:nitrmitg ef 
 
 No 
 
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 Received. 
 
PRACTICAL CHEMISTRY. 
 
LONDON: PRINTED BY 
 
 SPOTTISWOODE AND CO., NEW-STREET SQUARE 
 AND tAHLIAMENT STREET 
 
A COURSE 
 
 OF 
 
 PEACTICAL CHEMISTRY 
 
 ARRANGED FOR 
 
 THE USE OF MEDICAL STUDENTS. 
 
 BY 
 
 WILLIAM ODLING, M.B., F.E.S. 
 
 FELLOW OP THE ROYAL COLLEGE OF PHYSICIANS : 
 LECTURER ON CHEMISTRY AT ST. BARTHOLOMEW'S HOSPITAL. 
 
 FOUETH EDITION. 
 
 LONGMANS, GKEKN, AND CO. 
 
PREFACE 
 
 TO 
 
 THE FOUKTH EDITION. 
 
 IN this Fourth Edition of a Course of Practical Chemistry, 
 arranged for the use of medical students, several minor 
 improvements, suggested by further experience in teaching, 
 have been effected. 
 
 The analytical portion of the work, in so far as regards 
 the description of the methods employed, has been re- 
 arranged. 
 
 The new system of atomic weights and formulae has 
 been employed throughout ; but it has not been thought 
 necessary to introduce any general changes in the nomen- 
 clature. 
 
 W. 0. 
 
 ST. -BARTHOLOMEW'S HOSPITAL: 
 May, 1869. 
 
PREFACE 
 
 THE SECOND EDITION, 
 
 IN PREPARING a Second Edition of this Course of Practical 
 Chemistry for the press, the first having been for upwards 
 of three years out of print, many additions and alterations 
 have been made, which it is believed will much increase 
 its usefulness as a laboratory guide. 
 
 The first chapter, treating of chemical reactions and 
 manipulation, is quite new; the second, relating to general 
 analysis, has been rewritten ; and the third and fourth 
 chapters, treating respectively of toxicological and animal 
 chemistry, have been carefully revised. In the second 
 chapter more particularly, full explanations have been 
 given of the tables for the examination of the several 
 groups of bases and acids ; so that the paragraphs relating 
 to the individual members of the groups need scarcely be 
 considered by the learner save for purposes of reference. 
 
 To maintain its adaptability to the wants of the medical 
 student, the old scale of atomic weights has been ex- 
 clusively employed throughout the body of the work. 
 
Vlll PREFACE. 
 
 lu a short Appendix, however, some tables have been set 
 up, in which the new atomic weights are used, with a view 
 to illustrate the superior simplicity and mutual association 
 of the modern unitary over the older dualistic formulae. 
 This Edition of the work is, moreover, illustrated by 
 Mr. Branston with seventy woodcuts of microscopical 
 preparations and chemical apparatus, all of them made 
 expressly from drawings of the actual objects. 
 
 W. 0. 
 
 ST. BARTHOLOMEW'S HOSPITAL : 
 June, 1865. 
 
CONTENTS. 
 
 CHAPTER I. 
 INTRODUCTORY. 
 
 I. CHEMICAL REACTIONS. 
 
 PAGE 
 
 1. Equivalents I 
 
 2. Atoms .... a 
 
 3. Table of atomic weights . 3 
 
 4. Symbolic notation 4 
 
 5. Acids and salts . . 6 
 
 6. Basicity of acids . . 7 
 
 7. Multequi valent salts . S 
 
 8. Ammonium salts . . 9 
 
 9. Synoptic formulae . . 10 
 
 10. Anhydrides . . .11 
 
 11. Double decomposition . 12 
 
 II. CHEMICAL MANIPULATION. 
 
 PAGE 
 
 12. Sources of heat . . 13 
 
 13. Use of the blowpipe . 14 
 
 14. Glass-cutting and bending 18 
 
 15. Glass-blowing and sealing 19 
 
 1 6. Caoutchouc connectors &c. 22 
 
 1 7. Construction of apparatus 24 
 
 1 8. Filtration and decantation 28 
 
 19. Supports and baths . 32 
 
 20. Heating liquids . . 35 
 
 21. Heating solids . . 39 
 
 22. Weighing and measuring 42 
 
 23. Specific gravities . . 47 
 
 CHAPTER II. 
 ANALYTICAL CHEMISTRY. 
 
 24. Course of operations . . 52 
 I. BLOWPIPE EXAMINATION. 
 
 25. General effects , -. . 53 
 
 26. Special reactions . . 54 
 
 II. SOLUTION AND PRECIPITATION. 
 
 27. Solution in water and acids 61 
 
 28. Precipitation by reagents . 62 
 
 29. Examination for basic 
 
 groups . . . .64 
 
 III. EXAMINATION FOR BASES 
 OF GROUP I. 
 
 30. Detection of first group 
 
 31. Table 
 
 65 
 68 
 
 32. Action of sulphuretted hy- 
 
 drogen . . . .69 
 
 33. Sulphides soluble in sul- 
 
 phide of ammonium . 70 
 
 34. Action of potash . .71 
 
 IV. EXAMINATION FOE BASES 
 OF GROUP II. 
 
 35. Detection of second group . 
 
 36. Table .... 
 
 37. Action of sulphide of am- 
 
 monium . 
 
 38. Action of potash 
 
 39. Action of ammonia . 
 
 40. Behaviour of potash solu- 
 
 tion 
 
 73 
 76 
 
 77 
 78 
 79 
 
 81 
 
CONTENTS. 
 
 V. EXAMINATION FOR BASES OF 
 
 PAOB 
 
 GROUP III. 
 
 71. Silver . . . .116 
 
 PAGE 
 
 72. Copper . . . .116 
 
 41 . Detection of third group . 82 
 
 73. Cadmium. . . . 117 
 
 42. Table . . . .83 
 
 
 43. Action of carbonate of am- 
 
 IX. INDIVIDUAL BASES OP 
 
 monia . . . .84 
 
 GROUP II. 
 
 44. Bases unprecipitated by 
 
 74. Nickel . . . .118 
 
 carbonate of ammonia . 86 
 
 75. Cobalt . . . .118 
 
 VI. EXAMINATION FOR ACIDS. 
 
 76. Manganese . . .119 
 77. Iron .... 120 
 
 45. General remarks . . 88 
 
 78. Zinc .... 121 
 
 46. Table of preliminary re- 
 sults . . . .89 
 
 79. Chromium . . .122 
 80. Aluminium . . .122 
 
 47. Previous indications . . 90 
 48. Action of sulphuric acid . 93 
 49. Application of liquid tests . 94 
 
 X. INDIVIDUAL BASES OF 
 GROUP III. 
 
 50. Table . . . .96 
 
 81. Barium, strontium, calcium 123 
 
 51. Action of nitrate of silver . 96 
 
 82. Barium .... 123 
 
 52. Action of nitrate of barium 98 
 
 83. Strontium . . .124 
 
 53. Action of chloride of cal- 
 
 84. Calcium . . . .124 
 
 cium . . 9^ 
 
 85. Magnesium . . . 125 
 
 54. Action of sulphate of mag- 
 
 86. Potassium . . .125 
 
 nesium .... 100 
 
 87. Ammonium . . .126 
 
 55. Action of ferric chloride . 100 
 
 88. Sodium .... 1*6 
 
 56. Order of testing for acids . 101 
 
 
 
 XI. KEACTIONS OF INDIVIDUAL 
 
 VII. SPECIAL SUBSTANCES. 
 
 ACIDS. 
 
 57. General remarks . . 102 
 58. Insoluble compounds . 102 
 
 89. Chromates . . .127 
 90. Nitrates . . . .127 
 
 59. Earthy salts . . .105 
 
 91. Chlorates . . .127 
 
 60. Oxides and sulphides . 106 
 
 92. Carbonates ... 128 
 
 61. Acids or salts of hydrogen . 107 
 62. Miscellaneous salts . . 108 
 63. Liqxiid or dissolved sub- 
 
 93. Sulphides and sulphydrates 129 
 94. Sulphites . . .130 
 95. Sulphates . . . 130 
 
 stances . . . .109 
 
 96. Chlorides . . .13 
 
 64. Alkaline solutions of heavy 
 
 97. Bromides .. . . 131 
 
 metals , , -. v .no 
 
 98. Iodides . . . .131 
 
 VIII. INDIVIDUAL BASES OF 
 
 99. Cyanides . .132 
 100. Phosphates . . .132 
 
 GROUP I. 
 
 101. Oxalates . ^ . 133 
 
 65. Tin . . . ...'.'. . in 
 
 102. Tartrates . . . 134 
 
 66. Arsenic . . .112 
 
 103. Acetates . . . 135 
 
 67. Antimony "'. *'. . 113 
 
 104. Benzoates . . .135 
 
 68. Bismuth . . . .113 
 
 105. Borates . . . .135 
 
 69. Mercury . . . ' . 1 14 
 
 1 06. Fluorides . . .136 
 
 70. Lead . .-' "" . '"?'' .115 
 
 107. Silicates . . . 137 
 
CONTENTS. 
 
 XI 
 
 CHAPTER III. 
 TOXICOLOGICAL CHEMISTRY. 
 
 108. Introductory . <>3. 
 
 I. SULPHURIC ACID. 
 
 109. Concentrated . . 
 
 1 10. Diluted . 
 
 in. In organic liquids . 
 H2. Stains on clothing . 
 
 II. NITRIC ACID. 
 
 113. Concentrated . 
 
 114. Diluted . 
 -115. Nitrates . 
 
 1 1 6. In organic mixtures 
 
 III. HYDROCHLORIC ACID. 
 
 117. Concentrated . 
 
 1 1 8. Diluted . 
 
 119. In organic mixtures 
 
 IV. OXALIC ACID. 
 
 120. Solid 
 
 121. Dissolved 
 
 122. In organic mixtures 
 
 123. Insoluble salts 
 
 V. CORROSIVE SUBLIMATE. 
 
 124. Solid 
 
 125. Dissolved 
 
 126. In organic mixtures 
 
 VI. LEAD. 
 
 127. Solid compounds 
 
 128. Dissolved 
 
 129. In organic mixtures 
 
 PAGE 
 
 V 11. UOPPER. 
 
 PAGB 
 
 
 130. Dissolved 
 
 '55 
 
 
 131. In organic mixtures 
 
 . 156 
 
 139 
 I 4 
 
 VIII. ARSENIC. 
 
 
 HI 
 
 132. Arsenious acid 
 
 157 
 
 141 
 
 133. Dissolved 
 
 159 
 
 
 134. Marsh's test . 
 
 . 161 
 
 
 135. Original process 
 
 . 162 
 
 142 
 
 136. Modified process 
 
 . 164 
 
 I 4 2 
 
 137. Reinsch's test . 
 
 . 165 
 
 H3 
 
 I 4 4 
 
 138. Impediments thereto 
 139. Other forms of arsenic 
 
 . 167 
 . 168 
 
 ^ 
 
 140. In organic mixtures 
 
 . 169 
 
 144 
 
 IX. ANTIMONY. 
 
 
 145 
 
 /- 
 
 141. Antimonial salts 
 
 . 169 
 
 140 
 
 142. Dissolved 
 
 . 170 
 
 
 143. Marsh's test . 
 
 . 171 
 
 
 144. Reinsch's test . 
 
 . 172 
 
 I 4 6 
 
 145. In organic mixtures 
 
 173 
 
 147 
 
 
 
 H7 
 
 X. PRUSSIC ACID. 
 
 
 149 
 
 146. Aqueous solution 
 
 173 
 
 S. 
 
 147. In vapour 
 
 . 174 
 
 I 49 
 
 XI. STRYCHNIA. 
 
 
 150 
 151 
 
 O 
 
 148. In pure state . 
 
 175 
 
 
 149. In organic mixtures 
 
 . 178 
 
 153 
 
 XII. MORPHIA. 
 
 
 154 
 
 150. In pure state . 
 
 . 179 
 
 *54 
 
 151. Opiate liquids . . J 
 
 . 180 
 
 CHAPTER IV. 
 ANIMAL CHEMISTRY. 
 
 I. COMPOSITION OF TISSUES. 
 
 152. Organic and mineral con- 
 
 stituents . . .183 
 
 153. Ultimate organic consti- 
 
 tuents . . . .184 
 
 1 54. Ash of animal matter 
 
 II. NORMAL URINE. 
 
 155. General properties . 
 
 156. Urea 
 
 186 
 
 188 
 189 
 
Xll 
 
 CONTENTS. 
 
 PAGE 
 
 157. Uric acid . . .100 
 
 158. Hippuric acid . . .192 
 
 159. Colouring and extractive 
 
 matter " , { 'V . 193 
 
 1 60. Mineral salts . . . 194 
 
 III. ABNORMAL URINE. 
 
 1 6 1. Albuminous . . . 195 
 
 162. Saccharine . . .196 
 
 163. Biliary . . . -199 
 
 164. Fatty . . . -199 
 
 IV. URINARY DEPOSITS. 
 
 165. Chemical . . .201 
 
 166. Organised . . i . 203 
 
 V. CLINICAL EXAMINATION OF 
 URINE. 
 
 167. General examination . 205 
 
 PAGE 
 
 168. Chemical testing . . 206 
 
 VI. URINARY CALCULI. 
 
 169. General characters . .207 
 
 1 70. Preliminary examination .210 
 
 171. Special tests . . .211 
 
 172. Systematic analysis . 213 
 
 VII. BLOOD. 
 
 173. Coagulation . . .215 
 
 174. Fibrin . . . .216 
 
 175. Corpuscles . . .217 
 
 176. Blood stains . . .219 
 
 177. Serum .... 220 
 
 VIII. MISCELLANEOUS ANIMAL 
 PRODUCTS. 
 
 178. Bile 
 
 179. Milk 
 
 1 80. Bone 
 
 . 224 
 . 226 
 . 227 
 
PRACTICAL CHEMISTRY. 
 
 CHAPTER I. 
 INTKODUCTOKY. 
 
 L CHEMICAL REACTIONS. 
 
 ( i .) CHEMISTS are acquainted with about sixty different kinds 
 of matter which have hitherto proved undecomposible, and are 
 consequently termed simple bodies, or elements. These elements 
 unite with one another in certain definite proportions to form an 
 infinite variety of compounds ; each particular chemical compound 
 being always constituted of the same elements, combined together 
 in the same proportion. Common salt, for instance, no matter 
 how obtained, or when examined, is always found to consist of 
 sodium and chlorine, united in the ratio of 23 parts by weight of 
 the former element to 35*5 parts by weight of the latter. 
 
 The relative quantity of hydrogen which can enter into 
 chemical combination being less than that of any other element, 
 its combining proportion is taken as the standard of comparison 
 or unity. It is found that I part by weight of hydrogen unites 
 with 3 5' 5 parts by weight of chlorine to form hydrochloric acid ; 
 and further that in very many chemical compounds I part of 
 hydrogen may be displaced by 35*5 parts of chlorine to produce 
 chlorine- derivatives of the respective compounds. Again, when 
 hydrochloric acid is treated with metallic sodium, every 23 parts 
 of sodium is found to expel I part of hydrogen and form common 
 salt, by uniting with the 35*5 parts of chlorine previously com- 
 bined with the i part of hydrogen. 
 
 The proportion of an element which unites with i part by , 
 weight of hydrogen, or which displaces i part by weight of 
 hydrogen, to unite with 35-5 parts of chlorine, is called its equi- 
 valent. Thus 80 is the equivalent of bromine, 23 the equivalent 
 
2 CHEMICAL KEACTIONS. 
 
 of sodium, and 39 the equivalent of potassium, because 80 parts 
 of bromine, 23 parts of sodium, and 39 parts of potassium are 
 respectively exchangeable for, or equivalent in combination to, 
 i part of hydrogen. 
 
 (2.) But it is found in many cases that some multiple of the 
 proportion of an element which unites with or displaces i part 
 by weight of hydrogen, constitutes the smallest proportion of that 
 element which actually enters into chemical combination. Thus 
 although 25 parts of arsenic unite with i part of hydrogen to 
 form arsenetted hydrogen, and with 35*5 parts of chlorine to form 
 chloride of arsenic, yet it is allowed on all hands that the mole- 
 cule* of arsenetted hydrogen contains three separable equivalents 
 of hydrogen united with 75 parts of arsenic; and that the mole- 
 cule of chloride of arsenic contains three separable equivalents 
 of chlorine united with 75 parts of arsenic; and, in fact, that 75 
 parts of arsenic constitute the least indivisible proportion of 
 arsenic which ever enters into a combination. The least indivi- 
 sible proportion of an element which is found to enter into 
 chemical combination is termed its atom, and the number ex- 
 pressing that proportion is called its atomic weight. Hence the 
 atomic weight of an element sometimes coincides with its equiva- 
 lent weight, as in the case of sodium, and is sometimes a multiple 
 of its equivalent weight, as in the case of arsenic. 
 
 * The determination of the molecule of a compound body is based upon 
 very many considerations, physical as well as chemical, which cannot be 
 fully entered into here. The most important of these considerations relate 
 to specific heat, atomic volume, direct combination, analogy, mode of deriva- 
 tion, and, above all, to metamorphoses by substitution. Thus the mole- 
 cules of marsh gas, ammonia, water, and hydrochloric acid, might each be 
 represented with one equivalent of hydrogen. But the molecule of marsh 
 gas is represented with four equivalents of hydrogen, because in it | or f or 
 | or | of the hydrogen can be displaced by substitution at four successive 
 stages. The molecule of ammonia is represented with three equivalents of 
 hydrogen, because in it | or | or f of the hydrogen may be displaced at 
 three successive stages. The molecule of water is represented with two 
 equivalents of hydrogen, because in it f or f of the hydrogen can be dis- 
 placed at two successive stages ; while the molecule of hydrochloric acid is 
 represented with one equivalent of hydrogen, because in it the hydrogen 
 must be displaced at once or not at all. 
 
ATOMIC WEIGHTS. 3 
 
 The determination of equivalents is a purely experimental 
 question, which, in the majority of instances, has been answered 
 with almost absolute exactitude; but the determination of atomic 
 weights is a question of judgment, to which in many cases very 
 different answers were until lately accorded. Chemists are now 
 agreed, however, as to the atomic weights of all the most im- 
 portant elements, and their agreement extends equally to atomic 
 weights which are multiples of, as to those which are identical 
 with, the equivalents of the respective elements. It is only with 
 regard to a few of the less known elements that any great 
 difference of opinion now exists as to the correlations of their 
 respective equivalents and atomic weights. 
 
 (3.) The following tables exhibit lists of the most important 
 elements, with their accepted atomic weights, their symbols or 
 abbreviated names, and the names and symbols of their principal 
 compounds with hydrogen or chlorine. All the hydrides are 
 volatile, and when in the gaseous state occupy the same volume. 
 
 Element 
 
 Hydride 
 
 Atomic 
 weight 
 
 Symbol 
 
 Name 
 
 Symbol 
 
 Name 
 
 I 
 
 H 
 
 Hydrogen 
 
 H, 
 
 
 19 
 
 F 
 
 Fluorine 
 
 HF 
 
 Hydrofluoric acid 
 
 35*5 
 
 Cl 
 
 Chlorine 
 
 HC1 
 
 Hydrochloric acid 
 
 80 
 
 Br 
 
 Bromine 
 
 HBr 
 
 Hydrobromic acid 
 
 127 
 
 I 
 
 Iodine 
 
 HI 
 
 Hydriodic acid 
 
 16 
 
 
 
 Oxygen 
 
 H a O 
 
 Water 
 
 3* 
 
 S 
 
 Sulphur 
 
 H,S 
 
 Sulphuretted hydrogen 
 
 H 
 
 N 
 
 Nitrogen 
 
 H 3 N 
 
 Ammonia 
 
 3 1 
 
 P 
 
 Phosphorus 
 
 H 3 P 
 
 Phosphoretted hydrogen 
 
 ii 
 
 B 
 
 Boron 
 
 H 3 B 
 
 Hydride of boron ? 
 
 12 
 
 C 
 
 Carbon 
 
 H 4 C 
 
 Marsh-gas 
 
 28 
 
 Si 
 
 Silicon 
 
 H 4 Si 
 
 Silicated hydrogen 
 
CHEMICAL REACTIONS. 
 
 Perissad Metal, &c. 
 
 Artiad Metal, &c. 
 
 Atomic 
 weight 
 
 Name 
 
 Chloride 
 
 Atomic 
 weight 
 
 Name 
 
 Chloride 
 
 18 
 
 Ammonium 
 
 NH 4 C1 
 
 40 
 
 Calcium 
 
 CaCl 2 
 
 i 
 
 Hydrogen 
 
 HC1 
 
 87-5 
 
 Strontium 
 
 SrCl 2 
 
 7 
 
 Lithium 
 
 Li Cl 
 
 *37 
 
 Barium 
 
 Bad, 
 
 23 
 
 Sodium 
 
 NaCl 
 
 24 
 
 Magnesium 
 
 MgCl 2 
 
 39 
 
 Potassium 
 
 KC1 
 
 65 
 
 Zinc 
 
 Zn C1 3 
 
 108 
 
 Silver 
 
 AgCJ 
 
 112 
 
 Cadmium 
 
 CdCl 2 
 
 200 
 
 Mercury 
 
 HgCl* 
 
 200 
 
 Mercury 
 
 HgCl 2 
 
 63-5 
 
 Copper 
 
 CuCl* 
 
 63-5 
 
 Copper 
 
 Cu C1 2 
 
 27-5 
 
 Aluminum 
 
 Al C1 3 * 
 
 59 
 
 Nickel 
 
 NiCl 2 
 
 5^5 
 
 Chromium 
 
 Cr Cl,* 
 
 59 
 
 Cobalt 
 
 CoCl 2 
 
 56 
 
 Iron 
 
 Fe C1 3 * 
 
 56 
 
 Iron 
 
 FeCl 3 
 
 75 
 
 Arsenic 
 
 As CL 
 
 55 
 
 Manganese 
 
 MnCl a 
 
 122 
 
 Antimony 
 
 SbCl 3 
 
 118 
 
 Tin 
 
 SnCl 2 &SnCl 4 
 
 210 
 
 Bismuth 
 
 BiCl 3 
 
 207 
 
 Lead 
 
 PbCl 2 
 
 196 
 
 Gold 
 
 ( Au CL 
 { AuCl 
 
 197 
 
 Platinum 
 
 Pt Cl 2 &PtCl 4 
 
 It is observable that the metals mercury, copper, iron, tin, 
 gold, and platinum, form two distinct chlorides, and, as will be 
 afterwards seen, two distinct sets of oxides and salts, correspond- 
 ing respectively thereto. Several of the other metals also form 
 two chlorides and two sets of salts, but only the chlorides shown 
 in the table, and their corresponding salts, are familiarly known. 
 Cuprous, aurous, and platinous salts, moreover, are for the most 
 part very unstable, and rarely met with save when specially pre- 
 pared. 
 
 (4.) Each symbol, as exemplified in the above tables, represents 
 one combining proportion, or atom, of the element. Thus N 
 stands not for nitrogen in general, but for 14. parts by weight of 
 
 * It is doubtful whether the molecules and consequent formulae of some 
 or all of the chlorides corresponding to the formulae marked with asterisks 
 should not be doubled. The words ' perissad ' and ' artiad ' are applied to 
 both metals and non-metals, accordingly as they combine with an odd or 
 even number of atoms of chlorine or hydrogen. 
 
SYMBOLIC NOTATION. 5 
 
 nitrogen as compared with I part by weight of hydrogen. Che- 
 mical combination is represented by the apposition of symbols ; 
 thus KC1 signifies a compound of 39 parts of potassium and 35-5 
 parts of chlorine united to form 74*5 parts of chloride of potas- 
 sium. A small figure placed to the right of a symbol indicates 
 a multiple quantity of that particular element. Thus HgCl 2 , or 
 corrosive sublimate, signifies a compound of one atom of mercury 
 with two atoms of chlorine. A larger figure placed to the left of 
 an allocation of symbols multiplies the entire compound. Thus 
 3HN0 3 represents three proportions of nitric acid, a compound 
 body consisting of one atom of hydrogen, one atom of nitrogen, 
 and three atoms of oxygen. The single formula of a compound 
 body represents the atom, or smallest indivisible proportion, of 
 that particular compound, and its atomic weight is the sum of 
 the atomic weights of its constituents. Thus the atomic weight 
 of nitric acid HN0 3 =i + 14+ 16 x 3 = 63. 
 
 In writing the formula of compound bodies, it is sometimes 
 found advisable to break them up in different ways by means 
 of periods, brackets, parentheses, &c. Thus for sulphuric acid 
 we sometimes write H 2 O.S0 3 instead of H 2 S0 4 ; for nitrate of am- 
 monium, ]^II 4 N0 3 instead of N 2 H 4 3 ; and for phosphate of calcium 
 Ca 3 (P0 4 )-5 instead of Ca 3 P 3 8 . Sometimes these breaks are purely 
 arbitrary or conventional, and should then be dispensed with as 
 much as possible. At other times they indicate a real molecular 
 isolation of one portion of a compound from the remainder, when 
 their use is perfectly legitimate. 
 
 The symbol for the atom of an element is sometimes marked 
 with one or more dashes, to indicate its equivalency or inter- 
 changeable value for hydrogen. For instance, Ag is sometimes 
 marked with a single dash to show that the atom of silver may be 
 substituted for an atom of hydrogen, so as to combine with an 
 atom of chlorine, thus Ag'Cl. Again, Pb- is marked with two 
 dashes, and Bi with three dashes to indicate that the atoms of lead 
 and bismuth may be respectively substituted for two and three 
 atoms of hydrogen, so as to combine with two and three atoms of 
 chlorine, thus Pb"Cl a and Bi'"Cl 3 . 
 
6 CHEMICAL REACTIONS. 
 
 The signs -f, -, and = are used almost in their ordinary 
 algebraical sense. The sign + signifies addition to, or rather 
 mixture with ; the sign subtraction from ; and the sign = 
 equivalency with, or rather conversion into. Thus the equation 
 aHCl + CuO = CuCl a + H a O, implies that an gftom of hydrochloric 
 acid, mixed with an a^bm of oxide of copper, yields an atom 
 of chloride of copper together with an mbm of water. Or the 
 equation may of course be written zHCl + CuO - H 2 = CuCl 2 . In 
 modern chemistry the sign -f is no longer used to express com- 
 bination. 
 
 (5.) Those hydrogenised compounds which can readily ex- 
 change some or all of their hydrogen for its equivalent of metal 
 constitute the acids. From habit one particular reaction is 
 adopted as the conventional criterion of acidity, namely that 
 effected by the hydrates of potassium and sodium. An acid is 
 simply a hydrogenised body which, when treated with hydrate of 
 potassium, can exchange hydrogen for potassium with simultaneous 
 formation of water, thus : 
 
 H 4 C a O a + KHO = KH 3 C a O a + H a O. 
 
 The solutions of such bodies are generally found to have the 
 power of reddening blue litmus paper, and of effervescing with 
 alkaline carbonates, so that the possession of these properties 
 may be looked upon as more or less characteristic of an acid. 
 Oxygenised acids, such as the nitric HN0 3 , and acetic H 4 Cj,O a , are 
 also called ternary, while non-oxygenised acids, such as the 
 hydrochloric HC1, and sulphydric, H a S, are called binary. These 
 binary acids were formerly known as hydracids. In most ternary 
 acids the number of oxygen atoms is two, or three, or four, as 
 shown below : 
 
 HC10 a Chlorous. 
 H N O a Nitrous. 
 H B O a Boracic. 
 H 4 C 2 O a Acetic 
 H 3 PO a Hypophos. 
 
 HC10 3 Chloric. 
 
 H N 3 Nitric. 
 
 H 2 S 3 Sulphurous. 
 
 H a C 3 Carbonic. 
 
 H 3 P 3 Phosphorous. 
 
 HC10 4 Perchloric. 
 H I 4 Periodic. 
 H a S 4 Sulphuric. 
 H 2 C Z 4 Oxalic. 
 H 3 P 4 Phosphoric. 
 
 It is not uncommon to have one or more of the hydrogen atoms 
 
ACIDS AND SALTS. 7 
 
 of a ternary acid which are not replaceable by metal exchanged 
 for chlorine, and some or all of its oxygen atoms exchanged for 
 sulphur. Thus we have acetic acid H 4 C a O a , chloracetic acid 
 HCl 3 C a O a , and sulphacetic acid H 4 C 2 S a ; with their corresponding 
 salts, NaH 3 C a O a acetate, NaCl 3 C a O a chloracetate, and NaH 3 C a S a sulph- 
 acetate of sodium, for instance. 
 
 (6.) Acids in which only one atom of hydrogen can be replaced 
 by metal are called monobasic. The principal monobasic acids 
 with which the student will have to deal are the following : 
 
 HC1 
 
 Hydrochloric. 
 
 NaCI 
 
 Chloride of sodium. 
 
 HC10 3 
 
 Chloric. 
 
 Na Cl 3 
 
 Chlorate of sodium. 
 
 HBr 
 
 Hydrobromic. 
 
 NaBr 
 
 Bromide of sodium. 
 
 HI 
 
 Hydro-iodic. 
 
 Nal 
 
 Iodide of sodium. 
 
 HN 3 
 
 Nitric. 
 
 NaN0 3 
 
 Nitrate of sodium. 
 
 HBO, 
 
 Boracic.* 
 
 NaBO a 
 
 Borate of sodium. 
 
 H 4 C 2 O z 
 
 Acetic. 
 
 NaH 3 C a O a 
 
 Acetate of sodium. 
 
 Acids in which two atoms of hydrogen can be replaced by 
 metal are called dibasic. The most important of them are com- 
 prised in the following table : 
 
 H,0 
 
 Hydric acid . 
 
 ( 
 
 KHO 
 K a O 
 
 Potash. 
 Oxide of potassium. 
 
 H a S 
 
 Sulphydric acid 
 
 ( 
 
 NaHS 
 
 Na a S 
 
 Sulphydrate of sodium. 
 Sulphide of sodium. 
 
 H a S0 3 
 
 Sulphurous acid 
 
 I 
 
 NaHS0 3 
 
 Na a S0 3 
 
 Acid sulphite of sodium. 
 Sulphite of sodium. 
 
 H a S0 4 
 
 Sulphuric acid 
 
 { 
 
 KHS0 4 
 
 K a S0 4 
 
 Acid sulphate of K. 
 Sulphate of potassium. 
 
 H a Si0 3 
 
 Silicic acid 
 
 . 
 
 K a Si0 3 
 
 Silicate of potassium. 
 
 H a C0 3 
 
 Carbonic acid 
 
 1 
 
 KHC0 3 
 K a C0 3 
 
 Acid carbonate of K. 
 Carbonate of potassium. 
 
 H a C a 4 
 
 Oxalic acid . - 
 
 -( 
 
 ' KHC a 4 
 K a C a 4 
 
 Acid oxalate of K. 
 Oxalate of potassium. 
 
 H 6 C 4 6 
 
 Tartaric acid . 
 
 f KH 5 C 4 6 
 (KNaH 4 C 4 6 
 
 Cream of tartar. 
 Eochelle salt. 
 
 * Another variety of boracic acid has the formula H 3 B0 3> and is 
 tribasic. 
 
8 CHEMICAL REACTIONS. 
 
 Until lately many of these acids were considered as monobasic 
 and represented by the halves of the formulae here given ; but 
 the evidence of their dibasicity is at present indisputable. This 
 class of bodies includes sulphydric acid, or sulphuretted hydrogen, 
 the sulphur analogue of water, which itself often plays the part 
 of an acid, and is included in the foregoing list. 
 
 Acids in which three atoms of hydrogen may be replaced by 
 metal are called tribasic, the most important of which are 
 
 I KH Z P0 4 Phosphate of potassium. 
 
 H 3 P0 4 Phosphoric acid . j Na a HP0 4 Phosphate of sodium. 
 
 I Ag 3 P0 4 Phosphate of silver. 
 
 H 3 As0 4 Arsenic acid . . Ag 3 As0 4 Arseniate of silver. 
 H 8 C 6 7 Citric acid . . Ag 3 H 5 C 6 7 Citrate of silver. 
 
 Monometallic and dimetallic arseniates and citrates are also 
 familiarly known. 
 
 The monometallic salts of dibasic and tribasic acids closely re- 
 semble the acids themselves in their action on blue litmus paper 
 and on alkaline hydrates and carbonates. They constitute, indeed, 
 a mere variety of the class of acids. 
 
 In polyhydrogenised acids, it does not follow that the units of 
 basicity are equal to the units of hydrogen, acetic acid H 4 C 2 O a , 
 lartaric acid H 6 C 4 6 , and citric acid H 8 C 6 7 , for example, being 
 but monobasic, dibasic, and tribasic respectively, or capable 
 of exchanging respectively but one, two, and three atoms of 
 hydrogen for metal. 
 
 (7.) In the illustrative salts above adduced, each atom of 
 hydrogen in the acid has been displaced by one atom of uniqui- 
 valent metal. Thus we had nitrate of potassium KN0 3 , derived 
 from nitric acid HN0 3 ; oxalate of sodium Na a C 2 4 , derived from 
 oxalic acid H a C 2 4 ; phosphate of silver Ag 3 P0 4 , derived from 
 phosphoric acid H 3 P0 4 , &c. &c. But the salts of multiquivalent 
 metals have usually, though not invariably, a somewhat greater 
 complexity of constitution. Their chlorides, derived from two 
 or three atoms of hydrochloric acid, are given on page 4, and 
 their other salts derived from monobasic acids are found to cor- 
 respond closely with their chlorides. Thus dichloride and dini- 
 
MULTIQUIVALENT SALTS. 9 
 
 trate of tin, Sn"Cl a and Sn"(N0 3 ) 2 , are derived from two molecules 
 of hydrochloric and nitric acid, H 2 C1 2 and H a (N0 3 ) 2 , respectively ; 
 trichloride and trinitrate of bismuth, Bi'"Cl 3 and Bi'"(N0 3 ) 3 , derived 
 from three molecules of hydrochloric and nitric acid, H 3 C1 3 and 
 H 3 (N0 3 ) 3 respectively. But the formulae of the salts of dibasic 
 acids with diquivalent metals and of tribasic acids with triqui- 
 valent metals are very simple. Thus lead sulphate Pb"S0 4 , is 
 derived from sulphuric acid H 3 S0 4 , and bismuth phosphate Bi"T0 4 , 
 from phosphoric acid H 3 P0 4 , &c. On the other hand the salts of 
 dibasic acids with triquivalent metals, and of tribasic acids with 
 diquivalent metals, are highly complex. Sulphate of bismuth, 
 for example, must be represented by the formula Bi'" 2 (S0 4 ) 3 , de- 
 rived from three atoms of sulphuric acid H 6 (S0 4 ) 3 , and so in other 
 instances. 
 
 (8.) It will be perceived from the above tables and examples, 
 that a salt is usually derived from its corresponding acid by a 
 substitution of metal for hydrogen. Many salts, however, known 
 as salts of the alkaloids, are formed in a different way namely, 
 by a direct union of the acid with ammonia or some other alka- 
 loidal base ; as exemplified by hydrochloride of ammonia NH 3 HC1, 
 nitrate of ammonia NH 3 HN0 3 , &c. But salts of this character 
 may also be considered to contain a composite metal, or rather 
 metalloid, in place of the hydrogen of the acid. Thus by asso- 
 ciating with each atom of ammonia in the salt an atom of hydrogen 
 from the acid, each such atom of ammonia NH 3 , becomes con- 
 verted into an atom of ammonium NH 4 , a pseudo-metallic group- 
 ing, which in its combinations presents a most marked analogy 
 to potassium, as illustrated below : 
 
 Ammonia salts. 
 NH 3 HC1 Hydrochlor. 
 NH 3 HN0 3 Nitrate. 
 NH 3 H 2 S0 4 Acid sulph. 
 (NH 3 ) 2 H 2 S0 4 Sulphate. 
 
 Ammonium salts. 
 
 NH 4 N0 3 Nitrate. 
 NH 4 HS0 4 Acid sulpl 
 (NH 4 ) 8 S0 4 Sulphate. 
 
 Potassium salts. 
 
 KC1 Chloride. 
 
 KN0 3 Nitrate. 
 
 KHSO a Acid sulph. 
 
 K 2 S0 4 Sulphate. 
 
 Without assuming any knowledge of the actual molecular 
 arrangement of ammoniacal salts, it is found most convenient in 
 
10 CHEMICAL REACTIONS. 
 
 practice, especially when comparing them with metallic salts, to 
 regard them as salts of ammonium rather than as salts of ammonia. 
 But the salts of the correlated alkaloids aniline, morphia, strychnia, 
 &c., are usually represented after the manner of ammonia salts, 
 thus: 
 
 Hydrochlorides. 
 NH 3 . HC1 Ammonia. 
 C 6 H 7 N .HC1 Aniline. 
 C I7 H I9 N0 3 . HC1 Morphia. 
 C aI H aa N a O, . HC1 Strychnia. 
 
 Acetates. 
 
 NH 3 . H 4 C 2 O a Ammonia. 
 
 ' C 6 H 7 N . H 4 C 2 O a Aniline. 
 
 C 17 H I9 N0 3 . H 4 C 2 O a Morphia. 
 
 C aI H aa N a O a . H 4 C a O a Strychnia. 
 
 (9.) It was formerly the custom to regard ternary acids as 
 compounds of one or more equivalents of water with a special 
 oxidised grouping, and the corresponding salts as compounds of 
 one or more equivalents of metallic oxide with the same oxidised 
 grouping. Thus the formulae of chloric acid, and chlorate of 
 potassium were written H a O.Cl a 5 and K a O.Cl a 5 , corresponding to 
 aHC10 3 and aKC10 3 respectively. But this custom, which was 
 based on assumptions since shown to be erroneous, is now falling 
 gradually into disuse. Thus the acids of chlorine form the follow- 
 ing series, the ternary members of which may be obtained by 
 direct and successive oxidation of the binary member, hydro- 
 chloric acid, the hydrogen of which cannot possibly exist in the 
 state of water : 
 
 HC1 Hydrochloric. 
 
 HC10 Hypochlorous. 
 
 HC10 a Chlorous. 
 
 HC10 3 Chloric. 
 
 HC10 4 Perchloric. 
 
 KC1 Chloride. 
 
 KC10 Hypochlorite. 
 
 KC10 a Chlorite. 
 
 KC10 3 Chlorate. 
 
 KC10 4 Perchlorate. 
 
 It is true that many ternary acids and salts may be directly 
 or indirectly formed from, or separated into, a special oxidised 
 grouping and water or metallic oxide, but the same acids and 
 salts may also be formed from, or separated into, a variety of 
 other sub-compounds, and the one mode of composition or de- 
 composition has no more right than has each of the others to set 
 up for itself a rational formula. Thus if we act upon sulphate of 
 
SYNOPTIC FORMULAE. II 
 
 copper by metallic iron, magnesia, peroxide of barium, and sul- 
 phide of sod;um respectively, we have the following reactions: 
 
 CuS0 4 or Cu .S0 4 + Fe = FeS0 4 or Fe . S0 4 + Cu 
 
 CuS0 4 or CuO .S0 3 + MgO = MgS0 4 or MgO . S0 3 + CuO 
 
 CuS0 4 or CuO a .SO a + BaO a = BaS0 4 or BaO a . SO,, + Cu0 2 
 
 CuS0 4 or CuS . 4 + Na,S = Na a S0 4 or Na a S . 4 + CuS 
 
 From each of these reactions there might, with equal reason, be 
 inferred the pre-existence in sulphate of copper of the respective 
 groupings S0 4 , S0 3 , S0 a , and CuS, and the correctness of the 
 respective rational formulas Cu.S0 4 , CuO.S0 3 , CuO a .SO a , and CuS.0 4 , 
 in accordance with the theories of Dulong, Berzelius, Long- 
 champs, and Laurent respectively. Moreover, sulphate of copper 
 may be electrolysed into Cu and S0 3 + 0, Avhile it may be formed 
 by combining CuO with SO,, or CuO a with S0 a , or CuS with 4 . 
 From considerations of this kind chemists have thought it better 
 to employ, as much as possible, what are called synoptic formulas, 
 which express only the composition of acids and salts, and not 
 their internal molecular arrangement. 
 
 (10.) The anhydrous acids assumed to pre-exist in ternary 
 acids and salts are mostly hypothetical, but those which have an 
 actual independent existence are found to be quite devoid of 
 acid properties, and in their reactions upon various classes of 
 bodies to differ greatly from the corresponding acids. Hence the 
 appellation acid is altogether inapplicable to them, and conse- 
 quently the phrase anhydrous acid is become gradually disused, 
 and the word anhydride adopted in its stead. The only an|jy- 
 drides often concerned in chemical reactions are the carbonic, 
 silicic, stannic, sulphurous, and arsenious. With the carbonic 
 and sulphurous anhydrides may be associated carbonic oxide 
 and sulphuric anhydride respectively, as in the following table : . 
 
 CO Carbonic oxide. 
 
 C0 a Carbonic anhydride. 
 
 SiO a Silica. 
 
 SnO a Stannic anhydride. 
 
 S0 a Sulphurous anhydride. 
 
 S0 3 Sulphuric anhydride. 
 
 As a 3 Arsenious anhydride. 
 
12 CHEMICAL REACTIONS. 
 
 The carbonic, silicic, stannic, sulphurous, and arsenious acids 
 are unstable ill-defined bodies, which readily break up into water 
 and the respective anhydrides. 
 
 (n.) The general term salt is often taken to include the acid, 
 or salt of hydrogen, as well as the salt of a true metal, such as 
 sodium, or of a quasi-metal, such as ammonium. Using the term 
 in this broad sense, it may be said that whenever different salts 
 of different bases or basylides occur in solution, they undergo 
 mutual decomposition to a greater or less extent according to 
 circumstances. Thus when solutions of chloride of hydrogen and 
 nitrate of sodium are mixed together in equivalent proportions, 
 we have produced some chloride of sodium and nitrate of hydrogen 
 together with some unaltered chloride of hydrogen and nitrate of 
 sodium, or the two salts become four salts, thus : 
 
 o-HCl + arNaN0 3 = yNaCl + yHN0 3 + (x - y)HCl + (a: - y)NaN0 3 . 
 
 But whenever any one of the freshly formed salts is removed 
 from the sphere of chemical action by precipitation or volatilisa- 
 tion, there is a complete instead of a partial decomposition, 
 thus : 
 
 Hence we arrive at the following general law. Any two salts 
 which, by an exchange of their respective basylides, can, under 
 the conditions of the experiment, form an insoluble or volatile 
 compound, undergo a complete double decomposition with pre- 
 cipitation of the insoluble or evolution of the volatile compound. 
 Oxalate of calcium, for instance, being insoluble in water, we 
 know that when chloride of calcium solution is mixed with excess 
 of oxalate of ammonium solution, the whole of the calcium will 
 be precipitated in the form of oxalate of calcium, thus : 
 
 CaCl a + (NH 4 ) 2 C a 4 = zNH 4 Cl + CaC 3 4 . 
 
 Again, acetic acid or acetate of hydrogen being volatile at a 
 moderate temperature, we know that when acetate of sodium is 
 
CHEMICAL MANIPULATION. 13 
 
 heated with sulphate of hydrogen a double decomposition will 
 take place, and acetic acid be liberated, thus : 
 
 O a + H 2 S0 4 = H 4 C 2 O a + NaHS0 4 . 
 
 As will hereafter be seen, the deposition of characteristic pre- 
 cipitates and evolution of characteristic gases or vapours constitute 
 the most general means by which the presence of particular 
 bodies can be analytically established. 
 
 II. CHEMICAL MANIPULATION. 
 
 (12.) The spirit-lamp is very useful for many operations, 
 especially when a small, smokeless, not over hot flame is required. 
 The charcoal burner is scarcely necessary in a laboratory fur- 
 nished with gas, but is otherwise almost indispensable. In a 
 chauffer of the kind figured on page 38, one or two pieces of 
 charcoal may be kept slowly burning, by occasionally blowing 
 off the ash ; or a large brisk fire may be kept up, capable of 
 boiling a gallon or more of water. A few pieces of charcoal 
 may also be readily burnt on a coarse wire grating or trellis, 
 resting by its edges on a couple of bricks or other suitable 
 support. But gas is by far the most convenient fuel for ordinary 
 laboratory work. Among burners which are very generally 
 useful may be mentioned the bat's-wing-gauze burner. This 
 consists of a large bat's-wing nipple, screwed into an elbow of brass 
 tube standing on a flat iron ibot, and provided with a gallery of some 
 kind to support a brass chimney covered at the top with wire 
 gauze. The bat's-wing flame burnt without the chimney is 
 convenient for bending glass tube, and when reduced by partially 
 turning off the gas, is well fitted for blowpipe testing (fig. 4). 
 With the chimney on, and the ascending mixture of gas and air 
 burnt at the top of the gauze, as shown on page 34. a large 
 smokeless flame is obtained suitable for heating sand-baths, flasks, 
 test-tubes, &c. An argand burner, screwed into a flat iron foot 
 and provided with a short brass chimney, is also convenient for 
 
CHEMICAL MANIPULATION. 
 
 Fig. i. 
 
 many purposes, especially when a steady long-continued heat is 
 required. When small flasks, &c., have to be heated, a flat 
 brass ring with an aperture about the size of a shilling may be 
 placed on the top of the argand chimney so as to confine the heat. 
 In the Bunsen burner (fig. I ), gas issues from a short jet fixed 
 in the interior of an upright tube, having holes at the bottom 
 through which air is sucked in, so as to produce a mixture of 
 gas and air to be burnt at the top of the tube. The flame is 
 
 smokeless, and from its 
 great heat well suited for 
 ignitions on a small scale. 
 In many Bunsen burners 
 the gas may be either 
 burnt in a single upright 
 flame, as above described, 
 or in a flat rosette of 
 smaller jets well adapted 
 for evaporations, distil- 
 lations, &c., as shown on 
 page 37. The Bunsen 
 burner may be further 
 modified by slipping into 
 its upright tube, a some- 
 what narrower tube, hav- 
 ing an expanded, broad, flat openmg, the flat flame from which 
 is especially suitable for blowpipe use. Herapath's burner (fig. 2), 
 is a very useful instrument for effecting strong ignitions or 
 fusions, and for glass working. It consists of a large blowpipe 
 jet a, connected with the mouthpiece by a flexible tube, and 
 sliding in the interior of a brass tube b, furnished with a 
 supply of gas, through a lateral projection c, fitting on to an 
 elbow on which it moves easily, so as to allow of the flame being 
 turned in any direction. 
 
 (13.) The mode of using the mouth blowpipe, though difficult 
 to describe, is fortunately very easy to learn. The best blowpipe 
 for general laboratory use is that designed by Dr. Black (fig. 3 a). 
 
GAS-BURNERS. 1 5 
 
 It consists of a small conical tube of brass or tin plate- closed at 
 its broadband open at its narrow end, which is usually furnished 
 with a mouthpiece of bone or ivory. From the side of the cone 
 
 Fig. 2. 
 
 near its broad end, there projects a piece 01 narrow tube about 
 an inch long terminating in a jet, through which the current of 
 air issues. This jet or nozzle should be turned out of a solid 
 piece of metal, should be strictly conical both inside and out, 
 and should fit on to the conical end of the narrow tube by mere 
 pressure without screwing. It is advisable to have a fine jet for 
 testing, and a coarse jet for glass working and general heating; 
 but for these last purposes a common brazier's blowpipe (fig. 3 b\ 
 or even a bent glass tube drawn out to a fine point (fig. 3 c) will 
 usually suffice. 
 
 A coarse bat's-wing burner with the gas partly cut off, so as to 
 produce a flame scarcely larger than that of a candle, will be 
 found very convenient for blowpipe testing ; but in default of gas, 
 the flame of a large candle, or of a spirit lamp fed with solution 
 of turpentine in spirits of wine, may be employed. The candle- 
 
i6 
 
 CHEMICAL MANIPULATION. 
 
 wick should be cut of medium length, and turned in the same 
 direction as the blowpipe jet. 
 
 In using a blowpipe, the air must be projected by the muscles, 
 not of the chest, but of the mouth, which should be blown 
 
 Fig- 3- 
 1 
 
 Fig. 4- 
 
 out like a trumpeter's. The breathing has to be carried on 
 through the nose only ; and, after a little practice, it will be found 
 easy to keep up a continuous pressure with the cheeks and lips 
 
 quite unaffected 
 by the alternating 
 respiratory move- 
 ments of the trunk. 
 The mouth should 
 never be allowed 
 to get exhausted 
 of air, but be 
 constantly reple- 
 nished from behind through the nose. It will be requisite for 
 the student to acquire the power of producing either an oxidising 
 or reducing flame at will. To produce an oxidising flame (fig. 4), 
 
USE OF THE BLOWPIPE. 1 7 
 
 the extremity of the jet should be placed inside the gas- or 
 candle-flame, and a steady not too forcible current of air main- 
 tained. By this means a continuous, silent, lateral flame, of 
 sharply defined conical form, will be produced. The interior of 
 this flame close to the jet will be dark, and contain an excess 
 of cold air from the mouth ; 
 
 while surrounding it will be Fl S- 5- 
 
 seen a somewhat thick layer 
 of clear blue. This is the 
 cone of perfect combustion, 
 the pointed extremity of 
 which constitutes the hottest 
 part of the flame. Outside 
 this blue cone, more espe- 
 cially at its termination, will 
 
 be perceived a very slightly luminous yellow cone, in which the 
 external air is in excess and at a very high temperature. This con- 
 stitutes the oxidising portion of the flame, by exposure to which, 
 a small piece of metallic tin, the size of a pin's head, should 
 gradually swell up into a pulverulent mass of peroxide of tin. To 
 produce a reducing or deoxidising flame (fig. 5), the blowpipe jet, 
 which should be rather fine, is placed just outside the gas- or 
 candle-flame, and a somewhat forcible current of air maintained. 
 The resulting blowpipe flame is much less sharply defined than that 
 previously described, and consists principally of a large luminous 
 cone containing an excess of unconsumed carbon, which exerts 
 a powerful reducing action. A minute portion of peroxide of 
 tin, heated in this flame on a charcoal support, may be readily 
 brought to the metallic state even without the use of a flux. 
 
 The heating power of the blowpipe flame depends upon the 
 continuous impulsion of hot gaseous matter on to the substance 
 under examination, and upon its rapid removal so soon as it has 
 imparted its heat by contact. Moreover, a very perfect combus- 
 tion of the fuel is effected, partly by air projected through the 
 jet, partly by external air drawn in from the sides of the jet and 
 flame, and coinciding in direction with the projected stream. 
 
 c 
 
l8 CHEMICAL MANIPULATION. 
 
 (14.) Some amount of skill must be attained by the chemical 
 student in constructing apparatus of glass tubing, and in other- 
 wis^ working with glass. Ordinary tubing or rod may be cut of 
 any required length by making a firm scratch across it with a 
 triangular file, and then breaking it sharply at the file-mark by a 
 conjoint pull and bend. Glass may also be, as it were, sawn 
 through by means of a file, but the operation is rather tedious. 
 It may be much facilitated by occasionally wetting the file with 
 turpentine, or even with water. Glass may be bored through in 
 a similar manner by a drill or a hard bradawl dipped in turpen- 
 tine. When the neck of a flask, rim of a beaker, or portion 
 of other glass apparatus, becomes cracked, a piece of ignited 
 charcoal, or preferably of pastille, held in contact with the glass 
 immediately in front of the crack, will serve to extend it in any 
 desired direction, so as to cut off the neck or rim, &c. The 
 charcoal may be kept alight by gently blowing on it. Pastilles 
 are made of charcoal powder formed into a mass with thick gum, 
 and rolled into quill-sized sticks, which are dusted with charcoal 
 and dried. 
 
 Glass stirring rods are best made from a piece of solid rod or 
 cane long enough for two stirrers. This is to be heated at its 
 middle point in the blowpipe flame, turning it constantly round 
 and gently extending it, until a constriction is formed, which 
 when cold is scratched with a file. The two halves are then 
 snapped apart, and the ends of the stirrers rounded off by direct- 
 ing the flame upon them for a few moments. 
 
 Subliming or reduction tubes are made by taking a piece of 
 glass tubing of about 0-2 inch bore and six inches long, heating 
 it at its middle point in the blowpipe flame until the glass is 
 thoroughly softened, and then gently pulling the two halves 
 asunder. The glass of which these tubes are formed should be 
 clear, thin, and difficultly fusible. 
 
 Ordinary glass tubing, unless very thick, may be bent in the 
 flame of a bat's-wing or Bunsen burner. The piece of tubing 
 should be heated over a considerable portion of its length, either 
 at once or successively, and as it gradually softens be bent into 
 
GLASS-WORKING. 
 
 Fig. 6. 
 
 the required shape. The production of any constriction in the 
 bore may be avoided by causing some length of tube to take part 
 in the bend, which should never form a sharp angle, but anvell- 
 rounded curve, as in the syphon (fig. 6). 
 
 Glass tubing may be drawn out to an almost capillary point, as 
 in the jet of a wash bottle, end of a pipette, &c., by heating a 
 portion of it, about a quarter 
 of an inch long, until it just 
 softens and then steadily pull- 
 ing until a sufficient constric- 
 tion is produced, which is after- 
 wards scratched with a file and 
 snapped across. The point may 
 have its edges rounded, and 
 its aperture further diminished 
 if necessary, by holding it in 
 the flame for a few seconds or 
 so. In order to point the ex- 
 tremity of a piece of tubing, 
 another piece of tubing or rod 
 must first be joined to it by 
 the blowpipe, so that the neces- 
 sary extension may be made. It is often advisable to thicken a 
 tube slightly at the spot where it is to be drawn out, by rotating 
 it for some time in the flame, and gently pressing its ends to- 
 gether. In this way the conical aperture may be made both strong 
 and fine. 
 
 (15.) Glass-blowing is a valuable accomplishment to the 
 practical chemist, but there are only one or two small operations 
 with which it is actually necessary for the student to become 
 familiar. It will be rarely worth while for him to make his own 
 test-tubes, but he should be able to reseal any that have got 
 accidentally broken. By means of the blowpipe, a piece of waste 
 rod or tubing must first be joined firmly on to two or three pro- 
 jecting points of the broken end, and be made to coincide as 
 nearly as practicable with the axis of the test-tube, as in fig. 7. 
 
 c 2 
 
20 CHEMICAL MANIPULATION. 
 
 Then, at about half an inch or more from its broken end, the 
 tube is to be steadily heated in a large blowpipe-flame, and con- 
 stantly rotated until a considerable constriction is formed, when 
 gentle extension may be employed. The flame is next to be 
 directed upon what will form the bottom of the tube, just at its 
 
 Fig. 7. 
 
 bend or shoulder, and the extension continued. By this means 
 the end to be pulled away will be left irregularly conical, and 
 that of the new tube well rounded. Finally, the thread of glass 
 proceeding from the cone is to be strongly heated at its junction 
 with the tube until it melts and becomes detached. There is 
 thus always left on the bottom of the tube a little burr or projec- 
 tion of melted glass, which, if sufficiently small, may be made to 
 disappear by heating it and the whole bottom of the tube until 
 the glass is soft, and then blowing into the tube with moderate 
 force while rotating it in the mouth. The burr, if too large for 
 this treatment, may be melted in a small blowpipe-flame, and 
 then have a piece of waste tubing, previously warmed, applied to 
 it, and quickly drawn away, so as to bring the burr with it. In 
 this manner a smaller burr will be left, which may be melted 
 into the bottom of the tube as above described. The mouth of a 
 test-tube may be everted by softening it in the flame, and then 
 bending the edge uniformly outwards with the smooth end of an 
 old file previously heated nearly to redness; or else a conical 
 piece of charcoal may be twisted into the softened mouth of the 
 tube. 
 
 Glass tubes sealed at both ends constitute the best means of 
 preserving small specimens, either of liquid or solid. One end of 
 the tube is first sealed as if for a test-tube, save that the small 
 burr need not be interfered v/ith. The other end is then con- 
 stricted to a greater or less extent, according to the size of the 
 specimen to be introduced, so as to leave a funnel-shaped 
 
MAKING SEALED TUBES. 
 
 21 
 
 Fig. 8. 
 
 Fig. 9. 
 
 appendage, as in fig. 8. Liquids may be introduced through a 
 very constricted opening by alternately warming and cooling the 
 body of the tube while the liquid 
 is contained in the funnel. After 
 the substance has been introduced, 
 a small blowpipe-flame is gradually 
 brought to bear upon the con- 
 striction, and the sealing com- 
 pleted. Very careful heating is 
 more particularly required when 
 the constriction is moist from the 
 passage of liquid. For practice 
 the student should seal up small 
 tubes filled to within an inch or 
 so of their length with water, spirit, 
 sulphur, sugar, &c. When sealed 
 tubes are used for effecting reac- 
 tions under pressure, their ends 
 have to be made with great care 
 so as not to be less resisting than 
 the original sides. 
 
 When a small bulb has to be 
 blown upon the end of a piece of 
 tubing, the closed end must first 
 be thickened by rotating it in the 
 flame for some time, and pressing 
 it up with a piece of charcoal until 
 enough glass has accumulated. 
 This thick portion has next to be 
 strongly heated, then withdrawn 
 from the flame, and have air quick- 
 ly but gently blown into it from 
 
 the other end, during constant rotation of the tube in the mouth. 
 Or a bulb may be blown in the course of a tube, as in making a 
 bulbed pipette (fig. 9 #), for instance. For this purpose a portion 
 of the tube is to be thickened considerably by rotating it in the 
 
22 CHEMICAL MANIPULATION. 
 
 flame for* some time and gently pressing the two ends together. 
 The nearest end is then to be closed with a cork, and the thickened 
 portion, having been strongly heated, is to be distended into a bulb 
 by blowing into the tube at the other end, during its rotation in 
 the mouth. In making a pipette, a strong capillary termination 
 should be first formed, and the bulb afterwards blown. The 
 suction orifice may be everted or not at pleasure. The successful 
 blowing of even small bulbs will not be found easy save after 
 considerable practice. 
 
 (16.) Connections of tubing and apparatus are made in various 
 ways. Two pieces of tubing of the same diameter may be sealed 
 together, but the operation requires some amount of skill for its 
 performance. The two ends, well adapted and by preference 
 slightly everted, should be heated to softening in the Bunsen or 
 blowpipe flame, and then brought steadily into contact, taking 
 care that the edges exactly coincide. The junction has then to be 
 heated for some time, constantly rotating the tube, and alternately 
 pushing and pulling the free ends, one of which should be stopped 
 with a -cork, and the other occasionally blown into, so as to main- 
 tain a proper calibre. A piece of wide may be joined to a piece 
 of smaller tubing, by first drawing out the former to a point, and 
 then cutting it across just where its diameter coincides with 
 that of the narrow tube. The two can then be joined together 
 as if originally of equal size. In this way funnel-tubes may be 
 made. 
 
 Glass tubes of more or less similar diameter are best connected 
 by means of a short piece of vulcanite tubing, the internal diameter 
 of which should be rather less than the exterior diameter of the 
 glass tubes, so as to grasp them firmly by its contraction without 
 requiring to be tied. In the absence of vulcanite, small connec- 
 tors may be made of sheet india-rubber, a piece of which of the 
 required size is to be gently warmed, and wrapped round a glass 
 rod or tube ; when its opposite edges, having been cut obliquely 
 so as to overlap, and firmly pressed together with the thumb- 
 nails, will, if freshly cut and perfectly clean, adhere thoroughly. 
 The removal of the caoutchouc connector, from the tube or rod 
 
CONNECTIONS OF APPARATUS. 23 
 
 on which it has been made, may be facilitated by first moistening 
 the rod in the mouth or afterwards dipping it in water. Glass 
 tubes may often be advantageously connected by a considerable 
 length of vulcanite tubing, which can be closed at will anywhere 
 in its course by pressing it together with a clamp of some kind, 
 or even by tying it tightly with string. A stiff union of two 
 tubes may be made by wrapping a piece of well-soaked bladder 
 or parchment paper several times round their opposed ends, and 
 allowing it to dry on. Or they may be first connected by a piece 
 of vulcanite tubing, and then stiffened by tying on one or two 
 wooden splints made out of lucifer matches. In this way an 
 ordinary funnel may be readily converted into a funnel-tube. An 
 extempore funnel-tube may also be formed by merely resting 
 a small funnel in the suction-orifice of a plain straight pipette 
 (fig. 9 a). 
 
