IC-NRLF i :, V*. Division Range Shelf.... Received, ... ....(^C^V.... . .. 187^ fauriijan CHEMISTRY WILLIAMSON Hoution MACMILLAN AND CO. PUBLISHERS TO THE UNIVERSITY OF Series CHEMISTRY FOR STUDENTS BY ALEXANDER W. WILLIAMSON F.R.S., F.C.S., ETC. Professor of Chemistry and Practical Chemistry in University College, London Examiner in Chemistry at the University of London NEW EDITION AT THE CLARENDON PRESS M DCCC LXVIII [All rights reserved'} PREFACE. THIS little book is intended to supply to Students of Chemistry an outline of the most interesting and useful facts pertaining to the Science, and of the most important ideas which have been got from a study of those facts. The method of exposition differs from that which is adopted in most other treatises of .Chemistry ; for I describe and compare individual facts, so as to lead the mind of the reader towards general principles, instead of stating the general principles first and then proceeding to illustrate them by details. The book is intended for the use of beginners in Chemistry, and also of Students who, having made some progress in the Science, wish to have an outline of the chief facts and theories of mineral and of organic Chemistry. Those who wish to proceed further and to obtain full par- ticulars of any one part of the subject, will need to consult such books as Gmelin's Handbook, Watts's Dictionary, Miller's Elements, Gerhardt's Traite* de Chimie organique, or Kekule^s admirable Lehrbuch der organischen Chemie. It is not intended as a substitute for vivd voce and ex- perimental teaching, but rather as a guide and aid to Students and Teachers. A judicious Teacher will amplify the brief explanations and descriptions which I give; and will show experimentally the reactions and transformations which I mention. A Learner who wants to recall to mind what he has seen and heard may refer to the book for the substance of it. vi PREFACE. The absolute ' volume ' which I have for many years adopted in my classes is here employed in the calculations relating to gases. The knowledge of this absolute volume is of value to Learners because it leads them easily from a class of similar facts to an important general conclusion, and it supplies to Chemists a ready means of calculating the weight of any given measure of gas or vapour. This ab- solute volume is in round numbers 11.2 litres, which is the bulk of one gramme of hydrogen, of sixteen grammes of oxygen, of fourteen grammes of nitrogen, &c., at the normal temperature and pressure ; in fact the bulk of that quantity of any one of those gases which weighs as many grammes as there are units in the number expressing its atomic weight. Students will do well to work out the answers to the questions appended to the first few chapters, and thereby to practise themselves in using the elementary facts of Chemistry. Among the additions which have been made to the first edition, I may mention the following as amongst the most important : i st. Tables of acids, bases, sulphides, salts, &c. 2nd. Diagrams explanatory of the proportions of com- bination by volume and by weight. 3rd. Explanations respecting the atomic theory and the equivalence of atoms, &c. I have also employed more systematically than before, in the organic part of the volume, in describing hydrogen salts, names analogous to those applied to other salts. My friend M. Barff has been kind enough to revise the last sheets of the book. ALEX. W. WILLIAMSON. UNIVERSITY COLLEGE, LONDON, September, 1868. TABLE OF CONTENTS. INORGANIC CHEMISTRY. CHAP. SECT. I. Preparation of Oxygen, O= 16 . i Sprengel's Air Pump i Composition of Air . 2 Combustions in Oxygen . ..... 3 Change of properties in Combustion .... 4 Density of Oxygen . . . . . . . 5 Expansion of Oxygen by Heat ..... 5 Compression of Oxygen ...... 6 Physiological relations of Oxygen .... 7 Ozone 8 II. Preparation of Hydrogen, H = i . . . . 9 Purification of Hydrogen . . . . .10 Properties of Hydrogen . . . . . . 1 1 Diffusion of Hydrogen 12 Combustion of Hydrogen 13 Proportion of Hydrogen in Water . . . .14 A Mixture distinguished from a Compound . . -14 Heat of Combustion of Hydrogen . . . -15 Mineral Waters 16 Purification of Water 1 7 Decomposition of Water . . . . . .18 Oxides 18 Compounds of Water (Hydrates) . . . 19 Expansion of Water . . . . . . .20 Freezing of Water ....... 20 III. Evaporation of Water .21 Tension of Steam . . . . . . .21 Superheated Steam 22 Saturated Steam 23 Density of Steam 24 Mixtures of Steam and Air . . . . .25 CONTENTS. CHAP. SECT. Oxygen soluble in Water 26 Nitrogen soluble in Water ...... 26 IV. Specific Heat of Oxygen . . . . . .27 Specific Heat of Hydrogen 27 Specific Heat of Steam 27 Specific Heat at Constant Volume . . . .28 Work done in Expansion ...... 29 Mechanical Equivalent of Heat ..... 30 Latent Heat of Expansion . . . . . .31 Latent Heat of Evaporation .., . . . -32 Total Heat of Evaporation 33 Latent Heat of Fusion ...... 34 V. Atomic Symbols 35 Atomic Symbols of Combination 36 Molecular Formulae . . . . . . 36 Equations . . .. . . . . -37 Brackets . .. . . . . . . -37 Hydric Peroxide, H 2 O 2 38 Synthesis of Oxygen . . . . . . .39 Hydrides ......... 39 VI. Nitrogen, Preparation of, N= 14 40 Analysis of Air 40 Nitrogen, Properties of 41 Atmospheric Pressure 42 Barometer . . . . . . . .42 Weight of Air 43 Temperature of the Atmosphere 44 Formation of Dew 45 Minor Constituents of Air 46 Respiration ........ 46 Respiration of Plants ....... 47 Nutrition of Plants . . . . . . .47 VII. Nitrogen Oxides 48 Nitrate, Hydric, H N O 3 49 Nitrates, Reactions of 50 Nitrate, Monobasic 51 Nitrates 51 Nitric Acid, N* O 5 52 Nitric Peroxide, N 2 O* 52 CONTENTS. CHAP. SECT Nitrite, Hydric, N O 2 H 53 Nitrous Acid, N 2 O 3 53 Nitric Oxide, NO 54 Nitrous Oxide, N a O 55 VIII. Ammonia, N H 3 56 Ammonia, Liquid 57 Ammonic Hydrate, N H 5 O 58 Ammonium, NH 1 -59 Ammonic Salts 59 Ammonia, Reactions of .60 IX. Carbon, C= 12 61 Plumbago . . . . . . . . .61 Coke 62 Charcoal 62 Animal Charcoal 63 Lamp Black 63 Combustion of Charcoal ...... 64 Carbonic Acid, CO 2 65 Carbonates 66 X. Carbonic Oxide, CO .67 Furnaces, Action of . . . . . . .68 Carbonic Oxide, Reactions of . . . ,69 Oxalate, H 2 C 2 O*, Formation of 70 Oxalate, Reactions of 71 Formiate, Hydric, C H 2 O 2 72 XI. Marsh Gas, C H 4 73 Ethylene, C 2 H* 74 Acetylene, C 2 H 2 75 Coal Gas 76 Coal Tar 77 Coal Gas, Purification of 78 Benzole in Coal Gas ....... 79 Structure of Flame ....... 80 Bunsen Burner 80 XII. Cyanogen, CN 81 Cyanates 82 Urea 83 Cyanurates ........ 84 Isomerism 85 CONTENTS. CHAP. SECT. Cyanides 86 Prussia Acid ........ 86 Methylia, CNH 5 .87 XIII. Atoms 88 Molecules 89 Radicals 90 Equivalents . . . . . . . .91 Equivalents, Change of ...... 92 Atomic Weights, Table of 92 XIV. Chlorine, Cl= 35.5 ....... 93 Chlorates, &c 94 Chlorides 95 Hydrochloric Acid ....... 95 Chlorochromic Acid, Cr O 2 Cl 2 96 Nitric Chloride 97 Ammonic Chloride, N H 4 Cl 98 Chloro-carbonic Acid, CO Cl 2 99 Chlorine Action on Hydrocarbons . . . .100 Chloroform, C H Cl 3 101 Carbonic Chloride, C Cl* 102 Chlorides and Double Chlorides . . . . 102 XV. Bromine, Br == 80 103 Bromine, Compounds of . . . . .104 Iodine, 1=127 105 lodic Acid, I 2 ' O 5 105 Iodides ... . . . . . . .106 Periodate, H 3 I O 5 107 Iodides, Reactions of 108 Nitric Iodide . . . . . . . .109 Iodine with Hydrocarbons . . . . . .110 Cyanic Iodide, C N I no Fluorine, F = 1 9 in Fluorides . . . . . . . . .112 XVI. Sulphur, 8 = 32 113 Allotropic varieties of Sulphur . . . . .113 Sulphuretted Hydrogen, S H 2 . . . . .114 Sulphuretted Hydrogen, Action of, on Metallic Salts . 115 Sulphurous Acid, SO 2 1 1 6 Hydric Sulphate, H 2 SO 1 117 CONTENTS. CHAP. SECT. Sulphuric Acid, S O 3 118 XVII. Sulphamide, S O 2 (N H 2 ) 2 119 Sulphates 120 Hyposulphites . . . . . . . .121 Hyposulphates 121 Ammonic Sulphide, (N H 4 ) S 122 Carbonic Sulphide . . . . . . .123 Sulphocarbonates . . . . . . .124 Chlorides of Sulphur 124 Chlorosulphuric Acid, S O 2 Cl 2 125 Chlorhydrated Sulphuric Acid, S O 3 H Cl . . .125 Selenium, Se == 79.5 ".126 Selenious Acid, Se O 2 .... . .126 Tellurium, Te=i27 127 Telluric Acid, Te O 3 127 XVIII. Phosphorus, P = 31 128 Red Phosphorus . . . . . . .129 Phosphoric Acid, P 2 O 5 130 Hydric Phosphate, H 3 P O 4 131 Phosphates 131 Phosphates, Reactions of 132 Pyrophosphate, H 4 P 2 O 7 1 33 Metaphosphate 133 XIX. Phosphorous Acid, P 2 O 3 134 Phosphite, Hydric, H 2 H P O 3 134 Hypophosphite, H 3 P O 2 134 Phosphuretted Hydrogen, H 3 P 135 Phosphorous Chloride, P Cl 3 136 Phosphoric Chloride, P Cl 5 136 Chlorophosphoric Acid, P O Cl 3 . . . .136 Sulphides of Phosphorus . . . . . . 137 XX. Boron, B = ii 138 Boracic Acid, B 2 O 3 138 Silicon, 81=28 . 139 Silica, Si O 2 139 Silicates, Si O 4 H* Si O 3 H 2 139 Silicic Fluoride, Si F 1 140 Hydrofluosilicic Acid, Si F 2 H 6 140 XXI. 'Arsenic, As = 75 141 b 2 CONTENTS. CHAP. SECT. Arsenious Acid, As 2 O 3 . . . . . . 142 Arsenic Acid, As 2 O 5 143 Arseniates, H 3 As O 4 143 Arseniuretted Hydrogen, H 3 As 144 Arsenious Chloride, As Cl 3 . . . . .144 Realgar, As 2 S 2 145 Arsenious Sulphide, As 2 S 3 . . . . . -145 Arsenic Sulphide, As 2 S 5 145 XXII. Antimony, Sb = 1 2 2 146 Antimonious Acid, Sb a O 3 ...... 147 Antimonic Acid, Sb 2 O^ 147 Antimoniuretted Hydrogen, H 3 Sb . . . .148 Antimonious Chloride, Sb Cl 3 148 Antimonic Chloride, Sb Cl 5 148 Antimonious Sulphide, Sb 2 S^ 149 XXIII. Tin, Sn=n8 150 Stannous Oxide, Sn O . . . . . . 1 50 Stannic Oxide, Sn O 2 1 50 Stannous Chloride, Sn Cl 2 151 Stannic Chloride, SnCl 1 152 Titanium 1=2 Tungsten, W = 1 84 153 Tungstic Acid, W O 3 153 Molybdenum 153 Gold, Au = 1 96.5 154 Auric Chloride, Au Cl 3 154 Aurous Chloride, Au 2 Cl 2 154 Platinum, Pt= 197 155 Platinic Oxide, Pt O 2 . . . . . .155 Platinous Oxide, Pt O . . . . . . 155 Platinic Chloride 156 XXIV. Silver, Ag=io8 157 Argentic Oxide, Ag 2 O 158 Argentic Nitrate 158 Argentic Chloride, Ag Cl 159 Argentic Sulphide, Ag 2 S 160 Argentic Sulphate, Ag 2 S O* 1 60 XXV. Mercury, Hg = 2OO 161 Mercuric Oxide, Hg O 162 CONTENTS. xiii CHAP. SECT. Mercurous Oxide, Hg 2 O 162 Mercurous Chloride (Calomel), Hg 2 Cl 2 . . .163 Mercuric Chloride, Hg Cl 2 164 White Precipitate, Hg N H 2 Cl . . . .. .164 Mercuric Sulphide, Hg S . . . . . .165 XXVI. Lead, Pb = 20 7 166 Plumbic Oxide, Pb O 167 Red Lead 167 Plumbic Binoxide, Pb O 2 167 Plumbic Nitrate, Pb (N O 3 ) 2 168 White Lead i6S Plumbic Oxalate, Pb C 2 O 4 168 Plumbic Chloride, Pb Cl 2 168 Plumbic Sulphide, Pb S 169 Plumbic Sulphate, Pb S O* 169 Bismuth, Bi= 2 10 170 Bismuth Oxide, Bi 2 O 3 . . ., . . .170 Bismuth Chloride, Bi Cl 3 . . . . . . 1 70 XXVII. Copper, Cu = 63.5 171 Cuprous Oxide, Cu 2 O 172 Cupric Oxide, Cu O . . . , . . .172 Malachite, Cu 2 (C O 3 ) (HO) 2 172 Cuprous Chloride, Cu 2 Cl 2 . . . . . .172 Cupric Chloride, Cu Cl 2 172 Cupric Sulphate, Cu S O 4 172 Cadmium, Cd = 1 1 2 173 Cadmic Oxide, Cd O 173 XXVIII. Iron, Fe = 56 174 Blast Furnace 1 74 Spiegeleisen . . . . . . .174 White Iron . . . . . . . .174 Grey Iron 1 74 Malleable Iron 175 Puddling Furnace . . . . . . .175 Bessemer's Process . . . . . .175 Malleable Cast Iron . . . . . . 1 75 Oxidation of Iron 176 Steel [77 Ferrous Oxide, Fe O 178 CONTENTS. CHAP. SECT. Ferric Oxide, Fe 2 O s 178 Prussian Blue . . . . . . . .179 Ferrous Carbonate, Fe Co 3 179 Ferrous Chloride, Fe Cl 2 180 Ferric Chloride, Fe 2 Cl 6 180 Ferrous Sulphide, Fe S 180 Pyrites, FeS 2 180 Ferrous Sulphate, Fe S O 4 181 Ferric Sulphate, Fe 2 (S O 4 ) 3 . . . . . i?i XXIX. Aluminium, Al= 2 7.5 . . . . . .182 Alumina, A1 2 3 183 Mordants 183 Aluminic Chloride, Al 2 Cl 6 184 Alum, Al 2 K 2 (S O 4 ) 4 (H 2 O) 21 185 Clay 1 86 Chromium, Cr = 52.5 187 Chromous Oxide, Cr O 187 Chromic Oxide, Cr 2 O 3 187 Chromic Acid, Cr O 3 1 88 Chromic Chloride . . . . . . .189 Chlorochromic Acid 189 Uranium, Ur= 1 20 190 XXX. Cobalt, 00 = 58.5 191 Cobaltous Oxide, Co O 191 Cobaltous Chloride, Co Cl 2 191 Nickel, Ni = 58.5 ....... 192 Nickel Sulphate, Ni S O 4 192 Manganese, Mn = 55 193 Manganous Oxide, Mn O 193 Manganic Oxide, Mn 2 O 3 193 Manganic Peroxide, Mn O 2 . . . . .193 Manganous Chloride, Mn Cl 2 ..... 194 Manganous Sulphide, Mn S . . . .194 Manganic Sulphate, Mn SO 4 . . . . . 194 Manganate, Potassic 195 Permanganate, Potassic, Mn 2 O 8 K 2 . . . .195 Zinc, Zn = 65 196 Brass 196 Zinc Oxide, Zn O 197 CONTENTS. x CHAP. SECT. Zinc Carbonate, Zn C O 3 . . . . . 197 Zinc Chloride, Zn Cl 2 . . . . . 197 Zinc Sulphate, Zn S O 4 . . . . . 197 Cerium 198 Ceric Oxide, Ce O 198 Lanthanum 198 Didymium 198 Yttrium 198 G-lucinum 198 XXXI. Barium, Ba= 1 37 199 Baryta, Ba O 199 Barytic Nitrate, Ba (N O 3 ) 2 199 Barytic Carbonate, Ba C O 3 200 Barytic Chloride, Ba Cl 2 200 Barytic Sulphide, Ba S 200 Barytic Hyposulphate, Ba S 2 O 6 -200 Barytic Sulphate, Ba S O* 200 Barytic Fluosilicate, Ba Si F 6 200 Strontium, Sr = 8 7. 5 201 Calcium, Ca = 40 202 Lime, Ca O 202 Calcic Hydrate, Ca O 2 H 2 202 Calcic Carbonate, Ca C O 3 203 Calcic Hydrocarbonate, Ca H 2 (C O 3 ) 2 . . .203 Calcic Chloride, Ca Cl 2 203 Calcic Hypochlorite, Ca Cl 2 O 2 203 Calcic Sulphate, Ca S O* 204 Calcic Phosphate, Ca 3 (P O 4 ) 2 . . . . .204 Calcic Silicate 204 Magnesium, Mg = 24 205 Magnesia, Mg O . . . . . . 205 Magnesic Chloride, Mg Ci 2 205 Magnesic Sulphate, Mg S O 4 205 Ammonio-magnesic Phosphate, N H 4 Mg P O 4 (H 2 O) 6 . 205 XXXII. Potassium, K = 39 206 Potash, K 2 O 206 Potassic Hydrate, K H O 207 Potassic Nitrate, K N O 3 208 Gunpowder ........ 208 CONTENTS. Potassic Nitride, K 3 N Potassic Carbonate, K 2 C O 3 Hydropotassic Carbonate, K H C O 3 . Potassic Oxalate, K 2 C 2 O* Hydropotassic Oxalate, H K C 2 O* Potassic Cyanide, K C N . Potassic Cyanate, K C N O Potassic Sulphocyanate, K C N S Potassic Chloride, K Cl Potassic Chloroplatinate, K 2 Pt Cr 5 Potassic Chlorate, K Cl O 3 Potassic Iodide, K I . Potassic Fluoride, K F Hydropotassic Fluoride, F 2 K H Potassic Fluosilicate, K 2 Si F 6 . Potassic Sulphide, K 2 S Potassic Sulphhydrate, K S H Potassic Sulphite, K 2 SO 3 . Hydropotassic Sulphite, H K S O 3 Potassic Sulphate, K 2 S O 4 . Potassic Disulphate, K 2 S 2 O 7 Hydropotassic Sulphate, K H S O 4 Potassic Phosphate, K 3 P O 4 Hydrodipotassic Phosphate, K 2 H P O 4 Dihydropotassic Phosphate, H 2 K P O 4 Dihydropotassic Antimoniate, K H 2 Sb O 4 Potassic Chromate, K 2 Cr O 4 Potassic Dichromate, K 2 Cr 2 O 7 . Potassic Permanganate XXXIII. Sodium, Na = 23 .... Soda, Na 2 O Sodic Hydrate, Na H O . Sodic Nitrate, Na N O 3 . Sodic Carbonate, Na 2 CO 3 Hydrosodic Carbonate, H Na C O 3 . Sodio-potassic Carbonate, K Na C O 3 . Sodic Chloride, Na Cl Bay Salt Sodio-platinic Chloride, Na 2 Pt Cl 6 SECT. 208 20 9 2O9 2O9 20 9 210 21O 210 211 211 211 211 211 211 211 212 212 212 212 213 213 213 21 4 2I 4 2I 4 2I 4 2I 4 214 2I 4 2I 5 2I 5 2'5 2I 5 216 216 216 217 2TJ 217 CONTENTS. xv CHAP. SECT. Sodic Hyposulphite, Na 2 S 2 O 3 217 Sodic Sulphate, Na 2 S O* 218 Sodic Disulphate, Na 2 S 2 O 7 218 Rhombic Phosphate (Hydrodisodic Phosphate), HNa 2 PO' 219 Sodic Pyrophosphate . . . . . .219 Dihydrosodic Phosphate . . . . . .219 Sodic Phosphate, Na 3 P O 1 219 Microcosmic Salt, Na H N H* P O 4 . . . .219 Borax, B 4 O 7 Na 2 (H 2 O) 10 . . . . .219 Sodic Silicate, Na 2 Si O 3 220 Sodic Tetrasilicate, Na 2 Si 4 O' J 2 20 Glass 220 Coloured Glass . . . . . . 22"o Hydrosodic Antimoniate, H 2 Na 2 Sb 2 O 7 . . .220 Lithium, Li = 7 221 Lithia, Li 2 O 221 Lithic Hydrate, Li H O 221 Lithic Phosphate, Li 3 P O 1 221 Rubidium 222 Coesium 222 Thallium . . 222 Thallic Oxide, Tl 2 O 222 Thallic Chloride, Tl Cl 222 ORGANIC CHEMISTRY. XXXIV. Meaning of Organic Chemistry ..... 223 Complexity of Organic Molecules .... 224 Radicals not peculiar to Organic Chemistry. . .225 Types . . . . . . . . .225 Limited Oxidation of Organic Molecules . . .226 Synthesis of Organic Molecules 227 Fermentation, S:c. . . . . . . .228 XXXV. Organic Constituents of the Atmosphere . . . 229 Alcohol, H O C 2 H 5 230 Spirits of Wine . . . . . . .231 Solvent action of Alcohol 232 Decompositions of Alcohol 232 Monobasic Ethers . . . . . . -233 Ethyle, C 2 H 5 , the Radical of Alcohol . . .234 xviii CONTENTS. CHAP. SECT. XXXVI. Methylic Alcohol, H O C W 235 Wood Spirits 236 Decompositions of Methylic Alcohol . . . -237 Constitution of Methylic Alcohol . . . .238 Homologous Bodies 238 Oxidation of Methylic Alcohol ..... 239 Alcohols from the ' mark ' of the Grape . . . 239 Propylic Alcohol, H O C 3 H 7 240 Isopropylic Alcohols 240 XXXVII. Butylic Alcohols, H O C 4 H 9 241 Amylic Alcohols, H O C 5 H 11 242 Amylene, C 5 H 10 242 Caproic Alcohol, &c 243 Cetylic Alcohol, from Spermaceti . . . .244 Cerotic Alcohol ....... 245 Melissic Alcohol 245 XXXVIII. Vinic Ether, C 2 H 5 OC 2 H 5 246 Continuous Etherification ...... 247 Properties of Ether . ...... 248 Methylic Ether, C H 3 O C H 3 249 Vinomethylic Ether, C 2 H 5 O C H 3 . . . . 249 Amylomethylic Ether, C 5 H 11 C H 3 . . . .250 Evidence that Oxygen is divalent . . . .251 XXXIX. Sulphur Compounds of Alcohol Radicals . . .252 Action of Phosphoric Sulphide on Alcohol . . . 253 Action of Phosphoric Chloride on Alcohol . . .2:3 Marsh Gas Series 254 Constitution of Marsh Gas Series . . . . 255 XL. Ethylic Chloride and Homologues .... 256 Ethylic Iodide (C 2 H 5 1) and Homologues . . -57 Acetonitrile and Homologues, or Methylic Cyanides . 258 Methylic Cyanate and Homologues . . . .259 Ethylia 259 Ethylic Sulphocyanate 259 Methylic Nitrite, &c. 260 Ethylic Nitrate 260 Alcoholic Carbonates . . . . . .261 Alcoholic Sulphocarbonates . . . .261 Alcoholic Oxalates 262 Formation of Oxamates 262 CONTENTS. x CHAP. SECT. XLI. Sulphurous Ether 263 Vinic Sulphate, (C 2 H 5 ) 2 SO* 264 Sulphovinates ........ 264 Zinc Methyle, Zn (C H 3 ) 2 265 Zinc lodomethyle, Znl (CH 3 ) 265 Mercuric Methiodide, Hg C H 3 1 . . . .266 Mercuric Methide ....... 266 XLII. Phosphoric Ethers ....... 267 Boracic Ether ........ 267 Boric Ethide ........ 267 Methylia 268 Ethylia 268 Diethylia ........ 269 Triethylia ........ 269 Action of Oxalic Ether on Ethylia, &c. . . . 269 Tetrethylammonium, &c. ...... 269 Phosphorus Bases . . . . . . .270 Kakodyle . . . . . . . .271 Alcoholic derivatives of Arsenic . . . .272 XLIII. Stibethyle, Sb(C 2 H 5 ) 3 273 Aluminic Ethide, Al 2 (C 2 H 5 ) 6 273 Vinic Silicate, Si O 4 (C 2 H 5 ) 4 274 Silicic Ethide, Si (C 2 H r >) 4 274 Stannic Ethide, Sn (C 2 H 5 ) 4 274 Plumbic Ethide, Pb (C 2 H 5 / 274 Allyl, C 3 H 5 275 Phenilic Alcohol, H O C 6 H 5 276 Carbazotic Acid, H O C 6 H 2 (N O 2 ) 3 . . . .276 XLIV. Benzole, or Benzine, C 6 H 6 277 Nitrobenzole, C 6 H r> N O 2 277 Toluol, C 7 H 8 . . 277 Aniline, N H 2 C 6 H 5 2 78 Aniline Derivatives . . . . . . .279 Benzoic Aldehyde, or Oil of Bitter Almonds, H C 7 H 5 O 280 Cuminic Aldehyde . . . . . . .280 Aldehyde, C 2 H 4 O 281 Chloral, C 2 HC1 3 O 281 Cinnamic Aldehyde, H C 9 H 7 O 282 Furfurol, C 5 H 4 O 2 282 Acrolein, C 3 H 4 O 282 x CONTENTS. CHAP. SECT. Hydrobenzamide, C 21 H 18 N 2 282 Furfurine, C 15 H 12 O 3 N 282 XLV. Acetone, C 3 H 6 O 283 Benzophenone, C 7 H 5 OC 6 H 5 283 Hydric Acetate, H O C 2 H 3 O, Formation of . . 284 Hydric Acetate, Purification of . . . . . 285 Plumbic Acetate, Pb (C 2 H 3 O 2 ) 2 . . . .286 Emerald Green ....... 286 Acetic Ether ........ 286 Acetamide . . . . . . . .286 XLVI. Hydric Chloracetate 287 Hydric Thiacetate 287 Sulphacetates . . . . . . . .287 Propionate ........ 288 Butyrate 288 Valerate 289 Caproate ......... 289 Palmitate, H C 16 H 31 2 u 290 Margarate . . 290 Stearate ......... 291 XLVII. Oleate 292 Drying Oils 292 Cerotate 293 Acetic Chloride 294 Acetic Acid, (C 2 H 3 O) 2 O 295 Acrylic Series . . . . . . . 296 XLVIII. Benzoates 297 Benzoic Chloride 298 Acetamide ........ 299 Glycol, C 2 H 4 (H O) 2 300 Ethylenic Oxide . . . . . . .301 Polyethylenic Glycols 302 Ethylenic Sulph-hydrate 302 XLIX. Glycollates 303 Lactates, H 2 (C 3 H*0 3 ) 304 Lactic Series . . . . . . . 304 Oxybenzoic Series ....... 304 Oxalic Series 305 Constitution of Oxalic Series ..... 306 Ethylene Diamine, C 2 H 4 (NH 2 ) 2 . . . .307 CONTENTS. x CHAP. SECT. L. Glycerine, H 3 O 3 C 3 H 5 308 Acetine ......... 309 Glycerate . . . . . . . .310 Malate, C 4 H 6 O 5 310 Asparagine 310 Aniline-red, C 20 H 19 N 3 3 r I Aniline-blue . . . . . . . .311 Mauveine . . . . . . . . .311 LI. Erithrite, C 4 H 6 O 4 H 4 312 Tartrate, C 4 H 6 O 6 312 Tartrates 313 Racemates . . , . . . . .314 Citrates, C 6 H"O 7 315 Mannite, C 6 H 8 O 6 H 6 316 Saccharates and Mucates 317 LIT. Sugars 318 Glucosates . . . . . . . .319 Levulose 319 Cane-sugar, C 12 H 22 O 11 320 Compounds of Sugar 321 Milk-sugar . . . . . . . .321 LIII. Dextrine, C 6 H 10 O 5 322 Starch 322 Cellulose 323 Gun Cotton 323 Collodion 323 LIV. Urates, H 2 C 5 H 2 N 4 O 3 324 Alloxan, C 4 H 2 N 2 O* 325 Alloxantin, C 4 B 6 N 4 O 3 325 Mesoxalate, H 2 C : H 5 325 Constitution of Mesoxalates . . . . .326 Parabanate 327 Dialurate . . . . . . . . .327 Murexide -32; Barbiturate 328 Constitution of Urates 328 Allantoine, C 4 H 6 N 4 O 3 328 LV. Guanin, C 5 H 5 N 5 O 329 Guanidin, CH 5 N 3 329 Xanthin, C 5 H 4 N*O 2 330 a CONTENTS. CHAP. SECT. Sarkine, C 5 H 4 N 4 O 330 Glycocyamine, C 3 H 7 N 3 2 331 Creatine, C 4 H 9 N 3 2 332 Creatinine, C* H 7 N 3 O 332 Sarkosine, C 3 H 7 N O 2 332 Creatinine 333 LVI. Theine, C 8 H 10 N 4 2 334 Theobromine, C 7 H 8 N 1 2 334 Constitution of Theine and Theobromine . . . 335 Bile 336 Cholate, C 26 H 42 Na N O 6 337 Taurocholate, C 26 H 44 Na N O 7 S 337 Cholalate, C 24 H 39 Na O 5 337 Glycocoll, C 2 H 5 N0 2 337 Taurine, C 2 H 7 N0 3 S 338 Cholesterine, C 26 H 4 * O 338 LVII. Chinine, C 20 H 24 N 2 O 2 339 Cinchonine, C 20 H 21 N 2 O 340 Opium 341 Morphia, C 17 H 19 NO' 342 Narcotine, C^H^NO 7 342 Strychnia, C^H^N 2 2 343 Brucia, C 23 H 26 N 2 O' 343 Nicotine, C 10 H 14 N 2 344 LVIII. Indigo, C 8 H 5 NO 345 Isatine, C 8 H 5 N0 2 345 Indigo-white, C 16 H 12 N 2 2 345 Alizarine, C 10 H 6 3 346 Naphthalate, H 2 C 8 H 4 O l 346 Orceine, C 7 H 7 N O' 347 Orsellate, C 8 H 8 0* 347 Turpentine, C 10 H 16 348 Essential Oils 348 Camphor, C 10 H 16 O 349 Camphorate, H 2 C 10 H 11 4 . 349 Solutions to the Problems p. 352 Index p. 380 INORGANIC CHEMISTRY INTRODUCTION. THE science of Chemistry is generally considered to date from the discovery of the nature of combustion. Lavoisier shewed that when a substance is burnt in the air, combination takes place between that substance and a constituent of the air, and something is formed by the combustion which can by suitable means be collected and examined. In no pro- cess of combustion is matter destroyed, for the materials employed weigh exactly as much as the product formed by their combination. Thus mercury can be made to combine by a sort of combustion with a constituent of the air (called oxygen), and the compound thus formed (called mercuric oxide) weighs exactly as much as the mercury and the oxygen which were consumed in making it. We are accustomed to say that the mercuric oxide con- tains mercury and oxygen ; for 2 grammes of oxygen and 25 grammes of mercury are used to make 27 grammes of mercuric oxide ; and we can get 2 grammes of oxygen and 25 grammes of mercury from 27 grammes of the oxide. Weight is, however, the only property in which the com- pound is identical with its constituents ; and it is a charac- teristic of chemical combination that substances acquire new properties on combining with one another, their weight remaining unchanged. In order to decide whether two substances known to be intimately mixed with one another B L INTRODUCTION. are chemically combined or not, it is necessary to ascertain whether each of the substances has got in that mixture the same properties which it has by itself. Thus air is known to contain oxygen and nitrogen in- timately mixed ; but we know that the oxygen is not chemi- cally combined with nitrogen, because the oxygen in the air has the same properties as oxygen by itself, and the nitrogen in the air has the same properties as nitrogen by itself. We know several compounds of oxygen and nitrogen, but each of them has got peculiar properties of its own, different from those of free nitrogen and of free oxygen. A careful examination of numberless processes of com- bination and of decomposition has shewn that all kinds of matter known to us on the surface of the earth are com- posed of a comparatively small number of elements. Thus a piece of white marble can be decomposed into carbonic acid and lime. The first of these can be made from carbon and oxygen, the second from calcium and oxygen. As neither carbon, oxygen, nor calcium can be decomposed so as to yield other substances, they are accordingly the elements of the marble. Pure white sugar can be burnt, and no other products are formed than carbonic acid and water, and these substances are known to consist of carbon, oxygen, and hydrogen. The weight of oxygen in the products is, how- ever, greater than the weight of oxygen supplied during combustion. From these facts we infer that sugar contains the elements carbon, hydrogen, and oxygen. Chemists have found that all well-known substances are built up of small particles of elementary matter. These particles can be united with one another and separated from one another; but in no case has any one of them been broken up into smaller particles, nor built up from smaller ones. They are accordingly called atoms. The absolute weights of atoms have not yet been ascertained ; but 2 INTRODUCTION. chemists have proved that the atoms of hydrogen are lighter than those of any other element, and they have discovered how many times heavier each elementary atom is than an atom of hydrogen ; thus we know how many times heavier an atom of carbon is than an atom of hydrogen ; and the so-called 'atomic weight' of carbon is a statement of that ratio for carbon. In like manner we know how much heavier an atom of oxygen is than an atom of hydrogen. The atomic weight of each element is the ratio of the weight of its atom to that of hydrogen. These atomic weights have been found by comparing the different pro- portions in which different elements combine ; but the evidence upon which they rest can only be understood by those who know accurately the particulars of the very numerous chemical processes from the comparison of which they are derived. It is worthy of remark that philosophers (such as Descartes) had supposed that matter must be built up of atoms, long before Chemistry gave a definite experi- mental basis to the idea. The atomic theory as now used by chemists is a generali- zation of a well-established experimental fact. We assume that all substances are built up of atoms in the same sort of way in which every well-examined substance is found to be built up of atoms. It is a fact that carbon in those processes of chemical change which are accurately known has not been further divided than into particles twelve times as heavy as the smallest particles of hydrogen ; and we as- sume that the same peculiarity of carbon must belong to it in those other compounds which are as yet little known to us, or are entirely unknown. When a chemist investigates any new compound of carbon he has present to his mind the peculiarities which the element has been found to exhibit in its known compounds, and of them the atomic weight is one of the most important. The 'theory' leads him to expect B 2 3 INTRODUCTION. and to find many important truths which would escape notice if he did not look for them; and it is more and more trusted in proportion as it has been found to be a useful and faith- ful guide. Respecting the constitution of the elementary atoms chemists know nothing. Whether each atom is in itself an aggregate of smaller particles, or whether it is in its very nature indivisible, are questions upon which the chemical theory has at present no hold. The chemist cannot break up an atom of carbon or of oxygen any more than an astro- nomer can break up the planet Mars or Jupiter. But there is no reason to suppose the elementary atoms incapable of subdivision by processes beyond our present reach, any more than there is reason to suppose that the planets might not be divided into smaller masses. The atomic theory has been gradually consolidated and extended since Dalton established its first principles, and it has received particularly important additions of late years. Still it is but a beginning of a theory of chemical action. Many and many a patient and accurate worker and thinker will add his mite of facts and of ideas to the store, before the full and exact theory of the constitution of matter is established. Every student of the science should strive to learn how to draw his ideas from experiment, the fountain-head of knowledge, and for that purpose he cannot do better than study how our present stock of ideas in Chemistry has been derived from experiment. He ought to accumulate more and more exact knowledge of the characteristic re- semblances and distinctive differences among substances, stopping every now and then to look over the facts which he has accumulated, and to arrange them according to their resemblances. He will thus rise gradually to general theories in a sound and useful manner. 4 CHAPTER I. 1. Oxygen a is most conveniently prepared by heating pure potassic chlorate (chlorate of potash) in a glass flask Preparation of Oxygen. a Flask containing chlorate ; b Griffin's trough ; c jar collecting the gas ; d bent tube. or tube. The salt first melts and then appears to boil, the bubbles which come off from it, being oxygen, are a The symbol for the atom of oxygen is O, and the weight of the atom denoted by O is 16. The formula of the molecule of oxygen is O 2 . The density of oxygen in th hydrogen scale is 1 6. 5 1 PREPARATION OF OXYGEN. collected by displacement of water in a glass jar inverted in a pneumatic trough. The gas should be tested from time to Enlarged view of jar with its support. time as it comes off, by plunging into it the glowing end of a splint of wood. If the splint burst sharply into flame the gas may be assumed to be pure enough for most purposes. But if the purest obtainable oxygen be required, the operator ought to select a flask only just large enough to contain the quantity of chlorate which he wishes to decompose, and he ought to remove the air from the apparatus before de- composing the chlorate. For this purpose the Sprengel air- pump is employed as shewn in the annexed figure. The drops of mercury which fall successively down the tube of this instrument act like pistons, driving before them the air which enters at the horizontal tube b. When all the air has been pumped out of the apparatus the action of the pump is stopped while heat is applied to the tube containing the chlorate. The oxygen finds a free outlet at the bottom of the pump, and is collected by dis- placement of mercury in a small jar, as by passing through water it would get contaminated by nitrogen which was dis- 6 PREPARATION OF OXYGEN. 1 solved in the water. Some persons recommend the addition Sprengel's Air-pump attached to a small tube evolving Oxygen. a Tube containing chlorate ; b glass tube 'OO2 m diameter ; c funnel containing mercury ; d tube for collecting gas ; e trough of water surrounding an india-rubber joint. 