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              MANUAL   OF

QUALITATIVE     CHEMICAL

             ANALYSIS.
-x— * * * +--^
                  BY

   DR.  C.  REMIGIUS  FRESENIUS.

      PRIVY ACLIC COUNSELLOR OF THE DUKE OF NASSAU ;
    DIRECTOR OF THE CHEMICAL LABORATORY AT WIESRADEN;
PROFESSOR OP CHEMISTRY, NATURAL PHILOSOPHY, AND TECHKOLCliT AT THB
         WIESBADEN AGRICULTURAL ISSTITUTK.
jFrom tf)t last Bnglisf) anb Amman 3£^itfonjS.
                    EDITED BY

           SAMUEL W. JOHNSON, M.A.,

PROFESSOR OF ANALYTICAL AND AGRICULTURAL CHEMISTRY IN YALB COLLEGE, NSW HAYEN, OOSlt.
            NEW  YORK:
JOHN WILEY &  SON, 535 BROADWAY.
                1867. 
             Scored according to Act of Congress, in the year 1864, by
                                 JOHN  WILEY,
In the Clerk's Office  of  the District  Court of the United States  for the  Southern
                               District of New York.
     K. OBAIOHEAD,
:itrr, Mereolyper. ami Electrolyptr,
    Carton ©wining,
 81. Hi, and 83  CerUrt Strict. 
EDITOR'S  PREFACE.
  Notwithstanding the rapid multiplication of  Treatises  on
Qualitative Chemical Analysis,  the  Manual  of Fresenius  main-
tains a well deserved  popularity.  Though apparently somewhat
complicated in its arrangement, it is in use  incomparably the most
trustworthy guide the chemist can employ.
  The  present  contains all  the improvements of the eleventh
German and sixth English editions.  The editor has employed as
its basis the text of the fifth London issue, and has incorporated
with it his own translation of the corrections  and new matter of
the last German edition; the Appendix  alone excepted, which is
reprinted from the sixth English edition, just published.
  The  matter  newly added to this work  by the author relates
chiefly  to the  Rarer  Elements,  to  Flame-Tests,  Spectral
Analysis, Dialysis, and the  Reactions  op the Alkaloids.
The course of Analysis has also received some  important modifica-
tions.  The editor has added a few notes which are distinguished
by inclosure in brackets [ ].  In one or two instances he has sub-
stituted his own matter for that of the author, and he has omitted
altogether a few unimportant paragraphs.
  The  colored  spectrum-plate of the foreign editions, which is
not only incomplete but erroneous, has been replaced in this work
by the more recent and useful plain plate of Kirchhof and Bunsen.

                            SAMUEL W.  JOHNSON,
                      Sheffield Laboratory  of  Tale  College.
May, 1864. 
 
CONTENTS.
           PART I.


INTRODUCTORY   PART.
                               PAGE
       PRELIMINARY REMARKS.

Definition, objects, general princi-
  ples, utility, and importance of
  qualitative chemical analysis, the
  conditions and requirements for
  •a successful   study   of  that
  science.....................    2
SECTION I
Operations, § 1.
1.		3
9		fi
3.		7
4.		8
5.		9
6.		11
7.		12
R		13
9.		13
10.	Fusion and Fluxing, § 11....	14
11.	Deflagration, § 12...........	15
12.	The use .of the blowpipe, § 13	16
13.	Spirit and gas lamps, § 14....	20
14.	Colored flames and spectral	
		25
    Appendix to the First Section,

Apparatus and utensils, § 16.....  29
           SECTION II.

    Reagents, § 17.............   31

A.  Reagents in  the humid way.
                               pa 01
I. Simple Solvents.

 1.  Water, § 18................  34
 2.  Alcohol, § 19...............  35
 3.  Ether,             )
 4.  Chloroform, and     [-§20...  35
 5.  Sulphide of Carbon, )

II. Acids and halogens, § 21....  36

    a. Oxygen acids.

 1.  Sulphuric acid, § 22.........  37
 2.  Nitric acid, § 23...........  38
 3.  Acetic acid, § 24..........  39
 4.  Tartaric acid, § 25..........  40

    6. Hydrogen acids and halogens.

 1.  Hydrochloric acid, § 26......  40
 2.  Chlorine, §27..............  42
 3.  Nitrohydrochloric acid, § 28..  43
 4.  Hydrofluosilicic acid, § 29....  43

    c. Sulphur acids.

 1.  Hydrosulphuric acid, § 30....  44

III. Bases and metals, §  31.....  50

    a. Oxygen bases.

      a.  Alkalies.

 1.  Potassa and soda, § 32......  51
 2.  Ammonia, § 33.............  53

      /?.  Alkaline earths.

 1.  Baryta, § 34...............  5£ 
VI
CONTENTS.
                                PAGE
 2. Lime, § 35.................   56

       y. Heavy metals and their oxides.

 1. Zinc, 8 36.................   56
 2  Iron, § 37.................   57
 3. Copper, § 38...............   57
 4. Hydrate  of  teroxide of  bis-
       muth. § 39..............   57
 5. Binoxide of lead,  § 40.......   58

    b. Sulphur banes.

 1. Sulphide of ammonium, §  41.   58
 2. Sulphide of sodium, § 42___   60

IV. Salts.

    a. Salts of the alkalies.

 1. Sulphate of potassa, § 43.....   61
 2. Phosphate of soda, § 44.....   61
 3. Oxalate of ammonia, § 45....   61
 4  Acetate  of soda, § 46.......   62
 5. Carbonate of soda, § 47......   62
 6. Carbonate of ammonia, § 48..   63
 7. Bisulphite of soda, § 49.....   64
 8. Nitrite of potassa, § 50......   64
 9. Bichromate of potassa, § 51..   65
10. Antimonate of potassa. § 5'2..   65
11. Molybdate of ammonia, §  53.   66
12. Chloride of ammonium, § 54..   66
13. Cyanide of potassium, § 55...   67
14. Ferrocyanide   of  potassium,
       §56...................   68
15. Ferricyanide of potassium, § 57   69
16. Sulphocyanide  of potassium,
       §58....................   69

    b. Salts of the alkaline earths.

 1. Chloride of barium, § 59.....   70
 2. Nitrate of baryta,  § 60.......   71
 3. Carbonate of baryta, § 61....   71
 4. Sulphate of lime, § 62.......   72
 5. Chloride of calcium, § 63.....   72
 6. Sulphate of magnesia, § 64...   72

    c. Salts of the oxides of  the
       heavy metals.

 1. Sulphate of protoxide of iron,
       §65....................   73
 2. Sesquichloride of iron, § 66..   73
 3. Nitrate of silver, § 67.......   74
 4. Acetate of lead, § 68........   75
 5. Nitrate of suboxide of mercury,
       §69....................   75
 6. Chloride of mercury, § 70___   76
 7. Sulphate of copper, $71.....   76
 8.  Protochloride of tin, § 72.....   77
 9.  Bichloride of platinum, § 73..   77
10. Sodio-protochloride  of palla-
       dium, § 74..............   78
11. Terchloride of gold, § 75.....  78

V.  Coloring matters  and indif-
       ferent vegetable substan-
       ces, § 76.

  1. Test papers.
    a.  Blue litmus paper.........  79
    0.  Reddened litmus paper....  79
    y.  Georgina paper...........  79
    6.  Turmeric paper..........  80
  2. Indigo solution, § 77........  80

    B. Reagents in the dry way.

  I. Fluxes and decomposing agents.

  1. Mixture  of carbonate of soda
       and carbonate  of potassa,
       §78....................  81
  2. Hydrate of baryta.  § 79.....  82
  3. Fluoride of calcium, § 80  ...  83
  4. Carbonate of lime, § 81......  83
  5. Chloride of ammonium,  § 82..  83
  6. Nitrate of soda, § 83........  84

        [I. Blowpipe reagents.

  1.  Carbonate of soda, § 84......  84
  2.  Cyanide of potassium. §  85...  85
  3.  Biborate of soda, §  86.......  86
  4.  Phosphate of soda and ammo-
       nia, § 87................  87
  5.  Nitrate of protoxide of cobalt,
       §88....................  88

           SECTION  III.

Reactions, or the deportment of
    bodies with reagents, § 89..  89

A.  Deportment and properties of
    THE METALLIC OXIDES AND THEIR
    RADICALS, § 90.............  90

          FIRST GROUP, § 91.

  a. Potassa, § 92..............  91
  b. Soda, § 93................  93
  c. Ammonia, § 94............  95
Recapitulation and remarks, § 95..  96
  Caesia, rubidia, lithia, § 96 ....  98

    SECOND GROUP, § 97......... 100

  a. Baryta, § 98............. 100
  b. Strontia,  § 99............. 102
  c. Lime, §  100............... 104
  d. Magnesia, § 101........... 105
Recapitulation and remarks,  § 102. 107

    THIRD GROUP, § 103......... HO

  a. Alumina, § 104............ HO 
CONTENTS.
Vll
                                 PAGE
  b.  Sesquioxide of chromium,  §
       105.................... 112
Recapitulation and remarks, § 106. 113
  Glucina, thoria, zirconia, yttria,
     terbia, erbia, oxides of cerium,
     lanthanum,  and  didymium,
     titanic,  tantalic, and  hypo-
     columbic acids, § 107.....114-120

     FOURTH GROUP, § 108........ 120

  a. Oxide of zinc, § 109........ 120
  b.  Protoxide of manganese, §110 122
  c.  Protoxide of nickel, § 111.. 124
  d. Protoxide  of cobalt,  § 112... 126
  e.  Protoxide of iron, § 113____128
  /.  Sesquioxide of iron, § 114.. 130
Recapitulation and remarks, § 115. 131
  Oxides of uranium, vanadium,
     and thallium, § 116.....  134-136

     FIFTH GROUP, § 117........136

First  division  of the fifth group:
     oxides which are  precipitated
     by hydrochloric acid.

   a. Oxide of  silver, § 118...... 137
   6. Suboxide of mercury, § 119. 138
   c  Oxide of lead, § 120........ 139
Recapitulation and remarks, § 121. 141

Second division of the  fifth group:
     oxides which are  not precipi-
     tated by hydrochloric acid.

   a. Oxide of mercury,  § 122--- 142
   b. Oxide of  copper,  § 123.....  143
   c. Teroxide  of bismuth, § 124.. 146
   d. Oxide of cadmium,  § 125.... 147
Recapitulation and remarks, § 126.  148
   Protoxide of  palladium, oxide
     of rhodium, oxides of osmium
     and  ruthenium, § 127... 149-151

     SIXTH group, § 128......... 152

 First division :

   a. Teroxide of gold, § 129.....  152
   b Binoxide of platinum, S 130.  154
Recapitulation and remarks, § 131.  155

Second division:

   a. Protoxide of tin, § 132.....155
   b. Binoxide of tin, § 133......  157
   c. Teroxide  of antimony,  § 134.  159
   d. Arsenious acid, § 135....... 163
   e. Arsenic acid, § 136........173
Recapitulation and remarks, §137.  175
   Oxide   of  iridium,   oxides  of
     molybdenum, tungsten, tellu-
     rium, and selenium,  § 138.179-182
                                PAGE
B. Deportment  of the acids and
    THEIR RADICALS WITH REAGENTS.
    § 139..................... 182

         L Inorganic acids.

    first group, § 140......... 184

First division:

  Chromic  acid,  §  141........... 184
  Sulphurous, hvposulphurous, and
    iodic acids,'§ 142........186-188

Second division:

  Sulphuric acid, § 143  ........ 188
  Hydrofluosilicic  acid, § 144____189

Third division:

  a. Phosphoric acid, § 145...... 190
     Bi- and  tribasic  phosphoric
        acids, §  146............. 194
  6. Boracic acid,  § 147.........195
  c. Oxalic acid,  § 148......... 196
  d. Hydrofluoric acid, § 149____198
Recapitulation and remarks, § 150. 201
  Phosphorous acid, § 151........ 202

Fourth  division:

  a. Carbonic acid, § 152........ 203
  b. Silicic acid, § 153.......... 204
Recapitulation and remarks, § 154. 207

     SECOND GROUP.............. 207

   a. Hydrochloric acid. § 155.... 207
   b. Hydrobromic acid,  § 156.... 209
   c. Hvdriodic  acid, § 157....... 211
   d. Hydrocyanic acid, § 158----214
     Hydroferrocyanic   and  hy-
        droferricyanic acids...... 216
   e. Hydrosulphuric acid.  §  159.. 217
Recapitulation and remarks, § 160. 218
   Nitrous, hypochlorous, chlorous,
     and    hypochlorous    acids,
     § 161................220-221

             THIRD GROUP.

   a. Nitric acid, § 162..........222
   b. Chloric acid, § 163......... 223
Recapitulation and remarks, § 164. 225
   Perchloric acid, § 165......... 225
       II.  Organic acids.

  first group...............  226

a.  Oxalic acid...............  226
b.  Tartaric acid, §166........  226 
vm
CONTENTS.
                                 PAGE
  c.  Citric acid, § 167.......... 228
  d.  Malic acid, § 168.......... 229
Recapitulation and remarks, § 169. 230
  Racemic  or paratartaric  acid,
    § 170..................... 231

    second group.............. 232

  a.  Succinic acid, 8 171........232
  b.  Benzoic acid, § 172........233
                                 PAGE
Recapitulation and remarks, § 173.  234

    THIRD GROUP...............234

  a. Acetic acid, 8 174.........  234
  b. Formic acid, § 175.........236
Recapitulation and remarks, § 176.  237
  Lactic,  propionic,  and  butyric
    acids, § 177...............  238
PART II.
SYSTEMATIC COURSE OF QUALITATIVE CHEMICAL  ANALYSIS.
Preliminary remarks on the course
    of qualitative analysis in gene-
    ral, and the plan of this part
    of the present work in parti-
    cular..................... 243
            SECTION I.

          PRACTICAL PROCESS,

I.  Preliminary examination, § 178 246
A. The body under  examination
    is solid.................... 246
  I.  It is neither a pure  metal nor
       an  alloy, §179........... 246
  II.  The  substance  is a metal  or
       an  alloy. § 180........... 253
B. The substance under  examina-
    tion is a fluid, §  181........254
  II.  Solution of bodies, or classi-
       fication of substances  ac-
       cording to their deportment
       with certain solvents, § 182 255
A. The substance under examina-
    tion is neither a metal  nor an
    alloy,  § 183............... 256
B  The substance under  examina-
    tion is a metal or an alloy, §
     184...................... 258

         III.  Actual analysis..... 259

          SIMPLE COMPOUNDS.

A. Substances soluble in water.
    Detection of the base, § 185.. 259
    Detection of the acid.
  I.  Detection of inorganic acids,
       § 186................... 266
  II.  Detection of organic acids,
       § 187...................  269
B. Substances insoluble or sparingly
       soluble  in water, but soluble
       in hydrochloric acid,  nitric
       acid,  or  nilrohydrochloric
       acid.
    Detection of the base, § 188.  271
    Detection of the acid.
  I. Detection of inorganic acids,
       §189...................  273
  II. Detection of  organic acids,
       § 190...................  275
C. Substances insoluble or sparingly
       soluble in water, hydrochloric
       acid, nitric acid,  or  nitro-
       hydrochloric acid.
    Detection of the base and the
       acid, § 191..............  275

         COMPLEX COMPOUNDS.

A.  Substances soluble in water, and
       also such as are insoluble in
       water, but dissolve in hydro-
       chloric acid,  nitric  acid,  or
       nilrohydrochloric  acid.
    Detection of the bases, § 192
  I. Substances soluble  in water.
     Detection of silver and  sub-
       oxide of mercury.........278
  II. Substances soluble in hydro-
       chloric or nitrohydrochloric
       acid....................281
  III. Substances soluble in nitric
       acid.
     Detection of silver and sub-
       oxide of mercury.........  281
  Treatment  with hydrosulphuric
     acid, precipitation of the me- 
CONTENTS.
IX
  tallic oxides of Group V., 2d
  division, and of Group VI.,
  § 193..................... 282
Treatment of the precipitate pro-
  duced  by hydrosulphuric acid
  with sulphide of ammonium ;
  separation  of the  2d division
  of Group V. from  Group VI.,
  § 194.....................283
Detection of the metals of Group
  VI.   Arsenic,  antimony, tin,
  gold, platinum, § 195....... 285
Detection of  the metallic oxides
  of  Group   V,  2d  division.
  Oxide of lead, teroxide of bis-
  muth,  oxide of copper, oxide
  of  cadmium, oxide  of mer-
  cury, § 196................ 288
Precipitation  with sulphide  of
  ammonium,   detection   and
  separation  of  the oxides  of
  Groups III. and IV.  Alumi-
  na, sesquioxide of  chromium,
  oxide  of  zinc, protoxide  of
  manganese,    protoxide   of
  nickel,  protoxide  of cobalt,
  proto- and sesquioxide of iron,
  and also of those salts of the
  alkaline earths which are pre-
  cipitated  by ammonia  from
  their  solution in hydrochloric
  acid: phosphates, borates, ox-
  alates, silicates, and fluorides,
  § 197..................... 290
Separation and detection of the
  oxides of Group II.,  which
  are precipitated by carbonate
  of  ammonia iu  presence  of
  chloride of  ammonium, viz.,
  baryta, strontia, lime, §  198.. 299
Examination for magnesia, § 199 300
Examination for potassa  and
  soda, § 200................ 301
Examination for ammonia, § 201 302
       DETECTION OF THE ACIDS.

1.  Substances soluble in water.
  I.  In the  absence  of  organic
    acids, §  202...............  302
  II.  In presence of organic acids,
    § 203....................305
2.  Substances insoluble in water, but
       soluble in hydrochloric acid,
       nitric  acid,  or nilrohydro-
       chloric acid.
  I.  In the  absence  of  organic
    acids, §  204...............  308
  II.  In presence of organic acids,
    § 205.....................  309
B.  Substances insoluble, or sparing-
       ly soluble both in water and
       in hydrochloric acid, nitric
  acid,  or  nilrohydrochloric
  acid.
Detection of the bases, acids,
  and non-metallic elements,
  §206................... 309
            SECTION  II.

   practical course in particular
               cases.

I.  Special method of effecting the
       analysis of cyanides, ferro-
       cyanides,  &c,  insoluble in
       water, § 207.............314
II. Analysis of silicates, § 208... 316
   A.  Silicates  decomposable  by
       acids, § 209............. 317
   B.  Silicates which  are not de-
       composed  by acids, § 210.. 319
   C.  Silicates which are partially
       decomposed by  acids, § 211 322
III. Analysis of  natural  waters,
       §212.
   A.  Analysis of the fresh waters-
       (spring-water,   well-water,
       brook water,    river-water,
       &c.), § 213..............323
   B.  Analysis  of mineral  waters,
       §214................. 327
   1.  Examination of the water.
       a.  Operations at the spring,
         §215................. 328
       6.  Operations iu the labora-
         tory, § 216............ 329
   2.  Examination  of  the  sinter
       deposits, § 217........... 334
IV. Analysis of  soils,  § 218..... 337
   1.  Preparation and examination
       of the aqueous extract, § 219 338
   2.  Preparation and examination
       of the acid extract, § 220.. 340
   3.  Examination of the inorganic
       constituents  insoluble  in
       water and acids, § 221... 341
   4.  Examination  of the  organic
       constituents of the soil,   §
       222..................'. 341
V. Detection of inorganic  sub-
       stances  in presence of or-
       ganic substances, § 223... 343
   1.  General  rules for the detec-
       tion  of inorganic substances
       in presence of organic mat-
       ters, which by their color,
       consistence, &c,  impede the
       application of the reagents,
       or  obscure the reactions
       produced,  § 224......... 343
   2.  Detection of inorganic poisons
       in articles of food, in dead
       bodies, &c, in chemico-legal
       cases, § 225.............346 
CONTENTS.
                                PAGE
I.  Method  for the  detection  of
      arsenic and all other metal-
      lic poisons.
  A. Method  for the detection of
      undissolved arsenious acid,
      § 226................... 346
  B. Method  of detecting arsenic
      and other  metallic  com-
      pounds which are soluble
      in water, by means of  dialy-
      sis, § 227 .............. 347
  C. Method  for the detection of
      arsenic in whatever form of
      combination  it may  exist,
      which  allows  also a quanti-
      tative determination of that
      poison, and permits at  the
      same time the detection  of
      other metallic  poisons which
      may be present, § 22-*..... 349
II. Method for  the detection  of
      hydrocyanic acid, § 229... 358
[II. Method for the  detection of
      phosphorus, § 230........360
  3.  Examination of the inorganic
      constituents of plants, ani-
      mals, or parts of the  same,
      of  manures,  &c. (analysis
      of ashes), § 231......... 366
    A.  Preparation of the ash...  366
    B.  Examination of the ash .. 366
      a. Examination of the part
        soluble in water........ 367
      b. Examination of the part
        soluble in  hydrochloric
        acid.................. 368
      c. Examination of the resi-
        due   insoluble  in hydro-
        chloric acid............ 369
           SECTION III.

EXPLANATORY NOTK8 AND ADDITIONS
  TO THE  SYSTEMATIC  COURSE  OF
  ANALYSIS.

I. Additional  remarks to the pre-
      liminary  examination,   To
      §§  178-181.............. 370
II Additional remarks to the  so-
      lution of  substances, &c,
      To  §§ 182-184......... 371
III. Additional  remarks  to  the
      actual analysis, To §§ 185-
      207...................372
  A. General review and explana-
      tion of the analytical course 372
    a. Detection of the bases.... 372
    b  Detection of the acids.... 376
B. Special remarks and additions
      to the systematic course of
      auaiysis................. 379
  To 8 192.................... 380
                               PAGE
To 88 193 and 194........... 381
   §195................... 383
   8 196.................... 383
   §197................... 384
   8 198................... 386
   §206................... 386
   8 207................... 387
            APPENDIX.

I.  Deportment of the most import-
       ant medicinal alkaloids with
       reagents,  and  systematic
       method of effecting the de-
       tection of these substances,
       §232................... 389
  I. Volatile  alkaloids.
     1. Nicotia, § 233........... 390
     2. Conia, § 234............391
  II. Non-volatile alkaloids.

            FIRST GROUP.

  Morphia, § 235.............. 393

           SECOND GROUP.

  a. Narcotina, § 236........... 395
  b. Quina, § 237.............. 396
  c. Cinchonia, § 238........... 398
Recapitulation and remarks, § 239. 399

            THIRD  GROUP.

  a. Strychnia, § 240........... 400
  b. Brucia, § 241.............402
  c. Veratria, § 242............404
Recapitulation and remarks,  § 243. 405
  Salicine, § 244............... 406
Systematic course for the detection
       of the non-volatile alkaloids
       treated of in the preceding
       paragraphs, and of salicine. 406
I.  Detection  of the  alkaloids, and
     of salicine, in solutions sup-
     posed to contain only one of
     these substances, § 245...... 406
II.  Detection of the  alkaloids, and
     of salicine, in solutions sup-
     posed to contain several or all
     of these  substances, §246... 409
III. Detection of the alkaloids, in
     presence of coloring and ex-
     tractive  vegetable  or animal
     matter, § 247.............. 411
   1. Stas's method  of  detecting
       poisonous alkaloids....... 411
   2. Otto's  modification of Stas's
       method................. 4jj
  3. Method of L. von Uslar and
       J. Erdmann.............. 414
  4. Detection   of  strychnia  by
       means of chloroform...... 416 
CONTENTS.
xi
  5. Graham   and   Hoffmann's
       method of detecting strych-
       nia in beer.............. 417
  6. Dialysis of the alkaloids.....417
II.  General plan of the order and
    succession  in which substan-
    ces  should  be analyzed  for
    practice, § 248............418
ITI. Arrangement of  the  results
    of the analyses  performed for
    practice, § 249.............420
IV. Table of the  more frequently
    occurring forms and  combina-
    tions of the substances treated
    of in the present work;  ar-
                                 PAGH
     ranged with special regard to
     the class  to  which they  re-
     spectively belong, according
     to their solubility  in water, in
     hydrochloric acid, nitric acid,
     or  nitrohydrochloric acid, §
     250...................... 422
Preliminary remarks........  .   422
  Table....................... 424
  Notes....................... 424
V. Table  of weights  and  mea-
     sures............ ........427

Index.......................429 
 
          PAET   I.

INTRODUCTORY.
               PRELIMINARY  REMARKS.

DEFINITION", GENERAL PRINCIPLES, OBJECTS, UTILITY, AND IMPORT-
  ANCE OP QUALITATIVE  CHEMICAL ANALYSIS, THE CONDITIONS ANT
  REQUIREMENTS  FOR A  SUCCESSFUL STUDY OF THAT SCIENCE.

Chemistry is  the science which treats of the various materials
entering into the structure  of the  earth,  their  composition  and
decomposition, their mutual relations  and deportment in general.
A special branch of this science is designated Analytical Chemis-
try, inasmuch as it pursues a distinct and definite object—viz., the
analysis of compound  bodies, and the  examination  of their com-
ponent elements.   Analytical  chemistry, again, is subdivided into
two branches—viz., qualitative analysis, which simply studies the
nature and  properties of the component  parts  of bodies ;  and
quantitative analysis, which  ascertains  the quantity of every indi-
vidual element present.  The office of qualitative analysis, there-
fore, is to exhibit the constituent parts of a  substance of unknown
composition in forms of known composition, from which the consti-
tution of the body examined, and the presence of its several com-
ponent elements may be  positively inferred.  The efficiency of its
method depends  upon two  conditions—viz., it must attain the
object in view with unerring certainty, and  in the most expeditious
manner.  The object of quantitative analysis, on the other hand, is
to exhibit the elements revealed by the qualitative investigation in
forms which will permit the most accurate estimate of their weight,
or to  effect by other means the determination of their quantity.
  These different ends are, of course, attained respectively by very
different ways and means.  The study of qualitative  analysis must,
therefore, be pursued separately from that of quantitative analysis,
and must naturally precede it.
  Having thus generally  defined the meaning and scope of qualita- 
2
PRELIMINARY REMARKS.
tive analysis, we have now still to consider, in the  first  place, the
preliminary information required to qualify students for a success-
ful cultivation of this branch of science, the rank which it holds in
the domain of chemistry, the bodies that fall within the  sphere of
its operations, and its  utility and importance; and, in the second
place, the principal parts into which its study is divided.
  It is, above all, absolutely indispensable  for a  successful pursuit
of qualitative investigations, that the student should possess some
knowledge of the chemical elements, and  of  their most important
combinations, as well as of the  principles  of  chemistry in general;
and that he should combine with this knowledge some readiness in
the apprehension of chemical processes.  The practical part of this
science demands, moreover, strict order, great neatness, and a cer-
tain skill in  manipulation.   If the student joins  to  these qualifica-
tions the habit of invariably ascribing  the failures with which he
may happen to meet, to some error  or defect in  his operations, or,
in other  words, to the  absence of some condition or other indis-
pensable  to  the success of the  experiment—and a firm reliance on
the immutability of the laws of nature cannot  fail to create this
habit—he possesses every  requisite to render his study of analyti-
cal chemistry successful.
  Now, although chemical analysis is based on general chemistry,
and cannot be cultivated without some previous  knowledge of the
latter, yet, on the other hand, we have to look upon it as one of the
main pillars upon which the entire structure  of the  science  rests ;
<dnce it is of almost equal  importance for  all branches of theoreti-
cal as well as of practical chemistry; and I need  not expatiate here
on the advantages  which the physician, the pharmaceutist,  the
mineralogist, the rational farmer,  the  manufacturer, the artisan,
and many others derive from it.
  This consideration would surely in itself be sufficient  reason to
recommend  a thorough and diligent study of this  branch  of sci-
ence, even if its cultivation  lacked  those  attractions which yet it
unquestionably possesses for  every one who  devotes himself zeal-
ously and ardently to it.  The  human mind is constantly striving
for the attainment of truth; it delights in the solution of problems  ;
and where do we meet  with a greater variety of them, more  or less
difficult of solution, than in the province of chemistry ? but  as a
problem to which, after long pondering, we fail to discover the key,
wearies and discourages the mind :  so, in like manner, do chemical
investigations, if the object in view is not attained—if the results
do  not bear the stamp of truth, of unerring certainty.  A  half-
knowledge is therefore, as  indeed in every department  of science,
but more especially here, to be considered worse  than  no know-
ledge  at all; and a mere superficial cultivation of chemical analysis
is consequently to be particularly guarded against. 
§§ 1, 2.]                  SOLUTION.                         3

  A qualitative investigation may be made with a twofold view—
viz., either, 1st, to prove that a certain body is or is not contained
in a substance, e.g. lead in wine ;  or, 2nd, to ascertain all the con-
stituents of a  chemical compound or mixture.  Any substance
whatever may of course become the object of a chemical analysis.
  In this work, those bodies which, are most important in practi-
cal chemistry, from their wide distribut ion and their uses in medi-
cine and the arts, are treated of in full detail; while, to facilitate the
beginner's  progress, the rarer elements  are noticed more briefly,
and in such a manner that they may be separately studied.
  The study of qualitative analysis  is most properly  divided into
four principal parts—viz.,

     1.  Chemical operations.
     2.  Reagents and their uses.
     3.  Deportment of the various bodies with reagents.
     4.  Systematic course of  qualitative analysis.

   It will now be  readily understood that the pursuit of chemical
analysis requires practical skill and ability, as well as theoretical
knowledge ; and that, consequently, a mere  speculative study  of
that science can be as little  expected to lead to success as purely
empirical experiments.  To attain  the desired  end, theory and
practice must be combined.
SECTION  I.
                       OPERATIONS.

  The operations of analytical chemistry are essentially the same
as those of synthetical chemistry,  though modified to a certain
extent to adapt them to  the  different object in view, and to the
small quantities operated upon in analytical investigations.
  The following are the principal operations in qualitative analysis.

                             §  2.
                         1. Solution.
  The term "solution," in  its widest sense, denotes the perfect
union of a body, no matter  whether gaseous, liquid, or solid, with
a fluid, resulting in a homogeneous liquid.  However, when the
substance dissolved is gaseous,  the term "absorption" is more
properly made use of; and the solution of one fluid in another is
more generally called a  mixture.  The  application of the  term 
4
OPERATIONS.
L§2,
solution, in its usual and more restricted sense, is confined to the
perfect union of a solid body with a fluid.
  A solution is the more readily effected the more minutely the
body to be dissolved is divided.  The fluid by means of which the
solution is effected, is called the solvent.  We  call the solution
chemical, where the solvent enters into chemical combination with
the substance dissolved; simple, where  no definite combination
takes place.
  In  a simple solution the  dissolved body exists in the free state,
and retains all its original properties, except those  dependent on
its form and cohesion; it separates unaltered when the solvent is
withdrawn.  Common salt dissolved in water is a familiar instance
of a simple solution. The salt in this case imparts its peculiar taste
to the fluid.   On evaporating the water, the salt is left behind in its
original form.   A simple  solution is called saturated  when the
solvent has  received as  much  as  it can hold of  the dissolved
substance.  But as fluids dissolve generally larger quantities of a
substance, the higher  their temperature, the  term saturated, as
applied to  simple  solutions, is only relative, and refers invariably
to a certain temperature.  It may be laid down as a general rule,
that elevation of temperature facilitates and  accelerates  simple
solution.
  A chemical  solution contains the dissolved substance not in the
same  state nor possessed  of the same properties as before;  the dis-
solved body is no longer free, but intimately combined with the
solvent, which latter also  has lost its original properties ; a new sub-
stance has thus been produced, and the solution manifests therefore
now the properties of this new substance.  A chemical solution also
may be accelerated by elevation of temperature ; and this is  indeed
usually the case, since heat generally promotes the action of bodies
upon  each other.   But the quantity of the dissolved body remains
always the same in proportion to a given quantity of the solvent,
whatever may be  the  difference of temperature—the combining
proportions  of substances being  invariable, and altogether inde-
pendent of the gradations of temperature.
  The reason of this is, that in a chemical solution the solvent and
the body upon which it  acts have  invariably opposite  properties,
which they strive mutually to neutralize.  Further solution ceases
as soon as this tendency of mutual neutralization is satisfied. The
solution is in this case also said to be saturated, or, more properly,
neutralized, and the point which denotes it to be  so  is termed the
point of saturation or neutralization.
  The substances which  produce chemical solutions  are, in most
cases, either acids or alkalies.  With few exceptions, they have
first to be converted to the fluid state by means of a simple solvent.
When the opposite properties of acid and base are  mutually neu- 
§2.]
SOLUTION.
5
tralized, and the new compound is formed, the actual transition to
the fluid state will ensue only if the new  compound possesses the
property of forming  a  simple  solution with the  liquid present;
e. g. when solution of acetic acid in water is brought into contact
with oxide  of lead, there ensues, first, a chemical combination of
the  acid with the oxide, and then a  simple solution of the new-
formed acetate of lead in the water of the menstruum.
  In pharmacy, solutions are often made in a mortar by triturating
the body to be dissolved with the solvent added gradually in small
quantities at a time;  in chemical laboratories solutions  are  rarely
made in this  manner, but generally by digesting or heating the
substance to be dissolved with the fluid in beaker-glasses,  flasks,
test-tubes, or capsules.  In the preparation of chemical solutions,
the best way generally is to mix the body to be dissolved  in the
first place with water (or with whatever other indifferent fluid may
happen to be used), and then gradually add the  chemical  agent.
By this course of proceeding a large excess of the latter is avoided,
an  over-energetic action guarded  against,  the  process greatly
facilitated, and complete solution ensured, which is a matter of
some importance, as  it will not seldom happen in chemical com-
binations that the product formed refuses to dissolve if an  excess
of the chemical solvent is present; in which case  the molecules
first formed of the new salt,  being insoluble  in  the menstruum
present, gather round and  enclose the portion still  unacted  on,
weakening thereby or preventing altogether further chemical action
upon them.  Thus, for instance, Witherite (carbonate of baryta)
dissolves readily  when,  after being reduced to powder, water is
poured  upon  it,  and hydrochloric acid gradually added;  but it
dissolves with difficulty and  imperfectly when projected  into a
concentrated solution of hydrochloric aid  in water, for chloride of
barium  will indeed dissolve in water, but not in hydrochloric acid.
  Crystallization and precipitation are the reverse of solution,
since they  have for their object the  conversion of a fluid  or dis-
solved substance to the solid state.  As both generally depend on
the same cause, viz., on the  absence of a  solvent,  it is impossible
to assign exact limits  to either;  in many cases they merge into one
another. We must,  however, consider them separately here, as
they differ essentially in their extreme forms,  and  as the special
objects which  we  purpose to attain by their application are gene-
rally very different. 
6                        OPERATIONS.                     [§ 3.


                             §3.

                     2. Crystallization.

  We understand  by the  term crystallization,  in  a more  general
sense, every  operation,  or process, whereby bodies are made  to
pass from the fluid to the solid state, and to assume certain fixed,
mathematically definable,  regular forms.  But  as these forms,
which we call crystals, are the more regular, and consequently the
more perfect, the more slowly the  operation is carried  on, we
always connect with the term " crystallization " the accessory idea
of a slow separation—of a gradual conversion  to  the  solid state.
The formation of crystals  depends on the regular arrangement of
the ultimate constituent particles of bodies  [molecules  or atoms);
it can only take place, therefore,  if these  atoms possess perfect
freedom  of motion, and thus in general only when a substance
passes from the fluid or  gaseous to the solid state.  Those instances
in which the  mere ignition, or the softening or moistening of a
solid body, suffices to make the tendency  of the molecules to a
regular arrangement (crystallization) prevail over the diminished
force of  cohesion—such as, for instance, the turning white  and
opaque of moistened barley-sugar—are  to be regarded as excep-
tional cases.
  To induce crystallization, the causes of the fluid or gaseous form
of a substance must be removed.  These causes are  either heat
alone, e.  g., in the case of  fused metals; or solvents alone, as in the
case of an aqueous  solution of common salt; or both combined,
as in the case of a hot saturated solution of nitrate of potassa  in
water.  In the first case we obtain crystals by cooling the fused
mass; in the second, by evaporating  the menstruum; and in the
third by either of these means.   The most frequently occurring
case is that of crystallization by cooling hot saturated  solutions.
The liquors which remain after the separation of the crystals are
called mother-waters, or mother-liquors.   The term  amorphous is
applied to such solid bodies as have no crystalline form.
  We  have recourse to crystallization  generally either  to obtain
the crystallized substance  in a solid form, or to separate  it from
other substances dissolved in the same menstruum.   In many cases
also the form of the crystals or their deportment in the air, viz.,
whether  they remain unaltered or effloresce, or deliquesce, upon
exposure to the air, will  afford an excellent means of distinguishing
between bodies otherwise  resembling'  each other; for instance,
between sulphate  of soda and sulphate of potassa.  The process
of crystallization is  usually effected in  dishes,  or, in the  case  of
very small quantities, in watch-glasses.
  In cases where the quantity of fluid to be operated upon  is small. 
§ 3, 4.]
PRECIPITATION.
7
the surest way of getting well-formed crystals is to let the fluid
evaporate  in  the air, or, better still, under a  bell-glass, with an
open vessel half-filled with concentrated sulphuric acid.  Minute
ervstals  are examined best with a  lens,  or under the microscope.


                              M-

                       3. Precipitation.

   This operation differs from the preceding one in this much, that
the dissolved body is converted to  the solid state, not slowly and
gradually,  but suddenly, no matter whether the  substance separat-
ing is crystalline or amorphous, whether it sinks to the bottom of
the vessel, or ascends, or remains suspended  in  the liquid.  Preci-
pitation  is either caused by a modification of the solvent—thus
sulphate of lime  (gypsum) separates immediately from its solution
in water upon the addition of alcohol; or it ensues in consequence
of the separation of an educt insoluble in  the  menstruum—thus
when ammonia is added to a  solution of sulphate of alumina, the
latter  salt is decomposed, and the alumina, not being soluble in
water, precipitates.   Precipitation  takes place also when, by  the
action of simple or double  chemical affinity, new compounds  are
formed which are insoluble in the menstruum  ; thus oxalate of lime
precipitates upon adding oxalic acid to a solution of acetate of
lime ;  chromate of lead upon mixing  chromate of potassa with ni
trate of  lead.  In decompositions of this kind, induced by simple
or double affinity, one of the  new compounds remains  generally in
solution, and the same is sometimes the  case also with the  educt;
thus in the instances just mentioned the  sulphate of ammonia, the
acetic acid, and the nitrate of potassa, remain in solution.  It may,
however, happen also that both the product and  the educt, or two
products, precipitate, and that  nothing remains in solution ; this is
the case, for instance, when a solution of sulphate of magnesia is
mixed with water of baryta, or when a solution of sulphate of sil-
ver is precipitated with chloride  of barium.
   Precipitation is resorted to for the same purposes as crystalliza-
tion, viz., either to  obtain a substance  in  the  solid  form, or to
separate  it from other substances dissolved in the same menstruum.
But in qualitative analysis we have  recourse to this operation more
particularly for the  purpose of detecting and distinguishing  sub-
stances by the color, properties, and general deportment which they
exhibit when precipitated either in an isolated state or in combina-
tion  with  other  substances.  The  solid body separated by  this
process is  called the precipitate, and  the substance which acts as
the immediate cause  of the separation is termed the precipitant.
Various terms are applied to  precipitates by way of particularizing 
8
OPERATIONS.
[§§ 4, 5.
thftni according to their different nature ; thus we distinguish crys
Ulline, pulverulent, flocculent, curdy, gelatinous precipitates, &c.
  The  terms turbid, turbidity, are made use of to designate the
state of a fluid which contains a precipitate so finely divided and so
inconsiderable in amount,  that the  suspended particles, although
impairing the transparency of the fluid, yet cannot be clearly dis-
tinguished.  The separation of flocculent precipitates may generally
be promoted by a vigorous shake of the vessel;  that of crystalline
precipitates, by stirring the fluid and rubbing the sides of the vessel
with a glass rod ;  elevation of temperature is also  an effective
means  of promoting  the  separation of most  precipitates.  The
process is therefore conducted, according to circumstances, either
in test-tubes, flasks, or beakers.

  The  two  operations described respectively in §§ 5  and 6, viz.,
filtration and decantation,  serve to effect the mechanical separation
of fluids from matter suspended therein.

                             §5.
                        4. Filtration.
  This operation consists simply in passing the fluid from which we
wish to remove the solid particles mechanically  suspended therein
through a filtering apparatus, formed usually by a properly arranged
piece of unsized paper placed in a funnel; an  apparatus  of  this
description allows the fluid to trickle through with ease, whilst it
completely retains the  solid particles.  We  employ  smooth filters
and  plaited filters; the former in cases where the separated solid
substance is to be made use of, the latter in cases where it is simply
intended to clear the solution.   Smooth filters are prepared  by
double-folding a  circular piece of paper, with  the  folds at right
angles;  they must in every  part  fit close to  the funnel.  The
preparation of plaited  filters is more properly a matter for ocular
demonstration than for description.  In cases where the contents
of the  filter require washing, the paper must not project over the
rim of the funnel.  It is in  most cases advisable to moisten the filter
previously to passing the fluid through it; since  this not only tends
to accelerate the process,  but also  renders the solid particles less
liable to be carried through  the pores of  the  filter.   The paper
selected  for filters  must be as free as possible from inorganic  sub-
stances, especially such as  are dissolved by acids, e.g., sesquioxide
of iron and lime.  The common filtering paper of commerce seldom
comes up to our wants in this respect, and I would therefore always
recommend to wash  it carefully with dilute  hydrochloric acid
whenever it is intended for use in accurate analyses.  With the
stronger sorts of paper this may be done by placing the paper cut
in circular discs, in a layer of moderate thickness, in a shallow 
& 5, 6.]
DECANTATION.
9
porcelain dish, pouring over it a mixture of one part of hydrochloric
acid or nitric acid with  about nine parts of  water, and letting it
digest for  several hours at a moderate heat.  The  fluid is then
poured off, and the paper is repeatedly washed with water (finally
with distilled water),  until litmus paper is no longer reddened by
the washings : the water  is then  drained  off, and the entire layer is
carefully transferred to a quire  of blotting-paper, and left  there
until  they  can be taken  off singly without injury; they are then
hung up to dry on lines in a place
free from dust.  With the finer sorts
of paper (Swedish paper) I prefer
washing the filters in the  funnel.   To
this end they are first sprinkled with
a  little  moderately  diluted  hydro-
chloric or  nitric acid, and then  tho-
roughly  washed with water, finally
with distilled water. Filtering paper,
to be considered good, must, besides
being pure, also let fluids  pass readily
through, whilst yet completely retain-
ing even the finest pulverulent preci-
pitates,  such  as sulphate of baryta,
oxalate  of lime,  &c.   If a  paper
satisfying  these  requirements cannot be  readily procured, it is
advisable to keep two sorts, one of greater  density for the separa-
tion of very finely divided precipitates, and one of greater porosity
for the speedy separation of grosser particles.  The funnels must be
of  glass or porcelain (§ 16, 10); they are  usually placed on an
appropriate stand, to keep them in  a fixed position.  The stand
shown in Fig. 1 is particularly well adapted for the  reception of
the small-sized funnels used in qualitative analyses.
BM.....iiiiiiiiiiiiiiiiiiiiffliiwiiiiiiiiiwiiiiwiiiiiifl
  Fig. 1.
                              §6.
                        5. Decantation.
  This operation is frequently resorted to instead of filtration,  in
cases where the solid particles to be removed are of considerably
greater specific gravity than the liquid in which they are suspended;
as they will in such cases speedily subside to the bottom, thereby
rendering it easy either to decant the  supernatant fluid by simply
inclining the  vessel,  or  to  draw it  off by means of a  syphon  or
pipette.
  In cases where filtration or decantation are resorted to  for the
purpose of obtaining the solid substance, the latter has to be freed
afterwards by repeated washing from the liquid still adhering to it 
10
OPERATIONS.
[§&
Tlie operation is called washing or edulcoration.  The washing of
precipitates collected on a filter is usually effected by means of a
washing bottle, such as is shown in Fig. 2.
                       This consists of a flask or bottle, closed
                     with a twice-perforated, snugly-fitting cork,
                     through which pass two glass tubes, as in the
                     figure. The outer end of the tube, a, is drawn
                     to a moderately fine point.  By blowing into
                     the other tube, a stream of water is driven
                     out  from a with considerable force, which
                     adapts the  apparatus to removing  precipi-
                     tates from the sides of vessels as well as to
                     washing  them  on  filters.   This form  of
                     washing-bottle serves for edulcoration with
                     warm or even boiling water, provided the
                     vessel itself has a uniformly thin bottom, so
                     that it can be heated without fear of break-
                     ing.   It is improved by binding  about the
                     neck  a ring of cork, or winding it closely
                   It then may be handled with convenience when
                     [As  it is usually inclined when in use, it is
Fig. 2.
with smooth cord.
its contents  are hot.
further improved by bending the lower part of the tube a (after it
is fitted through the cork), so that its end closely approaches the
bottom of the bottle a^B. Its contents may then be used nearly
to the last drop without need of so frequent replenishing.]
  As the success of an analysis often depends upon the complete
or proper washing of a precipitate, we may here  remark that the
operator must accustom himself to continue the process until he is
certain that the  object in view has been actually accomplished.
In general, this is not the  case until the precipitate has been per-
fectly freed  from the liquid in which it was formed.   The analyst
must  not be  content to  guess that  a  precipitate is thoroughly
washed, but must prove that it is so, by applying appropriate tests.
If the body to be removed is non-volatile, slow evaporation of a
few drops of the last portions of the washings on a  clean surface
of glass  or  platinum, will usually serve to indicate the point at
which the process may terminate.
  There are four operations which serve to  separate volatile sub-
Btances from less volatile or from fixed bodies, viz., evaporation
distillation, ignition, and sublimation.  The two former  of these
operations are applied exclusively to fluids, the two  latter exclu-
sively to solids. 
§7.]
EVAPORATION.
11
                        6. Evaporation.
  This  operation is of very frequent occurrence.  It  serves  tc
separate volatile fluids from less volatile or from fixed bodies  (no
matter whether solid or fluid),  in  cases where the residuary sub-
stance alone is of importance, whilst the evaporating  matter is
entirely  disregarded;—thus, for instance, we  have recourse  to
evaporation for the  purpose of removing from  a saline solution
part of the water, in order to bring  about  crystallization  of the
salt;  we resort to this process also for the  purpose of removing
the whole of the water of the menstruum from the solution of a
non-crystallizable substance, so  as to  obtain the latter in a solid
form, &c.  The evaporated water is entirely disregarded in either
of these cases, the  only object in view being to obtain,  in  the
former case, a more  concentrated fluid, and in the latter  a dry sub-
stance.   These objects are invariably attained by converting  the
fluid which is to be removed to the gaseous state.  This is generally
done by the  application of heat; sometimes also by leaving  the
fluid for a certain time in contact with the atmosphere, or with  an
enclosed volume of air  constantly kept dry by  hygroscopic sub-
stances, such as concentrated sulphuric acid, chloride of calcium,
&c.; or, lastly,  in  many cases, by placing the  fluid in rarefied
air,  with  simultaneous  application  of  hygroscopic substances.
As it is of the utmost  importance  in  qualitative analyses to
guard against  the  least  contamination, and as an evaporating
fluid is the more liable to this the  longer the operation lasts,  the
process is  usually conducted, with proper  expedition,  over  the
flame of a  spirit or gas-lamp, in a  separate place free from dust and
not exposed to draughts of air.  If the operator has no place  of
the kind, he must have recourse to the much less suitable proceed-
ing of covering  the dish; the  best way of doing this is to  place
over the dish a large glass funnel secured by a retort holder, in a
manner to leave sufficient space between the  rim of the funnel and
the border of the dish; the funnel is placed slightly aslant that the
drops running down its sides may be received in a beaker. Or the
dish may also  be covered with a sheet of filter  paper previously
freed from inorganic substances by washing
with dilute hydrochloric or nitric acid  (see   a
§ 5); were common and  unwashed filter
paper used for  the purpose, the sesquioxide
of iron, lime, &c, contained in it, would
dissolve in  the vapors evolved (more espe-
cially if acid),  and  the  solution dripping
down into  the  evaporating fluid  would speedily contaminate  it.
These precautions are necessary of course only in accurate analyses;
 
12
OPERATIONS.
[§§ 7, 8.
 [In most ordinary cases, vessels may be covered with the very thin
 white paper used by grocers (tea-paper) without detriment, since the
 impurities  that can find their  way  into solutions from  so small a
 weight of  paper,  are too  slight  to  affect common  analyses.]
 Larger quantities of fluid are  evaporated  best  in glass  flasks
 standing aslant,  covered with  a cap of paper, over  a charcoal  fire
 or gas; or  also in retorts.   Evaporating processes at 212°  are
 conducted in an  appropriate steam apparatus, or in the water-baths
 shown in Fig. 3.
  Evaporation to dryness, instead of being conducted over a free
fire or lamp-flame, is best carried on either in a water or sand-batb
 or on a heated iron plate.

                             §8.
                       7.  Distillation.
  This operation serves to separate a  volatile  liquid from a less
volatile or a fixed substance  (no matter whether  solid or fluid),
where the object is to recover the evaporating fluid.  In  order to
attain this object,  it is  necessary to reconvert the  liquid from the
gaseous form in which it evaporates, into the fluid state.  A dis-
tilling apparatus consists  consequently always of three parts,  no
matter whether admitting of separation or not.  These three parts
are—1st, a vessel in which the liquid to be distilled is heated, and
thus converted into vapor; 2nd, an apparatus in which  this vapor
is  cooled again  or condensed, and thus reconverted to the fluid
state;  and 3rd, a vessel to receive the fluid thus reproduced by the
condensation of  the vapor  (the distillate).  For the distillation  of
                             Fig. 4

large quantities we use either a metallic  apparatus (a copper still
with head and condenser made ot tin or pewter), or large glas 
§§ 9, 10.]
SUBLIMATION.
13
retorts; in analytical investigations we generally employ the appa-
ratus shown in Fig. 4.

                              §  9.
                          8. Ignition.
  Ignition is, in a certain measure, for solid bodies what  evapora-
tion is with regard to fluids; since it serves (at least generally) to
separate volatile substances from less volatile or from fixed bodies,
in cases where the  residuary substance alone is of importance.
The process of ignition  always presupposes the  application of a
high temperature, in which it differs from that of  drying  or  exsic-
cation.  The form or state which the eliminated substance assumes
on cooling—whether it remains gaseous, as in  the ignition of car-
bonate of lime; or assumes the liquid state,  as in the ignition  of
hydrate of lime;  or solidifies, as in the ignition of a  mixture
containing chloride of ammonium—is a matter of perfect indiffe-
rence as regards the name given to the operation.
  The process of ignition is mostly employed, as  has just  been
said, to effect the elimination of a volatile body.  In some instances,
however, substances are ignited simply for the purpose of modifying
their state, without any volatilization taking place ; thus the sesqui-
oxide  of  chromium  is converted by ignition into its  insoluble
modification, &c.  In analytical  investigations substances  under
examination  are often ignited also, that the operator may from
their deportment at a red heat draw a conclusion as to their nature
in general; their fixity, their fusibility, the presence or absence of
organic matter, &c.
  Crucibles are the vessels made use of in ignition.   In operations
on a large scale Hessian or  black-lead crucibles are used, heated
by charcoal or coke; in analytical experiments small-sized crucibles
or  dishes are  selected, of porcelain, platinum, silver or  iron,  or
glass tubes sealed at one  end,  according to the  nature of the
substances to  be ignited;  these  crucibles,  dishes, or tubes are
heated over a Berzelius spirit-lamp or a properly-constructed gas-
lamp.

                              § 10.
                        9. Sublimation.
  The term  sublimation designates the process which serves to
expand solid  bodies into vapor by  the  application of heat, and
subsequently to recondense the vapor to the solid state by refrigera-
tion ; the  substance volatilized and recondensed is  called a subli
mate.  Sublimation  is consequently  a distillation of solid bodies
We have  recourse to this process mostly to effect  the separation
of  substances  possessed of  different degrees of  volatility.   Its
application is of the highest importance in analysis for the  detection 
14
OPERATIONS.
[§H.
 of certain substances, e. g. of arsenic.   The vessels  used in subli-
 mation are of various shapes, according to the different degrees of
 volatility of the  substances operated  upon.  In sublimations for
 analytical purposes we generally employ sealed glass tubes.


                             § H-
                   10. Fusion and Fluxing.
  We designate  by the term " fusion " the conversion of a solid
substance into the fluid form by the  application of heat; fusion
is most frequently resorted to  for the purpose of effecting the com-
bination  or the decomposition of bodies.  The term " fluxing " is
applied to this process in cases where substances  insoluble or diffi-
cult  of solution in water and acids are by fusion in conjunction
with some other body modified or decomposed in such a manner,
that they or the new-formed compounds will subsequently dissolve
in  water or  acids.  Fusion and fluxing are  conducted either in
porcelain, silver, or platinum crucibles, according to the  nature of
the compound.  The crucible is supported  on  a triangle of mode-
rately stout  platinum wire, resting  on, or attached to, the ring of
the spirit or  gas-lamp.  Triangles  of thick iron wire, especially
when laid upon the still stouter brass ring of the' lamp, carry off
too much heat to allow of the production of very high temperatures.
Small  quantities  of matter are also often fused in  glass tubes
sealed at one end.
  Resort to fluxing is especially required  for the analysis of the
sulphates of the alkaline earths, and also for that of many silicates.
The flux  most commonly used is carbonate of  soda or carbonate of
potassa, or, better still, a mixture of both in equal atomic propor-
tions  (see § "78).   In certain cases, hydrate of baryta is used instead
of the alkaline carbonates (see § 79). But in either case the opera-
tion is conducted in platinum crucibles.
  I have to add here a few precautionary rules for the  prevention
of damage to the platinum vessels used in these operations.   No
substance evolving chlorine ought to be treated in platinum vessels;
no nitrate of potassa, caustic potassa, metals,  sulphides  of  the
metals, or cyanides of the alkalies, should be fused in such vessels;
nor ought readily deoxidizable metallic oxides, organic metallic
salts,  or phosphates to be ignited in them in the presence of organic
compounds.  It is also  detrimental to platinum  crucibles,   and
especially to  their covers, to  expose them directly to  an intense
charcoal  fire, since the action of the ash, under such circumstances
gives readily rise  to the formation  of silicide of platinum, which
renders the vessel brittle.  It  is always advisable  to support  the
platinum crucible in which a process of ignition or fusion is to be
conducted, on a triangle  of platinum wire.  [When platinum ves- 
§§ 12, 13.]       THE USE  OF THE BLOWPIPE.               15

sels are ignited in the gas flame, especially over a blast lamp, they
are liable to assume a dull and soiled aspect  externally, and after
prolonged use  often become  cracked with rifts, that at first are
scarcely perceptible, but shortly extend so as  to ruin the vessel.
This detriment is prevented] and generally most kinds of stains
may be removed  from platinum apparatus by  gently rubbing th
surface with moist sea-sand as often as the lustre is impaired. The
grains of sand must be polished and free from sharp angles.  By
the proper use of sand of good quality, the metal  is not scoured,
but burnished.  If the stains or impurities in a platinum dish resist
this treatment, bisulphate of potassa or borax should be heated in it
to fusion for some time. The vessel is then cleaned with  hot water,
and finally, if needful, is burnished with sand as above described.
   We have still to speak  here  of another  operation which bears
 some affinity to fusion.

                             §  12.
                       11. Deflagration.
   We understand by the term " deflagration,''''  in a more general
 sense, every  process of  decomposition  attended with  noise  or
 detonation—(the cause of the decomposition is a matter of perfect
 indifference as regards the application of the term in this  sense).
   We use the same term, however, in a more restricted  sense,  to
 designate the oxidation of a substance in a dry way, at the expense
 of the oxygen of another substance mixed with it (usually a nitrate
 or a chlorate), and connect with it the idea of a sudden and violent
 combustion attended with vivid incandescence and noise or detona-
 tion.   Deflagration is  resorted to either to produce  the desired
 oxide—thus tersulphide of arsenic is  deflagrated with nitrate of
 potassa to obtain arsenate of potassa;—or it is applied as a means
 to prove the presence or absence of a certain substance—thus salts
 are tested  for nitric or chloric acid, by fusing them in  conjunction
 with  cyanide  of potassium,  and observing  whether this procesa
 will cause  deflagration or not, &c.
   To attain the former object, the  perfectly dry mixture  of the
 substance under examination and of the deflagrating agent is pro-
 jected in small portions into a  red-hot crucible.  Experiments of
 the latter description are invariably made with very minute  quan-
 tities ;  the  process is, in such cases, best conducted on a  piece of
 thin platinum foil, or in a small spoon.

                             § 13.
                12. The  Use of the Blowpipe.
  This operation belongs exclusively to the province of analytical
chemistry,  and  is of paramount importance in many analytical 
16
OPERATIONS.
[§13,
processes.  We have to examine here,  1, the apparatus; 2, the
mode of its application;  and, 3, the results of the operation.
  The blowpipe (Fig. 5)  is a  small instrument, usually made of
brass or German silver.  It consists of three distinct  parts;  viz.
1st, a tube (a b), fitted, for greater convenience, with a horn or
ivory mouthpiece,  through which  air is  blown from the mouth;
                     2nd,  a small cylindrical vessel (c d),  into
                     which a b is ground air-tight, and which
                     serves as  an air-chamber, and to retain  the
                     moisture of the air blown into the tube; and,
                     3rd, a smaller tube (fg), also fitted into the
                     vessel (c d).   This  small tube, which forms
                     a right angle with the larger one, is fitted at
                     its aperture either simply with a finely per-
                     forated platinum plate, or more conveniently
                     with a finely perforated platinum cap  (A)
                     ground on air-tight.  The construction of
                     the cap is shown in Fig. 6.  It is, indeed, a
                     little dearer than a  simple plate,  but it is
                     also  much  more  durable.   Whenever  the
                     opening of the cap happens  to be stopped
                     up, the obstruction may be removed by heat-
                     ing the cap to redness before  the blowpipe.
                     [A  cap of brass is in no way inferior  to one
                     of platinum.  It may be cleaned by a needle,
                     from the inside, and is much easier to obtain
of the thickness requisite to withstand continued use.]
  The proper length of the blowpipe depends upon the distance
to which the operator can see with distinctness; it  is usually from
eight to ten inches.  The form  of the mouthpieces  varies.  Some
chemists like them of a shape to be encircled by the lips;  others
prefer the form of a  trumpet  mouthpiece, which is only pressed
against the lips. The latter require less  exertion on the part of
the operator, and  are accordingly generally chosen by those who
have a great deal of blowpipe work.
  The blowpipe serves to  conduct a continuous fine  current of
air into  a  gas-flame, or into the flame of a candle or lamp.  The
flame of a candle  (and equally so that of gas or of an  oil lamp),
burning under ordinary circumstances, is seen to consist of three
distinct parts,  as shown in  Fig. V,  viz., 1st, a dark nucleus in  the
centre(a);  2nd, a luminous cone surrounding this nucleus (efg);
and, 3rd, a feebly luminous mantle encircling the  whole flame
(bed).  The  dark nucleus is formed by the gases which the heat
evolves  from the wax Or fat,  and which cannot  burn here  for
want of oxygen.  In the luminous cone these gases come in  con-
tact with a certain amount of air insufficient for  their complete
Figs. 5, 6. 
§ 13.]            THE USE OF THE BLOWPIPE.               17
Fig. 7.
 combustion.  In this part, therefore, it is principally the hydrogen
 of the carbides of  hydrogen  evolved  which  burns,
 whilst the carbon separates in a state of intense igni-
 tion, which imparts to the flame the luminous appear-
 ance observed  in  this part.  In the  outer coat, the
 access of air is no longer limited, and all the gases not
 yet burned are consumed here.  This part of the flame
 is the hottest; oxidizable bodies oxidize therefore with
 the greatest possible  rapidity when placed in it, since
 all the conditions of oxidation are here  united, viz.
 high temperature, and an unlimited supply of oxygen.
 This outer part of  the  flame  is therefore called the
 oxidizing flame.
   On the other  hand, oxides having a tendency to yield
 up their oxygen, suffer reduction when placed within
 the luminous part of the  flame,  the oxygen being withdrs /m from
 them by the carbon and the still unconsumed carbide of faydrogen
 present in this  sphere.   The  luminous part of the flame is there-
 fore called the reducing flame.
   Now the  effect  of blowing a fine current of air across a flame,
 is first to alter the shape of the latter, which, from tending upward,
 is now driven sideways  in the  direction of the blast, and at the
 same time  lengthened  and narrowed;   and,  in  the  second
 place, to extend the sphere of combustion  from  the outer to
 the inner part.   As  the  latter  circumstance  causes an extraordi-
 nary increase of the heat  of the  flame,  and the former a concentra-
 tion of that heat within narrower limits, it  is easy to understand
 the exceedingly energetic action of the blowpipe flame.  The way
 of holding the blowpipe and the nature of the current, will always
 depend upon the precise object in view, viz., whether the operator
 wants a reducing or an oxidizing flame.  The easiest way of pro-
 ducing most efficient flames of both kinds is by means of coal-gas
 delivered from a tube, terminating in  a flat top with a somewhat
 slantingly downward-turned slit 1  centimetre long and l£ to 2
 millimetres wide; as with the use of gas the operator is enabled to
 control  and regulate not  only  the blowpipe  flame, but the gas
 stream also.   The  task of keeping the blowpipe steadily in the
 proper position  may be greatly facilitated by firmly resting that
 instrument upon some moveable metallic support, such as, for in-
 stance, the ring of Bunsen's gas  lamp for supporting dishes, &c.
  Fig. 8 shows the flame  for  reducing, Fig. 9 the  flame for oxi-
dizing.  The luminous parts are shaded.
  The reducing flame is produced by keeping the jet of the blow-
pipe just on the border of a tolerably strong gas flame, and driving
a moderate blast across it.  The  resulting mixture of the air with
the gas is only imperfect, and there remains between the inner
                               2 
18                      OPERATIONS.                    [§ 13.

bluish  part of the flame and the outer barely visible part a lumi-
nous and reducing zone, of  which the hottest point lies somewhat
                              Fig. a

beyond the apex of the inner cone.  To produce  the oxidizing
flame, the gas is lowered, the jet of the blowpipe pushed a little
further into the flame, and the strength of the current somewhat
increased.  This serves to effect an intimate mixture of the air and
gas, and an inner pointed, bluish cone, slightly luminous towards
the apex, is formed, and surrounded by a thin, pointed, light-bluish,
barely visible mantle.   The hottest part of the flame is at the apex
of the inner  cone.  Difficultly fusible bodies are exposed to this
part to effect their fusion;  but bodies  to  be oxidized are held a
little beyond the apex, that there may be no want of  air for their
combustion.  An oil-lamp with broad  wick of  proper thickness
may be used instead of coal-gas; a thick wax candle also will do.
For an oxidizing flame, a  small spirit-lamp will in most  cases
answer the purpose.
                             Fig. o.

  The current is produced with the cheek muscles alone, and not
irith the lungs.  The way of doing this may be easily acquired by 
 § 13.]            THE  USE OF THE BLOWPIPE.              19

 practising for some time to breathe calmly with puffed-up cheeks,
 and with the blowpipe between the lips;  with a little patience the
 student will soon be able to produce an even and uninterrupted
 current.
   The supports on which substances are  exposed to the blowpipe
 name  are  generally either wood-charcoal, or  platinum wire or
 foil.
   Charcoal supports are used principally in the reduction of me-
 tallic oxides, &c, or in trying the fusibility of bodies.  The sub-
 stances to be  operated  upon are  put into  small  conical cavities
 scooped out with a penknife or with a little tin tube.  Metals that
 are volatile at the heat of the reducing flame, evaporate wholly or
 in part upon the reduction of  their oxides;  in passing through the
 outer flame, the metallic  fumes are  re-oxidized,  and  the  oxide
 formed is deposited around the portion of matter upon the support.
 Such deposits  are called  incrustations.  Many of these  exhibit
 characteristic  colors leading  to the  detection  of the  metals.
 Thoroughly-burnt pieces of charcoal only should be selected for
 supports in blowpipe experiments, as imperfectly-burnt  pieces  are
 apt to spirt and throw off  the matter  placed on them.  The char-
 coal of the wood of pine, linden, or willow is greatly preferable for
 supports to that of harder and denser woods.  Smooth pieces ought
 to be selected for supports, as knotty pieces are apt to  spirt  when
 heated, and throw off the  matter placed on them.  The most con-
 venient way is to saw the  charcoal of well-seasoned  and straight-
 split pinewood into parallelopipedic pieces, and to blow or brush
 off the dust; they may then be handled without fear of soiling the
 hands.  Those sides  alone are used  on which  the  annual  rings
 are visible as circles or segments, as  on the other sides the  fused
 matters are apt to spread  over the surface of the charcoal  (Ber-
 zelius).
   The properties which  make charcoal so valuable as  a material
 for supports in blowpipe  experiments are—1st, its infusibility;
 2nd, its low conducting power for heat, which admits of substances
 being heated more strongly upon a charcoal than upon any  other
 support; 3rd, its porosity, which makes it  imbibe readily fusible
 substances, such as borax, carbonate of soda, &c, whilst infusible
bodies remain on  the surface; 4th, its power of reducing oxides,
which  greatly contributes  to effecting the reduction of oxides in
the inner blowpipe flame.
  We  use platinum wire,  and occasionally also platinum foil, in
all oxidizing processes before the blowpipe, and also when fusing
substances with fluxes, with a view to try their  solubility in them,
and to watch the phenomena attending the solution, and mark the
color of the bead.
  The wire, which should be about the thickness of lute-strings, is 
20
OPERATIONS.
[§14-
 cut into lengths of three inches, and each length bent at both ends
 into a small loop (Fig. 10.)


             o---------—o
                            Fig. 10.

   When required for use, the loop is  moistened with a droplet of
 water, then dipped into the flux, and the portion adhering exposed
 to the flame of a gas or spirit-lamp.   The bead produced, which
 continues to adhere to the loop, is let cool, then moistened again,
 a small portion of the substance  to be examined  added to it, and
 the loop finally exposed, according to circumstances, to the  inner
 or to the outer blowpipe flame.
   What renders the  application of the blowpipe particularly useful
 in chemical experiments is the great expedition with which  the
 intended results are attained. These results are of a twofold kind,
 viz., either they afford us simply an insight  into  the general pro-
 perties of the examined body, and enable us  accordingly only to
 determine the class  to which it belongs, i. e., whether it is fixed,
 volatile, fusible, &c.; or the phenomena which we observe enable
 us at once to recognise the particular  body which we have before
 us. We shall have occasion to describe these phenomena when treat-
 ing of the deportment of the different substances with reagents.
   For most analytical purposes,  the  blowpipe may be replaced
 with  great advantage and  convenience by the non-luminous and
 smokeless flame of the Bunsen gas-lamp, which is  described in the
 subsequent paragraphs.

                            § 14.
                 13. Alcohol and Gas-lamps.
  In  chemical  analysis  the operator has constant occasion to
submit substances to the influence of heat in  evaporations, igni-
tions, &c.  As for the most part small quantities of matter  are
employed, the requisite heat may be usually obtained from suitable
lamps, for which alcohol, or better when it is at hand, illuminating
gas, may serve as fuel.
  Alcohol or  Spirit-Lamps are of two kinds;  the common or
plain  spirit-lamp  (Fig. 13)  is made of glass, has  a ground  glass
cap and a brass wick-holder, and suffices to give a moderate heat
for small operations.   The Berzelius lamp has a hollow wick with
double draught, and  is much more powerful in its effects.
  The form shown in Fig. 11 is convenient and serviceable.   It is
adjustable to any desired position upon a brass stand,  which also
bears a stout brass ring for supporting heavy vessels, and a second
ring of slender iron wire to carry a triangle for sustaining crucibles 
§ 14.]             ALCOHOL AND GAS-LAMPS.                21
in the processes  of ignition and fusion.   The part enclosing the
wick  and the vessel  containing the spirit of wine  must  be in
separate pieces, connected together by means  of a narrow tube;
otherwise disagreeable  explosions are apt to occur on lighting the
lamp.  The chimney must not be too narrow.   The stopper on the
mouth, through which the spirit of wine is poured in, must not fit
air-tight.
  [The Rose and Mitscherlich lamps are of essentially the same
construction.  The stand of the former usually has a flat  base,
covered with a plate of porcelain, which is convenient for resting
hot vessels  upon.  The latter is provided with  a glass feeding
reservoir arranged so as to maintain the alcohol about the wick, at
a constant level.]  Fig. 12 exhibits  a triangle of platinum wire
secured within a  larger one of iron wire.   It is useful for support-
ing crucibles while heating to redness.
Fig. 12.
Fig. n.
Fig. 18.
  Glass vessels, more particularly beakers, which it is intended to
heat over  the lamp, are most  conveniently rested  on a circular
piece of gauze made of fine iron wire such as is used in the making
of sieves of medium fineness.
  Of the  many gas-lamps  proposed, Bunsen's, as shown in its
simplest form in Fig. 15, is the  most  convenient; a b is a foot of
cast-iron measuring 7 centimetres in diameter.  In the centre of
this is fixed a square brass box, c d, which slightly slants towards
the top; the sides of this box are 25 millimetres high and 16 milli-
metres wide;  it has a cylindric  cavity 12 millimetres deep and 10
millimetres in diameter.  Each side  of  the box has 4 millimetres
from the upper rim, a circular aperture of 8 millimetres diameter, 
22
OPERATIONS.
[§1±-
leading to the inner cavity.  One  of the sides has fitted into it,
about 1 millimetre below the circular aperture, a tube, d, to which
is attached a vulcanized india-rubber hose, which serves to convey
FiS- 14-                                 Fig. 15.
the gas to the apparatus.  This  tube is turned  as  shown in Fig.
14; it has a bore  of 4 millimetres diameter.  The gas conveyed
into it through the india-rubber re-issues from a tube placed in the
centre of the cavity of the box.  This tube, which is 4 millimetres
thick  at the top,  thicker at the lower end, projects 3 millimetres
above the  rim of the box; the gas issues from a narrow  open-
ing which appears formed of  3  radii of a circle, inclined to each
other  at  an angle  of 120°.  The length of each radius is 1 mil-
limetre, the opening £ millimetre wide;  ef is  a brass  tube  75
millimetres long, open at both  ends, and having an inner diameter
of 9 millimetres  ; the screw at the lower end of this tube fits into
a nut  in the upper part of the  cavity of the box.  With this tube
screwed in, the lamp is completed.  On opening the stop-cock, the
gas rushes from the opening into tube e f, when it mixes with the
air coming in through the  circular apertures (c).  When this mix-
ture is kindled at/, it burns  with a straight, bluish flame, entirely
free from soot, which may be regulated at will by opening the stop-
cock more or less;  a partial opening of the cock suffices to give a 
§ 14.]             ALCOHOL  AND  GAS-LAMPS.                23
flame fully answering the purpose of  the common simple spirit
lamp; whilst, with the full stream of gas turned on, the flame, which
will now rise up to 2 decimetres in height, burning with a roaring
noise, affords a most  excellent substitute for the Berzelius lamp.
When  the gas burns low, it sometimes happens  that the flame
recedes to the bottom of the tube/ e, and burns there unmixed with
air and with smoke.  This difficulty is remedied by bending a bit
of wire-gauze over the top of the tube/e, so as to form a movable
cap.   Flasks, &c, which it is intended to heat over the gas-lamp, are
most conveniently supported on wire-gauze.  If it is wished to use
the gas-lamp for blowpipe operations, the tube g h must be inserted
into ef; this tube terminates in a flattened top slanting at an angle
of 68° to the  axis, and having an opening in it 1 centimetre  long and
l£ to 2 millimetres wide ; its insertion into e f serves to close up the
air-apertures  in the box, and  pure gas, burning with  a luminous
flame, issues  accordingly now from the top  of the tube.  Fig. 15
shows the apparatus complete, fixed in  the forked iron stand; this
arrangement  permits  the lamp being  moved backward and for-
ward between the prongs of the fork, and up and down the pillar
of the stand.   The  movable ring on the same pillar serves to sup-
port the object to be operated upon.   The 6 radii  round the tube
of the lamp serve to support a sheet-iron chimney (see Fig. 17), or
a porcelain plate used in quantitative analyses.
  When it is necessary to heat a crucible to an intense  red, or even
to a white heat, a blast-lamp must be em-
ployed.   The effect  of  the  Bunsen
burner  may,  however,  be  greatly in-
creased by a suitable  clay chimney, such
as recommended by O. L.  Erdmann.
Fig.  16   represents  the  arrangement.
The  chimney has a height of 4£ inches,
and  is 3  inches wide in the clear.  The
walls are three-eighths of an inch thick.
In order  to  make the gas-lamp  serve
as a substitute for the blowpipe in experi-
ments  of  reduction,  oxidation,  fusion,
&c, or in observing  the coloration  im-
parted by various substances  to the flame, Bunsen* has arranged
it as  shown  in Fig.  17.   Here  is seen a  ring, a, which, being
movable up and down on a screw, serves to regulate with perfect
nicety the access of air to the flame.  Again a conical sheet-iron chim-
ney, b, which has a diameter above of 30 millimetres, below of  55
millimetres, is so placed on the radii c c,  that the tube d  is in its axis
and terminates 45 millimetres below its  upper edge.   This chimney
Fig. 16.
* Ann. d. Chem. v. Pharm. Ill, 257. 
.24
OPERATIONS.
[§14-
has the effect of producing an elongated flame of a shape like that
represented in the Figure, which burns quietly and  with uniform-
ity.  By careful examination, this flame is perceived to be made
up  of  an interior part and two surrounding envelopes.  The  for-
mer corresponds to the dark centre of the ordinary luminous flame,
and contains  the  unconsumed mixture of gas and air.  If the gas-
cock be so turned that the point of this interior portion is on a
level with the top of the chimney, the flame becomes perfectly
steady and definite in its parts.  By this means it may always be
re-produced with the same form and qualities when desired.  The
mantle which immediately surrounds the interior  part contains un-
consumed hydro-carbons; the exterior  blue envelope  consists  of
the final products of combustion.   According to Bunsen's calcu-
lation, the hottest point in the flame has  a temperature of about
2300° C. (4172° Fah.)   It  is  situated in the  mantle that lies
within  the  outer blue envelope, and in a horizontal zone which
occupies  a  few millimetres of space above and  below the point
of the inner mantle.  This  zone affusion, as it may  be called, 
 § 25.]    COLORED FLAMES AND SPECTRAL ANALYSIS.       25

 serves  to examine the deportment of bodies at  a  temperature
 of about 2300° C.  Its external border  acts as  an oxidizing
 flame; within  it  has the effect of a reducing flame,  and most
 powerfully just  above the point of the interior part of the flame.
 The Bunsen lamp, thus regulated, serves admirably for observing
 the coloring which many substances communicate to flame,  and
 which furnishes the most ready and sensitive test of the presence
 of some bodies, enabling the operator to  discover the slightest
 traces  of them when all other means of recognition are useless.
 In the next paragraph this subject comes under notice.  Here we
 must further state that a great advantage of the gas over the blow-
 pipe-flame consists  in the fact that, by means of a suitable holder,
 the substance under examination may be kept for any length of
 time in a given  part of the flame.   Such a holder is represented in
 Fig. 18.  The arm a is maintained at any  desired height  on  the
 rod c, by means of the spring slide b /  d is a glass tube which
 passes over the  arm a.  Into one end of it a  platinum wire of about
 0.145 millimetre diameter is  fused, which is bent to a loop set its
 free extremity.   By bringing the moistened platinum loop in con-
 tact with the powder of  the substance  that is to be  examined, a
 portion of it adheres; and when the loop is held for a time near
 the flame and  finally within it,  the substance  sinters or fuses
 firmly upon the wire.  Matters that decrepitate must first be ignited
 in a covered platinum vessel.  For testing liquids the wire  of the
 loop is  flattened by a few blows with a  hammer; then, if dipped
 into the substance, it lifts a drop, which, by holding near the flame,
 slowly evaporates, and the residue, if any, maybe brought into the
 zone of fusion (Bunsen).
                                                     \
                             § 15-
        14.  Colored Flames and Spectral Analysis.
  Many substances, when brought into a  colorless or non-luminous
 flame, color it in a remarkable  manner.  The  colorations are, in
 many cases, characteristic of the elements yielding them, and furnish
 excellent means  of  detecting the latter, even in the minutest quan-
 tities, with great ease and  certainty.  Thus soda-salts  tinge  the
 flame yellow ; potassa-compounds violet; lithia-salts carmine-red ;
 and on account of this peculiarity they may  be  distinguished from
 each other by the simplest experiments.
  The Bunsen lamp, with  chimney, previously described (Fig.  17),
is  especially adapted to such observations.   The  substance to be
tested is brought by means of the platinum wire-loop, Fig. 18, into
the zone of fusion of the gas-flame.  The alkalies and alkaline earths
are most remarkable in their coloring effects on the flame.  If we
compare together various  salts of the same base, we find that they 
26
OPERATIONS.
[§16-
 all, if volatile at the temperature of the flame, give the same color,
 but the color differs  in  intensity, being strongest with the most
 volatile salts, and  vice versd.  Thus, chloride of potassium gives a
 deeper tinge to the flame than carbonate of potassa, and carbonate a
 stronger than  silicate of potassa.   Sometimes  a  non-volatile com-
 pound is made to  exhibit a characteristic tint by the addition of
 some flux or decomposing agent.  Silicates which contain but a few
per cent, of potassa, and  of themselves do not color the flame, give
a coloration after heating with some pure  sulphate of lime, which
 decomposes them, producing silicate of lime and volatile sulphate
of potassa.
  In  mixtures of  several substances which  may  be individually
detected without difficulty, when they exist  separately, it usually
happens that a mixed and indecisive coloration  is  produced, or  one
substance masks all  the  others.  Thus, in a mixture of soda  and
potassa-salts, only a  soda-flame—in one  of baryta and strontia-
salts,  only  a baryta-flame is evident to the  unassisted eye.  We
have recently learned  two methods of dissecting these mixed flames
so as  to recognize their  component colors with surprising facility
and distinctness.
  The first method, introduced into chemistry by  Cartmell,*  and
further  developed by Bunsen\ and Merz,\  consists  in observing
the colored flames through colored media (stained-glass, indigo-
solution, &c).   These act by extinguishing the color of one metal
and thus developing  that of the  other.  A mixture of soda and
potassa, which to  the eye has  a pure yellow flame, when seen
through a deep-blue  cobalt glass or a  solution of indigo, exhibits
the violet  tint of potassa without  any traces of the  yellow soda-
flame.  The apparatus for these observations is simple, viz:
  1.  A hollow prism, made of plate glass, Fig. 19, whose  princi.
pal section forms a triangle, with two sides of  150 millimetres  and
one of 35 millimetres long.  The solution with which it is filled is
prepared by dissolving 1 part of indigo in 8 parts of fuming oil-of-
                             Flg. 19.

vitriol, adding 1500 to 2000 parts of water and filtering.  In use,
the prism is held close before the eye and moved horizontally, so

  * Philosophical Magazine, XYI. 328.    f Ann. d. Chem. u. Pharm. III. 257.
  \ Jour. f. Prakt Chem. 80. 487. 
§ 15.]    COLORED FLAMES AND  SPECTRAL ANALYSIS.       27

as to  cause  the  light of the  colored flame to pass into  the  eye
through successively thicker portions of the absorbing medium.
  2. A blue, a violet, a red and a green glass.  The blue is colored
by protoxide of cobalt;  the violet, by sesquioxide of manganese;
the red, by suboxide of copper; and the green, by sesquioxide of
iron and oxide of copper.  The stained glasses found in commerce
and  employed  for  ornamenting windows,  generally possess  the
requisite shades of color.  The appearance of the colored flames
produced by various bodies, when  seen  through these' media, and
the combinations which  serve to recognize individual substances,
are described in Section III.
  The second method—that of spectral  analysis, discovered by
Kirchhoff and Bunsen, consists in letting the rays of the colored
flame,  after passing through a narrow slit, traverse a prism, and in
observing  the spectrum  thus  produced by means of a telescope.
Each of the metals  which give color to  the  flame, thus  yields a
peculiar spectrum, formed in  some cases, as in that of baryta, of
many contiguous colored lines; in  others of two more distant lines
of different color, as shown by lithia; or, again, of a single line,  as
in case of soda and thallium.  These  spectra are  characteristic in
two respects, viz. 1,  in the definite color of the spectral lines ; and
2, in the invariable relative position they occupy.
  The last named fact enables us  to detect, without  difficulty  in
most cases,  all the  spectrum-giving ingredients of  a   mixture.
Thus, when potassa, soda and lithia-salts are brought together into
the spectroscope, the lines characteristic of each metal appear  in
the utmost purity at one view. [Very minute traces of some ele-
ments  do  not, however, exhibit  their spectra in presence of large
quantities of other substances.]
  Kirchhoff' and Bunsen have described two instruments adapted
to spectral observations.   The larger and more complete is figured
in Poggendorff's Ann. 113, 374;  also  Fresenius'' Zeitschrift far
analytische Chemie, 1862. 49.  The smaller, simpler, and cheaper
instrument, which is perfectly adapted for ordinary uses, is  here
described.  It is represented in Fig. 20.
  The triangular glass prism, whose refracting surfaces are circles
of about  25 millimetres  in diameter, is placed at the centre  of a
circular iron plate, A, to which it is secured by a clamp.   To the
same iron plate the three brass tubes B,  C,  D, are permanently
attached.   Each  tube is soldered to  a block of metal (shown
enlarged in Fig. 21), which is secured by means of two screws
to the iron plate,  after the tube has been brought into its proper
position.   B is the  telescope  through which the  spectrum is seen.
It has  an objective of 20 millimetres aperture, and magnifies about
six diameters.
  The tube C has at its outer extremity the vertical slit  through 
28
OPERATIONS.
[§15
which the rays of the flame pass on their way to the prism.  The
tube J), at its outer end, bears a narrow, horizontal scale photo-
graphed on glass.   In  use, this scale is  illuminated by the  flame
of a lamp placed immediately before it.
Fig. 20.                       Fig. 21.
  The axes of the tubes B and B are equally inclined to one face
of the prism.  The tube  C is opposite to the other face.  By this
arrangement, the spectrum produced by refraction of the light that
traverses C, and  the image of the scale  in D, produced by total
reflection, are seen together by the eye looking into B, and thus the
position of the colored lines may be read off in degrees  of the
scale.  The prism is placed nearly in a position in which the devia-
tion of the rays of the soda line is a minimum, and the telescope is
so situated that the centre of the field lies equidistant between the
red and the violet potassa lines.
  Four inches from the  slit in  C is placed  the  colorless flame of
Bunsen's lamp, Fig. 17.  It is so regulated that the  upper edge of
the chimney lies about  -f$ of an inch below the bottom of the slit.
A bead  of sulphate of potassa is now brought  into the flame (as
described on page 25,)  and the  instrument is so adjusted that the
spectrum becomes as bright as possible.  To cut off external light,
a black cloth, having three  slits corresponding to the three tubes,
is hung  over them and the prism.
  [A cheap and  excellent spectroscope,  planned by  Prof. J. P.
Cooke, of Harvard  College, and  made by Alvan Clark, of Cam-
bridgeport, Mass., has the prism inclosed in a circular wooden box
into which the three tubes are firmly fixed.]
  [The  spectra which are the most  serviceable for  analytical pur- 
 §  16.]            APPARATUS AND UTENSILS.                29

 poses are  mapped on plate  I.  The scale employed is  that  of
 Kirchhoff and Bunsen's instrument, in which the degree  50 coin-
 cides with the yellow sodium line.  The topmost scale gives  the
 positions of some of the more important dark lines (Fraunhofer's),
 of the solar spectrum, which are distinguished by the letters A, B,
 C, &c, and a and b.  The limits of the seven colors are indicated
 with sufficient accuracy by the vertical lines  drawn below each
 spectrum.  The long dashes of black drawn at the upper  edge of
 the  spectra of potassa,  rubidia, cassia and  soda,  represent broad,
 continuous bands of color.  The proper  spectral lines are shown at
 the lower edge of each scale.  The width of each line is seen from
 the  number  of degrees it covers.  Its  brightness is indicated  by
 its vertical depth in the  engraving.  The most  characteristic or
 important lines are designated by the  Greek numerals.  Special
 notice of them is given in Section HI.
   In using the spectroscope it is not always sufficient to perceive a
 line  with its appropriate color; its position with relation to known
 standards must be likewise ascertained.  This is  done by making
 for each spectroscope a diagram of the spectra, similar to plate I.
 For  most purposes, it is however  only  needful to map the more
 important lines.  Any arbitrary scale being drawn, the lines  are
 placed against degrees corresponding to those seen  in the spec-
 troscope, when beads of the purest  accessible  compounds of  the
 various  alkalies and alkaline  earths are placed in the flame.  To
 insure uniformity the left edge of the  soda line, which is rarely
 absent even in specially prepared salts, is brought to coincide with
 the degree 50° or 100°  of the scale  of the instrument.  To  the
 position once  adopted, the scale must  always be brought before
 taking observations, if by any means it has  been disturbed.]
  In many respects the  spectroscope  opens a new era in chemical
analysis, for with its aid we are able to detect quantities of sub-
stances  that  are not recognizable in any other manner.  At the
same time the results possess the utmost possible certainty, and are
arrived  at in a few moments.
           APPENDIX  TO  SECTION  I.

                             §  16-
                  Apparatus  and Utensils.
  As many students of chemical analysis might find some difficulty
in the selection of the proper apparatus, &c, I append here a list
of the  articles which are required for  the  performance of simple 
30                      OPERATIONS.                   [§ 16-

experiments and investigations, together with instructions to guide
the student in the purchase or making of them.
  1. A Spirit-Lamp with Double Draught (§ 14, Fig. 11).
  2. A Plain Spirit-Lamp op Glass (§ 14, Fig. 13), or instead of
the above, when gas  is at  hand,  a  Bunsen's Gas-lamp with
chimney (§ 14, Figs. 14, 15 and 17).
  3. A Blowpipe (see § 13).
  4. A Platinum crucible which will contain about a quarter of
an ounce of water, with a cover of the form of a shallow dish; it
must not be too deep in proportion to its breadth.
  5. Platinum foil, as smooth and clean as possible, and not very
thin: length about 1| inches; width about 1  inch.
  6. Platinum wire (see § 13, and  § 14, Figs. 10 and 18); three
or four  stronger and  as many finer wires  are amply sufficient.
They are kept most conveniently in a glass half filled with dilute
hydrochloric acid, most of the beads being dissolved by that fluid
when left in contact with it for some time ; the wires may thus be
always kept clean.
  7. A Stand with twelve test tubes (Fig. 17); 6 to 8 inches is
about the proper length of the tubes; from % to one inch the proper
                            Fig. IT.

width.   The pegs on the  upper shelf serve for the clean tubes,
which may thus be always kept dry and ready for use.  The tubes
must be made  of thin white glass, and so well annealed that they
do not crack,  even though boiling  water be poured  into them.
The rim must be quite round, and slightly turned  over;  it ought
not to  have a lip, as  this  is  useless, simply preventing  the tube
being closely stopped with the finger, and also hindering the agita-
tion of its contents.
  8.  Several beaker glasses  and small  retorts of thins well
annealed glasses. 
§17.]
REAGENTS.
31
  9.  Several porcelain  evaporating dishes, and  a variety
of small porcelain crucibles.  Those of the royal manufacture
of Berlin are unexceptionable, both in shape and durability.
  10. Several glass funnels of various sizes.  Their sides must
incline at an angle of 60°, and merge abruptly into the neck.
  11. A Washing bottle of a capacity of about a pint (see § 6).
  12. Several glass rods  and  glass tubes.   The  latter are
bent, drawn out, &c, over a Berzelius spirit-lamp, or over the gas-
lamp ; the former are rounded at the ends by fusion.
  13. A  selection of small watch  glasses.
  14. A  small agate mortar.
  15. A  pair of small  steel or brass  pincers, about four or five
inches long.
  16. A  Wooden filtering stand (see § 5).
  17. A  Tripod of thin iron, to support the dishes, &c, which it
is intended to heat over the  small spirit or gas-lamp.
  18. The colored glasses  mentioned  in § 15, especially blue and
green.
                    SECTION   II.

                        REAGENTS.

                            § 17.
  A variety of phenomena may manifest  themselves upon  the
decomposition or combination  of bodies.  In some cases liquids
change  their color, in  others precipitates are formed; sometimes
effervescence takes place, and sometimes deflagration, &c.  Now,
if these  phenomena are very striking, and attendant only upon the
action of two definite  bodies upon one another, it is obvious that
the presence of one of these bodies may be detected by means
of the other: if we  know, for  instance, that a white  precipitate
of certain definite properties is formed  upon mixing baryta with
sulphuric acid, it is clear that if, upon adding bartya to any liquid,
we  obtain a precipitate exhibiting these properties, we may con-
clude that this liquid contains sulphuric acid.
  Those substances which indicate the presence of others by any
striking phenomena are called reagents.
  According to the different objects attained by their application
we  make a distinction between general and special reagents.   By
general reagents we understand those which serve to determine the
class or group to which  a  substance belongs j and by special
reagents those which serve to detect  and determine  bodies indivi-
dually.  That the line between the two divisions cannot be drawn 
32
REAGENTS.
[§17.
with any degree of precision, and that one and the same substance
is  often made to serve both as a general and  special reagent, can.
not well be held a valid objection  to this classification, which, in
fact, is simply intended  to induce  a  habit of employing reagents
always for a settled purpose—viz., either simply to find  out the
group to which the substance under examination belongs,  or to
determine the latter individually.
  Now whilst  the  usefulness  of general reagents depends princi.
pally upon their efficiency in strictly characterizing groups of bodies,
and often effecting a complete separation of the bodies belonging
to one group from those belonging  to  another, that of special
reagents  depends upon their being  characteristic, and upon their
being sensitive.  We call a reagent characteristic, if the alteration
produced by it, in the  event of the body tested for  being present,
is so distinctly marked as to admit of no mistake.  Thus, iron is a
characteristic reagent for copper, protochloride of tin for mercury,
because the  phenomena  produced by these  reagents—viz.,  the
separation of metallic copper  and of globules of mercury, admit
of no mistake.  We call a reagent sensitive or delicate, if its action
is  distinctly perceptible,  even  though a very minute  quantity only
of the substance  tested  for be  present;  such  is, for instance, the
action of starch upon iodine.
  Very many reagents are both characteristic  and  delicate; thus
for instance, terchloride of gold for protoxide of tin ; ferrocyanid
of potassium for sesquioxide of iron  and oxide of  copper, &c.
  I need hardly mention that, as a  general rule, reagents must be
chemically pure—i. e., they must consist purely and simply of their
essential  constituents, and must contain no admixture of foreign
substances.  We  must therefore make it  an invariable rule to test
the purity of our reagents before we  use  them, no matter whether
they be articles of our own production or purchased.   Although
the necessity of this is fully admitted on all hands, yet we find that
in practice it is too often neglected: thus it is by no means uncom-
mon to see alumina entered among the substances detected in an
analysis, simply because the solution of potassa used as one of the
reagents  happened to contain  that  earth;  or iron, because the
chloride of ammonium used was not free from that metal.   The
directions given in this section for testing the purity of the several
reagents, refer, of course, only to the presence of foreign matter
resulting from the mode of their preparation, and  not to mere acci-
dental admixtures.
  One of the most common sources of error in qualitative analysis
proceeds from missing the proper measure—the  light quantity—
in the application of reagents.  Such terms as " addition in excess,"
" supersaturation," &c, often induce  novices to suppose  that they
cannot add too much of the reagent, and thus some will fill a test 
§17.]
REAGENTS.
33
tube with acid, simply to  supersaturate a few drops of an alkaline
fluid, whereas every drop of acid added,  after the neutralization
point has  once been reached, is to be looked upon as an excess of
acid.   On the other hand, the addition of  an insufficient amount is
to be equally avoided, since a reagent, when added in insufficient
quantity,  often  produces phenomena quite different from  those
which  will appear if the same reagent be  added in excess: e. g., a
solution of chloride of mercury yields a white precipitate, if tested
with a small quantity of hydrosulphuric acid; but if treated with
the same  reagent in excess, the precipitate is black.  Experience
has, however, proved that  the  most  common mistake beginners
make,  is to add the reagents too copiously.  The reason why this
over-addition must impair the accuracy of the  results, is obvious;
we need simply bear in mind that the changes effected by reagents
are perceptible within certain limits only, and that therefore they
may be the more readily overlooked the nearer we approach these
limits by diluting the-fluid.
   No  special and definite  rules can be  given for avoiding this
source of error; a general rule may, however, be laid down, which
will be found to answer  the purpose, if not in all, at least  in the
great  majority of cases.   It is simply this : let  the student always
reflect, before the  addition of a reagent, for what purpose he applies
it, and what are the phenomena he intends to produce.
   We divide reagents into two classes, according to whether the
state of fluidity  which is indispensable for the  manifestation of
the action of reagents upon the various bodies, is brought about
by the application of heat,  or  by  means of liquid solvents; we
have  consequently, 1. Reagents  in the humid  way; and 2,
Reagents  in the dry way.   For greater  clearness we subdivide
these two principal classes as follows :—

A. REAGENTS IN THE  HUMID WAY.
    I. Simple Solvents.
   n. Acids (and Halogens).
       a.  Oxygen acids.
       b. Hydrogen acids and halogens.
       c. Sulphur acids.

 m. Bases (and Metals).
       a.  Oxygen bases.
       b. Sulphur bases.

 IV. Salts.
       a.  Of the alkalies.
       b.  Of the alkaline earths.
       c. Of the oxides of the heavy metals.
                               3 
34
WATER.
[§18.
   V.  Coloring  Matters  and Indifferent Vegetable  Sub-
stances.

B. REAGENTS IN THE  DRY WAY.
   I. Fluxes.
   H. Blowpipe  reagents.

          A. REAGENTS IN THE HUMID WAY.
                      I. Simple Solvents.
   Simple solvents are fluids which do not enter into chemical com-
bination with the bodies dissolved in them ; they will accordingly
dissolve any quantity of matter up to a  certain  limit,  which is
called the point of saturation, and is in a measure dependent upon
the temperature of the solvent.  The essential and characteristic
properties of the dissolved substances (taste, reaction, color, &c.)
are not destroyed by the solvent.  (See §  2.)

                             § 18.
                       1.  Water (H O).
   Preparation.—Pure water is obtained by distilling spring water
from a copper still, with head and  condenser made of pure tin, or
from a glass  retort; which latter apparatus, however, is less suita-
ble for  the  purpose.   The distillation is  carried  to about  three-
fourths  of the quantity operated upon.  If it is desired to have the
distilled water perfectly free from carbonic  acid, and carbonate of
ammonia, the portions passing over first must be thrown away.  In
the larger chemical, and in most pharmaceutical  laboratories, the
distilled water required is  obtained from the steam  apparatus
which serves for drying, heating, boiling, &c.  Rain water collected
in the open air may in many cases be substituted for distilled water.
   Tests. -Pure distilled  water  must be colorless, inodorous, and
tasteless, and must leave no residue upon evaporation in a platinum
vessel.  Sulphide of ammonium  must  not alter it  (copper,  lead,
iron) ; its transparency must not be in the least impaired by basic
acetate  of lead (carbonic acid, carbonate of ammonia), nor, even
after  long  standing, by oxalate of ammonia  (lime), chloride  of
barium  (sulphates), or nitrate of silver (metallic chlorides).
   Uses.—We use water* principally as a simple solvent for a great
variety  of substances; the most convenient way of using it is with
the washing bottle  (see  § 6, Fig. 2), by which means a large or
fine stream  may  be obtained.   It  serves  also  to effect the con-
version  of several neutral metallic salts  (more particularly terchlo-

  * In analytical experiments we use only distilled water; whenever, therefore, the
term "water" occurs in the present work, distilled water is meant. 
§§ 19, 20.]
SULPHIDE  OF CARBON.
35
ride of antimony and the salts of bismuth) into soluble acid, and
insoluble basic compounds.

                             § 19.
                     2. Alcohol (C4 H6 02).
  Preparation.—Two sorts  of  alcohol   are  used  in  chemical
analysis: viz., 1st, spirit  of wine of 0-83 or 0'84 spec.gr. (= 91 to
88 per cent, by volume, spiritus vini rectificatissimus of the shops) ;
and 2nd, absolute alcohol.   The latter may be prepared sufficiently
absolute  for most  purposes, by bringing together in a retort or
still 1 part of fused chloride of calcium, and 2 parts of commercial
alcohol of  about 90 per cent., digesting two or three days until the
chloride  of calcium is dissolved and  then slowly distilling.  The
distillate is tested  as to  its sp. gr. from time to time, and the first
portions which are  lighter than 0.81 (= 96.5 per cent, by volume,)
are reserved as absolute alcohol; those passing over later are sepa-
rately collected.
   Tests.—Pure alcohol must completely volatilize, and ought not to
leave the least smell of fusel oil, when rubbed between the  hands;
nor should it redden litmus  paper.   When kindled, it must burn
with a faint bluish, barely perceptible  flame.
   Uses.—Alcohol  serves  (a), to  effect the separation  of bodies
soluble in this fluid from others which  do not dissolve in it,  e.g., of
chloride of strontium from chloride of barium; (b)  to precipitate
from aqueous solutions  many substances  which  are insoluble in
dilute alcohol, e.g.,  gypsum, malate of lime; (c)  to produce  various
kinds  of ether,  e.g., acetic  ether,  which  is characterized by  its
peculiar  and  agreeable  smell;  (d) to reduce, mostly with  the
co-operation of  an acid, certain peroxides and metallic acids, e.g.,
binoxide of lead, chromic acid, &c.;  (e) to detect certain substances
which impart a characteristic tint  to its  flame, especially  boracic
acid, strontia, potassa, soda, and lithia.

                             §  20.
                3. Ether  (C, H5 O).
                4. Chloroform  (C2 H Cl3).
                5. Sulphide of Carbon  (C S2).
  These solvents find but very limited application in the analysis
of inorganic  bodies.  They are  chiefly used to detect and isolate
iodine and bromine.  Chloroform and  sulphide of carbon are much
preferable  to ether for this purpose.
  These  substances are most  conveniently purchased, as their pre-
paration on the small scale is troublesome.
   Tests.—Ether must have a sp. gr. of 0.725, and must require 9
parts of water for  its solution.  The  solution must not affect  test 
36                        REAGENTS.                     [§ 21.

papers.   Placed upon a watch glass, it must evaporate at ordinary
temperatures rapidly and completely.
  Chloroform must be colorless  and have  a  sp. gr. of 1.49.  It
must be free from acid reaction, and not be  rendered turbid by
solution of nitrate of silver.  When agitated in a tube with two
volumes of water, it must not suffer perceptible diminution of bulk.
It must  evaporate easily and completely at common temperatures.
  Sulphide of Carbon must be colorless, without action on carbonate
of lead, and  must volatilize readily and  perfectly at usual tem-
peratures.

               II. ACIDS AND HALOGENS.

                             § 21.
  The acids—at least those of more strongly pronounced character
—are soluble in water.  The solutions taste acid,  and redden
litmus paper.  Acids are divided into oxygen acids, sulphur acids,
and hydrogen acids.
  The oxygen acids, produced generally by the combination of  a
non-metallic element with  oxygen, combine with water in definite
proportions to hydrated acids.  It is with these hydrates that wc
have usually to  do  in analytical processes; they  are commonly
designated by the name of "free  acids," as the accession of the
water does hot  destroy their acid properties.  In the action of
hydrated acids upon oxides of metals, the oxide takes the place of
the water of hydration, and an oxygen salt is formed (H O, S 03
+ K O = K O, S  03 + H O).   Where these  salts  are  the
product of the  combination of an acid with  a strong base, their
reaction (supposing  the combining acid also to be a strong acid)
is neutral; the salts  formed with weaker  bases, for instance, with
the oxide of  a heavy metal, generally show acid reaction, but are
nevertheless called neutral  salts, if the oxygen of the base bear the
same proportion  to that of the acid in which it  is  found in the
distinctly neutral salts of the same acid, or, in other terms, if  it
corresponds  with the saturation  capacity of the  acid.   Sul-
phate of  potassa (K O, S  03) has  a  neutral reaction, whilst the
reaction of sulphate of copper (Cu O, S 03)  is acid; yet the latter
is nevertheless  called  neutral sulphate of copper, because  the
oxygen  of the oxide of copper in it bears a proportion of 1 : 3 to
that of the sulphuric  acid, which is the  same proportion as the
oxygen  of the potassa bears  to that of the sulphuric acid  in the
confessedly neutral sulphate of potassa.
  The hydrogen acids  are formed by the combination  of  the  salt
radicals with hydrogen.  Most of these possess  the characteristic
properties  of acids in a high degree.   They neutralize oxygen
bases with formation of haloid salts and water, H CI and Na O = 
§22.]
SULPHURIC ACID.
37
Na CI and H O, - 3 H CI and Fe2 03 =Fe2 Cl3 and 3 H O.  The
haloid salts produced by the action  of  powerful hydrogen  acids
upon strong bases, have a neutral reaction; whilst the solutions of
those  haloid salts which have been produced by the action of power-
ful hydrogen acids upon weak bases (such as the oxides of the heavy
metals), show acid reactions.
  The sulphur acids are more frequently the result of the combi-
nation of metallic than of non-metallic elements with sulphur; they
combine  with  sulphur bases to sulphur salts, H S +  KS = KS,
H S, - Sb S3  +  3 Na S  = 3 Na S, Sb  S5.    The sulphur  acids
being weak acids, the soluble sulphur salts have all of them alkaline
reaction.

                     a. OXYGEN ACIDS.

                             § 22.
                1. Sulphuric Acid (H O, S 03).
  We use—
  a.  Concentrated sulphuric acid of commerce, English oil  of
vitriol.
  b. Concentrated pure srdphuric acid.
  The surest plan of preparing pure and strong sulphuric acid is as
follows:
  Oil of vitriol  is  poured into 4  times its weight of water, and
a slow  stream of  hydrosulphuric acid gas is passed  through the
mixture for some hours.   The acid is now left at rest several days;
the clear liquid is then poured off from  the precipitated sulphur,
sulphide of lead and sulphide of arsenic, and heated in a tubulated
retort with the beak inclined upwards, and with open tubulure,
until vapors of sulphuric acid escape with those of the water.
  The acid so purified is fit for nearly all the purposes of chemical
analysis; if it is wished, however, to free it also from non-volatile
substances, it  may be  distilled from  a luted non-tubulated retort
resting  on a  reversed crucible cover,  and heated directly over
charcoal.
  The neck of the retort must reach  so far into  the receiver that
the acid distilling over drops directly into the body. Refrigeration
of the receiver by means of water is unnecessary and even dan-
gerous.   To prevent the flask coming into direct contact with the
hot neck of the retort, some asbestos in long fibres is wrapt round
that part of the neck where such contact might be apprehended.
  As  soon as the drops in the retort neck  become  oily in con-
sistence,  the  receiver is  changed  and  the  concentrated acid is
collected by itself.
  c. Dilute sulphuric acid.  This is prepared by adding to 5  parts
of water in  a leaden  or porcelain  dish, gradually,  and whilst 
33
NITRIC  ACID.
[§23.
stirring, 1 part of  concentrated  sulphuric acid.   The sulphate of
lead which  separates  is  allowed to subside, and the clear fluid
finally decanted from the precipitate.
   Tests.—Pure sulphuric  acid must be colorless; when colorless
solution of sulphate of protoxide of iron is poured upon it in a test
tube, no red tint must mark  the  line of contact of the two fluids
(nitric acid,  hypo-nitric acid);  when diluted with twenty parts of
water, it must not impart a blue  tint to a solution of iodide of
potassium mixed with starch paste  (nitrous acid).
  When mixed with pure zinc and water, it must yield hydrogen
gas; which,  on being passed through a red-hot tube, must not
deposit the  slightest  trace of arsenic.  It must leave  no residue
upon evaporation on  platinum, and must remain  perfectly  clear
upon dilution with  four or  five parts of spirit of wine (oxide of
lead, sesquioxide of iron, lime).  The presence of small quantities
of lead is detected most  easily by adding some hydrochloric acid
to the sulphuric  acid in  a  test tube.  If the  point  of contact is
marked by turbidity (chloride of lead), lead is present.  (Ldwen-
thai.)
   Uses.—Sulphuric acid has for most bases  a greater affinity than
almost any  other acid; it  is  therefore  used principally for the
liberation and expulsion of other acids, especially of phosphoric,
boracic, hydrochloric, nitric, and acetic acids.
  Several substances  which cannot exist in an anhydrous  state
(e. g.,  oxalic  acid), are decomposed when  brought into contact
with concentrated sulphuric acid;  this decomposition is owing to
the  great affinity which sulphuric  acid possesses for water.   The
nature of the  decomposed body may in  such cases be inferred from
the liberated products of the decomposition.  Sulphuric acid is also
frequently used for the evolution of certain gases, more particularly
of hydrogen, and hydrosulphuric acid.  It serves also as a special
reagent for the detection and precipitation of baryta, strontia, and
lead.  What kind of sulphuric acid is to be used,  whether the pure,
or the purified acid, or the ordinary acid of commerce, whether con-
centrated or dilute, depends upon what the  circumstances in each
case may require.   It will, however, be found that the necessary
directions on this point are generally given in the present work.

                             §23.
                 2. Nitric Acid (H O, N  05).
  Preparation.—a. Heat  crude nitric acid of commerce, as free as
possible from chlorine, and of a specific gravity of at least 1*31,* in a
glass retort, to boiling, with addition of some nitrate of potassa;
let the distillate run into a receiver kept cool, and try from time to
* A weaker acii will not suit this mode of preparation. 
§ 24.]
ACETIC ACID.
39
time whether it still continues to precipitate or trouble solution of
nitrate of silver.   As soon as this ceases to be the case, change the
receiver,  and distil until  a trifling quantity  only remains in the
retort.  Dilute the distillate with  water until the specific gravity
of the diluted acid is 1-2.
  b. Dilute crude nitric acid  of commerce of about  T38 specific
gravity, with two-fifths of its weight of water;  add solution of
nitrate of silver as long as a precipitate of chloride of silver con-
tinues to form, [and in considerable excess besides.  Mulder.—The
solution of a coin in the same  acid may be economically employed
instead of pure nitrate.]   Let the precipitate subside out of access
of light, decant the perfectly clear supernatant acid into a tubu-
lated retort ;  add some nitrate of  potassa, free from chlorine, and
distil until only a  small quantity remains, taking care to  attend to
the proper  cooling of  the fumes  distilling over.   Dilute the dis-
tillate, if necessary,  with water  until it has a  specific gravity
of 1-2.
   Tests.—Pure  nitric acid must be colorless, and  leave no residue
upon evaporation on platinum foil.   Addition of solution of nitrate
of silver, or of nitrate of  baryta, must not  cause  the slightest tur-
bidity in it.   It is advisable to  dilute the acid with water before
adding the reagents,  as otherwise nitrates may precipitate.
   Uses.—Nitric acid serves as a chemical solvent for metals, oxides,
sulphides, oxygen salts, &c. With metals, and sulphides of metals,
the acid oxidizes  the metal present first, at the expense of part oi
its  own oxygen, and then dissolves the oxide, forming a nitrate.
Most oxides are  dissolved by nitric acid at once as nitrates; and
so are also most of the insoluble salts with weaker acids, the latter
being expelled in  the process by the nitric acid.   Nitric acid dis-
solves also  salts with soluble,  non-volatile  acids, as e. g. phosphate
of lime, with  which it forms nitrate of lime and acid phosphate of
lime.  Nitric acid is used  also as an oxidizing agent: for instance,
to convert protoxide  of iron into sesquioxide, protoxide of tin into
binoxide, &c.

                              §24.
            3. Acetic Acid (H O, C, H3 O =H 0, A).
  A highly concentrated acetic  acid is not required in qualitative
analytical processes;  the common  acetic  acid of commerce, which
contains 25  per cent, of anhydrous acid, and has a specific gravity
of 1-04, answers the purpose.
  Tests.—Pure acetic acid must leave  no residue  upon evapora
tion, and—after saturation with  carbonate of soda—emit no empy
reumatic odor.  Hydrosulphuric acid, solution of  nitrate  of silver,
and solution of nitrate of  baryta must not impair the transparency 
4:0                  HYDROCHLORIC ACID.           [§§ 25, 26.

of the dilute acid, nor must sulphide of ammonium, after neutrali-
zation of the acid by oxide of ammonium.  Solution of indigo must
not lose its color, when heated with the acid.
  If the acid is not pure, add some acetate of soda  and  redistil
from a glass retort, not quite to dryness; if it contains sulphurous
acid (in which case hydrosulphuric acid will produce a white tur-
bidity in  it), digest it first with  some binoxide of lead or finely
pulverized binoxide of manganese, and then distil  with acetate of
soda.
   Uses.—Acetic acid possesses a  greater solvent power for some
substances than for others ; it is used, therefore, to distinguish the
former from  the latter;  thus it serves, for instance, to distinguish
oxalate of lime from phosphate of lime.  Acetic acid is occasionally
used also to acidulate fluids where  it is wished to avoid the employ-
ment of mineral acids.

                             § 25.
        4. Tartaric Acid  (2 H O, C3 H4 O10=2 H O, f).
  The tartaric acid of commerce  is sufficiently pure for the pur-
poses of chemical analysis.  It is kept best in powder, as its solu-
tion suffers decomposition after a  time, a white film forming upon
its surface.   For use, it  is dissolved in a little water with the aid
of heat.
   Uses.—The addition of tartaric  acid to solutions of sesquioxide
of iron, protoxide of manganese, and various other oxides of metals,
prevents the usual precipitation of these metals by an alkali; this
non-precipitation is owing to the formation of double tartrates,
which are not decomposed by alkalies.
  Tartaric acid may therefore be employed to effect the separation
of these metals from others, the precipitation of which it does not
prevent.   Tartaric acid forms a difficultly soluble salt with potassa,
but not so with soda ;  it is, therefore, one of our best reagents to
distinguish between the two alkalies.
  The bitartrate of soda is even better adapted for the detection
of potash than the free acid.  It is prepared by dividing a solution
of tartaric acid into two equal portions, neutralizing one with car-
bonate of soda (which is best done by adding solution of the latter
to the boiling solution of the  acid), adding  the other  portion of
acid, and evaporating the solution  to crystallization.  For use, one
part of the salt is dissolved in about 10 parts of water.

         b. HYDROGEN ACIDS AND HALOGENS.
                             § 26.
                1. Hydrochloric Acid (H CI).
  Preparation.—Pour a  cooled mixture of seven parts of concen.
trated sulphuric acid and two  parts of water over four parts of 
 § 26.]               HYDROCHLORIC ACID.                   41

 chloride of sodium in a retort; expose  the  retort, with slightly
 raised neck, to the heat of a sand-bath, until the evolution of gas
 ceases; conduct the evolved gas, by means of a double limbed tube,
 into a flask containing six  parts of water, and take care to keep
 this vessel constantly cool.   To prevent the gas from receding, the
 tube ought only to dip about one line into the water of the flask.
 When the operation is terminated, try the specific gravity of the
 acid produced, and  dilute with water until it marks from 1-11 to
 1*12.  If you wish to ensure the absolute purity of the acid, and its
 perfect freedom from every trace of arsenic and chlorine, you must
 take care to free the sulphuric acid, intended to be used in the pro-
 cess, from arsenic and the oxygen compounds of nitrogen, accord-
 ing to the directions of § 22.  A pure acid may also be prepared
 cheaply from the crude hydrochloric acid of commerce, by diluting
 the latter to a specific gravity of 1*12, and distilling the fluid, with
 addition of some  chloride of sodium.   If the  crude acid contains
 chlorine, this should be removed first by the  cautious  addition of
 solution of sulphurous acid, before proceeding to the distillation;
 if, on the other hand, it contains sulphurous acid, this  is removed
 in the same way by the cautious addition of some chlorine water.
  Commercial  hydrochloric acid not infrequently contains a very
 slight trace of chloride of arsenic, derived from arsenical  oil of
 vitriol.  To remove this, conduct into the acid a stream  of hydro-
 sulphuric  acid, decant  after  standing for  a  day or two, from the
 deposited sulphur and sulphide of arsenic, and heat until all hydro-
 sulphuric acid is  expelled.
   Tests.—Hydrochloric acid intended for the  purposes of chemical
 analysis, must be perfectly colorless,  and  leave no residue  upon
 evaporation.  It  must  not  impart  a  blue tint  to a solution  of
 iodide of potassium mixed with starch paste (chlorine), nor dis-
 color a fluid made faintly  blue with iodide of starch  (sulphurous
 acid).   Chloride  of barium ought not  to produce a precipitate in
 the  highly diluted  acid  (sulphuric acid).  Hydrosulphuric acid
 must leave it unaltered.    Sulphocyanide of potassium must not
 impart the least red tint to  the diluted acid.
   Uses.—Hydrochloric acid  serves as a solvent for a great many
 substances. It dissolves  many metals and sulphides of metals,
 forming chlorides, with evolution of hydrogen or of hydrosulphuric
 acid.  It dissolves lower and higher oxides in the form of chlorides,
 the solution being, in the case of the higher oxides, mostly attended
 with liberation of chlorine.  Salts with  insoluble or volatile acids
 are also converted by hydrochloric acid into  chlorides, with sepa-
ration  of the original acid; thus carbonate of lime is converted
into chloride of calcium, with liberation of carbonic acid.  Hydro-
chloric acid dissolves  salts with non-volatile and soluble  acids,
apparently without decomposing them (e. g., phosphate of lime) 
42
CHLORINE.
[§27.
but the fact is that, in cases of this kind, a metallic chloride and a
soluble acid salt of the acid of the dissolved compound are formed;
thus,  for instance, in the case of phosphate of lime, chloride of
calcium and acid  phosphate of lime are formed.  With salts of
acids  forming no  soluble acid compound with the  base present,
hydrochloric acid forms metallic  chlorides, the  liberated acids
remaining free in solution (borate  of lime).  Hydrochloric acid is
also applied as a special reagent for the detection and  separation
of oxide of silver, suboxide of mercury, and lead (see § 121) ;  and
likewise for the detection of free ammonia, with which it produces
in the air dense white fumes of chloride of ammonium.

                             §27.
            2. Chlorine (CI) and Chlorine Water.
  Preparation.—Mix 18 parts of common salt in coarse powder or
crystals with 15 parts of finely pulverized good binoxide of manga-
nese ;  put the mixture in a flask, pour a completely cooled mixture of
45 parts of concentrated sulphuric acid and 21 parts of water upon
it, and shake the flask:  a uniform and continuous evolution of
chlorine gas will  soon  begin,  which, when  slackening,  may be
easily increased again by the application  of a  gentle heat.  This
method of  Wiggers is excellent, and can be highly recommended.
Conduct the chlorine gas evolved, first through a flask containing
a little water, then into a bottle filled with cold water, and continue
the process until the fluid is  saturated.  To procure a solution of
chlorine entirely free from bromine, the wash-flask and receiving
bottle must be changed when about half the  gas has passed over.
The last portion  is pure.  The chlorine water  must be kept  in a
cellar, and  carefully protected from the action of light; since, if
this precaution is neglected, it speedily suffers complete decompo-
sition, being converted into dilute hydrochloric acid, with evolution
of oxygen  (resulting from the  decomposition of water).  Smaller
quantities, intended for use in the  laboratory,  are  best kept  in a
stoppered bottle, protected from the influence of light by a case of
pasteboard.   Chlorine  water which has lost its strong  peculiar
odor is unfit for use.
  Uses.—Chlorine has a greater affinity than iodine and bromine
for  metals  and  for hydrogen.  Chlorine water  is therefore an
efficient agent to effect the expulsion  of iodine  and bromine from
their compounds.   Chlorine serves, moreover, to convert sulphurous
acid into sulphuric acid, protoxide of iron  into sesquoxide, &c.;
and also to effect the destruction of organic substances, in presence
of water, as it withdraws hydrogen from the latter, enabling thus
the liberated oxygen to combine with the vegetable matters and to
effect  their decomposition.   For  this latter purpose  it is most
advisable to evolve the chlorine in the fluid which contains the 
 §§ 28, 29.]         HYDROFLUOSILICIC ACID.                43

 organic substances; this is effected by adding hydrochloric acid to
 the fluid, heating the mixture to boiling, and then adding chlorate
 of potassa.  This gives rise to the formation of chloride of potas-
 sium, water, free chlorine, and bichlorate  of chlorous acid, which
 acts in a similar manner to chlorine.

                              §28.
           3. Nltro-Hydrochloric  Acid.   Aqua regia.
   Preparation.—Mix one part of pure nitric acid with from three
 to four parts of pure hydrochloric acid.
   Nitric  acid  and hydrochloric acid decompose each other,  the
 decomposition  resulting, in most cases, as  Gay-Lussac has shown,
 in  the formation  of two  compounds  which  are  gaseous  at  the
 ordinary  temperature, N 02 Cl2 and N 02  CI, and of free chlorine
 and water.  If one equivalent of N Os is used to three equivalents
 of CI H, it may be assumed that only chloro-hyponitric acid  (N
 O, CI,),  chlorine and water, are formed  (N 05 -f  3 H CI = N
 O, Cl2 +  CI + 3 H O).
   This decomposition occurs as soon as the fluid is saturated with
 the gas; but it recommences the instant this state of saturation is
 disturbed  by the application of heat or by decomposition  of  the
 acid.  The presence of the free  chlorine, and also,  but in  a very
 subordinate degree, that of the acids named, makes aqua regia  our
 most powerful solvent for metals (with  the  exception of those
 which form insoluble compounds with chlorine).   Nitro-hydro-
 chloric acid serves principally to effect the  solution  of gold and
 platinum, which metals  are  insoluble both in hydrochloric  and in
 nitric acid; and also to decompose various  metallic sulphides, e. g.,
 cinnabar,  pyrites, &c.

                             § 29.
           4. Hydrofluosilicic Acid (H Fl, Si Fl2).
   Preparation.—Take quartz sand, wash off every particle of dust,
 and dry  thoroughly.  Mix one part of the dry sand  intimately
 with one part of perfectly dry fluor spar in powder; pour six parts
 of concentrated sulphuric  acid  over the mixture in a strong glass
 flask or in  a non-tubulated  retort, dry inside, and mix carefully by
 shaking the vessel.   As the mixture swells up, when getting warm,
 it must at first fill the vessel  only to one-third.   The mouth of the
 flask or retort must be closed with a perforated cork, or a cap of
india-rubber, into which  one end of a somewhat wide glass tube,
suitably bent at right angles,  is fitted air-tight; the other limb
reaching to the bottom  of  a tall  flat-bottomed glass jar with just
sufficient mercury to allow the end of the tube to dip into it to the
extent of several lines; the mercury in the jar is covered with four 
44
HYDROSULPHURIC ACID.
[§30.
parts of water.   Promote  the  disengagement  of  fluosilicic gas,
which commences even in the cold, by exposing  the flask or retort
to a moderate heat  in the  sand-bath.    Towards the end of the
process a pretty strong heat should be applied.   Every gas bubble
ascending through the mercury produces in the water a precipitate
of hydrated silicic acid.   The rationale of this process is that, of
every three equivalents of fluoride of silicon (Si Fl2), one equivalent
decomposes with two equivalents of water into silicic  acid (Si O^),
which separates, and hydrofluoric acid, which combines with the
two undecomposed equivalents of fluoride of silicon, forming hydro-
fluosilicic acid.
          3 Si Fl2 + 2 H O = 2 (H Fl, Si Fl2) + Si 02.
  The precipitated hydrate of silicic acid renders the liquid gela-
tinous, and it is for this reason that the aperture of the  exit tube
must be placed under mercury, since it would speedily be choked
if this precaution were neglected.  The same end may be attained
also  by attaching a funnel to the exit tube, by means of vulcanized
india-rubber, and letting  the funnel alone  dip into the water.  It
sometimes happens in  the  course, and especially towards the end
of the operation, that the gas forms  complete channels of silica in
the gelatinous liquid, through which it gains the surface without
undergoing decomposition, if the liquid is not occasionally stirred.
When the evolution  of gas has completely ceased, throw the gela-
tinous paste upon  a linen  cloth, squeeze the fluid through, and
filter it afterwards.   Keep the filtrate for use.
  Tests.—Hydrofluosilicic acid,  mixed with  two parts of water,
must produce no precipitate in solutions of salts  of  strontia.
   Uses.—Bases decompose  with  hydrofluosilicic  acid,  forming
water and metallic  silicofluorides.  Many of these are insoluble,
whilst others are soluble; the latter may therefore by means  of
this  reagent be distinguished from the former.  In the course  of
analysis, hydrofluosilicic  acid is  applied  simply  for the detection
of baryta.

                    c. SULPHUR ACIDS.

                             §30.
   5. Hydrosulphuric Acid (Sulphuretted Hydrogen) (H S).
  Preparation.—Hydrosulphuric acid  gas is evolved best  from
sulphide of iron, which is  broken  into small lumps, and then treated
with dilute sulphuric  acid.  Fused sulphide of iron may be procured
so cheaply in commerce  that it  is hardly worth while to take the
trouble  of preparing it expressly.  It  may, however, be made, if
necessary, by heating iron turnings or nails, from 1 to \\ inch long,
in a  Hessian crucible to a white heat, and then adding small lumps 
30.]
HYDROSULPHURIC  ACID.
45
Fig. 22.
 of roll-sulphur until the  entire  contents of  the crucible  are in
 fusion.  As soon as this is the
 case, the fused mass is poured
 out on  sand, or into an old
 Hessian crucible.  By making
 a hole in the bottom  of the
 crucible in which the mixture
 is fused, the sulphide of iron
 will, as  fast as it  forms, run
 through, and may be received
 in a coal-shovel placed in the
 ash-pit.   Or, introduce an in-
 timate mixture of thirty parts
 of iron filings and twenty-
 one parts of flowers of sul-
 phur, gradually and in small
 portions at a time, into a red-hot crucible, awaiting always  the
 incandescence of the portion last introduced, before proceeding to
 the addition of a fresh one.   When the whole mixture has been
 brought into the crucible, cover the latter closely, and expose it to
 a more intense heat, sufficient  to fuse the sulphide of iron.
   The evolution of the gas is  effected in the apparatus illustrated
 by Fig.  22.
   Pour  water over the sulphide of iron in a, add concentrated  sul-
 phuric acid, and shake  the  mixture; the evolved gas is washed in
 c.  When a sufficient  quantity of gas  is evolved, pour the fluid
 from off the still undecomposed sulphide of iron, wash the bottle
 repeatedly with water,  fill it with that fluid, and keep it for the next
 operation.  If you neglect this, the apparatus will speedily become
 incrusted  with crystals of sulphate of protoxide of iron, which is
 apt to interfere injuriously with subsequent processes of evolution
 of gas.
   For larger laboratories,  or for chemists, having to operate  often
 and largely with hydrosulphuric  acid, I can recommend the lead
 apparatus  designed by myself, which I have now for several years
 employed  with the most satisfactory results in my own laboratory*
 (see Figs.  23 and 24).
   abed and e f g h (Fig. 24) are two cylindrical leaden vessels,
soldered with pure  lead.  They are both of the same  size  (in  my
own apparatus 13 inches high, and 12 inches in diameter),   i is a
false bottom of lead, perforated like a sieve, placed about 2 inches
above the  actual bottom of the vessel, and resting on  leaden feet,
which support  it on  the sides as well as also more particularly in

  * The apparatus is made  by Mr. Siumpf of Wiesbaden, mechanist, and fullj
answers all reasonable demands, both as regards workmanship and price. 
46                 HYDROSULPHURIC ACID.              [§ 30.
                            Fig. 23.

                          the middle.   The numerous holes in
                          the sieve-like bottom have a diameter
                          of 0.06 of an inch; k shows the opening
                          through which the sulphide of iron is
                          introduced  into the vessel.   In  my
                          apparatus this aperture has a diameter
                          of 2f inches, and is closed by putting
                          a greased leather ring on its broad
                          smooth rim, and pressing down upon
                          this by means of three thumb-screws,
                          the  broad rim of the  smooth turned
                          cover.  I shows the  opening through
                          which the solution of sulphate of prot-
                          oxide of iron is drawn off; it will be
                          seen by the drawing that the  bottom
                          of the vessel (g h) slants towards the
                          part where  this opening  is  placed.
                          The aperture has a diameter of about
                          1| inches; it is closed by means of a
          Fig. 24            smooth-turned broad and thick leaden
                          cap, fitting on the smooth-turned broad
rim, and pressed down upon  it  with a thumb-screw.  The  semi-
 
§30.]
HYDROSULPHURIC ACID.
47
 elliptical clamp which carries  the female  screw is movable, and
 hinged to the  sides of I in a manner to admit of its being put out
 of reach of  the liquid on drawing off the latter.   The construction
 of the filling  tube,  m,  may be learned from the drawing, and
 equally so that of the tube d h, which is intended to convey the
 acid from the  upper to the  lower vessel, and vice versd.  It will
 be seen from the drawing that this tube reaches down into the
 slanting  and deepened part of the bottom g h, without, however,
 actually touching the latter.  The tube c e is closed at the top, and
 has, therefore, no communication with the upper vessel,  being
 simply intended  to  let off the  gas  evolved in  e f g h; to which
 end  it is connected laterally by a branch tube, with the tube o ;
 this latter tube is fitted with a stop-cock (?i).  The tube q is closed at
 both ends, and serves simply as  an additional support for the  upper
 vessel.  The tubes may have an inner diameter of half an inch.
   The process  of filling  is conducted as  follows:  put 3*3 kilo-
 grammes* of fused sulphide of iron, broken in lumps, through the
 mouth k, upon the perforated bottom i ; screw the covers properly
 down upon k and I, shut  the  cock n, and pour through the funnel
 of m first 7  litres of water, then 1 litre of concentrated  sulphuric
 acid, and then again 7 litres of water.   The air in a b c d escapes
 in this operation  through p, even when the latter tube is already
 connected with the flasks r, s, t.
   If the  cock n is now opened, and one of the cocks u, the acid
 will flow through the tube d I into efgh; and through  o air will
 escape at first, followed by the hydrosulphuric acid evolved in ef
 g h.   As is  seen  in  the  figure, the tube o rises only to a certain
 elevation, wrhen it makes a bend, running on thence in a horizontal
 direction. As many cocks, u u, are added as is thought desirable;
 these cocks are  common brass gas stop-cocks, close-fitting and well
 ground in.  They are connected with  a small washing bottle ; a
 double bent  tube conveys the  gas from the latter,  with the co
 operation of a straight  tube  connected  with  it  by means of
 vulcanized india-rubber,  into the fluid which  it is intended to
 operate on;  this arrangement greatly  facilitates the cleansing of
 the straight tube dipping into the fluid.  Upon  now opening one
 of the cocks, u, the cock  n being of course also  open, you will at
 once  obtain  a  current of gas of any strength desired, which will
 keep on for days  in a continuous and  steady stream.  If all  the
 cocks u, are shut, the gas  evolved in efg h forces the acid back to
 the upper vessel through the tube h d, and the evolution ceases.
   The cessation of the evolution of gas is not instantaneous, how-
 ever as the sulphide  of iron in efg h remains still moistened with

  * The quantities here given are calculated  for an apparatus of the  dimensions
stated. 
48
HYDROSULPHURIC  ACID.
[§30
acid ; moreover, small particles of the sulphides will always crum-
ble off, and dropping through the sieve, come into contact with the
rest of the acid covering the bottom, g h.  Now the gas which
still continues to be evolved in e f g h, being  no longer able to
escape through o, forces the fluid up h d, and passing through the
acid in a b c d, makes  its way out through  p.  To save this gas
and keep it from poisoning the air, the flasks r, s, t are  connected
with p.   r contains cotton, and serves the purpose of a washing bot-
tle ;* s and t contain solution of ammonia; but the two flasks toge-
ther should contain no more than either of them can conveniently
hold ; since, as the pressure of the gas increases or  relaxes, the fluid
is forced from s to t, or back from t to s.  It will be readily under-
stood that  sulphide of ammonium is formed in these flasks.
  The evolution of gas ceases completely when  all the acid is con-
sumed, but there remains still the one half of the  sulphide of iron,
as the quantity used is calculated for double the  amount of  acid.
The solution of sulphate of protoxide of iron is therefore  drawn
off,  and 1 litre of acid and 14 of water again poured in as directed.
This apparatus is now made also of much less dimensions to adapt
it for smaller laboratories.
  The  apparatus described by Pohl deserves  mention as being
simple of construction and convenient in use. It is represented in
Fig. 25.  The bottle A containing  the dilute sulphuric  acid  may
                      contain from 1 to 3 or more quarts.  In the
                      caoutchouc stopper B, a  stout glass-rod  G,
                      of at least § of an inch in diameter, passes
                      with considerable friction.   Below, it bears
                      a perforated basket, K, of hard rubber.  It
                      is  lined with  coarse  linen  and filled  with
                      lumps of fused sulphide of iron.   When the
                      glass-rod is so far depressed that the sul-
                      phide of iron  just reaches  the acid,  a  slow
                      evolution of gas takes place.  The flow of
                      gas is  increased by immersing the basket,
                      or checked by raising it above the  liquid.
                      The  wide tube R, which forms  a part of
                      the delivery tube, is filled loosely with cot-
                      ton and perfectly serves the purpose of a
                      wash-bottle.f
                        [In the Sheffield Laboratory of Yale Col-
                      lege the supply of hydrosulphuric acid is
       ^p^T^        obtained from two  large  self-regulating

  *  A common washing bottle filled with water could not well be used, as  the
water would very speedily recede.
  \\ This form of Kemps gas generator is still more easily constructed by adopting
 
§ 30.]               HYDROSULPHURIC  ACID.                 49

generators, like those commonly employed in the Dobereiner hydro-
gen lamp.  To construct such a generator, procure a glass cylinder 8
or 9 inches in diameter, and 12 to 15 inches high, and a stout tubu-
lated bell-glass 4 to 5 inches wide and 2 or 3 inches shorter than the
cylinder. Procure also a basket of sheet-lead 3 inches deep, and an
inch narrower than the bell-glass, whose sides and bottom are per-
forated with a number of small holes.   Cast a circular plate of lead,
of diameter l£ inches larger than that of the cylinder and  £ of an
inch thick.  On what is intended for its under side  solder three
equidistant leaden strips to keep the plate  in proper position as a
cover for the cylinder.   Obtain a well-made brass gas-cock, fit to
each end of it either by  its screws  or by soldering,  a piece of
brass or leaden tube 3 inches long, ^ to f inches wide and stout
in metal.   Perforate the centre of the leaden plate, so that one of
these tubes will snugly pass the orifice and secure it  by solder,
leaving 2  inches of the tube projecting below the plate.  Attach
a stout copper hook to the lower end of the tube by which to hang
the leaden basket.  By means of a good tightly fitting cork and
cement, secure this  tube into  the  neck of the bell-glass air-tight
and so firmly that a  weight of several pounds will not break the
joining.  Hang the  basket, filled with lumps of fused  sulphide of
iron, within the bell and two inches above the bottom of the latter.
To the tube, which extends above the stop-cock, attach, by a good
cork, the  neck of a 4 or 6 oz.  tubulated globular receiver, which
is to be   loosely stuffed  with cotton.   To  the  tubulure of the
receiver fit a  tube bent at a right  angle.  On  the depending arm
of the latter  tube is adapted,  by a  rubber connector, the wide
tube which is to convey the gas into any solution.  The cylinder is
now filled with dilute sulphuric acid  (1 vol. to 14 water) to within
l£ inches of the top, the bell-glass, full of air, being in its place.
By opening the cock the air is expelled, and by the action of the
acid upon  the sulphide of iron the bell-glass is speedily filled  with
hydrosulphuric acid which replaces itself without any  waste  until
either  the acid is saturated or the  sulphide of iron is dissolved.
In cold weather this apparatus operates best when slightly warmed,
especially if the acid be not fresh.]
  Sulphuretted hydrogen water (solution of hydrosulphuric acid)
is prepared by conducting the  gas into very cold water, which has
been previously freed from the air by  boiling.  The operation is
continued  until the water is completely saturated with the  gas,
which may be readily ascertained by closing the mouth of the flask

the following modifications.  Instead of a glass rod, as above prescribed, a stout
tube of the same diameter may be used.  The basket is simply made of sheet-lea.l
or of a bit of wide lead tubing, or even a linen bag will suffice. A good cork will
take the place of the caoutchouc stopper, particularly if it be soaked for some time in
melted tallow to fill up its pores.] 
50
REAGENTS.
[§31
with the thumb, and shaking it a little :  if, upon this, a pressure is
felt from within, tending to push the thumb off the aperture of the
flask, the operation may be considered  at an end;  but if, on the
contrary, the thumb feels sucked into the mouth of the flask, this
is a sure sign that the water is still capable of absorbing more gas.
  Sulphuretted hydrogen water must be kept  in well-closed vessels,
otherwise it will soon suffer complete decomposition, the hydrogen
being oxidized to water, and a small portion of the sulphur to sul-
phuric acid, the  rest of the sulphur separating.   The best way of
preserving it unaltered for a very long time is to pour the freshly-
prepared solution immediately into small phials, and to place the
latter, carefully corked, in an inverted position, into bottles  filled
with water.
  Tests.—Pure sulphuretted hydrogen water  must be  perfectly
clear, and strongly emit the peculiar odor of the gas; when treated
with sesquichloride of iron, it must yield  a copious precipitate of
sulphur.  Addition of ammonia must not impart a blackish appear-
ance to it.   It must leave no residue upon  evaporation on platinum.
  Uses.—Hydrosulphuric acid has a strong tendency to  undergo
decomposition with metallic oxides, forming water and  metallic
sulphides; and the latter, being mostly  insoluble in water, are
usually precipitated in the process.  The  conditions under which
the  precipitation of certain sulphides ensues  differ materially; by
altering or modifying these conditions, we  may therefore divide the
whole of the precipitable  metals  into  groups,  as will be found
explained below.  Hydrosulphuric acid is therefore an invaluable
agent to effect the  separation  of  metals into  principal  groups.
Some of the precipitated sulphides exhibit a characteristic color
indicative of the individual metals which they respectively contain.
Hydrosulphuric  acid serves thus more particularly for the special
detection of tin, antimony, arsenic, cadmium,  manganese, and
zinc.  For  more ample information upon  this point, I refer to the
third section. The great facility with which hydrosulphuric acid
is decomposed, renders this  substance also a useful reducing  agent
for  many compounds; thus it serves, for  instance, to reduce salts
of sesquioxide of iron to salts of protoxide, chromic acid to  the
state of sesquioxide of chromium, &c.  In these processes of
reduction, the sulphur separates in the form of a fine white powder.
Whether the hydrosulphuric  acid had better be  applied in the
gaseous form, or in aqueous  solution,  depends  always  upon  the
special circumstances of  the case.

                 in. BASES  AND METALS.
                             § 31.
  Bases are divided into oxygen bases and sulphur bases.  The
former result from the combination  of metals or of compound radi- 
§32.]
POTASSA AND SODA.
51
cals of similar character with oxygen, the latter from the combina.
tion of the same bodu s with sulphur.
  The oxygen bases  are  classified into alkalies,  alkaline earths,
earths proper, and  oxides of the heavy metals. The alkalies are
readily soluble in water; the alkaline earths dissolve with greater
difficulty in that menstruum;  and magnesia, the  last  member of
the class, is only very sparingly soluble in it.  The earths proper,
and the oxides of the heavy metals are insoluble in  water, or nearly
so.  The solutions of the  alkalies and  alkaline earths are caustic
when sufficiently concentrated; they have an alkaline taste, change
the yellow color of turmeric paper to brown, and restore the blue tint
of reddened litmus paper; they saturate acids completely, so that
even  the salts which they form with strong acids do  not change
vegetable colors, whilst those with weak  acids generally have an
alkaline reaction.  The earths proper and the oxides of the heavy
metals combine likewise with  acids to form  salts, but, as a rule,
they do not entirely take away the acid reaction of the latter.
  The sulphur bases resulting from the  combination of the metals
of the alkalies and alkaline earths with  sulphur, are soluble in
water.  The solutions have a strong alkaline reaction.   The  other
sulphur bases do  not dissolve in water.  All sulphur  bases form
with  sulphur acids sidphur salts.

                     a. OXYGEN BASES.

                         a. Alkalies.
                             §32.
             1. Potassa  (K O)  and Soda (Na  O).
  The preparation of perfectly pure  potassa or soda is  a difficult
operation.   It is advisable, therefore, to prepare, besides perfectly
pure  caustic alkali, also some which  is not quite  pure, and  some
which, being free from certain impurities, may in many cases bo
safely substituted for  the pure substance.
  a.  Common solution  of soda.
  Preparation.—Put into a clean cast-iron pan provided with a lid,
15 parts of crystallized carbonate of  soda of commerce and 3
parts of water, heat to boiling,  and add, in  small portions at a
time, milk of lime prepared by pouring  3 parts  of warm  water
upon  1 part of quicklime, and letting the mixture stand in  a covered
vessel until the  lime  is reduced  to a uniform pulpy mass.   Keep
the liquid  in  the pan boiling whilst adding the milk of  lime, and
for a  quarter of an hour longer, then filter off a small portion, and
try whether the filtrate still causes effervescence  in hydrochlorio
acid.   If this is the  case, the boiling must be continued, and, if
necessary,  some  more  milk of lime  added  to the fluid.  When 
52
POTASSA.
[§32
 the solution is  perfectly free  from carbonic acid, cover the pan,
 allow the fluid to cool a little, and then draw off the clear solution
 from  the residuary sediment, by means of a  syphon filled with
 water, and  transfer it to a glass flask.   Boil the  residue a second
 and a third time with water, and draw off the fluid in the  same
 way.  Cover the flask closely with a glass plate, and allow the lime
 suspended in the fluid to subside completely.  Scour the iron pan
 clean, pour  the clear solution back into it, and evaporate it to 6 or
 7 parts.  The solution so prepared has a sp. gr.  of 1.13 to 1.15, and
 contains from 9 to 10 per  cent, of soda.  It must be clear, color-
 less, and as free as possible from carbonic acid ; sulphide of ammo-
 nium must  not  impart a black color to it.   Traces of silicic  acid,
 alumina, and phosphoric acid, are usually found in a solution of soda
 prepared in this manner;  on which account it is  unfit  for use in
 accurate experiments.
  Solution of soda is kept best in bottles closed with ground  glass
 caps.  In default of capped bottles, common ones with ground stop-
 pers may be used; but in  that  case, the neck must be wiped per-
 fectly dry and clean inside, and a slip of writing paper rolled round
 the stopper  ; or, better, the stopper is smeared  with a little paraf-
 fine  before  putting it  into its  place.   If these  precautions are
 neglected, it will be found impossible, after  a time, to remove the
 stopper, particularly if the bottle is only rarely opened.
  b. Hydrate of potassa purified with alcohol.
  Preparation.—Dissolve some sticks of caustic potassa of  com-
 merce in rectified spirit of wine in a stoppered bottle, by digestion
 and shaking ; let the fluid stand, decant or filter if necessary, and
 evaporate the clear fluid in a covered silver dish  over the spirit-
 lamp, until no more aqueous  vapors escape; adding from time to
 time, during the evaporation, some  water, to prevent blackening
 of the mass.  Place the silver dish in cold water until it has  suffi-
 ciently cooled; remove the cake of caustic potassa from the  dish,
 break it into coarse lumps in a hot mortar, and keep in a well-closed
 glass bottle.  When required for use, dissolve some of it in water.
  The hydrate of potassa so prepared is sufficiently pure for most
purposes; it contains, indeed, a  minute trace of alumina, but is
usually free  from phosphoric acid, sulphuric  acid, and silicic  acid.
The solution must remain clear upon addition of sulphide of ammo-
nium ;  hydrochloric  acid must only produce  a barely perceptible
 effervescence in it.  The solution, acidified with hydrochloric acid,
must, upon evaporation to dryness, leave a  residue which dissolves
in water to a clear fluid ; when boiled with molybdate of ammonia,
it must exhibit no yellow color; when treated with  ammonia, it
 ought not to deposit slight flakes of alumina immediately; but only
 after standing several hours in a warm place.
  c.  Hydrate of potassa prepared with baryta. 

AMMONIA.
53
  Preparation.—Dissolve pure crystals of baryta (§ 34) by heating
with water, and add to the solution pure sulphate of potassa, until
a portion of the filtered fluid, acidified by hydrochloric  acid and
diluted, no longer gives a precipitate on addition of a further quan-
tity of the sulphate (16 parts of crystals of baryta require 9 parts
of sulphate of potassa).  Let the turbid fluid  clear,  decant, and
evaporate in a silver dish as in b.  The hydrate of potassa so pre-
pared is perfectly pure, except that it contains a trifling admixture
of sulphate of potassa, which is  left behind  upon  dissolving  the
hydrate in a little water.  This hydrate is but rarely  required, its
use being in  fact exclusively confined to the detection of minute
traces of alumina.
   Uses.—The great  affinity which the fixed alkalies  possess  for
acids renders these substances powerful agents to effect the decom-
position of the salts of most bases, and consequently the precipita-
tion of  those  bases which are insoluble in water. Many  of the so
precipitated oxides redissolve in an excess of the precipitant, as, for
instance,  alumina,  sesquioxide of chromium, and  oxide  of lead ;
whilst others remain undissolved, e. g., sesquioxide of iron, teroxide
of bismuth, &c.  The fixed alkalies serve therefore also as a means
to separate the  former from the latter.  Potassa and soda dissolve
also many salts  (e. g., chromate of lead),  sulphur compounds, &c,
and serve thus to separate  and distinguish them from other sub-
stances.  Many of the oxides precipitated by the action of potassa
or soda exhibit a peculiar color, or possess other characteristic pro-
perties  that may serve to lead to the detection of  the individual
metal which they respectively contain; such  are, for  instance, the
precipitate of protoxide of manganese, hydrate of protoxide of iron,
suboxide of mercury,  &g.  The fixed alkalies expel  ammonia from
its  salts, and enable us thus to detect that body by  its  smell, its
reaction on vegetable colors, &c.

