidity communicated to the latter from the production of insoluble carbonate of lime is very charac- teristic. Cold water dissolves about its own volume of carbonic acid, whatever be the density of the gas with which it is in contact: the solution temporarily reddens litmus paper. In common soda-water, and also in effervescent wines, examples may be seen of this solubility of the gas. Even boiling water absorbs a perceptible quantity. Some of the interesting phenomena attending the liquefaction of carbonic acid have been already described; it requires for the purpose a pressure of between 27 and 28 atmospheres at 32° (0°C), according to Mr. Addams. The liquefied acid is colorless and limpid, lighter than water and four times more expansible than air; it mixes in all proportions with ether, alcohol, naphtha, oil of turpentine, and bisulphide of carbon, and is insoluble in water and fat oils. It is probably destitute when in this condition of all properties of an acid.2 Carbonic acid exists, as already mentioned, in the air; relatively, its quan- tity is but small, but absolutely taking into account the vast extent of the atmosphere, it is very great, and fully adequate to the purpose for which it is designed, namely, to supply to plants their carbon; these latter having the power, by the aid of their green leaves, of decomposing carbonic acid, retain- ing the carbon, and expelling the oxygen. The presence of light is essential to this extraordinary effect, but of the manner in which it is produced we are yet ignorant. The carbonates form a very large and important group of salts, some of which occur in nature in great quantities, as the carbonates of lime and mag- nesia. Carbonic Oxide.—When carbonic acid-is passed over red-hot charcoal or metallic iron, one-half of its oxygen is removed, and it becomes converted into carbonic oxide. A very good method of preparing this gas is to intro- duce into a flask or retort filled with a bent tube some crystallized oxalic acid, or salt of sorrel, and pour upon it five or six times as much strong oil of 1 MM. Dulong and Berzelius. a [When relieved of pressure it immediately boils, and seven parts out of eisht assume the gaseous state, the rest becoming solid at —00° (67°7C) (Mitchell). Solid carbonic acid mixed with ether produces in vacuo a very intense cold (—165° [109°-4C] Faraday), capable of solidi- fying many gases \thcn aided by pressure. Liquid carbonic acid immersed in this mixture becomes a solid so clear aud transparent that its condition cannot be detected until a portion again becomes liquid.—It. B.] 148 SULPHUR. vitriol.1 On heating the mixture, the organic acid is resolved into water, car- bonic acid, and carbonic oxide: by passing the gases through a strong solu- tion of caustic potassa, the first is withdrawn by absorption, while the second Fig. 107. remains unchanged. Another, and it may be preferable method, is to heat finely-powdered yellow ferrocyanide of potassium with eight or ten times its weight of concentrated sulphuric acid. The salt is entirely decomposed, yielding a most copious supply of perfectly pure carbonic oxide gas, which may be collected over water in the usual manner.2 Carbonic oxide is a combustible gas; it burns with a beautiful pale blue flame, generating carbonic acid. It has never been liquefied. It is colorless, has very little odor, and is extremely poisonous, much more so than carbonic acid. Mixed with oxygen, it explodes by the electric spark, but with some difficulty. Its specific gravity is 0-973; 100 cubic inches weigh 30-21 grains. The relation by volume of these oxides of carbon may thus be made intelli- gible : carbonic acid contains its own volume of oxygen, that gas suffering no change of bulk by its conversion. One measure of carbonic oxide, mixed with half a measure of oxygen and exploded, yields one measure of carbonic acid; hence carbonic oxide contains half its volume of oxygen. Carbonic oxide unites with chlorine under the influence of light, forming a pungent, suffocating compound, possessing acid properties, called phosgene gas, or chloro-carbonic acid. It is made by mixing equal volumes of carbonic oxide and chlorine, both perfectly dry, and exposing the mixture to sunshine; the gases unite quietly, the color disappears, and the volume becomes reduced to one-half. A more convenient method for preparing this gas consists in passing carbonic oxide through pentachloride of antimony. It is decomposed by water. '■ This is an elementary body of great importance and interest. Sulphur is often found in a free state in connection with deposits of gypsum and rock- salt ; its occurrence in volcanic districts is probably accidental. Sicily fur- nished a large proportion of the sulphur employed in Europe. In a state of combination with iron and other metals, and as sulphuric acid, united to lime and magnesia, it is also abundant. HO,C203 Oxalic acid. '+ HO.SOa Concentrated sulphuric acid. + 2IIO,S03. Diluted sulphuric acid. 2 See a paper by the author in Memoirs of Chem. Soc. of London, i. 25,1. 1 eq. crystallized ferrocyanide of potassium and 6 eq. oil of vitriol yield 6 eq. carbonic oxide, 2 eq. sulphate of potassa, 3 eq. sulphate of ammonia, and 1 eq. protosulphate of iron. SULPHUR. 149 Pure sulphur is a pale yellow brittle solid, of well-known appearance. It melts when heated, and distils over unaltered, if air be exclnded. The cystals of sulphur exhibit two distinct and incompatible forms, namely, an octahedron with rhombic base, which is the figure of native sulphur, and that assumed Fig. 108. Fig. 109. Fig. 110. when sulphur separates from solution at common temperatures, as when a solution of sulphur in bisulphide of carbon is exposed to slow evaporation in the air: and a lengthened prism, having no relation to the preceding: this happens when a mass of sulphur is melted, and, after partial cooling, the crust of the surface broken and the fluid portion poured out. Fig. 109 shows the result of such an experiment. The specific gravity of sulphur varies according to the form in which it is crystallized. The octahedral variety has a specific gravity 2045; the pris- matic variety a specific gravity 1-982. Sulphur melts at 232° (111°-1C,) [238° (114°-5C,) Brodie]: at this tempe- rature it is of the color of amber, and thin and fluid as water; when farther heated, it begins to thicken, and to acquire a deeper color; and between 430° (221°C) and 480° (249°C) it is so tenacious that the vessel in which it is con- tained may be inverted for a moment without the loss of its contents. If in this state it be poured into water, it retains for many hours its remarkably soft and flexible condition, which should be looked upon as the amorphous state of sulphur. After awhile it again becomes brittle and crystalline. From the temperature last mentioned to the boiling-point, about 792° (400CC), sulphur again becomes thin and liquid. In the preparation of commercial flowers of sulphur the vapor is conducted into a large cold chamber, where it condenses in minute crystals. The specific gravity of sulphur-vapor is 6-654. Sulphur is insoluble in water and alcohol; oil of turpentine and the fat oils dissolve it, but the best substance for the purpose is bisulphide of carbon. In its chemical relations sulphur bears great resemblance to oxygen : to very many oxides there are corresponding sulphides, and the sulphides often unite among themselves, forming crystallizable compounds analogous to salts. A red and a black modification of sulphur have been discovered. When heated to 680° (360°C), and rapidly cooled, 40 per cent, of sulphur becomes insoluble in bisulphide of carbon ; by repeated heating to this temperature tho sulphur becomes more and more dark-red. It is heated with sulphide of car- bon to separate the soluble sulphur, and the insoluble yellow residue is re- peatedly heated to 212° (100°C), and treated with bisulphide of carbon, then heated to 572° (300°C) and suddjiii^cooled. Black sulphur remains insoluble in sulphide of carbon, alcohol, ether, benzol, oil of turpentine, and chloroform. If this black sulphur be heated from 266° to 302° (130° to 150°C), on cooling it becomes soluble in bisulphide of carbon; by slow evaporation yellow sul- phur crystallizes out, and a red fluid remains, which ultimately solidifies to red sulphur. 13* 150 SULPHUR. 16 16 16 24 32 16 32 40 48 40 64 40 80 40 Compounds of Sulphur and Oxygen. Composition by weight Sulphur. Oxygen. Sulphurous acid . . . . . Sulphuric acid1 ..... Hyposulphurous acid .... Hyposulphuric acid .... Sulphuretted hyposulphuric acid . Bisulphuretted hyposulphuric acid Trisulphuretted hyposulphuric acid2 Sulphurous Acid.—This is the only product of the combustion of sulphur in dry air or oxygen gas. It is most conveniently prepared by heating oil of vitriol with metallic mercury or copper clippings; a portion of the acid is decomposed, one-third of its oxygen being transferred to the metal, while the sulphuric acid becomes sulphurous.3 Sulphurous acid thus obtained is a colorless gas, having the peculiar suffocating odor of burning brimstone; it instantly extinguishes flame, and is quite irrespirable. Its density is 2-21; 100 cubic inches weighing 68-69 grains. At 0° (-17°-8C), under the pressure of the atmosphere, this gas condenses to a colorless, limpid liquid, very expan- sible by heat. Cold water dissolves more than thirty times its volume of sul- phurous acid. The solution may be kept unchanged so long as air is excluded, but access of oxygen gradually converts the sulphurous into sulphuric acid, in the presence of water, although the dry gases may remain in contact for any length of time without change. When sulphurous acid and aqueous vapor are passed into a vessel cooled to below 17° or 21° (-6° or - 8°C), a crystalline body forms, which contains about 24-2 acid to 75-8 water. One volume of sulphurous acid gas contains one volume of oxygen and £ of a volume of sulphur-vapor, condensed into one volume. Gases which, like the present, are freely soluble in water, must be col- lected by displacement, or by the use of the mercurial pneumatic trough. The manipulation with the latter is exactly the same in principle as with the ordinary water-trough, but rather more troublesome, from the great density of the mercury, and its opacity. The whole apparatus is on a much smaller scale. The trough is best constructed of hard, sound wood, and so contrived as to economise as much as possible the expensive fluid it is to contain. Sulphurous acid has bleaching properties ; it is used in the arts for bleaching woollen goods and straw-plait. A piece of blue litmus-paper plunged into the moist gas is first reddened and then slowly bleached. The salts of sulphurous acid are not of much importance: those of the alka- 1 The termininations ous and ic, applied to acids, signify degrees of oxidation, the latter being the highest: acids ending in ous form sails the names of which are made to end in ite, and those in ic terminate in ate—as sulphurous acid, sulphite of soda; sulphuric acid, sulphate of soda. 3 The more advanced student will be glad to see these stated in equivalents by the use of sym- bols, their relations becoming thereby much more evident. The numbers given are really the equivalent numbers, but are intended only to show the proportions of sulphur and oxygen without any reference to other bodies. The following are the quantities required to saturate one equivalent of a base:— Sulphurous acid...........gOj Sulphuric acid.......j^fe,......SOa Hyposulphurous acid . .4B5......g202 Hyposulphuric acid, Dithionic acid . ^fflP-.....S2O5 Sulphuretted hyposulphuric acid, Trithionic acid .... s3Os Bisulphuretted hyposulphnrio acid, lUrathionic acid . . . . s Os Trisulphuretted hyposulphuric acid, Pentathionic acid . . . S5O5 2(HO,S03) + Cu = S02 + CuO.SOs + 2HO Sulphuric acid. Copper. Sulphurous acid. Sulphate of copper. Water. SULPHUR. 151 lies are soluble and crystallizable; they are easily formed by direct combina- tion. Sulphites of baryta, strontia, and lime are insoluble in water, but soluble in hydrochloric acid. The strong acids decompose them; nitric acid converts them into sulphates. Sulphuric Acid.—Hydrated sulphuric acid has been known since the fifteenth century. There are two distinct processes by which it is at the present timo prepared, namely, by the distillation of green sulphate of iron, and by the oxi- dation of sulphurous acid by nitrous and hyponitric acids. The first process is still carried on in some parts of Germany, especially in the neighborhood of Nordhausen, in Prussia, and in Bohemia. The sulphate of iron, derived from the oxidation of iron pyrites, is deprived by heat of tho greater part of its water of crystallization, and subjected to a high red heat in earthen retorts, to which receivers are fitted as soon as the acid begins to distil over. A part gets decomposed by the very high temperature; the remainder is driven off" in vapor, which is condenssd by the cold vessel. The product is a brown oily liquid, of about 1-9 specific gravity, fuming in the air, and very corrosive. It is chiefly made for the purpose of dissolving indigo. The second method, which is, perhaps, with the single exception mentioned, always followed as the more economical, depends upon the fact that, when sulphurous acid, hyponitric acid, and water are present in certain proportions, the sulphurous acid becomes oxidized at the expense of the hyponitric acid, which by the loss of one-half of its oxygen sinks to the condition of binoxide of nitrogen. The operation is thus conducted: — A large and very long chamber is built of sheet-lead supported by timber framing; on the outside, at one extremity, a small furnace or oven is constructed, having a wide tube leading into the chamber. In this, sulphur is kept burning, the flame of which heats a crucible containing a mixture of nitre and oil of vitriol. A shallow stratum of water occupies the floor of the chamber, and sometimes a jet of steam is also introduced. Lastly, an exit is provided at the remote end of the chamber for the spent and useless gases. The effect of these arrange- ments is to cause a constant supply of sulphurous acid, atmospheric air, nitric acid vapor, and water in the state of steam, to be thrown into the chamber, there to mix and react upon each other. The nitric acid imme- diately gives up a part of its oxygen to the sulphurous acid, becoming hypo nitric ; it does not remain in this state, however, but suffers farther deoxida tion until it becomes reduced to binoxide of nitrogen. That substance iB contact with free oxygen absorbs a portion of the latter, and once more becomes hyponitric acid, which is again destined to undergo deoxidation by a fresh quantity of sulphurous acid. A very small portion of hyponitric acid, mixed with atmospheric air and sulphurous acid, may thus in time convert an indefinite amount of the latter into sulphuric acid, by acting as a kind of carrier between the oxygen of the air and the sulphurous acid. The presence of water is essential to this reaction. We may thus represent the change1: — f Nitrogen 14 _____^_ Binoxide of nitrogen 30. Hyponitric acid 46 -J Oxygen 16 (Oxygen 16, Sulphurous acid 64 {^^ f2 Water 18 Hydrated sulphuric acid 98. Such is the simplest view that can be taken of the production of sulphuric acid in the leaden chamber; but it is too much to affirm that it is strictly :+ 250a NOs 2(HO,SOs). Hyponitric Sulphurous Water. Binoxide of Hydrated acid. acid. nitrogen. sulphuric acid. 152 SULPHUR. true; it may be more complex. When a little water is put at the bottom of a large glass globe, so as to maintain a certain degree of humidity in the air within, and sulphurous and hyponitric acids are introduced by separate tubes, symptoms of chemical action become immediately evident, and after a little time a white crystalline matter is observed to condense on the sides of the vessel. This substance appears to be a compound of sulphuric acid, nitrous acid, and a little water.1 When thrown into water, it is resolved into sul- phuric acid, binoxide of nitrogen, and nitric acid. This curious body is certainly very often produced in large quantity in the leaden chambers; but that its production is indispensable to the success of the process, and constant when the operation goes on.well, and the hyponitric acid is not in excess, may perhaps admit of doubt. The water at the bottom of the chamber thus becomes loaded with sulphuric acid: when a certain degree of strength has been reached, it is drawn off and concentrated by evaporation, first in leaden pans, and afterwards in stills of platinum, until it attains a density (when cold) of 1-84, or thereabouts; it is then transferred to carboys, or large glass bottles fitted in baskets, for sale. In Great Britain this manufacture is one of great national importance, and is carried on to a vast extent. An inferior kind of acid is sometimes made by burning iron pyrites, or poor copper ore, or zinc-blende, as a substi- tute for Sicilian sulphur: this is chiefly used by the makers for their own consumption ; it very frequently contains arsenic, from which it may be freed, however, by heating the acid with a small quantity of chloride of sodium, or by passing through the heated acid a current of hydrochloric acid gas, when the arsenic is volatilized as terchloride. The most concentrated sulphuric acid, or oil of vitriol, as it is often called, is a definite combination of 40 parts real acid, and 9 parts water. It is a colorless, oily liquid, having a specific gravity of about 1-85, of intensely-acid taste and reaction. Organic matter is rapidly charred and destroyed by this substance. At the temperature of —15° (—26°-lC) it freezes; at 020° (326°-6C) it boils, and may be distilled without decomposition. Oil of vitriol has a most energetic attraction for water: it withdraws aqueous vapors from the air, and when diluted with water, great heat is evolved, so that the mixture always requires to be made with caution. Oil of vitriol is not the only hydrate of sulphuric acid ; three others are known to exist. When the fuming oil of vitriol of Nordhausen is exposed to a low temperature, a white crystal- line substance separates, which is a hydrate containing half as much water as the common liquid acid. Then, again, a mixture of 49 parts of strong liquid acid and 9 parts of water, congeals or crystallizes at a temperature above 32° (0°C), and remains solid even at 45° (7°-2C). Lastly, when a very dilute acid is concentrated by evaporation in vacuo over a surface of oil of vitriol, the evaporation stops when the real acid and water bear to each other the proportion of 40 to 27. When good Nordhausen oil of vitriol is exposed in a retort to a gentle heat, and a receiver cooled by a freezing mixture fitted to it, a volatile substance distils over in great abundance, which condenses into beautiful white, silky crystals, resembling those of asbestos: this bears the name of anhydrous 1 M. Gaultier de Claubry assigned to this curious substance the composition expressed by the formula 4IIO ,NOs + 5S03, and this view has generally been received by recent chemical writers. M. de la Provostaye has since shown that a compound, possessing all the essential properties of the body in- question, may be formed by bringing together, in a sealed glass tube, liquid sulphurous acid and liquid hyponitric acid, both free from water. The white crystalline solid soon begins to form, and at the expiration of twenty-six hours the reaction appears complete. The new product is accompanied by an exceedingly volatile greenish liquid having the characters of nitrous acid. The white substance, on analysis, was found to contain the elements of two equivalents of sulphuric acid and one of nitrous acid, or NO3 + 2SOS. M. de la Provostaye very ingeniously explains the anomalies in the different analyses of the leaden-chamber product, by showing that the pure substance forms crystallizable combinations with different proportions of liquid sulphuric acid. (Ann. Chim. et Phys. lxxiii. 362.) SULPHUR. 153 Bulphuric acid. When put into water it hisses like a hot iron, from the violence with which combination occurs; exposed to the air even for a few moments, it liquefies by absorption of moisture, forming common liquid sulphuric acid. It forms an exceedingly curious compound with dry ammo- niacal gas, quite distinct from ordinary sulphate of ammonia, and which indeed possesses none of the characters of a sulphate. This interesting sub- stance may also be obtained by distilling the most concentrated oil of vitriol with a sufficient quantity of anhydrous phosphoric acid, or by passing a mixture of dry sulphurous acid and oxygeu over heated spongy platinum. Sulphuric acid, in all soluble states of combination, may be detected with the greatest ease by solution of nitrate of baryta, or chloride of barium. A white precipitate is produced, which does not dissolve in nitric acid. Hyposulphurous Acid. — By digesting sulphur with a solution of sulphite of potassa or soda, a portion of that substance is dissolved, and the liquid, by slow evaporation, furnishes crystals of the new salt.1 The acid cannot bo isolated; when hydrochloric acid is added to a solution of a hyposulphate, the acid of the latter is almost instantly resolved into sulphur, which precipi- tates, and into sulphurous acid, easily recognized by its odor. The most remarkable feature of the alkaline hyposulphites is their property of dissolving certain insoluble salts of silver, as the chloride — a property which has lately conferred upon them a considerable share of importance in relation to the art of photogenic drawing. Hyposulphuric Acid; Dithionic Acid.—This is prepared by suspending finely-divided binoxide of manganese in water artificially cooled, and then transmitting a stream of sulphurous acid gas; the binoxide becomes protoxide, half its oxygen converting the sulphurous acid into hyposulphuric.2 The hyposulphate of manganese thus prepared is decomposed by a solution of pure hydrate of baryta, and the barytic salt, in turn, by enough sulphuric acid to precipitate the base. The solution of hyposulphuric acid may be concentrated by evaporation in vacuo, until it acquires a density of 1-347 ; pushed farther, it decomposes into sulphuric and sulphurous acids. It has no odor, is very sour, and forms soluble salts with baryta, lime, and protoxide of lead. Sulphuretted Hyposulphuric Acid; Trithionic Acid.—A substance accidentally formed by M. Langlois,* in the preparation of hyposulphite of potassa, by gently heating with sulphur a solution of carbonate of potassa, saturated with sulphurous acid. The salts bear a great resemblance to those of hyposul- phurous acid, but differ completely in composition, while the acid itself is not quite so prone to change. It is obtained by decomposing the potassa salt by hydrofluosilicic acid; it maybe concentrated under the receiver of the air- pump, but is gradually decomposed into sulphur, sulphurous and sulphuric acids. Bisulphuretted Hyposulphuric Acid; Tetrathionic Acid.—This was discovered by MM. Fordos and Gelis.4 When iodine is added to a solution of hyposulphite of soda, a large quantity of that substance is dissolved, and a clear colorless solution obtained, which, besides iodide of sodium, contains a salt of a peculiar acid, richer in sulphur than the preceding. By suitable means, the new substance can be eliminated, and obtained in a state of solution. It very closely resembles hyposulphuric acid. The same acid is produced by tho action of sulphurous acid on subchloride of sulphur. Trisulphuretted Hyposulphuric Acid; Pentathionic Acid.—Another acid of Bulphur has been announced by M. Wackenroder, who formed it by the action » KO,SOa + S = KO,SaOa Sulphite ofpotassa. Sulphur. Hyposulphite of potassa. » MnOa + 2SOa = MnO, S2O5 Binoxide of manganese. SulpAurous acid. Hyposulphate of manganese. « Ann. Chiin. et Phys., 3d series, iv. 77. * Ibid, 3d scries, vi. 454. 154 SELENIUM of sulphuretted hydrogen on sulphurous acid. It is described as colorlesa and inodorous, of acid and bitter taste, and capable of being concentrated to a considerable extent by cautious evaporation. Under the influence of heat, it is decomposed into sulphur, sulphurous and sulphuric acid, and sulphuretted hydrogen. The salts of pentathionic acid are nearly all soluble. The baryta salt crystallizes from alcohol in square prisms. The acid is also formed when hyposulphate of lead is decomposed by sulphuretted hydrogen, and when protochloride of sulphur is heated with sulphurous acid. Sulphurous acid unites, under peculiar circumstances, with chlorine, and also with iodine, forming compounds, which have been called chloro- and iodo- sulphuric acids. They are decomposed by water. It also combines with dry ammoniacal gas, giving rise to a remarkable compound ; and with nitric oxide also, in presence of an alkali. SELENIUM. This is a very rare substance, much resembling sulphur in its chemical relations, and found in association with that element in some few localities, or replacing it in certain metallic combinations, as in the selenide of lead of Clausthal, in the Hartz. Selenium is a reddish-brown solid body, somewhat translucent, and having an imperfect metallic lustre. Its specific gravity, when rapid]y cooled after fusion, is 4-3. At 212° (100°C), or a little above, it melts, and at 650° (343°-3C) boils. It is insoluble in water, and exhales, when heated in the air, a peculiar and disagreeable odor, which has been compared to that of de- caying horseradish : it is insoluble in alcohol, but slightly dissolves in bisul- phide of carbon, from which solution it crystallizes. There are three oxides of selenium, two of which correspond respectively to sulphurous and sulphu- ric acids, while the third has no known analogue in the sulphur-series. Composition by weight.1 Selenium. Oxygen. Oxide of Selenium.......39-5 8 Selenous acid ........ 39-5 16 Selenic acid........39-5 24 Oxide. — Formed by heating selenium in the air. It is a colorless gas slightly soluble in water, and has the remarkable odor above described. It has no acid properties. Selenous Acid. — This is obtained by dissolving selenium in nitric acid, and evaporating to dryness. It is a white, soluble, deliquescent substance, of dis- tinctly acid properties, and may be sublimed without decomposition. Sul- phurous acid decomposes it, precipitating the selenium. Selenic Acid.—Prepared by fusing nitrate of potassa or soda with selenium, precipitating the selenate so produced by a salt of lead, and then decompos- ing the compound by sulphuretted hydrogen. The hydrated acid strongly resembles oil of vitriol; but, when very much concentrated, decomposes, by the application of heat, into selenous acid and oxygen. The selenates bear the closest analogy to the sulphates in almost every particular. 1 In symbols — Oxide of Selenium..........SeO (?) Selenous acid...........SeO„ Selenic acid...........SeOa PHOSPHORUS. 155 PHOSPHORUS. Phosphorus in the state of phosphoric acid is contained in the ancient un- stratified rocks, and in the lavas of modern origin. As these disintegrate and crumble down into fertile soil, the phosphates pass into the organism of plants, and ultimately into the bodies of the animals to which these latter serve for food. The earthy phosphates play a very important part in the structure of the animal frame, by communicating stiffness and inflexibility to the bony skelton. This element was discovered in 1669 by Brandt, of Hamburg, who prepared it from urine. The following is an outline of the process now adopted. Thoroughly-calcined bones are reduced to powder, and mixed with two-thirds of their weight of sulphuric acid, diluted with a considerable quantity of water: this mixture, after standing some hours, is filtered, and the nearly insoluble sulphate of lime washed. The liquid is then evaporated to a syrupy consistence, mixed with charcoal powder, and the desiccation completed in an iron vessel exposed to a *iiigh temperature. When quite dry it is transferred to a stoneware retort, to which a wide bent tube is luted, dipping a little way into the water contained in the receiver. A narrow tube serves to give issue to the gases, which are conveyed to a chimney. This manufacture is now conducted on a very large scale, the consumption of phosphorus, for the ap- parently-trifling article of instantaneous-light matches, being something prodigious. Phosphorus, when pure, very much resembles in appearance imperfectly-bleached wax, and is soft and flexible at common temperatures. Its density is 1-77, and that of, its vapor 4-35, air being unity. At 108° (42°-2 C) it melts, and at 550° (287°-7 C) boils. On slowly cooling melted phosphorus, some- times well-formed dodecahedra are obtained. It is insoluble in water, and is usually kept immersed in that liquid, but dissolves in oils, in native naphtha, and especially in bisulphide of carbon. When set on fire in the air, it burns with a bright flame, generating phosphoric acid. Phosphorus is exceedingly inflammable; it sometimes takes fire by the heat of the hand, and demands great care in its management; a blow or hard rub will very often kindle it. A stick of phosphorus held in the air always appears to emit a whitish smoke, which in the darlois luminous. This effect is chiefly due to a slow combustion which the phosphorus undergoes by the oxygen of the air, and upon it depends one of the methods employed for the analysis of the atmosphere, as already described. It is singular that the slow oxidation of phosphorus may be entirely prevented by the presence of a small quantity of olefiant gas, or the vapor of ether, or some essential oil; it may even be distilled in an atmosphere containing vapor of oil of turpentine in considerable quantity. Neither does the action go on in pure oxygen, at least at the temperature of 60° (15°-5C), which is very remarkable; but if the gas be rarefied, or diluted with nitrogen, hydrogen, or carbonic acid, oxidation is set up. A very remarkable modification of this element is known by the name of amorphous phosphorus. It was discovered by Schrotter, and may be made by exposing for fifty hours common phosphorus to a temperature of about 550° (240° to 250° C) in an atmosphere which is unable to act chemically upon it. At this temperature it becomes red and opaque, and insoluble in bisulphide of carbon, whereby it may be separated from ordinary phosphorus. 156 PHOSPHORUS. It may be obtained in compact masses when common phosphorus is kept for eight days at a constant high temperature. It is a coherent, reddish-brown, infusible substance, of specific gravity between 2-089 and 2-106. It does not become luminous in the dark until its temperature is raised to about 393° (200° C), nor has it any tendency to combine with the oxygen of the air. When heated to 500° (260° C), it is reconverted into ordinary phosphorus. Compounds of Phosphorus and Oxygen.—These are three in number, and have the composition indicated below:— Composition by weight. Phosphorus. Oxygen. Hypophosphorous acid ...... 31 8 Phosphorous acid ....... 31 24 Phosphoric Acid1 . . . . . . .31 40 Oxide of Phosphorus.—W7hen phosphorus is melted beneath the surface of hot water, and a stream of oxygen gas forced upon it from a bladder, com- bustion ensues, and the phosphorus is converted in great part into a brick-red powder, which was formerlyjaelieved to be a, peculiar oxide of phosphorus^ Schrotter has shown that it is a mixture, consisting chiefly of amorphous phosphorus. Ilypophosphorus Acid.—When phosphorus is boiled with a solution of potassa or baryta, water is decomposed, giving rise to phosphoretted hydrogen, phos- phoric acid, and hypophosphorous acid, which combine with the baryta; the first escapes as gas, and the two acids remain in union with the baryta.2 By filtration the soluble hypophosphite is separated from the insoluble phosphate. On adding to the liquid the quantity of sulphuric acid necessary to precipitate the base, the hypophosphorous acid is obtained in solution. By evaporation it may be reduced to a syrupy consistence. The acid is very prone to absorb more oxygen, and is therefore a powerful deoxidizing agent. All its salts are soluble in water. Phosphorous Acid. — Phosphorous acid is formed by the slow combustion of phosphorus in the atmosphere; or by burning that substance by means of a very limited supply of air, in which case it is anhydrous, and presents the aspect of a white powder. The hydrated acid is more conveniently pre- pared by adding water to the terchloride of phosphorus, when mutual de- composition takes place, the oxygen of the water being transferred to the phosphorus, generating phosphorous acid, and its hydrogen to the chlorine, giving rise to hydrochloric acid.3 By evaporating the solution to the consist- ence of syrup, the hydrochloric acid is expelled, and the residue on cooling crystallizes. Hydrated phosphorous acid is very deliquescent and very prone to attract oxygen and pass into phosphoric acid. When heated in a close vessel, it is resolved into hydrated phosphoric acid and pure phosphoretted hydrogen gas. It is composed of 55 parts of real acid and 27 parts of water.4 The phosphites are of little importance. * In symbols — Hypophosphorous acid..........pg Phosphorous acid..........." P O Phosphoric acid..........! P O5 » 4P + 3BaO + ^110^ - 3BaOPO + pu3 Phosphorus. Baryta. Water. Hypophosphite 'Phosphoretted" of baryta. hydrogen. PCI* + 6HO = 3HO,POs + 3iici Terchloride Water. Hydrated " Hydrochloric* of phosphorus. phosphorous acid. acid. •Or, 3110,POs. CHLORINE. 157 Phosphoric Acid. — When phosphorus is burned under a bell-jar by the aid of a copious supply of dry air, snow-like anhydrous phosphoric acid is pro duced in great quantity. This substance exhibits as much attraction for water as anhydrous sulphuric acid: exposed to the air for a few moments it deliquesces to a liquid, and when thrown into water, combines with the latter with explosive violence. Once in the state of hydrate the water cannot again be separated. When nitric acid of moderate strength is heated in a retort to which a re- ceiver is connected, and fragments of phosphorus added singly, taking care to suffer the violence of the action to subside between each addition, the phosphorus is oxidized to its maximum, and converted into phosphoric acid. By distilling off the greater part of the acid, transferring the residue in the retort to a platinum vessel, and then cautiously raising the heat to redness, the hydrated acid may be obtained pure. This is the glacial phosphoric acid of the Pharmacopoeia. A third method consists in taking the acid phosphate of lime produced by the action of sulphuric acid on bone-earth, precipitating it with a slight ex- cess of carbonate of ammonia, separating by a filter the insoluble lime-salt, and then evaporating and igniting in a platinum vessel the mixed phosphate and sulphate of ammonia. Hydrated phosphoric acid alone remains behind. The acid thus obtained is not remarkable for its purity. One of the most ad- vantageous methods of preparing phosphoric acid on the large scale in a state of purity is to burn phosphorus in a stream of dry atmospheric air, by the aid of a proper apparatus, not difficult to contrive, in which the process may be carried on continuously. The anhydrous acid obtained may be preserved in that state, or converted into hydrate or glacial acid, by the addition of water and subsequent fusion in a platinum vessel. The hydrate of phosphoric acid is exceedingly deliquescent, and requires to be kept in a closely-stopped bottle. It contains 71 parts of real acid, and 9 parts of water.1 Phosphoric acid is a powerful acid; its solution has an intensely sour taste, and reddens litmus-paper; it is not poisonous. There are few bodies that present a greater degree of interest to the chemist than this substance: the ex- traordinary changes its compounds undergo by the action of heat, chiefly made known to us by the ad- mirable researches of Prof. Graham, will be found de- scribed in connection with the general history of saline compounds. CHLORINE. This substance is a member of a small natural group, containing besides iodine, bromine, and fluorine. So great a degree of resemblance exists between these bodies in all their chemical relations, especially between chlorine, bromine, and iodine, that the history of one will almost serve, with a few little alterations, for that of the rest. Chlorine2 is a very abundant substance; in common salt it exists in combination with sodium. It is most easily prepared by pouring strong liquid hydrochloric acid upon finely-powdered black oxide of manganese, contained in a retort or flask, and applying a gentle heat; a heavy yellow gas is disengaged, which is the Bubstance in question. It may be collected over warm water, or by displace- 1 HO,P05. a From ^Xupdj, yellowish-green, the name given to it by Sir H. Davy. Fig. 112. 158 CHLORINE. ment; the mercurial trough cannot be employed, as the chlorine rapidly acta upon the metal, and becomes absorbed. The reaction is very easily explained. Hydrochloric ncitl is a compound of chlorine and hydrogen: when this is mixed with a metallic protoxide, double interchange of elements takes place, water and chloride of the metal being produced. But when some of the binoxides are substituted, an additional effect ensues, namely, the decomposition of a second portion of hydrochloric acid by the oxygen in excess, the hydrogen of which is withdrawn and the chlorine set free. Hydrochloric J Chlorine-------------Chlorine. acid. \ Hydrogen-------__^ Water. Binoxide 0ff0xygen--- -< Manganese---.-----—=--Chloride of manganese. manganese j0xy|en SZ^^ Hydrochloric f Chlorine ^>-<:^--^^^ acid \ Hydrogen •------^"~~~-- Water.1 Chlorine was discovered by Scheele in 1774, but its nature was long mis- understood. It is a yellow gaseous body, of intolerably suffocating proper- ties, producing very violent cough and irritation when inhaled even in ex- ceedingly small quantity. It is soluble to a considerable extent in water, that liquid absorbing at 60° (15°-5C) about twice its volume, and acquiring the color and odor of the gas. When this solution is exposed to light, it is slowly changed by decomposition of water into hydrochloric acid, the oxygen being at the same time liberated. When moist chlorine gas is exposed to a cold of 32° (0°C), yellow crystals are form'ed which consist of a definite compound of chlorine and water containing 35-5 parts of the former to 90 of the latter. Chlorine has a specific gravity of 2-47, 100 cubic inches weighing 76-6 grains. Exposed to a pressure of about four atmospheres, it condenses to a yellow limpid liquid. This substance has but little attraction for oxygen, its chemical energies being principally exerted towards hydrogen and the metals. When a lighted taper is plunged into the gas, it continues to burn with a dull red light, and emits a large quantity of smoke, the hydrogen of the wax being alone con- sumed, and the carbon separated. If a piece of paper be wetted with oil of turpentine, and thrust into a bottle filled with chlorine, the chemical action of the latter upon the hydrogen is so violent as to cause inflammation, ac- companied by a copious deposit of soot. Although chlorine can, by indirect means, be made to combine with carbon, yet this never occurs under the cir- cumstances described. Phosphorus takes fire spontaneously in chlorine; it burns with a pale and feebly luminous flame. Several of the metals, as copper-leaf, powdered anti- mony, and arsenic, undergo combustion in the same manner. A mixture of equal measures of chlorine and hydrogen explodes with violence on the passage of an electric spark, or on the application of a lighted taper, hydrochloric acid gas being formed. Such a mixture may be retained in the dark for nny length of time without change; exposed to diffuse daylight the two gases slowly unite, while the direct rays of the sun induce instantaneous explosion. The most characteristic property of chlorine is its bleaching power • the MnOa + 2IIC1 = CI + MnCl + 2H0 Binoxide of Hydrochloric Chlorine. Protochloride Water manganese. acid. of manganese. CHLORINE. 159 most stable organic coloring principles are instantly decomposed and de- stroyed by this remarkable agent; indigo, for example, which resists the action of strong oil of vitriol, is converted by chlorine into a brownish substance, to which the blue color cannot be restored. The presence of water is essential to these changes, for the gas in a state of perfect dryness is incapable of even affecting litmus. Chlorine is largely used in the arts for bleaching linen and cotton goods, rags for the manufacture of paper, &c. For these purposes, it is sometimes employed in the state of gas, sometimes in that of solution in water, but more frequently in combination with lime, forming the substance called bleaching- powder. When required in large quantities, it is often made by pouring slightly diluted oil of vitriol upon a mixture of common salt and oxide of manganese contained in a large leaden vessel. The decomposition which ensues may be thus represented:— Chloride of } Chlorine-------------------------Chlorine. sodium ) Sodium---------------- Sulphuric acid------------ ~~~^^^z=*- Sulphate of soda. Binoxide of J^feTtfl^" manganese. { manganese. ~~~ZZZ==—$ Sulphate of manga- Sulphuric acid--------------------- } nese.1 Chlorine is one of the best and most potent substances that can be used for the purpose of disinfection, but its employment requires care. Bleaching- powder mixed with water, and exposed to the air in shallow vessels, becomes slowly decomposed by the carbonic acid of the atmosphere, and the chlorine evolved; if a more rapid disengagement be wished, a little acid of any kind may be added. In the absence of bleaching-powder, either of the methods for the production of the gas described may be had recourse to, always taking care to avoid an excess of acid. Chloride of Hydrogen; Hydrochloric, Chlorhydric or Muriatic Acid. — This substance in a state of solution in water, has been long known. The gas is prepared with the utmost ease by heating in a flask, fitted with a cork and bent tube, a mixture of common salt and oil of vitriol, diluted with a small quantity of water; it must be collected by displacement, or over mercury. It is a colorless gas, which fumes strongly in the air from condensing the at- mospheric moisture; it has an acid, suffocating odor, but is infinitely less offensive than chlorine. Exposed to a pressure of 40 atmospheres it liquefies. Hydrochloric acid gas has a density of 1-269. It is exceedingly soluble in water, that liquid taking up at the temperature of the air about 418 times its bulk. The gas and solution are powerfully acid. The action of oil of vitriol on common salt, or any analogous substance, is thus easily explained: —2 Chloride of sodium Water .... Sulphuric acid - 1 NaCl + MnOs \ Chlorine ) Sodium S Hydrogen ) Oxygen Hydrochloric acid. Chloride Binoxide of of sodium. manganese. » NaCl + + 2(HO,S03) = CI Sulphuric acid. Sulphate of soda. + NaO,S03 + MnO,SOs + 2110 Sulphate of soda. II0,S0s Sulphate of Wa manganese. + NaO,S03 Chloride of Sulphuric Hydrochloric Sulphate sodium. acid. acid. cf soda. $ 160 CHLORINE. The composition of this substance may be determined by synthesis: when a measure of chlorine and a measure of hydrogen are fired by the electric spark, two measures of hydrochloric acid gas result, the combination being unattended by change of volume. By weight it contains 35-5 parts of chlo- rine and 1 part of hydrogen. Solution of hydrochloric acid, the liquid acid of commerce, is a very im- portant preparation, and of extensive use in chemical pursuits; it is best prepared by the following arrangement: — A large glass flask, containing a quantity of common salt, is fitted with a cork and bent tube, in the manner represented in fig. 113; the latter passes Fig. 113. through and below a second short tube into a wide-necked bottle, containing a little water, into which the open fube dips. A bent tube is adapted to another hole in the cork of the wash-bottle so as to convey the purified gas into a quantity of distilled water, by which it is instantly absorbed: the joints are made air-tight by melting over the corks a little yellow wax. A quantity of oil of vitriol, about equal in weight to the salt, is then slowly introduced by the funnel; the disengaged gas is at first wholly absorbed by the water in the wash-bottle, but when this becomes saturated, it passes into the second vessel and there dissolves. When all the acid has.been added heat may be applied to the flask by a charcoal chauffer, until its contents appear nearly dry, and the evolution of gas almost ceases, when the process may be stopped. As much heat is given out during the condensation of the gas, it is necessary to surround the condensing-vessel with cold water. The simple wash-bottle figured in the drawing will be found an exceedingly- useful contrivance in a great number of chemical operations. It serves in the present, and in many similar cases, to retain any liquid or solid matter CHLORINE. 161 mechanically carried over with the gas, and it may be always employed when a gas of any kind is to be passed through an alkaline or other solution. The open tube dipping into the liquid prevents the possibility of absorption, by which a partial vacuum would be occasioned, and the liquid of the Becond vessel lost by being driven into the first. Fig. 114. The arrangement by which the acid is introduced also deserves a ^ moment's notice. The tube is bent twice upon itself, and a bulb blown in one portion, the liquid poured into the funnel rises upon the opposite side of the first bend until it reaches the second; it then flows over and runs into the flask. Any quantity can then be got into the latter without the introduction of air, and without the escape of gas from the interior. The funnel acts also as a kind of safety- valve, and in both directions; for if by any chance the delivery tube should be stopped, and the issue of gas prevented, its increased elastic force soon drives the little column of liquid out of the tube, the gas escapes, and the vessel is saved. On the other hand, any absorption within is quickly compensated by the entrance of air through the liquid in the bulb. The plan employed on the large scale by the manufacturer is the same in principle as that described; he merely substitutes a large iron cylinder, or apparatus made of lead, for the flask, and vessels of stoneware for those of glass. Pure solution of hydrochloric acid is transparent and colorless: when strong, it fumes in the air by disengaging a little gas. It leaves no residue on evaporation, and gives no precipitate or opacity with diluted solution of chloride of barium. When saturateil with the gas, it has a specific gravity of 1-21, and contains about 42 per cent, of real acid. The commercial acid lias usually a yellow color, and is very impure, containing salts, sulphuric acid, chloride of iron, and organic matter. It may be rendered sufficiently pure for most purposes by diluting it to the density of 1-1, which happens when the strong acid is mixed with its own bulk or rather less of water, and then distilling it in a retort furnished with a Liebig's condenser. A mixture of nitric and hydrochloric acids has long been known under the name of aqua regia, from its property of dissolving gold. When these two substances are heated together, they both undergo decomposition, hyponitric acid and chlorine being evolved. This at least appears to be the final result of the action; at a certain stage, however, two peculiar substances, consisting of nitrogen, oxygen, and chlorine (chlorohyponitric acid1 and chloronitrous acid-), appear to be formed. It is chiefly the chlorine which attacks the metal. The presence of hydrochloric acid, or any other soluble chloride, is easily detected by solution of nitrate of silver. A white curdy precipitate is pro- duced, insoluble in nitric acid; freely soluble in ammonia, and subject to blacken by exposure to light. 1 NOsCla. a VTr>,ni 14* 162 CHLORINE. Compounds of Chlorine and Oxygen Although these bodies never combine directly, they may be made to unite by circuitous means in five different proportions, as below: — Composition by weight. Hypochlorous acid Chlorous acid Hypochloric acid . Chloric acid Perchloric acid1 . Chlorine. Oxygen. . 35-5 8 . 35-5 24 . 35-5 32 . 35-5 40 . 35-5 56 Hypochlorous and chloric acids are generated by the action of chlorine on certain metallic oxides; the former in the cold, the latter at a high tempera- ture. Chlorous, hypochloric, and perchloric acids result from the decompo- sition of chloric acid. Hypochlorous Acid. — This is best prepared by the action of chlorine gas upon red oxide of mercury. It is a pale-yellow gaseous body, containing, in every two measures, two measures of chlorine and one of oxygen. It is very freely soluble in water, and explodes, although with no great violence, by slight elevation of temperature. The odor of this gas is peculiar, and but remotely resembles that of chlorine. It bleaches powerfully, and acts upon certain of the metals in a manner which is determined by their respective attractions for oxygen and chlorine. It forms with the alkalies a series of bleaching salts. The preparations called chloride of, or chlorinated, lime and soda, contain hypochlorous acid. A description of these will be found under the head of Salts of Lime. The reaction by which hypochlorous acid is produced may thus be illustrated: — Chlorine----------------- __^_~" Hypochloric acid. Oxide of K Mercury mercury ( Oxygen Chlorine ----------------------~ °"~ Chloride of mercury.2 The chloride of mercury, however, does not remain as such; it combines with another portion of the oxide, when the latter is in excess, forming a peculiar brown compound, an oxychloride of mercury.3 Chlorous Acid. — This substance is prepared by heating in a flask filled to the neck a mixture of 4 parts of chlorate of potassa and 3 parts of arsenious acid with 12 parts of nitric acid previously diluted by 4 parts of water. 1 Hypochlorous acid...........CIO Chlorous acid............C103 Hypochloric acid...........CIO4 Chloric acid............C106 Perchloric acid............ CIO7 » 2IIgO + 2C1 = HgCl,HgO + CIO Protoxide of Chlorine. Oxychloride of Hypochlorous mercury. mercury. acid. * A very convenient method of preparing hypochlorous acid has been described by M. Pelouze. Red oxide of mercury, prepared by precipitation, and dried by exposure to a strong heat, is introduced into a glass tube, kept cool, well washed, and dry chlorine gas is slowly passed over it. Chloride of mercury and hypochlorous acid are formed; the latter is collected by displacement. When the flask or bottle in which the gas is received is exposed to artificial cold by the aid of a mixture of ice and salt, the hypochlorous acid condenses to a deep-red liquid, slowly soluble in water, and very subject to explosion. It is remarkable that the crystalline oxide of mercury prepared by calcining the nitrate, or by the direct oxidation of tho metal, is scarcely acted upon by chlorine under the circumstances described. — Ann. Chim. et Phys. 3d series, vii. 179. CHLORINE. 163 During the operation, which must be performed in a water-bath, a greenish- yellow gas i3 evolved, which is sparingly soluble in water, and cannot bo condensed by exposure to a freezing mixture. It slowly combines with bases, producing a class of salts called chlorites. The process which gives rise to chlorous acid is rather complicated. The arsenious acid deprives the nitric acid of part of its oxygen, reducing it into nitrous acid, which is oxidized again at the expense of the chloric acid. This, by the loss of two-fifths of its oxygen, becomes chlorous acid. Hypochloric Acid; Peroxide of Chlorine.—Chlorate of potassa is made into a paste with concentrated sulphuric acid, and cooled: this is introduced into a small glass retort, and very cautiously heated by warm water; a deep- yellow gas is evolved, which is the body in question: it can be collected only by displacement, since mercury decomposes and water absorbs the gas. Hypochloric acid has a powerful odor, quite different from that of the preceding compounds, and of chlorine itself. It is exceedingly explosive, being resolved with violence into its elements by a temperature short of the boiling-point of water. Its preparation is, therefore, always attended by danger, and should be performed only on a small scale. It is composed by measure of one volume of chlorine and two volumes of oxygen, condensed into two volumes.1 It may be liquefied by cold. The solution of the gas in water bleaches. Salts of this acid have not yet been obtained. The euchlorine of Davy, prepared by gently heating chlorate of potassa with dilute hydrochloric acid, is probably a mixture of chlorous acid and free chlorine. ! The production of hypochloric acid from chlorate of potassa and sulphuric acid depends upon the spontaneous splitting of the chloric acid into hypochloric acid and perchloric acid, which latter remains in union with the potassa.2 When a mixture of chlorate of potassa and sugar is touched with a drop of oil of vitriol, it is instantly set on fire; the hypochloric acid disengaged being decom- posed by the combustible substance with such violence as to cause inflammation. If crystals of chlorate of potassa be thrown into a glass of water, a few small fragments of phosphorus added, and then oil of vitriol poured down a narrow funnel reaching to the bottom of the glass, the phosphorus will burn beneath the surface of the water by the assistance of the oxygen of the hypochloric acid disengaged. The liquid at the same time becomes yellow, and acquires the odor of that gas. Chloric Acid.—This is the most important compound of the series. When chlorine is passed to saturation into a moderately strong hot solution of caustic potassa, or the carbonate of that base, and the liquid concentrated by evaporation, it furnishes, on cooling, flat tabular crystals of a colorless salt, consisting of potassa, combined with chloric acid. The mother-liquor contains chloride of potassium. In this reaction a part of the potassa is decomposed; its oxygen Fig. 115. In equivalents, as already stated, CIO4. '- eq. chlorine ■ I S eq. oxygon I 7 eq. oxygen [1 eq. chlorine ■ 3(KO,C105) + 3(IIO,S03) = 2C10. + 13 equiv. chloric acid 2 eq. hypochloric acid. "1 eq. perchloric acid. CIO7 + 3(KO,SOs) 3HO Chlorate of Sulphuric Hypochloric Perchloric Sulphate of Water. potassa. acid. acid. acid. potassa. 164 BROMINE. combines with one portion of chlorine to form chloric acid, while the potassium is taken up by a second portion of the same substance.1 From chlorate of potassa chloric acid may be obtained by boiling the salt with a solution of hydrofluosilicic acid, which forms an almost insoluble salt with potassa, decanting the clear liquid, and digesting it with a little silica, which removes the excess of the hydrofluosilicic acid. Filtration through paper must be avoided. By cautious evaporation, the acid may be so far concentrated as to assume a syrupy consistence ; it is then very easily decomposed. It sometimes sets fire to paper, or other dry organic matter, in consequence of the facility with which it is deoxidized by combustible bodies. The chlorates are easily recognized; they give no precipitate when in solu- tion with nitrate of baryta or silver; they evolve pure oxygen when heated, pa iing thereby into chlorides; and they afford, when treated with sulphuric acid, the characteristic explosive yellow gas already described. The dilute solution of the acid has no bleaching power. Perchloric Acid.'2—Professor Penny has shown that when powdered chlorate of potassa is thrown by small portions at a time into hot nitric acid, a change of the same description as that which happens when sulphuric acid is used takes place, but with this important difference, that the chlorine and oxygen, instead of being evolved in a dangerous state of combination, are emitted in a state of mixture. The result of the reaction is a mixture of nitrate of potassa and perchlorate of potassa, which may be readily separated by their difference of solubility. By treating the potassa-salt in the manner directed for chloric acid, the free acid may be obtained tolerably pure. It may be concentrated by evapo- ration, and even distilled without change. The solution fumes slightly in the air, and has a specific gravity of 1-65. It is very deliquescent or hygroscopic, and has no bleaching properties. The perchlorates much resemble the chlo- rates ; they give off oxygen when heated to redness. This acid is the most stable of the compounds of chlorine and oxygen. Bromine3 dates back to 1826 only, having been discovered by M. Balard of Montpelier. It is found in «=ea-water, and is a frequent constituent of saline springs, chiefly as bromide of magnesium;—a celebrated spring of tho kind exists near Kreuznach, in Prussia. Bromine may be obtained pure by the following process, which depends upon the fact, that ether agitated with an aqueous solution of bromine, removes the greater part of that substance. The mother-liquor, from which the less soluble salts have separated by crys- tallization, is exposed to a stream of chlorine, and then shaken up with a quantity of ether; the chlorine decomposes the bromide of magnesium and the ether dissolves the bromine thus set free. On standing, the etherial solu- tion, having a fine red color, separates, and may be removed by a funnel or ' 6 eq. chlorine \\ £|; ^j°™e------^- 5 eq. chloride of potassium j~5 eq. potassium ■ 6 eq. potassa < 5 eq. oxygen—____ (.1 eq. potassa— --^ 1. eq. chlorate potassa. 6KO + 6C1 = KO,C105 + 5KCi Potassa. Chlorine. Chlorate of Chloride of P°mssa. potassium. * \Hyperchloric or oxichloric acid.—The liquid acid of 1C5 density when distilled with 4 to 5 parts of strong sulphuric acid is partly decomposed into chlorine and oxyo-en while the remainder condenses in crystals of two kinds. These are hydrates of the acid • "the' imi,wm„. acid has not been obtained.—U. B.] annyarous 3 From ftpS/pos, a noisome smell; a very appropriate term. IODINE. 165 pipette. Caustic potassa is then added in excess, and heat applied : bromide of potassium and bromate of potassa are formed. The solution is evaporated to dryness, and the saline matter, after ignition to redness to decompose the bromate of potassa, heated in a small retort with binoxide of manganese and sulphuric acid diluted with a little water, the neck of the retort being plunged into cold water. The bromine volatilizes in the form of a deep-red vapor, which condenses into drops beneath the liquid. Bromine is at common temperatures a thin red liquid of an exceedingly in- tense color, and very volatile; it freezes at about 19° (-7°-2C), and boils at 145°-4 (63°C). The density of the liquid is 2-976, and that of the vapor 5-39. The odor of bromine is very suffocating and offensive, much resembling that of iodine, but more disagreeable. It is slightly soluble in water, more freely in alcohol, and most abundantly in ether. The aqueous solution bleaches. Hydrobromic Acid.1—This substance bears the closest resemblance in every particular to hydriodic acid; it has the same constitution by volume, vw-y nearly the same properties, and may be prepared by means exactly similar, substituting the one body for the other. The solution of hydrobromic acid has also the power of dissolving a large quantity of bromine, thereby acquiring a red tint. Hydrobromic acid contains by weight 80 parts bromine, and 1 part hydrogen. Bromic Acid."1—Caustic alkalis in presence of bromine undergo the same change as with chlorine, bromide of the metal and bromate of the oxide being produced ; these may often be separated by the inferior solubility of the latter. Bromic acid, obtained from bromate of baryta, closely resembles chloric acid; it is easily decomposed. The bromates when heated lose oxygen and become bromides. No other compound of bromine and oxygen has yet been described. This remarkable substance was first noticed in 1812, by M. Courtois, of Paris. Minute traces are found in combination with sodium or potassium in sea-water, and occasionally a much larger proportion in that of certain mine- ral springs. It seems to be in some way beneficial to many marine plants, as these latter have the power of abstracting it from the surrounding water, and accumulating it in their tissues. It is from this source that all the iodine of commerce is derived. It has lately been found in minute quantity in some aluminous slates of Sweden, and in several varieties of coal and turf. Kelp, or the half-vitrified ashes of sea-weeds, prepared by the inhabitants of the Western Islands and the northern shores of Scotland and Ireland, is treated with water, and the solution filtered. The liquid is then concentrated by evaporation until it is reduced to a very small volume, the chloride of sodium, carbonate of soda, chloride of potassium, and other salts being removed as they successively crystallize. The dark-brown mother-liquor left contains very nearly the whole of the iodine, as iodide of sodium, magnesium, &c.; this is mixed with sulphuric acid and binoxide of manganese, and gently heated in a leaden retort, when the iodine distils over and condenses in the receiver. The theory of the operation is exactly analogous to that of the preparation of chlorine; it requires in practice, however, careful management, otherwise the impurities present in the solution interfere with the general result.3 The manganese is not really essential; iodide of potassium or sodium, heated with an excess of sulphuric acid, evolves iodine. This effect is due to a a BrOs. + MnOa + 2(H0,S0s) - I + KO,SOs + MnO,S03 Binoxide of Sulphuric Iodine. Sulphate of Sulphate of. uiaugaueso. acid. potassa. manganese. L66 IODINE. secondary action between the hydriodic acid first produced, and the excess of the sulphuric acid, in which both suffer decomposition, yielding iodine, water, and sulphurous acid. Iodine crystallizes in plates or scales of a bluish-black color and imperfect metallic lustre, resembling that of plumbago; the crystals are sometimes very large and brilliant. Its density is 4-948. At 225° (107°-2C) it fuses, and at 347° (175°C) boils, the vapor having an exceedingly beautiful violet color.1 It is slowly volatile, however, at common temperatures, and exhales an odor much resembling that of chlorine. The density of the vapor is 8-716. Iodine requires for solution about 7000 parts of water, which nevertheless acquires a brown color; in alcohol it is much more freely soluble. Solutions of hydri- odic acid and the iodides of the alkaline metals also dissolve a large quantity: these solutions are not decomposed by water, which is the case with the alco- holic tincture. This substance stains the skin, but not permanently; it has a very ener- getic action upon the animal system, and is much used in medicine. One of the most characteristic properties of iodine is the production of a splendid blue color by contact with the organic principle, starch. The iodine for this purpose must be free or uncombined. It is easy, however, to make the test available for the purpose of recognizing the presence of the element in question when a soluble iodide is suspected; it is only necessary to add a very small quantity of chlorine-water, when the iodine, being displaced from combination, becomes capable of acting upon the starch. Hydriodic Acid.—The simplest process for Fie-116- preparing hydriodic acid gas is to introduce into a glass tube, sealed at one extremity, a little iodine, then a small quantity of roughly- powdered glass moistened with water, upon this a few little fragments of phosphorus, and lastly more glass: this order of iodine, glass, phosphorus, glass, is repeated until the tube is half or two-thirds filled. A cork and nar- row bent tube are then fitted, and gentle heat applied. The gas is best collected by dis- placement of air. The experiment depends on the formation of an iodide of phosphorus, and its subsequent decomposition by water^ hydrated phosphorous acid and iodide of hy- drogen being produced.2 The glass merely serves to moderate the violence of the action of the iodine upon the phosphorus. Hydriodic acid gas greatly resembles the corresponding chlorine compound ; it is color- less, and highly acid; it fumes in the air, and is very soluble in water Its density is about 4-4. By weight it is composed of 127 parts iodine and 1 part hydrogen ; and by measure, of equal volumes of iodine-vapor and hydro- gen united without condensation. Solution of hydriodic acid may be prepared by a process much less trouble- some than the above. Iodine in fine powder is suspended in water and a stream of washed sulphuretted hydrogen passed through the mixture • sulphur is deposited, and the iodine converted into hydriodic acid. When the liouid has become colorless, it is heated, to expel the excess of sulphuretted hvdro- 1 Whence the name, from tai&rjs, violet-colored. 3 P + 31 + 6IIO = 3HO,P03 Phosphorus. Iodine. Water. Hydriodic acid. Hydrated phosphorous acid. FLUORINE. 167 Iodine. Oxygen. 127 40 127 56 gen, and filtered. The solution cannot long be kept, especially if it be strong; the oxygen of the air gradually decomposes the hydriodic acid, and iodine is Bet free, which, dissolving in the remainder, communicates to it a brown color. Compounds of Iodine and Oxygen. The most, important of these are the iodic and periodic acids. Composition by weight. Iodic acid ...... Periodic acid1 ..... Iodic acid may be prepared by the direct oxidation of iodine by nitric acid of specific gravity 1-5; 5 parts of dry iodine with 200 parts of nitric acid are kept at a boiling temperature for several hours, or until the iodine has disap- peared. The solution is then cautiously distilled to dryness, and the residue dissolved in water and made to crystallize. Iodic acid is a very soluble substance; it crystallizes in colorless, six-sided tables, which contain water. It is decomposed by heat, and its solution readily deoxidized by sulphurous acid. The iodates much resemble the chlo- rates ; that of potassa is decomposed by heat into iodide of potassium and oxygen gas. Periodic Acid.—When solution of iodate of soda is mixed with caustic soda, and a current of chlorine transmitted through the liquid, two salts are formed, namely, chloride of sodium and a combination of periodate of soda with hydrate of soda, which is sparingly soluble.2 This is separated, converted into a silver-salt, and dissolved in nitric acid: the solution yields on evapora- tion crystals of yellow periodate of silver; from which the acid may be sepa- rated by the action of water, which resolves the salt into free acid and inso- luble basic periodate. The acid itself may be obtained in crystals. It is permanent in the air, and capable of being resolved into iodine and oxygen by a high temperature. This element has never been isolated, at least in a state fit for examination ; its properties are consequently in great measure unknown; from the observa- tions made, it is presumed to be gaseous, and to possess color, like chlorine. The compounds containing fluorine can be easily decomposed, and the element transferred from one body to another; but its extraordinary chemical ener- gies towards the metals and towards silicium, a component of glass, have hitherto baffled all attempts to obtain it pure in a separate state. As fluoride of calcium it exists in small quantities in many animal substances, such as bones. Several chemists have endeavored to obtain it by decomposing fluoride of* silver by means of chlorine in vessels of fluor-spar, but eveu these experi- ments have not led to a decisive result. Hydrofluoric Acid.3—When powdered fluoride of calcium (fluor-spar) is heated with concentrated sulphuric acid in a retort of platinum or lead con- nected with a carefully-cooled receiver of the same metal, a very volatile colorless liquid is obtained, which emits copious white and highly-suffocating I05 and I07. NaOJOs + 3NaO + 2C1 : = 2NaO,I07 + 2\aCl Iodate of soda, Soda. Chlorine Basic Periodate of soda. Chloride of sodium. 1 IIF. 168 SILICIUM. fumes in the air. This was formerly believed to be the acid in an anhydrous state. M. Louyet, however, states that it still contains water, and that hydro- fluoric acid, like hydrochloric acid, when anhydrous, is a gas. The anhydrous acid may be prepared, according to Fremy, by distilling hydrofluate of fluo- ride of potassium in a platinunTvessel. The acid is gaseous at ordinary tem- peratures. In a frigorific mixture it exists as a fluid, which acts violently on water and evolves white fumes. When hydrofluoric acid is put into water, it unites with the latter with great violence: the dilute solution attacks glass with great facility. The con- centrated acid dropped upon the skin occasions deep and malignant ulcers, so that great care is requisite in its management. Hydrofluoric acid contains 19 parts fluorine and 1 part hydrogen. . In a diluted state, this acid is occasionally used in the analysis of siliceous minerals, when alkali is to be estimated; it is employed also for etching on glass; for which purpose the acid may be prepared in vessels of lead, that metal being but slowly attacked under these circumstances. The vapor of the acid is also very advantageously applied to the same object in the following manner: the glass to be engraved is coated with etching-ground or wax, and the design traced in the usual way with a pointed instrument. A shallow basin, made by beating up a piece of sheet-lead, is then prepared, a little powdered fluor-spar placed in it, and enough sulphuric acid added to form with the latter a thin paste. The glass is placed upon the basin, with the waxed side downwards, and gentle heat applied beneath, which speedily dis- engages the vapor of hydrofluoric acid. In a very few minutes the operation is complete; the glass is then removed and cleaned by a little warm oil of turpen- tine. When the experiment is successful, the lines are very clean and smooth. No combination of fluorine and oxygen has yet been discovered. SILICIUM. Silicium, sometimes called silicon, in union with oxygen constituting silica, or the earth of flints, is a very abundant substance, and one of great import- ance. It enters largely into the composition of many of the rocks and mineral masses of which the surface of the earth is composed. The following process yields silicium most readily. The double fluoride of silicium and potassium is heated in a glass tube with nearly its own weight of metallic potassium, violent reaction ensues, and silicium is set free. When cold, the contents of the tube are put into cold water, which removes the saline matter and any residual potassium, and leaves the silicium untouched. So prepared, silicium is a dark-brown powder, destitute of lustre. Heated in the air, it burns, and becomes superficially converted into silica. It is also acted upon by sulphur and by chlorine. When silicium is strongly heated in a covered crucible, its properties are greatly changed; it becomes darker in color, denser, and incom- bustible, refusing to burn even when heated by the flame of the oxyhydrogen blowpipe. According to recent researches by Wohler and Deville, silicium, like carbon, is capable of existing in three different modifications. The modification above mentioned corresponds to the amorphous variety of carbon (lampblack). The researches just quoted have established the existence of modifications corre- sponding to the diamond, and to the graphite-variety of carbon. The dia- mond modification of silicium is most readily obtained by introducing into a red- hot crucible a mixture of 3 parts of silico-fluoride of potassium, 1 part of sodium in small fragments, and 1 part of granulated zinc, and heating to per- fect fusion. On slowly cooling there is formed a button of zinc, covered and interspersed with needle-shaped crystals consisting of octohedra, joined in the direction of the axis. This crystallized silicium, which may be readily freed from zinc by treatment with acids, resembles crystallized hematite in color and appearance; it scratches glass, and fuses at a temperature approaching SILICIUM. 169 Fig. 117. the melting-point of cast-iron. The graphite modification of silicium is pre- pared by fusing, in a Hessian crucible, 5 parts of soluble glass (silicate of potassa), 10 parts of cryolith (fluoride of sodium and aluminium), with 1 part of aluminium. On treating the resulting button of aluminium with hydrochloric acid, the silicium remains in the form of scaly crystals, resem- bling graphite, but of somewhat brighter color, scratching glass, like the pre- vious modification. It is infusible. Its specific gravity is 2-49. Silica. — This is the only known oxide; it contains 21 -3 parts silicium, and 24 parts oxygen.1 Colorless transparent rock-crystal consists of silica very nearly in a state of purity: common quartz, agate, calcedony, flint, and seve- ral other minerals, are also chiefly composed of this substance. The experiment about to be described furnishes silica in a state of complete purity, and at the same time exhibits one of the most remarkable properties of silicium, namely, its attraction for fluorine. A mixture is made of equal parts fluor-spar and glass, both finely powdered, and introduced into a glass flask, with a quantity of oil of vitriol. A tolerably wide bent tube, fitted to the flask by a cork, passes to the bottom of a glass jar, into which enough mercury is poured to cover the extremity of the tube. The jar is then half filled with water, and heat is applied to the flask. The first effect is the disengagement of hydrofluoric acid: this substance, however, finding itself in contact with the silica of the powdered glass, under- goes decomposition, water and fluoride of silicium being produced. The latter is a permanent gas, which escapes from the flask by the bent tube. By contact with a large quantity of water, it is in turn decomposed, yielding silica, which separates in a beautiful gelatinous condition, and an acid liquid which is a double fluoride of silicium and hydrogen, commonly called hydrofluosilicic acid.2 The silica may be collected on a cloth filter, well washed, dried, and heated to redness to expel water. 1 SiOs. » (1) Reaction of hydrofluoric acid upon silica: — Hydrofluoricacid{^d0»-n^ t Silicium \ Oxygen + Si03 = Gaseous fluoride of silicium. Silica. Water. Terfluoride of silicium. (2) Decomposition of fluoride of silicium by water: — Fiuoride of silicium {^«-- Wator f Oxygen. \ llydrog. Fluoride of silicium --------- ~::5^. Hydrofluosilicic acid. + SiOa 3HF,2SiFs 15 170 BORON. The acid liquid is kept as a test for baryta and potassa, with which it forma nearly insoluble precipitates, the double fluoride of silicium and potassium being used, as was stated, in the preparation of silicium. The fluoride of silicium, instead of being conducted into water, may be collected over mer- cury: it is a permanent gas, destitute of color, and very heavy. Admitted into the air, it condenses the moisture of the latter, giving rise to a thick white cloud. It is important in the experiment above described to keep the end of the delivery-tube from touching the water of the jar; otherwise it almost instantly becomes stopped; the mercury effects this object. There is another method by which pure silica can be prepared, and which is also very instructive, inasmuch as it is the basis of the proceeding adopted in the analysis of all siliceous minerals. Powdered rock-crystal or fine sand is mixed with about three times its weight of dry carbonate of soda, and the mixture fused in a platinum crucible. When cold, the glassy mass is boiled with water, by which it is softened, and almost entirely dissolved. An excess of hydrochloric acid is then added to the filtered liquid, and the whole evapo- rated to complete dryness. By this treatment the gelatinous silica thrown down by the acid becomes completely insoluble, and remains behind when the dry saline mass is treated with acidulated water, by which the alkaline salts, alumina, sesquioxide of iron, lime, and many other bodies which may happen to be present, are removed. The silica is washed, dried, and heated to redness. The most prominent characters of silica are the following: it is a very fine, white, tasteless powder, not sensibly soluble in water or dilute acids (with the exception of hydrofluoric) unless recently precipitated. It dissolves, on the contrary, freely in strong alkaline solutions. Its density is about 2-66, and it is only to be fused by the oxyhydrogen blowpipe. Silica is in reality an acid, and a very powerful one; insolubility in water prevents the manifestation of acid properties under ordinary circumstances. When heated with bases, especially those which are capable of undergoing fusion, it unites with them and forms true salts, which are sometimes soluble in water, as in the case of the silicates of potassa and soda when the propor- tion of base is considerable. Common glass is a mixture of several silicates in which the reverse of this happens, the silica, or, as it is more correctly called, silicic acid, being in excess. Even glass, however, is slowly acted upon by water. Finely-divided silica is highly useful in the manufacture of porcelain. BOEON. This substance is closely related to silicium; it is the basis of boracic acid. Boron is prepared by a process very similar to that described in the case of silicium, the double fluoride of boron and potassium being substituted for the other salt, and the operation conducted in a small iron vessel instead of a glass tube. It is a dull greenish-brown powder, which burns in the air when heated, producing boracic acid. Nitric acid, alkalis in a fused condition, chlorine, and other agents, attack it readily. By processes perfectly analogous to those adopted for the preparation of the diamond and graphite variety of .silicium, Wohler and Deville have procured also the corresponding modifications of boron. The diamond modification of boron crystallizes in square octohedra, generally of a brownish color, posses- sing very nearly the hardness and refractive power of diamond. It is infusible in the flame of the oxyhydrogen blowpipe, but burns in oxygen at the same temperature at which the diamond is oxidized. Its sp. gr. is 2-68. The gra- phite modification of boron crystallizes in scaly hexagonal plates, which in every respect resemble the carbon graphite. Both modifications form fusible alloys with platinum. BORON. 171 There is but one oxide of boron, namely boracic acid, containing 10-9 parts of boron and 21 parts of oxygen.1 Boracic acid is found in solution in the water of the hot volcanic lagoons of Tuscany, whence a large supply is at present derived. It is also easily made by decomposing with sulphuric acid a hot solution of borax, a salt brought from the Fast Indies, consisting of boracic acid combined with soda. ^ Boracic acid crystallizes in transparent colorless plates, soluble in about ~o parts of cold water,'and in a much smaller quantity at a, boiling heat; the acid has but little taste, and feebly affects vegetable colors. When heated, it loses water, and melts to a glassy transparent mass, which dissolves many metallic oxides With great ease. The crystals contain 34-9 parts of real acid, and 27 parts of water.2 They dissolve in alcohol, and the solution burns with a green flame. Glassy boracic acid in a state of fusion requires for its dissipation in vapor a very intense and long-continued heat: the solution in water cannot, however, be evaporated without very appreciable loss by volatilization; hence it is pro- table that the hydrate is far more volatile than the acid itself. By heating in a glass flask or retort one part of the vitrified boracic acid, 2 of fluor-spar, and 12 of oil of vitriol, a gaseous fluoride of boron may be ob- tained, and received in glass jars standing over mercury. It is a transparent gas, very soluble in water, and very heavy; it forms a dense fume in the air like fluoride of silicium.3 > Bo08. a 3IIO,Bo03. * These two bodies are thus constituted—SiFs, and B0F3. 8* 172 COMPOUNDS OP CARBON AND HYDROGEN. ON CERTAIN IMPORTANT COMPOUNDS FORMED BY THE UNION OF THE PRECEDING ELEMENTS AMONG THEMSELVES. COMPOUNDS OF CAKBON AND HYDROGEN. The compounds of carbon and hydrogen already known are exceedingly numerous; perhaps all, in strictness, belong to the domain of organic che- mistry, as they cannot be formed by the direct union of their elements, but always arise from a decomposition of a complex body of organic origin. It will be found convenient, notwithstanding, to describe two of them in this part of the volume, as they very well illustrate the important subjects of combus- tion, and the nature of flame. Light Carbonetted or Carburetted Hydrogen; Marsh-gas; Fire-damp; Gas of the Acetates.—This gas is but too often found to be abundantly disengaged in coal-mines from the fresh-cut surface of the coal, and from remarkable aper- tures or "blowers," which emit for a great length of time a copious stream or jet of gas, which probably existed in a state of compression, pent up in the coal. The mud at the bottom of pools in which water-plants grow, on being stirred, suffers bubbles of gas to escape, which may be easily collected. This, on examination, is found to be chiefly a mixture of light carbonetted hydrogen and carbonic acid; the latter is easily absorbed by lime-water or caustic potassa. Until recently, no method was known by which the gas in question could be produced in a state approaching to purity by artificial means; the various illuminating gases from pit-coal and oil, and that obtained by passing the vapor of alcohol through a red-hot tube, contain large quantities of light car- bonetted hydrogen, associated, however, with other substances which hardly admit of separation. M. Dumas was so fortunate as to discover a method by which that gas can be produced at will, perfectly pure, and in any quantity. A mixture is made of 40 parts crystallized acetate of soda, 40 parts solid hydrate of potassa, and 60 parts quicklime in powder. This mixture is trans- ferred to a flask or retort, and strongly heated; the gas is disengaged in great abundance, and may by collected over water.1 Light carbonetted hydrogen is a colorless and nearly inodorous gas, which does not affect vegetable colors. It burns with a yellow flame, generating carbonic acid and water. It is not poisonous, and may be respired to a great extent without apparent injury. The density of this compound is about 0-559, 100 cubic inches weighing 17-41 grains; and it contains carbon and hydrogen 1 Ann. Chim. et Phys. Ixxiii. 93. The reaction consists in the conversion of the acetic acid by the aid of the elements of water, into carbonic acid and light carbonetted hydrogen ; the instability of the organic acid at a high temperature, and the attraction of the potassa for car- bonic acid, being the determining causes. The lime prevents the hydrate of potassa from fusing and attacking the glass vessels. This decomposition is best understood by putting it in the shape of an equation. Acetic acid C4II3O3 ) _$ Carbonic acid, 2 eq. C2 Ot Water HO j~(. Marsh-gas, 2 eq. C2II4 C4H4O4. C4U4O4. COMPOUNDS OF CARBON AND HYDROGEN. 173 associated in the proportion of 6 parts by weight of the former to 2 of tho latter.1 When 100 measures of this gas are mixed with 200 of pure oxygen in the eudiometer, and the mixture exploded by the electric spark, 100 measures of a gas remain which is entirely absorbable by a little solution of caustic potassa. Now carbonic acid contains its own volume of oxygen; hence one-balf the oxygen added, that is 100 measures, must have been consumed in uniting with the hydrogen. Consequently, the gas must contain twice its own mea- sure of hydrogen, and enough carbon to produce, when completely burned, an equal quantity of carbonic acid. When chlorine is mixed with light carbonetted hydrogen over water, no change follows, provided light be excluded. The presence of light, however, brings about decomposition, hydrochloric acid, carbonic acid, and sometimes other products being produced. It is important to remember that the gas is not acted upon by chlorine in the da-rk. Oirjiant (las.—Strong spirit of wine is mixed with five or six times its weight of oil of vitriol in a glass flask, the tube of which passes into a wash- bottie containing caustic potassa. A second wash-bottle, partly filled with oil of vitriol, is connected with the first, and furnished with a tube dipping into the water of the pneumatic trough. On the first application of ieat to the contents of the flask, alcohol, and afterwards ether, make their appear- ance ; but, as the temperature rises, and the mixture blackens, the ether-vapor diminishes in quantity, and its place becomes in great part supplied by a per- manent inflammable gas; carbonic acid and sulphurous acid are also gene- rated at the same time, besides traces of other products. The two last men- tioned gases are absorbed by the alkali in the first bottle, and the ether-vapor by the acid in the second, so that the olefiant gas is delivered tolerably pure. The reaction is too complex to be discussed at the present moment; it will be found fully described in another part of the volume. Olefiant gas thus pro- duced is colorless, neutral, and but sliglitly soluble in water. Alcohol, ether, oil of turpentine', and even olive oil, as Mr. Faraday has observed, dissolve it to a considerable extent. It has a faint odor of garlic. On the approach of a kindled taper it takes fire, and burns with a splendid white light, far sur- passing in brilliancy that produced by light carbonetted hydrogen. This gas, when mixed with oxygen and fired, explodes with extreme violence. Its den- sity is 0-981 ; 100 cubic inches weigh 30-57 grains.2 By the use of the eudiometer, as already described, it has been found that each measure of olefiant gas requires for complete combustion exactly three of oxygen, and produces under these circumstances two measures of carbonic acid. Whence it is evident that it contains twice its own volume of hydrogen, combined with twice as much carbon as in marsh gas. By weight, these proportions will be 12 parts carbon, and 2 parts hydrogen. Olefiant gas is decomposed by passing it through a tube heated to bright redness; a deposit of charcoal and tar takes place, and the gas becomes con- verted into light carbonetted hydrogen, or even into free hydrogen, if the temperature be very high. This latter change is of course attended by increase of volume. Chlorine acts upon olefiant gas in a very remarkable manner. When tho two bodies are mixed, even in the dark, they combine in equal measures, and give rise to a heavy oily liquid, of sweetish taste and ethereal odor, to which 1 The two carbides of hydrogen here described are thus represented in equivalents:— Light carbonetted hydrogen Clla, or Cill4- Olefiant gas C2II2, or C4II4. * [Olefiant gas. by pressure and intense cold, produced by the evaporation in a vacuum of solid carbonic arid and ether, is condensed into a colorless transparent liiuid, but not frozen. (Faraday.)—B. B.] 15* 174 COMPOUNDS OF CARBON AND HYDROGEN. the name of chloride of hydrocarbon, or Dutch liquid,1 is given. It is from this peculiarity that the term olefiant gas is derived. A pleasing and instructive experiment may also be made by mixing in a tall jar two measures of chlorine and one of olefiant gas, and then quickly apply- ing a light to the mouth of the vessel. The chlorine and hydrogen unite with flame, which passes quickly down the jar, while the whole of the carbon is set free in the form of a thick black smoke. Coal and Oil Gases.—The manufacture of coal-gas is at the present moment a branch of industry of great interest and importance in several points of view. The process is one of great simplicity of principle, but requires, in practice, some delicacy in management to yield a good result. When pit-coal is subjected to destructive distillation, a variety of products show themselves; permanent gases, steam, and volatile oils, besides a not inconsiderable quantity of ammonia from the nitrogen always present in the coal. These substances vary very much in their proportions with the tempe- rature at which the process is conducted, the permanent gases becoming more abundant with increased heat, but at the same time losing much of their value for the purposes of illumination. The coal is distilled in cast-iron retorts, maintained at a bright-red heat, and the volatilized products conducted into a long horizontal pipe of large dimensions, always half filled with liquid, into which the extremity of each separate tube dips: this is called the hydraulic main. The gas and its accom- panying vapors are next made to traverse a refrigerator, usually a series of iron pipes, cooled on the outside by a stream of water; here the condensation of the tar and the ammoniacal liquid becomes complete, and the gas proceeds onwards to another part of the apparatus, in which it is deprived of the sul- phuretted hydrogen and carbonic acid gases always present in the crude pro- duct. This is generally effected by hydrate of lime, which readily absorbs the compounds in question. The purifiers are large iron vessels, partly filled with a mixture of hydrate of lime and water,2 in which a churning machine or agitator is kept in constant motion to prevent the subsidence of the lime. The gas is admitted at the bottom of the vessel by a great number of minute apertures, and is thus made to present a large surface of contact to the puri- fying liquid. The last part of the operation, which indeed is often omitted, consists in passing the gas through dilute sulphuric acid, in order to remove ammonia. The quantity thus separated is very small, relatively, to the bulk of the gas, but in an extensive work becomes an object of importance. Coal-gas thus manufactured and purified is preserved for use in immense cylindrical receivers, closed at the top, suspended in tanks of water by chains to which counterpoises are attached, so that the gas-holders rise and sink in the liquid as they become filled from the purifiers or emptied by the mains. These latter are made of large diameter, to diminish as much as possible the resistance experienced by the gas in passing through such a length of pipe. The joints of these mains are still made in such an imperfect manner, that immense loss is experienced by leakage when the pressure upon the gas at the works exceeds that exerted by a column of water an inch in height.3 1 CallnCl, or C4IL.CI2. a A mixture of sulphate of lime and hydrated sesquioxide of iron is likewise frequently employed. s It may give some idea of the extent of this species of manufacture, to mention, that in the year 1838, for lighting London and the suburbs alone, there were eighteen public gas-works and £2,800,000invested in pipes and apparatus. The yearly revenue amounted to £450.000 and the consumption of coal in the same period to 180,000 tons, 1,400 millions of cubic feet of gas being made in the year. There were 134;300 private lights, and 30,400 street lamps. 890 tons of coals were used in the retorts in the space of twenty-four hours at mid-winter, and 7,120 000 cubic feet of gas consumed in the longest night.—Dr. Ure, Dictionary of Arts and Manufactures. Since that time the production of gas has been enormously increased. The amount of coal used in London for gas-making in 1857 is estimated at more than 800,000 tons, yielding not less than 7,000,000,000 of cubic feet of gas. In the same year the mains in the London streets had reached the extraordinary length of 2000 miles. COMBUSTION, AND STRUCTURE OP FLAME. 175 Coal-gas varies very much in composition, judging from its variable density and illuminating powers, and from the analyses which have been made. The difficulties of such investigations are very great, and unless particular pre- caution be taken, the results are merely approximative. The purified gas is believed to contain the following substances, of which the first is most abun- dant, and the second most valuable:— Light carbonetted hydrogen. Olefiant gas. Hydrogen. Carbonic oxide. Nitrogen. Vapors of volatile liquid carbides of hydrogen.1 Vapor of bisulphide of carbon. Separated by Condensation and by the Purifiers. Tar and volatile oils. Sulphate of ammonia, chloride and sulphide of ammonium. Sulphuretted hydrogen. Carbonic acid. Hydrocyanic acid, or C3ranide of ammonium. Hydrosulphocyanic acid, or sulphocyanide of ammonium. A very far better illuminating gas may be prepared from oil, by dropping it into a red-hot iron retort filled with coke: the liquid is in great part decom- posed and converted into permanent gas, which requires no purification, as it is quite free from the ammoniacal and sulphur compounds which vitiate gas from coal. A few years ago this article was prepared in London; it was com- pressed for the use of the consumer into strong iron vessels, to the extent of 30 atmospheres; these were furnished with a screw-valve of peculiar construc- tion, and exchanged for others when exhausted. The comparative high price of the material, and other circumstances, led to the abandonment of the undertaking. On the Continent gas is now extensively prepared from wood. COMBUSTION, AND THE STRUCTURE OF FLAME. When any solid substance, capable of bearing the fire, is heated to a certain point, it emits light, the character of which depends upon the temperature. Thus, a bar of platinum or a piece of porcelain, raised to a particular tempe- rature, becomes what is called red-hot, or emissive of red light: at a higher degree of heat this light becomes whiter and more intense, and when urged to the utmost, as in the case of a piece of lime placed in the flame of the oxyhydrogen blowpipe, the light becomes exceedingly powerful, and acquires , a tint of violet. Bodies in these states are said to be incandescent or ignited. Again, if the same experiment be made on a piece of charcoal, similar effects will bo observed, but something in addition; for whereas the platinum or porcelain, when removed from the fire, or the lime from the blowpipe flame, begin immediately to cool, and emit less and less light, until they become completely obscure, the charcoal maintains to a great extent its high tempera- ture. Unlike the other bodies, too, which suffer no change whatever, either of weight or substance, the charcoal gradually wastes away until it disappears. This is what is called combustion, in contradistinction to mere ignition • the charcoal burns, and its temperature is kept up by the heat evolved in the act of union with the oxygen of the air. 1 These bodies increase the illuminating power, and confer on the gas its peculiar odor. 176 COMBUSTION, AND STRUCTURE OF FLAME. In the most general sense, a body in a state of combustion is one in the act of undergoing intense chemical action: any chemical action whatsoever, if its energy rise sufficiently high, may produce the phenomenon of combustion, by heating the body to such an extent that it becomes luminous. In all ordinary cases of combustion, the action lies between the burning body and the oxygen of the air; and since the materials employed for the economical production of heat and light consist of carbon chiefly, or that sub- stance conjoined with a certain proportion of hydrogen and oxygen, all common effects of this nature are cases of the rapid and violent oxidation of carbon and hydrogen by the aid of the free oxygen of the air. The heat must be referred to the act of chemical union, and the light to the elevated temperature. By this principle it is easy to understand the means which must be adopted to increase the heat of ordinary fires to the point necessary to melt refractory metals, and to bring about certain desired effects of chemical decomposition. If the rate of consumption of the fuel can be increased by a more rapid intro- duction of air into the burning mass, the intensity of the heat will of neces- sity rise in the same ratio, there being reason to believe that the quantity of heat evolved is fixed and definite for the same constant quantity of chemical action. This increased supply of air may be effected by two distinct methods: it may be forced into the fire by bellows or blowing machines, as in the common forge, and in the blast and cupola-furnaces of the iron-worker, or it may be drawn through the burning materials by the help of a tall chimney, the fire- place being closed on all sides, and no entrance of air allowed, save between the bars of the grate. Such is the kind of furnace generally employed by the scientific chemist in assaying and in the reduction of metallic oxides by char- coal ; the principle will be at once understood by the aid of the sectional drawing, in which a crucible is represented, arranged in the fire for an opera- tion of the kind mentioned. (Fig. 118.) Fig. 118. Fig. 119. The " reverberatory" furnace (fig. 119) is one very much used in the arts when substances are to be exposed to heat without contact with the fuel. The fire- chamber is separated from the bed or hearth of the furnace by a "low wall or bridge of brick-work, and the flame and heated air are reflected downwards COMBUSTION, AND STRUCTURE OF FLAME. 177 -V—-A by the arohed form of the roof. Any degree of heat can be obtained in a furnace of this kind, from the temperature of dull redness, to that required to melt very large quantities of cast-iron. The fire is urged by a chimney, provided with a sliding-plate or damper to regulate the draught. Solids and liquids, as melted metal, enjoy, when sufficiently heated, the faculty of emitting light; the same power is possessed by gaseous bodies, but the temperature required to render a gas luminous is incomparably higher than in the cases already described. Gas or vapor in this condition consti- tutes flame, the actual temperature of which generally exceeds that of the white heat of solid bodies. The light emitted from pure flame is exceedingly feeble; illuminating power is almost entirely dependent upon the presence of solid matter. The flame of hydrogen, or of the mixed gases, is scarcely visible in full daylight: in a dusty atmosphere, however, it becomes much more luminous by igniting to intense whiteness the floating Fig. 120. particles with which it comes in contact. The piece of lime in the blowpipe flame cannot have a higher tem- perature than that of the flame itself; yet the light it throws off is infinitely greater. Flames burning in the air, and not supplied with oxy- gen from another source, arc, as already stated, hollow; th« chemical action is necessarily confined to the spot where the two bodies unite. That of a lamp or candle, when carefully examined, is seen to consist of three separate portions. The dark central part, a, easily ren- dered evident by depressing upon the flame a piece of fine wire-gauze, consists of combustible matter drawn up by the capillarity of the wick, and volatilized by the heat. This is surrounded by a highly-luminous cone or envelope, b, which, in contact with a cold body, deposits soot. On the outside a second cone, c, is to be traced, feeble in its light-giving power, but having an exceed- ingly high temperature. The explanation of these ap- pearances is easy: carbon and hydrogen are very un- equal in their attraction for oxygen, the latter greatly exceeding the former in this respect: consequently, when both are present, and the supply of oxygen limit- ed, the hydrogen takes all, to the exclusion of a great part of the carbon. Now this happens in the case under consideration at some little distance within the outer surface of the flame, namely, in the luminous portion; the little oxygen which has penetrated thus far inwards is entirely consumed by the hydrogen, and the particles of deposited charcoal, which would, were they cooler, form smoke, become intensely ignited by the burning hj-drogen, and evolve a light whose white- ness marks a very elevated temperature. In the exte- rior and scarcely visible cone, these particles of carbon undergo combustion. A jet of coal-gas exhibits these phenomena; but if the gas be previously mingled with air, or if air be forcibly mixed with or driven into the flame, no such separation of carbon occurs, the hydrogen and carbon burn together, and the illuminating power almost disap- Fig. 12L A pears. I*J The common mouth blowpipe is a little instrument of great utility; it is merely a brass tube fitted with an ivory mouthpiece, and 178 COMBUSTION, AND STRUCTURE OF FLAME. Fig. 122. terminated by a jet, having a small aperture by which a current of air is driven across the flame of a candle. The best form is perhaps that contrived by Mr. Pepys, and figured in the margin (fig. 121). The flame so produced is very peculiar. Instead of the double envelope just described, two long pointed cones are observed, which, when the blowpipe is good, and the aperture smooth and round, are very well defined, the outer cone being yellowish, and the inner blue. A double combustion is, in fact, going on, by the blast in the inside, and by the external air. The space between the inner and outer cones is filled with exceedingly hot combustible matter, possessing strong reduc- ing or deoxidizing powers, while the highly-heated air just beyond the point of the exterior cone ox- idizes with great facility. A small portion of matter, supported on a piece of charcoal, oi. fixed in a ring at the end of a fine platinum wire, can thus in an instant be exposed to a very high degree of heat under these contrasted cir- cumstances, and observations of great value made in a very short time. The use of the in- strument requires an even and uninterrupted blast of some duration, by a method easily acquired with a little patience; it consists in employing for the purpose the muscles of the cheeks alone, respiration being conducted through the nostrils, and the mouth from time to time replenished with air without intermission of the blast. The Argand lamp, adapted to burn either oil or spirit, but especially,the latter, is a very useful piece of chemical apparatus. In this lamp the wick is cylindrical, the flame being supplied with air both inside and outside; the combustion is greatly aided by the chimney, which is made of copper when the lamp is used as a source of heat. Fig. 123. Fig. 124. The accompanying drawing exhibits, in section, an excellent lamp of this kind for burning alcohol or wood-spirit. It is constructed of thin copper, and furnished with ground caps to the wick-holder and aperture1 by which the spirit is introduced in order to prevent loss when the lamp is not in use. 1 When in use this aperture must always be :pen, otherwise an accident is sure to happen; the heat expands the air in the lamp, and the spirit is forced out in a state of inflam- mation. COMBUSTION, AND STRUCTURE OF FLAME. 179 01 a-8 spirit-lamps, (fig. 121,) fitted with caps to prevent evaporation, are very convenient for occasional use, being always ready and in order.1 In London, and other large towns, where coal-gas is to be had, it is con- stantly used with the greatest economy and advantage in every respect as a source of heat. Retorts, flasks, capsules, and other ves- sels can be thus exposed to an easily-regulated and inva- Fio-125- riable temperature for many successive hours. Small ._<>_» platinum crucibles may be ignited to redness by placing _____^P%, them over the flame on a little wire triangle. The ar- 1^91"^ rangement shown, consisting of a common Argand gas- 'l|| burner fixed on a heavy and low foot, and connected with 1 a flexible tube of caoutchouc or other material, leaves J 1 nothing to desire. '^^M gF The kindling-point, or temperature at which combus- \&F lion commences, is very different with different sub- \f stances; phosphorus will sometimes take fire in the ^s^ hand; sulphur requires a temperature exceeding that of /^y^l^^t-^ boiling water, charcoal must be heated to redness. C\^ ^ _^J*~ Among gaseous bodies the same fact is observed: hydro- ^^mn^^^ gen is inflamed by a red-hot wire; carbonetted hydrogen requires a white heat to effect the same thing. When flame is cooled by any means below the temperature at which the rapid oxidation of the combustible gas occurs, it is at once extinguished. Upon this depends the principle of Sir H. Davy's invaluable safety-lamp. Mention has already been made of the frequent disengagement of great quantities of light carbonetted hydrogen gas in coal-mines. This gas, mixed with seven or eight times its volume of atmospheric air, becomes highly ex- plosive, taking fire at a light, and burning with a pale-blue flame ; and many fearful accidents have occurred from the ignition of large quantities of mixed gas and air occupying the extensive galleries and workings of a mine. Sir II. Davy undertook an investigation with a view to discover some remedy for this constantly-occurring calamity: his labors resulted in some exceedingly- important discoveries respecting flame, of which the substance has been given, and which led to the construction of the lamp which bears his name. When two vessels filled with a gaseous explosive mixture are connected by a narrow tube, and the contents of one fired by the electric spark, or other- wise, the flame is not communicated to the other, provided the diameter of the tube, its length and the conducting power for heat of its material, bear a cer- tain proportion to each other; the flame is extinguished by cooling, and its transmission rendered impossible. In this experiment high conducting power and diminished diameter compen- sate for diminution in length; and to such an extent can this be carried, that metallic gauze, which may be looked upon as a series of very short square 1 [The spirit-lamp represented in fig. 126 is one contrived by Dr. Mitchell. " It is made of tinned iron. The alcohol is poured in by means Of the hollow handle, and is admitted to the cylindrical burner by two or three tubes which are placed at the very bottom of the fountain. Hy such an arrangement of parts, the alcohol may be added as it is con- sumed, and the flame kept uniform; and as the pipes which pass to the burner are sore- mote from the flame, the alcohol never be- comes heated so as to fly off through the vent-hole, and thus to cause greater waste and danger of explosion." A cylindrical chimney is an advantageous addition for many purposes. It may be made 5f tin-plate or copper.—It. B.] lig. 126. 180 COMBUSTION, AND STRUCTURE OF FLAME. Fig. 127. ©>) tubes arranged side by side, arrests in the most complete manner the passage of flame in explosive mixtures, when of sufficient degree of fineness, depending upon the inflammability of the gas. Most providentially the fire-damp mix- ture has an exceedingly high kindling-point; a red heat does not cause inflam- mation; consequently, the gauze will be safe for this substance, when flame would pass in almost any other case. The miner's safety-lamp is merely an ordinary oil-lamp, the flame of which is enclosed in a cage of wire-gauze; made double at the upper part, containing about 400 apertures to the square inch. The tube for supplying, oil to the reservoir reaches nearly to the bottom of the latter, while the wick admits of being trimmed by a bent wire passing with friction through a small tube in the body of the lamp; the flame can thus be kept burning for any length of time, without the ne-'- cessity of unscrewing the cage. When this lamp is taken into an explosive atmosphere, although the fire-damp may burn within the cage with such energy as sometimes to heat the metallic tissue to dull redness, the flame is not communicated to the mixture on the outside. These effects may be conveniently studied by suspending the lamp in a large glass jar, and gradually admitting coal- gas below. The oil-flame is at first elongated, and then, as the proportion of gas increases, extinguished, while the inte- rior of the gauze cylinder becomes filled with the burning mixture of gas and air. As the atmosphere becomes purer, the wick is once more relighted. These appearances are so remarkable, that the lamp becomes an admirable indicator of the state of the air in different parts of the mine.1 The same great principle has been ingeniously applied by Mr. Hemming to the construction of the oxyhydrogen safety- jet before mentioned. This is a tube of brass about four inches long, filled with straight pieces of fine brass wire, the whole being tightly wedged together by a pointed rod, forcibly driven into the centre of the bundle. The arrangement thus presents a series of metallic tubes, very long in proportion to their diameter, the cooling powers of which are so great as to prevent the possibility of the passage of flame, even with oxygen and hydrogen. The jet may be used, as before men- tioned, with a common bladder, without a chance of explo- sion. The fundamental fact of flame being extinguished by contact with a cold body, may be elegantly shown by twisting a copper wire into a short spiral, about 0-1 inch in diameter, and then passing it cold over the flame of a wax candle; the latter is extinguished. If the spiral be now heated to red- ness by a spirit lamp, and the experiment repeated, no such effect follows.2 Fig. 129. Fig. 128. * This is the true use of the lamp, namely, to permit the viewer or superintendent, without risk to himself, to examine the state of the air in every part of the mine; not to enable work- men t/i continue their labors in an atmosphere habitually explosive, which must be unfit for human respiration, although the evil effects may be slow to appear. Owners of coal-mines should be compelled either to adopt efficient means of ventilation, or to close workings of this dangerous character altogether. a | Where coal-gas is to be had, it may be advantageously used as a source of heat, by taking NITROGEN AND HYDROGEN; AMMONIA. 181 NITROGEN AND HYDROGEN; AMMONIA. When powdered sal-ammoniac is mixed with moist hydrate of lime, and gently heated in a glass flask, a large quantity of gaseous matter is disengaged, which must be collected over mercury, or by displacement; advantage being taken of its low specific gravity. Ammoniacal gas thus obtained is colorless; it has a very powerfully-pun- gent odor, and a strongly-alkaline reaction to test paper, by which it may be at once distinguished from nearly all other bodies possessing the same phy- sical characters. Under a pressure of 6-5 atmospheres at 60° (15°-5C), am- monia condenses to the liquid form.1 Water dissolves about 700 times its volume of this remarkable gas, forming a solution which in a more dilute state has long been known under the name of liquor ammonice; by heat, a great '* part is again expelled. The solution is decomposed by chlorine, sal-ammoniac being formed, and nitrogen set free. Ammonia has a density of 0-589; 100 cubic inches weigh 18-26 grains._ It cannot be formed by the direct union of its elements, although it is sometimes produced under rather remarkable circumstances by the deoxidation of nitric acid. The great sources of ammonia are the feebly-compounded azotized prin- ciples of the animal and vegetable kingdoms, which, when left to putrefactive change, or subjected to destructive distillation, almost invariably give rise to an abundant production of this substance. The analysis of ammoniacal gas is easily effected. When a portion is con- fined in a graduated tube over mercury, and electric sparks passed through it for a considerable time, the volume of the gas gradually increases until it be- comes doubled. On examination, the tube is found to contain a mixture of 3 measures hydrogen gas and 1 measure nitrogen. Every two volumes of the ammonia, therefore, contained three volumes of hydrogen and one of nitrogen, . the whole being condensed to the extent of one-half. The weight of the two constituents will be in the proportion of 3 parts hydrogen to 14 parts nitrogen. Ammonia may also be decomposed into its elements by transmission through a red-hot tube. Solution of ammonia is a very valuable reagent, and is employed in a great number of chemical operations, for some of which it is necessary to have it perfectly pure. The best mode of preparation is the following:— Equal weights of sal-ammoniac and quicklime are taken; the lime is slaked in a covered basin, and the salt reduced to powder. These are mixed and in- troduced into the flask employed in preparing solution of hydrochloric acid,3 together with just enough water to damp the mixture, and cause it to aggre- gate into lumps; the rest of the apparatus is arranged exactly as in the former case, with an ounce or two of water in the wash-bottle, or enough to cover the ends of the tubes, and the gas conducted afterwards into pure distilled water, artificially cooled as before. The cork-joints are made tight with wax, a little mercury is put into the safety-funnel, heat cautiously applied to the flask, and the whole left to itself. The disengagement of ammonia is very regular and advantage of the above-mentioned faot. On passing a current of gas through a wide vertical tube, open at the bottom to afford a free mixture with atmospheric air, but closed at the top by wire gauze, and then kindling the mixture after its escape through the meshes, it will burn with feeble illuminating power, but no loss of heat. When the proportion of the gas to the atmospheric air is such as not to allow the flame to become yellow, the combustion will be complete, and no carbonaceous deposit will be formed on cold bodies held over the flames. The length and diameter of the cylinder are determined by the amount of gas to be burnt, and the length may be much decreased by interposing a second diaphragm of wire gauze about mid-length of the cylinder, the current of gas being introduced below this, by which means a more thorough and rapid mixture is made with the atmospheric air. — Sir John Kobinson, K. II. &c, Ed. New Phil. Journal, 1840.—R. B.] 1 [At the temperature of —103°(—75°C), liquid ammonia freezes into a colorless solid, heavier than tho liquid itself. — (Faraday.) — R. B.] a See fig. 113, p. 160. 16 182 NITROGEN AND HYDROGEN; AMMONIA. uniform. Chloride of calcium, with excess of hydrate of lime, remains in the flask. The decomposition of the salt is usually represented in the manner shown by the following diagram:— t Ammonia- Sal-ammoniac •? Hydrochloric I Hydrogen f acid . S Chlorine Lime S Oxygen ) Calcium -Ammonia. Water. Chloride of calcium.1 Solution of ammonia should be perfectly colorless, leave no residue on eva- poration, and when supersaturated by nitric acid, give no cloud or muddiness with nitrate of silver. Its density diminishes with its strength, that of the most concentrated being about 0-875: the value in alkali of any sample of liquor ammoniae is most safely inferred, not from a knowledge of its density, but from the quantity of acid a given amount will saturate. The mode of conducting this experiment will be found described under Alkalimetry. When solution of ammonia is mixed with acids of various kinds, salts are generated, which resemble in the most complete manner the corresponding compounds of potassa and soda: these are best discussed in connexion with the latter. Any ammoniacal salt can at once be recognized by the evolution of ammonia when it is heated with hydrate of lime, or solution of carbonate of potassa or soda. NITROGEN AND BORON. A combination of nitrogen with boron was first obtained by Balmain. Woehler prepared it by mixing one part of pure dry borax with two parts of dry sal-ammoniac, heating to redness, boiling with water and hydrochloric acid, filtering and washing with hot water, when the compound remained in the form of a white powder. As yet it has not been obtained quite free from oxygen. SULPHUR, SELENIUM, AND PHOSPHORUS WITH HYDROGEN. Sulphuretted Hydrogen ; Ilydrosulphuric and Sulphydric Acid.—There are two methods by which this important compound can be readily prepared, namely, by the action of dilute sulphuric acid upon sulphide of iron, and by the decomposition of tersulphide of antimony by hydrochloric acid. The first method yields it most easily, and the second in the purest state. Protosulphide of iron is put into the apparatus for hydrogen, already seve- ral times mentioned, together with some water, and oil of vitriol is added by the funnel, until a copious disengagement of gas takes place. This is to be collected over tepid water. The reaction is thus explained:__ Sulphide of iron > Sulphur I Iron Water . . . Sulphuric acid \ Hydrogen ) Oxygen Sulphuretted hydrogen. Sulphate of protoxide of iron.2 NEUCl + Sal Ammoniac. FeS + CaO = NH3 + CaCl + HO Ammonia. Chloride of Calcium. Water. + FeO,SOa Sulphate of protoxide of iroD. SULPnUR WITH HYDROGEN. 183 By the other plan, finely-powdered tersulphide of antimony is put into a flask, to which a cork and bent tube can be adapted, and strong liquid hydro- chloric acid poured upon it. On the application of heat, a double interchange occurs between the bodies present, sulphuretted hydrogen being formed and terchloride of antimony. The action only lasts while the heat is maintained. Hydrochloric acid { Hydrogen ( Chlorine Sulphide of antimony j ^timon Sulphuretted hydrogen. Chloride of antimony.1 Sulphuretted hydrogen is a colorless gas, having the odor of putrid eggs; it is most offensive when in small quantity, when a mere trace is present in the air. It is not irritating, but, on the contrary, powerfully narcotic. When set on fire, it burns with a blue flame, producing water and sulphurous acid when the supply of air is abundant; and depositing sulphur when the oxygen is deficient. Mixed with chlorine, it is instantly decomposed, with separation of the whole of the sulphur. This gas has a specific gravity of 1-171; 100 cubic inches weigh 36-33 grains. A pressure of 17 atmospheres at 50° (10°C) reduces it to the liquid form. Cold water dissolves its own volume of sulphuretted hydrogen, and the solution is often directed to be kept as a test; it is so prone to decomposition, however, by the oxygen of the air, that it speedily spoils. A much better plan is to keep a little apparatus for generating the gas always at hand, and ready for use at a moment's notice. A small bottle or flask, to which a bit of bent tube is fitted by a cork, is supplied with a little sul- phide of iron and water; when required for use, a few drops of oil of vitriol are added, and the gas is at once evolved. The experiment completed, the liquid is poured from the bottle, replaced by a little clean water, and the apparatus is again ready for use. When potassium is heated in sulphuretted hydrogen, the metals burns with great energy, becoming converted into sulphide, while pure hydrogen remains, equal in volume to the original gas. Taking this fact into account, and comparing the density of the gas with those of hydrogen and sulphur-vapor, it appears that every volume of sulphuretted hydrogen contains one volume of hydrogen and £ of a volume of sulphur-vapor, the whole condensed into one volume. This corresponds very nearly with its composition by weight, determined by other means, namely, 16 parts sulphur and 1 part hydrogen. When a mixture is made of 100 measures of sulphuretted hydrogen and 150 measures of pure oxygen, and exploded by the electric spark, complete combustion ensues, and 100 measures of sulphurous acid gas result. Sulphuretted hydrogen is a frequent product of the putrefaction of organic matter, both animal and vegetable; it occurs also in certain mineral springs, ns at Harrowgate, and elsewhere. When accidentally present in the atmos- phere of an apartment, it may be instantaneously destroyed by a small quantity of chlorine gas. There are few reagents of greater value to the practical chemist than this SbSs + 3HC1 3IIS Sulphuretted hydrogen. + SbCIa 184 PERSULPHIDE OF HYDROGEN. substance: when brought in contact with many metallic solutions, it gives rise to precipitates, which are often exceedingly characteristic in appearance, and it frequently affords the means also of separating metals from each other with the greatest precision and certainty. The precipitates spoken of are insoluble sulphides, formed by the mutual decomposition of the metallic oxides or chlorides and sulphuretted hydrogen, water or hydrochloric acid being produced at the same time. All the metals are, in fact, precipitated, whose sulphides are insoluble in water and in dilute acids. Sulphuretted hydrogen possesses itself the properties of an acid; its solu- tion in water reddens litmus paper. The best teat for the presence of this compound is paper wetted with solu- tion of acetate of lead. This salt is blackened by the smallest trace of the gas. -a Persulphide of Hydrogen. — This substance corresponds in constitution and™ instability to the binoxide of hydrogen; it is prepared by the following means: — Equal weights of slaked lime and flowers of sulphur are boiled with 5 or 6 parts of water for half an hour, when a deep orange-colored solution is pro- duced, containing, among other things, persulphide of calcium. This is fil- tered, and slowly added to an excess of dilute sulphuric acid, with constant agitation. A white precipitate of separated sulphur and sulphate of lime makes its appearance, together with a quantity of yellow, oily-looking matter, which collects at the bottom of the vessel: this is persulphide of hydrogen.1 If the experiment be conducted by pouring the acid into the solution of sulphide, then nothing but finely-divided precipitated sulphur is obtained. The persulphide is a yellow, viscid, insoluble liquid, exhaling the odor of sulphuretted hydrogen: its specific gravity is 1-769. It is slowly decomposed even in the cold into sulphur and sulphuretted hydrogen, and instantly by a higher temperature, or by contact with many metallic oxides. This compound probably contains twice as much sulphur in relation to the other element as sulphuretted hydrogen.2 • The reaction which ensues when hydrate of lime, sulphur, and water are boiled together is rather complex, bisulphide or pentasulphide of calcium being formed, together with hypo- sulphite of lime, arising from the transfer of the oxygen of the decomposed lime to another portion of sulphur. 2 en lime -f 2 e<1- calclum---------__2 eq. bisulphide of calcium. "*!• \ 2 eq. oxygen ^—-— 1 eq. lime-———-a-s^r^-^^^--^ 4 eq. sulphur--"""3*"11^---■—-_________"-v«^^ 2 eq. sulphur--------------^^ 1 eq. hyposulphite of lime. 3CaO + 6S = 2CaSa + Ca0,S20s Lime. Sulphur. Bisulphide of calcium. ■ The bisulphide of calcium, decomposed by an acid under favorable circumstances, yields a salt of lime and bisulphide (persulphide) of hydrogen. 1 eq. bisulph. S 2 eq. sulphur ---------- ^______■«■ 1 eq. bisulphide of hydrogen. calcium 11 e1- calcium _ , . ( 1 eq. hydrogen 1 eq. water . } x „* 0£ygen Sulphuric acid-------------------^==-. 1 eq. sulphate of lime. CaS2 + HO.SOs = HSa + CaO,SOa Bisulphide of Sulphuric Bisulphide of calcium. acid. hydrogen. When the acid is poured into the sulphide, sulphuretted hydrogen, water, and sulphate of lime are produced, while the excess of sulphur is thrown down as a fine white powder, the "precipitated sulphur" of the Pharmacopoeia. When the object is to prepare the latter sub- stance, hydrochloric acid must be used in the place of sulphuric. SELENIUM, ETC. 185 Hydrogen and Selenium; Selenetled Hydrogen. —This substance is produced by the action of dilute sulphuric acid upon selenide of potassium or iron; it very much resembles sulphuretted hydrogen, being a colorless gas, freely Boluble in water, and decomposing metallic solutions like that substance : in- Boluble selcnides are thus produced. This gas is said to act very powerfully upon the lining membrane of the nose, exciting catarrhal symptoms, and de- stroying the sense of smell. It contains 39-5 parts selenium, and 1 part hydrogen.1 Phosphorus and Hydrogen; Phosphoretted Hydrogen.—This body bears a slight analogy in some of its chemical relations to ammonical gas; its alkaline properties are, however, much weaker. Phosphoretted hydrogen may be obtained in a state of purity by heating in a small retort hydrated phosphorous acid, which is by such treatment decom- posed into phosphoretted hydrogen and hydrated phosphoric acid.2 Thus obtained, the gas has a density of 1-24. It contains 31 parts phos- phorus and 3 parts hydrogen, and is so constituted that every two volumes contain 3 volumes of hydrogen and half a volume of phosphorus vapor, con- densed into two volumes. It possesses a highly disagreeable odor of garlic, is slightly soluble in water, and burns with a brilliant white flame, forming water and phosphoric acid. Phosphoretted hydrogen may also be produced by boiling together in a re- tort of small dimensions caustic potassa or hydrate of lime, water, and phosphorus; the vessel should fte filled to the neck, and the extremity of the latter made to dip into the water of tho pneumatic trough. In the reaction which ensues the water is decomposed, and both its elements combine with the phosphorus. The alkali acts by its presence determining the decomposition of the water in the same manner as sulphuric acid determines the decompo- sition of water when in contact with zinc. Water f Hydrogen \ Oxygen Phosphorus Phosphorus Lime rhosphoretted hydrogen. Hypophosphite of lime.3 The phosphoretted hydrogen prepared by the latter process has the singular property of spontaneous inflammability when admitted into the air or into oxygen gas: with the latter, the experiment is very beautiful, but requires caution: the bubbles should be singly admitted. When kept over water for some time, the gas loses this property, without otherwise suffering any ap- preciable change; but if dried by chloride of calcium, it may be kept un- 1 HSe. a Decomposition of hydrated phosphorous acid by heat :- 4 eq. hydrated phosphorous acid. 4 eq real acid id. (. 12 eq. water. 4(3HO,P03) Hydrated phospho- rous acid. 1 eq. phosph. 3 eq. phosph. 12 eq. oxygen 3 eq. hydrog. 9 eq. hydrog. 3 eq. oxygen 9 eq. oxygen .1 eq. phosphoretted hydrogen, PHs. PHs S 3 eq. phos-' X phoric ac. 9 eq. water + Hydrated phos- phoric acid. 3(3HO,P06) Phosphoretted hydrogen. 3CaO + 3IIO = Hydrated phospho- rous acid. Lime. Water. Phosphoretted hydrogen. 3(CaO,PO) Hypophosphite of lime. 186 NITROGEN WITH CHLORINE AND IODINE. altered for a much longer period. M. Paul The'nard has shown that the spontaneous combustibility of the gas arises from the presence of the vapor of a liquid phosphide of hydrogen, which can be procured in small quantity, by conveying the gas produced by the action of water on phosphide of calcium through a tube cooled by a freezing mixture. This substance forms a color- less liquid of high refractive power and very great volatility. It does not freeze at 0° (-17°-8C). In contact with air it inflames instantly, and its vapor in very small quantity communicates spontaneous inflammability to pure phosphoretted hydrogen, and to all other combustible gases. It is decom- posed by light into gaseous phosphoretted hydrogen, and a solid phosphide which in often seen on the inside of jars containing gas which has lost the property of spontaneous inflammation by exposure to light. Strong acids occasion its instantaneous decomposition. Its instability is equal to that of binoxide of hydrogen. It is to be observed that the pure phosphoretted __ hydrogen gas itself becomes spontaneously inflammable if heated to the tern- "* perature of boiling water.1 Phosphoretted hydrogen decomposes several metallic solutions, giving rise to precipitates of insoluble phosphides. With hydriodic acid it forms a crystal- line compound somewhat resembling sal-ammoniac. Hydrogen and Silicium are likewise capable of combining. According to recent researches of Buff and Wohler, aluminium containing silicium, when used as the positive pole of a galvanic battery, disengages a spontaneously- inflammable gas containing hydrogen and silicium, the composition of which is not yet finally determined. NITROGEN WITH CHLORINE AND IODINE. Chloride of Nitrogen.—When sal-ammoniac or nitrate of ammonia is dissolved in water, and ajar of chlorine gas inverted into the solution, the gas is ab- sorbed, and a deep-yellow oily liquid is observed to collect upon the surface of the solution, which ultimately sinks in globules to the bottom. This is chloride of nitrogen, the most dangerously-explosive substance known. The. following is the safest method of conducting the experiment:— A somewhat dilute and tepid solution of pure sal-ammoniac in distilled water is poured into a clean basin, and a bottle of chlorine, the neck of which is quite free from grease, inverted into it. A shallow and heavy leaden cup is placed beneath the mouth of the bottle to collect the product. When enough has been obtained, the leaden vessel may be withdrawn with its dangerous contents, the chloride remaining covered with a stratum of water. The ope- rator should protect his face with a strong wire-gauze mask when experiment- ing upon this substance. The change is explained by the following diagram:— Chlorine------------------------—^^-Chloride of nitrogen. Chlorine----------------^_^ '~^\^-^ Hydrochloric acid. !( Nitrogen ^—" \ Hydrogen Hydrochloric Acid -------Hydrochloric acid.2 Chloride of nitrogen is very volatile, and its vapor is exceedingly irritating to the eye 3. It has a specific gravity of 1-653. It may be distilled at 160° 1 Ann. Chim. et Phys. 3d series, xiv. 5. According to M. P. Thenard the new liquid phosphide of hydrogen contains PHj and the solid PaH. The gas is represented by the formula PH3. 9 NH4C1 + 6C1 = NCI3 + 4HC1 Chloride of Chlorine. Terchloride of Hydrochloric Ammonium. Nitrogen. acid. OTHER COMPOUNDS OF NON-METALLIC ELEMENTS. 187 (71°-1C), although the experiment is attended with great danger. Between 200° (9:S°-3C) and -12° (100°C) it explodes with the most fearful violence. Contact with almost any combustible matter, as oil or fat of any kind, deter- mines the explosion at common temperatures: a vessel of porcelain, glass, or even of cast-iron, is broken to pieces, and the leaden cup receives a deep indentation. This body has usually been supposed to contain nitrogen and chlorine in the proportion of 14 parts of the former to 106-5 parts ot the latter; but recent experiments upon the corresponding iodine-compound induce a belief that it contains hydrogen.1 Iodide of Nitrogen.—When finely-powdered iodine is put into caustic ammonia it is in part dissolved, giving a deep-brown solution, and the residue is con- verted into a black powder, which is the substance in question, lhe brown. liquid consists of hydriodic acid, holding iodine in solution, and is easily separated from the solid product by a filter. The latter while still wet is dis- tributed in small quantities upon separate pieces of bibulous paper, and left to dry in the air. . Iodide of nitrogen is a black insoluble powder, which, when dry, explodes with tho slightest touch, even that of a feather: and sometimes without any obvious cause. The explosion is not nearly so violent as that of the compound last described, and is attended with-the production of violet fumes of iodine. According to Dr. Gladstone this substance contains hydrogen, and it may be viewed as ammonia, in which two-thirds of the hydrogen are replaced by iodine.2 According to the researches of Bunsen it must be viewed as a com- bination of teriodide of nitrogen with ammonia.3 It appears, however, that the substance called iodide of nitrogen varies in composition. Gladstone, by changing the mode of preparation, obtained several compounds of teriodide of nitrogen with ammonia. OTHER COMPOUNDS OF NON-METALLIC ELEMENTS. Chlorine with Sulphur and Phosphorus. — Chloride of Sulphur. -^The sub- chloride is easily prepared by passing dry chlorine over the surface of sulphur kept melted in a small glass retort connected with a good condensing arrange- ment. The chloride distils over as a deep orange-yellow mobile liquid, of peculiar and disagreeable odor, which boils at 280° (137°-8C). As this sub- stance dissolves both sulphur and chlorine, it is not easy to obtain it in a pure and definite state. It contains 32 parts sulphur and 35.5 chlorine.4 Subchloride of sulphur is instantly decomposed by water; hydrochloric and hyposulphurous acids are formed, and sulphur separated. The hyposulphurous acid in its turn decomposes into sulphur and sulphurous acid. Protochloride of sulphur is formed by exposing the above compound for a considerable time to the action of chlorine, and then distilling it in a stream of the gas. It has a deep-red color, is heavier than water, boils at 147° (63°-9C), and contains twice as much chlorine as the subchloride.5 Chlorides of Phosphorus.—Terchloride.6—This is prepared in the same manner as subchloride of sulphur, by gently heating phosphorus in dry chlorine gas, the phosphorus being in excess. Or, by passing the vapor of phosphorus over fragments of calomel (subchloride of mercury) contained in a glass tube and strongly heated. It is a colorless, thin liquid, which fumes in the air, and possesses a powerful and offensive odor. Its specific gravity is 1 -45. Thrown into water, it sinks to the bottom of that liquid, and becomes slowly decom- posed, yielding phosphorous acid and hydrochloric acid. This compound con- tains 32 parts phosphorus and 106-5 parts chlorine. Pentachloride of Phosphorus.''—The compound is formed when phosphorus is 1 Instead of NCU, it may in reality be NHCla. <• NIHa. 3 NI9 + NH* 'SaCl. »S01. ePCls. 'PClsT 188 OTHER COMPOUNDS OF NOX-METALLIC ELEMENTS. burned in excess of chlorine. Into a large retort, fitted with a cap and stop- cock, pieces of phosphorus are introduced; the retort is then exhausted, and filled with dry chlorine gas. The phosphorus takes fire, and burns with a pale flame, forming a white, volatile crystalline sublimate, which is the penta- chloride. It may be obtained in larger quantity by passing a stream of dry chlorine gas into the preceding liquid terchloride, which becomes gradually converted into a solid crystalline mass. Pentachloride of phosphorus is decom-- posed by water, yielding phosphoric and hydrochloric acids. Oxichloride of Phosphorus.1—If terchloride of phosphorus be heated with a quantity of water which is insufficient to convert it into phosphoric acid, it yields, together with hydrochloric acid, a compound of phosphorus, chlorine, and oxygen. This body may also be prepared by distilling protochloride of phosphorus with dehydrated oxalic acid, or by distilling a mixture of penta- chloride of phosphorus and anhydrous phosphoric acid. Oxichloride of phos- phorus is a colorless liquid of 1-7 sp. gr., possessing a very pungent odor, and boiling at 230° (110°C). By water it is readily decomposed into hydrochloric and phosphoric acids. Two bromides of phosphorus are known, closely corresponding in properties and constitution with the chlorides* Several compounds of iodine and phos- phorus also exist: they are fusible crystalline substances, which decompose by contact with water, and yield hydriodic acid and phosphorus, or phosphoric acid. Chlorine and Carbon.—Several compounds of chlorine and carbon are known. They are obtained indirectly by the action of chlorine upon certain organic compounds, and are described in connection with the history of alcohol, &c. Iodine loith Sulphur and Phosphorus. — These compounds are formed by gently heating together the materials in vessels from which the air is excluded. They present few points of interest. Chlorine icith Iodine.—Iodine readily absorbs chlorine gas, forming, when the chlorine is in excess, a solid yellow compound, and when the iodine pre- ponderates, a brown liquid. The solid iodide is decomposed by water, yielding hydrochloric and iodic acids.2 Another definite compound is formed by heating in a retort a mixture of 1 part iodine and 4 parts chlorate of potassa; oxygen gas and chloride of iodine are disengaged, and the latter may be condensed by suitable means. Iodate and perchlorate of potassa remain in the retort. This chloride of iodine is* a yellow, oily liquid, of suffocating smell and astringent taste; it is soluble in water and alcohol without decomposition. It probably consists of 127 parts iodine and 35-5 parts chlorine.3 Carbon and Sulphur.—Bisulphide of Carbon*—A wide porcelain tube is filled with pieces of charcoal which have been recently heated to redness in a covered crucible, and fixed across a furnace in a slightly-inclined position. Into the lower extremity a tolerably-wide tube is secured by the aid of a cork: this tube bends downwards, and passes nearly to the bottom of a bottle filled with fragments of ice and a little water. The porcelain tube being heated to a bright redness, fragments of sulphur are thrown into the open end, which is immediately afterwards stopped by a cork. The sulphur melts, and becomes converted into vapor, which at that high temperature combines with the carbon, forming an exceedingly volatile compound, which is condensed by the ice and collects at the bottom of the vessel. This is collected and redistilled with a very gentle heat in a retort connected with a good condenser. Bisul- phide of carbon is a transparent, colorless liquid of great refractive and.dis- persive power. Its density is 1-272. It boils at 110° (43°3C), and emits vapor of considerable elasticity at common temperatures. The odor of this 1 PCI3O2. a Hence it doubtless contains 1 eq. iodine, and 5 eq. chlorine, or ICU. 3 Or single equivalents. 4 CSa. OTHER COMPOUNDS OF NON-METALLIC ELEMENTS. substance is very repulsive. When set on fire in the air it burns with a blue flame, forming carbonic acid and sulphurous acid gases; and when its vapor is mixed with oxygen, it becomes explosive. Bisulphide of carbon, when heated with water in a sealed tube to about 302° (150°C), is converted into carbonic acid and sulphuretted hydrogen. In contact with nascent hydrogen (when heated with zinc and dilute sulphuric acid), it is converted into a white crystalline substance containing carbon, hydrogen, and sulphur,1 crystallizing in square prisms, insoluble in water, alcohol, and ether, but soluble in bisul- phide of carbon, subliming at 302° (150°C), and decomposing at 392° (200°L). Bisulphide of carbon freely dissolves sulphur, and by spontaneous evaporation deposits the latter in beautiful crystals; it also dissolves phosphorus. Pn.h.mlphide of Carbon. — This body has been recently discovered by Baudrimont. It is formed together with the bisulphide, if, in the preparation Mot the latter, the carbon predominates. It is also produced when the vapor ^ of bisulphide of carbon meets with hydrogen at a red heat, as when carbonic oxide and sulphuretted hydrogen are passed together through a red-hot tube. Protosulphide of carbon is a gas of an odor similar to that of the bisulphide: it burns with a blue flame. Water dissolves its own volume of protosulphide of carbon, which is, however, gradually decomposed into sulphuretted hydrogen and carbonic oxide. Chlorides of Silicium and Boron. — Both silicium and boron combine directly with chlorine. The chloride of silicium is obtained by mixing finely-divided silica with charcoal powder and oil, strongly heating the mixture in a covered crucible, and then exposing the mass so obtained in a porcelain tube, heated to full redness, to the action of perfectly dry chlorine gas. A good condensing arrangement, supplied with ice-cold water, must be connected with the por- celain tube. The product is a colorless and very volatile liquid, boiling at 122° (50°C), of pungent, suffocating odor. In contact with water it yields hydrochloric acid and gelatinous silica. This substance contains 21-3 parts Bilicium, and 106-5 chlorine.2 Bromide of Silicium3 may be obtained by a similar proceeding, the vapor of bromine being substituted for chlorine: it resembles the chloride, but is less volatile. Chloride of Boron* was formerly believed to be a permanent gas: recent researches have proved that it is a liquid, boiling at 62-6° (17°C), decomposed by water, with production of boracic and hydrochloric acids, and fuming strongly in the air. It may be most easily obtained by exposing to the action of dry chlorine at a very high temperature an intimate mixture of glassy boracic acid and charcoal. It resembles in constitution chloride of silicium. Bromide of boron5 likewise exists. Sulphides of Silicium and Boron. — Fremy has formed sulphide of silicium6 and sulphide of boron' by passing the vapor of bisulphide of carbon over strongly-heated pellets of lamp-black and precipitated silica in the one case; or in the other, of boracic acid with charcoal. The sulphide of silicium forms long silky needles soluble in water, with rapid evolution of sulphuretted hydrogen. The sulphide of boron is also occasionally obtained in crystals. •CallaSa. SiCl3. »SiBrs. «BoCls. i BoBr3. • Si Ss. 'Bo S3. 190 GENERAL 1RINCIPLES OF ON THE GENERAL PRINCIPLES OF CHEMICAL PHILOSOPHY. The study of the non-metallic elements can be pushed to a very considerable extent, and a large amount of precise and exceedingly important information acquired, without much direct reference to the great fundamental laws of chemical union. The subject cannot be discussed in this manner completely^ as will be obvious from frequent cases of anticipation in many of the foregoing foot-notes: still much may be done by this simple method of proceeding. The bodies themselves, in their combinations, furnish admirable illustrations of the general laws referred to; but the study of their leading characters and relations does not of necessity involve a previous knowledge of these laws themselves. It is thought that by such an arrangement the comprehension of these very important general principles may become, in some measure, facilitated by constant references to examples of combinations, the elements and products of which have been already described. So much more difficult is it to gain a clear and distinct idea of any proposition of great generality from a simple enunciation, than to understand the bearing of the same law when illustrated by a single good and familiar instance. Before proceeding farther, however, it is absolutely necessary that these matters should be discussed: the metallic compounds are so numerous and complicated, that the establishment of some general principle, some connecting link, becomes indispensable. The doctrine of equivalents, and the laws which regulate the formation of saline compounds, supply this deficiency. In the organic department of the science, the most interesting perhaps of all, a knowledge of these principles, and farther, an acquaintance or even familiarity with the beautiful system of chemical notation now in use, are absolutely required. This latter is found of very great service in the study of salts and other complex inorganic compounds, but in that of organic chemistry it cannot be dispensed with. It will be proper to commence with a notice of the principles which regulate the modern nomenclature in use in chemical writings. NOMENCLATURE. In the early days of chemistry the arbitrary and fanciful names which were conferred by each experimenter on the new compounds he discovered sufficed to distinguish these from each other, and to render intelligible the description given of their production. Such terms as oil of vitriol, spirit of salt, oil of tartar, butter of antimony, sugar of lead, flowers of zinc, sal enixum, sal mirabile, &c, were then quite admissible. In process of time, however, when the number of known substances became vastly increased, the confusion of lan- guage produced by the want of a more systematic kind of nomenclature became quite intolerable, and the evil was still further increased by the frequent use of numerous synonyms to designate the same substance. In the year 1787 Lavoisier and his colleagues published the plan of the remarkable system of nomenclature, which, with some important extensions since rendered necessary, has up to the present time to a great extent satisfied the wants of the science. It is in organic chemistry that the deficiencies of CHEMICAL PHILOSOPHY. 191 this plan are chiefly felt, and that something like a return to the old method has been rendered inevitable. Organic chemistry is an entirely new science, which has sprung up since the death of these eminent men, and has to deal with bodies of a constitution or type differing completely from that of the inorganic acids, bases, and salts, which formed the subjects of the chemical studies of that period. The rapid progress of discovery by which new com- pounds, and new classes of compounds, often of the most unexpected nature, are continually brought to light, sufficiently proves that the time to attempt the construction of a permanent systematic plan of naming organic bodies has not yet arrived. The principle of the nomenclature in use may be thus explained: — Ele- mentary substances still receive arbitrary names, generally, but not always, .deferring to some marked peculiarity of the body; a uniformity in the ter- /mination of the word has generalhy been observed, as in the cast of new metals whose names are made to end in turn. Compounds formed by the union of non-metallic elements with metals, or with other non-metallic elements, are collected into groups having a kind of generic name derived from the non-metallic element, or that most opposed in characters to a metal, and made to terminate in ide.1 Thus we have oxides, chlorides, iodides, bromides, &c, of hydrogen and of the several metals; oxides of chlorine; chlorides of iodine and sulphur; sulphides and phosphides of hydrogen and the metals. The nomenclature of oxides has been already described (p. 126). They are divided into three classes, namely, alkaline or basic oxides, neutral oxides, and oxides possessing acid characters. In practice the term oxide is usually restricted to bodies belonging to the first two groups, those of the third being simply called acids. Generally speaking these acids are derived from the non-metallic elements which yield no basic oxides: many of the metals, how- ever, yield acids of a more or less energetic description. The same element in combining with oxygen in more than one proportion may yield more than one acid: in this case it has been usual to apply to the acid containing most oxygen the termination ic, and to the one containing tho lesser quantity the termination ous. When more members of the same group came to be known, recourse was had to a prefix, hypo or hyper, (or per,) signifying deficiency or excess. Thus, the two earliest-known acids of sulphui wero named respectively sulphurous and sulphuric acid; subsequently two more were discovered, the one containing less oxygen than sulphurous acid, the other intermediate in composition between sulphurous and sulphuric acids. These were called hyposulphurous and hyposulphuric acids The names of the new acids of sulphur of still more recent discovery are not yet perma- nently fixed ; Lavoisier's system, even in its extended form, fails to furnish names for such a lengthened series. Other examples of the nomenclature of acids with increasing proportions of oxygen are easily found; as, hypophos- phorous, phosphorous, and phosphoric acids ; hypochlorous, chlorous, hypochloric, chloric, and perchloric acid-; nitrous, hyponitric, and nitric acids, &c. The nomenclature of salts is derived from that of the acid they contain; if the name of the acid terminate in ic, that of the salt is made to end in ate; if in ous, that of the saline compound ends in ite Thus sulphuric acid forms sulphates of the various bases; sulphurous acid, sulphites; hyposulphurous acid, hyposulphites; hyposulphuric acid, hyposulphates, &c. The rule is here very simple and obvious. The want of uniformity in the application of the systematic nomenclature is chiefly felt in the class of oxides not possessing acid characters, and in that of some analogous compounds. The old rule was to apply the word protoxide to the oxide containing least oxygen, to call the next in order binoxide, the 1 Formerly the termination urei was likewise frequently used. 192 GENERAL PRINCIPLES OF third tritoxide or teroxide, &c. But latterly this rule has been broken through, and the term protoxide given to that oxide of a series in which the basio characters are most strongly marked. Any compound containing a smaller proportion of oxygen than this is called a suboxide. An example is to be found in the two oxides of copper; that which was once called-binoxide is now prot- oxide, being the more basic of the two, while the former protoxide is degraded into suboxide. The Latin prefix per, or rarely hyper, is sometimes used to indicate the highest oxide of a series destitute of acidity, as peroxide of iron, chromium, manganese, lead, &c. Other Latin prefixes, as sesqui, bi or bin, and quad, applied to the names of binary compounds or salts have reference to the con- stitution of these latter expressed in chemical equivalents.1 Thus, an oxide in which the proportion of oxygen and metal are in equivalents, as 1-5 to 1^ or 3 to 2, is often called a sesquioxide; if in the proportion of 2 to 1, a bin-" oxide, &c. The same terms are applied to salts: thus we have neutral sul- phate of potassa, sesquisulphale of potassa, and bisulphate of potassa; the first containing 1 equivalent of acid to 1 of base, the second 1 -5 of acid to 1 of base, and the third 2 equivalents of acid to 1 equivalent of base. In like manner we have neutral oxalate, binoxalate, and quadroxalate of potassa, the latter having 4 eq. of acid to 1 eq. of base. Many other cases might be cited. The student will soon discover that the rules of nomenclature are often loosely applied, as when a Latin numeral prefix is substituted for one of Greek origin. We speak of tersulphide instead of tritosulphide of antimony, and quinquisulphide instead of pentasulphide of antimony. These and other small irregularities are not found in practice to cause serious confusion. THE LAWS OF COMBINATION BY WEIGHT. The great general laws which regulate all chemical combinations admit of being laid down in a manner at once simple and concise. They are four in number, and to the following effect: 1. All chemical compounds are definite in their nature, the ratio of the elements being constant. 2. When any body is capable of uniting with a second in several propor- tions, these proportions bear a simple relation to each other. 3. If a body, A, unite with other bodies, B, C, D, the quantities of B, C, D, which unite with A, represent the relations in which they unite among themselves, in the event of union taking place. 4. The combining quantity of a compound is the sum of the combining quantities of its components. (1.) Constancy of Composition.—That the same chemical compound invariably contains the same elements united in unvarying proportions, is a proposition almost axiomatic; it is involved in the very idea of identity itself. The con- verse, however, is very far from being true; the same elements combining in the same proportions do not of necessity generate the same substance. Organic chemistry furnishes numerous instances of this very remarkable fact, in which the greatest diversity of properties is associated with identity of chemical composition. These cases are chiefly met with in organic chem- istry ; but well-established and undoubted examples are known in the inor- ganic or mineral division of the science. 1 See a few pages forward. CHEMICAL PHILOSOPHY. 193 (2.) Multiple Proportions. — Illustrations of this simple and beautiful law abound on every side: let the reader take for example the compounds of nitro- gen and oxygen, five in number, containing the proportions of the two ele- ments so described that the quantity of one of them shall remain constant: Nitrogen. Oxygen Protoxide . .....14 8 Binoxide .....14 16 Nitrous acid .....14 24 Hyponitric acid . - .....14 32 Nitric acid . .....14 40 uU'O 8 35-5 24 35-5 32 35-5 40 35-5 56 It will be seen at a glance, that while the nitrogen remains the same, the quantities of oxygen increase by multiples of 8, or the number representing the quantity of that substance in the first compound; thus, 8, 8 X 2, 8 x 3, 8 X 1, and 8x5, give respectively the oxygen in the protoxide, the binoxide, nitrous acid, hyponitric acid, and lastly, nitric acid. Again, carbonic acid contains exactly twice as much oxygen in proportion to the other constituent as carbonic oxide; the binoxide of hydrogen is twice as rich in oxygen as water; the corresponding sulphides exhibit the same phenomena, while the metallic compounds offer one continued series of illustrations of the law, although the ratio is not always so simple as that of 1 to 2. It often happens that one or more members of a series are yet deficient: the oxides of chlorine afford an example. Chlorine. Oxygen. Hypochlorous acid Chlorous acid . Hypochloric acid Chloric acid Perchloric acid Here the quantities of oxygen progress in the following order: —8, 8 X •', 8 X -1' 8 X 5, 8 X 7; gaps are manifest between the first and second, and also between the fourth and fifth substances; these remain to be filled up by future researches. The existence of a simple relation among the numbers in tho second column is, however, not the less evident. Even when difficulties seem to occur in applying this principle, they are only apparent, and vanish when closely examined. In the highly-complex sulphur series, given at p. 150, the numbers placed in each column are multiples of the lowest among them; and, by making the assumption, which is not at all extravagant, that certain of the last-named bodies are intermediate combinations, we may arrange the four direct compounds in such a manner that the sulphur shall remain a constant quantity. Hyposulphurous acid Sulphurous acid . Hyposulphuric acid Sulphuric acid Compound bodies of all kinds are also subject to the law of multiples when they unite among themselves, or with elementary substances. There are two sulphates of potassa and soda: the second contains twice as much acid in relation to the alkaline base as the first. There are three oxalates of potassa, namely, the simple oxalate, the binoxalate, and the quadroxalate; the second has equally twice as much acid as the first; and the third twice as much as 17 lphur. Oxygen. 32. 10 32 32 32 40 32 48 194 GENERAL PRINCIPLES OF the second. Many other cases might be cited, but the student, once in pos- session of the principle, will easily notice them as he proceeds. (3.) Law of Equivalents.—It is liighly important that the subject now to be discussed should be completely understood. Let a substance be chosen whose range of affinity and powers of combina- tion are very great, and whose compounds are susceptible of rigid and exact analysis; such a body is found in oxygen, which is known to unite with all the elementary substances, with the single exception of fluorine. Now, let a series of exact experiments be made to determine the proportions in which the different elements combine with one and the same constant quantity of oxygen, which, for reasons hereafter to be explained, may be assumed to be 8 parts by weight; and let these numbers be arranged in a column opposite the names of the substances. The result is a table or list like the following, but of course much more extensive when complete. \ Oxygen ....... 8 Hydrogen . . . . 1 Nitrogen . 14 Carbon . 6 Sulphur . 16 Phosphorus 31 Chlorine 35-5 Iodine. ... 127 Potassium ... 39 Iron . ... 28 Copper 31-7 Lead . 103-7 Silver. • . . • 108 &c, &( Now the law in question is to this effect: — If such numbers represent the proportions in which the different elements combine with the arbitrarily fixed quantity of the starting-substance, the oxygen, they also represent the pro- portions in which they unite among themselves, or at any rate bear some exceed- ingly simple ratio to these proportions. Thus, hydrogen and chlorine combine invariably in the proportions 1 and 35-5; hydrogen and sulphur, 1 to 16; chlorine and silver, 35-5 to 108; iodine and potassium, 127 parts of the former to 39 of the latter, &c. This rule is never departed from in any one instance. The term equivalent is applied to these numbers for a reason which will now be perfectly intelligible; they represent quantities capable of exactly replacing each other in combination: 1 part of hydrogen goes as far in combining with or saturating a certain amount of oxygen as 28 parts of iron, 39 of potassium or 108 of silver; for the same reasons, the numbers are said to represent combining quantities, or proportionals. Nothing is more common than to speak of so many equivalents of this or that substance being united to one or more equivalents of a second; by this expression, quantities are meant just so many times greater than these relative numbers. Thus, sulphuric acid is said to contain 1 equivalent of sulphur, and 3 equivalents of oxygen; that is, a quantity of the latter represented by three times the combining number of oxygen; phosphoric acid is made up of 1 equivalent of phosphorus and 5 of oxygen; the red oxide of iron contains, as will be seen hereafter, 3 equivalents of oxygen to every 2 equivalents' of metal, &c. It is an expression which will henceforward be freely and con- stantly employed; it is hoped, therefore, that it will be understood. CHEMICAL PHILOSOPHY. 195 The nature of the law will easily show that the choice of the body destined to serve for a point of departure is perfectly arbitrary, and regulated by considerations of convenience alone. A body might be chos u which refuses to unite with a considerable number of the elements, and yet the equivalents of the latter would admit of being determined by indirect means, in virtue of the very peculiar law under dis- cussion. Oxygen does not unite with fluorine, yet the equivalent of the latter can be found by observing the quantity which combines with the equivalent quantity of hydrogen or calcium, already known. We may rest assured that if an oxide of fluorine be ever discovered, its elements will be associated m the ratio of 8 to 19, or in numbers which are either multiples or submultiples of these. Tho number assigned to the starting-substance is also equally arbitrary: if, in the table given, oxygen instead of 8 were made 10, or 100, or even a fractional number, it is quite obvious that although the other numbers would all bo different, the ratio, or proportion among the whole, would remain unchanged, and the law would still be maintained in all its integrity. There are, in fact, two such tables in use among chemists; one in which oxygen is made = 8, and a second in which it is made = 100; the former is generally used in this country, and the latter still to a certain extent on the Continent. The only reason for giving, as in the present volume, a preference to the first is, that the numbers are smaller and more easily remembered. The number 8 has "been chosen in this table to represent oxygen, from an opinion long held by the late Dr. Prout, and recently to appearance substan- tiated in some remarkable instances by very elaborate investigation, that the equivalents of all bodies are multiples of that of hydrogen; and consequently, by making the latter unity, the numbers would be all integers. The question must be considered as altogether unsettled. A great obstacle to such a view is presented by the case of chlorine, which certainly seems to be a fractional number; and one single well-established exception will be fatal to the hypothesis. As all experimental investigations are attended with a certain amount of error, the results contained in the following table must be looked upon merely as good approximations to the truth. For the same reason, small differences are often observed in the determination of the equivalents of the same bodies by different experimenters. TABLE OF ELEMENTARY SUBSTANCES, WITH THEIR EQUIVALENTS. Aluminium Antimony . Arsenic . . Barium . . Beryllium . Bismuth . . Boron . . . Bromine . . Padmiuni . Calcium . . Carbon . . Cerium . . Chlorine . . Chromium . Cobalt. . . Copper. . . Oxy. = 8 Oxy. = 100. Oxy. - 8. Oxy. = 100. . 13-7 171-25 Didymium . . 48 600 120-3 1503-7 Erbium 75 937-5 Fluorine. . . 19 237-5 68-5 856-25 Gold..... 197 2402-5 141 170-25 Hydrogen . . 1 12-5 208 2600 Iodine .... 127 1587-5 10-9 136-25 Iridium . . . 99 1237-5 80 1000 28 350 . 5G . ■ 700 Lanthanum . 47 587-5 20 • 250 103-7 1296-2-". 6 75 Lithium . . . 6-95 86-87 47 587-5 Magnesium . 12 150 Co-5 443-75 Manganese . 27-6 345 26-7 333-75 Mercury. . . 100 1250 29-5 368-75 Molybdenum 46 375 31-7 396-25 Nickel .... 29-6 370 196 GENERAL PRINCIPLES OF TABLE OF ELEMENTARY SUBSTANCES, WITH THEIR EQUIVALENTS-- Continued. Oxy. = 8. Oxy. = 100. Oxy. = 8. Oxy. — 100. Niobium Strontium . . 43-8 547-5 Nitrogen. . . 14 175 Sulphur . . 16 200 Norium Tantalum . . 184 2300 Osmium . . 99-6 1245 Tellurium . . 64-2 800 Oxygen . . 8 100 Terbium Palladium . 53-3 666-25 Thorium . . . 59-6 745 Phosphorus 31 387-5 Tin ... 58 725 Platinum . 98-7 1233-75 Titanium . . 25 312-5 Potassium . 39 4S7-5 Tungsten . . 92 1150 Rhodium . 52-2 652-5 Uranium. : . 60 750 Ruthenium 52-2 652-5 Vanadium . . 68-6 857-5 Selenium. . 39-5 493-75 Yttrium Silicium . . 21-3 266-25 Zinc . . . . • 32-6 407-5 Silver . . . 108 1350 Zirconium . . 33-6 420 Sodium . . 23 287-5 1 (4.) Combining Numbers of Compounds. — The law states that the equivalent or combining number of a compound is always the sum of the equivalents of • its components. This is also a great fundamental truth, which it is necessary to place in a clear and conspicuous light. It is a separate and independent law, established by direct experimental evidence, and not deducible from either of the preceding. The method of investigation by which the equivalent of a simple body is determined has been already explained ; that employed in the case of a com- pound is in nowise different. The example of the acids and alkalhj may be taken as the most explicit, and at the same time most important. An acid and a base, combined in certain definite proportions, neutralize, or mask each other's properties completely, and the result is a salt; these proportions are called the equivalents of the bodies, and they are very variable. Some acids have very high capacities of saturation, of others a much larger quantity must be employed to neutralize the same amount of base; the bases them- selves present also similar phenomena. Thus, to saturate 47 parts of potassa, or 116 parts of oxide of silver, there are required — 40 parts sulphuric acid, 54 " nitric acid, 75-5 " chloric acid, 167 " iodic acid, 51 " acetic acid. Numbers very different, but representing quantities which replace each other in combination. Now, if a quantity of some base, such as potassa, be taken, which is represented by the sum of the equivalents of potassium and oxygen, then the quantity of any acid requisite for its neutralization, as determined by direct experiment, will always be found equal to the sum of the equivalents of the different components of the acid itself. 