7 1 PREPARATION OF OXYGEN. of a little manganic peroxide to the chlorate which is to be heated, but although the chlorate is thus more rapidly decomposed, the advantage is dearly purchased, for the gas set free is liable to contain chlorine. Pure oxygen is com- pletely absorbed by a solution of pyrogallic acid in strong potash, and whatever remains undissolved by this re-agent (excepting a trace of carbonic oxide) must be some other gas which had been mixed with the oxygen. Potassic chlorate b , if completely decomposed by heat, yields 39.183 per cent, of its weight of oxygen gas, the remaining salt being potassic chloride, a compound of potassium with chlorine. Some of the chlorate employed is however usually carried away by the oxygen in the form of spray, and thus escapes decomposition ; and some oxygen is often retained in the form of potassic per-chlorate, a salt which requires for its decomposition a higher temperature than that at which the chlorate is decomposed. When oxygen is wanted in very large quantities, it is more economically prepared by heating a mineral called ' Man- ganese.' The process is performed in a stone -ware retort similar to those used for making coal gas. The mineral consists of the metal manganese combined with oxygen, but the utmost heat is unable to drive off more than one-third of the oxygen contained in the pure mineral c . 2. Oxygen is a component of atmospheric air, and can be prepared from it in a pure state. An experiment of Lavoisier's shews this result in a very interesting form. Mer- cury is boiled in a convenient vessel containing say 100 cubic centimetres of air, care being taken that no air shall escape. A red powder is formed by combination of some b A molecule of potassic chlorate is represented by the formula KC1O 3 . The decomposition which this salt undergoes is represented by the equation KClO 3 = KCl-i-3O. c The action of heat upon the ' manganese ' is represented by the equation 8 OXYGEN MADE FROM AIR. 2 of the mercury with oxygen, and if the process be allowed to continue about twelve days the mercury will absorb nearly Lavoisier's Preparation of Oxygen from Air. a Flask containing air and mercury and communicating with the air in the jar b. all the oxygen contained in the air. If the oxygen were completely removed, the residual gas would measure rather less than 80 cubic centimetres; so that oxygen constitutes rather more than one-fifth of the volume of atmospheric air. A burning taper plunged into the residual gas goes out. While losing its oxygen the air has lost the power of supporting combustion. When the red compound of mer- cury and oxygen is heated to a temperature sufficiently above that at which it was formed, it is decomposed into metallic mercury and oxygen d ; and if this oxygen be returned to the air from which it had been removed by the action of mercury, it restores to the air the power of supporting combustion. 3 COMBUSTION IN OXYGEN. 3. Iron wire can be lighted in an atmosphere of oxygen, by fixing a piece of tinder to its end, and kindling it before it is put into the gas. The iron burns with great intensity, while white hot globules are formed at the end of the wire, and increase in size till they drop off. These globules con- sist of iron combined with oxygen e . Phosphorus also burns in oxygen with great intensity. A small piece of that substance ought to be carefully dried, and put into a little copper spoon. It can very easily be lighted by a match while still surrounded by air, and if then lowered into a jar of oxygen it immediatery burns with far greater brilliancy and rapidity than in air, and gives off a dazzling light A -white powder called phosphoric acid is formed in this process, by combination of the phosphorus and oxygen f . When sulphur is burned in oxygen there is no solid or visible product formed, and the blue flame which is produced during the process is far less luminous than the white flame of the burning phosphorus. In proportion how- ever as the combustion proceeds the oxygen disappears, and in its place is found a gas of an exceedingly powerful and well-known smell. This gas, called sulphurous acid, is a compound of sulphur and oxygens. The combustion of charcoal affords another interesting instance of combination with oxygen. A piece of light wood charcoal should be selected for the purpose, and in proportion as it burns away, a gas is produced containing carbon combined with oxygen 11 , and possessing feebly acid properties. This gas (called carbonic acid) is readily ab- sorbed by caustic potash, and can thus be separated from oxygen. Metallic sodium burns very vividly in oxygen, forming a white powder which can easily be dissolved in water with effervescence. 10 DENSITY OF OXYGEN AT VARIOUS TEMPERATURES. 5 4. In all these processes of combustion there are pro- ducts formed which weigh exactly as much as the materials used in their formation ; and in no case of combustion is there a destruction of materials. Every kilogramme of sul- phur which is burnt takes up a kilogramme of oxygen, forming 2 kilogrammes of sulphurous acid; and if this sulphurous acid were collected, the sulphur could be reco- vered from it. In like manner every kilogramme of carbon fully burnt forms 3 kilogrammes of carbonic acid, by com- bining with 2 kilogrammes of oxygen, and both the carbon and oxygen can be got out of this compound by suitable processes. But except in the one particular of weight, these pro- ducts have different properties from the materials which formed them ; and the object of chemistry is to explain the changes of property which substances undergo by acting on one another. 5. Oxygen is a colourless gas devoid of taste and smell. It is a little heavier than atmospheric air. It is 1 6 times as heavy as hydrogen at the same temperature and pressure, and is accordingly described as having a density equal to 16 when that of hydrogen is represented by unity. Air is only 14.45 times as heavy as hydrogen. In the metrical system, which is the most convenient for calculations, the volume of a fixed weight of oxygen is thus stated: 16 grammes of oxygen measure 11.19 or very nearly IT. 2 litres at oC, and 760 millimetres of mercury pressure. The same measure (11.2 litres) of water of the maximum density weighs nearly 700 times as much; so that under these conditions of temperature and pressure oxygen has about T ig- the density (or specific gravity) of water. In grains and cubic inches the same relation may be thus stated : 1 6 grains of oxygen at oC and 29.9 inches pressure measure 44.473 cubic inches. When 100 measures of oxygen are ii 5 EFFECT OF PRESSURE. measured off at oC and then heated to iC they become 100.3665, when heated to 2C they become 100.7330, and so on, gaining .3665 for every degree rise of temperature counted from oC. It follows from this, that if 100 volumes of the gas were measured off at T5C, and then heated to j 6C, the increase of volume would be found by the follow- ing proportion: 1004- 15 x .3665 : 100+ 1 6 X-3665 = 100 : AT, or 105.4975 : 105.8640 = 100 : x, which gives us for the volume at i6C, .#=100.34. 6. If -oxygen were kept at the same temperature and sub- jected to greater and greater pressure, it would diminish in volume in proportion to the increase of pressure. Thus if a litre of oxygen were measured off in stormy weather while the barometer stood at 700 millimetres, and then put aside and measured at the same temperature, but after the barometer had risen to a height of 750 millimetres, it would be found to have diminished in volume in the proportion of 75 to 70, and would only measure 0.933 of a litre. It is convenient to state this law thus : the density of oxygen at a given temperature is proportional to the pressure to which it is subjected. By exposure to a pressure of about 300 atmospheres, oxygen has been reduced to -g-^-Q of its ordinary volume, but further pressure did not appear to pro- duce a corresponding diminution of volume. When oxygen is heated and yet not allowed to expand, it presses against the sides of the vessel in which it is contained with an amount of force which increases, with rise of temperature, in the same proportion in which ex- pansion takes place under constant pressure. Thus if we measure out i litre of oxygen at the temperature of oC, and if while heating the gas to 1 5C we wish to prevent it from expanding, we must increase the pressure upon it in round numbers in the proportion of 273 to 273 + 1 5. If at 12 RELATIONS TO ANIMALS AND PLANTS. 8 the commencement of the experiment a barometer in the same room stood at a height of 760 millimetres, the litre of oxygen was under a pressure of the air equal to a column of mercury 760 millimetres (or 30 inches) high; and the pres- sure required to prevent the air from expanding whilst it is being heated is found by the proportion: 273 : 288 = 760 : x which gives us x =801.7; so that we must increase the atmospheric pressure by an amount equal to a column of mercury rather more than 41 millimetres high to keep our oxygen to the bulk of a litre when it is heated from oC to isC. 7. Oxygen is absorbed by venous blood, and imparts to it a bright red colour. Carbonic acid is given off at the same time that the oxygen is absorbed. The respiration of animals takes place quite freely in oxygen, but the pure gas has too stimulating an action, and soon disturbs the regular working of the process, by inducing too rapid an oxidation for the requirements of the system. Fresh leaves of plants give off oxygen, when placed in the sunshine, in contact with carbonic acid. 8. Ozone. Under particular conditions, the oxygen which is given off in the decomposition of dilute sulphuric acid by the galvanic battery is found to have a sickly smell, owing to the presence in it of a substance of more actively oxidizing properties than ordinary oxygen. The same sub- stance is said to be formed by the action of an electrical brush discharge on pure oxygen. It is destroyed by passing the oxygen containing it through a glass tube heated to redness by a lamp ; and by contact with india-rubber, or cork, or any other vegetable or animal substance, it is immediately destroyed, producing water and carbonic acid, by the oxida- tion of the hydrogen and carbon of the vegetable substance. Even metallic silver is transformed into an oxide by contact with this powerful substance. 13 8 APPENDIX TO CHAPTER I. Until the substance is isolated and 4 fully examined, we cannot with certainty pronounce upon its nature, but some chemists are of opinion that it is nothing else than oxygen which has undergone a change of properties. The very great majority of the compounds of oxygen hold that substance so firmly that it cannot support combustion so easily as in the free state ; but there are some compounds of oxygen in which it has more active combining tendencies than in the free state, and some of them are known to produce effects similar to those by which ozone is usually tested. The atmosphere is said by some persons to contain ozone, when paper moistened with potassic iodide and starch turns blue by contact with it. Appendix to Chapter /. PROBLEMS. 1. What weight of oxygen is contained in one kilo- gramme of potassic chlorate? 2. ico litres of oxygen at oC, and 760 millimetres baro- metric pressure, are wanted. How much potassic chlorate must be decomposed for its production, assuming that all the oxygen can be expelled from the salt ? 3. 30 litres of oxygen were measured off at i5C. What would be the volume of the gas at oC, the pressure remain- ing unchanged? 4. What weight of oxygen is required to fill a globe of 13 litres capacity, at the temperature of 1 2C, and at the normal barometric pressure ? 5. 10 litres of oxygen are measured off at i4F. Required the volume of the gas at J5C. 14 APPENDIX TO CHAPTER 7. 6. 230 cubic centimetres of oxygen are measured off at i4C and 740 millimetres mercurial pressure. Required the volume of the gas at the normal temperature and pressure (oC and 760 millimetres). 7 . 43 grammes of oxygen were measured off at the normal pressure, and at a temperature such that their density was 18. Required the volume of the gas in litres, and the temperature at which it was measured. 8. A flask is filled with oxygen at oC, at 760 mm. pres- sure, and the flask is then tightly corked. The flask would burst if exposed to an outward pressure of 1500 mm. At what temperature would the oxygen exert this pressure, as- suming the capacity of the flask to remain unaltered ? 9. A litre of oxygen is confined in a glass flask at ioC by the atmospheric pressure, added to that of a column of mer- cury 60 millimetres high. The flask must be heated to 3ooC, without any increase of volume taking place in the oxygen. How high must the column of mercury then be which presses on the gas, supposing the atmospheric pressure to remain constant at 760 mm. ? 10. A litre of oxygen is required of the density of 100 at oC. What weight of potassic chlorate must be used for its preparation, and what total pressure must be applied to it ? PREPARATION OF HYDROGEN. CHAPTER II. 9. Hydrogen i is most conveniently prepared by pouring upon metallic zinc a very acid salt called hydric sulphate previously mixed with three or four times its volume of water .i. The gas comes off from the surface of the zinc and can be collected in the same way as oxygen. The process by which it is here given off is illustrative of the chemical nature of hydrogen, for the hydric sulphate consists of hydrogen combined with sulphur and oxygen, and the metal zinc actually pushes the hydrogen out of this compound and takes its place k . It will be seen that there are many other cases of a metal combining with the same elements as hydrogen. If a sufficient quantity of zinc be used to expel all the hydrogen from the sulphate employed in the experi- ment, it will be found that the liquid left in the bottle con- sists of a solution of a compound of zinc with sulphur and oxygen, called zinc sulphate. This salt can be obtained in the form of beautiful white crystals, by carefully evaporating off the water until the solution, on cooling, deposits some of the substance dissolved in it. Iron wire also dissolves in dilute hydric sulphate, giving off hydrogen gas, and forming i Atomic symbol H = I. Molecular formula H 2 . 11.19 litres of hydrogen weigh one gramme at oC, and an atmospheric pressure equal to 760 milli- metres of mercury (32F. and 30 inches). i This acid salt is often called sulphuric acid, a name which belongs to another compound obtained from it by the removal of the elements of water. 16 PURIFICA TION OF HYDROGEN. 10 a crystallizable salt, called ferrous sulphate, consisting of iron combined with sulphur and oxygen 1 . But the hydrogen prepared by the use of iron, usually has an unpleasant smell, owing to the presence in it of a compound of carbon and hydrogen. Sulphur, phosphorus, and arsenic are not uncommon impurities in hydrogen, and the vapour of water necessarily accompanies it from the generating flask. 10. To remove these impurities the gas should be passed slowly through a tube containing pieces of pumice-stone moistened with a solution of argentic nitrate, which keeps back the sulphuretted hydrogen, phosphuretted hydrogen, and arseniuretted hydrogen; and through a second tube containing pumice moistened with strong oil of vitriol, which absorbs the moisture in the gas. Many metals are capable of decomposing water and liberating hydrogen from it, just as zinc and iron decom- pose hydric sulphate" 1 ; but some of these metals, such as potassium and sodium, are too expensive to be used in the common preparation of the gas ; and others, such as iron n , only decompose water at high temperatures, which it is not always convenient to employ. In order to prepare hydrogen in small quantities free from any other impurity than moisture, an apparatus of the con- struction represented in the annexed woodcut is used with ad- vantage. It contains the same materials as those employed in the process just described, but the metallic zinc is dissolved in mercury before acting on the hydric sulphate. The action continues as long as mercury containing zinc is connected by a wire with the platinized silver plate e, and it ceases as soon as that contact is interrupted. The plate of platinized silver remains unchanged, and the bubbles of hydrogen are given off from its surface. The impurities contained in the i Fe + H 2 SO* = FeSO* + H 2 . Na 2 + 2H 2 O = aNaHO + H 2 4H' 2 . 17 10 PROPERTIES OF HYDROGEN. metallic zinc which in the ordinary form of apparatus would pass over into the hydrogen, are here left behind, as they are not soluble in the mercury. Apparatus for evolving pure Hydrogen. a Mercury containing metallic zinc ; b copper wire surrounded by glass tube ; c coiled plate of platinized silver ; d wide tube dipping into the mercury containing strip of zinc ; e tube for escape of hydrogen. The theory of this instrument will be understood by those who are acquainted with the laws of galvanic action. 11. Hydrogen, when collected pure, does not explode, but burns quietly when ignited. Mere traces of oxygen can be discovered in it by a diminution of the volume of the gas subjected to the prolonged action of electric sparks in a tube over mercury. Hydrogen is the lightest substance known, i gramme of it measures exactly as much as 16 grammes of oxygen, viz. 18 PROPERTIES OF HYDROGEN. 11 11.19 litres, so that oxygen is 16 times as heavy as hydro- gen. One grain of hydrogen at oC and 760 millimetres pressure measures 44.473 cubic inches. Hydrogen has less than T V the density of air (y^^g-), and it accordingly tends to rise to the top of any vessel containing air. Thus a glass bell-jar, suspended with its mouth downwards, may be filled a Bottle for evolving Hydrogen ; b bell-jar for collecting Hydrogen by displacement of air. with hydrogen by leading a rapid current of the gas up to the top of the bell-jar, by a tube, as shewn in the annexed figure. That the hydrogen remains for a short time in the 02 19 11 DIFFUSION OF HYDROGEN. bell-jar can be proved by passing a lighted taper up into it, when the taper is extinguished but sets fire to the hydrogen. Its extreme lightness makes this gas particularly suitable for filling balloons. Hydrogen conducts sound very feebly, as it is easy to prove by agitating a small bell in a jar full of the gas, and then agitating it in a similar jar full of air. 12. It is the most difficult gas to keep, for its particles are so exceedingly light and mobile that they find their way out through any crack or imperfect joint more rapidly than any other particles. This important pro- perty is well illustrated by the processes of dif- fusion. If hydrogen be contained in a bell- jar, of which the mouth is closed by a porous disc of plaster of Paris, whilst the narrow opening dips into water, the gas escapes through the porous disc so much more rapidly than the outer air can get in through it, that a partial vacuum is produced, and the water is rapidly sucked up into the bell-jar. It might be supposed that a mixture of oxygen and hydrogen would gradually separate, the heavy oxygen falling to the bottom of the vessel, and the hydrogen rising to the 20 Diffusion of Hydrogen. a Glass containing coloured liquid ; b jar closed at top by a porous disc. FORMATION OF WATER (H* 0). 13 top. Not only does no such separation of these gases by subsidence occur, but if a flask full of hydrogen be con- nected tightly, by means of a long narrow tube, with a second flask containing oxy- gen, and the tube placed in a vertical position, with the hydrogen in the upper flask, and the oxygen in the lower one, it is found that the two gradually but completely mingle, in opposition to the action of gravitation. 13. When a cold glass bottle is passed over a flame of hydrogen, it becomes coated with a dew-like film of moisture, which is formed by the combustion of the hydrogen, and at the same time the air loses some of its free oxygen. In order to prove that the combination of hydrogen and oxygen does form water, it is sufficient to heat some cupric oxide in a glass tube, and pass pure hy- drogen slowly over -it. The black oxide is speedily changed to red metallic copper, while the oxygen carried away from it by the hydrogen forms water which can be collected. The cupric oxide is obtained by burning metallic copper in the air. By taking due precautions the reduction of the oxide can be conducted in such a manner as to shew exactly the weight of oxygen taken from the cupric oxide, and the 2 [ Apparatus to shew the Mixing of Gases by Diffusion. a Flask full of oxy- gen ; b flask full of hydrogen. 13 FORMATION OF WATER (H 2 0). weight of water formed by the combination of this oxygen with hydrogen; and it will then be found that every 8 Apparatus for the reduction of Cupric Oxide by Hydrogen and for collecting the water. a Bottle for evolving hydrogen ; b c tubes containing mate- rials for purifying and drying the gas ; d tube containing cupric oxide ; e tube for collecting the water. grammes of oxygen taken from the copper form 9 grammes of water . So that -- of the weight of water is due to hy- drogen, and f of its weight to oxygen. 14. Another way of arriving at the same result is to mix Oxygen and hydrogen, in the proportion of one measure of oxygen and two measures of hydrogen, and to fire the mix- ture by means of an electric spark in a strong glass vessel. After the explosion there will be no free hydrogen and no free oxygen left, nothing but water formed ; whereas, if more than twice as great a volume of hydrogen be taken as of oxygen, the excess above the two volumes is left uncom- bined. By no expedient can the gases be got to combine 22 OXY HYDROGEN GAS. 15 directly with one another in any other proportion than that of one volume of oxygen to two volumes of hydrogen. Now we know that one volume of oxygen is sixteen times as heavy as one volume of hydrogen, and it follows that one volume of oxygen is eight times as heavy as the two volumes of hydrogen with which it combines to form water. The com- bustion of hydrogen in air is nothing else than a process of combination of hydrogen with the oxygen of the air, forming water, and every cubic centimetre of oxygen supplied by the air unites with 2 cubic centimetres of hydrogen. A mixture of oxygen and hydrogen in these proportions is called oxy-hydrogen gas. It could be distinguished from steam by the following amongst other differences : OXY-HYDROGEN GAS. 1. Has a density of 6. 2. Allows hydrogen to diffuse out more rapidly than oxygen. 3. Explodes when sufficiently heat- ed, forming steam. 4. Cannot be condensed by cold and pressure to the liquid state. 5. Allows its oxygen to be absorbed in the cold by phosphorus, pyrogallate, nitric oxide, &c. 6. Is not absorbed, by oil of vi- triol, calcic chloride, or phos- phoric acid, &c. STEAM. 1. Has a density of 9. 2. Does not allow its hydrogen to diffuse out from its oxygen. They go together uniformly. 3. Expands when heated, and re- turns on cooling to original state. 4. Is easily condensed to water. 5. Does not give its oxygen to any of these re-agents. 6. Is readily absorbed by any of these re-agents. 15. The combination of oxygen and hydrogen is accom- panied by the evolution of intense heat ; and a flame of hydrogen, fed with oxygen in the proper proportion, in a suitable burner, is used for very strong heating effects. It is generally known by the name of the oxy-hydrogen burner. A piece of lime held in the flame becomes heated to so intense a white heat as to be valuable as a source of light. One kilogramme of hydrogen gives off on combining with 23 15 PURIFICATION OF WATER. the requisite weight of oxygen (8 kilogrammes), enough heat to warm 34,462 kilos, of water from oC to iC, or what is usually called 34,462 'degrees of heat' (not degrees of temperature). 16. Water is seldom found in nature in a state of purity. The peculiar qualities which belong to some waters are owing to the presence of foreign substances dissolved in them. Thus sea water contains from 3.5 to 4 per cent, of its weight of salts, which are left behind w r hen the water itself is driven off by heat. These salts consist chiefly of sodium, potassium, magnesium, and calcium, combined partly as chlorides, partly as sulphates. Spring water presents the greatest varieties of composition, according to the nature of the soil through which it has percolated and the substances which it has taken up. Among mineral waters which are too strongly impregnated with foreign matter to be suitable for domestic use, and are confined to medical use, chalybeate waters are those which contain iron, hepatic waters contain sulphuretted hydrogen, whilst carbonic acid gas imparts to the waters which come in contact with it at high pressures the property of effervescing. Most kinds of spring water contain lime in solution, and possess the property of * hard- ness' in consequence of this lime. The hardness of water is measured by * degrees/ each degree representing i part by weight of carbonate of lime in 100,000 parts of water. 17. In order to remove mechanical admixtures with which it may happen to be contaminated, water is filtered ; but for the removal of dissolved solid matter the process of distilla- tion is most convenient. In chemical laboratories, where water is constantly used for operations in which the presence of lime, &c. would be perfectly inadmissible, spring water is usually distilled in an iron boiler, and condensed in a coil of copper tubing lined with tin. The spray which is usually carried up by the 24 DECOMPOSITION OF WATER. 18 steam from the surface of the water, ought to be allowed to collect in an intermediate chamber before the pure steam passes on to the condenser. At sea it is now becoming more and more customary to distil sea water for the use of the crew or passengers ; but when first collected from the condenser, the water, however free from saline impurities, has a peculiar sickly flavour which renders it unfit for drink. This flavour is completely re- moved by the customary practice of passing the water through a filter containing animal charcoal, and the water becomes charged at the same time with air, or ' aerated.' For domestic use, water should be kept in wooden or iron cisterns. Zinc is also used sometimes with advantage; but the use of leaden cisterns is exceedingly dangerous, especially for keeping rain water, and ought under no circumstances to be permitted. 18. It was stated above that water is the sole product of the combination of oxygen and hydrogen, and by its de- composition the oxygen and hydrogen can be recovered again, in their original quantity and with unaltered properties. The easiest way to decompose water, for the preparation of free oxygen and hydrogen, is by the action of a strong galvanic current, on a mixture of water with hydric sulphate. The wires which conduct the current should consist of platinum, and oxygen gas collects on the surface of one of them, rapidly rising in bubbles through the liquid, while hydrogen rises from the surface of the other. A small loss of oxygen usually occurs, but the gases are nearly in the proportion of one volume of oxygen to two volumes of hy- drogen if collected carefully. This fact of the decomposition of water into two sub- stances is an evidence of its containing two kinds of matter united together. Oxygen and hydrogen unite with one another to form water, and both of them can be recovered 25 18 COMPOUNDS OF OXYGEN. again from the water. Water is accordingly called a com- pound of oxygen and hydrogen. Oxygen has not ever been separated into different substances, and for this reason it is called an element. It undergoes various changes of property according to the conditions in which it is placed ; but it resumes its original properties without difficulty when these conditions are reversed. All the more permanent changes which oxygen undergoes are due to processes of combination like those mentioned above, where it unites with other substances forming compounds from which it can be recovered again. Similar facts prove hydrogen to be an element. Chemical investigations have proved the existence of sixty-two elements, and every substance which has been examined is found to consist of one or more of these elements. A list of the elements is given in 92, and appended to the name of each element is a symbol de- noting a particular weight of that element, called its atomic weight. When steam is passed through a tube intensely heated in a furnace, some of it is decomposed; but in order to collect any quantity of oxygen and hydrogen, it is necessary to separate them from contact with one another as soon as they are formed, as they would otherwise recombine. For this purpose the tube through which the steam passes is made of a porous material (unglazed earthenware) and is surrounded by a larger tube P. P There are other compounds of oxygen analogous in their constitution to water, such as Nitrous oxide, N 2 O. Hypochlorous acid, C1 2 O. Silver oxide, Ag 2 O. Potash, K 2 0. Soda, Na 2 O. A second class of oxides is represented by the following bodies, viz. Hydric peroxide H 2 O 2 , 4 Silver peroxide Ag 2 O 2 . Sodic peroxide Na 2 O 2 . 26 COMPOUNDS OF WATER. 19 19. Water combines with a great variety of substances, and the term Hydrate is used to designate a compound of water. Thus quick lime (calcic oxide) if merely moistened with water exhibits appearances which may be compared to combustion. Intense heat is evolved, and the light powder which is formed by the combination of the lime with A third class is illustrated by the following oxides, viz. Carbonic oxide, CO. Stannous oxide, SnO. Platinous oxide, PtO. Mercuric oxide, HgO. Plumbic oxide, PbO. Cupric oxide, CuO. Ferrous oxide, FeO. Manganous oxide, MnO. Cobaltic oxide, CoO. Nickelic oxide, NiO. Zinc oxide, ZnO. Baryta, BaO. Strontia, SrO. Lime, CaO. Magnesia, MgO. The fourth class is composed of oxides more acid in their properties, such as Carbonic acid, CO 2 . Sulphurous acid, SO 2 . Silicic acid ]n- , or Silica f bl Stannic oxide Sn O 2 . SiO 2 . The fifth class is represented by Nitrous acid, N 2 O 3 . Chlorous acid, C1 2 O 3 . Phosphorous acid, P 2 O 3 . Boracic acid B 2 O 3 . Arsenious acid, As 2 O 3 . Antimonious acid, Sb 2 O 3 . Platinic oxide, PtO 2 . Plumbic peroxide, Pb O 2 . Manganic peroxide, Mn O 2 . Barytic peroxide, BaO 2 . Bismuthic oxide, Bi 2 O 3 . Ferric oxide, Fe 2 O 3 . Manganic oxide, Mn 2 O 3 . Chromic oxide, Cr 2 O 3 . Alumina, A1 2 O 3 . The sixth class is less numerous : it contains Nitric peroxide, N 2 O 4 . Chloric peroxide, C1 2 O*. The seventh class consists of acids, such as Potassic peroxide, K 2 O*. Nitric acid, N 2 O 5 . Phosphoric acid, P 2 O 5 . Arsenic acid, As 2 O 8 . The eighth class also consists of acids Sulphuric acid, SO 3 . Selenic acid, SeO 3 . Telluric acid, TeO 3 . Antimonic acid, Sb 2 5 . Jodie acid, J 2 O 5 . Molybdic acid, MoO 3 . Tungstic acid, WO 3 . Chromic acid, CrO 3 . 2? 