 A small tube may be adapted to a considerably larger one, or 
 to the neck of a flask or bottle, by means of a well-fitting per- 
 forated cork, the size of which can be readily reduced to any 
 required extent by rasping and filing. A sound cork of slightly 
 conical shape, and of such a size as to require some little force 
 for its insertion, having been softened by pressure between the 
 fingers or rolling under the foot, should be pierced by thrusting 
 the point of a rat-tail file half way through it from each end, and 
 then right through. The hole so made must be enlarged by filing 
 until of a size to fit the tube tightly. When two or more holes 
 have to be made in the same cork, care must be taken to have 
 them all parallel, and as equidistant as possible from one another 
 and from the outside of the cork. For making the necessary 
 perforations variously-sized brass tubes with cutting edges, known 
 as cork-borers, may be used with advantage instead of files. 
 The holes made with them should always be rather too small at 
 first, so as to require some little enlargement by filing. By means 
 of cork-borers, very admirable substitutes for corks may be cut 
 out of solid vulcanite. The end of a tube to be inserted through 
 a perforation should always be rounded off by carefully heating it 
 to redness, so that it may not cut or tear the bore, through which 
 
CHEMICAL MANIPULATION. 
 
 it is, after cooling, to be gradually thrust with a screw-like motion. 
 If fitting very tightly, it may advantageously be greased before its 
 insertion. The cork, with its tube or tubes, is next to be fitted 
 to the neck of the flask or bottle by direct pressure with the 
 fingers* and by gentle screwing. That the junction is air-tight 
 may be ascertained by sucking out or blowing into the closed 
 apparatus, and noticing with the tongue whether any exhaustion, 
 or by the ear whether any compression, is produced. Lutes 
 should be avoided as much as possible, but sealing-wax, 
 varnish, white lead, and linseed meal paste are sometimes useful 
 to stop a leak. Occasionally two pieces of tubing of more 
 or less similar diameter are connected by being each of them 
 inserted half-wa}' through the opposite ends of a long perforated 
 cork. 
 
 (17.) By means of glass tubing, vulcanite connectors, and 
 perforated corks, together with flasks, bottles, or test-tubes, the 
 student may construct for himself a variety of useful apparatus, 
 
 such, for instance, as 
 
 Fig. 10. 
 
 the drop-bottle (fig. 
 10). From this, when 
 surrounded by the 
 warm hand and in- 
 verted, the water or 
 other contained liquid 
 issues in a succession 
 of drops ; but when 
 forcibly blown into and 
 quickly inverted, a jet 
 of water springs forth 
 with considerable but 
 gradually decreasing 
 force. This bottle, 
 which should never be 
 
 more than half filled, is convenient for moistening substances, 
 and for washing down into filters or evaporating dishes the fre- 
 quently adhering contents of inverted tubes and beakers. 
 
DROP- AND WASH-BOTTLES. 
 
 The wash-bottle also (fig. n), 
 when held in an upright position 
 and blown into through the short 
 tube, furnishes a fine strong jet of 
 water suitable for washing precipi- 
 tates; while, upon simple inver- 
 sion, it delivers a coarse stream of 
 water through the blow-tube, serv- 
 ing to dilute solutions, fill test- 
 tubes, &c. The blow-tube may 
 conveniently be made with a vul- 
 canite joint or mouthpiece, so as 
 to allow some freedom of move- 
 ment during its use. The jet also 
 may be attached by a cork joint, 
 whereby it can be pointed in any 
 direction. It is convenient to have 
 several wash-bottles, one for cold 
 distilled water, one made out of 
 a flat-bottomed flask for boiling 
 water, one of smaller size for alco- 
 hol, &c. The neck of the hot- 
 water flask should be bound round 
 with list or something of the kind, 
 so as to allow of its being handled. 
 The blow-tube of the alcohol flask 
 may be temporarily closed by a 
 short length of vulcanite, one end 
 of which has been stopped with a 
 bit of glass rod. 
 
 Retorts suitable for the genera- 
 tion of gases are readily made by 
 adapting a bent tube and cork 
 to a small flask or test-tube, as 
 in fig. 12. But when the gas is 
 liberable without the application 
 
 Fig. ii. 
 
 Fig. iz. 
 
26 
 
 CHEMICAL MANIPULATION. 
 
 Fig. 13- 
 
 of heat, a small phial, of such a shape as to stand firmly on the 
 table, may be used instead of a flask. The addition of a funnel- 
 tube is useful when fresh liquid has to be supplied from time to 
 time in order to maintain the effervescence. The bottom of this 
 tube must dip under 4he liquid in the 
 retort or bottle, so as to be cut off 
 from the liberated gas. 
 
 An arrangement of the kind shown 
 in fig. 13 is useful for testing the 
 nature of a gas generated by the 
 action of a known liquid, usually an 
 acid, upon some unknown substance. 
 The acid is poured upon the other 
 substance through the tube-funnel, 
 and the gas conducted by the bent 
 tube into the test solution, where its 
 effects, if any, are observable. 
 
 Gases often require to be purified 
 by acting on them with certain liquid 
 or solid reagents capable of retaining 
 their different impurities, of which 
 aqueous vapour is by far the most 
 common. The solid reagent, divided 
 into small pieces, is usually contained 
 in a glass tube, either straight or bent 
 in the form of the letter U, a little 
 cotton wool or tow being interposed 
 between it and the perforated corks 
 of the tube. The liquid reagent is 
 either absorbed into pieces of pumice 
 
 or other porous solid contained in a U-tube, or the current of gas 
 is allowed to bubble up through the liquid contained in a two- 
 necked bottle, or in a wide-mouthed bottle, or in a U-tube, ac- 
 cording to circumstances. Most insoluble gases, when required 
 in a pure state, are first 'd by their transmission through 
 
SULPHURETTED HYDROGEN APPARATUS. 2; 
 
 water, and then dried, if necessary, by being passed over chloride 
 of calcium or pumice soaked in oil of vitriol. 
 
 An apparatus for evolving sulphuretted hydrogen gas is indis- 
 pensable to the analyst. For ordinary testing the generating 
 bulb shown in fig. 14 is very convenient. Four or five small 
 lumps of sulphide of iron, not larger than peas, are slid down the 
 neck into the bulb, and covered to some depth with water. Sul- 
 phuric acid is then added little by little, until a brisk effer- 
 
 Fig. 14. 
 
 vescence is produced, which usually happens when the acid 
 measures about one-tenth part of the water previously introduced. 
 The mouth is then closed by a tightly fitting cork, or even by the 
 thumb, and the evolved gas transmitted through the solution to 
 be examined. In the absence of the above- described bulb, the 
 arrangement shown on page 26 may be employed. The gas 
 from either apparatus may be washed, if necessary, by trans- 
 mission through a little water contained in a second generating 
 bulb, or in a test-tube, as shown in fig. 42. But when a con- 
 tinuous supply of washed sulphuretted hydrogen is required, as in 
 some toxicological experiments, a different arrangement is pre- 
 ferable. The gas is developed in a Wolfe's bottle, into one neck 
 
28 
 
 CHEMICAL MANIPULATION. 
 
 of which there passes a tube-funnel, and from the other a delivery - 
 tube bent twice at right angles, which dips through a wider tube 
 into a second bottle charged with a very dilute solution of potash, 
 and furnished with a delivery-tube conveying the gas into the 
 solution to be precipitated, as in fig. 15. But contrivances of 
 
 this kind may be 
 infinitely varied, ac- 
 cording to the fancy 
 of the operator. 
 
 (18.) Filtration is 
 performed in order 
 to separate a mecha- 
 nically mixed liquid 
 and solid, with a 
 view to obtain the 
 clear liquid which 
 passes through the 
 filter, or the sus- 
 pended solid which 
 is retained on the 
 filter, or both liquid 
 and solid apart from 
 one another. For 
 analytical purposes, 
 a fine, thin, white 
 
 blotting-paper is employed as the ordinary filtering medium. Boil- 
 ing water should not dissolve anything from it, and when burnt 
 it should leave scarcely any appreciable ash. It is sold either in 
 sheets, or preferably cut into circles of various sizes. A round 
 or square piece of the paper is folded, in one or other of two ways, 
 into the form of a cone, which, unless very small, should rest in 
 a funnel of glass or fine porcelain. When the object of filtration 
 is merely to clarify the liquid, and especially when such liquid is 
 at all viscid, or requires to be very quickly filtered, as often 
 happens with a hot saturated solution, a ribbed filter is employed. 
 The mode of folding this filter is not easily described, though 
 
FOLDING FILTERS. 2Q 
 
 very easily learnt from demonstration. A circle or square of 
 paper is folded first into halves, then into quarters, and each 
 of the two double quarters again into quarters, all the creases 
 being made on the same side of the doubled paper ; each sector 
 is next to be divided into two by a crease down the middle made 
 on the opposite side of the still doubled paper. At this stage the 
 filter assumes the form of a child's fan (fig. 16 a), and in the 
 
 Fig. 1 6. 
 
 event of a square of paper having been used, the projecting ends 
 may be cut off while the fan is closed. The doubled halves are 
 now for the first time separated, which may be facilitated by 
 blowing on to the edge of the paper, when a deeply ribbed cone 
 will be produced, consisting everywhere of alternate internal and 
 external angles, except at two opposite places where two external 
 angles will be found together, between each of which a subsequent 
 fold must be made, so as to produce an internal angle between 
 them. The filter is now completed, and when gently opened out 
 has the form shown in fig. 16 b. The different creases should be 
 made very sharply at the circumference, but indistinctly at the 
 centre of the paper, for fear of weakening it too much. 
 
 But when the chief object of filtration is to collect the sus- 
 pended matter, most usually a precipitate especially thrown 
 down, a plain filter is much to be preferred. A piece of paper is 
 folded into halves and then into quarters, when it will have the 
 outline of an isosceles triangle, with two straight and one curved 
 side if folded from a circle, or with three straight sides if folded 
 
30 CHEMICAL MANIPULATION. 
 
 diagonally from a square, in which case the base must be cut 
 round, as shown in fig. 17 a. The filter is then opened out, 
 leaving three thicknesses on one side and one thickness on the 
 other, so as to form a smooth cone (fig. 1 7 b), which is carefully 
 fitted into a funnel in such a manner as to be well supported all 
 round. The funnel should be rather larger than the filter, so as 
 to project somewhat beyond it, while the filter itself should always 
 
 Fig. 17. 
 
 project beyond the contained liquid. Where it is necessary to 
 employ a double filter, the two should be folded separately, and 
 so arranged in the funnel that the three thicknesses of the one 
 may correspond to the one thickness of the other. The outside 
 filter is often made very small, so as merely to support the 
 bottom of the other. A filter should always be wetted before 
 receiving the mixture to be filtered. This is necessary in order 
 to swell the paper and thereby close its pores, which are otherwise 
 apt to become choked with the precipitate, if indeed some of it 
 be not carried through by the rapid imbibition which at first 
 takes place. When the liquid passes through the paper at all 
 turbid, it should be returned once or twice into the filter, after 
 which it will generally come through clear. It is usually advisable 
 to let the mixture to be filtered subside a little before beginning 
 its filtration, The comparatively clear liquid is then poured off 
 into the filter, and, when it has run through, the thick sediment 
 added separately. The interior of the tube, test-glass or beaker, 
 which contained the mixture, is next to be washed down by a 
 small forcible stream from the wash-bottle, and the rinsings 
 
FILTRATION. 
 
 Fig. i 8. 
 
 poured on to the deposit left in the filter by the draining away of 
 the previously added liquid. Lastly, by means of a wash-bottle, 
 any deposit extending up the sides of the filter is washed down to 
 its centre, so that the entire precipi- 
 tate may be collected into as small a 
 bulk as possible, for further treat- 
 ment. It is often necessary, more- 
 over, to wash a precipitate thoroughly, 
 so as to free it from every trace of 
 soluble matter. This is done by 
 projecting water upon it several times 
 by means of the wash-bottle, and al- 
 lowing the bulk of each addition to 
 filter away before repeating the pro- 
 cess, until, on evaporating down a 
 few drops of the filtered washings, 
 no residue whatever is left upon the 
 slip of glass or platinum foil. The 
 stream of water must not be too 
 forcible, for fear of making a hole in 
 the filter or causing a spurting of its 
 contents. Moreover, in pouring into 
 
 an empty filter, the liquid should be directed along the side and 
 not immediately upon the point of the filter, which is its most 
 unprotected and consequently weakest part ; while the filtered 
 liquid if received in a wide beaker or evaporating dish, should 
 be made to run along the side of the glass or dish, so as to avoid 
 spurting. Again, in pouring from one vessel into another, from 
 a beaker or wide-mouthed flask into a funnel for instance, a 
 glass rod should be applied to the lip of the flask or beaker, as 
 shown in fig. 1 8, not only to direct the course of the liquid into 
 the funnel, but also to prevent any of it being spilt by running 
 over the side of the delivering vessel. This running of liquid 
 over the side may also be avoided by greasing that part of the 
 lip which is poured from, with a little tallow or spermaceti 
 ointment. 
 
32 CHEMICAL MANIPULATION. 
 
 When it is necessary to remove a wet precipitate from the filter 
 on which it has been collected, the well-drained filter, carefully 
 removed from its funnel, may be spread out on two or three folds 
 of bibulous paper to absorb superfluous moisture, and the preci- 
 pitate be then carefully scraped off from it by a spatula of ivory, 
 platinum, or steel ; or the drained filter may be spread out on 
 one side of the funnel, and its contents washed quickly down by 
 a forcible stream from the wash bottle ; or, by means of a glass 
 rod, a hole may be made in the bottom of a filter in situ, and its 
 contents washed through ; or the precipitate may be dissolved off 
 the filter by causing some solvent, usually an acid, to pass through 
 it several times, preferably at a boiling temperature. 
 
 Decantation often furnishes a ready substitute for filtration in 
 cases where the solid part of a mixture has subsided to the bottom 
 of the precipitating glass. The speedy and complete subsidence 
 of a freshly formed precipitate may often be effected by violently 
 shaking up the mixture for a few minutes in a closed vessel, when, 
 after standing at rest for a little while, the clear supernatant liquor 
 may be poured off with a steady hand, or be withdrawn by a 
 syphon or pipette. In using a pipette great care must be taken 
 not to allow any of the liquid once sucked up to descend again 
 upon the sediment so as to disturb it. A deposit from which the 
 supernatant liquid has been removed by some form of decantation 
 may be washed by pouring water on to it, stirring it well up, and 
 letting it again subside for a second decantation, and so on. A 
 thin layer of liquid overlying a deposit may often be sucked up 
 very completely by a coil of bibulous paper, introduced with care 
 so as not to disturb the deposit. 
 
 Syphons and pipettes are useful not only for separating a super- 
 natant liquid from a deposited solid, but also for separating two 
 strata of different liquids from one another. 
 
 (19.) Apparatus to be heated over the several burners already 
 described, may, according to its nature, be supported in various 
 ways. It may rest on the ring, or be held by the clamp, of a re- 
 tort-stand ; or an independent upright clamp or tripod stand may 
 be employed. The tripod is often replaced with advantage by a 
 
SUPPORTS AND BATHS. 
 
 33 
 
 Fig. 19. 
 
 jacket of clay, or metal, surrounding the burner, and so prevent- 
 ing draughts, as shown in fig. 19. Iron triangles also to rest on 
 the top of the jacket, tripod, or retort-ring, are in constant requi- 
 sition. A triangle of iron wire, 
 sheathed with three pieces of 
 tobacco-pipe, is useful for sup- 
 porting small porcelain cruci- 
 bles that have to be made 
 red-hot, but the mass of the 
 tobacco-pipe interferes with the 
 attainment of a very high tem- 
 perature. Small triangles of 
 platinum wire are far more 
 convenient. 
 
 Flasks and retorts may be 
 heated at some little distance 
 over an argand flame without 
 the interposition of any me- 
 dium. But with the gauze 
 
 burner, and more particularly with the Bunsen burner, it is 
 advisable to protect the bottom of the vessel by a piece of stout 
 wire gauze. Beakers should be placed either on a flat iron plate 
 or sand-bath, and the heat be raised cautiously. Porcelain 
 evaporating dishes may be heated almost anyhow, according to 
 circumstances; but when the flame touches the bottom of the 
 dish some little care is necessary, both at the commencement of 
 the operation, and when the liquid is evaporated nearly to dry- 
 ness. Watch-glasses require very careful lieating. They are 
 best held by the thumb and finger over a small flame, but 
 may be supported by forceps, wire-triangle, or special watch- 
 glass holder. When containing liquid, to be heated by means 
 of a sand-bath, they should not be depressed into, but just 
 rest on, the top of the hot sand. Test tubes may be readily 
 heated in the flame of a spirit lamp or gauze-burner. They 
 should be held between the thumb and fingers, and be constantly 
 shaken from side to side, especially during boiling, to prevent any 
 
34 
 
 CHEMICAL MANIPULATION. 
 
 Fig. 20. 
 
 sudden expulsion of the contained liquid, with which they should 
 not be more than half filled. When the boiling has to be long 
 continued, a piece of paper or cloth may be bound or twisted 
 
 round the upper part of the tube, so 
 as to protect the fingers. Test tube 
 holders are rarely of much use. 
 
 Small capsules and crucibles, of 
 platinum or Berlin ware, may be 
 heated to redness over an argand 
 (fig. 20), or to full redness over a 
 Bunsen burner, or by the blowpipe 
 flame. They may be held either 
 with forceps or on triangles of wire 
 or tobacco-pipe. When a strong 
 heat is required, they should be 
 surrounded with a small jacket of 
 metal or clay. 
 
 Sand-baths are usually formed of sheet iron. Some are made 
 rather deep to receive flasks and retorts, others nearly flat for 
 
 beakers. The sand, which 
 must not be heaped above 
 the level of the liquid to be 
 heated, should be of uni- 
 form size and rather coarse. 
 An iron plate, or trellis of 
 thick iron wire, forms an 
 excellent substitute for a 
 flat sand-bath. 
 
 The water-bath is used 
 for heating substances to a 
 temperature not exceeding 
 1 00 C. A small saucepan, 
 with an evaporating dish for 
 a cover, forms a capital 
 makeshift. The saucepan lid 
 may be replaced by a series of broad rings of tin plate, having 
 
 Fig. 21. 
 
EVAPORATION. 35 
 
 apertures of different sizes to support small evaporating dishes 
 (fig. 21), capsules, watch-glasses, necks of flasks, &c. Beakers, 
 flasks, and retorts, to be heated in a water-bath, should not be 
 allowed to touch the bottom of the bath, but should rest on a 
 piece of tow or folded cloth, as well to avoid danger from bumping 
 as to prevent the communication of an increased temperature by 
 contact with the heated metal. , 
 
 (20.) Heat is applied to liquids in order to warm, evaporate, 
 boil, or distil them. Evaporations are performed on slips- of flat 
 glass, or on watch-glasses, or evaporating dishes. The crystalline 
 forms of various salts may often, be recognised by dissolving a 
 grain or so of the salt in a drop or two of water on a glass slip,, 
 evaporating until a solid margin appears, and setting aside to 
 crystallise. The residue may tken be examined by a lens, or- 
 under the low power of a microscope. The evaporation, of a 
 small quantity of liquid, contained in a watch-glass for instance, 
 may often be promoted by gently blowing on its surface for a 
 little while. A dish in which evaporation is taking place (fig. 19) 
 may be loosely covered with a piece of filtering paper, stiffened 
 by a glass strip passed through and across it ; and care should 
 be taken not to allow the liquid to boil. In evaporating to dry- 
 ness, it is well to have the heat lowered as the process approaches, 
 completion, and the residue, if considerable, kept constantly 
 stirred. 
 
 Ebullition is conducted on a small scale in test tubes, and oa 
 a larger scale in flasks, Florence oil flasks being among the best 
 and cheapest that can be employed. A flask of cold liquid, held 
 over a naked flame, quickly becomes covered with a deposit of 
 moisture, which it is advisable to wipe off once or twice. Ebul- 
 lition sometimes takes place intermittingly, and with considerable 
 jerking or bumping. This may often be prevented by introduc- 
 ing a coil of platinum wire or piece of tobacco pipe into the liquid, 
 either before boiling or after cooling down a degree or two. If 
 introduced during boiling, it is apt to produce a violent rush of 
 vapour. It is occasionally useful to adapt a long upright tube to 
 
 D z 
 
CHEMICAL MANIPULATION. 
 
 Fig. 22. 
 
 the mouth of a flask (fig. 22) in which a liquid has been heated, 
 
 so that any vapour given off may 
 be condensed in the tube, and flow 
 back again into the flask. 
 
 Distillation is usually conducted 
 in an apparatus composed of a 
 boiler, condenser, and receiver. 
 On a small scale the boiler is re- 
 presented by a glass retort, or 
 flask with its bent tube, the re- 
 ceiver by a test tube, flask or 
 bottle, and the condenser by a 
 long glass tube placed between the 
 retort and receiving flask, and sur- 
 rounded either by a constantly 
 changing layer of water, as in Lie- 
 big's condenser, or by a piece of 
 blotting-paper kept moist by the 
 constant dripping of water. Very 
 often a separate condensing tube 
 is dispensed with, and the long 
 neck either of the retort or receiv- 
 ing flask alone employed. Fig. 
 23 shows a very simple arrange- 
 ment of this description. The liquid is boiled in a long-necked 
 retort, and the distillate conducted by means of a bent adapter 
 into an upright bottle. A twist of thoroughly wetted tow, or 
 lamp-cotton, is tied somewhat tightly round the retort-neck, at 
 about an inch above the point where it enters the perforated 
 cork of the adapter, and the ends of the twist allowed to hang 
 down for two or three inches. A piece of filtering paper of 
 suitable size and shape to embrace almost the entire circumference 
 of the neck, and reach from just above the twist of tow almost 
 to the curve of the retort, is moistened with water, laid upon 
 the retort-neck and bent round it so as to adhere closely. A 
 second piece of filtering paper is at first folded by means of 
 
DISTILLATION. 
 
 37 
 
 three creases into four strips and then placed over the other, so 
 that the flaps being bent down, its middle portion will form a 
 
 small channel along the top of the retort-neck. It should be about 
 two-thirds the length of the other, and not reach so high up. By 
 this arrangement the water constantly dropping out of a partly 
 plugged funnel from the height of half an inch or so on to the 
 surface of the inner paper, at a little distance from its upper ex- 
 tremity, is conveyed along the channel, spread uniformly over the 
 retort-neck and drained away by the twist of tow. If the short 
 length of neck intervening between the twist and adapter be dry 
 at the beginning, it will continue so throughout the experiment. 
 For further security, however, it may be marked with a ring of 
 grease. Adapters are of all shapes and sizes. Such a one as that 
 shown in the woodcut is easily made out of a piece of tubing or 
 broken retort neck. Others, intended to act more or less as 
 condensers, are represented in fig. 24. Another convenient form 
 of distilling apparatus is shown in fig. 40. The boiler consists 
 of a round flask, from which a long wide bent tube dips through 
 a perforated cork into a Florence flask resting in a basin of water . 
 
CHEMICAL MANIPULATION. 
 
 The cork must either not fit tightly or have a slit cut in it, so as 
 to permit the escape of any uncondensed vapour. The neck and 
 upper surface of the receiving flask should be surrounded with 
 
 Fig. 24. 
 
 filtering paper, on to which water should drop from a funnel. A 
 bend of sheet lead may be placed over this flask so as to sink it 
 in 'the water. 
 
 One of the simplest varieties of Liebig's condenser is shown in 
 
 Fig. 25. 
 
 figure 25. It is merely a cylinder of tin-plate, having four 
 slightly conical tubular apertures two in the same plane with 
 each other at either side of the cylindrical surface, and two oppo- 
 
DRYING OF PRECIPITATES, ETC. 39 
 
 site each other in the terminal circular planes. By means of 
 well-fitting perforated corks a funnel tube of tin-plate or glass is 
 inserted into the distant horizontal aperture, and an exit tube of 
 tin or glass into the other, while the distilling tube extends 
 through the axis of the cylinder. The hot contents of the dis- 
 tilling tube pass downwards, becoming colder and colder in their 
 descent, while the stream of cold water entering the condenser 
 through the funnel passes upwards, becoming hotter and hotter 
 in its ascent until it escapes at the overflow pipe. The condenser 
 may be fastened to a retort-stand with string or wire, as in the 
 figure, or may be supported by a clamp of some kind. Liebig's 
 condensers are made in every variety of form, size, material, and 
 construction, some of them being provided with special supports, 
 which allow them to be heightened or lowered at will, and placed 
 at any desired inclination. 
 
 (21.) Heat is applied to solids in order to warm, dry, ignite, 
 fuse, or volatilise them. Any tube, flask, or retort, the interior 
 of which cannot be reached by the fingers, should, after thorough 
 cleaning,* be rinsed once or twice with distilled water, and then 
 drained as dry as possible by means of draining pegs or some 
 other mode of support. It should next be warmed carefully over 
 a gas flame or in front of a fire, and the hot moist air sucked out 
 of it from time to time by the aid of a long tube reaching into 
 it for some -p-i. 26. 
 
 considerable 
 distance, as 
 shown in fig. 
 26. Narrow 
 glass tubing is 
 
 * There is seldom much difficulty in cleaning laboratory glass from any 
 stain or dirtiness, when it is not of long standing, by means of cold or hot 
 water and dilute or strong acids or alkalis, aided by. extempore brushes 
 made of moist tow dipped in sand and fastened on to thick pieces of wire, 
 or by tube-brushes made specially for the purpose. Flasks, retorts, &C M 
 may often be very efficiently cleaned by shaking them up somewhat vio- 
 lently, after the introduction of a little water and a few pieces of soft paper 
 or rag. The interior of narrow glass tubing is best cleaned by pushing a 
 piece of moist filtering paper through it. 
 
4 o 
 
 CHEMICAL MANIPULATION. 
 
 Fig. 27. 
 
 dried by heating some length of it over a gas burner or spirit 
 lamp, and simultaneously sucking air through it with the mouth. 
 In the absence of an air- or water-oven, reduction tubes and 
 similar small pieces of apparatus may be dried by heating them 
 on a sand-bath standing over a burner ; or preferably on a flat 
 iron plate, which in many other cases also may be advantageously 
 substituted for a sand-bath. Moist powders of various kinds may 
 be dried on a water-bath, or sand-bath, or by ignition over an 
 argand burner, &c., according to circumstances. A washed pre- 
 cipitate retained in its filter and funnel may often be quickly 
 
 dried by supporting the fun- 
 nel on a broken beaker or 
 short lamp -glass standing 
 upon a trellis of iron wire, 
 underneath which a small 
 gas-flame is kept burning 
 (fig. 27). Or the filter may 
 be supported over a heated 
 iron plate by means of a 
 small tripod - stand, easily 
 made out of copper -wire. 
 When nearly dry, the filter 
 with its contents may be re- 
 moved from the funnel and 
 placed in a water-bath; or 
 the washed precipitate and 
 filter may be removed care- 
 fully from the funnel, pressed 
 gently between folds of blotting-paper, and placed at once in the 
 water -bath. At moderate temperatures, drying over oil of vitriol 
 in the exhausted receiver of an air-pump takes place with con- 
 siderable rapidity. Moreover, a shallow air-pump-jar standing 
 on a plate of ground glass over a dish of oil of vitriol or quick- 
 lime, forms a very convenient chamber in which all sorts of 
 bodies may be dried and kept dry. 
 
 Animal solids are frequently subjected to ignition in order to 
 
FUSIONS AND SUBLIMATIONS. 41 
 
 burn off their organic, and leave behind their mineral matter, or 
 ash. The tissue, &c., may be first carbonised in small portions 
 at a time in a thin Berlin capsule or crucible, heated over a gauze 
 burner, in some place where the ernpyreumatic vapour, &c., can 
 be readily got rid of. The resulting charcoal should then be 
 pulverised, and the powder heated steadily for some hours in a 
 shallow platinum capsule, or on a tray of platinum foil, supported 
 over an argand flame, when the charcoal will gradually burn 
 away, and a white or greyish ash be left. The temperature 
 should never exceed that of dull redness, as otherwise the ash, 
 save that of blood, is apt to fuse over the remaining charcoal, and 
 so prevent its combustion. The operation is much facilitated by 
 protecting the capsule from draughts, and particularly by placing 
 over, but not immediately upon it, a cover of thin platinum foil. 
 Carbonate of sodium and other fluxes employed in testing, are often 
 heated to dull redness over an argand flame just before being used. 
 Moreover, in quantitative analysis, filters and their contained 
 precipitates have constantly to be burnt, with a view to getting 
 rid of the filter-paper and leaving the precipitate in a state fit for 
 being weighed. The ignitions made on charcoal or platinum 
 wire in the course of blowpipe testing will be presently described. 
 Independently of the many fusions made in the course of blow- 
 pipe testing, others on a somewhat larger, though still very small 
 scale, have occasionally to be performed by the student. There 
 are, for instance, a few substances which require to be fused with 
 carbonate of sodium or potassium, either alone or mixed with 
 some other reagent, before they can be brought into a state of 
 solution, and so identified by ordinary analytical processes. The 
 insoluble substance is usually incorporated with three or four 
 times its bulk of a mixture of carbonate of sodium with carbonate 
 of potassium, or in some cases with either the nitrate or cyanide of 
 potassium, and heated to thorough fusion over a Bunsen or blow- 
 pipe flame, in a platinum or porcelain capsule, or in a small iron 
 spoon. In making these fusions, it is most important that both 
 the substance and flux be well dried, very finely powdered, and 
 intimately commixed. The capsule or crucible should be heated 
 
42 CHEMICAL MANIPULATION. 
 
 at first very gradually, but ultimately to the highest attainable 
 temperature. 
 
 The only volatilisations which the student will be called upon 
 to perform are made in narrow glass tubes, open at both ends 
 when a current of air is required to act upon the heated sub- 
 stance, or open at one end only when a simple sublimation is 
 intended. Powdered substances of various kinds may be intro- 
 duced into narrow tubes open at both ends, by first placing a 
 suitable quantity of the powder in a gutter of stiff glazed paper, 
 pushing this gutter with its contents into the tube held hori- 
 zontally, then inverting the tube and gutter, and, lastly, with- 
 drawing the gutter while still inverted. The same method may 
 sometimes be used with closed subliming tubes, so as to avoid 
 soiling their interiors, but is unnecessary when both substance 
 and tube are thoroughly dry. The tube, whether open or closed 
 at one end, should be made of hard glass, and be heated in the 
 flame of a spirit lamp or Bunsen burner. 
 
 (22.) Although quantitative analysis does not come within the 
 scope of this work, yet a few words on weighing and measuring 
 may not form an inappropriate addition to the foregoing remarks 
 on chemical manipulation. The general adoption of the French 
 metrical system, of which the gramme is the unit of weight, and 
 the cubic centimetre or bulk of a gramme of water at its greatest 
 density the most usual unit of measure, is highly desirable ; but 
 in default of this, the English decimal system, of which the 
 standard grain is the unit of weight, and the bulk of a grain of 
 water, at 62 F., the unit of measure, may be employed. In the 
 chemical laboratory we dispense altogether with the use of 
 ounces, drams, &c., and speak only of so many grammes and 
 cubic centimetres, or grains and grain-measures. Mr. Griffin 
 takes the bulk of seven grains of water as his unit of measure, 
 which he terms a septem, so that 1000 septems are equal to one 
 decigallon, or to the bulk of a pound of water. The use of this 
 decimal division of the gallon is often very convenient, and quite 
 compatible with that of the grain-measure, the septem and grain- 
 measure standing to one another in the simple relation of 7 to I, 
 
MEASURING. 
 
 43 
 
 as shown in the following table. The figures with a dot over 
 them are inexact. 
 
 
 Decigallong 
 
 Septems 
 
 Grain-measures 
 
 Gallon .... 
 
 
 10,000 
 1,000 
 
 2,500 
 1,250 
 62-5 
 
 62,32! 
 36-065 
 
 2,204-6 
 
 2-2 
 
 70,000 
 7,000 
 
 17,500 
 8,750 
 437*5 
 
 436,247-4 
 252-458 
 
 i5,43 2 ' 6 
 *5'4 
 
 Decigallon or pound . . . 
 Quart 
 
 
 2-50 
 1-25 
 -0625 
 
 62-321 
 2-204 
 
 Pint .... 
 
 
 Cubic foot ...... 
 
 Cubic inch . 
 
 Litre ...... ^^'- 
 
 Cubic centimetre . . *;%'- 
 
 Fig. 28. 
 
 One litre, or kilogramme of water-measure, equals I "j6 pints, 
 or 6 1 '027 cubic inches. One cubic centimetre, or gramme of 
 water-measure, equals *o6i cubic inch. 
 
 One decigallon or pound of water-measure equals '4535; litre, 
 or 453'$ cubic centimetres, or 0*0160 cubic 
 foot, or 27727 cubic inches, or 16 fluid ounces. 
 
 Some measures are made to contain or deliver 
 a definite quantity of liquid. Others are gra- 
 duated so that any indefinite quantity delivered 
 may be afterwards read off. A flat-bottomed 
 and somewhat narrow-necked flask, having a 
 horizontal scratch across its neck marking the 
 height to which it should be filled, forms a 
 very convenient measure of the former kind 
 (fig. 28). It is easy to select a couple of such 
 flasks, which shall measure either a deci- 
 gallon and half-decigallon respectively, or a 
 litre and half-litre, &e., &c. A pipette of the form shown in fig. 29 
 is also a very useful instrument of this class. It is filled by care- 
 fully sucking up liquid to a level somewhat above the mark on its 
 stem, and quickly closing its upper orifice by the finger. Then by 
 
44 
 
 CHEMICAL MANIPULATION. 
 
 
 relaxing the pressure of the finger, the contained liquid is allowed 
 to issue drop by drop until its height corresponds exactly with the 
 scratch, when the finger is again pressed 
 down ; after which, on removing the Fig- 3- 
 finger, the measured quantity of liquid 
 is allowed to flow out. A pipette of this 
 kind is so constructed that when filled 
 up to the mark on its stem it delivers 
 exactly the indicated quantity of liquid, 
 irrespective of what adheres to the inte- 
 rior of its elongated bulb. The last drop 
 should be gently blown out while the 
 point of the pipette is in contact with 
 the inside of the receiving vessel. It is 
 well to have a couple of such pipettes 
 delivering either 100 septems and 10 
 septems, or 50 and 5 cubic centimetres 
 respectively. For measuring indefinite 
 quantities a tall narrow cylinder (fig. 30), 
 graduated into divisions of 10 septems, 
 or 5 c. c. each, is most convenient. The 
 ordinary ounce measures of the apothe- 
 cary are very unsatisfactory instruments. 
 Their graduation is seldom accurate and 
 always difficult to read off exactly, on 
 account of the expanded conical form of the glass. 
 Where smaller quantities have to be delivered and 
 their volumes afterwards noticed, a Bink's burette or a 
 graduated straight pipette may be employed. The 
 burette (fig. 3 1 a) should be held near its upper end, 
 with its mouth guarded by the thumb or forefinger, and 
 its beak pointed not directly but obliquely downwards, 
 so that the 'side of the beak may be inclined to the 
 horizontal plane at a somewhat acute angle. The 
 orifice of the beak should be well greased with tallow 
 or spermaceti ointment, and any liquid remaining in it be sucked 
 
MEASURING. 
 
 45 
 
 Fig. 31, 
 
 a 
 
 down, both at the beginning and end of the experiment. More- 
 over, the burette must always be allowed to stand at rest for a 
 minute or two before observing the 
 height of the contained liquid. The 
 graduation should be from above to 
 below, as in the woodcut. 
 
 The graduated pipette (fig. 31 b) is 
 filled by suction, the contained liquid 
 adjusted to a proper height, the quan- 
 tity required allowed to flow out, and 
 the level of the remainder finally read 
 off. Inasmuch as the conical extremity 
 of this kind of pipette rarely delivers 
 its contents exactly, it is better not to 
 have it included in the graduation. 
 Whether the graduation of the pipette 
 is from above to below, or from below 
 to above, does not much matter; for 
 some purposes the one, and for some 
 purposes the other mode being most 
 convenient. 
 
 In reading off the height of a liquid 
 its upper surface should be brought as 
 nearly as possible to a level with the 
 eye. This surface in most liquids con- 
 tained in glass vessels, will be found 
 more or less deeply concave according 
 
 to the diametric smallness of the column, &c. ; but, in all cases, 
 the bottom of the curve is taken as the true level, and, in mea- 
 suring definite quantities, must be made to coincide exactly with 
 the mark. By right all measurements should be taken at 
 mean temperature, namely, I5'5 C. (60 F.), but the expansions 
 and contractions of aqueous liquids within the ordinary ranges 
 of temperature are so slight that, in most cases, they may be 
 safely disregarded. 
 
 A pair of the best description of dispensing scales suspended 
 
46 CHEMICAL MANIPULATION. 
 
 from a fixed support makes a very useful balance for ordinary 
 work. A set of accurate grain weights ranging from 0*05, or 0*1 
 grain to 1000 grains should be provided, and also a supplementary 
 short pan for taking specific gravities. The beam should turn 
 freely by an addition of o' i grain, even when the pans are each 
 loaded with a weight of twelve or fifteen hundred grains. It is 
 well to employ habitually the left-hand pan for the substance, 
 and the right-hand pan for the weights, which should be always 
 handled by pincers, and not by the fingers. It is sometimes 
 necessary to weigh out definite quantities of a substance such as 
 20, 50, or 100 grains; but it is better in most cases to take an 
 indefinite quantity and then ascertain its weight, exactly as in 
 weighing any particular specimen, the resultant of an experiment 
 for instance. When taking the weight of an indefinite quantity, 
 much time will be saved by trying the weights not at random 
 but in a definite order, always taking in succession the weight 
 next above or below in the series that particular weight which 
 was last found too little or too much. 
 
 It is convenient to provide counterpoises of sheet lead for 
 balancing exactly the several watch-glasses, capsules, crucibles, 
 bottles, &c., used for retaining a substance while being weighed ; 
 or their respective weights may be ascertained and scratched upon 
 them. When a definite quantity of substance has to be transferred 
 from the watch-glass or capsule on which it has been weighed 
 into some other vessel, the frequently adhering residue may be 
 washed off by a jet of water, or be gently brushed off by a 
 camel' s-hair pencil. But where an indefinite quantity has been 
 taken, it is better to reweigh the watch-glass or capsule and to sub- 
 tract the weight of adhering residue from the original weight of 
 substance. Or, what comes to the same thing, some portion of a 
 weighed quantity may be transferred, and its amount ascertained 
 by noticing the loss sustained by the originally weighed quantity. 
 
 Substances to be accurately weighed must always be first 
 brought to an uniform condition of dry ness, inasmuch as a greater 
 or less degree of dryness may cause considerable variation in the 
 
SPECIFIC GRAVITY. 47 
 
 weight of a body at different times. The substance may be dried 
 in vacuo over oil of vitriol, or in a water-bath, and its weight 
 determined from time to time until it becomss constant ; or, in 
 some cases, the substance may be heated at once to dull redness 
 and then weighed, not, however, until thoroughly cooled, as by 
 resting the containing crucible on a piece of metal, for instance, 
 otherwise an ascending current of heated air will be set up, 
 which will diminish its apparent weight appreciably. Hygro- 
 metric substances must be weighed in covered crucibles, or 
 between a pair of ground watch-glasses held together by a clip, 
 or in stoppered bottles made expressly for the purpose, or in short 
 wide test tubes. They may be cooled under a glass jar standing 
 over oil of vitriol. 
 
 (23.) By specific gravity is understood the weight of a unit of 
 volume, or, what comes to the same thing, the comparative weights 
 of equal bulks of different bodies. In this country water at the 
 temperature of I5'5 C. (60 F.) is taken as the standard to which 
 the specific gravities of liquids and solids are usually referred, 
 and its sp. gr. considered either as I 'o or I ooo according to cir- 
 cumstances. 
 
 In order to determine the specific gravity of a liquid, a small 
 flask or bottle of known weight is selected, which, when accu- 
 rately filled to a certain point, contains a known weight of pure 
 water at I5'5. This flask is filled with the liquid whose sp. gr. 
 is required, and weighed, when, after deducting the known weight 
 of the flask, the residuary weight of contained liquid is compared 
 with the known weight of the same bulk of water, according to 
 the proportion : 
 
 Wt. of water W' '. wt. of liquid W:: sp. gr. of water : sp. gr. of liquid; 
 
 that is, according to the equation, 
 
 _ ,. . , Wx 1000 
 Sp. gr. of liquid = yp- . 
 
 Thus, supposing the flask to be what is called a five-hundred 
 
CHEMICAL MANIPULATION. 
 
 grain flask, but to contain in reality 4997 grains of water, and 
 say 459 '8 grains of proof spirit, then the sp. gr. of the spirit 
 459800 
 
 wiibe-^^9*,. 
 
 Specific gravity flasks or bottles are made of various shapes, 
 one of the most convenient being that employed by Regnault and 
 shown in fig. 32 a, for which, however, any flat-bottomed narrow- 
 necked flask may 
 be substituted. It 
 is to be filled up 
 to the mark on its 
 neck with the li- 
 quid, previously 
 brought to the 
 temperature of 
 15*5 by immer- 
 sion in cooled or 
 warmed water, and 
 weighed. For tak- 
 ing the specific 
 gravities of very 
 volatile liquids 
 
 this kind of flask is provided with a solid stopper. The most 
 usual form of sp. gr. flask is shown in fig. 32 b ; when used, it is 
 nearly filled with the liquid to be examined, a tube thermometer 
 introduced, and the whole placed in a vessel of cooled or warmed 
 water until the contained liquid has acquired a temperature of 
 1 5' 5. The thermometer is then removed, and the flask filled 
 to the brim with more of the liquid previously brought to mean 
 temperature, the perforated stopper inserted, whereby the excess 
 of liquid is thrust out, and the exterior of the flask thoroughly 
 dried with a cloth, care being taken to avoid any communica- 
 tion of heat from the hand or elsewhere. As a rule sp. gr. flasks 
 should be made perfectly dry before being filled, and by preference 
 be rinsed out with some of the liquid under examination. 
 
SPECIFIC GRAVITY. 
 
 49 
 
 . 3 3- 
 
 The hydrometer (fig. 33) is useful for taking the specific gravi- 
 ties of different liquids, where rapidity rather than accuracy ot 
 determination is required. It is merely an upright float, weighted 
 below, and having a narrow graduated stem above^ so as to sink 
 to a greater or less extent in liquids of different densities. 
 Inasmuch as the bulk of any liquid displaced 
 by a floating body is equal in weight to the 
 floating body, it is obvious that equal weights of 
 different liquids will differ in volume according 
 to the depth to which the hydrometer sinks in 
 them; or, in other words, the heights to which 
 different liquids rise on the stem will be inversely 
 as their specific gravities. Some hydrometers, 
 those used in the examination of urine, for in- 
 stance, are so graduated that their degrees exprets- 
 the specific gravities directly. But in commerce- 
 various artificial scales are preferred, that of 
 Twaddell in particular being very generally used 
 in this country. The degree of gravity marked 
 on Twaddell's scale has to be multiplied by 5;, 
 and the product added to iooo, to give the actual 
 specific gravity. 
 
 The most usual method of taking the specific 
 gravity of a solid body heavier than water, con- 
 sists in weighing it first in air, or theoretically 
 in a vacuum, and afterwards in pure water at 
 15-5, when the ratio of the difference in the 
 weighings to the weight in air will give the sp. 
 gr., according to the proportion : 
 
 Dif.inwgs. W W : wt.inair JF:: sp. gr. of water : sp. gr. of solid 
 
 that is, according to the equation 
 
 For by a well-known principle in hydrostatics, the apparent loss 
 
 E 
 
5O CHEMICAL MANIPULATION. 
 
 of weight which a body experiences when immersed in a liquid 
 is identical with the weight of an equal bulk of that liquid.* 
 
 In order to weigh a solid body in water it must be attached by 
 a horse-hair to the hook of the sp. gr. pan, as shown in fig. 34, 
 f and have its surface thoroughly wetted 
 
 with a soft brush, so that, when immersed 
 in the water, there shall be no adhering 
 air bubbles. When the solid is soluble 
 in water it must be immersed in alcohol, 
 petroleum, or some other liquid of which 
 the specific gravity has been previously 
 ascertained, and the calculation made as 
 before, substituting the sp. gr. of the 
 liquid employed for the sp. gr. of water. 
 When the solid is lighter than water it 
 must, after its weight in air has been 
 taken, be attached to some heavy body 
 sufficient to sink it, a piece of lead, for 
 instance, and the weight of the solid 
 and piece of lead in water and of the piece of lead alone in 
 water ascertained. The weight of the volume of water displaced 
 by the light solid will equal the weight of the light solid in 
 air Wj plus the buoyancy it imparts to the immersed lead, as 
 measured by the difference between the weight of the lead in 
 water w, and the conjoint weight of the lead and light body in 
 water w f . Hence we have the proportion : 
 
 Wt. of water W+ wuf '. wt. of solid W : : sp. gr. of water : sp. gr. of solid ; 
 or the equation : 
 
 Sp. gr. of light solid =- 
 
 * Kelying on this principle, the specific gravities of different liquids 
 may be ascertained by immersing some solid of known weight in each of 
 them, and comparing the losses in weight which it experiences by the 
 upward pressures of the different liquids, equal in each instance to the 
 weight of the bulk of liquid displaced by it. 
 
SPECIFIC GRAVITY. 51 
 
 When the substance to be examined is in the pulverulent state, 
 its specific gravity may be ascertained by means of a sp, gr. flask. 
 A quantity of the powder is introduced into the flask and weighed. 
 It is then thoroughly wetted with water or some other liquid, of 
 which a further quantity is afterwards added, so as to fill up the 
 flask to the mark on its neck ; when the weighing is repeated. 
 The difference between the weight of liquid which the flask 
 ordinarily holds, and the weight of liquid added to fill up the 
 flask after the introduction of the dry powder, gives the weight 
 of the bulk of liquid displaced by the powder, the ratio of which 
 to the weight of the powder gives the specific gravity. 
 
52 ANALYTICAL CHEMISTRY. 
 
 CHAPTER II. 
 ANALYTICAL CHEMISTKY. 
 
 (24.) THE object of this part of the course is to make the student 
 practically acquainted with the chemical properties of such 
 bodies as are of the most importance, and of the most common 
 occurrence. 
 
 Of all chemical compounds, those known as salts will most 
 frequently present themselves to his notice. 
 
 Sulphate of iron and chloride of sodium may be taken as the 
 types of simple salts. The sulphuric acid and chlorine are 
 termed the electro -negative or acid constituents, or, more shortly, 
 the acids ; the iron and sodium the electro-positive or basic con- 
 stituents, or, more shortly, the bases. 
 
 In testing the substances distributed for examination, each of 
 which should contain but one basic and one acid constituent, the 
 student may first of all confine himself to the bases ; subse- 
 quently he must examine both for bases and acids. He will have 
 to pursue the following course of operations : 
 
 I. To examine the dry substance before the blowpipe. 
 (Pars. 25 and 26.) 
 
 II. To make a solution of the substance in water or acid. 
 (Pars. 27 and 28.) 
 
 III. To ascertain to which group the base of his substance 
 belongs. (Pars. 30, 35, and 41,) 
 
 IV. To identify the particular member of the group with 
 which he IB dealing. (Tables I. II. and III.) 
 
BLOWPIPE EXAMINATION. GENERAL EFFECTS. 53 
 
 V. To realise the special reactions described under the head of 
 his particular base. 
 
 VI. To identify the acid constituent of his substance. (Tables 
 IV. and V.) 
 
 VII. To realise the special reactions described under the head 
 of his particular acid. 
 
 As regards V. and VII., the student must remember that the 
 simple discovery of the base and acid of his salt is of much less 
 importance than the thorough verification of all their described 
 properties. 
 
 I. BLOWPIPE EXAMINATION. 
 
 (25.) A small shallow hole having been made on a piece of 
 charcoal, the student should put into it a little of the substance 
 under examination, a piece about the size of a mustard-seed, for 
 instance, or as much powder as will rest on the point of a 
 penknife. He must then heat the substance on its charcoal 
 support before the blowpipe, and notice what effects, if any, 
 are produced. It is often advisable to moisten a pulverulent 
 substance with water before submitting it to the blowpipe flame, 
 so as to make it cohere and remain on the charcoal. The sub- 
 stance may also be heated with advantage in a subliming tube 
 open at both ends ; whereby corroborative, and sometimes even 
 primary, evidence of its composition is obtainable, especially when 
 it happens to be wholly or partly volatile. In this way ammoniacal 
 and sulphurous acid gases may be recognised by their respective 
 smells ; deposits of acid or alkaline water, by their reaction to 
 test-paper; and sublimates of sulphur, arsenic, mercury, and 
 ammonium-salts, by their appearance and behaviour. 
 
 The following are the most important general effects observ- 
 able upon heating a substance on charcoal before the blowpipe. 
 
 AH hydrated salts give off their water of crystallisation, some 
 with intumescence, as borax; others with decrepitation, as 
 gypsum. Many anhydrous salts also, as chloride of sodium, 
 
$4 BLOWPIPE EXAMINATION. 
 
 for instance, decrepitate from the expulsion of water retained 
 mechanically within their crystals. Most hydrated salts, when 
 first heated, fuse in their water of crystallisation, and then solidify, 
 whether or not susceptible of again fusing at a higher tempera- 
 ture, (vide par. 26). 
 
 Most compounds of the heavy metals become darker when 
 heated, either permanently through decomposition, or temporarily 
 through some altered relation to light. Zinc compounds acquire 
 a deep greenish-yellow by the action of heat, and peroxide of 
 tin a pale brownish -yellow. 
 
 Certain metallic compounds, more especially those of silver, 
 lead, and bismuth, are quickly brought to the metallic state 
 when heated on charcoal in the reducing blowpipe flame, (vide 
 par. 26). 
 
 Some substances, whether or not inflammable, leave a black 
 carbonaceous residue, capable of being burnt away by prolonged 
 ignition. This charring indicates the presence of organic matter, 
 an organic acid or base, for instance, either free or in com- 
 bination. 
 
 Many bodies evolve a more or less marked smell when heated. 
 Thus sulphur and many sulphides give off sulphurous anhydride. 
 Tartaric and benzoic acids, and their respective salts, evolve 
 characteristic empyreuinatic odours. The fixed organic bases, 
 and some salts of ammonia and organic bases, give offammoniacal 
 vapour ; while arsenic compounds, when in contact with ignited 
 charcoal, give rise to a peculiar garlic-like smell. 
 
 Sometimes the heated substance volatilises wholly or in 
 great measure, usually with evolution of visible fumes, (vide 
 par. 26). 
 
 In a few cases the red-hot charcoal undergoes a rapid com- 
 bustion where it comes in contact with the heated compound. 
 This deflagration indicates the probable presence of a nitrate or 
 chlorate. 
 
 (26.) As regards their more special behaviour before the 
 blowpipe, metallic compounds may be classified into those which 
 are volatile (a), those which leave a white permanently fusible 
 
SPECIAL REACTIONS. 
 
 55 
 
 residue (/3), those which leave a white , infusible residue (y), 
 those which are reducible to the metallic state (3), and those 
 which give a colouration to the borax bead (e), as shown in the 
 following scheme : 
 
 BLOWPIPE EXAMINATION 
 
 a. Volatile 
 
 j3. White and 
 Fusible 
 
 y. White and 
 Infusible 
 
 8. Keducible 
 
 e. Colour borax 
 bead 
 
 AMMONIUM ^ 
 
 SODIUM 1..* 
 
 ZINC 
 
 SILVER 
 
 CHROMIUM "> 
 
 
 
 
 
 Green 
 
 MERCURY V 
 
 POTASSIUM 
 
 ALUMINUM 
 
 TIN 
 
 
 
 
 
 
 MANGANESE 
 
 Salts J 
 
 Salts 
 
 MAGNESIUM 
 
 
 Amethyst 
 
 
 
 
 LEAD ^ 
 
 
 
 
 1 
 
 
 IRON 
 
 ARSENIC 
 
 CALCIUM 
 
 CALCIUM ( 
 
 BISMUTH 
 
 Yellow-brown 
 
 Oxides 
 
 STRONTIUM 
 
 STRONTIUM 
 
 ANTIMONY 
 
 COBALT 
 
 
 
 
 
 Deep-blue \ 
 
 Sulphides 
 
 BARIUM 
 
 BARIUM 
 
 CADMIUM 
 
 
 
 
 
 
 NICKEL 
 
 
 Chlorides 
 
 Salts 
 
 Give incrus- 
 
 Reddish 
 
 ANTIMONY 
 
 
 
 tations. 
 
 
 
 Colour blow- 
 
 
 
 COPPER 
 
 Teroxide 
 OXALIC ACID 
 
 pipe flame. J 
 
 SILICIC "^ 
 STANNIC 
 
 ZiNCy 
 MERCURY a 
 
 Pale-blue 
 
 In oxidising 
 flame J 
 
 
 
 ANTIMONIC 
 
 
 
 
 
 
 ARSENIC a 
 
 
 
 
 Oxides J 
 
 
 
 
 
 
 COPPER e 
 
 
 a. The ordinary compounds of ammonium and mercury 
 are readily volatile. Phosphate of ammonium, however, leaves 
 a fused residue of phosphoric acid, which requires a strong 
 heat for its dissipation. The oxides and sulphides of arsenic 
 also are readily volatile ; the teroxide of antimony somewhat 
 less so. Oxalic acid melts and effervesces during its disappear- 
 ance without furnishing much incrustation. The compounds of 
 mercury, arsenic, and antimony, and many ammonium- salts, 
 deposit incrustations or sublimates upon the cold part of the 
 charcoal. Similar sublimates are procurable by heating the sub- 
 stance in a sealed or open subliming tube. 
 
 The various bodies which volatilise when heated on charcoal 
 
56 BLOWPIPE EXAMINATION. 
 
 may often be satisfactorily identified by a few rough tests, such 
 as the following : 
 
 Ammonium salts, when warmed with potash, evolve ammonia, 
 recognisable by its odour and alkaline reaction. Mercury 
 salts, save the black and red sulphide, are turned black by 
 sulphide of ammonium. Mixed with a large excess of car- 
 bonate of sodium, and heated in a reduction tube, they afford 
 a sublimate of mercurial globules. The oxides (white) and 
 sulphides (orange or yellow) of arsenic dissolve in sulphide of 
 ammonium to form a yellowish liquid, which on evaporation to 
 dryaess leaves a bright yellow residue. Mixed with soda-flux, 
 and heated in a reduction tube, they furnish sublimed crusts 
 of metallic arsenic. Teroxide of antimony dissolves in sul- 
 phide of ammonium, and the liquid, when evaporated down, 
 leaves a deep orange residue. It is, moreover, easily reducible 
 before the blowpipe (5). Oxalic acid, when moistened with 
 water, manifests a strongly acid reaction, and effervesces with 
 peroxide of manganese. 
 
 /3. The ordinary salts of sodium and potassium fuse at 
 a red heat, many of them into almost watery liquids, which are 
 absorbed by the porous charcoal. During their ignition, the salts 
 of sodium impart a bright yellow, and those of potassium a violet 
 colouration to the blowpipe flame. These colours are best seen by 
 taking up a minute quantity of the salt upon the end of a platinum 
 wire, and heating it at the point of the blowpipe flame. When 
 a potassium salt is contaminated with even a small proportion of 
 any sodium salt, the violet colour of its flame is liable to be 
 concealed by the strong yellow colour which the sodium salt 
 produces. But the proper potassium colour may be readily seen 
 by looking at the flame through a piece of smalt glass, which cuts 
 off the yellow sodium rays. 
 
 Unlike most salts of the alkaline earth-metals, the chlorides of 
 calcium, strontium, and barium are fusible in the blowpipe 
 flame. That of calcium fuses very readily, but the other two 
 chlorides are much less readily fusible than are the majority of 
 sodium and potassium salts. When strongly ignited on fine 
 
SPECIAL KEACTIONS. 57 
 
 platinum wire, chloride of barium imparts to the blowpipe flame 
 a marked apple green, chloride of strontium a deep crimson, and 
 chloride of calcium an orange-red colour. The platinum wire 
 used for testing by the blowpipe flame should be moderately 
 thin, to allow of its being strongly heated. It may be held 
 directly in the fingers, platinum being a bad conductor of heat. 
 Should the end to be used impart any colour to the flame, from 
 contamination either with soda, derived from the perspiration of 
 the fingers, or with the residues of former experiments, it must 
 be alternately dipped in hydrochloric acid, and strongly heated 
 in the blowpipe flame until all colouration ceases to appear. 
 
 The chlorides of the alkaline earth-metals, and most salts 
 of the alkali metals, fuse into colourless transparent liquids, 
 whereby they are distinguished from the fusible compounds of 
 the heavy metals, which yield coloured or opaque beads. More- 
 over, the temporary melting of hydrated salts in their water 
 of crystallisation must not be confounded with the permanent 
 fusion at a red heat which characterises the above-mentioned 
 classes of salts. l .i-:^ 
 
 y. Compounds of zinc, aluminum, and magnesium, with 
 nearly all calcium, strontium, and barium salts, whether 
 or not undergoing a preliminary aqueous fusion, leave after 
 strong ignition a white infusible residue; while the stannic, 
 silicic, and antimonic oxides are from the first infusible. 
 During strong ignition the aluminum residue manifests an in- 
 tense white incandescence, the zinc residue a deep greenish- 
 yellow, and the stannic and antimonic oxides a pale brownish- 
 yellow colour. In any case the white or yellowish-white in- 
 fusible residue may be moistened with solution of nitrate of cobalt, 
 and again strongly heated, whereby characteristic colourations 
 are produced with compounds of zinc, aluminum, and magne- 
 sium, and less definite colourations with the remainder. The 
 zinc residue acquhes a fine green, the aluminum residue a 
 bright blue, and the magnesium residue a very faint pink 
 colour. When the residue is pulverulent, it may be moistened 
 with sulphuric acid and re-ignited before being heated with 
 
58 BLOWPIPE EXAMINATION. 
 
 nitrate of cobalt, more especially in order to bring out the 
 magnesian colour. It must be borne in mind that nitrate of 
 cobalt also imparts a blue colour to many fused phosphates, 
 borates, and silicates, which, however cannot be confounded with, 
 the blue given to an infusible aluminum residue. 
 
 The other infusible residues receive a less distinct colour by 
 ignition with nitrate of cobalt, those of calcium and strontium 
 becoming grey, that of barium reddish-grey, those of the stannic 
 and silicic anhydrides bluish-grey, and that of antimony greenish- 
 grey ; but these substances may be further distinguished by other 
 means, calcium, strontium, and barium by their tinting the 
 blowpipe flame, antimony and tin by their reducibility, the 
 former with, and the latter without, any incrustation (3), and 
 silica by its behaviour with fused carbonate of sodium. In order 
 to test an infusible compound for calcium, strontium, or 
 barium, a small quantity, taken up on the end of a fine pla- 
 tinum wire, should be moistened with hydrochloric acid, and 
 ignited for some time in the hottest part of the blowpipe flame, 
 when the characteristic colour due to the volatilisation of each 
 metal will be clearly brought out, save indeed with their respec- 
 tive sulphates. Silica may be identified by making a small 
 loop at the end of a platinum wire, and fusing upon it a minute 
 quantity of carbonate of sodium, which will thus form a white 
 bead, transparent when hot, opaque when cold : in this fused 
 bead, silica, when strongly heated, will dissolve with effer- 
 vescence, and, if in sufficient quantity, render it permanently 
 transparent. 
 
 & Compounds of silver, tin, lead, bismuth, antimony, 
 and cadmium, often assume the metallic state, or produce 
 characteristic incrustations, when merely heated on charcoal in 
 the reducing blowpipe flame ; but their behaviour when heated 
 with a flux of carbonate of sodium, mixed or not with cyanide of 
 potassium, is more satisfactory. Carbonate of sodium alone will 
 answer the purpose, but the addition thereto of one-fourth of its 
 weight of cyanide of potassium often assists the reduction very 
 greatly, and is not in any case disadvantageous, save when the 
 
SPECIAL REACTIONS. 59 
 
 specimen itself deflagrates upon charcoal from the presence of a 
 nitrate or chlorate, in which case a slight explosion results from 
 the reaction of the cyanide and oxisalt. 
 