                              § 33.
         2.  Ammonia—Oxide of Ammonium—(N H4 O).
  Preparation.—The  apparatus illustrated by Fig.  22 (§ 30) may
also serve for the  preparation of solution of ammonia,  with  this
modification, however, that no funnel tube being required in the
process, the cork upon  the flask a has only one  perforation for the
reception of the tube which serves to conduct the evolved  ammonia
into the washing bottle.  Introduce into  a 4 parts  of chloride of
ammonium in pieces about the size of a  pea, and dry hydrate of
lime prepared from 5 parts of lime ; mix by shaking the flask,  and
add cautiously a sufficient quantity of water  to make the powder
into lumps.  Put a small quantity of water only into  the washing
bottle (which  should  be rather capacious); but have 10 parts of 
54
AMMONIA.
[§33
 water in the flask which is  intended for the final reception of the
 washed gas.  Set the flask a now in a sand bath, connect it with the
 rest of the apparatus,  place the flask d in a vessel of cold water,
 and apply heat.   The  evolution of gas speedily commences.   Con-
 tinue to heat until no more bubbles appear.  Open the cork of the
 flask a, to prevent the receding of the fluid.  The solution  of
 ammonia contained in  the washing bottle is  impure, but  that con
 tained in the receiver d is perfectly pure ; dilute it with water until
 the specific gravity is about 0-96 = 10 per cent, of ammonia.  Keep
 the fluid in bottles  closed with ground stoppers.  This  is the best
 way of  preparing solution of ammonia  in  small quantities.  That
 prepared on a large scale in cast-iron vessels is of course cheaper.
   Tests.—Solution of ammonia must be colorless, and ought not to
 leave the  least residue when evaporated on a watch-glass, nor
 should it cause the slightest turbidity in lime water (carbonic acid).
 [ Concentrated ammonia precipitates  lime-water though free from
 carbonic acid.   It should, therefore, be  diluted before  testing.]
 When supersaturated  with nitric acid, neither solution of nitrate
 of baryta, nor of nitrate of silver, must render it turbid, nor must
 sulphuretted hydrogen impart to it the slightest color.
   Uses.—Solution  of ammonia,  although  formed by  conducting
 ammoniacal gas  (N H3) into  water, and letting that  gas escape
 upon exposure to the  air, and much quicker when heated, is con-
 veniently regarded as a solution of oxide of ammonium (N H4 O)
 in  water, the equivalent of water  (H O) existing with N  H3 being
 assumed to form with the latter N H.4 O.  Solution of ammonia is
 accordingly regarded as corresponding to the solution of potassa
 and soda, which greatly serves to facilitate the explanation of many
 chemical transformations into  which the ammoniacal compounds
 enter, the oxygen salts resulting from the neutralization of oxygen
 acids by solution of ammonia being also assumed to contain oxide
 of ammonium N H, O, instead of  N H .  Ammonia is  one of the
most  frequently used  reagents.  It is  especially applied for the
saturation of acid fluids, and  also to effect the precipitation of a
great many metallic oxides and earths ;  many of these precipitates
redissolve in an excess  of ammonia, as, for instance, the oxides of
zinc,  cadmium,  silver,  copper, &c, whilst others are insoluble in
free ammonia.  This reagent may serve, therefore, to separate and
distinguish the former from the latter.  Some of these precipitates
 as  well as their solutions in ammonia, exhibit peculiar colors, which
may at once  lead to the detection of the  individual metal which
they respectively contain.
  Many of the  oxides  which  are precipitated  by ammonia from
 neutral  solutions,  are not precipitated by  this reagent from acid
 solutions, their precipitation from the latter being prevented by the
 formation of a salt of ammonia.  Compare § 54, chloride of ammonium. 
§34.]
BARYTA.
55
                   /3. ALKALINE EARTHS.
                              § 34.
                       1.  Baryta (Ba O).
   Preparation.—a. Prom  sulphate of baryta.  Mix  together  6
parts of finely pulverized  sulphate of baryta, 1 part of powdered
charcoal, and l| part of flour;  or 8 parts of sulphate of baryta, 2
parts of charcoal, and 1 part of common resin.  Put the mixture
in a crucible, and expose it in  a wind furnace to  a long-continued
red heat; or put the mixture in an earthen pot, lute the lid on with
clay, and expose the  pot to the heat of a brick-kiln.  Boil the crude
sulphide of barium obtained by this process for some time  with
water, and, when the crystallization point is attained, filter off hot:
let the  filtrate cool in a well-covered vessel.  Pour off the mother
liquor, which, together with the residue left from the boiling of the
sulphide of barium, may be used for the preparation of chloride
of barium; boil the  crystals with just sufficient water to dissolve
them ; keep boiling (taking care to replace the evaporated water);
add finely triturated  and sifted copper  scales in small portions at a
time, until a filtered  sample of the fluid gives a pure wrhite precipi-
tate when mixed with a little acetate of lead.  Filter boiling.  As
solution of baryta  eagerly absorbs carbonic acid from the air, great
care must be taken to  exclude the  air in the process of filtration
and crystallization.   To effect this it is necessary to place the beaker
intended to receive the filtrate on a flat dish or flat  iron pot con-
taining a  little milk of lime, invert  a bell-glass over it with  an
opening in the  top, insert the  funnel through this,  filter,  then
remove  the  funnel, close the opening in the top of the bell-glass
with an india-rubber cap,  and let the fluid thus  protected  from
access of air  stand for several days in a cool place.   After  this
decant the fluid (baryta water), let the crystals (Ba O, HO + 8 aq.)
drain in a well-covered funnel, dry them quickly between sheets
of blotting-paper, and keep them in well-stoppered bottles.  For
use dissolve  1 part in 20 parts of water, and filter.   The baryta
water so obtained is preferable to that  decanted from the crystals.
  b.  Prom Witherite.—Mix intimately 100 parts of finely pulverized
Witherite, 10 parts of powdered charcoal, and 5 parts of resin ; or
100  parts  of Witherite and  15 parts  of finely powdered caking
coal.  Put the mixture in  a pot or crucible, lute  on  the lid with
clay, and expose to the heat of a brick-kiln. Triturate the mass,
and boil the powder with water; filter, and proceed with the fil-
trate, as in a.  The  undissolved residue,  which consists of unde-
composed Witherite and coal, may be used in the  preparation of
chloride of barium.  This  is a  most excellent  method, both as
regards cheapness and purity of product.
  Tests.—Solution of baryta, or baryta water, must, after precipi- 
56
ZINC.
[§§ 35, 36
tation of the baryta by sulphuric acid,  give a filtrate remaining
clear when mixed with spirit of wine, and leaving no fixed residue
upon evaporation in a platinum crucible.
   Uses.—Caustic baryta, being  a strong  base, precipitates  the
earths and metallic oxides insoluble in water from the solutions of
their salts.  In the course of analysis we use it simply to precipitate
magnesia.  Baryta  water may also  be used  to precipitate those
acids which form insoluble compounds with this base ;  it is applied
with this view to effect the detection of carbonic acid, the removal
of sulphuric acid, phosphoric acid, &c.

                             § 35.
                        2.  Lime (Ca O).
  We use—
  a. Hydrate of lime.
  b. Lime water.
  The former is obtained by slacking  pure calcined lime in lumps,
in a porcelain dish, with half its weight of water.  Hydrate of
lime must be kept in a well-stoppered bottle.
  To prepare lime water, digest hydrate of lime for some time with
cold distilled water, shaking the mixture occasionally;  let the
undissolved portion of lime subside, decant, and keep the clear fluid
in a well-stoppered flask.
  If hydrate of lime  or lime water is required, entirely free from
traces  of alkalies which  usually exist in limestones, the  lime is
washed several times with water before it or its solution is preserved.
   Tests.—Lime water must impart a strongly-marked brown tint
to turmeric paper, and give a considerable precipitate with  carbo-
nate of soda.  It speedily loses these properties upon exposure to
air, and is thereby rendered totally unfit for analytical purposes.
   Uses.—Lime  forms with  many acids insoluble, with others solu-
ble salts.  Lime water may therefore serve to distinguish the former
acids, which it  precipitates from their solutions, from  the  latter,
which it will of course fail  to precipitate.  Many of the precipita-
ble acids are  thrown down only  under certain conditions, e. g., on
boiling (citric acid), which affords a ready means of distinguishing
between them by altering these conditions.  We use lime water in
analysis principally to effect the detection of carbonic  acid, and
also to distinguish between citric acid and tartaric acid.  Hydrate
of lime is chiefly used  to  liberate  ammonia from  the salts  of
ammonia.
         y.  HEAVY METALS AND THEIR OXIDES.
                              § 36.
                          1.  Zinc (Zn).
   Select  zinc of good quality, and, above all, perfectly  free from
 arsenic.  The method described, § 135, 10 will serve  to detect the 
 §§ 37, 38, 39.]  HYDRATE OF TEROXIDE OF BISMUTH.       57

 presence of the  slightest trace of this substance.  Fuse the metal,
 and pour the fused mass  in  a thin  unbroken stream into a large
 vessel  with water.  Should  the  zinc  contain arsenic, it must be
 rejected, as  no  practicable  process  of purifying it  is known.—■
 (Eliot and Storer.)
   Uses.—Zinc serves in qualitative analysis  for the  evolution of
 hydrogen, and also of arsenetted  and antimonetted hydrogen gases
 (compare §§ 134, 10 and  135, 10); it is occasionally used also to
 precipitate some metals from their solutions ;  in which process the
 zinc simply displaces the  other  metal (Cu O, S 0o + Zn=Zn O,
 S 03-f Cu).

                              §37.
                           2. Iron (Fe).
   Iron reduces many metals, and precipitates them from their solu-
 tions in the metallic state.  We  use it especially for the detection
 of copper, which precipitates upon it with its characteristic color.
 Any clean surface  of iron, such as a knife-blade, a needle, a piece
 of wire, &c, will serve for this purpose.

                              §  38.
                         3. Copper (Cu).
   We  use copper exclusively to  effect the reduction of mercury,
 which precipitates upon it as a white coating shining with silvery
 lustre when rubbed.   A copper coin scoured  with fine sand, or in
 fact any clean surface of copper, may be employed for this purpose.

                              §  39.
     4. Hydrate  of Teroxide  op Bismuth  (Bi 03, H O).*
   Preparation.—Dissolve  bismuth, freed  from arsenic by fusion
 with hepar stdphuris, in dilute nitric acid; dilute the solution as
 much as is practicable without producing a permanent precipitate ;
 filter, and evaporate  the filtrate to crystallization.  Wash the crys-
 tals with water containing nitric acid, triturate them with water,
 add  ammonia in excess, and let the mixture digest for some time ;
 then filter, wash, and dry the white precipitate,  and keep it for
 use.
   Tests.—Hydrosulphuric  acid must throw down from a solution
 of this reagent  in dilute  nitric  acid, a precipitate insoluble  in
 ammonia and sulphide of  ammonium; and, accordingly, the fluid
filtered off from the precipitate treated with ammonia must remain
perfectly clear upon  addition  of hydrochloric  acid, whilst in  that
  * The  basic nitrate of teroxide of bismuth of commerce, if perfectly free from
arsenic and antimony, may also be used instead of the hydrate of teroxide. 
58                SULPHIDE OF AMMONIUM.        [§§ 40, 41.

filtered off from the precipitate treated with sulphide qf ammonium,
that acid must only produce a pure white turbidity  (sulphur).
   Uses.—Teroxide of bismuth, when boiled with alkaline solutions
of metallic sulphides, decomposes with the latter, giving rise to the
formation of metallic oxides and sulphide of bismuth.  It is better
adapted to effect decompositions of this kind than oxide of copper,
since it enables the operator to  judge immediately upon the addi-
tion of a fresh portion whether the decomposition  is complete or
not. It has still another advantage over the oxide of copper, viz.,
it does not, like the latter, dissolve in the alkaline fluid in presence
of organic substances; nor does it act as a reducing agent upon
reducible  oxygen compounds.  We  use it principally to convert
tersulphide and pentasulphide of arsenic into arsenious and arsenic
acids, for which purpose oxide of copper is altogether inapplicable,
since it converts the arsenious acid immediately into arsenic acid,
being itself reduced to the state  of suboxide.

                            [§ 40.
                5.  Binoxide op Lead (Pb O,).
  Preparation.—Dissolve separately 4 parts of crystallized acetate
of lead and  3 parts of crystallized carbonate of soda in hot  water,
and filter if needful;  mix the  solutions, and pass well-washed
chlorine gas through the mixture until it has become  dark-brown
and all effervescence from escape of carbonic  acid gas has ceased.
Throw on a  filter and wash with  hot water until nitrate of silver no
longer  causes any turbidity in the washings.  The contents of the
filter are dried for use.— Wbhler.
   Tests.—Binoxide of lead, when boiled with thrice its bulk of pure
nitric acid for several minutes and allowed to settle, must not com-
municate the faintest red color to the acid (absence of manganese).
   Uses.—This reagent serves to oxydize sesquioxide of chromium
when in alkaline solution to chromic acid.  It also is a most deli-
cate and characteristic test for manganese.]

                    b.  SULPHUR  BASES.
                            §  41.
             1. Sulphide op Ammonium (N H4 S).
  We use in analysis—
  a. Colorless proto-sidphide of  ammonium.
  b. Tellow bi-, ter-, &c, sulphide of ammonium.
  Preparation.—Transmit hydrosulphuric acid gas through 3 part*
of solution of oxide of ammonium until no further absorption takes
place; then add 2 parts more  of the same solution of oxide of
ammonium.  The  action of hydrosulphuric acid upon  oxide of
ammonium gives rise to the formation, first of N  Hj, S (N H G 
§ 41.]             SULPHIDE OF  AMMONIUM.               53

and 11 S=N H, S and II O), then  of N H, S, H S;  upon addition
of the same quantity of solution of ammonia as has been saturated,
the oxide of ammonium  decomposes with the double sulphide of
ammonium and hydrogen, or, as it is commonly called, the hydro-
sulphate of sulphide of ammonium, and simple or  proto-sulphide
of ammonium is formed (N H, S, H S + N H, 0 = 2 (N H, S) + H 0.
The rule, however, is to add only two-thirds of the quantity of solu-
tion of ammonia, as it is better the preparation should contain a
little  hydrosulphate of  sulphide  of ammonium, than that free
ammonia should be present.  To employ, as has usually been the
case hitherto, hydrosulphate of sulphide of ammonium instead of
the simple  proto-sulphide, is unnecessary, and simply tends to
increase the smell of sulphuretted  hydrogen  in the laboratory, as
the preparation allows that gas to escape when in contact with
metallic sulphur acids.
   Sulphide of ammonium should be kept in  small  well-stoppered
bottles.  It is colorless at first, and deposits no sulphur upon addi-
tion of acids.  Upon  exposure  to  the  air, however, it acquires a
yellow tint, owing to  the formation of bisulphide  of ammonium,
which is attended also  with formation of ammonia and water:

             2  (N H  S) + 0=N H, S2+N H +H O.

Continued action of the oxygen of the air upon the sulphide of
ammonium tends at first to the  formation of still higher sulphides;
but afterwards  the fluid deposits  sulphur, and, in  the end, there
remains nothing in solution but pure ammonia, the whole of the
sulphur having  separated.
   The sulphide of ammonium, which has turned yellow by exposure
to the air, may be used for all purposes requiring the employment
of yellow sulphide of ammonium :  the yellow  sulphide may also be
expeditiously prepared by digesting the proto-sulphide with some
sulphur.  All kinds of yellow sulphide of ammonium deposit sul-
phur, and look  turbid and milky on being mixed with acids.
   Tests.—Sulphide of  ammonium  must strongly emit the odor
peculiar to it; with acids it must evolve abundance of sulphuretted
hydrogen; the  evolution of gas  may be attended by  the separation
of a pure white deposit,  but no  other precipitate must be  formed.
Upon  evaporation and exposure to a red heat on a platinum dish,
it must leave no residue.  It must not precipitate, nor even render
turbid, solution of magnesia or solution of  lime   (carbonate of
ammonia oi free ammonia).
   irses.—Sulphide of  ammonium  is one of the most frequently
employed reagents.  It serves (a) to effect the precipitation  of those
metals which hydrosulphuric  acid  fails to throw down from acid
solutions, e.  g. of iron, cobalt, &c.   (N H, S + Fe O,  S 0„=Fe S-f 
60
SALTS.
[§42.
N H, 0, S 0,), (b) to separate the metallic sulphides thrown down
from acid solutions by hydrosulphuric acid, as it dissolves some of
them to sulphur salts, as, for instance, the sulphides of arsenic and
antimony, &c.  (N H; S, As S=, &c), whilst leaving others undis-
solved—for instance,  sulphide of lead, sulphide  of cadmium, &o.
The sulphide  of ammonium used for this purpose must  contain an
excess of sulphur, if the metallic sulphides to be dissolved will dis-
solve only as higher sulphides, as, for instance, Sn S, which dissolves
with ease only as  Sn S.,.
  From solutions  of salts of alumina and sesquioxide of chromium,
sulphide of ammonium precipitates  hydrates of these oxides, with
escape of sulphuretted hydrogen, as the sulphur compounds corre-
sponding to these oxides cannot form in the humid way.  Al2 0„
3 S 03+3 N H< S+3 II 0=Ali 03, 3  H  0 + 3 (NH,  O, S 0) +
3 H S.  Salts insoluble in water are thrown down by sulphide of
ammonium unaltered  from their  solutions  in  acids; thus, for
instance, phosphate of lime is  precipitated unaltered from its solu-
tion in hydrochloric acid.

                             § 42.
               2. Sulphide  op Sodium (Na S).
  Preparation.—Same as sulphide of ammonium, except that solu-
tion of soda is substituted for solution of ammonia.  Keep the fluid
obtained in well-stoppered bottles.  If required  to contain some
higher sulphide of sodium, digest it with powdered sulphur.
   Uses.—Sulphide of sodium is substituted for sulphide of ammo-
nium  to  effect  the  separation  of sulphide of copper from  sulphur
compounds soluble in alkaline sulphides, e. g., from proto-sulphide
of tin, as sulphide of copper is not quite insoluble in sulphide of
ammonium.

                         IY. SALTS.
  Of  the many salts employed as reagents, those of potassa, soda,
and ammonia are used principally on account of their acids; salts
of soda  may, therefore, often be substituted for the corresponding
potassa  salts, &c.  Thus it is almost  always a matter of perfect
indifference whether  we use  carbonate of soda  or carbonate of
potassa, ferrocyanide of potassium or ferrocyanide of sodium, &c.
I have, accordingly, here classified the salts of the alkalies by their
acids.  With the salts  of the alkaline earths and  those of the
oxides of the  heavy metals the case is different; these are not used
for their acid, but for their base ; we may, therefore, often substi-
tute for one salt of  a base another similar one, as e. g., nitrate or
acetate of baryta for chloride of barium, &c.  For  this reason I
have  classified  the  salts of the  alkaline earths and of  the  heavj
metals by their  bases. 
§§ 43, 44, 45.]      OXALATE  OF AMMONIA.
61
                a. SALTS OF  THE ALKALIES.
                              § 43.
              1.  Sulphate of Potassa (K O, S 03).
   Preparation.—Purify sulphate of potassa of commerce by recrys-
 tallization, and dissolve 1 part of the pure salt in 12 parts of water.
   Uses.—Sulphate of potassa serves to detect and separate baryta
 and strontia.   It is in many cases used in preference to dilute sul-
 phuric acid, which is employed for the same purpose, as it does not,
 like the latter reagent, disturb the neutrality of the solution.

                              § 44.
       2. Phosphate  op  Soda (2 Na O, H O, P 05+24 aq.).
   Preparation.—Purify phosphate of soda of commerce by recrys-
 tallization, and dissolve one part of the  pure salt in  10 parts of
 water for use.
   Tests.—Solution of phosphate of soda must not become turbid
 when heated with  ammonia.  The precipitates which solution of
 nitrate of baryta and solution of nitrate of silver produce in  it, must
 completely, and without effervescence, redissolve upon addition of
 dilute nitric acid.
   Uses.—Phosphate of soda  precipitates  the  alkaline earths, and
 all metallic oxides,  by double affinity.  It serves, in the course of
 analysis, after  the separation of the oxides of the heavy metals, as
 a test for alkaline earths in general;  and, after the  separation of
 baryta, strontia, and lime, as a special test for the detection  of mag-
 nesia ;  for which latter  purpose it  is used  in conjunction  with
 ammonia, the magnesia precipitating, under these circumstances, as
 basic phosphate of  magnesia and ammonia.

                             § 45.
       3. Oxalate  op Ammonia (2 N H, O, C4 06+2 aq.).
   Preparation.—Dissolve commercial oxalic  acid which has  been
 purified by recrystallization,  in 2 parts of hot  water, add  caustic
 ammonia, or carbonate of ammonia, until the fluid begins to mani-
 fest a slight alkaline reaction ;  filter, and  set aside to cool.  The
 crystals that separate are allowed to  drain, and the mother liquors
 are further evaporated to crystallization.  Purify by recrystalliza-
 tion.  Dissolve 1 part of  the pure salt in 24 parts of water  for use.
   Tests.—The solution of oxalate of ammonia must not be precipi-
tated nor rendered  turbid by hydrosulphuric acid,  nor by sulphide
of ammonium.   The salt must leave no residue after ignition on
platinum foil.
   Uses.—Oxalic  acid forms writh lime, strontia, baryta, oxide of
lead, and other metallic oxides, insoluble or very difficultly  soluble 
 62                  CARBONATE OF SODA.           [§§ 46, 47

 compounds; oxalate of ammonia produces, therefore, in the aqueous
 solutions of the salts of these bases, precipitates of the correspond-
 ing oxalates.  In analysis it serves principally for the detection of
 lime.

                             §46.
 4. Acetate of Soda (Na O, C4 H3 03+6 aq., or Na O, A-r-6 aq.).
   Preparation.—Dissolve crystallized carbonate of soda in a little
 water, add to the solution acetic acid to slight excess, evaporate to
 crystallization, and purify the salt by  recrystallization.  For  use
 dissolve 1 part of the salt in 10 parts of water.
   Tests.—Acetate of soda must be colorless and free from empy-
 reumatic matters and inorganic acids.
   Uses.—The stronger  acids in the free state decompose acetate
 of soda, combining with the base, and setting the acetic acid free.
 In the course of analysis, acetate of soda  is  used principally to
 precipitate phosphate of sesquioxide of iron (which is insoluble in
 acetic acid) from its solution in hydrochloric acid.

                             § 47.
         5. Carbonate of Soda (Na O, C O24-10 aq.).
  Preparation.—Finely  pulverize bicarbonate of  soda  of com-
merce, put the powder into a funnel stopped loosely with some
cotton, make  the surface even, cover it with  a  disc of difficultly
permeable paper with turned-up edges, and  wash by pouring small
quantities of water  on the paper disc, until the filtrate, when acidi-
fied with nitric acid, is not  rendered turbid by solution of nitrate
of silver, nor by solution of chloride of barium.  Let the salt dry,
and then convert it by gentle ignition  into the simple carbonate.
This is effected best in a crucible or dish of silver or platinum ; but
it may be done also in a perfectly clean vessel of cast iron, or, on
a small scale, in a porcelain  dish.  Pure carbonate of soda may be
obtained also by repeated recrystallization of carbonate of soda of
commerce.  For use, dissolve 1  part of the anhydrous salt or 2-7
parts of the crystallized salt in 5 parts of water.
   Tests.—Carbonate of soda intended for analytical purposes must
be perfectly white.  Its  solution, when supersaturated with nitric
acid, must not be rendered turbid by  chloride of barium nor by
nitrate of silver; nor must addition of sulphocyanide of potassium
impart a red, or warming with molybdate of ammonia and nitri
acid a yellow  tint to it;  the residue which remains upon evaporat
ing  its solution to dryness, after previous supersaturation with
hydrochloric acid, must leave  no residue (silicic acid) when redis-
 solved in water.
   Uses.—With the exception of the alkalies, carbonate of soda 
 § 48.]             CARBONATE  OF AMMONIA.                63

 precipitates the  whole of the  bases, most of them as carbonates,
 but some also as hydrated oxides.  Those bases which are soluble
 in water as bicarbonates require boiling for their complete precipi-
 tation from acid  solutions.  Many of the precipitates produced by
 the action of carbonate of soda exhibit a characteristic color, which
 may  lead to  the detection of the individual  metals which they
 respectively contain.  Solution of carbonate of soda  serves, more-
 over, for the  decomposition of many insoluble salts of the alkaline
 earths or of the metals, more  particularly of those with organic
 acids.  Upon boiling with carbonate of soda, these salts  are con-
 verted into insoluble  carbonates, whilst the acids combine with
 the soda, and are thus obtained in  solution in the  form of salts of
 soda.   Carbonate  of  soda is often used  also to saturate free
 acids.


                              § 48.

           6. Carbonate  of  Ammonia (N Hj O, C O,,).

   Preparation.—We  use  for the  purpose of  chemical analysis
 purified  sesquicarbonate of ammonia, entirely free  from any smell
 of animal oil, such as is prepared on a large scale from chloride of
 ammonium and carbonate of lime by sublimation.  The outer and
 the inner surface of the mass  are carefully scraped.   One part  of
 the salt  is dissolved by digestion with 4 parts of  water, to which
 one part of solution of caustic ammonia has been added.
   Tests.—Pure carbonate of ammonia  must completely volatilize.
 Neither  solution of nitrate of baryta nor nitrate of silver, nor sul-
 phuretted hydrogen, must color or precipitate it, after supersatura-
 tion with nitric acid.
   Uses.—Carbonate of ammonia precipitates,  like  carbonate  of
 soda, most metallic oxides and earths ; it is generally employed in
 preference to the latter reagent, because it introduces no non-volatile
 body into the solution.   Complete  precipitation  of many of the
 oxides takes place only  on boiling.  Several of the precipitates
 redissolve again  in an  excess of the precipitant.   In like manner,
 carbonate of ammonia dissolves  many hydrated oxides and metal-
 lic sulphides, and thus enables us to distinguish and separate them
 from others which are insoluble in this reagent.
  Carbonate of ammonia, like  caustic ammonia, and  for the same
 reason, fails to precipitate from acid solutions many oxides which
it  precipitates  from neutral solutions.   (Compare  § 54.)   We use
carbonate of ammonia in  chemical analysis principally to effect the
precipitation of baryta, strontia, and lime,  and the separation  of
these substances from magnesia, as the latter is not precipitated by
this reagent in the presence of salts of ammonia. 
64                   NITRITE OF  POTASSA.           [§§ 49, 50


                             § 49.
            7. Bisulphite op Soda (Na O, 2 S O*).
  Preparation.—Heat 5 parts of copper shreds with  20 parts  of
concentrated sulphuric acid in a flask, and conduct the sulphurous
acid gas evolved, first through a washing bottle containing some
water, then into a flask containing 4 parts of purified bicarbonate
of soda (§ 47), or 7  parts of crystallized carbonate of soda, and
from  20 to 30 parts of water, and which is not much more than
half full ; continue  the transmission of the  gas until the evolution
of carbonic acid ceases.  Keep the  solution, which smells strongly
of sulphurous  acid, in a well-stoppered bottle.
  Tests.—Sulphite of soda, when evaporated to dryness with pure
sulphuric acid must leave a residue,* the aqueous solution of which
is not altered by hydrosulphuric acid, nor colored yellow by heat-
ing with  a solution of molybdate of ammonia  mixed with nitric
acid.
   Uses.—Sulphurous acid has a  great tendency to pass to the state
of sulphuric acid by absorbing oxygen.   It  is therefore one of our
most powerful reducing  agents.  Sulphite of soda, which has the
advantage of  keeping better than sulphurous acid, acts in an ana-
logous manner as a reducing agent upon acids and higher oxides.
We employ it principally to reduce arsenic  acid to arsenious acid,
chromic acid to sesquioxide of  chromium, and sesquioxide of iron
to  protoxide.   It is besides employed for  separating tersulphide
of arsenic from the  sulphides of antimony and tin;  the  former
being soluble, the latter insoluble in solution of this reagent.

                             § 50.
              8. Nitrite op Potassa  (K O, N 03).
  Preparation.—Heat 2  parts of starch in  lumps, with 8 parts of
crude  nitric acid, sp. gr. 1.4, and 8 parts of water  in a flask that
is but half filled with the mixture, and conduct the nitrous vapors
first through a large  empty bottle,  then into  a flask  containing 5
parts of potassa-ley of sp. gr. 1.27,  until the latter is  saturated, as
is  evinced by the  separation of alumina or silica when common
potassa is used.   As soon  as the evolution  of gas begins, the heat
must be removed for a while, as otherwise the action  becomes too
violent.  The  filtered solution  is evaporated  to dryness.   When
needed for use, dissolve 1 part of the solid salt in about 2 parts of
water.
   Tests.—Nitrite of potassa must, upon addition of dilute sulphuric
acid, copiously evolve nitric oxide gas.
   Uses.—Nitrite of potassa is  an  excellent means to effect  the
* The evaporation is attended with copious evolution of sulphurous acid. 
§§ 51, 52.]     GRANULAR ANTIMONATE OF POTASSA.        65

detection and separation of cobalt; in the solutions of which metal
it produces  a precipitate of nitrite of potassa and sesquioxide of
cobalt.   It  serves also  in presence of free acid to liberate iodine
from its compounds.


                             § 51.
           9.  Bichromate of Potassa (K O, 2 Cr 03).
  Preparation.—Purify the  salt of commerce by recrystallization,
and dissolve 1 part of the pure salt in 10 parts of water for use.
   Uses.—Chromate of potassa   decomposes most of the soluble
salts of metallic oxides, by double affinity.  Most of the precipi-
tated chromates are very  difficultly  soluble,  and many of them
exhibit characteristic colors which lead readily to the detection of
the  particular metal which  they  respectively contain.  We use
bichromate of potassa principally as a test for lead.


                             § 52.
  10. Granular Antimonate op  Potassa (K O, Sb Os-f-7 aq.).
  A mixture of equal parts of pulverized tartar emetic and nitrate
of potassa is projected little by little into a red-hot crucible.  The
mass is kept gently  ignited for £ of an hour  after  the deflagration
is finished;  it foams somewhat at first, but  afterwards enters into
calm fusion.  The crucible is allowed to cool and  the  whole is
treated with warm water.  The contents are thus easily removed,
and the  liquid  deposits a heavy white powder from which  it is
decanted.   The liquid  itself is  concentrated by  evaporation.
After 1 to  2 days a doughy mass separates.  This  is stirred by
means of a spatula with thrice its volume of cold water, until it is
converted  into  a  fine granular powder, which  is united with that
first obtained.  The whole is then washed with a little cold water
and dried upon blotting paper.  100 parts of tartar  emetic yield
about 36 parts of antimonate of potassa.  (Brunner.)
  Tests and Uses.—Granular antimonate of potassa  is quite  diffi-
cultly soluble in water; it requires  90 parts  of boiling and 250
parts of  cold water  for solution.  The  solution is best made just
before use,  by continued shaking of the pulverized salt with cold
water and filtering off from the undissolved portion.  The solution
thus procured must be clear and have  a neutral reaction; it must
not  be altered by solutions of chloride of potassium or chloride
of ammonium, but must yield with  chloride of sodium a crystal-
lized precipitate.  Antimonate of potassa is an excellent reagent
for  soda, but must  be  employed with much  caution.  Compare
§93.
                               5 
66                CHLORIDE OF AMMONIUM.         [§§ 53, 54.

                             § 53.
         11. Molybdate of  Ammonia (N H^ O, Mo 03).
  Preparation.—Triturate  sulphide of molybdenum with  an equal
bulk of coarse quartz sand washed with hydrochloric acid,  until the
mass is reduced to a moderately fine powder ; heat the powder to
feeble  redness, until the mass has acquired a lemon-yellow color
(which after cooling turns whitish).  With  small quantities, this
operation may be conducted in- a  flat  platinum dish, with large
quantities, in a muffle;  take  care  to stir the mixture repeatedly
during the operation.  After  cooling, digest  the impure molybdic
acid thus produced with solution of ammonia, filter, evaporate the
filtrate to dryness, ignite  the  residue gently until the mass has
become yellow or white, and digest this for some days in the water-
bath with nitric acid in order to convert any phosphoric acid into
the tribasic modification.  After the nitric acid is evaporated, dis-
solve the residue  in 4 parts of solution of ammonia, filter rapidly
and pour the solution into 15 parts by weight of nitric acid of sp.
gr. 1.20.   Allow the solution  to stand several days in a warm place
until any phospho-molybdate  of ammonia that may be present has
separated, pour off the colorless solution from the precipitate, and
keep for use.  When heated to 104° Fah. the  solution is unaltered;
at a  higher  tempei'ature a white precipitate of molybdic acid or
acid molybdate of ammonia deposits, unless more nitric or hydro-
chloric acid be added.  (Eggertz.)
  Uses.—Phosphoric and  arsenic acids form, with  molybdic acid
and ammonia, peculiar  compounds of a  yellow color,  which are
insoluble in a nitric acid solution of molybdate of ammonia.  This
reagent is therefore especially adapted for detecting minute traces
of these  acids in acid solutions containing oxide of iron,  alumina,
and alkaline earths.

                            §  54.
            12. Chloride  of Ammonium (N H^, CI).
  Preparation.—Select sublimed white sal-ammoniac of commerce.
If it contains iron, it must  be purified.  [This is most readily
accomplished by slowly passing chlorine  gas  into the nearly satu-
rated solution for a short time, or until ferricyanide of potassium
gives no blue color with a few drops of the  liquid.   Ammonia  is
then added in slight excess, the whole is  warmed, filtered  from the
separated sesquioxide of iron, and  evaporated  to  crystallization.
Care must be taken not to allow chlorine to react too long or in
too large  quantity on the sal ammoniac, else chloride of  nitrogen
might be formed which is dangerously explosive.]   For use, dissolve
one part  of the salt in 8 parts of water.
  Tests.—Solution of  chloride of ammonium must  upon  evapora- 
§55.]
CYANIDE  OF POTASSIUM.
67
tion on a platinum knife leave a  residue which volatilizes com-
pletely upon continued application of heat.  Sulphide of ammonium
must leave it unaltered.  Its reaction must be perfectly neutral.
   Uses.—Chloride  of ammonium  serves principally to retain in
solution certain oxides (e. g., protoxide of manganese, magnesia) or
salts (e.g., tartrate of lime), upon the precipitation of other oxides
or salts by ammonia or some other reagent.  This  application of
chloride of ammonium is based upon the tendency of the ammonia
salts to form double  compounds  with  other salts.  Chloride of
ammonium  serves  also to  distinguish between precipitates pos-
sessed of  similar properties ; for instance, to  distinguish the basic
phosphate of magnesia and ammonia, which is insoluble in chloride
of ammonium, from other precipitates  of magnesia.  It is used also
to  precipitate from their  solutions in potassa  various substances
which are  soluble in that alkali, but insoluble in ammonia; e. g.,
alumina, sesquioxide of chromium, &c.   In this process  the  ele-
ments  of  the  chloride of ammonium transpose  with those of  the
potassa, and chloride of potassium, water, and  ammonia are formed.
Chloride of ammonium is applied also  as a special reagent to effect
the precipitation of platinum as ammonio-bichloride of platinum.

                              § 55.
              13. Cyanide  of Potassium (K Cy).
   Preparation.—Heat ferrocyanide of potassium of commerce (per
fectly free from sulphate of potassa) gently, with stirring, until the
crystallization water is completely expelled; triturate the  anhy-
drous  mass, and mix 8 parts of the dry powder with 3 parts of
perfectly dry carbonate of potassa; fuse the  mixture in a covered
Hessian, or, better  still, in a covered iron crucible until the mass is
in a faint glow, and appears clear, and  a sample of it, taken  out
with an iron spatula, looks perfectly white.  Remove the crucible
now from the fire, tap it gently, and let it cool  a  little until the
evolution of gas has ceased ;  pour  the fused cyanide of potassium
into a  heated crucible-shaped vessel of clean scoured iron or silver,
or into a moderately hot Hessian crucible, with proper care to pre-
vent the running out of any of the minute particles of iron which
have separated in the  process of fusion and have subsided to the
bottom of the crucible.  Let the  mass now slowly cool in a some-
what warm place.  The cyanide of potassium so prepared is exceed-
ingly well adapted for analytical purposes,  although it contains
carbonate and cyanate of potassa;  which latter is upon solution in
water  transformed into carbonate of ammonia  and carbonate of
potassa (K O, C  N 0 + 4 H 0=K  O,  C 02+N H, O, C Oa).  Keep
it in the solid form  in a well-stoppered bottle, and for use dissolve
1 part in 4 parts of distilled water, without application of heat. 
68               FERROCYANIDE OF POTASSIUM.          [§56

[This salt occurs sufficiently pure for analytical  purposes in com-
merce.]
  Tests.—Cyanide of potassium must be of a milk-white color, and
quite free from particles of iron or charcoal.  It  must completely
dissolve in water to  a clear fluid.  It must contain  neither silicic
acid nor sulphide of potassium; the precipitate which salts of lead
produce in  its solution must accordingly be of a white color, and
the  residue which  its solution leaves upon  evaporation, after pre-
vious supersaturation  with hydrochloric  acid,  whereby hydro-
cyanic acid  escapes, must completely dissolve  in water to a clear
fluid.
  Uses.—Cyanide of potassium prepared in the manner described
produces in the solutions of most of the salts with metallic oxides,
precipitates  of  cyanides  of metals or of oxides or carbonates,
which are  insoluble in  water.  The precipitated cyanides are
soluble in cyanide of potassium, and may therefore be separated
from the oxides  or carbonates which are  insoluble in cyanide of
potassium, by further addition  of the reagent.  Some of the me-
tallic cyanides redissolve in the cyanide of potassium, even in pre-
sence of free hydrocyanic acid  and upon boiling, invariably as
double cyanides;  whilst others combine with cyanogen, forming
new radicals, which remain in solution in combination  with the
potassium.   The most  common  compounds  of  this nature are
cobalticyanide of potassium, and ferro- and ferricyanide of potas-
sium.  These differ from the double  cyanides of the other descrip-
tions particularly in this, that  dilute acids fail to precipitate the
metallic cyanides which they contain.  Cyanide of potassium may
accordingly serve also  to separate  the  metals which  form com-
pounds of the latter description from others, the cyanides of which
are precipitated by acids from their solution in cyanide  of potas-
sium.  In the course of analysis, this reagent serves to effect the
separation of cobalt from nickel, and also of copper whose sulphide
it dissolves, from cadmium whose sulphide is insoluble.

                             §56.
14. Ferrocyanide of Potassium  (2 K, Cj N3 Fe + 3 aq. = 2 K,
                          Cfy+3 aq.).
  Preparation.—The ferrocyanide of potassium is  found in com-
merce sufficiently pure for  the purposes  of chemical analysis.   1
part of the salt  is dissolved in 12 parts of water for use.
   Uses.—Ferrocyanogen forms with most metals compounds in-
soluble in water, and which frequently exhibit  highly character-
istic colors.  These  ferrocyanides are formed when ferrocyanide
of potassium is brought into contact with soluble salts of metallic
oxides, with chlorides, &c, the potassium changing places with the
metals.  Ferrocyanide of  copper and ferrosesquicyanide of iron 
§§ 57, 58.]     sulphocyanide  of potassium.              69

exhibit the most characteristic colors of all;  ferrocyanide of potas-
sium serves therefore particularly  as a test for oxide of copper and
Besquioxide of iron.

                              §57.
15. Ferricyanide of Potassium (3  K, Ci2 N6 Fe2 = 3 K Cfdy),
  Preparation.—Conduct chlorine gas slowly into  a solution of 1
part of ferrocyanide of potassium in 10 parts of water, with frequent
stirring, until the solution exhibits  a fine deep red color by trans-
mitted light (the light of  a candle answers best), and a portion  of
the fluid produces no longer a blue precipitate, in a solution  of
sesquichloride of iron, but imparts a brownish tint to it; evaporate
the fluid now  in a dish to \ of its weight,  and crystallize.  The
mother liquor  will upon further evaporation yield a second crop  of
crystals equally fit for use as the first.   Dissolve  the whole of the
crystals obtained in 3 parts of water, filter, if necessary ; evaporate
the solution briskly to half its volume, and crystallize again.  Dis-
solve  1 part of the crystals,  which are of a  splendid red color, in
10 parts of water for use.    The  solution, as already remarked,
must produce  neither a blue precipitate nor  a blue color in a  solu-
tion of sesquichloride of iron.  [The commercial salt is suited for
all analytical purposes. This salt undergoes decomposition when
long kept in solution.  It is therefore best applied in the state of a
fine powder.]
   Uses.—Ferricyanide of potassium decomposes  with  solutions  of
metallic oxides in the same manner as ferrocyanide of potassium.
Of the metallic ferricyanides, the ferriprotocyanide  of iron is more
particularly chnracterized by its color, and we apply ferricyanide
of potassium therefore principally  as a test for protoxide of iron.

                              § 58.
  16.  Sulphocyanide op Potassium  (K, C2 N S2 or K, Cy S2).
  Preparation.—Mix together 46  parts of anhydrous ferrocyanide
of potassium, 17 parts of carbonate of potassa, and 32 parts of sul-
phur ;  introduce the mixture into  an iron pan provided with a lid,
and fuse at a gentle heat;  maintain the same temperature  until
the swelling of the mass  which ensues at first has completely sub-
sided  and given place  to a state of tranquil  and clear fusion; in-
crease the temperature now, towards the end of the operation,  to
dull redness, in  order to  decompose the hyposulphite of potassa
which has been formed in this process.  Remove the half refrige-
rated and still soft mass from  the  pan, pulverize it, and boil  with
alcohol.  Let the alcoholic solution cool, when part  of the sulpho-
cyanide of potassium will separate in colorless crystals; to obtain
the remainder, distil the alcohol from the mother-liquor.   Dissolve
1 part of the salt in 10 parts of water for use. 
 70                 CHLORIDE OF BARIUM.                [§ 59.

   Uses.—Sulphocyanide of potassium serves for the detection of
 sesquioxide of iron; it is for that substance at once the most char-
 acteristic and  delicate test.   Its solution must remain colorless
 when heated with pure and dilute hydrochloric acid.

          b. SALTS OF THE ALKALINE  EARTHS.

                              §  59.
             Chloride op Barium (Ba CI+ 2 aq.).
  Preparation.—a. From heavy spar.  Triturate crude sulphide
 of barium (§  34), boil about T9o  of the powder with 4 times the
 quantity of water, and add hydrochloric acid until all effervescence
 of sulphuretted hydrogen  has ceased, and the fluid manifests  a
 feeble  acid reaction ;  add  now the remaining T\ part of the sul-
 phide of barium, boil for some  time longer, then filter,  and let the
 alkaline fluid crystallize.  Dry the crystals, redissolve them in water,
 and crystallize  again.
  b.  From Witherite. Pour 10 parts  of water  upon  1  part of
 Witherite, and gradually add  crude hydrochloric  acid until the
 Witherite is almost completely dissolved.  Add now a little more
finely pulverized Witherite, and heat,  with frequent stirring, until
 the fluid has entirely  or very  nearly lost  its acid reaction; add
some baryta water or solution  of sulphide  of barium, as long as a
precipitate forms; filter,  evaporate to  crystallization;  dry the
crystals, redissolve them in water, and crystallize again.  For use,
dissolve 1 part of  the chloride  of barium obtained in 10 parts of
water.
  Tests.—Pure chloride of barium must not alter vegetable colors ;
its solution must not be colored or precipitated by hydrosulphuric
 acid, nor  by sulphide  of ammonium.  Pure sulphuric acid must
 precipitate every fixed particle from it, so that  the fluid filtered
 from the  precipitate formed upon the addition of that reagent
 leaves not the  slightest residue when evaporated on platinum
 foil.
   Uses.—Baryta forms with many acids soluble, with others in-
 soluble compounds.  This property of baryta affords us, therefore,
 a means of distinguishing  the  former  acids which are not precipi-
 tated by  chloride of barium from the latter, in  the solution of
 the salts of which this reagent produces a precipitate.  The pre-
 cipitated salts of baryta severally show with other bodies (acids) a
 different deportment.   By subjecting these salts to the action of
 such bodies, we are therefore enabled  to subdivide the group of
 precipitable acids,  and  even to detect certain individual acids.  This
 makes chloride of barium  one of our  most important reagents to
 distinguish between certain groups of acids, and more especially
 also for the detection of sulphuric acid. 
§§ 60, 61, 62.]       SULPHATE OF LIME.
71
                              §  60.
              2. Nitrate  op Baryta (Ba O, N 05).
   Preparation.—Pour 12 parts of water upon 1 part of carbonate
 of baryta, no matter whether Witherite  or precipitated by carbo-
 nate of soda  from solution of sulphide of barium,  gradually add
 dilute nitric acid free from chlorine, and proceed exactly as directed
 in the preparation of chloride of barium from Witherite.  For use,
 dissolve 1 part of the salt in 15 parts of water.
   Tests.—Solution of nitrate of baryta must not be made turbid by
 solution of nitrate of silver.  Other tests the same  as for chloride
 of barium.
   Uses.—Nitrate of baryta is used instead of chloride of barium in
 eases where it is necessary to avoid the presence of a metallic chlo-
 ride in the fluid.
                              §61.
            3. Carbonate of Baryta (Ba O,  C 02).
   Preparation.—Dissolve crystallized chloride of barium in water,
 heat to boiling, and add a solution of carbonate of ammonia mixed
 with some caustic ammonia, or of pure carbonate of soda, as long
 as a precipitate forms ; let it subside, decant five or six times, trans-
 fer the precipitate to a filter, and  wash until the washing water is
 no longer rendered turbid by solution of nitrate of silver.  Stir
 the  precipitate  with water to the consistence of thick milk, and
 keep this mixture in  a stoppered bottle.  It must of course be
 shaken every  time it is required for use.
   Tests.—Pure sulphuric acid must precipitate every fixed particle .
 from a solution of carbonate of baryta in hydrochloric acid (com-
 pare caustic baryta).
   Uses.—Carbonate of baryta completely  decomposes the solutions
 of many metallic oxides, e. g., sesquioxide  of iron, alumina; precipi-
 tating from them the whole of the oxide as hydrate  and basic salt,
 whilst some other metallic  salts  are not precipitated by it.  It
 serves therefore to separate  the former from the latter, and is an
 excellent means to effect the separation of sesquioxide of iron and
 alumina from  protoxide of manganese, oxide of  zinc, &c, and also
 from lime and magnesia.  For this purpose it must be remembered
 that the  sulphates cannot be employed,  as from  them it throws
 down all the bases above mentioned.

                             § 62.
 4. Sulphate of Lime (Ca O, S 03, crystallized Ca O, S 03+2 aq.).
   Preparation.—Digest and shake powdered crystallized gypsum
for some  time with water; let the undissolved portion subside,
decant, and keep the clear fluid for use. 
 72                SULPHATE OF MAGNESIA.         [§§ 63,  64.

   Uses.—Sulphate of lime being a difficultly soluble salt, is a con-
 venient agent in cases where it is wished to apply a solution of a
 lime salt or of a sulphate of a definite degree of dilution.   As dilute
 solution of a lime salt, it is used  for the detection of oxalic  acid;
 whilst as dilute solution of a sulphate it affords an  excellent means
 of distinguishing between baryta, strontia, and lime.

                             § 63.
   5.  Chloride of Calcium (Ca  CI, crystallized Ca CI+6 aq.).
   Preparation.—Dilute 1 part of crude hydrochloric acid with 6
 parts of water, and add to the fluid marble or chalk until the last
 portion added remains undissolved;  add some hydrate of lime, and
 then  solution  of hydrosulphuric acid until a filtered sample is not
 affected by sulphide  of  ammonium. Let it  stand 12 hours at a
 gentle heat in a closed vessel; filter, exactly neutralize the filtrate,
 concentrate by evaporation, and crystallize.  Let the crystals drain,
 and dissolve 1 part of the salt in 5 parts of water for use.
   Tests.—Solution of chloride of calcium must be perfectly neutral,
 and neither be colored nor precipitated  by sulphide of ammonium ;
 nor ought it to evolve ammonia when mixed with hydrate of potassa
 or hydrate of lime.
   Uses.—Chloride  of calcium  is,  in its action  and application,
 analogous to  chloride of barium.   For,  as the  latter reagent is
 used to divide the inorganic acids into groups, so  chloride of cal-
 cium  serves in  the same manner to effect the separation of the
 organic acids into groups, since it precipitates  some of them, whilst
 it forms soluble compounds with  others.  And, as is the case with
 the baryta precipitates, the different conditions  under which the
 various insoluble lime salts are thrown down, enable us to subdi-
 vide the group  of precipitable acids, and even to detect certain
 individual acids.

                             § 64.
 6.  Sulphate of Magnesia (Mg O, S 03, crystallized Mg O, S 03,
                         HO + 6 aq.).
  Preparation.—Dissolve 1 part of sulphate  of magnesia  of com-
merce in 10 parts of water; if the salt is not perfectly pure, subject
it to recrystallization.
   Tests.—The solution of sulphate  of magnesia must have a neutral
reaction.  When mixed with sufficient chloride of ammonium  it
must  remain unaffected by ammonia,  carbonate and oxalate of
 ammonia, and sulphide of ammonium for the space of half an hour.
   Uses.—Sulphate of  magnesia serves  almost exclusively  for the
 detection of phosphoric and arsenic acids, which  it  precipitates
 from  aqueous  solutions of their salts in presence of ammonia and 
 §; 65, 66.]          SESQUICHLORIDE OF  IRON.              73

 chloride of ammonium, in the form of double salts (basic phosphate
 or arsenate of magnesia and ammonia), which are nearly insoluble,
 and  have  highly characteristic properties.   Sulphate of magnesia
 is, moreover, employed to test the purity of sulphide of ammonium
 (see §41).

  c. SALTS OF THE OXIDES  OF THE HEAVY METALS.
                             § 65.
 1. Sulphate of Protoxide of Iron (Fe O, S 03, crystallized Fe O,
                       S03,HO + 6 aq.).
  Preparation.—Heat an excess of iron nails free from rust, or of
 clean iron wire, with dilute sulphuric acid, until  the evolution
 of hydrogen  ceases; filter  the sufficiently  concentrated  solution,
 add  a few drops of dilute sulphuric acid to the nitrate, and allow
 it to cool.  Wash the crystals with water very slightly acidulated
 with sulphuric acid, dry, and keep for use.  The sulphate of prot-
 oxide of iron  may also be prepared from the solution of sulphide
 of iron in dilute sulphuric acid, which is obtained in the process
 of evolving hydrosulphuric  acid.
  Tests.—Sulphate  of protoxide  of iron must appear as fine, pale,
 green  crystals.  Those which  by action of the  air have become
 yellow, or which give with water a brownish-yellow solution, are
 to be rejected.  The solution, after addition of a little hydrochloric
 acid, must not be precipitated black by hydrosulphuric acid.
  Uses.—Sulphate  of protoxide of iron has a great disposition  to
 absorb  oxygen, and  to  be  converted  into  the  sulphate  of  the
 sesquioxide.  It acts, therefore, as a powerful reducing agent.  We
 employ it principally  for the reduction  of nitric  acid,  from which
it separates nitric oxide by withdrawing three  atoms of oxygen
from it.  The  decomposition of the nitric acid being attended, in
this  case,  with the formation of a very peculiar brownish-black
compound of nitric  oxide with an undecomposed portion of the salt
of the protoxide  of iron,   this  reaction  affords  a particularly
characteristic  and  delicate test for the detection of  nitric acid.
Sulphate of protoxide of iron serves,  also,  for  the detection of
hydroferricyanic acid, with which it produces a kind of  Prussian
blue, and also to effect the precipitation of metallic gold from solu-
tions of the salts of that metal.

                             § 66.
            2. Sesquichloride of  Iron  (Fe2 CI).
  Preparation.—Heat in a flask a mixture of 10 parts  of water
and 1 part of pure  hydrochloric acid with small iron nails until no
further evolution of  hydrogen is observed, even after adding  the
nails in excess ; filter the solution into another flask, and conduct 
74
NITRATE OF SILVER.
[§67.
 into it chlorine gas, writh frequent shaking, until the fluid no longer
 produces a blue precipitate in solution of ferricyanide of potassium.
 Heat until the excess of chlorine is expelled.   Dilute  until  the
 fluid  is twenty times  the  weight of  the iron dissolved, and keep
 the dilute fluid for use.
    Tests.—Solution  of sesquichloride  of iron must not  contain an
 excess of acid ; this may be readily ascertained by stirring a sam-
 ple of it with a glass rod dipped in ammonia, when the  absence of
 any excess of acid will be proved by the formation of a precipitate,
 which shaking the vessel and agitating  the fluid fail to redissolve.
 Ferricyanide of potassium must not impart a blue color to it.
    Uses.—Sesquichloride of  iron serves to subdivide  the group of
 organic acids which chloride of  calcium fails to precipitate ; as it
 produces precipitates in  solutions of benzoates and succinates, but
 not in solutions of acetates and formates.   The  aqueous solutions
 of the neutral acetate and formate of sesquioxide of iron  exhibit an
 intensely red  color ;  sesquichloride of iron is, therefore, a useful
 agent for detecting acetic acid and formic acid.   Sesquichloride  of
 iron is  exceedingly well adapted to  effect  the decomposition  of
 phosphates  of the  alkaline  earths  (see § 145).   It serves also for
 the detection of hydroferrocyanic  acid, with which it produces
 Prussian blue.

                                §67.
              3.  Nitrate of Silver  (Ag O, N 05).
   Preparation.—Dissolve pure  silver* in pure nitric  acid, evapo-
rate the  solution to dryness, and dissolve 1 part  of the salt in 20
parts of water.
   Tests.—Solution of nitrate of silver must be completely precipi-
tated by dilute hydrochloric acid,  so that the fluid filtered from the
precipitated chloride of silver leaves no residue when evaporated
on a watch-glass, and is neither  precipitated nor  colored by hydro-
sulphuric acid.
  [* Obtained from the silver-refiners usually in a state of sufficient purity, or pre-
pared free from all foreign matters by the following method :
  Silver coins are dissolved in nitric acid, and the solution is made perfectly clear by
rest and decantation, or by filtration. The clear solution  is  precipitated by excess
of common hydrochloric acid, which must also be free from suspended matters, and
the precipitated chloride  of  silver is boiled several times with renewed portions of
dilute hydrochloric acid.  It is then washed by decantation with hot water until
the washings have no longer  an acid reaction.  The pure chloride of silver thus ob-
tained is mixed, while still moist, with  its own weight of crystallized  carbonate of
soda which has been purified by recrystallization, and £ its weight  of pure nitre.
The  mixture is dried, being  well stirred during the process, brought into  a covered
porcelain crucible, heated at first gently, and finally to the fusing point  of  silver.
When cold the globule of silver is removed by breaking the crucible.  It is cleaned
from adhering flux by thoroughly washing in hot-water.—Mulder.] 
§§ 68, 69.]     NITRATE  OF SUBOXIDE OF  MERCURY.        75

   Uses.—Oxide of  silver forms  with many acids soluble,  with
others insoluble compounds.   Nitrate of silver may therefore serve,
like chloride of barium, to effect the separation and arrangement
of acids into groups.
  Most of the insoluble compounds of silver dissolve in dilute nitric
acid; chloride, bromide, iodide, cyanide, ferrocyanide, ferricyanide
and sulphide of silver, are insoluble in that menstruum.  Nitrate of
silver is therefore  a  most excellent agent to  distinguish and sepa-
rate from all  other acids, the hydracids corresponding to the last
enumerated compounds of silver.  Many of the insoluble salts of
silver  exhibit  a  peculiar color (chromate  of silver, arsenate of
silver), or  manifest  a  characteristic  deportment with other re-
agents, or upon the application of heat (formate of silver); nitrate
of silver is therefore an important agent for the positive  detection
of certain acids.

                             § 68.

   4. Acetate of  Lead (Pb  O, A, crystallized Pb O, A+ 3 aq.).
   The best  acetate of lead of commerce is sufficiently pure for the
purpose of chemical analysis; for use, dissolve 1 part of the salt in
10 parts of water.
   Tests.—Acetate of lead must dissolve in water to which a few
drops of acetic acid have been added, forming a clear and color-
less liquid.   Hydrosulphuric acid  must precipitate all the fixed
matter from  its  solution.   Mixed with excess of carbonate of
ammonia and filtered, the  filtrate must not have  a blue color
(copper).
   Uses.—Oxide of lead forms with a great many acids compounds
insoluble in wrater, which are marked either by peculiarity of color
or characteristic deportment.  The acetate of lead, therefore,  pro-
duces precipitates in the solutions of these acids, or of their salts,
and  essentially contributes to the detection of several  of them.
Thus, chromate of lead, for instance, is characterized by its yellow
color,  phosphate  of lead by its  peculiar deportment before the
blowpipe, and malate of lead by its ready fusibility.

                              § 69.

5. Nitrate of Suboxide of Mercury (Hg2 O, N Os, crystallized
                      Hg20, N05+2 aq.).
  Preparation.—Pour  1  part of pure  nitric  acid  sp. gr. 1.2 on 1
part  of mercury,  in a  porcelain  dish, and  let  the  vessel stand
twenty-four hours in a cool place; separate the  crystals  formed
from the undissolved mercury and the mother-liquor, and dissolve
them in water rriixed with  one-sixteenth part  of nitric  acid, by 
76                  SULPHATE  OF COPPER.          [§§ 70,  71

trituration, in  a mortar.  Filter the solution, and  keep  the  fil
trate in a bottle, with metallic mercury covering the bottom of the
vessel.
  Tests.—The solution of subnitrate of mercury must  yield with
dilute hydrochloric acid, a heavy white precipitate of subchloride
of mercury.  The liquid filtered from this precipitate should give
with hydrosulphuric acid none, or only a very slight black precipi-
tate (sxdphide of mercury).
   Uses.—Nitrate of suboxide of mercury acts in an  analogous
manner to the corresponding salt of silver.   In the first place, it
precipitates many  acids,  especially  the hydracids;  and, in the
second place, it  serves for the detection of  several readily oxidi-
zable bodies, e. g., of formic acid, as the oxidation  of such bodies,
at the expense  of the oxygen  of the suboxide  of mercury,  is
attended with the highly characteristic  separation  of  metallic
mercury.

                             § 70.
              6. Chloride of Mercury  (Hg CI).
  The chloride of mercury of commerce is sufficiently pure for the
purpose of chemical analysis.  For use, dissolve 1 part  of the salt
in 16 parts of water.
   Uses.—Chloride  of mercury gives with  several acids, e. g., with
hydriodic acid,  peculiarly colored precipitates, and may  accord-
ingly be used for the detection of these acids.  It is an important
agent for the detection of tin, when that metal is in solution in the
state of protochloride; if only the smallest  quantity of that com-
pound is present, the addition of chloride  of mercury in excess to
the solution is followed by separation of  subchloride of mercury
insoluble in water.   In a similar manner chloride of mercury serves
also for the detection of formic acid.

                             §  71.
7. Sulphate op Copper  (Cu O, S  03, crystallized  Cu 0, S  03,
                         H  0 + 4 aq.).
  Preparation.—This reagent may be obtained in a state of great
purity from the residue remaining in the retort in the  process of
preparing bisulphite of soda (§ 49), by treating that residue with
water, applying heat, filtering, crystallizing, and purifying the salt
by recrystallization. For use, dissolve 1 part  of the pure crystals
in 10 parts of water.
  Tests.—Pure sulphate of copper must be completely precipitated
from its solutions by hydrosulphuric acid; ammonia  and sulphide
of ammonium must accordingly leave the filtrate unaltered.
   Uses.—Sulphate of copper is employed in qualitative analysis to 
§§ 72, 73.]
BICHLORIDE  OF PLATINUM.
77
 effect the precipitation of hydriodic acid in the form of subiodide
 of copper.  For this purpose it is necessary to mix the solution of
 1 part of sulphate of copper with 2£ parts of sulphate of protoxide
 of iron, otherwise half of the iodine will separate in the free state.
 The protoxide of iron changes, in this process, to sesquioxide, at
 the expense of the oxygen of  the bxide of copper, which latter is
 thus reduced to the state of suboxide.   Sulphate of copper is used
 also for the detection of arsenious and arsenic acid; it serves, like-
 wise, as a test for the soluble ferrocyanides.

                              § 72.
   8. Protochloride op Tin  (Sn CI, crystallized Sn CI+2 aq.).
   Preparation.—Reduce English tin to powder by means of a file,
 or  fuse  it in  a  small porcelain  dish,  remove  from the fire,  and
 triturate the fused  liquid mass with a pestle until  it has passed
 again to the solid state; boil the powder for some time with con-
 centrated hydrochloric acid in a flask (taking care always to have
 an excess  of tin) until no more hydrogen gas is evolved; dilute
 the solution with 4 times the quantity of water slightly acidulated
 with hydrochloric acid, and filter.   Keep the filtrate for use in
 a well-stoppered bottle containing small pieces of metallic tin, or
 some pure tin-foil.   If these precautions are  neglected,  the pro-
 tochloride will soon  change  to bichloride with separation  of
 oxychloride, which will, of course, render the reagent totally unfit
 for the purpose for which it is intended.
   Tests.—Solution of protochloride of tin, when added to a  solu-
 tion of chloride of mercury, must immediately produce a white pre-
 cipitate of subchloride of mercury; when treated with hydrosul-
 phuric acid, it must give a dark brown precipitate;  it must not be
 precipitated nor rendered turbid by sulphuric acid.
   Uses.—The  great tendency  of protochloride of tin to absorb
 oxygen, and thus to form  binoxide, or  rather bichloride—as  the
 binoxide, in the moment of its  formation, decomposes with the free
 hydrochloric acid present—makes this substance one of our most
 powerful reducing agents.  We employ it in the course of analysis
 as a test for mercury, and also to effect the detection of gold, for
 which latter purpose it is previously mixed with some nitric acid,
 without heat.

                              y73.
 9.  Bichloride of Platinum (Pt CL, crystallized Pt Cl2 + 10 aq.)
  Preparation.—Treat platinum filings (purified  by boiling with
nitric acid), with concentrated hydrochloric acid and some nitric
acid, in a narrow-necked flask,  and apply a very gentle heat,  add-
ing occasionally fresh  portions of nitric acid, until the platinum is 
78                  TERCHLORIDE  OF GOLD.           [§ 74, 75

completely dissolved.*   Evaporate  the solution to dryness on the
water-bath, with addition of  hydrochloric acid, and  dissolve  the
residue in  10 parts of water for use.
  Tests.—Bichloride of  platinum must, upon evaporation  to  dry-
ness in the water-bath, leave a residue which dissolves completely
in spirit of wine.
   Uses.—Bichloride of platinum forms very sparingly soluble dou-
ble salts with  chloride of potassium  and chloride of ammonium,
but not so  with chloride  of sodium; it serves, therefore, to detect
ammonia  and  potassa, and  is, indeed, almost  our  most  delicate
reagent for the latter substance.

                               §74.
    10. Sodio-Protochloride of Palladium  (Na CI, Pd CI).
  Dissolve 5 parts of palladium in  nitrohydrochloric  acid (comp.
§ 73),  add 6 parts of pure  chloride of sodium, evaporate  in  the
water-bath to dryness, and dissolve  1 part of the residuary double
salt in 12 parts of water for use.  The brownish solution forms an
excellent means of detecting and separating iodine.

                               §75.
               11. Terchloride op Gold (Au Cl3).
  Preparation.—Take fine shreds of gold, which  may be  alloyed
with  silver or copper, treat them in a flask with nitrohydrochloric
acid in excess, and apply a gentle heat until no more  of the metal
dissolves.  If the gold was alloyed with copper, which is known
by the brownish-red precipitate produced by ferrocyanide of potas-
sium  in a  portion of the solution diluted with water, mix it with
solution o" sulphate of protoxide of  iron  in  excess; this  will re-
duce  the  terchloride  to  metallic gold, which will separate in  the
form of a fine brownish-black powder ; wash the powder in  a small
flask, and  redissolve it in nitrohydrochloric acid;  evaporate  the
solution to dryness  on the water-bath, and dissolve the residue in
30 parts of water.  If the gold was alloyed with silver, the latter
metal remains  as chloride upon treating the alloy with nitrohydro-
chloric  acid.   In  that case  evaporate the solution at  once to dry-
ness, and dissolve in water for use.
  [* When platinum scraps are to be converted into bichloride, the  process of solu-
tion is extremely tedious, unless the metal be first brought to a state of fine division.
This is most conveniently effected as follows:  Heat in a  clay crucible 5 parts ol
zinc to fusion, with sufficient common salt to  cover the surface and prevent its  oxi-
dation, then introduce 1 part of platinum scraps in small quantities at a time, into the
fused metal.  An alloy is formed from which  the zinc is to be removed by digesting
in common somewhat dilute hydrochloric acid, until all effervescence ceases, and
subsequent boiling for a time with fresh hydrochloric acid.  The residual  platinum
is completely washed with water and  boiled with nitric acid.  It is again washed
and finally treated with aqua regia, as above  directed.] 
§76.]
GEORGINA PAPER.
79
   Uses.—Terchloride of gold has a great tendency to yield up its
 chlorine ; it therefore readily converts protochlorides into higher
 chlorides,  protoxides, with the co-operation of water, into higher
 oxides.  These peroxidations are usually indicated by the precipi-
 tation of pure metallic gold in the form of a brownish-black pow-
 der.  In the  course  of analysis  this reagent  is used only for the
 detection of protoxide of tin, in the solutions of which it produces
 a purple color or a purple precipitate.


 V.  COLORING  MATTERS  AND  INDIFFERENT  VEGE-
                   TABLE SUBSTANCES.
                             § 76.
                        1.  Test Papers.
                    a. Blue Litmus Paper.
   Preparation.—Digest 1 part of litmus of commerce  with 6 parts
 of water, and filter the solution; divide the intensely blue filtrate
 into 2 equal parts;  saturate the free alkali in  the one part, by re-
 peatedly stirring with a glass rod dipped in very dilute sulphuric
 acid, until the color of the fluid just appears red; add  now  the
 other part of the blue filtrate, pour the whole fluid into a dish, and
 draw strips of fine unsized paper through it;  suspend these slips
 over threads and leave them to dry.  The color of litmus paper
 must be perfectly uniform, and neither too light nor too dark.
   Uses.—Litmus paper serves to detect the presence of free acid
 in fluids, as acids change its blue  color to red.  It must be borne
 in mind,  however, that the soluble neutral salts of most of  the
 heavy metallic oxides produce the same effect.

                 (3. Reddened Litmus Paper.
  Preparation.—Stir blue  solution  of litmus with  a glass  rod
 dipped  in  dilute sulphuric  acid,  and repeat this process  until  the
 fluid has just  turned distinctly red.  Steep slips of paper in  the
 solution, and dry them as in a.  The dried slips must look distinctly
 red.
   Uses.—Pure alkalies and  alkaline earths, and also the sulphides
 of their metals, restore the blue  color of  reddened litmus paper ;
 alkaline carbonates and the soluble salts of several  other  weak
 acids, especially of boracic  acid, possess the same property.  This
 reagent serves therefore for the detection of these bodies in general.

              y. Georgina Paper (dahlia paper).
  Preparation.—Boil the violet-colored petals of Georgina purpu-
rea (purple dahlia)  in  water, or  digest them with spirit of wine,
and steep slips of paper in the tincture obtained.  The latter should 
80
SOLUTION OF INDIGO.
[§77.
be neither more nor less concentrated than is  necessary to make
the paper, after drying, appear of a fine and light violet blue color.
Should the color too much incline to red, this may be remedied by
adding a very little ammonia to the tincture.
   Uses.—Georgina paper is reddened by acids, whilst alkalies im-
part  a beautiful green tint to it.  It is therefore an extremely con-
venient substitute both for the blue and the reddened litmus paper.
This reagent, if properly prepared, is a most delicate test both for
acids and alkalies.  Concentrated solutions of caustic alkalies turn
Georgina paper yellow, by destroying the coloring matter.

                      8. Turmeric Paper.
  Preparation.—Digest  and heat 1 part of bruised turmeric root
with six parts of weak spirit  of wine, filter the tincture obtained,
and steep slips of fine paper in the filtrate.  The dried slips must
exhibit a fine yellow tint.
   Uses.—Turmeric paper serves, like reddened litmus paper and
dahlia paper, for the detection of free alkalies, &c, as they change
its yellow color to brown.  It is not quite so delicate a test as the
other reagent  papers; but the change of color which it  produces
is highly characteristic, and is very distinctly perceptible in many
colored fluids; we cannot well dispense, therefore, with this paper.
When  testing with turmeric paper, it is to be  borne in mind that,
besides  the  substances  enumerated in  /3, several other  bodies
(boracic acid, for instance) possess the property of turning its yel-
low  color to brown-red.  It affords  an  excellent means  for the
detection of the latter substance.
  All test papers  are cut into slips, which are kept in small well-
closed boxes, or in bottles covered with black  paper, as continued
action of light destroys the color.

                             § 77.
                    2. Solution of Indigo.
  Preparation.—Take from 4 to 6 parts  of fuming sulphuric acid,
add  slowly, and in small portions  at a  time,  1 part of finely pul-
verized indigo, taking care to keep  the mixture well stirred.  The
acid has  at first imparted to it a brownish tint by the matter which
the indigo  contains in admixture, but it subsequently turns deep
blue.  Elevation of temperature to any considerable extent must
be avoided, as part of the indigo is thereby destroyed; it is there-
fore  advisable, when dissolving larger quantities of the substance,
to place  the vessel in cold water.  When the whole of the indigo
has  been added  to the  acid, cover the vessel, let it stand forty-
eight hours, then pour its  contents  into 20 times  the quantity ol
water, mix, filter, and keep the filtrate for use. 
§ 78.]        FLUXES AND  DECOMPOSING AGENTS.           81

   Uses.—Indigo is decomposed by boiling with nitric acid, yellow-
colored oxidation products being formed.  It serves, therefore, for
the detection  of  nitric acid.    Solution  of indigo is also well
adapted to effect the detection of chloric acid and of free chlorine.

               B. REAGENTS IN THE DRY WAT.
             I. Fluxes and Decomposing Agents.
                              § 78.
1. Mixture of Carbonate of Soda and Carbonate of Potassa
                   (Na  O, CO.+KO, C 02).
  Preparation.—Digest 10 parts of purified bitartrate of potassa in
powder with 10 parts of water and 1 part of hydrochloric acid for
several hours  on  the water-bath, with  frequent stirring; put the
mass into a funnel with a small filter inserted into the pointed end;
let  it drain; cover with a disc of rather  difficultly permeable fil-
tering paper with upturned edges, and wash by repeatedly pouring
upon this small quantities of cold water;  continue this  washing
process until the fluid running off is no longer rendered turbid by
solution of nitrate of silver, after addition of nitric acid.   Dry the
bitartrate of potassa freed in this manner from lime (and phosphoric
acid).  It is now necessary to prepare pure nitrate of potassa.   To
effect this, dissolve nitrate of potassa of commerce in half its weight
of boiling water, filter the  solution into a porcelain or stoneware
dish, using a hot funnel, and stir it well with  a wooden or porcelain
spatula until  cold.   Transfer the  crystalline powder to a funnel
loosely stopped with cotton, let it  drain, press down tight, make
it even at the top, and cover with a double  disc of  difficultly per-
meable filtering paper with upturned edges, and pour upon this at
proper intervals small portions of water, until the washings are no
longer made turbid by solution of nitrate of silver. Empty now the
contents of the funnel into a porcelain dish, dry in this vessel, and
reduce the mass to a fine powder by trituration.   Mix now 2 parts
of the pure bitartrate of potassa with 1 part of the pure nitrate of
potassa; put the perfectly dry mixture in  small portions at a time
into a clean-scoured cast-iron pot heated to gentle redness;  when
the mixture  has deflagrated, heat strongly, until a sample taken
from  the edges gives with  water  a  perfectly colorless solution.
Triturate the charred mass with water, filter, wash slightly, and
evaporate the filtrate in a porcelain, or, better still, in a silver dish,
until the fluid is covered with a persistent pellicle.   Let the mix-
ture now cool, with constant stining; put the crystals of carbonate
of potassa on  a funnel,  let them well drain, wash slightly, dry
thoroughly in a silver or porcelain dish, and keep the crystals in a
well-stoppered bottle.  The mother-liquor leaves, upon evaporation,
                               6 
82                  HYDRATE OF BARYTA.               [§ 79.

a salt which, though containing traces of alumina and silicic acid,
may still be turned to account for many purposes.
  Mix 13 parts of the pure carbonate of potassa prepared in  the
manner just now described, with  10 parts of pure anhydrous car-
bonate of soda, and  keep the mixture in a well-stoppered bottle.
The mixture of carbonate  of potassa and carbonate of soda may
also be prepared by deflagrating 20 parts  of pure bitartrate of
potassa with 9 parts  of pure nitrate of soda, treating with water,
and evaporating the  solution to dryness.
  Tests.—The purity of the mixed salt is tested as directed, § 41
(carbonate  of soda).   Should cyanide of potassium be present, it
is detected by adding a mixture of protosulphate and sesquichloride
of iron,  and then hydrochloric acid in  excess.  A bluish green
color is produced and  a  blue  precipitate separates after long
standing.
   Uses.—If silicic acid or  silicates are  fused  with  about 4 parts
(consequently with an excess) of carbonate of potassa or soda, car-
bonic acid escapes with effervescence, and a basic alkaline silicate
is formed, which, being soluble in water, may be  readily separated
from  such  metallic oxides as it may contain in  admixture; from
this basic alkaline silicate, hydrochloric acid  separates the silicic
acid as hydrate.   If a fixed alkaline carbonate  is fused together
with  sulphate of baryta, strontia, or lime, there are  formed cai-
bonates of the alkaline earths and sulphate  of  the alkali, in which
new compounds both the  base and the  acid of  the originally in-
soluble salt may now  be  readily detected.  However, we.do  not
employ carbonate of potassa separately,  nor carbonate of soda, to
effect the decomposition  of the insoluble silicates and sulphates;
but we apply for this purpose the above-described mixture of both,
because this mixture requires a far lower degree of heat for fusion
than  either of  its two components, and thus enables us to conduct
the operation over a Berzelius lamp, or over a simple gas-lamp.
[It is far better to be provided with a blast lamp (Bunsen's) or a
wind-furnace and employ  carbonate  of soda alone for fluxing
silicates, &c, than to take  the  trouble to prepare pure carbonate
of potassa for  this mixture.]  The fusion with alkaline carbonates
is invariably effected in a platinum crucible, provided no reducible
metallic oxides be present.

                             § 79.
             2. Hydrate op Baryta (Ba O,  H O).
   Preparation.—The  crystals of baryta prepared in the manner
directed, § 34,  are heated gently in a silver  or  platinum dish, until
the water of crystallization is completely expelled.  The residuary
white mass is pulverized, and kept for use in a  well-closed bottle. 
§§ 80, 81, 82.]     CHLORIDE OF AMMONIUM.
83
   Uses.—Hydrate  of baryta fuses at  a gentle  red  heat without
losing its water.  Upon fusing silicates together with about 4 parts
of hydrate of baryta, a basic silicate of baryta is formed, and the
oxides are  liberated.  If the fused mass is treated with hydro-
chloric acid, the solution  evaporated to dryness, and the  residue
digested  with hydrochloric acid,  the  silicic acid is left behind,
and the oxides are obtained in solution in the  form of chlorides.
We use hydrate of baryta as a flux when we wish to test silicates
for alkalies.   This reagent is preferable as a flux to the carbonate
or nitrate of baryta, since it does not require a very high tempera-
ture for its fusion, as is the case with the carbonate, nor  does it
cause any spirting in the  fusing mass, arising from disengagement
of gas, as is the case with the nitrate.   The operation is conducted
in silver  or platinum crucibles.

                              § 80.
               3. Fluoride of  Calcium (Ca Fl).
  Take fluor-spar as pure as can be  procured, and more particularly
free from alkalies, reduce to fine powder, and keep this for use.
   Uses.—Fluoride of calcium applied in conjunction with sulphuric
acid,  serves  to effect the  decomposition of silicates insoluble in
acids, and more  especially to detect the alkalies which they con-
tain.   Compare Section IH.  Silicic acid, § 153.

                             [§81.
              4. Carbonate of  Lime  (Ca O C 02).
  Preparation.—Solution of pure chloride of calcium, § 63, is heated
to boiling and precipitate by a slight excess of solution of carbon-
ate of ammonia with addition of some ammonia, § 48.  The pre-
cipitate is washed 5 or 6 times with hot water by decantation, then
is brought upon a filter and further edulcorated until the washings
give no turbidity with nitrate of silver.   The contents of the filter
are then  dried and bottled.
  Tests.—Carbonate of lime for use as a flux, must  be free from
Baits of  the  fixed  alkalies.  When washed with hot water  the
washings must yield no residue when evaporated to dryness.  For
uses, see  chloride of ammonium, § 82.]

                             [§ 82.
             5. Chloride  of  Ammonium (N H4 CI).
  Preparation.—Crystals  of chloride of ammonium, prepared as
described in § 54, are dried  and preserved in a wide-mouthed
bottle.
  Tests.—The salt  must be free from salts of the fixed alkalies. 
84                  CARBONATE OF  SODA.           [§§ 83, 84.

A considerable quantity of the salt, when ignited in a platinum ves-
sel, must leave no residue.
   Uses.—When a silicate containing alkalies, that is insoluble in
acids, is intimately mixed in a state of fine powder with chloride
of ammonium and carbonate of lime,  in suitable proportions, and
heated for some time  in  a platinum crucible, a mass results, from
which hot water extracts, besides  caustic lime and chloride of cal-
cium, the alkalies of the silicate in  the form of chlorides  ; while the
silica and other bases remain behind undissolved.   Carbonate (or
oxalate) of ammonia may be  used to remove the lime from  the
solution, and the filtrate on evaporation to dryness, and ignition
yields the alkalies as pure chlorides (or carbonates).  In this opera-
tion the larger share of the  carbonate  of lime,  at a red  heat, loses
carbonic acid and is  converted into caustic lime.   A smaller por-
tion, by  the action of  chloride of  ammonium, is  converted  into
chloride of calcium, which, readily fusing, allows the lime and sili-
cate to come into intimate contact, whereby insoluble basic silicate
of lime and soluble alkaline chlorides result.—(J. Lawrence Smith.)
This is incomparably the best  method of fluxing  silicates for  the
separation of the alkalies.  See § 210.  2. c]

                             § 83.
               6. Nitrate of  Soda (Na O, N05).
   Preparation.—Neutralize  pure nitric acid with pure carbonate of
soda exactly,  and evaporate to crystallization.  Dry the crystals
thoroughly,  triturate,  and keep the powder for use.
   Tests.—A solution of nitrate of soda  must not be made turbid by
solution of nitrate of silver or nitrate of baryta, nor precipitated by
carbonate of soda.
  , Uses.—Nitrate of soda serves as a  very powerful oxidizing agent,
by yielding oxygen to combustible  substances when heated with
them.  We  use this reagent principally to convert several metallic
sulphides, and more particularly the  sulphides of tin, antimony,
and arsenic, into oxides and acids ; and also to effect the rapid and
complete combustion of organic substances; for the latter purpose,
however, nitrate of ammonia is in many cases preferable; this lat-
ter reagent is  prepared by saturating nitric acid with carbonate of
ammonia.

                   n. Blowpipe Reagents.
                             § 84.
              1. Carbonate op Soda  (Na O, C 02).
   Preparation.—See  § 47.
   Uses.—Carbonate of soda serves, in the first place,  to promote
the reduction  of oxidized substances in the inner flame of the blow- 
§85.]
CYANIDE  OF POTASSIUM.
85
pipe.  In fusing it brings the oxides into the most intimate contact
with, the charcoai support, and enables the flame to embrace every
part of the substance under examination.  It co-operates  in this
process  also chemically by  the transposition of  its  constituents
(according to R. Wagner, in consequence of the formation of cyanide
of sodium).   If the quantity operated upon was very minute, the
reduced metal is often found in the pores of the  charcoal.  In  such
cases, the  parts surrounding the  little cavity which contained the
sample are dug out with a knife, and triturated  in a small mortar;
the charcoal is  then washed  off from  the metallic particles, which
now become visible either in the form of powder or  as small flat
spangles, according to the nature  of the particular metal or metals
present.
  Carbonate  of soda serves,  in  the  second place, as a solvent.
Platinum wire  is  the most convenient support for testing the  solu-
bility of substances in fusing carbonate  of soda.   A  few only of
the bases dissolve in  fusing carbonate of soda, but acids dissolve
in it with facility.  Carbonate of soda is, moreover,  applied as a
decomposing agent and flux, and more particularly to effect the
decomposition  of the  insoluble sulphates, with which it exchanges
acids, the newly formed sulphate of  soda being reduced  at the
same time to sulphide of sodium; and to effect the decomposition
of sulphide of arsenic, Avith which it forms a double sulphide of
arsenic and sodium, and arsenite or arsenate of  soda, thus convert-
ing it to a state which permits its subsequent reduction by hydro-
gen.  Finally, carbonate of soda is the most sensitive reagent in
the dry way for the detection of manganese, since when fused  in
the outer flame of the  blowpipe  together with a substance  con-
taining  manganese, it produces  a  green  opaque bead, owing  to
the formation of manganate  of soda.

                             § 85.
              2.  Cyanide op Potassium  (K Cy).
  Preparation.—See § 55.
   Uses.—Cyanide of potassium is an  exceedingly powerful reduc-
ing agent in the dry way; indeed it excels in its  action almost all
other reagents of the same class, and separates the metals not only
from most oxygen compounds, but also  from sulphur  compounds:
this reduction is  attended in  the former  case  with formation of
cyanate of potassa, by the absorption  of oxygen,  and  in the latter
case with formation of sulphocyanide  of potassium.  By means of
this reagent we may effect the reduction of metals from their  com-
pounds with  the  greatest possible  facility; thus we  may,  for in-
stance, produce metallic antimony from antimonious acid or  from
sulphide of antimony, metallic iron from sesquioxide  of iron, &c. 
86                   BIBORATE OF SODA.                [§ 86.

The readiness with which cyanide of potassium enters into fusion
facilitates the reduction  of the metals greatly; the process may
usually be  conducted even  in  a porcelain crucible over a spirit-
lamp.  Cyanide of potassium is a most valuable  and important
agent to  effect the reduction  of arsenites and arsenates,  and more
particularly of  tersulphide of arsenic (see § 135).  Cyanide of  po-
tassium is equally important as a blowpipe reagent.  Its action is
exceedingly energetic; substances like binoxide of tin, bisulphide
of tin, &c, the reduction of which by means of carbonate of soda
requires a tolerably strong flame, are reduced by cyanide of potas-
sium with the  greatest  facility.  In blowpipe  experiments we in-
variably  use  a  mixture of equal parts of carbonate of  soda and
cyanide  of potassium;  the admixture  of carbonate  of  soda is
intended here to check in  some measure  the excessive fusibility of
the cyanide of potassium.  This mixture of cyanide of potassium
with carbonate of soda, besides being a far more powerful reducing
agent than the  simple carbonate of  soda, has, moreover, this great
advantage  over the latter, that it is absorbed by the pores of  the
charcoal  with extreme facility, and thus permits the production of
the metallic globules in a state  of the greatest purity.

                             § 86.
3. Biborate of Soda (Borax) (Na O, 2 B 03, crystallized+10 aq.).
  The purity of commercial  borax may  be tested by adding to its
solution carbonate of soda, or after previous addition of nitric acid,
solution of nitrate of baryta or of nitrate  of silver.  The borax may *
be considered pure if these reagents fail to produce any alteration
in the solution; but if either of them causes  the  formation of a
precipitate, or renders  the  fluid  turbid,   recrystallization  is
necessary.  The pure crystallized borax is pulverized and kept for
use.
   Uses.—Boracic  acid manifests a great affinity for oxides when
brought into  contact with them in a state of fusion.  This affinity
enables  it in  the  first place,  to combine directly with oxides;
secondly, to expel weaker acids from  their salts;  and, thirdly, to
dispose metals, sulphides,  and haloid compounds to oxidize in the
outer flame of  the blowpipe, that it may combine with the oxides.
Most of the  thus produced borates fuse readily, even without the
aid of a  flux, but far more so in conjunction with borate of soda;
the latter salt acts in this  operation either as  a mere flux, or by
the formation  of double  salts.  Now, in the biborate of soda we
have  both free  boracic acid and borate of soda ; the union of these
two substances renders  it one  of our most important blowpipe re-
agents.  In the process of fluxing with borax, we usually select
platinum wire for a support; the loop  of the wire is heated to  red 
§ 87.]       PHOSPHATE OF SODA AND AMMONIA.           87

ness,  then dipped  into  the  powder, and exposed to  the  outer
flame; a colorless bead of fused borax is thus produced.  A small
portion of the substance under examination is then attached to the
bead, by bringing the latter into contact with it, either whilst still
hot or having previously moistened it.   The bead with the sample
of  the  substance intended  for analysis adhering to  it, is now
exposed  to the blowpipe flame, and the phenomena to the  mani-
festation of which this process gives rise are  carefully observed
and examined.   The following points  ought to be more particu-
larly watched:—(1) Whether or not the sample under examination
dissolves to a transparent bead, and whether or not the bead retains
its transparency on cooling;  (2) whether the bead exhibits a dis-
tinct color, which in many cases at once clearly indicates the indi-
vidual metal  which the analysed compound contains, as is the case,
for instance,  with cobalt; and (3)  whether the  bead manifests the
6ame  or a different deportment in the outer and in the inner flame.
Phenomena  of  the latter kind arise from the ensuing reduction  of
higher to lower oxides, or even to the metallic state, and are for
some  substances particularly  characteristic.

                             § 87
4. Phosphate  of  Soda and Ammonia  (Microcosmic Salt  or
   Salt of Phosphorus) (Na O, N  H4 O, H O, P 05, crystallized+
   8 aq.).
  Preparation.—a. Heat to boiling 6 parts of phosphate of soda
and 1 part of pure chloride  of ammonium with 2 parts of water,
and let the solution cool.  Free the crystals produced of the double
phosphate of soda  and  ammonia  by  recrystallization  from the
chloride  of sodium which adheres to them.  Dry the purified crys-
tals, and pulverize them for use.
  b. Of two  equal parts of common pure phosphoric acid, 1 part
has soda-lye  and the  other  ammonia  added   until  both liquids
acquire a decided alkaline reaction.  They are then mixed together
and evaporated to crystallization.
  Tests.—Phosphate of soda  and ammonia should dissolve in water
to a solution having  a  slightly  alkaline reaction.   The yellow
precipitate produced in it by nitrate of silver must perfectly dissolve
in nitric acid.  Fused on platinum wire it must give a clear and
colorless bead.
   Uses.—When phosphate of soda and ammonia is subjected to
the action of  heat, the ammonia escapes with the water of crystalli-
zation, and readily fusible metaphosphate of soda is left behind.
The action of microcosmic salt is quite analogous to that of biborate
of soda.  We prefer it, however,  in some cases, to borax as a sol-
vent or flux, the beads which it forms with many substances  being 
88           NITRATE OF PROTOXIDE OF COBALT.        [§ 88

more beautifully and distinctly colored than those of borax.  Pla-
tinum wire is also used for a support in the process of fluxing with
microcosmic salt; the loop of the wire must be made small and
narrow, otherwise the bead will not adhere to it.   The operation
is conducted as directed in the preceding paragraph.

                             § 88.
5. Nitrate  op Protoxide of  Cobalt  (Co  O,  N  05, crystal-
                         lized+5 aq.).
   Preparation.—Fuse in  a Hessian crucible 3 parts of bisulphate
of potassa, and add  to the  fused mass, in small portions at a time,
1 part of well roasted cobalt ore (the purest zaffre you can procure)
reduced to fine powder.  The mass thickens,  and acquires a pasty
consistence.  Heat now more strongly, until  it has become more
fluid again, and continue to apply heat until  the excess of sulphu-
ric acid is completely expelled, and the mass accordingly no longer
emits white fumes.  Remove the fused mass now from the crucible
with an iron spoon or spatula, let it cool, and reduce it to powder;
boil  this with water until the undissolved portion presents a soft
mass;  then filter  off  the  rose-red  solution, which is free from
arsenic and nickel, and mostly also from iron.
  Add to this liquid a little carbonate of soda so as to separate a
small quantity of carbonate of cobalt, boil and  filter.  The solution,
which is now free from oxide of iron, is precipitated boiling hot
with carbonate of soda, the precipitate is thoroughly washed, and
treated while still  moist with excess of oxalic acid.  The rose-red
oxalate of cobalt thus procured is washed, dried, and ignited in a
glass tube in a stream  of hydrogen gas.*  It  is hereby converted
into  carbonic acid which escapes and metallic cobalt.  The latter
is washed, first with water containing  some acetic acid, and after-
wards with  pure  water, and then dissolved in dilute  nitric acid.
The  solution, if needful, is treated with hydrosulphuric acid gas to
separate copper,  and filtered again.   It is  lastly  evaporated to
dryness and the residue dissolved in 10 times  its weight of water.
   Tests.—Solution of nitrate of protoxide  of cobalt must be free
from other  metals, and especially also from salts of the alkalies;
when precipitated with sulphide  of ammonium and  filtered, the
filtrate  must, upon  evaporation   on   platinum,  leave no fixed
residue.
   Uses.—Protoxide  of cobalt forms,  upon ignition with  certain
infusible bodies, peculiarly colored compounds, and may accord-
ingly serve for the detection of these bodies (oxides of zinc, alumina,
and  magnesia; see Section III.).

   [*  Most conveniently supplied from one of the forms of gas-generating apparatus
described in § 30.] 
§ 89.]    THE  DEPORTMENT OF BODIES WITH REAGENTS.     89
                   SECTION  III.

 ON THE  DEPORTMENT  OF BODIES WITH REAGENTS

                             § 89.
   I  stated in my introductory remarks that  the  operations and
 experiments  of qualitative analysis have for their object the con-
 version of the unknown constituents of any given compound into
 forms of which we know the deportment, relations, and properties,
 and which will accordingly permit us to draw correct inferences
 regarding the several constituents of which the analysed compound
 consists.  The greater or less value of such analytical experiments,
 like that of all other inquiries and investigations, depends upon the
 greater or less degree of certainty with which they lead to definite
 results, no  matter whether of a positive or negative nature.  But
 as a question does not render us any the wiser if we do not know
 the language in which the answer is returned, so, in like manner,
 will analytical investigations  prove unavailing  if we do not under-
 stand the mode of expression in which the  desired information is
 conveyed to us; in other words, if we do not know how to interpret
 the phenomena produced by the action of our reagents upon the
 substance examined.
   Before we can therefore proceed to enter upon  the practical
 investigations of analytical chemistry, it is  indispensable that we
 should  really possess the most perfect knowledge of the deport-
 ment,  relations, and properties of the new forms  into which we
 intend  to  convert the substances we wish to analyse.  Now, this
 perfect knowledge consists, in the first place, in a clear conception
 and comprehension of the  conditions necessary for the formation
 of the new compounds  and the manifestation of the various reac-
 tions ; and, in the second place, in a distinct impression of the color,
 form, and  physical properties  which characterize the new com-
 pound.   This section  of the work demands therefore not only the
 most careful and attentive study, but requires moreover that the
 student should examine and verify by actual experiment every fact
 asserted in it.
  The  method usually adopted  in elementary works on chemistry
 is  to treat  of the various  substances and their  deportment with
 reagents individually and separately, and to, point out their charac-
 teristic reactions.  I have, however, in the present work, deemed it
 more judicious and better adapted to its elementary character, to
 arrange those substances which are in many respects analogous
into  groups, and thus, by comparing  their analogies with their dif-
ferences, to place the latter in the clearest possible light. 
90
ALKALIES.
[§§ 90, 91.
A.—Deportment and  Properties  of  the  Metallic Oxides
                   and of their Radicals.
                              § 90.
  Before proceeding  to  the  special  study of the several metallic
oxides, I give here a general view of the whole  of them,  classified
in groups—showing which oxides belong to each  group.  The
grounds upon which  the classification  has  been  arranged will
appear from the special consideration of the several groups.
  First group—
  Potassa, soda,  ammonia (caesia, rubidia, lithia).
  Second group—
  Baryta, strontia, lime, magnesia.
  Third group—
  Alumina, sesquioxide of chromium (glucina, thoria, yttria, terbia,
erbia, zirconia ; oxides of cerium, lanthanum,  didymium;  oxide  ol
titanium and titanic acid; tantalic acid, hyponiobic acid).
  Fourth group—
  Oxides of zinc, manganese, nickel, cobalt,  iron (uranium, vana-
dium, thallium).
  Fifth group—
  Oxides of silver, mercury, lead, bismuth,  copper, cadmium (palla-
dium, rhodium, osmium, ruthenium).
  Sixth group—
  Oxides and  acids of  gold,  platinum,  tin, antimony, arsenic
(iridium, molybdenum, tellurium, tungsten, selenium).
  Of these metallic oxides only those printed in italics are found
extensively and in large quantities in  that portion of the  earth's
crust which is  accessible  to our investigations; these, therefore,
are most important to chemistry, arts and manufactures,  agricul-
ture, pharmacy, &c. &c.; and these therefore we shall dwell upon
at greater length.  The  remainder are more  briefly considered  in
supplementary  paragraphs, which are printed in smaller type,  so
that they can be omitted  by the beginner without inconvenience.
  The  deportment of  the metals I have given only in the case  of
those that are more frequently met with, in analytical operations, in
the metallic state.

                            § 91.
                   first group.  Alkalies.
      Of common occurrence: Potassa,  Soda, Ammonia.
      Of rare occurrence: Caesia,  Rubidia, Lithia.
  Properties of the group.—-The alkalies are  readily soluble  in
water, as well in the pure or caustic state as in the form of sulphides,
carbonates, and phosphates.  Accordingly  they  do  not precipitate 
§92.]
POTASSA.
91
one  another in the pure state, nor as carbonates or phosphates, nor
are they precipitated by hydrosulphuric acid  under any condition
whatever.   The  solutions of the pure alkalies, as well as of their
sulphides and carbonates, restore the blue color of reddened litmus-
paper, and impart an intensely brown tint to turmeric paper.


         Special Reactions of the more common Alkalies.

                               §92.
                        a.  Potassa (K O).
   1. Potassa and its hydrate and salts are not volatile at a faint
red-heat.   Potassa  and its hydrate  deliquesce in  the  air; the oily
liquids formed do not solidify by absorption of carbonic acid.
   2. Nearly the whole of the salts of potassa are readily soluble
in water.   They are colorless, if the constituent  acid is so.  The
neutral (see § 21) salts of potassa with  strong  acids  do not alter
vegetable colors.  Carbonate of potassa crystallizes with difficulty,
and deliquesces in the air.  Sulphate of potassa is anhydrous, and
suffers no alteration in the air.
   3. Bichloride of platinum produces in the neutral and acid solu-
tions* of the  salts  of potassa  a yellow, crystalline, heavy precipi-
tate of  bichloride  op platinum  and chloride of potassium
(platinchloride  of potassium) (K  CI, Pt  CL.).  In  concentrated
solutions this  precipitate separates  immediately upon the addition
of the reagent:  in dilute  solutions it forms only after some time,
often after a considerable time.  Very dilute  solutions are not pre-
cipitated by the  reagent.   The precipitate consists of octahedrons
discernable under the microscope.  Alkaline solutions must be acidi-
fied with hydrochloric  acid before the bichloride of platinum is
added.  The precipitate is difficultly soluble in water; the presence
of free acids does not greatly increase its solubility;  it is insoluble
in alcohol.  Bichloride of platinum  is therefore a particularly deli-
cate test for salts of potassa dissolved in spirit of wine.  The best
method of applying this reagent is  to evaporate the  aqueous solu-
tion of the potassa salt with bichloride of platinum nearly to dry-
ness on the water-bath, and to pour a little water on  the residue,
or, better still, some spirit of wine, provided no substances insolu-
ble in  that menstruum be present: the platinchloride of potassium

  * [While a neutral salt is one whose acid and base bear a certain ratio to each
other—an  acid salt being one that contains a larger proportion of acid, and a basic
salt one in which a larger proportion of base (alkali or other metallic oxide) exists;  a
neutral solution is simply one which is indifferent to vegetable colors—litmus, turme-
ric, (§ 76,) or has  a neutral reaction; an acid solution is one which has an acid reac-
tion—reddens  blue litmus; an alkaline solution is one that reacts  alkaline—tinges
turmeric paper brown.] 
92
POTASSA.
[§92
is left undissolved.   Care must be taken not to confound this double
salt with platinchloride of ammonium, which greatly resembles it
(see § 94.4).
  4.  Tartaric acid produces in neutral or alkaline solutions of salts
of potassa—(in the  latter case tartaric  acid must be  added  to
strong acid reaction)—a white, quickly subsiding, granular crystal-
line precipitate  of bitartrate of potassa (K  O,  H  O,  C8  H,
O10).  In  concentrated solutions this precipitate separates imme-
diately ;  in dilute solutions often only after the lapse of some time.
Vigorous shaking or stirring  of the fluid  promotes its  formation
considerably.  Very dilute solutions are not  precipitated by this
reagent.   Free  alkalies and free mineral  acids dissolve the pre-
cipitate ;  it is difficultly soluble in cold, but pretty readily soluble
in hot water.  In the case of  acid solutions, the free acid must, if
practicable, first be expelled by evaporation  and ignition, or the
solution  must be neutralized with soda  or carbonate of soda, before
we can proceed to test for potassa with tartaric acid.
  Bitartrate of Soda  (§ 25) is even a  better test of  potassa than
tartaric acid.  It  precipitates bitartrate  of potassa like  tartaric
acid, but  is a more sensitive  reagent than the  latter, because its
soda neutralizes the acid of the potassa  salt under examination, and
thus prevents any solvent action of this  acid  on the bitartrate of
potassa.    (e. g. K O, N 05 + Na O, H O, C8 H4 O10=K O, H O, C8
ILO10 +  NaO,NOs).
  5. If any salt of potassa that is volatile  at a bright red  heat,  be
brought  by means  of  a platinum wire  into the zone of fusion  of
the Bunsen gas-lamp  (§ 14), or into  the  inner blowpipe flame,* it
is vaporized and communicates to the flame a  bluish-violet color.
Chloride  of  potassium and nitrate of potassa  volatilize  rapidly,
carbonate and sulphate of potassa more slowly, phosphate of potas-
sa still more slowly ; all, however, give the reaction with  distinct-
ness.   If it is desired  to  render the coloration of the flame inde-
pendent of any acid which is accidentally present, and wThich may
impede the reaction, the substance under examination is  moistened
with sulphuric acid and dried  at the  edge of  the flame  before the
reaction is observed;  or, in case of silicates and other very fixed
compounds,  the  substance is  fused  with pure gypsum.   There is
thus formed  sulphate of potassa (in the latter instance  silicate of
lime  also) which  cannot fail to tinge the flame violet, unless soda
is present, when the reaction is more or less masked according to
the  quantity of the latter, only a  small  proportion of it  being
requisite  to obscure the potassa flame entirely.
   6. The spectrum of the potassa flame as seen in the spectroscope

  * Salts which decrepitate  are ignited in a platinum spoon before one attempts to rix
them on the wire. 
93.]
SODA.
93
(§ 15), is mapped on Plate 1.  It contains  two lines that are espe-
cially characteristic, viz., the red a and the indigo-blue (3.
   7. When the potassa flame is  observed through the indigo prism
(§ 15), its color appears sky-blue, violet,  and through the thickest
part of the prism even intense carmine-red.   Salts of lime, soda,
and lithia in admixture do not affect this reaction, because the yel-
low soda rays (§ 93, 3) cannot penetrate the indigo-prism  at  all,
arid the  lithia rays can only pass the thinner parts of the prism*.
Organic  matters which make  the flame  luminous may occasion
mistakes, and should therefore be destroyed  by heat.  Instead of
the indigo prism, cobalt glass (§  14) may be employed; it should be
so thick,  or  so many  thicknesses should  be used,  as  totally to
absorb the red rays of a lithia flame.
   8. If a salt  of potassa (more particularly chloride of potassium)
is heated with a  small quantity of  water,  alcohol (burning with
colorless flame) added, heated, and then kindled, the flame appears
violet.   The reaction is far less delicate than that given in 5, and
presence of soda obscures it entirely.

                             §93.
                        b.  Soda (Na O).
   1. Soda and its hydrate and  salts presents in general the same
deportment and properties  as potassa and its corresponding com-
pounds.   The oily fluid which soda forms  by deliquescing  in  the
air, resolidifies speedily by absorption of carbonic acid.  Carbonate
of soda  crystallizes readily; the tabular  crystals  (Na O, C 0.2 +
l0aq.) effloresce rapidly when exposed to the air.  The same applies
to the prismatic crystals of sulphate of soda (Na O, S  03  + 10 aq.).
   2. If to a sufficiently concentrated neutral or alkaline solution of
a soda salt, which is conveniently placed on a watch-glass, solution
of granular antimonate of potassa (prepared as directed in § 52)
is added, there appears at  first only a slight turbidity or none at
all.  On  rubbing the bottom of the watch-glass with a glass rod,
there speedily separates a crystalline precipitate of Antimonate op
Soda (Na O, Sb 05 +  7 aq.), which at first  appears  on the track
of the glass rod, and settles from the liquid as a heavy sandy depo-
sit.  From dilute solutions it is formed only after the lapse of some
time, e. g., 12 hours; in very dilute liquids it does  not appear at all.
The precipitate always has a distinct crystalline character.   When
slowly formed, it sometimes assumes the shape of  well  defined
microscopic square octahedrons, sometimes  of four  sided  prisms
with pyramidal terminations ; when it separates rapidly it appears
in minute boat-shaped  crystals.   The presence of large quantities oi

  * The prism should be marked at the point where the lithia rays cease to be per-
ceptible through it. 
94
SODA.
[§93.
potassa-salts  very perceptibly diminishes the delicacy of the reac-
tion.   Acid solutions cannot be tested with antimonate of potassa,
because free acid precipitates from this reagent hydrated antimonic
acid or acid antimonate of potassa.  If, therefore, free acid be pre-
sent, it must be removed, if possible, by evaporation or ignition, or
neutralized by addition of carbonate of potassa, before the reagent
is applied.  This test is  only applicable  to  such solutions as con-
tain no other bases than  potassa and soda.
  3. When salts of soda are brought into  the zone of fusion of
the Bunsen lamp, or into the inner blowpipe flame, they evince, as
to their volatility and deportment towards  decomposing agents, a
behavior similar to that  of  salts of potassa.   The  soda-salts are,
however, somewhat  less volatile than the  corresponding potassa
salts.  Highly characteristic for soda is the intense yellow color it
communicates to the flame,  a reaction which serves for detecting
the minutest  traces of soda,  and which is not  masked by the pre-
sence of large quantities  of potassa-salts.
  4. The Spectrum of  soda, Plate 1, contains a single yellow line.
a.  The spectral  reaction is so extraordinarily sensitive, that, as a
rule, the quantity of soda contained  in the atmospheric  dust suf-
fices to give at least a faint yellow line.
  5. The soda-flame is  characterized by its rendering a crystal  of
bichromate of potassa, which is illuminated by its  light, colorless.
Paper covered with iodide of mercury when seen by the soda-flame,
appears yellowish-white  (Bunsen).   Viewed  through green glass
its color is orange-yellow (Merz).  These reactions are not disguised
by presence of salts of potassa, lithia, or lime.
  6. If a  salt of soda (more particularly chloride of sodium) is
heated with a small quantity of water, alcohol added, and the latter
heated  and  then kindled,  the flame appears strongly  yellow.
The presence of a salt  of potassa does not impair the distinctness
of this reaction.
  7. Bichloride  of Platinum gives no precipitate in solutions  of
salts of soda.  The  Bichloride op  Platinum and Chloride  op
Sodium (platinchloride  of sodium) is easily  soluble  both  in
water and alcohol.  From concentrated solutions it crystallizes in
aurora-red prisms.  [The form of these crystals is characteristic for
soda when no other bases but potassa or ammonia are present.  By
slowly evaporating a drop of the solution of chloride of sodium to
which excess of bichloride of platinum has been added, on a slip of
glass, the crystals appear as needles or long prisms, usually dis-
tinguishable by the naked eye, and readily made out by help of a
magnifier.]
  8. Tartaric acid and Bitartrate of soda do not precipitate even
concentrated  neutral solutions of salts of soda. 
§94.]
AMMONIA.
95
                             § 94.
                     c.  Ammonia (N H, O).
   1. Anhydrous ammonia (N H) is gaseous at the common tempe-
rature ; but we have most frequently to  deal with it in its aqueous
solution, in which it betrays its presence at once by its penetrating
odor.  It is expelled from this solution by the application of heat.
It may be assumed that the solution contains it as oxide of ammo-
nium (N H4 O) (see § 33).
   2. All the salts of ammonia are volatile  at a high temperature,
either with or without decomposition.  Most of them are readily
soluble in water.  The solutions are  colorless.   The neutral com-
pounds of  ammonia with strong acids do not alter vegetable
colors.
   3. If salts of ammonia are triturated together with hydrate of
lime, best with the addition of a few  drops of water, or are, either
in a solid form or in solution, heated  with solution of soda or of
potassa, the ammonia is liberated in the gaseous state, and betrays
itself (1) by its characteristic odor; (2) by its reaction on moistened
test-papers; and (3) by giving rise to the formation of white fumes,
when any object (e. g., a  glass rod) moistened with hydrochloric
acid, nitric  acid, acetic  acid,  or  any  of  the volatile acids,  is
brought in contact with it.  These  fumes arise from the formation
of solid ammoniacal salts produced by the contact of the gases  in
the air.  Hydrochloric acid is the most delicate test in this respect J
acetic acid, however, admits less readily of a  mistake.  In  cases
where the quantity of ammonia present is only very small, the best
way of testing  the alkaline reaction of the fumes is to cover a  small
beaker containing the mixture of the substance with hydrate of
lime and a very little water, with a  watch-glass, having  a slip of
moistened turmeric or reddened litmus paper attached to the con-
vex side, to place it in hot sand, and  observe, after a few minutes,
whether the test-paper has changed color.
   4. Bichloride of platinum shows the same deportment with salts
of ammonia as with salts of  potassa;  the  yellow precipitate  of
bichloride  op platinum and  chloride op ammonium (platin-
chloride of ammonium N H4 CI, Pt Cl2) is, however, of  a some-
what lighter color  than  platinchloride of potassium.   It consists,
like the corresponding potassium  compound, of octahedrons, dis-
cernable under  the microscope.
   5. Tartaric acid added in excess to a very concentrated  neutral
solution of an ammonia salt, throws down a part of the ammonia as
bitartrate of ammonia (N H, O,  H O, C8 H4  O10).   Dilute solutions
are not precipitated.  Bitartrate of soda precipitates concentrated
solutions much more completely, and renders  dilute  solutions turbid.
Bitartrate of ammonia is a white crystalline precipitate.  Its for- 
96
AMMONIA.
[§95.
mation  is facilitated by agitation.  It deports itself towards  sol-
vents like  the corresponding  potassa-compound,  though  it is
somewhat more easily dissolved by water and acids.


                             §95.
  Recapitulation and remarks.—The  salts of potassa and soda are
not volatile at a moderate red heat, whilst  the  salts of ammonia
volatilize readily; the  latter may therefore  be easily  separated
from the former by ignition.  The expulsion of ammonia from its
compounds, by hydrate  of lime, affords the surest means of ascer-
taining  the presence of this substance.   Salts of potassa can be
detected positively only after the  removal of the ammoniacal salts
which may be present, since both classes of salts manifest the same
or a similar deportment with bichloride of platinum and tartaric
acid.  After the removal  of the ammonia, the potassa  is clearly
and positively characterized by either of these two reagents.
  It must be remembered that the reactions occur only in concen-
trated solutions.  The operator should therefore evaporate dilute
liquids to a small bulk before adding the reagents.  One drop of a
concentrated solution will  give at  once a decisive result; while no
satisfactory indications  can  be had  from any quantity of dilute
liquids.   The most simple way of detecting the potassa in the two
difficultly soluble compounds that have come under our  considera-
tion here—viz., the platinchloride  of  potassium and  bitartrate of
potassa—is to decompose these salts by ignition; the former, there-
upon, yields the potassa in the form  of  chloride of potassium, the
latter in the form of carbonate of potassa.  With respect to soda,
it  can be recognized in the humid way with entire  certainty, by
means of antimonate of potassa, provided that this reagent has been
properly prepared, its solution freshly made as directed, § 52, and
the soda solution be concentrated, neutral  or slightly alkaline in
its  reaction, and free from  other bases  save  potassa.   The anti-
monate  always appears crystalline and never flocculent.   If, by
this test, minute quantities of soda are to be looked for in presence
of much potassa, the latter is first precipitated by a slight excess
of bichloride  of platinum, the platinum is removed from the filtrate
by hydrosulphuric acid,  the  liquid is  again filtered, evaporated to
dryness, ignited gently,  and the residue is dissolved in a very little
water, and then the antimonate of potassa is applied.
  The coloration which  the  alkalies impart to the flame, furnishes,
however, the most ready and most sensitive means of recognizing
them.   The unassisted eye is indeed not able to detect  potassa in
presence of much soda;  but, by aid  of the indigo-prism  or blue
glass, the potassa flame  is brought out, while the iodide of mercury
paper or green glass serves to identify the soda flame. 
§ 95.]                     AMMONIA.                         97

  In  the spectroscope  the  characteristic  lines  of both  alkalies
appear at once with such distinctness as to preclude all chances of
mistake.  [Potassa is masked by much soda.]
  [For detecting soda in presence of potassa, antimonate of potassa
is somewhat troublesome to prepare and apply.   The spectral and
flame tests do not always enable  the  operator to discriminate be-
tween accidental traces  of soda and  such quantities as constitute
it an essential or weighable ingredient,  of a compound or mixture.
A method that supplies  this  deficiency, is moreover easy of appli-
cation to very small quantities of substance, and that serves for the
simultaneous detection of both alkalies, is the following, described
by J. Lawrence Smith.   The alkali metals must exist as  chlorides,
and  must be free from organic  acids  or  other  bases.   A  small
fragment of the  solid substance, which need not exceed \ „  of an
inch in diameter, or a drop of its concentrated aqueous solution, is
placed on a slip of glass, and to it is added a single drop of  aqueous
solution of bichloride of platinum. The plate is now gently warmed;
if potassa be present a yellow deposit  soon forms, which,  under a
good magnifier, is seen to consist of  octahedral  crystals of platin-
chloride of potassium;  the warming is continued until the liquid
begins to dry on the edges;  if it now be examined with the mag-
nifier the characteristic  slender yellow  prisms of platinchloride of
sodium will be seen.  If potassa  be present in such quantity that a
copious  precipitate of  platinchloride  of potassium separates on
addition  of bichloride of platinum, it is best to add another drop
of the reagent, and allow the precipitate to subside.  The liquid is
poured  off upon  another slip of glass, and warmed  as above
described.  When larger quantities of materials are employed, the
unassisted eye may usually recognize the  crystals of platinchloride
of sodium.    In  looking for minute  quantities  of soda,  recourse
must be had to the compound microscope.  If the slip of  glass be
viewed in the microscope by polarized light, the reaction becomes
extremely sensitive,  as  the crystals  of platinchloride  of sodium
assume prismatic colors, while those of  the  potassium salt do not
transmit polarized light.
  If  the beginner fails  to find prismatic crystals the first time he
evaporates the mixture  on the glass slip,  he should add a  drop of
water and repeat the evaporation more slowly.   This  reaction for
6oda is uncertain  in presence of lithia.]

  For the detection of exceedingly minute traces of ammonia a reaction first pointed
out by Ncssler may be employed.   Digest at  a gentle heat 2 grammes of iodide of
potassium, and 3 grammes of iodide of mercury, in 5 cub. cent, of water; add 20
cub. cent, of water, let the mixture stand for some  time, then filter; add to the
filtrate 30 cub. cent, of pure concentrated solution of potassa (1:4); and, should a
precipitate form,  filter again.  If to this solution  is added, in small  quantity, a
liquid containing ammonia or  an ammonia-salt, a  reddish brown precipitate, or with
                                7 
98      SPECIAL EEACTIONS OF  THE RARER  MEMBERS.      [§ 96.

exceedingly small quantities of ammonia, a yellow coloration is produced  by the
formation of hydrated tetrahydrargyro-iodide of ammonium (N  Hg4 1 + 2 H 0).
The chemical interchange is as  follows, viz.: 4 (Hg I, K I) + 3 K 0 -f N H3 = (N
Hg41 + 2H0) +  1KI + H0.   Application of a gentle heat favors its separation.
This precipitate redissolves in presence of an excess of ammoniacal salts; but repre-
cipitates upon further addition of potassa; it is soluble also in solution of iodide of
potassium, but the less so the more free  potassa  happens to be present.   When  a
considerable excess of potassa exists,  therefore, the precipitate is insoluble in iodide
of potassium.   Presence of chlorides  of  the alkali metals, or of salts of potassa and
soda, does not interfere with the reaction; but cyanides and sulphides of the alkali
metals prevent it.
   [According  to Bohlig, chloride  of mercury  is  the most  sensitive reagent for
ammonia, when in the free state or as carbonate.   It  gives a white precipitate or in
very dilute solutions (even when  containing but j^-0~~^  of ammonia) a white tur-
bidity due to the separation of  chloramide op mercury (Hg Cl + Hg N HL>).  In
solutions of the salts of ammonia with other acids than carbonic, a clear solution of
mixed carbonate of potassa and chloride of  mercury must  be employed,  which is
prepared by adding 10 drops of a solution of the purest carbonate of potassa  (§ 78),
(1 of salt to 50 of water) and 5  drops  of  a solution of chloride of mercury (§ 70) to
80 c. c. of water exempt  from  ammonia (such is the water  of  many springs, but
ordinary distilled water  rarely,  § 18).   This reagent may be kept in closed  vessels
for a time without change.  If much more concentrated, oxide of mercury separates
from it.  By its use the  ammonia  salt is first  converted  into  carbonate by  double
decomposition with the carbonate of  potassa,  and the further  reaction proceeds  as
before  mentioned]

                                     § 96.
            Special Reactions of the rarer Members of the First Group.
   1.  C^sia (Cs O,) and  2.  Rubidia (Rb O).   The compounds of Caesium  and
Rubidium  appear to be widely distributed in nature, though they occur  in small
quantities.   They have been found principally  in the mother-liquors of some mineral
waters and in some minerals (lepidolite).  They  have great  similarity to the com-
pounds of potassium.  Their volatile salts communicate a violet color to the flame,
and  their  concentrated  aqueous  solutions  give precipitates with  bichloride of
platinum and tartaric acid.  Characteristic of these metals is the great insolubility
of their platinchlorides.   Thus, at 50°   Fahr.  100  grm. of  water  dissolve  900
milligrm. of platinchloride of potassium, but  only 154  mgr.  of  the rubidium- and
60 mgr. of the csesium-platinchloride.  Their  spectra are especially adapted to their
detection, and characterize them most perfectly.   The spectrum of caesium (plate I.)
has the pale blue lines a  and 0  of extraordinary brilliancy and definiteness.   Next
to these in brilliancy is the line y.
   In  the spectrum of rubidium the  splendid indigo-blue lines  a and /? are most
prominent.  Less brilliant though not less characteristic are the deep red lines S and
y.  [Finally,  caesia may be separated from rubidia  by converting  both into bitar-
trates  and repeatedly recrystallizing these salts from  hot solution.—(Allen*).  Or
better, by uniting them with so much tartaric acid as will form bitartrate of  rubidia
and neutral tartrate of caesia, bringing the dried mixture on a funnel and placing it
in an  atmosphere kept  saturated with moisture; tartrate of ca?sia  deliquesces and
passes the funnel, while bitartrate of  rubidia remains behind.—(Bunscn)f ].
   3. Lithia (Li O), is of frequent  occurrence, though usually found in small quan-
tities.   It is commonly met with in analyses  of mineral waters and the  ashes of
plants, more rarely  in examining minerals, and very seldom in technical analyses

   * American Journal of Science [2]  xxxiv. 370.     f  Pogg. Annalen cxix. 3. 
§ 96.]     SPECIAL  REACTIONS  OF THE RARER  ALKALIES.      99

Lithia forms the transition  from the first to  the second group.  It is soluble in
water with difficulty, and does not become moist by exposure to the air.   Its salts
are mostly soluble in water, and some of them (chloride of lithium) are deliquescent.
Carbonate ol lithia is difficultly soluble, especially in cold water.
  Phosphate of soda produces in not too dilute solutions of lithia  salts, on boiling,
a white crystalline quickly subsiding precipitate  of tribasic phosphate of lithia,
(3 Li 0 P05).   This  characteristic reaction is far more sensitive  when the  solution
of the lithia salt together with phosphate  of soda, and so much  soda-lye as suffices
to maintain  an alkaline reaction is evaporated to dryness, the residue softened with
water, and an equal volume of solution of  ammonia  added.   In this way very small
quantities of lithia may  be separated as phosphate.   This precipitate fuses before the
blowpipe, with carbonate of soda melts to a clear bead;  fused on charcoal, it is ab-
sorbed by the latter.  It dissolves in hydrochloric acid to a solution which  remains
clear after addition of ammonia in excess;  but, on boiling, separates again  with its
original characters—(Distinction from the alkaline earths.).  Tartaric acid and bichlo-
ride of platinum do not affect even concentrated solutions of lithia-salts.  When a salt
of lithia is brought into the blowpipe or gas-flame (§  14.) the latter is tinged carmine-
red.  Silicates containing lithia are mixed with sulphate of lime.  Phosphate of lithia
colors the  flame  when tho fused salt is  moistened with  hydrochloric acid. The
lithia flame  is completely masked by that of soda, and when the latter substance  is
present the  flame must  be examined by a  blue glass or by the thinner parts of the
indigo prism.   A small quantity of potassa does  not disguise the lithia flame.  In
presence of  much potassa, lithia may be detected by comparing  through the indigo-
prism the flame of the  substance to be tested  with  that of a pure potassa-salt.  In
this experiment, the two substances are placed near each other on opposite sides of
the zone of  fusion of the Bunsen lamp.  The potassa-lithia flame, viewed through the
narrow part of the prism, appears redder in color than the  pure potassa flame ; at a
certain thicker point in the prism both flames  appear  equally  red if the  proportion
of lithia is  very small.   If lithia predominates, the  intensity of the flame reddened
by  it, diminishes perceptibly,  when seen  through the thicker parts of the  prism,
while  the  potassa flame is  scarcely affected.   In  this way a few  thousandths  of
lithia  may be  recognized iu salts of potassa.   Soda scarcely influences the result
unless it is present in very large quantity. — Cartmell, Bunsen.
  The spectrum of lithium (Plate I.) is  characterized by the fine carmine-red line a
and the faint  orange-yellow  line /?.  If chloride of lithium is  heated with  alcohol
and the latter be set on fire, it burns with a magnificent carmine-red color.  Soda-
salts disguise this reaction.
  In order to discover small quantities of caesia, rubidia and lithia when associated
with  a large  amount of potassa and  soda, the dry chlorides are extracted. with
alcohol of 90 per cent, and a few drops of hydrochloric acid, which leaves untouched
the greater share of the chlorides of sodium and potassium.   The alcoholic solution
is evaporated  to dryness, the  residue is dissolved in a little water and precipitated
with bichloride of platinum.  The precipitate  is repeatedly boiled  out  with fresh
quantities of  water, being tested each time in  the spectroscope.   If  rubidia and
caesia be present,  the spectra of these metals will shortly appear, while  that of
potassa becomes less marked.
  The filtrate  from the precipitate  of platinchlorides is evaporated to dryness, the
residue is gently heated in a  current of hydrogen gas  in  order to decompose  platin-
chloride of sodium and bichloride of platinum, it is then moistened with hydrochloric
acid, dried, and the  chloride of  lithium is extracted with  a mixture of ether and
absolute alcohol.   This  solution, on evaporation, leaves behind  chloride of lithium
in a nearly pure state, which can be  further tested.  Before deciding from  tho sim-
ple  flarao that lithia is present, the dilute aqueous  solution of a portion  of the
supposed chloride  of lithium must be  examined with  carbonate  of ammonia to 
100
BARYTA.
[§§ 97, 98.
demonstrate the absence of strontia and lime.  The addition of hydrochloric acid
before extraction with alcohol is needful, because  chloride of lithium on moderate
ignition is partially converted into caustic lithia, which, by absorbing carbonic acid
from the air, becomes insoluble in alcohol.

                              § 97.
              second group. alkaline earths.
             Baryta, Strontia,  Lime, Magnesia.
  Properties of the group.—The  alkaline earths in a pure (caustic)
state are soluble in water.  Magnesia, however, dissolves but very
sparingly in water.  The solutions manifest alkaline reaction ; the
alkaline reaction of magnesia is most  clearly apparent when that
earth is laid  upon moistened test-paper.   The neutral  carbonates
and phosphates of the alkaline earths are insoluble in water.  The
solutions of the salts of the alkaline earths are therefore precipitated
by alkaline carbonates and phosphates.   This deportment distin-
guishes the  oxides of the  second group from those of the first.
They are further distinguished from the oxides of the  subsequent
groups by not being thrown down from their solutions  by hydro-
sulphuric  acid and  sulphide of ammonium.   The  alkaline earths
and their salts are  colorless, and not volatile at a gentle red-heat;
the solutions of  their nitrates and chlorides are not precipitated by
carbonate of baryta.

                       Special Reactions.
                              § 98.
                       a. Baryta (Ba O).
  1.  Caustic baryta is pretty  readily  soluble in hot  water, but
rather difficultly so in  cold water; it dissolves  easily in  dilute
hydrochloric or nitric acid.  Hydrate of baryta fuses but does not
lose its water upon ignition.
  2. Most of the salts of baryta are insoluble in witter.   The solu-
ble salts do not  affect vegetable colors, and are decomposed upon
ignition, with the exception of chloride  of barium.  The insoluble
salts dissolve in  dilute hydrochloric acid, except sulphate of baryta
and  silicofluoride of barium.  Nitrate of baryta and chloride of
barium are insoluble in  alcohol, and do not deliquesce in the air.
Concentrated solutions of baryta are precipitated by hydrochloric
or nitric acid added in large proportions, as chloride of barium and
nitrate of baryta are  not soluble in the  aqueous solutions of  the
said acids.
  3 Ammonia (free from carbonic acid) produces no precipitate in
the aqueous solutions of salts  of baryta; soda  or potassa (free from
carbonic acid) only in highly concentrated solutions.  Water redis-
solves the bulky precipitate of crystals of baryta (Ba O, H O -f
8 aq.) produced by soda  or potassa. 
r
 § 98.]                      BARYTA.                        101

   4.  Alkaline carbonates throw down from solutions of baryta car-
 bonate of baryta (Ba O, C 02) in the form of a white precipitate
 When carbonate of ammonia is used as the precipitant, or if the
 solution was previously  acid, complete precipitation  takes  place
 only  upon heating the fluid.   In chloride of ammonium the precipi-
 tate is soluble to a trifling yet clearly perceptible  extent; in very
 dilute solutions of baryta, therefore, which contain much chloride
 of ammonium, carbonate of ammonia produces no precipitate.
   5.  Sulphuric acid and all the soluble sulphates, also solution of
 sxdphate of lime, produce even in very dilute solutions  of baryta, a
 heavy, finely pulverulent, white precipitate of sulphate of baryta
 (Ba O, S 03), which is insoluble in alkalies, and scarcely soluble in
 dilute acids; but is  perceptibly  soluble in  boiling concentrated
 hydrochloric and  nitric  acids.   In  strong solutions of ammonia
 salts, when excess of sulphuric acid is not present, it is also soluble.
 As a  rule, this precipitate is  formed immediately upon the addition
 of the  reagent; from highly dilute  solutions, however,  especially
 when strongly acid, it separates only after some time.
   6.  Hydrofluosilicic acid throws down from solutions  of baryta
 silicofluoride of barium (Ba Fl + Si Fl2), in form of  a  colorless,
 crystalline, quickly subsiding precipitate.  In dilute solutions this
 precipitate is formed only after the lapse of some time ;  it is per-
 ceptibly soluble in hydrochloric and nitric acids.  Addition of an
 equal volume of alcohol hastens the precipitation and makes  it so
 complete that the filtrate remains  clear upon addition of  sulphuric
 acid.
   7.  Phosphate of soda  produces in neutral or alkaline solutions
 of baryta a white precipitate of phosphate  of baryta (2 Ba O,
 II O, P 05),  which is soluble in free acids.  Addition of ammonia
 only slightly increases the quantity of this precipitate, and converts
 a  portion  of it into  basic phosphate of baryta (3 Ba O, P 05).
 Chloride of ammonium dissolves it to a clearly perceptible extent.
   8.  Oxalate of ammonia produces in moderately dilute solutions
 of baryta a white, pulverulent precipitate  of  oxalate  of baryta
 (2 Ba O, C4 Os -f 2 aq.) which is soluble in hydrochloric and nitric
 acids.   When  recently thrown down,  this precipitate  dissolves
 also in oxalic and acetic acids; but the  solutions speedily  deposit
 binoxalate of baryta (Ba O, II O, C4 06 + 2 aq.) in the form  of  a
 crystalline powder.
   9. Soluble  pulverized salts of baryta, when heated with dilute
 spirit  of wine, impart to the  flame  a greenish  yellow color,
 which, however, is not very characteristic.
   10.  Salts of baryta, when  exposed  on a platinum wire to the
inner  blowpipe flame, or the zone of fusion of the gas lamp, color
the flame yellowish-green.  The soluble baryta-salts, together
with the carbonate and sulphate, give the reaction at once, or after 
  102                       STRONTIA.                     [§ 99,

  a little time—phosphate of baryta and  silicates decomposable by
  acids, after moistening with sulphuric or hydrochloric acid. Silicates
  not decomposable by acids must be fluxed with carbonate of soda,
  and the carbonate of baryta  thus  obtained is  examined  in  the
  flame.  The presence of salts of lime and strontia does not prevent
  the reaction when the sulphates are employed.
   11. The baryta flame is characterized by  its appearing blue-
  green when viewed through the green glass.
   12. The spectrum of baryta is figured  on Plate I.  The green
  lines a and (3 are the most intense.   Less distinct but  still charac-
  teristic is the line y.
   13. Sulphate of  baryta is not all or but very slightly decom-
 posed by cold solutions of alkaline bicarbonates or of carbonate  of
 ammonia. It is also not  perceptibly decomposed by  a boiling
 solution of 1 part of carbonate and 3 parts of sulphate of potassa.
 Boiling solutions of neutral carbonates of the alkalies, if renewed
 sufficiently often,  decompose  it  completely.   By  fusing it with
 carbonate of soda or  potassa, it is easily and perfectly decomposed,
 there being formed  sulphate  of  the alkali which  is soluble, and
 carbonate of baryta which is insoluble in  water.

                              § 99.
                      b. Strontia (Sr O).
   1. Strontia and its hydrate and salts manifest nearly the same
 general  deportment and properties as baryta and its  correspond-
 ing  compounds.—Hydrate of  strontia is  more difficultly soluble
 in water than hydrate of baryta.—Chloride of strontium  dissolve?
 in absolute alcohol,  and deliquesces in moist  air.   Mtrate of
 strontia is  insoluble in absolute alcohol, and does not deliquesce in
 the air.
   2. The salts of strontia manifest with ammonia and potassa,
 and also with the alkaline carbonates and  with phosphate  of soda,
 nearly the  same deportment as  the salts of baryta.  Carbonate of
 strontia dissolves somewhat  more  difficultly in chloride of ammo-
 nium than  is the case  with carbonate of baryta.
  3.  Sulphuric acid  and  sulphates precipitate  from solutions of
 strontia  sulphate of strontia (Sr O, S  03), in form  of a  white
 powder.   Application of heat  greatly promotes the precipitation.
 Sulphate of strontia is far more soluble in water than sulphate of
baryta ; owing to this readier solubility, the  precipitated  sulphate
 of strontia separates from rather dilute solutions, in general, only
 after the lapse of some time; and this is invariably the  case  (even
in concentrated solutions) if solution of sidphate of lime is used  as
precipitant. Sulphate of strontia is insoluble  in alcohol;  addition
of the latter, therefore, facilitates its separation.   It is perceptibly 
 § 99.]                     STRONTIA.                       103

 soluble in hydrochloric and nitric acids, and the delicacy of this
 reaction is therefore greatly diminished when these  acids are pre-
 sent.  The solution of sulphate of strontia in hydrochloric acid is
 made turbid by chloride of barium, after addition of water.
   4. Hydrofluosilicic acid fails to produce  a precipitate  even in
 concentrated solutions of strontia; even upon addition of an equal
 volume  of  alcohol  no precipitation  takes place, except  in very
 highly concentrated solutions.
   5.  Oxalate  of ammonia precipitates even  from rather dilute
 solutions, oxalate of strontia (2 Sr 0, C4 06  + 5 aq.), in form
 of a white  powder, which dissolves readily in  hydrochloric and
 nitric acid, and perceptibly in salts of ammonia, but is  only spar-
 ingly soluble in oxalic and acetic acid.
   6. If salts of strontia soluble in water or  alcohol, are heated
 with dilute  spirit of wine, and the latter kindled, the flame appears
 of an intense carmine  color, more particularly upon stirring  the
 mixture.
   7. Salts of Strontia, when  exposed  on platinum wire to  the
 inner blowpipe flame, or brought into the zone of fusion of the
 gas lamp, impart an intense red color to the flame.  Chloride  of
 strontium  gives the   strongest  reaction.  With carbonate and
 sulphate  of strontia  the  coloration  is  less intense.   The com-
 pounds with fixed  acids scarcely affect the flame.  The  substance
 to be examined is therefore first placed by itself in  the flame and
 afterwards, when moistened with  hydrochloric acid, is  again sub-
 jected to its action.  If sulphate of strontia is suspected, it is first
 exposed a short time to a reducing  flame (whereby sulphide  of
 strontium is formed), before it is treated with hydrochloric acid.
   8. The strontia  flame, viewed  through the blue  glass, appears
 purple to rose colored, and is hereby distinguished from the lime
 flame which under  the same circumstances  has a faint green-gray
 tint.  In presence of baryta the strontia reaction only  appears at
 the moment when the substance moistened with hydrochloric acid
 is first brought into the flame.
  9. The spectrum of strontia is represented in Plate I.  It con-
 tarns numerous characteristic lines, especially the orange line, a,
 the red lines (3 and 7 and the blue line 8.   The last is  especially
 adapted for detecting strontia in presence  of lime.
  10. Sulphate  of strontia is completely  decomposed by long
 digestion with solutions of carbonate of ammonia or of bicarbo-
 nates of the alkalies ; also, and far more  readily, by boiling with
 a solution of 1 part of carbonate and three  parts of sulphate  of
potassa (important  distinction from sulphate of baryta). 
104
LIME.
[§ ioo.
                             §100.
                        c. Lime (Ca O).
  1. Lime and its  hydrate and  salts present, in their general
deportment and properties, a great similarity to baryta and strontia
and their corresponding compounds.  Hydrate of lime  is far more
difficultly soluble in water than the hydrates of baryta and strontia;
it  dissolves, besides, more sparingly in hot than in cold water.
Hydrate of lime loses its water upon ignition.   Chloride of calcium
and nitrate of lime are soluble in absolute alcohol, and deliquesce
in the air.
  2. Ammonia, alkaline carbonates, and phosphate of soda, pre-
sent nearly the same deportment with salts of lime as with salts
of baryta.  Recently precipitated carbonate of lime (Ca O, C Oa)
is bulky and amorphous—after a time, and immediately upon appli-
cation of heat, it falls down and assumes a crystalline form.  When
recently precipitated, it dissolves  pretty  readily in solution of
chloride of ammonium ; but the solution speedily becomes turbid,
and deposits the greater part of the dissolved salt in form of crystals.
  3. Sulphuric acid and sulphate of soda produce immediately in
very concentrated solutions of lime, white precipitates of sulphate
of lime (Ca O, S 03, H O + aq.), which redissolve completely in  a
large  proportion of water and are still far more soluble  in acids.
In less  concentrated  solutions the precipitates are formed only
after the lapse of some time ; and no precipitation whatever takes
place in dilute solutions.   Solution of sulphate of lime of course
cannot produce a precipitate in salts  of lime ; but even a cold satu-
rated solution of sulphate of potassa, mixed with 3 parts of water,
produces  a precipitate only after standing from twelve to twenty-
four hours.  In solutions of lime which are so very dilute that
sulphuric  acid  has  no apparent action  on them, a precipitate will
immediately form upon addition of alcohol.
  4. Hydrofluosilicic acid does not precipitate salts of lime.
  5. Oxalate of ammonia produces even in very dilute  solutions
of lime a white  pulverulent precipitate of oxalate of lime.  The
composition of this precipitate, when thrown down hot  or from
concentrated solutions, is  2 Ca O,  d  O   + 2 aq; whilst  when
thrown down cold from dilute solutions, it consists of a mixture of
the above salt with  2 Ca O, C4 06 +  6 aq.   In very dilute solutions
the precipitate forms only after some time.  It is readily soluble in
hydrochloric and nitric acids, but dissolves to a trifling extent only
in acetic and oxalic acids.
  6. Soluble salts of lime,  when heated with dilute spirit of wine,
impart to the flame  of the latter a yellowish-red  color,  which is
often confounded with that communicated to the flame of alcohol
by salts of strontia. 
§ 101.]
MAGNESIA.
105
   7. Salts of lime when brought into the inner  blowpipe flame or
 into the zone of fusion  of the Bunsen lamp communicate a yel-
 low-red color to the flame.   This reaction is most evident with
 chloride of calcium.  Sulphate of lime gives it after it has become
 basic.  Carbonate of lime manifests it most plainly when the carbo-
 nic acid has been expelled.  Compounds of lime with acids which
 are not volatile at a high temperature do  not tinge the flame ; if
 they are decomposed by hydrochloric acid, the coloration appears
 after moistening them with this acid.   To promote its action, the
 loop of the  platinum  wire  is flattened with a  hammer, a small
 quantity of the substance is brought upon it and heated until it has
 caked together, a drop of hydrochloric acid is added, and the whole
 brought at once into the flame.  At the moment when the drop of
 acid disappears the reaction is most plainly exhibited.—Bunsen.
   8. Viewed  through  green-glass,  the flame  obtained as  just
 described, appears siskin-green. This distinguishes it from strontia,
 which under the same  circumstances has a very faint yellow color.
 Merz.   In presence of baryta, the reaction is only manifest at the
 moment when the  substance moistened with hydrochloric acid is
 brought into the flame.
   9. The spectrum of lime is mapped on Plate I.   The bright green
 line (3 and the  orange line a are the  most characteristic.  The
 indigo-blue  line  at  the right of the spectrum is only seen  in a
 good  spectroscope.
   10. Sulphate of  lime manifests the same deportment towards
 alkaline carbonates and bicarbonates as sulphate of strontia.


                            § 101.
                     d.  Magnesia (Mg O).
   1. Magnesia and its hydrate are  white powders of far greater
 bulk than the other alkaline earths and their hydrates.  Magnesia
 and hydrate of magnesia are nearly insoluble both in cold and hot
 water.   Hydrate of magnesia loses its water upon ignition.
   2. Some of the salts of magnesia are soluble in water, others
 are insoluble in  that fluid.   The  soluble salts of magnesia have a
 nauseous bilter taste ; in  the neutral state they do not alter vegeta-
ble colors ; with the exception of sulphate of magnesia, they undergo
decomposition when gently ignited, and the greater part of them
even upon simple evaporation of their solutions.   Sulphate of mag-
nesia loses its acid at a strong white heat.  Nearly all the salts of
magnesia  which are insoluble in water dissolve in hydrochloric
acid.
  3. Ammonia throws  down  from the solutions of neutral  salts
of magnesia part of the magnesia as hydrate (Mg O, H O), in form
of a white, bulky precipitate.  The rest of the magnesia remains 
106
MAGNESIA.
[§ 101.
in solution as a double salt, viz., in combination with the ammoniacal
Bait which forms upon the decomposition of the salt of magnesia ;
these double salts are not decomposed by ammonia.  It is owing
to this tendency of salts of magnesia to form such double salts with
ammoniacal compounds, that ammonia fails  to precipitate them in
presence of  ammoniacal salts  in sufficient proportion,  or, what is
the same, that ammonia produces no precipitate in solutions of
magnesia containing a sufficient quantity of free acid; and that pre-
cipitates produced by  ammonia in neutral  solutions of magnesia
are redissolved  upon the addition of chloride of  ammonium.
  4. Soda, potassa, caustic  baryta and caustic  lime throw down
from  solutions of magnesia  hydrate  of magnesia. The  separa-
tion of the precipitate is greatly promoted by boiling the mixture.
Chloride of  ammonium  and other  similar  salts of ammonia redis-
solve  the precipitated  hydrate of magnesia  if the  precipitant has
not been added greatly in excess.  If the salts of ammonia are added
in sufficient quantity to the solution of magnesia before the addition
of the precipitant, small quantities of the latter fail altogether to
produce a precipitate.  However, upon boiling the solution after-
wards with an excess of soda, the precipitate will, of course, make
its appearance, since  this process causes the  decomposition of the
ammoniacal salt, removing thus the  agent which retains the hydrate
of magnesia in solution.
  5.  Carbonate of soda and carbonate of potassa produce in
neutral solutions of magnesia a white precipitate of basic carbon-
ate of magnesia 4 (Mg O, C02) + Mg O H O +10 aq.  One-fifth of
the carbonic acid of the decomposed alkaline carbonate is liberated
in the process, and combines with  a portion of  the  carbonate of
magnesia to bicarbonate, which remains in solution.   This carbonic
acid escapes upon ebullition and a further precipitate (Mg O C 02+
3 aq.) is  produced.  Chloride of ammonium and  other similar salts
of ammonia prevent this precipitation also, and redissolve the pre-
cipitates already formed.
  6.  Carbonate of ammonia added to solutions of magnesia does
not at once  cause a precipitate.  After a time, however, except in
very  dilute  solutions, a crystalline precipitate forms,  which is a
double carbonate of ammonia and magnesia (1ST H4 O, C02+Mg
O C02-f-4 aq.)  It separates the  more rapidly  the more concen-
trated are the solutions.  Excess of carbonate of ammonia and free
ammonia promote its formation.  Chloride of ammonium hinders,
but, in concentrated solutions, cannot  altogether prevent its  sepa-
ration.
   7.  Phosphate of soda precipitates from solutions of magnesia, if
they are not too  dilute, phosphate of magnesia  (2 Mg O,  H O,
P 03 + 14 aq.) as a white powder.   On boiling, basic phosphate of
magnesia (3 Mg O, P 05 + 7 aq.) is formed which separates even 
§ 102.]                    MAGNESIA.                       107

from quite dilute solutions.  But if the addition of the precipitant is
preceded by that of chloride of ammonium and ammonia, a white
crystalline  precipitate  of basic phosphate of  magnesia  and
ammonia (2 Mg O, 1ST Hi O, P 0.5+12 aq.)will separate, even from
very dilute solutions of magnesia; its separation  may be greatly
promoted and  accelerated by vigorous stirring with a glass rod:
even should the solution  be so extremely dilute as to forbid the
formation of a precipitate, yet the lines of direction in which the
glass rod has  moved  along the side of the vessel will,  after the
lapse of some time, appear distinctly as white streaks.  Water and
solutions  of  salts of  ammonia dissolve the precipitate but very
slightly ; but it is readily soluble in acids, even  in acetic acid.  In
water containing ammonia it is as good as insoluble.
  8. Oxalate  of ammonia produces no precipitate in highly dilute
solutions of magnesia; in  less dilute solutions no precipitate is
formed  at  first, but after some time crystalline crusts of various
oxalates  of ammonia  and magnesia  make  their appearance.   In
highly concentrated solutions oxalate of ammonia very speedily pro-
duces precipitates of oxalate of magnesia (2 Mg O, C4 0G-4-4  aq.),
which  contain  small quantities of the  above-named double salts.
Chloride of ammonium, especially in  presence  of free ammonia,
interferes with  the formation of these precipitates; but, as  a  rule,
it does not absolutely prevent it.
  9. Sulphuric acid and hydrofluosilicic acid do not precipitate
salts of magnesia.
  10. If magnesia, or  a salt of magnesia, is moistened with  water,
heated to redness on a charcoal support, then moistened with  1 drop
of solution of nitrate of protoxide of cobalt, and again heated at first
to gentle redness, ultimately to intense redness, in the oxidation flame,
a pinkish mass is obtained,  the  color of which becomes distinctly
apparent only  upon cooling, but is never very intense.   Alkalies,
alkaline earths, and heavy metallic  oxides prevent the reaction.
  11. Salts of magnesia impart no coloration to the flame.