19 COMPOUNDS OF WATER. the elements of water Q is called calcic hydrate, or in common language, 'slaked lime/ The elements of water in this com- pound have properties different from those of uncombined water. They are solid, and not only do they not evaporate at the ordinary atmospheric temperature, and boil at iooC, but it requires nearly a red heat for their expulsion from the compound. When phosphoric acid is moistened with water a similar combination takes place between the two bodies, forming a hydrate r . Soda also combines vigorously with water, forming a compound called sodic hydrate 8 . These hydrates are con- sidered to belong to the general class of compounds called salts. The calcic and sodic hydrates have the power of imparting a blue colour to red litmus-paper, or a brown colour to turmeric. The hydrate of phosphoric acid (called hydric phosphate) has an opposite action, for it restores the red colour of blue litmus or the yellow colour of brown turmeric ; and it is shewn by these properties to be an acid salt. Its taste is sour or acid. Calcic hydrate and sodic hydrate are called basic substances (meaning anti-acid). If either of them be added to a solution of the acid phosphate, its acidity is gradually diminished and may be completely destroyed by the basic substance, whilst the base thus employed also loses its pro- perties. The product thus obtained, if neither acid nor basic, is called neutral. There are many other oxides besides lime and soda which combine with water forming basic salts, and also many which like phosphoric acid form acid salts, when brought in contact with water. Oxides like lime and soda in this respect are called bases. Those like phosphoric acid are called acids. Water is a neutral oxide which does not neutralize the basic pro- Ca O + H 2 = Ca H 2 O 2 . r P 2 O 5 + 3 H 2 O = 2H 3 PO*. 28 EXPANSION OF WATER. 2O perties of bases nor the acidity of acids when it combines with either of them. When salts are decomposed by the galvanic current, acids and bodies analogous to acids make their appearance at the positive pole, and are called electro negative bodies; bases and substances analogous to bases appear at the negative pole and are called electro positive bodies. In some compounds water is contained in a feebler state of combination than when combined with a strong base like lime, or with an acid. For instance, the crystals obtained by evaporating a solution of zinc sulphate contain water which can be driven off by heat, leaving the zinc sulphate anhydrous. This water is called water of crystallization, as it is less powerfully combined with the other materials than the water in hydrates. Water of crystallization possesses properties less different from those of free water than the properties of water contained in hydrates. 20. The effects of heat upon water are very remark- able, and deserve a careful study. If water be cooled to the temperature of oC, which is easily done by stirring it up with pieces of ice and then allowed to absorb heat gradually in a warm room, it will be found that the water diminishes in volume while rising in temperature, and this goes on till the water has attained the temperature of 4C. This is the tem- perature at which water is densest ; for if heated above 4C it expands with every degree of rise of temperature. Thus a litre of water at oC becomes 0.99988 of a litre at 4C, and at 9C it has a volume somewhat greater than its original one, viz. 1.00005. Every degree further rise of temperature causes a greater proportional increase of volume: at i6C the volume of the water is 1.00085 >' at 3C it is 1.00406; at 5oC, 1.01177; at 7oC, 1.02225; at iooC, 1.04299. A litre measured off at 4C expands to 1.0431 15 at iooC. At 4C the litre of water weighs 1000 grammes, called 29 20 APPENDIX TO CHAPTER II. i kilogramme. At i6|C (62F) a gallon of water weighs 70,000 grains, but at 4C the gallon of water weighs 70007.2 grains. When cooled to the temperature of oC, water can be made to give up heat, by contact with substances of a still lower temperature, but it does not for a time become colder by the process. It merely passes into the solid state, or, as we generally say, it freezes. The ice formed is however con- siderably bulkier than an equal weight of water : 94 grammes weight of pure ice occupy the same volume as i oo grammes of water at 4C, thus the density of ice is 0.94. Under favourable conditions the particles of ice arrange themselves at the moment of their formation in the form of regular six-sided prisms. Appendix to Chapter II. PROBLEMS. 1 1 . What is the volume of \ 2 grammes of hydrogen at 1 5C ? 12. 100 cubic metres of hydrogen are supplied at i2C. Wanted, the weight of a balloon which, when filled with the hydrogen, would press upwards with a weight of 20 grammes. 13. At what temperature has air the density which hy- drogen possesses at the normal temperature (oC) ? 14. What loss of weight will 200 grammes of cupric oxide undergo when heated in contact with 2 grammes of hydro- gen ? What weight of water will be formed ? 15. 4 litres of hydrogen at oC and 760 mm. are passed over an excess of red hot cupric oxide. What loss of weight 3 APPENDIX TO CHAPTER II. does the oxide undergo? What volume of oxygen will be wanted to supply the place of that which was carried away by the hydrogen ? 1 6. What volume of air is required for the oxidation of that quantity of metallic copper which is reduced from its o^ide by i o grammes of hydrogen ? 17. 100 cubic centimetres of air are mixed with 50 cubic centimetres of hydrogen, and exploded by the electric spark. What is the volume of the residual mixture after explosion, supposing all the steam to be condensed ? 1 8. What weight of potassic chlorate is required for the evolution of that quantity of oxygen which is needed for the combustion of i o litres of hydrogen ? 19. 20 kilogrammes of water have to be heated from o to iC by the combustion of hydrogen. What weight of hydro- gen is needed for the purpose ? 20. 200 litres of oxy-hydrogen gas are burned. What weight of water can be heated from oC to iC by the heat thus evolved ? 2 r. An iceberg floating freely in sea water of density i .027- is found to have a volume of 30,000 cubic metres above water. What is the total bulk of the iceberg ? 22. A block of Wenham Lake ice weighs 280 kilogrammes. What is its volume ? 21 BOILING-POINT OF WATER. CHAPTER III. 21. When water at iooC is put over a fire, or otherwise exposed to heating action, it passes into steam, without get- ting hotter ; so that a thermometer immersed in the boiling water continues to indicate the temperature of i ooC as long as the steam is being freely formed. Any circumstances, however, which prevent the escape of steam enable water to undergo a rise of temperature when ex- posed to the action of heat. For instance, if the water be heated in a strong iron boiler, of which the outlet cock is closed, so that no steam can escape, the temperature rises above iooC; and if the boiler be strong enough to resist the force with which the steam then presses against its sides, the water may be heated up to 2ooC or 3ooC, and even to still higher temperatures. If the experiment were performed in a boiler heated by a furnace and provided with a safety-valve, and if the valve were loaded more and more heavily, so as to subject the steam to the necessity of overcoming greater and greater pressure in order to make its way out, it would be found that when heated to i 20C, the water would give off steam almost capable of lifting a valve loaded i .033 kilogrammes on the square centimetre (i4 Ibs. on the square inch), and at a very slight elevation of temperature the valve would be lifted, and the water would boil at i2oC. By loading the valve further this ebullition could be stopped, and a load of about 3.1 kilos, on the square centimetre (44 Ibs. on the square inch) would prevent the water from boiling till heated to about 32 DEPENDENT ON PRESSURE. 21 i44C. In like manner it would be found, that at i7oC the tension of the vapour of water is about equal to a pressure of 7.2,3 kilos, on the square centimetre (io2- Ibs. on the square inch). Now if the escape-pipe from the boiler be made to com- municate with a closed condenser, from which all the air has been pumped out, so that steam on making its way from the boiler does not blow into the air, but into an empty space ; it will be found that at the temperature of 100 the water in the boiler just boils when the valve is loaded 1.033 kilo, on the square centimetre (i4 Ibs. on the square inch) ; and at \ 2oC it boils at a pressure of 2.066 kilos. (29 J Ibs.) ; at i44C it boils at 4.13 kilos. (58! Ibs.); and at i7oC it boils under a pressure of 8.26 kilos. (117^ Ibs.) The removal of the atmo- spheric pressure by means of the air-pump is just made up for by an additional load on the valve of 1.033 kilo, on the square centimetre, or 1 4 Ibs. on the square inch, or 21 26.4 Ibs. on the square foot, and we are thus led to infer that the boiling-point of water is the temperature at which the tension of its vapour is able to overcome the atmospheric pressure of 1.033 kilo, on the square centimetre, or nearly 15 Ibs. on the square inch. A very simple experiment confirms the truth of this con- clusion. Introduce a few drops of water into the vacuum of a barometer, as shewn in the annexed figure, and heat the instrument gradually to i ooC by steam. The mercury in the tube will gradually descend, and will stand at the same level inside the tube as outside it, when the water is heated to O/~i ioo C. The tension of the vapour of water at temperatures below iooC is measured by the depression of the column of mer- cury, produced by water heated to measured temperatures in the vacuum above it. In the following table the results of observations of the D 33 21 BOILING-POINT OF WA TER DEPENDENT ON PRESSURE. tension of steam, made at low temperatures by the aid of a barometer-tube, and made at high temperatures in a strong Apparatus for heating water in a barometer. boiler provided with a so-called pressure-gauge, are arranged in order. The numbers given in the columns headed ' Tension in Millimetres' shew the height in millimetres of a column of mercury which could be supported by the steam. 34 SUPERHEATED STEAM. 22 By dividing any one of these numbers .by 760 the amount of tension in atmospheres is obtained. Tension (or Maximum Pressure} of Water-vapour between 32C and + 230^ (Regnaulf). Tem- perature. Tension in Millimetres. Tem- perature. Tension in Millimetres. Tem- perature. Tension in Millimetres. . o -32 0.320 o 55 117.478 o 145 3l 2 5-55 30 0.386 60 148.791 150 3581.23 25 0.605 65 186.945 155 4088.56 20 0.927 70 233-093 1 60 4651.62 15 1.400 75 288.517 165 5274-54 10 2.093 80 354-643 170 5961.66 5 3-"3 85 433-04I 175 67I7-43 o 4.600 90 52.v450 180 7=546.39 + 5 6.534 95 633.778 185 8453.23 10 9.165 100 760.000 190 9442.70 15 12.699 105 906.410 , '95 10519.63 20 I7-39I no 1075.370 200 11688.96 25 23-550 JI 5 1269.410 205 12955.66 30 31-548 1 20 1491.280 210 14324.80 35 41.827 125 1743.880 215 15801.33 40 54.906 130 2030.280 220 17390-36 45 71-39 1 IBS 2353-730 225 19097.04 50 91.982 i 4 o 2717.630 230 i 20926.40 22. When steam is heated by itself, without the presence of any liquid water, it is called superheated steam. But when there is water present, so that no excess of heat can accumu- late in the steam above the quantity needed for its formation, under the pressure at which it exists, the steam is called saturated, meaning saturated with water. And when steam is mixed with small drops of liquid water (visible as fog) it is called wet steam. When saturated steam is heated for a few degrees above the temperature at which it was formed, it expands more than oxygen or hydrogen for each degree of temperature; but at still higher temperatures this anomaly does not exist, and steam then has the co-efficient of expansion D 2 35 22 SATURATED STEAM. 2-y^-. It follows from this that dry saturated steam at i ooC heated to higher temperatures in a closed vessel of sufficient strength, would increase a little more than oxygen or hydrogen in pressure for each degree rise of temperature near the point of saturation. 23. When, however, steam and water together are heated in a closed vessel, every degree rise of temperature causes the evaporation of some additional water into the limited space occupied by the steam, and consequently an increase of the density of the steam. In order to calculate approxi- mately the density of saturated steam at any given tem- perature, it is necessary to ascertain by reference to the table what maximum pressure corresponds to the given temperature ; and starting from the known density of steam at the normal temperature and pressure, to reckon its density at the given pressure by assuming it to behave like oxygen, i.e. to increase in density proportionally to the increase of pressure; then using the ordinary co-efficient of expansion (g-fs), to compute how much the density calculated above would be reduced by heating the vapour from the normal temperature to that at which it has to be calculated. 24. The normal density of steam is best recollected in relation to that of hydrogen ; for when two volumes of hydro- gen weighing 2 grammes are combined with one volume of oxygen weighing 16 grammes, the 18 grammes of steam oc- cupy just two volumes, so that each volume of steam weighs 9 grammes, and steam is therefore exactly nine times as heavy as hydrogen. The proportions by volume in which oxygen and hydrogen combine may be represented gra- phically. Let a square figure be drawn of convenient size to represent one side of a cube of 11.2 litres capacity. This square figure represents a ' volume/ and it may be marked by the symbol and weight of any gaseous volume which has to be 36 EVAPORATION IN AIR. 25 represented. Thus weighing i gramme ; denotes a volume of hydrogen O = 16 denotes a volume of oxygen weighing 16 grammes, &c. The combination of hydrogen with oxygen is represented by the diagram H 2 H 2 O which tells us that two volumes of hydrogen each weigh- ing i gramme unite with one volume of oxygen weighing 1 6 grammes to form two volumes of steam each weighing 9 grammes. If it were required to calculate the density of saturated steam at 1 50, we should find by reference to the table that the tension corresponding to i5oC is about 4^ atmospheres, or 4.71 kilogrammes on the square centimetre (4! times i4flbs. on the square inch). The increase from the normal atmospheric pressure of 1.033 to 4-7 T kilos, will increase the density in like proportion, raising it from 9 to about 42. But the rise of temperature from o to i.$o C will diminish this density in the proportion of 154.97 to loc, i.e. from 42 to 27. i . So that 27.1 is the approximate density of saturated steam at 1 50, according to calculation. 25. When water evaporates into air, it is generally stated that it evaporates as into a vacuum; but this statement requires explanation. Suppose that a litre-flask were taken full of air at the pressure of 760 millimetres, and at the 37 25 EVAPORATION IN AIR. temperature of i5C, and that water were allowed to evaporate into this air until it was saturated with moisture at the same temperature. It is quite true that the litre-flask would then contain the same weight of steam as if no air were there. This weight can be ascertained by a calculation perfectly similar to that shewn for the weight of one volume of steam at i5oC, and it will be found that at i5C, and the cor- responding pressure of 12.7 millimetres, the density of steam is 0.1425; so that Ti.2 litres weigh 0.1425 gramme, and i litre of it weighs 0.0127 gramme. The aif in the flask continues to exert its original pressure, equal to 760 milli- metres of mercury, on the flask sides, and the pressure of the steam is added to that, making the whole pressure 760-1-12.7 = 772.7 millimetres. When, on the other hand, bubbles of air pass through water in an open vessel, the moist bubbles which are formed expand immediately to a greater volume than the dry air from which they were formed, by the addition of steam. The moist air is therefore at the same pressure as the original dry air, but has gained in volume as much as, if enclosed in a flask, it would have gained in pressure by taking up steam. Thus, if a litre of air at i5C and 760 millimetres mercurial pressure bubbled through water at 15 in an open vessel, the moist bubbles formed would occupy a volume greater than the litre in the proportion of 760 and 772.7, viz. 1.0167 litre, while remaining at the same temperature. The pressure exerted by a bubble of air is equal to that of the surrounding atmosphere upon it, and is therefore measured by the barometer. This barometric pressure we may call B, and the tension of the steam corresponding to the temperature of the experiment may be called T. Then the air in the moist bubbles has a pressure B T, while the tension of the steam makes up the loss of pressure caused by the expansion of the air. 38 WATER DISSOLVES AIR. 26 The boiling-point of water was described above as the temperature at which the tension of steam is equal to the atmospheric pressure, so that the slightest addition of heat to any part of the water causes it to form bubbles of steam, and to lift the atmosphere enough to make room for those bubbles. But when water evaporates into oxygen or hydro- gen gas at constant pressure, and forms a mixture of greater volume than the original dry gas, there is truly a lifting of the atmosphere to make room for the steam thus formed, as much as if it were by itself and unmixed with the perma- nent gas. So that at temperatures below its boiling-point water does evaporate, and lift the atmosphere, if in sufficiently close contact with a permanent gas ; but only to such an extent that its volume, calculated at atmospheric pressure, stands to the volume of the permanent gas in the same proportion as the tension of the steam stands to the barometric pressure. Thus, at ioC the tension of steam is equal to 2.093 millimetres of mercury. A litre of dry air at the barometric pressure of 760 millimetres, in contact with ice at ioC, . 1000 x 2.093 would cause the evaporation ot - - cubic centi- metres of steam. 26. When aerated water is gradually heated in a glass vessel it gives off small bubbles of air before actually begin- ning to boil ; and it must be kept briskly boiling for several hours, and cooled in a vessel to which atmospheric air has no access, if wanted perfectly free from air. If then brought in contact with oxygen gas at oC, it would dissolve about 4 per cent, of its volume of that gas. At ioC it dissolves only 3^ per cent, of oxygen, and at 2oC about 2.8 per cent. This dissolved oxygen is driven out again, with its original properties, by prolonged boiling. Hydrogen is rather less than half as soluble as oxygen at oC ; for i oo volumes of water take up, according to Bunsen, 39 26 APPENDIX TO CHAPTER III. 1.93 volumes of hydrogen, but at 10 and 20 the same volume is dissolved. Whether the experiment is tried at the atmospheric pressure or at a higher pressure, water still dis- solves these same volumes of the gases and weights propor- tional to the pressure. Hence it is that water saturated with oxygen under pressure effervesces as soon as the pressure is removed, and only retains in solution the quantity of gas corresponding to the lower pressure. Appendix to Chapter III. PROBLEMS. 23. Ascertain from the tables the tension of steam at the following temperatures, viz. 7oC, i2oC, i4oC, i8o c C; and calculate the density corresponding to each of these temperatures. 24. What is the density of steam at 760 mm. pressure, superheated to 2ooC ? 25. A room contains 83 cubic metres of air, saturated with moisture at i2C and 760 mm. pressure. What would be the volume of the air by itself, at the same temperature and pressure, after removal of the moisture ? 26. A glass globe of 10 litres capacity is full of dry air at iooC and 760 mm. pressure. Water is forced into it as long as it evaporates, the temperature being kept at 100. What will be the tension of the moist air ? 27. A mixture of air and steam is wanted containing one volume steam to two volumes air; and in order to obtain such a mixture it is proposed to bubble air through water kept uniformly at a temperature such that its vapour has the tension necessary. What is the temperature to which the water must be heated? 40 APPENDIX TO CHAPTER III. 28. A subterranean cavity contains 30 cubic metres of water, at the temperature of ioC. Hydrogen gas is bub- bling through this water, and escaping afterwards at a pres- sure equal to 7,600 mm. of mercury. What weight of hydrogen will be dissolved in the water when it is fully saturated ? 27 SPECIFIC HEAT OF STEAM. CHAPTER IV. 27. The quantity of heat which water requires in order to undergo a rise of temperature of one degree centigrade is used as a measure of the quantity of heat which other sub- stances require for iC elevation of temperature, and the term ' one degree of heat' means that quantity which heats i kilogramme of water from oC to iC. A kilogramme of oxygen undergoes i rise of temperature by about ^ of a degree of heat ; that is, it needs only about enough heat to warm i of a kilogramme of water from oC to iC. The number 0.2182 represents the exact quantity as determined by Regnault, and is usually referred to as the specific heat of oxygen. Hydrogen has the highest specific heat of all known substances, the co-efficient being 3.4046. It is con- venient to represent the specific heat of these two gases by volume instead of by weight; and as 16 parts by weight of oxygen occupy the same volume as i part by weight of hydrogen, we have only to multiply by 16 the specific heat of oxygen, in order to get the quantity of heat absorbed by 1 6 kilos, of oxygen, which are equal in volume to i kilo, of hydrogen. Now 16 x 0.2182 = 3.4912, which is nearly the same as the heat absorbed by an equal measure of hydrogen. The specific heat of steam is 0.4805, or rather less than half that of water. It is worthy of note that the oxygen and hydrogen contained in 9 kilos, of steam have, before com- bination, capacities for heat amounting together to 5.149, whereas the specific heat of 9 kilos, of the combined gases is only 4.3245. 42 SPECIFIC HEAT AT CONSTANT PRESSURE. 28 Ice has a specific heat of 0.504 if examined between oC and 2oC, but if examined for the whole range of temperature from oC to 7oC it has a mean specific heat of smaller amount, viz. 0.474. A careful comparison of the specific heat of water at different temperatures has shewn that at high temperatures the specific heat is somewhat greater than at low temperatures, as will be seen by the following examples calculated from a general formula which agrees with the observations at oC sp. H =1.0000; at 5oC sp. H= 1.0042. at iooC sp. H = i.oi3o; at i5oC sp. H= 1.0262. at 2ooC sp. H= 1.0440; at 23oC sp. H= 1.0568. Oxygen has the same specific heat at high temperatures as at low temperatures, and the same assertion no doubt holds good with regard to hydrogen. Oxygen is also found to have the same specific heat when examined under great pressure as when examined at its ordinary pressure and density. 28. The apparatus used for determining the specific heat of gases is so arranged as to allow the gas under exami- nation to expand while it is being heated, and to contract again while it is giving up its heat to the calorimetre for measure- ment. In this manner the gas is kept at a constant pressure (measured by the barometer at the time of experiment). If a kilogramme of oxygen were enclosed in a strong bottle, and heated without being allowed to expand, it would be found to have a smaller specific heat, viz. about ^x .2175, or .15; and in like manner a kilogramme of hydrogen if heated without expansion would have a specific heat, -f x 3.409. In other words, oxygen or hydrogen require about f- more heat if allowed to expand while they are being heated iC, than if heated without expansion. Representing as i the specific heat of these gases at constant volume, the specific heat at constant pressure is represented by the fraction 1.413. An example will help us to understand this wonderful law. 43 29 WORK DONE IN EXPANSION. 29. Let a kilogramme of oxygen be heated from oC to 1 00, and while expanding, let it drive before it a column of mercury 760 millimetres long, in a vertical tube of i square centimetre area. This column of mercury weighs 1.033 kilo- gramme; so that a weight of 1.033 kilo, is raised i metre, by every 100 cubic centimetres increase of volume of the gas. Now as 16 grammes of oxygen measure 11.2 litres at o, the 1000 grammes which are to be expanded measure =700 litres at oC, and their increase of volume in expanding to 100 is 5_J= 256.55 litres or 256550 cubic centimetres. As the expansion takes place in a tube of i square centimetre area, the oxygen raises a weight of 1.033 kilo, to a height of 2565.5 metres, and does 1.033 x 2565.5 = 2650.16 metre-kilogrammes of work; or in other words, the kilogramme of oxygen in expanding from o to 1 00 does work equivalent to that of raising i kilogramme to a height of 2650.16 metres. 30. The mechanical force expended in raising this weight can be recovered again, if the weight be allowed to fall, for the falling mercury may be made to turn a wheel, or some other suitable mechanism, so as to set other masses in motion, by the momentum which it accumulates in falling. It has been proved by Mr. Joule that if mechanical force be em- ployed in agitating water, so that the particles of the water rub against each other and get heated by friction, every 423.6 metre-kilogrammes of work so expended produce one degree of heat ; that is to say, enough heat to raise the temperature of i kilogramme of water from o to iC. 423.6 metre-kilogrammes accordingly represent the * me- chanical equivalent' of one degree of heat. Whenever heat is transformed into mechanical force, by the expansion of a gas which lifts the atmosphere while expanding, or by any 44 LA TENT HE A T OF EXPANSION. 31 other process, every degree of heat so expended produces 423.6 metre-kilogrammes of work. The knowledge of the mechanical equivalent of heat enables us to calculate how much heat is consumed by the work which the kilogramme of oxygen does in expanding. That work was computed at 2650. 1 6 metre-kilogrammes, and every 423.6 of these is equivalent to one degree of heat, so that = 6.25 is the quantity of heat which is transformed 423.6 into mechanical work, when i kilogramme of oxygen ex- pands and raises the atmosphere by being heated from o to iO3C. The heat absorbed by the kilogramme of oxygen is partly employed in heating it, partly in doing the work of lifting the weight of the atmosphere. This total quantity of heat is found by multiplying the specific heat of oxy- gen at constant pressure (0.2175) by the number of degrees that it is heated (ico), and accordingly 21.75 * s tne tota l quantity of heat absorbed by the oxygen. It was stated above that the specific heat of oxygen at constant volume is to its specific heat at constant pressure in the proportion of i to 1.41, and accordingly if the kilogramme of oxygen had been heated from oto 100 in a closed vessel, so that it could not do any work, it would only have absorbed = 15.4. The difference between this quantity of 1.41 heat and 21.75 is 6.35, or very nearly that same quantity of heat which, from the work done by the expansion of the oxygen, and the mechanical equivalent of heat, was computed to have been needed for the effort of expanding the oxygen, so as to keep it at atmospheric pressure while heated from o to 100. 31. There are other and more direct means of proving that oxygen by expanding under pressure is an agent for the transformation of heat into mechanical work ; for if a delicate 45 31 LA TENT HE A T OF EXPANSION. metallic thermometer, of Breguet's construction, be introduced into a bell-jar containing oxygen over mercury, and if the bell-jar be suddenly raised by the hand, so as to expand the gas without letting it out of the bell-jar, the thermometer will shew a fall of temperature. In this experiment the hand of the operator only applies enough force to lighten the pressure of the bell-jar and of the air on the oxygen, sufficiently to enable the expanding oxygen to lift them ; and the expanding oxygen does aid in producing the mechanical effect of raising these weights, and does use up heat in doing this work. Heat which thus disappears for the production of me- chanical work may be called latent whenever it can be re- covered again by reversing the process. Whenever oxygen or hydrogen are compressed, an expenditure of mechanical work is incurred, and the exact equivalent of this expended work makes its appearance as heat in the compressed gas. If the experiment of expanding the kilogramme of oxygen were to be continued so as to bring matters back to their original state, it would only be necessary to abstract heat from the heated oxygen, by putting it in contact with some cold surface, say metallic tubes kept at oC by ice-cold water circulating through them. The weight of 1.033 kilogramme would begin to fall from its full height (2565.5 metres) as soon as the oxygen began cooling, and it would have fallen through 2565.5 metres as soon as the kilogramme of oxygen was cooled down to oC. The heat taken out of the oxygen by this time would be 21.75 degrees of heat, that is, not only what it had retained while heating to iooC, but also the 6.35 which it had been an agent for transforming into work. The 1.033 kilo, of mercury in falling compresses the oxygen and evolves the 6.35 of heat by expenditure of mechanical work. Similar principles apply to the expansion of steam by rise of temperature, and its condensation by cooling agents. In order to make the comparison we will take the same volume 46 LATENT HEAT OF EXPANSION. 31 of steam at 100 which we just now took of oxygen at o, viz. 700 litres, and heat it until it expands to a volume greater by 256.55 litres, so that the steam may do the same amount of work in expanding which was done by the oxygen. We will assume that the steam expands at the same rate for each degree rise of temperature, which is only an approxima- tion to the truth. In order to gain 256... litres in volume by rise of tem- perature from 100 the steam must be heated to 236.3. The weight of 700 litres of steam at 100 is calculated at 415.3 grammes 4 ; and taking the specific heat at 0.4805 for the rise of temperature from 100 to 236.3, it appears that the steam absorbs rather more than 27. When 6.3 is deducted from this quantity as equivalent to the work done in ex- pansion, there remains 20.7 as absorbed by the steam, which is more than the quantity absorbed by the oxygen, on doing an equal amount of work. Another difference between steam, and either oxygen or hydrogen, would be discovered by allowing saturated steam to expand, by a gentle diminution of the pressure upon it. The steam would give up heat, and transform it into mechanical force, but in doing so, some of the steam would be condensed into water, as would be seen by a foggy appearance after ex- pansion. Superheated steam presents no condensation of water on expansion, but becomes cooler by doing work, just like oxygen, till its temperature is lowered to the point of saturation. If pressure be applied to saturated steam it becomes hotter ; but the heat evolved by the expenditure of mechanical force can be removed from the steam, and its temperature maintained constant, while its volume is being reduced by * According to the observations of the density of steam, Rankine assigns to a cubic foot at 100 the weight 0.03797 of a pound, which corresponds to 421.3 grms. as the weight of 693.75 litres. 