 The specimen having been intimately mixed with five or six 
 times its bulk of flux, a small portion of the resulting powder, 
 sometimes moistened with water so as to make it cohere, is heated 
 strongly on charcoal. The mixed mass should fuse readily 
 before the blowpipe, so that any minute globules of reduced 
 metal may run together. If not readily fusible, a fresh mixture 
 must be taken with a larger proportion of flux. When the 
 reduced metal volatilises at the temperature employed, its vapour 
 becomes oxidised outside the flame, and is deposited upon the 
 charcoal as a more or less abundant, white or coloured, incrusta- 
 tion. Silver gives no incrustation, and tin scarcely any : lead 
 gives a yellow, and bismuth a brownish-yellow, incrustation; 
 while antimony gives an abundant easily volatile bluish-white, 
 and cadmium a comparatively fixed brown-red incrustation. 
 Metallic antimony vaporises rapidly ; while cadmium is so vola- 
 tile that its reduction and vaporisation are simultaneous, where- 
 fore no globule, but only an incrustation, is producible with it. 
 Zinc compounds, heated with reducing flux, behave in this 
 respect like cadmium, furnishing no globule of metal, but only 
 an incrustation, which is yellow when hot, white when cold ; but 
 zinc will have been previously detected by its reaction with 
 nitrate of cobalt (y). Keduced arsenic and mercury are so 
 volatile that they can only be obtained in the form of sublimates 
 by performing the reduction in tubes as already described (a). 
 
 The different metals usually identified by their reduction on 
 charcoal, exhibit the following characters: Silver yields a 
 bead of white, moderately hard and malleable metal, with no 
 incrustation. Tin, which is less easily reducible, yields a bead 
 of white malleable metal, softer than silver, with very slight, if 
 any, incrustation. Lead yields a bead of soft bluish-white 
 metal, with yellow incrustation; bismuth, a bead of brittle 
 yellowish -white metal, with brownish -yellow incrustation ; anti- 
 mony, a bead of brittle bluish-white metal, with an abundant 
 
6o 
 
 BLOWPIPE EXAMINATION. 
 
 bluish-white incrustation ; and cadmium, no metallic bead, but 
 only a reddish-brown incrustation. 
 
 In addition, copper, iron, nickel, and cobalt are reducible, 
 though they do not afford incrustations, and are not easily 
 obtainable in the form of beads. But on crushing the fused 
 mass in a mortar, and washing away the lighter portions, copper 
 may often be recognised in the form of red spangles, and iron, 
 nickel, and cobalt as heavy powders affected by the magnet. 
 
 e. Compounds of those metals which tinge the borax bead 
 usually leave dark-coloured infusible residues when heated alone 
 on charcoal. In testing by the borax bead, a piece of platinum 
 wire is bent into a single or double loop, as shown of the actual 
 size in fig. 35, the loop dipped into powdered 
 Fig- 35- borax, and the adhering borax heated to red- 
 
 ness, when it first undergoes a highly charac- 
 teristic intumescence, and afterwards, when 
 more strongly heated, sinks into a colourless 
 transparent bead. To this bead is then at- 
 tached a minute quantity of the substance 
 under examination, and the whole strongly 
 heated in the blowpipe flame, when in some 
 cases the fused bead dissolves the specimen, 
 and thereby acquires a more or less definite 
 colour, the depth of which may be increased 
 by adding more of the specimen and again 
 heating strongly. 
 
 The metals iron and copper, which form 
 two classes of salts, also form beads of two 
 colours. Thus in the oxidising flame we 
 have a blue cnpric and a yellow-brown ferric bead, while in the 
 reducing flame we hare a cuprous bead of an almost colourless 
 or opaque reddish aspect, and a ferrous bead of a sea-green 
 colour. The chromium bead has an emerald green, and the 
 cobalt bead a sapphire blue colour. Manganese, when free 
 from iron, imparts an amethystine tint, and nickel a deep sherry 
 hue, which becomes amethystine when the bead is heated with a 
 
SOLUTION AND PRECIPITATION. 6 1 
 
 fragment of nitre. The borax may be replaced by microcosmic 
 salt, or even by ordinary glass. In these several reagents we 
 have, after ignition, an excess of melted boric, phosphoric, or 
 silicic anhydride, which at the temperature of the blowpipe 
 flame combines with the various metallic oxides to form coloured 
 fusible salts. -.--itt 
 
 II. SOLUTION AND PRECIPITATION. 
 
 (27.) Having made his examination in the dry way, by means 
 of the blowpipe, the student must next bring his substance, by 
 some means or other, into a state of solution, so that he may 
 submit it to the action of liquid reagents. As a general rule, 
 the substance to be dissolved should be in a finely divided state. 
 This is particularly necessary in the case of bodies which are 
 with difficulty soluble, such as many native oxides, sulphides, 
 &c. Any substance having a decided colour, a hard structure, 
 and an opaque aspect, whether earthy or lustrous, ought always 
 to be pulverised very finely before being treated with solvents. 
 The solution of the body under examination should be effected 
 by preference in water ; bat, if insoluble in water, it may be 
 acted upon with hydrochloric acid, or with nitro-muriatic acid, 
 or with nitric acid. 
 
 A small portion of the powdered substance is to be placed in a 
 test-tube, a moderate quantity of water* added, the whole 
 agitated, and heated over a spirit or gas-flame. While heating, 
 the tube should receive an occasional jerk, to facilitate mixture 
 and avoid the sudden escape of vapour. If the substance, by 
 this treatment, is obviously dissolved, the clear solution, filtered 
 if necessary from any insoluble portions, can be submitted at 
 once to the action of reagents. If the substance, however, is 
 not obviously dissolved, a few drops of the liquid may be filtered 
 on to a glass slip and gently evaporated to dryness. Should any 
 
 * By water is always meant pure or distilled water ; but clean rain water 
 may sometimes be employed as a substitute. 
 
62 SOLUTION AND PRECIPITATION. 
 
 definite amount of residue remain upon the glass, the whole mix* 
 ture must be thrown upon a filter, and the tests applied to the 
 clear nitrate. There are many substances which, unless taken in 
 very small quantity, do not disappear perceptibly when boiled in 
 water, but yet are sufficiently soluble to afford an aqueous solu- 
 tion that can be successfully tested. Should a mere trace of 
 residue, or none at all, be left upon the glass slip, as much of the 
 water as possible is to be poured away from the insoluble sub- 
 stance, and replaced little by little with hydrochloric acid, 
 warming between each addition. Should any obvious action 
 occur, more hydrochloric acid may be added, if necessary, and 
 the whole heated for some time until an available solution is 
 formed. Should there be no obvious action, nitric acid must 
 be added in the proportion of about one-fourth of the hydro- 
 chloric acid previously used, and heat again applied. By one or 
 other of these means a solution will generally be effected. There 
 are, indeed, a few substances which dissolve in nitric, but neither 
 in hydrochloric nor in nitre-hydrochloric acid. There are also 
 some substances which are quite insoluble in any ordinary men- 
 struum ; the consideration of these, however, is deferred for the 
 present. The solution of the substance, whether in water or 
 acid, to which no reagent has been added, is called in the tables 
 and elsewhere the original solution. The freshly-made acid solu- 
 tion should generally be diluted somewhat freely with water, and 
 filtered if necessary. The acidity, neutrality, or alkalinity of the 
 aqueous solution should be ascertained by means of test-paper. 
 
 (28.) Different reagents are next to be added to the original 
 solution in the order and manner described in paragraphs 30, 35, 
 and 41, and in the Tables I. II. III. and V. These reagents 
 produce in the solution certain effects, which are characteristic of 
 the various substances dissolved. The effect most usually pro- 
 duced by a liquid reagent is to cause a precipitate or solid deposit 
 of some insoluble compound of the substance sought for. Hence 
 the formation or non-formation of a particular precipitate usually 
 proves the presence or absence of a particular base or acid in the 
 solution under examination. Precipitates differ much in their 
 
ADDITION OF REAGENTS. 63 
 
 colour, consistency, rapidity of formation, and solubility in 
 different liquids, whence the student must make himself familiar 
 with their various aspects and habitudes. As regards aspect, he 
 must notice whether a precipitate is dense, crystalline, clotty, 
 gelatinous, opaque, transparent, coloured or colourless, &c. As 
 regards habitude, he will find that crystalline precipitates, unless 
 thrown down from concentrated solutions, do not usually appear 
 at once, but only after some little time. Their immediate for- 
 mation, however, may be often determined by rubbing the liquid 
 against the inside of the containing vessel with a glass rod. 
 Again, many precipitates are characterised by their solubility in 
 an excess of the precipitant, or in some other reagent. 
 
 Eeagents and solvents should always be added gradually, 
 except when special direction is given to the contrary. This 
 rule is of great importance, and applies equally to the formation 
 and solution of precipitates; in the latter case, the mixture 
 should be agitated between each addition of the solvent. Many 
 characteristic effects are occasionally overlooked through a neglect 
 of this rule. The student must also bear in mind, when directed 
 to employ an excess of any particular reagent or solvent, that 
 every minute quantity more than sufficient to produce the desired 
 effect is an excess. 
 
 In the tables, the word dissolved placed at the head of a column 
 signifies either that the substances written under it have not been 
 precipitated at all, or that, having been precipitated, they are now 
 redissolved by an excess of the reagent, in any case that they 
 remain in solution. 
 
6 4 
 
 BASIC GROUPS. 
 
 EXAMINATION FOR BASIC GROUPS. 
 
 (29.) The bases are divided into three principal groups, as 
 follows :' 
 
 I. 
 
 TIN 
 
 ARSENIC 
 ANTIMONY 
 BISMUTH 
 MERCURY 
 LEAD 
 SILVER 
 COPPER 
 CADMIUM 
 
 II. 
 
 NICKEL 
 
 COBALT 
 
 MANGANESE 
 
 IRON 
 
 CHROMIUM 
 
 ALUMINUM 
 
 ZINC 
 
 III. 
 
 BARIUM 
 STRONTIUM 
 CALCIUM 
 MAGNESIUM 
 POTASSIUM 
 SODIUM 
 AMMONIUM 
 
 The first object of the student must be to ascertain the group 
 to which the base of the salt under his examination belongs. 
 
 The members of the first group are precipitated from their acid 
 solutions by sulpJiydric acid. The members of the second group 
 are not precipitated from their acid solutions by sulphydric 
 acid, but are precipitated from their neutral solutions by sulphide 
 of ammonium. The members of the third group are precipitated 
 neither by sulphydric acid nor by sulphide of ammonium. 
 
 Having ascertained to which particular group the base of his 
 salt belongs, he will proceed according to the directions of the 
 table pertaining to that group, in order to identify the individual 
 member thereof with which he is dealing. Should, therefore, 
 sulphydric acid produce a precipitate, in an acidified solu- 
 tion, the student will proceed according to Table I. Should it 
 produce no obvious precipitate, he will render the solution nearly 
 neutral by ammonia, and then add sulphide of ammonium. Should 
 this reagent produce a precipitate he will proceed according to 
 Table II. Should no precipitate be produced by either of the 
 above reagents, he will proceed according to Table III. 
 
EXAMINATION FOR BASES OF GROUP I. 65 
 
 III. EXAMINATION FOR BASES OF GROUP I. 
 
 (30.) To recognise the presence of some member of this group 
 by means of sulphuretted hydrogen or sulphydric acid, the 
 solution to be tested should be moderately acid. In solutions 
 which are too acid, sulphuretted hydrogen may not give any 
 precipitate, despite the presence of a member of the group ; and 
 in solutions which are neutral or alkaline, it may give a precipi- 
 tate even in the absence of every member of the group ; inasmuch 
 as sulphuretted hydrogen precipitates some members of the second 
 group from their neutral or alkaline solutions. 
 
 AQUEOUS SOLUTIONS. These must consequently be acidulated 
 before being treated with sulphuretted hydrogen. A few drops 
 of either nitric or hydrochloric acid will answer the purpose, but 
 the use of the latter acid is generally preferable. The addition 
 of hydrochloric acid, however, sometimes produces a permanent 
 white precipitate, in which case the presence of silver, or lead, 
 or mercury is indicated. Solutions of silver invariably yield a 
 precipitate with hydrochloric acid, solutions of lead and mercury 
 only under certain conditions. But in the event of hydrochloric 
 acid producing a precipitate, it will suffice for the student to 
 distinguish between the above three metals, without following 
 out the directions of the general table for the group (page 68.) 
 
 The SILVER precipitate is soluble in excess of ammonia. 
 
 The MERCURY precipitate is turned black by excess of ammonia. 
 
 The LEAD precipitate is unaffected by ammonia, but is soluble 
 in boiling water; and, on cooling, is deposited therefrom in 
 crystalline needles. 
 
 These three precipitates are blackened by sulphuretted hydro- 
 gen, and are not produced by nitric acid, properties distinguishing 
 them from all other precipitates which hydrochloric acid occasion- 
 ally produces. 
 
 The acidification of a solution of tartar-emetic, with either 
 hydrochloric or nitric acid, is attended with the production of a 
 white turbidity, which, however, . disappears on gently warming 
 
66 EXAMINATION FOR BASIC GROUPS. 
 
 the liquid with a little more acid. Moreover, the acidification, 
 by either hydrochloric or nitric acid, of various alkaline solutions, 
 not unfrequently gives rise to whitish precipitates, which some- 
 times disappear in an excess of acid, and, at other times, remain. 
 Among those which are permanent, the principal are sulphur, 
 from the decomposition of an alkaline persulphide, &c. ; silica, 
 from the decomposition of an alkaline silicate; and boric acid 
 from the decomposition of an alkaline borate ; but this last pre- 
 cipitate is readily soluble in boiling water. 
 
 SOLUTIONS IN ACID. When the solution of the original sub- 
 stance has been made in an acid, it is important to get rid of any 
 great excess of acid ; or, at any rate, to reduce its activity. 
 
 a. By mere dilution with water. It is generally ad- 
 visable to dilute somewhat considerably solutions which have 
 been made by means of an acid. 
 
 /3. By evaporation. The solution may be evaporated 
 down to a small bulk, and then be diluted with water. This 
 process is especially necessary when the solution has been made 
 with nitre-muriatic acid. 
 
 y. By neutralisation with ammonia. When a large 
 quantity of acid has been employed to effect the solution of a 
 substance, it is occasionally useful to neutralise some of the excess 
 of acid with ammonia. 
 
 The acid solution of the substance, whether or not evaporated 
 down, or partly neutralised, should, after dilution with water, 
 be perfectly bright. If not bright, it must be rendered so by 
 nitration. 
 
 The addition of water to an acid solution sometimes produces 
 an obvious white precipitate, in which case the dilution should be 
 very slight or be dispensed with altogether. The formation of a 
 white precipitate on the addition of water indicates the presence 
 of ANTIMONY or BISMUTH. The precipitate produced in solutions 
 of the former metal is dissolved by tartaric acid and turned of an 
 orange colour by sulphuretted hydrogen ; while that produced in 
 solutions of the latter metal is not dissolved by tartaric acid, and 
 is turned black by sulphuretted hydrogen. Water does not 
 
PRECIPITATION OF FIRST GROUP. 67 
 
 invariably cause a precipitate in solutions containing antimony 
 or bismuth, but in the event of a precipitate being produced, it 
 will suffice to distinguish between the above two metals without 
 proceeding according to the general table for the group (page 68). 
 
 The acidified solution of the substance in water, or the diluted 
 solution of the substance in acid, is to be treated with sulphuret- 
 ted hydrogen. It may be sufficient to add sulphuretted hydrogen 
 water to the solution, but it is always preferable to use a current 
 of the gas itself. The production of a coloured precipitate is 
 indicative of the presence of some member of the first group ; in 
 which case, the gas should be passed into the liquid until it smells 
 permanently even after agitation. A little water should next be 
 added, and the whole well shaken or stirred, to promote the 
 subsequent subsidence of the precipitate, which, on setting the 
 tube aside for a few minutes, will soon collect at the bottom. 
 The supernatant liquid may then be poured off, and the pre- 
 cipitate treated according to the directions of Table I. /3. 
 
 Sulphuretted hydrogen, when added to certain solutions, not 
 containing any member of the first group, sometimes produces a 
 more or less considerable yellowish -white turbidity, due to a 
 liberation of finely divided sulphur, effected by some per-oxidated 
 or per-chlorinetted compound, thus : 
 
 H a S -f C1 3 = aHCl + S. 
 
 In yellow solutions, this white turbidity often appears decidedly 
 yellow, from the colour of the liquid through which it is seen. 
 "When, simultaneously with the liberation of sulphur, a brownish- 
 yellow solution becomes paler or colourless, the presence of a 
 per -salt of iron may be generally inferred; 'but when it be- 
 comes of a marked green colour the presence of chromic acid 
 is indicated. 
 
68 
 
 EXAMINATION FOR BASES OF GROUP I. 
 
 TABLE I. 
 
 (3 1 .) Examination of a solution containing some one member 
 of the first group ; namely, TIN, ARSENIC, ANTIMONY, BISMUTH, 
 SILVER, MERCURY, LEAD, COPPER, or CADMIUM; all of which 
 metals are precipitated from their acid solutions by Sulphuretted 
 hydrogen gas (a), or its solution in water. 
 
 ft. Having treated the not too acid solution of the substance with excess 
 of sulphuretted hydrogen, and poured off or filtered off the supernatant 
 liquid, warm the precipitate with some solution of Sulphide of Ammonium. 
 
 If the precipitated sulphide be of 
 
 TIN (protosalf), brown, 
 TIN (persalt), yellow, 
 ARSENIC, yellow, 
 ANTIMONY, orange, 
 
 it will dissolve entirely, and on ad- 
 dition of Hydrochloric Acid to the 
 resulting solution will be repre- 
 cipitated. 
 
 TIN, always yellow 
 ARSENIC, yellow 
 ANTIMONY, orange 
 
 7. Boil the precipitate thrown 
 down by sulphuretted hydrogen 
 with strong Hydrochloric Acid. 
 
 Undissolved 
 ARSENIC 
 
 Dissolved 
 TIN 
 ANTIMONY. 
 
 If the precipitated sulphide be of 
 BISMUTH 
 SILVER 
 
 MERCURY ^-blacker dark brown,, 
 LEAD 
 COPPER 
 
 CADMIUM, yellow, 
 it will remain undissolved. 
 
 8. Add Potash to a portion of the 
 original solution : in any case a 
 precipitate will be produced charac- 
 terised as follows : 
 
 LEAD, white, soluble in excess of the 
 reagent, unaffected by ammonia. 
 
 C MEECURY (protosalf), black, un- 
 affected by ammonia. 
 
 MERCURY (persalf), yellow, turned 
 white by ammonia. 
 
 BISMUTH, white, unaffected by 
 ammonia. 
 
 COPPER, blue ^ 
 
 CADMIUM, white L soluble in am - 
 
 monia, 
 SILVER, brown J 
 
 ^ Insoluble in excess of potash. 
 
EXAMINATION FOR BASES OF GROUP I. 69 
 
 (32.) a. SulpJiydric acid, or sulphuretted hydrogen, reacts 
 with the salts belonging to this group to form metallic sulphide?, 
 as shown by the following typical equations, in which M stands 
 for an atom of metal : 
 
 2MC1 + H Z S = aHCl + M 2 S 
 2MC1 3 + 3 H a S = 6HC1 + 
 
 In this manner the salts of perissad metals, as silver Ag', arsenic 
 As'", antimony Sb'", and bismuth Bi' x , are decomposed by sulphur- 
 etted hydrogen. 
 
 MCI, + H 4 S = 2HC1 + M'S 
 MC1 4 + 2H a S = 4HC1 + M"g a . 
 
 In this manner the salts of artiad metals, as lead Pb", mercury 
 Hg", copper Cu", cadmium Cd", tin (stannosum) Sn", and tin (stanni- 
 cum) Sn"" are decomposed by sulphuretted hydrogen. 
 
 The sulphides thus produced differ much from one another as 
 regards their solubility in mineral acids. They are all completely 
 dissolved by nitro-muriatic acid; except that of silver, which 
 is converted into insoluble chloride of silver ; and that of lead, 
 which is converted partly into the sparingly soluble chloride, 
 partly into the insoluble sulphate of lead, owing to an oxidation 
 of its constituent sulphur. 
 
 Hot nitric acid dissolves the sulphides of arsenic, bismuth, 
 silver, copper, and cadmium, but has no appreciable action on the 
 sulphides of mercury. It converts the sulphides of tin and anti- 
 mony into their insoluble oxides or anhydrides, SnOg and Sb a 4 
 respectively. When slightly diluted, it dissolves sulphide of lead 
 completely, but otherwise it converts a portion of it into inso- 
 luble sulphate of lead. The action of nitric acid upon the sul- 
 phides is generally attended with a separation of sulphur, which, 
 on boiling, gradually assumes the form of melted globules. 
 
 Strong hydrochloric acid at a boiling temperature has no 
 action on the sulphides of arsenic and mercury. It converts the 
 sulphides of silver and lead into their insoluble or sparingly 
 
70 EXAMINATION FOR BASES OF GROUP I. 
 
 soluble chlorides, and dissolves the remaining sulphides of the 
 group with greater or less facility. 
 
 (33.) /3. The disulphide of tin, and the trisulphides of arsenic 
 and antimony, unite with the sulphides of alkali-metal to form 
 soluble sulphur-salts corresponding to the well-known oxygen 
 salts, thus : 
 
 Ammonium sulpho-salts. 
 (NH 4 ) a S.SnS, = (NH 4 ) 3 SnS 3 
 
 3 (NH 4 ) a S.Sb a S 3 = 2(NH 4 ) 3 SbS 3 . 
 
 Hence these sulphides are distinguished from the remainder 
 by their solubility in sulphide of ammonium* Protosulphide of 
 tin is not soluble in pure colourless sulphide or sulphydrate 
 of ammonium ; but it is soluble in the ordinary yellow solution 
 of the persulphide, whereby it becomes converted into the above- 
 described compound of disulphide of tin, thus : 
 
 (NH 4 ) a S a + &S = (NH 4 ) a S.SnS a or (NH 4 ) a SnS 3 . 
 
 On the addition of hydrochloric acid to any of these sulpho- 
 salts, they are decomposed with reprecipitation of their respective 
 sulphides, thus: 
 
 (NH 4 ) a S.SnS a + aHCl = H a S + SnS a + 2NH 4 C1 
 3(NH 4 ) a S.As a S 3 + 6HC1 = sH,S + As a S 3 + 6NH 4 CL 
 
 It is advisable not to dissolve the sulphides of this sub-section 
 in an unnecessarily large quantity of yellow sulphide of am- 
 monium, lest the subsequent addition of hydrochloric acid should 
 separate so great a quantity of whitish sulphur as to conceal the 
 colour of the reprecipitated sulphides. 
 
 y. Sulphide of arsenic is distinguishable from the sulphides of 
 tin and antimony by its insolubility even in boiling hydrochloric 
 acid ; and by its solubility in a warm solution of sesquicarbonate 
 of ammonia. 
 
 * Sulphide of copper is quite insoluble in the sulphides of sodium and 
 potassium ; but is slightly soluble in sulphide of ammonium, especially 
 when it contains, as it usually does, some free ammonia. 
 
SULPHIDES SOLUBLE IN SULPHIDE OF AMMONIUM. JI 
 
 Sulphide of antimony and persulphide of tin are distinguishable 
 from one another by their difference in colour. When pure they 
 dissolve completely in hydrochloric acid ; but as usually obtained 
 they often contain excess of sulphur, which remains undissolved. 
 Upon evaporating down their hydrochloric acid solutions to a 
 small bulk, stannic and antimonious chlorides are obtained respect- 
 ively. The former chloride does not have its transparency affected 
 by dilution, neither does the diluted liquid yield any deposit upon 
 a surface of metallic tin : and again, an acid solution of chloride 
 of tin, in which a small fragment of zinc has been dissolved, gives 
 with corrosive sublimate a white precipitate of calomel, gradually 
 becoming grey from its conversion into metallic mercury (vide 
 par. 34). 
 
 The latter chloride is generally rendered opaque by diluting 
 its solution, which again becomes clear on the addition of tartaric 
 acid ; while the diluted liquid yields an abundant black deposit of 
 pulverulent antimony upon a surface of metallic tin. Moreover, 
 chloride of antimony reacts satisfactorily when examined by 
 Marsh's or Reinsch's process. 
 
 Solid compounds of arsenic are most readily recognised by the 
 reduction test (vide par. 66). 
 
 (34.) S. Potash reacts with the salts belonging to the second 
 section of this group, to precipitate the hydrated oxides of the 
 respective metals, thus : 
 
 aAgCl + aKHO = zKCl + Ag a O . H 2 
 2Bi'Cl 3 + 6KHO = 6KC1 + BC0 3 .3H a O. 
 
 The hydrated oxides of mercury, lead, copper, and cadmium are 
 produced according to the following general equation : 
 
 M'bl a + 2KHO = zKCl + MO.H^O. 
 
 Hydrate of lead is soluble in excess of potash ; the hydrates of 
 silver, copper and cadmium are soluble in excess of ammonia; 
 while those of bismuth and mercury are insoluble in either reagent. 
 Independently of their behaviour with sulphuretted hydrogen and 
 
72 EXAMINATION FOR BASES OF GROUP I. 
 
 caustic alkalis, the metals of this sub-section of the first group are 
 characterised by the following reactions. 
 
 Bismuth solutions, unless too acid, when they must first be 
 evaporated down, yield an opaque white precipitate on the 
 addition of water, due to the formation of some insoluble basic 
 salt, thus : 
 
 BiCl 3 + H a O = aHCl + BfOCl 
 
 Bi(N0 3 ) 3 + H a O = aHN0 3 + BiO.N0 3 or 4(Bi 4 3 .N a 5 ). 
 
 These basic salts of bismuth are insoluble in tartaric acid, and 
 are blackened by sulphuretted hydrogen or sulphide of ammo- 
 nium. 
 
 Mercury solutions yield with protochloride of tin a white 
 precipitate becoming grey spontaneously, or more rapidly on the 
 application of heat. The white precipitate is calomel, which is 
 formed from mercurous salts by double decomposition, thus : 
 
 + SnCl a = aHgCl + Sn(N0 3 ) a or SnO.N,0 5 . 
 But it is formed from mercuric salts by reduction, thus : 
 2HgCl a + SnCL, "" = zHgCl + SnCl 4 
 
 The grey deposit consists of finely divided metallic mercury, 
 produced by an abstraction of chlorine from the calomel first 
 precipitated : 
 
 zHgCl + Sn'Cl-5 = Hg a + SnCl 4 . 
 
 This grey deposit, when boiled with hydrochloric acid, acquires 
 the characteristic appearance of globules of mercury. 
 
 Lead solutions yield with sulphuric acid, or soluble sulphates, 
 a white precipitate of sulphate of lead, insoluble in cold nitric or 
 hydrochloric acid : 
 
 + H,S0 4 = 2HN0 3 + bS0 4 or PbO.S0 3 . 
 The precipitate is distinguished from the similar precipitate 
 
SULPHIDES INSOLUBLE IN SULPHIDE OF AMMONIUM. 73 
 
 produced with barium- and strontium- salts, by its solubility in 
 excess of potash, by its solubility in boiling hydrochloric acid, 
 and by its becoming blackened by sulphuretted hydrogen or sul- 
 phide of ammonium. 
 
 Silver solutions yield with hydrochloric acid or soluble 
 chlorides a white clotty precipitate of chloride of silver : 
 
 AgN0 3 + HC1 = HN0 3 + AgCl. 
 
 The precipitate is soluble in ammonia, but insoluble in the 
 strongest nitric acid, even when boiling. It is turned of a slate- 
 purple colour by exposure to light. 
 
 Copper solutions, even when very dilute, give with ferrocya- 
 nide of potassium a chocolate-red precipitate of ferrocyanide of 
 copper, or of ferrocyanide of copper and potassium, thus : 
 
 2 CuS0 4 + K 4 FeCy 6 = aK a S0 4 + Cu a FeCy 6 . 
 
 The precipitate is turned of a pale blue colour by potash, and 
 is then readily soluble in ammonia, forming a deep purple coloured 
 liquid, by which properties it is distinguished from the similarly 
 coloured ferrocyanide of uranium. 
 
 Cadmium solutions are specially recognised by the bright 
 yellow colour and insolubility in sulphide of ammonium, of the 
 precipitated sulphide of cadmium CdS, produced by sulphuretted 
 hydrogen or sulphide of ammonium. Of all the sulphides of the 
 first group of metals, sulphide of cadmium is the one most readily 
 soluble in acids. Cadmium-salts, moreover, are readily identified 
 by their behaviour before the blowpipe. 
 
 IV. EXAMINATION FOB BASES OF GROUP II. 
 
 (35.) The members of this group are precipitated by sulphide 
 or sulphydrate of ammonium, but are not precipitated from their 
 acidified solutions by sulphuretted hydrogen. Inasmuch as sul- 
 phide of ammonium also precipitates most of the metals of the 
 first group, their absence must be ascertained by the non-produc- 
 
74 EXAMINATION FOR BASES OF GROUP II. 
 
 tion of a precipitate with sulphuretted hydrogen, before the 
 reaction with sulphide of ammonium can be depended on as a 
 general test for members of the second group. 
 
 The solution to be tested with sulphide of ammonium should 
 be nearly neutral, but it may be slightly alkaline, or slightly 
 acid without disadvantage. It must not, however, be decidedly 
 acid ; for if so, there may not only be no precipitate produced 
 when some member of the group is present, but, owing to a 
 customary impurity in the reagent, there may even be a preci- 
 pitate produced when every member of the group is absent. 
 This last occurrence is consequent upon a deposition of sulphur 
 from the mutual decomposition of the acid solution and the 
 reagent, quite irrespective of the presence of any metal. Pure 
 colourless sulphide or sulphydrate of ammonium, indeed, is not 
 precipitated by mere acid solutions ; but the yellow persulphide 
 of ammonium, into which it becomes gradually converted, is 
 decomposed by all acid liquids with precipitation of sulphur, 
 thus : 
 
 aHCl + (NH 4 ) 3 S a = aNH 4 Cl + H a S + S. 
 
 The aqueous solution of a salt may be examined for members of 
 the second group, by adding sulphide of ammonium at once ; but 
 a solution of the salt in acid must be rendered neutral, or nearly 
 neutral, with ammonia before applying the test. The addition of 
 even an excess of ammonia to the acid liquid is no disadvantage. 
 It will sometimes, indeed, produce a precipitate, but the formation 
 of a precipitate by ammonia, equally with the formation of a 
 precipitate by sulphide of ammonium, indicates the presence of 
 a member of the second group ; though the non-production of a 
 precipitate by ammonia does not prove the absence of all mem- 
 bers of the group. The precipitate produced by ammonia 
 generally differs in its character, and frequently in its appearance, 
 from that produced by sulphide of ammonium, but the formation 
 of a precipitate by ammonia will not interfere with the action of 
 the more characteristic reagent for the group. 
 
PRECIPITATION OF SECOND GROUP. 75 
 
 The acidulous solution of the substance which has been tested 
 with sulphuretted hydrogen, but which has not yielded any pre- 
 cipitate therewith, may be examined for members of the second 
 group by treatment with ammonia. In this case, one portion of 
 the ammonia neutralises the excess of acid, while another portion 
 combines with the sulphuretted hydrogen to form sulphide or 
 sulphydrate of ammonium, which serves to precipitate any mem- 
 ber of the group, thus : 
 
 H a S + 2NH 3 = (NH 4 ) a S. 
 
 There are certain salts of barium, strontium, calcium, and 
 magnesium which do not dissolve in water, but which are readily 
 soluble in dilute mineral acids nitric or hydrochloric, for in- 
 stance without, at the same time, undergoing any obvious 
 decomposition. Hence, when such an acid solution is neutralised 
 by ammonia, or by sulphide of ammonium, the salts are repreci- 
 pitated in their original condition ; so that, although the alkaline 
 earths strictly belong to the third group, they are occasionally 
 precipitated along with the proper members of the second. These 
 salts are principally the fluoride of calcium the oxalates 
 of calcium, strontium, and barium and the phosphates 
 of magnesium, calcium, strontium, and barium. la 
 Table II. they are referred to under the general term of earthy 
 salts ; and the mode of distinguishing them from one another is 
 described in par. 59. 
 
7 6 
 
 EXAMINATION FOR BASES OF GROUP II. 
 
 TABLE II. 
 
 (36.) Examination of a solution containing some one member 
 of the second group of bases ; namely, NICKEL, COBALT, MANGA- 
 NESE, IRON, CHROMIUM, ALUMINUM, or ZINC ; all of which bodies 
 are precipitated by Sulphide of Ammonium (a), from their neutral, 
 or nearly neutral, solutions.* 
 
 )8. Add gradually a considerable excess of aqueous Potash to a portion of 
 the original solution. In any case a precipitate will be formed, which may 
 either remain or be redissolved. 
 
 Undissolved 
 NICKEL, pale green. 
 COBALT, pale blue. 
 MANGANESE, white, becoming brown. 
 IRON, olive-green, black, or red. 
 EARTHY SALTS, white. 
 
 7. Add to a fresh portion of the 
 original solution, some Chloride of 
 ammonium and an excess of Am- 
 
 Dissolved 
 CHROME, green. 
 ALUMINUM, white. 
 ZINC, white. 
 
 8. Boil the potash solution for 
 some time. 
 
 Precipitated 
 
 Dissolved 
 
 X" 
 
 Precipitated 
 
 ~~\ 
 
 Dissolved 
 
 IRON, red 
 
 NICKEL, blue. 
 
 CHROME, 
 
 ALUMINUM. 
 
 EARTHY SALTS, 
 
 COBALT, brownish 
 
 green 
 
 ZINC. 
 
 white. 
 
 pink. 
 
 
 
 
 MANGANESE, co- 
 
 
 To the potash solution 
 
 
 lourless, speedily 
 becoming brown 
 and turbid. 
 
 
 ^ e. Add 
 a few drops 
 of Sulphide 
 
 C Add~ 
 excess of 
 Chloride of 
 
 
 
 
 of Ammo- 
 
 Ammonium. 
 
 
 
 
 nium. 
 
 
 
 
 
 Precipitated 
 
 Precipitated 
 
 
 
 
 ZINC. 
 
 ALUMINUM. 
 
 * To work successfully, the student must supplement the brief directions 
 of the different tables, and more especially of this table, by the explanations 
 and limitations of the succeeding letterpress. 
 
PRECIPITATION BY SULPHIDE OF AMMONIUM. 77 
 
 (37.) a. Sulphide of ammonium reacts with salts pertaining to 
 this group, to form precipitates of various characters and aspects. 
 The precipitate is white in solutions of zinc, aluminum, and the 
 earthy salts; black in solutions of iron, nickel, and cobalt; 
 greenish in solutions of chrome ; and buff- coloured in those of 
 manganese. The student must not, however, attach too much 
 importance to the colour of a precipitate, as it is a quality very 
 liable to be interfered with by accidental circumstances. For 
 instance, the presence of a trace of iron, occurring as an impurity, 
 may effect a great alteration in the characteristic appearance of 
 precipitates due to chrome, manganese, zinc, aluminum, or earthy 
 salts, respectively, by imparting to them a black, grey, or greenish 
 colour. From its transparency, the precipitate produced in 
 aluminous solutions is very liable to be overlooked. 
 
 The salts of nickel, cobalt, manganese, iron and zinc are preci- 
 pitated by sulphide of ammonium, in the form of sulphides, 
 according to the general equation, 
 
 MCl a + (NH 4 ) a S 2NH 4 C1 + j&. 
 
 From their neutral solutions these metals are precipitated very 
 imperfectly by sulphuretted hydrogen, in consequence of the 
 formation during the reaction of hydrochloric or some other acid, 
 in which the respective sulphides are soluble, thus : 
 
 MC1 3 + H a S = 2HC1 + M&. 
 
 But the sulphides of nickel, cobalt, and zinc may be precipitated 
 completely from solutions which are acid only with acetic acid, 
 and in which, owing to the addition of an alkaline acetate, no 
 stronger acid than the acetic can be set free during the reaction ; 
 though even then sulphide of iron can be but partially precipi- 
 tated, and sulphide of manganese not at all. 
 
 Although the sulphides of nickel and cobalt are not precipitated 
 in the presence of hydrochloric acid, yet, when once produced, 
 they can only be dissolved in the acid with considerable difficulty ; 
 but they are readily soluble in nitric acid. The sulphides of 
 
7 8 EXAMINATION FOR BASES OF GROUP II. 
 
 zinc, iron, and manganese, however, are easily dissolved by cold 
 hydrochloric acid, and that of manganese by acetic acid. 
 
 The sulphides of aluminum and chromium cannot be produced 
 in the moist way. Hence the salts of these metals are precipitated 
 by sulphide of ammonium in the form, not of sulphides, but of 
 'hydrated sesquioxides, with liberation of sulphuretted hydrogen, 
 thus: 
 
 2A1C1 3 + 3(NH 4 ) 2 S + 6H,0 = 6NH 4 C1 + 3 H a S + Al a 3 . 3 H a O. 
 
 The earthy salts are precipitated as such by a mere neutralisation 
 of the acid in which they were dissolved, thus (vide page 75) : 
 
 Ca 3 (P0 4 ) a .4HCl + 2(NH 4 ) a S = Ca 3 (P0 4 ), + 4 NH 4 C1 + aH 2 S. 
 
 (38.) /3. From protosalts of nickel, cobalt, manganese, iron, 
 and zinc, potash throws down the respective prothydrates, pre- 
 cisely as it does the prothydrates of the metals of the first 
 group : 
 
 MCI, + zKHO = 2KC1 + MO.H,0. 
 
 From the tri- or sesquisalts of iron, chromium, and aluminum, 
 it precipitates the respective sesquihydrates, thus : 
 
 2 MC1 3 + 6KHO = 6KC1 + M;"0 3 . sH^O. 
 
 The earthy salts are precipitated as such by the neutralisation 
 of the acid in which they were dissolved. 
 
 The appearance of the manganese precipitate is very charac- 
 teristic. From being quite white it becomes rapidly brown by 
 an absorption of atmospheric oxygen. The precipitate given by 
 potash with perfectly pure protosalts of iron is greenish-white, 
 but the precipitate ordinarily obtained has a dark olive-green 
 colour, becoming ochrey-red by exposure to air : with mixed 
 proto- and sesqui-salts, a black precipitate, and with pure sesqui- 
 salts a red-brown precipitate is produced. The hydrates of 
 chromium, aluminum, and zinc are completely soluble in excess 
 
PRECIPITATION BY AMMONIA. 79 
 
 of potash, while the other precipitates are insoluble. Should the 
 excess of potash effect an obvious solution of the precipitate at 
 first thrown down, but the liquid at the same time not become 
 perfectly bright, it may be filtered off from the oxide of iron, or 
 other insoluble impurity, and tested for chromium, aluminum, 
 and zinc (3). 
 
 (39.) y. Ammonia throws down from solutions of nickel, 
 cobalt, manganese, iron, and earthy salts, precipitates 
 which have respectively the same composition as those thrown 
 down by potash. The precipitates produced in solutions of the 
 earthy salts and in sesquisalts of iron are equally insoluble in 
 excess of ammonia as in excess of potash; but the prothydrates 
 of nickel, cobalt, and manganese are readily soluble, and that of 
 iron sparingly soluble, in excess of ammonia, when chloride 
 of ammonium or some other neutral ammoniacal salt is also 
 present. Hence when the previous experiment with potash 
 has shown the probable presence of a protosalt of iron, it is neces- 
 sary, before adding ammonia, to boil the solution with a little 
 nitric acid for a few minutes, so as to convert the protosalt into a 
 sesquisalt, whereby all the iron may be precipitated as a red-brown 
 sesquihydrate, quite insoluble in excess of ammonia. 
 
 But when the colour of the precipitate produced by potash, or 
 some other reaction, has indicated the absence of a protosalt of 
 iron, the boiling with nitric acid may be dispensed with. The 
 presence of a protosalt of iron in the original solution is best 
 shown by the addition of ferridcyanide of potassium, which pro- 
 duces therewith an abundant dark blue precipitate of ferridcyanide 
 of iron, or Turnbull's blue : 
 
 aPeCl* + 2K 3 Fe'Cy 6 = 6KC1 + Fe^Fe'^'Cy,,. 
 
 The presence of a sesquisalt of iron is best shown by sul- 
 pliocyanate of potassium^ which produces therewith a blood-red 
 liquid, due to the formation of sesqui-sulphocyanate of iron : 
 
 FeCl 3 + sKCyS = sKCl + Fe(CyS) 3 . 
 
80 EXAMINATION FOR BASES OF GROUP II. 
 
 The mode of examining the earthy salts is described in 
 par. 59. 
 
 When excess of ammonia is added to a strongly acid solution, 
 or when chloride of ammonium and excess of ammonia are added 
 to a nearly neutral solution of nickel, cobalt, or manganese, the 
 precipitate at first produced is immediately redissolved. 
 
 The ammoniacal solution of nickel has a deep purple-blue 
 colour, closely resembling that of the similarly constituted solu- 
 tion of copper. Potash added to the ammoniacal nickel solution 
 throws down an apple-green precipitate of hydrate of nickel ; but 
 a very large quantity of potash may be added to the ammoniacal 
 copper solution without disturbing its transparency, and the pre- 
 cipitate finally produced is for the most part blue. Moreover, 
 ferrocyanide of potassium produces with ordinary salts of nickel a 
 pale green, and with ordinary salts of copper a chocolate-red, 
 precipitate of the respective ferrocyanides ; and the two metals 
 are otherwise well characterised. 
 
 The ammoniacal solution of cobalt has a brownish-pink 
 colour, which gradually becomes darker by exposure to air, until 
 eventually a brownish precipitate of hydrated sesquioxide of 
 cobalt is produced. But the cobalt solution, when made with 
 ammonia containing carbonate of ammonium, or even with car- 
 bonate of ammonium itself, has a fine pink colour, which is 
 tolerably permanent. Cobalt compounds are best recognised by 
 fusion with the borax bead, to which they impart a deep purple- 
 blue colour. 
 
 The ammoniacal solution of manganese is at first colourless, 
 but by exposure to air it speedily becomes brown and opaque, 
 from the conversion of the white soluble prothydrate into the 
 brown insoluble sesquihydrate. Manganese compounds are very 
 frequently contaminated with iron ; hence, when excess of am- 
 monia produces a brown precipitate, it is often worth while to 
 pour the mixture on to a filter, and to test the ammoniacal filtrate 
 with sulphide of ammonium; whereupon manganese, if present, is 
 precipitated as a flesh-coloured sulphide. Manganese is best 
 recognised before the blowpipe by fusing some carbonate of 
 sodium, to which a little nitre may be added, upon platinum foil, 
 
SOLUTION IN AMMONIA. 8 1 
 
 and then introducing a minute portion of the manganese com- 
 pound, whereby a bright green fusible mass of manganate of 
 sodium Na a Mn0 4> is produced. 
 
 (40.) S. The potash solution of chromium is of a green colour, 
 and when boiled for a longer or shorter time, according to the 
 relative proportions of potash and chrome present, deposits the 
 whole of its chrome in the form of a green precipitate. Chrome 
 compounds are best recognised by the emerald green colour they 
 impart to the borax bead ; and by the bright yellow mass of 
 chromate of alkali metal which they yield when ignited on 
 platinum foil, with carbonate of sodium and nitre, before the 
 blowpipe. 
 
 . The potash solution of zinc, when containing a considerable 
 excess of potash, is not affected even by prolonged ebullition ; 
 but when containing only a slight excess, it soon deposits an 
 opaque white precipitate. On adding a few drops of sulphide of 
 ammonium to potash solution of zinc, sulphide of zinc is formed, 
 which being, unlike the hydrate of zinc, insoluble in potash, is 
 thrown down as a white precipitate, frequently having a greyish 
 tinge from the accidental presence of a trace of lead in the potash 
 used as the reagent. 
 
 Zinc compounds when strongly heated leave a fixed infusible 
 residue, which when cold is quite white, but when hot has a 
 deep greenish-yellow tint. Moistened with nitrate of cobalt solu- 
 tion and re-ignited, it acquires a pure permanent chrome-green 
 colour. 
 
 . The potash solution of alumina is unaffected by boiling, 
 and also by the addition of a few drops of sulphide of ammonium, 
 unless indeed the potash contains an appreciable quantity of lead, 
 when a black precipitate of sulphide of lead is formed. 
 
 Ammonia or carbonate of ammonium gives a similar white 
 precipitate with zincous and aluminous salts, but the precipitate 
 produced with the former is freely soluble, while that produced 
 with the latter is insoluble in excess of the reagent. Hence the 
 addition of chloride of ammonium to potash solution of zinc 
 
 o 
 
82 EXAMINATION FOR BASES OF GROUP III. 
 
 produces no precipitate ; but when added in sufficient quantity 
 to potash solution of alumina, it throws down a white gelatinous 
 precipitate of hydrate of aluminum, owing to a substitution of free 
 ammonia for free potash, thus : 
 
 KHO = KC1 + NH 4 HO, or NH 3 .H Z 0. 
 
 Compounds of aluminum, when strongly heated in the blowpipe 
 flame, leave a white, infusible, highly incandescent residue, which, 
 when moistened with solution of nitrate of cobalt, and reignited, 
 assumes a fine permanent blue colour. 
 
 V. EXAMINATION FOE BASES OF GEOUP III. 
 
 (41.) This group includes the bases which are not precipitated 
 either by sulphuretted hydrogen, or by sulphide of ammonium. 
 A solution of the salt in water or acid may be at once examined, 
 according to the directions of Table III. Or the solution, which 
 has been successively treated with sulphuretted hydrogen and 
 sulphide of ammonium without the production of a precipitate, 
 may be tested for any of the metals of this group, except 
 potassium, sodium, and ammonium. If the original substance 
 required an acid to effect its solution, its base cannot be any one 
 of the last three, inasmuch as all simple salts of potassium, 
 sodium, and ammonium are soluble in hot water. 
 
EXAMINATION FOR BASES OF GROUP III. 
 
 TABLE III. 
 
 (42.) Examination of a solution containing some one member 
 of the third group of bases ; namely, BARIUM, STRONTIUM, CAL- 
 CIUM, MAGNESIUM, POTASSIUM, SODIUM, or AMMONIUM. The sul- 
 phides or sulphydrates of these metals being soluble in water, 
 the solutions of their salts are not precipitated either by sulphu- 
 retted hydrogen, or by sulphide or sulphydrate of ommonium. 
 
 o. Add Chloride and Carbonate of Ammonium to the original solution, and 
 warm gently. 
 
 Precipitated 
 BARIUM 
 STRONTIUM 
 CALCIUM. 
 
 ft. Add Sulphate of Potassium or 
 dilute Sulphuric Acid to the original 
 solution. 
 
 7N 
 
 Dissolved 
 MAGNESIUM 
 POTASSIUM 
 SODIUM 
 AMMONIUM. 
 
 y> Add Phosphate of Ammonium 
 to the above solution already con- 
 taining the ammoniacal salts, and 
 stir. < '} 
 
 /" 
 
 Precipitated 
 
 Dissolved 
 
 / 
 
 Precipitated 
 
 \ 
 
 Dissolved 
 
 BARIUM (quickly) 
 
 CALCIUM. 
 
 MAGNESIUM. 
 
 POTASSIUM 
 
 STRONTIUM (slowly). 
 
 
 
 SODIUM 
 
 
 
 
 AMMONIUM. 
 
 Add Chromate of Po- 
 tassium to the original 
 solution. 
 
 
 
 8. Add to the original 
 solution Tartaric Acid 
 
 ^ 
 
 
 
 in excess, and stir. 
 
 Precipitatedl Dissolved 
 BARIUM. {STRONTIUM. 
 
 
 
 Precipitated 
 
 ^ 
 
 Dissolved 
 
 
 
 
 POTASSIUM. 
 
 SODIUM. 
 
 
 
 
 AMMONIUM ? 
 
 G 2 
 
84 EXAMINATION FOR BASES OF GROUP III. 
 
 (43-) a - Carbonate of ammonium produces in solutions con- 
 taining barium, strontium, or calcium, a white precipitate, 
 the carbonates of these three metals being insoluble : 
 
 CaCl, + (NH 4 ) a C0 3 = aNH 4 Cl + CaC0 3 , or CaO.CO,. 
 
 When carbonate of ammonium is added to an acid solution of 
 the compound under examination, care must be taken to add a 
 quantity more than sufficient to neutralise the acid, or, in other 
 words, enough to render the solution alkaline. Inasmuch as the 
 carbonic gas evolved on adding carbonate of ammonium to an 
 acid liquid retains the carbonates of the alkaline earth-metals 
 in solution, it must be expelled by gentle warming. Carbonate 
 of magnesium also is insoluble in water, though readily 
 soluble in solutions containing chloride of ammonium or other 
 ammoniacal salt. Hence the necessity of adding chloride as 
 well as carbonate of ammonium to the aqueous solution of the 
 substance under examination, in order to prevent a precipitate 
 of carbonate of magnesium being formed, and confounded with 
 one of the other precipi table carbonates. But when the sub- 
 stance has been dissolved in an acid, the carbonate of ammonium 
 expended in neutralising the acid forms a sufficient quantity of 
 neutral ammoniacal salt to prevent the precipitation of carbonate 
 of magnesium ; and consequently the separate addition of chloride 
 of ammonium is rendered unnecessary. The addition of chloride 
 of ammonium may also be dispensed with, when the carbonate is 
 added to a portion of the solution with which a negative result 
 has been obtained by successive treatment with sulphuretted 
 hydrogen and sulphide of ammonium. Carbonate of ammonium 
 also precipitates most of the metals belonging to the first and 
 second groups, so that it can only be depended upon to indicate 
 the presence of the alkaline earth-metals, when the absence of 
 all other precipitable metals has been previously ascertained by 
 sulphuretted hydrogen and sulphide of ammonium respectively. 
 
 /3. Sulphate of calcium is very slightly soluble in water, 
 sulphate of strontium still less so, and sulphate of barium 
 
PRECIPITATION BY SULPHATE OF CALCIUM. 85 
 
 quite insoluble. Hence sulphuric acid and most soluble sulphates 
 give precipitates in the solutions of all three metals. But owing 
 to the sparing solubility of sulphate of potassium in water, its 
 solution does not usually precipitate the salts of calcium unless 
 very concentrated, though it is readily capable of precipitating 
 those of strontium and barium : 
 
 BaCl a + K 2 S0 4 = aKCl + BaS0 4 , or BaO.S0 3 . 
 
 Moreover, a solution of sulphate of calcium will not precipitate 
 salts of calcium under any circumstances, but will nevertheless 
 precipitate those of strontium and barium, the former slowly, the 
 latter immediately. 
 
 Oxalate of ammonium is the reagent usually employed to 
 demonstrate the presence of calcium, with neutral or alkaline 
 solutions of which it gives a white precipitate of oxalate of 
 calcium, soluble in nitric and hydrochloric, but insoluble in 
 acetic and oxalic acids : 
 
 CaCl 2 + (NH 4 ) 2 C 2 4 -= 2NH 4 C1 + CaC^ or CaO.C,0 3 . 
 
 But oxalate of ammonium produces precisely similar precipi- 
 tates in neutral salts of strontium and barium, the oxalates of 
 these two metals being also insoluble in water. That of barium, 
 however, is soluble in excess of warm oxalic acid. Moreover, 
 free oxalic acid precipitates neutral solutions of calcium and 
 strontium, but not of barium, unless very concentrated. 
 
 In solutions" acidified with acetic acid, chromate of potassium 
 has no action upon strontium and calcium salts, but throws down 
 from barium salts a yellow precipitate of chromate of barium, 
 soluble in the nitric and hydrochloric acids : 
 
 Ba(N0 3 ) a + K 2 Cr0 4 - zKN0 3 + BaCr0 4 . 
 
 Hydrofluosilicic acid also serves to distinguish barium salts 
 from those of strontium and calcium, with the first of which it 
 alone produces a precipitate, the fluosilicate of barium being alone 
 
86 EXAMINATION FOE BASES OF GEOUP III. 
 
 insoluble. This test is unaffected by the presence of nitric and 
 hydrochloric acids : 
 
 tfaCl, + H 2 SiF 6 = aHCl + BaSiF 6 , or BaF a .SiF 4 . 
 
 Most barium salts, especially when moistened with hydro- 
 chloric acid, impart an apple-green colour to the blowpipe flame ; 
 strontium salts a marked crimson ; and calcium salts an orange- 
 red. 
 
 (44.) y. Phosphate of ammonium, or of sodium, gives with 
 magnesian solutions, containing carbonate of ammonium or 
 free ammonia, a white crystalline precipitate of phosphate of 
 magnesium and ammonium, frequently known as triple phos- 
 phate : 
 
 MgCl a + (NH 4 ) a HP0 4 + NH 3 = aNH 4 Cl + Mg(NH 4 )P0 4 . 
 
 This precipitate does not usually form in warm solutions, and 
 is frequently produced only after brisk stirring, or rubbing the 
 inside of the tube with a glass rod. It must be remembered that 
 phosphate of ammonium gives precipitates with salts of barium, 
 strontium, and calcium, and of most metals belonging to the first 
 and second groups, so that it can only be relied upon as a test for 
 magnesium when the absence of all other metals precipitable by 
 it has been first ascertained. 
 
 5. Tartaric acid gives with neutral solutions of potassium- 
 salts a white crystalline precipitate of acid tartrate of potassium 
 or cream of tartar : 
 
 Kl + H 6 C 4 6 = HC1 + KH 5 C 4 6 . 
 
 The precipitate does not usually appear in a warm liquid. It 
 is produced very slowly in solutions of the more sparingly 
 soluble, and in dilute solutions of the more freely soluble potas- 
 sium-salts. From such solutions it is best obtained by cooling 
 the mixture under a tap, diluting it with a little alcohol, and 
 stirring it briskly with a glass rod, which should be rubbed 
 
PRECIPITATION OF ALKALI-METALS. 87 
 
 against the inside of the tube. In testing alkaline solutions for 
 the presence of potassium, care must be taken to add an excess of 
 tartaric acid. The precipitate of cream of tartar is not formed in 
 solutions of potassium-salts which have a marked acid reaction 
 from the presence either of oxalic acid, or of one of the strong 
 mineral acids. But on neutralising such solutions with caustic 
 soda, or carbonate of sodium, and then adding tartaric acid, the 
 characteristic precipitate is readily obtained. 
 
 Perchloride of platinum produces also in solutions of potas- 
 sium-salts, which should first be acidulated with hydrochloric 
 acid, a yellow crystalline precipitate of platino-chloride of potas- 
 sium 2KCl.PtCl 4 , the deposition of which is facilitated by stirring, 
 and by the addition of alcohol. 
 
 Solutions of ammonium-salts, when moderately concentrated, 
 resemble potassium- salts in their behaviour with tartaric acid, 
 yielding therewith a crystalline precipitate of acid tartrate of 
 ammonium (NH 4 )H 5 C 4 6 . Hence ammonia cannot be used to 
 neutralise those acid solutions which have to be tested with tartaric 
 acid for the presence of potassium. Moreover, moderately concen- 
 trated solutions of ammonium-salts give with dichloride of 
 platinum a yellow crystalline precipitate of platino-chloride of 
 ammonium 2NH 4 Cl.PtCl 4 , resembling the similar' compound of 
 potassium. Dilute solutions of ammoniacal salts behave like solu- 
 tions of sodium-salts in not furnishing any precipitate with 
 either tartaric acid or dichloride of platinum. But ammonium- 
 sales may be readily distinguished from those of potassium and 
 sodium by their partial or complete volatility, and by their solu- 
 tions evolving ammonia when boiled with potash or lime : , 
 
 NH 4 C1 + KHO = KC1 + NH 3 + H Z 0. 
 
 Sodium-salts impart an intense yellow colouration to flame, 
 and potassium-salts a marked violet. 
 
88 EXAMINATION FOR ACIDS. 
 
 VI. EXAMINATION EOE ACIDS. 
 
 (45.) The student should always ascertain the nature of the 
 metallic or basic constituent of his substance, before proceeding 
 to search for its acid or'chloroid constituent. In this search he 
 will be greatly assisted by a knowledge of the special characters 
 of particular salts, and of the general characters of various classes 
 of salts. Knowing, for instance, that sulphate of barium is 
 insoluble in all menstrua, he need not test a soluble barium salt 
 for sulphuric acid. On the other hand, a salt insoluble in water 
 is not likely to be a nitrate or chlorate. The following classes of 
 salts are, as a rule, soluble in water : Nitrates, excepting a few 
 superbasic salts ; acetates, except acetate of silver, which is only 
 sparingly soluble ; chlorides, except chloride of silver, which is 
 insoluble in boiling nitric acid, and mercurous chloride, or 
 calomel, which dissolves in boiling nitric acid with conversion 
 into a mercuric salt : chloride of lead is moderately soluble in 
 boiling, though very sparingly soluble in cold water. Sulphates, 
 except those of barium, strontium, and lead, which last is soluble 
 in boiling hydrochloric acid : the sulphates of silver and calcium 
 also are only sparingly soluble. The following classes of salts 
 are, as a rule, insoluble in water : Oxides or hydrates, and 
 sulphides or sulphydrates, except those of the alkali- and alkaline 
 earth- metals, and the sulphydrate of magnesium ; also car- 
 bonates, phosphates, and oxalates in general, except those of the 
 alkali metals, and many hyperacid salts. 
 
 The presence of any particular acid is indicated more or less 
 certainly by the behaviour of the substance when gently heated 
 in the solid state with three or four times its bulk of strong 
 sulphuric acid, and when under examination for the detection of 
 its metallic constituent. 
 
 The most usual decomposition which takes place between sul- 
 phuric acid and the salt of a more volatile or feeble acid consists 
 in an exchange of the hydrogen of the sulphuric acid for the 
 metal of the salt, thus : 
 
THEIR LIBERATION BY SULPHURIC ACID. 89 
 
 H a S0 4 + NaCl = NaHS0 4 + HC1 
 H a S0 4 + KNO ? = KES0 4 + HN0 3 . 
 
 Reactions similar to the above take place with the salts of 
 nearly all acids, provided the sulphuric acid employed is not too 
 strong, and the heat not too great; but with ordinary oil of 
 vitriol, especially at a somewhat high temperature, the liberated 
 acids themselves often undergo a partial or complete decomposi- 
 tion. 
 
 The tartaric and citric acids, for instance, are destroyed with 
 more or less charring. The nitric and chloric acids yield the 
 peroxides of nitrogen and of chlorine respectively, thus : 
 
 2HN0 3 = H a O + N a 4 + 
 2HC10 3 = H a O + C1 2 4 + 
 
 except that, in the former case, the decomposition is but slight, 
 while in the latter, the separated oxygen converts another portion 
 of the chloric into perchloric acid. 
 
 Oxalic acid breaks up into water, carbonous oxide, and carbonic 
 anhydride, thus: 
 
 H a C a 4 = H a O + CO + GO,. 
 
 The hydrobromic, hydroiodic, and sulphydric acids are decom- 
 posed with liberation of bromine, iodine, and sulphur, respec- 
 tively, thus : 
 
 + H a S0 4 = 2H a O + S0 a + Br a 
 2HI + H a S0 4 = 2H a O + S0 a + I a 
 H a S + H a S0 4 = 2H a O + S0 a + S 
 
 Hydrocyanic acid yields acid-sulphate of ammonia and carbon- 
 ous oxide, thus : 
 
 HCN + H a O + H a S0 4 => CO + NH 3 .H a S0 4 . 
 
 (46.) In the following table the principal acids are classified 
 according to the behaviour of their salts when under examination 
 for bases, and when warmed with strong sulphuric acid : 
 
9O EXAMINATION FOR ACIDS. 
 
 TABLE IV. PRELIMINARY TESTING FOR ACIDS. 
 
 a. Indicated during 
 previous examina- 
 tion. 
 
 /3. Corroborated 
 by sulphuric 
 acid. 
 
 y. Also react with 
 sulphuric acid. 
 