                            § 102.
  Recapitulation and remarks.—The difficult solubility of the
hydrate of magnesia,  the ready solubility of the sulphate, and the
disposition of salts of magnesia to form double salts with  ammo-
niacal compounds, are  the three principal points in which magnesia
differs  from the  other alkaline earths.   To  detect magnesia we
always first remove the baryta, strontia, and lime, if these  bodies
happen to be present.
  This is accomplished most conveniently (because the latter bases
are at the same time procured in the form best adapted for further
examination) by  precipitating with carbonate  of ammonia  with
addition of some caustic ammonia and chloride of ammonium, and 
108                      MAGNESIA.                    [§ 102.

gently heating.   If the solutions  are moderately dilute and the
precipitate is shortly brought upon  a filter, it consists of carbonates
of baryta, strontia, and lime,  while  all  the magnesia remains in
solution and  is found in the filtrate.   Since, however, chloride of
ammonium dissolves carbonate of  baryta and even carbonate of
lime to some, though but a slight extent, small quantities of these
bases pass into  the filtrate, and when but traces of them are pre-
sent they may remain entirely in solution.
  In exact investigations it  is therefore advisable  to divide  the
filtrate into three portions, in one of which any dissolved baryta is
detected by dilute sulphuric acid, while the second is tested for lime
by means of  oxalate of ammonia.  In case these reagents produce
no turbidity,  even after the lapse of  some time,  the third portion
is examined for magnesia by means of phosphate of soda.  If, on the
other hand, a precipitate appears in either of the first two portions,
it is filtered off after it has completely subsided, and the filtrate is
tested for magnesia.   If both the first and  second portions are
turbid they are mixed  together, after some  time are  filtered, and
the filtrate is tested with phosphate of soda.   To prove that a pre-
cipitate produced by oxalate of ammonia is really oxalate of lime,
and not an oxalate of ammonia and  magnesia, it is dissolved in a
little hydrochloric acid, and a  few drops of dilute  sulphuric  acid
and some alcohol are added, when sulphate of lime should separate,
if lime were present.
  The  precipitate by carbonate of ammonia may be examined for
baryta, strontia, and lime, as follows:
  It is dissolved, after  washing,  in dilute hydrochloric acid.  To
a small portion of the liquid, solution  of sulphate  of  lime is added;
an immediate precipitate is proof of the presence of  baryta.  The
rest of the hydrochloric solution is  evaporated to dryness and the
residue is treated with absolute alcohol (§ 19).  Chloride of barium
mostly remains undissolved while the chlorides of  strontium  and
calcium enter into solution.  The alcoholic solution  is mixed with
an equal volume of water and some drops of hydrofluosilicic  acid ;
the last traces of baryta are thus thrown down if  the  mixture is
allowed to stand for  several hours.  To the  alcoholic filtrate, sul-
phuric acid is added which precipitates from  it strontia  and lime.
The precipitated sulphates are collected on  a filter, washed with
weak alcohol [4 volumes of alcohol of 92 per cent, mixed with 5
volumes  of water], and converted into carbonates by boiling with
solution  of carbonate of soda.  The carbonates  thus  obtained are
well washed  with water, dissolved in  a little hydrochloric acid, the
solution is evaporated  to dryness, and the residue is  taken up by
a little water.  The aqueous solution is filtered, if  necessary, and
divided into  two portions.   To one of these, solution of sulphate
of lime is added ; a precipitate formed after some time, it may be 
§ 102.]
MAGNESIA.
109
a long time, indicates strontia.  The other portion is treated with
solution  of sulphate of potassa, heated to  boiling and filtered, to
remove strontia.  The filtrate from the  sulphate  of  strontia is
tested with oxalate of ammonia for lime.  In precipitating strontia
by sulphate of potassa, a portion of the lime may also be separated
if it is present in large quantity, but enough always remains in the
filtrate to detect with certainty.
  The best way of detecting the alkaline  earths, when in the form
of phosphates, is to decompose these latter by means  of sesqui-
chloride of iron with the addition of acetate of soda (§ 145).   The
oxidates  of the  alkaline  earths  are converted into carbonates by
ignition,  preparatory to  the detection of the individual  earths
which they contain.
  A mixture of the sidphates of the alkaline earths is first washed
with small quantities  of boiling water.  All the suJphate of mag-
nesia and a small quantity of sulphate of lime thus  pass into solu-
tion.   The residue, which must be finely pulverized,  is digested, as
Rose recommends, for 12 hours in a cold  solution of carbonate of
ammonia, or is  boiled 10 minutes in a solution of one  part of car-
bonate and three parts of sulphate of potassa, thrown on a filter,
thoroughly washed, and then treated with dilute hydrochloric acid,
which dissolves the carbonates  of lime and strontia,  and likewise a
slight  trace of baryta (Fresenius); but leaves  behind  sulphate of
baryta.  The latter can be  decomposed by fusion with carbonate
of soda.   The solutions thus obtained are to  be further tested as
previously directed.
  By aid of the spectroscope, baryta, strontia, and lime may be
detected,  even when occurring together, far more easily than by
following the highly instructive but  somewhat tedious  processes
of the humid  method.   The   substance  under examination  is
brought  into  the flame  of the  gas-lamp, either  directly or after
moistening with hydrochloric acid.
  [Minute quantities of baryta and strontia give no spectral lines
in  presence  of much lime.  Engelbach  directs that  the  mixed
carbonates be strongly ignited  by means of a blast-lamp for a few
minutes,  whereby, in  presence of carbonate  of lime, baryta and
strontia readily become  caustic.  The mass  is  extracted with  a
little  distilled  water,  the  solution evaporated to  dryness  with
hydrochloric  acid and the residue examined in the spectroscope.]
  The earths just named may also be severally recognized in their
mixtures,  without the spectroscope, by observing the   coloration
they impart to the flame.   The substance is repeatedly moistened
with sulphuric acid and cautiously dried.   It is then brought into
the zone of fusion of the  gas flame.  After any alkalies that may
be  present in  the mixture have volatilized, the baryta coloration
tppears by itself.  (§ 98, 10.) 
110
OXIDES.
[§§ 103, 104.
   After it has entirely disappeared, and the substance on moisten-
ing with hydrochloric acid gives, at the  moment when the latter
evaporates, no more a flame, that seen  through the green glass
appears blue-green, the substance is again  moistened with hydro-
chloric acid,  and its flame  examined  by help of the green glass
(§100, 8), for lime, and with the blue glass for strontia.—Merz.

                              §103.
                          THIRD GROUP.
   Of common occurrence: Alumina, Sesquioxide  of Chromium.
Of rare occurrence: Glucina, Thoria, Zirconia, Yttria, Terbia,
    Erbia, Oxides of Cerium, Lanthanum, Didymium ; Titanic,
    Tantalic, and Hyponiobic Acids :
  Properties of the group.—The oxides  of the  third  group are
insoluble in water, both in the pure state  and as hydrates.  Their
sulphides cannot be produced in the humid  way.  Hydrosulphuric
acid therefore fails  to precipitate their  solutions.  From salts in
which  the  oxides of the  third  group play the part of base,* sul-
phide of ammonium as well as ammonia, throws down the hydrated
oxides.  This deportment with sulphide of ammonium distinguishes
the oxides  of  the third from those of the  two preceding groups.

  Special Reactions  of the  more commonly occurring Oxides.

                     a.   Alumina (Al2 O ).
  1.  Aluminum is a nearly white metal.   It undergoes no oxida-
tion on exposure to the air, and when massive  scarcely oxidizes on
ignition.  It is very malleable  and may  be wrought by  the  file.
Its sp.  gr. is but  2.56.  It fuses at  a bright red heat.  The finely
divided, but not the compact metal, decomposes water at a boiling
heat.   Aluminum dissolves easily in hydrochloric acid as well as in
hot soda-lye,  with evolution of hydrogen.   It is but slowly dis-
solved even by hot nitric acid.
  2. Alumina is non-volatile and  colorless; the  hydrate is also
colorless.   Alumina  dissolves in acids (particularly when dilute)
slowly and with  very great  difficulty;  in  fusing  bisulphate of
potassa it  dissolves  readily to  a  mass  soluble  in  water.  The
hydrate in an amorphous  state,  and  recently precipitated,  is
readily soluble in acids; but after being left  some time in the fluid

  * The oxides  of the third group are mostly capable of uniting with acids  as
well as with  bases to produce saline compounds, e.  g. alumina unites with  potassa
forming aluminate of potassa, and with sulphuric acid  yields  sulphate of alumiua.
These oxides, therefore, stand in part on the boundary between bases and acid.
Those which  most nearly agree  in character with the latter are designated as acids. 
§ 104.]
OXIDES.
Ill
 from which it was precipitated, its solubility decreases, and in the
 crystallized state it dissolves  with very great difficulty in  acids.
 After previous ignition with alkalies, which leads to the formation
 of aluminates of the alkalies, alumina is readily dissolved by acids.
   3.  The salts of  alumina are mostly colorless, and non-volatile:
 some of them are soluble, others insoluble.  Anhydrous chloride of
 aluminum is a yellow crystalline volatile solid.  The soluble salts
 have a sweetish astringent taste,  redden litmus paper, and lose
 their acids  upon ignition.  The insoluble salts are  dissolved by
 hydrochloric acid, with the exception of certain native compounds.
 The  compounds of alumina which are insoluble in hydrochloric
 acid are decomposed and made soluble by ignition with  carbonate
 of soda and potassa, or bisulphate of potassa.  They may also be
 decomposed and brought into solution by heating for two hours at
 a temperature of 390° to 410Q Fah. with hydrochloric  acid of 25
 per cent, or  with a mixture of three parts of hydrated sulphuric
 acid and  1  part of water.   The substance must be in a state of
 fine  division.   The  heating is performed in  a sealed glass tube.
 —(A. Mitscherlich.)
   4.  Soda andpotassa throw down from solutions of alumina a bulky
 precipitate of hydrate of alumina (Al2 03 3 H O), which contains
 alkali, and  generally also  an  admixture of basic salt;  this pre-
 cipitate  re-dissolves readily and completely in an excess  of the
 precipitant, but from this solution  it is reprecipitated by addition
 of chloride  of ammonium, even in the cold, but more completely
 upon application of heat (compare  § 54).  The presence of salts
 of ammonia does not prevent the precipitation by potassa or soda.
   5. Ammonia also produces in solutions of alumina a precipitate
 of hydrate of alumina, containing ammonia  and an admixture
 of basic salt; this precipitate also redissolves in a very considerable
 excess of the precipitant, but with difficulty  only, which  is  the
 greater the  larger the quantity of salts  of ammonia contained in
 the solution.  It is  this  deportment which accounts  for the com-
 plete  precipitation of hydrate of alumina from solution in potassa,
 by an excess of chloride of  ammonium.
   6.   Carbonates  of the  alkalies  throw  down from  solutions of
 alumina basic carbonate of alumina, which  is insoluble or but
 very slightly soluble in excess of the precipitant.
   7.  If the  solution of a salt  of alumina  is digested with finely
 pulverized carbonate of baryta, the greater part of the acid of the
 alumina salt combines with  the baryta, the liberated carbonic acid
 escapes, and the alumina precipitates completely as hydrate mixed
 with basic salt of  alumina ; even digestion in the cold suffices to
produce this reaction.
  8.  If alumina or  one of its compounds is ignited upon charcoal
before the blowpipe, and afterwards moistened with a solution of 
 112              SESQUIOXIDE  OF CHROMIUM.  .        [§ 105

 nitrate of protoxide of cobalt, and then again strongly ignited, an
 unfused mass of a deep sky-blue color is produced, which consists
 of a compound of the two oxides.  The blue color becomes distinct
 only upon cooling.  By candlelight it appears  violet.   This reac-
 tion is decisive only in  the case of infusible or  difficultly fusible
 compounds of alumina pretty free from other oxides,  as solution
 of cobalt imparts a blue tint to  readily fusible  salts, even though
 no alumina be present.

                             § 105.
              b. Sesquioxide of Chromium (Cr2 Oj).
   1. Sesquioxide of Chromium is a green, its  hydrate a bluish
 gray-green powder.  The hydrate dissolves readily in  acids :  the
 non-ignited sesquioxide dissolves more  difficultly,  and the ignited
 sesquioxide is almost altogether insoluble.
   2. The  salts of sesquioxide of chromium have a green or
 violet color.   Many of them are soluble in water.  Most of them
 dissolve in hydrochloric acid.  The solutions exhibit either a fine
 green or a deep  violet color; the latter, however,  acquire a green
 tint when even  moderately heated. The  salts  of sesquioxide of
 chromium with volatile acids are decomposed upon ignition,  the
 acids being expelled.   The salts of sesquioxide of chromium which
 are soluble in water redden litmus.   Anhydrous sesquichloride of
 chromium is crystalline, difficultly volatile, insoluble in  water and
 acids, and of a fine violet color.
   3. Potassa and soda produce in solutions, both of the green and
 violet salts of sesquioxide of  chromium, a bluish-green  precipitate
 of hydrate of sesquioxide of chromium, which dissolves readily
 and completely in an excess  of the precipitant, imparting to  the
 fluid an emerald-green tint.  Upon long-continued ebullition of
 this  solution, the  whole of  the  hydrated sesquioxide separates
 again, and the supernatant fluid  appears perfectly colorless.   The
same reprecipitation takes place if chloride of ammonium is added
to the alkaline solution, and the mixture heated.
  4.  Ammonia precipitates from the green solutions of sesquioxide
of chromium  grayish-green, from the violet solutions, grayish-blue,
hydrate of sesquioxide  of chromium.  The former  precipitate
dissolves in acids with a green, the latter with a violet color.  The
color and composition of these precipitates is influenced  by various
circumstances; viz., the concentration  of the solutions, the mode
in which the precipitant is added, &c.  A small portion of these
hydrates may redissolve in an excess of the precipitant in the cold,
imparting to  the fluid a peach-blossom  red tint; but if, after  the
 addition of ammonia in excess, heat is applied to the mixture,  the
 precipitation  is complete. 
  § 106.]          SESQUIOXIDE OF CHROMIUM.              113

   5. Carbonates of the alkalies precipitate basic carbonate of
  sesquioxide of chromium, which is soluble in a  large excess of
  the precipitant.
   6. Carbonate of baryta precipitates from solutions of sesqui-
  oxide of chromium the whole of the sesquioxide as a greenish
  hydrate mixed with basic salt.  The precipitation takes  place
  in the cold, but is complete only after long-continued digestion.
   7. If the solution of sesquioxide of  chromium in soda or potassa-
  lye  is boiled a' short time with an excess of binoxide of lead, the
 sesquioxide of chromium is converted into chromic acid.  On filter-
 ing, a yellow fluid is obtained, which holds chromate of lead in
 solution, and upon supersaturation with acetic acid, chromate  of
 lead  separates  in form   of  a  yellow  precipitate.—(Chancel.)
 Minute traces of chromic acid may be detected in the alkaline solu-
 tion with more certainty by acidifying it by means of hydrochloric
 acid,  and adding binoxide of hydrogen   and  ether.  Compare
 chromic acid (§ 141, 8).
   8. The fusion of sesquioxide of chromium or of any of  its com-
 pounds with nitrate of soda and som,e carbonate of soda gives
 rise  to the formation  of yellow  chromate  of  sooa, part of the
 oxygen of the nitric acid separating from the nitrate of soda, and
 converting the sesquioxide  of chromium into chromic acid, which
 then combines  with the soda.  For the reactions of chromic acid,
 see § 141.
  9. Phosphate of soda and ammonia dissolves  sesquioxide of
 chromium and  its salts,  both in the oxidizing and reducing flame
 of the blowpipe or Bunsen's lamp, to  clear beads of a faint  yel-
 lowish-green tint, which upon cooling change to emerald-green.
 The  sesquioxide of chromium and its salts show a similar deport-
 ment with biborate of soda.

                            % 106.
  Recapitulation and remarks.—The solubility of hydrate  of
 alumina in solutions of  potassa and soda, and its  reprecipitation
 from the alkaline solutions by chloride of ammonium, afford a safe
 means  of detecting alumina only in the absence of  sesquioxide of
 chromium.  If the  latter is present, therefore, which is seen either
 from the color of the solution, or by the reaction with phosphate
 of soda and ammonia, it must be removed before we  can  proceed
to test for alumina.  The separation of sesquioxide of chromium
from alumina is effected the most completely by fusing 1  part of
the mixed oxides together with 2 parts of carbonate and 2 parts
of nitrate of soda, which may be done in a platinum crucible.   The
yellow mass obtained is  boiled with water; by  this process the
whole of the chromium is dissolved as chromate of  soda, and part
of the alumina as aluminate of soda, the rest of the alumina remain- 
114
GLUCINA.
[§107
ing  undissolved.  If  the solution is acidified with  nitric acid, it
acquires a reddish tint;  if ammonia is then added to feebly alka-
line  reaction, the dissolved portion of the alumina separates.
  The precipitation of sesquioxide of chromium, effected by boiling
its solution in solution of potassa or soda, is also tolerably complete
if the ebullition is continued a sufficient length of time; still it is
often liable  to mislead in  cases where only little sesquioxide of
chromium is present, or Avhere the solution contains organic matter,
even though in small proportion only.   The deportment of a solu-
tion of sesquioxide of chromium with  solution of potassa or soda
is completely changed by the presence of certain  other metallic
oxides, viz., protoxide of manganese, protoxide of nickel, protoxide
of cobalt, and especially  sesquioxide of iron.   In  presence of these
oxides, and according to the greater or less relative proportion in
which they happen  to be present, sesquioxide of chromium does
not dissolve, or dissolves only incompletely in  an  excess of solution
of potassa.  This circumstance should never be lost sight of in the
analysis  of  compounds containing   sesquioxide  of  chromium.
Further, it must  be borne in mind, also, that  alkalies produce no
precipitates in the solutions of alumina if non-volatile organic sub-
stances are present, such as sugar, tartaric acid,  &c.   The precipi-
tation of sesquioxide  of chromium is likewise interfered with by
the  presence  of  organic acids (oxalic, tartaric, acetic), since the
latter form with sesquioxide of chromium double  salts not decom-
posable by alkalies.  If, therefore, organic matters are present, the
substance is ignited ;  the residue, fused with carbonate and nitrate
of soda, and further treated  as directed above.

Special Reactions of the  more rarely occurring Oxides of the  Third
                               Group.
                                § 107.
  1.  Glucina  (Gl2 03).  This earth is found as  silicate in phenacite, and combined
with other silicates in beryl, euclase,  and a few not commonly occurring minerals.
In the  pure state glucina is a white tasteless  powder that is insoluble in water.
After ignition  it dissolves slowly but completely in acids. Fusion with bisulphate
of potassa  renders it easily soluble.  Its hydrate dissolves readily in acids.  Its
compounds have a great resemblance to those of alumina.  The soluble salts have
a sweet and astringent taste, and an acid reaction. Silicates containing glucina are
made soluble in  acids by fusion with 4 parts of carbonate of soda   Soda,  potassa,
ammonia and sulphide of ammonium produce in solutions of salts of glucina, a white
flocculent precipitate of hydrate of glucina.  This precipitate is insoluble in ammonia,
easily soluble in soda and potassa:  from these solutions it is reprecipitated by chlo-
ride  of ammonium.  The concentrated alkaline solutions remain clear on  boiling;
the dilute solutions on long boiling deposit all their glucina (distinction from alumina).
The freshly precipitated hydrate dissolves in solution of chloride of ammonium on
continued boiling as chloride of glucinum, ammonia being expelled (distinction from
 alumina).
   Carbonates of the alkalies precipitate white carbonate  of glucina which is soluble 
107.]                         ZIRCONIA.                              115
in a large excess of carbonate of soda and  carbonate of potassa, and in much  less
carbonate of  ammonia  (characteristic  distinction  from  alumina).  When  these
solutions are boiled, basic carbonate of glucina separates.   The  separation is com-
plete and speedy from solutions of  carbonate of ammonia;  from solutions in  the
fixed alkaline  carbonates, it takes place only upon dilution and is imperfect.   Ca?-
bonate of baryta partially throws down glucina in the  cold, completely on boiling.
It is not precipitated by oxalic acid or oxalates.   The compounds of glucina when
ignited with nitrate of cobalt yield a gray mass.
   2.  Thoria (Th 0) is of very rare occurrence in Thorite and Monazite.  It is white.
After ignition it dissolves when  heated in a mixture of equal parts  of concentrated
sulphuric acid  and water; but is not soluble in other acids  even after fusion with
alkalies.   Its hydrates dissolve easily in acids when moist, but with  difficulty  when
dry.  Thorite (silicate  of thoria) is  decomposed  by  concentrated hydrochloric acid.—
Potassa,  soda and sulphide of ammonium precipitate from solutions of salts of thoria
white hydrate of thoria which  is  insoluble in excess of these reagents.   (Its insolu-
bility in  excess of potassa and soda distinguishes thoria from alumina  and glucina.)—
Carbonate of potassa and carbonate of ammonia throw down basic carbonate which
is easily soluble in excess of the precipitant, when the latter is concentrated, diffi-
cultly when it is dilute (distinction  from alumina).  The  solution  in carbonate of
ammonia deposits  basic salt when heated  to  122° F.   Oxalic acid gives a  white
precipitate (distinction from alumina and  glucina),  which is insoluble in oxalic acid,
and scarcely soluble in other  acids.—A concentrated solution of sulphate of potassa
precipitates thoria  slowly but  completely, (distinction  from alumina and  glucina).
The precipitate—sulphate of thoria and potassa—is insoluble iu  strong solution of
Bulphate of potassa;  it dissolves slowly in cold, easily in  hot water.  The solution
deposits  basic salt on prolonged boiling.
   3. Zirconia  (Zr2 03)—is found in  zircon  and a  few other rare minerals.   It  is  a
white powder insoluble in hydrochloric acid, but is taken up by continued digestion
in a mixture of 2 parts  of strong sulphuric acid  and 1 part of  water, with final
addition  of  more water.   Its hydrate resembles hydrate of alumina   It is easily
soluble  in hydrochloric acid when freshly precipitated in  the cold; if precipitated
from hot solutions or when dried it is difficultly soluble.   Salts of zirconia which  are
soluble in water redden litmus.   The silicates of  zirconia, if finely elutriated,  are
decomposed by fusion at a high heat with 4 parts of carbonate of  soda.  The fused
mass yields to  water  silicate of  soda, while zirconate of soda remains as  a sandy
powder.  It is when washed soluble in hydrochloric acid.—Potassa,  soda, ammonia,
and sulphide of ammonium thrown down from solutions of salts of zirconia, the hydrate
in form of flocks, which is insoluble  in excess of  the precipitant  (distinction from
alumina and glucina) and is not taken up by chloride of ammonium (distinction from
glucina).   Carbonates of potassa, soda,  and ammonia throw down carbonate of zirconia
as a flocky precipitate, which is  soluble in a large excess  of  carbonate of potassa)
more easily in  bicarbonate of potassa and  most readily in carbonate of ammonia
(distinction  from alumina).   From these solutions  it  is  thrown  down on boiling.
— Oxalic acid gives a voluminous precipitate of oxalate of zirconia (distinction from
alumina  and glucina), which  is  insoluble in oxalic acid, and difficultly soluble in
hydrochloric acid.   A strong solution of sulphate of potassa  shortly produces a white
precipitate of sulphate of potassa  and zirconia (distinction from  alumina and glucina),
which—precipitated cold—is soluble  in a large  quantity of hydrochloric acid ; but,
precipitated  hot, is almost perfectly insoluble in water and hydrochloric acid (dis-
tinction   from  thoria).   Zirconia  is not thrown down completely by carbonate of
baryta even  upon boiling.—When turmeric paper is immersed in solutions of zirconia,
which have been rendered acid by a slight excess of hydrochloric or sulphuric acid(
the  paper  acquires  an orange yellow color.—(G. J.  Brush.)   (Distinction  from
thoria.) 
 116                       OXIDES OF  CERIUM.                   [§ 107.

   4. Ytteia (Y 0) is met with in the rare minerals gadulinite, orthite, and yttrotanta-
 lite.   The ignited earth is easily dissolved by hydrochloric acid (distinction  from
 zirconia and thoria).   When pure it is white, but  when it contains erbia and terbia
 has a brownish-yellow color.  Its hydrate is white, attracts carbonic  acid from  the
 air, when freshly precipitated is soluble in boiling  solution of chloride of  ammonium
 (distinction from alumina and zirconia).  The salts of yttria are white with an ame-
 thystine tinge.  Anhydrous chloride of yttrium is not volatile (distinction from alu-
 mina, glucina, thoria, and zirconia)—Potassa  throws down white hydrate which is
 insoluble in excess (distinction from alumina and glucina). Ammonia and  sulphide of
 ammonium act like potassa.  A small amount of chloride of ammonium does not
 prevent the precipitation by ammonia and sulphide of ammonium;  but in presence
 of a large excess of this salt uo precipitate is produced.
   Carbonates of the alkalies give a white precipitate, which dissolves  with difficulty
 in carbonate of  potassa, more easily in bicarbonate  of potassa and in carbonate of1
 ammonia (but not to nearly the same extent as carbonate of glucina).  The solution
 of pure hydrate of yttria in carbonate  of ammonia deposits all its yttria  on boiling
 Ifj however,  chloride of ammonium be  present, the precipitate redissolves on  further
 heating with separation of ammonia and formation  of chloride of yttrium.   It is to
 be observed further, that from saturated solutions of carbonate of yttria in carbonate
 of ammonia, double carbonate of yttria  and ammonia readily separates.  Oxalic acid
 gives a white precipitate (distinction from alumina  and glucina).   This precipitate is
 insoluble in oxalic, but soluble in hydrochloric acid. Sulphate of potassa precipitates
 double sulphate  of yttria and potassa, which is  soluble, though slowly, in  much
 water even when it has been thrown down from hot solutions (distinction  from zirco
 nia); it is somewhat more soluble in solution of sulphate of potassa (distinction from
 thoria), and still more soluble in solutions of salts of ammonia.   Carbonate of baryta
 does not precipitate yttria even on boiling.   Turmeric paper  is not affected  by the
 acidified solutions of yttria (distinction from zirconia).—Tartaric acid does not prevent
 the precipitation by alkalies (characteristic distinction from alumina, glucina,  thoria,
 and zirconia).  The precipitate is  tartrate of yttria.  The precipitation takes place
 only after the lapse of some time;  it is, however, complete.
   5. Terbia (Tr 0) and  6 Erbia  (E 0).  These oxides usually accompany  yttria.
 Gradual addition of  ammonia to  a solution  of the three bases first throws down
 erbia,  then terbia,  and lastly yttria.   Erbia after  ignition is yellow or orange-yel-
 low in color.   Terbia appears to be white, though  it is not known in the pure state.
 No further means of distinguishing these earths, or  separating them from each  other,
 are known.
   7. Oxides of Cerium.—Cerium occurs  as protoxide in the rare minerals, cerite,
 orthite, &c.  It forms two oxides, the protoxide (Ce 0), and the  sesquioxide (Ce2 03).
 The hydrated protoxide is white ; exposed to the air it absorbs oxygen and becomes
yellow ;  ignited in the air it passes into orange-red or red sesquioxide (distinction
 from  the previously described  earths).  The hydrated protoxide  easily dissolves in
acids.  The ignited sesquioxide, when it contains oxides of lanthanum and  didymium,
dissolves easily in hydrochloric acid with evolutbn of chlorine ; when pure, sesqui-
oxide of cerium  is scarcely  soluble  in boiling hydrochloric acid; on  addition  of
alcohol it,  however, dissolves  (distinction from thoria and zirconia); the solution
contains protochloride of  cerium.   The salts of protoxide of cerium are colorless,
sometimes with an amethystine tinge; those which  are soluble redden litmus.  Pro-
tochloride of cerium is  not volatile (distinction from alumina,  glucina., thoria and
zircouia).  Cerite (hydrous silicate  of protoxide  of  cerium,  (Ce 0, La 0,  Di  O), S.
0a -f 2 aq) is  insoluble in aqua regia,  is, however, decomposed by fusion with car-
bonate of soda, and by digestion  with concentrated sulphuric acid.   Potassa pre-
cipitates from solutions of protoxide of cerium white hydrate, which turns yellow
 in  the air, and is insoluble in excess of the  precipitant (distinction from alumina and 
§ 107.]
OXIDE  OF DIDYMIUM.
117
glucina).  Ammonia  throws  down a basic salt  insoluble in excess.   Carbonates
of the  Alkalies  give  white  precipitates  slightly  soluble  in  excess of carbo-
nate  of potassa,  more easily  soluble in carbonate of  ammonia.— Oxalic acid
precipitates  protoxide of cerium  completely,  even  from  moderately dilute solu-
tions  (distinction from alumina and glucina).  The precipitate is insoluble in oxalic
acid, but is taken up by a large quantity of hydrochloric acid.   A saturated solution
of sulphate of potassa throws down, even from somewhat acid solutions, white double
sulphate of potassa and protoxide of cerium (distinction from alumina and glucina),
which is very difficultly soluble in water, and totally insoluble m a saturated solution
of sulphate of potassa (distinction from yttria).  This precipitate may be dissolved in a
large quantity  of boiling water to which some hydrochloric acid is added.   Carbo-
nate of baryta precipitates cerium slowly but completely.   Tartaric acid  prevents
the precipitation by ammonia (distinction  from yttria), but not by potassa.  Borax
and  microcosmic salt dissolve cerium  in the  outer  flame  to red  beads (distinction
Irom  the previously mentioned earths), the color fades or even disappears on cool-
ing.   In the inner flame the beads are colorless.
  8.  Oxide op Lanthanum  is usually associated with protoxide of cerium.  It is
white, and does not change color on ignition (distinction from protoxide of cerium);
in contact with cold water  it  is  slowly, by hot water rapidly, converted into milk-
white hydrate.  The oxide and  its hydrate both turn  red litmus paper blue,  and
are dissolved  by boiling solution of chloride of  ammonium, and by dilute acids i
oxide of lanthanum thus resembles magnesia.   The salts are colorless; the saturated
solution of sulphate of lanthanum in cold water, deposits a portion of the salt upon
heating to 86° F. (distinction  from  protoxide of cerium).   Sulphate of potassa, oxalic
acid,  and carbonate of baryta  react as has been described  uuder  cerium.   Potassa
throws down  hydrate, which is insoluble  iu  excess, and  does not turn brown on
exposure to the air.  Ammonia precipitates  basic salts, which, when washed,  run
milky through the filter.  The precipitate by carbonate of ammonia is entirely inso-
luble in  excess of this reagent (distinction from Ce 0).  By supersaturating the
solution of acetate  of lanthanum  with ammonia, washing the precipitate several
times with cold water and  adding  a little powdered iodine, a blue color gradually
pervades the mass (characteristic distinction of lanthanum from all the other earths).
   9.  Oxide of Didymitm  occurs together with cerium and lanthanum, white after
strong ignition; moistened with nitric acid and gently ignited, dark brown;  becomes
white again on strong ignition.  In contact with water, slowly passes into hydrate ;
absorbs carbonic acid; is destitute of alkaline reaction; dissolves easily in acids.   Its
strong solutions have  a reddish  or faintly violet  color.   The  saturated solution of
the sulphate is  not precipitated by heating to 86° F., but, on boiling, salt is deposited.
Potassa throws down hydrated oxide  that  does not alter when exposed to the air,
and  is insoluble in  excess of the precipitant.   Ammonia precipitates basic salts
which are insoluble in ammonia,  but somewhat soluble  in  chloride of  ammonium.
Alkaline carbonates give copious precipitates which are insoluble in excess, even of
carbonate of ammonia (distinction from protoxide  of cerium), but  are somewhat
soluble in chloride  of ammonium   Oxalic acid precipitates oxide  of didymium
almost completely; the precipitate is soluble with  difficulty in cold, with ease in hot
hydrochloric acid.    Carbonate  of baryta throws down  oxide of didymium very
slowly (more slowly than protoxide of cerium,  and oxide of lanthanum), and never
completely.  Salts of didymium are more slowly and less completely precipitated by
sulphate  of potassa than salts of protoxide of cerium.   The  precipitate  is inso-
luble  in cold, and difficultly soluble in hot hydrochloric  acid.   Microcosmic salt  dis-
solves oxide of didymium  in  the reduction flame to a violet amethyst bead; with
soda in the outer flame a grayish mass is obtained (distinction from manganese).
  Entirely satisfactory methods of separating the oxides of cerium, lanthanum,  and
didymium from each other are not known.  Sesquioxide of cerium is obtained nearly 
118
TANTAL1C ACID.
[§ 107.
pure as a  residue, when the mixed oxides  are  ignited  in  the air  and afterwards
treated with concentrated nitric acid.   This process is repeated with the nitric acid
solution,  whereby nearly all the cerium is removed from it.   From the solution, the
oxides of lanthanum  and didymium  are  thrown down by an  alkali, washed and
dissolved  in  sulphuric acid.   Water at a  temperature of 41°  to 43° Fall., is now
saturated with the dry sulphates.   The saturated  solution is finally heated to 86°
Fah. when sulphate of lanthanum separates, while sulphate of didymium remains in
solution.
  10. Titanic Acid.—Titanium  forms  two  oxides;  the sesquioxide (Ti2 03) and
titanic acid (Ti 0 )    The latter is most frequently met with.   It  occurs free in
rutile and anatase, combined  in titanite, titanic  iron,  <fec.   It is  found in small
quantity  in many iron  ores, and in the slags of iron furnaces.   The small copper-rod
cubic crystals, sometimes seen  in iron slags, are cyano-nitride of titanium.   Gently
ignited titanic acid is  white, and when heated, transiently assumes  a yellow color.
When strongly ignited it is yellowish or brownish.   It is infusible, insoluble in water,
has a sp.  gr. of 3.9 to 4.25.
  a. Deportment  of titanic acid  to acids, d?id  reactions of its acid solutions. Ignited
titanic acid is insoluble  in  acids with exception of hydrofluoric acid  and strong
sulphuric acid.  Heated sufficiently long with bisulphate of potassa, it dissolves to a
clear mass which  is taken up by a considerable  quantity of water, forming a clear
solution.   Hydrated titanic  acid when  moist, or when  dried at ordinary  tempera-
tures, is soluble in dilute  acids,  especially hydrochloric and sulphuric.  From  all
the solutions of titanic acid in hydrochloric or sulphuric  acids, when highly diluted,
especially from the last, the titanic acid separates on long continued boiling, as a white
powder insoluble in  dilute acids.   Much free acid hinders the precipitation and
diminishes the quantity of the  precipitate.   The titanic acid thus separated from its
solution  in hydrochloric  acid  may be collected on  a filter, but runs through  on
washing,  unless  hydrochloric  acid or chloride of ammonium  be added.   Potassa
throws down from the hydrochloric or sulphuric solution of titanic acid, a voluminous
white precipitate of hydrated  titanic acid, which  is insoluble in excess of the pre-
cipitant.   The same effect is produced by ammonia, sulphide of ammonium, carbonates
of the alkalies, and carbonate of baryta.   The  precipitate when thrown  down in the
cold, and after washing  with cold water,  is soluble in dilute  hydrochloric and
sulphuric acids.  Tartaric acid prevents its  formation.   Ferrocyanide of potassium
gives with acid solutions of titanic acid, a dark brown precipitate ;  tincture of galls, a
precipitate which' is brownish at  first, but shortly changes to orange-red.  Zinc
reduces titanic acid  in acid solutions to  sesquioxide of titanium, causing at first a
blue coloration of the liquid,  and finally the  separation of blue hydrated sesqui-
oxide.
   b. Behavior of titanic acid to alkalies.  Freshly  precipitated hydrated titauic acid is
scarcely  soluble in solution of potassa.   If titanic acid be  fused with hydrate of
potassa, and treated with water,  the alkaline liquid contains  somewhat  more titanic
acid.  Fused  with carbonate of potassa or soda, carbonic acid is expelled and neutral
titanate  of the alkali is formed.  On treating the  fused mass with  water, carbonate
and hydrate of the alkali  are dissolved and  an acid titanate remains behind.  The
latter is  soluble in hydrochloric acid.  When  titanic  acid  is mixed with charcoal,
and ignited in a stream of chlorine gas, liquid, volatile and  fuming chloride of tita
nium is produced.  Microcosmic  salt dissolves titanic acid  with ease  in  the outer
flame to a clear bead,  which is yellowish while hot and  colorless when  cold.  In a
good reducing flame (more easily on addition of some  metallic tin) the bend becomes
yellow when  hot, red  when somewhat cooled,  and violet when cold.  If sulphate of
iron be added the bead obtained in the inner flame is blood-red.
   11. Tantalio acid.—There are two oxides of Tantalum, viz., Ta 02 and Ta 0i
 The last—tantalic acid—exists in tantalite, yttrotantalite and some  other rare mine 
§ 107.]
HYPONIOBIC  ACID.
119
rata  It is white and remains so after ignition (distinction from  titanic acid).   The
ignited Ta 03 has a  density of 1  to  8.   Tantalic  acid  unites  both to acids and
bases.
  a. Deportment to acids.   The ignited acid is dissolved neither by hydrochloric acid
nor even by strong sulphuric acid.   It fuses  together with  bisulphate of potassa.
On  treating the fused mass with water the tantalic acid  remains behind, combined
with sulphuric acid (distinction, but imperfect separation from Ti 02).  The  sulphate
of tautalic acid is converted into pure Ta 03 by ignition in an atmosphere of carbo-
nate of ammonia  If the solution of an alkaline tantalate has added to it excess of
hydrochloric  acid, the precipitate which  forms  at first afterwards  dissolves to an
opaline  liquid   Out  of this solution  ammonia and  sulphide of ammonium throw
down hydrated tantalic acid, or acid tantalate of ammonia; the precipitation is pre-
vented by tartaric acid.   Sulphuric acid throws  down  from  the opaline  solution
sulphate  of tantalic acid.  When tantalates of the alkalies  are strongly  acidified
with hydrochloric acid and put in contact with zinc, there ensues little or  no blue
coloration, even on further addition of sulphuric acid; if,  however, solid chloride of
tantalum  be dissolved in strong  sulphuric acid,  and water and zinc be  added, the
liquid acquires a blue color,  which on standing does not change to brown.
  b. Behavior towards alkalies. Tantalic acid, when long fused with hyd?-ale of potassa,
forms tantalate of potassa, which dissolves in water.   Fused with hydrate  of soda, it
gives a turbid mass;  when  this is treated with  a  little water  all the tantalic  acid
remains as tantalate of soda, this salt being insoluble in solution of soda; it dissolves,
nowever,  in water as soon as the  excess of soda is removed.   From  the  aqueous
solution it is  thrown down again in a crystalline state by gradual addition  of soda
lye.   Carbonic acid throws  down  from solutions  of  alkaline tantalates  acid  salts,
which do not dissolve when boiled with solution  of  carbonate of soda.  Sulphuric
acid throws down, even from dilute solutions of alkaline tantalates, sulphate of tan-
talic acid.  Ferrocyanide of potassium  and tincture of galls precipitate these solutions
only  on acidifying them.  The former  gives a yellow, the latter  a  light brown
precipitate.
  Ignited with  charcoal  in a stream  of chlorine  gas, tantalic acid yields a yellow,
solid  chloride of tantalum,  which  forms a crystalline  sublimate;  if the tantalic acid
contain  titanic acid,  the  fuming  chloride  of titanium appears.at the same time;
Microcosmic salt dissolves tantalic acid to a colorless bead both in  the inner and outer
flames.   It is not made blood-red by addition of sulphate of iron (distinction from
titanic acid).
  12. Hyponiobic acid.  Niobium (Columbium) forms with oxygen two compounds—
hyponiobic and  niobic acids.   (Nb2 03 and Nb 0*)  The first occurs in a few rare
minerals as columbite, samarskite,  &c.  It is white, on ignition is transiently yellow
(distinction from tantalic acid).  Its density is 4.6 to 6.5 (distinction from  tantalic
acid).  The hyponiobic acid combines both with bases and acids.
  a.  Acid solutions.   Hyponiobic acid is dissolved  by hot concentrated sulphuric acid.
On addition of much cold water a clear liquid is obtained from which sulphate of hypo-
niobic acid is precipitated gradually in the cold and quickly on boiling.  By washing
this precipitate with  solution of carbonate of ammonia and  finally with  very dilute
hydrochloric  acid, hydrated hyponiobic acid—by  igniting in an atmosphere of car
Donate of ammonia, anhydrous hyponiobic acid is  obtained.   Ammonia and  sulphide
of ammonium throw down from  the solutions,  acid  hyponiobate  of ammonia.—
Bisulphate of potassa in  fusion easily dissolves the acid;  on treating the fused mass
with hot water sulphate of  hyponiobic acid remains behind.
  ft. Alkaline solutions.   With caustic potassa the acid readily fuses to a clear mass,
soluble in water.   With caustic soda the fused  mass is turbid ; water  first  extracts
from it  the excess of soda, leaving hyponiobate of soda which dissolves  iu  pure
water.  The carbonate of soda gives, on fusion, similar  results.   Crystallized  hypo- 
120
FOURTH  GROUP.
[§108
niobate of soda is obtained by gradually adding soda-lye to its aqueous solution.
Solutions of the hyponiobates are not rendered turbid by boiling.   Sulphuric acid
throws down from them, on boiling, all the hyponiobic acid.  Chloride of ammonium
precipitates them  less  completely.  Hydrochloric acid gives a precipitate which
is insoluble in excess (distinction from titanic and tantalic acids)   The separated
hyponiobic acid in presence of hydrochloric acid gives with zinc at  first a blue and
afterwards a brown color  (distinction from tantalic acid).   Carbonic acid throws
down acid hyponiobates of the alkalies which are soluble in boiling dilute solution
of carbonate of soda (separation from tantalic acid).   In alkaline solutions, ferrocy-
anide of potassium and tincture  of galls have no effect;  on acidifying  the liquids,
the former gives a dark brown, the latter a deep orange-red precipitate.  On heating
the acid mixed with charcoal in a stream of chlorine gas, there are obtained white
solid Nb2 Cl3 and yellow solid but more volatile Nb Cl-2 —Microcosmic salt  dissolves
the acid copiously, the bead obtained in the inner flame has a violet  blue or brown
color, according to the quantity of hyponiobic acid added and the mode of its prepa-
ration ; with sulphate of iron the bead becomes red.
  The mode of proceeding to detect  most and perhaps all the oxides of the third
group in presence of each other is considered in Section III. Part II.


                               §108.

                           fourth group.

Op Common Occurrence : Oxide of Zinc, Protoxide op Manga-
  nese, Protoxide  of  Nickel,  Protoxide of Cobalt,  Prot-
  oxide of Iron, Sesquioxide of Iron.
Op Rare Occurrence : Oxides of Uranium, Oxides of Vana-
  dium, Oxides op Thallium.

  Properties of the  group.—The solutions of the  oxides of  the
fourth group, when containing a stronger free acid, are not  precipi
tated by hydrosulphuric  acid ;  neutral solutions also are  not, or
only  very incompletely, precipitated by that reagent; but alkaline
solutions are completely precipitated by hydrosulphuric acid; and
so are other solutions if a sulphide of an alkali-metal is used as the
precipitant, instead  of  hydrosulphuric acid.   The  precipitated
metallic sulphides corresponding to the respective oxides are insolu-
ble in water; some of them are readily  soluble in dilute acids ;
others (sulphide of nickel  and sulphide of cobalt) dissolve only with
very  great difficulty in these menstrua.  Some of them are insoluble
in sulphides of the alkali  metals; others  are  sparingly  soluble in
them, under  certain  circumstances (nickel) or completely soluble
(vanadium).
  The oxides of the  fourth group are therefore distinguished from
those of the first and second groups by the fact that their solutions
are precipitated by sulphide of ammonium; from those of the third
group by the  circumstance that they are thrown down  by  this
reagent as sulphides, and not, as is the case with alumina,  &c, as
hydrated oxides. 
§ 109.]
OXIDE OF  ZINC.
121
    Special Reactions of the more commonly occurring Oxides.
                             % 109.
                    a.  Oxide op Zinc (Zn O).
   1. Metallic Zinc is bluish-white and very bright; when exposed
 to  the air, a thin coating of basic  carbonate of zinc forms on its
 surface.   It is of medium  hardness, ductile at a  temperature of
 between  212°  and 302°  Fah., and  under ordinary circumstances
 more or less brittle; it fuses readily on charcoal before the blow-
 pipe, boils afterwards, and burns with a bluish-green flame, giving
 off white  fumes, and coating the  charcoal support  with oxide.
 Zinc dissolves in hydrochloric and sulphuric acids, with evolution
 of hydrogen gas; in dilute nitric  acid, with evolution of nitrous
 oxide ; in more  concentrated nitric acid, with evolution of nitric
 oxide.
   2. The oxide of zinc and its hydrate are white powders, which
 are insoluble in water, but dissolve  readily in hydrochloric, nitric,
 and sulphuric  acids.   The  oxide of zinc acquires  a lemon-yellow
 tint when heated, but  it reassumes its  original white color  upon
 cooling.   When  ignited  before the blowpipe, it shines with  con-
 siderable brilliancy.
   3. The salts of oxide op zinc  are colorless;  part of them are
 soluble in water, the  rest in acids.  The  neutral salts   of zinc
 which are  soluble in water redden litmus-paper, and  are  readily
 decomposed by heat, with the exception of sulphate of zinc, which
 can bear  a  dull red heat, without undergoing  decomposition.
 Chloride of zinc is volatile at a red heat.
   4. Hydrosulphuric acid precipitates from neutral solutions of
 salts of zinc a portion of the metal as white hydrated sulphide of
 zinc (Zn S).   In  acid solutions this  reagent fails altogether to pro-
 duce a precipitate if the free  acid  present is one of the stronger
 acids; but from a solution of oxide of zinc in acetic acid, it throws
 down the Avhole  of the zinc, even if the acid is present in excess.
 [Solutions of zinc, containing a free, strong  acid, are  partially, or
 even completely precipitated when very largely diluted with water.
 —Eliot and Storer.]
  5. Sulphide  of ammonium throws down  from  neutral,  and
 hydrosulphuric acid  from  alkaline solutions of salts of zinc, the
 whole of  the metal  as  hydrated sulphide of zinc, in form of a
 white precipitate.  Chloride of ammonium promotes the separation
 of this precipitate.  From  very  dilute solutions it deposits  only
 after long standing.  This  precipitate is not redissolved by an
 excess of  sulphide of ammonium, nor by potassa or ammonia ; but
 it dissolves readily in hydrochloric acid, nitric acid, and dilute sul-
phuric acid.  It is insoluble in acetic acid.
  6. Potassa and soda throw down from solutions of salts of zinc 
 122              PROTOXIDE  OF MANGANESE.           [§ 110.

 hydrated oxide of zinc (Zn  O, H O), in form of a white, gelati-
 nous precipitate, which is readily and completely redissolved by an
 excess of the  precipitant.   Upon  boiling these alkaline solutions
 they remain, if concentrated, unaltered; but from dilute solutions
 nearly the whole of the oxide of zinc  separates as a white precipi-
 tate.   Chloride of ammonium  does  not precipitate alkaline  solu-
 tions of oxide of zinc.
   7. Ammonia also produces in solutions of oxide of zinc, if they
 do not contain a large excess of free acid, a precipitate of hydrated
 oxide  of zinc, which readily dissolves in an excess of the precipi-
 tant.   The concentrated solution  turns turbid when  mixed  with
 water.  On boiling the concentrated solution, part of the oxide of
 zinc separates immediately ; on boiling the dilute solution, all the
 oxide of zinc precipitates.
   8. Carbonate of soda produces in  solutions of salts of zinc a
 precipitate of basic carbonate of zinc (3 [Zn O, H O] 4- 2 [Zn O,
 C 02]-f-4  aq.), which is insoluble  in an excess of the precipitant.
 Presence  of salts of ammonia in great excess  prevents the forma-
 tion of this precipitate.
   9. Carbonate of ammonia also produces in  solutions of salts of
 zinc the same precipitate of basic carbonate of zinc as carbonate
 of soda;  but this precipitate redissolves upon further addition of
 the precipitant.  On boiling the dilute solution, oxide of zinc pre-
 cipitates.
   10.   Carbonate of baryta fails to  precipitate solutions of oxide
of zinc in the cold,  solution of  the sulphate excepted.
   11.  If a mixture of oxide of zinc, or  one of its salts, with carbon-
ate of soda is exposed to the reducing flame of the blowpipe, the
charcoal  support becomes covered with  a slight coating of oxide
 of zinc, which presents a yellow color whilst hot, and turns while
upon cooling.  This coating is produced by the reduced  metallic
zinc volatilizing at the moment of its reduction, and being reoxidized
in passing through the outer flame.
   12.  If oxide of zinc or one of the salts of zinc is moistened with
solution of nitrate of protoxide of cobalt, and  then heated before
the blowpipe, an unfused  mass is obtained, of a  beautiful green
color:  this mass is a compound of oxide of zinc with protoxide of
cobalt.  If, therefore, in the experiment described in 11 the char-
coal is moistened, around  the little cavity, with solution of nitrate
of protoxide of cobalt, the coating appears green when cold.

                            § 110.
            b. Protoxide of Manganese (Mn O).
   1. Metallic manganese is whitish-gray in color, extremely hard,
eminently susceptible of polish, brittle, and fuses with very great
difficulty.   Exposed to  the air  it shortly tarnishes, on heating it al 
§ 110.]           PROTOXIDE  OF MANGANESE.               123

first acquires a colored tarnish like steel, afterwards becomes coated
with  brown oxide.  It oxidizes  slowly in cold  water, rapidly in
boiling water, and dissolves  readily in  acids.  The  solutions con-
tain protoxide.
  2. Puotoxide  of manganese  is grayish-green ; the hydrated
protoxide is white.   Both the protoxide  and its hydrate absorb
oxygen from the air, and are converted into the brown sesquioxide.
They are readily soluble in hydrochloric, nitric, and sulphuric acids.
  1. The  Higher Oxides op Manganese all dissolve in hot hydro-
chloric acid to protochloride, at the same time evolving chlorine.
On heating with  concentrated sulphuric acid they give off oxygen
and yield  protosulphate of Manganese.
  2. The  salts op protoxide of manganese are colorless or pale
red ;  part of them are soluble in water, the rest in acids. The salts
soluble in water are readily decomposed by a red heat, with the
exception of the sulphate.   The solutions  do not alter vegetable
colors.
  4. Hydrosulphuric acid does not precipitate acid  solutions of
salts of protoxide of manganese; neutral solutions also it fails to
precipitate, or precipitates them only very imperfectly.
  5. Sulphide of ammonium  throws  down from neutral,  and
hydrosulphuric acid from alkaline solutions of salts of protoxide of
manganese, the whole of the metal as hydrated sulphide  of man-
ganese (Mu S), in form of a light flesh-colored* precipitate, which
acquires a dark-brown color in the air;  this precipitate is insoluble
in sulphide of ammonium and in alkalies,  but readily soluble in
hydrochloric, nitric, and acetic acids.  From very dilute  solutions
the precipitate separates only after standing some time in a warm
place.  Solutions containing much free ammonia should be nearly
neutralized with hydrochloric acid.  The separation of the  precipi-
tate is facilitated by chloride of ammonium.
  6. Potassa, soda, and ammonia produce  whitish precipitates of
HYDRATE OF PROTOXIDE OP MANGANESE  (Mn O, H 0),  which Upon
exposure to the air speedily acquire  a brownish and finally a deep
blackish-brown color, owing to the conversion of the hydrated prot-
oxide into hydrated sesquioxide, by the absorption of oxygen from
the air. Ammonia and carbonate of ammonia  do not redissolve
this precipitate ;  but presence of chloride of ammonium prevents
the precipitation by ammonia altogether,  and that by  potassa
partly.  Of already-formed precipitates,  solution of  chloride of
ammonium redissolves only those parts, which have not yet under-
gone  peroxidation.  The solution of the  hydrated protoxide of
manganese in chloride of ammonium is owing to the disposition of

  * If  the quantity of the precipitate is only trifling, the color appears yellowish'
white. 
 121                PROTOXIDE OF NICKEL.             [§ 111.

 the salts of protoxide of manganese to form double salts with salts
 of ammonia.   The ammoniacal solutions  of the  double salts turc
 brown in the air, and deposit dark-brown hydrate of sesquioxide of
 manganese.
  7. If a few drops of a fluid containing protoxide  of  manganese,
 and free from chlorine,  are  sprinkled on binoxide  of lead, or red
 lead,  nitric acid free from chlorine  added, the mixture  boiled and
 allowed  to settle, the fluid is of a purple red color from the forma-
 tion of nitrate of sesquioxide of manganese, [according to Rose,—
 of permanganic acid, according to Crum, and Hoppe-Seyler.]
  8.  Carbonate  of baryta does not precipitate protoxide of manga-
 nese from its solutions, upon digestion  in the cold, solution of sul-
 phate of manganese excepted.
  9. If any compound of manganese, in a state of minute division,
 is fused  with carbonate  of  soda on a platinum wire in the outer
 flame of the blowpipe, or gas-lamp, manganate of soda (Na  O,
 Mn 03)  is formed,  which makes  the fused mass appear green
 while hot, and of a bluish-green tint after  cooling, the  bead at the
 same time becoming turbid.   This reaction  enables us to detect the
 smallest quantities of manganese.  The delicacy of the test maybe
 still further increased by the addition of a minute quantity of nitrate
 of potassa to the carbonate of soda.  [If the compound  is not solu-
 ble in carbonate  of soda, a little borax should be added.]
  10.  Borax  and. phosphate of soda and ammonia dissolve manga-
 nese compounds in the outer  flame of the blowpipe to clear violet-
 red beads, which  upon cooling acquire an amethyst-red tint:
they lose their color in the inner flame, owing to a  reduction of
the  sesquioxide  to protoxide.  The bead which borax  forms with
 manganese compounds, appears black when containing  a conside-
 rable portion of sesquioxide of manganese, but that formed by phos
phate  of soda and ammonia  never loses its transparency.  But the
 latter loses its color in the inner flame of the blowpipe far more
readily than the former.

                            § 111.
               c. Protoxide  of Nickel (Ni O).
  1. Metallic nickel in the fused state is  silvery white, inclining
 to gray;  it is bright,  hard, malleable, ductile, difficultly fusible ; it
does not oxidize in the air at common temperatures,  but it oxi-
 dizes slowly upon ignition ; it is attracted by the magnet, and may
 itself become  magnetic.   It slowly  dissolves in hydrochloric  acid
 and dilute sulphuric acid upon the application of heat, the solution
 being attended with evolution  of hydrogen  gas. It dissolves readi-
 ly in nitric acid.  The solutions contain protoxide of nickel.
  2. Hydrated protoxide of nickel is  green and inalterable iu 
§ 111.]             PROTOXIDE OF NICKEL.                125

the air.  By ignition it is converted into grayish-green protoxide.
Both are easily soluble in hydrochloric, nitric, and sulphuric acids.
The octahedrally crystallized protoxide of nickel is, however, inso-
luble in acids though soluble in fused bisulphate of potash.  Sesqui-
oxide of nickel is black  and soluble in hydrochloric acid with
evolution of chlorine, forming protochloride of nickel.
  3. Most of the salts of protoxide of  nickel are yellow in the
anhydrous,  green in the hydrated state; their solutions are of a
light green color. The soluble neutral salts slightly redden litmus-
paper, and are decomposed  at a red heat.
  4. Hydrosulphuric acid does not precipitate solutions of salts of
nickel Avhich contain  one of the stronger acids in the free state.
In absence of free acid these solutions gradually yield a slight pre-
cipitate of black sulphide  of nickel (Ni S).   Acetate of nickel,
containing excess of acetic acid, is not at all, or but slightly precipi-
tated ; in absence of free acid the larger part of the nickel is thrown
down by prolonged action of the reagent.
  5. Sulphide of ammonium produces in neutral, and*.hydrosulphu-
ric acid in alkaline solutions of salts of protoxide of nickel, a black
precipitate  of hydrated sulphide of nickel (Ni S), which is not
altogether insoluble  in sulphide of ammonium, especially if contain-
ing  free ammonia ;  the fluid from which the precipitate has  been
thrown down exhibits  therefore usually a brownish color.  Chlo-
ride of ammonium  greatly promotes the precipitation.  Sulphide
of nickel dissolves scarcely at all in acetic acid, with great difficulty
in hydrochloric  acid, but readily in nitrohydrochloric acid  upon
application of heat.
  6. Potassa  and soda produce  a light green  precipitate  of
hydrate of protoxide of nickel (Ni O, H O), which is insoluble
in an excess of the precipitants,  and unalterable in the  air.   Carbo-
nate  of ammonia dissolves this precipitate,  when  filtered and
washed, to a greenish-blue fluid, from which potassa or soda repre-
cipitates the nickel as an apple-green hydrate of protoxide of nickel.
  7. Ammonia added  in small quantity to solutions of protoxide of
nickel produces in them  a trifling greenish turbidity; upon further
addition of the reagent this  redissolves readily to a blue  fluid con-
taining a compound  of protoxide of nickel and  ammonia.   Potassa
and soda precipitate from this  solution hydrate of protoxide  of
nickel.  Solutions containing salts of ammonia or free  acid are not
rendered turbid  by ammonia.
  8. Cyanide of potassium  produces a yellowish-green precipitate
Df cyanide  op nickel (Ni Cy), which  redissolves  readily in  an
excess of the precipitant as a double cyanide of nickel and potas-
sium (Ni Cy + K Cy); the solution is brownish-yellow.  If sulphu-
ric acid or hydrochloric  acid is added to this solution, the cyanide
of potassium is decomposed, and the cyanide of nickel  reprecipi 
126                PROTOXIDE OF COBALT.              [§ 112

tated; the latter substance is very difficultly soluble  in an excess
of these acids in the cold, but more readily upon boiling.
   9. Carbonate of baryta does not precipitate protoxide of nickel
from its solutions, upon digestion in the cold solution of  sulphate
of nickel excepted.
   10. Nitrite of potassa, used in conjunction with acetic acid, fails
to precipitate even concentrated solutions of nickel.
   11. Borax and phosphate of soda and ammonia dissolve com-
pounds of protoxide of nickel in the outer flame to clear beads ; the
bead produced with borax is violet whilst hot, reddish-brown when
cold; the bead produced with the phosphate of soda and ammonia
is reddish, inclining to brown whilst hot, but turns yellow  or red-
dish yellow upon cooling.  The bead which phosphate of soda and
ammonia forms with salts of protoxide of nickel remains unaltered
in  the inner flame of the blowpipe, but that formed with borax
turns gray and turbid from reduced  metallic nickel.  Upon con-
tinued exposure to the blowpipe flame the particles of nickel unite,
but without fusing to a grain, and the bead becomes colorless.

                            §112.
               d.  Protoxide op Cobalt (Co O).
   1. Metallic cobalt in the fused state is steel-gray, pretty hard,
susceptible of polish, malleable, difficultly fusible, and magnetic;
it oxidizes very slowly in the air at the common temperature, more
rapidly at a red heat;  with acids it comports  itself like nickel.
The solutions contain protoxide of cobalt.
   2. Protoxide op cobalt is an olive-green, its hydrate a pale red
powder.   Both dissolve readily in hydrochloric, nitric, and sulphu-
ric acids.   The sesquioxide op cobalt (Co, 03)  is black, and dis-
solves in hydrochloric acid to protochloride of cobalt, with evolu-
tion of chlorine.
   3. The  salts of  protoxide op cobalt, containing water  of
crystallization,  are red, the anhydrous salts  mostly blue. The
moderately concentrated solutions appear of a  light red color,
which they retain even though  considerably diluted.  The soluble
neutral salts redden litmus-paper slightly, and are decomposed at a
red heat: sulphate of protoxide of cobalt alone can bear a mode-
rate red heat without suffering decomposition.  When a solution of
chloride  of cobalt is  evaporated, the  light  red  color changes
towards  the end of the operation to blue;  addition of water
restores the red color.
   4. Hydrosulphuric acid does not precipitate solutions of cobalt,
which contain one  of  the  stronger  acids in the free state.   In
absence of free acid there gradually separates from these solutions
a  portion  of the  cobalt, as black  sulphide  (Co S).   Acetate  of 
 § 112.]            PROTOXIDE OF COBALT.                 127

 cobalt containing free acid is scarcely or not at all precipitated; in
 absence of free acid, all or nearly all the cobalt is thrown down.
   5. Sulphide of ammonium precipitates from neutral, and hydro-
 sulphuric  acid from alkaline solutions  of salts of protoxide of
 cobalt, the whole of the metal as black  hydrated sulphide of
 cobalt (Co S).  Chloride of ammonium greatly favors its separa-
 tion.  This substance is insoluble in alkalies and sulphide of ammo-
 nium, scarcely soluble in acetic acid, very difficultly in hydrochlo-
 ric acid, but readily so in nitrohydrochloric acid upon application
 of heat.
   6. Potassa and soda produce in solutions of cobalt blue precipi-
 tates of basic salts of cobalt, which turn  green  upon exposure to
 the air, owing to the absorption  of oxygen; upon boiling, they are
 converted into pale  red hydrate  of protoxide of cobalt, which  con-
 tains alkali, and generally appears rather discolored from an admix-
 ture of sesquioxide formed in the process.  These precipitates are
 insoluble in solutions of potassa  and soda; but  neutral carbonate
 of ammonia  dissolves  them  completely to  intensely violet-red
 fluids, in which a somewhat larger  proportion of potassa or soda
 produces  a  blue precipitate, the fluid still  retaining its violet
 color.
   7. Ammonia produces the same precipitate as potassa, but  this
 redissolves in an excess of the ammonia  to a reddish-brown fluid,
 from which solution of potassa  or soda  throws down part of the
 cobalt  as  a  blue basic  salt.   Ammonia fails to precipitate  solu-
 tions of protoxide of cobalt containing salts of ammonia or  free
 acid.
   8.  Addition of cyanide of potassium to a solution of cobalt
 gives  rise to the formation  of  a brownish-white  precipitate of
 protocyanide op cobalt (Co Cy),  which dissolves readily  as a
 double cyanide of cobalt and potassium in an excess of solution of
 cyanide of potassium.   Acids precipitate from this solution cyanide
 of cobalt.  But if the solution is  boiled with cyanide of potassium
 in excess, in presence of free hydrocyanic acid  (liberated by addi-
 tion of one or two  drops of hydrochloric  acid), a  double com-
 pound of sesquicyanide of cobalt and cyanide of potassium (cobal-
 ticyanide of potassium,  K , Co2 Cy6 = K3 Ckdy)  is formed, in  the
 solution of which  acids produce no precipitate  (important distinc-
 tion from nickel).
  9. Carbonate of baryta does not precipitate solutions of prot-
 oxide of cobalt in  the cold, sulphate of cobalt excepted.
  10. If nitrite of potassa is added in not too small proportion to
a solution of protoxide of cobalt, then acetic acid to  strongly acid
reaction, and the mixture put in a moderately warm place, all  the
cobalt separates, from concentrated solutions immediately or very
soon, from  dilute solutions after some time, as nitrite  of  sesqup- 
 128                  PROTOXIDE  OF IRON.              [§ 113.

 oxide op cobalt and potassa (Co2 03, 3 K O, 5 N Oy, 2 H  0), in
 form of a crystalline precipitate of a beautiful yellow color.  The
 mode in  which this precipitate forms may be seen from the follow-
 ing equation:  2 (Co O, S 03) + 6 (K O, N 03) + A = K O, A + 2
 (K O, S  O,) + Co, 03, 3 K  O, 5 N 03 + N 0_.  The precipitate is
 only sparingly soluble in pure water, and  altogether insoluble in
 saline solutions and  in alcohol.  When boiled Avith water,  it dis-
 solves, though not copiously, to  a red fluid,  which remains clear
 upon cooling, and from which alkalies throw down hydrate of prot-
 oxide of cobalt (Fischer, Aug. Stromeyer).   This excellent reaction
 enables us to distinguish nickel from cobalt.  It is always  neces-
 sary to concentrate the solution of protoxide  of cobalt to  a con-
 siderable extent before adding the nitrite of potassa.
   11. Borax dissolves compounds of cobalt both in the inner and
 outer flame of the blowpipe, giving clear  beads  of a magnificent
 blue color, which appear violet by candle-light, and almost  black
 if the cobalt is present in considerable proportion.   This  test is as
 delicate as it is characteristic.  Phosphate of soda and ammonia
 manifests with salts of cobalt before the  blowpipe an analogous
 but less delicate reaction.

                             § H3.
                e. Protoxide of  Iron (Fe O).
   1. Metallic iron in the  pure state  has a light whitish-gray
 color (iron containing  carbon is more or less  gray); the metal is
 hard, lustrous, malleable, ductile, exceedingly difficult to fuse, and
 is attracted by the magnet.  In contact with air and  moisture a
 coating of rust (hydrate of sesquioxide of  iron) forms on its sur-
 face ; upon ignition in the air, a coating of black  protosesquioxide.
 Hydrochloric  acid and dilute sulphuric acid dissolve iron, with
 evolution of hydrogen  gas; if the iron contains carbon, the hydro-
gen is mixed  with carbide of hydrogen.   The  solutions contain
protoxide.  Dilute nitric acid dissolves iron in the cold to nitrate
of protoxide, with evolution of nitrous oxide; at a high  tempera-
ture, to nitrate of sesquioxide, with evolution of nitric oxide;  if
the iron contains carbon, some carbonic acid  is also evolved, and
there is  left undissolved  a brown  substance resembling humus,
 which is  soluble in alkalies, or in some cases, graphite remains.
   2. Protoxide of iron  is  a black powder;  its  hydrate is a
white powder,  which in  the moist state absorbs oxygen and
speedily  acquires a grayish-green, and ultimately a brownish-red
color.  Both the protoxide and its  hydrates are  readily dissolved
by hydrochloric, sulphuric, and nitric acids.
   3. The salts of protoxide of  iron  have in  the anhydrous
state a white, in the  hydrated state  a greenish  color; their solu- 
§ H3.]
PROTOXIDE OF IRON.
129
tions appear colored only when concentrated.  Exposed to the air,
they absorb oxygen and are converted into salts of the protoses-
quioxide with separation of  basic sesquisalts.  The soluble neutral
salts redden litmus-paper, and are decomposed at a red heat.
  4. Acid solutions of salts of protoxide of iron are not precipitated
by  hydrosulphuric acid / neutral solutions  of salts of protoxide
of iron with weak acids are precipitated by this reagent at the
most but very incompletely; the precipitates are of a black color.
  5. Sulphide of ammonium precipitates from neutral, and hydro-
sulphuric acid from alkaline solutions of salts of protoxide of iron,
the whole of the metal as black hydrated protosulphide of iron
(Fe S), which is insoluble in alkalies and sulphides of the alkali
metals, but  dissolves readily in hydrochloric  and nitric acids: this
black precipitate turns reddish-brown in the  air by oxidation.  To
highly dilute solutions of protoxide of iron, addition of sulphide of
ammonium imparts a  green color, and  it is  only after some  time
that the protosulphide of iron  separates as a black precipitate.
Chloride of ammonium greatly facilitates the precipitation.
  6. Potassa and ammonia produce a  precipitate of hydrate of
protoxide op iron (Fe O, H O), which in the first moment looks
almost  white, but acquires after a very short time  a  dirty green,
and ultimately  a reddish-brown  color, owing to  absorption of
oxygen from the air.   Presence of salts of ammonia prevents the
precipitation by potassa partly, and that by ammonia  altogether.
If  alkaline  solutions  of protoxide of  iron  thus obtained by the
agency of salts of ammonia are exposed to the air, hydrates of pro-
tosesquioxide and of sesquioxide of iron precipitate.
  7. Ferrocyanide of potassium produces in  solutions of protoxide
of iron  a bluish-white precipitate of ferrocyanide of potassium
and iron  (K, Fe„ Cfy2), which, by absorption of oxygen from the
air, speedily acquires a blue color.   Nitric acid or chlorine converts
it immediately into Prussian blue, 3 (K, Fe3, Cfy2) -f- 4  CI = 3 K
CI + Fe CI  + 2 (Fe, Cfy3).
  8. Ferricyanide  of potassium  produces  a magnificently blue
precipitate of ferricyanide  op iron (Fe3  Cfdy).  This precipi-
tate does not differ in color from Prussian blue.   It  is insoluble in
hydrochloric acid, but is readily decomposed by potassa.   In
highly dilute solutions of salts of protoxide of iron  the reagent
produces simply a deep blue-green coloration.
  9. Sulphocyanide of potassium does not alter solutions of prot-
oxide of iron free from sesquioxide.
  10. Carbonate of Baryta  does not precipitate solutions of prot-
oxide of iron in the cold, solution of the sulphate excepted.
  11. Borax dissolves salts of protoxide of iron in the oxidizing
flame, giving beads varying in  color from yellow to dark-red ;
when cold, the beads vary from colorless to  dark-yellow.  In the
                               9 
 130               • SESQUIOXIDE  OF IRON.              [§ 114.

inner flame the beads change to bottle-green, owing to the reduc-
tion of the newly-formed sesquioxide to protosesquioxide. Phosphate
of soda  and ammonia manifests a similar  deportment with the
salts of protoxide of iron; the beads produced with this reagent
lose their  color upon  cooling still  more  completely than is  the
case with those produced with borax; the signs of  the  ensuing
reduction in the reducing flame are also less marked.


                             § H4.
               f.  Sesquioxide op Iron (Fe2 03).
   1. The native crystallized  sesquioxide op iron is steel-gray;
the native as well  as the  artificially prepared sesquioxide  of iron
gives upon trituration a brownish-red powder ; the color of hydrate
of sesquioxide of iron is more inclined to reddish-brown.  Both the
sesquioxide and its hydrate dissolve in hydrochloric, nitric, and
sulphuric acids; the hydrate  dissolves readily in these acids, but
the anhydrous sesquioxide dissolves with greater  difficulty, and
completely  only  after long exposure to  heat.   The protoses-
quioxide (magnetic oxide Fe  O, Fe2 03) is black, and dissolves in
hydrochloric acid to a mixture of proto- and sesquichloride, in aqua
regia to sesquichloride of iron.
   2. The neutral  anhydrous  salts  op sesquioxide op iron are
nearly white;  the  basic  salts are yellow or reddish-brown.   The
color of  the solutions is brownish-yellow, and becomes  reddish-
yellow upon the application of heat.   The soluble neutral salts
redden litmus-paper, and are decomposed by heat.
   3. Hydrosulphuric acid produces in acid solutions of salts of
sesquioxide of iron containing the stronger acids, a  milky white
turbidity, proceeding from separated  sulphur.   At  the same time
the sesquisalt is converted into a protosalt.   Fe2 03, 3 S 03 -}- H S = 2
(Fe O, S 03) +  H O, S'03 +  S.  Solution of hydrosulphuric acid,
rapidly added to neutral solutions, imparts to the fluid a transitory
blackening. In  solution of neutral acetate of sesquioxide of iron
it precipitates  the greater part  of the iron.  In presence of a suf-
ficient quantity of  free acetic acid only sulphur separates.
  4. Sulphide of ammonium precipitates from neutral, and hydro-
sulphuric acid from alkaline  solutions of  salts  of sesquioxide of
iron, the  whole of  the metal as black hydrated protosulphide of
iron (Fe S) mixed with sulphur.  This precipitation  is preceded
by the reduction of the sesquioxide to protoxide.  Fe2  Cl3 + 3 N H, S
= 3 N H, CI + 2  Fe S + S.   In very dilute solutions the  reagent
produces only a blackish-green coloration.   The  minutely divided
protosulphide  of iron subsides  in such cases only after long stand-
ing. Its separation is greatly favored by presence of chloride of
ammonium.  Protosulphide of iron, as already stated (§113.5.), is 
§ -15.]
SESQUIOXIDE OF  IRON.
131
insoluble in alkalies and alkaline  sulphides, but dissolves  readily
in hydrochloric and nitric acids.
  5. Potassa  and  ammonia  produce  bulky reddish-brown  pre-
cipitates Of HYDRATE OF SESQUIOXIDE OF IRON (Fe2 03, H O), which
ure  insoluble in an  excess  of the precipitant  as well as in salts of
ammonia.
  6. Ferrocyanide of potassium produces even in highly dilute
solutions a magnificently  blue precipitate of ferrocyanide op
iron, or Prussian blue (Fe4 Cfy):   2 (Fe2 Cl3) + 3 (Cfy. 2 K)  = 6
K Cl+Fej Cfy3.  This precipitate is insoluble in hydrochloric acid,
but is decomposed  by potassa, with  separation of hydrate of sesqui-
oxide of iron.
  7. Ferricyanide  of potassium deepens the  color of solutions of
salts of sesquioxide of iron to reddish-brown; but it fails to produce
a precipitate.
  H. Sulphocyanide of potassium  imparts to neutral  or  slightly
acid solutions of salts of sesquioxide of iron a most intense blood-
red color, arising from the formation  of a soluble sulphocyanide
op  iron.*    Addition  of  acetate of  sodaf  destroys this color,
hydrochloric acid restores it again.  This test is the most delicate
of all;  it will indicate  the presence of sesquioxide  of iron  even in
fluids which are so highly dilute that  every other reagent  fails to
produce the  slightest visible  alteration.   The  red  coloration
may  in  such cases be detected most  distinctly by  resting the
test-tube upon a sheet of white paper, and looking through it from
the top.
  [9. When a solution containing  a sesquisalt of iron is rendered
nearly neutral by  carbonate of soda, and then  heated to  boiling
with addition of excess of acetate  of soda, all the iron is  precipi-
tated as  brown basic sesqui acetate, and  may  be  completely
removed from the  solution by filtering  hot and washing with boil-
ing water.  If it is allowed to remain in the solution it partially
redissolves as the latter becomes cold.]
  10. Carbonate of  baryta precipitates  even in the cold all the
iron as a basic salt mixed with hydrate of sesquioxide.
  11. The reactions before the blowpipe are the same  as with the
protoxide.

                              § H5.
  Recapitulation  and remarks.—On  observing the behavior of
the oxides  of the fourth group with solution of  soda, it would
appear that the separation of the oxide of zinc, which is soluble in
  [* A similar coloration is produced by sulphocyanide  of potassium in  solutions
containing binoxide of molybdenum or hyponitric acid.]
  [f So also phosphates, borates, fluorides,  oxalates, tartrates, racemates, malates,
citrates, succinates, and  the corresponding acids ] 
132
RECAPITULATION.
[§ H5.
an excess of this reagent, might be readily effected by its means;
however, in the actual experiment, we find that in the presence of
sesquioxide of iron, protoxide of cobalt, &c, some of the oxide of
zinc precipitates with these oxides; and if only a small quantity of
oxide of zinc is present, it frequently occurs that  no trace of this
metal can be detected in the alkaline  filtrate.   This method would
be entirely worthless in case sesquioxide of chromium were present,
because oxide of zinc and  sesquioxide of chromium mutually pre-
cipitate each other from their  alkaline solutions.
  Again, from the behavior of the different oxides with chloride
of ammonium and an excess of ammonia, one would conclude that
the separation of sesquioxide of iron from the protoxides of cobalt,
nickel, and manganese,  and from oxide of zinc, might be readily
effected by these  agents.  But this  method  also applied to the
mixed oxides, is inaccurate, since greater or smaller portions of
the other  oxides will always  precipitate with  the  sesquioxide of
iron;  and  it  may therefore  happen that, in  this process,  small
quantities of cobalt, manganese, &c,  altogether escape detection.
  It is far safer therefore to separate the other oxides of the fourth
group from sesquioxide of iron by carbonate of baryta (with addi-
tion of chloride of ammonium), as in that case the iron is precipi-
tated  free  from oxide  of zinc and protoxide of manganese, and
mixed only with a very trifling  quantity  of protoxides of  nickel
and cobalt.
  Protoxide of manganese may conveniently be separated from the
protoxides of cobalt and nickel and from oxide of zinc, by treating
the  precipitated and washed sulphides with  moderately  dilute
acetic acid, which dissolves the sulphide of manganese, leaving the
other  sulphides unacted on.  If the acetic acid solution is now
mixed with solution of soda, the least trace of a precipitate will be
sufficient  to recognize  the manganese  before the blowpipe with
carbonate of soda.
  If  the  sulphides  left undissolved by acetic  acid,  after being
washed are treated with very dilute hydrochloric acid, the sulphide
of zinc dissolves, leaving almost the whole of the sulphides of
cobalt and nickel behind.  If the fluid is then boiled and consider-
ably concentrated, to expel the hydrosulphuric acid, and afterwards
treated cold with solution  of  potassa or soda in excess, the zinc  is
sure to be detected in the filtrate by hydrosulphuric acid.
  If the filter which may contain the sulphides of nickel and cobalt
is dried and burned in  a small porcelain dish, and a portion  of the
residue tested with borax in  the inner blowpipe  flame, cobalt is
usually recognized without difficulty [or in its  absence, nickel  is
at once detected].  The detection of nickel in presence of cobalt is
not so easy. It succeeds best by the following method.  To the
concentrated solution, nitrite of potassa is added in  considerable 
§116.]
RECAPITULATION.
133
quantity, then acetic acid to  strongly acid reaction, and  the mix-
ture is finally set aside in a moderately warm place for at least
12 hours.  All the cobalt will thus separate as nitrite of cobalt and
potassa.  It is then filtered, the nickel in the filtrate is precipitated
with caustic soda, and tested before the blowpipe.
  Since in the course of analysis the oxides of the fourth group are
usually thrown down together by  sulphide of ammonium  as  sul-
phides, it is most convenient to separate the nickel and cobalt, or at
least, all but traces of these metals at  the outset.   For  this pur-
pose, the precipitated sulphides while still moist are agitated with
water and some hydrochloric acid in the cold.  Sulphides of nickel
and cobalt remain almost entirely undissolved, while the sulphides
of all the other metals of the fourth group at once go into solution.
The sulphides of nickel and  cobalt are  filtered off, washed, and
treated as above directed.  The filtrate is boiled with addition  of
some nitric acid, whereby the iron is converted into sesquioxide.
The free acid is now nearly neutralized with carbonate of soda and
the sesquioxide of iron is precipitated either in the cold by addi-
tion of carbonate of baryta, or by boiling with acetate of soda and
filtering hot.  The filtrate contains finally manganese  and zinc.
These are again thrown down with sulphide of ammonium, chloride
of ammonium being likewise added, filtered off, washed  and sepa-
rated as above described with acetic acid, or this solution is freed
from  baryta by addition of excess of sulphuric acid and filtration ;
the filtrate is reduced to a small bulk by  evaporation, and treated
with  soda-solution, which throws  down manganese and  retains
zinc in solution.  The small quantities of nickel and cobalt which
might have passed into solution in the first treatment of the preci-
pitated sulphides with hydrochloric acid,  remain with the sulphide
of zinc when this is  separated  from sulphide of manganese  by
acetic acid; or in case oxide of zinc was separated by soda-solution
from oxide of manganese, they are  found with the  latter.   In  the
former instance sulphide of zinc may be extracted from the black-
ish precipitate by dilute  hydrochloric  acid.  In  the latter  case
manganese may  be at  once  detected by means of carbonate  of
soda, in the  outer blowpipe flame, even in presence of  nickel and
cobalt.
  Protoxide and sesquioxide of iron may be detected in presence
of each other,  by testing for the former with  ferricyanide of potas-
sium, for the latter with ferrocyanide of potassium, or, better still,
with sulphocyanide of potassium.*
  In  conclusion,  it is  necessary  to mention that  alkalies  fail to
precipitate the oxides of the fourth group, and carbonate of baryta
does not throw down sesquioxide of iron, in presence of non-volatile
* [Compare Molybdenum, § 138. b.] 
134
OXIDES  OF VANADIUM.
[§116
organic substances  (such as sugar, tartaric acid, &c.)   We  have
already seen that the  same applies to alumina.

            Special Reactions of the rarer Oxides of the Fourth Group.
                                    §  116.
   1. Oxides of Uranium.  Uranium is  of comparatively rare occurrence in pitch-
blende,  uranium-ochre, &c.   Its sesquioxide is  employed  in making yellow-green
glass.   It forms two oxides, the protoxide (U 0) and the sesquioxide (Us 03).  The
first is brown and dissolves in nitric acid to nitrate of sesquioxide.   Hydrated sesqui-
oxide is yellow; at about 570c Fah. loses its water and becomes  red;  on ignition
it is converted into the dark blackish-green protosesquioxide..  The solutions of ses-
quioxide of uranium in acids are yellow.  They  are not altered by  hydrosulphuric
acid.  Sulphide of ammonium throws down,  after neutralization  of the  free acid, a
slowly subsiding precipitate, whose color varies from dirty yellow to red-brown, and
is sometimes even blood-red, according to the presence and relative quantities of
chloride of ammonium, ammonia, and sulphide of ammonium.   Chloride of ammo-
nium facilitates its separation.  The precipitate is readily soluble in  acids, even in
acetic acid;  it is insoluble in sulphide of ammonium.   It  is not pure sulphide of
uranium, but contains, besides uranium and sulphur, ammonium, oxygen, and water.
Ammonia, potassa,  and soda  produce yellow  precipitates of sesquioxide of ura-
nium  and alkali, insoluble  in excess of  the  precipitants.    Carbonate of ammonia,
and the bicarbonates of soda and potassa, produce yellow precipitates of carbonate of
sesquioxide  of uranium and alkali, which dissolve readily in an excess  of  the precipi-
tant. Potassa and soda throw down from these solutions the whole of the  sesquioxide
of uranium.   Carbonate of baryta completely precipitates  solutions of  sesquioxide
of uranium, even in  the cold.  Ferrocyanide  of potassium produces a reddish-brown
precipitate ;  this is a very delicate test for uranium.  Borax and phosphate of soda
and ammonia give with sesquioxide of uranium in the inner flame of the blowpipe
green beads, in the outer flame yellow beads, which upon cooling acquire a yellowish"
green tint.
  2. Oxides op Vanadium.  Vanadium is met with but very rarely in the form
of salts  of vanadic acid, sometimes  it exists in minute quantity in iron and copper
ores and in the slags which result from  their smelting.  Vanadium has three oxides,
viz.: suboxide (V 0>, binoxide (V 02), and vanadic acid (V 03). The lower oxides
of vanadium are converted into vanadic acid by heating with nitric or  nitrohydro-
chloric acids, and by fusion with nitrate of potassa.   Vanadic acid is yellowish-red,
fusible at an incipient red heat, not volatile, and becomes crystalliue on solidification.
It  is very slightly soluble  in  water, but reddens litmus-paper strongly.  It unites
both with acids and bases.
  a. Acid solutions.   Vanadic acid dissolves in the stronger acids, forming yellow or
red liquids.  The solutions  are often decolorized by boiling.   Sulphurous acid, many
metals,  organic matters, <fcc, color the solutions blue  by  reducing vanadic acid to
binoxide of vanadium.  Hydrosulphuric acid does not precipitate acidified solutions,
but colors them blue,  sulphur separating   Sulphide of ammonium colors the solu-
tions brown, and by acidifying with hydrochloric, or better with sulphuric acid, brown
tersulphide of vanadium separates, which is soluble in  excess of sulphide of ammo-
nium, giving a red-brown  liquid.   Ferrocyanide of potassium throws down a green
precipitate.   Tincture of galls, after some  time, gives a blue-black precipitate.
  b. Vanadates.  The neutral salts are mostly yellow.   The salts of the alkalies and
Bome  others, when  warmed  with  water,  become colorless.   The  acid  salts are
yellowish-red.   The salts withstand  a red heat; they are  mostly soluble in water,
and are  all dissolved by nitric  acid.   The alkaline  vanadates are the less soluble in
water the more free alkali  or  alkaline salt is present.   On saturating the  solution 
§ 116.]
OXIDES OF  THALLIUM.
135
of an alkaline vanadate with chloride of ammonium all  the vanadic acid  is thrown
down as a white vanadate of ammonia, which is insoluble  in excess of the precipi-
tant (especially characteristic reaction).  This  precipitate,  when  ignited, yields
vanadate of binoxide of vanadium.—On agitating the acidified solution of an alkaline
vanadate with binoxide of hydrogen, the solution  acquires  a red color,  the liquid
remains red even after shaking with ether, the latter being  unchanged (very delicate
reaction).—(Weriher.)   Borax  dissolves vanadic acid to a clear bead, which in the
outer flame  is colorless, or with  large quantities yellow: in the inner flame green,
or with large quantities brownish while hot, and green on cooling.
   [3. Oxides of Thallium.  Thallium occurs in minute quantities in many native
metallic sulphides, especially in iron and copper pyrites.  Hence it is often found in
commercial sulphur, in oil of vitriol, and in the sediment of  sulphuric acid  chambers,
in metallic copper,  bismuth,  and cadmium, and in preparations derived from these
substances; also in certain mineral springs, and in the flue-dust of furnaces.  Thal-
lium  is  a bluish-white, very soft and malleable, though not tenacious metal   Its
sp. gr. = 11.8:  it is brilliant  on a fresh  surface, but  shortly tarnishes.   It is easily
fusible and volatilizes at a red heat, and before the blowpipe emits copious fumes of
oxide which have a peculiar odor and exhibit white, reddish, and violet colors.  It
dissolves readily in sulphuric and  nitric acids, with  difficulty in hydrochloric  acid.
Boiled with hydrochloric acid or aqua regia, chloride of thallium escapes in the vapors.
It dissolves slowly as oxide in distilled water, especially when in a state of fine division.
—Of the compounds of oxygen with thallium there are known a protoxide, a sesqui-
oxide, and a teroxide.  Protoxide of thallium as hydrate, is largely soluble in water and
alcohol; its solution reddens litmus, is caustic and alkaline; by  evaporation  in vacuo
it is obtained crystallized in  the  form of yellow needles.  It absorbs carbonic acid
with avidity, unites  with acids yielding crystallizable  salts.—Hydrosulphuric acid
does not affect acid solutions of thallium, but throws  down from alkaline, as sulphide
of ammonium does from neutral and alkaline solutions, all the thallium they contain
as brownish-black (according  to Bottger  grayish-black) sulphide in form of a very
bulky flocculent precipitate, which becomes less voluminous on heating or agitation.
Sulphide of thallium  is  insoluble in  sulphide of ammonium, in alkalies,  alkaline
carbonates and cyanides.  It oxidizes  to  soluble sulphate  on  exposure to the air,
and must hence be washed  with dilute sulphide  of ammonium.   It is  slowly but
perceptibly soluble in cold dilute acetic, hydrochloric and sulphuric acids, especially
if exposed to the air, as happens v/hen treated on a filter with these acids.  It dis-
solves readily in nitric  acid.
   According to Bottger there exists a higher sulphide of thallium, which has  a red
color.   It is obtained  mixed with  sulphur, by cautious addition of hyposulphite of
soda to the boiling acid solutions of thallium.   It also appears  to be formed to some
extent when the solutions of thallium  are  treated  with  sulphide of ammonium, a
yellow, brownish-yellow  or  red-brown  coloration  appearing in cold dilute solutions,
and on  heating, the liquid assumes a purplish or blue color by transmitted, and ia
yellow or brownish-red by reflected light,  while, after standing, a brownish precipi-
tate separates, which, treated with dilute acids, leaves a slowly soluble or insoluble
red residue.   This  sulphide  is inalterable  in  the air.—Alkalies and alkaline carbon-
ates produce  no precipitates in solutions of thallium. Hydrochloric  acid throws
down  from solutions that  are not  too dilute, protochloride of  thallium as  a white,
curdy, quickly subsiding  precipitate, which requires 50 parts of boiling  water and
200 parts  of cold  water for its solution, and is  less  soluble  in water  containing
hydrochloric acid.  It is  but slightly soluble in ammonia or in alcohol.   Chromate
of potassa  gives yellow, and bichromate of potassa deep orange precipitates, which
are nearly insoluble in water and acids.  Phosphate of soda gives a crystalline precipi-
tate soluble in acids, but  almost insoluble in water and  alkaline liquids.
   Iodide of potassium,  a  very sensitive reagent,  gives  a  pale  yellow precipitate of 
136
FIFTH GEOUP.
[§H7
iodide of thallium, which appears to be but slightly soluble either in water or exce^
of the reagent.
  Bichloride of platinum throws down a pale orange precipitate  of platinchloride
of thallium, which is next to the sulphide, the least soluble salt of thallium yet
described
  Metallic zinc separates all the thallium  in the metallic state, from neutral solu-
tions often in form  of brilliant, radiated, needle shaped crystals, from acid solutions
as a heavy black powder.
  Thallium and its  compounds  are most easily and certainly detected by spectral
analysis.  The spectrum is characterized  by a single bright green line coincident
with Ba, 5, as seen in Plate I.   It is, however, usually perceptible for but a moment,
and its intensity and duration do not safely indicate the amount of thallium present
in sulphides, flue-dust, &c.
  To find thallium in native  sulphur the latter is mostly dissolved by sulphide of
carbon, and the residue  examined as above.  In pyrites, flue dust and sulphuric
acid-chamber sediment, it may be usually detected at once by the spectroscope.  The
sublimate obtained by strongly heating finely pulverized sulphides in a closed glass
aibe often gives the reaction when none can be obtained from the substance  itself]


                               § H7.

                           FIFTH GROUP.

Of Common  Occurrence : Oxide of  Silver,  Suboxide  of Mer-
  cury, Oxide of Mercury, Oxide  of  Lead, Teroxide  of Bis-
  muth, Oxide of  Copper, Oxide of Cadmium.
Of Rare Occurrence: Oxides of Palladium, Rhodium,  Osmium
  and Ruthenium.

  Properties of the group.—The  sulphides corresponding to the
oxides of this group are insoluble both in dilute acids and in alka-
line sulphides*   The solutions  of these oxides are therefore com-
pletely precipitated  by hydrosulphuric  acid,  no matter whether
their reaction  be neutral, alkaline, or acid.
  The circumstance that they are thrown down by hydrosulphuric
acid from acid solutions distinguishes the oxides  of the fifth group
from those  of the fourth, and all the former groups.
  For the sake of greater clearness and  simplicity, we divide the
oxides of this group into two divisions, and distinguish,
  1.  Oxides precipitable by hydrochloric  acid, viz.: oxide of
silver, suboxide of mercury, oxide of lead.
  2.  Oxides not precipitable by hydrochloric acid,  viz.: oxide
of mercury, oxide of copper, teroxide of bismuth, oxide of cadmium.
  Lead must be considered in both divisions, since the sparing solu-
Dility of its chloride might lead to confounding its oxide with sub-
oxide of mercury and oxide of silver, without affording us,  on the
other hand, any means of effecting its perfect separation  from  the
oxides of the second division.

  * Consult, however, the paragraphs on oxide of copper and suboxide and oxide ol
mercury, as the latter remark  applies only partially to them. 
§ 118.]
OXIDE OF  SILVER.
137
    Special Reactions of the more commonly occurring oxides.
first division : oxides which are precipitated bv hydrochlo-
                           ric ACID.

                       Special Reactions.
                             § 118
                 a. Oxide of Silver (Ag O).
  1. Metallic silver is white, very lustrous, moderately  hard,
highly malleable, ductile, rather difficultly fusible.  It is scarcely
oxidized by ignition in the air. Nitric acid dissolves silver readily .
the metal is insoluble in dilute  sulphuric acid and in hydrochloric
acid.
  2. Oxide of silver is a grayish-brown powder; it is not alto-
gether insoluble in water, and dissolves readily in dilute nitric acid.
li forms no  hydrate.  It is decomposed by heat into metallic silver
and  oxygen gas.  The  Suboxide  of silver (Ag2 O) and  the
binoxide (Ag 02) suffer the same decomposition by ignition.
  3. The salts of oxide of silver are non-volatile and colorless;
most  of them  acquire  a black tint upon exposure to light.  The
soluble neutral salts do not alter vegetable colors, and are decom-
posed at a red heat.
  4. Hydrosulphuric acid and sulphide of ammonium precipitate
from  solutions of salts of silver black  sulphide of silver (Ag S),
which is insoluble in dilute  acids, alkalies, alkaline sulphides, and
cyanide of potassium.  Boiling nitric acid decomposes and dis-
solves this precipitate readily, with separation of sulphur.
  5. Potassa and soda precipitate from solutions of salts of silver
the oxide of this metal in the form  of a  light  brown powder,
which is insoluble in an  excess  of  the precipitant, but dissolves
readily in ammonia.
  6. Ammonia, when added in very small quantity to neutral solu-
tions  of oxide of silver, throws down the oxide as a brown precipi-
tate,  which  readily redissolves in an  excess  of ammonia.  Acid
solutions of silver are not precipitated.
  7. Hydrochloric acid and  soluble metallic chlorides produce in
solutions of salts  of silver a white, curdy precipitate of chloride
of silver (Ag CI).  In very dilute solutions these reagents impart
at first simply a bluish-white  opalescent appearance to  the  fluid ;
by long standing, however, the chloride  of silver separates.  By
the action of light, chloride of silver is slowly decomposed, losing
chlorine, and acquiring at first a violet tint, but ultimately turning
black; it is  insoluble  in nitric acid,  but dissolves readily in ammo-
nia as ammonio-chloride of silver, from which double compound the
chloride of silver  is again separated  by acids. Concentrated hydro* 
 138                SUBOXIDE OF MERCURY.             [§ 119

 chloric acid and concentrated solutions of chlorides of the  alkali
 metals dissolve some  chloride of silver, more particularly upon
 application of heat;  but the dissolved chloride separates again upon
 dilution.  Upon exposure to heat, chloride of  silver fuses without
 decomposition, giving upon cooling a transparent horny mass.
   8. If compounds  of  silver, mixed with carbonate of soda, are
 exposed on a charcoal support to the inner flame of the blowpipe,
 white, brilliant, ductile metallic globules are obtained,  unat-
 tended with incrustation of the charcoal;  or, if the blast be intense
 and prolonged, with the formation of a slight dark-red sublimate.

                             § H9-
               b. Suboxide of Mercury (Hg2 O).
   1. Metallic mercury  is  grayish-white, lustrous,  fluid at the
 common temperature; it solidifies at —40°, and boils at 680° Fah.
 It is insoluble in hydrochloric acid ; in dilute cold nitric acid it dis-
 solves to nitrate of suboxide, in more concentrated hot nitric acid
to nitrate of oxide of mercury.
   2. Suboxide  of mercury is a black powder which is readily
soluble in  nitric acid, and is decomposed by the action  of heat,
the mercury volatilizing in the  metallic state.  It forms no hy-
drate.
   3. The salts of suboxide of mercury volatilize upon ignition;
most of them  suffer decomposition  in this process.   Subchloride
and subbromide of mercury volatilize unaltered.  Most of  the salts
of suboxide of mercury are colorless.  The soluble salts in  the neu-
tral state redden litmus paper.  Nitrate of suboxide of mercury  is
decomposed by addition of much water into a pale-yellow, insolu-
ble basic, and a soluble acid salt.
   4. Hydrosulphuric acid and sulphide of ammonium produce black
precipitates of subsulphide of mercury  (Hg2 S), which are insolu-
ble in dilute acids, sulphide of ammonium, and cyanide of potassium.
Protosulphide  of sodium in presence of some  caustic soda dissolves
this subsulphide to sulphide, with separation  of metallic mercury.
 Bisulphide of sodium dissolves the subsulphide to sulphide, without
 separation of metallic mercury.  Subsulphide of mercury is readily
 decomposed and dissolved by nitrohydrochloric acid,  but not by
 boiling concentrated nitric acids.
   5. Soda, potassa and ammonia produce in solutions of salts of
 suboxide of mercury black precipitates, which are insoluble  in an
 excess  of the precipitants.  The precipitates produced  by  soda and
 potassa consist of suboxide of  mercury ;  whilst those produced
 by ammonia consist of a basic double salt of suboxide  of mer-
 cury and ammonia,  e. g. (N H3, NOs + 2 Hg2 O).
   6. Hydrochloric acid and soluble chlorides precipitate from solu-
 tions of salts  of suboxide of mercury subchloride of mercury 
120.]
OXIDE OF  LEAD.
139
(Hg2 CI) as a fine powder of dazzling whiteness.  Cold  hydrochlo-
ric acid and cold nitric acid fail to dissolve this precipitate ;  it dis-
solves, however,  although very difficultly and slowly,  upon long
protracted boiling with these acids, being resolved by hydrochloric
acid into chloride of mercury and  metallic mercury, which sepa-
rates ;  and converted by nitric acid into chloride of mercury and
nitrate of oxide of mercury.  Nitrohydrochloric acid and chlorine
water  dissolve the subchloride  of mercury readily, converting it
into chloride.  Ammonia and potassa decompose the subchloride
of mercury, the first gives rise to the formation of amido-subchloride
of mercury, (Hg2 N IT, Hg2 CI) the latter separates black suboxide
from it.
  7. If a drop of a neutral or slightly acid solution  of suboxide of
mercury is put on a clean and smooth surface of copper, and washed
off  after some time, the spot will afterwards, on being gently rub-
bed with cloth, paper, &c, appear white and lustrous like silver.
The application of a gentle heat to the copper causes the  metallic
mercury precipitated on  its  surface to volatilize, and thus removes
the apparent silvering.
  8. Protochloride of tin  produces in solutions of suboxide of
mercury a gray precipitate  of metallic  mercury,  which may be
united into globules by boiling the metallic deposit,  after decanting
the fluid, with hydrochloric  acid, to which a drop of protochloride
of tin may be added.
  9. If an intimate mixture of an anhydrous compound of mercury
with anhydrous carbonate of soda is introduced into a  drawn-out
glass tube, and covered with a layer of carbonate of soda, and the
tube is then heated before the blowpipe, the mercurial  compound
invariably undergoes decomposition, and metallic  mercury sepa-
rates, forming a coat of gray sublimate above the heated part of
the tube.  The minute particles  of  mercury may  be united into
larger globules by rubbing this coating with a glass rod.

                             §  120.

                  c.  Oxide of  Lead  (Pb 0).

  1. Metallic lead is bluish-gray;  its surface recently cut exhi-
bits a  metallic lustre; it is soft, malleable, readily fusible, and
volatile at a white heat.  Fused upon charcoal before  the blow-
pipe, it forms a coating of yellow oxide on the charcoal.  Hydro-
chloric acid and moderately concentrated sulphuric acid act upon
it but little, even with the aid of heat; but dilute nitric acid dis-
solves it readily, more particularly on heating.
  2. Oxide of lead is a  yellow or reddish-yellow powder,* which
* While hot, the oxide of lead appears red. 
140
OXIDE OF  LEAD.
[§ 120,
upon exposure to a red heat fuses  to a vitreous mass.   Hydrated
oxide of lead is white.  Both the  oxide and  its hydrate dissolve
readily in nitric and acetic acids.  The suboxide of lead (Pb2 0)
is black, minium or red-lead (2 Pb O, Pb 02)  is red, the binoxide
Pb 02 is brown.   These are all converted  by ignition into oxide.
The binoxide is insoluble in hot nitric  acid, but dissolves on addi-
tion of alcohol, yielding nitrate of oxide of lead.
  3.  The salts of oxide of lead are  non-volatile ; most of them
are colorless; the neutral soluble  salts redden litmus paper, and
are decomposed at a red heat.   Chloride of lead when heated with
access of air, partially volatilizes and oxychloride  of lead remains
behind.
  4.  Hydrosulphuric acid and sulphide of ammonium produce in
solutions of salts of lead black precipitates of sulphide of lead
(Pb S), which are insoluble in cold dilute acids, in alkalies, alkaline
sulphides, and cyanide of potassium.   Sulphide of lead  is decom-
posed by boiling nitric acid.   If the acid be sufficiently dilute the
whole of the lead dissolves  as  nitrate of  lead, and sulphur sepa-
rates.  Fuming nitric acid oxidizes the sulphur entirely to sulphuric
acid, and  all the lead  separates as  insoluble sulphate of lead.
Nitric acid of medium strength causes the  separation of a portion
Df the lead as sulphate, while the remainder remains in the form of
nitrate.  In solutions of salts of lead containing an excess  of a
concentrated mineral acid, hydrosulphuric  acid produces a precipi-
tate only after the addition of water or after neutralization of the
free  acid by an alkali.   If a  solution of  lead is precipitated by
hydrosulphuric acid, in presence of a large quantity of free  hydro-
chloric acid, a red precipitate may be formed, consisting of  chlo-
ride  and sulphide  of  lead, which,  however, is converted by an
excess of hydrosulphuric acid into black sulphide of lead.
  5.  Soda, potassa and ammonia throw down basic salts of lead
in the form of white precipitates, which are insoluble in ammonia,
and difficultly soluble in soda and potassa.   In solutions of acetate
of lead ammonia (free from carbonate,) does not immediately pro-
duce a precipitate, owing to the formation of a soluble triacetate
of lead.
  6. Carbonate of soda throws down from  solutions of salts of
lead a white  precipitate of basic carbonate of lead (e.  g.  6
(Pb O, C 02) + Pb O, H O), which is insoluble in an excess of the
precipitant and also in cyanide of potassium.
  7. Hydrochloric acid  and soluble chlorides produce in concen-
trated solutions of salts of lead heavy, white precipitates of chlo-
ride of lead (Pb CI), which are soluble in a large  amount  of
water, especially upon application  of heat.  This chloride  of lead
is converted by  ammonia into oxychloride of lead (Pb CI, 3 Pb
0+HO), which is also a white  powder, but almost  absolutely 
§ 121.]
OXIDE OF  LEAD.
Ill
 insoluble in water.  In dilute  nitric and hydrochloric acids, chlo-
 ride of lead is more difficultly soluble than in water.
   8. Sulphuric acid and sulphates produce in solutions of salts of
 lead white precipitates of sulphate of lead  (Pb O, S 03), which
 are nearly insoluble in water and dilute acids.  From dilute solu-
 tions, especially from such as contain much free acid, the  sulphate
 of lead precipitates only after some, frequently after  a  long time.
 It is advisable under all circumstances to add a considerable excess
 of dilute sulphuric acid, since sulphate of lead is more insoluble
 in this menstruum than in water.  The separation of small quanti-
 ties of sulphate of lead is best effected by  evaporating, after the
 addition of the sulphuric acid,  as far as practicable on  the  water-
 bath, and then treating the residue with water.   Sulphate  of lead
 is slightly soluble in concentrated nitric  acid; it  dissolves with
 difficulty in  boiling  concentrated  hydrochloric  acid,  but more
 readily in solution of potassa.   It dissolves also  pretty readily in
 the solutions of some of the salts of ammonia, particularly in solu-
 tion of acetate of ammonia; dilute sulphuric  acid precipitates  it
 again from these solutions.
   9. Chromate of potassa produces in solutions of salts of lead a
 yellow precipitate of chromate  of lead  (Pb O, Cr 03) which is
 readily soluble in  potassa, but difficultly so in dilute nitric acid.
   10. If a mixture of a compound of lead with carbonate  of soda
 is exposed on a charcoal support to the reducing flame of the blow-
pipe, soft, malleable metallic globules of  lead are readily pro-
 duced, the charcoal becoming covered at the  same time  with a
 slight yellow incrustation of oxide of lead.


                             §121.
  Recapitidation  and remarks.—The metallic oxides of the first
 division of the fifth group are most distinctly characterized in their
corresponding chlorides; since the different respective deportment
of these chlorides with water and ammonia affords us a simple
means both of detecting them and effecting  their  separation from
one another.   For if the precipitate containing the three metallic
chlorides is boiled with a somewhat large  quantity  of water, or
boiling water is repeatedly poured over it on the filter, the chloride
of lead  dissolves, whilst the  chloride of silver and the subchloride
of mercury remain undissolved.  If these  two chlorides are then
treated  with  ammonia, the  subchloride of mercury is  converted
into  a  black  basic salt, insoluble in an excess of the  ammonia;
whilst the chloride of silver dissolves  readily in  that agent, and
precipitates from this solution again upon  addition of nitric acid.
When operating upon small  quantities, it is advisable first to expel
the greater part of the ammonia by heat.   In the  aqueous solution 
142
OXIDE OF  MERCURY.
IS122
of chloride of lead the metal may be readily detected by sulphuru
acid.

second division of the  fifth group: oxides  which are not
             precipitated by hydrochloric acid.

                      Special Reactions.

                            § 122.
                a. Oxide of Mercury (Hg O.)
  1. Oxide of Mercury is generally crystalline,  and has a bright
red color, which upon reduction to powder changes to a pale yel-
lowish-red ; the oxide precipitated from solutions  of the nitrate  of
the oxide, or from solutions of the chloride, forms  a yellow powder.
Upon exposure to heat it transiently acquires a deeper tint; at a
dull red heat it is resolved into metallic mercury and oxygen.
Both the crystalline and non-crystalline oxide dissolve readily in
hydrochloric and nitric acids.
  2. The  salts  of oxide of mercury volatilize upon ignition;
most of them suffer decomposition in this process; chloride, bro-
mide, and iodide of mercury, however, volatilize unaltered.  Most
of the salts of oxide of mercury are colorless.   The  soluble neutral
salts redden litmus paper.   The nitrate  and sulphate of oxide  of
mercury are decomposed by water added  in large  quantity, into
soluble acid and insoluble  basic salts.
  3. Addition of a very small quantity  of hydrosulphuric acid or
sulphide of ammonium produces in solutions of oxide of mercury,
after shaking, a  perfectly white precipitate.  Addition of a some-
what  larger quantity of these reagents causes the precipitate  to
acquire  a yellow, orange,  or brownish-red color,  according to the
less or greater proportion  added ; an excess of the precipitant pro-
duces a purely black precipitate of sulphide of mercury (Hg S).
This progressive variation of color from white  to black, which
depends on the proportion of the hydrosulphuric  acid or sulphide
of ammonium added, distinguishes the  oxide of mercury from  all
other bodies.  The white  precipitate which forms at first consists
of a double  compound of  sulphide of mercury with the still unde-
composed portion of the salt of oxide of mercury  (in a solution  of
chloride of mercury, for instance, Hg CI+ 2 Hg S); the gradually
increasing admixture of black  sulphide causes the precipitate to
pass through  the  several gradations of  color above mentioned.
Sulphide of mercury  is not dissolved  by sulphide of ammonium,
nor by potassa or  cyanide of potassium; it is altogether insoluble
in hydrochloric acid  and in  nitric acid, even  upon boiling.  It dis-
solves completely in sulphide of potassium, and is readily decom-
posed and dissolved by nitrohydrochloric acid. 
§ 123.]
OXIDE OF  COPPER.
143
   4.  Soda or potassa, added in small quantity, produces in neutral
 or slightly  acid  solutions of oxide of mercury a  reddish-brown
 precipitate, which acquires a yellow tint if the reagent is added in
 excess.  The reddish-brown precipitate is a basic salt ;  the yellow
 precipitate  consists  of oxide of  mercury.  An  excess of the
 precipitant  does not redissolve these  precipitates.   In very acid
 solutions  this reaction does not take place  at all, or at least the
 precipitation is very incomplete.   In presence of salts of ammonia,
 potassa produces in solutions  of salts of oxide of mercury, instead
 of reddish-brown or yellow,  white precipitates.  The  precipitate
 thrown down by potassa from a  solution of chloride of mercury
 containing  an  excess of chloride  of ammonium  is of  analogous
 composition to the precipitate produced by ammonia (see 5).
   5.  Ammonia produces in solutions of salts of oxide of mercury
 white precipitates quite analogous to those produced by potassa in
 presence  of chloride of ammonium; thus, for instance,  ammonia
 precipitates from solutions of chloride of mercury, chloramide of
 MERCURY (Hg Cl + Hg N Ha).
   6.  Protochloride of tin, added in small quantity to salts of oxide
 of mercury, reduces the oxide to  suboxide, thus giving rise to the
 formation of a  white precipitate of  subchloride of  mercury
 (2 Hg CI + Sn  CI = Hg2 CI + Sn Cl2); but if added in excess, the
 subchloride at first formed is reduced to metal (Hg2 CI + Sn CI =
 Sn Cl2 +  Hg2).  The precipitate, which was white at first, acquires
 therefore  now a gray tint, and may be readily united into globules
 of metallic  mercury by boiling with hydrochloric acid, and some
 protochloride of tin.
   7. The  salts of oxide of mercury present the same deportment as
 the salts  of the suboxide, both with  metallic copper and  when
 heated together with carbonate of soda in a glass tube before the
 blowpipe.

                             § 123.
                  b. Oxide of  Copper (Cu  O).
   1. Metallic copper has a peculiar red color, and a strong lustre;
 it  is moderately hard, malleable, ductile, rather difficultly fusible;
 in contact with  water and air it  becomes  covered with a green
 crust of basic carbonate of oxide of copper; upon ignition in the
 air it becomes coated over with black oxide.  In hydrochloric acid
 and dilute sulphuric  acid  it is insoluble or  nearly  so, even upon
 boiling.  Nitric  acid dissolves the metal  readily.  Concentrated
 sulphuric acid converts it into  sulphate of oxide of copper,with evo-
 lution of sulphurous acid.
  2. Suboxide of copper is red, its hydrate yellow ; both change
to  oxide upon ignition in  the air.   On  treating the  suboxide with
dilute sulphuric acid, metallic copper separates, whilst sulphate of 
144
OXIDE OF  COPPER.
[§ 123.
 oxide of copper dissolves; on  treating  suboxide of copper with
 hydrochloric  acid, white subchloride of copper is  formed, which
 dissolves in an excess of the acid, but is reprecipitated from this
 solution by water.
   3.  Oxide of copper is a black powder ; its hydrate (Cu O, H 0)
 is of  a light blue color.  Both the oxide of copper and its hydrate
 dissolve readily in hydrochloric, sulphuric, and nitric acids.
   4.  Most  of the neutral salts of oxide of copper are  soluble in
 water; the soluble salts  redden litmus, and suffer  decomposition
 when heated to gentle redness, with the exception of the sulphate,
 which can bear a somewhat higher temperature.  They are usually
 white in the anhydrous state; the hydrated salts are  usually of a
 blue,  or green color, which their solutions continue to exhibit even
 when much diluted.
   5.  Hydrosulphuric acid and sulphide of ammonium produce in
 alkaline, neutral, and  acid solutions of salts of oxide of copper,
 brownish-black precipitates of sulphide  of copper (Cu S).  This
 sulphide is insoluble in dilute acids and caustic alkalies.  Hot solu-
 tions  of sulphide of potassium and sulphide of sodium fail  also to
 dissolve it, or  dissolve it  only to a very trifling extent; but it is a
 little  more soluble in sulphide of ammonium.  [Sulphide of ammo-
 nium  may produce in the cold a  red-brown or  red precipitate
 which dissolves completely in an excess of the reagent, but is per-
 fectly or almost perfectly precipitated as black sulphide  when the
 solution is heated to boiling.]  The latter reagent is therefore not
 adapted to effect the perfect separation of sulphide of copper from
 other metallic sulphides.   Sulphide of copper is readily decomposed
 and  dissolved by  boiling concentrated  nitric  acid;  it dissolves
 completely in  solution of cyanide of potassium.  In  solutions  of
 salts of copper which contain an excess of a concentrated  mineral
 acid,  hydrosulphuric  acid produces  a precipitate only after the
 addition of water.
   6. Potassa  or soda produces in solutions of salts of oxide  of
 copper  a light blue, bulky precipitate of hydrate of  oxide  of
 copper (Cu O, II O).  If the solution is  highly concentrated, and
the potassa added in excess, the precipitate turns black after the
lapse  of some  time, and  loses its bulkiness, even in the  cold; but
the change takes place immediately if the precipitate is boiled with
the fluid in  which it is suspended (and which must,  if necessary, be
diluted for  the purpose).   In this process Cu O, H  O, is  converted
into 3 Cu O, H O.
   7.   Carbo'hate of  soda  produces in solutions of salts of oxide of
copper a greenish-blue precipitate of hydrated  basic carbonate
 of copper  (Cu O, C 02 4- Cu O, H O), which upon boiling  changes
 to brownish-black oxide of copper, and dissolves in ammonia to an
azure-blue,  and in cyanide of potassium to a brownish fluid. 
§ 1^.]
OXIDE OF  COPPER.
145
   8. Ammonia added  in small quantity to solutions of salts of
 oxide of copper produces a greenish-blue precipitate, consisting of
 a basic salt of copper. This precipitate redissolves  readily upon
 further addition of ammonia, giving a perfectly clear solution of a
 magnificent azure-blue,  which owes its color to the formation of a
 basic  double  salt of ammonio-oxide  of copper.  Thus, for
 instance, in a  solution of sulphate  of oxide of copper, ammonia
 produces a precipitate of N H3, Cu O 4- N II4 O, S 03.   The blue
 color ceases to be perceptible only in very dilute solutions.  Potassa
 produces in such blue  solutions in  the cold, after the lapse of
 some time, a precipitate of blue hydrate of oxide of copper; but
 upon boiling the fluid this reagent  precipitates the whole of the
 copper as black oxide.  Carbonate of ammonia presents the same
 deportment with salts of copper as pure ammonia.
   9. Ferrocyanide of potassium  produces even  in  moderately
 dilute  solutions a  reddish-brown precipitate of ferrocyanide of
 copper  (Cu,,  Cfy) which is insoluble in dilute acids, but suffers
 decomposition when acted upon by potassa or ammonia.  In very
 highly dilute solutions the reagent produces only a reddish colora-
 tion of the fluid.
   10. Metallic iron when brought into  contact with concentrated
 solutions of salts of copper is almost immediately covered with a
 coppery-red coating of metallic copper ;  very dilute solutions
 produce this coating only after some time. Presence of a little
 free acid accelerates the reaction.
  If a fluid containing copper and a little free hydrochloric acid
 is poured into  a small platinum dish (the lid  of  a platinum cruci-
 ble), and a small piece of zinc is introduced, the bright platinum
 surface speedily becomes covered with a coating of copper ;  even
 with very dilute solutions this coating is clearly discernible.
  11. If a  mixture of a compound of copper with carbonate of
 soda is exposed on a charcoal support to the reducing flame of the
 blowpipe, metallic  copper is  obtained, without  simultaneous
 incrustation of the charcoal.  The best method of freeing this cop-
 per from the particles of charcoal, is to triturate the fused mass in
 a small mortar with water, and to Avash off the  charcoal powder;
 when the coppery-red metallic particles will be left behind.
  12. Copper, its alloys, and other compounds, when exposed in
 even the minutest quantities to the inner blowpipe or gas-flame,
 impart an emerald green tint  to  the outer  flame.  Addition  of
 hydrochloric acid  considerably heightens  the delicacy of the
 reaction.
  13. Borax and phosphate of soda and ammonia readily dissolve
 oxide of copper in the outer flame.  The beads are green while
hot, blue when cold.  In the inner flame the bead produced with
borax appears colorless, that produced with phosphate of soda and
                              10 
146                TEROXIDE OF BISMUTH.             [§ 124

ammonia turns dark green; both acquire a brownish-red tint upon
cooling.

                             § 124.
               c. Teroxide of Bismuth (Bi 03).
  1. Bismuth has a reddish tin-white color and moderate metallic
lustre; it is of medium hardness, brittle, readily fusible; when fused
upon a charcoal support, it forms a coating of yellow teroxide on
the surface of the charcoal.  It dissolves readily in nitric acid, but
is nearly insoluble in hydrochloric acid, and altogether so in dilute
sulphuric acid.  Concentrated sulphuric acid converts it into sul-
phate  of teroxide  of  bismuth,  with  evolution  of sulphurous
acid.
  2. The teroxide of bismuth is a yellow powder; when heated,
it transiently acquires a deeper tint; it fuses  at a red heat.   Hy-
drate of teroxide of bismuth is white.   Both the teroxide and its
hydrate dissolve readily in hydrochloric, sulphuric, and nitric acids.
Grayish-black binoxide  of bismuth  (Bi 02) and red bismuthic
acid (Bi 05) are converted into teroxide  by ignition in the air, and
yield with hot nitric acid, nitrate of teroxide.
  3. The salts of teroxide of bismuth are  non-volatile, with the
exception of a few  (terchloride of bismuth).  Most of  them are
soluble  in water, whilst  others are insoluble in this menstruum.
The soluble  salts, in the neutral state, redden litmus-paper, and
are decomposed when treated with  a  large  amount of water,
insoluble basic salts separating, the greater portion of the acid and
a small quantity of bismuth remaining however in solution.
  4. Hydrosulphuric acid and sulphide of ammonium produce in
neutral and acid solutions of salts of bismuth black precipitates of
tersulphide  of  bismuth (Bi S3), which are insoluble  in dilute
acids, alkalies, alkaline sulphides,  and cyanide of potassium, but
are readily decomposed and dissolved by boiling nitric  acid.  In
solutions of salts of bismuth which contain  a considerable excess
of hydrochloric or nitric acid, hydrosulphuric acid produces a pre-
cipitate only after the addition of water.
  5. Potassa  and ammonia throw down  from  solutions  of salts
of bismuth hydrate of  teroxide of  bismuth as a white  precipi-
tate, which is  insoluble in an excess of the precipitant.
  6. Carbonate of soda throws  down from solutions of salts of
bismuth  basic carbonate  of bismuth  (Bi  03, C O.) as a white
bulky precipitate, which is insoluble in an excess of the precipitant,
and equally so in cyanide of potassium.
  7. Chromate of potassa precipitates from solutions of salts of
bismuth chromate  of  bismuth  (Bi  03,  2  Cr  03) as  a yellow
powder.  This substance differs from chromate of lead in being
soluble in dilute nitric acid and insoluble in potassa. 
§ 125.]
OXIDE OF  CADMIUM.
147
   8.  Dilute  sidphuric acid does not precipitate dilute solutions of
 nitrate of bismuth.   If the solution containing excess of sulphuric
 acid  be evaporated to dryness in the water-bath, there remains a
 white saline  mass, which dissolves perfectly in  water acidified with
 sulphuric acid  (characteristic distinction  from oxide of  lead).
 From this solution, after long standing (perhaps for days), basic
 sulphate  of bismuth  (Bi 03 S 03 +  2 aq.) crystallizes out in white
 microscopic needles which are soluble in nitric acid.
   9.  The reaction which especially characterizes the teroxide of
 bismuth,  is the decomposition of its neutral salts by water with the
 formation of insoluble basic salts.  The addition of a large amount
 of water to solutions of salts of bismuth, causes the immediate
 formation of a dazzling white precipitate, provided there be not too
 much free acid present.   This reaction is the most sensitive with
 terchloride  of bismuth,  as the basic  oxychloride  of bismuth
 (Bi CI, 2 Bi 03)  is nearly insoluble in water.  If water fails to
 produce a precipitate in nitric acid solutions of bismuth, owing to
 the presence of too much free acid,  adding solution of chloride of
 sodium nearly always causes an immediate precipitation.  From
 the basic salts of antimony which  are formed under analogous cir-
 cumstances, the precipitated basic salts of bismuth  may be readily
 distinguished by their insolubility in tartaric acid.
   10. If a mixture of a compound of bismuth with carbonate of
 soda  is exposed on a  charcoal support to the reducing flame of the
 blowpipe,hxitt\Q globules of bismuth are obtained, which fly into
 pieces  under the stroke of  a  hammer.   The charcoal becomes
 covered at the same time with a  slight incrustation of teroxide
 of bismuth, which is  orange when hot,  and yellow  when cold.

                             § 125.
                 d. Oxide  of Cadmium (Cd O).
   1. Metallic cadmium has a tin-white color; it is lustrous, not very
 hard,  malleable, ductile ; it  fuses at a temperature below red heat,
 and volatilizes at a temperature somewhat above  the boiling point
 of mercury.   It may therefore be easily sublimed in  a glass tube.
 Heated on charcoal before  the blowpipe, it takes fire  and burns,
 emitting brown fumes of oxide of cadmium, which form a coating
 on the charcoal.   Hydrochloric acid and dilute sulphuric acid dis-
 solve  it, with evolution of hydrogen; but nitric  acid  dissolves it
 most  readily.
  2. Oxide of cadmium is a yellowish-brown, fixed  powder; its
 hydrate is white.   Both the oxide and its hydrate dissolve readily
 in hydrochloric, nitric, and sulphuric acids.
  3. The salts of oxide of cadmium are colorless or white;  some
 of them are  soluble in water.  The soluble salts,  in  the neutral
state,  redden litmus-paper, and are decomposed at a red heat. 
148
OXIDE OF  CADMIUM.
[§ 126.
   4. Hydrosulphuric acid and sulphide of ammonium produce  in
alkaline, neutral, and  acid solutions of salts  of  cadmium,  bright
yellow precipitates of sulphide of  cadmium (Cd S),  which are
insoluble  in  dilute  acids, alkalies,  alkaline  sulphides,  and (dis-
tinction from copper) in cyanide of potassium.   They are readily
decomposed and dissolved by boiling nitric and hydrochloric acids,
and  (distinction from copper)  in boiling dilute sulphuric acid.  In
solutions of salts of cadmium which contain a considerable  excess
of acid, hydrosulphuric acid produces a precipitate only after dilu-
tion  with water.
   5.  Potassa  produces in solutions of salts of cadmium a white
precipitate of hydrate of oxide of cadmium (Cd O, H O), which
is insoluble in an excess of the precipitant.
   6.  Ammonia likewise precipitates from solutions of salts of cad-
mium white hydrate of oxide of cadmium, which, however, redis-
solves readily to a colorless fluid in an excess of the precipitant.
   7.  Carbonate of potassa and  carbonate of ammonia produce
white precipitates of carbonate  of cadmium (Cd O, C 02), which
are insoluble  in an  excess of the precipitants.  The presence of
salts of ammonia does not prevent  the formation of these precipi-
tates.  The precipitated carbonate of cadmium dissolves readily in
solution of cyanide of potassium.  From dilute solutions the pre-
cipitate separates only after some time.
   8.  If a mixture  of a  compound of cadmium with carbonate of
soda is exposed on a charcoal support to the reducing flame of the
blowpipe,  the charcoal becomes covered  with  a  reddish-brown
coating of oxide of cadmium, owing to the  volatilization  of the
reduced metal and its subsequent re-oxidation in passing through
the  oxidizing flame.   The  coating is seen most distinctly after
cooling.

                            § 126.
  Recapitulation  and remarks.—The perfect separation of the
metallic oxides of the second division of the fifth group from sub-
oxide of mercury  and oxide of  silver may, as already stated, be
effected by means of hydrochloric acid ; but this agent fails to sepa-
rate them completely from oxide of lead.   Traces of salts of oxide
of mercury which may adhere to the chloride of silver are com-
pletely dissolved by washing.—(67. J. Mulder.) The oxide of mer-
cury is distinguished from the other oxides of this division by the
insolubility of the  corresponding  sulphide  in boiling nitric acid.
This property affords a  convenient means for its  separation.  Care
must be taken that the sulphides be  completely freed from hydro-
chloric acid and metallic chlorides before treating them with nitric
acid, as otherwise, mercury would go into  solution.  Moreover,
the reactions  with protochloride of tin or with metallic copper, as 
§ 127.]           PROTOXIDE OF  PALLADIUM.               149

well as those in the dry way, will, after  the previous removal of
the suboxide, always readily indicate the presence  of oxide of
mercury.
  If the humid  method be  employed, it is best to dissolve the
sulphide of mercury in hot hydrochloric acid  with help of a frag-
ment of chlorate of potassa.
  From the still remaining oxides  the oxide of lead is separated by
addition of a sufficient quantity of dilute sulphuric acid; the sepa-
ration  is the most complete if the  fluid, after the addition of  sul-
phuric acid,  is evaporated on the water-bath, the residue diluted
with water containing some  sulphuric  acid and the insoluble  sul-
phate of lead immediately filtered off.  The latter can be examined
in the  dry way as described,  § 120.10, or  by heating a portion of
it  with solution of chromate of potassa.  The white precipitate is
thus converted into the yellow chromate of lead.   It is washed and
heated with  soda-solution in which  it dissolves.   Addition of
acetic  acid to the alkaline solution throws down again yellow chro-
mate of lead.  After removal of the oxides  of mercury and lead,
teroxide of bismuth may be separated from oxide of copper and
oxide of cadmium by addition of  ammonia in excess, as the latter
two oxides are soluble in an excess of this agent.  If the filtered
precipitate is  dissolved in one or two drops of hydrochloric acid on
a watchglass, and water added, the appearance of a milky turbidity
is  a confirmation of the presence of teroxide of bismuth.—The pre-
sence  of  a notable quantity of oxide  of copper is revealed by the
blue color of the ammoniacal solution ; smaller quantities are detect-
ed  by evaporating the  ammoniacal  solution nearly  to  dryness,
adding a  little acetic acid, and then  ferrocyanide of  potassium.
The separation of copper from cadmium may be effected by acting
on the mixed  sulphides of these metals by cyanide of potassium,
or by boiling dilute sulphuric acid.  The solution of the two metals
is precipitated by hydrosulphuric acid and the sulphides are filtered
off.  If the sulphides be now covered with water and a fragment of
cyanide of potassium added, the sulphide of copper dissolves, while
yellow sulphide of cadmium remains behind.  If the mixed sulphides
be boiled  with dilute sulphuric acid (1 part of strong acid to 6 parts
of water)  sulphide of cadmium is dissolved while sulphide of copper
is unattacked.   From the solution hydrosulphuric acid throws down
yellow sulphide of cadmium.—(A. W. Hoffman.)

            Special reactions of the rarer oxides of the fifth group.
                              §127.
  1. Protoxide op Palladium (Pd 0).—Palladium greatly resembles platinum,
with which it is usually associated in nature. Its color is, however, somewhat darker.
It fuses with great difficulty; when heated in the air  to dull redness, it becomes
covered with a blue coating; but. upon more intense ignition, it recovers its light
color and metallic lustre.  It is difficultly soluble in pure nitric acid, but dissolve* 
150                       OXIDES OF  OSMIUM.                  [§  127.

somewhat more  readily in nitric acid, containing nitrous acid ;  it dissolves very
sparingly in boiling concentrated sulphuric acid, but readily in nitro-hydrocliloric
acid.   It combines with 1 and 2 eq.  of oxygen to form protoxide and binoxide.  The
latter  in  black, and when  heated with dilute hydrochloric  acid,  evolves chlorine,
and gives solution of protochloride of* palladium.  Protoxide  of palladium is black,
its hydrate dark brown; both are, upon intense ignition, resolved into oxygen and
metallic palladium.  The salts of protoxide of palladium are mostly soluble in water;
they are brown, or reddish-brown; their solutions, when concentrated,  are reddish-
brown ; when dilute, yellow.  "Water precipitates from  a solution of nitrate of prot-
oxide  of palladium containing a slight excess of  acid, a brown-colored basic salt.
The oxygen salts, as well as the protochloride, are decomposed  upon ignition,  leav.
ing metallic  palladium behind.  Hydrosulphuric acid  and sulphide  of ammonium
throw down from acid  or neutral solutions of salts of protoxide of  palladium, black
protosulphide of palladium, which dissolves neither in sulphide of ammonium nor in
boiling hydrochloric acid,  and with difficulty in boiling nitric acid, but readily in
nitro-hydrochloric acid.  From the solution of the protochloride potassa precipitates
a brown  basic salt, soluble  in an excess of the  precipitant, ammonia,  flesh-colored
ammonio-protochloride  of palladium  (Pd CI, N  H3), cyanide of mercury, yellowish-
white gelatinous  protocyanide of palladium soluble in hydrochloric acid,  and in
ammonia (characteristic reaction).  Protochloride of tin produces, in absence of free
hydrochloric acid, a brownish-black precipitate ; in presence of free hydrochloric acid,
a red-colored solution,  which speedily turns brown, and ultimately  green, and,  upon
addition of water, brownish-red.  Sulphate of protoxide of iron produces a deposit of
palladium on the sides of  the glass.   Iodide of potassium precipitates black protio-
dide of palladium (characteristic reaction).   Chloride of potassium  precipitates from
highly concentrated solutions of protoxide of palladium,  potassio-protochloride of
palladium (K CI, Pd CI), in form of  golden-yellow needles, which dissolve  readily in
water, giving a dark red fluid, but are insoluble in absolute alcohol.
  2. Sesquioxide of  Rhodium.—(R2 03).   Rhodium is found  in  small quantity in
native platinum.   It is a steel-gray,  hard, brittle metal.   In the state of powder  it
acquires  oxygen at a red heat, and passes first into  protoxide, afterwards  into  pro-
tosesquioxide.   On stronger  ignition it  is  reduced again  to  the  metallic  state.
Rhodium is insoluble in all acids, even in nitro-hydrochloric.  It dissolves in the
latter when it is alloyed with platinum, copper, &c, but not when alloyed  with gold
and silver.  It is dissolved as sesquioxide  by fused hydrated  phosphoric  acid, as
well as bisulphate of potassa.   The  sesquioxide is black, its hydrate greenish  gray,
or brown; it is insoluble in acids, but soluble in the fluxes above named.   The
solutions are rose red.   Hydrosulphuric acid and sulphide of ammonium slowly pre-
cipitate,  especially from warm  solutions,  brown  sulphide  of  rhodium,  which  is
insoluble in sulphide of ammonium but dissolves in  boiling hydrochloric and  nitric
acids.  Potassa precipitates brown hydrate only on boiling.   If alcohol be added to
the solution,  made alkaline by potassa, rhodium is thrown  down  in the form  of  a
black powder.   The precipitation takes place only after the lapse of some  time,
when potassa is present in large excess.
  Ammonia  produces, after some time, a yellow precipitate  which is soluble  m
hydrochloric  acid   Zinc throws down black metallic rhodium.  All the solid com-
pounds of rhodium, when ignited in  a stream of hydrogen, yield the metal, which is
well characterized by  its insolubility in nitrohydrochloric acid, its solubility in fus-
ing bisulphate of potassa and the deportment of the solution towards potassa and
alcohol.
   3.  Oxides of Osmium.—Osmium  accompanies native platinum as  Iridosmine, &c.
It is either a black powder or a gray brilliant mass, and is infusible.  The metal as
well as its protoxide (0 0) and binoxide  (Os 02), oxidize easily when heated in the
air, to osmic acid (Os 04) which is volatile and recognizable by  its  highly character* 
§ 127.]                OXIDES OF  RUTHENIUM.                     151

istic, penetrating, and disagreeable odor, resembling that of chlorine and iodine.  If
osmium be placed on a strip of platinum foil, and brought into the outer mantel  of
the gas or alcohol flame at half its height, the flame becomes intensely luminous.  In
iridium containing minute traces of osmium, the latter may thus be  detected; the
reaction is, however, momentary;  it may be reproduced  by bringing the substance
for a time into the reducing flame and then again into the outer mantel.   Nitric acidt
especially when red and fuming, and  nitrohydrochloric acid, dissolve  osmium to
osmic acid. #  The solution is favored by heat, but with loss of osmic acid.  Osmium
which  has been intensely ignited does  not  dissolve in  acids.  It should  be fused
with nitrate of potassa and the fused mass distilled with  nitric  acid; osmic acid
passes into the distillate.
  When osmium is heated in chlorine, there are formed green  volatile  protochloride
of osmium (Os CI), and red, still more volatile  bichloride (Os  CU).   The bichloride
of osmium in solution rapidly decomposes,  unless an alkaline chloride  be present,
into hydrochloric acid, osmic acid, and metallic osmium.   All  compounds of osmium
yield, when heated in hydrogen gas, metallic  osmium.   Anhydrous osmic  acid  is
white  and crystalline, fusible at a gentle heat, boil3 at about 212°  Fah., giving off
vapors that attack the eyes and nostrils.  Heated with water, it fuses and dissolves
but slowly.   The solution has a faint acid reaction and a strong disagreeable  odor.
Its solution is colored yellow, and its odor  disappears  on addition  of alkalies.  On
heating with nitric or hydrochloric acid, the odor is again developed, and on distil-
ling the mixture, osmic acid passes over (highly characteristic reaction).  On evapo-
rating solutions of  alkaline osmates, especially if alkali  be in excess, osmous acid
(Os Oj) is formed.  The reduction is aided  by addition of alcohol.   Hydrosulphuric
acid produces brown sulphide of osmium (Os S4),  which only separates  in presence
of a strong acid; it is insoluble in sulphide of ammonium.  Sulphite of soda gives a
deep blue-violet color, and osmium gradually separates as a black powder.  Osmium
is also thrown down as a black powder by protosulphate of iron and by fo?-mic acid,
Bnd in presence of a strong acid, by zinc and  many other metals   The osmochlo-
ride of potassium is difficultly soluble in cold, more easily in  hot water;  it is inso-
luble in alcohol.   On heating its solution with tannic acid it becomes of a deep blue
color (characteristic); formate of soda throws down from  it black metallic osmium.
   4. Oxides  of  Ruthenium.—Ruthenium is found in small quantities in native
platinum.  It is  a  gray-white, brittle, very infusible  metal, not attacked by fusing
bisulphate of potassa, scarcely by aqua-regia;  ignited in the air, it  is converted into
bluish-black  sesquioxide (Ru2 03) which is insoluble  in acids; ignited in a stream
of chlorine  gas with chloride of  potassium, it  gives ruthenochloride of potassium ;
fused with hydrate, nitrate or chlorate of  potassa it  yields a greenish-black  mass
containing ruthenate of potassa (Ko Ru 03), which dissolves  in water to an orange-
yellow solution, that  colors the skin black, from  reduction and separation of black
sesquioxide.   From this solution, acids  precipitate black  oxide which is dissolved by
hydrochloric acid, to an orange yellow liquid.  The latter solution is decomposed by
heating, into hydrochloric acid and  brownish-black oxide of ruthenium; it  gives
when concentrated, crystalline, violet, shining precipitates with chlorides of ammo-
nium  and potassium, from  which  on  boiling, black  oxyprotochloride separates.
Potassa throws down black  hydrated oxide of  ruthenium,  which is  insoluble in
alkalies and  soluble in acids.   Hydrosulphuric acid at first, produces  no change.
After some time the solution becomes sky-blue, and brown  sulphide of ruthenium
separates (very characteristic reaction).   Sulphide of ammonium gives a brown-black
precipitate,  which  slightly dissolves in excess of the precipitant.   Sulphocyanide
of potassium produces (in  absence  of the other platinum metals), and after some time,
a red  coloration which  gradually becomes purple, and on  heating, violet  (very
characteristic reaction).  Zinc  causes at first a sky-blue coloration, and afterwards
a decoloration of  the liquid with separation  of metallic ruthenium. 
 152                  TEROXIDE  OF GOLD.         [§§ 128, 129.

                             § 128.
                       SIXTH  GROUP.
 Of common occurrence : Teroxide of Gold, Binoxide of Plati-
   num, Protoxide of Tin, Binoxide of Tin, Teroxide of Anti-
   mony, Arsenious Acid and Arsenic Acid.
 Of rare occurrence:  Oxides  of Iridium, Molybdenum, Tung-
                sten, Tellurium and  Selenium.
   The higher oxides of the elements belonging to the sixth group
 all possess more or less marked acid characters ; they are however
 noticed here because they cannot be conveniently considered apart
 from the lower  oxides of the same elements, especially as they
 deport themselves similarly towards hydrosulphuric acid.
   Properties of the  group.—The  sulphides corresponding to the
 oxides of the sixth group are insoluble in dilute acids.  These com-
 bine with alkaline sulphides either  directly, or by passing into a
 higher degree of sulphuration,  forming soluble  sulphur salts, in
 which they perform  the  part  of  the acid.  Hydrosulphuric acid
 precipitates these oxides therefore, like those of the fifth group,
 completely from  acidified solutions. The precipitated sulphides
 differ, however, from those of the fifth group in this, that they dis-
 solve in sulphide of ammonium, sulphide of potassium, &c, and
 are reprecipitated from these solutions on the addition of acids.
   We divide the  oxides of this group into two classes, and distin-
 guish,
   1. Oxides whose corresponding sulphides are  insoluble in
 hydrochloric  acid and in nitric acio, and are reduced to  the
 metallic state upon fusion in conjunction with nitrate and carbon-
 ate of soda: viz., teroxide of gold and binoxide of platinum.
   2.  Oxides  whose corresponding sulphides are soluble  in
 boiling hydrochloric acid or  nitric acid, and  are upon fusion
 with nitrate and carbonate of soda converted into oxides or acids,
which combine with the  soda:  viz., Teroxide of antimony, prot-
oxide and binoxide of tin, arsenious and arsenic acids.

                        FIRST DIVISION.
                       Special Reactions.
                            §129.
                a. Teroxide of Gold (Au 03).
   1. Metallic gold has a reddish yellow color, and a high metal-
lic lustre : it is rather soft, exceedingly malleable, ductile, difficultly
fusible: it does not oxidize upon ignition in the air, and is insolu-
ble in hydrochloric, nitric, and sulphuric acids; but it dissolves in
fluids containing  or evolving chlorine, e. g. in nitro-hydrochloric
 acid.  The solution contains terchloride of gold. 
§ 129.]
TEROXIDE  OF GOLD.
153
   2.  Teroxide of gold is a blackish-brown, its hydrate a chesnut-
 brown  powder.  Both are reduced by light and heat, and dissolve
 readily in hydrochloric acid, but not in dilute oxygen acids.   Con-
 centrated nitric and sulphuric  acids dissolve  a little teroxide of
 gold ; water reprecipitates it from these solutions.   The protoxide
 of gold (Au O) in violet-black, on heating it is resolved into gold
 and oxygen.
   3.  Salts of Gold with oxygen acids are nearly unknown.  The
 haloid  salts of gold are yellow,  and their  solutions continue to
 exhibit this color up to a high degree of dilution.   The whole  of
 them are  readily decomposed upon ignition.  Neutral solution  of
 terchloride of gold reddens litmus-paper.
   4. Hydrosulphuric acid precipitates from neutral and acid solu-
 tions of gold the whole of the metal in the cold, as brown black ter-
 sulphide of gold (Au Sj),  when hot, as protosulphide of gold
 (Au S).   These precipitates are insoluble in nitric or hydrochloric
 acid ; but dissolve in aqua regia.  They are insoluble in colorless
 sulphide of ammonium, but dissolve in the yellow alkaline sulphides,
 especially in yellow sulphides of potassium and sodium.
   5. Sulphide of ammonium throws down  tersulphide  of  gold.
 This  redissolves in an excess of the precipitant only if the  latter
 contains an excess of sulphur.
   6. Ammonia produces, but only in tolerably concentrated solu-
 tions of gold, reddish-yellow precipitates of aurate of ammonia
 (fulminating gold).  The more acid the  solution and the greater
 the excess of ammonia added, the more gold remains in solution.
   7. Protochloride of tin  containing  an admixture of bichloride
 (procured by adding a little  chlorine water to protochloride), pro-
 duces  even in  extremely dilute solutions of  gold,  a purple-red
 precipitate (or coloration at least), which  sometimes  inclines rather
 to violet or to brownish-red.  This precipitate, which has received
 the name  of purple of cassius, is insoluble  in hydrochloric acid.
 It is assumed to be a hydrated compound of binoxide of tin and
 protoxide of gold with protoxide  and  binoxide of tin (Au O,
 Sn 0.2 + Sn O,  Sn 02 + 4 H O).
   8. Salts of protoxide of iron reduce the teroxide  of gold, when
 added to  its solutions, and precipitate metallic gold in form of a
 most minutely divided brown powder, which shows metallic lustre
 when pressed  with the  blade of a  knife, or when  rubbed.   The
 fluid in  which the precipitate is  suspended  appears of a blackish-
blue color by transmitted light.
   9. If  to a solution of gold, potassa or soda be added in excess,
it remains clear; on addition of tannic acid  to the alkaline liquid
a  deep black precipitate of protoxide of gold (Au O) is formed,
which separates perfectly after a little time. 
154               BINOXIDE OF  PLATINUM.             [§ 130

                             § 130.
               b. Binoxide of  Platinum (Pt 02).
  1. Metallic platinum has a light steel-gray color; it is very
lustrous, moderately hard, very malleable and ductile, difficultly
fusible ; it does not oxidize upon ignition in the air, and is insoluble
in hydrochloric, nitric, and sulphuric acids.   It dissolves in  nitro-
hydrochloric acid, especially upon  heating.  The solution contains
bichloride of platinum.
  2. Binoxide of  platinum  is a blackish-brown, its hydrate a
reddish-brown powder.   Both are reduced by heat; they are both
readily soluble in hydrochloric acid, and difficultly soluble in oxygen
acids.   Hydrated protoxide of platinum is black,  and  when
heated, yields metallic platinum.
  3. The  salts of binoxide  of  platinum are decomposed at a
red heat.   They  are  yellow; bichloride of platinum is reddish-
brown, its solution reddish-yellow, which tint it retains up to a
high degree of dilution.  The solution reddens litmus-paper. Ex-
posure to a very low red heat converts bichloride of platinum to
protochloride;  application of  a stronger red heat reduces it to the
metallic state.   Solution of bichloride of platinum, containing proto-
chloride, has a dark-brown color.
  4. Hydrosulphuric  acid throws down from acid  and  neutral
solutions—(but not from alkaline  solutions, or, at all events, not
completely)—after  the  lapse of some time  a blackish-brown pre-
cipitate of bisulphide  of platinum (Pt S2).   If the solution is
heated after the addition of the hydrosulphuric acid the precipitate
forms immediately.  It  dissolves in  a great excess of alkaline sul-
phides, more particularly of the higher degrees of  sulphuration.
Bisulphide of platinum is insoluble in  hydrochloric  acid and  in
nitric acid;  but it dissolves in nitrohydrochloric acid.
  5. Sulphide of ammonium produces  the  same precipitate; this
redissolves slowly and with difficulty, but at  last completely in a
large excess of the precipitant, if the latter contains  an excess of
sulphur.  Acids reprecipitate  the bisulphide of platinum unaltered
from the red-brown solution.
  6. Chloride of potassium and chloride of ammonium (and also
potassa and ammonia in presence  of hydrochloric acid),  produce in
not too highly dilute solutions of  salts of platinum, yellow crystal-
line precipitates of platinchlorides of potassium and ammonium.
From dilute solutions these precipitates  are obtained by evaporat-
ing with chloride  of potassium  or chloride of ammonium on the
water-bath  to  dryness, and treating the residue with dilute spirit
of wine until the  alkaline chlorides are dissolved.  The precipitates
are no more soluble in acids than  in water, they dissolve, however,
by  heating with soda or potassa-lye.  Upon ignition platinchloride 
 §§ 131*  132.]         PROTOXIDE OF TIN.                   153

 of ammonium  leaves spongy platinum behind.   Platinchloride of
 potassium leaves platinum  and  chloride of potassium, but  its
 decomposition  is only complete when it is gently heated in a
 stream of hydrogen gas, or ignited with oxalic acid.
   7. Protochloride of tin imparts to solutions of salts of binoxide
 of platinum which contain much free hydrochloric acid an intensely
 dark brownish-red  color,  owing to a reduction of the binoxide
 or bichloride of platinum to protoxide or simple chloride.  But the
 reagent produces no precipitate in such solutions.
   8. Sulphate  of protoxide  of  iron  does not precipitate  solution
 of bichloride of platinum, unless the two are boiled together for a
 long time, when metallic platinum separates.