47 31 LATENT HEAT OF EVAPORATION. pressure. In this case the density of the steam will remain perfectly constant, and the diminution of its volume will be effected by the condensation of steam into water. The term * vapour' is usually applied to those aeriform bodies which are made by the action of heat upon liquids, and which return to the same liquid state, either by removal of heat or by pressure. 32. It was stated above that water does not become hotter by continuing to boil, and moreover the steam which escapes is no hotter than the water itself, so that the heat which passes into it produces the change of water at iooC into steam at iooC while disappearing thermometrically. When saturated steam at iooC is compressed as above described, so as gradually to be condensed into water, and the mixture kept at iooC until all the steam has been liquified, all the heat is recovered which had disappeared during the evaporation of the water ; so that the heat is called ' latent/ to convey the idea that it is stored up in connection with the steam, so as to be recoverable when the steam returns to the state of water. A very simple experiment serves to measure approximately the latent heat of steam. Put 5^ kilos, of ice-cold water into a jar, and blow steam into it till no more can be con- densed. Then weigh the boiling- hot water thus obtained. The first portions of steam condense to water, and are cooled by mixing with the ice-cold water ; but at the end of the ex- periment the original 5 J kilos, of water, together with the water formed by condensation of the steam, are left at the tem- perature of iooC; so that the steam may be considered to have been condensed without becoming cooler, and to have evolved 5j x iooC = 533 of heat by its condensation. The increase of weight is nearly i kilo. ; so that i kilo, of steam condenses to water of the same temperature, evolving about 533 of heat. 33. At temperatures above iooC and all corresponding 48 TOTAL HEAT OF EVAPORATION. 34 pressures, more heat is required to transform water at oC into steam. The quantity of heat for different temperatures is given by Regnault's formula, 606.5 + .305 t; which means that the number of degrees centigrade at which the saturated steam is to be formed is to be multiplied by .305 and added to the number 606.5, in order to shew how many degrees of heat are required for heating i kilogramme of water from o up to the given boiling-point, and evaporating it at the pressure corresponding to that boiling-point. Thus to heat water at oC up to iooC and evaporate it, we have 606.5 + 3 0.5 =63 7; to heat it up to 200 and evaporate it at that temperature, 667.5 of heat are required; and at oC every kilo, of water absorbs only 606.5 of heat in evaporating. 34. In the process of freezing water, heat is also given off, and the same quantity of heat is absorbed again when it is melted. A kilo, of water on cooling from 8oC to o gives off enough heat to melt i kilo, of ice at oC, the 2 kilos, of water which are thus obtained being at the same temperature (o) as the ice before fusion. The heat which water gives off on becoming ice can be made to boil liquids : for instance, ether can be made to boil at temperatures below oC if put in contact with a vessel containing water, while the pressure of the atmosphere is removed from the surface of the ether by a good air-pump. Ice-making machines have been constructed on this principle ; the ether vapour which is pumped out of the boiling ether being subsequently compressed into a condenser tube, and thus recovered for repeated use. Water can also be frozen by the evaporation of some of its particles. For this purpose an instrument called a eryophorus is constructed. It consists of two glass bulbs connected by a glass tube, and hermetically sealed. One of the bulbs is about half-full of water, and the remainder of the space in the apparatus contains nothing but steam, all the air having been expelled by long boiling, before the apparatus E 49 34 APPENDIX TO CHAPTER IV. was closed. The bulb containing steam can be brought to a temperature considerably below oC by immersion in 'a so- called frigorific mixture, and the steam in it is thereby con- densed. Fresh steam then comes over into the cold bulb from the one containing water, and steam is formed by evapo- ration of some of the water under the greatly reduced pres- sure, till the remaining water has at last parted with all its latent heat of fluidity and has become ice. Appendix to Chapter IV. PROBLEMS. 29. How many 'degrees of heat' are required to raise the temperature of 4 cubic metres of oxygen from oC to iooC ? What increase of volume will the oxygen undergo ? 30. What weight of hydrogen would you have to burn in order to evolve enough heat to heat i oo kilogrammes of steam from i2oC to 2ooC? 31. What quantity of heat is obtained by cooling 90 grammes of hydrogen from 3ooC to oC ? 32. A kilogramme of hydrogen is heated from oC to iooC, at the atmospheric pressure of 1.033 kilos, on the square centi- metre. How much work (in metre -kilogrammes) does it do in expanding ? 33. How many degrees of heat are evolved by the fall of i ooo kilogrammes from a height of i o metres ? 34. Translate into its equivalent of mechanical force the heat evolved by the combustion of 500 grammes of hydrogen. 35. Calculate the quantity of heat required to heat a kilo- gramme of water from oC to each of the following temperatures and to evaporate it at each temperature (under corresponding pressure) : viz. i5oC, 25oC, 5oC. APPENDIX TO CHAPTER IV. 36. A pond is calculated to contain noo cubic metres of ice. What quantity of heat will be required to melt it ? 37. What weight of saturated steam at iooC is needed for the fusion of a kilogramme of ice ? 38. 10 kilogrammes of oxygen at iooC have to be cooled to oC. What weight of ice will be required for the purpose ? 39. What quantity of heat will be needed to raise the temperature of a kilogramme of oxygen from oC to iooC in a closed and inextensible vessel ? 40. How much mechanical force will be required to con- dense to water by pressure 100 cubic metres of steam saturated at iooC ? The heat evolved by compression is removed as fast as it is evolved. E 2 35 ATOMIC NOTATION. CHAPTER V. 35. The letter O is used to denote an atom of oxygen, and in like manner H denotes an atom of hydrogen, and the symbol attached to the name of each element in 92 means an atom of that element. The juxtaposition of two symbols is used to denote combination of the respective atoms : but when two or more atoms of like kind are com- bined together it is customary to put after and above the symbol of the atom a number shewing how many such atoms are combined together. Thus CO means a compound of one atom of carbon with one atom of oxygen ; O 2 means a compound of two atoms of oxygen ; H 2 O means a compound of two atoms of hydrogen with one atom of oxygen. 36. Each cluster of atoms united together is called a molecule, and the formula for such a cluster is called a molecular formula. When several molecules have to be denoted the formula of jone such molecule is written after the appropriate number. Thus 2H 2 O means two molecules of water. Every molecular formula, like H 2 O, denotes a weight of the compound equal to the sum of the weights of the atoms contained in it, so that H 2 O means 1 8 parts by weight of water. The molecule of water occupies in the state of vapour exactly two volumes, whereas the three atoms which go to make it occupy together three volumes while uncombined. CO is in like manner the molecular formula of a com- pound called carbonic oxide, containing an atom of carbon weighing 12, united with an atom of oxygen weighing 16. 12+16 grammes, or 28 grammes, is its molecular weight taken in grammes ; and 28 grammes of carbonic oxide 52 MOLECULES. 37 measure exactly two volumes (2x11.19 litres at oC and 760 millimetres). The molecule of carbonic oxide occupies therefore the same volume as the molecule of steam. If two volumes of carbonic acid (C O 2 ) were measured out and then weighed, they would be found to weigh 44 grammes, the weight (in grammes) denoted by the molecular formula of the acid. Two volumes of sulphurous acid SO 2 weigh 64 grammes, and two volumes of sulphuric acid vapour (SO 3 ) weigh 80 grammes. One more example may suffice for the present purpose : viz. nitrous oxide N 2 O. Two volumes of this gas weigh 44 grammes. In all these cases, viz. H 2 O, CO, CO 2 , SO 2 , SO 3 , and N 2 O, the weight of two volumes of the vapour is called the molecular weight of the respective compound. The mole- cular weight of every substance which can be made to evaporate without decomposition is defined in like manner as the weight of two volumes of the vapour or gas. 37. The sign + interposed between symbols denotes addition of the atoms or molecules which the symbols re- present, and in the proportions by weight corresponding to those symbols. In like manner the sign between two symbols denotes the removal from one another of the atoms or molecules in the proportions described. The sign = is used to denote chemical changes. It denotes equality in weight, between the sum of the atoms of each kind on one side of it and the sum of the atoms of the same kind on the other side of it. Thus H -f O denotes a mixture of i part by weight of hydrogen with 16 parts by weight of oxygen. H 2 +-O = H 2 O means that 2 parts by weight of hydrogen, added to 16 parts by weight of oxygen, can be made to combine to form 18 parts by weight of water. 53 37 HYDRIC PEROXIDE (H* O 2 ). H 2 O O = H 2 means that if 16 parts by weight of oxygen are taken away from 18 parts by weight of water, 2 parts by weight of hydrogen are formed. Brackets are frequently used to facilitate the comparison of two formulae. Thus in comparing the formulae (S O 4 ) Zn and (S O 4 ) H 2 , the use of brackets inclosing those consti- tuents which are common to the two salts, serves to mark the fact that the difference between them is that one has got H 2 , two atoms of hydrogen, while the other has got Zn, one atom of zinc. When several symbols are enclosed by brackets, and a number put after the group, the whole group is multiplied by that number. 38. Hydric Peroxide (H 2 O 2 ). Oxygen and hydrogen do not unite directly in any other proportion than that in which they form water, but by indirect means a molecule of water can be made to combine with an atom of oxygen, forming hydric peroxide. For the preparation of this remarkable compound, barytic peroxide (BaO 2 ) should be ground to a fine powder under water, and left for some time in contact with the water. A combination takes place forming a hy- drated peroxide (Ba H 2 O 3 ). When this hydrate is dissolved in dilute hydrochloric acid, barytic chloride is formed, to- gether with hydric peroxide The barytic chloride can be removed from the solution by carefully dropping into it a solution of argentic sulphate as long as it continues to form a precipitate. The two soluble salts exchange metals, forming barytic sulphate and argentic chloride, both of which are insoluble Ba Cl 2 + Ag 2 S O 4 = 2 (Ag Cl) 4- Ba S O 4 ; and they settle at the bottom of the liquid, if it be allowed to stand; so that the solution of hydric peroxide can be poured off clear. In order to get rid of the greater part of the water which is mixed with the peroxide, the liquid is put 54 DECOMPOSITIONS. 39 into an open porcelain dish, under a glass bell-jar fitted on to the plate of an air-pump. A vessel containing strong oil of vitriol is also put under the bell-jar, and the air is then pumped out from it. In this vacuum the water evaporates rapidly, and is absorbed by the oil of vitriol, forming with it a compound far less volatile than water itself. In this manner a concentrated solution of peroxide is finally obtained of a specific gravity of 1.45. It bleaches litmus-paper. 39. This solution is rapidly decomposed by heat, giving off oxygen, and leaving water. It is also decomposed by various substances at the ordinary temperature. Thus, char- coal causes an immediate effervescence of oxygen in the solution, and finely-divided platinum, in the form called platinum-black, decomposes it still more rapidly. It is worthy of remark that the charcoal or platinum is found unchanged at the end of the decomposition, and although the peroxide gives up oxygen with the utmost readiness, it does not always allow other substances to combine with the oxygen which it is giving off. It frequently induces compounds containing oxygen to undergo a decomposition similar to its own, and to give off oxygen. Thus, potassic chromate, when dropped carefully into an acid solution containing hydric peroxide, is changed at first into a deep-blue body, and immediately afterwards turns green by giving off half the oxygen of the chromic acid with the oxygen which is escaping from the peroxide. Still more remarkable is the action of the peroxide on the oxides of manganese : a mixture of man- ganic peroxide with nitric acid is deoxidized by hydric peroxide. Half of the oxygen which is given off comes from the hydric peroxide, whilst the other half comes from the manganic peroxide. The manganous oxide formed in this reaction is reconverted into peroxide by the action of hydric peroxide, in presence of an alkali or substance op- posite to acids in its properties. 55 39 APPENDIX TO CHAPTER V. These remarkable phenomena have been investigated by Professor Brodie, and explained by him as due to the fact that oxygen from the one body combines with oxygen from the other, forming free oxygen of which the molecule O 2 contains two atoms. An atom of oxygen -cannot exist by itself, and a couple of atoms is the smallest quantity of the element which can take part in any reaction. The important rule stated in 36 respecting compounds is thus extended to the element oxygen. Two volumes of free oxygen contain 32 grammes, and 32 is the molecular weight of oxygen. In like manner hydrogen, nitrogen, chlorine, bromine, and iodine have the molecular formulae H 2 , N 2 , Cl 2 , Br 2 , and I 2 , each molecule containing two atoms u . Appendix to Chapter V. PROBLEM. 41. State in words the meaning of the following equations (ascertaining the signification of each elementary symbol from the table of atomic weights) : C1 2 + H 2 O=C1H + C1HO; BaCl 2 + H 2 S 4 =Ba S O 4 -f 2 (H Cl); Na Cl + H 2 S 4 -H C1=H Na S O 4 . u Among hydrogen compounds (hydrides) there is less variety than among oxides. The simplest hydrates can be classified in four groups, viz. FIRST Hydrochloric acid,_ClH. Hydrobromic, BrH. Hydriodic, I H. SECOND Water, OH 2 . Sulphuretted hydrogen, S H 2 . THIRD Ammonia, N H 3 . Phosphuretted hydrogen, PH 3 . Arseniuretted hydrogen, AsH 3 . FOURTH Marsh gas, C H*. Siliciuretted hydrogen, SiH 4 . Seleniuretted, Another class is formed by Hydric peroxide, O 2 H 2 , Hydric persulphide, S 2 H 2 , Cuprous hydride, Cu 2 H 2 . 56 PREPARATION OF NITROGEN FROM AIR. 40 CHAPTER VI. 40. Nitrogen x , in the free state, is one of the most inert of gases, and is characterized by its inability to burn or to support combustion, and generally by its disinclination to combine. When combined with oxygen and hydrogen it forms a strongly acid compound belonging to the class of salts called nitrates. This acid nitrate is commonly called nitric acidy; and with less oxygen and more hydrogen it forms the com- pound called ammonic hydrate 2 , which is a strongly basic, or in other words, a strongly anti-acid substance. Nitrogen is the chief constituent of atmospheric air, and is best prepared from that source. A tube containing metallic copper, as obtained by the reduction of cupric oxide by hy- drogen, is heated to redness, and a current of purified atmo- spheric air is then passed slowly into it at one end; pure nitrogen passes Out at the other end. The purification of the air is effected by first passing it through a plug, of cotton- wool in a tube, so as to strain off particles of dust, &c. which are contained in it, and then through a long tube or a bottle, containing solid potash, for the absorption of carbonic acid; and finally through a third long tube or bottle containing pumice moistened with strong sulphuric acid, for the absorption of water and ammonia. The oxygen is entirely absorbed by Atomic symbol, N = I4. Molecular formulae. N 2 = 2 vols. > NO 3 H. z NH 5 O. 57 40 WEIGHT OF NITROGEN IN AIR. the metallic copper, and pure nitrogen can be collected as it escapes from the tube. By arranging this experiment suitably, the relative weights of oxygen and nitrogen in air can be determined with Preparation of Nitrogen from Air. a gas-holder containing air; b bottle containing potash ; c bottle containing pumice and strong sulphuric acid ; d furnace containing tube ; e jar for collecting nitrogen. great accuracy. For this purpose a large glass globe, fitted with a good stop-cock, is exhausted by means of an air- pump, and then weighed. It is then connected with the end of the tube containing metallic copper, in such a way that all the nitrogen which passes through the tube shall go into the globe. The tube containing copper must also be weighed before it is connected with the globe. As soon as the tube of copper is red hot, purified air is allowed to pass slowly through it. All the oxygen is deposited on the copper, while the nitrogen goes over to the exhausted globe. At the end of the experiment the globe is weighed again, and its increase of weight shews how much nitrogen there was in the air ; the tube containing copper, now partially oxidized, is also weighed, and its increase of weight shews the quantity of oxygen in the air. 58 WEIGHT OF A TMOSPHERE MEASURED BY BAROMETER. 42 by volume, by weight f . . 20.9 23.1 of oxygen, i oo parts of air contain . 79.1 76.9 ot nitrogen. Nitrogen is somewhat lighter than air; its density is 14, the density of air being 14.45. 41. Nitrogen gas can also be obtained by heating am- monic nitrite. The salt is decomposed at temperatures below the boiling-point of water, forming nitrogen and water a , and an aqueous solution of the salt accordingly gives off nitrogen gas with effervesence when heated. The most convenient way of obtaining the salt is to mix ammonic chloride and potassic nitrite in presence of water. The salts interchange bases forming potassic chloride and ammonic nitrite b . When heated at constant pressure nitrogen expands in the same proportion as oxygen and hydrogen for each degree rise of temperature, and the quantity of heat which one volume of it absorbs in order to undergo a rise of tempera- ture of one degree is the same as the quantity absorbed by one volume of oxygen or of hydrogen. Nitrogen in- creases in density proportionally to the pressure to which it is subjected, and the greatest pressure and cold to which it has been subjected have failed to condense it to the liquid state. 42. The weight of the sea of air, or atmosphere, as it is generally called, is best investigated by means of a mercury barometer. A straight glass tube, nearly i metre long and closed at one end, is filled with mercury, care being taken to remove all the bubbles of air which at first adhere to its sides, by sweeping them away by means of one large bubble. The open end of the tube is then closed by. the finger till dipped under mercury in a little cup. If the tube be then held vertically, the mercury in it will fall several inches below the top of the tube ; but by inclining the tube the a N0 2 NH 4 =N 2 + 2 H 2 0. b KNO^NH^Cl 59 42 CURRENTS IN A TMOSPHERE. mercury can be made to fill the whole of it. In each posi- tion of the tube the column of mercury inside it will be the same height (measured vertically) above the mercury in the cup, if the tube be long enough to allow it to rise to that height. At the level of the sea and in the normal or ordinary state of the atmospheric - pressure this height is 760 milli- metres, or about 30 in- ches. When such a baro- meter is carried up to a height, so that there is a shorter column of air Moveable Barometer to shew uniform height i ., ,1 of mercurial column, with varying lengths. ab Ve !t > the ercury a cup containing mercury ; b moveable falls ; and in like man- ner the mercurial column rises to a greater height when the barometer is taken down any deep well or shaft. When the barometer is put under a bell-jar, and a part of the air enclosed with it is gradually pumped out, so that the portion of air remaining in the bell-jar is of lesser and lesser density and corresponding pressure, the mercury falls in proportion to this diminution of pressure. Thus, if the mer- cury stood first at a height of 760 millimetres (30 inches) the removal of half the air from under the bell-jar would lower the pressure of the remainder to 1 33 kilo, on the square centi- metre (^^ Ibs. on the square inch), and the mercury would fall to 380 millimetres (15 inches). If -5% of the air were removed from the bell-jar, the mercury would stand at a 60 FORMATION OF DEW. 43 height of only 76 millimetres (3 inches), the pressure of the remaining air on the surface of the mercury in the cup being 0.1033 n the square centimetre (1.47 Ibs. on the square inch). A perfect vacuum would not support the mercury in the barometer at all ; but even the best air-pumps are not perfect, they leave enough air to support half a millimetre or some- times less height of mercury. 43. According to the results of Regnault's experiments, a cubic metre of dry air, measured at oC and 760 milli- metres, mercurial pressure, weighs 1.2932 kilogramme (or ico cubic inches of dry air, measured at oC and 29.92 inches mercurial pressure, weigh 32.586 grains). In a cubic metre of air there are 10,000 columns of air of i metre high and of i square centimetre section, each of which weighs 0.00012932 of a kilogramme. In order to make up 1.033 kilo, (the actual weight of the air on each square centimetre) we should need 8,020 such columns of air i metre long, or a column of uniform density about 8,020 metres high. If the upper strata of the atmosphere were of this density as well as the lower strata, the height of the atmosphere \vould be 26,315 feet, or 5 miles all but 85 feet, above the level of the sea. But each stratum of air c has a density proportional to the superincumbent weight, and the higher strata have conse- quently a lesser density than the lower ones. If a bottle of i litre capacity were taken up to a mountain 5,486 metres high (about 18,000 feet), and there filled with air at oC, it would only take in half as great a weight as if filled at the level of the sea, viz. I^M. 2 grammes, because the stratum of air at that height has only half as great a pressure upon it as the lower air, and consequently only half as great a density. If the mouth of the vessel were closed by immersion in a vessel of mercury, and then brought down to the level of the sea while kept at the c At any fixed temperature. 61 43 MINOR CONSTITUENTS OF AIR. same temperature, it would be found that half a litre of mercury would be forced into the bottle by atmospheric pressure; so that the enclosed air would be at double as great a density as when collected on the top of the moun- tain. It is assumed that the level of the mercury inside the bottle is kept equal to the level outside, so as not to inter- fere with the atmospheric pressure on the contents of the bottle. It is computed that the air extends to a height of about 39,624 metres (130,000 feet), and that it is prevented by its own weight from expanding still further into the vacuum beyond it. 44. The temperature of the atmosphere is lower in elevated strata than near the surface of the earth, and this is easily accounted for by the fact that the air absorbs but a small part of the heat which is brought to it by the sun's rays, while the greater portion of the heat passes through the atmosphere, and heats the surface of the earth, or produces changes in its materials. The lower strata get heated in the day-time by contact with the hot ground, until their expan- sion renders them lighter than the upper strata, when a circu- lation immediately establishes itself. The evaporation of water in the lower atmospheric strata also causes a circu- lation ; for the density of steam is less than f that of air, and moist air is therefore lighter than dry air. 45. In the night-time, while the surface of the ground is receiving no heat from the sun, it is constantly giving off its heat, in the form of rays, more especially when the air above it is clear; and the lower strata of air are then cooled by contact with the cold earth. This cooling action often proceeds far enough to cause a condensation of moisture from the air, in the form of dew. The formation of dew from the air is best studied with the aid of a hygrometer. Daniell's hygrometer is a kind of cryophorous containing ether, and having one bulb blackened 62 DEW POINT. 46 internally while the other bulb is covered by cambric. This cambric bulb is gradually cooled by dropping ether upon it, until moisture begins to be deposited from the air on the blackened bulb. A small thermometer contained in the ether of the blackened bulb is then read off, and at the same time a thermometer in the outer air is read off. The difference between the two readings shews how much the air had to be cooled in order to begin to deposit ' moisture. The temperature at which air begins to deposit moisture is called the dew-point. When the dew-point is many degrees below the temperature of the air, the air is capable of taking up more moisture, or, in other words, it is capable of drying a moist surface more rapidly than when the dew-point is but few degrees below the prevailing temperature. Thus it is that air containing a given quantity of moisture would be practically considered drier at 24C than at i6C. If the dew-point of this air were at i6C, or, in other words, if it contained as much steam as it coukMiold dissolved at 16, it would have no drying action at that temperature, but a con- siderable one at 24. The quantity of steam dissolved in the air is too variable to admit of being estimated in any particular case by an average from many observations. In this country such an average would perhaps be about 1.5 per cent, of the volume of the air. 46. Two other essential constituents of air are carbonic acid and ammonia. 100 volumes of air usually contain about 0.04 of carbonic acid; but the proportion of carbonic acid is in many localities greater, and in ill-ventilated rooms is said to vary from o.i to 0.4, and even 0.7. The respiration of animals not only removes oxygen from the air but replaces it by carbonic acid. Herbivorous animals usually exhale carbonic acid, in volume equal to the 63 46 RESPIRATION OF ANIMALS. oxygen which they absorb, but carnivorous animals appear to exhale a volume of carbonic acid smaller by 40 per cent, than that of the inhaled oxygen. Dumas states that a man absorbs 220 to 245 cubic centi- metres (from 13 J to 15 cubic inches) of oxygen per minute, which amounts to a little more than 450 grammes (or about lib.) per day. From 100 cubic centimetres of inhaled air, a quantity of oxygen varying from 4 to 6 cubic centimetres are usually removed at each inspiration. The average weight of water exhaled from the lungs per day is upwards of 500 grammes (or 7, 71 6... grains), while that of carbonic acid is somewhat greater, viz. 550 grammes (or 8, 487... grains). To keep an inhabited room in a state of good ventilation for one person, 283 litres (10 cubic feet) of air should be re- moved every minute, and replaced by fresh air. The proportion of ammonia in air is far smaller and also more variable than that of carbonic acid. Ten million volumes of air have been found to contain from 1.3 to 3.3 volumes of ammonia. Both carbonic acid and ammonia are given off and oxygen absorbed by decomposing vegetable and animal matter, and in some districts carbonic acid is evolved from vegetable matter underground, and when it comes in con- tact with water at high pressure, gives rise to the effervescing springs. The processes of combustion of wood and coal which are now carried on for heating and mechanical purposes on a vast and increasing scale, constitute another drain of oxygen from the air and supply of carbonic acid. 47. The continual consumption of atmospheric oxygen in these various ways would gradually diminish its quantity, while replacing it by carbonic acid, were it not for the respiration of plants. Under the influence of sunshine, the leaves of plants absorb carbonic acid, and give off oxygen. At the same time plants feed upon ammonia, and by their vital pro- cesses the elements of these substances and of water are 64 APPENDIX TO CHAPTER VI. 47 elaborated into the varied compounds which we find in them such as sugar, starch, wood, volatile oils, fatty oils, gluten, &c., &c. The processes by which these substances are formed might be called processes of unburning; for they are exactly the opposite processes to combustion. Not only do plants produce these combustible compounds while liberating oxygen, but they absorb from the sun's rays a vast quantity of heat, which they render latent, or store up in the form of wood and oils, &c., and of free oxygen. The water of the sea, as well as of rivers and lakes, holds both oxygen and nitrogen in solution, and this air serves to support the respiration of fishes. It is richer in oxygen than atmospheric air, for 100 volumes of it contain upwards of 33 volumes of oxygen. This difference is owing to the fact that water dissolves nitrogen less freely than it does oxygen. At oC 100 volumes of water dissolve about 2 volumes of nitro- gen; at ioC only 1.6 volumes; and at 2oC, 1.4: in each case about half as much as of oxygen. Marine plants absorb the carbonic acid, which is exhaled by fishes, and give off oxygen in its stead, thus helping to keep the composition of the air in water suitable for the respiration of the fishes. Appendix to Chapter VI. PROBLEMS. 42. 50 cubic metres of nitrogen are in a gas-holder, and it is desired to add enough oxygen to make a mixture of the same composition as atmospheric air. How much potassic chlorate will be needed for the purpose ? 43. An experimentalist fills with dry and pure atmospheric air, at the temperature of ioC, a bottle of i litre capacity at a height in the atmosphere such that a barometer stands at a F '65 APPENDIX TO CHAPTER VI. height, of 350 millimetres. What volume of oxygen and what volume of nitrogen will he have at the normal temperature and pressure ? 