 8. No obvious 
 effect with sul- 
 phuric acid. 
 
 ARSENATES ) React 
 
 NITRATES. Brown 
 
 CHLORIDES. Pungent 
 
 BORATES. Give 
 
 CHROMATES J withH^S 
 
 acid vapours with 
 
 acid fumes. With 
 
 green flame with 
 
 
 copper 
 
 MnO z evolve chlo- 
 
 alcohol 
 
 
 
 rine 
 
 
 NITRATES \ Defla- 
 CHLORATES j" grate 
 
 CHLORATES. Brown 
 ing and crackling 
 
 BROMIDES. Brown 
 fumes, which bleach 
 
 OXALATES | Effer- 
 CYANIDES J vesce? 
 
 
 detonation 
 
 litmus, and turn 
 
 
 
 
 starch yellow 
 
 PHOSPHATES \ 
 
 
 
 
 ARSENATES j 
 
 TARTRATES i 
 CITRATES J Char 
 
 TARTRATES ) 
 CITRATES } Char 
 
 IODIDES. Violet va- 
 pours, which turn 
 starch paper purple. 
 
 SULPHATES > 
 SILICATES 
 OXIDES j 
 
 CARBONATES >, Effer- 
 
 CARBONATES ^ 
 
 FLUORIDES. Pungent 
 
 
 SULPHIDES 1 vesce 
 
 SULPHIDES ' Effer - 
 
 acid fumes, which 
 
 
 SULPHTFES, &c. [with 
 
 SULPHITES ) V68Ce 
 
 etch glass 
 
 
 PEROXIDES > HC1 
 
 
 
 
 
 
 ACETATES. Acid va- 
 
 
 , 
 
 
 pour. With alcohol 
 
 
 PERSULPHIDES \ 5 5 
 
 
 yield acetic ether 
 
 
 SILICATES [e>6 
 
 
 
 
 BORATES j ^S w 
 
 
 
 
 BENZOATES J |j 
 
 
 
 
 ' 
 
 
 
 
 (47.) a. Deflagration of the substance, when heated upon 
 charcoal before the blowpipe, shows the probable presence of a 
 nitrate or chlorate. 
 
 Charring of the substance, when heated upon platinum foil 
 or charcoal, usually indicates the presence of a tartrate or 
 citrate. 
 
 Effervescence from the substance, when its solution is being 
 effected in hydrochloric acid, occurs with several classes of 
 salts. 
 
 With nearly all carbonates there is evolution of carbonic 
 anhydride, thus : 
 
 aHCl + CaCO, = CaCL, 
 
 H a O 
 
 CO,. 
 
BEHAYIOUR OF SALTS WITH HYDROCHLORIC ACID. QI 
 
 The gas is free from any marked smell, and renders lime water 
 milky (vide par. 84). 
 
 With many sulphides there is evolution of sulphydric acid or 
 sulphuretted hydrogen, thus : 
 
 + FeS = Fe'CL, + H 2 S 
 6HC1 + Sb a S 3 = 2SbCl 3 + sH a S. 
 
 The gas smells most offensively, and turns lead paper of a black 
 or brown colour. 
 
 With sulphites and hyposulphites (vide par. 94) there is 
 evolution of sulphurous anhydride, thus : 
 
 + Na,S0 3 = aNaCl + H a O + S0 a . 
 
 The gas has the peculiar suffocating smell of burning sulphur, 
 and produces a purple discolouration on starch paper moistened 
 with iodic acid solution. 
 
 With peroxides there is evolution of chlorine, thus: 
 
 4 HCi + MnO a = 2H a O + MnCl a + Cl a . 
 
 The gas, which has a greenish colour and characteristic irrita- 
 ting smell, produces a purple colouration on starch paper moist- 
 ened with iodide of potassium. 
 
 Similar effects are observable on acidifying with hydrochloric 
 acid the strong aqueous solutions of soluble carbonates, sulphides 
 or sulphydrates, sulphites, and hyposulphites ; but the evolution 
 of chlorine under these circumstances would probably be due to 
 the presence of a hypochlorite. Moreover, most simple cyanides, 
 and the strong aqueous solutions of such of them as are soluble, 
 effervesce when warmed with hydrochloric acid, from an evolu- 
 tion of hydrocyanic acid gas, known by its characteristic smell, 
 and by its behaviour with sulphide of ammonium, &c. (vide par. 
 99)- 
 
 HC1 + KCN = KC1 + HCN. 
 
 The aqueous solutions of certain salts when acidified with 
 
92 EXAMINATION FOR ACIDS. 
 
 hydrochloric acid yield precipitates due, not to the metals silver, 
 lead, and mercury, but to the acids of the respective salts. 
 
 With persulphides there is formed a yellowish white 
 turbidity from liberated sulphur, always accompanied, however, 
 by an evolution of sulphuretted hydrogen : 
 
 2HC1 + K a S a = aKCl + H a S + S. 
 
 With hyposulphites, there is gradually produced a more de- 
 cidedly yellow precipitate of sulphur, and an evolution of 
 sulphurous anhydride, thus: 
 
 + Na a S a 3 = 2 NaCl + H a O + S0 a + S. 
 
 With soluble silicates there is produced a gelatinous precipi- 
 tate of silica, which separates out more completely, and becomes 
 gritty on evaporation : 
 
 + K a Si0 3 = aKCl + H a O + SiO a . 
 
 Borates and benzoates, if sufficiently concentrated, yield 
 crystalline precipitates of boric and benzoic acids respectively, 
 which dissolve in boiling water, and crystallise out again on 
 cooling : 
 
 HC1 + NaH 5 (B0 3 ) a = NaCl + 2H 3 B0 3 
 HC1 + KE 5 C 7 O a = KC1 + H 6 C 7 O a . 
 
 In testing for bases of the first group, by treating the acidi- 
 fied solution of the substance with sulphuretted hydrogen, strong 
 evidence of the presence of arsenates or chromates may also be 
 afforded. Acidified solutions of arsenates slowly yield a 
 yellow precipitate of mixed trisulphide of arsenic and sulphur, 
 thus: 
 
 s0 4 = 8H a O + aKCl + As a S 3 + S v 
 
 Acidified solutions of chromates yield a yellowish- white 
 deposit of sulphur, while the colour of the liquid changes from 
 
BEHAVIOUR OF SALTS WITH SULPHUEIC ACID. 93 
 
 orange-red to green, owing to the reduction of the chromic acid 
 to the state of a chrome-salt, thus : 
 
 3H,S + 6HC1 + 2Cr6 3 = 6H Z + 2CrCl 3 + S 3 . 
 
 (48.) (3. Nitrates, when heated with sulphuric acid, give off 
 nitric acid vapours, sometimes having a brownish tint from the 
 presence of peroxide of nitrogen. On the addition of a few 
 copper turnings the brown colour becomes very marked, from the 
 evolution of colourless nitric oxide N a 2 , and its immediate con- 
 version into brown peroxide of nitrogen N Z 4 , by an absorption 
 of atmospheric oxygen : 
 
 3H 2 S0 4 + sCu + 
 
 The vapour, whether before or after the addition of copper, 
 has a characteristic nitrous smell, reddens litmus paper, and gives 
 a purple colouration to starch paper moistened with iodide of 
 potassium : 
 
 Chlorates react somewhat violently with sulphuric acid, pro- 
 ducing an immediate browning, and, either at once or on the 
 slightest application of heat, a crackling, or even loud detona- 
 tion, from the breaking up of the peroxide of chlorine first 
 liberated. 
 
 Tartrates and citrates undergo more or less charring, the 
 tartrates becoming thoroughly blackened, the citrates merely 
 browned. 
 
 Carbonates, sulphites, and sulphides effervesce with sulphuric 
 as with hydrochloric acid ; except that in the last case some of 
 the liberated sulphydric acid reacts with the excess of sulphuric 
 acid to form sulphur, water, and sulphurous anhydride, as already 
 described (vide par. 45). 
 
 y. Most chlorides when warmed with sulphuric acid evolve 
 hydrochloric acid gas, which reddens litmus paper, and has a well 
 characterised pungent smell. On the addition of a little peroxide 
 
94 EXAMINATION FOR ACIDS. 
 
 of manganese, chlorine is evolved, recognisable by its peculiar 
 irritant smell : ': ? 
 
 H 3 S0 4 + MnO a + zHCl = MnS0 4 + 2H 3 + Cl a . 
 
 It bleaches litmus, and produces a purpling of starch paper 
 moistened with iodide of potassium solution. 
 
 Bromides evolve a mixture of hydrobromic acid with bromine 
 vapour, the latter recognisable by its brown colour, irritant 
 smell, and power of bleaching litmus. 
 
 Iodides yield iodine vapour, recognisable by its violet colour, 
 and by its rendering starch paper purple. 
 
 Fluorides give off pungent fumes of hydrofluoric acid, which 
 redden litmus and etch glass (vide par. 106). 
 
 Acetates give off acetic acid vapours, which redden litmus. 
 On the addition of a little alcohol the original sour smell of the 
 acid is changed into the fruity smell of acetic ether. 
 
 8. B orates do not react visibly with sulphuric acid, but on 
 adding alcohol, and then setting fire to the mixture in a capsule, 
 the flame presents a marked green colour. 
 
 Oxalates and cyanides are decomposed by heated sul- 
 phuric acid with liberation of carbonous oxide gas, accompanied 
 in the case of the former salts with carbonic anhydride ; but as 
 the evolution of gas is liable to be overlooked, and the gas itself 
 does not present any striking property, the oxalates arid cyanides 
 are here included among the salts with which sulphuric acid pro- 
 duces no obvious effect. 
 
 Phosphates, arsenates, sulphates, silicates, andoxides 
 do not react visibly with sulphuric acid ; except that with some 
 peroxides there is evolution of oxygen, transformable into that of 
 chlorine on the addition of chloride of sodium or hydrochloric acid. 
 
 (49.) The various liquid tests for the acids should be applied 
 by preference to an aqueous solution of the original substance. 
 But if insoluble in water, and consequently neither a nitrate nor 
 a chloride, it may be dissolved .in dilute nitric or hydrochloric 
 -acid, and the tests applied to the solution so formed. 
 
INFLUENCE OF BASES. 95 
 
 The presence of certain basic metals interferes occasionally 
 with the described reactions of several of the acids. Thus solu- 
 tion of hydrochloric acid or any chloride, when tested with 
 nitrate of silver, gives a white precipitate of chloride of silver, 
 said to be readily soluble in ammonia. But on adding nitrate of 
 silver to solution of mercuric chloride, and treating the resultant 
 white precipitate with ammonia, there is no obvious solution pro- 
 duced, because, although the precipitated chloride of silver does 
 actually and completely dissolve, a white insoluble mercuram- 
 monium compound is simultaneously thrown down from the 
 mutual reaction of the ammonia and mercuric salt. 
 
 Bearing in mind, however, the interference likely to be pro- 
 duced by the presence of the particular metal previously detected, 
 the tests for sulphuric, hydrochloric, and nitric acids can for the 
 most part be satisfactorily applied to any of their salts. 
 
 But in testing for phosphoric, oxalic, and tartaric acids more 
 particularly, and for other acids when any difficulty occurs, it is 
 important that the base of the salt should be one of the alkali 
 metals, potassium, or sodium, or ammonium. 
 
 The bases of the first group may be got rid of by saturating 
 the solution with sulphuretted hydrogen gas, filtering, evaporating 
 the filtrate until it ceases to smell, and neutralising it with car- 
 bonate of sodium or potassium. 
 
 The bases of the second group, together with barium, stron- 
 tium, calcium, and magnesium, may be removed by adding to the 
 acidulous, or occasionally to the aqueous, solution of the substance 
 an excess of carbonate of sodium or potassium, boiling for some 
 time, and filtering. The filtrate can afterwards be neutralised 
 with nitric or hydrochloric acid, which may be conveniently 
 added drop by drop from a pipette. 
 
 (50.) The following abridged table shows the action of some 
 general reagents upon the dissolved salts of the principal acids. 
 By its aid and that of the preceding table, the student will rarely 
 have much difficulty in quickly discovering the acid constituent 
 of his substance, although, indeed, the course of examination is 
 not so systematic as that for the bases. A more complete table 
 
9 6 
 
 EXAMINATION FOR ACIDS. 
 
 for the detection of the acids would include the reactions of a few 
 organic salts of comparatively rare occurrence, such as the formates, 
 succinates, citrates, meconates, gallates, tannates, and ferrid- 
 cyanides ; of a few mineral salts of similarly rare occurrence, 
 namely, the iodates, seleniates, and silico-fluorides ; of .a few 
 mineral salts rarely met with in the soluble form, namely, silicates 
 and fluorides ; and of the previously detected arsenates. It would 
 also mention the several precipitates given by nitrate of silver and 
 nitrate of barium respectively, which disappear on acidification, 
 and have, as a rule, but little practical interest. 
 
 TABLE V. COURSE FOE DETECTION or THE ACIDS. 
 
 a. NlTRATK OF 
 SlLVEB 
 
 /3. NITRATE OP 
 BARIUM 
 
 y. CHLORIDE OP 
 CALCIUM 
 
 e. PERCHLORIDE 
 OP IRON 
 
 From acid solutions 
 CHLORIDES \ 
 CYANIDES L White 
 BROMIDES J 
 IODIDES. Yellow 
 SULPHIDES. Black 
 
 From acid solutions 
 SULPHATES. White 
 
 From non-acid sols. 
 CHROMATES. Yellow 
 
 CARBONATES \ 
 [White 
 SULPHITES j 
 &c., &c. 
 
 From acetic acid sols. 
 OXALATES. White 
 
 From neutral sols. 
 TARTRATES. White 
 
 From acid solutions. 
 
 FERROCYANIDES. 
 D. blue pp. 
 
 SULPHOCYANIDES. 
 
 D. red colour. 
 
 From neutral sols. 
 BORATES | L>brown 
 
 BENZOATEsJ PP ' 
 
 ACETATES. D. red 
 colour 
 
 8. SULPHATE OP 
 MAGNESIUM 
 
 From ammon. sols. 
 PHOSPHATES. White 
 
 (51.) a. Nitrate of silver causes precipitates in the solutions of 
 very many classes of salts, the majority of silver salts being more 
 or less insoluble in water. The reactions consist in an exchange 
 of the silver of the nitrate of silver for the metal or quasi-metal 
 of the dissolved salt under examination, as illustrated by the 
 following examples : 
 
 AgN0 3 
 
 3 AgN0 3 
 aAgN0 3 
 
 3 AgN0 3 
 
 KI 
 
 FeCl 3 
 (NH 4 )A0 4 = 
 
 Na 8 HP0 4 = 
 
 KN0 3 
 
 Fe(N0 3 ) 3 
 
 Agl 
 
 3AgCl 
 AgA0 4 
 
 HNO, 
 
PRECIPITATION BY NITRATE OF SILVER. 97 
 
 All the precipitates produced by nitrate of silver disappear upon 
 the addition of nitric acid, or do not form in presence of .free 
 nitric acid, except the chloride, cyanide, bromide, iodide, and 
 sulphide. 
 
 With chlorides the silver precipitate is white, becoming 
 slate-coloured on exposure to light, and soluble in ammonia 
 before discolouration. Upon heating the original substance with 
 peroxide of manganese and sulphuric acid, chlorine gas is evolved. 
 
 With simple* cyanides the silver precipitate is white, soluble 
 in ammonia, and in boiling concentrated nitric acid : a portion of 
 the precipitate washed by decantation may be treated with yellow 
 sulphide of ammonium, whereby sulphide of silver and sulpho- 
 cyariate of ammonium are produced, which last strikes a deep red 
 colour on the addition of a ferric salt. An excess of sulphide of 
 ammonium must be avoided, or afterwards got rid of by evapo- 
 rating to dry ness. 
 
 With bromides the silver precipitate is white, and with diffi- 
 culty soluble in ammonia. Bromine is liberated from the original 
 salt, when treated with sulphuric acid, and from the solution of the 
 salt when treated with a few drops of nitro-hydrochloric acid or 
 chlorine- water, whereby the liquid assumes a red -brown colour 
 rendered more evident upon the addition of a little ether or 
 chloroform, which dissolves out the bromine to form a deep brown 
 stratum. 
 
 With iodides the silver precipitate has a pale yellow colour, 
 and is insoluble in, but turned white by, ammonia. Iodine is 
 liberated from the salt when treated with sulphuric acid, and from 
 the solution of the salt when treated with a few drops of yellow 
 nitric or nitro-hydrochloric acid or chlorine- water, its presence 
 being manifested by the purple colour it produces on starched 
 pap<-r, or with dilute starch paste added to the liquid, or by the 
 pink or crimson colour it imparts to chloroform. 
 
 * Ferrocyanide and sulphocyanate of silver occur as white precipitates, 
 and the ferridcyanide as a brown precipitate, all unaffected by nitric acid, 
 but soluble ferrocyanides, ferridcyanides, and sulphocjanates are recog- 
 nised immediately by their behaviour with iron solutions. 
 
98 EXAMINATION FOR ACIDS. 
 
 With sulphides the silver precipitate is black, and insoluble 
 in ammonia, but soluble in boiling nitric acid. Nitro-prusside 
 of sodium added to an alkaline sulphide produces a deep purple 
 colouration. 
 
 Of the silver precipitates which disappear on acidification with 
 nitric acid, the hydrate is brown, the chromate dark red, the ar- 
 senate brick-red, the phosphate bright yellow, though sometimes 
 white, the carbonate pale yellow, and the rest white. The oxa- 
 late is insoluble in acetic acid ; the acetate is thrown down from 
 concentrated solutions only ; the tartrates, formates, and sul- 
 phites are reduced to the metallic state on boiling ; while the 
 borates, benzoates, and citrates do not exhibit any characteristic 
 property. 
 
 (52.) (3. Nitrate or chloride of barium precipitates the solutions 
 of many classes of salts, most barium salts being insoluble or 
 sparingly soluble in water. The reaction consists in an exchange 
 of the barium of the nitrate or chloride of barium for the metal 
 or quasi-metal of the salt under examination, thus : 
 
 Ba(N0 3 ), + Na a S0 4 = 2 NaN0 3 + BaS0 4 
 
 Bad, + KHS0 4 = KC1 + HC1 + BaS0 4 
 
 With sulphates the barium precipitate is white, and, if in 
 any quantity, opaque. It does not disappear upon the addition 
 of nitric or hydrochloric acid, but is nevertheless slightly soluble 
 in concentrated nitric acid. The seleniate and silicofluoride of 
 barium also occur as white precipitates unaffected by acidification, 
 (vide par. 95). Of the barium precipitates which dissolve in nitric 
 or hydrochloric acid, the chromate is yellow and the remainder 
 are white. The carbonate and sulphite dissolve with effervescence. 
 The arsenate, borate, and tartrate do not form in the presence 
 of ammoniacal solutions, and, when once thrown down, disappear 
 more or less readily on the addition of chloride of ammonium. 
 The oxalate and phosphate exhibit no characteristic properties. 
 
 (53.) y. With a few exceptions, chloride of calcium causes 
 precipitates with the several classes of salts which are precipitated 
 by chloride or nitrate of barium ; but while sulphate of barium 
 
PRECIPITATION BY CHLORIDE OF CALCIUM. 99 
 
 is much more insoluble in water and acids than sulphate of cal- 
 cium, oxalate of calcium is more insoluble in water, and especially 
 in acetic acid, than oxalate of barium. 
 
 With solutions ofoxalates in which there is no free mineral 
 acid, chloride or sulphate of calcium produces an opaque white 
 precipitate of oxalate of calcium, the deposition of which, when in 
 small quantity, may be facilitated by stirring: 
 
 CaCl a + K a C a 4 = zKCl + CaC a 4 . 
 
 The precipitate is insoluble in ammonia and in acetic acid, but 
 soluble in dilute nitric or hydrochloric acid. Its solubility in 
 mineral acids distinguishes it from sulphate of calcium, which is 
 occasionally thrown down by chloride of calcium from strong 
 solutions of sulphates, as does also its property of effervescing 
 with sulphuric acid and peroxide of manganese; while its insolu- 
 bility in acetic acid distinguishes it from the phosphate, tartrate, 
 carbonate, and other salts of calcium insoluble in water. 
 
 The solution to be tested for oxalic acid with chloride of cal- 
 cium may be alkaline, or neutral, or acid from acetic acid only. 
 If an alkaline carbonate is present from its employment in pre- 
 paring the solution, it should be neutralised with acetic or hydro- 
 chloric acid. If an excess of mineral acid is present, it may 
 either be neutralised with ammonia, or acetate of ammonia may 
 be added, whereby the free mineral acid is replaced by free acetic 
 acid, thus : 
 
 HOI + (NH 4 )H 3 C a O a = NH 4 C1 + H 4 C a O a ; 
 
 but in practice it is better to add the ammonia and acetic acid 
 separately. 
 
 In neutral solutions of tartrates, chloride of calcium gives a 
 white precipitate of tartrate of calcium, soluble even in acetic 
 acid: 
 
 CaCL, -h KNaH 4 C 4 6 = KC1 + NaCl + CaH 4 C 4 6 . 
 
 On digesting the precipitate with potash, filtering, and boiling 
 the filtrate, a white turbidity is produced, which disappears on* 
 
 H 2 
 
IOO EXAMINATION FOB ACIDS. 
 
 cooling. This behaviour with potash distinguishes the tartrate 
 from the phosphate and other insoluble salts of calcium. Tartrate 
 of calcium is not thrown down in the presence of much ammoniacal 
 salt. 
 
 (54.) 3. Although phosphate solutions are precipitated alike 
 by nitrate of silver, nitrate of barium, chloride of calcium, sul- 
 phate of magnesium, and perch loride of iron, it is the magnesian 
 precipitate more especially which is characteristic of phosphoric 
 acid. From a neutral or alkaline phosphate solution, a mixture 
 of sulphate of magnesium, chloride of ammonium and ammonia 
 throws down a white crystalline precipitate of phosphate of 
 ammonium and magnesium, thus : 
 
 MiS0 4 + NH 3 + Na a HP0 4 = Na a S0 4 + NH 4 M'gP0 4 . 
 
 In common with all magnesian precipitates, it is readily soluble 
 in acids ; but, unlike any other magnesian salt, except, the arse- 
 nate, it is insoluble in ammonia and ammoniacal salts. The yellow 
 precipitate given with nitrate of silver is a useful confirmatory 
 test, as is also the reaction with molybdate of ammonium (vide 
 par. loo), although this last is common to the phosphoric and 
 arsenic acids. 
 
 (55.) e. Percliloride of iron, which, for most purposes, should 
 be free from any excess of acid, causes precipitates or characteristic 
 alterations of colour in the solutions of very many classes of salts, 
 among which may be mentioned the following : 
 
 With ferro cyanides a dark blue precipitate of Prussian 
 blue, Fe 7 Cy l8 or 3Fe"Cy a .4Fe'"Cy 3 , is thrown down; while with sul- 
 phocyanates a dark red colour, due to ferric sulphocyanate 
 Fe(CyS) 3 , is developed, neither of which results is affected by the 
 addition of hydrochloric acid. With n utral bo rates, benzo- 
 ates, or phosphates, there is produced a pale brown precipi- 
 tate of borate, benzoate, or phosphate of iron, which disappears 
 on the addition of hydrochloric acid. The phosphate, however, 
 Fe"'P0 4 , is scarcely affected by acetic acid, save in presence of a 
 large excess of iron. 
 
 With neutral acetates and sulphites, there is produced a 
 
NITRATES CHLOBATES. 
 
 101 
 
 dark reddish-brown colouration, which disappears on the addition 
 of hydrochloric acid, or on boiling: in the latter case with forma- 
 tion of a red-brown turbidity. 
 
 Nitrates and chlorates are unaffected by any of the general 
 reagents mentioned in the table. 
 
 (56.) Although nearly all of the acids react more or less cha- 
 racteristically with several reagents as above described, the 
 following list of acids or salts, with the tests by which their 
 presence is more particularly indicated or established, may 
 prove useful to the student : 
 
 Reaction with sulphydric acid. 
 I Deflagration on charcoal, and reaction with sulphuric acid. 
 
 CHROMATES 
 
 NITRATES 
 
 CHLORATES 
 
 CARBONATES 
 
 SULPHIDES 
 
 SULPHITES 
 
 SULPHATES 
 
 CHLORIDES 
 BROMIDES 
 IODIDES 
 CYANIDES 
 
 PHOSPHATES 
 
 OXALATES 
 TARTRATES 
 
 ACETATES 
 BENZOATES 
 
 BORATES 
 
 FLUORIDES 
 
 SILICATES 
 
 1- Effervescence with acids. 
 
 Precipitation by chloride of barium. 
 
 |- Precipitation by nitrate of silver. 
 
 Precipitation by sulphate of magnesium, 
 j- Precipitation by chloride of calcium. 
 
 ! Reaction with perchloride of iron. 
 \ Special tests. 
 
 In the paragraphs, 89 to 107, describing the several reactions 
 of the individual acids, the order of the above list is adopted. 
 
102 SPECIAL SUBSTANCES. 
 
 VII. SPECIAL SUBSTANCES. 
 
 (57.) It being scarcely possible to give general rules that 
 shall apply to every particular case, there yet remain for con- 
 sideration certain compounds, the detection of which according to 
 the directions of the preceding tables is impracticable, or difficult, 
 or liable to fallacy. There are some few substances, for instance, 
 which are insoluble in all ordinary menstrua, and which must 
 consequently be submitted to special modes of treatment, so that 
 they may be transformed into new and soluble combinations. 
 Again, there are those compounds of barium, strontium, calcium, 
 and magnesium, which are precipitated by sulphide of ammonium 
 along with the members of the second group, and which are 
 known by the laboratory-name of earthy salts. There are also 
 the oxides, or compounds without an acid, and the acids or com- 
 pounds without a base other than hydrogen, together with two 
 or three miscellaneous bodies. A lew remarks, moreover, are 
 appended on the examination of substances in the dissolved or 
 liquid condition, and on the solubility of the heavy metals in 
 alkaline solutions. 
 
 (58.) INSOLUBLE COMPOUNDS. 
 
 Many substances are known which do not dissolve in water or 
 in any ordinary acid, or in any combination of acids, even with 
 the aid of heat. Among bodies of this class, the following are 
 most likely to come under the notice of the student: namely, 
 peroxide of tin ; peroxide of antimony; chloride, bromide, and 
 iodide of silver ; the sulphates of barium, strontium, and perhaps 
 lead , chromic oxide ; alumina and some aluminates ; with silica 
 and some silicates. Several of these bodies may be met with in 
 the soluble as well as the insoluble form, but the silver com- 
 pounds and earthy sulphates are always alike insoluble. Sul- 
 phate of strontium, however, though practically insoluble, dis- 
 solves sufficiently in water to form a solution in which the presence 
 
INSOLUBLE COMPOUNDS. 103 
 
 of sulphuric acid can be detected by the addition of a barium- 
 salt. Again, sulphate of lead dissolves, though not very readily 
 or to any great extent, in boiling hydrochloric acid, forming a 
 solution from which chloride of lead crystallises out on cooling. 
 For analytical purposes these more or less insoluble bodies may 
 be classified into compounds of heavy metals easily recognisable 
 before the blowpipe (a), and earthy compounds for whose satis- 
 factory identification a further examination is required (fi). 
 
 a. The insoluble compounds of tin, antimony, silver, and 
 lead, when mixed with cyanide flux and heated on charcoal 
 before the blowpipe, yield beads of metal distinguishable from 
 one another by their appearance, texture, behaviour with acids, 
 and freedom from, or association with, incrustations of definite 
 character (vide par. 26, t). The sulphuric acid of the insoluble 
 lead compound may be recognised by boiling it with a solution 
 of carbonate of sodium or of potassium, filtering, and testing the 
 clear filtrate, with nitric acid and nitrate of barium, for the pre- 
 sence of any alkaline sulphate resulting from the decomposition 
 of the original sulphate of lead, thus : 
 
 PfcS0 4 + Na a C0 3 = Na,S0 4 + bC0 3 . 
 
 The chlorine, bromine, or iodine of the insoluble silver com- 
 pound may be detected by fusing the compound with a mixture 
 of the carbonates of sodium and potassium in a small porcelain 
 capsule or iron spoon, and treating the resulting saline mass with 
 sulphuric acid and peroxide of manganese, or the solution of 
 the mass with nitric acid and nitrate of silver. By fusing the 
 chloride, bromide, or iodide of silver with carbonated alkali, the 
 halogen is transferred from the silver to the alkali metal, thus: 
 
 aAgCl + Na a C0 3 = aNaCl + Ag a + C0 a + 0. 
 
 Chromic oxide is known by its dull green colour, by the 
 bright green colour it imparts to the borax bead, and by the 
 yellow mass of alkaline chi ornate into which it is converted by 
 fusion with a little nitre and carbonate of sodium. This mass 
 
IO4 SPECIAL SUBSTANCES. 
 
 may be dissolved in water, and to the yellow solution so formed 
 the ordinary tests for chromic acid applied. 
 
 /3. The remaining insoluble and non-reducible compounds may 
 be recognised by the following process. The substance in the 
 state of a very fine powder, and mixed with three or four times 
 its weight of the carbonates of sodium and potassium, is fused for 
 some time on a platinum capsule or on platinum foil, whereby a 
 decomposition of the kind represented below is effected : 
 
 BaS0 4 + Na a C0 3 = Na a S0 4 + !BaC0 3 
 
 Ai a (Si0 3 ) 3 + 3Na a C0 3 = 3Na a Si0 3 + A1 Z 3 + sC0 2 . 
 
 By boiling the fused mass in water and filtering, a clear 
 solution is obtained containing a sulphate or silicate, and perhaps 
 some aluminate of sodium ; while an undissolved residue is left 
 upon the filter consisting of alumina, or of carbonate of barium or 
 strontium, or possibly of the carbonate or oxide of some other 
 basylous metal, originally existing in the form of a silicate or 
 aluminate. This residue, after being washed with water, is dis- 
 solved in dilute hydrochloric acid, and the resulting solution 
 tested by the usual reagents, for aluminum, barium, strontium, 
 and the basylous metals generally. 
 
 The clear filtrate is acidified with hydrochloric acid, and a 
 portion of it, refiltered if necessary from any deposit caused by 
 the acidification, tested for sulphuric acid by means of nitrate or 
 chloride of barium. The remainder, whether or not turbid from 
 the acidification, must be evaporated to dryness, gently heated, 
 and again acted upon with hydrochloric acid and water. Any 
 undissolved gritty residue will consist of silica, which may be 
 further identified by fusion with a bead of carbonate of sodium 
 before the blowpipe ; while any alumina contained in the hydro- 
 chloric acid solution will be thrown down on neutralisation with 
 ammonia. 
 
EARTHY SALTS. 1 05 
 
 (59.) EARTHY SALTS. 
 
 These compounds being insoluble in water are precipitated 
 unchanged from their acidulous solutions upon the addition 
 thereto of any alkaline hydrate, carbonate, or sulphide ; whence 
 their occurrence among members of the second group of bases. 
 Perphosphate of iron, which resembles the earthy salts in the 
 behaviour of its acidulous solution with alkaline hydrates and 
 carbonates, may be conveniently associated with them, thus : 
 
 a. Iron . ." ' . ''.'* . / " Phosphate 
 Barium \ /Phosphate 
 
 0. Strontium^ , . . .. ' -1 Oxalate 
 Calcium i \ Fluoride 
 
 7. Magnesium :'- Phosphate 
 The identification of the different compounds when separated 
 from one another is easily effected by the under- mentioned 
 methods; while the more difficult process for the detection of 
 iron, calcium, magnesium, and phosphoric acid in presence of one 
 another is described in Chapter IV. 
 
 a. In the original acid solution, iron may be detected by sul- 
 phocyanate or ferridcyanide of potassium ; and phosphoric 
 acid by molybdate of ammonium and nitric acid. After any 
 excess of mineral acid, more than sufficient to keep the substance 
 in solution, has been neutralised with ammonia, the addition of 
 acetate of ammonium produces a buff-coloured precipitate of 
 phosphate of iron, unless, indeed, the ratio of phosphoric acid to 
 iron is very small. 
 
 (3. Barium and strontium may be detected in the original 
 solution by means of sulphate of potassium, and be distinguished 
 by the different behaviour of their salts, with hydrofluo.silicic 
 acid, or before the blowpipe. Calcium may also be detected in 
 the original solution by the addition thereto of sulphate of potas- 
 sium and proof spirit. The precipitated sulphate of calcium may 
 be collected on a filter, washed with proof spirit, dissolved in water, 
 and the resulting solution teste.d with oxalate of ammonium. 
 
106 SPECIAL SUBSTANCES. 
 
 Phosphoric acid may be detected in the original solution by 
 molybdate of ammonium and nitric acid. 
 
 Oxalic acid is recognisable by the effervescence produced on 
 adding dilute sulphuric acid and peroxide of manganese to the ori- 
 ginal substance. Or it may be detected by boiling the original acid 
 solution with excess of carbonate of sodium, filtering, rendering 
 the filtrate slightly acid with acetic acid, and then adding chloride 
 of calcium, when a white precipitate of oxalate of calcium will be 
 produced. Moreover, like phosphate of iron, oxalate of calcium 
 is thrown down from its original solution in hydrochloric acid by 
 addition of acetate of ammonium. 
 
 Fluorine may be detected by treating the original substance 
 with sulphuric acid, or with sulphuric acid and silica (vide par. 
 1 06). 
 
 y. Magnesium in any form is not precipitated from acid 
 solutions by sulphate of potassium and proof spirit, or by acetate 
 6f ammonium ; but, in presence of phosphoric acid, is thrown 
 down from its acid solution by excess of ammonia as a white 
 crystalline deposit of triple phosphate, which may be examined 
 microscopically, and if necessary be dissolved in acetic or hydro- 
 chloric acid, so as to form a solution that may be submitted to 
 further examination. 
 
 (60.) OXIDES AND SULPHIDES. 
 
 The oxides are generally recognised by their physical proper- 
 ties, and by their not answering to the tests for any of the acids. 
 Peroxides when boiled with hydrochloric acid, or with sulphuric 
 acid and common palt, give off chlorine gas. The soluble hydrates 
 or hydrated oxides are known by their alkalinity to test paper ; ; 
 by their effervescing not at all, or but very slightly, upon the; 
 addition of an acid ; and by their giving a brown precipitate \ 
 with solution of nitrate of silver. The solution of a hydrate is,: 
 moreover, distinguishable from that of a carbonate by the circum- : 
 stance that an admixture with it of excess of chloride of barium: 
 does not affect its alkaline reaction. - - 
 
ACIDS. IO7 ' 
 
 Such of the sulphides as are soluble only in nitro-hydro- 
 chloric, or in concentrated nitric acid, become by the action of the = 
 acid converted into sulphates. That the sulphuric acid did not, > 
 however, exist in the original substance, is shown by 1 fusing this 
 latter with carbonate of sodium, when the fused mass will afford 
 the reactions of a soluble sulphide instead of those of a soluble 
 sulphate. Some sulphides are extremely difficult to dissolve 
 completely in acid, in consequence of the deposition of sulphur, 
 which fuses round the unaltered substance, and prevents any action 
 of the acid upon it. This is particularly the case with the sulphides 
 of arsenic and mercury in their ordinary sublimed state. But 
 these sulphides are easily recognised by their colour, their vola- \ 
 tility, and by their reducibility with conversion into sublimed 
 metal, when heated with soda flux, for instance. 
 
 (6 1.) ACIDS OR SALTS OF HYDROGEN. 
 
 The ordinary solid acids are known by their solubility in cold 
 or hot water to form strongly acid liquids, which effervesce with 
 alkaline carbonates, are not precipitated by the several reagents 
 for the metals, and do not evolve ammonia when heated with 
 caustic potash. The boric and phosphoric acids yield, upon 
 ignition, fusible residues of boric anhydride, and metaphosphoric 
 acid respectively. 
 
 The oxalic, benzoic, tartaric, and citric acids are entirely dissi- 
 pated by a prolonged heat, the two last furnishing an intermediate 
 product of carbon. 
 
 The liquid acids, namely, the sulphuric, nitric, hydrochloric, 
 and acetic acids, are known by their liquidity, volatility, strongly- 
 marked acid reaction, and, except the sulphuric, by their charac- 
 teristic odours. They jrive only negative results when tested for 
 bases. The sulphuric and nitric acids are easily recognised by 
 their respective actions on metallic copper, and hydrochloric acid 
 by its action on peroxide of manganese (vide Chapter III.). 
 
 Acid salts, such, for instance, as the acid sulphates, oxalates, 
 and tartrates of alkali-metal or ammonium, manifest a strongly 
 
I08 SPECIAL SUBSTANCES. 
 
 acid reaction to test-paper, and effervesce with alkaline carbonates. 
 But they either evolve ammonia when treated with caustic potash, 
 or leave a fixed residue upon ignition, which, in the case of the 
 acid oxalates and tartrates, consists of alkaline carbonate. The 
 acid salts of potassium react with perchloride of platinum, but 
 not with tartaric acid, unless previously neutralised with soda. 
 
 (62.) MISCELLANEOUS SALTS. 
 
 Iodide of potassium solution reacts satisfactorily when 
 treated with tartaric acid, but yields a dark brown liquid with 
 perchloride of platinum. But after its iodine has been precipitated 
 with excess of nitrate of silver, and the excess of silver with 
 hydrochloric acid, the filtered liquid yields with perchloride of 
 platinum the characteristic yellow precipitate of potassio-chloride 
 of platinum. 
 
 Calomel occurs as a heavy, white, volatile powder. It is 
 readily soluble in concentrated nitric acid, but in the act of 
 solution becomes converted into a mercuric salt. That it was 
 originally a mercurous salt is shown by the powder itself becom- 
 ing black when agitated with potash-water. 
 
 White precipitate, amido-chk ride of mercury, or chloride 
 of mercurammonium, is a mercuric compound, readily distin- 
 guishable from calomel by heating it gently with potash-water, 
 whereby it becomes of an orange-yellow colour, while ammoniacal 
 vapours are given off. It is insoluble in water, soluble in nitric 
 and hydrochloric acids, and dissipated by heat. 
 
 The sulphides of arsenic, known as realgar and orpiment, 
 are orange or \ellow coloured volatile solids. When boiled with 
 nitro-hydrochloric acid, they are converted in great measure into 
 arsenic acid, which may be obtained st lid on evaporation. Its 
 solution is precipitated very slowly by sulphuretted hydrogen, 
 Unless previously reduced by treatment with sulphurous acid. 
 
LIQUID OR DISSOLVED SUBSTANCES. 1 09 
 
 (63.) LIQUID OR DISSOLVED SUBSTANCES. 
 
 A few drops of the liquid are evaporated on a glass slip, and 
 the residue, if any, examined microscopically. Should there be 
 an appreciable solid residue, a further quantity of liquid may be 
 evaporated down in a capsule, the vapour examined for its odour 
 and reaction, and the residue submitted to ignition, &c.; as de- 
 scribed in pars. 25 and 26. 
 
 The reaction of the liquid to test-paper is next ascertained. 
 Among volatile liquids, water, alcohol, and ether are neutral ; 
 ammonia, alkaline ; and the sulphuric, nitric, hydrochloric, and 
 acetic acids, strongly acid. These several liquids are readily 
 distinguishable from one another by a few simple tests. 
 
 Solutions which leave a saline residue on evaporation, and are 
 perfectly neutral, will most probably prove to contain some salt 
 of an alkali- or alkaline earth- rnetal; salts of the heavy metals, 
 with a few exceptions only, exhibiting a more or less marked 
 acidity. 
 
 Solutions which have an alkaline reaction, known by their 
 turning rose paper green, turmeric paper brown, or reddened 
 litmus paper blue, may contain the hydrate or sulphydrate of 
 an alkaline ear th -metal ; or the hydrate, sulphydrate, carbonate, 
 phosphate, borate, or .silicate of an alkali metal, or some heavy 
 metal dissolved in excess of alkaline hydrate or carbonate (vide 
 par. 64). 
 
 Solutions which have an acid reaction, known by their redden- 
 ing blue litmus paper, may contain a free acid, an acid salt, or 
 the normal salt of a heavy metal, in which last case the addition 
 of even a drop of potash will most probably cause a precipitate. 
 
 After the above preliminary examination, the solution may be 
 tested according to the directions of Tables I., II., III., and V. ; 
 or, in some cases, the evaporated residue may be dissolved in 
 water or acid, and the solution so formed be employed by pre- 
 ference. The original solvent, if suspected to be other than 
 water, may be distilled off, condensed in a receiver, and separately 
 examined. 
 
IIO . SPECIAL SUBSTANCES. 
 
 (64.) ALKALINE SOLUTIONS OF HEAVY METALS. 
 
 The hydrates of barium, strontium, and calcium, like those of 
 the alkali metals, are soluble in water. The hydrates of all other 
 metals are insoluble, and consequently, precipitable by caustic 
 alkalies. The hydrates of lead, chromium, aluminum, and zinc, 
 are readily soluble in excess of potash or soda ; those of silver, 
 copper, cadmium, nickel, cobalt, manganese, zinc, and magnesium 
 readily, and those of chromium and iron (ferrous salts) sparingly 
 soluble in excess of ammonia, especially in presence of neutral 
 ammoniacal salts ; while those of bismuth, mercury, and iron 
 (ferric salts), are insoluble in excess of either reagent. On boiling 
 alkaline solutions of chromium, the whole of the chromic hydrate 
 is reprecipitated. 
 
 The hydrates of the metals tin, antimony, and arsenic, 
 whose sulphides are soluble in sulphide of ammonium, have 
 no practical interest in analysis. The teroxide of arsenic is 
 slightly soluble in water, and freely soluble in ail alkaline 
 liquids. The hydrate of antimony and both hydrates of tin are 
 soluble in excess of potash, while stannic hydrate is soluble also 
 in excess of ammonia. The potash solution of stannous hydrate 
 is decomposed on boiling into metallic tin, which is deposited 
 as a black powder, and stannate of potassium which remains 
 dissolved. 
 
 The precipitates produced by carbonate of ammonium in solu- 
 tions of silver, copper, nickel, cobalt, zinc, and magnesium, are 
 readily soluble in excess of the reagent, especially when chloride 
 of ammonium is also present, while those of iron (ferrous salts) 
 and chrome are sparingly soluble. The precipitates produced in 
 solutions of cadmium and manganese are insoluble in excess, as 
 are also all those produced in solutions of metals whose hydrates 
 are insoluble in ammonia. The precipitates produced by fixed 
 alkaline carbonates are all insoluble in excess, except that pro- 
 duced in stannic salts, which dissolves in excess of the preci- 
 pitant, and is again thrown down on ebullition. 
 
EXAMINATION FOR BASES OF GROUP I. Ill 
 
 VIII. INDIVIDUAL BASES OF GROUP I. 
 
 The reactions of the individual bases of this group may be con- 
 veniently realised by operating with the following substances : 
 
 TIN . . The crystallised proto-chloride and precipitated peroxide. 
 ARSENIC . The white oxide. 
 
 ANTIMONY. The native tersnlphiHe and tartar-emetic. 
 BISMUTH . The crystallised nitrate and precipitated oxide. 
 MERCURY . Corrosive sublimate, t^e red mercuric oxide, and the crys- 
 tallised mercurous nitrate. 
 
 LEAD . . The oxide, carbonate, nitrate, and acetate. 
 SILVER. . The nitrate and oxide. 
 COPPER . The sulphate and oxide. 
 CADMIUM . The sulphate and carbonate. 
 
 (65.) TIN. 
 
 Tin salts are of two kinds, stannous or protosalts, represented 
 by protochloride of tin SnCl a , and stannic or persalts, represented 
 by perchloride of tin SnCl 4 . 
 
 a. When compounds of tin are heated upon charcoal with a 
 mixture of carbonate of sodium and cyanide of potassium, a 
 globule of white malleable metal is produced with very slight, if 
 any, incrustation. If this globule be hammered out, and dis- 
 solved in hydrochloric acid, the tests for stannoua salts can be 
 applied to the solution so formed. 
 
 STANNOUS SALTS. 
 
 a. Sulphydric acid produces a brown precipitate of proto- 
 sulphide of tin SnS, which dissolves in yellow sulphide of 
 ammonium with conversion into persulphide of tin SnS 2 , so that 
 on adding an acid to the solution, a yellow and not a brown pre- 
 cipitate is separated. The protosulphide of tin first thrown down 
 is converted by boiling nitric acid into a white insoluble powder 
 consisting of stannic anhydride SnO a . 
 
112 EXAMINATION FOR BASES OF GROUP I. 
 
 fi. Solution of corrosive sublimate, added carefully 1o stannous 
 solutions, produces a white precipitate of calomel HgCl, which 
 speedily becomes grey, and finally black, from its reduction to 
 the state of metallic mercury. 
 
 STANNIC SALTS. 
 
 a. Sulphydric acid produces a yellow precipitate of disulphide 
 of tin SnS a , which is insoluble in the carbonate, but soluble 
 in the hydrate and sulphide of ammonium, and reprecipitable 
 therefrom on the addition of an acid. It is likewise soluble 
 in boiling hydrochloric acid, more readily on the addition 
 of a little nitric acid also, and is converted by concentrated 
 nitric acid into a white insoluble powder of stannic anhydride 
 
 (66.) ARSENIC. 
 
 Arsenious acid is convertible into arsenic acid by boiling it 
 with concentrated nitric acid, to which a little hydrochloric acid 
 may be added with advantage. But in order to apply the various 
 tests successfully, the acid liquid must be evaporated to dryness, 
 and the residue dissolved in water. Arsenic acid is readily con- 
 vertible into arsenious acid by the passage of sulphurous acid gas 
 through its solution, or by heating it with sulphite of sodium and 
 dilute hydrochloric acid. 
 
 a. Sulphydric acid produces, in acidulated solutions of arse- 
 nious acid, or of arsenic acid after the addition of sulphurous 
 acid, a yellow precipitate of trisulphide of arsenic As a S 3 , which is 
 soluble in carbonate, hydrate, and sulphide of ammonium, and 
 reprecipitated on the addition of an acid. It is insoluble in 
 boiling hydrochloric acid, but is readily dissolved by hot nitric 
 or nitro-hydrochloric acid. 
 
 j3. Nitrate of silver produces in neutral or slightly ammoniacal 
 solutions of arsenious acid a yellow precipitate of arsenite of 
 silver Ag 3 As0 3 , and from similar solutions of arsenic acid a 
 brick -dust red precipitate of arseniate of silver Ag 3 As0 4 . Both 
 precipitates are soluble in excess of either ammonia or nitric acid. 
 
ARSENIC ANTIMONY BISMUTH. 113 
 
 y. Sulphate of copper produces, in neutral or very faintly 
 ammoniacal solutions of arsenious acid a grass-green precipitate 
 of arsenite of copper HCu"As0 3 , and in similar solutions of arsenic 
 acid a pale blue precipitate of arseniate of copper Cu" 3 (As0 4 ) a . 
 Both precipitates are soluble in excess of either ammonia or nitric 
 or hydrochloric acid. 
 
 ?. When a compound of arsenic is mixed with soda-flux, and 
 heated in a subliming tube, a steel-grey ring of reduced metal 
 condenses in the upper or cool part of the tube. 
 
 (67.) ANTIMONY. 
 
 o. Sulphydric acid produces an orange-coloured precipitate 
 of trisulphide of antimony Sb a S 3 , which is insoluble in carbo- 
 nate, but soluble in hydrate and sulphide of ammonium, and 
 reprecipi table on the addition of an acid. It is also dissolved by 
 hydrochloric acid with the aid of heat, and is converted almost 
 entirely by strong nitric acid into a white insoluble powder, con- 
 sisting of tetroxide of antimony Sb a 4 . 
 
 (3. Water, added to certain antimony solutions (not to all), 
 produces a white precipitate of a basic salt of antimony, soluble 
 in excess of tartaric, hydrochloric, or nitric acid. 
 
 y. Antimony compounds, when fused with carbonate of 
 sodium on charcoal in the reducing flame, yield a bead of brittle 
 metal with an abundant bluish-white incrustation. If the heat 
 be prolonged, the metal volatilises entirely with the production 
 of white fumes of teroxide of antimony Sb a O 3 . 
 
 (68.) BISMUTH. 
 
 a. Sulphydric acid produces a brownish -black precipitate of 
 trisulphide of bismuth Bi 2 S 3 , which is insoluble in sulphide of 
 ammonium. It dissolves readily in hot nitre-muriatic, nitric, or 
 hydrochloric acid. 
 
 /3. Caustic alkalies give a white precipitate of hydrate of 
 
 1 
 
114 EXAMINATION FOR BASES OF GROUP I. 
 
 bismuth Bi a 3 .H a O, insoluble in excess of either potash or am- 
 monia. 
 
 y. Water, when added to moderately- concentrated and not 
 over-acid solutions of bismuth, causes a dense white precipitate 
 of a basic bismuth salt, which does not disappear on the addition 
 of tartaric acid, but dissolves in excess of nitric or hydrochloric 
 acid. 
 
 3. Bismuth compounds, when mixed with carbonate of sodium 
 and heated upon charcoal in the reducing blowpipe flame, yield a 
 brittle metallic globule and a yellow incrustation. 
 
 (69.) MERCURY. 
 
 There are two classes of mercury salts, namely, the mercurous, 
 represented by calomel HgCl, and the mercuric, represented by 
 corrosive sublimate HgCl 2 . Certain reactions are common to 
 both, while others are distinctive between them. 
 
 a. An excess of sulphydric acid produces a black precipi- 
 tate of mercurous sulphide Hg a S, or of mercuric sulphide HgS, 
 which is insoluble in sulphide of ammonium, and also in strong 
 hot nitric and hydrochloric acids taken separately, but is readily 
 soluble in a mixture of the two. An insufficiency of sulphydric 
 acid produces in mercuric salts a highly characteristic white pre- 
 cipitate of doubtful composition, which, as the proportion of gas 
 increases, becomes orange, brown, and finally black. 
 
 ft. Protochloride of tin produces at first a white precipitate of 
 calomel HgCl, which becomes in succession grey and almost 
 black on adding more of the reagent and warming gently. If 
 the supernatant liquor be poured off, and the deposit boiled with 
 hydrochloric acid, globules of metallic mercury make their 
 appearance. 
 
 y. Mercury compounds mixed with carbonate of sodium, and 
 heated in a reduction -tube, furnish a sublimate of well-defined 
 mercurial globules. 
 
MERCURY LEAD. 115 
 
 MERCUROUS SALTS. 
 
 a. Potash and ammonia alike produce a black precipitate, the 
 former of mercurous hydrate Hg 2 O.H 2 0, the latter of some amido- 
 mercurous compound. 
 
 /3. Hydrochloric acid produces a white precipitate of calomel 
 HgCl, which dissolves in boiling nitric acid. It is turned black 
 by ammouia, being converted into amido- mercurous chloride. 
 
 MERCURIC SALTS. 
 
 a. Potash gives a yellow precipitate of mercuric oxide HgO, 
 which is turned white on the addition of ammonia, or in presence of 
 an ammoniacal salt. Ammonia produces a white precipitate of 
 some arnido-mercuric compound. 
 
 (3. Iodide of potassium, added carefully, produces a bright 
 orange-red precipitate of mercuric iodide Hgl z , which dissolves in 
 excess of the reagent, forming a colourless solution. 
 
 (70.) LEAD. 
 
 a. Sulphydric acid produces a black (occasionally red) pre- 
 cipitate of sulphide of lead PbS, which is insoluble in sulphide 
 of ammonium, but dissolves when heated with not too con- 
 centrated nitric or hydrochloric acid. Strong nitric acid con- 
 verts it into a white insoluble deposit of sulphate of lead PbS0 4 . 
 
 /3. Caustic alkalies give a white precipitate of hydrate of lead 
 PbO.H a O, soluble in excess of potash. 
 
 y. In moderately strong solutions, hydrochloric acid gives a 
 white crystalline precipitate of chloride of lead PbCl a , which is 
 soluble in boiling water, unaffected by ammonia, and soluble in 
 great excess of potash. 
 
 . Dilute sulphuric acid or a dissolved sulphate gives a dense 
 white precipitate of sulphate of lead PbS0 4 , which is insoluble in 
 dilute acids, soluble in strong hydrochloric acid with the aid of 
 heat, and also in a large excess of potash. 
 
 i2 
 
Il6 EXAMINATION FOR BASES OF GROUP I. 
 
 e. Lead compounds, when fused with carbonate of sodium and 
 charcoal in the reducing blowpipe flame, yield a globule of soft 
 metal and a brownish-yellow incrustation. 
 
 (71.) SILVER. 
 
 a. Sulphydric acid gives a black precipitate of sulphide of 
 silver Ag a S, insoluble in sulphide of ammonium, soluble in warm 
 nitric acid, and converted by ebullition with hydrochloric acid 
 into a white deposit of chloride of silver AgCl. 
 
 /3. Caustic alkalies give a brown precipitate of hydrate of 
 silver Ag a O.H 2 0, which is insoluble in excess of potash, but soluble 
 in ammonia, forming a colourless solution. 
 
 y. Hydrochloric acid gives in solutions of silver salts a white 
 precipitate of chloride of silver AgCl, which is insoluble even in 
 boiling nitric acid, but readily soluble in ammonia. The colour 
 of the precipitate changes to a slate-purple by exposure to light. 
 
 <L Silver compounds, when fused with carbonate of sodium 
 upon a charcoal support in the reducing blowpipe flame, yield a 
 button of hard white malleable metal, without any incrustation 
 being formed on the charcoal. 
 
 (72.) COPPER. 
 
 a. SulpJiydric acid produces a dark-brown precipitate of 
 sulphide of copper CuS, which is insoluble in sulphide of 
 potassium, and but sparingly soluble in sulphide of ammonium. 
 It dissolves readily in nitric but not in hydrochloric acid, save by 
 an application of heat. 
 
 j8. Potash gives a pale blue precipitate of hydrate of copper 
 CuO.H 2 0, which is insoluble in excess, and converted by ebullition 
 into black oxide of copper CuO. Ammonia gives a similar blue 
 precipitate of hydrate of copper, which is soluble in excess of the 
 reagent, forming a deep blue solution, the transparency of which 
 is not affected by the addition of a moderate quantity of potash. 
 
COPPER CA DMIUM. 1 1 7 
 
 The pale-blue precipitate produced by carbonate of ammonium is 
 also readily soluble in excess of the reagent, with production of a 
 deep blue liquid. 
 
 y. Ferrocyanide of potassium gives a chocolate-coloured preci- 
 pitate of ferrocyanide of copper Cu a FeCy 6 , which is decomposed by 
 caustic potash, and is then freely soluble in ammonia, forming a 
 deep blue liquid. 
 
 ?. A piece of clean iron or steel dipped into an acidulated 
 copper solution becomes coated with metallic copper, which may 
 be dissolved off by the conjoint action of ammonia and air into a 
 deep blue liquid. 
 
 e. The borax bead heated with a particle of any copper-com- 
 pound becomes blue or green in the oxidising, and nearly 
 colourless or reddish-grey in the reducing, flame. 
 
 (73.) CADMIUM. 
 
 a. The precipitate of sulphide of cadmium CdS, produced by 
 sulphydric acid, is of a bright yellow colour, and insoluble in 
 sulphide of ammonium. It disappears readily on the addition 
 of nitric or hydrochloric acid, and does not form in very acid 
 solutions. 
 
 ft. Caustic alkalies give a white precipitate of hydrate of 
 cadmium CdO.H 2 O, soluble in excess of ammonia, but not in that 
 of potash. The precipitate produced by carbonate of ammonium 
 does not disappear in excess of the reagent. 
 
 y. Cadmium compounds, fused with carbonate of sodium in. 
 the reducing blowpipe flame, give a reddish-brown incrustation 
 of oxide of cadmium CdO, but no bead of metal. 
 
1 1 8 EXAMINATION FOR BASES OF GROUP II. 
 
 IX. INDIVIDUAL BASES OF GROUP II. 
 
 The reactions of the individual bases of this group may be 
 conveniently realised by operating with the following substances: 
 
 NICKEL . . The oxide and sulphate. 
 
 COBALT . . The oxide. 
 
 MANGANESE. The sulphate, chloride, and carbonate. 
 
 IRON . . . The red and black oxides, the sulphate and sulphide. 
 
 ZINC . . . The oxide and sulphate. 
 
 CHROMIUM . The precipitated oxide and chrome alum. 
 
 ALUMINUM . The hydrate and sulphate. 
 
 (74.) NICKEL. 
 Solutions of nickel are generally of a green colour. 
 
 a. Sulphide of ammonium gives with nickel salts a black pre- 
 cipitate of sulphide of nickel NiS, not soluble in hydrochloric acid 
 until after the addition of a drop or two of nitric acid. 
 
 /3. Ammonia gives a slight greenish precipitate of hydrate of 
 nickel NiO.H.,0, soluble in excess of the reagent, forming a violet- 
 blue liquid, from which potash reprecipitates the green hydrate. 
 Moreover, potash throws down this hydrate readily from all ordi- 
 nary nickel solutions. 
 
 y. In the reducing flame, nickel renders the borax bead pur- 
 plish-grey and turbid, and in the oxidising flame of a dark sherry 
 colour with a tinge of violet. If a fragment of nitre be added, 
 and the bead again heated in the oxidising flame, a well-marked 
 purple colour is produced. 
 
 (75.) COBALT. 
 
 Cobalt solutions are pink when dilute, blue when concen- 
 trated. 
 
 a. Sulphide of ammonium gives with cobalt salts a black 
 precipitate of sulphide of cobalt CoS, not soluble in hydro- 
 chloric acid until after the addition of a few drops of nitric 
 acid. 
 
COBALT MANGANESE. 1 19 
 
 /3. Potash gives a blue precipitate of prothydrate of cobalt 
 CO.H 2 0, insoluble in excess of the precipitant. Excess of ammonia, 
 especially in presence of chloride of ammonium, produces a 
 brownish-pink solution, becoming brown and opaque on exposure 
 to air, from the deposition of the insoluble sesquihydrate. 
 
 y. Cobalt compounds impart to the borax bead, when heated 
 in either flame of the blowpipe, a deep sapphire-blue colour. 
 
 (76.) MANGANESE. 
 
 Manganese solutions are of a faint pink tinge, or altogether 
 colourless. 
 
 a. Sulphide of ammonium gives a buff-coloured precipitate of 
 sulphide of manganese MnS, soluble even in acetic acid. 
 
 ft. Potash gives a white precipitate of prothydrate of manga- 
 nese MnO.H z O, speedily becoming brown on exposure, from its 
 conversion into the sesquihydrate Mn z 3 .H 8 0. If to the solution 
 of a manganous salt containing chloride of ammonium, an excess 
 of ammonia be added at once, a clear colourless solution will be 
 produced, quickly becoming brown and opaque when exposed to 
 the air, from a conversion of the soluble proto- into the insoluble 
 sesqui-compou nd . 
 
 y. The borax bead with manganese is amethyst-red in the 
 oxidising, and nearly colourless in the reducing, flame. Its 
 appearance is much interfered with by the presence of a trace of 
 iron. 
 
 S. Compounds of manganese, fused upon platinum foil with 
 carbonate of sodium in the oxidising flame of the blowpipe, 
 either with or without the addition of a little nitre, yield a bluish- 
 green fusible mass of manganate of sodium Na a Mn0 4 . For this 
 experiment but a very small quantity of the manganese compound 
 should be employed. 
 
I2O EXAMINATION FOR BASES OF GROUP II. 
 
 (77.) IRON. 
 
 There are two classes of iron salts, namely, ferrous or proto- 
 salts, represented by green vitriol FeS0 4 , and ferric or persalts, 
 represented by sesquichloride of iron FeCl 3 or Fe,Cl 6 . The proto- 
 salts are rarely ever free from some admixture with persalts. 
 
 a. Sulphide of ammonium gives a black precipitate of protosul- 
 phide of iron FeS, readily soluble in hydrochloric acid. The 
 precipitate, when thrown down from ferric salts, is accompanied 
 by free sulphur. 
 
 ft. Iron compounds dissolve in the borax bead, forming a glass 
 which is of a bottle-green colour in the reducing, and of a yellow- 
 ish-brown colour in the oxidising, flame. Ferrous compounds 
 give the green, and ferric compounds the yellow, colour most 
 readily. 
 
 FERROUS SALTS. 
 