                            § 131.
   Recapitulation and remarks.—The reactions  of  gold and pla-
 tinum  enable  us, at least partially, to detect these  two metals in
 the presence of many other oxides, and also when platinum and
 gold are present in the same solution.  In the latter case the solu-
 tion is evaporated to dryness with chloride of ammonium, and the
 residue treated with Spirit of wine, in order to obtain the gold in
 solution, and  the  platinum  in the  residue.   The  latter yields
 metallic  platinum on ignition, while gold may be  thrown  down
 from the solution after  evaporating  off the  alcohol, by means of
 protosulphate of iron.

            second  division  of the sixth group.
                      Special Reactions.
                            §  132.
                 a. Protoxide of  Tin (Sn O).
   1. Tin has a light gray-white color and a high metallic lustre ;
 it  is soft  and malleable ;  when bent, it produces  a crackling sound.
 When  heated in the air, it absorbs oxygen, and is converted into
 grayish-white binoxide ;  heated on  charcoal before the  blowpipe,
 it  forms  a white coating on the  support.   Concentrated hydro-
 chloric acid dissolves tin  to protochloride, with evolution of hydro-
 gen gas; nitrohydrochloric acid dissolves it,  according to circum-
 stances, to bichloride or to a mixture of proto- and bichloride.  Tin
 dissolves with  difficulty  in  dilute  sulphuric acid;  concentrated
 sulphuric acid  converts it, with the aid of heat, into sulphate of
 binoxide; moderately concentrated nitric  acid oxidizes it readily,
 particularly with  the aid of  heat;  the white binoxide (hydrated
metastannic acid Sn 02, 2 H O) formed, does  not redissolve  in an
excess  of the acid.
   2. Protoxide of tin  is a black or grayish-black powder;  its
hydrate is  white.   Protoxide  of tin is reduced by fusion  with 
156
PROTOXIDE OF  TIN.
[§132
 cyanide of potassium.  It is  readily soluble in hydrochloric  acid
 Nitric acid converts it into hydrated metastannic acid, which is
 insoluble in an excess of the acid.
   3. The salts of protoxide of tin are colorless, and are de-
 composed by heat.  The soluble  salts, in the neutral state, redden
 litmus-paper.   The salts of protoxide of tin rapidly absorb oxygen
 from the air, and are partially or entirely converted  into salts of
 binoxide; hence a solution of protochloride of tin becomes speedily
 turbid (from ensuing separation of oxychloride of tin), if the glass is
 often opened and there is  only little free  acid present; hence it is
 only quite recently prepared protochloride of tin which will com-
 pletely dissolve in water free from air, and the  crystallized proto-
 chloride of tin dissolves to  a  clear liquid only in water acidified
 with hydrochloric acid.
   4. Hydrosulphuric  acid throws  down from  neutral and  acid
 solutions of salts of  protoxide of tin a dark brown precipitate of
 hydrated protosulphide  of tin (Sn S), which is  insoluble, or
 nearly so, in protosulphide of ammonium, but dissolves readily in
 the higher yellow sulphide.  Acids precipitate from  this solution
 yellow bisulphide of tin, mixed with sulphur.   Protosulphide of
 tin dissolves also in solution of soda or potassa.  Acids precipitate
 from these  solutions brown protosulphide.  Boiling  hydrochloric
 acid dissolves it, with evolution of hydrosulphuric acid gas ; boil-
 ing  nitric  acid converts it into  insoluble hydrated metastannic
 acid.  Alkaline solutions of protosalts of tin are  not, or at least
 only imperfectly, precipitated by hydrosulphuric acid.
   5. Sulphide  of ammonium  produces  the  same precipitate of
 hydrated protosulphide of tin.
   6. Soda, potassa, ammonia, carbonate of potassa, and carbonate
 of ammonia produce in solutions of salts of protoxide  of tin a
 white,  bulky precipitate of hydrate of  protoxide of tin  (Sn O,
 H O), which redissolves readily in  an excess of soda or potassa,
 but is insoluble in an excess of the other precipitants.  If the solu-
tion of hydrate of protoxide of tin in potassa is briskly evaporated,
a  compound of  binoxide of  tin and potassa  is formed,  which
remains in solution, whilst metallic tin precipitates ; but upon eva-
porating slowly, crystalline anhydrous protoxide  of tin separates.
   7. Terchloride of gold produces in solutions of protochloride or
protoxide of tin, upon addition of some nitric acid (without appli-
cation  of heat), a precipitate or  coloration of purple of cassius.
 (Compare § 129. 7.)
   8. Solution of chloride of mercury, added in excess, produces in
 solutions of protochloride of tin or  of protoxide  of tin in  hydro-
 chloric  acid, a white precipitate of subchloride  of mercury.
 owing to the protosalt of tin  withdrawing from the chloride of
 mercury half of its chlorine. 
133.]
BINOXIDE  OF TIN.
157
  9. If a  fluid containing protoxide or protochloride of tin and
hydrochloric acid is added to a mixture  of ferricyanide of potas-
sium  and sesquichloride of iron,  a precipitate of Prussian blue
(ferrocyanide  of  iron, Fe4  Cfy3) separates immediately,  owing to
the reduction of the ferricyanide (Fe4 Cfy4*-f 2 H CI + 2 Sn  CI =
Fe^ Cfy3 + ll2 Cfy +  2  Sn Cl2).  This reaction is extremely  deli-
cate, but  it can  be held to be decisive only in  cases where no
other reducing agent  is  present.
  10. If compounds of protoxide of tin, mixed with carbonate of
soda  and some  borax,  or, better still, with a mixture of  equal
parts of carbonate of soda and cyanide of potassium, are exposed
on  a  charcoal  support  to  the  inner blowpipe flame, malleable
grains of metallic tin are obtained.   The best way of making
quite sure of the  real nature  of these grains, is to triturate  them
and the surrounding  parts of charcoal  with  water forcibly  in a
small mortar; then to wash the charcoal off from the metallic par-
ticles.   Upon  strongly heating the grains of metallic tin  on a
charcoal support, the latter becomes covered with a  coating of
white binoxide.
                            § 133.
                 b. Binoxide  of Tin  (Sn 02).
  1. Binoxide of tin is a powder varying in color from white to
straw-yellow, and which upon heating transiently assumes a brown
tint.  It forms two different series of compounds with acids, bases,
and water.   The hydrate precipitated by alkalies  from solution
of bichloride of tin dissolves readily in hydrochloric acid; whilst
that formed by the  action of nitric acid upon  tin—hydrate of
metastannic acid—remains undissolved.   If the hydrated metastan-
nic  acid be  boiled a  short time with hydrochloric  acid, it unites
with the latter; on pouring off the excess of hydrochloric acid and
adding water the compound  dissolves.   The aqueous solution of
the common bichloride  of tin is not altered by addition of strong
hydrochloric acid, while  this reagent  throws  down  from the
aqueous solutions of metabichloride of tin, the latter salt as a white
precipitate.   The color  of  solution  of common bichloride  of
tin is not altered by protochloride of tin; solution of metabichloride
of tin becomes yellow by addition of the latter.  From the dilute
solutions of both the bichlorides of tin, the corresponding hydrates
of the  binoxide are thrown down on boiling.
  2. The salts of binoxide of tin are colorless; they are decom-
posed at a red heat.   The soluble salts  of binoxide  of tin, in the
neutral state, redden litmus paper.   Anhydrous bichloride of tin is
a volatile liquid, strongly fuming in the air.
  3. Hydrosulphuric  acid throws down from all  acid and neutral
        * (2  Fe2 Cfdy) = Fe4 Cfy4, because Cfdy = CJ2 N„ Fe2 = 2 Cfy. 
158
BINOXIDE  OF TIN.
[§133
solutions  of salts  of binoxide of tin, particularly upon heating, a
white flocculent precipitate, if the solution  of the binoxide is in
excess; a dull-yellow precipitate, if the hydrosulphuric acid is in
excess.  The former (the  white precipitate) may be assumed, in
the case of a solution of bichloride of tin, to consist of chloro-bisul-
phide of tin (however, it has not as yet been analysed); the latter
(the yellow precipitate) consists of hydrated bisulphide of tin
(Sn S2).  Alkaline solutions are not precipitated by hydrosulphuric
acid.   The precipitation is prevented by a very large excess of hy-
drochloric acid. The bisulphide of tin dissolves readily in potas-
sa,  alkaline sulphides, concentrated boiling hydrochloric acid and
aqua regia.  It dissolves with some difficulty in pure ammonia, and
is nearly insoluble in carbonate of ammonia.   Nitric acid converts
it into insoluble binoxide of tin.  It is insoluble in solution  of acid
sulphite of  potassa.  Upon  deflagrating  bisulphide  of tin  with
nitrate and carbonate of soda, sulphate of soda and binoxide of tin
are obtained.   If a solution of bisulphide of tin in potassa is boiled
with teroxide  of bismuth,  tersulphide  of bismuth and binoxide of
tin  are formed, which  latter substance remains  dissolved in the
potassa solution.
  4. Sulphide   of ammonium  produces the  same precipitate of
hydrated bisulphide of tin ; the precipitate redissolves readily in
an excess of the precipitant.  From this solution acids reprecipitate
the bisulphide of tin unaltered.
  5. Soda, potassa and ammonia, carbonate of soda and carbonate
of ammonia, produce in solutions of salts of binoxide of tin white
precipitates which, according to the nature of the solutions, consist
of hydrate of binoxide  of tin, or of hydrate of metastannic acid.
Both  dissolve readily in an excess of potassa.
  6. Sulphate  of soda, nitrate of ammonia (in fact, most neutral
salts), when added in excess, throw down from solutions  of both
modifications of binoxide of tin, provided they  are not too  acid, the
whole of  the tin as hydrated binoxide or hydrated metastan-
nic acid.  Heating promotes the precipitation:  Sn Cl2 + 4 Na 0,
S 03 + 4 H O = Sn 02 2 H O  + Na CI + 2 (Na O, H O, 2 S O ).
  7. Metallic zinc precipitates from solutions of bichloride of tin, in
the absence of free acid, in the first place, some metallic tin, then
white oxychloride; but in presence of a sufficient quantity of free
hydrochloric acid,  metallic tin, in the shape of small gray scales,
or as  a spongy mass. If the operation  is conducted in a platinum
dish, no blackening  of  the latter is observed (difference between
tin and antimony).
  8. The  compounds  of the binoxide  of tin manifest the  same
deportment before the blowpipe as those of the protoxide.  Binox-
ide of tin is also readily reduced when fused with cyanide of potas-
sium  in a glass tube. 
§ 134.]            TEROXIDE OF ANTIMONY.               159

                             §  134.
               c. Teroxide of Antimony (Sb 03).
  1. Metallic antimony has a bluish tin-white color and is very
lustrous ; it is hard, brittle, readily fusible.  When heated on char-
coal before the blowpipe, it emits thick white fumes of teroxide  of
antimony, which form a coating on the coal; this  combustion con-
tinues for some time, even after the removal of the metal from the
flame ; it is the most distinctly visible  if a current of air is directed
with the blowpipe directly upon the sample on the charcoal.  But
if the sample on the support is  kept steady,  that the fumes may
ascend straight, the metallic grain becomes surrounded with  a net
of brilliant crystals of teroxide of antimony.   Nitric acid oxidizes
antimony readily ; the dilute acid converting it almost entirely into
teroxide, the more  concentrated acid into antimonic acid; both are
nearly insoluble in nitric  acid; still in the acid fluid filtered from the
precipitate there are always  found  traces of antimony.  Hydro-
chloric acid, even boiling, does not attack antimony.  In nitrohy-
drochloric acid the metal dissolves readily.  The solution contains
terchloride of antimony  (Sb  Cl3), or  pentachloride  of antimony
(Sb  CI ), according to the degree of concentration of the acid and
the duration of the action.
  2. According to the different modes  of its preparation, Teroxide
of Antimony occurs either in the form of white, brilliant crystal-
line  needles, or as a grayish-white powder.  It fuses at a moderate
red  heat; when exposed to  a  higher temperature,  it volatilizes
without decomposition.   It is almost  insoluble in nitric acid, but
dissolves  readily in hydrochloric and  tartaric acids.  Boiled with
hydrochloric acid (free from chlorine) and with iodide of potassium
(free from iodic acid) iodine  is not liberated (Bunsen).  Teroxide
of antimony is easily reduced to the metallic state by fusion with
cyanide of potassium.
  3.  Antimonic acid (Sb 03)  is pale  yellow; its hydrates are
white.  Both the acid and its hydrates redden litmus-paper; they
are slightly soluble in water, and almost insoluble in nitric acid, but
dissolve pretty readily in hot concentrated hydrochloric acid: the
solution contains pentachloride of antimony (Sb Cl5), and  turns
turbid upon addition of water.   Antimonic acid when boiled with
hydrochloric acid and iodide of potassium liberates iodine which
dissolves in the hydriodic acid present, giving  a brown  color  to
the  liquid.  Upon ignition, antimonic acid loses oxygen, and  is
converted into antimonate of teroxide  of antimony (Sb  03, Sb 0.5).
Of the antimonates the potassa  and ammonia salts alone are solu-
ble in water: acids precipitate hydrate of antimonic acid from the
solutions, chloride  of sodium throws  down from them antimonate
of soda (§ 93.2.) 
 160                TEROXIDE  OF ANTIMONY.            [§ 134.

   4. Most of the salts of teroxide of antimony are decomposed
 upon ignition; the  haloid  salts volatilize readily and unaltered,
 The soluble neutral salts  of antimony redden litmus-paper.   When
 treated with a large amount  of  water, they are decomposed  into
 insoluble basic salts and acid solutions containing teroxide of anti
 mony.  Thus, for instance, water throws down from solutions of
 terchloride of antimony  in hydrochloric acid, a white bulky  pre-
 cipitate of oxyterchloride of antimony  (powder  of Algaroth)
 Sb Cl3 5 Sb Oj,  which after some time becomes heavy and crystal-
line.  Tartaric acid dissolves this precipitate readily, and therefore
prevents its formation if  mixed with the solution previously to the
addition of the water.  It is by this property that the oxyterchloride
of antimony is distinguished from the basic salts of bismuth formed
under similar circumstances.
  5. Hydrosulphuric acid precipitates  from  acid   solutions  of
teroxide of antimony the whole of the metal unless  a very large
excess of free (mineral) acid be present as orange-red tersulphide
of antimony (Sb S3).  In alkaline  solutions this  reagent fails to
produce a precipitate or,  at  least, it precipitates them only imper-
fectly ;  neutral  solutions also are only imperfectly thrown  down
by it.  The tersulphide of antimony produced is readily  dissolved
by potassa and by alkaline  sulphides, especially if the latter con-
tain  an excess  of sulphur; it is but sparingly soluble in ammonia,
and—if it  contains no free sulphur nor pentasulphide of antimony—
almost insoluble  in bicarbonate of  ammonia.  It is insoluble in
dilute acids.  Concentrated  boiling hydrochloric acid dissolves it,
with evolution of hydrosulphuric acid gas.   It is not dissolved by
an aqueous solution of acid sulphite of potassa.
  When heated in the air, the precipitate is converted into a mix-
ture of antimonate  of teroxide of  antimony with tersulphide of
antimony.  When deflagrated with nitrate of soda, it gives sulphate
and antimonate  of soda.  If a  potassa solution of tersulphide of
antimony is boiled with teroxide of bismuth, tersulphide of bismuth
precipitates, and teroxide of antimony dissolved in potassa remains
in the solution.    On fusing tersulphide of antimony with cyanide
 of potassium, metallic antimony and sulphocyanide  of potassium
 are produced.  If the operation is conducted  in a small tube  ex-
 panded into a bulb at the lower end, or in a  stream of carbonic
 acid gas (see §  135, 12), no  sublimate  of antimony is pi'oduced.
 But if a mixture of tersulphide of antimony with carbonate of soda
 or with cyanide  of potassium and carbonate of soda, is heated in
 a glass^tube  in  a stream of hydrogen gas  (compare §  135, 4), a
 mirror  of antimony is deposited on the inner surface of the tube,
 immediately behind the spot occupied by the mixture.
   From a solution  of antimonic acid  in hydrochloric acid,  sul-
 phuretted hydrogen throws  down pentasulphide of antimony (Sb 
 § 134.]             TEROXIDE OF ANTIMONY.               161

 S,), which dissolves readily when  heated with solution of soda  or
 ammonia, and equally so in concentrated boiling hydrochloric acid
 with evolution of hydrosulphuric acid gas and  separation of sul-
 phur.  It is very slightly soluble in cold solution of bicarbonate  of
 ammonia.
   6.  Sulphide of ammonium produces in  solutions of teroxide  of
 antimony an orange-red precipitate of tersulphide  of antimony,
 which readily dissolves in an excess of the precipitant if the latter
 contains an excess  of sulphur.   Acids throw down from this solu-
 tion  pentasulphide of  antimony (Sb S5).   However, the orange
 color appears in that case usually of a lighter tint, owing to  an
 admixture of free sulphur.
   7.  Soda, potassa, ammonia, carbonate of soda, and carbonate of
 ammonia throw down from solutions of terchloride  of antimony,
 and  also of  simple  salts  of  teroxide  of  antimony—but  far less
 completely and usually after the lapse of some time, from solutions
 of tartar emetic or analogous compounds—a white, bulky  precipi-
 tate of teroxide of antimony, which redissolves pretty readily in
 an excess of soda or  potassa, but requires  the application of heat
 for its re-solution in carbonate of soda, and is altogether insoluble
 in ammonia.
   8.  Metallic Zinc precipitates  from all solutions  of teroxide of
 antimony, if they contain no free  nitric  acid, metallic antimony
 as a black powder.  If a few drops of a  solution  of antimony, con-
 taining some  free hydrochloric acid, are poured into a platinum
 dish  (the inside of a platinum crucible cover), and a small piece of
 zinc  introduced, hydrogen  is  evolved  and antimony  separates,
 staining the part of the platinum covered  by the liquid brown  or
 black, even in the case of very dilute solutions; these new reactions
 I can therefore  recommend as being delicate  and characteristic.
 Cold hv drochloric acid fails to remove the stain, which, however,
 may be immediately removed by warm nitric acid.
   9.  If a solution  of  teroxide  of antimony in solution of potassa
 or soda is mixed with  solution  of nitrate  of silver, a deep black
 precipitate of suboxide of silver forms with the grayish-brown
 precipitate  of oxide  of  silver.   Upon  now adding ammonia  in
 excess, the oxide is redissolved, whilst the  suboxide is left undis-
 solved (H. Rose).   The following equation will explain the forma-
 tion of the suboxide of silver in this process:  K  O, Sb 03 + 4
 Ag O = K O, Sb O5  -f- 2 Ag2 O.   This exceedingly delicate reac-
 tion affords us an excellent means of detecting teroxide of antimony
 in presence of antimonic acid.
   10. If a solution of teroxide of antimony  is introduced into a
 flask in which hydrogen gas is being evolved from  pure zinc and
 dilute sulphuric  acid, the zinc oxidizes not  only at the expense of
the oxygen of the water, but also at the expense  of that of the ter-
                              11 
102                TEROXIDE  OF ANTIMONY.            [§ 134.

oxide of antimony, and the antimony separates accordingly in the
metallic state; but a portion of the metal combines in the moment
of its separation with the liberated hydrogen of the water, form-
ing antimonetted hydrogen  gas (Sb H3).  If this operation  is
conducted in a gas-evolution flask, connected by means of a perfo-
rated cork with the limb of a bent tube of  which the other limb
ends in a fine orifice,* and the hydrogen passing through the  fine
aperture of the tube  is ignited after the atmospheric air is com-
pletely expelled, the flame appears of a bluish-green  tint, which  is
imparted to it by the antimony separating in  a state of intense
ignition upon the combustion of the antimonetted hydrogen; white
fumes of teroxide of antimony rise from the flame, which condense
readily upon cold substances, forming spots on them which are not
dissolved by water.   But  if a cold body, a porcelain  dish, for
instance, is now  depressed  into the flame, metallic antimony  is
deposited upon  the  surface of the plate, in a state of the most
minute division,  forming a deep  black and almost lustreless spot.
If the middle part of the tube  through which the gas is passing is
heated to redness, the bluish-green tint of the flame decreases  in
intensity, and  a  metallic mirror  of antimony of silvery lustre  is
formed within the tube on both sides of the heated part.
  As the acids of arsenic give  under the same circumstances simi-
lar spots of metallic arsenic, it is always necessary to examine the
spots produced, in order to ascertain whether they really consist of
antimony or contain  any of that metal.  With spots deposited in a
porcelain dish the object in view is most readily attained by treat-
ing them with  a solution  of  chloride of  soda (a  compound of
hypochlorite of soda with chloride of  sodium, prepared by mixing
a solution of chloride of lime  with carbonate  of soda in excess,
and  filtering);   which will immediately dissolve arsenical spots,
leaving the spots proceeding from antimony untouched, or, at least,
removing them  only after  a  very protracted  action.  A  mirror
within the glass  tube, on the other hand, may be tested by heating
it whilst the current of hydrogen gas still continues to pass through
the tube: if the mirror volatilizes only at  a higher temperature,
and  the hydrogen gas then issuing from the tube does not smell
of garlic ; if it is only with a  strong  current that the ignited gas
deposits spots on porcelain,  and the mirror before volatilizing fuses
to small lustrous globules distinctly discernible through a magnify-
ing glass,—the presence  of antimony  may  be considered certain.
Or, better still, the metals may be identified by conducting through
the tube a very slow stream of dry hydrosulphuric acid gas, and
heating the mirror, by means of a spirit-lamp, proceeding from the
outer to the inner border, and accordingly in an opposite direction

  • la accurate experiments it is advisable to use Marsh's apparatus.  (§ 135, 10) 
 § 135.]  §             ARSENIOUS ACID.                    163

 to that of the gaseous current.  The antimonial  mirror is by  this
 means converted into tersulphide of antimony, which appears of a
 more or less reddish-yellow color, and almost black when in thick
 layers.   If a feeble  stream of dry hydrochloric acid  gas is now
 transmitted through the  glass tube, the tersulphide of antimony,
 if present in thin  layers  only,  disappears  immediately;  if  the
 incrustation is somewhat  thicker, it takes a short time  to dissipate
 it.  The reason for this is, that the tersulphide of antimony decom-
 poses readily with hydrochloric acid, and the terchloride  of anti-
 mony formed is exceedingly volatile in  a stream of hydrochloric
 acid  gas.  If the gaseous current is now  conducted into some
 water, the presence  of antimony in the latter fluid  may readily be
 proved by means of hydrosulphuric acid.  By this  combination of
 reactions, antimony may  be distinguished with  positive certainty
 from all other metals.
   The deportment of antimonetted hydrogen towards a solution
 of nitrate of silver is noticed in § 137, 6.
   11. If a mixture of a compound of antimony with carbonate of
 soda and cyanide of potassium  is exposed  on a charcoal support
 to the reducing flame of the blowpipe, brittle globules of metallic
 antimony are produced, which may be readily  recognised by the
 peculiar appearances  attendant  upon  their oxidation (compare
 § 134, 1).

                             §135.
                  d. Arsenious Acid (As 03).
   1. Metallic arsenic has a blackish-gray color  and high metallic
 lustre, which it retains in  dry air, but loses in moist air, becoming
 covered  with suboxide ; the metallic arsenic of commerce looks
 therefore rather dull, the planes of crystallization  appearing bronze-
 colored and feebly shining.  Arsenic is not very  hard, but brittle :
 at a dull red heat it volatilizes without fusion.   The fumes have a
 most characteristic  odor of garlic, which proceeds from the sub-
 oxide of arsenic  formed.   Heated with free  access of air, arsenic
 burns—at  an intense heat with a bluish flame—emitting white
 fumes of arsenious acid, which condense on cold bodies. If arsenic
 is heated in a glass  tube sealed at  the lower end, the greater part
 of it volatilizes unoxidized, and recondenses above the heated spot
 as a lustrous black sublimate (arsenical mirror);  a very thin coat-
ing of the sublimate  appears of a  brownish-black color.  In  con-
tact with air  and water arsenic oxidizes slowly to  arsenious acid.
Weak nitric acid converts it, with  the  aid of heat, into arsenious
acid, which dissolves only  sparingly in an excess of the acid; strong
nitric acid converts it partially into arsenic acid.  It is insoluble in
hydrochloric acid and dilute sulphuric acid;  concentrated boiling 
164
ARSENIOUS ACID.
[§ 135.
sulphuric acid oxidizes it to arsenious acid, with evolution of sul-
phurous acid.
  2. Arsenious acid generally presents the appearance either of a
transparent vitreous or of a white porcelain-like mass.  Triturated,
it gives a heavy, white, gritty powder.  When heated, it volatilizes
in white inodorous fumes.  If the operation is  conducted in a glass
tube, a sublimate is obtained  consisting of small brilliant octahe-
drons and tetrahedrons.  Arsenious acid is only difficultly moistened
by water;  it comports itself in this respect like a fatty substance.
It is difficultly soluble in cold, but more readily in hot water.  It is
copiously dissolved by hydrochloric acid, as well  as by solution of
soda and potassa.  Upon boiling with nitrohydrochloric acid it
dissolves to arsenic acid.   It is highly poisonous.
  3. The arsenites are  mostly decomposed  upon ignition either
into arsenates and metallic arsenic, which volatilizes, or into arse-
nious  acid  and the base with which  it was combined.   Of  the
arsenites those only  with  alkaline bases are soluble in water.  The
insoluble arsenites are dissolved, or at least decomposed, by hydro-
chloric acid.  Terchloride of arsenic is a  colorless, volatile liquid,
fuming in the air, which allows the addition of a little water,  but
is  decomposed by a  larger amount  into arsenious acid, which
partly  separates,  and hydrochloric acid, which retains the rest  of
the arsenious acid in  solution.  On  heating  and concentrating a
solution of arsenious acid in hydrochloric acid,  pentachloride  of
arsenic esapes with the vapors.
  4. Hydrosulphuric acid colors yellow the aqueous solutions of
arsenious acid without causing a precipitate.  It also does  not
precipitate the neutral arsenites,  but on adding one of the stronger
acids,  there separates at once  bright  yellow  tersulphide   of
arsenic (sulpharsenious acid).   It is  also produced in the hydro-
chloric solution of arsenites  that are insoluble in water.  The  for-
mation of this precipitate is  not prevented, even by a great excess
of hydrochloric acid.   Alkaline solutions are not precipitated.  The
tersulphide  of arsenic is easily and completely soluble in hydrates,
carbonates,  bicarbonates,  and sulphides of the alkalies.   Hydro-
chloric acid, even when concentrated and hot, scarcely attacks it.
It is easily  decomposed and dissolved by boiling nitric acid.
  If recently precipitated tersulphide of arsenic is  digested with
sulphurous acid and acid sulphite of potassa, the  precipitate is  dis-
solved ; upon heating the solution to boiling, the fluid turns turbid,
owing to the separation of sulphur, which upon continued boiling
is for the greater part redissolred.  The fluid contains, after expul-
sion of the  sulphurous acid, arsenite and hyposulphite of potassa:
2 As S3 + 8 (KO, 2 S02) = 2 (KO, As O ) + 6 (KO, S 02) + 3 S +
7 SO,.   Tersulphide of antimony and bisulphide of tin do not show
this reaction, as already stated (§ 133, 3 and 134, 5).—Bunsen. 
§ 135.]
ARSENIOUS ACID.
165
  The deflagration of tersulphide of arsenic with carbonate of soda
and nitrate of soda gives rise to the formation of arsenate and sul-
phate of soda.  If a solution of tersulphide of arsenic in potassa is
boiled with hydrated carbonate or basic nitrate of teroxide of bis-
muth, tersulphide of bismuth and arsenite of potassa are produced.
  If a mixture of tersulphide of arsenic with from 3 to 4 parts of
carbonate of soda is made  into a  paste with some  water, and this
spread over small glass splinters, and after being well dried, rapidly
heated to redness in a glass tube through which dry hydrogen gas
is transmitted, a large portion of the arsenic  present is  reduced to
the metallic state and expelled, if the  temperature applied is suffi-
ciently high.   Part of the reduced arsenic forms a  metallic mirror
on the  inner surface of the tube, the remainder is carried  away
suspended in the  hydrogen gas; the  minute particles of arsenic
impart a bluish tint to the flame when  the gas is kindled, and form
stains of arsenic upon  the surface of a  porcelain  dish depressed
upon the flame.  The fusion of the mixture of tersulphide of arsenic
with carbonate of soda first gives rise to the formation of a double
tersulphide of arsenic  and sulphide  of  sodium (sulpharsenite  of
sulphide of sodium), and of arsenite of soda: 2 As S3 + 4 (Na O,
CO,)  = 3 (Na S, As S3) + Na O, As 03  + 4 C 02.   Upon heating
these products the arsenite of soda is resolved into arsenic and
arsenate of soda (5 As 03 = 2 As + 3 As 03), and the  tersulphide
of arsenic and sulphide of sodium  into arsenic and pentasulphide
of arsenic and sulphide of sodium (5 As S3 = 2 As -f 3 As S5);
and by  the action of the hydrogen the  arsenate of soda  is also con-
verted into hydrate of soda, arsenic, and  water.  With the excep-
tion, therefore, of that portion of the  arsenic which constitutes a
component part of the  double  pentasulphide  of arsenic and sul-
phide of sodium formed in the process, a  sulphur salt which is not
decomposed by hydrogen, all the arsenic is expelled.—(H Rose.)
  This method of reduction gives indeed very accurate  results, but
it does not enable us to distinguish arsenic from antimony with a
sufficient degree of certainty, nor to detect the one in presence  of
the other.  (Compare § 134, 5.)
  The operation is conducted in the apparatus illustrated by Fig. 26.
a is the evolution flask, b a tube containing chloride of calcium, 0
the tube in which, at the point d, the glass splinter with the mix-
ture of  tersulphide  of arsenic and carbonate of soda is placed; this
tube is made of difficultly fusible glass free from lead.  When the
apparatus is completely filled with pure hydrogen gas, d is exposed
to a gentle heat at first, in order to expel all the moisture  which
may still be present, and then suddenly to a very intense heat,* to

 * The flame of the blowpipe or of  the Bunsen lamp with chimney, answers the
purpose best. 
ARSENIOUS ACID.                [§ 135.

                            Fig. 26.

prevent the sublimation of undecomposed tersulphide  of  arsenic.
The metallic mirror is deposited near the point e.  Another method
of effecting the reduction of tersulphide of arsenic to the metallic
state, and which combines with the very highest degree of delicacy
the advantage of precluding the possibility of confounding arsenic
with antimony, will be found described in number 12.
  5. Sulphide of ammonium also causes the formation  of ter-
sulphide of arsenic.   In neutral and alkaline solutions, however,
the tersulphide formed does not precipitate, but remains dissolved
as a double sulphide of arsenic and ammonium  (sulpharsenite of
sulphide of ammonium).  From this solution it precipitates imme-
diately upon the addition of a free acid.
  6. Nitrate of silver leaves aqueous solutions  of arsenious  acid
clear, or at most produces only a trifling yellowish-white turbidity
in them; but if a little ammonia is added, a yellow precipitate of
arsenite of silver (3 Ag O, As 03) separates. The same pre-
cipitate forms, of course, immediately  upon the addition of nitrate
of silver to the solution of a  neutral arsenite.   The  precipitate
dissolves readily in nitric acid as well as in ammonia, and is  not
insoluble in nitrate of ammonia;  if therefore  a  small  quantity of
the precipitate is dissolved in a large amount of nitric acid, and the
latter is afterwards neutralized with ammonia, the precipitate does
not make its appearance again, as it remains dissolved in the nitrate
of ammonia formed.
  7. Sulphate of copper produces under the same  circumstances
as the nitrate of silver a yellowish-green precipitate of arsenite
of COPPER.
  8. If to a solution of arsenious acid in an excess of concentrated
solution of soda or potassa, or to the solution of an alkaline arsenite
mixed with caustic potassa or soda a few drops of a dilute solution
of sulphate of copper are added,  a clear, blue  fluid is obtained,
which upon boiling deposits a red precipitate  of  suboxide of cop-
per, leavmg arsenate of  potassa  in  solution.   This  reaction is
166
 
§ 135.]
ARSENIOUS  ACID.
167
 exceedingly delicate,  provided not too much  of the solution of
 sulphate of copper be used.  Even should the  red precipitate of
 suboxide of copper be so exceedingly minute as  to escape detection
 by transmitted light, yet it will always be  discernible with great
 distinctness upon looking in at the top of the test tube.  Of course
 this  reaction,  although  really  of great importance  in  certain
 instances, as a confirmatory proof of the presence of arsenious acid,
 and more particularly also as a means of distinguishing that acid
 from  arsenic acid, is yet entirely inapplicable for the direct detection
 of arsenic, since grape sugar and other organic substances also pro-
 duce  suboxide of copper from salts of oxide  of copper in the same
 manner.
  9. If a solution of arsenious acid mixed with hydrochloric acid is
 heated  with a clean slip of copper, an iron-gray film  is deposited
 on  the  copper,  even  in highly  dilute solutions;  when  this film
 increases in thickness, it peels  off in black scales.   If the  coated
 copper  slip  is heated with solution of ammonia, the film peels off
 from the copper, and separates in form of minute spangles (Reinsch).
 It is  to be  observed that  this coating is not pure arsenic, but an
 arsenide of copper (Cu3 As).  On heating the dried compound, a
 relatively small part of the arsenic volatilizes  (in the open tube
 arsenious acid  is  formed), and  an alloy rich in copper remains
 behind.  (Fresenius, Lippert.)  Reinsch's test is only conclusive
 when the coating of the copper slip  is demonstrated to contain
 arsenic,  since  antimony and  other  metals are  precipitated on
 copper  under similar circumstances, with much  the same  appear-
 ance.
  10.  If an acid or neutral  solution of arsenious acid or any of its
 compounds  is mixed with  zinc, water, and diluted sulphuric acid,
 arse netted hydrogen (As H3) is formed, in  the same  manner
 as compounds  of antimony  give under analogous  circumstances
 antimonetted  hydrogen.   (Compare  § 134, 10.)  This reaction
 affords us a  means for the detection of even the most minute quan-
 tities  of arsenic.
  The operation is conducted in the apparatus  illustrated by Fig.
 27, or in one of similar construction.*   a is the evolution flask; b sl
bulb intended to receive the water mechanically  carried along with
the  gaseous  current; c a tube filled with cotton and small lumps of
chloride of calcium to remove the last traces  of water.   This tube
is connected w^th b and d by vulcanized india-rubber which must
be freed from adhering sulphur by warming for some time  in solu-
tion of soda  ; d should have an inner diameter of about one-fourth
of an  inch  (see Fig.  28),  and must be made of difficultly fusible

  *  I willingly adopt the very convenient form of Marsh's apparatus recommended
by Otto in his excellent Manual of Chemistry. 
168
ARSENIOUS  ACID.
[§ 135.
Fig. 27
Fig. 28.
glass free from lead.   In experiments requiring great accuracy the
tube should be drawn out as shown in Fig. 27.  The operation  is
           now commenced by evolving in a a somewhat rapid cur-
           rent  of hydrogen gas, from pure  granulated zinc and
           a previously cooled mixture of 1 part of concentrated
           sulphuric acid with  3 parts of water, to which a few
           drops of bichloride  of platinum  are advantageously
added.  When the evolution of  hydrogen has proceeded for some
time, so that it may safely be concluded the air has been completely
expelled  from the apparatus, the gas is kindled at the open end  of
the tube d.  It  is advisable to  wrap a piece of cloth round the
flask before kindling the gas, to  guard against accidents in case  of
an  explosion.   It is  now absolutely necessary first to  ascertain
whether  the zinc  and the sulphuric  acid are quite free from any
admixture  of arsenic.  This is  done by depressing  a porcelain
dish horizontally into the flame  to half the depth of the latter: if
the hydrogen  contains arsenetted hydrogen, brownish or brownish-
black stains of  arsenic  will appear on the porcelain; the non-ap-
pearance of such stains maybe considered as a proof of the freedom
of the zinc and sulphuric acid from arsenic.  In very  accurate
experiments,  however,  additional evidence is required to ensure
the positive certainty of the purity of the reagents employed;  for
this purpose the part of the tube d, shown in Fig. 27, is heated to
redness  with a Berzelius or gas-lamp, and kept some time in a
 state of ignition: if no arsenical coating makes its appearance in
 the narrowed part of the tube, the reagents employed may be pro- 
§ 135.]
ARSENIOUS ACID.
169
 nounced free from arsenic,* and the operation proceeded with, by
 pouring the fluid to be tested for arsenic through the funnel tube
 into the flask, and afterwards some  water to rinse the tube.   Only
 a very little of the fluid ought to be poured in at first, as in cases
 where the quantity of arsenic present is considerable, and a some-
 what large  supply of the fluid  is poured into the flask, the evolu-
 tion of gas often proceeds with such violence as to stop the further
 progress of the experiment.
   Now if the fluid contains arsenic, there is immediately evolved,
 with the hydrogen, arsenetted hydrogen, which at once imparts a
 bluish tint to the flame of the kindled gas, owing to the combustion
 of the particles of arsenic separating from the arsenetted hydro-
 gen in passing through the flame.  At  the  same time white fumes
 of arsenious acid arise, which condense  upon cold  objects.  If a
 porcelain capsule is now depressed into the flame, the separated
 and not yet reoxidized  arsenic condenses upon the plate in black
 stains, the same way as antimony.  (See §  134,  10.)  The stains
 formed  by arsenic incline, however, more to a blackish-brown tint,
 and show a  bright metallic lustre ; whilst the antimonial stains are
 of a deep black color and but feebly lustrous.  The arsenical stains
 may be distinguished moreover from the antimonial stains by solu-
 tion of  chloride of soda (compare §  134, 10), which will at  once
 dissolve arsenical spots, leaving  antimonial spots unaffected,  or
 removing them only after a considerable time.
  If the heat  of a  Berzelius, or gas-lamp,  is now applied to the
 part of the  tube d, shown in Fig. 27, a brilliant  arsenical  mirror
 makes its appearance in the narrowed portion  of  the tube  behind
 the heated part; this mirror is of a  darker  and less silvery white
 hue than that produced by antimony under  similar circumstances ;
 from which  it is, moreover, distinguished by the facility with which
 it may be dissipated in  a current of hydrogen gas without previous
 fusion, and  by the  characteristic odor of  garlic emitted by the
 escaping (unkindled)  gas.  If the gas is kindled whilst the  mirror
 in the tube is being heated, the flame will, even with a very weak
 current  of gas, deposit  arsenical stains on a porcelain plate.
  The reactions and properties just described are amply sufficient
 to enable us to distinguish between arsenical and antimonial stains
 and mirrors; but they will often  fail to detect arsenic with  posi-
 tive certainty in presence of antimony.  Now, in cases of this kind,
 the following process will serve to set at rest all possible doubt  as
to the presence or absence of arsenic:—
  Heat  the long tube through which the arsenetted hydrogen

  *  [If no mirror is obtained in 10 to 15 minutes the materials are pure enough foi
toxical examinations.  It  is  scarcely possible, however, to obtain reagents so fret
from arsenic as  not to give a faint arsenical mirror  in an hour or two.] 
170
ARSENIOUS  ACID.
[§ 135,
passes to redness in several parts, to produce distinct metallic mir-
rors ;  then transmit through the tube a very weak stream of dry
hydrosulphuric acid gas, and heat the metallic mirrors with a com-
mon spirit-lamp, proceeding from the outer towards the inner  bor-
der.  If arsenic alone is present, yellow tersulphide  of arsenic is
formed inside the tube;  if antimony alone is present, an orange-
red or black tersulphide of antimony is produced; and if the mir-
ror consisted of both metals, the two sulphides appear side by side,
the sulphide of arsenic as the more volatile lying invariably beyond
the sulphide of antimony.  If you now transmit through the tube
containing the  sulphide of arsenic, sulphide of antimony, or both
sulphides  together, dry  hydrochloric  acid gas, without applying
heat, no alteration will take  place if sulphide  of arsenic  alone is
present, even though the gas be transmitted through  the tube for
a considerable time.   If  sulphide of antimony alone is present, this
will entirely disappear, as already stated, and if both sulphides are
present, the  sulphide of antimony will  immediately volatilize,
whilst the yellow sulphide of arsenic will remain.  If a small quan-
tity of ammonia is now drawn into the tube, the sulphide of arsenic
is dissolved, and may thus be readily distinguished from sulphur
which perhaps may have separated.  My personal experience has
convinced me of the infallibility of these combined tests for  the
detection of arsenic.
  The deportment of arsenetted hydrogen  towards solution of
nitrate of silver is described § 137, 6.
   Marsh  was  the first who suggested the  method  of detecting
arsenic by the production of arsenetted hydrogen.
  11.  Ka small lump of arsenious acid (a) be introduced into the
pointed end of a drawn-out glass tube (Fig. 29) and a fragment of
very recently burnt charcoal  (b)  pushed down the tube to within a
short  distance of the arsenious acid, and the flame of a spirit-lamp
applied, first to the piece of charcoal, then to the arsenious acid, a
mirror of metallic arsenic will form at c, owing to the reduction
of the arsenious acid vapor by the red-hot charcoal.  If the tube
be now cut between b and c, and then heated in  an  inclined posi-
tion, with the cut end c turned  upwards, the metallic mirror will
volatilize, emitting the characteristic odor of garlic.  This is both
the simplest and safest way of recognizing pure arsenious acid.
  12.  If arsenites, or  arsenious acid, or tersulphide of arsenic  are
fused  together with a mixture of equal parts of dry carbonate of
soda and cyanide of potassium, the whole of the arsenic is reduced
to the metallic state, and so is the  base also, if easily reducible;
the eliminated oxygen converts part of the cyanide  of potassium
into cyanate of potassa.  In the reduction of tersulphide of arsenic,
sulphocyanide of potassium is formed.  The operation is conducted
as follows:—introduce the perfectly dry arsenical compound into 
§ 135.]                 ARSENIOUS  ACID
                            Fig. 29.

the bulb of a small bulb-tube (Fig. 30), and cover it with six times
the quantity of a perfectly dry mixture of equal parts of carbonate
of soda and cyanide of potassium.  The whole quantity must not
much more than half fill the bulb, otherwise the fusing cyanide of
potassium is likely to ascend into the tube.  Heat the  bulb now
gently with a gas or spirit-lamp;  should some water  still  escape
upon gently heating the mixture, wipe the inside of the  tube per-
fectly  dry with  a twisted slip of paper.  It is of the highest
importance for the success of the experiment to bestow great care
upon  the  expulsion  of the water, drying the mixture, and wiping
the tube clean and dry.  Apply now a strong  heat to the bulb, to
effect the reduction of  the arsenical compound, and continue  this
for awhile, as the arsenic often requires some time for its complete
                             Fig. 30.

sublimation.  The mirror, which is deposited at b, is  of exceeding
uurity.  It is obtained from all arsenites whose bases remain either
altogether untouched, or are reduced to such metallic arsenides as
lose their arsenic partly or totally upon the simple application  of
heat.  This method deserves to be particularly recommended  on
account of  its simplicity and neatness, as well as for  the accuracy
of the results attainable by it, even in cases where only very minute
quantities of arsenic are present.   It is more especially adapted
for the direct production of arsenic  from tersulphide  of arsenic,
and is in this respect superior in  simplicity and accuracy to all
other methods hitherto suggested.  The delicacy of the  reaction 
172
ARSENIOUS  ACID.
[§ 135.
may be very much heightened by heating the mixture in a stream
of dry carbonic acid gas.  A series of experiments  made by Dr.
 V. Babo and myself has shown that the most accurate and  satis-
factory results are obtained in the following manner:—
  Figs. 31 and 32 show the apparatus in which the process is con-
ducted.
  A is a capacious flask intended  for the  evolution  of  carbonic
acid; it  is half-filled with water  and lumps  of solid limestone or
marble (not chalk, as this would not give a constant stream of gas\.
B is a smaller flask containing  concentrated  sulphuric acid.   The
flask A is closed with a doubly-perforated cork, into the one aper-
ture of which is inserted a funnel-tube (a), which reaches nearly to
the bottom of the flask; into the other perforation is fitted a tube
(b), which serves to conduct the evolved gas into the sulphuric
acid in B, where it is thoroughly freed from moisture.  The tube
c conducts the dried gas into the reduction-tube C, of which Fig.
32 give a representation  on the  scale of one-third of the actual
length.   The tube may  have  an inner  diameter of about three-
eicrhths of an inch.
                             Fig. 32.

  When the apparatus is fully prepared for use, triturate the per-
fectly dry  sulphide  of arsenic, or arsenite, in a slightly heated
morta* with about twelve parts of a well-dried mixture consisting
of three parts  of carbonate of soda and one part of  cyanide of
potassium.   Put the powder upon a narrow slip of paper bent into
the shape of a gutter, and push this into the reduction-tube  down 
§ 136.]
ARSENIC ACID.
173
to e /  turn the tube now half-way round its axis, which will cause
the mixture to drop into the tube between e and d, every other part
remaining  perfectly clean.  Connect  the tube now with  the gas-
evolution apparatus, and  evolve a moderate stream  of  carbonic
acid, by pouring  some  hydrochloric acid into the flask A.   Heat
the tube C in its  whole length very gently with a spirit-lamp, until
t he mixture in it is quite dry; when every trace of water is expelled,
and the gas-stream has become so slow that the  single bubbles
pass through the  sulphuric acid  in B at intervals of one second,
heat the reduction-tube to redness at c, by  means of a  spirit or
gas-lamp ; when  c is red-hot, apply the flame of a second  gas or
larger  spirit-lamp to the mixture, proceeding  from d to e,  until the
whole  of the arsenic is expelled.  The  far greater portion  of the
volatilized  arsenic recondenses  at h, whilst  a small portion only
escapes through i, imparting to  the surrounding air the  peculiar
odor of garlic.  Advance the flame of the second lamp slowly and
gradually up to c, by which means the whole of the arsenic  which
may have condensed in  the wide  part of the tube is driven to h.
When  you have effected this, close the tube at the point i by fusion,
and apply heat, proceeding from i towards h, by which means the
extent of the mirror is narrowed, whilst its beauty and lustre are
correspondingly  increased.   In this manner perfectly  distinct
mirrors of arsenic are produced  from as little as the 3^otn Par* of
a grain of tersulphide of arsenic.  No mirrors are obtained by this
process from tersulphide  of  antimony,  nor from any other com-
pound  of antimony.
  13. If arsenious acid or one of its compounds is exposed on  a
charcoal support  to the reducing flame of the blowpipe, a highly
characteristic garlic odor  is emitted, more especially if some car-
bonate of soda is added to the examined sample.  This odor has
its origin in the reduction and re-oxidation of the arsenic, and ena-
bles us to detect very minute quantities.  This test, however, like
all others that are based upon the mere indications of the sense of
smell, cannot be implicitly relied on.

                            §136.
                   e. Arsenic Acid (As O.,)
  1. Arsenic acid is a transparent or white mass, which gradually
deliquesces in the air, and dissolves slowly but in large quantity in
water.   It fuses at a gentle red heat without suffering decomposi-
tion ; but at a higher  temperature it is  resolved into  oxygen and
arsenious acid, which volatilizes.  It is highly poisonous.
  2. Most of the  arsenates are insoluble in water.   Of the so-
called neutral arsenates  those with alkaline bases  alone are soluble
in water.  Most  of the neutral  and basic arsenates  can bear  a 
 174                     ARSENIC ACID.                  [§ 136

 strong red heat without suffering  decomposition.   The acid arse-
 nates lose  their excess of acid  upon ignition, the  free acid being
 resolved into arsenious acid and oxygen.
   3. Hydrosulphuric acid fails to precipitate alkaline and neutral
 solutions of arsenates;  but in acidified solutions it causes at first, a
 reduction of arsenic to arsenious acid, with simultaneous  separa,
 tion of sulphur, and then throws down  tersulphide of arsenic.
 This process goes on, until finally, all the arsenic is precipitated as
 As S3 mixed with 2 S.—(Wackenroder, Ludwig, H. Rose.)
   The precipitate never forms  instantaneously, and in dilute solu-
 tions frequently only after the lapse of a considerable time (twenty-
 four hours, for instance).   Heating (to about 160° Fah.) promotes
 its separation.  If a solution of arsenic acid, or of an arsenate, is
 mixed with sulphurous acid,  or with  sulphite of soda and  some
 hydrochloric acid, the  sulphurous acid is converted into sulphuric
acid, and the arsenic acid reduced to arsenious acid; application
 of heat promotes the change.  If hydrosulphuric acid is now added,
the whole of the arsenic is thrown  down at once as tersulphide.
   4. Sulphide of ammonium converts  the arsenic acid in neutral
and alkaline solutions of arsenates into pentasulphide of arsenic
 (As S3), which  remains in solution as ammonio-pentasulphide of
arsenic (sulpharsenate of sulphide of ammonium).   Upon the addi-
tion of an acid to the solution, this  double sulphide is decomposed,
and pentasulphide of arsenic precipitates.   The separation of this
precipitate proceeds more  rapidly than is the case  when acid solu-
tions of arsenates are precipitated with hydrosulphuric acid.  It  is
promoted by heat.  This precipitate is really As S5 and not a mix-
ture of As S3 with 2 S.
   5. Nitrate of silver produces under  the  circumstances stated
 §  135,  6,  a highly characteristic  reddish-brown precipitate of
 arsenate of silver (3 Ag O, As 05), which is readily soluble in
 dilute nitric acid and in  ammonia, and dissolves  also slightly in
 nitrate  of  ammonia.  Accordingly, if a little of the precipitate  is
 dissolved in a large proportion  of  nitric acid,  neutralization with
 ammonia often fails to reproduce the precipitate.
   6. Sulphate of copper produces under the circumstances stated
 § 135, 7, a greenish-blue precipitate of arsenate of copper (2 Cu
 O, H O, As O:).
   7. When a dilute solution of arsenic acid to which a little hydro-
 chloric  acid has been  added, is heated with metallic copper, the
 latter remains perfectly unaltered.  If, however, the liquid is mixed
 with twice its volume of concentrated hydrochloric acid, the copper
 acquires a gray coating as described  under  arsenious acid.  The
 reaction under the circumstances above  described is as sensitive  as
 in the presence of arsenious acid (Reinsch).
   8. With zinc in presence of sulphuric acid, with  cyanide of 
§ 137.]
RECAPITULATION.
175
 potassium, and before the blowpipe, the compounds of arsenic acid
 comport themselves in the same way as those of arsenious acid.  If
 the reduction of arsenic acid by zinc is effected in a platinum dish,
 the platinum does not  turn  black, as is the case in the reduction
 of antimony by zinc  (§ 134, 8).
   9. If a solution of arsenic acid, or of an arsenate soluble in water,
 is added to a clear mixture  of sulphate of magnesia,  chloride of
 ammonium* and  a  sufficient  quantity of ammonia, a crystalline
 precipitate of  arsenate of ammonia and  magnesia (2  Mg O,
 N Hi 0, As 05  + 12 aq.) separates;  from concentrated  solutions
 immediately, from dilute solutions after some time.
   If a  portion  of the precipitate be dissolved in a few drops of
 nitric acid, a drop of nitrate of silver added, and into the mixture
 be placed a glass rod previously dipped  in  ammonia, brown-red
 arsenate of silver is formed  (distinction of arsenate from phosphate
 of ammonia-magnesia).

                               §137.
   Recapitulation  and remarks.—I  will  here  describe  first the
 different ways best adapted to effect the detection or separation of
 tin, antimony,  and  arsenic, when present together  in the same
 compound  or  mixture,  and  afterwards  the most  trustworthy
 means of distinguishing between the several oxides of each of the
 three metals.
   1. If you have a mixture of sulphide of tin, sulphide of antimony,
 and sulphide of arsenic, triturate 1 part of it, together with 1 part
 of dry carbonate of soda, and 1 part of nitrate of soda,  and transfer
 the mixed powder gradually to a small porcelain crucible contain-
 ing 2 parts of nitrate of soda kept in a state of fusion at a not over-
 strong heat; oxidation of the sulphides ensues, attended with slight
 deflagration.  The fused mass contains binoxide  of tin, arsenate
 and antimonate of  soda, with sulphate,  carbonate, nitrate,  and
 nitrite of soda.   You must take care not to raise the heat to  such
 a degree, nor continue the fusion so long, as to  lead to a reduction
 of the nitrite of soda to the caustic state so-that soluble stannate
 of soda  be not formed.  Treat the fused mass, poured out upon a
 piece of porcelain  and pulverized, with a little cold water until
 it is completely  softened; then  filter  the fluid  off from the undis-

  [* The operator will save time and avoid mistakes by keeping among his reagents
 the mixture here alluded to, which is often needed in testing for arsenic and  phos-
 phoric acids.  It is properly  prepared by dissolving in water 24.6 grammes of
 crystallized sulphate of magnesia and 33 grammes of chloride of ammonium  (the
commercial salts will answer), adding some ammonia and diluting to the volume of
a litre. From the mixture thus made no hydrate of magnesia separates by addition
of more ammonia.  If a precipitate (sesquioxide of iron, &c.) should form, filter off
and use the clear solution.] 
176
RECAPITULATION.
[§ 137.
solved residue, which contains the binoxide of tin and antimonate
of soda.  Mix the filtrate, which contains the arsenate of soda and
the other salts, with nitric acid to distinctly acid reaction, and heat
to expel carbonic  and nitrous acids, then with a sufficient pro-
portion of solution of nitrate of silver; a precipitate of chloride
of silver forms  (if the reagents employed or the precipitated sul-
phides contained a chlorine  compound).   Filter,  and carefully add
to the filtrate dilute solution of ammonia, whereupon the presence
of arsenic  is manifested by the characteristic  reddish-brown pre-
cipitate of arsenate of oxide of silver which makes its appearance,
first in the uppermost stratum  of the fluid where the solution of
ammonia comes first into contact with it, but  subsequently, upon
complete neutralization of the free acid, in every part of the fluid.
Arsenic may also be tested by a mixture of sulphate of  magnesia,
chloride of ammonium and ammonia, see § 136, 9.
  Wash now  the filter containing  the residuary binoxide of tin
and  antimonate of soda once with water, then three times with  a
mixture of equal parts of water and spirit of wine.  Transfer the
residue into a small platinum capsule (or a porcelain capsule into
which a piece of platinum foil is  placed), and  heat gently with
some hydrochloric acid.  The mass  either dissolves entirely, or in
case much  tin is present, a white precipitate remains.  Add now a
fragment of zinc.  Both  tin  and antimony are  reduced, and the
presence of antimony is at once made evident by the black stain
which appears upon the platinum.   When the evolution  of hydro-
gen has nearly ceased, what remains of  the  zinc is removed, and
the contents  of the capsule are heated with a little hydrochloric
acid,  antimony remains undissolved  in black flocks, while tin goes
into solution as protochloride.  In the filtered solution, the tin may
now be detected by chloride of mercury or  a mixture  of  sesqui-
chloride of iron and ferricyanide of potassium ;  while the antimony,
after  washing with water, may be dissolved in a little nitrohydro-
chloric  acid and further  tested  by hydrosulphuric acid.   This
method of separation is further detailed in § 192.
  2. If the mixed sulphides, after removing the greater share of thd
water that adheres  to them  by placing the filter on blotting-paper,
are treated with warm fuming hydrochloric  acid, the sulphide of
antimony and sulphide of tin dissolve, whilst the sulphide of arse-
nic is left nearly altogether undissolved.   If the residuary sulphide
of arsenic is treated with ammonia, and the solution obtained eva-
porated, after adding to it a very little carbonate of soda, an arse-
nical  mirror may readily be produced from the residue with cyanide
of potassium and carbonate of soda in a stream of carbonic acid
gas.  The  solution,  which  contains the tin and antimony, may be
treated as directed in 1.
  Or, if there is a considerable excess  of antimony, the solution 
§ 137.]
RECAPITULATION.
177
may be mixed with  sesquicarbonate  of ammonia in excess, and
boiled.  A considerable proportion  of the  antimony present dis-
solves  in this process, whilst binoxide of tin  mixed with a small
quantity of teroxide of antimony remains undissolved.  The pre-
sence of the tin may now be the  more readily proved  by the
method given in 1 (Bloxam).
  3. On digesting the mixed sulphides with some solid sesquicar-
bonate of ammonia and water at a gentle heat, sulphide of arsenic
dissolves,  while the sulphides of antimony and tin remain  behind.
This separation is not, however,  complete, a trace of sulphide of
antimony easily passes into solution, and some  sulphide of arsenic
remains in the residue.  It is, therefore, necessary to examine the
precipitate which is thrown down by acidifying the alkaline solu-
tion with hydrochloric acid, especially when it is in small quantity,
by dissolving it, after washing, in ammonia,  evaporating  with a
little carbonate of soda and igniting the residue with a mixture of
cyanide of potassium and carbonate of soda in a stream of carbonic
acid.  A metallic mirror thus obtained is decisive proof of the pre-
sence of arsenic.   The residue  insoluble in carbonate of ammonia
is to be examined according to 2.
  4. If sulphide of antimony, sulphide of tin, and sulphide of arse-  .
nic  are dissolved in sulphide of potassium, a large excess of a con-
centrated solution of  sulphurous acid added, the mixture digested
for  some time in the water-bath, then  boiled  until  all sulphurous
acid is expelled, and filtered, the filtrate contains  all the arsenic as
arsenious acid (which may be precipitated from it by hydrosulphu-
ric  acid),  whilst  tersulphide of antimony and bisulphide  of tin
are  left behind undissolved (Bunsen).  After dissolving the residue
in hydrochloric acid,  the  antimony  and tin may be detected as
directed in 2.
  5. In the analysis of alloys, binoxide of tin f,nd teroxide  of anti-
mony are  often obtained together as  a residue insoluble in nitric
acid.  This is best treated by fusing the dried mass with hydrate of
soda in a silver crucible, softening  the contents of the crucible with
water and  adding to  the solution  one-third its volume of alcohol.
The whole is now brought upon a filter, antimonate of soda remains
upon the latter and is to be washed with weak alcohol to which a
few drops  of solution of carbonate of soda have been added.—The
filtrate is  acidified with hydrochloric acid, and tin and arsenic are
thrown down by hydrosulphuric acid with  the aid of heat.  The
sulphides thus obtained are  heated in a current of hydrosulphuric
acid gas, when all the tin remains behind as bisulphide, while all
sulphide of arsenic volatilizes and may be collected in ammonia
(H. Rose).
  6. For the most accurate way of  separating antimony and arse-
nic,  and distinguishing between the two metals, viz.,  by treating
                               12 
178
RECAPITULATION.
[§137
with hydrosulphuric acid the mirror produced by Marsh's method;
and separating the resulting sulphides  by means of hydrochloric
acid gas, I refer to § 135, 10.  Antimony and  arsenic may,  how-
ever, when mixed  together in form of hydrides,  be separated also
in the following way:  Conduct the gases mixed with an excess of
hydrogen, first through a tube containing glass splinters moistened
with  solution of acetate of lead (to retain  the hydrochloric and
hydrosulphuric gases), then in  a slow  stream  into a solution  of
nitrate of silver.   All the antimony in the gas falls down  as black
antimonide of silver (Ag3 Sb), whilst the arsenic goes into solution as
arsenious acid, silver being at the same time reduced to the metallic
state.  The arsenic may be detected in the solution as arsenite  of
silver (by cautious addition of ammonia),  or  by hydrosulphuric
acid after precipitating the excess of silver by hydrochloric  acid.
In the precipitated antimonide  of  silver which is often mingled
with considerable  metallic silver, antimony is most easily detected
by boiling the well-washed precipitate with tartaric acid and water.
Antimony alone is dissolved, and may be recognized in the  solu-
tion by hydrosulphuric acid after acidifying with hydrochloric acid.
(A. W. Hofmann.)
   7. Protoxide and binoxide of tin may be detected and identified
in presence of each other, by testing one portion  of the  solution
containing both oxides for the protoxide with chloride of mercury,
terchloride of gold or a mixture  of ferricyanide of potassium and
sesquichloride of iron, and another portion for the binoxide, by
pouring it into  a hot concentrated solution of sulphate of soda.
   8. Teroxide of antimony in presence of antimonic acid may  be
identified by the reaction described in §131, 9.   Antimonic acid in
presence of teroxide of antimony, by heating the teroxide suspect-
ed to contain an admixture of the acid, but without any other admix-
ture, with hydrochloric acid free from chlorine, and iodide of potas-
sium free from  iodate of potassa (§  134, 2 and 3).
   9. Arsenious acid and arsenic acid in the same solution may be
distinguished by means of nitrate of silver.   If the precipitate con-
tains little arsenate  and much  arsenite of silver, it is necessary, in
order to identify the former, to add  cautiously and drop by drop
very highly diluted nitric acid, which dissolves the yellow arsenite
of silver first.
   A still safer way to detect small  quantities of arsenic acid in pre-
sence of arsenious acid, is to precipitate the solution which contains
the two acids, with a mixture of sulphate of magnesia, chloride of
ammonium, and ammonia (§ 136, 9), whereby complete separation
of the two acids is attainable.
   Arsenious acid in presence of arsenic acid may also be identified
by the  immediate  precipitation of the acidified solution of the
former evnin the cold by hydrosulphuric acid, as well as by the 
 § 138.]              OXIDES OF  MOLYBDENUM.                  179

 reduction  of alkaline  solutions  of oxide of copper effected  by its
 agency.   To distinguish between the ter- and the pentasulphide of
 arsenic in sulphur salts, boil the potassa  solution of the salt under
 examination with hydrate of teroxide of bismuth, filter off from the
 tersulphide of bismuth formed, and test whether the filtrate contain
 arsenious or arsenic acid.   Ter-  and pentasulphide of  arsenic are
 distinguished from  each other by first  removing any admixture of
 sulphur by means of sulphide of carbon, then dissolving  the resi-
 due in  ammonia, adding excess of nitrate  of silver, filtering off from
 sulphide of silver and cautiously adding  dilute nitric acid  to the
 filtrate to see whether yellow arsenite or brown-red arsenate of
 silver is produced.

             Special Reactions of the rarer Oxides of the Sixth Group.

                                   % 138.
   a. Binoxide of Iridium.—(Ir 0^).  Iridium occurs associated  with platinum, espe-
 cially in  iridosmine.   It is now employed in alloy with platinum, for making cruci-
 bles, &c. It is similar to platinum in appearance, is brittle and exceedingly infusible.
 When compact or when  reduced by hydrogen  at a red-heat, it is insoluble in all
 acids, even in aqua regia (distinction from gold and platinum).   When reduced in
 the wet way, as by formic acid, or when alloyed with a large proportion of platinum
 i  dissolves in aqua-regia to bichloride (Ir Cl2).   It is oxidized but not dissolved by
 bisulphate of potassa in a state of fusion (distinction from rhodium). It is also oxi-
 dized by fusing with hydrate of soda with access of  air or with nitrate of soda. The
 resulting  combination  of  sesquioxide  (Ir2 03)  with soda is  partially soluble  in
 water;  heated with aqua regia it dissolves with  a dark red color to  bichloride of
 iridium and chloride of sodium.
   When a mixture of pulverized iridium and common salt is heated in a stream o'
 chlorine gas to incipient redness, there is formed  iridiochloride of sodium, which dis-
 solves iu water  to a dark reddish-brown  liquid.   Addition of potassa in excess to
 the solution decolorizes it, while some iridiochloride  of potassium is  thrown down
 as a brownish black substance.  On heating the  solution and then exposing it for  a
 considerable time to the air,  it at first acquires a  reddish, afterwards an  azure-blue
 color (characteristic distinction from platinum);  by evaporating it to  dryness and
 treating with water, we obtain a colorless liquid and a blue residue. Hydrosulphuric
 acid at first, decolorizes the solutions of bichloride of iridium,  protochloride and free
 sulphur  being formed ;  afterwards,  brown sulphide of iridium precipitates.  The
 Bame precipitate is produced by sulphide  of ammonium: it is easily soluble in excess
 of the latter reagent.   Chloride of  ammonium  throws down  from  concentrated
 solutions a blackish-red precipitate of iridiochloride of ammonium, which consists of
 microscopic octahedrons.  Protochloride  of tin gives a  light-brown precipitate in
 solutions of  iridium.  Protosulphate  of iron decolorizes  but does not precipitate
 them.   Zinc causes the separation of metallic iridium as a black  powder.
  6. Oxides of Molybdenum.—Molybdenum is of  comparatively rare occurrence.
 It is found chiefly as sulphide (molybdenite) and as molybdate of lead. It has latterly
 acquired importance in practical chemistry from the use of molybdate of ammonia as
a test for phosphoric acid.  Molybdenum is a silver-white, very infusible metal. Its
protoxide (Mo 0) is black,  its binoxide  is dark brown.  The  metal and both the
oxides are converted into molybdic acid (Mo 03), either by heating to redness in the
air or by  boiling with nitric acid.   Molybdic acid is a white porous  mass which
when placed in water falls into a multitude of minute scales.  It  fuses at a red heat, 
 180                     OXIDES  OF  TUNGSTEN.                 [§  138

 in close vessels volatilizes only at a bright red heat; in the air it sublimes at low
 redness and condenses in the  form of transparent needles and  plates.   The  unig.
 nited substance dissolves in ordinary acids, yielding colorless solutions, which in con-
 tact with zinc or tin, become fir3t blue, then green, and finally black under separation
 of protoxide.   By digesting with copper the solution in  sulphuric  acid  acquires a
 blue, that in hydrochloric acid acquires a brown color.   The reaction is often not
 perceptible until after the lapse of some time.  Ferrocyanide of potassium produces
 a reddish-brown precipitate, infusion  of galls a green  precipitate.  Hydrosulphwir.
 aad, when added in small proportion,  imparts a blue tint to solutions of molybdic
 acid; when added in larger proportion, it  produces a brownish-black precipitate;
 the fluid over the latter at first  appears green, but after standing some time, and
 upon application of  heat  with renewed transmission  of hydrosulphuric acid gas
 through the liquid, all the molybdenum may be finally thrown  down as  brownish-
 black tersulphide of molybdenum (Mo S3).  The precipitated tersulphide  of molyb-
 denum  dissolves in sulphides of the  alkali metals;  acids reprecipitate from the
 Sulphur salts  the sulphur  acid (Mo S3).  "Warming facilitates the separation.  When
 roasted at a red-heat  in the air or heated with uitric 'acid, sulphide- of molybdenum
 is converted into molybdic acid.
  Molybdic acid dissolves readily in solutions of pure alkalies and carbonates of the
 alkalies; from rather concentrated solutions, nitric, and hydrochloric acids throw down
 molybdic acid,  which redissolves  upon further  addition of the precipitant.  The
 solutions  of molybdates of the alkalies are colored yellow by hydrosulphuric  acid,
 and  give afterwards, upon addition of  acids, a brownish-black precipitate.  For the
 deportment of molybdic  acid with phosphoric acid and ammonia, see § 145, 10.
  [By putting a fragment of zinc into a hydrochloric solution of molybdic  acid or of
 a molybdate, adding a few drops of strong solution of sulphocyanide of potassium and
 finally a few  drops of sulphuric or hydrochloric acid, so  that a gentle evolution of
 hydrogen is excited, the liquid shortly acquires a  carmine color.  The reaction is
 very delicate. —(Braun.)   To recognize molybdenum in presence of sesquioxide of
 iron  and peroxide of nitrogen, which likewise give  a red  color with  sulphocyanide
 of potassium, the solution is treated with sulphurous acid  or an alkaline sulphite and
 hydrochloric acid, until no coloration is produced in it by sulphocyanide of potassium
 silone.   Sesquioxide of iron is thus reduced to protoxide, and peroxide of nitrogen
 to a  lower oxide.  On now adding solution of sulphocyanide of potassium and a
 fragment of zinc, the reaction at once becomes manifest.—(Fdiior.)]
  [Solutions of molybdic acid acidified  with  dilute hydrochloric acid impart a brown
 tint to turmeric paper.—(A. Miiller.)   (Compare zirconia and boracic acid).]
  When molybdic acid is heated on charcoal in the  oxidizing flame it volatilizes: at
 the same time  the  support  acquires a  yellow,  often  crystalline coating, which
 becomes white on cooling.   In the reducing flame  metallic molybdenum is formed
 which  may  bo obtained as a  gray powder on washing the pulverized charcoal.
 Sulphide of molybdenum when heated  in the oxidizing flame yields sulphurous acid
gas and a sublimate of molybdic acid.
  c. Oxides of Tungsten.—Tungsten  is of rare occurrence,  the commonest minerals
containing it are  Seheelite (tungstate of lime) and  Wolfram (tungstate of protoxides
of iron and manganese).  Tungsten as  obtained by the reduction of tungstic  acid in
a stream of hydrogen gas at a strong red heat, is a  very difficultly fusible,  iron-
gray powder.   Ignited  in the air pulverulent tungsten  is  converted  into tungstic
acid (W 03), heated to redness in  chlorine gas it yields a sublimate of red chloride
(W Gli): the latter decomposes with water into hydrochloric acid and oxide of tung-
 sten  (W 02), which on exposure to air  absorbs oxygen and is converted into the blue
 "ungstate of tungsten  (W 02, W 03).   Tungsten is not dissolved by acids, not  even
by aqua regia.   It is also insoluble in solution of potassa,  but dissolves in  a mixtura
of potassa with hypochlorite of an alkali.  Oxide of tungsten is black, when strongly 
 § 138.]                OXIDES  OF TELLURIUM.                     181

 ignited in the  air it  is converted  into  tungstic acid.  Tungstic acid is a lemon-
 yellow, non-volatile powder, insoluble in water and acids.  By fusing it with bisul-
 phate of potassa and treating the fused mass with water, there is at first obtained an
 acid solution free from tungstic  acid.  After its removal, the residual tungstate of
 potassa dissolves.   Tungstates of the alkalies are obtained with difficulty by boiling
 tungstic acid with solutions of alkaline carbonates: by fusing the acid with  th6
 carbonates, the  tungstates of potassa and soda are easily prepared.  They are soluble
 in water.  Hydrochloric, nitric, and  sulphuric acids throw down from  solutions of
 tungstates white precipitates which are insoluble in excess of acid (distinction from
 molybdic acid); but  soluble in ammonia.  By evaporating tungstates to dryness
 with excess of hydrochloric acid and treating the  residue with water, tungstic acid
 remains undissolved.   Chlorides of  barium and calcimn, and nitrates of silver and
 protoxide of mercury  throw down white precipitates.   Ferrocyanide of potassium on
 addition of some acid gives with solutions of tungstates a brown-red  coloration, and
 after some time, a brown-red precipitate.  Tincture of galls, by addition of an acid,
 throws down a  brown precipitate.   Hydrosulphuric acid scarcely affects acid solu-
 tions ; sulphide  of ammonium does not precipitate alkaline solutions; but by acidify-
 ing  the latter light-brown sulphide of tungsten (WS3) separates,  which is somewhat
 Boluble  in pure water, but is  insoluble in saline solutions.  Protochloride of tin
 gives a yellow precipitate;  if the mixture be  acidified with  hydrochloric acid and
 heated,  it acquires a  fine  blue color (characteristic and sensitive  reaction).   By
 supersaturating the solution of an alkaline tungstate with hydrochloric, or, better,
 with phosphoric acid and  adding zinc, a fine blue color is  obtained.   Microcosmic
 salt  dissolves tungstic acid: in the oxidizing flame  the bead is clear, colorless or
 yellowish : in the  reducing flame it  becomes blue  and by addition of protosulphate
 of iron, blood-red.   Heated with a very little soda in the reducing flame  on charcoal,
 tungsten is obtained as a powder which may be separated by washing the pulverized
 charcoal.  The  tungstates  which are insoluble in water are mostly decomposed by
 acids.  Wolfram,  which is  difficultly decomposed by acids, may be fused with carbo-
 nate of soda.   Water extracts tungstate of soda from the fused mass.
   d.  Oxides of Tellurium.—Tellurium is found native,  alloyed with other elements,
 and  in the form of tellurous acid. It is extremely rare.  It is a white, brittle, easily
 fusible metal; may be sublimed in   a glass tube;  heated in the air it burns with a
 greenish-blue flame with production of  dense white  vapors of tellurous acid.   Tellu-
 rium is insoluble in hydrochloric  acid; but in nitric acid readily dissolves  to tellurous
 acid (Te 02).  Tellurium  in the state  of powder, dissolves in strong sulphuric acid
 with  purple color: on addition of  water  it is thrown down  from this solution.
 Tellurous acid is white, fuses at a moderate heat to  a yellow liquid, is volatile in the
 air at a strong red heat, does not yield a crystalline  sublimate.  The anhydrous acid
 easily dissolves  in  hydrochloric  acid, to a slight extent  in  nitric acid, largely in
 caustic  potassa, slowly in  ammonia, and is  nearly insoluble in water.  Hydrated
 tellurous acid is white, perceptibly soluble in cold water, soluble in hydrochloric
 and nitric acids.   Water throws down from  the  solutions the white hydrate: from
 the solution in nitric acid crystallized anhydrous tellurous acid separates after some
 time.  Alkalies  and alkaline carbonates precipitate  from the  hydrochloric solution,
 white hydrate which is soluble  in excess of the precipitant.  Hydrosulphuric  acid
 throws  down from acid solutions,  brown sulphide of tellurium (Te S^) which is
 readily soluble in sulphide of ammonium.  Sulphite of soda, protochloride of tin and
 zinc  precipitate  metallic tellurium as  a black powder.   Telluric acid (Te  03) is
 obtained by fusing  tellurium or tellurites with nitrate and carbonate  of  soda.   The
fused mass is insoluble in water; it remains clear in  the cold after acidifying with
hydrochloric acid;   but on boiling evolves chlorine with formation of tellurous acid;
the liquid therefore now gives a precipitate with water if the excess  of  acid be not
ioo great. 
182         DEPORTMENT  OF ACIDS  WITH  REAGENTS.      [§ 139

  When tellurium, its sulphides  or oxides are fused with cyanide of potassium in  a
Btream  of hydrogen, tellurocyanide of potassium is formed.  The fused mass v
Boluble in water, a stream of air  precipitates from it all the tellurium (distinction and
separation from selenium).   Tellurous or telluric acid fused with carbonate of potassa
and  charcoal, yields telluride of potassium  from which  acids evolve telluretted
hydrogen as a fetid gas.  Compounds of tellurium, when mixed with carbonate of
soda and subjected to the iuner blowpipe flame, suffer reduction and volatilize.  The
vapors of tellurium oxidize again in the outer flame and coat the charcoal support
with a white incrustation of tellurous acid.
  e.  Selenium exists sparingly in nature in combination with various metals.   It is
sometimes found in the flue dust  of roasting furnaces, and in Nordhausen oil-of-vitriol.
It is on  the one hand,  related  to tellurium; on  the other,  to sulphur; and  thus
stands on the boundary between  the metals and non-metallic elements.  In the fused
state it has a gray-black color, it volatilizes  and sublimes at high temperatures, and
when heated in the air burns with a characteristic odor of decaying horse-radish, to
selenious acid (Se 0^).  It dissolves, without oxidizing, in strong sulphuric acid and
is precipitated by dilution, in red flocks.  It is dissolved and oxidized  by nitric and
nitrohydrochloric acids to selenious acid.  Selenious acid, when produced by sublima-
tion, forms white four-sided needles; its hydrate gives crystals resembling those of ni-
trate of potassa. Both dissolve readily in water, producing a strongly acid liquid; of
the neutral selenites only those with alkaline base are soluble in water; their solutions
react alkaline;  selenites of lead and silver dissolve with difficulty—all other selenites
dissolve with ease, in nitric  acid. Hydrosulphuric acid in presence of  hydrochloric
acid, produces in solutions of selenious acid or of selenites a precipitate (sulphido of
selenium), which is yellow in cold and reddish-yellow in hot solutions, and is soluble
in sulphide of ammonium.  In neutral solutions of selenites chloride of barium yields
a white precipitate of selenite of baryta which is soluble  in hydrochloric or nitrio
acid.  Protochloride of tin or sulphurous acid on addition of  hydrochloric acid, pro-
duce a red, or in hot liquids, a gray  precipitate of selenium.   Selenic acid is  formed
by heating selenium or its compounds  with nitrate and  carbonate  of soda.  The
fused mass  is soluble in water;  treated with hydrochloric acid it remains clear, on
boiling,  it evolves chlorine while  selenic acid is reduced to selenious acid.—Selenium
and its compounds when fused with cyanide of potassium in a current of hydrogen
gas,  yield selenocyanide of potassium from which selenium  does not separate by the
action of air (distinction from tellurium); by continued  boiling with  hydrochloric
acid  selenium is, however, precipitated.  On charcoal  in the reducing flame, sele-
nium compounds emit the highly characteristic odor of decaying horse-radish above
mentioned, which  serves for their ready detection.

B.—Deportment  of  the  Acids and  their  Radicals   with
                               Reagents.

                                   §139.

  The reagents which serve for the  detection of  the  acids  are
divided, like those used for the detection of the bases, into general
reagents, i. e., such as indicate the group to which the acid under
examination belongs;  and special reagents,  i.e.,  such as serve
to effect the detection and identification of the individual acids.
The  groups  into which we  classify the various  acids can scarcely
be defined and limited with  the same degree of precision as those
into  which the bases are divided
  The two principal groups into which acids are divided are those 
§ 139.]           CLASSIFICATION OF ACIDS.               183

of inorganic and organic  acids.  We  base this division upon
those characteristics by which,  irrespectively of theoretical con-
siderations, the ends  of  analysis are most  easily attained.   We
select therefore here, as the  characteristic mark to guide us in the
classification into organic and inorganic acids,  the  deportment
which the various acids manifest at a high temperature, and call
organic those acids of which  the salts—(particularly those which
have  an  alkali  or an alkaline earth  for base)—are  decomposed
upon ignition, the decomposition being  attended with separation
of carbon.
  By selecting  this deportment  at  a  high temperature as the dis-
tinctive characteristic of organic acids, we are enabled to determine
at once  by a  most simple preliminary experiment the class to
which an acid  belongs.  The  salts  of organic  acids with alkalies
or alkaline earths are converted into carbonates when  heated to
redness.
  Before proceeding to the special  study of the several acids con-
sidered in this work, I give here, the same as I have done with the
bases, a general view of the  whole of  them classified in groups.

         CLASSIFICATION OF ACIDS IN GROUPS.
I. Inorganic Acids.
     first group :
  Division a.  Chromic acid (sulphurous and hyposulphurous acids,
             iodic acid).
  Division b. Sulphuric acid (hydrofluosilicic acid).
  Division c. Phosphoric acid,  boracic acid, oxalic acid, hydro-
             fluoric acid (phosphorous acid).
  Division d.  Carbonic acid, silicic acid.
     second group:
   Chlorine and hydrochloric acid, bromine and hydrobromic acid,
           iodine and hydriodic acid, cyanogen and hydrocyanic
           acid together with hydroferro-  and hydroferricyanic
           acids, sulphur and hydrosulphuric acid  (nitrous, hypo-
           chlorous,  chlorous and hypophosphorous acids).
     THIRD GROUP I
  Nitric acid, chloric acid (perchloric acid).
II. Organic Acids.
    first group :
   Oxalic acid, tartaric  acid, citric  acid,  malic  acid  (racemic
           acid).
     second group:
  Succinic acid, benzoic acid.
    third group :
  Acetic acid,  formic acid (propionic acid, butyric acid, lactic
           acid). 
184                    CHROMIC ACID.            [§§ 140, 141,

  The acids which are printed in italics  are  the  most important
from their frequent occurrence in the various  natural or industrial
subjects  of  chemical investigation: the others are comparatively
rare.
                     I.  Inorganic Acids.
                             § 140.
                          First Group.
Acids which are precipitated from Neutral  Solutions  by
                     Chloride of Barium.
  This group is again subdivided into four divisions, viz.:
  1. Acids  which are decomposed in acid solution by  hydrosul-
phuric acid, and to which attention has  therefore been  directed
already in the testing for bases, viz., chromic acid, sulphurous acid,
and hyposulphurous  acid, the latter because it  is  decomposed
and detected by the mere addition of hydrochloric acid to the
solution of one of its salts; and also iodic acid.*
  2. Acids  which are not decomposed in acid solution by hydro-
sulphuric acid, and the  baryta compounds of which are insoluble
in hydrochloric acid, sulphuric acid (hydrofluosilicic acid).
  3. Acids which are not decomposed in an acid solution by hydro-
sulphuric acid, and the baryta compounds of which dissolve in
hydrochloric acid,  apparently without decomposition, inasmuch
as the acids eannot be completely separated from the hydrochloric
acid solution by heating or evaporation ; phosphoric acid, boracic
acid,  oxalic Acid, and hydrofluoric acid  (phosphorous  acid).
(Oxalic  acid belongs more properly to the organic group.  We
consider it,  however, here  with  the acids of the inorganic class, as
the property of its  salts to be decomposed upon ignition without
actual carbonization may lead to its being overlooked as an organic
acid.)
  4. Acids  which are not decomposed in acid solution by hydro-
sulphuric acid, and the baryta salts of which  are soluble in hydro-
chloric acid, with  decomposition (separation  of the acid); car-
bonic acid,  silicic acid.

  First Division of the First  Group of the  Inorganic Acids.
                             § 141.
                      Chromic Acid (Cr  03).
  1. Chromic acid presents the appearance of a  scarlet-red crys-
talline mass, or of distinct acicular crystals.   Upon ignition it is

  *  All the oxides  of the  sixth group of metals which possess decided acid
characters, viz., arsenic, antimonic, selenious and selenic acids, properly belong to the
first  division of the first group of acids.  On account, however, of their deportment
towards hydrosulphuric  acid they are most conveniently considered in connection
with the bases. 
§ 141.]
CHROMIC  ACID.
185
 resolved into sesquioxide of chromium and oxygen.   It deliquesces
 rapidly upon exposure to the air.  It dissolves in water, imparting
 to the fluid a deep reddish-brown tint, which remains still visible
 in very dilute solutions.
   2. The chromates are all red or yellow, and for the most part
 insoluble in water.  Part of them are decomposed  upon ignition;
 those  with alkaline bases  are fixed, and soluble  in water; the
 solutions of the neutral  alkaline  chromates  are  yellow, those of
 the alkaline  bichromates  are red.  These tints are  still visible in
 highly dilute solutions.   The  yellow color  of the  solution  of a
 neutral salt changes  to  red on the addition of a  mineral  acid,
 owing to the formation of an acid chromate.
   3. Hydrosulphuric acid acts upon acidified solutions of chromates
 producing at first a brown and finally a green coloration of the
 liquid whereby a salt of sesquioxide of  chromium is formed with
 simultaneous separation of sulphur, which gives to the solution a
 milky appearance (KO, 2 Cr 03 + 4 S03 +  3 HS  = KO, S03 +
 Crs 03, 3 S03  + 3 HO +  3  S).  The reaction  is  facilitated  by
 warming, when a portion of the sulphur is oxidized to  sulphuric
 acid.
   4. Chromic acid may also be reduced to sesquioxide of chromium
 by means of many other  substances, and  more particularly by sul-
 phurous acid,  or by heating  with hydrochloric acid, especially
 upon the addition of alcohol (in which case chloride of ethyle and
 aldehyde are evolved);  also by metallic  zinc, or by heating with
 tartaric  acid,  oxalic acid, &c. All  these  reactions are  clearly
 characterized by the change of the red or yellow  color of the
 solution to the green tint of the salt of sesquioxide  of chromium.
   5. Chloride  of barium produces in  aqueous solutions  of  chro-
 mates  a  yellowish-white precipitate  of chromate of baryta (Ba
 0, Cr 0(), which is soluble in dilute hydrochloric acid and nitric acid.
   6. Nitrate of silver produces in aqueous solutions of chromates
 a dark purple-red precipitate of chromate  of silver (Ag  O, Cr
 Oj),  which  is  soluble  in  nitric acid and in ammonia; in feebly
 acid solutions it produces a precipitate of bichromate of silver
 (Ag O, 2 Cr O,).
   7. Acetate of lead throws down from aqueous or acetic solutions
 of a chromate  a yellow precipitate of chromate of lead (Pb O,
 Cr 03), which  is soluble in potassa, but  only difficultly soluble in
 dilute nitric  acid, and is  insoluble in acetic acid.  Upon heating
 with alkalies, the yellow  neutral salt is  converted into basic red
 chromate of lead (2 Pb O, Cr O).
   8.  On placing at the bottom of a tube  6 to 8 cubic centimetres
 of a dilute acid solution  of binoxide of  hydrogen* pouring upon
  * To be prepared by pulverizing a fragment of binoxide of barium of the size of a
pea, with a little water, and gradually adding the same with stirring to a mixture 
186
SULPHUROUS ACID.
[§ 142.
it a layer of ether £  of an inch  in  depth  and  adding  finally  a
solution containing chromic acid, the binoxide of hydrogen im-
mediately assumes a fine blue color.   On closing the tube with the
thumb  and  reversing  its position several times without violent
agitation the solution is decolorized, while the ether becomes blue.
  The latter phenomenon is especially characteristic.   One part of
chromate of potash in 40000 parts of water gives  a perceptible
reaction (Storer);  vanadic  acid impairs  its  delicacy (Werthcr);
compare § 116, 2.  The blue coloration is doubtless due to a com-
pound of chromic  acid and binoxide  of hydrogen, and not to the
formation  of a higher acid of chromium.  After some time  the
ether becomes  colorless, the chromic  acid suffering reduction to
sesquioxide of chromium.
  9. If insoluble chromates are fused together with  carbonate of
soda  and  nitrate  of soda,  and the  fused mass is  treated with
water, the fluid produced appears yellow from the alkaline  chro-
mate  which it holds in solution ; upon the addition of an  acid  the
yellow color changes to red.  The oxides remain behind either in
the pure state or as carbonates, if they are not soluble in the caustio
soda formed from the nitrate.
  10. Chromates  (not containing  metallic  oxides giving  colored
beads) give the same reactions with  borax and microcosmic salt
in the blowpipe flame as are exhibited by sesquioxide of chromium
(§ 105).
   Remarks.—When testing for bases, we always find the chromic
acid as sesquioxide of chromium, since hydrosulphuric acid reduces
it to that state.  The characteristic color of the solution frequently
renders the application of any further test unnecessary.   The reac-
tions with salts of silver and salts of lead afford positive and  con-
firmatory proof of the presence of chromic acid in aqueous solu-
tions.   Acid solutions are tested with binoxide of hydrogen.


              More rarely occurring Acids of the First Division.
                              § 142.
  a. Sulphurous acid (S 02) is a colorless, uninflammable gas,  which  exhales the
stifling odor of burning sulphur. It dissolves copiously in water.  The solution haa
the odor of the  gas, reddens  litmus paper, and  bleaches Brazil-wood paper.  It
absorbs oxygen from the air, and is  thereby converted into sulphuric acid.  The
salts of sulphurous acid are colorless.   Of the neutral sulphites those with  alkaline
base only are readily soluble in water; many of the sulphites insoluble or difficultly

of about 30 c. c. of hydrochloric acid, and 120 c. c. of water.  Instead of binoxide of
barium the impure peroxide  of sodium obtained by heating a piece  of sodium in
a porcelain capsule until it inflames, and then allowing it to burn completely, may
be employed.  The solution may be kept  a long time without  suffering decompo-
sition. 
§ 142.]
IODIC  ACID.
187
soluble in water dissolve in an aqueous solution  of sulphurous acid, but  fall  down
again upon boiling.   All the sulphites  evolve sulphurous acid when  treated  with
sidphuric acid or hydrochloric acid.   Chlorine  water dissolves most sulphites to sul-
phates.  Chloride of barium precipitates neutral sulphites, but not free sulphurous acid.
The precipitate dissolves in hydrochloric acid.  Hydrosulphuric acid decomposes free
sulphurous acid, water and pentathionic acid being formed and free sulphur  elimi-
nated, which latter separates from  the  fluid.  If a trace of sulphurous acid or of a
sulphite is introduced into a flask in which hydrogen is being evolved from zinc  and
hydrochloric acid, hydrosulphuric acid is immediately evolved along with the hydro-
gen, and the gas now produces a black coloration or a black precipitate in a solution
of acetate of lead to which has been added a sufficient quantity of solution of soda
to redissolve the precipitate which forms at first.  Sulphurous acid is a  powerful
reducing agent; it reduces chromic acid, permanganic acid, chloride of mercury (to
Bubchloride), decolorizes iodide of starch, produces a blue precipitate in  a mixture of
ferricyanide of potassium and sesquichloride of iron, &c.   With a hydrochloric acid
solution of protochloride of tin, a  brown  precipitate of protosulphide  op tin is
formed after some time.
  When an aqueous solution of an alkaline sulphite is made just acid by acetic acid
and poured into a relatively large amount of  solution of sulphate of zinc mixed with
a very little nitroprusside of sodium there  is produced, when the quantity of sulphu-
rous acid is not too small, a red color.  If  but a trace of sulphurous acid be present
the color is developed by adding a  little ferrocyanide of potassium.   By addition of
the latter substance a purple precipitate is thrown  down if the sulphurous  acid be
not too small in amount (Boedeker).  (Hyposulphites do not manifest this reaction.)
  b. Ht/posulphurous acid (S, 02).  This acid  does  not  exist  in the free state.  Its
salts are generally soluble in water.  The  solutions of most hyposulphites may be
ooiled without suffering decomposition; hyposulphite of lime is resolved upon boil-
in"' into sulphite of  lime and sulphur.   If Hydrochloric acid or  sulphuric acid is
added to the solution of a hyposulphite, the fluid remains at first clear and inodor-
ous, but after a short time—the  shorter the more concentrated the  solution—it
becomes more and more turbid, owing to the separation  of sulphur, and exhales the
odor of sulphurous acid.  Application of heat promotes  this decomposition.  Nitrate
of silver produces a white precipitate of hyposulphite of silver, which is soluble in
an excess of the hyposulphite;  after a little while (upon heating almost immediately)
the precipitate turns black, being decomposed into  sulphide of silver and sulphuric
acid.   Hyposulphite of  soda dissolves chloride of silver; upon the addition of an
acid the solution remains clear at first, but shortly, and  upon boiling  immediately,
sulphide of silver separates.   Chloride of barium produces a white precipitate,
which is soluble in much  water, more especially hot water, and is decomposed by
hydrochloric acid.
  When, as often happens, it is desired  to  test for sulphites and  hyposulphites in
presence of an alkaline sulphide, sulphate of zinc is added to the mixture until  the
alkaline sulphide is fully decomposed ; the  sulphide of zinc is filtered off, a portion
of the filtrate is tested for hyposulphurous  acid  by addition of hydrochloric acid,
another portion is treated with  nitroprusside of sodium, &&, to detect sulphurous
acid.
  Iodic acid (I 05).  Iodic acid crystallizes in white, six-sided tables; at a moderate
heat it  is resolved into iodine  vapor and  oxygen; it is  readily soluble  in  water.
Tho  salts are decomposed upon ignition, being resolved either into oxygen and a
metallic iodide, or into iodine,  oxygen,  and metallic oxide;  the iodates with an
alkaline base alone dissolve  readily in water.  Chloride of barium throws down
from solution of iodates of the  alkalies  a white precipitate  of  iodate of  baryta,
which is soluble in nitric acid; nitrate of silver, a white, granular-crystalline precipi- 
188
SULPHURIC ACID.
[§ 143.
tate of iodate of silver which dissolves readily in ammonia, but only sparingly ir
nitric acid.  Hydrosulphuric acid throws down from  solutions of iodic acid, with
simultaneous separation of sulphur, iodine, which then dissolves in hydriodic acid;
if an excess of hydrosulphuric acid is  added, the fluid  loses its color, and sulphur
separates, the iodine being converted into hydriodic acid.  The iodates are likewise
decomposed by hydrosulphuric acid. Sulphurous acid  throws down iodine,  which
upon addition of an excess of the acid is converted into  hydriodic acid.

   Second Division of the First Group of the Inorganic Acids.

                              § 143.

                     Sulphuric Acid (SO).
   1. Anhydrous sulphuric acid is a white,  feathery-crystalline
mass, which emits  strong fumes upon exposure to the air ; hydrated
sulphuric acid forms  an oily liquid, colorless and  transparent like
water.  Both the  anhydrous and hydrated acid char organic sub-
stances, and combine with water in all proportions, the process  of
combination being attended with considerable elevation of tem-
perature, and in the case of the  anhydrous acid, with a hissing
noise.
   2. The neutral sulphates are easily soluble in water, with excep-
tion of the sulphates  of baryta, strontia, lime and lead.   The basic
sulphates of many heavy metallic oxides are insoluble  in water;
but all dissolve in hydrochloric and nitric  acids.  The sulphates
are mostly colorless  or white.   The  sulphates  of  the  alkalies are
not decomposed by  ignition.   Of the  other sulphates,  some are
decomposed easily, some with difficulty on ignition, and some alto-
gether resist decomposition at high temperature.
   3. Chloride of barium produces even in exceedingly dilute  solu-
tions of sulphuric acid  and of the sulphates a finely-pulverulent,
heavy,  white  precipitate of sulphate  of baryta (Ba  O,  S 03),
which is  insoluble in dilute hydrochloric acid  and  in nitric  acid.
From  very dilute  solutions the  precipitate  separates  only  after
standing some time.   Concentrated acids and strong solutions  of
many salts, impair  the  delicacy of this reaction.
   4. Acetate of lead  produces  a heavy, white  precipitate of sul-
phate of  lead (Pb O, S 03)  which  is  sparingly soluble in dilute
nitric acid, but dissolves completely in  hot concentrated hydro-
chloric acid.
   5. The salts of sulphuric acid with the alkaline earths  which are
insoluble  in water and acids are  converted into carbonates,  by
fusion with alkaline carbonates.   But the sulphate of lead is reduced
to the state of pure  oxide when treated in this manner.   Both
the conversion of the former into carbonates, and the reduction  of
the latter  to  the  state of oxide, are  attended with  the  formation
of an alkaline sulphate.  The  sulphates of the  alkaline earths and 
§ 144.]             HYDROFLUOSILICIC ACID.                189

sulphate of lead, are  also resolved into insoluble carbonates and
soluble  alkaline sulphate when boiled with concentrated solutions
of carbonates of the alkalies (compare §§ 98, 99,  100).
  6. Upon fusing sulphates with carbonate of soda on charcoal in
the inner flame of the blowpipe, the sulphuric acid is reduced, and
sulphide of sodium formed, which may be readily recognized by
the odor of hydrosulphuric acid emitted upon moistening the sam-
ple and the part of the  charcoal  into which the fused mass has
penetrated, and adding some acid.  If the fused mass is transferred
to a clean silver plate, or a polished silver coin, and then moistened
with water and some acid, a black  stain of sulphide of silver is
immediately formed.
  Remarks.—The  characteristic and exceedingly delicate reaction
of sulphuric acid with salts of baryta renders the detection of this
acid an  easier task than that of almost any other.   It  is  simply
necessary to take  care not to confound with sulphate of baryta,
precipitates of chloride  of barium,  and particularly of nitrate  of
baryta, which are  formed  upon mixing  aqueous solutions of these
salts with fluids containing a large proportion of free hydrochloric
acid or free nitric acid.   It is very easy to distinguish these precipi-
tates from  sulphate of baryta,  since they redissolve immediately
upon diluting the acid fluid with water.
  In  testing  for sulphuric acid with chloride of barium, the ope-
rator should make  the solution tolerably dilute ; he should also add
some hydrochloric acid,  without which, certain  salts, e. g. alkaline
citrates, may entirely prevent the separation of sulphate of baryta.
In case very dilute solutions are to be examined  for sulphuric acid,
they should be allowed to stand for  several hours in a warm place,
after addition of chloride of barium. To be certain that a precipi-
tate is really sulphate of baryta it may  be  examined according to
§ 143,6.—To detect free sulphuric acid  in presence of a sulphate,
the fluid under examination is mixed with a very little cane-sugar,
and the  mixture evaporated to dryness in a porcelain dish at 212°
Fah.   If free sulphuric acid was present, a black residue remains,
or,  in the case of most minute quantities, a blackish-green residue
Other free  acids do not decompose cane-sugar in this way (Runge)

                             §144.
  Hydrofluosilicic Acid  (H F, Si F2).—Hydrofluosilicic acid is a very acid fluid,
when evaporated on platinum, it volatilizes completely as  fluoride of silicon and
hydrofluoric acid.  When evaporated on glass, it etches  the latter.  With bases it
forms water and  silico-fluorides of the metals, which are most of them soluble in
water, redden litmus paper, and are resolved upon ignition  into metallic fluorides
and fluoride of silicon.
  Chloride of barium  forms  a crystalline precipitate with hydrofluosilicic acid 
190
PHOSPHORIC ACID.
[§ 145.
(§ 98, 6).  Chloride of strontium and acetate of lead form no precipitates with thia
acid; salts  of potassa  precipitate transparent  gelatinous silico-fluoride of
potassium;  ammonia in excess precipitates hydrated silicic acid, with forma-
tion of  fluoride of ammonium. When metallic  silico-fluorides  are heated  with
concentrated sulphuric acid, a fuming mixture of hydrofluoric acid and fluoride of
silicon escapes.  If the experiment is conducted in a platinum vessel covered with
glass, the glass is etched (§ 149, 5).  The bases remain as sulphates.


Third  Division of the  First Group of  the Inorganic Acids.
                             §145.
                  a. phosphoric Acid (P Os).
  1. Phosphorus is usually  a colorless, transparent, solid body, of
2-089 specific gravity; it has  a waxy appearance.  Taken internally,
it acts  as  a virulent poison.  It fuses at 113°, and boils at 554° Fah.
By the  influence of light, phosphorus kept under water turns first
yellow, then  red,  and is finally covered with  a white  crust.   If
phosphorus  is  exposed  to the air, at the common temperature, it
exhales a characteristic, highly disagreeable odor, and gradually
oxidizes into phosphorous and  phosphoric acids.  At  the same
time, heavy fumes are formed  [which, according to Meissner, con-
sist of  antozone combined with water].   Exposed to  the air in the
dark,  phosphorus appears luminous.   Phosphorus  very readily
takes  fire spontaneously,  and burns with a luminous flame, being
converted into phosphoric acid, which  is dissipated for the most
part in  white fumes  through the surrounding air.  Nitric acid and
nitrohydrochloric acid  dissolve phosphorus pretty  readily upon
heating.  The  solutions contain at first, besides phosphoric acid,
also phosphorous acid.   Hydrochloric acid does not dissolve phos-
phorus ; if phosphorus is boiled with solution of soda or potassa, or
with milk of  lime,  hypophosphites and phosphates are formed,
whilst   spontaneously inflammable  phosphoretted hydrogen  gas
escapes.
  When  a substance containing unoxidized phosphorus, is placed
at the bottom  of a  flask, in  the body of which is hung, by means
of a loosely fitting cork, a slip of filter-paper moistened with solu-
tion of nitrate of silver, and  the whole is warmed to 85° to 100°
Fah., the  paper becomes black from the reducing action of even
the minutest traces  of phosphorus.   If, when the reaction is  com-
plete, the  blackened part of the paper is treated with boiling water,
the liquid, after removal of  silver by hydrochloric acid and filtra-
tion, gives on evaporation in the water-bath to a very small volume,
a solution in which phosphoric acid may be detected by the tests
below  described  (J. Scherer).   It must not be forgotten that a
blackening of  paper saturated with  silver solution, may also be
produced  by hydrosulphuric acid, formic acid, the volatile products 
§ 145.]
PHOSPHORIC ACID.
191
of putrefaction, &c.  The detection of phosphoric acid in the slip
of paper has no value as a test  for phosphorus unless the paper be
itself free from phosphates.  The deportment of phosphorus upon
boiling with dilute sulphuric acid,  and on  bringing into a vessel
from which hydrogen is evolved by the  action of zinc and dilute
sulphuric acid, is described, § 230.
   2. Anhydrous phosphoric acid is a white, snowlike mass, which
rapidly deliquesces in the air, and dissolves in water with a hissing
noise.   It forms with water  and bases, three different series  of
compounds: viz., with three equivalents of water or base, hydrate
of common phosphoric acid or common phosphates (tribasic) ; with
two equivalents of water or base, hydrate of pyrophosphoric acid
or pyrophosphates (bibasic); with one equivalent of water or base,
hydrate of metaphosphoric acid or metaphosphates (monobasic).
   The phosphates which we generally meet with in nature and in
analytical investigations belong, as a rule,  to  the  tribasic series;
we therefore make them alone  the object of a fuller study in this
place,  devoting a supplemental paragraph to a briefer considera-
tion of monobasic and bibasic phosphoric acids, and their salts.
   3. The hydrate of tribasic phosphoric acid  (3 H O, P 05)
forms  colorless and  pellucid crystals, which deliquesce rapidly in
the air to a syrupy non-caustic  liquid.  The action of heat changes
it into hydrated pyro- or metaphosphoric  acid, according as either
one  or two equivalents of water are expelled.  Heated in an open
platinum dish, the  hydrate of  common  phosphoric acid, if pure,
volatilizes completely, though with difficulty, in white fumes.
  4. The action of heat fails to decompose the tribasic phosphates
with fixed bases, but converts  them into pyrophosphates, if they
contain one  equivalent of basic water or ammonia, and into meta-
phosphates,  if they contain two equivalents.   The tribasic phos-
phates with alkaline base alone  are soluble in water, in the neutral
state.  The  solutions manifest  an  alkaline  reaction.  If  pyro-  or
metaphosphates are fused with carbonate of soda, the  fused mass
contains the phosphoric acid invariably in the tribasic state.
  5. Chloride  of barium produces in  aqueous  solutions of the
neutral or basic phosphates, but not in  solution of the hydrate, a
white precipitate of phosphate of baryta 2  Ba  O, H O, P 0.,;
or 3 Ba O,  P  05,* which is  soluble in hydrochloric acid and  in
nitric acid, but difficultly soluble in chloride  of ammonium.
  6.  Solution of sulphate of lime produces in neutral or  alkaline
solutions of phosphates, but not in solutions of the hydrate, a white
precipitate  of phosphate of lime (2 Ca O, H  O, P 05 or 3 Ca O,

  * Precipitates of the former composition are produced in solutions containing an
alkaline phosphate with two equivalents of a fixed base or ammonia; whilst precipi-
tates  of  the latter composition are formed in solutions which contain an alkaline
phosphate with three equivalents of a fixed base or ammonia. 
 192                   PHOSPHORIC ACID.                [§ 145.

 P 05) which  dissolves readily in acids, even in acetic acid, and to
 some extent in chloride of ammonium.
   7.  Sulphate of magnesia produces in  concentrated solutions of
 neutral phosphates a white precipitate of phosphate of magnesia
 (2 Mg O, H O, P 03 + 14 aq.), which  often  separates only  after
 some time ; upon boiling, however, a precipitate of basic salt (3 Mg
 0, P 05 -f 5 aq.) is thrown down immediately.  The latter precipi-
 tate forms also upon addition of sulphate of magnesia to the solu-
 tion of a basic alkaline phosphate.  But if sulphate of magnesia,
 mixed with a sufficient quantity of chloride of ammonium to leave
 the solution clear upon addition of ammonia,* is added to a solution
 of free phosphoric acid or of an alkaline phosphate, and  ammonia
 in excess is then added, a white, crystalline, and quickly subsiding
 precipitate of basic phosphate of magnesia  and ammonia (2 Mg
 O, N H, O, P 05 -f- 12 aq.) is formed,  even in highly dilute solu-
 tions.   This  precipitate  is insoluble in  ammonia and  most  spar-
 ingly soluble  in chloride of ammonium, but dissolves readily in
 acids, even in acetic  acid.  It makes its appearance often  only
 after the lapse of  some time ; stirring promotes its separation (see
 § 101, 7).  This reaction  is only  decisive in absence of  arsenic
 acid (§  136, 9).
  8. Nitrate of silver throws  down from solutions of neutral and
basic alkaline phosphates  a light-yellow precipitate of phosphate
 of silver (3 Ag O, P  05), which  is readily soluble in  nitric  acid
and in ammonia.   If the solution contained a basic phosphate, the
fluid in  which the precipitate is suspended manifests a neutral  reac-
tion ; whilst the reaction is acid if the solution contained a neutral
phosphate.  The  acid reaction in the  latter case arises from the
circumstance that the nitric acid receives for the 3 equivalents  of
oxide of silver which it yields to the phosphoric ao.d, only 2 eq. of
alkali and 1 eq. of water ; and as the latter does n-yt neutralize the
acid properties of  the nitric acid, the solution becomes acid.
  9.  If  to a solution containing phosphoric acid and the least possi-
ble excess of hydrochloric or nitric acid, a tolerably large amount of
acetate  of soda is added, and then a drop of sesquichloride of iron,
a yellowish-white, flocculent-gelatinous precipitate  of  phosphate
of  sesquioxide  of iron (Fea 03, P Os + 4 aq.) is formed.   An
 excess of sesquichloride of iron must be avoided,  as acetate of ses-
 quioxide of iron (of red color)  would thereby be formed, in which
the precipitate is not insoluble.  This reaction is  of  importance, as
 it enables us to detect  the phosphoric acid in phosphates  of the
 alkaline earths ; but only  in absence of arsenic acid, which exhibits
 the same behavior towards sesquichloride  of  iron.  To effect the
 complete separation of the phosphoric acid from the alkaline earths
* [See§ 136,9.] 
§ 145.]
PHOSPHORIC ACID.
193
 a sufficient quantity of sesquichloride  of iron is added to impart a
 reddish  color to the solution, which is  then boiled (whereby the
 whole of the sesquioxide of iron is thrown down, partly as phos-
 phate, partly as basic  acetate), and filtered hot.  The filtrate  con-
 tains the alkaline  earths  as chlorides.  If you wish to detect, by
 means of this reaction, phosphoric acid in presence of a large pro-
 portion of sesquioxide of  iron, boil the hydrochloric acid solution
 with sulphite of soda  until the sesquichloride is reduced to  proto-
 chloride, which reduction  is indicated by the  decoloration of the
 solution ; add carbonate of soda until the fluid  is nearly neutral,
 then acetate of soda, and finally one drop of sesquichloride of iron.
 The reason for this proceeding is, that acetate  of protoxide of iron
 does not dissolve phosphate of sesquioxide of iron.
  10. When 2 or 3 drops of a  neutral or acid  solution containing
 phosphoric acid, are poured into a test tube  filled to the depth of
 £ to 1 inch with solution of molybdate of ammonia  in nitric acid
 (§ 53), there  is formed in the cold, either immediately or after the
 lapse of a short time,  unless  the solution under  examination con-
 tains only a very minute amount of phosphoric acid, a pulverulent
 pale-yellow precipitate, which gathers upon the sides and bottom
 of  the tube. If the  precipitate does not  appear within a  few
 minutes, the  operator may  add cautiously and by degrees, more of
 the substance to be tested.   Only when the phosphoric acid is pre-
 sent in exceedingly minute quantity, e.  g., 0.00002 grm.,  is it
 requisite to wait  some hours and to apply  a  gentle heat, not to
 exceed 100° Fahr.,  before the precipitate appears.  When other
 coloring matters are not present, the liquid above the precipitate is
 colorless.  It is indispensable not to add too  much of the solution
 to  be  tested for phosphoric  acid, as the yellow precipitate is
 soluble in phosphoric and other acids (and therefore is not formed)
 unless a considerable excess of the molybdic solution be present.
 A yellow coloration of the  liquid is not to be regarded as proof of
 the  presence  of phosphoric acid.
  The  yellow  precipitate  (often termed  phospho-molybdate of
 ammonia) contains  molybdic acid, ammonia, water, and a  small
 amount (about 3 per cent.)  of phosphoric  acid.  Its formation is
 prevented not only by  excess of phosphoric acid, but likewise by
 certain organic  substances, e. g. tartaric acid.*  The precipitate is
 easily recognized even in dark-colored liquids, by giving it time to
 settle.  If it be washed with the same  molybdic solution  employed
in producing  it (in which it is  totally insoluble) and be then  dis-
solved in  ammonia, addition of a mixture of chloride of ammonium,
sulphate  of  magnesia and ammonia  to the solution will  throw
down phosphate of ammonia-magnesia.

          *  [This is probably a mistake as regards tartaric acid.]
                              ]3 
194
PHOSPHORIC  ACID.
[§ 146.
   By operating in the manner above described, there is no danger
of mistaking any  other substance for phosphoric acid; because,
arsenic acid  gives  in the cold, no precipitate with the  molybdic
solution,  though  a yellow precipitate is formed on heating and
especially on boiling  (the liquid  above the  arsenical precipitate
has a  yellow color), and  silicic acid does not react at all  in  the
cold, though  on  heating it causes a strong yellow  coloration, but
gives no precipitate.
   11. If a  finely  powdered substance  containing phosphoric acid
(or also a metallic phosphide) is intimately mixed with  5 parts  of
a flux consisting of 3 parts of carbonate  of soda, 1 part of nitrate
of potassa,  and 1 part of silicic acid, the mixture fused in  a pla-
tinum  spoon  or  crucible, the fused mass boiled with water, the
solution obtained  decanted, carbonate of ammonia added to it, the
fluid boiled again, and the silicic acid which is  thereby precipitated
filtered off,  the filtrate now  holds  in solution  alkaline  phosphate,
and may accordingly be tested for phosphoric  acid  as  directed  in
7, 8, 9, or 10.
   12.  White of egg is not precipitated by solution  of hydrate  of
tribasic phosphoric acid, nor  by solutions of  tribasic  phosphates,
mixed  with acetic acid.

                                 § 146.
                               Supplement.
  a.  Bibasic phosphoric acid.   The solution of the hydrate 2 H 0, P 05 is converted
by boiling into solution of the hydrate 3 H 0, P 0>  The solutions of the salts beai
heating without suffering decomposition; but upon boiling with a strong acid,  the
phosphoric acid  is converted  into the tribasic state.   If the salts are fused with
carbonate of soda in excess, tribasic phosphates are produced.   Of the neutral pyro-
phosphates only those with alkaline bases are soluble in water; the acid salts (e. g.,
Na 0, H 0, P 05) are  by ignition converted into metaphosphates (Na 0,  P  0S).
Chloride of barium fails to precipitate fhe free acid; from solutions  of the salts it
precipitates pyrophosphate op  baryta (2 Ba 0, P 0.5).   Nitrate of silver throws
down from a solution  of the hydrate, especially upon addition of an alkali, a white,
earthy-looking precipitate  of  pyrophosphate  of silver (2 Ag 0, P 03), which
is soluble in nitric acid and in ammonia.  Sulphate of magnesia  precipitates pyro-
phosphate op magnesia  (2 Mg 0, P 05).   The precipitate  dissolves in an excess
of the phosphate, as well as in an excess of the sulphate  of  magnesia.  Ammonia
fails to precipitate it  from these solutions.  Upon boiling the solution, it separates
again.   While of egg is not precipitated by solution of the hydrate, nor by solutions
of the salts, mixed with acetic acid.   Molybdate of ammonia, with addition of nitric
acid, fails to produce a precipitate.
  /?. Monobasic phosphoric acid.   Five sorts of  monobasic phosphates  are known,
and the  hydrates also of most of these have been produced.  The several reactions
by which to distinguish between  these I  will  not enter upon  here, and  confine
myself to the simple observation that the monobasic phosphoric acids differ from the
bibasic and tribasic phosphoric acids in this, that the solutions of the  hydrates of
the monobasic acids precipitate white of egg at once, and the solutions of their salts.
after addition  of acetic  acid.  Those hydrates  and salts which are precipitated by
nitrate of silver produce with that reagent a white precipitate.  A mixture of sulphate 
§ 147.]
BORACIC ACID.
195
 of magnesia, chloride of ammonium, and ammonia fails to precipitate the monobasic
 phosphoric acids and their salts, or produces precipitates soluble in chloride of
 ammonium.  All monobasic phosphates yield upon fusion with carbonate of soda
 tribasic phosphate of soda.
                              §  14V.
                    b. Boracic  Acid (B 03).
   1. Boracic acid, in  the anhydrous state,  is a  colorless, fixed
 glass,  fusible at a red heat; hydrate  of boracic acid  (H  O, B 03)
 is a porous, white mass; in the crystalline state (H O, B 03-f 2  aq.),
 it presents small scaly laminae.   It is soluble in water and in spirit
 of  wine; upon evaporating  the solutions, a large proportion of
 boracic acid volatilizes along with the aqueous and alcoholic vapors.
 The solutions redden  litmus-paper, and impart to turmeric paper a
 faint red tint, which acquires intensity upon drying.  The borates
 are not decomposed upon ignition ; those with alkaline bases alone
 are readily soluble in  water.  The  solutions are  colorless, and all
 of them, even those of the acid salts, manifest alkaline reaction.
  2. Chloride  of barium produces  in solutions of borates, if not
 too highly dilute,  a white precipitate of borate of baryta, which
 is soluble in acids and ammoniacal salts.   The formula of this pre-
 cipitate, when thrown down from  solutions of neutral borates, is
 Ba O, B 03 -f aq.;  when thrown down from solutions of  acid
 Dorates,  3 Ba O, 5 B 03 + 6 aq.  (H Rose.)
  3. Nitrate of silver produces in concentrated solutions of neutral
 borates  of the  alkalies  a white  precipitate,  inclining slightly to
 yellow from admixture of free oxide of silver (Ag O, B 03 +HO);
 in concentrated solutions  of acid borates, a white precipitate of
 3 Ag O, 4 B 03.  Dilute  solutions of borates give with nitrate of
 silver  a  grayish-brown precipitate  of oxide of  silver (H. Rose).
 All these precipitates  dissolve in nitric acid and in ammonia.
  4. If dilute sulphuric acid or hydrochloric acid is added to highly
 concentrated,  hot  prepared  solutions  of  alkaline borates,  the
 boracic  acid separates upon cooling, in the form of shining crys-
 talline  scales.
  5. If alcohol is poured over free  boracic acid or a borate—with
 addition, in the latter  case, of a sufficient quantity of concentrated
 sulphuric acid  to  liberate  the  boracic acid—and the alcohol  is
 kindled,  the  flame appears of  a very distinct yellowish-green
 color, especially upon  stirring the mixture ; this tint is imparted to
 the  flame by the  ignited boracic acid which volatilizes  with  the
 alcohol.   The  delicacy  of this reaction  may  be considerably
 heightened by heating the dish which contains the alcoholic mix-
ture, kindling the alcohol, allowing  it to burn for a  short time,
then extinguishing the flame, and afterwards rekindling it. At the
first flickering of the flame its borders will now appear green, even
though the quantity of the boracic  acid be  so minute that it fails 
196
OXALIC ACID.
[§ 148.
 to produce a perceptible coloring of the flame, when treated in the
 usual manner.   The sulphuric  acid employed must be concen-
 trated, and must be added  in  considerable quantity.  As
 salts of copper also impart a green tint to the flame  of alcohol, the
 copper which might be present must  first be removed by means of
 hydrosulphuric acid.  Presence of metallic chlorides also may lead
 to mistakes, as the chloride of ethyle  formed in that  case colors the
 borders of the flame greenish.
   6.  If the  solution of boracic  acid or of  an alkaline or earthy
 borate  is mixed with hydrochloric acid to slight, but distinct, acid
 reaction, and a  slip of turmeric paper is half dipped into  it, and
 then dried on a watch-glass  at 112° Fah., the dipped half shows a
 peculiar red tint (H. Rose).
   This reaction is  very delicate; care  must be taken not to con-
 found the characteristic red coloration with  the blackish-brown
 color which turmeric paper acquires  when moistened with rather
 concentrated hydrochloric  acid, and then dried or with the brown-
 ish-red occasioned by sesquichloride of iron or by acid solutions of
 molybdic acid [or the orange-red produced by acid solutions of
 zirconia.]
   When turmeric paper that has been reddened by boracic acid
 is moistened with solution of an alkali or alkaline  carbonate, its
 color passes into  bluish  or greenish-black.  Hydrochloric acid
 restores the red tint.   (A.  Vbgel, H  Ludwig.)
   7  If a substance containing boracic acid  is reduced to a fine
 powder, this, with  addition of a drop  of water, mixed with 3
 times its weight of a flux  composed  of A\ parts of bisulphate of
 potassa and  1 part of finely pulverized fluoride  of calcium, free
 from boracic acid, and the paste exposed on the loop of a platinum
 wire to the inner flame of the blowpipe, fluoride of boron escapes,
 which imparts to the flame—though only for a few  instants—a
 yellow-gfeen tint.   This  reaction may  be prpduced with  easily
 decomposable substances by moistening them with hydrofluosilicic
 acid and then bringing into the flame.

                             § 148-
                 c.  Oxalic Acid (C4 Og = O).

  1. The  hydrate  of oxalic acid  (2 H   O, C4 06)  is  a  white
powder; the crystallized acid (2 H  O, C4 O   + 4 aq.) forms color-
less rhombic prisms.  Both dissolve readily in water and in spirit
 of wine.  When heated   rapidly in open   vessels,  part of the
hydrated acid  undergoes  decomposition, whilst  another portion
volatilizes unaltered.  The  fumes of the volatilizing acid are very
 irritating  and provoke coughing.  If the hydrate is heated in a
 test-tube, the greater part of it sublimes unaltered. 
§ 148.]
OXALIC ACID.
197
   2.  All the oxalates undergo decomposition  at a red  heat, the
 oxalic acid being converted into carbonic acid and carbonic oxide.
 Those  with an  alkali or an  alkaline earth  for base are in this
 process converted  into carbonates  (if pure, almost  without sepa-
 ration of charcoal) ;  oxalate of magnesia  yields pure magnesia  on
 gentle ignition;  those with a metallic base leave either  the pure
 metal or the oxide behind, according to the greater or less degree
 of reducibility of the metallic  oxide.  The alkaline oxalates, and
 also some of the oxalates with metallic bases,  are soluble in water.
   3.  Chloride of barium produces in neutral solutions of oxalates
 a  white precipitate of oxalate of baryta  (2 Ba  O,  C, 06 + 2
 Aq.), which is  very slightly soluble in water, more largely in acetic
 or oxalic acid,  and in solution of chloride of  ammonium, easily in
 nitric acid and in hydrochloric acid.   From solution in the last
 named acids it is reprecipitated by ammonia unaltered.
   4.  Nitrate of silver produces in aqueous solutions of oxalic acid
 and alkaline oxalates a white precipitate of oxalate of silver
 (2 Ag  O, C4 Or,),  which  is  almost insoluble in water, difficultly
 soluble in dilute nitric acid, easily soluble in hot strong nitric acid
 and in ammonia.
   5.  Lime-xoater and all the soluble salts of lime, and consequently
 also  solution of sulphate  of lime,  produce in even highly dilute
 solutions of free oxalic acid or of oxalates, white, finely pulverulent
 precipitates of oxalate of lime (2 Ca  O,  C, 06 + 2 aq. and some-
 times 2 Ca O, C4 0G -f- 6 aq.) which dissolve readily in hydrochloric
 acid and in nitric acid, but are nearly insoluble in oxalic acid and
 in acetic acid, and almost totally insoluble in water.  The presence
 of salts of  ammonia does not  interfere  with the formation  of these
 precipitates.  Addition of ammonia considerably promotes the pre-
 cipitation of the free oxalic acid by salts of lime.  In highly dilute
 solutions the precipitate is only formed after some time.
   6. If hydrated oxalic acid (or an oxalate),  in the  dry state, is
 heated  with an excess of concentrated sulphuric acid, the latter
 withdraws from the oxalic acid its constitutional water, and thus
 causes its  decomposition into carbonic acid  and carbonic oxide
 (C4 Ofl = 2 CO -f- 2 CO,), the two gases escaping with effervescence.
 If the quantity operated upon is not too minute, the escaping car-
 bonic oxide gas m;iy be kindled ; it burns with a blue flame. Should
 the sulphuric acid acquire a dark color in this reaction, this is a proof
 that the oxalic acid contained some organic substance in admixture.
   7. If  oxalic acid or an oxalate is  mixed with some finely pulve-
 rized  binoxide of manganese (which must be free from carbonates),
a little  water added and  a few drops  of  sulphuric acid,  a  lively
effervescence ensues,  caused by the escaping carbonic acid:  2 Mn
O, +  C, O  +2 SO, = 2 (Mn  O SO,) + 4CO,.
  8.  If oxalates of  the alkaline earths are  boiled with a concentra- 
198                 HYDROFLUORIC ACID.              [§ 149

ted solution of carbonate of soda, and the fluid filtered, the  oxalic
acid is obtained in the filtrate in combination with soda, whilst the
precipitate contains the base as carbonate.  Some oxalates of the
heavy metals, e. g., oxalate of nickel, are not entirely decomposed
in this manner, soluble double oxalates being formed.   Sulphide of
ammonium or hydrosulphuric acid must, therefore, be employed to
separate these bases.

                            §149.
                d. Hydrofluoric Acid (H F).
   1. Anhydrous Hydrofluoric acid is a colorless, corrosive gas,
which fumes when exposed to the air,  and is freely absorbed by
water.  Aqueous hydrofluoric acid is distinguished from all other
acids by the exclusive property it  possesses of dissolving crystalliz-
ed silicic acid, and also the silicates which are insoluble in hydro-
chloric acid. Fluoride of silicon and water are formed in the pro-
cess of  solution  (2 H F + Si 02 = Si F2 -f- 2 H O).   Hydrofluoric
acid decomposes with metallic oxides in the same manner, metallic
fluorides and water being formed.
   2. The fluorides of the alkali metals are soluble in water ; the
solutions have an alkaline reaction. The fluorides of the metals of
the alkaline earths are either altogether insoluble in water, or they
dissolve in that menstruum only with very great difficulty. Fluoride
of aluminum is readily soluble.   Most of the fluorides correspond-
ing to the oxides of the heavy metals  are very difficultly soluble in
water, for instance, fluorides of copper, lead, and zinc ; many other
of the fluorides of the heavy metals dissolve in water without diffi-
culty, as, for instance, the sesquifluoride of iron,  protofluoride of
tin, fluoride of mercury, &c.  Many of the fluorides insoluble or
difficultly soluble in water dissolve in free hydrofluoric acid, others
do not.   Most of  the fluorides bear ignition in a crucible without
suffering decomposition.
   3.  Chloride of barium precipitates free hydrofluoric acid imper-
fectly, more completely the solutions  of alkaline fluorides ; the volu-
minous  white precipitate of Fluoride of Barium (Ba F) is quite
insoluble in water, but dissolves in a  large excess of hydrochloric
or nitric acid.  From these solutions it is thrown down incompletely
or not at all by ammonia, being somewhat soluble in ammonia salts.
   4.  Chloride of calcium produces in aqueous solutions of hydro-
fluoric acid or of fluorides a gelatinous precipitate of fluoride
of calcium (Ca F), which is so transparent, as at first to induce
the belief that the fluid  has remained perfectly clear.  Addition
of ammonia promotes the complete separation of the precipitate.
The precipitated fluoride  of calcium is  insoluble in water, is  very
slightly soluble in hydrochloric acid and nitric acid in the cold; it
dissolves somewhat  more largely upon boiling with hydrochloric 
§ 149.]
HYDROFLUORIC ACID.
199
acid.   Ammonia produces no precipitate in the solution, or only a
very trifling one, as the salt of ammonia formed retains it in solu-
tion.   It is scarcely more soluble in free hydrofluoric acid than in
water.  It is insoluble in alkaline fluids.
  5. If a finely pulverized fluoride, no matter whether soluble  or
insoluble, is treated in a platinum  crucible with just enough con-
cent rated sulphuric acid to make a thin paste, the crucible covered
with  the  convex  face of a watch-glass of hard glass coated with
bees-wax,*  which  has been removed  again in some places by
tracing lines in it with a pointed bit of wood, the  hollow of the
glass filled with water, and the crucible gently heated for the space
of half an hour or an hour, the exposed lines will, upon the removal
of the  wax, be found  etched into the  glass.  If the quantity of
hydrofluoric acid disengaged by the sulphuric acid was very minute,
the etching is often invisible upon  the removal of the wax; it will,
however, in such  cases  reappear when the plate is breathed upon.
This  reappearance  of the etched  lines is owing to the unequal
capacity of condensing water which the etched and the untouched
parts of the plate respectively possess.
  The appearance of lines, after breathing on the glass, is not neces-
sarily evidence of  the presence of hydrofluoric acid  in the  sub-
stance under examination, unless they can be reproduced after the
glass has been rinsed, dried and wiped, though their  non-appear-
ance  is proof of its absence.
  This reaction (5) fails if there is too much silicic acid  present,  or
if the body under  examination  is not  decomposed by sulphuric
acid.   In such cases the one or the  other of the  two following
methods is resorted to, according to circumstances.
  G. If we have to deal with a fluoride decomposable by sulphuric
arid,  but  mixed with a large proportion of silicic acid,  the fluorine
in it  may be detected by heating the  mixture in a test-tube with
concentrated sulphuric acid, as  fluosilicic gas is evolved in this
process, which forms dense white fumes in moist air.  If the gas is
conducted into water, through a bent tube moistened  inside, the
latter has its transparency more or less impaired, by the separation
of silicic acid.   If the  quantity operated upon is rather considera-
ble, hydrate of silicic acid separates in  the water, and  the fluid is
rendered  acid by hydrofluosilicic acid.

  * The coating with wax may be  readily effected by heating the glass cautiously,
putting a small piece of wax upon  the convex face, and spreading the fused mass
equally over it. The  removal of the wax coating is effected by heating the glass
gently, and wiping the wax off with a cloth.
  f  The statement of  Nickles, that sulphuric acid and all acids adapted to decom-
pose fluorides, etch glass, I have not been able to confirm when employing Bohemian
glass.  It is, however, advisable to  prove by trial that the sulphuric acid one usea
really does not attack the glass. 
200
HYDROFLUORIC ACID.
[§ 149.
  The following process answers best for the detection of smaller
quantities of fluorine.   The substance is heated with concentrated
sulphuric acid in a flask closed by a perforated cork bearing two
tubes.   Through one tube which should reach nearly to the bottom
of the flask, is passed a  slow current of dried air which finds exit
through the other short tube, and is made then to stream through
some ammonia contained in a U tube by attaching the latter to an
aspirator.  The fluoride of silicon carried over by the stream of air,
is decomposed on reaching the  ammonia, especially when the  latter
is heated, fluoride of ammonium  and hydrated silica being formed.
The liquid is filtered, the filtrate is evaporated to dryness in a plati-
num crucible and the residue tested according to 5.
  In the  case of more difficultly decomposable substances  bisul-
phate of potassa is used instead of sulphuric acid, and the mixture,
to which some marble is likewise added, heated to fusion, and kept
in that state for  some time.
  7. Compounds not decomposable by sulphuric acid must first be
fused with four parts of carbonate of soda and potassa.  The fused
mass is treated with water, the  solution filtered, the filtrate concen-
trated  by evaporation, allowed to cool,  transferred to a platinum
or silver vessel, hydrochloric acid added to feebly  acid  reaction,
and the fluid allowed to stand until the  carbonic acid has escaped.
It  is then supersaturated  with ammonia, heated, filtered into a
bottle, chloride of calcium added to the still hot  fluid, the bottle
closed, and  allowed to stand  at  rest.  If a precipitate separates
after some time, it is collected  on a filter, dried, and examined by
the method described in 5.   (H. Rose.)
  8. Minute quantities of metallic fluorides in minerals, slags, &c,
may also be readily detected by means  of the blowpipe.  To this
end, bend a piece of platinum foil, gutter-shape, then insert it in a
   ,ramisi!=____==_[ra___         glass tube as shown in Fig. 29,
  H!^^/                  "THi  introduce  the  finely triturated
                                 substance mixed with powdered
              Fi„ 29.              phosphate of soda and ammo-
                                 nia  fused  on charcoal, and let
the blowpipe flame  play upon it in a manner to make the products
of combustion pass into the tube.  If fluorides of metals are pre-
sent, hydrofluoric acid gas  is evolved, which  betrays its  presence
by its pungent odor, the dimming of the glass tube, and the yellow
tint which the acid air issuing from the  tube imparts to a moist
slip of Brazil-wood paper* (Berzelius, Smithson).  When silicates
containing metallic fluorides are treated  in  this manner, gaseous
fluoride  of silicon is formed, which also colors yellow a moist slip

  * Prepared by moistening slips of fine printing-paper with decoction of Brazil
wood. 
§ 150.]
RECAPITULATION.
201
of Brazil-wood paper inserted in the tube, and leads to silicic acid
being deposited within the tube.  After washing  and drying the
tube, the latter appears here and there dimmed.  In the case of
minerals containing water, presence of even a small proportion of
metallic fluorides  will, upon heating, even without  addition of
phosphate  of soda  and  ammonia,  usually  suffice  to color yel
low  a moistened slip of Brazil-wood paper  inserted in the tube
(Berzelius).

                             §  150.
  Recapitulation and remarks.—The baryta  compounds of the
acids of the third  division  are dissolved  by hydrochloric acid,
apparently without undergoing  decomposition; alkalies therefore
reprecipitate them unaltered, by neutralizing the hydrochloric acid.
The  baryta  compounds of chromic, sulphurous,  hyposulphurous,
and  iodic acids show, however, the same deportment; these acids
must, therefore, if  present, be removed before any conclusion
regarding  the  presence of phosphoric acid, boracic  acid, oxalic
acid, or hydrofluoric acid, can be  drawn from the reprecipitation
of a salt of baryta by alkalies.  But even leaving this point alto-
gether out of the question, no great value is to be  placed on this
reaction, not even so far as the simple detection of these acids is
concerned, and far less still as regards their separation from other
acids, since ammonia fails to reprecipitate from hydrochloric acid
solutions the salts of baryta in question, and more particularly the
borate of baryta and the fluoride of barium, if the solution con-
tains any considerable proportion  of free acid or of an ammoniacal
salt.  Boracic acid may be invariably detected by the characteris-
tic tint Avhich it communicates to  the flame of alcohol, as well as
by its reaction with turmeric paper.   The latter reaction is particu-
larly adapted to detect minute quantities.  Care should be  taken
to concentrate the solution sufficiently before testing.   Solutions of
free  boracic acid must be combined with an  alkali before  evapora-
ting, otherwise a large portion of the acid will volatilize along with
the aqueous vapors.  Metallic oxides, if present, should be removed,
which may be done by hydrosulphuric acid or sulphide of ammo-
nium.
  The detection of phosphoric acid in compounds soluble in water
is not difficult;  the reaction with  sulphate of magnesia is the best
adapted to effect the purpose.  To compounds which are insoluble
in water,  sulphate of magnesia  cannot be applied.   In phosphates
of the alkaline earths, phosphoric acid may be detected and sepa-
rated by means of sesquichloride  of iron (§  145, 9).  In  presence
of alumina and sesquioxide of iron, solution of molybdate of ammo-
nia  in nitric acid is best employed.  Both  reagents must be used
strictly according to the directions already given (§ 145, 9 and 10), 
202                  PHOSPHOROUS  ACID.                [§ 151

if satisfactory results are looked for.  Phosphates of the oxides of
groups 4, 5, or  6, may be treated either as described, § 145, 11 or
the base being thrown down by hydrosulphuric acid or sulphide of
ammonium, the acid may be looked for ii»the filtrate.
   Oxalic acid may always be easily detected in aqueous solutions
of alkaline oxalates by solution of sulphate  of lime.  The forma-
tion of a finely pulverulent precipitate, insoluble in  acetic  acid,
leaves hardly a doubt on the point, as racemic acid alone, which
occurs so very rarely, gives  the same reaction.  In case  of doubt,
the oxalate of lime may be readily distinguished from the para-
tartrate, or racemate, by simple ignition, with exclusion  of the air,
as the decomposed paratartrate leaves a considerable proportion of
charcoal behind ;  the paratartrate dissolves moreover  in cold solu-
tion of potassa  or soda, in which oxalate of lime is insoluble.  The
deportment of the oxalates  with  sulphuric acid, or with binoxide
of manganese and sulphuric acid, affords also sufficient means to
confirm  the  results  of other tests.   In insoluble salts the oxalic
acid is detected most safely by decomposing the insoluble  com-
pound by boiling with solution of carbonate of soda, by hydrosul-
phuric acid or sulphide of ammonium, according to circumstances.
(See § 148, 8).  I must finally call attention here  to the fact that
there are certain soluble oxalates which are not  precipitated by
salts  of  lime; these are more  particularly oxalate of sesquioxide
of  chromium, and oxalate of  sesquioxide of iron.  Their  non-
precipitation  is owing to the circumstance that  these  salts  form
soluble double salts with oxalate of lime.  In salts decomposable
by sulphuric acid, the hydrofluoric acid is readily detected;  only,
it must be borne in mind that too much sulphuric acid hinders the
free escape of hydrofluoric acid gas, and thus impairs  the  delicacy
of the reaction, and that the glass cannot  be distinctly etched, if,
instead of hydrofluoric gas, fluosilicic gas alone is evolved. There-
fore, in the case of compounds abounding in silica, the safer way is
to try, besides  the reaction given § 149, 5, also the one given in
§ 149, 6.  In silicates which  are not decomposed by sulphuric acid,
the presence of fluorine is often overlooked, because the analyst omits
to examine the  compound carefully by the method given §  149, 7.

                             §  151.
  Phosphorous acid (P 03), when anhydrous, is a white powder which may be
sublimed in close vessels but burns if heated in contact with the air.  In combina.
tion with water it  forms  a syrupy liquid. On long standing it crystallizes, when
heated it decomposes into hydrated phosphoric  acid and non-spontaneously inflam-
mable phosphoretted hydrogen gas.  It is easily soluble  in water.  Its salts with
alkaline bases are readily soluble in water, the  other  phosphites are with difficulty
dissolved by water, but easily by dilute acids.  On ignition, the phosphites are
converted into phosphates, hydrogen gas or a mixture of hydrogen and phosphoretted
hydrogen being evolved.  With nitrate of silver, especially on  addition of ammonia 
§ 152.]
CARBONIC ACID.
203
and warming, they cause reduction and separation of metallic  silver  with  nitrate
of protoxide of mercury, under similar circumstances, separation of metallic mercury.
From sdu tion of chloride of mercury in excess, phosphorous acid, after some time, more
speedily on heating, throws down subchloride of mercury.  Chloride of barium and
chloride of calcium with addition  of ammonia, yield in moderately dilute solutions,
white precipitates  which are soluble in acetic acid.  A  mixture of sulphate  of
magnesia, chloride  of ammonium and ammonia precipitates only somewhat concen-
trated  solutions.  Acetate of lead throws down white phosphite of  lead which is
insoluble in acetic acid. When phosphorous  acid  is heated to boiling with excess
of sulphurous acid, sulphur separates  and phosphoric acid is produced.  Phosphorous
acid when placed in contact with zinc and dilute sulphuric acid, evolves a mixture
of  hydrogen  and phosphoretted hydrogen which smokes in the air, burns with an
emerald green flame and throws down phosphide of silver from a solution of nitrate
of  silver.

    Fourth Division of the First Group of Inorganic Acids.
                              §152.
                    a.  Carbonic Acid (C (X).
   1. Carbon is a  solid, tasteless, and inodorous body.   The very
highest degrees of heat alone can effect its fusion and volatilization
(Silliman, Despretz).   Carbon is combustible, and yields carbonic
acid when burnt with a sufficient supply of oxygen or atmospheric
air.  In the diamond the carbon is crystallized, transparent, exceed-
ingly hard, difficultly combustible; in the form  of graphite, it is
opaque, blackish-gray, soft, greasy to  the touch, difficultly combusti-
ble, and stains the fingers; as charcoal, produced by the decomposi-
tion (destructive distillation) of organic matters, it is black, opaque,
noncrystalline—often dense, shining,  difficultly combustible—often
porous, dull, readily combustible.
   2. Carbonic acid,  at the common temperature and common
atmospheric  pressure,  is  a  colorless gas of  far higher specific
gravity than  atmospheric air, so that it  may be poured from one
vessel into another.   It is almost inodorous, has  a sourish  taste,
and reddens moist litmus-paper; but the red tint  disappears again
upon drying.   Carbonic  acid is readily  absorbed by solution  of
potassa; it dissolves pretty copiously in water.
   :i. The aqueous solution of carbonic acid has a feebly acid,
pungent taste ; it transiently imparts  a red tint to litmus-paper, and
colors solution of litmus wine-red ; it loses its carbonic acid upon the
application of heat, and also  when shaken with air in a half-filled
bottle.   Many  of the  carbonates lose  their carbonic  acid upon
ignition; those with  colorless oxides are white or colorless.   Of
the neutral carbonates, only  those with  alkaline bases are soluble
in  water.  The solutions manifest a  very strong alkaline reaction.
Besides the  carbonates with alkaline bases, those also with  an
alkaline earth  for  base, and  some of those  with  a metallic base,
dissolve as acid or bicarbonates. 
204                     silicic acid.                  [§ 153.

  4. The carbonates are decomposed by all free acids soluble  in
water, with the exception of hydrocyanic acid  and hydrosulphuric
acid.   The decomposition  of the  carbonates by acids is attended
with  effervescence, the  carbonic  acid being disengaged as a
colorless and  almost  inodorous gas,  which transiently imparts a
reddish tint to litmus-paper.  It is necessary to apply the decom-
posing acid in excess, especially when operating upon carbonates
with alkaline  bases, since the formation of bicarbonates  will fre-
quently prevent effervescence, if too little of the decomposing acid
be  added.   Substances which  it is intended to test for  carbonic
acid by this method, should first be heated with a little water,  to
prevent any mistake  which might arise from the escape  of air-
bubbles upon treating the  dry substances with the  acid.  Lime-
water may be substituted for pure water if it is feared that carbonic
acid will escape  on boiling.  If it is wished  to determine by a
direct  experiment whether  the disengaged gas is  really carbonic
acid or not, this may be  readily accomplished  by dipping the end
of a glass rod in baryta-water, and inserting the rod into the test-
tube, bringing the moistened end near the surface of the fluid in
the tube, when ensuing turbidity of the  baryta-water on  the glass
rod will prove that the evolved gas is really carbonic acid, since
  5. Lime-water and baryta-water, when brought into contact with
carbonic acid or with soluble carbonates, produce  white preci-
pitates of neutral carbonate  of lime  (Ca O, C  0-2), or neutral
carbonate of bartta  (Ba O, C 0^).  When testing for free
carbonic acid, the reagents ought always to be added in excess, as
the acid carbonates of the  alkaline  earths are soluble in water.
The precipitated carbonates of lime and baryta dissolve in acids,
with  effervescence, and  are not reprecipitated from such solutions
by  ammonia, after the complete expulsion  of the carbonic acid  by
ebullition.
  Since a  minute quantity of carbonate  of lime  is taken up  by
lime-water, the latter should be saturated with carbonate of lime
by  continued digestion  with it for some time before being em-
ployed for  detecting very small traces of  carbonic acid.—( Welter,
Berthollet.)
  6.  Chloride of calcium and chloride of barium immediately pro-
duce  in solutions of neutral alkaline carbonates,  precipitates  of
carbonate of lime or of carbonate  of baryta ; in dilute solu-
tions of bicarbonates these precipitates are formed  only upon ebul-
lition ; with free carbonic acid these reagents give  no precipitate.