44. Atmospheric air at the temperature of i5C, and of which the dew-point is at ioC, is passed over a moist sur- face of earth. What weight of water can each cubic metre of this air take up, supposing its temperature to remain at 66 OXIDES OF NITROGEN. 49 CHAPTER VII. 48. Nitrogen can be made to combine with oxygen, by mixing it with a large quantity of hydrogen, and burning the mixture. Electrical sparks passed through moist air also cause the formation of compounds of nitrogen, oxygen, and hydrogen, but both of these processes are too slow and costly for the preparation of large quantities of the compounds. Five compounds of nitrogen with oxygen are known, viz. those represented by the formulae N 2 O 5 Nitric acid. N 2 O 4 Nitric peroxide. N 2 O 3 Nitrous acid. N O Nitric oxide. N 2 O Nitrous oxide, or laughing-gas. Compounds of nitric acid are formed spontaneously by the contact of air with decomposing animal or vegetable matter containing nitrogen, in presence of bases. It is necessary that some base, such as lime, or potash, or soda, be present, to combine with the acid in proportion as it forms. 49. Potassic nitrate, or saltpetre, or nitre, as it is popu- larly termed, is generally used for preparing hydric nitrate on a small scale. The salt is mixed with an equal weight of hydric sulphate, and distilled in a retort until the con- tents of the retort fuse tranquilly, without giving off any more red fumes or condensable vapour. The yellow liquid which collects in the receiver has a density approaching to 1.5. It emits dense white fumes when brought in contact F 2 67 49 HYDRIC NITRATE (HNO'X). with moist air, by combining with the moisture of the air to form a compound less volatile than the original acid or Preparation of Hydric Nitrate. a Retort containing potassic nitrate and hydric sulphate ; b receiver to collect distilled nitrate; c wet bibulous paper. water. Even when mixed with large quantities of water the acid compound imparts a bright red colour to blue litmus- paper, and the original blue colour is restored by immersion in a solution of potash, or of soda, or lime, or any other substance possessing in a sufficiently strong degree the pro- perty of reversing the effect produced by an acid. When the acid is poured into a solution of potash, intense heat is evolved, and if a good deal of water were not present with 68 HYDRIC NITRA TE (H N 3 ). 49 the substances, so great an elevation of temperature would be produced as to cause the mixture to boil, by the action of the opposite liquids on one another. By using dilute potash, and examining the liquid by litmus-paper after each addition, it is possible to destroy the power of blueing red litmus which the potash possessed, without imparting to the liquid the acid property of reddening blue litmus. The liquid is then termed neutral, and the compound of potassium which it contains is called potassic nitrate d . It is the very salt from which our acid was prepared by the action of sulphuric acid. In order to explain the process by which hydric nitrate is prepared, it is best to compare the composition of the materials used in the process, with the composition of the products finally obtained. Oil of vitriol (hydric sulphate) is represented by the for- mula H 2 S O 4 ; S being 32 parts by weight of sulphur, O being 16 parts by weight of oxygen, and accordingly O 4 being 64 parts by weight, and H 2 being 2 parts by weight of hydrogen. Potassic nitrate has the formula KNO 3 , N being 14 parts by weight of nitrogen, and K 39 parts by weight of potassium. When the operation is complete, the fused mass in the retort, called hydro-potassic sulphate, has the composition H K S O 4 ; so that it is the same thing as hydric sulphate, from which i part by weight of hydrogen is taken away, and to which 39 parts by weight of potassium are added. The hydric nitrate collected in the receiver has a composition represented by the formula H N O 3 , so that it is formed from potassic nitrate by removing K and putting in H. The following equation The process which takes place is represented by the equation, H N O 3 + O = KN0 3 + H 2 0. 69 49 PROPERTIES OF HYDRIC NITRATE. describes the process in its simplest form, as an interchange of K in nitre for H in oil of vitriol. It generally happens that the oil of vitriol contains a little water mixed with it, and this water goes over with the product. Some of the hydric nitrate, moreover, is decomposed by the heat, giving oif oxygen-gas, and forming nitrous acid, a volatile com- pound of a yellowish red colour, which is generally seen in the distilling vessel, and which condenses in part with the acid in the receiver. By adding together the weight of sulphur, oxygen, and hydrogen, indicated by the formula of hydric sulphate, we have 98 as the weight of S O 4 H 2 > and in like manner 101 as the weight of NO 3 K. The pro- portions represented by the formula are thus seen to be very nearly those of the experiment. The hydric nitrate is an exceedingly acid salt; but the hydrogen contained in it acts the part of basic metal, and being endowed with feeble basic (or anti-acid) pro- perties it does not neutralize the acidity which the com- pound owes to its oxygen. Hydric nitrate is so very acid a salt that it has very commonly been called 'nitric acid/ a name which properly belongs to the compound N 2 5 . 50. Hydric nitrate gives up a part of its oxygen with great facility to substances capable of combining with oxygen. When diluted with water its action is, however, less energetic than in the concentrated state, and by mixing it with oil of vitriol (a substance which tends to take water away from other compounds), the action of the nitrate is in most cases rendered even more violent than it is by itself. Metallic copper thrown into dilute nitric acid of density 1.2 rapidly dissolves in it, while deep red fumes are given off in torrents ; but if the experiment be performed in a vessel from which all atmospheric air has been previously removed, a colourless gas called nitric oxide is given off. The solu- 70 FORMATION OF OTHER NITRATES. 51 tion left at the end of the operation contains cupric nitrate. The changes which take place in the process are repre- sented by the equation 8H N O 3 + 3 Cu = 2N O 4- sCu (N O 3 ) 2 + 4H 2 O This reaction affords a very good means of detecting a nitrate. Strong sulphuric acid should be added to the liquid so as to form hydric nitrate from any other nitrate which may be present in the solution, and if much water be present sulphuric acid should be added in still greater quantity. The nitric oxide which comes off is easily re- cognized by the red fumes which it forms on coming in contact with atmospheric oxygen. Nitrates are also detected by pouring a solution of ferrous sulphate into a mixture of equal volumes of strong sulphuric acid and the solution containing the nitrate. A brown colour shews itself immediately in the ferrous sulphate, if the quantity of nitrate present be considerable, or after some time if only a trace of the salt be present. Metallic zinc dissolves in dilute nitric acid even more readily than metallic copper, and a part of the nitric acid is reduced to nitrous oxide (N 2 O). By using the acid still more dilute, some of it is not only deprived of all its oxygen but combined with hydrogen, at the same time forming ammonia. This transformation is complete when the acid is reduced by metallic zinc in presence of metallic iron, in a great excess of caustic potash. 51. Nitric acid reacts on potash only in one proportion, and from this circumstance it is termed a monobasic acid. The process, when hydric nitrate combines with potassic hydrate, consists in a replacement of the hydrogen of the acid salt by potassium, in the proportion represented by the symbol of that element (K) ; and the hydrogen which leaves the acid takes the place of the metal, forming water accord- ing to the equation H N O 3 + K H O = K N O 3 + H 2 O. 51 DOUBLE DECOMPOSITIONS. The process is therefore an interchange of metals (H and K) between two salts, forming two new compounds which are nearly neutral. The weights of these substances are N O 3 H=63, and HKO=56; and the equation states that hydric nitrate and potassic hydrate react on one another in the proportion of 63 parts of the acid salt to 56 of the basic salt. That they react on one another in no other proportion can be proved, by bringing the substances together in other pro- portions, on each side of this one that is, with a greater proportion of base to the acid, so as to see if the acid can combine with more base; and then with more acid in pro- portion to the potash, in order to ascertain whether the base can combine with more acid, or the acid with less base. When an excess of potash is used the mixture is found to be alkaline to test-paper ; and if a part of the water be care- fully driven off from it by evaporation, the solution deposits crystals of nitre of the same composition as if no excess of potash had been present at their formation, and the excess of potash remains uncombined in the liquid from which the crystals have been deposited, or what is called the mother liquid. By using an excess of nitric acid to the potash, a perfectly similar result is obtained in an even more striking manner, for not only does the excess of acid remain uncom- bined with the potassic nitrate, but it can be distilled off from the salt and recovered unchanged. It is thus proved that hydric nitrate and potassic hydrate react on one another in no other proportion than that re- presented by our equation. We have here a case of vigorous action between two substances of very opposite properties giving off great heat and causing a disappearance of those properties; but it is proved to consist of both separations and combinations. If we write the formulae of the ' acid' and 'base' for con- venience thus, H (NO 3 ) and K (HO), and the formulae of the 72 NITRIC ACID (N? O 5 .) 52 products similarly, K (N O 3 ) and H (H O), we see that H is separated from (N O 3 ) and K is separated from (H O), while K combines in the place of H, and H in the place of K. An atom is taken away from each of the compounds and another atom combines with each of the residues. Processes of this kind are called 'double decompo- sitions.' Their general results present so much analogy with those which ensue in processes of apparently direct combination, such as we considered in 4, that it is cus- tomary and proper to include them all under the general term chemical combination. The forces which hold the substances together in the products are greater than those which held them together in the original compounds, so that weak forces are overcome in the separations by the exertion of the strong forces of combination 6 . 52. Anhydrous nitric acid (N 2 O 5 ) has not been obtained by removal of water from the hydrogen salt. It is prepared by passing chlorine gas over argentic nitrate, and condensing the products in a receiver cooled to a very low temperature. It is a solid crystalline compound, possessing the above e Nitrates may be classified similarly to hydrates in four chief families ; the first being composed of such salts as Hydric nitrate, H N O 3 . I Sodic nitrate, Na N O 3 . Potassic nitrate, K N O 3 . Argentic nitrate, AgN O 3 . The second class is composed of nitrates such as Stannous nitrate, Sn (N O 3 ) 2 . - Platinous nitrate, Pt (N O 3 ) 2 . Mercuric nitrate, Hg (N O 3 ) 2 . Plumbic nitrate, Pb (N O 3 ) 2 . Cupric nitrate, Cu (N O 3 ) 2 . Cadmic nitrate, Cd (N O 3 ) 2 . Ferrous nitrate, Fe (N O 3 ) 2 . Manganous nitrate, Mn (N O 3 ) 2 . The third class contains such nitrates as Bismuth nitrate, Bi (N O 3 ) 3 . The fourth salts like Platinic nitrate, Pt (N O 8 )*. 73 Cobaltous nitrate, Co (N O 3 ) 2 . Nickelous nitrate, Ni (N O 3 ) 2 . Zinc nitrate, Zn (N O 3 ) 2 . Barytic nitrate, Ba (N O 3 ) 2 . Strontic nitrate, Sr (N O 3 ) 2 . Calcic nitrate, Ca (N O 3 ) 2 . Magnesic nitrate, Mg (N O 3 ) 2 . 52 NITRIC PEROXIDE composition. When brought in contact with water it com- bines, with evolution of heat, to form hydric nitrate according to the equation N 2 O 5 + H 2 O = 2 N O 3 H. When kept in a closed tube it has been found to explode with violence, and without any external aid. Nitric Peroxide (N 2 O 4 ) is most conveniently obtained by heating plumbic nitrate in a stone-ware retort, and con- densing in a cold receiver the red fumes which escape. The process consists in a breaking-up of the salt into plumbic oxide, which remains in the retort, and nitric peroxide and oxygen which pass off The peroxide is at the ordinary atmospheric temperature a yellowish red liquid, but when cooled a few degrees below oC it becomes colourless. In contact with water it is decom- posed, forming hydric nitrate and a lower oxide of nitrogen. It does not appear to combine with bases. When evaporated by the aid of heat in the pure state its vapour has a density corresponding to N 2 O 4 = 4 vols. But when evaporated at a lower temperature in presence of a permanent gas it approaches the normal density corresponding to N 2 O 4 = 2 vols. 53. Hydric Nitrite (HNO 2 ) is a very unstable compound, and is but little known even in its saline derivatives. The red colour of nitric acid which has been exposed to the action 74 NITROUS ACID (A^O 3 ). 54 of light is owing to the presence of nitrous acid. It is decomposed by water, forming nitrate, nitric oxide, and water. The nitrites have much resemblance to nitrates. Nitrous acid is easily obtained by heating starch with a large quantity of nitric acid of density 1.25. Anhydrous nitrous acid (N 2 O 3 ) is formed by mixing nitric oxide (NO) with free oxygen, in the proportion of not more than one-fourth of its volume. The red vapour which is formed does not condense at oC, but if the vessel containing it be cooled to a temperature of about 2OC the acid condenses to a deep blue liquid. 54. Nitric Oxide 1 ' is most conveniently prepared by dissolving copper in nitric acid of density 1.2 to 1.3. Its theoretical molecule (N 2 O 2 ) N 2 2 " NW T- I5 N 2 O 2 N 2 2 =I5 =I5 4 4 occupies four volumes, the same as that occupied by a mixture of nitrogen and oxygen in these quantities. Its density is therefore 15. The gas has not been condensed to a liquid, by the greatest pressure and cold hitherto applied to it. Nitric oxide does not support the combustion of some kinds of wood ; but more powerful combustibles, such as phosphorus or charcoal, burn very rapidly if kindled and then plunged into the gas. It combines with anhydrous sulphuric acid. When two volumes of nitric oxide are mixed with not less N O = 2 vols. 75 54 NITROUS OXIDE (N*O). than five volumes of hydrogen, and passed through a red- hot tube containing spongy metallic platinum, the mixture is transformed into ammonia and water g . 55. Nitrous Oxide, or laughing-gas (N 2 O = 2 vols.), is most readily prepared by gently heating ammonic nitrate. Water and nitrous oxide are the only products, and the decomposition takes place according to the equation The gas dissolves in water at oC to the extent of 1.3 of its volume, and at i5C water dissolves more than two- thirds of its volume. It is therefore customary to collect the gas by displacement of hot water in the pneumatic trough. It may also be collected by displacement of air, if led to the bottom of a jar full of air, as it is about half as heavy again as air. Its exact density is 22. N=i 4 + = N 2 = 22 2 = i6 N=I 4 N 2 O =22 2 Nitrous oxide is a colourless gas, devoid of odour; but it produces when inhaled inebriating effects, which have gained for it the trivial name of laughing-gas. It supports the combustion of most substances with an intensity so nearly equal to that with which oxygen supports combustion that it might be mistaken for that gas, if carelessly examined. A kindled splint bursts into flame in 'nitrous oxide as in oxygen. Phosphorus burns with dazzling splendour in nitrous oxide, liberating nitrogen in volume equal to the g N O + 5H = N H 3 + H 2 O. 76 APPENDIX TO CHAPTER VII. 55 original gas, This circumstance affords a distinction be- tween nitrous oxide and oxygen. Nitric oxide does not produce red fumes when mixed with nitrous oxide. Potassic pyrogallate does, not absorb nitrous oxide as it does oxygen. Nitrous oxide can be condensed into a liquid at the temperature of oC by a pressure of about 36 atmospheres, and the liquid nitrous oxide is one of the most powerful cooling agents known. When some of the liquid is re- moved from the vessel' in which it was formed by pressure, and brought out into an open vessel, it boils with great violence, and the portion which evaporates absorbs so much heat, that the remaining liquid is cooled to a temperature of about 88C, at which it boils under the common atmo- spheric pressure. A still lower temperature is obtained by placing this liquid in a vacuum, maintained by a powerful air-pump, and the accelerated evaporation which takes place at that greatly reduced pressure, serves to freeze some of the nitrous oxide into a transparent solid like ice. The co-efficient of expansion of nitrous oxide gas is very slightly greater than that of oxygen. The specific heat of the gas is .2238. The specific heat of a mixture of oxygen and nitrogen in the same proportions is .2284. Appendix to Chapter VII. PROBLEMS. 45. What weight of hydric nitrate H N O 3 ought to be obtained from i kilogramme of sodic nitrate Na NO 3 , sup- posing none of the product to be decomposed ? 46. How much hydric sulphate is required for the decom- position of 500 grammes of potassic nitrate, according to the equation H 2 S0 4 + 2 KN O 3 = K 2 S O 4 + 2 HNO 3 ? 77 APPENDIX TO CHAPTER VII. 47. 10 grammes of nitric oxide are required; what weight of the materials would you require for their formation ? 48. What weight of water is formed by the reaction of 200 grammes of hydric nitrate upon potassic hydrate, ac- cording to the equation HNO 3 + HKO = KNO 3 + H 2 O? 49. 300 grammes of pure hydric nitrate are mixed with 800 grammes of potassic hydrate. How much more of the nitrate must be added in order to render the mixture neutral ? 50. What weight of oxygen is liberated by the gradual action of heat on 300 grammes of plumbic nitrate ? 51. What volume of nitric oxide is required for the com- bustion of 10 cubic centimetres of hydrogen? and what will be the volume of the nitrogen liberated ? 52. What volume of oxygen is needed for the conversion of 10 grammes of nitric oxide (in presence of water) into hydric nitrate ? 53. What weight of nitrous oxide is obtained from a kilo- gramme of ammonic nitrate? and what is the volume of the gas at the normal temperature and pressure ? 54. What volumes of the free gases would you obtain by the decomposition of a litre of nitrous oxide ? 55. What volume of hydrogen could be burnt by 10 grammes of nitrous oxide ? AMMONIA (NH 3 ). 56 CHAPTER VIII. 56. Ammonia (N H 3 ) is a minor constituent of the atmo- sphere, and is given off by putrifying animal and vegetable sub- stances containing nitrogen. It is also one of the products of the decomposition of coals by heat, and is collected in large quantities at gas-works. It is usually obtained by the action of lime on sal-ammoniac. The lime should be previously slaked, that is, combined with water, and the light powder thus obtained should be mixed with about two-thirds of its weight of finely-powdered sal-ammoniac, and the mixture heated in a flask similar to that used for evolving oxygen, fitted however with a wash-bottle to wash the gas. The sal-ammonia is a compound of ammonia with hydrochloric acid, and the lime takes the hydrochloric acid from it, whilst ammonia is liberated, together with the water from the lime. The reaction is thus described by an equation : 2 NH 4 C1 + CaH 2 2 = 2 NH 3 + CaCl 2 + 2 H 2 O. The ammonia gas is usually led into water, and the solu- tion thus obtained goes commonly by the name of ammonia. The gas itself can be collected by displacement of mercury, or for some purposes it might be collected like hydrogen, by displacement of air, by leading it up to the top of a bottle suspended mouth downwards. Its density is 8.5. If re- quired free from moisture it should be passed through a tube containing powdered potassic hydrate. Ammonia is remark- able for its pungent smell, and it exerts so powerful a cor- rosive action on moist animal tissues that the most serious consequences might arise from inhaling any considerable quantity of it. A piece of red litmus-paper immediately 79 56 AMMONIA turns blue by contact with ammonia, and nitric acid is neu- tralized by ammonia as effectually as by potash itself, so that Preparation of Ammonia Solution. a Flask containing sal-ammoniac and lime ; b safety tube ; c wash-bottle ; d bottle containing distilled water to be saturated. ammonia is justly entitled to the name which is frequently given to it, of volatile alcali. When a glass rod, moistened by nitric acid of such strength as not to fume in the air, is 80 AMMONIA 56 brought in contact with ammonia, dense white fumes are formed, owing to the formation of solid ammonic nitrate in the air, by contact of the vapour of the nitrate with the volatile alkali. Ammonia burns with the greatest difficulty; but when mixed with oxygen it can be exploded, and if sufficient oxy- gen be present ammonic nitrate is formed by the explosion. A gradual oxidation of ammonia, forming ammonic nitrite acid, takes place at the common atmospheric temperature, in presence of finely-divided metallic copper. When passed through a red-hot tube ammonia is decom- posed, and the same result can be obtained by passing a suc- cession of electric sparks through ammonia gas confined in a glass tube over mercury. The mixture of nitrogen and hydro- gen formed by the decomposition of ammonia occupies exactly double the volume of the compound of the two gases. T"=* The expansion of ammonia gas by heat takes place very nearly in the same proportion as that of oxygen, hydrogen, or nitrogen, the coefficient of expansion of ammonia being slightly greater than that of the permanent gases. The specific heat of ammonia is .5083, which is considerably less than that of the nitrogen and hydrogen contained in it. The specific heat of a mixture of hydrogen and nitrogen in the proportions in which these gases are contained in ammonia is .802. G 81 57 LIQUEFACTION OF AMMONIA. 57. Ammonia can be condensed into a liquid of about 0.76 density, by passing the gas slowly into a tube cooled by a powerful frigorific mixture below the temperature of 38.5, at which liquid ammonia boils at the ordinary atmospheric pressure. At the temperature of i oC it requires a pressure of about 6 atmospheres for its liquefaction. The Preparation of Liquid Ammonia. a Heated end of tube containing com- pound of silver-chloride and ammonia ; b cooled end of tube where liquid ammonia collects. easiest way to prepare this liquid on a small scale is to satu- rate some dry silver chloride with ammonia gas, and to put the compound into a strong glass tube, sealed up at one end and bent in the middle at an angle of about 1 20. The tube is then sealed up at the other end, by the aid of a blow-pipe flame, and when cold is ready for use. If the empty end of 82 SOLUTION OF AMMONIA. 58 the tube be surrounded by ice, whilst the end containing the compound of ammonia and chloride is heated by means of a water bath, the ammonia is gradually expelled from the com- pound, and is confined by the narrow dimensions of the tube at so great a pressure, that a considerable proportion of it condenses in the cold end of the tube. Liquid ammonia solidifies at about 9oC. A solution of ammonia in water, saturated with the gas at a low temperature, gives off a large part of the gas when heated, and a strong solution of am- monia can therefore be used for the preparation of liquid ammonia. The operation is performed in iron vessels from which all atmospheric air has been removed, and if the water from which ammonia has been expelled by heat be cooled again, it condenses the ammonia gas above it, and causes an evaporation of the liquid ammonia which has been previously condensed. The evaporation of this liquid ammonia serves to freeze water outside the vessel. 58. Ammonia dissolves in water with great rapidity, and gives off a considerable quantity of heat in the process. At OC water takes up more than 1000 times its volume of the gas, at i5C upwards of 700 volumes, and at 24C nearly 600. The solutions smell strongly of ammonia, and when saturated give off a part of the gas with extreme readiness. Their density is less than that of water, and the strongest solutions have the smallest density. Quantitative deter- minations have been made of the proportion of ammonia and water, in solutions of various densities, and the re- sults of these determinations are recorded in tables, which should be consulted whenever it is wanted to know the strength of a solution of which the density has been ascertained. One of these tables will bz found at the end of the volume. Ammonia, when dissolved in water, must be con- sidered to be in combination with one molecule of water, in G 2 83 58 COMPOUNDS OF AMMONIA. the form of the compound N H 5 O. In the reaction of aqueous ammonia on hydric nitrate, forming ammonic nitrate and water, there is a process perfectly similar to that which occurs when aqueous potash reacts upon the salt; but in order to see the resemblance, we must arrange the elements of the compound of ammonia and water, so as to shew its analogy with the potassic hydrate (K) H O. For that pur- pose we can write it (NH 4 )HO, so that the group of ele- ments N H 4 is contained in the aqueous ammonia instead of the element K in the potassic hydrate. We have then to represent the reaction of the nitrate by the following equa- tion, viz. H N O 3 + (N H 4 ) H O = (N H 4 ) N O 3 + H H O ; just like H N O 3 4- (K) H O = (K) N O 3 + H H O. The action of solution of ammonia on nitrates containing other weak bases is analogous to the action of potash upon them. Thus, potash precipitates plumbic hydrate from a solution of plumbic nitrate, and ammonia effects a similar decomposition, though rather less effectually : Pb(NO 3 ) 2 + 2 KHO = 2 KNO 3 + Pb(HO) 2 . Pb(N O 3 ) 2 + 2(N H 4 ) H O = 2N H 4 N O 3 + Pb(HO) 2 . The alkalies and alkaline earths are stronger bases than ammonia, and are not separated from acids by it. 59. It will be seen by the further study of ammonia that it reacts on nearly all acids in a similar manner to potash, and that NH 4 plays the same part in the salts of ammonia which K plays in the salts of potassium. In fact this group of elements (N H 4 ) is in its compounds like the metal potassium. For these reasons it is found convenient to give to this group of elements a name bearing some resem- blance to the names of metals, and the object is attained by 84 AMMONIC NITRATE (NH*NO 3 ). 60 calling it ammonium 11 . Ammonium is at present only known in compounds, as it is always decomposed into ammonia and hydrogen as soon as it is turned out of combination. The nearest approach to free ammonium is a compound of mer- cury with if, a substance in which the metal mercury is united with the compound metal ammonium so feebly that the properties of the constituents are less altered than in firmer compounds. The compound is easily obtained by putting sodium amalgam into a strong solution of sal-ammoniac. The sodium rapidly dissolves, taking the chlorine from the ammonium, while the ammonium combines with the mercury. A soft buttery mass is thus obtained, occupying an enor- mous volume compared with that of the original mercury NaHga + NH 4 Cl = NH 4 Hgn + NaCl. The ammonium amalgam very rapidly decomposes when removed from the liquid, and gives off a mixture of two volumes of ammonia to one volume of hydrogen. 60. Ammonic Nitrate (empirical formula N 2 O 3 H 4 , rational formula NO 3 N H 4 ) is easily prepared by dissolving ammonic carbonate in nitric acid, and evaporating the so- lution till it crystallizes. The salt is then deposited in the shape of needle-shaped crystals, which can be dried on bibulous paper. Ammonic nitrate dissolves in water very rapidly, and in very large quantity. Its liquefaction absorbs a considerable quantity of heat, which is evolved again w r hen the salt crystallizes out from its solution. The salt is h AMMONIUM COMPOUNDS Ammonic chloride, N H 1 Cl. cyanide, N H 1 C N. nitrate, N H* N O 3 . hydrate, N H 4 H O. sulphate, (NH f ) 2 SO*. sulphite, (N H 4 ) 2 S O 3 . oxalate, (N H 4 ) 2 C 2 C*. carbonate, (NH 4 , 2 CO 3 , phosphate, (NH') 3 P0 4 - POTASSIUM COMPOUNDS Potassic chloride, K Cl. cyanide, K C N. nitrate, K N O 3 . hydrate, K H O. sulphate, K 2 S O 4 . sulphite, K 2 SO 3 , oxalate, K a C 2 O l . carbonate, K 2 C O 3 . phosphate, K 3 P O*. 85 60 APPENDIX TO CHAPTER VIII. frequently used for producing a low temperature for the for- mation of ice, and is recovered again after use by evaporation of its solution. When thrown on to red-hot coals the salt explodes, but when heated gradually by means of a lamp it decomposes entirely into nitrous oxide and water. Ammonic nitrite (N 2 H 4 O 2 or NO 2 (NH 4 )) is a very un- stable salt. It can be obtained by decomposing plumbic nitrite by ammonic sulphate. The solution decomposes when heated, giving off nitrogen gas. A solution of ammonia precipitates a solution of cupric sulphate, but when added in greater quantity it dissolves the precipitate, forming a deep azure-blue solution. Ammonic chloride forms with platinic chloride a compound very slightly soluble in water, and insoluble in alcohol. It possesses the composition Pt (N H 4 ) 2 Cl 6 . The most deli- cate test for ammonia is Nessler's test, viz. potassic iodide saturated with mercuric iodide. When mixed with an excess of potash, this solution gives a reddish yellow colour with a liquid containing the least trace of ammonia, and gives a precipitate with very small quantities of ammonia. Appendix to Chapter VIII. PROBLEMS. 56. What will be the dimensions of a flask capable of con- taining 20 grammes of ammonia gas, at i2C and 730 mm. pressure ? 57. What weight of sal-ammoniac must be taken to obtain i kilogramme of ammonia ? 58. What volume of nitrogen is obtained by the com- bustion of i o cubic centimetres of ammonia ? 59. What volume of nitrogen will be evolved by the action of nitrous acid on 10 grammes of ammonia? 86 APPENDIX TO CHAPTER VIII. 60. ico grammes of nitre (K N O 3 ) are distilled with hydric sulphate. What weight of ammonia will be required to neutralize the distillate ? and what will be the weight of the nitrate formed ? 6 1. 3 grammes of nitric oxide are mixed with an excess of hydrogen and passed over moderately heated platinum sponge. What weight of ammonia is formed ? 62. 2.14 grammes of ammonic chloride (N H 4 Cl) were obtained by the action of metallic zinc in presence of iron on a mixture of a nitrate with potash solution. W T hat weight of anhydrous nitric acid was required for its formation ? 63. A weighed quantity of an organic substance containing nitrogen was heated with soda-lime, and the ammonia was passed into hydrochloric acid and combined with platinic chloride. 