 Ferrous solutions are generally colourless, or of a pale green 
 tint. 
 
 a. Caustic alkalies give a dingy green precipitate of ferrous 
 hydrate FeO.H s O, which becomes red on exposure to air. The 
 pure, nearly white prothydrate is sparingly soluble in excess of 
 ammonia and chloride of ammonium. 
 
 j3. Ferrocyanide of potassium gives a pale blue precipitate of 
 double ferrocyanide of iron and potassium K a Fe a Cy 6 , which be- 
 comes dark blue on exposure to air. 
 
 y. Ferridcyanide of potassium gives a dark-blue precipitate of 
 ferridcyanide of iron Fe 5 Cy Ia , or Fe" 3 Fe z '"Cy IJ5 , insoluble in dilute 
 acids and decomposible by caustic alkalies. 
 
 FERRIC SALTS. 
 
 Ferric solutions are generally of a yellow, brown, or red 
 colour. 
 
 a. Caustic and carbonated alkalies alike give a brick- dust red 
 nrecipitate of ferric hydrate Fe,0 3 .H,0, accompanied in the case 
 
IRON ZINC. 121 
 
 of the carbonates by an evolution of carbonic acid. The 
 precipitate is quite insoluble in the hydrates of potassium and 
 ammonium, and also in their respective carbonates at a boiling 
 heat. 
 
 j3. Ferrocyanide of potassium gives a deep blue-coloured 
 precipitate of sesquiferrocyanide of iron Fe 7 Cy l8 , or Fe" 3 Fe'" 4 Cy l8 , 
 insoluble in dilute acids, and decomposible by caustic alkalies. 
 The ferridcyanide does not produce any precipitate, but gives to 
 the ferric solution a colour which is brown or red according to 
 circumstances. 
 
 y. Sulphocyanate of potassium imparts to ferric solutions a 
 deep red colour, from the formation of ferric sulphocyanate 
 FeCy 3 S 3 , or Fe(CyS) 3 . 
 
 (78.) ZlNC. 
 Zinc solutions are usually colourless. 
 
 a. Sulphide of ammonium gives a white precipitate of sulphide 
 of zinc ZnS, which is insoluble in acetic, but readily soluble in 
 hydrochloric, acid. Unlike most zinc precipitates, it is insoluble 
 in any alkaline solution. 
 
 /3. Caustic alkalies give with solutions of zinc a white pre- 
 cipitate of hydrate of zinc ZnO.H a O, soluble in a large excess of 
 the precipitant. Alkaline carbonates also give a white precipi- 
 tate of a highly basic carbonate of zinc, insoluble in excess of the 
 fixed alkaline carbonates, but soluble in presence of ammoniacal 
 salts. 
 
 y. Zinc salts, heated on platinum foil, leave a fixed infusible 
 residue, which is yellow when hot, white when cold. After being 
 moistened with solution of nitrate of cobalt, and reignited in the 
 blowpipe flame, it assumes a fine green colour. 
 
 B. Zinc salts, mixed with carbonate of sodium or cyanide flux, 
 and heated in the reducing blowpipe flame, deposit upon the 
 charcoal an incrustation which is yellow when hot, white when 
 cold, and green after ignition with nitrate of cobalt. 
 
122 EXAMINATION FOR BASES OF GROUP II. 
 
 (79.) CHROMIUM. 
 
 Solutions of chromic salts are mostly of a green or violet 
 colour. 
 
 a. Caustic alkalies, their sulphides or sulphydrates, and car- 
 bonates throw down from chrome solutions a greenish precipitate 
 of 'hydrate of chrome Cr a 3 .H a O, which is slightly soluble in excess 
 of ammonia, more so in excess of potash, and in each instance 
 reprecipitable on boiling. Its production by sulphides and car- 
 bonates respectively is accompanied by an evolution of sulphydric 
 or carbonic acid. 
 
 /3. Chrome imparts to the borax bead a fine green colour, per- 
 manent in both flames of the blowpipe. 
 
 y. When a chrome compound is fused on platinum foil with 
 a little carbonate of sodium and nitre, a yellow mass of chromate 
 .of sodium Na a Cr0 4 , is produced, which dissolves in water to form 
 a solution, giving with acetate of lead a yellow precipitate of 
 chromate of lead PbCrO 4 . 
 
 (80.) ALUMINUM. 
 
 a. Caustic alkalies, their carbonates and sulphides or sulphy- 
 drates, give with aluminous solutions a white gelatinous precipi- 
 l ate of hydrate of aluminum Al,0 3 .H a O, which is soluble in excess 
 rf potash, but reprecipitated on the addition of chloride of am- 
 monium. The action of the carbonates and sulphides respec- 
 tively is accompanied by an evolution of carbonic or sulphydric 
 acid. 
 
 /3. Salts of aluminum, when heated on charcoal or platinum 
 foil, leave a white, infusible, highly incandescent residue, which, 
 when moistened with nitrate of cobalt solution and reignited in 
 the blowpipe flame, assumes a bright blue colour. 
 
GROUP III. BARIUM STRONTIUM CALCIUM. 123 
 
 X. INDIVIDUAL BASES OF GROUP III. 
 
 The reactions of the individual bases of this group may be 
 conveniently realised by operating with the following substances : 
 
 BARIUM . . The carbonate, nitrate, and chloride. 
 
 STRONTIUM . The carbonate and nitrate. 
 
 CALCIUM . . The hydrate, carbonate, phosphate, oxalate, and sulphate. 
 
 MAGNESIUM . The oxide, carbonate, and sulphate. 
 
 POTASSIUM . The nitrate and sulphate. 
 
 SODIUM . . The carbonate, sulphate, chloride, and phosphate. 
 
 AMMONIUM . The sulphate, chloride, carbonate, phosphate, and oxalate. 
 
 (8 1.) BARIUM, STRONTIUM, CALCIUM. 
 These three metals possess many properties in common. 
 
 a. Their hydrates MO.H a O or M(HO) 2 , are all soluble in water, 
 so that the addition of caustic alkali, if perfectly free from car- 
 bonate, does not disturb their solutions. Their sulphides and 
 sulphyd rates are also soluble. 
 
 /3. The following salts of these metals are insoluble in water, 
 namely, the oxalates, phosphates, carbonates (even in the presence 
 of ammoniacal salts), and sulphates, sulphate of barium being 
 the most insoluble, sulphate of calcium the least so. Hence 
 neutral barium, strontium, and calcium salts are precipitated by 
 soluble oxalates, pi osphates, carbonates and sulphates. 
 
 y. When a barium, strontium, or calcium salt is ignited on 
 platinum foil, a Avhite fixed residue remains, which, except in the 
 case of the chlorides, is usually infusible. When moistened with 
 solution of nitrate of cobalt and reignited, the infusible mass 
 acquires an ill- defined grey colour. 
 
 (82.) BARIUM. 
 
 a. Sulphuric acid and solutions of all sulphates, even when very 
 dilute, give with barium salts a white precipitate of sulphate of 
 barium BaS0 4 , insoluble in acids and alkalies. 
 
1 24 EXAMINATION FOR BASES OF GROUP III. 
 
 /3. Hydrofluosilicic acid produces in acid and neutral solutions 
 a somewhat transparent precipitate of fluosilicate of barium 
 BaSiF 6 , tlie deposition of which is much facilitated by the addition 
 of a little alcohol. 
 
 y. Barium salts, when intensely heated before the blowpipe 
 upon a fine platinum wire, impart a marked apple-green colour to 
 the flame. 
 
 (83.) STRONTIUM. 
 
 a. Sulphuric acid and solutions of most sulphates, give a pre- 
 cipitate of sulphate of strontium SrS0 4 , insoluble in acids and 
 alkalies, very sparingly soluble in water. Strontium salts are not 
 precipitated by solution of sulphate of strontium, and very slowly 
 by solutions of the sulphates of calcium and potassium. 
 
 /3. Strontium salts, when intensely heated before the blowpipe 
 upon a fine platinum wire, impart a deep crimson colour to the 
 flame. 
 
 (84.) CALCIUM. 
 
 a. Sulphuric acid and strong solutions of sulphates give with 
 moderately strong calcium solutions a white precipitate of sulphate 
 of calcium CaS0 4 , slightly soluble in water, insoluble in proof- 
 spirit. But dilute calcium solutions are not precipitable by any 
 sulphate ; while even strong solutions are not precipitable by the 
 sulphates of strontium, calcium, and scarcely by that of potassium. 
 
 /3. Oxalate of ammonium produces in neutral calcium solutions 
 a white precipitate of oxalate of calcium CaC a 4 , soluble in nitric 
 and hydrochloric acids, insoluble in acetic and oxalic acids, and 
 insoluble in ammonia. 
 
 y. Calcium salts impart a fine orange-red colour to the blow- 
 pipe flame. 
 
 (85.) MAGNESIUM. - ' 
 
 a. Sulphydrate and sulphate of magnesium are soluble in 
 water. Hence magnesian salts are not precipitated by soluble 
 sulphydrates and sulphates. 
 
MAGNESIUM POTASSIUM. 125 
 
 j3. Hydrate, carbonate, oxalate, phosphate, and arseniate of 
 magnesium, are insoluble in water. Hence magnesian salts are 
 precipitated by soluble hydrates, carbonates, oxalates, phosphates, 
 and arseniates. But all magnesian precipitates, excepting the 
 phosphate and arseniate, are soluble in ammoniacal solutions. 
 When phosphate of sodium or ammonium is added to a solution 
 of magnesium containing chloride of ammonium and rendered 
 alkaline by ammonia, a white crystalline precipitate of triple 
 phosphate Mg(NH 4 )P0 4 , is produced, which is soluble in dilute 
 acids, insoluble in ammonia and ammoniacal salts. 
 
 y. Magnesium compounds, heated on charcoal or platinum 
 foil, leave a white fixed infusible residue, which when moistened 
 with nitrate of cobalt solution and reignited in the blowpipe 
 flame assumes a faint pink colour. 
 
 (86.) POTASSIUM. 
 
 a. All simple potassium salts, except the acid-tartrate, are 
 moderately soluble in water. Tartaric acid added in excess to 
 the neutral or alkaline solution of a potassium salt throws down a 
 white crystalline precipitate of cream of tartar KH 5 C 4 O 6 , which 
 frequently does not appear immediately. Its deposition is facili- 
 tated by stirring the mixed liquids, and by the addition of a little 
 alcohol to them. It is soluble in mineral acids, in hot water, and 
 in a large excess of cold water. 
 
 j3. Percliloride of platinum when added to neutral or acid 
 solutions of potassium throws down a yellow crystalline precipi- 
 tate of potassio- chloride of platinum K z PtCI 6 , or 2KCl.PtCl 4 . The 
 solution should generally be acidulated with a few drops of 
 hydrochloric acid before being tested. The precipitate does not 
 always appear immediately : its production is facilitated by stir- 
 ring and by the addition of a little alcohol. 
 
 y. Potassium salts when heated on charcoal or platinum foil 
 leave a fixed and generally fusible residue. When heated before 
 the blowpipe they impart to the flame a marked violet colour, 
 
126 EXAMINATION FOR ACIDS. 
 
 which, however, is not recognisable in the presence of even a 
 small quantity of sodium. 
 
 (87.) AMMONIUM. 
 
 a. All simple ammoniacal salts, except the acid tartrate, are 
 freely soluble in water. Tartaric acid reacts upon ammoniacal 
 as upon potassium salts. The resulting precipitate of acid tartrate 
 of ammonium (NH 4 )H 5 C 4 6 , is, however, more soluble in water 
 than the corresponding potassium compound, and consequently 
 does not form, save when the ammoniacal solution is moderately 
 concentrated. 
 
 (3. Per chloride of platinum reacts upon ammoniacal salts to form 
 the ammonio- chloride of platinum (NH 4 ) 2 PtCl 6 , or 2NH 4 Cl.PtCl 4 , 
 which closely resembles the corresponding potassium compound 
 in its appearance, solubility, and mode of deposition. 
 
 y. When any ammoniacal salt is boiled with potash or lime, 
 ammoniacal vapour is given off, which is recognisable by its 
 smell, by its action on te^t paper, and by its forming opaque 
 fumes when brought into contact with the vapour of hydro- 
 chloric acid. 
 
 3. All ammoniacal salts volatilise partly, most of them entirely, 
 when heated upon platinum foil or charcoal. 
 
 (88.) SODIUM. 
 
 a. Sodium solutions are non-precipitable, all simple sodium 
 salts being soluble in water. 
 
 /3. Sodium salts when heated on platinum foil or charcoal leave 
 a fixed residue, almost always fusible, and impart an intense 
 yellow colour to flame. 
 
 XI. KEACTIONS OF INDIVIDUAL ACIDS. 
 (89.) CHROMATES. 
 
 Chromates are usually of a yellow or red colour, and, except 
 those of the alkali metals, are more or less insoluble in water. 
 
CHROMATES NITRATES CHLORATES. 12 J 
 
 a. Chromates acidified with hydrochloric acid, and treated 
 with sulphuretted hydrogen, yield a deposit of sulphur, and a 
 green solution of chromic chloride, CrCl 3 or Cr a Cl 6 . The same 
 compound is produced on boiling the solution of a chromate with 
 hydrochloric acid and a little alcohol. To it the ordinary tests 
 for chrome salts can be applied. 
 
 ft. Nitrate of silver gives a dark red precipitate of chromate of 
 silver Ag a O0 4 , soluble in nitric acid. Nitrate of barium and 
 acetate of lead throw down yellow precipitates of the chromates 
 of the respective metals. 
 
 (90.) NITRATES. 
 
 The nitrates are soluble or non-precipitable salts, which de- 
 flagrate when ignited upon charcoal or with organic matter. 
 
 a. When a nitrate, or the concentrated solution of a nitrate, is 
 gently heated with sulphuric acid and a few copper turnings, 
 brown fumes of peroxide of nitrogen N 2 4 , are evolved, which 
 redden, but do not bleach, litmus paper, and produce 
 a purple colouration on starch paper moistened with J ^* ' ' 
 iodide of potassium. 
 
 ft. A solution of protosulphate of iron carefully 
 poured upon sulphuric acid, to which a minute por- 
 tion of a solid or dissolved nitrate has been added, 
 produces a deep brown halo at the junction of the 
 two liquids, as seen in fig. 36. 
 
 y. When a minute quantity of gold-leaf is boiled 
 in hydrochloric acid, no action is produced ; but, on 
 the addition of a little nitric acid or a nitrate, the 
 gold quickly disappears, and may be detected in 
 solution by protochloride of tin, which gives rise to 
 a purplish precipitate. 
 
 (91.) CHLORATES. 
 The chlorates, like the nitrates, are soluble or non-precipitable 
 
128 EXAMINATION FOR ACIDS. 
 
 salts, which deflagrate when ignited upon charcoal or with organic 
 matter. 
 
 a. Strong sulphuric acid added to a solid chlorate produces a 
 brown colouration with crackling detonation, especially when 
 gently warmed. The experiment should be made carefully, and 
 with but a small quantity of the salt, for fear of an explosion and 
 scattering of the acid. 
 
 ft. The addition of some solid or dissolved chlorate to hydro- 
 chloric acid enables it to bleach litmus and dissolve gold-leaf. 
 Strong hydrochloric acid reacts with a moderate quantity of 
 a solid chlorate to produce a greenish-yellow gas known as 
 euchlorine. 
 
 y. Chlorates of alkali-metal, when heated alone, and other 
 chlorates, when heated with carbonate of sodium in a reduction 
 tube, evolve oxygen, known by its inflaming a piece of incan- 
 descent wood ; and leave a residue of alkaline chloride, recog- 
 nisable by adding nitrate of silver to its solution previously 
 acidified with nitric acid, when a white precipitate of chloride of 
 silver is thrown down. 
 
 (92.) CARBONATES. 
 
 On adding hydrochloric or slightly diluted sulphuric acid to a 
 solid or dissolved carbonate, effervescence of carbonic anhydride 
 C0 a , is produced, either immediately or on gently warming. The 
 gas is free from any marked smell, and does not affect lead paper, 
 but turns lime water milky, from the precipitation of carbonate 
 of calcium CaC0 3 . It may be tested by means of the apparatus 
 shown in fig. 37 ; or, being one and a half times as heavy as air, 
 it may be generated in one test tube, and then carefully poured 
 into another containing some lime water, with which it is to be 
 agitated. The lime water may be replaced by baryta- water or a 
 solution of basic acetate of lead. 
 
 /3. Soluble carbonates give precipitates with salts of silver, 
 barium, calcium, &c., &c., which disappear with effervescence on 
 the addition of any acid. 
 
SULPHIDES AND SULPHYDRATES. 
 
 I2 9 
 
 (93.) SULPHIDES AND SULPHYDRATES. 
 
 a. Most sulphides when acted upon by hydrochloric or mode- 
 rately dilute sulphuric acid, especially -p. ^ 
 
 on the application of heat, evolve sul- 
 phuretted hydrogen, which is known 
 by its offensive smell, and by the 
 brown or lustrous black stain it pro- 
 duces on lead paper. All sulphides, 
 when fused with carbonate of sodium 
 in a porcelain capsule, leave a residue 
 which disengages sulphuretted hydro- 
 gen upon the addition of an acid. 
 The residue, moistened with water, 
 gives a black stain to silver coin, and 
 a purple colouration with nitroprus- 
 side of sodium (vide /3 and y). 
 
 /3. Soluble sulphides, including sul- 
 phide of hydrogen, give with nitrate 
 of silver a black precipitate of sul- 
 phide of silver Ag a S, which does not 
 disappear on the addition of cold nitric 
 acid. They also produce a black stain 
 on metallic silver, or acetate of lead 
 paper. The precipitate of sulphide 
 of lead PbS, thrown down from any 
 dissolved lead salt, is not affected by 
 dilute mineral acids, save on the ap- 
 plication of heat. 
 
 y. Nitroprusside of sodium produces a magnificent purple 
 colouration with soluble sulphides, even when extremely dilute. 
 The effect, however, is not obtained with sulphide of hydrogen 
 until after the addition of a drop or so of alkali. 
 
 . Many sulphides, when heated in a glass tube open at both 
 ends, evolve sulphurous anhydride S0 a , which is known by its 
 
I3O EXAMINATION FOR ACIDS. 
 
 smell of burning sulphur, and by its producing a purple stain on 
 starch paper moistened with iodic acid. 
 
 (94.) SULPHITES. 
 
 a. Hydrochloric or sulphuric acid causes an effervescence of 
 sulphurous acid or anhydride S0 2 , known by its smell of burning 
 sulphur, and by the purple colouration it gives to starch paper 
 moistened with iodic acid. On the addition of a fragment of 
 zinc, the sulphurous is replaced by sulphydric acid, known by its 
 effect on lead paper. Hyposulphites behave in a similar 
 manner, except that the effervescence of sulphurous acid is 
 accompanied by a deposition of yellow sulphur. 
 
 ft. Perchloride of iron produces in neutral solutions a red 
 colouration, which disappears on the addition of a strong acid, 
 and is destroyed by boiling, with formation of a brown deposit of 
 ferric oxide. 
 
 (95.) SULPHATES. 
 
 a. Nitrate or chloride of barium throws down an opaque white 
 precipitate of sulphate of barium BaS0 4 , which does not dis- 
 appear on the addition of hydrochloric or nitric acid even at a 
 boiling heat. But in presence of a large excess of nitric acid 
 a portion of sulphate of barium remains in solution. The seleniate 
 and silicofluoride of barium resemble the sulphate in being 
 precipitable from acid solutions ; but, when boiled with strong 
 hydrochloric acid, the seleniate dissolves with evolution of 
 chlorine, while the silicofluoride, which is very transparent, 
 dissolves, with the exception of a little silica. 
 
 (96.) CHLORIDES. 
 
 a. Nitrate of silver produces a white clotty precipitate of 
 chloride of silver AgCl, which becomes slate-coloured on ex- 
 posure to light. It is insoluble even in boiling concentrated 
 nitric acid, but is readily soluble in ammonia. When heated in a 
 
BROMIDES IODIDES. 1 3 1 
 
 porcelain capsule, it does not undergo decomposition, but simply 
 fuses. 
 
 /3. Chlorides, when heated with strong sulphuric acid, save 
 those of mercury, silver, and tin, evolve hydrochloric acid gas, 
 known by its pungent smell and acid reaction. When heated 
 with peroxide of manganese and sulphuric acid, chlorine gas is 
 given off, recognisable by its irritant odour, green colour, power 
 of bleaching litmus, &c., and by the purple stain it produces on 
 a piece of starch paper moistened with iodide of potassium. 
 
 (97.) BROMIDES. 
 
 a. The precipitate of bromide of silver AgBr, produced by 
 nitrate of silver in solutions of bromides, closely resembles the 
 chloride, except that it has a faint tinge of yellow and is less 
 readily soluble in ammonia. 
 
 J3. Bromides when heated with strong sulphuric acid, with or 
 without the addition of peroxide of manganese, evolve bromine, 
 which is recognised by the red colour and irritant smell of its 
 vapour, by its bleaching litmus, and turning starch paper yellow. 
 
 (98.) IODIDES. 
 
 a. The precipitate of iodide of silver Agl, produced by nitrate 
 of silver in solutions of iodides, is of a pale yellow colour, in- 
 soluble in, but turned white by, ammonia, and in other respects 
 similar to the chloride. 
 
 /3. A sufficiency of chloride of mercury produces a scarlet pre- 
 cipitate of iodide of mercury HgI 2 ; while acetate of lead throws 
 down a yellow precipitate of iodide of lead PbI 2 , somewhat soluble 
 in boiling water, and deposited therefrom on cooling, in golden 
 scales. 
 
 y. Iodides when acted upon by strong sulphuric acid with or 
 without peroxide of manganese, evolve iodine, known by its violet 
 Vapour, staining starch paper purple. 
 
132 EXAMINATION FOR ACIDS. 
 
 5. A drop or two of chlorine water, or of nitric or preferably 
 nitre-hydrochloric acid, added to a dissolved iodide, causes a 
 liberation of its iodine, which, if in any quantity, imparts a yellow- 
 brown colour to the liquid. But in presence of dilute starch 
 paste, a deep purple colour is developed ; and chloroform or 
 disulphide of carbon shaken with the liquid becomes of a bright 
 pink or crimson colour. 
 
 (99.) CYANIDES. 
 
 a. Nitrate of silver throws down a white clotty precipitate of 
 cyanide of silver AgCl, not altered in colour by exposure to 
 light. It is readily soluble in ammonia, insoluble in cold, but 
 soluble in boiling concentrated nitric acid. 
 
 The white precipitates produced by nitrate of silver in ferro- 
 cyanide and sulphocyanate solutions, and the brown preci- 
 pitate produced in ferridcyanide solutions are insoluble in 
 nitric acid. 
 
 /3. When a mixture of ordinary sulphate of iron and potash is 
 added to a simple cyanide, no obvious effect is produced, but on 
 acidification with hydrochloric acid the unaltered hydrates of 
 iron are dissolved, and Prussian blue or sesquiferrocyanide of 
 iron, Fe 7 Cy l8 or Fe 3 "Cy 6 , Fe 4 "'Cy la , is left as a deep blue precipitate. 
 
 y. Cyanides, including cyanide of silver, when acted upon by 
 yellow sulphide of ammonium, are converted into sulphocyanates 
 MCyS 3 . After evaporating to dryness, to expel the excess 
 of sulphide of ammonium, perchloride of iron gives a deep 
 red colouration due to the production of ferric sulphocyanate 
 Fe'"(CyS) 3 . 
 
 (100.) PHOSPHATES. 
 
 a. Sulphate of magnesium added to a phosphate solution 
 rendered alkaline by ammonia, and containing chloride of ammo- 
 nium, produces a white crystalline precipitate of phosphate of 
 magnesium and ammonium Mg(NH 4 )P0 4 , readily soluble in acids. 
 The formation of the precipitate is facilitated by rubbing the 
 
PHOSPHATES OXALATES. 133 
 
 inside of the tube with a stirring rod. Chloride of barium or 
 calcium produces in neutral or ammoniacal phosphate solutions a 
 white precipitate of phosphate of calcium or barium, soluble even 
 in acetic acid. 
 
 /3. Nitrate of silver added to a neutral or nearly neutral phos- 
 phate solution, produces a yellow (under certain circumstances 
 white) precipitate of phosphate of silver Ag 3 P0 4 , soluble in 
 ammonia and dilute nitric acid. 
 
 y. Perchloride of iron produces in phosphate solutions which 
 are neutral, or acid only with acetic aci J, a pale brown precipitate 
 of phosphate of iron Ffe"T0 4 . An excess of acetate of ammo- 
 nium may be added to a solution of phosphate of magnesium or 
 calcium in the smallest sufficient quantity of hydrochloric acid, 
 whereby the free hydrochloric is replaced by free acetic acid. 
 Then, on adding a drop of perchloride of iron, a deep red 
 colour, speedily changing into an opaque white cloud, is pro- 
 duced. On adding more perchloride of iron gradually, until the 
 liquid remains permanently red, and afterwards boiling and filter- 
 ing, a colourless nitrate is obtained, free alike from phosphoric acid 
 and iron, but containing chloride of calcium or magnesium. 
 
 8. Excess of molybdata of ammonium added to a phosphate 
 solution containing free nitric acid, produces, either immediately 
 or on gentle warming, a bright yellow precipitate of a phospho- 
 molybdate of ammonium of uncertain composition. 
 
 Except that the arseniate of silver is brick red instead of yellow 
 or white, all the above described reactions apply equally to 
 arsenic and phosphoric acids. Arsenic acid may, however, be 
 got rid of by treatment of its solution with sulphurous acid and 
 sulphydric acid in succession, or by prolonged treatment with 
 sulphydric acid alone (vide par. 66). 
 
 (101.) OXALATES. 
 
 Unlike most organic acids, save those which volatilise without 
 decomposition, neither oxalic acid nor its salts become charred by 
 
134 EXAMINATION FOR ACIDS. 
 
 the action of heat or strong sulphuric acid. They effervesce with 
 dilute sulphuric acid and peroxide of manganese. 
 
 a. Oxalates soluble in water, or oxalates soluble in acid after 
 the addition of acetate of ammonium, give with chloride or even 
 sulphate of calcium a white precipitate of oxalate of calcium 
 CaC a 4 , insoluble in ammonia and in acetic acid, but soluble in 
 dilute mineral acids. 
 
 /3. Nitrate of silver and chloride of barium give with neutral 
 oxalates white precipitates of oxalate of silver Ag a C 3 4 , and 
 oxalate of barium BaC 2 4 , respectively, soluble in dilute nitric, 
 but insoluble or very sparingly soluble in acetic acid. 
 
 (102.) TARTRATES. 
 
 Tartaric acid and tartrates, when ignited, evolve a peculiar 
 odour, and leave an abundant charcoal. They become blackened 
 when heated with strong sulphuric acid ; whereas citric acid and 
 the citrates acquire only a yellow colour. 
 
 a. Chloride of calcium produces in neutral tartrates a white 
 precipitate of tartrate of calcium Ca"H 4 C 4 6 , soluble even in 
 acetic acid. On heating the washed precipitate with aqueous 
 potash, filtering the mixture and boiling the filtrate, a white tur- 
 bidity is produced which disappears on cooling. Chloride of 
 calcium does not precipitate neutral citrates in the cold ; but, upon 
 boiling, a temporary white turbidity is produced. 
 
 p. Nitrate of silver throws down from neutral tartrates a white 
 precipitate of tartrate of silver Ag a H 4 C 4 6 , soluble in dilute nitric 
 acid and in ammonia, and decomposed on boiling, with black- 
 ening and reduction. Chloride of barium does not precipitate 
 tartrates in the presence of ammoniacal salts or free acid. 
 
 y. Neutral tartrates of potassium, and of sodium and ammo- 
 nium in presence of chloride of potassium, yield, on acidification 
 with acetic acid, a white crystalline precipitate of cream of 
 tartar, or acid tartrate of potassium KE 5 C 4 6 , which deposits 
 
ACETATES BENZOATES EQUATES. 1 35 
 
 most readily on stirring, and is soluble in boiling water and 
 mineral acids. 
 
 (103.) ACETATES. 
 
 a. Perchloride of iron added to a neutral acetate produces 
 a deep red colour, from the formation of peracetate of iron 
 Fe'"(H 3 C a 2 ) 3 . The colour is destroyed on the addition of a 
 mineral acid, or on boiling ; in the latter case with formation of 
 an ochry deposit. 
 
 /3. Nitrate of silver produces, in concentrated solutions only, a 
 white precipitate of acetate of silver AgH 3 C a 2 , soluble in hot 
 water, in dilute nitric acid, and in ammonia. 
 
 y. On warming a solid acetate, or its concentrated solution, 
 with sulphuric acid, acetic acid is liberated, recognisable by its 
 well-known smell ; but in presence of alcohol the fragrant vapour 
 of acetic ether (C,.H 5 )H 3 C a O a , is evolved instead, 
 
 (104.) BENZOATES. 
 
 Benzoates evolve the characteristic smell of benzene upon 
 ignition, and yield a sublimate of benzoic acid when warmed 
 with strong sulphuric acid ; but in neither case do they undergo 
 much charring. 
 
 a. Perchloride of iron gives with neutral benzoates a brownish- 
 yellow precipitate of perbenzoate of iron Fe'"(H 5 C 7 O a ) 3 , which 
 dissolves completely in warm dilute hydrochloric acid forming a 
 solution from which benzoic acid crystallises out on cooling. 
 
 /3. Nitrate of silver gives a white clotty precipitate of benzoate 
 of silver AgH 5 C 7 0.,, soluble in hot water, in dilute nitric acid, 
 and in ammonia. 
 
 (105.) BORATES. 
 
 Borate solutions have usually an alkaline reaction to test-paper. 
 Several borates are sparingly soluble, but none of them insoluble 
 in water ; whence dilute solutions of borates are non-precipitable. 
 
136 EXAMINATION FOR ACIDS. 
 
 a. Alcohol added to a mixture of sulphuric acid and a bonite, 
 burns with a marked green flame, the colour of which is best 
 brought out on stirring the burning mixture. 
 
 /3. The solution of a borate, acidified with hydrochloric acid, 
 has the property of turning turmeric paper of the brown colour 
 usually caused by alkalis. Even with dilute solutions the 
 colouration becomes well marked on drying the paper. The 
 acidification of not too dilute borate solutions is attended with 
 the precipitation of boric or boracic acid H 3 B0 3 . 
 
 (106.) FLUORIDES. 
 
 a. Fluorides, when gently heated with strong sulphuric acid, 
 evolve hydrofluoric acid vapour HF, which becomes opaque in 
 moist air, and has a very pungent, irritating smell. The expe- 
 riment is best made in a platinum crucible, but should a test- 
 tube or watch-glass be employed, its interior will afterwards 
 be found corroded. When a piece of flat glass, covered with a 
 layer of beeswax, through which some markings have been 
 scratched, is exposed for a little while to the action of the 
 vapour, the markings become permanently etched upon the glass, 
 and even if very slight may be rendered evident by breathing 
 upon its well- polished surface. 
 
 /3. Fluorides, mixed with silica or any silicate, and warmed 
 with sulphuric acid, evolve gaseous fluoride of silicon SiF 4 , as a 
 pungent, irritating gas, rendered opaque and acid by moist air, 
 in consequence of the following decomposition : 
 
 3 SiF 4 + 3 H a O = aH a SiF 6 + H a Si0 3 or H 8 O.Si0 3 . 
 
 Hence the wetted surface of a strip of glass, dipped into the 
 gas, or the moist interior of a tube through which it is trans- 
 mitted, as shown in fig. 38, soon acquires an opaque coating of 
 silica. 
 
 y. The soluble fluorides of potassium and sodium give with 
 
SILICATES. 137 
 
 chloride of calcium or chloride of barium a gelatinous white pre- 
 cipitate, soluble in hydrochloric acid, slightly soluble in am- 
 moniacal salts, and scarcely at all soluble in acetic acid ; though, 
 indeed, the precipitated fluoride of calcium CaP a , or of barium 
 BaF,,, is often accompanied by some silicofluoride insoluble in 
 hydrochloric acid. Fluor-spar, or native fluoride of calcium, is 
 not readily soluble in hydrochloric acid, but an available solution 
 may be obtained by digesting the finely-powdered 
 spar for some time in the strong acid, and then boiling & 3- 
 the mixture after dilution with water. 
 
 (107.) SILICATES. 
 
 Silicates of potassium and sodium, when not con- 
 taining an excess of silica, are soluble in water, but all 
 other silicates are insoluble. 
 
 a. On acidifying the solution of a silicate of alkali- 
 metal with hydrochloric acid complete decomposition 
 takes place, most usually with precipitation of some 
 silicic acid in the gelatinous form, while another por- 
 tion remains dissolved in the acid liquid. Under cer- 
 tain circumstances, however, as when the silicate solu- 
 tion is rather dilute, or when it is added at once to an 
 excess of hydrochloric acid, there may not be any pre- 
 cipitation whatever. But in any case, upon evaporating 
 down the clear acidified solution, the whole of the dissolved silicic 
 acid separates out in the form of silica, which, after drying, is 
 insoluble both in acid and alkaline solutions. The precipitate of 
 gelatinous silicic acid is readily soluble in solutions of caustic 
 alkali, and even of carbonated alkali when gently warmed there- 
 with ; but upon drying at a moderate heat, it becomes hard, 
 gritty, and insoluble. 
 
 (3. Owing to the incompetency of silicic acid to form a salt 
 with ammonia, chloride or carbonate of ammonium added to a 
 dissolved silicate of alkali-metal precipitates gelatinous silica, 
 
138 EXAMINATION OF ACIDS. 
 
 which separates more completely on evaporation, at the same 
 time becoming anhydrous. 
 
 y. Carbonate of sodium fused before the blowpipe on a loop of 
 platinum wire furnishes a bead which is transparent while hot, 
 opaque when cold ; but a little silica added to the strongly heated 
 bead dissolves therein with effervescence, and, if in sufficient 
 quantity, renders it permanently transparent, 
 
TOXICOLOGICAL CHEMISTRY. 139 
 
 CHAPTER III. 
 TOXICOLOGICAL CHEMISTKY. 
 
 (108.) FOR the performance of this part of the course, the student 
 should be provided in succession with the principal poisons in the 
 various forms in which they ordinarily occur in medico-legal 
 practice. He must examine each poison in the several conditions in 
 which it is presented to him, and verily all its described reactions. 
 The different poisons may be met with in the ordinary state in 
 which they are sold; dissolved in or diluted with water; in 
 various organic liquids, either the vehicles in which they were 
 administered, or the contents of the stomach for instance ; mixed 
 with solid food; in the tissues of different organs, more particu- 
 larly the liver and kidney ; and as stains upon clothing. They 
 may be roughly classified into acid poisons, including the sulphuric, 
 nitric, hydrochloric and oxalic acids ; metallic poisons, including 
 compounds of mercury, lead, copper, arsenic and antimony ; and 
 organic poisons, including prussic acid, strychnia, and opium. 
 
 I. SULPHURIC ACID. 
 (109.) CONCENTRATED. 
 
 a. Appearance. Concentrated sulphuric acid, or oil of 
 vitriol, occurs as a heavy, somewhat oily liquid, usually having a 
 more or less marked brownish tint. 
 
 /3. Volatility. A few drops of the acid, when cautiously 
 
140 SULPHURIC ACID. 
 
 heated upon a watch-glass, or on platinum foil, disappear entirely 
 with the formation of opaque white acrid fumes. 
 
 y. Heat on admixture with water. Upon agitating a 
 drachm or so of the strong acid with about an equal bulk of water, 
 the temperature of the mixture rises very considerably, and the 
 outside of the tube or other containing vessel becomes insup- 
 portably hot to the hand. 
 
 3. Charring organic matter. A piece of paper, wood, or 
 sugar, dipped into the strong acid, speedily becomes blackened or 
 carbonised. 
 
 . Evolution of sulphurous acid. Upon gently heating 
 sulphuric acid in a test tube with some chips of wood, copper 
 turnings, or mercury, a vapour having the peculiar suffocating 
 smell of burning sulphur is evolved ; while a piece of starch- 
 paper, moistened with iodic acid solution and held over the mouth 
 of the tube, acquires a purple colour, which, however, the pro- 
 longed action of the vapour ultimately causes to disappear. 
 
 (no.) DILUTED. 
 
 a. Acid reaction, &c. Dilute sulphuric acid is entirely 
 volatilisable by heat, has a marked acid reaction to test paper, 
 and dissolves a fragment of carbonate of ammonium or sodium 
 with rapid effervescence. 
 
 (3. Charring after concentration. Marks upon paper 
 made with the dilute acid appear simply wet, but become 
 gradually black from carbonisation, on carefully drying the paper 
 over a stove or gas flame. 
 
 y. Precipitation of sulphate of barium. Solution of 
 nitrate or chloride of barium throws down from dilute sulphuric 
 acid a white precipitate of sulphate of barium, not affected by 
 the addition of nitric or hydrochloric acid. 
 
 c. Recognition of sulphur in precipitate. The pre- 
 cipitate having been collected on a filter, is washed, dried, and 
 intimately mixed with about an equal quantity of black flux. 
 
IN ORGANIC LIQUIDS. 141 
 
 The mixture is then heated to redness in a reduction tube or 
 before the blowpipe, whereby a fused residue is obtained, from 
 which hydrochloric acid causes an evolution of sulphuretted 
 hydrogen gas, recognisable by means of lead paper, to which it 
 imparts a glistening black or brown discolouration. 
 
 (in.) IN ORGANIC LIQUIDS. 
 
 a. Sulphuric acid contained in an organic liquid, such as coffee, 
 beer, or the contents of the stomach, readily manifests all the 
 above described properties of the dilute acid, except that of 
 volatility. Should the liquid be viscid or turbid, it must be 
 diluted freely with water or proof spirit, and strained through 
 fine muslin, or, if practicable, filtered through paper. The filtrate 
 is precipitable by nitrate or chloride of barium (vide 1 10) ; and 
 upon being evaporated down, becomes more strongly acid, chars, 
 and evolves sulphurous acid gas {vide 109). Although, from the 
 administration of antidotes in cases of sulphuric acid poisoning, 
 the contents of the stomach or vomited matters may not exhibit 
 any, or only a very, slight acid reaction, they may, nevertheless, 
 yield an abundant precipitate of sulphate of barium. 
 
 (i 12.) STAINS ON CLOTHING. 
 
 a. The concentrated acid produces, upon black cloth, for 
 instance, a farown stain with or without a red border ; and the 
 diluted acid a red stain, gradually becoming brown. The stains 
 remain moist for a long time, and in all cases the fibre becomes 
 destroyed with greater or less rapidity. By treating the stained 
 pieces with water, a solution of sulphuric acid is obtained, which 
 manifests acidity to test paper, and yields a white precipitate with 
 nitrate of barium. A portion of the stained stuff heated in a 
 reduction tube evolves sulphurous acid, recognisable by its smell, 
 and by its reaction upon starch paper moistened with iodic acid 
 solution. 
 
142 NITRIC ACID. 
 
 II. NITEIC ACID. 
 (113.) CONCENTRATED. 
 
 o. Appearance. Nitric acid when pure is colourless ; but 
 when containing peroxide of nitrogen is straw-yellow or orange, 
 and sometimes even green or blue. 
 
 ft. Volatility. The concentrated acid when exposed to the 
 air at ordinary temperatures gives off colourless or orange fumes, 
 having a characteristic smell, and a strongly marked acid reaction. 
 A few drops of the acid heated upon a watch-glass disappear 
 without leaving any residue. 
 
 y. Action on organic matter. A strip of flannel or other 
 nitrogenised organic tissue dipped into strong nitric acid becomes 
 stained distinctly yellow ; the colour being rendered darker and 
 browner by the subsequent action of caustic alkali. Black and 
 coloured cloths likewise become stained of a yellow colour, and 
 rapidly corroded by the strong acid. 
 
 S. Action on metals. When nitric acid is gently warmed 
 in a test-tube with a drop or two of mercury or a few copper- 
 turnings, violent chemical action takes place, as evidenced by the 
 solution of the metal, and the copious evolution of orange-brown 
 vapours which redden but do not bleach litmus paper, and 
 produce a purple colouration on starch paper moistened with 
 iodide of potassium. 
 
 e. Reaction with sulphate of iron. Nitric acid added 
 to a cold moderately concentrated solution of sulphate of iron, 
 produces a dark greenish-brown discolouration, which disappears 
 on the application of heat with evolution of orange fumes. 
 
 . Solution of gold. Gold leaf is unacted upon by boiling 
 nitric acid, but upon the addition thereto of a little hydrochloric 
 acid it undergoes rapid solution. 
 
 (114.) DILUTED. 
 
 a. Acid reaction, &c. Dilute nitric acid is completely 
 volatilised by heat ; has a marked acid reaction ; when evaporated 
 from paper moistened with it, does not leave a black, but only a 
 
EE ACTIONS OF NITRATES. 143 
 
 slightly yellow stain ; produces upon black cloth a stain, red at 
 first, but ultimately yellow ; and, if pure, gives no precipitate with 
 solutions of chloride of b^ri^m and nitrate of silver respectively. 
 When neutralised by the hydrate or carbonate of sodium, potas- 
 sium, or barium, it is converted into a nitrate which may be ob- 
 tained solid and crystalline by careful evaporation. 
 
 (115.) NITRATES. 
 
 a. Crystalline form. A drop or so of the aqueous solution 
 of a nitrate heated slowly upon a glass plate until a solid margin 
 appears round the edge of the 
 liquid, yields upon cooling a well 
 crystallised residue, which may 
 be examined by a pocket lens or 
 the low power of a microscope. 
 The potassium salt crystallises in 
 long fluted six-sided prisms, the 
 sodium salt (fig. 39), in rhombic 
 plates, and the barium salt in 
 octahedrons. 
 
 (3. Deflagration with char- 
 coal. A solid nitrate heated upon 
 
 charcoal, or heated with charcoal powder on platinum foil, un- 
 dergoes deflagration ; while a piece of filtering paper moistened 
 with the solution of a nitrate and dried, burns in the characteristic 
 manner of touch paper. 
 
 y. Evolution of peroxide of nitrogen. When a mix- 
 ture of a little powdered nitrate with a few copper filings is acted 
 upon by sulphuric acid and gently warmed, orange-brown fumes 
 are given off, which redden but do not bleach litmus paper, and 
 produce a purple colouration on starch paper moistened with 
 iodide of potassium. This experiment may be performed satis- 
 factorily with less than one-tenth of a grain of nitre. 
 
 I. Keaction with sulphate of iron. When a solution of 
 sulphate of iron is poured carefully upon some sulphuric acid, to 
 which a minute fragment of a nitrate has been added, or upon a 
 
144 HYDROCHLORIC ACID. 
 
 cooled mixture of sulphuric acid with a little nitrate solution, 
 a deep greenish-brown halo is produced at the junction of the 
 .two liquids, as shown in fig. 36. This test is also extremely 
 delicate. 
 
 . Solution of gold. Gold leaf when boiled in hydro- 
 chloric acid remains unchanged, but upon the addition of a little 
 nitrate becomes dissolved wholly or in part. To demonstrate the 
 solution of the gold in the latter case, protochloride of tin may be 
 added, which will give rise to a purplish precipitate or turbidity. 
 
 (116.) IN ORGANIC MIXTURES. 
 
 a. Solid matters should be digested for some time in cold water, 
 and the liquid filtered off. This method is applicable to stains 
 on clothing, when not of too long standing. Viscid and turbid 
 liquids are simply mixed with water and filtered. The suspected 
 filtrate is next tested with blue litmus paper, and if found to be 
 acid, neutralised carefully with a solution of carbonate or hydrate 
 of sodium, evaporated down to the crystallising point, and set 
 aside. If practicable, the resulting deposit may be collected, dried 
 by pressure between folds of bibulous paper, dissolved in a little 
 warm water, and the solution, filtered if necessary, evaporated, and 
 recrystallised. Lastly, the crystalline residue is to be examined 
 microscopically, and by the several chemical tests mentioned in 
 the preceding section. The acid reaction may be wanting in 
 organic mixtures, through a neutralisation of the nitric acid 
 originally administered. 
 
 III. HYDRO CHLOEIC ACID. 
 (117.) CONCENTRATED. 
 
 a. Appearance. The pure solution is colourless, or of a 
 scarcely perceptible greenish tinge ; but the commercial acid has 
 frequently a bright yellow colour, from the presence of perchloride 
 of iron. 
 
 /3. Volatility. At ordinary temperatures the strong acid 
 evolves colourless, almost transparent fumes, which have a marked 
 
IN CONCENTRATED AND DILUTED STATE. 145 
 
 acid reaction, a characteristic smell, and, in common with other 
 acid fumes, become opaque upon admixture with ammoniacal 
 vapour. The liquid acid heated on a watch-glass evaporates 
 without leaving any residue. 
 
 y. Action on organic matter. Most organic tissues are 
 gradually corroded and tinged of a yellow colour by immersion 
 in the strong acid ; but the stains produced on black cloth are at 
 first distinctly red, and after some days reddish-brown. 
 
 5. Want of action on metals. Hydrochloric acid boiled 
 with a little copper or mercury simply evaporates, leaving the 
 metal unchanged, or very nearly so. 
 
 e. Evolution of chlorine. Peroxide of manganese warmed 
 with hydrochloric acid in a test tube produces an abundant 
 evolution of chlorine gas, recognisable by its greenish-yellow 
 colour and irritating smell. It quickly bleaches litmus paper, and 
 produces a purple colouration on starch paper moistened with 
 iodide of potassium. 
 
 (118.) DILUTED. 
 
 o. Neutralisation by carbonates, &c. Dilute hydro- 
 chloric acid is completely volatile, has a marked acid reaction, and 
 dissolves most carbonates with effervescence, forming chlorides, 
 which may be obtained in the solid state on evaporation ; the al- 
 kaline chlorides, and particularly chloride of sodium, crystallising 
 in cubical or stauroid forms. Chlorine may be liberated from the 
 evaporated residue by the action of sulphuric acid and peroxide 
 of manganese. 
 
 /3. Precipitation of chloride of silver. Solution of 
 nitrate of silver added to hydrochloric acid throws down a white 
 clotty precipitate of chloride of silver, which subsides readily 
 after brisk agitation, and by exposure to light acquires a grey or 
 purplish colour. One portion of the precipitate may be treated 
 with ammonia, in which it will dissolve, and another portion 
 boiled with nitric acid, by which it will be unaffected, while the 
 remainder may be washed, dried, and ignited in a porcelain cap- 
 sule, when it will fuse into a horny mass. 
 
 L 
 
HYDROCHLORIC ACID. 
 
 (119.) TN ORGANIC LIQUIDS OR SOLIDS. 
 
 o. Distillation, &c. The liquid having shown an acid 
 reaction to test paper, may be strained or filtered if necessary, 
 and then distilled nearly to dryness from a retort, or a flask to 
 which a cork and delivery tube have been adapted, as in fig. 40. 
 
 Fig. 40. 
 
 The earlier portions ot the distillate are usually little else than 
 water, but the later portions should manifest all the properties ol 
 dilute hydrochloric acid. Solid substances may be digested in 
 distilled water, and the resulting solution examined with test 
 paper and nitrate of silver. If possible, a portion of the liquid 
 should be evaporated to thorough dryness, and the dissolved 
 residue again tested with nitrate of silver to ascertain the absence 
 or comparative absence of metallic chlorides. 
 
 IV. OXALIC ACID. 
 (120.) SOLID. 
 
 1 a. Appearance, &c. Oxalic acid generally occurs in 
 colourless, more or less well-defined four-sided prisms, which 
 dissolve readily in boiling water to form a solution having a 
 marked acid reaction. 
 
OXALIC ACID IN SOLUTION. 147 
 
 /3. Volatility without charring. A few crystals of the 
 acid, when heated upon platinum foil, melt, evolve fumes, and 
 disappear without leaving any carbonaceous residue. 
 
 y. Effervescence with manganese. A little peroxide 
 of manganese, free from carbonates, when added to oxalic acid 
 moistened with water, sets up an active effervescence of carbonic 
 acid gas. 
 
 (121.) DISSOLVED. 
 
 a. Crystalline form. One or two drops of the strongly 
 acid liquid evaporated cautiously upon a glass plate until a solid 
 white margin appears, yield on 
 spontaneous cooling a crystalline 
 residue of delicate, long flat prisms, 
 as shown in fig 41. 
 
 /3. Precipitation of oxalate 
 of silver. Nitrate of silver pro- 
 duces in solution of oxalic acid, 
 more abundantly after its neutra- 
 lisation or partial neutralisation 
 with ammonia, an opaque white 
 precipitate of oxalate of silver, 
 which is not discoloured by ebul- 
 lition, but may dissolve if the excess of oxalic acid be large, and 
 is readily soluble in dilute nitric acid. The precipitate collected 
 on a filter, washed, dried, and then ignited upon platinum foil, is 
 dissipated with a slight explosion, leaving an inconsiderable 
 pulverulent residue of metallic silver. 
 
 y. Precipitation of oxalate of calcium. Solution of 
 sulphate of calcium added freely to aqueous oxalic acid, throws 
 down a white precipitate of oxalate of calcium, insoluble in acetic, 
 but readily soluble in dilute nitric acid. By ignition, the pre- 
 cipitate is converted into carbonate of calcium, which dissolves 
 in acetic acid with effervescence. 
 
 (122.) IN ORGANIC LIQUIDS. 
 
 a. Eeaction to test paper, &c. The acid reaction is verv 
 
 J 
 
148 
 
 OXALIC ACID. 
 
 decided even when the poison exists but in very small proportion. 
 It is often necessary to filter the liquid, after previous dilution with 
 water or proof spirit, or at any rate to strain it through muslin, 
 before applying any reagent. 
 
 /3. Precipitation of oxalate of lead. Solution of acetate 
 of lead added to the strained or filtered liquid, throws down a 
 precipitate of oxalate of lead, either white or discoloured by the 
 organic matter present. The addition of the reagent is to be 
 continued until it no longer produces a fresh precipitate. This 
 point is easily ascertained by repeatedly testing the supernatant 
 liquid, which separates readily after briskly agitating the mixture. 
 
 y. Production of oxalic acid. The above precipitate of 
 oxalate of lead having been collected on a filter and thoroughly 
 
 Fig. 42. 
 
 washed, is made into a thin magma with water, and treated with 
 a current of washed sulphuretted hydrogen evolved from some 
 
CORROSIVE SUBLIMATE. 149 
 
 such arrangement as that shown in figs. 42 and 15, until the 
 mixture, after agitation and standing at rest for a minute or so, 
 smells strongly of the gas; when, with or without previous 
 warming, it is to be thrown on to a filter. The nitrate will be 
 an aqueous solution of oxalic acid, which will yield crystals on 
 evaporation, and manifest all the above-described reactions of the 
 dissolved acid. 
 
 3. Production of oxalate of ammonium. Or instead 
 of treating the washed precipitate of oxalate of lead with sul- 
 phuretted hydrogen, it may be boiled for a short time with a 
 small quantity of dilute sulphuric acid, the mixture filtered, and 
 the filtrate neutralised with ammonia. The resulting solution of 
 oxalate of ammonium may be concentrated by evaporation and 
 tested with nitrate of silver and sulphate of calcium, when cha- 
 racteristic precipitates of the oxalates of silver and calcium 
 respectively will be obtained. 
 
 (123.) INSOLUBLE. 
 
 a. Oxalic acid is sometimes met with as a calcium or mag- 
 nesium salt, owing to the exhibition of chalk or magnesia as an 
 antidote. The insoluble white deposit, when boiled for some 
 time with carbonate of sodium, yields a solution of oxalate of 
 sodium, which after filtration and careful neutralisation with dilute 
 nitric acid, may be tested with nitrate of silver and sulphate of 
 calcium respectively. It is recognisable also by effervescing upon 
 treatment with peroxide of manganese and a dilute mineral acid. 
 
 V.COREOSIVE SUBLIMATE. 
 (124.) SOLID. 
 
 a. Appearance, solubility. &c. Corrosive sublimate usually 
 occurs as a heavy, white, glistening powder, turned black by 
 sulphide of ammonium, yellow by potash, and scarlet by iodide 
 of potassium. Boiled with a little water in a test-tube it under- 
 goes speedy solution. 
 
 /3. Volatility. A small portion of the powder, heated on 
 charcoal or platinum foil, disappears completely with production 
 
150 CORROSIVE SUBLIMATE. 
 
 of opaque white fumes. Heated in a narrow tube it yields a 
 white crystalline sublimate. 
 
 y. Metallic reduction. When a little of the powdered salt, 
 mixed with three or four times its bulk of recently calcined car- 
 bonate of sodium, is introduced into a thoroughly dry reduction 
 tube, the mixture covered with some additional carbonate of 
 sodium, and the heat of a spirit or gas-flame applied, first to the 
 carbonate and then to the mixture, volatilisation of metallic 
 mercury takes place, and a sublimate of well-defined mercurial 
 globules condenses in the cold part of the tube. 
 
 3. Detection of chlorine in residue. The bottom of 
 the tube containing the fused residue having been snapped off at 
 a file-mark and boiled in water, the resulting solution may be 
 acidulated with nitric acid and tested with nitrate of silver, when 
 a white precipitate of chloride of silver will be formed, insoluble 
 in nitric acid, but soluble in ammonia. 
 
 (125.) DISSOLVED. 
 
 a. Crystalline form. A little of the solution evaporated 
 cautiously on a glass plate until a solid margin appears, and set 
 Fig. 43. aside to crystallise, furnishes a 
 
 residue of slender opaque inter- 
 secting needles (fig. 43), which 
 afford the above- described reac- 
 tions of the solid poison. 
 
 /3. Precipitation of sul- 
 phide of mercury. Sulphu- 
 retted hydrogen gas, or its aqueous 
 solution, added to corrosive subli- 
 mate solution, produces at first a 
 white turbidity, gradually becom- 
 ing orange-brown, and finally changing into a dense black pre- 
 cipitate of sulphide of mercury, which may also be thrown down 
 by sulphide of ammonium. The washed precipitate is insoluble 
 even in boiling nitric acid. 
 
 y.- Precipitation of oxide of mercury. Excess of 
 
REACTIONS OF SOLUTION. 151 
 
 potash or lime water produces an orange-yellow precipitate of 
 mercuric oxide, the nitrate from which may be tested for chlorine 
 by means of nitrate of silver and nitric acid. 
 
 5. Precipitation of iodide of mercury. Iodide 
 of potassium produces, in corrosive sublimate solution, an orange 
 or scarlet precipitate of iodide of mercury, which disappears in 
 excess of the precipitant, forming a colourless liquid. This re- 
 action is very characteristic, though liable to be interfered with 
 by the presence of various saline compounds. 
 
 e. Reduction by a stannous salt. Protochloride of 
 tin, added to a solution of corrosive sublimate acidulated with 
 hydrochloric acid, produces at first a white precipitate of calomel, 
 which, on adding more of the reagent, becomes slate-coloured, 
 and finally almost black, from its conversion into metallic 
 mercury. The precipitate subsides rapidly upon the applica- 
 tion of heat ; afterwards the supernatant liquid may be poured 
 off, replaced by hydrochloric acid, and heat again applied, when 
 the originally bulky deposit will shrink into a few globules of 
 liquid mercury having a highly characteristic aspect. 
 
 . Deposition on copper. A piece of thin copper 
 foil or gauze immersed in the solution, previously diluted very 
 considerably and acidulated with hydrochloric acid, quickly 
 acquires a silver-like coating of mercury. On heating the 
 washed and dried piece of coated copper in a subliming tube,, 
 the mercury volatilises, yielding a sublimate of metallic globules, 
 while the copper resumes its original red colour. 
 
 rj. Electrolytic test. When a few drops of the so- 
 lution, preferably acidulated with hydrochloric acid, are placed 
 on a sovereign or other piece of gold, and the coin touched 
 through the liquid with a key or other steel instrument, a 
 deposition of mercury takes place upon the gold at the point 
 of contact, forming a silvery stain, which disappears upon the 
 application of heat. 
 
 (126.) IN ORGANIC LIQUIDS AND SOLIDS. 
 a. General processes. The strained or filtered liquid, 
 
152 CORROSIVE SUBLIMATE. 
 
 acidulated with hydrochloric acid and gently warmed, may 
 sometimes be treated with a solution of protochloride of tin, as 
 above described ; but the electrolytic test, and especially the test 
 of metallic reduction upon copper, are in most cases much to be 
 preferred. It is generally sufficient to prove the presence of 
 dissolved mercury in an organic liquid, without taking the 
 chlorine of the salt into consideration ; but occasionally the entire 
 salt may be extracted by agitating the liquid with ether, evapo- 
 rating the ethereal solution, and treating the residue with water. 
 Organic solids, thoroughly broken up or otherwise finely divided, 
 are boiled for an hour or so with dilute hydrochloric acid, and 
 the solution tested by immersing in it a piece of clean copper ; or, 
 if necessary, the copper may be boiled in the liquid for a con- 
 siderable length of time. 
 
 (3. Special process. After boiling the broken-up tissue 
 with dilute hydrochloric acid for an hour or so as above described, 
 and filtering off the acid decoction, the undissolved residue should 
 be made into a thin paste with hydrochloric acid diluted with twice 
 its bulk of water, and the mixture heated on a water bath. 
 Then, from time to time, finely powdered chlorate of potassium 
 is to be added little by little until the colour of the undissolved 
 substance is reduced to a pale yellow tint, when the filtered de- 
 coction may be returned, the whole boiled for a few minutes, 
 allowed to cool, and filtered, the filtrate evaporated to a small 
 bulk, again filtered if necessary, and treated with excess of washed 
 sulphuretted hydrogen gas. The resulting sulphide of mercury, 
 mixed with much sulphur, may be collected on a filter, washed 
 with water, dissolved in hydrochloric acid, to which a minute 
 quantity of chlorate of potassium has been added, the liquid 
 evaporated to dryness, the residue dissolved in water, and the 
 resulting solution of mercuric chloride examined by any of the 
 usual tests. This method is one of general applicability for the 
 detection of metals absorbed into the tissues. The original 
 precipitate produced by sulphuretted hydrogen may in all cases 
 be dissolved in hydrochloric acid, aided by the smallest sufficient 
 quantity of chlorate of potassium as above described, the result- 
 
SOLID COMPOUNDS OF LEAD. 153 
 
 ing solution treated afresh with sulphuretted hydrogen, and the 
 precipitate then obtained examined for mercury, lead, copper, 
 arsenic, antimony, bismuth, tin, &c. 
 
 VI. LEAD. 
 (127.) SOLID COMPOUNDS. 
 
 n. Metallic reduction. Lead may be readily procured 
 in the metallic state from substances containing it in moderate 
 quantity. When a small portion of any lead compound, mixed 
 Avith three or four times its weight of carbonate of sodium, is 
 heated on charcoal in the reducing blowpipe flame, a malleable 
 metallic globule is soon produced, while the charcoal receives a 
 yellow incrustation. The globule may be dissolved in dilute nitric 
 acid, and the liquid tests applied to the solution so formed. 
 
 (3. Carbonate of lead. This salt occurs as an opaque 
 white powder, which melts and becomes yellow when heated, is 
 turned black by sulphide of ammonium, is insoluble in water, 
 but dissolves in dilute nitric acid with effervescence, forming a 
 solution to which the liquid tests for lead can be applied. 
 
 y. Acetate of lead. Aspect, &c. Acetate of lead gene- 
 rally occurs as a heavy crystalline powder, of a white colour, 
 a peculiar sour smell, and a sweetish astringent taste. It is 
 moderately soluble in distilled water, and forms a milky liquid 
 with common water, containing sulphates or carbonates. Its 
 solution when evaporated upon a glass plate yields opaque white 
 prismatic crystals. 
 
 S. Acetate of lead. Eeactions. The salt is turned 
 of a black colour by sulphide of ammonium, and of a yellow 
 colour by iodide of potassium. When heated in a reduction 
 tube, it melts, resolidifies, becomes dark in colour, gives out a 
 smell of acetone, and leaves a carbonaceous residue containing 
 very finely divided metallic lead. When heated in a test tube 
 with sulphuric acid it gives off the smell of acetic acid, convertible 
 into that of acetic ether upon the addition of a little alcohol. 
 
154 LEAD. 
 
 Treated with solution of persulphate of iron it yields a white 
 residue of sulphate of lead, and a dark red solution of peracetate 
 of iron. 
 