                             § 153.
                     b.  Silicic Acid (Si 02).
   1.  Silicic acid is colorless or white, even in the hottest blowpipe
flame unalterable and infusible. It fuses in the flame of the oxyhy- 
 §  153.]                   silicic  acid.                      205

 drogen blowpipe.   It is met with in two modifications (more cor-
 rectly speaking, in the crystalline and in the amorphous state).   It
 is insoluble in water and acids, with the exception of hydrofluoric
 acid ;  whilst its hydrate is soluble in acids, but only at the moment
 of its  separation.   The amorphous silicic acid and the hydrate dis-
 solve in hot aqueous solutions of caustic alkalies and  of fixed alka-
 line carbonates ;  but the crystallized acid is insoluble or  nearly so
 in these fluids.  If either of the two is fused with pure alkalies or
 alkaline  carbonates, a basic silicate of the alkali is obtained, which
 is soluble in water.  The silicates with  alkaline bases  alone are
 soluble in water.
   2. The solutions  of the alkaline  silicates are decomposed by all
 acids.    If  a large proportion of hydrochloric acid is  added  at
 once to even concentrated solutions of alkaline silicates,  the sepa-
 rated silicic acid remains in solution;  but if the hydrochloric acid
 is added gradually drop by drop,  whilst stirring the fluid, the
 greater part of the silicic acid separates as  gelatinous hydrate. The
 more dilute the fluid, the more silicic acid remains in solution, and
 in highly dilute solutions no precipitate is formed.  But if the solu-
 tion of an alkaline silicate, mixed with hydrochloric or nitric acid
 in excess, is evaporated  to dryness, silicic acid separates in propor-
 tion as the acid escapes; upon treating the residue with hydrochlo-
 ric acid and water,  the silicic acid remains  in  the free state (or, if
 the temperature in the process of drying was restricted to 212°, as
 hydrate, II  O, 4 Si O.), as an insoluble white powder.  Chloride of
 ammonium produces in moderately dilute solutions of alkaline sili-
 cates precipitates of hydrate of  silicic acid containing alkali.  The
 separation is facilitated by warming.
   3. Part of the  silicates insoluble in  water are decomposed by
 hydrochloric acid or nitric acid, part of them are not affected by
 these acids, not even upon boiling.  In  the decomposition of the
 former, the greater  portion  of  the silicic acid separates usually as
 gelatinous, more rarely as pulverulent hydrate.  To effect the com-
 plete separation of the silicic acid,  the hydrochloric  acid  solution,
 wilh the precipitated hydrate of silicic acid suspended in  it, is eva-
 porated to dryness,  the residue heated at a temperature somewhat
 above the boiling point  of water until no more acid fumes escape,
 then moistened with hydrochloric acid, heated with water, and the
 fluid containing the  bases filtered from the residuary insoluble silicic
 acid.
  4. Of the silicates not decomposed by hydrochloric acid, many,
e. g., kaolin, are completely decomposed by heating with a mixture
of 8 parts of hydrated sulphuric acid and three parts of water, the
decomposition being attended with separation of silicic acid in the
pulverulent form;  many others are acted upon  to some extent by
this reagent. 
206
SILICIC ACID.
[§153
   5. If any silicate, reduced to a fine powder, is fused with 4 parts
of carbonate of potassa and soda until the  evolution of carbonic
acid has ceased, and the fused mass is then boiled with  water, the
greater portion of  the silicic acid  dissolves as alkaline  silicate,
whilst the alkaline earths, the earths  proper (with the exception of
alumina and glucina, which are more or  less perfectly  dissolved),
and the heavy metallic oxides are left behind.  If the fused mass
is treated with water,  then, without previous filtration,  hydrochlo-
ric or nitric acid added to  strongly  acid  reaction, and the fluid
evaporated to dryness  as directed in 3,  the silicic acid is left undis-
solved, whilst the bases are dissolved.  If the powdered silicate is
fused with 4 parts of  hydrate of baryta, the fused mass  digested
with water, with addition  of hydrochloric  or nitric acid, and the
acid solution evaporated to dryness as directed in 3, the  silicic acid
separates, and the  bases,  especially the  alkalies, are found in the
filtrate.
   [6. If an insoluble  alkaline silicate is mixed in the state of powder
with 3 times its weight of precipitated carbonate of lime  and one-
half its weight of chloride of ammonium in powder, and the mix-
ture is heated  in a  platinum crucible  in a  slow charcoal fire for
half an hour, too high a heat being  avoided, a somewhat sintered
mass is obtained, which, on  being digested in hot  water, falls to
powder, and yields  a  solution containing, besides chloride of cal-
cium and hydrate of lime,  all, or nearly all the  alkalies  of the sili-
cate, in the form of  chlorides.—(J. Lawrence Smith) ]
   7. When hydrofluoric acid, in concentrated aqueous  solution or
as gas, is allowed to act on silicic  acid, gaseous fluoride of silicon
is formed (Si 02 +  2 H F  = Si F2 + 2 H O) :  dilute hydrofluoric
acid dissolves silica to hydrofluosilicic acid (Si 02 + 3 H  F = Si F„
H F 4- 2 H O).  By the action of hydrofluoric  acid upon silicates,
silicofluorides are produced (Ca O, Si 02 -f 3 H F = Si F2, Ca F, +
3 II O), which when heated with strong sulphuric acid are  con-
verted into  sulphates with  evolution of  hydrofluoric acid  and
fluoride of silicon.   If the powdered silicate is  mixed with 5 parts
of fluoride of calcium in  powder, the  mixture made into a paste
with hydrated sulphuric acid, and heat  applied (best in the open
air), until no more  fumes escape, the whole of the silicic acid pre-
sent volatilizes as fluosilicic gas.  The  bases present are found, in
the residue as sulphates, mixed with  sulphate of lime.
   8. If silicic acid or a silicate  is fused with carbonate of soda on
the loop of  a platinum wire, a frothing 'is  observed in the fusing
bead, owing to the disengagement of carbonic acid.  If the proper
proportion of carbonate of soda is not exceeded, the bead of silicate
of soda formed in the  process will remain transparent on cooling.
   9. Phosphate of  soda and  ammonia, in  a state of fusion, fails
nearly altogether to dissolve  silicic acid.  If therefore  silicic acid 
§§ 151, 155.]        HYDROCHLORIC ACID.                 207

or a silicate is heated, in small fragments, with phosphate of soda
and ammonia on a platinum wire, the bases  are dissolved, whilst
the silicic acid separates and floats about in the clear bead, as a
more or less transparent mass, exhibiting the shape of the fragment
used in the experiment.

                             § 154-
  Recapitulation and  remarks.—Free  carbonic  acid is readily
known by  its deportment with lime-water; the carbonates  are
easily detected by the evolution of a nearly inodorous gas, which
takes  place when they are treated with acids.  When operating
upon compounds which, besides carbonic  acid, evolve other gases,
the disengaged gas is to be tested with lime-water or baryta-water.
Silicic acid, both in the free state  and in  silicates, may usually be
readily  detected by the  reaction with phosphate of  soda and
ammonia.  It  differs, moreover, from all other bodies in the form
in which it is always  obtained  in analyses,  by its insolubility in
acids (except hydrofluoric acid), and in fusing bisulphate of potassa,
and its solubility in boiling solutions of pure alkalies and alkaline
carbonates.  It  also differs from many bodies by its completely
volatilizing when repeatedly evaporated in a platinum dish with
hydrofluoric acid or a mixture of fluoride of ammonium and  sul-
phuric acid.

            second group of the inorganic acids.
Acids which are precipitated by Nitrate of Silver, but not
  by  Chloride  of Barium :  Hydrochloric  Acid,  Hydrobromic
  Acid,  Hydriodic Acid,  Hydrocyanic Acid, Hydroferro-, and
  Hydroferricyanic Acid, Hydrosulphuric Acid.   (Nitrous acid,
  Hypochlorous acid, Chlorous acid, Hypophosphorous acid.)
  The  silver compounds corresponding  to the hydrogen  acids of
this group are insoluble in dilute nitric  acid.   These acids decom-
pose with metallic oxides, the metals combining with the chlorine,
bromine, cyanogen, iodine, or sulphur,  whilst  the  oxygen of  the
metallic oxide forms water with the hydrogen of the hydracid.

                             §155.
                a. Hydrochloric Acid (H CI).
  1. Chlorine is a heavy, yellowish-green gas of a disagreeable,
suffocating  odor, and which has a  most  injurious action upon  the
respiratory organs; it  destroys vegetable colors  (litmus, indigo-
blue, <fcc.); it is incombustible, and supports the combustion of few
bodies  only.  Minutely-divided antimony, tin, &c, spontaneously
ignite in it, being converted  into chlorides.   It  dissolves  pretty
largely in water ;  the chlorine water formed has a faint yellowish- 
208
HYDROCHLORIC ACID.
[§ 155,
green color, smells  strongly of the gas, bleaches vegetable colors,
is  decomposed by the action of light (§ 2V), and loses its odor
when shaken with mercury ;  in this process the latter is converted
into a mixture of subchloride and metallic mercury.   Small quan-
tities of chlorine may be readily detected in a fluid, by adding the
latter to a solution of pure protoxide of iron, mixed with sulpho-
cyanide of potassium: the solution is at once colored red by the
action of the free chlorine ;—or, in the absence of nitrous acid, by
adding the fluid to  a dilute solution of iodide of potassium, mixed
with starch-paste.   (See § 157, 9.)
   2. Hydrochloric acid, at the common temperature and common
atmospheric pressure, is a colorless gas, which  forms dense fumes
in the air, is  suffocating and very irritant, and  dissolves in water
with exceeding facility.   The more concentrated solution  (fuming
hydrochloric acid) loses a large portion of its gas upon heating.
   3. The neutral metallic chlorides are readily soluble in water,
with the exception  of chloride of lead, chloride of silver, and sub«
chloride of mercury ; most of the chlorides are white or colorless.
Many of them volatilize at a  high temperature, without suffering
decomposition;  others  are decomposed upon ignition,  and many
of them are fixed.
   4. Nitrate of silver produces in even  highly dilute solutions of
free hydrochloric acid or of metallic chlorides  white precipitates
of chloride of  silver (Ag  CI), which upon exposure  to light
change  first to violet, then to black; they are insoluble in nitric
acid,  but dissolve  readily in  ammonia,  as  well as in cyanide of
potassium, and fuse without decomposition, when  heated.  (Com-
pare § 118, 7).
   5. Nitrate of suboxide of'mercury and acetate of lead  produce
in solutions containing free hydrochloric acid or metallic chlorides
precipitates of subchloride of  mercury (Hg, CI) and chloride
of lead  (Pb CI).   For the properties of these  precipitates see
§  119, 6, and § 120,7.
   6. If hydrochloric acid is heated with binoxide of manganese,
or a chloride with  binoxide of manganese and  sulphuric acid,
chlorine gas is  evolved, which may be readily recognised by its
yellowish-green  color, its odor and  its  bleaching  action on
vegetable  colors.  To observe the  last named effect, a slip of
moistened litmus-paper is exposed to its  action.
   7. If a metallic chloride is triturated together wi'h chromate of
potassa, the mixture treated  with concentrated sulphuric acid in
a tubulated retort,  and a gentle heat  applied, a deep brownish-red
gas is copiously evolved (chloro-chromic acid (Cr  02 CI), which
condenses into a fluid of the  same color, and passes over into the
receiver.   If this distillate is  mixed with ammonia in excess, a
yellow-colored liquid is produced; the  yellow tint is imparted to 
§ 156.]
HYDROBROMIC ACID.
209
 the fluid by the chromate of ammonia which  forms in this process
 (Cr 02 CI -f 2 N 11^ O = N H4 CI 4- N H4 O,  Cr Oa); upon  the
 addition of an acid, the color of the solution  changes to a reddish
 yellow, ow7ing to the formation of acid chromate of ammonia.
   8. In the metallic chlorides insoluble in water and nitric acid,
 the chlorine is detected by fusing them with  carbonate of soda
 and potassa, and treating the fused mass with water, which will
 dissolve, besides the excess  of the alkaline carbonate, the chloride
 of the alkali metal formed in the process of fusion.
   9. If in  a bead  of phosphate of soda  and ammonia on  a pla-
 tinum wire, oxide  of copper be  dissolved in the outer blowpipe
 flame in sufficient quantity to make the mass nearly opaque, a trace
 of a substance containing chlorine added to it while still in fusion,
 and the bead then exposed to the reducing flame, a fine  blue-
 colored flame, inclining to  purple, will  be seen encircling it so
 long as chlorine is present (Berzelius).

                             §156.
                b.  Hydrobromic Acid  (H Br).
   1. Bromine is a heavy, reddish-brown fluid, of a very disagreea-
 ble chlorine-like odor; it boils at 116-6° F., and volatilizes rapidly
 even  at  the common  temperature.  The  vapor  of bromine is
 brownish-red.  Bromine bleaches  vegetable colors  like  chlorine;
 it is rather difficultly soluble in water, but dissolves more easily in
 alcohol, and very readily in ether.  The solutions are yellowish-red.
   2. Hydrobromic acid gas, its aqueous solution and the metal-
 lic bromides offer in their general deportment a great analogy to
 the corresponding chlorides.
   3. Nitrate of silver produces  in  aqueous  solutions of hydro-
 bromic acid or  of bromides  a yellowish-white precipitate of bro-
 mide of silver (Ag Br), which changes to gray upon exposure to
 light; this  precipitate is insoluble in nitric acid,  and somewhat
 difficultly soluble in ammonia, but dissolves with facility in cyanide
 of potassium.
   4. Nitrate of protoxide of palladium, but not protochloride of
 palladium,  produces in neutral solutions of metallic bromides  a
 reddish-brown precipitate of protobromide of palladium (Pd
 Br).  In concentrated solutions this precipitate is formed imme-
 diately, in dilute solutions it makes its appearance only after stand-
 ing some time.
   5. Nitric acid decomposes hydrobromic acid and the bromides,
 v, ith the exception  of bromide of silver and bromide of mercury,
 upon the application of heat, and liberates the bromine, by oxidi-
zing the hydrogen or the metal.  The liberated bromine colors the
solution yellow or yellowish-red.  When operating upon bromides
in  the solid state, brownish-red (if diluted, brownish-yellow) vapors
                              14 
 210                  HYDROBROMIC ACID.               [§ 156.

 of bromine escape,  which, when  evolved in. sufficient quantity,
 condense in the cold part of the test-tube to small drops.   In the
 cold, even  red fuming nitric acid as well  as  solution of peroxide
 of nitrogen in hydrated sulphuric acid, or  a mixture  of hydro-
 chloric acid  and nitrite of potassa, fail to  liberate the bromine
 contained in rather dilute solutions of metallic bromides.
   6. Chlorine, in  the  gaseous state or in solution, immediately
 liberates bromine in the  solutions of its compounds; the fluid
 assuming a yellowish-red tint, if the quantity of the bromine pre-
 sent is not too minute.   A  large excess of chlorine is to be avoided
 since  it nearly or quite discharges  the  color by forming chloride
 of bromine.  This reaction becomes far more sensitive by adding
 to the mixture some liquid  which dissolves  the bromine and at the
 same time does not mingle with the water, such as bisulphide of
 carbon or chloroform.  The neutral or slightly acid solution of the
 substance under examination  is placed in a test-tube, and a little
 of one of the above-mentioned liquids is poured in, which gathers
 as a globule at the bottom ; dilute chlorine water is then added,
 drop by drop, the whole being agitated.   When bromine is present
 in considerable quantity (e.g., 1 of bromine to  1000 of water),
 the  globule  acquires a reddish-yellow  color,—with very  minute
 quantities (e. g., 1 of bromine to 30,000 of water),  it still has a per-
 ceptible  pale-yellow tint.  Ether is far  less adapted to this test.
 In these experiments also,  a large  excess  of chlorine water must
 be avoided, and  this reagent  is only applicable, if when  shaken
 with much water and some bisulphide of carbon or chloroform it
 communicates no color  to the  latter.  If the solution of bromine
 in bisulphide  of carbon, chloroform (or ether) is mixed with some
 solution of  potassa, and the mixture shaken, the yellow tint disap-
 pears,  and the solution  now contains bromide of potassium and
 bromate of potassa.  Upon evaporation  and subsequent ignition
 of the residue, the bromate of  potassa is converted into bromide
 of potassium, and the ignited mass may then be further tested as
 directed in 7.
   7. If bromides are heated with binoxide of manganese and con-
 centrated sulphuric acid, brownish-red vapors of  bromine  are
 evolved.   Presence of large quantities  of metallic chlorides is un-
favorable to this reaction, and  makes it necessary to add a little
 water,  and to apply the  sulphuric acid repeatedly, but in very small
proportions, until the bromine vapors appear.  If the bromine is
present only in very minute quantjty, the color of these vapors is
not visible.  The experiment should, in that case, be conducted in
a small retort, and the  evolved  vapors transmitted through a long
glass condensing  tube;  generally, the color will be perceptible by
looking lengthwise through the tube. The first drops of the distillate
 will  also appear yellow.  These and the vapors that first go over 
 § 157.]                HYDRIODIC ACID.                   211

 are conveniently received  into  small test-tubes, containing some
 starch moistened with water; since
   8. If moistened starch is brought into contact with free bromine,
 especially when the latter is in the gaseous state, yellow bromide
 of starch is formed.  The coloration is not always instantaneous.
 The reaction is rendered most delicate by hermetically sealing the
 test-tube which contains the moistened starch and the fluid under
 examination, and then inverting it, so as to cause the moist starch
 to occupy the upper part of the tube whilst the fluid occupies the
 bottom.   The presence of  even the slightest trace of bromine will
 now, in the course of from twelve to twenty-four hours, impart a
 yellow tint to the  starch,  which, however, after some time, will
 again disappear.  The reaction  is obtained more simply and with
 scarcely impaired delicacy, by warming  the  distillate containing
 bromine, or the  original mixture of a  bromide with  binoxide of
 manganese, &c, in  a very small beaker, which  is covered with a
 watch-glass, to whose under side  is attached  a piece  of paper
 moistened with starch-paste and sprinkled with dry starch.
  9. If sulphuric acid is poured over a mixture of a bromide with
 chromate  of potassa, and heat is then applied, a brownish-red gas
 is evolved, exactly as in the case of chlorides.   But this gas  con-
 sists of pure bromine, and therefore the  fluid passing over does
 not turn yellow, but becomes colorless, upon supersaturation with
 ammonia.
  10. In the metallic bromides  which are insoluble in water and
 nitric acid, the bromine is detected in the same way as the chlo-
 rine in the corresponding chlorides.
  11. A phosphate of soda  and ammonia bead saturated with oxide
 of copper,  mixed with a substance containing bromine, and then
 ignited in the  inner blowpipe flame, colors the flame blue, inclin-
 ing to green, more particularly at the edges (Berzelius).

                        .    §  157.
                   c. Hydriodic Acid  (H I).
  1.  Iodine is a solid, soft  body, of a peculiar, disagreeable odoi.
 It is generally seen in the form  of black, shining, crystalline scales.
 It fuses at a gentle heat; at a somewhat  higher temperature, it is
 converted  into iodine  vapor,  which has a beautiful violet-blue
 color, and condenses upon cooling to a black sublimate.  It is very
 sparingly soluble in water,  but  readily in alcohol and ether; the
 aqueous solution  is   of a light-brown, the alcoholic and ethereal
 solutions are a deep red-brown color.  Iodine destroys vegetable
 colors only slowly and imperfectly; it stains the skin brown; with
 starch it forms a compound of an intensely deep blue color.   This
compound is formed invariably when iodine vapor or a  solution
containing  free iodine  comes in contact with  starch, best with 
212                    HYDRIODIC ACID.                [§ 157.

starch-paste.   It is decomposed  by alkalies,  and also by chlorine
and bromine.
  2.  Hydriodic acid gas resembles hydrochloric and hydrobromic
acid  gases; it dissolves copiously in water.  The colorless hydrated
hydriodic acid turns speedily to a reddish-brown when in contact
with the air, owing to  the formation of water, and a solution  of
iodine in hydriodic acid.
  3.  The iodides also correspond in many respects with the  chlo-
rides.  Of the iodides of the heavy metals, however, many more
are insoluble in water than is the case with the corresponding chlo-
rides.  Many  iodides, as those of lead and mercury, have charac-
teristic colors.
  4.  Nitrate of silver  produces in  aqueous solutions of hydriodic
acid and of iodides yellowish-white precipitates of iodide of sil-
ver  (Ag I), which blacken on exposure to light; these precipitates
are insoluble in dilute nitric acid, and very  sparingly soluble in
ammonia, but dissolve readily in cyanide of potassium.
  5.  Protochloride of palladium and nitrate  of protoxide of pal-
ladium  produce even in very dilute solutions of hydriodic acid or
metallic iodides  a  brownish-black  precipitate  of protiodide of
palladium  (Pd I), which  dissolves to a trifling  extent  in  saline
solutions (solution of chloride of sodium, chloride of magnesium,
&c), but is insoluble or nearly so in dilute cold hydrochloric and
nitric acids.
  6. A  solution of 1 part  of sulphate of oxide of copper and 2|
parts of sulphate of protoxide of iron throws down from neutral
aqueous solutions of the iodides subiodide of copper (Cu2 I), in
the form of a dirty-white precipitate.  The addition of ammonia
promotes the complete precipitation of the iodine.  Chlorides and
bromides are not precipitated by this reagent.
   7. Pure nitric acid, free from nitrous  acid, decomposes hydrio-
dic acid or iodides only when acting upon them in its concentrated
form, particularly  when aided by the application  of heat.  But
nitrous acid and hyponitric acid  decompose hydriodic  acid and
iodides with the greatest facility even in the most dilute  solutions.
Colorless solutions  of iodides  therefore  acquire immediately a
brownish-red color,  upon addition of some red fuming nitric acid,
or a mixture of this  with concentrated sulphuric acid, or, better
still, a solution  of hyponitric acid  in hydrated sulphuric  acid or
nitrite of potassa and  some sulphuric or hydrochloric acid.   From
more concentrated solutions the iodine  separates  under  these cir-
 cumstances in the form of small black plates or scales, whilst nitric
 oxide gas and iodine vapors escape.
   8. As the blue coloration of iodide of starch remains still visible
 in much more highly dilute solutions than the yellow color of solu-
 tions of iodine in water, the delicacy of the reaction just now de 
§ 157.]
HYDRIODIC ACID.
213
 scribed  (7) is  considerably heightened  by mixing the fluid  to  be
 tested for  iodine first with some thin, clear starch-paste, then add-
 ing one or two drops  of dilute sulphuric acid, to  make the fluid
 acid, and adding finally one or the other of the reagents given in
 7.   Of the solution of hyponitric acid in sulphuric acid a  single
 drop on a  glass rod suffices to produce the reaction most distinctly.
 I can therefore strongly recommend this reagent, which was first
 proposed by Otto.  Red fuming nitric acid must be added in  some-
 what larger quantity, to call forth the reaction in its highest  inten-
 sity ; this reagent therefore  is  not well adapted to  detect very
 minute quantities of iodine.  The reaction with nitrite of potassa
 also is  of the  utmost  delicacy.   The fluid to be tested is mixed
 with dilute sulphuric  acid or with  hydrochloric acid to distinctly
 acid reaction,  and a drop or two  of a concentrated solution  of
 nitrite of  potassa is then added.  In cases where the quantity of
 iodine present is  very minute, the  fluid turns  reddish  instead  of
 blue.  An excess of the fluid containing nitrous acid or hyponitric
 acid does  not materially impair  the delicacy of the  reaction.  As
 iodide of  starch dissolves in hot water to a colorless  liquid, the
 fluids must of necessity be  cold; the  colder they are, the  more
 delicate  the reaction.   When it is desired to attain the extreme
 limit of delicacy, the  mixture is cooled with  ice, the starch is
 allowed  to settle to the bottom  of the  tube, and it is placed upon
 white paper for observing the coloration. (See also Recapitulation,
 §160.)
   9.  Chlorine  gas and chlorine water decompose compounds of
 iodine also, setting the iodine free ; but if the chlorine is applied
 in excess, the liberated iodine combines with it to colorless chloride
 of iodine.   A  dilute solution  of a metallic iodide, mixed  with
 starch-paste, acquires therefore, upon addition  of a little chlorine
 water, at once a blue tint, but becomes  colorless again upon  addi-
 tion of more chlorine  water.  As it is therefore  difficult not  to
 exceed the proper limit, especially where the quantity of iodine
 present is  only small,  chlorine water is not well adapted for the
 detection of minute quantities of iodine.
  10. If a solution  in  which iodine has been set free by nitrous
 acid (nitrite of potassa and hydrochloric acid), &c, is mixed with
 some chloroform, or bisulphide of carbon, and the mixture shaken,
 leaving a few drops of the reagent undissolved, these will subside
 to the bottom of the fluid, exhibiting a lighter or darker red color.
 This reaction also is extremely sensitive.  If the solution is mixed
 with ether,  and the mixture shaken, the ether dissolves the liberated
iodine, and acquires thereby a reddish-brown or yellow color.   The
 color imparted to the  ether by iodine is much more intense  than
that imparted to that fluid by an  equal quantity of bromine.
  11. If  metallic iodides are  heated with  concentrated sulphuric 
214
HYDROCYANIC  ACID.
[§ 158.
acid or with sulphuric acid and binoxide of manganese, or with
sulphuric acid and chromate of potassa, iodine separates, which
may be known by the color of its vapor, and, in the case of very
minute  quantities, also by its  action upon a slip of paper coated
with starch-paste.
  12.  The  iodides which are insoluble  in water and nitric acid
comport themselves upon fusion with carbonate of soda and potassa
in the same manner as the corresponding chlorides.
  13.  A phosphate of soda and ammonia  bead, saturated with
oxide of copper, when mixed with a substance containing iodine,
and ignited in the inner blowpipe flame, imparts an intense Green
color to the flame.

                            § 158.
                d. Hydrocyanic Acid (H Cy).
  1. Cyanogen is a colorless gas of a peculiar, penetrating odor;
it burns with a crimson flame, and is pretty soluble in water.
  2. Hydrocyanic acid is a colorless, volatile, inflammable liquid,
the odor of which resembles that of bitter almonds ; it is miscible
with water in all proportions ;  in the pure state  it speedily suffers
decomposition. It is extremely poisonous.
  3. The cyanides of the metals of the 1st and 2d groups are soluble
in water; the solutions smell of hydrocyanic acid.   They are readily
decomposed by acids, even  by  carbonic  acid; but ignition fails to
decompose them,  if the access of air is precluded. When fused
with oxides of lead, copper, antimony, tin, &c, the cyanides reduce
these oxides,  and are converted into cyanates.   Only a few of the
cyanides with heavy metals are soluble in water; all of them are
decomposed upon ignition, the cyanides  of the noble metals being
converted into cyanogen gas and metal, the  cyanides of the other
heavy metals into nitrogen  gas and  metallic carbides.  Many of
the cyanides with heavy metals are not decomposed  by dilute
oxygen acids, and  only with difficulty by concentrated nitric acid.
By heating and evaporating with a strong sulphuric acid they are
all  decomposed,  hydrochloric acid  decomposes some  of them,
hydrosulphuric acid many others.
  4. The  cyanides have  a  great tendency to  combine with each
other; hence most of the cyanides  of the heavy metals dissolve in
cyanide of potassium.  The resulting compounds are either:
  a. True  double salts,  e.  g.,  K Cy +  Ni Cy.   From  solutions
of such double salts, acids,  by  decomposing  the  cyanide  of potas-
sium, precipitate the metallic  cyanide which was combined with
it.—Or they  are:
  b. Simple haloid salts,  in which a metal, e. g., potassium, is corn*
bined with a compound radical consisting of cyanogen and another
metal  (iron,  cobalt, manganese, chromium).   Compounds of thia 
§ 158.]
HYDROCYANIC ACID.
215
 kind are the ferro- and ferricyanide of potassium, K2 Cy3 Fe or K,
 Cfy, and K3  Cy6 Fe2 or K3 Cfdy, cobalticyanide  of potassium,
 K  Cy,; Co., &c.  From solutions  of compounds  of this  nature
 dilute acids do not separate metallic cyanides in the cold.   If the
 potassium is replaced by hydrogen, peculiar hydracids are formed,
 which must not be confounded with hydrocyanic acid.
   We will now first consider the reaction of hydrocyanic acid and
 the simple  cyanides, then, in an appendix to this paragraph, those
 of hydroferro- and hydroferricyanic acid.
   5. Nitrate of  silver produces in solutions of free hydrocyanic
 acid and of cyanides of the alkali metals white precipitates of
 cyanide of silver (Ag  Cy), which are readily soluble in cyanide
 of potassium,  dissolve with some  difficulty  in ammonia, and are
 insoluble in nitric acid; these precipitates are decomposed upon
 ignition, leaving metallic silver with some paracyanide of silver.
   6. If solution of sulphate of protoxide of iron which has been
 for some time in contact  with the air  is added to a solution of free
 hydrocyanic acid, no alteration takes place; but if solution  of
 potassa or  soda  is now added, a  bluish-green precipitate  forms,
 which consists of a mixture of Prussian-blue (Fe4 Cfy3), and hydrate
 of protosesquioxide of iron. Upon now adding hydrochloric acid
 (best after  previous application of heat),  the hydrate of protoses-
 quioxide of iron dissolves, whilst  the  Prussian-blue remains
 undissolved.   If only a  very minute  quantity of hydrocyanic acid
 is present, the fluid simply appears  green  after the addition of the
 hydrochloric acid, and it is only after long standing that a trifling
 blue precipitate separates from it.  The same reactions are observed
 when sulphate of  protoxide  of iron containing sesquioxide, is
 added to the solution of an alkaline cyanide, with subsequent addi-
 tion of hydrochloric acid.
  7. If  a liquid containing a small quantity of hydrochloric acid
 or cyanide of potassium is mixed with so much yellow sulphide of
 ammonium  that the solution appears yellowish, and with a little
 ammonia, and the  mixture warmed in  a porcelain  dish with
 renewal of  water, if necessary, until  it has become colorless, and
 all excess of sulphide of ammonium is destroyed or volatilized,
 sulphocyanide of ammonium is formed, and the fluid, after being
 acidified with hydrochloric  acid (whereby no evolution  of  hydro-
 sulphuric acid should occur), acquires a blood-red tint upon addition
 of sesquichloride  of iron (Liebig).  This reaction is exceedingly
 delicate. The  following formula expresses the transformation of
hydrocyanic acid  into sulphocyanide of ammonium:  N IL,, S + 2
 (N H4, O)  + 2 H Cy = 2  (N H, Cy S2) + N  H„ S + 2 H O.
 If an  acetate [a phosphate,  borate, fluoride, oxalate, or salt of an
 organic acid] is present, addition of  more hydrochloric acid may
be necessary to develope the red color. 
216                HYDROSULPHURIC ACID.             [§ 158.

   8. Neither  of  the  above  methods will serve  to  effect the
detection of cyanogen in cyanide of mercury.  To detect cyanogen
in that compound, the solution is mixed with hydrosulphuric acid:
sulphide of mercury precipitates, and the solution contains free
hydrocyanic acid.  In solid cyanide of mercury the cyanogen  is
most readily detected by heating in a glass tube.  Compare 3.

                          Appendix.
  a. Hydroferrocyanic acid (H2 Cfy). Hydroferrocyanic acid  is
soluble  in water.  Some of the ferrocyanides,  as  those of the
alkalies and alkaline earths, are soluble  in water, most of them
: re however insoluble.  They are all decomposed by ignition.  If
strongly heated  while containing  water they yield hydrocyanic
acid, carbonic  acid, and ammonia;  when anhydrous they give off
on ignition nitrogen, and sometimes cyanogen.
  In solutions of this acid or of soluble ferrocyanides, sesquichlo.
ride of iron produces a blue precipitate of ferrocyanide of iron
(F4 Cfy3); sulphate of oxide  of copper, a brownish-red precipitate
of ferrocyanide  of copper (Cu2 Cfy); nitrate of silver, a white
precipitate of ferrocyanide of silver  (Ag2 Cfy), which is insoluble
in nitric  acid and in'  ammonia, but dissolves  in cyanide  of pot-
assium.   Insoluble ferrocyanides of metals are decomposed by
boiling with solution of soda,  ferrocyanide of sodium being formed
and  the oxides thrown down  unless the  latter are  themselves
soluble  in soda.   When heated with 3 parts of sulphate and  1
part of nitrate of ammonia, they yield sulphates of the metals
contained in them, the whole of the cyanogen volatilizing in form
of cyanide of ammonium and the  products of its decomposition
(Bolley).
  b. Hydroferricyanic acid.   (H3 Cfdy.)   Hydroferricyanic  acid
and  many ferricyanides are soluble in water.   The ferricyanides
are all decomposed  at a strong heat,  in a  manner similar to the
ferrocyanides.   In the  aqueous solutions of hydroferricyanic acid
and its  salts, sesquichloride of iron produces no blue precipitate,
but sulphate of protoxide  of iron produces a  blue precipitate of
irotoferricyanide of iron (3  Fe, Cfdy); sulphate of copper, a
yellowish-green  precipitate of ferricyanide of copper (3 Cu,
Cfdy), which is insoluble in  hydrochloric acid;  nitrate of silver,
an orange-colored precipitate of ferricyanide of  silver (3 Ag,
Cfdy), which  is insoluble  in nitric acid, but dissolves readily in
ammonia and in cyanide of potassium.  The insoluble ferricyanides
of metals are decomposed by boiling with solution of soda, the
metallic oxides being thrown down; in the  fluid filtered  off from
them, either ferrocyanide  of  sodium alone is found, or a mixture
of ferro- with  ferricyanide  of sodium.  By heating  with sulphate 
 § 159.]             HYDROSULPHURIC ACID.                217

 and nitrate of ammonia the ferricyanides are decomposed the same
 as the ferrocyanides.

                             § 159.
                e.  Hydrosulphuric Acid (H S).
                    Sulphuretted Hydrogen.
   2. Sulphur  is a  solid, brittle,  friable, tasteless body, insoluble
 in water.   It occurs sometimes in the form of yellow or brownish
 crystals, or crystalline masses of a yellow or brownish  color, and
 sometimes in that of a yellow or yellowish-white or grayish-white
 powder.  It melts at a moderate heat; upon the application  of a
 stronger heat it is converted into brownish-yellow vapors, which,
 in cold air, condense  to a yellow powder, and on  the  sides of the
 vessel, to drops.  Heated in  the air, it  burns  with bluish flame
 to sulphurous  acid, which betrays its presence in the air at once
 by its suffocating  odor.   Concentrated  nitric acid,  nitrohydro-
 chloric acid, and a mixture of chlorate of potassa and hydrochloric
 acid dissolve sulphur gradually, with the aid of a  moderate heat,
 and convert it into sulphuric acid; in  boiling solution of soda
 sulphur dissolves to  a  yellow fluid,  which  contains  sulphide of
 Bodium and hyposulphite of soda; in ammonia sulphur is insoluble.
   2. Hydrosulphuric  acid, at the common temperature and un-
 der common atmospheric  pressure, is a  colorless, inflammable gas,
 soluble in water, and which may be readily recognised by its  cha-
 racteristic  smell of rotten eggs; it transiently imparts a red tint
 to litmus paper.
   3. Of the sulphides only those with alkalies and alkaline earths
 are soluble in water.  These, and the sulphides of iron, manganese,
 and  zinc, are decomposed by dilute mineral acids, with evolution
 of hydrosulphuric acid  gas, which may be readily detected by its
 peculiar smell, and  by its action upon  solution of lead  (see 4).
 The decomposition of higher sulphides is attended also with sepa-
 ration  of  sulphur in a finely-divided  state;  the white  precipitate
 may be  readily distinguished  from similar precipitates by its
 deportment on heating.   Part of the sulphides of the metals of the
 fifth and sixth groups are  decomposed by concentrated and boiling
 hydrochloric acid, with evolution of hydrosulphuric acid gas, whilst
 others  are not dissolved by hydrochloric acid, but by concentrated
 and boiling nitric acid.  The compounds of sulphur with mercury,
 gold and platinum  resist  the action of  both acids, but dissolvo
 readily in nitrohydrochloric acid.  Upon  the solution of sulphides
 in nitric acid,  and in  nitrohydrochloric acid,  sulphuric  acid  is
formed, and the process of solution is moreover attended, in most
cases, with separation of  sulphur, which  is readily recognised by
its color and by its deportment upon heating.  Many metallic sul- 
218
RECAPITULATION.
[§ 160.
 phides, more  especially of a higher degree of sulphuration, give a
 sublimate of sulphur when heated in a test-tube.
   4. If hydrosulphuric acid, in the gaseous state or in solution, is
 brought into contact with nitrate of silver or acetate of lead, black
 precipitates of sulphide of  silver  or sulphide of lead  are
 formed.  In  cases, therefore, where the odor of  the  gas fails to
 ;tfford sufficient proof of the presence of hydrosulphuric acid, these
 reagents will remove all doubt.   If the hydrosulphuric acid is pre-
 sent in the gaseous form, the air suspected to contain it is tested
 by placing in  it a small slip of paper moistened with solution of
 neutral acetate of lead and a little ammonia ; if the gas is present,
 the slip becomes covered with a thin, brownish-black, shining film
 of sulphide of lead.   To detect a trace of an alkaline sulphide in
 presence of a free alkali or an alkaline carbonate, the best way is
 to mix the fluid with a solution of oxide of lead in solution of
 soda, which  is prepared by  mixing  solution of  acetate  of lead
 with solution  of  soda until the precipitate which forms at first is
 redissolved.
  5. If a fluid containing hydrosulphuric acid or  an alkaline sul-
 phide  is  mixed with solution of soda, then with nitroprusside  of
 sodium* it acquires a fine reddish-violet tint.  The reaction is very
 delicate; but that with solution of oxide of lead in solution of soda
is still more sensitive.
  6. If metallic sulphides are exposed to  the oxidizing flame of the
 blowpipe, the sulphur burns with a blue flame, emitting at the same
time the well-known odor of sulphurous acid.  If a metallic sulphide
is heated in a glass  tube open at both ends, in the upper part oi
 which a slip of blue litmus paper is inserted, and the tube is held in
a slanting position during the  operation, the escaping sulphurous
acid reddens the  litmus paper.
  7. If a finely-pulverized metallic sulphide is boiled in a porcelain
dish with solution of potassa, and the mixture heated  to incipient
fusion  of the hydrate of potassa, or if the test specimen is fused in
a platinum spoon with hydrate  of potassa, and the mass is, in either
case, dissolved in a little water, a piece of bright silver (a polished
coin) put into  the solution, and the fluid warmed, a brownish-black
film  of sulphide  of silver forms  on the metal.  This film may be
 removed afterwards  by rubbing the metal with leather and quick-
 lime (v. Kobell).

                             § 160.
  Recapitulation and remarks.—Most of the acids  of the first
 group are also precipitated by nitrate  of silver, but the precipitates
 cannot well be confounded with the silver compounds of the acids
  * Nitroprusside of sodium  being a reagent  which can very well be dispensed
 with, I have omitted giving it a place among the reagents. 
§ 160.]
RECAPITULATION.
219
 of the  second group, since the former are soluble in dilute nitric
 acid, whilst the latter are  insoluble in that menstruum.  The pre-
 sence of hydrosulphuric acid interferes more or less with the test-
 ing for the other acids of the second group ;  this acid must there-
 fore, if present, be  removed first before the  testing for the other
 acids can be proceeded with.  The removal of the hydrosulphuric
 acid, when  present  in the free state, may be  effected by simple
 ebullition ;  and when present in the form of  an alkaline sulphide,
 by the  addition of a metallic salt, such as will not precipitate any
 of the  other  acids,  or at least will not precipitate  them from  acid
 solutions.  Hydriodic  and hydrocyanic  acids may be  detected,
 even in presence of hydrochloric or hydrobromic acid,  by the
 equally characteristic and delicate reactions with starch (with addi-
 tion of a fluid containing  nitrous acid), and with solution  of pro-
 tosesquioxide of iron.  But  the detection of  chlorine and bromine
 is more or less difficult in presence of iodine and cyanogen.  These
 latter must therefore, if present, be removed first before the proper
 tests for chlorine and bromine  can be applied.  The  separation of
 the cyanogen may be readily effected by converting the whole of
 the radicals present into salts  of silver, and igniting the mixture:
 the cyanide of silver is decomposed in this process, whilst the chlo-
 ride, bromide, and iodide of silver remain unaltered.   Upon fusing
 the ignited residue with carbonate of soda and potassa, and boiling
 the fused mass with water,  chloride, bromide, and  iodide  of the
 alkali metals are obtained in solution ; or the  fused silver salts may
 be easily decomposed by means of  zinc.   For this purpose, the
 fused mass is covered with water, a little dilute sulphuric acid and
 a fragment of zinc added, and the whole allowed to stand for some
 time.   The  solution containing the soluble chloride, bromide, or
 iodide of zinc is filtered off from the metallic silver.
   Iodine may be separated from chlorine and  bromine, by treating
 the mixed silver compound with ammonia, but more accurately by
 precipitating the iodine as protiodide of copper.  From bromine
 the iodine is separated most accurately by protochloride of palla-
 dium, which only precipitates the iodine ; from chlorine it is sepa-
 rated by nitrate of protoxide of palladium.
   Bromine in presence of iodine and chlorine may be identified by
 the following simple operation : Mix the fluid with a few drops of
 dilute sulphuric acid, then with some starch-paste, and add a little
 red fuming nitric acid, or, better still, a solution of hyponitric acid
 in sulphuric acid,* whereupon the iodine reaction will show itself
 immediately.  Add  now chlorine water drop by drop until that
 reaction has disappeared ; and then add some more chlorine water

  * [This compound may be prepared by passing the gases that result from the
action of nitric  acid on starch (§ 50) into oil of vitriol.] 
 220                    HYPOCHLOROUS ACID.              [§ 161.

 to  set the bromine also free, which may  then be  separated  and
 identified by means of chloroform, or  bisulphide of carbon.  Or
 the liberated iodine may also be removed first by means of chlo-
 roform, or  bisulphide of carbon, and  the  fluid then tested for
 bromine, by means of chlorine  water and one of the just named
 solvents.
  Metallic chlorides are  detected in presence of metallic bromides
 by  the reaction with chromate of potassa and sulphuric acid.
  In conclusion may be mentioned that  besides the reagents above
 noticed many others have been employed for liberating iodine from
 its  combinations,  e. g. iodic acid,  or  iodates of the alkalies with
 hydrochloric acid—(Liebig) : sesquichloride of iron with sulphu-
 ric   acid,  or  bichloride of  platinum  with hydrochloric acid—
 (Hempel): permanganate of potassa in slightly acidified solution.
 —(Henry.)
  With regard to  these  reagents, it  must  be remarked that iodic
 acid  should be employed with great caution, because, in the first
 place, iodine may  be  liberated  from  it by reducing agents, and
 because, in the second place, when used in excess, it destroys  the
 reaction.—Sesquichloride of iron with  addition of  sulphuric acid
 does  not act immediately; if time be given it  the reaction ensues
 with  the greatest delicacy, and an excess of it is  not greatly inju-
 rious.—Permanganate of potassa also reacts at once, even in  the
 dilutest solutions.   Since, however, a  liquid containing a trace of
 iodide of starch, has a  reddish appearance, mistakes may arise from
the color of this reagent.  The reaction  can  therefore not be con-
 sidered decisive until after the lapse of 6 to  12 hours.—It is obvious
that the mode of operating may be greatly varied for the purpose
 of making the starch-test in the highest  degree sensitive.  For  the
particulars of such modifications as have  been  found  useful in
examinations of the utmost nicety, the operator may profitably
consult the papers  of Morin* and Hempel.\

                              §  161.
             More rarely occurring Acids of the Second Group.
  1. Nitrous acid (N 03). Nitrous acid, in the free state, at the common tempera-
ture, is a brownish-red gas.  In contact with water it is converted into nitric acid,
which  dissolves, and nitric oxide gas, which remains undissolved (3 N 03 = N Os -f-
2 N  02). The nitrites  are decomposed by ignition; many  of  them are soluble in
water.   When nitrites or concentrated solutions of nitrites  are treated with dilute
 Bulphuric acid, it is not nitrous acid gas which is evolved, but nitric  oxide  gas,
 attended with formation of nitric acid. In solutions of nitrites of tbe alkalies nitrate
 of silver produces a white precipitate, which dissolves in a very large proportion of
 water, especially upon application of heat; sulphate of protoxide of iron, upon addi-
 tion of a small quantity of acid,  produces a dark blackish-brown coloration, which  ia
* Jour. f. Prakt. Chem. 78. 1.
f Ann. d. Chem. u. Pharm. 107. 102. 
§ 162.]
NITRIC  ACID.
221
due to nitric oxide gas in the solution of the sulphate of protoxide of iron.   Hydro-
sulphuric acid produces in neutral as well as in acid solutions  copious precipitates
of sulphur,  attended with formation of nitrate of ammonia.  Solution  of iodide of
potassium, mixed with starch paste and sulphuric acid, is,  however, the most delicate
test of nitrous  acid.  (Price,  Schonbein.)  Water which  contains the one-hundred-
thousandth part of  nitrite of  potassa gives in a few  seconds, and  water containing
but one-millionth of  this salt gives in a few  minutes a perceptible blue color, from
the liberation of iodine and formation  of iodide of starch.  This  reaction  is only
proof of the presence  of nitrous acid when other substances that decompose iodide
of potassium (iodic acid, sesquioxide  of iron, &c.) are not present.
   2. Hypochlorous acid (CI 0) at ordinary temperatures  is a deep yellowish-green
gas of an unpleasant irritating odor like that of chlorine.   It is soluble in water, and
the dilute aqueous  solution may  be distilled  without decomposition.   The hypo-
chlorites usually occur combined with  metallic  chlorides,  as in so-called chloride of
lime,  Eau-de-Javelle, &c.   The solutions decompose  on boiling, with formation of a
chloride and a chlorate; while from concentrated solutions, oxygen is evolved.  If a
solution of chloride of lime is  mixed with sulphuric or hydrochloric acid, chlorine is
set free, while  by  addition of  nitric  acid in small quantity hypochlorous acid is
liberated.   Nitrate of silver throws down from  solution of chloride  of lime, chloride
of silver (the hypochlorite of silver at first formed rapidly  decomposing into chloride
and chlorate of silver  3 (Ag 0, CI 0) = Ag 0, CI Os + 2 Ag CI): nitrate of lead pro-
duces at first a  white precipitate which gradually becomes orange-red, and finally—
from formation  of binoxide of lead—brown.  Salts of protoxide of manganese  give
brownish-black precipitates of hydrated binoxide.  A solution of permanganate of
potassa is not decolorized.  Litmus and indigo solutions are bleached by the alkaline,
more  rapidly by the  acidulated solutions of hypochlorites.  When a solution of
arsenious acid in hydrochloric acid is made blue by indigo, and poured  into  a solu-
tion of chloride of  lime, with constant stirring, decolorization only takes place after
the arsenious acid has been wholly converted into arsenic acid.
   3.  Chlorous acid (CI 03) is a yellowish-green  gas of a peculiar unpleasant odor.  It
dissolves in water,  forming even when dilute an intensely yellow liquid.   The chlo-
rites are mostly soluble in water; the solutions readily decompose into a mixture
of chloride and chlorate.   Nitrate of silver throws white chlorite of silver, which is
soluble in a large amount of water;  a solution of permanganate of potassa is at once
decolorized, after some time hydrated  sesquioxide of manganese separates.  Litmus
and indigo solutions are at once  bleached  even in  presence of excess of arsenious
acid.   If the slightly  acidulated dilute solution of a protosalt of iron is added to a
dilute solution of chlorous acid, the mixture  transiently  acquires an amethyst color
and only alter some moments assumes the  yellowish tinge of sesquisalts  of iron.
(Lennsen.)
   4. Hypophosphorous acid (P 0), in concentrated solution forms a syrupy liquid similar
to that of phosphorous acid (§ 151),  with which it agrees further by decomposing on
application of heat into hydrated phosphoric acid and non-spontaneously inflammable
phosphoretted hydrogen gas.   The hypophosphites are all soluble in water,  and on
ignition are all resolved into  phosphates, and in general,  spontaneously inflammable
phosphoretted hydrogen gas.   Chlorides of barium and calcium, and acetate of lead
give no precipitates (distinction  from  phosphorous acid); nitrate  of silver yields in
solutions of hypophosphites a precipitate which at first is white, but which, even at
ordinary temperatures, more rapidly by heating, blackens from separation of metallic
silver.  Hypophosphorous acid throws down from au excess of  chloride of mercury,
slowly in  the  cold, rapidly on  heating,  a precipitate of subchloride of mercury.
Brought in contact with zinc and  dilute sulphuric  acid, hypophosphorus acid yields
hydrogen  gas mixed with phosphoretted hydrogen.   (Compare  phosphorous acid,
§  161.) 
222
NITRIC  ACID.
[§ 162.
             third group of the inorganic acids.
Acids which are  not precipitated by Salts of Baryta nor
    by  Salts  of Silver : Nitric  Acid,  Chloric  Acid.  (Per-
    chloric Acid.)
                             §162.
                    a. Nitric Acid (NO).
  1. Anhydrous nitric acid crystallizes in six-sided prisms.   It
fuses at 85-2° F., and boils at 113° F. (Deville).   The pure hydrate
is a colorless, exceedingly corrosive fluid, which emits fumes in the
air, exercises a rapidly destructive action upon organic substances,
and colors  nitrogenous matter intensely yellow.   Hydrate  of nitric
acid containing nitrous acid has a red color.
  2. All the neutral salts of nitric acid are soluble in water;
only some  of the basic nitrates are insoluble in this  menstruum.
All nitrates without exception undergo decomposition at an intense
red heat.  Those with alkaline bases yield  at first  oxygen, and
change to nitrites, which are then further resolved into oxygen and
nitrogen; the others yield oxygen and nitrous or hyponitric acid.
  3. If a nitrate is thrown upon red-hot charcoal, or if charcoal or
some  organic substance, paper for instance, is brought into contact
with a nitrate in fusion, deflagration takes place, i.e., the charcoal
burns at the  expense of the oxygen of the nitric acid, the  combus-
tion being  attended with vivid scintillation.
  4. If a mixture of a nitrate with cyanide of potassium in powder
is  heated on a  platinum plate, a vivid  deflagration will ensue,
attended  with  distinct  ignition  and   detonation.   Even very
minute quantities of nitrates may be detected by this reaction.
  5. If a nitrate is mixed with copper  filings, and  the  mixture
heated in  a  test-tube with concentrated  sulphuric acid, the air in
the tube acquires a yellowish-red tint, owing to the nitric oxide
gas which  is liberated upon the oxidation  of  the copper by the
nitric acid, combining with the oxygen  of the air to nitrous acid.
The coloration may be observed most distinctly by looking length-
ways through the tube.
  6. If the solution of a nitrate is mixed with an equal volume of
concentrated sulphuric acid, free from nitric and hyponitric acid,
the mixture allowed to cool, and  a concentrated solution of  sul.
phate of protoxide of iron then cautiously added to it so that the
fluids do not mix, the stratum, where the  two fluids are in imme-
diate contact, shows  a purple, afterwards a brown, or,  in cases
where only a very minute  quantity of nitric acid is present, a red-
dish  color.  If  the solutions are now  mixed,  a clear, brownish-
purple liquid is obtained.   In this process the nitric acid is decom-
posed by the protoxide of iron, three-fifths of its oxygen combining
with  the protoxide and converting a portion of it into sesquioxide, 
§ 163.]
CHLORIC ACID.
223
 whilst the remaining  nitric oxide combines with  the remaining
 portion  of  the protoxide of iron,  and forms  with it a peculiar
 compound, which dissolves in water, imparting a brownish-black
 color to  the fluid.
   A similar coloration is obtained with selenious acid ; on mixing
 the solutions and allowing them to stand  for some time, selenium
 separates as a red powder.  ( Wittstock.)
   7. If some hydrochloric  acid is heated  to boiling in a test-tube,
 and one  or  two drops of a very dilute solution of sulphate of in-
 digo are added, and the boiling continued, the liquid remains blue
 (if the hydrochloric acid be free from chlorine).  If now there be
 added to the faint-blue liquid  a nitrate, either solid or  in solution,
 and the  mixture be again  boiled [and, if needful, evaporated to
 one-half  or  to a less volume], the liquid is decolorized by the de-
 struction of the  indigo-blue.  This  is a highly sensitive reaction.
 It must  not be overlooked that some  other bodies, especially free
 chlorine, have the same bleaching effect.
   8. If a little  brucia  is dissolved in  concentrated sulphuric acid,
 and a little  of a fluid containing nitric acid added to the solution,
 the latter immediately acquires a  magnificent red color.  This re-
 action is  exceedingly characteristic and delicate.
   9. Very minute quantities of nitric acid maybe detected also, by
 reducing, in the first place, the nitric acid to nitrous acid.  This is
 accomplished in the wet way,  by heating the solution of nitric acid
 or of a nitrate, for some  time with zinc filings, or better with an
 amalgam of zinc, and then filtering off the liquid: in the dry way,
 by fusing the substance under examination with carbonate of soda
 and potassa  at a moderate heat, extracting the mass, after cooling,
 with water, and filtering.  On  now adding  the filtrate to a solution
 of iodide of potassium mixed with starch-paste, and then adding
 hydrochloric acid, the liquid becomes blue from the formation  of
 iodide of starch.   In  making  the  experiment, the  operator has to
 ascertain whether the  solution of iodide of potassium  mixes with
 the hydrochloric  acid without being colored blue by it, since this
 blue coloration would indicate the presence of iodic acid in the
iodide of potassium,  or of free  chlorine in the  hydrochloric acid.
 (Compare §  161, 1.)

                             §163.
                   b.  Chloric  Acid  (CI  05).
   1.  Chloric acid, in its most highly concentrated solution, is a
colorless  or yellow, oily fluid ;  its odor  resembles that of nitric acid.
It first reddens litmus and then bleaches it. Dilute  chloric acid is
colorless  and inodorous.
   2.  All  Chlorates  are  soluble  in water.  When chlorates are 
224
CHLORIC ACID.
[§ 163.
heated to redness, the whole of their  oxygen escapes and metallio
chlorides remain.
   3. Heated with charcoal,  or some  organic substance, the chlo-
rates deflagrate,  and this with far greater violence than the
nitrates.
   4. If a mixture of a chlorate with cyanide of potassium is heated
on platinum foil, deflagration takes place, attended with strong
detonation and ignition, even though  the chlorate be present only
in very  small  quantity.  This experiment should be  made  with
very minute  quantities only.
   5. Free chloric acid oxidizes and decolorizes indigo  in the same
manner as nitric acid; consequently if the solution of a chlorate is
mixed with sulphuric acid and solution of indigo, and the mixture
heated, the  same reaction  is observed  as with nitric  acid  (see
§ 162, 7).
   6. If the solution of a chlorate is colored  light-blue with solution
of indigo in sulphuric acid,  a little dilute  sulphuric acid added,
and a solution of sulphite of soda  dropped  cautiously into the blue
fluid, the color  of the indigo disappears immediately.   The  cause
of this equally characteristic and delicate  reaction is, that the sul-
phurous  acid deprives the chloric acid of its oxygen, thus setting
free chiorine or a lower  oxide of it, which then decolorizes the
indigo.
   7. When  chlorates are treated with hydrochloric  acid, the con-
stituents of the two acids transpose,  forming water, chlorine, and
chlorochloric acid (2 CI 05, CI O.,).  Application of heat promotes
the reaction.  The test-tube  in which the experiment is made be-
comes filled in  this  process with a greenish-yellow gas of a very
disagreeable odor resembling that of chlorine; the hydrochloric
acid acquires a greenish-yellow color.  In case the hydrochloric
acid had been tinged blue with indigo solution, the color would be
at once bleached, even by a very minute quantity of  a chlorate.
   8. Concentrated sulphuric acid, poured over a chlorate, converts
two-thirds of the metallic oxide into a sulphate and  the remaining
one-third into perchlorate ; this conversion is  attended, moreover,
with liberation of chlorochloric acid, which imparts an intensely
yellow tint  to  the  sulphuric  acid, and  betrays its  presence also
by its  odor and the greenish  color of the  evolved  gas [3 (K O,
CI 05) + 4  S 03  = (K O, 2 S 03)  + K O, CI 07  + (CI 05, CI 03)].
The application of  heat must be avoided  in this  experiment, and
the quantities operated upon should be very small, since otherwise
the decomposition might take place with such violence  as to cause
an explosion. 
§§ 164,  165.]           PERCHLORIC  ACID.                    225

                              §  164.
   Recapitulation and remarks.—Of the reactions which have been
suggested to effect the  detection of nitric acid, those with sulphate
of protoxide of iron and sulphuric  acid, with copper filings and sul-
phuric acid, with brucia, and also those based upon the  reduction
of the nitrates to nitrites, give the most positive results ; with re-
gard to deflagration with charcoal, detonation with  cyanide  of
potassium, and discoloration  of solution of indigo, we have seen
that these reactions belong equally to chlorates as to nitrates, and
are  consequently decisive  only  when no  chloric  acid is present.
The presence of free nitric acid  in  a fluid may be detected by eva-
porating the fluid, in a  porcelain dish on the water-bath, to dryness,
having first thrown  in a few quill-cuttings:  yellow coloration  of
these indicates the presence of nitric acid (Runge).  The best way
to ascertain  whether chloric acid is present or not, is to ignite the
sample under examination, dissolve the mass, and test the solution
with nitrate of silver.   If a  chlorate is present, this is converted
into a chloride upon  ignition, and nitrate  of silver will now preci-
pitate chloride  of silver from the  solution.  However, the process
is thus simple only if no chloride is present along with the chlorate.
But in presence  of a chloride, the latter must be removed first by
adding nitrate of silver to the solution as long as a  precipitate con-
tinues to form, and  filtering the  fluid from  the precipitate;  the
filtrate is then, after addition of pure carbonate of soda, evaporated
to dryness, and the  residue ignited.   It is, however, generally un-
necessary to pursue  this circuitous way, since the reactions with
concentrated sulphuric  acid, and with indigo and sulphurous acid,
are sufficiently marked  and characteristic  to  afford positive  proof
of the presence of chloric acid.
   To detect nitric acid in presence of a large quantity of chlorio
acid, the mixture  is  mixed with excess of carbonate of soda, eva-
porated  to dryness if necessary, and the residue  is ignited with
moderate intensity, but long enough to convert all chlorate into
chloride.  The residual mass is now tested for nitric (or nitrous)
acid.
                              8 165.
  Perchloric  Acid  (CI 07).—"When  anhydrous this acid is  a colorless  mobile
liquid which explodes violently when dropped upon charcoal, and on exposure to
the air, forms  thick white fumes.—(Roscoe.) The  hydrated  acid crystallizes in
needles, the concentrated aqueous solution is  heavy and has an oily consistence.
The dilute solution on distillation yields in the distillate first water, then the dilute,
and finally the strong acid. The perchlorates are all soluble in water, most of them
with ease ; they are all decomposed on  ignition, the alkaline perchlorates give off
oxygen  and alkaline chloride remains.   Potassa salts produce in not too dilute solu-
tions a white crystalline precipitate of perchlorate of potassa (KO CI 07), which is
difficultly soluble in water and insoluble in  alcohol.  Salts of baryta and silver are
not affected.  Concentrated sulphuric acid does not decompose perchloric acid in the
                                 15 
226
TARTARIC  ACID.
[§ 166.
cold and with difficulty when heated (distinction from chloric acid).  Hydrochloric,
nitric and sulphurous acids do not decompose an aqueous solution of perchloric acid;
previously added indigo solution is, therefore, not  decolorized  (distinction from
all other oxacids of chlorine).

                       H. Organic  Acids.
                          First Group.
Acids which are invariably precipitated by Chloride of Cal-
  cium: Oxalic  Acid, Tartaric  Acid (Paratartaric or Racemic
  Acid), Citric Acid, Malic Acid.

                              §166.
                        a. Oxalic Acid.
  For the reactions of oxalic acid I refer to § 148.

              b. Tartaric Acid (2 H O, CA H4 OI0).
  1. The hydrate of tartaric acid forms colorless crystals of an
agreeable acid taste, which are persistent in the air, and soluble in
water and in spirit of wine.   Tartaric  acid when heated  to  212°
Fah. loses no water,  at 340°  Fah. it fuses and at a higher tem-
perature becomes carbonized, emitting during the process a very
peculiar and highly characteristic odor, which resembles that of
burnt sugar.  The aqueous solutions of tartaric acid and of nearly
all  tartrates, produce  right-handed rotation of a ray of polarized
light.
  2. The tartrates with alkaline base are soluble in water, and
so  are  those with  the metallic oxides of the third  and fourth
groups.  The solution of tartrate of  sesquioxide of iron, when
evaporated in the water-bath to the consistence of syrup, deposits
a basic salt in the form of powder.   The tartrates, which are inso-
luble in water, dissolve in hydrochloric or nitric  acid.  The tar-
trates suffer  decomposition  when heated to  redness;  charcoal
separates, and the  same  peculiar odor is emitted as  attends the
carbonization of  free tartaric acid.
  3. If to a solution of tartaric acid, or to that of a tartrate, solu-
tion of sesquioxide  of iron, protoxide of manganese  or alumina is
added in not too large quantity, and then ammonia or potassa, no
precipitation of sesquioxide  of iron, protoxide of manganese or
alumina will ensue, since the double tartrates formed are not decom-
posed by alkalies.   Tartaric acid prevents also the precipitation of
several other oxides by alkalies.
  4.  Free tartaric acid produces with salts of potassa, and more
particularly  with the acetate, a difficultly soluble precipitate of
bitartrate  of  potassa.  A similar precipitate is formed  when
acetate of potassa and free  acetic acid are added to the  solution
of  a neutral tartrate.   The acid  tartrate  of potassa  dissolves 
§ 166.]
TARTARIC  ACID.
227
 readily in alkalies and mineral  acids;  tartaric acid and acetic acid
 do not increase its  solubility in water.  The separation of the
 bitartrate of potassa precipitate is greatly promoted by shaking, or
 by rubbing the sides of the vessel with a glass-rod.  If it is desired
 to make this reaction delicate, the  solution of tartaric acid should
 be concentrated.  If then a few drops are mixed  on a watch glass
 with a drop of strong solution of acetate of potassa and stirred
 with a glass-rod, the  minute crystals  of bitartrate of potassa  are
 formed in the track of the rod.   Addition of an equal volume of
 alcohol heightens the  delicacy of the reaction.
   5.  Chloride  of calcium throws down from  solutions of neutral
 tartrates a white precipitate of tartrate of lime (2 Ca O, C8 H4
 O,0 + 8 aq.).   Presence of ammoniacal salts retards the formation
 of this precipitate for a more  or less  considerable space of time
 (often for a long time).  Agitation of the fluid or friction on the
 6ides of the vessel promotes the separation of the precipitate.   The
 precipitate is crystalline or it invariably assumes a crystalline form
 after some time ; it dissolves in a cold not over dilute solution of
 potassa or soda, pretty free from carbonic acid,  to a clear fluid.
 But upon boiling this  solution, the dissolved tartrate of lime sepa-
 rates again in  the  form of a gelatinous precipitate,  which redis-
 solves upon cooling.
  6. Lime-water produces in solutions of neutral tartrates—and
 also in a solution of free tartaric acid, if added to  alkaline reaction
 —white precipitates which, flocculent at first, assume afterwards a
 crystalline form ; so long as they remain flocculent, they are readily
 dissolved by tartaric  acid  as well  as  by solutions of chloride of
 ammonium.  From  these  solutions the tartrate of lime separates
 again, after the lapse of several hours, in the form of small crystals
 deposited upon the sides of the vessel.
  7. Solution of sulphate of lime fails  to produce a precipitate in
 a solution of tartaric acid; in solutions of neutral tartrates it pro-
 duces a trifling precipitate after the lapse of some time.
  8. If solution of  ammonia is poured upon even a  very minute
 quantity of tartrate of lime, a small fragment of crystallized nitrate
 of silver added, and the mixture  slowly and gradually heated, the
 sides of the test-tube are covered with a bright coating of metallic
 silver.  If instead of a crystal, solution of nitrate of silver be used,
 or heat be applied more rapidly, the reduced silver will separate in
pulverulent form (Arthur  Casselmann).
  9. Acetate of lead produces white precipitates in solutions of
tartaric acid and its  salts.  The precipitate (2 Pb O, C8 H4 O10) dis-
solves readily in nitric acid and in ammonia.
  10. Nitrate of silver does not precipitate  free tartaric acid; but
in solutions of neutral tartrates it produces a white precipitate of
tartrate of silver (2 Ag  0, Cg H O10), which dissolves  readily 
228                      CITRIC  ACID.                  [§ 167.

in nitric acid and in ammonia; upon boiling it turns black, owing
to ensuing reduction of the silver to the metallic state.
   11. Upon heating hydrated  tartaric acid, or a  tartrate,  with
concentrated sulphuric acid the sulphuric acid acquires a brown
*olor almost simultaneously with the evolution of gas.

                             §  167.
               c.  Citric Acid (3 H O, C« H5 Ou).
   1. Crystallized citric acid, obtained by the  cooling of its
solution, has  the formula, 3 H  0, C12 H5 Oa -f 2 aq.  It crys-
tallizes in pellucid, colorless, and inodorous crystals of an agreeable
acid taste, which dissolve readily in water and  in spirit of wine,
and effloresce slowly  in the air.   Heated at 112° F., the crystal-
lized acid loses its water of crystallization; when subjected to the
action of a stronger heat, it fuses at first, and  afterwards carbon-
izes, with evolution of pungent acid fumes, the odor of which  may
be  readily distinguished from that emitted by tartaric acid upon
carbonization.
   2. The citrates with alkaline base are  readily soluble in water,
as well in the neutral as in the acid state ; solution  of  citric acid
is therefore not precipitated by acetate of potassa.  The compounds
of citric acid with such of the metallic oxides as are weak bases,
sesquioxide  of iron, for instance, are also readily soluble in water;
solution  of  citrate  of  sesquioxide of iron does not deposit basic
salt on  evaporating in the water bath to a syrupy consistency,
Citrates, like  tartrates, and  for  the   same reason,  prevent the
precipitation of  sesquioxide  of  iron,  protoxide of manganese,
alumina, &c, by alkalies.
   3. Chloride of calcium fails to produce a precipitate in solution
of free citric acid, even upon boiling; but  a precipitate of neutral
citrate  of lime (3 Ca O, Ci2 H5 Ou + 4 aq.) forms  immediately
upon saturating with potassa  or  soda the  concentrated solution of
citric acid, mixed with chloride  of calcium in excess.   The  pre-
cipitate  is insoluble in potassa, but it dissolves readily in solution
of chloride of ammonium; upon boiling  this chloride of ammonium
solution, neutral  citrate of lime of the same  composition separates
again in the form  of  a white crystalline precipitate, which, how-
ever, is  now no  longer soluble  in chloride of ammonium.  If a
solution of citric acid mixed with chloride of calcium is saturated
with ammonia, a precipitate will form in the cold only after many
hours' standing; but upon boiling the  clear fluid, neutral citrate
of  lime  of the properties just  stated will suddenly precipitate.
When citrate of lime is heated with ammonia and nitrate of silver,
no reduction of the latter salt ensues.
   4. Lime-water produces no precipitate in cold solutions of  citric 
§ 168.]
MALIC ACID.
229
acid or of citrates.  But  upon heating the solution to boiling,
with a tolerable excess of hot prepared lime-water, a white pre-
cipitate of citrate of lime is formed, of which the greater por-
tion redissolves upon cooling.
   5. Acetate of lead, when added in excess to a solution  of citric
acid, produces a white precipitate of citrate of lead (3  Pb O,
C,2 H5 On), which, after washing, dissolves readily in ammonia.
   6. Nitrate of silver produces in solutions  of neutral citrates of
the alkalies a white, flocculent precipitate  of citrate of silver
(3 Ag O, C,2 H5 On), which does not become black on boiling.
   7. Upon heating citric  acid or citrates with concentrated sul-
phuric acid, carbonic  oxide  and carbonic acid escape at  first, the
sulphuric acid retaining its natural color; upon continued ebullition,
however, the solution acquires a dark color, and sulphurous  acid
is evolved.
                               §168.
                d.  Malic Acid (2 H O, C3 H4 08).
   1. Hydrate of  malic  acid crystallizes  with great difficulty,
forming crystalline  crusts, which deliquesce in the air, and dissolve
readily in water and in alcohol.  Exposed  to  a temperature of
300° Fah., hydrated malic acid loses 2 eq. of water, and  slowly
passes  into  hydrated fumaric acid  (2 H O, C3 H2 O,;); by heating
to  356°  Fah. it is  resolved  into  water, Maxeic acid (2  H O,
C8  Ha Os)  which  volatilizes,  and  fumaric acid  which  remains
behind; if, finally, the temperature exceeds 392° Fah., the fumaric
acid also volatilizes.  This  deportment of malic acid is  highly
characteristic.  If the experiment is made in a  small  spoon, pun-
gent acid  vapors are evolved with frothing  effervescence.  If the
experiment is made in a small tube, maleic acid first, and afterward
fumaric acid will condense to crystals  in the colder part  of the
tube.
   2. Malic acid forms with most bases salts soluble in water.  The
acid malate of  potassa is not very difficultly soluble  in water,
hence solution of  malic  acid is not precipitated by acetate of
potassa.  Malic acid prevents, like tartaric acid, the precipitation
of sesquioxide of iron, &c, by alkalies.
   3. Chloride of calcium fails to produce a precipitate in solutions
of free malic acid.   Even after saturation with potassa or soda no
precipitate is formed.  But upon boiling, a precipitate  of  malate
of  lime  (2 Ca 0, Cs Hj 08 + 6 aq.) separates from  concentrated
solutions.  If the precipitate is  dissolved  in a very little hydro-
chloric acid, ammonia added to the solution, and the fluid boiled,
the malate of lime separates  again; but if it is dissolved in a
somewhat larger quantity  of hydrochloric acid, it will not  repre-
cipitate, after addition of ammonia in excess, even upon continued 
230
RECAPITULATION.
[§ 169.
 boiling.   Alcohol precipitates it immediately from a solution of the
 kind.  Malate of lime, when heated  with ammonia and nitrate
 of silver, nearly or altogether fails to  effect the reduction of the
 latter to the metallic state.
   4. Lime-water produces no precipitate, either in solutions of free
 malic acid or in solutions of malates.   Even on boiling, the liquid
 remains  clear, if the lime-water was prepared with boiling water.
   5. Acetate of lead throws down from solutions of malic acid and
 of malates a white precipitate of malate of lead (2 Pb O, C8 H4
 08 + 6 aq.).  The precipitation is the  most complete, if the fluid
 is neutralized  by .ammonia,  as the precipitate is  slightly soluble in
 free malic acid and acetic acid, and also in ammonia.   If the fluid
 in which the precipitate is suspended is heated to boiling, a portion
 of the precipitate dissolves, the remainder fuses to a mass resem-
 bling resin melted under water.   This reaction is distinctly marked
 only when  the  malate of lead is tolerably pure; if mixed  with
 other salts  of lead—if, for instance, ammonia is added to alkaline
 reaction,  it is  only imperfect or fails  altogether to. make  its
 appearance.
   6. Nitrate  of silver throws  down from solutions of neutral
 malates of the alkalies  a  white precipitate of malate of silver,
 which upon boiling turns a  little gray.
   7. Upon heating  malic acid  with concentrated sulphuric acid,
 carbonic  acid and carbonic oxide gas are  evolved at first;  the
 fluid then turns  brown and ultimately black, with  evolution of
 sulphurous acid.


                             § 169.
   Recapitulation and remarks.—Of the organic acids of this group,
 oxalic acid is characterized by the precipitation of its lime-salt from
 its solution in  hydrochloric  acid by ammonia, and also by acetate
 of soda,  as well as by the immediate precipitation of the free acid
by solution of sulphate of lime.   Tartaric acid is characterized by
the difficult  solubility of the acid potassa  salt, the solubility of the
lime salt in cold solution of soda and  of potassa, the deportment
of the lime salt with ammonia and nitrate of silver, and the peculiar
odor which the acid and its  salts emit upon  heating.   In presence
of the other acids it is most certainly  detected  by aid of acetate
of potassa (§ 166, 4).   Citric acid is most strongly characterized
by its deportment with lime-water, or with chloride of calcium and
ammonia in presence of chloride of ammonium.  But for its detec-
tion, oxalic and tartaric acids must have been previously removed
from the solution. Malic acid would be sufficiently characterized
by the deportment  of malate of lead when heated  under water,
 were this reaction more sensitive, and not so easily prevented by 
§ 170.]
RACEMIC ACID.
231
 the presence of other acids.  The safest means of identifying malic
 acid is to convert it into malseic acid by heating in a glass tube;
 but this conversion can  be effected successfully only with pure
 hydrate  of malic acid.   Malate of lead is  difficultly soluble  in
 ammonia, whilst  citrate  and tartrate of lead dissolve readily  in
 that agent;  this  different deportment of the lead salts of the acids
 affords also a means of distinguishing malic from citric and tarta-
 ric acids.  If only  one of the  four  acids is present in a  solution,
 lime-water will suffice to indicate which of  the four is  present;
 since malic acid is not precipitated by this reagent, citric acid only
 upon boiling, tartaric acid and oxalic acid already in the cold; and
 the tartrate of lime redissolves  upon addition of chloride of ammo-
 nium,  whilst  the  oxalate does  not.  If the four  acids together are
 present in a solution, the oxalic acid and tartaric acid  are precipi-
 tated  first by  chloride of calcium  and ammonia, in  presence of
 chloride of ammonium (the tartrate  of lime separates  under these
 circumstances  completely only after some time;  it is  separated
 from the oxalate by treating with  solution  of  soda); the citrate
 of lime is then thrown down by boiling, and the malate finally by
 means of spirit of wine.   (The precipitate  produced by  spirit of
 wine must never  be taken positively for malate of lime, without
 further proof, since the sulphate and other salts of lime are also
 precipitated by that  agent under the same circumstances.  Posi-
 tive conviction can only be attained by the production of hydrate
 of malic acid from the lime-salt.  To effect this, the precipitate  is
 dissolved in acetic acid, spirit of wine added,  and the fluid filtered,
 if necessary.   The filtrate is precipitated with acetate  of  lead, the
 fluid neutralized with  ammonia, the precipitate washed, stirred  in
 water, decomposed by hydrosulphuric acid, and the filtrate evapo-
 rated  to dryness.)
   To find a little citric or malio acid in presence  of much tartaric
 acid, the latter  is  first  thrown down by  acetate of potassa with
 addition of an equal volume of strong alcohol.   From the filtrate,
 the other acids may be precipitated by chloride of calcium if some
 more alcohol be added.

                               §170.
          Racemic Acid, or Paratartaric Acn> (2 H 0, Cs H4 O10).
  The formula of crystallized racemic acid is 2 H 0, C8 H4 0i0 + 2  aq.   The crys-
 tallization water escapes slowly in the air, but rapidly at 212° F. (difference between
 racemic  acid and tartaric acid).  Towards solvents racemic acid comports itself like
 tartaric  acid.  The racemates also show very similar deportment to that of the tar-
 trates.  However, many of them differ in the amount of water they contain, and iu
 form and solubility from the corresponding tartrates.  Aqueous solutions of racemio
 acid and racemates  do not deviate the ray of  polarized light.   Chloride  of calcium
precipitates from the solutions of free racemic  acid, and of racemates racemate ov
umk (2 Ca 0, C» H, do + 8 aq.), as a white crystalline powder.   Ammonia throws 
 232                       SUCCINIC ACID.                   [§ 171,

 down the precipitate from its solution in hydrochloric acid, either immediately or at
 least very speedily (difference between racemic acid and tartaric acid).   It dissolves
 in solution of soda and potassa, but is reprecipitated from this solution by boiling
 (difference between racemic acid and  oxalic acid).  Lime-water added in excess,
 produces immediately a white precipitate insoluble in chloride of ammonium (differ-
 ence between racemic acid and tartaric acid).   Solution of sulphate of lime does not
 immediately produce a precipitate in  a solution of racemic acid (difference between
 racemic acid and oxalic acid); however, after ten or fifteen minutes,  racemate of
 lime  separates (difference between racemic acid and tartaric acid); in solutions of
 neutral racemates the precipitate forms immediately.  With salts of potassa racemic
 acid comports itself like tartaric acid.
   If a solution of the double racemate of soda and potassa, or of the racemate of soda
 and of ammonia, is allowed to crystallize slowly, two kinds of crystals are obtained
 which differ from each other in appearance as the direct image of an  object differs
 from its image reflected from a mirror.  One set of (dextro-hemihedral) crystals con-
 tains the  ordinary (right  polarizing) tartaric  acid (dextro-tartaric acid), the other
 flaevo-hemihedral) crystals contain an acid which scarcely differs from ordinary tartaric
 acid except that it rotates the plane  of polarization to the left.   It is termed
 laevo-tartaric acid.  When the two kinds of crystals are dissolved together, the solu-
 tion has all the reactions of racemic acid.


                second group  of the organic acids.

 Acids which  Chloride of  Calcium  fails to precipitate under
   any  Circumstances,  but which are  precipitated from Neu-
   tral  Solutions  by Sesquichloride of Ibon : Succinic  Acid,
   Benzoic Acid.

                                §171.

                a. Succinic Acid (2 H O, C8 H, 06).

   1.  Hydrate  of  Succinic  acid forms  colorless and  inodorous
prisms or tables  of  slightly acid taste, which are readily soluble in
water, alcohol, and  ether, difficultly soluble in nitric acid, and vola-
tilize when exposed to the action of heat, leaving only a little char-
coal behind.   The  officinal acid  has  an empyreumatic odor, and
leaves a somewhat larger carbonaceous residue upon volatilization.
Succinic acid is not  destroyed  by heating with nitric acid, and may
therefore be  easily  obtained in the pure state by boiling with that
acid for half an hour,  by which means the oil of amber, if present,
will be destroyed.   By sublimation crystalline needles of  silky lus-
tre are obtained; the hydrate  loses water  in  this process, so that
by repeated sublimation  anhydrous acid  is  ultimately  obtained.
Heated in the air, succinic acid burns  with a  blue flame, free from
soot.
   2.  The succinates  are decomposed at a red heat; those which
have an alkali or alkaline earth for base, are converted into  carbo-
nates in this process, the change being attended with separation of
charcoal.  Most of the succinates are soluble in water.
   3.  Sesquichloride of iron produces in solutions of  neutral succi« 
§ 172.]
BENZOIC ACID.
233
nates of the alkalies a brownish pale-red, bulky precipitate of suc-
cinate of sesquioxide of  iron (Fe2 03, C8 H4 0();  one-third of
the succinic acid is liberated in this  reaction,  and retains part of
the precipitate in solution, if the fluid is filtered off hot.   The pre-
cipitate dissolves readily in mineral acids; ammonia decomposes it,
causing the separation of a less bulky precipitate of a highly basic
succinate of sesquioxide  of iron, and combining with the greater
portion of the acid to succinate of ammonia, which dissolves.
   4. Acetate of lead gives with succinic acid a white precipitate of
neutral succinate of lead (2 Pb O,  Cd H4 06), which is very spar-
ingly soluble in water, acetic acid, and succinic acid, but dissolves
readily in solution of acetate of lead and in nitric acid.  Treated
with ammonia,  the  neutral  succinate of lead is converted into a
basic salt (6 Pb O, C8 H4 Oe).
   5. A mixture of alcohol, ammonia, and solution of chloride of
barium produces in solutions of free succinic acid and of succinates
a white precipitate of succinate of baryta  (2 Ba O, C H, 06).
   6. Nitrate of suboxide of mercury and nitrate of silver  also pre-
cipitate the succinates ; the precipitates, however, are not possessed
of any characteristic properties.

                             § 1?2.
               b.  Benzoic Acid (H  O, Ch H5 03).
   1. Pure hydrate  of benzoic acid forms inodorous white scales
or needles, or simply a crystalline powder.  When heated, it fuses,
and afterwards volatilizes completely.  The  fumes of  benzoic acid
cause a peculiar irritating sensation in  the throat, and  provoke
coughing; when  cautiously cooled,  they condense  to  brilliant
needles,  when  kindled, they burn with  a luminous  sooty flame.
The common officinal hydrate of benzoic acid has the odor of ben-
zoin, and leaves a small carbonaceous residue  upon volatilization.
Hydrate of benzoic acid  is very sparingly soluble  in  cold water,
but it dissolves pretty readily in hot water and in alcohol.  Addi-
tion  of water, therefore, imparts  a milky turbidity to a saturated
solution of benzoic acid in alcohol.
  2.  Most of the benzoates are soluble in water; only those with
weak bases, e. g., sesquioxide of iron, are insoluble.   The soluble
benzoates have  a peculiar,  pungent taste.  The  addition of a strong
acid to aqueous solutions  of benzoates displaces the benzoic acid,
which separates as hydrate in  the form of a dazzling white, spar-
ingly soluble powder.  Benzoic acid  is expelled in  the same way
from the insoluble benzoates, by such strong acids as form soluble
salts with the bases with which the benzoic acid is combined.
  3.  Sesquichloride of iron  precipitates solutions of free benzoic
acid incompletely; solutions of neutral benzoates  of the  alkalies
completely.   The precipitate  of benzoate  of  sesquioxide op 
234                     ACETIC  ACID.            [§§ 173, 174.

tRON (2 Fe2 03, 3 [Cu H5 03]  + 15 aq.) is bulky, flesh-colored, in-
soluble in water.  It is decomposed by ammonia in the same man-
ner as succinate of sesquioxide of iron, from which salt it differs in
this, that it dissolves  in a little hydrochloric acid, with separation
of the greater portion of the benzoic acid.
  4. Acetate  of  lead fails  to precipitate  free  benzoic acid and
benzoate of ammonia, at least immediately; but it produces white,
flocculent precipitates in solutions of benzoates  with a fixed alka-
line base.
  5. A mixture of alcohol, ammonia, and solution  of chloride of
barium produces no precipitate in solutions of free benzoic acid or
of the alkaline benzoates.

                            § !73.
  Recapitulation and remarks.—Succinic and  benzoic  acids  are
distinguished  from all other  acids by the facility with which they
may be sublimed, and by their deportment with  sesquichloride of
iron.  They are distinguished from one another by the different
color of their salts with sesquioxide of iron, and also by their differ-
ent deportment with chloride of barium and alcohol; but princi-
pally by their different degrees of solubility, succinic acid being
readily soluble in water, whilst benzoic acid  is very difficult of solu-
tion.  Succinic acid  is seldom perfectly pure, and may therefore
often be detected by the odor of oil of amber which it emits.
  The detection of the two  acids, when present in the same solu-
tion with other acids, may be effected  as follows: precipitate with
sesquichloride of iron, warm the washed precipitate with ammonia,
filter, concentrate the solution, divide  it into two parts, and mix
one part with hydrochloric acid, the other with chloride of barium
and alcohol.
  Succinic acid and benzoic acid  do not prevent the precipitation
of sesquioxide of iron, alumina, &c, by alkalies.

            third  group of the inorganic group.
Acids  which are  not  precipitated  by Chloride  of Calcium
    nor  by  Sesquichloride of Iron :  Acetic  Acid,  Formic
    Acid.  (Lactic Acid, Propionic Acid, Butyric Acid).

                             § 174.
                a.  Acetic Acid (H O, C4 H3 03).
 . 1. The  hydrate of acetic acid forms  transparent  crystalline
scales, which fuse at 62'6° F. to a colorless fluid  of a peculiar, pun-
gent  and  penetrating odor, and exceedingly acid taste.  When
exposed to the action  of  heat, it volatilizes completely, forming
pungent inflammable vapors, which burn with a blue flame.  It is 
§ 174.]
ACETIC ACID.
235
miscible with water in all proportions; it is to such mixtures of the
acid with water that the name of acetic acid is commonly applied.
The hydrate of acetic acid is also soluble in alcohol.
   2. The  acetates undergo decomposition at a red heat;  among
the products  of this decomposition we generally find hydrate  of
acetic acid, and almost invariably acetone (C6 H3 O,).   The acetates
of the alkalies and alkaline earths are converted into carbonates in
this process ; of the acetates with metallic bases many leave the
metal behind in the pure  state, others in the form of oxide.  Most
of the residues which the acetates  leave upon ignition are carbo-
naceous.  Nearly all acetates dissolve  in water and in alcohol;
most of them are readily soluble in water, a few only are difficult
of solution in that menstruum.  If acetates are distilled with dilute
sulphuric acid, the free acetic acid is obtained in the distillate.
   3. If sesquichloride of  iron is added to acetic acid, and the acid
is then nearly saturated with ammonia, or if  a  neutral acetate is
mixed with sesquichloride of iron, the fluid acquires  a deep dark-
red color, owing to the formation  of acetate of  sesquioxide of
iron.  Upon boiling, the fluid becomes colorless if it  contains an
excess of acetate, the whole of the sesquioxide of iron  precipitating
as a basic acetate, in the  form of brown-yellow flocks.  Ammonia
precipitates from it the whole of the sesquioxide of iron as hydrate.
Upon  addition  of hydrochloric acid,  a fluid which  appears red
from the presence of acetate of sesquioxide of  iron turns  yellow
(difference from sulphocyanide of iron).
   4. Neutral acetates (but not free acetic  acid) give with nitrate
of silver white, crystalline precipitates of acetate of silver (Ag
0, C, H, 03), which are very sparingly soluble in cold water.  They
dissolve more easily in hot water, but separate again upon cooling,
in the form of very fine crystals.  Ammonia dissolves them readily;
free acetic acid does not increase their solubility in water.
  5. Nitrate of suboxide of mercury produces in solutions of acetic
acid, and more readily still in  solutions of acetates, white, scaly
crystalline precipitates of acetate of suboxide of mercury (Hg,
0, C4 H3 03), which are sparingly soluble in water and acetic acid
in the cold, but dissolve without difficulty in an excess of the pre-
cipitant.  The  precipitates dissolve in water upon heating, but
separate again upon cooling, in  the form of small crystals;  in this
process  the salt undergoes partial decomposition: a portion of the
mercury separates in the metallic  state, and imparts  a gray color
to the precipitate.  If the acetate of suboxide of mercury is boiled
with dilute acetic acid instead of water, the  quantity of the me-
tallic mercury which separates is exceedingly minute.
  6.  Chloride of mercury heated with solutions  of acetic acid or
of acetates yields no precipitate of subchloride of mercury.
  '7.  When acetates are heated with concentrated sulphuric acid, 
236                     FORMIC ACID.                  [§ 175

hydrate of acetic acid is evolved, which may be known by its
pungent odor.  But if the acetates are  heated with a mixture of
about equal volumes  of concentrated sulphuric  acid and  alcohol,
acetic ether (C4 H5 O, C4 H3 03) is formed.   The odor of this ether
is  highly characteristic and agreeable; it  is  most distinct upon
shaking the mixture when somewhat cooled, and is much less liable
to lead to mistakes than the pungent odor of the free acetic acid.
  7. If  acetates are distilled  with dilute sulphuric acid,  and the
distillate is digested with an  excess of oxide of lead, part of the
latter dissolves  as basic acetate  of lead, which may  be readily
recognised by its alkaline reaction.

                             §  175.
                b. Formic Acid (H O, Ca H 03).
  1. The  hydrate  of formic acid is  a transparent, colorless,
slightly fuming liquid,  of a  characteristic and exceedingly pene-
trating  odor.  When  cooled  to below  32° F., it crystallizes in
colorless plates.  It is miscible  in all proportions with water and
with alcohol.  When  exposed to  the action of heat, it volatilizes
completely;  the vapors are  inflammable and burn with a  blue
flame.
  2. The formates, like the corresponding acetates, leave upon
ignition either  carbonates,  oxides, or metals behind, the process
being attended with separation of charcoal, and escape of carbide
of hydrogen, carbonic acid,  and water.  All the compounds of
formic .acid with bases are  soluble in water; alcohol likewise dis-
solves some of them.
  3. Formic acid presents the same deportment with sesquichloride
of  iron as acetic acid.
  4. Nitrate  of silver  fails to  precipitate  free formic acid, and
affects the alkaline formates only in concentrated  solutions.  The
white,  sparingly  soluble, crystalline  precipitate  of formate of
silver (Ag O, C2 H 03) acquires very rapidly a darker tint, owing
to the separation of metallic  silver.  Complete reduction of the
oxide of silver to the metallic  state takes place, even in the cold,
after the lapse of some time ; but immediately, upon applying heat
to the fluid containing the precipitated  formate of silver.  The
same reduction of the  oxide  of silver to the metallic state takes
place in a solution of free formic acid, and also in solutions of for-
mates so dilute that the addition  of the nitrate of silver failed to
produce a precipitate in them.   But it does not take place in pre-
sence of an excess of ammonia. The rationale of this reduction is as
follows : the formic acid, which may be looked upon as a compound
of carbonic oxide with water, deprives the  oxide  of silver  of its
oxygen, thus causing the formation   of  carbonic acid, which 
§ 176.]                 RECAPITULATION.                   237

escapes, and of water, whilst the  reduced silver separates in  the
metallic state.
  5.  Nitrate of suboxide of mercury gives no precipitate with free
formic acid; but in concentrated solutions of alkaline formates this
reagent produces a white, sparingly soluble precipitate of formate
of suboxide of mercury (Hg20, C2 H 03), which rapidly becomes
gray, owing  to  the separation of metallic mercury.   Complete
reduction ensues, even in the cold, after  the  lapse  of some time,
but is immediate upon application of heat.   This  reduction is
also attended with the formation of carbonic  acid and water, and
takes place, the same as with the oxide of silver, both in solutions
of free formic acid and in fluids so highly dilute that the  formate
of suboxide of mercury is retained in solution.
  6.  If formic acid or an alkaline formate is heated with chloride
of mercury to from 140° to  158° F., subchloride of  mercury
precipitates.  Free hydrochloric acid, as well  as a large quantity
of alkaline chlorides  prevent this reaction.
  7.  If  formic acid or  a formate is heated  with concentrated
sulphuric acid, the formic acid is resolved into water and carbonic
oxide gas, which latter escapes with effervescence, and if kindled,
burns with a  blue flame. The fluid  does not  turn black in this
process.  The rationale of the  decomposition  of the formic acid is
this: the sulphuric acid withdraws from the formic acid the water or
the oxide  necessary for the existence of the latter  acid, and thus
occasions a transposition of its elements (C2 H03 = 2 CO-f-HO).
Upon heating  formates with  dilute sulphuric  acid in a distilling
apparatus, free formic  acid is  obtained in the distillate, and may
mostly be  readily detected  by its  odor.  Upon  heating a  for-
mate with  a  mixture  of sulphuric acid  and alcohol, formic ether
is  evolved, which is  characterized  by  its  peculiar arrack-like
smell.
  8.  If dilute formic acid is heated with oxide of lead, the latter
dissolves.   On cooling the solution, which, if  necessary,  is concen-
trated by  evaporation, the formate  of lead (Pb O,  Ca H  03)
separates in brilliant prisms or  needles.

                            §176.
  Recapitulation and remarks.—Acetic acid and formic acia may
be distilled over with water, and form with sesquioxide  of iron
soluble neutral salts  which dissolve in water, imparting to the fluid
a blood-red color, and are decomposed upon boiling.  These reac-
tions distinguish the two acids  of  the third group from the other
organic acids.  From  each other  the two acids are distinguished
by the odor of their hydrates and ethyle compounds, and by their
different deportment with sails  of silver and  salts of mercury,
oxide of lead, and concentrated sulphuric  acid.  The separation 
 238                         PROPIONIC ACTD.                    [§  177,

 of acetic acid from formic  acid  is  effected  by heating the mixture
 of the two  acids with an excess of  oxide  of mercury or oxide of
 silver.   Formic acid reduces the oxides, and  suffers decomposition,
 being resolve!  into  carbonic  oxide and water; whilst  the  acetic
 acid combines with  the  oxides, forming acetates, which  remain L
 Bolution.

                                    ? 177.
             Mo". rarC-j otcurriig Organic Aciii of i'rie T\ir& Group.
  1. Lactic acid i2HO, Cu H1tOu) is found in some of the liquids of the animal
 oodv. in milk and in vegetable juices which have soured.  When pore, its hydrate
 e a syrupy liquid which has no odor, but possesses a purely acid  and bit-? taste.
 When slowly heated at -2-j-i' Fan., it yields a d-sallate  of water and a little h7i.-i-.ri
acid, and leaves a residue of lactic anhydride (Ca Hit  On), which at higher tem-
peratures  i'4i'j:-370° Fah. i3 resolved into  earoonic oxide, carbonic acid, lactide
and other products.  Lactic acid  dissolves  with ease  in water, alcohol  and ether
Cm boiling the  aqueous solution a portion  of the acid e=teres with the vapors of
 water.  The  lactates are all soluble in water and alcohol, most of them, however
with difficulty.   In ether they are all insoluble.  The best mode  of proceeding for
the detection of lactic arid consists  in p-eoirlig certain of its salts, and observi:.?
their form under the microscope.  The salts best adapted for this purpose are those
of lime and zinc   To prepare the lime salt from animal or ve^etehle juices the
method cf .5 '-vrer is  to  be recommended.   Tr.e liquid is  dilute! if needful  with
water, treated with baryta water,  and altered from the precipitate.  The filtrate is
disti.led with a  little  sulphuric acid  to remove volatile acids) and  the residue is
digested :';r  several days with strong alcohoL  The acid solution is distilled with
addition of milk  of lime, filtered warm  from  the  excess  of lime and frjm pre
capitated sulphate of lime, and subjected to  a  stream of carbonic acid gas. a?ain
heated to boiling, and  filtered from carbonate of lime, and  evaporated  to dryness.
The  residue is  wanned and digested with  strong alcohol filtered and the neutral
nitrate set aside for some days for the lactate of lime to deposit.  If so little lactic
a::d be present that no crystals separate, the liquid is  evaporated to the consistence
of syrup, strong alcohol is added,  the mixture allowed to stand some time, and the
alcoholic solution poured or  filtered Into a stoppered vessel and a small : u.:.:t
of ether is added by degrees.  By this treatment even trace; of lactate of lime may
be broutrht to crystallization.   Under the microscope this  salt appears  in tufts cf
needles, of which there are always some specimens that resemble two brusies joined
base to base.  Lactate of zinc when rapidly deposited appears under  the m::r:sccpe
in the form of globular groups  of needles.   When it  crystallizes  slowly it  at  urst
yields crystals with curved faces, and narrower at one end than at the other, like a
club.   Their crystals gradually increase in  size, the extremities become narrower,
while the middle thickens i'fV:>:.
  2  PBOPioyic acid  iH  O,  C«  H5 Os) and 3. Bttttbic actd (H 0. d H7  Cm
 Prttl :.c add is produced under  a gr^at  variety of circumstances, it is found
 especially in fermented liquids.   The pure hydrated add crystallizes In minute plates,
 it boils  at 2 = 4=—-li3~^ Pal:., is easily soluble in  water, upon hydrated phosphoric acid
 or chloride of calcium  solution, it floats as an ofly layer.  It  has a peculiar  odor.
 remind in?  at  once of acetic  and butyric  acids.  On distilling its  aqueous  -.*>
 tion. it passes over with the water.   Butyric acid occurs in animal and vegetable
 matters, especially  in fermented  liquids of  the most  various kinds.  The  pure
 hydrate is a colorless, mobile, caustic, very sour liquid which bolls  at about  320°
 Fak, and has a disagreeable odor,  partaking of that of  rancid butter and acetic acid,
 t is  soluble in water  and alcohol in all proportions; from  concentrated aqueous 
§ 177.]
PROPIONIC ACID.
239
solutions it is separated by chloride of calcium, strong acids, &c, in the form of a
thin oil  Its odor is especially marked in its aqueous solution.   It distils over when
heated with water.
  Propionic and butyric acids occur in fermented liquids, in guano and in many
mineral waters, often associated with formic and acetic acids.  In such mixtures ono
may operate as follows, to  detect the  individual acids: The  substance, sufficiently
diluted with water, is acidulated with sulphuric acid and distilled.  The distillate is
saturated with baryta  water, evaporated   to dryness, and the  residue  repeatedly
extracted with boiling alcohol of 85 per cent.   By this means a solution is obtained
in which exist the propionate, butyrate, and a part of the acetate of baryta, while
the  formate and a part of the acetate remain undissolved.   The alcoholic solution is *
evaporated  to dryness,  the  residue dissolved in water, decomposed by cautious addi-
tion of sulphate of silver (of which not quite enough to  throw down  the  baryta,
rather than  an excess, should be employed), boiled, filtered, and the solution evapo-
rated in a desiccator.  The crystals which form at first, an intermediate crop, and a
final crop, are collected and examined separately.  The acetate of silver when dis
solved in concentrated  sulphuric acid, gives the odor of acetic acid, and no oily drop-
lets ; propionate and butyrate of silver under the same treatment yield oil-drops (in
Bmall quantities to be recognized only by  the  help  of a  microscope), and further,
give the odor peculiar to these acids.  In order, however, to decide with certainty
between propionic and butyric acids, it is necessary to determine the per centage of
silver in the  salts  separated by  crystallization, and thence calculate  the atomic
weight of the acids.
  In a solution which  contains a large quantity of acetic acid with but little pro-
pionic and butyric acids, that portion  of the  baryta salts taken up by alcohol is
Drought into aqueous   solution,  from it the  baryta  is exactly thrown down  by
Bulpliuric acid; one-half of the  acid solution  is now  neutralized by  carbonate of
soda, the other  half added and  the whole subjected to distillation.   The distillate
which contains, principally, the propionic and butyric acids is saturated with baryta,
decomposed by sulphate of silver and further treated as above directed. 
• 
PART  II.
SYSTEMATIC  COUESE .
QUALITATIVE CHEMICAL  ANALYSIS. 
 
PART   II.
               PRELIMINARY  REMARKS

                            ON THE

COURSE  OF QUALITATIVE ANALYSIS IN GENERAL AND ON THE PLAN
     OF THIS PART OF THE PRESENT WORK IN PARTICULAR.

The knowledge of reagents and of the deportment of other bodies
with them enables us  to ascertain at once whether a compound of
which the  physical properties permit an inference as to its nature,
is in reality what we suspect it to be.  Thus,  for instance, a  few
simple reactions suffice to show whether a body which appears to
be calcareous spar, is really carbonate of lime, and that another,
which we  hold to be gypsum, is actually sulphate of  lime.   This
knowledge usually suffices  also to ascertain whether a certain body
is present or not in a compound ; for instance,  whether or  not a
white powder contains subchloride of mercury.  But if our design
is to ascertain the chemical nature of a substance entirely unknown
to us—if we wish to discover all the constituents of a mixture or
chemical compound—if we intend to prove that, besides certain
bodies which we have detected in a mixture or compound, no other
substance can possibly be present—if consequently a complete quali-
tative analysis  is our object, the mere knowledge of the reagents,
and of the reactions of other bodies with them, will not suffice for
the  attainment of this end ; this requires the additional knowledge
of a systematic  and progressive course of analysis, in other words,
the  knowledge  of the order and succession in which solvents, and
general and special reagents, should be applied,  both  to effect the
speedy and certain detection of every component element of a.com-
pound or mixture, and to  prove with certainty the absence of all
other substances.   If we do not possess the knowledge of this sys-
tematic  course, or if, in  the hope  of attaining our object more
rapidly, we adhere to no  method whatever in  our investigations
and experiments,  analyzing becomes  (at least in  the  hands  of a
novice) mere guess-work, and the results obtained are no longer
the  fruits  of scientific calculation, but mere matters  of accident,
which sometimes may prove lucky hits, and at others total failures. 
244
PRELIMINARY REMARKS.
  Every analytical investigation must therefore be based upon a
definite method.  But it  is not by any means nece=sary that thia
method should be the same in all cases.  Practice,  reflection,  and
a due  attention to circumstances  will, on the contrary,  generally
lead to the adoption of different methods for different cases.   How-
ever, all analytical methods agree in this, that the substances pre-
sent or supposed to be present in a compound or mixture, are in
the first place  classed into certain groups, which are then again
subdivided, until the individual detection of the various substances
present is finally  accomplished.   The  diversity  of analytical
methods depends partly on the order  and succession in which rea-
gents are applied, and partly on their selection.
  Before we can venture upon inventing methods  of our own for
individual cases,  we must first make  ourselves thoroughly conver-
sant with a certain definite course, or system, of chemical analysis
in general.  This system must have passed through  the ordeal of
experience, and must be adapted to every imaginable case, so that
afterwards, when we have acquired some  practice in analysis, we
may be able to determine which modification of the general method
will in  certain  given  cases  most  readily  and rapidly lead to  the
attainment of the object in view.
  The exposition of such a systematic course, adapted to  all cases,
tested  by experience, and combining simplicity with the greatest
possible security,  is the object of  the First Section of the second
part of this work.
  The  elements  and  compounds  comprised  in it  are  the same
which  we have  studied in  Part  I., with the  exception of those
given in that part simply by way of appendix,  or printed in
smaller type.
  The  First Section  of the Second Part consists of practical
instructions in  analysis, wherein I have laid down a systematic
course  which, with due care and attention, will, by  progressive
steps, lead speedily and safely to the attainment of the end in view.
  The  subdivisions of this practical course are :
  1, Preliminary examination ;
  2, Solution;
  3, Actual analysis.
  The  third  subdivision  (the actual  analysis) is again  subdi-
vided into, (1)  Examination of compounds in which but one base
and one acid are assumed to be present; and, (2) Examination of
mixtures or compounds in which all  the substances treated of in
the present work are  assumed to  be present.  With respect to the
latter section, I have to remark that where the preliminary exami-
nation  has not clearly demonstrated the absence of certain groups
of substances, the student cannot safely disregard any  of the para-
graphs to which reference is made in consequence of the reactions 
PRELIMINARY  REMARKS.
245
observed.  In cases where the intention  is simply to test a com-
pound or mixture for certain substances, and not to ascertain all its
constituents, it will be easy to select the particular numbers which
ought to be attended to.
  As the construction of a universally applicable systematic course
of analysis requires due regard to, and provision for, every contin-
gency that may possibly arise, it is self-evident that, though in the
system here laid down the various bodies comprised in it have been
assumed to be mixed up together in every conceivable way, it was
absolutely indispensable  to proceed throughout upon the supposi-
tion that no foreign organic matters whatever were present, since
the presence  of such matters would of course  tend to prevent or
obscure many reactions, and variously modify others.
  Although the general analytical course laid down here is devised
and arranged in a manner to suit all possible  contingencies,  with a
very few exceptions, still there are special cases in which it may
be advisable  to  modify  it.  A preliminary treatment of the sub-
stance is also sometimes necessary, before the  actual analysis can be
proceeded with; the presence of coloring, slimy,  organic matters
more especially requires certain preliminary operations.
  Not to leave the student without a guide in these special cases,
the Second Section of this Part will be found to contain a detailed
description of the  methods employed to effect the analysis of a few
important compounds and mixtures which chemists are frequently
called upon to examine.  Some of these  methods show  how the
analytical process becomes simplified as the number of substances
decreases to which regard must be had in  the analysis.
  In conclusion,  as an intelligent and successful pursuit of analysis
is  possible only  with  an accurate  knowledge of the principles
whereon the  detection and separation of  bodies depend, since this
knowledge alone can furnish the student with a guide to the selec-
tion of the proper reagents, and the  order in which they ought to
be applied, I  have  given in the  Third Section of  the Second Part
an explanation and elucidation of the general analytical process,
with numerous additions to the practical operations.   As this third
section may properly be regarded as the key to the first and second
sections, I strongly recommend students to make themselves early
and thoroughly acquainted with  it.   I have  devoted  a special sec-
tion to this theoretical explanation of the process, as I think it will
be understood better in a connected form, than it would have been
by explanatory additions to the several paragraphs, which, more-
over might have materially interfered with the plainness and per-
spicuity of the plan of the practical process.
  In this Third Section  I have  also indicated  in what residues,
solutions, precipitates, &c, as obtained in the systematic course,
the operator may look for the elements of more rare occurrence, 
246
PRELIMINARY EXAMINATION.     [§§ 178, 179
and how these bodies may be systematically and surely detected in
analyses where they are likely to be present.
                     SECTION  I.

PRACTICAL  PROCESS FOR THE  ANALYSIS OF  COM
       POUNDS AND  MIXTURES IN  GENERAL.

                I. Preliminary Examination.*
                            § 178.
  1. Examine, in the first  place, the physical  properties— if
color, shape, hardness, gravity,  odor, &c.—of the substance
intended for analysis, since these will often enable you in some
measure to infer  its  nature.  Before proceeding to the appli-
cation of any chemical process,  you must  always consider
how much of the substance to be analyzed you have at com-
mand, since it  is necessary, at this early period of the exa-
mination, to  calculate the quantity which may safely be used
in the preliminary investigation.   A reasonable economy is in
all cases advisable,  even  though you may  possess the sub-
Btance in large quantities; but, under all circumstances, let it
be a fixed  rule, never to  use  at once the whole of what you
possess of a substance, but always to keep a portion of it for
unforeseen contingencies, and for confirmatory experiments.

         A. The Body under  Examination is Solid.
       I. It is neither a Pure Metal nor an Alloy.
                            § 179.
  1.  The substance is fit for examination if in powder or in 2
minute crystals ; but if in larger crystals or in solid pieces, it
is necessary in  the first place to  reduce  a portion of it to fine
powder, if  practicable.  Bodies of the  softer kind  may be
triturated in a porcelain  mortar; those of a harder nature
must first be broken into  small  pieces in a steel mortar, or
upon a steel anvil, and the pieces  then be triturated in  an
agate mortar.
  2.  Put some of the powder  into a glass tube, sealed 3
at one end, about 2  inches long and fgths  of an  inch
wide, and heat, first gently over the spirit  or gas-lamp, then
intensely in the blowpipe flame.  The reactions resulting may

     * Consult also the observations and additions in the Third Section.
     \ These marginal numbers are simply intended to facilitate reference. 
§ 170.]          preliminary examination.             247

lead to many positive  or probable conclusions  regarding the
nature of the substance.  The following are the most import-
ant of these reactions, to which particular attention  ought to
be paid ;  it often occurs that several of them are observed in
the case of one and the same substance.
      a.  The substance  remains unaltered: absence of 4
    organic matters, salts containing water of crystallization,
    readily fusible matters, and volatile bodies.
      b.  The  substance  does not fuse  at a moderate 5
    heat, but simply  changes color.  From white to yel-
    low,  turning white again on cooling, indicates oxide of
    zinc: from white to  yellowish-brown, turning to a dirty
    light yellow on cooling, indicates binoxide  of tin ; if the
    color changes from white or reddish-yellow to brownish-
    red, turning to yellow on cooling,  and the body is fusible
    at a  red heat, this indicates  the  presence  of oxide of
    lead ; if the color changes from white to orange-yellow,
    or a deeper and more reddish  tint, up to reddish-brown,
    turning pale yellow on cooling, and the  body fuses at an
    intense  red heat, this indicates the  presence  of teroxide
    of bismuth ; if the color changes from red to black, turn-
    ing red again on cooling, this indicates the presence of
    sesquioxide of iron ;  if from yellow to dark orange the
    substance being fusible at a strong heat, it indicates neu-
    tral chromate of potassa, &c.
      c. The substance fuses without expulsion of aque- 6
    ous vapor.  If on intense heating, gas (oxygen) is  evolved,
    and a small fragment  of charcoal thrown  in is energe-
    tically consumed,nitrates or chlorates maybe  assumed
    to be present.
      d. Aqueous vapors are  expelled, which condense 7
    in the colder part of the tube :  this indicates  the pre-
    sence either  (a) of substances containing water of
    crystallization, in which case they will generally readily
    fuse, and re-solidify after expulsion  of the water;  many of
    these  swell considerably whilst yielding up  their water,
    e. g. (borax, alum); or (8) of decomposable hydrates, in
    which case the bodies often will not fuse ; or (7) of anhy-
    drous salts, holding water, mechanically enclosed between
   their lamellae—in which case the bodies will decrepitate ;
    or (S)  of bodies with moisture externally adhering to them.
     Test the reaction of the  condensed  fluid  in the  tube:
   if it is alkaline, ammonia may be assumed to be present;
   if acid,  a volatile  acid (sulphuric acid, sulphurous acid,
   hydrofluoric acid, hydrochloric, hydrobromic, or hydriodic
   acids, nitric acid, &c). 
preliminary examination.          [§
  e. Gases  or fumes escape.  Observe whether they
have a  color, smell, acid or alkaline reaction, whether
they are inflammable, cfcc.
    aa. Oxygen.  The disengagement of this gas indi-
  cates the presence of peroxides, chlorates, nitrates, &c.
  A glimmering slip of wood is relighted in  the gaseous
  current.
    bb.  Sulphurous acid.   This is often produced by
  the  decomposition of sulphates; it may be known by
  its peculiar odor and by its acid reaction.
    cc.  Hyponitric acid, resulting from  the decomposi-
  tion  of nitrates, especially with oxides of the  heavy
  metals; it may be known by the brownish-red color of
  the fumes.
    dd. Carbonic acid.  The evolution of carbonic acid
  indicates the presence of  carbonates decomposable by
  heat [or if accompanied by carbonization (see  10) of
  organic bodies].  The gas  evolved is colorless and taste-
  less, non-inflammable; a drop of lime-water on a watch-
  glass becomes turbid on exposure to the gaseous current.
    ee.  Carbonic  oxide  gas.   The  escape  of this  gas
  indicates the presence of oxalates, and,  when attended
  with actual carbonization, also of formates.  The gas
  burns with a blue flame.  When evolved from oxalates,
  it is mingled with carbonic acid, and is more difficult to
  kindle.  Oxalates when placed with a little water  and
  pulverized binoxide of manganese on a watch-glass and
  a few drops of oil of vitriol added, effervesce from  evo-
  lution of carbonic acid, formates do not.
   ff.  Cyanogen.  The  evolution of cyanogen gas de-
  notes the presence of cyanides decomposable by heat.
  The gas may be known by its odor, and the crimson
  flame with which it burns.
   gg.  Hydrosulphuric acid gas.  The escape of hydro-
  sulphuric acid gas indicates the presence of sulphides
  containing water ; the gas may be readily known by its
  odor.
    hh. Ammonia, resulting from the decomposition of
  ammoniacal salts, or also of cyanides  or  nitrogenous
  organic matters,  in which latter cases browning or car-
  bonization  of  the  substance takes place,  and either
  cyanogen  or offensive empyreumatic oils escape with
  the ammonia.
  /. A sublimate forms.  This indicates the presence of
volatile bodies: the following are those more frequently
met with:— 
§ 179.]          preliminary examination.
     aa. Sulphur.   Separated from  mixtures or from
  many of the metallic sulphides.  Sublimes in reddish-
  brown drops which become solid  on cooling, and turn
  yellow, or yellowish-brown.
     bb. Ammonia salts give white sublimates;  heated
  with soda and a drop of water on  platinum foil, they
  evolve ammonia.
     cc. Mercury and compounds of mercury.  Metallic
  mercury forms  globules; sulphide of  mercury is
  black, but acquires a red tint when rubbed; chloride
  of mercury fuses before volatilizing; subchloride of
  mercury sublimes without previous fusion; the sub-
  limate,  which  is  yellow whilst  hot, turns white  on
  cooling. The red iodide of mercury  gives a yellow
  sublimate.
     dd. Arsenic and compounds of that metal.  Metal-
  lic arsenic  forms the  well-known  arsenical mirror;
  arsenious acid forms small shining crystals; the sul-
  phides  of  arsenic give sublimates which  are reddish-
  yellow whilst hot, and turn yellow on cooling.
     ee. Teroxide of antimony fuses to a yellow liquid
  before subliming.  The sublimate consists of brilliant
  needles.
    ff. Benzoic acid and  succinic acid, which may be
  known by the odor of their fumes.
     gg. Hydrated oxalic acid.  White  crystalline sub-
  limate,  thick fumes in  the tube.   Heating a small
  sample  on  platinum  foil with  a  drop of concentrated
  sulphuric acid  gives rise  to  a  copious  evolution of
  gas.
  g. Carbonization takes place : organic substances.
This is always attended with evolution of gases (in the
case of acetates,  of acetone) and water, which latter has
an alkaline or  acid  reaction.  If the  residue effervesces
with acids, whilst  the  original  substance  did  not show
this  reaction, organic acids may be assumed to be pre-
sent in combination with alkalies or  alkaline  earths.
[Since the observations suggested by this paragraph will
decide the operator, whether or not to look for an organic
acid in the subsequent  analysis, it may be well to caution
the  beginner not to be too hasty in concluding  that car-
bonization does or does not occur.   In addition to what
is stated above, we may mention that: 1.  Blackening is
not  necessarily carbonization, for salts of volatile acids
with certain oxides, as  those of copper, nickel and cobalt,
blacken on ignition from  separation   of the  oxide.  2. 
250              preliminary examination.          [§ 179

    Carbonization, i. e., the separation  of carbon, is usually
    attended with the  disengagement of vapors, which often
    condense  in oily droplets, or as an oily film on the cold
    part of the tube, and  which have  a  " burnt" odor.  3.
    The carbon remaining  after these vapors cease to  escape
    usually takes fire when heated in cogtact with the air, and
    glows with red-heat until it is consumed.  4.  Carboniza-
    tion is, in general, best observed when the body is heated
    rapidly to a high temperature.]
  3. Put a small portion of the substance on a charcoal i i
SUPPORT (IN THE CAVITY SCOOPED OUT FOR THE PURPOSE), AND
EXPOSE TO THE INNER BLOWPIPE FLAME.
  As most of the reactions  described under 2 (3—10) are also
produced  by this process, I will here  enumerate  only those
which result more particularly and exclusively from its appli-
cation.   Evolution  of sulphurous acid in this  experiment,
usually denotes the presence of a metallic sulphide.
        a. The body  fuses, and is absorbed by the char- 1 a
       coal or forms a  bead in the cavity without  incrus-
       tation of the charcoal: this denotes more particularly
       the presence of salts of the alkalies.
        b. An infusible  white  residue  remains on  the l.l
       charcoal, either at once or after previous melting in the
       water  of crystallization.  This indicates more particu-
       larly the presence of baryta,  strontia, lime, magnesia,
       alumina, oxide of zinc (which appears  yellow whilst
       hot), and silicic acid. Among these substances,  stron-
       tia, lime, magnesia, and oxide of zinc,  are  distin-
       guished by strong luminosity in the  blowpipe flame.
       Moisten the white residue with  a drop  of solution of
       nitrate  of protoxide of cobalt, and expose  again  to  a
       strong heat.  If the mass assumes a fine blue  tint, this
       indicates the presence of alumina;  if a reddish  tint, of
       magnesia; if a green  color, of  oxide of  zinc.  If
       silicic  acid is present, the mass also assumes a  faint
       bluish tint, which must  not be  confounded with that
       proceeding from the presence of alumina.
  In cases a. and b. further examination  may be made for
the alkalies and alkaline earths by the flame-tests.  A little of
the substance is  brought  upon the  loop of a fine  platinum
wire, moistened repeatedly with sulphuric acid, and cautiously
dried near the edge of  the  gas flame, and  finally brought into
the zone of fusion.  The alkalies first volatilize  and tinge the
flame; after they are dissipated, the baryta  coloration, and
lastly,  on wetting with hydrochloric acid, the strontia  and
lime reactions appear.   For details see § 95 and § 102. 
§ 179.]           preliminary examination.

      c. The  substance  leaves  a residue  of  another
    COLOR,  OR REDUCTION TO THE METALLIC  STATE  TAKES
    PLACE, OR  THERE  IS FORMED AN INCRUSTATION ON THE
    charcoal.  Mix a portion of the powder with  carbo-
    nate of  soda,  and heat on charcoal  in  the reducing
    flame; observe the residue in  the cavity,  as well  as the
     acrustation on the charcoal.
        a. The sustained application of a strong flame pro-
      duces a  metallic globule, without incrustation of the
      charcoal; this indicates the presence of  gold, or cop-
      per.  The  oxides of platinum, iron, cobalt, and nickel,
      are indeed also  reduced, but they yield  no metallic
      globules.
        /3. The  charcoal  support  is coated with an  incrus-
      tation, either with  or without simultaneous formation
      of a metallic globule.
          aa.  The  incrustation  is white, at  a  long dis-
        tance  from the  test specimen, and is very readily
        dissipated by heat, emitting a  garlic-like  odor;
        ARSENIC.
          bb.  The incrustation is white,  is nearer the test
        specimen than aa, and may be driven  from one part
        of  the  support  to  another:  antimony.   Metallic
        globules are generally observed at the  same time,
        which continue to evolve white fumes  long after the
        blowpipe jet is discontinued, and upon cooling may,
        if the metal is quite pure, become surrounded with
        crystals  of teroxide of antimony; the globules are
        brittle.
           cc. The  incrustation  is yellow whilst hot, but
        turns white on cooling; it is near the  test specimen,
        and is with difficulty volatilized: zinc.
          dd.  The incrustation has a faint yelloio tint whilst
        hot, but turns white on cooling;  it  surrounds the
        test specimen, and both the inner and outer flame fail
        to volatilize it: tin.  The metallic globules formed
        at the same time  (but only  in a good reducing  flame),
        are bright, readily fusible,  and malleable.
          ee.  The incrustation has  a lemon-yellow color, turn-
        ing on cooling to sulphur  yellow;  when exposed  to
        the  reducing flame, it volatilizes tinging the flame
        azure-blue: lead.    Readily  fusible,  malleable glo-
        bules  are formed at the same time with the  incrus-
        tation.
          ff. The  incrustation is  of a dark  orange-yellow
        oolor whilst hot, which changes to lemon-yellow  on 
252             preliminary examination.          [§ 179.

        cooling; when  exposed to the reducing flame, it
        changes its place without imparting any color to the
        flame: bismuth.  The metallic globules formed at
        the same time as the incrustation are readily fusible
        and brittle.
          gg. The  incrustation is reddish-brown,  in  thin
        layers, orange-yellow; it volatilizes without  tinging
        the flame: cadmium.
          hh.  The  slight incrustation  is dark-red:  silver.
        In presence  of a little lead or  antimony it is crim-
        son-red.

          To learn, in cases of doubt, whether reduced metal
        has been separated in this experiment, the charcoal
        cavity is moistened with water, the charcoal cut out
        for  a  little   space  around and below the  cavity,
        brought into an agate mortar, finely pulverized, and
        the charcoal powder cautiously washed away.  Any
        metal  that may be present remains in the mortar;
        gold in yellow,  copper in red, silver in white, tin in
        grayish-white, lead in gray plates or  streaks.   Bis-
        muth will remain as  a reddish-gray,  zinc a bluish-
        gray, antimony a gray powder.  When copper and
        tin, or copper and  zinc are simultaneously present,
        yellow alloys of these metals may be formed.  [Iron,
        nickel and cobalt, when reduced on charcoal, remain
        after washing as black or dark-gray powders, which
        are lifted by the magnet.]
  4. Fuse a small portion together with a bead of micro- 17
cosmic salt, and expose  for some  time  to the outer flame
of the blowpipe.
    a. The  substance  dissolves  readily   and  rather
  LARGELY TO A CLEAR BEAD (WHILST HOT).
       a. The hot bead is colored:                          18
        Blue, by candlelight inclining to violet—cobalt ;
        Green, upon cooling blue; in  the reducing flame,
           after cooling,  red—copper ;
        Green, particularly fine on cooling, unaltered in the
           reducing flame—chromium ;
        Brownish-red,  on cooling light yellow or colorless;
           in the reducing flame red whilst hot, yellow whilst
           cooling, then  greenish—iron ;
        Dark yellow to reddish, turning lighter or altoge-
           ther colorless on cooling; in the  reducing flame
           unaltered—nickel ;
         Yellowish-brown, on cooling changing  to  light- 
§ 180.]          preliminary examination.             253
          yellow  or losing  its  color  altogether;  in  the
          reducing flame almost colorless (especially  after
          addition of a very little tin foil), blackish-gray on
          cooling—bismuth ;
        Bright-yellowish to  opal,  when  cold  somewhat
          turbid; in the reducing flame whitish-gray—silver.
        Amethyst-red, especially on cooling; colorless in the
          reducing flame, not quite clear—manganese.
      (3. The hot bead is colorless:                         19
        It remains clear on cooling :  antimony, alumina,
          ZINC, CADMIUM, LEAD, LIME, MAGNESIA J the latter
          five metals, when added in somewhat large propor-
          tion to the microcosmic salt, give enamel-white
          beads;  the bead of  oxide of lead is yellowish
          when saturated;
        It becomes enamel-white on cooling, even when
          only a small portion of the powder has been adS'ed
          to the microcosmic salt: baryta, strontia.
    b.  The substance dissolves slowly and only in small 20
  QUANTITY :
      a. The bead is colorless, and  remains so  even after
    cooling; the undissolved portion looks semi-transparent;
    upon addition of a little  sesquioxide of  iron, it  acquires
    the characteristic color of an iron  bead:  silicic acid.
      /3. The bead is colorless, and remains so after  addition
    of a little sesquioxide of iron: tin.
    c. The substance does not dissolve,  but floats (in 21
  the metallic state) in the bead : gold, platinum.
  5. Minerals should be examined for fluorine according
to § 149, 8.
  As the body under examination may  consist of a mixture of
the  most  dissimilar elements, it is impossible to  give well
defined cases that shall offer at the same time the  advantage
of general applicability.   If, therefore, reactions are observed
in an experiment which proceed from a combination of two
or several cases, the conclusions drawn  from these reactions
must of course be modified accordingly.
  On concluding the Preliminary Examination, solution may
be proceeded with  according to § 183 (32).

                           § 180.
        n.  The Substance is a Metal or  an Alloy.
  1. Heat a small portion of the substance with water 22
ACIDULATED WITH ACETIC ACID.   If HYDROGEN GAS  is evolved
this indicates the  presence of a light  metal  (a metal of the 
254             the  substance is a fluid.          [§181

alkalies or alkaline  earths),  possibly also  of  metallic man-
ganese.
  2. Heat a  sample of the substance on  charcoal in the 23
reducing flame of the blowpipe, and watch the reactions;
for instance, whether the substance fuses, whether an incrusta-
tion is formed, or an odor emitted, &c.
  In this operation the  following metals maybe detected with
more or less certainty : arsenic by its garlic odor; mercury
by  its volatility:  antimony,  zinc, lead,  bismuth,  cadmium,
tin and silver by their fusibility and yielding incrustations on
the charcoal,  compare (l6), copper  by its  tinging the outer
flame green; only when a single pure or nearly pure metal  is
present, is it possible to form further conclusions, thus gold is
fusible  without  incrusting the  charcoal;  platinum, iron,
manganese, nickel and cobalt when pure are infusible.
  3. Heat a sample of the substance  before the blow- 24
PIPE INJA glass tube sealed at one end.
       a. No  sublimate is formed in the  colder  part of
    the tube : absence of mercury.
       b. A sublimate is formed ;  presence of mercury,
    cadmium, or arsenic.  The sublimate of mercury, which
    consists of small globules, cannot possibly be confounded
    with that of cadmium or arsenic.
       When the Preliminary Examination is finished, proceed to
    bring the substance into solution according to § 184 (^2).

                            § 181.
       B. The Substance under Examination is a Fluid.
  1. Evaporate a small  portion of the  fluid in a plati-  25
num dish, or in a small porcelain  crucible, to ascertain whe-
ther it actually contains any matter in solution; if a residue
remains, examine this as directed §179.
  2. Test with litmus paper (blue and red).                26
       a. The fluid reddens blue litmus paper.  This reac-
    tion may be caused by a  free  acid or  an acid salt, as  well
    as  by a  metallic  salt soluble in water.   To distinguish
    between these two  cases, pour a small quantity of the fluid
    into a watch-glass, and dip into it a small glass rod, the
    extreme  point of  which  has  previously been moistened
    with dilute solution  of  carbonate of soda; if the fluid
    remains clear, or  if the  precipitate  which may form  at
    first, redissolves upon stirring the liquid, this proves the
    presence  of a free acid or of an acid salt; but if the  fluid
    becomes  turbid and remains so, this generally denotes the
    presence of a soluble metallic  salt.
       b. Reddened litmus paper turns blue : this indicates  21
o 
§ 182.]              solution of  bodies.                 255

    the presence of free alkalies or alkaline carbonates, free
    alkaline earths,  alkaline sulphides, and of a number of
    other salts which contain an alkali or an alkaline earth in
    combination with a weak acid.
  3. Smell the fluid, or, should this fail to give satisfactory  2§
results, distil, to ascertain whether the  simple  solvent pre-
sent is water, alcohol, ether, &c.   If you find it is not water,
evaporate the  solution to dryness,  and treat the residue as
directed 179.
  4. If the  solution is aqueous, and manifests an acid reac-  29
tion, dilute a  portion of it largely with water.  Should
this impart a milky and turbid appearance to it,  the presence
of antimony, bismuth (possibly also of tin) may be inferred.
  On completing the Preliminary Examination the operator  30
may proceed to the Actual Analysis.  If the solution is aque-
ous and reacts neutral, only bodies which are soluble in water
can be present; if, on the contrary, it has an acid reaction,
which may be due to the presence of a free acid,  it can  no
longer be considered simply aqueous, and the subsequent exa-
mination must  accordingly be conducted with  regard to the
possible presence  of substances insoluble in  water but soluble
in acids.
  These circumstances being properly considered, the analyst
passes over, when but one acid and one base are to be sought,
to § 185 or to  § 188—if several acids  or bases are  possibly pre-
sent to § 192—solutions having an alkaline reaction are examin-
ed according to § 185 when containing  but one acid and one
base, otherwise according to §192.

H.  Solution  of  Bodies, or Classification of Substances
  ACCORDING  TO  THEIR DEPORTMENT  WITH  CERTAIN  SOL-
  VENTS *

                            §182.
  Water,  hydrochloric or nitric  acid, and aqua regia are the  3|
solvents used to classify simple  or compound substances, and
to isolate the component parts  of  mixtures.  We divide the
various substances into three classes, according  to  their re-
spective behavior  with these solvents.
      First class.—Substances soluble in water.
      Second  class.—Substances insoluble  or sparingly
    SOLUBLE IN WATER, BUT SOLUBLE IN  HYDROCHLORIC ACID,
    NITRIC ACID OR  AQUA REGIA.
      Third class.—Substances  insoluble or  difficultly
Consult the remarks in the third section. 
256         NEITHER  A METAL  NOR  AN ALLOY.        [§ 183.

     SOLUBLE IN WATER AS WELL AS IN HYDROCHLORIC  ACID,
     NITRIC ACID, AND AQUA REGIA.
  The solution of alloys being more appropriately effected in a
different manner from that pursued with other bodies,  I  shall
give a special method for these substances (see § 184).
  The process  of solution is conducted in the following manner

A.   The  Substance  under  Examination is neither  a
                    Metal nor an Alloy.
                             §183.
  1. Put about a gramme (15*5 grains) of the finely-pulverized 32
substance under examination  into a small flask or a test-tube,
add from ten to twelve times the  amount of distilled water,
and heat to boiling over a spirit or gas-lamp.
       a. The  substance  dissolves completely.   In that 33
     case (regard being had to what has been stated in (30)
     concerning the reactions with test-papers), the substances
     may be reckoned in the first class.  Treat the solution
     either as directed § 185, or as directed  § 192, according
     as either one  or several acids and bases are supposed to
     be present.
       b. An insoluble residue remains, even after pro- 34
     tracted boiling.  Let the residue  subside, and filter the
     fluid off, if practicable, in such a manner as to retain the
     residue in  the test-tube;  evaporate a few drops of the
     clear filtrate slowly on platinum foil; if  nothing remains,
     the substance  is completely insoluble in  water; in which
     case proceed as directed (35).  But if a residue remains,
     the  substance  is at least partly  soluble; in which case
     boil again with water, filter, add the filtrate to the ori-
     ginal solution, and treat the fluid, according to  circum-
     stances, either as directed § 185, or according to § 192.
    Wash the  residue with water, and proceed as directed
     (35).
  2. Treat a small portion of the residue which has been boiled 35
with water (34) with dilute hydrochloric acid.  If it does not
dissolve, heat to boiling, and if this fails  to effect complete
solution decant the fluid into another test-tube, boil the resi-
due with concentrated hydrochloric acid, and if it  dissolves,
add it to the fluid in the other  test-tube.  The reactions which
may manifest themselves in this operation, and which ought to
be  carefully observed are, (a) Effervescence, which indicates
the presence of carbonic  acid  or hydrosulphuric  acid; (3)
Evolution of chlorine, which  indicates  the  presence  of per-
oxides, chromates, &c.; (7) Emission of the odor  of hydro- 
§ 183.]
SOLUTION.
257
 cyanic acid, wrhich indicates the presence of insoluble cyanides.
 The analysis of the latter bodies being effected in a somewhat
 different manner, a special paragraph will be devoted to them
 (see § 207).
        a. The residue is  completely dissolved by the hy- 3<j
     droculoric acid (except  perhaps that sulphur separates,
     which may be known by its color and light specific gravity,
     and may, after boiling some time longer, be  removed by
     filtration ; or that gelatinous hydrate of silicic acid sepa-
     rates).  Proceed, according to circumstances, either as
     directed  § 188,  or as  directed  § 193, after previous fil-
     tration  if  necessary.  The body belongs  to the  second
     class.  To make quite  sure of the actual nature of the sul-
     phur or hydrated silicic acid filtered off, examine these
     residuary matters as directed § 191, or as directed §  206.
        b. There is still a residue left.  In that case  put 37
     aside the test-tube  containing  the  specimen which  has
     been  boiled with the  hydrochloric  acid, and try and dis-
     solve another sample of the substance under examination,
     or of the residue from the treatment with water, by boil-
     ing with nitric  acid, and subsequent addition of water.
     In case binoxide of nitrogen or nitrous acid are evolved
     in this operation, it indicates that an oxidizing process is
     going on.
         a. The  sample  is completely dissolved,  or leaves no 3§
       other residue but sidphur or  the gelatinous hydrate of
       silicic  acid; in this case also the body belongs to the
       second class.   Use this solution to test further for bases,
       according to § 188,  or, as the case may be (109), and
       for the rest proceed  as directed in (36).
         (3. After boiling with nitric acid there is still a residue 39
       left.   Pass on to (40).
   3. If the residue insoluble in water will not entirely dissolve 40
 in hydrochloric acid or in  nitric acid, try to effect complete
 solution of it by nitrohydrochloric acid.   To this end mix the
 contents of the tube treated with nitric acid with the contents
 of the tube treated with concentrated hydrochloric acid; heat
 the mixture to boiling, and should this fail to effect complete
 solution, decant the clear fluid off from the undissolved residue
 boil the latter for  some  time with concentratej^nitrohydro-
 chloric  acid,  and add the decanted  solution  in dilute  aqua
 regia  as well as the  solution in dilute hydrochloric acid de-
 canted in (35).  Heat the entire mixture once more to boilino-,
 and observe whether complete solution has now been effected,
or whether  the  action of the  concentrated nitrohydrochloric
acid has still left a residue.   In the latter case, filter the  solu-
                               17 
258     THE  SUBSTANCE IS A METAL OR AN ALLOY.    [§ 184.

tion—if necessary, after addition  of some water*—wash  the
residue with boiling water, and proceed with the filtrate, and
the washings  added to  it, as  directed § 188, or as  directed
§193 ;—in the former case, proceed with the clear solution in
the same way.f
  4. If boiling nitrohydrochloric acid  has left an undissolved  41
residue, wash it thoroughly with water, and  then proceed as
directed § 41, or as directed §  206.

    B. The Substance under Examination is  a Metal or
                            an Alloy.
                               § 184.
  The metals  are  best classed according to their respective  42
behavior with nitric acid:  this gives us,
  I. Metals which are not attacked by nitric acid :  gold,
platinum.
  H  Metals which  are  oxidized by  nitric  acid, but of
which the oxides do not dissolve in an excess of the acid
or  in water : antimony, tin.
  IH. Metals which are oxidized by nitric acid and con-
verted  into nitrates, which dissolve in an excess of the
acid  or in water :  all other metals.
  Pour  nitric acid of  1*20 sp.  gr. over  a  small portion of the
metal or alloy under examination, and apply heat.
  1.  Complete solution takes place,  either  at  once or  43
upon addition of  water ; this proves  the absence of  pla-
tinum,;];  gold, antimony,§ and tin.   Proceed, according to  cir-
cumstances, either  as directed § 188, or  as  instructed § 192,
m. (109).
  2.  A RESIDUE IS LEFT.
       a. A metallic residue.  Filter, and treat the  filtrate as  44
     directed  § 192,  III.,  (109)  after having examined, in
     the first place, whether anything has  really been dissolved.

  * If the fluid turns turbid upon addition of  water, this indicates  the presence
of bismuth or antimony; the turbidity disappears again upon addition of hydro-
chloric acid.
  f If the acid solution on cooling deposits acicular crystals, the latter generally
consist of chloride of lead; it is in that case often advisable to decant the fluid off
from the crystals, and to examine fluid and crystals separately.  If on boiling with
aqua regia, metabichloride of tin has been formed (by the action of the  solvent on
binoxide of tin), the wash waters, which dissolve it, will become turbid on  falling into
the acid solution which first passed the filter.  In  this  case  the two  solutions are
collected  separately and separately treated with hydrosulphuric acid, according to
§ 193, both are however filtered afterwards through the same filter.
  \ Alloys of silver with a little platinum dissolve completely in nitric acid.
  § Very minute traces of antimony nevertheless often pass  wholly into the
solution. 
 § 185.]     ACTUAL ANALYSIS—SIMPLE COMPOUNDS.        259

     Wash the residue thoroughly, dissolve in nitrohydrochlo-
     ric acid, and examine the solution for gold and platinum,
     according to § 131.
        b. A white, pulveruUnt residue;  this indicates the pre- 45
     sence  of antimony  and tin.  Filter,  ascertain whether
     anything has been  dissolved, and  treat the  filtrate  as
     directed § 192, III. (109).   Wash the residue thoroughly,
     and examine according to § 137, 5, for antimony, tin,
     and arsenic acid (of which last  a  portion may exist  in
     this residue, united to tin or antimony).

                      in.  Actual Analysis.
                       Simple Compounds.*
                A. Substances  soluble  in water.
                     Detection  of the Base.\
                              §185.
   1. Add some hydrochloric acid to a portion of the aqueous 46
 solution.
       a. No precipitate is formed ; this is a positive proof
     of the absence of silver and suboxide of mercury, and  is
     likewise an indication of the probable absence of lead.
     Pass on to (50).
       b. A precipitate  is  formed.   Divide  the fluid in 47
     which  the precipitate is suspended into two  portions, and
     add ammonia in excess to the one.
         a.  The precipitate redissolves, and the fluid becomes
       clear / this shows the precipitate  to  have  consisted of
       chloride of silver, and is consequently indicative of the
       presence of silver.  To arrive at a positive conviction
       on this point,  the original solution must be tested with
       chromate of potassa, and with hydrosulphuric acid (see
       § 118, 4, and§ 141, 6).
         (3.  The precipitate  turns black:  this shows the pre-4§
       cipitate to have consisted of subchloride of mercury,
       which has now been converted by the ammonia into

  * This term is used here, and wherever it happens to occur hereafter  in the pre-
sent work, to designate compounds supposed to contain only one base and one acid,
or one metal, and one non-metallic element.
  This course of analysis of " simple compounds" is especially intended to facilitate
the acquisition of a knowledge of the analytical method, it being on many accounts
advantageous for the student to practise at first on bodies of simple composition
before attempting to analyze complex substances.  In other than analyses for mere
practice, this course is only useful in a few exceptional cases, because there are no
external indications which enable one to judge positively whether a  body contains
one or several acids or bases.
  f  Arsenious acid, arsenic acid, and silicic acid are included here. 
260
TESTING FOR BASES.
[§185
       subamidochloride of mercury; it  is consequently indi-
       cative of the presence of suboxide of  mercury.  To
       set  all doubt  on this point  at rest, test the original
       solution with protochloride of tin,  and with metallic
       copper (see § 119).
         y. The precipitate remains  unaltered; it consists in 49
       that case of chloride of lead,  which is not dissolved by
       ammonia;  this  reaction  is  accordingly indicative  of
       the  presence of lead.  Whether the precipitate consists
       really of chloride  of lead or not is  conclusively ascer-
       tained:  1st, by diluting the second portion  of the fluid
       in which the precipitate produced by hydrochloric acid
       is suspended, with a large amount of water, and apply-
       ing  heat; the precipitate must dissolve if it consists of
       chloride of lead; and 2nd, by adding dilute sulphuric
       acid to the original solution (§ 120, 8).
  2. Add  to the  fluid acidified  with  hydrochloric acid (46) 50
solution of hydrosulphuric acid until it smells distinctly of
that gas, even after shaking; heat the mixture, add again some
hydrosulphuric acid and let the whole stand a short time.*
       a. The fluid remains clear.  Pass on to  (56), since
     this is a proof that lead, bismuth, copper, cadmium, oxide
     of mercury,  gold, platinum, tin, antimony, arsenic, and
     sesquioxide of iron, are not present.
       b. A precipitate is formed.
         a. This precipitate is white ; it consists in that case 51
       of separated sulphur, and is indicative of the presence
       of sesquioxide  of  iron (§ 114, 3).   However, as the
       separation of sulphur may also be caused by other sub-
       stances, it is indispensable that you should satisfy your-
       self whether the substance  present is really sesquioxide
       of iron or not.   For this purpose test the original solu-
       tion with ammonia, and with ferrocyanide of potassium
       (§ 114, 5 and 6).
        8. The precipitate is  yellow ;  in that case it may 52
       consist either  of  sulphide of cadmium, sulphide  of
       arsenic,  or  bisulphide of tin;  it indicates accordingly
       the presence of either cadmium, arsenic, or binoxide of
       tin.   To distinguish between them, mix a portion of the
       fluid wherein the precipitate is suspended with ammo-
       nia in excess, add some sulphide of ammonium, and heat.
  *  If a precipitate ensues immediately on addition of hydrosulphuric acid, warm
ino- and repeated addition of the  reagent are  not needful.  If, however, the liquid
remains clear, or becomes but slightly turbid,  the above directions must be closely
followed or else arsenic acid, binoxide of  tin  and oxide of mercury may be over
looked. 
§ 185.]    ACTUAL ANALYSIS.—SIMPLE COMPOUNDS.        261

          aa. The precipitate  does not dissolve; it consists
        of cadmium ; for sulphide of cadmium is insoluble in
        ammonia and sulphide  of ammonium.  The blowpipe
        is resorted to as a confirmatory test (§ 125, 8).
          bb. The Precipitate dissolves: binoxide  of tin
        or  arsenic ; add ammonia to a small portion of the
        original solution.
             h«. A white precipitate  is formed. Binoxide of
          tin is the substance present.  Positive conviction
          is obtained by reducing the precipitate before the
          blowpipe, with cyanide of potassium and carbonate
          of soda  (§ 133, 8).
             83. No precipitate  is formed.   This indicates
          the presence of arsenic  Positive  conviction may
          be arrived at by the  production of  an arsenical
          mirror,  which is effected by reducing  the original
          substance or the precipitated sulphide of arsenic,
          either with cyanide of potassium and carbonate of
          soda, or in some other way; and w.oreover by ex-
          posing the original substance in conjunction with
          carbonate of soda to the inner  flame of the blow-
          pipe (§  135,12 and 13).  If the solution (50) con-
          tained arsenious acid, the yellow precipitate (52)
          formed immediately upon the addition of the hydro-
          sulphuric acid; if arsenic acid, it formed only upon
          the application  of heat,  or after  long  standing.
          For further information respecting the means of
          distinguishing between the two acids see § 137, 9.
        y. The  precipitate is  orange-colored ; in that case
      it consists of tersulphide of antimony, and indicates the 53
      presence of teroxide of antimony.  For confirmation,
      the original  solution is tested with zinc  in a small pla-
      tinum dish (§ 134, 8).
        8. The  precipitate is brown.  It consists of proto- 54
      sulphide of tin, and indicates the presence of protoxide
      of  tin.  To remove  all doubt, test a  portion of the
      original solution with solution of chloride  of mercury
      (§ 132, 8).
        s. The precipitate is brownish-black or black.  It 55
      may in that case  consist of sulphide of lead, sulphide
      of copper, tersulphide of bismuth, tersulphide  of gold,
      bisulphide of  platinum,  or sulphide of mercury. To
      distinguish between these different sulphides, the fol-
      lowing experiments are resorted to.
          aa. Add dilute sulphuric acid to a  portion of the 
262
TESTING FOR BASES.
[§ 185.
      original  solution; if a white precipitate is formed,
      this indicates lead.  To dispel all doubt,  test with
      chromate of potassa (§ 120).
        bb. Add solution of soda to a portion of  the origi-
      nal solution; if a yellow precipitate is formed, this
      indicates  oxide of mercury.  The reactions  with
      protochloride of tin and metallic copper, afford posi-
      tive certainty on the point (§ 122).
        The presence of oxide of mercury is usually suffi-
      ciently indicated  by the  several  changes  of  color
      through which the precipitate produced by the solu-
      tion of hydrosulphuric acid in the fluid under exami-
      nation is observed to pass ;  this precipitate is white
      at first, but changes upon the addition of an excess ol
      the precipitant to yellow, then to orange, and finally
      to black  (§ 122, 3).
        cc. Add ammonia in  excess to  a portion of the
      original  solution; if a  bluish precipitate is  formed
      which redissolves in an excess of the  precipitant,
      imparting an azure color to the fluid,  this  indicates
      copper.   To remove all doubt, test with ferrocyanide
      of potassium (§ 123).
        dd.  If the precipitate produced  by ammonia  was
      white, and excess of ammonia has failed to redissolve
      it, filter the fluid off, wash the precipitate, dissolve it
      on  a watch-glass  in 1 or  2 drops of hydrochloric
      acid, with addition of 2  drops  of Avater,  and then
      add some more water.  If the solution turns turbid
      and milky, this is caused by basic terchloride of bis-
      muth : the reaction consequently indicates  bismuth.
      The blowpipe is  resorted to as  a conclusive  test
      (§ 124).
        ee. Add solution of sulphate of protoxide of iron to
      a portion of  the original solution.   The formation of
      a fine black precipitate is indicative of the presence
      of gold.  To remove all doubt as  to the  nature of
      the precipitate, expose it to the flame of the blow-
      pipe, or test the original solution with protochloride
      of  tin (§ 129).
        ff. Add chloride of potassium and alcohol to a por-
      tion of the original solution; the formation of a. yel-
      low crystalline precipitate is indicative of the presence
      of platinum.   To remove  all doubt, heat the precipi-
      tate to redness (§ 130).
3.  Mix a small portion of the original solution with chloride 56 
 § 185.]   ACTUAL EXAMINATION—SIMPLE COMPOUNDS.    263

 of ammonium,*  add ammonia to alkaline reaction, and then,
 no matter whether the latter reagent has produced a preci-
 pitate or not, a little sulphide of ammonium, and apply heat,
 if a precipitate fail to separate in the cold.
       a. No precipitate is formed ; pass on to (62); for iron,
     cobalt, nickel, manganese, zinc, chromium, alumina, and
     silicic acid, are not present.
       b. A precipitate is formed.
         a. The precipitate is black: protoxide of iron, nickel, 57
       or cobalt.  Mix a portion of the original solution with
       some solution of potassa or soda.
           aa. A  dirty greenish-white precipitate is formed,
         which soon changes to reddish-brown, upon exposure
         to  the  air:  protoxide  of iron.  To  remove  all
         doubt, test with ferricyanide of potassium (§ 113).
           bb. A precipitate of a  light  greenish tint is pro-
         duced, which does not change  color: nickel.  The
          reaction with ammonia, and the precipitation of the
         ammoniacal solution by potassa or soda, will afford
         positive certainty on the point (§ 111).
           cc.  A sky-blue precipitate is  formed,  which is dis-
         colored  upon boiling, and acquires a  dark  tint:
         cobalt.   The blowpipe is resorted to as a conclusive
         test(§ 112).
       8. The precipitate is not black.                        5§
           aa. If the precipitate is distinctly flesh-colored,  it
         consists of  sulphide  of  manganese, and  is  conse-
         quently indicative of the presence of protoxide of
         manganese.   To remove all doubt, add soda to the
         original solution, or try before the blowpipe (§110).
           bb.  If the precipitate is bluish-green, it consists of
         hydrated  sesquioxide of chromium, and is conse-
         quently indicative of the presence of sesquioxide of
         chromium.  To  dispel  all  doubt, test the  original
         solution with soda, and  apply the blowpipe tests
         (§105).
           cc. If the precipitate  is white, it may consist of 59
         hydrate of alumina,  or hydrate of silicic acid, or sul-
         phide of zinc,  and may accordingly  point to the pre-
         sence of either alumina or oxide of zinc or silicic acid;
         the  latter, in that case, is generally  contained in the
         original  solution  as  an alkaline silicate.  To distin-
         guish between these three bodies, add to a portion of

  * The addition of chloride of ammonium is made  to prevent the  precipitation ol
magnesia by the ammonia. 
264
TESTING FOR BASES.
[§185
          the original  solution, solui ion  of soda drop by drop,
          wait to see whether this produces a precipitate, and
          then  add some more solution  of soda, until the pre-
          cipitate formed is dissolved.
             aa. If solution of soda fails to produce a precipi- 60
           tate, there is reason to test  for silicic acid.  For
           that purpose, evaporate a portion of the original
           solution with  hydrochloric  acid to dryness, and
           treat the residue with hydrochloric acid and water
           (§ 153,  2), when the  silicic acid will be left undis-
           solved.   Determine the nature of the alkali which
           has been dissolved, as directed (66).
             88. If solution of soda produces a  precipitate,
           which redissolves in an excess of the  precipitant,
           add to a portion of this alkaline fluid hydrosulphu-
           ric acid; the formation of a  white precipitate indi-
           cates the  presence of zinc  The reaction with
           solution of nitrate of protoxide of cobalt before
           the blowpipe will afford conclusive proof (§ 109).
           If hydrosulphuric acid fails to produce a precipitate,
           add to the remaining- portion  of the alkaline fluid
           chloride of ammonium, and  apply  heat.  The for-
           mation  of a white  precipitate indicates the pre-
           sence of alumina.   The reaction with solution of
           nitrate of protoxide of cobalt before the blowpipe
           will afford conclusive proof (§  104).