39 = equivalent of potassium. 8 = " oxygen. 47 = assumed equivalent of potassa, CHEMICAL PHILOSOPHY. 197 47 parts of potassa are found to be exactly neutralized by 40 parts of real sulphuric acid, or of 54 parts of real nitric acid. These quantities are evidently made up by adding together the equivalents of their constituents:— 1 equivalent of sulphur =-16 1 equivalent of nitrogen = 14 3 " oxygen =24 5 " oxygen = 40 1 " sulphuric acid =-. 40 1 " nitric acid =■ 54 And the same is true if any acid be taken, and the quantities of different bases required for its neutralization determined; the combining number of the compound will always be found to be the sum of the combining numbers of its components, however complex the substance may be. Even among Buch bodies as the vegeto-alkalis of organic chemistry, the same universal rule holds good. When salts combine, which is a thing of very common occurrence, as will hereafter be seen, it is always in the ratio of the equivalent numbers. Apart from hypothetical considerations, no & priori reason can bo shown why such should be the case: it is, as before remarked, an independent law, established like the rest by experiment. A curious observation was very early made to this effect: — If two neutral salts which decompose each other when mixed, be brought in contact, the new compounds resulting from their mutual decomposition will also be neutral. For example, when solution of nitrate of baryta and sulphate of potassa are mingled, they both suffer decomposition, sulphate of baryta and nitrate of potassa being simultaneously formed, both of which are perfectly neutral. The reason of this will be at once evident; interchange of elements can only take place by the displacement of equivalent quantities of matter on either side. For every 51 parts of nitric acid set free by the decomposition of the baryta salt, 17 parts of potassa are abandoned by the 40 parts of sul- phuric Acid with which they were previously in combination, now transferred to the baryta. But 54 and 47 arc the representatives of combining quantities; licuce the new compound must be neutral. COMBINATION BY VOLUME. _ Many years ago M. Gay-Lussac made the very important and interesting discovery that when gases combine chemically union invariably takes place either between equal Volumes, or between volumes which bear a simple rela- tion to each other. This is not only true of elementary gases, but of compound bodies of this description, as it is invariably observed that the contraction of bulk which so frequently follows combination itself also bears a simple relation to tho volumes of the combining gases. The consequence of this is that compound gases and the vapors of complex, volatile liquids (which are truly gases to all intents and purposes) fullow the same law as elementary bodies when they unite with these latter or combine among themselves. The ultimate reason of the law in question is to be found in the very remarkable relation established by the hand of Nature between the specific. gravity of a body in the gaseous state and its chemical equivalent;—a relation of such a kind that quantities by weight of the various gases expressed by their equivalents, or in other words quantities by weight which combine, occupy under similar circumstances of pressure and temperature either equal volumes or volumes bearing a simple proportion to each other. In the example cited below, equivalent weights of hydrogen, chlorine, and iodine- vap n- occupy equal volumes, while the equivalent of oxygen occupies exactly half that measure. 17* 198 . GENERAL PRINCIPLES OF Cubic inches. 8-0 grains of oxygen occupy at 60° (15°-5C) and 30 in. barom. . 23.3 1-0 grain of hydrogen ...•••••• 4b*7 35-5 grains of chlorine ....■••••• ~. " 127-0 grains of iodine-vapor (would measure).....46'' If both the specific gravity and the chemical equivalent of a gas be known, its equivalent or combining volume can be easily determined, since it will be represented by the number of times the weight of an unit of volume (the specific gravity) is contained in the weight of one chemical equivalent of the substance. In other words, the equivalent volume is found by dividing the chemical equivalent by the specific gravity. The following table exhibits the relations of specific gravity, equivalent weight, and equivalent volume of the principal elementary substances:— Hydrogen Nitrogen Chlorine Bromine-vapor Iodine-vapor . Carbon-vapor1 Mercury-vapor Oxygen . Phosphorus-vapor Arsenic-vapor Sulphur-vapor Thus it appears that hydrogen, nitrogen, chlorine, bromine, iodine, carbon, and mercury, in the gaseous state, have the same equivalent volume; oxygen, phosphorus, and arsenic, one-half of this; and sulphur one-sixth. The slight discrepancies in the numbers in the third column result chiefly from errors in the determination of the specific gravities. Compound bodies exhibit exactly similar results: — Sp. gravity. Equiv. weight. Equiv. volume. . 1-0 . 14-43 or 1 0-972 . 14-0 . 14-37 " 1 • 2-470 . 35-5 . 14-33 " 1 5-395 80-0 . 14-82 « 1 8-716 . 127-0 . 14-57 " 1 0-418 . 6-0 . 14-34 " 1 7-000 . 100-0 . 14-29 " 1 1-106 . 8-0 . 7-23 " $ 4-350 . 320 . ■ ■ 7-35 « \ 10-420 . 750 . 7-19 « i 6-654 . 160 . 2-40 " \ Water vapor Protoxide of nitrogen . Sulphuretted hydrogen Sulphurous acid . Carbonic oxide Carbonic acid Light carbonetted hydrogen Olefiant gas Binoxide of nitrogen . Hydrochloric acid Phosphoretted hydrogen Ammonia . Ether-vapor. Acetone-vapor Benzol-vapor Alcohol-vapor Sp. gravity. 0-625 1-525 , 1-171 . , 2-210 , . 0-973 1-524 . 0-559 . 0-981 , 1-039 . 1-269 . 1-240 . 0-589 . 2-586 . 2-022 . . 2-738 1-613 , Equiv. weight. 9-0 . 220 . 17-0 . 320 . 14-0 . 22-3 . 8-0 . 14-0 . 30-0 . 36-5 . 350 . 17-0 . 37-0 . 29-0 . 780 . 46-0 . In the preceding tables the ordinary standard of specific gravity for gases atmospheric air, has been taken. It is, however, a matter of pei Equiv. volume. 14-40 or 1 14-43 14-51 14-52 14-39 14-43 14-31 14-27 28-87 28-70 28-22 28-86 14-31 14-34 28-49 28-52 feet indiffer- ence what substance be chosen for this purpose; the numbers representing 1 See farther on. CHEMICAL P III L 0 S O P H Y. 199 the combining volumes will change with the divisor, but the proportions they bear to each other will remain unaltered. And the same remark applies to the equivalent weights; either of the scales in use maybe taken, provided that it be adhered to throughout. The law of volumes often serves in practice to check and corroborate the results of experimental investigation, and is often of great service in this respect. There is an expression sometimes made use of in chemical writings which it is necessary to explain, namely, the meaning of the words hi/pothelicai density of vapor, applied to a substance which has never been volatilized, such as carbon, whose real specific gravity in that state must of course be unknown. It is easy to understand the origin of this term. Carbonic acid contains a volume of oxygen equal to its own; consequently, if the specific gravity of the latter be subtracted from that of the former gas, the residue will express the proportion borne by the weight of the carbon, certainly then in a vaporous state, to that of the two gases. The specific gravity of carbonic acid is 1-5240 That of oxygen is ...... 11057 0-4183 On the supposition that carbonic acid contains equal volumes of oxygen and this vapor of carbon, condensed to one-half, the latter will have the specific gravity represented by 0-4183 and the combining volume given in the table. But this is merely a supposition, a guess; no proof can be given that carbonic acid gas is so constituted. All that can be safely said is contained in the prediction, that, should the specific gravity of the vapor of carbon ever bo determined, it will be found to coincide with this number, or to bear some simple and obvious relation to it. For many years past attempts have been made to extend to solids and liquids the results of Gay-Lussac's discovery of the law of gaseous combination by volume, the combining or equivalent volumes of the bodies in question being determined by the method pursued in the case of gases, namely, by dividing the chemical equivalent by the specific gravity. The numbers ob- tained in this manner representing the combining volumes of the various solid and liquid elementary substances, present far more cases of discrepancy than of agreement. The latter are, however, sufficiently numerous to excite great interest in the investigation. Some of the results pointed out. are exceedingly curious as far as they go, but are not as yet sufficient to justify any general conclusion. Tho inquiry is beset with many great difficulties, chiefly arising from the unequal expansion of solids and liquids by heat, and the great differences of physical state, and consequently of specific gravity, often pre- sented by the former. Such is a brief account of the great laws by which chemical combinations, of every kind, are governed and regulated; and it cannot be too often repeated, that the discovery of these beautiful laws has been the result of pure experi- mental inquiry. They have been established on this firm and stable founda- tion by the joint labors of very many illustrious men ; they are the expression of fact, and are totally independent of all hypothesis or theories whatsoever. CHEMICAL NOTATION; SYMBOLS. For convenience in communicating ideas respecting the composition and supposed constitution of chemical compounds, and explaining in a clear and simple manner the results of changes they may happen to undergo, recourse 200 GENERAL PRINCIPLES OF is had to a kind of written symbolical language, the principle of which must now be explained. To represent compounds by symbols is no novelty, as the works of the Alchemists will show, but these have been mere arbitrary marks or characters invented for the sake of brevity, or sometimes perhaps for that of obscurity. The plan about to be described is due to Berzclius : it has been adopted, with slight modifications, wherever chemistry is pursued. Every elementary substance is designated by the first letter of its Latin name, in capital, or by the first letter conjoined with a second small one, the most characteristic in the word, as the names of many bodies begin alike. The single letter is usually confined to the earliest discovered, or most import- ant elements. Farther, by a most ingenious idea, the symbol is made to repre- sent not the substance in the abstract, but one equivalent of that substance. Table of Symbols of the Elementary Bodies Aluminium . Al Antimony (Stibium). Arsenic . . Sb . As Barium . . Ba Beryllium Bismuth . . Be . Bi Boron . Bo Bromine . . Br Cadmium. . Cd Calcium . . Ca Carbon . . C Cerium . Ce Chlorine . . CI Chromium . Cr Cobalt . . Co Copper(Cuprum) Didymium Erbium . . Cu • • Dy . Er Fluorine . . F Gold (Aurum) . Hydrogen Iodine . Au . H . I Iridium . . Ir Iron (Ferrum) . . Fe Lantanum . Ln Lead (Plumbum) Lithium . . Pb . L Magnesium . Mg Manganese . Mn Mercury (Hydrargyrum) Molybdenum . • Hg . Mo Combination between b )dies in the mere juxtaposition of the symbols, or Nickel . . Ni Niobium . Nb Nitrogen . N Norium . No Osmium . Os Oxygen . 0 Palladium . . Pd Phosphorus . . P Platinum . Pt Potassium (Kalium) . K Rhodium . R Ruthenium . . Ru Selenium . Se Silicium . Si Silver (Argcntum) • Ag Sodium (Natrium) . Na Strontium . . Sr Sulphur . S Tantalum . Ta Tellurium . Te Terbium . Tb Thorium . Th Tin (Stannum) . Sn Titanium . Ti Tungsten (Wolframiumj . W Vanadium . . V Uranium . U Yttrium . Y Zinc . Zn Zirconium . . Zr cumcB "y interposing the sign of addition. For example:— b Water . . . HO, or II + 0 Hydrochloric acid HC1, or II -f- CI Protoxide of iron FeO, or Fe -f- 0 When more than one equivalent is intended, a suitable number is addpd sometimes being placed before the symbol, like a coefficient in algebra, somel CHEMICAL PHILOSOPHY. 201 times appended after the manner of an exponent, but more commonly placed a little below on the right. P.innxide of hydrogen......II-f-20, or HO2, or H02 Sulphuric acid........S+30, or SO3, or S03 Hyposulphuric acid......2S-4-50, or S205, or S205 Combination between bodies themselves compound is indicated by the sign of addition, or by a comma. When both are used in the same formula, the latter may be very conveniently'applied, as Professor Graham has suggested, to indicate the closest and most intimate union. A number standing before symbols, enclosed within a bracket, signifies that the whole of the latter are to be multiplied by that number. Occasionally the bracket is omitted, when the number affects all the symbols between itself and the next sign. A few examples will serve to illustrate these several points. Sulphate of soda.......NaO+S03, or NaO, S03 Nitrate of potassa.......KO-f N05, or KO, N05 The base being always placed first. Double sulphate of copper and potassa. . . CuO,S034-KO,S03 The same in a crystallized state.....CuO,S03-r-K:0,SOa4-6HO Common crystallized alum, or double sulphate of alumina and potassa, is thus written: — A1203, 3S03+KO, S03+24HO. In expressing organic compounds, where three or more elements exist, the Bame plan is used. Sugar...........^.^,,0,, Alcohol..........Cyi6()2 Acetic acid.........HO,C4 IT3 03 Morphine..........C^H^NOg Acetate of morphine......CWIT19N06, HO, C4H303 Acetate of soda........NaO, C4H303 By such a system, the eye is enabled to embrace the whole at a glance, and gain a distinct idea of the composition of the body, and its relations to others similarly described. Some autnors are in the habit of making use of contractions, which, how- ever, are by no means generally adopted. Thus, two equivalents of a sub- stance arc indicated by the symbol with a short line drawn through or below it; an equivalent'of oxygen is signified by a dot, and one of sulphur by a comma. These alterations are sometimes convenient for abbreviating a long formula, but easily liable to mistakes. Thus, Sesquioxide of iron F 0-\ or FO3, or Fe, instead of Fe203 Bisulphide of Carbon C, instead of CS2 Crystallized alum as before Al S3, K S+24H. 202 GENERAL PRINCIPLES OF THE ATOMIC THEORY. That no attempt should have been made to explain the reason of the very remarkable manner in which combination occurs in the production of chemi- cal compounds, and to point out the nature of the relations between the different modifications of matter which fix and determine these peculiar and definite changes, would have been unlikely, and in contradiction to the specu- lative tendency of the human mind. Such an attempt, and a very successful and ingenious one it is, has been made, namely, the atomic hypothesis of Dr. Dalton. From very ancient times, the question of the constitution of matter with respect to divisibility has been debated, some adopting the opinion that this divisibility is infinite, and others, that when the particles become reduced to a certain degree of tenuity, far indeed beyond any sfate that can be reached by mechanical means, they cease to be farther diminished in magnitude ; they become, in short, atoms.1 Now, however the imagination may succeed in figuring to itself the condition of matter on either view, it is hardly necessary to mention that we have absolutely no means at our disposal for deciding such a question, which remains at the present day in the same state as when it first engaged the attention of the Greek philosophers, or perhaps that of the sages of Egypt and Hindostan long before them. Dr. Dalton's hypothesis sets out by assuming the existence of such atoms or indivisible particles, and states, that compounds are formed by the union of atoms of different bodies one to one, one to two, &c. The compound atom joins itself in the same manner to a compound atom of another kind, and a combination of the second order results. Let it be granted, farther, that the relative weights of the atoms are in the proportions of the equivalent num- bers, and the hypothesis becomes capable of rendering consistent and satis- factory reasons for all the consequences of those beautiful laws of combina- tion lately discussed. Chemical compounds must always be definite; they must always contain the same number of atoms, of the same kind, arranged in a similar manner. The same kind and number of atoms need not, however, of necessity produce the same substance, for they may be differently arranged; and much depends upon this circumstance. Again, the law of multiple proportions is perfectly well explained; an atom of nitrogen unites with one of oxygen to form laughing gas; with two, to form binoxide of nitrogen; with three, to produce nitrous acid; with four, hyponitric acid; and with five', nitric acid, — perhaps something after the manner below represented, in which the circle with a cross represents the atom of nitrogen, and the plain circle that of oxygen. Fig. 131. Protoxide of Binoxide of Nitrous Hyponitric Nitric nitrogen. nitrogen. acid. acid. acid. eeoro Two atoms of one substance may unite themselves with three or even with seven of another, as in the case of one of the acids of manganese; but such combinations are rare. 1 "Atop the metals amounts to forty-nine in Physical Properties -One of the most remarkable and striking characters possessed by the metals is their peculiar lustre ; this is so characteristic™ £t the expression metallic lustre has passed into common speech. This property xs no doubt connected with the extraordinary degree of opacity which the metals present » every instance. The thinnest lea°ves or pla?es the edges of crystalline lamina, arrest the passage of light in the most complete manner An exception to this; rule is usually made in favor of gold-leaf, which, when held up to the daylight, exhibits a greenish, and in some cases a purple c^ or as ifit were really endued with a certain degree of translucency; the metalKo film is, however, generally so imperfect that it became difficult to say whether he observed effect might not be in some measure due to multitudes of 1 ttle holes, many of which are visible to the naked eye; but recent experiment bylWessor Faraday have established the translucency of gold beyond all In point of color, the metals present a certain degree of uniformity with two exceptions, viz. copper, which is red, and gold, which is yellow, an'the e bodies arcincluded between the pure white of silver, and the bluish-gray tint of lead; b.smu h it is true, has a pinkish color, and calcium and stro2m yellowish tint, but they are very feeble. m d The differences of specific gravity are very wide, passing from lithium potas- sium and sodium which are lighter than water,'to platinum, whicH'nearly twenty-one times heavier than an equal bulk of that fluid. y Table of the Specific Gravities of Metals at 60° (15°-5C).- Platinum .... 90-98 19*26 17-60 13-57 11-30 to 11-8 11-35 10-47 9-82 9-00 Gold Tungsten Mercury Palladium Lead Silver Bismuth . Uranium . . 19 ' Dr. Turner's Elements, eighth edition, p. 345 218 CHEMISTRY OF THE METALS. Copper . . Cadmium . Cobalt Nickel Iron Molybdenum Tin Zinc Manganese Antimony Tellurium Arsenic Aluminium Magnesium Sodium Potassium Lithium . 8-89 8-60 8-54 8-28 7-79 7-40 7-29 7-86 to 7-1 6-85 6-70 6-11 5-88 2-56 to 2-67 1-75 0-972 0-865 0-593 The property of malleability, or power of extension under the hammer, or between the rollers of the flatting-mill, is enjoyed by certain of the metals to a very great extent. Gold-leaf is a remarkable example of the tenuity to which a malleable metal may be brought by suitable means. The gilding on silver wire used in the manufacture of gold lace is even thinner, and yet presents an unbroken surface. Silver may be beaten out very thin ; copper also, but to an inferior extent; tin and platinum are easily rolled out into foil; iron, palladium, lead, nickel, cadmium, the metals of the alkalis, and mercury, when solidified, are also malleable. Zinc may be placed midway between the malleable and brittle division; then perhaps bismuth, and, lastly, such metals as antimony and arsenic, which are altogether destitute of malleability. The specific gravity of malleable metals is usually very sensibly increased by pressure or blows, and the metals themselves rendered much harder, with a tendency to brittleness. This condition is destroyed and the former soft state restored by the operation of annealing, which consists in heating tho metal to redness out of contact with air (if it will bear that temperature with- out fusion), and cooling it quickly or slowly according to the circumstances of the case. After this operation, it is found to possess its original specific gravity. Ductility is a property distinct from the last, inasmuch as it involves the principle of tenacity, or power of resisting ten- sion. The art of wire-drawing is one of great antiquity; it consists in drawing rods of metal through a succession of trumpet-shaped holes in a steel plate, each being a little smaller than its predecessor, until the requisite degree of fine- ness is attained. The metal often becomes very hard and rigid in this process, and is then liable to break; this is reme- died by annealing. The order of tenacity among the metals susceptible of being easily drawn into wire is the following; it is determined by observing the weights required to break asunder wires drawn through the Bame orifice of the plate: — Fig. 142. Iron Gold Copper Zinc Platinum Tin Silver Lead Metals differ as much in fusibility as in density. The following tnblp extracted from the late Dr. Turner's excellent work, will give an idea of their CHEMISTRY OF THE METALS. 219 relations to heat. The melting points of the metals which only fuse at a tem- perature above ignition, and that of zinc, are on the authority of Mr. Daniell, having been observed by the help of the pyrometer before described: — ' Mercury . —39 Potassium . 136 Sodium . 194 Lithium . 356 Tin ... . 442 Fusible below Cadmium (about) 442 a red heat Bismuth . 497 Lead . . . . . 612 Melting points. F. C —39°-44 57-77 90 180 227-77 227-77 258-33 322-77 Infusible below a red heat Tellurium — rather less fusible than lead. Arsenic — unknown. Zinc....... Antimony—just below redness. f Silver . Copper Gold . Cast iron Pure iron . Nickel . . Cobalt . . Manganese Palladium . - Molybdenum Uranium . Tungsten . Chromium Titanium . Cerium Osmium Iridium Rhodium . Platinum . Tantalum . 773 411-66 1873 1022-77 1996 1091-11 2016 1102-22 2786 1530 Fusible only in an excellent wind- furnace. Imperfectly melted in wind-furnace. Infusible in furnace; fusible by oxy- hydrogen blowpipe. Some metals acquire a pasty or adhesive state before becoming fluid: this is the case with iron and platinum, and also with the metals of the alkalis. It is this peculiarity which confers the very valuable property of welding, by which pieces of iron and steel are united without solder, and the finely-divided metallic sponge of platinum converted into a solid and compact bar. Volatility is possessed by certain members of this class, and perhaps by all, could temperatures sufficiently elevated be obtained. Mercury boils and distils below a red heat; potassium, sodium, zinc, magnesium, and cadmium rise in vapor when heated to a bright redness; arsenic and tellurium are volatile. CHEMICAL RELATIONS OP THE METALS; CONSTITUTION OF SALTS. Metallic combinations are of two kinds, namely, those formed by the union of metals among themselves, which are called alloys, or where mercury is concerned, amalgams, and those generated by combination with the non- metallic elements, as oxides, chlorides, sulphides, &c. In this latter case, the 220 CHEMISTRY OF THE METALS. metallic characters are very frequently lost. The alloys themselves are really true chemical compounds, and are not mere mixtures of the constituent metals; their properties often differ completely from those of the latter. The oxides of the metals may be divided, as already pointed out, into three classes; namely, those which possess basic characters more or less marked, those which refuse to combine with either acids or alkalis, and those which have distinctly acid properties. The strong bases are all protoxides; they contain single equivalents of metal and oxygen; the weaker bases are usually sesquioxides, containing metal and oxygen in the proportion of two equivalents of the former to three of the latter; the peroxides or neutral compounds arc still richer in oxygen, and, lastly, the metallic acids contain the maximum proportion of that element. The gradual change of properties by increasing proportions of oxygen is well illustrated by the case of manganese. Metal. Oxygen. Symbols. Characters. Protoxide . 1 eq. 1 eq. MnO Strongly basic Sesquioxide 2 eq. 3 eq. Mnj.0, Feebly basic. Binoxide 1 eq. 2 eq. Mn02 Neutral. Manganic acid . Permanganic acid 1 eq. 2 eq. 3 eq. 7 eq. Mn03 \ Mn207 / Strongly acid. The oxides of iron and chromium present similar, but less numerous grada- tions. When a powerful oxygen-acid and a powerful metallic base are united in such proportions that they exactly destroy each other's properties, the resulting salt is said to be neutral: it is incapable of affecting vegetable colors. Now, in all these well-characterized neutral salts, a constant and very remarkable relation is observed to exist between the quantity of oxygen in the base and the quantity of acid in the salt. This relation is expressed in the following manner: — To form a neutral combination, as many equivalents of acid must be present in the salt as there are of oxygen in the base itself. In fact, this has become the very definition of neutrality, as the action on vegetable colors is sometimes an unsafe guide. It is easy to see the application of this law. When a base is a protoxide, a single equivalent of acid suffices to neutralize it; when a sesquioxide, not less than three are required. Hence, if by any chance the base of a salt should pass by oxidation from the one state to the other, the acid will be insufficient in quantity by one-half to form a neutral combination. Sulphate of the protoxide of iron offers an example: when a solution of this substance is exposed to the air, it absorbs oxygen, and a yellow insoluble sub-salt, or basic-salt, is produced, which contains an excess of base. Four equivalents of the green compound absorb from the air two equivalents of oxygen, and give rise to one equivalent of neutral and one equivalent of basic sulphate of the sesquioxide, as indicated by the diagonal zigzag line of division. 1 eq. iron -f- 1 eq. oxygen . . . . 1 eq. sulphuric acid. 1 eq. iron + 1 eq. oxygen .... 1 eq. sulphuric acid. | -f- 1 eq. oxygen from air. 1 eq. iron -j- 1 eq. oxygen '. ; \ ~\ 1 eq. sulphuric acid. 1 eq. iron + 1 eq. oxygen . . . . 1 eq. sulphuric acid. -j- 1 eq. oxygen from air. Such sub-salts or basic salts are very frequently insoluble. The combinations of chlorine, iodine, bromine, and fluorine with the metals possess in a very high degree the saline character. If, however, the definition formerly given of a salt be rigidly adhered to, these bodies must be excluded from the class, and with them the very substance from which the name is CHEMISTRY OF THE METALS. 221 derived, that is, common salt, which is a chloride of sodium. To obviate this anomaly, it has been found necessary to create two classes of salts: in the first division will stand those constituted after the type of common salt, which contain a metal and a salt-radical, as chlorine, iodine, &c.; and, in the second, those which, like sulphate of soda and nitrate of potassa, are generally sup- posed to be combinations of an acid with an oxide. The names haloid1 salts, and oxygen-acid-, or oxy-salts, are given to these two kinds. When a haloid salt is dissolved in water, it might be regarded as a combi- nation of a metallic oxide with a hydrogen-acid, the water being supposed to undergo decomposition, its hydrogen being transferred to the salt-radical, and its oxygen to the metal. This view is unsupported by evidence of any value: it is much more probable, indeed, that no truly saline compounds of hydrogen-acids exist, at any rate in inorganic chemistry. When a solution of any hydrogen acid is poured upon a metallic oxide, we may rather suppose that both are decomposed, water and a haloid salt of the metal being produced. Take hydrochloric acid and potassa by way of example. Hydrochloric acid \ CMorine ----------^_^ Chloride of Potassium. J } Hydrogen -^^^^_--- Potassa 1 Potassium -X-— ( Oxygen -----------^"~~~-> Water. On evaporating the solution, the chloride of potassium crystallizes out. When hydrochloric acid and ammoniacal gases are mixed, they combine with some energy, and form a white solid salt, sal-ammoniac. Now this substance bears such a strong resemblance in many important particulars to chloride of potassium and common salt, that the ascription to it of a similar constitution is well warranted. If chloride of potassium, therefore, contain chlorine and metal, sal-ammo- niac may also contain chlorine in combination with a substance having the chemical relations of a metal, formed by the addition of the hydrogen of the acid to the elements of the ammonia. Hydrochloric acid \ ] c* f,h 1rino ---------- Chlorine ") Q , •> ) 1 eq. Hydrogen f Sal- Ammonia . . 5 3 eq. Hydrogen__-^ f ammoniac. ( 1 eq. Nitrogen____ ^-^^ Ammonium ) The term ammonium is given to this hypothetical body, NH4; it is supposed to exist in all the ammoniacal salts. Thus we have chloride of ammonium, sulphate of the oxide of ammonium, &c. This view is very strongly supported by the peculiarities of the salts themselves, and by the existence of a series of substances, intimately related to these salts in organic chemistry, as will hereafter be seen. Many of the sulphides also possess the saline character and are soluble in water, as those of potassium and sodium. Sometimes a pair of sulphides will unite in definite proportions, and form a crystallizable compound. Such bodies bear a very close resemblance to oxygen-acid salts; they usually contain a protosulphide of an alkaline metal, and a higher sulphide of a non- nictallic substance or of a metal which has little tendency to form a basic oxide, the two sulphides having exactly the same relation to each other as the oxide and acid of an ordinary salt. Hence the expressions sulphur-salt, sulphur-acid, and sulphur-base, which Berzelius applies to such compounds: they contain sulphur in the place of oxygen. Thus, bisulphide of carbon is a sulphur-acid; it forms a crystallizable compound with protosulphide of potassium, which is a sulphur-base. Were oxygen substituted for the sulphur m this product, we should have carbonate of potassa. 1 5Xf, sea-salt, and siios, form. 19* 222 CHEMISTRY OF THE METALS. KS + CS2 sulphur-salt. KO -f- C02 oxygen salt. These remarkable compounds are very numerous and interesting; they have been studied by Berzelius with great care. Salts often combine together, and form what are called double-salts, in which the same acid is in combination with two different bases. AVhen sulphate of copper and sulphate of potassa, or chloride of zinc and sal-ammoniac, are mixed in the ratio of their equivalents, dissolved in water, and the solution made to crystallize, double salts are obtained. These latter are often more beautiful, and crystallize better than their constituent salts. Many of the compounds called super-, or acid-salts, such as bisulphate of potassa, which have a sour taste and acid reaction to test-paper, ought strictly to be considered in the light of double-salts, in which one of the bases is water. Strange as it may at first sight appear, water possesses considerable basic powers, although it is unable to mask acid reaction on vegetable colors; hydrogen, in fact, very much resembles a metal in its chemical relations. Bisulphate of potassa will, therefore, be a double sulphate of potassa and water, while oil of vitriol must be assimilated to neutral sulphate of potassa. KO + S03 and HO + S03. Water is a weak base: it is for the most part easily displaced by a metallic oxide; yet cases occur now and then in which the reverse happens, and water is seen to decompose a salt, in virtue of its basic power. There are a few acid salts which contain no water; as the bichromate of potassa, and a new anhydrous sulphate of potassa discovered by M. Jacque- lain.1 It will be necessary, of course, to adopt some other view in these cases. The simplest will be to consider them as really containing two equivalents of acid to one of base. By water of crystallization is meant water in a somewhat loose state of com- bination with a salt, or other compound body, from which it can be disengaged by the mere application of heat, or by exposure to a dry atmosphere. Salts which contain water of crystallization have their crystalline form greatly in- fluenced by the proportion of the latter. Green sulphate of iron crystallizes in two different forms, and with two different proportions of water, according to the temperature at which the salt separates from the solution. Many salts containing water effloresce in a dry atmosphere, crumbling to powder, and losing a part or the whole of their water of crystallization ; while in a moist atmosphere they may be preserved unchanged. The opposite effect to this, or deliquescence, results from a strong attraction of the salt for water in virtue of which it absorbs the latter from the air, often to such an extent as to produce liquefaction. Crystallization; Crystalline Forms.—Almost every substance, simple and compound, capable of existence in the solid state, assumes, under favorable circumstances, a distinct geometrical form or figure, usually bounded by plane surfaces, and having angles of fixed and constant value. ■ The faculty of crys- tallization seems to be denied only to a few bodies, chiefly highly-complex organic principles, which stand, as it were, upon the very verge of organiza- tion, and which, when in a solid sta'te, are frequently characterized by a kind of beady or globular appearance, well known to microscopical observers The most beautiful examples of crystallization are to be found among natural minerals, the results of exceedingly slow changes constantly occurring within the earth. It is invariably found that artificial crystals of salts and other soluble substances, which have been slowly and quietly deposited alwavs surpass in size and regularity those of more rapid formation. ' Solution in water or some other liquid is one very frequent method of effecting crystallization. If the substance be more soluble at a high than at 'Ann. Chim. et Phys. lxx. 311. CHEMISTRY OF THE METALS. a low temperature, then a hot and saturated solution by slow cooling will generally be found to furnish crystals: this is a very common case with salts and various organic principles. If it be equally soluble, or nearly so, at all temperatures, then slow spontaneous evaporation in the air, or over a surface of oil of vitriol, often proves very effective. Fusion and slow cooling may be employed in many cases; that of sulphur is a good example: the metals usually afford traces of crystalline figure when thus treated, which sometimes become very beautiful and distinct, as with bismuth. A third condition under which crystals very often form is in passing from a gaseous to a solid state, of which iodine affords a good instance. AVhen by any of these means time is allowed for the symmetrical arrangement of the particles of matter, at the moment of solidification, crystals are produced. That crystals owe their figure to a certain regularity of internal structure, is shown both by their mode of formation and also by the peculiarities attend- ing their fracture. A crystal placed in a slowly-evaporating saturated solu- tion of the same substance grows or increases by a continued deposition of fresh matter upon its sides, in such a manner that the angles formed by the meeting of the latter remain unaltered. The tendency of most crystals to split in particular directions, called by mineralogists cleavage, is a certain indication of regular structure, while the curious optical properties of many among them, and their remarkable mode of expansion by heat, point to the same conclusion. It may be laid down as a general rule that every substance has its own crystalline form, by which it may very frequently be recognized at once ; not that each substance has a different figure, although very great diversity in this respect is to be found. Some forms are much more common than others, as the cube and six-sided prism, which are very frequently assumed by a number of bodies, not in any way related. The same substance may have, under different sets of circumstances, as high and low temperatures, two different crystalline forms, in which case it is said to be dimorphous. Sulphur and carbon furnish, as already noticed, examples of this curious fact: another case is presented by carbonate of lime in the two modifications of calcareous spar and arragonite, both chemically the same, but physically different. A fourth example might be given in the iodide of mercury, which also has two distinct forms, and even two distinct colors, offering as great a contrast as those of diamond and graphite. The angles of crystals are measured by means of instruments called gonio- meters, of which there are two kinds in use, namely, the old or common goniometer, and the reflective goniometer of Dr. Wollaston. The common goniometer consists of a pair of steel blades moving with friction upon a centre, as shown in the cut (fig. 143). The Fig. 113. edges a a are carefully adjusted to tho faces of the crystal, whose inclination to each other it is required to ascertain, and then the instrument being ap- plied to the divided semicircle, the contained angle is at once read off. An approximative measurement, within one or two degrees, can be easily ob- tained by this instrument, pro- vided the planes of the crystal be tolerably perfect, and large enough for the purpose. Some practice is of course required before even this amount of accuracy can be attained. 224 CHEMISTRY OF THE METALS. The reflective goniometer is a very superior instrument, its indications being correct within a fraction of a degree : it is applicable also to the measurement of the angles of crystals of very small size, the only condition required being that their planes be smooth and brilliant. Fig. 114. The annexed sketch will convey an idea of its nature and mode of use. a is a divided circle or disc of brass, the axis of which passes stiffly and with- out shake through the support b. This axis is itself pierced to admit the passage of a round rod or wire, terminated by the milled-edged head c, and destined to carry the crystal to be measured by means of the jointed arm d. A vernier, e, immovably fixed to the upright sup- port, serves to measure with great accu- racy the angular motion of the divided circle. The crystal at / can thus be turned round, or adjusted in any desired position, without the necessity of moving the disc. The principle upon which the measure- ment of the angle rests is very simple. If the two adjacent planes of a crystal be successively brought into the same position, the angle through which the crystal will have moved will be the supplement to that contained between the two planes. If, for example, in a small crystal cab be the angle which is desired to be determined, and the reflect- ing surface a 6 be placed in such a position that the reflection of the image of a distant point S seen from 0 exactly covers a point E lying in the line of the reflected ray, then the other side a c of the angle cab must be turned through the arc caf, in order to assume the same position, and to give the same phenomena as the plane a b j, ...--'' previously did. The angle c a/is ----±^1 the complement of the angle c a b. All that is required to be done, therefore, is to measure the angle c af with accuracy, and subtract its value from 180° ; and this the goniometer effects. One method of using the instrument is the following: —The goniometer is placed at a convenient height upon a steady table in front of a well-illuminated window. Horizontally across the latter, at the height of eight or nine feet from the ground, is stretched a narrow black ribbon, while a second similar ribbon, adjusted parallel to the first, is fixed beneath the window, a foot or eighteen inches above the floor. The object is to obtain two easily-visible black lines, perfectly parallel. The crystal to be examined is attached to the arm of the goniometer at / by a little wax, and adjusted in such a manner that the edge joining the two planes whose inclination is to be measured shall nearly coincide with, or be parallel to, the axis of the instrument. This being done, the adjustment is completed in the following manner:—The divided circle is turned until the zero of the vernier comes to 180°; the crystal is then moved round by means of the inner axis c (fig. 144) until the eye placed near it perceives the image of the upper black line reflected from the surface of one of the planes in question. Following this image, the crystal is still CHEMISTRY OF THE METALS. 225 cautiously turned until the upper black line seen by reflection approaches and overlaps the lower black line seen directly by another portion of the pupil. It is obvious, that if the plane of the crystal be quite parallel to the axis of the instrument (the latter being horizontal), the two lines will coincide completely. If, however, this should not be the case, the crystal must be moved upon the wax until the two lines fall in one when superposed. The second face of the crystal must then be adjusted in the same manner, care being taken not to derange the position of the first. When by repeated observation it is found that both have been correctly placed, so as to bring the edge into the required condition of parallelism with the axis of motion, the measurement of the angle may be made. For this purpose the crystal is moved as before by the inner axis until the image of the upper line, reflected from the first face of the crystal, covers the lower line seen directly. The great circle, carrying the whole with it, is then cautiously turned until the same coincidence of the upper with the lower line is seen by means of the second face of the crystal; that is, the second face is brought into exactly the same position as that previously occupied by the first. Nothing then remains but to read off by the vernier the angle through which the circle has been moved in this operation. The division upon the circle itself is very often made backwards, so that the angle of motion is not obtained, but its complement, or the angle of the crystal required. It may be necessary to remark, that, although the principle of the opera- tion described is in the highest degree simple, its successful practice requires considerable skill and experience. If a crystal of tolerably simple form bo attentively considered, it will become evident that certain directions can be pointed out in which straight lines may be imagined to be drawn, passing through the central point of the crystal from side to side, from end to end, or from one angle to that opposed to it, &c, about which lines the particles of matter composing the crystal may be conceived to be symmetrically built up. Such lines or axes are not always purely imaginary, however, as may be inferred from the remarkable optical properties of many crystals: upon their number, relative lengths, position, and inclination to each other, depends the outward figure of the crys- tal itself. All crystalline forms may upon this plan be arranged in six classes or systems; these are the following: — 1. The regular system.—The crystals of this division have three equal axes, all placed at right angles to each other. Tho most important forms are the cube (1), the regular octahedron (2), and the rhombic dodecahedron (3). The letters a — a (fig. 146) show the termination of the three axes, placed as stated. Fig. 146. 12 3 Very many substances, both simple and compound, assume these forms, as most of the metals, carbon in the state of diamond, common salt, iodide of potassium, the alums, fluor-spar, bisulphide of iron, garnet, spinelle, &c. 226 CHEMISTRY OF THE METALS. 2. The square prismatic system. — Three axes are here also observed, at right angles to each other. Of these, however, two only are of equal length, the third being usually longer or shorter. The most important forms are, a right square prism, in which the lateral axes terminate in the central point of each side (1); a second right square prism, in which the axes terminate in the edges (2) ; a corresponding pair of right, squar-e-based octahedra (3 and 4). Fig. 147. 2 3 »--•!"*• V a—a. Principal, or vertical axis. 6—6, c—c. Secondary, or lateral axes. Examples of these forms are to be found in zircon, native binoxide of tin, apophylite, yellow ferrocyanide of potassium, &c. 3. The right prismatic system. — This is characterized by three axes of un- equal lengths, placed at right angles to each other, as in the right rectangular prism (1), the right rhombic prism (2), the right rectangular-based octahedron (3), and the right rhombic-based octahedron (4). Fig. 148. /■■ * A a—a. Principal axis. 6—6, c—c. Secondary axeo. The system is exemplified in sulphur crystallized at a low temperature ar- senical iron pyrites, nitrate and sulphate of potassa, sulphate of baryta &c 4. The oblique prismatic system.—Crystals belonging to this group have also three axes which may be all unequal, two of these (the secondary) are placed at right angles, the third being so inclined as to be oblique to one and per- pendicular to the other. To this system may be referred the four followine forms: — The oblique rectangular prism (1), the oblique rhombic prism (21 the oblique rectangular-based octahedron (3), the oblique rhombic-based octahedron (4) Such forms are taken by sulphur crystallized by fusion and cooline ren W sulphate carbonate and phosphate of soda, borax, green vitriol, and many CHEMISTRY OF THE METALS. 227 Fig. 149. a—a. Principal axis. 6—6, c—c. Secondary axes. 5. The doubly-oblique prismatic system.—The crystalline forms comprehended in this division are, from their great apparent irregularity, exceedingly diffi- cult to study and understand. In them are traced three axes, which may be nil unequal in length, and are all oblique to each other, as in the two doubly- oblique prisms (1 and 2), and in the corresponding doubly-oblique octahedra (3 and 4). Fig. 150. a—a. Principal axis, as before. 6—6, c—c. Secondary axes. Sulphate of copper, nitrate of bismuth, and quadroxalate of potassa afford illustrations of these forms. 6. The rhombohedral system. — This is very important and extensive ; it is characterized by the presence of four axes, three of which are equal, in the same plane, and inclined to each other at angles of 60°, while the fourth or principal axis is perpendiular to all. The regular six-sided prism (1), the quartz-dodecahedron (2), the rhombohedron (3), and a second dodecahedron, whose faces are scalene triangles (4), belong to the system in question. Examples are readily found; as in ice, calcareous spar, nitrate of soda, beryl, quartz or rock crystal, and the semi-metals, arsenic, antimony, and tel- lurium. If a crystal increase in magnitude by equal additions on every part, it is quite clear that its figure must remain unaltered; but if from some cause this increase should be partial, the newly-deposited matter being distributed une- qually, but still in obedience to certain definite laws, then alterations of form 228 CHEMISTRY OF THE METALS. Fig. 151. i.i^iy a—a. Principal axis. 6—6. Secondary axes. are produced, giving rise to figures which have a direct geometrical connection with that from which they are derived. If, for example, in the cube, a regular omission of successive rows of particles of matter in a certain order be made at each solid angle, while the crystal continues to increase elsewhere, the result will be the production of small triangular planes, which, as the process advanceSj gradually usurp the whole of the surface of the crystal, and con- vert the cube into an octahedron. The new planes are called secondary, and their production is said to take place by regular decrements upon the solid angles. The same thing may happen on the edges of the cube; a new figure, the rhombic dodecahedron, is then generated. The modifications which can thus be produced of the original or primary figure (all of which are subject to exact geometrical laws) are very numerous. Several distinct modifications may be present at the same time, and thus render the form exceedingly complex. Fig. 152. Passage of cube to octahedron. It is important to observe, that in all these deviations from what maybe regarded as the primary or fundamental figure of the crystal, the modifying planes are in fact the planes of figures belonging to the same natural group or cryslallographical system as the primary form, and having their axes coincident with those of the latter. The crystals of each system are thus subject to a peculiar and distinct set of modifications, the observation of which very fre- quently constitutes an excellent guide to the discovery of the primary form itself. J Crystals often cleave parallel to all the planes of the primary figure as in calcareous spar, which offers a good illustration of this perfect cleavage Sometimes one or two of these planes have a kind of preference over the rest in this respect, the crystal splitting readily in these directions only. A very curious modification of the figure sometimes occurs by the excessive growth of each alternate plane of the crystal; the rest become at length obli- terated, and the crystal assumes the character called hemihedral or half sided This is well seen in the production of the tetrahedron from the regular octa' CHEMISTRY OF THE METAL8. 229 Fig. 153. Passage of octahedron to tetrahedron. hedron, and of the rhombohedric form by a similar change from the quartz- dodecahedron already figured. Relations of Form and Constitution; Isomorphism.—Certain substances, to which a similar chemical constitution is ascribed, possess the remarkable pro- perty of exactly replacing each other in crystallized compounds without alte- ration of the characteristic geometrical figure. Such bodies are said to be isomorphous J For example, magnesia, oxide of zinc, oxide of copper, protoxide of iron, and oxide of nickel, are allied by isomorphic relations of the most intimate nature. The salts formed by these substances with the same acid and similar proportions of water of crystallization, are identical in their form, and, when of the same color, cannot be distinguished by the eye: the sulphates of mag- nesia and zinc may be thus confounded. The sulphates, too, all combine with Bulphate of potassa and sulphate of ammonia, giving rise to double salts, whose figure is the same, but quite different from that of the simple sulphates. Indeed, this connection between identity of form and parallelism of constitu- tion runs through all their combinations. In the same manner alumina and sesquioxide of iron replace each other continually without change of crystalline figure; the same remark may be made of potassa, soda, and ammonia, with an equivalent of water, or oxide of ammonium, these bodies being strictly isomorphous. The alumina in com- mon alum may be replaced by sesquioxide of iron, the potassa by ammonia or by soda, and still the figure of the crystal remains unchanged. These replace- ments may be partial only: we may have an alum containing both potassa and ammonia, or alumina and sesquioxide of chromium. By artificial manage- ment—namely, by transferring the crystal successively to different solutions— we may have these isomorphous and mutually-replacing compounds distri- buted in different layers upon the same crystal. For these reasons mixtures of isomorphous salts can never be separated by crystallization, unless their difference of solubility is very great. A mixed solution of sulphate of protoxide of iron and sulphate of nickel, isomorphous salts, yields on evaporation crystals containing both iron and copper. But if before evaporation the protoxide of iron be converted into sesquioxide by chlorine or other means, then the crystals obtained are free from iron, except that of the mother-liquor which wets them. The salt of sesquioxide of iron is no longer isomorphous with the nickel salt, and easily separates from the latter. When compounds arc thus found to correspond, it is inferred that the ele- ments composing them are also sometimes isomorphous. Thus, the metals magnesium, zinc, iron, and copper are presumed to be isomorphous: arsenic aud phosphorus have not the same crystalline form, nevertheless they are said to bo isomorphous because arsenic and phosphoric acids give rise to combina- tions which agree most completely in figure and constitution. The chlorides, ' From loos, equal, and /^p^fy shape or form. 20 230 CHEMISTRY OF THE METALS. . 105° 5' . 107° 25' ■ 107° 20' . 107° . 107° 40' iodides, bromides, and fluorides agree, whenever they can be observed, in tho most perfect manner; hence the elements themselves are believed to bo also isomorphous. Unfortunately, for obvious reasons, it is very difficult to observe the crystalline figure of most of the elementary bodies, and this difficulty is increased by the frequent dimorphism they exhibit. Absolute identity of value in the angles of crystals is not always exhibited by isomorphous substances. In other words, small variations often occur in the magnitude of the angles of crystals of compounds which in all other respects show the closest isomorphic relations. This should occasion no sur- prise, as there are reasons why such variations might be expected, the chief perhaps being the unequal effects of expansion by heat, by which the angles of the same crystal are changed by alteration of temperature. A good example is found in the case of the carbonates of lime, magnesia, manganese, iron, and zinc, which are found native crystallized in the form of obtuse rhombohedra (figs. 151, 3), not distinguishable from each other by the eye, or even by the common goniometer, but showing small differences when examined by the more accurate instrument of Dr. Wollaston. These compounds are isomor- phous, and the measurements of the obtuse angles of their rhombohedra are as follows: — Carbonate of lime ..... " magnesia .... " protox. manganese " " iron ... " zinc ..... Anomalies in the composition of various earthy minerals, which formerly threw much obscurity upon their chemical nature, have been in great mea- sure explained by these discoveries. Specimens of the same mineral from different localities were found to afford very discordant results on analysis. But the proof once given of the extent to which substitution of isomorphous bodies may go without destruction of what may be called the primitive type of the compound, these difficulties vanish. Another benefit conferred on science by the discoveries in question, is that of furnishing a really philosophical method of classifying elementary and compound substances, so as to exhibit their natural relationships: it would be perhaps more proper to say that such will be the case when the isomorphic relations of all the elementary bodies become known, — at present only a cer- tain number have been traced. Decision of a doubtful point concerning the constitution of-a compound may now and then be very satisfactorily made by a reference to this same law of isomorphism. Thus, alumina, the only known oxide of aluminum is judged to be a sesquioxide of the metal from its relation to sesquioxide of iron, which is certainly so; the black oxide of copper is inferred to be really the protoxide, although it contains twice as much oxygen as the red oxide because it is isomorphous with magnesia and zinc, both undoubted prot- oxides. r The subjoined table will serve to convey some idea of the most important families of isomorphous elements; it is taken from Professor Graham's sys- tematic work,! to which the pupil is referred for fuller details on this interest- ing subject. 1 Second edition, p. 175. CHEMISTRY OF THE METALS. 231 Isomorphous Groups. (1) Sulphur Selenium (3.) Barium Strontium (7-) Sodium Silver Tellurium. Lead. Gold «(2>) • (4-) Potassium Magnesium Calcium Tin Titanium. Ammonium. (8.) Manganese Iron (5.) Platinum Chlorine Iodine Cobalt Iridium Bromine Nickel Osmium. Fluorine Zinc Cadmium (6.) Tungsten Cyanogen. (9.) Copper Chromium Molybdenum Tantalum. Phosphorus Arsenic Aluminum Beryllium Vanadium Antimony Bismuth. Zirconium. There is a law concerning the formation of double salts which may now be mentioned; the two bases are never taken from the same isomorphous family. Sulphate of copper or of zinc may unite in this manner with sulphate of soda or potassa, but not with sulphate of iron or cobalt; chloride of magnesium may combine with chloride of ammonium, but not with chloride of zinc or nickel, &c. It will be seen hereafter that this is a matter of some importance in the theory of the organic acids. Polybasic Acids.—There is a particular class of acids in which a departure occurs from the law of neutrality formerly described: these are acids requiring two or more equivalents of a base for neutralization. The phosphoric and arsenic acids present the best examples yet known in mineral chemistry; but in the organic department of the science cases very frequently occur. Phosphoric acid is capable of existing in three different states or modifica- tions, forming three separate classes of salts, which differ completely in pro- perties and constitution. They are distinguished by the names tribasic, bibasic, and monobasic acids, according to the number of equivalents of base required to form neutral salts. Tribasic or Common Phosphoric Acid.—When commercial phosphate of soda Is .dissolved in water, and the solution mixed with acetate of lead, an abun- dant white precipitate of phosphate of lead falls, which may be collected on a filter, and well washed. While still moist, this compound is suspended in distilled water, and an excess of sulphuretted hydrogen gas passed into it. The protoxide of lead is converted into sulphide, which subsides as a black insoluble precipitate, while phosphoric acid remains in solution, and is easily deprived of the residual sulphuretted hydrogen by a gentle heat. The soda-salt employed in this experiment contains the tribasic modification of phosphoric acid. Of the three equivalents of base, two consist of soda and one of water: when mixed with solution of lead, a tribasic phosphate of the oxide of that metal falls, which, when decomposed by sulphuretted hydrogen, yields sulphide of lead and a hydrate of the acid containing three equivalents of water in intimate combination. 232 CHEMISTRY OF THE METALS. (2 eq. soda___________-? 2 eq. acetate of soda. 1 ,, water_________S 7^ " flydrated acetic acid. 1 ,, phos- \ // phoricacid / " ^-y// „ r 2 eq. acetic acid ©/^^ Z^'ll - gffig& ^^-1 ^triphosphate of lead. 2NaO,HO,P06 + 3PbO,~A = 3PbO,P05 + HO, T + 2(NaO,"A) (3 eq. lead ------------7 3 eq. sulphide of lead. 3 ,, oxygen 1 ,, phos- "1 phoric acid J 3 eq. sulphuretted $ 3 eq. sulphur ^^^. . , • hydrogen ) 3 ,, hydrogen------^ 1 eq. tribasic hydrate of J 6 ' " J 6 phosphoric acid. 3PbO,P05 -f- 3HS = 3HO,P06 + 3PbS. The solution of the tribasic hydrate of phosphoric acid may be concentrated by evaporation in vacuo over sulphuric acid until it crystallizes in thin deli- quescent plates. The same compound in beautiful crystals, resembling those of sugar-candy, has been accidentally formed.1 It undergoes no change by boiling, with water, but when heated alone to 400° (204°-4C) loses some of its combined water, and becomes converted into a mixture of the bibasic and mo- nobasic hydrates. At a red heat it becomes entirely changed to monohydrate, which, at a still higher temperature, sublimes. Tribasic phosphoric acid is characterized by the yellow insoluble salt it forms with protoxide of silver. • Bibasic Phosphoric Acid, or Pyrophosphoric Acid.—When common phosphate of soda, containing 2NaO,HO,P05 + 24HO, is gently heated, the 24 equivalents of water of crystallization are expelled, and the salt becomes anhydrous; but if the heat be raised to a higher point, the basic water is also driven off, and the acid passes into the second or bi- basic modification. If the altered salt be now dissolved in water, this new compound, the bibasic phosphate of soda, crystallizes out. When mixed with solution of acetate of lead, bibasic phosphate of lead is thrown down, which, decomposed by sulphuretted hydrogen, furnishes a solution of the bibasic hydrate. This solution may be preserved without change at common tempe- ratures ; but when heated, an equivalent of water is taken up, and the sub- stance passes back again into the tribasic modification. Crystals of this hydrate have also been observed by M. Pe"ligot. Their pro- duction was accidental. The bibasic phosphates soluble in water give a white precipitate with solution of silver. Monobasic, or Metaphosphoric Acid.—When common tribasic phosphate of soda is mixed with solution -of tribasic hydrate of phosphoric acid, and ex- posed, after proper concentration, to a low temperature, prismatic crystals are obtained, which consist of a phosphate of soda having two equivalents of basic water. NaO,2HO,P05 -f 2HO. When this salt is very strongly heated, both the water of crystallization and that contained in the base are expelled, and monobasic phosphate of soda remains. This may be dissolved in cold water, precipitated with acetate of lead, and the lead-salt as before decomposed by sulphuretted hydrogen. The solution of the monobasic hydrate is decomposed rapidly by heat 1 Peligot, Ann. Chim. et Phys. lxxiii. 286. CHEMISTRY OF THE METALS. 233 becoming converted into tribasic hydrate. It possesses the property of coagu- lating albumen, which is not enjoyed by either of the preceding modifications. Monobasic alkaline phosphates precipitate nitrate of silver white. The glacial phosphoric acid of pharmacy is, when pure, hydrate of mono- basic phosphoric acid; it contains HO, P06. Anhydrous phosphoric acid, prepared by burning phosphorus in dry air, when thrown into water, forms a mixture in variable proportions of the three hydrates. When heated, a solution of the tribasic hydrate alone remains.1 See also phosphates of soda. Binary Theory of Salts.—The great resemblance in properties between the two classes of sal.ne compounds, the haloid and oxy-salts, has very naturally led to the supposition that both might possibly be alike constituted, and that the latter, instead of being considered compounds of an oxide and an acid, might with greater propriety be considered to contain a metal in union with a compound salt-radical, having the chemical relations of chlorine and iodine. On this supposition sulphate and nitrate of potassa will be constituted in the same manner as chloride of potassium, the compound radical replacing the Bimple one. Old View. New View. KO-f-S03 K-f S04 KO-f-NOg K-fN06 Hydrated sulphuric acid will be, like hydrochloric acid, a hydride of a salt radical, H+S04 When the latter acts upon metallic zinc, the hydrogen is- simply displaced, and the metal substituted; no decomposition of water is supposed to occur, and, consequently, the difficulty of the old hypothesis is at an end. When the acid is poured upon a metallic oxide, the same reaction occurs as in the case of hydrochloric acid, water and a haloid salt arc produced. All acids must be, in fact, hydrogen acids, and all salts haloid salts, with either simple or compound radicals. This simple and beautiful theory is not by any means new; it was sug- gested by Davy, who proposed to consider hydrogen as the acidifying prin- ciple in the common acids, .and lately revived and very happily illustrated by Liebig. It is supported by a good deal of evidence derived from various Bources, and has received great help from a series of exceedingly interesting experiments on the electrolysis of saline solutions, by the late Professor Daniell.* The necessity of creating a great number of unknown compounds is often urged as an objection to the new view; but the same objection applies to the old mode of considering the subject. Hyposulphurous acid and hypo- sulphuric acid are unknown in their free states. The compounds S202 and S2<)4 are as hypothetical as the substances S203 and S206. The same remark applies to almost every one of the organic acids; and, what is well worthy of notice, those acids which, like sulphuric, phosphoric, and carbonic acids, may be obtained in a separate state, are destitute of all acid properties so long as the anhydrous condition is retained. The general application of the binary theory still presents a few difficulties. But it is very probable that the progress of discovery will ultimately lead to its universal adoption, which would greatly simplify many parts of the science. One great inconvenience will be the change of nomenclature involved. 1 The three modifications of phosphoric acid possess properties so dissimilar that they might really be considered three distinct, although intimately related bodies. It is exceedingly re- markable, that when their salts are subjected to electro-chemical decomposition, the acids travel unaltered, a tribasic salt giving at the positive electrode a solution of common phosphoric acid; a bibasic salt, one of pvruphosphorie acid; and a monobasic salt, one of metaphosphoric acid (Professor Daniell and Dr. Miller, Phil. Trans, for 1S41. p. IV J Sec Daniell's Introduction to Chemical l'hilosophv, Al edition, p. 5o3. 1.0* 234 CHEMISTRY OF THE METALS. CLASSIFICATION OF METALS. Metals of the Alkalies. Potassium Lithium Sodium Ammonium. Metals of the Alkaline Earths. Barium Calcium Strontium Magnesium. 3. Metals of the Earths Proper. Aluminum Norium Beryllium Thorium Yttrium Cerium Erbium Lanthanum Terbium Didymium. Zirconium 4. Oxidable Metals Proper, whose Oxides form powerful Bases. Manganese Zinc Iron Cadmium Chromium Bismuth Nickel Lead Cobalt Uranium. Copper 5. Oxidable Metals Proper, whose Oxides form iveak Bases, or Acids. Vanadium Tin Tungsten Antimony Molybdenum Arsenic Tantalum Tellurium Niobium Osmium. Titanium 6. Metals Proper, whose Oxides are reduced by Heat; Noble Metals. Gold Palladium Mercury Iridium Silver Ruthenium Platinum Bhodium. Am'te 2SSln tt^Snel!8 ""^ **"** "^ ** ""*"" to the Sake of convenience, POTASSIUM. 235 SECTION I. METALS OF THE ALKALIS. POTASSIUM. Potassium was discovered by Sir II. Davy in 1807, who obtained it in very small quantity by exposing a piece of moistened hydrate of potassa to the action of a powerful voltaic battery, the alkali being placed between a pair of platinum plates put into connection with the apparatus. Processes have since been devised for obtaining this curious metal in almost any quantity that can be desired. An intimate mixture of carbonate of potassa and charcoal is prepared by calcining, in a covered iron pot, the crude tartar of commerce; when cold it is rubbed to powder, mixed with one-tenth part of charcoal in small lumps, and quickly transferred to a retort of stout hammered iron; the latter may be one of the iron bottles in which mercury is imported, a short and somewhat wide iron tube having been fitted to the aperture. The retort is placed upon its side, in a furnace so constructed that the flame of a very strong fire, fed with dry wood, may wrap round it, and maintain every part at a uniform degree of heat, approaching to whiteness. A copper receiver, divided in the centre by a diaphragm, is connected with the iron pipe, and kept cool by the application of ice, while the receiver itself is partly filled with naphtha or rock-oil, in which the potassium is to be preserved. Arrangements being thus completed, the fire is gradually raised until the requisite temperature is reached, when decomposition of the alkali by the charcoal commences, car- bonic oxide gas is abundantly disengaged, and potassium distils over, and falls in large melted drops into the liquid. The pieces of charcoal are introduced for the purpose of absorbing the melted carbonate of potassa, and preventing its separation from the finely-divided carbonaceous matter. If the potassium, be wanted absolutely pure, it must be afterwards re-dis- tilled in an iron retort, into which some naphtha has been put, that its vapor may expel the air, and prevent oxidation of the metal. Potassium is a brilliant white metal, with a high degree of lustre; at the common temperature of the air it is soft, and may be easily cut with a knife, but at 32° (0°C) it is brittle and crystalline. It melts completely at 136° (o7°77C), and distils at a low red heat. The density of this remarkable metal is only 0-8G5, water being unity. Exposed to the air, potassium oxidizes instantly, a tarnish covering the sur- face of the metal, which quickly thickens to a crust of caustic potassa. Thrown upon water, it takes fire spontaneously, and burns with a beautiful purple flame, yielding an alkaline solution. When brought into contact with a little water in a jar standing over mercury, the liquid is decomposed with great energy, and hydrogen liberated. Potassium is always preserved under the surface of naphtha. The equivalent of potassium (kalium) is 39; and its symbol, K. There are two compounds of this metal with oxygen,—potassa and teroxide of potassium. 236 POTASSIUM. Potassa, potash, or protoxide of potassium, KO, is produced when potas- sium is heated in dry air ; the metal burns, and becomes entirely converted into a volatile, fusible, white substance, which is anhydrous potassa. Moist- ened with water, it evolves great heat, and forms the hydrate. The hydrate of potassa, KO,HO, is a very important substance, and one of great practical utility. It is always prepared for use by decomposing tho car- bonate by hydrate of lime, as in the following process, which is very conve- nient: —10 parts of carbonate of potassa are dissolved in 100 parts of water, and heated to ebullition in a clean untinned iron, or still better, silver vessel; 8 parts of good quicklime are meanwhile slaked in a covered basin, and the resulting hydrate of lime added, little by little, to the boiling solution of car- bonate, with frequent stirring. When all the lime has been introduced, the mixture is suffered to boil for a few minutes, and then removed from the fire, and covered up. In the course of a very short time, the solution will have become quite clear, and fit for decantation, the carbonate of lime, with the excess of hydrate, settling down as a heavy, sandy precipitate. The solution should not effervesce with acids. It is essential in this process that the solution of carbonate of potassa be dilute, otherwise the decomposition becomes imperfect. The proportion of lime recommended is much greater than that required by theory, but it is always proper to have an excess. The solution of hydrate, or, as it is commonly called, caustic potassa, may be concentrated by quick evaporation in the iron or silver vessel to any desired extent: when heated until vapor of water ceases to be disengaged, and then suffered to cool, it furnishes the solid hydrate, containing single equivalents of potassa and water. Pure hydrate of potassa may also be easily obtained by heating to redness for half an hour fh a covered copper vessel one part of pure powdered nitre with two or three parts of finely-divided copper foil. The mass, when cold, is treated with water. This compound is a white solid substance, very deliques- cent and soluble in water; alcohol also dissolves it freely, which is the case with comparatively few of the compounds of this base: the solid hydrate of commerce, which is very impure, may thus be purified.' The solution of this substance possesses, in the very highest degree, the properties termed alka- line : it restores the blue color to litmus which has been reddened by an acid • neutralizes completely the most powerful acids; has a nauseous and peculiar taste, and dissolves the skin, and many other organic matters, when the latter are subjected to its action. It is frequently used by surgeons as a cauterv being moulded into little sticks for that purpose. Hydrate of potassa, both in the solid state and in solution, rapidly absorbs carbonic acid-from the air; hence it must be kept in closely-stopped bottles. an aci™13 Prepared, or partly altered by exposure, it effervesces with The water in this compound cannot be displaced by heat, the hydrate vola- tilizing as such at a very high temperature. The following table of the densities and value in real alkali of different solutions of hydrate of potassa is given on the authority of Dr Dalton • — Density. 1-68 1-60 1:52 1-47 1-44 1-42 1-39 1-36 Percentage of real alkali. . 51-2 . 46-7 . 42-9 . 39-6 . 36-8 . 34-4 . 32-4 29-4 Density. 1-33 1-28 1-23 1-19 115 111 1-06 Percentage of real alkali. 26-3 23-4 19-5 16-2 130 9-5 4-7 POTASSIUM 237 Teroxide of potassium, K03.—This is an orange-yellow fusible substance, generated when potassium is burned in excess of dry oxygen gas, and also formed to a small extent, when hydrate of potassa is long exposed, in a melted state, to the air. When nitre is decomposed by a strong heat, peroxide of potassium is also produced. It is decomposed by water into potassa, which unites with the latter, and into oxygen gas. Carbonate of totassa, KO,C02-f-2HO.—Salts of potassa containing a vege- table acid are of constant occurrence in plants, where they perform important, but not yet perfectly understood, functions in the economy of those beings. Tho potassa is derived from the soil, which, when capable of supporting vege- table life, always contains that substance. When plants are burned, the organic acids are destroyed, and the potassa left in the state of carbonate. It is by these indirect means that carbonate, and, in fact, nearly all the salts of potassa, are obtained; the great natural depository of the alkali is the felspar of granitic and other unstratified rocks, where it is combined with silica, and in an insoluble state. Its extraction thence is attended with too many difficulties to be attempted on the large scale; but when these rocks disintegrate into soils, and the alkali acquires solubility, it is gradually taken up by plants, and accumulates in their substance in a condition highly favor- able to its subsequent applications. Potassa-salts are always most abundant in the green and tender parts of plants, as may be expected, since from these evaporation of nearly pure water takes place to a large extent; the solid timber of forest trees contains com- paratively little. In preparing the salt on an extensive scale, the ashes are subjected to a process called lixiviation: they are put into a large cask or tun, having an aperture near the bottom, stopped by a plug, and a quantity of water is added. After some hours the liquid is drawn off, and more water added, that the whole of the soluble matter may be removed. The weakest solutions are poured upon fresh quantities of ash, in place of water. The solutions are then evaporated to dryness, and the residue calcined, to remove a little brown organic matter: the products are the crude potash and pearlash of commerce, of which very large quantities are obtained from Russia and America. This salt is very impure; it contains silicate and sulphate of potassa, chloride of potassium, &c. Tho purified carbonate of potassa of pharmacy is prepared from the crude article by adding an equal weight of cold water, agitating, and filtering: most of the foreign salts are, from their inferior degree of solubility, left behind. The solution is then boiled down to a very small bulk, and suffered to cool, when the carbonate separates in small crystals containing 2 equiv. of water, which are drained from the mother-liquor, and then dried in a stove. A still purer salt may be obtained by exposing to a red-heat purified cream of tartar (acid tartrate of potassa), and separating the carbonate by solution in water and crystallization, or evaporation to dryness.1 Carbonate of potassa is extremely deliquescent, and soluble in less than its own weight of water ; the solution is highly alkaline to test paper. It is in- soluble in alcohol. By heat the water of crystallization is driven off, and by a temperature of full ignition the salt is fused, but not otherwise changed. This substance is largely used in the arts, and is a compound of great im- portance. Bicarbonate of potassa, KO,CO,-f- HO,C02.—When a stream of carbonic acid gas is passed through a cold solution of carbonate of potassa, the gas is rapidly absorbed, and a white, crystalline, and less soluble substance separated, "Crystals of bicarbonate when exposed to heat yield pure carbonate. In saturating carbonate with carbonic acid, silica is separated, and in the subsequent crystallization the sulphate of potassa, by which means the more common impurities are withdrawn, and by heat the carbonio acid which has been added is driven off.—It. B.] 238 POTASSIUM. which is the new compound. It is collected, pressed, re-dissolved in warm water, and the solution left to crystallize. Bicarbonate of potassa is much less soluble than simple carbonate; it requires for that purpose 4 parts of cold water. The solution is nearly neutral to test-paper, and has a much milder taste than the preceding salt, When boiled, carbonic acid is disengaged. The crystals, which are large and beauti- ful, derive their form from a right rhombic prism; they are decomposed by heat, water and carbonic acid being extricated, and simple carbonate left behind. Nitrate of potassa ; nitre; saltpetre, KO,NOg.—This important com- pound is a natural product, being disengaged by a kind of efflorescence from the surface of the soil in certain dry and hot countries. It may also be pro- duced by artificial means, namely, by the oxidation of ammonia in presence of a powerful base. In France, large quantities of artificial nitre are prepared by mixing animal refuse of all kinds with old mortar or hydrate of lime and earth, and placing the mixture in heaps, protected from the rain by a roof, but freely exposed to the air. From time to time the heaps are watered with putrid urine, and the mass turned over, to expose fresh surfaces to the air. When much salt has been formed, the mixture is lixiviated, and the solution, which contains nitrate of lime, mixed with carbonate of potassa; carbonate of lime is formed, and the nitric acid transferred to the alkali. The filtered solution is then made to crystalline, and the crystals purified by re-solution and crystallization, the liquid being stirred to prevent the formation of large crystals. All the nitre used in this country comes from the East Indies: it is dissolved in water, a little carbonate of potassa added to precipitate lime, and then the salt purified as above. Nitrate of potassa crystallizes in anhydrous six-sided prisms, with dihedral summits: it is soluble in 7 parts of water at 60° (15°-5C), and in its own weight of boiling water. Its taste is saline and cooling, and it is without action on vegetable colors. At a temperature below redness it melts, and by a strong heat is completely decomposed. When thrown on the surface of many metals in a state of fusion, or when mixed with combustible matter and heated, rapid oxidation ensues, at the ex- pense of the oxygen of the nitric acid. Examples of such mixtures are found in common gunpowder, and in nearly all pyrotechnic compositions, which burn in this manner independently of the oxygen of the air, and even under water. Gunpowder is made by very intimately mixing together nitrate of potassa, charcoal, and sulphur, in proportions which approach 1 eq. nitre, 3 eq. carbon, 1 eq. sulphur. These quantities give, reckoned to 100 parts and compared with the pro- portions used in the manufacture of the English Government powder,1 ±hc following results: — Theory. Proportions J in practice. Nitrate of potassa.....74-8 . 75 Charcoal.......13-3 [ [ 15 Sulphur.......H-9 _ _ 10 100- 100 The nitre is rendered very pure by the means already mentioned, freed from water by fusion, and ground to fine powder; the sulphur and charcoal the latter being made from light wood, as dogwood or elder, are also finely ground after which the materials are weighed out moistened with water, and thorou°-hly 1 Dr. M'Cullocb, Ency. Brit. POTASSIUM. 239 mixed, by grinning under an edge-mill. The mass is then subjected to great pressure, and the mill-cake thus produced broken in pieces, and placed in sieves made of perforated vellum, moved by machinery, each containing, in addition, a round piece of heavy wood. The grains of powder broken off by attrition fall through the holes in the skin, and are easily separated from the dust by sifting. The powder is, lastly, dried by exposure to steam-heat, and sometimes glazed or polished by agitation in a kind of cask mounted on an axis. When gunpowder is fired, the oxygen of the nitrate of potassa is transferred to the carbon, forming carbonic acid; the sulphur combines with the potas- sium, and the nitrogen is set free. The large volume of gas thus produced, and still farther expanded by the very exalted temperature, sufficiently accounts for the explosive effects. Sulphate of rorASSA, KO,S03.—The acid residue left in the retort when nitric acid is prepared is dissolved in water, and neutralized with crude car- bonate of potassa. The solution furnishes, on cooling, hard transparent crystals of the neutral sulphate, which may be re-dissolved in boiling water, and re-crystallized. Sulphate of potassa is soluble in about 10 parts of cold, and in a much smaller quantity of boiling water; it has a bitter taste, and is neutral to test- paper. The crystals much resemble those of quartz in figure and appearance ; they are anhydrous, and decrepitate when suddenly heated, which is often the case with salts containing no water of crystallization. They are quite insolu- ble in alcohol. Bisulphate of potassa, KO,S03 + HO,S03.—The neutral sulphate in powder is mixed with half its weight of oil of vitriol, and the whole evapo- rated quite to dryness in a platinum vessel, placed under a chimney; the fused salt is dissolved in hot water, and left to crystallize. The crystals have the figure of flattened rhombic prisms, and are much moresoluble than the neutral salt, requiring only twice their weight of water at 60° (15°-5C), and less than half that quantity at 212° (100°C). The solution has a sour taste and strongly- acid reaction. Bisulphate of potassa, anhydrous, K0,2S03.—Equal weights of neutral sulphate of potassa and oil of vitriol are dissolved in a small quantity of warm distilled water, and set aside to cool. The anhydrous sulphate crystallizes out in long delicate needles, which if left several days in the mother-liquor disap- pear, and give place to crystals of the ordinary hydrated bisulphate above described. This salt is decomposed by a large quantity of water.1 Sksquisulphate of potassa, 2(K0,S03)4- HO,S03. — A salt, crystallizing in fine needles resembling those of asbestos, and having the composition stated, was obtained by Mr. Phillips from the nitric acid residue. M. Jacquelain was unsuccessful in his attempts to reproduce this compound. Ciilohate of potassa, KO,C105.—The theory of the production of chloric acid, by the action of chlorine gas on a solution of caustic potassa, has been already described (p. 164). Chlorine gas is conducted by a wide tube into a strong and warm solution of carbonate of potassa, until absorption of the gas ceases. The liquid is, it necessary, evaporated, and then allowed to cool, in order that the slightly- soluble chlorate may crystallize out. The mother-liquor affords a second crop of crystals, but they are much more contaminated by chloride of potassium. It may be purified by one or two re-crystallizations. Chlorate of potassa is soluble in about 20 parts of cold and 2 of boiling water; the cryst.ils are anhydrous, flat, and tabular; in taste it somewhat resembles nitre. Heated, it disengages oxygen gas from both acid and base, and leaves chloride of potassium. By arresting the decomposition when the 1 Jacquelain, Ann. Chim. et Phys. vol. vii. p. 311. 240 POTASSIUM. evolution of gas begins, and re-dissolving the salt, perchlorate of potassa and chloride of potassium may be obtained. This salt deflagrates violently with combustible matter, explosion often oc- curring by friction or blows. When about one gram weight of chlorate and an equal quantity of sulphur are rubbed in a mortar, the mixture explodes with a loud report; hence it cannot be used in the preparation of gunpowder instead of nitrate of potassa. Chlorate of potassa is now a large article of commerce, being employed, together with phosphorus, in making instantaneous- light matches. , . Perchlorate of potassa, KO,C10r—This has been already noticed under the head of perchloric acid. It is best prepared by projecting powdered chlorate of potassa into warm nitric acid, when the chloric acid is resolved into perchloric acid, chlorine and oxygen gases. The salt is separated by crystallization from the nitrate. Perchlorate of potassa is a very feebly- Boluble salt; it requires 55 parts of cold water, but is more freely taken up at a boiling heat. The crystals are small, and have the figure of an octahe- dron, with square base. It is decomposed by heat, in the same manner as chlorate of potassa. Sulphides of potassium.—There are not less than five or six distinct com- pounds of potassium and sulphur, of which, however, only three are of suffi- cient importance to be noticed here: these'are the compounds, containing KS, KS8, and KS6. Simple or protosulphide of potassium is formed by directly combining the metal with sulphur, or by reducing sulphate of potassa at a red-heat by hy- drogen or charcoal powder. Another method is to take a strong solution of hydrate of potassa, and after dividing it into two equal portions, saturate the one with sulphuretted hydrogen gas, and then add the remainder. The whole is then evaporated to dryness in a retort, and the residue fused. The protosulphide is a crystalline cinnabar-red mass, very soluble in water. The solution has an exceedingly offensive and caustic taste, and is decomposed by acids, even carbonic acid, with evolution of sulphuretted hydrogen, and formation of a salt of the acid used. This compound is a strong sulphur- base, and unites with the sulphides of hydrogen, carbon, arsenic, &c, forming crystallizable saline compounds. One of these, KS-f-HS, is produced when hydrate of potassa is saturated with sulphuretted hydrogen, as before mentioned. The higher sulphides are obtained by fusing the protosulphide with different proportions of sulphur. They are soluble in water, and decomposed by acids, in the same manner as the foregoing compound, with this addition, .that the excess of sulphur is precipitated as a fine white powder. Hepar sulphuris is a name given to a brownish substance, sometimes used in medicine, made by fusing together different proportions of carbonate of potassa and sulphur. It is a variable mixture of the two higher sulphides with hyposulphite and sulphate of potassa. When equal parts of sulphur and dry carbonate of potassa are melted together at a temperature not exceeding 482° (250°C), the decomposition of the salt is quite complete, and all the carbonic acid is expelled. The fused mass dissolves in water, with the exception of a little mechanically-mixed sulphur, with dark-brown color, and the solution is found to contain nothing besides pentasulphide of potassium and hyposulphite of potassa. f 2 eq. potassium-------- 2 eq. pentasulphide of potas- 3 eq. potassa 4 2 eq. oxygen ^^^ sium ( 1 eq. potassa^^x^^ ,0 , , S 10 eq. sulphur~^>'<~-©^>>^ 12 eq. sulphur < 0 ^ ,r, ^^-^s^ n , \ 2 eq. sulphur---------=^a- i eq. hyposulphite of potassa. 3KO + 12S = 2KSB+ KO,S202. POTASSIUM. 241 When the mixture has been exposed to a temperature approaching that of ignition, it is found, on the contrary, to contain sulphate of potassa, arising from the decomposition of the hyposulphite which then occurs. U ea f * e(l- potassium ------—^ \ eq. pentasulphide /posulph. X 3 eq. sulphur \acid. (. 8 eq. oxygen - ^^ 3 eq. sulphate of po- tassa. 4(KO,S202) = KS5+ 3(KO,S03). From both these mixtures the pentasulphide of potassium may be extracted by alcohol, in which it dissolves. When the carbonate is fused with half its weight of sulphur only, then the tersulphide, KS3, is produced instead of that above indicated; 3 eq. of potassa and 8 eq. of sulphur containing the elements of 2 eq. sulphide and 1 eq. hyposulphite. The effects described happen in the same manner when hydrate of potassa is substituted for the carbonate; and, also, when a solution of the hydrate is boiled with sulphur, a mixture of sulphide and hyposulphite always results. Chloride of potassium, KC1. —This salt is obtained in large quantity in the manufacture of chlorate of potassa; it is easily purified from any por- tions of the latter by exposure to a dull red-heat. It is also contained in kelp, and is separated for the use of the alum-maker. Chloride of potassium closely resembles common salt in appearance, assum- ing, like that substance, the cubic form of crystallization. The crystals dis- solve in three parts of cold, and in a much less quantity of boiling water; they are anhydrous, have a simple saline taste, with slight bitterness, and fuse wheu exposed to a red-heat. Chloride of potassium is volatilized by a very high temperature. Iodide of potassium, KI. — There are two different methods of preparing this important medicinal compound. (1.) When iodine is added to a strong solution of caustic potassa free from carbonate, it is dissolved in large quantity, forming a colorless solution con- taining iodide of potassium and iodate of potassa; the reaction is the same as in the analogous case with chlorine. When the solution begins to be per- manently colored by the iodine, it is evaporated to dryness, and cautiously heated tb redness ; by which the iodate of potassa is entirely converted into iodide of potassium. The mass is then dissolved in water, and, after filtra- tion, made to crystallize. (2.) Iodine, water, and iron-filings or scraps of zinc, are placed in a warm situation until the combination is complete, and the solution colorless. Tho resulting iodide of iron or zinc is then filtered, and exactly decomposed with solution of pure carbonate of potassa, great care being taken to avoid excess of the latter. Iodide of potassium and carbonate of protoxide of iron, or zinc, are obtained; the former is separated by filtration, and evaporated until the solution is sufficiently concentrated to crystallize on cooling, the washings of the filter being added to avoid loss. Iodide of iron . . ) ™™ ^* Iodide of potassium. ! f Potassium ^xT 1 otassa j oxygen -~-__JX. Carbonic acid ------ ^ Carbonate of protoxide of iron. Fcl + K0,C02 = KI + FeO,C02. f 242 sodium. The second method is ort the whole to be preferred. Iodide of potassium crystallizes in cubes, which are often, from some un- explained cause, milk-white and opaque; they are anhydrous, and fuse readily when heated. The salt is very soluble in water, but not deliquescent, when pure, in a moderately-dry atmosphere ; it is dissolved by alcohol. Solution of iodide of potassium, like those of all the soluble iodides, dis- solves a large quantity of free iodine, forming a deep-brown liquid, not de- composed by water. Bromide of potassium, KBr. — This compound may be obtained by pro- cesses exactly similar to those just described, substituting bromine for the iodine. It is a colorless and very soluble salt, quite indistinguishable in ap- pearance and general characters from the iodide. The salts of potassa are colorless, when not associated with a colored metal- lic oxide or acid. They are all more or less soluble in water, and may be distinguished by the following characters: —■ (1.) Solution of tartaric acid, added to a moderately-strong solution of potassa-salt, gives, after some time, a white, crystalline precipitate of cream of tartar; the effect is greatly promoted by strong agitation. (2.) Solution of bichloride of platinum, with a little hydrochloric acid, if necessary, gives, under similar circumstances, a crystalline yellow precipitate, which is a double salt of bichloride of platinum and chloride of potassium. Both this compound and cream of tartar are, however, soluble in about 60 parts of cold water. An addition of alcohol increases the delicacy of both tests. (3.) Perchloric acid, and hydrofluosilicic acid, give rise to slightly-soluble white precipitates when added to a potassa-salt. (4.) Salts of potassa usually color the outer blowpipe-flame purple or vio- let : this reaction is clearly perceptible only when the potassa-salts are pure. SODIUM. This metal was obtained by Davy very shortly after the discovery of potas- sium, and by similar means. It may be prepared in large quantity by de- composing carbonate of soda by charcoal at a high temperature. Six parts of anhydrous carbonate of soda are dissolved in a little hot water, and mixed with two parts of finely-powdered charcoal and one part of char- coal in lumps. The whole is then evaporated to dryness, transferred to the iron retort before described, and heated in the same manner to whiteness. A receiver containing rock-oil is adapted to the tube, and the whole operation carried on in the same way as when potassium is made. The process, when well conducted, is easier and more certain than that of making potassium. Very important improvements have been made in the manufacture of sodium by M. Deville, consisting partly in the simplification of the receiver, partly in the addition of carbonate of lime to the mixture, which appears to facilitate the reduction in a most remarkable manner. Sodium is a silver-white metal, greatly resembling potassium in every re- spect ; it is soft at common temperatures, melts at 194° (90°C), and oxidizes very rapidly in the air. Its specific gravity is 0-972. Placed upon the sur- face of cold water, sodium decomposes that liquid with great violence but seldom takes fire unless the motion of the fragment be restrained, and its rapid cooling diminished, by adding gum or starch to tho water. With hot water it takes fire at once, burning with a bright-yellow flame, and giving rise to a solution of soda. The equivalent of sodium is 23, and its symbol Na (Natrium). There are two well-defined compounds of sodium and oxygen ; the protoxide anhydrous soda, NaO, and the binoxide, Na02, or perhaps, teroxide, NaO : sodium. 243 they are formed by burning sodium in air or oxygen gas, and resemble in every respect the corresponding compounds of potassium. Hydrate of soda, NaO, HO.—This substance is prepared in practice by decomposing a somewhat dilute solution of carbonate of soda by hydrate of lime: the description of the process employed in the case of hydrate of potassa, and the precautions necessary, apply word for word to that of soda. The solid hydrate is a white, fusible substance, very similar in properties to hydrate of potassa. It is deliquescent, but dries up again after a time in consequence of the absorption of carbonic acid. The solution is highly alkaline, and a powerful solvent for animal matter: it is used in large quantity for making soap. The strength of a solution of caustic soda may be roughly determined from a knowledge of its density, by the aid of the following table drawn up by Dr. Dalton. TABLE OF PERCENTAGE OF SODA IN SOLUTIONS OF DIFFERENT DENSITY. )ensity. Percentage of real soda. Density. Percentage of real soda. 2-00 . . ' . . 77-8 1-40 .... 29-0 1-85 . 63-6 1-36 26-0 1-72 . 53-8 1-32 23 0 1-63 . 46-6 1-29 190 153 . 41-2 1-23 16-0 1-50 . 36-8 1-18 130 117 . 340 - 1-12 90 1-44 . 31-0 1-06 4-7 Carbonate of soda, NaO,CO2-f-10RO. — Carbonate of soda was once ex- clusively obtained from the ashes of sea-weeds, and of plants, such as the Salsola soda, which grew by the sea-side, or, being cultivated in suitable localities for the purpose, were afterwards subjected to incineration. The barilla, yet employed to a small extent in soap-making, is thus produced in several places on the coast of Spain, as Alicante, Carthagena, &c. That made in Brittany is called varec. Carbonate of soda is now manufactured on a stupendous scale from common salt, or rather from sulphate of soda, by a process of which the following is an outline: — A charge of 600 lbs. of common salt1 is placed upon the hearth of a well- heated reverberatory furnace, and an equal weight of sulphuric acid of sp. gr. 1-6 poured upon it through an opening in the roof, and r'g- 154- thoroughly mingled with the ^//^^/Zw^m salt; hydrochloric acid gas is disengaged, which is either allowed to escape by the chimney, or condensed by suitable apparatus, and the salt is converted into sulphate of soda. This part of" the process takes for completion about four hours, and requires much care and skill The sulphate is next reduced to powder, and mixed with an equal weight of chalk or limestone, and half as much small coal, both ground or crushed. V//////////'// ■'//„ ™ + efficient appears to be the method of Dr. Kitterband, which consists in throwinsr into th h •? a small quantity of sal-ammoniac, when carbonate of ammonia is formed which i«V l +-r 1 with the steam, chloride of calcium remaining in solution. It need scirroW v,Q «, !,• j.f . this plan is inapplicable in the case of permanently-hard waters. """""J De mentioned that CALCIUM. 261 boid, whose angles measure 105°-5/ and 74°-55/: its density varies from 2-5 to 2-8. The rarer variety, or arragonite, is found in crystals whose primary form is a right rhombic prism; a figure having no geometrical relation to the preceding; it is, besides, heavier and harder. Phosphates of lime.—A number of distinct compounds of lime and phos- phoric acid are known. Two tribasic phosphates, 2CaO,HO,P06 and 3CaO, P05, are produced when the corresponding soda-salts are added in solution to chloride of calcium ; the first is slightly crystalline, and the second gelatinous. When the first phosphate is digested with ammonia, or dissolved in acid, and rcprecipitated by that alkali, it is converted into the second. The earth of bones consists principally of what appears to be a combination of these two salts. Another phosphate, containiug 2 equivalents of basic water, has been described, which completes the series; it is formed by dissolving either of the preceding in phosphoric, hydrochloric, or nitric acid, and evaporating until tho salt separates on cooling in small platy crystals. It is the substance which yields phosphorus, when heated with charcoal, in the ordinary process of manufacture before described. Bibasic and monobasic phosphates of lime also exist. These phosphates, although insoluble in water, dissolve readily in dilute acids, even acetic acid. The mineral apatite is chiefly phosphate of lime. Fluobide of calcium; fluor-spar; CaF.—This substance is important as the most abundant natural source of hydrofluoric acid and the other fluorides. It occurs beautifully crystallized, of various colors, in lead-veins, the crystals having commonly the cubic, but sometimes the octahedral form, parallel to the faces of which latter figure they always cleave. Some varieties, when heated, emit a greenish, and some a purple phosphorescent light. The fluo- ride is quite insoluble in water, and is decomposed by oil of vitriol in the manner already mentioned, vide p. 167. Chloride of lime; bleachinq-powder. — When hydrate of lime, very slightly moist, is exposed to chlorine gas, the latter is eagerly absorbed, and a compound produced which has attracted a great deal of attention ; this is the bleaching-powder of commerce, now manufactured on an immense scale, for bleaching linen and cotton goods. It is requisite, in preparing this sub- stance, to avoid with the greatest care all elevation of temperature, which may be easily done by slowly supplying the chlorine in the first instance. The product, when freshly and well prepared, is a soft, white powder, which attracts moisture from the air, and exhales an odor sensibly different from that of chlorine. It is soluble in about 10 parts of water, the unaltered hydrate being left behind; the solution is highly alkaline, and bleaches feebly. When hydrate of lime is suspended in cold water, and chlorine gas trans- mitted through the mixture, the lime is gradually dissolved, and the same peculiar bleaching compound produced; the alkalies also, either caustic or carbonated, may by similar means be made to absorb a large quantity of chlorine, and give rise to corresponding compounds; such are the "disinfect- ing solutions" of M. Labarraque. The most consistent view of the constitution of these curious compounds is that which supposes them to contain salts of hypochlorous acid, a substance as remarkable for bleaching powers as chlorine itself; and this opinion seems borne out by a careful comparison of the properties of the bleaching salts • with those of the true hypochlorites. Hypochlorous acid can be actually obtained from good bleaching-powder, by distilling it with dilute sulphuric or nitric acid, in quantity insufficient to decompose the whole; when the acid is used in excess, chlorine is disengaged.1 If this view be correct, chloride of calcium must be formed simultaneously with the hypochlorite, as in the following diagram: 1 M. Gay Lussac, Ann. Chim. et Phys. 3rd series, v. 296. 262 CALCIUM. Chloride of calcium. -.Hypochlorite of lime. 2CaO + 2C1 = CaCl + CaO,C10. When the temperature of the hydrate of lime has risen during the absorption of the chlorine, or when the compound has been subsequently exposed to heat, its bleaching properties are impaired or altogether destroyed ; it then contains chlorate of lime and chloride of calcium; oxygen, in variable quantity, is usually set free. The same change seems to ensue by long keeping, even at the common temperature of the air. In an open vessel it is speedily destroyed by the carbonic acid of the atmosphere. Commercial bleaching-powder thus constantly varies in value with its age, and with the care originally bestowed upon its preparation: the best may contain about 30 per cent, of available chlorine, easily liberated by an acid, which is, however, far short of the theo- retical quantity. The general method in which this substance is employed for bleaching is the following: — the goods are first immersed in a dilute solution of chloride of lime, and then transferred to a vat containing dilute sulphuric acid. Decom- position ensues; both the lime of the hypochlorite and the calcium of the chloride are converted into sulphate of lime, while the free hypochlorous and hydrochloric acid yield water and free chlorine. The chlorine thus disengaged in contact with the cloth causes the destruc- tion of the coloring matter. This process is often repeated, it being unsafe to use strong solutions. White patterns are on this principle imprinted upon colored cloth, the figures being stamped with tartaric acid thickened with gum- water, and then the stuff immersed in the chloride bath, when the parts to which no acid has been applied remain unaltered, while the printed portions are bleached. For purifying an offensive or infectious atmosphere, as an aid to proper ven- tilation, the bleaching-powder is very convenient. The solution is exposed in shallow vessels, or cloths steeped in it are suspended in the apartment, when the carbonic acid of the air slowly decomposes it in the manner above de- scribed. An addition of a strong acid causes rapid disengagement of chlorine. The value of any sample of bleaching-powder may be easily determined by the following method) in which the feebly-combined chlorine is estimated by its effect in peroxidizing a protosalt of iron, of which two equivalents require one of chlorine: the latter acts by decomposing water and liberating a corre- sponding quantity of oxygen — 78 (more correctly 78-16) grains of green sulphate of iron are dissolved in about two ounces of water, and acidulated by a few drops of sulphuric or hydrochloric acid: this quantity will require for peroxidation 10 grains of chlorine. Fifty grains of the chloride of lime to be examined are next rubbed up with a little tepid water, and the whole transferred to the alkalimeter1 before described, which is then filled up to 0 with liquid water, after which the contents are well mixed by agitation. The liquid is next gradually poured into the solution of iron, with constant stirring, until the latter has become peroxidized, which may be known by a drop ceas- ing to give a deep-blue precipitate with ferricyanide of potassium. The num- ber of grain-measures of the chloride solution employed may then be read off: since these must contain 10 grains of serviceable chlorine, the quantity of the latter in the 50 grains may be easily reckoned. Thus, suppose 72 such measures have been taken, then Chlorine Lime\£Y?en / Calcium Chlorine Lime 1 Vide p. 246. MAGNESIUM. 263 Mensnres. Gr?. chlorine. Measures. Grs. chlorine. 72 : 10 = 100 : 13-89 The bleaching-powder contains, therefore, 27-78 per cent.1 Baryta, strontia, and lime are thus distinguished from all other substances, and from each other. Caustic potassa, when free from carbonate, and caustic ammonia, occasion no precipitates in dilute solutions of the earths, especially l2 the first two, the hydrates being soluble in water. Alkaline carbonates, and carbonate of ammonia, give white precipitates, insoluble in excess, of the precipitant, with all three. Sulphuric acid, or a sulphate, added to very dilute solutions of the earths in question, gives nn immediate white precipitate with baryta, a similar pre- cipitate after a short interval with strontia, and occasions no change with the lime-salt. The precipitates with baryta and strontia are insoluble in nitric acid. Solution of sulphate of lime gives an instantaneous cloud with baryta, and one with strontia after a little time. Sulphate of strontia is itself sufficiently soluble to occasion turbidity when mixed with chloride of barium. Lastly, the soluble oxalates give a white precipitate in the most dilute solu- tions of lime, which is not dissolved by a drop or two of hydrochloric or by an excess of acetic acid. This is an exceedingly characteristic test. The chlorides of strontium and calcium dissolved in alcohol color the flame of the latter red or purple; salts of baryta communicate to the flame a pale- green tint. MAGNESIUM. A few pellets of sodium are placed at the bottom of a test-tube of hard Cer'man glass, and covered with fragments of fused chloride of magnesium. The heat of a spirit-lamp is then applied until reaction has been induced: this takes place with great violence and elevation of temperature, chloride of sodium being formed, and metallic magnesium set free. When the tube and its contents are completely cold, it is broken up, and the fragments put into cold water, by which the metal is separated-from the salt. _ Bunsen has lately succeeded in reducing the magnesium by the decomposi- tion of fused chloride of magnesium, by means of the electric battery.2 Magnesium is a white, malleable metal, of 1-75 sp. gr., fusible at a red heat; it is almost as volatile as zinc, and can therefore be purified by distil- lation. Magnesium is not sensibly acted upon by cold water; it is oxidized by hot water. Heated in the air, it burns and produces magnesia, which is the only oxide. Sulphuric and hydrochloric acids dissolve it readily, evolving hydrogen. The equivalent of this metal is 12, and its symbol Mg. Macnesia; calcined magnesia; MgO. — This is prepared with great ease by exposing the magnesia alba of pharmacy to a full red heat in an earthen or platinum crucible. It forms a soft, white powder, which slowly attracts moisture and carbonic acid from the air, and unites quietly with water to a hydrate which possesses a feeble degree of solubility, requiring about 5000 parts of water at 60° (15°-5C) and 36,000 parts at 212° (100°C). The alka- 1 Graham"s Elements, p. 414. « Matthicssen states that instead of the pure chloride it is simpler to use a mixture of three oquivalents of chloride of potassium and four of chloride of magnesium; some chloride of ammonium is added, the mixture is then fused and electrolyzed. 264 MAGNESIUM. Unity of magnesia can only be observed by placing a small portion in a moist- ened state upon test-paper; it neutralizes acids, however, in the most com- plete manner. It is infusible. _ Chloride of magnesium, MgCl.—When magnesia, or its carbonate, is dis- solved in hydrochloric acid, there can be no doubt respecting the simultaneous production of chloride of magnesium and water; but when this solution comes to be evaporated to dryness, the last portions of water are retained with such obstinacy, that decomposition of the water is brought about by the concurring attractions of magnesium for oxygen, and of chlorine for hydrogen; hydro- chloric acid is expelled, and magnesia remains. If, however, sal-ammoniac or chloride of potassium happen to be present, a double salt is produced, which is easily rendered anhydrous. The best mode of preparing the chloride is to divide a quantity of hydrochloric acid into two equal portions, to neutralize one with magnesia, and the other with ammonia, or carbonate of ammonia; to mix these solutions, evaporate them to dryness, and then expose the salt to a red-heat in a loosely-covered porcelain crucible. Sal-ammoniac sublimes, and chloride of magnesium in a fused state remains; the latter is poured out upon a clean stone, and when cold, transferred to a well-stopped bottle. The chloride so obtained is white and crystalline. It is very deliquescent and highly soluble in water, from which it cannot again be recovered by eva- poration, for the reasons just mentioned. When long exposed to the air in a melted state, it is converted into magnesia. It is soluble in alcohol. Sulphide of magnesium is formed by passing vapor of sulphide of carbon over magnesia, in capsules of coke, at a strong red-heat. Sulphate of magnesia; Epsom salt; MgO,S03-f- 7HO.—This salt occurs in sea-water, and in that of many mineral springs,, and is now manufactured in large quantities by acting on magnesian limestone by diluted sulphuric acid, and separating the sulphate of magnesia from the greater part of the slightly-soluble sulphate of lime by the filter. The crystals are derived from a right rhombic prism; they are soluble in an equal weight of water at 60° (15°-5C), and in a still smaller quantity at 212° (100°C). The salt has a nauseous bitter taste, and, like many other neutral salts, purgative properties. AVhen exposed to heat, 6 equivalents of water readily pass off, the seventh being energetically retained. Sulphate of magnesia forms beautiful double salts with the sulphates of potassa and ammonia, which contain 6 equivalents of water of crystallization. Carbonate of magnesia.—The neutral carbonate MgO,C02, occurs native in rhombohedral crystals, resembling those of calcareous spar, embedded in talc- slate: a soft earthy variety is sometimes met with. When magnesia alba is dissolved in carbonic acid water, and the solution left to evaporate spontaneously, small prismatic crystals are deposited, which consist of carbonate of magnesia, with 3 equivalents of water. The magnesia alba itself, although often called carbonate of magnesia, is not so in reality ; it is a compound of carbonate with hydrate. It is prepared by mixing hot solutions of carbonate of potassa or soda, and sulphate of mag- nesia, the latter being kept in slight excess, boiling the whole a few minutes, during which time much carbonic acid is disengaged, and then well washing the precipitate so produced. If the solution be very dilute, the magnesia alba is exceedingly light and bulky; if otherwise, it is denser. The compo- sition of this precipitate is not perfectly constant. In most cases it contains 4 (MgO,C02)+ MgO.HO-f- 6HO. Magnesia alba is slightly soluble in water, especially when cold. Phosphate of magnesia, 2MgO,HO,P05-f- 14H0.— This salt separates in small colorless prismatic crystals when solutions of phosphate of soda and sulphate of magnesia are mixed and suffered to stand some time. According to Professor Graham, it is soluble in about 1000 parts of cold water. Phos- MAGNESIUM. 265 phate of magnesia exists in the grain of the cereals, and can be detected in considerable quantity in beer. Phosphate of magnesia and ammonia, 2MgO,NH40,P05+ 12HO.—When a soluble phosphate is mixed with a salt of magnesia, and ammonia or its car- bonate added, a crystalline precipitate, having the above composition, sub- Bides immediately if the solutions are concentrated, and after some time if very dilute; in the latter case, the precipitation is promoted by stirring. This salt is slightly soluble in pure water, but scarcely so in saline and ammoniacal liquids. When heated, it is resolved into bibasic phosphate (pyrophosphate) of magnesia, containing 35-71 per cent, of magnesia. At a strong red-heat it fuses to a white enamel-like mass. The phosphate of magnesia and am- monia sometimes forms an urinary calculus, and occurs also in guano. In practical analysis, magnesia is often separated from solutions by bring- ing it into this state. The liquid, free from alumina, lime, &c, is mixed with phosphate of soda and excess of ammonia, and gently heated for a short time. The precipitate is collected upon a filter and thoroughly washed with water containing a little ammonia, after which it is dried, ignited to redness, and weighed. The proportion of magnesia is then easily calculated. Silicates of magnesia.—The following natural compounds belong to this class:—Steatite*or soap-stone, MgO,Si03, a soft, white, or pale-colored, amor- phous substance, found in Cornwall and elsewhere ;—Meerschaum, MgO,Si03 -f- HO, from which pipe-bowls are often manufactured; Chrysolite, 3MgO, Si03, a crystallized mineral, sometimes employed for ornamental purposes; a portion of magnesia is commonly replaced by protoxide of iron, which commu- nicates a green color;—Serpentine is a combination of silicate and hydrate of magnesia; Jade, an exceedingly hard stone, brought from New Zealand, con- tains silicate of magnesia combined with silicate of alumina; its green color is due to sesquioxide of chromium; Augite and hornblende are essentially double salts of silicic acid, magnesia, and lime, in which the magnesia is moro or less replaced by its isomorphous substitute, protoxide of iron. The salts of magnesia are strictly isomorphous with those of the protoxides of zinc, of iron, of copper, &c. ; they are usually colorless, and are easily recognized by the following characters:— A gelatinous white precipitate with caustic alkalis, including ammonia, insoluble in excess, but soluble in solution of sal-ammoniac. A white precipitate with the carbonates of potassa and soda, but none with carbonate of ammonia in the cold. A white crystalline precipitate with soluble phosphates, on the addition of a little ammonia. 23 266 ALUMINIUM. SECTION III. METALS OF THE EARTHS PROPER. aluminum or aluminium. Alumina, the only known oxide of this metal, is a substance of very abun- dant occurrence in nature in the state of silicate, as in felspar and its asso- ciated minerals, and in the various modifications of clay thence derived. Aluminium was first obtained by Wohler: it is prepared in the same manner as magnesium, but with rather more difficulty: a platinum or iron tube closed at one extremity may be employed. Sesquichloride of aluminium is first intro- duced, and upon that about an equal bulk of potassium loosely wrapped in platinum foil. The lower part of the tube is then heated so as to sublime the chloride and bring its vapors in contact with the melted potassium. The re- duction takes place with great disengagement of heat. The metal, separated by cold water from the alkaline chloride, has a tin-white color and perfect lustre. It is obtained in small fused globules by the heat attained in the reduction, which are malleable, and have a specific gravity of 2-6. When heated in the air or in oxygen it takes fire and burns with brilliancy, pro- ducing alumina.1 Aluminium has for its equivalent the number 13-7 ; its symbol is AI. Alumina, A1203.—This substance is inferred to be a sesquioxide, from its isomorphism with the red oxide of iron. It is prepared by mixing solution of alum with excess of ammonia, by which an extremely bulky, white, gela- tinous precipitate of hydrate of alumina is thrown down. This is washed, dried, and ignited to whiteness. Thus obtained, alumina constitutes a white, tasteless, coherent mass, very little acted upon by acids. The hydrate, on the contrary, when simply dried in the air, or by gentle heat, dissolves freely in dilute acid, and in caustic potassa or soda, from which it is precipitated by the addition of sal-ammoniac. Alumina is fusible before the oxyhydrogen blowpipe. The mineral called corundum, of which the ruby and sapphire are transparent varieties, consists of nearly pure alumina in a crystallized state, with a little coloring oxide: emery, used for polishing glass and metals, is a ' The metal, like magnesium, has been obtained by Bunsen by electrolysis, and also by De- ville, who has moreover prepared the metal in large ingots from the chloride of aluminium by sodium. Some chloride of aluminium is put into a glass tube, through which hydrogen gas is passed. Sodium is then introduced, and the tube is heated to melt the sodium, and to cause the vapor of the chloride of aluminium to be decomposed by it. The aluminium remains in a melted mass, which is washed with water. Dr. Percy and H. Rose heat powdered cryolite (flu- oride of aluminium and sodium) with potassium to bright redness in a small iron crucible and thus obtain aluminium with greater ease than from chloride of aluminium. On a larger scale aluminium is obtained by heating (for half an hour) equal parts of chloride of potassTum and cryolite with two parts of sodium and five of cryolite. The chloride of potassium fuses the fluoride of sodium which is formed. When cold, the melted mass is immersed in water- after twelve hours it is crushed, and the globules of aluminium separated. To obtain a mass the globules of aluminium are melted with ohloride of potassium. ' ALUMINIUM. 267 coarse variety of corundum. Alumina is a very feeble base, and its salts havo often an acid reaction. Sesqoichloride of aluminium, A12C13.—The solution of alumina in hydro- chloric acid behaves, when evaporated to dryness, like that of magnesia, the chloride being decomposed by the water, and alumina and hydrochloric acid produced. The chloride may be thus prepared;—Pure precipitated alumina is dried and mixed with lampblack, and the mixture strongly calcined in a covered crucible. It is then transferred to a porcelain tube fixed across a furnace, and heated to redness in a stream of chlorine gas, when the alumina, yielding to the attraction of the chlorine on the one hand and the carbon on the other, for each of its constituents, suffers decomposition, carbonic oxide being disengaged, and sesquichloride of aluminium formed; the latter sub- limes, and condenses in the cool part of the tube. Sesquichloride of aluminium is a crystalline yellowish substance, excessively greedy of moisture, and very soluble. Once dissolved, it cannot be again recovered. Sulphide of aluminium, A12S3.—The vapor of sulphide of carbon is passed over alumina at a bright-red heat; a glassy melted mass remains, which is instantly decomposed by water with evolution of sulphuretted hydrogen. Sulphate of alumina, A1203,3S034- 18HO.—Prepared by saturating dilute sulphuric acid with hydrate of alumina, and evaporating; or, on a large scale, by heating clay with sulphuric acid. It crystallizes in thin pearly plates, soluble in 2 parts of water; it has a sweet and astringent taste, and an acid reaction. Heated to redness, it is decomposed, leaving pure alumina. Two other sulphates of alumina, with excess of base, are also described, one of which is insoluble in water. Sulphate of alumina combines with the sulphates of potassa, soda, and am- monia, forming double salts of great interest, the alums. Common alum, the source of all the preparations of alumina, contains Al203,3SOs -f- KO,S03 -\- 24 HO. It is manufactured, on a very large scale, from a kind of slaty clay, loaded with bisulphide of iron, which abounds in certain localities. This is gently roasted, and then exposed to the air in a moistened state; oxygen is absorbed, the sulphur becomes acidified, sulphate of protoxide of iron and sul- phate of alumina are produced", and afterwards separated by lixiviation with water. The solution is next concentrated, and mixed with a quantity of chloride of potassium, which decomposes the iron-salt, forming protochloride of iron and sulphate of potassa, which latter combines, with the sulphate of alumina, to form alum. By crystallization the alum is separated from the highly-soluble chloride of iron, and afterwards easily purified by a repetition of that process. Other methods of alum-making exist, and are sometimes employed. Potassa-alum crystallizes in colorless, transparent octahedra, which often exhibit the faces of the cube. It has a sweetish and astringent taste, reddens litmus-paper, and dissolves in 18 parts of water at 60° (15-5°C,) and in its own weight of boiling water. Exposed to heat, it is easily ren- dered anhydrous, and, by a very high temperature, decomposed. The crys- tals have little tendency to change in the air. Alum is largely used in the arts, in preparing skins, dyeing, &c.; it is occasionally contaminated with oxide of iron, which interferes with some of its applications. The celebrated Roman alum, made from alum-stone, a felspathic rock, altered by sulphurous vapors, was once much prized on account of its freedom from this impurity. A mixture of dried alum and sugar, carbonized in an open pan, and then heated to redness, out of contact of air, furnishes thepyrophorus of Homberg, which ignites spontaneously on exposure to the atmosphere. The essential ingredient is, in all probability, finely-divided sulphide of potassium. Soda-alum, in which sulphate of soda replaces sulphate of potassa, has a form and constitution similar to that of the salt described: it is, however, much more soluble, and difficult to crystallize. 268 ALUMINIUM. Ammonia-alum, containing NII40,S03, instead of KO,S03, very closely re- sembles common potassa-alum, having the same figure, appearance, and con- stitution, and nearly the same degree of solubility as that substance. It is sometimes manufactured for commercial use. When heated to redness, it yields pure alumina. Few of the other salts of alumina, except the silicates, present points of interest: these latter are of great importance. Silicates of alumina enter into the composition of a number of crystallized minerals, among which felspar occupies, by reason of its abundant occurrence, a prominent place. Granite, porphyry, trachyte, and other ancient unstratified rocks, consist in great part of this mineral, which, under peculiar circumstances, by no means well un- derstood, and particularly by the action of the carbonic acid of the air, suffer complete decomposition, becoming converted into a soft, friable mass of earthy matter. This is the origin of clay: the change itself is seen in great perfec- tion in certain districts of Devonshire and Cornwall, the felspar of the fine white granite of those localities being often disintegrated to an extraordinary depth, and the rock altered to a substance resembling soft mortar. By wash- ing, this finely-divided matter is separated from the quartz and mica, and the milk-like liquid, being collected in tanks and suffered to stand, deposits the suspended clay, which is afterwards dried, first in the air and afterwards in a stove, and employed in the manufacture of porcelain. The composition as- signed to unaltered felspar is Al203,3Si03 + KO,Si03, or alum, having silicic acid in the place of sulphuric. The exact nature of the change by which it passes into porcelain clay is unknown, although it evidently consists in the abstraction of silica and alkali. ■ When the decomposing rock, contains oxide of iron, the clay produced is colored. The different varieties of shale and slate result from the alteration of ancient clay-beds, apparently in many instances by the infiltration of water holding silica in solution: the dark appearance of some of these deposits is due to bituminous matter. It is a common mistake to confound clay with alumina; all clays are essen- tially silicates of that base; they often vary a good deal in composition. Dilute acids exert little action on these compounds; but by boiling with oil of vitriol, alumina is dissolved out, and finely-divided silica left behind. Clays containing an admixture of carbonate of lime are termed marls, and are recognized by effervescing with acids. A basic silicate of alumina, 2Al203,Si03, is found crystallized, constituting the beautiful mineral called cyanite. The compounds formed by the union of the silicates of alumina with other silicates are almost innumerable; a soda- felspar, albite, containing that alkali in place of potassa, is known, and there are two somewhat similar lithia-compounds, spodumene and petalite. The zeolites belong to this class; analcime, nepheline, mesotype, &c, are double silicates of soda and alumina, with water of crystallization. Stilbite, heulandite, laumonite, prehnite, &c, consist of silicate of lime, combined with silicate of alumina. The garnets, axinite, mica, &c, have a similar composition, but are anhydrous. Sesquioxide of iron is very often substituted for alumina in these minerals. Alumina, when in solution, is distinguished without difficulty. Caustic potassa and soda occasion white gelatinous precipitates of hydrate of alumina, freely soluble in excess of the alkali. Ammonia produces a similar precipitate, insoluble in excess of the reagent. The alkaline carbonates and carbonate of ammonia precipitate the hydrate' with escape of carbonic acid. The precipitates are insoluble in excess! ' CERIUM, LANTHANIUM, AND DIDYMIUM. 269 beryllium (glucinfm). This metal is prepared from the chloride in the same manner as aluminium, which it very much resembles in its properties. It is not altered when exposed to the air. Even in the flame of the blowpipe, or in oxygen, it is but slightly coated with a thin film of berylla. Beryllium is malleable; it fuses at a temperature lower than the fusing point of silver. Its sp. gr. is 2-1. The equivalent of beryllium is 14-1, and the symbol Be. Berylla, Be203, is a rare earth found in the emerald, beryl, and enclose, from which it may be extracted by a tolerably simple process. It very much resembles alumina, but is distinguished from that substance by its solubility, when freshly precipitated, in a cold solution of carbonate of ammonia, from which it is again thrown down on boiling. The salts of berylla have a sweet taste, whence its former name glucina (yXu His. Permanganic acid, Mn207. — When manganate of potassa, free from any great excess of alkali, is put into a large quantity of water, it is resolved into hydrated binoxide of manganese, which subsides, and a deep-purple liquid, containing permanganate of potassa. This effect is accelerated by heat. The changes of color accompanying this decomposition are very remarkable, and have procured for the substance the name mineral chameleon; excess of alkali hinders, in some measure, the reaction, by conferring greater stability on the manganate. Permanganate of potassa is easily prepared on a considerable scale. Equal parts of very finely-powdered binoxide of manganese and chlo- rate of potassa are mixed with rather more than one part of hydrate of potassa dissolved in a little water, and the whole exposed, after evaporation to dry- ness, to a temperature just short of ignition. The mass is treated with hot vyater, the insoluble oxide separated by decantation, and the deep-purple liquid concentrated by heat, until crystals form on its surface; it is then left to cool. The crystals have a dark-purple color, and are not very soluble in cold water. The manganates and permanganates are decomposed by contact with organic matter: the former are said to be isomorphous with the sulphates, and the latter with the perchlorates. Salts of the protoxide of manganese are very easily distinguished by re- agents. The fixed caustic alkalies, ammonia, give white precipitates, insoluble in excess, quickly becoming brown. The carbonates of the fixed alkalies, and carbonate of ammonia, give white precipitates, but little subject to change, and insoluble in excess of carbonate of ammonia. Sulphuretted hydrogen gives no precipitate, but sulphide of ammonium throws down insoluble, flesh-colored sulphide of manganese which is very characteristic. Ferrocyanide of potassium gives a white precipitate. Manganese is also easily detected by the blowpipe; it gives with borax an amethystine bead in the outer or oxidizing flame, and a colorless one in the inner flame. Heated upon platinum foil with carbonate of soda, it yields a green mass of manganate of soda. This is by very far the most important member of the group of metals under discussion: there are few substances to which it yields in interest, when it is considered how very intimately the knowledge of the properties and uses of iron is connected.with human civilization. _ Metallic iron is of exceedingly rare occurrence; it has been found at Canaan in Connecticut,1 forming a vein about two inches thick in mica-slate, but it invariably enters into the composition of those extraordinary stones known to fall from the air, called meteorites. Isolated masses of soft malleable iron also of large dimensions, lie loose upon the surface of the earth in South America and elsewhere, and are presumed to have had a similar origin: these latter contain, in common with the iron of the undoubted meteorites, nickel. In an oxidized condition, the presence of iron may be said to be universal: it con- stitutes a great part of the common coloring matter of rocks and soils; it is contained in plants, and forms an essential component of the blood of the animal body. In the state of bisulphide it is also very common. Pure iron may be prepared, according to Mitscherlich, by introducing into a Hessian „ * Phillips' Mineralogy, 4th edit. p. 208. 278 IRON. crucible 4 parts of fine iron wire cut small, and 1 part of black oxide of iron. This is covered with a mixture of white sand, lime, and carbonate of potassa, in the proportion used for glass-making, and a cover being closely applied, the crucible is exposed to a very high degree of heat. A button of pure metal is thus obtained, the traces of carbon and silicium present in the wire having been removed by the oxygen of the oxide. Pure iron has a white color and perfect lustre: it is extremely soft and tough, and has a specific gravity of 7-8. The crystalline form is probably the cube, to judge from appearances now and then exhibited. In good bar-iron or wire a distinct fibrous texture may always be observed when the metal has been attacked by rusting or by the application of an acid, and upon the per- fection of this fibre much of its strength and value depends. Iron is the most tenacious of all the metals, a wire ^ of an inch in diameter bearing a weight of 60 lbs. It is very difficult of fusion, and before becoming liquid passes through a soft or pasty condition. Pieces of iron pressed or hammered to- gether in this state cohere into a single mass: the operation is termed welding, and is usually performed by sprinkling a little sand over the heated metal which combines with the superficial film of oxide, forming a fusible silicate, which is subsequently forced out from between the pieces of iron by the pressure applied; clean surfaces of metal are thus presented to each other, and union takes place without difficulty. Iron does not oxidize in dry air at common temperatures: heated to redness, it becomes covered with a scaly coating of black oxide, and at a high white- heat burns brilliantly, producing the same substance. In oxygen gas the combustion occurs with still greater ease. The finely-divided spongy metal, prepared by reducing the red oxide by hydrogen gas, takes fire spontaneously in the air.1 Pure water, free from air and carbonic acid, does not tarnish a surface of polished iron, but the combined agency of free oxygen and moisture speedily leads to the production of rust, which is a hydrate of the sesquioxide. The rusting of iron is wonderfully promoted by the presence of a little acid vapor.2 At a red-heat iron decomposes water, evolving hydrogen, and passing into the black oxide. Dilute sulphuric and hydrochloric acids dissolve it freely with separation of hydrogen. Iron is strongly magnetic up to a red heat, when it loses all traces of that remarkable property. The equivalent of iron is 28, and its symbol Fe. Four compounds of iron and oxygen are described. Protoxide ...... FeO Sesquioxide (peroxide) . . . Fe203 Proto-sesquioxide (bla'ck oxide) . . Fe30. = FeO, Fe203 Ferric acid . . . . . . Fe 03. Protoxide, FeO.— This is a very powerful base, neutralizing acids com- pletely, and isomorphous with magnesia, oxide of zinc, &c. It is almost unknown in a separate state, from its extreme proneness to absorb oxygen and pass into the sesquioxide. When a salt of this substance is mixed with caustic alkali or ammonia, a bulky whitish precipitate of hydrate of the protoxide falls, which becomes nearly black when boiled, tho water beino- separated. This hydrate exposed to the air, very rapidly changes, becoming green and 1 [When obtained at a heat below redness.—It. B.] * [The rusting of iron proceeds with rapidity after it once begins, extending from the point first affected Iron rust contains ammonia, resulting from the combination of the nascent hydrogen of decomposed water uniting with dissolved nitrogen. This is an inmortant noint in medico-legal investigations, as it is considered, that, when stains on a steel instrument Vield ammonia by the action of potassa, the presence of organic matter is proved • but as mst con- ting wThTorss^-rS.f neCe$Sary t0 aSCertaln US abSeUCe' °r drive " off>Vevious to opera- iron. 279 ultimately red-brown. The soluble salts of protoxide of iron have commonly a delicate pale-green color, and a nauseous metallic taste. Sixm-ioxide, Fe203. — A feeble base, isomorphous with alumina. Sesqui- oxide of iron occurs native, most beautifully crystallized, as specular iron ore, in the island of Elba, and elsewhere: also as red and brown hccmatites, the latter being a hydrate. It is artificially prepared by precipitating a solution of sulphate of the sesquioxide or the sesquichloride of iron by excess of ammonia, and washing, drying, and igniting the yellowish-brown hydrate thus produced: fixed alkali must not be used in this operation, as a portion is retained by the oxide. In fine powder, this oxide has a full-red color, and is used as a pigment, being prepared for the purpose by calcination of the sul- phate of the protoxide; the tint varies somewhat with the temperature to which it has been exposed. This oxide is unaltered in the fire, although easily reduced at a high temperature by carbon or hydrogen. It dissolves in acids, with difficulty after strong ignition, forming a series of reddish salts, which have an acid reaction and an astringent taste. Sesquioxide of iron is not acted upon by the magnet.1 Black oxiije; magnetic oxide; loadstone, Fe304, or probably FeO-f-Fe203. —A natural product, one of the most valuable of the iron ores, often found in regular octahedral crystals, which are magnetic. It may be prepared by mixing due proportions of salts of the protoxide and sesquioxide of iron, pre- cipitating them by excess of alkali, and then boiling the mixed hydrates, when the latter unite to a black sandy substance, consisting of minute crystals of the magnetic oxide. This oxide is the chief product of the oxidation of iron at a high temperature in the air and in aqueous vapor. It is incapable of forming salts. Feiuuc acid, Fe03. — A very remarkable compound of recent discovery. The simple^ mode of preparing it is to heat to full redness, for an hour, in a covered crucible, a mixture of one part of pure sesquioxide of iron, and four parts of dry nitre. The brown, porous, deliquescent mass is treated when cold with ice-cold water, by which a deep amethystine red solution of ferrate of potassa is obtained. This gradually decomposes even in the cold, evolving oxygen gas, and depositing sesquioxide; by heat the decomposition is very rapid. Tho solution of ferrate of potassa gives no precipitate with salts of lime, magnesia, or strontia, but when mixed with one of baryta, a deep crimson, insoluble compound falls, which is a ferrate of that base, and is very permanent. Protochloride of iron, FeCl.—Formed by transmitting dry hydrochloric acid gas over red-hot metallic iron, or by dissolving iron in hydrochloric acid. The latter solution yields, when duly concentrated, green crystals of proto- chloride, containing 4 equivalents of water; they are very soluble and deli- quescent, and rapidly oxidize in the air. ' Sesquiciilouide of iron, Fe2Cl8. — Usually prepared by dissolving sesqui- oxide in hydrochloric acid. The solution, evaporated to a syrupy consistence deposits red, hydrated crystals, which are very soluble in water and alcohol! It forms double salts with chloride of potassium and sal-ammoniac. When evaporated to dryness and strongly heated, much of the chloride is decomposed yielding sesquioxide and hydrochloric acid: the remainder sublimes and afterwards condenses in the form of small brilliant red crystals, which deliquesce rapidly. The solution of sesquichloride of iron is capable of dis- solving a large »xerss of recently-precipitated hydrate of the sesquioxide by which it acquires a much darker color. Anhydrous sesquichloride of iron is also produced by the action of chlorine upon the heated metal. • fin the form of hydrate. Fej03+3IIO, as recently precipitated from the persulphate bv am monia, it oou.Utu es the antidote for arseuious acid. The affinity for water in tln7ca«its -lor pa^nVfrom 280 IRON. Protiodide of iron, Fel.—This is an important medicinal preparation; it is easily made by digesting iodine with water and metallic iron. The solution is pale green, and yields, on evaporation, crystals resembling those of the chloride, which rapidly oxidize on exposure to air. It is best preserved in solution'in contact with excess of iron.1 A sesqui-iodide of iron exists, which is yellowish-red and soluble. Sulphides of iron.—Several compounds of iron and sulphur are described. of these the two most important are the following. Protosulphide, FeS, is a blackish, brittle substance, attracted by the magnet, formed by heating together iron and sulphur. It is dissolved by dilute acids with evolution of sulphuretted hydrogen gas, and is constantly employed for that purpose in the laboratory, being made by projecting into a red-hot crucible a mixture of 2J parts of sulphur and 4 parts of iron filings or borings of cast-iron, and ex- cluding the air as much as possible. The same substance is formed when a bar of white-hot iron is brought in contact with sulphur. The bisulphide of iron, FeS2, iron pyrites, is a natural product, occurring in rocks of all ages, and evidently formed in many cases by the gradual deoxidation of sulphate of iron by organic matter. It has a brass-yellow color, is very hard, not attracted by the magnet, and not acted upon by dilute acids. Exposed to heat, sulphur is expelled, and an intermediate sulphide, analogous probably to the black oxide, is produced. This substance also occurs native, under the name of magnetic pyrites. The bisulphide is sometimes used in the manufacture of sulphuric acid. Compounds of iron with phosphorus, carbon, and silicium exist, but little is known respecting them in a definite state. The carbide is contained in cast- iron and in steel, to which it communicates ready fusibility; the silicium- compound is also found in cast-iron. Phosphorus is a very hurtful substance in bar-iron, as it renders it brittle or cold-short. Sulphate of protoxide of iron; green vitriol, FeO,S03-f-7HO.—This beautiful and important salt may be obtained by directly dissolving iron in dilute sulphuric acid; it is generally prepared, however, and that on a very large scale, by contact of air and moisture with common iron pyrites, which, by absorption of oxygen, readily furnishes the substance in question. Heaps of this material are exposed to the air until the decomposition is sufficiently advanced; the salt produced is then dissolved out by water, and the solution made to crystallize. It forms large green crystals, of the composition above stated, which slowly effloresce and oxidize in the air; it is soluble in about twice its weight of cold water. Crystals containing 4, and also 2 equivalents of water, have been obtained. Sulphate of protoxide of iron forms double salts with the sulphates of potassa and ammonia. Sulphate of sesquioxide of iron, Fe203,8S03.—Prepared by adding to a solution of the protosalt exactly one-half as much sulphuric acid as it already contains, raising the liquid to the boiling-point, and then dropping in nitric acid until the solution ceases to blacken by such addition. The red liquid thus obtained furnishes, on evaporation to dryness, a buff-colored amorphous mass, which, when put into water, very slowly dissolves. With the sulphates of potassa and ammonia, this salt yields compounds, having the form and constitution of alums; the crystals are nearly destitute of color. These latter are decomposed by water, and sometimes by long keeping when in a dry state. They are best prepared by exposing to spontaneous evaporation a solution of sulphate of sesquioxide of iron, to which sulphate of potass*, or of ammonia has been added. Nitrate of the protoxide of iron, FeO,NOg. —When dilute cold nitric acid is made to act to saturation upon protosulphide of iron and the solution » [Or protected from the action of oxygen by pure honey, or other saccharine substance, in the proportion of one part to three of the solution.—R. B.] ^ IRON. 281 evaporated in vacuo, pale-green and very soluble crystals of protonitratc are obtained, which are very subject to alteration. The nitrate of the sesquioxide is readily formed by pouring nitric acid, slightly diluted, upon iron; it is a deep-red liquid, apt to deposit an insoluble basic salt, and is used in dying. Carbonate of protoxide of iron, FeO,C02. — The white precipitate ob- tained by mixing solutions of protosalt of iron and alkaline carbonate: it cannot be washed and dried without losing carbonic acid and absorbing oxygen. This substance occurs in nature as spathose iron ore, associated with variable quantities of carbonate of lime and of magnesia; and also in the common clay iron-stone, from which nearly all the British iron is made. It is often found in mineral waters, being soluble in excess of carbonic acid ; such waters are known by the rusty matter they deposit by exposure to the air. No carbonate of the sesquioxide is known. The phosphates of iron are all insoluble.1 Salts of the protoxide of iron are thus distinguished: — Caustic alkalies, and ammonia, give nearly white precipitates, insoluble in excess of the reagent, rapidly becoming green, and ultimately brown, by ex- posure to air. Alkaline carbonates, and carbonate of ammonia, throw down the white carbonate, also very subject to change. Sulphuretted hydrogen gives no precipitate, but sulphide of ammonium throws down black protosulphide of iron, soluble in dilute acids. Ferrocyanide of potassium gives a nearly-white precipitate, becoming deep blue on exposure to air. Salts of the sesquioxide are thus characterized : — ('au-itic alkalies, and ammonia, give foxy-red precipitates of hydrated ses- quioxide. insoluble in excess. The carbonates behave in a similar manner, the carbonic acid escaping. Sulphuretted hydrogen gives a nearly-white precipitate of sulphur, and re- duces the soMpiioxide to protoxide. Sulphide of ammonium gives a black precipitate, slightly soluble in excess. Ferrocyanide of potassium yields Prussian blue. Tincture or infusion of gall-nuts strikes intense bluish-black with the most liluto solutions of salts of sesquioxide of iron. Iron manufacture.—This most important branch of industry consists, as now conducted, of two distinct parts; viz., the production from the ore of a fusible (carbide) of iron, and the subsequent decomposition of the carbide, and its conversion into pure or malleable iron. The clay-iron ore is found in association with coal, forming thin beds or nodules: it consists, as already mentioned, of carbonate of iron mixed with clay; sometimes lime and magnesia arc also present. It is broken in pieces, and exposed to heat in a furnace resembling a lime-kiln, by which the water and carbonic acid are expelled, and the ore rendered dark-colored, denser and also magnetic; it is then ready for reduction. The furnace in which this operation is performed is usually of very large dimensions, fifty feet or more • [Phosphate of protoxide or Irox, 2FeO,TIO,P05, is formed when a solution of common phosphate of soda .s added to a solution of protosulphate of iron. It falls as a white1?™U>1 tat-, gradually become bluish by the action of the air; it is soluble in acids, from whfch am l'lKisi-iuTE of sesquioxidk OF irox is formed by adding common phosphate of soda to nersnl S^flT h' f ,r"aLa Whit" Pr-i>'itate is produced insoluble^ ammonia un£™2," ta£n.-l«vf *°da * Pl'eseUt- Uig,;sted witU the fixed alkali3 or »n,I»°»ia U beame" 24* 282 IRON. in height, and constructed of brick-work with great solidity, the interior being lined with excellent fire- Fig. 162. bricks: the figure will be at once understood from the sectional drawing. The furnace is close at the bottom, the fire being main- tained by a powerful artificial blast introduced by two or three tuyere-pipes, as shown in the sec- tion. The materials, consisting of due proportions of coke or carbonized coal, roasted ore, and limestone, are constantly supplied from the top, the operation pro- ceeding continuously night and day, often for years, or until the furnace is judged to require re- pair. In the upper part of the furnace, where the temperature is still very high, and where com- bustible gases abound, the iron of the ore is probably reduced to the metallic state, being dissemi- nated through the earthy matter of the ore. As the whole sinks down and attains a still higher degree of heat, the iron becomes converted into carbide by cemen- tation, while the silica and alu- mina unite with the lime, pur- posely added, to a kind of glass or slag, nearly free from oxide of iron. The carbide and slag, , . , , „ , „ both in a melted state, reach at last the bottom of the furnace, where they arrange themselves in the order of their densities: the slag flows out at certain apertures contrived for the purpose, and the iron is discharged from time to time, and suffered to run into rude moulds of sand by opening an orifice at the bottom of the recipient previously stopped with clay. Such is the origin of crude or cast-iron of which there are several varieties, distinguished by differences of color hard- ness, and composition, and known by the names of gray, black, and white iron. The first is for most purposes the best, as it admits of being filed and cut with perfect case. The black and gray kinds probably contain a mechani- cal admixture of graphite, which separates during solidification A great improvement has been made in the above-described process, by substituting raw coal for coke, and blowing hot air, instead of cold, into the furnace This is effected oy causing the air, on leaving the blowinsr'machine to circulate through a system of red-hot iron pipesS until itl emSS becomes high enough to melt lead This alteration'has air■ dyXted Z;PTductSaVmS m ' ' aPPearS' any "W t0 th/quSSr of The conversion of cast into bar iron is effected hv or, „__*• « i puddling; previous to which, however, it commonly under™? If theory of which is not perfectly intelligible. It is remS ^T,' ^ cooled, by which it becomes white, crystalline, and excepti- Wl*"^J state it is called fine metal The puddling process is cond„et£^ d '' r **"' veverberatory furnace, into whiclftbe chaise o/fiue-Te^ IRON. 283 Bide aperture. This is speedily melted by the flame, and its surface covered with a crust of oxide. The workman then, by the aid of an iron tool, dili- gently stirs the melted mass, so as intimately to mix the oxide with the metal; he now and then also throws in a little water, with the view of promoting more rapid oxidation. Small jets of blue flame soon appear upon the surface of the iron, and the latter, after a time, begins to lose its fluidity, and ac- quires, in succession, a pasty and a granular condition. At this point the fire is strongly urged, the' sandy particles once more cohere, and the contents of the furnace now admit of being formed into several large balls or masses, which are then withdrawn, and placed under an immense hammer, moved by machinery, by which each becomes quickly fashioned into a rude bar. This is reheated, and passed between grooved cast-iron rollers, and drawn out into a long bar or rod. To make the best iron, the bar is cut into a number of pieces, which arc afterwards piled or bound together, again raised to a weld- ing heat, and hammered or rolled into a single bar; and this process of piling or fagoting is sometimes twice or thrice repeated, the iron becoming greatly improved thereby. The general nature of the change in the puddling furnace is not difficult to explain. Cast-iron consists essentially of iron in combination with carbon and silicium. When strongly heated with oxide of iron, those compounds un- dergo decomposition, the carbon and silicium becoming oxidized at the ex- pense of the oxygen of the oxide. As this change takes place, the metal gradually loses its fusibility, but retains a certain degree of adhesiveness, so that when at last it comes under the tilt-hammer, or between the rollers, the particles of iron become agglutinated into a solid mass, while the readily- fusible silicate of the oxide is squeezed out and separated. All these processes are, in Great Britain, performed with coal or coke, but the iron obtained is, in many respects, inferior to that made in Sweden and Russia from the magnetic oxide, by the use of wood charcoal, a fuel too dear to be extensively employed in England. Plate-iron is, however, sometimes made with charcoal. Steel.—A very remarkable, and most useful substance, prepared by heating iron in contact with charcoal. Bars of Swedish iron,,. nr___• c „ Genth and Gibbs. (Transactions of the Smithsonian Institute) * Mem0lr 0f Me8srSl ZINC. 291 At 773° (111°-GC) it melts: at a bright red-heat it boils and volatilizes, and, if the air be admitted, burns with a splendid greenish light, generating the oxide. Dilute acids dissolve zinc very readily; it is constantly employed in this manner in preparing hydrogen gas. The equivalent of zinc lias been fixed at 32-6; its symbol is Zn. Protoxide of zinc, ZnO.— Only one oxide of this metal is known to exist; it is a strong base, in its compounds isomorphous with magnesia; it is pre- pared either by burning zinc in atmospheric air, or by heating to redness the carbonate. Oxide of zinc is a white tasteless powder, insoluble in water, but freely dissolved by acids. When heated it is yellow, but turns white again on cooling. It is getting into use as a substitute for white lead. Sulphate of zinc ; white-vitriol; ZnO, S03+7HO. This salt is hardly to be distinguished by the eye from sulphate of magnesia; it is prepared either by dissolving the metal in dilute sulphuric acid, or more economically, by roasting the native sulphide, or blende, which, by absorption of oxygen, becomes in great part converted into sulphate of the oxide. The altered mineral is thrown hot into water, and the salt obtained by evaporating the clear solution. Sulphate of zinc has an astringent metallic taste, and is used in medicine as an emetic. The crystals dissolve in 2h parts of cold, and in a much smaller quantity of hot water. Crystals containing 6 equivalents of water have been observed. Sulphate of zinc forms double salt's with tho sulphates of potassa and ammonia. Carbonate of zinc, ZnO,C02.—The neutral carbonate is found native; tho white precipitate obtained by mixing solutions of zinc and of alkaline carbo- nates is a combination of carbonate and hydrate. When heated to redness, it yields pure oxide of zinc. Chloride of zinc, ZuCl.—The chloride may be prepared by heating metallic zinc in chlorine; by distilling a mixture of zinc-filings and corrosive subli- mate ; or, more easily, by dissolving zinc in hydrochloric acid. It is a nearly white, translucent, fusible substance, very soluble in water and alcohol, and very deliquescent. A strong solution of chloride of zinc is sometimes used as a bath for obtaining a graduated heat above 212° (100°C). Chloride of zinc unites with sal-ammoniac and chloride of potassium to double salts: the former of these, made by dissolving an equivalent of zinc in the requisite quantity of hydrochloric acid, and then adding an equivalent of sal-ammoniac, is very useful in tinning and soft-soldering copper and iron. A salt of zinc is easily distinguished by appropriate reagents. Caustic potassa and soda give a white precipitate of hydrate, freely soluble in excess of alkalL Ammonia behaves in the same manner ; an excess re-dissolves the precipi- tate instantly. The carbonates of potassa and soda give white precipitates, insoluble in excess. Carbonate of ammonia gives also a white precipitate, which is rc-dissolvcd by an excess. Ferrocyanide of potassium gives a white precipitate. Sulphuretted hydrogen causes no change.1 Sulphide of ammonium throws clown white sulphide of zinc. The applications of metallic zinc to the purposes of roofing, the construc- tion of water-channels, &c, are well known; it is sufficiently durable, but inferior in this respect to copper. With neutral solutions, or zinc-salts of an organic acid, a white precipitate ensues. 292 CADMIUM. — BISMUTH. CADMIUM. This metal was discovered in 1817 by Stromeycr, and by Hermann; it accompanies the ores of zinc, especially those occurring in Silesia, and, being more volatile than that substance, rises first in vapor when the calamine is subjected to distillation with charcoal. Cadmium resembles tin in color, but is somewhat harder; it is very malleable, has a density of 8 7, melts below 500° (260°C), and is nearly as volatile as mercury. It tarnishes but little in the air, but, when strongly heated, burns. Dilute sulphuric and hydrochloric acids act but little on this metal in the cold ; nitric acid is its best solvent. The equivalent of cadmium is 56; its symbol is Cd. Protoxide of cadmium, CdO. — The oxide maybe prepared by igniting either the carbonate or the nitrate: in the former case it has a pale-brown color, and in the latter a much darker tint, and forms octohedral microscopic crystals. Oxide of cadmium is infusible; it dissolves in acids, producing a series of colorless salts; it attracts carbonic acid from the atmosphere and turns white. Sulphate of cadmium, CdO,S03 -f- 4110. — This is easily obtained by dis- solving the oxide or carbonate in dilute sulphuric acid ; it is very soluble in water, and forms double salts with the sulphates of potassa and of ammonia, which contain respectively CdO,S03 + KO,S03-f- 6HO and CdO,S03 -4- NII.O S03 + GHO. Chloride of cadmium, CdCl. — This is a very soluble salt, crystallizing in small four-sided prisms. SuLrniDE of cadmium is a very characteristic compound, of a bright-yellow color, forming microscopic crystals, fusible at a high temperature. It is obtained by passing sulphuretted hydrogen gas through a solution of the sul- phate, nitrate, or chloride. This compound is useful as a yellow coloring matter, of great beauty and permanence. It occurs native as greenokite. The salts of cadmium are thus distinguished: — Fixed caustic alkalis give a white precipitate of hydrated oxide, insoluble in excess. Ammonia gives a similar white precipitate, readily soluble in excess. The alkaline carbonates, and carbonate of ammonia, throw down whito carbonate of cadmium, insoluble in excess of either precipitant. Sulphuretted hydrogen and sulphide of ammonium precipitate the yellow sulphide of cadmium. BISMUTH. Bismuth is found chiefly in the metallic state, disseminated through various rocks, from which it is separated by simple exposure to heat. The metal is highly crystalline and very brittle ; it has a reddish-white color, and a density of 9-9. Crystals of great beauty may be obtained by slowly coolin«- a con- siderable mass of this substance until solidification has commenced, and then piercing the crust, and pouring out the fluid residue. Bismuth melt's at about 500° (260°C), and volatilizes at a high temperature: it is little oxidized by the air, but burns when strongly heated with a bluish flame. Nitric acid somewhat diluted, dissolves it freely. ' The equivalent of bismuth is 208, its symbol is Bi. Teroxide of bismuth, Bi03. — This is the base of all the salts It is a straw-yellow powder, obtained by gently igniting the neutral or basic nitrate It is fusible at a high temperature, and in that state acts towards siliceous matter as a powerful flux. Bismuthic acid, Bi06.—If teroxide of bismuth be suspended in a strong solution of potassa, and chlorine be passed through this liquid, decomposition of water ensues; hydrochloric acid being formed and the teroxide berm- con verted into the pentoxide. To separate any teroxide which may have escaped U R A X I U M . 293 oxidation, the powder is treated with dilute nitric acid, when the bismuthic tcid is left as a reddish powder, which is insoluble in water. This substance combines with bases, but the compounds are not very well known. AVhen heated it loses oxygen, an intermediate oxide Bi04 being formed, which may be considered as bismuthate of bismuth, 2Bi04 = Bi03, Bi05. Nitrate of bismuth, Bi03,3N05 -4- 10HO. — When bismuth is dissolved in moderately-strong nitric acid to saturation, and the whole left to cool, large, colorless, transparent crystals of the neutral nitrate are deposited. Water decomposes these crystals; an acid solution containing a little bismuth is obtained, and a brilliant white crystalline powder is left, which varies to a certain extent in composition according to the temperature and the quantity of water employed, but which frequently consists of a basic nitrate of the teroxide Bi03,N05, -f- 2110. A solution of nitrate of bismuth, free from any great excess of acid, poured into a large quantity of cold water, yields an inso- luble basic nitrate, very similar in appearance to the above, but containing rather a larger proportion of teroxide of bismuth. This remarkable decom- position illustrates at once the basic property of water, and the feeble affinity of teroxide of bismuth for acids, the nitric acid dividing itself between the two bases. The decomposition of a neutral salt by water is by no means an uncommon occurrence in the history of the metals; a solution of terchloride of antimony exhibits the same phenomenon; certain salts of mercury are affected in a similar manner, and other cases might perhaps be cited, less conspicuous, where the same change takes place to a smaller extent. The basic nitrate of teroxide of bismuth was once extensively employed as a cosmetic, but is said to injure the skin, rendering it yellow and leather-like. It has been used in medicine. The other salts of bismuth possess few points of interest. ^ Bismuth is; sufficiently characterized by the decomposition of the nitrate by vater, and by the blackening the nitrate undergoes when exposed to the action of sulphuretted hydrogen gas. A mixture of 8 parts of bismuth, 5 parts of lead, and 3 of tin, is known under the name of fusible metal, and is.employed in taking impressions from dies and for other purposes; it melts below 212° (100°C). The discrepancies so frequently observed between the properties of alloys and those of their con- stituent metals, plainly show that such substances must be looked upon as true chemical compounds, and not as mere mixtures: in the present case the proof is complete, for the fusible metal has lately been obtained in crystals. URANIUM. This metal is found in a few minerals, as pitchblende and uranitc, of which the former is the more abundant. According to M. PeUigot, the substance obtained by the action of hydrogen gas upon the black oxide, and formerly taken for metallic uranium, is not in reality the metal, but a protoxide, capable of uniting directly with acids, and like the protoxide of manganese, not decomposable by hydrogen at a red-heat. The metal itself can be obtained ouly by the intervention of potassium, applied in the same manner as in the preparation of magnesium. It is described as a black coherent powder, or a white malleable metal, according to the state of aggregation, not oxidized by air or water, but eminently combustible when exposed to heat. It unites also with great violence with chlorine and with sulphur. M. Peligot admits three distinct oxides of uranium, beside? two other compounds of the metal and oxygen, which he designates as suboxides. The equivalent of uranium is 60. Its symbol is U. Protoxide of uranium, UO. —This is the body formerly considered as the 25 * 294 COTPER. metal; it is prepared by several processes, one of which has been already mentioned. It is a brown powder, sometimes highly crystalline. When in minute division it is pyrophoric, taking fire in the air, and burning to black oxide. It forms with acids a series of green salts. A corresponding chloride exists, which forms dark-green octahedral crystals, highly deliquescent and soluble in water. M. Peligot attributes a very extraordinary double function to this substance, namely, that of acting as a protoxide and forming salts with acids, and that of combining with chlorine or oxygen after the fashion of an elementary body. Proto-sesquioxide of uranium ; black oxide ; U405, or 2UO-|-U203.