 (128.) DISSOLVED. 
 
 a. Precipitation of sulphide of lead. Sulphuretted 
 hydrogen gas or its solution in water, when added to any solu- 
 tion containing lead, gives a black or dark brown precipitate of 
 sulphide of lead, insoluble in cold dilute hydrochloric acid, and 
 unaffected by sulphide of ammonium. But in some cases, espe- 
 cially in presence of much chloride of hydrogen or iron, the 
 precipitate comes dowa of a red colour, and is then turned black 
 by sulphide of ammonium. 
 
 /3. Precipitation of sulphate of lead. Dilute sulphuric 
 acid produces an opaque white precipitate of sulphate of lead, 
 insoluble in nitric acid, soluble in boiling and in a large excess 
 of cold hydrochloric acid, and in a considerable excess of potash 
 water. The precipitate is turned black by sulphuretted hydrogen 
 or sulphide of ammonium. 
 
 y. Precipitation of iodide of lead. Iodide of potassium 
 added to the lead solution, which should be free from any great 
 excess of free acid or alkali, throws down a bright yellow preci- 
 pitate of iodide of lead, soluble in hot hydrochloric acid and in a 
 large excess of potash water. It is also sparingly soluble in boil- 
 ing water, and is reprecipitated on cooling in golden scales. 
 
 (129.) IN ORGANIC LIQUIDS OR SOLIDS. 
 
 a. Organic liquids. The liquid, strained or filtered if 
 necessary, and acidulated with a few drops of nitric or hydro- 
 chloric acid, is treated with a current of washed sulphuretted 
 hydrogen, until it acquires a marked smell of the gas, persistent 
 after agitation. The resulting black or dark brown precipitate is 
 allowed to subside, collected on a filter, thoroughly washed with 
 water, and boiled, until its colour is destroyed, in nitric acid 
 diluted with about four times its bulk of water. The solution 
 
REACTIONS OF COPPER IN SOLUTION. 155 
 
 so obtained, filtered if necessary and concentrated by evaporation, 
 is then submitted to the action of the ordinary tests for dissolved 
 lead salts. 
 
 /3. Organic solids. The tissue suspected to contain lead may 
 be treated with hydrochloric acid and chlorate of potassium, as 
 described in par. 1 16 /3. Or it may be dried in an oven, burnt 
 in a capsule, and the resulting charcoal heated to dull redness for 
 several hours until a grey ash is left, which must be dissolved in 
 dilute nitric acid by the aid of heat. The solution of the ash is 
 then to be treated with sulphuretted hydrogen, and the black pre- 
 cipitate further examined. 
 
 VII. COPPER. 
 (130.) DISSOLVED. 
 
 a. Solubility, &c. Most salts of copper are soluble in 
 water or dilute mineral acids, except the sulphide, which, however, 
 dissolves readily in strong nitric acid. The solutions whether 
 aqueous or acidulous have a decidedly blue or green colour. 
 
 (3. Precipitation of sulphide of copper. Sulphuretted 
 hydrogen or an alkaline sulphide throws down a dark brown pre- 
 cipitate of sulphide of copper, which is scarcely affected by 
 treatment with cold hydrochloric acid, but dissolves readily in 
 nitric acid, is partly soluble in ordinary sulphide of ammonium, 
 but insoluble in sulphide of sodium or potassium. 
 
 y. Formation of c up r ammonium salt. Ammonia 
 added carefully to a cupric solution produces a bluish white 
 precipitate, which dissolves in excess of the precipitant, forming 
 a deep purple-blue liquid, of highly characteristic appearance, 
 save when very dilute, in which case it resembles the similarly 
 constituted but strong arnmoniacal solution of nickel. It is, 
 however, distinguishable therefrom by means of caustic potash, 
 which, unless added in very large proportion, does not disturb 
 the transparency of the cuprous, but affords a pale green pre- 
 cipitate with the nickel solution. 
 
156 COPPER. 
 
 . Precipitation of ferrocyanide of copper. 
 Ferrocyanide of potassium produces a gelatinous chocolate pre- 
 cipitate of ferrocyanide of copper, insoluble in mineral acids. 
 Potash changes it into a pale blue magma readily soluble in ammo- 
 nia, forming a deep blue liquid. By these properties it is distin- 
 guished from the similarly coloured precipitate of ferrocyanide of 
 uranium. Ferrocyanide of nickel has a pale green colour. 
 
 e. Metallic precipitation on iron. A steel needle 
 or piece of polished iron wire immersed in a feebly acidulated 
 cupric solution soon acquires a coating of metallic copper, 
 having its characteristic red appearance. When the proportion 
 of copper is very minute, the iron should continue immersed for 
 several hours. Occasionally the deposit is not sufficient in quan- 
 tity to present the ordinary aspect of metallic copper, but appears 
 simply brown or black. 
 
 . Examination of metallic deposit. The coated wire, 
 having been washed in water, is acted upon by a drop or two of 
 ammonia when by exposure to air the copper gradually dissolves 
 in the ammonia, forming a deep blue solution, in which, after 
 acidification with acetic acid, ferrocyanide of potassium causes a 
 chocolate red turbidity of ferrocyanide of copper. 
 
 77. Electrolytic test. When a few drops of an acidulated 
 solution of copper are placed in a platinum capsule, and a piece of 
 zinc foil introduced so as to touch the capsule through the liquid, 
 metallic copper is quickly deposited upon the platinum, either 
 with its characteristic appearance, or simply as a brown stain. 
 The deposit can be examined with ammonia and ferrocyanide 
 of potassium as above described. The process possesses no 
 advantage over that with the iron wire. 
 
 (131.) IN ORGANIC LIQUIDS AND SOLIDS. 
 
 a. Organic liquids. These, when containing any appreciable 
 quantity of copper, have usually a more or less marked greenish 
 tint. They may be acidulated with hydrochloric acid, and allowed 
 to act upon clean iron wire as above described ; or the filtered 
 
REACTIONS OF ARSENIOUS ANHYDRIDE. 157 
 
 acidulated solution may be treated with a current of sulphuretted 
 hydrogen gas, and the resulting dark brown precipitate collected 
 upon a filter, washed with water, and dissolved in dilute nitric or 
 in strong hydrochloric acid. The acid solution evaporated nearly 
 to dryness, and diluted with water, can then be examined by the 
 usual tests. 
 
 (3. Organic solids. These, when containing copper even 
 in small quantity, acquire a deep blue colour by immersion in 
 ammonia. They may be cut into small pieces, boiled for some 
 time in dilute hydrochloric acid, and the resulting liquid, after 
 being concentrated by evaporation, examined with a steel needle 
 or a current of sulphuretted hydrogen gas (a). Or the tissue 
 may be destroyed, either with hydrochloric acid and chlorate of 
 potassium, as described in par. 116 /3, or by incineration, as de- 
 scribed in par. 1 1 9 /3, and the residues further examined. 
 
 VIII. ARSENIC. 
 (132.) ARSENIOUS ACID o ANHYDRIDE. 
 
 a. Appearance. Commercial arsenious acid, white arsenic, 
 or arsenious anhydride, usually occurs as a heavy white powder, 
 but maybe met with in transparent vitreous masses, or in opaque 
 porcellanous masses, or in masses which are opaque externally 
 and glassy in the centre. 
 
 /3. Volatility. A minute quan- 
 tity of the powder heated on plati- 
 num foil volatilises entirely with 
 evolution of opaque white fumes ; 
 any fixed residue being due to im- 
 purity, probably sulphate of cal- 
 cium. A little of the powder heated 
 in a subliming tube also volatilises, 
 and deposits an iridescent sub- 
 limate in the cool part of the tube. 
 Or the volatilisation may be ef- 
 fected in a short wide test tube, 
 and the sublimate condensed on a flat strip of glass held over the 
 
i 5 8 
 
 ARSENIC. 
 
 mouth of the tube. Upon examination with a lens, the sublimate 
 in the tube or on the glass will be seen to consist chiefly of octa- 
 hedral crystals, as shown in fig. 44, which do not polarize. 
 
 y. Action of sulphide of ammonium. When a drop or 
 so of sulphide of ammonium is added to a little white arsenic 
 contained in a watch glass, there is no alteration of colour pro- 
 duced, but on applying a gentle heat, solution takes place, and 
 on evaporating to dryness, a yellow film of sulphide of arsenic is 
 left, soluble in alkalies, insoluble in hydrochloric acid. 
 
 3. Solubility. Powdered white arsenic when agitated with 
 water in a test tube, does not perceptibly dissolve, but remains 
 partly as a film over the surface, partly in small aggregations at 
 the bottom. This state of immiscibility, which is very cha- 
 racteristic, does not disappear even on prolonged boiling. By 
 filtration, however, a clear aqueous solution of arsenious acid is 
 obtained. Moreover on adding a little potash or hydrochloric 
 acid to the hot mixture of water and white arsenic, complete 
 solution is very easily effected. 
 
 e. Reducibility. A minute quantity of the powder sprinkled 
 upon red-hot charcoal evolves 
 scarcely visible vapours having a 
 peculiar garlic-like odour. When a 
 little white arsenic mixed with three 
 or four times its bulk of dry soda- 
 flux, produced by the incineration of 
 acetate of sodium with some addi- 
 tional charcoal, is introduced into a 
 narrow reduction tube of hard glass, 
 made perfectly dry and warm, there 
 is produced, on subjecting the mix- 
 ture to the heat of a spirit flame, a 
 sublimate of reduced arsenic which 
 condenses in the upper cool part of the 
 tube in the form of a metallic ring, 
 as shown of the actual size in fig. 45. 
 
 Kg. 45- 
 
DEDUCTION -TEST. 159 
 
 Or a minute quantity of white arsenic may be placed in the re- 
 duction-tube, covered with a considerable thickness of powdered 
 charcoal, and heat applied from above to below, so that the ar- 
 senic may volatilise through the red-hot charcoal, when a ring of 
 reduced metal will appear as before. 
 
 . Characters of the metallic ring. The arsenical 
 ring is characterised as follows: a. By its lustrous steel grey 
 appearance. Should it present an opaque brownish -black colour, 
 its proper aspect may be brought out by the cautious application 
 of heat, when the characteristic metallic grey ring will remain, 
 and a more volatile dark-coloured compound of arsenic be vola- 
 tilised. The interior surface of the metallic sublimate, rendered 
 visible by breaking the tube, presents a crystalline appearance. 
 b. By its volatility. Upon heating the sublimate to a tempera- 
 ture considerably below redness, it may be readily volatilised 
 from one part of the tube to another, c. By its conversion into 
 arsenious anhydride. After repeated volatilisations up and down 
 the tube, the ring of metal is gradually replaced by a ring of 
 iridescent crystals of white arsenic, shown by a lens to consist of 
 variously modified octahedrons. These may be boiled in a small 
 quantity of water for some time, when a solution of arsenious 
 acid will be formed, to which the ordinary liquid reagents 
 can be applied, d. By its conversion into arsenic acid. The 
 ring of metal, when warmed with a drop or two of nitro-muriatic 
 acid, disappears, and on evaporating to dryness, a residue of 
 arsenic acid is left, which may be dissolved in water, and tested 
 with nitrate of silver solution, when a brick-red precipitate of 
 arseniate of silver will be produced. 
 
 (133.) DISSOLVED. 
 
 a. Reaction, &c. The aqueous solution of arsenious acid 
 is clear, colourless, tasteless, inodorous, and has a faintly acid 
 reaction to test-paper. When evaporated upon a glass plate, it 
 leaves a white residue of minute octahedral non -polarising crystals, 
 which may be volatilised by a further application of heat. 
 
l6o ARSENIC. 
 
 /3. Precipitation of arsenite of silver. Ammonio- 
 nitrate of silver, added to aqueous arsenious acid, throws down 
 an opaque yellow precipitate of arsenite of silver, soluble in 
 ammonia and in dilute nitric acid. The reagent is made by 
 adding a weak solution of ammonia drop by drop to a strong 
 solution of nitrate of silver, until the brown precipitate at first 
 produced is just redissolved. 
 
 y. Precipitation of arsenite of copper. Ammonio- 
 sulphate of copper, added to aqueous arsenious acid, produces 
 a light green precipitate of arsenite of copper, soluble in am- 
 monia and in dilute acids. When collected on a filter, washed, 
 dried, and heated in a reduction tube, it yields a crystalline sub- 
 limate of arsenious anhydride. Ammonio- sulphate of copper is 
 made by carefully adding ammonia drop by drop to a somewhat 
 dilute solution of sulphate of copper, until the precipitate at 
 first produced is nearly redissolved. 
 
 5. Precipitation of trisulphide of arsenic. When 
 a current of washed sulphuretted hydrogen gas is passed through 
 a solution of arsenious acid acidulated with hydrochloric acid, 
 an abundant bright yellow precipitate of arsenious sulphide or 
 orpiment is produced. Sulphide of ammonium does not give 
 any precipitate with aqueous arsenious acid until some other 
 acid is added ; while sulphuretted hydrogen produces only a 
 yellow discolouration. 
 
 e. Characters of the above precipitate. The 
 yellow precipitate may be collected on a filter, washed with 
 water, and tested as follows. Boiled with hydrochloric acid it 
 does not perceptibly dissolve, but, on the addition thereto of a 
 little nitric acid, disappears with the formation of red fumes, a 
 globule of melted sulphur frequently remaining undissolved. 
 Treated with sulphide, hydrate, or carbonate of ammonium, it 
 undergoes solution, and is again thrown down by the addition of 
 hydrochloric acid. Dried and heated in a reduction tube, it sub- 
 limes unchanged or nearly so. Dried and heated in a reduction 
 tube, after thorough mixture with four or five times its bulk of 
 soda-flux, it yields a sublimate or ring of reduced metal. 
 
NATURE OF MARSH'S TEST. 
 
 161 
 
 Fig. 46. 
 
 (134.) MARSH'S TEST. 
 
 a. Nature of process. When a substance containing 
 arsenic is acted upon by nascent hydrogen, usually developed 
 by the reaction of metallic zinc and dilute sulphuric or hydro- 
 chloric acid, a gaseous compound of arsenic and hydrogen, 
 known by the name of arsenetted hydrogen, is given off. This 
 gas may be generated in any ordinary form of hydrogen-appa- 
 ratus ; even the adaptation to one another of a flat-bottomed 
 vial, perforated cork, and piece of glass tube, either straight or 
 bent, according to circumstances, and drawn out to a moderately 
 fine point, will answer the pur- 
 pose. The arrangement shown 
 in fig. 47 is in some cases very 
 convenient; while in others, the 
 original bent tube devised by 
 Marsh may be most advanta- 
 geously employed. It may be 
 made quite plain, as in fig. 46, 
 or be provided with a couple of 
 large strong bulbs, one in the 
 upper part of the long, and one 
 in the lower part of the short 
 limb. This short limb is fur- 
 nished with a movable stopcock, 
 into which is screwed either a 
 short jet, for burning the issuing 
 gas, as shown in the figure, or 
 an elbow, to which a horizontal 
 piece of glass tubing may be 
 readily adapted. Arsenetted 
 hydrogen is identified by its property of yielding deposits ot 
 metallic arsenic, either upon imperfect combustion, as originally 
 pointed out by Marsh, or by exposure to a dull red heat, as 
 recommended by a committee of the French Academy. 
 
1 62 ARSENIC. 
 
 (135.) ORIGINAL MARSH'S PROCESS. 
 
 When it is intended to obtain deposits by an imperfect com- 
 bustion of the gas, Marsh's apparatus (fig. 46) is usually em- 
 ployed in the following manner. The stopcock being removed, 
 a piece of stout glass rod is carefully dropped into the shorter 
 limb of the tube. It should be sufficiently small to reach the 
 bend, but not small enough to pass into the longer limb : a glass 
 stopper will often answer the purpose extremely well. Two or 
 three compact lumps of metallic zinc are then let fall upon the 
 piece of glass, the open stopcock replaced, and cold diluted sul- 
 phuric acid, in the proportion of about one part of acid to six 
 or seven of water, poured into the longer limb ; so that when 
 the liquid is level in the two limbs, there may yet remain some 
 little free space beneath the stopcock. The dilute acid is allowed 
 to act upon the zinc for a few minutes, and the stopcock then 
 closed, whereby the shorter limb becomes gradually filled with 
 hydrogen gas, the acid being gradually driven up into the longer 
 limb. The stopcock is then opened, and the issuing hydrogen 
 quickly inflamed. It ought to burn with a scarcely visible 
 flame, which should not produce a deposit or even a discoloura- 
 tion upon a piece of clean glass or porcelain momentarily de- 
 pressed upon it. As soon as all the hydrogen is driven out of 
 the shorter limb by the descending acid r the stopcock is reclosed 
 while another accumulation of gas takes place, which is then 
 released, inflamed, and examined as before. Or the issuing gas, 
 without being inflamed, may be allowed to impinge on paper 
 moistened with nitrate of silver solution, which should not 
 thereby acquire any discolouration. When, after several exa- 
 minations, the purity of the hydrogen, and consequently of the 
 materials used to generate it, has been satisfactorily ascertained, 
 the arsenical liquid is introduced and the experiment repeated. 
 
 a. Appearance of flame, &c. The hydrogen gas subse- 
 quently evolved is contaminated to a greater or less extent with 
 arsenetted hydrogen, and produces a metallic -looking discoloura- 
 tion upon paper moistened with nitrate of silver solution. It 
 
MARSH'S TEST. 163 
 
 burns with a bluish flame, and evolves a white smoke of arse- 
 nious anhydride. 
 
 (3. Reactions of the smoke. The smoke or vapour 
 may be tested by holding over the summit of the flame a piece of 
 porcelain moistened with ammonio-nitrate of silver, when a yellow 
 turbidity due to arsenite of silver will make its appearance; or by 
 enclosing the flame more than once if necessary by a short wide 
 test-tube moistened on its interior with water, whereby a weak 
 solution of arsenious acid will be formed, which may be tested 
 with sulphuretted hydrogen, or other appropriate reagent. 
 
 y. Formation of deposit. When a piece of clean 
 glass, porcelain, or talc is momentarily depressed upon the flame so 
 as to cut off about two-thirds of its height, there is produced upon 
 the cold surface a dark stain or deposit which is constituted of three 
 products, in the centre of metallic arsenic, in the exterior of arse- 
 nious anhydride, and in the intermediate zone of a compound 
 considered to be a suboxide of arsenic. That the stain is really 
 arsenical is shown by its possessing the following characters : 
 a. Metallic brilliancy. The lustrous appearance of the arsenical 
 stain is best seen on its free surface, but is recognisable through the 
 glass, b. Hair-brown colour. This colour appertains particularly 
 to slight stains, and to the intermediate portion of larger stains, 
 in which last it is best manifested by means of transmitted light, 
 c. Volatility. The arsenical stain disappears readily on the appli- 
 cation of a heat considerably below redness; this property of vola- 
 tility is very evident when the stain has been produced on a thin 
 plate of talc. During its volatilisation the metallic arsenic becomes 
 converted into arsenious anhydride, d. Solubility in chloride 
 of lime. When the arsenical stain is warmed with a few drops of 
 bleaching liquid, complete solution speedily takes place. For the 
 application of this test it is convenient to produce the stain on the 
 interior of a watch-glass, e. Non- solubility in cold disulphide 
 of ammonium. The arsenical stain is not perceptibly affected by 
 treatment with a drop of yellow sulphide of ammonium solution. 
 But on heating to dryness, a bright yellow stain of orpiment i$ 
 
 xS 
 
i6 4 
 
 ARSENIC. 
 
 produced, containing a dark nucleus of undissolved metallic 
 arsenic. (Guy.) f. Conversion into arsenic acid. The arsenical 
 stain disappears completely when gently warmed with a drop 
 or two of nitric or nitro -muriatic acid. By evaporating to dry- 
 ness, a slight residue of arsenic acid is left, recognisable by its 
 ready solubility in a drop of water, so as to form a solution in 
 which nitrate of silver produces a brick-dust-red turbidity. 
 
 (136,) MODIFIED MARSH'S PROCESS. 
 
 Marsh's apparatus may also be used for generating arsenetted 
 hydrogen when it is intended to decompose the gas by extraneous 
 heat. In this case the jet of the stopcock is unscrewed and 
 replaced by a metal elbow, to which a horizontal piece of narrow 
 hard glass tubing is adapted. But some such apparatus as that 
 shown in fig. 47 is on the whole to be preferred. It consists of a 
 
 Fig. 47. 
 
 small flask furnished with a cork through which passes a long 
 funnel tube, and a short wide rectangular tube, loosely plugged 
 with a little cotton wool, arid connected by means of a perforated 
 
REINSCH'S TEST. 165 
 
 cork with a long horizontal piece of narrow hard glass-tubing, bent 
 downwards at its extremity so as to dip into a solution of nitrate 
 of silver. The apparatus is charged with pure zinc and dilute sul- 
 phuric acid, so as to cause an evolution of hydrogen gas, which 
 passes through the cotton wool, where it deposits any mechanical 
 impurities, along the horizontal tube, and into the silver solution. 
 During the transmission of the gas, the flame of a spirit lamp is 
 applied steadily to some particular part of the horizontal tube, and 
 if after a little time there is not produced any deposit within the 
 tube, or precipitate in the silver solution, the materials are known 
 to be pure, and the arsenical liquid may be introduced. 
 
 a. Decomposition by heat. The resulting arsenetted hy- 
 drogen is decomposed in its passage through the heated portion 
 of the tube, and deposits a steel-grey ring of metallic arsenic at 
 some little distance beyond the flame. The ring may be identi- 
 fied by its appearance, its position at a little distance beyond the 
 flame, its volatility, its conversion into arsenious anhydride by 
 repeated sublimations, and its conversion into arsenic acid by 
 treatment with nitre-muriatic acid and evaporation to dryness. 
 
 j3. Decomposition by nitrate of silver. Any 
 arsenetted hydrogen that may escape decomposition by the flame, 
 or that may be purposely allowed to escape, is arrested by the 
 nitrate of silver solution, with formation of a black deposit of 
 metallic silver. On the termination of the experiment, the 
 excess of silver may be precipitated with hydrochloric acid, the 
 filtrate evaporated to dryness, and the residue of arsenic acid dis- 
 solved in water and tested with the usual reagents. 
 
 (137.) REINSCH'S TEST. 
 
 This test is particularly useful for the detection of arsenic in 
 organic liquids or solids. The suspected liquid is simply acidu- 
 lated with about one-eighth of its bulk of pure hydrochloric acid, 
 and boiled. The solid tissue is cut up into very small pieces and 
 boiled for some time in a mixture of about one part of hydro- 
 chloric acid with six of water. 
 
1 66 ARSENIC. 
 
 a. Deposit on copper. A small piece of clean copper 
 foil, or preferably of fine gauze, is introduced into the hot acidu- 
 lated liquid, and the boiling continued for a period varying from 
 a few minutes to a quarter of an hour or longer. Should the 
 copper acquire a grey metallic discolouration, other pieces thereof 
 may be added from time to time, and the supply continued so 
 long as the last added piece assumes any perceptible alteration 
 in colour. 
 
 j3. Character of deposit. The pieces of coated foil or 
 gauze are removed from the liquid, washed in water, and dried 
 between folds of bibulous paper. The deposit unless very thick 
 adheres firmly to the subjacent copper, presents a well-marked 
 metallic lustre, and has a dark steel-grey colour, or, if very thin, 
 a somewhat bluish tint. On the application of heat it disappears 
 entirely, while the copper resumes its ordinary appearance. 
 
 y. Crystalline sublimate. A piece of the coated copper, 
 held between the fingers, is warmed over a flame, coiled up into 
 a small bulk, and introduced into an ordinary reduction tube 
 (fig. 45). The heat of a small spirit flame is then carefully applied, 
 at first a little above the coil, and afterwards to the coil itself, 
 whereby the arsenic is volatilised, oxidised, and condensed in the 
 cool part of the tube as a crystalline sublimate. If necessary, 
 several pieces of coated copper may be thus heated successively in 
 the same tube until a sufficiently obvious sublimate of arsenious 
 anhydride is produced, which, when examined by a lens or the low 
 power of a microscope, will exhibit highly iridescent octahedral 
 forms. A small piece of tubing open at both ends, one of 
 which is drawn out to a long, almost capillary, termination, as 
 
 Fig. 48- 
 
 shown in fig. 48, is convenient for volatilising a very slight de- 
 posit. The coated foil having been introduced and tilted down 
 
KEINSCH'S TEST. 167 
 
 to the shoulder, the tube is sealed by the blowpipe at the point a, 
 and the resulting cylindrical bulb containing the foil heated in a 
 spirit-flame, from its capillary shoulder backwards to its sealed 
 extremity, whereby a crystalline ring becomes condensed in the 
 capillary projection at b. 
 
 3. Reactions of the sublimate. By means of a 
 couple of file-marks, the short length of tubing containing the 
 sublimate may be broken off from the two ends of the tube, and 
 the sublimate itself be acted upon by reagents. Moistened with 
 sulphide of ammonium solution and dried in a water-bath, it 
 yields a yellow residue of orpiment. Moistened with a mixture 
 of nitric and a little hydrochloric acid and evaporated to dryness, 
 it leaves a slight residue of arsenic acid, which produces a red 
 turbidity when treated with a drop of nitrate of silver solution. 
 
 (138.) IMPEDIMENTS TO KEINSCH'S TEST. 
 
 a. Influence of oxygenants. Reinsch's process is not 
 applicable in the presence of oxidising bodies, which moreover 
 enable dilute hydrochloric acid to dissolve metallic copper. But 
 the majority of such compounds may be reduced by the action 
 of sulphite of sodium upon the acidified liquid, while any excess 
 of sulphurous acid from the decomposition of the salt may be got 
 rid of by ebullition before introducing the foil or gauze. 
 
 /3. Purity of the acid. This may be ascertained by 
 diluting a sufficient quantity of the hydrochloric acid with about 
 four times its bulk of water, and boiling a very small piece of 
 foil or gauze in the diluted liquid for a period of twenty minutes 
 or half an hour. 
 
 y. Purity of the copper. As even in the most satisfac- 
 tory performance of Reinsch's test, there is always some, although 
 but an extremely minute quantity of the copper dissolved, and 
 as commercial copper is rarely quite free from arsenic, it is 
 important that the foil or gauze employed in the experiment 
 should be specially tested as to its purity. If ; however, the 
 
1 68 ARSENIC. 
 
 solution of four or five grains of the copper does not yield an^ 
 evidence of arsenic, the metal is quite pure enough for the 
 purpose, even though a trace of arsenic should be detected in a 
 larger quantity of it. A few grains of the copper cut into fine 
 pieces are placed in a small tube-retort, or in a bulb- tube, such 
 as that shown in fig. 14, with not less than twice their weight 
 of precipitated peroxide of iron, and an excess of hydrochloric 
 acid. The mixture is then distilled to dryness, great care being 
 taken at the last to prevent spurting. Any arsenic originally 
 contained in the copper is in this manner carried over in the form 
 of chloride of arsenic, and may be condensed in a little water 
 with the excess of aqueous hydrochloric acid. The resulting 
 liquid may then be tested for the presence of arsenic by boiling 
 in it a fresh piece of clean copper gauze or foil. 
 
 <$. Modified processes. The peroxide of iron mentioned 
 above may be replaced by an equivalent quantity of perchloride 
 of iron. Indeed it is better to dissolve the peroxide in excess of 
 hydrochloric acid, and then employ the residue left on evaporating 
 to dryness, which will be free from any trace of arsenic the 
 peroxide itself may have originally contained. Moreover, oxide 
 or chloride of copper may be substituted for the peroxide or 
 perchloride of iron, though not with advantage. Or the copper 
 may be dissolved in hydrochloric acid alone, without the addition 
 of any special oxygenant, by moistening the metal with the acid 
 and exposing both to the air for several days. The addition of 
 a few drops of a solution of perchloride of iron or chloride of 
 copper to the acid greatly facilitates this solution by exposure 
 to air. The hydrochloric solution, no matter how obtained, is 
 eventually distilled to dryness, and the distillate tested for arsenic. 
 
 (139.) OTHER FORMS OF ARSENIC. 
 
 a. Orpiment and realgar. These sulphides of arsenic 
 are yellow or orange-coloured compounds, which volatilise un- 
 changed upon the application of heat. Mixed with soda flux and 
 heated in reduction tubes, they give rise to sublimates of metallic 
 
IN ORGANIC MIXTURES. 169 
 
 arsenic ; and the residues, when moistened with hydrochloric acid, 
 evolve sulphuretted hydrogen, recognisable by its smell and action 
 on lead paper. Orpiment and realgar are not dissolved by boil- 
 ing hydrochloric acid, but disappear more or less completely in 
 nitro-hydrochloric acid, forming solutions from which arsenic 
 acid may be obtained by evaporating to dryness. They also 
 dissolve in sulphide of ammonium, and are redeposited on eva- 
 porating the liquid to dryness. 
 
 /3. Scheele's green. This well-known green pigment is 
 an impure arsenite of copper. Heated in a reduction tube, it 
 yields a crystalline sublimate of arsenious anhydride, and a black 
 residue of oxide of copper, which may be dissolved in hydro- 
 chloric acid, and tested by the usual reagents. Arsenite of 
 copper dissolves in dilute hydrochloric acid, forming a solution 
 in which, after precipitation of the copper by excess of oxalate of 
 ammonium, arsenic may be detected by sulphuretted hydrogen, 
 or by Marsh's or Reinsch's tests. 
 
 (140.) IN ORGANIC MIXTURES. 
 
 a. A hydrochloric acid decoction may be prepared as already 
 described and tested by Keinsch's process. Or the organic sub- 
 stance may be distilled to dryness with hydrochloric acid, the 
 residue redistilled with fresh hydrochloric acid, the two distillates 
 collected in water, and the product examined by sulphuretted 
 hydrogen, or by Marsh's or Reinsch's process. Or the tissue, &c., 
 may be destroyed with hydrochloric acid and chlorate of potas- 
 sium, the solution submitted to the prolonged action of sulphu- 
 retted hydrogen, and the resulting precipitate further examined 
 (vide par. 116 /3). 
 
 IX. ANTIMONY. 
 (141.) ANTIMONIAL SALTS. 
 
 a. Tartar emetic. This compound usually occurs as a white 
 powder, or in ill-defined crystalline masses. It becomes charred 
 by heat, and when ignited with a little carbonate of sodium on 
 charcoal before the blowpipe, yields a bead of brittle metal and 
 
170 
 
 ANTIMONY. 
 
 Fig. 49. 
 
 an abundant white incrustation. It is turned of an orange colour, 
 and finally dissolved by sulphide of ammonium. Its solution in 
 
 water when carefully evaporated 
 yields beautifully polarising crys- 
 tals (fig. 49), chiefly tetrahedral, 
 but here and there cubical and 
 octahedral. When acidified by 
 nitric or hydrochloric acid, it fur- 
 nishes a white precipitate soluble 
 in excess of either acid. 
 
 ft. Chloride of antimony. 
 This is a highly corrosive fuming 
 liquid, usually having a yellow or 
 orange colour from the presence of 
 
 chloride of iron. Poured into water, it gives rise to an abundant 
 white precipitate, which, after thorough washing with water, is 
 turned of an orange colour and finally dissolved by sulphide of 
 ammonium. The precipitate is also readily soluble in tartaric acid. 
 Mixed with carbonate of sodium and heated on charcoal before 
 the blowpipe, it yields a bead of brittle metal and an abundant 
 white incrustation. 
 
 (142.) IN SOLUTION. 
 
 a. Precipitation of trisulphide of antimony. 
 A current of sulphuretted hydrogen gas passed into an antimonial 
 solution acidified with tartaric acid, throws down an orange pre- 
 cipitate, which after washing with water, is insoluble in carbonate, 
 but soluble in sulphide of ammonium, forming a solution from 
 which it may be reprecipitated on the addition of an acid. 
 
 ft. Precipitation of oxichloride of antimony. 
 Precipitated trisulphide of antimony dissolves completely in hot 
 hydrochloric acid with evolution of sulphuretted hydrogen gas. 
 The resulting trichloride of antimony, freed from excess of hydro- 
 chloric acid by evaporation to a small bulk, gives when poured 
 into water an abundant white precipitate of oxichloride of anti- 
 mony, soluble in tartaric acid. 
 
MARSH'S TEST. 171 
 
 y Metallic precipitation on tin. A piece of tin 
 foil or bar immersed in the above tartaric acid solution, becomes 
 speedily covered with a pulverulent black deposit of metallic 
 antimony. 
 
 (143.) MARSH'S TEST. 
 
 The antimonial solution, acidulated with tartaric acid, may be 
 introduced into the original or modified form of Marsh's appa- 
 ratus, previously charged with pure zinc and dilute sulphuric 
 acid, and the resulting gas examined as follows : 
 
 a. Appearance of flame, &c. Hydrogen contaminated 
 with antimonetted hydrogen produces a black discolouration on 
 paper moistened with nitrate of silver solution. It burns with an 
 opaque bluish white flame, and evolves a white smoke of teroxide 
 of antimony, which, unlike the arsenical smoke, does not produce 
 a yellow turbidity with ammonio -nitrate of silver. 
 
 /3. Characters of deposit. When a piece of talc, 
 porcelain, or glass is depressed upon the flame, a dark stain or 
 deposit is produced, distinguishable from the arsenical stain by 
 the following properties : a, by its comparative want of metallic 
 lustre ; b, by its smoky black colour ; c, by its non- volatility 
 save at a heat approaching redness ; d, by its insolubility in 
 chloride of lime; e, by its ready solubility in yellow sulphide of 
 ammonium, so as to form a solution which on evaporation to dry- 
 ness leaves a bright orange stain ; and /, by its yielding after 
 treatment with nitro-muriatic acid and evaporation to dryness, a 
 residue which does not give a red precipitate with nitrate of silver 
 solution. 
 
 y. Decomposition by heat. Instead of burning the 
 antimonetted hydrogen, it may be transmitted through a tube 
 heated to redness, and finally through a solution of nitrate of 
 silver. The- deposit of antimony produced in the tube is charac- 
 terised by its position, just before and beyond the exact spot 
 where the heat is applied, by its want of volatility, by its non- . 
 
1 72 ANTIMONY. 
 
 convertibility into arsenious anhydride or arsenic acid, and by its 
 ready solubility in yellow sulphide of ammonium to form a solu- 
 tion which leaves a bright orange stain on evaporation. 
 
 5. Reaction with nitrate of silver. Antimonetted 
 hydrogen produces in nitrate of silver solution a black deposit of 
 antimonide of silver, from which, after washing with water, the 
 antimony may be dissolved away by a boiling solution of cream 
 of tartar, and precipitated from the resulting solution by sulphu- 
 retted hydrogen. 
 
 (144.) REINSCH'S TEST. 
 
 a. Deposit on copper. The deposition of antimony 
 upon copper foil or gauze boiled in a hydrochloric acid decoction 
 of organic matter contaminated with antimony, or in a weak 
 acidulated solution of some antimonial salt, takes place exactly as 
 does the deposition of arsenic under similar circumstances. The 
 highly lustrous deposit of antimony differs from that of arsenic 
 in having a marked violet colour, and in being less easily dissipated 
 by heat. When a piece of the coated foil or gauze is strongly 
 heated in a reduction tube, it either does not afford any sublimate 
 at all, or else a very slight white deposit situated close to the 
 heated end of the tube, not having a crystalline character, and 
 being practically non-volatile. 
 
 /3. Solution of deposit. When boiled for a few minutes 
 in a weak feebly alkaline solution of permanganate of potassium, 
 the antimonial coating is dissolved away from the copper, while 
 the permanganate loses its colour and furnishes a slight turbidity 
 of manganic hydrate. The filtered liquid acidulated with hydro- 
 chloric acid and treated with sulphuretted hydrogen, acquires a 
 yellowish colour, and on standing deposits an orange precipitate, 
 which may be further examined if necessary. Or, if the anti- 
 monial coating be not very thick, it will suffice to boil the copper 
 for some time, with frequent exposure of its surface to the air, in 
 a weak solution of caustic potash only, and to treat -the resulting 
 liquid, after acidification by hydrochloric acid, with sulphuretted 
 hydrogen. 
 
PRUSSIC ACID. 173 
 
 (145.) IN ORGANIC MIXTURES. 
 
 The processes of precipitation by sulphuretted hydrogen and 
 deposition on copper, are perfectly applicable to acidified organic 
 liquids, and to the hydrochloric acid decoctions of organic 
 tissues. Or the tissue may be destroyed by hydrochloric acid 
 and chlorate of potassium, the solution after evaporation treated 
 by sulphuretted hydrogen, the resulting precipitate dissolved in 
 boiling hydrochloric acid, and the solution so formed tested in 
 Marsh's apparatus, or by the process of Reinsch; 
 
 X. PEUSSIC ACID. 
 (146.) IN AQUEOUS SOLUTION. 
 
 a. Appearance, &c. Prussic or hydrocyanic acid CNH, 
 occurs in the state of aqueous solution as a colourless, perfectly 
 volatile, feebly acid, mobile liquid. Its vapour, which is given 
 off at all ordinary temperatures, is invisible, has an odour said 
 to be like that of bitter almonds, and when inspired even in 
 minute quantity causes a peculiar sensation in the fauces. 
 
 /3. Formation of Prussian blue. The turbid greenish 
 liquid made by adding excess of potash to solution of ordinary 
 sulphate of iron, does not undergo any visible alteration when 
 mixed with aqueous prussic acid ; but, on acidifying the mixture 
 with hydrochloric acid, a bright blue, or sometimes a greenish 
 blue colour is developed, due to the production of finely divided 
 Prussian blue, which gradually separates as a distinct precipitate. 
 Or the potash and sulphate of iron may be added separately to 
 the suspected liquid, and the mixture be afterwards acidulated 
 with hydrochloric acid. 
 
 y. Formation of sulphocyanate of iron. Aqueous 
 prussic acid, mixed with a drop or two of yellow sulphide of 
 ammonium solution and evaporated to dryness at a low tem- 
 perature, leaves a residue of sulphocyanate of ammonium, which, 
 when moistened with water and tested with a drop of per- 
 
174 PRUSSIC ACID. 
 
 chloride of iron, produces a dark-red solution of persulphocyanate 
 of iron. 
 
 3. Formation of cyanide of silver. Solution of 
 nitrate of silver added to aqueous prussic acid throws down a 
 white precipitate of cyanide of silver, which quickly subsides 
 after agitation. It is not affected by cold nitric acid, but when 
 separated from the supernatant liquid dissolves more or less 
 completely in the strong boiling acid. The precipitate collected 
 on a filter, washed, dried, and heated in a reduction tube, evolves 
 cyanogen gas, which if ignited at the mouth of the tube, will 
 burn with its peculiar rose-coloured flame. 
 
 . Decompositions of precipitate. The precipitate 
 treated with hydrochloric acid evolves prussic acid vapour, 
 which may be received on the interior of a watch-glass mois- 
 tened either with yellow sulphide of ammonium, or with a 
 mixture of potash and sulphate of iron, as described under the 
 head of the vapour reactions. Or a portion of the precipitate 
 may be treated with a drop of yellow sulphide of ammonium, 
 dried at a low temperature, and the residue, after being mois- 
 tened with water, tested by a drop of perchloride of iron, when a 
 dark red liquid will be produced, easily distinguishable from the 
 black precipitate of sulphide of silver. Or a portion of the pre- 
 cipitate may be treated first with potash, then with a drop of 
 sulphate of iron, and lastly with a little hydrochloric acid, when 
 Prussian blue will be formed, together with white chloride of 
 silver. 
 
 (146.) IN VAPOUROUS STATE. 
 
 The succeeding tests may be applied to the vapour of the pure 
 liquid acid, or to the vapour produced by the action of hydro- 
 chloric acid upon precipitated cyanide of silver, or to the vapour 
 evolved spontaneously from organic liquids or solids containing 
 prussic acid. Organic substances which do not react satisfac- 
 torily with these vapour tests may be distilled in a water-bath, 
 and the distillate treated similarly to the pure aqueous acid as 
 above described. 
 
STRYCHNIA. 175 
 
 a. Formation of Prussian blue. When a mixture of 
 potash and sulphate of iron, smeared upon the interior of a watch- 
 glass, or preferably on a flat glass slip ~. 
 (fig. 50), is exposed for a few minutes 
 to the action of prussic acid vapour, 
 there is produced on acidification with 
 hydrochloric acid, a solution of the iron 
 magma and development of Prussian 
 blue. 
 
 /3. Formation of sulphocyanate 
 of iron. A drop of yellow sulphide 
 
 of ammonium placed on a watch-glass or glass slip and exposed 
 for a short time to the action of prussic acid vapour, yields, when 
 evaporated to dryness at a low temperature, a residue of sulpho- 
 cyanate of ammonium, which produces a dark red colour, on, the 
 addition of perchloride of iron. 
 
 y. Formation of cyanide of silver. A drop of nitrate 
 of silver, placed on a watch-glass or glass slip and exposed to the 
 action of the vapour, becomes white and opaque from the forma- 
 tion of cyanide of silver, convertible into Prussian blue, or 
 sulphocyanate of iron, as previously described. 
 
 When the prussic acid vapo'ur from some organic mixture is 
 contaminated with sulphuretted hydrogen, it produces a blacken- 
 ing of the silver salt ; but no interference with the sulphocyanate 
 reaction is manifested under the same circumstances. 
 
 XI. STRYCHNIA. 
 (148.) IN PURE STATE. 
 
 a. Nature, solubility, &c. Strychnia is a vegetable alka- 
 loid, having the formula C at H la N 4 0,,. It is more or less freely 
 soluble in alcohol, chloroform, benzole, and ether ; scarcely at all 
 soluble in pure water ; but readily soluble in acidulated water. 
 It is capable of uniting with and neutralising acids, to form 
 definite crystallisable salts, of which the sulphate, nitrate, hydro- 
 
STRYCHNIA. 
 
 chlorate, oxalate, tartrate, and acetate are soluble in water. 
 Most other strychnia compounds are more or less insoluble, 
 whence solutions of strychnia salts are precipitated by a very 
 great number of reagents, including hydrate, carbonate, iodide, 
 sulphocyanate and chromate of potassium, carbazotic acid, 
 phospho-molybdate of sodium, iodide of potassium with iodine, 
 potash double iodide of mercury and potassium, perchloride of 
 platinum, trichloride of gold, &c. 
 
 /3. Appearance. Strychnia usually occurs in the form of a 
 crystalline powder, or of well-defined prismatic crystals, either 
 white, or of a pale buff colour. The ordinary salts of strychnia 
 are generally met with as crystalline powders. Strychnia and its 
 salts when heated, melt, burn with a smoky flame, and leave a 
 carbonaceous residue. 
 
 y. Bitter taste. The bitterness of strychnia is peculiar, 
 and has been sometimes spoken of as metallic. Its intensity is 
 so great, that one drop of a gallon of water, in which a grain of 
 strychnia is dissolved, presents a recognisable bitter taste ; while 
 with ^^ part of strychnia in solution, the bitterness is well 
 marked and persistent. The taste of strychnia salts is but 
 slightly less intense than that of the alkaloid itself. In very 
 dilute solutions only is the bitterness capable of partial conceal- 
 ment by other sapid bodies. 
 
 3. Crystalline form. A drop or so of a spirituous or ethe- 
 real solution of strychnia allowed to evaporate spontaneously on a 
 glass slip, furnishes a crystalline residue consisting of rectangular 
 prisms often terminated by double or single oblique planes, and 
 in variously modified octahedra, as shown in fig. 51. The forms 
 deposited from a chloroformic solution are, for the most part, 
 not well characterised. 
 
 e. Precipitation. Aqueous solutions of strychnia salts, con- 
 taining from ^ to ~ part of strychnia, are precipitated by 
 the several reagents mentioned above, either immediately or 
 on stirring ; the most delicate though least characteristic preci- 
 pitants being the phospho-molybdate of sodium, and the potash 
 
COLOUR TESTS. 177 
 
 
 
 solution of hydrargyro-iodide of potassium. Hydrate or carbo- 
 
 nate of potassium causes a gradual deposition of well-defined 
 
 strychnia crystals, insoluble in ex- 
 
 cess of the precipitant (fig. 51). 
 
 The precipitates thrown down by 
 
 iodide, sulphocyanate, and chromate 
 
 of potassium, carbazotic acid, and 
 
 the chlorides of platinum and gold, 
 
 are also crystalline. 
 
 . Action of acids. Strong 
 sulphuric acid is without action on 
 strychnia, even at and above the 
 temperature of boiling water. Strong 
 
 nitric acid usually produces a yellow, or yellow-brown, dis- 
 colouration ; but is said to be without visible action on perfectly 
 pure strychnia, although this seems doubtful. 
 
 rj. Colour tests. When a little peroxide of lead is added 
 to a fragment of strychnia, dissolved in a drop of strong sul- 
 phuric acid mixed with ~ of its bulk of strong nitric acid ; or 
 preferably, when a little peroxide of manganese, or bichromate, or 
 ferridcyanide, or permanganate of potassium, is added to a frag- 
 ment of strychnia dissolved in a drop of strong sulphuric acid, 
 there is produced a magnificent purple-blue colour, becoming 
 gradually crimson, and finally reddish pink. The delicacy of this 
 test, when special precautions are taken, is almost illimitable, less 
 than ~> of a grain having been stated to give the reaction. 
 
 With from to j-^j- of a grain it is easily obtainable. In 
 operating on small quantities, the following plan may be adopted 
 with advantage. The dry strychnia, usually the residue of an 
 evaporation, in which case it must be allowed to become quite 
 cold, is moistened with the smallest sufficient quantity of strong 
 sulphuric acid. By the side of it is next placed a minute drop 
 of a mixture of sulphuric acid with a little very finely-powdered 
 amorphous peroxide of manganese, and the two then brought 
 into contact. The experiment should be made on a surface of 
 
 N 
 
iy8 STRYCHNIA. 
 
 white porcelain, or on a flat watch-glass or glass slip, resting on a 
 sheet of white paper. 
 
 0. Physiological test. When a minute quantity of solid 
 or dissolved strychnia is introduced underneath the incised skin 
 of a small frog, well-marked tetanic convulsions are manifested 
 by the animal, usually within a quarter of an hour ; and with a 
 strong dose almost immediately. This tetanus is said to have 
 been produced with so small a quantity as -^ of a grain of 
 strychnia ; but the delicacy of the test varies much with the state 
 of the animal, freshly- caught young frogs being the most excitable. 
 
 (149.) IN ORGANIC MIXTURES. 
 
 a. If a liquid, it is merely acidified, mixed in some cases with 
 a little spirit of wine, filtered, evaporated nearly to dryness, and 
 the residue extracted with strong alcohol. If a solid, it is brought 
 into a state of fine division, and mixed with a little proof spirit 
 acidulated with dilute sulphuric or other acid, acetic, oxalic, tar- 
 taric, &c. After digestion for some time in a water bath, the mix- 
 ture is filtered, the insoluble matters washed with proof spirit, the 
 washings added to the filtrate, the whole of the clear liquid 
 evaporated down to a small bulk, and the residue so obtained 
 extracted with strong alcohol. The alcoholic solution is then 
 evaporated to dryness, the residue dissolved in a little water, the 
 liquid filtered into a long tube or bottle, and rendered alkaline 
 with carbonate of potassium. Two or three times its volume of 
 ether are next added, and the whole shaken up briskly for some 
 time. After subsidence, the ethereal solution is poured off, and 
 allowed to evaporate spontaneously, whereby a residue is left of 
 more or less well crystallised strychnia. This may be further 
 purified by moistening it with strong sulphuric acid, and heating 
 it for some time in a water bath, then diluting with water, 
 supersaturating the acid liquid with potash, again extracting with 
 ether, and evaporating. The final product may be examined 
 under the microscope, by the colour and physiological tests, and 
 by the tongue. In the above process, chloroform or benzole may 
 be substituted for the ether. 
 
MORPHIA. REACTIONS OF. 
 
 179 
 
 XII. MORPHIA. 
 (150.) IN PURE STATE. 
 
 a. Nature, solubility, &c. Morphia is a vegetable 
 alkaloid, having the formula C I7 Hj 9 NO r It neutralises acids to 
 form salts, one of which, the raeconate of morphia, exists largely 
 in opium, and is the source from which the alkaloid is obtained. 
 Morphia is readily soluble in hot, less so in cold alcohol, very 
 sparingly soluble in ether, and almost insoluble in water, save in 
 the presence of acids. Its ordinary salts dissolve readily in water 
 to form solutions, which are precipitable by a great number of 
 reagents, including most of those which precipitate strychnia. 
 Solutions of morphia and its salts have a well marked bitter taste. 
 
 13. Appearance, &c. Morphia is usually met with in the 
 state of acetate or hydrochlorate, which salts sometimes occur 
 iinely crystallised, but more often as imperfectly crystalline pow- 
 ders of a buff- tinted white colour. The alkaloid itself occurs 
 in quadrangular prisms, frequently having two opposite edges 
 truncated so as to produce hexagonal forms. Morphia and its 
 salts when heated, melt, burn with 
 a smoky flame, and leave a carbo- 
 naceous residue. 
 
 y. Cry stalline form. Mor- 
 phia, when deposited by the spon- 
 taneous evaporation of its alcoholic 
 or ethereal solution, or when slowly 
 precipitated by caustic or carbona- 
 ted alkalies from aqueous solutions 
 of its salts, occurs in the form of va- 
 riously modified prismatic crystals, 
 as shown in fig. 52. 
 
 . Precipitation by potash. A single drop of potash 
 added to the somewhat concentrated solution of a morphia salt, 
 produces after some time, or on brisk stirring, a white precipitate 
 
 N2 
 
l8o MORPHIA. 
 
 of morphia, very soluble in excess of the precipitant, but repro- 
 ducible by an absorption of carbonic acid from the air. 
 
 . Colouration by nitric acid. Strong colourless 
 nitric acid added, in considerable quantity, to the cold solution 
 of a morphia salt, produces a deep orange-red colouration. Or a 
 drop or two of the acid may be added to a little powdered 
 morphia or morphia salt, on a watch-glass or capsule, when an 
 intense colouration will be at once developed. But the behaviour 
 is not peculiar to morphia. 
 
 . Colouration by a persalt ofiron. A drop or 
 two of a carefully neutralised solution of perchloride of iron, 
 added to a morphia solution, or to the dry alkaloid or salt, 
 produces a deep blue colour, rendered bluish green by any excess 
 of the iron solution. 
 
 r). Decomposition of iodic acid. A few drops of 
 aqueous iodic acid produce, in solutions of morphia, a brown 
 discolouration, only in part due to the liberation of iodine. 
 Ammonia, added after a little while, deepens the colour con- 
 siderably. A piece of starched paper, dipped into the coloured 
 liquid before it has been treated with ammonia, acquires a 
 purple colour, save when the quantity of the alkaloid is very 
 small. 
 
 6. Reduction of bichromate of potassium. 
 Strong sulphuric acid produces no colouration with morphia 
 salts or solutions. But a little bichromate of potassium solution 
 dropped carefully on to the sulphuric acid mixture is quickly 
 reduced with production of a bright green colour. 
 
 (151.) OPIATE LIQUIDS. 
 
 In the examination of liquids supposed to contain opium, the 
 presence of both morphia and meconic acid is usually sought for. 
 The last named body is not indeed poisonous, but is character- 
 istic of opium, and possessed of well marked properties. 
 
['OPIATE LIQUIDS. 181 
 
 a. Preliminary test for morphia with nitric 
 aci d. Strong nitric acid, added in considerable quantity to an 
 opiate liquid, will often produce a very perceptible darkening or 
 even a distinct orange-red colouration. If necessary, the original 
 liquid may have its colour reduced by moderate dilution with 
 water before the addition of the acid. 
 
 /3. Preliminary test for meconic acid with 
 perchloride of iron. To the opiate solution reduced to 
 a pale colour by dilution with even a very large proportion of 
 water, a few drops of perchloride of iron are added, when, if 
 meconic acid be present even in small quantity, a distinct red- 
 dening of the liquid will be produced. 
 
 y. Precipitation ofmeconate of lead. The opiate 
 liquid acidulated with acetic acid, is treated with acetate of lead, 
 so long as a precipitate continues to be produced, when the whole 
 is well agitated, and after partial subsidence, thrown upon a wet 
 filter. Meconate of lead remains as an insoluble deposit on the 
 paper, while the filtrate contains acetate of morphia, together 
 with the excess of acetate of lead. 
 
 3. Production of meconic acid from precipitate. 
 The precipitate having been thoroughly washed with water, is 
 boiled for some minutes with a small quantity of dilute sulphuric 
 acid, and the mixture thrown upon a filter, whereby a solution of 
 meconic acid is obtained. Or the washed precipitate suspended in 
 a little water may be treated with excess of sulphuretted hydrogen 
 gas, and the clear liquid filtered off, and gently evaporated. 
 
 e. Test for meconic acid by persalt of iron. The 
 filtrate produced by either of the above means is then tested with 
 a few drops of perchloride of iron, which should produce a dark 
 logwood red colour, through the formation of meconate of iron. 
 The red liquid does not alter its colour on boiling, in which 
 respect it differs from the similarly coloured solution of peracetate 
 of iron, neither is it bleached by treatment with corrosive sub- 
 limate, in which respect it differs from the similarly coloured 
 solution of sulphocyanate of iron. 
 
1 82 MORPHIA. 
 
 . Separation of morphia. Through the liquid filtered 
 from the precipitate of meconate of lead, but having more or less 
 acetate of lead in solution, a current of washed sulphuretted 
 hydrogen is passed, until the smell of the gas is persistent even 
 after agitaticn, when the whole is thrown upon a filter. The 
 clear filtrate containing acetate of morphia, is evaporated down 
 to a small bulk, supersaturated with carbonate of potassium, and 
 agitated with an ethereal solution of acetic ether. After subsi- 
 dence, the ethereal solution is poured off and allowed to evapo- 
 rate spontaneously, when there is left a residue of morphia in 
 more or less well defined crystals, to which the several tests for 
 the alkaloid can be successfully applied. 
 
ANIMAL CHEMISTRY. 183 
 
 CHAPTER IV. 
 ANIMAL CHEMISTKY. 
 
 L COMPOSITION OF TISSUES, &c. 
 (152.) ORGANIC AND MINERAL CONSTITUENTS. 
 
 a. The animal fluids and tissues consist of water together with 
 a certain amount of solid matter. When an animal tissue or 
 fluid is kept for some time at, or a little above, the temperature 
 of boiling water, its aqueous portion evaporates off more or less 
 completely, leaving the dry solids behind. This residuum, when 
 heated upon platinum foil, undergoes combustion ; some of its 
 constituents are dissipated, and a black carbonaceous mass 
 remains. If this carbonaceous residue be further heated for some 
 time, especially in a current of air, the black colour will gradually 
 disappear, and a white ash, fusible or infusible according to cir- 
 cumstances, will be left upon the foil. The components of dried 
 animal matter are thus separated into two classes ; one comprising 
 the substances which are destroyed by iire, and which are called 
 the organic constituents ; the other comprising the substances 
 which resist the action of fire, and which are called the inorganic 
 constituents, or more simply the ashes. This distinction, how- 
 ever, is not absolute. 
 
 The organic components of animal matter consist principally 
 of 
 
 CARBON. NITROGEN. 
 
 HYDROGEN. SULPHUR and 
 
 OXYGEN. PHOSPHORUS. 
 
184 COMPOSITION OF TISSUES, ETC. 
 
 These are also called the elementary or ultimate principles of 
 organic bodies. 
 
 The ashes consist principally of 
 
 SODIUM. SULPHURIC ACID. 
 
 POTASSIUM. PHOSPHORIC ACID. 
 
 CALCIUM. CARBONIC ACID. 
 
 MAGNESIUM. CHLORINE. 
 
 IRON. FLUORINE. 
 
 Nearly all animal products are composed of both organic and 
 inorganic constituents. Some few substances, however, pertain 
 almost entirely to one class : thus, while the enamel of the teeth 
 contains scarcely any organic matter, some of the crystals of uric 
 acid met with in the urine afford scarcely any ash. 
 
 In animal tissues or fluids, the ultimate organic elements are 
 combined with one another in a variety of ways, constituting 
 definite compounds, which are known as proximate organic 
 principles : thus in urine we may have all the above-mentioned 
 ultimate principles united with one another, to form the proximate 
 principles, urea, uric acid, sugar, albumen, &c. 
 
 The muscular tissue is a very suitable material to be employed 
 for the demonstration of the principal organic and mineral con- 
 stituents of animal bodies : the same general plan is adopted in 
 other instances. 
 
 (153.) ULTIMATE ORGANIC CONSTITUENTS. 
 
 a. Desiccation. The flesh or other tissue is cut into small 
 pieces and dried in a water bath until it ceases to lose weight. 
 By this means it is divided into an aqueous portion which has 
 evaporated, and a solid portion which remains. Nearly all animal 
 matters behave in a similar way ; but nitrogenous substances 
 having an alkaline reaction, give off water containing a variable 
 amount of ammonia. 
 
 /3. Destructive distillation. A few fragments of the dried 
 
ULTIMATE ORGANIC CONSTITUENTS. 185 
 
 flesh are placed in a reduction tube, into the mouth of which are 
 inserted a narrow strip of red litmus paper, and a similar strip of 
 lead paper. On applying the heat of a spirit-lamp, water will 
 condense in the upper part of the tube, proving the presence of 
 oxygen and hydrogen in the flesh a smell of ammonia will 
 be given off, and the litmus paper become blue, results indicating 
 the presence of nitrogen the lead paper will become blackened, 
 showing the presence of sulphur and lastly, a black mass 
 consisting chiefly of carbon will remain in the tube. 
 
 y. Incineration. If some of the dried flesh be heated 
 upon a piece of platinum foil, or in a shallow capsule, it will swell 
 up, burn with a smoky flame, and leave an abundant carbonaceous 
 residue. On continuing the application of heat for some time, 
 the carbon will gradually burn away. Its disappearance may be 
 facilitated by occasionally pulverising the coherent residue result- 
 ing from the ignition. Throughout the process the temperature 
 should not exceed, or indeed scarcely arrive at, a full red heat. 
 As soon as a pale grey or ochry red ash is produced, the heating 
 may be discontinued. 
 
 3. Detection of nitrogen. A little of the finely divided 
 dry substance is intimately mixed with ten or twelve times its bulk 
 of soda-lime (made by slacking quicklime with caustic soda solu- 
 tion) and the mixture heated in a reduction tube, whereby 
 ammonia is given off, recognisable by its smell and reaction on 
 test-paper. 
 
 . Detection of sulphur. Bodies of a moderately light 
 colour may be tested for sulphur by boiling them in aqueous 
 potash, to which solution of acetate of lead has been added in 
 quantity insufficient to render the liquid permanently opaque. 
 Should the substance so treated contain sulphur it will become 
 stained of a brown or black colour, which cannot be removed by 
 subsequent washing with water. If a substance is stained in the 
 above manner when boiled in a potash solution of lead, and IB 
 scarcely or not at all deepened in colour when boiled in a solution 
 of pure potash (free from lead), the presence of sulphur is certain. 
 
1 86 COMPOSITION OF TISSUES, ETC. 
 
 In the case of bodies readily soluble in potash water, the results 
 are not quite so characteristic. 
 
 . Deflagration with nitre. A little of the dried and 
 finely divided animal matter is mixed with about an equal bulk 
 of powdered nitre, and the mixture projected in small portions at 
 a time into a porcelain crucible kept at a red heat. Deflagration 
 immediately takes place, and, in the fused residue, the presence of 
 carbonic, sulphuric, and phosphoric acids, resulting from the 
 oxidation of carbon, sulphur, and phosphorus respectively, may be 
 ascertained by the usual tests. 
 
 In performing the above experiments, very different results 
 will be obtained with different substances, such, for instance, as 
 pieces of flannel, hard white of egg, refined gelatine, sugar, 
 fat, &c. 
 
 (154.) ASH OF ANIMAL MATTER. 
 
 a. A small portion of the ash, resulting from the incineration 
 of any kind of animal matter, is placed on a watch-glass, moistened 
 with water and examined by test-papers. Should it not have an 
 acid reaction, a drop or so of nitric acid is to be added, and any 
 effervescence due to carbonic acid carefully noted. The re- 
 mainder of the ash is boiled in a small quantity of water for 
 some time, a few drops of carbonate of ammonium solution added, 
 the whole thrown upon a filter, and the filtrate set aside for ex- 
 amination. The residue is then well washed with water, boiled 
 in a little hydrochloric acid with which a few drops of nitric acid 
 have been mixed, the liquid evaporated just to dryness, diluted 
 with water, and filtered. In this manner an aqueous and an 
 acidulous solution are obtained, containing respectively : 
 
 Aqueous Solution. Acid Solution. 
 