                    Note to (58), and  (59).
  As very slight contaminations may impair the distinctness of
the tints exhibited by the precipitates  considered in (58), and
(59), it is advisable, in all cases where  the least  impurity is
suspected, to adopt the following method for the detection of
manganese, chromium, zinc, alumina, and silicic acid.
  Add solution of soda to  a portion of  the original solution,
first in small quantity, then in excess.
         aa. No precipitate is formed: silicic acid maybe  61
      assumed to be present; proceed as directed  (60).
         bb. A  whitish precipitate is formed,  which does not
      redissolve in  an excess of  the precipitant, and speedily
      turns blackish-brown upon exposure to the air: man-
      ganese.  The blowpipe is resorted to  as a conclusive
      test (§110).
        cc. A precipitate  is formed  which redissolves in an
      excess of the precipitant:  sesquioxide of chromium,
      alumina, oxide of zinc.
          aa. Add hydrosulphuric acid  water to a portion  of 
§ 185.]     ACTUAL ANALYSIS—SIMPLE COMPOUNDS.
        the alkaline solution.   The formation of a white pre-
        cipitate indicates the presence of zinc.
          88. If the original or the alkaline solution is green,
        and if the precipitate produced by soda and redissolv-
        ed by an excess of the precipitant, was of  a bluish
        color,  sesquioxide  of chromium  is  present.   To
        remove all doubt, heat the alkaline solution to boil-
        ing, or try the reaction before the blowpipe  (§ 105).
          yy. Add chloride of ammonium to the alkaline solu-
        tion.   The formation of a white precipitate indicates
        the presence of alumina.  The reaction with solution
        of nitrate of protoxide of cobalt before the blowpipe
        will afford conclusive proof (§ 104).
  4. Add  to a portion  of the original solution chloride of  62
ammonium and carbonate of ammonia, mixed  with some caus-
tic ammonia, and heat gently.
      a. No precipitate is formed : absence of baryta, stron-
    tia, and lime.  Pass on to  (64).
      b. A precipitate is formed ;  presence  of baryta, stron-  63
    tia, or lime.
      Add a considerable quantity of solution of sulphate of
    lime to a portion of the original solution.
        a. The solution does not become turbid, not even after
      the  lapse of from five to ten minutes: lime. To remove
      all doubt, test with oxalate of ammonia (§ 100).
        8. The solution becomes  turbid, but only after the
      lapse of some time: strontia.
        This reaction is only conclusive when the  solution is
      neutral  or but slightly  acid.    The coloration of the
      flame is looked to for confirmation (§ 99, 6 or 7).
        y. A  precipitate is immediately formed:  baryta.
      To  remove all doubt, test with hydrofluosilicic acid
      (§ 98).
  5. Mix that  portion of the solution of (62) in which carbo-  64
nate  of ammonia has,  after previous addition of chloride of
ammonium, failed to produce a  precipitate, with phosphate of
soda, add  some more ammonia, and rub the sides of  the ves-
sel with a  glass rod.
      a. No precipitate is formed : absence  of  magnesia.
    Pass on to (65)-
      b. A crystalline precipitate is formed : magnesia.
  6. Evaporate a drop  of  the  original solution on perfectly  65
clean platinum foil as slowly as possible, and gently ignite the
residue.
      a. There is no fixed ft:smuE left.  Test for ammo-
    nia, by adding  to^rtworiginal  solution  hydrate of lime, 
 266           DETECTION OF INORGANIC ACIDS.        [§ 186,

     and observing the odor and reaction of the escaping gas,
     and the fumes which it forms with acetic acid (§ 94).
       b. There  is a fixed residue left : potassa or soda. 66
     Add bichloride of platinum to  a  portion of the original
     solution, having first  concentrated it by  evaporation if
     dilute, and shake the mixture.
         a.  No precipitate is formed, not even after the  lapse
       of ten or fifteen minutes: soda.  The coloration of the
       flame is selected  as a  conclusive test, or the reaction
       with antimonate  of potassa is resorted to for the pur-
       pose (§ 93).
         8. A  yellow crystalline precipitate is formed: po-
       tassa.  The reaction with tartaric acid, and the color-
       ation of  the flame are selected  as conclusive  tests
       (§ 92).

                     Simple  Compounds.

A. Substances soluble in Water.  Detection of the Acid.

               I.  Detection of Inorganic Acids.
                             § 186.
  Reflect in the first place which of  the inorganic acids form
soluble compounds with the detected base (compare Appendix
TV.), and bear this in mind in your subsequent operations.
  1.  Arsenious acid and  arsenic  acid  have  already been 67
considered in the preceding paragraph (detection of the base).
These two acids are  distinguished from each other by their
respective behavior with nitrate of silver, or with potassa and
sulphate of copper (see § 137, 9).
  2.  The presence of carbonic acid, hydrosulphuric acid,
and  chromic acid, is also indicated already in  the  course
of the process pursued for the detection of the bases.  The two
former betray  their  presence by effervescing   upon   the
addition of hydrochloric  acid ;  they  may be  distinguished
from one another by their odor.    Should additional  proof
be required, the presence  of  carbonic acid may be ascertain-
ed  beyond a doubt by the  reaction with lime-water (see §
 152), and that  of hydrosulphuric  acid by the  reaction with
solution of acetate of lead (§ 159).   The presence of chromic
acid is invariably indicated by the yellow or red  tint of the
solution, as well as by the transition  of the red or yellow  color
to green, accompanied by the separation of sulphur, upon the
addition of hydrosulphuric acid water.  To remove all doubt,
try the reactions with solutions of aoetate of lead and of nitrate
of silver (§ 141). 
§ 186.]     ACTUAL ANALYSIS—SIMPLE  COMPOUNDS.        2(>7

  3.  A portion of the solution is slightly acidified with hydro-
chloric acid (or in case oxide  of silver or protoxide of mer-
cury has  been detected, with nitric  acid), and  chloride of
barium (or nitrate  of baryta) is added.
         a. The fluid remains clear. Absence of sulphuric
      acid.  Pass on to  (70).
         b. A WHITE  finely pulverulent precipitate is
      formed.  Sulphuric acid.  The precipitate must re-
      main undissolved on  addition of more hydrochloric (or
      nitric) acid.
  4.  Add solution of sulphate of lime  to  another portion of  70
the solution (which, if it has  an acid reaction, must first be
neutralized, or made slightly alkaline, by means of ammonia).
      a. No precipitate is formed : absence of phosphoric
     acid, silicic acid, oxalic  acid, and fluorine. Pass on to (73).
      b. A precipitate is formed.  Add acetic acid in excess.  71
         a.  The precipitate redissolves readily: phosphoric
      acid or silicic acid.   To a  portion of the original
      solution hydrochloric acid is added in slight  excess, the
      liquid is evaporated to  dryness, and the residue treated
      with a little hydrochloric acid and water.  If an insolu-
      ble residue  remains it is silica.  If no residue remains
      a portion of the original solution is mixed with chloride
      of ammonium, ammonia, and a little sulphate of mag-
      nesia.*  The formation of a  crystalline precipitate is
      proof of the presence of phosphoric acid (§ 145).
         8. The precipitate remains undissolved or dissolves  72
      with difficulty: oxalic acid or fluorine.   Oxalate of
      lime is pulverulent, fluoride of calcium flocculent and
      gelatinous.   The reaction wTith binoxide of manganese
      and sulphuric acid (§ 148) will afford conclusive  proof
      of the  presence of oxalic acid; the reaction on  glass
      (etching) of the presence of fluorine (§  149).
  5.  Acidify a fresh portion of the original solution with nitric  73
acid, and add solution of nitrate of silver.
      a. The fluid remains clear.  This  is  a proof of the
     absence of chlorine, bromine, iodine,  ferrocyanogen, and
     ferricyanogen; the absence of cyanogen (in simple  cyan-
     ides) is also probable.  (Of the soluble  metallic cyanides,
     cyanide of mercury is not precipitated by nitrate of silver;
     if therefore, in the analytical process for the detection of
     the  bases, mercury  has been found,  cyanide  of mercury
     may be present. For the manner of detecting the cya-
     nogen in the latter,  see § 158, 8.)  Pass on to (76).
* [See § 136, 9, note.] 
268            DETECTION OF INORGANIC  ACIDS.         [§ 166.

       b. A precipitate is formed.
       «. The precipitate is orange  colored: ferricyanogen ; 74
    the reaction with sulphate of protoxide  of iron is resorted
    to as a confirmatory test (§ 158, appendix).
       3. The precipitate is  white  or yellowish-white.  Treat
    the precipitate with ammonia  in  excess—at once, if the
    base be of  the  1st or  2d groups—after filtering  and
    washing if a base  of the  3d or subsequent groups be
    present.
           aa.  The precipitate is  not dissolved: iodine or
        ferrocyanogen.  In the former case the precipitate
        is pale-yellow,  in the  latter white and gelatinous.
        The reaction with starch  and hyponitric acid i§ 157)
        will afford conclusive proof of the presence of iodine,
        the reaction with sesquichloride  of iron  of the  pre-
        sence  of ferrocyanogen (§ 15S, appendix).
           33. The precipitate is  dissolved: chlorine, bro- 75
        mine, or cyanogen.  If the original substance smells
        of hydrocyanic acid, and the silver precipitate dis-
        solves with some difficulty in the ammonia, the  pre-
        cipitate  may be assumed to consist  of cyanide  of
        silver, and, consequently, to indicate the presence  of
        cyanogen.  To remove all doubt  on  the point, add
        to the original solution sulphate of protoxide of iron,
        solution of soda, and hydrochloric acid  (§ 158).  If
        addition of chlorine  water imparts a yellow tint  to
        the original solution the precipitate may be held  to
        consist of bromide  of silver, and  consequently indi-
         cates  the presence of bromine ; if the bromine is pre-
         sent  only in very  small  proportion,  chloroform  or
        bisulphide  of carbon must be used  in conjunction
         with chlorine water  to make the  reaction   distinctly
         apparent  (§ 156).  In the  proved absence of both
         bromine and  cyanogen,  the precipitate consists  of
         jhloride  of silver, and consequently shows the pre-
         sence of chlorine.
   6. AcLrto a small portion of the aqueous solution hydro-  7b
 chloric acid, drop by  drop, until a distinct acid reaction is
 just imparted  to the fluid, then dip in a slip of turmeric paper,
 take it out, and#dry it at 212°.  If the dipped portion looks
 brownish-red, borack acid is present.  To settle all doubt on
 the point, add  sulphuric acid and  alcohol, and  set fire to the
 latter (§147).
   7.  With regard to nitric acid and chloric  acid, these are  77
 usually discovered already in the course  of the preliminary
 examination (6).  The reaction with sulphate of protoxide of 
§ 187.]
SIMPLE COMPOUNDS.
269
 iron and sulphuric acid (§ 162) will afford conclusive evidence
 of  the presence  of the former, treatment of the solid salt
 with concentrated sulphuric acid, of the presence of the lat-
 ter acid (§163).

                      Simple  Compounds.

 A. Substances soluble in Water.  Detection  of the Acid,

               LI. Detection of  Organic Acids.*
                              § 187.
  The analyst should in the first place ascertain by reference
 to the Index of solubilities (see Appendix IV.) what  organic
 acids form soluble salts with the base which has  been found
 in the substance under examination.   Those which form  inso-
 luble salts, of course, cannot be present.
  The following course implies that the organic acid is either
 in the free state or combined with an alkali  or  alkaline earth.
 If, therefore, any other base besides those belonging to groups
 I. and II. is present it must be removed. If the base belongs
 to the 5th or 6th groups it may be separated by hydrosulphu-
 ric acid; if it belongs to the 4th group, by sulphide of ammo-
 nium.   After the metallic sulphide is filtered off, and excess of
 sulphide of  ammonium is disposed  of by acidulating  with
 hydrochloric acid, warming  and  filtering off the sulphur, the
 clear liquid  is examined according to (7§).  In case alumina
 or sesquioxide of chromium is the base present, the attempt
 should be made to throw it down by boiling with carbonate of
 soda.  If this plan does not succeed, as will be the case when
 a non-volatile acid is present, the  acid itself is precipitated by
 neutral acetate of  lead, the precipitate  is washed,  diffused in
 a little water  and  hydrosulphuric  acid gas passed through
 until the lead salt  is decomposed.  The sulphide of lead is fil-
 tered off and the  filtrate examined according  to  (7§).   Alu-
 mina may also be thrown down  from  its  combinations  with
 non-volatile organic acids, by means of a solution of silicate of
 soda, in the form of a silicate of alumina.
  1. Add ammonia to a  portion of the aqueous solution of the 7§
 compound under  examination to slight  alkaline reaction,  then
 chloride of calcium.  If the  solution  was neutral, or  only

  [* The indications of the preliminary examination (10 and note) are always suffi
cient to prove the presence or absence of an organic acid in "simple compounds."
 If, from iuexperience, the operator is uncertain whether an organic acid  be present
he will do well to go carefully  through the following course, and  then to repeat the
preliminary examination (10), interpreting its results by the more positive proof of
the actual analysis.] 
270             DETECTION OF  ORGANIC  ACIDS.         [§ 187,
 slightly acid,  add  chloride  of ammonium before adding the
 chloride of calcium.
        a. No PRECIPITATE IS FORMED, NOT EVEN AFTER SHAK-
     ING THE FLUID NOR AFTER THE LAPSE  OF A FEW MINUTES '.
     absence of oxalic  acid  and  tartaric  acid.*  Pass on to
     (80).
        b. A precipitate is  formed.  Add lime-water in  ex- 79
     cess to a fresh portion  of the original solution, and then
     add solution of chloride of ammonium to the precipitate
     formed.
          a.  The precipitate  redissolves: tartaric acid.  The
        reaction with acetate of potassa may be resorted to as
        a confirmatory test; positive proof will also be afforded
        by the deportment which the precipitate produced by
        the chloride of calcium, and properly washed, exhibits
        with solution of soda or with ammonia and nitrate of
        silver (§ 166).
         8.  The precipitate does  not redissolve :  oxalic acid.
       To remove all doubt, try the reaction with concentrated
       sulphuric acid (§ 148).
  2. Heat the fluid of 1, a, to boiling, keep at that temperature 80
 or some time, and add some more ammonia to the boiling fluid.
       a.  It remains clear : absence of citric acid.  Pass  on
     to  (§1).
       b. It becomes turbid, and deposits  a  precipitate :
     citric acid.  To remove all doubt as to the nature of the
     acid, add solution of acetate of lead in excess, wash the
     precipitate formed, and  see whether it dissolves  readily
     in ammonia (§ 167).
  3. Mix the fluid of 2,  a, with alcohol.                      §1
       a.  It remains clear : absence of malic acid.  Pass on
     to  (§2).
       b. A precipitate is formed :  malic acid.  To  remove
     all doubt, it is invariably necessary to try the reaction
     with acetate of lead, to  see whether the precipitate pro-
     duced by that reagent  dissolves with difficulty in ammo-
     nia, and to examine its  deportment when  the fluid in
     which it is suspended is heated to boiling (§ 168).
  4. Neutralize a portion of the original solution exactly\ (if not
  * [To be certain of the absence of tartaric acid, the solution must be concentrated.]
  f [For this purpose, place a very small slip of blue litmus paper, and also one of
red litmus or turmeric in the solution, and add, from the  reagent bottle, either am
inonia or hydrochloric acid, as is needed, a single drop at a time, agitating, to mix
the liquids thoroughly, until the reagent is in excess.  Then dilute a drop of the other
reagent with enough water to fill a test-tube to the depth of half an inch, and apply
this to the solution by means of a glass rod, until it is just in excess, when the point
of neutralization is attained with sufficient accuracy.] 
§ 188.]
SIMPLE COMPOUNDS.
271
already absolutely neutral) with ammonia or with hydrochloric  §2
acid, and add solution of sesquichloride of iron.
       a. A BULKY PRECIPITATE FORMS, OF A CINNAMON BROWN,
    or dirty yellow color.  Wash  the  precipitate, heat it
    with ammonia, filter, concentrate  the  filtrate by  evapo-
    ration to a  small bulk, divide into two parts, and  add to
    the one  some hydrochloric acid, to the other alcohol and
    chloride of barium.  The  formation of a precipitate  in
    the first portion indicates the presence of benzoic acid,
    a precipitate in the  second denotes the presence of succi-
    nic acid.  Compare § 171 and § 172.
       b. The liquid acquires a rather  intense deep red  §3
    TINT, AND, UPON PROTRACTED BOILING, A LIGHT REDDISH-
    BROWN  precipitate separates :   acetic  acid or  formic
    acid.  Heat a portion of the solid salt under examination,
    or, if the substance  is in the fluid state, of the residue left
    upon evaporating the fluid (which, if acid, you must neu-
    tralize first with soda), with  sulphuric acid and  alcohol
    (§ 174).   The characteristic odor of acetic ether indicates
    the preesnce of acetic acid.
       If you do not detect acetic acid in the fluid, you may
    conclude that the substance  under examination  contains
    formic acid : to remove all doubt, try the reactions with
    nitrate of silver and chloride of mercury (§ 175).

                      Simple Compounds.
B. Substances insoluble or sparingly soluble in Water,  but
  soluble  in Hydrochloric Acid, Nitric Acid, or Nitrohydro-
  chloric  Acid.
                     Detection of the  Base.*
                             § 188.
  Dilute a  portion  of the solution in hydrochloric acid, nitric  84
acid, or nitrohydrochloric acid with  water, f  and proceed  to
examine for  bases  of the 2d, 5th, and 6th groups exactly as
directed §  185, beginning at (46), in cases where the substance
is dissolved in nitric acid, and at (50), if the  solution already
contains hydrochloric acid.
  In testing for  bases of the 3d  and 4th groups by means of
sulphide  of ammonium  according to  (56)  the usual course of

  * Regard is also had here to certain salts of the alkaline earths, as  this course of
examination leads directly to their detection.
  f If upon  the addition of water the liquid becomes white and turbid or deposits
a  white precipitate, this indicates the presence of antimony or bismuth, possibly also
of tin: compare § 124, 9, and 134, 4.  Heat with hydrochloric acid until the fluid
has become clear again, and then begin at (50). 
272               DETECTION OF THE  BASE.            [§ 188

analysis sometimes requires to be modified.  Particular regard
must therefore be had to the following observations:   In cases
where we have a substance soluble in  water, we obtain, in
the course of the examination, a white precipitate upon adding
chloride of ammonium, ammonia, and sulphide of ammonium;
this  precipitate  can  consist  only  of sulphide  of  zinc, or
alumina, or hydrate of siltcic acid as  we have  already seen
(59).  But the case is  different  if the body is insoluble in
water, but dissolves in  hydrochloric acid; for in that  case a
white  precipitate produced by sulphide of ammonium, in pre-
sence of chloride of ammonium, may consist also of phosphates,
BORATES, OXALATES, SILICATES  OF THE ALKALINE EARTHS, Or of
fluorides of their metals, as all these bodies are insoluble
in water, but dissolve in hydrochloric acid, and (being only
very sparingly soluble also in  solution of chloride of ammo-
nium) accordingly separate again upon neutralization of that
acid.   If, therefore, a white precipitate is produced upon test-
ing an  acid solution, under the circumstances stated, and ac-
cording to the directions of § 185, (56) proceed as follows:—
  1. If the results of the preliminary examination have given §5
you reason to suspect the presence of silicic acid [20],  evapo-
rate a portion of the hydrochloric acid solution  to  dryness,
moisten the residue with hydrochloric acid and add water.  If
silicic acid is present, it will remain undissolved.  Determine the
base in the solution as directed (56), or (62), as the case may
require.
  2. Add  to  a portion  of the  original  hydrochloric acid
solution, some tartaric acid, and after this ammonia in excess.
       a. No permanent precipitate is formed : absence of §6
    the above enumerated salts of the alkaline earths.  Mix
    another portion of  the original solution  with solution of
    soda in excess, and add to the one half of the clear fluid
    chloride  of ammonium, to the other half hydrosulphuric
    acid.   The formation of a precipitate in the former indi-
    cates  the presence of alumina ; in the latter, the presence
    of ZINC
       b. A permanent precipitate is formed : presence of
    a salt of an alkaline earth.
        a. A portion of the original substance is placed on a
       watch-glass, with a little binoxide of manganese, a few
       drops of water and some concentrated sulphuric acid.
       If evolution of carbonic acid forthwith takes place, the
       salt is an oxalate.  Heat a sample of the original sub-
       stance to redness, dissolve the residue in hydrochloric
       acid, and ascertain the  nature of the alkaline earth in
       the solution as directed (62). 
§ 189.]              SIMPLE COMPOUNDS.                  273

         8.  Add to a portion of the hydrochloric acid solution §§
       ammonia until a precipitate forms ; then acetic acid until
       this is redissolved;  lastly, acetate of soda and a drop
       of solution of sesquichloride of iron: the  formation of
       a  white  flocculent precipitate indicates the presence of
       phosphoric acid.  Add now some more sesquichloride
       of iron until the  fluid has acquired a distinct red color,
       boil, filter boiling, and test  the filtrate, which is now
       free from phosphoric acid, for the alkaline earth with
       which the phosphoric acid was combined, as directed
       (62), after having previously removed, by precipitation
       with ammonia, the iron which may have been dissolved.
         y. Test a portion of the original substance, or of the §9
       precipitate produced in the  hydrochloric  acid  solution
       by ammonia, with sulphuric acid for fluorine (§ 149).
       After removal of the fluorine, ascertain the nature of the
       alkaline  earth  now  in the residue, combined with sul-
       phuric acid (§ 191).
         S. Boracic acid is detected in the hydrochloric acid
       solution  by means of turmeric paper (§ 147), and the
       base combined with  it, by boiling a portion of the origi-
       nal substance with dilute solution of carbonate of soda,
       filtering, washing well the precipitated carbonate, dis-
       solving it in the least possible quantity of dilute hydro-
       chloric acid, and  further proceeding with this solution
       according to (62).

                      Simple Compounds.

B. Substances  insoluble or sparingly soluble in Water, but
    soluble in  Hydrochloric Acid, Nitric  Acid, or Nitro-
    hydrochloric Acid.

                   detection  of  the acid.

               I. Detection of Inorganic Acids.
                            §  189.
  1.  Chloric acid cannot be present, since all chlorates with- 90
out exception are soluble in water; nitric acid, which may
be present in form of a basic salt,  must have been revealed
already by ignition  of the  body in  a  glass tube, and so must
cyanogen (§).  For the analysis of the metallic cyanides in-
soluble in water see § 207.  The results of the test with phos-
phate of soda and ammonia will have directed attention to the
presence  of silicic acid  (20).   Evaporation of the  hydro-
chloric acid solution to dryness, and treatment of the residue
                              18 
 274           DETECTION  OF INORGANIC ACIDS.        [§ 189

 with hydrochloric acid and water will set all doubt at rest on
 the point (§ 153, 3).
   2. The course of examination laid down here for the detec- 91
 tion of the bases leads likewise to that of arsenious and
 ARSENIC ACIDS, CARBONIC ACID, HYDROSULPHURIC ACID,  and
 chromic acid.  With regard to the latter acid, I repeat that
 its presence is  indicated by the yellow or red color  of the
 compound, the evolution of chlorine which ensues upon  boiling
 with hydrochloric acid, and the subsequent presence of sesqui-
 oxide of chromium in the solution.  Fusion of the compound
 under examination with  carbonate of soda is, however, the
 most conclusive test for chromic acid (§ 141).
   3.  Boil a portion of the substance with nitric acid.          92
       a. If nitric  oxide gas is evolved, and sulphur separates,
     this is confirmative of the presence of a metallic sulphide.
       b. If violet vapors escape, the compound is a metallic
     IODIDE.
       c. If reddish-brown fumes of a chlorine-like smell are
     evolved, the  compound is  a  metallic bromide, in which
     case the fumes will color starch yellow (§ 156).
   4. Dilute a portion of the solution obtained by boiling with 93
nitric acid (92)—or of the filtrate of this solution, should the
nitric acid have  left  an undissolved residue—with water, and
add solution  of  nitrate of silver to  the fluid.  The formation
of a white precipitate which,  after  washing, is soluble in
ammonia, and fuses without decomposition when heated, indi-
cates the presence  of  chlorine.
   5. Boil a portion of the  substance with hydrochloric acid, 94
filter, if necessary, dilute with water, and  add  chloride of
barium.  The formation of a white precipitate, which does not
redissolve even  upon  addition of a large quantity of  water,
indicates the presence of sulphuric acid.
  6. Test for boracic acid as directed § 147, 6.
  7. If  none of  the acids  enumerated from 1 to 6 are present, 95
there is reason  to suspect the presence  of phosphoric acid,
oxalic acid, or fluorine, or the total absence of  acids.   To
the presence  of oxalic acid your attention will  have been
called already in the  course of the preliminary examination
(8).   If the acids  named  had been combined with  an alkaline
earth, they would have already been detected in the course of
the examination for these  bases; they need therefore here be
tested for, only in  case the  examination has revealed the  pre-
sence of some other base.  To  that end, precipitate the base,
according to circumstances, either with  hydrosulphuric  acid
or with  sulphide of ammonium and filter.  If you have precipi-
tated with sulphide of ammonium  add to the filtrate  hydro- 
§§ 190, 191.]   SIMPLE INSOLUBLE  COMPOUNDS.            275

chloric acid to acid reaction, expel in either case the hydro-
Rulphuric acid by boiling, and filter if necessary.  Test a portion
of this solution for phosphoric acid, oxalic acid, and fluorine, as
directed (70).  If the base is alumina or sesquioxide of chro-
mium, phosphoric acid is  tested by means of the nitric acid
solution of molybdate of ammonia (§  145,10), oxalic acid with
binoxide of manganese and oil of vitriol (§ 148), fluorine with
oil of vitriol (§ 149).

                    Simple Compounds.
B. Substances insoluble or sparingly soluble in Water, but
                      soluble  in Acids.

                   detection of the acid.

              H.  Detection of Organic Acids.*

                            § 190-
  1. Formic acid  cannot be present, as all the formates  are 96
soluble in water.
  2. Acetic acid has been revealed  already in the  course of
the preliminary examination, by the disengagement of acetone.
The reaction with sulphuric acid and  alcohol (§ 174) will afford
conclusive proof.
  3. Boil a portion of the substance for some time with solution 97
of carbonate of soda in excess, and filter hot.  You have now
in most cases the organic acid in solution in combination with
soda.  Acidulate the solution slightly -with hydrochloric acid,
expel the carbonic acid by heat, and test  as directed § 187.
When a base of the 4th group, or oxide of lead is present,  the
separation by  carbonate  of soda is not complete.  In  such a
case, after boiling with carbonate  of soda, add to the filtrate
sulphide  of  ammonium in slight excess, filter again and test
the solution thus obtained.

                     Simple Compounds.
C.  Substances  insoluble  or  sparingly  soluble  in Water,
  Hydrochloric  Acid, Nitric  Acid, and  Nitrohydrochloric
  Acid.

            detection of the  base and the acid.
                            § 191.
  Under  this  head we have to consider here, sulphate of 98
BARYTA, SULPHATE OF STRONTIA,  SULPHATE OF LIME, FLUORIDE
OF  CALCIUM, SILICA, SULPHATE OF  LEAD, Compounds of LEAD
* [See Note § 187.] 
276             DETECTION OF  BASE AND ACID.         [§ 191

with chlorine and bromine, compounds of silver with chlo-
rine, bromine, iodine, and cyanogen, and  lastly,  sulphur
and carbon, as the only bodies belonging to this class which
are more frequently met wdth.  For the simple silicates I refer
to §  208, for  the ferro- and ferricyanides, to § 207.   The pre-
liminary examination will  have informed  you whether you
need  pay any regard to the  possible presence of these com-
pounds.
  Sulphate of lime and  chloride  of lead are not altogether
insoluble in water, and sulphate of lead may be  dissolved in
hydrochloric acid.   However,  as these compounds are so diffi-
cultly soluble that complete solution of them is seldom effected,
they are included here also among the class  of insoluble sub-
stances, to insure their detection, should they have been over-
looked in the course of the examination of the aqueous or acid
solution of the body to be analyzed.
  1.  Free sulphur must have been detected already in  the
course of the preliminary examination.
  2.  Carbon is  usually black; it is insoluble in  aqua regia;
put on platinum foil, with the blowpipe flame playing upon the
under side of the foil, it is always  consumed; by deflagration
with nitrate of potassa it yields carbonate of potassa.
  3.  Pour sulphide of ammonium over a very small quantity 90
of the substance under examination.
       a. It turns black ;  this indicates the presence of lead
     or a salt of  silver.
         ol. The  body fused in the glass  tube without decompo-
       sition (s)'  chloride of  lead, bromide of lead, chloride
       of silver, bromide  of silver, iodide  of silver.  Fuse 1
       part of the compound with 4 parts of carbonate of
       soda and potassa in a small porcelain crucible, let
       cool, boil the residue  with water, and test the  fil-
       trate for  chlorine, bromine,  and iodine, as directed
       (73).   Dissolve the residue, which consists either of
       metallic silver or oxide of lead,  in nitric  acid,  and
       test the solution as directed (46).
         8.  The body  evolved cyanogen, and left metallic sil-
       ver behind: cyanide of silver.
         y. The body remained unaltered: sulphate of lead.
       Boil a sample of it with solution of  carbonate of soda,
       filter,  acidulate  the filtrate with hydrochloric acid,
       and test with chloride  of barium for sulphuric acid ;
       dissolve the washed residue in nitric acid, and  test
       the solution with hydrosulphuric acid and  with  sul-
       phuric acid for lead.
       b. It remains white : absence of an oxide of a heavy 100 
§ 191.]          SOLUBLE  COMPLEX  COMPOUNDS.            !

    metal.   A small sample is ground together with quartz
    sand, the mixture  is placed on a watch-glass, moistened
    with a few drops of oil of vitriol and gently warmed.
         a.  White vapors  are evolved which redden litmus y
      this  indicates the presence of fluoride of calcium.
      Reduce a portion of the substance to a fine powder,
      decompose  this  in  a  platinum  crucible  with  sul-
      phuric acid, and  try  the reaction on glass  (§  149),
      to prove the  presence of fluorine ; boil  the  residue
      with hydrochloric acid,  filter,  neutralize  the filtrate
      with ammonia,  and  test  for  lime  with  oxalate  of
      ammonia.
         8. Vapors that redden litmus are not evolved.  Mix
      a  small portion  of  the very finely pulverized  sub-
      stance with 4 times the quantity of pure carbonate of
      soda and potassa, and fuse the mixture in a platinum
      crucible, or else on  platinum foil.   Boil the fused mass
      with water, filter, should a residue be left, and wash
      the  latter.   Acidulate a  portion  of the filtrate with
      hydrochloric acid, and then test with chloride of barium
      for sulphuric acid ; and in case you do not  find that
      acid, test another portion of the filtrate for silicic acid
      by evaporating the fluid  acidified with  hydrochloric
      acid (§ 153, 2).
         If the silicic acid was present  in the pure state, the
      mass resulting  from the fusion of  the  substance with
      carbonate of soda and potassa must  have dissolved in
      water to a clear fluid;  but if silicates also happened to
      be present,  their bases are  left behind undissolved,  and
      may be further examined.
         If, on the other hand, sulphuric  acid has been found,
      the  alkaline earth which was combined  with it is found
      on the filter as a  carbonate.  Wash this, then dissolve
      it in dilute  hydrochloric  acid, and test the solution for
      baryta, strontia, and lime, as directed (62).
                     Complex Compounds.*

A. Substances soluble in Water, and also such as are inso-
    luble in  Water,  but  dissolve  in Hydrochloric  Acid,
    Nitric Acid, or Nitrohydrochloric Acid.

  * I use this term here, and hereafter in the present work, to designate compounds
in which all the more frequently occurring bases, acids, metals, and metalloids are
supposed to be present. 
278   AQUEOUS SOLUTION—DETECTION OF  THE BASES.   [§ 192
                     Detection of the Bases. *

                             § 192. f
(Treatment with Hydrochloric Acid:  Detection  of Silver, Sub
                    oxide of Mercury [Lead].)
  The systematic  course for the detection of the bases is 1©1
essentially the same for bodies soluble in water, as for those
which are soluble only in acids.  Where, in consequence of the
different nature of the original  solution,  deviations are ren-
dered necessary, the fact will be distinctly stated.

                     I. Solution in Water.
  Mix the portion intended for the  detection of  the
bases with some hydrochloric acid.
  1. The solution had an acid or neutral reaction pre- 102
viously to the addition of the hydrochloric acid.
      a. No  precipitate  is formed ;  this  indicates the
    absence of silver and suboxide of mercury.  Pass on to
    § 193.
      b. A precipitate is formed.   Add more hydrochloric
    acid  drop by drop  until the  precipitate  ceases to in-
    crease ; then add about six or eight drops more of hydro-
    chloric acid, shake the  mixture, and filter.
      The  precipitate produced by  hydrochloric acid may
    consist of chloride of  silver,  subchloride of  mercury,
    chloride of lead, a basic salt of antimony, basic oxychlo-
    ride of bismuth, possibly also of benzoic acid.  The basic
    salts of antimony and oxychloride of bismuth,  however,
    redissolve  in the  excess of hydrochloric acid; conse-
    quently, if the instructions given have been  strictly fol-
    lowed, the precipitate  collected upon the filter can con-
    sist  only of chloride of silver,  subchloride  of mercury,
    or  chloride  of  lead—(possibly also of  benzoic  acid,
    which, however, is altogether disregarded here).
      Wash the  precipitate collected upon the filter, twice
    with cold water, add the washings  to  the filtrate, and
    examine the solution as directed § 190,  even though the
    addition of the washings  to the acid filtrate should pro-

  *  The beginner should not fail to study the explanations in the Third Section
thoroughly before attempting the  analysis of a complex substance.   He will also
do well to review these explanations frequently during the course of his practice.
  Regard is here had also to the presence of the acids of arsenic, and of those salts of
the  alkaline earths which dissolve in hydrochloric acid, and separate again from
that solution unaltered, upon neutralization of the acid by ammonia.
  f  Consult the remarks in the Third Section. 
§ 192.]         SOLUBLE COMPLEX COMPOUNDS.            279

    duce turbidity in the fluid (which indicates the presence
    of compounds of antimony or bismuth).
      Treat the washed  precipitate on the filter as follows:   103
        a. Pour hot water over it upon the filter, and test the
      fluid running  off  with sulphuric acid for lead.  The
      non-formation of a precipitate upon the addition of the
      sulphuric acid simply proves that the precipitate pro-
      duced by hydrochloric acid contains no lead, and does
      not by any means  establish the  total absence  of this
      metal, as hydrochloric acid fails to precipitate lead from
      dilute solutions.
        8. Pour over the now thrice-washed precipitate upon
      the filter, solution of ammonia. If this changes its color
      to black or gray, it is a proof of the presence of subox-
      ide OF MERCURY.
        y. Add to the  ammoniacal fluid running off in 8
      nitric acid to strongly acid reaction.  The formation of
      a white,  curdy precipitate or opalescence indicates the
      presence of silver. (If the  precipitate did contain lead,
      the ammoniacal solution  generally appears  turbid,
      owing to the separation of a basic salt of lead.  This,
      however, does not interfere with the testing for silver,
      since the  basic salt of lead redissolves upon the addition
      of nitric  acid.)
  2.  The  original  aqueous  solution had an  alkaline  104
reaction.
      a. The addition of hydrochloric acid to  strongly
    ACID REACTION FAILS TO PRODUCE EVOLUTION OF  GAS OR
    A PRECIPITATE, OR  THE PRECIPITATE WHICH  FORMS AT
    FIRST  REDISSOLVES UPON FURTHER ADDITION OF  HYDRO-
    CHLORIC acid : pass on to § 193.
      b. The addition of hydrochloric acid to the origi-
    nal SOLUTION PRODUCES A  PRECIPITATE WHICH DOES NOT
    REDISSOLVE IN  AN  EXCESS OF THE PRECIPITANT, EVEN
    UPON  BOILING.
        a. The formation of  the precipitate is attended  105
      neither with evolution of hydrosulphuric acid nor of
      hydrocyanic  acid.  Filter, and  treat the filtrate as
      directed  § 193.
          aa.  The precipitate is white.   It  may,  in that
        case, consist of  a salt of lead or silver, insoluble  in
        water  and hydrochloric acid (chloride of lead,
        sulphate of lead, chloride of silver, &c.) or may
        be hydrated silicic  acid. Test for the  bases and
        acids of these compounds as directed § 206,  bearing
        in mind that the chloride of lead or chloride of silver 
280   AQUEOUS  SOLUTION—DETECTION OF THE BASES.   [§ 192,

         which may be present may possibly have been form-
         ed in the process.
           bb. The precipitate is yellow or orange.  In
         that case it may consist of sulphide of arsenic (and
         if the fluid from which it has separated was not boil-
         ed for  a long time, or only with very dilute hydro-
         chloric  acid, also of sulphide of  antimony  or
         bisulphide of tin), which substances were original-
         ly dissolved in solution of ammonia, soda, potassa,
         phosphate of soda, or some other alkaline fluid, with
         the exception of solutions of alkaline sulphides and
         cyanides.  Examine the precipitate which may also
         contain hydrated silica, as directed (40).
         8. The formation of the precipitate is attended with 106
      evolution of  hydrosulphuric  acid gas,  but not  of
      hydrocyanic acid.*
           aa. The precipitate  is of a pure white color,
         and consists of separated sulphur.  In that case
         a  sulphuretted,  alkaline  sulphide   is  present.
         Boil, filter, proceed  with  the  filtrate according to
         §  197, with the  residue as directed § 206.
           bb. The precipitate  is colored.  In that case
         you may conclude that a metallic sulphur salt is
         present, i. e., a combination of  an alkaline sulphur
         base  with a metallic  sulphur acid.  The precipitate
         may accordingly consist of sulphide  of gold, sul-
         phide OF PLATINUM,  SULPHIDE OF TIN, SULPHIDE  OF
         ARSENIC, Or SULPHIDE OF ANTIMONY.  It might, flOW-
         ever, consist also of sulphide  of  mercury or of
         sulphide of copper,  or  sulphide of nickel, or con-
         tain  these  substances, as  the first is readily soluble
         in sulphide of potassium, and the last two are slightly
         soluble in sulphide of ammonium.  Filter, and treat
         the  filtrate according to  § 197, the precipitate as
         directed (40)-
         y. The formation of the precipitate is attended with  107
      evolution of hydrocyanic acid, with or without  simul-
      taneous disengagement  of hydrosulphuric acid.   This
      indicates the presence of an alkaline cyanide, and,
      if the  evolution of the hydrocyanic acid is  attended
      with that of  hydrosulphuric acid, also of an alkaline
      sulphide.  In that  case the precipitate may, besides
  * Should the odor of the evolved gas leave any doubt regarding the presence 01
absence of hydrocyanic acid, add some chromate of potassa to a portion of the fluid
previously to the addition of the hydrochloric acid. 
§ 192.]         SOLUBLE COMPLEX COMPOUNDS.            281
  the compounds enumerated in a (105) and 8 (106),
  contain many other substances (e. g., cyanide of nickel,
  cyanide of silver,  &c).  Boil,  with further addition
  of hydrochloric acid, or of nitric acid, until the whole
  of the hydrocyanic acid is expelled, and treat the
  solution,  or, if an  undissolved  residue has been left,
  the filtrate, as  directed § 193 ; and the residue (if any)
  according to § 206.
  c. The addition of hydrochloric acid fails to pro-  10§
DUCE A PERMANENT PRECIPITATE, BUT CAUSES EVOLUTION
OF GAS.
    a.  The escaping  gas smells of hydrosulphuric acid ;
  this indicates the presence of a  simple alkaline sul-
  phide.  Proceed as in § 197.
    8. The escaping gas is inodorous y in that case it is
  carbonic  acid which was combined with an alkali.
  Pass on to § 193.
    y.  The  escaping gas  smells of hydrocyanic  acid
  (no matter whether hydrosulphuric acid or carbonic
  acid is evolved at the same time or not).   This  indi-
  cates  the presence of an  alkaline  cyanide.   Boil
  until the  whole of the hydrocyanic acid is expelled,
  and then pass  on to § 193.
II. Solution in Hydrochloric Acid or in  Nitrohydro-
                        chloric Acid.

  Proceed as directed § 193.

                HI. Solution in  Nitric Acid.

  Dilute a small sample of it  with water; should this pro- 109
duce turbidity or a precipitate  (indicative of the  presence of
bismuth) add nitric  acid until  the  fluid is clear  again, then
hydrochloric acid.
    1. No  precipitate is  formed.   Absence of silver and
  suboxide  of  mercury.  Treat  the principal  solution  as
  directed § 193.
    2. A precipitate is formed.   Treat a larger portion of
  the nitric acid solution the same way as the sample, filter,
  and examine the precipitate as directed (l03), the filtrate
  as directed §  193. 
282       TREATMENT WITH HYDROSULPHURIC ACID.    [§ 193.
                               § 193*
(Treatment  with  Hydrosulphuric  Acid,  Precipitation  of
  the Metallic Oxides of Group  V.  2nd Section,  and  of
   Group VI.)
  Add to  a small portion of  the  clear acid solution
HYDROSULPHURIC ACID WATER, UNTIL THE ODOR OF HYDROSUL-
PHURIC ACID IS DISTINCTLY PERCEPTIBLE  AFTER  SHAKING THE
MIXTURE, AND WARM GENTLY.
       1. No precipitate is formed, even after the lapse of  no
     some time.  Pass on to  § 197, for lead, bismuth, cad-
     mium, copper, mercury, gold,  platinum, antimony, tin,
     and arsenic,f  are not  present ;J the absence of sesqui-
     oxide of iron and  of chromic acid  is also indicated  by
     this negative reaction.
       2. A PRECIPITATE IS FORMED.
         a.  The precipitate is of a pure white color, light and  m
       finely pulverulent, and does not redissolve on addition
       of hydrochloric  acid.  It  consists of  separated  sul-
       phur, and indicates  the presence of sesquioxide  of
       iron.§   None of the other metals  enumerated in (110)
       can  be  present.   Treat  the principal  solution  as
       directed § 197.
         b.  The precipitate  is colored.
         Add to the larger proportion of the acid or acidified  112
       solution, best in  a small  flask,  hydrosulphuric acid
       water in excess, i. e., until the fluid smells distinctly of
       it, and  the  precipitate  ceases to  increase upon con-
       tinued addition of the reagent; apply a  gentle heat,
       shake vigorously for  some time, filter, keep the filtrate
       (which contains the oxides  present of Groups I.—IV.)
       for further examination, according to the instructions
  * Consult the remarks in the Third Section.
  f  Should the preliminary examination have led you to suspect  the presence of
arsenic acid, you must endeavor  to obtain the most conclusive evidence of the
absence of this acid;  this may be done by allowing the fluid to stand for some time
at a gentle heat (about 158" Fah.) or by heating it with sulphurous acid previous to
the addition of the hydrosulphuric acid.  (Compare § 136, 3.)
  \  In solutions containing much free acid, the  precipitates are frequently formed
only after dilution  with water.
  § Sulphur will precipitate also  if sulphurous acid, iodic acid, or bromic acid  is
present (which substances are  not included in  our analytical course), and also  if
chromic acid, chloric acid, or free chlorine is present.  In presence of chromic acid,
the separation of the sulphur is attended with reduction of the acid to sesquioxide
of  chromium, in consequence of which  the reddish-yellow color of the solution
changes to green.  (Compare § 141.)  The white  sulphur suspended in the green
solution looks at first like a green precipitate, which frequently tends  to mislead
beginners. 
191.]         SOLUBLE COMPLEX  COMPOUNDS.             283
       of § 197, and thoroughly wash (compare page 10) the
       precipitate which contains the sulphides of the metals
       present of Groups V. and VI.
           In many cases,  and more particularly when there
         is any reason to suspect the presence of arsenic, it
         will be found more convenient to  transmit  hydro-
         sulphuric  acid gas through the solution diluted
         with water, instead of adding hydrosulphuric acid
         water.
         If the precipitate is yellow, it consists  principally  lis
       of sulphide of arsenic, sulphide  of tin, or  sulphide of
       cadmium; if orange-colored, this indicates sulphide of
       antimony; if brown  or black, one at least of the fol-
       lowing oxides is present:  oxide of lead, teroxide of
       bismuth, oxide of copper, oxide  of mercury, teroxide
       of gold, binoxide of platinum, protoxide of tin.   How-
       ever, as a yellow precipitate may contain small admix-
       tures of an orange-colored, a  brown, or even a black
       precipitate, and yet its color not be very perceptibly
       altered thereby, it will always prove the  safest way
       to assume the presence  of all  the metals named in
       (110), in any precipitate  produced by hydrosulphuric
       acid,  and  to  proceed  accordingly as the next  para-
       graph directs.


                              §  194.
 (Treatment of the Precipitate produced by Hydrosulphuric Acid
   with Sulphide of Ammonium; Separation of the  2nd  Section
   of Group V. from  Group VI.)
   Introduce a small portion of the (thoroughly washed)  114
 PRECIPITATE  PRODUCED BY  HYDROSULPHURIC  ACID IN THE
 ACIDIFIED  SOLUTION  INTO A TEST-TUBE,* ADD A LITTLE WATER,
 AND TEN TO TWENTY DROPS  OF YELLOW SULPHIDE  OF AMMO-
 NIUM,  AND EXPOSE THE MIXTURE  FOR  A  SHORT TIME  TO  A
 GENTLE HEAT.f

  * If there is a somewhat large precipitate, this may be readily effected by means
 of a small spatula of platinum or horn; but if you have only a very trifling precipi-
 tate, make a hole in the bottom of the filter, insert the perforated point into the
 mouth of the test-tube, rinse the precipitate into the latter by means of the washing-
 bottle, wait until the precipitate has subsided, and then decant the water.
  f If the solution contains copper, which is generally revealed by the color of the
fluid,  and may be ascertained positively by testing with a  clean  iron rod (see
§ 123 10), use solution of sulphide of sodium instead of sulphide of ammonium (in
which sulphide of copper is not absolutely insoluble, see § 123, 5), and boil the mix 
284  TREATMENT OF THE  HS  PRECIPITATE WITH NH4S.  [§ 194.

   1. THE PRECIPITATE  DISSOLVES COMPLETELY IN SULPHIDE  Hg
of ammonium (or sulphide of  sodium, as the  case may be):
absence of the metals of Group V.—cadmium,  lead, bismuth,
copper, mercury.  Treat the remainder of the  precipitate (of
which you have digested a  portion with sulphide  of ammo-
nium) as  directed § 195.—If the precipitate  produced  by
hydrosulphuric acid was so trifling  that you have used the
whole of it in  treating with sulphide of ammonium, precipi-
tate the  solution  obtained  in  that  process by addition of
hydrochloric acid, filter, wash the precipitate, and treat the
latter as directed §  195.
   2. The precipitate is not redissolved, or  at least not  lie
completely :  presence of the metals  of  Group  V.
       Dilute with 4 or 5 parts  of water, filter, and mix the
     filtrate with hydrochloric acid in slight excess.
       a.  The fluid simply turns  milky, owing  to the separa-
     tion of sulphur.  Absence of the metals of Group VI.—
     gold, platinum, tin, antimony, and  arsenic*  Treat the
     rest of the precipitate (of which  you  have  digested a
     portion with sulphide  of ammonium), according to the
     directions of  §  196.
       b. A colored precipitate is formed: presence of metals  117
     of Group VI. by the side  of those  of Group V.  Treat
     the entire precipitate produced  by hydrosulphuric acid
     the same as you have treated a portion of  it, i. e., digest
     it with yellow sulphide of ammonium,  or, as the case
     may  be,  sulphide  of sodium,  let  it subside, pour the
     supernatant liquid on a filter, digest the residue in the
     tube once more with yellow  sulphide of ammonium  (or

ture.   But if the fluid, besides copper, also contains oxide of mercury (the presence
of which is generally sufficiently indicated by the several changes of color exhibited
by the precipitate forming upon the addition of the hydrosulphuric acid (§122, 3), and
which, in doubtful cases, may be detected with positive certainty by testing a por-
tion of the original solution acidified with  hydrochloric  acid, with  protochloride of
tin, sulphide of ammonium must be used, although the separation of the sulphides
of the antimony group from the  sulphide of copper is not fully  effected  in such
cases; since, were sulphide of sodium used, the sulphide of mercury would dissolve
in this reagent, and this would impede the ulterior examination of the sulphides of
the antimony group.  [If the mixture is heated to boiling before filtering off, sulphide
of ammonium may be  used in all cases, only the very minutest traces of copper, or
none at all being dissolved.—Editor.]
  * That this inference becomes uncertain if the precipitate  produced by hydro-
sulphuric acid, instead of being digested with a small quantity of sulphide of ammo-
nium, has been treated with a larger quantity of that reagent, is self-evident; for the
large quantity of sulphur which separates in  that case will, of course,  completely
conceal any slight traces of sulphide of  arsenic or bisulphide of tin which may have
been thrown down.  In case of doubt, proceed according to  (117). 
§ 195.]          SOLUBLE COMPLEX COMPOUNDS.             285

     sulphide of sodium), and filter.  Wash the residue* (con-
     taining the sulphides of Group V.),  and treat it after-
     wards as  directed  §  194.   Dilute   the filtrate—which
     contains the metals of Group VI.  in  the form of sulphur
     salts—with water, add hydrochloric acid to slightly acid
     reaction,  heat gently, filter  the  precipitate  formed—
     which contains the sulphides of the metals of Group VI.
     mixed with  sulphur—wash thoroughly, and proceed as
     directed next paragraph (§ 195).

                               § 195.
     (Detection of the Metals of  Group VI.:  Arsenic, Anti-
                  mony, Tin, Gold, Platinum.)
  If the precipitate consisting of the sulphides of Group VI.  11 §
has a pure yellow color, this indicates principally arsenic
and tin ;  if it is distinctly  orange-yellow, antimony is pre-
sent ; if it is brown or black, this denotes the presence of
platinum or gold.
  Beyond these general indications, the color of the precipi-
tate affords no safe  guidance.  It is  therefore  always  advi-
sable to  test yellow precipitate also for antimony, gold, and
platinum, since minute  quantities of the  sulphides of  these
metals  are completely hid by a large  quantity of bisulphide
of tin  or tersulphide  of arsenic.  Proceed  accordingly as
follows:
  Heat a little of the precipitate on the lid of a porcelain cru-
cible, or on a fragment of porcelain or glass.f
       1.  Complete volatilization ensues: probably presence  119
     of  arsenic,  absence of  the other metals of  Group VI.
     Reduction of  a portion of the precipitate with cyanide
     of  potassium and carbonate of  soda (§ 135, 12)J will

  * If the residue suspended in the fluid containing sulphide of ammonium, and
insoluble therein, subsides readily, it is not transferred to the filter, but washed in
the tube by decantation.  But if its subsidence  proceeds slowly and with difficulty,
it is transferred to the filter, and washed there;  a hole is then made in the bottom
of the filter, and the residue rinsed into a small porcelain basin by means of a wash-
ing bottle; the application of a gentle heat will  now materially aid the  subsidence
of the residue, and the  supernatant water may then be decanted.  Sometimes  the
suspended sulphides are so finely divided  as to  run  through the filter.  In such a
case add  to the liquid a little chloride of ammonium.
  f  That this  preliminary examination  may be omitted if the precipitate is  not
yellow, and that it can give a decisive result only if the sulphur precipitate submit-
ted to the test has been thoroughly washed, is self-evident.
  t  If the precipitate contains much free sulphur,  it is digested for some time with
ammonia which  dissolves the tersulphide of  arsenic.  The  filtered  solution is
evaporated k) dryness at a gentle heat with addition of a little carbonate of soda,
and this residue is heated with cyanide of potassium and soda as above directed. 
286     DETECTION OF THE METALS  OF GROUP VI.     [§ 195
     afford  positive proof  of the presence or absence  of
     arsenic.  Whether  that metal was present  in  the form
     of arsenious acid or in that of arsenic acid, may be ascer-
     tained by the method described § 137, 9.
       2.  A fixed residue is left.   In that case all the metals 120
     of Group VI. must be  sought for.  Dry the remainder
     of the precipitate thoroughly upon the filter, triturate it
     together with about 1  part  of anhydrous  carbonate  of
     soda and 1 part of nitrate of soda, and transfer the mix-
     ture in small  portions at a time to a small porcelain cru-
     cible, in  which you have  previously heated 2 parts  of
     nitrate of soda to  fusion.*  As soon as complete oxida-
     tion  is effected, pour the mass out on  a piece  of  por-
     celain.
       After  cooling, soak the fused mass (the  portion still
     sticking  to the inside of the crucible as well as the por-
     tion  poured out on the porcelain) in cold  water, filter
     the insoluble  residue—which will remain if the mass con-
     tained antimony, tin, gold, or platinum—and wash well
     with a mixture of about equal parts of water and alcohol.
     (The alcohol is added to prevent the solution of the anti-
     monate of soda.   The  washings are not added to the
     filtrate.)   The filtrate and the residue are now examined
     as follows:
         a. Examination  of  the filtrate  for  arsenic 121
       (which must be present  in it in  the form of arsenate
       of soda).
         To  the  filtrate add  nitric acid  cautiously to faint
       acid reaction,! heat to expel  carbonic and nitrous acids,
       and then  divide the liquid into two  portions.—To one
       portion add some nitrate of silver (not too little), filter

  * Should the  amount of the precipitate be so minute that this operation cannot
be conveniently  performed, cut the filter,  with the dried precipitate adhering to it,
into small pieces, triturate these together with some carbonate of soda and nitrate
of soda, and project both the powder and the  paper into the fusing nitrate of soda.
It is preferable,  however, in such  cases, to procure at once, if  practicable, a suffi-
ciently large amount of the precipitate, as otherwise there will be but little hope of
effecting the positive detection of  all the metals of Group  VI.  Supposing all the
metallic sulphides of the sixth group to have been present, the fused mass would
consist  of antimonate and arsenate of soda, binoxide of tin, metallic gold and pla-
tinum, sulphate, carbonate,  nitrate,  and some nitrite of  soda.   Compare  also
§ 137, 1.
  \ In some cases where a somewhat  larger proportion  of  carbonate of soda had
been used, or a very strong heat applied, a trifling  precipitate  (hydrated binoxide
of tin)  may separate upon  the acidification of  the filtrate  with nitric acid.  This
may be  filtered off, and then treated in  the  same manner as the undissolved
residue. 
$ 195.]         SOLUBLE COMPLEX COMPOUNDS.             287

      (in case some  chloride  of silver* or nitrite of silver
      should  have separated), pour upon the filtrate, along
      the  side of the tube  held slanting, a layer of  dilute
      solution of ammonia,—2  parts  of water to 1 part of
      solution of ammonia—and let  the mixture stand for
      some time without shaking. The formation of a red-
      dish-brown precipitate, which floats cloud-like between
      the two layers (and may be seen  far more readily and
      distinctly by reflected than by transmitted light), de-
      notes the presence of arsenic
         If the arsenic is present in  some quantity, and the
      free nitric acid  of the solution  is exactly  saturated
      with ammonia, the fluid being stirred during this pro-
      cess, the  precipitate  of   arsenate  of silver  which
      forms  imparts  a  brownish-red  tint to  the  entire
      fluid.
         To the other portion of this acidified solution, add  122
      ammonia, then a mixture of sulphate of magnesia and
      chloride of ammoniumf and rub the sides  of the test-
      tube with a glass rod.  The formation  of the crystal-
      fine  precipitate  of arsenate of ammonia-magnesia,
      which often forms only after the lapse  of some time
      and  especially on the sides  of the tube, is further evi-
      dence of the presence of arsenic.  For additional con-
      firmation the arsenic  may  be procured in  the metallic
      state.   (Compare  § 135 and § 136.)
         Whether the arsenic was present in the form  of
      arsenious acid or in that of arsenic acid, may be ascer-
      tained by the method described,  § 137, 9.
         b. Examination of the residue for antimony, tin,  128
      gold, platinum.  (As the  antimony, if present in the
      residue, must exist as white, pulverulent antimonate of
      soda, the tin as white, flocculent binoxide, the gold and
      platinum in the metallic state, the appearance of  the
      residue  is in itself indicative of its nature.)  The preci-
      pitate is placed in a small vessel  of platinum [or in a
      porcelain dish in contact with a slip of platinum foil] and
      heated with a little hydrochloric acid.   Water is now
      added,  and (disregarding  any undissolved residue) a
      compact piece  of pure (lead-free) zinc is put into the
      liquid. Gold and platinum, through all these operations,
      from the fusion forward, exist in the metallic state. Tin
      and antimony are  now reduced to the metallic state by
  * Chloride of silver will separate if the  reagents were not perfectly pure, and the
precipitate has not been thoroughly washed.
  f [See§ 136, 9, note.] 
288   DETECTION OF THE METALS OF  GROUP V. 2d SEC.   [§ 19(j
       the zinc.   Antimony is however at once, or shortly, re-
       cognized by the black stain it produces on the platinum.
       As soon as hydrogen gas  has nearly ceased to escape,
       what remains of the zinc is removed, the liquid—a solu-
       tion of chloride of zinc—is carefully poured off, and the
       residual metals are warmed with hydrochloric acid. In
       the solution thus procured, which, if tin be present, con-
       tains protochloride of tin,  this metal is tested by means
       of chloride of mercury (§  132, 8).
         The contents of the platinum vessel (123) are freed 121
       from tin by repeatedly boiling with hydrochloric acid,
       and in case an insoluble residue is left—the acid is also
       removed by washing it with water.  The residue is then
       examined in the following  manner : It is warmed in the
       platinum dish with some water and a little tartaric acid,
       and lastly  with addition of a few drops  of nitric acid.
       If it dissolves completely, gold and platinum are not
       present; if an insoluble residue remains these metals
       must be looked for.
         The acid solution is decanted (in it the presence of
       antimony  may be confirmed  by hydrosulphuric acid),
       the residue  is  washed  several times by decantation,
       transferred to a porcelain  dish and dissolved by aid of
       a little nitrohydrochloric acid.  The solution is evapo-
       rated to a very small bulk and further tested as directed
       § 131 for gold and platinum.

                            § 196.
(Detection of the Metallic  Oxides of Group V. 2 c? Section:— Oxide
    of Lead.  Teroxide of Bismuth.   Oxide of Copper.  Oxide
    of Cadmium.  Oxide of Mercury.
  Thoroughly wash the precipitate which has not been 125
dissolved by sulphate of ammonium, and boil with nitric
acid.   This  operation is  performed best in a small porcelain
dish; the boiling mass must be constantly stirred with a glass
rod during  the process.   A great  excess  of  acid must be
avoided.
  1. The precipitate dissolves, and there remains float- 126
ing in the fluid only the separated, light, flocculent,
yellow sulphur ;  this indicates the absence of mercury.
Cadmium, copper, lead,  and bismuth may be present.
  Filter  the fluid from the separated sulphur, and treat the
filtrate as follows (should there be too much nitric acid pre-
sent, the greater part  of this must first be driven off by
evaporation) : add to a portion of the filtrate dilute sulphuric 
§ 196.]         SOLUBLE COMPLEX COMPOUNDS.            289

acid in moderate quantity, heat gently, and let the fluid stand
Borne time.
      a. No precipitate forms ; absence of lead.   Mix the  127
    remainder of the nitrate with  ammonia in excess, and
    gently heat.
        a.  No precipitate  is formed; absence of bismuth.  128
      If the liquid is blue, copper is present; very minute
      traces of copper, however, might be overlooked, if the
      color  of the  ammoniated fluid alone were consulted.
      To be quite safe, and also to test for cadmium,  evapo-
      rate  the ammoniated solution nearly to dryness, add
      a little  acetic  acid, and, if necessary, some  water,
      and
          aa. Test a small portion of the fluid for copper  129
        with ferrocyanide  of potassium.  The formation of
        a reddish-brown precipitate, or a light brownish-red
        turbidity, indicates the presence of copper (in the
        latter case only to a very trifling amount).
          bb.  Mix the remainder of the fluid with solution  130
        of  hydrosulphuric  acid in excess.  The formation
        of  a yellow  precipitate denotes cadmium.   If, on
        account of the presence of copper, the sulphide of
        cadmium cannot be distinctly recognised, allow the
        precipitate produced by the hydrosulphuric acid to
        subside, decant the supernatant fluid, and add to the
        precipitate solution of cyanide of potassium until the
        sulphide of copper is dissolved.   If a yellow residue
        is left undissolved, cadmium is  present; in the con-
        trary  case, not.
        8. A  precipitate is formed.  Bismuth is present.  131
      Filter the fluid, and test the filtrate for copper and
      cadmium, as directed in  a (i2§).   To test the washed
      precipitate  more fully for bismuth, dry the filter con-
      taining  it somewhat between blotting-paper, remove
      the still  moist precipitate with a platinum spatula, dis-
      solve  in a watch-glass in the  least possible quantity of
      hydrochloric acid, and then add a considerable quantity
      of .water.   The appearance of a milky turbidity con-
      firms  the presence of bismuth.
      b. A precipitate is formed.  Presence of lead.  Bring  132
    the  entire nitric solution  into a porcelain capsule, add
    enough  dilute  sulphuric acid to form sulphate with the
    lead  and evaporate in the water-bath until all nitric acid
    is expelled, add to the residue a little water mixed with
    dilute sulphuric acid, filter off immediately from the inso-
    luble sulphate of lead, and examine the filtrate for bis-
                              19 
290   PRECIPITATION WITH SULPHIDE OF AMMONIUM.   [§ 197.
     muth, copper, and cadmium, as directed in a (127).*
     Test the precipitate, after washing, by one of the me-
     thods described in § 126.
  2. The precipitate of the metallic sulphides does not  133
completely dissolve in the boiling nitric acid, but leaves
a residue, besides the sulphur  that floats in the  fluid.
Probable presence of oxide of mercury (which may be pro-
nounced almost certain, if the precipitate is heavy and black).
Allow the precipitate  to  subside, filter off the fluid,  which
must still be tested for cadmium, copper, lead, and bismuth ;
mix a small portion of the filtrate with a large amount of solu-
tion of hydrosulphuric  acid, and should a precipitate form or
a coloration become visible, treat the remainder according to
the directions of (126).
  Wash the residue (which, besides sulphide of mercury, may
also contain sulphate of lead, (formed by the action of nitric
acid upon sulphide of lead), and also binoxide of tin, and pos-
sibly sulphides of gold and platinum, as the complete separa-
tion of these sulphides from the sulphides of the metals of
Group V. is rather difficult), and  examine one half of it for
mercury,f by dissolving  it in some hydrochloric acid, with
addition of a very small proportion of  chlorate of potassa,
and testing the solution with copper, or protochloride of tin
(§ 122); fuse the  other half with cyanide of potassium and
carbonate of soda.  If on treating the fused mass with water,
you obtain metallic grains or a metallic powder, wash, heat
with nitric acid, and test the solution obtained, with sulphuric
acid for  lead.  If nitric acid leaves a residue, this is washed
and any hydrated metastannic acid it may contain is extract-
ed from it in the form of metabichloride of tin by boiling for a
time with hydrochloric acid, pouring off the acid and adding
water (see §  133,  1).
  If a heavy metallic powder remains after this  treatment  it
is dissolved in aqua regia and the solution tested for gold and
platinum according to  § 131.

                             § 197.
(Precipitation with Sulphide of Ammonium, Separation and De-
  tection of the  Oxides  of  Groups ni. and IV.: Alumina,  SeS'
  quioxide  of  Chromium ;— Oxide of Zinc, Protoxide of Man-
  * For another method of distinguishing cadmium, copper, lead, and bismuth from
each other, I refer to the Third Section (additions and remarks to §  196).
  \ If you have an aqueous solution, or a solution in very dilute hydrochloric acid,
the oxide of mercury formed was present in the original substance in that form; but
if the solution has been prepared by boiling with concentrated hydrochloric acid, or
by  heating with nitric acid, the mercury may most likely have been originally pre-
sent in the form of suboxide, and may have been converted into oxide in the process. 
 § 197.]          SOLUBLE COMPLEX  COMPOUNDS.            291

   ganese, Protoxide of Nickel, Protoxide of  Cobalt, Proto- and
   Sesquioxide of Iron ;  and also of those Salts of the Alkaline
   Earths which are precipitated by Ammonia from their Solution
   in Hydrochloric Acid; Phosphates, Borates,  Oxalates, Silicates
   and Fluorides.)
   Put a small portion of the fluid  in  which  solution of  134
 hydrosulphuric acid has failed to  produce a precipitate
 (110) or of the fluid which has been filtered from the
 precipitate  formed (112) in a test tube, observe whether it
 is colored or not,* boil to expel the hydrosulphuric acid which
 may be present,  add  a  few drops of nitric acid, boil, and
 observe again the color of the fluid ; then cautiously add am-
 monia to  alkaline reaction, observe whether this produces a
 precipitate, and then add some sulphide of ammonium, no mat-
 ter whether ammonia has produced a precipitate or not.
       a. Neither ammonia  nor  sulphide of ammonium  135
     produces a precipitate.  Pass  on to  § 198, for iron,
     nickel, cobalt, zinc, manganese, sesquioxide of chromium,
     alumina, are not  present, nor  are phosphates, borates,f
     silicates, and oxalates J of the  alkaline earths ; nor fluo-
     rides of the metals of the alkaline earths ; nor silicic acid
     originally united to alkalies.
       b. Sulphide of ammonium produces  a  precipitate,  136
     ammonia having failed  to do so ; absence  of phos-
     phates,  borates,!  silicates,  and oxalates^  of the alkaline
     earths; of the fluorides  of  the  metals of  the alkaline
     earths; of silica originally united to alkalies, and also, if
     no organic  matters are present, of  iron, sesquioxide of
     chromium,  and alumina.  Pass on to (138).
       c. Ammonia produces a precipitate before the addi-  137
     tion of sulphide of ammonium.   The course of proceed-
     ing  to  be pursued now  depends upon whether (a)  the
     original solution is simply aqueous, and has a neutral
  * If the fluid is colorless, it contains no chromium or but  a very minute quantity.
If colored, the tint will to some extent act as a guide to the  nature of the substance
present; thus  a green tint, or a violet tint turning  green upon boiling, points to the
presence of chromium ; a light green tint to that of nickel; a reddish color to that
of cobalt • the  turning yellow  of the fluid upon boiling with nitric acid, to that of
iron.  It must, however, be always  borne in mind that  these tints are perceptible
only if the metallic oxides are present in larger quantity, and also that complement-
ary colors, such as. for instance, the green of the nickel solution and the red of the
cobalt solution, will destroy each other, and that, accordingly, a  solution  may con-
tain both metals and yet appear colorless.
  + Presence of much chloride of ammonium has a great tendency to prevent the
precipitation of borates of the alkaline earths.
  ± Oxalate of magnesia is thrown down from hydrochloric solution by ammonia
only after  the lapse  of some time, and never completely:  dilute solutions are not
t^eciriitated at all. 
292  BASES OF GROUPS III. AND IV. IN ABSENCE OF P06, ETC. [§ 197
     reaction, or (8) the original solution is acid.or alkaline.  In
     the former case, pass on to (l3§), for phosphates, borates,
     oxalates, and silicates  of the alkaline earths  cannot be
     present; nor can fluorides of the metals of  the  alkaline
     earths nor silica in combination with alkalies.  In the lat-
     ter case, regard must be had to the possible presence of
     all the bodies enumerated in (l35); pass on to  (150).
   1.  Detection of the bases of Groups HE. and IV. if  13§
PHOSPHATES,  &C,  OF THE  ALKALINE EARTHS ARE NOT PRE-
SENT.*
   Mix the fluid mentioned at the beginning of the paragraph
(.134) (a portion of which you have submitted to  a  prelimi-
nary examination) with some chloride of ammonium, then with
ammonia,  just  to alkaline reaction; lastly, with sulphide of
ammonium, until the fluid, after being shaken, smells distinctly
of that  reagent; shake  the mixture  until the precipitate
begins to separate in flocks, warm gently for a time,  and  fil-
ter.
   Keep the filtrate,!  which contains, or may contain, the
bases of Groups H.  and I., for subsequent examination accord-
ing to the  directions of § 198.   Wash the precipitate with
water, to which a very little sulphide of ammonium has been
added, and then proceed  with it  as follows :—
      a. It is  perfectly  white; absence of  iron, cobalt,  139
     nickel.  You must test for all the  other bases of Groups
     IH. and TV., as the faint tints of sesquioxide of chromium
     and sulphide of manganese are imperceptible in  a  large
     quantity of a white precipitate.  Dissolve the precipitate
     by heating it  in a  small  dish with the least possible
     amount of hydrochloric acid ; boil—should hydrosulphu-
     ric acid be evolved—until this gas is completely expel-
     led, concentrate by evaporation to a small bulk, neutral-
     ize  with carbonate of soda, then add solution of  soda in
     excess, heat to boiling, and keep the mixture for  some
     time in a state of ebullition.
         a. The precipitate formed at first dissolves complete- 140
      ly in the excess of solution of soda.  Absence of man-
      ganese and chromium, presence  of alumina or oxide of
      zinc.  Test a portion of the alkaline solution with solu-

  * This  simpler course is quite good enough for most purposes; in  very accurate
analyses, however, the course beginning at (150) is to be followed, since it leads to
the detection of the traces of alkaline earths which are thrown down with alumina
and sesquioxide of chromium.
  \ If the filtrate has a brownish color, this points to the presence  of nickel, sul«
phide of nickel, as is well known, being slightly soluble in sulphide of ammoniurr
this, however, involves no modification of the analytical course. 
197.]        SOLUBLE COMPLEX COMPOUNDS.            293

     tion  of hydrosulphuric  acid for  zinc; acidify  the
     remainder with hydrochloric acid, add ammonia slight-
     ly in excess, and  apply heat.   The formation of a
     white, flocculent precipitate  shows  the  presence  of
     ALUMINA.
      (3.  The precipitate formed does not dissolve, or die- in
     solves only partially, in the excess of  solution of soda.
     Filter and test the filtrate, as in a (i40), for zinc
     and  alumina. With  the  undissolved  precipitate
    which, when much  manganese is present, has a brown
    or brownish color, proceed as follows:—
        aa. Should the color of the solution  indicate the
      absence of chromium,  test a portion of the precipi-
      tate for Manganese by means of the reaction with
      carbonate of soda in the outer blowpipe flame.
        bb. If chromium is  indicated by the color of the 142
      solution, the examination of the residue insoluble  in
      solution of soda becomes more  complicated, since it
      may contain zinc, and indeed, perhaps all the zinc of
      the original substance (§115). The precipitate is dis-
      solved in hydrochloric acid, the  solution is  evapo-
      rated to a small bulk, diluted, the  free acid nearly
      neutralized by means of carbonate of soda, a slight
      excess of carbonate of  baryta added, and the whole
      digested in the cold with  occasional agitation until
      the solution has become colorless.   It is now filter-
      ed  and the precipitate is tested for chromium by
      fusion with carbonate of soda and nitrate of soda or
      potassa (§ 105,  8). The solution is  treated hot with
      excess of  dilute  sulphuric  acid  and filtered, to
      remove baryta, the filtrate is evaporated to a small
      volume  and  supersaturated with strong solution of
      soda.   If any precipitate is formed, it is filtered off
      and tested as in aa. for manganese ; the filtrate is
      examined for zinc with hydrosulphuric acid.
    b. It is not white ; this points to the presence of chro- 143
 mium, manganese, iron, cobalt, or nickel.  If it is black, or
 inclines to black, one of the three metals last mentioned
 is present.  Under  all circumstances, all the oxides of
 Groups III. and IV. must be looked for.
    Remove the washed precipitate from  the filter with a
 spatula, or by rinsing it, with the aid of a washing-bottle,
 into a test-tube, through a hole made in the bottom of
 the filter, and pour over it rather dilute cold hydrochloric
 acid in moderate excess.
     a. It dissolves  completely  (except perhaps  a little 141 
294 BASES OF GROUPS III. AND IV. IN ABSENCE OF P05, ETC. [§ 197

      sulphur, which may separate); absence of cobalt and
      nickel, at  least of notable  quantities of these two
      metals.
        Boil until the hydrosulphuric acid is completely ex-
      pelled, filter if particles of sulphur are suspended in
      the fluid, concentrate by evaporation to a small volume,
      then add solution  of potassa or  soda in excess, boil,
      filter the fluid from the insoluble  precipitate which is
      sure to remain, wash  the latter, and proceed first to
      examine the filtrate, then  the precipitate.
          aa. Test  .a portion of the filtrate with hydrosul- 145
        phuric  acid for  zinc;  acidify the remainder  with
        hydrochloric acid, and then test it with ammonia for
        alumina.   Compare (140).
           bb. Dissolve a portion of the precipitate in hydro- 146
        chloric acid, and test the solution with sulphocyanide
        of potassium for iron.   Test another portion  for
        chromium  by fusing it with carbonate and nitrate
        of  soda (§  105, 8).   If chromium is not thus  de-
        tected, the  remainder of the precipitate is examined
        with carbonate  of soda in the  oxidizing flame for
        manganese.  If, on  the contrary, chromium be pre-
         sent, the remainder  of the  precipitate, which may
        in that  case contain manganese and zinc  (and in-
         deed the whole  of  the latter metal, § 115), is exa-
         mined according to (142).
         8. The precipitate  is not completely dissolved, a  147
       black residue  being left;  this indicates the presence of
       cobalt and nickel.  Filter, wash  the undissolved pre-
       cipitate, and  test  the  filtrate as directed (144); pro-
       ceed with the residuary precipitate as follows :—
           aa. Test a portion  of  it with  borax, first in the  148
         outer, then in the inner blowpipe flame.  If the bead
         in the oxidizing flame  is violet whilst hot,  and of a
         pale reddish-brown  when cold, and turns in the re-
         ducing flame gray and turbid, nickel is present; but
         if the color of the bead is and remains blue, in both
         flames, and whether hot or cold, cobalt is present.
         As in the latter case the  presence of  nickel cannot
         be distinctly recognized; examine
           bb. The  remainder  of  the precipitate  by incine-  149
         rating it together with the filter in a small  porcelain
          capsule or crucible, heating the ash with  some hy-
          drochloric  acid, filtering the solution,  then evapo-
          rating  nearly  to  dryness,  and  adding nitrate of
          potassa, and then acetic acid (§ 112, 10).   The for- 
§ 197.]         SOLUBLE COMPLEX COMPOUNDS.            295

        mation of a yellow precipitate after standing in a
        warm place for some time confirms  the  presence of
        cobalt.   Let the fluid,  with the precipitate in it,
        stand for  about 12  hours, then filter, and test the
        filtrate with solution of soda for nickel.
  2. Detection of  the bases of groups HI. and IV. in  150
CASES WHERE PHOSPHATES, BORATES, OXALATES, OR SILICATES
OF THE ALKALINE EARTHS, OR FLUORIDES OF THE METALS
OF THE ALKALINE EARTHS, OR HYDRATED SILICA, MAY POSSI-
BLY  HAVE BEEN THROWN DOWN  ALONG WITH THESE BASES,
i.e., in cases where the original solution was  acid or alkaline
and a precipitate was produced by ammonia  in the prelimi-
nary examination.  See (134).
  Mix the fluid mentioned in the beginning of this paragraph
(l3l) with  some  chloride of ammonium, then with ammo-
nia just to  alkaline reaction, lastly with sulphide of ammo-
nium, until the fluid, after being  shaken, smells distinctly of
this  reagent;  shake  the mixture  until the precipitate begins
to separate in flocks, warm gently for a time and filter.
  Keep the  filtrate, which contains,  or may contain, the
bases of Group H. and I., for subsequent examination accord-
ing  to  the  directions  of §  198.   Wash  the precipitate
thoroughly with water to which a very little  sulphide  of
ammonium has been added, and  then  proceed with it as fol-
lows.  To give a clear notion of the obstacles to be overcome
in this analytical process I must remind  you  that it is neces-
sary to examine the precipitate  for the following bodies:
Iron, nickel, cobalt  (these show their presence to  a certain
extent by the black or blackish coloration of the precipitate),
manganese,  zinc, sesquioxide of chromium  (the  latter  gene-
rally reveals its presence by the color of the solution), alu-
mina ;— baryta, strontia,  lime, magnesia, which latter sub-
stances may have fallen down in combination with phosphoric
acid, boracic acid,  oxalic acid,  silicic  acid, or in form  of
fluorides.  Besides these bodies, free silicic  acid may also be
contained in the precipitate as hydrate.
  As the original substance must, under all circumstances, be  151
afterwards examined for all acids that might possibly be pre-
sent, it is not indispensable to test for the above enumerated
acids at this stage of the analytical process; still, as it is often
interesting to know the presence of these acids at once, more
especially in  cases where a  somewhat  large  proportion  of
some alkaline earth  has  been found in the precipitate pro-
duced by sulphide of ammonium, a method for the  detection
of the acids  in question will  be  found  appended by way of
supplement to the method for the detection of the bases. 
296 BASES OF GROUPS III. AND IV. IN PRESENCE OF P05, ETC. [§ 197.

  Remove the precipitate from the filter as soon as it is com-  152
pletely washed [else it  may partially oxidize and be lost],
with a small spatula, or  by rinsing it off with the washing-
bottle, and pour  over it  cold dilute hydrochloric acid in
moderate excess.
      a. A residue remains.  Filter, and treat the filtrate  153
    as directed in  (154).  The residue, if it is black, may con-
    tain sulphide  of nickel, and sulphide of cobalt, and be-
    sides these, sulphur and silicic acid.   Wash, and examine
    a sample of it in conjunction with phosphate of soda and
    ammonia before the blowpipe, in the outer flame.  If a
    silica skeleton remains undissolved (§ 153, 8), this proves
    the presence of silicic acid.  If the color of the bead is
    blue, cobalt is present; if reddish, turning yellow  on
    cooling, nickel.  Should the color leave you in doubt,
    incinerate the filter containing the remainder of the resi-
    due, and test for cobalt and nickel by means of nitrite of
    potassa, as directed  (149).
      b.  No  residue  is left  (except perhaps  a little  sul-  154
    phur, which may separate): absence of nickel and cobalt,
    at least in any notable  proportion.
      Boil the solution until the  sulphuretted  hydrogen is
    expelled, and then proceed as follows:
         a. Mix a  small portion of the solution with dilute   155
      sulphuric acid.  If a precipitate forms, this may con-
      sist of sulphates of baryta and  strontia, possibly
      also of sulphate of lime.  Filter, wash the precipitate
      and test it either by the flame, according to the latter
      part of § 102, or decompose it by boiling or fusion with
      carbonated  alkali, wash the  carbonates produced, dis-
      solve them in hydrochloric  acid, and test the  solution
      as directed § 198.  Mix the  fluid which has not been
      precipitated  by dilute  sulphuric acid,  or the  fluid fil-
      tered from  the  precipitate produced,  with 3 volumes
      of spirit of wine.  If a precipitate forms, this  consists
      of sulphate of lime.  Filter, dissolve in water, and add
      oxalate of ammonia to the solution, as a confirmatory
      proof of the presence of lime.
        8. Boil a  somewhat larger sample with some nitric   156.
      acid, and test a small portion of the fluid with sulpho-
      cyanide of  potassium for iron ;* mix  the remainder
      with sesquichloride  of iron in sufficient  quantity  to
  * "Whether the iron was present  as sesquioxide or as protoxide, must  be ascer-
tained by testing the original  solution in hydrochloric acid with ferrocyanide 0/
potassium and sulphocyanide of potassium.   [Compare § 114, 8, note.] 
§ 197.]          SOLUBLE  COMPLEX COMPOUNDS.            297
       make a drop of the fluid give a yellowish precipitate*
       when mixed, on a watch-glass, with a drop of  ammo-
       nia ;  concentrate the fluid now until there  is  only a
       small quantity left; add to this some water, then a few
       drops of solution of carbonate of soda, just sufficient to
       nearly neutralize the free acid, and lastly carbonate of
       baryta in slight excess; stir  the  mixture, and let it
       stand in the cold until the fluid above the precipitate
       has become colorless.   Filter now the precipitate (aa)
       from the solution (bb),  and wash.
           aa. Boil the precipitate for some time with solu-  157
         tion of soda, filter, and test the filtrate for alumina,!
         by heating with  chloride of ammonium in  excess.
         The part of the precipitate insoluble in solution of
         soda is examined for chromium by fusion with car-
         bonate and nitrate of soda (§ 105, 8).
           bb. Add to the solution hydrochloric acid  to acid
         reaction, heat  to boiling, add dilute sulphuric acid
         as long as a precipitate of sulphate of baryta forms,
         and filter.  Supersaturate the filtrate with ammonia
         and add sulphide of ammonium.
              aa. No precipitate forms: absence of manga-  158
           nese and zinc.  Mix the solution with oxalate  of
           ammonia.   If a  precipitate  of  oxalate of lime
           (which may be   distinguished   from   separated
           sulphur by  its being  readily soluble   in  dilute
           hydrochloric acid)  forms, filter, and test the filtrate
           with phosphate of soda for magnesia.
              BB. A precipitate forms.   Filter,  and proceed  159
           with the  filtrate according to the directions of aa
          (l5§).   The precipitate may consist of sulphide of
           manganese and sulphide of zinc, and may  contain
           traces also of  sulphide  of cobalt and sulphide of
           nickel.   Wash it with water containing  some sul-
           phide of ammonium, and then treat it with acetic
           acid, which will dissolve  the  sulphide of  manga-
           nese if any is present, leaving the other  sulphides
  * The addition of sesquichloride of iron is necessary, to  effect the separation of
phosphoric acid and silicic acid which may be present.
  f If  the solution contains silicic acid, the precipitate taken for alumina may con-
tain also silicic acid.   A simple trial with  phosphate  of soda  and ammonia, on a
platinum wire, in the blowpipe flame, will show whether the precipitate really con-
tains silicic acid.  Should this be the case, ignite the remainder of the supposed
alumina precipitate on the cover of a platinum crucible, add some acid sulphate of
potassa, fuse the mixture, and treat the fused mass with water, which will dissolve
the alumina, leaving the silicic acid undissolved; precipitate the alumina from the
eolution by ammonia. 
298 BASES OF GROUPS III. AND IV. IN PRESENCE OF P06, ETC. [§ 197.

          undissolved.  Filter, boil the filtrate with solution
          of soda, and test the precipitate, which may form,
          with carbonate  of soda in the lower  blowpipe
          flame for manganese.   Free the residuary part of
          the  precipitate, which acetic  acid  has  failed to
          dissolve, by washing,  from the acetic acid solu-
          tion still adhering  to it, and  then treat it with
          dilute hydrochloric acid, which will dissolve the
          zinc, if any is present.  Filter, add some nitric
          acid to the filtrate, and concentrate the mixture
          considerably by boiling ;  then  add  to it solution
          of soda in excess, boil, filter, if necessary, and test
          the filtrate with  sulphide of ammonium for zinc.'
          Should a   precipitate  insoluble in solution  of
          soda remain in the  last  operation, or  should
          the  dilute hydrochloric acid  have  left a black
          residue, test this precipitate and residue  for co-
          balt and nickel,  if you have not already pre-
          viously detected the  presence of these bodies;
          compare (i4§ and  149).
      /. If you have found alkaline  earths in a  or B, and 160
    wish to know the acids in combination with which they
    have passed into  the precipitate produced by sulphide
    of ammonium, this may be ascertained by making the
    following experiments with the remainder  of the hydro-
    chloric acid solution:—
          aa. A portion is  evaporated in  a small capsule  or 161
        watch-glass in the water-bath to  complete dryness,
        the residue is treated with hydrochloric  acid, and
        subsequently with water.  If silicic acid were pre-
         sent it remains undissolved.   The solution is tested
        by phosphoric acid by means of the nitric solution
        of molybdate of ammonia (§ 145, 10).
          bb. Mix another portion with  carbonate of soda
        in excess, boil  for some time, filter, and test one-half
        of the filtrate for oxalic acid, by acidifying it with
         acetic acid, and adding solution of sulphate of lime;
        the other half for boracic acid, by slightly acidify-
        ing  it with hydrochloric  acid, and testing with tur-
        meric paper (§147 and § 148).
          cc. Precipitate the remainder  with  ammonia,  fil- 162
        ter, wash and  dry the precipitate, and  examine it for
        fluorine according to § 149, 5. 
§ 198.]     SOLUBLE COMPLEX COMPOUNDS, GROUP  II.     299


                           §  198.
(Separation and Detection of the Oxides of Group II, which
  are precipitated  by Carbonate of Ammonia in Presence
  of Chloride of Ammonium, viz., Baryta, Strontia, Lime.)
  TO A SMALL PORTION OF THE FLUID IN WHICH AMMONIA AND
SULPHIDE OF AMMONIUM HAVE FAILED TO PRODUCE A PRECIPI-
rATE (135), OR OF THE FLUID FILTERED FROM THE PRECIPITATE
FORMED, ADD CHLORIDE OF AMMONIUM, IF THE SOLUTION CON-
TAINS  NO AMMONIACAL SALT, THEN CARBONATE OF AMMONIA
AND SOME CAUSTIC AMMONIA, AND HEAT FOR SOME  TIME VERY
ge.vtly (not to boiling).
  1. No precipitate forms : absence of any notable quantity  163
of baryta, strontia, and lime. Traces of these alkaline earths
may, however, be present;  to  detect them, add to another
portion of the fluid some sulphate of ammonia (prepared by
supersaturating dilute sulphuric acid with ammonia):  if the
fluid becomes turbid, it contains traces  of baryta ; add to a
third portion  some  oxalate  of  ammonia; if the fluid turns
turbid—which  reaction may perhaps require some time to
manifest itself—traces of lime are present.  Treat the re-
mainder of the fluid as directed § 199, after having previously
removed the traces  of lime and baryta which may have been
found, by means of the reagents that have served to effect
their detection.
  2. A precipitate  is formed.  Presence of lime, baryta,  164
or strontia.   Treat the entire solution with ammonia  and
carbonate of ammonia as above directed.   After gently heat-
ing, filter, test  portions of the filtrate with sulphate and
oxalate  of ammonia, for traces  of  lime and baryta, which it
may possibly still  contain, remove  such traces, should they
be found, by means of the said reagents, and examine the
fluid, thus perfectly freed from baryta, strontia, and lime, for
magnesia according to  the directions of § 199.   Wash the
precipitate produced by carbonate of ammonia, dissolve it in
the least possible amount of dilute hydrochloric acid, and add
to a small portion of the fluid some  solution of sulphate of
lime (not too little).
      a. No  precipitate  is formed, not even after  the
    lapse of some time.   Absence  of baryta and strontia ;
    presence  of lime.  To remove  all doubt, mix another
    sample with oxalate of ammonia.
      b. A precipitate is formed by solution of sulphate of
    lime.
        a.  It is formed immediately ; this indicates baryta.  165 
300             EXAMINATION FOR  MAGNESIA.          [§ 199
      Besides this, strontia and lime may also be present.
        Evaporate the remainder  of  the hydrochloric acid
      solution  of the precipitate produced by carbonate of
      ammonia to  dryness, digest the residue with strong
      alcohol, decant the fluid from the undissolved chloride
      of barium, dilute with an equal  volume of water, mix
      with  a few  drops  of hydrofluosilicic   acid—which
      throws down the small portion of baryta that had dis-
      solved in form of chloride of barium—allow the mix-
      ture  to  stand for some  time;  filter, and treat  the
      filtrate with dilute sulphuric  acid.  The  formation  of
      a precipitate indicates strontia  or lime or both these
      substances.   The precipitate is filtered off after some
      time,  washed  with weak alcohol  [a mixture of  4
      volumes  of so-called alcohol of 95 per  cent, with  5
      volumes  of water],  and boiled  with solution of car-
      bonate of soda  to convert the sulphates into car-
      bonates.   The  carbonates are  collected on  a small
      filter  and washed with water dissolved in hydrochloric
      acid,  and the  solution is evaporated to dryness.  Dis-
      solve  the residue  in a little water and test a portion
      of the fluid with a dilute solution of sulphate of potassa
      (§ 99, 3).  If a precipitate forms immediately, or in
      the course of half an hour, the presence of strontia is
      demonstrated.  In that case, let the fluid with the pre-
      cipitate in it stand  at rest for some time, then filter,
      and add ammonia and oxalate  of ammonia to the fil-
      trate.  The formation of  a white precipitate indicates
      lime.   If sulphate of potassa has failed  to produce a
      precipitate, the remainder of the solution of the residue
      left upon evaporation is tested at once with ammonia
      and oxalate of ammonia for lime.
        8. It is formed only after some time.  Absence of 166
      baryta, presence of strontia.   Mix the  remainder of
      the hydrochloric acid solution with sulphate of potassa,
      let the mixture stand for some time, then filter, and test
      the filtrate with ammonia and oxalate of ammonia  for
      LIME.

                            § 199.
                 (Examination for 3fagnesia.)
  TO A PORTION OF THE FLUID IN WHICH CARBONATE, SULPHATE,
AND OXALATE OF AMMONIA  HAVE FAILED  TO PRODUCE A PRE-
CIPITATE (163)  OR OF THE FLUID FILTERED FROM THE PRECIPI-
TATES FORMED  (164), ADD  AMMONIA,  THEN SOME PHOSPHATE 
 § 200.]    SOLUBLE COMPLEX COMPOUNDS.   ALKALIES.    301

 OF SODA, AND, SHOULD A PRECIPITATE NOT AT ONCE FORM, RUB
 THE INNER SIDES  OF THE VESSEL WITH A GLASS ROD, AND THEN
 LET THE MIXTURE STAND FOR SOME TIME.
   1. No precipitate is formed:  absence of magnesia.  Eva- 167
 porate  another  portion  of  the fluid to dryness, and ignite
 gently.   If a residue remains, treat the  remainder of the
 fluid the same as the sample, and examine the  residue, which
 by the moderate ignition to which it has been subjected has
 been freed from ammonia, for potassa and soda, according  to
 the directions of § 200.—If no residue is left, this is a proof
 of the absence of the fixed alkalies; pass on to § 201.
   2. A precipitate is formed: presence of  magnesia.  As 16§
 testing for alkalies can proceed with certainty  only after the
 removal of magnesia, evaporate the remainder of the fluid  to
 dryness, and ignite until all ammoniacal salts are removed.
 Warm the residue with water, add baryta-water  (prepared
 from crystals of hydrate  of baryta), as long as a  precipitate
 continues to form,* boil, filter, add to the  filtrate  a mixture  of
 carbonate  of ammonia with some caustic ammonia  in slight
 excess, heat for some time gently, filter, evaporate the filtrate
 to dryness, adding some chloride of ammonium during the
 process (to convert into chlorides the caustic alkalies that may
 have formed), ignite the residue gently, then dissolve it in a
 little water, precipitate, if necessary, once more, with ammonia
 and carbonate of ammonia,  evaporate again, and if a residue
 remains, ignite this gently, and finally examine  it  according  to
 the directions of § 200.
                             § 200.
             (Examination for Potassa and Soda.)
   YOU HAVE NOW TO EXAMINE FOR POTASSA  AND SODA THE
 GENTLY IGNITED RESIDUE, FREE FROM SALTS  OF AMMONIA  AND
 ALKALINE  EARTHS, WHICH HAS BEEN OBTAINED IN (l67), OR
 IN (16§).
   Dissolve it in  a little water, filter, if necessary, evaporate
 until there is only a small quantity of fluid left, and transfer
 one half of this to a watch-glass, leaving  the other half  in
 the porcelain dish.
   1. To the one-half in the  porcelain dish add, after cooling, 169
 a few drops of solution of bichloride of platinum.  If a yel-
 low, crystalline precipitate  forms  immediately, or after  some
 time, potassa is present.  Should no precipitate form, evapo-
 rate to dryness at a gentle heat, and treat the  residue with a
 very small quantity of water or, if  chlorides alone are present,
  * [In absence of sulphuric acid, or after it has been thrown down by baryta water
or  chloride  of barium, milk of  lime may be  advantageously used to  separate
magnesia.] 
302   AQUEOUS  SOLUTION—DETECTION  OF ACIDS. [§§ 201, 202

with a mixture  of water and alcohol, when the presence  of
minute traces of potassa will be revealed by a small quantity
of a heavy yellow powder being left undissolved, § 92, 3.
  2.  To the other half of the  fluid (in the  watch-glass) add 170
some antimonate of potassa.  If this produces at once or after
some time a crystalline precipitate, soda is present.  If the
quantity of soda present is only very trifling, it often takes
twelve hours before minute crystals of antimonate of soda
will separate; the operator should therefore wait that time
for the possible manifestation of the reaction, before deciding,
from its non-appearance, that no soda is present.  As regards
the form of  the crystals, consult § 93, 2.
  [The alkalies may also be conveniently tested for by J.  L.
Smith's method  (§ 95), but care must be taken not to operate
in an atmosphere containing ammonia vapors.]

                            § 201.
                 (Examination for  Ammonia.)
  There  remains still  the  examination for ammonia. 171
Triturate some of the body under examination, or, if a fluid, a
portion of the latter, together with an excess of hydrate  of
lime, and, if necessary, a little water.   If the escaping gas
smells of ammonia, if it restores  the  blue color of reddened
litmus paper, and forms white  fumes  with hydrochloric acid
vapors, brought into  contact with it by means of a glass rod,
ammonia is present.  The reaction is the most sensitive, if the
trituration is made in a small beaker, and the latter covered
with a glass plate with a slip of moistened turmeric  or moist
reddened litmus  paper adhering to the under side.

                     Complex Compounds.
            A.  1. Substances soluble in Water.
                    DETECTION OF ACIDS.*
            I.  In the  Absence of Organic Acids.
                            § 202.
  Consider,  in the  first  place, which  are  the acids that form
with the bases found, compounds soluble in water, and let this
guide you in the examination.   To beginners the table given
in Appendix IV. will prove of  considerable  assistance.
  1.  The acids of arsenic, as well as carbonic acid, hydro- 172
sulphuric acid,  chromic acid, and silicic acid, have generally
been detected already in the course of testing for the  bases;
compare (67) and (68).
  2. Add to a portion  of the solution chloride of barium, or
              *  Consult also the explanations in Section ILL. 
§ 202.]     COMPLEX  COMPOUNDS.—AQUEOUS SOLUTION.    303

if lead, silver, or suboxide of mercury are present, nitrate of
baryta, and,  should the  reaction of the  fluid be acid,  add
ammonia to neutral or slightly alkaline reaction.
       a. No  precipitate is formed : absence of sulphuric 173
     acid, phosphoric acid, chromic acid,  silicic  acid,  oxalic
     acid, arsenious  and  arsenic  acids, as  well as  of notable
     quantities of boracic  acid  and hydrofluoric acid.*   Pass
     on to (175).
       b. A precipitate is formed.  Dilute the fluid, and add 174
     hydrochloric acid; if the precipitate does not redissolve,
     or at least not completely, sulphuric  acid is present.
  3. Add nitrate of silver to a portion of the solution.   If this 175
fails to produce a precipitate, test the reaction, and add to the
fluid, if it is acid, some dilute ammonia, taking care to add the
reagent so gently and  cautiously that  the two fluids  do not
intermix; if the reaction  is  alkaline, on the  other hand, add
with the same care some dilute nitric acid, instead of ammonia,
and watch attentively, whether a precipitate or a cloud forms
in the layer between the two fluids.
       a. NO  PRECIPITATE IS FORMED IN THE LAYER BETWEEN 176
     THE TWO  FLUIDS, NEITHER IMMEDIATELY NOR AFTER SOME
     time.   Pass on  to (i§i) ;  there is neither chlorine, bro-
     mine, iodine, cyanogen,f ferro- nor ferricyanogen present,
     nor sulphur; nor  phosphoric acid, arsenic acid, arsenious
     acid, chromic acid, silicic  acid, oxalic acid; nor boracic
     acid, if the solution was not too dilute.
       b. A precipitate is formed.  Observe the color J of it, 177
     then add nitric acid,  and shake the mixture.
         a.  The precipitate redissolves completely: absence of
       chlorine, bromine,  iodine, cyanogen, ferro- and ferricya-
       nogen, and also of sulphur.  Pass on to (l§l).
         8. A  residue is left:  chlorine, bromine,  iodine, cy- 178
       anogen, ferro- or ferricyanogen may be present; and if
       the residue is black or blackish, hydrosulphuric acid
       or a soluble metallic  sulphide.—The presence  of sul-
       phur may, if  necessary, be readily  established beyond

  * If the solution contains an ammoniacal salt in somewhat  considerable  propor-
tion  the non-formation of a precipitate cannot be considered a conclusive proof of
the absence of these acids, since the baryta salts of most of them (not the sulphate)
are  in presence of ammoniacal  salts, more or less soluble in water.
  + That the cyanogen in cyanide of mercury is not indicated by nitrate of silver
has been mentioned (73).
  1 Chloride, bromide, cyanide, and ferrocyanide of silver, and oxalate,  silicate, and
borate of silver are white; iodide of silver, tribasic phosphate,  and arsenite  of silver
are yellow; arsenate of silver and ferricyanide of silver are brownish-red; chromate
of Bilver is purple-red;  sulphide of silver is black. 
304            DETECTION OF  INORGANIC  ACIDS.        [§ 202
       doubt, by mixing another portion of the solution with
       some solution of sulphate of copper.
           aa. Test another  portion of the  fluid for iodine,
         and  subsequently for  bromine, by  the methods  de-
         scribed in § 160.
           bb. Test a small portion  of the fluid with sesqui-179
         chloride  of iron for  ferrocyanogen ;  and,  if the
         color of the silver precipitate leads you to suspect the
         presence of ferricyanogen, test another portion  for
         this latter substance with protosulphate of iron.—If the
         original solution has an alkaline reaction, some hydro-
         chloric acid must be added before the addition of the
         sesquichloride or  the protosulphate of iron.
           cc. Cyanogen,  if present  in form of  a simple
         metallic  cyanide soluble  in water, may usually  be
         readily recognised by the smell of hydrocyanic acid
         which the body under examination emits, and  which
         is rendered more strongly perceptible by addition of
         a little dilute sulphuric acid.—If no ferrocyanogen is
         present, the presence of cyanogen may be ascertained
         by the method  given in § 158, 6.
           dd. Should bromine, iodine, cyanogen, ferrocyano- i§0
         gen, ferricyanogen,  and sulphur not be present, the
         precipitate which nitric acid  has failed to  dissolve,
         consists of chloride of silver.
           However, should  the  analytical process  have  re-
         vealed the presence of any of the  other  bodies, a
         special examination for chlorine may become neces-
         sary, viz., in cases where the quantity of the precipi-
         tate will not  enable  the operator to pronounce with
         positive certainty on the presence or absence of the
         latter element.*  In such cases, which are of rare
         occurrence, however, the  methods given in § 160 are
         resorted  to.
  4. Test another portion for nitric acid, by means of protosul-181
phate of iron and sulphuric acid (§ 162).
  5. To  ascertain whether chloric acid is  present, pour a
little concentrated sulphuric acid over  a  small sample of the
solid  body  under  examination:   ensuing yellow  coloration
of  the  acid  resolves   the   question  in  the  affirmative
(§ 163).
  You  have still  to test  for phosphoric acid,  boracic acid,
  * Supposing, for instance, the solution of nitrate of silver to  have produced a
copious precipitate insoluble in nitric  acid, and the subsequent examination to have
shown mere traces of iodine and bromine, the presence of chlorine may be held to
be demonstrated without requiring additional proof. 
§ 203.]   COMPLEX COMPOUNDS.—AQUEOUS SOLUTION.       305

silicic acid, oxalic acid, and chromic acid, as well as for hy-
drofluoric acid.
  For the first five acids test only in cases where both chlo-
ride of barium and nitrate of silver have produced precipitates
in neutral solutions.   Compare also  foot note to (173).
  6. Test for phosphoric acid, by adding to a portion of the 182
fluid, ammonia in excess, then chloride of ammonium and sul-
phate of magnesia (§ 145, 7).   Very minute quantities of
phosphoric  acid  are  detected  most  readily  by means of
molybdic acid (§ 145,  10).
  7. To  effect  the  detection  of oxalic acid and hydrosul-
phuric acid, add chloride  of calcium  to a portion of  the
solution, which, if acid, must be rendered slightly alkaline
by addition  of ammonia.  If chloride of calcium produces  a
precipitate which is not redissolved by addition of acetic acid,
one or both bodies are present.  Examine therefore now  a
sample of the original substance for fluorine, according to the
directions of §  149, 5,  another sample for oxalic acid, by the
method given in § 148, 7.
  8. Acidulate  a portion of the fluid slightly with hydrochlo- 183
ric acid, and then test for boracic acid, by means of turmeric
paper (§ 147, 6).
  9. Should silicic acid not have yet been found in the course
of testing for the bases, acidulate a portion of the fluid with
hydrochloric acid, evaporate to dryness, and treat the residue
with hydrochloric acid (§ 153, 3).
  10. Chromic acid is readily recognised  by the yellow or
red color of the solution, and  by the purple-red color of the
precipitate produced by nitrate of silver.—If there remains
the least doubt  on the  point, test for chromic acid with ace-
tate of lead and acetic  acid (§  141, 7).

                      Complex  Compounds.
             A. 1.  Substances soluble in Water.
                      DETECTION OF ACIDS.
               II. In presence of Organic Acids.
                             §  203.
  1. The examination  for inorganic  acids, inclusive of oxalic  184
acid, is made in the manner described in § 202.  As the tar-
trates and citrates of baryta and silver are insoluble in water,
tartaric  acid and citric acid  can be present  only in cases
where both chloride of barium and nitrate of silver have  pro-
duced precipitates in  the neutral fluid ; still, in drawing  a
conclusion,  you  must bear in mind that the said salts are
slightly soluble  in solutions of salts of ammonia.
                               20 
 306            DETECTION OF  ORGANIC ACIDS.          [§ 203

   Before testing for organic acids it is necessary to remove
 all those bases whose presence might disturb the reactions,
 viz., all those belonging to Groups III. IV. V. and VI.   This
 is accomplished  by the  methods already described at the
 beginning of § 187, to which the operator is referred.
   The examination for the organic acids  is then conducted
 as follows: —
   2. Make  a portion of the fluid feebly alkaline by addition  185
 of ammonia, add some chloride of ammonium, then chloride
 of  calcium, shake vigorously, and let the mixture  stand  at
 rest from ten to twenty minutes.
       a. No PRECIPITATE IS FORMED, NOT EVEN AFTER THE
     lapse of some time.  Absence of tartaric acid,*  pass
     on to (186).
       b. A precipitate is formed immediately, or after
     some time.   Filter, wash, and keep the filtrate for fur-
     ther examination according to the directions of (186).
       Digest and shake the precipitate with solution of soda,
     without applying heat, then  dilute with a little water,
     filter, and boil the filtrate some time.  If a precipitate
     separates, tartaric acid may be  assumed to be present.
     Filter hot, and  subject the precipitate to the  ammonia
     and nitrate of silver test described in § 166, 8.
  3. Mix the fluid in which chloride of calcdum has failed to 18«
produce  a  precipitate, or that which  has  been filtered from
the precipitate-*—in which latter case some more chloride of
oalcium is to be added—with alcohol.
       a. No precipitate is formed.   Absence of citric  acid 187
     and malic acid.   Pass on to (190).
       b. A  precipitate is formed. Filter and treat the fil-
     trate  as directed in (l90).   As regards the precipitate, 188
     treat this as follows :—
       After washing with some alcohol, dissolve on the filter
     in a little dilute hydrochloric acid, add ammonia to the
     filtrate to feebly alkaline reaction, and  then boil for some
     time.
        a. The filtrate remains clear.  Absence of citric
       acid.   Probable presence of malic acid.  Add alcohol
       again to the fluid, and test the lime precipitate in the
       manner directed § 169, to  make sure whether malic
       acid is really present or not.
        8.  A heavy, white precipitate is formed.   Pre- 189
       sence  of  citric  acid.   Filter  boiling,  and  test  the
       filtrate for malic acid in the same manner as in a.  To

   [* Tartaric acid may be easily overlooked unless the solution is concentrated.] 
§ 203.]  COMPLEX COMPOUNDS.—AQUEOUS SOLUTION.      307
       remove  all  doubt  as to whether the  precipitate  is
       citrate of lime  or not, it is advisable to dissolve once
       more in some hydrochloric acid, to supersaturate again
       with ammonia,  and to boil;  if the precipitate  really
       consisted of citrate of lime,  it will  now  be thrown
       down again.  (Compare § 167, 3).
   4. Heat the filtrate of (iss) (or the fluid in which addition  190
of alcohol has failed to produce a precipitate) (187), to expel
the  alcohol, neutralize exactly with hydrochloric acid,  and
add sesquichloride of iron.  If this fails to produce  a light
brown, flocculent  precipitate, neither succinic nor benzoic
acid is present.  If a precipitate of the kind is formed, filter,
digest, and heat the  washed precipitate with ammonia in
excess; filter, evaporate  the filtrate nearly  to dryness,  and
test a  portion for succinic acid with chloride of barium  and
alcohol (§ 171); the remainder for benzoic acid with hydro-
chloric acid (§ 172).   Benzoic acid may generally be readily
detected also in the original substance, by pouring  some dilute
hydrochloric  acid  over  a small portion of  the latter, which
will leave the benzoic acid undissolved;  it is then filtered and
heated on platinum foil (§ 172,  1).
   5. Evaporate a portion of the solution to  dryness—if acid,  191
after previous saturation with soda—introduce the residue,
or a portion of the original dry substance, into a  small tube,
pour some alcohol over it, add about an equal volume of con-
centrated sulphuric acid, and heat to boiling.  Evolution of
the odor of acetic ether demonstrates the presence of acetic
acid.  This odor is rendered more distinctly perceptible by
shaking the cooling or cold mixture.
   6. To effect the detection of formic acid, add to a portion  192
of the  solution nitrate of silver in not too small a proportion,
then soda until the fluid is exactly neutralized, and boil.   If
formic acid is present,  reduction of the  silver to the metallic
state  ensues (§ 175, 4).   The  reaction  with nitrate of sub-
oxide of mercury may  be had recourse to as a conclusive  test
(§ 175, 5).*

  * In  presence of chromic acid the  reduction of oxide of silver and  suboxide of
mercury is not a positive proof of the presence of formic acid.  In cases where the
two acids are present, the following method must be resorted to:—Mix the original
solution with some nitric acid, add oxide of lead in excess, shake the mixture, filter,
add to the filtrate dilute  sulphuric acid in excess, and distil.   Test the distillate as
directed 8 176.  In presence of tartaric acid also it is the safest way to distil the
formic acid first, with addition of dilute sulphuric acid. 
308
ACID  SOLUTION,—IN ORGANIC ACIDS.      [§ 204
                      Complex  Compounds.
 A. 2. Substances insoluble in Water, but soluble  in  Hydro-
    chloric Acid,  Nitric Acid, or Nitrohydrochloric Acid.
                    detection  of the acids.
               I. In the absence of Organic Acids.
                             §  204.
   In the examination of these  compounds attention must be
 directed to  all  acids,  with the exception  of chloric  acid.
 Cyanogen compounds and silicates are not examined by this
 method.   (Compare § 207 and § 208.)
   1.  Carbonic acid, sulphur (in form of metallic sulphides),  193
 arsenious acid,  arsenic acid, and chromic acid, if present,
 have been found  already in the course of the examination for
 bases ;  nitric acid,  if present, has been  detected in the
 course of the preliminary examination, by the ignition of the
 powdered substance in a glass tube (s).
   2.  Mix a sample of the substance with 4 parts of pure car-  194
 bonate of soda and potassa, and, should it contain a metallic
 sulphide, add some nitrate of soda ; fuse the mixture in a pla-
 tinum crucible if there  are no reducible metals present, in a
 porcelain crucible if reducible  metals  are present; boil the
 fused mass with  water, and add a little  nitric acid, leaving
 the reaction of the fluid, however, still alkaline; heat again,
 filter, and proceed with the filtrate according to the directions
 of §  202, to  effect the detection of  all the acids which  were
 combined with the bases.*
   3.  As  the phosphates of the alkaline earths are only incom- 195
 pletely decomposed by fusion in conjunction with  carbonate
 of soda  and potassa, it is always advisable in cases where
 alkaline  earths are present, and phosphoric acid has not yet
 been  detected, to  dissolve  a fresh sample  of the body under
 examination in hydrochloric acid or  nitric acid, and after re-
moval of silicic acid (§ 153, 3) and of arsenic acid (§ 136, 3  or 4)
to test the solution for phosphoric acid with molybdic acid.
  4. If in the  course of the examination for bases, alkaline
earths have been  found,  it is also advisable to test a separate
portion of the body under examination for fluorine, by the
method described in § 149,  5.
  5. That portion of the substance under examination which 196
 is  treated as directed in (194), can be tested for silicic acid

  * If the  body examined has been found to contain a metallic sulphide, a separate
 portion of  it must be examined for sulphuric acid, by heating it with hydrochloric
 acid, filtering, adding water to the filtrate, and then testing the fluid with chloride
 of barium. 
§§ 205, 206.]  COMPLEX COMPOUNDS.—ACIDS, BASES, ETC.  309

only in cases where the fusion has been effected in a platinum
crucible: in cases where a porcelain  crucible has been used,
it is necessary to examine a separate portion of the body for
silicic acid, by evaporating the hydrochloric or nitric acid
solution (§ 153, 3).
  6. Examine a separate sample of the body for oxalic acid
as directed in (§ 148, 6 or 7).

                     Complex Compounds.
A.  2. Substances insoluble in Water, but soluble in Hydro-
    chloric Acid, Nitric Acid,  or Nitrohydrochloric Acid.
                    detection of the acids.
               II. In presence of Organic Acids.
                             § 205.
   1. Conduct the examination for inorganic acids according  197
to the directions of § 204.
   2. Test for acetic acid as directed § 174, 7.
   3. Dissolve a portion of the compound under examination  198
in  the least  possible amount of  hydrochloric  acid, filter, if
necessary, and test the undissolved residue which may be left,
for benzoic acid by application of heat;  add to the filtrate
solution of carbonate of soda  in considerable excess, and, be-
sides this, also a little solid carbonate of soda, boil the mixture
for a few minutes, and then filter  the fluid from the precipi-
tate.  In  the  filtrate you have  now all  the organic acids in
solution, combined  with soda.   Acidify the  filtrate with
hydrochloric acid, heat, and proceed according to (185).

                     Complex  Compounds.
B.  Substances insoluble or sparingly soluble both in Water
      and in Hydrochloric Acid, Nitric Acid,  or  Nitrohy-
      drochloric Acid.
  detection of the bases, acids, and non-metallic elements.
                             § 206.
  To this class belong the following bodies and compounds.  199
  Sulphate  of baryta,  sulphate of  strontia,  and  sul-
phate OF  LIME.*
  Sulphate  of lead| and chloride of lead.J

  * Sulnhate of lime passes partially into  the  solution effected by water, and often
completely into that effected by acids.
  +  Sulphate of lead may pass completely  into the solution effected by acids.
  ±  Chloride of lead can here only be found if the precipitate insoluble in acids haa
not been thoroughly washed with hot water. 
310           SUBSTANCES  INSOLUBLE  IN ACIDS.        [§ 206

   Chloride of silver, bromide  of silver, iodide of silver,
cyanide of silver,* ferro- and ferricyanide of silver.f
   Silicic acid and many silicates.
   Native alumina, or alumina which has passed through a
process of intense ignition, and many aluminates.
   Ignited sesquioxide of chromium and chrome-ironstone (a
compound of sesquioxide of chromium and protoxide of iron).
   Ignited, and native binoxide of tin (tin-stone).
   Some metaphosphates and some arsenates.
   Fluoride of calcium and a  few  other compounds of
fluorine.
   Sulphur.
   Carbon.
   Of these compounds those printed in small capitals are more
frequently met with.  As the silicates perform a highly im-
portant part in mineral analysis, a special chapter (§ 208—
211) is devoted to them.
   The substance under examination which  is insoluble in
water and in acids  is in the first place subjected to the pre-
liminary experiments here described in a—e, if the quantity
at your disposal is  not absolutely too smaU  to admit of this
proceeding; in cases where the quantity is insufficient for the
purpose, the operator must  omit  this  preliminary examina-
tion, and at once pass on to (205)  bearing in mind, however,
that the body may contain all the aforesaid  substances and
compounds.
   a. Examine closely and attentively the  physical  state and 200
condition of the substance, to ascertain whether you have to
deal with a homogeneous mass or  with a mass  composed of
dissimilar particles;  whether the body is sandy or pulveru-
lent, whether it has the same color throughout, or is made up
of variously-colored particles, &c.   The microscope, or even
a simple magnifying  glass, will be found very useful at this
stage of the examination.
   b. Heat a small sample in  a glass  tube sealed at one end. 201
If brown fumes arise, and sulphur sublimes, this is of course
a proof of the presence of that substance.
  c. If the substance is black, this indicates, in most cases, 202
the presence of carbon  (wood-charcoal, pit-coal, bone-black,
lamp-black, graphite,  &c).  Heat a small sample on platinum

  * Bromide, iodide, and cyanide of silver are  decomposed by boiling with nitro-
hydrochloric acid, and converted into chloride of silver; they can accordingly be
found here only in cases where the operator has to deal with a substance which—
aa nitrohydrochloric acid has failed  to effect its solution—ia examined directly by
the method described in this paragraph (§ 206).
  f With regard to the examination of these compounds, compare also § 207. 
§ 206.]        INSOLUBLE COMPLEX COMPOUNDS.           311

foil over the blowpipe flame; if the substance (which blackens
the fingers) is consumed, this may be held to be a positive
proof of the presence of carbon in some  shape or other.
Graphite, which may be  readily recognized  by its  property
of communicating its  blackish-gray color to the fingers, to
paper, &c, requires the application  of  oxygen for its  easy
combustion.
  d. Warm a small sample, together with  a small lump of 203
cyanide of potassium  and some water,  for some time, filter,
and test the filtrate with sulphide of ammonium.   The  for-
mation of  a brownish-black precipitate shows that the sub-
stance under examination contains a compound of silver.
  e.  If an undissolved residue  has been left in d, wash this  4<*04
thoroughly with water, and, if white, sprinkle a few drops of
sulphide of ammonium over it; if it turns black, salts of lead
are present.  If, however, the residue left in d is black, heat
it with some acetate of ammonia, adding a few drops of ace-
tic acid, filter, and test the filtrate for lead, by means of sul-
phuric acid and hydrosulphuric acid.*
  The  results obtained  by these  preliminary experiments
serve to guide the operator now in his further course of  pro-
ceeding.
   1, a. Salts of lead are not present.  Pass on to (206).  205
      b. Salts  of  lead are  present.   Heat  the   sub-
     stance repeatedly with a concentrated solution of acetate
     of ammonia, until the salt of lead is completely dissolved
     out.  Test a portion of the filtrate for chlorine, another
     for sulphuric acid, and the remainder for lead, by
     addition of sulphuric  acid in excess, and by hydrosul-
     phuric  acid.   If  acetate  of ammonia has left a residue,
     wash this, and treat it as directed in (206).
  2, a. Salts of silver are not present.   Pass on to (207). 206
      b. Salts  of silver are present.  Digest the  sub-
     stance free from lead, or which has been freed from that
     metal by acetate  of ammonia, repeatedly with cyanide
     of potassium and water, at a gentle heat (in presence of
     sulphur, in the cold), until all the salt of silver is removed.
     If an undissolved residue is left, wash this, and then pro-
     ceed with it according to the directions of  (207).  Of
     the filtrate, which contains cyanide of potassium,  mix
     the larger  portion with  sulphide of ammonium, to  pre-
     cipitate  the  silver.   Wash the precipitated sulphide of
     silver  then dissolve it in nitric acid, dilute the solution,

  * The presence of lead in silicates, e. g. in glass containing lead, cannot be de-
tected by this method. 
 312            DETECTION OF BASES, ACIDS,  ETC.        [§ 20G

     and add hydrochloric acid, to ascertain whether the pre-
     cipitate really consisted of sulphide of silver.  Test ano-
     ther small portion of the filtrate for sulphuric acid.*
   3. a. Sulphur is not present.   Pass on to (208).         207
       b. Sulphur is present.   Heat the substance free from
     silver and lead in a covered  porcelain crucible until all
     the sulphur is expelled, and, if a residue is left, treat this
     according to the  directions of (208).
   4. Mix  the substance free from  silver, lead, and sulphur  208
 with 2 parts of carbonate of soda, 2 parts of carbonate of po-
 tassa, and  1  part of nitrate of potassa,f heat the mixture  in
 a platinum crucible until the mass is in a state of calm fusion,
 place the red hot crucible on a thick, cold iron plate, and let
 it  cool.  By this means you will  generally succeed  in remov-
 ing the fused mass  from the crucible in an unbroken  lump.
 Soak the mass now in water, boil, filter, and wash the residue
 until chloride  of  barium no longer produces a precipitate in
 the washings.   (Add  only the first washings to the filtrate.)
       a.  The  solution  obtained  contains  the acids  which  209
     were  present in the substance decomposed by fluxing.
     But it  may,  besides these acids,  contain  also  such
     bases  as are  soluble in caustic alkalies.  Proceed as fol-
     lows :—
         a. Test a small portion of the solution for sulphuric
       acid.
         8. Test  another  portion with  molybdic  acid for
       phosphoric acid and arsenic acid.  If a yellow pre-
       cipitate forms, remove  the  arsenic  acid which may
       be  present  with  hydrosulphuric  acid, and then test
       once more  for phosphoric acid.
         y. Test another portion for fluorine (§ 149, 7).
         S. If the solution is  yellow,  chromic acid is pre-
       sent.   To remove all doubt on the point, acidify a por-
       tion of the solution with acetic  acid, and test with
       acetate of lead.
         s. Acidify the remainder of the solution with hydro-  210
       chloric acid, evaporate to dryness, and treat the residue

  * As the carbonate of potassa contained in the cyanide of potassium may have
produced a total or partial decomposition  of any sulphates of the alkaline earths
 which happened to be present.
  \ Addition of nitrate of potassa is useful even in the case of white powders, as it
counteracts the injurious action of silicate of lead, should any be present, upon the
platinum crucible.  In the  case of black powders, the proportion of nitrate of potassa
must  be correspondingly increased, in order that carbon, if present, may be consumed
 as  completely as possible, and that any chrome ironstone existing in  the compound
 may be more thoroughly decomposed. 
§ 206.J        INSOLUBLE COMPLEX COMPOUNDS.           313

      with  hydrochloric  acid and  water.   If  a residue is
      left which refuses to dissolve even in boiling water,
      this consists of silicic acid.   Test the hydrochloric
      acid  solution now in the usual way for  those bases
      which,  being  soluble in caustic alkalies, may  be
      present.
      b. Dissolve  the residue left in  (208) in  hydrochloric  211
    acid  (effervescence indicates the  presence  of alkaline
    earths), and test the solution for the bases as directed in
    § 193.  (If much silicic acid has been found in (210), it
    is advisable to evaporate the solution of the residue  to
    dryness, and to treat the residuary mass with hydrochlo-
    ric  acid and water, in order that the silicic acid remain-
    ing may also be removed as completely as possible.)
  5. If you have found in 4 that the residue insoluble in acids  212
 contains a silicate, treat a separate portion of it according to
 the directions  of (22§), to ascertain whether or not this sili-
 cate contains alkalies.
  6. If  a  residue is still left undissolved upon  treating the  213
 residue  left  in (208)  with hydrochloric acid (21l), this may
 consist  either  of silicic acid, which has separated, or of  an
 undecomposed portion of sulphate  of baryta; it may, how-
 ever, also be  fluoride of calcium, and if it is dark-colored,
 chrome-ironstone, as the last-named  two compounds are only
 with difficulty decomposed by the method given in (208).   I
 would therefore remind the student  that fluoride of calcium
 may be  readily decomposed by means of sulphuric acid; and,
 as  regards  the  decomposition of  chrome-ironstone,  I can
 recommend the following  method, first  proposed by Hart:
 Project  the  fine powder into  8  times the quantity of fused
 borax, stir the mixture frequently, and keep the  crucible  for
 half-an-hour at a bright red heat.   Add now to the  fusing
 mass carbonate of  soda so long as  effervescence  continues,
 and then finally add 3 times  the weight of the  chrome-iron-
 stone of a mixture  of equal parts of carbonate  of soda  and
 nitrate of potassa,  whilst actively stirring the mixture with a
 platinum  wire.  Let  the  mass cool, and, when  cold, boil it
 with water.
  7. If  the residue insoluble  in acids contained silver, you  211
 have still to ascertain whether that metal was present in the
 original substance as chloride, bromide, iodide, &c, of silver,
 or whether  it has been converted into the form of chloride of
 silver by the treatment employed to effect the solution of the
 orio-inal substance.   For that purpose, treat a portion of the
 original substance with boiling water until the soluble part
is completely removed; then treat  the residuary portion in 
314             ANALYSIS OF CYANIDES, ETC.         [§ 207

the same way with dilute nitric acid, wash the undissolved
residue with water, and test a  small sample of it for silver
according to the directions of  (203).   If silver is present,
proceed to ascertain the salt-radical with which the metal is
combined; this may easily be effected by boiling the remain-
der of the residue in the first place with rather dilute  solu-
tion of soda, filtering, and testing the filtrate, after acidifying
it, for ferro- and ferricyanogen.  Digest  the washed residue
now with finely granulated zinc and water, with addition of
some sulphuric acid, and filter after the lapse of ten minutes.
You may now at once test the filtrate for chlorine, bromine,
iodine, and cyanogen;  or you may first throw down the zinc
with carbonate of soda, in order to obtain the  salt-radicals in
combination with sodium.
                       SECTION II.

                PRACTICAL COURSE

                     IN PARTICULAR  CASES.

I. Special Method of effecting the Analysis of Cya-
   nides, Ferrocyanides, etc., insoluble in Water, and
   also of insoluble mixed substances  containing such
   Compounds.*
                            §  207.
  The analysis  of ferrocyanides,  ferricyanides, &c, by  the 215
common method is often  attended by the manifestation of
such  anomalous  reactions  as  easily mislead the  analyst.
Moreover, acids often fail to effect their complete solution.
For these reasons it is advisable to analyze  them, and mix-
tures  containing such compounds, by the following  special
method:—
  Treat the substance with water until the soluble parts are
entirely removed, and boil the residue with strong solution of
potassa or soda; after a few minutes' ebullition add some car-
bonate of soda, and boil again for  some time; filter, should a
residue remain, and wash the latter.
       1. The residue, if any has been left, is now free from 210
    cyanogen, unless the substance under examination  con-
    tains cyanide of silver, in which case the residue would

  * Before entering upon this course of analysis, study well the special remarks to
the paragraph (§ 207) in the Third Section. 
§ 207.]              ANALYSIS OF CYANIDES.               315

    of course still contain cyanogen.   Examine the residue
    now by the common method, beginning at (35).
      2. The solution or filtrate, which,  if combinations of  217
    compound  cyanogen  radicals (ferrocyanogen, cobalti-
    cyanogen, &c.)  were originally present,  contains these
    combined with  alkali  metals, may also  contain  other
    acids,  which have been separated from their bases by the
    process of boiling  with carbonate of soda, and  lastly
    also, such oxides as are soluble in caustic alkalies.
  Treat the solution  as follows:—
      a. Mix the alkaline fluid with a little solution  of hydro-  218
    sulphuric acid.  The addition of solution of hydrosulphu-
    ric acid or the passage of the gas  through the solution
    until the liquid smells of it (i.e. until all the alkali is con-
    verted into a sulphuretted sulphide—hydrosulphate) is to
    be avoided, else alumina, and even sulphides of metals
    of the sixth group might be thrown down.
        a. No permanent  precipitate  is formed.  Absence
      of zinc and lead.  Pass on to (219)-
        (3.  A permanent precipitate  is form.ed.  Add to
      the   fluid   sulphide   of sodium,  drop by drop, just
      sufficient to throw down from the alkaline solution the
      metals of groups IY.  and V., heat moderately, filter,
      wash the precipitate, and treat the  filtrate as directed
      in (219).   Dissolve the washed  precipitate  in  nitric
      acid, whereby sulphide of mercury may remain undis-
      solved, and examine the solution for copper, lead, zinc,
      and  other  metals of the fourth  group, which may, in
      the  same way as copper, have passed into the alkaline
      solution by the agency of organic matters.
      b. Mix the alkaline fluid, which contains now also sul-  219
    phide  of an alkali metal (and may therefore contain  the
    sulphides of  the  sixth group (as sulphur salts), as well as
    sulphide of mercury, which is soluble in sulphides of the
    fixed alkalies), with water and with dilute nitric acid  to
    acid reaction, and, if necessary, add more hydrosulphuric
    acid until the liquid smells strongly of the gas.
        a. No precipitate is formed.   Absence of  mercury
      and of the oxides of the sixth group.  Pass onto (220).
        (8. A precipitate  is formed.   Filter,  wash the pre-
      cipitate, and then examine  it  for  mercury, and the
      metals of the sixth group, according to  the directions
      of § 194.
      c. The fluid,  acidified  with nitric acid, and therefore 220
   abundantly supplied with nitrates  of alkalies, may still
   contain the metals which, in combination with cyanogen, 
 316                ANALYSIS  OF SILICATES.             [j

     form compound radicals (iron, cobalt, manganese, chro-
     mium), and, besides these,  also alumina.  You  have to
     test it also for cyanogen, respectively, ferrocyanogen,
     cobalticyanogen, &c,  and for other acids.  Divide it,
     therefore, into two portions, a and 8.   Examine a for
     the acids acording to the directions of § 202 or § 203.
     (Cobalticyanogen may be recognised as such by its giving
     with salts of nickel greenish, with salts of manganese and
     zinc white precipitates  in which cobalt may be detected
     with borax before the blowpipe.)
       Evaporate 8 to dryness, and heat the residue to fusion.
     Pour the fused mass upon a piece of porcelain, boil with
     water, filter, and examine the residue for iron, manga-
     nese, cobalt, and alumina.   Test  a portion of the fil-
     trate (if yellow) for chromic acid, the remainder for
     alumina—which may have passed partially or complete-
     ly  into the solution, through the agency  of the caustic
     alkalies formed, in the process of fusion, from the nitrates
     of the alkalies present.

                   n. Analysis of Silicates.
                             §208.
  Whether the body to be analyzed is a silicate, or  contains
one, is ascertained by the preliminary examination with phos-
phate of soda and ammonia before the blowpipe ; since, in the
process of fusion, the metallic oxides dissolve, whilst the sepa-
rated silicic acid floats about in the liquid bead as a transpa-
rent, swollen mass (§ 153, 8).
  The analysis of the silicates differs, strictly speaking, from
the  common course only in so far as  the preliminary treat-
ment is concerned, which is  required to effect  the separation
of the silicic acid from the  bases, and to obtain the latter in
solution.
  The silicates and  double  silicates are divided into two dis-
tinct classes,  which require respectively a different method of
analysis; viz., (1) silicates easily decomposable by acids (hy-
drochloric acid, nitric acid, sulphuric acid) and (2)  silicates
which are not decomposed or decomposed with difficulty, by
acids. Many rocks are mixtures of these two kinds of silicates.
  To ascertain  to  which of  these  two classes a silicate
belongs, reduce it to a very  fine powder, and digest a portion
with hydrochloric acid at  a temperature near the boiling
point.   If this fails to decompose it, try another portion with
tolerably concentrated  sulphuric  acid, and  apply heat.  If
this  also fails, after  some time, to produce the  desired effect, 
§ 209.]       SILICATES DECOMPOSABLE  BY ACIDS.           317

the silicate belongs to the second class.  Whether  decompo-
sition has been effected by the acid or not may generally be
learned from external indications, as a colored solution forms
almost invariably, and the separated gelatinous, flocculent, or
finely-pulverulent hydrate of silicic acid takes the place of the
original heavy powder which grated under the glass rod with
which it was stirred.
  To ascertain  whether the decomposition is  complete  the
separated hydrate of silicic acid, after filtering and washing,
is treated with boiling solution of carbonate of soda.
  If complete solution takes place it shows  that the silicate
was wholly decomposed.  If after repeated treatment a resi-
due remains, it indicates that the silicate  (or mixture of sili-
cates) is but partially decomposed.
  These preliminary tests decide whether the substance shall
be further examined according to § 209 or §  210 or § 211.
  Before proceeding further, test a portion of the pulverized
compound also for xoater, by heating it in a perfectly dry glass
tube.  If the substance contains hygroscopic moisture it must
first  be  dried by  protracted exposure to a temperature of
212° F.  Apply  a gentle heat  at  first,  but ultimately an
intense heat,  by means  of the blowpipe  ; you may also con-
veniently combine with this a  preliminary  examination for
fluorine (§ 149, 8).


            A.  Silicates  decomposable by Acids.
                             § 209.
  a. Silicates decomposable by hydrochloric  acid or by nitric
acid.*                          •
  1.  Digest the  finely pulverized silicate with  hydrochloric  222
acid (or nitric acid) at a temperature near the boiling point,
until complete decomposition is effected, filter off a small por-
tion  of the fluid, evaporate the  remainder, together with the
silicic acid suspended therein, to dryness,  and expose the resi-
due to a temperature somewhat exceeding 212° F., with con-
stant stirring, until no more, or very few, hydrochloric acid
fumes escape; allow it to  cool, moisten the  residue with
hydrochloric  acid,  or as  the case may be,  with nitric acid,
afterwards add a little water, and heat gently for some time.
  This operation effects the separation of the silicic acid,  and
the solution of the bases in the form of chlorides (or nitrates).
Filter, wash the residue thoroughly,  and examine the solu-

 * Nitric acid is preferable to hydrochloric acid in cases where compounds of sil-
ver or lead are present. 
318           SILICATES  DECOMPOSABLE BY  ACIDS.        [§ 209

tion by  the common method, beginning at §  192, II. or III*
To be  quite  safe, the residuary silicic acid may be  digested
with ammonia, filtered, and the filtrate tested for  silver, by
supersaturation with nitric acid.
   2.  As in silicates,  and more  particularly  in those  decom-  223
posed by hydrochloric acid, there are often found other acids,
as well as metalloids, the following observations and instruc-
tions must be attended to, that none of these substances may
be overlooked:—
       a. Sulphides of metals and carbonates are detected
     in the process of treating  with hydrochloric acid.
       8.  If the separated silicic acid is  black, and turns sub-
     sequently white upon  ignition in the air, this indicates
     the presence of carbon or of organic substances.   In
     presence of the latter, the silicates emit an  empyreuma-
     tic odor upon being heated in a glass tube.
       y. Test the portion of the hydrochloric acid solution
     filtered off before evaporating (222), for sulphuric acid,
     phosphoric acid, and arsenic acid : for  sulphuric acid
     with  chloride of barium, in a sample diluted with water:
     for arsenic acid by passing a stream of hydrosulphuric
     acid  gas  into the  solution  heated to  160°  Fah., and
     further  examination of the  precipitate: for phosphoric
     acid by means  of molybdic acid.  The  filtrate  from the
     sulphide of arsenic, in case  arsenic acid was present,
     will  serve,  after  expulsion of excess of hydrosulphuric
     acid, to test for phosphoric acid.
   * Minute traces of titanic acid are occasionally met with in silicates.  The titanic
acid  present mostly passes into the hydrochloric  acid solution, if the separation of
the silicic acid has been effected on the water-bath, while a small portion  separates
with the silica.   The titanic acid is detectea in the following manner :
   a.  The silica is heated  in a platinum dish with a mixture of hydrofluoric acid, and
sulphuric acid, and this is repeated until  all the silica is dissipated as  fluoride of
silicon.  Finally the residue is evaporated to dryness.
   b.  The solution that has been filtered from silica is precipitated with ammonia, the
precipitate (which contains alumina, oxide of iron,  Ac,  together with the rest of the
titanic acid) is washed, dried, and ignited.  It is now added to the residue  obtained
in a, the whole is fused with enough bisulphate of potassa to bring it into solution, and
the heat  is kept up until the greater  part of the excess of sulphuric acid is driven
off.  After  cooling the fused mass is dissolved in cold water (whereby  a perfectly
clear solution is obtained if the process  has been successfully carried out, and all
silica was removed).  The solution is filtered if needful and largely diluted with
water. Hydrosulphuric acid gas is now transmitted through the liquid until all ses-
quioxide of iron is reduced to protoxide.  The liquid is now (without removal of the
suspended sulphur) maintained for half an hour at a boiling heat, while a  stream of
carbonic acid gas is passed through it  without interruption. The titanic acid is in thia
way gradually thrown down while all the bases  remain in solution (Th. Scheerer\
   The precipitate is collected on a filter, washed, ignited,  and the residue is examined
 according to § 107, 10 
§ 210.]      SILICATES  NOT  DECOMPOSED  BY  ACIDS.         319
       8. Boracic acid is best detected by fusing a portion  224
     of the  substance in a platinum spoon with carbonate of
     soda, boiling the fused mass with water, and examining
     the  solution  for  boracic acid by  the method given in
     § 147, 6.
       s. With many  silicates, boiling with water is sufficient
     to dissolve the metallic chlorides present, which may
     then be readily detected in the filtrate by means of solu-
     tion of nitrate of silver; the  safest way, however, is to
     dissolve the mineral in dilute nitric  acid, and test the
     solution with nitrate of silver.
       £. Metallic fluorides, which often  occur in silicates in
     greater or smaller proportion, are detected by the method
     described § 149, 6.
   b. Silicates which resist  the  action of hydrochloric acid,
 but are decomposed by concentrated sulphuric acid.
   Heat the finely pulverized mineral with a mixture of 3 parts  225
 of concentrated pure sulphuric acid, and 1 part of water
 (best in a platinum dish), finally drive off  nearly all the  sul-
 phuric acid, boil the residue with hydrochloric  acid, dilute,
 filter, and treat the filtrate as directed § 193 ;  and the residue,
 which, besides the  separated silicic  acid, may  contain also
 sulphates of the alkaline earths, &c, according  to  the  direc-
 tions of  § 206.  If you wish to examine silicates of this class
 for acids and salt-radicals, treat a separate portion of the sub-
 stance according to the directions of § 210.

     B.  Silicates which are  not decomposed by Acids*
                              § 210.
   As the silicates  of this class are most conveniently decom-  220
 posed by fusion with carbonate of soda and potassa, the por-
 tion so treated cannot, of course,  be examined  for alkalies.
 The analytical process is therefore  properly divided into two
 principal parts, viz., a portion of the mineral is examined for
 the silicic acid and the bases, with the exception of the alka-
 lies, whilst another portion  is specially examined for the  lat-
 ter.—Besides   these,  there  are  some  other  experiments
 required, to obtain information  as to the presence or absence
 of other  acids.
   1. Detection of the silicic acid and the bases, with the excep-
 tion of the alkalies.
  * Silicates which are unaffected by boiling acids are with few exceptions decom-
posed when heated with a mixture of 3 parts concentrated sulphuric acid and 1
part of water, as well as by hydrochloric acid, to a temperature of 390° to 410° Fah.
The silicate must be finely pulverized, and the heating is conducted in a sealed
lube of Bohemian glass.  (Al.  Mitscherlich.) 
320         SILICATES  NOT DECOMPOSED  BY ACIDS.      [§210,

  Reduce the mineral to a very fine  powder, mix this with 4  227
parts of carbonate of soda and potassa, and heat the mixture
in a platinum crucible  over a  gas  or Berzelius  spirit-lamp,
until the mass is in a state of calm  fusion.  Put  the red-hot
crucible on a thick, cold iron plate, and let  it cool there ;  this
will generally enable you to remove the fused cake from the
crucible, in which case break the mass to pieces, and keep a
portion for  subsequent  examination  for  acids.  Put  the
remainder, or, if the mass still adheres to the crucible, the
latter, with its  contents,  into  a porcelain  dish, pour  water
over it, add hydrochloric acid, and heat gently until the mass
is dissolved, with the exception of the silicic acid, which sepa-
rates in flocks.   Remove the crucible from the dish,  if neces-
sary,  evaporate the contents  of the latter to dryness,  and
treat the residue as directed (222).
  2.  Detection of the alkalies.
  To effect  this, the  silicates under examination must be  22§
decomposed  by  means of a  substance free from  alkalies.
Hydrofluoric acid or a metallic fluoride answers this purpose
best; but fusion with hydrate of baryta will also  accomplish
the end in view.
       a. Decomposition by  means of a metallic  fluo-
    ride.—Mix 1 part of the very finely pulverized mineral
    with 5 parts of fluoride of barium, or pure, finely pulver-
    ized fluoride of calcium, stir the mixture in  a platinum
    crucible with concentrated sulphuric  acid to a  thickish
    paste, and heat gently for some  time in a place affording
    a  free escape to the vapors; finally heat a little more
    strongly, until the excess of sulphuric  acid is completely
    expelled. Boil the residue now with water, add chloride
    of barium cautiously as long as a precipitate continues
    to form,  then  baryta-water to alkaline reaction,  boil,
    filter, mix with carbonate of ammonia and some ammonia
    as long as a precipitate forms, and proceed  exactly as
    directed (l6§).
       b. Decomposition  by means  of hydrate of baryta.  229
    Mix 1 part of the very finely pulverized substance with
    4 parts of hydrate of baryta, expose the mixture for half
    an hour in a platinum crucible to the  strongest possible
    heat of a good Berzelius or gas-lamp, and treat the fused
    or agglutinated mass with hydrochloric acid  and water
    until it is dissolved;  precipitate the solution with ammo-
    nia and carbonate of ammonia, filter,  evaporate to  dry-
    ness,  ignite, dissolve the  residue in  water,  precipitate
    again with  ammonia and  carbonate  of ammonia, filter,
    evaporate, ignite, and test the  residue  for potassa  and 
§ 210.]      SILICATES  NOT DECOMPOSED BY  ACIDS.         321

    soda  as directed § 200.   If the  residue  still  contains
    magnesia, this may be readily removed, by adding to the
    aqueous solution of the residue a little pure oxalic acid,
    evaporating to dryness, igniting the dry mass, and then
    treating it with  water, which will dissolve the  alkalies
    as chlorides, and leave the magnesia undissolved.  Fil-
    ter, acidulate the filtrate with hydrochloric acid, evapo-
    rate to dryness,  and examine the residue for potassa and
    soda.
      [c. Decomposition by means of carbonate of lime 229*
    and chloride of ammonium.   Mix 1  part  of  the pul-
    verized  substance with 6 parts of precipitated carbonate
    of lime, and % part of pulverized chloride of ammonium,
    place in a platinum crucible and treat to bright redness
    for  30  to 40  minutes.  The crucible with its  contents
    (which  should  be  in a  coherent,  sintered, but  not
    thoroughly fused condition),  is  placed in  a  beaker,
    covered with water and heated to near the boiling point
    for  half an hour.  The whole  is  then  brought upon a
    filter, the filtrate, containing the alkalies, chloride  of cal-
    cium and caustic  lime, is treated with a little ammonia
    and with carbonate  of ammonia  in slight excess,  and
    heated to boiling, filtered, and the filtrate evaporated to
    dryness and gently ignited to  expel salts of ammonia.
    The residue is dissolved in a  little water, one or two
    drops of carbonate of ammonia, and a drop of oxalate of
    ammonia added, the mixture is heated, filtered, the  fil-
    trate is evaporated to dryness, ignited, and the  residual
    alkaline chlorides examined according to § 200.   (J.  L.
    Smith).]
  3. Examination for fluorine, chlorine, boracic acid, phos-
phoric acid, arsenic acid, and sulphuric acid.
  Use for this purpose the portion of the fused mass reserved 230
in (22T), or, if necessary, fuse a separate portion of the finely
pulverized substance with 4 parts of pure carbonate of soda
and potassa until the mass flows calmly ; boil the fused mass
with water, filter the solution, which contains all the fluorine
as fluoride of sodium, all the chlorine as chloride of  sodium,
all the boracic acid as borate,  all the  sulphuric acid as sul-
phate, all the arsenic acid as arsenate, and at least part of the
phosphoric  acid as phosphate  of soda, and treat the filtrate
as follows:—
      a. Acidify a portion of  it with nitric acid, and test
    for chlorine with nitrate of silver.
      b. Test another portion for boracic  acid as  directed
    §  147, 6.
                               21 
 322     SILICATES PARTIALLY DECOMPOSED BY  ACIDS.   [§211.

       c. Examine a third portion according to §149, 7 for
     fluorine.
       d. The remainder is acidified with hydrochloric acid,
     and a small portion is tested with chloride of barium for
     sulphuric acid ; the  rest of the solution is heated to
     158° Fah., and tested for arsenic acid by hydrosulphuric
     acid.  If no  precipitate is formed, the liquid—or if a
     precipitate separates, the  filtrate from it—is evaporated
     to dryness, the residue is treated with hydrochloric acid
     and water, and the solution thus  obtained is examined
     for phosphoric acid by means of sulphate of magnesia,
     or a nitric solution of molybdate of ammonia (§ 145).