—The black oxide, formerly considered as protoxide, is produced when either pro- toxide or sesquioxide is strongly heated in the air, the former gaining, and the latter losing, a certain quantity of oxygen. It forms no salts, but is resolved by solution in acids into protoxide and sesquioxide. It is extensively used in painting on glass and porcelain. Sesquioxide of uranium, U203. —The sesquioxide is the best known and most important of the three; it forms a number of extremely beautiful greenish- yellow salts. When caustic alkali is added to a solution of nitrate of sesqui- oxide of uranium, a yellow precipitate of hydrated oxide falls, which retains, however, a portion of the precipitant. The hydrate cannot be exposed to a heat sufficient to expel the water without a commencement of decomposition, A better method of obtaining the sesquioxide is to heat by means of an oil- bath the powdered and dried crystals of the nitrate to 480° (249°C), until no more nitrous fumes are disengaged. Its color in this state is chamois- yellow. Nitrate of sesquioxide of uranium, U203,N06-f-6HO; or (U202) 0, NO5-4-6HO; U202 being the supposed quasi-metal.—This nitrate is the start- ing-point in the preparation of all the compounds of uranium: it may be prepared from pitchblende by dissolving the pulverized mineral in nitric acid, evaporating to drynesss, adding water and filtering; the liquid furnishes by due evaporation crystals of nitrate of uranium, which are purified by a repetition of the process, and, lastly, dissolved in ether. This latter solution yields the pure nitrate. The green salts of uranium are peroxidized by boiling with nitric acid. A yellow precipitate with caustic alkalies, convertible by heat into black oxide; a brown precipitate with sulphide of ammonium; and no precipitate with sulphuretted hydrogen gas, sufficiently characterize the salts of sesqui- oxide of uranium. A solution suspected to contain protoxide may be boiled with a little nitric acid, and then examined. The only application of uranium is that to enamel painting and the staining of glass; the protoxide giving a fine black color, and the sesquioxide a delicate yellow. copper. Copper is a metal of great value in the arts: it sometimes occurs in the metallic state, crystallized in octahedra, or more frequently in dodecahedra, but is more abundant in the condition of red oxide, and in that of sulphide combined with sulphide of iron, as yellow copper ore, or copper pyrites. Large quantities of the latter substance are annually obtained from the Cornish mines and taken to South Wales for reduction, which is effected by a somewhat complex process. The principle of this may, however, be easily made intelli- gible. The ore is roasted in a reverberatory furnace, by which much of the sulphide of iron is converted into oxide, while the sulphide of copper remains COPPER. 295 unaltered. The product of this operation is then strongly heated with siliceous sand ; the latter combines with the oxide of iron to a fusible slag, and sepa- rates from the heavier copper-compound. When the iron has, by a repetition of these processes, been got rid of, the sulphide of copper begins to decom- pose in the flame-furnace, losing its sulphur and absorbing oxygen ; the tem- perature is then raised sufficiently to reduce the oxide thus produced, by the aid of carbonaceous matter. The last part of the operation consists in thrusting into the melted metal a pole of birch-wood, the object of which is probably to reduce a little remaining oxide by the combustible gases thus generated. Large quantities of extremely valuable ore, chiefly carbonate and red oxide, have lately been obtained from South Australia and Chili. Copper has a well-known yellowish-red color, a specific gravity of 8-96, and is very nialleable and ductile; it is an excellent conductor of heat and elec- tricity ; it melts at a bright red-heat, and seems to be a little volatile at a very high temperature. Copper undergoes no change in dry air; exposed to a moist atmosphere, it becomes covered with a strongly-adherent green crust, consisting in a great measure of carbonate. Heated to redness in the air, it is quickly oxidized, becoming covered with a black scale.. Dilute sulphuric and hydrochloric acids scarcely act upon copper; boiling oil of vitriol attacks it with evolution of sulphurous acid; nitric acid, even dilute, dissolves it readily with evolution of binoxide of nitrogen. Two oxides are known which form salts; a third, or peroxide, is said to exist. The equivalent of copper is 31-7; its symbol Cu. Protoxide of copper; black oxide; CuO.—This is the base of the ordinary blue and green salts. It is prepared by calcining metallic copper at a red-heat, with full exposure to air, or, more conveniently, by heating to redness the nitrate, which suffers complete decomposition. When a salt of this oxide is mixed with caustic alkali in excess, a bulky pale-blue precipitate of hydrated oxide falls, which, when the whole is raised to the boiling-point, becomes converted into a heavy dark-brown powder: this also is anhydrous oxide of copper, the hydrate suffering decomposition, even in contact with water. The oxide prepared at a high temperature is perfectly black and very dense. Protoxide of copper is soluble in acids, and forms a series of very important salts, being isomorphous with magnesia. Suboxide of copper; red oxide ; Cu20. — The suboxide may be obtained by heating in a covered crucible a mixture of 5 parts of black oxide and 4 parts of fine copper-filings: or by adding grape-sugar to a solution of sulphate of copper, and then putting in an excess of caustic potassa, the blue solution, heated to ebullition, is reduced by the sugar, and deposits suboxide. It often occurs in beautifully transparent ruby-red crystals, associated with other ores of copper, and can be obtained in this state by artificial means. This sub- stance forms colorless salts with acids, which are exceedingly unstable, and tend to absorb oxygen. The suboxide communicates to glass a magnificent red tint, while that given by the protoxide is green. Si i.phate of copper; blue vitriol; CuO,S03-|-5IlO.—This beautiful salt is prepared by dissolving oxide of copper in sulphuric acid, or at less expense, by oxidizing the sulphide. It forms large blue crystals, soluble in 4 parts of cold and two of boiling water; by heat it is rendered anhydrous and nearly white, and by a very high temperature decomposed. Sulphate of copper combines with the sulphates of potassa and of ammonia, forming pale-blue salts, which contain 6 equivalents of water, and also with ammonia, generating a remarkable compound of deep-blue color, capable of crystallizing. Nitrate of copper, CuO, NOg-j-3110.—The nitrate is easily made by dis- solving the metal in nitric acid; it forms deep-blue crystals, very soluble and deliquescent. It Is highly corrosive. An insoluble subnitrate is known; it is green. Nitrate of copper also combines with ammonia. Carbonates of copper. —When carbonate of soda is added in excess to a 296 LEAD. solution of sulphate, of copper, the precipitate is at first pale blue and floccu- lent, but by warming it becomes sandy, and assumes a green tint; in this state it contains CuO,C02+ CuO,HO + HO. This substance is prepared as a pigment. The beautiful mineral malachite has a similar composition, but con- tains one equivalent of water less. Another natural compound, not yet artificially imitated, occurs in large transparent crystals of the most intense blue; it contains 2(CuO,C02) -4- CuO,HO. Verditer, made by decomposing nitrate of copper by chalk, is said, however, to have a somewhat similar com- position. Chloride of copper, CuCl-|-2HO. The chloride is most easily prepared by dissolving the black oxide in hydrochloric acid, and concentrating the green solution thence resulting. It forms green crystals, very soluble in water and in alcohol; it colors the flame of the latter green. AVhen gently heated, it parts with its water of crystallization and becomes yellowish-brown ; at a high temperature it loses half its chlorine and becomes converted into the sub- chloride. The latter is a white fusible substance, but little soluble in water, and prone to oxidation; it is formed when copper-filings or copper-leaf are put into chlorine gas. A basic chloride CuCl-f- 3(CuO, HO) occurs in nature as atacamite. Arsenite of copper; Scheele's green. — This is prepared by mixing solutions of sulphate of copper and arsenite of potassa; it falls as a bright- green insoluble powder. The characters of the protosalts of copper are well marked. Caustic potassa gives a pale-blue precipitate of hydrate, becoming blackish- brown anhydrous protoxide on boiling. Ammonia also throws down the hydrate; but, when in excess, re-dissolves it, yielding an intense purplish-blue solution.1 Carbonates of potassa and soda give pale-blue precipitates, insoluble in excess. Carbonate of ammonia, the same, but soluble with deep-blue color. Ferrocyanide of potassium gives a fine red-brown precipitate of ferrocyanide of copper. Sulphuretted hydrogen and sulphide of ammonium afford black sulphide of copper. The alloys of copper are of great importance. Brass consists of copper alloyed with from 28 to 34 per cent, of zinc; the latter may be added directly to the melted copper, or granulated copper may be heated with calamine and charcoal-powder, as in the old process. Gun-metal, a most trustworthy and valuable alloy, consists of 90 parts copper and 10 tin. Bell and speculum metal contain a still larger proportion of tin; these are brittle, especially tho last named. A good bronze for statues is made of 91 parts copper, 2 parts tin, 6 parts zinc, and 1 part lead. The brass of the ancients is an alloy of copper with tin. LEAD. This abundant and useful metal is altogether obtained from the native sul- phide or galena, no other lead-ore being found in quantity. The reduction is effected in a reverberatory furnace, into which the crushed lead-ore is intro- duced and roasted for some time at a dull red-heat, by which much of the sul- phide becomes changed by oxidation to sulphate. The contents of the fur- nace are then thoroughly mixed, and the temperature raised, when the 1 This solution has the remarkable property of dissolving cellulose and vegetable fibres LEAD. 297 sulphate and sulphide react upon each other, producing sulphurous acid and metallic lead.1 Lead is a soft bluish metal, possessing very little elasticity; its specific gra- vity is 111). It may be easily rolled out into plates, or drawn into coarse wire, but has a very trifling degree of strength. Lead melts at 600° (315°-5C) or a little above, and at a white-heat boils and volatilizes. By slow cooling it may be obtained in octahedral crystals. In moist air this metal becomes coated with a film of gray matter, thought to be suboxide, and when exposed to the atmosphere in a melted state it rapidly absorbs oxygen. Dilute acids witli the exception of nitric, act but slowly upon lead. Chemists are familiar with four oxides of lead, only one of which possesses basic properties. Tho equivalent of lead is 103-7; its symbol is Pb. Protoxide ; litharge ; massicot ; PbO.—This is the product of the direct oxidation of the metal. It is most conveniently prepared by heating the car- bonate to dull redness; common litharge is impure protoxide which has under- gone fusion. Protoxide of lead has a delicate straw-yellow color, is very heavy, and slightly soluble in water, giving an alkaline liquid. Protoxide of lead is soluble in potassa; from this solution it crystallizes in rhombic prisms. At a red-heat it melts, and tends to crystallize on cooling. In a melted state it attacks and dissolves siliceous matter with astonishing facility, often pene- trating an earthen crucible in a few minutes. It is easily reduced when heated with organic substances of any kind containing carbon or hydrogen. 1'rotoxide of lead forms a large class of salts, which are colorless if the acid itself bo not colored. Bed oxide; red-lead; Pb304, or 2FbO -f- Pb02.— The composition of this substance is not very constant; it is prepared by exposing for a long time to the air, at a very faint red-heat, protoxide of lead which has not been fused; it is a brilliant red and extremely heavy powder, decomposed with evolution of oxygen by a strong heat, and converted into a mixture of protoxide and binoxide by acids. It is used as a cheap substitute for vermillion. Binoxide of Lead; puce or brown oxide; Pb02.—This compound is ob- tained without difficulty by digesting red-lead in dilute nitric acid, when nitrate of protoxide is dissolved out, and insoluble binoxide left behind in the form of a deep-brown powder. The binoxide is decomposed by a red heat, yielding up one-half of its oxygen. Hydrochloric acid converts it into chlo- ride of lead with disengagement of chlorine; hot oil of vitriol forms with it sulphate of lead, and liberates oxygen. The binoxide is very useful in sepa- rating sulphurous acid from certain gaseous mixtures, sulphate of lead being then produced. Suboxide of lead, Pb20.—When oxalate of lead is heated to dull redness in a retort, a gray pulverulent substance is left, which is resolved by acids into protoxide of lead and metal. It absorbs oxygen with great rapidity when heated, and even when simply moistened with water and exposed to the air. Nitrate of lead, PbO, N05.—The nitrate may be obtained by dissolving carbonate of lead in nitric acid, or by acting directly upon the metal by the same agent with the aid of heat; it is, as already noticed, a by-product in the preparation of the binoxide. It crystallizes in anhydrous octahedra, which are usually milk-white and opaque; it dissolves in 7.1, parts of cold water, and is decomposed by heat, yielding nitrous acid, oxygen, and protoxide of lead, which obstinately retains traces of nitrogen. When a solution of this salt is boiled with an additional quantity of oxide of lead, a portion of the latter is dis- ! Oxide of j Lead_________________. Freo. lead j Oxygen .------____„_ -j Sulphurous acid. Sulphuric ( Sulphur ■ acid / 3 Oxyiren ■ Sulphide of lead Sulphur- I head-------------------Free. PbO,S03 + PbS = 2Pb + 2SO.<. 298 LEAD. solved, and a basic nitrate generated, which may be had in crystals. Car- bonic acid separates this excess of oxide in the form of a white compound of carbonate and hydrate of lead. Neutral and basic compounds of oxide of lead with nitrous, and the elements of hyponitric acid, have been described. These last are probably formed by the combination of a nitrite with a nitrate. Carbonate of lead; white-lead; PbO, C02.—Carbonate of lead is some- times found beautifully crystallized in long white needles, accompanying other metallic ores. It may be prepared artificially by precipitating in the cold a solution of the nitrate or acetate by an alkaline carbonate: when the lead solu- tion is boiling, the precipitate is a basic salt containing 2 (PbO, C02)-{- IIO, PbO ; it is also manufactured to an immense extent by other means for the use of the painter. Pure carbonate of lead is a soft, white powder, of great specific gravity, insoluble in water, but easily dissolved by dilute nitric or acetic acid. Of the many methods put in practice, or proposed, for making white-lead, the two following are the most important and interesting:—One of these con- sists in forming a basic nitrate or acetate of lead by boiling finely-powdered litharge with the neutral salt. This solution is then brought into contact with carbonic acid gas: all the excess of oxide previously taken up by the neutral salt is at once precipitated as white-lead. The solution strained or pressed from the latter is again boiled with litharge, and treated with carbonic acid: these processes being susceptible of indefinite repetition, when the little loss of neutral salt left in the precipitates is compensated. The second, and by far the more ancient method, is rather more complex, and at first sight not very intelligible. A great number of earthen jars are prepared, into each of which is poured a few ounces of crude vinegar; a roll of sheet-lead is then introduced in such a manner that it shall neither touch the vinegar nor pro- ject above the top of the jar. The vessels are next arranged in a large build- ing, side by side, upon a layer of stable manure, or, still better, spent-tan, and closely covered with boards. A second' layer of tan is spread upon the top of the latter, and then a second series of pots; these are in turn covered with boards and decomposing bark, and in this manner a pile of many alter- nations is constructed. After the lapse of a considerable time the pile is taken down and the sheets of lead removed and carefully unrolled; they arc then found to be in great part converted into carbonate, which merely requires washing and grinding to be fit for use. The nature of this curious process is generally explained by supposing the vapor of vinegar raised by the high temperature of the fermenting matter merely to act as a carrier between the carbonic acid evolved from the tan, and the oxide of lead formed under the influence of the acid vapor; a natural acetate, a basic acetate, and a carbonate being produced in succession, the action gradually travelling from the surface inwards. The quantity of acetic acid used is, in relation to the lead, quite trifling, and cannot directly contribute to the production of the carbonate. A preference is still given to the product of this old mode of manufacture on ac- count of its superiority of opacity, or body, over that obtained by precipitation. Commercial white-lead, however prepared, always contains a certain propor- tion of hydrate. It is sometimes adulterated by sulphate of baryta. When clean metallic lead is put into pure water and exposed to the atmo- sphere, a white crystalline, scaly powder begins to show itself in a few hours, and very rapidly increases in quantity. This substance may consist of hy- drated protoxide of lead, formed by the action of the oxygen dissolved in the water upon the lead. It is slightly soluble, and may be readily detected in the water. In most cases, however, the formation of this deposit is due to the action of the carbonic acid dissolved in the water; it consists of carbonate in combination with hydrate, and is very insoluble in water. When common river or spring water is substituted for the pure liquid, this effect is less observable LEAD. 299 the little sulphate, almost invariably present, causing the deposition of a very thin but closely adherent film of sulphate of lead upon the surface of the metal, which protects it from farther action. It is on this account that leaden Cisterns arc used with impunity at least in most cases, for holding water; if the latter were quite pure, it would be speedily contaminated with lead, and the cistern be soon destroyed. Natural water highly charged with carbonic acid cannot, under any circumstances, be kept in lead or passed through leaden pipes with safety; the carbonate, though very insoluble in pure water, being slightly soluble in water containing carbonic acid. Chloride of lead, PbCl.—This salt is prepared by mixing strong solutions of acetate of lead and chloride of sodium ; or by dissolving litharge in boiling dilute hydrochloric acid, and setting aside the filtered solution to cool. Chlo- ride of lead crystallizes in brilliant, colorless needles, which require 135 parts of cold water for solution. It is anhydrous ; it melts when heated, and solidi- fies on cooling to a horn-like substance. Iodide of lead, Pbl.—The iodide of lead separates as a brilliant yellow precipitate when a soluble salt of lead is mixed with iodide of potassium. This compound dissolves in boiling water, yielding a colorless solution, which deposits the iodide on cooling in splendid golden-yellow scales. The soluble salts of lead thus behave with reagents:— Caustic potassa and soda precipitate a white hydrate freely soluble in excess. Ammonia gives a similar white precipitate, not soluble in excess.1 _ The carbonates of potassa, soda, and ammonia, precipitate carbonate of lead, insoluble in excess. _ Sulphuric acid or a sulphate causes a white precipitate of sulphate of lead, insoluble in nitric acid. Sulphuretted hydrogen and sulphide of ammonium throw down black sul- phide of lead. Ati alloy of 2 parts of lead and 1 of tin constitutes plumber's solder; these proportions reversed give a more fusible compound called fine solder. The lead employed in the manufacture of shot is combined with a little arsenic. 1 Ammonia gives no immediate precipitate with the acetate. 300 TIN. SECTION V. OXIDABLE METALS PROPER, WHOSE OXIDES FORM WEAK BASES OR ACIDS. TIN. This valuable metal occurs in the state of oxide, and more rarely as sul- phide : the principal tin mines are those of the Erzgebirge in Saxoriy and Bohemia, Malacca, and more especially Cornwall. In Cornwall the tin-stone is found as a constituent of metal-bearing veins, associated with copper ore, in granite and slate-rocks; and as an alluvial deposit, mixed with rounded pebbles, in the beds of several small rivers. The first variety is called mine- and the second stream-tin. Oxide of tin is also found disseminated through the rock itself in small crystals. To prepare the ore for reduction, it is stamped to powder, washed, to sepa- rate as much as possible of the earthy matter, and roasted to expel sulphur and arsenic; it is then strongly heated with coal, and the metal thus obtained cast into large blocks, which, after being assayed, receive the stamp of the Duchy. Two varieties of commercial tin are known, called grain- and bar-tin; the first is the best; it is prepared from the stream ore. Pure tin has a white color, approaching to that of silver; it is soft and malleable, and when bent or twisted emits a peculiar crackling sound; it has a density of 7-3 and melts at 442° (227C-77C). Tin is but little acted upon by air and water, even conjointly; when heated above its melting-point it oxidizes rapidly, becoming converted into a whitish powder, used in the arts for polishing under the name of putty-powder. The metal is easily attacked and dissolved by hydrochloric acid, with evolution of hydrogen: nitric acid acts with great energy, converting it into a white hydrate of the binoxide. There are two well-marked oxides of tin, which act as feeble bases or acids, according to circumstances, and a third, which has been less studied. The equivalent of tin is 58; its symbol is Sn. Protoxide of tin, SnO.—When solution of protochloride of tin is mixed with carbonate of potassa, a white hydrate of the protoxide falls, the carbonic acid being at the same time expelled. AVhen this is carefully washed, dried, and heated in an atmosphere of carbonic acid, it loses water, and changes to a dense black powder, which is permanent in the air, but takes fire on the approach of a red-hot body, and burns like tinder, producing binoxide. It may be obtained in a state of great division by heating oxalate of tin in con- tact with the air. The hydrate is freely soluble in caustic potassa; the solu- tion decomposes by keeping into motallic tin and binoxide. Sesquioxide of tin, Sn203. — The sesquioxide is produced by the action of hydrated sesquioxide of iron upon protochloride of tin; it is a grayish, ' slimy substance, soluble in hydrochloric acid, and in ammonia. This oxide has been but little examined. TIN. 301 Binoxide of tin, Sn02. — This substance is obtained in two different states, having properties altogether dissimilar. When bichloride of tin is pre- cipitated by an alkali, a white bulky hydrate appears, which is freely soluble in acids. If, on the other hand, the bichloride be boiled with excess of nitric acid, or if that acid be made to act directly on metallic tin, a white substance is produced, which refuses altogether to dissolve in acids, and possesses pro- perties differing in other respects from those of the first modification. Both these varieties of binoxide of tin have the same composition, and when ignited, leave the pure binoxide of a pale lemon-yellow tint. Both dissolve in caustic alkali, and are precipitated with unchanged properties by an acid. The two hydrates redden litmus-paper.1 Protochloride of tin, SnCl. —The protochloride is easily made by dis- solving metallic tin in hot hydrochloric acid. It crystallizes in needles con- taining 2 equivalents of water, which are freely soluble in a small quantity of water, but are apt to be decomposed in part when put into a large mass, unless hydrochloric acid in excess be present. The anhydrous chloride may be obtained by distilling a mixture of calomel and powdered tin, prepared by agitating the melted metal in a wooden box until it solidifies. The chloride is a gray, resinous-looking substance, fusible below redness, and volatile at a high temperature. Solution of protochloride of tin is employed as a deoxidiz- ing agent; it reduces the salts of mercury and other metals of the same class. Bichloride, or perchlobide of tin, SnCl2. — This is an old and very curious compound, formerly called fuming liquor of Libavius. It is made by exposing metallic tin to the action of chlorine, or, more conveniently, by dis- tilling a mixture of 1 part of powdered tin, and 5 parts of corrosive subli- mate. Tho bichloride is a thin, colorless, mobile liquid; it boils at 248° (120°C), and yields a colorless invisible vapor. It fumes in the air, and when mixed with a. third part of water, solidifies to a crystalline mass. The solu- tion of bichloride is much employed by the dyer as a mordant; it is commonly prepared by dissolving metallic tin in a mixture of hydrochloric and nitric acids, care being taken to avoid too great elevation of temperature. Sulphides of tin.—Protosulphide, SnS, is prepared by fusing tin with excess of sulphur, and strongly heating the product. It is a lead-gray, brittle substance, fusible at a red-heat, and soluble with evolution of sulphuretted hydrogen in hot hydrochloric acid. A sesquisulphide may be formed by gently heating the above compound with a third of its weight of sulphur ; it is yel- lowish-gray, and easily decomposed by heat. Bisulphide, SnS2, or Mosaic gold, is prepared by exposing to a low red-heat, in a glass flask, a mixture of 12 parts of tin, 6 of mercury, 6 of sal-ammoniac, and 7 of flowers of sulphur. Sal-ammoniac, cinnabar, and protochloride of tin sublime, while the bisul- phide remains at the bottom of the vessel in the form of brilliant gold-colored scales ; it is used as a substitute for gold-powder. Salts of tin are thus distinguished: — Protoxide. Caustic alkalies; white hydrate soluble in excess. Ammonia; carbonates of potassa, "I White hydrate, nearly insoluble in soda, and ammonia . . . . J excess. Sulphuretted hydrogen . . . . ■> „, . . ., . „ , , .. Sulphide of ammonium . . . .} Black precipitate of protosulphide. 4 Frcmy has called the first of these oxides stannic acid, SnOa. The second he has named m.tastannic acid, Sn6Oi°. See also II. Rose, Pogg, Ann., Ixxv. 1, who thinks that there are oilier modifications of this oxide of tin. 26 302 TUNGSTEN. Binoxide. Caustic alkalies; white hydrate soluble in excess. Ammonia; white hydrate, slightly soluble in excess. Alkaline carbonates; white hydrates, slightly soluble in excess. Carbonate of ammonia; white hydrate, insoluble. Sulp*huretted hydrogen; yellow precipitate of sulphide. Sulphide of ammonium; the same, soluble in excess. Terchloride of gold, added to a dilute solution of protochloride of tin, gives rise to a brownish-purple precipitate, called purple of Cassius, very charac- teristic, the nature of which is not thoroughly understood; it is supposed to be a combination of oxide of gold and sesquioxide of tin, in which the latter acts as an acid. Heat resolves it into a mixture of metallic gold and binoxide of tin. Purple of Cassius is employed in enamel-painting, and in staining \ glass. The useful applications of tin are very numerous. Tinned-plate consists of iron superficially alloyed with this metal; pewter, of the best kind, is chiefly tin, hardened by the admixture of a little antimony, &c. Cooking- vessels of copper are usually tinned in the interior. TUNGSTEN (WOLFRAMIUM). Tungsten is found, as tungstate of protoxide of iron, in the mineral wolfram, tolerably abundant in Cornwall; a native tungstate of lime is also occasionally met with. Metallic tungsten is obtained in the state of a dark-gray powder, by strongly heating tungstic acid in a stream of hydrogen, out requires for fusion an exceedingly high temperature. It is a white metal, very hard and brittle ; it has a density of 17-4. Heated to redness in the air, it takes fire, and reproduces tungstic acid. The equivalent of tungsten is 92, its symbol is W (wolframium). Binoxide of tungsten, W02. —This is most easily prepared by exposing tungstic acid to hydrogen, at a temperature which does not exceed dull red- ness. It is a brown powder, sometimes assuming a crystalline appearance and an imperfect metallic lustre It takes fire when heated in the air, and burns, like the metal itself, to tungstic acid. The binoxide forms no salts with acids. Tungstic acid, W03. — When tungstate of lime can be obtained, simple digestion in hot nitric acid is sufficient to remove the base, and liberate the tungstic acid in a state of tolerable purity; its extraction from wolfram, which contains tungstic acid or oxide of tungsten in association with the oxides of iron and manganese, is more difficult. Tungstic acid is a yellow powder, in- soluble in water, and freely dissolved by caustic alkalies. When strongly ignited in the open air, it assumes a greenish tint. Intermediate or blue oxide of tungsten, W205,=W02,WOs.—This sub- stance is obtained by heating tungstate of ammonia, or by exposing the brown binoxide to the action of hydrogen at a very low temperature. The same compound appears to be produced if tungstic acid be separated from one of its salts, by hydrochloric acid, and the liquid be digested with metallic zinc, when the solution or the precipitate assumes a beautiful blue color, which is very characteristic of this metal. Two chlorides and two sulphides of tungsten are known to exist. MOLYBDENUM..— VANADIUM. 303 MOLYBDENUM. Metallic molybdenum is obtained by exposing molybdic acid in a charcoal- lined crucible to the most intense heat that can be obtained. It is a white, brittle, and exceedingly-infusible metal, having a density of 8-6, and oxidiz- ing, when heated in the air, to molybdic acid. The equivalent of molybdenum is 46; its symbol is Mo. Protoxide of molybdenum, MoO. — Molybdatc of potassa is mixed with excess of hydrochloric acid, by which the molybdic acid first precipitated is redissolved; into this acid solution zinc is put: a mixture of chloride of zinc and protochloride of molybdenum results. A large quantity of caustic potassa is then added, which precipitates a black hydrate of the protoxide of molyb- denum, and retains in solution the oxide of zinc. The freshly-precipitated protoxide is soluble in acids and in carbonate of ammonia; when heated in the air, it burns to binoxide. Binoxide of molybdenum, Mo02.—This is obtained in the anhydrous condition by heating molybdate of soda with sal-ammoniac, the molybdic acid being reduced to binoxide by the hydrogen of the ammoniacal salt; or, in a hydrated condition, by digesting metallic copper in a solution of molybdic acid in hydrochloric acid, until the liquid assumes a red color, and then adding a large excess of ammonia. The anhydrous binoxide is deep brown, and insoluble in acids; the hydrate resembles hydrate of sesquioxide of iron, and dissolves in acids, yielding red solutions. It is converted into molybdic acid by strong nitric acid. Molybdic acid, Mo03. —The native bisulphide of molybdenum is roasted, at a red-heat, in an open vessel, and the impure molybdic acid thence resulting dissolved in ammonia. The filtered solution is evaporated to dryness, the salt taken up by water, and purified by crystallization. It is, lastly, decomposed by heat, and the ammonia expelled. Molybdic acid is a white crystalline powder, fusible at a red-heat, and slightly soluble in water. It is dissolved with ease by the alkalies. It forms two series of salts, namely, neutral molybdatcs, MO,Mo03, and acid molybdates, MO,2Mo03. A solution of molybdate of ammonia in an excess of nitric acid forms a valuable reagent for phosphoric acid, with which it gives a beautiful yellow precipitate, phospho- molybdate of ammonia. Three chlorides, and as many sulphides of molybde- num, are described. vanadium. Vanadium is found, in small quantity, in some iron ores, and also as vanadate of lead. It has also been discovered in the iron slag of Staffordshire. The most successful process for obtaining the metal is said to be the follow- ing : — The liquid chloride of vanadium is introduced into a bulb blown in a glass tube, and dry ammoniacal gas passed over it; the latter is absorbed, and a white saline mass produced. When this is heated by the flame of a spirit-lamp, chloride of ammonium is volatilized, and metallic vanadium left behind. It is a white brittle substance, of perfect metallic lustre, and a very high degree of infusibility; it is neither oxidized by air nor water, nor attacked by sulphuric, hydrochloric, nor even hydrofluoric acid; aqua legia dissolves it, yielding a deep-blue solution. The equivalent of vanadium is 68-6; its symbol is V. Protoxide of vanadium, VO.—This is prepared by heating vanadic acid iu contact with charcoal or hydrogen; it has a black color and imperfect metallic lustre, conducts electricity, and is very infusible. Heated in the air, it burns to binoxide. Nitric acid produces the same effect, a blue nitrate of the binoxide being generated. It does not form salts. Binoxide of vanadium, V02.—The binoxide is obtained by heating a mix- ture of 10 parts protoxide of vanadium, and 12 of vanadic acid in a vessel 304 NIOBIUM AND PELOPIUM. filled with carbonic acid gas: or by adding a slight excess of carbonate of soda to a salt of the binoxide: in the latter case it falls as a grayish-white hydrate, readily becoming brown by absorption of oxygen. The anhydrous oxide is a black insoluble powder, convertible by heat and air into vanadic acid. It forms a series of blue salts, which have a tendency to become green, and ultimately red, by the production of vanadic acid. Binoxide of vanadium also unites with alkalies. Vanadic acid, V03.—The native vanadate of lead is dissolved in nitric acid, and the lead and arsenic precipitated by sulphuretted hydrogen, which at the same time reduces the vanadic acid to binoxide of vanadium. The blue filtered solution is then evaporated to dryness, and the residue digested in ammonia, which dissolves out the vanadic acid reproduced during evaporation. In this solution a lump of sal-ammoniac is put: as that salt dissolves, vanadate of ammonia subsides as a white powder, being scarcely soluble in a saturated solution of chloride of ammonium. By exposure to a temperature below redness in an open crucible, the ammonia is expelled, and vanadic acid left. It has a dark-red color, and melts even below a red-heat; water dissolves it sparingly, and acids with greater ease; the solutions easily suffer deoxidation. It unites with bases, forming a series of red or yellow salts, of which those of the alkalies are soluble in water. Chlorides of vanadium. — The bichloride is prepared by digesting vanadic acid in hydrochloric acid, passing a stream of sulphuretted hydrogen, and evaporating the whole to dryness. A brown residue is left, which yields a blue solution with water and an insoluble oxichloride. The terchloride is a yellow liquid obtained by passing chlorine over a mixture of protoxide of vanadium and charcoal. It is converted by water into hydrochloric and vanadic acids. Two sulphides, corresponding to the chlorides, exist. tantalium (columbium). This is an exceedingly rare substance; it is found in the minerals tantalile and yttro-tantalile, occurring in Sweden and Finland, and may be obtained pure by heating with potassium the double fluoride of tantalium and potas- sium. It is a gray metal, but little acted on by the ordinary acids, and burn- ing to tantalic acid when heated in the air, or when fused with hydrate of potassa. The equivalent of tantalium is 184; its symbol is T. Binoxide of tantalium, T02. — When tantalic acid is heated to whiteness in a crucible lined with charcoal, the greater part is converted into this sub- stance. It is a dark-brown powder, insoluble in acids, and easily changed by oxidation to tantalic acid. Tantalic acid, T03. —The powdered mineral is fused with three or four times its weight of carbonate of potassa, and the product digested with water; from this solution acids precipitate a white hydrate of the body in question! It is soluble in acids, but forms with them no definite compounds; with alkalies it yields, on the contrary, crystallizable salts. The specific gravity of the acid varies from 7'03 to 8-26. Chloride of Tantalium. — Tantalic acid in a glass tube is mixed with sugar, and burnt, then heated to redness in a current of dry carbonic acid gas; when cold, chlorine is passed over it and heated. Chloride of tantalium sublimes of a yellow color when pure. NIOBIUM AND PELOPIUM. The oxides of these two metals are said to exist in the tantalile of Boden- mais, in Bavaria. When the supposed tantalic acid from this source is mixed TITANIUM. 305 with dry powdered charcoal, and heated to redness in a current of chlorine gas, a sublimate is obtained, of a yellow, readily-fusible, and very volatile substance, the chloride of pelopium, and a white, infusible, less volatile body the chloride of niobium. The true chloride of tantalium, from the Finland tantalite, much resembles chloride of pelopium. The American tantalite contains niobic, pelopic, and tungstic acids, the former in greatest quantity. All these chlorides are decomposed by water, with production of hydro- chloric acid and the insoluble acids of the metals in the hydrated state. In properties these bodies greatly resemble each other. When heated to redness, they exhibit strongly the phenomenon of incandescence. While hot, tantalic acid remains white, pelopic acid is rendered slightly yellowish, and has a specific gravity varying from 5-79 to 6-37, and niobic acid becomes dark yellow, with a specific gravity between 4-56 and 5-26. Tantalium, niobium, and pelopium may be obtained in a finely-divided metallic state by the action of ammonia on their respective chlorides at a high temperature. So prepared, they are black, pulverulent, not acted on by ivatcr, but burning, when heated in the air, to acids. According to the latest researches of H. Rose, who has been chiefly engaged in the examination of these bodies, the existence of pelopium is Yery doubtful. TITANIUM. Crystallized titanic acid is found in nature in the form of rutile, brookite, and anatase. Occasionally in the slag adherent to the bottom of blast-furnaces in which iron ore is reduced, small brilliant copper-colored cubes, hard enough to scratch glass, and in the highest degree infusible, are found. This substance, of which a single smelting furnace in the Hartz produced as much as SO pounds, was formerly believed to be metallic titanium. Recent researches of Wohler, however, have shown it to be a combination of cyanide of titanium, with nitride of titanium. AVhen these crystals are powdered, mixed with hydrate of potassa and fused, ammonia is evolved, and titanate of potassa is formed. Metallic titanium in a finely-divided state may be obtained by heat- ing fluoride of titanium and potassium with potassium. This element is remarkable for its affinity for nitrogen: when heated in the air, it simulta- neous^- absorbs oxygen and nitrogen. There are two compounds of this substance with oxygen; viz., an oxide and an acid: very little is known respecting the former. The equivalent of titanium is 25 ; its symbol is Ti. Titanic acid, Ti02. —Rutile, or titaniferous iron ore, is reduced to fine powder, and fused with twice its weight of carbonate of potassa, powdered, dissolved in dilute hydrofluoric acid, when titano-fluoridc of titanium and potassium soon begins to separate. From its hot aqueous solution snow-like titanate of ammonia is precipitated by ammonia, which is easily soluble in hydrochloric acid, and when ignited gives pure titanic acid. When pure the acid is quite white : it is, when recently precipitated from solutions, soluble in acids, but the solutions are decomposed by mere boiling. After ignition it is no longer soluble, passing over into metatitanic acid. Titanic acid, on the whole, very much resembles silica, and is probably often overlooked and confounded with that substance in analytical researches. Bichloride of titanium. — This is a colorless, volatile liquid, resembling bichloride of tin; it is obtained by passing chlorine over a mixture of titanic acid and charcoal at a high temperature. It unites very violently with water. On passing the vapor with hydrogen through a red-hot tube, hydrochloric acid and a new compound Ti2Cl3 are formed. 26* 306 ANTIMONY. ANTIMONY. This important metal is found chiefly in the state of sulphide. The ore is freed by fusion from earthy impurities, and is afterwards decomposed by heating with metallic iron or carbonate of potassa, which retain the sulphur. Antimony has a bluish-white color and strong lustre; it is extremely brittle, being reduced to powder with the utmost ease. Its specific gravity is 6-8; it melts at a temperature just short of redness, and boils and volatilizes at a white heat. This metal has always a distinctly crystalline, platy structure, but by particular management it may be obtained in crystals, which are rhombohedral.1 Antimony is not oxidized by the air at common temperatures; strongly heated, it burns with a white flame, producing teroxide, which is often deposited in beautiful crystals. It is dissolved by hot hydrochloric acid with evolution of hydrogen and production of terchloride. Nitric acid oxidizes it to antimonic acid, which is insoluble in that menstruum. There are three compounds of antimony and oxygen ; the first has doubtful basic properties, the second is indifferent, and the third is an acid. The equivalent of antimony is 120. Its symbol is Sb (stibium). Teroxide of antimony, Sb03.—This compound may be prepared by several methods; as by burning metallic antimony at the bottom of a large red-hot crucible, in which case it is obtained in brilliant crystals ; or by pouring solu- tion of terchloride of antimony into water, and digesting the resulting pre- cipitate with a solution of carbonate of soda. The teroxide thus produced is anhydrous; it is a pale buff-colored powder, fusible at a red-heat, and vola- tile in a close vessel, but in contact with air, at a high temperature, absorbs oxygen, and becomes changed to the intermediate oxide. There exist a sul- phate, nitrate, and oxalate of teroxide of antimony. When boiled with cream of tartar (bitartrate of potassa), it is dissolved, and the solution yields on evaporation crystals of tartar-emetic, which is almost the only compound of teroxide of antimony with an acid which bears admixture with water without decomposition. An impure oxide for this purpose is sometimes prepared by carefully roasting the powdered sulphide in a reverberatory furnace, and rais- ing the heat at the end.of the process, so as to fuse the product; it has long been known under the name of glass of antimony. Intermediate oxide, Sb04 or Sb03,Sb06.—This is the ultimate product of the oxidation of the metal by heat and air; it is a grayish-white powder, infu- sible, and destitute t>f volatility; it is insoluble in water and in acids, except when recently precipitated. When treated with tartaric acid or bitartrate of potassa, teroxide of antimony is dissolved, antimonic acid remaining behind; alkalies, on the other hand, remove antimonic acid, teroxide of antimony being left. Antimonic acid, Sb05.—When strong nitric acid is made to act upon metallic antimony, the metal is oxidized to its highest point, and antimonic acid is pro- duced, which is insoluble. By exposure to a heat short of redness, it is ren- dered anhydrous, and then presents the appearance of a pale straw-colored powder, insoluble in water and acids. It is decomposed by a red-heat, yield- ing the intermediate oxide, with loss of oxygen. Antimonic acid is likewise obtained by decomposing pentachloride of anti- mony with an excess of water, when, together with the metallic acid, hydro- chloric acid is produced. The hydrated antimonic acid produced by the two processes mentioned, differs in many of its proporties, and especially in its deportment with bases. The substance produced by nitric acid is monobasic, 1 On electrolyzing a solution of terchloride of antimony (1 part of tartar-emetic in 4 parts of ordinary chloride of antimony) by a small battery of two elements, metallic antimony forming the positive, and metallic copper the negative pole, crusts of antimony are obtained, •which possess the remarkable property of exploding and catching fire when scratched or broken, (Gore, Proceedings of Royal Society, vol. ix.) A N T I M 0 N Y. 307 producing salts of the formula MO,SbOB, the other is bibasic, and forms two series of the salts of the composition 2MO,Sb06 and MO,HO,Sb05. In order to distinguish the two modifications, M. Fremy, who first pointed out the bibasic nature of the acid obtained from the pentachloride, has proposed to distinguish it as metantimonic acid. Among the salts of the latter, an acid metantimonate of potassa, KO,HO,Sb06-f- 6HO, is to be noticed, which yields a precipitate with soda-salts. It is the only reagent which precipitates soda, but must be employed with great care and circumspection. It is obtained by fusing antimonic acid with an excess of potassa in a silver crucible, dissolving the fused mass in a small quantity of cold water, and allowing it to crystallize in vacuo. The crystals which form are metantimonate of potassa, 2KO,Sb06, which, when dissolved in pure water, are decomposed into free potassa and acid metantimonate. Terchloride of antimony: butter of antimony; SbCl3.—This sub- stance is produced when sulphuretted hydrogen is prepared by the action of strong hydrochloric acid on tersulphide of antimony. The impure and highly- acid solution thus obtained is put into a retort and distilled, until each drop of the condensed product, on falling into the aqueous liquid of the receiver, produces a copious white precipitate. The receiver is then changed, and the distillation continued. Pure terchloride of antimony passes over, and solidi- fies on cooling to a white and highly-crystalline mass, from which the air requires to be carefully excluded. The same compound is formed by distilling metallic antimony in powder with 2J times its weight of corrosive sublimate. Terchloride of antimony is very deliquescent; it dissolves in strong hydro- chloric acid without decomposition, and the solution poured into water gives rise to a white bulky precipitate, which, after a short time, becomes highly crystalline, and assumes a pale fawn-color. This is the old powder of Alga- roth ; it is a compound of terchloride and teroxide of antimony. Alkaline solutions extract the chloride and leave teroxide of antimony. Finely-pow- dered antimony thrown into chlorine gas inflames. Pentachloride of antimony, corresponding to antimonic acid, is formed by passing a stream of chlorine gas over gently-heated metallic antimony; a mix- ture of the two chlorides results, which may be separated by distillation. The pentachloride is a colorless volatile liquid, which forms a crystalline compound with a small portion of water, but is decomposed by a larger quantity into antimonic and hydrochloric acids. Teusi-lphide of antimony; crude antimony: SbS3. — The native sul- phide is a lead-gray, brittle substance, having a radiated crystalline texture, and is easily fusible. It may be prepared artificially by melting together antimony and sulphur. When a solution of tartar-emetic is precipitated by sulphuretted hydrogen, a brick-red precipitate falls, which is the same sub- stance combined with a little water. If the precipitate be dried and gently heated, the Water may be expelled without other change of color than a little darkening, but at a higher temperature it assumes the color and aspect of the native sulphide. This remarkable change probably indicates a passage from the amorphous to the crystalline condition. When powdered tersulphide of antimony is boiled in a solution of caustic potassa, it is dissolved, teroxide of antimony and sulphide of potassium being produced. The latter unites with an additional quantity of tersulphide of antimony to a soluble sulphur-salt," fh which the sulphide of potassium is the sulphur-base, and the tersulphide of antimony is the sulphur-acid. 3KO -f- 2SbS3 = Sb03-f- 3KS,SbS3. The teroxide of antimony separates in small crystals from the boiling solu- tion when the latter is concentrated, and the sulphur-salt dissolves an extra portion of tersulphide of antimony, which it again deposits on cooling as a red amorphous powder, containing a small admixture of teroxide of antimony and 308 TELLURIU M. sulphide of potassium. This is the kermes mineral of the old chemists. The filtered solution mixed with an acid gives a salt of potassa, sulphuretted hydrogen, and precipitated tersulphide of antimony. Kermes may also be made by fusing a mixture of 5 parts tersulphide of antimony and 3 of dry carbonate of soda, boiling the mass in 80 parts of water, and filtering while hot: the compound separates on cooling. Pentasulphide of antimony, SbS6, formerly called sulphur auratum, also exists; it is a sulphur-acid. 18 parts finely-powdered tersulphide of anti- mony, 17 parts dry carbonate of soda, 13 parts lime in the state of hydrate, and Z\ parts sulphur, are boiled for some hours in a quantity of water; car- bonate of lime, antimonate of soda, pentasulphide of antimony, and sulphide of sodium are produced. The first is insoluble, and the second partially so; the two last-named bodies, on the contrary, unite to a soluble sulphur-salt, which may by evaporation be obtained in beautiful crystals. A solution of this substance, mixed with dilute sulphuric acid, furnishes sulphate of soda, sulphuretted hydrogen, and pentasulphide of antimony, which falls as a golden- yellow flocculent precipitate. Antimonetted hydrogen.—A compound of antimony and hydrogen exists, but has not yet been isolated: when zinc is put into a solution of teroxide of antimony, and sulphuric acid added, part of the hydrogen combines with the antimony. This gas burns with a greenish flame, giving rise to white fumes of teroxide of antimony. When the gas is conducted through a red-hot glass tube of narrow dimensions, or burned with a limited supply of air, such as is the case when a cold porcelain surface is pressed into the flame, metallic anti- mony is deposited. On passing a current of antimonetted hydrogen through a solution of nitrate of silver a black precipitate is obtained, containing Sb Ag0; from the formation of this compound it is inferred that the gas has the composition SbH3. The few salts of antimony soluble in water are amply characterized by the orange or brick-red precipitate with sulphuretted hydrogen, which is soluble in a solution of sulphide of ammonium, and again precipitated by an acid. Besides its application to medicine, antimony is of great importance in the arts, inasmuch as it forms with lead type-metal. This alloy expands at the moment of solidifying, and takes an exceedingly sharp impression of the mould. It is remarkable that both its constituents shrink under similar cir- cumstances, and make very bad castings. Tersulphide of antimony enters into composition of the blue signal-light used at sea.1 TELLURIUM. This metal, or semi-metal, is of very rare occurrence: it is found in a few scarce minerals in association with gold, silver, lead, and bismuth, apparently replacing sulphur, and is most easily extracted from the sulpho-telluride of bismuth of Chemnitz, in Hungary. The finely-powdered ore is mixed with an equal weight of dry carbonate of soda, the mixture made into a paste with oil, and heated to whiteness in a closely-covered crucible. Telluride and sul- phide of sodium are produced, and metallic bismuth set free. The fused mass is dissolved in water and the solution freely exposed to the air, when the sodium and sulphur oxidize to caustic soda and hyposulphite of soda, while the tellurium separates in the metallic state. Tellurium has the color and lustre of silver: by fusion and slow cooling it maybe made to exhibit the form of rhombohcdral crystals similar to those of antimony and arsenic. It is 1 Blue or Bengal light: — Dry nitrate of potassa . . .6 parts, Sulphur......2 " Tersulphide of antimony . . . 1 part, All in fine powder, and intimately mixed. ARSENIC. 309 brittle, and a comparatively bad conductor of heat and electricity: it has a density of 6-26, melts at little below a red-heat, and volatilizes at a higher temperature. Tellurium burns when heated in the air, and is oxidized by nitric acid. Two compounds of this substance with oxygen are known, having acid properties; they much resemble the acids of arsenic. The equivalent of tellurium is 64-2; its symbol is Te. Tellurous acid, Te02. — This is obtained by burning tellurium in the air, or by heating it in fine powder with nitric acid of 1-25 specific gravity: a solution is rapidly formed, from which white anhydrous octahedral crystals' of tellurous acid are deposited on standing. The acid is fusible at a red-heat, and slightly volatile at a higher temperature; it is but feebly soluble in water or acids, easily dissolved by alkalies, and reduced when heated with carbon or hydrogen. A hydrate of tellurous acid is thrown down when tellurite of potassa is mixed with a slight excess of nitric acid; it is a white powder, soluble to a certain extent in water, and reddens litmus. " Telluric .acid, TeO^—Equal parts of tellurous acid afid carbonate of soda are fused, and the product dissolved in water; a little hydrate of soda is added, and a stream of chlorine passed through the solution. The liquid is next saturated with ammonia, and mixed with solution of chloride of barium, by which a white insoluble precipitate of tellurate of baryta is thrown down. This is washed and digested with a quarter of its weight of sulphuric acid, diluted with water. The filtered solution gives, on evaporation in the air, large crystals of telluric acid. Telluric acid is freely, although slowly, soluble in water; it has a metallic taste, and reddens litmus-paper. When the crystals are strongly heated, they lose water, and yield the anhydrous acid, which is then insoluble in water, and eveu in a boiling alkaline liquid. At the temperature of ignition, telluric acid loses oxygen, and passes into tellurous acid. The salts of the alkalies are soluble, but do not crystallize: those of the earths are nearly, or quite, insoluble. There are two chlorides of tellurium, and also a hydride, which closely resemble sulphuretted hydrogen. arsenic. Arsenic is sometimes found native: it occurs in considerable quantity as a constituent of many minerals, combined with metals, sulphur and oxygen In the oxidized state it has been found in very minute quantity in a great many mineral waters. The largest portion is derived from the roasting of natural arsenides of iron, nickel, and cobalt: the operation is conducted in a reverbe- ratory furnace, and the volatile products condensed in a long and nearly hori- zontal chimney, or in a kind of tower of brickwork, divided into numerous chambers The crude arsenious acid thus produced is purified by sublima- tion and then heated with charcoal in a retort; the metal is reduced, and readily sublimes. Arsenic has a steel-gray color, and high metallic lustre; it is crystalline and very brittle; it tarnishes in the air, but may be preserved unchanged in pure water Its density is 5-7 to 5-9. When heated, it volatilizes without fusion, and, if air be present, oxidizes to arsenious acid. The vapor has the odor of garlic. This substance combines with metals in the same manner as sulphur and phosphorus, which it resembles, especially the latter, in many respects. _ \\ ith oxygen it unites in two proportions, giving rise to arsenious and arsenic acids. There is no basic oxide of arsenic. Tho equivalent of arsenic is 75; its symbol is As. Arsenious acid ; white oxide of ars"exic ; As03.—The origin of this sub- stance is mentioned above. It is commonly met with in the form of a heavy white, glassy-looking substance, with smooth conchoidal fracture, which' ha« evidently undergone fusion. When freshly-prepared, it is often transparent" but by keeping becomes opaque, at the same time slightly diminishing ia 310 ARSENIC. density, and acquiring a greater degree of solubility in water. 100 parts of that liquid dissolve, at 212° (100°C), about 11-5 parts of the opaque variety ; the largest portion separates, however, on cooling, leaving about 3 parts dis- solved : the solution feebly reddens litmus. Cold water, agitated with pow- dered arsenious acid, takes up a still smaller quantity. Alkalies dissolve this substance freely, forming arsenites; also compounds with ammonia, baryta, strontia, lime, magnesia, and oxide of manganese, have been formed; the compound with oxide of silver is a beautifully lemon-yellow precipitate. Ar- senious acid is easily soluble in hot hydrochloric acid. The vapor of arsenious acid is colorless and inodorous. It crystallizes on solidifying in brilliant trans- parent octahedra. The acid itself has a feeble sweetish and astringent taste, and is a most fearful poison.1 Arsenic acid, As05. —Powdered arsenious acid is dissolved in hot hydro- chloric acid, and oxidized by the addition of nitric acid, the latter being added as long as red vapors are produced; the whole is then cautiously evaporated to complete dryness. The acid thus produced is white and anhydrous. Put into water, it slowly but completely dissolves, giving a highly-acid solution, which, on being evaporated to a syrupy consistence, deposits, after a time, hydrated crystals of arsenic acid. When strongly heated, it is decomposed into arsenious acid and oxygen gas. This substance is a very powerful acid, comparable with phosphoric, which it resembles in the closest manner, forming salts strictly isomorphous with the corresponding phosphates; it is also tribasic. An arsenate of soda, 2NaO, HO,As05-j- 24HO, indistinguishable in appearance from common phosphate of soda, may be prepared by adding the carbonate to a solution of arsenic acid, until an alkaliue reaction is apparent, and then evaporating. This salt also crystallizes with 14 equivalents of water. Another arsenate, 3NaO,As05 -f- 24HO, is produced when carbonate of soda in excess is fused with arsenic acid, or when the preceding salt is mixed with caustic soda. A third, NaO, 2HO,As05 + 2HO, is made by substituting an excess of arsenic acid for the solution of alkali. The alkaline arsenates which contain basic wafer lose the latter at a red-heat, but, unlike the phosphates, recover it when again dis- solved.2 The salts of the alkalies are soluble in water; those of the earths and other metallic oxides are insoluble, but are dissolved by acids. The pre- cipitate with nitrate of silver is highly characteristic of arsenic acid; it is reddish-brown. Three Sulphides of arsenic are known.—Realgar, AsS2, occurs native. It is formed artificially, by heating arsenious acid with the proper proportion of sulphur. It is an orange-red, fusible, and volatile substance, employed in painting and by the pyrotechnist in making white-fire. Orpiment, AsS3, which is also a product of the mineral kingdom, is made by fusing arsenious acid with excess of sulphur, or by precipitating a solution of the acid by sulphuretted hydrogen. It is a golden-yellow crystalline substance, fusible and volatile by heat. A higher sulphide, AsS5, corresponding to arsenic acid, is produced when sulphuretted hydrogen is transmitted through a solution of arsenic acid. 1 [The antidotes for arsenious acid are magnesia and the hydrate of the sesquioxide of iron of which the latter is best. In its recently precipitated gelatinous condition it is mo«t efficient' It acts by forming au insoluble arseniate of the protoxide of iron ; for the peroxide'is reduced to protoxide by losing oxygen, which, passing to the arsenious acid, forms arsenic acid. This change is represented by the following formula: 2Fe203 and As03 = 4FeO + As05. The hydrate is incapable of decomposing the arsenites. The red oxide, to act as an antidote to the arsenical salts, requires to be combined with an acid, which may separate the has* ind then the arsenious acid aud red oxide react on each other as above The ,™t,t„ „f ,^L ™i oxide is the salt used. ' aceiate oi the red Magnesia has also been recommended. In the state of recently precipitated hvrlvnt,. it ant* on a solution of arsenious acid with nearly the same rapidity as the hvdr^rt nflv • i ' i • In the condition usually found in the shops, it cannot be depended on Litn t^L de °/"T having beeu too highly calcined.-R. B.J «<-pcnata on w ith the same certainty, a Graham, Elements, p. 532. ARSENIC. 311 The solution of arsenic acid is not immediately precipitated, the pentasulphide being deposited only after some hours' standing. Its precipitation is consi- derably accelerated by ebullition. It is a yellow, fusible substance, capable of sublimation. Realgar, orpiment, and pentasulphide of arsenic are sulphur-acids. Arsenic unites with chlorine, iodine, &c. The terchloride, AsCl3. is formed by distilling a mixture of 1 part of arsenic, and 6 parts of corrosive subli- mate: it is a colorless, volatile liquid, decomposed by water into arsenious and hydrochloric acids. The same substance is produced, with disengagement of heat and light, when powdered arsenic is thrown into chlorine gas. The teriodide, Asl3, is formed by heating metallic arsenic with iodine; it is a deep- red crystalline substance, capable of sublimation. The bromide and fluoride are both liquid. Arsenic also combines with hydrogen, forming a gaseous compound, AsH3, analogous to phosphoretted hydrogen. It is obtained pure by the action of strong hydrochloric acid on an alloy of equal parts of zinc and arsenic, and is produced in greater or less proportion whenever hydrogen is set free in con- tact with arsenious acid. Arsenetted hydrogen is a colorless gas, of 2-695 specific gravity, slightly soluble in water, and having the smell of garlic. It burns when kindled with a blue flame, generating arsenious acid. It is also decomposed by transmission through a red-hot tube. Many metallic solutions arc precipitated by this substance. It is, when inhaled, exceedingly poisonous, even in very minute quantity. Arsenious acid is distinguished by characters which cannot be misunderstood. _ Nitrate of silver, mixed with a solution of arsenious acid in water, occa- sions no precipitate, or merely a faint cloud ; but if a little alkali, as a drop of ammonia, be added, a yellow precipitate of arsenite of silver immediately falls. The precipitate is exceedingly soluble in excess of ammonia; that sub- stance must, therefore, be added with great caution; it is likewise very soluble in nitric acid. Sulphate of copper gives no precipitate with solution of arsenious acid, until the addition has been made of a little alkali, when a brilliant yellow- green precipitate (Scheele's green) falls, which also is very soluble in excess of ammonia. Sulphuretted hydrogen passed into a solution of arsenious acid, to which a few drops of hydrochloric or sulphuric acid have been added, occasions the production of a copious bright-yellow precipitate, of orpiment, which is dis- solved with facility by ammonia, and reprecipitated by acids. Solid arsenious acid, heated by the blowpipe in a narrow glass tube with small fragments of dry charcoal, affords a sublimate of metallic arsenic in the shape of a brilliant steel-gray metallic ring. A portion of this, detached by the point of a knife and heated in a second glass tube, with access of air, yields, in its turn, a sublimate of colorless, transparent, octahedral crystals of arsenious Tig. 163. acid. All these experiments, which jointly give de- monstrative proof of the presence of the sub- stance in question, may be performed with perfect precision and certainty, upon exceed- ingly small quantities of material. The detection of arsenious acid in complex mixtures containing organic matter and com- mon salt, as beer, gruel, soup, &c, or the fluid contents of the stomach in cases of poison- ing, is a very far more difficult problem, but one which is unfortunately often required to be solved. These organic matters interfere completely with the liquid tests, and render 312 ARSENIC . their indications worthless. Sometimes the difficulty may be eluded by a diligent search in the suspected liquid, and in the vessel containing it, De- fragments or powder of solid arsenious acid, which, from its small degree of solubility, often escapes solution, and from the high density of the substance may be found at the bottom of the vessels in which the fluids are contained. If anything of the kind be found, it may be washed by decautation with a little cold water, dried, and then reduced with charcoal. For the Fig. 164. latter purpose, a small glass tube is taken, having the figure re- presented in the margin; white German glass, free from lead, is to be preferred. The arsenious acid, or what is suspected to be such, is dropped to the bottom, and covered with splinters or little fragments of charcoal, the tube being filled to the shoulder. The whole is gently heated, to expel any moisture that may be present in the charcoal, and the deposited water wiped from the interior of the tube with bibulous paper. The narrow part of the tube containing the charcoal, from a to b, is now heated by the blowpipe flame; when red-hot the tube is inclined, so that the bottom also may become heated. The arsenious acid, if present, is vaporized, and reduced by the charcoal, and a ring of metallic arsenic deposited on the cool part of the tube. To complete the experiment, the tube may be melted a-t a by the point of the flame, drawn off, and closed, and the arsenic oxidized to arseni- ous acid, by chasing it up and down by the heat of a small spirit- lamp. A little water may afterwards be introduced, and boiled in the tube, by which the arsenious acid will be dissolved, and to this solution the tests of nitrate of silver and ammonia, sulphate of copper and ammonia, and sulphuretted hydrogen may be applied. When the search for solid arsenious acid fails, the liquid itself must be examined; a tolerably limpid solution must be obtained, from which the arsenic may be precipitated by sulphuretted hydrogen, and the orpiment col- lected, and reduced to the metallic state. It is in the first part of this opera- tion that the chief difficulty is found: such organic mixtures refuse to filter, . or filter so slowly as to render some method of acceleration indispensable. Boiling with a little caustic potassa or acetic acid will sometimes effect this object. The following is an outline of a plan, which has been found success- ful in a variety of cases, in which a very small quantity of arsenious acid had been purposely added to an organic mixture. Oil of vitriol, itself perfectly free from arsenic, is mixed with the suspected liquid, in the proportion of about a measured ounce to a pint, having been previously diluted with a little water, and the whole is boiled in a flask for half an hour, or until a complete separation of solid and liquid matter becomes manifest. The acid converts any starch that may be present into dextrin and sugar; it coagulates com- pletely albuminous substances, and casein, in the case of milk, and brines the whole in a very short time into a state in which filtration is both easy and rapid. Through the filtered solution, when cold, a current of sulphuretted hydrogen is transmitted, and the liquid is warmed, to facilitate the'deposition of the tersulphide, which falls in combination with a large quantity of organic matter, which often communicates to it a dirty color. This is collected upon a small filter, and washed. It is next transferred to a capsule, and heated with a mixture of nitric and hydrochloric acids, by which the organic impuri- ties are in a great measure destroyed, and the arsenic oxidized to arsenic acid. The solution is evaporated to dryness, the soluble part taken up by dilute hydrochloric acid, and then the solution saturated with sulphurous acid whereby the arsenic acid is reduced to the state of arsenious acid the sul- phurous being oxidized to sulphuric acid. The solution of arsenious'acid may be precipitated by sulphuretted hydrogen without any difficulty. The liquid is warmed, and the precipitate washed by decantation, and dried. It is then ARSENIC. 313 mixed with black-flux, and heated in a small glass tube, similar to that already described, with similar precautions: a ring of reduced arsenic is obtained, which may be oxidized to arsenious acid, and farther examined. The black- flux is a mixture of carbonate of potassa and charcoal, obtained by calcining cream of tartar in a close crucible; the alkali transforms the sulphide into arsenious acid, the charcoal subsequently effecting the deoxidation. A mix- ture of anhydrous carbonate of soda and charcoal may be substituted with advantage for the common black-flux, as it is less hygroscopic. Other methods of proceeding, different in principle from the foregoing, have been proposed, as that of the late Mr. Marsh, which is exceedingly delicate. The suspected liquid is acidulated with sulphuric acid and placed in contact with metallic zinc; the hydrogen reduces the arsenious acid and combines witli the arsenic, if any be present. The gas is burned at a jet, and a piece of glass or porcelain held in the flame, when any admixture of arsenetted hydrogen is at once known by the production of a brilliant black metallic spot of reduced arsenic on the porcelain. It has been observed (page 308) that antimonetted hydrogen gives a similar result. In order to distinguish the two substances, the gas may be passed into a solution of nitrate of silver. Both gases give rise to a black precipitate, which, hi the case of antimonetted hydrogen, consists of antimonide of silver, Sl>Ags, "whilst it is a pure silver in the case of arsenetted hydrogen, the arsenic being then converted into arsenious acid, which combines with a por- tion of oxide of silver. The arsenite of silver remains dissolved in the nitric acid which is liberated by the precipitation of the silver, and may be thrown down with its characteristic yellow color by adding ammonia to the liquid filtered off from the black precipitate. The black antimonide of silver, when carefully washed and subsequently boiled with a solution of tartaric acid, yields a solution containing antimony only, and from which sulphuretted hydrogen separates the character- istic orange-yellow precipitate of tersulphide of anti- mony. A convenient form of Marsh's instrument is that shown in the drawing: it consists of a bent tube having two bulbs blown upon it, fitted with a stop-cock and narrow jet. Slips of zinc are put into the lower bulb, which is afterwards filled with the liquid to be ex- amined. On replacing the stop-cock, closed, the gas collects and forces the fluid into the upper bulb, which then acts by its hydrostatic pressure, and expels the gas through the jet so soon as the stop-cock is opened. It must be borne in mind that both common zinc and sulphuric acid often contain traces of arsenic.1 A slip of copper-foil boiled in the poisoned liquid previously acidulated with hydrochloric acid, with- draws tho arsenic and becomes covered with a, white alloy. By heating the metal in a glass tube, the arsenic is expelled, and oxidized to arsenious acid. (hen orange do not disappear on exposure. ^i^clZ^to^lJ^^s^^tni hydrogen solution, but are not then soluble in ammonia. - K.B.] g y sulPhurctte*l 314 SILVER. SECTION VI. METALS WHOSE OXIDES ARE REDUCED BY HEAT. silver. Silver is found in the metallic state, as sulphide in union with sulphide of antimony and sulphide of arsenic, and also as chloride, iodide, and bromide. Among the principle silver mines may be mentioned those of the Hartz moun- tains in Germany, of Konigsberg in Norway, and, more particularly, of the Andes in both North and South America. The greater part of the silver of commerce is extracted from ores so poor as to render any process of smelting or fusion inapplicable, even where fuel could be obtained, and this is often difficult to be procured. Recourse, therefore, is had to another method, that of amalgamation, founded on the easy solubility of silver and many other metals in metallic mercury. The amalgamation-process, as conducted in Germany, differs somewhat from that in use in America. The ore is crushed to powder, mixed with a quantity of common salt, and roasted at a low red-heat in a suitable furnace, by which treatment any sulphide of silver it may contain is converted into chloride. The mixture of earthy matter, oxides of iron, copper, soluble salts, chloride of silver, and metallic silver, is sifted and put into large barrels, made to revolve on axes, with a quantity of water and scraps of iron, and the whole agitated together for some time, during which the iron reduces the chloride of silver to the state of metal. A certain proportion of mercury is then intro- duced, and the agitation repeated; the mercury dissolves out the silver together with gold, if there be any, metallic copper, and other substances, forming a fluid amalgam easily separable from the thin mud of earthy matter by subsidence and washing. This amalgam is strained through strong linen cloth, and the solid portion exposed to heat in a kind of retort, by which the remaining mercury is distilled off and the silver left behind in an impure condition. A considerable quantity of silver is obtained from argentiferous galena; in fact, almost every specimen of native sulphide of lead will be found to con- tain traces of this metal. When the proportion rises to a certain amount it becomes worth extracting. The ore is reduced in the usual manner, the whole of the silver remaining with the lead; the latter is then re-melted'in a large vessel, and allowed slowly to cool until solidification commences. The portion which first crystallizes is nearly pure lead, the alloy with silver being more fusible than lead itself; by particular management this is drained away and is found to contain nearly the whole of the silver. This rich mass is'next exposed to red-heat on the shallow hearth of a furnace, while a stream of air is allowed to impinge upon the surface; oxidation takes place with great rapidity, the fused oxide or litharge being constantly swept from the metal by the blast. When the greater part of the lead has been thus removed the residue is transferred to a cupel or shallow dish made of bone-ashes, and again SILVER. 315 heated ; the last of the lead is now oxidized, and the oxide sinks in a melted state into the porous vessel, while the silver, almost chemically pure, and exhibiting a brilliant surface, remains behind. Pure silver may be easily obtained. The metal is dissolved in nitric acid; if it contain copper, the solution will have a blue tint; gold will remain undis- solved as a black powder. The solution is mixed with hydrochloric acid or with common salt, and the white, insoluble curdy precipitate of chloride of silver washed and dried. This is then mixed with about twice its weight of anhydrous carbonate of soda, and the mixture, placed in an earthen crucible, gradually raised to a temperature approaching whiteness, during which the carbonate of soda and the chloride react upon each other, carbonic acid and oxygen escape, while metallic silver and chloride of sodium result; the former fu-es into a button at the bottom of the crucible, and is easily detached. I'ure silver has a most perfect white color and a high degree of lustre: it is exceedingly malleable and ductile, and is probably the best conductor both of heat and electricity known. Its specific gravity is 10-5. In hardness it lies between gold and copper. It melts at a bright red-heat, about 1873° (1023°C), according to the observations of Mr. Daniell. Silver is unalterable by air and moisture: it refuses to oxidize at any temperature, but possesses the extraor- dinary faculty, already noticed in an earlier part of the work, of absorbing many times its volume of oxygen when strongly heated in an atmosphere of that gas, or in common air. This oxygen is again disengaged at the moment of solidification, and gives rise to the peculiar arborescent appearance often remarked on the surface of masses or buttons of pure silver. The addition of 2 per cent, of copper is sufficient to prevent this absorption of oxygen. Silver oxidizes when heated with fusible siliceous matter, as glass, which it stains yellow or orange, from the formation of a silicate. It is little attacked by hydrochloric acid; boiling oil of vitriol converts it into sulphate with evo- lution of sulphurous acid ; nitric acid, even dilute and in the cold, dissolves it readily. The tarnishing of surfaces of silver exposed to the air is due to sulphuretted hydrogen, the metal having a strong attraction for sulphur. There are three oxides of silver, one of which is a powerful base isomorphous with potassa, soda, and oxide of ammonium. The equivalent of silver is 108; its symbol is Ag (argentum). Suboxide of silver, Ag20. — When dry citrate of silver is heated to 212° (100°C) in a stream of hydrogen gas, it loses oxygen and becomes dark brown. The product dissolved in water, gives a dark-colored solution containing free citric acid and citrate of the suboxide of silver. The suboxide is then pre- cipitated by potassa. It is a black powder, very easily decomposed, and soluble in ammonia. The solution of citrate is rendered colorless by heat, being resolved into a salt of the protoxide and metallic silver. According to Wohlcr, suboxide of silver is also formed by boiling arsenite of silver with caustic alkalies. In this case it is mixed with metallic silver. Protoxide of silver, AgO.—Caustic potassa added to a solution of nitrate of silver throws down a pale-brown precipitate, which consists of protoxide of silver. It is very soluble in ammonia, and is dissolved also to a small extent by pure water; the solution is alkaline. Recently-precipitated chloride of silver, boiled with a solution of caustic potassa of specific gravity 1-25, ac- cording to the observation of Dr. Gregory, is converted, although with diffi- culty, into oxide of silver, which in this case is black and very dense. The protoxide of silver neutralizes acids completely, and forms, for the most part, colorless salts. It is decomposed by a red-heat, with evolution of oxygen, Bpongy metallic silver being left: the sun's rays also effect its decomposition t<> a small extent. Peroxide of silver. — This is a black crystalline substance which forms upon the positive electrode of a voltaic arrangement employed to decompose a solution of nitrate of silver. It is reduced by heat, evolves chlorine when acted upon by hydrochloric acid, explodes when mixed with phosphorus and 316 SILVER. struck, and decomposes solution of ammonia with great energy and rapid disengagement of nitrogen gas. Nitrate of silver, AgO,N05.—The nitrate is prepared by directly dissolving silver in nitric acid, and evaporating the solution to dryness, or until it is strong enough to crystallize on cooling. The crystals are colorless, transparent, anhydrous tables, soluble in an equal weight of cold, and in half that quantity of boiling water: they also dissolve in alcohol. They fuse when heated like those of nitre, and at a higher temperature suffer decomposition : the lunar caustic of the surgeon is nitrate of silver which has been melted and poured into a cylindrical mould. The salt blackens when exposed to light, more particularly if organic matters of any kind be present, and is frequently employed to communicate a dark stain to the hair; it enters into the compo- sition of the "indelible" ink used for marking linen. The black stain has been thought to be metallic silver; it may possibly be suboxide. Pure nitrate of silver may be prepared from the metal alloyed with copper: the alloy is dissolved in nitric acid, the solution evaporated to dryness, and the mixed nitrates cautiously heated to fusion. A small portion of the melted mass is removed from time to time for examination; it is dissolved in water, filtered, and ammonia added to it in excess. While any copper salt remains undecom- posed, the liquid will be blue, but when that no longer happens, the nitrate may be suffered to cool, dissolved in water, and filtered from the insoluble black oxide of copper. Sulphate of silver, AgO,S03.—The sulphate may be prepared by boiling together oil of vitriol and metallic silver, or by precipitating a concentrated solution of nitrate of silver by an alkaline sulphate. It dissolves in 88 parts of boiling water, and separates in great measure in a crystalline form on cooling, having but a feeble degree of solubility at a low temperature. It forms a crystallizable compound-with ammonia, freely soluble in water, con- taining AgO,S03+ 2NH3. Hyposulphate of Silver, AgO,S205-f-HO, is a soluble crystallizable salt, per- manent in the air. The hyposulphite is insoluble, white, and very prone to decomposition: it combines with the alkaline hyposulphites, forming soluble compounds distinguished by an intensely-sweet taste. The alkaline hyposul- phites dissolve both oxide and chloride of silver, and give rise to similar salts, an oxide or chloride of the alkaline metal being at the same time formed. Carbonate of silver is a white insoluble substance obtained by mixing solutions of nitrate of silver and of carbonate of soda. It is blackened and decom- posed by boiling. Chloride of silver, AgCl.—This substance is almost invariably produced when a soluble salt of silver and a soluble chloride are mixed. It falls as a white curdy precipitate, quite insoluble in water and nitric acid ; but one part of chloride of silver is soluble in 200 parts of hydrochloric acid when concen- trated, and in about 600 parts when diluted with double its weight of water. When heated it melts, and on cooling becomes a grayish crystalline mass, which cuts like horn; it is found native in this condition, constituting the horn-silver of the mineralogist. Chloride of silver is decomposed by light both in a dry and wet state, very slowly if pure, and quickly if organic matter be present: it is reduced also when put into water with metallic zinc or iron. It is soluble with great ease in ammonia and in a solution of cyanide of potas- sium. In practical analysis the proportion of chlorine or hydrochloric acid in a compound is always estimated by precipitation by solution of silver. The liquid is acidulated with nitric .acid, and an excess of nitrate of silver added- .the chloride is collected on a filter, or better by subsidence, washed, dried and fused; 100 parts correspond to 24-7 chlorine, or 25-43 of hydrochloric acid. Iodide of silver, Agl. — The iodide is a pale-yellow insoluble precipitate, produced by adding nitrate of silver to iodide of potas'sium: it is insoluble or GOLD. 317 nearly so in ammonia, and forms an exception to the silver-salts in general in this respect. Deville has obtained a crystalline iodide of silver by the action of concentrated hydriodic acid upon metallic silver which it dissolves with disengagement of hydrogen. Hydriodic acid converts chloride of silver into iodide. The bromide of silver very closely resembles the chloride. Sulphide of silver, AgS.—This is a soft, gray, and somewhat malleable substance, found native in a crystallized state, and easily produced by melting together its constitutents. or by precipitating a solution of silver by sulphu- retted hydrogen. It is a strong sulphur-base, and combines with the sulphides of antimony and arsenic: examples of such compounds are found in the beautiful minerals, dark and light-red silver ore. Ammonia-compound of silver ; Berthollet's fulminating silver. — When precipitated oxide of silver is digested in ammonia, a black substance is produced, possessing extremely dangerous explosive properties. It ex- plodes while moist, when rubbed with a hard body, but when dry the touch of a feather is sufficient. The ammonia retains some of this substance in solution, and deposits it in small crystals by spontaneous evaporation. A similar compound containing oxide of gold exists. It is easy to understand the reason why these bodies are subject to such violent and sudden decompo- sition by the slightest cause, on the supposition that they contain an oxide of nn easily-reducible metal and ammonia: the attraction between the two con- stituents of the substance is \cry feeble, while that between the oxygen of the one and the hydrogen of the other is very powerful. The explosion is caused by the sudden evolution of nitrogen gas and vapor of water, the metal being set free. A soluble salt of silver is perfectly characterized by the white curdy preci- pitate of chloride of silver, darkening by exposure to light, and insoluble in hot nitric acid, which is produced by the addition of any soluble chloride. Lead is the only metal which can be confounded with it in this respect; but chloride of lead is soluble to a great extent in boiling water, and is deposited in brilliant acicular crystals when the solution cools. Solutions of silver are reduced to the metallic state by iron, copper, mercury, and other metals. The economical uses of silver are man}': it is admirable for culinary and other similar purposes, not being attacked in the slightest degree by any of the substances used for food. It is necessary, however, in these cases to diminish the softness of the metal by a small addition of copper. The stan- dard silver of England contains 222 parts of silver and 18 parts of copper. (Jold. in small quantitres, is a very widely-diffused metal; traces are con- stantly found in the iron pyrites of the more ancient rocks. It is always met with in the metallic state, sometimes beautifully crystallized in the cubic form, associated with quartz, oxide of iron, and other substances, in regular mineral veins. The sands of various rivers have long furnished gold derived from this source, and separable by a simple process of washing; such is the gold-dust of commerce. When a veinstone is wrought for gold, it is stamped to powder, and shaken in a suitable apparatus with water and mercury: an amalgam is formed, which is afterwards separated from the mixture and de- composed by distillation. The pure metal is obtained by solution in nitro-hydrochloric acid and pre- cipitated 1>\ a salt of protoxide of iron, which, by undergoing peroxidation, 27*' 318 GOLD. reduces the gold. The latter falls as a brown powder, which acquires the metallic lustre by friction. Golo. is a soft metal, having a beautiful yellow color. It surpasses all other metals in malleability, the thinnest gold-leaf not exceeding, it is said, onTyWo" of an m°k *n fhickness> while the gilding on the silver wire used in the manufacture of gold-lace is still thinner. It may also be drawn into very fine wire. Gold has a density of 19-5 ; it melts at a temperature a little above the fusing-point of silver. Neither air nor water affect it in the least at any temperature : the ordinary acids fail to attack it singly. A mixture of nitric and hydrochloric acids dissolves gold, however, with ease, the active agent being the liberated chlorine. Gold forms two compounds with oxygen, and two corresponding compounds with chlorine, iodine, sulphur, &c. Both oxides refuse to unite with acids. The equivalent of gold is 197. Its symbol is Au (aurum). Protoxide of gold, AuO.—The protoxide is produced when caustic potassa in solution is poured upon the protochloride. It is a green powder, partly soluble in the alkaline liquid: the solution rapidly decomposes into metallic gold, which subsides, and into teroxide, which remains dissolved. Teroxide of gold; auric acid; Au03. — When magnesia is added to the terchloride of gold, and the sparingly-soluble aurate of that base well washed and digested with nitric acid, the teroxide is left as an insoluble reddish-yellow powder, which, when dry, becomes chestnut-brown. It is easily reduced by heat, and also by mere exposure to light: it "is insoluble in oxygen acids, with the exception of strong nitric acid, insoluble in hydro- fluoric acid, easily dissolved by hydrochloric and hydrobromic acids. Alka- lies dissolve it freely; indeed, the acid properties of this substance are very strongly marked: it partially decomposes a solution of chloride of potassium when boiled with that liquid, potassa being produced. When digested with ammonia, it furnishes fulminating gold. Protochloride of gold, AuCL — This substance is produced when the terchloride is evaporated to dryness, and exposed to a heat of 440° (226°-6C), until chlorine ceases to be exhaled. It forms a yellowish-white mass, insoluble in water. In contact with that liquid it is decomposed slowly in the cold and rapidly by the aid of heat, into metallic gold and terchloride. Terchloride of gold, AuC13. — This is the most important compound of the metal; it is always produced when gold is dissolved in nitro-hydro- chloric acid. The deep-yellow solution thus obtained yields, by evaporation yellow crystals of the double chloride of gold and hydrogen • when this is with a number of metallic chlorides, forming a series of double salts "ofwhich the general formula in the anhydrous state is MCl+AuCl3, M representing an equivalent of the second metal. These compounds are mostly yellow when in crystals, and red when deprived of water. A mixture of terchloride of gold with excess of bicarbonate of potassa or soda is used for gilding small ornamental articles of copper: these are cleaned by dilute nitric acid, and then boiled in the mixture for some time bv which means they acquire a thin but perfect coating of reduced gold ' The other compounds of gold are of very little importance. The presence of this metal in solution may be known by the brown nrecini- tate with sulphate of protoxide of iron, fusible before the Wowdidp into « W of gold; and by the purple compound formed when th^iS^S loldfc added to a solution of protochloride of tin. nae 0I g01ct 1S MERCURY, OR QUICKSILVER. 319 Gold intended for coin, and most other purposes, is always alloyed with a certain proportion of silver or copper to increase its hardness and durability ; the first-named metal Confers a pale-greenish color. English standard gold contains ^ of alloy, now always copper. Gold-leaf is made by rolling out plates of pure gold as thin as possible, and then beating them between folds of membrane by a heavy hammer, until the requisite degree of tenuity has been reached. The leaf is made to adhere to wood, &c, by size or varnish. Gilding on copper has very generally been performed by dipping the articles into a solution of nitrate of mercury, and then shaking them with a small lump of a soft amalgam of gold with that metal, which thus becomes spread over their surfaces: the articles are subsequently heated to expel the mer- cury and then burnished. Gilding on steel is done either by applying a solu- tion of terchloride of gold, in ether, or by roughening the surface of the metal, heating it, and applying gold-leaf, with a burnisher. Gilding by electrolysis —an elegant and simple method, now rapidly superseding many of the others —has already been noticed. The solution usually employed is obtained by dissolving oxide or cyanide of gold in a solution of cyanide of potassium.1 MERCURY, OR QUICKSILVER. This very remarkable metal has been known from an early period, and per- haps more than all others has excited the attention and curiosity of experi- menters, by reason of its peculiar physical properties. Mercury is of great importance in several of the arts, and enters into the composition of many valuable medicaments. Metallic mercury is occasionally met with in globules disseminated through the native sulphide, which is the ordinary ore. This latter substance, some- times called cinnabar, is found in considerable quantity in several localities, of which the most celebrated are Almaden in Spain, and Idria in Austria. Only recently it has been discovered in great abundance, and of remarkable purity, in California and Australia. The metal is obtained by heating the sul- phide in an iron retort with lime or scraps of iron, or by roasting it in a fur- nace, and conducting the vapors into a large chamber, where the mercury is condensed, while the sulphurous acid is allowed to escape. Mercury is im- ported into this country in bottles of hammered iron, containing seventy-five pounds each, and in a state of considerable purity. When purchased in smaller quantities, it is sometimes found adulterated with tin and lead, which metals it dissolves to some extent without much loss of fluidity. Such admix- ture may be known by the foul surface the mercury exhibits when shaken in a bottle containing air, and by the globules, when made to roll upon the table, having a train or tail. Mercury has a nearly silver-white color, and a very high degree of lustre: it is liquid at all ordinary temperatures, and only solidifies when cooled to —40° (—40°C). In this state it is soft and malleable. At GG2° (350°C) it boils, and yields a transparent, colorless vapor, of great density. The metal volatilizes, however, to a sensible extent at all temperatures above 68° (20°C) or 70° (21°C); below this point its volatility is imperceptible. The volatility of mercury at the boiling-heat is singularly retarded by the presence of minute quantities of lead or zinc. The specific gravity of mercury at 00° (15°-5C) is 13-59; that of frozen mercury about 14, greatcontraction taking place in the act of solidification. Pure quicksilver is quite unalterable in the air at common temperatures, but when heated to near its boiling-point it slowly absorbs oxygen, and be- comes converted into S crystalline dark-red powder, which is the highest oxide. At a dull-red heat this oxide is again decomposed into its constituents. 1 Messrs. Elkington, Application of Electro-Metallurgy to the Arts. 320 MERCURY, OR QUICKSILVER. Hydrochloric acid has little or no action on mercury, and the same may be said of sulphuric acid in a diluted state: when the latter is concentrated and boiling-hot, it oxidizes the metal, converting it into sirlphate of the red oxide, with evolution of sulphurous acid. Nitric acid, even dilute and in the cold, dissolves mercury freely, with an evolution of binoxide of nitrogen. Mercury combines with oxygen in two proportions, forming a gray and a red oxide, both of which are salifiable. As the salts of the red oxide are the most stable and permanent, that substance may be regarded as the true prot- oxide, instead of the gray oxide, to which the term has formerly been applied. Until, however, isomorphous relations connecting mercury with the other metals shall be established, the constitution of the two oxides and that of the corresponding chlorides, iodides, &c, must remain somewhat unsettled.1 The equivalent of mercury, on the above supposition, will be 100; its sym- bol is Hg (hydrargyrum). Suboxide of mercury ; gray oxide ; Hg20.—The suboxide'is easily pre- pared by adding caustic potassa to the nitrate of this substance, or by digest- ing calomel in solution of caustic alkali. It is a dark-gray, nearly black, heavy powder, insoluble in water. It is slowly decomposed by the action of light into metallic mercury and red oxide. The preparations known in phar- macy by the names blue pill, gray ointment, mercury with chalk, &c, often sup- posed to owe their efficacy to this substance, merely contain the finely-divided metal. Protoxide of mercury; red oxide; HgO.—There are numerous methods by which this compound may be obtained ; the following may be cited as the most important:—(1) By exposing mercury in a glass flask, with a long nar- row neck, for several weeks to a temperature approaching 600° (315°-5C); the product has a dark-red color, and is highly crystalline; it is the red pre- cipitate of the old writers. (2) By cautiously heating any of the nitrates of either oxide to complete decomposition, when the acid is decomposed and ex- pelled, oxidizing the metal to a maximum, if it happen to be in the condition of suboxide. The product is in this case also crystalline and very dense, but has a much paler color than the preceding ; while hot it is nearly black. It is by this method that the oxide is generally prepared; it is opt to contain undecomposed nitrate, which may be discovered by strongly heating a portion in a test-tube: if red fumes are produced, or the odor of nitrous acid exhaled, the oxide has been insufficiently heated in the process of manufacture. (3) By adding caustic potassa in excess to a solution of corrosive sublimate, by which a bright-yellow precipitate of oxide is thrown down, which only differs from the foregoing preparations in being destitute of crystalline texture and much more minutely divided. It must be well washed and dried. Red oxide of mercury is slightly soluble in water, communicating to the latter an alkaline reaction and metallic taste ; it is highly poisonous. When strongly heated, it is decomposed, as before observed, into metallic mercury and oxygen gas. Nitrates of the oxides of mercury.—Nitric acid varies in its action upon mercury, according to the temperature. When cold and somewhat diluted, only salts of the gray oxide are formed, and these are neutral or basic (i. e. with excess of oxide), as the acid or the metal happens to be in ex- cess. When, on the contrary, the nitric acid is concentrated and hot, the mercury is raised to its highest state of oxidation, and a salt of the red oxide produced. Both classes of salts are apt to be decomposed by a large quan- tity of water, giving rise to insoluble, or sparingly soluble', compounds con- taining an excess of base. Neutral nitrate of the suboxide, Hg20,N05-f- 2IIO, forms large colorless crys- * [By referring to cyanogen, it will be perceived that when the equivalent of mercury is con- sidered to be 100, the constitution of the cyanide of mercury is analogous to the other metallic cyanides, but when taken at 200, it becomes a bicyanide, and then differs from all others.__R. B.l MERCURY, OR QUICKSILVER. 321 tals soluble in a small quantity of water without decomposition; it is made by dissolving mercury in an excess of cold dilute nitric acid. When excess of mercury has been employed, a finely-crystallized basic salt is, after some time, deposited, containing 3IIg20,2N06 4- 3HO: this is also decomposed by water. The two salts are easily distinguished when rubbed in a mortar with a little chloride of sodium; the neutral compound gives nitrate of soda and calomel; the basic salt, nitrate of soda and a black compound of calomel with oxide of mercury. A black substance, called Hahneman's soluble mercury, is produced when ammonia in small quantity is dropped into a solu- tion of the nitrate of the suboxide; it contains 3Hg20,N05+NH3 or, according to Sir B. Kane, 2IIgO,N054- NH„: the composition of this preparation evidently varies according to the temperature and the concentration of the solutions. Nitrates of the Protoxide (Red Oxide) of Mercury.—By dissolving red oxide of mercury in excess of nitric acid, and evaporating gently, a syrupy liquid is obtained, which, enclosed in a bell-jar over lime or sulphuric acid, deposits voluminous crystals and crystalline crusts. The crystals and crusts have the Bame composition. 2(IIgO,X05) + HO. The same substance is deposited from the syrupy liquid as a crystalline powder by dropping it into concentrated nitric acid. The syrupy liquid itself appears to be a definite "compound con- taining HgO,NOs-f 2H0. By saturating hot dilute nitric acid with the red oxide, a salt is obtained on cooling which crystallizes in needles, permanent in the air, containing 2HgO,N06-f- HO. The preceding crystallized salts are decomposed by water, with production of compounds more and more basic as the washing is prolonged or the temperature of the water raised. The nitrates of the protoxide of mercury combine with ammonia. Sulphate of the Suboxide of Mercury, Hg20,S03, falls as a white crystalline powder when sulphuric acid is added to a solution of the nitrate of the sub- oxide ; it is but slightly soluble in water. Sulphate of the protoxide, HgO,S03, is readily prepared by boiling together oil of vitriol and metallic mercury until the latter is wholly converted into a heavy white crystalline powder, which is the salt in question; the excess of acid is then removed by evaporation, car- ried to perfect dryness. Equal weights of acid and metal may be conveni- ently employed. Water decomposes the sulphate, dissolving out an acid salt, and leaving an insoluble, yellow, basic compound, formerly called turpith or turbeth mineral, containing, according to Kane's analysis, 3HgO,S03. Long- continued washing with hot water entirely removes the remaining acid, and leaves pure protoxide of mercury. Subchloride of mercury; calomel: IIg2Cl. — This very important sub- stance may be easily and well prepared by pouring a solution of the nitrate of the suboxide into a large excess of dilute solution of common salt. It falls as a dense white precipitate, quite insoluble in water; it must be thoroughly w.ashed with boiling distilled water, and dried. Calomel is generally procured by another and more complex process. Dry sulphate of the red oxide is rubbed in a mortar with as much metallic mercury as it already contains, and a quantity of common salt until the globules disappear, and an uniform mix- ture been produced. This is subjected to sublimation, the vapor of the calomel .being carried into an atmosphere of steam, or into a chamber containing air; it is thus condensed into a minutely-divided state, and the laborious process of pulverization of the sublimed mass avoided. The reaction is thus explained:—J 1 If tho gray oxide be considered as protoxide, the sulphate will be sulphate of the binoxide, HgOa. 2.-0>, and the decomposition will stand thus: — 1 eq. sulphate} \ **• mcrcuT -------------—pr- eq. calomel, HgCl. of mercury ) * cq- ox?'£n . —TT ' ( - eq. sulphuric acid. 1 eq,. metallic mercury 2 on. common ( 2 eq. chlorine salt . . ( 2 eq. sodium ------- —^ 2 eq. sulphate of soda. IlgOs, 2SOs + Ilg + 2NaCl = 2HgCl + 2(NaO, S03). 322 MERCURY, OR QUICKSILVER. {1 eq. mercury_______-----——Calomel, Hg2Cl. 1 eq. oxygen 1 eq. sul- phuric acid 1 eq. metallic mercury -""^ 1 eq. common "l 1 eq. chlorine / "~^\ salt / 1 eq. sodium___________^S, Sulphate of soda. HgO,S03 + Hg + NaCl = Hg2Cl + NaO,S03. Pure calomel is a heavy, white, insoluble, tasteless powder; it rises in vapor at a temperature below redness, and is obtained by ordinary sublima- tion as a yellowish-white crystalline mass. It is as insoluble in cold diluted nitric acid as the chloride of silver; boiling-hot strong nitric acid oxidizes and dissolves it. Calomel is instantly decomposed by an alkali, or by lime-water, with production of suboxide. It is sometimes apt to contain a little chloride, which would be a very dangerous contamination in calomel employed for medical purposes. This is easily discovered by boiling with water, filtering the liquid, and adding caustic potassa. Any corrosive sublimate is indicated by a yellow precipitate. Protochloride of mercury; corrosive sublimate; HgCl.—The chloride may be obtained by several different processes. (1) When metallic mercury is heated in chlorine gas, it takes fire and burns, producing this substance. (2) It may be made by dissolving the i-ed oxide in hot hydrochloric acid, when crystals of corrosive sublimate separate on cooling. (3) Or, more economically, by subliming a mixture of equal parts of sulphate of the red oxide of mercury and dry common salt; and this is the plan generally followed. The decompo- sition is thus easily explained:1 — fl eq. mercury ■-----------^.Corrosive sublimate. 1 eq. sulphate J 1 eq. oxygen of mercury | 1 eq. sul- [ phuric acid J 1 eq. common j 1 eq. chlorine salt \ 1 eq. sodium -^'Sulphate of soda. HgO,S03 -f- NaCl = HgCl + NaO,S03. The sublimed protochloride forms a white transparent crystalline mass, of great density; it melts at 509° (265°C), and boils and volatilizes at a some- what higher temperature. It is soluble in 16 parts of cold and 3 of boiling water, and crystallizes from a hot solution in long white prisms. Alcohol and ether also dissolve it with facility; the latter even withdraws it from a watery solution. Chloride of mercury combines with a great number of other metallic chlorides, forming a series of beautiful double salts, of which the ancient sal alembroth maybe taken as a good example: it contains HgCl-f-NH4Cl-f- HO. Corrosive sublimate absorbs ammoniacal gas with great avidity, generating a compound supposed to contain 2HgCl-(- NH3. When excess of ammonia is added to a solution of corrosive sublimate, a white insoluble substance is thrown down, long known under the name of white precipitate. Sir Bobert Kane, who has devoted much attention to the salts of mercury, represents this white precipitate as a double amide and * Or on the other supposition : — l , .-, flM. mercury__________________Bichloride of mercury. 1 eq. sulphate^ _, ^ } ___^—_^-~^ of mercury ^„ ^ BJp^urte£dd><^ 2 eq. common j 2 eq. chloriue ■-- " ^^j^ salt . . X 2 eq. sodium ,_____________^S»».2 eq. sulphate of soda. UgOa, 2s03 + 2-\aCl = HgCl -f 2(XaO,S03). • MERCURY, OR QUICKSILVER. "323 chloride of mercury, or IlgCl^- Hg\fl2, 2 equivalents of chloride of mercury and 1 of ammonia, yielding 1 equivalent of the new body and 1 of hydrochloric acid. A corresponding black compound, Hg2Cl + HgXH2, is produced when ammonia is digested with calomel, which must be carefully distinguished from the suboxide. Several compounds of protochloride of mercury with protoxide of mercury also exist. These are produced by several processes, as when an alkaline carbonate or bicarbonate is added in varying proportions to a solution of corrosive sublimate. They differ greatly in color and physical character, and are mostly decomposed by water. Corrosive sublimate forms insoluble compounds with many of the azotized organic principles, as albumin, &c. It is perhaps to this property that its great antiseptic virtues are due. Animal and vegetable substances are pre- served by it from decay, as in Mr. Kyan's method of preserving timber and cordage. Albumin is on this account an excellent antidote to corrosive subli- mate in cases of poisoning. Subiouide of mercury, Hg2T.—The subiodide is formed when a solution of iodide of potassium is added to nitrate of the suboxide of mercury; it separates as a dirty yellow, insoluble precipitate, with a cast of green. It may be prepared by rubbing together in a mortar mercury and iodine in the proportion of 2 equivalents of the former to 1 of the latter, the mixture being moistened from time to time with a little alcohol. Protiodioe of mercury, HgL—When solution of iodide of potassium is mixed with protochloride of mercury, a precipitate falls, which is at first yellow, but in a few moments changes to a most brilliant scarlet, which color is retained on drying. This is the neutral iodide; it may be made, although of rather duller tint, by triturating single equivalents of iodine and mercury with a little alcohol. When prepared by precipitation, it is better to weigh out the proper proportions of the two salts, as the iodide is soluble in an excess of ether, more especially in excess of iodide of potassium. The iodide of mercury exhibits a very remarkable case of dimorphism, attended with difference of color, the latter being red or yellow, according to the figure assumed. Thus, when the iodide is suddenly exposed to a high temperature, it becomes bright yellow throughout, and yields a copious sublimate of minute but brilliant yellow crystals. If in this state it be touched by a hard body, it instantly becomes red, and the same change happens spontaneously after a certain lapse of time. On the other hand, by a very slow and careful heating, a sublimate of red crystals, having a totally different form, may be obtained, which are permanent, flic same kind of change happens with the freshly- precipitated iodide, as Mr. Warington has shown, the yellow crystals first formed breaking up in the course of a few seconds from the passage of the salt to the red modification.1 Suhselfhioe of mercury, Hg2S.—The black precipitate thrown down from a solution of the nitrate of suboxide of mercury by sulphuretted hydrogen is a subsulphide; it is decomposed by heat into metallic mercury and neutra, sulphide. Sulphide of mercury; artificial cinnabar; vermilion; HgS.—Sulphu- retted hydrogen gas causes a precipitate of a white color when passed in small quantity into a solution of corrosive sublimate or nitrate of the red oxide; this is a combination of sulphide with the salt itself. An excess of the gas converts the whole into sulphide, the color at the same time changing to black. When this black sulphide is sublimed, it becomes dark red and crystalline, but undergoes no change of composition: it is then cinnabar. The sulphide is most easily prepared by subliming an intimate mixture of 6 parts of mercury ami 1 of sulphur, and reducing to very fine powder the resulting cinnabar, 1 Memoirs of Chemical Society of London, i. 85. 324 PLATINUM. the beauty of the tint depending much upon the extent to which division is carried. The red or crystalline sulphide may also be formed directly, without sublimation, by heating the black precipitated substance in a solution of pen- tasulphide of potassium; the sulphide of mercury is in fact soluble, to a certain extent, in the alkaline sulphides, and forms with them crystallizable compounds. When vermilion is heated in the air, it yields metallic mercury and sul- phurous acid; it resists the action both of caustic alkali in solution, and of strong mineral acids, even nitric, and is only attacked by aqua regia. When protoxide of mercury is put into a large excess of pure caustic am- monia, a compound is obtained, the color of which varies with the state of the oxide. If the latter be amorphous, it is pale yellow; if crystalline, then the action of the ammonia is much less energetic, and the product darker in color. This substance possesses very extraordinary properties, namely, those of a most powerful base, and probably belongs to the same class as the compound bases containing platinum, described under that metal. The body in question bears a temperature of 260° (126°5C), without decomposition, becoming brown and anhydrous by the loss of 3 equivalents of water. In this state it contains NH2Hg403 = NH2Hg20-f-2HgO, or NHg40-f 2HO. It is insoluble in water, alcohol, and ammonia; cold solution or potassa has no action on the hydrate, but at a boiling heat some ammonia is disengaged. The anhydrous base is only acted on by hydrate of potassa in fusion. It combines directly and energetically with acids, forming well-defined compounds; it absorbs carbonic acid with avidity from the air, like baryta or lime. It even decom- poses ammoniacal salts by boiling, expelling the ammonia and combining with the acid.1 The salts of mercury are all volatilized or decomposed by a temperature of ignition: those which fail to yield the metal by simple heating may in all cases be made to do so by heating in a test-tube with a little dry carbonate of soda. The metal is precipitated from its soluble combinations by a plate of copper, and also by a solution of protochloride of tin, used in excess. The behavior of the protochloride and soluble salts of the red oxide with caustic potassa and ammonia is also highly characteristic. Alloys of mercury with other metals are termed amalgams; mercury dis- solves in this manner many of the metals, as gold, silver, tin, lead, &c. These combinations sometimes take place with considerable violence, as in the case of potassium, where light and heat are produced; besides this, many of the amalgams crystallize after a while, becoming solid. The amalgam of tin used in silvering looking glasses, and that of silver and of copper sometimes employed for stopping hollow-teeth, are examples. platinum. Platinum, palladium, rhodium, iridium, ruthenium, and osmium, form a small group of metals, allied in some cases by properties in common,'and still more closely by their natural association. Crude platinum, a native alloy of platinum, palladium, rhodium, iridium, and a little iron, occurs in grains and rolled masses, sometimes of tolerably large dimensions, mixed with gravel and transported materials, on the slope of the Ural Mountains in Russia, in Brazil and Ceylon, and in a few other places. It has never been seen in' the rock 1 Ann. Chim. et Phys., 3d series, xviii. 333. PLATINUM. 325 which, however, is judged, from the accompanying materials, to have been serpentine. It is stated to be always present in small quantities with native silver. From this substance platinum is prepared by the following process: — The crude metal is acted upon as far as possible by nitro-hydrochloric acid, con- taining an excess of hydrochloric acid, and slightly diluted with water, in order to dissolve as small a quantity of iridium as possible; to the deep yellowish-red and highly acid solution thus produced sal-ammoniac is added, by which nearly the whole of the platinum is thrown down in the state of ammonia-chloride. This substance is washed with a little cold water, dried and heated to redness; metallic platinum in the spongy state is left. This metal can only with difficulty be fused into a compact mass by ordinary furnace-heat, but the same object may be accomplished by taking advantage of its property of welding, like iron, at a high temperature. The spongy platinum is made into a thin uniform paste with water, introduced into a slightly-conical mould of brass, and subjected to a graduated pressure, by which the water is squeezed out, and the mass rendered at length sufficiently solid to bear handling. It is then dried, very carefully heated to whiteness, and hammered, or subjected to powerful pressure by suitable means. If this operation be properly conducted, the platinum will then be in a state to bear forging into a bar, which can afterwards be rolled into plates, or drawn into wire, at pleasure. Becently Deville has constructed a blast furnace, the heat of which is capable of fusing as much as an ounce of platinum. Platinum is in point of color a little whiter than iron; it is exceedingly malleable and ductile, both hot and cold, and is very infusible, melting only before the oxy-hydrogen blowpipe, or in powerful blast furnaces. It is the heaviest substance known, its specific gravity being 21-5. Neither air, moisture, rtor the ordinary acids attack platinum in the slightest degree at any temperature; hence its great value in the construction of chemical vessels. It is dissolved by aqua regia, and superficially oxidized by fused hydrate of potassa, which enters into combination with the oxide. The remarkable property of the spongy metal to determine the union of oxygen and hydrogen has been already noticed. There is a still more curious state in which platinum can be obtained, that of platinum-black, where the division is pushed much farther. It is easily prepared by boiling a solution of bichloride of platinum, to which an excess of carbonate of soda and a quantity of sugar have been added, until the precipitate formed after a little time becomes perfectly black, and the supernatant liquid colorless. The black powder is collected on a filter, washed, and dried by gentle heat. This sub- stance appears to possess the property of condensing gases, more especially oxygen, into its pores to a very great extent: when placed in contact with a solution of formic acid, it converts the latter, with copious effervescence, into carbonic acid; alcohol, dropped upon the platinum-black, becomes changed by oxidation to acetic acid, the rise of temperature being often sufficiently great to cause inflammation. When exposed to a red-heat, the black substance shrinks in volume, assumes the appearance of common spongy platinum, and loses these peculiarities, which arc no doubt the result of its excessively- comminuted state. Platinum forms, two compounds with oxygen, chlorine, &c. The equivalent of platinum is 98-7. Its symbol is Pt. Protoxide of platinum, PtO.—When protochloride of platinum is digested with caustic potassa, a black powder, soluble in excess of alkali, is produced: this is the protoxide. It is soluble in acids with brown color, and the solutions are not precipitated by sal-ammoniac. When binoxide of platinum is heated with solution of oxalic acid, it is reduced to protoxide, which remains dissolved. The liquid has a dark-blue color, and deposits fine copper-red needles of oxalate of the protoxide of platinum. Binoxide of platinum, Pt02. — This is best prepared by adding nitrate of 28 326 P L A T I N U M . baryta to sulphate of the binoxide of platinum; sulphate of baryta and nitrate of the binoxide are produced. From the latter, caustic soda precipitates one- half of the binoxide of platinum. The sulphate is itself obtained by acting with strong nitric acid upon the bisulphide of platinum, which falls as a black powder when a solution of bichloride is dropped into sulphide of potassium. The hydrate of the binoxide is a bulky brown powder, which, when gently heated, becomes black and anhydrous. It may also be formed by boiling bichloride of platinum with a great excess of caustic soda, and then adding acetic acid. It dissolves in acids, and also combines with bases: the salts have a yellow or red tint, and a great disposition to unite with salts of the alkalies and alkaline earths, giving rise to a series of double compounds, which are not precipitated by excess of alkali. A combination of binoxide of platinum with ammonia exists, which is explosive. Both oxides of platinum are reduced to the metallic state by ignition. Protochloride of platinum, PtCl. — The protochloride is produced when bichloride of platinum, dried and powdered, is exposed for some time to a heat of 400° (204°-5C), by which half of the chlorine is expelled ; also, when sulphurous acid is passed into a solution of the bichloride until the latter ceases to give a precipitate with sal-ammoniac. It is a greenish-gray powder, insoluble in water, but dissolved by hydrochloric acid. The latter solution, mixed with sal-ammoniac or chloride of potassium, deposits a double salt jp fine red prismatic crystals, containing, in the last case, PtCl -f- KC1. The corresponding sodium-compound is very soluble and difficult to crystallize. The protochloride is decomposed by heat into chlorine and metallic platinum. Bichloride, or perchloride of platinum, PtCl2. — This substance is always formed when platinum is dissolved in nitro-hydrochloric acid. The acid solution yields on evaporation to dryness a red or brown residue, deli- quescent, and very soluble both in water and alcohol; the aqueous solution has a pure orange-yellow tint. Bichloride of platinum combines to double salts with a great variety of metallic chlorides; the most important of these compounds are those containing the metals of the alkalies and ammonium. Bichloride of platinum and chloride of potassium, PtCl2, KC1, form a bright yellow crystalline precipitate, being produced whenever solutions of the chlorides of platinum and of potassium are mixed, or a salt of potassa, mixed with a little hydrochloric acid, added to bichloride of platinum. It is feebly soluble in water, still less soluble in dilute alcohol, and is decomposed with some difficulty by heat. It is readily reduced by hydrogen at a high tempera- ture, furnishing a mixture of chloride of potassium and platinum-black; the latter substance may thus, indeed, be very easily prepared. The sodium-salt, PtCl2, NaCl -|- 6IlO, is very soluble, crystallizing in large, transparent, yellow-red prisms of great beauty. The ammonio-chloride of platinum, PtCl2, NH4C1, is indistinguishable, in physical characters, from the potassium-salt; it is thrown down as a precipitate of small, transparent, yellow, octahedral crystals, when sal-ammoniac is mixed with chloride of platinum; it is but feebly soluble in water, still less so in dilute alcohol, and is decomposed by heat, yielding spongy platinum, while sal-ammoniac, hydrochloric acid, and nitrogen are driven off. Compounds of platinum with iodine, bromine, sulphur, and phosphorus, have been formed, but are comparatively unim- portant. Some very extraordinary compounds have been derived from the protoxide of platinum. When ammonia in excess is added to a hot solution of the protochloride of platinum in hydrochloric acid, a green crystalline salt separates after a time, which is quite insoluble in water, and is not affected by hydrochloric or sulphuric acids, ammonia, or even a boiling-hot solution of potassa. This substance is known as the green salt of Magnus, and contains the elements of protochloride of platinum and ammonia, or PtCl -j- NH3. PLATINUM. 327 When the above compound is heated with concentrated nitric acid, it becomes converted into a white, granular, crystalline powder, which, on addition of water, dissolves, leaving a residue of metallic platinum. The solution yields on standing, small, brilliant, colorless prisms of a substance very soluble in water, containing the elements of protochloride of platinum, ammonia, nitric acid, and an additional equivalent of oxygen: — PtCl,N2H60 + N05. The platinum and chlorine in this curious body are insensible to ordinary reagents, and ammonia is evolved from it only on boiling with caustic alkali; the presence of nitric acid can be detected immediately by gently heating a small portion with copper-filings and oil of vitriol. From this substance a series of salt-like bodies can be obtained, some of which have been carefully studied by M. Gros. Thus, when treated with hydrochloric acid, the nitric acid is wholly displaced, and a compound formed which crystallizes in small, transparent, yellowish octahedra, sparingly soluble in boiling water, containing PtCl, N2H6C1. With sulphuric acid it gives a substance which crystallizes in Bmall, slightly soluble, colorless needles, containing PtCl, N2H60 + S03. The oxalic acid compound is white and insoluble ; it contains PtCl, N2H60 -f- C2%j. Crystallizable compounds containing phosphoric, tartaric, citric, malic, formic, and even carbonic acids, were obtained by similar means. The substances have very much the characters of salts of a compound base or a quasi-metal containing PtCl,N2II6, and which yet remains unknown in a separate state. M.Raewsky has repeated and extended the observations of M. Gros. MM. Beiset and Peyrone have also described two other basic bodies con- taining platinum in the same remarkable condition: these differ from the preceding in being free from chlorine. Protochloride of platinum put into ammonia becomes rapidly converted into a green powder, which, by boiling, slowly dissolves; the solution, on evapora- tion and cooling, furnishes beautiful yellowish crystals of the chlorine-com- pound of one of these bases, compounded of platinum and the elements of ammonia. The crystals contain PtN2H6Cl + HO. The equivalent of water is easily expelled by heat, and regained by absorption from the air. The green salt of Magnus, boiled with ammonia, yields the same product. A solution of this substance, mixed with nitrate of silver, gives chloride of Bilver and the nitrate of the new base, which crystallizes on evaporation in fine, white, transparent needles, containing PtN2H60 -f- N06. The sulphide, iodide, and bromide are all crystallizable. Two carbonates exist. By adding baryta-water to a solution of the sulphate, or by treating the chloride with protoxide of silver, and evaporating the filtered liquid in vacuo, a white, crys- talline deliquescent mass is obtained, which is the hydrate of the base, PtNjHgO -f- HO. It is almost comparable in point of alkalinity with potassa itself, absorbing carbonic acid with energy, and decomposing ammoniacal salts. When this hydrate is heated to 230° (110°C), it abandons water and ammonia, and leaves a grayish, porous, insoluble mass containing PtNHg,0. This is probably an isomeric modification of the second base, whose salts are mentioned below. When a solution of the iodide, PtN2H6I, is long boiled, it deposits a sparingly- soluble yellow powder, the composition of which is expressed by the formula PtXHjI: this is the iodine-compound of a second basic substance, PtNIf3 ; and from it by double decomposition a series of analogous salts can be obtained. When the iodine-compound is treated with protoxide of silver, the base itself is obtained in the form of a powerfully-alkaline solution. The green salt of Magnus has the same composition as the chloride of this new base, which is yellow and soluble in boiling water, and may be converted into it. The salts of the first base are generally convertible into those of the second by heat, and the converse change may also be often effected by ebullition with ammonia. 328 PALLADIUM. The subject of the platinum-bases appears to be by no means exhausted. Lately another remarkable basic compound containing ammonia and platinum has been discovered by M. Gerhardt. The chloride of Reiset's second base, the compound PtNH3Cl, when treated with chlorine, absorbs this element, and becomes converted into a lemon-yellow powder consisting of small octahedra, and having the composition PtNH3Cl2. Boiled with nitrate of silver, this sub- stance yields chloride of silver, and, according to the quantity of nitric acid present, a salt, PtNH302, 2N06, or PtNH302, N05 + 3HQ» On adding am- monia to the latter nitrate, a crystalline precipitate takes place, which con- sists of PtNH302 -f- 2HO. This substance, which is slightly soluble in water, may be viewed as the hydrated base existing in the bichloride and in the nitrates previously described. The bichloride, or a solution of binoxide of platinum, can be at once recog- nized by the yellow precipitate with sal-ammoniac, decomposable by heat, with production of spongy metal. # ---- Bichloride of platinum and the sodio-chloride of platinum are employed in analytical investigations to detect the presence of potassa, and separate it from soda. For the latter purpose, the alkaline salts are converted into chlorides, and in this condition mixed with four times their weight of sodio- chloride of platinum in crystals, the whole being dissolved in a little water. When the formation of the yellow salt appears complete, alcohol is added, and the precipitate collected on a weighed filter, washed with weak spirit, care- fully dried and weighed. The chloride of potassium is then easily reckoned from the weight of the double salt, and this, subtracted from the weight of the mixed chlorides employed, gives that of the chloride of sodium by difference; 100 parts of potassio-chloride of platinum correspond to 35-06 parts of chloride of potassium. Capsules and crucibles of platinum are of great value to the chemist; the latter are constantly used in mineral analysis for fusing siliceous matter with alkaline carbonates. They suffer no injury in this operation, although the caustic alkali roughens and corrodes the metal. The experimenter must be particularly careful to avoid introducing any oxide of an easily-fusible metal, as that of lead or tin, into a platinum crucible. If reduction should by any means occur, these metals will at once alloy themselves with the platinum, and the vessel will be destroyed. A platinum crucible must never be put naked into a charcoal fire, but be always placed within a covered earthen crucible. palladium. The solution of crude platinum, from which the greater part of that metal has been precipitated by sal-ammoniac, is neutralized by carbonate of soda, and mixed with a solution of cyanide of mercury ; cyanide of palladium sepa- rates as a whitish insoluble substance, which, on being washed, dried, and heated to redness, yields metallic palladium in a spongy state. The palladium is then welded into a mass, in the same manner as platinum. Palladium closely corresponds with platinum in color and appearance • it is also very malleable and ductile. In density it differs very much from' that metal, being only 11-8. Palladium is more oxidable than platinum. When heated to redness in the air, especially in the state of sponge, it acquires a blue or purple superficial film of oxide, which is again reduced at a white heat. This metal is slowly attacked by nitric acid; its best solvent is aqua regia. There are two compounds of palladium and oxygen. The equivalent of palladium is 53-3 ; its symbol is Pd. RHODIUM. 329 Protoxide of palladium, PdO. — This is obtained by evaporating to dry- ness,'and cautiously heating, the solution of palladium in nitric acid. It is black, and but little soluble in acids. The hydrate falls as a dark-brown pre- cipitate when carbonate of soda is added to the above solution. It is decom- posed by a strong heat. Binoxide of palladium, Pd02. — The pure binoxide is very difficult to obtain. When solution of caustic potassa is poured, little fey little, with con- stant stirring, upon the double chloride of palladium and potassium in a dry state, the latter is converted into a yellowish-brown substance, which is the binoxide, in combination with water and a little alkali. It is but feebly solu- ble in acids. Protochloride of palladium, PdCl.—The solution of the metal in aqua regia yields this substance when evaporated to dryness. It is a dark-brown mass soluble in water when the heat has not been too great, and forms double salts with many metallic chlorides. The potassio- and ammonio-chlorides of palladium, are much more soluble than those of platinum; they have a brownish-yellow tint.1 Bichloride of palladium only exists in solution, and in combination with the alkaline chlorides. It is formed when the protochloride of palladium is digested in aqua regia. The solution has an intensely brown color, and is decomposed by evaporation. Mixed with chloride of potassium or sal-ammo- niac, it gives rise to a red crystalline precipitate, which is but little soluble in water. A sulphide of palladium, PdS, is formed by fusing the metal with sulphur, or by precipitating a solution of protochloride by sulphuretted hydrogen. A palladium-salt is well marked by the pale yellowish-white precipitate with solution of cyanide of mercury, convertible by heat into the spongy metal. This precipitate is a double salt, having the formula PdCy.HgCy, HO. Palladium is readily alloyed with other metals, as copper: one of these sompouuds, namely, the alloy with silver, has been applied to useful pur- poses. An amalgam of palladium is now extensively used by dentists for stopping teeth. A native alloy of gold with palladium is found in the Brazils, and imported into England. rhodium. The solution from which platinum and palladium have been separated in the manner described is mixed with hydrochloric acid, and evaporated to dry- ness The residue is treated with alcohol of specific gravity 0-837, which dis- solves everything except the double chloride of rhodium and sodium. This is well washed with spirit, dried, heated to whiteness, and then boiled with water; chloride of sodium is dissolved out, and metallic rhodium remains. Thus obtained, rhodium is a white, coherent, spongy mass, which is more 1 Chloride of palladium furnishes with ammonia results similar to those obtained with chloride of platinum. By mixing a tolerably concentrated solution of chloride of palladium with small excess of ammonia, a compound is formed containing PdCl + jSIIs. When this substance is heated, moist to 212° (100° C), dry to ;;<.t2° (200° C), it is changed into another body, which dissolves in dilute caustic potassa without evolving ammonia; out of this substance NIMlTs, CI, Miiller has separated the base palladamine. A salt of palladamine is formed when chloride of palladium is precipitated by ammonia, the precipitate dissolved in excess of ammo- nia, and the solution neutralized with hydrochloric acid. The chloride of palladamine, thus produced, forms a yellow crystalline precipitate. Palladamine, N1MII3. 0, may be obtained from tho chloride by oxide of silver. The carbonate, sulphate, nitrate, sulphide, iodide, bromide, aud chloride of palladamine have been formed. M tiller also obtained another compound by excess of ammonia, to which he gives the name of palladdiamine; it contains N'lMII6. 28* 330 IRIDIUM. infusible and less capable of being welded than platinum. Its specific gravity varies from 10-6 to 11. Rhodium is very brittle: reduced to powder and heated in the air, it be- comes oxidized, and the same alteration happens to a greater extent when it is fused with nitrate or bisulphate of potassa. None of the acids, singly or conjoined, dissolve this metal, unless it be in the state of alloy, as with plati- num, in which it is attacked by aqua regia. The equivalent of rhodium is 52-2; its symbol is R. Protoxide of rhodium, RO, is obtained by roasting finely-divided metallic rhodium. It is but little known. Sesquioxide of rhodium, R203.—Finely-powdered metallic rhodium is heated in a silver crucible with a mixture of hydrate of potassa and nitre; the fused mass boiled with water leaves a dark-brown insoluble substance, con- sisting of sesquioxide of rhodium in union with potassa. This is digested with hydrochloric acid, which removes the potassa, and leaves a greenish-graj hydrate of the sesquioxide of rhodium, insoluble in acids. A soluble modifi- cation of the same substance, retaining, however, a portion of alkali, may be had by adding an excess of carbonate of potassa to the double chloride of rhodium and potassium, and evaporating. Sesquichloride of rhodium, R2C)3.—The pure sesquichloride is prepared by adding hydrofluosilicic acid to the double chloride of rhodium and potas- sium, evaporating the filtered solution to dryness, and dissolving the residue in water. It forms a brownish-red deliquescent mass, soluble in water, with a fine red color. It is decomposed by heat into chlorine and metallic rhodium. The chloride of rhodium and potassium, R2C13 -J- 2KC1 -f- 2HO, is prepared by heating in a stream of chlorine a mixture of equal parts of finely-powdered rhodium and chloride of potassium. The salt has a fine red color, is soluble in water, and crystallizes in 4-sided prisms. Chloride of rhodium and sodium is also a very beautiful red salt, obtained by a similar process; it contains R2C13 -f- 3NaCl -f- 18HO. The chloride of rhodium and ammonium resembles the potassium-compound. Sulphate of rhodium, B203.3S03.—The sulphide of rhodium, obtained by precipitating one of the salts by a soluble sulphide, is oxidized by strong nitric acid. The product is a brown powder, nearly insoluble in nitric acid, but dissolved by water; it cannot be made to crystallize. Sulphate of rhodium and potassium is produced when metallic rhodium is strongly heated with bisulphate of potassa. It is a yellow salt, slowly soluble in cold water. An alloy of steel with a small quantity of rhodium is said to possess ex- tremely valuable properties. IRIDIUM. When crude platinum is dissolved in aqua regia, a small quantity of a gray scaly metallic substance usually remains behind, having altogether resisted the action of the acid: this is a native alloy of iridium and osmium; it is reduced to powder, mixed with an equal weight of dry chloride of sodium, and heated to redness in a glass tube, through which a stream of moist chlorine gas is transmitted. The farther extremity of the tube is connected with a receiver containing solution of ammonia. The gas, under these circumstances is rapidly absorbed, chloride of iridium and chloride of osmium being pro- duced: the former remains in combination with the chloride of sodium- the latter, being a volatile substance, is carried forward into the receiver where it is decomposed by the water into osmic and hydrochloric acids, which com- bine with the alkali. The contents of the tube when cold are treated with water, by which the double chloride of iridium and sodium is dissolved out: IRIDIUM. 331 this is mixed with an excess of carbonate of soda, and evaporated to dryness. The residue is ignited in a crucible, boiled with water, and dried; it then consists of a mixture of sesquioxide of iron, and a combination of oxide of iridium with soda; it is reduced by hydrogen at a high temperature, and treated successively with water and strong hydrochloric acid, by which the alkali and the iron are removed, while metallic iridium is left in a divided state. By strong pressure and exposure to a white heat, a certain degree of compactness may be communicated to the metal. Iridium is a white brittle metal, fusible with great difficulty before the oxy- hydrogen blowpipe.1 It is not attacked by an acid, but is oxidized by fusion with nitre, and by ignition to redness in the air. The equivalent of iridium is 99. Its symbol is Ir. Oxides of iridium. — Four of these compounds are described. Protoxide of iridium, IrO, is prepared by adding caustic alkali to the protochloride, and digesting the precipitate in an acid. It is a heavy black powder, insoluble in acids. It may be hud in the state of hydrate by precipitating the protochlo- ride of iridium and sodium by caustic potassa. The hydrate is soluble in acids with dirty green color. Sesquioxide, lr203, is produced when iridium is heated in the air, or with nitre ; it is best prepared by fusing in a silver cru- cible a mixture of carbonate of potassa and the terchloride of iridium and potassium, and boiling the product with water. This oxide is bluish-black, and is quite insoluble in acids. It is reduced by combustible substances with explosion. Binoxide of iridium, IrO__, is unknown in a separate state; it is supposed to exist in the sulphate, produced when the sulphide is oxidized by nitric acid. A solution of sulphate heated with excess of alkali evolves oxygen gas, and deposits sesquioxide of iridium. Teroxide of iridium, Ir03, is pro- duced when carbonate of potassa is gently heated with the terchloride of iri- dium ; it forms a grayish-yellow hydrate, which contains alkali. Chlorides of iridium.—Protochloride, IrCl, is formed when the metal is brought in contact with chlorine at a dull red-heat; it is a dark olive-green insoluble powder. It is dissolved by hydrochloric acid, and forms double salts with the alkaline chlorides, which have a green color. The sesquichlo- ride, Ir2Cl3, is prepared by strongly heating iridium with nitre; adding water and enough nitric acid to saturate the alkali, warming the mixture, and then dissolving the precipitated hydrate of the sesquioxide in hydrochloric acid, it forms a dark yellowish-brown solution. This substance combines with metallic chlorides. Bichloride of iridium is obtained in solution by adding hydrofluo- silicic acid to the bichloride of iridium and potassium, formed when chlorine is passed over a heated mixture of iridium and chloride of potassium. It forms with metallic chlorides a number of double salts, which resemble the platinum-compounds of the same order. Terchloride of iridium, IrCl3, is unknown in a separate state. Terchloride of iridium and potassium is obtained by heating iridium with nitre, and then dissolving the whoje in aqua regia, 'and evaporating to dryness. The excess of chloride of potassium may be extracted by a small quantity of water. The crystallized salt has a beautiful red color. The variety of tints exhibited by the different soluble compounds of iridium is very remarkable, and suggested the name of the metal, from the word iris. Platinum, palladium, and iridium combine with carbon when heated in the flame of a spirit-lamp ; they acquire a covering of soot, which, when burned, leaves a kind of skeleton of spongy metal. 1 [It is the heaviest substance known, its specific gravity, according to Professor Hare, being 21-8. Proceedings of the Amer. Phil. Soc, May and June, 1812.—K. P..] 332 R U T II E N I U M . — OSMIUM. RUTHENIUM. M. Claus has described under this name a new metal contained in the residue from crude platinum, insoluble in aqua regia. It closely resembles iridium in its general characters, but yet possesses distinctive features of its own. It was obtained in the form of small angular masses, with perfect metallic lustre, very brittle and infusible. Its specific gravity is 8-6. It resists the action of acids, but oxidizes readily when heated in the air. The equivalent of ruthenium is 52-2, and its symbol Ru. Oxides of ruthenium.—Protoxides of ruthenium, RuO, is a grayish-black metallic-looking powder, obtained by heating bichloride of ruthenium with excess of carbonate of soda in a stream of carbonic acid gas, and then wash- ing away the soluble saline matter. It is insoluble in acids. The sesquioxide, Ru203, in the anhydrous condition, is a bluish-black powder formed by heat- ing the metal in the air. It is also precipitated by alkalies from the sesqui- chloride as a blackish-brown hydrate, soluble in acids with orange-yellow color. The binoxide, Ru02, is a deep-blue powder, procured by roasting the bisulphide. A hydrate of this oxide is known in an impure condition. An acid of ruthenium is also supposed to exist. Sesquichloride of ruthenium, Ru2Cl3, is an orange-yellow soluble acid of astringent taste; when the solution is heated it becomes green and finally blue, by reduction, in all probability, to protochloride. Sesquichloride of ruthenium forms double salts with the chlorides of potassium and ammonium. osmium. The solution of osmic acid in ammonia, already mentioned, is gently heated for some time in a loosely-stopped vessel; its original yellow color becomes darker, and at length a brown precipitate falls, which is a combination of sesquioxide of osmium with ammonia; it results from the reduction of the osmic acid by the hydrogen of the volatile alkali. A little of the precipitate is held in solution by the sal-ammoniac, but may be recovered by heating tho clear liquid with caustic potassa. The brown substance is dissolved in hydro- chloric acid, a little chloride of ammonium is added, and the whole evaporated to dryness. The residue is strongly heated in a small porcelain retort; the oxygen of the oxide combines with hydrogen from the ammonia, vapor of water, hydrochloric acid, and sal-ammoniac are expelled, and osmium left behind, as a grayish porous mass, having metallic lustre. In the most compact state in which this metal can be obtained, it has a bluish-white color, and although somewhat flexible in thin plates, is yet easily reduced to powder. Its specific gravity is 10; it is neither fusible nor vola- tile. It burns when heated to redness, yielding osmic acid, which volatilizes. Osmate of potassa is produced when the metal is fused with nitre. When in a finely-divided state, it is oxidized by strong nitric acid. The equivalent of osmium is 99-6; its symbol is Os. Oxides of osmium. —Five compounds of osmium with oxygen are known. Protoxide, OsO, is obtained, in combination with a little alkali, when caustic potassa is added to a solution of protochloride of osmium and potassium. It is a dark-green powder, slowly soluble in acids. Sesquioxide, Os203, has already been noticed; it is generated by the deoxidation of osmate of ammo- nia; it is black, and but little soluble in acids. It always contains ammonia, and explodes feebly when heated. Binoxide of osmium, Os02, is prepared by strongly heating in a retort a mixture of carbonate of soda and of the bichlo- ride of osmium and potassium, and treating the residue with water, and after- wards with hydrochloric acid. The binoxide is a black powder, insoluble in acids, and burning to osmic acid when heated in the air. Osmious acid, OsO., OSMIUM. 333 is known only in combination. On adding alcohol to a solution of osmate of potassa, the alcohol is oxidized at the expense of the osmic acid, and a rose- red crystalline powder of osmite of potassa is produced. On attempting to separate the acid, it is decomposed into the binoxide and osmic acid. Osmic acid, Os04, is by far the most important and interesting of the oxides of this metal. It is prepared by heating osmium in a current of pure oxygen gas; it condenses in the cool part of the tube in which the experiment is made in colorless transparent crystals. Osmic acid melts and even boils below 212° (100°C) ; its vapor has a peculiarly offensive odor, and is exceedingly irri- tating and dangerous. Water slowly dissolves this substance. It has acid properties, and combines with bases. Nearly all the metals precipitate osmium from a solution of osmic acid. By the action of ammonia on osmic acid, a new acid has been formed, containing osmium, nitrogen, and oxygen; it has been called osman-osmic acid or osmanic acid. Some doubts exist respecting the formula of this substance. It produces salts with many bases. Chlorides of osmium.—Protochloride, OsCl, is a dark-green crystalline substance, formed by gently heating osmium in chlorine gas. It is soluble in a small quantity of water, with green color, but decomposed by a large quan- tity into osmic and hydrochloric acids and metallic osmium. It forms double salts with the metallic chlorides. The sesquichloride, Os2Cl3, has not been isolated; it exists in the solution obtained by dissolving the sesquioxide in hydrochloric acid. Bichloride, OsCl2, in combination with chloride of potas- sium, is produced when a mixture of equal parts metallic osmium and the last-named salt is strongly heated in chlorine gas. It forms fine red octahe- dral crystals, containing OsCl2 -\- KC1. Osmium combines also with sulphur and with phosphorus. PART III. ORGANIC CHEMISTRY. introduction. Obgaxic substances, whether directly derived from the vegetable or animal kingdom, or produced by the subsequent modification of bodies which thus originate, are remarkable as a class for a degree of complexity of constitution far exceeding that observed in any of the compounds yet described. And yet the number of elements which enter into the composition of these substances is extremely limited; very few, comparatively speaking, contain more than four, viz., carbon, hydrogen, oxygen, and nitrogen; sulphur and phosphorus are occasionally associated with these in certain natural products; and com- pounds containing chlorine, bromine, iodine, arsenic, antimony, zinc, &c, have been formed by artificial means. This paucity of elementary bodies is compensated by the very peculiar and extraordinary properties of the four first-mentioned, which possess capabilities of combination to which the re- maining elements are strangers. There appears to be absolutely no limit to the number of definite, and often crystallizable, substances which can be thus generated, each marked by a perfect individuality of its own. The mode of association of the elements of organic substances is in general altogether different from that so obvious in the other division of the science. The latter is invariably characterized by what may be termed a binary plan of combination, union taking place between pairs of elements, and the com- pounds so produced again uniting themselves to other compound bodies in the same manner. Thus, copper and oxygen combine to oxide of copper, potassium, and oxygen to potassa, sulphur and oxygen to sulphuric acid; sul- phuric acid, in its turn, combines both with oxide of copper and oxide of potassium, generating a pair of salts, which are again capable of uniting to form the double compound, CuO,S03-f- KO,S03. The most complicated products of organic chemistry may be thus shown to be built up by this repeated pairing on the part of their constituents. With organic bodies, however, the case is strikingly different; no such arrangement can here be traced. In sugar C12HnOn, or morphine, C34HI9N06, or the radical of bitter-almond oil, C14H502, and a multitude of similar cases, the elements concerned are, as it were, bound up together into a single whole, which can enter into combination with other substances, and be thence disengaged with properties unaltered. A curious consequence of this peculiarity is to be found in the comparatively instable character of organic compounds, and their general proneness to de- composition and change, when the balance of opposing forces, to which they owe their existence, becomes deranged by some external cause. If a complex inorganic substance be attentively considered, it will usually be found that the elements are combined in such a manner as to satisfy the (334) ORGANIC CHEMISTRY. 335 most powerful affinities, and to give rise to a state of very considerable per- manence and durability. But in the case of an organic substance, containing three or four elements associated in the way described, this is very far from being true: the carbon and oxygen strongly tend to unite to form carbonic acid ; the hydrogen and oxygen attract each other in a powerful manner; and the nitrogen, if that body be present, also contributes its share to these in- ternal sources of weakness by its disposition to generate ammonia. While the opposing forces remain exactly balanced, the integrity of the compound is preserved ; but the moment one of them, from some accidental cause, ac- quires preponderance over the rest, equilibrium is destroyed, and the organic principle breaks up into two or more new bodies of simpler and more°per- manent constitution. The agency of heat produces this effect by exalting the attraction of oxygen for hydrogen and carbon-; hence the almost universal de- structibihty of organic substances by a high temperature. Merc molecular disturbance of any kind may cause destruction when the instability is very great. As a general rule, it may be assumed that those bodies which are most complex from the number of elements, and the want of simplicity in their equivalent relations, are by constitution weakest, and least capable of resist- ing the action of disturbing forces; and that this susceptibility of change di- minishes with increased simplicity of structure, until it reaches its minimum in those bodies which, like the carbides of hydrogen, like cyanogen, and oxalic acid, connect, by imperceptible gradations, the organic and the mineral departments of chemical science. The definite organic principles of the vegetable and animal kingdoms form but a very small proportion of the immense mass of compounds included within the domain of organic chemistry: by far the greater number of these are produced by modifying by suitable means the bodies furnished by the plant or the animal, and which have themselves been formed from the elements of the air by processes for the most part unknown, carried on under the con- trol of vitality. Unlike these latter, the artificial modifications referred to, by oxidation, by the action of other powerful reagents, by the influence of heat, and by numerous other sources of disturbance, are, for the most part, changes of descent in order of complexity, new products being thus generated more simple in constitution and more stable in character than the bodies from which they were derived. These, in turn, by a repetition of such treatment under perhaps varied circumstances, may be broken up into other and still simpler organic combinations ; until at length the binary compounds of inor- ganic chemistry, or bodies so allied to them that they may be placed indiffe- rently in either group, are by such means reached. Organic substitution-products: Law of Substitution.—The study of the action of chlorine, bromine, iodine, and nitric acid, upon various organic substances, has led to the discovery of a very remarkable law regulating the formation of chlonnetted and other analogous compounds, which, without being of necessity absolute in every case, is yet of sufficient generality and importance to require careful consideration. This peculiar mode of action consists in the replacement of the hydrogen of the organic substance by chlorine, bromine, iodine, the elements of hyponitric acid, and more rarely other substances of the same class, equivalent for equivalent, without the destruction of the pri- mitive type or constitution of the compound so modified. The hydrogen thus removed takes of course the form of hydrochloric or hydrobromic acid, &c, or that of water, by combination with another portion of the active body. Strange as it may appear, and utterly opposed to the ordinary views of the functions of powerful salt-radicals, this loss of hydrogen and assumption of the new element do actually occur with a great variety of substances, belong- ing to different groups, with comparatively trifling disturbance of physical and chemical properties; the power of saturation, the density of the vapor, S36 ORGANIC CHEMISTRY. and other peculiarities of the original substance remain the same, saving the modification they may suffer from the difference of the equivalent weights of hydrogen and the body by which it is replaced. This change may take place by several successive steps, giving rise to a series of substitution-compounds, which depart more and more in properties from the original substance with each successive increase in the proportion of the replacing body. The substitution may even be total, the whole of the hydrogen being lost, and its place supplied by a similar number of equivalents of the new element. And even in these extreme cases, of very common oc- currence, however, with one class of substances, the resulting compound re- tains generally the stamp of its origin. Although numerous examples of these changes will be found described in detail in the following pages, if will be well perhaps to mention here two or three cases by way of illustration. Dutch-liquid, the compound formed by the union of equal measures of ole- fiant gas and chlorine, containing C4H4C12, is affected by chlorine in obedience to the law of substitution; one, two, three, four equivalents of hydrogen being successively removed by the prolonged action of the gas aided by sun- shine, and one, two, three, or four equivalents of chlorine introduced in place of the hydrogen withdrawn as hydrochloric acid. In the last product, the sesquichloride of carbon, C4C16, the replacement is total; the intermediate products are volatile liquids not differing very much in general characters from Dutch-liquid itself. A great number of compound ethers of the ethyl- and methyl- series are attacked by chlorine and bromine in a similar mariner; indeed, the majority of the examples of the law in question are to be found in the history of this class of bodies. Concentrated acetic acid, placed in a vessel of dry chlorine and exposed to the sun, gives rise to chloracetic acid, containing C4C1303, HO, and in which consequently the whole hydrogen of the real acid is replaced by chlorine. Chloracetic acid is a stable substance, of strong acid characters, and forms a series of salts, some of which bear no slight resemblance to the normal acetates. Basic substitution-products have beeii likewise obtained; chloraniline, bromaniline, and iodaniline are the most striking examples. These will be found fully described in the section on organic bases. The action of fuming nitric acid upon organic substances very commonly indeed gives rise to substitution-products containing the elements of hyponitric acid, N04, in place of hydrogen. The benzoyl-compounds, and several of the essential oils natural and derived from resins, will be found to furnish illus- trations. In formulae representing substitution-compounds retaining some hydroo-en, the practice is often adopted of placing the substituting body beneath or beside this residual hydrogen, and uniting them by a bracket on each side. Thus, the formulae of the first two products of the action of chlorine on Dutch-liquid are thus written : — C4 { £» } Cl2, and C4 { **« } Cl2, or C4 (H3C1) Cl2 and C4 (H2C12) Cl2. And pyroxylin, or gun-cotton, which is supposed to be a substitution-product from lignin, C^H^O^, having five equivalents of hydrogen replaced by the elements of hyponitric acid, will stand:— C"{5N04}0w or Cm [H,5 (N04)5] O20. Isomeric bodies, or substances different in properties, yet identical in com- position, are of constant occurrence in organic chemistry, and stand indeed ORGANIC CHEMISTRY. 337 among its most striking and peculiar features. Every year brings to light fre-h examples of compounds so related. In most cases, discordance in pro- perties is fairly and properly ascribed to difference of constitution, the ele- ment* being differently arranged. For instance, formic ether and acetate of methyl are isomeric, both containing C6H604; but then the first is supposed to consi-t of formic acid, t'2II03, combined with ether, C4H50 ; while the second is imagined, in accordance with the same views, to be made up of acetic acid, C4II803, and the ether of wood-spirit, C2H30. And this method of explana- tion is generally sufficient and satisfactory: when it can be shown that a diffe- rence of constitution, or even a difference in the equivalent numbers, exists between two or more bodies identical in ultimate composition, the reason of their discordant characters becomes to a certain extent intelligible. The action of heat on organic substances presents many important^ and interesting points, of which a few of the more prominent may be noticed. Bodies of simple constitution and of some permanence, which do not sublime unchanged, as many of the organic acids, yield, when exposed to a high, but regulated temperature, in a retort, new compounds, perfectly definite and often crystallizable, which partake, to a certain extent, of the properties of the original substance; the numerous pyro-acids, of which many examples will occur in the succeeding pages are thus produced. Carbonie acid and water are often eliminated under these circumstances. If the heat be sud- denly raised to redness, then the regularity of the decomposition vanishes, while the products become more uncertain and more numerous; carbonic acid and watery vapor are succeeded by inflammable gases, as carbonic oxide and carbonetted hydrogen; oily matter and tar distil over, and increase in quan- tity until the close of the operation, when the retort is found to contain, in nmst cases, a residue of charcoal. Such is destructive distillation. • If the organic substance contain nitrogen, and be not of a kind capable of taking a new and permanent form at a moderate degree of heat, then that nitrogen is in most instances partly disengaged in the shape of ammonia, or Bub-tances analogous to it, partly left in combination with the carbonaceous matter in the distillatory vessel. The products of dry distillation thus become still more complicated. A much greater degree of regularity is observed in the effects of heat on fixed organic matters, when these arc previously mixed with an excess of strong alkaline base, as potassa or lime. In such cases an acid, the nature of whioh is chiefly dependent upon the temperature applied, is produced, and remains in uniou with the base, the residual element or elements escaping in some volatile form. Thus, benzoic acid distilled with hydrate of lime, at a dull-red heat, yields carbonate of lime and a bicarbide of hydrogen, benzole; woody fibre and caustic potassa, heated to a very moderate temperature, yield ulmic acid and free hydrogen; with a higher degree of heat, oxalic acid appears in the place of the ulmic; and, at the temperature of ignition, car- bonic acid, hydrogen being the other product. The spontaneous changes denominated decay and putrefaction, to which many of the more complicated organic, and more particularly, azotized prin- ciples arc subject, have always attracted much attention. By the expression decay,1 Liebig and his school understand a decomposition- of moist organic matter, freely exposed to the air, by the oxygen of which it is gradually burned and destroyed, without sensible elevation of temperature ; the term putrefaction, on the other hand, is limited to changes occurring in and beneath the surface of water, the effeet being a mere transposition of elements, or metamorphosis of the organic body. The conversion of sugar into alcohol and carbonic acid furnishes, perhaps, the simplest case of the kind. It is proper to remark, however, that contact of oxygen is indispensable, in the first 29 1 Or eramacausis, that is, with slow burning. 