 POTASSIUM. IRON PEROXIDE. 
 
 SODIUM. CALCIUM. 
 
 SULPHATES. MAGNESIUM. 
 
 CHLORIDES. PHOSPHATES. 
 PHOSPHATES. 
 
ASH OF ANIMAL MATTER. 187 
 
 /3. Treatment of acid solution. A little of this solution 
 may be examined for phosphoric acid by molybdate of am- 
 monium (par. 100 .), and another portion tested for iron by 
 ferrocyanide or sulphocyanate of potassium (par. 77). To the 
 remainder of the solution acetate of ammonium is added, and, in 
 the event of there being no decided reddening produced, a little 
 perchloride of iron also. The whole is then boiled for some 
 time, whereby a red precipitate of basic phosphate of iron is 
 thrown down, the deposition of which may sometimes be facili- 
 tated by the careful addition of ammonia in quantity not suffi- 
 cient to produce neutrality. The boiling liquid is next filtered, 
 whereby a clear colourless solution should be obtained, perfectly 
 free from both iron and phosphoric acid. Excess of oxalate of 
 ammonium added to this solution throws down a precipitate of 
 oxalate of calcium. The resulting turbid mixture, having been 
 well shaken or stirred, is set aside for a little while, and, after 
 partial subsidence, passed once or twice through filtering paper, 
 when magnesium may be tested for in the clear liquid by- 
 means of ammonia and phosphate of ammonium. 
 
 y. Treatment of aqueous solution. Separate portions 
 of this solution, acidified with nitric acid, may be tested for 
 sulphates by chloride or nitrate of barium (par. 95 a.) ; for 
 chlorides, by nitrate of silver (par. 96 a,); and for phos- 
 phates, by molybdate of ammonium, or by sulphate of magne- 
 sium and ammonia (par. 100 S. a). Or a single portion of the 
 acidified solution may be tested with a few drops of nitrate of 
 barium to precipitate sulphates ; then filtered and treated with 
 excess of nitrate of silver to precipitate chlorides ; then again 
 filtered and carefully neutralised with dilute ammonia to throw 
 down the yellow phosphate of silver which the previously free 
 nitric acid held in solution. 
 
 The remainder of the liquid has to be evaporated to dryness, 
 and the residue, after gentle ignition, dissolved in a small quan- 
 tity of water. The solution, filtered if necessary, and acidulated 
 with hydrochloric acid, is carefully evaporated down in a watch- 
 
l88 NORMAL URINE. 
 
 glass or capsule, when cubes of common salt will crystallise out, 
 showing the presence of sodium. The mother liquor from these 
 crystals is then to be treated with perchloride of platinum and 
 alcohol, when, on stirring, a crystalline yellow precipitate of 
 platino-chloride of potassium will be deposited. Or the solu- 
 tion, acidified with hydrochloric acid, may be treated at once with 
 perchloride of platinum and alcohol, the yellow liquid filtered 
 from the potassium precipitate and evaporated down, when 
 yellow crystals of platino-chloride of sodium will make their 
 appearance. 
 
 II. NOEMAL UKINE. 
 (155.) GENERAL PROPERTIES. 
 
 a. Appearance, &c. Healthy human urine is an aqueous 
 liquid in which various compounds, organic and mineral, are 
 dissolved, and certain other substances held in suspension. It 
 has an amber colour, a slightly acid reaction, a characteristic 
 though not powerful odour, and a sp. gr. usually ranging within 
 a few degrees of 1020. The substances suspended in urine are 
 epithelium and mucus. Its dissolved organic constituents are 
 urea, uric acid, and hippuric acid, with colouring and other extrac- 
 tive matters. Its inorganic or mineral constituents are sodium, 
 potassium, calcium, and magnesium, in the form of phosphates, 
 sulphates, and chlorides. The student is expected to identify 
 these several substances, to make himself acquainted with their 
 characteristic appearances, and to realise their principal reac- 
 tions. A good quarter-inch object-glass is requisite for micro- 
 scopic examination. 
 
 /3. Mucus, epithelium, &c. Recent urine set aside for 
 some little time in a glass vessel gradually deposits a loose 
 flocculent sediment, readily visible upon holding the specimen 
 between the eye and the light. When examined microscopically 
 it is seen to consist of epithelial cells, derived from different por- 
 tions of the urinary apparatus, together with granular or mucus- 
 corpuscles. By nitration, these suspended urinary constituents 
 
PREPARATION OF UREA. 189 
 
 remain on the filtering paper as a scarcely visible deposit, while 
 the urine itself passes through perfectly bright. On gently 
 drying the filtering paper, the deposit assumes a varnish-like 
 aspect. 
 
 (156.) UREA. 
 
 a. Its detection. A little of the filtered urine, concen- 
 trated by careful evaporation in a watch-glass, and treated with 
 a few drops of strong colourless nitric acid, yields either at once 
 or very speedily a crystalline deposit of nitrate of urea. This 
 deposit, when examined under the microscope, is seen to consist 
 of delicate six-sided plates, superimposed upon one another so as 
 usually to prevent more than three or 
 four of the sides of any one crystal 
 beingrecognisable, as shown in fig. 5 3 . 
 The nitrate of urea maybe formed in 
 a watch-glass and then transferred 
 to a slide, or it may be dissolved in 
 water and recrystallised on a slide, 
 or nitric acid may be added to some 
 concentrated urine previously placed 
 in the field of the microscope, and 
 the actual process of crystallisation 
 observed. 
 
 (3. Preparation of urea. A couple of ounces or so of 
 fresh and filtered urine are evaporated on a water-bath or gently 
 heated sand-bath to a syrupy consistency, and a quantity of 
 strong colourless nitric acid about equal in bulk to the concen- 
 trated urine added thereto, when the mixture, upon cooling, 
 becomes semi-solid from the formation of nitrate of urea. The 
 crystalline mass is drained on a tile, or pressed between several 
 folds of blotting paper, then dissolved in a little warm water, 
 and the resulting solution treated with an excess of carbonate 
 of barium. Upon concentrating the filtered liquid, nitrate of 
 barium crystallises out first, while urea remains in the mother 
 liquor, which is evaporated to dryness over a water-bath. From 
 
NORMAL URINE. 
 
 this residue warm alcohol extracts the urea, and, on cooling or 
 slow evaporation, deposits it in the form of long flattened pris- 
 matic crystals, as shown in fig. 54.. 
 
 y. Properties of urea. Urea 
 behaves in some respects like an 
 organic base, being capable of unit- 
 ing with certain acids, notably the 
 nitric and oxalic acids, to form salts. 
 It dissolves readily in water and 
 alcohol, producing solutions which 
 are neutral to test-paper. The for- 
 mula of urea is CH 4 N 2 0, and that 
 of nitrate of urea CH 4 N 2 O.HN0 3 . 
 Urea is isomeric with cyanate of 
 ammonium NH 4 CNO, which undergoes spontaneous conversion 
 into it ; and also isomeric, if not identical, with carbamide 
 N a H 4 (CO)". Heated with water under pressure, it is trans- 
 formed into carbonate of ammonium, thus : CH 4 N a O + 2H a O 
 = (NH 4 ) a C0 3 . The same change takes place spontaneously in 
 putrefying urine, and is also brought about by acting on urea 
 with strong potash or sulphuric acid, except that the result- 
 ing carbonate of ammonium is then broken up by the reagent 
 employed. 1,000 parts of urine contain, on the average, about 
 1 5 of urea. 
 
 (157.) URIC ACID. 
 
 a. Its detection. This compound occurs but in small 
 quantity in healthy human urine, 100 parts of which con- 
 tain, on the average, not more than half a part of uric 
 acid. In order to detect its presence, a couple of ounces 
 or so of filtered urine are reduced to one-half the original 
 bulk by evaporation, a little hydrochloric acid added to the 
 concentrated liquid, and the whole set aside in a cool place 
 for some hours, when the interior of the vessel will be found 
 studded with small brown crystals of impure uric acid. In 
 
CHARACTERS OF URIC ACID. 19! 
 
 the case of urine having a moderately high specific gravity, con- 
 centration is unnecessary. After pouring off the supernatant 
 liquid, the crystals are detached, washed with water, and dissolved 
 in a few drops of warm potash. The resulting solution of urate 
 of potassium is then filtered, and acidulated with hydrochloric 
 acid, whereby a crystalline precipitate of uric acid is thrown 
 down, which may be examined microscopically and by the action 
 of nitric acid, as described below. 
 
 j3. Preparation of uric acid. Uric acid cannot well be 
 prepared, in any quantity, from normal human urine. But it 
 may be easily obtained from the common brickdust urinary 
 deposit, collected on a filter and washed with water ; or from 
 powdered uric calculi ; or the excreta of serpents. Any one of 
 these substances is boiled with caustic potash, the solution diluted 
 with water, filtered, and supersaturated with hydrochloric acid, 
 whereby a very considerable opacity is at first produced, which, 
 however, speedily disappears, and is replaced by a dense crystal- 
 line precipitate, from which the supernatant liquid may be readily 
 poured off. 
 
 y. Properties of uric acid. Uric acid furnishes two 
 classes of salts, acid and neutral, and is consequently dibasic. 
 Its formula is C 5 H 4 N 4 3 . The formula for a scarcely soluble or 
 acid urate is C 5 MH 3 N 4 O a , and that for a soluble or neutral urate 
 C 5 M a H a Isr 4 3 . Uric acid itself is extremely insoluble, both in 
 water and alcohol ; but is soluble in alkaline solutions, forming 
 neutral urates, and reprecipitated therefrom on the addition of an 
 acid. It always occurs in the crystalline state, the appearance of 
 the crystals, however, being very various. Occasionally the acid 
 is met with in its normal form of the rhombic prism, more fre- 
 quently in rhombic plates with the obtuse angles more or less 
 rounded off, or in acuminated doubly-convex lozenge-shaped 
 plates, or in elongated flat plates with excavated ends. Some of 
 the forms of uric acid crystals are shown in figs. 55 and 56. 
 Uric acid dissolves readily, with effervescence, in nitric acid, and 
 
I 9 2 
 
 NORMAL URINE. 
 
 on evaporating the solution to dryness an amorphous pinkish 
 residue is left. This, when moistened with ammonia, assumes a 
 
 Fig- 55- 
 
 fine crimson colour, which is changed to violet on the addition 
 of a small quantity of caustic potash. 
 
 (158.) HIPPURIC ACID. 
 
 a. Its preparation. 'Although this acid exists, in healthy 
 human urine, in nearly the same proportion as uric acid, yet its 
 presence therein does not so readily admit of demonstration. It 
 can, however, be easily procured from the urine of herbivora, 
 and from that of patients who have been taking benzoic acid as 
 a medicine. To prepare it from either of these sources, the 
 recent filtered urine is evaporated down to one-fourth of its bulk r 
 and then treated with an equal volume of ordinary hydrochloric 
 acid, when, on cooling, long prismatic needles of impure hippuric 
 acid crystallise out. These, after being washed with a little cold 
 water, are dissolved in boiling water, and the solution set aside to 
 crystallise. 
 
 /3. Properties of hippuric acid. The hippuric is a 
 monobasic acid, represented by the formula C 9 H 9 N0 3 . It is 
 soluble in water, alcohol, and ether. The crystals obtained by 
 cooling the hot aqueous solution on a slide consist of delicate 
 
COLOURING AND EXTRACTIVE MATTERS. 1 93 
 
 prisms, often presenting the appearance of elongated six-sided 
 plates, as shown in fig. 57. 
 
 By prolonged boiling with con- ^ 57 ' 
 
 centrated hydrochloric acid, hip- 
 puric or glyco-benzoic acid absorbs 
 a molecule of water, and breaks up 
 into benzoic acid and glycocine or 
 sugar of gelatine, thus: C 9 H 9 N0 3 
 + H 2 = C 7 H 6 O a + C a H 5 NO a . The 
 larger proportion of the former pro- 
 duct is dissipated by evaporation ; 
 but the glycocine may be detected 
 by adding to the liquid a drop or so 
 of aqueous sulphate of copper and an excess of potash, whereby a 
 deep blue-coloured solution is produced, unaffected by ebullition. 
 
 (159.) COLOURING AND EXTRACTIVE MATTERS. 
 
 a. Purpurine, &c. When healthy urine is boiled in a test- 
 tube with about one-fourth its bulk of hydrochloric acid, a deep 
 brownish-purple colour is produced, due to the metamorphosis of 
 a peculiar highly carbonised pink colouring matter, known as 
 purpurine. The common pink deposits of alkaline urates owe 
 their colour to this purpurine, which has a great tendency to 
 become precipitated with them. Hence, when perfectly white 
 urate of ammonia, boa's excrement, for instance, is boiled in 
 urine containing much purpurine, it is deposited on cooling of 
 a pink colour, from its carrying down some purpurine with it. 
 When these coloured deposits, natural or artificial, are boiled in 
 alcohol, the purpurine is dissolved, forming a pinkish-red solution. 
 The relation in which purpurine stands to the yellow colouring 
 matter of urine is not satisfactorily established. 
 
 /3. Extractives. The remaining organic urinary constituents 
 are called by this name. They generally amount to about one 
 per cent, of the urine. Included among them is some principle 
 containing sulphur in an un oxidised form, also kreatine and 
 
 o 
 
194 NORMAL URINE. 
 
 kreatinine, substances derived from the oxidation of muscle, and 
 found more largely in the juice of flesh. Schunck has noticed 
 in urine the habitat presence of a substance, allied to indican, 
 decomposible by an absorption of water into grape sugar and 
 indigo-blue. 
 
 (160.) MINERAL SALTS. 
 
 a. Ash of urine. This may be examined according to the 
 directions previously given for the analysis of animal ashes 
 (par. 144). It will be usually found to contain calcium, mag- 
 nesium, sodium, and a small quantity of potassium, in the form 
 of carbonates, sulphates, phosphates, and chlorides. The residue 
 left after the ash has been acted upon by acid, consists principally 
 of carbon. When this residue is ignited for some time, a 
 minute white ash remains, which is said to contain silica and 
 fluorine. 
 
 /3. Most of the inorganic constituents of urine may be de- 
 tected in the secretion itself after simple filtration. On the 
 addition of ammonia a white precipitate is produced, which, 
 when examined microscopically, is seen to consist of amor- 
 phous granules of phosphate of calcium and characteris- 
 tic stellate feathery crystals of ammonio - phosphate of 
 magnesium. If healthy urine, especially that passed after a 
 -p. 8 night's rest, be evaporated very gra- 
 
 dually upon a glass slide, minute 
 octahedral crystals of chloride of 
 sodium may be detected by mi- 
 croscopic examination. Generally 
 speaking, however, the common salt 
 is seen in the form of very complex 
 right-angled crosslets (stauroid crys- 
 tals), arranged somewhat like che- 
 vaux de frise. On the axes and 
 extremities of these forms, octahe- 
 drons may occasionally be recog- 
 nised by a good defining glass. Fig. 58 shows one of the 
 many appearances presented by carefully evaporated urine. 
 
ABNORMAL URINE. 195 
 
 Sulphuric and hydrochloric acids may be detected in urine by 
 the usual testa. 
 
 in. AENOEMAL UEINE.. 
 
 The abnormal constituents of urine which do not necessarily 
 give rise to deposits, are albumen, sugar, biliary matters, and fat. 
 
 (161.) ALBUMINOUS URINE. 
 
 a. Appearance, &c. The general appearances of albuminous 
 urine vary considerably. Sometimes it presents nothing un- 
 usual in its aspect; often the flocculent deposit formed by 
 repose is larger in amount than that of the healthy secretion ; 
 occasionally the urine has a faintly opalescent appearance, 
 not removable by nitration ; and very frequently it" is met 
 with, black, brown, or red, from the presence of altered blood, 
 with or without the occurrence of a deposit of blood globules. 
 Albuminous urine when shaken retains the froth for a long time ; 
 its specific gravity is very variable. 
 
 (3, Testbyboiling. Some of the suspected urine is boiled 
 in a test-tube, when should albumen be present, a turbidity will 
 be produced, the amount of which may vary from a faint cloud 
 to a bulky precipitate rendering the urine nearly solid. Impedi- 
 ments. a. Albumen when dissolved in alkaline nuid& is not 
 necessarily deposited upon boiling, the formation or non-forma- 
 tion of a precipitate having reference to the relative quantities of 
 albumen and alkali respectively present. Therefore, in testing an 
 alkaline urine for albumen, the liquid should first be rendered very 
 faintly acid with acetic acid. b. A previously opaque condition 
 of the urine interferes with the action of this test. This inter- 
 ference may be lessened, if not removed, by filtering the urine 
 before applying heat thereto. In urine containing deposits, the 
 clear liquid can generally be poured off and tested separately. 
 But deposits of urates do not impede the action of this test, as, 
 upon heating the urine, their dissolution takes place before 
 the precipitation of any albumen, c. Albuminous urine, to 
 
196 ABNORMAL URINE. 
 
 which a very minute quantity of nitric acid has been added, 
 is not rendered turbid by heat. Fallacy. Upon boiling certain 
 varieties of urine, a precipitate of the earthy phosphates occa- 
 sionally takes place, which can, however, be distinguished from 
 that of albumen by the addition of a little dilute nitric acid, 
 whereby the former is dissolved, the latter unaffected. 
 
 y. Nitric acid test. On adding nitric acid to albuminous 
 urine, a white turbidity is produced, varying in amount with the 
 proportion of albumen present. Impediments. a. The reagent 
 should be added drop by drop, since a minute quantity does not 
 cause any precipitate, and a great excess dissolves any precipitate 
 which may have formed, b. When the urine is opaque, it should 
 be rendered slightly alkaline with potash, agitated, filtered, and 
 then tested with nitric acid. Fallacies. a. In some varieties of 
 urine the addition of nitric acid produces a precipitate of uric 
 acidj which, however, speedily shrinks very much in bulk, and, 
 when .examined microscopically, is seen to be crystalline, whereas 
 the deposit of albumen is amorphous, b. Nitric acid produces a 
 whitish turbidity in the urine of patients who have been taking 
 copaiva, cubebs, and probably other oleo- and resinous medicines. 
 But while the precipitate of albumen subsides to the bottom of 
 the test-tube in the course of a few hours, the precipitate of oleo- 
 resinous matters remains suspended in the urine for two or three 
 days. Moreover, inquiry can always be made on these points. 
 
 8. Ferrocyanide of potassium test. Solution of ferro- 
 cyanide of potassium added to albuminous urine previously 
 acidulated with acetic acid, throws down a white precipitate. 
 Impediment.- The mere addition of acetic acid to urine occa- 
 sionally produces a precipitation of mucus, in which case the 
 acidulated urine must be filtered before being tested with the 
 ferrocyanide, 
 
 '(162.) SACCHARINE URINE. 
 
 a. Appearance, &c. Saccharine urine cannot be distin- 
 guished by the eye from the normal secretion. It has generally 
 a high specific gravity, a rather fragrant odour, and when agitated 
 
SACCHARINE URINE. 197 
 
 retains its froth for some time. It is said to have a distinctly sweet 
 taste. Minute traces of sugar exist habitually in normal urine. 
 
 /3. Potash test. To the suspected urine, an equal bulk of 
 the ordinary solution of caustic potash is added, and the whole 
 boiled ; whereon a deep orange-brown, frequently almost black, 
 colour is produced if sugar be present in abnormal quantity. 
 Fallacies. Should a deep brown colour be produced, the test 
 is free from fallacy ; but there are many specimens of non-sac- 
 charine urine which, when bailed with caustic potash, acquire a 
 tolerably dark sherry colour. Moreover, caustic potash fre- 
 quently contains lead, and this impure reagent, acting upon the 
 sulphur of ordinary urine, or more decidedly in albuminous 
 specimens, will occasion a brown discoloration. The potash 
 should, therefore, be first tested for lead. 
 
 y. Copper test. The urine is mixed with about half its 
 bulk of caustic potash solution, whereby a precipitate of earthy 
 phosphates is produced, which, in questionable cases f should be 
 separated by filtration. To the alkaline liquid, filtered or un- 
 filtered, a drop or two of a dilute solution of sulphate of copper 
 is added, when, if sugar be present, the greenish-blue precipitate 
 first thrown down will disappear upon agitation, forming a deep 
 blue-coloured liquid. On heating this liquid, and even before 
 it arrives at the boiling point, a red or orange-coloured preci- 
 pitate will be formed, characteristic of sugar. Fallacies 
 
 Although the precipitate produced by the addition of sulphate of 
 copper to a mixture of normal urine and caustic potash does not 
 disappear upon agitation, still the disappearance of the precipitate 
 with formation of a blue liquid is no proof of the presence of 
 sugar. Moreover, the application of heat should not be continued 
 after the blue liquid has acquired a boiling temperature, as many 
 substances by prolonged ebullition effect a deposition of the red 
 suboxide of copper. 
 
 ft. Modified copper test. Instead of taking separate so- 
 lutions of sulphate of copper and potash, a ready-made alkaline 
 solution of tartrate of copper may be added to the suspected 
 
ABNORMAL URINE. 
 
 Fig. 59- 
 
 urine, and the whole heated to the boiling point, when the pro- 
 duction of an orange precipitate of suboxide of copper will show 
 the presence of sugar. The test solution is made 'by dissolving 
 about 20 grains of sulphate of copper and 40 grains of neutral 
 tartrate of potassium in an ounce of the officinal solution of potash, 
 whereby a clear deep blue liquid should be produced, which may 
 be filtered if necessary. 
 
 t. Tin test. The reductions of salts of tin, bismuth, silver, 
 and chromic acid by grape sugar at a moderate heat, have been 
 made the bases of separate tests. The tin test is best performed 
 T^y having ready-prepared strips of merino or other woollen (not 
 cotton or linen) tissue dipped in solution of dichloride of tin and 
 then dried in a water-bath. On moistening one of these strips 
 with diabetic urine, and holding it near 
 the fire, or otherwise heating it to a 
 temperature of about 300 F., a brown- 
 ish-black coloration quickly makes its 
 appearance. This is a convenient cli- 
 nical test, and one of great delicacy. 
 
 . Fermentation test. Ordinary 
 yeast, or the dried "German yeast, is 
 mixed with water, and a long test-tube 
 completely filled with the suspected 
 urine, to which a little of the yeast 
 liquid has been added. The tube is 
 then closed with the thumb, and in- 
 verted in a saucer containing a little 
 of the urine under examination, so 
 that no air may enter the tube ; and 
 the whole set aside in a tolerably warm 
 situation. The temperature ought not 
 to be below 70 Fahrenheit. Should 
 the urine be saccharine, minute air-bubbles will speedily make 
 their appearance, and in the course of an hour or so a very 
 definite quantity of gas will occupy the upper part of the tube, 
 
BILIARY AND FATTY URINE. 
 
 I 99 
 
 Fig. 60. 
 
 as shown in fig. 59 ; but other forms of apparatus may be em- 
 ployed. The sporules and thallus of the sugar fungus, or yeast 
 plant, are said to be recognisable in stale saccharine urine. 
 
 (163.) BILIARY URINE. 
 
 a. Appearance, &c. Biliary urine has a yellowish-brown 
 colour, and a persistent bitter taste. It is doubtful whether the 
 urine as voided ever contains more than a trace of the true biliary 
 salts, for the detection of which substances only is 
 Pettenkofer's test adapted (vide par. 178); but 
 Heller's test, and the nitric acid test, react upon the 
 colouring matter of bile, which not unfrequently 
 finds its way into the urine. 
 
 /3. Nitric acid test. A little of the urine, 
 previously concentrated if necessary, is poured on to 
 a white plate, so as to form a thin layer, upon which 
 a few drops of strong nitric acid are then let fall. 
 Where the acid comes into contact with the biliary 
 urine, a peculiar play of colours is produced green, 
 pink, violet, and yellow, being readily recognisable. 
 Or a mixture of the urine with dilute nitric acid may 
 be carefully poured on to some strong sulphuric acid, 
 when the characteristic colouration will take place 
 at the junction of the two liquids, as seen in fig. 60. 
 
 y. Heller's test. For the application of this test the urine 
 is required to contain albumen ; hence it must be mixed, if 
 necessary, with a little diluted white of egg, serum of blood, or 
 some other urine containing albumen. Nitric acid is then added, 
 when, if bile be present, tlie precipitate will have a faintly 
 bluish or greenish colour ; but the test is not very satisfactory. 
 
 (164.) FATTY URINE. 
 
 a. Fat globules, &c. The conditions in which fat occurs in 
 the urine have not been ascertained with any degree of precision. 
 
2OO URINARY DEPOSITS. 
 
 Occasionally, when examining the ordinary flocculent deposit of 
 urine by means of the microscope, isolated fat globules may be 
 recognised. Fat occurring only in this state is believed by some 
 observers to be necessarily of extraneous origin. In some forms 
 of Bright's disease the fibrinous casts of tubes and the epithe- 
 lial cells, particularly those derived from the kidney, are seen 
 loaded with fat, and at the same time isolated fat globules may be 
 detected. 
 
 /3. Chylous urine. Occasionally this curious variety of 
 urine is met with : the secretion is more or less opaque, always 
 contains albumen, frequently gelatinises on cooling, and, when 
 examined microscopically, displays an abundance of minutely 
 divided granular matter, and a few granular cells similar to those 
 found in the chyle, but no fat globules. Fat, however, may be 
 readily obtained by agitating the urine with ether, and evapo- 
 rating the ethereal solution. 
 
 y. Kie stein-urine. In the urine of pregnant women the 
 so-called kiestein may be recognised. The secretion has generally 
 an acid reaction, and by repose becomes faintly opaque. In the 
 course of two or three days a fat-like scum rises to the surface, 
 remains there for two or three days, and then sinks to the bottom 
 of the vessel, the urine becoming at the same time ammoniacal. 
 When this scum is examined microscopically, it is seen to consist 
 of crystals of triple phosphate, with a few fat globules, imbedded 
 in a dense granular matter, which appears to be of an albuminous 
 character, containing, however, minutely divided fat. Kiestein 
 urine, by keeping, frequently evolves a powerful odour of putres- 
 cent cheese. Its occurrence is no longer regarded as positively 
 diagnostic of pregnancy. 
 
 IV. UEINAEY DEPOSITS. 
 
 These may be distinguished into chemical compounds either 
 crystalline or amorphous, and structural or organised compounds. 
 
URATES AND PHOSPHATES. 
 
 201 
 
 (165.) CHEMICAL DEPOSITS. 
 
 a. Urates or lithates. Every deposit which disappears 
 upon the application of heat, consists of uric acid in combination 
 with various bases. These urates are sometimes white, but 
 generally more or less coloured with purpurine, which may be 
 partially extracted from them by means of boiling alcohol. They 
 form a bulky deposit, nearly always amorphous, occasionally 
 appearing in the form of minute spheres with protruding spicula. 
 Urate sediments dissolve readily on the addition of caustic 
 potash, the solution when boiled giving off ammonia. Moreover, 
 they yield a residue of murexide, when treated with strong nitric 
 acid, evaporated to dryness, and held over the vapour of am- 
 monia. The urine in which these deposits occur has generally 
 an acid reaction. 
 
 /3. Earthy phosphates. Nearly every deposit which dis- 
 appears upon the addition of hydrochloric acid consists of earthy 
 phosphates. These salts form a bulky opaque white deposit, 
 which, unless associated with mucus, is easily diffusible upon 
 agitation. The urine itself is mostly alkaline, or neutral, or 
 but very faintly acid. Deposited 
 phosphate of calcium is usually 
 amorphous, save in acid urine, 
 where it sometimes occurs in pe- 
 culiar radiated or penniform crys- 
 tals. The ammonio-phosphate of 
 magnesium crystallises in variously 
 modified triangular prisms, often 
 simulating irregular six-sided plates, 
 as shown in fig, 61 ; and in very 
 ammoniacal urine is met with in the 
 form of stellate feathery crystals. 
 In some cases this deposit is seen as an iridescent pellicle, and 
 occasionally it remains for a long time suspended in the urine. 
 
 y. Uric acid. Every obviously crystalline deposit, having a 
 
 Fig. 61. 
 
202 
 
 URINARY DEPOSITS. 
 
 Fig. 62. 
 
 distinctly yellow or red colour, consists of uric acid. The colour, 
 specific gravity, and acidity of urine yielding uric acid sediments 
 are generally rather- above than below the average. The deposit 
 is compact in its appearance, and subsides quickly after agitation. 
 It is readily soluble in potash, from which solution it is repre- 
 cipitated on the addition of hydrochloric acid. When treated 
 with strong nitric acid, evaporated to dryness, and held over the 
 vapour of ammonia, it yields murexide. Uric acid deposits are 
 very rarely indeed devoid of colour. They are met with in 
 variously modified crystalline forms (vide par. 147). 
 
 jb. Oxalate of calcium. This salt seldom if ever forms a 
 distinct sediment. It may be detected by allowing the urine to 
 stand at rest for some time, and then pouring away all but the 
 
 last portions, which must be ex- 
 amined microscopically. It occurs in 
 well-marked octahedrons, the crys- 
 tals generally appearing to have a 
 square outline, and their opposite 
 angles being connected by markings, 
 as shown in fig. 62. The sediment 
 may be rendered apparent to the 
 naked eye, by warming the residue 
 of urine, left after pouring away the 
 greater portion, giving it a rotatory 
 motion, and allowing it to stand for 
 
 a few minutes. Then on pouring off the remainder of the urine, 
 and replacing it by water, a white glistening deposit becomes 
 visible. The deposit of oxalate of calcium is scarcely at all 
 affected by cold potash. It dissolves without effervescence in dilute 
 hydrochloric acid, forming a solution which effervesces on the 
 addition of a little peroxide of manganese. There are occasion- 
 ally found associated with octahedrons of oxalate of calcium, 
 certain dumbbell-shaped crystals, said to consist of oxalurate of 
 calcium. They are insoluble in potash, soluble in hot hydro- 
 chloric acid, and when incinerated leave a residue of carbonate of 
 
ORGANISED DEPOSITS. 
 
 203 
 
 FIG. 63. 
 
 calcium. Deposits of uric acid and phosphates have been occa- 
 sionally met with in the dumb-bell form. 
 
 e. Cystine. This deposit occurs somewhat rarely, in the 
 form of a bulky, easily diffusible deposit, resembling in its appear- 
 ance the white or pale lithates. When examined microscopically 
 it is seen to consist of rosette-like plates, in which a hexagonal 
 outline may sometimes be recognised. After pouring off the 
 supernatant urine, the sediment will be found to be insoluble in 
 acetic acid, soluble in hydrochloric acid, and very soluble in 
 ammonia. When the ammoniacal 
 solution is allowed to evaporate 
 spontaneously on a slide, very well- 
 defined, transparent hexagonal 
 plates crystallise out, as shown in 
 fig. 63. Cystine is remarkable for 
 containing twenty- six per cent, of 
 sulphur, so that when cystic urine 
 is boiled with a solution of acetate 
 of lead to which potash has been 
 added in sufficient excess to dis- 
 solve the precipitate at first thrown 
 down, the whole becomes nearly black, from the formation of 
 sulphide of lead. Cystic urine has when recent an aromatic, 
 when decomposing a very fetid odour. The formula of cystine 
 is C 3 H 7 NSO a . 
 
 (166.) ORGANISED DEPOSITS. 
 
 a. Normal sediment A flocculent deposit, varying 
 slightly in quantity and appearance, always separates from urine 
 by repose. When examined microscopically it may show, in 
 addition to the usual mucus-corpuscles and epithelium- cells, 
 torulas characteristic of saccharine urine, casts of uriniferous tubes 
 indicative of Bright's disease, fat globules, whether free or con- 
 tained in a cell wall, vibriones, spermatozoa, blood globules, 
 exudation globules, minute crystals of oxalate of calcium, and 
 occasionally of uric acid, &c. &c. 
 
204 
 
 URINARY DEPOSITS. 
 
 Fig. 64. 
 
 (3. Pus. This substance presents a different appearance 
 accordingly as it occurs in acid or alkaline urine. In acid 
 urine, purulent deposits sink to the bottom of the vessel, and 
 form a greenish-yellow opaque layer, having a creamy con- 
 sistency, an easy diffusibility on agitation, and a slow subsidency 
 on repose, gelatinising when agitated with an equal bulk of 
 caustic potash, and in fact presenting all the ordinary qualities, 
 physical and microscopical, of pus. In alkaline urine the deposit 
 is viscid, tenacious, ropy, not diffusible on agitation, and is 
 mixed up with the earthy phosphates, which may, however, be 
 separated by the action of dilute hydrochloric acid. Purulent 
 urine is necessarily albuminous. When a deposit of pus has been 
 
 agitated with ether, the resulting 
 ethereal solution, upon being poured 
 off and evaporated, leaves a consi- 
 derable residue of oily globules. 
 
 The pus corpuscles, which, how- 
 ever, can scarcely be said to exist 
 after the action of an alkali, consist 
 of circular granulated cells, some- 
 what larger than blood globules, as 
 shown in fig. 64. When acted on 
 by acetic acid, they swell up very 
 considerably, their margins become 
 distinct, and two, three, or four small granular masses appear in 
 their centres. 
 
 y. Mucus. A little mucus is always met with, even in 
 normal urine. It may be much increased in quantity without 
 being appreciably altered in character; but oftener it occurs 
 in the form of gelatinous masses, which sink to the bottom of the 
 vessel, or, from the entanglement of air-bubbles, remain for a 
 long time suspended in the urine. 
 
 Mucus deposits have a more or less marked alkaline reaction, 
 even when the supernatant urine is acid : they do not diffuse 
 readily by agitation, and are frequently associated with a very 
 
CLINICAL EXAMINATION OF CHINE. 205 
 
 considerable sediment of the earthy phosphates. The presence of 
 even a large amount of mucus does not of itself render the urine 
 albuminous. The microscopical characters of the mucus corpuscle 
 are very similar to those of the pus corpuscle, but the granular 
 character is perhaps not quite so well marked. 
 
 5. Blood. Urine containing blood is necessarily albuminous. 
 On allowing the urine to stand, and examining the sediment 
 microscopically, blood globules may be recognised by their 
 uniform size, non-granular surface, and yellow colour. The ap- 
 pearance of urine containing blood is very variable : its colour 
 may be light-red, dark-red, reddish-brown, smoke-brown or 
 scarcely altered. The sediment also varies much in its appear- 
 ance : sometimes its nature is evident to the unassisted eye, at 
 other times it occurs but in very minute quantities, and can only 
 be identified microscopically. Urine may contain altered colour- 
 ing matter of blood, and yet the blood-corpuscles escape recog- 
 nition. 
 
 V. CLINICAL EXAMINATION OF UEINE. 
 (167.) GENERAL EXAMINATION. 
 
 a. Appearance, &c. It is advisable to notice the colour, 
 whether pale from a dilute urine, or dark from a concentrated 
 urine, or reddish yellow from purpurine, or brownish yellow 
 from bile, or red or brown from blood the taste, whether sweet 
 from sugar, or bitter from bile the smell, whether fragrant from 
 cystine or from sugar, or foetid from alkalinity, with or without 
 mucus, or from cystine any opalescence or milkiness due to fat, 
 kiestein, mucus, or a modification of albumen, &c. 
 
 /3. Specific gravity. The specific gravity should be taken 
 by means of a gravimeter (fig. 65.) It may be too low, from an 
 accidentally diluted urine, or from Diabetes insipidus, or from 
 certain forms of Morbus Brightii, &c. ; too high, from a concen- 
 
206 
 
 CLINICAL EXAMINATION OF URINlT. 
 
 trated urine or from the presence of sugar, <fec. Dr. Golding 
 Bird pointed out the very curious coincidence, that the last two 
 Fig. 65. figures, expressing the specific gravity, represent very 
 nearly the number of grains of solid matter con- 
 tained in an ounce of the secretion : thus in urine 
 of the specific gravity 10.17, every fluid ounce con- 
 tains about 1 7 grains of solid matter. This, however, 
 must be regarded as but a very rough approxi- 
 mation to the truth, trifling variations in the amount 
 of the saline constituents of urine effecting greater 
 alterations of density than considerable variations in 
 its organic constituents. 
 
 y. Quantity. In order to determine the quantity 
 of urine passed in twenty-four hours, the patient 
 should be caused to make water at some definite 
 hour in the day, say 10 A.M., the amount then 
 voided being neglected. After this he should save 
 all the urine he passes until 10 o'clock on the next 
 day, at which time he must again empty his bladder, 
 and add the contents to the specimen to be measured. 
 He should moreover be desired always to mictu- 
 rate before going to the closet. By multiplying 
 the number of ounces passed, by the last two figures 
 of the specific gravity, an approximation will be 
 arrived at as to the total amount of solids excreted 
 by the kidneys in twenty -four hours. 
 
 (168.) CHEMICAL EXAMINATION. 
 
 a. Reaction to test-paper. Normal urine has a slightly 
 acid reaction. If alkaline, it will restore the blue colour of 
 reddened litmus- paper. Should the blue colour remain after the 
 paper has become dry, the alkalinity is due to the presence of a 
 
URINARY CALCULI. 2OJ 
 
 fixed alkaline salt ; but should the red colour reappear on drying 
 the paper, the alkalinity is due to ammonia. 
 
 /3. Testing the urine. The supernatant urine is to be 
 poured away from any deposit which may have formed, and be 
 examined for albumen, sugar, purpurine, and if necessary fat and 
 bile. Should the urine have a high specific gravity and be free 
 from sugar, it may be examined for an excess of urea by pouring 
 a little of the secretion into a watch-glass, and adding about two- 
 thirds its bulk of cold concentrated nitric acid. The formation 
 of a crystalline deposit of nitrate of urea is, with certain restric- 
 tions, indicative of an excess of that base. It is, perhaps, 
 generally advisable to concentrate the urine slightly, before 
 adding the acid. 
 
 y. Testing the deposit. The appearance of the deposit 
 generally indicates the order in which the tests, both micro- 
 scopical and chemical, should be applied. The lithates are dis- 
 solved by heat, dissolved by potash, undissolved by hydrochloric 
 acid; the phosphates are undissolved by heat, undissolved by 
 potash, dissolved by hydrochloric acid ; uric acid is undissolved 
 by heat, dissolved by potash, undissolved by hydrochloric acid ; 
 cystine is undissolved by heat, dissolved by ammonia or potash, 
 and dissolved by hydrochloric acid ; oxalate of calcium is un- 
 dissolved by heat, undissolved by potash, dissolved by hydro- 
 chloric acid. In mixed deposits the different ingredients are 
 readily recognised by their different microscopical appearances, 
 and by their different behaviour with the above reagents. 
 
 VI. URINARY CALCULI. 
 (169.) GENERAL CHARACTERS. 
 
 a. Construction, &c. Urinary calculi are for the most 
 part built up of concentric layers. This structural arrangement 
 is readily seen on making a section of a calculus through its 
 
208 
 
 URINARY CALCULI. 
 
 centre. All the layers of a calculus may have the same composi- 
 tion, or may differ very much from one another in this respect. 
 One single uniform layer of a calculus may be, and generally is, 
 composed of several ingredients. The internal arrangement of a 
 
 mixed mulberry and fusible calculus, 
 belonging to the museum of St. Bar- 
 tholomew's Hospital, is shown in 
 fig. 66 (No. 79 in catalogue). 
 
 It is probable, that if a very exact 
 analysis were made, each of the 
 layers of nearly every calculus would 
 be found to contain uric acid, alka- 
 line urates, phosphate of calcium, 
 and ammonio-phosphate of mag- 
 nesium, with or without the other 
 constituents of calculi. Moreover, 
 most calculi contain traces of all 
 
 the salts naturally existing in the urine, as well as of colouring 
 matter, mucus, &c. 
 
 From these considerations it is obvious that the chemical 
 examination of a calculus need have reference only to its general 
 composition, and not to its exact analysis. It is important, how- 
 ever, to bear in mind, that even a homogeneous layer of a calculus 
 rarely ever consists of one constituent only. 
 
 (3. Appearance, &c. The general appearances, &c., of the 
 different varieties of calculi are as follows: a. Uric calculi 
 consist of uric acid, with or without variable proportions of the 
 alkaline urates. They have usually an uniform outline, a compact 
 laminated structure, and an orange or yellow colour : sometimes 
 the laminated appearance is wanting, and sometimes they have a 
 light fawn colour, resembling the paler varieties of oxalate of 
 lime concretions. A greater or less amount of uric acid is found 
 in the centres of most calculi. 
 
 b. Earthy phosphates consist of phosphates of calcium and 
 ammonio-phosphate of magnesium. It rarely if ever happens that. 
 
THEIR VARIETIES. 20Q 
 
 where one of these constituents is present the other is wholly 
 absent. When the two exist in about equal quantities, the con- 
 cretion is known by the name of the fusible calculus, in consequence 
 of the readiness with which it fuses in the blowpipe flame. But 
 when either constituent is present in great excess, this fusion 
 cannot be effected. The distinctly laminated character appears 
 to be more frequently wanting in the fusible than in most other 
 varieties of calculi. Phosphatic calculi differ much in their 
 appearance ; they have usually a smooth uniform surface, and a 
 pale, white, or even chalk-like aspect. Sometimes they are 
 compact and hard, at other times light and friable ; sometimes 
 the layers adhere very closely to one another, and at other times 
 are just as easily separable. The earthy phosphates may con- 
 stitute the greater part of a calculus, or may be disseminated 
 through the other constituents, or may form distinct layers : they 
 give a more or less thick external coating to most calculi. 
 
 c. Oxalate of calcium calculi are generally recognised by 
 their dark colour, hard compact laminated structure, and irregular 
 surface. The term mulberry calculus does not give any idea of 
 the degree of this irregularity. But some small oxalate of cal- 
 cium calculi, known as hemp-seed concretions, have a smooth 
 contour. Occasionally, oxalate of calcium concretions, especially 
 when forming layers in other calculi, or when mixed with uric 
 or phosphatic deposits, have a pale colour, and very finely lami- 
 nated structure. The central portions of oxalate of calcium calculi 
 generally contain more or less uric acid. 
 
 d. Cystine calculi are of comparatively rare occurrence. 
 They have an irregular or oval shape, a rough and crystalline- 
 looking surface, a fawn-brown colour when recent, and a sea- 
 green colour when long kept. Cystine rarely ever enters into the 
 constitution of composite calculi. 
 
 y. Action ofheat. Some of the ingredients of calculi are 
 destructible by heat, some indestructible, as seen in the following 
 table : 
 
210 URINARY CALCULI. 
 
 URIC ACID. 
 
 URATE OF AMMONIUM. 
 
 CYSTINE. 
 
 OXALIC ACID, from oxalate of calcium. 
 
 AMMONIA, from triple phosphate. 
 
 URIC ACID, from urates of calcium and sodium. 
 
 T PHOSPHATE OF CALCIUM. 
 CARBONATE OF CALCIUM. 
 
 PHOSPHATE OF MAGNESIUM, from triple phosphate. 
 
 CARBONATE OF SODIUM, from urate of sodium. 
 
 CARBONATE OF CALCIUM, from oxalate and urate of calcium 
 
 If the heat be sufficiently prolonged and intense, the carbonate 
 of calcium will become converted into caustic lime. Carbonate of 
 calcium is not an unfrequent constituent of calculi which have 
 undergone partial decomposition in the bladder. 
 
 (170.) PRELIMINARY EXAMINATION. 
 
 a. Pulverisation, &c. The calculus to be examined 
 should be sawn through its centre, so as to expose its internal 
 arrangement. Should it consist of layers obviously differing from 
 one another each of them must be separately examined. For 
 this purpose, a sufficient quantity of each layer may be consecu- 
 tively removed by means of a pocket-knife. The determination 
 of the nature of any one layer should be ascertained before re- 
 moving a specimen of the next one. In friable calculi, great care 
 must be exercised in obtaining specimens of the different layers. 
 The smooth appearance of the flat surface can be readily restored 
 by grinding, so that a calculus may be analysed without any 
 necessary disfigurement. The specimen removed from each layer 
 is to be reduced to a fine powder. 
 
 /3. Ignition. A little of the powder is to be heated upon 
 platinum foil, and careful attention paid to any of the following 
 results, &c. 
 
PKELIMINART EXAMINATIONS. 211 
 
 Charring. All urinary calculi undergo a slight amount of 
 charring. In oxalate of calcium calculi this is very slight, and 
 speedily disappears, leaving a bulky white pulverulent residue. 
 In phosphatic calculi the charring is more complete, and the 
 carbon not so easily burnt off. 
 
 Decrepitation. This is always very slight: when occurring 
 simultaneously with the formation of a white smoke and a great 
 degree of mobility in the heated powder, it is indicative of urate 
 of ammonium. 
 
 Odour. Oxalate of calcium calculi do not evolve much odour 
 when heated : most others do. The odour produced by the igni- 
 tion of cystine is well marked and characteristic. 
 
 Volatilisation. Should the calculus powder burn away almost 
 entirely, it will suffice to test for uric acid, urate of ammonium, 
 and cystine. 
 
 Fusion. The heat of a spirit-lamp is sometimes sufficient to 
 fuse the mixed earthy phosphates. 
 
 Alkalinity. When only the heat of a lamp has been employed, 
 any alkalinity to test paper, shown by the moistened residue, is 
 probably due to carbonate of sodium, derived from the ignition of 
 urate of sodium. 
 
 Effervescence. The moistened residue is treated with a drop or 
 two of nitric acid. Effervescence denotes the presence of a car- 
 bonate, whether orginally existing as such, or derived from the 
 ignition of oxalate of calcium or of the fixed alkaline urates ; 
 in which latter case the amount of effervescence is usually very 
 small. 
 
 Blowpipe. Should the ordinary flame have proved incapable 
 of fusing the ash, the acidified residue may now be dried, and 
 strongly heated before the blowpipe ; when, if the mixed earthy 
 phosphates are present, a more or less complete fusion, or at any 
 rate cohesion of the particles, will take place. 
 
 (171.) SPECIAL TESTS. 
 In addition to noticing the above described effects of heat, it 
 
212 URINARY CALCULI. 
 
 will often suffice to make special tests for the phosphoric, oxalic, 
 and uric acids, without subjecting the calculus to a more complete 
 analysis. 
 
 a. Phosphoric acid. The residue upon the foil after its 
 ignition before the blowpipe is treated with a drop or two of 
 nitric acid and a little water, whereby its solution is usually 
 effected without appreciable effervescence, any carbonate of 
 calcium having been converted into caustic lime. A drop or 
 two of nitrate of silver solution is then added, and the mixed 
 liquid carefully neutralised with dilute ammonia, when the pro- 
 duction of a yellow precipitate will indicate the presence of phos- 
 phoric acid. Under certain circumstances, especially when triple 
 phosphate constitutes the great mass of the calculus, or when the 
 silver salt has been added in very small quantity, the precipitate 
 is white. Or the nitric acid solution of the ignited calculus may 
 be tested with molybdate of ammonium (vide par. 92 <5). Triple 
 phosphate are distinguished from bone 
 earth calculi by their solubility in acetic 
 acid. 
 
 /3. Oxalic acid. Some of the ori- 
 ginal calculus powder is mixed with a 
 drop or so of dilute sulphuric acid, and 
 a little finely divided peroxide of man- 
 ganese added, whereby any oxalic acid 
 is at once oxidised into carbonic acid, 
 which is liberated with effervescence. 
 
 7. Uric acid. A little of the 
 original calculus powder, placed in a 
 watch-glass, is treated with a drop or two of strong nitric acid 
 in which, if uric acid or a urate be present, it will dissolve 
 with effervescence. , On carefully evaporating to complete dry- 
 ness over a small flame, as shown in fig. 67, a pinkish residue 
 is left, which, when cold, is to be moistened with a drop of 
 ammonia, whereby murexide will be produced with its cha- 
 racteristic crimson colour, convertible into violet on the addition 
 
SYSTEMATIC ANALYSIS. 213 
 
 of a little caustic potash. Or the watch-glass may be held in 
 the fingers as a precaution against using too strong a heat. 
 
 (172.) SYSTEMATIC ANALYSIS. 
 
 a. Solution. Some of the powdered calculus is boiled for a 
 few minutes with a little distilled water in a test tube, the mix- 
 ture thrown upon a filter, the filtrate collected apart, and the 
 residue thoroughly washed with boiling water. The first portion 
 of the washings may be reserved for use on an emergency. The 
 filtrate A may contain urate of ammonium, urate of sodium, and 
 urate of calcium. 
 
 The washed residue is next boiled in dilute hydrochloric acid, 
 observation being made as to whether or not any effervescence 
 indicative of the presence of carbonate of calcium takes place. 
 The acid liquid is thrown on a filter, the resulting filtrate B, col- 
 lected apart, and the residue therefrom, if any, washed with 
 water. The acid solution B may contain chloride of calcium 
 from the decomposition of the carbonate, oxalate of calcium, 
 cystine, phosphate of calcium, and ammonio-phosphate of mag- 
 nesium. The residue C left upon the filter will consist of uric 
 acid. 
 
 /3. Aqueous solution. A few drops of the solution A 
 are evaporated upon a glass plate, when, should a mere trace only 
 of residue be left, the remainder of this solution may be disre- 
 garded, and the calculus considered as free from any appreciable 
 amount of alkaline urates. But should an obvious residue be 
 left, about one-fourth part of the solution may be boiled in a test 
 tube with a little caustic potash, when ammonia, if present, 
 will be given off so as to be recognisable by its odour and by its 
 reactions with test-paper and hydrochloric acid vapour, &c. The 
 remainder of the solution is reduced to a very small bulk by 
 evaporation, treated with strong nitric acid, and evaporated 
 cautiously to dryness, when the production of a pinkish residue, 
 rendered crimson when moistened with ammonia, will be indica- 
 
214 URINARY CALCULI. 
 
 tive of uric acid. The contents of the capsule are next in- 
 cinerated, the residue treated with a few drops of water, and the 
 liquid divided into two portions. One is slightly acidified with 
 acetic acid and tested with a drop of oxalate of ammonium, when 
 the production of a white turbidity will indicate the presence of 
 calcium. The other is acidified with hydrochloric acid and 
 evaporated cautiously to dryness, when the production of micro- 
 scopic cubical crystals will show the presence of s. odium. 
 
 y. Acid solution. By means of dilute ammonia, the solu- 
 tion B is made as nearly neutral as it can be, without having its 
 transparency affected. Acetate of ammonia is then added, the 
 production by which of a white precipitate will indicate the 
 presence of oxalate of calcium, or cystine. The latter body 
 rarely occurs in mixed calculi, and could be readily separated 
 from the oxalate by treatment with ammonia : on evaporating 
 the ammoniacal solution, it would be deposited in the form of 
 hexagonal tablets. To the clear liquid, if no precipitate has 
 formed, or otherwise to the filtrate therefrom, oxalate of am- 
 monium is added in excess, when the deposition of a white 
 precipitate will indicate the presence of calcium, which did not 
 previously exist in the state of an oxalate. Filtration is next 
 performed, if necessary, and an excess of ammonia added to the 
 clear liquid, when the production of a white crystalline precipitate, 
 after stirring for a little while, will prove the presence of 
 phosphoric acid and of magnesium. Should there be no 
 obvious precipitate, sulphate of magnesium is to be added, when 
 the presence of phosphoric acid will be indicated by the 
 formation, after brisk stirring, of a white crystalline precipitate. 
 
 3. Insoluble residue. The residue C is to be treated with 
 concentrated nitric acid, and the whole evaporated to dryness, 
 whereby a pink mass will be left, which held over the vapour ot 
 ammonia will become crimson, and if subsequently moistened with 
 potash will become purple, reactions characterising uric acid. 
 
BLOOD. 215 
 
 VII. BLOOD. 
 (173.) COAGULATION. 
 
 a. Blood as existing in the vessels is seen to consist of red 
 corpuscles floating in a clear liquid, termed the liquor 
 sanguinis. When removed from the living vessels it speedily 
 separates into two portions, a clear yellow liquid, the serum, 
 and a solid red mass, the clot. The liquor sanguinis consists 
 of fibrin and serum ; the clot, of fibrin and corpuscles, as seen in 
 the following diagram : 
 
 f Ll UOK SANGUINIS. | *" 
 BLOOD, i ' ~ 
 
 1 CORPUSCLES i ^,V : '>.^ 1 CLOT ' 
 
 Thus the chemical investigation of the blood naturally divides 
 itself into separate examinations of the clot and serum. 
 
 (3. The coagulation of blood is due to the solidification of 
 fibrin, which entangles in its meshes the corpuscles and a con- 
 siderable portion of the serum, so as to form a firm jelly-like 
 mass. While the blood is circulating through the vessels of living 
 animals, the fibrin exists in a state of perfect solution. The 
 circumstances which determine this state of solution are not well 
 understood ; but intimate contact with the living tissues appears 
 to be one very important condition. Out of the body the fibrin 
 speedily solidifies, the coagulation, which is accompanied by a 
 slight evolution of ammonia, being generally complete in about 
 ten minutes' time. Variations of temperature, movement, and 
 exposure to air, modify but never prevent the coagulation. 
 Where the fibrin exists in large quantity, the coagulation takes 
 place more slowly, but the coagulum is firmer and more compact. 
 When blood is removed from persons suffering from an in- 
 flammatory condition of system, or when it contains an excess of 
 fibrin, or a deficiency of corpuscles, or when it is collected in a 
 deep narrow vessel, or when its coagulation is retarded by any 
 means, the corpuscles sinking before the coagulation is complete, 
 
21 6 BLOOD. 
 
 exist principally in the lower portion of the clot, while the tipper 
 layer consists of nearly colourless fibrin. This colourless layer is 
 termed the huffy coat ; it is extremely tenacious, and frequently 
 by its slow contraction draws up the edges of the clot, so as to 
 form a cup-like depression. 
 
 (174.) FIBRIN. 
 
 a. From liquid blood. Fibrin is most easily procured 
 from this source. The blood, before it has had time to coagulate, 
 is rapidly whipped with a few twigs of wood, or well shaken in a 
 bottle with two or three irregular pieces of lead. In this way the 
 fibrin separates more or less completely from the corpuscles, and 
 adheres to the twigs or pieces of lead in the form of loose fibrous 
 masses. These are to be well washed with water, and also with 
 ether, when it is desired to remove the adherent fat. 
 
 /3. From the clot. The preparation of fibrin from 
 coagulated blood is rather more tedious. The clot should be 
 placed upon a cloth, thoroughly broken up by the hand, and 
 washed under a stream of water ; when, by alternate washing 
 and kneading, the serum and colouring matter of the clot will 
 pass through the cloth, and a residue of tolerably white fibrin be 
 left thereon. 
 
 y. Properties of fibrin. Fibrin possesses all the 
 chemical properties of coagulated albumen (vide par. 176 y). 
 When examined microscopically it is seen to differ from coagu- 
 lated albumen in manifesting an organised structure, though of 
 the lowest type, viz., the simply fibrous. This fibrillated arrange- 
 ment is best seen in the buffy layer of inflammatory blood. 
 When moist fibrin, especially that obtained from the clot, is 
 covered with water rendered faintly alkaline by soda, and left at 
 rest for some days in a tolerably warm .situation, the greater part 
 of it dissolves, and albumen may be detected in the filtered liquid 
 by the action of heat and nitric acid. Fibrin constitutes about 
 0*25 per cent, of normal blood. 
 
CORPUSCLES. 
 
 2I 7 
 
 Fig. 68. 
 
 (175.) CORPUSCLES. 
 
 a. Their appearance. When a drop of uncoagulated 
 blood, or a drop of the deep red-coloured serum squeezed out of 
 the clot, is examined under a good quarter-inch object glass 
 with a high eye-piece, the field of the microscope is seen covered 
 with minute coloured cells, of uni- 
 form size, circular outline, and non- 
 granular structure, as shown in 
 fig. 68. According to the focussing 
 the edges will appear dark and the 
 centre transparent, or vice versd. 
 Some of the globules may be seen 
 lying upon their edges, some of them 
 adhering to one another by their 
 flat surfaces, forming rouleaus. In 
 the case of the previously uncoagu- 
 lated blood, a delicate net- work of 
 fibrin will speedily appear. Blood corpuscles appear to consist 
 of a transparent membrane containing a red-coloured fluid. The 
 phenomena of osmose may be readily seen under the microscope : 
 thus if a concentrated solution of sulphate of sodium be added, 
 the corpuscles become distorted, their edges uneven, and their 
 dark centres more prominent ; if, however, water be added, the 
 corpuscles swell up, their dark centres and defined margins 
 gradually disappear, and finally the cells burst with discharge of 
 their contents. 
 
 In addition to the above- described red corpuscles, there may 
 generally be seen a few of the colourless or lymph corpuscles. 
 In healthy blood, these exist in a variable but very small propor- 
 tion compared with the red, than which they are rather larger 
 in size, and less uniform in outline. Moreover, they manifest 
 a faintly granular structure. 
 
 /3. Their separation. If blood as it is flowing be 
 received into a saturated solution of sulphate of sodium, all 
 
2l8 BLOOD, 
 
 coagulation will be prevented, and by repose the corpuscles will 
 form a bright scarlet layer at the bottom of the vessel. The 
 supernatant fluid may be poured off, and the sediment collected 
 in a filter, and washed with a solution of sulphate of sodium. Or 
 the red liquor, from which the fibrin has been removed by agita- 
 tion, may be allowed to subside ; or the clot may be broken up, 
 well shaken with the serum, and the red fluid so formed be 
 allowed to subside. From either of these fluids a gradual but 
 incomplete deposition of the corpuscles will take place. The 
 supernatant serum may then be poured away, and replaced by a 
 solution of sulphate of sodium, when the corpuscles will behave 
 as in the first instance, and may be collected upon a filter and 
 washed with sulphate of sodium as before. 
 
 y. Red colouring matter. Haematosine, or the red 
 colouring matter of blood, is remarkable for the amount of iron 
 which it contains. The ash of blood corpuscles yields fully 30 
 per cent, of peroxide of iron. The presence of iron in any of the 
 other tissues or fluids, with the exception of the chyle, appears to 
 be due to an admixture of blood. It is possible indeed to obtain 
 a modified hsematosine free from iron ; but no inference can 
 be drawn from the experiment. The chemical reactions of the 
 colouring matter may be recognised by throwing the corpuscles, 
 well washed with sulphate of sodium and drained, into a consider- 
 able excess of cold water, when the cell walls burst by endosmosis, 
 and the coloured contents of the cells dissolve in the water, form- 
 ing a deep-red solution, which by filtration may be made per- 
 fectly bright. This red colouring matter is unaffected by 
 ammonia, and is entirely destroyed by ebullition, with the for- 
 mation of a dirty-coloured coagulum, which dissolves in caustic 
 potash with an indistinct greenish colour. 
 
 3. Hsematocrystallin, or blood crystals. The forma- 
 tion of these crystals was first discovered by Dr. Otto Funke, 
 of Leipsic. It appears that by the bursting of the red cor- 
 puscles as above described an aqueous solution of their con- 
 tents is obtained, which by very slow evaporation yields crystals 
 
BLOOD STAINS. 2 19 
 
 having very definite forms. The blood of some of the lower 
 animals, particularly of the rodents, yields these crystals with 
 great facility, but their production from human blood is always 
 an uncertain operation. A drop or so of the deeply coloured 
 liquid from a portion of clot a day or two old, may be squeezed 
 on to a glass slide and diluted with less than its own bulk of 
 proof spirit. Upon covering the whole loosely with a piece of 
 microscopic glass and setting it aside in a light but not too warm 
 situation, flattened, prismatic red-coloured crystals will some- 
 times make their appearance in the course of a few hours. 
 
 (176.) BLOOD STAINS. 
 