3.428 grammes of the double chloride were thus obtained. How much nitrogen is contained in this ? 61 CARBON (C = 12. CHAPTER IX. 61. Carbon occurs as diamond, plumbago, charcoal, &c. It is remarkable for the great difference between the properties which it possesses in these different substances, differences which are not owing to the presence of any foreign substance in any of these varieties of carbon, but which belong to the carbon itself. Diamonds have a density of about 3.55, whilst plumbago has only a density of about 2.2. Diamond is the hardest known substance, whereas plumbago is so soft, that even paper rubs off particles from it. Diamond is transparent, plumbago is opaque. Diamond is a very bad conductor of electricity, and usually ranks among non-con- ductors. Plumbago, on the contrary, conducts well, and equals some metals in this respect. Diamond crystallizes in octo- hedral forms, or in forms nearly related to them, plumbago crystallizes in six-sided plates. The specific heat of diamond is .14687, while that of plumbago is .2008, and that of char- coal .2415. These substances are so entirely different in their properties that they could not be classed together at all, were it not for the fact that both of them can be made to combine with oxygen, and, once combined, retain no traces of the original differences between them, for carbonic acid made from diamonds is identical with carbonic acid made from plumbago. At a very high temperature, such as that obtained by discharging a powerful galvanic battery between two carbon points, diamonds swell up, become opaque, and are transformed into a material nearly resembling plumbago. The inverse transformation has not yet been effected. 88 COKE. 62 Plumbago, or black-lead, as it is commonly but very improperly called, is obtained from mines in Cumberland, Ceylon, and some other districts. A very similar substance is formed by the gradual cooling of large masses of cast-iron. The molten mass contains carbon in solution, and a part of this carbon crystallizes out on the surface of the iron while it is cooling. A very pure and dense variety of carbon is found in the roof of old gas-retorts, where it had been gradually de- posited, by the action of the high temperature upon the coal- gas which was passing out. 62. Coke is a dense variety of carbon, prepared by heating coals to a bright red heat, and thereby expelling, as gas, oils, &c., all the hydrogen and oxygen of the native coal, with some of its carbon. Coals which are rich in compounds of hydrogen become semi-fluid before decomposition, and the coke which is left from them is in large coherent masses. Such coals are called caking coals. Welsh coal and anthra- cite contain little hydrogen, and burn with very little flame or smoke. They approach more nearly to the composition of coke than the bituminous coals. Coke generally contains earthy matter, which remains as an ash when the carbon is burnt away, and sometimes a good deal of sulphur in the form of ferric sulphide or pyrites, which diminishes its value con- siderably for foundry use. Charcoal is the name given to the carbon obtained by expelling all the hydrogen and oxygen from wood by heat, the necessary heat being usually obtained by burning some of the wood. The ashes of charcoal contain potassic car- bonate. Few persons can have used successively coke and charcoal for fuel without noticing the comparative difficulty of lighting coke ; inasmuch as those parts of it to which heat is applied allow the heat to escape from them into the rest of the heap, far more rapidly than is the case with charcoal. This superior conducting power for heat which 89 62 CONDENSATION OF GASES, &c. BY CHARCOAL. belongs to coke, is mainly owing to the comparatively dense state of aggregation of its particles, acquired by the high temperature to which they have been exposed ; for if a piece of soft porous charcoal be heated to a good white heat in a closed vessel it is found to become harder and more difficult of ignition than before, in fact very much like coke itself. At no temperature to which it has been exposed does carbon evaporate, or even shew signs of fusion. 63. When prepared at a comparatively low temperature charcoal possesses the power of condensing large quantities of gas on its surface, and the gas so condensed is capable of producing effects which it cannot produce under similar circumstances when uncondensed. Thus, the oxygen of atmospheric air when condensed by charcoal combines rapidly with all volatile combustible bodies which come in contact with it. Many of the most dangerous impurities in atmospheric air, such as the fetid products given off by putrefying animal or vegetable matter, can be removed from it completely by a process of total oxidation, by passing the impure air through a sufficient thickness of powdered char- coal. The air is thus rendered inodorous and harmless. Respirators have been constructed by Dr. Stenhouse, for purifying in this manner the air which passes into the lungs, and their efficacy is increased by a small quantity of finely- divided platinum spread over the charcoal. It is much to be regretted that this most valuable safeguard to health is not more generally known and adopted. Animal charcoal, bone black, ivory black, &c., are names given to mixtures of carbon with calcic phosphate, obtained by heating bones in a closed vessel until the organic matter contained in them is completely decomposed, leaving char- coal intimately mixed with the incombustible materials of the bones. The presence of the phosphate in this animal char- coal enables the carbon to remove various colouring matters 90 COMBINATIONS OF CARBON. 64 from liquids, and the substance is accordingly much used by sugar-refiners and others for the purpose of decolorizing solutions. An exceedingly striking illustration of the action of animal charcoal is obtained by putting some of it, in the form of a fine powder, into water coloured deep blue by sulphindigotic acid. The colouring matter is speedily ab- sorbed by the animal charcoal, and a colourless liquid is obtained by filtration. The charcoal obtained by calcining blood with potassic carbonate is found very efficacious for some purposes of decolorization. Lamp-black is a fine powder of charcoal, usually contami- nated by oily matter. It is made by burning hydro- carbons, such as turpentine, with a supply of air insufficient for their complete combustion. The smoke from these flames, or better still, from very bituminous coal, is made to pass through long horizontal flues, where the lamp-black gradually collects. Lamp-black, when mixed with linseed-oil and soap, forms printing-ink. 64. When heated to redness in contact, with free oxygen carbon burns, forming carbonic acid. Dumas found that by burning diamonds in oxygen gas, 44 parts by weight o carbonic acid are formed from every 1 2 parts by weight of carbon. The compound is therefore represented by the formula CO 2 . When heated in carbonic acid, carbon also burns at the expense of the oxygen of that compound, C-fCO 2 =2(CO); and when air passes up through a thick layer of red-hot char- coal or coal, there is a formation of carbonic acid at the bottom, but this carbonic acid in passing over the red-hot charcoal takes up carbon, and becomes reduced to carbonic oxide. At very high temperatures carbon combines also with hydrogen, forming the gaseous compound C 2 H 2 , called acetylene. This is obtained by discharging a powerful gal- vanic battery by carbon points, separated from one another 91 64 CARBONIC ACID (CO 2 ). by an atmosphere of hydrogen. With nitrogen, carbon does not combine without the intervention of other substances. Steam at very high temperatures is reduced by charcoal, according to the equation At a red heat carbonic acid is formed, as well as carbonic oxide. Ammonia is also decomposed by charcoal at a red heat. The products of the action are free nitrogen, hydrogen, and ammonic cyanide (C N 2 H 3 ). Charcoal evolves 8,080 of heat on burning to form car- bonic acid. Only two compounds of carbon and oxygen are known, viz. carbonic acid and carbonic oxide. 65. Carbonic Acid gas (CO 2 2 vols.) is prepared by dissolving chalk or white marble in hydrochloric acid Ca C 3 + 2 (H Cl) = CaCl 2 + H 2 O + C O 2 . Sulphuric acid is used instead of common hydrochloric acid, if carbonic acid be required for purposes in which the pre- sence of a little arsenic would be injurious. The gas is about half as heavy again as atmospheric air ; its density being like that of nitrous oxide, 22, C O 2 2 vols. i6 0=i6 = CO 2 CO 2 It neither burns nor supports combustion, so that a lighted taper is extinguished when lowered into carbonic acid gas. It can be poured from one vessel to another by displace- ment of air, but should not be left long in an open vessel, as it gradually escapes by diffusion. Clear lime-water is precipitated by carbonic acid, the precipitate being calcic carbonate. When subjected to a pressure of 35.4 atmospheres, at the 92 CARBONATES. 65 temperature of oC, carbonic acid is condensed into a liquid. At 25C it only requires 17.2 atmospheres pressure for its condensation. The liquid carbonic acid is frequently pre- pared by putting hydro-sodic carbonate (often called bicar- bonate of soda) and water into a strong wrought-iron bottle, together with a narrow pot nearly full of sulphuric acid. The bottle is closed by a screw-plug, and then agitated so as to shake the acid out of its pot, and bring it in contact with the carbonate. Liquid Carbonic Acid is said to have a density of 0.9 at 2oC, and a density of 0.6 at 30; so that a rise of tem- perature of 50 increases its volume about 50 per cent., or about three times as much as if it were a gas. The liquid acid is usually distilled out into another vessel before use. When brought out to the open air a portion of the carbonic acid boils so rapidly as to freeze the remainder into a white solid, looking very much like snow. An alcohol thermo- meter immersed in this solid carbonic acid falls to 78C. The solid dissolves readily in ether, and can be most con- veniently used in that form for freezing purposes. Metallic mercury is instantly frozen into a solid mass like lead by contact with the solution ; and if it comes in contact with the skin, a blister is said to be produced very similar to that produced by a burn. The solid acid can, however, be taken up by the hand without producing any painful sensation, as it does not come in contact with the surface of the hand sufficiently to absorb much heat from it. The specific heat of gaseous carbonic acid, between 10 and 2ooC, is .2169. At the ordinary atmospheric tem- perature of i5C water dissolves about its own volume of carbonic acid, and the solution has a slightly acid reaction to litmus-paper. At oC the exact volume of carbonic acid absorbed by water is 1.7967; at ioC it is 1.1847; at 2oC it is 0.9014. A piece of litmus, reddened by the solution of 93 65 CARBONATES, carbonic acid, resumes its blue colour on exposure to the air for a few minutes, by evaporation of the acid. The aqueous solution no doubt contains hydric carbonate (CO 3 H 2 ), although that compound has never been separated from the water. 66. Carbonic acid reacts in two distinct proportions upon potash, forming a normal carbonate called potassic carbonate (CO 3 K 2 ) and a double salt hydro-potassic carbonate, often called bicarbonate of potash (C O 3 H K). The former salt is decidedly alkaline in its reaction and properties, proving that carbonic acid is by no means capable of neutralizing two molecules of potassium. Even the second salt is slightly alkaline. Ammonia combines with carbonic acid, forming a solid and very volatile compound, well known by the name of volatile salt of hartshorn. In the pure state the commercial salt has the composition 2(N H 4 ) 2 O 3C O 2 , and is called ammonic sesqui-carbonate*. 1 Among the oxides enumerated in 1 8, all which are strong bases can be obtained in combination with carbonic. Thus, there are the following car- bonates corresponding to the first class of oxides, viz. Silver carbonate, Ag 2 CO 3 . Sodio-potassic carbonate, Na K C O 3 . Potassic carbonate, K 2 C O\ Sodic carbonate, Na 2 C O 3 . Hydro-potassic carbonate. H K C O 3 . The peroxides (2nd and 4th classes) do not possess basic properties, and they form no compounds with carbonic acid. Many oxides of the third class form carbonates, such as Barytic carbonate, Ba C O 3 . Calcic carbonate, Ca C O 3 . Strontic carbonate, Sr C O 3 . Magnesic carbonate, Mg C O 3 . Others, such as cupric oxide, cannot form regular or so-called normal car- bonates, but when supplied with it in due proportion allow some of the acid to escape and form a compound of oxide and carbonate. Others, again, such as mercuric oxide, are unable to hold carbonic acid in combination. 94 APPENDIX TO CHAPTER IX. Appendix to Chapter IX. PROBLEMS. 64. What weight of air is needed for the complete com- bustion of i kilogramme of carbon ? 65. A chamber contains 60 cubic metres of air at i4C and 760 mm. pressure. 500 grammes of carbon are com- pletely burnt in the room and nothing allowed to escape. What is the percentage composition of the residual mixture, assuming the original air to have consisted of 21 per cent, oxygen and 79 per cent, nitrogen by volume ? 66. \Vhat weight of hydro- sodic carbonate, and what weight of hydric sulphate, must be used in order to evolve i kilo- gramme of carbonic acid according to the equation HNaCO 3 + H 2 SO 4 =HNaSO 4 + H 2 O + CO 2 ? 67. What volume of carbonic acid would be obtained by combining j oo grammes of oxygen in the proper proportion with carbon? 68. What weight of carbon is contained in a litre of carbonic acid ? 69. What weight of calcic carbonate must be dissolved for the evolution of 20 litres of carbonic acid at J5C and 760 mm. pressure ? 95 67 CARBONIC OXIDE (C 0). CHAPTER X. 67. Carbonic Oxide (C O = 2 vols.) is most conveni- ently prepared in large quantities by passing dry carbonic acid through a red-hot tube containing charcoal, and then through a bottle containing pieces of coke soaked in potash. In most cases it is best made by mixing potassic formiate with sulphuric acid, in sufficient quantity to form a thin mud, and heating the mixture. The reaction which ensues is this CHKO 2 + SO 4 H 2 = CO + SO 4 HK + H 2 O. Carbonic oxide is a little lighter than atmospheric air; its density being 14, the same as that of nitrogen. It burns in CO CO = 14 2 2 air with a pale blue flame, forming carbonic acid, and every two volumes of carbonic oxide combine with one volume of oxygen to form two volumes of carbonic acid. When the CO CO + O 16 = CO 2 CO 2 -=22 2 2 a " 2 mixture in these proportions is fired by the electric spark it explodes with force about equal to that of the explosion of oxy-hydrogen gas. The heat of combustion of carbonic oxide is 2,403 degrees ; and as 28 parts by weight of the gas contain 16 parts by weight of oxygen and 12 of carbon, it 96 PROPERTIES OF CARBONIC OXIDE. 68 follows that one part by weight of carbon in carbonic oxide evolves 5,607 degrees of heat on taking up the additional oxygen to form carbonic acid. If this quantity of heat be deducted from 8,080 degrees, which charcoal gives off when it burns to carbonic acid, the difference, namely 8080 5607 = 2473, shews how much heat is evolved by one part by weight of carbon burning to form carbonic oxide. 68. Some furnaces are occasionally to be seen at work under such conditions that the air, after forming carbonic acid with the fuel with which it first comes in contact, is then forced over red-hot coals, so as to reduce this carbonic acid to carbonic oxide, which escapes unburnt or burns outside the furnace : and the above calculation shews that in such cases there is less than one-third the total quantity of heat of combustion of the fuel given off in the furnace. To rectify the working of such a furnace the mixture of nitrogen and carbonic oxide which passes out from the coals should be intimately mixed, while still hot, with as great a volume of air as that which passed through the coals. The weight of air needed for burning completely i kilo, of coal is nearly 12 kilos., and these occupy at the common temperature about pf cubic metres. To verify these numbers we should first calculate the weight of oxygen needed to burn a kilo, of coal, and then how much air must be taken in order to supply the needful quantity of oxygen. The formula C O 2 shews that for every 1 2 parts by weight of carbon 3 2 parts by weight of oxygen are needed, or /or one of carbon 2| of oxygen. As air contains 23 per cent, of oxygen by weight, we have the proportion 23 : 100 = 2 : x, whence 11.56 kilos, is the weight of air needed to burn i kilo, of carbon. Coals, however, usually contain some unburnt hydrogen, and this renders a greater proportion of oxygen necessary ; so that 1 2 kilos, of air is by no means too much to allow. Allowing 1.293 kilo, as the weight of a cubic metre of air at o, or H 97 68 OXALIC ACID (C 2 O s ). 1.2256 at i5C, the proportion 1.22 56 : i = 12 : x gives us 9.7584, or in round numbers g|, as the number of cubic metres of air at 15 weighing 12 kilos., needed for the com- bustion of i kilo, of coal. 69. The specific heat of carbonic oxide is .2450. When it combines with oxygen the carbonic acid formed would have a specific heat equal to .235 if it retained that of the oxygen and of the carbonic oxide without loss, whereas the specific heat of carbonic acid is only .2103. Carbonic oxide has never been condensed by cold or pres- sure into a liquid. Carbonic oxide is stated to be poisonous when taken into the lungs for some time, and the deadly effects produced by a charcoal fire in an unventilated room are attributed to its action. It is rather less soluble than oxy- gen in water. A solution of potash does not absorb it in the cold, but carbonic oxide is slowly absorbed by semi-fluid potash at iooC, producing potassic formiate CO + HKO = KCHO 2 . Carbonic oxide is absorbed by a solution of cuprous chloride (Cu 2 Cl 2 ) in aqueous hydrochloric acid. Melted potassium also absorbs carbonic oxide. 70. Oxalic Acid (C 2 O 3 ) is not known in the free state. Its salts are contained in the juice of many plants, such as sorrel, lichens, &c. Its compound with water (hydric oxalate, H 2 C 2 O 4 ), generally called oxalic acid, is now prepared on a large scale by heating sawdust with a mixture of po- tassic and sodic hydrate. The alkaline oxalates thus obtained are dissolved in water and boiled with milk of lime. The lime carries down the acid as an insoluble salt, and the alka- line hydrates are left in solution ready for using with some fresh sawdust as soon as they have been boiled down Na 2 C 2 O 4 + Ca O 2 H 2 = 2 (Na O H) + Ca C O 4 . The calcic oxalate is, decomposed by dilute hydric sulphate CaC 2 4 + H 2 S0 4 = H 2 C 2 4 + CaSO 4 . 98 OXALATES. 71 Hydric oxalate may easily be made on a small scale by the action of nitric acid on sugar or starch. Eight parts of nitric acid of 1.37 density are heated with one part of sugar, and the mixture evaporated to about ^ of its original volume, when crystals of the hydrogen salt are deposited on cooling. The crystals contain two molecules of water C 2 H 2 4 (H 2 0) 2 , which can be expelled by gentle heat, and a white powder is then left consisting of the hydrogen salt H 2 C 2 O 4 . When heated more strongly the salt decomposes chiefly into carbonic acid and carbonic oxide, whilst water is libe- rated, C 2 H 2 O 4 = CO 2 + CO + H 2 O; but a small quan- tity of the compound is carried up by the escaping gases, and condenses on any cold surface over which it is led, whilst a little formic acid is formed at the same time. When an oxalate is heated with strong sulphuric acid it breaks up entirely into carbonic acid and carbonic oxide, whilst water is liberated C 2 H 2 O 4 = C O 2 + C O + H 2 O. When hydric oxalate is heated to a temperature of 100 with glycerine, it breaks up entirely into hydric formiate and carbonic acid 71. Hydric oxalate dissolves readily in water, and has an intensely acid taste, and acid reaction to litmus-paper. Its solution expels carbonic acid from its salts, whilst water is formed at the same time, and it destroys the alkaline reaction of potash and soda. With either of these bases it reacts in two distinct proportions, forming first a double salt of hydrogen and potassium or, with twice as much base, it forms the normal potassic oxalate H 2 99 71 FORMIC ACID (C 2 # 2 3 ). There is also another double salt containing hydrogen and potassium, tri-hydro-potassic binoxalate, H 3 KC 4 O. Ammonia combines with hydric oxalate to form either a neutral ammonic oxalate, (N H 4 ) 2 C 2 O 4 (H 2 O), or hydr- ammonic oxalate, H (N H 4 ) C 2 O 4 (H 2 O). The salts of oxalic acid, containing calcium, barium, or the heavy metals, such as zinc, iron, lead, &c., are insoluble in water but soluble in acids. One of the most important of its salts is the calcic oxalate (Ca C 2 O 4 ), which is insoluble in water and in acetic acid, though soluble in hydrochloric or in nitric acid. When the salt is cautiously heated it decomposes, leaving a colourless residue of calcic carbonate, whilst carbonic oxide escapes. The residue dissolves with effervescence in acetic acid. When mixed with manganic peroxide, in presence of hydrochloric acid, the oxalic acid in oxalates is completely oxidized to carbonic acid. Commercial oxalic acid generally contains some mineral impurities, which are left as an ash when the acid is burnt. If it be required in a state of purity it should be made from distilled vinic oxalate, which is easily decomposed by water. 72. Formic Acid (C 2 H 2 O 3 ) is not known in the free state. Its hydrogen salt, CH 2 O 2 , was originally ex- tracted from red ants, and was named from that source. It is formed by the partial oxidation of a great variety of organic bodies, such as sugar, gum, tartaric acid, alcohol, &c. ; but by far the best way of making it is by the action of glycerine on dried oxalic acid. A tubulated retort is about one-quarter filled with concentrated glycerine, and as much dry oxalate thrown in as the glycerine can cover. The mouth of the retort is inserted into a flask receiver, and its body is sur- rounded by boiling water. The formiate distils over into the receiver, whilst carbonic acid escapes ; and when it ceases to come over some fresh oxalate is put into the retort, and the process is thus repeated with the same portion of glycerine 100 FORMIC ACID (C 2 H z O 3 ). 72 until enough acid has been collected. If the compound be required free from uncombined water, it should be made by the action of sulphuretted hydrogen on dry plumbic for- miate Pb (C H O 2 ) 2 + H 2 S = Pb S + 2 (C H 2 O 2 ). It is then obtained as a liquid of 1.235 density, and boiling at 100. Compounds of formic acid greatly resemble those of acetic acid (or vinegar) in their properties. One of the least soluble of the formiates is the plumbic salt. With calcium it forms an exceedingly soluble salt, obtained by dissolving lime in hydric formiate Ca O + 2 (H C H O 2 ) = H 2 O + Ca (C H O 2 ) 2 . Mercuric and argentic formiates are completely decomposed by heat in presence of water, the metal being reduced and carbonic acid making its escape with effervescence. For- mic acid resembles nitric acid in reacting on potash in one proportion only, forming the salt K C H O 2 , containing one atom of potassium in the place of one atom of hydrogen in the hydrogen salt. This neutral salt forms an unstable compound with the acid hydrogen salt, having the com- position (KCHO 2 ) (HCHO 2 ); but this substance is a very unstable chemical compound, for the hydric formiate contained in it is driven off at 100, just like free hydric formiate. There are many compounds of carbon and hydrogen, but only one of them (acetylene) has been made by the direct combination of the elements. Several hydrocarbons are gaseous, many are liquid, and some, as paraffine, are solids. The three simplest hydrocarbons will alone be described at present ; and first of these marsh gas. lot APPENDIX TO CHAPTER X. Appendix to Chapter X. PROBLEMS. 70. What volume of carbonic acid must be passed over white-hot charcoal for the preparation of 10 litres of car- bonic oxide ? 71. What volume of carbonic oxide will be obtained by passing a litre of oxygen over an excess of white-hot char- coal ? 72. 10 litres of a mixture of carbonic oxide and oxygen, in the combining proportions, are fired by the electric spark. What volume of carbonic acid is formed ? 73. A ton of carbon has to be burnt to carbonic oxide by means of air. What volume of air is needed for the pur- pose ? What will be the volume of the mixture formed ? How much heat will be evolved in the process ? How much heat will be obtained by burning the carbonic oxide ? 74. What weight of water, supplied at cC, would be evaporated at atmospheric pressure by the total heat of combustion of i kilogramme of carbon? 75. How much heat is evolved by the combustion of a litre of carbonic oxide, measured at oC and 760 mm. 76. 50 grammes of crystallized 'oxalic acid' are decom- posed by sulphuric acid. What volume of carbonic oxide is evolved? 77. What weight of ammonia would be neutralized by a kilogramme of hydric oxalate (H 2 C 2 O 4 )? 78. What weight of pure hydric formiate would be formed from a kilogramme of hydric oxalate by the action of glyce- rine? and what weight of ammonia would this formiate neutralize ? IC2 MARSH GAS (C# 4 ). 73 CHAPTER XL 73. Marsh Gas (C H 4 = 2 vols.). It is formed by the putrefaction of vegetable matter under water, and has thence obtained its name. It is also given off from the coal mines, and by mixing with air in the shafts and galleries gives rise to an explosive mixture, which it is the duty of the super- intendent to remove by thorough ventilation, before it accumulates in sufficient quantity to do harm. Marsh gas is formed by the action of a high tempera- ture on many volatile and fixed organic bodies, and is a chief constituent of coal gas ; but the most convenient way to prepare it for use is, to mix potassic acetate with two or three times its weight of slaked lime, and to heat the mixture in a flask coated with Stourbridge clay. Marsh gas is given off below a red heat, and carbonic acid re- mains in combination with the bases, partly potash, partly lime. The product requires purification by oil of vitriol. The equation C 2 H 3 K O 2 + H K O = C H 4 + C O 3 K 2 represents the process, assuming potassic hydrate to react on the acetate. Marsh gas burns with a yellowish blue flame, but if previously heated by passing through a red-hot tube it is said to yield a far more luminous flame. One molecule of the gas, occupying two volumes, requires four atoms of oxygen, occupying four volumes, for its complete combustion, and the mixture explodes even more strongly than oxy-hydrogen gas. The products are two volumes of carbonic acid, four volumes of steam, of which latter the greater part condenses at the ordinary temperature and 103 73 ETHYLENE OR OLEFIANT GAS (C 2 # 4 ). pressure. Marsh gas is the lightest known substance, next to hydrogen its density being only 8. All attempts to con- ., H 2 O ~~T~ = 9 i CH< II 8 O = i6 CO 2 =22 2 H 2 I" =9 + O = i6 + CH' , CO 2 =22 H 2 =9 2 2 2 0=i6 dense marsh gas, by combined cold and pressure, have failed. Marsh gas is rather more soluble than oxygen in water, for at oC one volume of water dissolves 0.054; at ioC 0.044; an d at 2oC 0.035. A succession of electric sparks decomposes marsh gas, carbon being deposited, and hydrogen being left, of volume double the marsh gas employed. 74. Ethylene or Oleflant Gas (C 2 H 4 = 2 vols.) is one of the minor constituents of coal gas. It is best made by heating spirits of wine with about double its bulk of strong sulphuric acid. Some dry sand should be added, in sufficient quantity to form a thick mud with the mixture, as it is other- wise liable to froth very much. The gas comes over with water, which is formed at the same time, by decomposition of the alcohol Alcohol, C 2 H 6 O = C 2 H 4 + H 2 O. 104 ETHYLENE OR OLEFIANT GAS 74 Some alcohol vapour is also carried over, as well as ether, and these impurities are best removed by passing the gas through oil of vitriol spread over pumice-stone. There is also sulphurous acid and carbonic acid formed, by the combustion of some of the alcohol at the expense of the sulphuric acid, and to remove these impurities the gas should be passed through caustic potash. It is then obtained as a colourless and nearly inodorous gas, of the same density as nitrogen and carbonic oxide, viz. 1 4. Olefiant gas dissolves considerably in water. One volume at oC dissolves 0.256 of the gas, at 10 0.184, and at 20 0.149. Faraday compressed olefiant gas to a liquid, by using a very great cold, together with pressure. At 76 the liquid was found to exert a pressure of 4.6 atmospheres, and at 1 7.8 as much as 26.9 atmospheres. Olefiant gas burns with a bright luminous flame, consuming C 2 H' 2 C 2 H 4 =I 4 = i6 CO 2 =22 2 i6 O=i6 CO 2 =22 2 + CO 2 =22 2 H 2 2 H 2 2 = 9 H 2 2 = 9 H 2 2 = 9 in the process three times its own volume of oxygen, and forming twice its own volume of carbonic acid. It is easily 10! 74 ACETYLENE (C 2 # 2 ). decomposed by heat, and if passed through a red-hot tube, it deposits carbon and* forms marsh gas, together with other compounds ; but at very high temperatures the marsh gas is in its trn decomposed, liberating hydrogen. defiant gas is rapidly absorbed by anhydrous sulphuric acid, or by the fuming sulphuric acid (hydric disulphate), which is a compound of the acid with the hydric sulphate, and this re-agent is usually employed for absorbing olefiant gas in any mixture, such as coal gas, in which its quantity has to be determined. It is also absorbed, though very slowly, by common oil of vitriol (hydric sulphate), and the compound thus formed is a double salt of ethyle (C 2 H 5 ) and hydrogen. By mixing this double salt with "water, and boiling the mix- ture, alcohol is distilled over, thus (C 2 H 5 ) H S O 4 + H 2 O = S O 4 H 2 + C 2 H 6 O. Through the agency of sulphuric acid, alcohol can therefore be built up again from olefiant gas and water, the very products into which it is decomposed, at a high temperature, by the acid itself. Olefiant gas has obtained its name from the circumstance of its forming with chlorine an oily compound called Dutch liquid (C 2 H 4 C1 2 ). 