338 THE ULTIMATE ANALYSIS OF instance, to the change, which, when once begun, proceeds, without the aid of .any other substance external to the decomposing body, unless it be water or its elements. Every case of putrefaction thus begins with decay ; and if the decay, or its cause, namely, the absorption of oxygen, be prevented, no putrefaction occurs. The most putrescible substances, as animal flesh intended for food, milk, and highly-azotized vegetables, are preserved indefinitely, by enclosure in metallic cases, from which the air has been completely removed and excluded. Some of the curious phenomena of communicated chemical activity, where a decomposing substance seems to involve others in destructive change, which, without such influence, would have remained in a permanent and quiescent state, will be found noticed in their proper places, as under the head of Vinous Fermentation. These actions are yet very obscure, and require to be discussed with great caution. the ultimate analysis of organic bodies. As most organic substances cannot be produced at will from their elements, the analytical method of research is alone applicable to the investigation of their exact chemical composition ; hence the ultimate analysis of these sub- stances becomes a matter of great practical importance. The operation is always executed by causing complete combustion of a known weiglit of the body to be examined, in such a manner that the carbonic acid and water produced shall be collected, and their quantity determined: the carbon and hydrogen they respectively contain may from these data be easily calculated. When nitrogen, sulphur, phosphorus, chlorine, &c, are present, special and separate means are resorted to for their estimation. The method to be described for the determination of the carbon and hydro- gen owes its convenience and efficiency to the improvements of Professor Liebig; it has superseded all other processes, and is now invariably employed in inquiries of the kind. AVith proper care, the results obtained are wonder- fully correct; and equal, if not surpass in precision, those of the best mineral analyses. The principle upon which the whole depends is the following: — When an organic substance is heated with the oxides of copper, lead, and several other metals, it undergoes complete combustion at the expense of the oxygen of the oxide, the metal being at the same time reduced, either com- pletely or to a lower state of oxidation. This effect takes place with greatest ease and certainty with the black oxide of copper, which, although unchanged by heat alone, gives up oxygen to combustible matter with extreme facility. When nothing but carbon and hydrogen, or those bodies together with oxygen, are present, one experiment suffices; the carbon and hydrogen are deter- mined directly, and the oxygen by difference. It is of course indispensable that the substance to be analyzed should pos- sess the physical characters of purity, otherwise the inquiry cannot lead to any useful result; if in the solid state, it must also be freed with the most scrupulous care from the moisture which many substances retain with great obstinacy. If it will bear the application of a moderate heat, this desic- cation is very easily accomplished by a water or steam bath: in other cases, exposure at common temperature to the absorbent powers of a large sur- face of oil of vitriol in the vacuum of an air-pump must be substituted. The operation of weighing the dried powder is conducted in a narrow open tube, about 2£ or 3' inches long: the tube and ORGANIC BODIES. 339 substance are weighed together, and, when the latter has been removed, the tube with any little adherent matter is re-weighed. This weight, subtracted from the former, gives the weight of the substance employed in the experi- ment. As only 5 or 6 grains are used, the weighings should not involve a greater error than ^fa part of a grain. The protoxide of copper is best made from the nitrate by complete ignition in an earthen crucible : it is reduced to powder, and reheated just before use, to expel hygroscopic moisture, which it absorbs, even while warm, with avidity. The combustion is performed in a lube of hard white Bohemian glass, having a diameter of 0-4 or 0-5 inch, and in length varying from 14 to 18 inches: this kind of glass bears "a moderate red-heat without becoming soft enough to loose its shape. One end of the tube is draAvn out to a point, as shown in fig. 167, and closed ; the other is simply heated to fuse and soften the sharp edges of the glass. The tube is now two-thirds filled with the yet warm prot- oxide of copper, nearly the whole of which is transferred to a small porcelain or Wedgwood mortar, and very intimately mixed with the organic substance. Fig. 167. Oxide copper. Mixture. Oxide copper. The mixture is next transferred to the tube, and the mortar rinsed with a little fresh and hot oxide, which is added to the rest; the tube is, lastly, filled to within an inch of the open end with oxide from the crucible. A few gentle taps on the table suffice to shake together the contents, so as to leave a free passage for the evolved gases from end to end. The arrangement of the mix- ture and oxide in the tube is represented in the sketch. The tube is then ready to be placed in the furnace or chauffer; this is con- structed of thin sheet-iron, and is furnished with a series of supports of equal height, which serve to prevent flexure in the combustion-tube when softened by heat. The chauffer is placed upon flat bricks or a piece of stone, so that but little air can enter the grating, unless the whole be properly raised. A slight inclination is also given towards the extremity occupied by the mouth of the combustion-tube, which passes through a hole provided for the purpose. To collect the water produced in the experiment, a small light tube of the form represented in fig. 169, filled with fragments of spongy chloride of cal- cium, is attached by a perforated cork, thoroughly dried, to the open extre- mity of the combustion-tube. The carbonic acid is absorbed by a solution of caustic potassa, of specific gravity 1-27, which is contained in a small'glass apparatus on the principle of a Woulfe's bottle, shown in fig. 170. The con- nection between the latter and the chloridc-of-calcium tube is completed by a little tube of caoutchouc, secured with silk cord. The whole is shown in fig, 171, as arranged for use. Both the chloride-of-calcium tube and the pot- ash-apparatus are weighed with the utmost care before the experiment. 340 THE ULTIMATE ANALYSIS OF Fig. 170. The tightness of the junctions may be ascertained by slightly rarefying the included air by sucking a few bubbles from the interior through the liquid, using the dry lips, or, better, a little bent tube with a perforated cork: if the difference of level of the liquid in the two limbs of the potash-apparatus bo preserved for several minutes, the joints are perfect. Red-hot charcoal is now placed around the anterior portion of the combustion-tube, containing the pure oxide of copper; and when this is red-hot, the fire is slowly extended towards the farther extremity by shifting the moveable screen represented in the drawing. The experiment must be so conducted that an uniform stream Fig. 171. ff Drawing of the whole arrangement. of carbonic acid shall enter the potash-apparatus by bubbles which may be easily counted: when no nitrogen is present, these bubbles are towards the termination of the experiment almost completely absorbed by the alkaline liquid, the little residue of air alone escaping. In the case of an azotized body, on the contrary, bubbles of nitrogen gas pass through the potassa-solu- tion during the whole process. When the tube has become completely heated from end to end, and no more gas is disengaged, but, on the other hand, absorption begins to be evident, the coals are removed from the farther extremity of the combustion-tube, and the point of the latter broken off. A little air is ('own through the whole apparatus, by which the remaining carbonic acid and watery vapor are se- cured. The parts are, lastly, detached, and the chloride-of-calcium tube and potash-apparatus reweighed. The mode of heating the combustion-tube with red-hot charcoal is the ori- ginal process, and still extensively employed, the construction of the furnace being most simple, and charcoal everywhere accessible. However, since the use of coal-gas has been universally adopted in laboratories, many contrivances have been suggested, by means of which this convenient fuel may be employed also in organic analysis. An apparatus of this kind1 is the one represented 1 Hofmann, Journal of the Chemical Society, vol. xi. p. 30. ORGANIC BODIES. 341 in fig. 172, in which the combustion-tube is heated by a series of perforated clay-burners. These clay-burners are fixed on pipes provided with stopcocks, so that the gas may be lighted according to the requirements of the case. Fig. 172. m 'i'...... ..'. '••■■'i'!;K!# The stopcocks being appropriately adjusted, the gas burns on the surface of the burners with a smokeless blue flame, which renders them in a short time incandescent. The construction of this furnace is readily intelligible by a glance at figures 173 and 174, which exhibit the different parts of the appa- Fig. 174. ratus in section, fig. 173 representing a large furnace with five rows, and fig. 174 a smaller furnace with three rows of clay-burners. The following account of a real experiment will serve to illustrate the cal- culation of the results obtained in the combustion of crystallized sugar: Quantity of sugar employed Potash-apparatus weighed after experiment " " before experiment Carbonic acid . Chloride-of-calciuna-tube after experiment. " '• before experiment. 4-750 grains. 781-13 773-82 •31 226-05 223-30 Water 342 THE ULTIMATE ANALYSIS OF 7-31 gr. carbonic acid — 1-994 gr. carbon: and 2-75 gr. water = 0-3056 gr. hydrogen; or in 100 parts of sugar,1 Carbon........41-98 Hydrogen... ..... 6-43 Oxygen, by difference.....51-59 100-00 When the organic substance cannot be mixed with the protoxide of copper in the manner described, the process must be slightly modified to meet the particular case. If, for example, a volatile liquid is to be examined, it is enclosed in a little glass bulb with a narrow stem, Fig. 175. which is weighed before and after the introduction of the liquid, the point being hermetically sealed. The combustion-tube must have, in this case, a much greater length ; and, as the protoxide of cop- per cannot be introduced hot, it must be ignited and cooled out of contact with the atmosphere to prevent absorption of watery vapor. This is most conveniently effected by transferring it, in a heated state, to a large platinum crucible to which a closely-fitting cover can be adapted. AVhen quite cold, the cover is removed and instantly replaced by a dry glass funnel, by the assistance of which the oxide may be directly poured into the combus- tion-tube, with merely momentary exposure to the air. A little oxide is put in, then the bulb, with its stem broken at a, a file-scratch having been pre- viously made; and, lastly, the tube is filled with the cold and dry protoxide of copper. It is arranged in the chauffer, the chloride-of-calcium tube and potash-apparatus adjusted, and then, some six or eight inches of oxide hav- ing been heated to redness, the liquid in the bulb is, by the approximation of a hot coal, expelled, and slowly converted into vapor, which, in passing over the hot oxide, is completely burned. The experiment is then terminated in the usual manner. Fusible fatty substances, and volatile concrete bodies, as camphor, require rather different management, which need not be here described. Protoxide of copper, which has been used, may be easily restored by moist- ening with nitric acid, and igniting to redness; it becomes, in fact, rather improved than otherwise, as, after frequent employment, its density is in- creased, and its troublesome hygroscopic powers diminished. For substances which are very difficult of combustion, from the large proportion of carbon they contain, and for compounds into which chlorine enters as a constituent fused and powdered chromate of lead is very advantageously substituted for the protoxide of copper. Chromate of lead freely gives up oxygen to com- bustible matters, and even evolves, when strongly heated, a little of that gas, which thus insures the perfect combustion of the organic body. Analysis of Azotized Substances. — The presence of nitrogen in an organic compound is easily ascertained by heating a small portion with solid hydrate of potassa in a test-tube: the nitrogen, if present, is converted into ammonia, which may be recognised by its odor and alkaline reaction. There are seve- 1 The theoretical composition of sugar C12II11O11, reckoned to 100 parts, gives — Carhon.......4211 Hydrogen.......G-43 Oxygen.......51-4(1 10000 ORGANIC BODIES. 343 ral methods of determining the proportion of nitrogen in azotized organic sub- stances, the experimenter being guided in his choice of means by the nature of the substance and its comparative richness in that element. The carbon and hydrogen are first determined in the usual manner: a longer tube than usual is employed, and four or five inches of its anterior portion filled with spongy metallic copper, made by reducing the protoxide by hydrogen ; this serves to decompose any nitrous acid or binoxide of nitrogen, which may be formed in the act of combustion. During the experiment some idea of the abundance or paucity of the nitrogen may be formed from the number of bub- bles of incondensible gas which traverse the solution of potassa. In the case of compounds abounding in nitrogen, and readily burned by protoxide of copper, a mcthed may be employed, which is very easy of exe- cution : this consists in determining the ratio borne by the liberated nitrogen to the carbonic acid produced in the combustion. A tube of hard glass, of the usual diameter, and about 15 inches long, is sealed at one end; a little of the organic substance, mixed with protoxide of copper, is introduced, and allowed to occupy about two inches of the tube; about as much pure oxide is placed over it, and- then another portion of a similar mixture; after which the tube is filled up with a second and larger portion of pure oxide, and a quantity of spongy metallic copper. A short bent tube, made movable by a caoutchouc joint, is fitted by a perforated cork, and made to dip into a mer- curial trough, while the combustion-tube itself rests in the chauffer. (Fig. 176.) Fig. 176. Fig. 177. (G3i Fire is first applied to the anterior part of the tube containing the metal and unmixed oxide, and, when this is red-hot, to the extreme end. Combustion of the first portion of the mixture takes place, the gaseous products sweeping before them nearly the whole of the air of the apparatus. AVhen no more gas , issues the tube is slowly heated by half an inch at a time, in the usual manner, and all the gas very carefully collected in a graduated jar, until the operation is at an end. The volume is then read off, and some strong solution of caustic potassa thrown up into the jar by a, pipette (fig. 177,) with a curved extremity. \\ hen the absorption is complete, the residual volume of nitrogen is observed, and compared with that of the mixed gases, proper correction being made for differences of level in the mercury; and from these data the exact pro- portion borne by the nitrogen to the carbon can be at once determined.1 1 Volumes of the two gases represent equivalents; for 100 cubic inches carbonic acid weigh 47-26 grains. 100 " nitrogen " 30-14 ». . .. 47-26 : 3014 = 22 : 14. iqwivrient o°f wton"0 thC cauhalont numbe«; one equivalent of carbonic acid contains one 344 THE ULTIMATE ANALYSIS OF If the proportion of nitrogen be but small, the error from the nitrogen of the residual atmospheric air becomes so great as to destroy all confidence in the result of the experiment; and the same thing happens when the sub- stance is incompletely burned by protoxide of copper: other means must then be employed. The absolute method of determination, also known by the name of Dumas's method, may be had recourse to when the foregoing, or compara- tive method, fails from the first cause mentioned: it gives excellent results, and is applicable to all azotized substances. A tube of good Bohemian glass, 28 inches long, is securely sealed at one end; into this enough dry bicarbonate of soda is put to occupy 6 inches. A little pure protoxide of copper is next introduced, and afterwards the mixture of oxide and organic substance, the weight of the latter, between 4-5 and 9 grains, in a dry state, having been correctly determined. The remainder of the tube, amounting to nearly one-half of its length, is then filled up with pure protoxide of copper and spongy metal, and a round cork, perforated by a piece of narrow tube, is securely adapted to its mouth. This tube is con- nected by means of a caoutchouc joint with a bent delivery-tube, a, and the combustion-tube, arranged in the furnace, A few coais are now applied to the farther end of the tube, so as to decompose a portion of the bicarbonate of soda, the remainder of the carbonate as well as of the other part of the tube being protected from the heat by a screen n. The current of carbonic acid thus produced is intended to expel all the air from the apparatus. In order to ascertain that this object, on which the success of the whole operation de- pends, is accomplished, the delivery-tube is depressed under the level of a mercurial trough, and the gas, which is evolved, collected in a test-tube filled with concentrated potassa-solution. If the gas be perfectly absorbed, or, after the introduction of a considerable quantity, only a minute bubble be left, the air may be considered as expelled. The next step is to fill a graduated glass jar two-thirds with mercury and one-third with a strong solution of potassa and to invert it over the delivery-table, as represented in fig. 178. Fig. 178. This done, fire is applied to the tube, commencing at the front end, and gradually proceeding to the closed extremity, which still contains some unde- composed bicarbonate of soda. This, when the fire at length reaches it, yields up carbonic acid, which chases forward the nitrogen lingering in the tube. The carbonic acid generated during the combustion is wholly absorbed by the potassa in the jar, and nothing is left but the nitrogen. AVhen the operation is at an end, the jar, with its contents, is transferred to a vessel of water, and the volume of the nitrogen read off. This is properly corrected for tempera- ture, pressure, and aqueous vapor, and its weight determined by calculation. AVhen the operation has been very successful, and all precautions minutely observed, the result still leaves an error in excess, amounting to 0-3 or 0-5 ORGANIC BODIES. 345 per cent., due to the residual air of the apparatus, or that condensed in the pores of the protoxide of copper. A most elegant process for estimating nitrogen in all organic compounds, except those containing the nitrogen in the form of nitrous, hyponitric, and nitric acids, and in some organic bases, has been put in practice by MM. AYill and Varrentrapp. AVhen a non-azotized organic substance is heated to red- ness with a large excess of hydrate of potassa or soda, it suffers complete and speedy combustion at the expense of the water of the hydrate, the oxygen combining with the carbon of the organic matter to carbonic acid, which is retained by the alkali, while its hydrogen, together with that of the substance, is disengaged, sometimes in union with a little carbon. The same change happens when nitrogen is present, but with this addition: the whole of the nitrogen thus abandoned combines with a portion of the liberated hydrogen to form ammonia. It is evident, therefore, that if this experiment be made on a weighed quantity of matter, and circumstances allow the collection of the whole of the ammonia thus produced, the proportion of nitrogen can be easily calculated. „ An intimate mixture is made of 1 part caustic soda, and 2 or 3 parts quick- lime, by slaking lime of good quality with the proper proportion of strong caustic soda, drying the mixture in an iron vessel, and then heating it to red- ness in an earthen crucible. The ignited mass is rubbed to powder in a warm mortar, and carefully preserved from the air. The lime is useful in many ways; it diminishes the tendency of the alkali to deliquescence, facilitates mixture with the organic substance, and prevents fusion and liquefaction. A proper quantity of the substance to be analyzed, namely, from 5 to 10 grains, is dried and accurately weighed out: this is mixed in a warm porcelain mortar with enough of the soda-lime to fill two-thirds of an ordinary combustion-tube, the mortar being rinsed with a little more of the alkaline mixture, and, lastly, with a small quantity of powdered glass, which completely removes everything adherent to its surface; the tube is then filled to within an inch of the open end with the lime-mixture, and arranged in the chauffer in the usual manner. The ammonia is collected in a little apparatus of three bulbs, contain- Fig. 179. ing moderately-strong hydrochloric acid, attached by a cork to the combustion-tube. Matters being thus adjusted, fire is applied to the tube, commencing with the anterior extremity. AVhen ignited through- out its whole length, and when no ' more gas issues from the apparatus, the point of the tube is broken, and a little air drawn through the whole. . The acid liquid is then emptied into a capsule, the bulbs rinsed into the same, first with a little alcohol, and then repeatedly with distilled water; an excess of pure bichloride of platinum is added, and the whole evaporated to dryness in a water-bath. The dry mass, when cold, is treated with a mixture of alcohol and ether, which dissolves out the superfluous bichloride of platinum, but leaves untouched the yellow crys- talline double chloride of platinum and ammonium. The latter is collected upon a small weighed filter, washed with the same mixture of alcohol and ether, dried at 212° (100°C), and weighed; 100 parts correspond to 6-272 parts of nitrogen; or, the salt with its filter may be very carefully ignited, and the filter burned in a platinum crucible, and the nitrogen reckoned from the weight of the spongy metal, 100 parts of that substance corresponding to 14-18 parts of nitrogen. The former plan is to be preferred in most cases. Bodies very rich in nitrogen, as urea, must be mixed with about an equal 346 THE ULTIMATE ANALYSIS OF quantity of pure sugar, to furnish incondensible gas, and thus diminish the violence of the absorption which otherwise occurs; ond the same precaution must be taken, for a different reason, with those which contain little or no hydrogen. A modification of this process has been suggested by M. P^ligot, which is very convenient if a large number of nitrogen-determinations is to be made. By this plan the ammonia, instead of being received in hydrochloric acid, is conducted into a known volume (from £ to 1 cubic inch) of a standard solution of sulphuric acid, contained in the ordinary nitrogen-bulbs. After the com- bustion is finished, the acid containing the ammonia is poured out into a beaker, colored with a drop of tincture of litmus, arid then neutralized with a standard solution of soda in water or of lime in sugar-water, the point of neu- tralization becoming perceptible by the sudden appearance of a blue tint. The lime-solution is conveniently poured out from the graduated glass-tube, described under the head of Alkalimetry. The volume of lime-solution neces- sary to neutralize the same amount of acid, which is used for condensing the ammonia, having been ascertained by a preliminary experiment, it is evident that the difference of the quantities used in the two experiments gives the am- monia collected during the combustion in the acid. The amount of nitrogen may thus be calculated. If, for instance, an acid be prepared, containing 20 grains of pure hydrated sulphuric acid (S03,HO) in 1000 grain-measures— 200 grain-measures of this acid—the quantity introduced into the bulbs—cor- respond to 1-38 grains of ammonia, or 1-14 grains of nitrogen. The alkaline solution is so graduated that 1000 grain-measures will exactly neutralize the 200 grain-measures of the standard acid. If we now find that the acid, partly saturated with the ammonia disengaged during the combustion of a nitrogenous substance, requires only 700 grain-measures of the alkaline solution, it is evi- dent that —rpr™— = 00 grain-measures were saturated by the ammonia, and the quantity of nitrogen is obtained by the proportion 200: 1-14 = GO: x, 1-14 V 00 wherefore x =---—---- — 0-342 grains af nitrogen. Estimation of Sulphur in Organic Compounds. — When bodies of this class containing sulphur are burned with protoxide of copper, a small tube, con- taining binoxide of lead, may be interposed between the chloride-of-calcium tube and the potassa-apparatus to retain any sulphurous acid which may be formed. It is better, however, to use chromate of lead in such cases. Tho proportion of sulphur is determined by oxidizing a known weight of the sub- stance by strong nitric acid, or by fusion in a silver vessel with ten or twelve times its weight of pure hydrate of potassa and half as much nitre. The sul- phur is thus converted into sulphuric acid, the quantity of which can be determined by dissolving the fused mass in water, acidulating with nitric acid, and adding a salt of baryta. Phosphorus is, in like manner, oxidized to phosphoric acid, the quantity of which is determined by precipitation in com- bination with sesquioxide of iron, or otherwise. Estimation of Chlorine.—The case of a volatile liquid containing chlorine is of very frequent occurrence, and may be taken as an illustration of the general plan of proceeding. The combustion with protoxide of copper must be very carefully conducted, and two or three inches of the anterior portion of the tube kept cool enough to prevent volatilization of the chloride of copper into the chloride-of-calcium tube. Chromate of lead is much better for the pur- pose. The chlorine is correctly determined by placing a small" weighed bulb of liquid in a combustion-tube, which is afterwards filled with fragments of pure quicklime. The lime is brought to a red-heat, and the vapor of the liquid driven over it, when the chlorine displaces oxygen from the lime, and EMPIRICAL AND RATIONAL FORMULAE. 347 gives rise to chloride of calcium. When cold, the contents of the tube are di-solved in dilute nitric acid, filtered, and the chlorine precipitated by nitrate of silver. empirical and rational formulae. A chemical formula is termed empirical when it merely gives the simplest possible expression of the composition of the substance to which it refers. A rational formula, on the contrary, aims at describing the exact composition of one equivalent, or combining proportion of the substance, by stating the abso- lute number of equivalents of each of its elements essential to that object, as well as the mere relations existing between them. The empirical formula is at once deduced from the analysis of the substance, reckoned to 100 parts; the rational formula requires in addition a knowledge of its combining quan- tity, which can only be obtained by direct experiment, by synthesis, or by the careful examination of one or more of its most definite compounds. Farther, the rational may either coincide with the empirical formula, or it may be a multiple of the latter. Thus, the composition of acetic acid is expressed by the formula CHO, which exhibits the simplest relations of the three elements; if we want to express the quantities of these, in equivalents, required to make up an equivalent of acetic acid we have to adopt the formula C41I404 = C4H303.1I0. Again, the empirical formula of crystallized kinic acid is C7U606, while its rational formula, determined by its capacity of saturation, is double, or C14H12012, = ^M^u^ii'lfO. In like manner, the empirical formula; of the artificial alka- loids furfurine and amarinc are respectively C,5H6N03 and C2lU9N. The equi- valents of these substances, that is to say, the quantities required to form neutral salts with one equivalent of any well-defined monobasic acid will, however, be expressed by the formula; C30H12N2O6 and C42H18N2; hence these latter deserve the name of rational formula;. The deduction of an empirical formula from the ultimate analysis is very easy : the case of sugar, already cited, may be taken as an example. This contains, according to the analysis, in 100 parts — Carbon.....• . , .41-98 Hydrogen . . . . . . .0-43 Oxygen........51-59 10000 If each of these quantities be divided by the equivalent of the element, the quotients will express in equivalents the relations existing between them : these are afterwards reduced to their simplest expression. This is the only part of the calculation attended with any difficulty: if the numbers were rigidly correct, it would only be necessary to divide each by the greatest divisor com- mon to the whole; as they are, however, only approximative, something is of necessity left to the judgment of the experimenter, who is obliged to use more indirect means. 41-98 51-59 —^— = 6-99; 6-43; —g- = 6-44. or 069 eq. carbon, 643 eq. hydrogen, and 644 eq. oxygen. It will be evident, in the first place, that the hydrogen and oxygen are present in the proportion to form water, or as many equivalents of one as of the other. Again, the equivalents of carbon and hydrogen are nearly in the proportion of 12 :11, so that the formula C^H.jOj, appears likely to be cor- 348 DETERMINATION OF THE DENSITY OF VAPORS. rect. It is now easy to see how far this is admissible, by reckoning it back to 100 parts, comparing the result with the numbers given, by the actual analysis, and observing whether the difference falls fairly in direction and amount within the limits of error of what may be termed a good experiment, viz., two- or three-tenths per cent, deficiency in the carbon, and not more than one-tenth or two-tenths per cent, excess in the hydrogen. Carbon '......6 x 12 = 72 Hydrogen......11 eq. = 11 Oxygen......8x11=88 171 : 72 = 100: 42-11 171 : 11 = 100: 6-43 171 : 88 = 100: 51-46 Organic acids and salt-radicals have their proper equivalents most fre- quently determined by an analysis of their lead- and silver-salts, by burning these latter with suitable precautions in a thin porcelain capsule, and noting the weight of the protoxide of lead or metallic silver left behind. If the prot- oxide of lead be mixed with globules of reduced metal, the quantity of the latter must be ascertained by dissolving away the oxide by acetic acid. Or the lead-salt may be converted into sulphate, and the silver compound into chloride, and both metals thus estimated. An organic base, on the contrary, or a basyle, has its equivalent fixed by the observation of the quantity of a mineral acid, or an inorganic salt-radical, required to form with it a combina- tion having the characters of neutrality. DETERMINATION OF THE DENSITY OF VAPORS. The determination of the specific gravity of the vapor of a volatile sub- stance is frequently a point of great importance, inasmuch as it gives the means, in conjunction with the analysis, of representing the constitution of the substance by measure in a gaseous state. The following is a sketch of the plan of operation usually followed: — A light glass globe, about three inches in diameter, is taken, and its neck softened and Fig. ISO. drawn out in the blowpipe-flame, as represented in the figure: this is accurately weighed. About one hundred grains of the volatile liquid are then introduced, by gently warming the globe and dipping the point into the liquid, which is then forced upwards by the pressure of the air as the vessel cools. The globe is next firmly attached by wire to a handle, in such a manner that it may be plunged into a bath of boiling water or heated oil, and steadTly held with the point projecting upwards. The bath must have a temperature considerably above that of the boiling-point of the liquid. The latter becomes rapidly converted into vapor, which escapes by the narrow orifice, chasing before it the air of the globe. AVhen the issue of vapor has wholly ceased, and the temperature of the bath, carefully observed, appears pretty uniform, the open extremity of the point is hermetically sealed by a small blowpipe-flame. The globe is removed from the bath, suffered to cool, cleansed if necessary, and weighed, after which the neck is broken off beneath the sur- face of water which has been boiled and cooled out of contact of air, or (better) 171 DETERMINATION OF THE DENSITY OF VAPORS. 349 mercury. The liquid enters the globe, and, if the expulsion of the air by the vapor has been complete, fills it; if otherwise, an air-bubble is left, whose volume can be easily ascertained by pouring the liquid from the globe into a jar graduated to cubic inches, and then refilling the globe, and repeating the same observation. The capacity of the vessel is thus at the same time known: and these are all the data required. An example will render the whole intelligible. Determination of the density of the vapor of Acetone. Capacity of globe ....... Weight of globe filled with dry air at 52° (11°-11C) and 30.24 inches barometer . . . . Weight of globe filled with vapor at 312° (100°C) temp, of the bath at the moment of sealing the point, and 30°-24 inches barometer Residual air, at 45° (7°-22C), and 30-24 inches barometer ........ 31-61 cubic inches. 2070-88 grains. 2076-81 grains. 0-60 cubic inches. 31-01 cub. inches of air at 52° and 30-24 in. bar. =32-36 cub. inches at 60° (15°-5C) and 30 inch, bar., weighing .... 10035 grains. Hence, weight of empty globe . . 2070-88 —10-035 = 2060-845 grains. 0G c. inch of air at 45° = 0-8 c. inch at 212°; weight of do, by calcula- tion = 0-191 grain. 31 -61— 0-8 = 30-81 cubic inches of vapor at 212° and 30-24 in bar., which, on the supposition that it could bear cooling to 60° without liquefaction, would, at that temperature, and under a pressure of 30 inch bar., become reduced to 24-18 cubic inches. Hence, AVcight of globe and vapor " residual air Weight of globe. AVeight of the 24-18 cubic inches of vapor. . . 15-774 Consequently, 100 cubic inches of such vapor must weigh.........65-23 grains. 100 cubic inches of air, under similar circumstances, weigh.........3101 --—— =2-103, the specific gravity of the vapor in question, air being d1'01 unity. 2076-810 grains. 0-191 2076-619 2060-845 In the foregoing statement a correction has been, for the sake of simplicity, omitted, which, in very exact experiments, must not be lost sight of, viz., the expansion and change of capacity of the glass globe by the elevated tempera- ture of the bath. The density so obtained will be always on this account a little too high. The error to which the mercurial thermometer is, at high temperatures, liable, tends in the opposite direction. 30 350 DETERMINATION OF THE DENSITY OF VAPORS, It is easy to compare the actual specific gravity of the vapor found in tho manner above described with the theoretical specific gravity deduced from the formula of the substance : — The formula of acetone is C3H30.—In combining volumes this is represented by 3 vols, of the hypothetical vapor of carbon, 3 vols, of hydrogen, and half a volume of oxygen. Or the weight of the unit of volume of acetone-vapor will be equal to three times the specific gravity of carbon-vapor, three times that of hydrogen, and one-half that of oxygen added together, one volume of the compound vapor containing 6i_- volumes of its components: — 3 vols, hypothetical vapor of carbon . . 0-4183x3 = 1-2549 3 vols, hydrogen......0-0693x3 = 0-2079 jV vol. oxygen...... = 0-5528 Theoretical specific gravity .... 2-0156 • CANE- AND GRAPE-SUGAR. 351 NON-AZOTIZED BODIES OF THE SACCHARINE AND AMYLACEOUS GROUP. SUGAR, STARCH, GUM, LIONIN, AND ALLIED SUBSTANCES. The members of this remarkable and very natural group present several interesting cases of isomerism. They are characterized by their feeble apti- tude to enter into combination, and also by containing, with a few exceptions, oxygen and hydrogen in the proportions to form water. Table of Saccharine and Amylaceous Substances. Cane-sugar, crystallized. Cane-sugar, in combination . Grape-sugar, crystallized Grape-sugar, in combination . Milk-sugar, crystallized. Milk-sugar in combination Melitose from Eucalyptus manifera Eucalyne from the same. Inosite . Sorbin . Sugar from Secale cornutum (Mycose) Caramel Mannite Dulcosc. Erythromannite Pinite . Quercite Starch, unaltered, dried at 212° (100°C) Amidin, or gelatinous starch . Dextrin, or gummy starch Starch from Cetraria Islandica Inulin ..... Gum-arabic .... Gum-tragacanth . Lignin, or cellulose 124 HjgOjjj ^24 H18^ IS C24" 28^28 C24H2102, C24H24024 L24H]gO|g 124H24024 C24H24024 tfcl" 24^24 c6ir6o6 *-24"26('26 C24H18018 C12H14O12 C14H 14^)2 C-8^10^8 C^H 24O20 t24H24()20 *-'24™ 20^20 C24"20 '20 ^24"2O^'20 C24H20O20 C24H2I02I C24H22()22 *-24 20 20 C24H20O20 Cane-sugar; ordinary-sugar, C^H^O^. — This most useful substance is found in the juice of many of the grasses, in the sap of several forest-trees, in the root of the beet and the mallow, and in several other plants. It is •extracted most easily and in greatest abundance from the sugar-cane, culti- vated for the purpose in many tropical countries. The canes are crushed 352 CANE- AND GRAPE-SUGAR. between rollers, and the expressed juice suffered to flow into a large vessel, where it is slowly heated nearly to its boiling-point. A small quantity of hy- drate of lime mixed with water is then added, which occasions the separation of a coagulum consisting chiefly of earthy phosphates, waxy matter, a pecu- liar albuminous principle, and mechanical impurities. The clear liquid sepa- rated from the coagulum thus produced is rapidly evaporated in open pans heated "by a strong fire made with the crushed canes of the preceding year, dried in the sun and preserved for the purpose. AVhen sufficiently concen- trated, the syrup is transferred to a shallow vessel, and left to crystallize, during which time it is frequently agitated in order to hasten the'change and hinder the formation of large crystals. It is, lastly, drained from the dark uncrystallizable syrup, or molasses, and sent into commerce, under the name of raw or Muscovado sugar. The refining of this crude product is effected by rcdissolving it in water, adding a quantity of albumen in the shape of serum of blood or white of egg, and sometimes a little lime-water, and heating the whole to the boiling-point; the albumen coagulates, and forms a kind of net- work of fibres, which enclose and separate from the liquid all mechanically- suspended impurities. The solution is decolorized by filtration through animal charcoal, evaporated to the crystallizing-point, and put into conical earthen moulds, where it solidifies, after some time, to a confusedly-crystalline mass, which is drained, washed with a little clean syrup, and dried in a stove: the product is ordinary loaf-sugar. When the crystallization is allowed to take place quietly and slowly, sugar-candy results, the crystals under these circum- stances acquiring large volume and regular form. The evaporation of the de- colorized syrup is best conducted in strong close boilers exhausted of air; the boiling-point of the syrup is reduced in consequence from 230° (110°C) to 150 (65°-5C) or below, and the injurious action of the heat upon the sugar in great measure prevented. Indeed the production of molasses in the rude colonial manufacture is chiefly the result of the high and long-continued heat applied to the cane-juice,, and might be almost entirely prevented by the use of vacuum-pans, the product of sugar being thereby greatly increased in quantity, and so far improved in quality as to become almost equal to the refined article. In many parts of the continent of Europe sugar is manufactured On a large scale from beet-root, which contains about 8 per cent, of that substance. The process is far more complicated and troublesome than that just described, and the product much inferior. When refined, however, it is scarcely to be dis- tinguished from the preceding. The inhabitants of the AVestern States of America prepare sugar in considerable quantity from the sap of the sugar maple, Acer saccharinum, which is common in those parts. The tree is tapped in the spring by boring a hole a little way into the wood, and inserting a small spout to convey the liquid into a vessel placed for its reception. This is boiled down in an iron pot, and furnishes a coarse sugar, which is almost wholly employed for domestic purposes, but little finding its way into commerce. Pure sugar slowly separates from a strong solution in large, transparent, colorless crystals, having the figure of a modified oblique rhombic prism. It has a pure, sweet taste, is very soluble in water, requiring for solution only one-third of its weight in the qpld, and is also dissolved by alcohol, but with more difficulty. AVhen moderately heated'it melts, and solidifies on cooling to a glassy amorphous mass, familiar under the name of barley-sugar; at a higher temperature it blackens and suffers decomposition: and the same effect is produced, as already remarked, by long-continued boiling of the aqueous solution, which loses its faculty of crystallizing and becomes colored. The crystals have a specific gravity of 1-6, and are unchangeable in the air. The deep-brown soluble substance called caramel, used for coloring spirits CANE- AND GRAPE-SUGAR. 353- and other purposes, is a product of the action of heat upon cane-sugar. It contains C^II^O^, and is isomeric with cane-sugar in combination. The following is the composition assigned to the principal compounds of cane-sugar by M. Peligot, who has devoted much attention to the subject.1 Crystallized cane-sugar .... C24II18018-f-4HO Compound of sugar with common salt . C24ll18()18-j- NaCl 4- 3HO Compound of sugar with baryta . . . C^Il^O^-j- 2BaO -f- 4110 Compound of sugar with lime . . . C24H]8Ol8-)--CaO-j-4110 Compound of sugar with protoxide of lead . 024H,80,8-J- 4Pb0 The compounds with baryta and lime are prepared by diges ing sugar at a gentle heat with the hydrates of the earths. The lime-compound has a bitter taste, and is more soluble in cold water than in hot. Both are readily decom- posed by carbonic acid, crystals of carbonate of lime being occasionally pro- duced. The combination with protoxide of lead is prepared by mixing sugar with a solution of acetate of lead, adding excess of ammonia, and drying the white insoluble product out of contact with air. The compound with common salt is crystallizable, soluble, and deliquescent. Grape-sugar; glucose; sugar of fruits, C24H28028.—This variety of sugar is very abundantly diffused through the vegetable kingdom ; it may be extracted in large quantity from the juice of sweet grapes, and also from honey, of which it forms the solid crystalline portion, by washing with cold alcohol, which dissolves the fluid syrup. It may also be prepared by artificially modifying cane-sugar, starch, and woody fibre, by processes presently to be described. The appearance of this substance, to an enormous extent, in the urine, is the most characteristic feature of the disease called diabetes. Grape-sugar is easily distinguished by several important peculiarities from cane-sugar: it is much less sweet, and less soluble in water, requiring lj- parts of the cold liquid for solution. Its mode of crystallization is also com- pletely different: instead of forming, like cane-sugar, bold, distinct crystals, it separates from its solutions in water and alcohol in granular warty masses, which but seldom present crystalline faces. AVhen pure, it is nearly white. AVhen heated, it melts, and loses 4 eq. of water, and, at a higher temperature, blackens and suffers decomposition. Grape-sugar combines with difficulty with lime, baryta, and oxide of lead, and is converted into a brown or black substance when boiled with a solution of caustic alkali, by which cane-sugar is but little affected. It dissolves, on the contrary, in strong oil of vitriol without blackening, and gives rise to a peculiar compound acid, whose baryta- salt is soluble. Cane-sugar is, under these circumstances, instantly changed to a black mass resembling charcoal. When solutions of cane- and grape-sugar are mixed with two separate portions of solution of sulphate of copper, and caustic potassa added in excess to each, deep-blue liquids are obtained, which, on being heated, exhibit different characters: the one containing cane-sugar is at first but little altered; a small quantity of red powder falls after a time, but the liquid long retains its blue tint: with the grape-sugar, on the other hand, the first application of heat throws down a copious greenish precipitate, wrhich rapidly changes to scarlet, and eventually to dark-red suboxide of copper, leaving a nearly colorless solution. This is an excellent test for distinguishing the two varieties of sugar, or discovering an admixture of grape- with-cane-sugar. Grape-sugar unites with common salt, forming a soluble compound of sweetish saline taste, which crystallizes in a regular and beautiful manner. • Ann. Chim. et Phys, lxvii. 113. 30* 354 LIQUORICE-SUGAR. Compounds of Grape-sugar, according to Peligot. Crystalline grape-sugar, dried in the air . . C24H21021 -4- 7IIO The same, dried at 260° (130°C) . . . C24H21021 -f- 3HO Compound of grape-sugar with common salt . C24H2l021 -j- NaCl -f- 5HO The same, dried at 266° (130°C) . . . C24H21021 + NaCl + 2HO Compound of grape-sugar with baryta . . C24H2)021 -j- SBaO-f- 7HO Compound of grape-sugar with lime . . . C24H2]021 -[- 3Cao -f- 7HO Compound of grape-sugar with protoxide of lead . C24H2102, + 6PbO Sulphosaccharic Acid, C24H20O20SO3.—Melted grape-sugar is cautiously mixed with concentrated sulphuric acid, the product dissolved in water, and neutral- ized with carbonate of baryta; sulphate of baryta is formed together with a soluble sulphosaccharate of that earth, from which the acid itself may be after- wards eliminated. It is a sweetish liquid, forming a variety of soluble salts, and very prone to decompose into sugar and sulphuric acid. Action of dilute Acids upon Sugar.—Cane-sugar dissolved in dilute sulphuric acid is gradually but completely converted, at the common temperature of the air, into grape-sugar. The same solution, when long boiled, yields a brownish- black and nearly insoluble substance, which is a mixture of two distinct bodies, one having the appearance of small shining scales, and the other that of a dull-brown powder. The first, called by Boullay and Malaguti ulmin, and by Liebig sacchulmin, is insoluble in ammonia and alkalies; the second, ulmic acid, the sacchulmic acid of Liebig, dissolves freely, yielding dark-brown solutions precipitable by acids. By long-continued boiling with water, sacch- ulmic acid is converted into sacchulmin. Both these substances have the same composition, expressed by the empirical formula C2HO. Hydrochloric acid, in a dilute state, produces the same effects.1 Action of Alkalies upon Sugar.—AVhen lime or baryta is dissolved in a solu- tion of grape-sugar, and the whole left to itself several weeks in a close vessel, the alkaline reaction will be found to have disappeared from the formation of an acid substance. By mixing this solution with basic acetate of lead, a voluminous white precipitate is obtained, which, when decomposed by sul- phuretted hydrogen, yields sulphide of lead, and the new acid, to which the term glucic acid is applied. Glucic acid is very soluble and deliquescent, has a sour taste and acid reaction: its salts, with the exception of that containing protoxide of lead, are very soluble. It contains C8H6Os. AArhen grape-sugar is heated in a strong solution of potassa, soda, or baryta, the liquid darkens and at length assumes a nearly black color. The addition of an acid then gives rise to a black flocculent precipitate of a substance called melasinic acid, containing C24H,2O,0. Cane-sugar long boiled with alkalies undergoes the same changes, being probably first converted into grape-sugar. Sugar of diabetes insipidus.—A substance having the general properties of a sugar, but destitute of sweet taste, has been described by M. Th6nard as having been obtained from the above-mentioned source. It was capable of furnishing alcohol by fermentation, and of suffering conversion into grape- sugar by dilute sulphuric acid. Its composition is unknown. These obser- vations require confirmation. Liquorice-sugar; glycyrrhizin. — The root of the common liquorice yields a large quantity of a peculiar sweet substance, which is soluble in water, 1 Under the names ulmin a^ ulmic acid have been confounded a number of brown or black uncrystallizable substances produced by the action of powerful chemical aeents upon sugar lignin, &c, or generated by the putrefactive decay of vegetable fibre. Common garden-mould' for example, treated with dilute, boiling solution of caustic potassa. yields a deep-brown solu- tion, from which acids precipitate a flocculent, brown substance, having but a slight decree of solubility in water. This is generally called ulmic or humic acid, and its origin ascribed"to the reaction of the alkali on the ulmin or humus of the soil. It is known that°thesc bodies differ exceedingly in composition : they are too indefinite to admit of ready investigation. MANNA-SUGAR. 355 but refuses to crystallize; it is remarkable for forming with acids compounds which have but sparing solubility. Glycyrrhizin cannot be made to ferment. The formula of this substance is not definitely settled. Panaquilon, from Panax quinquefol., very much resembles glycyrrhizin, but is not precipitated from its solution by sulphuric acid. Sugar of milk; lactin ; lactose, C24H24024.— This curious substance is an important constituent of milk; it is obtained in large quantities by evapo- rating whey to a syrupy state, and purifying the lactin, which, slowly crystal- lizes out, by animal charcoal. It forms white, translucent, four-sided prisms, of great hardness. It is slow and difficult of solution in cold water, requiring for that purpose 5 or 6 times its weight; it has a feeble, sweet taste, and in the solid state feels gritty between the teeth. AVhen heated, it loses water, and at a high temperature blackens and decomposes. Milk-sugar forms several compounds with protoxide of lead, and is converted into grape-sugar by boiling with dilute mineral acids. It is not directly fermentable, but can be made under particular circumstances to furnish alcohol. Melitose and eucalyne, C24H24024. — The Australian manna, which is the produce of Eucalyptus mannifera, according to recent researches of Berthelot, contains two different isomeric sugars, called mellitose and eucalyne. They exist in a state of combination in the crystallized manna, obtained by extract- ing the original secretion with boiling alcohol. If a solution of this substance be submitted to the action of yeast, the melitose is decomposed into alcohol and carbonic acid, whilst eucalyne, not being fermentable, is set free. On evaporating the liquid, eucalyne is obtained as a syrupy mass. Inosite, C24ll2.,024. occurs in almost all parts of the animal system, and is identical with phaseomanito, which occurs in unripe beans (Phaseolus). It forms prismatic crystals of the form of gypsum, is soluble in water, but insoluble in alcohol and ether. If this sugar be evaporated with nitric acid nearly to dryness, the residue be mixed with a little ammonia and chloride of calcium, and again evaporated, a beautiful rose tint is produced, which is quite characteristic of this substance. Sorbin, C6H606 or C12I112<)12. —M. Pelouze has observed that the juice of the berries of the mountain ash, when allowed to stand for some time in open vessels, deposits a brown crystalline matter, which, on recrystallization, may be obtained in transparent colorless crystals. This substance is almost insoluble in alcohol, but easily soluble in water, which assumes an exceedingly sweet taste. Sorbin is, however, no sugar; it is not capable of fermenting, nor can it, by the action of acids, be converted into grape-sugar. A solution of sorbin, when mixed with ammonia and a solution of acetate of lead, furnishes a white flocculent precipitate, which contains 2PbO, C6H404. Sugar from ERGdT of Bye : mycose.—This variety of sugar, extracted by alcohol from the ergot, crystallizes in transparent colorless prisms, which have a sweet taste, and are very soluble in water. It differs from cane-sugar in not reducing the acetate of copper when boiled with a solution of that sub- • stance. It contains C^H^O^. M. Berthelot has recently obtained compounds of nearly all the sugars with acids, especially with the so-called fatty acids. These compounds resemble in their constitution and properties the fats. Manna-sugar; mannite, C6H706 or Ci2H14012. — This is the chief compo- nent of manna, an exudation from a species of ash; it is also found in the juice of certain other plants, and in several sea-weeds, and may be formed artificially from ordinary sugar by a peculiar kind of fermentation. It is best prepared by treating manna with boiling alcohol, and filtering the solution whilst hot: the mannite crystallizes on cooling in tufts of slender colorless needles. It is fusible by heat without loss of weight, is freely soluble in water, possesses a powerfully sweet taste, and has no purgative properties. Mannite refuses to ferment. This substance combines with sulphuric acid, giving rise 35G STARCH. to a new acid, the composition of which is not yet definitely established. It is likewise acted on by concentrated nitric acid. The product of this action will be noticed farther on. The substance formerly described as mushroom- sugar is merely mannite. Dulcose, C6H706, orCi2HH012. —Closely allied to, and identical in composi- sition with mannite, is a substance, imported into Europe from Madagascar, the origin of which is uncertain, but which has been examined by Messrs. Soubeiran, Laurent, and Jaquelain. It forms large crystals, which fuse at 374° (190°C). Dulcose is insoluble in boiling alcohol, and not precipitated by basic acetate of lead. It is not capable of undergoing fermentation. Erythromannite, Phycite, C8H10O8, or C24H30O24.—This sugar is found in Protococcus vulgaris. It was originally discovered by Dr. Stenhouse among the products of decomposition of erythric acid (see the chapter on lichens). It crystallizes in large transparent prisms, is readily soluble in water, but with difficulty soluble in alcohol. It is not fermentable. Pinite, C24H24O20.—A secretion of a California pine-tree (Pinus lambertiana); gives, on extraction with water, a substance which crystallizes in botryoidal forms, of a sweet taste, like sugar-candy. This kind of sugar is not soluble in alcohol, is not fermentable, and does not reduce an alkaline solution of tar- trate of copper, not even after previous treatment with sulphuric acid. Quercite, C^H^Ojjq.—This sugar is found in acorns. Being unfermentable, the juice of the acorn is submitted to fermentation. The fermented liquor, on evaporation, yields small prisms of quercite. This sugar is soluble in water and dilute alcohol. Starch ; fecula. —This is one of the most important and widely diffused of the vegetable proximate principles, being found to a greater or less extent in every plant. It is most abundant in certain roots and tubers, and in soft stems: seeds often contain it in large quantity. From these sources the fecula can be obtained by rasping or grinding to pulp the vegetable structure, and washing the mass upon a sieve, by which the torn cellular tissue is re- tained, while the starch passes through with the liquid, and eventually settles down from the latter as a soft, white, insoluble powder, which may be washed with cold water, and dried with very gentle heat. Potatoes treated in this manner yield a large proportion of starch. Starch from grain may be pre- pared in the same manner, by mixing the meal with water to a paste, and washing the mass upon-a sieve: a nearly white, insoluble substance, called oluten or glutin, remains behind, which contains a large proportion of nitro- gen. The glutin of wheat flour is extremely tenacious and clastic. The value of meal as an article of food greatly depends upon this substance. Starch from grain is commonly manufactured on the large scale by steeping the mate- rial in water for a considerable period, when the lactic acid, always developed under such circumstances from the sugar of the seed, disintegrates, and in part dissolves the azotized matter, and greatly facilitates the mechanical sepa- ration of that which remains. A still more easy and successful process has lately been introduced, in which a very dilute solution of caustic soda, con- taining about 200 grains of alkali to a gallon of liquid, is employed with the same view. Excellent starch is thus prepared from rice. Starch is insoluble in cold water, as indeed its mode of preparation sufficiently shows; it is equally insoluble in alcohol and other liquids which do not effect its decomposition. To the naked eye it presents the appearance of a soft, white, and often glis- tening powder: under the microscope it is seen to be altogether destitute of crystalline structure, but to possess, on the contrary, a kind of organization, being made up of multitudes of little rounded transparent bodies, upon each of which a series of depressed parallel rings, surrounding a central spot or hilum, may often be traced. The starch-granules from different plants vary both in magnitude and form ; those from the Canna coccinea, or tous les mois, and potato being largest; and those from wheat, and the cereals in general, very DEXTRIN. 357 Pig. 181. much smaller. The figure (181) will serve to convey an idea of the appear- ance of the granules of potato starch, highly mag- nified. AVhen a mixture of starch and water is heated to near the boiling-point of the latter, the granules burst and disappear, producing, if the proportion of starch be considerable, a thick gelatinous mass, very slightly opalescent, from the shreds of fine membrane, the envelop of each separate granule. By the addition of a large quantity of water, this gelatinous starch, or amidin, may be so far diluted as to pass in great measure through filter-paper. It is very doubtful, however, how far the sub- Btance itself is really soluble in water, at least when cold ; it is more likely to be merely sus- pended in the liquid in the form of a swollen, trans- parent, insoluble jelly, of extreme tenuity. Gela- tinous starch, exposed in a thin layer to a dry at- mosphere, becomes converted into a yellowish, horny substance, like gum, which, when put into water, again softens and swells. Thin gelatinous starch is precipitated by many of the metallic oxides, as lime, baryta, and protoxide of lead, and also by a large addition of alcohol. Infusion of galls throws down a copious yellowish precipitate containing tannic acid, which redissolves when the solution is heated. By far the most charac- teristic reaction, however, is that with free iodine, which forms with starch a deep indi^o-blue compound, which appears to dissolve in pure water, although it is insoluble in solutions containing free acid or saline matter. The blue liquid has its color destroyed by heat, temporarily if the heat be quickly with- drawn, and permanently if the boiling be long continued; in which case the compound is decomposed and the iodine volatilized. Starch in the dry state, put into iodine-water, acquires a purplish-black color. The unaltered and the gelatinous starch, in a dried state, have the same composition, namely, C24H2pO20. A compound of starch and protoxide of lead was found to contain, when dried at 212° (100°C), C24H20O20-f- 4PbO. Dextrin.—When gelatinous starch is boiled with a small quantity of dilute sulphuric, hydrochloric, or, indeed, almost any acid, it speedily loses its con- sistency, and becomes thin and limpid, from having suffered conversion into a soluble substance resembling gum, called dextrin.1 The experiment is most conveniently made with sulphuric acid, which may be afterwards withdrawn by saturation with chalk. The liquid filtered from the n'early insoluble gyp- sum may then be evaporated in a water-bath to dryness. The result is a gum- like mass, destitute of crystalline structure, soluble in cold water, and preci- pitable from its solution by alcohol, and capable of combining with protoxide of lead. When the ebullition with the dilute acid is continued for a considerable period, the dextrin first formed undergoes a farther change, and becomes con- verted into grape-sugar, which can be thus artificially produced with the greatest facility. The length of time required for this remarkable change depends upon the quantity of acid present; if the latter be very small, it is necessary to continue the boiling many successive hours, replacing the water which evaporates. With a larger proportion of acid, the conversion is much more speedy. A mixture of 15 parts potato-starch, 60 parts water, and 6 parts sulphuric acid, may be kept boiling for about four hours: the liquid neutralized with chalk, filtered, and rapidly evaporated to a small bulk. By 1 From its action on polarized light, twisting the plane of polarization towards the right hand. 358 INULIN. digestion with animal charcoal, and a second filtration, much of the color will be removed, after which the solution may be boiled down to a thin syrup and left to crystallize: in the course of a few days it solidifies to a mass of grape- sugar. There is another method of preparing this substance from starch, which deserves particular notice. Germinating seeds, and buds in the act of development, are found to contain a small quantity of a peculiar azotized sub- stance, formed at this particular period from the glutin or vegetable albumin- ous matter, to which the name diastase is given. This substance possesses the same curious property of effecting the conversion of starch into dextrin, and ultimately into grape-sugar, and at a much lower temperature than that of ebullition. A little infusion of malt, or germinated barley, in tepid water, mixed with a large quantity of thick gelatinous starch, and the whole main- tained at 160° (71°C). or thereabouts, occasions complete liquefaction in the space of a few minutes from the production of dextrin, which in its turn becomes in three or four hours converted into sugar. If a greater degree of heat be employed, the diastase is coagulated and rendered insoluble and inac- tive. Very little is known respecting diastase itself; it seems very much to- resemble vegetable albumen, but has never been got in a state of purity. The change of starch or dextrin into sugar, whether produced by the action of dilute acid or by diastase, takes place quite independently of the oxygen of the air, and is unaccompanied by any secondary product. The acid takes no direct part in the reaction ; it may, if not volatile, be all withdrawn without loss after tho experiment. The whole reaction lies between the starch and the elements of water; a fixation of the latter occurring in the new product, as will be seen at once on comparing their composition. The sugar, in fact, so produced, very sensibly exceeds in weight the starch employed. Dextrin itself has exactly the same composition as the original starch. Dextrin is used in the arts as a substitute for gum: it is sometimes made in the manner above described, but more frequently by heating dry potato-starch to 400° (204°-5C), by which it acquires a yellowish tint and becomes soluble in cold water. It is sold in this state under the appellation of British Gum. Starch is an important article of food, especially when associated as in ordi- nary meal with albuminous substances. Arrow-root, and the fecula of the Canna coccinea, are very pure varieties, employed as articles of diet: arrow- root is obtained from the Maranta arundinacea, cultivated in the AVest Indies; it is with difficulty distinguished from the potato-starch. Tapioca is prepared from the root of the Ialropha manihot, being thoroughly purified from its poi- sonous juice. Cassava is the same substance modified whilst moist by heat. Sago is made from the soft central portion of the stem of a palm-tree. Starch from Iceland Moss.—The lichen called Cetraria Islandica, purified by a little cold solution of potassa from a bitter principle, yields, when boiled in water, a slimy and nearly colorless liquid, which gelatinizes on cooling, and dries up to a yellowish amorphous mass, which does not dissolve in'cold water, but merely softens and swells. A solution of this substance in warm water is not affected by iodine, although the jelly, on the contrary, is rendered blue. It is precipitated by alcohol, acetate of lead, and infusion of galls, and is converted by boiling with dilute sulphuric acid into grape-sugar. Accord- ing to Mulder, lichen-starch likewise contains C24H20O20. The jelly from cer- tain algae, as that of Ceylon, and the so-called Carragheen moss, closely resem- bles the above. Inulin.— This substance, which differs from common starch in some im- portant particulars, is found in the root of the Inula helenium, the Ilelianlhus luberosus, the dahlia, and several other plants: it may be easily obtained by washing the rasped root on n sieve, and allowing the inulin to settle down from the liquid; or by cutting the root into thin slices, boiling these in water and filtering while hot; the inulin separates as the solution cools. It is a, white, amorphous, tasteless substance, nearly insoluble in cold water but LIGNIN. 359 freely dissolved by tho aid of heat; the solution is precipitated by alcohol, but uot by acetate of lead or infusion of galls. Iodine communicates a brown color. Inulin has been analyzed by Mr. Parnell, who finds it to contain, when dried at 212° (100°C), C24H2I021. Gum.—Gum arabic, which is the produce of several species of acacia, may be taken as the most perfect type of this class of bodies. In its purest and finest condition, it forms white or slightly-yellowish irregular masses, which are destitute of crystalline structure, and break with a smooth conchoidal fracture. It is soluble in cold water, forming a viscid, adhesive, tasteless solution, from which the pure soluble gummy principle, or arabin, is precipi- tated by alcohol and by basic acetate of lead, but not by the neutral acetate.1 Arabin is composed of t,24H22022, and is consequently isomeric with crystallized cane-su^ar. Mucilage, so abundant in linseed, in the roots of the mallow, in salep, the fleshy root of Orchis mascula, and in other plants, differs in some respects from the foregoing, although it agrees in the property of dissolving in cold water. The solution is less transparent than that of gum, and is precipitated by neu- tral acetate of lead. Gum-lragacanth is chiefly composed of a kind of mucilage to which the name bassorin has been given, and which refuses to dissolve in water, merely softening and assuming a gelatinous aspect. It is dissolved by caustic alkali. Cerasin is the term given to the insoluble portion of the gum of the cherry-tree; it resembles bassorin. The composition of those various substances has been carefully examined by M. Schmidt, who finds that it closely agrees with that of starch. Mucilage invariably contains hydrogen and oxygen in the proportion in which they form water, and when treated with acid, yields grape-sugar. Pectin, or the jelly of fruits, is, in its physical properties, closely allied to the foregoing bodies. It may be extracted from various vegetable juices by precipitation by means of alcohol. It forms when moist a transparent jelly, soluble in water, and tasteless, which dries up to-a translucent mass. It is to this substance that the firm consistence of currant- and other fruit-jellies is ascribed. According to M. Fr6my, the composition of pectin is C64H48064. By ebullition with water and with dilute acids it is changed into two isomeric modifications, to which the names parapectin and metapectin have been given. In contact with bases, these three substances become converted into pectic acid, which, except that it possesses feeble acid properties, and is insoluble in water, resembles in the closest manner pectin itself. By long boiling with solution of caustic alkali, a farther change is produced, and a new acid, the metapectic, developed, which does not gelatinize. The salts of these two acids, are incapable of crystallizing. Their composition is represented by the fol- lowing formulae: — Pectic acid.......2HO,C32H20O23 Metapectic acid......2HO,C24H,502S. Much doubt still exists respecting the composition of the various bodies of tho pectin series; they do not appear, from the analyses yet made, to contain oxygen and hydrogen in equal equivalents, and consequently scarcely belong to the starch-group. Lignin; cellulose. — This substance constitutes the fundamental material of tho structure of plants; it is employed in the organization of cells, and vessels of all kinds, and forms a large proportion of the solid parts of every vegetable. It must 'not be confounded with ligneous or woody tissue, which 1 [The precipitate produced by sub-salts of lead is a compound of arabine and oxide of lead, r.'4ll«0w + 2l'b0. By the action of very dilute sulphuric acid arabine is slowly changed into dextrine, and by prolouged contact into glucose. Nitric acid decomposes gum and producos first uiucic and ultimately oxalic acid.—K. B.] 360 OXALIC ACID. is in reality cellulose, with other substances superadded, which encrust the walls of the original membranous cells, and confer stiffness and inflexibility. Thus woody tissue, even when freed as much as possible from coloring matter and resin by repeated boiling with water and alcohol, yields on analysis a result indicating an excess of hydrogen above that required to form water with the oxygen, besides traces of nitrogen. Pure cellulose, on the other hand, is a tertiary compound of carbon and the elements of water, closely allied in composition to starch, if not actually isomeric with that substance.1 The properties of lignin may be conveniently studied in fine linen and cot- ton, which are almost entirely composed of the body in question, the associated vegetable principles having been removed or destroyed by the variety of treat- ment to which the fibre has been subjected. Pure lignin is tasteless, insoluble in water and alcohol, and absolutely innutritious; it is not sensibly affected by boiling water, unless it happens to have been derived from a soft or imper- fectly-developed portion of the plant, in which case it is disintegrated and rendered pulpy. Dilute acids and alkalies exert but little action on lignin, even at a boiling temperature; strong oil of vitriol converts it, in the cold, into a nearly colorless, adhesive substance, which dissolves in water, and pre- sents the characters of dextrin. This curious and interesting experiment may be conveniently made by very slowly adding concentrated sulphuric acid to half its weight of lint, or linen cut into small shreds, taking care to avoid any rise of temperature, which would be attended with charring or blacken- ing. The mixing is completed by trituration in a mortar, and the whole left to stand a few hours; after which it is rubbed up with water, and warmed, and filtered from a little insoluble matter. The solution may then be neutral- ized with chalk, and again filtered. The gummy liquid retains lime, partly in the state of sulphate, and partly in combination with a peculiar acid, com- posed of the elements of sulphuric, in union with those of the lignin, to which the name sulpholignic acid is given. If the liquid, previous to neutralization, be boiled during three or four hours, and the water replaced as it evapo- rates, the dextrin becomes entirely changed to grape-sugar. Linen rags may, by these means, be made to furnish more than their own weight of that substance. Lignin is not^colored by iodine. PRODUCTS ARISING FROM THE ALTERATION OF THE PRECEDING SUBSTANCES BY CHEMICAL AGENTS. ACTION OF NITRIC ACID. Oxalic acid, C203,HO+ 2HO, or 0406,2110 + 4110.—This important com- pound occurs ready-formed in several plants, in combination with potassa as an acid salt, or with lime. It is now manufactured in large quantities as an article of commerce, by the action of nitric acid on sugar, starch, and dextrin. AVith the exception of gum and sugar of milk, which yield another product, all the substances comprehended in the saccharine and starch group furnish oxalic acid, as the chief and characteristic result of the long-continued action of moderately-strong nitric acid at an elevated temperature. One part of sugar is gently heated in a retort with 5 parts of nitric acid of sp. gr. 1 -42, diluted with twice its weight of water; copious red fumes are dis- engaged, and the oxidation of the sugar proceeds with violence and rapidity. When the action slackens, heat may be again applied to the vessel, and the 1 Dumas, Chimie appliquee aux Arts, vi. 5. OXALIC ACID. 361 liquid concentrated, by distilling off the superfluous nitric acid, until it > "* deposits crystals on cooling. These are drained, redissolved in a small quan- tity of hot water, and the solution set aside to cool. The acid separates from a hot solution in colorless, transparent crystals derived from an oblique rhombic prism, which contain three (six) equivalents of water, one (two) of these being basic and inseparable, except by substitution ; the other two (four) may be expelled by a very gentle heat, the crystals crumbling down to a soft white powder, which may be sublimed in great measure without decomposition. The crystallized acid, on the contrary, is decomposed by a high temperature into carbonic and formic acids and carbonic oxide, without leaving any solid residue. The crystals of oxalic acid dissolve in 8 parts of water at 60° (15°-5C), and in their own weight, or less, of hot water; they are also soluble in spirit. The aqueous solution has an intensely sour taste and most powerfully acid reaction, and is highly poisonous. The proper antidote is chalk or magnesia. Oxalic acid is decomposed by hot oil of vitriol into a mixture of carbonic oxide and carbonic acid; it is slowly converted into carbonic acid by nitric acid, whence arises a considerable loss in the process of manufacture. The binox- ides of lead and manganese effect the same change, becoming reduced to prot- oxides, which combine with the unaltered acid. The relation of oxalic acid to sugar is obvious from the following dia- gram : — 1 eq. sugar = C24II180,9) f 12 eq. oxalic acid = C24 0^ 30 ex. oxygen =______0^ J ~~ \18 eq. water = H180,8 ^24lli8^54 C24H18054 The most important salts of oxalic acids are the following — Neutral oxalate of potassa, KO,C203-f- III).—This is prepared by neu- tralizing oxalic acid by carbonate of potassa. It crystallizes in transparent rhombic prisms, which become opaque and anhydrous by heat, and dissolve in 3 parts of water. Oxalate of potassa is often produced when a variety of organic substances are cautiously heated with excess of caustic alkali. Binoxalate of potassa, KO,2C203-t- 3110. — Sometimes called.sail of sor- rel, from its occurrence in that plant. This, or the substance next to be men- tioned, is found also in the rumex and oxalis acelosella, and in the garden rhu- barb, associated with malic acid. It is easily prepared by dividing a solution of oxalic acid, in hot water, into two equal portions, neutralizing one with carbonate of potassa, and adding the other; the salt crystallizes, on cooling, in colorless rhombic prisms. The crystals have a sour taste, and require 40 parts of cold, and 6 of boiling water for solution. Quadroxalate of potassa, KO,4C203-}- 7110.—Prepared by a process similar in principle to that last described. The crystals are modified octahe- dra, and are less soluble than those of the binoxalate, which the salt in other respects resembles. Oxalate of soda, NaO,C203, has but little solubility ; a binoxalate exists. Oxalate of ammonia, NI140,C203 -|- HO. — This beautiful salt is prepared by neutralizing by carbonate of ammonia a hot solution of oxalic acid. It crystallizes in long, colorless, rhombic prisms, which effloresce in dry air from loss of water of crystallization. They are not very soluble in cold water, but freely dissolve by the aid of heat. Oxalate of ammonia is of great value in analytical chemistry, being employed to precipitate lime from its solutions. When oxalate of ammonia is heated in a retort, it is completely decomposed, yielding water, ammonia and carbonate of ammonia, cyanogen and carbonic acid gases, anil a small quantity of a peculiar grayish-white sublimate. The latter bears the name of oxamide; it is a very remarkable body, and forms the tvpe of a large class of substances containing the elements of an ammoniacal 31 862 SACCHARIC ACID. salt, minus those of water. Oxamide is composed of C2TT2N02, i- e., NIT40, C203 — 2HO, or the elements of 1 eq. amidogen, and 2 eq. carbonic oxide. It is insoluble in water and alcohol: when boiled with an alkali it furnishes an oxalate of the base, and ammonia, which is expelledf and when heated with an acid, it produces an ammoniacal salt. When treated with nitrous acid it likewise reproduces oxalic acid, pure nitrogen being evolved, C2H2N02 -f- NO, = C203,HO -f- HO -f- 2N. Oxamide is the representative of a tolerably large class of bodies having very analogous chemical relations, and apparently*^ common constitution. Oxamide is obtained purer and more abundantly from oxalic ether; its preparation will be found described under the head of that substance. Oxalate of ammonia, when distilled with anhydrous phosphoric acid, loses four equivalents of water, and yields a considerable quantity of cyanogen, NH40,C203 — 4HO = C2N. There are, however, other compounds simultaneously produced. The binoxalate of ammonia is still less soluble than the oxalate. AVhen this salt is heated in an oil-bath to 450° (232°-2C), among other products an acid called the oxamic is generated, containing C4H2N05,HO, i. e., NH40,C203-f HO, C^Oj — 2HO, and may be viewed as a compound of oxalic acid with oxamide. It forms soluble compounds with lime and baryta. AVhen heated with alka- lies it yields ammonia and an oxalate; hot oil of vitriol resolves it into car- bonic oxide and carbonic acid; and water converts it, at a boiling tempera- ture, into binoxalate of ammonia. Oxamic acid, too, is interesting as the type of a very large class of similarly-constructed compounds. Oxalate of lime, CaO,C203 -f- 2HO.—This compound is formed whenever oxalic acid or an oxalate is added to a soluble salt of lime ; it falls as a white powder, which acquires density by boiling, and is but little soluble in dilute hydrochloric, and entirely insoluble in acetic acid. Nitric acid dissolves it easily. When dried at 212° (100°C) it retains an equivalent of water, which may be driven off by a rather higher temperature. Exposed to a red heat in a close vessel, it is converted into carbonate of lime, with escape of carbonic oxide. The oxalates of baryta, zinc, manganese, protoxide of iron, copper, nickel, and cobalt, are nearly insoluble in water; that of magnesia is sparingly soluble, and that of the sesquioxide of iron freely soluble. The double oxalate of chro- mium and potassium, made by dissolving in hot water 1 part bichromate of potassa, 2 parts binoxalate of potassa, and 2 parts crystallized oxalic acid, is one of the most beautiful salts known. The crystals appear black by reflected light from the intensity of their color, which is pure deep blue : they are very soluble. The salt contains 3(KO,C203), -f- Cr203,3C203 + 6IIO. A corres- ponding compound containing sesquioxide of iron has been formed ; it crystal- lizes freely, and has a beautiful green color. Saccharic acid, C6II407,HO. — This substance was once thought to be identical with malic acid, which is not the case: it is formed by the action of dilute nitric acid on sugar, and is often produced in the preparation of oxalic acid, being, from its superior solubility, found in the mother-liquor from which the oxalic acid has crystallized. It may be made by heating together 1 part sugar, 2 parts nitric acid, and 10 parts water. AVhen the reaction seems terminated, the acid liquid is diluted, neutralized with chalk, and the filtered liquid mixed with acetate of lead. The insoluble saccharate of lead is washed, and decomposed by sulphuretted hydrogen. The acid slowly crystallizes from a solution of syrupy consistence in long colorless needles; it has a sour taste, and forms soluble salts with lime and baryta. AVhen mixed with nitrate of silver, it gives no precipitate, but, on the addition of ammonia, a white insoluble substance separates, which is reduced, by gently warming the whole, to metallic silver, the vessel being lined with a smooth and. brilliant coating of the metal. Nitric acid converts the saccharic into oxalic acid. MELLITIC ACID. 363 Xyloidin and pyroxylin.—AVhen starch is mixed with nitric acid of specific gravity 1 G. it is converted without disengagement of gas, into a transparent, colorless jelly, which, when put into water, yields a white, curdy, insoluble substance: this is the new body xyloidin. AVhen dry, it is white and tasteless, insoluble even in boiling water, but freely dissolved by dilute nitric acid, and the solution yields oxalic acid when boiled. Other substances belonging to the same class also yield xyloidin; paper dipped into the strongest nitric acid, quickly plunged into water, and afterwards dried, becomes in great part bo changed: it assumes the appearance of parchment, and acquires an extra- ordinary degree of combustibility. If pure finely-divided ligneous matter, as cotton-wool, be steeped for a few minutes in a mixture of nitric acid of sp. gr. 1-5 and concentrated sulphuric acid, squeezed, thoroughly washed and dried by very gentle heat, it will be found to have increased in weight about 70 per cent., and to have become in the highest degree explosive, taking fire at a temperature not much above 300° (148°-8C), and burning without smoke or residue. This is pyroxylin, the gun-cotton of Professor Schoenbein. Two modifications of pyroxylin are known; the one is insoluble in a mixture of ether and alcohol, whilst the other is readily dissolved. To a solution of this description the name collo- dion has been given; it is largely used in photography and occasionally in surgery. Both xyloidin and pyroxylin appear to be substitution-compounds, in which the elements of hyponitric acid replace respectively 1, 2, or 3 equivalents of hydrogen in starch and lignin. The analytical results are not very uniform, but the formulae which best agree with them arc, xyloidin C12H9N014 = C12(II9,NO4)Ow,andpyroxylinC12II8N2O,8 = C)2[H8,(NO4)2]O10andC12H7N3O22 = t'«["7-(ND4),]O10. _ . An analogous compound is produced by the action of nitric acid upon mannite (vide p. 356). This substance may be crystallized from spirit, and contains C6II4N()18; it may be viewed as mannite, in which three equivalents of hydrogen are replaced by hyponitric acid. Mucic acid, C12[I80,4.2HO. — Sugar of milk and gum, heated with nitric acid, somewhat diluted, furnish, in addition to a small quantity of oxalic acid, a white and nearly insoluble substance called mucic acid. It may be easily prepared by heating together in a flask or retort 1 part of milk-sugar, or guin, 1 parts of nitric acid, and 1 of water; the mucic acid is afterwards col- lected upon a filter, washed and dried. It has a slightly-sour taste, reddens vegetable colors, and forms salts with bases. It requires for solution 66 parts of boiling water. Oil of vitriol dissolves it with production of a red color. Mucic acid is decomposed by heat, yielding, among other products, a volatile acid, the pyromucic, which is soluble in water, and crystallizes in a form re- sembling that of benzoic acid. Pyromucic acid is monobasic; it contains C10H3O6,HO. Subeiuc acid, C,6H)206,2HO, is formed by the action of nitric acid on the peculiar ligneous matter of cork, and also on certain fatty bodies; it much resembles mucic acid, but is more soluble in water. It is a bibasic acid. See further on, the section on Oils and Fats. . The following bodies are closely allied in composition to oxalic acids: — Mellitio acid, C403,1IO.—This substance occurs in combination with alu- mina, in a very rare mineral called mellite or honey-stone, found in deposits of lignite. It is soluble in water and alcohol, and is crystallizable, forming color- less needles. It combines with bases : the mellitates of the alkalies are solu- ble and crystallizable; those of the earths and metals proper are mostly insoluble. Alellitato of ammonia yields by distillation two curious compounds, para- wide and euchronic acid. " The former is a white, amorphous, insoluble sub- btance, containing C8HN04, (»'. e., bimcllitatc of ammonia —4 eq. of water), 364 FERMENTATION OF SUGAR. and convertible by boiling with water into bimellitatc of ammonia. Tic latter forms colorless, sparingly-soluble crystals, containing in the anhydrous state Ci2N06,2HO. In contact with metallic zinc and deoxidizing agents in general, euchronic acid yields a deep-blue insoluble substance called euchrone. Bhodizonic and croconic acids. — AVhen potassium is heated in a stream of dry carbonic oxide gas, the latter is absorbed in large quantity, and a black porous substance generated, which, when put into water, evolves in- flammable gas, and produces a deep-red solution containing the potassa-salt of a peculiar acid, the rhodizonic: by adding alcohol to the liquid, the rhodi- zonate of potassa is precipitated. This and the lead-salt are the only two compounds which have been fully examined; the acid itself cannot be iso- lated. Bhodizonate of potassa is composed of C707.3KO ; hence the acid would appear to be tribasic. When solution of rhodizonate of potassa is boiled, it becomes orange-yellow from decomposition of the acid, and is then found to contain oxalate of potassa, free potassa, and a salt of an acid to which the term croconic is applied. This acid can be isolated; it is yellow, easily crystallizable, and soluble both in water and alcohol. Crystallized croconic acid contains C604,HO. THE FERMENTATION OF SUGAR AND ITS rBODUCTS. The term fermentation is applied in chemistry to a peculiar metamorphosis of a complex organic substance, by a transposition of its elements under the agency of an external disturbing force, different from ordinary chemical attraction, and more resembling those obscure phenomena of contact already noticed, to which the expression kalalysis is sometimes applied. The expla- nation which Liebig has suggested of the cause and nature of the fermenta- tive change is a very happy one, although of necessity only hypothetical. It has long been known that one of the most indispensable conditions of that process is the presence in the fermenting liquid of certain azotized substances, called ferments, whose decomposition proceeds simultaneously with that of the body undergoing metamorphosis. They all belong to the class of albuminous principles, bodies which in a moist condition putrefy and decompose spontane- ously. It is imagined that when these substances, in the act of undergoing change,-are brought into contact with neutral ternary compounds of slight stability, as sugar, the molecular disturbance of the body, already in a state of decomposition, may be, as it were, propagated to the other, and bring about destruction of the equilibrium of forces to which it owes its being. The complex body, under these circumstances, breaks up into simpler pro- ducts, which possess greater permanence. AVhatever may be the ultimate fate of this ingenious hypothesis, it is certain that decomposing azotized bodies not only do possess very energetic and extraordinary powers of exciting fermenta- tion, but that the kind of fermentation set up is, in a great degree, dependent on the phase or stage of decomposition of the ferment. Alcohol ; vinous fermentation.—A solution of pure sugar, in an open or close vessel, may be preserved unaltered for any length of time; but, if pu- trescible azotized matters be present, in the proper state of decay, the susrar is converted into alcohol, with escape of carbonic acid. Putrid blood, white of egg, or flour-paste, will effect this._ By far the most potent alcoholic fer- ment is, however, to be found in the insoluble, yellowish, viscid matter depo- sited from beer in the act of fermentation, called yeast. If the sugar be dis- solved in a large quantity of water, a due proportion of active yeast added and the whole maintained at a temperature of 70° (21°-1C) or 80° (26°-6C) the change will go on with great rapidity. The gas disengaged will be found to be nearly pure carbonic acid; it is easily collected and examined, as tho fermentation, once commenced, proceeds perfectly well in a close vessel as a large bottle or flask, fitted Avith a cork and conducting-tube. AVhen the efi'er- FERMENTATION OF SUGAR. 365 vescence is at an end, and the liquid has become clear, it will yield alcohol by instillation. Such is the origin of this important compound; it is a product of the metamorphosis of sugar, under the influence of a ferment. The composition of alcohol is expressed by the formula C4H602 ; it is pro- duced by the breaking up of an equivalent of grape-sugar, C24H28028, into 4 eq. of alcohol, 8 of carbonic acid, and 4 of water. It is grape-sugar alone which yields alcohol, the ferment in the experiment above related first con- verting the cane-sugar into that substance. Milk-sugar may sometimes appa- rently be made to ferment; but a change into grape-sugar always really pre- cedes the production of alcohol. The spirit first obtained by distilling a fermented saccharine liquid is very weak, being diluted with a large quantity of water. By a second distillation, in which the first portions of the distilled liquid are collected apart, it may be greatly strengthened: the whole of the water cannot, however be thus re- moved. The strongest rectified spirit of wine of commerce has a density of about 0-83-3, and yet contains 13 or 14 per cent, of water. Pure or absolute alcohol may be obtained from this by redistilling it with half its weight of fresh quicklime. The lime is reduced to coarse powder, and put into a retort; the alcohol is added, and the whole mixed by agitation. The neck of the retort is securely stopped with a cork, and the mixture left for several days. The alcohol is distilled off by the heat of a water-bath. Pure alcohol is a colorless, limpid liquid, of pungent and agreeable taste and odor; its specific gravity at 60° (15°-5C) is 0-7938, and that of its vapor 1-613. It is very inflammable, burning with a pale-bluish flame, free from smoke: it has never been frozen. Alcohol boils at 173° (78°-4C) when in the anhydrous condition; in a diluted state, the boiling-point is higher, being progressively raised by each addition of water. In the act of dilution a contraction of volume occurs, and the temperature of the mixture rises many degrees : this takes place not only with pure alcohol, but with rectified spirit. It is miscible with water in all proportions, and, indeed, has a great attraction for the latter, absorbing its vapor from the air, and abstracting the moisture from mem- branes and other similar substances immersed in it. The solvent powers of alcohol are very extensive ; it dissolves a great number of saline compounds, and likewise a considerable proportion of potassa. With many of these sub- stances it forms definite compounds. The substance which is produced by potassa contains C4HsO.KO; it may be likewise formed by acting with potas- sium upon anhydrous alcohol, when hydrogen is evolved. Alcohol dissolves, moreover, many organic substances, as the vegeto-alkalies, resins, essential oils, and various other bodies; hence its great use in chemical investigations and in several of the arts. The strength of commercial spirit is inferred from its density, when free from sugar and other substances added subsequent to distillation; a table ex- hibiting the proportions of real alcohol and water in spirits of different den- sities will be found at the end of the volume. The excise proof spirit has a sp. gr. of 0 9108 at 00° (15°-5C), and contains 49£ per cent, by weight of real alcohol. Methylated Spirit is a mixture of 90 per cent, of spirits and 10 per cent, of wood spirit. (See Wood Spirit.)1 1 The high duty on spirits of wine iu Great Britain, has hitherto interfered with the deve- lopment of many branches of industry, which aro dependent on the free use of this important liquid. The labors of the scientific chemist have been likewise often checked by this inconve- nience. A remedy for the evil has been supplied by a very important measure proposed and carried out by the late .Mr. John Moot/, Chairman of the Board of Inland lievenue. This mea- sure consists in issuing for manufacturing and scientific purposes, duty free, a mixture of 90 per rent, of spirits of wine of not less strength than corresponds to a density of 0-S30 with 10 per cent, of purified wood spirit, which is now sold by licensed dealers under the name of Me.- tlii/hiled Spirit. It appears that a mixture of this kind is rendered permanently unfit for human consumption, the separation of the two substances, in consequence of their close analogy, being not only difficult, but lo all appearance impossible; at the same time, and for the same reasons, this mixture is not materially impaired for the greater number of the more valuable purposes 366 ALCOHOL. AVine, beer, &c, owe their intoxicating properties to the alcohol they con- tain, the quantity of which varies very much. Port and sherry, and some other strong wines, contain, according to Mr. Brande, from 19 to 25 per cent, of alcohol, while in the lighter wines of France and Germany it sometimes fulls as low as'l2 per cent. Strong ale contains about 10 per cent. ; ordinary spi- rits, as brandy, gin, whisky, 40 to 50 per cent., or occasionally more. These latter owe their characteristic flavors to certain essential oils, present in very small quantity, either generated in the act of fermentation or purposely added. In making wine, the expressed juice of the grape is simply set aside in large vats, where it undergoes spontaneously the necessary change. The vegetable albumin of the juice absorbs oxygen from the air, runs into decomposition, and in that state becomes a ferment to the sugar, which is gradually con- verted into alcohol. If the sugar be in excess, and the azotized matter defi- cient, the resulting Avine remains sweet; but if, on the other hand, the pro- portion of sugar be small, and that of-albumin large, a d?y wine is produced. When the fermentation stops, and the liquor becomes clear, it is drawn off from the lees, and transferred to casks, to ripen and improve. The color of red wine is derived from the skins of the grapes, which in such cases are left in the fermenting liquid. Effervescent wines, as champagne, are bottled before the fermentation is complete; the carbonic acid is disen- gaged underpressure, and retained in solution in the liquid. A certain quan- tity of sugar is frequently added. The process requires much delicate ma- nagement. During the fermentation of the grape-juice, or must, a crystalline, stony matter, called argol, is deposited. This consists chiefly of acid tartrate of potassa, with a little tartrate of lime and coloring matter, and is the source of all the tartaric acid met with in commerce. The salt in question exists in the juice in considerable quantity; it is but sparingly soluble in water, but still less so in dilute alcohol; hence, as the fermentation proceeds, and the quan- tity of spirit increases, it is slowly deposited. The acid of the juice is thus removed as the sugar disappears. It is this circumstance which renders grape-juice alone fit for making good wine; when that of gooseberries or cur- rants is employed as a substitute, the malic and citric acids which these fruits contain cannot be thus withdrawn. There is, then, no other resource but to add sugar in sufficient quantity to mask and conceal the natural acidity of the liquor. Such wines are necessarily ascescent, prone to a second fermentation, and, to many persons at least, very unwholesome. Beer is a well-known liquor, of great antiquity, prepared from germinated grain, generally barley, and is used in countries where the vine does not flou- rish. The operation of malting is performed by steeping the barley in water until the grains become swollen and soft, then piling it in a' heap or couch, to favor the elevation of temperature caused by the absorption of oxygen from the air, and afterwards spreading it upon a floor, and turning it over from time to time, to prevent unequal heating. AVhen germination has proceeded far enough, the vitality of the seed is destroyed by kiln-drying. During this process, the curious substance already referred to, diastase, is produced, and a portion of the starch of the grain converted into sugar, and rendered soluble. In brewing, the crushed malt is infused in water at about 170° (76°-6C), in the arts for which spirits are usually employed. Methylated spirit may be used, instead of pure spirit, as a solvent of resinous substancea, as a solvent employed in the manufacture of many chemical preparations, especially of the alkaloids and other organic products. It may be used for the production of fulminating mercury, of ether, of chloroform, iodoform, olefiant gas and all it* derivatives—in fact, for an endless number of laboratory purposes. Methylated spirits may be substituted for pure spirits in the preservation of anatomical preparations. The introduction of this spirit has already exerted a very beneficial effect upon the development of organic chemistry in Great Britain. !-'<•<: Report on the Supply of Spirits of Wine, free from duty, for use in the Arts and Mat.n factures, addressed to the Chairman of Inland Revenue, by Professors Graham, Ilofmanu., ai.d Redwood. Quarterly Journal of Chemical Society, vol. viii. p. 120. ALCOHOL. 367 and the mixture left to stand during the space of two hours or more. The easily soluble diastase has thus an opportunity of acting upon the unaltered starch of the grain, and changing it into dextrin and sugar. The clear liquor, or wort, strained from the exhausted malt, is next pumped up into a copper boiler, and boiled with the requisite quantity of hops, for communicating a pleasant bitter flavor, and conferring on the beer the property of keeping with- out injury. The flowers of the hop contain a bitter, resinous principle, called lupulin, and an essential oil, both of which are useful. When the wort has been sufficiently boiled, it is drawn from the copper, and cooled, as rapidly as possible, to near the ordinary temperature of the air, in order to avoid an irregular acid fermentation, to which it would other- wise be liable. It is then transferred to the fermenting vessels, which in large breweries are of great capacity, and mixed with a quantity of yeast, the pro- duct of a preceding operation, by which the change is speedily induced. This is the most critical part of the whole operation, and one in which the skill and judgment of the brewer are most called into play. The process is in some measure under control by attention to the temperature of the liquid; and the extent to which the change has been carried is easily known by the diminished density, or attenuation, of the wort. The fermentation is never suffered to run its fulf course, but is always stopped at a particular point, by separating the yeast, and drawing off the beer into casks. A slow and almost insensible fermentation succeeds, which in time renders the beer stronger and less sweet than when new, and charges it with carbonic acid. Highly-colored beer 'is made by adding to the malt a small quantity of strongly-dried or charred malt, the sugar of which has been changed to cara- mel : porter and stout are so prepared. The yeast of beer is a very remarkable substance, and has excited much attention. To the naked eye it is a grayish-yellow soft solid, nearly insoluble in water, and dries up to a pale-brownish mass, which readily putrefies when moistened, and becomes offensive. Under the microscope it exhibits a kind of organized appearance, being made up of little transparent globules, which sometimes cohere in clusters or strings, like some of the lowest members of the vegetable kingdom. AVhatever may be the real nature of the substance, no doubt can exist that it is formed from the soluble azotized portion of the grain during the fermentative process. No yeast is ever produced in liquids free from azotized matter; that added for the purpose of exciting fermenta- tion in pure sugar is destroyed, and rendered inert thereby. AVhen yeast is deprived, by straining and strong pressure, of as much water as possible, it may be kept in a cool place, with unaltered properties, for a long time; other- wise it speedily spoils. The distiller, who prepares spirits from grain, makes his wort, or wash, much in the same manner as the brewer; he uses, however, with the malt a large quantity of raw grain, the starch of which suffers conversion into sugar by the diastase of the malt, which is sufficient for his purpose. He does not boil his infusion with hops, but proceeds at once to the fermentation, which he pushes as far as possible by large and repeated doses of yeast. Alcohol is manufactured in many cases from potatoes: the potatoes are ground to pulp, mixed with hot water, and a little malt, to furnish diastase, made to ferment, and then the fluid portion distilled. The potato-spirit is contami- nated by a very offensive volatile oil, again to be mentioned; the crude pro- duct from corn contains a substance of a similar kind. The business of the rectifier consists in removing or modifying these volatile oils, and in replacing them by others of a more agreeable character. In making bread, the vinous fermentation plays an important part; the yeast added to the dough converts the small portion of sugar the meal naturally contains into aleoliol and carbonic acid. The gas thus disengaged forces the tough and adhesive materials into bubbles, which are still further 368 LACTIC ACID. expanded by the heat of the oven, which at the same time dissipates the alco hoi; hence the light and spongy texture of all good bread. Sometimes car bonate of ammonia is employed with the same view, being completely volatil- ized by the high temperature of the oven. Bread is now sometimes made by mixing a little hydrochloric acid and carbonate of soda in the dough ; if proper proportions be taken, and the whole thoroughly mixed, the operation appears to be very successful. The use of leaven is one of great antiquity: this is merely dough in a state of incipient putrefaction. AVhen mixed with a large quantity of fresh dough, it excites in the latter the alcoholic fermen- tation, in the same manner as yeast, but less perfectly; it is apt to communi- cate a disagreeable sour taste and odor. Lactic acid; lactic acid fermentation ; butyric acid fermentation.—• Azotized albuminous substances, which in an advanced state of putrefactive change act as alcohol-ferments, often possess, at certain periods of decay, the property of inducing an acid fermentation in sugar, the consequence of which is the conversion of that substance into lactic acid. Thus, the azotized matter of malt, when suffered to putrefy in water for a few days, acquires the power of acidifying the sugar which accompanies it, while in a more advanced state of decomposition it converts, under similar circumstances, the sugar into alcohol. The glutin of grain behaves in the same manner: wheat flour, made into a paste with water, and left four or five days in a warm situation, becomes a true lactic acid ferment: if left a day or two longer, it changes its character, and then acts like common yeast. Moist animal membranes, in a slightly- decaying condition, often act energetically in developing lactic acid. Cane-sugar, probably by previously becoming grape-sugar, and the sugar of milk, both yield lactic acid, the latter, however, most readily, the grape- sugar having a strong tendency towards the alcoholic change. A good method of preparing lactic acid is the following. An addition quantity of milk-sugar is dissolved in ordinary milk, which is then set aside in a warm place, until it becomes sour and coagulated. The casein of the milk absorbs oxygen from the air, runs into putrefaction, and acidifies a portion of the sugar. The lactic acid formed, after a time coagulates and renders insoluble the casein, and the production of that acid ceases. By carefully neutralizing, however, the free acid by carbonate of soda, the casein becomes soluble, and resuming its activity, changes a fresh quantity of sugar into lactic acid, which may be also neutralized, and by a sufficient number of repetitions of this process all the sugar of milk present may, in time, be acidified. AVhen this has taken place, the liquid is boiled, filtered, and evaporated to dryness in a water-bath. The residue is treated with hot alcohol, which dissolves out the lactate of soda. The alcoholic .solution may then be decomposed by the cautious addition of sulphuric acid, which precipitates sulphate of soda, insoluble in spirit. The free acid may, if needful, be neutralized with lime, and the re- sulting salt purified by recrystallization and the use of animal charcoal, after which it may be decomposed by oxalic acid. The following process will be found more economical on a large scale: A mixture is made of two gallons of milk, which may be stale or skimmed milk, six pounds of raw sugar, twelve pints of water, eight ounces of putrid cheese, and four pounds of chalk, which should be mixed up to a creamy consistence with some of the liquid. This mixture is exposed in a loosely-covered jar to a temperature of about 86° (30°C), with occasional stirring. At the end of two or three weeks it will be found converted into a semi-solid mass of lactate of lime, which may be drained, pressed, and purified by re-crystallization from water. The lactate of lime may be decomposed by the necessary quantity of pure oxalic acid, the filtered liquor neutralized with carbonate of zinc, and, after a second filtration, evaporated until the zinc-salt crystallizes out on cooling. LACTIC ACID. 369 The latter may, lastly, be re-dissolved in water, and decomposed by sulphu- retted hydrogen, in order to obtain the free acid. If in the first part of the process the solid lactate of lime be not removed at the proper period from the fermenting liquid, it will gradually re-dissolve and disappear. On examination the liquid will then be found to consist chiefly of a solution of butyrale of lime. This second stage of the process, to which the name of butyric acid fermen- tation has been given, is attended with an evolution of hydrogen and carbonic acid. It will be mentioned more in detail under the head of butyric acid. Lactic acid may be extracted from a great variety of liquids containing de- composing organic matter, as sauerkraut, a preparation of white cabbage; the sour liquor of the starch-maker, &c. It has been supposed to exist in the blood, urine, and other animal fluids. Most careful researches have, however, failed to detect it in either blood or urine, although it has been shown by Lie- big to exist in considerable quantity in the juice of flesh or muscle. Lactic acid has been produced artificially in a most remarkable manner by the action of nitrous acid upon alanine. (See the Section on Organic Bases.) Quite recently it has been produced by the oxidation of propyl-glycol. (See further on.) Solution of lactic acid may be concentrated in the vacuum of the air-pump, over a surface of oil of vitriol, until it appears as a colorless, syrupy liquid, of sp. gr. 1-215. It has an intensely-sour taste and acid reaction ; it is hy- groscopic, and very soluble in water, alcohol, and ether. It forms soluble salts with all the metallic oxides. The syrupy acid contains C6H505+HO, the water being basic, and susceptible of replacement by a metallic oxide. AVhen syrupy lactic acid is heated in a retort to 266° (130°C), water con- taining a little lactic acid distils over, and the residue on cooling forms a yel- lowish solid fusible mass, very bitter, and nearly insoluble in water. This is anhydrous lactic acid, C6H505. Long-continued boiling with water converts it into ordinary lactic acid. AVhen this substance is further heated it decom- poses, yielding numerous products. One of these is lactide, formerly errone- ously called anhydrous lactic acid, a volatile substance, crystallizing in brilliant colorless rhombic plates, which, when put into water, slowly dissolve, with production of common lactic acid. Lactide contains C6H404; it combines with ammonia, forming lactamide, C6II7N04, a colorless, crystallizable, soluble substance, resembling in its chemical relations oxamide. Another product of the action of heat on lactic acid is lactone, a colorless volatile liquid, boil- ing atl98° (92°-2C). Acetone is also formed, and carbonic oxide and carbo- nic acid arc disengaged. _ A salt of lactic acid, gently heated with five or six parts of oil of vitriol, yields an enormous quantity of perfectly pure carbonic oxide gas. The most important and characteristic of the lactates are those of lime and the oxide of zinc. Lactate of Lime, CaO, C6H505-f 5HO, exists ready-formed, to a small extent, in Nux vomica, AVhen pure, it crystallizes in tufts of minute white needles grouped in concentric layers. It dissolves in 10 parts of cold, and in- definitely in boiling water, melting in its water of crystallization at that tem- perature. Lactate of zinc, ZnO,C6H,;06-f- 3HO, is deposited from a hot solution in small brilliant -1-sided prismatic crystals, which require for solution 58 parts of cold and 6 of boiling water. Lactate of protoxide of iron, FeO,C6Hs064- 3IIO, is now used in medi- cine. It is prepared by adding alcohol to a mixture of lactate of ammonia and protochloride of iron, when the salt is precipitated in the form of small yellowish needles. When the expressed juice of the beet is exposed to a temperature of 90° (32°-9C) or 100° (37°-7C) for a considerable time, the sugar it contains suffers 370 ETHER. a peculiar kind of fermentation, to which the term viscous has been applied. Gases are evolved which contain hydrogen, and when the change appears complete, and the products come to be examined, the sugar is found to have disappeared. Mere traces of alcohol are produced; but, in place of that substance, a quantity of lactic acid, mannite, and a mucilaginous substance resembling gum-arabic, and said to be identical with gum in composition. Pure sugar can be converted into this substance : by boiling yeast or the glutin of wheat in water, dissolving sugar in the filtered solution, and exposing it to a tolerably high temperature, the viscous fermentation is set up, and a large quantity of the gummy principle generated. A little gas is at the same time disengaged, which is a mixture of carbonic acid and hydrogen. products of the action of acids on alcohol. Ether; oxide of ethyl.—When equal weights of rectified spirit and oil of vitriol are mixed in a retort, the latter connected with a good condensing arrangement, and the liquid heated to ebullition, a colorless and highly-vola- tile liquid, long known under the name of ether, or sulphuric ether, distils over. The process must be stopped as soon as the contents of the retort blacken and froth, otherwise the product will be contaminated with other substances, which then make their appearance. The ether obtained may.be mixed with a little caustic potassa, and re-distilled by a very gentle heat. Pure ether is a colorless, transparent, fragrant liquid, very thin and mobile. Its sp. gr. at 60° (15°-5C) is about 0-720; it boils at 96° (35°-5C) under the pressure of the atmosphere, and bears without freezing the severest cold. AVhen dropped on the hand it occasions a sharp sensation of cold, from its rapid volatilization. Ether is very combustible; it burns with a white flame, generating water and carbonic acid. Although the substance itself is one of the lightest of liquids, its vapor is very heavy, having a density of 2-586. Mixed with oxygen gas, and fired by the electric spark, or otherwise, it ex- plodes with the utmost violence. Preserved in an imperfectly-stopped vessel, ether absorbs oxygen, and becomes acid from the production of acetic acid: this attraction for oxygen is increased by elevation of temperature. It is de- composed by transmission through a red-hot tube into olefiant gas, light car- bonetted hydrogen, and a substance yet to be described, aldehyde. Ether is miscible with alcohol in all proportions, but not with water; it dis- solves to a small extent in that liquid, 10 parts of water taking up 1 part, or thereabouts, of ether. It may be separated from alcohol, provided the quantity of the latter be not excessive, by an addition of water, and in this manner samples of commercial ether may be conveniently examined. Ether is a solvent for oily and fatty substances generally, and phosphorus to a small extent, a few saline compounds and some organic principles, but its powers in this respect are much more limited than those of alcohol or water. Ether was the first of a great number of analogous substances in which the property of producing temporary insensibility to pain was recognised. In surgical operations, the use of ether is now superseded by that of chloroform. Ether is found by analysis to contain C4H60; it therefore differs from alco- hol, C4H602, by the elements of water. Alcohol is often regarded as the hydrate of ether; but as ether cannot be made to combine with water directly, and as alcohol cannot be converted into ether by the abstraction of water by the aid of substances known to possess a strong affinity for that body, such a view was always looked upon as hypothetical. Recent experiments have, in fact, shown that a very different relation exists between alcohol and ether. COMPOUND ETHERS. 371 AVe shall return to these researches when we consider the theory of the pro- duction of ether, which will bo discussed partly in connection with the history of sulphovinic acid, and partly with that of the methyl-compounds. Compound ethers; etiiye-tiieort; ethyl.—The so-called compound ethers constitute a very large and important class of substances derived from alco- hol, and containing either the elements of ether, in combination with those of an oxygen-acid, inorganic or organic, or the elements of olefiant gas in union with those of a hydrogen-acid. The relations of these compounds to alcohol and the acids are most simply and clearly illustrated by comparing them with ordinary salts, in which the metal is replaced by a salt-basyle, termed ethyl, containing C4II5. This substance forms haloid-salts by combining with chlo- rine, iodine, bromine, &c, and its oxide, identical or isomeric with common ether, with oxygen-acids, like basic metallic oxides in general. A body con- taining carbon and hydrogen in the proportions indicated by the formula ('4I15, has been obtained by Dr. Frankland, from one of the members of this group of compounds, and described under the name of ethyl. It is formed by exposing dry iodide of- ethyl, in sealed tubes, for several hours, to the action of finely-divided metallic zinc, at a temperature of from 320° (160°C) to 338° (170°). In this reaction, the iodine of the iodide of ethyl, C4H5T, combines with the zinc, and ethyl is set free. On opening the sealed tubes, and allowing the gas, which is ethyl mixed with several secondary products (especially olefiant gas), to pass into a freezing mixture, the temperature of which is kept below -9a (-23°C), the ethyl condenses to a colorless mobile liquid. It is not attacked by concentrated sulphuric and nitric acids. Chlorine acts upon it under the influence of light but not in the dark. Hitherto no compound ether has been reproduced from ethyl. The ethyl-theory, proposed by Liebig long before the separation of ethyl itself, will be found very useful as an aid to the memory ; it must not, however, be forgotten that the compound ethers are distinguished by important characters from real and undoubted salts. Table of Ethyl-Compounds. Ethyl, symbol Ae .... C4H-5 Oxide of ethyl; ether . C4H60 Hydrate of the oxide; alcohol C4II50,HO Chloride of ethyl .... . C4H5C1 Bromide of ethyl .... C.li6Br Iodide of ethyl .... 3 Hydride of ethyl .... C4H5II Zinc-ethyl ...... 0. „ C. „ C4H6Zn &c, &c. The ethers of many of the acids may be formed by the direct action of the latter upon alcohol at a high temperature, the elements of water being dis- placed by those of the acid: this is chiefly conspicuous with the volatile acids. A more ready general method of forming them, however, is to distil a mix- ture of alcohol, sulphuric acid, and a salt of the acid the ether of which is required. The fatty acids, which in general cannot be distilled without more or less decomposition, yield their ethers with great facility by the action of hydrochloric acid gas upon an alcoholic solution of the acid. The compound ethers are mostly volatile aromatic liquids, in a few cases crystallizable solids, without action on vegetable colors, sparingly soluble in 372 CO M POUND ETHERS. water, but dissolved in all proportions by alcohol and ether. They are not acted upon in the cold by alkaline carbonates, but suffer decomposition with more or less difficulty when heated with aqueous solutions of caustic alkali, a salt of the acid of the ether being usually generated, and alcohol formed and set free. An alcoholic solution of hydrate of potassa or soda is more active in this respect. The same kind of decomposition is often brought about by the prolonged contact of boiling water. Chloride of ethyl ; light hydrochloric ether ; AeCl.—Bectified spirit of wine is saturated with dry hydrochloric acid gas, and the product distilled with very gentle heat; or a mixture of 3 parts oil of vitriol and 2 of alcohol is poured upon 4 parts of dry common salt in a retort, and heat applied; in either case the vapor of the hydrochloric ether should be conducted through a little tepid water in a wash-bottle, and then conveyed into a small receiver surrounded by ice and salt. It is purified from adhering water by contact with a few fragments of fused chloride of calcium. Hydrochloric ether is a thin, colorless, and excessively volatile liquid, of a penetrating, aromatic, and somewhat alliaceous odor. At the freezing point of water, its sp. gr. is 0-921, and it boils at 50° (12°-5C); it is soluble in 10 parts of water, is not decomposed by solution of nitrate of silver, but is quickly resolved into chlo- ride of potassium and alcohol by a hot solution of caustic potassa. Bromide of ethyl ; hydrobromic ether ; AeBr. — This is prepared by distilling a mixture of 8 parts bromine, 1 part phosphorus, and 32 parts alcohol. The phosphorus is converted into phosphorous acid by the oxygen of the alcohol, when the ethyl combines with the bromine; 3 equivalents of alcohol, 3 equivalents of bromine, and 1 equivalent of phosphorus, yield 3 equivalents of bromide of ethyl, 3 equivalents of water, and 1 equivalent of phosphorous acid. It is a very volatile liquid, boiling at 106° (41°C), of pene- trating taste and smell, and superior in density to water. Iodide of ethyl; hydriodic ether; Ael.—Obtained by gradually mixing, with precaution, 1 part of phosphorus, 5 parts of alcohol, and 10 parts of iodine (1 eq. of phosphorus, 3 eq. of alcohol, and 3 eq. of iodine), and dis- tilling. The reaction is analogous to that described in the case of the bro- mide. Iodide of ethyl is a colorless liquid, of penetrating ethereal odor, having a density of 1-92, and boiling at 158° (70°C). It becomes red by exposure to light from a commencement of decomposition. This substance has become highly important as a source of ethyl, and from its remarkable deportment with ammonia, which will be discussed in the Section on Organic Bases. Sulphide of ethyl ; AeS.—Formed by the action of chloride of ethyl upon a solution of the protosulphide of potassium. It is colorless, has a disagree- able garlic odor, and boils at 180° (82°C). Cy-anide of ethyl, AeCy. — This is produced when a mixture of sulphovi- nate of potassa and cyanide of potassium, both in a dry state, is slowly heated. It is colorless; when perfectly pure it*has a powerful, not disagreeable odor, and a sp. gr. of 0-788. It boils at 190°-4 (88°C). This substance has been studied by Drs. Kolbe and Frankland. They have found that cyanide of ethyl differs from the ordinary ethers in its deportment with the alkalies. Instead of yielding cyanide of potassium and alcohol, it is converted into ammonia and propionic acid, C6H503,HO, a peculiar acid closely allied to acetic acid, and which will be noticed more in detail in the Propyl series. Cyanide of ethyl, in this reaction, absorbs 4 equivalents of water: — 1 eq. of cyanide of ethyl C6H5N 1 eq. of propionic acid . C6H6 04 4 eq. of water . . H4 04 1 eq. of ammonia . . H3N C6H9N04 C6H9N04 COMPOUND ETHERS. 373 (See also Cyanide of Methyl.)—AVhen acted upon by potassium, cyanide of ethyl furnishes a gas, the nature of which is not definitely settled; the residue continues cyanide of potassium and an organic alkali, cyanethine, which contains cis" 15^3- and is formed by the coalescence of three equivalents of the cyanide. Sii.piiite of oxide of ethyl; sulphurous ether; AeO,S02-—This sub- stance is obtained by adding absolute alcohol in excess to subchloride of sul- phur. Hydrochloric acid is evolved, and sulphur deposited, while the sulphite of ethyl distils as a limpid strongly-smelling liquid, of sp. gr. 1-085, boiling at 3:)8° (170°C); it is slowly decomposed by water. Sulphate of oxide of ethyl; sulphuric t.ther; AeO,S03.—This sub- stance has been only recently obtained. It is formed by passing the vapor of anhydrous sulphuric acid into perfectly anhydrous ether. A syrupy liquid is produced, which is shaken with 4 vols, of water and 1 vol of ether, when two layers arc formed; the lower contains sulphovinic acid (see this substance, page 375) and various other compounds, while the upper layer consists of an ethereal solution of sulphate of ethyl. At a gentle dieat the ether is vola- tilized, and the sulphate of ethyl remains as a colorless liquid. It cannot be distilled without decomposition. Phosphate of oxide of ethyl; phosphoric ether. — See Phosphovinic Acid. Nitrate of oxide of ethyl; nitbic ether; AeO,N05.—The nitrate is prepared by cautiously distilling a mixture of equal weights of alcohol and moderately-strong nitric acid, to which a small quantity of nitrate urea has been added. The action of nitric acid upon alcohol is peculiar: the facility with which that acid is deoxidized by combustible bodies, leads, under ordi- nary circumstances, to the production of nitrous acid on the one hand, and an oxidized product of alcohol on the other, a nitrite of the oxide of ethyl being generated instead of a nitrate. M. Millon has shown that the addition of urea, from reasons to be explained when this compound will be described, entirely prevents the formation of that substance, and at the same time pre- serves tho alcohol from oxidation by undergoing that change in its place, the sole liquid product being the new ether. The experiment is most safely con- ducted on a small scale, and the distillation must be stopped when seven- eighths of the whole have passed over: a little water added to the distilled product separates tho nitric ether. Nitric ether has a density of 1-112 ; it is insoluble in water, has an agreeable sweet taste and odor, and is not decom- posed by an aqueous solution of caustic potassa, although that substance dis- solved in alcohol attacks it even in the cold, with production of nitrate of potassa. Its vapor is apt to explode when strongly heated. Nitrite of oxide of ethyl; nitrous ether; AeO,N03.—Pure nitrous ether can only be obtained by the direct action of the acid itself upon alcohol. 1 part of starch, and 10 parts of nitric acid, are gently heated in a capacious retort or flask, and the vapor of nitrous acid thereby evolved conducted into alcohol mixed with half its weight of water, contained in a two-necked bottle, which is to be plunged into cold water, and connected with a good condensing nrrangement. All deviation of temperature must be carefully avoided. The product of this operation is a pale-yellow volatile liquid, possessing an exceed- ingly agreeable odor of apples; it boils at 62° (16-6C), and has a density of 0-947. It is decomposed by potassa, without darkening, into the nitrite of the base, aud alcohol. Nitrous ether, but contaminated with aldehyde, may be prepared by the following simple method :—Into a tall cylindrical bottle or jar are to be intro- duced successively 9 parts of alcohol of sp. gr. 0-830, 4 parts of water, and 8 parts of strong fuming nitric acid ; the two latter are added by means of a long funnel with a very narrow orifice, reaching to the bottom of the bottle, so that the contents may form three distinct strata, which slowly mix from the solution of tho liquids in each other. The bottle is then loosely stopped, 374 COMPOUND ETHERS. and left two or three days in a cool place, after which it is found to contain two layers of liquids, of which the uppermost is the ether. It is purified by rectification. A somewhat similar product may be obtained by carefully dis- tilling a mixture of 3 parts rectified spirit and 2 of nitric acid of 128 sp. gr.: the fire must be withdrawn as soon as the liquid boils. The sweet spirits of nitre of pharmacy, prepared by distilling three pounds of alcohol with four ounces of nitric acid, is a solution of nitrous ether, alde- hyde, and perhaps other substances, in spirit of wine. Silicic and boracic ethers. — A number of these compounds appears to exist, containing different proportions of the acids. Silicic ether, containing 3AeO,Si03, was obtained by M. Ebelmen by the action of anhydrous alcohol upon chloride of silicium. It is a colorless, limpid, aromatic liquid, of sp. gr. 0-933, boiling at 329° (165°C), and decomposed by water with production of silicic acid and alcohol. In contact with moist air it is gradually resolved into translucent hydrate of silica, which becomes in the end hard enough to scratch glass. By substituting ordinary spirit for absolute alcohol, other compounds containing a larger portion of silicic acid are obtained. Boracic ether was procured by a similar process, substituting the chloride of boron for chloride of silicium. It forms a thin, limpid liquid of agreeable odor, having the sp. gr. of 0-885, and boiling at 246° (118°C). It is decom- posed by water. Its alcoholic solution burns with a fine green flame, throw- ing off a thick smoke of boracic acid. It contains 3x\eO,Bo03. A second boracic ether, in the form of a solid glassy fusible substance, containing AeO, 2BoOa, was formed by the action of fused boracic acid upon absolute alcohol. It is volatile in the vapor of alcohol only, and is decomposed by water. Of the ethers of the organic acids, the following are the most important: — Oxalate of the oxide of ethyl ; oxalic ether ; AeO,C203. — This com- pound is most easily obtained by distilling together 4 parts binoxalate of potassa, 5 parts oil of vitriol, and 4 parts strong alcohol. The distillation may be pushed nearly to dryness, and the receiver kept warm to dissipate any ordinary ether that may be formed. The product is mixed with water, by' which the oxalic ether is separated from the undecomposed spirit; it is re- peatedly washed to remove adhering acid, and re-distilled in a small retort, the first portions being received apart and rejected. Another very simple- process consists in digesting equal parts of alcohol and dehydrated oxalic acid, in a flask furnished with a long glass tube, in which the volatilized spirit may condense. After 6 or 8 hours' digestion, the mixture generally contains only traces of oxalic acid which is not etherified. Pure oxalic ether is a colorless, oily liquid, of pleasant aromatic odor, and 1-09 sp. gr. It boils at 363° (183°-8C), is but little soluble in water, and is readily decomposed by caustic alkalies into an oxalate and alcohol. AVith solution of ammonia in excess, it yields oxamide and alcohol. C4H50,C203 -4- NH3 = C202,NH2 -f- C4H50,HO. This is the best process for preparing oxa- mide, which is obtained perfectly white and pure. (See page 361). AVhen dry gaseous ammonia is conducted into a vessel containing oxalic ether, the gas is rapidly absorbed, and a white solid substance produced, which is solu- ble in hot alcohol, and separates on cooling, in colorless, transparent, scaly crystals. They dissolve in water, and are both fusible and volatile.' The name oxamethane is given to this body; it consists of C8H7N06 = C4H50, C4H2N06, i. e., the ether of oxamic acid (see page 362). The same substance is formed when ammonia in small quantity is added to a solution of oxalic ether in alcohol. AVhen oxalic ether is treated with dry chlorine in excess in the sunshine a white, colorless, crystalline, fusible body is produced, insoluble in water and instantly decomposed by alcohol. It contains C6C1504, or oxalic ether in which the whole of the hydrogen is replaced by chlorine. Carbonate of oxide of ethyl ; carbonic ether ; AeO,C02. — Fragments COMPOUND ETHERS. 375 of potassium or sodium are dropped into oxalic ether as long as gas is disen- gaged ; the brown pasty product is then mixed with water and distilled. The carbonic ether is found floating upon the surface of the water of the receiver as a colorless, limpid liquid of aromatic odor and burning taste. It boils at 259° (126°C), and is decomposed by an alcoholic solution of potassa into car- bonate of that base and alcohol. The reaction which gives rise to this sub- stance is unexplained. The ethers of many of the vegetable acids have been obtained. The de- scription of these substances and of some of their products of decomposition is postponed until the history of the acids themselves has been given. Chlorocarbonic. ether.—Although the constitution of this substance is doubtful, it may be here described. Absolute alcohol is introduced into a glass globe containing chlorocarbonic acid (phosgene gas, see p. 148); the gas is absorbed in large quantity, and a yellowish liquid produced, from which water separates the chlorocarbonic ether. AVhen freed from water by chloride of calcium, and from adhering acid by rectification from litharge, it forms a thin, colorless, neutral liquid, which burns with a green flame. Its density is 1-133; it boils at 202° (94°-5C). The vapor, mixed with a large quantity of air, has an agreeable odor, but when nearly pure is extremely suffocating. It contains C6H6C104 =t!4II60,C2C103. The density of the vapor is 3-82. The action of ammonia, gaseous or liquid, upon this substance, gives rise to a very curious product, called by M. Dumas urethane; sal-ammoniac is at the same time formed. Urethane is a white, solid, crystallizable body, fusi- ble below 212° (100°C), and distilling unchanged, when in a dry state, at about 356° (180°); if moisture be present, it is decomposed, with evolution of ammonia. AVater dissolves this substance very easily: the solution is not affected by nitrate of silver, and yields, by spontaneous evaporation, large aud distinct crystals. It contains C6H7N04, or the elements of carbonic ether and urea, —whence the name. compound acids containing the elements of ether. Sulphovinic acid, C4HsO,2S03,HO. — Strong rectified spirit of wine is mixed with twice its weight of concentrated sulphuric acid: the mixture is heated to its boiling-point, and then left to cool. AVhen cold, it is diluted with a large quantity of water, and neutralized with chalk: much sulphate of lime is produced. The mass is placed upon a cloth filter, drained, and pressed; the clear solution is evaporated to a small bulk by the heat of a water-bath, filtered from a little sulphate, and left to crystallize: the product is sulphovinate of lime, in beautiful colorless, transparent crystals, containing CaO,C4H60,2S03 -f- 2HO. They dissolve in an equal weight of cold water, and effloresce in a dry atmosphere. A similar salt, containing baryta, BaO,C4H50,2S034- 2HO, equally soluble, and still more beautiful, may be produced by substituting, in the above pro- cess, carbonate of baryta for chalk; from this substance the hydrated acid may be procured by exactly precipitating the base by dilute sulphuric acid, and evaporating the filtered solution, in vacuo, at the temperature of the air. It forms^a sour syrupy liquid, in which sulphuric acid cannot be recognized, and is very easily decomposed by heat, and even by long exposure in the vacuum of the air-pump. All the sulphovinates are soluble; the solutions are decomposed by ebullition. The lead-salt resembles the baryta-compound. That of potassa, easily made by decomposing sulphovinate of lime by car- bonate of potassa, is anhydrous ; it is permanent in the air, very soluble, and crystallizes well. Sulphovinate of potassa, distilled with concentrated sulphuric acid, gives 376 COMPOUND ACIDS CONTAINING ether; with dilute sulphuric acid, alcohol; and with strong acetic acid, acetic ether. Heated with hydrate of lime or baryta, the sulphovinates yield a sul- phate of the base and alcohol. Phosphovinic acid, C4H50,P05,2HO. —This acid is bibasic. The baryta- salt is prepared by heating to 180° (82°-2C) a mixture of equal weights of strong alcohol and syrupy phosphoric acid, diluting this mixture, after the lapse of 24 hours, with water, and neutralizing by carbonate of baryta. The solution of phosphovinate, separated by filtration from the insoluble phosphate, is evaporated at a moderate temperature. The salt crystallizes in brilliant hexagonal plates, which have a pearly lustre, and are more soluble in cold than in hot water; it dissolves in 15 parts of water at 68° (20°C). The crystals contain 2BaO,C4H50,P05 -4- 12HO. From this substance the hydrated acid may be obtained by precipitating the baryta by dilute sulphuric acid, and evaporating the filtered liquid in the vacuum of the air-pump; it forms a colorless, syrupy liquid of intensely-sour taste, which sometimes exhibits appearances of crystallization. It is very soluble in water, alcohol, and ether, and easily decomposed by heat when in a concentrated state. The phospho- vinates of lime, silver, and lead p'ossess but little solubility; those of the alkalies, magnesia, and strontia, are freely soluble. Voegeli has lately observed that, by the action of syrupy phosphoric acid upon alcohol, together with phosphovinic acid, another acid is formed, to which he gives the name phosphobiethylic acid, phosphovinic acid being designated as phosphethylic acid. The baryta- silver- and lead-salts of this acid are more soluble than the corresponding phosphovinates. The lead-salt and lime-salt are anhydrous, and contain respectively, PbO,2C4H50,P05 and CaO,2C4H50,P05. The former of these salts, when heated to a temperature of between 356° and 374° (180° and 190°C), yields an aromatic, limpid liquid, which is tribasic phosphoric ether, 3C4H60,P05. It boils at 288°5 (142°-5C). Its formation is represented by the equation: 2Pb(0,2C4H60,P05) = 3C4H50,P06-f 2PbO,C4H50,P05. Oxalovinic acid, C4H50,2C203 HO.—Oxalic ether is dissolved in anhydrous alcohol, and enough alcoholic solution of caustic potassa added to neutralize one-half of the oxalic acid present, whereupon the potassa salt of the new acid precipitates in the form of crystalline scales, insoluble in alcohol, but easily dissolved by water. The free acid is obtained as a sour and exceedingly instable liquid by the addition of hydrofluosilicic acid to a solution of the preceding salt in dilute alcohol. It forms with baryta a very soluble salt. A iartrovinic acid has been described, and many other compounds of the same type exist. Another, and a different view, is very frequently taken of the substances just described, and of many analogous compounds. The sulphovinates, phosphovinates, &c, are supposed to possess a constitution resembling that of ordinary double salts, one of the bases being a metallic oxide, and the other ether. Thus, anhydrous sulphovinate of baryta is written BaO,S03 -4- C4H50,S03, or double sulphate of baryta and ether; hydrated sulphovinic acid is HO,S03 + C4H50,S03, or bisulphate of ether. There are, however, grave objections against this mode of viewing the subject: in every true double salt the characters both of acid and bases remain unchanged: alum gives the reactions of sulphuric acid, of alumina, and of potassa; while in sulphovinic acid or sulphovinate not a trace of sulphuric acid can be detected by any method short of actual decomposition, by heat or otherwise. If sul- phovinate of baryta contain sulphate of baryta ready formed, it is very difficult to understand how that salt can be decomposed by an addition of sulphuric acid. The student must, however, bear in mind that all views of the consti- THE ELEMENTS OF ETHER. 377 tution of complex organic compounds must, of necessity, be to a great extent hypothetical, and liable to constant alteration with the progress of science. Products of the Decomposition of Sulphovinic Acid by Heat. A solution of sulphovinic acid, or, what is equivalent to it, a mixture, in due proportions, of oil of vitriol and strong alcohol, undergoes decomposition when heated, yielding products which differ with the temperature to which the liquid is subjected. The cause of the decomposition is to be traced to the instability of the compound itself, to the basic power of water, and the attrac- tion of sulphuric acid for the latter, in virtue of which it determines the pro- duction of that substance, and liberates the elements of ether. AVhen the sulphovinic acid is so far diluted as to boilmt 260° (126°6C) or below, or when a temperature not exceeding this is applied to a stronger solution by the aid of an oil-bath, the compound acid is resolved into sul- phuric acid, which remains behind in the retort or distillatory vessel, while alcohol, and mere traces of ether, are volatilized. An acid whose boiling-point lies between 260° and 310° (126°-6 and lo4°-5C) is decomposed by ebullition into hydrated sulphuric acid and ether, which is accompanied by small quantities of alcohol. Lastly-, when, by the addition of a large quantity of oil of vitriol, the boil- ing-point of the mixture is made to rise to 320° (160°C) and above, the pro- duction of ether diminishes, and other substances begin to make their appear- ance, of which the most remarkable is olefiant gas. The mixture in the retort blackens, sulphurous acid and carbonic acid are disengaged, a yellow, oily aromatic liquid passes over, and a coaly residue is left, which contains sul- phur. The chief and characteristic product is olefiant gas; the others may be considered tho result of secondary actions. The three modes of decompo- sition may be thus contrasted: — Below 260° C4H50,2S03,HO 4-2IIO = C4H50,HO 4-2(S03.HO) 2G0°—310°C4H5O,2SO3,HO + HO = C4H50 + 2(S03,HO) Above 320° C4H50,2S03,HO = C4H4 -f- 2(S03,HO) The other-producing temperature is thus seen to be circumscribed within narrow limits. In the old process, however, in which a mixture of equal weights of alcohol and sulphuric acid is subjected to distillation, these condi- tions can be but partially complied with. At first the temperature of the mixture is too low to yield either in any quantity, and towards the end of the process, long before all the sulphovinic acid has been decomposed, it becomes too high, so that olefiant gas and its accompanying products appear instead. The remedy for this inconvenience consists in restraining the temperature of ebullition of the mixture within its proper bounds by the introduction of a constant supply of alcohol, to combine with the liberated sulphuric acid, and reproduce the sulphovinic acid as fast as it becomes destroyed. The improved, or continuous ether process, in which the same acid is made to etherify an almost indefinite quantity of spirit, may be thus elegantly conducted upon a small scale. A wide-necked flask is fitted with a sound cork, perforated by three aper- tures, one of which is destined to receive a thermometer, with the graduation on the stem ; a second, the vertical portion of a long narrow tube, terminating in an orifice of about Jff of an inch in diameter; and the third, a wide bent tube, connected with the condenser, to carry off the volatilized products. A mixtuie is made of 8 parts by weight of concentrated sulphuric acid, and 5 parts of rectified spirit of wine, of about 0-834 sp. gr. This is introduced into the flask, and heated by a lamp. The liquid soon boils, and the thermometer 378 COMPOUND ACIDS. very shortly indicates a temperature of 300° (149°C). When this happens, alcohol of the above density is suffered slowly to enter by the narrow tube, which is put into communication with a reservoir of that liquid, consisting of a large bottle perforated by a hole near the bottom, and furnished with a small brass stopcock, fitted by a cork: the stopcock is secured to the end of the long tube by a caoutchouc connector, tied, as usual with silk cord. As the tube passes nearly to the bottom of the flask, the alcohol gets thoroughly mixed with the acid liquid, the hydrostatic pressure of the fluid column being sufficient to insure the regularity of the flow; the quantity is easily adjusted by the aid of the stopcock. For condensation, a Liebig's condenser may be used, supplied with ice-water. The arrangement is seen in figure 182. Fig. 182. Apparatus for the preparation of ether, a. Flask containing the mixtures of oil of vitriol and alcohol, b. Reservoir with stopcock, for applying a constant stream of alcohol, c. Wide bent tube connected with the condenser for conveying away the vapors, d. The thermo- meter for regulating the temperature of the boiling liquid. The intensity of the heat, and the supply of alcohol, must be so adjusted that the thermometer may remain at 300° (149°C), or as near that tempera- ture as possible, while the contents of the flask are maintained in a state of rapid and violent ebullition — a point of essential importance. Ether and water distil over together, and collect in the receiver, forming two distinct strata; tho mixture slowly blackens, from some slight secondary action of the acid apon the spirit, or upon the impurities in the latter, but retains, after many nSAVY OIL OF WINE. 379 hours' ebullition, its etherifying powers unimpaired. The acid, however, slowly volatilizes, partly in the state of oil of wine, and the quantity of liquid in the flask is found, after the lapse of a considerable interval, sensibly dimin- ished. This loss of acid constitutes the only limit to the duration of the pro- cess, which might otherwise be continued indefinitely. On the large scale, the flask may be replaced by a vessel of lead, the tubes being also of the same metal; the stem of the thermometer may be made to pas- air-tight through the cover, and heat may, perhaps, be advantageously applied by high-pressure steam, or hot oil, circulating in a spiral tube of metal, immersed in the mixture of acid and spirit. The crude ether is to be separated from the water on which it floats, agi- tated with a little solution of caustic potassa, and re-distilled by the heat of warm water. The aqueous portion, treated with an alkaline solution, and dis- tilled, yields alcohol, containing a little ether. Sometimes the spontaneous separation before mentioned does not occur, from the accidental presence of a larger quantity than usual of undecomposed alcohol; the addition of a little water, however, always suffices to determine it. We shall once more return to the formation of ether, when we discuss the methyl-compounds. Heavy oil of wine.—AVhen a mixture of 2£ parts of concentrated sul- phuric acid, and 1 part of rectified spirit of wine, of 0-833 sp. gr., is subjected to distillation, a little ether comes over, but is quickly succeeded by a yellow- ish, oily liquid, which may be freed from sulphurous acid by agitation with water, and from ether and undecomposed alcohol by exposure in the vacuum of the air-pump, beside two open capsules, the one containing hydrate of potassa, and the other concentrated sulphuric acid. This substance may be prepared in larger quantity by the destructive distillation of dry sulphovinate of lime; alcohol, oil of wine, and a small quantity of an exceedingly volatile liquid, yet imperfectly examined, are produced. Pure oil of wine is colorless, or greenish, of oily consistence, and heavier than water; it has an aromatic taste, and an odor resembling that of peppermint. Its boiling-point is tolerably high. It is soluble in alcohol and ether, but scarcely so in water. By analysis it is found to contain C8H90,2S03, or perhaps C4H4.S034- C4H50,S03; that is, neutral sulphate of ether, in combination with the sulphate of a hydro-carbon, ctherole. In contact with boiling water, oil of wine is resolved into sulphovinic acid, and a volatile liquid, known by the name of light, or sweet oil of wine: with an alkaline solution this effect is produced with even greater facility. Light oil of wine, left in a cool place for several days, deposits crystals of a white solid matter, which is tasteless, and has but little odor; it is called etherin. The fluid residual portion is yellowish, oily, and lighter than water; it has a high boiling-point, solidifies at a very low temperature, and is freely soluble in alcohol and ether; it bears the name of etherole. Both ctherole and etherin have the same composition, namely, C4H4, and are consequently isomeric with olefiant gas. Olefiant gas; ethylene.—This substance may also be advantageously prepared on the principle described, by restraining the temperature within certain bounds, and preventing the charring and destruction of the alcohol, which always occurs in the old process, and which, at the same time, leads to the production of sulphurous and carbonic acids, which contaminate the gas. If the vapor of alcohol be passed into somewhat diluted sulphuric acid, maintained at a boiling-heat, it is absorbed with production of sulphovinic acid, which is shortly afterwards decomposed into water and olefiant gas. The process is thus conducted: — A wide-necked flask, containing rectified spirit of wine, is fitted with a cork, through which pas» an ordiuary safety- tube, with a little water, and the bent glass tube, intended to convey the vapor of the spirit into the acid. The latter must be of such strength as to 380 OLEFIANT GAS. have a boiling-point between 320° and 330° (100° and 165°-5C); it is pre- pared by diluting strong oil of vitriol with rather less than half its weight of water. The acid is placed in a second and larger flask, also closed by a cork, into which are inserted two tubes and a thermometer. The first is a piece of straight tube, wide enough to allow the tube conveying the alcohol-vapor to Fig. 183. Fig. 184. pass freely down it, and dipping a little way into the acid; the second is a narrow bent tube, the extremity of which is immersed in the water of the pneumatic trough. Both flasks are heated; and as soon as it is seen that the acid is in a state of tranquil ebullition, while the thermometer marks the tem- perature above mentioned, the spirit is made to boil, and its vapor carried into the acid, which very soon begins to evolve olefiant gas and vapor of water, accompanied by a little ether and oil of wine, but no sulphurous acid. The acid liquid does not blacken, and the experiment may be carried on as long as may be desired. This is a very elegant and instructive, although some- what troublesome, method of preparing the gas. The essential parts of the apparatus are shown in fig. 184. The properties of olefiant gas have been described in a previous part uf this jvork. We mention here only an interesting experiment lately made by M. Berthelot. Olefiant gas, when agitated for a long time with concentrated sulphuric acid, is at last absorbed. The solution, when diluted with water and submitted to distillation, furnishes an appreciable quantity of alcohol. Chloride of olefiant gas ; Dutch-liquid. — It has long been known that when equal measures of olefiant gas and chlorine are mixed over water absorption of the mixture takes place, and a yellowish oily liquid is produced' which collects upon the surface of the water, and ultimately sinks to the bottom in drops. It»may be easily prepared, in quantity, by causing the two gases to combine in a, glass globe, having a narrow neck at the lower part, dipping into a small bottle, destined to receive (he product. The two CHLORIDES OF CARBON. 381 gases are conveyed by separate tubes, and allowed to mix in the globe, the olefiant gas being kept a little in excess. The chlorine should be washed with water, and the olefiant gas passed through strong oil of vitriol, to remove vapor of ether: the presence of eulphurous and carbonic acids is not injurious. Combination takes place very rapidly, and the liquid product trickles down the sides of the globe into the receiver. AVhen a considerable quantity has been collected, it is agitated first with water, and afterwards with concentrated sulphuric acid; it is, lastly, purified by re-distillation. If impure olefiant gas be employed, the crude product contains a large quantity of a substance called by M. Begnault chloro-sulphuric acid, S02C1, which, on contact with water, is converted, by the decomposition of the latter, into sulphuric and hydrochloric acids. Pure Dutch-liquid is a thin, colorless liquid, of agreeably-fragrant odor and sweet taste; it is slightly soluble in water, and readily so in alcohol and ether. It is heavier than water, and boils when heated to 180° (82°-3C); it is unaffected by oil of vitriol and solid hydrate of potassa. When inflamed, it burns with a greenish, smoky light. This substance yields, by analysis, C4H4C12. When Dutch-liquid is treated with an alcoholic solution of caustic potassa, it is slowly resolved into chloride of potassium, which separates, and into a new and exceedingly volatile substance, containing C4H3C1, whose vapor re- quires to be cooled down to 0° (—17°-7C ) before it condenses. At this temperature it forms a limpid, colorless liquid. Chlorine is absorbed by this substance, and a compound produced, which contains C4H3C13: this is in turn decomposed by an alcoholic solution of hydrate of potassa into chloride of potassium and a new volatile liquid, C4H2"C12. Bromide and iodide of olefiant gas, C4H4Br2 and C4H4I2. These com- pounds correspond to Dutch-liquid; they are produced by bringing olefiant gas in contact with bromine and iodine. The bromide is a colorless liquid, of agreeable ethereal odor, and has a density of 2-16: it boils at 265° (129°-5C), and solidifies, when cooled to near 0° (— 17°-7C). The iodide is a colorless, crystalline, volatile substance, of penetrating odor; it melts at 174° (78°-8C), resists the action of sulphuric acid, but is decomposed by caustic potassa. Sulphocyanide of ethylene. — According to Buff, Dutch-liquid, when boiled for some time with sulphocyanide of potassium, furnishes a beautifully crys- tallized compound, of a peculiar, mustard-like odor, containing CH NJ3.. = C4II4 (C2NS2)2. » s 4 2 4 Products of the action of chlorine on Dutch-liquid; chlorides of carbon. — Dutch-liquid readily absorbs chlorine gas, and yields several new compounds, produced by the abstraction of successive portions of hydrogen, and its replacement or substitution by equivalent quantities of chlorine. This regular substitution of chlorine, bromine, iodine, &c, in place of hydrogen, as before stated, is a phenomenon of constant occurrence in reactions between these bodies and very many organic compounds. In the present case four such steps may be traced, giving rise, in each instance, to hydrochloric acid and a new substance. Three out of the four new products are volatile liquids, containing respectively, C4H3C13, C4H2C14 and C4HC15; the fourth C4C16, in which the substitution of chlorine for hydrogen is complete, is the chloride of carbon, long ago obtained by Mr. Faraday by putting Dutch-liquid into a vessel of chlorine gas, and exposing the whole to the influence of light. Sesquichloride or Perchloride of Carbon, CC16, is a white, solid, crystalline substance, of aromatic odor, insoluble in water, but easily dissolved by alcohol and ether; it melts at 320° (160°Cj, and boils at a temperature a little above. It burns with difficulty, and is un.affected by both acids and alkalies. It is prepared as above stated. Protochloride of Carbon, C4C14.—When the vapor of the preceding substance 382 ET II IONIC AND ISET II IONIC ACID. is transmitted through a red-hot porcelain tube filled with fragments of glass or rock-crystal, it is decomposed into free chlorine, and a second chloride of carbon, which condenses in the form of a volatile colorless liquid, which has a density of 1-55, and boils at 248° (120°C). The density of vapor is 5-82. It resembles in chemical relations the perchloride. Subchloride of Carbon, C4C12, is produced when the protochloride is passed many successive times through an ignited porcelain tube: it is a white, volatile, silky substance, soluble in ether. Bichloride of Carbon, C2C14.—A fourth chloride of carbon is known and will be described here, although it is not derived from the alcohol group. It is formed by passing the vapor of bisulphide of carbon, together with chlorine, through a red-hot porcelain tube. A mixture of chloride of sulphur and bichloride of carbon is formed, which is distilled with potassa, when the chloride of sulphur is decomposed, and pure bichloride passes over. It is a colorless liquid of 1-56 sp. gr., and boils at 170°.6 (77°C). An alcoholic solution of potassa converts this compound into a mixture of chloride of potassium and carbonate of potassa. The same compound is formed by exhausting the action of chlorine upon marsh-gas and chloride of methyl in the sunshine. Combustible Platinum-salts of Zeise. — A solution of bichloride of platinum in alcohol is mixed with a little chloride of potassium dissolved in hydrochloric acid, and the whole digested some hours at a high temperature. The alcohol is distilled off, the acid residue neutralized by carbonate of potassa, and left to crystallize. The distilled liquid contains hydrochloric ether and aldehyde. The platinum-salt forms yellow, transparent, prismatic crystals, which become opaque on heating from loss of water; when introduced into the flame of a spirit-lamp, the salt burns vividly, leaving metallic platinum. It is soluble in 5 parts of warm water. When dried at 212° (100°C), this substance contains Pt2Cl2,C4H4-f- KC1. Corresponding compounds, containing Pt2Cl2C4H4 + NaCl, and Pt2Cl2,C4H4 + NH4C1, are known to exist. The chloride of potassium can be separated from the above compound by the cautious addition of bichloride of platinum: the filtered solution yields by evaporation in vacuo a yellow, gummy, acid mass. The solution is slowly decomposed in the cold, and rapidly at a boiling heat, with separation of a black precipitate. These compounds are of uncertain constitution. products of the action of anhydrous sulphuric acid on alcohol and olefiant gas. AVhen absolute alcohol is made to absorb the vapor of anhydrous sulphuric acid, a white, crystalline, solid substance is produced, fusible at a gentle heat, which, when purified from adhering acid, is found to consist of carbon' hydrogen, and the elements of sulphuric acid, in the relation of the equivalent numbers, or probably, C4H4,4S03. To this substance Magnus supplies the name sulphate of carbyl. A body very similar in appearance and properties, and probably identical with this, had previously been produced by M. Beg- nault, by passing pure and dry olefiant gas over anhydrous sulphuric acid contained in a bent tube. AVhen the crystals of sulphate of carbyl are dissolved in alcohol, water added, the whole neutralized by carbonate of baryta, and the filtered solution concentrated by very gentle heat to a small bulk, and then mixed with a quantity of alcohol, a precipitate falls, which consists of baryta, in combina- tion with a peculiar acid closely resembling the sulphovinic, but yet differing in many important particulars. By the cautious addition of dilute 'sulphuric acid, the base may be withdrawn, and the hydrate of the new acid left in CHLORAL. 383 solution ; it bears the name of ethionic acid, and contains C4H50,4S03 + 2HO. The ethionates differ completely from the sulphovinates; all are soluble in water, and appear to be anhydrous. Those of lime, baryta, and oxide of lead refuse to crystallize; the ethionates of potassa, soda, and ammonia, on the contrary, may readily be obtained in good crystals. AVhen a solution of ethionic acid is boiled, it is decomposed into sulphuric acid, and a second new acid, the isethionic, isomeric with sulphovinic acid. The isethionic acid and its salts are very stable: their solutions may be boiled without decomposition. The isethionates of baryta, lead, copper, potassa, soda, and ammonia crystallize with facility, and cannot be confounded with the sulphovinates. Isetbionate of ammonia has been lately converted into taurin. (See Taurin.) The hydrated acid contains C4H50,2S03-f HO. The action of anhydrous sulphuric acid on ether, as has been already mentioned, gives rise to the formatian of neutral sulphate of ethyl (see page 27.'<). Together with this substance, sulphuric acid and several other acids, methionic (see Disnlphometholic Acid) and althionic, are obtained; the latter acid is not yet sufficiently studied. products of the action of chlorine on alcohol, ether, and its compounds. Chloral.—Perfectly dry chlorine is passed into anhydrous alcohol to satu- ration ; the gas is absorbed in large quantity, and hydrochloric acid abundantly produced. Towards the end of the process the reaction must be aided by heat. AVhen no more hydrochloric acid appears, the current of chlorine is interrupted, and the product agitated with three times its volume of concen- trated sulphuric acid. On gently warming this mixture in a water-bath, the impure chloral separates as an oily liquid, which floats on the surface of the acid ; it is purified by distillation from fresh oil of vitriol, and afterwards from a small quantity of quicklime, which must be kept completely covered by the liquid, until the end of the operation. Chloral has been obtained from starch, by distillation with hydrochloric acid and binoxide of manganese. Chloral is a thin, oily, colorless liquid, of peculiar and penetrating odor, which excites tears; it has but little taste. AVhen dropped upon paper it leaves a greasy stain, which is not, however, permanent. It has a density of 1-502. and boils at 201°-2 (94°C). Chloral is freely soluble in water, alcohol, and ether; it forms, with a small quantity of water, a solid, crystalline hy- drate; the solution is not affected by nitrate of silver. Caustic baryta and lime decompose the vapor of chloral when heated in it with appearance of ignition; the oxide is converted into chloride, carbon is deposited, and car- bonic oxide set free. Solutions of caustic alkalies also decompose it, with production of a formate of the base, and a volatile liquid, chloroform. Chloral contains C4HC1302. When chloral is preserved for any length of time, even in a vessel herme- tically sealed, it undergoes a very extraordinary change — it becomes con- verted into a solid, white, translucent substance, insoluble chloral, possessing exactly the same composition as the liquid itself. The new product is but very slightly soluble in water, alcohol, or ether: when exposed to heat, alone, or in contact with oil of vitriol, it is reconverted into ordinary chloral. Solution of caustic potassa resolves it into formic acid and chloroform. Bro- mine acts upon alcohol in the same manner as chlorine, and gives rise to a product very similar in properties to the foregoing, called bromal, which con- tains C4HBr302. It forms a crystallizable hydrate with water, and is decom- 384 ALCOHOL. posed by strong alkaline solutions into formic acid and bromoform. A corres- ponding iodine-compound probably exists. Chlorine acts in a different manner upon alcohol which contains water: when very dilute, the principal products are hydrochloric acid and aldehyde, the change being one of oxidation at the expense of the water. AVith strong spirit the reaction is more complex, one of its products being a volatile, oily, colorless liquid, of uncertain composition, long known under the name of heavy muriatic ether. The mode of action of dry chlorine on pure ether conforms strictly to the law of substitution before mentioned; the carbon remains intact, while a por- tion or the whole of the hydrogen is removed, and its place supplied by an equivalent quantity of chlorine. Ether exposed to a current of the dry gas for a considerable period, the temperature being at first artificially reduced, yields a heavy oily product, having the odor of fennel. This is found by analysis to contain C4H3C120, or ether, in which 2 eq. of chlorine have been substituted for 2 eq. of hydrogen. It may be termed bichlorinetted ether. By the further action of chlorine, aided by sunlight, the remaining hydrogen is removed, and a white crystalline solid substance, closely resembling sesqui- chloride of carbon produced. This is composed of C4C150 ; it is called penta- chlorinetted ether. In a substance called chloretheral, C4H4C10, accidentally formed by M. d'Arcet, in the preparation of Dutch-liquid, from the ether- vapor mixed with the olefiant gas, we have evidently the first member of this series. AVith the compound ethers, the same remarkable law is usually followed. The change is, however, often complicated by the appearance of secondary products. Thus, chlorinetted acetic ether, a dense, oily liquid, very different from common acetic ether, was found to contain C8H6C1204, being a substitu- tion-product of C8H804 = C4H50,C4H303; and chlorinetted formic ether, CCH4C1204, is formed, in like manner, by the substitution of 2 eq. chlorine for 2 eq. hydrogen in ordinary formic ether, C6H604 = C4H50,C2H03. A most remarkable and interesting set of compounds, due to substitution of this kind, are formed by the action of chlorine on chloride of ethyl, or light hydrochlo- ric ether. AVhen the vapor of this substance is brought into contact with chlorine gas, the two bodies combine to a colorless oily liquid, very like Dutch-liquid, but yet differing from it in several important points; it has, however, precisely the same composition, and its vapor has the same density. By the prolonged action of chlorine three other compounds are successively obtained, each poorer in hydrogen and richer in chlorine than the preceding, the ultimate product being the well-known sesquichloride of carbon of Mr. Faraday. Hydrochloric ether . Monochlorinetted hydrochloric ether Bichlorinetted " " Tri chlorinetted " ' Quadrichlorinetted " ' Sesquichloride of carbon . C4H5C1 C4H4C12 C4H3C13 C4H2C14 C4H Cl6 C4 Cl6 derivatives of alcohol containing sulphur. Mercaptan.