   C. Silicates which are partially decomposed by Acids.
                              § 211.
  Most native rocks are mixtures of several silicates, of which 231
the one is often decomposed by acids, the other not.  If such
mixtures were analyzed by the  same method  as the  absolutely
insoluble silicates, the analyst would indeed detect all the ele-
ments present, but the  analysis would  afford no satisfactory
insight into the actual composition of the rock.
  It is, therefore, advisable to examine separately those  parts
which show a different deportment with acids.  For this pur-
pose digest the  very finely pulverized substance for  some
time with hydrochloric  acid* at a very gentle heat, then filter
off a small portion, evaporate the remainder to dryness, and
expose to a temperature somewhat exceeding 212° F., with
stirring,  until no  more,  or very little hydrochloric acid vapor
is evolved; let the residue cool, moisten it when cold with
hydrochloric acid, heat gently  with water, and filter.
  The filtrate contains the  bases of the decomposed part of
the mixed mineral; examine this as directed (222).  Test tbe
portion first filtered off according to (223) /, and portions of
the  original substance  for other acids  according to (224).
The residue  contains, besides the silicic acid separated from
the bases by the action of the hydrochloric acid, that part of
the mixed mineral which has resisted the  action of the acid.
Boil this residue with an excess  of solution of carbonate of
soda,f filter hot, and wash, first with hot solution of carbonate
of soda, finally with boiling water.  Treat the residuary un-
decomposed part of the mineral, from which  the admixed free

  * [Evolution of hydrogen gas  may be due, in certain trap rocks, to presence of
finely-divided metallic iron.]
  f [According to A. Miiller, caustic  Boda must be employed instead of carbonate
of soda for taking up silica.] 
§§ 212, 213.]        ANALYSIS OF  WATERS.
323
silicic acid has thus been removed, according to the instruc-
tions given in § 210.  In cases where it is of no consequence
or interest to effect the separation of the silicic acid of the
part decomposed by acids, you may omit the laborious treat-
ment with carbonate of soda, and may proceed at once to the
decomposition of the residue.

              IU. Analysis  of Natural Waters.
                            § 212.
   In the examination of natural waters the analytical process  232
is simplified by the circumstance that we know from expe-
rience the elements  and compounds which are usually found
in them.  Now, although  a quantitative analysis alone  can
properly inform us as to the true  nature and character of a
water, since  the differences between the various waters are
principally caused by the  different proportions in which the
several  constituents are respectively present,  a qualitative
analysis  may yet render very good service,  especially if the
analyst  notes with proper  care, whether  a reagent  produces
a faint or distinctly marked turbidity, a slight or copious pre-
cipitate,  since these circumstances will enable him  to make
an approximate  estimation  of  the  relative proportions  in
which the several constituents are present.
   I  separate here the analysis of the  common fresh  waters
(spring-water,  well-water,  brook-water,  river-water,  &c.)
from that of the  mineral waters, in which  we may also in-
clude sea-water; for, although no well-defined limit  can be
drawn between the two classes, still the  analytical  examina-
tion of the former is necessarily far more  simple than that of
the latter, as the  number  of substances to  be looked for is
much more limited than in the case of mineral  waters.

   A. Analysis of Fresh Waters (Spring-water,  Well-
          water, Brook-water, River-water,  &c).
                            § 213.
  We know  from experience that the substances to be had  233
regard to in the analysis of such waters are the following :—
  a. Bases :  Potassa, soda, ammonia, lime, magnesia, prot-
oxide of iron.
  b.  Acids, &c. :  Sulphuric acid, phosphoric  acid, silicic acid,
carbonic  acid, nitric acid, nitrous acid,  chlorine.
  c.  Organic Matters.
  d.  Mechanically suspended substances  : Clay, &e.
  The  fresh  waters contain  indeed also other constituents
besides those enumerated here, as  may be inferred from  the 
324              ANALYSIS OF FRESH WATERS.          [§ 213.
 origin and  formation of springs, &c, and as has, moreover,
 been fully established by the results of analytical  investiga-
 tions ;* but the quantity of such  constituents is so trifling
 that they escape detection, unless hundreds of pounds of the
 water are subjected to the analytical process.  I omit, there-
 fore,  here the mode of their detection, and refer to § 214.
   1.  Boil one to two litres of the carefully collected water in 234
 a glass flask or retort to one-half.   This generally produces a
 precipitate.  Pass the fluid through a perfectly clean filter
 (free  from  iron and lime), wash the precipitate well, after
 having removed the filtrate, and  then  examine both as  fol-
 lows :—
   a.  Examination  of the precipitate.
       The precipitate contains those constituents of the water 235
    which were only kept in solution through the  agency of
    free carbonic acid, or, as the case may be, in the form of
    bicarbonates, viz., carbonate of lime,  carbonate of mag-
    nesia, hydrated sesquioxide of iron (which was in solu-
    tion as bicarbonate of protoxide  of  iron, and  precipi-
    tates upon boiling as sesquioxide, and if  phosphoric acid
    is present, also  in combination with that acid), phosphate
    of lime; and besides, silicic acid,  and  sometimes  also
    sulphate of lime, if that  substance is present  in large
    proportion; and clay which was mechanically suspended
    in the water.
       Dissolve the  precipitate on the  filter in the least pos-
    sible quantity of dilute hydrochloric  acid (effervescence
    indicates the presence of carbonic acid), and mix sepa-
    rate portions of the solution :—
         a.  With sulphocyanide of potassium: red coloration
       indicates the presence of iron.
         8. After previous boiling, with  ammonia: filter, if 236
       necessary, mix the filtrate with  oxalate of ammonia,
       and let the mixture stand for some time in a warm
       place.  The formation of a white precipitate indicates
       the presence  of lime—in the form of carbonate, or also
       in  that of sulphate if  sulphuric acid is" detected in y.
       Filter, mix the filtrate again with ammonia, add some

  * Chatin ('; Journ. de  Pharm. et de Chim.," 3 Ser. t. xxvii. p. 418) found iodine
in all fresh-water plants,  but not in land plants, a proof that the water of rivers,
brooks, ponds,  Ac,  contains traces, even though  extremely minute,  of  metallic
iodides.  According to Marchand (" Compt.  Rend.," t. xxxi. p. 495),  all natural
waters contain iodine, bromine, and lithia. Van Ankum  has  demonstrated  the
presence of iodine in almost all the potable waters of Holland.  And it  may be
affirmed with the same certainty that all, or at all events most, natural waters con-
tain compounds of strontia, fluorine, &c. 
§ 213.]          ANALYSIS OF FRESH WATERS.              325

       phosphate of soda, stir with a glass rod, and let the
       mixture stand for twelve hours.   The  formation of a
       white,  crystalline precipitate, which is often visible
       only on the sides of the vessel when the fluid is poured
       out, indicates the presence of magnesia (carbonate of);
         y. With  chloride  of barium,  and let the  mixture
       stand for twelve hours in a warm place.   The forma-
       tion of a precipitate—which, when very inconsiderable,
       is best seen if the supernatant clear fluid is cautiously
       decanted, and  the  small quantity remaining shaken
       about in the glass—indicates the presence  of  sulphu-
       ric acid.
         8. Evaporate another portion to dryness, treat the  239
       residue with hydrochloric acid and water, filter and
       test the filtrate for phosphoric acid by means of molyb-
       dic acid or sesquichloride of iron and acetate of soda
       (§ 145).
   b. Examination of the filtrate.
         a. Mix a portion of the filtrate with a little hydro-  23§
       chloric acid and  chloride of barium.  The formation
       of a white precipitate,  which makes its appearance at
       once or  perhaps  only after standing some time, indi-
       cates SULPHURIC ACID.
         8.  Mix another portion with nitric  acid,  and add
       nitrate of silver.  A white precipitate or  a white tur-
       bidity  indicates the presence of chlorine.
         y.  Test a portion of the filtrate after acidifying with
       hydrochloric acid, for phosphoric acid as  in (237).
         8. Evaporate another and larger portion of the fil-
       trate until  highly concentrated, and test the  reaction
       of the fluid.  If it  is alkaline, and a drop  of the con-
       centrated clear solution effervesces when  mixed on  a
       watch-glass with a  drop of acid, a carbonate of an
       alkali is present.   Should this be the case, evaporate
       the fluid to perfect dryness, boil the residue with spirit
       of wine, filter, evaporate the alcoholic solution to dry-
       ness, dissolve the residue in a little water,  and test the
       solution for nitric acid* as directed § 162, 7, 8 or 9.
         e. Mix the remainder of the filtrate  with some chlo-
       ride of ammonium, add ammonia and oxalate of ammo-
       nia, and let the mixture stand for a considerable time.
       The formation of a precipitate indicates the  presence
       of lime.  Filter, and test,—

  * In many cases this circuitous but safe process is unnecessary, nitric acid being
•eadily detected directly in the highly concentrated water. 
326             ANALYSIS  OF FRESH WATERS.          [§ 132.

           aa.  A small portion with ammonia and phosphate
         of soda for magnesia.
           bb. Evaporate the remainder to dryness, heat the
         residue to redness, remove the magnesia, which may
         be present (168)  and test  for  potassa and soda,
         according to the directions of §  200.
  2. Acidify a tolerably large portion  of the filtered water  239
with pure hydrochloric acid, and evaporate nearly to dryness;
divide the residue into 2 parts, and—
       a.  Test the one part with hydrate of lime for ammo-
    nia (compare § 94, 3).
       b. Evaporate the other part to  dryness, moisten with
    hydrochloric acid, add water, warm, and filter, if a resi-
    due remains.  The residue may consist of silicic acid,
    and of clay  which has been mechanically suspended  in
    the water; these two substances may be separated from
    each other by boiling with solution of carbonate of soda.
    The precipitate is often dark-colored from the presence
    of organic substances; but it becomes perfectly white
    upon ignition.
  3. Mix another portion of the water, fresh taken from the  240
well,  &c, with lime-water.  If a precipitate is thereby pro-
duced, free carbonic acid or bicarbonates are present.  If
the former (free carbonic acid) is present, no permanent pre-
cipitate is obtained when  a larger portion of the  water is
mixed with only a small amount of lime-water, since in that
case soluble bicarbonate of lime is formed.
  4. A portion is examined for nitrous acid* by mixing with  241
iodide  of potassium-starch-paste  (1  part of pure  KI.   20
parts starch and 500 parts of pure water) and pure dilute
sulphuric acid, and observing whether a blue coloration is
produced at once or in a few minutes (§  161, 1).
  5. To detect the presence of organic matters, evaporate a 242
portion of the water to dryness, and gently ignite the residue:
blackening of the mass denotes the presence of organic sub-
stances.   If this experiment is to give conclusive results, the
evaporation of the  water, as well as the ignition of the resi-
due, must be conducted in a glass flask or a retort.
  6. To  detect putrefying organic matters  or other sub-
stances recognisable by the odor, a flask is filled  two-thirds
full of the water, closed with the palm of the hand, and
vigorously shaken; the  smell  is then noted.   If hydro-
sulphuric acid  is perceived proceed  according to § 215, 3.
To examine for organic odors in presence of hydrosulphuric
* Found by Schonbein in all rain and snow-waters. 
 § 214.]         ANALYSIS OF MINERAL WATERS.            327

 acid combine the latter with help of a little sulphate of cop-
 per and test the odor again.
   7. If  you wish  to examine the matters  mechanically  243
 suspended in a water (in muddy brook or river-water, for
 instance),  fill  a large  glass  bottle  with the  water,  cork
 securely, and let it stand at rest for  several days, until the
 suspended matter has subsided ; remove now the clear super-
 natant fluid with the aid of a syphon, filter the remainder,
 and examine  the sediment remaining on  the filter.  As this
 sediment may consist of the finest dust  of  various minerals,
 treat it  first with  hydrochloric  acid, and  examine the part
 insoluble in that menstruum in the manner directed § 208.
   8. In order not to overlook oxide of lead, which sometimes
 exists in waters which  are  served through leaden pipes,  a
 considerable quantity of the  water is  treated  with hydro-
 sulphuric acid gas left at rest for some time, and a black pre-
 cipitate, should one be formed, is examined according to §196.
 For detecting extremely minute traces of lead 6 to 8 litres of
 water are acidulated with acetic acid and evaporated almost
 to dryness with addition of some acetate of ammonia to pre-
 vent the precipitation of sulphate  of lead.  The residue is
 filtered and precipitated with hydrosulphuric acid.

               B. Analysis  of Mineral Waters.
                            § 214.
   The analysis of mineral waters embraces a larger number  244
 of constituents than that of fresh water.  The following are
 the principal of the additional elements to  be looked for:—
   Caesia rubidia, lithia, baryta, strontia, alumina, prot-
 oxide  OF manganese, boracic acid, bromine, iodine, fluo-
 rine, hydrosulphuric acid (Hyposulphurous Acid),* crenic
 acid, and  apocrenic acid (Formic Acid,  Propionic Acid,
 tkc., Nitrogen, Oxygen, Marsh Gas).
   The analyst has, moreover, to examine the muddy ochreous
 or hard  sinter-deposits  of the spring for arsenious acid,
 arsenic  acid, oxide  of antimony, oxide of copper, oxide
 of lead, oxide of  cobalt, oxide of nickel, and the oxides
 of other  heavy metals.  The greatest care  is required in this
 examination, to ascertain whether these oxides  come  really
 from the water, and  do  not  proceed from metal pipes, stop-
 cocks, &c.f  The absolute purity of the reagents employed
  * With regard to the  substances enclosed in  parentheses consult my treatise on
Quantitative Analysis, § 206, et seq.
  + Compare " Chemische Untersuchung der wichtigsten Mineralwasser des Herzog.
thums Nassau," von Professor Dr. Fresenius; I. Der Kochbrunnen zu Wiesbaden;
II  Die Mineralquellen zu Ems;  IIL die Quellen zu Schlangenbad; IV. die Quellen 
328              OPERATIONS AT THE SPRING.           [§ 215
 in these delicate investigations must also be ascertained with
 the greatest care.

                1.  Examination of the Water.
                 a. Operations at the Spring.
                              §  215.
   1.  Filter the water at the  spring, if  not perfectly clear,  245
 through Swedish filter paper,  and collect the filtrate in large
 bottles with glass stoppers.  The sediment remaining on the
 filter, which contains, besides the flocculent matter suspended
 in the water, also those  constituents which separate at once
 upon coming in contact with the air (hydrate of sesquioxide
 of iron, and compounds of sesquioxide of iron with phosphoric
 acid, silicic acid, arsenic  acid), is taken to the laboratory, to
 be examined afterwards according to the directions of § 21V.
   2. The presence of free carbonic acid is usually sufli-  246
 ciently visible to the eye.  However, to convince yourself by
 positive reactions, test the water with fresh-prepared solution
 of litmus, and with lime-water.  If carbonic acid is present,
 the former acquires a wine-red color;  the latter  produces
 turbidity, which must disappear  again upon addition  of the
 mineral water in excess.
   3. Free hydrosulphuric acid is detected with the greatest  247
 delicacy by the smell.  For this purpose half fill a bottle with
 the mineral water, close with the hand, shake, remove the
 hand,  and smell the  bottle.  In  this way distinct traces of
 hydrosulphuric  acid  are often  found, which would escape
 detection by reagents.   However,  if you wish  to  produce
 visible reactions,  fill a large white bottle with the water, add
 a few drops of solution of acetate of lead in solution of soda,
 place the bottle on a white surface, and look in at the top, to
 see whether the water acquires a brownish color or deposits a
blackish precipitate ;—or half fill  a large bottle with the water,
and close with a  cork to  which is attached a small  slip of
paper, previously steeped in solution of acetate of lead and
then moistened with a little  solution of carbonate of ammo-
nia ;  shake the bottle gently from time to time, and observe
whether the paper slip acquires a brownish tint in the course
of a few hours.  If the addition  of the solution of acetate of
lead to the water has imparted a brown color to  the fluid or
produced a  precipitate  in  it, whilst the  reaction  with the

ku Langenschwalbach; die Schwefelquelle zu Weilbach; die Mineralquelle zu Geil-
nau ; VII. die neue Natronquelle zu Weilbach ; published at Wiesbaden, by Kriedel
uud Niedner.   1850-1860. 
§ 216.]         ANALYSIS  OF MINERAL WATERS.           329

paper slip gives no result, this indicates that the water  con-
tains an alkaline sulphide, but no free hydrosulphuric acid.
  4.  Mix a wineglass-full of the water with some tannic acid,  248
another wineglass-full with some gallic  acid.   If the former
imparts a blue violet, the latter a red violet color to the water,
protoxide of iron  is present.   Instead  of  the two acids,
you may employ infusion of galls, which contains them both.
The coloration ensues only after some time, and increases from
above where the air  has access, downwards.

             b.  Operations in the Laboratory.
                            § 216.
  As it is always  desirable to obtain even in the qualitative
examination some information as to the quantitative compo-
sition of a mineral water, i. e. as to the  proportions in which
the several constituents are contained  in it, it is  advisable
to analyze  a  comparatively small portion for the  principal
constituents, and to ascertain, as far as  may  be practicable,
the relative proportions in which these constituents exist, and
thus to  determine the character of the  water; and  then  to
examine a large sample for substances  that  exist  in smaller
proportion, and finally a very large amount of the water or of
sinter, for those  elements which  are present only in minute
quantities.  For this purpose proceed as follows:—
   1. Examination for those constituents  of the water  219
which  are present in larger  quantities.
      a. Boil about 3lbs. of the clear water, or of the filtrate,
     brought from the spring, in  a glass flask for 1  hour,
     taking care, however, to add  from time to time some dis-
     tilled water, that the  quantity of liquid may remain un-
     diminished,  and thus  the  separation of  any  but those
     salts  be  prevented which  owe their solution to the pre-
     sence  and agency of carbonic acid.   Filter  after  an
     hour's ebullition, and  examine the precipitate  and the
     filtrate as directed § 213.
       b. Test for ammonia, silica, organic matters,  &c,
     as described  § 213.
   2. Examination for those fixed constituents of the  250
water  which are present in minute  quantities  only.—
Evaporate a large quantity (at least 20  lbs.)  of the water in
a silver or porcelain  dish to dryness ; conduct this operation
with the  most scrupulous cleanliness  in a place as free as
possible from dust.   If the water contains no carbonate of
an alkali, add pure carbonate  of  potassa to slight  predomi-
nance.   The process of evaporation may be conducted in the 
330           OPERATIONS IN THE LABORATORY.        [§ 216,
first place over a gas-lamp, but ultimately the sand-bath must
be employed.   Heat the dry mass to very faint redness ; if in
a silver dish, you may at once proceed to ignite it; but if you
have it in a porcelain dish,  first transfer it to a silver or pla-
tinum  vessel  before  proceeding  to ignition.  If the mass
turns black in this process, organic matters may be assumed
to be present.*
  Mix the residue thoroughly, that it may have  the same
composition throughout, and  then divide  it  into 3 portions,
one (c) amounting  to  about one-half, and  each of the other
two (a and b) to one-fourth.
       a.  Examination for iron, and phosphoric acid.
       Warm  the portion a  with some water, add perfectly 251
    pure  hydrochloric acid in moderate  excess, digest for
    some time at a temperature near the boiling point, filter
    through paper washed with hydrochloric acid and water,
    and test.
         a. A sample for iron, by means of sulphocyanide
       of  potassium.
         6. The remainder is examined for phosphoric acid
       with nitric solution of molybdate of ammonia (§ 145,
   .    10).
    b. Examination for fluorine.
       Heat the portion b with water, add chloride of calcium  252
    as long as a precipitate continues to form, let deposit;
    filter the  fluid from the precipitate, which consists chiefly
    of carbonate of lime and carbonate of magnesia.  After
    having washed and dried the precipitate,  ignite, then
    pour water over it in a  small dish,  add acetic acid in
    slight excess,  evaporate on the water-bath to dryness,
    heat  until all smell of acetic acid has disappeared, add
    water, heat again, filter the  solution  of the acetates of
    the alkaline earths, wash, dry or ignite the residue, and
     test it for fluorine as directed §  149, 5.
       c.  Examination for  the remaining constituents  253
    present in minute quantities.
       Boil the portion c  repeatedly  with water, filter, and
     wash the undissolved residue with boiling water.  You
     have now a residue (a), and a solution (8).
         a. The residue consists chiefly of carbonate of lime,

  * This inference is, however, correct only if  the water has been  effectually pro
tected from dust  during the process of evaporation ;  if this  has not been the case,
and you yet wish to ascertain beyond doubt whether organic matters are present,
evaporate a separate portion of the water in a retort.  If you find organic matter,
and wish to know whether it consists of crenic acid or of apocrenic acid, treat a
portion of the residue as directed § 217, 3. 
16.]         ANALYSIS  OF MINERAL WATERS.            331

   carbonate  of magnesia, silica,  and—in  the  case  of
   chalybeate springs—hydrate of  sesquioxide of iron.
   But it may contain also minute quantities of baryta,
   STRONTIA,  ALUMINA, and PROTOXIDE OF MANGANESE,
   and must  accordingly be  examined for these sub-
   stances.
     Put the residue  in a platinum or porcelain dish,
   pour water over it,  add hydrochloric acid to slightly
   acid reaction, then 4 or 5  drops of dilute sulphuric
   acid, evaporate to dryness, moisten with hydrochloric
   acid, then  add  water,  warm gently, filter, and wash
   the residue which is left undissolved.
       aa. Examination of the residue insoluble  in 254
     hydrochloric acid for  baryta and strontia.
       This residue will generally consist of silicic acid ;
     but  it may contain also  sulphates of  the  alkaline
     earths and carbon.  If there is much silicic acid pre-
     sent, remove  this in the first place, as far as practi-
     cable, by boiling with dilute solution of soda; filter,
     wash the residue, if any has been left, dry, incine-
     rate the filter in a platinum crucible, add some car-
     bonate   of  soda  and  potassa,  and, in  presence  of
     carbon,  some  nitrate of potassa, and ignite for some
     time.  If the residue contains but little silicic acid,
     the treatment with solution of soda may be omitted,
     and the  fusion with  carbonate of potassa and soda,
     &c, at once proceeded with.   Boil the fused mass
     with water, filter, wash thoroughly, dissolve the resi-
     due (which must have been left, if sulphates of  the
     alkaline earths were  present) on  the  filter in the
     least possible  quantity of dilute hydrochloric acid,
     add an equal volume of  spirit of wine, then some
     pure hydrofluosilicic acid, and  let the mixture stand
     12 hours.   If in the course or at the end of the 12
     hours  a precipitate makes its appearance, this de-
     notes the  presence  of baryta.   Filter, and warm
     the filtrate in a platinum  dish, adding from time to
     time some water,  until the spirit  of wine  is quite
     driven off.  Mix  the fluid now with saturated solu-
     tion of sulphate of lime.   If this produces a precipi-
     tate, whether after some time or after several hours'
     standing, this  precipitate consists of sulphate  of
     strontia.   To make  quite sure, examine it before
     the blowpipe  (see § 99, 1).
       The examination for baryta and strontia may be
     much more easily accomplished by help of the spec- 
332          EXAMINATION FOR NITRIC ACID,  ETC.       [§ 216,
         troscope.   For this purpose,  ignite what remains
         of the residue (free from  silica), strongly over a
         blast lamp, wash the ignited mass with a little water,
         evaporate the clear liquid with hydrochloric acid to
         dryness and test the residue as directed § 102.
           bb.  Examination of the  hydrochloric acid  255
         SOLUTION  FOR  PROTOXIDE  OF  MANGANESE  AND
         ALUMINA.
           Mix the solution in a flask with some pure chloride
         of ammonium, add ammonia until the fluid  is just
         turning alkaline, then some yellow sulphide of am-
         monium,  close the flask, which should be filled very
         nearly full, and let it stand for 24 hours in a  mode-
         rately warm place.  If a precipitate has formed at
         the end of that time, filter, dissolve the precipitate in
         hydrochloric  acid,  boil, add  solution  of potassa
         (§ 32, c) in excess, boil again, filter and test  the fil-
         trate for alumina with chloride of ammonium ;*  the
         residue with carbonate of soda before the blowpipe
         for MANGANESE.
         8. The alkaline solution  contains the  salts  of  the  256
      alkalies, and usually also magnesia and traces of lime.
      You have  to  examine  it now for nitric AciD,f  bo-
      racic acid, iodine,  bromine, and lithia.  Evapo-
      rate the fluid until highly concentrated, let it cool,  and
      place the dish in a slanting position, that  the small
      quantity of liquid may separate from the saline mass ;
      pour a few drops of the concentrated solution in a
      watch-glass, acidify very slightly with  hydrochloric
      acid, and test with turmeric  paper for boracic acid.
      Pour back into the dish  the  remainder  of the  liquid,
      of which you have just tested a few drops, evaporate,
      with stirring, to perfect  dryness, and divide the resi-
      duary powder into 2  portions, one (aa) of two-thirds,
      the  other (bb) of one-third.
           aa. Examine the  larger  portion  for  nitric  257
         ACID,  IODINE, AND BROMINE.
           Put the powder into a flask, pour pure spirit of

  * You are  not justified in regarding this substance as an ingredient of the water,
except in cases where  the process of evaporation has been conducted in a platinum
or silver dish, but not in a porcelain dish.
  \ The nitric acid originally present may have been destroyed by the ignition of
the residue in (250), if the latter contained organic matter.  If you have reason to
fear that such has been the case, and  you  have not already found nitric acid in
(249), examine a larger portion of non-ignited  residue for that acid,  according to
the directions of (2 57). 
§ 216.]         ANALYSIS OF MINERAL WATERS.            333

        wine of 90 per cent, over it, boil on the water bath,
        and filter hot; repeat the same operation a second
        and a third time.  Mix the alcoholic extract with a few
        drops of solution of potassa, distil the spirit of wine
        off to within a small quantity, and let cool. If minute
        crystals  separate, these may consist of nitrate of
        potassa ; pour off the fluid, wash the crystals with
        some spirit of wine, dissolve them in  a very little
        water, and test the solution for nitric acid, by means
        of  indigo, brucia,  or iodide  of potassium, starch-
        paste, and zinc  (§  162).  Evaporate the alcoholic
        solution  now to dryness.  If you have not yet found
        nitric acid, dissolve a small portion of the residue in
        a very little water, and examine the solution for that
        acid.  Treat the remainder of the  residue or,  if it
        has been unnecessary to search for nitric acid, the
        entire residue, three times with warm alcohol, filter,
        evaporate  the filtrate to dryness with addition  of a
        drop of potassa lye, dissolve the residue  in  a  very
        little water,  add some  starch-paste, acidify slightly
        with sulphuric acid, and test for iodine by adding
        some nitrite of potassa in solution, or  a drop  of
        solution  of hyponitric acid in sulphuric acid.  After
        having  carefully observed the  reactions,  test  the
        same fluid for bromine  with chloroform or bisul-
        phide of carbon and chlorine water in the manner
        described in  § 160.
           bb. Examine the smaller portion for lithia.
           Warm the smaller portion of the residue,  which,  258
        if lithia  is present, must contain that alkali as  car-
        bonate or phosphate, with water, add hydrochloric
        acid to distinctly acid reaction, evaporate nearly to
        dryness, and then mix with pure spirit of wine of 90
        per cent., which will separate the greater portion of
        the chloride  of sodium, and give all the lithia in the
        alcoholic solution.  Drive off the alcohol by  evapo-
        ration, and test the residue for lithia by means  of
        the spectroscope.  (§ 96, 3.)
           If no spectroscope be at hand dissolve the residue
        in  water mixed with a  few drops of hydrochloric
        acid, add a little sesquichloride of iron, then ammo-
        nia in slight  excess, and a small quantity of oxalate
        of ammonia, and  let the  mixture stand for some
        time ; then filter off the fluid, which is now entirely
        free from phosphoric acid  and lime; evaporate the
        nitrate to dryness, and gently  ignite the residue, 
334        EXAMINATION  OF THE SINTER-DEPOSIT.      [§217.

         until the salts of ammonia are expelled; treat the
         residue with  some  chlorine water (to remove the
         iodine and bromine) and a few drops of hydrochloric
         acid, and evaporate to dryness; add a  little water
         and (to remove  the  magnesia) some finely divided
         oxide of mercury,  evaporate to dryness, and gently
         ignite the residue, until the chloride of mercury is
         completely driven off; treat the residue  now with a
         mixture of absolute  alcohol and anhydrous ether,
         filter the solution obtained, concentrate  the filtrate
         by evaporation, and  set fire to the  alcohol.   If it
         burns with a  carmine flame, lithia is present.   By
         way of confirmation, convert the lithia  found into
         phosphate of lithia.  (§ 96, 3.)

  3. Examination for substances which are present in  259
extremely minute quantities.
  1. Evaporate 2 or 3  cwt. of the water in a large, perfectly
clean iron  kettle until the salts which are soluble in water
begin to separate.  In  case the water contains no carbonate
of soda, add previously to  the evaporation enough of this salt
to give the water an alkaline reaction.   Filter after the eva-
poration, wash the residue without uniting the washings  to
the  first filtrate and examine:—
      a. The  precipitate  according to the course beginning
    at (261).
      b. The  solution is  acidulated with hydrochloric acid,
    chloride of barium added  until all sulphuric  acid  is
    just thrown  down, filtered, evaporated to dryness, and
    the residue extracted  with alcohol of 90 per cent.   The
    alcoholic solution is tested according § 96, last paragraph,
    for caesia and rubidia.
  2. Test a sample  of the  original water for nitrous  actd  260
according to (24l).  Should hydrosulphuric acid be present
it must be removed by very cautious addition  of  sulphate of
silver (silver must on no account remain in the solution).


           2.  Examination of  the Sinter-Deposit.
                            § 217.
  1. Free the  ochreous or sinter-deposit from impurities, by  261
picking, sifting, elutriation,  &c,  and from the soluble  salts
adhering to it, by washing with water ; digest a large  quan-
tity (about 200 grammes)  of the  residue with  water and
hydrochloric acid (effervescence:  carbonic acid) until the 
§ 217.]         ANALYSIS  OF MINERAL WATERS.            335

Boluble part is  completely dissolved;  dilute,  cool, filter, and
wash the residue.
      a. Examination of  the filtrate.
        a. The larger share of the filtrate is heated nearly  262
      to boiling, and solution of pure hyposulphite of soda
      added until all the  iron  is reduced  to the  state of
      protochloride.   Carbonic acid  is now passed through
      the still heated liquid until all or nearly all sulphurous
      acid is expelled, then hydrosulphuric acid is  trans-
      mitted through it.   The solution being diluted if neces-
      sary, the liquid is let stand in a moderately  warm
      place until the  odor of hydrosulphuric acid becomes
      faint, and is then filtered  and washed.
        It is now  advantageous  to  displace the water by  263
      alcohol and to digest the precipitate  with  bisulphide
      of carbon until the larger portion of the  free sulphur
      is removed.   It is now gently warmed  with yellow
      sulphide  of ammonium,  filtered,  washed with water
      containing sulphide of ammonium, and the filtrate and
      wash waters  are  evaporated  to  dryness in a small
      porcelain capsule.   The residue is moistened with pure
      red fuming nitric acid, warmed until most of the acid
      is expelled, carbonate of soda  is added in excess and
      then nitrate  of soda, and the whole heated to fusion.
      The fused mass is  treated with cold water, filtered,
      the residue washed with dilute alcohol, and the aqueous
      solution  tested  for arsenic acid (l2l)  and (122);
      the residue for antimony, tin and  copper, by dis-
      solving it in dilute hydrochloric acid and treating one-
      half in a platinum vessel with  zinc (123) and adding
      to the other half ferrocyanide of potassium.
        If a residue has been left upon treating the precipi-  264
      tate produced by hydrosulphuric  acid with  sulphide
      of ammonium, boil it, together with the filter, with  a
      very little dilute nitric acid, filter, wash, and examine
      the contents of the filter, at first by pouring hydro-
      sulphuric acid over it, that  you may not overlook the
      possible  presence  of  sulphate  of  lead, and  test for
      baryta and strontia as directed (254).
        Mix the filtrate (the nitric acid solution) with some
      pure sulphuric acid,  evaporate on the water-bath  to
      dryness,  and  treat the residue with  water.  If this
      leaves an undissolved residue, the latter consists of sul-
      phate  of lead.  To make quite sure, filter, wash the
      residue treat it with hydrosulphuric acid water, and
      observe whether that reagent imparts a black color to 
336        EXAMINATION OF  THE  SINTER-DEPOSIT.      [§ 217.

      it.  Test the fluid  filtered from the sulphate of lead
      which  may have separated, a with ammonia, b with
      ferrocyanide of potassium, for  copper.
        Of the fluid  filtered from the precipitate produced 265
      by hydrosulphuric  acid,  examine in the first place  a
      portion, after having evaporated to dryness and treated
      the residue with hydrochloric acid and water, with
      nitric solution  of molybdate  of ammonia  for  phos-
      phoric  acid;  mix the remainder in  a  flask  with
      chloride of ammonium, ammonia, and yellow sulphide
      of ammonium,  close the flask, and let  it stand in  a
      moderately warm place until the fluid above the pre-
      cipitate looks no longer greenish,  but yellow;  filter,
      and  wash the  precipitate with  water to which some
      sulphide of ammonium has been added.  Dissolve the
      washed precipitate  in hydrochloric acid, and test for
      COBALT, NICKEL, IRON, MANGANESE,  ZINC, ALUMINA and
      silica  as directed (152) to (l60).  Examine now the
      fluid filtered from the precipitate produced by sulphide
      of ammonium, for lime and magnesia in the usual way.
        8. Mix a portion of the highly diluted hydrochloric
      acid solution with chloride of barium, and let the mix-
      ture stand  12 hours in a warm place.   The  formation
      of a white precipitate indicates the presence of sul-
      phuric  acid.
    b. Examination  of the residue.
      This consists usually of silicic acid, clay, and organic 266
    matters, but it may also contain  sulphate of baryta and
    sulphate of strontia.  Boil in the first place with solution
    of soda or potassa, to dissolve the silicic acid ; then fuse
    the residue with  carbonate of soda and potassa, and  a
    little nitrate of potassa.  Boil the mass with water, wash
    the residue, and then dissolve it in some hydrochloric acid,
    separate  any silica which may be  present, add to the
    hydrochloric  solution  ammonia, filter the fluid from the
    alumina, &c, which  may precipitate, evaporate the fil-
    trate to dryness, gently ignite the residue, redissolve  it
    in very little water, with addition of a  drop of hydro-
    chloric acid, and  test for baryta  and  strontia  as
    directed (254).
  2.  As regards the examination for fluorine, the best way  £67
is to take for this purpose a separate portion of the ochreous
or sinter-deposit.   Ignite  (which operation will  also  reveal
the presence of organic matters), stir with water, add acetic
acid  to  acid reaction, evaporate until the acetic acid is com-
pletely expelled, and proceed as described in (25&). 
§ 218.]
ANALYSIS OF SOILS.
  3.  Boil the ochreous  or sinter-deposit  for  a considerable
time with concentrated solution of potassa or soda, and filter.
      a. Acidify a portion of the filtrate with acetic acid,
     add ammonia, let the mixture stand  12 hours, and then
     filter the fluid  from the precipitate  of alumina and hy-
     drated silicic acid, which usually forms; again add acetic
     acid to acid reaction, and then a solution of neutral acetate
     of copper.  If a brownish precipitate is formed, this con-
     sists  of  apocrenate of copper.   Mix the fluid filtered
     from the precipitate with carbonate  of  ammonia, until
     the  green color has  changed to blue, and warm. If  a
     bluish-green  precipitate is produced, this  consists of
     crenate of copper.
      b. If you have detected arsenic, use the remainder of
     the alkaline fluid to ascertain whether the arsenic existed
     in the sinter as arsenious acid or as arsenic acid. Com-
     pare § 137, 9.

                    rV. Analysis of  Soils.
                             §  218.
   Soils must  necessarily contain all the constituents which are
 found in the  plants growing upon them,  with the  exception
 of those supplied by the  atmosphere  and the rain.  When
 we find, therefore, a plant the constituent elements of which
 are known, growing  in a certain soil,  the mere  fact of its
 growing there gives us some insight into  the composition of
 that soil, and may accordingly  save  us, to some extent, the
 trouble of a  qualitative analysis.
   Viewed in this light, it would appear quite  superfluous to
 make a qualitative analysis of soils still capable of producing
 plants; for it is well known that the ashes of plants contain
 almost invariably  the same constituents, and  the  differences
 between them are caused principally by differences in  the
 relative proportions in which the several constituents are pre-
 sent.  But if, in the qualitative analysis  of a  soil, regard  is
 had also—in so far as may be done by a simple estimation—
 to the quantities and proportions of the  several constituent
 ingredients,  and to the state and condition in  which they are
 found to be  present in the soil, an analysis  of the kind;  if
 combined with an examination  of the  physical properties of
 the soil, and a mechanical separation of its component parts,*
   * With regard to the mechanical separation of the component' parts of a soil, and
 the examination of its physical properties and chemical condition, compare Ir.
 Schuhe's paper,  " Anleitung zur Untersuchung der Ackererden auf ihre wichtigsten
 physikalischen Eigenschaften uud Bestandtheile."—Journal f. prakt. Chemie, Vol
 «)P.24L                       22 
338       EXAMINATION OF  THE AQUEOUS EXTRACT.    [§ 219.

may give most useful results, enabling the analyst  to judge
sufficiently of  the condition  of the  soil, to supersede the
necessity of  a  quantitative analysis,  which would  require
much time, and is a far more difficult task.
  As plants can only absorb substances in a state of solution,
it is a matter of especial importance, in the qualitative analy-
sis  of a soil, to know which  are the  constituents that are
soluble in water ;*  which those that require an acid for their
solution (in nature principally carbonic  acid); and, finally,
which those that are  neither soluble in water nor  in acids,
and are not, accordingly, in a position for the time being  to
afford nutriment to the plant.   With regard to the  insoluble
substances, another interesting question to answer is, whether
they suffer disintegration readily, or  slowly and with diffi-
culty, or whether they altogether resist the action of  disinte-
grating agencies; and also what are the products which they
yield upon their disintegration.!
  In the analysis of soils, the constituents soluble in water,
those soluble in acids, and the insoluble constituents must be
examined separately.  The  examination of the organic por-
tion also demands a separate process.
  The analysis is therefore properly divided into  the follow-
ing four parts:

   1. Preparation  and Examination  of the Aqueous  Extract.
                               § 219.
  About two pounds (1000  grammes) of the  air-dried soil are  269
used for the preparation  of  the aqueous extract.   To  prepare
this extract quite clear is a matter of  some difficulty; in fol-
lowing the usual course,  viz., digesting or boiling  the earth
with water, and then filtering, the fine particles  of clay are
speedily found to impede the operation, by choking up the
pores of the  filter; they  also  almost  invariably render the
  * Since the discovery that the soil, like porous charcoal, possesses the power of
removing dissolved matters from solutions, the formerly received notion  that  those
matters which are soluble in water, or in water containing carbonic acid, are free to
move in the soil has been necessarily modified.   We must conclude that the  water
extract of a soil does not accurately represent  what is present  in  the soil in a form
accessible to plants.  Certainly it cannot contain these  substances in the proportion
in which they exist in the soil, because the absorptive power  of the soil is exerted
more forcibly towards some substances  than towards others.  Although for these
reasons  the analysis of the aqueous solution  of a soil can no longer be valued as
formerly, yet it is often of interest  to know what substances really are dissolved by
water from an earth, and I have therefore retained this chapter.
  \ For more ample information  on this subject I refer the reader to Fresenius'
" Chemie fur Landwirthe, Forstmivnner und Cameralisten;" published at Brunswick
by  F. Vieweg & Son, 1847, p. 485. 
§ 219.]     ANALYSIS  OF SOILS—AQUEOUS  EXTRACT.        339

filtrate turbid, at least the portion which passes through first.
I have found the following method the most practical.*5 Close
the neck of several middle-sized funnels with small filters of
coarse blotting paper, moisten the paper, press it close to the
Bides of the funnels, and then introduce the air-dried soil, in
small lumps ranging from the size of a pea to that of a wal-
nut, but not pulverized  or even crushed; fill the funnels with
the soil to the extent  of about two-thirds.  Pour distilled
water into them,  in sufficient quantity to  cover the  soil; if
the first portion of the  filtrate is turbid, pour it back  on the
filter.  Let the operation proceed  quietly.  When the first
quantity^ of the fluid has passed, pour on more  and continue
the lixiviation until the  weight of the filtrate is two or three
times as great as that of the soil employed.   Unite the  several
filtrates and set  aside  a portion  of  the  washed earth for
further examination.
      a. Concentrate two-thirds of the aqueous solution by 270
    cautiously  evaporating in a porcelain dish, filter off a
    portion, and test  its reaction;  put aside a portion  of the
    filtrate for the subsequent examination for  organic mat-
    ters, according to the directions  of (2§0).  Warm the
    remainder, and add nitric  acid.   Evolution of gas  indi-
    cates  the presence  of an  alkaline carbonate.   Then
    test with nitrate of silver for  chlorine,   b. Transfer
    the remainder of the concentrated fluid, together with
    the  precipitate which usually  forms  in  the  process of
    concentration, to  a  small porcelain, or, wdiich  is  prefer-
    able, a small platinum  dish, evaporate to dryness, and
    cautiously heat the  brownish residue over the lamp until
    complete destruction of the organic matter is effected.
    In  presence of nitrates this operation is attended with
    deflagration, which  is more or less violent according to
    the greater or smaller proportion in which these salts are
    present,  c. Test a  small portion  of the  gently ignited
    residue with carbonate of soda before  the blowpipe for
    manganese,  d. Warm  the remainder with water, add
    some hydrochloric acid (effervescence indicates the  pre-
    sence  of carbonic  acid), evaporate to dryness, heat a
    little more strongly, to effect the complete separation of
    the  silicic  acid,  moisten with hydrochloric acid,  add
    water, warm, and filter.  The washed  residue generally
    contains some carbon, and also a little clay—if the aque-
  * Recommended by Fr. Schulze "Anleitung zur Untersuchung der Ackererden auf
ihre wichtigsten physikalischen Eigenschaften und Bestandtheile."—Journ. f. prakt.
Chemie, vol. 47, p. 241. 
 340         EXAMINATION OF THE ACID EXTRACT.      [§ 220

     ous extract was not perfectly clear—and  lastly silicic
     acid.  To detect the latter, make a hole in the  point of
     the filter, rinse the residue through, boil with solution of
     carbonate of soda, filter, saturate with hydrochloric acid,
     evaporate to dryness, and treat  the residue with water,
     which will leave the silicic acid undissolved.
       e.  Test  a  small portion of the hydrochloric acid solu- 271
     tion with chloride of barium for sulphuric acid ; another
     portion with nitric solution of molybdate of ammonia for
     phosphoric acid ; a third portion with sulphocyanide of
     potassium for sesquioxide of iron.  Add to the remain-
     der a few  drops of sesquichloride of iron (to remove the
     phosphoric acid), then ammonia cautiously until the fluid
     is  slightly alkaline, warm a little, filter, throw down the
     lime from the  filtrate by means of  oxalate  of  ammonia,
     and proceed for the detection of magnesia, potassa, and
     soda, in the  usual way, strictly  according to the direc-
     tions of § 199.
      /. Alumina  is not likely to be found in the aqueous  272
     extract.  (Fr.  Schulze never  found any.)  However, if
     you  wish  to test for it, boil the  ammonia precipitate
     obtained in (271) with pure solution of soda or potassa,
     filter, and test  the filtrate with chloride of ammonium.
      g.  If you  have  detected iron, test a portion of the  273
     remaining third of the aqueous extract with ferricyanide
     of potassium, another with sulphocyanide of potassium,
     both after previous addition of some hydrochloric acid :
     this will indicate the degree  of oxidation in which the
     iron is present.   Mix the remainder of  the aqueous
     extract with a little  sulphuric acid,  evaporate  on the
     water-bath nearly to dryness, and  test the residue for
     ammonia, by adding hydrate of lime.


     2.  Preparation and Examination of the Acid Extract.
                             § 220.
  1. Heat about 50 grammes of the soil from which the part 274
soluble in water has been removed as far as practicable,* with
moderately strong hydrochloric acid (effervescence  indicates
carbonic acid) for several hours on the water-bath, filter, and
make the following experiments  with the filtrate,  which,
owing to the presence  of sesquichloride  of iron, has in most
cases a yellow color:—
  Test a small portion of it with sulphocyanide of potassium 275
* Complete lixiviation is generally impracticable. 
§§ 221, 222.]         ANALYSIS  OF SOIL.
341
for sesquioxide of iron, another with ferrocyanide of potas-
sium for PROTOXIDE OF IRON.
  2.  Test a small portion with chloride of barium for sulphu-
ric acid, another with molybdate of ammonia for phosphoric
acid.
  3.  Mix  a larger portion  of the  filtrate with ammonia to  276
neutralize  the  free  acid, then  with yellowish sulphide  of
ammonium ; and let the mixture stand in a warm place until
the fluid looks  yellow; then filter, and test the filtrate in the
usual way for lime, magnesia, potassa, and soda.
  4.  Dissolve the precipitate obtained in 3,  in hydrochloric  277
acid, evaporate the solution to  dryness, moisten the residue
with hydrochloric  acid, add water, warm, filter, and examine
the filtrate according to the  directions  of (150),  for iron,
manganese, alumina, and, if necessary,  also for lime and
magnesia, which may have been thrown down by the  sul-
phide of ammonium, in combination with phosphoric acid.
  5.  The  separated silicic acid  obtained  in 4  is usually
colored by organic matter.  It must, therefore, be ignited to
obtain it pure.
  6.  If it is a  matter of interest to ascertain  whether the  278
hydrochloric  acid extract contains arsenic acid, oxide of
copper, &c, treat the remainder  of the solution first with
hyposulphite  of soda,  then  with  hydrosulphuric  acid,  as
directed in (262) to (264).
  7.  Should you wish to look for fluorine, ignite  a  fresh
portion of the earth, and then proceed according to the direc-
tions of (230).
   3.  Examination  of the Inorganic Constituents insoluble in
                       Water and Acids.
                             § 221.
  The operation of heating the lixiviated soil with hydro-  279
chloric acid (274) leaves still the greater portion of it undis-
solved. If you wish to subject  this undissolved residue  to  a
chemical examination,  wash, dry,  and  sift, to  separate the
large and small stones from  the clay and sand; moreover,
separate the two latter from each other by elutriation.   Sub-
ject the several portions to the analytical process given for
the silicates (§  208).
   4.  Examination of the  Organic Constituents of the Soil.*
                             §  222.
  The organic  constituents of the  soil,  which exercise so
great an influence upon its fertility, both by their physical
  * Compare Fresenius' "Chemiefur Landwirthe. Forstmilnner und Cameralisten;"
published at Brunswick, by F. Vieweg and Son, 1847, §§ 282-285. 
342       EXAMINATION OF ORGANIC CONSTITUENTS.    [§ 222,

and chemical action, are partly  portions of plants  in which
the structure  may  still be recognised (fragments  of straw,
roots, seeds  of weeds, &c), partly products of vegetable
decomposition, which are usually called by the general name
of humus, but differ in their constituent elements and proper-
ties, according to whether they result from the  decay of the
nitrogenous or non-nitrogenous parts of plants—whether alka-
lies or alkaline earths have or have not had a share in their
formation—whether they are in  the  incipient or in a more
advanced stage of decomposition.  To separate these several
component parts  of humus would be an exceedingly difficult
task, which, moreover, would hardly repay the trouble;  the
following operations are amply  sufficient  to  answer all the
purposes of a qualitative analysis of  the organic constituents
of a soil.

  a.  Examination  of the Organic Substances soluble in Water.
  Evaporate the portion of the  filtrate of (270), which  has 280
been put aside for the purpose of examining the organic con-
stituents, on the water-bath to perfect dryness, and  treat the
residue  with water.  The ulmic,  humic, and geic acids, which
were in the solution in combination with bases, remain undis-
solved,  whilst crenic acid and apocrenic acid are dissolved in
combination with ammonia;  for the manner of detecting the
latter acids, see (268).

           b.  Treatment with an Alkaline Carbonate.
  Dry a portion of  the lixiviated soil, and  sift to separate the 281
fragments  of straw, roots,  &c,  together with  the  small
stones,  from the finer  parts; digest the  latter for several
hours, at a temperature of  176°—194° F., with solution of
carbonate of soda,  and filter.  Mix the filtrate  with  hydro-
chloric acid to acid  reaction.   If brown flakes separate, these
proceed from ulmic acid,  humic  acid, or geic acid.   The
larger the  quantity of ulmic acid present the lighter, the
larger that of humic acid or  geic acid, the darker the brown
color of the flakes.

               c. Treatment with Caustic Alkali.
  Wash the soil boiled with  solution of carbonate of soda (b)  2§2
with  water,  boil several hours with  solution of potassa,
replacing the water in proportion as it evaporates,  dilute, fil-
ter and wash.  Treat the brown fluid as in b.  The ulmic and
humic acids which separate now, are new products resulting
from the action of boiling solution of potassa upon the ulmine
and humine originally present. 
 §§ 223, 224.]     DESTRUCTION OF ORGANIC  MATTERS.      343

    V. Detection of Inorganic Substances in Presence
                   of Organic Substances.
                             § 223.
   The impediments which the presence of coloring, slimy, and
 other organic substances throws in the way of  the detection
 of inorganic bodies, and that the latter can often be effected
 only after the total destruction of the organic admixture, will
 be readily conceived, if we reflect that in dark-colored fluids
 changes of color or the formation of precipitates escape the
 eye, that slimy fluids cannot  be filtered, &c.  Now, as these
 difficulties are very often met with in  the analysis of medi-
 cinal  substances, and more  especially in the  detection  of
 inorganic poisons in articles of food or in the contents of the
 stomach, and, lastly,  also in  the examination of plants and
 animals, or  parts of  them, for their inorganic constituents,
 I will here  point out the processes best adapted to lead to
 the attainment of  the object in view, both in the  general
 way and in special cases.

 1. General Rules for the Detection of Inorganic Substances in Pre-
    sence of Organic Matters, which by their  Color, Consistence,
    t&c,  impede  the Application of the Reagents, or  obscure the
    Reactions produced.
                            § 224.
  We confine  ourselves here, of course, to the description  of
 the most generally applicable methods, leaving the  adapta-
tion of the modifications which circumstances may require  in
special cases, to the discretion of the analyst.
  1.  The  substance under  examination  dissolves in  283
water, but the  solution is dark colored or of slimy
consistence.
      a.  Boil a portion  of the solution  with  hydrochloric
    acid, and  gradually  add chlorate  of potassa, until the
    mixture is decolorized and perfectly fluid;  heat until
    it no longer  exhales the odor of  chlorine, then dilute
    with water, and filter.  Examine the filtrate in the usual
    way, commencing with § 193.  Compare also § 228.
      b. Boil another portion of the solution for some time
    with nitric acid,  filter, and test the filtrate for silver,
    potassa, and hydrochloric  acid.  If the nitric acid
    succeeds in effecting the ready and complete destruction
    of the  coloring and  slimy matters, &c, this method  is
    often altogether preferable to all others.
      c. Alumina  and sesquioxide  of  chromium  might
    escape detection  by this  method, because ammonia and 
 344         DESTRUCTION OF ORGANIC MATTERS.       [§ 224.

     sulphide of  ammonium  fail  to  precipitate these oxides
     from fluids  containing non-volatile organic substances.
     Should you have reason to suspect the presence of these
     oxides, mix  a  third portion  of the substance with car-
     bonate of soda and chlorate  of  potassa, and project the
     mixture, in small portions at a time, into an ignited cru-
     cible.   After cooling, the fused  mass is  treated  with
     water, the solution is tested for chromic aeid and alumina,
     and the residue for alumina as directed  § 106.   The
     alumina is  now found by acidifying with nitric acid, and
     then adding ammonia; the chromium—as alkaline chro-
     mate—in the filtrate, by means  of acetate of lead, after
     addition of acetic acid.
  2. Boiling water fails to dissolve the substance, or  284
effects only  partial  solution ;  the  fluid admits of
filtration.
  Filter, and treat the filtrate either as directed § 192, or,
should it require decolorization, according to  the directions
of (283).   The residue may be of various kinds.
      a. It is fatty.  Remove the fatty matters by means of
    ether, and should a residue be left, treat this as directed
    § 1V8.
      b. It is  resinous.   Use alcohol instead of ether,  or
    apply both liquids successively.
      c. It is of a different nature, e.g., woody fibre, &c.
        a. Dry, and ignite a portion of the dried residue in
      a porcelain or platinum vessel,  until total or partial
      incineration  is effected; boil  the residue with  nitric
      acid and water, and  examine the solution as directed
      (109); if a residue has been left, treat this according
      to the directions of § 206.
        6.  Examine another portion  for the  heavy metals
      and  for  acids in the manner directed in (283) and
      (284) ; since in a, besides the compounds of mercury
      which may be present, arsenic, cadmium, zinc, &c,
      may volatilize.
        y.  Test the remainder for ammonia, by triturating it
      together with hydrate of lime.
  3. The substance does not admit of filtration or any 285
other means of separating the dissolved from the un-
dissolved  part.
  Treat the substance  in the same manner as the residue in
(284).   As regards the charred mass (284) c.  a, it is often
desirable to boil the mass, carbonized  at a gentle heat, with
water, filter, examine the filtrate,  wash the residue, incinerate
it, and examine the ash. 
 § 225.]        DETECTION OF INORGANIC POISONS.          345

     2.  Detection of Inorganic Poisons in Articles of Food,
          in Dead Bodies, dtc, in Chemico-legal Cases*
                              § 225.
  The chemist is sometimes called upon to examine an article  286
 of food, the contents of the  stomach of an individual, a dead
 body, <fec, with a view to detect the presence of some poison,
 and thus to establish the fact of a wilful or accidental poison-
 ing ; but it is  more frequently the case that the question put
 to him is of a less general nature, and that he is called upon
 to determine whether a certain  substance placed before him
 contains a metallic poison ;  or, more pointedly still, whether
 it contains arsenic, or hydrocyanic acid, or some other par-
 ticular poison—as it may be that the symptoms point clearly
 in the direction of that poison, or«that the examining magis-
 trate has, or believes he has, some  other reason to put this
 question.
  It is obvious that the task of the chemist will be the easier,
 the  more special  and pointed the  question which  is put  to
 him.  However, the analyst  will always act most wisely, even
 in cases where he is simply  requested to state whether a cer-
 tain poison, e.g., arsenic, is present or  not, if he adopts a
 course of proceeding which will not only permit the detection
 of the one poison specially named, the presence of which may
 be suspected on insufficient grounds, but will moreover inform
 him as to the presence or absence of other similar poisons.
  But we must not go too far in this direction either; if we
 were to attempt to devise a method that  should embrace all
 poisons, we  might unquestionably succeed in elaborating such
 a method at the writing-desk ; but practical experience would
 but too speedily convince us that the intricate  complexity in-
 separable from such  a course,  must necessarily  impede the
 easy  execution of  the process, and impair the certainty  of
 the results, to such an extent indeed, that the drawbacks
 would be greater than the advantages derivable from it.
  Moreover, the attendant  circumstances permit usually  at
 least a tolerably safe inference as to the group to which the
 poison belongs.  Acting on  these views, I give here —
  1. A method which  ensures the  detection of the minutest
traces of arsenic, allows of its quantitative determination, and
permits at the same time the detection of all other metallic
poisons.
  *  Compare: a. F-esenius, " die Stellung des Chemikers bei gerichtlich chemischen
Untersuchungen," &c.  Annal. der Chemie und Pharm. 49, 275); and b. Freseniu*
and v Bubo's " Abhandlung uber ein neuea, unter alien Urastanden sicheres Verfahreu
zur Ausmittelung und quantitativen Bestimmung des Arsens bei Ve^^ngst-allen."
—Annal der Chemie und Pharmacie, 49, 287. 
346          DETECTION OF INORGANIC  POISONS.       [§ 226,

  2. A method to  effect the detection of hydrocyanic acid,
which leaves the substance still fit to be examined both for
metallic poisons and for vegeto-alkalies.
  3. A method to effect the detection of phosphorus, which
does not interfere with the examination for other poisons.
  This section  does not, therefore, profess to supply a com-
plete guide in every possible case or contingency of chemico-
legal investigations.   But the  instructions given in  it are the
tried and proved results of my own practice and experience.
Moreover, they will be found sufficient in most cases, the more
so as I shall append to the Section on the vegeto-alkalies, the
description of a process by which  the detection of these latter
poisons in criminal cases may be effected.

I. Method for  the Detection of  Arsenic (with due  Re-
       gard TO THE  POSSIBLE PRESENCE OF OTHER METALLIC
       Poisons).
                         § 226.
  Of  all metallic poisons arsenic is the most dangerous, and 287
at the same time the one most frequently used, more particu-
larly for the wilful poisoning of others.  And again, among
the  compounds  of arsenic, arsenious acid (white arsenic)
occupies  the  first place, because—(1) It kills even in small
doses; (2) It does not betray itself,  or at least very slightly,
by the taste; and (3) It is but too readily procurable.
  As  arsenious acid dissolves in  water only sparingly and—
on account of the difficulty with  which moisture adheres to
it—very slowly, the greater portion of the quantity swallowed
exists usually in the body still in  the undissolved  state; as,
moreover, the smallest grains  of  it may be readily detected
by means of an exceedingly simple  experiment; and lastly,
as—no matter what opinion may be entertained about the
normal presence of arsenic  in the bones, &c.—this much is
certain, that at all events arsenious acid in grains or powder
is never normally present in  the body, the particular care and
efforts of the analyst ought always to be directed to  the
detection of the arsenious acid in substance—and  this  end
may indeed usually be attained.

   A. Method for the Detection  of undissolved Arsenious
                           Acid.
  1. If you have to examine some article of food, substances 288
rejected from the stomach, or some other matter of the kind,
mix the whole  as  uniformly as may be  practicable, reserve
one-third for unforeseen  contingencies,  and mix  the other 
§ 227.]      DETECTION OF  ARSENIC BY  DIALYSIS.         347

two-thirds in a  porcelain dish with  distilled water, with a
stirring rod; let the mixture stand a little, and then pour off
the fluid, together with the lighter suspended particles, into
another porcelain dish.  Repeat this  latter operation several
times, if possible,  with the same fluid, pouring it from the
second dish back into the first, &c.   Finally, wash once more
with pure water, remove the  fluid, as far as practicable, and
try whether you can find in the dish small,  white, hard grains
which feel gritty and grate under the glass rod.   If not, pro-
ceed as directed § 227 or § 228.   But if so, put the grains,
or part of them, on  blotting-paper, removing  them from the
dish with the  aid of pincers, when dry weigh them and try
the deportment of one or several grains  upon heating in a
glass tube, and of some other grains upon ignition with a
splinter of charcoal (compare §135,2, and 11).  If you obtain
in the former experiment  a white crystalline sublimate, in
the latter a lustrous arsenical mirror, the  fact is clearly de-
monstrated that the  grains selected and examined consisted
really of arsenious acid.  If you wish to determine the quan-
tity of the poison, unite the contents of both dishes,  and pro-
ceed as directed § 227, or § 228.
   2. If a stomach is submitted to you for analysis, empty the
contents into a porcelain dish, turn the stomach inside out, and
(a), search the inside coat for small, white, hard, sandy grains.
The spots occupied by such grains  are often reddened; they
are also frequently found firmly imbedded  in  the membrane.
(b) Mix the contents in the  dish  uniformly, put aside one-
third for unforeseen contingencies,  and  treat  the other two-
thirds as in 1.   The same  course  is  pursued also with the
intestines.   In other parts of the body—with the exception
perhaps  of the pharynx and oesophagus—arsenious acid can-
not be  found in grains, if the poison  has been introduced
through the mouth.  If you  have  found grains of the kind
described, examine  them as  directed in  1;  if not, proceed
according to the instructions of §227 or §228.

B. Process for detecting  Compounds  of Arsenic  and of
     other Metals, which are  Soluble in  Water, by means of
     Dialysis.
         *                   § 227.
   If in method A. no arsenious  acid, in the solid state, has  289
been found and the operator proceeds directly to the process
described in § 228, in which the organic matters are destroyed
by chlorate  of potassa and hydrochloric acid,  he must remain
ignorant  of the condition in which any arsenic that may be
found  exists  for  the  solution will contain  arsenic acid no 
348           DETECTION OF  INORGANIC POISONS.        [§ 227

matter what may  have been the  compound originally pre-
sent.   Any compound  of  arsenic or of other metals that is
soluble in water, may, however, be detected by a dialytic*
experiment.
  For this purpose the dialyser shown in Fig. 34, may be
employed. A hoop of wood, or gutta-percha, or of glass (cut
from  a broken jar), of 2 or more inches in depth, and 8 to 10
inches in diameter, has a  wetted  disk of  parchment-paper
(which should exceed the hoops in diameter by 3 or 4 inches),
rather loosely secured to it by thread or a ring of elastic rub-
ber.  The parchment-paper must not be porous.   Its sound-
ness will be ascertained by sponging the  upper surface  with
water, and then observing that no wet  spots show themselves
on the opposite side.  Defects  may be  remedied by applying
liquid albumin, and then coagulating the same by heat.  When
the dialyser is ready, the  mass to be examined (residue and
liquid of § 226, A), after  the addition of two-thirds  of the
stomach, intestines, &c, cut into  small pieces, if these  are
under investigation, and allowing the whole to digest  for 24

  * Dialysis, which is a late discovery  of  Graham's (Phil.  Mag.  (4) xxiii.,  and
Ann. Ch. u.  Ph. cxxi. 63), is founded on the  different relation of substances in
aqueous solution towards moist membranes.  One class of bodies,  the crystalloids,
rapidly penetrate permeable membranes; the other class, the colloids, are compara-
tively destitute of this  power.  The first class  comprises all crystallizable bodies.
The second class includes the uncrystallizable substances, such as glue, gum, dextrin,
caramel, tannin, albumin, so-called extractive  matters,  hydrated silica, &c.   The
membrane used for dialysis must consist of a  colloidal substance,  e.g., bladder, or
best of all, parchment paper.  It  is placed  in contact with pure water ou one side.
The action, Graham explains by supposing that  crystalloids attract and take up the
water which exists in the moist  colloid membrane, and thus acquire a medium for
diffusion, whereas the  colloids are incapable of separating water from the mem-
brane, and therefore cannot penetrate it 
§ 228.]             DETECTION OF  ARSENIC.                 349
hours at a temperature of about 90° Fah., is brought into the
dialyser so as not to fill it to more than the depth of \ an inch,
and  the whole  is then floated or supported on the  surface
of pure water,  contained in  a larger vessel, the amount of
which should be about 4 times that of the liquid in the dialyser.
When 24 hours have elapsed, one-half to three-fourths of the
crystalloids that were placed in the dialyser have passed into
the  outer  vessel  whose  contents  usually  appear  colorless.
This diffusate is now concentrated  in the water bath, acidu-
lated with hydrochloric acid, and finally treated with hydro-
sulphuric acid and further examined as  directed (291).  In
case a soluble compound of  arsenic  or  of any  other metal
was present, the  corresponding  sulphide is thus procured in
a state  of almost entire purity.  By continuing the dialysis—
placing under  the dialyser fresh portions  of water—all the
crystalloid substances may be  ultimately obtained in nearly
a pure  state.   Afterwards, the residue may be examined for
insoluble metallic compounds according to § 228.
 C. Method for the Detection of Arsenic in whatever Form of
   Combination it may exist, which allows also  a Quantita-
   tive Determination of that  Poison, and permits  at  the
   same time the  Detection  of other Metallic Poisons which
   may be present.*
                              § 228.
   If you have found no arsenious acid by the method  de-
 scribed in A, nor any soluble compound of arsenic by dialysis,
 evaporate the  mass in the porcelain  dish, which  has been
 diluted by washing with water  (see A, 1), on the water-bath,
 to a pasty consistence.   If you have  to  analyze a stomach,
 intestinal tube, &c, cut this into pieces, and add two-thirds
 to the mass in  the dish, in case this has not been done already
 in the dialysis.
   In examining other parts of the body (the lungs, liver, &c.),
 cut them also into pieces, and use two-thirds for the analysis.
 The process is  divided as follows :f

  * This method is essentially the same as that which I have elaborated and pub-
 lished in 1844, jointly with L. v. Babo; compare " Annal. der Chemie und Pharma-
 cie," Bd. 49, p. 308.   I have since that  time had frequent occasion to  apply it; I
 have also had it tried  by others, under  my own inspection, and / have invariably
 found it to answer the purpose perfectly.
  I It is hardly needful  to observe that in such extremely delicate experiments the
vessels and reagents used in the process must be perfectly free from arsenic, from
heavy metals in general,  and indeed from every impurity. 
350         DETECTION OF INORGANIC POTFONS.        [§ 229

                1. Decolorization and Solution.
  Add to the matters in the porcelain dish, whose quantity 290
e. g., may equal 4 to 8 ounces,  an amount of pure hydro-
chloric  acid about  equal to,  or somewhat  exceeding the
weight of the dry substances present, and sufficient water to
give to the entire mass the consistence of a thin paste.  In no
case should the amount of hydrochloric acid exceed one-third
that of the  liquid  employed.  Heat  the  dish now on the
water-bath,  adding every five minutes about two  grammes
(half a drachm) of chlorate of  potassa to the hot fluid, with
stirring, and continue the same operation until the contents
of the dish show a light-yellow color  and a perfectly homo-
geneous appearance, and are quite fluid.  The water which
is lost by evaporation, should be renewed from time to time.
When this point is attained, add again a portion of chlorate
of potassa, and then remove the dish from the water-bath.
When the contents are quite cold, transfer them  cautiously
to a linen  strainer or  to  a white  filter,  according to the
greater or less quantity of substance; allow the whole of the
fluid to pass through, and put the filtrate aside.  Wash the
residue well with hot water, and dry it;  then mark it I., and
reserve for further examination, according to the instructions
of (303).  Evaporate the  washings  on the  water-bath  to
about 3 or 4 oz. (about  100 grm.), add this, together with
any precipitate that may have formed therein, to the princi-
pal filtrate, and then heat the whole in the water-bath, replac-
ing the water that evaporates, until the odor of chlorine has
entirely or nearly vanished.

2. Treatment of  the Solution with  Hydrosulphuric Acid 291
  (Separation of the Arsenic  as Tersulphide,  and, respec-
  tively, of  all the Metals of Groups V. and  VI. in form of
  Sulphides.)
  The fluid obtained in 1, which amounts to about three or
four times the quantity of hydrochloric acid used, is brought
into a flask,  heated to about 158° Fah., and a slow stream of
washed hydrosulphuric acid gas is transmitted through it for
about 12 hours, and then, the gas being still passed into it, it
is allowed to cool.   Now rinse  the delivery pipe with  some
ammonia, add the  ammoniated  solution  thus  obtained, after
acidulating it, to the principal fluid, cover the  beaker lightly
with unsized paper, and put it in a moderately  warm place
(about 86° F.), until the  odor of hydrosulphuric  acid has
nearly disappeared.  Collect the precipitate obtained in this
manner on a moderately sized filter, and wash, until the wash- 
  5 228.]     PURIFICATION OF THE HS  PRECIPITATE.         351

  ings are quite free from  chlorine.   Concentrate the filtrate
  and washings somewhat, mix the fluid in a suitably sized flask
  with ammonia to alkaline reaction, then with  sulphide  of
  ammonium, closely cork the flask, which must now be nearly
  full, and reserve for  further  examination according to the
  instructions of (307).

     3. Purification  of the Precipitate produced by Hydro-  292
                        sulphuric Acid.
   Thoroughly dry the precipitate obtained  in  2—which,
  besides organic matters and free  sulphur, must  contain,  in
  form of tersulphide, the whole of the arsenic present in the
  analyzed substance, as well as, in form of sulphides, all the
  metals of Groups V. and VI.  which may happen to  be  pre-
  sent—together  with  the  filter, in   a small  porcelain  dish,
  heated on the water-bath; add pure fuming nitric acid  (per-
  fectly free from chlorine), drop by drop, until the  mass  is
  completely moistened, and then evaporate on the water-bath
  to dryness.  Moisten the residue uniformly all over with pure
  hydrated sulphuric acid, previously warmed; then heat for
 two or three hours on the water-bath, and finally on  the air-
 Band- or oil-bath at a somewhat higher, though  still moderate
 temperature (338° F.), until the charred mass becomes friable,
 and a small sample of it—to  be returned afterwards to the
 mass—when mixed with water and  then allowed to  subside,
 gives a colorless fluid; should the fluid  standing over the
 sediment show a brownish tint, or the  residue, instead of
 being friable, consist of a brown, oily liquid, add to the mass
 some cuttings of pure Swedish filtering paper,  and continue
 the application of heat.  By attending to these  rules you will
 always completely  attain the object  in view, viz., the  destruc-
 tion of the organic substances, without loss of any of the
 metals.  Warm the residue on the water-bath, with a  mixture >
 of 8 parts of water and 1 part of hydrochloric acid, filter,
 wash  the undissolved part  thoroughly with  hot, distilled
 water, with addition  of a little hydrochloric  acid, and add
 the washings, which  must be  concentrated if necessary, to
 the filtrate.
  Dry the  washed carbonaceous residue, then mark it  II.,
 and reserve for further examination  according to the instruc-
 tions given in (304).

4. Preliminary Examination  for  Arsenic  and  other 293
  Metallic Poisons  of Groups V. and VI.   (Second Pre-
  cipitation with Hydrosulphuric Acid.)
  The clear fluid obtained in  3 contains all the arsenic which 
352          DETECTION OF INORGANIC POISONS.       [§ 228.

may have been present, in form  of arsenious acid, and may
contain also tin, antimony, mercury,  copper, bismuth,  and
cadmium.  Supersaturate a small portion of it cautiously and
gradually with a mixture of carbonate  of ammonia and some
ammonia, and observe whether a precipitate  is thereby pro-
duced.  Acidify the supersaturated sample of the fluid with
hydrochloric acid, which will redissolve the  precipitate that
may have been produced by ammonia;  then return the sample
to the fluid, and treat the latter with hydrosulphuric acid in
strict accordance with the directions of (291).
  This process may lead to three different results, which are
to be carefully distinguished.
      a. The hydrosulphuric acid fails at first to produce a 294
    precipitate /  but after the fluid has stood for some time,
    a trifling white or yellowish-white precipitate separates.
    In this case  probably no metals  of Groups V. and VI.
    are present.   Nevertheless, treat the  filtered and washed
    precipitate as directed  in (297), to guard even against
    overlooking the minutest traces of arsenic, &c.
      b. A precipitate is formed, of a pure yellow color like 295
    that of tersulphide of arsenic.  Take a small portion of
    the fluid, together with the precipitate suspended therein,
    add some ammonia, and shake the mixture for some time,
    without application of heat.   If the precipitate dissolves
    readily and, with the exception of a  trace  of sulphur,
    completely,  and  if,  in  the preliminary  examination
    (293), carbonate  of ammonia has failed to produce a
    precipitate, arsenic alone is present, and no other  metal
    (tin or antimony), at all events, no quantity worth notic-
    ing.   Mix the solution  of the small' sample in ammonia
    with hydrochloric acid to acid reaction, return the acidu-
    lated sample to the fluid from which it was taken, and
    which contains the yellow precipitate produced by the
    hydrosulphuric acid, and proceed  as  directed  in (297).
    If, on the other hand, the addition of ammonia to  the
    sample completely or partially fails to redissolve the pre-
    cipitate, or  if, in the  preliminary examination (293),
    carbonate of ammonia has produced a precipitate, there
    is reason to  suppose that another metal is present, per-
    haps with arsenic.  In  this latter case also, add to  the
    sample in the test-tube hydrochloric acid to acid reaction,
    return the acidulated sample to  the fluid from which it
    was  taken, which contains  the yellow precipitate pro-
    duced by the  hydrosulphuric  acid, and  proceed  as
    directed in (298).
      c.  A precipitate is formed, which is  not yellow.   In  296 
§ 228.]   TREATMENT OF THE YELLOW  PRECIPITATE.       353

     that case you have to assume that other metals  are pre-
     sent, perhaps  with  arsenic.   Proceed as  directed  in
     (298).

5. Treatment of the Yellow Precipitate produced by Hydro- 297
  sulphuric Acid, in Cases where the Results of the Exami-
  nation in (295) lead to the Assumption  that Arsenic alone
  is present.  Determination of the Weight of the Arsenic.
  As soon as the fluid precipitated according to the directions
of (293) has nearly lost the smell  of sulphuretted hydrogen
transfer  the  yellow  precipitate   to   a  small filter,  wash
thoroughly, pour upon the still moist precipitate  solution of
ammonia, and wash the filter—on which, in this case, nothing
must remain undissolved, except sulphur—thoroughly with
dilute ammonia ; evaporate the ammoniacal fluid in a small,
accurately tared porcelain dish, on the water-bath,  dry the
residue at 212° F. until its weight suffers no further diminu-
tion, and, weigh.  If it is found, upon reduction,  that the
residue consisted of perfectly pure tersulphide of arsenic, cal-
culate for every part of it 0*8049 of arsenious acid, or 0"6098
of arsenic.  Treat the residue  in the  dish according to the
instructions given in (300).

6. Treatment of the Yellow Precipitate produced by Hydro- 298
  sulphuric  Acid, in Cases where the Results of the Exami-
  nation in (295),  or in (296), lead to the Assumption that
  another Metal is present—perhaps with  Arsenic.   Separa-
  tion of  the Metals from each other.   Determination of the
  Weight of the Arsenic.
  If you have reason to suppose that the precipitate produced
by hydrosulphuric acid (293) contains  other metals,  perhaps
with arsenic, proceed as follows:—As soon as the precipita-
tion  is thoroughly accomplished, and the smell of sulphuretted
hydrogen  nearly disappeared, pour the  precipitate on a  small
filter, wash thoroughly, perforate the  point of  the filter, and
rinse the  contents with the washing-bottle  into a little  flask,
using the least  possible quantity of water for the purpose;
add  to the fluid in which the precipitate is now suspended,
first  ammonia, then some yellowish sulphide of ammonium,
and  let the  mixture digest for some time at a gentle  heat.
Should part  of the precipitate remain undissolved, filter this
off, wash, perforate the filter,  rinse off the residuary preci-
pitate, mark  it III.,  and reserve for further examination
according to the instructions given  in (305).  Evaporate the
filtrate, together with the washings, in a small porcelain dish,
to drvness   Treat the  residue with some  pure fuming  nitric
     J    '                    23 
354
DETECTION OF INORGANIC POISONS.
[§ 228.
 acid  (free from chlorine),  nearly expel the acid by evapora-
 tion, and then add, as C. Meyer was the first to recommend,
 gradually, and in small portions at a time, a solution of pure
 carbonate of soda until it predominates.   Add now a mixture
 of 1 part of carbonate and 2 parts of nitrate of soda, in suffi-
 cient, yet not excessive quantity, evaporate to  dryness, and
 heat  the residue very gradually  to fusion.  Let  the fused
 mass cool, and, when cold, extract it with cold  water.  If a
 residue remains undissolved,  filter,  wash with a mixture of  299
 equal parts of spirit of wine and  water, mark it IV., and
 reserve for further examination, according to the direction of
 (306).   Mix the solution, which must contain all the arsenic
 as arsenate of soda, with the washings, previously freed from
 alcohol  by evaporation, add  gradually and cautiously pure
 dilute sulphuric acid to strongly acid reaction, evaporate in a
 small porcelain dish,  and when the fluid is tolerably concen-
 trated, add again sulphuric acid, to see whether the quantity
 first added has been sufficient to expel all nitric and nitrous
 acids ; heat now very  cautiously until heavy fumes of hydrated
 Bulphuric acid begin to escape  ; then let the liquid cool, dilute
 with  water, bring into a small flask, and, while  the liquid is
 kept  at  a temperature of 158° Fah., pass a slow current of
 washed hydrosulphuric acid gas  into it for at least 6 hours,
 then, continuing the stream of gas, let it cool.   If  arsenic is
 present, a yellow precipitate will form.  When the precipitate
 has completely  subsided, and the fluid  has nearly lost the
 smell of sulphuretted hydrogen, filter, wash the precipitate,
 dissolve  it in ammonia, and  proceed with the solution  as
 directed in (297), to  determine the weight of the arsenic.

           7.  Reduction  of the Sulphide of Arsenic.
  The production of metallic arsenic from the sulphide, which  300
may be regarded as the keystone of the whole process, de-
mands the greatest care and attention.   The method recom-
mended  in § 135, 12, viz., to fuse the  arsenical compound,
mixed with cyanide of potassium and carbonate  of  soda, in a
slow  stream of carbonic acid gas,  is  the best and safest,
affording, besides the advantage  of great accuracy, also a
positive  guarantee against the chance   of  confounding the
arsenic with some other body, more particularly antimony;
 on which account it is more  especially adapted  for medico-
legal investigations.
  The reduction should be made with great care; the apparatus
 should be entirely filled with carbonic acid, and the stream of
 this gas should be made sufficiently slow before applying heat
 to the mixture. It is best to employ an apparatus which admits 
§228.
REDUCTION OF  THE SULPHIDE OF  ARSENIC.
Fig. 35.
of perfectly regulating the gase-
ous current.   For the evolution
flask § 135, 12 maybe  conveni-
ently substituted the  arrange-
ment shown in Fig. 35, which is
easily constructed from the ordi-
nary stock of a laboratory.  The
stoppers are best made of vul-
canized rubber  [though corks
soaked in melted tallow answer
a good purpose].  The clamp by
which  the issue of gas  is  con-
trolled should be adjustable by
means  of a screw [or wedge].
  For the process of reduction,
you may  proceed at once with
the sulphide of  arsenic.  Take
care, if possible, not to use the
whole  of  the residue  in  the
dish, obtained  by the evapora-
tion of the ammoniacal solution, but only a portion  of it, so
that the process may be repeated several times, if necessary.
Should the residue be too trifling to admit  of being divided
into several portions, dissolve it in a few drops of ammonia,
add a little carbonate of soda, and evaporate on  the water-
bath to dryness, taking  care to stir the mixture during the
process;  divide the dry mass into several portions,  and pro-
ceed to reduction.
   Otto* recommends to convert the sulphide first into arsenic
acid, and then to reduce the latter with cyanide of potassium.
The following is  the  process given by him  to effect the con-
version  of the sulphide into the  acid;  pour concentrated
nitric acid over the sulphide of arsenic in the dish, evaporate,
and repeat the same operation  several times, if necessary,
and then  remove every trace of nitric acid by repeatedly
moistening the residue with water, and drying again ; when
the nitric  acid  is completely expelled,  treat  the residue with
a few drops of water, add carbonate  of soda in powder, to
form an alkaline mass, and thoroughly dry this in the dish,
with frequent stirring, taking  care to collect the mass within
the least possible space in the middle of the dish.   The dry
mass thus obtained is admirably adapted for reduction.  I
can, from the results of my own experience,  fully confirm this
statement of Otto; but I must once  more repeat,  that it is
301
Anleitung zur Ausmittelung der Gifte," von Dr. Fr. Jul. Otto, p. 36. 
356          DETECTION OF INORGANIC POISONS.       [§ 228.

indispensable for the success of the operation that the residue
should be perfectly free from every trace  of nitric  acid or
nitrate; otherwise  deflagration is sure to take place during
the process of fusion with cyanide of potassium, and, of course,
the experiment will fail.
  When the operation is finished, cut  off the reduction tube  302
at c (see Fig. 30), set aside the fore  part, which contains the
arsenical mirror, put the other part of the tube into a cylinder,
pour water over it, and let it stand some time; then filter
Fig. 36.
the solution obtained, add to the filtrate hydrochloric acid to
acid reaction; then again  some  hydrosulphuric acid,  and
observe whether this produces a precipitate.   In cases where
the reduction of the sulphide of arsenic has been effected in
the direct way, without previous  conversion to arsenic acid,
a trifling yellow precipitate  will usually form;  had traces of
antimony been present, the precipitate  would be  orange-
colored and insoluble in carbonate  of ammonia.  When all
the soluble salts of the fused mass  have been dissolved out,
examine the metallic residue, which may be left behind, for
traces of tin and antimony; these being the only metals that
can possibly be present if the instructions here given have
been strictly followed.  Should appreciable traces of these
metals, or of either of  them, be found, proper deduction and
correction must be  made in calculating the weight of the
arsenic.
Examination of the reserved Residues, marked severally
  I., II., III., and IV., for other Metals  of the Fifth and
  Sixth Groups.
a. Residue I.  Compare (290).
    This  may  contain chloride of silver and sulphate of  303
  lead, possibly also binoxide of tin.  Incinerate the resi-
  due  (I.) in a porcelain dish, burn the carbon with the
  aid of some nitrate of ammonia, extract the residue with
  water,  dry the  part left undissolved, and then fuse it
  with cyanide of potassium in a porcelain crucible.  When
  the fused mass  is  cold, treat it with water until all that
  is soluble in it is completely removed; warm the residue
   with nitric acid, and proceed as directed in § 184.
5. Residue II.   Compare (292).
     The  carbonaceous residue which is obtained by  the  304 
§ 228.]          EXAMINATION FOR METALS.              357

    purification of the crude sulphide by means of nitric acid
    and  sulphuric acid, may  more  especially  contain lead,
    mercury,  and tin; antimony and bismuth may also  be
    present.
       Heat the residue for some time with nitrohydrochloric
    acid, and  filter the solution; wash the undissolved resi-
    due with  water mixed with some hydrochloric acid, add
    the washings to  the filtrate, and treat the dilute fluid
    thus obtained with hydrochloric acid; should a precipi-
    tate form, examine this according  to  the instructions
    given in § 194.   Incinerate the residue insoluble in nitro-
    hydrochloric  acid,  fuse  the ash in conjunction with
    cyanide of potassium, and  proceed with the fused mass
    as directed in (303).
  c. Residue III  Compare (298)-
       Examine the precipitate insoluble in sulphide of ammo-  305
    nium for the metals of the  fifth group  according to the
    instructions given in § 196.
  d. Residue  IV.  Compare (299).                         306
       This may contain tin and antimony, perhaps also cop-
    per.  Proceed as directed  (123).   If  the color  of the
    residue was black  (oxide of copper), treat the  reduced
    metals according to the instructions given in § 184.

 9. Examination of the Filtrate reserved in (291) for Metals
    of the Fourth and Third  Groups, especially for Zinc
    and  Chromium.
  a. As we have seen in (29l), the fluid filtered from the  307
    precipitate produced by hydrosulphuric acid, and tempo-
    rarily reserved for further examination, has already been
    mixed with  sulphide of ammonium.   The addition of
    this reagent  to the filtrate is usually attended with the
    formation of a precipitate, consisting of sulphide of iron
    and phosphate of lime, but  which may possibly also con-
    tain sulphide of  zinc.   Filter the fluid from this precipi-
    tate, and  treat the filtrate  as directed in  (30s); wash
    the precipitate with water mixed with some sulphide of
    ammonium, dissolve by warming with hydrochloric acid,
    and boil  the  solution with nitric acid, to convert  the
    protoxide of iron into sesquioxide;  add,  if necessary,
    sufficient  sesquichloride of  iron for carbonate of soda to
    produce a brownish-yellow precipitate in a sample of the
    fluid- neutralize almost completely with  carbonate  of
    soda, precipitate with  carbonate of  baryta, and filter;
    the precipitate contains all the sesquioxide of iron and
    all the phosphoric acid.   Concentrate  the filtrate, pre- 
358           DETECTION  OF INORGANIC POISONS.        [§ 229.
     cipitate the baryta with dilute sulphuric acid, filter, add
     to the filtrate ammonia to alkaline reaction, and precipi-
     tate with sulphide of ammonium the zinc which may be
     present.  For the further examination of the precipitate,
     see § 109.
  b. If the analysed substance contained chromium, this will  308
     be found in  the fluid filtered from  the  precipitate pro-
     duced by sulphide  of ammonium, since this reagent is
     incapable  of throwing down chromium from liquid con-
     taining  organic matters.    If  you  wish  to  ascertain
     whether chromium is really present, evaporate  the fil-
     trate to dryness, mix the residue with 3  parts of nitrate
     of potassa and 1 part of carbonate of soda, and gradually
     introduce the mixture into a crucible heated to moderate
     redness.  Allow the fused mass  to cool, and, when cold,
     boil with water: yellow coloration of the fluid shows the
     presence of alkaline chromate, and accordingly of chro-
     mium.  For confirmatory tests, see § 141.

  II. Method for the Detection  of Hydrocyanic  Acid.
                             § 229.
  In cases of  actual or suspected poisoning with hydrocyanic  309
acid, where it is required to separate that acid from  articles
of food  or  from the contents of the  stomach, and thus to
prove  its presence, it is  highly necessary  to  act with the
greatest  expedition, as the hydrocyanic acid speedily under-
goes decomposition.  Still this decomposition is not quite so
rapid as  is generally supposed, and indeed it requires some
time before  the  decomposition  of  the whole  of the acid
present is effected.*
  Although hydrocyanic acid betrays its presence, even in
minute quantities, by its peculiar odor,  still this sign must
never be looked upon as conclusive.  On the contrary, to ad-
duce positive proof of the presence  of the acid, it is always
indispensable  to  separate it,  and to convert it into  certain
known compounds.
  The method of accomplishing this  is based upon distilla-
tion of the  acidified mass, and examination of the distillate
for hydrocyanic acid.  Now, as the non-poisonous salts, ferro-
and ferricyanide  of potassium, on distillation, likewise yield
  * Thus I succeeded in separating a notable quantity of hydrocyanic acid from the
stomach of a man who had poisoned himself with that acid in very hot weather, and
whose intestines were handed to me full 36 hours after death.—A dog was poisoned
with hydrocyanic acid, and the contents of the stomach, mixed with the blood, were
left for 24 hours exposed to an intense summer-heat, and then examined; the acid
was still detected. 
§ 229.]
HYDROCYANIC ACID.
359
a distillate containing hydrocyanic acid, it is, of course, indis-
pensable—as Otto very properly observes—first to ascertain
whether one of these salts may not be present.  For this
purpose, stir a small portion of the mass to be examined with
water, filter, acidify the filtrate with hydrochloric acid, and
test a sample of it with sesquichloride of iron,  another with
sulphate of protoxide of iron.   If no blue precipitate forms in
either, soluble ferro- and ferricyanides are not present, and
you may safely proceed as follows:
  Test, in the  first place, the reaction  of the mass under 310
examination; if necessary, after mixing and stirring it with
water.  If it is not already strongly acid,  add solution of tar-
taric acid until the fluid  strongly reddens litmus paper;  in-
troduce the mixture  into a  retort,  and place the body  of
the retort,  with the neck pointing  upwards, in an iron  or
copper vessel, but so that  it does not touch the bottom, which
should, moreover, by way of  precaution,  be covered with a
cloth;  fill the vessel with a solution  of chloride of calcium,
and apply heat, so  as to  cause  gentle ebullition of the con-
tents  of the retort. Conduct the vapors passing over, with
the aid of a tight-fitting  tube,  bent  at a very  obtuse  angle
through a Liebig^s condensing apparatus, and receive the
distillate in a small, weighed flask.   When about half-an-
ounce of distillate has passed over, remove the  receiver, and
replace it by a somewhat  larger flask, also previously tared.
Weigh the  contents of the  first  receiver  and proceed   as
follows:
      a. Mix  one-fourth  of the distillate with solution  of 311
    potassa or soda to strongly alkaline reaction, and then
    add a small quantity of solution of sulphate of protoxide
    of iron, mixed with a little sesquichloride of iron.   Heat
    now gently for some minutes and finally supersaturate
    with dilute hydrochloric  acid.   If a  blue  precipitate  is
    formed, it indicates a relatively large amount of hydro-
    cyanic acid;   if a bluish-green  liquid is obtained from
    which, on long standing, blue flocks deposit,  a small quan-
    tity is present.
      b. Treat another fourth as directed § 158, 7, to convert 312
    the hydrocyanic acid into  sulphocyanide of iron. Aa
    the distillate might, however, contain acetic acid, do not
    neglect to  add some hydrochloric acid after the sesqui-
    chloride of iron,  in order to  neutralize  the  adverse
    influence of the acetate of ammonia.  Compare § 114,  8,
    note.
      c.  If the experiments a and b have demonstrated the 318
    presence of hydrocyanic acid, and you wish now also to 
360           DETECTION OF INORGANIC  POISONS.       [§ 230.

    approximately determine its quantity, continue the dis-
    tillation, until the fluid passing over contains no longer
    the least trace of hydrocyanic acid;  add one-half of the
    contents of the second receiver to the  remaining half of
    the contents of the first, mix the fluid with nitrate of
    silver, then with ammonia  until  it predominates, and
    finally with nitric acid to strongly acid reaction.  Allow
    the precipitate which forms to subside, filter on a tared
    filter, dried at 212° F., wash the  precipitate, dry it tho-
    roughly at 212° F.,  and weigh.   Ignite  the weighed
    precipitate in a small porcelain crucible, to destroy the
    cyanide of silver, fuse the residue with carbonate of soda
    and potassa—to effect the decomposition of the chloride
    of silver which it may contain—boil the mass Avith water,
    filter, acidify the filtrate  with nitric acid, and precipitate
    with  nitrate of silver;  determine  the weight of the
    chloride of silver which may precipitate, and deduct the
    amount found from the total weight of the chloride and
    cyanide of silver: the difference  gives the quantity of
    the latter; by multiplying the quantity found of the
    cyanide of silver by 0*2017, you find the corresponding
    amount of anhydrous hydrocyanic acid; and by multi-
    plying this again by 2—as only one-half of the distillate
    has been  used—you  find the total quantity of hydro-
    cyanic acid which  was present in the examined  mass.
    Instead of decomposing the precipitate by fusion with
    an  alkaline carbonate it may be treated with zinc and
    dilute sulphuric  acid,  and the chlorine  determined in the
    solution after the reduction is complete.
      Instead  of pursuing this indirect method, you  may 311
    also determine the quantity of the hydrocyanic acid by
    the following direct method :  Introduce half of the dis-
    tillate into  a retort, together with powdered borax;
    distil  to a small  residue, and determine the hydrocyanic
    acid in the distillate as cyanide of silver.   Hydrochloric
    acid can no longer be  present in this distillate, as the
    soda of the borax retains it in the  retort ( Wackenroder).

      HI. Method  for the Detection of Phosphorus.
                             § 230.
  Since phosphorus paste has been  employed to poison  mice, 315
&c, and the poisonous action of lucifer matches has become
more  extensively known, phosphorus  has  not unfrequently
been resorted to  as  an agent for committing murder.   The
chemist is therefore occasionally called upon to  examine some 
§ 230.]     DETECTION OF  UNOXIDIZED  PHOSPHORUS.       361

article of food, or the contents of a  stomach, for this sub-
stance.   It is obvious that, in cases  of the kind, his whole
attention must be directed to the separation of the phospho-
rus in the free state, or to  producing such reactions as will
enable him to infer the presence of free phosphorus;  since
the mere finding of phosphorus in form of phosphates would
prove nothing, as phosphates invariably form constituents of
animal and vegetable bodies.
           A. Detection of Unoxidized Phosphorus.

   1.  Test in the first  place  the suspected matters as  to  316
 whether free  phosphorus is recognizable by its odor or  by
 its luminosity in  the  dark, exposing, for this purpose, the
 materials to  the  air,  as much  as is necessary, by rubbing,
 stirring, or shaking.
   2. A portion of the substance  is placed, according to the  317
 plan of J. Scherer* in a small flask, suspend in it, above the
 substance, by aid  of the loosely  fitted  cork, a slip  of filter
 paper moistened with neutral solution of nitrate of silver and
 warm the whole to 85° to  105° Fah.  In case the paper is
 not colored black after some  time, unoxidized phosphorus
 cannot  be  present, and it is then unnecessary to proceed fur-
 ther by the methods 3 and 4.   The operator  may go on to
 (324).  If, on the other hand, the paper blackens, this is no
 certain  evidence of the presence of phosphorus, because  vari-
 ous substances, viz., hydrosulphuric acid (detectable by means
 of a slip of paper moistened with  solution of 'lead or terchlo-
 ride of  antimony), formic acid,  products  of putrefaction,  &c,
 may produce  the  same result.   Proceed then  with the  sub-
 stance as directed  in 3 and  4.
  3.  The luminosity of phosphorus, of all its characters, fur-  31 §
 nishes the  most striking evidence of its presence  in the free
 state.   A large sample  of  the substance is  accordingly ex-
 amined  by the following well-proved and admirable  method
 of E. Mitscherlich.\
  Mix the substance under  examination with water and some
sulphuric acid, and subject the mixture to  distillation  in a
flask, A (see Fig. 37).  This flask is connected with an evolu-
tion tube b, and the latter again with a glass cooling or  con-
densing tube,  c c c, which passes through a perforated cork,
a,  in the bottom  of a  cylinder,  B, into a glass vessel, C.
Cold water runs from  D, through a stopcock, into a funnel,

 * Ann. d. Chem. u. Pharm., 112, 214.     f Jour. f. Prakt Chem., 66, 233. 
362           DETECTION  OF INORGANIC POISONS.       [§ 230.
                             Fig. 8T.

t, which extends to the  bottom of B; the  warmed water
flows off through g.*
  Now, if the substance in A contains phosphorus, there will
appear, in the dark, in the upper part of the condensing tube
at the point r, where the aqueous vapors distilling over enter
that part of the tube, a strong luminosity, usually a luminous
ring.  If you take for distillation 5 oz. of a mixture containing
only ^gth of a grain of phosphorus,  and accordingly only 1
part of phosphorus in 100,000 parts of mixture, you may dis-
til over 3 oz.  of  it—which will take  at least half-an-hour—
without the luminosity ceasing; Mitscherlich, in one of his
experiments, stopped  the distillation after  half-an-hour,  al-
lowed the flask  to  stand uncorked  a fortnight, and then
recommenced the distillation:  the  luminosity was as strong
as at first.   If the fluid contains substances which prevent the
luminosity of  phosphorus in  general, such as ether, alcohol,
or oil of turpentine, no luminosity is observed so long as these

  * [Instead of this vertical condenser, the  apparatus shown  in Fig. 4 may be
used.] 
 § 230.]           DETECTION  OF PHOSPHORUS.              363

 substances continue to distil over.  In the  case of ether and
 alcohol,  however, this is soon effected,  and the luminosity
 accordingly very speedily makes its  appearance ; but it is
 different with oil of turpentine, which  exercises a lasting pre-
 ventive influence upon the manifestation of this reaction.
   After the termination of the process,  globules of phosphorus  319
 are  found at  the bottom of the receiver, C.  Mitscherlich
 obtained from 5 oz. of a mixture containing i grain of phos-
 phorus, so many globules of that body that the one-tenth part
 of them would have been amply sufficient to demonstrate its
 presence.   In  medico-legal   investigations  these  globules
 should first be washed with  alcohol and then weighed.   A
 portion may afterwards be subjected to a confirmatory  ex-
 amination, to make  quite sure  that  they really consist  of
 phosphorus: the remainder, together  with a portion of the
 fluid which shows the luminosity upon distillation, should be
 sent in with the report.
   The experiment should be made in  a perfectly dark room,
 best at night.  If it is made  in the daytime the room should
 be darkened by aid of curtains  or blinds, so that no reflections
 whatever from the surfaces of the glass vessels or  of the
 liquids moving in them shall occasion  mistakes.  It is advis-
 able, even, especially when very minute traces of phosphorus
 are searched for, to pass the evolution-tube through a screen,
 at b, to prevent such reflections being occasioned by the light
 of the lamp by which the flask is heated.
   The residue of the distillation is further examined accord-
 ing to (324) for phosphorous  acid.  The  distillate, also, may
 be tested in  the same manner to confirm the  presence  of
 phosphorus, or of phosphorous  acid arising from its oxidation.
   4. Another   sample  of the  substance  may be examined,  320
 according to experiments made by Neubauer and myself*  in
 the following manner.   It is brought into a flask with doubly-
 perforated stopper, water is added, if necessary, and dilute
 Bulphuric  acid to acid reaction.  Washed carbonic acid gasf
 is now slowly conducted through the mixture by means of a
 glass tube passing through the cork and reaching nearly down
 to the bottom of the  flask.  From a  short tube above, the
 current of gas is led  through one  or two V-formed tubes
 which  contain neutral solution of nitrate of silver.   When
 the flask is filled with carbonic acid it  is warmed in a water-
 bath.  The experiment is kept up for several hours.  If free
 phosphorus be present, a portion of it volatilizes unoxidized
 in the stream of carbonic acid, and on passing into the silver-
solution,  produces  there an insoluble black precipitate  of
     * Zeitschrift f Analyt. Chem., 1, 336.
     \ The apparatus, Fig. 35 (300), may be conveniently employed. 
364          DETECTION  OF INORGANIC POISONS.       [§ 230.

phosphide of silver, together with phosphoric acid.   Since a
black insoluble precipitate  may be caused by various volatile
reducing agents or by hydrosulphuric acid, its appearance is
not proof of the presence of phosphorus, though its non-forma-
tion demonstrates conclusively that free phosphorus is absent.
  A precipitate formed in  the silver solution in the above 321
experiment is collected on  a filter (which has been previously
washed with dilute nitric acid and water), and is well washed
with water. The phosphide of silver, which may be contained
in this precipitate, is detected by the method of Blondlot, im-
proved by Dussard.* a Fig. 38. is an apparatus for evolving hy-
drogen ; b is filled with  fragments of pumice-stone drenched
with concentrated potassa-lye ;  c  is a common spring clamp;
d a clamp that can be nicely adjusted by means  of a screw
or wedge; e is a platinum jet which is kept cool by means of
moistened  cotton.  This platinum jet is essential, since the
flame would  be  colored yellow  if burned directly from a
glass tube.
  At the outset it is needful to test the sulphuric acid and
zinc to demonstrate that they yield hydrogen free from phos-
phuretted hydrogen.    For  this  purpose allow the gas to
evolve until air is displaced  from the apparatus, then close c
until the acid has been forced into/, then close cl, open c, and
lastly open d, cautiously inflaming the gas at the jet  and
properly regulating its  issue.  If the flame, when  examined
in a rather dark place, is colorless, exhibits  no trace of a
green cone in its  interior and no emerald-green tinge when a
                  * Zeitschrift f. Aualyt. Chem. 1, 129.
89999999999996 
§ 230.]        DETECTION OF PHOSPHOROUS ACID.

porcelain dish is depressed  into  it,  the  hydrogen  is pure.
After verifying this  result by a second trial, the precipitate
to be examined is rinsed into /, care being  taken  that  it
passes completely into a, and the flame is again observed as
before.   In case but a minimum of phosphide  of silver be
present the green inner  cone and  emerald-green coloration
of the flame will be perceptible.
  The solution filtered from the  silver  precipitate, is freed
from excess of silver by hydrochloric acid, filtered through a
well  purified  filter, strongly  concentrated in  a porcelain
capsule, and finally tested for  phosphoric  acid  by means of
molybdate  of ammonia or magnesia mixture.
   In this manner we have most plainly detected  the phospho-
rus of a common match mixed with a large quantity  of putre-
fied blood,  and in presence of those substances which prevent
luminosity in the method of Mitscherlich.
   5. When enough phosphorus  is present to weigh, its  esti-
mation is practicable by adopting Scherer's modification  of
the process of Mitscherlich.  The mass, acidified with sul-
phuric acid, is distilled in an  atmosphere  of carbonic  acid
gas.  For this purpose it is  best to  fit into the cork of the
flask in which  the mixture is  distilled, a second tube  through
which pure carbonic acid may be transmitted into the distill-
ing apparatus, until it is completely filled, when  the stream of
gas may be cut off and the process continued as usual.   The
receiver may consist  of a flask with a  doubly perforated cork,
one opening of which passes over the end of the condensing
tube,  the other carrying a bent glass tube which is connected
with a U tube containing solution of nitrate of  silver.
   When the distillation  is finished, globules of phosphorus
are found in the receiver, which, after again establishing a
gentle stream of carbonic acid, are united by gently heating
and then are washed and weighed as described (319).   The
solution poured off from the globules  is luminous in the dark,
when shaken, though not to the same degree as in Mitscher-
lich's process.   The  phosphorus in this liquid may be deter-
mined, after oxidation, by nitric acid or chlorine, as phosphoric
acid; though, only, when the operator is  certain that none
of the contents of the distilling flask, which usually contain
phosphoric acid, have spirted into the condenser.  The entire
quantity of phosphorus is obtained by adding  to that,  thus
determined, what exists in the U tube.    Its  contents are
treated with nitric acid, the  silver thrown down by hydro-
chloric acid filtered through a washed  filter, concentrated,
precipitated as phosphate of ammonia-magnesia,  and  weighed
as phosphate of magnesia. 
366
ANALYSIS OF ASHES.
[§ 231
             B. Detection of Phosphorous Acid.
  In case free phosphorus itself has not been detected by the 321
above methods, it  is needful to look for the first product of
its oxidation, viz. phosphorous acid.   To this end the residue
of the distillation (318) or (323), or also the residue of (320) is
brought into the apparatus, Fig. 38, and tested as described
(321), as to any green coloration of the evolved hydrogen.
If the phosphorous reaction appears it is sufficient; otherwise,
organic matters may have  hindered its  production.   If,
therefore, the  flame is not colored, the clamp is closed and a
U tube containing neutral solution  of nitrate  of  silver is
affixed to the apparatus and the gas is allowed to stream
slowly through the silver solution for many hours.   In pre-
sence of phosphorous acid, phosphide of silver is  formed,
which is filtered off and examined as  directed in (32l).

3. Examination of the Inorganic Constituents of Plants, Animals,
  or Parts of the  same, of Manures,  &c. (Analysis of Ashes.)
                              § 231.
                A. Preparation of the  Ash.
  It is sufficient for the purposes of a qualitative analysis to  325
incinerate a comparatively  small quantity of the substance
which it is intended to examine for its inorganic constituents;
the  substance must  previously  be  most  carefully cleaned.
The incineration is effected best in a small clay muffle, but it
may be  conducted also  in  a Hessian crucible placed in a
slanting position, or, under  certain circumstances, even in a
small porcelain or platinum dish, over which a wide glass
tube  (lamp  chimney) is  supported to increase the  access of
air.   The heat must always be  moderate,  to guard against
the volatilization  of certain  constituents, more especially of
metallic chlorides.  It is not always necessary  to  continue
the combustion until all the  carbon is consumed.  With ashes
containing a large proportion of fusible salts, as, e. g. the ash
of beetroot molasses, it is even advisable to effect, iu the first
place, complete carbonization, then to boil the charred mass
with water,  and finally  to incinerate the washed and dried
residue.  For further  particulars  see Quantitative Analysis,
4th Edition, § 250.
                  B.  Examination of the Ash.
  As the qualitative analysis  of the ash of a vegetable sub-  326
stance is usually undertaken, either as a practical exercise, or
for the purpose of determining its general character, and the
state or condition  in which any given constituent may happen
to be  present, or  also with  a view to make, as far as prac- 
§ 231.]              ANALYSIS OF  ASHES.                 367
 ticable, an approximate estimation of the respective quantities
 of the several constituents, it is usually the best way to examine
 separately ;  (l) the part soluble in water ; (2) the part soluble
 in hydrochloric acid; and (3) the residue which  is insoluble
 in either menstruum.  This can be done the more readily, as
 the  number of bodies to which regard must  be had in the
 analysis is only small, and the several processes may accord-
 ingly be expeditiously performed.

          a. Examination of the Part Soluble in Water.
  Boil  the ash with water, filter, and whilst  the residue is
 being washed, examine the solution as follows :—
  1. Add  to a portion, after  heating it, hydrochloric acid in  327
 excess,  warm, and let the fluid  stand at rest.   Effervescence
 indicates  carbonic acid, combined with alkalies;  odor of
 hydrosulphuric acid indicates  the  sulphide  of an  alkali
 metal, formed from an alkaline sulphate by the reducing ac-
 tion of the carbon.  Turbidity from separation  of  sulphur,
 with odor  of sulphurous  acid, denotes a hyposulphite (which
 occurs occasionally in the ash of coal).   Filter, if necessary,
 and add to the filtrate—or  to the fluid  if no filtration is
 required—some chloride of barium ; the formation of a white
 precipitate indicates the presence of sulphuric acid.
  2. Evaporate another  portion of the solution until it is  323
 reduced to a small volume, add hydrochloric acid to acid re-
 action—effervescence indicates the presence of carbonic acid
 —evaporate now to dryness, and treat the residue with hydro-
 chloric acid and water.  The portion left undissolved consists
 of silicic acid.  Filter, add ammonia, chloride  of ammonium,
 and  sulphate of magnesia; the formation of a white precipi-
 tate indicates the presence of phosphoric acid.  Instead of
 this  reaction, you  may  also  mix the fluid filtered from the
 silicic acid with acetate of soda, and then cautiously add, drop
 by drop, sesquichloride of iron, or you  may test with molyb-
 date of ammonia (§ 145).
  3. Add to another portion  of  the solution  nitrate of silver  329
 as long as  a precipitate continues to form ; warm gently, and
 then cautiously add ammonia ;  if a  black residue is left, this
 consists of sulphide of silver, proceeding from the sulphide of
 an alkali metal, or from a hyposulphite.  Mix the ammoniacal
 solution  now—after previous  filtration  if  necessary—with
nitric acid  in slight excess, so that phosphate of silver, which
 at first falls, is redissolved,  and only chloride (iodide  and
  *  To detect the iodine  in aquatic plants, dip  the plant in a weak solution  of
potassa (Chatin), dry, incinerate, treat with water, and examine the aqueous solution
as directed (257). 
 368                  ANALYSIS  OF ASHES.               [§ 231.

 bromide) of silver remains.  Filter off the precipitate, which
 is to be further examined according to (l78) and neutralize
 the filtrate cautiously and exactly with ammonia.  If this pro-
 duces a bright yellow  precipitate, phosphoric acid is present
 in  the tribasic;  if  a  white precipitate, it is present in the
 bibasic form.
   4. Acidify a portion of the solution with hydrochloric acid,  330
 and then make it alkaline with ammonia; mix the alkaline fluid
 with oxalate of ammonia, and let it stand at rest.  The forma-
 tion of a white precipitate indicates lime.  Filter, and mix
 the filtrate with ammonia and phosphate of soda; the forma-
 tion of a crystalline precipitate, which often  becomes visible
 only after long standing, indicates  magnesia.  Magnesia is
 often found in distinctly appreciable lime, only in exceedingly
 minute quantity, even when  alkaline carbonates and phos-
 phates are present.
  5. For  potassa and soda examine as directed § 200.  If
 magnesia  is  present, neutralize that portion  of the solution
 intended  for detecting alkalies with hydrochloric acid, and
 separate the magnesia as directed § 199, 2.
  6. Lithia, which is more frequently an ingredient of ashes
 than has been hitherto  suspected, and rubidia,  which nearly
 always accompanies potassa, may be detected by the spectro-
 scope (§ 96), in the residue of alkaline salts.

    b. Examination  of the Part Soluble in Hydrochloric Acid.
  Warm  the residue left undissolved by water with hydro- 331
 chloric  acid*—effervescence indicates carbonic  acid,  com-
 bined with  alkaline earths;  evolution of chlorine denotes
 oxides of manganese—evaporate to dryness, and heat a little
more strongly, to effect the  separation  of the silicic acid:
moisten the  residue with hydrochloric acid and some  nitric
acid, add  water, warm, and filter.
  1. Test with hydrosulphuric  acid.  If this produces any
other than a perfectly white precipitate, you must examine it
in the  usual way.  The ashes of  plants  occasionally contain
copper ; if the plant has been manured with excrements de-
odorized by nitrate of lead, they may contain lead [if with
superphosphate made from arsenical oil of vitriol, arsenic,
J. Davy].
  2. Mix  a portion of the original solution with carbonate of 332
soda, as long as the precipitate formed redissolves upon stir-
ring ; then add acetate of soda, and some  acetic acid.   This
produces,  in most cases, a white precipitate  of phosphate of
sesquioxide of iron.  If the fluid in which this  precipitate
  * If the residue still contains much carbon, after further incineration. 
§ 231.]
ANALYSIS  OF ASHES.
369
is suspended is reddish, there is more sesquioxide of iron pre-
sent than corresponds to the phosphoric acid; if it is  color-
less, add sesquichloride of iron, drop by drop, until the fluid
looks reddish.  (From the quantity of the precipitate of phos-
phate of sesquioxide of iron formed you  may  estimate  the
phosphoric acid present.)  Heat to boiling,* filter hot, and
mix the filtrate, after addition  of ammonia, with yellow  sul-
phide of ammonium, in a  stoppered flask; should  a precipi-
tate form, after long standing, examine  this  according to
(l4l) for manganese and ziNc,f and tne fluid filtered from it
for lime and magnesia, in the  usual way (330).
  3. To examine for baryta  and strontia, add dilute  sul-
phuric acid to a portion of the hydrochloric solution, let the
mixture stand for a considerable time, and test any precipitate
that may form as directed (254).

  c.  Examination of the Residue Insoluble in Hydrochloric  Acid.
  The residue  insoluble in hydrochloric acid contains,
  1. The silicic  acid, which has separated on  treating with 333
hydrochloric acid.
  2. Those ingredients  of the ash which  are insoluble in
hydrochloric acid.  These are, in most  ashes, sand, clay,  car-
bon ; substances, therefore, which are present in consequence
of defective cleaning or imperfect combustion of the plants,
or matter derived from the crucible.  It is only the  ashes of
the stems of cereals and others abounding in silicic acid, that
are not completely decomposed by hydrochloric acid.
  Boil the washed residue with solution of carbonate of soda 334
in excess, filter hot, wash with boiling water, and  test for,
silicic acid in the filtrate by evaporation  with hydrochloric
acid (§ 153, 2).   If the ash was of a kind to be completely
decomposed by hydrochloric acid, the analysis  may be con-
sidered as finished—for the accidental admixture of clay and
sand will rarely interest the analyst sufficiently  to warrant a
more  minute  examination  by fluxing.  But, if the  ash
abounded in silicic acid, and it may therefore  be supposed
that the hydrochloric acid has failed to effect complete decom-
position, evaporate half of the residue  insoluble in  solution
of carbonate of soda, with pure solution of soda in excess, in
a silver or platinum  dish, to dryness.   This  decomposes  the
silicates  of the  ash,  whilst but little affecting  the  sand.
Acidify now with hydrochloric acid, evaporate to dryness,
&c, and  proceed as in (33l).   For  the detection of  the
alkalies use the other half of the residue (22s).
  * If this should fail to decolorize the fluid, add some more acetate of soda.
  + TZinc is found in a species ot violet growing in the neighborhood of zinc minea]
  ' '                           24 
370
EXPLANATORY NOTES, ETC.,  TO §§ 178-181.
                    SECTION  III.

   EXPLANATORY  NOTES AND ADDITIONS TO THE
          SYSTEMATIC COURSE OF ANALYSIS.

  I. Additional Remarks to the Preliminary Examination.

                        To §§ 178-181.
  The inspection  of the physical properties of a body may, as
already stated, § 178, in many cases enable the analyst to draw
certain general inferences as to its nature.  Thus, for instance, if
the analyst has a white substance before him, he may at once con-
clude that it is not cinnabar, or if a light substance, that it is not a
compound of lead, &c.
  Inferences of this kind are quite admissible to a certain extent;
but if carried too far, they are apt  to mislead the operator, by
blinding him to every reaction not exactly in accordance  with his
preconceived notions.
  As regards the examination  of substances at a high temperature,
platinum foil or small iron spoons may also be used in the process;
however, the experiment  in the glass  tube gives, in most  cases,
results more clearly evident, and affords, moreover, the advantage
that volatile bodies are less likely to  escape detection, and that  a
more correct and precise notion can be formed of the nature of the
heated substance,  than exposure  on platinum foil  or in an iron
spoon will permit.  To ascertain  the products  of oxidation of  a
body, it is sometimes advisable also to heat it in a short glass-tube,
open at both ends, and  held in a slanting position; small quantities
of a metallic sulphicre} for instance, may be readily detected by
this means.  (Compare § 159,  6.)
  With respect to the  preliminary examination  by  means of the
blowpipe, I have to remark that the  student must avoid drawing
positive conclusions  from pyrochemical experiments, until he has
acquired some practice  in this branch of analytical chemistry.  A
slight incrustation of  the charcoal  support, which  may seem to
denote the presence of  a certain metal, is not always a conclusive
proof of the presence  of that metal; nor would it be safe to assume
the absence of a substance simply because the blowpipe flame fails
to effect reduction, or  solution of nitrate  of protoxide  of  cobalt
fails to impart a color to the ignited mass, &c.  The blowpipe
reactions are, indeed, in most cases, unerring, but it is not always
easy to produce them, and they are moreover liable to suffer modi-
fication by accidental circumstances.
  The student should never omit the  preliminary examination ; the
notion that this omission will save time and trouble, is very errone- 
            SOLUTION  OF SUBSTANCES, §§ 182-184.         371

 ous.  The beginner may, for example, spend hours in searching for
 organic acids, when the simple preliminary test would show that
 they are all absent.


 H. Additional Remarks to the Solution  of Substances, etc.
                         To§§ 182-184.
   It is a task of some difficulty to fix the exact limit between sub-
 stances which are soluble in water and those that are insoluble in
 that menstruum, since the number of bodies  which are  sparingly
 Boluble in water is very considerable, and the transition from spar-
 ingly soluble to insoluble is very gradual.  Sulphate of lime, which
 is soluble in 430 parts  of water, might  perhaps serve  as a limit
 between  the two classes, since this salt  may still be positively
 detected  in aqueous solution, by the delicate  reagents which we
 possess for lime and sulphuric acid.
   When  examining an aqueous fluid by evaporating a few drops
 of it upon platinum foil, to  see  whether it holds a solid body in
 solution, a very minute residue sometimes remains, which leaves the
 analyst in doubt respecting the nature of the substance;  in  cases
 of the kind test, in the  first  place, the reaction of the fluid with
 litmus papers;  in the second place, add to a portion of it a drop of
 solution of chloride of barium; and lastly, to another portion some
 carbonate of soda. Should the fluid  be  neutral, and remain unal-
 tered upon the addition  of these reagents, the  analyst  need not
 examine it any further for bases or acids;  since if the fluid  con-
 tained any of those bases  or acids which principally form sparingly
 soluble compounds, the  chloride of barium  and the carbonate of
 soda would have revealed their presence.   The analyst may there-
 fore feel assured that the detection of the substance of which the
 residue left upon evaporation consists, will be more readily effected
 in the class of bodies insoluble in water.
  If water has dissolved any part of the substance under examina-
 tion, the student will always do well to examine the solution both
 for acids  and bases, since this  will lead more readily to a correct
 apprehension of the nature of the compound—an advantage which
 will amply counterbalance the drawback of sometimes meeting with
 the same  substance both in the aqueous and in the acid solution.
  The following  substances  (with few exceptions) are insoluble in
 Water  but soluble in hydrochloric acid or in nitric acid : the phos-
 phates,  arsenates, arsenites, borates, carbonates,  and oxalates  of
 the earths and metals; and also several tartrates, citrates, malates,
 benzoates, and succinates; the oxides and  sulphides of the heavy
metals ; alumina, magnesia;  many of the metallic iodides and cya-
nides &c.  Nearly the  whole  of these compounds are, indeed,
decomposed, if not by dilute, by boiling concentrated hydrochloric 
 372       explanatory notes,  etc., to  §§ 185-207.

 acid ;* but this decomposition gives rise to the formation of inso-
 luble  compounds when oxide of silver is present, and of sparingly
 soluble compounds in the presence of suboxide of mercury and lead.
 This  is not  the case with nitric acid, and accordingly the latter
 effects complete solution in many cases where hydrochloric acid has
 left a residue.  But, on the other hand, nitric acid leaves, besides
 the bodies insoluble in any simple acid, teroxide  of antimony, bi-
 noxide of tin,  binoxide of lead, &c, undissolved, and fails also to
 effect  the complete solution of many other substances, e. g. sesqui-
 oxide  of iron and alumina.
   Substances  not soluble in water are,  therefore, treated as fol-
 lows :  try to dissolve them in dilute  or concentrated hydrochloric
 acid, cold or boiling; if this fails to effect complete solution, try to
 dissolve a fresh portion in nitric acid;  if this  also  fails,  treat the
 body with aqua regia, which is  an excellent  solvent, more particu-
 larly for metallic sulphides.  To examine separately the solution in
 hydrochloric acid or  in nitric  acid, on the one hand, and that in
 nitrohydrochloric acid on the other, is, in most cases, unnecessary.
 To prepare a  nitric  or nitrohydrochloric solution is  disadvan-
 tageous when not necessary, because a hydrochloric solution is much
 better adapted for precipitation with hydrosulphuric acid.  To
 evaporate an  aqua-regia  solution  for  the  purpose  of removing
 excess of acid is  unadvisable,  since volatile chlorides, especially
 chloride of arsenic, may thus be lost.  Use, therefore, no more acid
 at the  outset than is necessary in making the solution.
  With  regard to the solution of metals  and alloys, I have  to
 remark that, upon boiling them  with nitric acid, white precipitates
 will frequently form, although neither tin nor antimony be present.
Inexperienced  students often confound  such precipitates  with  the
oxides of these two metals, although their appearance is quite dif-
ferent.  These  precipitates consist simply of nitrates sparingly solu-
ble in the nitric acid present, but readily soluble in water.  Conse-
quently the analyst should ascertain whether these white precipi-
tates will dissolve in water or not, before  he  concludes them to
consist of tin or antimony.

     III. Additional Remarks to the Actual Analysis.
                        To §§  185-207.
A.  General  Review and  Explanation of the Analytical
                           Course.
                  a. detection of the bases.
  The  classification of the bases into six groups, and the methods
which  serve to  detect and isolate them individually, have been fully
* For the exceptions, see § 206. 
             detection of the  bases,  §§ 185-207.        373

 explained in Part I., Section IH.  The systematic course of ana-
 lysis, from § 192 to § 201, is founded upon this classification of the
 bases; and  as  a correct apprehension of it is of primary import-
 ance, I will  here subjoin a brief explanation of the grounds upon
 which this division rests.  Respecting the detection of the several
 bases individually, I refer the student to the recapitulations and
 remarks in §§ 95, 102, 106, 115, 121, 126, 130 and 137.
   The general reagents which serve to divide the bases into princi-
 pal groups  are—hydrochloric acid, hydrosulphuric acid, sul-
 phide of ammonium, and carbonate of ammonia ; this is likewise
 the order of succession in  which they are applied.  Sulphide of
 ammonium performs a double part.
   Let us  suppose we have in solution  the whole of the bases,
 together  with arsenious and arsenic acids, and also phosphate  of
 lime—which latter may serve as a type for the salts of the alkaline
 earths, soluble in acids, and reprecipitated unaltered by ammonia.
   Chlorine forms insoluble  compounds only with  silver and mer-
 cury ; chloride of lead is sparingly soluble in water.  The insolu-
 ble subchloride  of  mercury  corresponds to the suboxide of that
 metal.  If, therefore, we add to our solution:

   1. Hydrochloric Acid,

 we remove from it the metallic oxides of  the  first division of the
 fifth group, viz. the whole of the oxide of silver and the whole of
 the suboxide of  mercury.  From concentrated solutions, a por-
 tion of the lead may likewise precipitate as chloride ; this is, how-
 ever, immaterial, as a sufficient quantity of the lead remains in the
 solution to permit the subsequent detection of this metal.
   Hydrosulphuric acid completely precipitates the oxides of the
 fifth and sixth group from solutions containing a free mineral acid,
 since the affinity  of the metallic radicals of these oxides for sulphur,
 and that  of  the hydrogen for oxygen, are sufficiently powerful to
 overcome  the affinity between the metal and the oxygen, and that
 between the  oxide and  a strong acid, even though the acid be
 present in excess.   But none of the other bases are precipitated
 under these  circumstances, since  those of the first,  second, and
 third group  form no sulphur compounds insoluble in water; and
 the affinity which the metallic radicals of the oxides  of  the fourth
 group possess for sulphur, combined with that manifested by hydro-
 gen for oxygen, is not sufficiently powerful to overcome the affinity
 of the metal for oxygen and of the oxide for a strong acid, if the
 LATTER IS PRESENT IN EXCESS.
  If therefore, after the removal of the oxide of silver and sub-
oxide of mercury, by means of  hydrochloric acid, we add to the
solution, which still contains free hydrochloric acid, 
 374       EXPLANATORY NOTES,  ETC., TO  §§ 185-207.

   2. Hydrosulphuric Acid,
 we remove from it the remainder of the oxides of the fifth, toge-
 ther with those of the sixth group, viz., oxide of lead, oxide of
 MERCURY,  OXIDE OF COPPER,  TEROXIDE OF BISMUTH, OXIDE OF CAD-
 MIUM, TEROXIDE OF GOLD, BINOXIDE  OF PLATINUM, PROTOXIDE OF
 TIN, BINOXIDE OF TIN, TEROXIDE OF ANTIMONY, ARSENIOUS  ACID, and
 arsenic acid.   All the other oxides remain in solution, either unal-
 tered, or reduced to a lower degree of oxidation, e. g. sesquioxide
 of iron to protoxide ; chromic acid to sesquioxide of chromium, &c.
  The sulphides corresponding to the  oxides of the  sixth group
 combine with basic metallic sulphides (the sulphides  of  the  alkali
 metals),  and form with them sulphur  salts soluble in water;  while
 the sulphides corresponding to the oxides of the fifth group do not
 possess this property, or possess it only to a limited extent.*   If,
 therefore,  we  treat the whole of the sulphides precipitated by
 hydrosulphuric acid from an acid solution, with—

  3. Sulphide  of Ammonium (or, in  certain cases,  Sulphide of
 Sodium),

 if necessary, with addition of some sulphur  or  yellow sulphide of
 ammonium, the sulphides  of mercury, lead, copper, bismuth, and
 cadmium remain undissolved, whilst the other sulphides dissolve as
 double compounds of sulphide of gold, platinum, antimony, tin,
arsenic, with  sulphide of ammonium (or,  as the case  may  be,
sulphide of sodium), and precipitate again from this solution upon
the addition of an  acid, either unaltered, or, as regards the proto-
sulphide  of tin and the tersulphide of antimony, in a state of higher
sulphuration—these  two compounds taking up sulphur from the
yellow sulphide of ammonium.  The rationale of this precipitation
is as follows :—The acid decomposes the sulphur salt formed.  The
 sulphur base (sulphide of ammonium or  sulphide of sodium) trans-
poses with the  constituents  of the water, forming  an oxygen base
 (oxide of ammonium or soda) and hydrosulphuric acid; the former
 combines with  the acid added, the latter escapes, and the liberated
 electro-negative sulphide (sulphur acid) precipitates.   If  the  acid
 is an hydracid, its radical combines with the  ammonium, its hydro-
 gen with the sulphur.  Sulphur precipitates  at  the same time, the
 sulphide of ammonium containing generally an excess of that ele-
 ment.  The analyst must bear in  mind that this eliminated sulphur
 makes the precipitated sulphides appear  of a  lighter color than
 they are naturally.
  The alkalies, the alkaline earths,  alumina, and sesquioxide of

  * Sulphide of mercury combines  with sulphide of potassium and sulphide of
 Bodium, but not with sulphide of ammonium; sulphide of copper dissolves a little it
 sulphide of ammonium, but not in sulphide of potassium or sulphide of sodium. 
           DETECTION OF THE BASES.—§§ 185-207.        375

chromium have remained in  solution, because their sulphur com-
pounds are soluble in water, or because their salts are not affected
in the least by hydrosulphuric acid ; the  sulphides  corresponding
to the oxides  of the  fourth  group are insoluble  in  water, and
would have been precipitated accordingly by hydrosulphuric acid,
but for the free acid present. If, therefore, this free acid is removed,
i. e., if the solution is made alkaline, and then treated with hydro-
sulphuric acid,  or, what answers both purposes at once, if

  4. Sulphide  of Ammonium,

is added to the solution,* the sulphides corresponding to the oxides
of the fourth group will precipitate : viz., the sulphides of  iron,
manganese,  cobalt, nickel,  and zinc.   But in conjunction with
them, alumina, sesquioxide of chromium, and phosphate of lime
are thrown down, because the affinity which the oxide of ammo-
nium possesses for the acid of the salt of alumina or of sesquioxide
of chromium, or for that which keeps the phosphate of lime in solu-
tion, causes the elements of the sulphide of ammonium to transpose
with those of the water, thus giving rise to the formation of  oxide
of ammonium  and  of hydrosulphuric acid. The former combines
with the acid, the latter escapes, being incapable of entering into
combination  with the liberated oxides or with the phosphate of
lime,—the oxides and the lime-salt precipitate.
  There remain now  in solution only the alkaline earths and the
alkalies.   The  neutral carbonates of the former  are insoluble in
water, whilst those of  the latter are soluble in that menstruum. If,
therefore, we now add

  5. Carbonate of Ammonia,

and some  ammonia, in order to prevent the formation of bicarbo-
nates, the whole of the alkaline earths ought to precipitate.  Thia
is, however, the case only as regards baryta,  strontia, and lime ;
of magnesia we know  that, owing to its disposition to form double
compounds with salts of ammonia, it precipitates only in part; and
that the presence of an additional salt of ammonia will altogether
prevent  its  precipitation.    To  guard against any  uncertainty
arising from this cause, chloride of ammonium is added previously
to the addition of the  carbonate of ammonia, and thus the precipi-
tation of the magnesia is altogether prevented.
  We have now in  solution magnesia and the  alkalies.  The detec-
tion of magnesia may be effected by means of phosphate of soda

  * After previous neutralization of the free acid by ammonia,  to prevent unneces-
sary evolution of hydrosulphuric acid; and the addition also, if necessary, of chloride
of ammonium to prevent the precipitation of magnesia by ammonia. 
376         ADDITIONAL REMARKS TO §§ 185-207.
and ammonia;  but its separation requires a different method, since
the presence of phosphoric acid would impede the further progress
of the analysis.  The process which serves to effect the removal of
the magnesia is based upon the insolubility of that earth in the
pure state. The substance under examination is accordingly ignited
in order to expel the salt of ammonia, and  the magnesia is  then
precipitated  by means  of .baryta, the alkalies, together with the
newly formed salt of baryta and the excess  of the caustic baryta
added,  remaining in solution.  By the addition  of carbonate of
ammonia, the compounds of baryta are removed from the solution,
which now only contains the fixed alkalies, the salt of ammonia
formed, and the excess of the salt of ammonia added.   If the salts
of ammonia are then removed by ignition, the residue  consists of
the fixed alkalies  alone.  This method of  separating  the baryta
affords the advantage over  that  of effecting the removal of that
earth by means of sulphuric acid, that the alkalies are obtained in
the most convenient  form for their subsequent individual detection
and isolation, viz., as chlorides.   But as carbonate of baryta is
slightly soluble in salts  of ammonia,  and gives, upon evaporation
with  chloride of ammonium, carbonate of baryta and  chloride of
barium, it is usually necessary, after  the expulsion of the salts of
ammonia by ignition, to precipitate it once more with carbonate
of ammonia,  in  order to obtain a solution perfectly free from baryta.
Lastly, to effect the  detection of the ammonia, a fresh portion of
the substance must of course be taken.

                 b.  Detection  dF the Acids.
  Before passing on  to the examination for acids and salt radicals,
the analyst should first ask himself which  of these substances may
be expected to  be present, from the nature of the detected bases
and the class to which the substance under examination belongs
with respect  to its solubility in water  or acids, since this will save
him the trouble of unnecessary experiments.  Upon this point I
refer the student to the  table in Appendix IV., in which the various
compounds are arranged according to their several degrees of solu-
bility in water and acids.
  The general reagents applied for the detection of the  acids are,
for the inorganic acids chloride of barium and nitrate of silver,
for the organic acids chloride of calcium and sesquichloride of
iron.  It is  therefore indispensable that the analyst  should  first
assure himself whether the substance under examination contains
only  inorganic  acids, or whether the presence of  organic  acids
must also be looked for.  The latter  is invariably the  case, if the
body, when ignited,  turns black, owing to separation of carbon.—
In the examination for bases the different reagents serve to effect
the actual separation  of the several groups of bases from each 
            DETECTION OF THE ACIDS.—§§ 185-207.       377

 other;  but  in  the examination for  acids  they serve  simply  to
 demonstrate the presence or absence of the acids belonging to the
 different groups.
   Let  us  suppose we have  an aqueous solution  containing the
 whole of the acids, in combination with soda, for instance.
   Baryta forms insoluble compounds with  sulphuric acid, phos-
 phoric acid,  arsenious acid, arsenic acid, carbonic acid, silicic  acid,
 boracic acid, chromic acid,  oxalic acid, tartaric acid, and citric
 acid; fluoride of barium also  is insoluble  or, at least, difficultly
 soluble ; all  these compounds are soluble in hydrochloric acid, with
 the exception of sulphate of baryta.  If, therefore, to a portion  of
 our neutral or, if necessary, neutralized solution, we add,
   1.  Chloride of Barium,
 the formation of a precipitate will denote the presence of at  least
 one of these acids.  By treating the precipitate with hydrochloric
 acid, we learn at once whether sulphuric acid is present or not, as
 all the salts of baryta being  soluble in this  menstruum, with the
 exception of the sulphate, a residue left undissolved by the hydro-
 chloric acid can consist only of the latter salt.   When sulphate of
 baryta is present, the reaction with chloride of barium fails to lead
 to the positive detection  of the whole of the other acids  enume-
 rated.  For  upon filtering the hydrochloric solution  of the precipi-
 tates and  supersaturating  the  filtrate with  ammonia, the borate,
 tartrate, citrate, &c, of baryta do not always fall down again, being
 kept in solution by the chloride of ammonium formed.  For this
 reason, chloride of barium cannot serve to effect the  actual separa-
 tion of the whole of the acids named, and except as regards sul-
 phuric acid, we set no value upon this reagent as a means of effect-
 ing their individual detection.   Still it is  of great importance  as a
 reagent, since the non-formation of a precipitate upon its  applica-
 tion in neutral or alkaline solutions, proves at once the absence of
 so considerable a number of acids.

   The compounds of silver with sulphur,  chlorine, iodine, bromine,
 cyanogen, ferro- and ferricyanogen, and of the oxide of silver with
 phosphoric acid, arsenious acid, arsenic acid, boracic acid, chromic
 acid,  silicic acid, oxalic  acid, tartaric acid, and citric acid, are
 insoluble in water.  The  whole of these compounds are soluble  in
 dilute nitric acid, with the exception  of  the  chloride, iodide, bro-
 mide, cyanide, ferrocyanide,  ferricyanide, and sulphide of silver.
 If therefore, we add  to  our solution, which, for the  reason  just
 now stated, must be perfectly neutral,
   2.  Nitrate of  Silver,
and precipitation ensues, this shows at once the presence of one or
several of the acids enumerated • chromic acid, arsenic acid, and 
 378         ADDITIONAL REMARKS TO §§ 185-207.

 several others, which form colored salts  with  silver, may be  indi-
 vidually recognised with tolerable certainty by the mere colw  of
 the precipitate.  By treating the precipitate now  with nitric  acid,
 we see whether it contains any of the haloid compounds of silver,
 or sulphide of silver, as these remain undissolved, whilst all the
 oxide salts dissolve.—Nitrate of silver fails to effect the complete
 separation of those  acids which form  with oxide of silver  com-
 pounds insoluble in water, from the same cause which  renders the
 separation of acids by chloride of barium uncertain, viz. the ammo-
 niacal salt formed  prevents  the reprecipitation of several of the
 salts  of silver by ammonia, from the acid solution.  Nitrate of sil-
 ver, besides effecting the separation of chlorine, iodine, bromine,
 cyanogen, &c, and indicating the presence of chromic  acid,  &c,
 serves,  like the  chloride  of barium, to demonstrate  at once the
 absence of a great many acids, where it produces no precipitate in
 neutral solutions.
  The deportment  which the solution under examination exhibits
 with  chloride of barium and with nitrate of silver,  indicates there-
 fore at once the further course of the  investigation.   Thus, for
 instance,  where chloride  of barium  has produced a precipitate,
 whilst nitrate of silver  has  failed to do so, it is not  necessary to
 test for phosphoric acid, chromic  acid,  boracic acid, silicic acid,
 arsenious acid, arsenic acid, oxalic  acid, tartaric acid, and citric
 acid, provided always the solution did not already contain salts of
 ammonia.  The  same circumstance is to be considered in case we
 obtain a precipitate  by nitrate of silver, but none by chloride of
 barium.
  Returning now to the supposition which we have assumed here,
 viz., that the whole  of the acids are present in the solution under
 examination, the reactions with chloride of barium and nitrate of
 silver would accordingly have demonstrated already the presence of
 sulphuric acid, and led to the application of the  special tests for
 CHLORINE,  BROMINE,  IODINE, CYANOGEN,  FERROCYANOGEN, FERRI-
CYANOGEN, and sulphur ;* and there would be reason  to test for all
the other acids precipitable by these two reagents.  The detection
of these acids is based upon the results of a series of special ex-
periments, which have already been fully described and explained
in the course of the present work: the same  remark applies to
the rest of the inorganic acids, viz., nitric acid and chloric acid.
  Of  the  organic acids, oxalic acid, paratartaric acid, and tartaric
acid, are precipitated by chloride of calcium in the cold, in presence
of chloride of ammonium; the two  former immediately, the latter
often  only after some time ; but the  precipitation of citrate of  lime
is prevented by the presence of salts of ammonia, and ensues  only

  * For the separation and special detection of these substances, I refer to § 1G0. 
           THE COURSE OF ANALYSIS.—§§ 185-207.        379

upon  ebullition  or upon mixing the solution  with  alcohol; the
latter agent serves also to effect the separation of malate of lime
from aqueous solutions.  If, therefore, we add to our fluid,—

  3. Chloride of Calcium and Chloride of Ammonium,

oxalic acid, paratartaric acid, and tartaric acid are precipitated,
but the lime-salts  of several inorganic  acids, which have  not yet
been separated, phosphate of lime, for  instance, precipitate  along
with them.  We must therefore select for the individual detection
of the precipitated organic acids such reactions only as  preclude
the possibility of confounding the organic acids with the inorganic
acids  that have been thrown  doAvn along  with  them.  For the
detection of oxalic acid we select accordingly solution of sulphate of
lime, with addition of acetic acid (§ 148); to effect the detection of
the tartaric and paratartaric acids, we  treat the precipitate pro-
duced by chloride of calcium with solution of soda, since the lime-
salts of these two acids only are soluble in this menstruum  in the
cold, but insoluble upon ebullition.
  Of the organic acids we have  now still in solution citric acid and
malic acid, succinic acid and benzoic acid,  acetic acid  and formic
acid.   Citric acid and Malic  acid precipitate upon addition of
alcohol to the fluid filtered from the oxalate, tartrate, &c, of lime,
and which still contains an excess of chloride of calcium.  Sulphate
and borate of lime invariably precipitate along with the  malate and
citrate of lime, if sulphuric acid and boracic acid happen to be pre-
sent ; the analyst must therefore carefully guard against confound-
ing the lime precipitates of these acids with those of citric  acid and
malic acid.  The  alcohol is now removed by  evaporation, and to
the perfectly neutral solution,—

  4. Sesquichloride of Iron

is added.  This reagent precipitates succinic acid and benzoic
acid, in combination with sesquioxide  of iron, whilst formic acid
and acetic acid remain in  solution.  The methods which serve to
effect the separation of the several groups from each other, and the
individual detection of the various acids, have been fully described
and explained in the former part of this work.

  B.  Special Remarks and  Additions  to  the Systematic
                      Course  of Analysis.

  In this section attention will be directed to various points which
could not  be noticed in the course of  analysis, and explanations
will be given, in small type, how to proceed when the presence  of
the rarer elements is suspected. 
380        ADDITIONAL REMARKS, ETC.,  TO § 192.


                           To § 192.
  At the commencement of § 192, the  analyst is directed to mix
neutral or acid aqueous solutions  with hydrochloric acid.   Thia
should be done drop by drop.  If no precipitate forms, a few drops
are sufficient, since the only object in that case is to acidify the fluid
in order to prevent the subsequent  precipitation  of the  metals  of
the iron group, by hydrosulphuric acid.   In the case of the forma-
tion of a precipitate, some chemists recommend that a fresh portion
of the solution should be acidified with nitric acid.   However, even
leaving the fact out of consideration that nitric acid also produces
precipitates in many  cases—in a  solution  of potassio-tartrate  of
antimony, for  instance—I prefer the use of hydrochloric  acid, i. e.
the complete precipitation by that acid of all that is precipitable
by it, for the following reasons :—1. Metals are more readily pre-
cipitated  by hydrosulphuric  acid  from solutions  acidified  with
hydrochloric acid, than from those acidified with  nitric  acid;—2.
In cases where the solution contains silver, suboxide of mercury,
or lead, the further analysis is materially facilitated by the total or
partial precipitation of these three  metals in the form of chlorides;
—and 3.  This latter form is the best adapted for the  individual
detection of these three metals  when present in the same solution.
Besides, the application of hydrochloric acid saves  the necessity of
examining whether the mercury, which  may be subsequently de-
tected with the other metals of the fifth group, was originally pre-
sent in the form of oxide or in that of suboxide.  That the lead, if
present in large proportion, is obtained partly in  the form of' a
chloride, and partly in the precipitate produced by hydrosulphuric
acid in the acid solution, can hardly be thought an  objection to the
application of this method, as the removal of the larger portion of
the lead from the solution, effected  at the commencement, will only
serve to facilitate the examination  for other metals of the fifth and
sixth groups.
  As already remarked, a basic salt of teroxide  of antimony may
separate from potassio-tartrate of  antimony, for instance, or from
some other analogous compound,  and precipitate along with the
insoluble  chloride  of silver and subchloride of mercury, and the
sparingly soluble chloride of lead.  This precipitate, however, is
readily soluble  in  the excess of hydrochloric acid which is sub-
sequently  added, and exercises therefore  no influence  whatever
upon the  further process.   The application of heat to the fluid
mixed  with hydrochloric acid  is  neither necessary nor even  ad-
visable, since  it might cause  the  conversion of  a  little  of  the
precipitated subchloride of mercury into chloride.
  Should bismuth or chloride of antimony be present, the addition
of the washings of the precipitate produced by hydrochloric acid 
           THE  COURSE  OF ANALYSIS.—§§  193, 194.       381

to the first filtrate will cause turbidity, if the amount of free hydro-
chloric acid present is not sufficient to prevent the separation of the
basic salt.  This turbidity exercises, however, no  influence upon
the further  process,  since hydrosulphuric acid as readily converts
these finely-divided  precipitates into  sulphides, as if the  metals
were in actual solution.
   In the case of alkaline solutions, the addition of hydrochloric
acid must be continued until the fluid shows a strongly acid reaction.
The substance which causes the alkaline reaction  of the fluid com-
bines with  the hydrochloric  acid,  and the bodies  originally dis-
solved in that acid separate.  Thus, if the alkali was present in the
free state, oxide of zinc, for instance, or alumina,  &c, may pre-
cipitate.  But these  oxides redissolve in an excess of hydrochloric
acid, whereas chloride of  silver would not redissolve, and chloride
of lead only with  difficulty.   If a  metallic sulphur  salt was  the
cause of the  alkaline reaction, the  sulphur acid, e. g., tersulphide
of antimony,  precipitates  upon the  addition  of the  hydrochloric
acid, whilst the sulphur base, e. g., sulphide of sodium, transposes
with the constituents of the hydrochloric acid, forming chloride of
sodium  and  hydrosulphuric  acid.    If  an alkaline  carbonate,  a
cyanide, or the sulphide of an alkali metal was  the cause  of the
alkaline  reaction,  carbonic acid, hydrocyanic  acid,  or hydrosul-
phuric acid escapes.   All these  phenomena should  be  carefully
observed by the analyst, since they not only indicate the presence
of certain substances, but demonstrate also the  absence of entire
groups of bodies.