75. Acetylene (C 2 H 2 = 2 vols.) is said to be formed by passing the vapour of Dutch liquid through a red -hot tube. It burns with a rather smoky flame. Its most characteristic property is that of forming a solid compound of a red-brown colour when led into a solution of cuprous chloride in am- monia. This compound is explosive. By the action of hydrochloric acid the compound is decomposed with libera- tion of acetylene. When warmed in contact with zinc, in a solution of am- monia, it gradually combines with the hydrogen which is being given off, and forms olefiant gas. 76. Coal G-as is a mixture of gaseous compounds given 106 PURIFICATION OF COAL GAS. 78 off by coals, when rapidly heated to redness in an iron or earthenware retort. The quality of coal used for preparing gas is by no means a matter of indifference. The resinous coals yield far more gas than those harder varieties which do not cake on heating. Anthracite is of ^11 Jdods ih most useless for gas making, as it approaches most nearly to coke in its composition. Cannel coal, and especially a substance known by the name of Boghead Cannel, are the best gas coals, and a ton of these yields as much as 15,000 cubic feet of gas. Ordinary varieties of blazing coal yield from 8,000 to 11,000 cubic feet per ton. 77. The gas deposits a good deal of semi-fluid matter known by the name of tar, also water containing ammonia. Coal tar is alkaline to test-paper, and hydrochloric acid dis- solves out from it a mixture of bases, containing carbon, hy- drogen, and nitrogen, bases which can be precipitated from the hydrochloric acid by potash, and which appear as heavy oils. One of these is aniline (C 6 H 7 N), which is now largely manufactured for the preparation of dyes. Coal tar also contains oily acids, which can be dissolved out from it by lime, and which are precipitated by hydro- chloric acid. These are used for preserving meat and timber and other organic bodies from putrefaction and decay, and are generally called coal tar creosote. One chief antiseptic constituent of creosote is a crystalline body of the composition C 6 H 6 O, a kind of alcohol called phenylic hydrate. Besides these basic and acid oils, coal tar contains several neutral oils and crystalline compounds. Among these benzole (C 6 H 6 ) and naphthaline (C 10 H 8 ) deserve special mention. The former is the material from which aniline is artificially prepared, and the latter is a volatile solid which contributes materially to the peculiar smell of coal gas. 78. After it has deposited the tar, coal gas has to be purified before use. The worst impurity which it contains is 107 78 COMPOSITION OF COAL GAS. sulphur, and this element is present partly in the form of sulphuretted hydrogen (S H*), partly in the form of carbonic sulphide (CS 2 ). The sulphuretted hydrogen is removed by passing the gas over ferric hydrate, iron combining with sul- phur and water being formed. The carbonic sulphide is left in the gas for want of a convenient method of removing it. Ammonia should also be removed as completely as possible from the gas, not only for the sake of its commercial value for agricultural and other purposes, but also because it cor- rodes the brass tubes through which gas is passed. Saw- dust soaked with dilute sulphuric acid is used for absorbing ammonia. 79. The greater proportion of the volume of coal gas consists of hydro- gen and marsh gas, the former of which evolves heat and scarcely any light on combustion, while the latter is of very small illuminating value. In spite of this, hydrogen itself contributes to the il- luminating value of coal gas, by keeping in it the vapour of benzole and of other highly illuminating liquids. A very sim- ple experiment may prove this, for if a jet of hydrogen, which is burning at a 108 Apparatus to shew flame ot Hydrogen charged with Benzole. a Bottle containing zinc and dilute acid. STRUCTURE OF FLAME. 80 fine point, be supplied with benzole, by pouring a few drops of the oil into the bottle in which the gas is being evolved, the flame immediately becomes white, or sometimes even smoky. Hydrogen and marsh gas are therefore of value by enriching the coal gas by benzole, or when present in the gas from Boghead Cannel they aid the evaporation of hydro- carbons, such as C 5 H 12 . Carbonic oxide is a minor con- stituent of coal gas, which has a similar value. The actual illuminating gas contained in coal gas is olefiant gas, of which there is generally three to four per cent, of the volume of the mixture. In some varieties of gas there is besides olefiant, gas a more easily condensible hydrocarbon, con- taining carbon and hydrogen in the same proportion as olefiant gas, but differing from that body by its density, which is twice as great viz. 28. This can be seen from its formula C 4 H 8 = 2 vols. This gas is often named after its illustrious discoverer, Faraday's gas. It is sometimes called butylene. Carbonic acid and nitrogen are generally present in gas, in very small quantities. As an example of a coal gas, the following result of an analysis of a Manchester coal gas by Bunsen may be quoted. The numbers represent volumes of each constituent in 100 volumes of the gas. Hydrogen . . . . 45.58 Marsh gas .... 34.90 Carbonic oxide . . 6.64 Olefiant gas . . . 4.08 Butylene . . . . 2.38 Sulphuretted hydrogen 0.29 Nitrogen .... 2.46 Carbonic acid . . . 3.67 Acetylene is also frequently contained in coal gas. 80. Structure of flame. A burning candle or oil lamp differs from a flame of gas mainly in one respect ; namely, that it is a gas manufactory as well as a gas burner. For the liquid fat or oil is drawn up by the wick, in the midst of the flame, where it is made into gas by the action of heat, and the gas burns all round the wick as fast as it is formed, evolving 109 80 STRUCTURE OF FLAME. (by its combustion) heat, which keeps up the supply of gas. Immediately round the wick of a candle the flame does not give light. This dark zone extends usually to some height above the wick. It consists of combustible gases, on their way from the wick to the outer part of the flame, where they get burnt. Immediately round this inner and non-luminous zone is the brighter part of every flame. It consists mainly of steam, formed by the combustion of hydrogen, and solid particles of carbon, heated to a bright white heat. Of course nitrogen penetrates into it, with the oxygen which goes to form steam. A clear bead of glass held in this part of the flame by a platinum wire or forceps gets blackened by collecting soot, and metallic oxides such as plumbic oxide which part with their oxygen easily are reduced to the metallic state. This flame, containing free carbon, is therefore called the reducing flame. The outer surface and the top of the flame is usually of a pale blue or violet colour, and consists of carbonic acid and steam, mixed with nitrogen and heated to a high tempera- ture by the complete combustion of the gas. This outer flame is called the oxidizing flame, as it produces powerful effects of oxidation, owing to the presence in it of atmospheric air, at a high temperature. Whenever hydrocarbons are very imperfectly burnt, there is a deposition of carbon, as the more active hydrogen gets oxidized first ; and this temporary deposition of carbon is an essential condition for the production of the white light re- quired in an ordinary flame. When coal gas is wanted for heating purposes it can be burnt in Bunsen burners, which are so constructed that the coal gas mixes in a tube with a certain limited quantity of air, and the mixture burns in the open air on coming out of this tube. Under these circumstances a pale violet no APPENDIX TO CHAPTER XI. 80 colour is alone visible in the flame, and it is scarcely more luminous than a similar flame of hydrogen. When a more intense heat is needed, the flame is supplied by a jet of air from the nozzle of a mouth blow-pipe, or, better still, a blow-pipe worked by bellows; and in this manner glass tubes or rods can be readily heated so as to bend to any required angle, or even to draw out to a fine point. Appendix to Chapter XL PROBLEMS. 79. What is the weight of 10 litres of marsh gas at oC and 760 mm. ? 80. What volume of air is needed for the complete com- bustion of a litre of marsh gas ? What will be the volume (calculated at oC and 760 mm.) of the steam formed by its combustion ? 8 1. What weight of marsh gas would be obtained from a kilogramme of potassic acetate, according to the equation K C 2 H 3 O 2 + K H O = C H 4 + K 2 C O 3 ? 82. What is the volume of a kilogramme of ethylene ? 83. What volume of oxygen is needed for the complete combustion of a litre of ethylene ? What volume of carbonic acid, and what volume of steam, are formed ? 84. What volume of hydrogen would be obtained from a litre of ethylene if the carbon were entirely removed ? 85. What volume of acetylene could be burned by a litre of oxygen ? What would be the volumes of the products ? 86. What is the weight of a litre of acetylene ? 87. A thousand litres of ethylene are burned in a chamber containing 100 cubic metres of dry and pure air, both at oC and 760 mm. W T hat is the percentage composition of the air at the end of the process, supposing nothing to escape or enter ? in 81 CYANOGEN (C 2 .iV 2 ). CHAPTER XII. 81. Cyanogen k (C 2 N 2 = 2 vols.) is best prepared by heating mercuric cyanide in a glass tube. It should be collected over mercury, or by displacement of air, as water dissolves it to a considerable extent. Metallic mercury is set free, together with cyanogen gas ; but some of the cyanogen is transformed into a dark brown mass containing carbon and nitrogen. Cyanogen is a heavy gas of pungent odour.- Its density is 26. It burns with a purple flame, absorbing twice its bulk of oxygen. When passed through a tube cooled to a tem- perature of 25 to 3QC it condenses to a liquid, and at oC the liquid was found by Bunsen to exert a pressure of 2.7 atmospheres; at 2oC of 5 atmospheres. The liquid freezes at 34-4. When dissolved in water cyanogen speedily decomposes, forming a variety of products ; amongst them is ammonic oxalate, formed by cyanogen taking up the elements of water C 2 N 2 + 4 (H 2 O) = C 2 (N H 4 ) 2 O 4 . Cyanogen combines with potassium, but the compound (K C N) is easily decomposed by acids, in presence of water. Cyanogen is remarkable for the stability of the double salt, which it forms with iron and potassium, and for the insta- bility of its compounds with the alkali metals by themselves With iron it forms the valuable blue colours known by the name of Prussian blue. 82. Cyanic Acid is assumed to exist in the so-called cyanates, represented by hydric cyanate (HCNO). It is k Hg(CN) 2 = Hg + C 2 N 2 . 112 UREA (CN*H*0). 83 prepared by distilling hydric cyanurate or cyamelide ; the condenser should be surrounded by a freezing mixture. It is a very volatile liquid, of pungent odour and violent action on the skin. Even at the temperature of oC this compound speedily changes into a solid inert substance, called cyam- elide ; but at the ordinary atmospheric temperature the change is complete in five minutes. When dissolved in water, cyanic acid is recognized for a short time by its peculiar odour, but it soon takes up the elements of water, and becomes con- verted into hydr-ammonic carbonate CNOH + 2 (H 2 0) = C0 3 H(NH 4 ). 83. Urea (CON 2 H 4 ) is a weak base contained in human urine, and constituting the chief nitrogenized excretion. It can be obtained by adding nitric acid to urine, previously evaporated to a small bulk. Impure crystals of urea nitrate are thus deposited, and urea can be obtained from them by evaporating their solution in water to dryness with barytic carbonate in slight excess, and dissolving up the urea by alcohol, which leaves barytic nitrate undissolved. Urea contains the elements of ammonic cyanate NH 4 (CNO); and this suggested to Wohler the possibility of making it artificially by combining ammonia and hydric cyanate. The usual plan is to mix a solution of potassic cyanate in water with ammonic sulphate, and to evaporate the mixture to dry- ness. The quantity of sulphate should be sufficient to supply fully as much sulphuric acid as the potassium in the cyanate requires. Alcohol is added to the dry mixture, and dissolves out urea from it, leaving potassic sulphate and the excess of ammonic salt. The process consists of an interchange of bases, between the potassic cyanate and ammonic sul- phate, forming ammonic cyanate and potassic sulphate 2 (K C N O) + (N H 4 ) 2 S O 4 = K 2 S O 4 + 2 (N H 4 C N O) ; and part of the ammonic salt is changed into urea, while I n3 83 CYANURATES. another part takes up water, becoming neutral ammonic car- bonate. By evaporation of its solution urea is obtained in the form of white needle-shaped crystals, which dissolve readily in water. The urea nitrate is considerably less soluble in water than the base itself. Its composition is represented by the formula (N O 3 H) CN 2 H 4 O. Nitrous acid immediately de- composes urea with effervescence ; carbonic acid and nitrogen being given off whilst water is formed. When mercuric nitrate is added to a solution of urea, a white precipitate is formed, containing urea combined with mercuric oxide and a part of the nitric acid. Urea oxalate is precipitated when a concentrated aqueous solution of urea is mixed with oxalic acid. Its formula is (C N 2 H 4 O) 2 H 2 C 2 O 4 . In contact with decomposing animal or vegetable matter urea combines with the elements of water, and is transformed into ammonic carbonate. Hence the presence of that salt in decomposed urine C O N 2 H 4 + 2 (O H 2 ) = C O 3 (N H 4 ) 2 . Urea is decomposed by heat. It first melts, and then gives off ammonia. When as much ammonia as possible has been expelled by heat, the residue possesses the com- position of hydric cyanate or cyamelide, but different properties from either of these bodies. It is called ' cyanuric acid/ 84. Cyanurates. The hydrogen salt H 3 C 3 N 3 O 3 is a solid crystallizable compound of great stability. It is puri- fied by dissolving in oil of vitriol with the aid of heat, and adding nitric acid as long as there is any effervescence. Water then precipitates a snowy-white powder, which is pure cyanurate. A solution of cyanurate in water does not decompose like the corresponding solution of a cyanate. The basic metal in cyanurates is replaceable in three pro- portions, forming double salts of the three following classes ; viz. ist, those in which one atom of hydrogen is replaced ISOMERISM. 85 by the more basic metal, for instance, KH 2 C 3 N 3 O 3 ; 2nd, salts which are formed by the substitution of metal for two atoms of hydrogen, such as HAg 2 C 3 N 3 O 3 ; and, finally, salts in which all the three atoms of hydrogen are replaced by basic metal, such as Ag 3 C 3 N 3 O 3 . This shews that the molecule of the hydrogen salt contains three atoms of hydrogen. Hydric cyanate has only one atom of hydrogen in each molecule, for we cannot remove a part of the hydrogen in one molecule without removing the whole. Hydric cyanurate passes over into the cyanate by mere distillation, without taking up or losing anything ; and cyam- elide can be transformed in like manner into hydric cyanate without any change in the proportions of the elements con- tained in it. 85. The term 'isomerism' is used to denote the existence of differences of physical or chemical properties among bodies of the same composition. When two compounds have the same percentage composition but different molecular weights they are frequently called ' Polymerism/ A fourth substance of considerable importance (besides cyanilic acid) is isomeric with these three, viz. fulminic acid. This body is only known in its salts, the fulminates, of which the commonest is the mercury salt, a detonating compound used for charging percussion caps. The salt is made by the action of nitrous acid on alcohol, in presence of a salt of mercury, and the violence with which it detonates when struck or heated finds no parallel in the case of any other of the isomeric bodies. Argentic fulminate is represented by the formula Ag 2 C 2 N 2 O 2 ; and there is a double salt containing silver and potassium according to the proportions Ag K C 2 N 2 O 2 , which leads to the inference that the hydrogen salt itself, if prepared, would be found to possess the composition H 2 C 2 N 2 O 2 . I 2 115 85 CYANIDES. We have therefore the series of salts Cyanate HCNO, Fulminate .... H 2 C 2 N 2 O 2 , Cyanurate .... H 3 C 3 N 3 O 3 . 86. Cyanides (H C N = 2 vols.). The symbol Cy is sometimes used for an atom of cyanogen, Cy = C N. H Cy is then the formula for prussic acid. Hydric cyanide, com- monly called prussic acid, is most conveniently prepared by adding dry calcic chloride gradually to the aqueous solution of the acid, until considerably more is added than the liquid can dissolve, and then distilling the mixture at a very gentle heat, using as a condenser a vessel surrounded by a freezing mixture. In the dry state, as thus obtained, prussic acid is so exceedingly dangerous a substance, that it ought never to be made without a very good reason, and extreme care. It is a light mobile liquid, which boils at about 27C, and evaporates in large quantities far below its boiling-point. A small quantity of the vapour is sufficient to produce instan- taneous death. It burns rapidly in the air, absorbing i-J times its volume of oxygen in the process. It dissolves in water in all proportions, but is held with very little force, so that even when diluted with much water the acid evaporates very easily. To prepare a solution of prussic acid the usual plan is to decompose a solution of potassic ferro-cyanide by dilute sul- phuric acid, and distil with a good condenser, and some cold water in the receiver. The best proportions are : i o grammes of the crystallized ferro-cyanide dissolved in 50 grammes of water; 3.5 grammes of common sulphuric acid are then mixed with 25 grammes of water, and the mixture when cold is poured into the solution of the salt. On distilling this mixture a greenish white precipitate is formed, containing half the cyanogen of the salt employed, in combination with all the iron and one-quarter of the potassium. 116 CYANIDES. 86 The reaction is thus stated by equation 2 (Fe K* ^ N) 6 ) + 3 (H 2 S O 4 ) + Aq = Fe 2 K 2 (C N) 6 + + 3 (K 2 S0 4 ) + 6(HCN) + Aq. The solution of prussic acid has a strong smell of the acid. It reddens litmus-paper very slightly indeed; has so little ten- dency to take potassium in place of its hydrogen that it is not even able to decompose a solution of potassic carbonate. When mixed with a solution of potash, prussic acid is de- composed, forming potassic cyanide and water CNH + HKO = CNK+H 2 O; but the solution is as alkaline to test paper as caustic potash itself. It is decomposed by carbonic acid of the air or breath : thus, CNK + C0 3 H 2 = CNH + CO 3 HK; hence the smell of prussic acid which it possesses J . A solution of prussic acid is liable to undergo decomposi- tion, especially when exposed to the sunshine. A small quantity of hydrochloric acid impedes the decomposition, and is therefore usually added to prussic acid in order to preserve it ; but concentrated hydrochloric acid decomposes the cyanide immediately, forming ammonic chloride and formic acid : thus, CNH + 2 (H 2 0) + HC1 = NH 3 HC1 + CH 2 O 2 . When prussic acid is boiled with an excess of potash, ammonia is evolved, and formic acid remains in combination with the potash. Strong sulphuric acid not only acts like hydrochloric acid, in decomposing prussic acid, but when 1 The following table shews the similarity of constitution between metallic cyanides and the corresponding chlorides Potassic cyanide, K C N. Sodic cyanide, Na C N. Argentic cyanide, Ag C N. Mercuric cyanide, Hg (C N) 2 . Ferrous cyanide, Fe (C N) 2 . Plumbic cyanide, Pb (C N) 2 . Auric cyanide, Au (C N) 3 . Platinic cyanide, Pt (C N) 4 . Potassic chloride, K Cl. Sodic chloride, Na Cl. Argentic chloride, Ag Cl. Mercuric chloride, Hg Cl 2 . Ferrous chloride, Fe Cl 2 . Plumbic chloride, Pb Cl 2 . Auric chloride, Au Cl 3 . Platinic chloride, Pt Cl 4 . 117 86 METHYLIA (CNH 5 ). heated with the products causes a secondary decomposition of the formic acid into carbonic oxide and water. The action of heat upon ammonic formiate gives rise to prussic acid and water (C N H 4 H O 2 - 2 (H 2 O) = C N H). Prussic acid is recognized by a variety of tests, which are characteristic and delicate. When added to argentic nitrate it forms a precipitate consisting of argentic cyanide, and this precipitate dissolves in ammonia or in boiling nitric acid. With solution of mercurous nitrate it forms a grey precipi- tate consisting of metallic mercury, whilst mercuric cyanide remains in the solution. When neutralized by potash and heated with a solution of ferrous sulphate it forms potassic ferro- cyanide, which can be separated by filtration from ferric oxides and discovered by acidulation with hydrochloric acid, and addition of ferric chloride, which precipitates Prussian blue. By evaporation to dryness with yellow ammonic sulphide, prussic acid combines with sulphur, and the residue, dissolved in water, gives a deep blood-red colour when mixed with ferric chloride 6(NH 4 CNS) + Fe 2 Cl 6 = Fe 2 (CNS) 6 +6(NH 4 Cl). Ammonic sulphocyanate can also be obtained by the action of an excess of aqueous ammonia in carbonic sul- phide CS 2 + 4 (NH 3 ) = CNSNH 4 + S(NH 4 ) 2 . Potassic sulphocyanate (K C N S) is most easily obtained by fusing the cyanide with sulphur. It is remarkable for not decomposing in contact with water like potassic cyanate. It is used as a test for ferric salts. 87. Methylia (CNH 5 ). In the presence of spongy platinum prussic acid vapour combines with hydrogen, form- ing a compound wonderfully like ammonia in its properties, and called methylia. This remarkable base will be more fully described hereafter. Its vapour has the same power of 118 APPENDIX TO CHAPTER XII. 87 saturating acids as an equal volume of ammonia, and C N H 5 may be considered equivalent to N H 3 . Methylia can be condensed to a liquid at the atmospheric pressure, at a tem- perature but little below oC. Its vapour burns easily, forming carbonic acid and water, and liberating nitrogen. Appendix to Chapter XII. PROBLEMS. 88. What is the weight of a litre of cyanogen? 89. What volume of air is needed for the combustion of a litre of cyanogen ? What volume of each product is formed ? 90. What weight of ammonia could be obtained from i gramme of urea ? 91. What weight of urea nitrate could be obtained by satu- rating i gramme of urea with nitric acid ? 92. If a gramme of argentic fulminate were broken up into metallic silver, carbonic oxide, and nitrogen, what volume of each of the gases would you obtain ? 93. What weight of hydrocyanic acid is obtained by distilling 500 grammes of crystallized 'ferro-cyanide' ((CN) 6 FeK 4 (H 2 O) 3 ) with dilute sulphuric acid? 94. What is the volume of i o grammes of methylia ? What volume of oxygen is needed for their combustion ? What volume of each product is formed? 119 88 ATOMIC THEORY. CHAPTER XIII. 88. Atoms. Each element consists of small indivisible particles called atoms. The elementary atoms are capable of uniting with one another, forming compounds, but they cannot be destroyed by any known process. Each atom of oxygen has the same weight as any other atom of oxygen, so also with hydrogen, nitrogen, carbon, &c. ; in fact all the atoms of one element have the same weight ; and chemistry teaches that an atom of oxygen is 16 times as heavy as an atom of hydrogen, and this is meant when we say that 1 6 is the atomic weight of oxygen. An atom of nitrogen is 14 times as heavy as an atom of hydrogen, so that the atomic weight of nitrogen is 14; and an atom of carbon is 12 times as heavy as an atom of hydrogen, so that the atomic weight of carbon is 1 2. In like manner the atomic weight of each of the other elements tells us the weight of every atom of that element, taking the weight of the atom of hydrogen as one. Each atom has different properties under different circum- stances : its own weight is, however, a property which each atom retains under all circumstances. Thus the volume or tension of oxygen increases with rise of temperature, and the velocity with which its atoms diffuse through an opening in a vessel increases also. With some substances, such as mer- cury, oxygen does not combine at the ordinary temperature ; but at a higher temperature the oxygen is converted by con- tact with mercury into a solid red powder which contains the atom of mercury united with the atom of oxygen in couples (HgO). The atoms of mercury are in as solid a state as those 120 MOLECULES. 89 of a solid bar of the metal frozen by carbonic acid ; and the atoms of oxygen, which no combination of cold and pressure has yet been sufficient to reduce even to the liquid state, are in the mercuric oxide perfectly solid. 89. Molecule is the name given to the smallest cluster of atoms of any substance, whether an element or a com- pound, that is believed capable of existing by itself, and every pure compound consists of similar molecules. The following formulae represent the molecules of the gaseous substances which have been described in the pre- ceding pages, and each formula taken in grammes represents 22.4 litres, or 2 volumes of the respective gas, and may be called the ' absolute molecule :' Oxygen, O 2 . Hydrogen, H 2 . Nitrogen, N 2 . Steam, H 2 O. Nitrous oxide, N 2 O. Nitric oxide, N O. Nitric peroxide, N 2 O 4 . Carbonic oxide, C O. Carbonic acid, C O 2 . Ammonia, N H 3 . Marsh gas, C H*. Ethylene, C 2 H*. Acetylene, C 2 H 2 . Butylene, C 4 H 8 . Cyanogen, C 2 N 2 . Prussic acid, C N H. Formiate, C H 2 O 2 . None of these absolute molecules (containing hydrogen) has got less than i gramme of hydrogen. Some contain 2, 3, or 4 grammes of it, but no molecule has got a fraction of an atom of hydrogen. So also with regard to oxygen, some of our absolute molecules contain 16 grammes of oxygen, others contain entire multiples of 1 6 grammes of oxygen. Nitrogen in like manner combines in the proportion of 14 grammes in one molecule and entire multiples of that num- ber, and carbon in the proportion of 12 grammes and multiples of 12 grammes. None of these molecules con- tains a fraction of any atomic weight. 121 89 MOLECULES. Thus it is that the study of the constitution of gaseous jnolecules proves the truth of the atomic theory. There are, however, many compounds which cannot be Obtained in the state of vapour, and of any such compound the formula which represents the smallest cluster which can be shewn (by an accurate comparison of the various reactions of the compound) to exist by itself is the formula of the molecule. Hydric oxalate (C 2 O 4 H 2 ) might, consistently with the atomic weights of its elements, be represented by the formula C O 2 H, but the study of the oxalates has shewn that C O 2 H does not exist by itself, and that C 2 O 4 H 2 is the smallest group of the oxalate which can take part in any reaction; for we can take out one atom of hydrogen and put in one atom of potassium in its place, forming the hydro- potassic oxalate C 2 O 4 H K ; or we can replace both atoms of hydrogen by potassium in a similar manner, forming the neutral potassic oxalate C 2 O 4 K 2 . The molecule of am- monia is represented by the formula N H 3 ; for one-third of the hydrogen can be taken out and replaced by an atom of another kind, or two-thirds of the hydrogen can be taken out and replaced, or, finally, the whole of the hydrogen can be replaced by three atoms of some other element. The molecular weight of a hydrogen salt is that weight which contains as many atoms of hydrogen replaceable by potassium or silver as have been separately replaced by such a metal. Hydric oxalate and carbonate have the molecular formulae C 2 O 4 H 2 and CO 3 H 2 , because potassium can re- place either one or both atoms of hydrogen in these weights of the compound. Nitrate and chlorate have the molecular formulae N O 3 H and Cl O 3 H, because potassium never replaces part of the hydrogen in one of the acids, so as to form a compound derivable from any multiple of these formulae, having part of the hydrogen replaced by potassium. 122 ATOMIC EQUIVALENCE. 91 There is no hydropotassic nitrate or hydropotassic chlorate with such a formula as N 2 O 6 HK, or N 3 O 9 H 2 K, or N 3 O 9 HK 2 , &c. 90. The term ' atom' was explained above only in its ap- plication to elements. It is, however, applied to compounds, in accordance with the same principles which regulate its ap- plication to elements. Whenever a group of elements forms a compound corresponding to one formed by an element, or in fact, whenever a group behaves like an element, such group of elements is called a radical, and the term ' atom' is applied to radicals exactly in the same way as it is applied to elements. Thus N H 4 is a radical analogous to potas- sium, and N H 4 is capable in many compounds of taking the place of K. N H 4 is called an atom of ammonium. So also C N combines in a similar manner to Cl, and is a radical comparable to the element chlorine. C N is called an atom of cyanogen. But neither N H 4 nor C N are believed capable of existing by themselves, any more than Cl. If ammonium be ever made, its molecule will doubt- less be found to correspond to the formula (N H 4 ) 2 , just as the molecule of cyanogen is found to be (CN) 2 , and the molecule of chlorine is Cl 2 . 91. The elements oxygen, nitrogen, and carbon, form with hydrogen the compounds H 2 O, H 3 N, H 4 C. Each atom of oxygen in water is combined with two atoms of hydrogen, each atom of nitrogen in ammonia is combined with three atoms of hydrogen, and each atom of carbon in marsh gas is combined with four atoms of hydrogen; and these quantities of the three compounds occupy pre- cisely the same volume in the state of vapour, so that a cubic centimetre of ammonia gas has got three atoms of hydrogen in it, for every two atoms of hydrogen in a cubic centimetre of steam ; and a cubic centimetre of marsh gas has got four atoms of hydrogen in it for every two atoms 123 01 ATOMIC EQUIVALENCE. of hydrogen in an equal volume of steam, or for every three atoms of hydrogen in the cubic centimetre of am- monia H 2 O = 2 vols, N H 3 = 2 vols, C H 4 = 2 vols. There are other elements, such as chlorine, potassium, silver, &c., which resemble hydrogen in the atomic consti- tution of their compounds with oxygen, nitrogen, and carbon. They form, for instance, the compounds Cl 2 O, K 2 O, Ag 2 O, Cl 3 N, K 3 N, Ag 3 N, Cl 4 C, &c., so that one atom of oxygen combines with two atoms of hydrogen, or of these other elements. Nitrogen combines with three atoms of hydrogen, or three of these other elements ; and so also the atom of carbon combines with four atoms of elements of the hydro- gen class. When hydrogen combines with chlorine, or any other element of its own class, it is always in the proportion of one atom of each; and the molecule of hydrochloric acid occupies in the state of vapour the same volume as any other molecule, Cl H = 2 vols. When chlorine in hydrochloric acid is replaced by oxygen the process takes place in the following proportions, viz. H 2 Cl 2 f O = H 2 O + Cl 2 . One atom of oxygen takes the place of two atoms of chlorine, and it is spoken of as equivalent to two atoms of chlorine. It is not necessary for the establishment of this relation between oxygen and chlorine that one atom of oxygen be capable of turning out two atoms of chlorine from hydrochloric acid, for even if no such decomposition were possible we might compare a molecule of water H 2 O with that quantity of hydrochloric acid which is equal to it in hydrogen, viz. with two mole- cules of hydrochloric acid 2 (H Cl), and we might say that to transform one of the compounds into the other a change of place between two atoms of chlorine and one atom of oxygen would be needed. Oxygen is from this peculiarity 124 EQUIVALENT INTERCHANGES. 