—A solution of caustic potassa, of 1-28 or 1-3 sp. gr., is satu- rated with sulphuretted hydrogen, and mixed in a retort with an equal volume of solution of sulphovinate of lime of the same density. The retort is ALCOHOL. 385 connected with a good condenser, and heat is applied by means of a bath of salt ami water. Mcreaptan and water distil over together, and are easily separated by a separating funnel. The product thus obtained is a colorless, limpid liquid, of sp. gr. 0-812, but slightly soluble in water, easily miscible, on the contrary, with alcohol. ' It boil's at 97° (36°C). The vapor of mer- captan has a most intolerable odor of onions, which adheres to the clothes and person with rrreat obstinacy; it is very inflammable, and burns with a blue flame. Mcreaptan contains C4II6S2 = C4H5S,HS; or alcohol, having sulphur in the place of oxygen. AVhen brought into contact with red oxide of mercury, even in the cold, violent reaction ensues,1 water is formed, and a white substance is produced, soluble in alcohol, and separating from that liquid in distinct crystals, which contain C4H6S,IIgS. This compound is decomposed by sulphuretted hydro- gen, sulphide of mercury being thrown down, and mercaptan reproduced. By adding solutions of the oxides of lead, copper, silver, and gold, to an al- coholic solution of mercaptan, corresponding compounds containing those metals are formed. Caustic potassa produces no effect upon mercaptan, but potassium displaces hydrogen, and gives rise to a crystallizable compound soluble in water. Xanthic acid.—The elements of ether and those of bisulphide of carbon combine in presence of an alkali to a very extraordinary substance, possess- ing the properties of an oxygen-acid, to which the name xanthic is applied, on account of the yellow color of one of its most permanent and character- istic salts, that with oxide of copper. Alcohol of 0-800 sp. gr. is saturated, whilst boiling, with potassa, and into this solution bisulphide of carbon is dropped until it ceases to be dissolved, or until the liquid loses its alkalinity. The whole is then cooled to 0° (—17°-8C), when the potassa-salt separates in the form of brilliant, slender, colorless prisms, which must be quickly pressed between folds of bibulous paper, and dried in vacuo. It is freely soluble in water and alcohol, but insoluble in ether, and is gradually destroyed by exposure to air by oxidation of a part of the sulphur. Hydrated zanthic acid may be prepared by decomposing the foregoing compound by dilute sulphuric or hydrochloric acid. It is a color- less, oily liquid, heavier than water, of powerful and peculiar odor, and very combustible; it reddens litmus-paper, and ultimately bleaches it. Exposed to gentle heat, it is decomposed into alcohol and bisulphide of carbon: this happens at a temperature of 75° (23°-8C). Exposed to the air, or kept beneath tho surface of water open to the atmosphere, it becomes covered with a whitish crust, and is gradually destroyed. The xanthates of the alka- lies and of baryta are colorless and crystallizable; the lime-salt dries up to a gummy mass; the xanthates of the oxides of zinc, lead, and mercury are white, and but feebly soluble, that of copper is a flocculent, insoluble sub- stance, of beautiful yellow color. Hydrated xanthic acid contains C6TI6S40,IIO; or C4Ii50,C2S4,IIO. In the salts this water is replaced by one equivalent of a metallic oxide. derivatives of alcohol containing metals. Zinc-etiiyl.—In heating iodide of ethyl with zinc in sealed glass-tubes (see Compound Ethers; Ethyl-theory, p. 371), a white substance remains in the tube, which is a mixture of iodide of zinc and a peculiar volatile com- pound, to which Dr. Frankland has given the name zinc-ethyl. It may be sepa- 1 AVhenoe the name, mercurium captans. 33 386 ALCOHOL. rated from the residue by distilling it in a current of hydrogen, when it is obtained in the form of a liquid of a disagreeable odor, which contains C4H5Zn. In contact with atmospheric air it is so rapidly oxidized as to take fire. AVhen mixed with water this compound is violently decomposed with evolution of a carbonetted hydrogen, having the formula C4H6= C4II5.II, which may be viewed as the hydride of ethyl. Zinc-ethyl forms, with bin- oxide of nitrogen, a peculiar compound of dinitroethylate of zinc with zinc- ethyl = ZnO,C4H5N203, C4H5Zn. This substance takes fire when exposed to the action of the air; with water hydride of ethyl and basic dinitroethylate of zinc is produced. Dinitroethylic acid, separated from its saline compounds, possesses but very little stability. It forms a series of well-defined salts. The action of anhydrous sulphurous acid on zinc-ethyl gives rise to the formation of a crystalline compound, which is the zinc-salt, of a peculiar acid, ethylo- trithionic acid, ZnO,C4H5S305,HO (Hobson). Zinc-ethyl, when treated with potassium or sodium, produces potassium- ethyl and sodium-ethyl, two bodies, which, in their general characters, closely resemble zinc-ethyl (Wanklyn). Stannethyl.—A series of substances have been lately described by Frank- land and by Loewig, which contain the elements of ethyl, associated with the metal tin. AVhen iodide of ethyl is submitted in sealed tubes to the action of metallic tin at a temperature of 302°-320° (150°-1G0°C), iodide of stannethyl, C4II6SnI, is obtained in the form of yellow crystals, which fuse at 107°6 (42°C) and sublime at 464° (240°C). They are -easily soluble in alcohol and ether, but difficultly soluble in water. The iodine of this compound may be readily separated by the action of metals, such as potassium and zinc, when a metallic iodide is formed, stannethyl, C4H5Sn, being liberated in the form of a dense, oily liquid, having a sp. gr. of 1-55. Exposed to the action of the at- mosphere, stannethyl absorbs oxygen, and is converted into oxide of stannethyl, C4II5SnO, which is an inodorous and tasteless powder of a whitish color. This substance combines with most acids, giving rise to a series of well-crystallizable salts, which are soluble in water and alcohol, but dissolve only with difficulty in ether. As yet only the following terms of this series have been analyzed by Frankland. Stannethyl Oxide of stannethyl Chloride of stannethyl Bromide of stannethyl Iodide of stannethyl Nitrate of stannethyl C4H6Sn C4H6SnO C4H5SnCl C4H6SnBr C4H5SnI C4II5SnO,N05. Several other analogous substances have been discovered by Loewig: the action of an alloy of six parts of tin with one part of sodium on iodide of ethyl, at the common temperature, gives rise to the formation of a series of compounds, which may be extracted from the residue by means of ether, but which are difficult to separate. This mixture is left behind, on evaporating the ether, in the form of a thick, oily liquid, emitting dense fumes in contact with the air. It absorbs oxygen from the atmosphere, and becomes converted into a mixture of oxides, of which oxide of stannethyl constitutes the chief part. They are partly soluble in water and alcohol, and partly insoluble, and can, by means of these solvents, be separated to a certain extent. They form crystallizable salts with the acids. Loewig distinguishes the following series, some of which exhibit a very unusual ratio of composition:__ C4II3SnO ■) ^n2ol: 2(C4H5)Sn20 } Insoluble in water. 4(C4H5)Sn40j 3(C4H5)Sn20 )..... 5(C4H6)Sn40 ) Soluble m water- ALCOHOL. 387 Bism-ethtl.—This substance is formed by the action of iodide of ethyl upon an alloy of bismuth and potassium; from the residue it is extracted with ether. It contains BiC12H,5 = Bi:3C4fI5, and forms a yellow liquid of 1-82 sp. gr., which possesses a most nauseous odor, and emits fumes which inflame when coming in contact with the air. It combines with oxygen, chlorine, bromine, iodine, and with nitric acid. Plum is ethyl.—The product of the action of iodide of ethyl upon an alloy of lead and sodium is exhausted with ether, which dissolves a mixture of seve- ral compounds of lead with ethyl. On exposing the ethereal solution to the air, a white amorphous powder is obtained, containing Pb2C12H15=Pb23C4H6. This substance is capable of forming salts. As yet only the nitrate (Pb2 3C4H5)0,N05, the sulphate (Pb23C4H6)0,S03, and carbonate (Pb23C4H5)0,C02, have been obtained. The nitrate, decomposed by potassa, yields to ether the hydrated oxide, which remains upon evaporation of the ether as a viscid mass, which gradually crystallizes. This substance is easily soluble in water, alco- hol, and ether; the solution possesses a powerfully alkaline reaction. By decomposing zinc-ethyl by chloride of lead, Mr. Buckton has lately ob- tained another plumbethyl of the formula PbC8HI0=Pb2C4Hs. It is a liquid, boiling above 392° (200°C), which produces crystalline salts with the acids. Hyduaiigyrethyl.—According to Frankland, iodide of ethyl is readily at- tacked by mercury. The mixture solidifies after some time into a white crys- talline mass, which is iodide of hydrargyrethyl, C4H5IIg2I. It is insoluble in water, soluble in alcohol and ether, readily fusible, and may be sublimed with- out decomposition. There is a corresponding nitrate and chloride known:— Nitrate of hydrargyrethyl.....C4H5Hg20,NOs Chloride of hydrargyrethyl.....C4H6Hg2Cl They are both crystallizable compounds. The action of zinc-ethyl on chloride of mercury gives rise to the formation of a liquid body, C4ILHg, of sp. gr. 2-4, and boiling at 320° (160°C). Phosphetiiyl.—The compounds of ethyl and phosphorus will be considered in the section on the organic bases. Stibethyl.—Iodide of ethyl, when distilled with an alloy of antimony and potassium, yields a curious substance, which MM. Loewig and Schweizer have described under the name of stibethyl. It contains SbC|2H15=Sb 3(C4H5). Arsenethyl.—This substance is obtained analogously to stibethyl by the action of an alloy of arsenic and sodium upon iodide of ethyl. It contains Asri2H16=As:SC4H6. A\ e shall return to this and the preceding compound, When treating of the compound ammonias. products of the oxidation of alcohol. AVhen alcohol and ether burn with flame in free air, the products of their combustion are, as with all bodies of like chemical nature, carbonic acid and water. Under peculiar circumstances, however, these substances undergo partial oxidation, in which the hydrogen alone is affected, the carbon remain- ing untouched. The result is the production of certain compounds, which form a small scries, supposed by some chemists to contain a common radical, to which the name acetyl is applied. It is derived from ethyl by the oxidation and removal of 2 eq. of hydrogen. Table of Acetyl-Compounds Acetyl (symbol Ac) . Oxide of acetyl (unknown) Hydrate of oxide of acetyl; aldehyde . Acetylous acid; aldehydic acid . Anhydrous acetic acid Acetylic acid ; acetic acid .... CVI3 C4H30 C4H30,HO C4H302,HO C4H303 C4H303,HO 388 ALCOHOL. Acetyl and its protoxide are alike hypothetical. Aldehyde, C4H402 or AcO.HO.—This substance is formed, as already no- ticed, amono- other products, when the vapor of ether or alcohol is transmitted through a red-hot tube ; also, by the action of chlorine on weak alcohol. It is best prepared by the following process:—6 parts of oil of vitriol are mixed with 4 parts of rectified spirit of wine, and 4 parts of water; this mixture is poured upon 6 parts of powdered binoxide of manganese, contained in a ca- pacious retort, in connection with a condenser, cooled by ice-cold water. Gentle heat is applied ; and when six parts of liquid have passed over the pro- cess is interrupted. The distilled product is put into a small retort, with its own weight of chloride of calcium, and redistilled: this operation is repeated. The aldehyde, still retaining alcohol and other impurities, is mixed with twice its volume of ether, and saturated with dry ammoniacal gas; a crystalline compound of aldehyde and ammonia separates, which may be washed with a little ether, and dried in the air. From this substance the aldehyde may be separated by distillation in a water-bath, with sulphuric acid, diluted with an equal quantity of water: by careful rectification from chloride of calcium, at a temperature not exceeding 87° (30°5C), it is obtained pure and anhydrous. An interesting formation of aldehyde will be mentioned under the head of formic acid. Aldehyde1 is a limpid, colorless liquid, of characteristic ethereal odor, which, when strong, is exceedingly suffocating. It has a density of 0-790; boils at 72° (22°-3C), and mixes in all proportions with water, alcohol, and ether; it is neutral to test-paper, but acquires acidity on exposure to air, from the pro- duction of acetic acid: under the influence of platinum-black this change is very speedy. AVhen a solution of this compound is heated with caustic potassa, a remarkable brown resin-like substance is produced, the so-called aldehyde-resin. Gently heated with protoxide of silver, it reduces the latter without evolution of gas, the metal being deposited on the inner surface of the vessel as a brilliant and uniform film; the liquid contains aldehydate of silver. When treated with hydrocyanic acid, aldehyde yields a substance called alanine, which was already noticed, when treating of lactic acid, and which will be described more in detail in the section on vegeto-alkalies, under the head of bases from aldehyde. The action of sulphuretted hydrogen upon the ammonia-compound gives rise to the formation of thialdine, noticed likewise under the head of bases from aldehyde. The ammonia-compound above mentioned forms transparent, colorless crys- tals, of great beauty: it has a mixed odor of ammonia and turpentine: it dis- solves very easily in water, with less facility in alcohol, and with difficulty in ether: it melts at about 170° (76°C), and distils unchanged at 212° (100°C). Acids decompose it, with production of an ammoniacal salt and separation of aldehyde. The crystals, which are apt to become yellow, and lose their lustre in the air, contain C4II402-4-NH3. When pure aldehyde is long preserved in a closely-stopped vessel, it is some- times found to undergo spontaneous change into one, and even two isomeric modifications, differing completely in properties from the original compound. In a specimen kept some weeks at 32° (0°C), transparent acicular crystals were observed to form in considerable quantity, which, at a temperature little exceeding that of the freezing-point of water, melted to a colorless liquid, mis- cible'with water, alcohol, and ether; a few crystals remained, which sublimed without fusion, and were probably composed of the second substance. This new body received the name elaldehyde; it was found to be identical in com- position with aldehyde, but to differ in properties and in the density of its 1 Alcohol dehydrogenaius. ALDEHYDIC ACID___ACETAL. 389 vapor; the latter has a sp. gr. of 4-515, while that of aldehyde is only 1-502, or one-third of that number. It refuses to combine with ammonia, is not ren- dered brown by potassa, and is but little affected by solution of silver. The second modification, or metaldehyde, is sometimes produced in pure alde- hyde, kept at the common temperature of the air, even in hermetically-sealed tubes: the conditions of its formation are unknown. It forms colorless, trans- parent, prismatic crystals, which sublime without fusion at a temperature above 212° (100°C), and are soluble in alcohol and ether, but not in water. They also were found, by analysis, to have the same composition as aldehyde. The substance which we have described by the term of chloral may be viewed as bichlorinetted aldehyde. Alokiiydic acid. C4H30,HO.—AVhen solution of aldchydate of silver, obtained by digesting oxide of silver in excess with alhehyde, is precipitated by sulphuretted hydrogen, an acid liquid is obtained, which neutralizes alka- lies, and combines with the oxides of the metals. It is very easily decom- posed. Aldehydate of silver, mixed with baryta-water, gives rise to aldehy- date of baryta and oxide of silver: if this precipitate be heated in the liquid, the metal is reduced, and neutral acetate of baryta formed ; whence it is inferred that the new acid contains the elements of acetic acid, minus an equivalent of oxygen. Acetal. — This substance, is one of the products of the slow oxidation of alcohol-vapor under the influence of platinum-black. Spirit of wine is poured into a large, tall, glass jar, to the depth of about an inch, and a shallow cap- sule, containing slightly-moistened platinum-black, arranged above the surface of the liquid; the jar is loosely covered by a glass plate, and left during two or three weeks in a warm situation. At the expiration of that period the liquid is found highly acid; it is to be neutralized with carbonate of potassa, as much chloride of calcium added as the liquid will dissolve, and the whole subjected to distillation, the first fourth only being collected. Fused chloride of calcium added to the distilled product now throws up a light oily liquid, which is a mixture of acctal with alcohol, aldehyde, and acetic ether. By fresh treatment with chloride of calcium, and long exposure to gentle heat in a retort, the aldehyde is expelled. The acetic ether is destroyed by caustic potassa, and the alcohol removed by washing with water, after which the acctal is again digested with fused chloride of calcium, and redistilled. Pure aeetal is a thin, colorless fluid, of agreeable ethereal odor, of sp. gr. 0-821 at 72° (22°-2C), and boiling at 220° (104° C). It is soluble in 18 parts of water, and miscible in all proportions with alcohol and ether. It is un- changed in. the air; but, under the influence of platinum-black, becomes converted into aldehyde, and eventually into acetic acid. Nitric and chromic acids produce a similar effect. Strong Fig. 185. boiling solution of potassa has no action on this substance. Acctal contains C12II1404. or the elements of 2 eq. ether and 1 eq. aldehyde, C12tl1404 = 2C4H50-f-C4H402. See also further on, ethyleue-alcohol, glycol. When a coil of fine platinum wire is heated to redness, and plunged into a mixtuie of ether, or alcohol-vapor, and atmospheric air, it determines upon its surface the partial combustion of the former, and gives rise to an excessively pungent acrid vapor, which may be condensed to a colorless liquid by suitable means. The heat evolved in the act of oxidation is sufficient to maintain the wire in an incandescent state. The experiment may be made by put ting a little ether into an ale-glass, and suspending over it tho heated spiral from a card; or by slipping the coil over the wick of a spirit-lamp, so that the greater part may be raised above the cotton; the lamp is supplied with ether or spirit of wine, lighted for a 33* 390 ACETIC ACID. moment, and then blown out. The coil continues to glow in the mixed atmo- sphere of air and combustible vapor, until the ether is exhausted. This is the lamp without flame of Sir II. Davy. A ball of spongy platinum may be substi- tuted for the coil of wire. The condensed liquid contains acetic and formic aeids, with aldehydic acid. Acetic acid. —Pure alcohol, exposed to the air, or thrown into a vessel of oxygen gas, fails to suffer the slightest change by oxidation: when diluted with water, it remains also unaffected. If, on the other hand, spirit of wine be dropped upon dry platinum-black, the oxygen condensed into the pores of the latter reacts so powerfully upon the alcohol as to cause its instant inflam- mation. AVhen the spirit is mixed with a little water, and slowly dropped upon the finely-divided metal, oxidation still takes place, but with less energy, and vapor of acetic acid is abundantly evolved. It is almost unnecessary to add, that the platinum itself undergoes no change in this experiment. Dilute alcohol, mixed with a little yeast, or almost any azotized organic matter, susceptible of putrefaction, and exposed to the air, speedily becomes oxidized to acetic acid. Acetic acid is thus manufactured in Germany, by suffering such a mixture to flow over wood-shavings, steeped in a little vine- gar, contained in a large cylindrical vessel, through which a current of air is made to pass._ The greatly-extended surface of the liquid expedites the change, which is completed in a few hours. No carbonic acid is produced in this reaction. The best vinegar is made from wine by spontaneous acidification in a par- tially-filled cask to which the air has access. Vinegar is first introduced into the empty vessel, and a quantity of wine added; after some days a second portion of wine is poured in, and after similar intervals a third and a fourth. AVhen the whole has become vinegar, a quantity is drawn off equal to that of the wine employed, and the process is recommenced. The temperature of the building is kept up to 86° (30°C). Such is the plan adopted at Orleans.! In England vinegar is prepared from a kind of beer made for the purpose. The liquor is exposed to the air in half-empty casks, loosely stopped, until acidifi- cation is complete. Frequently a little sulphuric acid is afterwards added. with a view of checking further decomposition, or mothering, by which the product would be spoiled. There is another source of acetic acid besides the oxidation of alcohol: when dry, hard wood, as oak and beech, is subjected to destructive distillation at a red-heat, acetic acid is found among the liquid condensable products of the operation. The distillation is conducted in an iron cylinder of large dimensions, to which a worm or condenser is attached; a sour watery liquid a quantity of tar, and much inflammable gas pass over, while charcoal of ex- cellent quality remains in the retort. The acid liquid is subjected to distilla- tion, the first portion being collected apart for the sake of a peculiar volatile body, shortly to be described, which it contains. The remainder is saturated with lime, concentrated by evaporation, and mixed with solution of sulphate of soda; sulphate of lime precipitates, while the acetic acid is transferred to the soda. The filtered solution is evaporated to its crystallizing-point • the crystals are drained as much as possible from the dark, tarry mother-liquor and deprived by heat of their combined water. The dry salt is then cautiously fused by which the last portions of tar are decomposed or expelled • it is then redissolved in water, and recrystallized. Pure acetate of soda, thus obtained readily yields hydrated acetic acid by distillation with sulphuric acid The strongest acetic acid is prepared by distilling finely-powdered anhy- drous acetate of soda with three times its weight of concentrated oil of vitriol The liquid is purified by rectification from sulphate of soda, accidentally thrown up, and then exposed to a low temperature. Crystals of hydrate of acetic acid form in large quantity, which may be drained from the weaker fluid portion, 1 DumaF, Chimie appliauoc aux Arts, vi. 537. ACETIC ACID. 391 and then suffered to melt. Below 60° (15°-5C) this substance forms large, colorless, transparent crystals, which above that temperature fuse to a thin, colorless liquid, of exceedingly pungent and well-known odor; it raises blis- ters on the skin. It is miscible in all proportions with water, alcohol, and ether, and dissolves camphor and several resins. AVhen diluted it has a plea- sant acid taste. The hydrate of acetic acid in the liquid condition has a den- sity of 1-063, and boils at 240° (119°C); its vapor is inflammable. Acetic acid forms a great number of exceedingly important salts, all of which are Boluble in water; the acetates of silver and mercury are the least soluble. Dilute acetic acid, or distilled vinegar, used in pharmacy, should always be carefully examined for copper and lead: these impurities are contracted from the metallic vessel or condenser sometimes employed in the process. The Btrength of any sample of acetic acid cannot be safely inferred from its den- sity, but is easily determined by observing the quantity of dry carbonate of soda necessary to saturate a known weight of the liquid.1 The hydrate of acetic acid contains C4H303,IIO=Ac03,HO: it is formed from alcohol by the substitution of 2 eq. of oxygen for 2 eq. of hydrogen. The water is basic, and can be replaced by metallic oxides. Dr. AVilliamson assumes in acetic acid a peculiar radical, which he terms otbyl, C4H302, i. e., ethyd in which 2 eq. of hydrogen are replaced by 2 eq. of oxygen. The con- stitution of acetic acid thus becomes analogous to that of benzoic acid in which Liebig and AVohler assume a peculiar radical, benzoyl, C14H502. Sec the article on this substance. Benzoic acid, HO,(C,4H602)0, Hydrated oxide of benzoyl. Acetic acid, HO,(C4H302)0, Hydrated oxide of othyl. This view is supported by the existence of several bodies which may be considered as othyl-compounds. The most remarkable of these substances is the chloride of othyl, discovered by M. Gerhardt. This compound, C4H303C1, which is also often called chloride of acetyl, is formed by the action of penta- chloride of phosphorus upon the pure hydrate of acetic acid, C4H303,HO + PC16 = C4H302C1 -f PC1302 + IIC1. Acetic acid. Pentachloride Chloride Oxychloride of phosphorus, of othyl. of phosphorus. Or, more readily, by distilling acetate of soda with oxychloride of phos- phorus. 3(NaO,C4II303) -f- PC1302 = 3C4H302C1 -f 3NaO,P05, Acetate of soda. Oxychloride Chloride of Phosphate of phosphorus. othyl. of soda. Chlorido of othyl is a colorless liquid, of suffocating odor. It fumes in con- tact with moist air. The boiling point is 131° (55°C). It is heavier than water, with the elements of which it produces acetic and hydrochloric acids. A different view regarding the constitution of acetic acid has been proposed by Prof. Kolbe; it is chiefly based upon the remarkable decomposition which * [Acetic acid increases in density by the addition of water, and reaches its maximum 1-079 when SO parts have been mixed with 100 of the strongest acid; it then decreases in density, and when 135 parts have been added its specific gravity is the same as the hydrate, 1063°. The most ready method to test its strength is to suspend in it a fragment of pure marble of known weight; the loss of weight resulting will be five-sixths of the weight of the hydrated acid present, 50 parts of carbonate of lime being required to saturate 60 parts of acetic acid.— K. B.] 392 ACETIC ACID. acetic acid undergoes when submitted to the action of the galvanic current. AVe shall return to this subject when speaking of valeric acid. M. Gerhardt has lately made the remarkable discovery that anhydrous acetic acid, the substance C4H303, may be obtained by a process which is of general applicability for the isolation of the anhydrous acids. Anhydrous acetic acid may be obtained by the action of chloride of othyl upon dry acetate of soda. NaO,C4H303 + C4H302C1 ■= NaCl + 2C4H303, Chloride Anhydrous of othyl. acetic acid. There is another method of procuring this compound which deserves to be mentioned, as it is the only one by which anhydrous acetic acid was originally obtained. In one of the subsequent chapters a substance will be described nndef the name of chloride of benzoyl, which may be viewed as the chloride of the radi- cal of benzoic acid. If this body be heated with anhydrous acetate of soda, a lively reaction ensues, and anhydrous acetic acid distils over, while a mix- ture of chloride of sodium and benzoate of soda remains in the retort. 2(NaO,C4H303) + C14H502C1 = NaCl 4" NaO£,4H£3 4- 2(C4H303) Acetate of Chloride of Chlor. of Benzoate of Anhydrous Soda. Benzoyl. Sodium. Soda. Acet. Acid. Anhydrous acetic acid is a heavy oil which combines only slowly with water, giving rise to the formation of ordinary hydrated acetic acid. Acetate cf totassa, KO,C4H303.—This salt crystallizes with great diffi- culty : it is generally met with as a foliated, white, crystalline mass, obtained by neutralizing carbonate of potassa by acetic acid, evaporating to dryness. and heating the salt to fusion. The acetate is extremely deliquescent, and soluble in water and alcohol; the solution is usually alkaline from a little loss of acid by the heat to which it has been subjected. From the alcoholic solu- tion, carbonate of potassa is thrown down by a stream of carbonic acid. Acetate of soda, NaO,C4H3034- OHO.—The mode of preparation of this salt on the large scale has been already described; it forms large, transparent, colorless crystals, derived from a rhombic prism, which are easily rendered anhydrous by heat, effloresce in dry air, and dissolve in 3 parts of* cold, and in an equal weight of hot water, — it is also soluble in alcohol. The taste of this substance is cooling and saline. The dry salt undergoes the igneous fusion at 550° (287°-8C), and begins to decompose at 600° (315°-5C). Acetate of ammonia; spirit of Mindeuerus ;.NH40,C4H303. — The neu- tral solution obtained by saturating strong acetic acid by carbonate of ammo- nia cannot be evaporated without becoming acid from loss of base: the salt passes off in large quantity with the vapor of water. Solid acetate of ammonia is best prepared by distilling a mixture of equal parts acetate of lime and pow- dered sal-ammoniac; chloride of calcium remains in the retort. A saturated solution of the solid salt in hot water, suffered slowly to cool in a close vessel, deposits long slender crystals, which deliquesce in the air. Acetonitrile. —Acetate of ammonia when distilled with anhydrous phos- phoric acid, loses 4 eq. of water, being converted into a colorless liquid, diffi- cultly soluble in water, of an aromatic odor, and boiling at 170° (77°C), which has received the name of acetonitrile. AVhen boiled with acids or alkalies, it reassimilatcs the 4 eq. of water, being converted again into acetic acid and ammonia. This substance is the type of a class; a great many ammonia-salts of acids, analogous to acetic acid, undergoing a similar change when treated BASIC ACETATES OF LEAD. 393 with anhydrous phosphoric acid. It is likewise obtained by a perfectly differ- ent process, which will be described when treating of the methyl compounds. (See cyanide of methyl, page 402). The acetates of lime, baryta, and strontia, are very soluble, and can be pro- cured in crystals; acetate of magnesia crystallizes with difficulty. Acetate of alumina. —This salt is very soluble in water, and dries up in the vacuum of the air-pump to a gummy mass without trace of crystallization. If foreign salts be present, the solution of the acetate becomes turbid on heat- ing, from the separation of a basic compound, which redissolves as the liquid cools. Acetate of alumina is much employed in calico printing; it is prepared, in combination with the alkaline base of the alum, by mixing solutions of ace- tate of lead and alum, and filtering from the insoluble sulphate of lead. The liquid is thickened with gum or other suitable material, and with it the design is impressed upon the cloth by a wood-block, or by other means. Exposure to a moderate degree of heat drives off the acetic acid, and leaves the alumina in a state capable of entering into combination with the dye-stuff. Some very interesting researches on acetate of alumina have been published by Mr. AV. Crum.1 The solution obtained by decomposing sulphate of alumina Al2033SOs by acetate of lead may be supposed to contain the neutral acetate of alumina Alg033(.'4H303. This salt cannot, however, be obtained in the dry state. If the solution be rapidly evaporated at low temperatures, by being spread in thin layers on glass or porcelain, a basic soluble acetate is obtained, having the composition A12032C4H303 -f- 4HO, but if the solution be left to stand, or submitted to the action of heat, insoluble basic salts are precipitated, differing in composition from the former only by containing instead of 4 eq. of water either 2 or 5 eq. The soluble acetate of alumina, when exposed in a dilute solution to the temperature of boiling-water for several days, undergoes a very remarkable change. The whole, or nearly the whole, of the acetic acid, is expelled by the action of heat, and a peculiar allotropic modification of alumina remains in solution. At the temperature of boiling-water this alumina retains 2 eq. of water; it entirely redissolves in water. The soluble modification of alumina is instantaneously coagulated, that is, reconverted into the insoluble modification, by mineral and vegetable acids, by the alkalies, and by a great number of salts. Acetate of manganese forms colorless, rhombic, prismatic crystals, permanent in the air. Acetate of protoxide of iron crystallizes in small, greenish-white needles, very prone to oxidation ; both salts dissolve freely in water. Acetate of sesquioxide of iron is a dark-brownish red, uncrystallizable liquid, of power- ful astringent taste. Acetate of cobalt forms a violet-colored, crystalline, deli- quescent mass. The nickel-salt separates in green crystals, which dissolve in 6 parts of water. Acetate of lead, PbO,C4H3034- 3HO.—This important salt is prepared on a large scale by dissolving litharge in acetic acid; it may be obtained in co- lorless, transparent prismatic crystals, but is generally met with in commerce as a confusedly crystalline mass, somewhat resembling loaf-sugar. From this circumstance, and from its sweet taste, it is often called sugaf of lead. The crystals are soluble in about 1£ part of cold water, effloresce in dry air, and melt when gently heated in their water of crystallization ; the latter is easily driven off, and the anhydrous salt obtained, which suffers the igneous fusion, and afterwards decomposes, at a high temperature. Acetate of lead is soluble in alcohol. The watery solution has an intensely sweet, and at the same time astringent taste, and is not precipitated by ammonia. It is an article of great value to the chemist. Basic acetates (sub-acetates) of lead.— Sesqui-basic acetate is produced when the neutral anhydrous salt is so far decomposed by heat as to become * Chem. Soc. Quar. Jour, vi 216. 39-4 ACETATE OF OXIDE OF ETHYL. converted into a porous white mass, decomposable only at a much higher tem- perature. It is soluble in water, and separates from the solution evaporated to a syrupy consistence in the form of crystalline scales. It contains 3l'bO, 2C4H303. A sub-acetate with 3 eq. of base is obtained by digesting at a mo- derate heat, 7 parts of finely-powdered litharge, 6 parts of acetate of lead, and 30 parts of water. Or, by mixing a cold saturated solution of neutral acetate with a fifth of its volume of caustic ammonia, and leaving the whole some time in a covered vessel; the salt separates in minute needles, which contain 3PbO, C4H303 4- HO. The solution of sub-acetate prepared by the first method is known in pharmacy under the name of Goulard water. A third sub-acetate exists, formed by adding a great excess of ammonia to a solution of acetate of lead, or by digesting acetate of lead with a large quantity of oxide. It is a white, slightly crystalline substance, insoluble in cold, and but little soluble in boiling water. It contains 6PbO,C4H303. The solutions of the sub-acetates of lead have a strong alkaline reaction, and absorb carbonic acid with the greatest avidity, becoming turbid from the precipitation of basic carbonate. Acetate of copper.—The neutral acetate, CuO,C4H3034- HO, is prepared by dissolving verdigris in hot acetic acid, and leaving the filtered solution to cool. It forms beautiful dark-green crystals, which dissolve in 14 parts of cold and 5 parts of boiling water, and are also soluble in alcohol. A solution of this salt, mixed with sugar and heated, yields suboxide of copper in the form of minute red octahedral crystals: the residual copper solution is not precipitated by an alkali. Acetate of copper furnishes, by destructive distil- lation, strong acetic acid, containing acetone, and contaminated with copper. The salt is sometimes called distilled verdigris, and is used as a pigment. Basic acetates'(sub-acetates) of copper.—Common verdigris, made by spreading the marc of grapes upon plates of copper exposed to the air du- ring several weeks, or by substituting with the same view, pieces of cloth dipped in crude acetic acid, is a mixture of several basic acetates of copper which have a green or blue color. One of these, 3CuO,2C4H303+ 6IIO, is ob- tained by digesting the powdered verdigris in warm water, and leaving the soluble part to spontaneous evaporation. It forms a blue, crystalline mass, but little soluble in cold water. AVhen boiled, it deposits a brown powder, which is a subsalt with large excess of base. The green insoluble residue of the verdigris contains 3CuO,C4H303 4- "HO; it may be formed by digesting neutral acetate of copper with the hydrated oxide. By ebullition with water it is resolved into neutral acetate and the brown sub-salt. Acetate of silveb, AgO,C4H303, is obtained by mixing acetate of potassa with nitrate of silver, and washing the precipitate with coid water to remove the nitrate of potassa. It crystallizes from a warm solution in small colorless needles, which have but little solubility in the cold. Acetate of suboxide of mercury forms small scaly crystals, which are as feebly soluble as those of acetate of silver. The salt of the red oxide of mercury dis- solves with facility. Acetate of oxide of ethyl; acetic ether; AeO,C4H303.—Acetic ether is conveniently made by heating together in a retort 3 parts of acetate of po- tassa, 3 parts of strong alcohol, and 2 of oil of vitriol. The distilled product is mixed with water, to separate the alcohol, digested first with a little chalk, and afterwards with fused chloride of calcium, and, lastly, rectified. The pure ether is an exceedingly fragrant limpid liquid; it has a density of 0-890, and boils at 165° (73°-8C). Alkalies decompose it in the usual manner. AVhen treated with ammonia, it yields acetamide, a crystalline substance soluble in water and alcohol, which contains C4H5N02 = C4H302,NH2, i.e., acetate of am- monia— 2 equivalents of water. Its formation is analogous to that of oxa- mide. Alkalies and acids reconvert it into ammonia and acetic acid. AVhen treated with nitrous acid, it yields acetic acid, water, and nitrogen gas C4H5N02 + N03 = C4II303,HO + HO + 2N. b b ' M 0 X O B R 0 M A C E T I C ACID. 395 TmciiLORAfETic acid.—AVhen a small quantity of crystallizable acetic acid is introduced into a bottle of dry chlorine gas, and the whole exposed to the direct solar rays for several hours, the interior of the vessel is found coated with a white crystulline substance, which is a mixture of the new product, trichloracetic acid, with a small quantity of oxalic acid. The liquid at the bottom contains the same substances, together with the unaltered acetic acid. Hydrochloric and carbonic acid gases are at the same time produced, together with a suffocating vapor, resembling chloro-carbonic acid The crystalline matter is dissolved out with a small quantity of water, added to the liquid contained in the bottle, and the whole placed in the vacuum of the air-pump, with capsules containing fragments of caustic potassa, and concentrated sul- phuric acid. The oxalic acid is first deposited, and afterwards the new sub- stance in beautiful rhombic crystals. If the liquid refuse to crystallize, it may be distilled with a little anhydrous phosphoric acid, and then evapora- ted. The crystals are spread upon bibulous paper to drain, and dried in vacuo. Trichloracetic acid is a colorless and extremely deliquescent substance; it has a faint odor, and a sharp, caustic taste, bleaching the tongue and destroy- ing the skin; the solution is powerfully acid. At 115° (16°C) it melts to a clear liquid, and at 390° (218°-8C) boils and distils unchanged. The density of the fused acid is 1-617; that of the vapor, which is very irritating, is probably 5-6. The substance contains, according to the analysis of M. Dumas, C4C!303,IIO, or the elements of hydrated acetic acid from which 3 eq. of hydrogen have been withdrawn, and replaced by 3 eq. of chlorine. Trichloracetic acid forms a variety of salts, which have been examined and described; it combines also with ether, and with the ether of wood-spirit. These compounds correspond to the ethers of the other organic acids. Tri- chloracelate of potassa crystallizes in fibrous, silky needles, which are perma- nent in the air, and contain K0,C4C1303 -f- HO. The ammoniacal salt is also crystallizable and neutral; it contains NH40,C4C1303 4- 5HO. Trichloracetate of silver is a soluble compound, crystallizing in small grayish scales, which are easily altered by light; it gives, on analysis, AgO,C4<;]303. and is conse- quently anhydrous. When trichloracetic acid is boiled with an excess of ammonia, it is decom- posed, with production of chloroform and carbonate of ammonia. C4H C1304 = C2II Cl3 + 2C02. AVith caustic potassa, it yields a smaller quantity of chloroform, chloride of potassium, carbonate and formate of potassa. The chloride and the formate are secondary products of the reaction of the alkali upon the chloroform. Acetic acid may be reproduced from this curious substitution-compound. When an amalgam of potassium and mercury is put into a strong aqueous solution of trichloracetic acid, chemical action ensues, the temperature of the liquid rises, without disengagement of gas, and the solution is found to con- tain acetate of potassa, chloride of potassium, and some caustic potassa. Monociiloracetic acid; C4H2C103,HO, according to B. Hoffmann, is pro- duced by the action of chlorine on boiling glacial acetic acid in sunlight. On submitting the product of this reaction to repeated distillation a substance is obtained which boils at 307° (186°C) and solidifies to a crystalline mass, which fuses at 147° (64°C) and dissolves with facility in water. This acid and its salts, when heated, are converted into glycolic acid and glycolates. C4H2C103,KO 4- H202 = C4H40B 4- KC1. Monobhomacetic acid ; C4H2Br03,HO, obtained by Perkin and Duppa, resembles in every respect the former. It is formed by acting with bromiue on glacial acetic acid in sealed tubes at a temperature above that of boiling water. 396 ACETONE. This acid, when treated with ammonia, is converted into glycocin (glycocoll), C4H5N04 and bromide of ammonium. C4H3Br04 -f- 2NII3 = NH4Br 4- C4H5N04. Thiacetic acid.—A compound has been discovered by Kekule\ which may be viewed as acetic acid, in which 2 equivalents of oxygen are replaced by 2 equivalents of sulphur. C4H302,0,HO. Acetic acid, or hydrated oxide of othyl. C4N302,S,HS. Thiacetic acid, or sulphuretted sulphide of othyl, It is formed by the action of pentasulphide of phosphorus upon pure hydrate of acetic acid. 5(C4N303,HO) 4- 2PS5 = 5(C4H302S,HS) 4- 2r05. Acetic acid. Thiacetic acid. Thiacetic acid is a colorless liquid, boiling at 199°-4 (93°C), combining the odor of acetic with that of hydrosulphuric acid. It forms, with solution of acetate of lead, a crystalline precipitate containing PbS,C4N302S. Sulpiiacetic acid. — Pure acetic acid is mixed with 4; of its weight of anhydrous sulphuric acid, and the mixture digested for several days at a temperature of from 140° to 167° (60— 75°C). The solution of the mass in water, when saturated with carbonate of baryta or lead, deposits a crystalline baryta salt, or lead salt, containing respectively 2BaO,C4H2S208 -4- 3Aq. and 2PbO,C4H2S208. From these salts the acid may be separated by means of sulphuric or hydrosulphuric acid. Sulphacetic acid is also obtained by the action of Nordhausen acid upon acetamide (see p. 394) or acetonitrile (see p. 392.) Disulphometholic acid. — This name has been given to an acid, which is produced by the protracted action of Nordhausen acid upon sulphacetic acid, or upon acetic acid, acetamide, or acetonitrile, when carbonic acid is evolved. The product, diluted with water, and saturated with carbonate of baryta, furnishes a beautifully-crystallized and rather difficultly-soluble baryta com- pound, containing 2BaO,C2H2S4O10, from which the acid may be separated by means of sulphuric acid. Both sulphacetic acid and. disulphometholic acid are bibasic acids. The latter is identical with methionic acid (see p. 383). Acetone : pyroacetic spirit. — AVhen metallic acetates in an anhydrous state are subjected to destructive distillation, they yield, among other products, a peculiar inflammable volatile liquid, designated by the above names. It is most easily prepared by distilling carefully dried acetate of lead in a large earthen or coated glass retort, by a heat gradually raised to redness; the retort must be connected with a condenser well supplied with cold water. Much gas is evolved, chiefly carbonic acid, and the volatile product, but slightly contaminated with tar, collects in the receiver. The retort is found after the operation to contain minutely-divided metallic lead, which is some- times pyrophoric. The crude acetone is saturated with carbonate of potassa, and afterwards rectified in a water-bath from chloride of calcium. This com- pound may also be prepared by passing the vapor of strong acetic acid through an iron tube heated to dull redness ; the acid is resolved into acetone, carbonic acid, carbonic oxide, and carbonetted hydrogen. Pure acetone is a colorless limpid liquid, of peculiar odor: it has a density of 0'792, and boils at 132° (55°-5C); the density of its vapor is 2022. Acetone is very inflammable, and burns with a bright flame; it is miscible in all proportions with water, alcohol, and ether. The simplest formula of this substance, which is produced by the resolution of acetic acid into acetone and carbonic acid, is C3H30; but it is probable that this formula must be doubled. AVhen acetone is distilled with half its volume of Nordhausen sulphuric acid, ETHYLENE-ALCOHOL. 397 an oily liquid is obtained, which in a state of purity has a feeble garlic odor. It is lighter than water, and very inflammable. It contains C,eH,2, and is produced by the abstraction of the elements of water from acetone. It has received the name mesitilole. If pentachloride of phosphorus be dropped into carefully-cooled acetone, and the whole mixed with water, a heavy oil liquid separates, which is stated to contain C6H6C1. AVhen this is dissolved in alcohol, and mixed with caustic potassa, a second oily product results. This is lighter than water, has an aromatic odor, and contains C6H50. Sir Bobert Kane has described a number of other compounds formed by the action of acids, and other chemical agents, on acetone, from which he has inferred the existence of an organic salt-basyle, containing C6H5, and to which the name of mesityl has been given. Beise, on the other hand, has shown that by the action of chloride of platinum upon acetone, a yellow crys- tallizable compound can be obtained, having a composition expressed by the formula C0H6O 4- PtCl2. Acetic acid is not the only source of acetone: it is produced in the destruc- tive distillation of citric acid, and may be procured from sugar, starch, and gum, by distillation with 8 times their weight of powdered quicklime. The acetone is, in this case, accompanied by an oily, volatile liquid, separable by water, in which it is insoluble. This substance is called metaceione or propione; it contains C6H60; its boiling point is 212° (100°C). When acetate of potassa is heated with a great excess of caustic alkali, it is converted, as has been already remarked,1 into carbonic acid and light car- bonetted hydrogen, by the reaction of the oxygen of the water of the hydrate upon the carbon of the acid. C4II303,HO = C204 + C2H4. Etiiyi.f.ne-alcohol, glycol.—Becent researches, chiefly by AVurtz and Buff, have pointed out the existence of an alcohol-like body, C4H604, differing from ordinary alcohol only by containing two additional equivalents of oxygen. Among the derivatives of olefiant gas compounds of this body with chlorine, bromine, and iodine have been mentioned, containing C4H4C12, C4H4Br2, and r4H4l2, which by their chemical deportment are closely allied to chloride, bromide, and iodide of ethyl. The latter bodies, as has been stated before, are capable of exchanging chlorine, bromine, and iodine, for oxygen, and of simultaneously assimilating the elements of water, it being thereby converted into ethylic alcohol. The chloride, bromide, and iodide of olefiant gas, under favorable circumstances, exhibit a similar deportment, an alcoholic body being formed, to which the name ethylene-alcohol, or glycol, has been given. The analogy of these two reactions will be shown by a glance at the following equations: C4H5I 4- 2H0 == C4II50,HO -f . HI. Iodide Ethylic of ethyl. alcohol. C4H4T2 4- 4HO = ^C4Ijjl(V2HO 4- 2 III. Iodide of Ethylene-alcohol, ethylene. glycol, On distilling a mixture of iodide of ethylene with acetate of silver, an oily mixture is obtained, from which acetate of ethylene may be separated by fractional distillation. This is a liquid heavier than water, and boiling at 365° (185°C); treated with caustic potassa it furnishes the corresponding alcohol. 1 See page 172. 34 398 ETHYLENE-ALCOIIOT,. C4H4I2 4- 2(AgO,C4H303) = 2AgI 4- C4H402,2C4H303 Iodide of Acetate of ethylene. ethylene. C4H402.2C4H303 4- 2KO,HO = 2(KO,C4H303) 4- .C^^HO Acetate of Ethylene- ethylene, alcohol. Ethylene-alcohol is a colorless liquid, of a sweetish taste, soluble in water, alcohol, and ether, boiling at 383° (195°C). AVhen submitted to the action of dilute nitric acid, it is converted into oxalic acid, which stands to the new alcohol in the same relation as acetic acid to ethylic alcohol. C4H50, HO 4- 40 = C4H303, HO 4- 2110. C4H402,2HO 4- 80 = C406,2HO 4- 4H0. It has been pointed out that in the oxidation of ethylic alcohol the forma- tion of acetic acid is invariably preceded by that of aldehyde, C4H402. In a similar manner oxalic acid is not the direct product of oxidation of ethylene- alcohol. When treated with very dilute nitric acid this alcohol furnishes gly- colic acid, C4H305,HO, which was originally obtained from glycocoll (see Ani- mal Chemistry). It is highly probable that by modifying the process of oxidation, other intermediate substances will be obtained. By treating ethy- lic alcohol with nitric acid, M. Debus has obtained two compounds — an alde- hyde-like body, glyoxal, C4H204, and an acid, glyoxalic acid, C4H206, which obviously belong to the same series. Ethylene-alcohol (glycol) .... C4H604 Ethylene-aldehyde (isomeric with acetic acid). C4H404 (unknown) Glycolic acid .......C4H406 C4H408 (unknown) Glyoxalic aldehyde (glyoxal) .... C4H204 Glyoxalic acid ...... C4H206 Oxalic acid.......C4H2Og In describing the constitution of ethylic alcohol, and of acetic acid, we have represented these bodies as hydrated oxide of ethyl and as hydrated oxide of othyl. In the conception of this view alcohol and acetic acid may be derived from 2 molecules of water, by the substitution respectively of ethyl and othyl for 1 equivalent of hydrogen. Water . -. . . . g J02 Alcohol.....C4JJs J02 Acetic acid .... CA°2 j q2 In a similar manner ethylene-alcohol and oxalic acid may be derived from 4 molecules of water, in which 2 equivalents of hydrogen are replaced re- spectively by one molecule of C4H4 (ethylene) and C404 (oxalyl), To these molecules, accordingly, we attribute a biatomic character, that is, the power of replacing 2 equivalents of hydrogen, which may be conveniently indicated by two dashes on the right of the symbol. ETHYLENE-ALCOHOL. 399 Water ..... % JoA Ethylene alcohol . . . (C4{|4)"}04 Oxalic acid .... (C<2t)" }04 Alcohols containing biatomic molecules are designated as biatomic alcohols; thus ethylene alcohol is a biatomic alcohol, whilst ethyl-alcohol is a monatomic alcohol. The substance mentioned under the name of acetal among the products of oxidation of alcohol is the ethylic ether of ethylene-alcohol. ^12ll14U4 — c4n5 ;u< 400 METHYL SERIES. SUBSTANCES MORE OR LESS ALLIED TO ALCOHOL. METHYL-SERIES.—WOOD-SPIRIT AND ITS DERIVATIVES. In the year 1812, Mr. P. Taylor discovered, among the liquid products of the destructive distillation of dry-wood, a peculiar volatile inflammable liquid, much resembling spirit of wine, to which allusion has already been made. This substance has been shown by MM. Dumas and Peligot to be another alcohol, forming an ether and a series of compounds, exactly corresponding with those of vinous spirit. Wood-spirit, like ordinary alcohol, may be regarded as an hydrated oxide of a body like ethyl, containing C2H3, called methyl.1 A very great number of compound methyl-ethers have been described ; they present the most complete parallelism of origin, properties, and constitution with those derived from common alcohol. Wood-spirit Series. Methyl (symbol, Me) Oxide of methyl Hydride of methyl (marsh-gas) Chloride of methyl . Iodide of methyl, &c. Zinc-methyl .... AVood-spirit .... Sulphate of oxide of methyl . Nitrate of oxide of methyl, &c. Sulphomethylic acid. Formic acid .... Chloroform .... ^2^3 C2H30 C2H3H C2H3C1 C2H3I C2II3Zn C2H30,HO C2H30,S03 C2H30,N05 C2H30,2S03,IIO C2H03,HO C-H CI. Hydrated oxide of methyl: pyroxylic spirit; wood-spirit; MeO,HO. __The crude wood-vinegar probably contains about y1^ part of this substance, which is separated from the great bulk of the liquid by subjecting the whole to distillation, and collecting apart the first portions which pass over. The acid solution thus obtained is neutralized by hydrate of lime, the clear liquid separated from the oil which floats on the surface, and from the sediment at the bottom of the vessel, is again distilled. A volatile liquid, which burns like weak alcohol, is obtained: this may be strengthened in the same manner as ordinary spirit, by rectification, and ultimately rendered pure and anhy- drous, by careful distillation from quicklime, by the heat of a water-bath. 1 From pi6v, wine, and v\v, -wood; the termination 8X17, or yl, is very frequently employed in the sense of matter, material. AVOOD-SPIRIT AND ITS DERIVATIVES. 401 Pure wood-spirit is a colorless, thin liquid, of peculiar odor, quite different from that of alcohol, and burning, disagreeable taste: it boils at 152° (66°6C), and has a density of 0-798 at 68° (20°C). The density of its vapor is 1-12. AVood-spirit mixes in all proportions with water, when pure ; it dissolves resins and volatile oils as freely as alcohol, and is often substituted for alcohol in various processes in the arts, for which purpose it is prepared on a large scale. It may be burned instead of ordinary spirit in lamps; the flame is pale-colored, like that of alcohol, and deposits no soot. AVood-spirit dissolves caustic baryta ; the solution deposites, by evaporation in vacuo, acicular crys- tals, containing BaO 4- MeO.HO. Like alcohol, it dissolves chloride of cal- cium in large quantity, and gives rise to a crystalline compound, resembling that formed by alcohol, and containing, according to Kane, CaCl 4- 2 (MeO,IIO). Oxide of methyl; wood-ether; MeO.—One part of wood-spirit and 4 parts of concentrated sulphuric acid are mixed and exposed to heat in a flask fitted with a perforated cork and bent tube; the liquid slowly blackens, and emits large quantities of gas, which may be passed through a little strong strong solution of caustic potassa, and collected over mercury. This is the wood-spirit ether, a permanently gaseous substance, which does not liquefy at the temperature of 3° (-16°-1C). It is colorless, has an ethereal odor, and burns with a pale and feebly-luminous flame. Its specific gravity is 1-617. Cold water dissolves about 33 times its volume of this gas, acquiring thereby the characteristic taste and odor of this substance: when boiled, the gas is again liberated. Alcohol, wood-spirit, and concentrated sulphuric acid, dis- solve it in still larger quantity. Under the head of ether it has been mentioned that the generally-received relation of this substance to the other ethyl-compminds had been rendered doubtful by recent researches. The same remark of course applies to me- thylic ether, which is in every respect analogous to common ether. It was fust proposed by Berzelius, and has long been urged by MM. Laurent and Gcrhardt, that the composition of alcohol being expressed by the formula C4H602. the true formula of ether was C8II10O2, and not C4H50. The correct- ness of this view has lately been established by a series of beautiful experi- ments carried out by Prof. Williamson. He found that the substance pro- duced by dissolving potassium in alcohol, which has the formula C4H50,KO, wheu acted upon by iodide of ethyl, furnishes iodide of potassium and per- fectly pure ether. This reaction may be expressed by the two following equa- tions : — C4H50,KO 4- C4H5I = KI 4- 2C4H60, or C4H50,KO 4- C4H8l = KI 4- C8H10O2. That in this reaction, not two equivalents of ether are formed, as represented in the first equation, but that a compound CsH,0O2 is formed, as expressed in the second, is clearly proved by substituting, when acting upon the compound C4H60,KO, for the iodide of ethyl, the corresponding methyl-compound. In this case neither common ether nor methyl-ether is formed, but an interme- diate compound C6H802 = C4H5O.02H3O. This substance is insoluble in water, and has a peculiar odor similar to that of ether, but boils at 50° (10°C). It is very probable that the substances, which have been described by the terms ethyl and methyl, likewise are not C4H5 and C2H3, but C8Hl0 and C4H6. The limits of this elementary work will not permit us at present to enter into the details of this question, which is still under the discussion of chemists. Chloride of methyl, MeCl.—This compound is most easily prepared by heating a mixture of 2 parts of common salt, 1 of wood-spirit, and 3 of con- centrated sulphuric acid; it is a gaseous body, which may be conveniently collected over water, as it is but slightly soluble in that liquid. Chloride of methyl is colorless ; it has a peculiar odor and sweetish taste, and burns, 34* 402 METHYL SERIES. when kindled, with a pale flame, greenish towards the edges, like most com- bustible chlorine-compounds. It has a density of 1-731, and is not liquified at 0° (—17°-7C). The gas is decomposed by transmission through a red-hot tube, with slight deposition of carbon, into hydrochloric acid gas and a car- bonetted hydrogen, which has been but little examined. Iodide of methyl, Mel, is a colorless and feebly-combustible liquid, ob- tained by distilling together 1 part of phosphorus, 8 of iodine, and 12 or 15 of wood-spirit. It is insoluble in water, has a density of 2-237, and boils at 111° (43°-8C). The density of its vapor is 4-883. The action of zinc upon iodide of methyl in sealed tubes furnishes a colorless gas, apparently a mixture of several substances, among which methyl does occur.1 The residue con- tains iodide of zinc, together with a volatile substance of very disagreeable odor, which absorbs oxygen with so much avidity, that it takes fire when coming in contact with the air. It is zinc-methyl, C2H3Zn, corresponding to zinc-ethyl (see page 385), and may be obtained by distilling the residue of the reaction of zinc upon iodide of methyl in an apparatus filled with hydrogen. AVhen mixed with water it yields oxide of zinc and light, carbonetted hydrogen! Cyanide of methyl, MeCy.—If a dry mixture of sulphomethylate of baryta and cyanide of potassium are heated in a retort, a very volatile liquid of a powerful odor distils over. It generally contains hydrocyanic acid and water, from which it is separated by distillation, first over red oxide of mer- cury, and then over anhydrous phosphoric acid. When thus purified, it has an agreeable aromatic odor, and boils at 170°-6 (77°C). AVhen boiled with potassa, it undergoes a decomposition analogous to that of cyanide of ethyl (see page 372); it absorbs 4 eq. of water, and yields acetic acid and ammonia. MeCy = C4H3N H4O4 C,H,NO, C4H30,HO = C4H4 04 H9N C4H7N04 It has been mentioned that this compound may be obtained by abstracting 4 eq. of water from acetate of ammonia by means of phosphoric acid. (See page 392). v "Compounds of Methyl with bromine, fluorine, and sulphur have also been obtained. Sulphate of oxide of methyl, MeO,S03. — This interesting substance is prepared by distilling 1 part of wood-spirit with 8 or 10 of strong oil of vitriol: the distillation may be carried nearly to dryness. The oleaginous liquid found in the receiver is agitated with water, and purified by rectifica- tion from powdered caustic baryta. The product, which is the body sought is a colorless oily liquid, of alliaceous odor, having a density of 1-324 and boiling at 370° (187°-7C). It is neutral to test-paper, and insoluble in water but decomposed by that liquid, slowly in the cold, rapidly and with violence at a boiling temperature, into sulphomelhylic acid and wood-spirit which is thus reproduced by hydration of the liberated methylic ether. Anhydrous lime or baryta have no action on this substance; their hydrates, however and those of potassa and soda, decompose it instantly, with production of a sul- phomethylate of the base, and wood-spirit. When neutral sulphate of methvl is heated with common salt, it yields sulphate of soda and chloride of methyl • with cyanide of mercury or potassium, it gives a sulphate of the base and cyanide of methyl; with dry formate of soda, sulphate of soda and formate of methyl. These reactions possess great interest. Nitrate of the oxide of methyl, MeO,N05.— One part of nitrate of potassa is introduced into a retort, connected with a tubulated receiver to which is attached a bottle, containing salt and water, cooled by a freezi'ne- mixture; a second tube serves to carry off the incondensable gases to a 1 The same compound is believed to occur among the substances ni-r>Hi„>ort k„ ♦», i- the galvanic current upon acetic acid. See valeric acid. UDStances Pr°1uced by the action of WOOD-SPIRIT AND ITS DERIVATIVES. 403 chimney. A mixture of one part of wood-spirit and 2 of oil of vitriol is made, and immediately poured upon the nitre; reaction commences at once, and requires but little aid from external heat. A small quantity of red vapor is seen to arise, and an ethereal liquid condenses, in great abundance, in the receiver, and also in the bottle. When the process is at an end, the distilled products are mixed, and the heavy oily liquid obtained separated from the water. It is purified by several successive distillations by the heat of a water-bath from a mixture of chloride of calcium and litharge, and, lastly, rectified alone in a retort, furnished with a thermometer passing through the tubulature. The liquor begins to boil at about 140° (60°C); the temperature soon rises to 150° (65°-5C), at which point it remains constant; the product is then collected apart, the first and most volatile portions being contaminated with hydrocyanic acid and other impurities. Even with these precautions, the nitrate of methyl is not quite pure, as the analytical results show. The pro- perties of the substance, however, remove any doubts respecting its real nature. Nitrate of methyl is colorless, neutral, and of feeble odor; its density is 1-182; it boils at 150° (6-3°-5C), and burns, when kindled, with a yellow flame. Its vapor has a density of 2-64. and is eminently explosive; when heated in a flask or globe to 300° (149°C), or a little above, it explodes with fearful violence; the determination of the density of the vapor is, conse- quently, an operation of danger. Nitrate of methyl is decomposed by a solu- tion of caustic potassa into nitrate of that base and wood-spirit. Oxalate of oxide of methyl, MeO,C203. — This beautiful and interesting substance is easily prepared by distilling a mixture of equal weights of oxalic acid, wood-spirit, and oil of vitriol. A spirituous liquid collects in the receiver, which, exposed to the air, quickly evaporates, leaving the oxalic methyl-ether in the form of rhombic transparent crystalline plates, which may be purified by pressure between folds of bibulous paper, and redistilled from a little oxide of lead. The product is colorless, and has the odor of common oxalic ether ; it melts at 124° (51°-1C), and boils at 322° (161°C). It dissolves freely in alcohol and wood-spirit, and also in water, which, however, rapidly decomposes it, especially when hot, into oxalic acid and wood-spirit. The alkaline hydrates effect the same change even more easily. Solution of am- monia converts it into oxamide and wood-spirit. AVith dry ammoniacal gas it yields a white, solid substance, which crystallizes from alcohol in pearly cubes: this new body, designated oxamelhylane, or oxamate of methyl, con- tains C6H5N06 = C2H30,C4H2N05. Many other salts of oxide of methyl have been formed and examined. The acetate, MeO,C4H303, is abundantly obtained by distilling 2 parts of wood- spirit with 1 of crystallizable acetic acid, and 1 of oil of vitriol. It much resembles acetic ether, having a density of 0.919, and boiling at 136° (57°-8C): the density of its vapor is 2-563. This compound is isomeric with formic ether. Formate of methyl, MeO,C2H03, is prepared by heating in a retort equal weights of sulphate of methyl and dry formate of soda. It is very vola- tile, lighter than water, and is isomeric with hydrate of acetic acid. Chloro- carbonic methyl-ether is produced by the action of phosgene gas upon wood- spirit, it is a colorless, thin, heavy, and very volatile liquid, containing C4H3C104 = C2II3O,C2C103. It yields with dry ammonia a solid crystallizable substance, called, urelhylane. (See page 375). Sulphomethylic acid, MeO,2S03,HO.—Sulphomethylate of baryta is pre- pared in the same manner as the sulphovinate: 1 part of wood-spirit is slowly mixed with 2 parts of concentrated sulphuric acid, the whole heated to ebulli- tion, and left to cool, after which it is diluted with water and neutralized with carbonate of baryta. The solution is filtered from the insoluble sulphate, and evaporated, first in a water-bath, and afterwards in vacuo to the duo degree of concentration. The salt crystallizes in beautiful square colorless tables, 404 METHYL 8 E II I E S . containing BaO,C2H30,2S03 4- 2HO, which effloresce in dry air, and are very soluble in water. By exactly precipitating the base from this substance by dilute sulphuric acid, and leaving the filtered liquid to evaporate in the air, hydrated sulphomethylic acid may be procured in the form of a sour, syrupy liquid, or as minute acicular crystals, very soluble in water and alcohol. It is very instable, being decomposed by heat in the same manner as sulpho- vinic acid. Sulpho-methylate of potassa crystallizes in small, nacreous, rhombic tables, which are deliquescent; it contains KO,C2H30,2S03. The lead-salt is also very soluble. Formic acid. — As alcohol by oxidation under the influence of finely- divided platinum gives rise to acetic acid, so wood-spirit, under similar cir- cumstances, yields a peculiar acid product, produced by the substitution of 2 eq. of oxygen for 2 eq. of hydrogen, to which the term formic acid is given, from its occurrence in the animal kingdom, in the bodies of ants. The expe- riment may be easily made by enclosing wood-spirit in a glass jar with a quan- tity of platinum-black, and allowing moderate access of air; the spirit is gradually converted into formic acid. There has not been found an interme- diate product corresponding to aldehyde. Anhydrous formic acid, as in the salts, contains C2H03, or the elements of 2 eq. carbonic oxide, and 1 eq. water. Pure hydrate of formic acid, C2II03.HO, is obtained by the action of sul- phuretted hydrogen on dry formate of lead. The salt, reduced to fine powder, is very gently heated in a glass tube connected with a condensing apparatus, through which a current of dry sulphuretted hydrogen gas is transmitted. It forms a clear, colorless liquid, which fumes slightly in the air, of exceedingly penetrating odor, boiling at 209° (98°-5C), and crystallizing in large brilliant plates, when cooled below 32° (0°C). The sp. gr. of the acid is 1-235; it mixes with water in all proportions ; the vapor is inflammable, and burns with a bine flame. A second hydrate, containing 2 eq. of water, exists; its density is 1-11, and it boils at 223° (136°-1C). In its concentrated form this body is extremely corrosive; it attacks the skin, forming a blister or an ulcer, painful and difficult to heal. A more dilute acid may be prepared by a variety of processes. Starch, sugar, and many other organic substances often yield formic acid when heated with oxidizing agents: a convenient method is the following: — 1 part of sugar, 3 of binoxide of manganese, and 2 of water, are mixed in a very capacious retort, or large metal still; 3 parts of oil of vitriol, diluted with an equal weight of water, are then added, and when the first violent effervescence from the disengagement of carbonic acid has subsided, heat is cautiously applied, and a considerable quantity of liquid distilled over. This is very impure ; it contains a volatile oily matter, and some substance which communicates a pungency not proper to formic acid in that dilute state. The acid liquid is neutralized with carbonate of soda, and the resulting for- mate purified by crystallization, and, if needful, by animal charcoal. From this, or any other of its salts, solution of formic acid may be readily obtained by distillation with dilute sulphuric acid. It has an odor and taste much re- sembling those of acetic acid, reddens litmus strongly, and decomposes the alkaline carbonates with effervescence. Another process for making formic acid consists of distilling dry oxalic acid, mixed with its own weight of sand or pumice-stone in a glass retort. Car- bonic oxide and carbonic acid are disengaged, while a very acid liquid distils, which is formic acid contaminated with a small quantity of oxalic acid. By redistilling this mixture pure formic acid is obtained. This process yields a very strong acid, but only a small quantity in proportion to the oxalic acid employed. A still better result is obtained by distilling oxalic acid with glycerin. Formic acid, in quantity, may be extracted from ants by distilling the in- sects with water, or by simply macerating them in the cold liquid. WOOD SPIRIT AND ITS DERIVATIVES. 405 Formic acid is readily distinguished from acetic acid by heating it with a little solution of oxide of silver or mercury; the metal is reduced, and precipi- tated in a pulverulent state, while carbonic acid is evolved: this reaction is sufficiently intelligible. The protochloride of mercury is reduced, by the aid of the elements of water, to calomel, carbonic and hydrochloric acids being formed. Formic acid, when heated with concentrated sulphuric acid, splits into carbonic oxide and water; on the other hand carbonic oxide, when heated with caustic potassa, furnishes formate of potassa. The most important salts of formic acid are the following:—Formate of soda crystallizes in rhombic prisms containing 2 eq. of water; it is very soluble, and is decomposed like the rest of the-salts by hot oil of vitriol with evolution of pure carbonic oxide. Fused with many metallic oxides, it causes their reduc- tion. Formate of potassa is with difficulty made to crystallize from its great solubility. Formate of ammonia crystallizes in square prisms ; it is very soluble, and is decomposed by a high temperature into hydrocyanic acid and water, the elements of which it contains, NH40,C2H03—4HO = C2NH. This decom- position is perfectly analogous to that of acetate of ammonia (see page 392). The salts of baryta, strontia, lime, and magnesia form small prismatic crystals, soluble without difficulty. Formate of lead crystallizes in small, diverging, colorless needles, which require for solution 40 parts of cold water. The for- mates of manganese, protoxide of iron, zinc, nickel, and cobalt are also crystal- lizable. That of copper is very beautiful, constituting bright blue rhombic prisms of considerable magnitude. Formate of silver is white, but slightly soluble, and decomposed by the least elevation of temperature. Formates, when mixed with acetates and submitted to distillation, yield car- bonates and acetic aldehyde. MO,C2H034- MO,C4H303, =C4H402+ (MO,C02). Formate of the oxide of ethyl ; formic ether ; AeO, C2H03.—A mixture of 7 parts of dry formate of soda, 10 of oil of vitriol, and 6 of strong alcohol, is to be subjected to distillation. The formic ether, separated by the addition of water to the distilled product, is agitated with a little magnesia, and left several days in contact with chloride of calcium. Formic ether is colorless, has an aromatic smell, and density of 0-915, and boils at 133° (56°C). AVater dissolves this substance to a small extent. Chloroform.—This substance is produced, as already remarked, when an aqueous solution of caustic alkali is made to act upon chloral. It may be ob- tained with greater facility by distilling alcohol, wood-spirit, or acetone with a solution of chloride of lime. 1 part of hydrate of lime is suspended in 24 parts of cold water, and chlorine passed through the mixture until nearly the whole lime is dissolved. A little more hydrate is then added to restore the alkaline reaction, the clear liquid mixed with one part of alcohol or wood- spirit, and, after an interval of 24 hours, cautiously distilled in a very spacious vessel. A watery liquid containing a little spirit and a heavy oil collect in the receiver; the latter, which is the chloroform, is agitated with water, digested with chloride of calcium, and rectified in a water-bath. It is a thin, colorless liquid of agreeable ethereal odor, much resembling that of Dutch- liquid, and of a sweetish taste. Its density is 1-48, and it boils at 141°-8 (01°C); the density of its vapor is 4-1116. Chloroform is with difficulty kin- dled, and burns with a greenish flame. It is nearly insoluble in water, and is not affected by concentrated sulphuric acid. Alcoholic solution of potassa decomposes it, with production of chloride of potassium and formate of potassa. Chloroform may be prepared on a larger scale by cautiously distilling together good commercial chloride of lime, water, and alcohol. The whole product distils over with the first portions of water, so that the operation may be soon interrupted with advantage. This substance has been called strongly into notice from its remarkable effects upon the animal system in producing temporary insensibility to pain when its vapor is inhaled. 406 METHYL SERIES. Chloroform contains C2HC13: it is changed to formic acid by the substitution of 3 eq. of oxygen for the 3 eq. of chlorine removed by the alkaline metal. Bromoform, C2HBr3, is a heavy, volatile liquid, prepared by a similar pro- cess, bromine being substituted in the place of chlorine. It is converted by alkali into bromide of potassium and formate of potassa. Iodoform, C2HI3, is a solid, yellow, crystallizable substance, easily obtained by adding alcoholic solution of potassa to tincture of iodine, avoiding excess, evaporating the whole to dryness, and treating the residue with water. Iodoform is nearly insoluble in water, but dissolves in alcohol, and is decomposed by alkalies in the same manner as the preceding compounds. Formomf.thylal.—This is a product of the distillation of wood-spirit with dilute sulphuric acid and binoxide of manganese. The distilled liquid is satu- rated with potassa, by which the new substance is separated as a light oily fluid. AVhen purified by rectification, it is colorless, and of agreeable aromatic odor; it has a density of 0-855, boils at 170° (41 °C), and is completely soluble in three parts of water. It contains C6Hg04. It corresponds to acetal, and may be viewed as a compound of 2 eq. of ether with 1 eq. of the yet-unknown aldehyde of the methyl-series, C6H804 = 2C2H30,C2H202. It may also be derived from an alcohol, C2H404 = C2H202,2HO, standing to methylic alcohol in the same relation which obtains between ethylic and ethy- lenic alcohols. Methylene alcohol.......(C2H2)" 1 q4 Formomethylal . .....f p2!]2!" } °4 Methyl-mercaptan is prepared by a process similar to that recommended for ordinary mercaptan, sulphomethylate of potassa being substituted for the sulphoviuate of lime. It is a colorless liquid, of powerful alliaceous odor, and lighter than water; it boils at 68° (20°C), and resembles mercaptan in its action on red oxide of mercury. Products of the action of chlorine on the compounds of methyl.— Chlorine acts upon the methylic compounds in a manner strictly in obedience to the law of substitution; the carbon invariably remains intact, and every proportion of hydrogen removed is replaced by an equivalent quantity of chlorine. Methylic ether and chlorine, in a dry and pure condition, yield a volatile liquid product, containing C2H2C10: the experiment is attended with great danger, as the least elevation of temperature gives rise to a violent ex- plosion. This product in its turn furnishes, by the continued action of the gas, a second liquid containing C2HCI20. The whole of the hydrogen is even- tually lost, and a third compound, C2C130, produced. Chloride of methyl, C2H3C1, in like manner gives rise to three successive products. The first, C2H2CI2, is a volatile liquid, much resembling chloride of olefiant gas; the second, C2HC13, is no other than chloroform; the third is bichloride of carbon, C2C14. Some of these substances, especially chloroform and bichloride of carbon, have been obtained also by the action of chlorine on light carbonetted hydro- gen (marsh-gas), which thus becomes connected with the methyl-series. It may be regarded as hydride of methyl, a view which is likewise supported by its formation from zinc-methyl (see page 402); thus we have the following series:— Hydride of methyl . . . C2H3II. Light carbonetted hydrogen. Chloride of methyl . . C2H3C1. Chlorinetted chloride of methyl C2H2C12. Bichlorinetted ,, ,, " C2HC13. Chloroform. Trichlorinetted „ „ C2C14. Bichloride of carbon. KAKODYL AND ITS COMPOUNDS. 407 The acetate of methyl, C6H604, gives CGH4C1204, and C6H3C1304; the other methyl-ethers are without doubt affected in a similar manner. Commercial wood-spirit is very frequently contaminated with other sub- Stances, some of which are with great difficulty separated. It sometimes con- tains aldehyde, often acetone and propione, and very frequently a volatile oil, which is precipitated by the addition of water, rendering the whole turbid. The latter is a mixture of several hydro-carbons, very analogous to those con- tained in coal-tar. A specimen of wood-spirit, from AA'attwyl, in Switzerland, was found by Gmelin to contain a volatile liquid, differing in some respects from acetone, to which he gave the term lignone. A very similar substance is described by Schweizer and AVeidmann, under the name of xylite. Lastly, Mr. Scanlan has obtained from wood-spirit a solid, yellowish-red, crystallizable substance, called eblanin. It is left behind in the retort when the crude spirit is rectified from lime; it is insoluble in water, sublimes without fusion at 273° (133°-9C), and contains, according to Gregory, C2,H904. KAKODYL AND ITS COMPOUNDS. The substance long known under the name of fuming liquor of Cadet, pre- pared by distilling a mixture of dry acetate of potassa and arsenious acid, has been shown by M. Bunsen to be the oxide of an isolable organic basyl, capable of forming a vast number of combinations displacing other bodies, and being in turn displaced by them, in the same manner as a metal. The investigation of this difficult subject reflects the highest honor on the patience and skill of the discoverer. Kakodyl, so named from its poisonous and offensive .nature, contains three elements, viz., carbon, hydrogen, and arsenic; it may be viewed as a combination of 1 eq. of arsenic and 2 eqs. of methyl. Table of the most important Kakodyl-Compounds. Kakodyl (symbol Kd) .... C4H6As Oxide of kakodyl. .... KdO Chloride of kakodyl .... KdCl Chloride of kakodyl and copper . . KdCl -f- Cu2Cl Oxy-chloride of kakodyl . . . 3KdCl-4-KdO Terchloride of kakodyl . . . KdCl3 Bromide of kakodyl .... KdBr Iodide of kakodyl .... Kdl Cyanide of kakodyl .... KdCy Kakodylic acid.....Kd03 Kakodylate of silver .... AgO,Kd03 Kakodylate of kakodyl . . . KdO,Kd03 Sulphide of kakodyl .... KdS Sulphide of kakodyl and copper . . KdS -4- 3CuS Tersulphide of kakodyl . . . KdS3 Sulphur-salts, containing tersulphide of \ KdS,KdS3 — AuS,KdS3 kakodyl....../CuS,KdS3 —PbS,KdS3 Selenide of kakodyl .... KdSe Oxide of kakodyl; Cadet's-fuming liquid; alkarsin ; KdO. — Equal weights of acetate of potassa and arsenious acid are intimately mixed and introduced into a glass retort connected with a condenser and tubulated re- ceiver, cooled by ice : a tube is attached to the receiver to carry away the permanently-gaseous products to some distance from the experimenter. Heat is then applied to the retort, which is gradually increased to redness. At the close of the operation, the receiver is found to contain two liquids, besides a 408 METHYL SERIES. quantity of reduced arsenic: the heavier of these is the oxide of kakodyl in a colored and impure condition; the other chiefly consists of water, acetic acid, and acetone. The gas given off during distillation is principally carbo- nic acid. The crude oxide of kakodyl is repeatedly washed by agitation with water, previously freed from air by boiling, and afterwards redistilled from hydrate of potassa in a vessel filled with pure hydrogen gas. All these ope- rations must be conducted in the open air, and the strictest precautions adopted to avoid the accidental inhalation of the smallest quantity of the vapor or its products. Oxide of kakodyl is a colorless, ethereal liquid of great refractive power; it is much heavier than water, having a density of 1-462. It is very slightly soluble in water, but easily dissolved by alcohol; its boiling-point approaches 302° (150°C), and it solidifies to a white crystalline mass at 9° (-12°-GC). The odor of this substance is extremely offensive, resembling that of arsenetted hydrogen; the minutest quantity attacks the eyes and the mucous membrane of the nose: a larger dose is highly dangerous. When exposed to the air, oxide of kakodyl emits a dense white smoke, becomes heated, and eventually takes fire, burning with a pale flame, and producing carbonic acid, water, and a copious cloud of arsenious acid. It explodes when brought into contact with strong nitric acid, and inflames spontaneously when thrown into chlorine gas. The density of the vapor of this body is about 7-5. Oxide of kakodyl is generated by the reaction of arsenious acid on the elements of acetone, car- bonic acid being at the same time formed; the accompanying products are accidental: — 2 eq. acetone, C6H602, and 1 eq. arsenious acid, As03=l eq. oxide kako- dyl, C4H6AsO, and 2 eq. carbonic acid, C204. Chloride of kakodyl, KdCl.—A dilute alcoholic solution of oxide of kakodyl is cautiously mixed with an equally dilute solution of corrosive sub- limate, avoiding an excess of the latter; a white crystalline, inodorous pre- cipitate falls, containing KdO 4-2HgCl: when this is distilled with concen- trated liquid hydrochloric acid, it yields corrosive sublimate, water, and chloride of kakodyl, which distils over. The product is left some time in con- tact with chloride of calcium and a little quicklime, and then distilled alone in an atmosphere of carbonic acid. The pure chloride is a colorless liquid, which does not fume in the air, but emits a vapor even more fearful in its effects, and more insupportable in odor than that of the oxide. It is heavier than water, and insoluble in that liquid, as also in ether; alcohol, on the other hand, dissolves it with facility. The boiling-point of this compound is a little above 212° (100°C); its vapor is colorless, spontaneously inflammable in the air, and has a density of 4-56. Dilute nitric acid dis- Fi,„ 186 solves the chloride without change; with the concentrated acid ignition and explosion occur. Chloride of kakodyl combines with subchloride of copper to a white, insoluble, crystalline double salt, containing KdC14-Cu2Cl, and also with oxide of kakodyl. Kakodyl in a free state may be obtained by the action of metallic zinc, iron, or tin upon the above-described com- pound. Pure and anhydrous chloride of kakodyl is digested for three hours, at a temperature of 212° (100°C), with slips of clean metallic zinc contained in a bulb blown upon a glass tube, previously filled with carbonic acid gas, and her- metically sealed. The metal dissolves quietly without evolu- tion of gas. AVhen the action is complete, and the whole cool, the vessel is observed to contain a white saline mass which, on the admission of a little water, dissolves, and libe- rates a heavy oily liquid,, the kakodyl itself. This is ren- dered quite pure by distillation from a fresh quantity of zinc, the process being conducted in the little apparatus shown in the margin, KAKODYL AND ITS COMPOUNDS. 409 which is made from a piece of glass tube, and is intended to serve the purpose both of retort and receiver. The zinc is introduced into the upper bulb, and the tube drawn out in the manner represented. The whole is then filled with carbonic acid, and the lower extremity put into communication with a little hand-syringe. On dipping the point a into the crude kakodyl, and making a slight movement of exhaustion, the liquid is drawn up into the bulb. Both extremities are then sealed in the blowpipe flame, and after a short digestion at 212° (100°C), or a little above, the pure kakodyl is distilled off into the lower bulb, which is kept cool. It forms a colorless, transparent, thin liquid, much resembling the oxide in odor, and surpassing that substance in inflammability. AVhen poured into the air, or into oxygen gas, it ignites instantly; the same thing happens with chlorine. AVith very limited access of air it throws off white fumes, passing into oxide, and eventually into kakodylic acid. Kakodyl boils at oua° (170°C), and when cooled to 21° (-6°-lC) crystallizes in large, transparent, square prisms. It combines directly with sulphur and chlorine, and, in fact, may readily be made to furnish all the compounds previously derived from the oxide. It constitutes one of the most perfect types of an organic quasi-metal which chemistry yet possesses. Kakodyl is decomposed by a temperature inferior to redness into metallic arsenic, and a mixture of 2 measures light carbonetted hydrogen (marsh-gas, hydride of methyl), and 1 measure olefiant gas. This decomposition connects kakodyl most intimately with the methyl series; a connection which is also clearly proved by the formation of small quantities of kakodyl by the action of iodide methyl upon an alloy of arsenic and sodium. AVe shall return to this reaction. Chloride of kakodyl forms a hydrate, which is thick and viscid, and readily decomposable by chloride of calcium, which withdraws the water. In the preparation of the chloride, and also in other operations, a small quantity of a red amorphous powder is often obtained, called erytrarsin. This is insoluble in water, alcohol, ether, and caustic potassa, but is gradually oxidized by ex- posure to the air, with production of arsenious acid. It contains C4H603AS3. Iodide of kakodyl, Kdl.—This is a thin, yellowish liquid, of offensive odor, and considerable specific gravity, prepared by distilling oxide of kako- dyl with strong solution of hydriodic acid. A yellow crystalline substance is at the same time formed, which is an oxyiodide. Bromide and fluoride of kako- dyl have likewise been obtained and examined. Sulphide of kakodyl, KdS, is prepared by distilling chloride of kakodyl with a solution of the hydrosulphate of sulphide of barium. It is a clear, thin, colorless liquid, smelling at once of alkarsin and mercaptan, insoluble in water, and spontaneously inflammable in the air. Its boiling-point is high, but it distils easily with the vapor of water. The substance dissolves sulphur, and generates tersulphide of kakodyl, KdSa, which is a sulphur-acid, and combines with the sulphides of gold, copper, bismuth, lead, and antimony. Cyanide of kakodyl, KdCy. — The cyanide is easily formed by distilling alkarsin with strong hydrocyanic acid, or cyanide of mercury. Above 91° (32°-7C) it is a colorless, ethereal liquid, but below that temperature it crys- tallizes in colorless, four-sided prisms, of beautiful diamond lustre. It boils at about 284° (140°C), and is but slightly soluble in water. It requires to be heated before inflammation occurs. The vapor of this substance is most fearfully poisonous: the atmosphere of a room is said to be so far contami- nated by the evaporation of a few grains, as to cause instantaneous numbness of the hands and feet, vertigo, and even unconsciousness. Kakodylic acid (alkargen) ; Kd03.—This is the ultimate product of the action of oxygen at a low temperature upon kakodyl or its oxide: it is best prepared by adding oxide of mercury to that substance, covered with a layer of water, and artificially cooled, until the mixture loses all odor, and aSter- 35 410 PROPYLIC ALCOHOL. wards'decomposing any kakodylate of mercury, that may have been formed, by the cautious addition of more alkarsin. The liquid furnishes, by evapora- tion to dryness and solution in alcohol, crystals of the new acid. The sul- phide, and other compounds of kakodyl, yield, by exposure to air, the same substance. Kakodylic acid forms brilliant, colorless, brittle crystals, which have the form of a modified square prism ; it is permanent in dry air, but de- liquescent in a moist atmosphere. It is very soluble in water and in alcohol, but not in ether ; the solution has an acid reaction. AVhen mixed with alka- lies and evaporated, a gummy, amorphous mass results AVith the oxides of silver and mercury, on the other hand, it yields crystallizable compounds. It unites with oxide of kakodyl, and forms a variety of combinations with metallic salts. Alkargen is exceedingly stable; it is neither affected by red, fuming, nitric acid, aqua regia, nor even chromic acid in solution: it may be boiled with these substances without the least change. It is deoxidized, however, by phosphorous acid and protochloride of tin to oxide of kakodyl. Dry hydriodic acid gas decomposes it, with production of water, iodide of kakodyl, and free iodine; hydrochloric acid, under similar circumstances, converts it into a corresponding terchloride, which is solid and crystallizable. Lastly, what is extremely remarkable, this substance is not in the least degree poisonous. Parakakodylic oxide.—When air is allowed access to a quantity of alkar- sin, so slowly that no sensible rise of temperature follows, that body is gradually converted into a thick syrupy liquid, full of crystals of kakodylic acid. Long exposure to air, or the passage of a copious current through the mass, heated to 158° (70°C), fails to induce crystallization of the whole. If in this state water be added, everything dissolves, and a solution results which contains kakodylic acid, partly free, and partly in combination with the oxide of kakodyl. When this liquid is distilled, water, having the odor of alkarsin, passes over, and afterwards an oily liquid, which is the new compound. Impure kakodylic acid remains in the retort. Parakakodylic oxide, purified by rectification from caustic baryta, is a color- less, oily liquid, strongly resembling alkarsin itself in odor, relations to sol- vents, and in the greater number of its reactions. It, however, neither fumes in the air, nor takes fire at common temperatures; its vapor mixed with air, and heated to 190° (87°-8C), explodes with violence. By analysis, it is found to have exactly the same composition as ordinary oxide of kakodyl. propyl sebies. propylic alcohol. In the manufacture of spirits from saccharine liquids derived from the vege- table kingdom, ethyl-alcohol, the principal product of the fermentation is always accompanied by certain acrid volatile oils, generally called fusel-oils which are very difficult to separate. These oils consist of various substances' but almost invariably contain compounds which are analogous to methylic and ethylic alcohols. The fusel-oil of the marc-brandy of the south of France, according to the researches of M. Chancel, contains several alcohols, which boil at different temperatures, and may be separated by distillation. By repeatedly rectify- ing the first products obtained in the distillation of this fusel-oil, a substance is at last procured, which boils at 240°-8 (96°C), and the composition of which is represented by the formula CcII802 = C6H70, HO. This substance stands to ethylic alcohol in the same relation in which the latter stands to AND ITS DERIVATIVES. 411 methylic alcohol. Chancel designates this compound as trityl-alcohol, or hydrated oxide of trityl. AVe prefer the name propylic alcohol, or hydrated oxide of propyl. Propylic alcohol is very soluble in water, but does not dis- solve in that liquid in all proportions. This substance possesses all the pro- perties of an alcohol: heated with concentrated sulphuric acid, it yields a conjugate acid analogous to sulphovinic acid, the potassa-salt of which has the formula C6H7O.S03.KO,S03. Propylic alcohol, when submitted to the action of dehydrating agents, such as sulphuric or phosphoric acid, will probably yield the hydrocarbon, C6H6, analogous to olefiant gas. This hydrocarbon propylene is known; it is ob- tained by a variety of processes (see below), and especially from glycerin, among the derivatives of which it will be noticed. Berthelot has observed that this hydrocarbon propylene, C6H6, dissolves in sulphuric acid, and that this solution, when diluted with water and dissolved, furnishes propylic alcohol. Propionic acid. —Under the influence of oxidizing agents, propylic alcohol undergoes a change similar to that of ordinary alcohol. It is converted into an acid analogous to acetic acid, which is called propionic acid. This sub- stance, which contains C6H604 = C6H603,HO, is a colorless, transparent liquid, of a peculiar, somewhat pungent odor, similar to that of acetic acid. It boils at 287° (142°C). Propionic acid is soluble in water, and is separated again from this solution by the addition of chloride of calcium or phosphoric acid. AVith the metallic oxides it forms crystalline salts, which are soluble in water. The baryta-salt, BaO,C6H5034- aq, is very soluble in water, tolerably soluble in spirits of wine, and nearly insoluble in absolute alcohol. Submitted to dry distillation it yields propione (Morley). The occurrence of this substance among the products of the dry distillation of the acetates has been already noticed, p. 397. Propione treated with oxidizing agents is reconverted into propionic acid. This acid is also formed by the action of hydrate of potassa, in a melted state, upon sugar, and is among the products of fermentation of glycerin. The formation of propionic acid by the action of potassa upon cya- nide of ethyl has been already mentioned, p. 373. Quite recently Mr. Wanklyn has observed that potassium-ethyl (see page 386) absorbs carbon!.? acid with formation of propionate of potassa, KC4H6 -f- 2C02 = KO,C6H50.. APPENDIX TO THE PROPYL SERIES. Allyl series. —In the preceding paragraphs, the hydrocarbon propylene, CGli6, has been repeatedly mentioned. This hydrocarbon was originally ob- served by Captain Beynolds, who produced it, together with other hydrocar- bons, by the destructive distillation of fusel-oil. Reynolds prepared several of the derivations of this compound, especially the products C6H6CI2, C6H6Br2, and C6H5C1 and C6II6Br. He pointed out the close relation of these latter com- pounds with the essential oils of garlic and mustard, that they might be con- sidered as chloride and bromide of allyl, C6H5, the radical generally assumed in these oils, and that the action of these substances upon sulphide and sul- phocyanide of potassium would probably lead to the artificial production of garlic-oil and mustanf-.oil. The difficulty of procuring the chlorine- and bro- mine-compounds by this method in sufficient quantity and purity, prevented Beynolds from establishing by experiment the relation which he had pointed out. A new source of propylene-compounds has since been opened by MM. Berthelot and De Luca, who have found that the action of iodide of phosphorus upon glycerin gives rise to the formation of an oily body, which is the iodide 412 PROPYLIC ALCOHOL to the chloride and bromide above mentioned. The* best proportions for producing this compound are, 200 parts of iodide of phosphorus and 57 parts of glycerin. By submitting this iodide to the action of sulphocyanide of potassium, MM. Berthelot and De Luca have actually produced oil of mustard with all its properties. Treated with bromine, iodide of allyl is converted into a bromide of the formula C6H,;Br3. The close analogy of oil of garlic and oil of mustard, sulphide, and sulpho- cyanide of ally] with sulphide and sulphocyanide of ethyl, rendered it probable that these two substances might be derived from an alcohol analogous to com- mon alcohol. This alcohol has been lately discovered by Cahours and Ilof- mann. Allylic alcouol. — Iodide of allyl (iodide of propylene, the iodine-com- pound obtained from glycerin), dissolved in dry ether, and submitted to the action of oxalate of silver, furnishes, together with iodide of silver, an oily liquid boiling at 404° (207°C). AgO,C203 -f C6H6I = Agl 4- C6H50,C203 Oxalate of Iodide of' Iodide of Oxalate of silver. allyl. silver. allyl. Oxalate of allyl, when treated with dry ammonia, suffers exactly the same decomposition as oxalate of ethyl (page 374), being converted into oxamide, with separation of allylic alcohol. C6H60,C203 4- NH3 = NH2,C202 4- C6H50,HO Oxalate of allyl. Oxamide. Allylic alcohol. Allylic alcohol is a colorless, very mobile liquid, soluble in water in all pro- portions, which boils at 217° (103°C). It has a slightly acrid odor, resem- bling mustard. It dissolves potassium with evolution of hydrogen, being con- verted into a gelatinous mass, which is violently attacked by iodide of ally], iodide of potassium and allylic ether being produced. KO,C6H50 4- C6H5I = KI -f 2C6H50. By distilling allyl-alcohol with chloride, bromide, and iodide of phosphorus, the hydrochloric, hydrobromic, and hydriodic ether of the series are readily obtained. Allylic alcohol dissolves in concentrated sulphuric acid, producing a conjugated acid similar to sulphovinic acid, which forms crystallizable salts, represented by the general formula C6H50,S03,MO,S03. Allylic alcohol is powerfully attacked by oxidizing agents. A mixture of bichromate of potassa and sulphuric acid acts with extraordinary violence, giving rise to the forma- tion of acrolein and acrylic acid, the aldehyde and the acid of the series. Pla- tinum black produces the same effects. The compound ethers of allyfic alcohol may be obtained by the processes which have furnished the corresponding terms of the ethyl-series, or frequently more conveniently by the action of iodide of allyl on the silver salts of the acids. The acetate, benzoate, buty- rate, and cyanate have been thus obtained. The radical of this series, C6H5, which is an oily substance, boiling at a hio-h temperature, has been lately isolated by Berthelot and De Luca. It is ob- tained by the action of sodium upon iodide of allyl. Acrolein and acrylic acid.—When a neutral fat is subjected to destruc- tive distillation, it furnishes, as has been already mentioned, among other nro- ducts, an excessively volatile acrid substance, which attacks the eyes and the mucous membrane of the nose most distressingly. As the neutral fats alone AND ITS DERIVATIVES. 413 yield this body, and the fatty acids never, it is known to arise from the ele- ments of the glycerin ; and glycerin itself under certain circumstances may be made to produce acrolein abundantly. It is best prepared by distilling gly- cerin with bisulphate of potassa; both the preparation and purification are attended with great difficulties. Pure acrolein is a thin, colorless, highly-volatile liquid, lighter than water, and boiling at 126° (52°-9C). Its vapor is irritating beyond description. It is sparingly soluble in water, freely in alcohol and ether. According to M. Itcdtenbacher it contains C6H402. Acrolein, by keeping, undergoes partial decomposition, yielding a white, flocculent, indifferent body, disacryle; the same substance is sometimes pro- duced together with acrylic acid by exposure to the air. In contact with alka- lies, acrolein suffers violent decomposition, producing, like aldehyde, a resinous body. When exposed for some time to the air, or when mixed with oxide of silver, acrolein oxidizes with avidity, and passes into acrylic acid, which resembles in very many particulars acetic and propionic acids; it contains C6H303,HO. Acrolein, allylic alcohol, and acrylic acid stand to each other in the same relation which obtains between ethylic alcohol, aldehyde, and acetic acid. The analogy of the acetyl- and allyl-series becomes obvious by the following synopsis: — Alcohol . . C4H602 Allylic alcohol . . C6H602 Aldehyde . . C4H402 Acrolein . . C6H402 Acetic acid . . C4ll404 Acrylic acid . . C6H404 The following table represents the principal allyl-compounds: — Allyl.........C6H5 Allylic alcohol.......C6H50,HO Allylic ether.......C6H50,C6H50 Ethyl-allylic ether......C6H50,C4HB0 Chloride of allyl.......C6H6C1 Bromide of allyl . . •.....C6H5Br Iodide of allyl . . . ... . C6H5I Sulphide of allyl (garlic oil).....C6H5S Hydrosulphide of sulphide of allyl (allyl mercaptan) C6H5S,HS Sulpho-cyanide of allyl (mustard oil) . . . C6H5S,C2NS Carbonate of allyl......C6H50,C02 Acetate of allyl.......C6H50,C4H303 Oxalate of allyl . .'.....C6H50,C203 Sulphallylic acid.......C6H50,S03,HO,S03 Propylene........C6H6 Acrolein, acrylic aldehyde.....C6H402 Allylic acid........C6H603,HO Propylene alcohol or propyl-glycol.—By submitting bromide of propy- lene, C6H6Br2, to the succession of processes which have been mentioned under the head of ethylene-alcohol, M. AA'urtz has obtained the biatomic alco- hol, C61I804. It is a liquid boiling at 370° (188°Cj, which by slow oxidation is converted into lactic acid C6H606 (see page 368), corresponding to the gly- culic acid of the ethylene-series. C6TI6Br2 + 2(AgO,C4H303) = C6TI602,2C4H303 4- 2AgBr Bromide of Acetate of silver. Acetate of propyl- propylene, glycol. 33* 414 BUTYLIC ALCOHOL. C6H602,2CJI303 4- 2KOIIO = C6H602,2HO -f- 2(KO,C4H303) Acetate of pro- pyl-glycol. Propyl- glycol. Acetate of potassa. C6H602,2HO + 40 = C6H606 2H0 Propyl- glycol. Glycerin.—In the paragraph on the allyl-series an oily bromine compound, C6II6Br3, has been mentioned, which is formed by the action of bromine upon iodide of allyl. This substance, tribromide of allyl, when submitted to the action of acetate of silver, furnishes a new acetate. C6H5Br3-4- 3(AgO,C4H303) = Tribro- mide of allyl. C6H5034-3C4H303 -f SAgBr New acetate. The acetate boiled with potassa furnishes glycerin, a body of alcohol-like deportment, widely diffused in nature, whose various compound ethers con- stitute the extensive group of fatty bodies. C6H503,3C4H303 4- 3(K0,H0) = C6H503,3HO 4- 3(KO,C4H303) Acetate. Glycerin. Acetate of potassa. Glycerin, which will be more fully described in connection with the fatty bodies, yields, when submitted to the action of nitric acid, a peculiar acid, glyceric-acid, C6H608. Glycerin is the type of a triatomic alcohol. • It is extremely probable that corresponding alcohols, C2H03,3HO, and C4H303',3HO, will be discovered in the methyl- and ethyl-series. Chloroform, C2HC13, bromoform, C2HBr3, and iodoform, C2HI3, may, in fact, be viewed as the hydrochloric, hydrobromic, and hydriodic ethers of methyl-glycerin. The propyl-series is remarkable for its numerous representatives of the type alcohol. Propylic alcohol, C6H802 Propylene-alcohol, C6H804 Glycerin alcohol, C6Hg06 Allylic alcohol, C6H602 C6H70,HO (Monatomic). C6H602, + 2H° (Biatomic). C6H503,3HO (Triatomic). C6H50,HO (Secondary monatomic alcohol). BUTYL SERIES. Butylic alcohol.—This substance has been found by M. AVurtz to be pre- sent in the fusel-oil obtained by fermenting the molasses of beet-root sugar. In order to obtain it, the potato-oil is submitted to fractional distillation, and the liquid boiling between 226° and 244° (108° and 118C) repeatedly rectified over hydrate of potassa, until the boiling-point becomes constant at 228°-2 (109°C). Pure butylic alcohol is a colorless liquid,"of a powerful odor, lighter than water, in which it dissolves to a certain extent. Its formula is CaH. 0 = AMYLIC ALCOnOL. 415 CgHgO.HO, i. e., hydrated oxide of butyl. AVith sulphuric acid it furnishes a conjugate acid, analogous to sulphovinic acid, the potassa-salt of which con- tains C8H90,S03,KO,S03. Butylic alcohol has been lately minutely examined by M. Wurtz, who has prepared the ether of this series, C8H90; the hydrocarbon butylene, C8H8, an extremely volatile liquid, which had been previously observed as a very gene- ral product of the action of heat upon organic bodies ; chloride of butyl, C8H9C1, an ethereal liquid of pungent odor, boiling at 158° (70°C); bromide of butyl, CgH9Br, boiling at 192°-2 (89°C): and iodide of butyl, C8H9I, boiling at 2-j6° (121°C). If iodide of butyl be submitted to the action of potassium, several compounds are generated; the principal product of which is butyl, the radical of the series. Butyl, C8H9, which is also produced by the electro- lysis of valeric acid, (seep. 419), is a colorless, transparent liquid, lighter than water, boiling at 221° (105°C). AVhen fused with potassa, or submitted to the action of other oxidizing agents, butylic alcohol is converted into buty- ric acid, C8H804 = C8II703,HO, which has been noticed already in page 369, and which will be mentioned again in the section on Oils and Fats. Butyric acid, when pure, is a thin colorless liquid, of pungent rancid odor and sour taste. It is miscible in all proportions with water and alcohol. Its density is 0-963, and it boils and distils unchanged at 327° (164°C). It is attacked by chlorine, with production of oxalic acid and of a chlorinetted compound. Butyric acid has acquired a certain degree of importance from the curious discovery of MM. Pelouze and Gelis, that sugar, under particular circum- stances, is susceptible of becoming converted into that substance. A tolerably strong solution of common sugar mixed with a small quantity of casein and some chalk, and exposed for some time to a temperature of 95° (35°C), yields, by a species of fermentation, in which the casein is the active ferment, a large amount of butyrate of lime; carbonic acid and hydrogen gases are evolved during the whole period. This change may be thus expressed: — C24H28028 = 4HO -f 811 -f 8C02 4- 2(C8H703,HO) Grape-sugar. Butyric acid. The mixture directed for lactic acid ansAvers well (see page 368): lactate of lime is first formed in large quantity, and afterwards gradually dissolved and converted into butyrato, which may be decomposed by sulphuric acid and dis- tilled. This is an exceedingly interesting case of the half-artificial formation of an animal product. Butyric ether, AeO,C8H703, is a liquid of a fragrant pine-apple odor. It is sometimes used in confectionary. amyl series. In the manufacture of potato-brandy the crude spirit is found to be conta- minated with an acrid fusel-oil, which is extremely difficult to separate in a complete manner. Towards the end of the distillation, it passes over in con- siderable quantity; it may be collected apart, agitated with several successive portions of water to withdraw the spirit with which it is mixed, and redis- tilled. According to the researches of M. Cahours, this substance exhibits properties indicative of a constitution analogous to that of alcohol; it may be considered as the hydrate of the oxide of the hydrocarbon, called amyl, containing C10H„. The ether of potato-oil, and a variety of other compounds, euresponding in every point to those of ordipary alcohol, have been formed, as will be manifest from an inspection of the following table: — 4L6 AMYLICALCOIIOL Amyl (symbol Ayl) ..... Amyl-ether ...•••• Hydride of amyl ..•••■ Potato-oil ...•••• Chloride of amyl ..•••• Bromide of amyl ...••• Iodide of amyl ....•• Zinc-amyl ....... Acetate of amyl ...... Sulphamylic acid ...... Amylene ....... Anhydrous valeric acid..... Valeric acid ....... Hydrated oxide of amyl; fusel-oil; AylO,HO.—The crude fusel-oil of potato-brandy is washed with water, and distilled in a retort furnished with a thermometer, the bulb of which dips into the liquid. The portion which dis- tils between 260° (126°-6C) and 280° (137°-8C) is collected apart and redistilled in the same manner, until an oil is obtained, having a fixed boiling-point at 268°— 269° (131°-1C—131°-7C). Thus purified, it is a thin fluid oil, exhaling a powerful and peculiarly suffocating odor, and leaving a burning taste; it inflames with some difficulty, and then burns with a pure blue flame. Its density is 0-818. It undergoes little change by contact with air under ordi- nary circumstances ; but when warmed, and dropped upon platinum-black, it oxidizes to valeric acid, which bears the same relation to this substance that acetic acid does to ordinary alcohol, or formic acid to methyl-alcohol. The action of heat upon fusel-oil has been studied by Captain Beynolds. The vapor of this alcohol when passed through a red-hot glass tube, yields a mixture of gases, among which a carbo-hydrogen C6II6 predominates, which has the chemical character of olefiant gas, and to which the name propylene has been given (see page 411). The separation of this gaseous mixture has hitherto failed, but on bringing the gas in contact with chlorine a compound C6H6C12 is formed. This is a heavy liquid, boiling at 217°-4 (103°C). It is in every respect analogous to the Dutch-liquid (see page 380), originating under similar circumstances from olefiant gas. Amyl-ether, AylO.—If amyl-alcohol is distilled with concentrated sulphuric acid, a mixture of several substances is obtained, which has to be separated by distillation. After several rectifications, an oil is obtained, which has a sp. gr. 0-779 and boils at 348°-8 (176°C). This is amyl-ether. The compo- sition is C10H,,O, or, if we adopt the double formulae for the ethers, C^H^X),,. Intermediate ethers between amyl- and ethyl-, and likewise between amyl- and methyl-ether, have been prepared. They contain respectively C.H.-O,, =- C4H5O,C10HuO and C12H1402 = C2H3O,C10HnO. Chloride of amyl, Ayl CI.—The chloride is procured by subjecting to dis- tillation equal weights of potato-oil and pentachloride of phosphorus, wash- ing the product repeatedly with alkaline water, and rectifying it from chloride of calcium. Less pure it may be obtained by saturating fusel-oil with hydro- chloric acid. It is a colorless liquid, of agreeable aromatic odor, insoluble in water, and neutral to test-paper; it boils at215° (101°-7C), and ignites readily, burning with a flame green at the edges. By the long-continued action of chlorine, aided by powerful sunshine, a new product, chlorinetted chloride of amyl, was obtained in the form of a volatile colorless liquid, smelling like camphor, and containing C10H3C19: the whole of the hydrogen could not how- ever, be removed. Bromide of amyl, Ayl Br, is a volatile, colorless liquid, heavier than water It is obtained by distilling fusel-oil, bromine, and phosphorus together. (See bromide of ethyl, page 372). Its odor is penetrating and alliaceous. The ■ GI0HM • C10HuO,C10IInO • C,0IIMH . c'oHnO.HO ■ c10unci • C,0HnBr . C10HUI ■ C10N„Zn • C10HnO,C4TI3O3 . C10HnO,2SO3,llO • CI0HI0 • C10lI9O3 . C10H9O3,IIO. AND ITS DERIVATIVES. 417 bromide is decomposed by an alcoholic solution of potassa, with production of bromide of the metal. Iodide of amyl, Ayl I, is procured by distilling a mixture of 15 parts of potato-oil, 8 of iodine, and 1 of phosphorus. It is colorless when pure, heavier than water, volatile without decomposition at 294°-8 (146°C), and re- sembles in other respects the bromide; it is partly decomposed by exposure to light. Iodide of amyl, when heated in sealed tubes with zinc to 374° (1!»0°C), yields amyl, a colorless liquid of an ethereal odor containing C]0Hn, ami boiling at 311° (155°C). Together with this substance there is formed iodide of zinc and zinc-amyl, C10HnZn, which, when coming in contact with water, is decomposed into oxide of zinc and hydride of amyl, C,0Hl2 = Cj0H,1H, an exceedingly volatile substance, boiling at 86° (30°C). Cyanide of amyl, Ayl Cy.—Colorless liquid of 0-806 sp. gr., and boiling at 394° (140°C), wbich is obtained by distilling cyanide of potassium with sul- phamylate of potassa. Boiled with potassa, this compound undergoes a decomposition analogous to that of cyanide of ethyl and methyl (see pages 372 and 402); it absorbs 4 eq. of water, and furnishes ammonia and the potassa-salt of caproic acid, C12HI204, one of the constituents of butter, CUH„N 4- 4HO = C12HI204 4- NH3. Acetate of oxide of amyl, AylO, C4H303. — This interesting product is easily obtained by submitting to distillation a mixture of 1 part of potato-oil, 2 parts of acetate of potassa, and one part of concentrated sulphuric acid; it is purified by washing with dilute alkali, and distillation from chloride of calcium. It presents the appearance of a colorless, limpid liquid, which is insoluble in water, soluble in alcohol, boils at 272° (133°-3C), and becomes converted by an alcoholic solution of potassa into an acetate of that base, with reproduction of fusel-oil. This ether possesses in a remarkable manner the odor of the Jargonelle-pear. It is now manufactured upon a large scale for flavoring liquors and confectionary. Carbonate of oxide of amyl, AylO,C02.—This ether has been lately obtained by Dr. Medlock by saturating fusel-oil with phospene-gas (chloro- carbonic acid). A compound, AylO,C2C103, analogous to chloro-carbonic ether, is first produced, which, when treated with water, yields hydrochloric and carbonic acids, together with carbonate of amyl (AylO,C2C103 4- HO — AylO,C02 -f- HC1 -\- C02). Carbonate of amyl is a colorless liquid of an aro- matic odor, boiling at 438°-8 (226°C). Alcoholic solution of potassa converts this ether into fusel-oil, carbonate of potassa being formed at the same time. Sulphide of amyl, amyl-mercaptan, and numerous other compounds of like nature, have been described. Sulphamylic acid.—AVhen equal weights of potato-oil and strong sulphuric acid are mixed, heat is evolved, accompanied by blackening and partial de- composition. The mixture diluted with water, and saturated with carbonate of baryta, affords sulphate of that base, and a soluble salt corresponding to the sulphovinate. The latter may be obtained in a crystalline state by gentle evaporation, and purified by resolution and the use of animal charcoal. It forms small, brilliant, pearly plates, very soluble in water and alcohol, con- taining BaO,C10H_,O,2SO3 4- HO. The baryta may be precipitated from the salt by dilute sulphuric acid, and the hydrated sulphamylic acid concentrated by spontaneous evaporation to a syrupy, or even crystalline state; it has an acid and bitter taste, strongly reddens litmus-paper, and is decomposed by ebullition into potato-oil and sulphuric acid. The potassa-salt forms groups of small radiated needles, very soluble in water. The sulphamylates of lime and protoxide of lead are also soluble and crystallizable. Amylene.—By the distillation of potato-oil with anhydrous phosphoric acid, a volatile, colorless, oily liquid is procured, quite different in properties from the original substance. It is lighter than water, boils at 102°-2 (39°C), and 418 AMYLIC ALCOHOL contains no oxygen. Its composition is represented by the formula ClrtIIm; consequently it not only corresponds to olefiant gas in the alcohol-sei-ie-. but is isomeric with that substance. Like olefiant gas it combines directly with chlorine and bromine, giving rise tn compounds C,0H]0C12 and C,olI,0T»'2- The vapor, however, has a density of 2-68, which is 1\ times that of olefiant gas, every measure containing 5 measures of hydrogen. The bromide C10H_0Brg has lately furnished amylene-alcohol or amyl-glycol, Cl0HI0O2,2HO. Amylene has been successfully employed as an anesthetic agent. Together with this substance several other hydrocarbons are formed, especially one to which the name paramylene has been given. It contains C^II^,, and boils at 320° (100°C). Valeric or valerianic acid.—M. Dumas has shown that when a mixture of equal parts quicklime and hydrate of potassa is moistened with alcohol, and the whole subjected to a gentle heat, out of contact of air, the alcohol is oxidized to acetic acid, with evolution of pure hydrogen gas. At a higher temperature the acetate of potassa produced is in turn decomposed, yielding carbonate of potassa and light carbonetted hydrogen. Wood-spirit, by similar treatment, yields hydrogen and formate of potassa, which, as the heat in- creases, becomes converted into carbonate, with continued disengagement of hydrogen. In like manner potato-oil, amylic alcohol, suffers, under similar circumstances, conversion into a new acid, bearing to it the same relation that acetic acid does to common alcohol and formic acid to wood-spirit, hydrogen being at the same time evolved. The body thus produced is found to be identical with a volatile oily acid distilled from the root of the Valeriana officinalis. In preparing artificial valeric acid, the potato-oil is heated in a flask with about ten times its weight of the above-mentioned alkaline mixture during the space of 10 or 12 hours; the heat is applied by a bath of oil or fusible metal raised to the temperature of 390° (198°-8C) or 400° (204°-4C). AVhen cold, the nearly-white solid residue is mixed with water, an excess of sul- phuric or phosphoric acid added, and the whole subjected to distillation. The distilled liquid is supersaturated with potassa, evaporated nearly to dryness, to dissipate any undecomposed potato-oil, and then mixed with somewhat diluted sulphuric acid in excess. The greater part of the valeric acid then separates as an oily liquid, lighter than water: this is a terhydrate of the acid, containing three equivalents of water, one of which is basic.1 AVhen this hydrate is distilled alone, it undergoes decomposition: water, with a little of the acid, first appears, and eventually the pure acid, in the form of a thin, fluid, colorless oil, of the persistent and characteristic odor of valerian- root. It has a sharp and acid taste, reddens litmus strongly, bleaches the tongue, and burns when inflamed with a bright, yet smoky light. Valeric acid has a density of 0-937 ; it boils at 370° (175°C). Placed in contact with water, it absorbs a certain quantity, and is itself to a certain extent soluble. The salts of this acid present but little interest, as few among them seem to be susceptible of crystallizing. The liquid acid is found by analysis to con- tain C,0H9O3,IIO, and the silver-salt, AgO,C10H9O3. The ether of valeric acid, AeO,C10H9O3, is obtained by passing hydrochloric acid into an alcoholic solution of valeric acid. By treatment with ammonia this ether is converted into valeramide, C10HMNO2 = C10H9O2,NII2 (analogous to acetamide), which, 1 [Anhydrous valerianic acid is formed by the reaction between valerianate of potassa and oxychloride of phosphorus, 5(KO,CioIl903) and VCI3O2 = 2KO,P05, and 3KC1, and 5(C,0II9O3). It is an oleaginous liquid lighter than water. Boiling water changes it slowlv into tho hydrated acid, while this transformation is rapidly affected hy solutions of the ilbnlioa u boils at 419° (215°C). and distils unchan-ed. - K. 15.] lDe alKSUles. It AND ITS DERIVATIVES. 419 under the influence of anhydrous phosphoric acid, loses 2 more eq. of water, booming valeronitiilc, CI0H9\ - OsIJ,.C..N. or cyanide of butyl. The former is a fusible crystalline substance, the latter a volatile liquid, having a boiling-point of 1^07° (12o°(J). It was first obtained by the action of oxidi- zing agents upon gelatine. (See Animal Chemistry). A more advantageous mode of preparing valeric acid is the following: — 4 parts of bichromate of potassa in powder, 6 parts of oil of vitriol, and 8 parts of water are mixed in a capacious retort: 1 part of pure potato-oil is then added by small portions, with strong agitation, the retort being plunged into cold water to moderate the violence of the reaction. AVhen the change appears complete, the deep-green liquid is distilled nearly to dryness, the product mixed with excess of caustic potassa, and the aqueous solution sepa- rated mechanically from a pungent, colorless, oily liquid which floats upon it, and which is valerate of amyl. The alkaline solution is then evaporated to a small bulk, and decomposed by sulphuric acid, as already directed. If an open jar be set in a plate containing a little water, and having be- neath it a capsule with heated platinum-black, upon which potato-oil is slowly dropped in sucli quantity as to be absorbed by the powder, the sides of the jar become speedily moistened with an acid liquid, which collects in the plate, and may be easily examined. This liquid, saturated with baryta-water, evaporated to dryness, and the product distilled with solution of phosphoric acid, yields valeric acid. Valeric acid is found in angelica root, in the berries of Viburnum, opulus, and probably exists in many other plants; it is generated by the spontaneous decomposition of azotized substances, animal and vegetable, and is produced in many chemical rcactions,in which oxidizing agents are employed. Some very beautiful, and for the progress of organic chemistry, highly im- portant results have been obtained by the action of electricity upon valeric acid. By submitting a solution of valerate of potassa to a galvanic current, produced by 4 elements of Bunsen's battery, Dr. Kolbe observed that potassa and pure hydrogen were evolved at the negative pole, while at the positive pole valeric and carbonic acids, an odorous inflammable gas, and an ethereal liquid, made their appearance. The inflammable gas obtained in this reaction is the caibohydrogen C8H8, which had been previously isolated by Mr. Fara- day from the oily products separated from compressed oil gas, and which has been mentioned among the members of the butyl-series (page 414). This substance, to which the name butylene has been given, is perfectly analogous to olefiant gas (ethylene), propylene, and amylcne, which have been previ- ously described. It combines with chlorine and bromine, forming substances analogous to Dutch-liquid. The oily liquid formed together with butylene, in the electrolysis of valeric acid, is a mixture of several substances, among which a hydrocarbon, of the remarkable composition'C8H9, predominates. This body appears to be identical with butyl, the hydrocarbon which M. Wurtz subsequently separated from iodide of butyl (see page 415). Kolbe considers butyl to be one of the proximate consituents of valeric acid, which he views as an intimate combination of butyl with oxalic acid, butyl-oxalic acid C10H9O3,HO = C8H9.C203,HO. According to this view, the transforma- tion of valeric acid under the influence of the galvanic current is readily explained. The oxygen evolved at the positive pole by the electrolysis of water oxidizes the oxalic to carbonic acid, and liberates the butyl, portions of which are farther attacked by the oxygen, and deprived of 1 eq. of hydro- gen, thus giving rise to the simultaneous evolution of butylene. If this view holds good for valeric acid, it must be equally true of butyric, propionic, acetic, and formic acid, and of a great number of analogous acids, which will be described in the subsequent chapters of this Manual. Butyric acid will be propyl-oxalic acid ; propionic acid, ethyl-oxalic ; acetic acid, methyl-oxalic, and lastly, formic acid, hydro-oxalic acid, thus — 420 AMYLIC ALCOHOL AND ITS DERIVATIVES. Formic acid .... C2H03,HO = H,C203,HO Acetic acid .... C4H303,HO = C2H3,C203,HO Propionic acid .... C6H60,,HO = C4H5,C203,HO . C8H703,HO = C6H7,C203,HO . C10H&O3,HO=C8H9,C2O3,HO Butyric acid Valeric acid This view is borne out by the electrolytic decomposition of acetic acid, which yields a gas, considered by Kolbe to be methyl. Several collateral facts have furnished additional support to this theory: amongst which may be quoted the remarkable deportment of the ammonia-salts of these acids under the in- fluence of anhydrous phosphoric acid. In this reaction, oxalic, formic, acetic, propionic, and valeric acids, yield respectively cyanogen and the cyanides of hydrogen, methyl, ethyl, and butyl. NH40, C203 — 4HO = C2N NH40, H, C203 — 4HO =±= H, C2N NH40,C2H3,C203 — 4HO = C2H3,C2N NH40,C4H5,C203 — 4HO = C4H5,C2N NH40,C8H9,C203 — 4HO = C8H9,C2N AVe have seen, moreover, that the cyanides of methyl and ethyl, when treated with the alkalies, are readily reconverted into acetic and propionic acid, and in the section on cyanogen, it will be shown that this substance and hydro- cyanic acid are indeed easily convertible into oxalate and formate of ammonia. All these facts are readily intelligible by the view proposed by Dr. Kolbe. Trichlorovaleric acid.—AVhen dry chlorine is* passed for a long time into pure valeric acid, in tho dark, the gas is absorbed in great quantity, and much hydrochloric acid produced: towards the end of the operation a little heat becomes necessary. The product is a semi-fluid transparent substance, hea- vier than water, odorless, and of acrid burning taste. It does not congeal when exposed to a very low temperature, but acquires complete fluidity when heated to 86° (30°C). It cannot be distilled without decomposition. AVhen put into water it forms a thin, fluid hydrate, which afterwards dissolves to a considerable extent. This body is freely soluble in alkalies, from which it is again precipitated by the addition of an acid. Trichlorovaleric acid contains CI0(H6Cl3)O3,HO. Quadrichlorovaleric acid. — This is the ultimate product of the action of chlorine on the preceding substance, aided by exposure to the sun. It re- sembles trichlorovaleric acid in appearance and properties, being semi-fluid and colorless, destitute of odor, of powerful pungent taste, and heavier than water. It can neither be solidified by cold, nor distilled without decomposi- tion. In contact with water, it forms a hydrate containing 3 eq. of that sub- stance, which is slightly soluble. In alcohol and ether it dissolves with" fa- cility. It forms salts with bases, of which the best defined is that of silver. Quadrichlorovaleric acid is composed of C10(H5C14)03,HO. Fusel-oil of grain-spirit.—The fusel-oil, separated in large quantities from grain-spirit by the London rectifiers, consists chiefly of potato-oil (hy- drated oxide of amyl) mixed with alcohol and water. Sometimes it contains in addition more or less of the ethyl or amyl-compounds of certain fatty acids thought to have been identified with cenanthic and margaric acids. These last-named substances form the principal part of the nearly-solid fat produced in this manner in whisky-distilleries conducted on the old plan. Mulder has described, under the name of corn-oil, another constituent of the crude fu«el- oil of Holland; it has a very powerful odor, resembling that of some of "the umbelliferous plants, and is unaffected by solution of caustic potassa. Accord- ing to Mr. Kowney, the fusel-oil of the Scotch distilleries contains in addition a certain quantity of capric acid, C20H20O4, which is one of the constituents HOMOLOGOUS SERIES. 421 of butter. Potato-oil, in addition to butylic alcohol (seep. 414), has been separated from the spirit distilled from beet-molasses, and from artificial grape-sugar made by the aid of sulphuric acid. Although much obscurity yet hangs over the history of these substances, it is generally supposed that they are products of the fermentation of sugar, and have an origin contemporaneous with that of common alcohol. HOMOLOGOUS SERIES. It is impossible to leave the history of the alcohols without alluding to some results of great importance for the elucidation of organic compounds gene- rally, which the study of these substances has elicited. When describing the Beveral alcohols, discussed in the preceding chapter, we have repeatedly pointed out the remarkable analogy presented by the properties and the general de- portment of these bodies. If we compare the composition of these alcohols — Methyl-alcohol Ethyl-alcohol Propyl-alcohol Butyl-alcohol Amyl-alcohol C2 H4 02 C4 II6 02 c6n8o2 C10lli2O2 we find that their formula; present an unmistakable symmetry. All contain the same amount of oxygen, only the carbon and hydrogen vary. This varia- tion, however, takes place iu very simple relations. Thus we find the differ- ence of ethyl and methyl-alcohol to be C4H602 — C„H402 = C2H2, the differ- ence of methyl and propyl-alcohol to be C6Hg02 — C2ll402 = C4H4 =■ 2C2H2, the difference of amyl and methyl-alcohol to be C10H |202 — C2H402 = C8H8 = 4C2H2. The same elementary difference of course prevails likewise between all the derivatives of the three alcohols: — Iodide of methyl . . . C2 H31 Iodide of ethyl . . . C4 H51 = C,H,I 4- C2IT2 Iodide of propyl . . . C6 H7 I = C2H3I -j- 2C2EI2 Iodide of amyl . . . C)0HnI = C2H3I -j- 4C2H2 or Formic acid .... C2II03,HO Acetic acid . . . C4 H303,HO = C2H03,HO -f C2H2 Propionic acid . . . C6 Il503,HO = C2H03.HO-j-2C2H2 Valeric acid . . . C10H9O3,HO = C2H03,HO -f 4C2H2 Methylic, ethylic, propylic, butylic, and amylic alcohols are by no means the only members of this class which are known. In the succeeding pages of this work a series of compounds will be noticed, evidently of a perfectly analogous character, which have been discovered in various departments of organic chem- istry. By submitting castor-oil to a series of processes, M. Bouis has formed an alcohol, which has been called " caprylic alcohol." According to M. Dumas, spermaceti contains another analogous substance, cetylic alcohol, which is a solid: and Mr. Brodie has prepared two alcohols, cerotylic and melissic, from bees-wax. The composition of (these substances stands in exactly the same relation to that of the preceding alcohols, which we have pointed out, as will be seen from the following table: — Caprylic alcohol . . . C16H1802 = C2H402 -4- 7C2H2 Cetylic alcohol . . . CgjlI^Oj == C\II4Oa-j- 15C2H2 Cerotylic alcohol . . . C^H^O,, = C2H402 -f 26C2H2 Melissic alcohol . . . C60H62O2 = C2H402 -f 29C2H2 422 HOMOLOGOUS SERIES. These four alcohols, when submitted to the action of oxidizing agents, aro converted into four acids, analogous to formic and acetic acid, and which stand to each other, and to formic and acetic acid, in exactly the same rela- tion as the several alcohols do to each other. Caprylic acid . . Cl6nis03,HO = C2H03,HO 4- 7C2H2 Cetylic acid . . C32H3103,HO = C2H03,HO -f 15C2Hg Cerotylic acid . . C54H5303,HO = C2H03.HO 4- 26C2I12 Melissic acid . . Cfl0H59O3,HO = C2H03,HO-j-29C2H2 A glance at these tables shows that all the alcohols known differ from methyl-alcohol by C2H2, or a multiple of it. At the same time, it is evident that the series by no means regularly ascends. Thus we perceive that between amylic and caprylic alcohols, two alcohols still remain to be discovered; in like manner between caprylic and cetylic alcohols, not less than eight different alcohols are wanting. Even now the parallel series of volatile acids is far more complete than that of the alcohols. At present the following members of this group are known, C2 H2 04 C4 H4 04 c6 u6 04 ^8 H8 04 ^10^ 10^4 C12H]204 C14H1404 C16 H 16^4 C19"I804 ^20"20"4 &C We might continue the series of acids uninterruptedly to C38H3804 (balenic acid), and with intervals even much higher up to acids containing 54 and even more equivalents of carbon. Most of the acids belonging to this series have been separated from fats, and hence this series is frequently designated by the name of the series of fatty acids. A series of analogous substances, whose composition varies by C2H2, or a multiple of it, is called a series of homologous bodies— a name first used by Gerhardt, to whom we are much indebted for the elucidation of this subject. It is evident that there exist as many such homologous series as there are derivatives of any one of the alcohols. AVe may construct a series of homo- logous radicals, or ethers, or hydrocarbons. Inch are placed in juxta Methyl-alcohol position witn tn . C2 II4 02 e collateral alcohols: -Formic acid . Ethyl-alcohol ■ c4 II6 02 Acetic acid Propyl-alcohol . C6 H8 02 Propionic acid Butyl-alcohol C8 H]0O2 Butyric acid Amyl-alcohol . ^10^12^2 Valeric acid . Ci2H1402 Caproic acid C14Hl602 ■(Enanthylic acid Capryl-alcohol C16H1302 Caprylic acid ^18'*20^2 Pelargonic acid ^20 " 22^2 Capric acid &c. &c. &c. Methyl Ethyl Propyl Butyl Amyl Caproyl C2 H3 C4H5 C6H7 c8 u9 ^10^11 C,2H13 CI4H15 ^16^17 Methyl-ether Ether Butyl-ether Amyl-ether Capryl-ether C2H30 C4H50 C6H70 C8H90 C10HuO Cl2H130 C,4H130 C|fiH„0 Ethylene . Propylene . Butylene . Ainylene . Caproylene Caprylene . P2F2 C4H4 C6H6 C8H, ^10^10 C]2H12 U14U14 CirH,r All these series of homologous bodies still present numerous gaps • none perhaps more than that of the alcohols, which may be taken as the'pro'totvpe of all the rest; but since the existence of these homologous series was first pointed out, many gaps have been filled, and it may be expected that before long the rapid strides of organic chemistry will render these series complete OILS AND FATS. 423 The properties of the various members belonging to the homologous series gradually change as we ascend in the series. The most characteristic altera- tion is the diminution of volatility A regular difference between the boiling- points of homologous substances was first pointed out by II. Kopp. As an example the series of fatty acids may be taken:— Boiling-points. Differences. F. C. F. C. 20°-5 Formic acid . C2 H2 04 209° 98° 5 Acetic acid . C4 II4 04 246° 119° \ /"o0 oVo Propionic acid. C6 H6 04 284° 140° / V'L, f- Butyric acid . C8 H8 04 314°-6 157° "^ J 330.4 \[ Valeric acid . C,0M|0O4 347° 175 Caproic acid . Cl2U1204 388°-4 198 } 33°-4 18° 4 23° | 41° From this table it is evident that the boiling temperature of the homologous acids rises on an average 36°-3 (19°-9C) for every increment of C2H2. A similar regular difference has been observed in the boiling-points of many other homologous compounds. As yet, however, the number of cases in which discrepancies occur is very considerable. OILS AND FATS. The oils and fats form an interesting and very natural group of substances, which have been studied with great success. The vegetable and animal fats agree so closely in every respect, that it will be convenient to discuss them under one head. Oily bodies are divided into volatile and fixed: the former are capable of being distilled without decomposition, the latter are not. AVhen dropped or spread upon paper, they all produce a greasy stain: in the case of a volatile oil, this stain disappears when the paper is warmed, which never happens with a fixed fatty substance. All these bodies have an attraction, more or less energetic, for oxygen: this in some cases reaches such a height as to oc- casion spontaneous inflammation, as in the instance of large masses of cotton or flax moistened with rape or linseed oil. The effect of this absorption of oxygen leads to a further classification of the fixed oils into drying and non- drying oils, or those which become hard and resinous by exposure to air, and those which thicken slightly, become sour and rancid, but never solidify. To the first class belong the oils used in painting, as linseed, poppy-seed, and walnut; and to the second, olive- and palm-oils, and all the oils and fats of animal origin. The parts of plants which contain the largest quantities of oil ore, in general, the seeds. Olive-oil is, however, obtained from the fruit itself. The leaves of many plants are varnished on their upper surface with a cover- ing of waxy fat. Among the natural orders, that of the cruciferce is conspicu- ous for the number of oil-bearing species. The fixed oils in general have but a feeble odor, and scarcely any taste; whenever a sapid oil or fat is met with, it is invariably found to contain some volatile oily principle, as in the case of common butter. They are all insoluble in water, and but slightly soluble in alcohol, with the exception of castor-oil; in ether and in the essential oils, on the other hand, they dissolve in large quantity. The consistence of these substances varies from that of the thinnest olive-oil to that of solid, compact suet: and this difference proceeds from the variable 424 OILS AND FATS. proportions in which the proximate solid and fluid fatty principles are asso- ciated in the natural product. All these bodies may, in fact, by mere mecha- nical means, or by the application of a low temperature, be separated into two, or sometimes three, different substances, which dissolve in, or mix with, each other in all proportions. Thus, olive-oil exposed to a cold of 40° (4°-5C) de- posits a large quantity of a crystalline solid fat, which may be separated by filtration and pressure ; this is termed margarin, from its pearly aspect. That portion of the oil which retains its fluidity at this, or even a greater degree of cold, has received the name olein or elain. Again, a solid animal fat may, by pressure between folds of blotting-paper, be made much harder, more brittle, and more difficult of fusion. The paper becomes impregnated with a permanently-fluid oil, or olein, while the solid part is found to consist of a mixture of two solid fats, one resembling the margarin of olive-oil, and tho other having a much higher melting-point, and other properties which distin- guish it from that substance; it is called stearin. These remarks apply to all ordinary oils and fats: it is, however, by no means proved that the olein and margarin of all vegetable and animal oils are identical; it is very possible that there may be essential differences among them, more especially in the case of the first-named substance. Fixed fatty bodies, in contact with alkaline solutions at a high temperature, undergo the remarkable change termed saponification. AVhen stearin, mar- garin, or olein are boiled with a strong solution of caustic potassa or soda, they gradually combine with the alkali, and form a homogeneous, viscid, trans- parent mass, or soap, freely soluble in warm water, although insoluble in saline solutions. If the soap so produced be afterwards decomposed by the addition of an acid, the fat which separates is found completely changed in character; it has acquired a strongly-acid reaction when applied in a melted state to test-" paper, and it has become soluble with the greatest facility in warm alcohol; it is, in fact, a new substance, a true acid, capable of forming salts, and a compound ether, and has been generated out of the elements of the neutral fat under the influence of the base. Stearin, when thus treated, yields stearic acid, margarin gives margaric acid, olein gives oleic acid, and common animal fat, which is a mixture of the three neutral bodies, affords by saponification by an alkali and subsequent decomposition of the soap, a mixture of the three fatty acids in question. These bodies are not, however, the only products of saponification; the change is always accompanied by the formation of a very peculiar sweet substance, called glycerin (see page 414), which remains in the mother-liquor from which the acidified fat has been separated. The process of saponification itself proceeds with perfect facility in a close vessel; no gas is disengaged; the neutral fat, of whatsoever kind, is simply resolved into an alkaline salt of the fatty acid, or soap, and into glycerin.1 Hence the neutral fats may be viewed as a species of salt, in which the glycerin plays the part of base, similarly to oxide of methyl and ethyl, &c, in the compound ethers. Stearin and stearic acid.—Pure animal stearin is most easily obtained by mixing pure mutton-fat, melted in a glass flask, with several times its weight of ether, and suffering the whole to cool. Stearin crystallizes out, while mar- garin and olein remain in solution. The soft pasty mass may then be trans- ferred to a cloth, strongly pressed, and the solid portion still further purified by recrystallization from ether. It is a white friable substance, insoluble in water, and nearly so in cold alcohol; boiling spirit takes up a small quantity. Boiling ether dissolves it with great ease, but when cold retains only —l of 1 We are indebted to M. Chevreul for the first series of scientific researches on the fixed oils and fat?, and on the theory of saponification. These admirable investigations are detailed in the early volumes of the " Annales de Chimie et de Physique," and were afterwards published in a separate form in 1S23, under the title of " Jiecherches Chimvjue sur les Corps nrasWOriaint animate." J OILS AND FATS. 425 its weight. The melting-point of pure stearin, which is one of its most im- portant physical characters, may be placed at about 130° (54°-5C). \\ hen stearin is saponified, it yields, as already stated, glycerin and stearic acid. The latter crystallizes from hot alcohol in milk-white needles, which are inodorous, tasteless, and quite insoluble in water. It dissolves in its own weight of cold alcohol, and in all proportions at a boiling-heat; it is likewiso soluble in ether. Alkaline carbonates are decomposed by stearic acid. Ex- posed to heat it fuses, and at a higher temperature, if air be excluded, vola- tilizes unchanged. The melting-point of stearic acid is about 158° (70°C). Margarin and margaric acid.—The ethereal mother-liquor from which stearin has separated in the process just described, yields on evaporation a soft-solid mixture of margarin and olein with a little stearin. By compression between folds of blotting-paper, and resolution in ether, it is rendered tolerably pure. In this state margarin very much resembles stearin ; it is, however, more fusible, melting at 116° (4ft°-0C), and very much, more soluble in cold ether. By saponification it yields glycerin and margaric acid. The proper- ties of this last-named substance resemble, in the closest manner, those of stearic acid; it is different in composition, however, more soluble in cold spi- rit, and has a lower melting-point, viz., 140° (60°C) or thereabouts. Its salts also resemble those of stearic acid. A more or less impure mixture of stearic and margaric acids is now very extensively used as a substitute for wax and spermaceti in the manufacture of candles. It is prepared by saponifying tallow by lime, decomposing the insoluble soap so formed by boiling with dilute sulphuric acid, and then press- ing out the fluid or oily portion from the acidified fat. The solid part of olive-oil is said to be a definite compound of true margarin and olein, inasmuch as its melting-point, 68° (20°C), is constant; it gives by saponification a mixture of margaric and oleic acids. Recent researches made by Heintz have thrown some doubts on the exist- ence of margarin and margaric acid. Heintz considers margarin as a mixture of stearin and palmitin, margaric acid as a mixture of stearic and palmitic acid (see page 427). The subject is still under discussion. Olein and oleic acid.—It is doubtful.whethcr a perfectly-pure olein has yet been obtained: the separation of the last portions of margarin, with which it is always naturally associated, is a task of extreme difficulty. Any fluid oil, animal or vegetable, which has been carefully decolorized, and filtered at a temperature approaching the freezing-point of water, may be taken as a representative of the substance. Oleic acid much resembles olein in physical characters, being colorless and lighter than water; but it has usually a dis- tinctly-acid reaction, a sharp taste, and is miscible with alcohol in all propor- tions. AVhen submitted to the action of nitric acid, it yields almost the whole series of acids, of which formic, acetic, propionic, butyric, &c, are members, and which have been mentioned in a previous section of this work. AVhen stearic or margaric acid, or ordinary animal fats, are exposed to des- tructive distillation, they yield margaric acid, a fatty body, incapable of sapo- nification, termed margarone, a liquid carbide of hydrogen, and .'arious per- manent gases. The neutral fats furnish besides an extremely pungent and even poisonous volatile principle, called acrolein, (see page 412.) In the manufacture of ordinary soaps both potassa and soda are used; the former yielding soft, and the latter hard soaps. Animal and vegetable fats arc employed indifferently, and sometimes resin is added. Composition of the preceding Substances.—The following are the formulae at present generally assigned to the fatty acids in question: — Margaric acid ....... C^IIggOjj.IIO. Stearic acid ....... C^H^Og, 110. " 36* 426 OILS AND FATS. If these formulae be correct, stearic and margaric acids are homologues of formic and acetic acid. The formula of margaric acid is, however, by no means well established. Oleic acid, from almond-oil, butter, and beef-suet, gave results agreeing pretty well, and leading to the formula C^H^O.,, II0, the oleic acid of goose- fat and olive-oil having the same composition. Former researches had led to different results, which are explained by the extreme proneness to oxidation of the substance itself. The oleic acid obtained from linseed-oil appears to differ from the preceding substance, its analysis having led to the formula C«,H4806,HO. Margarone probably contains C^H^O, or margaric acid minus 1. eq of carbonic acid. Margaric, stearic, and oleic acids have many properties in common: their salts much resemble each other, those of the alkalies being soluble in pure water when warm, but not in saline solntions. A large quantity of cold water added to an alkaline margarate or stearate occasions the separation of a crystalline, insoluble acid salt. The margarates, stearates, and oleates of lime, baryta, and the oxides of the metals proper are insoluble in water. They are easily obtained by double decomposition, and in some few cases by direct action on the neutral fat. A solution of soap in alcohol is sometimes used as a test for the presence and quantity of lime, &c, in waters under examination (see page 260). Ethers of the fatty acids. — Stearic ether is obtained by passing hydro- chloric acid gas into an alcoholic solution of stearic acid; it contains AeO,C36H3503. It resembles white wax, is inodorous and tasteless, melts at 86° (30°C) and cannot be distilled without decomposition. It is readily decomposed by boiling with caustic alkalies. Margaric ether is prepared by a similar mode of proceeding. AVhen purified from excess of acid by agitation with successive small quantities of weak spirit, and afterwards made to crys- tallize slowly from the same menstruum, it forms regular, brilliant, colorless crystals, fusible at 70° (21°-1C), and distilling without decomposition; when less pure it is in great part destroyed by this latter process. Margaric ether is said to contain AeO,C34H3303. An oleic ether, and corresponding compounds of several other less important fatty acids, have been formed and described. They greatly resemble each other in character. Glycerin, C6H806. — This substance was originally obtained by heating together olive or other suitable oil, protoxide of lead, and water, as in the manufacture of common lead-plaster; an insoluble soap of lead is formed, while the glycerin remains in the aqueous liquid. The latter is treated with sulphuretted hydrogen, digested with animal charcoal, filtered and evacuated in vacuo at the temperature of the air. It is now produced in verv large quan- tity and of perfect purity in the decomposition of fatty substances, by means of overheated steam, a process which Mr. George Wilson has lately introduced into the manufacture of candles. In this reaction, both the fatty acid and the glycerin assimilate the elements of water, and the excess of steam carries over a mechanical mixture of glycerin and fatty acids, which rapidly separates into two layers in the receiver. In a pure state glycerin forms a nearly colorless and very viscid liquid of sp. gr. 1-27, which cannot be made to crystallize. It has an intensely-sweet taste, and mixes with water in all proportions: its solution does not undergo the alcoholic fermentation, but when mixed with yeast and kept in a warm place, it is gradually converted into propionic acid (see page 411). Glycerin has no action on vegetable colors. Exposed to heat, it volatilizes in part darkens, and becomes destroyed, one of its products of destruction being a substance possessing a most powerfully-penetrating odor, called acrolein which has been already mentioned under the head of propyl series (see page 412). Concentrated nitric acid converts it into glyceric acid, C H 0 dilute OILS AND FATS. 427 acid into oxalic acid. A mixture of nitric and sulphuric acids produces a Bubstitution-compound, nilro-glycerin, C6Hs(N04)306. a heavy oily liquid, powerfully exploding by concussion. ' Glycerin combines with the elements of sulphuric acid, forming a compound acid, the sulphoglyeerie, C6H,05,2S03,HO, which gives soluble salts with lime, baryta, and protoxide of lead. Submitted to the action of iodide of phosphorus, glycerin is converted into iodide of propylene and other compounds. M. Berthelot has succeeded in combining glycerin with a great number of acids, and producing in this manner artificially a series of compounds, which are partly identical with the fats occurring in nature, and partly analogous to these substances. They are generally obtained by the direct action, during several hours, of the acids upon glycerin in closed vessels at temperatures varying, according to circumstances, from 212° to 536° (100 to 280°C). Three compounds of stearic acid with glycerin have been thus produced, which M. Berthelot distinguishes as monostearin, bistearin, and tristearin. There are likewise several artificial margarins, palmitins, and oleins. The deportment of these bodies is perfectly analogous to that of neutral fats. Compounds with acetic, butyric, and valeric, benzoic, camphoric, and even with hydrochloric acid have likewise been obtained. The study of these artificial compounds has thrown much light upon the nature of glycerin, and the compounds of the substances which occur in nature, that is, the neutral fatty bodies. It results from these researches that glycerin is a substance analogous to alcohol in general character, but differing from the latter by the variety of proportions in which it can be combined with the acids. In fact, M. Berthelot has pointed out three classes of compounds which glycerin is capable of forming with the acids. AVith acetic acid, for instance, it forms three combinations, — monacetin, diacetin, and triacetin,—which may be formulated in the following manner: — Glycerin.....C6 H8 06 = C6TT503,3HO Monacetin .... C10II10O8 = C6H503,2H0, C4H303 Diacetin.....C14I112010 = C6H503. HO,2C4H303 Triacetin .... CI8H14012 = QA\£>3, 3C4H303 In a similar manner, three different stearins may be distinguished: — Monostearin . . . C42 H42 08 = C6H503,2HO, C^H^O., Bistearin . . . . C78 H76 OI0 = C6II503, 110,20^0, Tristearin .... CI14H110O]2 = C6H503, SC^H^O^ Tristearin is the stearin which occurs in nature. The formation of glycerin from tribromide of allyl has been mentioned under the head of propyl-series. Palm and cocoa oils. — These substances, which at the common tempera- ture of the air have a soft-solid or buttery consistence, are now largely con- sumed in this country. Palm-oil is the produce of the Elais guianensis, and comes chiefly from the coast of Africa. It has, when fresh, a deep orange- red tint, and a*very agreeable odor; the coloring matter — the nature of which is unknown — is easily destroyed by exposure to light, especially at a high temperature, and also by oxidizing agents. The oil melts at 80< (26°-6C). By cautious pressure it may be separated into a fluid olein and a solid substance, palmitin, which, when purified by crystallization from hot ether, is perfectly white, fusible at 118° (47°-8C), soluble to a small extent only in boiling alcohol, and convertible by saponification into palmitic acid. The latter resembles, in the closest manner, margaric acid, and has the same melting-point; it differs in composition, however, containingC32H3103,HO. By keeping, palm-oil seems to suffer a change similar to that produced by saponi- fication : in this stato it is found to contain traces of glycerin, and a con- siderable quantity of oleic acid, together with a solid fatty acid, first supposed 428 OILS AND FATS. to be margaric, but which is probably palmitic acid. The oil becomes harder and rancid, and its melting-point is raised at the same time. Cocoa-oil, extracted from the kernel of the common cocoa-nut, is white, and has a far less agreeable smell than the preceding. It contains olein and a solid fat, often used as a substitute for tallow in making candles, which by saponification gives a crystallizable fatty acid, cocinic acid, having the usual properties of these bodies, and melting at 95° (35°-5C). It is composed of CjgH^Ojj.IIO. Both this and palmitic acid are monobasic. The solid vegetable fat from the Myristica moschata contains a volatile oil, a fluid olein, and a solid, crystallizable, fatty principle; this, when saponified, which takes place with difficulty, yields myristic acid. This substance has been examined by Dr. Playfair: it melts at 120° (48°-8C), and contains Cggl^Oj.IIO. It is monobasic. Cacao-butter, extracted from the crushed beans by boiling with water, yields by saponification a fatty acid, identical, according to Dr. Stenhouse, with the stearic acid from animal fat. Elaidin and elaidic acid.—AVhen olive-oil is mixed with a small quantity of nitrous acid, nitric acid containing that substance, or solution of nitrate of mercury made in the cold, it becomes after a few hours a yellowish, soft-solid mass, which, pressed and treated with alcohol, furnishes a peculiar white, crystalline, fatty substance, termed elaidin. It resembles a neutral fat in properties, melts at 90° (32°-2C), dissolves with difficulty in boiling alcohol, easily in ether, and is resolved by saponification into glycerin and elaidic acid, which much resembles margaric acid. Oleic acid is directly convertible by nitrous acid into elaidic acid. It is not every kind of oil which furnishes elaidin; the drying oils, as those of linseed, poppy-seed, walnuts, &c, refuse to solidify; almond-, olive-, and castor-oils, possess the property in a high degree. Elaidic acid appears to have the same composition as oleic acid, or CgsII^.HO. The action of sulphuric acid upon olive-oil has been studied by M. Fremy. When the oil is slowly and cautiously mixed with half its volume of concentrated sulphuric acid, all rise of temperature being avoided, a homogeneous liquid is obtained, which, when mixed with a little water, separates into two la vers, the lower consisting of sulpho-glyceric and free sulphuric acid, and the upper " and syrupy portion of two compound acids, the sulphomargaric and sulpholeic. These latter dissolve in a large quantity of water, but after some time undergo decomposition into sulphuric acid and several new fatty acids, to which the names melamargaric, hydromargaric, hydromargarilic, metoleic, and hydroleic were given. The first three are derived from the elements of the sulphomargaric acid; they are solid and crystallizable, and much resemble ordinary margaric acid, differing slightly from that substance and from each other in their melting-points, degree of solubility in alcohol, &c. The metoleic and hydroleic acids are fluid, and are derived from the sulpholeic acid of the mixture. They yield carbonic acid and liquid hydrocarbons by destructive distillation. The composition of these fatty acids is yet uncertain, but in all probability they only differ from margaric and oleic acids by the elements of water. The action of sulphuric acid upon the oil is thus somewhat similar to the effect of saponification, the neutral fat being resolved into margaric and oleic acids and glycerin, the whole of which then combine with the°clements of sulphuric acid to form compounds belonging to the lam-e group of sub- stances, of which sulphovinic acid is the typical member. The sulphuipic saponification of fatty bodies is now carried out on a very large scale for producing cheaper varieties of "stearin candles." For this purpose, inferior fatty bodies, such as palm-oil, are mixed with 5 or 6 per cent, of concentrated sulphuric acid, and exposed to a temperature of 3")0° (177°C) produced by overheated steam. After cooling, the black mass thus OILS AND FATS. 429 obtained crystallizes to a tolerably-solid fat, which is washed once or twico with water, and then submitted to distillation by the aid of steam, heated to about 560° (293°-5C). The product of the distillation, which is beautifully white, may be at once used for making candles; frequently, however, it undergoes the processes of cold and hot pressing, whereby a much more solid fat is obtained. Spermaceti. — The soft-solid matter found in very large quantity in a remarkable cavity in the head of the spermaceti whale, when submitted to pressure, yields, as is well known, a most valuable fluid oil, and a crystalline brownish substance, which, when purified, becomes the beautiful snow-white article of commerce, spermaceti. This substance appears, by more recent experiments, to be a neutral fatty body of the constitution of compound ethers. It melts at 120° (48°-8C), and when cooled under favorable circumstances, forms distinct crystals. Boiling alcohol dissolves it in small quantity, and ether in much larger proportion. Spermaceti is saponified with great diffi- culty : two products arc obtained, a substance, C^H^O^ belonging to the series of alcohols (see page 421), to which the name {cetylic) ethalic alcohol has been given, and palmitic (cetylic, ethalic) acid, C32H3304; the first is a crys- tallizable fat, whose melting-point is nearly the same as that of spermaceti itself, but its solubility in alcohol is much greater ; it is also readily sublimed without decomposition. Palmitic acid stands to ethylic alcohol in the same relation as acetic acid to ordinary alcohol, and maybe actually procured from the latter by oxidation; it resembles in many respects margaric acid. By oxidation by nitric acid spermaceti yields a large quantity of succinic acid. Spermaceti is composed of C64H6404== CjjHjjOjCajH^Ojj; it is cetylate of oxide of cetyl, and represents in the cetyl-series the acetic ether of the com- mon alcohol-series. According to the recent researches of Heintz, the consti- tution of spermaceti is less simple. He believes that it is a mixture of several homologous compounds, which are difficult to separate. Wax. — Common bees'-wax, freed from its yellow coloring matter by bleach- ing, may be separated by boiling alcohol into two different proximate princi- ples, cerin and myricin. The first is a white crystalline substance, soluble in about 1G parts of boiling spirit, and melting at 144° (62°-2C); it is the more abundant of the two. It is easily saponified by a solution of caustic potassa. According to Brodie's valuable experiments it consists chiefly of cerotic acid (C54IIs3O3.HO), which belongs to the scries of fatty acids (see page 421). The same body in a very interesting form of combination exists in Chinese wax, which, according to Brodie, is a compound ether containing cerotic acid com- bined with the ether of cerotylic alcohol, C51H650,HO. It may be viewed as cerotate of oxide of cerotyl, C5in650>C64Hs303, corresponding to the acetic ether of the wine-alcohol series. AVhen heated with potassa it undergoes the changes peculiar to compound ethers, yielding on the one hand cerotate of potassa, and on the other hand cerotylic alcohol. Myricin is very much less soluble in alcohol, and rather more fusible. It is saponified with difficulty by a dilute solution of caustic potassa, palmitic acid, C32H3103.HO (see page 421), combines with the potassa, and a substance, C60H61O,HO, belonging to the series of alcohols, is set free, which has been termed melissic alcohol. Hence myricin is likewise a compound ether, namely, palmitate of oxide of melissyl, ^98*'92**4 — ^60^6lO>C32H3,O3. Butter; volatile acids of butter.