 These occasionally form important objects of medico-legal 
 enquiry. The chemical evidence has reference to the colouring 
 matter of the blood ; the microscopical to the form of the globules, 
 and the production of hsemine crystals. Kecent blood stains 
 are of a bright red colour ; older stains of a reddish brown : 
 when on linen or other stuffs, the fibre becomes more or less 
 stiffened. 
 
 a. Reactions of colour. Supposing the stain to be on 
 some stuff, a strip of the stained portion is cut off, and suspended 
 by means of a thread in a test tube containing a little distilled 
 water. Gradually, streaks of colouring matter will be seen 
 descending from the stuff to the bottom of the tube, and there 
 forming a layer, of a deep-red if the stain be recent, or a reddish- 
 brown colour if the stain be of an older date. If necessary, 
 several of the stained strips may be thus successively treated in 
 the same portion of water, until a sufficiently dark solution is 
 obtained. Stains on knives and other articles are likewise to be 
 treated with cold water, so as to obtain a solution of the colouring 
 matter. To this red or reddish-brown solution a little dilute 
 ammonia is added, whereby the colour will be unaltered or simply 
 brightened, but not changed to a green or crimson. When the 
 solution of the colouring matter is boiled, its colour is entirely 
 destroyed, and a dirty brown precipitate produced. Every stain 
 
22O BLOOD. 
 
 forming a reddish solution with cold water, which is unaffected' 
 by dilute ammonia, but has its colour destroyed by ebullition, 
 with the formation of a precipitate, is due to blood. 
 
 /3. Form of the corpuscles. A little of the stained 
 fibre, or, if possible, a little of the dried stain scraped away from 
 the article under examination, is placed upon a glass slide and 
 moistened with a solution of sugar (syrup diluted with about 
 twice its bulk of water) or of pure glycerine reduced to the 
 sp. gr. of 1028. After some time a red coloured liquid will be 
 obtained, which may be covered with apiece of microscopic glass, 
 and examined by a good quarter-inch object-glass. Should the 
 stain be due to blood, the corpuscles, with their characteristic 
 appearances, may in this way be readily detected. In the event 
 of their appearing shrivelled, the addition of a drop or two of 
 water will cause them to expand. 
 
 y. Hsemine crystals. The dry blood stain is extracted with a 
 little glacial acetic acid, and the resulting liquid evaporated at a 
 
 very gentle heat. In the event of no 
 crystals being thus obtained, a mi- 
 nute quantity of common salt maybe 
 added to the dry residue, and the 
 moistening with glacial acetic acid 
 and gentle evaporation repeated. In 
 some cases the moistening with acid 
 has to be performed a third time, 
 before the characteristic dark- 
 coloured rhombic crystals, often ar- 
 ranged in stellate groups, as shown 
 in fig. 69, make their appearance. 
 The formation of the crystals seems to be facilitated by moistening 
 the residue with water and evaporating therewith, after each 
 evaporation with acetic acid. 
 
 (177.) SERUM. 
 
 a. General characters. The serum is a pale yellow, 
 transparent, somewhat viscid fluid, having a specific gravity of 
 
SERUM. 221 
 
 about 1030, while that of blood averages about 1055. It has a 
 faintly alkaline reaction, and consists of water holding in solution 
 albumen, fat, certain ill-defined extractive matters, and the inor- 
 ganic salts. When serum is evaporated to dryness in a water- 
 bath, its aqueous portion is driven off, and a hard, nearly 
 transparent, horny residue left behind. Water constitutes about 
 80 per cent, of normal blood. 
 
 /3. Separation of albumen. For this purpose, either 
 of the following methods may be adopted : a. The serum is put 
 into a small capsule, an equal bulk of coarsely powdered crystals 
 of sulphate of sodium added to it, and the whole boiled until 
 complete coagulation takes place, when, on filtering the boiling 
 liquid, a perfectly clear and nearly colourless solution, quite free 
 from albumen, will rapidly pass through. This method is equally 
 applicable to serum containing any amount of colouring matter, 
 and even to the broken-up clot itself, b. The serum is made 
 neutral or very faintly acid with acetic acid, boiled and filtered. 
 By this means the whole of the albumen will coagulate in flakes 
 and remain on the filtering paper, while a clear liquid, termed the 
 serosity, will pass through. The precipitate of albumen is to 
 be washed with hot water, and dried in a water-bath ; moreover, 
 a minute amount of earthy salts may be removed from it by boil- 
 ing dilute hydrochloric acid, as also a small proportion of fat by 
 boiling alcohol. 
 
 y. Properties of albumen. Albumen, as it exists in 
 the blood and other animal fluids, is in a state of solution, but is 
 capable of being coagulated by heat. The temperature at which 
 coagulation takes place varies with the alkalinity of the fluid, and 
 with the amount of albumen present. Serum of blood coagulates 
 at the temperature of about 160 Fahr. Albumen once coagulated 
 cannot again be obtained in the form of a solution coagulable by 
 heat. Normal blood contains on the average about 7 per cent, of 
 dissolved albumen. Fibrin and coagulated albumen agree in the 
 following characters : they are insoluble in water, alcohol, and 
 ether ; but are soluble in potash, from which solution they are 
 
222 BLOOb. 
 
 reprecipitated by neutralisation with an acid. If to the potash 
 solution acetic acid be freely added, the albumen will be at first 
 precipitated, but subsequently redissolved in the excess of acid. 
 Moreover, coagulated albumen and fibrin are soluble, though 
 with difficulty, in acetic acid. Albumen and fibrin dissolve in 
 boiling hydrochloric acid, forming deep purple solutions. 
 
 When albumen or fibrin is heated upon platinum foil, a minute 
 white ash, consisting principally of phosphate of calcium, remains. 
 This proportion of earthy phosphate appears to be an integral 
 constituent of the albuminous principles. If dried albumen or 
 fibrin be heated in a reduction tube, into the mouth of which there 
 have been inserted a piece of red litmus and a piece of lead 
 paper, the red litmus will become blue and the lead paper black, 
 reactions indicating respectively the presence of nitrogen and 
 sulphur. 
 
 <L Fat of blood. The condition in which fat exists in the 
 serum is not well understood. Some portion of it is precipitated 
 with the albumen, the remainder being dissolved in the serosity. 
 As a rule, serum is perfectly bright, and fat globules cannot be 
 detected in it by microscopical examination ; yet the fat being 
 soluble in ether, does not appear to be saponified. In order to 
 extract the fat, the dried residue left by the evaporation of serum 
 upon a water-bath is pulverised, and the powder agitated for 
 some time, with three or four times its bulk of ether ; the whole 
 is allowed to subside, and after some hours the ether poured off 
 and evaporated to dryness on a water-bath, when a small quantity 
 of a yellow semi-solid fat will be left. This may be treated with 
 cold alcohol, when a crystalline fat will be dissolved and an oily 
 fat be left unacted upon. 
 
 e. Extractives and salts. The serosity consists of an 
 aqueous solution of certain ill- defined organic compounds, known 
 as extractives, and of the usual alkaline salts. All the organic 
 constituents of the serum, with the exception of the albumen and 
 fat, receive the name of extractives. If the serosity be carefully 
 evaporated almost to dryness, very beautiful cubes of common salt 
 
SERUM. 223 
 
 crystallise out. Moreover, sulphuric and phosphoric acids can 
 readily be detected ; the former by the production of a white 
 precipitate with nitrate of barium and nitric acid ; the latter by 
 the addition of sulphate of magnesium, ammonia, and chloride ot 
 ammonium, when on stirring a white crystalline precipitate is 
 thrown down. If the serosity be evaporated to dryness, and 
 ignited, a white fusible ash will remain, which may be examined 
 according to the directions for the analysis of animal ashes, and 
 will be found to contain chlorine, carbonic, phosphoric, and sul- 
 phuric acids, with sodium, potassium, and traces of calcium. 
 
 . Serum containing urea. It is probable that the 
 blood always contains minute traces of urea ; while in certain 
 forms of disease, particularly in Bright's disease, its amount 
 becomes very sensible. In order to detect it, the albumen is 
 removed from the serum by either of the methods described in 
 par. /3, and the serosity evaporated carefully to dryness. If the pro- 
 cess b be adopted, and the chloride of sodium in the dried residue 
 be seen to crystallise in well-marked octahedrons instead of cubes, 
 the presence of urea is tolerably certain. In any case the dry 
 residue is warmed with a little strong alcohol and filtered, the alco- 
 holic filtrate evaporated to dryness, the residue dissolved in a very 
 small quantity of distilled water, and the aqueous solution filtered 
 and concentrated in a watch-glass. To the cold concentrated 
 liquid, an equal bulk of cold colourless nitric acid is next added, 
 when, if urea be present, a crystalline deposit of nitrate of urea 
 will be produced, which can be examined microscopically. The 
 production of a crystalline deposit on the addition of nitric acid is 
 in itself almost conclusive as to the presence of urea. 
 
 /. Serum containing bile. In jaundice, the serum 
 of the blood is of a much darker yellow colour than usual, owing 
 to the presence of biliary colouring matter, which may be identi- 
 fied by adding to the serum a little nitric acid, when the albumen 
 will be precipitated of a bluish or greenish colour : or some of the 
 serum, just neutralised with acetic acid, may be precipitated with 
 excess of alcohol, the alcoholic solution evaporated to a small bulk 
 
224 MISCELLANEOUS ANIMAL PRODUCTS. 
 
 in a water-bath, and residue examined by Pettenkofer's test, and 
 by the nitric acid test (par. 153 /3). 
 
 6. Serum containing sugar. Sugar exists abundantly 
 in the blood, in cases of diabetes. Eecent researches have more- 
 over shown that the post-mortem blood of the inferior cava, and of 
 the right side of the heart, habitually contains sugar in very defi- 
 nite amount. In order to detect it, the albumen of the blood 
 must be removed by means of sulphate of sodium, as in par. 
 177/3, and to the clear filtrate a drop or two of a solution of 
 sulphate of copper, and then an excess of caustic potash be added, 
 whereby a deep blue-coloured liquid will be produced, which, on 
 the application of heat, will deposit a red or orange-yellow coloured 
 precipitate of suboxide of copper. The alkaline solution of tar- 
 trate of copper described in par. 162 3. may be conveniently 
 substituted for the mixture of sulphate of copper and caustic 
 potash. 
 
 VIII. MISCELLANEOUS ANIMAL PKODUCTS. 
 (178.) BILE. 
 
 a. Composition. Human bile contains the sodium salt of 
 a peculiar acid known as glycocholic acid, having a similar con- 
 stitution to the glycobenzoic or hippuric acid found in urine. It 
 also contains in small quantity the sodium salt of taurocholic 
 acid. These glycocholates and taurocholates, when boiled with 
 dilute hydrochloric acid, absorb water, and break up into cholic 
 acid and glycocine and taurine respectively, thus : 
 
 Glycocholic, C 36 H 43 N0 6 + H^O = C 24 H 40 5 + C 2 H 5 NOs 
 Taurocholic, C a6 H 45 N0 3 S + H,0 = C 24 H 40 5 + C 4 H 7 N0 3 S 
 
 The bile also contains water, mucus, cholesterine, fat and 
 colouring matter, the reactions of which last have been described 
 under the head of biliary urine (par. 153). 
 
 /3. Detection of cholic acid. This is effected by 
 Pettenkofer's test, which is performed in the following manner : 
 To a little diluted bile, or any liquid containing bile, rather more 
 
BILE. 
 
 225 
 
 than half its bulk of strong sulphuric acid is added very gradu- 
 ally, the tube in which the mixture is made being kept cool by 
 immersion in water. A minute quantity of powdered white 
 sugar, or its equivalent of syrup, is then introduced, the liquid 
 well agitated and mixed with more sulphuric acid. By this 
 means the temperature is gradually raised to the requisite point, 
 when a deep purplish-crimson colour makes its appearance. Very 
 minute quantities of bile may be detected by evaporating any 
 suspected liquid with a drop of sulphuric acid and a decigrain of 
 sugar in a water-bath. 
 
 y. Biliary calculi. Concretions of variable appearance 
 are occasionally formed in the gall-bladder, sometimes in very 
 considerable numbers. When numerous, they are of about the 
 size of peas, and have an irregular angular shape, with flattened 
 sides. When solitary, they are usually of larger bulk and of an 
 oval form. They have a soapy feel, a fawn-yellow colour, and 
 are easily crushed by pressure. They consist principally of choles- 
 terine and an insoluble combination of bile pigment with lime. 
 When rich in cholesterine, they 
 float upon water. To detect cho- 
 lesterine, the powdered calculus is 
 boiled in alcohol, and the solution 
 filtered, when, on cooling, colour- 
 less transparent plates crystallise 
 out of the yellow liquid. These 
 crystals, when examined microsco- 
 pically, are seen to consist of deli- 
 cate, nearly square, rhombic plates, 
 superimposed one upon the other 
 as shown in fig. 70. Cholesterine 
 CtfH^O, is soluble in ether and hot alcohol, very slightly soluble 
 in cold alcohol, not at all soluble in water. It seems to be a 
 species of solid alcohol. 
 
 70. 
 
226 
 
 MISCELLANEOUS ANIMAL PRODUCTS. 
 
 71- 
 
 (i79-) MILK. 
 
 This secretion consists of water holding in solution casein, 
 1 a c t i n e, and salts, and holding in suspension an abundance of 
 
 fat globules, to the presence of 
 which the opaque white appearance 
 of milk is due. Normal milk has 
 an alkaline reaction to test paper. 
 The specific gravity of human milk 
 averages about 1030. 
 
 a. Fat globules. These may 
 be easily recognised under the mi- 
 croscope : they are of various sizes, 
 andhave well-defined dark margins, 
 as shown in fig. 7 1 . They appear 
 to be surrounded by delicate cell- 
 membranes, as they cannot be made to unite by pressure until 
 after the addition of a little acetic acid. The milk secreted soon 
 after delivery contains large, granular, fatty corpuscles, known as 
 colostrum corpuscles. In milk abscess &c., pus and blood globules 
 may be occasionally detected. 
 
 ft. Casein. When ordinary or skimmed milk is evaporated, 
 a scum forms on its surface, which, if removed, is soon replaced 
 by a fresh one, and so on repeatedly. This property of forming 
 a scum on evaporation was formerly considered peculiar to fluids 
 containing casein. Casein differs from the other albuminous 
 bodies in being coagulable not by heat, but by the addition of a 
 little very dilute acid, or by contact with decomposing animal 
 membrane. Cheese is casein which has been precipitated by 
 rennet, the dried decomposing lining membrane of the stomach 
 of the calf. When skimmed milk is rendered slightly acid with 
 acetic acid, and gently warmed, the casein coagulates, and may be 
 collected on a filter, washed with hot water, and subsequently 
 with hot alcohol : it manifests all the usual properties of the 
 albuminous bodies. 
 
BONE. 227 
 
 y. L a c t i n e. Sugar of milk, or lactine, may be readily 
 detected in whey which has been separated by nitration from the 
 coagulated casein. On adding a drop or two of sulphate of 
 copper, and then an excess of potash, a red precipitate of sub- 
 oxide of copper will be produced on boiling the mixture. Sugar 
 of milk may be obtained crystalline by careful evaporation of 
 the whey. It does not readily undergo the alcoholic fermenta- 
 tion ; but by the action of putrefying curd becomes rapidly con- 
 verted into lactic acid. 
 
 5. Mineral salts. The ash of milk contains the same 
 constituents as most animal ashes ; the relative proportion of 
 earthy phosphates is very large, and potassium exists in it to a 
 greater extent than sodium. 
 
 (180.) BONE. 
 
 Bone consists principally of phosphate of calcium, deposited 
 in an animal basis. When bone is soaked for some time in 
 dilute hydrochloric acid, its earthy matter is dissolved out, and a 
 flexible elastic mass, having the exact form of the original bone, 
 is left unacted upon. This residue consists of gelatine, which by 
 long boiling dissolves in water, forming a solution that gelatinises 
 on cooling. The solution is precipitated by tannic acid, but not 
 by acetic acid or by ferrocyanide of potassium. Pure gelatine does 
 not contain sulphur. By the incineration of bone, its animal 
 matter is burnt off, and a brittle, white, earthy residue, having 
 the exact form of the original bone, remains. This earthy resi- 
 due consists principally of phosphate of calcium, with a little 
 carbonate of calcium and phosphate of magnesium, also minute 
 quantities of fluoride of calcium ; which latter substance may be 
 detected more readily, however, in fossil bones. 
 
 Q 2 
 
INDEX. 
 
 ACE 
 
 ACETATES, reactions of, 135 
 Acid, arsenious, 157 
 
 cholic, 224 
 
 hippuric, 192 
 
 hydrochloric, toxicology of, 144 
 
 hydrofluosilicic, as a reagent, 85 
 
 nitric, toxicology of, 142 
 
 oxalic, 147 
 
 prussic, 173 
 
 C 88 
 
 sulphuric, as a reagent, I 
 
 toxicology of, 139 
 
 tartaric, as a reagent, 68 
 
 uric, 190 
 Acidity, criterion of, 6 
 Acids and bases, 52 
 
 anhydrous, 1 1 
 
 binary, 6 
 
 dibasic, 7, 8 
 
 monobasic, 7 
 
 reactions of, 107 
 
 solutions to be tested for, 95 
 
 table for detection of, 96 
 preliminary testing, 90 
 
 ternary, 6 
 
 tribasic, 8 
 Adapters, 37 
 
 Albumen from blood, 220 
 Albuminous urine, 195 
 
 Alkaline solutions, reactions of, no 
 Alkaloidal salts, 9 
 Aluminum, reactions of, 122 
 Ammonia, as a precipitant, 74 
 
 reagent, 79 
 
 solvent, 80 
 
 Ammonium, carbonate of, as a pre- 
 cipitant, 83 
 
 oxalate of, as a reagent, 85 
 
 ATO 
 
 Ammonium, phosphate of, as a re- 
 agent, 68 
 
 salts of, 9 
 
 sulphide of, as a precipitant, 73 
 as a solvent, 70 
 
 Analysis, course of operations in, 
 
 5* 
 
 Anhydrides, n 
 Anhydrous acids, 1 1 
 Animal matter, ashes of, 184-186 
 components of, 183 
 
 products, various, 224 
 Antimonial salts, reactions of, 169 
 Antimony in organic mixtures, 173 
 
 Marsh's test for, 171 
 
 reactions of, 113, 169 
 
 Reinsch's test for, 172 
 
 toxicology of, 169 
 
 in solution, 170 
 
 Apparatus, cleaning glass, 39 
 
 connections of, 22 
 
 supports for, 32 
 Arsenic, Marsh's test for, 161 
 
 original process, 1 62 
 
 modified process, 164 
 
 metallic ring, 158 
 
 reactions of ; 112 
 
 Reinsch's test for, 165 
 impediments to, 167 
 
 various forms of, 168 
 Arsenious acid, reactions of, 157 
 toxicology of, 157 
 
 crystals of, 157 
 
 dissolved, 159 
 
 reduction of, 159 
 
 in organic mixtures, 169 
 
 Ashes of animal matter, 184, 186 
 Atomic weights, 2 
 
2 3 
 
 INDEX. 
 
 BAR 
 
 CON 
 
 BAEIUM, chloride of, as a re- 
 agent, 98 
 
 reactions of, 1 2 3 
 Bases and acids, 52 
 
 classification of, 64. 
 
 first group of, recognised, 65 
 table of, 68 
 
 second group of, recognised, 73 
 table of, 76 
 
 third group of, recognised, 82 
 
 table of, 83 
 
 Baths, sand, 33 
 
 water, 34 
 Beads, borax, 60 
 Benzoates, reactions of, 135 
 Biliary calculi, 224 
 
 urine, 199 
 Bile, 224 
 
 from blood, 223 
 Binary acids, 6 
 Bink's burette, 45 
 Bismuth, reactions of, 113 
 
 solutions, 72 
 
 Blood, albumen from, 220 
 
 bile in, 223 
 
 coagulation of, 215 
 
 colouring matter of, 218 
 
 composition of, 215 
 
 corpuscles, 217 
 
 crystals, 218 
 
 extractives and salts of, 222 
 
 fat of, 222 
 
 fibrin from, 216 
 
 in urine, 205 
 
 serum from, 220 
 
 stains, reactions of, 219 
 
 sugar in, 224 
 
 urea in, 222 
 Blowing glass bulbs, 21 
 Blowpipe, Black's, 16 
 
 brazier's, 1 6 
 
 examination, 53 
 
 flame, colouration of, 56 
 
 flames, 17 
 
 Herapath's gas, 1 5 
 
 incrustations, 59 
 
 the use of, 17 
 Bone, 226 
 
 Borates, reaction of, 135 
 Borax beads, 60 
 Boring corks, 23 
 
 Bottle, drop, 24 
 wash, 25 
 
 Bromides, reactions of, 131 
 Bulbs, blowing, 21 
 Burette, Bink's, 45 
 Burners, charcoal, 14 
 gas, 14 
 
 CADMIUM, reactions of, 117 
 \J Calcium, chloride of, as a re- 
 agent, 198 
 
 oxalate of, urinary deposit of, 202 
 calculus, 209 
 
 reactions of, 124 
 Calculi, action of heat on, 209 
 
 analysis (systematic) of, 213 
 
 biliary, 225 
 
 construction of, 207 
 
 cystine, 209 
 
 earthy phosphate, 208 
 reactions of, 212 
 
 examination of, 210 
 
 ignition of, 210 
 
 mulberry, 208 
 
 oxalate of calcium, 209 
 reactions of, 212 
 
 pulverising, 210 
 
 solution of, 213 
 
 tests, special for, 211 
 
 uric, acid, 208 
 
 reactions of, 212 
 
 Carbonates, reactions of, 119 
 Casein, 226 
 
 Charcoal burners, 13 
 Chemical equations, 6 
 
 formulae, 5 
 
 urinary deposits, 201 
 Chlorates, reactions of, 127 
 Chlorides, formulse of, 4 
 
 reactions of, 130 
 Cholic acid, 224 
 Chromates, reactions of, 126 
 Chromium, reactions of, 122 
 Chylous urine, 200 
 Cleaning-glass apparatus, 39 
 Cobalt, nitrate of, ignitions with, 57 
 
 reactions of, 1 1 8 
 Colouring-matter of blood, 218 
 Combining proportions, I 
 Complex salts, 9 
 Condenser, Liebig's, 38 
 
INDEX. 
 
 2 3 I 
 
 CON 
 
 HTD 
 
 Connections of apparatus, 22 
 Copper, reactions of, 116, 155 
 
 solutions, 73 
 
 toxicology of, 155 
 
 dissolved, 155 
 
 in organic mixtures, 156 
 
 Corks, boring, 23 
 
 Corpuscles, blood, 217 
 
 Corrosive sublimate, reactions of, 
 
 149 
 toxicology of, 149 
 
 solid, 149 
 
 dissolved, 150 
 
 crystals of, 150 
 
 in organic mixtures, 152 
 
 Counterpoises, 46 
 Crucibles, heating, 34 
 Crystals, blood, 218 
 
 hsemine, 220 
 Cyanides, reactions of, 132 
 Cystine, 203 
 
 calculi, 209 
 
 DASH'D SYMBOLS, 5 
 Decantation, 32 
 Decimal weights, 46 
 Deposits, urinary, 200 
 
 chemical, 201 
 
 organised, 203 
 
 Desiccation, 39, 46 
 Dibasic acids, 6 
 Distillation, 37 
 Drop-bottle, 24 
 Drying apparatus, 39 
 
 precipitates, 40 
 
 T7AKTHY SALTS, reactions of, 105 
 
 JJ Ebullition, 35 
 
 Elementary bodies, I 
 
 Elements, table of, 3 
 
 Equations, chemical, 6 
 
 Equivalents, i 
 
 Evaporation, 35 
 
 FAT of blood, 222 
 Fatty urine, 199 
 Ferric salts, reactions of, 120 
 Ferrous salts, reactions of, 120 
 
 Fibrin, 216 
 Filters, double, 30 
 Filters, making, 29 
 
 plain, 30 
 
 ribbed, 29 
 Filtration, 28 
 Flame, blowpipe, 17 
 
 colouration of, 56 
 
 oxidising, 1 7 
 
 reducing, 17 
 
 Flasks, measure, 43 
 
 specific gravity, 48 
 Fluorides, reactions of, 136 
 Formulae, chemical, 5 
 
 of chlorides, 4 
 
 of hydrides, 3 
 
 of salts, rational, 10 
 Funnel tubes, 26 
 Fusible salts, 56 
 Fusions, 41 
 
 /~1 ALLON, decimal division of, 43 
 \JT Gas blowpipe, Herapath's, 15 
 
 burners, 14 
 
 evolving tubes, 27 
 
 washing tubes, 27 
 Glass bending, 19 
 
 tube and rod, cutting, 18 
 
 vessels, heating, 3 5 
 
 working, 1 8 
 Graduated measures, 44 
 
 pipettes, 44 
 Gravity, specific, 47 
 
 H^MATO-CKYSTALLINE, 218 
 Hsemine crystals, 220 
 Heat, action of, on calculi, 209 
 Heating glass vessels, 35 
 
 crucibles, 34 
 Hippuric acid, 192 
 Hydracids, 7 
 Hydrides, formulae of, 3 
 Hydrochloric acid, as a precipitant, 
 
 65 
 
 reactions of, 144 
 
 toxicology of, 144 
 
 concentrated, 144 
 
 diluted, 145 
 
 in organic mixtures, 146 
 
2 3 2 
 
 INDEX. 
 
 HYD 
 
 PLA 
 
 Hydrofluosilicic acid as a reagent, 
 
 85 
 Hydrometer, 49 
 
 TGNITIONS, 41 
 
 JL with nitrate, of cobalt, 57 
 
 Incrustations, blowpipe, 59 
 
 Infusible salts, 57 
 
 Insoluble compounds, in acids, 102 
 
 oxalates, 149 
 Iodides, reactions of, 131 
 
 Iron, perchloride of, as a reagent, TOO 
 
 reactions of, 120 
 
 "ACKET STANDS, 33 
 
 T7IESTEIN UKINE, 200 
 
 A 
 
 T ACTINE, 226 
 
 JLJ Lead solutions, 72 
 
 reactions of, 115, 133 
 
 toxicology of, 153 
 
 solid, 153 
 
 dissolved, 154 
 
 in organic mixtures, 1 54 
 
 Liebig's condenser, 38 
 
 Liquids, analysis of, 109 
 specific gravity of, 48 
 Lithates, urinary deposits of, 201 
 Lutes, 24 
 
 MAGNESIUM, reactions of, 124 
 Manganese, reactions of, 119 
 Marsh's antimony test, 171 
 
 arsenic test, 161 
 
 original process, 1 62 
 
 modified process, 1 64 
 
 Measure flasks, 44 
 Measures, graduated, 45 
 Measuring, 44. 
 
 Mercuric salts, reactions of, 115 
 Mercurous salts, reactions of, 115 
 Mercury, dichloride of, toxicology 
 of, 149 
 
 reactions of, 114 
 
 solutions, 72 
 
 Milk, 226 
 
 casein of, 226 
 
 fat globules of, 226 
 
 lactine of, 226 
 
 mineral salts of, 226 
 Molecular weights, 2 
 Monobasic acids, 7 
 Morphia in solution, 1 80 
 
 toxicology of, 179 
 Mucus from urine, 204 
 Mulberry calculus, 208 
 Multequivalent salts, 8 
 
 "VTEUTKALISATION, 74 
 JLl Nickel, reactions of, 1 1 8 
 Nitrates, reactions of, 127, 143 
 Nitric acid, toxicology of, 142 
 
 concentrated, 142 
 
 diluted, 143 
 
 in organic mixtures, 144 
 
 Notation, symbolic, 5 
 
 OPIATE LIQUIDS, 180 
 Organic constituents, ultimate, 
 
 184 
 
 Oxacids, 6 
 Oxalate of calcium, urinary deposit 
 
 of, 202 
 
 Oxalates, reactions of, 133 
 insoluble, 105, 149 
 Oxalic acid, reactions of, 147, 212 
 
 toxicology of, 147 
 
 dissolved, 147 
 
 in organic mixtures, 148 
 
 insoluble form, 149 
 
 solid, 147 
 
 Oxides, reactions of, 106 
 Oxidising blowpipe flame, 1 6 
 
 PASTILLES, 1 8 
 
 JL Phosphates, reactions of, 132 
 
 earthy, urinary deposits of, 201 
 Pipettes, delivery, 44 
 
 graduated, 45 
 
 making, 22 
 
 Platinum, perchloride of, as a re- 
 agent, 86 
 
INDEX. 
 
 233 
 
 POT 
 
 EEA 
 
 Potash, as a reagent, 71, 78 
 
 solutions, 8 1 
 
 Potassium, sulphate of, as a reagent, 
 
 84 
 
 Powders, specific gravity of, 5 1 
 Precipitant, carbonate of ammo- 
 nium as a, 83 
 
 hydrochloric acid as a, 65 
 
 sulphide of ammonium as a, 73 
 
 sulphuretted hydrogen as a, 69 
 Precipitates, aspects of, 63 
 
 drying, 40 
 
 formation of, 62 
 removal of, 32 
 
 washing, 3 1 
 Precipitation by ammonia, 74 
 
 by water, 66 
 Proportions, combining, i 
 Prussic acid, toxicology of, 173 
 Purpurine, 193 
 
 Pus from urine, 204 
 
 HEACTIONS of acetates, 135 
 
 it acids, 107 
 
 alkaline solutions, no 
 
 aluminum, 122 
 
 ammonium, 126 
 
 antimony, 113, 169 
 
 arsenic, 112, 157 
 
 barium, 123 
 
 benzoates, 135 
 
 bismuth, 113 
 
 blood stains, 219 
 
 borates, 135 
 
 bromides, 131 
 
 cadmium, 117 
 
 calcium, 124 
 
 carbonates, 128 
 
 chlorates, 127 
 
 chlorides, 130 
 
 chromates, 126 
 
 chromium, 122 
 
 cobalt, 118 
 
 compounds in solution, 109 
 
 copper, 116, 155 
 
 corrosive sublimate, 149 
 
 cyanides, 132 
 
 earthy salts, 105 
 
 ferric salts, 120 
 
 ferrous salts, 120 
 
 ^Reactions of fluorides, 106 
 
 hippuric acid, 193 
 
 hydrochloric acid, 144 
 
 iodides, 131 
 
 iron, 120 
 
 lead, 115, 153 
 
 liquid substances, 109 
 
 magnesium, 124 
 
 manganese, 119 
 
 mercuric salts, 115 
 
 mercurous salts, 115 
 
 mercury, 114 
 
 miscellaneous salts, 108 
 morphia, 179 
 
 nickel, 1 1 8 
 
 nitrates, 127, 143 
 
 nitric acid, 143 
 
 oxalates, 133 
 
 oxalic acid, 147 
 
 - calculi, 212 
 
 oxides, 1 06 
 
 phosphates, 132 
 
 phosphatic calculi, 212 
 
 potassium, 125 
 
 prussic acid, 173 
 
 silicates, 137 
 
 silver, 116 
 
 sodium, 126 
 
 stannic salts, i la 
 
 stannous salts, in 
 
 strontium, 124 
 
 strychnia, 175 
 
 sulphates, 130 
 
 sulphides, 106, 129 
 
 sulphites, 130 
 
 sulphuric acid, 139 
 
 sulphydrates, 129 
 
 tartrates, 1 34 
 
 tin, in 
 
 urea, 1 89 
 
 uric acid, 190 
 
 calculi, 212 
 
 zinc, 121 
 
 Keagent, ammonia as a, 79 
 
 chloride of barium as a, 98 
 calcium as a, 98 
 
 hydrofluosilicic acid as a, 85 
 
 nitrate of silver as a, 96 
 
 oxalate of ammonium as a, 
 
 perchL 
 
 perchloride of iron as a, 100 
 
234 
 
 INDEX. 
 
 REA 
 
 TOX 
 
 Reagent, perchloride of platinum as 
 a, 86 
 
 phosphate of ammonium as a, 68 
 
 potash as a, 71, 78 
 
 sulphate of potassium as a, 84 
 
 sulphuric acid as a, 88, 93 
 
 tartaric acid as a, 86 
 Keagents, addition of, 63 
 Reducing blowpipe flame, 17 
 Reduction tubes, 18 
 Reinsch's test for antimony, 172 
 arsenic, 165 
 
 impediments to, 1 67 
 
 Retorts, tube, 25 
 
 SACCHARINE URINE, tests for, 
 196 
 Salts, alkaloidal, 9 
 
 ammonium, 9 
 complex, 9 
 
 double decomposition of, 12 
 
 earthy, nature of, 75 
 reactions of, 105 
 
 fusible, 56 
 
 infusible, 57 
 
 mineral, of milk, 226 
 of urine, 194 
 
 miscellaneous, 108 
 
 multequivalent, 8 
 
 rational formulae of, 1 1 
 
 reducible, 58 
 
 simple, 8 
 
 volatile, 55 
 Sand-baths, 34 
 Sealed tube making, 21 
 Sealing test tubes, 20 
 Sediment from normal urine, 203 
 Serum of blood, 216 
 Silicates, reactions of, 137 
 Silver, nitrate of, as a reagent, 96 
 
 reactions of, 1 1 6 
 
 solutions, 73 
 Simple salts, 9 
 
 Solids, specific gravity of, 50 
 Solutions made, 61 
 Solvent, ammonia as a, 80 
 
 sulphide of ammonium as a, 70 
 Solvents, addition of, 63 
 Specific gravity, 47 
 
 flasks, 48 
 
 Specific gravity of liquids, 48 
 
 of powders, 5 1 
 
 of solids, 50 
 
 Stains, blood, reactions of, 219 
 Stands, jacket, 33 
 
 tripod, 3 3 
 
 Stannic salts, reactions of, 112 
 Stannous salts, reactions of, 1 1 1 
 Stirring rods, 1 8 
 Strontium, reactions of, 124 
 Strychnia, appearance of, 176 
 
 colour tests, 177 
 
 in organic mixtures, 178 
 
 toxicology of, 17.5 
 Subliming tubes, 1 8 s 
 Sugar in blood, 224 
 Sulphates, reactions of, 130 
 Sulphides, reactions of, 106, 129 
 Sulphites, reactions of, 130 
 Sulphuretted hydrogen as a precipi- 
 tant, 65 
 
 bulb, 27 
 
 Sulphuric acid, as a reagent, 93 
 
 reactions of, 139 
 
 toxicology of, 139 
 
 concentrated, 139 
 
 diluted, 140 
 
 in organic mixtures, 141 
 
 stains on clothing, 141 
 
 Sulphydrates, reactions of, 129 
 Supports for apparatus, 3 3 
 Symbolic notation, 5 
 Symbols, dash'd, 5 
 Synoptic formulae, 1 1 
 
 TABLE for detection of acids, 96 
 of bases of group one, 
 
 68 
 
 of group two, 7 6 
 of group three, 84 
 
 of blowpipe reactions, 55 
 
 of elements, 3 
 
 of preliminary testing for acids, 
 
 90 
 
 Tartrates, reactions of, 1 34 
 Ternary acids, 6 
 Test tubes, sealing, 20 
 Tin, reactions of, in 
 Tissues, composition of, 183 
 Toxicological examinations, 139 
 
INDEX. 
 
 235 
 
 TOX 
 
 Toxicology of antimony, 169 
 
 arsenious acid, 157 
 
 copper, 155 
 
 corrosive sublimate, 149 
 
 hydrochloric acid, 144 
 
 hydrocyanic acid, 173 
 
 lead, 153 
 
 mercury, 149 
 
 morphia, 179 
 
 nitrates, 143 
 
 nitric acid, 142 
 
 oxalic acid, 147 
 
 prussic acid, 173 
 
 strychnia, 175 
 
 sulphuric acid, 139 
 
 Tripod stands, 34 
 Tube retorts, 25 
 Tubes, funnel, 26 
 
 gas-evolving, 26 
 
 joined, 23 
 
 subliming, 18 
 
 reduction, 18 
 Tubing, vulcanite, 22 
 
 TTEATES, urinary deposits of, 201 
 U Urea, crystals of, 190 
 
 from blood, 222 
 
 its detection, 189 
 
 preparation of, 189 
 
 properties of, 190 
 
 Uric acid, crystalline form of, 192 
 
 its detection, 190 
 
 preparation of, 191 
 
 properties of, 191 
 
 urinary deposit of, 201 
 
 calculus, 208 
 
 Urinary calculi, 207 
 construction of, 207 
 
 deposits, 200 
 
 chemical, 201 
 
 of cystine, 203 
 
 earthy phosphates, 201 
 
 lithates, 201 
 
 oxalate of calcium, 
 
 202 
 
 urates, 201 
 
 uric acid, 201 
 
 ZIN 
 
 Urinary deposits, organised, 203 
 
 of blood, 205 
 
 mucus, 204 
 
 normal sediment, 203 
 
 pus, 204 
 
 Urine, 188 
 
 abnormal, 195 
 
 albuminous, 195 
 tests for, 195 
 
 appearance of, 205 
 
 ash of, 194 
 biliary, 199 
 
 chemical examination of, 206 
 
 chylous, 200 
 
 clinical examination of, 205 
 
 colouring-matters of, 193 
 
 crystals from evaporation of, 194 
 
 extractive matters of, 193 
 
 fatty, 199 
 
 kiestein, 200 
 
 mineral salts of, 194 
 
 normal, properties of, 188 
 
 quantity of, 206 
 
 saccharine, 196 
 tests for, 197 
 
 specific gravity of, 205 
 
 TTOLATILE SALTS, 55 
 V Volatilisations, 42 
 Vulcanite tubing, 22 
 
 WASH BOTTLE, 25 
 Washing precipitates, 3 1 
 
 tube, gas, 28 
 Water baths, 34 
 
 precipitations by, 66 
 Weighing, 46 
 Weights, atomic, 2 
 
 decimal, 47 
 
 molecular, a 
 
 r/INC, blowpipe examination of, 
 
 L 57 
 
 reactions of, 121 
 
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INDEX. 
 
 ACTON'S Modern Cookery 
 
 Afterglow (The) 
 
 ALCOCK'S Residence in Japan 
 
 ALLIES on Formation of Christendom 
 
 Alpine Guide (The) 
 
 APJOHN'S Manual of the Metalloids 
 
 ARNOLD'S Manual of English Literature.... 
 
 ARNOTT'S Elements of Physics 
 
 Arundines Cami 
 
 Autumn holidays of a Country Parson .. 
 AYRE'S Treasury of Bible Knowledge 
 
 BACON'S Essays, by WHATELY 
 
 Life and Letters, by bpEDDiNo 
 
 Works, edited by SPKDDINO 
 
 BA;N"S Mental and Moral Science 
 
 -on the Emotions and Will 
 
 on the Senses and Intellect 
 
 on the Study of Character . 
 
 BALL'S Alpine Guide 
 
 BARNARD'S Drawing from N ature 
 
 BAYLDON'S Rents and Tillages 
 
 Beaten Tracks 
 
 BECKER'S Charicles mitf Gallus 
 
 BENFEY'S Sanskrit Dictionary 
 
 BLACK'S Treatise on Brewing 
 
 BLACKLEY'S Word-Gossip 
 
 BLACKI.EY and FRIEDLANDER a German ana 
 
 English Dictionary 
 
 ELAINE'S Rural Sports 
 
 Veterinary Art 
 
 BOOTH'R Epigrams 
 
 BOURNE on Screw Propeller 
 
 BOURNE'S Catechism of the Steam Engine.. 
 
 Handbook of Steam Engine 
 
 Treatise on the Steam Engine... 
 
 Examples of Modem Engines . . 
 
 BOWDLER'S Family SHAKSPEARK 
 
 BRANDB'S Dictionary of Science, Liter ature, 
 
 and Art 
 
 BRAY'S (C.) Education of the Feelings 
 
 . Philosophy of Necessity 
 
 on Force .... 
 
 BRINTON on Food and Digestion 
 
 BRODIE'S (Sir C. B.) Works 
 
 BROWNE'S Exposition of the 39 Articles 
 
 BUCKLE'S History of Civilization 
 
 BULL'S Hints to Mothers 
 
 Maternal Management of Children. 
 
 BUNSEN'S (Baron) Ancient Egypt 
 
 God in History 
 
 Memoirs 
 
 BUNSEN (E.DE)on Apocrvpha 
 
 's Keys of St. Peter 
 
 BUR KE'S Vicissitude* of Families 
 
 BURTON'S Christian Church 
 
 CabinetLawyer 28 
 
 CALVERT'S Wife's Manual .................. 
 
 CAN NON 's Grant's Campaign ................ 
 
 CARPENTER'S Six Months in India .......... 
 
 CATES'S Biographical Dictionary .......... 
 
 CATS' and FARLIE'S Moral Emblems ........ 
 
 Changed Aspects of Unchanged Truths.. 
 CHESNEY'S Euphrates Ex 
 IndianPolity 
 
 -- Waterloo Campaign ............ 
 
 CHILD'S Physiological Essays .............. 
 
 Chorale Book for England ................ 
 
 Christian Schools and Scholars ............ 
 
 Churchman's Daily Remembrancer ........ 
 
 CLOUOH'S Lives from Plutarch .............. 
 
 COBBE'S Norrnan Kings of England ...... .. 
 
 COLE N so (Bishop) on Pentateuch and BOOK 
 
 of Joshua ................................. 
 
 Commonplace Philosopher in Town and 
 
 Country ................................... 
 
 CONINOTON'S Chemical Analysis ............ 
 
 --- - Translation of VIROIL'S jEneid 
 
 CONTANSEAU'S French-English Dictionaries 
 CONYBEARE and HOWSON'S Work on St. Paul 
 Coos on the Acts ............................ 
 
 COOK'S Voyages ............................ 
 
 COPLAND'S Dictionary of Practical Medicine 
 COULTHART'S Decimal Interest Tables ...... 
 
 Counsel and Comfort from a City Pulpit . . 
 Cox's (G. W.) Manual of Mythology ...... 
 
 --- Tale of the Great Persian War 
 --- Tales of Ancient Greece ...... 
 
 - (H.) Ancient Parliamentary Elections 
 __ History of the Reform Bills .... 
 
 -- Whig and Tory Administrations 
 CRESY'S Encyclopaedia of Civil Engineering 
 Critical Essays of a Country Parson ........ 
 
 Caoss'sOld Story ........................... 
 
 CROWE'S History of France ................ 
 
 CRUMP on Banking, Currency, & Exchanges 
 CULLEY'S Handbook of Telegraphy ........ 
 
 CUSACK.'S History of Ireland ................ 
 
 DART'S Iliad of Homer ...................... 26 
 
 D'AumoNE's History of the Reformation in 
 
 the time of CALVIN ........................ 2 
 
 DAVIDSON'S Introduction to New Testament 19 
 
 DAYMAN'S Dante's Divina Commedia ...... '26 
 
 Dead Shot (The), by MARKSMAN .......... 26 
 
 DE LA RIVE'S Treatise on Electricity ...... 11 
 
 DE MORGAN on M atter and Spirit .......... 9 
 
 DE TOCQUEVILLE'S Democracy in America.. ! 
 
 DOBSON on the Ox .......................... 25 
 
 DOVE on Storms ............................ 11 
 
 DvBR'sCity ot Rome ...................... 2 
 
 EASTI.AKE'S Hints on Household Taste .... 17 
 History of Oil Painting 15 
 
30 
 
 NEW "WORKS PUBLISHED BY LONGMANS AND CO. 
 
 EDGINTON'S Odyssey 26 
 
 EDWARUS'S Shipmaster's Guide 27 
 
 Elementsof Botany 13 
 
 ELLICOTT'S Commentary on Ephesians .... 19 
 
 Lectures on Life ot Christ 19 
 
 Commentary on Galatians 19 
 
 Pastoral Epist... 19 
 
 Philippians,&c.. 19 
 
 Thessalonians ... 19 
 
 Essays and Contributions of A. K. H. B. .. 8 
 
 Essays and Reviews 21 
 
 EWALD'S History of Israel 19 
 
 FAIRBAIRN on Iron Shipbuilding 17 
 
 FAIRBAIRN'S Application of Cast and 
 
 Wrought Iron to Building 17 
 
 Information for Engineers... 17 
 
 Treatise on Mills & Millwork 17 
 
 18 
 
 FARRAR'S Chapters on Language 
 
 FBLKIN on Hosiery and Lace Manufactures 
 FPOULKES'S Christendom's Divisions iO 
 
 FITZOIBBON'S Ireland 
 
 FLIEDNER'S (Pastor) Life 
 
 FORBRS'S Earls of Granard 
 
 FRANCIS'S Fishing Book 
 
 FROUDE'S History of England 
 
 Short Studies on Great Subjects 
 
 GANOT'S Elementary Physics ll 
 
 GILBERT and CHURCHILL'S Dolomite Moun- 
 tains 23 
 
 GILLY'S Shipwrecks of the Navy 23 
 
 GOLDSMITH'S foems. Illustrated 25 
 
 GOODEV E'S Elements of Mechanism 17 
 
 gouLo's Silver Store 26 
 
 RAHAM'S Book about Words 7 
 
 GRANT'S Ethics of Aristotle 
 
 Graver Thoughts of a Country Parson .... 9 
 
 GRAY'S Anatomy 14 
 
 GREENE'S Coi als and Sea Jel lies 12 
 
 Sponges an d Animalculae 12 
 
 GREENHOW on Bronchiiis 14 
 
 ROVE on Correlation of Physical Forces.. 12 
 
 WILT'S Encyclopaedia of Architecture .... 16 
 
 Handbook of Angling, by EPHEMERA 26 
 
 HARE on Election of Representatives 7 
 
 HARTWIG'S Harmonies of Nature 13 
 
 Polar World 13 
 
 Sea and its Living Winders. . . . 13 
 
 Tropical World 13 
 
 HAUGHTON'S Manual of Geology 12 
 
 HAWKER'S Instructions to Young Sportsmen 26 
 HENDERSON'S Folk-Lore of the Northern 
 
 Counties 10 
 
 HERSCHEL'S Outlines of Astronomy 10 
 
 HEWITT on Diseases of Women 14 
 
 HODGSON'S Time and Space 9 
 
 HOLM ES'S System of Surgery 14 
 
 Surgical Diseases of Infancy .... 14 
 
 HOOKER and WALKER-ARNOTT'S British 
 
 Flora 13 
 
 HORNE'S Introduction to the Scriptures .... 19 
 
 - Compendium of ditto 19 
 
 HORSLEY'S Manual of Poisons 15 
 
 How we Spent the Summer 22 
 
 HOWARD'S Gymnastic Exercises 15 
 
 HOWITT'S Australian Discovery 22 
 
 Northern Heights of London 23 
 
 , Rural Life of England 23 
 
 Visitsto Remarkable Places 23 
 
 HUGHES'S (W.) Manual of Geography 11 
 
 HULLAH'S Collection of Sacred Music 16 
 
 Lectures on Modern Music 15 
 
 HOLLAH'S Transition Musical Lectures .... 15 
 HUMPHREYS' Sentiments of Shakspeare .... 16 
 
 INGELOW'S Poems 25 
 
 StoryofDoom 25 
 
 JAMESON'S Legends of the Saints and Mar- 
 tyrs 16 
 
 Legends of the Madonna 16 
 
 Legends of the Monastic Orders 16 
 
 JAMESON and EASTLAKE'S History of Our 
 
 Lord 16 
 
 TENNER'S Holy Child 25 
 
 JOHNSTON'S Gazetteer, or Geographical Dic- 
 tionary 11 
 
 JORDAN on Vis Inertias in the Ocean 11 
 
 JUKES on Second Death ; 21 
 
 on Types of Genesis 21 
 
 KALISCH'S Commentary on the Bible 
 Hebrew Grammar. . . 
 
 7 
 7 
 
 KEITH on Fulfilment of Prophecy 19 
 
 Destiny of the World 19 
 
 KERL'S Metallurgy by CROOKFS and ROHRIO IS 
 
 KESTEVEN'S Domestic Medicine 15 
 
 KIRBY and SPENCE'S Entomology 13 
 
 LANDON'S (L. E . L.) Poetical Works 25 
 
 LATHAM'S English Dictionary 7 
 
 River Plate 11 
 
 LECK Y'S History of European Morals 3 
 
 Rationalism J 
 
 LEIGHTON'S Sermons and Charges IS 
 
 Leisure Hours in Town 8 
 
 Lessons of Middle Age 9 
 
 LEWES' History of Philosophy 3 
 
 LIDDEI.I, and SCOTT'S Greek-English Lexicon 8 
 
 Abridged ditto 8 
 
 Life of Man Symbolised 16 
 
 LINDLEY and MOORE'S Treasury of Botany 13 
 
 LONGMAN'S Edward the Third 2 
 
 Lectures on the History of Eng- 
 land 2 
 
 LOUDON'S Agriculture Ifr 
 
 Gardening 18> 
 
 Plants 13 
 
 LOWNDES'S Engineer's Handbook 17 
 
 Lyra Domestica 21 
 
 Eucharistica 22 
 
 Germanica 16,22 
 
 Messianica 22 
 
 Mystica 22 
 
 MAC AULA Y 's (Lord) Essays 
 
 History of England 
 
 Lays of Ancient Rome . 
 
 Miscellaneous Writings 
 
 Speeches 
 
 Complete Works 
 
 MACFARREN'S Lectures on Harmony 
 
 MACLEOD'S Elements of Political Economy 
 
 Dictionary of Political Economy 
 
 Elementsof Banking 
 
 Theory and Practice of Banking 
 
 McCuLLOcn's Dictionary of Commerce 
 
 Geosrraphical Dictionary 
 
 MAOUIRE'S Irish in America 
 
 Lifeof Father Mathew 
 
 MALLKSON'S French in India 
 
 MANNING'S England and Christendom 
 
 MARSHALL'S Physiology 
 
 MARSHMAN'S Life of Havelock 
 
 History ot India 
 
NEW WORKS PUBLISHED BY LONGMANS AND CO. 
 
 31 
 
 MARTTNEAU'S Endeavours after the Chris- 
 tian Life 22 
 
 MASSEY'S History of England 2 
 
 MAsstNOBERn's History of the Reformation.. 4 
 
 MADNDER'S Biographical Treasury 5 
 
 Geographical Treasury 11 
 
 Historical Treasury 4 
 
 i Scientific and Literary Treasury 13 
 
 Treasury of Knowledge 28 
 
 . Treasury of Natural History .. 13 
 
 MAIJRY'S Physical Geosraphy 
 
 MAY'S Constitutional Historv of Eneland. . 2 
 
 MEISSNER'S Biographical and Critical Essays 5 
 
 MELIA on Virgin Mary 20 
 
 MELVILLE'S Digby Grand 24 
 
 General Bounce 24 
 
 Gladiators , 24 
 
 Good for Nothing 24 
 
 Holmby House 24 
 
 Interpreter 24 
 
 KateCoventry 24 
 
 Queen's Maries 24 
 
 MENDELSSOHN'S Letters 5 
 
 MERivALE's(H.HIistorical Studies 2 
 
 (C.) Fall of the Roman Republic 3 
 
 Romans under the Empire 3 
 
 MERRIPIELD and EVKRS'S Navigation 10 
 
 MILES on Horse's Foot and Horseshoeing... 27 
 
 on Horses' Teeth and Stables 27 
 
 MILL (JO on the Mind 10 
 
 MILL (.J. S.) on Liberty 6 
 
 on Representative Government 6 
 
 on Utilitarianism 6 
 
 MILL'S (J. S.) Dissertations and Discussions 6 
 
 Political H'conomy 6 
 
 System of Logic 6 
 
 . Hamilton's Philosophy 6 
 
 Inaugural Address 7 
 
 MILLER'S Elements of Chemistry 14 
 
 Hymn- Writers 21 
 
 MITCHELL'S Manual of Assaying 18 
 
 Modern Ireland 3 
 
 MONSELL'S Beatitudes 21 
 
 His Presence not his Memory .. 21 
 
 ' Spiritual Songs ' 21 
 
 MOOBE'S Irish Melodies 25 
 
 LallaRookh 25 
 
 Poetical Works 24 
 
 (Dr. G.) First Man 12 
 
 Power of the Soul over the Body . . 21 
 
 MORELL'S Elements of Psychology 10 
 
 Mental Philosophy 10 
 
 MOUNTPTELD on National Church 19 
 
 MCLLER'S (MAX) Chips from a German 
 
 Workshop 10 
 
 Lectures on the Science of 
 
 Language 
 
 (K. CO Literature of Ancient 
 Greece 
 
 2 
 
 MURCHISON on Continued Fevers 14 
 
 on Liver Complaints 14 
 
 MURK'S Language and Literature of Greece 2 
 
 New Testament,illustrated with Wood En- 
 gravings from the Old Masters 16 
 
 NEWMAN'S History of his Religious Opinions 4 
 
 NICHOLAS'S Pedigree of the English People 9 
 
 NICHOLS' Handbook to the British Museum 28 
 
 NIGHTINGALE'S Note* on Hospitals 28 
 
 NILSSON'S Scandinavia 12 
 
 NORTHCOTE'S Sanctuaries of the Madonna. . 20 
 
 NORTKCOTT'S Lathes and Turning 17 
 
 NORTON'S City of London 23 
 
 ODLINO'S Animal Chemistry 14 
 
 Course of Practical Chemistry. . . . 14 
 
 ODLING'S Manual of Chemistry 14 
 
 Original Designs for Wood Carving 17 
 
 OWJSN'S Lectures oa the Invertebrate Ani- 
 mals 12 
 
 Comparative Anatomy and Physio- 
 logy of Vertebrate Animals 12 
 
 PACKE'S Guide to the Pyrenees 23 
 
 PAOKT'S Lectures on Sursrical Pathology .. 14 
 
 PEREIRA'S Manual of Materia Medica 22 
 
 PERKINS'S Italian and Tuscan Sculptors.... 17 
 
 PHILMPS'S Guide to Geology 12 
 
 PHILLIPPS'S Horse and Man 27 
 
 Pictures in Tyrol 22 
 
 PIESSE'S Art of Perfumery 18 
 
 Chemical, Natural, and Physical 
 
 Magic 18 
 
 PIKE'S English and their Origin 9 
 
 Playtime with the Poets 25 
 
 PLOWDEN'S Travels in Abyssinia 23 
 
 POLKO'S Reminiscences of Mendelssohn 5 
 
 PHATT'S Law of Building Societies 28 
 
 PRESCOTT'S Scripture Difficulties 20 
 
 PROCTOR'S Saturn 10 
 
 Handbook of the Stars lo 
 
 PYCKOFT'S Cricket Field 26 
 
 Quarterly Journal of Science 13 
 
 Q,UICK'S Educational Reformers 5 
 
 Recreations of a Country Parson 8 
 
 RRILV'S Map of Mont Blanc 22 
 
 RKIMANNOII Aniline Dyes 15 
 
 RICHARDSON'S Life, by MC!LWRAITH 5 
 
 RILEY'S Memorials of London 23 
 
 RIVERS'S Rose Amateur's Guide IS 
 
 ROBBINS'S Cavalry Catechism 27 
 
 ROOERS'S Correspondence of Greyson 9 
 
 Eclipse of Faith 9 
 
 Defence of ditto 9 
 
 Essays from the Edinburgh Review 9 
 
 Reason and Faith 9 
 
 ROOET'S Thesaurus of English Words and 
 
 Phrases 7 
 
 Roma Sotteranea 24 
 
 RONALDS'S Fly-Fisher's Entomology 26 
 
 ROWTON'S Debater 7 
 
 RUOD'S Aristophanes 25 
 
 RUSSELL on Government and Constitution. . l 
 
 SANDARS'S Justinian's Institutes 6 
 
 SCHEFFLER on Oc.ular Defectsand Spectacles 14 
 
 SCHUBERT'S Life, translated by COLERIDGE.. 4 
 
 SCOTT'S Lectures on the Fine Arts 15 
 
 SEEBOHM'S Ox'ord Reformers of 1498 2 
 
 SENIOR'S Journals &c. relating to Ireland . . 3 
 
 SEWELL'S After Life 24 
 
 A my H erbert 24 
 
 CleveHall 2 4 
 
 Earl 's Daughter 24 
 
 Examination for Confirmation ... 21 
 
 Experience of Life 24 
 
 Gertrude 24 
 
 Glimpse of the World 
 
 History of the Early Church 4 
 
 Ivors 24 
 
 Journal of a Home Life 24 
 
 Katharine Ashton 24 
 
 Laneton Parsonage 2* 
 
 Margaret Percival 24 
 
 Passing Thoughts on Religion.... 21 
 
 Preparation for Communion 21 
 
 Principles ot Education 21 
 
 Readings for Confirmation 21 
 
 Readings for Lent 21 
 
 Tales and Stories 23 
 
32 
 
 NEW WORKS PUBLISHED BY LONGMANS AND CO. 
 
 SEWELL'S Ursula 
 
 SHAW'S Work on Wine 
 
 SHAKESPKARE'S Midsummer Night's Dream 
 
 illustrated with Silhouettes 
 
 SHEPHERD'S Iceland 
 
 SHIPLEY'S Church and the World 
 
 Short Whist 
 
 SHORT'S Church History 
 
 SMART'S WALKER'S Pronouncing Dictionary 
 SMITH'S (SOUTHWOOD) Philosophy of Heolth 
 
 (J.) Paul's Voyage and Shipwreck. . 
 
 i , . (SYDNEY) Miscellaneous Works 
 
 -WitandWisdom 
 
 24 | TYNDALL'S Lectures on Heat.. 
 28 Sound 
 
 FARADAY as a Discoverer 
 
 SOUTHEY'S (Doctor) 
 
 Poetical Works 
 
 STAFFORD'S Life of the Blessed Virgin 
 
 STANLEY'S History of British Birds 
 
 STEBBINO'S Analysis of MILL'S Logic 
 
 STEPHEN'S Essays in Ecclesiastical Bio- 
 graphy 
 
 STIRLING'S Secret of Hegel 
 
 STOKES'sLlfeOfPETRIE 
 
 STONEHENOE on the Dog 
 
 ___ on the Greyhound 
 
 STRICKLAND'S Tudor Princesses 
 
 Sunday Afternoons at the Parish Church of 
 a Scottish University City (.St. Andrew's) 
 
 TAYLOR'S (Jeremy) Works, edited by EDEN 
 (E.) Selections from some Contem- 
 porary Poets 
 
 TENNENT'S Ceylon 
 
 5aiRLwALL's History of Greece 
 HOMSON'S (Archbishop) Laws of Thought 
 
 . (A. T.~> Conspectus 
 nlains(The) 
 
 Three Foum 
 
 TIMBS'S Curiosities of London 
 
 TODD (A.) on Parliamentary Government.. 
 TODD and BOWMAN'S Anatomy and Phy- 
 siology of Man 
 
 TRRNCH'S Realities of Irish Life 
 
 TROLLOPE'S Barchester Towers 
 
 . Warden 
 
 Twiss's Law pf K atious 
 
 UNCLBPRTER'S Fairy Tale 24 
 
 URE'S Dictionary of Arts, Manufactures, 
 and Mines 17 
 
 VAN DER HOEVEN'S Handbook of Zoology. . 12 
 
 WARBURTON'S Hunting Songrs 26 
 
 WATSON'S Principles and Practice of Physic 14 
 
 WATTS'* Dictionary of Chemistry 13 
 
 WEBB'S Objects for Common Telescopes 10 
 
 WEBSTER & WILKINSON'* Greek Testament 20 
 
 WELD'S Florence 22 
 
 WELLINGTON'S Life, by the Rev G. K. 
 
 GLEIO * 
 
 WELLS on Dew 11 
 
 WEST on Children's Diseases 14 
 
 WHATELY'S English Synonymea 6 
 
 Logic 6 
 
 Rhetoric 6 
 
 Life and Correspondence 4 
 
 WHATELY on the Truth of Christianity 22 
 
 Religious Worship 22 
 
 Whist, what to lead, by CAM 28 
 
 WHITE and RIDDLE'S Latin-English Dic- 
 tionaries 8 
 
 WILCOCKS'S Sea Fisherman ". 28 
 
 WINSLOW on Light 11 
 
 WOOD'S Bible Animals 12 
 
 Homes without Hands 12 
 
 WRIOHT'S Homer's Iliad 26 
 
 YEO'S Manual of Zoology 12 
 
 YONOE'S English-Greek Lexicons 
 
 Editions of Horace 25 
 
 :ontheDog 27 
 
 . onthe Horse 27 
 
 YOL 
 
 ZELLER'S Socrates 
 
 ^. r 
 
 LONDON : PRINTED EY 
 
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LOAN DEPT. 
 

 
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 LIBRARY USE 
 
 :BTORN TO DESK FROM WHICH BORROWED 
 
 LOAN DEPT. 
 
 JCli 
 
 LD 62A-50m-2,'64 
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 . General Library 
 
 University of California 
 
 Berkeley