  In solutions which contain alkaline salts of antimonic, tantalic, hyponiobic, molyb-
dic or tungstic acids, hydrochloric acid likewise throws down precipitates. Those
yielded by antimonic, tantalic and molybdic acids, dissolve in excess (the tantalic
precipitate to an opaline liquid).  Hyponiobic and tungstic acids are, on the contrary,
insoluble in excess of hydrochloric acid.  The last two acids therefore remain with
the precipitate, which may also contain chloride of silver, subchloride of mercury,
chloride of lead, and silicic acid.   The separation of sulphur, beginning some time
subsequent to the addition of hydrochloric acid and attended by the evolution of sul-
phurous acid, indicates hyposulphites.
                       To §§ 193 and 194.
  To make  an analysis in the shortest possible time, the experi-
menter must accustom  himself to  carry on  several processes  at
once, and not to stand in idleness during an operation that requires
time.  Thus, after having procured  a hydrosulphuric acid precipi-
tate, instead of waiting until it is completely washed before going
further the analyst  may test  the first drops of  the filtrate with
hydrosulphuric acid  to  make sure that the precipitation is perfect,
and such being the  case, he  may add  sulphide  of ammonium  to
learn whether bases of Groups III. and IV. are present, and in their
absence  carbonate of  ammonia may be  employed to decide  the 
382         ADDITIONAL REMARKS TO §§  193,  194.
presence or absence  of alkaline earths.  When these experiments
are finished, the filtrate will usually be ready to treat with sulphide
of ammonium  or  carbonate of ammonia as the case may require,
and the second precipitate may be brought upon a filter while the
first is being washed.  As  soon as the first is washed sufficiently,
it may be digested with sulphide of ammonium, while at the same
time the second precipitate is washing.  In this way, after a little
practice, the analyst  will learn  to  occupy his  time fully, and will
be able  to accomplish double  the work that would  otherwise be
possible.   [The beginner  should  not fail to use the  necessary
means to avoid confusion.  For this purpose his precipitates, solu-
tions, &e., should be labelled, especially when several operations
are going on side by side or when his  products must stand over
night.   In most cases it is only necessary to write upon the paper
cover of the vessel or upon a slip of gummed paper attached to its
side, the marginal number of the  analytical course belonging to
the paragraph  according to which the solution or  precipitate is to
be treated on resuming work.   No matter how powerful may be
one's memory, the habit of labelling will often save from perplexing
uncertainty and effect a real economy of time.]
  In cases where  the analyst has simply to  deal with metallic
oxides of the sixth group—e. g., teroxide of antimony—and of the
fourth or fifth group—e. g., iron or bismuth—he need not precipi-
tate the acidified solution with hydrosulphuric acid, but may, after
neutralization, at once add sulphide of ammonium in  excess.   The
sulphide of iron, &c, will in that case precipitate, whilst the anti-
mony, &c, will remain in  solution, from which they will, by addi-
tion of an acid, at once be thrown down as tersulphide of antimony,
&c.   This method has the advantage that the fluid is diluted less than
is the case where solution of hydrosulphuric acid is employed, and
that the operation is performed more expeditiously and  conve-
niently than is the case where hydrosulphuric acid gas is conducted
into the fluid.  The beginner  must bear well in  mind that he is
very liable to fall into error in the precipitation by hydrosulphuric
acid, by employing  a solution  of  the  latter  that is  too weak or
altogether spoiled, or by adding it in too small quantity, as well as
by passing the  gas into a solution that is  too  concentrated or con-
tains too great an excess of hydrochloric or nitric acid.   Suppose,
for instance, that a very strongly acid solution of iron and bismuth
is in hand; addition  of a little  solution of hydrosulphuric acid, or
transmission of the gas, produces no precipitate on account of the
large excess  of acid.  It is thence concluded that no  base, pre-
cipitable  by  hydrosulphuric  acid,  is  present, and  the analyst
naturally proceeds to add sulphide of ammonium,  and thus obtains
sulphide of bismuth,  together with the sulphide of iron.   On treat-
ing this precipitate with  dilute  hydrochloric acid, a black residue 
             THE  COURSE OF ANALYSIS.—§§ 195,  196.        383

remains which is at once mistaken for cobalt or nickel.   When the
beginner has  thus lost  his  way it is very difficult to set himself
right again.   Acid solutions must therefore be sufficiently diluted,
and it must not  be neglected to warm them, as otherwise arsenic
acid may be overlooked.
   On treating acid solutions with hydrosulphuric acid, or on acidi-
fying the sulphide  of ammonium in which the hydrosulphuric  pre-
cipitate has been digested, precipitates are often  obtained which
so closely  resemble  pure  sulphur that  the  operator  is  in doubt
whether to test  them for metals.   In  such  cases, the precipitate
may be washed first with  water, then  with  alcohol, and finally
digested with bisulphide of  carbon, which  takes up sulphur, leav-
ing in a pure state any metallic sulphide.

   The precipitate produced by hydrosulphuric acid in acid solutions may contain the
Bulphides of the following rarer elements: Palladium, rhodium, osmium, ruthenium,
iridium,* molybdenum,  tellurium, selenium.f
   The following cause a separation of sulphur, by  oxidizing the hydrogen  of the
hydrosulphuric acid, viz.:  The higher oxides and chlorides of manganese and cobalt,
vanadic acid (the liquid becoming blue), nitrous, sulphurous, hyposulphurous, hypo-
chlorous, chlorous, bromic and iodic acids.
   On digesting  the  precipitate with sulphide of ammonium (sulphide of sodium)
there pass into solution (with sulphides of antimony, arsenic, &c), the  sulphides of
iridium, molybdenum, tellurium,  and selenium, while the sulphides of palladium,
rhodium, osmium, and ruthenium remain undissolved.

                                To § 195.
   When the precipitate which contains all the sulphides  of metals of group VI.,
viz., tin, antimony, arsenic, tellurium, selenium, molybdenum,  gold, platinum, and
iridium, is fused with carbonate and nitrate of soda,  and the fused mass is treated
with cold  water, as directed § 195, there pass into solution with arsenic acid, tel-
luric, selenic, and molybdic acids, while iridium remains in the  residue, with binox-
ide of tin, antimonate of soda, gold and platinum.
   The mode of detecting  the rarer elements in the solution and residue may be
gathered from § 138.

                               To  § 196.

   Besides the methods described in  the  systematic  course to  dis-
tinguish between cadmium,  copper, lead, and bismuth, the follow-
ing process will also  be found to give highly satisfactory  results.
Add carbonate of  soda to  the nitric acid  solution as long as a pre-

   * The platinum metals are not easy to precipitate completely by  hydrosulpkuric
acid.  The gas must be passed into the solution a long time with application  of a
gentle heat.
  + Tunesten and vanadium are not found in the precipitate produced by hydrosul-
phuric acid in  acid solution.  When the solution is  first treated  with sulphide of
ammonium, and then with hydrochloric or other strong acid in  excess, they remain
undissolved (as do sulphides of nickel and cobalt), and mixed with the sulphides o'
groups V.  and VI. 
384             ADDITIONAL REMARKS  TO  § 197.
cipitate continues to form, then solution of cyanide of potassium in
excess, and heat gently.  This effects the complete separation  of
lead  and  bismuth  in  the  form  of carbonates, whilst copper and
cadmium are obtained in solution in the form of cyanide of copper
and potassium, and cyanide of cadmium and potassium.   Lead and
bismuth may now be readily separated from one another by means
of sulphuric acid.   The separation of the copper from the cadmium
is effected by adding to the solution of the  cyanides  of these two
metals in cyanide  of  potassium, hydrosulphuric acid  in excess,
gently heating, and then  adding some more cyanide of potassium,
in order to redissolve the sulphide of copper which may have pre-
cipitated along with the sulphide of cadmium.  A residuary yellow
precipitate  (sulphide  of cadmium),  insoluble in  the cyanide of
potassium,  demonstrates  the  presence of  cadmium.   Filter  the
fluid  from this precipitate, and add hydrochloric acid to the filtrate,
when the formation  of a  black precipitate (sulphide of popper)
will demonstrate the presence of copper.

  If the sulphides of palladium, rhodium, osmium, and ruthenium  are suspected in
the  precipitate containing sulphide of copper, sulphide of bismuth, &c, proceed aa
follows:
  Fuse the precipitate with hydrate and chlorate of potassa, carrying the heat
finally to redness.  Treat the cooled mass with water.  The solution now contains
osmate and ruthenate  of potassa, and is colored deep yellow by the latter salt.
Neutralize cautiously with nitric acid, when black oxide of ruthenium separates. Add
to the filtrate more nitric acid and distil;  osmic acid passes over.
  The residue undissolved in water is gently ignited in a stream of hydrogen gas (in
which process cadmium may volatilize) and cautiously treated with dilute nitric
acid which dissolves copper, lead, &c,  and leaves behind rhodium and palladium.
Aqua  regia dissolves palladium,  while rhodium remains unaffected.  As  to the
further examination  of  the metals thus separated, refer to § 127.  Mercury maybe
looked for in a separate  portion of the precipitated sulphides.

                               To § 191.
  In case the solution filtered from the hydrosulphuric  acid precipitate contains all
the  elements  of groups III. and IV. we obtain, when  the solution is treated with
chloride and sulphide of ammonium and ammonia in excess, a precipitate in which
occur.
    a. As sulphides: Cobalt, nickel, manganese, iron, zinc, uranium and [thallium].
    6.  As oxides:  Aluminum, glucinum, thorium, zirconium, yttrium, terbium,
  erbium,  cerium,  lanthanum,  didymium,  chromium, titanium,  tantalum  and
  niobium*.
  When the rarer elements are suspected, the following course of analysis is in
many  cases the most satisfactory :
  Wash and dry the precipitate, roast it in a porcelain crucible and then fuse it  in
a platinum crucible with bisulphate of potassa for a considerable time.  Digest the
cooled mass for some time in cold water and filter.
  The residue which may contain tantalum and niobium, as well as silica and some

  * A small quantity of hyponiobic acid, redissolved  by hydrochloric acid in the
precipitation by that reagent, may be present. 
THE COURSE  OF  ANALYSIS.—§  197.            385
undissolved oxides of iron and chromium,  is fused with hydrate and a little nitrate
of soda, and digested  in soda-lye.   Chromate and silicate  of  soda are  dissolved,
while tantalate and hyponiobate  of  soda (which are insoluble in soda-lye) remain
with  oxide of iron.   After  removing the excess  of soda-lye the residue is treated
repeatedly with a very dilute solution of carbonate  of  soda  in  which the hyponio-
bate of soda dissolves much more easily than the tantalate.   Test further accord-
ing to § 107, 11 and 12.
   The solution which  contains all the other  elements of  groups  III. and IV. is
first treated with hydrosulphuric acid  to reduce sesquioxide of iron, then largely
diluted and heated for  a long time to boiling,  a current of carbonic acid  being at
the same time passed through it.   Any precipitate thus produced is to be examined
for titanic acid ;  it may also possibly contain  some zirconia.
   The filtrate is concentrated by evaporation with addition of nitric acid and precipi-
tated with ammonia: the  washed precipitate  is dissolved in hydrochloric acid and
again precipitated with ammonia.  In this manner zinc, manganese, nickel, cobalt
[and thallium]* are obtained almost completely in solution while  the earths and
other oxides remain in the precipitate.   The latter is again dissolved in hydrochloric
acid and  treated cold with excess of concentrated solution of potassa.  Chromium,
alumina and glucina pass into the  solution, while the other earths remain  with  the
oxides of  iron and uranium.  On diluting the alkaline solution and boiling it for
some time the glucina  and oxide  of  chromium are thrown down while alumina
remains dissolved and may be precipitated by means of chloride of ammonium.
   The precipitate is fused with  carbonate and nitrate of soda,  and chromic acid and
glucina are separated as  directed § 106 for the separation of alumina and chromic
acid.
   The precipitate which  consists of the sesquioxides of iron and uranium and the
earths  insoluble in potassa, may also under some  circumstances, viz. in presence of
yttria and oxide of cerium, contain glucina and alumina.  [It may likewise consist
in part  or entirely of  alumina and magnesia which are sometimes thrown down
together by ammonia in a combination which requires  a large excess of chloride of
ammonium to prevent its formation, and which is quite insoluble in potassa.   Before
examining for rare earths resolve this  precipitate if possible by repeatedly dissolv-
ing in hydrochloric acid and precipitating in presence of chloride of ammonium.   If
it remain undiminished by this treatment, and if no magnesia be found in the solu-
tions after precipitating by ammonia, proceed as follows]
   The precipitate is dissolved in hydrochloric acid,  and the excess of acid is mostly
removed by evaporation.   To the cold solution  carbonate of baryta is added and  the
mixture is allowed to stand 4 to 6  hours.
   The precipitate thus  formed, contains the sesquioxides of iron and uranium, and
any alumina that escaped  previous precipitation,  after dissolving  in hydrochloric
ncid, the uranium is removed from the iron and alumina by  an  excess of carbonate
of ammonia.
   The liquid filtered from the precipitate by carbonate  of baryta is freed from baryta
by a slight excess of sulphuric  acid, brought to a small bulk by evaporation, exactly
or at least very nearly  neutralized  by means of potassa (the reaction should be acid
rather than alkaline),  and crystals of neutral  sulphate of potassa are added, after

   * [In the solution thallium may be detected by the yellow precipitate it  yields
with iodide of potassium, or by the reaction with bichloride of platinum (confirm by
the flame test and spectroscope).   It may  be separated from all the other bases of
the fourth group by boiling the solution with carbonate of soda (if ammonia salts are
present until these'are  decomposed and ammonia completely dissipated) carbonate of
thallium  remains in the solution  especially while hot, and  all  the other bases  are
converted into insoluble carbonates or oxides.]
                                       25 
 386      ADDITIONAL REMARKS, ETC., TO  §§  198-201,  206.

 which the liquid is boiled a short time and then left at rest for 12 hours.   Any pre-
 cipitate is filtered off and washed with a solution of sulphate of potassa.
   The filtrate contains that portion of the glucina which may have escaped solution
 by potassa, also yttria (together with erbia  and terbia).   These substances are pre-
 cipitated by ammonia, and may then be easily separated by treating with a concen-
 trated warm  solution of oxalic  acid, in which  the  glucina is soluble, whilst the
 oxalates of yttria and of erbia  and  terbia are left undissolved.  Now boil the
 precipitate of the double sulphates of zirconia, &c, and potassa repeatedly  in water,
 with addition of some hydrochloric  acid, which will  dissolve the thoria  and the
 oxides op  cerium,  lanthanum and didymium, leaving the sulphate  of  zirconia
 and potassa undissolved.  The thoria and  the  oxides of cerium, <kc, may then be
 precipilated from the solution by ammonia, and tested by the reactions described
 in § 107.

                                To  §§  198—201.
   The fluid filtered from the precipitate produced by sulphide of ammonium may not
 only contain the alkaline earths and the alkalies, but some nickel, and  also vanadic
 acid and that portion of the tungstic acid which has been left unprecipitated by
 hydrochloric acid.  The  nickel, the vanadic acid, and the tungstic acid, are present
 as sulphides dissolved in excess of  sulphide of ammonium; they are thrown down
 in that form by just acidifying the  fluid with hydrochloric acid.   Filter the precipi-
 tate, wash, dry, fuse with carbonate of soda and nitrate of potassa, and  treat the
 fused mass with water;  this will dissolve the vanadate  and tungstate of potassai
 leaving the protoxide of nickel  undissolved.  From this solution the  vanadic
 acid may be separated by means of solid chloride of ammonium, the tungstic acid
 by evaporating with hydrochloric acid and treating the residue with water.   The
 two acids may then be examined as directed § 116, b, and § 138, c.
   For the  detection  of  lithium,  caesium, and rubidium, I  refer  to the analysis of
 mineral waters (258) and (259).

                                  To § 206.
   If the rarer elements are taken into account, the-number  of bodies which are left
 undissolved by treating  a  substance  under  examination with water, hydrochloric
 acid, nitric acid, and  aqua regia, is much enlarged.   The following bodies,  more
 especially, are either altogether, or in the ignited state, or in certain combinations,
 insoluble or slowly and sparingly soluble in acids:
   Glucina, thoria, and zirconia;  the oxides of cerium, lanthanum, and didymium;
titanic acid and tantalic acid;  hyponiobic acid and niobic  acid; molybdic  acid and
tungstic acid; rhodium, iridium, osmio-iridium, ruthenium.
  When you have, in the systematic course  of analysis, arrived at (20§), fuse the
substance, free  from  silver, lead, and sulphur,  with carbonate of soda and  some
nitrate of potassa, extract the fused  mass repeatedly with hot water, and, if a residue
is left, fuse this some time, in a silver crucible, with hydrate of potassa and nitrate of
potassa, and again treat the fused mass repeatedly with water.    The alkaline solu-
tions, which may be examined  separately  or  together,  may contain glucina,  a
portion of the  titanic acid, the tantalic acid, the niobic  acids, the molybdic acid,
the tungstic acid, the  osmic  and  ruthenic  acids,  and a  portion of  the  iridium
present.
   If the residue left  undissolved by  the preceding operation is fused with acid sul-
phate of potassa, and the fused mass treated with water, the thoria and zirconia, the
oxides of  cerium, the remainder  of the titanic acid, and the rhodium may dissolve.
A  residue left by  this operation may consist  of platinum metals  that have escaped
decomposition by fluxing,  and had best be mixed with chloride of  sodium, and
ignited in  a stream of chlorino. 
ANALYSIS  OF CYANIDES.—§ 207.            387
  With respect to the separation and individual detection of the several elements
that have passed into the different solutions, the requisite directions and instructions
have been given  in the third section of Part I., and in the additional remarks to
§§ 192—201.

                           To  § 207.
  The analysis of cyanogen compounds is not very easy in certain
cases, and it is sometimes a difficult task even to ascertain whether
we have really a cyanide before  us or not.  However, if the reac-
tions of  the  substance under examination upon ignition (§) be
carefully  observed,  and also whether upon boiling with hydro-
chloric  acid any odor  of  hydrocyanic acid is emitted  (35), the
presence or absence of a cyanide will generally not long remain a
matter of doubt.
  It must above all be borne in mind that the insoluble  cyanogen
compounds  occurring in pharmacy, &c, belong  to two distmct
classes; viz. they are either simple cyanides, or  compounds of
metals with  ferrocyanogen or some other analogous compound
radical.
  All the simple cyanides are decomposed by boiling with concen-
trated hydrochloric acid into  metallic chlorides  and hydrocyanic
acid.  Their analysis is therefore never difficult.   But  the ferro-
cyanides,  &c, to which indeed  the method described § 207 more
exclusively  refers, suffer by acids such complicated  decompositions
that their analysis by means of acids is a task not so easily accom-
plished.   Their decomposition  by potassa  or soda is  far more
simple.  The alkali yields its oxygen to the metal  combined with
the  ferrocyanogen, &c, the oxide thus  formed  precipitates, and
the reduced potassium or sodium forms with the liberated radical
soluble  ferrocyanide, &c, of potassium  or sodium.  But several
oxides are soluble in an excess of potassa, as, e. g.,  oxide of lead,
oxide of  zinc, &c.   If, therefore, the double ferrocyanide of  zinc
and potassium, for  instance, is boiled with  solution  of caustic
potassa, it dissolves completely in that  menstruum, and we may
assume  that the solution contains ferrocyanide of  potassium and
oxide of  zinc dissolved in potassa.  Were we to  add an acid to
this solution, we should of course simply re-obtain the original pre-
cipitate of the double ferrocyanide of zinc and potassium, and the
experiment  would consequently be of no avail.  To prevent  this
failure we conduct hydrosulphuric acid into the solution in potassa,
but only until the precipitable oxides are completely thrown down,
and not until the solution smells of sulphuretted  hydrogen.  This
serves to  convert into  sulphides all the  heavy metals  which the
potassa holds in solution  as oxides.  Those sulphides which are
insoluble in  potassa, such as sulphide of lead, sulphide of zinc, &c,
precipitate,  whilst those which  are soluble in alkaline  sulphides, 
388        ADDITIONAL  REMARKS, ETC., TO §  207.

such as bisulphide of tin, tersulphide of antimony, &c, remain in
solution.   To  effect  the detection of these also, the fluid is  now
acidified with  nitric  acid, and, if necessary, hydrosulphuric acid ia
conducted into the solution.  (The liquid must be  diluted before
adding the nitric acid, and too great an excess of the last must be
avoided, as, otherwise, the solution may acquire a blue color from
decomposition of hydroferrocyanic acid set at liberty by the nitric
acid.)
  The fluid filtered from the  precipitated oxides and sulphides
accordingly always contains the cyanogen as ferrocyanide, &c, of
potassium—provided, of course, the analyzed compound is really
a double  ferrocyanide, &c.  From most of these compounds—
ferrocyanide, ferricyanide, chromicyanide, and manganocyanide of
potassium—the  cyanogen partly separates  as  hydrocyanic acid,
upon boiling  the  solutions with sulphuric acid, and may thus be
readily detected by this means, should the direct way of detecting
the radicals not  succeed.  But the cobalticyanide of potassium is
not decomposed by sulphuric acid, and the analyst is accordingly
directed to  effect the detection  of the compound radical in  that
salt by means of solution of nickel, manganese, zinc, &c.  By fusion
with nitrate of potassa, all these double  compounds suffer decom-
position, cobalticyanide of potassium not excepted.  The fusion of
these double compounds  with nitrate of potassa should be  pre-
ceded by evaporation with  an excess of nitric  acid, to  prevent
the occurrence of explosions.  Caution is highly  advisable in this
operation.
  If you simply wish to examine  for bases in simple or compound
cyanides, and for that purpose to destroy the cyanogen compound,
drench it in the state of powder with concentrated sulphuric acid
diluted with a little water, and heat in a platinum vessel  so  long
and so highly as is needful to  expel nearly  all the free sulphuric
acid.  The  residue now consists of sulphates which are dissolved
in water and in hydrochloric acid for further analysis.  H. Rose*
* Zeitschrift fur Analytische Chem. 1, 194 
APPENDIX.
                              I.

Deportment of  the most important Medicinal Alkaloids
  with Reagents,  and Systematic Method of  effecting the
  Detection of these Substances.

                            §  232.
The detection and separation of the vegeto-alkalies, or alkaloids, is
a task of far greater difficulty than that  of most of the inorganic
bases.  Although this difficulty is in some measure owing to the
circumstance that scarely one of the compounds which the alkaloids
form with other substances is absolutely insoluble or particularly
characterized by its color or any striking property, yet the principal
cause of it must be ascribed to the want of accurate and minute in-
vestigations of the salts and other compounds of the alkaloids, and
of the products of their decomposition. We consequently generally
see  and apprehend the reactions only in their external manifestation,
but without being able to connect them with the causes producing
them, which makes it impossible to understand all the conditions
which may exercise a modifying influence.
  Although, therefore, in the present imperfect state of our know-
ledge of these bodies, an attempt to define their deportment with
reagents, and base thereon a method of effecting their separation
or, at least, their  individual  detection in presence of each other,
must of necessity fall very short of perfection,  yet,  having made a
great many experiments  on  the nature and deportment of these
substances, I will  attempt here, for the benefit of young chemists,
and more particularly pharmaceutists, to describe in some measure
the  reactions which the most important of the alkaloids manifest
with other bodies, and lay down a systematic method of effecting
their individual detection.
  The classification  of the  alkaloids into groups which  I have
adopted  is  based  upon their  deportment with certain general re-
agents.   I have verified by  numerous experiments the  whole of
the  reactions described in the succeeding paragraphs.
  Recent investigations have shown that several of the alkaloids, 
390
APPENDIX.
[§ 233.
in the state  in which they are obtained by the usual methods of
preparing them, and in which they occur in  commerce or are used
in pharmacy, must not be looked upon as simple  organic bodies,
but as consisting of several, often even of many, very closely allied
alkaloids.  Thus, for instance, common narcotine contains three or
four homologous bases ;  thus Schutzenberger has produced from
so-called brucia, by fractional crystallization, ten alkaloids, analo-
gous in form of crystallization and in deportment with nitric acid,
but differing in  composition and in solubility in water.  As these
varieties have not as yet been studied with  regard to their re-
actions, I have of course  been obliged to disregard them altogether
in the subjoined course  of analysis, which therefore must be held
to refer simply to the vegeto-alkalies in the pure state, such as they
have hitherto been assumed to exist.

                    I. Volatile  Alkaloids.
  The volatile alkaloids  are fluid at the common temperature, and
may be volatilized in the pure state as well as when mixed with
water.  They are accordingly obtained in the distillate when  their
salts are distilled with strong fixed bases and water.  Their vapors,
when brought in contact with those of volatile acids, form a white
cloud.

              1. Nicotina, or Nicotine (C,0,H7 N).
                             § 233.
  1. Nicotina, in its pure state, forms a colorless, oily liquid, of
1*048 sp. gr.; the action of air imparts a yellowish or brownish
tint to it.  It boils at 482° F., suffering, however, partial decom-
position in the process ;  but, when heated in a stream of hydrogen
gas, it distils over unaltered, between 212° and 392° F. It is mis-
cible in all proportions with water, alcohol, and ether.
  Nicotina has a peculiar, disagreeable, somewhat ethereal, tobacco-
like  odor, an acrid, pungent taste, and very poisonous properties.
Dropped on paper, it makes a transparent stain, which slowly dis-
appears ; it turns turmeric-paper brown, and reddened litmus-paper
blue.   Concentrated aqueous solution of nicotina  shows these re-
actions more distinctly than the alkaloid in the pure state.
  2. Nicotina has the character of a pretty strong base ; it precipi-
tates  metallic oxides from  their  solutions,  and forms  salts  with
acids.   The salts of nicotina are freely soluble in water and alcohol,
insoluble in ether; they are inodorous, but  taste strongly  of to-
bacco ; part of them are crystallizable.  Their solutions,  when
distilled with solution of potassa, give a distillate  containing nico-
tina.   By  neutralizing  this  with oxalic acid,  and  evaporating,
oxalate of nicotina is produced, which may be freed from any ad- 
§ 234.]
APPENDIX.
391
 mixture of oxalate of ammonia, by means of spirit of wine, in which
 the former salt is soluble, the latter insoluble.
   3.  If an aqueous  solution of nicotina, or a  solution of salt of
 nicotina mixed with solution of soda or potassa,  is shaken with
 ether, the  nicotina is dissolved by the ether ; if the latter is then
 allowed to evaporate on a watch-glass, the nicotina remains behind
 in drops and streaks ; on warming the watch-glass, it volatilizes in
 white fumes of strong odor.
   4.  Bichloride of platinum produces in aqueous solutions of nico-
 tbna  whitish-yellow flocculent precipitates.   On heating the fluid
 containing the precipitate, the latter dissolves, but  upon continued
 application of heat it very speedily separates again in form of an
 orange-yellow, crystalline, heavy powder, which, under the micro-
 scope, appears to be  composed of roundish crystalline grains.  If a
 rather dilute solution of nicotina, supersaturated with hydrochloric
 acid, is mixed with bichloride of platinum, the fluid at first remains
 clear; after some time, however, the double salt separates in small
 crystals  (oblique, four-sided prisms),  clearly discernible with the
 naked eye.
   5.  Terchloride of gold  produces a reddish-yellow flocculent pre-
 cipitate, sparingly soluble in hydrochloric acid.
   6.  Solution of iodine in iodide of potassium  and water, when
 added in small quantity to an aqueous  solution of nicotina, produces
 a yellow precipitate, which after a time disappears.  Upon further
 addition of iodine solution, a copious  kermes-colored  precipitate
 separates; but this also disappears again after a time.
   7.  Solution of tannic acid produces  a copious white precipitate,
 which redissolves upon addition of hydrochloric acid.
   8.  If an aqueous solution  of nicotina is  added to a solution of
 chloride  of mercury in excess,  an  abundant, flocculent, white pre-
 cipitate is  formed.  If solution of chloride of ammonium is now
 added to the mixture in sufficient  quantity, the entire  precipitate,
 or the greater part of it, redissolves.   But the fluid very soon turns
 turbid, and deposits a heavy white precipitate.

                2. Conia, or Conine (Ci6 Hi5 N).
                             §  234.
   1.  Conia forms a colorless oily liquid, of  0*87 sp.  gr.; the action
 of the air imparts to it a brown tint.   In the pure state it boils at
 about 392° F.;  when heated in a stream of hydrogen gas, it distils
 over unaltered ;  but when  distilled  in vessels containing air, it turns
 brown and suffers partial  decomposition;  with aqueous vapors it
distils over freely.   It dissolves sparingly in water, 100 parts of
water of the  common temperature dissolving 1 part of conia.  The
solution turns turbid on warming.   Conia is miscible in all propor- 
392
APPENDIX.
[§ 234.
tions with alcohol and ether.  The aqueous and alcoholic solutions
manifest strong  alkaline reaction.   Conia has a very strong, pun-
gent, repulsive odor, which affects the head, a most acrid and dis-
agreeable taste, and very poisonous properties.
  2. Conia is a strong base;  it accordingly precipitates metallic
oxides from their solutions, in a similar way to ammonia,  and forms
salts with acids.   The salts  of conia are  soluble in water and  in
spirit of wine, but nearly insoluble in ether. Hydrochlorate of conia
crystallizes readily;  the  smallest quantity of this base, brought in
contact with  a trace  of hydrochloric acid,  yields  almost imme-
diately a corresponding quantity of  non-deliquescent  rhombic
crystals (Th. Wertheim).  The solutions  of the salts of conia turn
brownish upon evaporation, with  partial decomposition of the
conia.   The dry salts  of  conia do not smell of the alkaloid;  when
moistened, they smell only feebly of it; but upon addition of solu-
tion of soda, they at once emit a  strong  conia odor.  When salts
of conia are distilled with solution  of soda, the distillate contains
conia.   On  neutralizing this with  oxalic  acid, evaporating to dry-
ness, and treating the residue with spirit  of wine,  the oxalate of
conia formed is dissolved, whilst any oxalate  of ammonia that may
be present is left undissolved.  As  conia  is  only sparingly soluble
in water, and dissolves with still greater  difficulty  in solutions of
alkalies, a concentrated solution of a salt of conia turns milky upon
addition of solution of  soda.  The minute drops which separate
unite gradually, and collect on the surface.
  3. If an aqueous solution of  a salt of conia is shaken  with solu-
tion of soda and ether, the conia is dissolved by the ether.  If the
latter  is then allowed to evaporate on a  watch-glass, the  conia is
left in  yellowish-colored oily drops.
  4. Concentrated nitric acid imparts  a fine blood-red tint  to
conia;  sulphuric acid, a purple-red color, which subsequently turns
to olive-green.
  5. Terchloride of gold produces  a yellowish-white precipitate,
insoluble in  hydrochloric  acid;  chloride of mercury,  a copious
white  precipitate, soluble in hydrochloric  acid.  Bichloride of pla-
tinum  does not precipitate  aqueous solutions of salts of  conia, the
conia compound  corresponding to ammonia-bichloride of platinum
being  insoluble in spirit of  wine and ether, but soluble in water.
  6. To  solution of iodine  in iodide of potassium and water,
and to solution of tannic acid, conia comports itself the same as
nicotina.
   7. Chlorine water produces in  a mixture  of water and conia a
strong, white turbidity.
   8. If an aqueous solution  of conia is mixed with  a solution of
albumen, the albumen coagulates.   Aniline  is the only other vola-
tile  vegeto-alkali which shows this reaction. 
§ 235.]
APPENDIX.
393
   The volatile alkaloids  are easily recognised when  pure; the
 great object  of the analyst must  accordingly always be to obtain
 them m that  state.  The way of effecting this is the same for
 nicotina as for conia, and has already been given in the foregoing
 paragraphs, viz., to distil with addition of solution of soda, neutral-
 ize with oxalic acid, evaporate, dissolve  in  alcohol, evaporate the
 solution, treat the residue with water, add solution  of soda, shake
 the mixture with ether, and let the latter evaporate spontaneously.
 Conia is distinguished from nicotina chiefly by its odor,  its  sparing
 solubility in water, and  its comportment with chlorine water, and
 bichloride of platinum.

                  II. Non-volatile Alkaloids
   The non-volatile alkaloids are solid, and cannot be distilled over
 with water.

                          first group.
 Non-volatile Alkaloids which  are precipitated by Potassa
   or  Soda from  the  Solutions of their  Salts, and redis-
   solve  readily in an Excess  of the Precipitant.
   Of the alkaloids of  which  I propose to treat here, one only
 belongs  to this group, viz.,

         Morphia,  or Morphine (C34 H19 N 06 = Mo).
                             §235.
                            +
   1.  Crystallized morphia (Mo + 2 aq.) usually appears  in  the
 form of  colorless, brilliant four-sided prisms, or, when obtained by
 precipitation,  as a white crystalline powder.  It has a bitter taste,
 and dissolves very sparingly in cold, but somewhat more  readily
 in boiling water.  Of cold alcohol  it  requires about  90 parts by
 weight for solution; of  boiling alcohol from 20 to 30 parts.  The
 solutions of morphia  in alcohol  as well as in hot water manifest
 distinctly alkaline reaction.   This  alkaloid is nearly insoluble in
 ether; it dissolves in amyl-alcohol in the cold, but more freely with
 the aid of heat.  At a moderate heat the  crystallized morphia loses
 the two equivalents of water.
   2. Morphia neutralizes acids  completely, and forms with them
 the salts of morphia.   These salts are  readily soluble in water
 and in spirit of wine, but insoluble in ether and amyl-alcohol; their
 taste  is disagreeably bitter.  Most of them are crystallizable.
   3. Potassa  and ammonia precipitate from the solutions of salts
                                             +
 of morphia—generally only after some time—Mo + 2 aq., in thv
form of a white crystalline powder.  Stirring  and friction on the
sides  of the vessel promote the separation  of the  precipitate, which 
394
APPENDIX.
[§235
redissolves with great readiness in an excess of potassa, but  more
sparingly in ammonia.  It dissolves also in chloride of ammonium
and, though with difficulty only, in carbonate of ammonia.
  4.  Carbonate of potassa and carbonate of soda produce the same
precipitate as potassa and ammonia, but fail  to redissolve it upon
addition in excess.   Consequently if  a fixed alkaline bicarbonate is
added to a solution of morphia in caustic potassa, or if  carbonic
                                    +
acid is conducted into the solution, Mo -f 2 aq. separates,—espe-
cially after previous  ebullition—in the form of a crystalline powder.
A more minute inspection, particularly through a magnifying glass,
Bhows this powder to consist of small acicular  crystals;  seen
through  a glass which magnifies 100 times, these crystals present
the form of four-sided prisms.
  5. Bicarbonate of soda and bicarbonate of potassa speedily pro-
duce in solutions of neutral salts of morphia  a precipitate of hydrat-
ed  morphia, in the form of a crystalline powder.   The precipitate
is insoluble in an excess of the  precipitants.   These reagents fail to
precipitate acidified  solutions of salts  of morphia in the cold.
  6. The action of strong nitric acid upon morphia or one of its
salts,  in the solid state or in  concentrated  solutions, produces a
fluid varying from red to yellowish-red.  Dilute solutions  do not
change their color upon addition of nitric acid in the cold, but upon
heating they acquire a yellow tint.
  7. If morphia or  a compound of  morphia  is treated with pure
concentrated sulphuric acid, and heat applied,  a colorless solution
is obtained; if, after cooling, 8 to 20 drops  of sulphuric acid mixed
with some nitric acid* are added, and 2 or 3 drops of water, the
fluid acquires a violet-red coloration (gentle heating promotes the
reaction) ; and if from 4 to 6 clean lentil-sized fragments  of binox-
ide of manganese  are now added, or  a fragment of chromate of
potassa  (Otto), the fluid acquires an intense mahogany-brown
color.  If the fluid is then diluted with 4 parts of water,  properly
cooled in a test tube, and ammonia added until  the reaction is
almost neutral, a dirty-yellow  color makes  its appearance, which
turns brownish red  upon supersaturation with ammonia,  without
depositing an appreciable precipitate (J. Erdmann).
  8. Neutral sesquichloride of iron imparts to neutral solutions of
salts of morphia a beautiful dark blue color, which disappears upon
the addition of an acid.   If the solution contains  an admixture of
animal or vegetable  extractive matters, or of acetates, the  color
will appear clouded  and less distinct.
  9. If iodic acid is added to a solution of  morphia or of a salt of
morphia, iodine separates.  In concentrated aqueous solutions  the
  * Mix 6 drops of nitric acid of 1*5*5 sp. gr. with 100 cubic centimetres of water,
and add 10 drops of this mixture to 20 grammes of pure concentrated sulphuric acid 
§ 236.]
APPENDIX.
395
separated iodine appears as a kermes-brown precipitate, whilst to
alcoholic and dilute aqueous solutions it imparts a brown or yellow-
ish-brown color.   The addition of starch-paste to the fluid, no mat-
ter whether made before or after that  of the iodic acid, considera-
bly heightens the delicacy of the reaction, since the blue tint of the
iodide of starch remains still perceptible in exceedingly dilute solu-
tions, which is not  the  case  with the brown  color imparted by
iodine.  As other nitrogenous bodies (albumen, caseine, fibrine,
&c.) likewise reduce iodic acid, this  reaction has only a relative
value; however, if ammonia is added after the iodic acid, the fluid
becomes  colorless if the separation of iodine has been caused by
other substances, whilst the coloration becomes much more intense
if it is  owing to the nresence of morphia (Lefort).*

                         second group.
Non-volatile Alkaloids  which are precipitated by  Potassa
  from  the Solutions of their Salts, but do not redissolve
  to a perceptible Extent in an Excess of the Precipitant,
  and are precipitated by Bicarbonate  of Soda even from
  Acid Solutions,  if the latter  are not diluted in a  larger pro-
  portion than 1 : 100;  Narcotina, Quina, Cinchonia.
                                                     +
       a. Narcotina, or Narcotine  (CJ6 H25 NOH = Na).
                             § 236.
                            I-
  1. Crystallized narcotina (Na + aq.) appears usually in the form
of colorless,  brilliant, right rhombic prisms, or,  when  precipi-
tated by alkalies, as a white, loose, crystalline powder.  It is insolu-
ble in water.  Alcohol and  ether dissolve it  sparingly in the cold,
but somewhat more readily upon heating.  Solid narcotina is taste-
less, but the alcoholic and  ethereal solutions are intensely bitter.
Narcotina does not alter vegetable colors.  At  338° F. it fuses,
with loss of 1 eq. of water.
  2. Narcotina dissolves readily in acids, combining  with them to
salts.   These  salts have  invariably an acid reaction.  Those  with
weak acids  are decomposed by a large amount of water, and, if the
acid is volatile, even  upon simple evaporation.  Most of  the salts
of narcotine  are amorphous, and  soluble in water, alcohol,  and
ether ; they have a bitter taste.

  * Lefort (Zeitschrift f. Anal. Chem. I., 134)  recommends  the following  method
for the detection of small quantities of morphia:  moisten strips of very white unsized
paper with the morphia solution, dry, and repeat the operation several times, so as to
ensure absorption by the paper of a tolerably large quantity of the fluid ;  the dried
paper contains the morphia in the solid state, most finely divided.  Nitric acid, ses-
auichloride of iron, and iodic acid and ammonia will readily and with positive dis-
tinctness show the characteristic reactions on paper so prepared. 
396
APPENDIX.
[§237
   3. Pure alkalies, and alkaline carbonates and bicarbonates, imme
                                                          +
 diately precipitate from  the solutions of salts of narcotine Na -f
 aq. in the form of a white powder, which,  seen through a lens mag-
 nifying 100 times, appears an  aggregate of small crystalline nee-
 dles.   The precipitate is insoluble in an excess of the precipitants.
 If solution of narcotina is mixed with ammonia, and ether added in
 sufficient  quantity, the narcotine which  has separated  upon the
 addition of the ammonia, redissolves  in  the ether, and the clear
 fluid presents two distinct layers.  If a drop of the ethereal solu-
 tion is  evaporated on a watch-glass, the residue is seen,  upon
 inspection through a lens magnifying a hundred times, to consist of
 small, distinct, elongated, and lance-shaped crystals.
   4. Concentrated nitric acid dissolves narcotine to a colorless
 fluid, which acquires a pure yellow tint upon application of heat.
   5. If a small quantity of pure narcotine is treated with from 4 to
 6 drops of pure  concentrated  sulphuric acid, no coloration is ob-
 served, not even on  the application of a gentle heat, or, at least,
the heated fluid acquires only a barely perceptible yellow tint, but
upon  adding now, after cooling, from  8 to 20 drops  of sulphuric
acid mixed with  a little nitric acid (§  235, 7) and 2  or 3 drops of
water,  the  fluid acquires an  intense  red  color.   Addition  of
binoxide of manganese  does not materially change the  color.   If,
after dilution, ammonia is  added to nearly neutral  reaction, the
color becomes less intense, in consequence of the  dilution.   Addi-
tion of ammonia in excess  produces a  copious dark brown preci-
pitate (J.Erdmann).
  6. If the solution of a salt of narcotine is mixed with chlorine
water, it acquires a yellow color, slightly inclining to  green: if am-
monia is then added,  a much more intensely colored yellowish-red
fluid is obtained.
  7. If narcotine or  one of its salts is dissolved in an  excess  of
dilute sulphuric acid, some finely levigated binoxide of manganese
added, the mixture heated to boiling, and kept in ebullition for the
space of several minutes, the narcotine absorbs oxygen and is con-
verted into opianic acid, cotarnine  (a base soluble  in water), and
carbonic acid.  Ammonia will now of course fail  to precipitate
narcotine  from the filtrate.

                                               +
             b. Quina, or Quinine (C4oH24N204=Q).

                             § 237.
                        +
   1. Crystallized quina (Q + 6 aq.) appears either in the form of
 fine crystalline needles of silky lustre, which are frequently aggre-
 gated into tufts, or as a loose white powder.  It is sparingly soluble 
§ 237.]                    appendix.                       397

in cold, but somewhat more readily in  hot water.  It is readily
soluble in  spirit  of wine, both  cold  and hot, but less so in ether.
The taste of quina is intensely bitter; the solutions of quina mani-
fest alkaline reaction.  Upon exposure to heat it loses the 6 eq. of
water.
  2. Quina neutralizes acids completely.   The salts taste intensely
bitter; most of them are crystallizable,  difficultly soluble  in cold,
readily soluble in hot water and in spirit of wine.  The acid salts
dissolve very freely in water;  the solutions reflect a bluish tint.
If a cone of light is thrown  into them, by means of a lens either
horizontally or vertically, a blue cone  of light is seen even in highly
dilute solution.
  3. Potassa, ammonia,  and the neutral carbonates of the alkalies
produce in solutions  of salts of quina (if they are not too dilute)
a white,  loose, pulverulent precipitate of hydrated quina, which
immediately after precipitation  appears opaque and amorphous un-
der the microscope, but assumes, after the lapse of some time, the
appearance of an aggregate of crystalline needles. The precipitate
redissolves  only to a scarcely perceptible extent in an excess of
potassa, but more so in  ammonia.  It is hardly more soluble  in
fixed alkaline carbonates than in pure water.  If a solution of quina
is mixed with ammonia, ether added, and the mixture shaken, the
quina which has  separated  upon the addition  of the ammonia, re-
dissolves in the  ether, and the clear fluid  presents  two  distinct
layers.  In this point quina differs essentially from cinchonia; by
means of this reaction, the former may therefore be readily detected
in presence of the latter, and separated from it.
  4. Bicarbonate of soda also produces both in neutral and acid solu-
tions of salts of quina a  white  precipitate.  In acidified solutions
containing 1 part of quina to 100 parts of acid and water, the pre-
cipitate forms immediately; if  the proportion of the quina to the
acid and water is as 1  :  150, the  precipitate separates only after
an hour  or two, in the form of distinct needles, aggregated into
groups.  If the proportion is as 1 : 200, the fluid remains clear, and
it is only after from twelve to  twenty-four  hours' standing that a
slight precipitate makes  its  appearance.  The precipitate is not
altogether  insoluble in  the  precipitant,  and the  separation  is
accordingly the more complete the  less the excess of the preci-
pitant ;  the precipitate contains carbonic acid.
  5. Concentrated nitric acid dissolves quina to a colorless fluid,
turning yellowish upon application of heat.
  6. The addition of chlorine water to the solution of a salt of quina
fails to impart a color to  the fluid, or, at  least, imparts to it only a
very faint tint; but if ammonia is now added, the fluid acquires an
intense emerald-green color.  If, after the addition of the chlorine
water  some solution of ferrocyanide of potassium is added, then 
398
APPENDIX.
[§238
a few drops  of ammonia or some other alkali, the fluid acquires a
magnificent  deep red tint, which, however, speedily changes to a
dirty brown.  This reaction  is delicate and characteristic.  Upon
addition of  an acid* to  the red fluid, the color vanishes, but re-
appears  afterwards   upon  cautious addition  of ammonia.   (O.
Livonius, communicated in a letter to the author; A. Vogel.)
   7. Concentrated sulphuric acid likewise dissolves pure quina and
pure salts of quina  to a colorless  or very faint yellowish fluid;
application of a gentle heat turns the fluid yellow,  application of a
stronger heat brown,  Sulphuric  acid containing an admixture of
nitric acid dissolves quina to  a  colorless or very faint yellowish
fluid.
   8. As  regards Herapath's  quinine reaction, based upon  the
polarizing properties  of  sulphate of iodide of quinine, I refer to
Phil. Mag. vi. 171.
                                                    +
        c. Cinchonia, or Cinchonine (C40H2i N2 02 = Ci).
                             § 238.
   1. Cinchonia appears either in the form of transparent, brilliant,
four-sided prisms, or fine white crystalline  needles, or if precipitated
from concentrated solutions,  as a loose white powder.  At first it
is  tasteless, but after some time  the bitter taste of the bark  becomes
perceptible.  It is nearly  insoluble  in cold water, and dissolves
only with extreme  difficulty in hot water ; it dissolves sparingly in
cold dilute spirit of  wine, more readily in hot spirit of wine, and
the most freely in absolute alcohol.   From hot alcoholic solutions
the  greater  portion  of the  dissolved  cinchonia  separates upon
cooling in a  crystalline form.   Solutions of cinchonia taste bitter,
and manifest alkaline reaction.  Cinchonia is insoluble in ether.f
   2. Cinchonia neutralizes acids completely.   The  salts have  the
bitter taste of the bark ; most of them are crystallizable :  they are
generally more readily soluble in water and in spirit  of wine than
the corresponding quina compounds.  Ether fails to dissolve them.
   3. Cinchonia, when heated cautiously, fuses at first without loss
of water; subsequently white fumes  arise  which, like benzoic acid,
condense.upon cold substances, in the form of small  brilliant nee-
dles, or  as  a  loose  sublimate, a peculiar aromatic odor being
exhaled at the  same time. If the operation is conducted in a stream
of hydrogen  gas, long brilliant  prisms are obtained (Hlasiwetz).
   4. Potassa, ammonia, and  the neutral carbonates of the alkalies
produce in solutions of salts of cinchonia a white loose precipitate
  * Acetic acid answers the purpose best.
  \ The cinchonia of commerce  usually contains in admixture another alkaloid,
called cinchotina,  which  is soluble  in ether. This alkaloid crystallizes in  large
rhomboidal crystals of brilliant lustre, which fuse at a high temperature, and cannot
be sublimed even in a stream of hydrogen gas (Hlasiwetz). 
§ 239-1                   appendix.                      399

of cinchonia, which does not redissolve in an excess of the precipi-
tants.  If the solution was concentrated,  the  precipitate  does not
exhibit a  distinctly crystalline appearance,  even though viewed
through a lens magnifying 200 times; but  if the solution was so
dilute that the precipitate formed  only after some time, it appears
under  the microscope to consist  of distinct crystalline needles
aggregated into star-shaped tufts.
  5. Bicarbonate of soda and bicarbonate  of potassa precipitate
cinchonia in the same  form as in 4, both from neutral and acidified
solutions  of cinchonia salts, but  not so completely as the simple
carbonates of the alkalies.  Even in solutions  containing  1 part of
cinchonia to 200  of water and acid, the precipitate forms immedi-
ately ;  its quantity increases after  standing  some time.
  6. Concentrated sulphuric acid  dissolves  cinchonia to a colorless
fluid, which upon application of heat first  acquires a brown, and
finally  a black color.   Addition of some nitric acid leaves the solu-
tion colorless in the cold, but upon application of heat  the fluid,
after passing through  the intermediate  tints of yellowish-brown
and brown, turns finally black.
  7. The  addition of chlorine water to the solution of a salt of cin-
chonia fails to impart a color to the fluid ; if ammonia is now added,
a yellowish-white precipitate is formed.
  8. If the solution of a cinchonia salt containing only very little or
no free acid, is mixed  with ferrocyanide  of potassium, a  flocculent
precipitant of ferrocyanide of cinchonia is formed.  If an excess of
the precipitant is added, and a gentle heat very slowly applied,  the
precipitate dissolves, but separates again upon cooling, in brilliant
gold-yellow scales, or in  long  needles,  often  aggregated in  the
shape of a fan.  With the  aid of the microscope, this reaction is as
delicate as it is characteristic  (Ch. Dollfus: Bill;  Seligsohn).

                  Recapitulation  and Remarks.
                             §239.
  The  non-volatile alkaloids of the second group are altered or pre-
cipitated by various other reagents besides those mentioned above ;
the reactions are, however, not adapted to effect their individual
detection and separation.  Thus, for instance, bichloride  of plati-
num produces in solutions  of the salts of the three alkaloids belong-
ing to  this group a yellowish-white precipitate, chloride of mercury
a white precipitate, tincture  of galls  a  yellowish-white  flocculent
precipitate, solution of iodine in iodide of potassium a reddish-
brown, phospho-molybdic acid a yellow precipitate, &c.
  Narcotina and quina being soluble in ether, whilst  cinchonia is
insoluble in that menstruum, the two former alkaloids may be most
readily separated by this means from the latter.   For this purpose 
400
APPENDIX.
[§ 240.
the analyst need simply mix the aqueous solution of the three alka
loids with ammonia in excess,  then add ether, and separate the solu
tion of quina and narcotina from the undissolved cinchonia.   If the
ethereal solution is now evaporated, the residue dissolved in hydro-
chloric acid and a sufficient  amount of water to make the dilution
as 1: 200, and bicarbonate  of soda is  then added, the  narcotina
precipitates, whilst the quina remains in solution.  By evaporating
the solution,  and treating the residue with water, the quina  is
obtained in the free state.*

                          third  group.

Non-volatile Alkaloids which are  precipitated  by Potassa
  from  the  Solutions of  their  Salts, and  do  not  redis-
  solve TO A PERCEPTIBLE EXTENT IN  AN  EXCESS  OF THE PRE-
  CIPITANT ;  but  are  not precipitated  from (even  somewhat
  concentrated)  Acid Solutions by the  Bicarbonates of  the
  Fixed Alkalies :  Strychnia, Brucia, Veratria.
                                                       +
       a. Strychnia, or Strychnine (C42  H^ N2 04 = Sr)
                              § 240.
  1. Strychnia appears either in  the form of white brilliant rhom-
bic prisms, or, when produced by precipitation or rapid evapora-
tion,  as a white powder.  It has  an  exceedingly bitter taste.  It
is nearly insoluble in cold, and barely soluble in  hot water.   It  is
almost insoluble in absolute alcohol and ether, and only sparingly
Boluble in dilute  spirit of wine.   It dissolves  freely in amyl-alcohol,
more especially with  the aid of heat. It does not fuse when heated.
It is exceedingly poisonous.
   2.  Strychnia neutralizes acids completely.  The salts  of  strych-
nia are, for the most  part, crystallizable ; they are soluble in water.
All the salts  of strychnia have an intolerably bitter taste and are
exceedingly poisonous.
   3.  Potassa and carbonate of soda produce in solutions of salts of
strychnia white precipitates  of strychnia,  which are insoluble in
an excess of the precipitants.  Viewed under a microscope  magni-

  * The reaction with ammonia and  ether, though well adapted to effect the separa-
tion of quina from cinchonine, fails to effect the separation of the former  vegeto-alkali
from the  other bases found in bark, which are not as yet officinal, viz., a quinidine,
0 quinidine, y quinidine, and cinchonidine; since, as G. Kerner (Zeitschrift f. Analyt.
Chem., 1,  150) has shown, several of these other vegeto-alkalies are  pretty freely
soluble in ether.  In fact, no qualitative reaction will enable the analyst to fully
effect this purpose; but  it may be accomplished by means of a simple volumetrical
method, based upon the  circumstance that the quina thrown down by ammonia
from a solution of the sulphate, requires  less ammonia  to redissolve it than all the
other vegeto-alkalies of the bark.  For further particulars I refer to Kerner's papei
 on  the subject. 
 § 240.]                   APPENDIX.                       401

 fying one  hundred times the precipitate appears as an aggregate
 of small crystalline needles.  From  dilute solutions the  strychnia
 separates only after the lapse  of some time, in the form of crystal-
 line needles, which are distinctly visible even to the naked eye.
   4. Ammonia produces the  same precipitate  as  potassa.   The
 precipitate redissolves in an excess of ammonia ;  but after a short
 time—or if the solution is highly dilute, after a more considerable
 lapse of time—the strychnia crystallizes from the ammoniacal solu-
 tion in the form of needles,  which are distinctly  visible to the
 naked eye.
   5. Bicarbonate of soda produces in neutral solutions of salts of
 strychnia a precipitate of strychnia, which separates in fine needles
 shortly after the addition of the reagent, and is insoluble in  an ex-
 cess of the precipitant.  But  upon adding one drop of acid (so as
 to leave the fluid still alkaline), the precipitate dissolves readily in
 the  liberated carbonic acid.  The addition of bicarbonate of soda
 to an acid solution of strychnia causes no precipitation, and it js
 only after the lapse of twenty-four hours, or even a longer period,
 that strychnia crystallizes from the fluid in distinct prisms, in pro-
 portion as the free  carbonic acid escapes.  If a concentrated solu-
 tion of strychnia, supersaturated with bicarbonate  of soda, is boiled
 for  some time,  a precipitate forms at  once; from dilute  solutions
 this precipitate  separates only after concentration.
   6.  Sulphocyanide of potassium produces  in concentrated solu-
 tions of salts of strychnia immediately, in dilute solutions after the
 lapse of some time, a white crystalline precipitate,  which appears
 under the microscope as an aggregate  of flat needles,  truncated or
 pointed at  an acute angle,  and is but little soluble in an excess
 of the precipitant.
   7.  Chloride of mercury produces in solutions of salts of strychnia
 a white precipitate, which changes after some time to crystalline
 needles, aggregated into stars, and distinctly visible through a lens.
 Upon heating the fluid these  crystals redissolve, and upon sub-
 sequent cooling of the solution the double  compound recrystallizes
 in larger needles.
   8. If a few drops of pure concentrated sulphuric acid are added
 to a  little strychnia in  a porcelain  dish, solution ensues, without
 coloration  of the fluid.  If small quantities  of oxidizing agents
 (chromate  of potassa, permanganate  of potassa,  ferricyanide of
 potassium, peroxide of lead, binoxide of manganese) are now added
—best in the solid form, as dilution is prejudicial to the reaction—
the fluid acquires a magnificent blue-violet color, which, after some
time, changes to wine-red, then to reddish-yellow.  With chromate
of potassa and permanganate of potassa the reaction  is immediate ;
on inclining the dish, blue violet streaks  are seen  to flow from the
salt fragment, and by pushing  the latter about, the coloration is
                               26 
402
APPENDIX.
[§ 241.
Roon imparted to the entire fluid.  With ferricyanide of potassium
the reaction is less  rapid;  but it is slowest with peroxides.  The
more speedy the manifestation of the reaction the more rapid is
also the change  of  color from one tint to another.  I prefer chro-
mate of potassa, recommended by Otto,  or permanganate  of
potassa, recommended by Guy, as the most sensitive, to all other
oxidizing agents.  Jordan succeeded, with chromate of potassa, in
distinctly showing the presence of JV^^^tib grain of strychnia.  J.
Erdmann prefers binoxide of manganese  in lentil-sized fragments.
Metallic chlorides and considerable quantities of nitrates, also large
quantities of organic substances, prevent  the manifestation of the
reaction or impair its delicacy.  It is therefore  always advisable to
free the  strychnia first, as far as practicable, from all foreign  mat-
ters before proceeding to try this reaction.  If the solution colored
red (by binoxide of manganese) is mixed with from 4 to 6 times
its volume of water, and ammonia is then  added until the reaction
is nearly neutral, the fluid shows a  magnificent violet-purple tint;
upon addition of more ammonia the color becomes yellowish-green
to  yellow  (J. Erdmann).   I have  found, however,  that this
reaction is seen only  where larger, though still very minute,
quantities of strychnia are present.
  9. Strong chlorine water produces in solutions of salts of strych-
nia a white precipitate, which dissolves in ammonia to a colorless
fluid.
  10. Concentrated nitric acid dissolves  strychnia and its salts to
a colorless fluid, which turns yellow upon the application of heat.

                                                +
           b. Brucia, or Brucine (C16 H^ N2 08 = Br).

                              § 241.
                         +
  1. Crystallized brucia (Br -+- 8 aq.) appears either in the form of
transparent right rhombic prisms, or in that of crystalline needles
aggregated into  stars, or as a white powder composed of minute
crystalline scales.   Brucia  is  difficultly soluble in cold, but some-
what more readily  in  hot water.  It dissolves freely in alcohol,
both in absolute and dilute, also in cold, but more readily still in
hot, amyl-alcohol; but it is  almost insoluble in ether.  Its taste is
intensely bitter.  When heated, it fuses with loss of its water of
crystallization.
  2. Brucia neutralizes acids completely.  The salts of brucia  are
readily soluble in water, and of an intensely bitter taste.   Most of
them are crystallizable.
   3. Potassa and carbonate of soda throw down from solutions of
salts of brucia a white  precipitate  of brucia, which is insoluble in
an  excess  of the precipitant.  Viewed under  the microscope,  im- 
§ 241.]
APPENDIX.
4 OS
 mediately after precipitation, it appears to consist of very minute
 grains; but upon further inspection, these grains are seen—with
 absorption of water—to  suddenly form into  needles, which latter
 subsequently arrange themselves without exception into concentric
 groups.  These successive changes of the precipitate may be traced
 distinctly even with the naked eye.
   4. Ammonia produces  in  solutions of salts of brucia a whitish
 precipitate, which appears at first like a  number of minute drops
 of oil, but changes subsequently—with  absorption  of water—to
 small needles.  The precipitate redissolves, immediately after sepa-
 ration, very readily in an excess of the precipitant; but after a very
 short time—or, in dilute solutions, after a more considerable lapse
 of time—the  brucia, combined with crystallization water, crystal-
 lizes from  the ammoniacal fluid  in small concentrically  grouped
 needles, which addition of ammonia fails to redissolve.
   5. Bicarbonate of soda produces in neutral solutions of salts  of
 brucia a precipitate of brucia, combined with crystallization water ;
 this precipitate separates after the lapse of a short time, in form of
 concentrically aggregated needles of silky lustre, which are insoluble
 in an excess  of the precipitant, but dissolve in free carbonic acid
 (compare strychnia).   Bicarbonate of soda fails to precipitate acid
 solutions of salts  of brucia ; and it is only after the lapse of a con-
 siderable time, and with the  escape of the carbonic acid,  that the
 alkaloid separates from the fluid in regular and comparatively large
 crystals.
   6.  Concentrated nitric  acid dissolves brucia and its salts to  in-
 tensely red fluids, which subsequently acquire a yellowish-red tint,
 and turn yellow upon application of heat.  Upon addition of pro-
 tochloride of tin  or sulphide of ammonium to the heated fluid,  no
 matter whether concentrated or after dilution with water, the faint
 yellow color changes to a  most intense violet.
   7.  If a little brucia is treated with from 4 to 6 drops of pure con-
 centrated sulphuric acid, a solution of a faint rose color is obtained,
 which afterwards turns yellow.  If from 8 to 20 drops of sulphuric
 acid  mixed with  some nitric  acid (p. 394) are  added, the fluid
 transiently acquires a red, afterwards a yellow color.  Addition  of
 binoxide of manganese transiently imparts a red, then a gamboge
 tint to the  fluid.   If the fluid is  then, with proper cooling, dilu-
 ted with 4 parts of water, ammonia added to nearly neutral reac-
 tion  or even to alkaline reaction,  the  solution acquires  a gold-
 yellow color (J. Erdmann).
   8. Addition of chlorine water to the solution of a salt of brucia im-
parts to the fluid a fine bright red tint; if ammonia is then added,
the red color changes to yellowish-brown.
  9  Sulphocyanide of potassium produces in concentrated solu
tions of salts of brucia immediately, in dilute  solutions  after some 
404
APPENDIX.
[§ 242.
 time, a granular crystalline precipitate, which, when viewed under
 the  microscope,  appears composed of variously aggregated  poly-
 hedral  crystalline grains.  Friction  applied  to  the sides of the
 vessel promotes the separation of the precipitate.
   10. Chloride of mercury also produces  a white granular preci-
 pitate, which,  when viewed under  the microscope,  appears  com-
 posed of small roundish crystalline grains.

                                                    +
          c. Veratria, or Veratrine (C^HgjNaOjg) Ve.
                             § 242.
   1. Veratria appears in the form of small prismatic crystals, which
 acquire a  porcelain-like look in the air, or as a white or yellowish-
 white powder of acrid  and burning, but not bitter taste;  it is
 exceedingly poisonous.   Veratria acts with great energy upon the
 membranes of the nose;  even the most minute quantity of the
 powder excites the most violent sneezing.   It is insoluble in water;
 in alcohol it dissolves readily, but  more sparingly in ether.  At
 239° Fah. it fuses like wax, and solidifies upon cooling to a trans-
parent yellow mass.
   2. Veratria neutralizes acids completely.  Some salts of veratria
 are crystallizable, others  dry up to  a  gummy mass.  They are
 soluble in water, and have an acrid and burning taste.
   3. Potassa, ammonia, and  the mono-carbonates of the alkalies
 produce in solutions  of salts  of veratria a flocculent white preci-
 pitate, which,  viewed under  the microscope,  immediately  after
 precipitation,  does not  appear crystalline.  After the lapse  of a
 few minutes, however, it alters its appearance, and small scattered
clusters of short prismatic crystals are observed, instead of the ori-
ginal coagulated flakes.  The  precipitate does not redissolve in an
excess of potassa or of carbonate of potassa.  It is slightly soluble
in ammonia in the cold, but the dissolved portion separates again
upon application of heat.
  4. With bicarbonate of soda and bicarbonate of potassa the salts
of veratria comport themselves like those of strychnia and brucia.
However, the  veratria  separates  readily upon boiling, even  from
dilute solutions.
  5. If veratria is  acted upon  by concentrated nitric acid, it agglu-
tinates into small resinous lumps, which afterwards dissolve slowly
in the acid.  If the veratria is pure the solution is colorless.
  6. If veratria is treated with concentrated sulphuric acid, it also
agglutinates at first into  small resinous lumps;  but these  dissolve
with great readiness to  a faint yellow fluid, the color of which
gradually increases in depth and intensity, and changes afterwards
to a reddish-yellow, then to an intense blood-red.  The color per 
§ 243.]
APPENDIX.
405
 gists 2 or 3 hours, then disappears gradually.  Addition of sulphurio
 acid, containing nitric acid, or of binoxide of manganese causes no
 great change of color.  If the fluid is then diluted with water, and
 ammonia  added until the reaction is nearly neutral,  a yellowish
 solution is obtained, in which ammonia added in excess produces
 a greenish light-brown precipitate (J. Erdmann).
   7. Sulphocyanide  of potassium  produces only  in concentrated
 solutions of salts of veratria flocculent-gelatinous precipitates.
   8. Addition of chlorine-water to the solution of a salt of veratria
 imparts to the fluid a yellowish tint, which, upon addition of  am-
 monia, changes to a faint brownish color. In concentrated solutions
 chlorine produces a white precipitate.
   [9.  Cold concentrated hydrochloric acid dissolves veratria to a
 colorless solution, which, on prolonged boiling, assumes a red color
 that finally becomes very intense and resembles that of perman-
 ganate of potassa.  The colored liquid remains unaltered for a long
 time.  This reaction is very sensitive.  Trapp.*

                   Recapitulation and remarks.
                               §  243.
   The alkaloids of the third group also are precipitated by many
 other reagents besides those  above mentioned, as, for instance, by
 tincture of galls, bichloride of platinum, solution of iodine in iodide
 of potassium, phosphomolybdic  acid,  &c.  But  as  these reactions
 are  common  to all, they are  of  little importance  in an analytical
 point of view.f
   Strychnia  may be  separated from brucia and veratria by means
 of absolute alcohol, since it is insoluble in that menstruum, whilst
 the  two  latter alkaloids readily dissolve  in it.   The identity of
 strychnia  is  best established by the  reaction with sulphuric  acid
 and the above-mentioned oxidizing agents ;\ also  by the form of
 its crystals—when thrown down by alkalies—viewed under  the
 microscope;  and lastly, by  the form  of the  precipitate  which
 sulphocyanide  of potassium  and chloride  of mercury produce in
  * Polytechnisches Notizblatt, 1863, 96.
  \ If the precipitate produced in the solution of a salt of strychnia by iodide of potas-
 sium containing  iodine, is dissolved in spirit of wine mixed with some sulphuric acid
and the solution  is evaporated, strongly polarizing prismatic crystals of sulphate of
 iodide of strychnia are obtained. De Vrij and Tan der Burg (Jahresber v. Liebig,
and Kopp, 1857, 602).  "Whether this reaction is characteristic for strychnia, can
 be known only after the optical properties of analogous compounds of the other
alkaloids shall have been studied.
  t The only substance which shows somewhat analogous reactions in this respect,
is aniline.  A. Guy has, however, called attention to the fact that aniline, treated
 with sulphuric acid and oxidizing agents, acquires a pale green color at first, which
gradually deepens, and  only then changes to a magnificent blue, which, after  per-
sisting some time turns finally black. 
 406                       appendix.             [§§ 244, 245.

 solutions of its salts.  Brucia and veratria are not readily separated
 from one  another, but may be detected in presence of each other.
 The identity of brucia is best established  by the reactions  with
 nitric acid and protochloride  of tin or sulphide of ammonium, or
 by the form of the crystalline precipitate which ammonia produces
 in solutions of salts of brucia.  Veratria is sufficiently distinguished
 from brucia and the other alkaloids which we have treated of, by
 its characteristic deportment at a gentle heat, and also by the form
 of the precipitate which alkalies produce in  solutions of its  salts.
 To distinguish veratria in  presence of brucia,  the  reaction with
 concentrated sulphuric acid is selected.
  To these alkaloids I will add salicine, though this substance does
 not properly  belong to the same class of chemical compounds.

                             § 244.
                       Salicine (Gx H18 014).
  1. Salicine appears either in the form of white crystalline  needles
and scales of silky lustre, or, where the crystals  are very small, as
a powder  of  silky lustre.   It has a bitter taste, is readily soluble
in water and  in alcohol, but insoluble in ether.
  2. No reagent precipitates salicine as such.
  3. If salicine is  treated with  concentrated sulphuric acid, it
agglutinates  into a resinous lump, and acquires an intensely blood-
red color, without dissolving in the acid; the color of the sulphuric
acid is at first unaltered.
  4. If an aqueous solution of salicine is mixed with hydrochloric
acid or dilute sulphuric acid, and the mixture  boiled for  a short
time, the fluid suddenly becomes turbid, and deposits a fine granu-
lar crystalline precipitate  (saliretine).

 Systematic  Course for  the Detection  of  the  Alkaloids
 treated of in the preceding Paragraphs, and  of Salicine.
  The analytical course which I am now about to describe is based
 upon the supposition that  the analyst has to examine a concentrated
 aqueous solution—effected  by the agency of an acid—of one or
 several of the non-volatile alkaloids, which solution is free  from
 any admixture of substances that might tend to  obscure or modify
 the reactions.  For the modifications which the  presence of color-
 ing or extractive matters, &c, requires, I refer to § 247.

 I. Detection of the Alkaloids, and  of Salicine, in  Solutions
    SUPPOSED TO CONTAIN ONLY ONE OF THESE SUBSTANCES.*
                             § 245.
  1. Add dilute solution  of potassa or  soda, drop  by drop,  to a
  * Where  the detection of one of the five more frequently occurring poisonous
 alkaloids alone is the object, the following simple methcd. devised by J. Erdmann,
 will fully answer the purpose : 
§ 245.]
APPENDIX.
407
  portion of the aqueous  solution  until the fluid acquires a scarcely
  perceptible alkaline reaction; stir, and let the fluid stand for some
  time.
    a. No precipitate is formed ; this proves the total absence of
  the alkaloids, and indicates the presence of salicine.  To set all
  doubt  at  rest,  test the  original  substance  with  concentrated
  sulphuric acid, and also with hydrochloric acid.   Compare §  244.
    b. A precipitate is formed.   Add solution  of potassa or  soda,
  drop by drop, until the fluid manifests a strongly alkaline reaction!
         a. The precipitate  redissolves: morphia.  To arrive  at a
      positive conclusion  on  this point, test another portion  of the
      solution with iodic  acid  (§ 235, 9), and a portion  of the ori-
      ginal substance with sulphuric acid, &c, (§ 235, 7).

   In this method, which is more especially applicable in cases where the disposable
  quantity of substance is very small, the alkaloids are supposed to be present in the
  pure state and in the solid form.
   1. Treat the substance under examination with from 4 to 6 drops of pure concen-
  trated sulphuric acid.
   Yellow color, speedily changing to red:  Veratria.
   Rose color,  changing afterwards to Brucia.
   The other alkaloids, if pure, impart no color to the sulphuric acid.
   2. No matter whether there is color or not; add to the fluid obtained in 1,  from 8
 to 20 drops of concentrated sulphuric acid mixed with nitric acid (see foot-note to
 § 235, 7), then two or three drops of water.   After a quarter or half-hour the tuid
 shows:
   a.  a violet-red color: Morphia ;
   6. an onion-red color: Narcotina ;
   c. a transient red tint, changing to yellow:  Brucia •
   d. the red color of the sulphuric acid solution of Veeatria is not materially
 altered;
   e. with stryounia no coloration is observed.
   3. Put iuto the fluid obtained in 2, no matter whether colored or not, from 4 to 6
 clean fragments of binoxide of manganese, of the size of a lentil.   After an hour the
 fluid shows;
   a. a mahogany-brown color:  Morphia ;
   b. a yellowish-red to blood-red color:  Narcotina ;
   c.  a transient purple-violet tint, changing to deep onion-red: Strychnia •
   d. a transient red tint, changing to gamboge-yellow: Brucia •
   e.  a dark dirty cherry-red color:  Veratria ;
   4.  Pour  the colored fluid obtained in 3, into a test tube containing 4 times the
 volume of water,  and add ammonia  until the neutralization point is almost attained.
 Heat must be as much as possible avoided in these operations.
   a.  dirty-yellow color, changing to  brownish-red upon supersaturation with ammo-
nia, without immediate deposition of a notable  precipitate: Morphia •
   b.  reddish coloration, more or less intense according  to the degree of dilution;  upon
supersaturation with ammonia, copious dark-brown precipitate: Narcotina ;
  c.  violet-purple colored solution, becoming yellowish-green to yell; w upon addition
of ammonia in excess :  Strychnia ;
  d.  gold-yellow solution, not materially changed by excess of ammonia: Brucia ;
  e. faint brownish solution, turning yellowish upon further addition of ammonia, and
depositing a greenish light-brown precipitate: Veratria. 
408                      appendix.                    [§ 245.

       8.   The precipitate remains undissolved: Presence  of an
     alkaloid of the second or third group.   Pass on to 2.
  2. Add to a second portion of* the original solution two or three
drops of dilute  sulphuric acid, then a saturated solution of bicar-
bonate of soda until the acid reaction is just neutralized; vigorously
rub  the inside of the vessel, and allow the  mixture to stand for
half an hour.
  a. No precipitate is produced : Absence of narcotina and cin-
chonia.  Pass on to 3.
  b. A precipitate is formed : Narcotina, cinchonia,  and perhaps
also quina, as the precipitation of the latter substance by bicarbonate
of soda depends entirely upon the degree of dilution  of the fluid.
Add to a portion of the  original solution ammonia in excess, then
a sufficient quantity of ether, and shake the mixture.
      a. The precipitate which forms at first upon the addition of
     the ammonia redissolves  in the ether, and the clear fluid pre-
     sents two distinct layers:  narcotina  or quina.   To distinguish
     between the two, test a fresh portion of the original solution
     with  chlorine  water and  ammonia.  If the  solution  turns
     green,  quina,  if yellowish-red, narcotine is present.   The
     reaction with  a  mixture  of  sulphuric  acid  and  nitric  acid
     (§ 236, 5) is resorted to as a conclusive test.
      8.  The precipitate which forms  upon the addition of am-
     monia  does  not redissolve  in the ether—cinchonia.   The
     deportment of cinchonia at a high temperature (§ 238, 3),  or
     the reaction with ferricyanide of potassium  (§ 238, 8),  may
     serve as a conclusive test.
  3. Put a  portion of the original substance,  or  of  the  residue
remaining upon the evaporation of the solution, on a  watch-glass,
and treat with concentrated sulphuric acid.
  a. A rose-coloured solution is obtained, which becomes intensely
red upon addition of nitric acid : brucia.   The reaction with nitric
acid and protochloride of tin  is resorted to as a  conclusive test
(§ 241, 6).
  b. A yellow solution is obtained, the color of which gradually
changes to yellowish-red, then to blood-red, and turns  finally crim-
son : VERATRIA.
  c. A colorless fluid  is obtained, which  remains colorless  after
standing for some time.
  Add to the fluid a fragment of chromate  of  potassa; if this
imparts to it a deep blue color, strychnia is present;  if it leaves
the fluid unaltered, quina is present.  The reaction with chlorine
water and ammonia is resorted to as a conclusive test. 
§ 246.]
APPENDIX.
409
II. Detection of the Alkaloids, and of Salicine, in Solutions
   SUPPOSED TO CONTAIN SEVERAL OR ALL OF THESE SUBSTANCES.
                             § 246.
  1.  Add to a portion of the aqueous  solution dilute solution of
potassa or soda, drop  by drop, until the fluid acquires a scarcely
perceptible alkaline reaction; stir, and let the fluid stand  for  some
time.
  a.  No precipitate is formed ; this proves the total absence of
the alkaloids, and indicates the presence  of  salicine.  To  remove
all doubt on the point, test the original substance with concentrated
sulphuric acid, and with hydrochloric acid.   Compare § 245,  1, a.
  b.  A precipitate is formed : add solution of  potassa or  soda,
drop by drop, until the fluid manifests a strongly  alkaline reaction.
       a. The precipitate redissolves.  Absence of the alkaloids of
     the second and third  groups.   Presence of  morphia is indi-
     cated.  The reactions  with iodic acid (§ 235, 9), and with sul-
     phuric acid, &c. (§ 235, 7), are resorted to  as conclusive  tests.
     Examination for salicine, see 4.
       8.  The precipitate does not redissolve, or  at least not com-
    pletely.  Filter, and treat  the precipitate as directed  in  2.
     Saturate the filtrate with carbonic  acid, or mix it with bicar-
     bonate of soda or bicarbonate of potassa, and boil nearly to
     dryness.  Treat the residue with water; if it dissolves  com-
     pletely, this is a sign that no morphia is present; but  if there
     is an insoluble residue left,  this indicates  the  presence  of
     morphia.   The reactions with iodic acid (§  235, 9), and with
     sulphuric acid, &c. (§ 235, 7), are resorted  to as conclusive
     tests.
  2.  Wash the filtered  precipitate of 1, b, 8, with cold water, dis-
solve in a slight excess  of dilute sulphuric acid, and add solution of
bicarbonate of soda to  the fluid until the acid reaction is neutraliz-
ed ;  stir the mixture, vigorously rubbing the sides of the vessel, and
allow the fluid to stand for an hour.
  a.  No Precipitate is formed.   Absence  of  narcotina and cin-
chonia.  Boil the solution nearly to dryness, and treat  the  residue
with cold water..  If it dissolves completely, pass on to  4 ; but if
an insoluble  residue  is left,  examine this for  quina—of which a
minute quantity might be present—and for  strychnia, brucia, and
veratria, according to the directions of 3.
  b.  A precipitate is formed.  This may  contain narcotina, cin-
chonia, and also quina, compare § 245, 2, b.  Filter, and treat the
filtrate as  directed § 246, 2,  a.  Wash the precipitate with cold
water dissolve in a little hydrochloric acid, add ammonia in excess,
then a sufficient quantity of ether.
       a.  The precipitate which forms at first upon the addition of 
410
APPENDIX.
[§ 246.
     the ammonia redissolves completely in the ether, and the clear
    fluid presents two distinct layers.  Absence of cinchonia ; pre
     sence of quina  or narcotina.  Evaporate the ethereal solution,
     dissolve the residue in a little hydrochloric acid and a sufficient
     amount of water to make the dilution at least as 1 : 200; add
     bicarbonate  of soda  to neutralization, and allow the fluid to
     stand for some  time.  The formation of a precipitate indicates
     the presence of narcotina.  Filter, and test the precipitate
     with chlorine water and ammonia, and with a mixture of sul-
     phuric acid and nitric acid (§ 236).  Evaporate the filtrate,  or
     the fluid if no precipitate has formed, to dryness, and treat the
     residue with water.   If part of it remains undissolved, wash
     this, dissolve in hydrochloric acid,  and add chlorine water and
     ammonia.   Green color: quina.
      8. The precipitate produced by the ammonia does not redis-
     solve in the ether, or at least not completely:  cinchonia. Quina
     or narcotina may also be present.   Filter, and examine the fil-
     trate for quina  and narcotina as in a.  The precipitate consists
     of cinchonia, and may be further examined according to § 238,
     3, or 8.
  3. Wash the  insoluble  residue of § 246, 2, a, with water, dry on
the water-bath, and digest with absolute alcohol.
  a. It dissolves completely : absence of strychnia ; presence of
(quina) brucia or veratria.  Evaporate the alcoholic solution on the
water-bath to  dryness, and, if quina  has already been detected,
divide the residue into two portions, and test one part for  brucia,
with  nitric  acid  and protochloride of tin (§ 241,  6), the other for
veratria, by means of concentrated sulphuric acid (§ 242, 6) ; but
if no quina  has  as yet been detected, divide the residue into three
portions, a, b, and c; examine  a and  b  for brucia and veratria,
in the manner just stated, and c for quina, with chlorine-water and
ammonia.  However, if brucia is present, dissolve c in hydrochloric
acid, add ammonia  and ether, let the mixture stand for some time,
evaporate the ethereal solution, and examine the residue for quina.
  b. It does not dissolve,  or at least not completely : presence of
strychnia  ; perhaps also  of (quina) brucia and veratria.   Filter,
and examine the filtrate for (quina) brucia and veratria as direct-
ed  § 246, 3, a.   The identity of  the precipitate with strychnia is
demonstrated by the reaction with sulphuric acid and chromate of
potassa (§ 240,  8).
  4. Mix a portion  of the original solution with hydrochloric acid,
and boil the mixture for some time.  The formation  of a  precipi-
tate indicates the presence of salicine.  To  set all doubt  on thi*
point at rest, test the original substance with concentrated sulphu-
ric  acid (§ 244, 3). 
§ 247.]
APPENDIX.
411
III.  Detection of the  Alkaloids, in  presence of coloring
       AND  EXTRACTIVE VEGETABLE OR ANIMAL MATTERS.
                             §247.
  The presence of mucilaginous, extractive,  and coloring matters
renders the  detection of the alkaloids a task of considerable diffi-
culty.  These matters obscure the reactions  so much that we are
even unable to determine by a preliminary experiment, whether the
substance under examination contains one of the alkaloids we have
treated of in the  foregoing paragraphs,  or not.  I will now give
Beveral methods by means of which the separation of the alkaloids
from such extraneous matters may be effected, and their detection
made practicable.  Which of these methods to select will, of course,
always depend upon the particular circumstances of the case.

1. Stas's Method for effecting the Detection of Poisonous
                          Alkaloids.*
  This method is based, a, upon the solubility of the acid salts  of
the alkaloids in water and in spirit of wine  ; b, upon the fact that
the alkaloids, even those sparingly soluble in ether, will pass into
the ethereal solution upon  mixing the  aqueous solution of any of
their salts with a fixed alkali or with the carbonate of a fixed alkali
in excess, and shaking the mixture repeatedly with ether;—lastly,
c, the removal from the alkaloids of other matters soluble in ether,
is based upon the insolubility  of the salts of  the alkaloids in ether,
owing to which an aqueous solution  of the  acid sulphate of the
alkaloid can be obtained, by  shaking the ethereal solution of the
pure alkaloid with dilute sulphuric acid.  I will give here, first the
original  method of Stas, then,  in 2, Otto's  modifications of that
method.
  a. If you have to look for the  suspected organic bases  in the
contents of  the stomach or intestines, or in  articles of food, or in
pappy matters in general, heat the suspected  substance with double
its weight of strong alcohol, acidified with from 0*5 grm. to 2 grin.
of tartaric acid or  oxalic acid,  to from 158°  F. to 167° F.  When
quite cold,  filter, and wash the undissolved  part with strong alco-
hol, adding  the washings to the filtrate.
  If you have to deal with the heart, liver, lungs, or similar organs,
cut them into fine shreds, moisten with the acidified alcohol, press,
and  repeat  the same operation, until the soluble parts are com-
pletely extracted ;  collect the fluids obtained, and filter.
  b. Concentrate the alcoholic fluid at a temperature not exceeding
95° F. and   if no insoluble matter separates, continue to evaporate

  * " Bulletin  de l'Academie de Medecine de Belgique," IX. 304.  " Jahrb.  f. prakt
Pharm  " XXIV. 313.   " Jahresbericht" von Liebig und Kopp, 1851, p. 640. 
412
APPENDIX.
[§ 247.
nearly to dryness.  Conduct this process either under a bell-glass
over sulphuric acid, with or without rarefaction of the air, or in a
tubulated retort, through which a current of air is passed.  If fatty
or other insoluble matters separate in the process of  concentra-
tion, pass the concentrated fluid  through a moistened filter, and
evaporate the filtrate nearly to dryness, conducting the process, as
above, either under a bell-glass or in a retort.
  c.  Digest the residue with cold absolute alcohol, filter, wash the
insoluble residue thoroughly with alcohol, and let  the alcoholic
solution evaporate in the air or in vacuo; dissolve the acid residue
in a little water, and add bicarbonate  of soda as long as  efferves-
cence ensues.
  d. Add to  the mixture four or five  times its volume of pure
ether, free from oil of wine, and shake ; then  allow it to  stand at
rest, and  let  a little of the supernatant ether evaporate  spon-
taneously on a watch-glass.  If this leaves  oily streaks upon the
glass, which gradually collect into a drop, and emit, upon the appli-
cation of a gentle heat a disagreeable, pungent, and  stifling odor,
there is reason  to infer the  presence of a liquid volatile base;
whilst a solid residue or a  turbid fluid, with solid particles sus-
pended in it, indicates a non-volatile, solid base.  In the latter case
the base may emit a disagreeable animal smell, but not a pungent
odor, as is the case with volatile bases.  The blue color of reddened
litmus-paper is permanently restored.  If no residue  is left,  add to
the fluid some solution of soda or potassa, and shake with repeatedly
renewed ether, which will now  dissolve  the base.  It follows from
the assumption that the bases present will pass into the ethereal
solution, that Stas's method is principally calculated for the detec-
tion of the  poisonous alkaloids which are soluble in  ether, though
some of them only sparingly.  The following  are the vegeto-alka-
lies which Stas enumerates as discoverable by his method :  Conia,
Nicotina, Aniline,  Picoline,  Petinine,  Morphia, Codeia,  Brucia,
Strychnia, Veratria, Colchicia,  Delphia, Emetine,  Solania,  Aconi-
tina, Atropia, and Hyoscyamia.
  a. There is reason to infer the presence of a volatile base.
  Add to the contents of the vessel from which you have taken the
small portion  of ether for evaporation on the watch-glass, one or
two cubic centimetres of strong solution of potassa or soda, shake
the  mixture, let  it  stand at rest, pour the  supernatant fluid into a
flask, and treat the residue again three or four times with ether,
until the last portion poured off leaves no longer a residue upon
evaporation.  Mix  the ethereal fluid now with some dilute sul-
phuric acid (1 part of acid  to 5 parts of water) until the well-shaken
fluid manifests acid reaction;  allow the mixture  to  stand  at rest,
decant the supernatant ether from the acid aqueous fluid, and treat
the latter once more with  ether in the same way. 
§ 247.]
APPENDIX.
413
       aa.  Mix the  residual acid solution (which may contain sul-
    phates of ammonia, nicotina, aniline, picoline, and petinine—
    indeed which must contain these bases, if they are present in
    the examined substance, since their compounds with sulphuric
    acid are quite insoluble in ether ; and in which, if conia is pre-
    sent, the  greater  part  of the latter  alkaloid is also found)
    with concentrated solution of • soda  or potassa in excess, and
    treat with ether, which will again dissolve the liberated bases ;
    decant the ether, and leave  it to spontaneous evaporation, at
    the lowest possible temperature ; place the dish with the resi-
    due in vacuo over sulphuric acid.   In this process  the  ether
    and ammonia escape, leaving the volatile organic base in the
    pure state.  The nature of  the organic  base is  then finally
    ascertained.
       bb.  The ether decanted from the acid solution  contains the
    animal matters  which it has  removed from the alkaline fluid.
    It leaves, therefore, upon spontaneous evaporation, a trifling faint
    yellow residue  of nauseous  odor, which contains also  some
    sulphate of conia, if that base was present in the  examined
    matter.
  8.  There is reason to infer the presence of a solid base.
  Add a few drops  of alcohol to the ethereal solution obtained by
treating with ether  the previously acid residue mixed either simply
with  bicarbonate of soda, or first with that reagent, then with
solution of soda or potassa (see c  and d), and leave the mixture to
spontaneous evaporation.   If this fails to  give the  base in a
distinctly crystalline form and sufficiently pure,  add a few drops of
water slightly acidified with sulphuric acid, which will usually serve
to separate the mass into a fatty portion, adhering to the dish, and
an acid aqueous solution, which contains the base as  an acid sul-
phate.  Decant or filter, wash with a little slightly acidified water,
and evaporate  the solution to a considerable extent, under a bell-
glass  over  sulphuric acid.   Mix the  residue with a highly  concen-
trated solution of pure carbonate  of potassa, treat  the mixture
with absolute alcohol, decant, and let the alcoholic fluid evaporate,
which will generally leave the base in a state of perfect purity, or
nearly so.

         2. Otto's  Modifications of Stas's Method.*
  a.  In the method just  described, the morphia which may be
present will only pass into the ethereal solution if the  solution ob-
tained in 1  c, is shaken with ether immediately after  the addition
of the bicarbonate of soda, and  the ether  then quickly decanted.
But if the operation of shaking with ether is delayed, so as to af-
                 * Annal. d. Chem. u. Pharm., 100, 44. 
414
APPENDIX.
[§ 247.
ford the morphia time to crystallize, the crystals will deposit, being
almost  absolutely insoluble  in  ether  (P.  Pollnitz) ;  and  if the
ethereal solution is allowed to stand some time, the dissolved mor-
phia will separate in small crystals, on the sides of the vessel.—As
it is therefore,  under the circumstances  stated,  always likely to
happen that the morphia may remain, wholly or in part, undissolved
by the ether, it is of the highest importance never to neglect mix-
ing the alkaline fluid obtained in 1, d—after repeated extraction
with ether,  and subsequent addition of some solution of soda, to
dissolve the morphia, which may have separated, and after evapo-
rating the ether still present—with  a concentrated  solution of
chloride of ammonium, and letting the mixture stand exposed to
the open air, to  allow the morphia to crystallize.
   b. Instead of the process described in 1, 8, to effect the detection
of non-volatile alkaloids, Otto recommends the following method,
which is in principle the same as that recommended by Stas for the
detection of the volatile bases.
   Let the ethereal solution evaporate, dissolve the residuary impure
alkaloid in a little water mixed with sulphuric acid, and shake the
solution repeatedly with ether, which will remove the foreign orga-
nic matters present, and leave  the acid vegeto-alkaline  sulphate
unaffected.  Mix now the acid aqueous solution with carbonate of
soda in excess, shake repeatedly with  ether  (to dissolve the libe-
rated alkaloids), and let the ethereal solution evaporate, when the
alkaloids held in solution by the  ether will be left in  a very pure
state and, to a great extent, in the crystalline form.  This  method
has stood the test of numerous experiments.
   c.  But what Otto  recommends most, is the treatment with ether
of the alkal oid in the form of salt, before its  separation, by means
of an alkali,  and its solution  in ether.—If,  therefore, you  wish to
follow this method, shake the acid aqueous fluid of 1, c, which con-
tains the alkaloid in  combination with tartaric acid or  oxalic acid,
repeatedly with ether, so long as  the ether becomes colored and
leaves a residue upon evaporation ; then, and not before, add car-
bonate  of soda, dissolve  the  alkaloid by means of ether, and
proceed generally as  directed in  1, d.   Upon evaporating the ether,
the alkaloid is now left at once in a very pure state.

        3. Method  of L. V. Uslar and J. Erdmann.*
  This may be considered an improvement upon Stas's method, as
regards non-volatile  alkaloids,  more  especially  morphia, whilst
Stas's method deserves the preference for volatile alkaloids.  The
new method is the same in principle as that of Stas's,  simply sub-
stituting amyl-alcohol for ether.
        * Annal. d. Chem. u. Pharm., 120, page 121; and 122, page 360. 
§ 247.]
APPENDIX.
415
   Mix the matters to be examined with water, if necessary, to the
consistence of a thin paste, acidify slightly with hydrochloric acid,
digest  one  or two hours  at from 140°  to 176° Fah., and  pass
through a linen cloth moistened with water.   Extract the residue
with water acidified with hydrochloric acid,  add  the solution ob-
tained to the first fluid, supersaturate with ammonia, and evaporate
to dryness, with addition of pure quartz sand, which will enable
you to reduce the residue to powder.  Boil the powder repeatedly
with amyl-alcohol,  to extract the whole  of the  alkaloid from it.
Filter the extracts hot through paper moistened with amyl-alcohol.
The filtrate, which is mostly colored  yellow, holds, besides the alka-
loid, fatty and coloring matters in solution.  To remove these latter,
transfer the filtrate to a cylindrical vessel, mix it with from ten to
twelve  times  its  volume of almost  boiling water, acidified with
hydrochloric acid, and vigorously shake the mixture for some time.
The hydrochlorate of the alkaloid passes into the aqueous solution,
whilst the fatty and coloring matters remain dissolved in the amyl-
alcohol.*   Remove the latter by means of an India-rubber pipette,
then shake  the acid solution  repeatedly with fresh quantities of
amyl-alcohol, until all the fatty and coloring matters are completely
removed.  Concentrate now by  evaporation, mix with ammonia in
slight excess, add hot amyl-alcohol, and shake vigorously.  When
the liquid has separated into two distinct layers, draw off, by means
of a pipette, the upper layer,  which contains the solution of the
alkaloid in amyl-alcohol, treat the fluid once more with hot amyl-
alcohol, then completely drive off the latter by heating on the water-
bath, which  will  often  leave the alkaloid  sufficiently pure  for
examination by the usual reactions.   Should it, however, still look
yellowish or brownish, dissolve it once  more in dilute hydrochloric
acid, shake the solution with amyl-alcohol, remove the latter with
the pipette, then  supersaturate  with ammonia,  shake again with
amyl-alcohol, draw off the latter with the pipette,  and evaporate it
on the water-bath.  It is only  in very rare  cases that the alkaloid
left  by this evaporation  requires a  repetition of this process of
purification.   The last evaporation of the pure alkaloid is best con-
ducted  in  a small porcelain  crucible, placed obliquely.  Before
proceeding to the decisive reaction,  pour a few drops  of concen-
trated sulphuric acid over  the  alkaloid, and observe whether it
still turns brown on the application of this test; in which case  the
process of purification  must be  repeated.—Uslar and Erdmann
have detected and isolated by  this method very minute traces of

  * If less water is used, traces of the  hydrochlorate of the alkali are apt to remain
in the amyl-alcoholie solution.  J  Erdmann recommends always to put aside the
first portion of amyl-alcohol, as well as that used to effect the removal of the fatty
matters that they may, if necessaiy, be shaken once more with the stated quantity
of acidulated water. 
416
APPENDIX.
[§247
 alkaloids, e.g., 5 milligrammes of hydrochlorate of morphia, 1 drop
 of nicotine, 9 milligrammes of strychnine, mixed with from 2 to 3
 pounds of contents of the stomach.   In  his  second paper on  the
 subject Erdmann calls particular attention to the fact that he suc-
 ceeded, in separating by this method the  poisonous  alkaloids from
 quite putrid intestines of poisoned  animals, from a  fortnight to  a
 month after death.  The latter  experiments referred to strychnia
 and morphia.   Of course only those  portions of the alkaloids can
 be detected which have not yet  suffered  decomposition.  With
 regard to morphia, there would seem to  exist no doubt but that
 this alkaloid suffers decomposition in the organism.  A rabbit had
 given it 0.1 grm. of hydrochlorate of morphia, and was killed three
 and a half hours after : no morphia was found in the urine, brain,
 and spinal marrow ; only very little of it in the blood, a little in
 the stomach and the small intestines, more in the other intestines.


 4. Methods of detecting Strychnia, based upon the Use of
                         Chloroform.*

            a. RODGERS AND GlRDWOOD's  METHOD.f

  Digest the substance under examination with dilute hydrochlorio
acid (1 part of acid to 10 parts of water) and filter;  evaporate the
filtrate on the  water-bath to dryness,  extract the residue with spirit
of wine, evaporate the solution, treat the residue with water, filter,
supersaturate the filtrate with ammonia, add £ oz. (15 grammes) of
chloroform, shake, transfer the chloroform to a dish, by means of a
pipette, evaporate  on the water-bath, moisten the residue with con-
centrated sulphuric acid, to effect carbonization of foreign organic
matters, treat  with water, after the  lapse of several hours, then
filter.   Supersaturate the filtrate again with ammonia, and shake it
with about 1 drachm (4 grammes)  of chloroform.  Repeat the same
operation until the residue left upon the evaporation of the chloro-
form is no longer charred by sulphuric acid.  Transfer the  chloro-
form  solution  which leaves a pure residue, no longer affected by
 sulphuric acid, drop by drop, by means of a  capillary tube, to the
 same spot on a heated porcelain dish, letting it evaporate, then test
 the residue with sulphuric acid and chromate of potassa. Rodgers
 and Girdwood succeeded  in detecting by  this method so small  a
 quantity of strychnia as the^ „'a ^th part of a grain.

  * These methods are no doubt useful also for effecting the separation of other alka-
 loids; however, the deportment of the latter with chloroform  has  not yet been
 sufficiently studied.
  f Liebig and  Kopp'S " Jahresbericht,"  1857, 603.—Pharm. Journ. Trans., xvi
 497. 
§ 247.]
APPENDIX.
417
           b. Method recommended by E. Prollius.
   Boil twice with spirit of wine, mixed with some tartaric acid,
 evaporate at a gentle heat, filter the residuary acid aqueous solu-
 tion through a moistened filter, add ammonia in slight excess, then
 from 20 to 25 grains (about \\ grm.) of chloroform, shake, free the
 deposited  chloroform thoroughly from  the ley, by decanting and
 shaking with water, mix the chloroform so purified with 3 parts of
 spirit of wine, and let the fluid evaporate.   If there is any notable
 quantity of strychnia present, it is obtained in crystals.

 5. Method of effecting the Detection of Strychnia in Beer,
               by Graham and A. W. Hofman.j
   This method, which is based on the known fact that a solution
 of a  salt of strychnia, when mixed and shaken with animal char-
 coal, yields its strychnia to the charcoal, will undoubtedly be found
 applicable also for the detection  of other alkaloids.  The process
 is conducted as follows:—
   Shake 2 ounces of animal charcoal in  half-a-gallon of the aqueous
 neutral or feebly acid  fluid under examination;  let the mixture
 stand for from 12 to 24 hours, with occasional shaking, filter, wash
 the  charcoal  twice with water, then boil for half-an-hour with 8
 ounces of spirit  of wine of 80-90 per cent., avoiding loss  of alco-
 hol by evaporation.  Filter the  spirit  of wine hot from the char-
 coal, and distil the filtrate ; add a few drops of solution of potassa
 to the residual watery fluid, shake with  ether, let the mixture stand
 at rest, then decant  the supernatant  ether.   The ethereal fluid
 leaves, upon  spontaneous evaporation, the strychnia  in  a state
 of sufficient purity to admit of its further examination by reagents
 (see § 240).
  MacadamJ employed  the same method in his numerous experi-
 ments to detect strychnia in the bodies of dead animals.  He treated
 the comminuted matters with  a dilute  aqueous solution of oxalic
 acid in the cold, filtered through muslin, washed with water, heated
 to boiling, filtered still warm, from the coagulated albuminous mat-
 ters,  shook  with charcoal, and proceeded in the manner just
 described.  According to his statements, the  iesidue  left  by the
evaporation of the alcoholic solution was generally at once fit to be
tested for strychnia.  Where it was not so, he treated  the  residue
ao-ain  with solution of  oxalic acid, and repeated the process with
animal charcoal.

                  6. Separation by Dialysis.
  The dialytic method devised by Graham, and described in § 227,
                  * Chem. Centrabl., 1557, 231.
                  f Chem. Soc. Quart. Journ., v. 173.
                  $ Pharm. Journ. Trans., xvi. 120,  160. 
418
APPENDIX.
[§ 248.
may also be advantageously employed to effect the separation of
alkaloids from the contents of the stomach, intestines, &c. Acidify
with hydrochloric acid, and place the matter in the dialyser.  The
alkaloids, being crystalline bodies, penetrate the membrane, and
are found, for the greater part, after 24  hours, in the outer  fluid ;
from this they may, then, according to  circumstances, either be
thrown down at once, after concentration by evaporation; or they
may be purified by one of the above described methods.
                             n.

   General Plan of the Order and Succession in which
       Substances should be analyzed for Practice.

                            § 248.
  It is not a matter of indifference whether the student, in analyz-
ing for the sake of practice, follows no rule or order whatever in
tvj selection  of the substances which he intends to  analyze,
or whether, on the contrary,  his investigations  and experiments
proceed systematically.   Many  ways,  indeed,  may lead to the
desired end, but one of them will invariably prove the shortest.  I
will, therefore, here point out a course which experience has shown
to lead safely and speedily to the attainment of the object in view.
  Let the student take 100 compounds,  systematically arranged
(see below), and let him analyze these  compounds successively in the
order in which they are placed.  A careful and  diligent examina-
tion of these will be amply sufficient to impart to him the necessary
degree of skill in practical analysis.  When analyzing for the sake
of practice only,  the student must above all things possess the
means of verifying the results obtained by his experiments.   The
compounds to be examined ought, therefore, to be mixed for him
by a friend who knows their exact composition.

                       A. From 1 to 20.
   Aqueous solutions of  simple salts : e. g., sulphate  of  soda,
nitrate of lime, chloride of copper, &c.   These investigations will
serve to  teach the student the  method of analyzing  substances
soluble in water  which contain but one base.  In these investi-
gations it is only intended to ascertain which base is present in the
fluid  under examination;  but  neither the  detection of the  acid,
nor the proof of the absence  of all  other bases besides the one
detected, is required. 
§ 248.]
APPENDIX.
419
                      B. From  21  to 50.
  Salts, etc., containing one base and one acid, or one metal
and one metalloid (in form of powder: e. g., carbonate of baryta,
borate of  soda, phosphate  of lime, arsenious acid,  chloride of
sodium, bitartrate of potassa, acetate of copper, sulphate of baryta,
chloride of lead, &c.  These investigations will serve to teach the
student how to make a preliminary examination of a solid sub-
stance, by heating in a tube or before the blowpipe ;  how to con-
vert it into a proper form for analysis,  i. e., how to dissolve or
decompose it; how to detect one metallic oxide, even in substances
insoluble in water ;  and how to demonstrate the  presence  of one
acid.  The detection of both the base and the acid is required, but
it is not necessary to prove that no other bodies are present.

                      C. From  51  to 65.
  Aqueous or acid solutions of several bases.  These investiga-
tions will serve to teach the student  the method of separating and
distinguishing several metallic oxides from each other.  The proof
is required that no other bases are present besides  those detected.
No regard is paid to the acids.

                      D. From  G6  to 80.
  Dry mixtures of  every description.  A portion of the  salts
should be organic, another inorganic; a portion of the compounds
soluble in water or hydrochloric acid; another insoluble; e. g., mix-
tures of chloride of sodium, carbonate of lime, and oxide of cop-
per;—of  phosphate  of magnesia and  ammonia, and arsenious
acid; of tartrate of lime, oxalate of lime, and sulphate of baryta ;—
of phosphate of soda, nitrate of ammonia, and acetate of potassa, &c.
  These investigations will serve to teach the student how to treat
mixtures of different substances with  solvents;  how  to  detect
several acids in presence of each other ; how to detect the bases
in presence of phosphates of the alkaline earths; and they will
serve as a general introduction to scientific and practical analysis.
All the component parts must be detected, and the nature  of the
substance ascertained.

                     E.  From 81 to 100.
  Native compounds, articles of  commerce, &c.  Mineral and
other waters, minerals of every description, soils, potash, soda.
alloys, colors, &c. 
420
APPENDIX.
[§ 249.
                             m.
 Arrangement of the Results of the Analysis performed
                       for Practice.
                           § 249.
  The manner  in  which the results of analytical investigations
ought to be arranged is not a matter of indifference.  The follow-
ing examples will serve to illustrate the method which I have found
the most suitable in this respect.
Plan of arranging the Results of Experiments, Nos. 1—20.
             Colorless fluid of neutral reaction.
HC1	HS	NH4S	N H 0, C 0 and
no precipitate,	no precipitate,	no precipitate,	NHiCl
consequently no	noPb 0	noFeO	a white precipitate,
AgO	„Hg0	„MnO	consequently either
Hg20	„CuO	„NiO	Ba 0, Sr 0, or Ca 0,
	„ Bi 03	„CoO	no precipitate by
	„CdO	„ZnO	solution of sul-phate of lime,
			
	„ As 03	„ A1203	consequently
	„As05	„Cr203	LIME.
	„ Sb 03		Confirmation by
	„ Sn 02		means of
	„SnO		0
	„ Au O3		
	„ Pt 0,		
	„ Fe203		
Plan of arranging the Results of Experiments, Nos. 21-50.
White powder, fusing in the water of crystallization upon applica-
  tion of heat, then remaining unaltered—soluble  in water—reac-
  tion neutral.
HC1	HS	NH4S	NHO,CO,	2NaO,HO,P05and
no preci-	no preci-	no preci-	andNH CI	NH40
pitate.	pitate.	pitate.	no preci-pitate.	a white precipitate, consequently MAGNESIA.
  The detected base being Mg O, and the analyzed substance being
soluble in water, the acid can only be CI, I, Br, SO , NO, A, &c.
The  preliminary examination has proved the absence of the or-
ganic acids, and of nitric acid.
  Ba CI produces a white precipitate which H CI fails to dissolve ;
consequently sulphuric acid. 
                         Plan of arranging the  Results  of Experiments, nos. 51—100.

A white powder, acquiring a permanent yelloxo tint upon application of heat, without forming a sublimate, and without
  emitting visible fumes marked by acid or alkaline reaction.  Before the blowpipe, a ductile metallic globule, and yellow
  incrustation, with white border upon cooling.  Insoluble in water,  effervescing with hydrochloric acid, incompletely
  soluble  in that  acid, readily soluble in nitric  acid to a colorless fluid.
to
CD
        HCl
  White  precipitate,
insoluble in an excess
of the precipitant, un-
altered by ammonia;
quite soluble  in  hot
water; S03 producing
a white precipitate in
the solution:  lead.
        HS
  Black  precipitate,
insoluble in sulphide
of ammonium, readi-
ly soluble  in nitric
acid.   S03 produces
a white  precipitate:
lead.  Examination
for Cu, Bi, and Cd:
results negative.
        N Hf, S
  White precipitate; am-
monia, applied by itself,
produces no  precipitate;
solution of precipitate in
hydrochloric acid remains
clear upon  addition of so-
da in excess.
 NH„ CI
no  precipi-
tate.
  HS
white pre-
cipitate :
  ZINC
      N H4 O, C02
 White precipitate; upon
dissolving this  in hydro-
chloric  acid,  and adding
solution of  sulphate  of
lime to  the fluid, a white
precipitate  forms  after
some time:   strontia.
Precipitation  with  sul-
phate of potassa, filtrate
tested for  lime  with O:
results negative.
   No fixed
residue upon
evaporation
  Hydrate
of lime has
failed to
evolve
ammonia.
Of the acids carbonic acid has already been found.  Of the remaining acids the following cannot be present:
  The preliminary examination has proved the absence of organic acids with nitric acid.
  CI 05 cannot be present, because the analyzed substance is insoluble in water.
  S and S 03 not, because the analyzed substance is readily soluble in nitric acid.
  Cr 03 not, as the nitric acid solution is colorless.
  P 05, Si Oi, H F, and O not, because the solution filtered from the sulphide of lead was not precipitated by simple
    addition of ammonia.
  B 03 might be present in trifling quantity; the examination for it gave a negative result.
CI, I, Br might be present in the form of basic  compounds of lead.  However, nitrate of silver has produced no pre-
  cipitate in the nitric acid solution:  accordingly, they cannot be present.
mi „    i    j          j    4.  •   it,   *    \ bases:  oxide of lead, oxide of zinc, strontia.
The  analyzed  compound contams, therefore \   .,  . n^n-  ^
I acids:
fe 
422
APPENDIX.
f§ 250.
                            IV.


                       TABLE


                           OF THE

         MORE FREQUENTLY OCCURRING FORMS AND
   COMBINATIONS OF THE SUBSTANCES TREATED OF IN THE
                      PRESENT  WORK,


                          ARRANGED
 WITH ESPECIAL REGARD TO THE CLASS TO WHICH THEY RESPECTIVELY BELONG
                 ACCORDING TO THEIR SOLXJBILITT

IN  WATER,  IN  HYDROCHLORIC  ACID,  IN  NITRIC  ACID,
            OR IN NITROHYDROCHLORIC ACID.
                            § 250.

                    PRELIMINARY remarks.
  The class to which the several compounds respectively belong
according to  their solubility in  water or acids (see § 182), is
expressed by figures.  Thus 1 or I means a substance soluble in
water; 2 or II a substance insoluble in water, but soluble in hydro-
chloric acid, nitric acid, or nitrohydrochloric acid; 3 or III a sub-
stance insoluble in water, in hydrochloric acid, and in nitric acid.
For those substances which stand as it were on the limits between
the various classes, the figures of the  classes in question are jointly
expressed: thus  1—2 signifies a substance sparingly soluble in
water, but soluble in hydrochloric acid or nitric acid ;  1—3 a body
sparingly soluble in water, and of which the solubility is not nota-
bly increased by the addition of acids; and 2—3 a substance inso-
luble  in  water, and  sparingly soluble in acids.   Wherever the
deportment of a substance with hydrochloric acid differs materially
from that which it  exhibits with  nitric acid, this is stated in the
notes.
  The Roman figures denote ofiicinal and more commonly occurring
compounds.
  The haloid salts and sulphur compounds are placed in the col- 
§ 250.]                   APPENDIX.                      42b

umns of the corresponding  oxides.  The  salts given  are, as  a
general rule, the neutral salts; the basic, acid, and double salts, if
officinal, are mentioned in the notes; the small figures placed near
the corresponding neutral or simple salts refer to these.
  Cyanogen, chloric acid, citric acid, malic acid, benzoic acid, suc-
cinic acid, and formic acid, are of more common occurrence in com-
bination with a few bases only, and have therefore been  omitted
from the table.  The most frequently occurring compounds of these
substances are:  cyanide of potassium I, ferrocyanide of potassium
I, ferricyanide of potassium I, sesqui-ferricyanide of iron (Prussian
blue) HI,  ferrocyanide  of zinc and potassium H—HI, chlorate  of
potassa I, the citrates of the alkalies I, the malates of the alkalies
I, malate of sesquioxide of iron I, the benzoates of the alkalies I,
the succinates of the alkalies I, and the formates of the alkalies I. 
424                       APPENDIX.

                         INDEX  OF THE SOLUBILITY OF
	KO	NaO	NH40	BaO	SrO	CaO	MgO	ALA	MnO	FeO	F&A	CoO	NiO	Zno
	I			I	1	I-II	II	II	2	2	II	II	II	II
s	I			I	1	I-II	2		II	II	2	2l5	2,6	2,7
CI	I		I12	I	I	I	1	I		I	Ik	I	I	1
I	I			1	1	1	1			I	1			1
S03	I.		I13	III	III	I-III	I	Il-l3		I	I	I	I	I
NO,	I			I	I	1	1	1		1	1	I	1	1
P06	1	I10	lio	2	2	n„	2	2	2	2	II	2	2	2
C02	I2	In		II	II	11	II		n	II		II	2	II
D	I3			2	2	11	2	2	2	1-2	1-2	2	2	2
B03	U	I<		2	2	2	2	2	2	2	2	2	2	2
A	I			I	1	1	1	1	1	1	I	1	1	I
T	I4.3	I7	16	2	2	11	1-2	1	1-2	1-2	18	1	2	2
As06	I			2	2	2	2	2	2	2	2	2	2	2
As03	I			2	2	2	2			2	2	2	2	
Cr03	I			2	2	2	1	2	1		1		2	1
                         NOTES.

 1.  Sulphate of potassa and alumina I.
 2.  Bicarbonate of potassa I.
 3.  Binoxalate of potassa I.
 4.  Tartarized borax (bitartrate of potassa and borate of soda) I
 5.  Bitartrate of potassa I-H.
 6.  Tartrate of potassa and ammonia I.
 7.  Tartrate of potassa and soda I.
 8.  Tartrate of potassa and sesquioxide of iron I.
 9.  Tartrate of antimony and potassa I.
10.  Phosphate of soda and ammonia I.
11.  Bicarbonate of soda I.
12.  Sesquichloride of iron and chloride of ammonium I.
13.  Sulphate of alumina and ammonia I.
14.  Basic phosphate of lime II.
15.  Sulphide  of cobalt is pretty readily decomposed  by nitric
     acid, but very difficultly by hydrochloric acid.  This sub-
     stance is not officinal.
16.  The same applies to sulphide of nickel. 
APPENDIX.                      425
SUBSTANCES IN WATER OR ACIDS.
	CdO	PbO	SnO	Sn02	Bi03	CuO	HgsO	HgO AgO		Pt02 Au03		Sb03	Cr203
	2	n18	2	2&3	2	na	II	H	2	2		1185	II & III
s	2	II	2ao	2ao	2	223	H	II	230	231		II*	
CI	1	I-III	I	I	I	1*	H-IH	1*8	III	I3233	I34	137	I&HI
T	1	I-II	1	1			II	H	3				
S03	I	n-in	1		1	125	1-2	I99	I-II	1		2	I-II
N05	1	1		1	I21	I	127	I	I	1			I
P05	2	2	2			2	2	2	2				2
co2	2	11			2	II	2	2	2				
0	2	2	2	1	2	2	2	2	2			1-2	1
B03	1-2	2	2		2	2	1						2
A	1	Il9	1	1	1	126	1-2	1	1				1
T	1-2	2	1-2		2	1	1-2	2	2			I33	1
Afe05		2			2	2	2	2	2			2	2
As03		2				n	2	2	2			2	
Cr03		II-III	2		2	1	2	1-2	2			2	2
 17. Sulphide of zinc is readily soluble in nitric acid, somewhat
       more sparingly soluble in hydrochloric acid.
 18. Minium is converted by  hydrochloric acid into chloride of
      lead; by nitric acid  into oxide, which redissolves  in  an
      excess of the acid, and into brown binoxide of lead, which
      is insoluble in nitric acid.
 19. Trisacetate of lead I.
 20. Proto- and bisulphide of tin are decomposed and dissolved
      by hydrochloric acid; by nitric acid they are  converted
      into binoxide, which is  insoluble in an excess of the acid.
      Sublimed bisulphide  of tin  dissolves  only in nitrohydro-
      chloric acid.
 21. Basic nitrate of teroxide of bismuth II.
 22. Ammoniated oxide of copper 1.
 23. Sulphide of copper is difficultly decomposed by hydrochloric
      acid, but with facility by nitric acid.
 24. Chloride of copper and ammonium I.
25. Sulphate of copper and ammonia I.
26. Basic acetate of copper, partially soluble in water, and com
      pletely in acids. 
426
APPENDIX.
27. Basic nitrate of suboxide of mercury and ammonia H.
28. Ammonio-chloride of mercury H.
29. Basic sulphate of oxide of mercury H.
30. Sulphide of silver soluble only in nitric acid.
31. Bisulphide of platinum is not affected by hydrochloric acid,
     and but little by boiling nitric acid; it dissolves in  hot
     nitrohydrochloric acid.
32. Bichloride of platinum and chloride of potassium 1—3.
33. Bichloride of platinum and chloride of ammonium 1—3.
34. Terchloride of gold and chloride of sodium I.
35. Teroxide of antimony is soluble in hydrochloric acid, but not
     in nitric acid.
36. Tersulphide of antimony and sulphide of calcium I—IL
37. Basic terchloride of antimony H.
38. Tartrate of teroxide of antimony and potassa I. 
APPENDIX.
427
V.
TABLE OF WEIGHTS AND MEASURES.
GRAMMES.	GRAINS.	DECIGRAMMES.	GRAINS.
1 =	15-4323	1 =	1-5432
2	30-8646	2	3-0864
3	46-2969	3	4-6296
4	61-7292	4	6-1728
5	77-1615	5	7-7160
6	92-5938	6	9-2592
7	108-0261	7	10-8024
8	123-4584	8	12-3456
9	138-8907	9	13-8888
CENTIGRAMMES.	GRAINS.	MILLIGRAMMES.	GRAINS.
1 =	•1543	1 —=	•0154
2	•3086	2	•0308
3	•4630	3	•0463
4	•6173	4	•0617
5	•7717	5	•0771
6	•9260	6	•0926
7	1-0804	7	•1080
8	1-2347	8	•1234
9	1-3891	9	•1389
METRES.	INCHES.	DECIMETRES.	INCHES.
1 =	39-37	1 =,	3-937
2	78-74	2	7-874
3	118-11	3	11-811
4	157-48	4	15-748
5	196-85	5	19-685
6	236-22	6	23-622
7	275-59	7	27-559
8	314-96	8	31-496
9	354-33	9	35-433
CENTIMETRES.	INCHES.	MILLIMETRES.	INCHES.
1 =	•3937	1 S3	•03937
2	•7874	2	•07874
3	1*1811	3	•11811
4	1-5748	4	•15748
5	1-9685	5	•19685
6	2-3622	6	•23622
7	2-7559	7	■27559
8	3-1496	8	•31496
9	3-5433 |	9	•35433
One kilogramme
One cubic centimetre
One litre
15432 grains.
0-0610 cubic inch.
61-0270 cubic inches. 
 
ALPHABETICAL   INDEX.
Acetic acid (as reagent)   .   .    .    .39
          deportment with reagents    . 234
          detection  of, in  simple com-
            pounds   .    .    .    271, 275
                      in  complex com-
                       pounds  .  807, 309
Acids, as reagents.....86
Actual analysis......259
Alcohol (as reagent).....85
Alkaloids, detection of     .... 406
                 in presence of coloring
                   and extractive vege-
                   table or animal mat-
                   ter   ...      411
Alkaline solutions, examination of   .     . 279
Alloys, examination of              253, 256
Alumina, deportment with  reagents .    . 110
         detection of,  in  soluble simple
                   compounds 264, 265, 272
                In soluble complex  com-
                   pounds    .    . 293, 294
                in insoluble complex com-
                   pounds    .    .     . 313
Ammonia (as reagent)     ....  53
         deportment with reagents .     .  95
         detection of,  in  simple  com-
          pounds   .....265
                       in complex com-
                         pounds  .     . 802
                       in soils    .    . 340
                       in fresh waters . 826
         carbonate of (as reagent) .    .  63
         molybdate of (as reagent) .     .  66
         oxalate of (as reagent)    .     .  61
Antimonic acid, detection of              881
Antimony, detection of, in  alloys    .     . 259
          properties of       .    .     . 159
          teroxide of, detection  of, in
                     simple compounds 261
                 in complex compounds 28S
                 in sinter deposits .     . 335
                 in food, &c.  .    .     . 357
                 deportment   with   re-
                   agents    .    .     . 159
Apocrenic acid, detection of, in soils .    . 842
                       in mineral waters 837
Apparatus and utensils    .    .    .     .29
Aqua regia  •    •.....-^
Arsenic, properties of     .    .    .     • lbs
        acid, deportment with reagents . 173
        produced from arsenious acid    . 171
                      the tersulphide   . 172
Arsenious acid, deportment with reagents  168
Arsenious and  arsenic acids, detection of,
              in simple compounds .    . 261
              in complex compounds   . 287
              in mineral waters    .    . S85
              in food, Ac.     ... 846
              in sinter deposits    .    . 385
Arsenious from arsenic acid, how to distin-
    guish   .......178
Ashes of plants, animals, manures, Ac,
    examination of.....866
                    B.

Baryta, deportment of, with reagents    . 100
       detection  of,  in  soluble simple
                     compounds  .     . 265
                  in  insoluble simple
                     compounds  .     . 277
                  in soluble  complex
                     compounds  .  296, 299
                  in insoluble complex
                     compounds  .     . 318
                  in mineral waters   . 831
                  in sinter deposits    . 836
        carbonate of (as reagent)  .    .  71
        hydrate of (as reagent)    .    .  82
        nitrate of (as  reagent) .   .     .71
        water (as reagent)    .   .    .55
Bases (as reagents).....50
Beaker glasses......30
Benzoic acid, detection of, in simple com-
                      pounds   .     . 271
                     In  complex  com-
                      pounds   .     . 807
            deportment with reagents   . 238
Bismuth, detection of, in alloys .   .     . 254
                    in  articles of food,
                     Ac.              357
                    properties of .     . 146
         teroxide, deportment of, with re-
                     agents  .   .    . 146
                 detection  of, in simple
                     compounds  .     . 262
                  in  complex   com-
                     pounds .   .     .289
                 hydrated (as reagent) .  57
Blowpipe.......15
         flame  ....   16, 17, IS
Boracic acid, deportment with reagents  . 195
            detection of, in simple com-
              pounds    .    . 268,  273, 274
                    in   complex  com-
                     pounds .   .  298, 305
                    in silicates   .  319, 821
                    in mineral waters  . 832
Borax (as reagent).....86
Bromic acid, detection of  .    .   •     . 888
Bromine, properties and deportment  with
            reagents     .... 209
         detection of               268, 276
                   in mineral waters  . 832
Brucia, deportment with reagents        .402
       detection of, in simple  compounds
                                  407, 408
                 in  complex compounds 410
Butyric acid, deportment with reagents   . 288 
430
ALPHABETICAL  INDEX.
Ceri
  19
 268
 223
\, 83
  70
  72
  76
  42
Cadmium, properties of   ...     147
          oxide, detection  of,  in simple
                            compounds 261
                           in   complex
                            compounds 289
                deportment  with   re-
                   agents    .    .   .147
Caesium,  oxide, deportment with reagents  98
               detection of             334
Carbon, detection of, in compound bodies 276
                   in silicates    .   . 818
       properties of.....203
Carbonic acid, deportment with reagents . 208
             detection of, in simple com
                           pounds    . 266
                         in    complex
                           compounds . 802
                         in soils  .   . 340
                        to  well   and
                mineral waters 823, 826, 328
       , oxides, deportment with reagents 116
               detection of
         for blowpipe experiments  .
      ' acid, detection of .
            deportment with reagents
Chloride of ammonium (as reagent) .  66,
        of barium (as reagent)
        of calcium (as reagent
        of mercury (as reagent)
Chlorine (as reagent).....
        properties and deportment  with
                         reagents .   . 207
        detection  of,  in soluble simple
                        compounds 268, 274
                      in insoluble  sim-
                        ple compounds . 276
                      in soluble complex
                        compounds    . 304
                      in insoluble  com-
                        plex compounds 318
                      in soils .    .    .839
                       in fresh and mine-
                        ral waters.   . 825
                      in silicates   .   . 821
Chloroform (as reagent)  .    .    .    .86
Chlorous acid, deportment with reagents
Chrome-ironstone, analysis of  .
Chromic acid, deportment with reagents
             detection of, in simple com-
                           pounds  266, 274
                         in    complex
                           compounds'. 805
                         in    insoluble
                           compounds  . 818
Chromium, sesquioxide, deportment with
               reagents  .... 112
            detection of, in soluble simple
                         compounds 263, 865
                       in  complex  com-
                         pounds 294, 297, 813
Cinchonia, deportment with reagents     . 898
          detection  of,  in  simple   com-
                          pounds  .    . 408
                        in  complex com-
                          pounds  .    . 410
Citric acid, deportment with  reagents    . 228
           detection of, in  simple   com-
                         pounds  .    . 270
                        in complex com-
                          pounds  .    . 806
Cobalt, properties of.....126
       protoxide,  deportment  with  re-
                         agents   .    . 126
                  detection of, in simple
                      compounds   . 263, 298
                   in   complex    com-
                     pounds    294, 295, 296
       nitrate (as reagent)     .    .    .88
Coloration of flame.....26
Conia, deportment with -eagents    .    . 392
Copper (as reagent).....57
221
313
184
Copper, properties of.....143
       oxide, deportment witt reagents  . 148
             detection of, in simple com-
                           pounds    . 262
                       in complex com-
                           pounds    . 289
                       in sinter deposits 335
       sulphate (as reagent)    .    .    .76
Crenic acid, detection of, in soils    .    . 342
                       in mineral waters 837
Crystallization......6
Cyanide of potassium (as reagent)  .    .  67
                    in the moist way   .  67
                    in the dry way     .  85
Cyanides, insoluble in water, analysis of  . 814
Cyanogen,  detection of,  in simple  com-
                          pounds   268, 276
                        in complex com-
                          pounds   804, 314
           properties of   ...     214
                    D.

Decantation......9
Deflagration......15
Dialysis.......847
Didymium, oxide, deportment with  re-
                       agents    .    . 117
                  detection of   .    . 886
Distillation.......12
Distilling apparatus.....12
                    E.

Edulcoration......10
Erbium, oxide, deportment with reagents 116
        detection of.....886
Ether (as reagent).....85
Evaporation......11
Ferricyanide of potassium (as reagent)   .  69
Ferricyanogen, detection  of,  in  simple
                         compounds   . 268
                      in  complex com
                         pounds  .
Ferrocyanide of potassium (as reagent)
Ferrocyanogen, detection  of,  in  simple
                         compounds
in
complex  com
pounds
814
 68
268
314
  8
  9
Filtering paper  .
        stands  .
Filtration
Flame, coloration of.....25
       parts of......16
Fluoride of calcium (as reagent)
Fluorine, detection  of, in simple compounds
                           267, 273, 275, 277
                    in  complex  com-
                       pounds    .    . 298
                    in  insoluble  com-
                       pounds    .    . 812
                    in mineral waters  . 880
                    In sinter deposits   . 836
                    in silicates    .    . 817
Fluxing.......14
Formic acid, deportment with reagents   . 236
            detection of,  in simple com-
                            pounds    . 271
                         in    complex
                            compounds  307
Funnels.......81
Fusion........14
Gas-lamp
21,  11 
ALPHABETICAL  INDEX.
431
                                      PAGB
Geic acid, detection of, in soils .    .    .  342
Georgina paper......79
Glucina, deportment towards reagents   .  114
        detection of.....385
Gold, properties of.....152
      detection of, in alloys    .    .    .  259
      terchloride of (as reagent)    .    .   78
      teroxide, deportment with reagents  152
               detection  of, in  simple
                             compounds  262
                           in  complex
                             compounds  288
Halogens (as reagents)    .    .    .    .36
Humic acid, detection of, in soils    .    .  842
Hydriodic acid, deportment with reagents  211
Hydrobromic  acid,  deportment with re-
    agents  .......209
Hydrochloric acid (as reagent) .    .    .40
                 deportment  with  re-
                      agents .     .    .207
Hydrocyanic  acid, deportment  with re-
                      agents .     .    .  214
                        in organic mat-
                           ters    .    .  858
Hydroferricyanic acid,  deportment with
    reagents......216
Hydroferrocyanic  acid, deportment with
    reagents......216
Hydrofluoric acid, properties and deport-
    ment with reagents    ....  198
Hydrofluosilicic acid (as reagent)    .    .   48
                   deportment with re-
                     agents  .    .    .189
Hydrogen acids (as reagents)  .    .    .40
Hydrosulphuric acid (as reagent)    .    .   44
                   deportment with re-
                       agents     .    .  217
                   detection of, in sim-
                       ple compounds  .  266
                     in  complex   com-
                       pounds     .    .  805
                     in mineral waters .  828
Hypochlorous  acid,  deportment with re-
    agents  .......221
Hyponiobic  acid,  deportment with re-
                     agents  .     .    .  119
                  detection of     . 884,  885
Hypophosphorous  acid, deportment with
    reagents......221
Hyposulphurous acid, deportment with re-
                       agents     .    .  187
                     detection of  .    .  881
                     L

Ignition.......18
Indigo solution (as reagent)     .        .  80
Inorganic bodies, detection of, in presence
    of organic bodies.....848
Iodic acid, deportment with reagents    . 187
          detection of    ...      888
Iodine, detection of, in simple compounds
      *                        268, 274, 276
                    in   complex  com-
                     pounds .    .  804, 814
                   In mineral waters   . 832
       properties of.....211
Iron (as reagent).....°J
     properties of.....t.%*
     protoxide, deportment with reagents . 128
              detection of, in simple com-
                         pounds  .    . 268
                     in  complex com-
                         pounds  .    . 296
                     in well and mineral
                         waters 824,829, 880
     sulphate of protoxide (as reagent)   .  78
     sesquichloride (as reagent)...  78
Iron,  sesquioxide, deportment  with  re-
                     agents   .    .    . 130
                  detection of, in simple
                          compounds  . 260
                       in  complex com-
                        pounds  .    . 296
                       in  soils    . 840, 341
                       in well and mine-
                        ral waters 824, 836
Iridium, oxide, deportment with reagents  . 179
              detection  .... 8S8
Lactic acid, deportment with reagents
Lamps, use of.....
Lanthanum,  oxide, deportment with re
238
 20
117
                   detection of
Lead, properties  of, and  deportment of
           oxide with reagents    .     . 189
      oxide, detection of, in soluble simple
                       compounds   260, 262
                     in insoluble simple
                       compounds      . 276
                     in soluble complex
                       compounds   279, 289
                     in insoluble complex
                       compounds      . 811
                     In organic matters  856
                     in sinter deposits  . 885
      acetate (as reagent)     .    .     .75
      binoxide (as reagent)    .    .     .58
Lime, deportment with reagents    .     . 104
      detection of, in soluble simple  com-
                    pounds   .    .     . 265
                  in   soluble   complex
                    compounds 296, 299, 800
                  in   insoluble  simple
                    compounds   .     . 277
                  in  insoluble  complex
                    compounds   .     . 813
                  in soils.    .    .     .840
                  in  well and  mineral
                    waters   .    .  824, 881
      sulphate (as reagent)
      water (as reagent)  .
Lithia, deportment with reagents
       detection of, in mineral waters
Litmus-paper.....
384
 79
M.
Magnesia, deportment with reagents .     . 105
          detection  of, in  simple com-
                           pounds     . 265
                       in complex com-
                           pounds  297, 301
                       in soils    .     . 840
                       in  well and mi-
                           neral  waters
                                   825, 826
          sulphate of (as reagent)  .     .  71
Malic acid, detection of,
                 in  simple compounds 270
                 in complex compounds 806
          deportment with  reagents     . 229
Manganese, properties of  .         .     . 122
          protoxide, detection  of,   in
             simple compounds    .  263, 264
          in complex  compounds  293,
                                   294, 298
          in soils.....841
          in mineral waters  .    .     . 832
          protoxide,  deportment  with
             reagents    .... 123
Marsh's apparatus.....163
Mercury, detection of, in articles of food,
             Ac......856
         properties of   .     .    .     .188
         chloride (as reagent)  .         .  76 
432
ALPHABETICAL INDEX.
Mercury, oxide, deportment with reagents 142
               detection  of,  in soluble
                          simple   com-
                            pounds    . 262
         oxide,  detection of, in soluble
           complex compounds     .    . 290
         suboxide, deportment  with re-
           agents    .....138
                  detection of, in simple
                             compounds 260
                          in  complex
                             compounds 279
                  nitrate of (as reagent)   75
Metallic poisons, detection of, in articles
    of food, Ac.......346
Metals (as reagents).....50
Mineral waters, analysis of                327
Molybdenum, deportment of oxide of, with
                reagents ....  179
             detection of .    .     .    .883
Morphia, deportment with reagents  .    .  393
         detection  of,  in  simple  com-
                        pounds   .    .  407
                      in complex com-
                         pounds  .   . 409
                     N.

Narcotina, deportment with reagents    . 395
           detection  of,  in simple  com-
                          pounds  407, 408
                        in complex com-
                          pounds .    . 410
Nickel, properties of.....124
       protoxide,  deportment with  re-
                      agents  .     .    .  124
                  detection of, in simple
                             compounds 263
                         in    complex
                            compounds,
                                   296, 298
Nicotina, deportment with reagents  .    . 890
Nitric acid (as reagent)   .    .     .    .88
           deportment with reagents    . 222
           detection   of,  in  simple  com-
                           pounds     . 268
                        in complex com-
                           pounds     . 296
                        in soils    .    . 889
                        in well and mi-
                           neral  waters
                                   325, 332
Nitrohydrochloric acid (as reagent)   .    .  43
Nitrous acid, deportment with reagents   .  220
            detection of  .    .     .    .383
                       in fresh waters  .  826
                       in mineral waters  834
0.
Osmium, oxides, deportment with reagents 150
               detection of             884
Oxalic acid, properties of  .    .    .    . 196
           deportment with reagents    . 196
           detection of,  in  simple com-
                     pounds   267, 270, 275
                  in   complex   com-
                     pounds  .    . 298, 805
Oxidizing flame......17
Oxygen acids (as reagents).    .    .    .87
        bases (as reagents)     .    .    .51
Palladium, properties of  ...    . 149
          protoxide of, deportment with
            reagents    .... 149
          detection of              388, 884
          sodio-chloride as reagent .    .  78
 Paratartaric  acid,  deportment  with re-
     agents  .......231
 Percholoric acid, deportment with reagents 225
 Phosphate of soda and ammonia  (as re-
     agent)  .......87
 Phosphates of alkaline earths, detection of,
     in simple compounds   .... 878
 Phosphates in complex compounds   .    . 812
 Phosphoric acid, deportment with reagents 190
                monobasic    .     .    .194
                bibasic    .... 194
                detection  of,  in   simple
                              compounds
                               267, 278, 275
                           in    complex
                              compounds
                                    298, 805
                           in soils   340, 341
                           in    mineral
                              waters 826, 330
                           in    silicates
                                    318,  322
 Phosphorous  acid, deportment with re-
    agents  .......202
 Phosphorus, properties of .    .    .    .  190
            detection of, in food    .    . 361
 Pincers.......81
 Platinum, detection of, in alloys     .    . 859
         properties of    ...     154
         bichloride of (as reagent)  .    .  77
         binoxide  of,  deportment  with
                         reagents .    . 154
                 detection of, in simple
                             compounds 262
                           in  complex
                             compounds 288
         crucibles and their use    .   14, 30
         foil and wire    .    .    .19, 80
Porcelain dishes and crucibles   .    .    .31
Potassa (as reagent).....51
       antimonate (as reagent) .    .    .65
       bichromate (as reagent) .    .    .65
       nitrite (as reagent) ....  64
       sulphate (as reagent)   .    .    .61
       deportment with reagents    .    .  91
       detection  of,   in   simple   com-
                        pounds   .    . 266
                      in complex  com-
                         pounds   .    . 302
                      in well  and  mine-
                        ral waters    .  826
                      in silicates  .    .  321
in soils
Potassium, ferricyanide of (as reagent)
          ferrocyanide of (as reagent)
          sulphocyanide of (as reagent)
Precipitation.....
Preliminary examination of solid bodies
                       of fluids
Propionic acid,  deportment   with  r<
340,  841
 69
 68
 69
  7
246
254

238
                    0.

Quina, detection of, in simple  compounds
                                   407, 408
Quina, detection  of,  in  complex   com-
         pounds    .....410
       deportment with reagents   .    . 896
                    E.

Racemic acid, deportment with reagents  . 281
Reactions.......89
Reagents.......81
Reducing flame......17
Retorts.......30
Rhodium, sesquioxide, deportment with re-
                        agents     .    . 150
                     detection of   .    . 888 
ALPHABETICAL  INDEX.
438
                                       PAGE
Rubidium, oxide, deportment with reagents  98
                detection  in   mineral
                  waters .... 334
Ruthenium, oxides of, deportment with re-
                       agents .    .     . 151
                     detection of    883, 384
                      S.

 Salicine, deportment with reagents   .     . 406
         detection of, in simple compounds 407
                     in   complex  com-
                       pounds .    .    . 409
 Salts (as reagents).....60
 Selenium, properties of         .    .    .189
           oxides  of, deportment with re-
             agents   .....189
           detection of     .... 383
 Silicates, analysis of.....316
 Bilicic acid, properties and deportment with
              reagents    .... 204
            detection of, by the blowpipe  . 253
                    in soluble compounds
                                264, 267, 272
                    in  insoluble   simple
                       compounds   .    . 278
                    in  soluble complex
                       compounds
                            279, 280, 296, 298
                    in insoluble complex
                       compounds   .    . 313
                    in soils    .    . 340, 341
                    In mineral waters    . 329
 Silver, detection of, in articles of food, Ac. 856
       properties of.....137
       oxide of, deportment with reagents 187
                detection   of,  in   simple
                              compounds
                                    259, 276
                        In complex com-
                          pounds   .     . 279
                nitrate (as reagent) .     .  74
 Sinter deposits, analysis of .    .    .     . 334
 Soda (as reagent).....51
      deportment with reagents  .    .     .93
      detection of, in simple compounds   . 266
                  in complex compounds . 302
                  in  well  and  mineral
                    waters     .    .     .826
                  in silicates    .    .     . 821
                  in soils  .     .    .840, 841
      acetate of (as reagent)     .    .     .62
      biborate of (as reagent)        .     .86
      carbonate of (as reagent)   .    .   62, 84
      nitrate of (as reagent)    .    .     .84
      phosphate of (as reagent) .    .     .61
      sulphite of (as reagent)    .    .     .64
      and  ammonia, phosphate  of  (as re-
       agent)    ......87
      and potassa, carbonate of (as reagent)  81
 Bodio-protochloride  of palladium  (as re-
    agent)  .......78
 Soils, analysis of......837
 Solubility, table indicating  degrees of     . 422
 Solution.......8
        of bodies for analysis   .    .     . 255
 Spectroscope......28
 Spectrum analysis.....27
 Spirit-lamps.......20
 Strontia, deportment with reagents   .     . 10'2
         detection  of,  in  soluble  simple
                         compounds    . 265
                       in  insoluble simple
                         compounds    . 277
                       In  soluble complex
                         compounds 296, 801
                       In  insoluble com-
                         plex compounds 813
                       in  mineral waters  831
                       in  sinter deposits . 885
Strychnia, deportment with reagents .    . 400
Strychnia, detection  of,  in simple  com-
                          pounds . 407, 408
                        in complex com-
_ ...  tI                  pounds .     . 410
Sublimation.......\%
Succinic acid, detection of, in simple com-
                           pounds     . 271
                         in     complex
                           compounds  . 307
             deportment with reagents   . 232
Sulphate of lime (as reagent)    .    .     .71
Sulphide of ammonium (as reagent)  .     .  58
         of carbon (as reagent)  .    .     .  ;',6
           iron......44
           sodium (as reagent).    .     .60
Sulphides, metallic, detection of, in simple
                     compounds  .     . 266
                   detection of, in  com-
                     plex compounds   . 802
                   detection  of, in  sili-
                     cates    .    .     .318
Sulphocyanide of potassium (as reagent)   .  69
Sulphur acids (as reagents)     .    .    .44
        bases (as reagents).     .    .     .53
        detection of, in insoluble  complex
          compounds......310
        properties of.....217
Sulphuretted hydrogen (as reagent)  .     .  44
Sulphuric acid (as reagent).     .    .     .37
              deportment with reagents  . 183
              detection of, in soluble sim-
                            ple   com-
                            pounds 267, 274
                      in  soluble  com-
                        plex compounds 302
                      in insoluble  sim-
                        ple compounds
                                   ^, 277
                      In insoluble com-
                        plex compounds 812
                      in soils .    .    .840
              detection of, in well and mi-
                        neral waters   . 826
                      in silicates .    . 822
Sulphurous  acid,  deportment  with  re-
    agents  ...         ... 186
Tantalic acid, deportment with reagents  .118
             detection of  .    .    .381, 885
Tartaric acid (ns reagent)  .    .    .    .40
            deportment with reagents  . 226
            detection of, in simple  com-
                           pounds     . 270
                         in complex com-
                           pounds     . 806
Tellurium,  oxides,  deportment  with re-
                      agents  .    .    . 181
                   detection of    .    .883
Terbium,  oxide,  deportment  with  re-
                 agents  .... 116
               detection of               886
Test-paper.......79
Test-tubes.......30
Thallium  oxides,   deportment with  re-
                      agents  .    .    .135
                note on detection of    . 385
Thoria, deportment with reagents    .    .115
       detection of.....886
Tin, properties of    .    .    .     .    .  155
    binoxide, deportment with reagents  .  157
             detection of, in soluble sim-
                         ple compounds 261
                      in   soluble  com-
                        plex compounds 288
                      in  insoluble com-
                        pounds    .    .  818
                      in articles of food,
                        Ac.  .    .    . 856
    protochloride (as  reagent) .     .    .77 
434
ALPHABETICAL  INDEX.
Tin, protoxide, deportment with reagents . 155
              detection  of,  in  simple
                        compounds    . 261
                      in  complex  com-
                        pounds   .    . 280
                      in articles of food,
                        Ac.  .    .    . 356
Titanic acid, deportment with reagents   . 118
            detection of .    . 818, 885, 836
Tungsten,  oxides,  deportment with  re-
                     agents  .    .    . 180
                   detection of   . 881, 886
Turmeric paper......80
                    U.

TJlmlc acid, detection of, In soils     .     . 842
Uranium, oxides of, deportment with re-
                      agents  .   .     . 184
                   detection of   .     . 886
                    V.

Vanadium,  oxides,  deportment with  re-
                      agents  .    .    . 184
                   detection of   . 883, 886
Veratria, deportment with reagents  .    . 404
        detection of, in simple compounds
                                  407, 408
                                      FASH
Veratria, detection  of, In complex com-
    pounds .......410


                    W.

Washing.......10
        bottles.....10, 81
Water (as reagent).....84
      bath.......H
Waters, analysis of natural     .    .    . 828
Well-water, analysis of    ...    . 828
Wolfram, see Tungsten.
                    Y.

Yttria, deportment with reagents    .    .116
      detection of.....386


                    Z.

Zinc (as reagent)......56
    properties of.....121
    oxide of, deportment with reagents  . 121
    detection  of, in  simple compounds
                              264, 265, 272
                 in complex compounds 293
                 in sinter deposits     . 835
Zirconia, deportment with reagents   .    . 115
        detection of .    .    .     . 885, 386
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>

 Pi
Or
Fresenius, Remigius, Manual of qualitative chemical analysis, HMD Bluncat 2001-168
Cleaning: The outer cover and top edge were surface cleaned with a soft brush.  Extreme grime
on the covers was cleaned using grated vinyl eraser (Staedtler). The top edge and foredge of the
text block were cleaned using grated eraser crumbs.  Mold on the back flyleaf and paste down
was reduced using a soft brush and grated eraser crumbs and was then deactivated using ethyl
alcohol (Fischer Scientific).
Treatment carried out by Rachel-Ray Cleveland, HMD Paper Conservator, 11/2001.