—Common butter chiefly consists of a solid, crystallizable, and easily-fusible fat, a fluid oily substance, and a yellow coloring matter, besides mechanical impurities, as casein. The oily part ap- pears to be a mixture of olein and a peculiar odoriferous fatty principle, buty- rin, which by saponification yields four distinct volatile acids, the butyric, the caproic, the caprylic, and the capric or rutic: these are most easily obtained by saponifying butter with potassa or soda, adding an excess of sulphuric acid, and distilling. The acid watery liquid obtained may then be saturated with 430 OILS AND FATS. an alkali, evaporated to a small bulk, and then distilled with excess of sul- phuric or phosphoric acid in a retort. The mixed acids are separated by taking advantage of the unequal solubility of their baryta-salts; the less solubte salts of the mixture amounting to about ^ of the whole mass, contain capric and caprylic acids: the larger and more soluble portion, the caproic and butyric acids. The properties of butyric acid are described under the head of butyl-series. Cai>roic acid forms a colorless liquid, of sp. gr. 0-922, boiling at 388°-4 (198°C): it has a feeble odor, somewhat resembling that of acetic acid, and is much less soluble in water than butyric acid. It contains C12H,]03,IIO. The artificial formation of this acid from cyanide of amyl has been already noticed (see page 417). Caproic acid has been submitted to the action of the galvanic current. Messrs. Brazier and Gossleth have proved that its effect upon this acid is analogous to that upon valeric acid, and that the principal product is the hydrocarbon amyl, C,0HU, previously obtained by Dr. Frankland by the action of zinc upon iodide of amyl (see page 417). Caprylic acid is chiefly remarkable for exhaling a powerful and disgust- ing odor of perspiration. It contains C,6H]503,HO. This acid has been lately obtained by a very interesting reaction, namely, by the oxidation of the new caprylic alcohol discovered by M. Bouis among the products of decomposition of castor-oil (see below). Capric or rutic acid much resembles caproic; it has a mixed odor of acetic acid, and the smell of the goat, and is very sparingly soluble in water. Its formula is C^H^O^HO. The simple relation existing between the formulae of the volatile acids of butter, which are all members of the series of fatty acids, has been already pointed out (see page 422). These acids exist ready formed in rancid butter and in cheese, associated with valeric acid. They are produced in small quantity by the saponification of most animal and some vegetable fats, together with other products. Bu- tyric acid has been observed also as a product of the spontaneous decompo- sition of fibrin, and pre-exists in the leguminous fruit known as St. John's bread. Whale- and seal-oil yield by saponification a volatile acid greatly resem- bling the preceding, calledphocenic or delphinic acid: it was formerly believed to be a peculiar acid, but it is, according to recent experiments, nothing but valeric acid. Castor-oil, which differs in some respects from the ordinary vegetable oils, yields, by oxidation with nitric acid, a peculiar product, namely, a volatile fatty acid, to which the term cenanthylic has been applied. It forms a color- less, oily liquid of aromatic odor and burning taste, and slightly soluble in water. It refuses to solidify at a very low temperature, and cannot be dis- tilled alone without some decomposition, although its vapor passes over readily with that of water. This body has distinct acid properties, forms a series of salts and an ether, and contains C14H,303,IIO. Under the influence of the galvanic current it. undergoes a decomposition similar to that of valeric acid according to Messrs. Brazier and Gossleth, the principal product beino-' together with a hydrocarbon containing equal equivalents of carbon and hydro- gen, an oily substance, C12H13, boiling at 395°-6 (202°C), to which the name caproyl has been given, and which may be viewed as the radical of the alcohol of caproic acid, Cl2HI30,HO, still to be discovered. Castor-oil has lately become the source of a new alcohol in the hands of M Bouis. According to his researches, there is present in castor-oil a peculiar oleic acid, ricinoleic acid, which contains CggllggOs.HO, i. e. 2 ca of ox - more than common oleic acid. If this acid, or more 'conveniently castor-oil itself, be heated with solid hydrate of potassa, an oily liquid distils: nvVv v>«;i ingat 356° (180°C), which is the alcohol of caprylic acid. It contains C HO OILS AND FAT8. 431 ITO. and is readily converted into caprylic acid (see page 430), by treatment with oxidizing agents. The residue in the retort contains sebacate of potato,. This transformation is represented by the following equation: — ^V!_3iA_HO + 2(KO,HO) = 2£aCi2Hi60? +>C2n4!OHO-+'2H Bicinoleic acid. Sebacate of Caprylic potassa. alcohol. The ether corresponding to caprylic alcohol is not yet known. Compounds, however, of this ether with methylic, ethylic, and amylic ethers have been lately described by Mr. Wills. The base corresponding to this alcohol, caprylamine, has been obtained by Mr. Squire and M. Cahours. It contains C16HI9N. (See further on, the sec- tion on the Organic Bases.) The acids derived from butter and from castor-oil are also produced, together with formic, acetic, and propionic acids, by the action of nitric acid upon oleic acid. This reaction furnishes, moreover, an acid not contained in butter, but closely allie.d to the butter acids. This acid is, Pklargonic acid, Ci8II]703, HO, which occupies the place between caprylic and capric acid. It is a liquid of a slightly-disagreeable odor, which boils at 500° (200°C). It was first obtained from the leaves of the geranium (Pelar- gonium roseum), in which it exists ready formed. It may be procured in larger quantity by the action of nitric acid, upon the essential oil of rue (see further on). The ether of pelargonic acid may be easily produced by dissolv- ing the acid in strong alcohol, and passing a current of hydrochloric acid through the solution. This ether contains C22H2204 = AeO,C18H)703: its spe- cific gravity is 0-862; its boiling point 482° (250°C). It posesses a powerful and a most intoxicating vinous odor. The aroma possessed by certain wines appears to be due to the presence of the ether of pelargonic acid, which, in this case, is probably generated during fermentation. AVhen such wines, or the residues of their fermentation, are distilled on the large scale, an oily liquid passes over towards the close of the operation, which consists, in great measure, of the crude ether; it may be purified by agitation with solutions of carbonate of potassa, freed from water by a few fragments of chloride of calcium, and redistilled. The pelargonic ether obtained by this process was originally described as cenanthic ether, and the acid as cenanthic acid. AVc prefer the name pelargonic acid, in order to distinguish this substance better from cenanthylic acid, C_4Hl303,HO. Suberic, succinic, and sebacic acids.—Suberic acid has long been known as a product of the oxidation of cork by nitric acid; succinic acid is obtained by the distillation of amber, a fossil resin. Becently both have been produced by the long-continued action of nitric acid upon stearic and margaric acids. Suberic acid is a white crystalline powder, sparingly soluble in cold water, fusible and volatile by heat; it contains C,6H)2O0,2HO. Succinic acid forms regular colorless crystals, soluble in 5 parts of cold, and in half that quantity of boiling water; it is also fusible and volatile without decomposition, and contains r8H406,2IIO. The remarkable production of this substance from malic acid by a process of fermentation has been already mentioned. Sebacic acid is a constant product of the destructive distillation of oleic acid, olein, and all fatty substances containing those bodies; it is extracted by boiling the dis- tilled matter with water; it has also been lately formed by the action of potassa on castor-oil (see above). It forms small pearly crystals resem- bling those of benzoic acid. It has a faintly-acid taste, is but little soluble in cold water, melts when heated, and sublimes unchanged. Sebacic acid is composed of C^H^Oe^HO. Suberic, succinic, and sebacic acid belong to a series of homologous bibasic 432 BITTER-ALMOND OIL acids, of which oxalic acid, the bibasic character of which we have repeatedly pointed out, is the type. This series, which includes, moreover, adipic and pimelic acid's, two substances produced by the action of oxidizing agents upon fatty bodies, and anchoic acid, lately observed by M. Buckton among the pro- ducts of oxidation of Chinese wax, runs parallel with the series of volatile monobasic acids, as seen in the following table : — Monobasic Acids. Bibasic Acids. Formic acid C2 H 03,HO Acetic acid C4H303,HO Oxalic acid . C4 06.2HO Propionic acid . ; C6H503,HO 1 . C6H206.2HO Butyric acid C8H703.HO Succinic acid . . CsH406,2HO Valeric acid C10H9O3.HO Pyrotartaric acid . C10H6O6.21IO Caproic acid C12HH03,HO Adipic acid . C12H806,2HO QSnanthylic acid C14H13O3,H0 Pimelic acid . . C14M)0OG,2HO Caprylic acid . Cl6H1503,HO Suberic acid . . C16H1206,2I10 Pelargonic acid C1BH)703,HO Anchoic acid . . C18HI406,2I10 Capric or rutic acid . GajH^Og.HO Sebacic acid . . C^H^^ 110 Cholesterin. — This substance is found in small quantity in various parts of the animal system, as in the bile, in the brain and nerves, and in the blood; it forms the chief ingredient of biliary calculi, from which it is easily extracted by boiling the powdered gall-stones in strong alcohol, and filtering the solution while hot: on cooling, the cholesterin crystallizes in brilliant colorless plates. It has the characters of a fat, is insoluble in water, taste- less and inodorous; it is freely soluble in boiling spirit, and also in ether. It altogether resists saponification. Cholesterin melts at 278° (136°C), and contains probably C^H^O. Cantharidin, the active principle of the Spanish fly, may be here men- tioned. It is a colorless, crystallizable, fatty body, extracted by ether or alcohol from the insect; it is insoluble in water and dilute acids, and volatile when strongly heated. The vapor attacks the eyes in a very painful manner. Cantharidin contains C,nHfiO.. BITTER-ALMOND OIL AND ITS PRODUCTS, B ENZ 0 YL SERIES. The volatile oil of bitter almonds possesses a very high degree of interest, from its study having, in the hands of MM. Liebig and AVohler, led to the first discovery of a compound organic body capable of entering into direct combi- nation with elementary principles, as hydrogen, chlorine, and oxygen, and playing in some degree the part of a metal. The oil is supposed to be the hydride of a salt-basyle, containing C,4H502 called benzoyl, from its relation to benzoic acid, which radical is to be traced throughout the whole series: it has been isolated, and will be described among the products of distillation of the benzoates. Table of Benzoyl-Compounds. Benzoyl, symbol Bz . Hydride of benzoyl; bitter-almond oil Oxide of benzoyl; anhydrous benzoic acid Hydrated oxide of benzoyl; benzoic acid Chloride of benzoyl Bromide of benzoyl Iodide of benzoyl Sulphide of benzoyl Benzoic alcohol . C 14^5^2 C14H502H C14H5020 C14"5020,HO CI4H502C1 CuH502Br c,4"5o2i C,4H502S C,4H70,HO AND ITS PRODUCTS. 433 Hydride of benzoyl ; bitter-almond oil ; BzH.—This substance is pre- pared in large quantities, principally for the use of the perfumer, by distilling Vkith water the pa-te of bitter almonds, from which the fixed oil has been ex- pressed. It certainly does not pre-exist in the almonds ; the fat oil obtained from them by pressure is absolutely free from every trace of this principle; it is formed by the action of water upon a peculiar crystallizable substance, hereafter to be described, called amygdalin, aided in a very extraordinary manner by the presence of the pulpy albuminous matter of the seed. The crude oil has a yellow color, and contains a very considerable quantity of hydrocyanic acid, the origin of which is contemporaneous with that of the oil itself: it is agitated with dilute solution of protochloride of iron mixed with hydrate of lime in excess, and the whole subjected to distillation: water passes over, accompanied by the purified essential oil, which is to be left for a short time in contact with a few fragments of fused chloride of calcium to free it from water. Pure hydride of benzoyl is a thin, colorless liquid, of great refractive power, and peculiar and very agreeable odor; its density is 1-043, and its boiling- point 356° (180°C): it is soluble in about 30 parts of water, and is misciblc in all proportions with alcohol and ether. Exposed to the air, it greatly absorbs oxygen, and becomes converted into a mass of crystallized benzoic acid. Heated with solid hydrate of potassa, it disengages hydrogen, and yields benzoate of the base. AVith the alkaline bisulphites it forms beautiful crystalline compounds. The vapor of the oil is inflammable, and burns with a bright flame and much smoke. It is very doubtful whether pure bitter- almond-oil is poisonous ; the crude product, sometimes used for imparting an agreeable flavor to puddings, custards, &c, and even publicly sold for that purpose, is in the highest degree dangerous. Oxide of benzoyl ; benzoic acid ; BzO,HO. — This is the sole product of the oxidation, at a moderate temperature, of bitter-almond oil: it is not, how- ever, thus obtained for tho purposes of experiment and of pharmacy. Several of the balsams yield benzoic acid lit'-187. in great abundance, more especially the concrete resi- nous variety known under the name of gum-benzoin. AVheu this substance is exposed to a gentle heat in a subliming vessel, the benzoic acid is volatilized, and may be condensed by a suitable arrangement. The simplest and most efficient apparatus for this and all similar operations is the contrivance of Dr. Mohr; it consists of a shallow iron pan, over the bottom of which the substance to be sublimed is thinly spread; a sheet of bibulous paper, pierced with a number of pin-holes, is then stretched over the vessel, and a cap made of thick, strong drawing or cartridge-paper, secured by a string or hoop over the whole. The pan is placed upon a sand-bath, and slowly heated to the requi- site temperature; the vapor of the acid condenses in the cap, and the crystals are kept by the thin-paper diaphragm from falling back again into the pan. Benzoic acid thus obtained assumes the form of light, feathery, colorless crystals, which exhale a fragrant odor, not belonging to the acid itself, but duo to a small quantity of a volatile oil. A more productive method of pre- paring the acid is to mix the powdered gum-benzoin very intimately with an equal weight of hydrate of lime, to boil this mixture with water, and to de- compose the filtered solution, concentrated by evaporation to a small bulk, with excess of hydrochloric acid; the benzoic acid crystallizes out on cooling in thin plates, which may be drained upon a cloth filter, pressed, and dried in the air. By sublimation, which is then effected with trifling loss, the acid is obtained perfectly white. 37 434 BITTER-ALMOND OIL Benzoic acid is inodorous when cold, but acquires a faint smell when gently warmed; it melts just below 212° (100°C), and sublimes at a temperature a little above; it boils at 462° (288°-8C) and emits a vapor of the density of 4-27. It dissolves in about 200 parts of cold, and 25 parts of boiling water, and with great facility in alcohol. Benzoic acid is not affected by ordinary nitric acid, even at a boiling heat. The crystals obtained by sublimation, or by the cooling of a hot aqueous solution, contain an equivalent of water, which is basic, or C)4H503,IIO. Lately M. Gerhardt has succeeded in obtain- ing anhydrous benzoic acid, Ci4H603. This substance crystallizes in beauti- ful oblique prisms, which fuse at 91-4° (33°C), and are soluble in alcohol and ether, but insoluble in water. Boiled with water it is gradually converted into common benzoic acid. The mode of formation of this substance is men- tioned under Chloride of Benzoyl, see page 436. All the benzoates have a greater or less degree of solubility; they are easily formed, either directly or by double decomposition. Benzoates of the alkalies and of ammonia are very soluble, and somewhat difficult to crystallize. Ben- zoate of lime forms groups of small colorless needles, which require 20 parts of cold water for solution. The salts of baryta and strontia are soluble with difficulty in the cold. Neutral benzoate of the sesquioxide of iron is a soluble compound; but the basic salt obtained by neutralizing as nearly as possible by ammonia a solution of sesquioxide of iron, and then adding benzoate of ammonia, is quite insoluble. Sesquioxide of iron is sometimes thus separated from other metals in practical analysis. Neutral and basic benzoate of lead are freely soluble in the cold. Benzoate of silver crystallizes in thin transpa- rent plates, which blacken on exposure to light. Nitrobenzoic acid.—AVhen benzoic acid is boiled for several hours with fuming nitric acid, until red fumes cease to appear, it yields a new acid body, in which the elements of hyponitric acid are substituted for an equivalent of hydrogen of the original benzoic acid. Nitrobenzoic acid greatly resembles benzoic acid in character, and contains CI4H4NO ,HO = C,4(H4N04)03,IIO. The remarkable transformation of the amide of this acid, of nitrobtnzamide, will be noticed under the head of aniline. The continued action of nitric acid gives rise to the formation of a second acid, called binitrobenzoic acid, and con- taining Cl4{ H3(N04)2|03,HO. By the action of reducing agents, such as sulphide of ammonium, nitrobenzoic and binitrobenzoic acid are converted into amidobenzoic acid, C14H7N03,HO and biamidobenzoic acid, C14H9N2O3,H0. This mode of transformation is more fully considered under the head of aniline. Sulphobenzoic acid. — Benzoic acid is soluble without change in concen- trated oil of vitriol, and is precipitated by the addition of water; it combines, however, the anhydrous sulphuric acid, generating a compound acid analo- gous to sulphovinic, but bibasic, forming a neutral and an acid series of salts. The baryta-compound is easily prepared by dissolving in water the viscid mass produced by the union of the two bodies, and saturating the solu- tion with carbonate of baryta. On adding hydrochloric acid to the filtered liquid, and allowing the whole to cool, acid sulphobenzoate of baryta crystal- lizes out. This salt has an acid reaction, and requires 20 parts of cold water for solution; the neutral salt is much more soluble. The hydrated acid is easily obtained by decomposing the sulphobenzoate of baryta by dilute sul- phuric acid; it forms a white, crystalline, deliquescent mass, very stable and permanent, which contains C14H402,2S03,2HO. Benzone, benzopiienone.—When dry benzoate of lime is distilled at a hi"-h temperature, it yields a thick, oily, colorless liquid, of peculiar odor. This°is a mixture of several compounds, from which, however, a crystalline substance C,3H50, or CjgH^Oj,, may be isolated, to which the name benzone or benzophe- none has been given. Carbonate of lime remains in the retort; the reactior AND ITS PRODUCTS. 435 is thus perfectly analogous to that by which acetone is produced by the dis- tillation of a dry acetate. CaO,CI4H603 = C13H50 + CaO,C02. The benzophenone is, however, always accompanied by secondary products, due to the irregular and excessive temperature, solid hydrocarbons, carbonic oxide, and benzol, a body next to be described. Benzol, or Benzine. — If crystallized benzoic acid be mixed with three times its weight of hydrate of lime, and the whole distilled at a temperature Blowly raised to redness in a coated glass or earthen retort, water, and a vola- tile oily liquid termed benzol, pass over, while carbonate of lime, mixed with excess of hydrate of lime, remains in the retort. The benzol separated from the water, and rectified, forms a thin, limpid, colorless liquid, of strong agree- able odor, insoluble in water, but miscible with alcohol, having a density of 0-885, and boiling at 176° (80°C); the sp. gr. of its vapor is 2-738. Cooled to 32° (0°C), it solidifies to a white, crystalline mass. Benzol contains carbon and hydrogen only, in the proportion of 2 eq. of the former to 1 of the latter, or probably C,2H6. It is produced by the resolution of benzoic acid into benzol and carbonic acid, the water taking part in the reaction. C14H604 = C12H6 + 2C02. Benzol is identical with the bicarbide of hydrogen, many years ago dis- covered by Mr. Faraday in the curious liquid condensed during the compres- sion of oil-gas, of which it forms the great bulk, being associated with an excessively volatile hydrocarbon, containing carbon and hydrogen in the ratio of the equivalents, the vapor of which required for condensation a tempera- ture of 0° (—17°-7C). This is the substance which has been described under the name of butylene, when treating of butylic alcohol (see page 415), and valeric acid (sec page 418). A copious source of benzol has been shown by Mr. Mansfield to exist in the lightest and most volatile portions of coal-tar oil, which will be noticed in its place under the head of that substance. Sulphobenzide and sulphobenzolic acid.—Benzol combines directly with anhydrous sulphuric acid to a thick viscid liquid, soluble in a small quantity of water, but decomposed by a larger portion, with separation of a crystalline matter, the sulphobcnzide, (sulphobenzol) which may be washed with water, in which it is nearly insoluble, dissolved in ether, and left to crystallize by spon- taneous evaporation. It is a colorless, transparent substance, fusible at 212° (100°C), bearing distillation without change, and resisting the action of acids and other energetic chemical agents. Sulphobenzide contains C12H5S02. It may be viewed as benzol in which 1 eq. of hydrogen has been replaced by 1 eq. of sulphurous acid. The acid liquid from which the preceding substance has been separated, neutralized by carbonate of baryta and filtered, yields sulpho- benzolate of baryta,, which is a soluble salt, but crystallizes in an imperfect manner. By double decomposition with sulphate of copper, a compound of the oxide of that metal is obtained, which forms fine, large, regular crystals. The hydrate of sulphobenzolic acid is prepared by decomposing the copper- salt with sulphuretted hydrogen; a sour liquid is obtained, which furnishes, by evaporation, a crystalline residue, containing C12H5S03, -\- HO,SO,. The salts of potassa, soda, ammonia, and of the oxides of zinc, iron, and silver, crystallize freely. This compound acid can be prepared by dissolving benzol in Nordhausen sulphuric acid. The long-continued action of Nordhausen acid converts benzol into a second acid, containing C,2H64S03, called disulphobenzo-^ lie acid. 43G BITTER-ALMOND OIL Nitbobenzol.—Ordinary nitric acid, even at a boiling temperature, has no action on benzol; the red fuming acid attacks it with the aid of heat, with great violence. The product, on dilution, throws down a heavy, oily, yellow- ish, and intensely-sweet liquid, which has an odor resembling that of bitter- almond oil. Its density is 1-209; it boils at 415° (212°-8C), and distils, but not without being slightly changed. It is but little affected by acids, alkalies, or chlorine, and is quite insoluble in water. Nitrobenzol contains C,2H5N04, and may be viewed as benzol, in which 1 eq. of hydrogen is replaced by 1 eq. of hyponitric acid. AVhen nitrobenzol is heated with an alcoholic solution of caustic potassa, and the product subjected to distillation, a red oily liquid passes over: this is a mixture of several substances from which, on cooling, large red crystals separate, which are nearly insoluble in water, but dissolve with facility in ether and alcohol. This compound, which is called azobenzol, melts at 149° (48°-3C), and boils at 379° (192°-2C); it contains C12H5N. To- gether with the azobenzol an oil is produced, which contains C,2H7N, and has, like ammonia, the power of combining with acids. It has received the name of aniline, and will be described in the section on Organic Bases. The reac- tion which gives rise to azobenzol and aniline, in this case, is not yet perfectly understood, several other substances being simultaneously produced, and a large quantity of nitrobenzol being charred. Nitrobenzol may, however, bo entirely converted into aniline, by a most elegant process, discovered by Zinin, namely, by the action of sulphide of ammonium, which will be noticed when treating of aniline. Binitrobenzol. — If benzol is dissolved in a mixture of equal volumes of concentrated nitric and sulphuric acids, and the liquid be boiled for some minutes, it solidifies on cooling to a mass of crystals, which are easily fusible, insoluble in water, and readily soluble in alcohol. They contain CI2H4N208 = C12{ H4(N04)2}, and may be viewed as benzol, in which 2 eq. of hydrogen are replaced by 2 eq. of hyponitric acid. Benzol and chlorine combine when exposed to the rays of the sun: the pro- duct is a solid, crystalline, fusible substance, insoluble in water, containing Cl2H6Cl6, called chlorobenzol. When this substance is distilled, it is decom- posed into hydrochloric acid, and a volatile liquid, chlorobenzide, composed of C]2H3C13. In its chemical relations, benzol exhibits the character of a substance ana- logous to hydride of methyl (marsh-gas), hydride of ethyl, and hydride of amyl. Benzol.....C12H6H = Hydride of phenyl. Sulphobenzol (sulphobenzide) . C,2H6S02 Nitrobenzol . . . . C]2H5N04 The alcohol belonging to this hydride is known: it contains C,2H602 = C12H50,HO, and will be described among the volatile principles of coal-tar. Chlortde of benzoyl, BzCl. —This compound is prepared by passing dry chlorine gas through pure bitter-almond oil, as long as hydrochloric acid con- tinues to be formed; the excess of chlorine is then expelled by heat. Chlo- ride of benzoyl is a colorless liquid of peculiar, disagreeable, and pungent odor. Its density is 1-106. The vapor is inflammable, and burns with a°tint of green. It is decomposed slowly by cold, and quickly by boiling water, into benzoic and hydrochloric acids; with an alkaline hydrate, benzoate of the base, and chloride of the metal, are generated. Chloride of benzoyl has become very interesting on account of some im- portant researches of Gerhardt, who succeeded by the aid of this substance in obtaining anhydrous benzoic acid. This compound is produced by the action of chloride of benzoyl upon benzoate of soda. AND ITS PRODUCTS. 437 ^01CJ4H50, + CI4H502C1 = NaCl + 2C14H503 Benzoate of Chloride of Chloride Anhydrous soda. benzoyl. of benzoic sodium. acid. This reaction is of considerable interest, since it is of general application for the separation of anhydrous acids; and has furnished already a very large number of new bodies. If chloride of benzoyl is made to act upon the soda-salt of another organic acid, peculiar anhydrous double acids are pro- duced. Thus chloride of benzoyl and valerate of potassa furnish on distilla- tion an oily liquid of a pungent odor, which excites tears. NaO,C10H9O3 + C14II502C1 = NaCl + C10H9O3,C)4H5O3 Valerate of Chloride of Chloride Anhydrous soda. benzoyl. of valero-benzoic sodium. acid. AVhen submitted to distillation, valero-benzoic acid splits into anhydrous benzoic and valeric flcids. The latter is a colorless liquid which boils at 419° (215°C). Gerhardt is of opinion that the so-called anhydrous acids, obtained by his process, are far from being the anhydrous acids which chemists are in the habit of assuming in the salts. He considers them as a sort of saline bodies, as the common hydrate, in which the hydrogen is re- placed by an organic radical. Hydrated benzoic acid .... (C,4H502)0,110 Benzoate of soda.....(CI4H502)0,NaO Benzoate of benzoyl.....(C14H502)0,(C14H502)0 (Anhydrous benzoic acid) Valero-benzoic acid.....(CI4H5O2)O,(C10H0O2)O Hydrated valeric acid .... (CI0H9O2)O,HO Valerate of soda.....(C10H9O2)O,NaO Valerate of valeryl. ... (C10H9O2)O,(C10H9O2)O (Anhydrous valeric acid) Benzamide. —AVhen pure chloride of benzoyl and dry ammoniacal gas are presented to each other, the ammonia is energetically absorbed, and a white, solid substance produced, which is a mixture of sal-ammoniac and a highly- interesting body, benzamide. The sal-ammoniac is removed by washing with cold water, and the benzamide dissolved in boiling water, and left to crystal- lize. It forms colorless, transparent, prismatic, or platy crystals, fusible at 239° (115°C), and volatile at a higher temperature. It is but slightly soluble iu cold, freely in boiling water, also in alcohol and ether. Benzamide cor- responds to oxamide, both in composition and properties; it contains C14117N02==C,411602,NH2, or benzoate of oxide of ammonium, minus 2 eq. of water, and it sutlers decomposition by both acids and alkaline solutions, yielding, in the first case, a salt of ammonia and benzoic acid, and, in the second, free ammonia and a benzoate. AVhen distilled it loses again 2 eq. of water, and becomes benzonitrile. (See page 439.) Iouide of benzoyl, Bzl. — This is prepared by distilling the chloride of benzoyl with iodide of potassium; it forms a colorless, crystalline, fusible mass, decomposed by water and alkalies, in the same manner as the chloride. The bromide of benzoyl, BzBr, has very similar properties. The sulphide BzS, is a yellow oil, of offensive smell, which solidifies at a low temperature, to a soft, crystalline mass. Cyanide of benzoyl, BzCy, obtained by heating the 37* 438 BITTER-ALMOND OIL chloride with cyanide of mercury, forms a colorless, oily, inflammable liquid, of pungent odor, somewhat resembling' that of cinnamon. All these com- pounds°yield benzamide with dry ammonia. Benzoic alcohol.—Becently M. Cannizzaro has made the interesting dis- covery that the action of an alcoholic solution of potassa on oil of bitter- almonds gives rise to the formation of an oily body, heavier than water, and boiling at 400° (204°C), which contains C14H8<)2, and exhibits in every respect the deportment of an alcohol. AVhen treated with oxidizing agents it fur- nishes benzoic acid. The action of hydrochloric acid gives rise to the for- mation of a chloride of the formula C,4H7C1, which boils at about 356° (180°C). Distillation with acetic and sulphuric acid converts benzoic alcohol into a compound ether of the formula C,8H10O4 = C1.1H70,C4H303 which has an aromatic pear odor, and boils at 410° (210°C). The relation of this new group of substances to ethyl-alcohol and its derivatives will become obvious from the following formulae : — Ethyl-series. Benzoyl-series. Ethylic alcohol . C4II50,HO ■ Acetic acid . . C4H303,HO Chloride of ethyl . C4H6C1 • Benz. of ethyl. . C4H50,C14H503 Benzoic alcohol . C14II70,HO Benzoic acid . . C14H603,HO Chloride. . . C14H7C1 Acetate . ." . C14H70,C4H303 Formobenzoic acid.—Crude bitter-almond oil is dissolved in water, mixed with hydrochloric acid, and evaporated to dryness: the residue is boiled with ether, which dissolves out the new substance, and leaves sal-ammoniac. Formobenzoic acid forms small, indistinct, white crystals, which fuse, and afterwards suffer decomposition by heat, evolving an odor resembling that of the flowers of the hawthorn, and leaving a bulky residue of charcoal. It is freely soluble in water, alcohol, and ether, has. a strongly acid taste and re- action, and forms a series of crystallizable salts with metallic oxides. This substance contains C,6H705,HO = C14H6024-C2H03,HO, or the elements of bitter-almond oil and formic acid: it owes its origin to the peculiar action of strong mineral acids on the hydrocyanic acid of the crude oil, by which that body suffers resolution into formic acid and ammonia. It is decomposed by oxidizing bodies, as binoxide of manganese, nitric acid, and chlorine, into bitter-almond oil and carbonic acid. Hydrobenzamide.—Pure bitter-almond oil is digested for some hours at about 120° (49°C) with a large quantity of strong solution of ammonia: the resulting white crystalline product is washed with cold ether, and dissolved in alcohol; the solution, left to evaporate spontaneously, deposits the hydro- benzamide in regular, colorless crystals, which have neither taste nor smell. This substance melts at a little above 212° (100°C), is readily decomposed by heat, dissolves with ease in alcohol, but is insoluble in water: the alcoholic solution is resolved by boiling into ammonia and bitter-almond oil; a similar change happens with hydrochloric acid. Hydrobenzamide contains C42H18N2, or the elements of 3 equivalents of bitter-almond oil, and 2 of ammonia minus 6 equivalents of water. AVhen impure bitter-almond oil is employed in this experiment, the products are different, several other compounds being obtained. But even with the pure oil frequently a great variety of substances are formed. Hydrobenzamide when submitted to the action of chemical pro- cesses furnishes a great number of derivatives, of which, however, only one substance, namely, amarine, will be described in the section on the Organic Bases. Benzoin. — This substance is found in the residue contained in the retort from which bitter-almond oil has been distilled with lime and oxide of iron to free it from hydrocyanic acid: it is a product of the action of alkalies and alkaline earths on the crude oil, and is gaid to be only generated in the nre- AND ITS PRODUCTS. 439 Bencc of hydrocyanic acid. It is easily extracted from the pasty mass, by dissolving out the lime and oxide of iron by hydrochloric acid, and boiling the residue in alcohol. Benzoin forms colorless, transparent, brilliant, pris- matic crystals, tasteless and inodorous; it melts at 248° (120°C), and distils without decomposition. AVater, even at a boiling heat, dissolves but a small quantity of this body; boiling alcohol takes it up in a larger proportion ; it dissolves in cold oil of vitriol, with violet color. Benzoin contains C14H602, or C28H]2C4, and is, consequently, an isomeric modification of bitter-almond oil. Benzile.—This curious compound is a product of the action of chlorine on benzoin: the gas is conducted into the fused benzoin as long as hydrochloric acid continues to be evolved. It is likewise formed by treating benzoin with fuming nitric acid. The crude product is purified by solution in alcohol. It forms large, transparent, sulphur-yellow crystals, fusible at 200° (93°-3C), unaltered lay distillation, and quite insoluble in water. It dissolves freely in alcohol, ether, and concentrated sulphuric acid, from which it is precipitated by water. Benzile is composed of CI4H602, or C28H_0O4, and is therefore iso- meric with the radical of the benzoyl-series. Benzilic acid.—Benzoin and benzile dissolve with violet tint in an alcoholic solution of caustic potassa. By long boiling the liquid becomes colorless, and is then found to contain a salt of a peculiar acid, called the benzilic, which is easily obtained by adding hydrochloric acid to the filtered liquid, and leaving the whole to cool. Benzilic acid forms small, colorless, transparent crystals, slightly soluble in cold, more readily in boiling water; it melts at 248° (120°C), and cannot be distilled without decomposition. It dissolves in cold concentrated sulphuric acid with a fine carmine-red color. Benzilic acid contains C^lln*^, HO, or 2 eq. benzile and 2 eq. water. Benzonitkile.—AVhen benzoate of ammonia is exposed to destructive dis- tillation, among other products a yellowish volatile oil makes its appearance. having exactly the odor of bitter-almond oil. It is heavier than water, slightly soluble in that liquid, boils at 376° (191°-1C), and contains C,4HSN. It is benzoate of ammonia—4 eq. of water, (NII40,C14II503—4HO=C14If5N,) and stands to this salt in the same relation as cyanogen to oxalate, hydro- cyanic acid to formate, and cyanide of methyl to acetate of ammonia. Ben- zonitrile likewise may be viewed as a cyanide when it becomes a member of the phenyl-series, C14H5N = CKII5,C2N. Benzoyl. — Benzoate of copper, by dry distillation cautiously conducted, gives a residue containing salicylic and benzoic acid, and an oily distillate which crystallizes on cooling. This substance possesses the odor of the ge- ranium, melts at 158° (70°C), and contains C14H502. It was discovered by Ettling, and subsequently studied by Stenhouse, and is evidently the radical of the benzoyl-series. By heating with hydrate of potassa it is instantly converted into benzoic acid with disengagement of hydrogen. Benzimiue.—This is a white, inodorous, shining, crystalline substance, occa- sionally found in crude bitter-almond oil. It is insoluble in water, and but slightly dissolved by boiling alcohol and ether. Oil of vitriol dissolves it with dark indigo-blue color, becoming green by the addition of a little water. This reaction is characteristic. Benzimide contains C28II„N04. It may be viewed as derived from an acid benzoate of ammonia by the separation of 4 eq. of water. A great number of other compounds derived from bitter-almond oil, directly or indirectly, have been described by Laurent and others. Many of these contain sulphur; sulphuretted hydrogen and sulphide of ammonium being employed in their preparation. Hippuric ACin. —This interesting substance is in some measure related to the benzoyl-compounds. It occurs, often in large quantity, in combination with potassa or soda, in the urine of horses, cows, and other graminivorous animals. It is prepared by evaporating in a water-bath perfectly fresh cows' 440 BENZOYL SERIES. urine to about a tenth of its volume, filtering from the deposit, and then mix- ing the liquid with excess of hydrochloric acid. Cows' urine frequently depo- sits hippuric acid without concentration, when mixed with a considerable quantity of hydrochloric acid, in which the acid is less soluble than in water. The brown crystalline mass which separates on cooling is dissolved in boiling water, and treated with a stream of chlorine gas until the liquid assumes a light amber color, and begins to exhale the odor of that substance; it is then filtered, and left to cool. The still impure acid is redissolved in water, neu- tralized with carbonate of soda, and boiled for a short time with animal charcoal; the hot filtered solution is, lastly, decomposed by hydrochloric acid. Hippuric acid in a pure state crystallizes in long, slender, milk-white, and exceedingly delicate square prisms, which have a slightly-bitter taste, fuse on the application of heat, and require for solution about 400 parts of cold water; it also dissolves in hot alcohol. It has an acid reaction, and forms salts with bases, many of which are crystallizable. Exposed to a high temperature, hippuric acid undergoes decomposition, yielding benzoic acid, benzoate of am- monia, and benzo-nitrile with a coaly residue. AVith hot oil of vitriol, it gives off benzoic acid: boiling hydrochloric acid converts it into benzoic acid and glycocine (gelatin-sugar), which is described in the Animal Chemistry. Hip- puric acid contains C18H8N05,HO. The constitution of hippuric acid has been frequently discussed by chemists. Very different views have been proposed. The most probable one is, that it is the amidogen-compound of a peculiar acid — glycobenzoic acid. If hippu- ric acid be treated with nitrous acid, it undergoes the decomposition peculiar to amidogen compounds, which has been explained when treating of oxamide (page 361. A new non-nitrogenous acid is formed together with water and pure nitrogen, C18IT8N05, HO + N03 = C18H707, H 0 -4- HO + 2N. Glycoben- zoic acid is a crystalline substance, slightly soluble in water, but readily dis- solved by alcohol and ether. It may be viewed as a conjugate acid, contain- ing benzoic and glycolic acids—2 eq. of water, C]8H707,HO = C14H604,C4H406 —2HO. Under the influence of boiling water it splits indeed into benzoic and glycolic acids. Glycocine must be considered as glycolamide, NH40,C4H406— 3HO = C4H5N04, and this explains the conversion of hippuric acid into ben- zoic acid and glycocine. Becently M. Dessaignes has succeeded in regenerating hippuric acid by the action of chloride of benzoyl upon the zinc-compound of glycocine. C4H5N04,ZnO + C,4H502C1 == C18II9N06 + ZnCl + HO Zinc-compound • Chloride of Hippuric of glycocine. benzoyl. acid. If, in the preparation of hippuric acid, the urine be in the slightest degree putrid, the hippuric acid is all destroyed during the evaporation, ammonia is disengaged in large quantity, and the liquid is then found to yield nothing but benzoic acid, not a trace of which can be discovered in the unaltered secre- tion. Complete putrefaction effects the same change: benzoic acid might thus be procured to almost any extent. AVhen benzoic acid is taken internally, it is rejected from the system in tho state of hippuric acid, which is then found in the urine. BENZOYL SERIES. 441 APPENDIX TO THE BENZOYL SERIES. STILBYL-ALCOHOL. If oil of bitter-almonds be treated with pentachloride of phosphorus, an oily liquid is produced, boiling at 402° (206°C), which contains C14H6C12. C14H602 -f PC16 = PC1302 + C:4H6C12. This compound represents in the benzoyl-series the Dutch-liquid of the ethyl-series; and recent experiments of AVicke have proved that this chloride, when distilled with acetate of silver, furnishes a crystalline body containing CBHI20„=CMHiOlP2C4H30,. This substance is the acetate of a biatomic alcohol, C14H602,2HO, which may be designated stilbylic alcohol, but which has not yet been isolated. HOMOLOGUES OF THE BENZOYL SERIES. Toluylic Acid, C16H703,HO.—This substance, which differs from benzoic acid by C2H2, has been discovered by Dr. Noad, who obtained it by the action of very dilute nitric acid upon cymol, a carbo-hydrogen occurring in cumin- oil. It is a substance exhibiting the closest analogy with benzoic acid, both in its physical characters and in its chemical relations. Like benzoic acid, when treated with fuming nitric acid, it yields a nitro-acid, nitrotoluylic acid, C16H6N07,HO = Cl6(H6N04)03,HO: distilled with lime or baryta, it furnishes a hydrocarbon C]4H8, homologous to benzol. The latter substance, which has received the name of toluol, is also obtained from other sources, especially from coal-tar and Tolu balsam. An acid of the formula C18H903,HO, is not yet known, but we may confi- dently expect that the progress of science will not fail to elicit this substance: even now wo are acquainted with a hydrocarbon Cl6HI0, homologous to benzol and toluol. This substance, which is called xylol, is found in wOod-tar and coal-gas naphtha, and stands to the unknown acid C18H903.HO, in the same relation as benzol to benzoic acid. Should the above acid be discovered, we may with certainty predict that, when distilled wUh_-exeess of U$ev," it will yield xylol. ,-i-v Cumic acii,, Cjq^hOj,HO. — Another acid, homologous to.-k§jp£©ic acid, was discovered some, thne ago by Cahours and Gerhardt. It is formed by the oxi- dation of one of the constituents of cumin-oil, cuminol C^H^O^ which corre- sponds to oil of bitter almonds. Cumic acid is very similar in its properties to benzoic acid. Boiled with a mixture of sulphuric acid and bichromate of potassa, it is converted into a new acid, insolinic acid, containing C18H8Og. Cumic acid likewise yields a nitro-acid, nitro-cumic acid, C^H^NO^HO = Cao(H|0^T(-')4)Os,HO' anc* wnen distilled with lime is converted into cumot, Cl8HI2, a hydrocarbon, homologous to benzol, toluol, and xylol. -i-- Of the next series only the hydrocarbon is known. This is cymol, C^II^,.., the substance which, as has been mentioned above, is the source of toluylic acid. The homology of these substances is clearly exhibited by the following table: — 442 SALICYL SERIES. Benzoyl-series Toluyl-series Xylil-series Cumyl-series Cymyl-series Hydrides. C14H502H Cl6H702H C20HnO2H C14H503,IIO C16H703,HO C^O^HO Hydrocarbons derived from the acid. C,2IT6 c14wa L ik tl ,n C18H,2 ^20^ 14 This table shows that up to the present moment only the series of hydro- carbons is without a gap, while two acids and two hydrides remain to be dis- covered. SALICYL SERIES. Salicin. — The leaves and young bark of the poplar, willow, and several other trees, contain a peculiar crystallizable, bitter principle, called salicin, which in some respects resembles the vegeto-alkalies cinchonine and quinine, being said to have febrifuge properties. It differs essentially, however, from these bodies in being destitute of nitrogen, and in not forming salts with acids. Salicin may be prepared by exhausting the bark with boiling water, concentrating the solution to a small bulk, digesting the liquid with powdered protoxide of lead, and then, after freeing the solution from lead by a stream of sulphuretted hydrogen gas, evaporating until the salicin crystallizes out on cooling. It is purified by treatment with animal charcoal and re-crystalliza- tion. Salicin forms small, white, silky needles, of an intensely bitter taste, which have no alkaline reaction. It melts and decomposes by heat, burning with a bright flame, and' leaving a residue of charcoal. It is soluble in 5-6 parts of cold water, and in a much smaller quantity when boiling hot. Oil of vitriol colors it deep red. The last experiments of M. Piria give for salicin the for- mula C26H18014. AVhen salicin is distilled with a mixture of bichromate of potassa and sul- phuric acid, ityields, among other products, a yellow, sweet-scented oil, which is found to be identical with the volatile oil distilled from the flowers of the Spiroza ulmaria, or common meadow-sweet. Table of Salycil- Compounds. Salicylous acid. Salicylite of potassa. Chlorosalicylous acid Iodosalicylous acid . Bromosalicylous acid Saligenin Salicylic acid . Cl4H503,HO C14H503,KO C14(H4C1)03,H0 C14(H4I)03,HO C14(H4Br)03,HO C,4H804 C14H404,2H0 Salicylous acid; artificial oil of meadow-sweet, C]4H503,HO.__One part of salicin is dissolved in 10 of water, and mixed in a retort with 1 part of powdered bichromate of potassa, and 2J parts of oil of vitriol diluted with 10 parts of water; gentle heat is applied, and after the cessation of the effer- vescence first produced, the mixture is distilled. The yellow oily product is separated from the water, and purified by rectification from chloride of cal- cium. It is thin, colorless, and transparent, but acquires a red tint by exno- sure to the air. Water dissolves a sensible quantity of this substance acquir- ing the fragrant odor of the oil, and the characteristic property of strikinir a SALICYL SERIES. 443 deep violet color with a salt of sesquioxide of iron, a property, however, which is also enjoyed by salicylic acid. Alcohol and ether dissolve it in all propor- tions. It has a density of 1-173, and boils at 385° (166°-1C), when heated alone. Salicylous acid decomposes the alkaline carbonates, even in the cold: it is acted upon with great energy by chlorine and bromine. By analysis it is found to contain C14H604, or the same elements as crystallized benzoic acid; and the density of its vapor is also the same, being 4-276. Salicyliti: of potassa, KO,C]4H503.—This compound is easily prepared by mixing the oil with a strong solution of caustic potassa; it separates, on agi- tation, as a yellow crystalline mass, which may be pressed between folds of blotting-paper, and recrystallized from alcohol. It forms large, square, golden- yellow tables, which have a greasy feel, and dissolve very easily both in water and alcohol: the solution has an alkaline reaction. AVhen quite dry, the crys- tals are permanent in the air; but in a humid state they soon become greenish, ond eventually change to a black, soot-like substance, insoluble in water, but dissolved by spirit and by solution of alkali, called melanic acid. Acetate of potassa is formed at the same time. Melanic acid is said to contain O^lIgO,,,. The crystals of salicylite of potassa contain water which cannot be expelled without partial decomposition of the salt. Salicylite of ammonia, NH40,C,4Il503, crystallizes in yellow needles, which are quickly destroyed with liberation of ammonia and the acid. Salicylite of baryta, BaO,C,4Ti503-f- 2HO, forms fine yellow acicular crystals, which are but slightly soluble in the cold. Salicylite of copper is a green insoluble pow- der, containing CuO,C14H503. Salicylite of copper by destructive distillation gives, among other products, salicylous acid, and a solid body forming colorless prismatic crystals, fusible and volatile. This body is insoluble in water, but dissolved by alcohol and ether. Nitric acid converts it into anilic and picric acids. (See Indigo.) It contains C14H603, and is isomeric with anhydrous benzoic acid. Ciiloro-salicylous Acii), C]4(H4C1 )03.HO. — Chlorine acts-very strongly upon salicylous acid; the liquid becomes heated, and disengages large quan- tities of hydrochloric acid. The product is a slightly-yellowish crystalline mass, which, when dissolved in hot alcohol, yields colorless tabular crystals of the pure compound, having a pearly lustre. The substance is insoluble in water; it dissolves freely in alcohol, ether, and solutions of the fixed alkalies; from the latter it is precipitated unaltered by the addition of an acid. It is not even decomposed by long ebullition with a concentrated solution of caustic potassa. Heated in a retort, it melts and volatilizes, condensing in the cool part of the vessel in long, snow-white needles. The odor of this substance is peculiar and by no means agreeable, and its taste is hot and pungent. Chloro-salicylous acid combines with the metallic oxides; with potassa it forms small red crystalline scales, very soluble in water. The corresponding compound of baryta, prepared from the foregoing, by double decomposition, is an insoluble crystalline, yellow powder, containing BaO,C,4(H4Cl)03. Bromo-salicylous acid, CI4(H4Br)03.HO.—The bromine-compound is pre- pared by the direct action of bromine on salicylous acid: it crystallizes in small colorless needles, and very closely resembles in properties the chlorine- compound. Salicylous acid dissolves a large quantity of iodine, acquiring thereby a brown color, but forming no combination; the iodine-compound may, however, be procured by distilling iodide of potassium with chloro-sali- cylous acid. It sublimes as a blackish-brown fusible mass. Chlorosajiide.—The action of dry ammoniacal gas on pure chloro-salicy- lous acid is very remarkable; the gas is absorbed in large quantity, and a Bolid yellow, resinous-looking compound produced, which dissolves in boiling ether, and separates as the solution cools in fine yellow iridescent crystals: this and a little water are the only products, not a trace of sal-ammoniac can be detected. Chlorosamide is nearly insoluble in water; it dissolves without 444 SALICYL SERIES. change in ether, and in absolute alcohol; with hot rectified spirit it is partially decomposed, with disengagement of ammonia. Boiled with an acid, it yields an ammoniacal salt of the acid and chloro-salicylous acid; with an alkali, on the other hand, it gives free ammonia, while chloro-salicylous acid remains dissolved. Chlorosamide contains C42(HI5C13)N206; it is formed by the addi- tion of 2 eq. of ammonia to 3 eq. of chloro-salicylous acid, and the subsequent separation of 6 eq. of water. A corresponding and very similar substance, bromosamide, is formed by the action of ammonia on bromo-salicylicous acid. Saligenin.—This curious substance is a product of the decomposition of salicin under the influence of the emulsion or synaptase of sweet almonds; it is also generated by the action of dilute acids. In both cases the salicin is resolved into saligenin and grape-sugar. Saligenin forms colorless, nacreous scales, freely soluble in water, alcohol, and ether. It melts at 180° (82°C), and decomposes at a higher temperature. Dilute acids at a boiling-heat con- vert it into a resinous-looking substance C,4H602, called saliretin. Many oxi- dizing agents, as chromic acid and oxide of silver, convert this substance into salicylous acid: even platinum-black produces this effect. Its aqueous solu- tion gives a deep indigo-blue color with salts of sesquioxide of iron. Salige- nin contains C14H804. Hence the transformation of salicin is represented by the equation:— SC^O., + 8HO = CAO^ + 2CI4H804 Salicin. Grape-sugar. Saligenin. Salicin yields with chlorine substitution-compounds containing that element, which are susceptible of decomposition by synaptase, with production of bodies termed chloro- and bichloro-saligenin. Chloro-saligenin very closely resembles saligenin, and contains C14(H7C1)04. Certain products, called by M. Piria helicin, helicoidin, and anilotic acid are described as resulting from the action of dilute nitric acid upon salicin. AVith strong acid at a high tempera- ture nitro-salicylic acid (anilic acid), C,4(H5N04)06, is produced. Salicylic acid, C14H404.2HO.—This compound is obtained by heating sali- cylous acid with excess of solid hydrate of potassa; the mixture is at first brown, but afterwards becomes colorless; hydrogen gas is disengaged during the reaction. On dissolving the melted mass in water, and adding a slight excess of hydrochloric acid, the salicylic acid separates in crystals, which are purified by re-solution in hot water. This substance very much resembles benzoic acid; it is very feebly soluble in cold water, is dissolved in large quan- tities by alcohol and ether, and may be sublimed with the utmost ease. It is charred and decomposed by hot oil of vitriol, and attacked with great violence by strong, heated nitric acid.1 Salicylic acid can also be prepared with great ease by fusing salicin with excess of hydrate of potassa, and also by the action of a concentrated and hot solution of potassa upon the volatile oil of Gaultheria procumbens, which is the methyl-compound of this acid occurring in nature (see essential oils contain- ing oxygen). AVhen salicylic acid is mixed with powdered glass or sand, and exposed to strong and sudden heat in a retort, it is almost entirely converted into carbonic acid and hydrate of phenyl, C12H602, a substance found in con- siderable proportion in coal-tar naphtha,—and the same change happens to many of its salts with even greater facility. Populin.—This substance closely resembles salicin in appearance and solu- bility, but has a penetrating sweet taste: it is found accompanying salicin in 1 [Both toluylic acid and salicylic acids when taken internally are rejected from the system in urine, as compound amidojien acids analogous to hippuric acid. The toluylurio acid has the position CaoIIioNOs, and salicyluric CisIItNOb, or glycocine and toluylic or salicvlie aoi.la ectively, less two equivalents of water.—R. B.l ' ™ ba"cyuc acius Cull] respectively CINNAMYL AND ITS COMPOUNDS. 445 the bark and leaves of the aspen According to the researches of Piria, pop- ulin contains C^H^O^ + 4H0. It is a conjugate compound of salicin and benzoic acid. C40IVV = C14H604 + C«H180M + 2HO CryBtall. populin. Benzoic acid. Salicin. By the action of reagents it is converted into benzoic acid, and the products of decomposition of salicin. AVith dilute acid it yields benzoic acid, grape- sugar, and saliretin ; when treated with a mixture of sulphuric acid and bi- chromate of potassa, it furnishes a considerable quantity of salicylous acid. Phloridzin.—This is a substance bearing a great likeness to salicin, found in the root-rind of the apple and cherry tree, and extracted by boiling alco- hol. It forms fine, colorless, silky needles, soluble in 1000 parts of cold water, but freely dissolved by that liquid when hot; it is also soluble without diffi- culty in alcohol. It contains C^H^Oj,, + 4HO. Dilute acids convert phlo- ridzin into grape sugar and a crystallizable sweet substance called phloretin, Ca0II14O,0. 2(C^Ao^4HO) + 4HO = C^sA. + 2C80HI4O10 Phloridzin. Grape-sugar. Phloretin. Phloridzin, when fused with hydrated potassa, yields phloretic acid, C,8H10O6, a beautifully-crystalline acid, homologous to salicylic and anisic acid. Cumarin.—This is the odoriferous principle of the tonka-bean. It may bo often seen forming minute, colorless crystals under the skin of the seed, and between the cotyledons. It is best extracted by macerating the sliced beans in hot alcohol, and, after straining through cloth, distilling off the greater part of the spirit. The syrupy residue deposits on standing crystals of cumarin, which must be purified by pressure from a fat oil which abounds in the beans, and then crystallized from hot water. So obtained, cumarin forms slender, brilliant, colorless needles, fusible at 122° (50°C), and distilling with- out decomposition at a higher temperature. It has a fragrant odor and burn- ing taste; it is very slightly soluble in cold water, more freely in hot water, and also in alcohol. It is unaffected by dilute acids and alkalies, which merely dissolve it. Boiling nitric acid converts it into picric acid, and a hot concentrated solution of potassa into cumaric, and eventually into salicylic acid. Cumarin exists in several other plants, as the Melilotus officinalis, the Asperula odorala, and the AMhoxanlhum odoratum. According to M. Bleibtreu it contains C,8H604. Cumaric acid is C19H806. CINNAMYL AND ITS COMPOUNDS. The essential oil of cinnamon seems to possess a constitution analogous to that of bitter-almond oil; it passes by oxidation into a volatile acid, the cin- namic, which resembles in the closest manner benzoic acid. The radical as- sumed in these substances bears the name of cinnamyl; it has not been isolated. Table of Cinnamyl-Compounds. Cinnamyl (symbol Ci) . • ^is^A Chloride of cinnamyl . . . . . • C,8H702C1 Hydride of cinnamyl; oil of cinnamon . CISH702H Hydrated oxide of cinnamyl; cinnamic acid . CI8H,020,H0 Cinnamylic alcohol .... . C18H90,HO Cinnamate of cinnamyl . 38 . C,8H90,C,8H703 446 CINNAMYL AND ITS COMPOUNDS. Hydride of cinnamyl; oil of cinnamon, Cill.—Cinnamon of excellent quality is crushed infused twelve hours in n saturated solution of common salt, and then the'whole subjected to rapid distillation. AVater passes over, milky from essential oil, which after a time separates. It is collected and left for a short time in contact with chloride of calcium This fragrant and costly substance has, like most of the volatile oils, a certain degree of solubility in water; it is heavier than that liquid, and sinks to the bottom of the receiver in which the distilled products have been collected. It contains, according to M. Dumas, C18H802. Cinnamic acid, CiO,HO. — When pure oil of cinnamon is exposed to the air, or enclosed in a jar of oxygen, it is quickly converted by absorption of the gas into a mass of white crystalline matter, which is hydrated cinnamic acid : this is the only product. Cinnamic acid is found in Peruvian and Tola balsams, associated with benzoic acid, and certain oily and resinous sub- stances: it may be procured by the following process in groat abundanoe, and in a state of perfect purity. Old, hard Tolu balsam is reduced to powder and intimately mixed with an equal weight of hydrate of lime : this mixture is boiled for some time in a large quantity of water, and filtered hot. On cool- ing, cinnamate of lime crystallizes out, while benzoate of lime remains in solu- tion. The impure salt is redissolved in boiling water, digested with animal charcoal, and, after filtration, suffered to crystallize. The crystals are drained and pressed, once more dissolved in hot water, and an excess of hydrochloric acid being added, the whole is allowed to cool; the pure cinnamic acid sepa- rates in small plates or needle-formed crystals of perfect whiteness. Prom the original mother-liquor much benzoic acid can be procured. The crystals of cinnamic acid are smaller and less distinct than those of benzoic acid, which in most respects it very closely resembles. It melts at 248° (120°C), and enters into ebullition and distils without change at 560° (293°-3C); the vapor is pungent and irritating. Cinnamic acid is much less soluble, both in hot and cold water, than benzoic; a hot saturated solution becomes on cooling a soft-solid mass of small nacreous crystals. It dissolves with perfect ease in alcohol. Boiling nitric acid decomposes cinnamic acid with great energy, and with production of copious red fumes; bitter-almond oil distils over, and benzoic acid remains in the retort in which the experi- ment is made. AVhen cinnamic acid is heated in a retort with a mixture of strong solution of bichromate of potassa and oil of vitriol, it is almost in- stantly converted into benzoic acid, which afterwards distils over with the vapor of water: the odor of bitter-almond oil is at the same time very per- ceptible. On fusing cinnamic acid with an excess of hydrate of potassa, it is decomposed into benzoic and acetic acids. This observation has led to the synthesis of cinnamic acid by M. Bertagnini. When oil of bitter-almonds is heated in a sealed tube with chloride of acetyl, cinnamic acid is produced together with hydrochloric acid. C„H„0, + C4H302C1 = Cl8H804 -f HC1. Cinnamic acid forms with bases a variety of salts which are very similar to the benzoates. The crystallized acid contains C18H703,HO. When dis- tilled with an excess of lime or baryta, cinnamic acid undergoes a decomposi- tion analogous to that of benzoic acid; an oily liquid, cinnamol, CI6H8, distils over, whilst a carbonate of the alkaline earth remains behind, C, II 0 4- 2BaO = 2(BaO,C02) -f- C,6H8. This oil is also found in liquid storax, and is fre- quently described by the term styrol. (See Besins and Balsams). Chlorocinnose.—This is the ultimate product of the action of chlorine on oil of cinnamon by the aid of heat. AVhen purified by crystallization from alcohol, it forms brilliant, colorless needles, fusible, and susceptible of vola- tilization without change. It is not affected by boiling oil of vitriol and CINNAMYL AND ITS COMPOUNDS. 447 may be distilled without decomposition in a current of ammoniacal gas. Chlorocinnose contains C,8H4C1402; it is formed by the substitution in the oil of cinnamon of 4 eq. of chlorine for 4 eq. of hydrogen. The true chloride of cinnamyl, CiCl, seems to be first formed in considerable quantity, and subse- quently decomposed by the continued action of the chlorine ; it appears as a very thin, fluid oil, convertible into a crystalline mass by strong solution of potassa. AVhen cinnamon oil is treated with hot nitric acid, it undergoes decomposi- tion, being converted into hydride of benzoyl and benzoic acid. AVith a boil- ing solution of chloride of lime the same thing happens, a benzoate of the base being generated. If the oil be heated with solution of caustic potassa it remains unaffected; with the solid hydrate, however, it disengages pure hydrogen, and forms a potassa salt, which appears to be the cinnamato. AVhen brought into contact with cold concentrated nitric acid, a crystalline, yellowish, scaly compound is obtained, which is decomposed by water with separation of the oil. AVith ammonia a solid substance is produced. Two varieties of oil of cinnamon are met with in commeree of very unequal value, viz., that of China and that of Ceylon ; the former being considered the better: both are, however, evidently impure. The pure oil may be extracted from them by an addition of cold, strong, nitric acid ; the crystalline matter which forms after the lapse of a few hours, separated and decomposed by water, yields pure hydride of cinnamyl. There can be no douot that the cinnamic acid in Tolu and Peru balsams is gradually formed by the oxidation of a substance very closely related to the alcohols. AVhen these balsams are first imported they are nearly fluid, but gradually acquire consistence by keeping. By the aid of an alcoholic solu- tion of potassa, a compound sometimes oily, sometimes solid, may be sepa- rated from these balsams, which cannot be distilled without partial decom- position. This compound, described respectively under the name of cinna- mein (when oily), and stryacin (when solid), when distilled with hydrate of potassa, is converted into cinnamic acid and a neutral substance, which like- wise occurs in an oily and crystalline modification, and has been called, re- spectively peruvin and styrone. These substances are related to each other in a very remarkable manner. Peruvin may be viewed as the alcohol of cinna- mic acid, when cinnamein becomes the compound ether, consisting of this alcohol and cinnamic acid. This relation will become.obvious by the follow- ing formulas: — Ethyl-series. Cinnamyl-series. Alcohol . . C4IIsO,IIO Peruvin . . C]8H90,HO Acetic acid. . C4H303,HO Cinnamic acid . C)8H703,HO Acetic ether . C4H50,C4H303 Ciunamein , . C18H90,C,8H703 When treated with oxidizing agents, peruvin yields cinnamic acid, or its products of decomposition, oil of bitter-almonds and benzoic acid. Cinnamic alcohol and cinnamic acid belong to a series of alcohols and acids of which, as yet, very few terms are known. They stand to the alcohols and acids, of which the benzoic compounds may be considered as the prototypes, in the relation which obtains between propylic alcohol and propionic acid on the one hand, and allylic alcohol and acrylic acid on the other hand. 448 VEGETABLE ACIDS. VEGETABLE ACIDS. The vegetable acids constitute a very natural and important family or group of compounds, many of which possess the property of acidity, t. e., acid reaction to litmus-paper, and power of forming stable, neutral, and often crystallizable compounds with bases, to an extent comparable with that of the mineral acids. Some of these bodies are very widely diffused through the vegetable kingdom; others are of much more limited occurrence, being found in some few particular plants only, and very frequently in combination with organic alkaline bases, in conjunction with which certain of them will be found described. Many of the vegetable acids are polybasic; and it is re- markable that in the new products, or pyro-acids, to which they often give rise under the influence of heat, this character is usually lost. The particular acids now to be described are for the most part of exten- sive and general occurrence; mention will be made of some of the rarer ones in connection with their respective sources. Table of Vegetable A cids. Tartaric acid . Pyrotartaric acid Bacemic acid . Citric acid Aconitic, or equisetic Citraconic acid. Itaconic acid . Malic acid Fumaric acid . Maleic acid Meconic acid . Comenic acid . Pyrocomenic acid Einic acid Tannic acid Gallic acid acid . C8II4OI0,2HO . C10H6O6, 2HO . C8H4O]0,2HO . C)2H6Ou,3HO . Cl2H4O10,2HO . C10H4O6, 2HO . C10II4O6, 2HO . C8H408, 2HO . C8 II206, 2HO . C8 H206, 2 HO . C14H On,3HO . C,2H208, 2HO . CI0H3O5, HO . C14H10O10,2HO • C54H19031,3HO . C7 H 03, 2HO Tartaric acid.—This is the acid of grapes, of tamarinds, of the pine-apple, and of several other fruits, in which it occurs in the state of an acid potassa- salt ; tartrate of lime is also occasionally met with. The tartaric acid of commerce is wholly prepared from the tartar or argol, an impure acid tar- trate of potassa, deposited from wine, or rather grape-juice, in the act of fer- mentation. This substance is purified by solution in hot water, the use of a little pipe-clay, and animal charcoal to remove the coloring matter of the wine, and subsequent crystallization; it then constitutes cream of tartar and serves for the preparation of the acid. The salt is dissolved in boiling water and powdered chalk added as long as effervescence is excited or the liquid VEGETABLE ACIDS. 449 exhibits an acid reaction; tartrate of lime and neutral tartrate of potassa result; the latter is separated from the former, which is insoluble, by filtra- tion. The solution of tartrate of potassa is then mixed with excess of chloride of calcium, which throws down all the remaining acid in the form of lime-salt: this is washed, added to the former portion, and then the whole digested with a sufficient quantity of dilute sulphuric acid to withdraw the base and liberate the organic acid. The filtered solution is cautiously evaporated to a sj-rupy consistence, and placed to crystallize in a warm situation. Tartaric acid forms colorless, transparent crystals, often of large size, which have the figure of an oblique rhombic prism more or less modified; these are permanent in the air, and inodorous; they dissolve with great facility in water, both hot and cold, and are soluble also in alcohol. The solu- tion reddens litmus strongly, and has a pure acid taste. The aqueous solu- tion, as has been mentioned (page 89), possesses right-handed polarization. This solution is gradually spoiled by keeping. Tartaric acid is bibasic; tho crystals contain C8H4O,0,2HO. This substance is consumed in large quanti- ties by the-calico-printer, being employed to evolve chlorine from solution of bleaching powder in the production of white or discharged patterns upon a colored ground. Tartrates of potassa; neutral tartrate: solurle tartar; 2KO, C8H4O,0. —The neutral salt may be procured by neutralizing cream of tartar with chalk, as in the preparation of the acid, or by adding carbonate of potassa to cream of tartar to saturation; it is very soluble, and crystallizes with difficulty in right rhombic prisms, which are permanent in the air, and have a bitter saline taste. Acid tartrate of potassa ; cream of tartar; KO,HO,C8H4Oi0.—The origin and mode of preparation of this substance have been already described. It forms small transparent or translucent prismatic crystals, irregularly grouped together, which grit between the teeth. It dissolves pretty freely in boiling water, but the greater part separates as the solution cools, leaving about B'(T or less dissolved in the cold liquid. The salt has an acid reaction, and a sour taste. When exposed to heat in a close vessel, it is decomposed with evolution of inflammable gas, leaving a mixture of finely-divided char- coal and pure carbonate of potassa, from which the latter may be extracted by water. Cream of tartar is almost always produced when tartaric acid in excess is added to a moderately-strong solution of a potassa-salt, and the whole agitated. Tartrates of soda. — Two compounds of tartaric acid with soda are known: a neutral salt, 2N'aO,C8H4O10 -f- 4IIO; and an acid salt, NaO, HO, C8H4<)10-|- 2HO. Both are easily soluble in water, and crystallize. Tartaric acid and bicarbonate of soda form the ordinary effervescing draughts. Tartrate of potassa and soda; Bochelle or seionette salt; KO,NaO, C8H4()I0 -f- 8IIO. — This beautiful salt is made by neutralizing with carbonate ot soda a hot solution of cream of tartar, and evaporating to the consistence of thin syrup. It separates in large, transparent, prismatic crystals, tho faces of which are unequally developed; these effloresce slighly in the air, and dissolve in 11 part of cold water. Acids preeipitate cream of tartar from the solution. Rochelle salt has a mild, saline taste, and is used as a purgative. Taktbates of ammonia. — The neutral tartrate is a soluble and efflorescent salt containing 2NH4O,C8H4O10 -f- 2HO. The acid tartrate, NH4O,HO,C8II4O,0, closely resembles ordinary cream of tartar. A salt corresponding to Bochelle salt also exists, having oxide of ammonium in place of soda. The tartrates of lime, baryta, strontia, magnesia, and of the oxides of most of the metals proper, are insoluble, or nearly so, in water. Tartrate of antimony and potassa; tartar emetic. —This salt is easily made by boiling teroxide of antimony in solution of cream of tartar; it is deposited from a hot and concentrated solution in crystals derived from an octahedron 3S* 450 VEGETABLE ACIDS. with rhombic base, which dissolve without decomposition in 1 •"> parts of cold and 3 of boiling water, and have an acrid and extremely disagreeable metallic taste! The solution is incompatible with, and decomposed by, both acids and alkalies : the former throws down a mixture of cream of tartar and teroxide of antimony, and the latter the teroxide, which is again dissolved by great excess of the reagent. Sulphuretted hydrogen separates all the antimony in the state of tersulphide. Heated in a dry state on charcoal before the blow- pipe, it yields a globule of metallic antimony. The crystals contain KO,Sb03, C8H4O10+4HO.i An analogous compound, containing arsenious acid (As03), in place of ter- oxide of antimony, has been described. It has the same crystalline form as tartar emetic. A solution of tartaric acid dissolves hydrated sesquioxide of iron in large quantity, forming a brown liquid which has an acid reaction, and dries up by gentle heat to a brown, transparent, glassy substance, destitute of all traces of crystallization. It is very soluble in water, and the solution is not precipi- tated by alkalies, fixed or volatile. Indeed, tartaric acid, added in sufficient quantity to a solution of sesquioxide of iron or alumina, entirely prevents tho precipitation of the bases by excess of ammonia. Tartrate and ammoniacal tartrate of iron are used in medicine, these compounds having a less disagree- able taste than most of the iron preparations. Solution of tartaric acid gives white precipitates with lime and baryta- water, and with acetate of lead, which dissolve in excess of the acid: with neutral salts of lime and baryta no change is produced. The effect on solu- tions of potassa-salts has been already noticed. Action of heat on tartaric acid.—When crystallized tartaric acid is exposed to a temperature of 400° (204°-5C) or thereabouts, it melts, loses water, and passes through three different modifications, called in succession tartralic, tartrelic, and anhydrous tartaric acid. The two first are soluble in water, and form salts which have properties completely different from those of ordinary tartaric acid. The third substance, or the anhydrous acid, is a white insoluble powder. All three, in contact with water, slowly pass into common tartaric acid. Their composition is thus expressed : Ordinary tartaric acid .... C8H4O10,2HO Tartralic acid......2C8H4O10,3HO Tartrelic acid......C8H4O10,HO Anhydrous acid.....C8H4Oi0 The analogy borne by these bodies to the several modifications of phos- phoric acid will be at once evident. Pyrotartaric acid.—AVhen crystallized tartaric acid is subjected to de- structive distillation, a heavy acid liquid containing this substance passes over, accompanied by a large quantity of carbonic acid; in the retort is left a semi- fluid black mass, which, by further heating, gives combustible gases, an em- pyreumatic oil, and a residue of charcoal. The distilled product exhales a powerful odor of acetic acid, and is with great difficulty purified. Pyrotar- taric acid contains CI0H6O6,2IIO. It forms two series of salts. * According to Dumas, KO,Sb03,CeIl40io + HO. Dried at 212° (IO0°C), an equivalent of water is lost, and at 428° (220°C), two additional equivalents, leaving the compound KO SbOs CeHaOn. which can no longer contain ordinary tartaric acid. Nevertheless, when dissolved in w-\ter the crystals again take up the elements of water and reproduce the original salt ' ' VEGETABLE ACIDS. 451 AVhen tartaric acid is heated to 400° (204-5°C) with excess of hydrate of potassa, it is resolved witliout charring or secondary decomposition into oxalic and acetic acids, which remain in union with the base, and only undergo decomposition at a much higher temperature. Racemic acid; paratartaric acid.—The grapes cultivated in certain dis- tricts of tho Upper Rhine, and also in the Vosges, in France, contain, in asso- ciation with tartaric acid, another and peculiar acid body, to which the term racemic acid is given ; it is rather less soluble than tartaric acid, and separates first from the solution of that substance. Between these two acids, however, the greatest possible resemblance exists ; they have exactly the same compo- sition, and yield, when exposed to heat, the same products; the salts of race- mic acid correspond also, in the closest manner, with the tartrates. A solution of this acid precipitates a neutral salt of lime, which is not the case with tar- taric acid. A solution of racemic acid does not rotate the plane of polariza- tion. Bacemic acid has been the subject of some exceedingly interesting researches by M. Pasteur, which have thrown much light upon the relation of this acid to tartaric acid. If racemic acid be saturated with potassa, or soda, or with most other bases, crystals are obtained, which are identical in form and phy- sical properties. By saturating racemic acid, however, with two bases, by forming, for instance, compounds corresponding to Ro'chelle-salt, which con- tain potassa and soda or ammonia and soda, and allowing the solution to crys- tallize slowly, two varieties of crystals are produced, which may be distin- guished by their form, namely, as the image and.the reflection of the image, or us right-handed and left-handed. If the two kinds of crystals are carefully selected and separately crystallized, in each case crystals of the one variety only are deposited. The composition, the specific gravity, and, in fact, most of the physical properties of these two varieties of racemate of potassa and soda, are invariably the same. They differ, however, somewhat in their chemical characters, and especially in one point, they rotate the plane of polarization in opposite directions. (See page 89.) M. Pasteur assumes, in tho two varieties of crystals, the existence of two modifications of the same acid, which he distinguishes, according as the salt possesses right- or left- handed polarization, by the terms dextro-racemic and levo-racemic acids. These acids can be separated by converting the above compounds into lead- or baryta- salts, and decomposing them by means of sulphuric acid. In this manner two crystalline acids are obtained, identical in every respect excepting in their deportment with polarized light, and in their crystals behaving as image and reflection. Dextro-racemic acid is nothing but common tartaric acid. A mixture of equal parts of the two acids has no longer the slightest effect on polarized light, and exhibits in every respect the deportment of racemic acid. At a later period M. Pasteur, in continuing his beautiful researches, has made the important discovery that racemic acid may be artificially produced by the action of heat upon certain compounds of tartaric acid which are • eapable of resisting a high temperature. If tartrate of cinchonine (see fur- ther on, the article on cinchonine in the section of the Organic Bases) or tar- taric ether be exposed to a temperature of about 338° (170°C), and the pro- duct thus formed be repeatedly boiled with water, a solution is obtained, which yields when mixed, after cooling, with an excess of chloride of calcium, a con- siderable precipitate of racemate of lime. Compounds of levo-racemic acid, when submitted to the action of heat, likewise furnish racemic acid. The for- mation of racemic acid in these reactions is accompanied by the production of a fourth modification of tartaric acid, which M. Pasteur calls inactive tartaric acid. Like racemic acid it has no action on polarized light, but cannot, like the latter, be resolved into levo- and dextro-racemic acids. Citric acid.—Citric acid is obtained in large quantity from the juice of lemons: it is found in many other fruits, as in gooseberries, currants, &c, in 452 VEGETABLE ACIDS. conjunction with another acid, the malic. In the preparation of this acid, the juice is allowed to ferment a short time, in order that mucilage and other impurities may separate and subside; the clear liquor is then carefully satu- rated with chalk, which forms, with the citric acid, an insoluble compound. This is thoroughly washed, decomposed by the proper quantity of sulphuric acid, diluted with water, and the filtered solution evaporated to a small bulk, and left to crystallize. The product is drained from the mother-liquor, re- dissolved, digested with animal charcoal, and again concentrated to the crystal- lizing-point. Citric acid forms colorless, prismatic crystals, which have a pure and agreeably acid taste; they dissolve with great ease, in both hot and cold water; the solution strongly reddens litmus, and when long kept, is subject to spontaneous change. Citric acid is tribasic; its formula in the gently-dried and anhydrous silver- salt is C12H50„. The hydrated acid crystallizes with two different quantities of water, assuming two different forms. The crystals, which separate by spontaneous evaporation from a cold saturated solution, contain C|2H5On, 3HO -f- 2HO, the last being water of crystallization; while, on the other hand, those which are deposited from a hot solution contain but 4 equivalents of water altogether, three of which are basic. Citric acid is entirely decomposed when heated with sulphuric and nitric acids; the latter converts it into oxalic acid. Caustic potassa,' at a high temperature, resolves it into acetic and oxalic acids.1 When subjected to the action of chlorine, the alkaline citrates yield, among other products, chloroform. The citrates are very numerous, the acid forming, like ordinary phosphoric acid, three classes of salts, which contain respectively 3 eq. of a metallic oxide ; 2 eq. of oxide, and 1 eq. of basic water; and 1 eq. oxide and 2 eq. basic water, besides true basic salts, in which the water of crystallization is perhaps replaced by a metallic oxide. The citrates of the alkalies are soluble and crystallizable with greater or less facility; those of baryta, strontia, lime, lead, and silver are insoluble. Citric acid resembles tartaric acid in its relations to sesquioxide of iron; it prevents the precipitation of that substance by excess of ammonia. The citrate, obtained by dissolving the hydrated sesquioxide in solution of citric acid, dries up to a pale-brown, transparent, amorphous mass, which is not very soluble in water; an addition of ammonia increases the solubility. Citrate and ammonio-citrate of iron are elegant medicinal preparations. Very little is known respecting the composition of these curious compounds; the absence of crystallization is a great bar to inquiry. Citric acid is sometimes adulterated with tartaric: the fraud is easily de- tected by dissolving the acid in a little cold water, and adding to the solution a small quantity of acetate of potassa. If tartaric acid be present, a white crystalline precipitate of cream of tartar will be produced on agitation. Aconitic, or equisetic acid. — AVhen cuystallized citric acid is heated in a retort until it begins to become colored, and to undergo decomposition, and the fused, glassy product, after cooling, dissolved in water, an acid is obtained, differing completely in properties from citric acid, but identical with an acid extracted from the Aconitum napellus and the Equisetum fluviatile.. Aconitic acid forms a white, confusedly-crystalline mass, permanent in the air, and very soluble in water, alcohol, and ether: the solution has an acid and astrin- gent taste. The salts of aconitic acid possess but little interest; that of baryta forms an insoluble gelatinous mass; aconitate of lime, which has a certain 1 The easy conversion of tartaric and citric acids into a mixture of oxalic and acetic acids hy the action of heat, aided by the presence of a powerful base, has led to the idea of the possible pre-existence of these last-named bodies in the two vegetable acids, which may thus be • -im- pounded of two acids of timpler constitution, forming coupled or conjugate acids, of wnich several are known to exist. These views, although sometimes useful, are not at present sun- ported by evidence of great importance. » VEGETABLE ACIDS. 453 degree of solubility, is found abundantly in the expressed juice of the monks- hood, and aconitate of magnesia in that of the equiselum. Hydrated aconitic acid contains CI2H4Ol0,2HO; it is formed in the artificial process above described, by the elimination of 2 eq. of water from 1 eq. of hydrated citric acid, C12IIgO,4. There are, however, invariably many secondary products formed, such as acetone, carbonic oxide, and carbonic acid. The further action of heat upon aconitic acid gives rise to several new acids, espe- cially cilraconic and ilaconic acids, both expressed by the formula C)0H4Oe,2HO. The limits of this elementary work will not permit us to enter into a descrip- tion of these further products of decomposition. . ^Ialic acid.—This is the acid of apples, pears, and various other fruits: it is often associated, as already observed, with citric acid. An excellent process for preparing the acid in question is that of Mr. Everitt, who has demonstrated its existence, in great quantity, in the juice of the common garden rhubarb; it is there accompanied by acid oxalate of potassa. The rhubarb stalks are peeled, and ground or grated to pulp, which is subjected to pressure. The juice is heated to the boiling-point, neutralized with carbonate of potassa, and mixed with acetate of lime; insoluble oxalate of lime falls, which is removed by filtration. To the clear and nearly colorless liquid, solution of acetate of lead is added as long as a precipitate continues to be produced. The malate of lead is collected on a filter, washed, diffused through water, and decomposed by sulphuretted hydrogen.1 The filtered liquid is carefully evaporated to the consistence of syrup, and left in a dry atmosphere until it becomes converted into a solid and somewhat crystalline mass of malic acid: regular crystals have not been obtained. From the berries of the mountain-ash (Sorbus aucuparia), in which malic acid is likewise present in considerable quantity, especially at the time they commence to ripen, the acid may be prepared by the same process. Malic acid is bibasic, its formula being C8H408,2HO ; it forms a variety of salts, some of which are neutral, others acid. In the presence of fermenting substances, especially of putrefying casein, it is itself decomposed, yielding succinic, acetic, and carbonic acid. 3^C8HiOJ£HO)^ =*= 2(CgH/)e.2HO) +^£g$BO^+ 4C02 + 2HO Malic acid. Succinic acid. Acetic acid. Sometimes also butyric acid and hydrogen are observed among the products of this decomposition. Mafic acid is colorless, slightly deliquescent, and very soluble in water; alcohol also dissolves it. The aqueous solution has an agreeably acid taste ; it becomes mouldy, and spoils by keeping. The most characteristic of the malates are the acid malate of ammonia, NH40,HO,C8H,Os, which crvs- talhzes remarkably well, and the malate of lead, which is insoluble in pure water, but dissolves, to a considerable extent, in warm dilute acid, and sepa- rates, on cooling, in brilliant, silvery crystals, which contain water. The acid ™ u\, yi tI1^feature' be distinguished. The acid malate of lime, CaO.HO, V8H4^8+ OHO, is also a very beautiful salt, freely soluble in warm water. It is prepared by dissolving the sparingly soluble neutral malate of lime in hot dilute nitric acid, and leaving the solution to cool. The researches of M. Piria have established a most intimate relation between malic acid and two substances—asparagin and aspartic acid, which will be described in one of the succeeding sections. These compounds may be viewed as nialamide and malamic acid, analogous to oxamide and oxamic acid. Oxalic acid' . C406,2HO Malic acid . C8H408,2HO • '-Jf» ^e IV? be .r^luired Pure, crystallized malate of lead must be used, the freshly-pre- cipitated salt invariably carrying down a quantity of lime, which cannot be removed by simple • We have here doubled the formula of oxalic acid, when it becomes bibasic, like malic acid. i iSE."- ' t ir" ?a?y features in the history of oxalic acid, which render it probable that it U Dibasic. In the text we have still retained the generally-received formula. 454 VEGETABLE ACIDS. Neutral oxalate \ p n 9mr 0 J Neutral malate A c „ Q oNu 0 of ammonia. } CA-2NfU° { of ammonia . | ^U*-*1 aV Oxamide . . C4H4N204 j' asparagin . } C8H8Nz06 Binoxalate of | c o6,HO,NH40 { Bi™^G °f""" } C8H408,HO,NH40 ammonia . f 4 B * I monia . . j Oxamic acid . C4H2N05,HO {M^0 ^d}c8H6N07,HO Hitherto neither asparagin nor aspartic acid have been actually obtained from malic acid. On the contrary, these substances are converted with the greatest facility into malic acid. On passing a current of nitrous acid into a solution of asparagin or aspartic acid, pure nitrogen is evolved, malic acid being liberated. C8H8N206 + 2N03 = C8H408,2IIO + 2110 + 4N Malic acid. Fumaric and Maleic acids. — If malic acid be heated in a small retort, nearly filled, it melts, emits water, and enters into ebullition; a volatile acid passes over, which dissolves in the water of the receiver. After a time, small solid, crystalline scales make their appearance in the boiling liquid, and in- crease in quantity, until the whole becomes solid. The process may now be interrupted, and the contents of the retort, after cooling, treated with cold water; unaltered malic acid is dissolved out, and the new substance, having a smaller degree of solubility, is left behind; it is called fumaric acid, from its identity with an acid extracted from the common fumitory. Fumaric acid forms small, white, crystalline laminae, which dissolve freely in hot water and alcohol, but require for that purpose about 200 parts of cold water; it is unchanged by hot nitric acid. AVhen heated in a current of air it sublimes, but in a retort undergoes decomposition. This is a phenomenon often observed in organic bodies of small volatility. Fumaric acid forms salts, which have been examined by M. Bieckher, and an ether, which, by the action of ammonia, yields a white, amorphous, insoluble powder, called fumaramide, corresponding in properties and constitution with Oxamide. Hydrated fumaric acid contains C8H206,2HO; hence it is isomeric with aconitic acid. The volatile acid produced simultaneously with fumaric acid is called maleic acid; it may be obtained in crystals by evaporation in a warm place. It is very soluble in water, alcohol, and ether; it has a strongly-acid taste and reaction, and is convertible by heat into fumaric acid. Hydrated maleic acid contains C8H206,2HO. Maleic and fumaric acids are thus seen to have pre- cisely the same composition; they are formed by the separation of 2 eq. of water from hydrated malic acid. Meconic acid.—This acid is one of the constituents of opium, from which it may be extracted by water. The liquid thus obtained, neutralized by powdered marble and precipitated by chloride of calcium, furnishes meconate of lime, which is suspended in warm water and treated with hydrochloric acid; on cooling, impure meconic acid crystallizes, which may be purified by repeated treatment with hydrochloric acid. The pure acid crystallizes in mica-like plates, easily soluble in boiling, difficultly soluble in cold water, and soluble likewise in alcohol. It contains C14HO,,,3HO -\- 6Aq. The water escapes at 212° (100°C). As the formula indicates, meconic acid is a tribasic acid- the salts, for the most part, contain one or two equivalents of metallic oxide' Two silver salts of meconic acid are known ; the one, 3AgO,C,.HO is vellnw" the other, 2AgO,HO,CI4HOll, is white. AVith salts of sesquioxide of iron' meconic acid produces a deep-red color. ' VEGETABLE ACIDS. 455 Cmir.Nic acid. —This substance is a product of decomposition of meconic acid. AVhen an aqueous, or, better, a hydrochloric solution of meconic acid is boiled, carbonic acid is evolved, and the solution now contains comenic acid, which crystallizes on cooling, being very difficultly soluble in cold water. The same acid may be obtained by heating meconic acid to 392° (200°C). Comenic acid contains C12H208,2HO; it is bibasic ; its formation is represented by the equation C14H40I4 = C12H4OI0 + 2C02 Meconic acid. Comenic acid. Pyrocomenic acid is formed by submitting either meconic or comenic acid to dry distillation. Pryocomenic acid contains C]0H3O5,HO; it is monobasic. It arises from comenic acid by the elimination of carbonic acid. CI2H4O)0 C10H4O6 + 2C02 Pyrocomenic acid. Pyrocomenic acid is a weak acid; it is soluble in water and alcohol; from these solutions it crystallizes in long colorless needles, which fuse at 248° (120°C), and begin to sublime at the boiling point of water. Both comenio and pyrocomenic acid3 exhibit the red coloration with salts of sesquioxide of iron. The salts of meconic acid and comenic acid, together with several deriva- tives of these substances, have been studied by Mr. How,1 but our space will not permit us to describe these compounds. An acid much resembling the meconic has been extracted from the Chelido- nium ma jus; it is combined with lime, and associated with malic and fumaric acids. Chelidonic acid is tribasic, forming three classes of salts, and a pyro- acid with evolution of water and carbonic acid when exposed to a high tem- perature. It crystallizes in slender colorless needles, of considerable solubi- lity, containing C14H09,3HO -f 2110. Kink: acid. —Kinate of lime is found in the solution from which the alka- lies of quinine bark have been separated by hydrate of lime, and is easily obtained by evaporation, and purified by animal charcoal. From the lime- salt the acid can be extracted by decomposing it by diluted sulphuric acid. Tho clear solution evaporated to a syrupy consistence deposits large, distinct crystals, which resemble those of tartaric acid. It is soluble in 2 parts of water, and contains C]4H10O10,2HO. Wheu kinic acid is heated with a mixture of sulphuric acid and binoxide of manganese, it furnishes a very volatile substance termed kinone, the vapor of which is exceedingly irritating to the eyes. This new body forms crystals both by sublimation and by solution in boiling water; it melts with gentle heat, and crystallizes on cooling, colors the skin permanently brown, and contains C,2H404. By destructive distillation, kinic acid yields numerous and interesting pro- ducts, which have been studied by Wohler, as benzoic acid, carbolic acid, sali- cylous acid, benzol, a tarry substance not examined, and a new body, colorless hydrokinone, which possesses very curious relations with the kinone above described. It forms colorless six-sided prismatic crystals; is neutral, desti- tute of taste and odor, fusible, and easily soluble both in water and alcohol. With care it may be sublimed unchanged. It contains C12H604. 1 Chem. Soc. Quar. Jour., iv. page 363. 456 VEGETABLE ACIDS. Colorless hydrokinone can be easily and directly produced from kinone by the assimilation of hydrogen, as by addition of hydriodic acid to a solution of the latter, when iodine is set free, or by sulphurous acid. An intermediate product of reduction is green hydrokinone. This is ob- tained by the incomplete action of sulphurous acid upon kinone, or by the action of sesquichloride of iron, chlorine, nitrate of silver, or chromic acid upon colorless hydrokinone; or by mixing together solutions of kinone and colorless hydrokinone. It forms slender green crystals of the color of the wing-case of the rose-beetle, and of the greatest brilliancy and beauty. It is fusible, has but little odor, and dissolves freely in boiling water, crystallizing out on cooling. This substance contains C,2H504. If kinic acid be submitted to distillation with an ordinary chlorine-mixture, an acid liquid and a crystalline sublimate are formed. The former is a solu- tion of formic acid, the latter a mixture of 4 chlorinetted compounds, which are chlorokinone CI2(H3C1)04, bichlorokinone C12(H2C12)04, tricliloroki- none C12(HC13)04, and tetrachlorokinone C12C1404. They are all yellow cry- stalline substances, which can be separated only with great difficulty. Like kinone itself, they possess the faculty of combining with 1 or 2 eq. of hydro- gen, producing 2 series of substances analogous to green and colorless hydro- kinone. Tetrachlorokinone, better known by the name chloranile, likewise occurs among the products of decomposition of indigo. Other products were obtained by the action of sulphuretted hydrogen and strong hydrochloric acid upon kinone, which possess less interest than the preceding. Tannic and gallic acids.—These are substances in which the acid charac- ter is much less strongly marked than in the preceding bodies; they consti- tute the astringent principles of plants, and are widely diffused, in one form or other, through the vegetable kingdom. It is possible that there may be several distinct modifications of tannic acid, which differ among themselves in some particulars. The astringent principle of oak-bark and nut-galls, for example, is found to precipitate salts of sesquioxide of iron bluish-black, while that from the leaves of the sumach and tea-plant, as well Fig. 188. as infusions of the substances known in commerce under the names of kino and catechu, are remarkable for giving, under similar circumstances, precipitates which have a tint of green. The color of a precipitate is, however, too much influenced by external causes to be relied upon as a proof of essential difference. Unfortunately, the tannic acid or acids refuse to crystallize; one most valuable test of individuality is therefore lost. After the reaction with salts of sesquioxide of iron, the most cha- racteristic feature of tannic acid and the other astringent infusions referred to, is that of forming insoluble compounds with a great variety of organic, and especially animal substances, as solutions of starch and gelatin, solid muscular fibre and skin, &c, which then acquire the property of resisting putrefaction: it is on this principle that leather is manufactured. Gallic acid, on the con- trary, is useless in the operation of tanning. Tannic Acid of the Oak. — This substance may be prepared by the elegant method of M. Pelouze, from nut-galls, which are ex- crescences produced on the leaves of a species of oak, the Quer- cus infectoria, by the puncture of an insect. A glass vessel, having somewhat the figure of that represented in the margin, is loosely stopped at its lower extremity by a bit of cotton wool, and half or two-thirds filled with powdered Aleppo-galls. Ether, prepared in the usual manner by rectification, and containing, as it inva- riably does, a little water, is then poured upon the powder and the vessel loosely stopped. The liquid, which after some'time VEGETABLE ACIDS. 457 collects in the receiver below, consists of two distinct strata: the lower, which is almost colorless, is a very strong solution of nearly pure tannic acid in water; the upper consists of ether holding in solution gallic acid, coloring matter, and other impurities. The carefully-separated heavy liquid is placed to evaporate over a surface of oil of vitriol in the vacuum of the air-pump. Tannic acid, or tannin, thus obtained, forms a slightly-yellowish, friable, porous mass, without the slightest tendency to crystallization. It is very soluble in water, less so in alcohol, and very slightly soluble in ether. It reddens litmus, and possesses a pure astringent taste without bitterness. A strong solution of this substance mixed with mineral acids gives rise to precipitates, which consist of combinations of the tannic acid with the acids in question: the compounds are freely soluble in pure water, but scarcely so in acid solutions. Tannic acid precipitates albumin, gelatin, salts of the vegeto-alkalies, and several other substances; it forms soluble compounds with the alkalies, which, if excess of base be present, rapidly attract oxygen, ond become brown by destruction of the acid ; the tannates of baryta, strontia, and lime are sparingly soluble, and those of the oxides of lead and antimony insoluble. Salts of protoxide of iron are unchanged by solution of tannic neid; salts of the sesquioxide, on the contrary, give with it a deep bluish- black precipitate, which is the basis of writing-ink; hence the value of an infusion of tincture of nut-galls as a test for the presence of that metal. The action of acids upon tannic acid gives rise to the formation of gallic acid, which will be presently described, with simultaneous separation of grape- sugar. Hence tannic acid would appear to be a conjugated sugar-compound. Tannic acid, carefully dried, contains C^^H^O^, or CgJI^Oj,-)- 3H0.1 Tannic acid, closely resembling that obtained from galls, may be extracted by cold water from catechu; hot water dissolves out a substance having feebly acid properties, termed catechin. This latter compound, when pure, crystal- lizes in fine colorless needles, which melt when heated, and dissolve very freely in boiling water, but scarcely at all in the cold. Catechin dissolves also in hot alcohol and ether. The aqueous solution acquires a red tint by exposure to air, and precipitates acetate of lead and corrosive sublimate white, reduces nitrate of silver on the addition of ammonia, but fails to form insoluble com- pounds with gelatin, starch, and the vegeto-alkalies. It strikes a deep-green color with the salts of sesquioxide of iron. This body is said to be conver- tible by heat into tannic acid. The formulae which have been assigned to catechin are C18II908, C14H606, and C,7H,2O10. Japonic and rubic acids are formed by the action of alkali in excess upon catechin ; the first in the caustic condition, and the second when in the state of carbonate. Japonic acid is a black and nearly insoluble substance, soluble in alkalies and precipitated by acids, containing C12H404,HO ; it is perhaps identical with a black substance of acid properties, formed by M. Peligot by heating grape-sugar with hydrate of baryta. Bubic acid has been but little studied; it is said to form red insoluble compounds with the earths and cer- tain oxides of the metals. Several acids closely allied to tannic acid have been found in coffee and Paraguay tea. Gallic acid. — Gallic acid is not nearly so abundant as tannic acid; it is produced by an alteration of the latter. A solution of tannic acid in water 1 The formula, CsJL^Osi, seems now established beyond a doubt. M. Strecker, who has ob- served the formation of sugar from tannic acid, represents the change of tannic acid under the influence of acids by the equation 2C5ai2sO3< + 20IIO = 6CnIIcOio + C24llae02e Tannic acid. Gallic acid. Grape-sugar. 39 458 VEGETABLE ACIDS. exposed to the air, gradually absorbs oxygen, and deposits crystals of galho acid, formed by the destruction of the tannic acid. The simplest method of preparing this acid in quantity is to take powdered nut-galls, which, when fresh and of good quality, contain 30 or 40 per cent, of tannic acid, with scarcely more than a trace of gallic, to mix this powder with water to a thin paste, and to expose the mixture to the air in a warm situation for the space of two or three months, adding water from time to time to replace that lost by drying up. The mouldy, dark-colored mass produced may then be strongly pressed in a cloth, and the solid portion boiled in a considerable quantity of water. The filtered solution deposits on cooling abundance of gallic acid, which may be drained and pressed, and finally purified by recrystallization. It forms small, feathery, and nearly colorless crystals, which have a beautiful silky lustre; it requires for solution 100 parts of cold and only 3 parts of boiling water; the solution has an acid and astringent taste, and is gradually decomposed by keeping. Gallic acid does not precipitate gelatin; with salts of protoxide of iron no change is produced, but with those of the sesquioxide a deep bluish-black precipitate falls, which disappears when the liquid is heated, from the reduction of the sesquioxide to the protoxide at the expense of the gallic acid. The salts of gallic acid present but little interest; those of the alkalies are soluble, and readily destroyed by oxidation in presence of excess of base, the solution acquiring after some time a nearly black color; the gallates of most of the other metallic oxides are insoluble. Gallic acid, dried at 212° (100°C), contains C7H03,2HO; the crystals contain an additional equivalent of water. The insoluble residue of woody fibre and other matters from which the gallic acid has been withdrawn by boiling water, contains a small quantity of another acid substance, which may be extracted by an alkali, and afterwards precipitated by an addition of hydrochloric acid, as a grayish, insoluble powder. It contains C7H204, when dried at 248° (120°C), or gallic acid minus 1 eq. of water. The term ellagic acid is given to this substance. M. Pelouze once observed its conversion into ordinary gallic acid. The conversion of tannic into gallic acid by oxidation is accompanied by a disengagement of carbonic acid, the volume of which equals that of the oxygen absorbed; the oxidizing action must therefore be confined to the carbon, and may perhaps be thus represented: — 1 eq. tannic acid C^H^O^") f 6 eq. gallic acid C^H^Ogo eq. water H 40 4 ^54H22Q34J f 6 Oj (12 24 24 eq. oxygen O^, J (12 eq. carbonic acid C,2 0, C54IJ220S8 C^H^O^ Much of the gallic acid is subsequently destroyed, in all probability only a part of that first produced escaping. The changes which gallic acid suffers when exposed to heat are very inte- resting. Heated in a retort by means of an oil-bath, the temperature of which is steadily maintained at 420° (215°C), or thereabouts, it is resolved into carbonic acid, and a new acid which sublimes into the neck of the retort in brilliant, crystalline plates, of the most perfect whiteness: an insignificant residue of black matter remains behind. The term pyrogallic acid is given to the volatile product. It dissolves with facility in water, but the solution cannot be evaporated without blackening and decomposition ; it communicates a blackish-blue color to salts of the protoxide of iron, and reduces those of the sesquioxide to the state of protoxide. An alkaline solution of this acid absorbs a very considerable quantity of oxygen, and has been employed with great advantage by Professor Liebig for the purpose of determining the VEGETABLE ACIDS. 459 amount of oxygen in atmospheric air. (See page 138.) The acid characters of this substance are very indistinct. Pyrogallic acid contains C6H303. AVhen dry gallic acid is suddenly heated to 480° (249°C). or above, it is decomposed into carbonic acid, water, and a second new acid, the melagallic, which remains in the retort as a black, shining mass, resembling charcoal: a few crystals of pyrogallic acid are formed at the same time. Mctagallic acid is insoluble in water, but dissolves in alkalies, and is again precipitated as a black powder by the addition of an acid. It combines with the oxides of lead and silver, and is composed of C6H202. Pyrogallic acid, also, exposed to the requisite temperature, yields metagallic acid, with separation of water. These changes admit of simple explanation. C7H,05 = C6H303 + C02 Dry gallic acid. Pyrogallic acid. CeH,0, = C6H202 + HO Pyrogallic acid. Metagallic acid. These phenomena present admirable illustrations of the production of pyrogen-acids by the agency of heat. Tannic acid, under similar circumstances, furnishes the same products as gallic acid. Dr. Stenhouse has shown that pyrogallic acid may be procured in considerable quantity by carefully heating the dried aqueous extract of gall-nuts in Dr. Mohr's subliming apparatus, already described. 2* 460 CYANOGEN, AZOTIZED OBGANIC PBINCIPLES OF SIMPLE CONSTITUTION. cyanogen, its compounds and derivatives. Cyanogen1 forms the most perfect type of a quasi-simple salt-radical that chemistry presents, as kakodyl does of the basyle class; it is interesting also from being the first-discovered body of the kind. Cyanogen may be prepared with the utmost ease by heating in a small retort of hard glass the salt called cyanide of mercury, previously reduced to powder, and Well dried. The cyanide undergoes decomposition, like the oxide under similar circumstances, yielding metallic mercury, a small quantity of a brown substance of which mention will again be made, and cyanogen itself, a colorless, permanent gas, which must be collected over mercury. It has a pungent and very peculiar odor, remotely resembling that of peach- kernels, or hydrocyanic acid: exposed while at the temperature of 45° (7°-2C) to a pressure of 3-0 atmospheres, it condenses to a thin, colorless, transparent liquid. Cyanogen is inflammable; it burns with a beautiful purple, or peach- blossom-colored flame, generating carbonic acid and liberating nitrogen. The specific gravity of this gas is 1-800; it is composed of carbon and nitrogen in the proportion of 2 equivalents of the former to 1 equivalent of the latter, or C2N : this is easily proved by mixing- it with twice its measure of pure oxygen, and firing the mixture in the eudiometer; carbonic acid is formed equal in volume to the oxygen employed, and a volume of nitrogen equal to that of the cyanogen is set free. Cyanogen, in its capacity of quasi-element, is designated by the symbol Cy. Water dissolves 4 or 5 times its volume of cyanogen-gas, and alcohol a much larger quantity; the solution rapidly decomposes, yielding oxalate of ammonia C2N -f- 4HO ^= NH40,C203, brown insoluble matter, and other products. Paracyanogen.—This is the brown or blackish substance above referred to, which is always formed in small quantity when cyanogen is prepared by heat- ing the cyanide of mercury, and probably, also, by the decomposition of solutions of cyanogen and of hydrocyanic acid. It is insoluble in water and alcohol, is dissipated by a very high temperature, and contains, according to Professor Johnson, carbon and nitrogen in the same proportions as in cyanogen. Cyanide of hydrogen; hydrocyanic or prussic acid, HCy. — This very important compound, so remarkable for its poisonous properties, was dis- covered as early as 1782 by Scheele. It may be prepared in a state of purity, and anhydrous, by the following process: —A long glass tube, filled with dry cyanide of mercury, is connected by one extremity with an arrangement for furnishing dry sulphuretted hydrogen gas, while a narrow tube attached to the other end is made to pass into a narrow-necked phial plunged into a freezing-mixture. Gentle heat is applied to the tube, the contents of which suffer decomposition in contact with the gas, sulphide of mercurv and cyanide of hydrogen being produced; the latter is condensed in the receiver to the liquid form. A little of the cyanide of mercury should be left undecomuosed, to avoid contamination of the product by sulphuretted hydrogen. The pure 1 So called from xvaios, blue, and yevvdu>, I generate. ITS COMPOUNDS AND DERIVATIVES. 461 acid is a thin, colorless, and exceedingly volatile liquid, which has a density of 0-7058 at 45° (7°-0C), boils at 79° (26°-lC), and solidifies when cooled to 0° (— 17°-8C); its odor is very powerful, and most characteristic, much resembling that of peach-blossoms or bitter-almond oil; it has a very feeble acid reaction, and mixes with water and alcohol in all proportions. In the anhydrous state this substance constitutes one of the mos,t formidable poisons known, and even when largely diluted with water, its effects upon the animal system are exceedingly energetic; it is employed, however, in medi- cine, in very small doses. The inhalation of the vapor should be carefully avoided in all experiments in which hydrocyanic acid is.concerned, as it pro- duces headache, giddiness, and other disagreeable symptoms: ammonia and chlorine are the best antidotes. The acid in its pure form can scarcely be preserved : even when enclosed in a carefully-stopped bottle it is observed after a very short time to darken, and eventually to deposit a black substance containing carbon, nitrogen, and perhaps hydrogen ; ammonia is formed at the same time, and many other products. Light favors this decomposition. Even in a dilute condition it is apt to decompose, becoming brown and turbid, but not always with the same facility ; some samples resisting change for a great length of time, and then suddenly solidifying to a brown, pasty mass in a few weeks. AVhen hydrocyanic acid is mixed with concentrated mineral acids, hydro- chloric for example, the whole solidifies to a crystalline paste of sal-ammoniac and hydrated formic acid; a reaction which is explained in a very simple manner, 1 eq. of hydrocyanic acid and 4 eq. of water, yielding 1 eq. of ammo- nia and 1 eq. of formic acid. C2NII 4- 4IIO = NIL, 4- C2H03,HO. On the other hand, when dry formate of ammonia is heated to 392° (200°C), it is almost entirely converted into hydrocyanic acid and water. NH40,C2H03 = C2N,H + 4110. Aqueous solution of hydrocyanic acid may be made by various means. The most economical, and by far the best, where considerable quantities are wanted, is to decompose at a boiling-heat the yellow ferrocyanide of potas- sium by diluted sulphuric acid. For example, 500 grains of the powdered ferrocyanide may be dissolved in four or five ounces of warm water, and in- troduced into a capacious flask or globe, capable of being connected by a perforated cork and wide bent tube with a Liebig's condenser well supplied with colli water; 300 grains of oil of vitriol are diluted with three or four times as much water and added to the contents of the flask; distillation is carried on until about one-half of the liquid has distilled over, after which the process may be interrupted. The theory of this process has been carefully studied by Mr. Evciitt;1 it is sufficiently complicated. 2 eq. ferrocy- anide of po- tassium. '6 eq. 0 eq. carbon carbon 3 eq. water 6 eq 3 eq. nitrogen 1 eq. nitrogen 1 eq. potassium 3 eq. potassium 2 eq. iron J 3 eq. hydrogen \3 eq. oxygen- ulphuric acid—------- Insoluble yellow salt. 3 eq. hydrocyanic acid. eq. bisulphate of po- tassa. 39* Phil. Magazine, Feb., 1835. 462 CYANOGEN, The substance described in the above diagram as insoluble yellow salt re- mains in the flask after the reaction, together with the bisulphate of potassa; it contains the elements of 2 eq. cyanide of iron, and 1 eq. cyanide of potas- sium, but its constitution is unknown. On exposure to the air, it rapidly becomes blue. AVhen hydrocyanic acid is wanted for the purposes of pharmacy, it is best to prepare a strong solution in the manner above described, and then, having ascertained its exact strength, to dilute it with pure water to the standard of the Pharmacopoeia, viz., 2 per cent, of real acid. This examination is best made by precipitating with excess of nitrate of silver a known weight of the acid to be tried, collecting the insoluble cyanide of silver upon a small filter previously weighed, washing, drying, and lastly reweighing the whole. From the weight of the cyanide that of the hydrocyanic acid can be easily calculated, an equivalent of the one corresponding to an equivalent of the other; or the weight of the cyanide of silver may be divided by 5, which will give a close approximation to the truth. Another very elegant method for determining the amount of hydrocyanic acid in a liquid has been suggested by Prof. Liebig. It is based upon the property possessed by cyanide of potassium of dissolving a quantity of chloride of silver sufficient to produce with it a double cyanide containing equal equivalents of cyanide of silver and of potassium (KCy,AgCy). Hence a solution of hydrocyanic acid, which is supersaturated with potassa, and mixed with a few drops of solution of common salt, will not yield a permanent precipitate with nitrate of silver before the whole of the hydrocyanic acid is converted into the above double salt. If we know the amount of silver in a given volume of the nitrate solution, it is easy to calculate the quantity of hydrocyanic acid, for this quantity will stand to the amount of silver in the nitrate consumed, as 2 eq. of hydrocyanic acid to 1 eq. of silver, i. e. 108 : 54 = silver consumed : x. It is a common remark, that the hydrocyanic acid made from ferrocyanide of potassium keeps better than that made by other means. The cause of this is ascribed to the presence of a trace of mineral acid. Mr. Everitt actually found that a few drops of hydrochloric acid, added to a large bulk of the pure dilute acid, preserved it from decomposition, while another portion, not so treated, became completely spoiled. A very convenient process for the extemporaneous preparation of an acid of definite strength, is to decompose a known quantity of cyanide of potas- sium by solution of tartaric acid : 100 grains of crystallized tartaric acid in powder, 44 grains of cyanide of potassium, and 2 measured ounces of dis- tilled water, shaken up in a phial for a few seconds, and then left at rest, in order that the precipitate may subside, will yield an acid of very nearly the required strength. A little alcohol may be added to complete the separation of the cream of tartar; no filtration or other treatment need be employed. The production of hydrocyanic acid from bitter almonds has been already mentioned in connection with the history of this volatile oil. Bitter almonds the kernels of plums and peaches, the seeds of the apple, the leaves of the cherry-laurel, and various other parts of plants belonging to the great natu- ral order rosacea?, yield on distillation with water a sweet-smelling liquid, con- taining hydrocyanic acid. This is probably due in all cases to the decomposi- tion of the amygdalin, pre-existent in the organic structure. The change in question is brought about, in a very singular manner, by the presence of a soluble azotized substance, called emulsin or synaptase, which forms a large proportion of the white pulp of both bitter and sweet almonds. This sub- stance bears a somewhat similar relation to amygdalin, that diastase which it closely resembles in many particulars, does to starch. Hydrocyanic acid exists ready-formed to a considerable extent in the juice of tire bitter cassava. ITS COMPOUNDS AND DERIVATIVES. 463 Amygdalin is prepared with facility by the following process: — The paste of bitter almonds, from which the fixed oil has been expressed, is exhausted with boiling alcohol: this coagulates and renders inactive the synaptase, while at the same time it dissolves out the amygdalin. The alcoholic liquid is dis- tilled in a water-bath, by which much of the spirit is recovered, and the syrupy residue diluted with water, mixed with a little yeast, and set in a warm place to ferment: a portion of sugar, present in the almond, is thus destroyed. The filtered liquid is then evaporated to a syrupy state in a water-bath, and mixed with a quantity of alcohol, which throws down the amygdalin as a white crystalline powder; the latter is collected on a cloth filter, pressed, redissolved in boiling alcohol, and left to cool. It separates in small crystalline plates, of pearly whiteness, which are inodorous and nearly tasteless ; it is decomposed by heat, leaving a bulky coal, and diffusing the odor of the hawthorn. In water, both hot and cold, amygdalin is very soluble; a hot saturated solution deposits, on cooling, brilliant prismatic crystals, which contain water. In cold alcohol it dissolves with great difficulty. Heated with dilute nitric acid, or a mixture of dilute sulphuric acid and binoxide of manganese, it is resolved into ammonia, bitter-almond oil, benzoic acid, formic acid, and carbonic acid: with permanganate of potassa, it yields a mixture of cyanate and benzoate of that base. Amygdalin is composed of C^H^NO^. Synaptase itself has never been obtained in a state of purity, or fit for analysis; it is described as a yellowish-white, opaque, brittle mass, very solu- ble in water, and coagulable, like albumin, by heat, in which case it loses its specific property. In solution it very soon becomes turbid, and putrefies. The decomposition of amygdalin under the influence of this body may be elegantly studied by dissolving a portion in a large quantity of water, and adding a little emulsion of sweet-almond ; the odor of the volatile oil immedi- ately becomes apparent, and the liquor yields, on distillation, hydrocyanic acid. The nature of the decomposition may be thus approximately repre- sented : — fl eq. hydrocyanic acid . . C 2H N 1 eq. amygdalin, J ? e* bitter-almond oil . . C^ll., 04 ( I! NO \ *Cq' Sugar • * ' • C6H7 07 ^4o"27-M'22 2 eq. formic acid . . . C 4H 4 08 [ 3 eq. water . . . . H 3 03 ^40 "27^^22- It may be observed, that in preparing bitter-almond oil, the paste should be well mixed with about 20 parts of warm water, and the whole left to stand some hours before distillation ; the heat must be gently raised, to avoid coagu- lating the synaptase before it has had time to act upon the amygdalin. Almond- paste, thrown into boiling water, yields little or no bitter-almond oil. , Amygdalic acid.—AVhen amygdalin is boiled with an alkali or an alkaline earth, it is decomposed into ammonia, and a new acid called the amygdalic, which remains in union with the base. This is best prepared by means of baryta-water, the ebullition being continued as long as ammonia is evolved. From the solution thus obtained, the baryta may be precipitated by dilute sulphuric acid: the filtered liquid is evaporated in a water-bath. Amygdalic acid forms a colorless, transparent, amorphous mass, very soluble in water, and deliquescent in moist air; the solution has an acid taste and reaction. It is converted by oxidizing agents into bitter-almond oil, formic, and benzoic acids. The amygdalates are mostly soluble, but have been but little studied; the acid contains C^IIj^O^. HO. The presence of hydrocyanic acid is detected with the utmost ease; its re- markable odor and high degree of volatility almost sufficiently characterize it. 464 CYANOGEN, AYith solution of nitrate of silver it gives a dense curdy white precipitate, much resembling the chloride, but differing from that substance in not blacken- ing so readily by light, in being soluble in boiling nitric acid, and in suffering complete decomposition when heated in a dry state, metallic silver being left: the chloride, under the same circumstances, merely fuses, but undergoes no chemical change. The production of Prussian blue by " Scheele's test" is an excellent and most decisive experiment, which may be made with a very small quantity of acid. The liquid to be examined is mixed with a few drops of solution of sulphate of protoxide of iron and an excess of caustic potassa, „ and the whole exposed to the air for 10 or 15 minutes, with agitation; hydro- chloric acid is then added in excess, which dissolves the oxide of iron, and, if hydrocyanic acid be present, leaves Prussian blue as an insoluble powder. The reaction becomes quite intelligible when the production of a ferrocyanide, described'a few pages hence, is understood. See page 472. Another elegant process for detecting hydrocyanic acid is mentioned in the article upon hydrosulphocyanic acid. The most important of the metallic cyanides are the following: they bear the most perfect analogy to the haloid-salts. Cyanide of potassium, KCy.—AVhen potassium is heated in cyanogen gas, it takes fire and burns in a very beautiful manner, yielding cyanide of the metal; the same substance is produced when potassium is heated in the vapor of hydrocyanic acid, hydrogen being liberated. If pure nitrogen gas be trans- mitted through a white-hot tube, containing a mixture of carbonate of potassa and charcoal, a considerable quantity of cyanide of potassium is formed, which settles in the cooler portions of the tube as a white amorphous powder; carbonic oxide is at the same time evolved. If azotized organic matter of any kind, capable of furnishing ammonia by destructive distillation, as horn- shavings, parings of hides, &c, be heated to redness with carbonate of potassa in a close vessel, a very abundant production of cyanide of potassium results, which cannot, however, be advantageously extracted by direct means, but in practice is always converted into ferrocyanide, which is a much more stable substance, and crystallizes better. There are several methods by which cyanide of potassium may be prepared for use. It may be made by passing the vapor of hydrocyanic acid into a cold alcoholic solution of potassa; the salt is deposited in a crystalline form, and may be separated from the liquid, pressed and dried. Ferrocyanide of potassium, heated to whiteness in a nearly-close vessel, evolves nitrogen and other gases, and leaves a mixture of charcoal, carbide of iron, and cyanide of potassium, which latter salt is not decomposed unless the temperature be excessively high. Mr. Donovan recommends the use in this process of a wrought-iron mercury-bottle, which is to be half filled with the ferrocyanide, and arranged in a good air-furnace, capable of giving the requisite degree of heat; a bent iron tube is fitted to the mouth of the bottle and made to dip half an inch into a vessel of water; this serves to give exit to the gas. The bottle is gently heated at first, but the temperature ultimately raised to white- ness. AVhen no more gas issues, the tube is stopped with a cork, and, when the whole is completely cold, the bottle is cut asunder in the middle by means of a chisel and sledge-hammer, and the pure white fused salt carefully sepa- rated from the black spongy mass below, and preserved in a well-stopped bottle: the black substance contains much cyanide, which may be extracted by a little cold water. It would be better, perhaps, in the foregoing process to deprive the ferrocyanide of potassium of its water of crystallization before introducing it into the iron vessel. Professor Liebig has published a very easy and excellent process for making cyanide of potassium, which does not, however, yield it pure, but mixed with cyanate of potassa. For most of the applications of cyanide of potassium as, for example, electro-plating and gilding, for which a considerable quantity ITS COMPOUNDS AND DERIVATIVES. 465 is now required, this impurity is of no consequence. 8 parts of ferrocyanide of potassium are rendered anhydrous by gentle heat, and intimately mixed with 3 parts of dry carbonate of potassa: this mixture is thrown into a red- hot earthen crucible, and kept in fusion, with occasional stirring, until gas ceases to be evolved, and the fluid portion of the mass becomes colorless. The crucible is left at rest for a moment, and then the clear salt decanted from the heavy black sediment at the bottom, which is principally metallic iron in a Btate of minute division. In this experiment, 2 eq. of ferrocyanide of potas- Bium and 2 eq. carbonate of potassa yield 5 eq. cyanide of potassium, 1 eq. cyanate of potassa, 2 eq. iron, and 2 eq. carbonic acid. The product may be advantageously used, instead of ferrocyanide of potassium, in the preparation of hydrated hydrocyanic acid, by distillation with diluted oil of vitriol. Cyanide of potassium forms colorless cubic or octahedral crystals, deliques- cent in the air, and exceedingly soluble in water; it dissolves in boiling alcohol, but separates in great measure on cooling. It is readily fusible, and undergoes no change at a moderate red- or even white-heat, when excluded from air; otherwise, oxygen is absorbed and the cyanide of potassium becomes cyanate of potassa. Its solution always has an alkaline reaction, and exhales when exposed to the air the smell of hydrocyanic acid; it is decomposed by the feeblest acids, even the carbonic acid of the atmosphere, and when boiled in a retort is slowly converted into formate of potassa with separation of am- monia. This salt is anhydrous: it is said to be as poisonous as hydrocyanic acid itself. Cyanide of potassium has been derived from a curious and unexpected source. In some of the iron furnaces in Scotland, where raw-coal is used for fuel with the hot-blast, a saline-looking substance is occasionally observed to issue in a fused state from the tuyere-holes of the furnace, and concrete on the outside. This proved, on examination by Dr. Clark, to be principally cyanide of potassium. Cyanide of sodium, NaCy, is a very soluble salt, corresponding closely with the foregoing, and obtained by similar means. Cyanide of ammonium, NH4Cy.—This is a colorless, crystallizable, and very volatile substance, prepared by distilling a mixture of cyanide of potassium and sal-ammoniac, or by mingling the vapor of anhydrous hydrocyanic acid with ammoniacal gas, or, lastly, according to the observation of M. Langlois, by passing ammonia over red-hot charcoal. It is very soluble in water, subject to spontaneous decomposition, and is highly poisonous. Cyanide of mercury, HgCy.—One of the most remarkable features in the history of cyanogen is its powerful attraction for certain of the less-oxidable metals, as silver, and more particularly mercury and palladium. Dilute hydrocyanic acid dissolves finely-powdered red oxide of mercury with the utmost ease; the liquid loses all odor, and yields on evaporation crystals of cyanide of mercury. Cyanide of potassium is in like manner decomposed by red oxide of mercury, hydrate of potassa being produced. Cyanide of mer- cury is generally prepared from common ferrocyanide of potassium; 2 parts of the salt are dissolved in 15 parts of hot water, and 3 parts of dry sulphate of mercury added; the whole is boiled for 15 minutes, and filtered hot from the oxide of iron, which separates. The solution, on cooling, deposits the new salt in crystals. Cyanide of mercury forms white, translucent prisms, much resembling those of corrosive sublimate; it is soluble in 8 parts of cold water, and in a much smaller quantity at a higher temperature, and also in alcohol. The solution has a disagreeable metallic taste, is very poisonous, and is not precipitated by alkalies. Cyanide of mercury is used in the laboratory as a source of cyanogen. Cyanide of silver, AgCy, has been already described. Cyanide of zinc, ZnCy, is a white insoluble powder, prepared by mixing acetate of zinc with hydrocyanic acid. Cyanide of cobalt, CoCy, is obtained by similar means; it 466 CYANOGEN, is dirty-white, and insoluble. Cyanide of palladium forms a pale-whitish pre- cipitate when the chloride of that metal is mixed with a soluble cyanide including that of mercury. Tercyanide of gold, AuCy3, is yellowish-white and insoluble, but freely dissolved by solution of cyanide of potassium Protocya- nide of iron has not been obtained, from the tendency of the metal to pass into the radical, and generate a ferrocyanide. An insoluble green compound con- taining FeCy,F2Cy3 was formed by M. Pelouzc by passing chlorine gas into a boiling solution of ferrocyanide of potassium. Cyanic and cyanuric acids.— These are two remarkable isomeric bodies related in a very close and intimate manner, and presenting phenomena of great interest. Cyanic acid is the true oxide of cyanogen; it is formed in conjunction with cyanide of potassium, when cyanogen gas is transmitted ""^r,^ heated hydrate or "carbonate of potassa, or passed into a solution of the alka-^M| line base, the reaction resembling that by which chlorate of potassa and V chloride of potassium are generated when the oxide and the salt-radical ^ are presented to each other. Cyanate of potassa is, moreover, formed when the cyanide is exposed to a high temperature with access of air; unlike the chlorate, it bears a full red-heat without decomposition. Hydrated Cyanic Acid, CyO.HO, is procured by heating to dull redness in a hard glass retort connected with a receiver cooled by ice, cyanuric acid, deprived of its water of crystallization. The cyanuric acid is resolved, without any other product, into hydrated cyanic acid, which condenses in the receiver to a limpid, colorless liquid, of exceedingly pungent and penetrating odor, like that of the strongest acetic acid: it even blisters the skin. AVhen mixed with water, it decomposes almost immediately, giving rise to bicarbonate of ammonia. C2NO,HO + 4HO = NH40,HO,2C02. This is the reason why the hydrated acid cannot be separated from a cyanate by a stronger acid. A trace of cyanic acid, however, always escapes decom- position, and communicates to the carbonic acid evolved a pungent smell similar to that of sulphurous acid. The cyanates may be easily distinguished by this smell, and by the simultaneous formation of an ammonia-salt, which remains behind. The pure hydrated cyanic acid cannot be preserved: shortly after its pre- paration it changes spontaneously, with sudden elevation of temperature into a solid, white, opaque, amorphous substance, called cyamelide. This curious body has the same composition as hydrated cyanic acid: it is insoluble in water, alcohol, ether, and dilute acids; it dissolves in strong oil of vitriol by the aid of heat, with evolution of carbonic acid and production of ammonia: boiled with solution of caustic alkali, it dissolves, ammonia is disengaged, and a mixture of cyanate and cyanurate of the base generated. By dry distillation it is again converted into the hydrate of cyanic acid. Cyanate of potassa, KO,CyO.—The best method of preparing this salt is, according to Liebig, to oxidize cyanide of potassium by means of litharge. The cyanide, already containing a portion of cyanate, described p. 464, is re- melted in an earthen crucible, and finely-powdered protoxide of lead added by small portions; the oxide is instantaneously reduced, and the metal, at first in a state of minute division, ultimately collects to a fused globule at the bottom of the crucible. The salt is poured out, and, when cold, powdered and boiled with alcohol; the hot filtered solution deposits crystals of cyanate of potassa on cooling. The great deoxidizing power exerted by cyanide of potassium at a high temperature promises to render it a valuable agent in many of the finer metallurgic operations. . Another method of preparing the cyanate is to mix dried and finely-pow- dered ferrocyanide of potassium with half its weight of equally dry binoxide of manganese; to heat this mixture in a shallow iron ladle with free exposure ITS COMPOUNDS AND DERIVATIVES. 46? to air and frequent stirring until the tinder-like combustion is at an end, and to boil the residue in alcohol, which extracts the cyanate of potassa. This salt crystallizes from alcohol in thin, colorless, transparent plates, which suffer no change in dry air, but on exposure to moisture become gra- dually converted, without much alteration of appearance, into bicarbonate of potassa, ammonia being at the same time disengaged. AVater dissolves the cyanate of potassa in large quantity; the solution is slowly decomposed in the cold, and rapidly at a boiling heat, into bicarbonate of potassa and ammonia. AVhen a concentrated solution is mixed with a small quantity of dilute mineral acid, a precipitate falls, which consists of acid cyanurate of potassa. Cyanate of potassa is reduced to cyanide of potassium by ignition with charcoal in a covered crucible. Cyanate of potassa, mixed with solutions of lead and silver, gives rise to insoluble cyanates of the oxides of those metals, which are white. Cyanate of ammonia ; urea.—When the vapor of hydrated cyanic acid is mixed with excess of ammoniacal gas, a white, crystalline, solid substance is produced, which has all the characters of a true, although not neutral, cyanate of ammonia. It dissolves in water, and, if mixed with an acid, evolves car- bonic acid gas; with an alkali, it yields ammonia. If the solution be heated, or if the crystals be merely exposed a certain time to the air, a portion of am- monia is dissipated, and the properties of the compound completely changed. It may now be mixed with acids witliout the least symptoms of decomposition, while cold caustic alkali, on the other hand, fails to disengage the smallest trace of ammonia. The result of this curious metamorphosis of the cyanate is a substance called urea, a product of the animal body, the chief and cha- racteristic constituent of urine. This artificial formation of one of the pro- ducts of animal life cannot fail to possess great interest. Its discovery is due to Wohler. The properties of urea, and the most advantageous methods of preparing it, will be found described a few pages hence. Cyanuric acid.—The substance called melam, of which further mention will be made, is dissolved by gentle heat in concentrated sulphuric acid, the solu- tion mixed with 20 or 30 parts of water, and the whole maintained at a tem- perature approaching the boiling-point, until the specimen of the liquid, on being tried by ammonia, no longer gives a white precipitate: several days are required. The liquid, concentrated by evaporation, deposits on cooling cya- nuric acid, which is purified by recrystallization. Another, and perhaps sim- pler method, is to heat dry and pure urea in a flask or retort: the substance melts, boils, disengages ammonia in large quantity, and at length becomes converted into a dirty-white, solid, amorphous mass, which is impure cyanuric acid. This is dissolved by the aid of heat in strong oil of vitriol, and nitric acid added by little and little until the liquid becomes nearly colorless ; it is then mixed with water, and suffered to cool, whereupon the cyanuric acid separates. The urea may likewise be decomposed very conveniently by gently heating it in a tube, while dry chlorine gas passes over it. A mixture of cya- nuric acid and sal-ammoniac results, which is separated by dissolving in water. Cyanuric acid in a pure state forms colorless crystals, seldom of large size, derived from an oblique rhombic prism, which effloresce in a dry atmosphere from loss of water. It is very little soluble in cold water, and requires 24 parts for solution at a boiling heat; it reddens litmus feebly, has no odor, and but little taste. The acid is tribasic; the crystals contain C6N303,3HO + 4HO, and are easily deprived of the 4 eq. of water of crystallization. In point of stability, it offers a most remarkable contrast to its isomer, cyanic acid: it dissolves, as above indicated, in hot oil of vitriol, and even in strong nitric acid, without decomposition, and in fact crystallizes from the latter in an an- hydrous state, containing 0aX3O3.3HO. Long-continued boiling with these powerful agents resolves it into ammonia and carbonic acid. 468 CYANOGEN, The connection between cyanic acid, urea, and cyanuric acid, may be thus recapitulated:— Cyanate of ammonia is converted by heat into urea. Urea is decomposed by the same means into cyanuric acid and ammonia. Cyanuric acid is changed by a very high temperature into hydrated cyanic acid. In the latter reaction, 1 eq. of hydrated cyanuric acid splits into 3 eq. hydrated cyanic acid. C6N303,3HO == 3(C2NO,HO). Cyanate and cyanurate of oxide of ethyl.—If a dry mixture of cyanate of potassa and sulphovinate of potassa be distilled, a product is obtained which consists of a mixture of the above ethers. They are separated without diffi- culty, the cyanate boiling at 140° (60°C), while the boiling-point of the cya- nurate is much higher, namely, 528°-8 (27G°C). Cyanate of ethyl is a mobile liquid, the vapor of which excites a flow of tears. The composition of cyanate of ethyl is C6H5N02 = C4H50,C2NO — AeO,CyO. The formation is repre- sented by the equation KO,CyO + KO, AeO,2S03 = AeO,CyO + 2(KO,S03). The cyanurate of ethyl contains 3AeO,C6N303; it arises in this reaction from the coalescence of 3 eq. of cyanate of ethyl. It may be likewise obtained by distilling a mixture of sulphovinate of potassa with cyanurate of potassa. Cyanurate of ethyl is a crystalline mass, slightly soluble in water, readily soluble in alcohol and ether, fusing at 185° (85°C). By substituting for sul- phovinate of potassa, salts of sulphomethylic and sulphamylic acid, the cor- responding methyl- and amyl- compounds may be obtained. The study of the cyanic and cyanuric ethers, which were discovered by Wurtz, has led to very important results, which will be fully described in the section on the Organic Bases. Fulminic acid.—This remarkable compound, which is isomeric both with cyanic and cyanuric acids, originates in the peculiar action exercised by nitrous acid upon alcohol in presence of a salt of silver or mercury. Neither absolute fulminic acid nor its hydrate has ever been obtained. Fulminate of silver is prepared by dissolving 40 or 50 grains of silver, which need not be pure, in f oz. by measure of nitric acid of sp. gr. 1-37 or there- abouts, by the aid of a little heat; a sixpence answers the purpose very well. To the highly-acid solution, while still hot, 2 measured ounces of alcohol are added, and heat applied until reaction commences. The nitric acid oxidizes part of the alcohol to aldehyde and oxalic acid, becoming itself reduced to nitrous acid, which in turn acts upon the alcohol in such a manner as to form nitrous ether, fulminic acid, and water; 1 eq. nitrous ether and 1 eq. of nitrous acid containing the elements of 1 eq. fulminic acid and 5 eq. water. C4II50,N03 + NOs = C4N202 + 5HO. The fulminate of silver slowly separates from the hot liquid in the form of small, brilliant, white, crystalline plates, which may be washed with a little cold water, distributed upon separate pieces of filter-paper in portions not ex- ceeding a grain or two each, and left to dry in a warm place. AVhen dry, the papers are folded up and preserved in a box. The only safe method of keep- ing the salt is by immersing it under water. Fulminate of silver is soluble in 36 parts of boiling water, but the greater part crystallizes out on cooling: it is one of the most dangerous substances to handle that chemistry present's • it explodes when strongly heated, or when rubbed or struck with a hard body, or when touched with concentrated sulphuric acid, with a degree of violence almost indescribable; the metal is reduced, and a large volume of "-aseous matter suddenly liberated. Strange to say, it may, when very cautiously mixed with oxide of copper, be burned in a tube with as much facility as any ITS COMPOUNDS AND DERIVATIVES. 469 other organic substance. Its composition thus determined is expressed in the formula 2AgO,C4N202. The acid is evidently bibasic: when fulminate of silver is digested with caustic potassa, one-half of the oxide is precipitated, and a compound pro- duced containing AgO,KO,C4N202, which resembles the neutral silver-salt, and detonates by a blow. Corresponding compounds containing soda and oxide of ammonium exist; but a pure fulminate of an alkaline metal has never been formed. If fulminate of silver be digested with water and copper, or zinc, the silver is entirely displaced, and a fulminate of the new metal produced. The zinc-salt mixed with baryta-water gives rise to a precipitate of oxide of zinc, while fulminate of zinc and baryta, ZnO,BaO,C4N202, remains in solution. Ful- minate of mercury is prepared by a process very similar to that by which the silver-salt is obtained: one part of mercury is dissolved in 12 parts of nitric acid, and the solution mixed with an equal quantity of alcohol; gentle heat is applied, and if the reaction becomes too violent, it may be moderated by the addition from time to time of more spirit: much carbonic acid, nitrogen, and red vapors are disengaged, together with a large quantity of nitrous ether and aldehyde: these are sometimes condensed and collected for sale, but are said to contain hydrocyanic acid. The fulminate of mercury separates from the hot liquid, and after cooling may be purified from an admixture of reduced metal by solution in boiling water and recrystallization. It much resembles the silver-salt in appearance, properties, and degree of solubility, and con- tains 2Hg20,C4N202. It explodes violently by friction or percussion, but, un- like the silver-compound, merely burns with a sudden and almost noiseless flash when kindled in the open air. It is manufactured on a large scale for the purpose of charging percussion-caps; sulphur and chlorate of potassa, or more frequently nitre, are added, and the powder, pressed into the cap, is secured by a drop of varnish. The relations of composition between the three isomeric acids are beauti- fully seen by comparing their silver-salts; the first acid is monobasic, the Becond bibasic, and the third tribasic. Cyanate of silver......AgO , C2NO. Fulminate of silver.....2AgO , C4N202. Cyanurate of silver.....3AgO , C6N303. Until quite recently, beyond the accidental one of identity of composition, no relation existed between fulminic acid and its isomers. Dr. Gladstone has however, shown that, when a solution of fulminate of copper is mixed with excess of ammonia, filtered, treated with sulphuretted hydrogen in excess, and again filtered from the insoluble sulphide of copper, the liquid obtained is a mixed solution of urea and sulphocyanide of ammonium. Another view regarding the constitution of fulminic acid was proposed by M. Gerhardt. The fulminates may be considered as cj-anide of methyl (ace- tonitrile), in which 1 eq. of hydrogen is replaced by N04, and 2 eq. of hydro- gen by mercury or silver. C2 H3 C2N. MS (C'N- This view has received some support by the interesting observation lately made by M. Kekule", that the action of chlorine upon fulminate of mercury gives rise to the formation of chloropicrin, C2CI3N04, a substance originally obtained by Stenhouse, which may be viewed as chloroform, the hydrogen of 40 470 FERROCYANOGEN. which is replaced by N04. The connection of fulminic acid with the methyl- series is thus established. Fulminuric acid.—Quite recently, a fourth acid, isomeric with cyanic, ful- minic, and cyanuric acids, has been discovered simultaneously by Liebig and by Schischkoff. This acid, to which the name fulminuric acid has been given, is obtained by the action of a soluble chloride upon fulminate of mercury. On boiling fulminating mercury with an aqueous solution of chloride of potassium, the mercury salt gradually dissolves; the clear solution, after some time, becomes turbid, in consequence of a separation of protoxide of mercury; it now contains fulminurate of potassa. Two phases may be distinguished in this reaction. If, for the sake of simplicity, we halve the formula of fulminate of mercury, the first stage may be represented by the equation 3(HgO,CyO) + 3KC1 = 3(KO,CyO) + 3HgCl. In the second stage, 2 equivalents of water participate in the reaction: 3(KO,CyO) + 2HO + 3HgCl = KO,Cy3H206 + 2HgO + HgCl + 2KC1. Fulminurate of potassa. If, instead of chloride of potassium, chloride of sodium or ammonium be employed, the corresponding soda and ammonia compounds are obtained. The fulminurates crystallize with great facility: they are not explosive. Fulminuric acid has the same composition as cyanuric acid, but it is mono- basic ; cyanuric acid being tribasic. Chlorides of cyanogen.—Chlorine forms two compounds with cyanogen, or its elements, which are isomeric, and correspond to cyanic and cyanuric acids. Gaseous chloride of cyanogen, CyCl, is formed by conducting chlorine gas into strong hydrocyanic acid, or by passing chlorine over moist cyanide of mercury contained in a tube sheltered from the light. It is a permanent and colorless gas at the temperature of the air, of insupportable pungency, and soluble to a very considerable extent in water, alcohol, and ether. At 0° (-17°-8C) it congeals to a mass of colorless crystals, which at 5° (-15°C) melt to a liquid whose boiling-point is 11° (-11°-6C). At the temperature of the air it is condensed to the liquid form under a pressure of four atmospheres, and when long preserved in this condition in hermetically-sealed tubes it gra- dually passes into the solid modification. Solid chloride of cyanogen is gene- rated when anhydrous hydrocyanic acid is put into a vessel of chlorine gas, and the whole exposed to the sun; hydrochloric acid is formed at the same time. It forms long colorless needles, which exhale a powerful and offensive odor, compared by some to that of the excrement of mice; it melts at 284° (140°C), and sublimes unchanged at a higher temperature. AVhen heated in contact with water, it is decomposed into cyanuric and hydrochloric acids. This compound may be represented by the formula Cy3Cl3, or C6N3C1». It dis- solves in alcohol and ether without decomposition. Bromide and iodide of cyanogen correspond to the first of the preceding compounds, and are prepared by distilling bromine or iodine with cyanide of mercury. They are colorless, volatile, solid substances, of powerful odor. FERROCYANOGEN AND ITS COMPOUNDS. When a solution of cyanide of potassium is digested with iron-filings at a gentle heat in an open vessel, oxygen is absorbed from the air, the- iron dis- solves quietly and disappears, and a highly alkaline, yellow liquid is obtained" which on evaporation deposits lemon-yellow crystals containing potassium in combination with a new salt-radical composed of the metal iron and the ele- AND ITS COMPOUNDS. 471 mcnts of cyanogen: in the mother-liquid hydrate of potassa is found. 3 eq. cyanide of potassium, 1 eq. iron, and 1 eq. oxygen, yield 1 eq. of the new Bait, and 1 eq. of potassa. 3KCy 4- Fe 4- 0 = KO 4- K2.C6N3Fe. The new substance is called ferrocyanogen, and is designated by the symbol Cfy; it is bibasic, neutralizing 2 equivalents of metal or hydrogen, and con- tains the elements of 3 equivalents of cyanogen combined with 1 eq. of iron. It has never been isolated. AVhen iron in filings is heated in a small retort with a solution of cyanide of potassium, it is dissolved with evolution of hydrogen, caustic potassa and the new substance being generated; the oxygen in this case is derived from the decomposition of water. Sulphide of iron and cyanide of potassium give rise, under similar circumstances, to sulphide of potassium and ferrocyanide of potassium. Hydroferrocyanic acid, H2Cfy.—Ferrocyanide of lead or copper, both of which are insoluble, may be suspended in water, and decomposed by a stream of sulphuretted hydrogen gas. The filtered solution evaporated in the vacuum of the air-pump over a surface of oil of vitriol, furnishes the acid in a solid form. If the aqueous solution be agitated with ether, nearly the whole of the acid separates in colorless, crystalline laminae; it may even be made in large quantity by adding hydrochloric acid to a strong solution of ferrocya- nide of potassium in water free from air, and shaking the whole with ether. The crystals may be dissolved in alcohol, and the acid again thrown down by ether, which possesses the remarkable property of precipitating this substance from solution. Hydroferrocyanic acid differs completely from hydrocyanic acid; its solution in water has a powerfully acid taste and reaction, and decom- poses alkaline carbonates with effervescence; it refuses to dissolve oxide of mercury in the cold, but when heat is applied, undergoes decomposition, form- ing cyanide of mercury and a peculiar compound of iron, cyanogen, and oxy- gen, with reduction of some of the oxide. In a dry state the acid is very permanent, but when long exposed to the air in contact with water it becomes entirely converted into. Prussian blue. This interesting substance was disco- vered by Mr. Porrett. Ferrocyanide of potassium, frequently called Yellow prussiate of potash, K2Cfy+ 3HO, or K^NgFe + 3HO. — This most beautiful salt is manufac- tured ou a large scale by the following process, which will now be easily intel- ligible : — Dry refuse animal matter of any kind is fused at a red-heat with impure carbonate of potassa and some iron-filings in a large iron vessel, from which the air should be excluded as much as possible: cyanide of potassium is generated in large quantity. The melted mass is afterwards treated with hot water, which dissolves out the cyanide and other salts; the cyanide being quickly converted by the oxide or sulphide1 of iron into ferrocyanide. The filtered solution is evaporated, and the first-formed crystals purified byre-solu- tion. If a sufficient quantity of iron be not present, great loss is incurred by tho decomposition of the cyanide into formate of potassa and ammonia. Ferrocyanide of potassium forms large, transparent, yellow crystals, derived from an octahedron with a square base; they cleave with facility in a direc- tion parallel to the base of the octahedron, and are tough and difficult to pow- der. They dissolve in 4 parts of cold, and in two of boiling water, and are insoluble in alcohol. They are permanent in the air, and have a mild saline taste. The salt has no poisonous properties, and in small doses, at least, is merely purgative. Exposed to a gentle heat, it loses 3 eq. of water, and becomes anhydrous; at a high temperature it yields cyanide of potassium, carbide of iron, and various gaseous products; if air be admitted, the cyanide becomes cyanate. 1 The sulphur is derived from the reduced sulphate of the crude pearl-ashes used in this manufacture. 472 FERROCYANOGEN The ferrocyanidcs are often described as double salts, in which protocyanide of iron is combined with other metallic cyanides, or with hydrogen. Thus hydroferrocyanic acid is written FeCy,2IICy, and ferrocyanide of potassium, FeCy,2KCy + 3HO ; the oxygen and hydrogen of the water of crystallization being respectively adequate to convert the metals into protoxides and the cya- nogen into hydrocyanic acid. This view has the merit of simplicity, and will often prove a useful aid to the memory; but there are insuperable objections to its adoption as a sound and satisfactory theory. Ferrocyanide of potassium is a chemical reagent of great value: when mixed in solution with neutral or slightly-acid salts of the metals proper, it gives rise to precipitates which very frequently present highly characteristic colors. In most of these compounds the potassium of the base is simply dis- placed by the new metal: the beautiful brown ferrocyanide of copper contains, for example, Cu2Cfy or Cu2C6N3Fe, and that of lead, Pb2Cfy. AVith salts of protoxide of iron it gives a bluish precipitate, which becomes rapidly dark blue by exposure to air: this appears to be a compound of the neutral ferro- cyanide of iron, Fe2Cfy, with ferrocyanide of potassium. AVhen a ferrocyanide is added to a solution of a salt of sesquioxide of iron, Prussian blue is produced. Although this remarkable substance has now been long known, and many elaborate researches have been made with a view of determining its exact composition, the problem cannot be said to be completely solved. This difficulty arises in great measure from the existence of several distinct deep-blue compounds formed under different circumstances, and having many properties in common, which have been frequently confounded. The following is a summary of the account given by Berzelius, who has paid much attention to this subject. Ordinary Prussian Blue, C,8N9Fe7, or Fe4Cfy3. — This is best prepared by adding nitrate of sesquioxide of iron to solution of ferrocyanide of potassium, keeping the latter in slight excess. It forms a bulky precipitate of the most intense blue, which shrinks to a comparatively small compass when well washed and dried by a gentle heat. In a dry state it is hard and brittle, much resembling in appearance the best indigo; the freshly-fractured surfaces have a beautiful copper-red lustre, similar to that produced by rubbing indigo with a hard body. Prussian blue is quite insoluble in water and dilute acids, with the exception of oxalic acid, in a solution of which it dissolves, forming a deep-blue liquid, which is sometimes used as ink ; concentrated oil of vitriol converts it into a white, pasty mass, which again becomes blue on the addi- tion of water. Alkalies destroy the color instantly; they dissolve out a ferro- cyanide, and leave sesquioxide of iron. Boiled with water and red oxide of mercury, it yields a cyanide of the metal, and sesquioxide of iron. Heated in the air, Prussian blue burns like tinder, leaving a residue of sesquioxide of iron. Exposed to a high temperature in a close vessel, it disengages water, cyanide of ammonium, and carbonate of ammonia, and leaves carbide of iron. This substance forms a very beautiful pigment, both an oil and a water color, but has little permanency. The Prussian blue of commerce is always exceed- ingly impure; it contains alumina and other matters, which greatly diminish the brilliancy of the color. The production of Prussian blue by mixing a salt of sesquioxide of iron and ferrocyanide of potassium or sodium may thus be elucidated :__ 3 eq. ferrocyanide f 3 eq. ferrocyanogen -----^^^. Prussian blue. potassium \ 6 eq. potassium ->^^_~—----- 2 eq. nitrate of ( 4 eq. iron ----~"^<;\^^ sesquioxide of -< 6 eq. oxygen —'—-------____^\^^ iron (. 6 eq. nitric acid---- ^^ 0 eq. nitrate of potassa. 3K2Cfy + 2(Fe203,3N05) = Fe4Cfy3 + 6(KO,NO.) AND ITS COMPOUNDS, 473 In the above formula no account is taken of the elements of water which Prussian blue certainly contains; in fact, it must be looked upon as still requiring examination. The theory of the beautiful test of Scheele for the discovery of hydrocyanic acid, or any soluble cyanide, will now be clearly intelligible. The liquid is mixed with a salt of protoxide of iron and excess of caustic alkali; the prot- oxide of iron quickly converts the alkaline cyanide into ferrocyanide. By exposure for a short time to the air, another portion of the hydrated oxide becomes peroxidized ; when excess of acid is added, this is dissolved, together with the unaltered protoxide; and thus presented to the ferrocyanide in a state fitted for the production of Prussian blue. Basic Prussian Blue, Fe4Cfy3+ Fe203. — This is a combination of Prussian blue with sesquioxide of iron: it is formed by exposing to the air the white or pale-blue precipitate caused by a ferrocyanide in a solution of protosalt of iron. It differs from the preceding in being soluble in pure water, although not in a saline solution. The blue precipitate, obtained by adding nitrate of sesquioxide of iron to a large excess of ferrocyanide of potassium, is a mixture of insoluble Prussian blue, with a compound containing that substance in union with ferrocyanide of potassium, or Fe4Cfy3+ 2K2Cfy. This also dissolves in water as soon as the salts have been removed by washing. The other ferrocyanides may be despatched in a few words. The soda-salt, Na2Cfy 4/- 12HO, crystallizes in yellow four-sided prisms, which are efflorescent in the air and very soluble. Ferrocyanide of ammonium, (NH4)2Cfy -{- 3110, is isomorphous with ferro- cyanide of potassium: it is easily soluble, and is decomposed by ebullition. Ferrocyanide of barium, Ba8Cfy, prepared by double decomposition, or by boil- ing Prussian blue in baryta-water, forms minute yellow, anhydrous crystals, which have but a small degree of solubility even in boiling water. The corre- sponding compounds of strontium, calcium, and magnesium, are more freely soluble. The ferrocyanides of silver, lead, zinc., manganese, and bismuth are white and insoluble; those of nickel and cobalt are pale-green and insoluble; and, lastly, that of copper has a beautiful reddish-brown tint. Ferrocyanides with two basic metals are occasionally met with: when, for example, concentrated solutions of chloride of calcium and ferrocyanide of potassium are mixed, a sparingly-soluble crystalline precipitate falls, contain- ing KCaCfy, the salt-radical being half saturated with potassium and half with calcium; many similar compounds have been formed. Ferui-, or ferridcyanogen, C|2N6Fe2; or Cfdy.—This name is given to a substance, by some thought to be a new salt-radical, isomeric with ferrocya- nogen, but differing in capacity of saturation ; it has never been isolated. Ferricyanide of potassium is thus prepared : — Chlorine is slowly passed, with agitation, into a somewhat dilute and cold solution of ferrocyanide of potas- sium, until the liquid acquires a deep-reddish-green color, and ceases to pre- cipitate a salt of the sesquioxide of iron. It is then evaporated until a skin begins to form upon the surface, filtered, and left to cool; the salt is purified by recrystallization. It forms regular prismatic, or sometimes tabular crys- tals, of a beautiful ruby-red tint, permanent in the air, and soluble in 4 parts of cold water; the solution has a dark-greenish color. The crystals burn when introduced into the flame of a candle, and emit sparks. Ferricyanide of potassium contains K3Cfdy ; hence the radical is tribasic ; the salt is formed by the abstraction of an equivalent of potassium from 2 eq. of the yellow ferrocyanide of potassium. It is decomposed by excess of chlo- rine, and by deoxidizing agents, as sulphuretted hydrogen.. The term red pruxsiale of potash is often, but very improperly, given to this substance. Ferricyanide of hydrogen is obtained in the form of a reddish-brown acid liquid, by decomposing ferricyanide of lead with sulphuric acid; it is very 40* 474 SULPHOCYANOGEN; ITS CO M POUNDS. .nstablc, and is resolved, by boiling, into an hydrated sesquicyanide of iron, an insoluble dark-green powder, containing Fe2Cy3 -f- 3HO, and hydrocyanic acid. The fenicyanides of sodium, ammonium, and of the alkaline earths are soluble; those of most of the other metals are insoluble. Ferricyanide of potassium, added to a salt of the sesquioxide of iron, occasions no precipitate, but merely a darkening of the reddish-brown color of the solution ; with prot- oxide of iron, on the other hand, it gives a deep-blue precipitate, containing Fe3Cfdy, which, when dry, has a brighter tint than that of Prussian blue • it is known under the name of TurnbulVs blue. Hence, ferricyanide of potas- sium is as excellent a test for protoxide of iron, as the yellow ferrocyanide is for the sesquioxide. Cobalticyanogen.—A series of compounds analogous to the preceding, containing cobalt in place of iron, have been formed and studied; a hydrogen- acid has been obtained, and a number of salts, which much resemble those of ferricyanogen. Several other metals of the same isomorphous family are found capable of replacing iron in these circumstances. Nitroprussides. —The action of nitric acid upon ferrocyanides and ferri- cyanides gives rise to the formation of a very interesting series of new salts, which were discovered by Dr. Playfair. The general formula of these salts appears to be M2Fe2Cy5NO, which exhibits a close relation with those of the ferro- and ferri-cyanides. 2M2Cfy = M4 Fe2 Cy6 = ferrocyanides. M3Cfdy = M3 Fe2 Cy6 = ferricyanides. M2 Fe2 -j j& = nitroprussides. _ According to this formula, the formation of the nitroprussides would con- sist in the reduction of the nitric acid to the state of protoxide of nitrogen, which replaces 1 eq. of cyanogen in 2 eq. of ferricyanide. The formation of these salts is attended by the production of a variety of secondary products, such as cyanogen, oxamide, hydrocyanic acid, nitrogen, carbonic acid, &c. One of the finest compounds of this series is the nitroprusside of sodium, Na2,Fe2Cy5NO + 4HO, which is readily obtained by treating 2 parts of the powdered ferrocyanide with 5 parts of common nitric acid, previously diluted with its own volume of water. The solution, after the evolution of gas has ceased, is digested on the water-bath, until salts of protoxide of iron no longer yield a blue but a slate-colored precipitate. The liquid is now allowed to cool, when much nitrate of potassa, and occasionally oxamide, is deposited: it is filtered and neutralized with carbonate of soda, which yields a green or brown precipitate, and furnishes a ruby-colored filtrate. This, on evaporation, gives a crystallization of nitrate of potassa and soda, together with the new salt The'crystals of the latter are selected and purified by crystallization • they are rhombic, and of a splendid ruby color. The soluble nitroprussides'strike a most beautiful violet tint with soluble sulphides. This reaction is recom- mended by Dr. Playfair as the most delicate test for alkaline sulphides. sulphocyanogen; its compounds and derivatives. The elements of cyanogen combine with sulphur, forming a very important and well-defined salt-radical, called sulphocyanogen, which contains C NS and is monobasic; it is expressed by the symbol Csy. 2 2' Sulphocyanide of potassium, KCsy. — Yellow ferrocyanide of potassium deprived of its water of crystallization, is intimately mixed with half its weight of sulphur, and the whole heated to tranquil fusion in an iron pot and kent for some time in that condition. AVhen cold, the melted mass is boiled with water, which dissolves out a mixture of sulphocyanide of potassium and sul sulphocyanogen; its compounds. 475 phooyanide of iron, leaving little behind but the excess of sulphur employed in the experiment. This solution, which becomes red on exposure to the air from the oxidationof the iron, is mixed with carbonate of potassa, by which the oxide of iron is precipitated, and potassium substituted; an excess of the carbonate must be, as far as possible, avoided. The filtered liquid is concen- trated, by evaporation over an open fire, to a small bulk, and left to cool and crystallize. The crystals are drained, purified by re-solution, if necessary, or dried by enclosing them, spread on filter-paper, over a surface of oil of vitriol, covered by a bell-jar. The reaction between the sulphur and the elements of the yellow salt is easily explained: 1 eq. of ferrocyanide of potassium, and 6 eq. sulphur, yielded 2 eq. of sulphocyanide of potassium, and 1 eq. of sulphocyanide of iron. C6N3FeK2 4- 6S = 2(KC2NS2) + FeC2NS2. Another and even better process consists in gradually heating to low redness in a covered vessel a mixture of 46 parts of dried ferrocyanide of potassium, 32 of sulphur, and 17 of pure carbonate of potassa. The mass is exhausted by water, the aqueous solution evaporated to dryness and extracted with alcohol. The alcoholic liquid deposits splendid crystals on cooling or evapo- ration. The new salt crystallizes in long, slender, colorless prisms, or plates, which are anhydrous; it has a bitter saline taste, and is destitute of poisonous pro- perties; it is very soluble in water and alcohol, and deliquesces when exposed to a moist atmosphere. AVhen heated, it fuses to a colorless liquid, at a tem- perature far below that of ignition. AVhen chlorine is passed into a strong solution of sulphocyanide of potas- sium, a large quantity of a bulky, deep yellow, insoluble substance, resem- bling some varieties of chromate of lead, is produced, together with chloride of potassium, which tends to choke up the tube delivering the gas; the liquid sometimes assumes a deep-red tint, and disengages a pungent vapor, probably chloride of cyanogen. This yellow matter may be collected on a filter, well washed with boiling water, and dried ; it retains its brilliancy of tint. The term sulphocyanogen has generally been applied to this substance, from its supposed identity with the radical of the sulphocyanides: it is, however, inva- riably found to contain both oxygen and hydrogen ; and a formula much more complex than that belonging to the true sulphocyanogen, namely, C8H2N4S80, has been assigned to it. The yellow substance is quite insoluble in water, alcohol, and ether; it dissolves in concentrated sulphuric acid, from which it is precipitated by dilution. Caustic potassa also dissolves it, with decompo- sition ; acids throw down from this solution a pale-yellow, insoluble body, having acid properties. AVhen heated in a dry state, the so-called sulpho-cya- nogen evolves sulphur and bisulphide of carbon, and leaves a curious, pale straw-yellow substance, called mellon, which contains C]SN)3, and is known to combine with hydrogen, and the metals. Mellon bears a dull red-heat with- out decomposition, but is resolved by strong ignition into a mixture of cya- nogen and nitrogen gases. It is quite insoluble in water, alcohol, and dilute acids. Hydrosulpiiocyanic acid, HCsy, is obtained by decomposing sulphocya- nide of lead, suspended in water, by sulphuretted hydrogen. The filtered solution is colorless, very acid, and not poisonous ; it is easily decomposed, in a \cry complex manner, by ebullition, and by exposure to the air. By neu- tralizing the liquid with ammonia, and evaporating, very gently, to dryness, sulphocyanide of ammonium, NIT4Csy, is obtained as a deliquescent, saline mass. This salt may be conveniently prepared by digesting hydrocyanic acid with yellow sulphide of ammonium, and boiling off the excess of the latter (NH4S34-HCy—NH4Csy+HS). The sulphocyanides of sodium, barium, slron- 476 sulphocyanogen; its compounds. Hum, calcium, manganese, and iron are colorless and very soluble: those of lead and silver are white and insoluble. A soluble sulphocyanide, mixed with a salt of the sesquioxide of iron, gives no precipitate, but causes the liquid to assume a deep blood-red tint, hence the occasional use of sulphocyanide of potassium as a test for iron in the state of sesquioxide. The red color produced by sulphocyanides in solution of sesquioxide of iron is exactly like that caused under similar circumstances by meconic acid. The two substances may, however, be readily distinguished by the addition of a solution of chlo- ride of gold, which destroys the color produced by sulphocyanides. The me- conate of iron may also be distinguished from the sulphocyanide, as Mr Everitt has shown, by an addition of corrosive sublimate, which bleaches the sulphocyanide, but has little effect upon the meconate. This is a point of considerable practical importance, as in medico-legal inquiries, in which evi- dence of the presence of opium is sought for in complex organic mixtures, the detection of meconic acid is usually the object of the chemist; and since traces of alkaline sulphocyanide are to be found in the saliva, it becomes very desirable to remove that source of error and ambiguity. The great facility with which hydrocyanic acid may be converted into sul- phocyanide of ammonium enables us to ascertain its presence by the iron test just described. The cyanide to be examined is mixed in a watch-glass with some hydrochloric acid and covered with another watch-glass, to which a few drops of yellow sulphide of ammonium adhere. On heating the mixture, hydrocyanic acid is disengaged, which combines with the sulphide of ammo- nium, and produces sulphocyanide of ammonium ; this, after expulsion of the excess of sulphide, yields the red color with solution of sesquichloride of iron. Selenocyanogen.—A series of salts containing selenium, and correspond- ing in their composition and properties with the sulphocyanides, exist. They have been studied by Mr. Crookes. Melam. —Such is the name given by Liebig to a curious buff-colored, in- soluble, amorphous substance, obtained by the distillation at a high tempera- ture of sulphocyanide of .ammonium. It maybe prepared in large quantity hy intimately mixing 1 part of perfectly dry sulphocyanide of potassium with 2 parts of powdered sal-ammoniac, and heating the mixture for some time in a retort or flask; bisulphide of carbon, sulphide of ammonium, and sulphu- retted hydrogen are disengaged and volatilized, while a mixture of melam, chloride of potassium, and some sal-ammoniac remains: the two latter sub- stances are removed by washing with hot water. Melam contains Cl2H9N_.; it dissolves in concentrated sulphuric acid, and gives, by dilution Avith water and long boiling, cyanuric acid. The same substance is produced with dis- engagement of ammonia when melam is fused with hydrate of potassa. When strongly heated, melam is resolved into mellon and ammonia. If melam be boiled for a long time in a moderately-strong solution of caus- tic potassa, until the whole has dissolved, and the liquid be then concentrated a crystalline substance separates on cooling, which is called melamine. By re- ciystallization it is obtained in colorless crystals, having the figure of an oc- tahedron with rhombic base; it is but slightly soluble in cold water, fusible by heat, and volatile with trifling decomposition. It contains C6II N , and acts as a base, combining with acids to crystallizable compounds. A second basic substauce called ammeline, very similar in properties to melamine is found in the alkaline mother-liquor from which the melamine has separated • it is thrown down on neutralizing the liquid with acetic acid. The precipitate' dissolved in dilute nitric acid, yields crystals of nitrate of ammeline from which the pure ammeline may be separated by" ammonia. It forms a brilliant white powder of minute needles, insoluble in water and alcohol, and contains C6H5N602. AVhen ammeline is dissolved in concentrated sulphuric acid and the solution mixed with a large quantity of water, or, better, spirit of wine urea; uric acid and its products. 477 a white, insoluble powder falls, which 13 designated ammelide, and is found to contain C12II9N90j. AVhen long boiled with dilute sulphuric acid, melamine, ammeline, and ammelide are converted into cyanuric acid and ammonia. Mellon and its compounds.—The formation of this compound as a re- siduary product of the action of heat upon the so-called sulphocyanogen, and upon melam, has been mentioned. This substance, which it would appear has never been obtained in a state of purity, possesses the properties of an organic radical. At a high temperature it combines directly with potassium, producing a well-defined saline compound, mellonide of potassium, and the same salt is produced in the action of mellon upon bromide and iodide of potassium, when bromine and iodine are liberated. A better process of pro- ducing mellonide of potassium consists in fusing crude mellon with sulphocy- anide of potassium. In this reaction we may assume that, in the first place, mellon expels the sulphocyanogen, which in its turn yields a fresh quantity of mellon at the temperature at which the reaction takes place; mellonide of potassium may therefore be produced likewise by fusing the ferrocyanide of potassium with half its weight of sulphur. The fused mass obtained by either process is dissolved in boiling water, from which the mellonide of potassium crystallizes on cooling, and is purified by repeated crystallizations. Mellonide of potassium contains K3C18N,3. Acetic acid converts this salt into a new salt still soluble, having the composition K2H,C18N13. Hydrochloric acid produces an insoluble compound, KH2C]3N)3. These three salts, it will be observed, stand to each other in the same relation as the several salts of phosphoric and cyanuric acid. Mellonide of potassium produces with soluble silver-salts a white precipitate, Ag3ClsNI3; with lead-salts and mercury-salts, precipitates containing respectively Pb3C]8N]3, and Hg3C18N,3. The latter dis- solved in hydrocyanic acid, and treated with sulphuretted hydrogen, furnishes the hydromellonic acid, H3Ci8N13. It is only known in solution, which has an acid taste; on evaporation it is decomposed. UREA ; URIC ACID AND ITS PRODUCTS. These bodies are closely connected with the cyanogen-compounds, and may be most conveniently discussed in the present place. Urea. — Urea may be extracted from its natural source, the urine, or it may be prepared by artificial means. Fresh urine is concentrated in a water- bath, until reduced to an eighth or a tenth of its original volume, and filtered through cloth from the insoluble deposit of urates and phosphates. The liquid is mixed with about an equal quantity of a strong solution of oxalic acid in hot water, and the whole vigorously agitated and left to cool. A very copious fawn-colored crystalline precipitate of oxalate of urea is obtained, which may be placed upon a cloth filter, slightly washed with cold water, and pressed. This is to be dissolved in boiling-hot water, and powdered chalk added until effervescence ceases, and the liquid becomes neutral. The solu- tion of urea is filtered from the insoluble oxalate of lime, warmed with a little animal charcoal, again filtered, and concentrated by evaporation, avoiding ebullition, until crystals form on cooling: these are purified by a repetition of the last part of the process. Urea can be extracted in great abundance from the urine of horses and cattle duly concentrated, and from which the hippuric aeid has been separated by the addition of hydrochloric acid; oxalic acid then throws down the oxalate in such quantity as to render the whole semi-solid. Another process consists in precipitating the evaporated urine with concentrated nitric acid, when nitrate of urea is precipitated, which is purified by recrystallization with animal charcoal, and lastly decomposed by 478 urea; uric acid and its products. carbonate of baryta. A mixture of nitrate of baryta and urea is formed, which is evaporated to dryness on the water-bath, and exhausted with alcohol, from which the urea crystallizes on cooling. By artificial means urea is produced by heating solution of cyanate of am- monia. The following method of proceeding yields it in any quantity that can be desired. Cyanate of potassa, prepared by Liebig's process,1 is dis- solved in a small quantity of water, and a quantity of dry neutral sulphate of ammonia, equal in weight to the cyanate, added. The whole is evaporated to dryness in a water-bath, and the dry residue boiled with strong alcohol, which dissolves out the urea, leaving the sulphate of potassa and the excess of sulphate of ammonia untouched. The filtered solution, concentrated by distilling off a portion of the spirit, deposits the urea in beautiful crystals of considerable magnitude. Urea forms transparent, colorless, four-sided prisms, which are soluble in an equal weight of cold water, and in a much smaller quantity at a high tem- perature. It is also readily dissolved by alcohol. It is inodorous, has a cool- ing saline taste, and is permanent in the air, unless the latter be very damp. AVhen heated it melts, and at a higher temperature decomposes with evolution of ammonia and cyanate of ammonia; cyanuric acid remains, which bears a much greater heat without change. The solution of urea is neutral to test- paper ; it is not decomposed in the cold by alkalies or by hydrate of lime, but at a boiling heat emits ammonia, and forms a carbonate of the base. The same change happens by fusion with the alkaline hydrates. Brought into contact with nitrous acid, it is decomposed instantly into a mixture of nitro- gen and carbonic acid gases: this decomposition explains the use of urea in preparing nitric ether (see page 373). AVith chlorine it yields hydrochloric acid, nitrogen and carbonic acid. Crystallized urea is anhydrous: it contains C2H4N202, or the elements of cyanate of oxide of ammonium. It differs from carbonate of ammonia by the elements of water; hence it might with some propriety be called carbamide. It is easily converted into carbonate of ammo- nia by assimilating the oxygen and hydrogen of 2 eq. of water. A solution of pure urea shows no tendency to change by keeping, and is not decom- posed by boiling: in the urine, on the other hand, where it is associated with putrefiable organic matter, as mucus, the case is different. In putrid urine no urea can be found, but enough carbonate of ammonia to cause brisk effer- vescence with an acid; and if urine, in a recent state, be long boiled, it gives off ammonia and carbonic acid from the same source. Urea acts as a salt-base; with nitric acid it forms a sparingly-soluble com- pound, which crystallizes, when pure, in small, indistinct, colorless plates, containing single equivalents of urea, nitric acid, and water. AVhen color- less nitric acid is added to urine, concentrated to a fourth or a sixth of its volume, and cold, the nitrate crystallizes out in large, brilliant, yellow laminae, which are very insoluble in the acid liquid. The production of this nitrate is highly characteristic of urea. The oxalate, when pure, crystallizes in large, transparent, colorless plates, which have an acid reaction, and are sparingly soluble; it contains an equivalent of water. Urea forms several compounds with metallic salts, e. g., with those of mercury. On mixing a liquid containing urea with a solution of nitrate of protoxide of mercury, a white precipitate takes place, which is a compound of urea with 4 eq. of prot- oxide of mercury. If the nitric acid, which is thus set free, be neutralized by the addition of an alkali or baryta-water, the whole of the urea is re- moved from the liquid in the form of the above compounds. Prof. Liebi°- to whom we are indebted for this observation, has based upon this deportment a process of determining the amount of urea in urine. The details of this method, which is equally interesting to the chemist and the physiologist have been published.2 » See page 466 a Journal of the Chemical Society, vol. vi. p. 1. URIC ACID AND ITS PRODUCTS. 479 A series of substances analogous to urea which have lately been discovered and described under the name of methylaminc-urea, ethylamine-urea, biethyl- ainine-uiea, &c, will be noticed in the section on the Vegeto-alkalies. Uric, or Litiiic acid. — This is a product of the animal organism, and has never been formed by artificial means. It may be prepared from human urine by concentration, and addition of hydrochloric acid; it crystallizes out after some time in the form of small, reddish, translucent grains, very difficult to purify. A much preferable method is, to employ the solid white excrement of serpents, which can be easily procured: this consists almost entirely of uric acid and urate of ammonia. It is reduced to powder, and boiled in dilute solution of caustic potassa; the liquid, filtered from the insignificant residue of feculent matter and earthy phosphates, is mixed with excess of hydrochloric acid, boiled for a few minutes, and left to cool. The product is collected on a filter, washed until free from chloride of potasssium, and dried by gentle heat. trie acid, thus obtained, forms a glistening, snow-white powder, tasteless, inodorous, and very sparingly soluble. It is seen under the microscope to consist of minute, but Fig. 189. regular crystals. It dissolves in concentrated sul- phuric acid without apparent decomposition, and is precipitated by dilution with water. By destructive distillation, uric acid yields cyanic, hydrocyanic, and carbonic acids, carbonate of ammonia, and a black coaly residue, rich in nitrogen. By fusion with hydrate of potassa, it furnishes carbonate and &***$/£\ ^^%_ £s cyanate of the base, and cyanide of the alkaline metal. AVhen treated with nitric acid and with binoxide of lead, it undergoes decomposition in a manner to be presently described. Uric acid is found by analysis to contain Cl0H2N4O4.2IIO. It is a bibasic acid. The only salts of uric acid that have attracted any attention are those of the alkalies ; acid urate of potassa contains KO,HO,C10H2N4O4; it is deposited from a hot, saturated solution of uric acid in the dilute alkali as a white, sparingly-soluble concrete mass, composed of minute needles; it requires about 500 parts of cold water for solution, is rather more soluble at a high temperature, and much more soluble in excess of alkali. Urate of soda resembles the salt of potassa; it forms the chief constituent of the gouty concretions in the joints called chalk-stones. Urate of ammonia is also a sparingly-soluble compound, requiring for the purpose about 1000 parts of cold water; the solubility is very much increased by the presence of a small quantity of certain salts, as chloride of sodium. This is the most common of the urinary deposits, forming a buff-colored or-pinkish cloud or muddiness, which disappears by re-solution when the urine is warmed: the secretion from which this is deposited has an acid reaction. It occurs also as a calculus. The following substances result from the oxidation of uric acid by binoxide of lead and nitric acid: they are some of the most beautiful and interesting bodies known, most of which have been discovered by Liebig and AVohler. Allantoin. —Allantoin occurs ready-formed in the allantoic liquid of the foetal calf. It is produced artificially by boiling together water, uric acid, and pure, freshly-prepared binoxide of lead: the filtered liquid, duly con- centrated by evaporation, deposits crystals of allantoin on cooling, which are purified by re-solution and the use of animal charcoal. It forms small, but most brilliant prismatic crystals, which are transparent and colorless, destitute of taste, and without action on vegetable colors. Allantoin dissolves in 160 parts of cold water, and in a smaller quantity at the boiling temperature. It is decomposed by boiling with nitric acid, and by oil of vitriol when concen- 480 URIC ACID AND ITS PRODUCTS. trated and hot, being in this case resolved into ammonia, carbonic acid, and carbonic oxide. Heated with concentrated solution of caustic alkalies, it is decomposed into ammonia and oxalic acid, which latter combines with the base. These reactions are explained by the analysis of the substance, which shows it to be composed of the elements of two equivalents of oxalate of or ammonia minus those of five equivalents of water, or C4H3N203. The production of allantoin from uric acid and binoxide of lead is also perfectly intelligible: 1 eq. of uric acid, 2 eq. of oxygen from the binoxide, and 3 eq. of water, contain the elements of allantoin, 2 eq. of oxalic acid, and 1 eq. of urea. C10H4N4O6 4- 20 A _ / C4H3N203 4- 2(HO,C203) + 3HO }~\ + C2H4N202. The insoluble matter from which the solution of allantoin is filtered consists in great part of oxalate of lead; and the mother-liquor, from which the crystals of allantoin have separated, yields, on further evaporation, a large quantity of pure urea. Alloxan.—This is the characteristic product of the action of concentrated nitric acid on uric acid in the cold. An acid is prepared, of sp. gr. 1 -45, or thereabouts, and placed in a shallow open basin: into this a third of its weight of dry uric acid is thrown, by small portions, with constant agitation, care being taken that the temperature never rises to any considerable extent. The uric acid at first dissolves with copious effervescence of carbonic acid and nitrogen, and eventually the whole becomes a mass of white, crystalline, pasty matter. This is left to stand some hours, drained from the acid liquid in a funnel whose neck is stopped with powder and fragments of glass, and after- wards more effectually dried upon a porous tile. This is alloxan in a crude state ; it is purified by solution in a small quantity of water, and crystallization. Alloxan crystallizes with facility from a hot and concentrated solution, slowly suffered to cool, in solid, hard, anhydrous crystals of great regularity, which are transparent, nearly colorless, have a high degree of lustre, and the figure of a modified rhombic octahedron. A cold solution, on the other hand, left to evaporate spontaneously, deposits large foliated crystals, which contain G eq. of water; they effloresce rapidly in the air. Alloxan is very soluble in water; the solution has an acid reaction, a disagreeably-astringent taste, and stains the skin, after a time, red or purple. It is decomposed by alkalies, and both by oxidizing and deoxidizing agents; its most characteristic property is that of forming a deep-blue compound with a salt of protoxide of iron and an alkali. Alloxan contains C8H4N2O10; its production is thus illustrated: 1 eq. of uric acid, 4 eq. of water, and 2 eq. of nitric acid contain the elements of alloxan, 2 eq. of carbonic acid, 2 eq. of free nitrogen, and 1 eq. of nitrate of ammonia. ■** C+421h6,N025)10} = C»H«N»°» + 2C0* + N* + NH40,N05. When to a solution of alloxan, heated to 140° (60°C), baryta-water is added, as long as the precipitate first produced redissolves, and the filtered solution is then left to cool, a substance is deposited in small, colorless, pearly crystals, which consists of baryta in combination with a new acid, the alloxamic. From this salt the base may be separated by the cautious addition of dilute sul- phuric acid: the filtered liquid by gentle evaporation yields alloxanic acid in small radiated needles. It has an acid taste and reaction, decomposes car- bonates, and dissolves zinc with disengagement of hydrogen. It is a bibasic acid, and contains in the hydrated state C8H2N208,2HO; hence it is isomeric with alloxan. The alloxanates of the alkalies are freely soluble • those of the earths dissolve in a large quantity of tepid water, and that of silver is quite insoluble and anhydrous. URIC ACID AND ITS PRODUCTS. 481 If a warm saturated solution of alloxanate of baryta be heated to ebullition, a precipitate falls, which is a mixture of carbonate and alloxanate of baryta, with an insoluble salt of a second new acid, the mesoxalic; the solution is found to contain unaltered alloxanate of baryta and urea. Mesoxalic acid is best prepared by slowly adding solution of alloxan to a boiling-hot solution of acetate of lead.- the heavy granular precipitate of mesoxalate of lead thus produced is washed and decomposed by sulphuretted hydrogen: urea is also formed in this experiment. Hydrate of mesoxalic acid is crystallizable; it has a sour taste and powerfully-acid reaction, and resists a boiling heat; it forms sparingly-soluble salts with baryta and lime, and a yellowish insoluble compound with oxide of silver, which is reduced with effervescence when gently heated. This remarkable acid contains as hydrate C304,2HO, and is consequently bibasic; it is formed by the resolution of alloxan into urea, and 2 eq. of mesoxalic acid: CsI^Ao 4- 4IIO = C2H4N202 4- 2(2HO,C304). AVhen ammonia in excess is added to A solution of alloxan, the whole heated to ebullition, and afterwards supersaturated with dilute sulphuric acid, a yellow, light precipitate falls, which increases in quantity as the liquid cools. This is mykomelinic acid; it is but feebly soluble in water, easily dissolved by alkalies, and forms a yellow compound with oxide of silver. Mykomelinic acid contains C8H6N405; it is produced by the conversion of alloxan and 2 eq. of ammonia into 1 eq. of mykomelinic acid and 5 eq. of water. Parabanic acid. — This is the characteristic product of the action of moderately-strong nitric acid on uric acid or alloxan, by the aid of heat; it is conveniently prepared by heating together 1 part of uric acid-and 8 parts of nitric acid until the reaction has nearly ceased; the liquid is evaporated to a syrupy state, and left to cool; the acid is drained from the mother-liquor and purified by recrystallization. Parabanic acid forms beautiful colorless, trans- parent, thin, prismatic crystals, which are permanent in the air; it is easily soluble in water, has a pure and powerfully acid taste, and reddens litmus strongly. Neutralized with ammonia, and mixed with nitrate of silver, it gives a white precipitate. Crystallized parabanic acid contains C6N204,2HO; its production is thus explained: 1 eq. of uric acid, 4 eq. of water, and 4 eq. of oxygen from the nitric acid, yield 1 eq. of parabanic acid, 4 eq. of carbonic acid, and 2 eq. of ammonia; or, alloxan and 2 additional equivalents of oxygen furnish 1 eq. of parabanic acid, 2 eq. of carbonic acid, and 2 eq. of water. The alkaline parabanates undergo a singular change by exposure to heat: if a solution of the acid be saturated with ammonia, boiled for a moment, and then left to cool, a substance separates in tufts of beautiful colorless needles • tfiis is the ammonia-salt of an acid called the oxaluric. The hydrated acid is procured by adding an excess of dilute sulphuric acid to a hot and strong solution of oxalurate of ammonia, and cooling the whole rapidly. It forms a white, crystalline powder, of acid taste and reaction, capable of combining with bases; the salts of baryta and lime are sparingly soluble; that of silver crystallizes from the mixed hot solution of nitrate of silver and oxalurate of ammonia in long, silky needles. Oxaluric acid is composed of CfiH3N207,HO: or the elements of 1 eq. of parabanic acid, and 2 eq. of water. A solution of oxaluric acid is resolved by ebullition into free oxalic acid and oxalate of urea. Thionuric acid.—A cold solution of alloxan is mixed with a saturated solu- tion of sulphurous acid in water, in such quantity that the odor of the gas remains quite distinct; an excess of carbonate of ammonia mixed with a little caustic ammonia is then added, and the whole boiled for a few minutes. On cooling, thionurate of ammonia is deposited in great abundance, forming beau- tiful colorless, crystalline plates, which by solution in water and recrystalliza- tion acquire a fine pink tint. A solution of this salt gives with acetate of lead a precipitate of insoluble thionurate of the oxide, of that metal, which is at 41 482 URIC ACID AND ITS PRODUCTS. first white and gelatinous, but shortly becomes dense and crystalline; from this compound the hydrated acid may be obtained by the aid of sulphuretted hydrogen. It forms a white, crystalline mass, permanent in the air, very soluble in water, of acid taste and reaction, and capable of combining directly with bases. When its solution is heated to the boiling-point it undergoes de- composition, yielding sulphuric acid, and a very peculiar and nearly insoluble substance, called uramile. Thionuric acid is bibasic; the hydrate contains C8H6N3S2Ol2,2HO; or the elements of alloxan, an equivalent of ammonia, and 2 eq. of sulphurous acid. Uramile.—The product of the decomposition by heat of hydrated thionuric acid. Thionurate of ammonia is dissolved in hot water, mixed with a small excess of hydrochloric acid, and the whole boiled in a flask: a white, crystal- line substance begins in a few moments to separate, which increases in quan- tity until the contents of the vessel often becomes semi-solid: this is uramile. After cooling, it is collected on a filter, washed with cold water to remove the sulphuric acid, and dried by gentle heat, during which it frequently becomes pinkish. Examined by a lens, it is seen to consist of minute acicular crys- tals. It is tasteless and nearly insoluble in water, but dissolves in ammonia and the fixed alkalies. The ammoniacal solution becomes purple in the air. It is decomposed by strong nitric acid, alloxan and nitrate of ammonia being generated. Uramile contains C8H6X306; or thionuric acid minus the elements of 2 eq. of sulphuric acid. Uramilic acid.—AVhen a cold saturated solution of thionurate of ammonia is mixed with dilute sulphuric acid, and evaporated in a water-bath, instead of uramile, another substance, uramilic acid, is formed and deposited in slender, colorless prisms, soluble in 8 parts of cold water. Uramilic acid dissolves in concentrated sulphuric acid without apparent decomposition; it has a feebly- acid taste and reaction, and combines with bases. The salts of the alkalies are easily soluble; those of the earths much less so, and that of the oxide of silver is insoluble. Uramilic acid contains Cl6HI0N5O,5 ; 2 eq. of uramile and 3 eq. of water contain the elements of uramilic acid and 1 eq. of ammonia. It is a substance difficult of preparation. Alloxantin. — This is the chief product of the action of hot dilute nitric acid upon uric acid: the surest and best method of preparing it, however, is by passing a stream of sulphuretted hydrogen gas through a moderately-strong and cold solution of alloxan. The impure mother-liquor from which the crys- tals of alloxan have separated answers the purpose perfectly well; it is diluted with a little water, and a copious stream of gas transmitted through it. Sul- phur is deposited in large quantity, mixed with a white, crystalline substance, which is the alloxantin. The product is drained upon a filter, slightly washed, and then boiled in water: the filtered solution deposits the alloxantin on cool- ing. Alloxantin forms small, four-sided, oblique rhombic prisms, colorless and transparent; it is soluble with difficulty in cold water, but more freely at a boiling temperature. The solution reddens litmus, gives with baryta-water a violet-colored precipitate, which disappears on heating, and when mixed with nitrate of silver produces a black precipitate of metallic silver. Heated with chlorine or nitric acid, it is changed by oxidation to alloxan. The crys- tals become red when exposed to ammoniacal vapors. Alloxantin contains C8H5N2O10; or alloxan plus 1 eq. of hydrogen. This substance is readily decomposed: when a stream of sulphuretted hydrogen is passed through a boiling solution, sulphur is deposited and an acid liquid produced, supposed to contain a new acid, to which the term dia- luric is applied. AVhen neutralized by ammonia it yields a salt which crystal- lizes in colorless, silky needles, containing NH40,C8N204 + 3HO. They become deep-red when heated to 212° (100°C) in the air. A hot saturated solution of alloxantin mixed with a neutral salt of ammonia instantly assumes a purple color, which however quickly vanishes, and the liquid becomes turbid from URIC ACID AND ITS PRODUCTS. 483 the formation of uramile ; the liquid is then found to contain alloxan and free acid. AVith oxide of silver alloxantin disengages carbonic acid, reduces a por- tion of the metal, and converts the remainder of the oxide into oxalurate. Boiled with water and binoxide of lead, alloxantin gives urea and carbonate of lead. Murexide ; purpurate of ammonia of Dr. Prout. — There are several different methods of preparing this magnificent compound. It may be made directly from uric acid, by dissolving that substance in dilute nitric acid, evaporating to a certain point, and then adding to the warm, but not boiling liquid, a very slight excess of ammonia. In this experiment alloxantin is first produced, which becomes afterwards partially converted into alloxan: the presence of both is requisite to the production of murexide. This process is, however, very precarious, and often fails altogether. An excellent method is to boil for a few minutes in a flask a mixture of 1 part of dry uramile, 1 part of red oxide of mercury, and 40 parts of water, to which two or three drops of ammonia have been added; the whole assumes in a short space of time an intensely deep-purple tint, and when filtered boiling-hot, deposits on cooling, splendid crystals of murexide, unmixed with any impurity. A third, and perhaps even still better process is that of Dr. Gregory: 7 parts ofalloxan and 4 parts of alloxantin are dissolved in 240 parts of boiling-water, and the solution added to about 80 parts of eold, strong solution of carbonate of am- monia ; the liquid instantly acquires such a depth of color as to become opaque, and gives on cooling a large quantity of murexide; the operation succeeds best on a small scale. Murexide' crystallizes in small square prisms, which by reflected light exhibit a splendid green metallic lustre, like that of the wing-cases of the rose-beetle and other insects: by transmitted light they are deep purple-red. It is soluble with difficulty in cold water, much more easily at a boiling tem- perature, and is iusoluble in alcohol and ether. Mineral acids decompose it with separation of murexan, and caustic potassa dissolves it, with production of a most magnificent purple color, which disappears when the solution is boiled. Murexide contains, according to Liebig and AVohler, C12H6N508; its production may be thus explained: —4 eq. of uramile and 6 eq. of oxygen from the protoxide of mercury give rise to 2 eq. murexide, 1 eq. of alloxanic acid, and 4 eq. of water. 4C3H6N306 + 60 = 2(C12H6N508) + C8H2N208,2HO + 4HO. Or, on the other hand, 1 eq. of alloxan, 2 eq. of alloxantin, and 4 eq. of ammonia, yield 2 eq. of murexide and 14 eq. of water. C8H4N2O10 + 2C8H5N2O10 + 4NII3 = 2C12H6N508 + 14HO. Murexan: purpuric acid of Dr. Prout. — Liebig directs this substance to be prepared by dissolving murexidc in caustic potassa, heating the liquid until the color disappears, and then adding an excess of dilute sulphuric acid. It separates in colorless or sligb.tly-yellowish scales, nearly insoluble in cold water. In ammonia it dissolves, and the solution acquires a purple color by exposure to the air, the murexide being then reproduced. Murexan is said to contain C6H4N205. This substance and its relation to murexide require re-ex- amination. A series of substances closely related to the derivatives of uric acid will be noticed under the head of Caffeine (see page 490). Connected with uric acid by similarity of origin, but not otherwise, are two curious aud exceedingly rare substances called xanthic oxide and cystic oxide. 1 So called from tho Tyriun dye, said to havo been prepared from a species of murex, a shell- fish. 484 XANTHIC OXIDE. Xanthic oxide was discovered by Dr. Marcct; it occurs as an urinary cal- culus, of pale-brown color, foliated texture, and waxy lustre, and is extracted by boiling the pulverized stone in dilute caustic potassa and precipitating by carbonic acid. The xanthic oxide falls as a white precipitate, which, on dry- ing, becomes pale yellow, and resembles wax when rubbed. It is nearly in- soluble in water and dilute acids. Its characteristic property is to dissolve without evolution of gas in nitric acid, and to give on evaporation a deep- yellow residue, which becomes yellowish-red on the addition of ammonia or solution of potassa. Xanthic oxide gives on analysis C5H2N202. Cystic oxide.—Cystic oxide calculi, although very rare, are more frequently met with than those of the preceding substance; they have a pale color, a concentric structure, and often a waxy external crust. The powdered cal- culus dissolves in great part without effervescence in dilute acids and alka- lies, including ammonia; the ammoniacal solution deposits, by spontaneous evaporation, small but beautiful colorless crystals, which have the form of six-sided prisms and square tables. It forms a saline compound with hydro- chloric acid. Caustic alkalies disengage ammonia from this substance by con- tinued ebullition. Cystic oxide contains sulphur; it is composed of C6H6NS204. Uric acid is perfectly well characterized, even when in very small quantity, by its behavior with nitric acid. A small portion heated with a drop or two of nitric acid in a small porcelain capsule dissolves with copious effervescence. When this solution is cautiously evaporated nearly to dryness, and, after the addition of a little water, mixed with a slight excess of ammonia, the deep- red tint of murexide is immediately produced. Impure uric acid, in a remarkable state of decomposition, is now imported into this country, in large quantities, for use as a manure, under the name of guano or huano. It comes from the barren and uninhabited islets of the weitern coast of South America, and is the production of the countless birds that dwell undisturbed in those regions. The people of Peru have used it for ages. Guano usually appears as a pale-brown powder, sometimes with whit- ish specks; it has an extremely offensive odor, the strength of which, how- ever, varies very much. It is soluble in great part in water, and the solution is found to be extremely rich in oxalate of ammonia, the acid having been generated by a process of oxidation. Guano also contains a peculiar sub- stance called guanine, which closely corresponds with xanthic oxide. Like urea it combines with acids forming a series of crystallizable salts. Guanine contains C10H5N5O2. VEGETO-ALKALIS. 485 THE VEGETO-ALKALIS. The vegcto-alkalis, alkaloids, or organic bases, constitute a remarkable and most interesting group of bodies: they are met with in various plants, always in combination with an acid, which is in many cases of peculiar nature, not occurring elsewhere in the vegetable kingdom. They are, for the most part, sparingly soluble in water, but dissolve in hot alcohol, from which they often crystallize in a very beautiful manner on cooling. Several of them, however, are oily, volatile liquids. The taste of these substances, when in solution, is usually intensely bitter, and their action upon the animal economy exceed- ingly energetic. They all contain a considerable quantity of nitrogen, and are very complicated in constitution, having high combining numbers. This class of bodies is very numerous. The limits of this elementary work permit us to study only the more important members of this group. None of the organic bases occurring in plants have yet been formed by arti- ficial means; analogous substances have, however, been thus produced. Morphine, or morphia.—This is the chief active principle of opium; it is tho best and most characteristic type of the group, and the earliest known, dating back to the year 1804, when it was discovered by Sertiirner. r Opium, the inspissated juice of the poppy-capsule, is a very complicated substance, containing besides morphine a host of other alkaloids in very variable quantities, combined with sulphuric acid and an organic acid called meconic acid (see page 451). In addition to these, there are gummy, resinous, and coloring matters, caoutchouc, &c, besides mechanical impurities, as chopped leaves. The opium of Turkey is the most valuable, and contains the largest quantity of morphine; the opiums of Egypt and of India are con- siderably inferior. It has beeji produced in England of the finest quality, but at great cost. If ammonia be added to a clear, aqueous infusion of opium, a very abun- dant buff-colored or brownish-white precipitate falls, which consists princi- pally of morphine and narcotine, rendered insoluble by the withdrawal of the acid. The product is too impure, however, for use. The chief difficulty in the preparation of these substances is to get rid of the coloring matter, which adheres with great obstinacy, redissolving with the precipitates, and being again in part thrown down when the solutions are saturated with an alkali. The following method, which succeeds well upon a small scale, will serve to give the student some idea of a process very commonly pursued when it is desired to isolate at once an insoluble organic base, and the acid with which it is in combination: —A filtered solution of opium in tepid water is mixed with acetate of lead in excess; the precipitated meconate of lead is separated by a filter, and through the solution containing acetate of morphine, now freed to a considerable extent from color, a stream of sulphuretted hydro- gen is passed. The filtered and nearly-colorless liquid, from which the lead has been thus removed, may be warmed to expel the excess of gas, once more filtered, aud then mixed with a slight excess of caustic ammonia, which throws down the morphine and narcotine : these may be separated by boiling 486 VEGETO-ALKALIS. ether, in which the latter is soluble. The meconate of lead, well washed, suspended in water, and decomposed by sulphuretted hydrogen, yields solu- tion of meconic acid. Morphine and its salts are advantageously prepared, on the large scale, by the process of Dr. Gregory. A strong infusion of opium is mixed with a solution of chloride of calcium, free from iron ; meconate of lime, which is nearly insoluble, separates, while the hydrochloric acid is transferred to the alka- loids. By duly concentrating the filtered solution, the hydrochlorate of mor- phine may be made to crystallize, while the narcotine, and other bodies, are left behind. Bepeated recrystallization, and the.use of animal charcoal, then suffice to whiten and purify the salt, from which the base may be precipitated in a pure state by ammonia. Other processes have been proposed, as that of M. Thiboumery, which consists in adding hydrate of lime in excess to an infusion of opium, by which the meconic acid is rendered insoluble, while the morphine is taken up with ease by the alkaline earth. By exactly neutralizing the filtered solution with hydrochloric acid, the morphine is precipitated, but in a somewhat colored state. Morphine, when crystallized from alcohol, forms small but very brilliant prismatic crystals, which are transparent and colorless. It requires at least 1000 parts of water for solution, tastes slightly bitter, and has an alkaline reaction. These effects are much more evident in the alcoholic solution. It dissolves in about 30 parts of boiling alcohol, and with great facility in dilute acids; it is also dissolved by excess of caustic potassa or soda, but scarcely by excess of ammonia. When heated in the air, morphine melts, inflames like a resin, and leaves a small quantity of charcoal, which easily burns away. Morphine in powder strikes a deep-bluish color with neutral salts of ses- quioxide of iron, decomposes iodic acid with liberation of iodine, and forms a deep-yellow or red compound with nitric acid : these reactions are by some considered characteristic. Crystallized morphine contains C^IIjgNOg + 2HO. The most characteristic and best-defined salt of this substance is the hydro- chlorate. It crystallizes in slender, colorless needles, arranged in tufts or stellated groups, soluble in about 20 parts of cold water, and in its own weight at a boiling temperature. The crystals contain 6 eq. of water. The sulphate, nitrate, and phosphate are crystallizable salts ; the acetate crystallizes with great difficulty, and is usually sold in the state of a dry powder. The artificial meconate is sometimes prepared for medicinal use. Narcotine.—The marc, or insoluble portion of opium, contains much nar- cotine, which may be extracted by boiling with dilute acetic acid. From the filtered solution the narcotine is precipitated by ammonia, and afterwards purified by solution in boiling alcohol, and filtration through animal charcoal. Narcotine crystallizes in small, colorless brilliant prisms, which are nearly insoluble in water. The basic powers of narcotine are very feeble ; it is desti- tute of alkaline reaction, and, although freely soluble in acids, refuses, for the most part, to form with them crystallizable compounds. According to Dr. Blyth narcotine contains C4SH25NO]4. Narcotine yields some curious products by the action of oxidizing agents, as a mixture of dilute sulphuric acid and binoxide of manganese, or a hot solution of bichloride of platinum. They have been chiefly studied by AVohler and Blyth, and lately also by Anderson. The most important of these is opianic acid, a substance forming colorless, prismatic, reticulated crystals, sparingly soluble in cold water, easily in hot. It melts when heated, but does not sublime. After fusion it becomes quite insoluble in dilute alkali.es, but without change of composition. This acid forms crystallizable salts and an ether; it contains CgoHgO^HO. The ammonia-salt, by evaporation to dryness, yields a nearly-white insoluble powder, called opiammon, containing C H NO » convertible by strong acids into opianic acid and ammonia. Sulphurous acid VEGETO-ALKALIS. 487 yields with opianic acid two products containing sulphur. A mixture of binoxide of lead, opianic acid, and sulphuric acid, gives rise to a crystallizable bibasic acid termed hemipinic acid, containing C20H8O10,2HO. A basic sub- stance, cotarnine C_,6H13N06, is contained in the mother-liquor from which opianic acid has crystallized; it forms a yellow crystalline mass, very soluble, of bitter taste, and feebly-alkaline reaction. Its hydrochlorate is a well-de- fined salt. Another basic substance, narcogenine, was accidentally produced in an attempt to prepare cotarnine by bichloride of platinum. It formed long orange-colored needles, and contained Cj^H^NO^. Codeine.—Hydrochlorate of morphine, prepared directly from opium as in Gregory's process, contains codeine-salt. When dissolved in water, and mixed with a slight excess of ammonia, the morphine is precipitated, and the codeine left in solution. Pure codeine crystallizes, by spontaneous evapora- tion, in colorless transparent octahedra ; it is soluble in 80 parts of cold, and 17 of boiling water, has a strongly-alkaline reaction, and forms crystallizable salts. Codeine is composed of C36H2IN06; it is homologous to morphine. This base has lately been the subject of a careful investigation by Dr. Anderson, who has prepared a great number of its derivatives, all of which establish the formula given. Thebaine or paramorphine. — This substance is contained in the precipi- tate formed by hydrate of lime in a strong infusion of opium in Thiboumery's process for morphine. The precipitate is well washed, dissolved in dilute acid, and mixed with ammonia in excess, and the thebaine thrown down crystallized from alcohol. It forms when pure colorless needles like those of narcotine, but sparingly soluble in water, readily soluble in the cold in alco- hol and ether. It melts when heated, and decomposes at a high temperature. With dilute acid it forms crystallizable compounds, and when isolated and in solution has a powerfully-alkaline reaction. The composition of thebaine is C38HnN06. A series of other bases, papaverine, pseudo-morphine, narceine, meconine, opi- anine, andphorphyroxine, are also, at least, occasionally, contained in opium; they are of small importance, and comparatively little is known respecting them. Papaverine contains C40H2,NO8. A considerable number of deriva- tives of papaverine have been prepared which confirm this formula. Cinchonine (Cinchonia) and Quinine (Quinia).— It is to these vegeto- alkalis that the valuable medicinal properties of the Peruvian barks are due. They are associated in the bark with sulphuric acid, and with a special acid, not found elsewhere, called the kinic. Cinchonine is contained in largest quantity in the pale bark, or Cinchona condaminea; quinine in the yellow bark, or Cinchona cordifolia; the Cinchona oblongifolia contains both. The simplest, but not the most economical, method of preparing these sub- stances, is to add a slight excess of hydrate of lime to a strong decoction of the ground bark, in acidulated water; to wash the precipitate which ensues, and boil it in alcohol. The solution, filtered while hot, deposits the vegeto- alkali on cooling. AVhen both bases are present, they may be separated by converting them into sulphates; the salt of quinine is the least soluble of the two, and crystallizes first. Pure cinchonine, or cinchonia, crystallizes in small, but beautifully brilliant, transparent, four-sided prisms. It is but very feebly soluble in water, dis- solves readily in boiling alcohol, and has but little taste, although its salts are excessively bitter. It is a powerful base, neutralizing acids completely, and forming a series of crystallizable salts. Cinchonine turns the plane of polari- zation to the right. Qunine, or quinia, much resembles cinchonine; it does not crystallize so well, however, and is much more soluble in water; its taste is intensely bitter. Quinine turns the plane of polarization towards the left. 488 VEGETO-ALKALIS. Cinchonine is composed of . . . . C^H^N^, and Quinine of.......C40H24N2O4. Sulphate of quinine is manufactured on a very large scale for medicinal use; it crystallizes in small white needles, which give a neutral solution. This substance contains C<0Ha4N2O4,HO,SO9 + 7HO. The solubility of this com- pound is much increased by the addition of a little sulphuric acid, whereby the acid salt C40H24N2O4,HO,SO3HO,SO3 -f-14HO is formed. A very interesting compound has been produced by Dr. Herapath, by the action of iodine upon the sulphate of quinine. It is a crystalline substance of a brilliant emerald color, which appears to consist of equal equivalents of the sulphate of quinine and of iodine. This remarkable compound possesses the optical properties of the mineral tourmaline. (See page 88). Quinidine (Quinidia). — In manufacturing sulphate of quinine, a new base has been obtained, which differs from quinine, in some of its physical properties, but is said to have the same composition as quinine. It has been described under the name of quinidine, and appears to have the same medicinal proper- ties as quinine. This substance has lately been carefully examined by M. Pasteur, and his researches have led to the following interesting results. The substance which is found in commerce under the name of quinidine is generally a mixture of two alkaloids, of which the one is isomeric with qui- nine, and the other isomeric with cinchonine. M. Pasteur designates these two substances respectively as quinidine and cinchonidine. They differ from quinine and cinchonine in several minor properties, but particularly in their deportment with polarized light, for while quinine turns the plane of polari- zation considerably towards the left, quinidine exerts a powerful action to- wards the right, Again, while cinchonine deflects considerably towards the right, the action of the isomeric cinchonidine is in the opposite direction, namely, towards the left. It is evident that quinine and quinidine on the one hand, and cinchonidine and cinchonine on the other, stand to each other in about the same relation as levo-and dextro-racemic acids (see page 451). Nor are the terms wanting which correspond to racemic acid itself. M. Pas- teur has in fact proved, that both quinine and quinidine, and likewise cincho- nine and cinchonidine, are peculiarly modified by the action of heat; exposed for several hours to a temperature varying between 248° and 266° (120° and 130°C), quinine and quinidine are converted into a third isomeric alkaloid, which M. Pasteur terms quinicine, while cinchonine and cinchonidine furnish an isomeric cinchonicine under the same circumstances. In racemic acid the right-handed action of dextro-racemic, and the left-handed action of levo- racemic acid, are exactly balanced, racemic acid possessing no longer any action upon polarized light: in the two new products, in quinicine and cincho- nicine, such a perfect balance is not observed, both still exert a feeble right- handed action, which is, however, very slight when compared with the powers of the alkaloids, which give rise to them. The following table exhibits the relations of the six alkaloids, and their analogy with the racemic group, in a more conspicuous manner : — Quinine Quinicine Quinidine Left-handed, Right-handed, Right-handed, powerfully. feebly. very powerfully. Cinchonine Cinchonicine Cinchonidine Right-handed, Right-handed, Left-handed, very powerfully. feebly. powerfully. Dextro-racemic Bacemic acid Levo-racemic (tartaric) acid neutral. acid Right-handed. Left-handed. VEGETO-ALKALIS. 489 Chinoidine, quinoidine, or amorphous quinine, is contained in the refuse, or mother-liquors of the quinine manufacture. In its purest state it forms a yellow or brown resin-like mass, insoluble in water, freely soluble in alcohol and ether. It is easily soluble also in dilute acids, and is thence precipitated by ammonia. Quinoidine possesses powerful febrifuge properties, and is identical in composition with quinine. It evidently bears the quinine the same relation that uncrystallizable syrup does to ordinary sugar, being pro- duced from quinine by the heat employed in the preparation. From Cusco- or Arika-bark, and likewise from the Cinchona ovata, or white quinquina of Condamine, a substance denominated aricine, or cinchovatine, has been extracted; it closely resembles cinchonine, and contains C^H^NOg. If this formula be doubled, it exhibits a close analogy with the formula? of cinchonine and quinine, differing, in fact, from the latter only by containing two more equivalents of oxygen. This substance is useless in medicine. Strychnine and brucine, also called strychina and brucia, are contained in Nux vomica, in St. Ignatius' bean, and in false Auguslura bark; they aro associated with a peculiar acid, called the igasuric. Nux-vomica seeds are boiled in dilute sulphuric acid until they become soft; they are then crushed, and the expressed liquid mixed with excess of hydrate of lime, which throws down the alkaloids. The precipitate is boiled in spirit of wine of sp. gr. 0-850, and filtered hot. Strychnine and brucine are deposited together in a colored and impure state, and may be separated by cold alcohol, in which the latter dissolves readily. Pure strychnine crystallizes under favorable circumstances in small but exceetlingly brilliant octahedral crystals, which are transparent and colorless. It has a very bitter, somewhat metallic taste (1 part in 1,000,000 parts of water is still perceptible), is slightly soluble in water, and is fearfully poison- ous. It dissolves in hot, and somewhat dilute spirit, but neither in absolute alcohol, ether, nor in solution of caustic alkali. This alkaloid may be readily identified by moistening a crystal with concentrated sulphuric acid, and adding to the liquid a crystal of bichromate of potassa, when a deep violet tint is produced, which disappears after some time. Strychnine forms with acids a series of well-defined salts, which were examined by Messrs. Nicholson and Abel, who established for strychnine the formula, C42H22N204. Brucine is easily distinguished from the preceding substance, which it much resembles in many respects, by its ready solubility in alcohol, both hydrate and absolute. It dissolves also in about 500 parts of hot water. The salts of brucine are, for the most part, crystallizable. Brucine contains C^H^NjOg. Veratiune or veratria is obtained from the seeds of Veratrum sabadilla. In its pure state it is a white or yellowish-white powder, which has a sharp burning taste, and is very poisonous. It is remarkable for occasioning violent sneezing. It is insoluble in water, but dissolves in hot alcohol, in ether, and in acids; the solution has an alkaline reaction. Veratrine contains C^HsjjNjjCk1 A substance called colchicine, extracted from the Colchicum autumnale, and formerly confounded with veratrine, is now considered distinct; its history is yet imperfect. Harmaline.—This compound is extracted by dilute acetic acid from the seeds of the Peganum harmala, a plant which grows abundantly in the Step- pes of Southern Bussia, and the seeds of which are used in dyeing. AVhen pure, it forms yellowish prismatic crystals, soluble in alcohol and dilute acids, but scarcely forming crystallizable salts. By oxidation it gives rise to another 1 [Several of these bases may be distinguished by nitric acid. Brucia becomes bright red, which is soon changed to purple by chloride of tin. Pure strychnine becomes yellow. Veratria, orange red, soou changing to yellow. Morphia, bright red, changed to yellow by chloride of Un.—R. B.l 490 VEGETO-ALKALIS. compound, harmine, which itself possesses basic properties. The seeds are used for dyeing. Harmaline contains C26Hl4N202, and harmine C26H)2\202. Caffeine or theine.—This remarkable substance occurs in four articles of domestic' life, infusions of which are used as beverages over the greater part of the known world, namely, tea and coffee, and in the leaves of Gua- rana officinalis, or Paullinia sorbilis, and in those of Ilex paraguayensis ; it will probably be found in other plants. A decoction of common tea, or of raw coffee-berries, previously crushed, is mixed with excess of solution of basic acetate of lead. The solution, filtered from the copious yellow or greenish precipitate, is treated with sulphuretted hydrogen to remove the lead, filtered, evaporated to a small bulk, and neutralized by ammonia. The caffeine crys- tallizes out on cooling, and is easily purified by animal charcoal. It forms tufts of delicate, white, silky needles, which have a bitter taste, melt when heated with loss of water, and sublime without decomposition. It is soluble in about 100 parts of cold water, and much more easily at a boiling heat, or if an acid be present. Alcohol also dissolves it, but not easily. Caffeine contains Cl6HI0N4O4. The basic properties are feeble. The salts with hydro- chloric and sulphuric acid are obtained only with difficulty. It forms, how- ever, splendid double-salts with bichloride of platinum and terchloride of gold. The products of oxidation of caffeine, which have been lately studied by Bochleder, are of considerable interest, inasmuch as both their composi- tion and their properties establish a close connection of these products with the derivatives of uric acid. Under the influence of chlorine, caffeine yields a substance of feebly-acid properties, which contains C,2H7N208. This com- pound, which has received the name amalic acid, is homologous to alloxantin. When treated with oxidizing agents, it yields choleslrophane, C10H6N2O6, cor- responding to parabanic acid of the uric-acid series. The murexide of the caffeine series lastly is formed by the treatment of amalic acid with ammonia, exactly as the murexide par excellence is formed by the action of ammonia upon alloxantin. The new murexide imitates its prototype, not only in com- position, but likewise- in the green metallic lustre of its crystals, and the deep- crimson color of its solutions. The homology of these compounds with the members of the uric-acid series is well illustrated by a comparison of their formulae: — Alloxantin . . C8H3N208 + 2C2H2 = C,2H7N208 Amalic acid. Parabanic acid . C6H2N2064-2C2H2 = Cl0H6N2O6 Cholestrophane. Murexide . . C12H6N5084- 3C2H2 = C^H^NjOg Caffeine-murexide. Theobromine. — The seeds of the Theobroma cacao, or cacao-nuts, from which chocolate is prepared, contain a crystallizable principle to which the preceding name is given. It is extracted in the same manner as caffeine, and forms a white, crystalline powder, which is much less soluble than the last- named substance. It contains, according to Glasson, C14H8N404. Accordingly it is homologous to caffeine. The products obtained from theobromine by oxidation appear to be likewise homologous with several terms of the uric- acid series. Berberine. — A substance crystallizing in fine yellow needles, slightly soluble in water, extracted from the root of the Berberis vulgaris. It? has feeble basic properties, and contains C42H19NO10. This must not be con- founded with bebeerine, an uncrystallizable basic substance, from the bark of the green-heart timber of Guiana, which has the composition CggH^NOg. Piperine.—A colorless, or slightly-yellow crystallizable principle, extracted from pepper by the aid of alcohol. It is insoluble in water. Formula C68H38N2°i2- Piperine readily dissolves in acid; definite compounds, how- ever, are obtained only with difficulty. Conine (conicine, or conia), nicotine, and sparteine differ from the VEGETO-ALKALIS. 491 other vegetable bases in physical characters; they are volatile oily liquids. The first is extracted from hemlock, the second from tobacco, and the third from broom (Spartium scoparium). They agree in most of their characters, having high-boiling points, very poisonous properties, strong alkaline reac- tion, and the power of forming with acids crystallizable salts. The formula of nicotine is C10H7N; that of conine, C18H]3N; and that of sparteine C|6HI3.\. A series of substances as it appears closely related to nicotine will be mentioned among the artificial organic bases. Closely allied to conine is conydrine, C)6H17N02, a crystalline base, lately extracted by AVcrtheim from hemlock. AVhen distilled with anhydrous phos- phoric acid, it splits into conine and 2 eq. of water. The basic substance obtained from the juice of animal flesh, creatinine, will be found described among the components of the animal body. There are very many other bodies, more or less perfectly known, having to a certain extent the properties of salt-bases; the following statement of the names and modes of occurrence of a few of these must suffice. Hyoscyamine (Daturine.) — A white, crystallizable substance, fromllyoscya- mus niger : it occurs likewise in Datura stramonium. Atropine.—Colorless needles, from Atropa belladonna; formula C^H^NOg.1 Solanine.—A pearly crystalline substance, from various solanaceous plants ; formula C42H35N014. (?) Aconitine. —A glassy, transparent, mass, from Aconitum napellus; formula L60n47->WI4- Delphinine. — A yellowish, fusible substance, from the seeds of Delphinium staphisagria. Emetine.—A white and nearly tasteless powder from ipecacuanha root. Curarine. — The arrow-poison of Central America. There exists an extensive series of neutral, usually bitter, and sometimes poisonous vegetable principles, which are allied in some measure to the vege- table alkalis. Some of these are destitute of nitrogen. Three of the number, salicin, phloridzin, and populin, have been already described (see pages 442 and 444); the most important of the remainder are the following: — Gentianin. — The bitter principle of the gentian root, extracted by ether.- It crystallizes in golden-yellow needles, is sparingly soluble in cold water, more soluble in hot water, and freely dissolved by alcohol and ether. Its composition is C,4H506. (?) Daphnin.—Extracted from the bark of the Daphne mezereum ; it forms color- less, radiated needles, freely soluble in hot water, alcohol, and ether. Hksperiimn.—A white, silky, tasteless substance, obtained from the spongy part of oranges and lemons. It dissolves in 60 parts of hot water: also in alcohol and ether. Elaterin. — The active principle of Mormodica elaterium. It is a white, silky, crystalline powder, insoluble in water. It has a bitter taste, and ex- cessively violent purgative properties. Alcohol, ether, and oils dissolve it. Exposed to heat, it melts and afterwards volatilizes. It contains C20H14O6. Antiarin.—The poisonous principle of the Upas antiar. It forms small pearly crystals, soluble in 27 parts of boiling water, and also in alcohol, but scarcely so in ether; it cannot be sublimed without decomposition. Iutro- * [Crystallizes from a saturated hot aqueous solution in silky tufts; colorless, inodorous, very bitter, soluble in 25 parts of ether, 2000 parts cold and 54 of hot water. Has a strong alkaline reaction, and forms crystallizable salts. It is probably identical with daturine.—It. B.] 8 [Crystallises from an alcoholic solution in small grains; soluble readily in alcohol and ether, and also in 100 parts cold and 50 boiling water; has a sharp, bitter taste, and alkaline reaction. Its salts are not crystallizable.—K. B.] 492 ORGANIC BASES OF ARTIFICIAL ORIGIN. duced into a wound it rapidly brings on vomiting, convulsions, and death. Antiarin contains C14H10O6. Piceotoxin.__It is to this substance that Cocculus indicus owes its active properties. Picrotoxin forms small, colorless, stellated needles, of inexpres- sibly bitter taste, which dissolve in 25 parts of boiling alcohol. It contains C10H6O4. _ _ Santonin. — This substance is the crystalline principle of several varieties of Artemisia. In order to obtain it, the seeds are crushed, and digested with lime and spirit of wine, when a yellow liquid is obtained, from which the alcohol is separated by distillation. The residuary liquid is saturated with acetic acid, when the santonin crystallizes. The substance is easily soluble in water and alcohol, and contains CjoH^Oe- Santonin possesses the character of a weak acid. Asparagin.—This and the following are azotized bodies. Asparagin is found in the root of the marsh-mallow, in asparagus sprouts, and in several other plants. The mallow-roots are chopped small, and macerated in the cold with milk of lime; the filtered liquid is precipitated by carbonate of ammo- nia, and the clear solution evaporated in a water-bath to a syrupy state. The impure asparagin, which separates after a few days, is purified by recrystalli- zation. Asparagin forms brilliant, transparent, colorless crystals, which have a faint, cooling taste, and are freely soluble in water, especially when hot. When dissolved in a saccharine liquid, which is afterwards made to ferment, when heated with water under pressure in a close vessel, or when boiled with an acid or an alkali, it is converted into ammonia and a new acid, the aspar- tic. Asparagin contains C8H8N206, and aspartic acid C8H7NOg. The re- markable relation in which these substances stand to malic acid has been already noticed under the head of malic acid (see page 453). ORGANIC BASES OF ARTIFICIAL ORIGIN. The constitution of the alkaloids, which occur ready formed in nature, is not yet clearly understood. The fact that all these substances contain nitro- gen, — the alkaline reaction, which the greater part of them exhibits with vegetable colors, and especially their faculty of combining with acids to crystallizable salts, establish an obvious relation between the alkaloids and ammonia. This has never been doubted, and the views of chemists have been divided only as to the nature of this relation. At a certain time Berze- lius assumed that all the alkaloids contained ammonia ready formed, and that their basic properties were due to this ammonia. According to this view the formulae of quinine and morphine would be — Quinine.....C40H24N2O4 = C40H21NO4,NH3. Morphine.....C34H19N06 = C34H,606,NH3. This view, in the general form in which it was proposed, is certainly inad- missible. It is supported by very scanty experimental evidence, and was never universally adopted. There may be some alkaloids so constituted as to be represented by the theory of Berzelius. There are, however, a great many, the constitution of which is obviously different. Several of these sub- stances have been lately the subject of extensive and careful inquiries • but these researches, although they have established their formulae, and increased our knowledge regarding their salts, have as yet elicited but few facts which promise to afford a clearer insight into the nature of these bodies. On the other hand, the labors of the last twelve years have brought to light a very numerous group of substances perfectly analogous to the alkaloids which are found in plants, but produced by artificial processes in the labora- ORGANIC BASES OF ARTIFICIAL ORIGIN. 493 tory. These bodies, which are termed artificial alkaloids or artificial organic bases, are mostly volatile. Their constitution is much simpler than that of the native bases. The very processes which give rise to their formation often permit a very clear insight into the mode in which the elements are grouped, and in the relation existing between these substances and ammonia. In a former section of this volume (page 251), it has been stated that the majority of chemists are inclined to assume in the ammoniacal salts the ex- istence of a compound metal ammonium NH4, Chloride of ammonium. ..... NH4Ci Sulphate of ammonia......NH40,S03. Now, recent researches have shown, that in these salts, 1,2, 3, or even the 4 eq. of hydrogen may be replaced by compound radicals, containing variable proportions of carbon and hydrogen, without any change in the fundamental properties of these salts. It is evident that we obtain in this manner, in addition to the ammoniacal salts, four new series of compounds very closely allied to the former. Let A B C D represent radicals capable of replacing hydrogen, then the following series of salts may be formed: — Ammonium salts. . . N< „ >C1 . . . N < tt VO,S03 Ih] UJ First group of compound \ N J II ( p, tj J H I n bU3 Second group of compound 1 „ I B I ™ w J ^ I o en ammonium-salts . . / M II fU ' * " M H >°'bU3 Third group of compound \ N J B I p) NrJBlnQn ammonium-salts . . / M C fU • ' ' N "A C >0>b03 Fourth group of compound \ N J B I n nJBIo0,bOa It need scarcely be mentioned that it is by no means necessary that the several hydrogen-equivalents in ammonium should be replaced by different radicals, as assumed in the preceding table. Substances of the formulae — are even more easily prepared and more frequently met with. This synopsis sljpows that the number of salts capable of being derived from the ordinary ammoniacal salts must be very considerable. Even now a very extensive series has been prepared, although the number of radicals at our disposal at present is still comparatively limited. It has been mentioned that all attempts at isolating both ammonium and 42 494 ORGANIC BASES OF ARTIFICIAL ORIGIN. its oxide have hitherto failed (see page 251). On treating chloride of ammo- nium or sulphate of ammonia with mineral oxides, such as potassa, lime, and baryta, decomposition ensues, chloride of potassium or sulphate of potassa, &c, is formed, and the separated oxide of ammonium splits into ammonia gas and water, NH40 = NH3+HO. The compound ammonium-salts are likewise decomposed by mineral oxides. AVith the first three classes the change is perfectly analogous to that of ammo- niacal salts, the separated oxide is decomposed into water and a volatile base, the properties of which, according to the nature of the replacing radicals, are more or less closely approximated to those of ammonia itself. AVe arrive in this manner at three groups of organic bases, differing from one another by the amount of hydrogen which is replaced; they have been distinguished by the terms Primary Amines (Amidogen bases), Secondary Amines (Imidogen bases), and Tertiary Amines (Nitrile bases). Ammonia. The last group of ammoniacal salts, in which the 4 eq. of hydrogen are replaced by radicals, differ in their deportment from the former classes. These salts are not decomposed by potassa, but yield, by appropriate treat- ment, a series of substances of a very powerfully-alkaline character which are expressed by the general formulas:— 0, HO, and are evidently analogous to hydrated oxide of ammonium ; from which they differ, however, in a remarkable manner, by their great stability. These general statements will become more intelligible if we elucidate them by the description of several individual substances: the limits of this work compel us, however, to confine ourselves to the more important members of this already very numerous group, which is, moreover, daily increasing. It may at once be stated that by far the greater number of these compounds are derived from the alcohols or substances analogous to them; and that the radicals which in the preceding sketch have been designated by the letters A, B, C, and D, are chiefly the hydrocarbons previously described under the names ethyl, methyl, and amyl. BASES OF THE ETHTL-SERIES. Etiiylamine, Ethyl-ammonia, C4H7N = N(H2,C4H5) = N(H2Ae).—On di- gesting bromide or iodide of ethyl (see page 372) with an alcoholic solution of ammonia, the alkaline reaction of the ammonia gradually disappears. On evaporating the solution on the water-bath, a white crystalline mass is ob- tained, which consists chiefly of bromide of ethyl-ammonium, Ael 4- NH = N(H3Ae)I. On distilling this salt in a retort provided with a'good condenser with caustic lime, the ethylamine is liberated and distils o^er. N(H3Ae)I + KO = N(H2Ae) + HO -f- KI. Another method of preparing this compound, and indeed the method by ORGANIC BASES OF ARTIFICIAL ORIGIN. 495 which this remarkable substance was first obtained by M. AVurtz, consists in submitting cyanate of ethyl to the action of hydrate of potassa. In describing cyanic acid (see page 466), the interesting change has been mentioned, which this substance undergoes when treated with boiling solution of potassa. In this case cyanic acid splits into 2 eq. of carbonic acid and 1 eq. of ammonia; cyanate of ethyl (see page 408) suffers a perfectly-analogous decomposition, and instead of ammonia we obtain ethylamine. CgNO,HO + 2(KO,HO) = 2(KO,C02) + NH3 Hydrated Ammonia. cyanic acid. C2NO,AeO -f 2(KO,HO) = 2(KO,C02) + N(H2Ae) Cyanate of Ethylamine. ethyl. Cyanurate of ethyl, isomeric with the cyanate, likewise furnishes ethylamine. Ethylamine is a very mobile liquid, of 0-6964 sp. gr., at 46°-4 (8°C), which boils at 64°-4 (18°C). The sp. gr. of the vapor is 1-57. It has a most pow- erfully-ammoniacal odor, and restores the blue color to reddened litmus paper. It produces white clouds with hydrochloric acid, and is absorbed by water with great avidity. AVith the acids it forms a series of neutral crystallizable salts perfectly analogous to those of ammonium. This substance imitates, moreover, in a remarkable manner, the deportment of ammonia with metallic salts. It precipitates the salts of magnesia, alumina, iron, manganese, bismuth, chromium, uranium, tin, lead, and mercury. Zinc salts yield a white precipitate which is soluble in excess. Like ammonia, ethylamine dissolves chloride of silver, and yields with copper salts a blue precipitate, which is soluble in an excess of ethylamine. On adding ethyla- mine to oxalic ether, a white precipitate of ethyl-oxamide, N(HAe),C202, is produced: even a.compound analogous to oxamic acid (see page 362) has been obtained. Ethylamine may, however, be readily distinguished from am- monia; its vapor is inflammable, and it produces, with bichloride of platinum, a salt N(H3Ae)Cl,PtCl2, crystallizing in golden scales, which are rather soluble in water. If ethylamine be treated with chlorine, it furnishes chloride of ethyl-ammonium and a yellow liquid of a penetrating odor, exciting tears, which contains NCl2Ae. This substance is bichlorethylamine. AVhen treated with potassa it is converted into ammonia, acetate of potassa, and chloride of potassium, NCI.2.C4H5 + 3KO -f HO = KO,C4H303 -4- NH3 -f 2KC1. Ethylamine-urea.—On passing into a solution of ethylamine, the vapor of hydrated cyanic acid, the liquid becomes hot and deposits, after evaporation fine crystals of cthylamine-urea. C4H7N -f C2NO,HO = C6H8N202 = C2(H3' C4H5)N202 = C2(H3Ae)N202. This substance, which may be viewed as ordil nary urea (see page 467), in which 1 eq. of hydrogen is replaced by ethyl, may be prepared also by treating cyanic ether with ammonia, C4H50,C2NO -j- NH3 = C6H8N202. Ethylamine-urea is very soluble in water and alcohol: the concentrated aqueous solution, unlike that of ordinary urea, yields no preci- pitate with nitric acid; but on gently evaporating the mixture, a very soluble crystalline nitrate of ethylamine-urea is obtained. Boiled with potassa, this substance yields a mixture of equal equivalents of ammonia and ethylamine C2(H3Ae)N202 + 2(KO,HO) = 2(KO,C02) + NH3 + N(H2Ae). Bietiiylamine, Biethyl-ammonia, C8HnN = MH,2C4H5 =• N(HAe2). — A mixture of solution of ethylamine and bromide of ethyl, heated in a sealed tube for several hours, solidifies to a crystalline mass of bromide of biethyl- ammonium, N(HaAe) + AeBr = N(H2Ae2)Br. The bromide, when distilled 496 ORGANIC BASES OF ARTIFICIAL ORIGIN. with potassa, furnishes a colorless liquid, still very alkaline, and soluble in water, but less so than ethylamine. This compound boils at 133° (55°C). It forms beautifully-crystallizable salts with acids. A solution of chloride of biethyl-ammonium furnishes, with bichloride of platinum, a very soluble double salt, N(H2Ae2)Cl,PtCl2, crystallizing in orange-red grains, very differ- ent from the orange-yellow leaves of the corresponding ethyl-ammonium-salt. Biethylamine-urea.—Biethylamine probably behaves with cyanic acid like ammonia and ethylamine, giving rise to biethylamine-urea. This substance has been produced by the action of cyanic ether upon ethylamine, C4H50, C2NO -f C4H7N = C10H12N2O2 = C2(H22C4H6)N202 == C2(H2Ae2)N202. Bi- ethylamine-urea is very crystallizable, and readily forms a crystalline nitrate. Boiled with potassa, biethylamine-urea yields pure ethylamine, C2(H2Ae2)N20_> + 2(KO,HO) = 2(KO,C02) -f 2N(H2Ae). Triethylamine, Triethyl-ammonia, CI2HI5N = N 3(C4H6) = NAe3.—The formation of this body is perfectly analogous to those of ethylamine and bi- ethylamine. On heating for a short time a mixture of biethylamine with bro- mide of ethyl in a sealed glass tube, a beautiful fibrous mass of bromide of triethyl-ammonium is obtained, from which the triethylamine is separated by potassa. Triethylamine is a colorless, powerfully-alkaline liquid, boiling at 195°-8 (91°C). The salts of this base crystallize remarkably well. AVith bi- chloride of platinum it forms a verj' soluble double salt, N(HAe3)Cl,PtCl2, which crystallizes in magnificent large orange-red rhombs. Hydrated Oxide of Tetrethyl-ammonium, C,6H21N02 = N 4(C4H5)0,HO = NAe40,HO.—AVhen anhydrous triethylamine is mixed with dry iodide of ethyl, a powerful reaction ensues, the mixture enters into ebullition, and solidifies on cooling to a white crystalline mass of iodide of tetrethyl-ammonium, NAe3 -f- Ael = NAe4I. The new iodide is readily soluble in hot water, from which it crystallizes on cooling in beautiful crystals of considerable size. This sub- stance is not decomposed by potassa; it maybe boiled with the alkali for hours without yielding a trace of volatile base. The iodine may, however, be readily removed by treating the solution with silver-salts. If in this case sul- phate or nitrate of silver be employed, we obtain, together with iodide of silver, the sulphate or nitrate of oxide of tetrethyl-ammonium, which crystal- lize on evaporation; on the other hand, if the iodide be treated with freshly- precipitated protoxide of silver, the oxide of tetrethyl-ammonium itself is sepa- rated. On filtering off the silver-precipitate, a clear colorless liquid is obtained, which contains the isolated base in solution. It is of a strongly- alkaline reaction, and has an intensely-bitter taste. Solution of oxide of tetrethyl-ammonium has a remarkable analogy to potassa and soda. Like the latter substance, it destroys the epidermis and saponifies fatty substances with the formation of true soaps. AVith the salts of the metals, this substance ex- hibits exactly the same reactions as potassa. On evaporating a solution of the base in vacuo, long slender needles are deposited, which are evidently the hydrate of the base, with an additional amount of water of crystallization. After some time these needles disappear again, and a semi-solid mass is left which is the hydrate of oxide of tetrethyl-ammonium. A concentrated solution of this substance in water may be boiled without decomposition, but on heat- ing the dry substance, it is decomposed into pure triethylamine and olefiant gas: NAe40,HO = 2HO + NAe3 -f C4H4. Oxide of tetrethyl-ammonium forms neutral salts with the acids. They are mostly very soluble; several yield beautiful crystals. The platinum-salt NAe4Cl,PtCl2. forms orange-yellow octahedra, which are of about the same solubility as the corresponding bichloride of platinum and potassium. Oxide of tetrethyl-ammonium is obviously perfectly analogous to the hitherto Hypothetical oxide of ammonium. It is a compound of remarkable ORGANIC BASES OF ARTIFICIAL ORIGIN. 497 stability, the existence and properties of which must be regarded as powerful supports of the ammonium-theory. bases of the methyl series. Methylamine. Methyl-ammonia, C2H6N = N(H2,C2rT3) = N(II2Me).— The formation and the method of preparing this compound from the cyanate of methyl are perfectly analogous to those of ethylamine (see page 495): how- ever, methylaminc being a gas at the common temperature, it is necessary to cool the receiver by a freezing mixture. The distillate, which is an aqueous Rolution of methylaminc, is saturated with hydrochloric acid, and evaporated to dryness. The crystalline residue, which is the chloride of methyl-ammo- nium, when distilled with dry lime, yields methylamine gas, which, like am- monia gas, has to be collected over mercury. It is distinguished from ammo- nia by a slightly-fishy odor, and by the facility with which it burns. Methyl- amine is liquefied at about 0°(17°-8C); its sp. gr. is 108. This substance is the most soluble of all gases at 53°-6 (12°C); 1 volume of water absorbs 1040 volumes of gas. It is likewise very readily absorbed by charcoal. In its chemical deportment with acids and other substances, methylamine resem- bles in every respect ammonia and ethylamine. Methylamine appears to be produced in a great number of processes of destructive distillation ; it has been formed by distilling several of the natural organic bases, such as codeine, morphine, caffeine, and several others, with caustic potassa; frequently a mixture of several bases is produced in this manner. Among the numerous derivatives already obtained with this substance, me- thylamine-urea, C2(H3Me)N202, and bimethylamine-urea, C2(H2Me2)N202, and even a methyl-ethylamine-urea, C2(ll2MeAe)N202, may be quoted. The latter substance has been produced by the action of cyanate of ethyl upon methyla- mine. Kven a scries of platinum-bases, analogous to those produced by the act'nm of ammonia upon protochloride of platinum (see page 326), has been obtained with methylamine. Bimkthylamine, C4H7N = N(H2C2II3) =• N(HMe2) is not easily prepared in a pure state by the action of ammonia or iodide of methyl. It has been, however, obtained by the destructive distillation of the compound of aldehyde with alkaline sulphites. Trimethylamine, Trimethyl-ammonia, C6H9 = N 3(C2H3) =. NMe3.—This substance is readily obtained, in a state of perfect purity, by submitting oxide of tetramethyl-ammonium (see the following compound) to the action of heat. It is gaseous at the common temperature, but liquefies at about 48°-2 (9°C) to a mobile fluid of very powerfully-alkaline reaction. Trimethylamine pro- duces with acids very soluble salts. The platinum-salt, N(IIMe3)Cl,PtCl2. is likewise very soluble and crystallizes in splendid orange-red octahedra. Ac- cording to Mr. Winkles, large quantities of trimethylamine are found in the liquor in which salt herrings are preserved. Hydrated oxide op tetkamktiiyl-ammonii-m, C8Hl3N02 = N 4|'C2H3),(), 110= NMe_O.H().—The corresponding iodide maybe obtained by adding iodide of methyl to the preceding compound. Both substances unite with a sort of cxplnMon. The same iodide is prepared, however, with less difficulty, simply by digesting iodide of methyl with an alcoholic solution of ammouia. In this reaction, a mixture of the iodides of ammonium, methyl-ammonium, bimethyl-ammonium, tiimethyl-ammonium, and tetramethyl-ammonium is produced. The first and last compound are formed in largest quantity, and may be separated by crystallization, the iodide of tetramethyl-ammonium being rather difficultly soluble in water. From the iodide the base itself is separated by means of protoxide of silver. The properties are similar to those of the corresponding ethyl-compound. It differs, however, from oxide of tetrethyl-ammonium in its behavior when heated (see page 496), yielding 49b ORGANIC BASES OF ARTIFICIAL ORIGIN. as it does trimethylamine, and pure methyl-alcohol, NMe40,H0 = NMe3 + MeO.HO. rases of the amyl-series. The formation of these bodies being perfectly analogous to that of the cor- responding terms in the ethyl-series, we refer to the more copious statement given in page 494, and confine ourselves to a brief description of their prin- cipal properties. Amylamine, Amyl-ammonia, C10HI3N = N(H2,C10H„) = N(H2Ayl), is a colorless liquid of a peculiar penetrating aromatic odor, slightly soluble in water, to which it imparts a strongly-alkaline reaction. AVith the acids it forms crystalline salts, which have a fatty lustre. Amylamine boils at 199°-4 (93°C). An amylamine-urea has been prepared. Biamylamine, Biamyl-ammonia, C^H^N = N(II,2CI0H11) = N(HAyl2), an aromatic liquid, less soluble in water, aud less alkaline than amylamine. It boils at about 338° (170°C). Triamylamine, Triamyl-ammonia, C^H^N = N 3(C10H„) = NAyl3, a color- less liquid, of properties similar to those of the two preceding bases, but boiling at 494°-6 (257°C). The salts of triamylamine are very insoluble in water, and fuse, when heated, to colorless liquids, floating upon water. Hydrated oxide oftetramyl-ammonium, C40H45NO2 = N4(C10H,i)O,HO:= NAyl40,HO. —This substance is far less soluble than the corresponding bases of the methyl- and ethyl- series. On adding potassa to the aqueous solution the compound separates as an oily layer. On evaporating the solution in an atmosphere free from carbonic acid, the alkali may be obtained in splendid, crystals of considerable size. AVhen submitted to distillation it splits into water, triamylamine, and amylene, NAylO,HO = 2HO -4-NAyl3+ CJ0H10. BASE OF THE PHENYL-SERIES. Aniline, phenylamine, C12H7N = N(H2,C,2H5) =N(H2Pyl).— Under the head of salicylic acid a volatile substance has been noticed by the name of hydrated oxide of phenyl. This substance, of which a fuller, description is given further on, imitates to a certain extent the deportment of an alcohol, but several very characteristic transformations of the alcohols, and especially the conversion into the corresponding acid, have not as yet been realized. Tho organic base, however, which is derived from this alcohol in the same manner as methylamine, ethylamine, and amylamine, from methyl-, ethyl-, and amyl- alcohol, is known under the term aniline, a name given to it on account of its relation to the indigo-series. On heating phenyl-alcohol with ammonia in sealed tubes, aniline is produced, PylO,HO -j- NH3 = 2HO 4- N(H2Pyl). This process, however, although interesting as establishing clearly the relation of aniline and phenyl-alcohol, is not calculated to yield large quantities of Ahis substance. Aniline is invariably obtained either from indigo or from nitro- benzol. Powdered indigo boiled with a highly-concentrated solution c%" hydrate of potassa dissolves with evolution of hydrogen-gas to a brownish-red liquid con- taining a peculiar acid, the chrysanilic, which becomes gradually converted into another acid, the anthranilic. If this matter be transferred to a retort and still further heated, it swells up and disengages aniline, which condenses in the form of oily drops in the neck of the retort and in the receiver. Sepa- rated from the ammoniacal water by which it is accompanied, and redistilled, it is obtained nearly colorless. ' The formation of aniline from indigo is repre- sented by the following equation: — C16H5N02 + 4(KO,HO) + 2IIO = C12H7N + 4(KO,C02) + 4H. Lndigo. Aniline. ORGANIC BASES OF ARTIFICIAL ORIGIN. 499 In order to prepare aniline from nitrobenzol (see page 436), this substance is submitted to a process discovered by Zinin, which has proved a very abun- dant source of artificial organic bases. An alcoholic solution of nitrobenzol is treated with ammonia and sulphuretted hydrogen, until after some hours a precipitate of sulphur takes place. The brown liquid is now saturated again with sulphuretted hydrogen, and the process repeated until sulphur is no longer separated. The reaction may be remarkably accelerated by occasion- ally heating or distilling the mixture. The liquid is then mixed with excess of acid, filtered, boiled to expel alcohol and unaltered nitrobenzol, and then distilled with excess of caustic potassa. The transformation of nitrobenzol into aniline is represented by the equation: — Cl2H5NO, -f 6HS = C12H7N + 4HO -f 6S. Nitrobenzol. Aniline. If the aniline be required quite pure, it must be converted into oxalate, the salt several times crystallized from alcohol, and again decomposed by hydrate of potassa. M. Be"champ8 has lately shown that the reduction of nitrobenzol may be effected even more conveniently by the action of acetate of protoxide of iron. The distillation of nitrobenzol, acetic acid, and iron filings, seems, in fact, to be the best process for preparing aniline. The mass violently swells up, and very capacious retorts are required. Aniline exists among the products of the distillation of coal, and probably of other organic matters; it is formed in the distillation of anthranilic acid, and occasionally in other reactions. When pure, aniline forms a thin, oily, colorless liquid, of faint vinous odor, and aromatic, burning taste. It is very volatile, but has, nevertheless, a high boiling-point, 359°-6 (182°C). In the air it gradually becomes yellow or brown, and acquires a resinous consistence. Its density is 1-028. Water dissolves aniline to a certain extent, and also forms with it a kind of hydrate; alcohol and ether are miscible with it in all proportions. It is destitute of alkaline reaction to test-paper, but is quite remarkable for the number and beauty of the crystallizable compounds it forms with acids. Two extraordinary reactions characterize this body and distinguish it from all others, viz., that with chromic acid, and that with solution of hypochlorite of lime. The former gives with aniline a deep-greenish or bluish-black precipitate, and the latter an extremely beautiful violet-colored compound, the fine tint of which is, how- ever, very soon destroyed. The production of a purple coloring matter by the action of chromic acid on aniline has lately been patented by M. Perkin. Substitution-products of aniline. — Under the head of indigo, a product of oxidation of this substance will be noticed, to which the name isatin has been given. AVhen isatin is distilled with an exceedingly-concentrated solution of caustic potassa, it is, like indigo, resolved into aniline, carbonic acid, and free hydrogen. In like manner, when chlorisatin or bichlor isatin, two chloro-substi- tutes of isatin, are similarly treated, they yield products analogous to aniline, but containing one or two equivalents of chlorine respectively in the place of hydrogen. The chloranUine, CI2(H6C1)N, and bichlor aniline C_2(H5C12)N, thus produced, cannot, however, be obtained directly from aniline by the action of chlorine, thus differing from ordinary substitution-compounds; but aniline maybe reproduced from them by the same reagent, which is capable of recon- verting chloracetic acid into ordinary acetic acid, namely, an amalgam of potassium (see page 395). They are the first cases on record of organic bases containing chlorine. Chloraniline forms large, colorless octahedra, having exactly the odor and taste of aniline, very volatile, and easily fusible ; it distils without decompo- sition at a high temperature, and burns, when strongly heated, with a red 500 ORGANIC BASES OF ARTIFICIAL ORIGIN. smoky flame with greenish border. It is heavier than water, indifferent to vegetable colors, and, except in being solid at common temperatures, resem- bles aniline in the closest manner. It forms numerous and beautiful crystal- lizable salts. If aniline be treated with chlorine-gas, the action goes further, trichloraniline, C,2(H4C13)N, being produced, a volatile crystalline body which has no longer any basic properties. The corresponding bromine-compounds have also been formed and described. Nitraniline.—If nitrobenzol be heated with fuming nitric acid, or, still bet- ter, with a mixture of that acid and oil of vitriol, it is converted into a sub- stance called binitrobenzol, containing C12H4N208, or nitrobenzol in which an additional equivalent of hydrogen is replaced by the elements of hyponitric acid. AVhen this is dissolved in alcohol, and subjected to the reducing action of sulphide of ammonium in Zinin's process, it furnishes a new substance of basic properties, nitraniline, having the constitution of a hyponitric acid sub- stitution product of ordinary aniline. The attempts to prepare it direct from aniline by means of nitric acid were unsuccessful, the principal product being usually carbazotic acid. Nitraniline forms yellow, acicular crystals, but little soluble in cold water, although easily dissolved by alcohol and ether. When warmed it exhales an aromatic odor, and melts. At a higher temperature it distils unchanged. By very gentle heat it may be sublimed witliout fusion. It is heaver than water, does not affect test-paper, and like chlor- and brom- aniline, fails to give with hypochlorite of lime the characteristic reaction of the normal compound. Nitraniline forms crystallizable salts, of which the hydrochlorate is the best known. This substance contains the elements of aniline with an equivalent of hydrogen replaced by hyponitric acid, or C]2H6 N204 = C]2(H6N04)N. Biphenylamine is not known. Triphenylamine, NCggH.s = N3C12H5 = NPyl3. or a substance isomeric with it, is formed by submitting to destruc- tive distillation the compound of cinnamic aldehyde with alkaline sulphides together with an excess of lime. Cyaniline is formed by the action of cyanogen upon analine; it is a crystal- line substance capable of combining with acids like aniline, but very prone to decomposition. Cyaniline contains CI4H7N2 = CI2H7NCy. Hence it is formed by the direct union of 1 eq. of cyanogen and 1 eq. of aniline. The constitution of the substitution-products of aniline is readily-intelligible: it is evident that these substances owe their origin to a double substitution, namely, first, of 1 equivalent of hydrogen in ammonia by phenyl; and, secondly, of one or several equivalents of hydrogen in phenyl by chlorine, bromine, &c. The arrangement of the elements may be conveniently illus- trated by the following formute : — Ammonia Aniline Chloraniline Bromaniline Bibromaniline Tribromaniline Nitraniline . NH, . NH2,C12H5 • • • NH2,C)2(H4C1) • NH2,C12(H4Br) . NH2,C12(H3Br2) . . . NH2,C12(II2Br5) . . NH2,C12(H4N04). The constitution of cyaniline is more complicated. Melaniline.—The action of dry chloride of cyanogen upon anhydrous aniline gives rise to the formation of a resinous substance, which is the chlorine- compound of a very peculiar basic substance to which the name melaniline has been given. Dissolved in water and mixed with potassa. the above salt furnishes melaniline in the form of an oil, which rapidly solidifies to a beautiful crystalline mass. Melaniline contains C26H13N3. The following equation represents its formation: — 2C12H7N 4- C2NC1 = C^H.^Cl. ORGANIC BASES OF ARTIFICIAL ORIGIN. 501 Melaniline, when treated with chlorine, bromine, iodine, or nitric acid, yields basic substitution-products, in which invariably 2 eq. of hydrogen are replaced. It combines with 2 eq. of cyanogen. Phenyl-melaniline. — Aniline, when exposed to the action of bichloride of carbon at a temperature of 202° (150°C) solidifies into a resinous mass, con- sisting of the hydrochlorates of several bases, from which, by appropriate treatment, a beautiful basic compound maybe extracted, containing C38HI7N3. The formation of this body, which in its properties closely resembles melani- line, may be represented by the equation — 6C12H7N + C2C14 = 3(C12H7N,HC1) 4- CS8H)7N3,HC1. It may be viewed as melaniline, in which 1 eq. of hydrogen is replaced by phenyl. Ethylene-aniline. — Aniline, when submitted to the action of bromide of ethylene, C4H4Br2, solidifies to a crystalline mass, from which potassa sepa- rates a beautifully-crystalline base, which is soluble in alcohol and ether, but insoluble in water. The simplest formula of this substance is Cl6H9N. The deportment, however, of the new base with iodide of methyl and ethyl appears to indicate that the true expression representing this compound is C^H^Nj, for it forms with the alcoholic iodides two compounds, containing respectively C^H^NjI, and C^H^N^, from which two very soluble bases, C34H2lN20,HO, and C36H23N20,HO, have been isolated. Formylaniline. — A mixture of aniline and chloroform exposed in sealed tubes to a temperature of 356° (180°C) solidifies to a crystalline mass, con- sisting of hydrochlorate of aniline, and the hydrochlorate of a crystalline base, containing CjgH^N,,, 4C12H7N + C2HC13 = 2(C12H7N,HC1) 4- C26H12N2,HC1. By washing with cold water the hydrochlorate of aniline is removed, and the residue, when treated with potassa, furnishes the base in a state of purity. It is insoluble in water, soluble in alcohol and in ether. Melaniline, phenylmelaniline, ethyleneaniline, and formylaniline may be derived from a double molecule of ammonia, N2H6, in which the hydrogen is more or less replaced by radicals. In melaniline and phenylmelaniline, 3 and 4 eq. of hydrogen of ammonia are replaced by cyanogen, and respectively 2 or 3 eq. of phenyl; in ethylene-aniline the 6 eq. of hydrogen are replaced by 2 eq. of phenyl and 2 eq. of ethylene, the biatomic character of which has been already pointed out under the head of glycol.1 In formylaniline, lastly, we have 2 eq. of hydrogen replaced by phenyl, and 3 equivalents by the triatomic molecule formyl. The bases derived from 2 molecules of ammonia have been designated by the term diamines. The constitution of the four bases last described may be thus stated: Diammonia . . . . . . . N2< H6 Melaniline Cyanbiphenyldiamine Phenylmelaniline . Cyantriphenyldiamine . Ethylenaniline Biethylenbiphenyldiamine Formylaniline . . . Forniylbiphenyldiamine }N2j(C12H H C2N (C12Hs)3 H, }*.{<*' (CI2H5)2 C,HK" }n2|(cI2h5) 1 The action of bibromide of ethylene on ammonia gives rise to the formation of a series of bases, which are not yet perfectly studied. 502 ORGANIC BASES OF ARTIFICIAL ORIGIN. Aniline-compounds corresponding to the amides and amidogen-acids, Sec. — In describing the ammonia-salts of various acids, attention has been repeatedly called to the power possessed by many of them to yield several new groups of compounds by the loss of a certain amount of water (see page 3bl). lhese groups are perhaps best elucidated by the derivatives of oxalic acid. NH40,C203 — 2HO = C202,NH2 Neutral oxalate of ammonia. NH40,C2O3,H0,C2O3 Binoxalate of ammonia. NH40,C203 Neutral oxalate of ammonia. 2HO = — 4HO Oxamide. C202,NH2; C203,HO Oxamic acid. C2N Oxalonitrile or cyanogen. The terms corresponding to oxamide and oxamic acid have also been obtained in the aniline-series: they are produced by the distillation of neutral and acid oxalate of aniline, and have been called oxanilide and oxanilic acid. Oxanilide = C; Oxanilic acid = C ,H6N02=C202NH(Pyl) 5H8N06 = C202,NH(Pyl),C203,HO. Compounds analogous to the nitriles have not been obtained in the aniline- series, and the reason is intelligible if we glance at the formula of oxalate of aniline, N(H3Pyl)0,C203. It is obvious that 4 eq. of water cannot be elimi- nated from this salt without touching the hydrogen of the phenyl, i.e., with- out destroying the compound altogether. A great many anilides and anilic acids have been formed. Aniline-urea. — On passing the vapor of cyanic acid into aniline, the sub- stance becomes hot, and solidifies on cooling to a crystalline mass, containing CI4H8N202 = C2(H3Pyl)N202. This is the composition of aniline-urea. This •substance, ^however, does not combine with acids like the ureas (see pages 495 and 496); it is-only isomeric with the true aniline-urea, which is obtained by another process. Among the derivatives of benzoic acid, nitrobenzoic acid, C14(H4N04)03,HO, has been mentioned. The ether of this acid, C4H50,C14 (H4N04)03, like oxalic ether, and many other ethers, furnishes an amide when treated with ammonia. This substance, nitrobenzamide, CI4(H4N04)02,NH2, under the influence of sulphide of ammonium, suffers a change, which is perfectly analogous to that of nitrobenzol under similar conditions (see page 499). The mixture soon deposits sulphur, and yields on evaporation crystals of aniline-urea. CMH6Nj|08 4- 6HS = C14H8N202 + 4HO + 6S. Nitrobenzamide. Aniline-urea. This substance, which was discovered by M. Chancel, combines with nitric and hydrochloric acid, and even with bichloride of platinum. Bases homologous to Aniline. In a former section of this Manual (page 441), a series of hydrocarbons have been mentioned, which are homologous to benzol. Each of these sub- stances, when treated with fuming nitric acid, yields a nitro-substitute cor- responding to nitrobenzol, which, under the influence of sulphuretted hydrogen ORGANIC BASES OF ARTIFICIAL ORIGIN. 503 is converteil into a basic compound homologous to aniline. AVe thus obtain the following group: — Benzol, C)2H 5H Nitrobenzol, C12H SN04 Aniline, N(H2,C,2H A Toluol, C14ll 7H Nitrotoluol, C14H 7N04 Toluidine, N(H2,C14II 7) Xylol, C16H9H Nitroxylol, C16H 9N04 Xylidine, N(H2,C,6H9) C'umol, <18HUH Nitrocumol, C,8H„N(.)4 Cumidine, N(H2.C,gH„) Cymol, CjoHaH Nitrocymol, C^H^^ Cymidine, ^(Hz.C^H^) Toluidine, CmH9N == N(II2,C14H7) = N(H2Tyl).—This is prepared exactly like aniline. Toluidine forms colorless platy crystals, very sparingly soluble in water, but easily in alcohol, ether, and oils; it is heavier than water, has an aromatic taste and odor, and a very feebly-alkaline reaction. At 104° (40°C), it melts, and at 388° (19-8°C), boils and distils unchanged: it forms a series of beautiful crystallizable salts. Xylidine, Cl6H„N = N(H2,Cl6H9) = N(H2Xyl). — Of this compound little more than its existence is known. _ Cumidine, Cl8H13N4-N(H2,C18Hn) = N(H2Cul). —This substance is an oil which boils at 437° (225°C). It forms magnificent salts with the acids. Cymidine, C^H^N = N(H2,C20H]3) = N(H2Cyl).—Oily base, similar to the preceding ones, but less stable, and more readily oxidizable. It boils at about 482° (250°C). Cymidine is less easily prepared than the homologues previously described, owing to the powerful action of concentrated nitric acid upon cymol, which furnishes generally toluylic and nitrotoluylic acids (p. 441), instead of the nitrocymol, C^H^NO^). But Mr. Barlow has lately shown that the latter compound may be readily obtained by exposing both acid and hydrocarbon, previous to being mixed, to a frigorific mixture. The product of the action of nitric acid yields on addition of water, nitrocymol, which may be converted into cymidine by means of iron filings and acetic acid. The following base is likewise closely allied to the group of aniline bases, both by their mode of formation and by their constitution, Naphthalidine, C20H9N = N(H2,C20H7) = N(H2Nyl). — This substance is interesting, as being one of the first of its kind produced by Zinin s process. It is obtained by the action of sulphide of ammonium upon an alcoholic solution of nitronaphthalase, one of the numerous products of the action of nitric acid upon the hydrocarbon naphthalin, which will be noticed in a subse- quent section of the Manual. AVhen pure it forms colorless silky needles, fusible, and volatile without decomposition. It has a powerful, not disagree- able odor and burning taste, is nearly insoluble in water, but readily dissolves in alcohol and ether: the solution has no alkaline reaction. Naphthalidine forms numerous crystallizable salts. mixed rases. In one of the preceding paragraphs it has been mentioned that the several hydrogen-equivalents in ammonium may be replaced by different hydrocarbon- radicals. In fact, on treating aniline or toluidine with bromide, or iodide of ethyl, as described under the head of ethylamine, the following series of com- pounds arc obtained: — Aniline N(H2Pyl) Toluidine N(H2Tyl) Ethylaniline N(HPylAe) Ethylotoluidine N(HTylAe) Biethylaniline N(BylAe2) BiethylotoluidrneN(TylAe2) Ammonium-base N(PylAc3)0,HO Ammonium-base N(TylAe3)0,HO. Ethylaniline (ethylophenylamine) and rietuylaniline (biethylophenyla- minc) are liquids greatly resembling aniline. They boil respectively at 399°-2 (204°C) and 416°-5 (213°-5C). The ammonium-base, to which the 504 METHYLATED AND ETIIYLATED DERIVATIVES. name Oxide of biethylophenyl-ammonium may be given, is soluble in water, with a powerful alkaline reaction, corresponding in its general properties to oxide of tetrethyl-ammonium (see page 496). The series of bases which may be ob- tained by changing the radicals is almost without limits: even now a con- siderable variety has been produced, of which, however, only a few will be mentioned here, as remarkable for the diversity of the materials with which they are constructed. Hydrated oxide of triethyl-amyl-ammonium, C22lI27N02 = N(3C4H5, C,0H„)0,HO = N(Ae3Ayl)0,HO. Triethylamine (see page 496), when boiled with iodide of amyl, is slowly converted into a crystalline mass of iodide of Triethylamyl-ammonium. The base liberated with protoxide of silver and sub- mitted to distillation yields olefiant gas, and Biethylamylamine, C,8H2)N = N(2C4H5,C,0Hn) -= N(Ae2Ayl), a liquid boiling at 309°-2 (154°C). This compound is most powerfully attacked by iodide of methyl. Both substances immediately solidify to a beautifully-crys- talline iodide, from which protoxide of silver separates. Hydrated oxide of metiiyl-biethyl-amyl-ammonium, C20H25NO2 = N(C2U3,2C4H5,C10Hn)O,HO = N(MeAe2Ayl)O,HO. This substance, which is a powerfully-alkaline base, soluble in water, when distilled undergoes the same decomposition as the other members of the fourth«group of bases, yield- ing olefiant gas, and Metiiyl-etiiyl-amyl-amine, or ammonia, in which 1 eq. of hydrogen is replaced by methyl, another by ethyl, and a third by amyl, C)6H19N = N(C2H3, C4H5,C10HM) = N(MeAeAyl). This is a basic oil of a peculiar aromatic odor, boiling at 275° (135°C), and forming crystallizable salts with the acids. Ethyl-amyl-aniline, C^H^N = N(C12H5,C4H5,C,0H„) = N(PylAeAyl). Ethylaniline (see page 503) treated with iodide of amyl yields the iodide of the above base, which is separated by distillation with potassa. It is an aromatic oil, boiling at 503°-5 (262°C). The action of iodide of methyl upon this sub- stance gives rise to a new iodide, from which protoxide of silver separates. Hydrated oxide of methyl-ethyl-amyl-phenyl-ammonium, 0^11^02 = N(C2H3,C4n5,C.0Hn,C12H5)O,HO = N(MeAeAylPyl)0,HO. This compound is very soluble in water, is powerfully alkaline, and of an extremely bitter taste. The composition, established by the examination of a platinum-salt, is cer- tainly remarkable, for this compound contains the radicals of not less than four different alcohols. METHYLATED AND ETIIYLATED DERIVATIVES OF NATURAL BASES. Becent researches have shown that many of the natural bases, when sub- mitted to the action of iodide of methyl or ethyl, are capable of absorbing a smaller or greater number of equivalents of methyl and ethyl. There can be no doubt that the natural alkaloids, like the artificial bases, are substitution- products of ammonia, and the deportment of these substances with the alco- hol-iodides, permits us to ascertain with great precision the degree of substi- tution. If a natural alkaloid, when submitted to the action of iodide of ethyl, be found to require for conversion into a base of the formula__ 0,H0 either 1, or 2, or 3 equivalents of ethyl, we may infer that the alkaloid in question belongs to the class of bases represented by the formulae__ (A (A rA N \ B . N \ B or N \ H, lc U (I! BASES OF UNCERTAIN CONSTITUTION. 505 t. e., that it is a tertiary, a secondary, or a primary amine base. All natural alkaloids which have been examined, with the exception of the conine, are nitrilc-bases. Morphine.—An alcoholic solution of morphine, when heated in sealed tubes with iodide of methyl, furnishes a crystalline compound, CjgH^NOel = C34(H)9,C2H3)N06I. This substance yields, with oxide of silver, a very alka- line solution, obviously containing an ammonium-base. Morphine is there- fore a tertiary amine-base; C34HI906 representing one or several radicals, which are together capable of replacing 3 equivalents of hydrogen. Codeine.—AVith iodide of ethyl codeine forms a crystalline iodide, ^011^06,1 = C36(H21,C4H5)N06,I, furnishing with oxide of silver a soluble base. Codeine being considered as a tertiary-amine-base, 036112,06 represent 3 equivalents of hydrogen. Cinchonine and quinine yield with iodide of methyl-compounds represented respectively by the formulse C40(Il24,C2ll3)N2O2I and C4n(H24,C2H3)N204I, which by oxide of silver are converted into soluble bases of the fourth class. Strychnine forms with iodide of ethyl a crystalline compound, C42(H22, 04H6)X2O4I, yielding with oxide of silver a soluble base. Nicotine.—A mixture of this base with iodide of methyl or ethyl solidifies after a short time to crystalline masses, containing C10(H7,C2H3)NI andC10(H7, C4H5)NI, convertible by oxide of silver into soluble bases. Conine is a secondary-amine-base. Treated with iodide of ethyl, this base yields successively two iodine-compounds, namely, C16(H15,C4H5)NI and i60[Hl4(C4H6)j]NI. The latter furnishes with oxide of silver a soluble base. BASES OF UNCERTAIN CONSTITUTION. In addition to the artificial bases which have just been described, several others have been formed by processes less simple and less calculated to afford a clear insight into their constitution. The destructive distillation of nitro- genous substances has furnished a rich harvest of similar substances. A few of the most interesting may be briefly mentioned. Chinoline C1RH,N")..., ~ , ., , . , Lepidine C20H 9N } obtamed from coal 0l1 an<* cinchonin. Cryptidine C^H,^ obtained from coal-oil. Chinoline (Leucoline) Cl3H17N.—Quinine, cinchonine, strychnine, and probably other bodies of this class, when distilled with a very concentrated solution of potassa, yield an oily product resembling aniline in many respects, and possessing strong basic powers; it is, however, less volatile than that sub- stance, and boils at 460° (235°C). AVhen pure it is colorless and has a faint odor of bitter almonds. Its density is 1-081. It is slightly soluble in water, and miscible in all proportions with alcohol, ether, and essential oils. Chino- leine has no alkaline reaction, but forms salts with acids, which, generally speaking, do not crystallize very freely. M. AVilliams has lately shown that the basic oil obtained by distilling cinchonine contains in addition to chino- leine two other bases of very similar properties, to which the names lepidine and cryptidine have been given. Lepidine contains C20H9N, cryptidine C^HnN. Bases from Coal-Tar Oil. Kyanol and Leukol.—The volatile basic bodies described under these names have been identified, the first with aniline and the second with chino- leine. They are separated from the coal-tar oil by agitating large quantities of that liquid with hydrochloric or diluted sulphuric acid, and then distilling the acid liquid with excess of potassa or lime. They are readily separated by distillation. 43 500 BASES OF UNCERTAIN CONSTITUTION. Picoline, C12H7N. —Dr. Anderson has described under the foregoing name a third volatile, oily base, which is present in certain varieties of coal-tar naphtha, being there associated with aniline, chinoleine, and several other volatile substances, but imperfectly understood. It is separated without diffi- culty from the two bases mentioned by distillation, in virtue of its superior volatility. Picoline, when pure, is a colorless, transparent, limpid liquid, of powerful and persistent odor, and acrid, bitter taste. It is unaffected by a cold of 0° (—17°-7C). It is extremely volatile, evaporates rapidly in the air, and does not become brown like aniline when kept in an ill-stopped bottle. Picoline has a sp. gr. of 0-955, and boils at 272° (133°-3C). It mixesin all proportions with pure water, but is insoluble in caustic potassa and most saline solutions. The alkalinity of this substance is exceedingly well marked; it restores the blue color of reddened litmus, and forms a series of crystallizable salts. This substance, as seen from the above formula, is isomeric with aniline, but numerous characteristic reactions completely distinguish it from this body. Bases from Animal Oil. The oily liquid obtained by the distillation of bones and animal matter generally, frequently designated by the term Dippel's oil, contains several vo- latile organic bases. Together with some of the substances already described, such as methylamine, ethylamine, picoline, and aniline, Dr. Anderson has found in it several peculiar bases. Petinine, C8HnN.—The properties of this substance are very analogous to those of biethylamine and triethylamine. It has the same composition as bi- ethylamine, but differs from it by its higher boiling-point, which is 175° (79°-5C), that of biethylamine being 133° (55°C) (see page 495). Some che- mists are inclined to explain this difference by assuming that petinine is an ammonia-base, containing the radical butyl, which was mentioned under the head of valeric acid (see also page 415); in one word, that it is butylamine N(H2,C8H9), homologous to ethylamine. This assumption may be correct, but is not as yet supported by any experimental evidence. The true butyl- amine has lately been obtained by M. AVurtz from butyl-alcohol (page 415), in the same manner as ethylamine is obtained from common alcohol (page 494). Pyridine, C,0H5N.—It much resembles picoline, and is obtained by re- peatedly rectifying the bases of Dippel's oil, which distil at 239° (115°C). Lutidine, C14H9N.—Oily base contained in the portion which distils at 309° (154°C). Collidine, CtfH,^.—Oily base very similar to the preceding ones. Boil- ing-point 354° (179°C). To the same series also belongs an oily base, lately isolated by Mr. "Wil- liams from tfie basic products of the distillation of Dorsetshire shale, and de- scribed by him under the name of parvoline. Parvoline is said to contain C18H13N. It will be observed that these bases, the constitution of which is not yet clearly made out, are isomeric with the bases homologous to aniline. ? Aniline . Toluidine Xylidine Cumidine Cymidine The first term of the aniline-series, and the last of the pyridine-series are unknown. In addition to the above compounds, Dippel's oil contains some peculiar C10H5N . . . Pyridine. CI2H7N Picoline. CUH9N . . Lutidine. C16H„N . . Collidine. C18H13N . Parvoline C20H15N . . ? BASES OF UNCERTAIN CONSTITUTION. 507 bases, often called pyrrole-bases, which are said to have the remarkable pro- perty of escaping from their saline combination by mere ebullition. Bases obtained by the action of Ammonia upon Volatile Oils. Furfurine.—AVhen sulphuric acid diluted with an equal bulk of water is carefully mixed with twice its weight of wheat-bran, and the adhesive pasty mass obtained exposed in a proper vessel to the action of a current of steam, which is afterwards condensed by a worm or refrigerator, a liquid is obtained which holds in solution a peculiar volatile oil, to which the term furfurole has been given. By redistillation several times repeated, the first half of the liquid only being collected, .the furfurole can be extracted from the water, and then by distillation alone obtained in a state of purity. It has a pale-yellow color, and a fragrant odor like that of oil of cassia; its specific gravity is 1-165, and it boils at 325° (1G2°8C), distilling unchanged. It dissolves in all proportions in alcohol and to a very considerable extent in water, and is readily destroyed by strong acids and caustic alkalies, especially when aided by heat. Furfu- role contains C6H202. The specific gravity of its vapor is 3-493. The product of furfurole is very greatly increased, and the operation much facilitated, by previously depriving the bran of all starch, gluten, and soluble matter, by steeping it in a cold dilute solution of caustic potassa, and washing and drying by gentle heat or in the sun. Maceration in cold water for some time answers the same purpose, owing to the lactic acid formed in that case. In contact with solution of ammonia, furfurole becomes converted in the space of a few hours into a yellowish-white, crystalline, insoluble substance, furfurolamide, C,-H6N03: this body is slowly decomposed in contact with water, and instantly by an acid into ammonia and furfurole. It may be crystallized from alcohol, however, in which it dissolves witliout much change. AVhen boiled with a somewhat dilute solution of caustic potassa, no ammonia is dis- engaged ; but the substance is slowly dissolved if the quantity of liquid be con- siderable, and the solution deposits on cooling, small, white, silky needles, of a substance having the same composition as furfurolamide itself. There is no other product. This new body, to which the name furfurine has been given, is a powerful organic base, forming with acids a series of beautiful crystal- lizable salts, and decomposing at a boiling heat the saline compounds of am- monia. Furfurine is very sparingly soluble in cold water, but dissolves in about 135 parts at 212° (100°C). Alcohol and ether dissolve it freely: the solutions have a strongly-alkaline reaction. It melts below the boiling-point of water, and when strongly heated inflames and burns with a red and smoky light, leaving but little charcoal. Its salts are intensely bitter. Furfurine contains in 1 equivalent C30H]2N2O6.1 Fucusink.—By treating several varieties of fucus with sulphuric acid in exactly the same manner as in the preparation of furfurole, Dr. Stenhouse ob- tained a series of substances, which he designates by the terms fucusol, fucus- amide, and fucusine. They have exactly the same composition as the corres- ponding terms in the furfurol-series, and also most of their properties, bu+ differ in some details. Amarine (bknzoline).—The hydrobenzamide of Laurent, C42Hl8N2, pro- duced by the action of ammonia on pure bitter-almond oil (see page 438), when long boiled with a solution of caustic potassa, suffers the same kind of change as furfurolamide, becoming entirely converted into a new body iso- meric with hydrobenzamide, having the characters of a salt base, and to which the preceding name has been given. Precipitated by ammonia from a cold solution of the hydrochlorate or sulphate, amarine separates in white curdy 1 This remarkable substance, the nearest approach to the native alkaloids yet made, was dis- covered by the author of this Manual.—Eds. t \ ■■•' 508 BASES OF UNCERTAIN CONSTITUTION. masses, which when washed and dried become greatly reduced in volume. Tn this state it is singularly electric by friction with a spatula. It is insoluble in water, but dissolves abundantly in alcohol: the solution is highly alkaline to test-paper, and if sufficiently concentrated deposits the amarine on stand- ing in the form of small, colorless, prismatic crystals. Below 212° (100°C) it melts, and on cooling assumes a glassy or resinous condition. Strongly heated in a retort it decomposes with production of ammonia, and a volatile oil not yet examined, and a new body, pyrobenzoline or lophine, C42ITl6N2(?), which ap- pears to be a neutral substance, insoluble in water, soluble in boiling alcohol, and containing a large quantity of nitrogen. It is fusible by moderate heat, and on cooling becomes a mass of colorless, radiating needles or plates. The salts of amarine are mostly sparingly soluble; the sulphate, nitrate, and hy- drochlorate are crystallizable and very definite. Amarine contains C42HI8N2. Thiosinamine.—The volatile oil distilled from black mustard-seed, C8H5NS2, which has been already mentioned under the head of allyl-series, and which will be noticed further on, in contact with solution of ammonia, yields a com- pound having the characters of an organic base, and forming colorless, pris- matic crystals, bitter in taste and soluble in water. The solution does not affect test-paper. It melts when heated, but cannot be sublimed. Acids com- bine with it, but form no crystallizable salts: the double salts of the hydro- chlorate with bichloride of platinum and corrosive sublimate are the most de- finite. This substance contains sulphur; its formula is C8H8N2S2. It is the only product of the action of ammonia on the oil. Thiosinamine is decomposed by metallic oxides, as protoxide of lead, with production of a metallic sulphide and a new body of basic properties, free from sulphur, called sinnamine. This latter substance crystallizes very slowly from a concentrated aqueous solution in brilliant, colorless crystals which contain water. It has a powerfully-bitter taste, is strongly alkaline to test-paper, and decomposes ammoniacal salts by boiling. With the exception of the oxalate, it forms no crystallizable salts. Sinnamine contains in the crystallized state C8H6N2,HO. When mustard-oil is treated with protoxide of lead or baryta, the whole of the sulphur is withdrawn, and carbonic acid and another basic substance pro- duced, which, when pure, crystallizes in colorless plates, soluble in water and in alcohol; the solution has a distinctly-alkaline reaction. Sinapoline, the body so formed, contains C,4Hl2N202. Bases from Aldehyde. Thialdine.—The crystalline compound of aldehyde with ammonia (see page 388) is dissolved in from 12 to 16 parts of water, mixed with a few drops of caustic ammonia, and then the whole subjected to a feeble stream of sulphu- retted hydrogen. After a time the liquid becomes turbid, and deposits a white crystalline substance, which is the body in question. It is separated, washed, dissolved in ether, and the solution mixed with alcohol and left to evaporate spontaneously, by which means the base is obtained in large, regu- lar, rhombic crystals, having the figure of those of common gypsum. The crystals are heavier than water, transparent and colorless. They refract light strongly. The substance has a somewhat aromatic odor, melts at 110° (43°-3), and volatilizes slowly at common temperatures. It distils unchanged with the vapor of water, but decomposes when heated alone. It is very spa- ringly soluble in water, easily in alcohol and ether. It has no action on vege- table colors, but dissolves freely in acids, forming crystallizable salts. Heated with hydrate of lime it yields chinoleine. Thialdine contains C]2H,„NS4. A very similar compound containing selenium exists. Alanine.—This substance is likewise obtained from aldehyde. It has been discovered by Strecker, who obtained it in a reaction, which promises many APPENDIX TO THE ORGANIC BASES. 509 interesting results. If an aqueous solution of the ammonia-compound of alde- hyde be treated with hydrocyanic and hydrochloric acid, chloride of ammo- nium is formed, together with hydrochlorate of alanine. On adding to this solution a mixture of alcohol and ether, the greater portion of the chloride of ammonium is precipitated; the filtrate is then treated with protoxide of lead to remove a small quantity of ammonium and hydrochloric acid, and separated from the lead by sulphuretted hydrogen. The liquid thus obtained deposits feathery crystals of alanine. The composition of alanine is C6H7N04, and its formation represented by the equation:— C4H402 4- HC2N 4- 2HO = C6H7N04 Aldehyde. Hydrocyanic Alanine. acid. Alanine crystallizes in rhombic prisms of the lustre of mother-of-pearl. They are pretty soluble in cold, but more so in boiling water; they dissolve but little in alcohol, and not at all in ether; the solution has a sweetish taste, but no effect upon vegetable colors. Alanine is a weak base: as yet only a crystalline nitrate has been obtained, but several combinations with metallic oxides have been produced. This substance has the same composition as lactamide (see page 369), urethrane (see page 375), and sarcosine, which will bo described in the section on the Components of the Animal Body. But it is only isomeric with those substances from which it differs in its physical and chemical properties. The most interesting feature in the history of alanine is its behavior with nitrous acid. Under the influence of this reagent it is con- verted into lactic acid, identical in every respect with that obtained in the fermentation of sugar (see page 368). This reaction is represented by the following equation: — C6H7N04 4- N03 := C6H505,HO + 2N 4- HO Alanine. Lactic acid. appendix to the organic bases. All the numerous members of this extensive group, which have been con- sidered in the preceding section, invariably contain nitrogen. Recent re- searches, however, have shown that there exist three series of analogous substances which contain phosphorus, antimony, and arsenic, in the place of nitrogen. These remarkable compounds, which are not yet sufficiently known, will be briefly noticed in the subsequent paragraphs. Phosphorus-bases. If a current of chloride of methyl (see page 401), be passed over a layer of phosphide of calcium (see page 259), heated to about 356° (180°C), a mixture of several phosphoretted bodies is produced, which are partly liquid and partly solid. M. Paul The"nard, who has investigated this subject, has separated from this mixture three compounds, containing carbon, hydrogen, and phosphorus, which he believes to correspond to the three hydrides of phosphorus (see page 185). 43* 510 APPENDIX TO THE ORGANIC BASES. Phosphoretted Phosphoretted hydrogens. methyl bodies. P2H........P2C2H3 = P2Me PH .....P2C2H3=PMe2 PH3 '. '.......P3C2H3=PMe3. As far as can be seen from the results obtained by M. Thenard, which have not been published in detail, the two last substances are powerful bases analo- gous to the bases of the nitrogen-series. These substances are very difficult to prepare, one of them is even spontaneously inflammable, so that their study has been attended with great difficulty and even danger—circumstances which sufficiently account for the insufficiency of the description. The subject of the phosphorus-bases has-been lately examined again by MM. Cahours and Hofmann, who have discovered a method of preparing these substances by means of a process which yields very definite results. In the former sections of this work, two remarkable substances have been noticed, discovered by Dr. Frankland, and described by him under the name of zinc- methyl and zinc-ethyl (page 386). These substances, when submitted to the action of terchloride of phosphorus, furnish saline compounds containing respectively PMe3,3ZnCl, and PAe3,3ZnCl, from which, by distillation with potassa, the bases PMe3 and PAe3, may be liberated. Triethylphosphine, C,2HI5P = PAe8.—This substance is a colorless oil of a very penetrating phosphorus odor, which boils at 266° (130°C). It is slowly oxidized in atmospheric air. The vapor, heated with air or oxygen, explodes. In chlorine gas it burns with separation of carbon, hydrochloric acid and pentachloride of phosphorus being produced. AVith the acid it forms crystalline compounds, which are very deliquescent. With iodide of methyl, ethyl, and amyl, it solidifies after a few moments to crystalline compounds, containing respectively P(Ae3Me)I,-PAe4I and P(Ae3Ayl)I, which are decom- posed by oxide of silver, yielding powerfully-alkaline liquids, containing the hydrates P(Ae3Me)0,HO-PAe40,HO and P(Ae3Ayl)0,HO, which resemble in every respect the ammonium-bases of the fourth class. Trimethyl-phosphine, C8H9P = PMe3.—This substance is very similar to the corresponding ethyl-base, but more volatile. When left to contact with atmospheric air, it furnishes a compound which crystallizes in beautiful white needles. With iodide of methyl, ethyl, and amyl it furnishes the iodides PMe4I, P(Me3Ae)I, and P(Me3Ayl)I, from which three analogous hydrates can be produced by means of oxide of silver. Antimony-bases. Among the derivatives of alcohol, a compound of antimony with 3 eq. of ethyl has been briefly noticed (see page 387) under the name of stibethyl. The composition of this remarkable compound approximates it to triethyla- mine. • Triethylamine, NAe3 .... { ^^^} SbAe,. A closer examination has shown that this substance differs in many points from triethylamine; but that, in one very essential character, the two substances agree in the most perfect manner. The properties of stibethyl are the following: it is a transparent, very mobile liquid, of a penetrating odor of onions. It boils at 317° (158°-3C). In contact with atmospheric air, it emits a dense white fume, and frequently even takes fire, burning with a white brilliant flame. It combines directly with 2 eq. of oxygen, sulphur, chlorine, and iodine. Binoxide of stibethyl, SbAe302, forms a viscid transparent mass soluble in APPENDIX TO THE ORGANIC BASES. 511 water and alcohol. It is extremely bitter and not poisonous. This substance cannot be volatilized without decomposition. Binoxide of stibethyl combines with acids, giving rise to the formation of crystallizable salts containing 2 eq. of acid. Bisulphide of stibethyl, SbAe3S2. — Beautiful crystals of silvery lustre, solu- ble in water and alcohol. Their taste is bitter, and their odor similar to that of mercaptan. The solution of this compound exhibits the deportment of an alkaline sulphide; it precipitates the solution of the metals as sulphides, a soluble salt of slibethyl being formed at the same* time. This deportment, indeed, affords the simplest means of preparing the salts of stibethyl. Bichloride of stibethyl, SbAe3Cl2. — Colorless liquid of the odor of oil of turpentine. Biniodide of stibethyl, SbAe3T2.—Colorless needles of intensely-bitter taste. The analogy of stibethyl with triethylamine is best exhibited in its deport- ment with iodide of ethyl. The two substances combine to a new iodide, containing SbAe4I, from which a powerful alkaline base may be separated by the action" of protoxide of silver. This substance, which must evidently be analogous to oxide of tetrethyl-ammonium, NAe40,HO SbAe40,HO, has not yet been minutely examined. A series of analogous substances exist in the methyl-series. They have been examined by M. Landolt, who has described several of its compounds, and separated the methyl-antimony-base corresponding to oxide of tetrethyl- ammonium. The iodide, SbMe4I, produced by the action of iodide of methyl upon stibme- thyl, crystallizes in white six-sided tables, which are easily soluble in water and alcohol, and slightly soluble in ether. It has a very bitter taste, and is decomposed by the action of heat. When treated with protoxide of silver, it yields a powerfully-alkaline solution, exhibiting all the properties of potassa, from which, on evaporation, a white crystalline mass, the hydrate of the base, SbMe40,H0, crystallizes. This compound forms an acid salt with sul- phuric acid, which crystallizes in tables. It contains SbMe40,S034- HO,S03. Arsenic-bases. It has been mentioned already (page 387), that an alloy of arsenic and sodium, when submitted to the action of iodide of ethyl, gives rise to the for- mation of an arsenic compound analogous to stibethyl, which has been described under the name of arsenethyl, but which more appropriately might be called triethylarsine, since its composition may be expressed by the for- mula C12H,,As — Ae3As. Together with this substance another body, con- taining C8li10As = Ae2As, is formed, which is perfectly analogous to cacodyl, C,H6.\.s = AsMe2. Both compounds are liquids of powerful odor, which may be separated by distillation in an atmosphere of carbonic acid, when the tri- ethylarsine passes over last. Triethylarsine is a colorless liquid of a most disagreeable odor, similar to that of arsenietted hydrogen, soluble in water, alcohol, and ether, and boiling at 284° (140°C). Triethylarsine combines directly with oxygen, sul- phur, bromine, and iodine, giving rise to a series of compounds containing 2 equivalents of oxygen, sulphur, bromine, and iodine. They are analogous to the corresponding compounds of stibethyl. When triethylarsine is submitted to the action of iodide of ethyl, a crystal- line compound is formed, containing AsAe4I, from which freshly-precipitated oxide of silver separates the corresponding oxide, AsAe40,I10, which is a 512 APPENDIX TO THE ORGANIC BASES. powerfully-alkaline substance, similar to the corresponding nitrogen-, phos- phorus-, and antimony-compounds. Analogous substances exist in the methyl-series. Trimethylarsine, AsMe3, is formed, together with cacodyl, AsMc2, when an alloy of arsenic and sodium is submitted to the action of iodide of methyl. It unites with iodide of methyl, producing a compound, AsMeJ, from which oxide of silver separates the body AsMe40,HO. The iodide just mentioned is formed, together with iodide of cacodyl, when cacodyl is acted upon by iodide of ethyl. 2(AsMe2) 4- 2MeI AsMe4I + AsMe2T. By substituting iodide of ethyl for iodide of methyl a compound, As(Me2Ae2)I, is formed. All these compounds are decomposed by oxide of silver. The following table exhibits the groups of phosphorus-, antimony-, and arsenic-bases, in juxtaposition with the nitrogen-series: — Nitrogen Phosphorus Antimony Arsenic series. series. series. series. Hydrogen compound • HH3 PH3 SbH3 AsAe3 Ethyl-base . . NH2Ae — — — Biethyl-base . NHAe2 — — — Triethyl-base . NAe3 PAe3 SbAe3 AsAes Ammonium-base . . NAe4O,H0 PAe40,H0 SbAe40,HO AsAe40,HO, INDIGO. 513 ORGANIC COLORING PRINCIPLES. The organic coloring principles are substances of very considerable practi- cal importance in relation to the arts: several of them, too, have been made the subjects of extensive and successful chemical investigation. With the exception of one red dye, cochineal, they are all of vegetable origin. The art of dyeing is founded upon an affinity or attraction existing between the coloring matter of the dye and the fibre of the fabric. In woollen and silk this affinity is usually very considerable, and to such tissues a permanent stain is very easily communicated, but with cotton and flax it is much weaker. Recourse is then had to a third substance, which does possess in a high degree such affinity, and with this the cloth is impregnated. Alumina, sesquioxide of iron, and oxide of tin are bodies of this class. AVhen an infusion of some dye-wood, as logwood, for example, is mixed with alum and a little alkali, a precipitate falls, consisting of alumina in combination with coloring matter, called a lake; it is by the formation of this insoluble substance within the fibre that a permanent dyeing of the cloth is effected. Such applications are termed mordants. Sesquioxide of iron usually gives rise to dull, heavy colors; alumina and oxide of tin, especially the latter, to brilliant ones. It is easy to see that, by applying the mordant partially to the cloth, by a wood-block or otherwise, a pattern may be pro- duced, as the color will be removed by washing from the other portions. indigo. Indigo is the most important member of the group of blue coloring matters. It is the product of several species of the genus indigofera, which grow prin- cipally in warm climates. AVhen the leaves of these plants are placed in a vessel of water and allowed to ferment, a yellow substance is dissolved out, which by contact of air becomes deep blue and insoluble, and finally precipi- tates. This, washed and carefully dried, constitutes the indigo of commerce. It is not contained ready-formed in the plant, but is produced by the oxida- tion of some substance there present. Neither is the fermentation essential, as a mere infusion of the plant in hot water deposits indigo by standing in the air. The occurrence or production of small quantities of indigo in urine had been observed by Hassel and others: it was, however, generally considered as a morbid secretion; but lately Dr. Schunck has proved that traces of indigo may be procured from healthy urine. The process by means of which this object may be attained is rather complicated. For a description of this, pro- cess, and for a full account of his researches on the formation of indigo-blue, which would overstep the limits of this elementary work, the reader is re- ferred to Dr. Schunck's original papers.1 Indigo comes into the market in the form of cubic cakes, which, rubbed 1 Memoirs of the Literary and Philosophical Society of Manchester, vol. xii. 177; xiv., 181, 239. 514 INDIGO. with a hard body, exhibit a copper-red appearance; its powder has an in- tensely deep-blue tint. The best is so light as to swim upon water. In addition to the blue coloring matter, or true indigo, it contains at least half its weight of various impurities, among which may be noticed a red resinous matter, the indigo-red of Berzelius; these may be extracted by boiling the powdered indigo in dilute acid, alkali, and afterwards in alcohol. Pure indigo is quite insoluble in water, alcohol, oils, dilute acids, and alka- lies ; it dissolves in about 15 parts of concentrated sulphuric acid, forming a deep-blue pasty mass, entirely soluble in water, and often used in dyeing: this is sulphindylic or sulphindigotic acid, a compound analogous to sulphovinic acid, capable of forming with alkaline bases blue salts, which, although easily soluble in pure water, are insoluble in saline solutions. If an insufficient quantity of sulphuric acid has been employed, or digestion not long enough continued, a purple powder is left on diluting the acid mass, soluble in a large quantity of pure water. The Nordhausen acid answers far better for dissolv- ing indigo than ordinary oil of vitriol. Indigo may, by cautious management, be volatilized; it forms a fine purple vapor, which condenses in brilliant copper-colored needles. The best method of subliming this substance is, ac- cording to Mr. Taylor, to mix it with plaster of Paris, make the whole into a paste with water, and spread it upon an iron plate. 1 part indigo, and 2 parts plaster, answer very well. This, when quite dry, is heated by a spirit- lamp : the volatilization of the indigo is aided by the vapor of water disengaged from the gypsum, and the surface of the mass becomes covered with beautiful crystals of pure indigo, which may be easily removed by a thin spatula. At a higher temperature, charring and decomposition take place. In contact with deoxidizing agents, and with an alkali, indigo suffers a very curious change; it becomes soluble and nearly colorless, perhaps returning to the same state in which it existed in the plant. It is on this principle that the dyer prepares his indigo-vat: — 5 parts of powdered indigo, 10 parts of green vitriol, 15 parts of hydrate of lime, and 60 parts of water, are agitated together in a close vessel, and then left to stand. The hydrated protoxide of iron, in conjunction with the excess of lime, reduces the indigo to the soluble state; a yellowish liquid is produced, from which acids precipitate the white or deoxidized indigo as a flocculent insoluble substance, which absorbs oxygen with the greatest avidity, and becomes blue. Cloth, steeped in the alkaline liquid, and then exposed to the air, acquires a deep and most permanent blue tint by the deposition of solid insoluble indigo in the substance of the fibre. Instead of the iron salt and lime, a mixture of dilute caustic soda- and grape- sugar dissolved in alcohol may be used; the sugar becomes oxidized to formic acid, and the indigo reduced. On allowing a solution of this description to remain in contact with the air, it absorbs oxygen and deposits the indigo in the crystalline condition. The following formulas represent the composition of the bodies described:— Blue insoluble indigo.....C16H5N02 AVhite, or reduced indigo1. . . . Ol6H6N02 Sulphindylic acid.....Cl6H4NO,2S03, HO. Products of the Decomposition of Indigo. The products of the destructive modifications of indigo by powerful chemi- cal agents of an oxidizing nature are both numerous and interesting, inas- 1 Properly liydrogenizcd indigo, if the above be the correct view ; white indigo may, however, be viewed as a hydrate, and blue indigo as an oxide of one and the same substance. White indigo...........CuIIsNO+HO Blue indigo...........C1CU5NO + O. INDIGO. 515 much as they connect this substance in a very curious manner with several other groups of organic bodies, especially with those of the salicyl- and phenyl-series. Many of them are exceedingly beautiful, and possess very re- markable properties. Isatin. — One part of indigo reduced to fine powder, and rubbed to a paste with water, is gently heated with a mixture of one part of sulphuric acid and one part of bichromate of potassa dissolved in 20 or 30 parts of water. The indigo dissolves with very slight disengagement of carbonic acid towards the end, forming a yellow-brown solution, which, on standing, deposits im- pure isatin in crystals. These are collected, slightly washed and redissolved in boiling water: the filtered solution deposits on cooling the isatin in a state of purity. Or, powdered indigo may be mi::ed with water to a thin paste, heated to the boiling-point in a large capsule, and nitric acid added by small portions until the color disappears; the whole is then largely diluted with boiling water, and filtered. The impure isatin which separates on cooling is washed with water containing a little ammonia, and re-crystallized. Both these processes require careful management, or the oxidizing action proceeds too far, and the product is destroyed. Isatin forms deep yellowish-red prismatic crystals of great beauty and lustre; it is sparingly soluble in cold water, freely in boiling water, and also in alcohol. The solution colors the skin yellow, and causes it to emit a very disagreeable odor. It cannot be sublimed. Isatin contains the elements of indigo plus 2 eq. of oxygen, or C16H5N04. A solution of potassa dissolves isatin with purple color: from this solution acids precipitate the isatin unchanged. AVhen boiled, however, the color is destroyed, and the liquid furnishes on evaporation crystals of the potassa-salt of a new acid, the isatic, containing C16H6N05,HO. In the free state this is a white and imperfectly-crystalline powder, soluble in water, and easily decom- posed into isatin and water. By chlorine isatin is converted into the substitution product chlorisatin, C,6(H4C1)N04, a body closely resembling isatin itself in properties. If an alcoholic solution and excess of chlorine be employed other products make their appearance, as chloranile, CI2C1404, trichlorophenol, C12(H3C13)02, and a resinous substance. The former of these substances, the position of which in the kinone-series has been already noticed (page 456), yields other products with potassa and ammonia. Bromisalin is easily formed. The change which isatin, and its chlorinetted and brominetted congeners, undergo when submitted to the action of fusing hydrate of potassa, has been already considered in the section on the Artificial Organic Bases (see page 499). Exposed to the action of sulphuretted hydrogen and sulphide of ammonium, isatin furnishes several-new compounds, as isathyde, sulfesathyde, sulfasathyde. A hot solution of isatin, when treated with sulphide of ammonium, gives rise to a deposit of sulphur, a white crystallized substance being produced at the same time: it has received the name of isathyde, and contains C16H6N04. It is obvious that it bears to isatin the same relation as white to blue indigo. If the sulphide of ammonium be replaced by sulphuretted hydrogen, bisulphi- sathyde, Cl6H8N02S:. is produced, which is the former, 2 eq. of oxygen being replaced by 2 eq. of sulphur. An alcoholic solution of potassa converts this into sulphisathyde, C16H6N03S, in which only one-quarter of the oxygen in isatin is replaced by sulphur. Under the influence of cold aqueous solution of potassa, bisulphisathyde yields indin, C16116N02, which is isomeric with white indigo. AVhen treated with boiling potassa, indin fixes the elements of 2 eq. of water, and becomes indie acid, Ci6H7N03,HO, the potassa-salt of which forms fine black needles. Ammoniacal gas and solution of ammonia yield with isatin a series of inte- resting substances, containing the nitrogen of the ammonia in addition to that of the isatin. 516 INDIGO. Action of chlorine on indigo. — In the dry state chlorine has no action whatever on indigo, even at the temperature of 212° (100°C)- In contact with water, the blue color is instantly destroyed, and cannot again be restored. The same thing happens with the blue solution of sulphindylic acid. When chlorine is passed into a mixture of powdered indigo and water until tho color disappears, and the product is then distilled in a retort, water contain- ing hydrochloric acid and a mixture of two volatile bodies, trichloraniline, C,2(H4C13)N, and trichlorophenol, C12(H3C]3)02, pass over into the receiver, while the residue of the retort is found to contain chlorisatin, already men- tioned, and bichlorisatin, C,6(H3C12)N04, much resembling the former, but more freely soluble in alcohol. Both these bodies yield acids in contact with boil- ing solution of potassa, by assimilating the elements of water. The action of bromine on indigo is very similar. Anilic and picric acids.—Anilic or indigotic acid is prepared by adding powdered indigo to a boiling mixture of 1 part of nitric acid and 10 parts of water, until the disengagement of gas ceases, filtering the hot dark-colored liquid, and allowing it to stand. The impure anilic acid so obtained is con- verted into the lead-salt, which is purified by crystallization and the use of animal charcoal, and then decomposed by sulphuric acid. Anilic acid forms fine white or yellowish needles, which have a feebly-acid taste, and very spa- ring degree of solubility in cold water. In hot water and in alcohol it dissolves easily. It melts when heated, and on cooling assumes a crystalline structure. By careful management it may be sublimed unchanged. Anilic acid contains C14H6NO10 = C,4(H6N04)06. It has been mentioned that the same acid is rea- dily prepared from salicylic acid (see page 444). Hence it is more appropri- ately called nitro-salicylic acid. Picric, carbazotic, or nitrophenisic acid, is one of the ultimate products of the action of nitric acid upon indigo and numerous other substances, as silk, wool, several resins, especially that of Xanthorrhoza hastilis (yellow gum of Botany Bay), salicin and some of its derivatives, cumarin, and phenyl-alcohol and other bodies belonging to the phenyl-series. It may be prepared from indigo by adding that substance in coarse powder, and by small portions, to 10 or 12 times its weight of boiling nitric acid of sp. gr. 1-43. AVhen the last of the indigo has been added, and the action, at first extremely violent, has become moderated, an additional quantity of nitric acid may be poured upon the mixture, and the boiling kept up until the evolution of red fumes nearly ceases. AVhen cold, the impure piric acid obtained may be removed, converted into potassa-salt, several times recrystallized, and, lastly, decom- posed by nitric acid. In the pure state it forms beautiful pale-yellow scaly crystals, but slightly soluble in cold water, and of insupportably bitter taste. Picric acid is used in dyeing; it forms a series of crystallizable salts of a yel- low or orange color: that of potassa forms brilliant needles, and is so little soluble in cold water, that a solution of picric acid is occasionally used as a precipitant for that base. The alkaline salts of this acid explode by heat with extraordinary violence. The crystals of picric acid contain C1()H0N„ 013HO. * 3 If a solution of picric acid be distilled with hypochlorite of lime, or a mix- ture of chlorate of potassa and hydrochloric acid, an oily liquid of a pene- trating odor is obtained, having a sp. gr. of 1-665, and boiling between 237° and 239° (114° and 115°C). This substance, chloropicrin, was discovered by Stenhouse, who gave the formula C4Cl7N2O10; MM. Gerhardt and Cahours assign to it the formula C2C13N04. According to the latter formula, which is more probable, chloropicrin would be chloroform, in which the hydrogen is replaced by the elements of hyponitric acid. Chloroform, C2(HC13); Chloropicrin, C2 (N04C13). Products of the action of hydrate of potassa upon indigo.__One of the most remarkable of these, aniline, has been already described (see page 499). LICHENS. 517 AVhen powdered indigo is boiled with a very concentrated solution of caustic potassa, it is gradually dissolved, with the exception of some brownish floc- culent matter, and the liquid on cooling deposits yellow crystals of the potassa- salt of a new acid, the chrysanilic, which can be procured in a purer state, by dissolving the crystals in water, filtering from reproduced indigo, and adding a slight excess of mineral acid. Chrysanilic acid can be obtained in indis- tinct crystals from weak alcohol: it is supposed to contain C^H^N^g,HO; but it is very probable that it is a mixture of several substances, especially isatic acid. AVhen this substance is boiled with mineral acids, it is decomposed into an- other new acid, the anthranilic, which remains in solution, and a blue insoluble matter resembling indigo: a similar effect is slowly produced by the action of the air upon an alcoholic solution of chrysanilic acid. Anthranilic acid is colorless, sparingly soluble in cold water, easily soluble in alcohol. It melts when heated, sublimes under favorable circumstances, but decomposes entirely when heated in a narrow tube into carbonic acid and aniline. It contains C14H6N03,HO. By treatment with nitrous acid, anthranilic acid is converted into salicylic acid, C14H6N03,HO -f N03 = C14H505,HO 4- HO -f- 2N. According to M. Cahours, pure indigo can also be converted into salycilic acid by fusion with hydrate of potassa: a particular temperature is required, somewhat above 570°(298°C), and the operation is by no means always suc- cessful. lichens. Litmus is used by the dyer as a red coloring matter; the chemist employs it in the blue state as a test for the presence of acid, by which it is instantly reddened. In preparing test-papers for chemical use with infusion of litmus, good writing or drawing paper, free from alum and other acid salts, should be chosen. Those sheets which after drying exhibit red spots, or patches, may be reddened completely by a little dilute acetic acid, and used, with much greater advantage than turmeric-paper, to discover the presence of free alkali, which restores the blue color. Many lichens, when exposed in a moistened state to the action of ammonia, yield purple or blue coloring principles, which, like indigo, do not pre-exist in the plant itself. Thus, the Roccella linctoria, the Variolaria orcina, the Leca- nora tartarea, &c, when ground to paste with water, mixed with putrid urine or solution of carbonate of ammonia, and left for some time freely exposed to the air, furnish the archil, litmus, and cudbear of commerce, very similar substances, differing chiefly in the details of the preparation. From these the coloring matter is easily extracted by water or a very dilute solution of am- monia. The lichens have been extensively examined by Schunck, Stenhouse, and several other chemists. The whole subject has been lately revised by Strecker, whose formulas have been adopted in the following succinct account: — Ekythric acid. —The lichen Roccella tinctoria, from which the finest kind of archil is prepared, is boiled with milk of lime, the filtered solution is pre- cipitated by hydrochloric acid, and the precipitate dried and dissolved in warm, not boiling, alcohol, from which on cooling crystals of erythric acid are depo- sited. This is a very feeble acid, colorless, inodorous, difficultly soluble in cold and even in boiling water, readily soluble in ether. Its solution, when mixed with chloride of lime, assumes a blood-red color. Boiled with water for some time, erythric acid absorbs 2 eq. and yields picro-erythrin, a crys- tallizable, bitter principle, and a new acid presently to be described, which is termed by some chemists lecanoric, by others orsellinic acid. If the ebullition be continued, the orsellinic acid undergoes a further change, being converted into a crystalline substance, orcin, of which mention will shortly be made. 44 518 LICHENS, Picro-erythrin, when boiled with baryta water, is decomposed into orchin, crythromannite (see page 444), and carbonic acid. The composition of these various substances is expressed by the following formulae: — Erythric acid Orsellinic acid . Picro-erythrin . Orcin C20Hn^ic ^16*1 8^ 8 C24H,60,4 CMH sO 4 And the successive changes which occur by ebullition are represented by the following equations : — 2C20HnO104-2HO = Erythric acid. C,6H808 = Orsellinic acid. C24H160144-2IIO Picro-erythrin. L'aiH.fiO, C14H804 4- C8H10O8+2CO2 Orcin. Eyrthro-mannite. Alphaorsellic acid is obtained from the South American variety of Roc- cella tinctoria. The preparation and the properties of this substance are per- fectly analogous to those of erythric acid. Alphaorsellic acid contains C38H14014; by boiling with baryta-water it likewise furnishes orsellinic acid. C.11,,0,,+ 2110 Alphaorsellic acid. 2C]6H808 Orsellinic acid. If the ebullition be continued too long, a great portion of the orsellinic acid is converted into orcin. Orsellinic acid, frequently called lecanoric acid, whether prepared from erythric or alphaorsellic acid, forms crystals which are far more soluble in water than either of the acids from which it has been prepared. Its taste is somewhat bitter. Boiled with water, it yields, as has been stated, orcin ; under the influence of air and ammonia, it assumes a beautiful purple color. If the lichens, instead of being treated with milk of lime, be exhausted with boiling alcohol, the erythric and alphaorsellic acids are likewise decomposed; but instead of orsellinic acid, the ether of .this substance, C4H50,Cl6H707 is formed. This ether was formerly described under the name pseudo-erylhrin, until Dr. Schunck pointed out the true nature of the substance. Orsellinate of ethyl may be likewise produced by boiling pure orsellinic acid with alcohol. It crystallizes in colorless lustrous plates, which are readily soluble in boiling water, alcohol, and ether. Betaorsellic acid is found in Roccella tinctoria grown at the Cape : it is ob- tained like erythric and alphaorsellic acid, which it resembles in properties. Betaorsellic acid contains C34Hl6Ol5: by boiling with water, it yields likewise orsellinic acid, together with hair-like crystals of a silvery lustre of a sub- stance called roccellinin, which has the composition C,8H807. LICHENS. 519 CmH^Ou = CI8H808 4- C18H807 Betaorsellic acid. Orsellinic acid. Roccellinin. The decomposition of betaorsellic acid icj obviously analogous to that of erythric acid, the roccellinin representing the picro-erj'thrin. Evernic acid is extracted by milk of lime from Evernia prunastri, which was formerly believed to contain orsellinic acid. Evernic acid is very difficultly soluble even in boiling water; it assumes a yellow color with chloride of lime. When boiled with the alkalies, it yields another crystalline acid, everninic acid, differing from the preceding by its free solubility in boiling water. The com- position of evernic acid is represented by the formula C34H)6014, that of ever- ninic acid by C,8H10O3. Evernic acid, when boiled for a considerable time with baryta, yields orcin : everninic acid does not give a trace of this substance ; it is therefore probable that evernic acid, under the influence of alkalies, yields in addition to everninic acid likewise orsellinic acid, from which the orcin is derived, and that this decomposition is represented by the equation:— C3iHieOM+2HO = C16H808 4- C18HI0O8 Evernic acid. Orsellinic acid. Everninic acid. Parellic acid. — Lecanora parella contains an acid probably analogous to erythric, alphaorsellic, betaorsellic, and evernic acids, the composition of which is, however, still unknown. By boiling with baryta it yields orsellinic acid and parellic acid, C18H608. Orcin is the general product of decomposition of the acids previously described, under the influence of heat or alkaline earths. Orcin is best prepared by boiling lecanoric or orsellinic acid, pure or impure, with baryta-water, precipitating the excess of baryta by carbonic acid, and evaporating the filtered liquid to a small bulk. It forms, when pure, large, square prisms, which have a slightly-yellowish tint, an intensely-sweet taste, and a high degree of solubility both in water and alcohol. AVhen heated, orcin loses water and melts to a syrupy liquid, which distils unchanged. The crystals of orcin contain C14II804,2HO. Orcein.—AVhen ammonia is added to a solution of orcin, and the whole ex- posed to the air, the liquid assumes a dark-red or purple tint by absorption of oxygen ; a slight excess of acetic acid then causes the precipitation of a deep-red powder, not very soluble in water, but freely dissolving in ammonia and fixed alkalies, with a purple or violet color. This powder is an azotized substance, formed from the elements of the ammonia and the orcin, called orcein; it probably constitutes the chief ingredient of the red dye-stuff of the commercial articles before mentioned. The composition of orcein is less cer- tain than that of orcin; it probably contains C14H7N06, when its formation from orcin, under the joint influence of oxygen and ammonia, would be repre- sented by the equation: — CI4II804,2HO 4- 604- NH3 = C14H7N064- 6H0 Orcin. Orcein. Other substances are occasionally present in lichens: thus, the Usnca barbata and several other lichens contain usnic acid, a substance crystallizing from alcohol in fine yellowish-white needles with metallic lustre, having the formula C38H180,4. It gives no orcin by distillation, but a substance similar to it which probably contains C34HI806, and has been designated by the name of betaorcin. Its formation, which is attended by an evolution of carbonic acid, is repre- sented by the equation — 520 RED AND YELLOW DYES. C38HlSOl4 = C84H1806+4C08 Usnic acid. Betaorcin. The Parmelia parietina furnished another new substance, chrysophank acid, crystallizing in fine golden-yellow scales, and containing C10H4O3. It is a very stable substance, and may be sublimed without much decomposition. The same body is present in rhubarb, together with emodin, a principle closely resembling chrysophanic acid. RED AND YELLOW DYES. Cochineal.—This is a little insect, the Coccus cacti, which lives on several species of cactus, found in warm climates, and cultivated for the purpose, as in Central America. The dried body of the insect yields to water and alcohol a magnificent red coloring matter, precipitable by alumina and oxide of tin; carmine is a preparation of this kind. In cochineal the coloring matter is associated with several inorganic salts, especially phosphates and nitrogenous substances. Mr. AVarren De La Rue, who has published a very elaborate in- vestigation of cochineal,1 has separated the pure coloring matter, which he calls carminic acid, by the following process. The aqueous decoction of the insect is precipitated by acetate cf lead, and the impure carminate of lead washed and decomposed by hydrosulphuric acid: the coloring matter thus separated is submitted again to the same treatment. A solution of carminic acid is thus obtained, which is evaporated to dryness, re-dissolved in absolute alcohol, and digested with crude carminate of lead, whereby a small quantity of phosphoric acid is separated, and lastly mixed with ether, which separates a trace of a nitrogenous substance. The residue now obtained on evaporation is pure carminic acid. It is a purple-brown mass, yielding a fine red powder, soluble in water and alcohol in all proportions, slightly soluble in ether. It is soluble without decomposition in concentrated sulphuric acid, but readily attacked by chlorine, bromine, and iodine, which change its color to yellow. It resists a temperature of 276°-8 (136°C), but is charred when heated more strongly. Carminic acid is a feeble acid. The composition of the substance, dried at 248° (120°C), is represented by C28H14016, which formula is corrobo- rated by the analysis of a copper compound, CuO,C28H,40]6. By the action of nitric acid upon carminic acid, together with oxalic acid, a splendid nitrogenetted acid, crystallizing in yellow rhombic plates, is obtained. This substance, to which the name nitrococcusic acid was given, is bibasic; it contains Cl6H3N3Ol6,2HO. It is soluble in cold, more so in boiling water, and readily soluble in alcohol and ether. Nitrococcusic acid is evidently derived from a non-nitrogenous compound, in which part of the hydrogen is replaced by the elements of hyponitric acid. Like the substances of this class, A, explodes when heated. In the mother-liquor, from which the carminic acid has been separated, Mr. AVarren De La Rue discovered a white, crystalline, nitrogenous substance, for which he established the formula C18HnN06. This substance is identical with tyrosine, which will be mentioned in the section on Animal Chemistry. Madder.—The root of the Rubia tinctorum, cultivated in southern France the Levant, &c, is the most permanent and valuable of the red dye-stuffs. In addition to several yellow coloring matters, which are of little importance for the purposes of the dyer, madder contains two red pigments which are called alizarin and purpurin. These substances have been the subject of very exten- sive researches by Debus, Higgins, and especially by Schunck. The latest 1 Mem. of the Chem. Soc. vol. iii. p. 454. RED AND YELLOW DYES. 521 papers on madder have been published by Wolff and Strecker, whose formulae are quoted in the following abstract. Alizarin.—The aqueous decoction of madder is precipitated by sulphuric acid, and the precipitate washed and boiled with sesquichloride of aluminum, which dissolves the red pigments; an insoluble brownish residue remaining behind. The solution, when mixed with hydrochloric acid, yields a precipitate consisting chiefly of alizarin, however, still contaminated with purpurin. The impure alizarin thus obtained may be further purified by again throwing down the alcoholic solution with hydrate of alumina, and boiling the precipitate with a concentrated solution of soda, which leaves a pure compound of alu- mina and alizarin behind. From this the alizarin is separated by hydrochloric acid and recrystallized from alcohol. Pure alizarin crystallizes in splendid red prisms, which may be sublimed. It is but slightly soluble in water and in alcohol, but dissolves in concentrated sulphuric acid with a deep-red color. On addition of water, the coloring matter is reprecipitated unchanged. It is also soluble in alkaline liquids, to which it imparts a magnificent purple color. It is insoluble in cold solution of alum. Alizarin is the chief coloring matter of madder; it contains C^HgOg 4- 4HO, and is a feeble acid; but a few definite compounds with mineral oxides have been prepared, among which a lime-com- pound, C2?H606,3Ca0 4- 3HO, may be quoted. The action of nitric acid upon alizarin gives rise to the formation of oxalic acid and phthalic acid, a sub- stance which will again be mentioned among the products of decomposition of naphthalin. C20H6O6 + 2IIO + 80 = 2(C203,H0) + Cl6H608 Alizarin. Phthalic acid. runruRiN. — Madder is allowed to ferment and then boiled with a strong solution of alum. The solution, when mixed with sulphuric acid, yields a red precipitate, which is purified by recrystallization from alcohol. Purpurin thus obtained, crystallizes in red needles, which contain C,8H606 4- 2H0, i. e., 2 eq. of carbon less than alizarin. AVhen treated with nitric acid, purpurin, like alizarin, furnishes oxalic and phthalic acids. Purpurin likewise con- tributes to the tinctorial properties of madder, but less so than alizarin. Together with alizarin and purpurin several other substances occur in madder, among which may be noticed an orange pigment, rubiacin, convertible by oxidizing agents into a peculiar acid, rubiacic acid, a yellow pigment, xanthin, a bitter principle, rubian, sugar, pectic acid, and several resins, &c. Garancin is a coloring material, which is produced by the action of sulphuric acid upon madder. This substance possesses a higher tinctorial power than madder itself. The beautiful Turkey red of cotton cloth is a madder-color; it is given by a very complicated process, the theory of which is not perfectly elucidated. Safflower. —This substance contains a yellow and a red coloring matter, the latter being insoluble in water, but soluble in alkaline liquids. The safflower may be exhausted with water acidulated with acetic acid, and the solution mixed with acetate of lead, and filtered from the dark-colored impure pre- cipitate. The lead compound of the yellow pigment may then be thrown down by addition of ammonia, and decomposed by sulphuric acid. In its purest form the yellow matter forms a deep yellow, uncrystallizable, and very soluble substance, very prone to oxidation. In its lead-compound it has probably the composition C24H12013. The red matter or carthamin is obtained from the residual safflower by a dilute solution of carbonate of soda; pieces of cotton wool are immersed in the liquid, and acetic acid gradually added. The dried cotton is then digested in a fresh quantity of the alkaline solution, and the liquid supersaturated with citric acid, which throws down the carthamin in carniinc-rcd flocks It 44* 522 RED AND YELLOW DYES. forms, when pure and dry, an amorphous, brilliant, green powder, nearly insoluble in water, but soluble in alcohol with splendid purple color. It contains C14H807. Brazil-wood and logwood give red and purple infusions, which are largely used in dyeing; the coloring principle of logwood is termed hematoxylin, and has been obtained in crystals. This substance contains C40H7O,5 + 8HO. Acids brighten these colors, and alkalies render them purple or blue. Among yellow dyes, quercitron bark, fustic-wood, and saffron, may be men- tioned, and also turmeric; these all give yellow infusions to water, and furnish more or less permanent colors. Purree or Indian yellow, a body of unknown origin, used in water-color painting, according to the researches of Stenhouse and Erdmann, is a com- pound of magnesia with a substance termed purreic or euxanthic acid. The latter, when pure, crystallizes in nearly-colorless needles, sparingly soluble in cold water, and of sweetish-bitter taste. It forms yellow compounds with the alkalies and earths, and is decomposed by heat, with production of a neutral crystalline sublimate, purrenone or euxanthone. Purreic acid contains C40H16O21, purrenone C13H404. By the action of chlorine, bromine, and nitric acid, a series of substitution-products are formed. Frangulin, C12II606, from Rhamnus frangula, crystallizes in scales resem- bling chrysophanic acid. The action of nitric acid converts frangulin into a nitro-compound, said to contain C40HnN3O37, very similar to chrysamnic acid, to be noticed further on. Moeindin, C28H150]5, yellow crystalline coloring matter, occurring in the root of Morinda citrifolia, which is called Soranjee in the East Indies. When heated it is converted into a beautiful crystalline body, morindon, containing C28 " 10^*10- Aloes. — Certain of the products of the action of nitric acid upon aloes resembles very much some of the derivatives of indigo, without, however, it seems, being identical with them. Powdered aloes, heated for a considerable time with excess of moderately-strong nitric acid, yields a deep-red solution, which deposits on cooling a yellow crystalline mass. This, purified by suitable means, constitutes chrysammic acid; it crystallizes in golden-yellow scales, which have a bitter taste, and are but sparingly soluble in water. Its potassa- salt has a carmine-red tint, and exhibits a green metallic lustre, like that of murexide. The formula of chrysammic acid is not perfectly established. It is probably Ci4HN20,,,HO. Like picric acid, it yields, with chloride of lime, chloropicrin. The mother-liquor from which the chrysammic acid has been deposited contains a second acid, the chrysolepic, which also forms golden- yellow, sparingly-soluble, scaly crystals. The potassa-salt forms small, yellow prisms, of little solubility. It explodes by heat. Chrysolepic acid contains Cl2H2N3013,HO : it is identical with picric acid. To these may be added the styphnic acid, described by MM. Boettger and AVill, produced by the action of nitric acid of sp. gr. 1 -2 upon assafcetida and several other gum-resins and extracts. Purree, when treated with excess of nitric acid, likewise yields styphnic acid. It crystallizes, when pure, in slender, yellowish-white prisms, sparingly soluble in water, readily dissolved in alcohol and ether. It has a purely astringent taste, and stains the skin yellow. By a gentle heat it melts, and on cooling becomes crystalline; suddenly and strongly heated, it burns like gunpowder. It also furnishes chloropicrin. The salts of this substance mostly crystallize in orange-yellow needles, and explode with great violence by heat. Styphnic acid contains C,2H2N3015,HO, i. e. picric acid + 2 eq. of oxygen. VOLATILE OILS. 523 VOLATILE OILS. The volatile oils of the vegetable kingdom are exceedingly numerous ; they are secreted by plants, and confer upon their flowers, fruits, leaves, and wood their peculiar odors. These substances are mostly procured by distilling the plant, or part of the plant, with water: their points of ebullition almost always lie above that of water; nevertheless, at 212° (100°C) the oils emit vapor of very considerable tension, which is carried over mechanically, and condensed with the steam. The milky or turbid liquid obtained, when left at rest, separates into oil and water. Sometimes the oil is heavier than tho water, and sinks to the bottom; sometimes the reverse happens. The volatile oils, when pure, are colorless : they very frequently, however, have a yellow, and, in rarer cases, a green color, from the presence of impurity. The odor of- these substances is usually powerful, and their taste pungent and burning. They resist saponification completely, but when exposed to the air frequently become altered by slow absorption of oxygen, and assume the character of resins. They mix in all proportions with fat oils, and dissolve freely both in ether and alcohol: from the latter solvent they are precipitated by the addition of water. As already mentioned, the volatile oils communicate a greasy stain to paper, which disappears by warming; by this character any adulteration with fixed oils can be at once detected. A solid crystalline matter, corresponding to the margarin of the common oils, frequently separates from these bodies; it bears the general name of stearop- tene, and differs probably in almost every case. The essential oils may be conveniently divided into three classes: viz., those consisting of carbon and hydrogen only; those consisting of carbon, hydrogen, and oxygen; and those containing in addition sulphur and nitrogen. Oils composed of Carbon and Hydrogen. Oil, or essence of turpentin. — This substance may be tauen as the typo or representative of the class; it is obtained by distilling with water the soft or semi-fluid balsam called in commerce crude turpentine, which exudes from various pines and firs, or flows from wounds made for the purpose in the wood. The solid product left after distillation is common rosin. Oil of tur- pentin, when further purified by rectification, is a thin, colorless liquid, of powerful and well-known odor: its density in the liquid state is 0-865, and that of its vapor 4-764; it boils at 312° (155°C). In water it dissolves to a small extent, and in strong alcohol and ether much more freely; with fixed oils it mixes in all proportions. Strong sulphuric acid chars and blackens this substance; concentrated nitric acid and chlorine attack it with such violence that inflammation sometimes ensues. Oil of turpentin is composed of C5H4 or C^Hjg. AVith hydrochloric acid tho oil forms a curious compound, which has been called artificial camphor, from its resemblance in odor and appearance to that Bubstance. It is prepared by passing dry hydrochloric acid gas into the pure 524 VOLATILE OILS. oil, cooled by a freezing mixture. After some time, a white crystalline sub- stance separates, which may be strained from the supernatant brown and highly-acid liquid, and purified by alcohol, in which it dissolves very freely. This substance is neutral to test-paper, does not affect nitrate of silver, and sublimes without much decomposition: it contains C^I^Cl, or perhaps C^Hjg, HC1. The dark mother-liquor contains a somewhat similar, but fluid com- pound. Different specimens of oil of turpentin yield very variable quantities of these substances, which may, perhaps, arise from the coexistence of two very similar and isomeric oils in the ordinary article. When these hydrochlo- rates are decomposed by distillation with lime, they yield liquid oily products differing in some particulars from the original oil of turpentin, but having the same composition as that substance. That from the solid has received the name of camphylene, and that from the liquid compound terebylene. The hypo- thetical and non-isolable modifications of the oil supposed to exist in the solid and liquid camphor are termed respectively camphene and terebene. Another isomeric compound, colophene, is produced by distilling oil of tur- pentin with concentrated sulphuric acid. It is a viscid, oily, colorless liquid, of high boiling-point, and exhibiting by reflected light a deep-bluish tint, —a phenomenon often remarked in bodies of this class. Bromine and iodine also form compounds with oil of turpentin. Oil of turpentin is very largely used in the arts, in painting, and as a sol- vent foi>resins in making varnishes. Bottles in which rectified oil of turpentin, not purposely rendered anhydrous, has been preserved, are often studded in the interior with groups of beautiful, colorless, prismatic crystals, which form spontaneously. These have the com- position of a hydrate of oil of turpentin. These crystals contain C20HI6H6O6. Oil of lemons is expressed from the rind of the fruit, or obtained by dis- tillation with water. This oil differs very much from the last in odor, but closely resembles it in other respects. It has the same composition as oil of turpentin, and forms with hydrochloric acid two compounds, one solid and crystalline, the other fluid. The solid contains C]6H8,IIC1. The oils of orange-peel, bergamot, pepper, cubebs, juniper, capivi, elemi, the laurel-oil of Guiana, the East Indian grass-oil, and the principal part of oil of hop, are hydrocarbons, isomeric with the oils of turpentin and lemons. Essential Oils containing Oxygen. The essential oils containing oxygen are very numerous, and, in fact, make up the great bulk of the bodies of this class employed in medicine and per- fumery. They are seldom homogeneous, and in consequence do not often exhibit fixed boiling-points. Some of these oils have been made the subjects of much chemical research, but the majority yet require examination. Three of the most interesting, viz., those of bitter almonds, cinnamon, and the Spiraea ulmaria, have been already described. Oil of aniseed. —The oil distilled from the fruit of the Pimpinella anisum consists of two substances, one of which is a fluid oil, and the other a solid crystalline substance, so abundant as to cause the whole to solidify at the tem- perature of 50° (10°C). By pressure between folds of bibulous paper, and crystallization from alcohol, the solid essence may be obtained pure. It forms colorless pearly plates, more fragrant than the crude oil, which melt when gently heated, and distil at a high temperature. It contains G^H^O,,. This substance is attacked energetically by chlorine, bromine, and nitric acid; it combines with hydrochloric acid, but is unaffected by solution of caustic potassa. AVith bromine the solid essence yields a white inodorous crystallizable compound, bromanisal, containing C^HgBr^O. The action of chlorine is more Complex, several successive compounds being produced. AVith sulphuric acid two products are obtained, a compound acid analogous to sulphovinic VOLATILE OILS. 525 acid, and a white, solid neutral substance, anisoin, isomeric with tho essence. The products of the action of nitric acid vary with the strength of the acid employed; the most important are hydride of anisyl; anisic acid, a substance very much resembling salicylic acid in properties, sparingly soluble in cold water, freely in alcohol and ether; nilranisic acid, a yellowish-white, crystal- line, sparingly-soluble powder; and nitraniside, a resinous body, produced by fuming nitric acid. The hydride of anisyl in a pure state is a yellowish oily liquid, having an aromatic odor of hay: it is heavier than water, and boils at 400° (254°-5C). Caustic potassa, concentrated and boiling, slowly decomposes it: with fused hydrate of potassa, it is instantly converted into anisic acid with disengage- ment of hydrogen; air and oxidizing bodies in general produce the same effect. Ammonia forms with it a crystalline compound analogous to hydrobenzamide. Hydride of anisyl contains"C)6H804. This body exhibits, with an alcoholic solution of potassa, the same deportment as hydride of benzoyl (see page 438); it is converted into a mixture of anisate of potassa and a crystalline body, which, when purified by distillation, boils at 482° (250°C). The composition of this compound, which may be viewed as the alcohol of anisic acid, is repre- sented by the formula C)6H,0O4. Anisic acid contains C,6H706,HO, i. e., hydride of anisyl and 2 eq. of oxygen. AVhen tested with an excess of lime or baryta, it suffers a decomposition, ana- logous to that of benzoic and salicylic acid, losing 2 eq. of carbonic acid, and being converted into an oxygenated oil, boiling at 302° (150°C), to which the name anisol has been given. CI6H705,HO 4- 2CaO = 2(CaO,CO)2 4- C14H802 Anisic acid. Anisol. The action of nitric acid upon anisol gives rise to the formation of three substitution products, nitro-, binitro-, and trinitro-anisol, the former of which is a liquid, while the two latter are crystalline solids. They contain respec- tively C14(HN04)02; C)4(H6 [N04]2)02, and C,4(H5[N04]3)02. Treated with sulphuretted hydrogen these substances are converted into three organic bases, anisidine C14H9N02, nitranisidine C14(H8N04)N02, and binitranisidine C,4(H7 [NO/j2)N02. Nitranisic acid is the nitro-substitute of anisic acid; it contains Cj6(H6N04) 06,HO. The solid portion of the oils of bitter fennel and badian is identical with that of oil of anised. The fluid component of the fennel-oil is isomeric with oil of turpentin. Draconic acid, obtained by the action of nitric acid upon the oil of Artemisia dracunculus, is identical with anisic acid. The various substances belonging to this group are homologous to the mem- bers of the salicyl-series, described in a former part of the Manual (see page 442), as may be seen from the following comparison : — Salicylous acid C14 H6 04; C16 H8 04 Hydride of auisyL Salicylic acid . C,4 H6 06; C16 H8 06 Anisic acid. N;ScfS. M&.H c»{\}°> »"»—«"■ 526 VOLATILE OILS. Binitrophenol (Ni- A Q f H. \ 02; C14 { *L«n , ) 02 Binitranisol. trophenesic acid) / 12\(N04)2 j 2' 14 \ (N04)2 ( * Trinitrophenol (Ni-") f tt -. f II 1 • trophentsic acid) lC,J fi?n x y02; C,J ,J0 > V 02 Trimtranisol. Carbazotic acid J ^ ^°^ ' l ^0i>3i C14 H9 N02 Anisidine. CI41 ^0 } N02 Nitranisidine. C141 ,X, . | N02 Binitranisidinc. Oil of cumin is a mixture of two bodies, separable in great measure by dis- tillation, cymol, a liquid hydrocarbon, containing CcjqH,^ the most volatile por- tion of the oil, and cuminol, a colorless transparent oil, of powerful odor, easily changed in the air, and only to be distilled in a current of carbonic acid gas. Cuminol contains C20H12O2, and is consequently isomeric with the solid essence of aniseed. By oxidation, this substance, which is homologous to oil of bitter almonds, yields cumic acid, a white, fatty, volatile substance, insoluble in water, having but little odor, and crystallizing in prismatic tables. It con- tains CjjjHj.Og.HO (see homologues of benzoic acid, page 441). AVhen treated with an alcoholic solution of potassa, cuminol is converted into cumate of potassa and an oil, boiling at 469° (243°C), containing C^H,^, which may be viewed as the alcohol of the cumyi-series. According to recent researches the oil of Cicuta virosa is identical with cumin-oil. Oil of thyme. — The essential oil of Thymus vulgaris, like cumin oil, is a mixture of several bodies, from which a crystalline substance, fusible at 1110 (44°C), and boiling at 446° (230°C), may be separated. This substance, thy- mol, contains C^H,^, and is therefore isomeric with cumin-alcohol, from which it differs, however, by not yielding cumic acid. By oxidation with bin- oxide of manganese and sulphuric acid, thymol is converted into a volatile, crystalline body, thymoil, C24H1604, homologous to kinone (see page 442), which it resembles in its properties and chemical character. The oil of Pty- chotis ayowan appears to be identical with oil of thyme. Oil of rue. — The principal constituent of the oil of Rula graveolens is the compound C^H^O^ It may be separated from the oil by the addition of bi- sulphate of soda or ammonia, when a crystalline compound, CjjqHj.O.NI^O, 2S02 + 4 eq., is formed, which may be purified by crystallization. Treated with an acid this compound yields the oil in a state of purity. It boils at 446° (233°). Cooled to 30° or 28-5° (—1° or 2°C), the oil solidifies into a crystal- line mass. Oil of rue has the general character of an aldehyde. Heated with weak oxidizing agents it furnishes rutic or capric acid, C^ll 1903,UO. Boiled with strong nitric acid, carbon is eliminated; and instead of rutic acid, pelar- gonic acid, its lower homologue, is formed. Oil of cedar-wood, in like manner, contains two substances, a solid crystal- line compound, having the formula C^H^O^ and a volatile liquid hydrocar- bon, cedrene, C32H24, which can also be obtained by distilling the solid with anhydrous phosphoric acid. Oil of gaultheria procumbens.—This very remarkable substance is now known in commerce under the name of winter-green-oil; it consists almost wholly of a definite principle which distils unchanged at 435° (223°-8C), and contains, according to the analysis of M. Cahours, C16H806. AVhen mixed with dilute caustic potassa, it solidifies to a crystalline mass, which is a potassa-salt, from which the oil may be separated again unchanged on addi- tion of an acid. AVhen distilled, however, with a concentrated solution of caustic potassa, the oil of gaultheria is resolved into salicylic acid and wood- VOLATILE OILS. 527 spirit, thus exactly resembling in its behavior the compound ethers which have bucn described in a previous section of the Manual (see page 371). This oil is, in fact, a veritable compound ether, salicylate of oxide of methyl. It is one of the ethers which the bibasic salicylic acid is capable of form- ing : that is salicylic acid in which one of the equivalents of water is replaced by oxide of methyl. The crystalline potassa-salt, formed by the addition of potassa to gaultheria-oil, which was formerly called gaultherate of potassa, is salicylate of methyl and potassa. AVhen treated in sealed tubes with iodide of methyl, this potassa-salt furnishes the second methyl-ether-compound of salicylic acid, which boils at 248°. The constitution of these compounds will be more intelligible by the following formulae: — . C14H404.2HO . CUH404,HO,KO . C14H404,2KO ;}ci4H404,HO,MeO •lci4H404,KO,MeO .' CI4H404,2McO. AVith ammonia oil of gaultheria yields salicylamide, C14TTrX04=C,4H504,NIT2, isomeric with anthranilic acid (see page 517), which is converted by fuming nitric acid into the nitro-substitute, nitro-salicylamide, C14(H4N04)04.NH2, crystallizing in yellowish-white needles. Gaultheria oil is isomeric with ani- sic (see page 525), and yields by distillation at a high temperature with an- hydrous lime and baryta, anisol, C)4H802, the same volatile liquid which is obtained from anisic acid by a similar process. Oil of valerian.—The oil obtained by distilling valerian-root with water has usually a viscid consistence, a yellowish color, and a powerful and dis- agreeable odor. It consists of at least three principles, namely, valeric (vale- rianic) acid, borneene (see camphor), a light volatile liquid hydrocarbon, much resembling and isomeric with oil of turpentin, and valerol, a neutral oily body, much less volatile than the preceding, of feeble odor, and convertible by oxi- dizing agents into valeric acid. It contains Cl2III0O2. Borneene, under cer- tain circumstances not well understood, assimilates the elements of water, and yields the solid camphor of Borneo, or borneol. Camphor.—Common camphor yields a good example of a concrete essential oil; it is obtained by distilling with water the wood of the Laurus camphora. AVhen pure, it forms a solid, white, crystalline, and translucent mass, tough, and difficult to powder, and having a powerful and very familiar odor. It melts when gently heated, and boils, distilling unchanged at a high tempera- ture. It slowly sublimes at the temperature of the air, and often forms beau- tiful crystals on the sides of bottles or jars containing it exposed to the light. Camphor is very sparingly soluble in water, but readily soluble in alcohol, ether, and strong acetic acid. It contains C10H8O, or C^lI^Og. By the action of nitric acid aided by heat, camphor is gradually oxidized and dissolved with production of camphoric acid: this substance forms small colorless needles or plates, of acid and bitter taste, sparingly soluble in cold water, and containing C,0H7O3,HO. It melts when heated, and yields by dis- tillation a colorless crystalline, neutral substance, containing C,0H7-O3, generally termed anhydrous camphoric acid. AVhen camphorate of lime is submitted to distillation, it yields a volatile oil containing oxygen: its formation and constitution are similar to that of ace- tone (page 396) or benzophcnone (page 434). This substance, phorone, contains C H,402? By the action of anhydrous phosphoric acid it loses water, and furnishes the hydrocarbon cumol, C18Hl2 (see page 441). Salicylic acid . Acid salicylate of potassa . Neutral salicylate of potassa Acid salicylate of methyl . Gaultheria oil . Salicylate of methyl and potassa Gaultherate of potassa Neutral salicylate of methyl 528 VOLATILE OILS. When camphor in vapor is passed over a mixture of hydrate of potassa and quicklime strongly heated in a tube, it is resolved without disengagement of gas into an acid body termed campholic acid, white, crystalline, and sparingly soluble in water, containing C20H1703,HO. By distillation with anhydrous phosphoric acid, this acid gives a volatile hydrocarbon, campholene. Camphor itself, by a similar mode of treatment, yields a colorless volatile liquid, CjjqII ,4, formerly called camphogen, but since found to be identical with the hydrocar- bon cymol, occurring in the oil of cumin. The camphor of Borneo, procured from the Dryabalanops camphora, con- tains C20HI3O2; it is accompanied by borneene, identical with that of the oil of valerian, and yields the same substance when distilled with anhydrous phosphoric acid. Nitric acid converts it into common camphor. The oils of peppermint, lavender, rosemary, orange-flowers, rose-petals, and many others, belong to the class of oxygenated essential oils. Essential Oils containing Sulphur. In the preparation of the sulphuretted volatile oils, distillatory vessels of copper, tin, or lead, must be avoided, as those metais are attacked by the sulphur. In other respects their manufacture offers no peculiarities. Oil of mustard. — The most remarkable member of the class is the oil obtained by distillation from black mustard-seed. White mustard yields none. Both varieties give, by expression, a bland fat oil. The volatile oil does not pre-exist in the seed, but is formed in the same manner as bitter-almond oil, by the joint action of water and a peculiar tfoagulable albuminous matter upon a substance yet imperfectly known, present in the grain, and termed myronic acid. The distilled oil, when pure, is colorless; it has a most powerful, pungent, and suffocating smell, and a density of 1-015. Applied to the skin, it pro- duces almost instant vesication. It boils at 289° (145°-8C). Water dissolves it in small quantity, and alcohol and ether very freely. The oil itself, at a high temperature, dissolves both sulphur and phosphorus, and deposits them in a crystalline form on cooling. It is oxidized with violence by nitric acid, and by aqua regia. Alkalies decompose it by the aid of heat, with production of ammonia, an alkaline sulphide, and a sulphocyanide. The remarkable compound with ammonia, thiosinamine, has been already described (see page 508). Mustard-oil gives by analysis C8H6NS2. The Oil of horse-radish, and that obtained from the roots of the Alliaria officinalis by distillation with water, are identical with the oil of black mustard- seed. Oil of garlic. —The crude oil procured by distilling the sliced bulbs with water is not a homogeneous product; by the action of metallic potassium, however, renewed until it is no longer tarnished, a small portion of oxyge- netted oil which it contains may be decomposed and withdrawn, after which the sulphuretted compound may be obtained pure by redistillation. In this state it forms a colorless liquid, lighter than water, of high refractive power, possessing in a high degree the peculiar odor of the plant, and capable of being distilled without decomposition. It contains C6HSS. Garlic-oil dis- solved in alcohol, and mixed with solutions of platinum, silver, and mercury, gives rise to crystalline compounds having the characters of double salts, containing the elements of the oil with the sulphur replaced by oxygen or chlorine. The curious and interesting relation existing between the oils of mustard and garlic has been already pointed out under the head of allyl-series. In both these substances, we may assume the existence of a radical C6H6, to RESINS AND BALSAMS. 529 which the name allyl has been given, when mustard-oil becomes the sulpho- cyanide, and garlic-oil the sulphide of allyL, Mustard-oil. . C8HrNS = C6H5C2NS2. Sulphocyanide of allyl. Garlic-oil . . C6H5S =C6H5S Sulphide of allyl. This relation has been experimentally established. By mixing the oil with hydrate of soda and quicklime, and exposing the whole in a hermetically- sealed tube to a temperature superior to that of boiling water, sulphocyanide of sodium is produced, together with an oily substance which is oxide of allyl; a substance chiefly known in combination, and which is the oxygenetted con- stituent of crude garlic-oil. Again, if mustard-oil be treated in a similar manner with sulphide of potassium, sulphocyanide of potassium and garlic- oil are formed. On the other hand, when the compound of garlic-oil and chloride of mercury is gently heated with sulphocyanide of potassium, mus- tard-oil, with all its characteristic properties, is called into existence. The oils of assafcetida, and onions, contain sulphur, and consequently belong to the same series: they have not yet been thoroughly examined. RESINS AND BALSAMS. Common resin, or colophony, furnishes perhaps the best example of the class. The origin of this substance has been already described. It is a mix- ture of two distinct bodies, having acid properties, called pinic and sylvic acids, separable from each other by their difference of solubility in cold and some- what dilute alcohol, the former being by far the more soluble of the two. Pure sylvic acid crystallizes in small, colorless, rhombic prisms, insoluble in hot strong alcohol, in volatile oils, and in ether. It melts when heated, but cannot be distilled without decomposition. The properties of pinic acid are very similar. Both have the same composition, viz., C^H^O^,. A third resin- acid also isomeric with the preceding, pimaric, has been found in the turpen- tin of the Pinus maritima of Bordeaux. Lac is a very valuable resin, much harder than colophony, and easily solu- ble in alcohol; three varieties are known in commerce, viz., stick-lac, seed-lac, and shellac. It is used in varnishes, and in the manufacture of hats, and very largely in the preparation of sealing-wax, of which it forms the chief ingredient. Crude lac contains a red dye called lac-dye, which is partly soluble in water. Lac dissolves in considerable quantity in a hot solution of borax; Indian ink, rubbed up with this liquid, forms a most excellent label- ink for the laboratory, as it is unaffected by acid vapors, and, when once dry, becomes nearly insoluble in water. Mastic, Dammar-resin, and sandarac are resins largely used by the varnish- maker. Dragon's-blood is a resin of a deep-red color. Copal is also a very valuable substance; it differs from the other resins, in being with difficulty dissolved by alcohol and essential oils. It is miscible, however, in the melted state with oils, and is thus made into varnish. Amber appears to be a fossil resin ; it is found accompanying brown-coal or lignite. Caoutchouc, india-rubber.—This curious and now most useful substance is the produce of several trees of tropical countries, which yield a milky juice, hardening by exposure to the air. In a pure state it is nearly white, the dark color of commercial caoutchouc being due to the effects of smoke and other impurities. Its physical characters are well known. It is softened, but not dissolved by boiling water; it is also insoluble in alcohol. In pure ether, 45 530 RESINS AND BALSAMS. rectified native naphtha, and coal-tar oil, it dissolves, and is left unchanged on the evaporation of the solvent. Oil of turpentin also dissolves it, forming a viscid, adhesive mass, which dries very imperfectly. At a temperature a little above the boiling-point of water caoutchouc melts, but never afterwards returns to its former elastic state. Few chemical agents affect this substance; hence its great practical use, in chemical investigations, for connecting appa- ratus, &c. Analysis shows it to contain nothing but carbon and hydrogen. By destructive distillation caoutchouc yields a large quantity of a thin volatile oily liquid, of naphtha-like odor, to which the name caoutchoucine has been applied. This is probably a mixture of several hydrocarbons, scarcely to be separated from each other by distillation or otherwise. It dissolves caoutchouc with facility. Caoutchouc combines with variable proportions of sulphur. The mixtures thus obtained are called vulcanized India-rubber: they are more permanently elastic than pure caoutchouc. A substance much resembling caoutchouc in certain respects, and of similar origin, has lately been introduced under the name of gutta percha. It has already afforded many useful applications. Most of the resins, when exposed to destructive distillation, yield liquid oily pyro-products, usually carbides of hydrogen, which have been studied with partial success." Great difficulties occur in these investigations: the task of separating from each other, and isolating bodies which scarcely differ but in their boiling-points, is exceedingly troublesome. Balsams are also, as before hinted, natural mixtures of resins with volatile oils. These differ very greatly in consistence, some being quite fluid, others solid and brittle. By keeping, the softer kinds often become hard. Balsams may be conveniently divided into two classes, viz., those which, like common and Venice turpentin, Canada balsam, copaiba balsam, &c, are merely natural varnishes, or solutions of resins in volatile oils, and those which contain benzoic or cinnamic acid in addition, as Peru and Tola balsams, and the solid resinous benzoin, commonly called gum-benzoin. Tolu-balsam, by distillation with water, yields three products; namely, benzoic acid, the cinnamein of M. Fr6my, (p. 447,) and tolene, a volatile color- less hydrocarbon, boiling at 338° (170°C), and containing C^H^. The balsam freed in this manner from essential oils, exposed to destructive distillation, yields in succession a viscous liquid which crystallizes in the receiver, and a thin liquid heavier than water; carbonic acid and carbonic oxide are largely evolved, and the retort is afterwards found to contain a residue of charcoal. The solid product is chiefly a mixture of benzoic and cinnamic acids: the volatile oil contains at least two substances differing in their boiling-points, and easily separated, namely, toluol (benzoene, see page 441), and an oily liquid heavier than water, of high boiling-point, and having the composition and characters of benzoic ether. Toluol is a thin, colorless liquid, insoluble in water, sparingly soluble in alcohol, more freely in ether; it has the odor of benzol; its sp. gr. is -870 and it boils at 226° (108°C). The density of its vapor is 3-26, and its' formula C14ll8. It combines with fuming sulphuric acid to the compound sulphotoluolic acid; with nitric acid it yields two products, nitrotoluol, C)4H7N"04, and binitro- toluol, C14H6N208. The former is fluid heavier than water, and bears a great resemblance in odor and other properties to nitrobenzol; the latter is a solid fusible, crystallizable substance. The conversion of nitrotoluol into the organic base toluidine, has been already described (see page 503). Liquid storax distilled with water, holding in solution a little carbonate of 6oda, yields a small and variable quantity of volatile oil, not homogeneous but from which, by careful distillation, a liquid volatile hydrocarbon, termed styrol, can be extracted in a state of purity. It is thin and colorless, of power- ful aromatic odor, refuses to solidify when cooled to 0° ( — 17°-7C) and boils RESINS AND BALSAMS. 581 at 293° (145°C). Its sp. gr. is -924; it is nearly insoluble in water, but mixes freely with alcohol and ether. Styrol contains Cl6H8, and is conse- quently isomeric with benzol. Storax, from which the styrol has been separated by distillation, when treated with carbonate of soda, yields a considerable quantity of cinnamate of soda. The residue consists of resinous bodies, with which a crystalline substance is associated, removable by alcohol, and containing C^H^. This substance, long known as styracin, has lately been found to be cinnamate of cinnamyl, C36H,604 .= C,8H90, C18H703 (see cinnamyl-series, page 445). When a portion of styrol is hermetically sealed in a glass tube, and then exposed for half an hour to a temperature approaching 400° (200°C) by means of an oil-bath, it undergoes a most remarkable change, becoming con- verted into a solid, transparent, glassy, fusible substance, called metastyrol, isomeric, as might be expected, with styrol itself. The same change is slowly produced by the influence of sunshine. A portion of metastyrol is always formed when styrol is distilled in a retort without water. Metastyrol is again convertible by distillation at a high temperature into liquid styrol.1 Certain of the products of the distillation of dragon's-blood appear to be identical with these bodies. » Mem. Chem. Soc., ii. 334. 532 SUBSTANCES OBTAINED FROM TAR ON CERTAIN PRODUCTS OF THE DESTRUCTIVE DISTILLATION AND SLOW PUTREFACTIVE CHANGE OF ORGANIC MATTER. substances obtained from tar. There are three principal varieties of tar: — (1.) Tar of the wood-vinegar maker, procured by the destructive distillation of dry hard wood; (2.) Stock- holm tar, so largely consumed in the arts, as in ship-building, &c, which is obtained by exposing to a kind of rude distillatio per decensum the roots and useless parts of resinous pine and fir-timber; and, lastly, (3.) Coal or mineral tar, a by-product in the manufacture of coal-gas. This is viscid, black, and ammoniacal. All these tars yield by distillation, alone or with water, oily liquids of ex- tremely complicated nature, from which a number of curious products, to be presently described, have been procured: the solid brown or black residue constitutes pitch. Hard-wood tar furnishes the following : — Paraffin ; tar-oil stearin. —This remarkable substance is found in that part of the wood-oil which is heavier than water; it is extracted by redis- tilling the oil in a retort, collecting apart the last portions, gradually adding a quantity of alcohol, and exposing the whole to a low temperature. Thus obtained, paraffin appears in the shape of small, colorless needles, fusible at 110° (43°-3C) to a clear liquid, which on solidifying becomes glassy and trans- parent. It is tasteless and inodorous; volatile without decomposition; and burns, when strongly heated, with a luminous yet smoky flame. It is quite insoluble in water, slightly soluble in alcohol, freely in ether, and miscible in all proportions, when melted, with both fixed and volatile oils. The most energetic chemical reagents, as strong acids, alkalies, chlorine, &c, fail to exert any action on this substance: it is not known to combine in a definite manner with any other body, whence its extraordinary name, from parum affinis.1 Paraffin contains carbon and hydrogen only, and in the same proportions as in olefiant gas, or CH. M. Lewy makes it C20H21. The rational formula is unknown. Eupione.2 — This is the chief component of the light oil of wood tar; it occurs also in the tar of animal matters, and in the fluid product of the dis- tillation of rape-seed oil. Its separation is effected by the agency of concen- trated sulphuric acid, or of a mixture of sulphuric acid and nitre, which oxidizes and destroys most of the accompanying substances. In a pure state, it is au exceedingly thin, colorless liquid, of agreeable aromatic odor, but destitute of taste: it is the lightest known liquid, having a density of 0-655. At 116° (46°-6C) it boils and distils unchanged. Dropped upon paper, it makes a greasy stain, which after a time disappears. Eupione is very inflam- 1 This substance likewise occurs amongst the products of distillation of peat, and in several mineral tars and some kinds of petroleum. 3 From tf, good, beautiful, and niov, fat. SUBSTANCES OBTAINED FROM TAR. 533 mable, and burns with a bright luminous flame. In water it is quite insoluble, in rectified spirit nearly so, but with ether and oils freely miscible. Eupione is a hydrocarbon: according to Hess it consists of C5H6. It is very probable that eupione frequently contains and sometimes entirely consists of hydride of amyl (see page 417). Other volatile oils, having a similar origin, and perhaps a similar composi- tion, but differing from the above in specific gravity and boiling-point, are sometimes confounded with eupione. The study of these substances presents many serious difficulties. It is even doubtful whether the eupione be not formed by the energetic chemical agents employed in its supposed purification; _ and this remark applies with even greater force to the next three or four tar- y products to be noticed. Picamar.1—A component of the heavy oil of wood ; it is a viscid, colorless, oily liquid, of feeble odor, but intensely-bitter taste. Its density is 1-095, and it boils at 518° (270°C). It is insoluble in water, but dissolves in all pro- portions in alcohol, ether, and the oils The most characteristic property of picamar is that of forming with the alkalies and ammonia crystalline com- pounds, which, although decomposed by water, are soluble without change in spirit. The composition of this substance is unknown. Kapnomor.2—Such is the name given by Dr. Reichenbach to another oily liquid obtained from the same source as the last, by a long and complex pro- cess, in which strong solutions of caustic potassa are freely used. It is de- scribed as a colorless volatile oil, of high boiling-point, and rather lighter than water; it has an odor of ginger, and a taste feeble at first, but afterwards becoming connected with an insupportable sense of suffocation. AVater refuses to dissolve it; alcohol and ether take it up easily; and oil of vitriol combines with it, giving rise to a complex acid, the potassa salt of which is crystallizable. Its composition is unknown. Cedriret.3—The lighter oil of hard-wood tar contains a substance, separable from the eupione, &c, by caustic alkalies, which in contact with oxidizing agents, as sulphate of sesquioxide of iron, chromic acid, or even atmospheric air, yields a mass of small, red, reticulated crystals, infusible by heat, and soluble in concentrated sulphuric acid with deep indigo-blue color. The sub- stance is insoluble in water, alcohol, and ether; nothing is known respecting its composition. Kreosote.4—This is by far the most important and interesting body of the group. Its discovery is due to Reichenbach: it is the principle to which wood-smoke owes its power of curing and preserving salted meat and other provisions. Kreosote is most abundantly contained in the heavy oil of beech- tar, as procured from the wood-vinegar maker, and is thence extracted by a most tedious and complicated series of operations; it certainly pre-exists, however, in the original material. The tar is distilled in a metallic vessel, and the different products are collected apart; the most volatile portion, which is lighter than water, and consists chiefly of eupione, is rejected; the second portion is denser, and contains the kreosote, and is set aside; the dis- tillation is stopped when paraffin begins to pass over in quantity. The im- pure kreosote is first agitated with carbonate of potassa to remove adhering acid, separated and redistilled, the first part being again rejected; it is next strongly shaken with a solution of phosphoric acid, and again distilled: a quantity of ammonia is thus separated. Afterwards, it is dissolved in a solu- tion of caustic potassa of specific gravity 1-12, and decanted from the insolu- ble oil which floats on the surface: this alkaline liquid is boiled, and left Bome time in contact with air, by which it acquires a brown color, from the 1 From pix, and amarus, in allusion to its bitter taste. a From Kavvbs, smoke, jioipa, part. 8 From cedrium, the old name for acid tar-water, and rete, a net. 4 Derived from tpias, flesh and o blood. /rwr©)© ^ © The blood-discs are found to present different ^v>^ © ^ jgv appearances in the blood of different animals: in © © the mammifers they look like little round red or yellowish discs, thin when compared with their diameter, being flattened or depressed on opposite sides. In birds, lizards, COMPOSITION OF THE BLOOD. 553 frogs, and fish, the corpuscles are elliptical. In magnitude, they seem to be pretty constant in all the members of a species, but differ with the genus and order. In man they are very small, varying from ^^q- to ^Vo" °^ an inch in breath, while in the frog the long diameter of the ellipse measures at least four times as much. The corpuscles consist of an envelope con- taining a fluid in which the red coloring-matter of the blood is dissolved. The coagulation of blood effects a kind of natural proximate analysis; the clear, pale serum, or fluid part, is an alkaline solution of albumin, containing various soluble salts; the clot is a mechanical mixture of fibrin and blood globules, swollen and distended with serum, of which it absorbs a large but variable quantity. AVhen the coagulum of blood is placed upon bibulous paper, and drained as much as possible from the fluid portion, and then put into water, the enve- lope, which consists of globulin, dissolves and sets free the coloring matter, forming a magnificent crimson solution, which has many of the characters of a dye-stuff. It contains albumin and globulin, and coagulates by heat and by the addition of alcohol; this albumin and globulin cannot be separated, and attempts to isolate the hemalosin or red pigment, have consequently failed. From its extreme susceptibility of change, it is not known in a state of purity. The above watery solution, exposed with extensive surface in a warm place, dries up to a dark-red, brittle mass, which is again soluble in water. After coagulation it becomes quite insoluble, but dissolves, like albu- min, in caustic alkalies. Carbonic and sulphurous acids blacken the red solu- tion : oxygen, or atmospheric air, heightens its color; protoxide of nitrogen renders it purple; while sulphuretted hydrogen, or an alkaline sulphide, changes it to a dirty greenish-black. Hematosin differs from the other animal principles in containing as an essential ingredient a remarkable quantity of the oxide of the metal iron. If a little of the dried clot of blood be calcined in a crucible, and digested with dilute hydrochloric acid, a solution will be obtained rich in oxide of iron; or if the solution of 6oloring matter just referred to be treated with excess of chlorine gas, the yellow liquid separated from the grayish coagulum formed will be found to give, in a striking manner, the well-known reactions of the sesquioxide of iron. There is little doubt either about the condition of the metal: sesquioxide of iron is withdrawn from the dry clot by the cautious addition of sulphuric acid, and without much alteration of the color of the mass.1 It is well known that certain organic matters, as sugar and tartaric acid, prevent the precipitation of sesquioxide of iron by alkalies, and its re- cognition by ferrocyanide of potassium, and it is very likely that the blood may contain a substance or substances capable of doing the same. Hematosin, necessarily in a modified state, contains, according to Mulder, in 100 parts : — Carbon . Hydrogen Nitrogen Oxygen . Iron 100-0 The following table represents the composition of healthy human blood as a whole ; it is on the authority of M. Lecanu : —2 1 Liebig, Handworterbuch, i. 885. 3 Ann. Chim. et de Phys. xlviii. 320. 47 65-3 5-4 10-4 11-9 70 554 NERVOUS SUBSTANCE. AVater . Fibrin . Albumin Coloring matter Crystallizable fat Fluid fat Extractive matter of uncertain nature, solu- ble in both water and alcohol Albumin in combination with soda . Chlorides of sodium and potassium; carbo- nates, phosphates, and sulphates of po- tassa and soda Carbonates of lime and magnesia; phos- phates of lime, magnesia, and iron; , quioxide of iron . ... Loss...... 0-) (2.) . 780-15 785-58 210 3-57 . 6509 69-41 . 133-00 119-63 2-43 4-30 1-31 2-27 1-79 1-92 1-26 2-01 ilOS- A ses- 1- 8-37 7-30 2-10 1-42 2-40 2-59 1000-00 1000-00 In healthy individuals of different sexes these proportions are found to vary: the fibrin and coloring matter are usually more abundant in the male than in the female; in diseases, variations of a far wider extent are often apparent. It appears singular that the red corpuscles, which are so easily dissolved by water, should remain uninjured in the fluid portion of the blood. This seems partly due to the presence of saline matter, and partly to that of albumin, the corpuscles being alike insoluble in a strong solution of salt and in a highly- albuminous liquid. In the blood the limit of dilution within which the cor- puscles retain their integrity appears to be nearly reached, for when water is added they immediately become attacked. nervous substance; elastic tissue; BONES. Nervous substance.—The brain and nerves contain from 7 to 9 per cent. of an albuminous substance, also several remarkable fatty principles, consti- tuting from 5 to 14 per cent., capable of being extracted by alcohol and ether, some of which are yet very imperfectly known, and from 75 to 80 per cent. of water. According to Fremy, if the nervous substance be boiled with alcohol, elain, cholesterin, oleic and margaric acids are extracted, partly com- bined with soda, potassa, or lime; if then the residue be treated with boiling ether, cholesterin, cerebric acid, and oleo-phosphoric acid are dissolved. These acids are also in combination with soda and lime. The first is solid, white, and crystalline, soluble without difficulty in boiling alcohol and ether, and forming with hot water a soft gelatinous mass. It melts when heated, and decomposes almost immediately afterwards, exhaling a peculiar odor, and leaving a quantity of charcoal which contains free phosphoric acid, and is, in consequence, very difficult to burn. It combines with the alkalies, but forms insoluble compounds. Cerebric acid contains in 100 parts:— Carbon . Hydrogen Nitrogen Oxygen . Phosphorus 66-7 10-6 2-3 19-5 0-9 1000 KERATIN, BONES. 555 Cerebric achl has been found in the yolk of eggs, in seminal fluid, in the Bpleen, in pus, and in other products of disease. The oleo-phosphoric acid has been even less perfectly studied than the pre- ceding substance. It is of soft oily consistence, soluble in hot alcohol and ether, and saponifiable. AVhen boiled with water, it is resolved into a fluid neutral oil, called cerebrolein, and phosphoric acid, which dissolves. Fre"my gives about 2 per cent, of phosphoric acid. The oily matter of the brain is sufficient in quantity to form with the albu- minous portion a kind of emulsion, which, when beaten up, remains long suspended in water. Elastic tissue; skin.—The skin and tendons contain a substance which resists the action of boiling water even for 60 hours. It is insoluble in cold concentrated acetic acid, and in tolerably concentrated caustic potassa. By long-continued boiling in acetic acid it is gradually dissolved ; it is more easily so in hydrochloric acid. Tilanus found in the ligamentum nuchse, carbon 55-75, hydrogen 7-41, nitrogen 17-74. The principle of tanning, of such great practical value, is easily explained. When the skin of an animal, carefully deprived of hair, fat, and other im- purities, is immersed in a dilute solution of tannic acid, the cellular and elastic tissues gradually combine with that substance as it penetrates inwards, forming a perfectly insoluble compound, which resists putrefaction completely: this^ is leather. In practice, lime-water is used for cleansing and preparing the skin, and an infusion of oak-bark or sometimes catechu, or other astringent matter, for the source of tannic acid. The process itself is necessarily a slow one, as dilute solutions only can be safely used. Of late years, however, various contrivances, some of which show great ingenuity, have been adopted, with more or less success, for quickening the operation. All leather is not tanned: glove leather is dressed with alum and common salt, and afterwards treated with a preparation of the yolk of eggs, which contain an albuminous matter and a yellow oil. Leather of this kind still yields a size by the action of boiling WQ/tcr Horny substance ; keratin.—This is chiefly found in hair, nails, feathers, and epithelium. It is obtained by finely dividing their substances, treating them with warm water, and afterwards with boiling alcohol and ether: the horn substance is then very soluble in caustic potash, and precipitable by acids. By long-continued boiling with water it is decomposed. It putrefies with difficulty. Sherer found — Skin of the sole IIair Ox-horn. Nails. Feathers. Quill. of the foot. Carbon. . . 50-20 50-37 51-13 5015 52-10 5200 Hydrogen. . 6-78 6-66 6-71 6-82 711 7-21 Nitrogen 17-22 17-94 17-28 16 90 17-68 17-89 Oxygen \ 25.g0 25-03 24-88 26-13 23-11 22-90 Sulphur / ' Bones —At the age of 21 years the weight of the skeleton is to that of the whole body as 10-5 to 100 in man, and as 8-5 to 100 in woman, the weight of the bodv heing about 125 or 130 lbs. Bones are constructed of a dense cellu- lar tissue of membranous matter, made stiff and rigid by insoluble earthy salts, of which phosphate of lime (3CaO,P05) is the most abundant. The oroportions of earthy and animal matter vary very much with the kind of bone and with the age of the individual as will be seen in the following table, in which the corresponding bones of an adult and of a still-born child are compared: — 556 BONES. Child. Inorganic Organic Inorganic Organic matter. matter. matter. matter. Femur . 62-49 37-51 57-51 42-49 Humerus . . 63-02 36-98 58-08 41-92 Badius . 60-51 39-49 56-50 43-50 Os temporum . 63-50 36-50 55-90 44-10 Costa . 57-49 42-51 53-75 46-25 The bones of the adult being constantly richer in earthy salts than those of the infant. The following complete comparative analysis of human and ox bones is due to Berzelius: — Animal matter soluble by boiling . Vascular substance .... Phosphate of lime, with a little fluoride of calcium ...... Carbonate of lime . Phosphate of magnesia .... Soda, and a little common salt Human bones. Ox bones. . 32-17 A . 1-13/ 33-30 . 53 04 57-35 . 11-30 3-85 . 116 2-05 1-20 3-45 100-00 10000 The teeth have a very similar composition, but contain less animal matter: their texture is much more solid and compact. The enamel does not contain more than 2 or 3 per cent, of animal matter, whilst 81 to 88 per cent, of phos- phate of lime, with 7 or 8 per cent, of carbonate of lime, are present. FUNCTION OF RESPIRATION. 557 ON THE EXCRETIONS AND SECRETIONS.-ON RESPIRATION. The simplest view that can be taken of a respiratory organ in an air- breathing animal, is that of a little membranous bag, saturated with moisture, and containing air, over the surface of which meanders a minute blood-vessel, whose contents, during the passage, are thus subjected to the chemical action of the air, through the substance of the membranes, and in virtue of the solu- bility of the gaseous matter itself in the water with which the membranes are imbued. In some of the lower classes of animals, where respiration is slug- gish and inactive, these air-cells are few and large; but in the higher kinds they are minute, and greatly multiplied in number in order to gain extent of surface, each communicating wkh the external air by the windpipe and its ramifications. Respiration is performed by the agency of the muscles which lie between aud about the ribs, and by the diaphragm. In an ordinary expiration from 22 to 43 cubic inches of air are thrown out. It has been said that as little as 3 and as much as 100 cubic inches have been expired. By a forced effort ordinarily from 50 to 60 cubic inches are expelled, and after a full inspiration possibly from 100 to 300 cubic inches may be expired. Even then the lun^s are not emptied of air. The residual quantity has been estimated at from 40 to 260 cubic inches. After an ordinary expiration a further quantity of air, amounting to from 77 to 170 cubic inches, may be expired, and after an ordi- nary inspiration by the deepest sigh, from 119 to 200 more cubic inches may be drawn into the lungs. Usually about 15 respirations are made in a minute; the number, however, even in health varies from 9 to 20. The expired air is found to have undergone a remarkable change; it is loaded with aqueous vapor, while a very large proportion of oxygen has dis- appeared, and its place been supplied by carbonic acid; air once breathed containing enough of that gas to extinguish a taper. The quantity of this gas is very liable to variation, usually from 3 3 to 6-2 per cent, of carbonic acid is found to be present: when the respirations are few, the carbonic acid is greatest, when many, least: thus with 6 respirations per minute, 5-5 per cent, has been found; with 48 respirations, 2-9 per cent. A full meal, cold weather, and increased barometric pressure increase the carbonic acid. Heat alcohol, tea, and diminished pressure, lessen the carbonic acid: age and sex produce definite effects. It appears most probable that nitrogen in small quantities is exhaled. Whatever may be the difficulties attending the investigation of these sub- jects— and difficulties there are, as the discrepant results of the experiments prove, — one thing is clear; namely, that quantities of hydrogen and carbon are daily oxidized in the body by the free oxygen of the atmosphere, and their products expelled from the system in the shape of water and carbonic acid. Now, if it be true that the heat developed in the act of combination is a con- stant quantity, and no proposition appears more reasonable, the high tempera- ture of the body may be the simple result of this exertion of chemical force. The oxidation of combustible matter in the blood is effected in the capilla- 558 URINE. ries of the whole body, not in the lungs, the temperature of which does not exceed that of the other parts. The oxygen of the air is taken up in the lungs, and carried by the blood to the distant capillary vessels: by the aid of which, secretion, and all the mysterious functions of animal life, are undoubt- edly performed : here the combustion takes place, although how this happens, and what the exact nature of the combustible may be, beyond the simple fact of its contaning carbon and hydrogen, yet remains a matter of conjecture. The carbonic acid produced is held in solution by the now venous blood, and probably confers, in great measure, upon the latter its dark color and delete- rious action upon the nervous system. Once more poured into the heart, and by that organ driven into the second set of capillaries bathed with atmospheric air, this carbonic acid is conveyed outwards, through the wet membrane, by a kind of false diffusion, constantly observed under such circumstances; while at the same time oxygen is, by similar means, carried inwards, and the blood resumes its bright-red color, and its capability of supporting life. Much of this oxygen is, no doubt, simply dissolved in the serum: the corpuscles, ac- cording to Professor Liebig, act as carriers of another portion, in virtue of the iron they contain, that metal being alternately in the state of sesquioxide and of carbonate of the protoxide, — of sesquioxide in the arteries, and of carbo- nate of protoxide in the veins, by loss of oxygen, and acquisition of carbonic acid. M. Mulder considers the fibrin to act in the same manner; being true fibrin in the veins, and, in part at least, an oxide of protein in the arteries. It would be very desirable to show, if possible, that the quantity of combus- tible matter daily burned in the body is adequate to the production of the heating effects observed. Something has been done with respect to the car- bon. Comparison of the quantities and composition of the food consumed by an individual in a given time, and of the excretions, shows an excess of carbon in the former over the latter, amounting, in some cases, according to Liebig's high estimate,1 to 14 ounces; the whole of which is thrown off' in the state of carbonic acid, from the lungs and skin, in the space of twenty-four hours. The statement applies to the case of healthy, vigorous men, much employed in the open air, and supplied with abundance of nutritious food. Females, and persons of weaker habit, who follow in-door pursuits in warm rooms, consume a much smaller quantity; their respiration is less energetic, and the heat generated less in amount. Those who inhabit very cold countries are well- known to consume enormous quantities of food of a fatty nature, the carbon and hydrogen of which are, without doubt, chiefly employed in the production of animal heat. These people live by hunting: the muscular exertion re- quired quickens and deepens the breathing; while, from the increased density of the air, a greater weight of oxygen is taken into the lungs, and absorbed into the blood at each inspiration. In this manner the temperature of the body is kept up, notwithstanding the piercing external cold: a most marvel- lous adjustment of the nature of the food, and even of the inclinations and appetite of the man, to the circumstances of his existence, enable him to bear with impunity an atmospheric temperature which would otherwise injure him. The carbon consumed in respiration in one day, by a horse moderately fed, amounted, in a valuable experiment of M. Boussingault, to 77 ounces; that consumed by a cow to 70 ounces. The determination was made in the manner just mentioned, viz., by comparing the quantity and composition of the food. Urine. — The urine is the great channel by which the azotized matter of those portions of the body which have been taken up by the absorbents is con- veyed away and rejected from the system in the form of urea. It serves also to remove superfluous water and foreign soluble matters which get introduced into the blood. 1 Animal Chemistry, p. 14. URINE. 559 The two most remarkable and characteristic constituents of urine, urea and uric acid, have already been fully described; in addition to these, it contains sulphates, chlorides, phosphates of lime, and magnesia, alkaline salts, and certain yet imperfectly-known principles, including an odoriferous and a coloring substance (see foot-note to page 560). Healthy human urine is a transparent, light, amber-colored liquid, which, while warm, emits a peculiar, aromatic, and not disagreeable odor. This is lost on cooling, while the urine at the same time occasionally becomes turbid from a deposition of urates, which re-dissolve with slight elevation of tempera- ture. It is very decidedly acid to test-paper:1 this acidity has been ascribed » to acid phosphate of soda, to free uric acid, and to free lactic acid; lactic acid can, however, hardly coexist with urate of ammonia, and the amorphous buff- colored deposit obtained from fresh urine by spontaneous evaporation in vacuo is not uric acid, but the ammonia-salt of that substance, modified as to crys- talline form by the presence of minute quantities of chloride of sodium. That a free acid is sometimes present in the urine is certain: in this case the reac- tion to test-paper is far stronger, and the liquid deposits on standing, little red, hard crystals of uric acid; but this is no longer a normal secretion. An alkaline condition of the urine from fixed alkali is sometimes met with. Such alkalinity can always be induced by the administration of neutral potassa- or soda-salts of a vegetable acid, as tartaric or acetic acid: the acid of the salt is burned in the blood in the process of respiration, and a portion of the base appears in the urine in the state of carbonate. The urine is often alkaline in cases of retention, from carbonate of ammonia produced by putre- faction in the bladder itself; but this is easily distinguished from alkalinity from fixed alkali, in which it is secreted in that condition. The density of the urine varies from 1-005 to 1-030: about 1-020 to 1025 may be taken as the average specific gravity. A high degree of density in urine may arise from an unusually large proportion of urea: in such a case, the addition of nitric acid will occasion an almost immediate production of crystals of nitrate of urea, whereas with urine of the usual degree of concen- tration at least very many hours will elapse before the nitrate begins to sepa- rate. The quantity of urine passed depends as much upon circumstances,as upon the activity of the skin. It is usually more deficient in quantity and of higher density in summer than in winter. Perhaps about 32 ounces in the 24 hours may be assumed as a mean. When kept at a moderate temperature, urine after some days begins to decompose; it exhales an offensive odor, becomes alkaline from the produc- tion of carbonate of ammonia, and turbid from the deposition of earthy phos- phates. The carbonate of ammonia is due to the putrefactive decomposition of the urea, which gradually disappears, the ferment, or active agent of the change, being apparently the mucus of the bladder, a portion of which is always voided with the urine. It has been found also that the yellow adhe- sive deposit from stale urine is a most powerful ferment to the fresh secretion. In this putrefied state urine is used in several of the arts, as in dyeing: and forms, perhaps, the most valuable manure for land known to exist. Putrid urine always contains a considerable quantity of sulphide of ammo- nium : this is formed by the deoxidation of sulphates by the organic matter. The highly-offensive odor and extreme pungency of the decomposing liquid may be prevented by previously mixing the urine, as Liebig suggests, with sulphuric or hydrochloric acid, in sufficient quantity to saturate all the ammonia that can be formed. The following is an analysis of human urine by Berzelius. 1000 parts con- tained 1 The degree of acidity appears to vary in the Fame person at different times. See Philoso- phical Trans., 1849. 56ft URINE. Water..........933-00 Urea..........30-10 Lactates and extractive matter1 . • . . . .1714 Uric acid.........100 Sulphates of potassa and soda.....6-87 Phosphates of soda.......2-92 " ammonia ...... 1-65 " lime and magnesia.....100 Chloride of sodium.......4-45 Sal-ammoniac ........ 1-50 Silica..........0-03 Mucus of bladder.......0-32 1000-00 In certain states of disorder and disease substances appear in the urine which are never present in the normal secretion: of these the most common is albumin. This is easily detected by the addition of nitric acid in excess, which then causes a white cloud or turbidity, which is permanent when boiled, or by corrosive sublimate, the urine being previously acidified by a little acetic acid; boiling causes usually a precipitate which is not dissolved by a drop or two of acid. Mere turbidity by boiling is no proof of albumin, the earthy phosphates being often thrown down Fig. 191. from nearly neutral urine under such circum- stances ; the phosphatic precipitate is, however, instantly dissolved by a drop of any acid. In diabetes the urine contains grape-sugar, the quantity of which commonly increases with the progress of the disease, until it becomes enormous, the urine acquiring a density of 1040 and beyond. It does not appear that the urea is deficient abso- lutely, although more difficult to discover from being mixed with such a mass of syrup. The smallest trace of sugar may be discovered in urine by Trommer's test, formerly mentioned: a few drops of solution of sulphate of copper are added to the urine, and afterwards an excess of caustic potassa; if sugar be present, a deep-blue liquid results, which, on boiling, deposits red suboxide of copper. AVith proper management, this test is very valuable; it will even detect sugar in the blood of diabetic patients."-1 Urine containing sugar, when mixed with a little yeast, and put in a warm place, readily undergoes vinous fermentation, and afterwards yields, on dis- tillation, weak alcohol, contaminated with ammonia. 1 All dark-colored, uncrystallizable substances soluble both in water and alcohol, were con- founded by the old chemists under the general name of extractive matter. The progress of modern science constantly tends to extricate from this confused mass one by one many definite organic principles therein contained in a more or less modified form, and to restrict within narrower limits the application of the term. In the above instance the coloring matter of the urine, and it may be several other substances, are involved. Professor Liebig states that all his endeavors to obtain direct evidence of the existence of lactic acid in the urine, either in a fresh or putrid state, completely failed. Putrid urine yielded a volatile acid in a notable quantity, which turned out to be acetic acid; a little benzoic acid was also noticed, and traced to a small amount of hippuric acid in the recent urine. The. acid reaction of urine is ascribed to an acid phosphate of soda produced by the partial decomposition of some of the common phosphate, the reaction of which is alkaline, by the organic acids (uric and hippurie) generated in the system, aided by the sulphuric acid constantly produced by the oxidation of the protein-compounds of the food, or rather of the body. — Lancet, June, 1844. Still more recently Liebig has announced the discovery in the urine of kreatin and kreati- nine, already described. Putrid nrine contains kreatinine only. a Dr. Bence Jones, Med. Chirur. Trans., vol. xxvi. Great care must be taken in using this test, which depends on the instantaneous reduction of the oxide of copper. By long boiling very many organic substances produce this reaction. URINARY CALCULI. 561 The urine of children is said sometimes to contain benzoic acid: it is pos- sible that this may be produced by the decomposition of hippuric acid, which frequently occurs in the urine or healthy persons. AVhen benzoic acid is taken, the urine after a few hours yields on concentration, and the addition of hydrochloric acid, needles of hippuric acid, soiled by adhering uric acid. The deposit of buff-colored or pinkish amorphous sediment, which so fre- quently occurs in urine upon cooling, after unusual exercise or slight derange- ments of health, consists chiefly of uncrystallized urate of soda or urate of ammonia: it may be at once distinguished from a deposit of ammonio- magnesian phosphate by its instant disappearance on the application of heat. The earthy phosphates, besides, are hardly ever deposited from urine which has an acid reaction. The coloring matter of the urine is constantly under- going change: by means of neutral and basic acetate of lead it may be sepa- rated into two substances which contain different amounts of carbon. The substance which contains most carbon maybe obtained as a dark-blue powder: when dry it has a copper color like indigo, and dissolves in alcohol, giving a purple-blue solution. It is said to occur most evidently in Bright's disease. Virchow states that he met with this blue pigment in crystals in unhealthy urine. Three coloring matters have been distinguished in urine, which have received the names, uroxanthin, uroglaucin, and urorhodin: they have not been perfectly examined on account of the difficulty of preparing them. One of them has many properties of indigo. The yellow principle of bile may be observed in urine in cases of jaundice. The urine of the carnivorous mammifera is small in quantity, and highly acid; it has a very offensive odor, and quickly putrefies. In composition it resembles that of man, and is rich in urea. In birds and serpents the urine is a white pasty substance, consisting almost entirely of urate of ammonia. In herbivorous animals it is alkaline and often turbid from earthy carbonates and phosphates: urea is still the characteristic ingredient, while of uric acid there is scarcely a trace; hippuric acid is usually, if not always, present, sometimes to a very large extent. AVhen the urine putrefies, this hippuric acid, as already noticed, becomes changed to benzoic acid. Urinary calculi. —Stony concretions, differing much in physical charac- ters and in chemical composition, are unhappily but too frequently formed in the bladder itself, and give rise to one of the most distressing complaints to which humanity is subject. Although many endeavors have been made to find some solvent or solvents for these calculi, and thus supersede the neces- sity of a formidable surgical operation for their removal, success has been but very partial and limited. Urinary calculi are generally composed of concentric layers of crystalline or amorphous matter, of various degrees of hardness. Very frequently the central point or nucleus is a small foreign body: curious illustrations of this will be seen in any large collection. Calculi are not confined toman: the lower animals are subject to the same affliction ; they have been found in horses, oxen, sheep, pigs, and almost constantly in rats. The following is a sketch of the principal characters of the different varie- ties of calculi: — 1. Uric Acid.— These are among the most common: externally they are smooth or warty, of yellowish or brownish tint; they have an imperfectly crystalline, distinctly Fig. 192. concentric structure, and are tolerably hard. Be- fore the blowpipe the uric acid calculus burns away, leaving no ash. It is insoluble in water, but dissolves with facility in caustic potassa, with but little ammoniacal odor; the solution mixed with acid gives a copious white curdy precipitate of uric acid, which speedily becomes dense and crystalline. Cautiously heated with nitric acid, 562 URINARY CALCULI. and then mixed with a little ammonia, it gives the characteristic reaction of uric acid, viz., deep purple-red murexide. 2. Urate of Ammonia. — Calculi of urate of Fig.193. ammonia much resemble the preceding; they are easily distinguished, however. The powder boiled in water dissolves, and the solution gives a precipitate of uric acid when mixed with hydrochloric acid. It dissolves also in hot carbonate of potassa with copious evolution of ammonia. 3. Fusible Calculus; Phosphate of Lime with Phosphate of Magnesia and Ammonia. — This is one of the most common kinds. The stones are usually white or pale-colored, smooth, earthy, and soft; they often attain a large size. Before the blowpipe this substance Fig. 194. blackens from animal matter which all calculi always contain; then becomes white, and melts to a bead with comparative facility. It is insoluble in caustic alkali, but readily soluble in dilute acids, and the solution is precipitated by ammonia. Calculi of unmixed phosphate of lime are rare, as also those of phosphate of magnesia and ammonia; the latter salt is sometimes seen forming 6mall brilliant crystals in cavities in the fusible calculus. 4. Oxalate of Lime Calculus; Mulberry Calculus.—The latter name is derived from the rough, warty character, and dark blood-stained aspect of this variety; it is perhaps the worst form of calculus. It is ex- Fig. 195. ceedingly hard; the layers are thick and imper- fectly crystalline. Before the blowpipe the oxalate of lime burns to a carbonate by a moderate red- heat, and, when the flame is strongly urged, to quicklime. It is soluble in moderately-strong hy- drochloric acid by heat, and very easily in nitric acid. When finely powdered and long boiled in a solution of carbonate of potassa, oxalate of potassa may be discovered in the filtered liquor when care- fully neutralized by nitric acid, by white precipi- tates with solutions of lime, lead, and silver. A sediment of oxalate of lime in very minute, transparent, octahedral crystals, only to be seen by the micro- scope, is of common occurrence in urine, in which a tendency to deposits of urates exists. 5. Cystic and Xanthic Oxides have already been described; they are very rare, especially the latter. Calculi of cystic oxide are very crystalline, and often present a waxy appearance externally; sediments of cystic oxide are sometimes met with. As before mentioned, this substance is a definite crys- tallizable organic principle, containing sulphur to a large amount; it is soluble both in acids and alkalies. When the solution in nitric acid is evaporated to dryness, it blackens; when dissolved in a large quantity of caustic potassa, a drop of solution of acetate of lead added, and the whole boiled, a black pre- cipitate containing sulphide of lead makes its appearance. By these charac- ters cystic oxide is easily recognised. Xanthic oxide, also a definite organic principle, is distinguished by the peculiar deep-yellow color produced when its solution in nitric acid is evapo- rated to dryness; it is soluble in alkalies, but not in hydrochloric acid. Very many calculi are of a composite nature, the composition of the dif- ferent layers being occasionally changed, or alternating: thus, urate of 8WEAT.—BILE. 563 ammonia and oxalate of lime are not unfrequently associated in the same stone. Sweat.—The watery fluid poured out by the skin contains from $ to 2 per cent of solid matter: the acidity of the secretion depends on organic acids, chiefly formic; acetic and butyric acids also exist in it. Lactic acid has been Btated to be absent even in rheumatism: a new acid named sudoric acid, and Bomewhat resembling in composition uric acid, is said to be always present, C10H8NO13. In disease, if not in health, small quantities of urea also exist in sweat. The salts in the sweat are chlorides of sodium and potassium. Phos- phoric acid, lime, magnesia, and oxide of iron have been found. Saliva is a mixture of several fluids secreted by different glands of the mouth. Its specific gravity is from 1002 to 1009. It is usually alkaline: during and after eating.the alkaline reaction increases, whilst it decreases by fasting. It contains an albuminous substance, ptyalin, which acts on starch, rapidly changing it into sugar. The secretion of the submaxillary gland with the mucus of the mouth chiefly"produces this effect. On the passage of the food into the acid gastric juice, this conversion of starch into sugar ceases. The second remarkable substance in saliva is sulphocyanide of potassium, which exists in very small quantities, but is very easily detected. The solid constituents of saliva are about 1 per cent., and in 100 parts of solid consti- tuents from 7 to 21 parts are fixed salts, chiefly chlorides. Gastric juice contains from 1 to 2 per cent, of solid constituents. It con- tains an albuminous substance, pepsin, by some called chymosin or better gas- terase. AVith the acids and water of the gastric juice the albuminous food is much more quickly dissolved than by water and acids alone. The free acids of the stomach are the hydrochloric, lactic, butyric, and acetic; and very probably sulphuric and phosphoric acids in very minute quantities are also free. The saline substances that are present are chlorides of sodium, cal- cium, magnesium, and traces of protochloride of iron and phosphate of lime, but these substances are present in very small quantities. From experiments lately made on a woman who had a fistulous opening in the stomach, it is said that as much as 31 pounds of fluid may sometimes be secreted by the stomach daily. Bile.—This is a secretion of a very different character from the preceding: the largest internal organ of the body, the liver, is devoted to its preparation, which takes place from venous, instead of arterial blood. The composition of the bile has been made the subject of much investigation; the following is a summary of the most important facts which have been brought to light. In its ordinary state bile is a very deep-yellow, or greenish, viscid, trans- parent liquid, which darkens by exposure to the air, and undergoes changes which have been yet imperfectly studied. It has a disagreeable odor, a most nauseous, bitter taste, a distinctly-alkaline reaction, and is miscible with water in all proportions. When evaporated to dryness at 212° (100°C), and treated with alcohol, the greater part dissolves, leaving behind an insoluble jelly of mucus of the gall-bladder. This alcoholic solution contains coloring- matter and cholesterin; from the former it may be freed by digestion with animal charcoal, and from the latter by a large admixture of ether, in which the bile is insoluble, and separates as a thick, syrupy, and nearly colorless liquid. The coloring-matter may also be precipitated by baryta-water. Pure bile thus obtained, when evaporated to dryness by a gentle heat, forms a slightly-yellowish brittle mass, resembling gum-arabic. It is completely soluble in water and absolute alcohol. The solution is not affected by the vegetable acids; hydrochloric and sulphuric acids, on the contrary, give rise to turbidity, either immediately or after a short interval. Acetate of lead partially precipitates it: the tribasic acetate precipitates it completely; the precipitate is readily soluble in acetic acid, in alcohol, and to a certain extent 564 BILE AND URINARY CALCULI. in excess of acetate of lead. When carbonized by heat, and incinerated, bile leaves between 11 and 12 per cent, of ash, consisting chiefly of carbonate of soda, with a little common salt and alkaline phosphate. The recent beautiful researches of Strecker show that bile is essentially a mixture of the soda- salts of two peculiar conjugate acids, very distinctly resembling the resinous and fatty acids. One of these contains nitrogen, but no sulphur, and is termed cholic acid, or better, glyco-cholalic, being a conjugated compound of a non-nitrogenous acid, cholalic acid,1 with the nitrogenetted substance glycocine (see page 549); the other, containing nitrogen and sulphur, has received the name choleic acid, or better, tauro-cholalic acid, being a conjugated compound of the same cholalic acid with a body to be presently described under the name of taurin, containing both nitrogen and sulphur. The relative proportion in which these acids occur in bile, remains pretty constant with the same ani- mal, but varies considerably with different classes of animals. Glyco-cholalic acid may be thus obtained : — AVhen ox-bile is perfectly dried and extracted with cold absolute alcohol, and after filtration is mixed with ether, it first deposits a brownish tough resinous mass, and after some time, stellated crystals which consist of glychocholalate of soda and potassa. These mixed crj'stals were first obtained by Platner, and they compose his so-called crystallized bile. Glyco-cholalic acid may be obtained by decomposing the glyco-cholalate of soda by sulphuric acid; it crystallizes in fine white needles of a bitterish- sweet taste, is soluble in water and alcohol, but only slightly in ether, and ha3 a strong acid reaction. It is represented by the formula C52H42NOn,HO. When boiled with a solution of potassa, the acid divides into cholalic acid C48H3909,HO, and glycocine or gelatin-sugar: — C52H42NOn,HO -f- 2HO = C48H3909,HO + C4H5N04. Glyco-cholalic acid. Cholalic acid. Glycocine. Boiled with concentrated sulphuric or hydrochloric acids, it yields likewise glycocine, but instead of cholalic acid, another white amorphous acid, choloidinic acid (C48H3909 = cholalic acid — 1 eq. of water), or if the ebullition has continued for some time, a resinous substance, from its insolubility in water called dyslysin, (C^HagOg = cholalic acid — 4 eq. of water). Tauro-cholalic acid is thus procured: — Ox bile is freed as far as possible from glyco-cholalic acid by means of neutral acetate of lead, and it is then precipitated by basic acetate of lead, to which a little ammonia is added. The precipitate is decomposed by carbonate of soda, when tolerably pure tauro-cholalate of soda is obtained. By decomposing the tauro-cholalate of lead by sulphuretted hydrogen, tauro-cholalic acid is liberated. This sub- stance, however, which was previously called choleic acid and bilin, has never been obtained in the pure state. Its formula, as inferred from the study of its products of decomposition, would be C52H44NS20)3,HO. When boiled with alkalies it divides into cholalic acid and taurin: — ^H^SgO^HO + 2HO = C48H3909,HO^ + C4H7NS206 Tauro-cholalic acid. Cholalic acid. Taurin. With boiling acids it gives likewise taurin, but instead of cholalic acid either choloidinic acid or dyslysin, according to the duration of the ebullition! 1 Also called cholic acid by some authors. BILE AND URINARY CALCULI. 565 Taurin, C4II7NS206, crystallizes in colorless regular hexagonal prisms, Which have no odor and very little taste. It is neutral to test-paper, and permanent in the air. -AVhen burnt, it gives rise to much sulphurous acid. It contains upwards of 25 per cent, of sulphur. It is easily prepared by boiling purified bile for some hours with hydrochloric acid. After filtration and evaporation, the acid residue is treated with five or six times its bulk of boiling alcohol, from which the taurin separates on cooling. Strecker made many attempts to prepare taurin artificially. Ultimately he found that when isethionate of ammonia (see page 383), which fuses at 266° (130°C,)is heated to 410° (210°C) or 428° (220CC,) it loses two equivalents of water, and becomes taurin. The substance is dissolved in water, and, on the addition of alcohol, gives crystals having all the properties of taurin. Cholalic or cholic acid, C4SU3909,I10, crystallizes in tertahcdra. It is Boluble in sulphuric acid, and on the addition of a drop of this acid, and a solution of sugar (1 part of sugar to 4 parts of water), a purple-violet color is produced, which constitutes Pettcnkofer's test for bile. At 383° (195°C) it loses an atom of water, and is converted into choloidinic acid ; which change, as-has been pointed out, is also produced by ebullition with acids. Cholalic acid is best obtained by boiling the resinous mass precipitated by ether from the alcoholic solution of the bile with a dilute solution of potassa for 24 or 36 hours, till the amorphous potassa-salt that has separated begins to crystallize. When the dark-colored soft mass is removed from the alkaline liquid, dissolved in water, and hydrochloric acid added, a little ether causes the deposition of the cholalic acid in crystals. The principal coloring matter of the bile has been called cholepyrrhin. AVhen dry it is reddish-brown and uncrystallizable, insoluble in water, more soluble in alcohol which becomes yellow, and most soluble in caustic alkali. On the addition of nitric acid to the yellow alkaline solution a change ensues. It passes through green, blue, violet, and red: after some time it again turns yellow, probably in consequence of a gradual process of oxidation. Another coloring matter has been called biliverdin. It is dark green, amor- phous without taste or smell, insoluble in water, slightly soluble in alcohol, but soluble in ether. Berzelius considers it to be identical with the chloro- phyll, or green coloring matter of leaves. According to the researches of Strecker and Gundelach, pigs' bile differs from the bile of other animals. This bile contains an acid, to which the name hyocholic acid has been given, which may be prepared in the following manner: — fresh pigs' bile is mixed with a solution of sulphate of soda, the precipitate obtained is dissolved in absolute alcohol, and decolorized by animal charcoal. From this solution ether throws down a soda-salt, yielding on addition of sulphuric acid, hyocholic acid as a resinous mass, which is dissolved in alcohol and rcprecipitated by water. Hyocholic acid contains C54H43NO,0. AVhen heated with solutions of the alkalies, the acid undergoes a decomposition perfectly analogous to that of glyco-cholalic acid, hyocholic acid splitting into glj'cocine and a crystalline acid, very soluble in alcohol, less so in ether, which has been termed hyocho- lalic acid. This substance contains CgoH^O^HO; and the change is repre- sented by the following equation: — ao 0°°° 4j0(9 sist of a perfectly-transparent fluid, in which o o ®o ® ©a 1 float about numbers of transparent globules: these <$>°©$'@®<^<>'0°?Q^> consist of fat surrounded by an albuminous enve- !S?®@S0,|P0 dfe'b ^ove, which can be broken mechanically as in o| §t® ° 1° 8° the churning, or dissolved by the chemical action 00°®t!5,0,-.o J^£®& of caustic potassa, after which, on agitating the 3 o°^»«|fo "° 0 niilk with etheT> the fat can be dissolved. AVhen milk is suffered to remain at rest some hours at the ordinary temperature of the air, a large proportion of the fat-globules collect at the surface into a layer of cream; if this be now removed and exposed for some time to strong agita- tion, the fat-globules coalesce into a mass, and the remaining watery liquid is expelled from between them and separated. The butter so pro- duced must be thoroughly washed with cold water, to remove, as far as possible, the last traces of casein, which readily putrefies, and would in that case spoil the -whole. A little salt is usually added. Ordinary butter still, however, contains some butter-milk, and when in- tended for keeping should be clarified, as it is termed, by fusion. The watery part then subsides, and carries with it the residue of the azotized matter. The flavor is unfortunately somewhat impaired by this process. The con- sistence of butter, in other words, the proportions of margarin and olein is dependent upon the season, or more probably upon the kind of food: in sum- mer the oily portion is always more considerable than in winter. The volatile odoriferous principle of butter, buiyrin, has been already referred to. The casein of milk, in the state of cheese, is in many countries an import- ant article of food. The milk is usually heated to about 120° (49°C) and coagulated by rennet, or an infusion of the stomach of the calf in water- the curd is carefully separated by a sieve from the whey, mixed with a due pro- portion of salt, and sometimes some coloring-matter, and "then subjected to strong and increasing pressure. The fresh cheese so prepared, being con- stantly kept cool and dry, undergoes a particular kind of putrefactive fermen- tation, very little understood, by which principles are generated which com- MILK. 569 municate a particular taste and odor. The goodness of cheese, as well as much of the difference of flavor perceptible in different samples, depends in great measure upon the manipulation: the best kinds contain a considerable quantity of fat, and are made with new milk; the inferior descriptions are made with skimmed milk. Some of the Tartar tribes prepare a kind of spirit from milk by suffering it to ferment, with frequent agitation. The casein converts a part of*the milk- Bugar into lactic acid, and another part into grape-sugar, which in turn be- comes converted into alcohol. Mare's milk is said to answer better for this purpose than that of the cow. In a fresh state, and taken from a healthy animal, milk is always feebly alkaline. AVhen left to itself, it very soon becomes acid, and is then found tc contain lactic acid, which cannot be discovered in the fresh condition. The alkalinity is due to the soda which holds the casein in solution. In this soluble form casein possesses the power of taking up and retaining a very con- siderable quantity of phosphate of lime. The density of milk varies exceed- ingly; its quality usually bears an inverse ratio to its quantity. From an analysis of cow-milk in the fresh state by M. Haidlen,1 the following state- ment of its composition in 1000 parts has been deduced:— Water..... 873 00 Butter .... 30 00 Casein . . . . . 48-20 Milk-sugar . 43-90 Phosphate of lime 2-31 ,, magnesia. 0-42 ,, iron 007 Chloride of potassium . . 1-44 ,, sodium 0-24 Soda in combination with cas ein 0-42 1000-00 Human milk is remarkable for the difficulty with which it coagulates; it generally contains a larger proportion of sugar than cow-milk, but scarcely differs in other respects. * Annalen der Chimie und Tharmacie, xlv. 263. 48* 570 ANIMAL NUTRITION. ON THE FUNCTION OF NUTRITION IN THE ANIMAL AND VEGETABLE KINGDOMS. The constant and unceasing waste of the animal body in the process of respiration, and in the various secondary changes therewith connected, neces- sitates an equally constant repair and renewal of the whole frame by the de- position or organization of matter from the blood, which is thus gradually impoverished. To supply this deficiency of solid material in the circulating fluid is the office of the food. The striking contrast which at first appears in the nature of the food of the two great classes of animals, the vegetable feeders and the carnivorous races, diminishes greatly on close examination: it will be seen that, so far as the materials of blood, or, in other words, those devoted to the repair and sustenance of the body itself, are concerned, the process is the same. In a flesh-eating animal great simplicity is observed in the construction of the digestive organs ; the stomach is a mere enlargement of the short and simple alimentary canal; and the reason is plain : the food of the creature, flesh, is absolutely identical in composition with its own blood, and with the body that blood is destined to nourish. In the stomach it under- goes mere solution, being brought into a state fitted for absorption by the lacteal vessels, by which it is nearly all taken up, and at once conveyed into the blood ; the excrements of such animals are little more than the comminuted bones, feathers, hair, and other matters which refuse to dissolve in the stomach. The same condition, that the food employed for the nourishment of the body must have the same or nearly the same chemical composition as the body itself, is really fulfilled in the case of animals that live exclusively on vegetable substances. It has been shown1 that certain of the azotized principles of plants, which often abound, and are never altogether absent, have a chemical composition and assemblage of properties which assimilate them in the closest manner, and it is believed even identify them, with the azotized principles of the animal body: vegetable albumin, fibrin, and casein are scarcely to be distinguished from the bodies of the same name extracted from blood and milk. If a portion of wheaten flour be made into a paste with water, and cautiously washed on a fine metallic sieve, or in a cloth, a grayish, adhesive, elastic, in- soluble substance will be left, called gluten or glutin, and a milky liquid'will pass through, which by a few hours' rest becomes clear by depositing a quan- tity of starch. If now this liquid be boiled, it becomes again turbid from the production of a flocculent precipitate, which, when collected, washed dried and purified from fat by boiling with ether, is found to have the same compo- sition as animal albumin. The glutin itself is a mixture of true vegetable fibrin and a small quantity of a peculiar azotized matter called gliadin to which its adhesive properties are due. The gliadin may be extracted by boil- ing alcohol, together with a thick, fluid oil, which is separable by ether- it is gluey and adhesive, quite insoluble in water, and, when dry, hard and trans- 1 Liehig, Ann. der Chim. und Pharm. xxxix. 129. ANIMAL NUTRITION. 571 lucent like horn; it dissolves readily in dilute caustic alkali, and also in acetic acid. The fibrin of other grain is unaccompanied by gliadin; barley and oat- meal yield no glutin, but incoherent filaments of nearly pure fibrin. Vegetable albumin in a soluble state abounds in the juice of many soft succulent plants used for food: it may be extracted from potatoes by macera- ting the sliced tubers in cold water containing a little sulphuric acid. It coagulates when heated to a temperature dependent upon the degree of con- centration, and cannot be distinguished when in this state from boiled white of egg in a divided condition. Almonds, peas, beans, and many of the oily seeds, contain a principle which bears the most striking resemblance to the casein of milk. AVhen a solution of this substance is heated, no coagulation occurs, but a skin forms on tho surface, just as with boiled milk. It is coagulable by alcohol, and by acetic -acid; the last being a character of importance. Such a solution, mixed with a little sugar—an emulsion of sweet almonds, for instance—left to itself, soon becomes sour and curdy, and exhales an offensive smell; it is then found to contain lactic acid. All these substances dissolve in caustic potassa, with production of a small quantity of alkaline sulphide: the filtered solutions mixed with excess of acid give precipitates of protein. The following is the composition in 100 parts of vegetable albumin and fibrin: it will be seen that they agree very closely with the results before given: — Alhumin. Fibrin. Carbon........5501 54-60 Hydrogen.......7-23 7-30 Nitrogen.......15-92 15-81 Oxygen, sulphur, and phosphorus . . . 21-84 22-29 10000 10000 The composition of vegetable casein, or legumin, has not been so well made out: so much discrepancy appears-in the analyses as to lead to the supposi- tion that different substances have been operated upon. The great bulk, however, of the solid portion of the food of the herbivora consists of bodies which do not contain nitrogen, and therefore cannot yield sustenance in the manner described: some of these, as vegetable fibre or lignin, and waxy matter, pass unaltered through the alimentary canal; others, as starch, sugar, gum, and perhaps vegetable fat, are absorbed into the system, and afterwards disappear entirely: they are supposed to contribute very largely to the production of animal heat. On these principles, Professor Liebig1 has very ingeniously made the dis- tinction between what he terms plastic elements of nutrition and elements of respiration ; to tho former class belong ATegetable fibrin, A'egetable albumin, Vegetable casein, Animal flesh, Blood. To the latter, Fat, Starch, Gum, Cane-sugar, Grape-sugar, Milk-sugar, Pectin, Alcohol? 1 Animal Chemistry, p. 96. O < JS VEGETABLE NUTRITION. In a flesh-eating animal, the waste of the tissues is very rapid, the tempe- rature being, as it were, kept up in great measure by the burning of azotized matter; in a vegetable feeder it is probably not so great, the non-azotized substances being consumed in the blood in place of the organic fabric. AVhen the muscular movements of a healthy animal are restrained, a genial temperature kept up, and an ample supply of food containing much amyla- ceous or «ily matter given, an accumulation of fat in the system rapidly takes place : this is well seen in the case of stall-fed cattle. On the other hand, when food is deficient, and much exercise is taken, emaciation results. These effects are ascribed to differences in the activity of the respiratory function: in the first instance, the heat-food is supplied faster than it is consumed, and hence accumulates in the form of fat; in the second, the conditions are reversed, and the creature is kept in a state of leanness by its rapid consump- tion. The fat of an animal appears to be a provision of nature for the main- tenance of life during a certain period under circumstances of privation. The origin of fat in the animal body has at one time been made the subject of much animated discussion. On the one hand it was contended that satis- factory evidence exists of the conversion of starch and saccharine substances into fat, by separation of carbon and oxygen, the change somewhat resembling that of vinous fermentation: it was argued, on the other side, that oily or fatty matter is invariably present in the food supplied to the domestic animals, and that this fat is merely absorbed and deposited in the body in a slightly- modified state. The question has now been decided in favor of the first of these views, which was enunciated by Professor Liebig, by the very chemist who formerly advocated the second opinion. By a series of very beautiful experiments, MM. Dumas and Milne Edwards proved that bees exclusively feeding upon sugar were still capable of producing wax, which was pointed out as a veritable fat. The food of animals, or rather that portion of the food which is destined to the repair and renewal of the frame itself, is thus seen to consist of substances iaentical in composition with the body it is to nourish, or requiring but little chemical change to become so. The chemical phenomena observed in the animal system resemble so far those produced out of the body by artificial means, that they are all, or nearly all, so far as is known, changes in a descending series. Albumin and fibrin are probably more complex compounds than gelatin or the membrane which furnishes it: this, in turn, has a far greater complexity of constitution than urea, the regular form in which rejected azotized matter is conveyed out of the body. The animal lives by the assimilation into its own substance of the most complex and elaborate products of the organic kingdom;__products which arc, and, apparently, can only be, formed under the influence of vege- table life, e The existence of the plant is maintained in a manner strikingly dissimilar- the food supplied to vegetables is wholly inorganic; the carbonic acid and nitrogen of the atmosphere, the water which falls as rain, or is deposited as dew; the minute trace of ammoniacal vapor present in the air; the alkali and saline matter extracted from the soil; —such are the substances which vield to plants the elements of their growth. That green healthy vegetables do possess, under circumstances to be mentioned immediately, the propertv of decomposing carbonic acid absorbed by their leaves from the air or conveved thither in solution through the medium of their roots, is a fact positively proved by direct experiment, and rendered certain by considerations of a verv stringent kind. To effect this very remarkable decomposition the influence of light is indispensable; the diffuse light of day suffices in some decree but the direct rays of the sun greatly exalt the activity of the process ' Thp carbon separated in this manner is retained in the plant in union with the elements of water, with which nitrogen is also sometimes associated while the VEGETABLE NUTRITION. 573 oxygen is thrown off into the air from the leaves in a pure and gaseous Condition. The effect of ammoniacal salts upon the growth of plants is so remarkable, as to leave little room for doubt concerning the peculiar function of the am- monia recently discovered in the air. Plants which in their cultivated state contain, and consequently require, a large supply of nitrogen, as wheat, and the cereals in general, are found to be greatly benefitted by the application to the land of such substances as putrefied urine, which may be looked upon as a solution of carbonate >of ammonia, the guano1 of the South Seas, which usually contains a large proportion of ammoniacal salt, and even of a pure sulphate of ammonia. Some of these manures doubtless owe a part of their value to the phosphates and alkaline salts they contain; still, the chief effect is certainly due to the ammonia. Upon the members of the vegetable kingdom thus devolves the duty of building up, as it were, out of the inorganic constituents of the atmosphere,— the carbonic acid, the water, and the ammonia, — the numerous complicated organic principles of the perfect plant, many of which are afterwards destined to become the food of animals, and of man. The chemistry of vegetable life is of a very high and mysterious order, and the glimpses occasionally obtained of its general nature are few and rare. One thing, however, is manifest, namely, the wonderful relations between the two orders of organized beings, in virtue of which the rejected and refuse matter of the one is made to con- stitute the essential and indispensable food of the other. While the animal lives, it exhales incessantly from its lungs, and often from its skin, carbonic acid; when it dies, the soft parts of its body undergo a series of chemical changes of degradation, which terminate in the production of carbonic acid, water, carbonate of ammonia, and, perhaps, other products in small quantity. These are taken up by a fresh generation of plants, which may in their turn serve for food to another race of animals. 1 Guano is the partially-decomposed dung of birds, found in immense quantities on some of the barren islets of the western coast of Southern America, as that of Peru. Jlore recently, similar deposits have been found on the coast of Southern Africa. The guano now imported into England from these localities is usually a soft, brown powder, of various shades of color. White specks of bone-earth, and sometimes masses of saline matter, may be found in it. That which is most recent, and probably most valuable as manure, often contains undecomposed uric acid, besides much oxalate or hydrochlorate of ammonia, and alkaline phosphates, and other salts; it has a most offensive odor. The specimens taken from older deposits have but little smell, are darker in color, contaiu ro uric acid, and much less ammoniacal salt; the chief components are bone-earth, a peculiar dark-colored organic matter, and soluble inorganic salts. See also p. 48i. \ APPENDIX. (575) 76 APPENDIX. HYDROMETER TABLES. COMPARISON OF THE DEGREES OF BAUME's HYDROMETER WITH THE SPECIFIC GRAVITIES. 1. For liquids heavier than water. Degrees. 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Specific Gravity. 1-000 1-007 1013 1020 1-027 1-034 1-041 1-048 1-056 1-063 1-070 1-078 1-085 1-094 1-101 1-109 1-118 1-126 1-134 1-143 1-152 1-160 1-169 1-178 1-188 1-197 Degrees. 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 Specific Gravity. 1-206 1-216 1-225 1-235 1-245 1-256 1-267 1-277 1-288 1-299 1-310 1-321 1-333 1-345 1-357 1-369 1-381 1-395 1-407 1-420 1-434 1-448 1-462 1-476 1-490 1-495 Degrees. 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 Specific Gravity. 1-520 1-535 1-551 1-567 1-583 1-600 1-617 1-634 1-652 1-670 1-689 1-708 1-727 1-747 1-767 1-788 1-809 1-831 1-854 1-877 1-900 1-924 1-949 1-974 2-000 APPENDIX. D/7 2. Baumffs Hydrometer for liquids lighter than water. Degrees. Specific Gravity. Degrees. Specific Gravity. Degrees. Specific Gravity. 10 1000 27 0-896 44 0-811 11 0-993 28 O-890 45 0-807 12 0-986 29 0-885 46 0-802 13 0-980 30 0-880 47 0-798 14 0-973 31 0-874 48 0-794 15 0-967 32 0-869 49 0-789 16 0-960 33 0-864 50 0-785 17 0-954 34 0-859 51 0-781 18 0-948 35 0-854 52 0-777 19 0-942 36 0-849 53 0-773 20 0-936 37 0-844 54 0-768 21 0-930 38 0-839 55 0-7G4 22 0-924 39 0-834 56 0-760 23 0-918 40 0-830 57 0-757 24 0-913 41 0-825 58 0-753 25 0-907 42 0-820 59 0-749 26 0-901 43 0-816 60 0-745 These two tables are on the authority of M. Francceur; they are taken from the Handuorterbuch der Chemie of Liebig and Poggendorff. Baume's hydrometer is very commonly used on the Continent, especially for liquids heavier than water. For lighter liquids, the hydrometer of Cartier is often employed in France. Cartier's degrees differ but little from those of Bauui6. In the United Kingdom, Twaddell's hydrometer is a good deal used for dense liquids. This instrument is so graduated that the real sp. gr. can be deduced by an extremely simple method from the degree of the hydrometer, namely, by multiplying the latter by 5, and adding 1000; the sum is the sp. gr., water being 1000. Thus 10° Twaddell indicates a sp. gr. of 1050, or 1-05; 90° Twaddell, 1450, or 1-45. In the Customs and Excise, Sike's hydrometer is used. 49 c«c«wc^cj.>*k*.rfkrf^^cocococococococo 05Cr\rf».COtai-»Ot000^01C7thKCON)l-'OCOOO~^OiOlrfi.COI>S o I ■a re p c a MMK)t-'MOOOOO(»-4MO>OJOlOll^»MlOIOMMOO o o o o oooooo ooooooo oooooo oo cb-^ItbosKJoi I^.C»CO-^Itil63K'Cn *.00C0^lt005hJ6lO -4 Oi Ol^03(OKIMOO 00CCCDOlH000lC0M(C0D0JOllM»WC0*>.OlMa3i-'l^-^O Force. 0000^T^J^l^t-4^1--J^l^l^JO5C5O>O5C5O5O5OiOiO5Ol—» O CO 00 -J 0 B 2" tOO)OJCOi|MMKlU)tOi-'MOOtOOOCltl-OiOl|M» ooooo ooo ooooo ooooooo ooooo t^.diH-'cjt **-6ooo-*-'0\ tf^cbeo-^itboii^'cn ** ob M^C5 00 -~4 Ol Ol 00-JO CO 13 i-^^OOOOOOOOOOOOOOOOOOOOOOO hJocociscDcbcboc-^i-^i^i-^id^OTdidiwcJiciicJicJic^cji^^ MOM*.M(X)01|s5(0-.l^MOMa)MMCO-iail^K10fflS ooHOOOi-'cooioaiHeDffltnoiaMoooM^Mo^ Force. 00>^COUIMMOtO(»^1050l|^*kWCONll3MMOOtO<0 OOOOOtSOOOOOOOWOCJiOOiOCnOdOOiO o p § 13 (D 8-cs (M5MMOOtOtOCOOO^I-10iffiiOOiOl(yi*>^l^*M0505 coi-'dOrf».ooow«4t>3ci>-'C''ico~j^i-'oocscoo-^iCNM ooooo oooo ooo ooooooooooooo OOt-'Cn rf*. 00C0--It>3aii-'Cji^i to^CiOOi-'WOi-.l to oo oo --i o -^ os oo -j o 0 hJCrc*k^.COCOlOK)t-»i->p-» MOO«5p-Ji^OOO(»<»OiK)tD-lfflOiOi*.COCOb5HMMWM o a>Mo»JOOcofflOi-'M^l(.oi-JOCij»iW!OCii-'cocnco p 3 > IS W fd H H 2 W H « 2 a 2 APPENDIX. 579 TABLE OP THE PBOPORTION BY WEIGHT OF ABSOLUTE OR REAL ALCOHOL IN 100 PARTS OF SPIRITS OF DIFFERENT SPECIFIC GRAVITIES. (FOWNES.) Sp. Gr. at 60° (15°-5C). i Per cent. of real Alcohol. Sp. Gr. at 60° (15°-5C.) Per cent. of real Alcohol. Sp. Gr. at 60° (15°-5C). Per cent. of real Alcohol. 0-9991 0-5 0-9511 34 0-8769 68 0-9981 1 0-9490 35 0-8745 69 B-9965 2 0-9470 36 0-8721 70 0-9947 3 0-9452 37 0-8696 71 0-9930 4 0-9434 38 0-8672 72 0-9914 5 0-9416 39 0-8649 73 0-9898 6 0-9396 40 0-8625 74 0-9884 7 0-9376 41 0-8603 75 0-9869 8 0-9356 42 0-8581 76 0-9855 9 0-9335 43 0-8557 77 0-9841 10 0-9314 44 0-8533 78 0-9828 11 0-9292 45 0-8508 79 0-9815 12 0-9270 46 0-8483 80 0-9802 13 0-9249 47 0-8459 81 0-9789 14 0-9228 48 0-8434 82 0-9778 15 0-9206 49 0-8408 83 0-9766 16 0-9184 50 0-8382 84 0-9753 17 0-9160 51 0-8357 85 0-9741 18 0-9135 52 0-8331 86 0-9728 19 0-9113 53 0-8305 87 0-9716 20 0-9090 54 0-8279 88 0-9704 21 0-9069 55 0-8254 89 0-9691 22 0-9047 56 0-8228 90 0-9678 23 0-9025 57 0-8199 91 0-9665 24 0-9001 58 0-8172 92 0-9652 25 0-8979 59 0-8145 93 0-9638 26 0-8956 60 0-8118 94 0-9623 27 0-8932 61 0-8089 95 0-9609 28 0-8908 62 0-8061 96 0-9593 29 0-8886 63 0-8031 97 0-9578 30 0-8863 64 0-8001 98 0-9560 31 0-8840 65 0-7969 99 0-9544 32 0-8816 66 0-7938 100 0-9528 33 0-8793 67 580 APPENDIX. DR. SCHWEITZER'S OF THE PRINCIPAL MINERAL WATERS OF GERMANY Grains of Anhydrous Ingredients in One Pound Troy. Carlshad. Ems. Schlesischer. Obersalz-Brunnen. Carbonate of Soda.......... 7-2712 0-0150 0-0055 1-7775 1-0275 0-0048 0-0208 0-0012 00019 14-9019 5-9820 00184 0-4329 8-0625 0-0405 00022 0 0080 0-8555 0-5915 00028 0-0120 00014 0-4050 0-0338 5-7255 0-0014 0-3104 7-6211 00170 1-5464 1-5496 0-0026 00356r 0-3160 2-5106 0-0164 0-8682 0-0051 0-2423 Ditto (proto) of Manganese Sub-Phos. of Lime.......... Ditto of Alumina............ Sulphate of Potassa........ Ditto of Soda................. Ditto of Lithia............... Ditto of Lime................ Ditto of Strontia............ Ditto of Potassium......... Ditto of Sodium............. • Ditto of Calcium............ Ditto of Barium............. Ditto of Strontium......... Bromide of Sodium......... Iodide of Sodium............ Fluoride of Calcium........ Total.......................... 31-4606 58 Sprud. 165° (73°-8C) Neub. 138° (58°-8C) Muhl. 128° (53°-3C) Ther. 122° (50°C) Berzelius. 16-0525 51 Kess. 117° (47°-2C) Kr'an. 84° (28°-8C) Struve. 14-7309 98 58° (14° 5C) Struve. Carbonic Acid Gas in 100 cubic inches } Analyzed by............... APPENDIX. 581 TABLE OF ANALYSES AND OF THE SARATOGA CONGRESS SPRING OF AMERICA. Saratoga Congress Spring. Kissengen. Kagozi. Marienbad. Kreutbr. Auschowitz. Ferdinauds-Brunnen. Eger. Franz en s-Brunnen. 0-8261 0-0672 5-8531 41155 0 0202 00173 0-1379 01004 00326 1-6256 19-6053 01613 0-0046 00069 0-1112 0-0592 4-8180 1-3185 0-0121 0-1397 1-2540 5-5485 0-0364 39-3733 3-6599 0-3331 0-1609 5-3499 00858 0-0028 2-9509 20390 20288 0-1319 28-5868 10-1727 0-0023 0-2908 4-5976 0 0507 00040 3-0085 2-2867 00692 0-2995 0-0040 16-9022 6-7472 0-5023 3-8914 0-0282 0-0023 1-3501 0-5040 0-0322 01762 0-0172 0-0092 18-3785 6-9229 0-3548 32-7452 114 50° (10°C) Schweitzer. 56-7136 96 53° (11°-6C) Struve. 51-6417 105 53° (11°-6C) Berzelius. 34-4719 146 49° (9°-5C) Steinman. 31-6670 154 54° (12°-2C) Berzelius. 49* 582 APPENDIX. DR. SCHWEITZER'S OF THE PRINCIPAL MINERAL WATERS OF GERMANY Grains of Anhydrous Ingredients in One Pound Troy. Pyrmont. Spa Pouhon. Fachingen. Carbonate of Soda.......... 4-7781 00364 0-3213 00110 0-0314 1-6092 00067 5-0265 0-0154 2-3684 0-8450 0-3727 0-5531 0-7387 0-8421 00389 0-2813 00102 00064 00593 0 0281 0-3371 0-3739 12-3328 1-8667 1-2983 00061 0-1267 3-2337 00657 Ditto of Lithia............... Ditto of Strontia............ Ditto (proto) of Manganese Ditto (proto) of Iron....... Sub-Phos. of Lime.......... Ditto of Alumina............ Ditto of Soda................. Ditto of Lithia............... Ditto of Lime................ Ditto of Strontia............ Ditto of Magnesia.......... Ditto of Potassium......... Ditto of Sodium............. Ditto of Lithium............ Ditto of Calcium............ Ditto of Barium............. Ditto of Strontium......... Bromide of Sodium......... Iodide of Sodium............ Fluoride of Calcium........ Total......................... 15-4221 160 56° (13°-3C) Struve. 3-2691 136 50° (10°C) Struve. 18-9300 135 50° (10°C) Bischoff. Carbonic Acid Gas in 100 1 Temperature (F.)............ APPENDIX. 583 TABLE OF ANALYSES AND OF THE SARATOGA CONGRESS SPRING OF AMERICA, Continued. Selters. Scidschiitz. Ptillna. Kreuznach. Elisen-Brunnen. Adelheids-Quelle. 4-6162 0-0014 0-0144 1-4004 1-5000 0-0007 0-0020 0-2978 0-2085 12-9690 00013 0-2265 5-1045 0-8235 0-0032 0-0095 00117 0-0088 3-6705 17-6220 1-1287 00347 62-3535 5-9302 1-2225 0-0900 0-5775 4-8045 00026 3-6000 92-8500 1-9500 69-8145 14-7495 01320 0-2058 1-1812 0-0072 0-1495 0-7287 54-6917 00562 9-7358 0-2366 0-5494 0-2304 00024 00086 0-2355 5-2443 0-0902 00024 0-0387 0-4703 0-2980 0-001S 00121 0-0066 0-1845 28-4608 0-3060 0-1500 0-0166 0-1922 21-2982 126 58° (14°-5C) Struve. 98-0133 20 58° (14°-5C) Struve. 188-4806 7 58° (14°-5C) Struve. 68-0190 12 47° (8°-3C) Struve. 35-4739 10 58° (14°-5C) Struve. 584 APPENDIX. WEIGHTS AND MEASURES 4800 grains Troy = 1 oz. Troy. 437-5 " = 1 oz. Avoirdupoids. 70000 " = 1 lb. Avoirdupoids. 5760-0 " =1 lb. Troy. The imperial gallon contains of water at 60° (15°-5C) 70,000- grains The pint (£ of gallon)........................................ 8,750- " The fluid-ounce (^V of pint)................................ 437-5 " The pint equals 34-66 cubic inches. The French kilogramme =. 15,433-6 grains, or 2-679 lb. Troy,or 2-205 lb. avoirdupoids. The grammme — 15-4336 grains. " decigramme — 1-5434 " " centigramme = 0-1543 " " milligramme = 0-0154 " The metre of France — 39-37 inches. " decimetre _ 3-937 " " centimetre _ 0-394 " " millimetre = 0 0394 «« COMPARISON OF FRENCH AND ENGLISH MEASURES. By Dr. Warren De La Rue. MEASURES OF LENGTH. In English Inches. In English Feet _: 12 Inches. In English Yards _: 3 Feet. In English Fathoms = 6 Feet. In English Miles = 1700 yards. 003937 0-39371 3-93708 39-37079 393-70790 3937-07900 39370-79000 393707-90000 0-0032809 0-0328090 0-3280899 3-2808992 32-8089920 328-0899200 3280-8992000 32808-9920000 0.0010936 00109363 0-1093633 1-0936331 10-9363310 109-3633100 1093-6331000 10936-3310000 0-0005468 0-0054682 0-0546816 0-5468165 5-4681655 54-6816550 546-8165500 5468-1655000 0-0000006 0-0000062 00000621 0-0006214 0-0062138 00621382 0-6213824 6-2138244 Metre.................................... 1 Inch = 2-539954 Centimetres. 1 Foot = 3-0479449 Decimetres. 1 Yard = 0-91438348 Metre. 1 Mile = 1-6093149 Kilometre. MEASURES OF SURFACE. In English Square Feet. In English Sq. Yards _: 9 Square Feet. In English Boles = 272-25 Sq. Feet. In English Roods = 10,890 Sq. Feet. In English Acres _: 43,560 Sq. Feet. 10-7642993 1076-4299342 107642-9934183 1-1960333 119-6033260 11960-3326020 0-0395383 3-9538290 395-3828959 0-000988457 0-098845724 9-884572398 0.0002471143 0-0247114310 2-4711430996 1 Square Inch —: 6-4513669 Square Centimetres. 1 Square Foot = 92899683 Square Decimetres. 1 Square Yard = 0-83609715 Square Metre oi 1 Acre = 0-404671021 Hectare. Centiare. MEASURES OF CAPACITY. Millilitre, or cubic centimetre............. Centilitre, or 10 cubic centimetres........ Decilitre, or 100 cubic centimetres........ Litre, or cubic decimetre................... Decalitre, or centistere...................... Hectolitre, or decistere.................. Kilolitre, or stere, or cubic metre......... Myriolitre, or decastere .................... 1 Cubic Inch = 16-3861759 Cubic Centimetres In Cubic Inches 0-061027 0-610271 6-102705 61-027052 610-270515 6102-705152 61027-051519 610270-515194 In Cubic Feet = 1728 Cubic Inches. 0-0000353 0 0003532 0-0035317 0-0353166 0-3531658 3-5316581 35-3165807 353-1658074 In Pints _: 34-65923 Cubic Inches. 0-001761 0-017608 0-176077 1-760773 17-607734 176-077341 1760-773414 17607-734140 In Gallons _: 8 Pints = 277-27384 Cubic Inches. 0-00022010 0-00220097 0-02200967 0-22009668 2-20096677 22-00966767 220-09667675 2200-96676750 In Bushels=8 Gal- lons = 221819075 Cubic Inches. 1 Cubic. Foot = 28-3153119 Cubic Decimetres. 1 Gallon =: 4-543457969 Litres. 0-000027512 0-000275121 0-002751208 0-027512085 0-275120846 2-751208459 27-512084594 275-120845937 MEASURES OF CAPACITY. Milligramme.. Centigramme . Decigramme .. Gramme....... Decagramme.., Hectogramme. Kilogramme.... Myriogramme. In English Grains. 0-015432 0154323 1-543235 15-432349 154-323488 1543-234880 15432-348800 154323-488000 In Troy Ounces = 480 Grains. 0-000032 0-000322 0-003215 0032151 0-321507 3-215073 32-150727 321-507267 In Avoirdupois Lbs. = 7000 £ Grains. 0-0000022 0-0000220 0-0002205 0-0022046 00220462 0-2204621 2-2046213 22-0462126 In Cwts. = 112 Lbs. == 784,000 Grains. 0-00000002 000000020 0-00000197 000001968 0-00019684 0-00196841 0-01968412 0.19084118 Tons = 20 Cwts. = 1680,000 Grains. 0-000000001 0-000000010 0-000000098 0000000984 0-000009842 0-000098421 0-000984206 0-009842059 1 Grain = 0-064798950 Gramme. 1 Troy oz. = 31-103496 Gram. 1 lb. Avd. = 0-45359265 Kilogr. 1 Cwt. = 50-80237689 Kilo™ INDEX. PAGE Absorption of heat... 96 Acetal. tx.t^Gtr-Mj. . ■ 389 Acetamide......394 Acetate of oxide of amyl. 417 Acetates.......392 Acetic acid......390 manufacture of . . . 390 anhydrous.....392 ether.......394 Acetone.......396 determination of vapor- density of.....448 Acetonitrile......392 Acetyl .(■'..' . Oc-Mq ■ • 387 compounds of ... . 387 Acid, acetic . C^Wi \? ^ Q 390 anhydrous^*, .^y. --... . 392 aconitic . . ...''. 452 acrylic.......412 aldehydicr, Jj..fi. . .389 alloxanic . v. J.i- . . 480 alphaorsellic.....518 althiouic......3S2 amalic.......490 amygdalic.....463 amido-benzoic . . . '. 434 anchoic......431 anilic.......516 anilotic......444 anisic.......525 anthranilic. . . . 498, 517 antimonic.....306 arsenic.......310 arsenious......309 aspartic......453 auric.......318 azotic.......140 balenic.......422 benzilic......439 benzoic...... . 433 anhydrous.....434 betaorsellic.....518 biamido-benzoic . . . 434 binitro-benzoic. . . . 434 bismuthic......293 boracic.......171 bromic.......165 bromo-phenisic. . . . 537 butyric .... 415,429 campholic......528 camphoric.....527 capric.......430 caproic.......430 caprylic......430 carbazotic.....517 carbolic......535 carbonic......146 liquefaction of . . . 75 Acids —cont. page carminic......520 cerebric......554 cerotic.......42!) cerotylic......429 cetylic.......429 chelidonic.....455 chloracetic.....395 chlorhydric.....159 chloric.......163 chlorocarbonic . . . 148 chlorochromic .... 287 chlorohyponitric . . . 161 chloronaphthalic . . . 539 chloi-onitrous .... 161 chlorophenisic .... 536 chlorophenusic. . . . 537 chlorosalieylous . . . 443 chlorosulphuric . . . 154 chlorous......162 cholalic......564 choleic.......564 cholic.......564 choloidinic.....564 chrysammic.....522 chrysanilic . . . 498, 517 chrysolepic.....522 chrysophanic .... 520 chromic......286 cinnamic......446 citraeonic......453 citric.......451 cobaltic......289 cocinic.......428 comenic......455 croconic......364 cumaric......445 cumic.....441, 526 cyanic.......466 cyanuric......467 delphinic......430 dextro-racemic. . . .451 dial uric......4S2 dinitro-ethylic .... 386 disulphometholic . 382, 396 dithionic......153 draconic.....• 525 elaidic.......428 ellagic.......458 equisetic......452 erythric......517 ethalic.......529 ethionic......382 euchronic......363 euxanthic.....522 evernic.......519 everninic......519 ferric.......279 formic.......400 Acids — cont. paqb formobenzoic .... 438 fulminic......468 fulminuric.....470 fumaric......454 gallic.......456 glucic.......354 glyceric......415 glyco-benzoic .... 440 glyco-cholalic .... 564 glyco-hyo-cholalic . . . 565 glycolic.....398, 549 glyoxalic acid .... 390 hemipinic......487 hippuric......439 regeneration of . . . 440 hydrobromic.....165 hydrochloric.....159 hydrocyanic.....460 hydroferricyanic . . . 474 hydroferrocyanic . . . 471 hydrofluoric.....167 hydrofluosilicic . . . 169 hydroleic......428 hydromargaric .... 428 hydromargaritic . . . 428 hydrosulphocyanic . . 475 hydrosulphuric. . . . 182 hyocholalic.....565 hyocholic......565 hypochloric ..... 163 hypochlorous .... 162 hyponitric.....143 hypophosphorous. . . 157 hyposulphuric .... 153 sulphuretted.... 153 hyposulphurous . . . 153 igasuric......4S'J indinic.......516 inosinic......552 itaconic......453 iodic.......167 iodo-sulphuric .... 154 insolinic......441 isatinic......515 isethionic......363 japonic......457 kakodylic......409 kinic.......455 lactic...... . 368 lecanoric......517 levo-racemic.....451 lithic.......479 lithofellinic.....566 malamic......453 maleic.......454 malic.......453 manganic......276 margaric......425 (587) 588 INDEX. Acres—cont. page meconic......454 melanic......443 melasinicc^^^ . . 364 melissic . . . .". . 42^ mellitic......363 mesoxalic.....481 metacetonic.....411 metagallic.....459 metamargaric .... 428 ^netapectic.....359 metaphosphoric . . . 233 methionic.....383 metoleic......428 molybdic......303 monobromacetic . . . 395 monochloracetic . . . 395 mucic.......363 muriatic......159 mykomelinic .... 481 myristic......428 myronic......528 niobic.......305 nitric.......140 nitranisic......525 nitrobenzoic.....434 nitrococcusic .... 520 nitrocumic.....441 nitrophenasic .... 537 nitrophenesic .... 537 nitrophenisic . . 516, 537 nitro-phthalic .... 538 nitrosalicylic .... 515 nitrotoluylic .... 441 nitrous......143 cenanthic......422 cenanthylio . . . 422, 430 oleic.......426 oleophosphoric. . . . 554 opianic......486 orsellinic .... 517, 518 osmic.......333 osmious......332 oxalic . £ O . . . .360 oxalovinic ..... 376 oxaluric......481 oxamic......362 oxanilic...... 502 palmitic .... 427, 429 parabanic.....481 paratartaric.....451 parellic......519 pectic.......359 pelargonic.....431 pelopic......305 pentathionic .... 153 perchloric.....164 perchromic.....260 periodic......167 permanganic .... 277 phloretic......445 phocenic......430 phosphethylic .... 376 phosphobiethylic . . . 376 phosphoric.....157 anhydrous .... 157 bibasic......232 glacial......157 monobasic .... 232 tribasic......231 phosphorous .... 156 phosphovinic .... 376 phthalic .... 521, 538 picric.......616 pimaric......529 Acids — cont. page pimelic . . T. . . . 430 pinic.......529 propionic......411 prussic.......460 purpuric......483 purreic......522 pyrocomenic .... 455 pyrogallic.....459 pyromucic.....363 pyrophesphoric . . . 233 pyrotartaric .... 450 quadrichlorovaleric . . 420 racemic......451 artificial production of. 451 retinic.......541 rhodizonic.....364 ricinoleic......430 rubiacic ...... 521 rubic..... . 457 rutic.......430 saccharic......362 sacchulmic.....354 salicylic.....• 444 salicylous.....442 salicyluric.....444 sebacic.......431 selenic.......154 selenious......154 silicic.......169 stearic.......424 styphnic......522 suberic .... 363,431 succinic......431 sudoric......563 sulphacetic.....396 sulphamylic .... 417 sulphindigotic .... 514 sulphindylic .... 514 sulphobenzoic .... 434 sulphobenzolic . . . 435 sulphoglyceric .... 427 sulpholeic.....428 sulpholignic .... 360 sulphomargaric . . . 42S sulphomethylic . . . 402 sulphonaphthalic . . 538 sulphophenic .... 535 sulphosaccharicga^/j^Sto, sulphotoluolic .... 530^ sulphovinic.....375 sulphuric.....151 sulphuric, anhydrous . 152 sulphurous.....150 sylvic.......529 tannic.......456 tantalic......304 tartaric......448 tartaric, anhydrous . . 450 inactive.....450 tartralic......450 tartrelic......450 tajjtrovinic.....376 tauro-cholalic .... 564 tauro-hyo-cholalic . . 566 telluric......309 tellurous......309 tetrath ionic.....I.ri3 thiacetic......396 thionuric......481 titanic.......305 toluylic......641 toluyluric.....444 trichloracetic .... 395 trichlorovaleric . . . 420 Acids —cont. page trith ionic......153 tungstic......302 ulmic.......354 uramilic......481 uric........479 usnic.......519 valerianic.....418 valeric.......418 valero-benzoic .... 437 vanadic......3(i4 xanthic......385 anhydrous . 233,392,434 bibasic.......232 fatty.......422 hydrogen-theory of . . 233 monobasic.....232 notation of.....233 oxygen-theory of . . . 233 polybasic......231 terminology of . . . 150 tribasic......231 vegetable.....448 Aconitates......453 Aconitic acid ..... 452 Aconitine......491 Acrolein.......412 Acrylic acid.....413 Actinism......91 Adelheidsquelle, water of 583 Adipic acid......431 Affinity, chemical . . . 203 disposing......206 After-damp of coal-mines . 147 Air-pump......47 Air, atmospheric .... 137 Air-thermometer ... 55 Alanine.....508, 549 Albite........268 Albumin ...... 543 test for......544 Albuminous principles 543, 571 Albuminose.....548 Alcohol Cif/r'{G1_- ■ • 364 absolute......365 acrylic.......413 allylic.......413 amylenic......418 amylic.......416 anisic.......525 benzoic......438 butylic......414 caprylic .... 422, 430 cerotylic .... 421, 429 cetylic .... 421, 429 cinnamylic.....445 cresyl ic......537 cumic.......526 ethalic.......429 ethylenic .... 379, 397 melissic .... 421, 429 phenyl-alcohol .... 535 products of oxidation of 387 propylen......414 propylic......414 Btilbylic......441 xylilic.......441 Alcohols, generally, table of, in aqueous mix- tures ......579 Aldehyde C, *J-, £_ . . 388 bases from . . f . . 508 resin.......388 Aldehydic acid .... 389 Alembroth, sal .... 322 INDEX. 589 PAGE Algaroth, powder of . . 307 Alizarin.......521 Alkalimeter.....245 Alkalimetry.....244 Alkalies.......235 Alkaline earths .... 255 Alkaloids......4S5 artificial......492 Alkargen......410 Alkarsin......407 Allantoin......479 Alloxan.......480 Alloxanic acid.....480 Alloxantin......4S2 Alloys of copper .... 296 Allyl series......411 alcohol ...... 412 oxide of......413 sulphide of.....413 sulphocyanide of . . . 413 Almonds, oil of bitter . . 433 Aloes........522 Alphaorsellic acid . . . 51S Althionic acid.....382 Alums.......207 Arum, common .... 207 ltoman......2ij? Alumina......266 acetate of.....393 analytical remarks . . 208 silicates of.....26S sulphate of.....267 Aluminium.....266 chloride of.....267 sulphide of.....267 26' 251 324 314 490 507 Alum stone Amalgam, ammoniacal Amalgams..... Amalgamation . . . Amalic acid .... Amarine ..... Amber.......529 Amidin.......357 Amidogen . 3.....253 Amidogen-bases .... 494 Amines.......494 Ammelide......477 Ammeline......476 Ammonia......1S1 acetate of.....392 alum.......267 analytical remarks on . 253 benzoate of.....434 carbonates of ... . 252 cyanate of.....467 nitrate of......252 oxalate of Jrfao6j.Ofi.ttd[^ purpurate of ... . 4s.'j sulphate of.....252 sulphites of.....253 tartrates of.....449 urate of......480 Ammoniacal amalgam . 251 Ammonium.....251 chloride of.....251 cyanide of.....46a ferrocyanide of. . . . 471 sulphocyanide of . . . 474 sulphides of.....252 Amorphous phosphorus . 155 Amides, new.....327 Amidobenzoic acid . . . 434 Amygdalio acid .... 463 Amvgdalin......463 page Amylaceous group . . . 351 Amyl and its compounds 415 series, bases of the . .498 Amylamine.....498 urea.......498 Amyl-ammonia . . . . 498 Amylene......41" bromide of.....418 Amyl-glycol.....418 Amylene-alcohol .... 418 Amylic ether.....416 mercaptan.....417 Amylotriethyl-ammonium, oxide of.....49S Analcime......268 Analysis, ultimate, of or- ganic bodies .... 338 Analysis of hydrates and carbonates of the alka- lies .....244, 24S Analytical method of che- mical research . . . 338 Anatase.......305 Anhydrous acids 232, 392, 434 Anilic acid......516 Aniline.......498 homologues of ... . 502 -urea.......502 Anilotic acid.....444 Animal heat.....542 body, components of . 543 Aniseed, oil of .... 524 Anisic acid......524 Anisoin.......525 Anisol . . . 525,527, 536 Anisic alcohol.....525 Anisidine......525 Anisyl, hydride of . . . 525 Anthranilic acid .... 517 Antiarin ......491 Antimonic acid . .■ . . 306 Antimony......306 bases.......510 crude.......307 explosive......306 potassa, tartrate of . . 4-19 Aqua regia......161 Arabin.......359 Archil.......517 Archimedes theorem . . 41 Argand lamp.....178 Argol........448 Aricine.......489 Arragonite......260 Arrow poison of Central America.....491 Arrowroot......358 Arsenethyl .... 387, 511 Arsenic acid.....310 Arsenic and its com- pounds......309 analytical details . . . Gil detection in organic mix- tures ......312 Arsenic bases.....511 Arsenious acid .... 310 Arterial blood .... 552 Assafoetida......522 Asparagin . . . 453, 492 Aspartic acid.....453 Asphaltene ...... 540 Asphaltum ....'.. 540 Astatic needle ..... 116 Atacamite......296 page Atmosphere, chemical re- lations of.....137 composition and ana- lysis .•.:.. 137,139 physical constitution of 46 purifying......26 vapor of water in . . . 74 Atmospheric electricity . 113 Atomic theory . . . .i202 Atomic weight .... 2_ff Atoms.......* Atropine......491 Attenuation of wort . .367 Attraction......203 Augite.......265 Auric acid......318 Auschowitz, water of . . 581 Axes of crystals .... 225 Axinite.......208 Azobenzol......436 Azotic acid......140 Azotized substances, ana- lysis of......342 B. Badian oil......525 Balenic acid.....422 Balsams.......529 Balsam, Canada .... 530 copaiba......530 Peru.......530 Tolu .......530 Barilla.......243 Barium.......255 chloride of.....255 sulphide of.....256 Barley sugar.....352 Barometer.....50, 52 Baryta and its hydrate, 255 analytical remarks on.....256, 263 nitrate of.....256 sulphate of.....256 Bases ....-„.-. 126 from aldehyde .... 508 amidogen-.....494 from animal oil . . . 507 antimony-.....510 organic, containing chlo- rine .......499 from coal-tar oil . . . 506 of the ethyl-series . . 494 imidogen-.....494 arsenic-......511 artificial, containing mercury.....324 methylated and ethy- lated derivatives of natural.....504 mixed artificial . . . 503 nitrile-......494 from volatile oils by am- monia ......507 organic......485 organic artificial .' . . 492 phosphorus-.....509 containing platinum . 327 Bassorin.......359 Battery, constant . . . 213 dissected ...... 212 Baume's hydrometer 574, 575 Bay salt.......250 Bechamp's process . . . 499 Beer........360 50 590 INDEX. page Beetroot, sugar from . . 352 290 Bengal light..... 308 437 439 439 439 455 434 Benzoate of benzoyl 437 536 433 anhydrous . . . 434 ,437 438 438 435 homologues of . . . 502 507 Benzone ...... 434 432 and its compounds . 433 437 490 490 Berthollet's fulminatiuj. 317 Beryl....... 269 ?fiq vm Betaorcin ..... 519 Bezoar stones . . . , 566 Biamidobenzoic acid 434 498 Biamyl-ammonia . . 498 •m Bi borate of soda . . . 250 Bicarbonate of potassa. 237 Bicarbonate of soda. . 244 499 Bichlorethylamine . . 495 Bichloride of tin . . . 301 516 Bichromate of potassa . 286 495 496 Biethyl-ammonia. . . 496 Biethyl-amylamine . . 504 504 Biethyl-phenylamine . 504 Biethyl - phenyl - ammoni um, oxide of . . . 504 Biethylo-toluidine . . 503 43--! Bile........ 563 test of PettenkoHer . 565 Bilin....... 564 565 Bimethylamine . . . 497 Binary theory of salts . 233 Binary combinations . 334 Binitranisidinc . . . 525 ftVfi Binitrobenzoic acid . . 434 Binitrobenzol . . . 430 , 500 537 53(1 Binoxide of barium . . 255 '>5S of manganese . . . 274 '/56 547 303 PAGE . . 272 Bism-cthyl,.; ... t, . . 387 Bismuth . . . . \ . 292 analytical remarks . . 293 Bismuthic acid . . . . 292 Bisulphide of carbon . . 188 Bisulphisathyde . . . . 515 Bitter almonds, oil of . . 433 . . 540 . . 262 Bleaching powder . . . 260 testing its value . . . 262 . . 162 arterial .... ■ . 552 circulation of the . . . 552 composition of . . . . 553 venous..... . . 552 . . 177 sympathetic. . . . . 289 light..... . . 308 Prussian- .... . . 472 . . 474 Bohemian plate-glass . . 271 Boilers, deposits in . . . 260 Boiling point .. . . . . 67 Boracic acid.... . . 171 Bcrneo camphor . . . . 528 . . 170 . . 189 . . 171 . . 396 . ^366 . .358 BromalCv»j'^,Oj_ . . . 383 . . 524 . . 165 . . 164 . . 515 Bromoform .... 383, 406 Bromo-salicylous acid . . 443 Bromophenisic acid . . 537 Bromosamide . . . . . 444 Brookite..... . . 305 Bunsen's battery . . . . 214 Burmese naphtha . . . 541 429, 568 of antimony . . . . 307 . . 415 . . 414 . . 415 PAGE C. . 4W Cadet's fuming liquid . . 407 analytical remarks . . 292 Calcium and its com . 258 , 261 analytical remarks . . 263 . 2C0 Calculi, biliary . . . . 432 . 561 . 562 . 562 . 322 Calotype process . . . . 92 524 Camphogen..... 528 5?8 Campholic acid . . . 528 527 524 Camphoric acid . . . 527 524 Canada balsam . . . 530 Cane-sugar*^ tf compounds of . . . 351 353 Candle, flame of . . . 177 432 530 540 630 Capric acid..... 430 Capivi, oil of ... . 524 Caproic acid .... 430 430 430 431 422 526 4?.?, 478 Carbazotic acid . . . . 516 Carbides of hydrogen . 172 280 535 144 chlorides of . . . 188 381 bisulphide of ... . 188 compounds with oxygen 146 with hydrogen . . . 172 estimation in organic 338 Carbonate of baryta. 256 ,381 289 ?95 281 of lead...... 298 260 264 of manganese . . . 276 288 237 316 243 991 147 analysis of ... . 244 252 Carbonetted hydrogen light...... 172 INDEX. 591 page Chloride — cont. Carbonic acid.....146 ether.......374 oxide.......14" Carbyl, sulphate of . . .382 Casciforme......548 Carlsbad, water of . . .580 Carmine.......520 Carminic acid.....520 Cartier's hydrometer . . 577 Carthamin.....-521 Carragheen moss.... 358 Casein........541 Cassava.......359 Cassius, purple of . . . 302 Castor-oil......430 Catechu.......457 Catechin.......457 Caustic potash.....236 Cedrene.......526 Cedriret.......533 Cellulose.......359 Cement.......258 Cements, lime.....258 Cement, Parker's, or Ro- man .......258 Cerasin.......359 Cerebric acid.....554 Cerebrolein......555 Cerin........429 Cerite........269 Cerium.......269 Cerotate of oxide of ceroty 1 429 Cerotic acid......429 Cerotyl.......429 Cerotylic acid.....429 alcohol......429 Cetyl-series......429 Cetylic acid......429 alcohol......429 Chalk........260 stones.......479 Chameleon, mineral . . 277 Charcoal, animal and vege- table ......145 Chelidonic acid .... 455 Chemical philosophy . . 190 relations of the metals . 219 Chimneys, action of . . . 63 Chinese wax.....431 Chinoline .... 506, 508 Chinoidine......489 Chloracetic acid .... 395 ChloralC, *«/, ,3J5 Dippel's oil . . . '. . ^. ~$07 Disacryle......418 Disinfection . . . 159,261 Disinfecting solution of La- barraque.....261 Disposing influence . . . 205 Distillation......70 Dithionic acid.....153 Double salts.....222 compound ethers . . . 371 Draconic acid.....525 Drairnn's blood .... 529 Ductility of metals . . .218 Dulcose 0i#7Os- ■ • -356 Dutch liquid . . . . .380 Dyes, red or yellow . . . 520 Dyeiuc. action of. . . . 513 Dj'sh.-in.......564 _. Earthenware.....273 Eblanin.......407 Ebullition......66 Effervescing draughts . . 449 Efflorescence.....222 Eger, water of.....581 Egg, white of . . . . . 543 Elaidic acid......428 Elaidin.......428 Elain........424 Elaldehyde......288 Elaterin.......-i'-'l Electric eel......115 machine......110 battery......112 electrical current . . . 114 Electricity, positive and negative.....108 of vaj)0^|. ..... 120 Eleetro-chemicaL decompo- sition ..:.'.. 207 Electrodes......207 Electrolysis ,.....207 Electro-magnetism . . . 115 Electrometers.....109 Electromotive power . . 211 Electrophorus.....113 Electro-plating .... 215 Electrolytes ..... 219 Electrotype.....215 Elementary bodies . . . 121 substances.....195 table of symbols of . 200 Elements......121 Ellagic acid.....458 Emerald.......209 Emery.......266 Emetine ...... 491 Emodin.......520 Ems, water of.....580 Emulsin.......463 Epsom salt......264 Equator, magnetic . . . 105 Equisetic acid.....452 Equivalents, table of . . 195 volume......198 law of....., . 194 Erbium.......269 Eremacausis.....338 Erythroniannite^^^tfJ'BSd * Erytrarsin......409 Erythric acid.....517 Erythroprotide .... 545 Essence of turpentine . . 523 Essential oils . . . . .523 Ethalic acid.....429 alcohol......429 Ether. C<,.#r-o . ■ .370 acetic, chlorinetted . . 384 acrylic.......413 boracic 3M(X#03 . . . 374 butylic......415 carbonic JUOCo%. . . 374 chlorocarbonicC #rC£Oi, 3"5 cyanic ....... 468 cyanuric......468 formation of ... . 377 formic.......405 formic, chlorinetted . . 384 hydriodic......372 hydrobromic .... 372 light hydrochloric . . 372 margaric......426 muriatic heavy . , . 385 nitric JUO&Qr. . 373 nitrous......373 oenanthic......431 oleic.......426 oxalic MO4t.0j . . .374 oxamic......374 pelargonic.....431 phosphoric.....373 preparation of ... . 377 silicic 3JU.Otu(2j . . 374 stearic.......426 INDEX. 593 372 371 Ether — cont. page sulphuric.....373 sulphurous.....373 valeric.......418 Etherin . c //.. . . . 379 Etherole jC+Hi. .... 379 Ethers, compound . . . 371 of fatty acids .... 426 Ethionic acidtf,,*-^.^ .W383 Kthyl .**r<%. formula ot . . ✓ hydrarayr-.....387 iodide of £„ Mj-J . . 372 oxide of ffM H}r0 . . . 370 oxide of, acetate Cv HjJ) &,3K4 oxide of, compounds with acids, see ether . 371 oxide of, cyanate of . . 468 oxide of, cyanurate . . 408 plumb-......387 potassium.....3S6 -series, bases of sodium......386 stann-.......3C6 stib-......387, 51ft sulphide of Jk$ . . . 372 -theory......371 zinc-.......383 Ethylamine.....494 -urea.......495 Et'.iylamylaniline . . . 504 Ethyl-ammonia .... 494 Ethylaniline.....503 Kthylenc ^^^a * . 379 •-.Ethylene-alcohol . . . . 397 Ethylene-aniline .... 503 Jithylophenylamine . . 503 Ethylo-toluidine .... 503 Ethyl-oxamide .... 495 tiucalyne......355 Kuchlorine......163 'Duchrone......363 Euchronic acid .... 363 Audiometer .... 1.53,138 jiuclase.......269 Eupione.......532 Xuxantbic acid .... 522 Euxanthone.....02,2 Evaporation.....71 Evernic acid.....419 ICverninic acid.....519 Vvernia prunastri . . . 519 expansion by heat ... 53 of fluids......53 of gases......61 power of......46 of solids......53 Exsudation fluid.... 567 F. Fachingen, water of . . 582 Fats........403 Fatty acids......424 Fecula ....... 356 Felspar.......268 fermentation . . . . . 364 butyric . . . . . .368 lactic ....... 368 vinous....... 364 viscous......369 PAGE Ferments......364 Ferricyanide of hydrogen 473 Ferricyanides.....473 Ferricyanogen.....473 Ferridcyanogen . . . .473 Ferrocyanides.....471 Ferrocyanogen and its compounds .... 470 Fibrin .... 544, 545, 570 Fire, blue......308 -damp.......172 red and green .... 257 Flame, structure of. 175,177 Flint-glass......271 Fluids, expansion of . . 58 Fluoride of boron . . .171 of calcium.....261 of silicium.....169 Fluorine.......167 Fluor-spar......261 Food........570 Formates......405 Formic acid.....404 ether.......405 Formo-benzoic acid . . . 438 -methylal......406 Formulas......347 empirical......347 rational......347 Formyl-aniline .... 501 Frangulin......522 French weights and meas- ures .......585 Frigorific mixtures ... 66 Fruit-sugar......353 Fucusamide.....507 Fucusine......507 Fucusol.......507 Fulminates......408 Fulminating silver of Ber- thollet . '.....317 Fulminic acid.....468 Fulminuric acid .... 470 Fumaramido.....454 Fumaric acid.....454 Furfurine......507 Furfurolamide .... 507 Furfurole......507 Furnace, reverberatory . 177 for combustion . . . 340 Fusel-oil.......416 of spirit......420 Fusibility of metals. . . 218 Fusible metal.....293 Fustic wood.....522 G. Gadolinite......269 Galena.......296 Gallates.......458 Gallic acid......457 Oalls, nut......458 Galvanism......115 Galvanometer.....99 Galvanoscope.....116 Garancin.......521 Garlic, oil of.....528 Garnets.......268 Gas, coal, and oil. . . . 174 olefiant .... 173, 379 Gases, diffusion of . . . 129 expansion of.....61 physical constitution of 46 specific heat of .... 79 PAGk Gas-holder......124 Gasterase......563 Gastric juice.....563 Gaultheria procunibens, oil of......526 Gelatin.......548 -sugar.......548 Gcntianin......491 German silver.....2S8 Geyser springs of Iceland . 136 Gilding.......319 Glass, colored.....272 manufacture of . . . 270 variety of.....270 soluble......272 Glauber's salt.....248 Gliadin.......570 Globulin.......548 Glucic acid......354 Glucinum......269 Glucose ....... 353 Glue........550 Gluten.....356,570 Glutin.......356 Glyceric acid.....414 Glycerin . . . 414, 424,426 -compounds.....427 Glyco-benzoic acid . . . 440 Glycocine .... 549,564 Glycocoll . . 396,549, 564 Glyco-cholalic acid . . . 566 Glycogenic substance . . 560 Glycohyocholalic acid . . 565 Glycol........397 Glycolamide.....440 Glycolic acid.....440 Glycyrrhizin.....354 Glyoxal ....... 398 Glyoxalic acid.....398 Goniometry . ... 223 Gold, analytical remarks . 318 and its compounds . . 317 cyanide of.....466 -dust.......317 -leaf.......319 standard of Engl and .319 Goulard water .... 394 Gouty concretions . . . 479 Granite.......268 Grape sugar Ci^^-Oir ' 353 compounds or ... . 354 Graphite.......146 Gravitation......46 Gravity, specific .... 39 of metals......217 Green fire......257 Greenokite......292 Green salt of Magnus . . 226 Groups, isomorphous . . 231 Grove's battery .... 214 Guanine.......484 Guano.....484,573 GTabk^?~ : : :l9 benzoin .... 433, 530 British......358 of cherry tree .... 359 tragacanth.....359 Gun-cotton......363 Gun-metal......296 Gunpowder.....238 Gutta percha.....530 Gypsum.......259 J&rhtZfau* 594 INDEX. II. Hahnemann's soluble mer- cury .......321 Halitus.......552 Haloid salts.....221 Hardness of water . . . 259 permanent.....260 temporary.....260 Harmaline......489 Harmine......489 Hatehetin......541 Heat, absorption ... 96 animal......571 capacity for.....78 conduction of .... 64 latent.......65 phenomena of . . . . 53 radiation......95 reflection......95 sources of.....81 specific......78 transmission .... 98 Heavy spar......256 Heliein.......444 Helicoidin......444 Hemihedral crystals . . 225 Heniipinic acid .... 487 Hematite......279 Hematocrystalline . . . 647 Hematosin.....,553 Hematoxylin.....522 Hepar sulphuris .... 240 Hesperidin......491 Heulandite......268 Hippuric acid.....439 regeneration of . . . 440 Homologues, term . . . 421 Homologues of aniline . . 502 of benzol......441 of the glycocine-series . 549 of the salicyl series . . 516 Honeystone.....363 Hops, oil of......524 Hornblende.....295 Horn silver......316 Horny substance .... 555 Huano.......484 Humie acid......354 Humus.......354 Hydrarg-ethylQ AS/ V-, ^ . 387 chloride of'C\»,-/.,\_ .'.' . 387 nitrate of£,,/.%. i . -.; ■ ,yJQS7 Hydrate of oil o'f turpen- tin .......524 Hydrates, term .... 135 Hydride of anisyl . . . 525 of benzoyl.....433 of cinn amyl.....446 Hydriodic acid.....166 ether.......372 Hydrobenzamide . . 437, 507 Hydrobromic acid . . .165 ether.......372 Hydrocarbon, chloride of. 174 Hydrochloric acid . . . 159 ether, heavy.....384 Hydrocyanic acid.... 460 Hydroferricyanic acid . . 473 Hydroferrocyanic acid . . 471 Hydrofluoric acid . . . 167 Hydrofluosilicic acid . . 169 Hydrogen......127 antimonetted .... 308 arsenetted . . . . . 311 Hydrogen — cont. binoxide of . carbides of . . carbonetted . . PAGE . 130 . 172 . 172 estimation in organic bodies......338 ferricyanide of ... . 473 persulphide.....184 phosphoretted .... 185 silicietted......186 selenietted.....185 sulphuretted .... 182 teroxide of.....130 Hydrokinone, colorless . 454 green ........ 456 Hydroleic acid.....428 Hydromargaric acid. . . 428 Hydromargaritic acid . . 428 Hydrometer.....44 Hydrometer tables . . . 574 llydrosulphocyanic acid . 475 Hydrosulphuric acid . . 182 Hygrometer, dew-point . 78 wet-bulb-......74 Hyocholalic acid .... 565 Hyocholic acid.....565 Hyoscyamine.....491 Hyodyslysin.....565 Hypochloric acid.... 163 Hypochlorous acid . . . 162 Hyponitric acid .... 143 Hypophosphorous acid . 156 Hyposulphate of silver . 316 Hyposulphite of soda . . 248 of silver......316 Hyposulphites.....153 Hyposulphuric acid. . . 153 bisulphuretted .... 153 sulphuretted .... 153 trisulphuretted . . . 153 Hyposulphurous acid . . 153 I. Iceland moss.....358 Idrialin.......541 Idryl .......541 Igasuric acid.....489 Ignition.......175 Imidogen-bases .... 569 Inclination, magnetic . . 104 Incrustations in boilers . 260 Indian yellow.....522 India rubber.....529 vulcanized ..... 530 Indigo.......513 red........514 vat........514 white or deoxidized . . 514 Indin........515 Indinic acid ..... 516 Inosinic acid.....551 Inosite 6_i#2j,0»* • 355, 551 Ink, label . ... . . 529 blue, sympathetic . . 289 Inulin <,«x* • • 355 Mellon .... T .. 477 its compounds . * . . 477 Mellonides......477 Membraneous tissue . . 555 Membranes, mucous . . 567 Mercaptan 4L..Mt K*;. • ^ Mekcaptan—cont. page methyl-......406 Mercury.......319 acetates of.....394 analytical remarks on . 324 cyanide of.....465 fulminate of.....469 its compounds .... 320 Meridian, magnetic . . . 105 Mesitilol.......397 Mesityl.......397 Mesotype......268 Mesoxalic acid.....481 Metacetone......397 Metacetonic acid .... 411 Metaldehyde . . . . .389 Metagallic acid .... 459 Metals.......217 classification .... 234 physical properties of . 217 Metamargaric acid . . . 428 Metapectin......359 Metapectic acid_*«<.M/^ —359 O 3 * Metaphosphoric acid . v. z3% Metastyrol......531 Meteorites......277 Methionic acid .... 383 Methyl.......400 Methylated spirit . . .400 acetate of......403 formate of.....403 Methylamine.....497 -urea/,,,......497 Methyl-pmmonia . . . 497 Methyl-compounds . . . 400 chlorinetted.....406 Methyl-ether ..... 401 Methyl-ethyl-amyl-amine. 504 -urea.......497 Methyl-ethyl-amylo-phenyl- ammouium .... 504 oxide of......504 Methyl-mercaptan . . . 406 Methylo-biethyl-amyl-am- monium, oxide of. . 504 Methyl, salicylate of oxide of........527 Methyl-series, bases of the 497 Metoleic acid.....428 Mica........208 Microscomic salt .... 249 Milk........568 composition of ... . 569 spirit from.....569 Milk sugar......355 Mindererus, spirit of . . 392 Mineral chameleon . . . 277 waters, tables of . . . 5S0 Molasses.......352 Molecular actions . . • 203 Molybdenum.....303 Monacetin......427 Monobasic acids .... 231 Monobromacetic acid . . 395 Monochloracetic acid . . 395 Monostearin.....427 Mordant.......301 Mordants......513 Morindin......522 Morindon......522 Morphia.....485, 505 Morphine .... 485,505 Mortar.......258 Mosaic gold...... 301 Mucic aeid....., 363 596 INDEX. PAGE Mucilage.......559 Mucin.......567 Mucous membranes . . 567 Mucus.......567 Mulberry calculus . . . 562 Multiplier......116 Murexan......483 Murexide......483 caffein-......490 Muriatic acid.....159 ether, heavy .... 384 Muscovado sugar . . . 352 Mushroom sugar . . . 356 Must........366 Mycose C_^/**£.£> _t ■ ■ 355 Mykomelinic acid . . . 481 Myricin.......429 Myristic acid.....428 Myristica mosch .... 428 Myronic acid . . . ' . . 528 N. Naphtha.......539 Naphthalidin.....503 Naphthalin......538 Narceine......487 Narcogenine.....487 Narcotine......486 Nefte-digil......541 Nepheline......268 Nervous substance . . . 554 Neutrality of salts . . '. 220 Neutralization .... 196 Nickel.......287 analytical remarks on . 288 oxalate of.....362 Nicotine.....491, 505 Niobium......304 Nitraniline......500 Nitranisic acid .... 525 Nitraniside......525 Nitranisidine.....625 Nitranisol......625 Nitrate of ammonia . . 252 of baryta.....256 of bismuth.....293 of copper.....295 of iron......280 of lead......297 of oxide of methyl . . 402 of potassa.....238 of soda......248 of silver......316 of strontia.....257 of uranium.....294 of urea......477 Nitrates.......141 of mercury.....320 Nitre........238 cubic.......248 sweet spirits of jD^OJUO^ 373 Nitric acid......140 action of, upon organic substances .... 360 acid, fuming .... 141 Nitrile-bases.....494 Nitro-benzamide .... 502 Nitrobenzoic acid . . . 434 Nitro-benzol.....436 Nitro-coccusjc acid . . . 520 Nitro-cumic acid .... 441 Nitro-cumol.....503 Nitro-cymol.....503 Nitroglycerine .... 427 Nitrogen......137 Nitrogen — cont. page binoxide of.....142 chloride of.....186 compottnds with oxygen 139 with hydrogen .... 181 with boron.....182 estimation in organic bodies......342 iodide of......187 Nitro-naphthalese . . . 538 Nitro-phenasic acid . . . 537 Nitro-phenesic acid . . . 537 Nitro-phenisic acid . . . 537 Nitro-phenol.....537 Nitro-phthalic acid . . . 538 Nitrc-prussides .... 474 Nitro-salicylamide . . . 527 Nitre-salicylic acid . . . 516 Nitro-toluol.....530 Nitro-toluylic acid . . . 441 Nitrous acid.....143 ether.......373 oxide ....... 142 Nitro-xylol......503 Nomenclature.....190 Norium.......270 Notation, chemical . . . 199 Nutgalls.......458 Nutrition......670 plastic elements of . . 571 O. CEnanthylic acid . . 422, 431 Oil gas.......174 of allaria officinalis . . 528 of aniseed.....024 of assafcetida .... 529 ofbadian ....... 525 ofbergamot.....524 of bitter almonds . . . 432 of bitter fennel . . . 525 of capivi......524 of cedar wood .... 526 ofcicuta......526 of cinnamon . . 445,446 ofelemi......524 of cubebs . . . . . . 524 of cumin......526 of garlic......528 of gaultheria procum- bens.......526 of Guiana-laurel . . . 524 of hops . : Y" . . . 524 of horseradish .... 528 of juniper.....524 of laurel......527 of lavender.....528 of lemon......524 of meadow-sweet . . . 442 of mustard.....528 of onions......529 of orange flowers . . .528 of orange peel .... 524 of pepper......524 of peppermint .... 528 ofptychotis.....526 of rosemary.....528 of rose petals .... 528 of rue.......526 of spiraea ulmaria . .442 of thynre......526 of turpentin .... 523 of valerian.....527 of vitriol......151 *'i*f ■ • -356 Picamar.......533 Picoline.....506, 535 Picric acid ...... 516 Picro-erythrin.....517 Picrotoxin......492 Pimaric acid.....529 Pimelic.......431 Pinic acid......529 Pinite_»_»*i%^. • -356 Piperine.......490 Pipette.......343 Pitch........532 Pitch blende.....393 Pitch, mineral.....540 Plants, supply of carbon to 147 Plumbago......145 Plumbetbyl .' ^ i Gf &,-. 387 Pneumatic trough . . . 123 Polarity, magnetic . . . 103 Polarization, circular . . 90 Poles, electric.....207 Poly basic acids .... 231 Populin.......444 Porcelain......273 clay........273 Porphyry......268 Potash.......236 crude.......237 Potassa . . . . . . .236 acetate of......392 alum * ." \ .-' . . . 267 analytical remarks on . 242 benzoate of.....434 bicarbonate of ... . 237 bisulphate of ... . 239 carbonate of .... 237 chlorate of.....239 cyanate of.....466 hydrate of.....236 nitrate of.....238 oxalate of/f^r C^c3-i~ff& 361 perchlorate of ... . 240 prussiates of .... 473 sulphate of.....239 tartrates of.....449 urate of......479 Potassium and its com- pounds ......235 bromide of.....242 chloride of.....241 cyanide of.....464 ethyl.......386 ferricyanide of ... . 473 ferrocyanide of ... 471 iodide of......241 sulphides of.....240 Bulphocyanide of . . . 474 teroxide of.....237 Potato-oil......418 Precipitate, red .... 320 white.......322 Prehnite.......268 Prisms, Nichols' .... 88 Proof spirit......365 Propione......411 Propionic acid.....411 Proportionals.....193 Proportionals, multiple . 193 Propyl-series.....410 Propyl-glycol.....413 Propylene......413 Propylene-alcohol . . . 413 Propylic alcohol .... 410 Protein.......547 binoxide of.....547 teroxide of.....547 Protide.......547 Protiodide of iron . . . 280 Protochlorido of tin . . . 301 of chromium .... 285 Protoxide of tin . . . . 300 Prussian blue.....472 Plaster of Paris . . . .269 Prussiate of potash, Platinum and its com- pounds ...... 324 analytical remarks on . 328 bases.......328 black.......326 surface-action of . . . 325 red........473 yellow.......471 Prussic acid.....4G0 l'seudo-erythrin .... 518 I'seudo-morphine . . . 487 Ptyalin.....563, 566 598 INDEX. PAGE Puddling......283 Pullna, water of . . . .583 Purple of Cassius . . . 302 Purpura te of ammonia .483 Purpuric acid.....483 Purpurin......521 Purree.......522 Purreic acid.....522 Purrenone......522 Pus........567 Putrefaction.....337 Putty powder.....298 Pyin........568 Pyren........534 Pyridine.......506 Pyrites.......280 Pyrmont, water of . . . 582 Pyroacetic spirit .... 396 Pyro-acids......337 Pyrobenzolin.....508 Pyrocomenic.....455 Pyrogallic acid .... 45'J Pyrolusite......275 Pyromucic acid CM*t^0t-W^ Pyrophorus of IlbmWrg '. 267 Pyrophosphoric acid . . 232 Pyrotartaric acid . . . 451 Pyroxylic spirit .... 400 Pyroxylin Qi+HfJXz&tf 363 Pyrrole bases.....607 Q. Quadrichlorovaleric acid . 420 Quercite &it,//t^e^- • 356 Quercitron bark .... 522 Quicksilver......319 Quina........487 Quinicine......488 Quinidine......488 Quinine.......487 Quinine, amorphous . . 489 Quinodine......489 R. Radiation of heat ... 95 Racemic acid.....451 artificial production of . 451 Rangoon tar.....541 Realgar.......310 Red lead.......297 Red oxide......297 Reflection of heat ... 95 of light......83 Refraction, double ... 87 of light......84 Rennet.......568 Resins.......529 Respiration .... 125, 557 Respiration, elements of . 571 Retinic acid.....541 Retinite.......541 Reverbcratory furnace . 176 Rhodium . . . . . .329 Rhodizonic acid Q Y0y • 364 Ricinoleic acid. . . '. . 430 Rocella tinctoria .... 518 Rocellinin......518 Rochelle salt.....449 Rock oil.......539 Rock salt.......251 Roman alum . . . . . 267 Rosemary, oil of . . . . 528 Rue, oil Of......528 Rubia tinctorum.... 520 PAGE Rubiacin.......521 Rubiacic acid.....521 Rubiau.......521 Rubic acid......457 Run-steel......284 Rust........278 Ruthenium......332 Rutile.......305 S. Saccharic acid<* f'f/.WSM Saccharic grou .... 351 Saccharometer .... 89 Sacchulmic acid .... 354 Sacchulmin.....354 Safety lamp.....180 Safflower.......521 Saffron.......522 Sago........358 Sal-alembroth.....322 Sal-ammoniac.....251 Salicin.......442 Salicylamide.....527 Salicyl and its compounds 442 series.......442 Salicylate of oxide of methyl......527 Salicylic acid.....444 Salicylites......443 Salicylous acid .... 442 Saligenin......444 Saliretin.......444 Saliva........563 Salsola soda.....243 Salt, common.....250 definition......126 of sorrel......361 -radical......221 Salts, super or acid . . . 222 subsalt, or basic salt. . 220 binary theory of . . . 233 constitution of. . . . 219 double.......222 neutral......220 Saltpetre......238 Sandarift.......529 Santonin......492 Saponification.....424 Saratoga Congress spring. 581 Sarcosine......551 Saturation......197 Scagliola. . . . ' . . .259 Schlesischer Obersalz Brun- nen.......580 Scheele's green .... 296 Sea water, composition of 135 Sebacic acid . . , . 431 Seed lac.......529 Seggars.......272 SeidschUtz, water of . . 583 Seignette salt.....449 Selenic acid . . . . . 154 Selenetted hydrogen . . 185 Selenious acid.....154 Selenite.......259 Selenium......154 Seleno-cyanogen .... 476 Selters, water of . . . .583 Serpentine......265 Serum of blood .... 553 Shellac......529 Sike's hydrometer . . . 577 Silica........168 Silicates of alumina . . 268 Silicates — cont. pagb of magnesia.....265 Silicic ether ... . '",74 Silicium.......1 l,v> chloride of.....189 fluoride of.....109 Silver........314 acetate of.....394 analytical remarks . . 317 benzoate of.....434 cyanate of.....469 cyanide of.....465 cyanurate of ... . 469 ferrocyanide of. . . . 473 fulminate of.....469 its compounds .... 314 standard of England . 317 Sinapoline......608 Sinnamine......508 Size........550 Skin........555 Smalt........290 Smee's battery .... 215 Soap......424, 425 Soap-stone......265 Soap-test of Dr. Clark 258, 395 Soda, acetate of.....3'J2 analytical remarks on . 251 ash........244 ash, testing its value . 245 bicarbonate of . . . . 244 biborate......250 bisulphate of . . ■ . 248 carbonate of.....243 hydrate of . . . . .243 hyposulphite of . . . 248 nitrate of......248 oxalate of -S&oGvOj .361 phosphates of ... . 248 sulphate of.....248 *- tartrates of".....449 urate of......479 Sodium.......242 bromide of.....251 cyanide of.....465 ferrocyanide of. . . .471 iodide of......251 oxides of......242 sulphide of.....250 Solanine.......491 Solder........299 Soleil's saccharometer . . 89 Solids, expansion of . . 56 Soranjee.......522 Sorbin Cc,#(,4<, ■ • -355 Sorrel, salt or.....361 Spa Pouhon, water of . . 582 Spar, calcareous .... 260 Sparteine......490 Spathose iron ore . . . 281 Specific gravities of metals 219 gravity of solids and liquids......39 of gases......125 heat.......79 Speculum metal .... 296 Spectrum......86 Speis ........ 287 Spermaceti ...... 429 Spirit of Mindererus . . 392 pyroxylic......400 Spirits, table of spec. gr. of........577 Spodumenc......254 Springs.......135 INDEX. 599 PAGE Stannethyl Ctf //r S^. . 3S6 oxide nf Cj i ..^.J . .386 chloride of /. .'£.£4 . 386 bromide of . .^(.^.. 386 iodide of . . . -'»v.,< . 386 nitrate of . . ■ ^ j, . 386 Starch G-t^^ o'ra ■ • 35ti animal.......566 State, change of—by heat 65 Steam-bath......69 Steam engine.....69 specific gravity of. . . 134 latent heat of.....65 Stearic acid......424 biearin.......424 candles......428 Stearoptene.....523 Steatite.......205 Steel........283 Stibethyl .... 387, 510 bichloride of .... 511 biniodideof.....511 binoxide of.....510 bisulphide of ... . 511 Stieklac.......529 Stilbite.......268 Stilbyl-alcohol .... 441 Stoneware......273 Storax.......530 Stronlia.......257 analytical remarks on . 203 Strontium and its com- pounds ......257 Strychnine .... 489, 505 Styphnic acid ..... 522 Styracin ,......531 Styrol -..'.-".". . 446, 530 Styrono.......44" Suberic acid $»«/t,(i2£\fl% Sublimate, corrosive . . 322 Sublimation.....70 Substitution, law of . . 335 products, organic . . . 335 Succinic acid.....431 Sudoric acid.....663 Sugar........351 action of dilute acids upon......354 action of alkalies upon . 354 candy.......352 copper test, for the varie- ties of ......363 from diabetes .... 354 from diabetes insipidus 354 from starch or dextrin . 356 of fruits......353 from ergot of rye . . . 355 gelatin-......649 of lead.......393 of milk......355 Sulphamylic acid . . .417 Sulphasatyde.....515 Sulphate of alumina . . 267 of ammonia.....262 of baryta......256 of cadmium.....292 of cobalt......289 of copper......295 of iron.......280 of lime......259 of magnesia.....264 of manganese .... 276 of methyl.....402 of nickel......287 Sulphate—cont. page of potassa.....239 of silver......316 of soda......248 of zinc.......291 Sulphates of mercury . .321 Sulphesatyde.....515 Sulphide of allyl .... 412 of amyl......417 of arsenic......310 of barium.....250 of benzoyl.....433 of boron......189 of cadmium ; . . . . 292 of calcium ..... 259 of ethyl......372 of kakodyl.....409 of silicium.....189 of silver......317 of sodium.....256 Sulphides . . . . . .149 of ammonium .... 253 of antimony .... 307 of carbon......188 of iron.....280 of mercury.....323 of potassium .... 240 of tin.......301 test for......474 Sulphindigotic acid . . .514 Sulphindylic acid . . . 614 Sulphisathyde .... 515 Sulphites......150 Sulphobenzide .... 535 Sulphobenzoic acid . . . 634 Sulphocyanide of allyl .413 Sulphocyanides .... 474 Sulphocyanogen and its compounds .... 474 Sulphoglyceric acid . . . 427 Sulphoniethylie acid . .403 Sulphonaphthalic acid . 538 Sulphophenic acid . . . 535 Sulphosaccharic acid . . 354 Sulphotoluolic acid . . . 536 Sulphovinic acidA t^ti^f. decomposed by heat . Sulphovinates.....375 Sulphur.......148 acids.......221 auratum......308 bases.......221 chloride of.....187 compounds with oxygen 150 estimation in organic bodies......347 salts.......221 Sulphuretted hydrogen . 182 Sulphuric acid .... 151 ether J«0+ ■ ■ 375 Urethylane .... 375, 403 Uric acid . . products from Urinary calculi Urine.... analysis of . in disease . coloring matter of Usnea barbata Usnic acid . . PAGE 479, 561 479 561 558 560 560 561 519 519 418. 418. Valeracetonitrile Valeramide. . Valerianic acid ether . . . Valerian, oil of Valeric acid . . anhydrous . Valero-benzoic acid Valerol . . Valeronitrile Vanadium . Vapor of water, tension . Vapors, determination of the density of . . . hypothetical density of 199, maximum density of . tension of..... Varec........ Variolaria...... Varvacite...... Vegetable acids .... table of ...... nutrition...... Vegeto-alkalies . . Venous blood..... Ventilation...... Veratria....... Veratrine...... Verdigris...... Verditer....... Vermillion...... Vinous fermentation . . Viscous fermentation . . Vitriol, blue..... Vitriol, green..... oil of....... oil of, fuming .... Volatile oils..... Volatility of metals . . . Volume, combination by . equivalent..... Voltaic battery .... pile, chemistry of the . Voltameter...... Volta's'pile...... W. Wash, distiller's .... 367 Water........132 Water — cont. page analysis of.....132 distilled......135 expansion by heat . . 58 hardness of.....259 of crystallization . . . 222 oxygenated.....136 tension of its vapor . . 71 Wax........429 fossil.......541 Weights.......585 specific.......39 Welding.......278 Whey........546 White lead......298 of egg .......543 Winds.......62 Wine........366 clarifying of .... 550 Witherite......256 Wolframium.....302 Wood ether......401 spirit.......400 Woody tissue.....359 Wootz.......2S4 Wort........367 Xanthic acid( &^,-?., Q. U&5 oxide . . . . "T 484,562 Xanthin.......521 Xylidine.......503 Xylite........407 Xyloidin C/t Ate J-/U 5GZ. 566 Xylol . . . 7 ■ 7 441, £38 Xylyl, hydrate, oxide of . 538 Yeast........367 Yellow dyes.....520 Yttria........26J Yttro-tantalite . . . .304 Yttrium.......269 Z. Zaffer ........ 290 Zeise's combustible plati- num salts.....382 Zeolites.......268 Zinc........290 analytical remarks . . 291 cyanide of.....465 -amyl.......402 -ethyl £y-vj-.?>t, . . .385 lactate of. 1" . . . .369 Zinin's process .... 499 Zircon.......270 Zirconia.......270 Zirconium......270 THE END. :> •*''■»■■«■ / I I ">ttf',Wc \ - *: II <1, .'■;.:-'.r^ ->•, i_l>w^>,,';;v -v:-,-.-:- :v."'f r A7»U!