01 called a di-valent element. A similar reasoning shews nitrogen to be tri-valent ; and carbon is tetra-valent. Many of the most important peculiarities of compounds depend upon the equivalence of the elements contained in them. When marsh gas is burnt, the formula CH 4 + 2 O 2 = CO 2 +2H 2 O describes the atomic proportions in which the process takes place. The product CO 2 has been formed from C H 4 by taking away the four atoms of hydrogen and putting in two atoms of oxygen in their place. And in like manner the other product, 2 H 2 O, is formed by taking out one atom of carbon from each molecule of marsh gas, and replacing it by two atoms of oxygen. In describing this result it is cus- tomary to say that two atoms of oxygen are ' equivalent to* four atoms of hydrogen, and that two atoms of oxygen are ' equivalent to' one atom of carbon. The term ' equivalent' is not intended to convey the idea of any equality of pro- perties. When prussic acid is burnt, the equation represents the atomic proportions of the process; and the carbonic acid is formed by four di-valent atoms of oxygen taking the place of two tri-valent atoms of nitrogen, and of two mono-valent atoms of hydrogen. The sum of the equivalences of the oxygen going into combination, is equal to the sum of the equivalences of the elements going out of the compound. This relation holds good in all de- compositions in which the elements retain their original equivalences. The equivalence of any atom is equal to the number of atoms of hydrogen or chlorine, or potassium or silver, with which one atom of element can^ combine, or the number of such atoms which it can be represented as replacing. 92 CHANGES OF EQUIVALENCE. 92. When carbon is burnt so as to form carbonic oxide, each molecule of the compound C O contains one tetra-valent atom of carbon united with one di-valent atom of oxygen, and in carbonic oxide one of the two atoms has accordingly an equivalence different from usual. We might say that the carbon is di-valent in carbonic oxide, or else that oxygen is tetra-valent. When carbonic oxide is burned forming CO 2 , the elements are both in their usual equivalence, and we must admit that one of them underwent a change of equivalence during the combustion. When olefiant gas is completely burnt the reaction is C 2 H 4 + 3 O 2 = 2 C O 2 + 2H 2 O. The four mono-valent atoms of hydrogen in the olefiant gas are here replaced by four di-valent atoms of oxygen, and the apparent equivalence of the carbon is doubled. If four atoms of oxygen only were supplied to each mole- cule of olefiant gas, and half of it combined with the hydro- gen, while the other half combined with the carbon, forming carbonic oxide C 2 H 4 + 2 O 2 = 2 CO 2 +2 H 2 O, the four mono-valent atoms of hydrogen would be replaced by two di-valent atoms of oxygen, and the carbon would continue apparently di-valent. 126 ATOMIC WEIGHTS OF ELEMENTS. Elements of Uneven Equivalence, 1V1OI> Hydrogen - Fluorine (ADS. - H = i -- F = 19 1RI f Nitrogen 1 Phosphorus - ADS. - N - P = H - 31 Chlorine - Cl = 35.5 -| Arsenic - - - As = 75 Bromine - Br = 80 1 Antimony - - Sb = 122 Iodine - - - I = 127 i. Bismuth - Bi = 210 f Lithium - - - Li = 7 Boron - - - B = II Sodium - - - Na = 23 Gold - - - - Au = 196 | Potassium - - K = 39 Vanadium - - V = 51-3 Rubidium - - Rb = 8s LCossium - - - Cs = 133 Thallium - - Tl = 203 Silver - - - Ag = 108 Elements of Even Equivalence. DYADS, TETRADS, &c. ( Oxygen - - - = 16 Yttrium - - - Y = 64 1 Sulphur - - - s = 32 Cerium - - - Ce = 92 \ Selenium - Se = 79.5 Lanthamum La = 92 ( Tellurium - - Te = 129 Didimium - - Di = 96 Calcium - - - Ca = 40 Uranium - - U = 120 Strontium - - Sr = 87.5 Zirconium - - Zr - 89.5 Barium - - - Ba = 137 Tantalum - - Ta = 138 Lead- - - - Pb = 207 Niobium - - Nb = I 9 s Mercury - Hg = 200 Thorinum - - Th = 238 Magnesium - - Mg - 24 Carbon - - - C - 12 Zinc - - - - Zn = 65 Silicon - - - Si = 28 Cadmium - - Cd = 112 Tin - - - - Sn = 118 Indium - - - In = 74 Titanium - - Ti = 50 Aluminium - - Al = 27.5 ( Molybdenum - Mo = 96 Iron - - - - Fe = 56 ( Tungsten - - W = 184 Chromium - - Cr = 52.5 Platinum - - Pt = 197 Manganese - - Mn = 55 Iridium - - - Ir = 197 Cobalt - - - Co = 58.5 Osmium - - - Os = 199 Nickel - - - Ni = 58.5 Rhodium - - Ro = 104 Copper - - - Cu = 63.5 Ruthenium - - Ru = 104 Glucinum - - G = 9 Palladium - - Pd = 106.5 127 CHLORINE (Cl 2 ; 01 = 35.5). CHAPTER XIV. 93. Chlorine (Cl 2 = 2 vols.) is most conveniently pre- pared by heating finely-powdered manganic peroxide with strong hydrochloric acid. The manganese seems at first to dis- solve as perchloride (Mn Cl 4 ), but chlorine gas speedily comes off, leaving manganous chloride MnO 2 + 4(HCl) = MnCl 2 + Cl 2 + 2(H 2 O). When the mixture is heated in a closed tube, similar to that described for the preparation of liquid ammonia, liquid chlorine is obtained. At 15.5 it requires a pressure of four atmospheres for its liquefaction. At the ordinary atmospheric pressure chlorine is a yellow gas, about two and a-half times as heavy as air. Its density is 35.5. At i5C water dissolves about twice its volume of chlorine gas, and for this reason it is customary to collect the gas by displacement of air. The gas has a most suffocating odour, and even two or three per cent, of it renders air quite irrespirable, as it dis- organizes the tissues of the air-passages of the lungs. It forms a crystalline hydrate of the composition Cl (H 2 O) 5 . Chlorine combines with metals, and its compounds are called chlorides. Powdered metallic antimony showered into the gas catches fire. Finely-divided metallic iron also burns in chlorine. In the dry state chlorine does not affect the colour of litmus-paper, but a drop of water thrown on the paper causes the immediate destruction of the colour by chlorine. Some colouring matters are bleached by chlorine alone, but the greater number of bleaching effects produced by it are with the co-operation of water. 128 OXYGEN ACIDS OF CHLORINE. 94 When passed with steam through a red-hot tube, chlorine combines with hydrogen, and liberates oxygen from a portion of the steam. When passed into a solution of ammonia it gives off nitrogen gas by taking hydrogen from the ammonia. But when passed into a solution of sal-ammoniac, chlorine forms oily drops of nitric chloride, which fall to the bottom of the liquid and detonate with great violence on very slight provocation. A solution of caustic potash absorbs chlorine, the first product being potassic chloride and a salt of potash with hypochlorous acid C1 2 + 2 (KHO)= C1K + C1KO + H 2 0. 94. Chlorine forms four acid compounds with hydrogen and oxygen, and salts corresponding to them. They are called perchlorates (such as C1O 4 H), chlorates (such as Cl O 3 H), chlorites (such as Cl O 2 H), and hypochlorites (such as Cl O H). Anhydrous acids corresponding to two of these are known, viz. chlorous acid (Cl 2 O 3 ), and hypochlorous acid (Cl 2 O). There is also a neutral peroxide, C1 2 O 4 = 4 vols. Hydric perchlorate (H Cl O 4 ) can be obtained by decomposing a solution of potassic perchlorate by hydrofluosilicic acid. The potassium is carried down as fluosilicate, while hydric perchlorate is formed SiFl 6 H 2 + 2 (C10 4 K) = SiFl 6 K 2 + 2 (C1O 4 H). When obtained as a monohydrate, perchloric acid is a liquid of 1.78 density at 15.5 (Roscoe). In contact with charcoal it explodes with great violence. The acid forms a crystalline hydrate, Cl O 4 H H 2 O. Dilute solutions of per- chloric acid dissolve zinc with evolution of hydrogen, and formation of zinc perchlorate. Hydric chlorate is best prepared by adding dilute sulphuric acid to a solution of barytic chlorate, in quantity exactly sufficient to remove all the barium, without leaving any sulphuric acid mixed K 129 94 OXYGEN ACIDS OF CHLORINE. with the chloric acid. Barytic sulphate is completely pre- cipitated Ba (Cl O 3 ) 2 + S O 4 H 2 = 2 (Cl O 3 H) + S O 4 Ba. The solution of chloric acid may be concentrated, by evapo- ration at a gentle heat ; but the process should be completed by putting the partially concentrated acid into a vacuum beside some strong sulphuric acid. Chloric acid, when con- taining but a little free water, is decomposed by light, and becomes yellow, owing to the formation of chlorous acid. It is decomposed by distillation, perchloric acid being formed, besides other products. A piece of blue litmus-paper is reddened by strong chloric acid, but a bleaching action immediately follows. Chlorates are powerful oxidizing agents, and present many points of analogy with nitrates. They are monobasic, and are remarkable for their solubility. Even the argentic, plumbic, and barytic chlorates are soluble in water. Strong sulphuric acid decomposes a chlorate, with evolu- tion of a deep yellow gas, which explodes when gently heated. Oxygen is given off at the same time, and the yellow gas called chloric peroxide appears to have the com- position Cl 2 O 4 = 4 vols. Chlorous acid is obtained by the partial desoxidation of chloric acid. It is a weaker acid than chloric acid, but pre- sents in other respects great resemblance to it. Hypochlorites. The hydrogen salt (Cl O H) is obtained by shaking up chlorine water with mercuric oxide. Its so- lution in water is colourless, and has a peculiar sickly odour. It is an exceedingly weak acid, being expelled by carbonic acid from its salts in presence of water. It is an ex- ceedingly powerful bleaching agent, and is present together with hydrochloric acid in the solution of chlorine in water. There is no difficulty in removing the hydrochloric acid from the solution, by adding to it a solution of argentic nitrate 130 HYDROCHLORIC ACID (HCl). 95 as long as any precipitate is formed. The decomposition is thus represented Cl 2 + H 2 + N0 3 Ag = ClAg + C10H + N0 3 H. After the action of the nitrate has removed half the chlo- rine the solution retains all the bleaching power which it had before the silver salt was added. When a concentrated hypochlorite is mixed with concentrated hydrochloric acid, an action takes place in the reverse direction to that of chlorine on water C1H + C1OH = C1 2 + H 2 O. Anhydrous hypochlorous acid (Cl 2 O = 2 vols.) is obtained in the form of a yellow gas by passing chlorine over red mercuric oxide, both substances being dry. The compound so much used by the name of bleaching powder is a mixture of calcic hypochlorite with calcic oxi- chloride. Hypochlorous acid can be liberated by adding dilute sulphuric acid, little by little, to bleaching powder mixed with water, and agitating the mass whilst the acid is running into it. In this manner the weak hypochlorite is alone decomposed and hydric hypochlorite can be distilled over. If too much sulphuric acid were to be added, hydro- chloric acid would also be evolved from the calcic chloride, and by acting on the hypochlorite would evolve chlorine. 95. Hydrochloric Acid (H Cl = 2 vols.), frequently called muriatic acid, is formed when a mixture of equal volumes of chlorine and hydrogen is exposed to the sunshine ; the mixture explodes, forming hydrochloric acid gas of the same volume HCl 2 - = 18.35 HCl 2 =18.25 as the mixture. The elements are not known to combine in K 2 11 95 REACTIONS OF HYDROCHLORIC ACID. any other proportion. On a small scale the gas is most con- veniently made by heating strong sulphuric acid with lumps of table salt, of the size of hazel nuts, obtained by melting the salt in an earthen crucible, and pouring it out to cool on a stone, then breaking up the cake into fragments of the size described. Half of the hydrogen of the sulphate is replaced by the sodium of the salt, forming hydrosodic sulphate, and the hydrogen which leaves the sulphate goes away in com- bination with chlorine from the salt. Thus, H 2 S O 4 + Na Cl = Na H S O 4 + H Cl. For manufacturing purposes a similar operation is per- formed with only half the proportion of sulphuric acid, aided by much stronger heat. The first part of the process then takes place as above, but the hydrosodic sulphate subse- quently reacts on a molecule of salt, forming neutral sodic sulphate and hydrochloric acid HNaS0 4 + NaCl= Na 2 SO 4 + HCl. The density of the gas is 18.25. At ioC a pressure of 40 atmospheres is required to liquefy hydrochloric acid. Hydrochloric acid forms dense fumes when allowed to escape into moist air. It dissolves in water with great avidity, giving off considerable heat, and forming a solution of greater density than water. When containing about 40 per cent, of acid, the solution has a density of 1.2. Strong 'solutions give off hydrochloric acid gas when heated, and they boil constantly at noC. Weak solutions give off water, with but little hydrochloric acid, until their boiling- point has risen to uoC at the ordinary atmospheric pres- sure. At this temperature the solution distils uniformly, and contains about 20 per cent, of hydrochloric acid. Roscoe finds that if the solution be distilled under a pressure of 2 atmospheres, it distils over undecomposed when containing 19 per cent, of acid ; and at a pressure of 3 atmospheres it dis- tils regularly only when containing about 18.3 per cent. H Cl. 132 CHLOROCHROMIC ACID. 97 96. Hydrochloric acid is an exceedingly acid salt, and by double decomposition with potassic hydrate it forms potassic chloride and water, both neutral bodies. There is only one proportion in which the hydrogen of hydrochloric acid can be removed, in whatever proportions the acid salt may be mixed with the basic compound. The process is this : H Cl + H K O = K Cl + H 2 O. A chloride can be detected in any solution by the cha- racteristic curdy precipitate which it forms with argentic nitrate. The precipitate, which consists of argentic chloride, is insoluble in nitric acid, even on boiling, but dissolves readily in ammonia. Mercurous nitrate is also decomposed by soluble chlorides, forming a precipitate of mercurous chloride, generally known by the name of calomel (N O 3 ) 2 Hg 2 + 2 (H Cl) = 2 H N O 3 + Hg 2 CP. One of the most characteristic properties of chlorides is that of yielding a volatile compound with chromium and oxygen, called chlorochromic acid. The compound is easily obtained by evaporating the chlorides to dryness (having previously added potash if the solution was acid), and mixing the dry residue with potassic dichromate and plenty of strong sulphuric acid, and distilling the mix- ture in a retort, when a deep-red vapour having the com- position Cr O 2 Cl 2 goes over into the receiver. Strong hydrochloric acid and other chlorides are oxidized by strong nitric acid, chlorine and oxides of nitrogen being evolved. The mixture is called aqua regia, from its property of dissolving gold or platinum, metals which are not attacked by either nitric or hydrochloric acid alone. Commercial hydrochloric acid is very liable to contain arsenic, and not unfrequently sulphurous acid. 97. Nitric Chloride (N Cl 3 ) is obtained by passing chlo- rine into a solution of sal-ammonia. It gradually goes to the bottom of the liquid, and is most safely collected in a hollow 133 97 AMMONIC CHLORIDE (NH'Cl). block of lead. A great number of organic bodies possess the property of causing this compound to explode, and the vio- lence with which it explodes is so great as to shatter any glass or earthenware vessel. The products of the decomposition are free nitrogen and chlorine. Chloronitric Acid (N O 2 C1) is obtained by the action of chlorophosphoric acid on plumbic nitrate. It is a heavy liquid, which is decomposed by contact with water, forming hydrochloric and nitric acids N O 2 Cl + H 2 O = H Cl + N O 3 H. Chloronitroiis Acid (N O Cl = 2 vols.) is one of the sub- stances formed by the action of nitric acid on hydrochloric acid. It can be condensed by a frigorinc mixture from the vapours given off by aqua regia. Nitric oxide combines directly with chlorine, forming this compound. 98. Ammonic Chloride (N H* Cl = 4 vols.). This salt is commonly called sal-ammoniac, and sometimes muriate of ammonia. It is usually made in this country by adding hydrochloric acid to the so-called gas liquor, which is an impure solution of ammonia, containing carbonic acid, sulphuretted hydro- gen, and other weak acids. The crude salt is purified by crystallization, by heating the crystals, and finally by sub- limation. It is very soluble in water, and by evaporation of its solution the salt can be obtained in cubical, or sometimes in octohedral, crystals. When heated by itself it evaporates, and the vapour formed by the evaporation of one molecule of the salt occupies the volume occupied by free ammonia, plus that occupied by free hydrochloric acid ; and from this circumstance it is concluded that the salt is decomposed by evaporation into free hydrochloric acid and free ammo- nia, just as mercuric oxide is decomposed by heat into free mercury and oxygen. 134 CHLOROCARBONIC ACID (C Cl 2 ). 99 Ammonic chloride is formed by adding a solution of ammonic carbonate to a solution of calcic chloride; calcic carbonate being precipitated, while the ammonic chloride remains in solution Ca Cl 2 + (N H 4 ) 2 C O 3 = C O 3 Ca + 2 (N H 4 Cl) ; but if the mixture of calcic carbonate and sal-ammoniac be boiled, the reverse process takes place, ammonic carbonate being carried away by the steam as fast as it is formed, while calcic chloride remains in the solution. Iron exposed to the air becomes rusty very rapidly when moistened with a solution of sal-ammoniac. 99. Chlorocarbonic Acid (C O Cl 2 = 2 vols.) is fre- quently called phosgene gas. The most easy way of obtaining this gas is to pass a mixture of equal volumes of chlorine and carbonic oxide through a long glass tube exposed to bright sunshine. The mixture condenses into half its volume of a colourless gas, consisting of chloro-carbonic acid, possessing a most suffo- cating odour. Its density is 49.5. CO = 14 C1=35-S 2 COC1 2 -49-5 CO _=,4 C1=3S-S COC1 2 : 49-5 The gas may be considered as carbonic acid, in which one atom of oxygen is replaced by an equivalent quantity, namely two atoms, of chlorine. In contact with moisture it is rapidly decomposed, with formation of hydrochloric and carbonic acids ; C O Cl 2 + H 2 O = C O 2 + 2 (H Cl). 135 99 ACTION OF CHLORINE ON HYDROCARBONS. With dry ammonia phosgene forms a compound of ami- dogen (N H 2 ) with carbonic oxide, called urea, together with ammonic chloride 4 (N H 3 ) + C O Cl 2 = C O (N H 2 ) 2 + 2 (N H 4 Cl). 100. The action of chlorine on compounds of carbon and hydrogen is of two kinds. With some hydrocarbons it combines in the proportion of two atoms of chlorine to one molecule of the hydrocarbon. Olefiant gas affords an instance of this action, for when equal volumes of chlorine and olefiant gas are mixed in presence of water, the gases combine, forming a heavy oily liquid of the composition C 2 H 4 Cl 2 = 2 vols. This substance has obtained the name " Dutch liquid." It is not dissolved or acted upon by water, nor by a solution of potash in water. It boils without decomposition at about 84 C, and its vapour has a sweetish and agreeable odour not unlike that of chloroform. The liquid has a density of 1.28 at oC, and its vapour has a density of 49.5. C 2 H 4 C1 2 =49-5 C 2 H*C1 2 -=49-5 The other kind of action of chlorine on hydrocarbons is illustrated by the case of marsh gas. Two atoms of chlo- rine react on one molecule of that hydrocarbon, but one of these atoms of chlorine takes hydrogen out of the hydro- carbon, forming hydrochloric acid, while the other atom of chlorine takes the place of the atom of hydrogen in the 136 METHYLIC CHLORIDE (C 1P-CI). 100 hydrocarbon. Thus, a mixture of two volumes of chlorine with two volumes of marsh gas forms two volumes of hydro- chloric acid, and a compound of C H 3 with one atom of chlorine ; C H 4 + Cl 2 = C H 3 Cl + H Cl. CH 4 2 CH 4 = 8 The compound C H 3 Cl is called methylic chloride. It dissolves in water, at the temperature of 14, to the extent of several times the volume of the water ; and at tempera- tures below 6C it forms a crystalline compound with water. When heated to iooC with potassic hydrate it is decom- posed, the potassium combining with its chlorine, and the group C H 3 , called methyle, taking the place of the potas- sium, forming methylic hydrate O = KC1 + CH 3 HO. Methylic chloride can be condensed to the liquid state by the aid of a powerful frigorific mixture, and boils at 23.73. A mixture of equal volumes of chlorine and methylic chlo- ride is in its turn decomposed by sunshine, the action of the chlorine being an exact repetition of the process by which the chloride itself was formed : viz. CH 3 C1 + C1 2 = CH 2 C1 2 + HC1. This body is an oil, insoluble in water, having a density of 137 100 CHLOROFORM (C H Cl 3 ). 1.344 at i8C, and a boiling-point of 30.5. Its vapour has the same volume as that of methylic chloride CH 2 C1 2 = 2 vols.; so that the atom of chlorine has taken the place of one atom of hydrogen in methylic chloride, without disturbing the other atoms of the compound. By repeating the action of chlorine, a still further substitu- tion of hydrogen by chlorine can be effected in a precisely similar manner (C H 2 Cl 2 + Cl 2 = C H Cl 3 + H Cl), and the compound thus obtained is the well-known 101. Chloroform (C H Cl 3 - 2 vols.). This compound is prepared on a large scale by distilling spirits of wine with bleaching powder mixed with a large quantity of water. It is heavier than the compound C H 2 Cl 2 , and has a higher boiling- point, its density being 1.491 at i7C, and its boiling-point 6o.i6C. It is not acted upon by water under iooC, nor can its chlorine be discovered by a watery solution of argentic nitrate. It is, however, dissolved by alcohol, and potash can then be mixed with it, when on the application of heat a brisk decom- position takes place, forming potassic chloride and formiate C H Cl 3 + 4 (K H O) = K C H O 2 + 3 (K Cl) + 2 (H 2 O). Chloroform is much used for allaying temporarily the sensation of pain, an action which is termed anaesthetic. When inhaled in sufficient quantity with air, it entirely sus- pends the consciousness of the patient. Its vapour is decomposed by passing through a red-hot tube, and if moisture be present hydrochloric acid is thus ob- tained in abundance. 102. Carbonic Chloride (C Cl 4 = 2 vols.). By passing the vapour of chloroform with an excess of chlorine through a red-hot glass tube this compound is formed. Its density is i .599, and it boils at 76.05. When potassium-amalgam is put into a solution of carbonic chloride in alcohol, the chlorine is gra- dually taken out of it, and replaced atom for atom by hydrogen. 138 CHLORIDES OF CARBON. 102 In this manner marsh gas can be recovered from the chlo- ride. The intermediate compounds C H Cl 3 , C H 2 Cl 2 , and C H 3 Cl are, however, formed at the same time, and the pro- cess must be considered as a substitution of one atom of chlorine at a time by hydrogen. Thus CC1 4 + H 2 = CHC1 3 + HC1, CHC1 3 + H 2 = CH 2 C1 2 + HC1, &c. The hydrogen must for this purpose be in the nascent state, as free hydrogen does not produce the effect. There is also a chloride of carbon (C 2 Cl 4 ) corresponding to olefiant gas, a liquid which boils at i22C, and another formed from it at high temperatures corresponding to acety- lene and having the formula C 2 Cl 2 . This protochloride is a crystalline solid which evaporates without fusion at 2ooC. Cyanogen forms three polymeric compounds with chlorine a gaseous, a liquid, and also a solid, chloride. They are obtained by the action of chlorine on prussic acid or mer- curic cyanide ; C N H + Cl 2 = C N Cl + H Cl. The solid chloride corresponds to cyanuric acid, and con- sists of three molecules of the gaseous chloride united in one, C 3 N 3 Cl 3 . m Examples of chlorides and double chlorides : Carbonic chloride, C Cl 4 . Stannic chloride, Sn Cl 4 . Platinic chloride, Pt Cl 4 . Hyd-auric chloride, H Au Cl*. Sod-auric chloride, Na Au Cl*. Potassio mercuric chloride, K 2 HgCl 4 . Potassio cupric chloride, K 2 Cu Cl*. Ferric chloride, Fe 2 Cl 6 . Aluminic chloride, Al 2 Cl 6 . Hydro-platinic chloride, H 2 Pt Cl 6 . Potassio platinic chloride, K 2 Pt Cl 6 . Ammonio platinic chloride, (N H*) 2 Pt Cl 6 . Bari platinic chloride, Ba Pt Cl 15 . Potassio stannic chloride, K 2 Sn Ci 6 . 139 Hydric chloride, H Cl. Potassic chloride, K Cl. Argentic chloride, Ag Cl. Stannous chloride, Sn Cl 2 . Calcic chloride, Ca Cl 2 . Zinc chloride, Zn Cl 2 . Cupric chloride, Cu Cl 2 . Cuprous chloride, Cu 2 Cl 2 . Mercuric chloride, Hg Cl 2 . Mercurous chloride, Hg 2 Cl 2 . Antimonious chloride, Sb Cl 3 . Boric chloride, B Cl 3 . Auric chloride, Au Cl 3 . Potassio mercuric chloride, KHgCl 3 . Potassio magnesic chloride, KMgCl 3 . APPENDIX TO CHAPTER XIV. Appendix to Chapter XIV. PROBLEMS. 95. What volume of hydrogen would be obtained by pass- ing a litre of hydrochloric acid gas over hot metallic iron ? 96. What weight of common salt would be needed for the preparation of a kilogramme of hydrochloric acid gas ? What volume will the gas occupy ? 97. What weight of pure " manganese" is needed for the evolution of i oo grammes of chlorine ? 98. A litre of chlorine is passed with an excess of steam through a red-hot porcelain tube. What volume of oxygen is liberated, assuming that all the chlorine combines with hydrogen ? 99. What weight of potassic hydrate is needed for the neu- tralization of 100 grammes of hydrochloric acid gas? 100. What volume of ammonia gas is required for the neutralization of 10 grammes of hydrochloric acid gas ? 1 01. 20 grammes of an aqueous solution of hydrochloric acid were mixed with an excess of argentic nitrate. The precipitate (argentic chloride) was collected, washed, dried, and weighed. It amounted to 4.53 grammes. Calculate the percentage of hydrochloric acid in the original solution. 102. What is the weight of a litre of sal-ammoniac vapour, reduced to the normal temperature and pressure ? 103. A litre of phosgene gas is completely decomposed into carbonic acid and hydrochloric acid by the action of water. What is the volume of each product ? 104. What volume of chlorine can be made to combine 140 APPENDIX TO CHAPTER XIV. directly with a litre of olefiant gas ? What is the vapour- volume of the product ? 105. What is the weight of a litre of chloroform vapour ? 1 06. Suppose a litre of carbonic chloride to be decom- posed by water according to the formula C Cl 4 f 2 (H 2 O) = C O 2 + 4 (H Cl), what volume of each product would be formed ? 141 103 BROMINE (Br = 80). CHAPTER XV. 103. Bromine (Br = 80. Br 2 = 2 vols.) is found in the mother liquor of sea-water in combination with sodium and potassium, and can be set free from those compounds by the action of chlorine. On a larger scale it is prepared by pro- cesses similar to those adopted for the preparation of chlo- rine. Bromine is a dark-red liquid of 2.966 density. It dissolves slightly in water, and the solution has the powerful odour of bromine, an odour which is even more distressing to the respiratory organs than chlorine itself. Bromine boils at 4 7, and evaporates very freely at ordinary temperatures. Its vapour has a deep-red colour, not unlike that of nitric peroxide. The vapour of bromine has a density equal to 80. 104. In its compounds bromine exhibits great analogy with chlorine, but it is decidedly less energetic than chlorine in its action. Thus a mixture of equal volumes of bromine vapour and hydrogen cannot be made to combine with ex- plosion; and hydrobromic acid once formed by indirect means is more easily decomposed than hydrochloric acid. In proof of this it is sufficient to heat potassic bromide with strong sulphuric acid, so as to evolve hydrobromic acid, in contact with hot sulphuric acid. There is an immediate action between these two acids, liberating bromine, by de- composition of some of the hydrobromic acid : thus, H 2 S O 4 + 2 (H Br) = S O 2 + Br 2 + 2 (H 2 O). Bromates, such as hydric-bromate (BrO 3 H), can be ob- tained by processes similar to those employed for the pre- 142 BROMIDES. 104 paration of chlorates. The silver bromate is insoluble in water. Hypobromites such as Br O H are very much like hypochlorites. The hydrogen salt is readily obtained by agi- tating bromine water with red mercuric oxide. Hydrobromic acid (Br H = 2 vols.) is most conveniently prepared by decomposing phosphoric bromide by the action of water ; P Br 5 + 4 (H 2 O) = P O 4 H 3 + 5 (H Br). The aqueous solution of the acid has much resemblance to hydrochloric acid, and by double decomposition with bases it forms metallic bromides analogous to the corre- sponding chlorides. Argentic bromide has much resem- blance to the chloride. It is however less soluble in am- monia, so that when potassic bromide is added to ammonia saturated by argentic chloride, a precipitate of argentic bromide is obtained. Bromine does not, like chlorine, form a volatile compound with chromium and oxygen, so that when a bromide is distilled with potassic di-chromate and sulphuric acid, bro- mine vapour escapes, without carrying over any chromium. The action of bromine on hydrocarbons is of the same kind as that of chlorine. The compound of bromine with olefiant gas (C 2 H 4 Br 2 ) is an oil of 2.16 density and i32C boiling-point. It crystallizes easily. The chloride was de- scribed above as having a density of 1.28 and the boiling- point 84 ; and whenever chlorine and bromine form similar liquid and volatile compounds the bromide is heavier and has a higher boiling-point than the chloride. Iodine (I = i27;I 2 =2 vols.) is found chiefly in the mother liquor from kelp (the ashes of sea-weeds) in combination with the alkali metals. The process of its preparation is very similar to that for liberating bromine, but the iodine which is driven off condenses easily into shining black scales of 4.95 sp. gr. Iodine is precipitated as a black powder by the action of chlorine or of bromine on a solution of an iodide, being very '43 104 IODINE (7=1 27). slightly soluble in water. The most convenient way of re- covering for use iodine which has been combined with metals is by the action of nitrous acid, such as is obtained by the reduction of nitric acid in the cells of a galvanic battery. Iodine melts at io7C and boils at i75C. Its vapour has a beautiful violet colour, and a density of 127. It dissolves in alcohol with a red colour, and also in a solution of potassic iodide, but its solution in carbonic sulphide has a violet colour. Free iodine forms with starch a deep blue com- pound, by which even the minutest traces of the element can be detected. Two oxygen acids of iodine are known, namely, iodic acid, forming iodates such as the hydrogen salt H I O 3 , and periodic acid, forming periodates such as HIO 4 or Na 2 HIO 5 . 105. Anhydrous Iodic Acid (I 2 O 5 ) is obtained by boil- ing iodine with nitric acid. It crystallizes readily from a con- centrated aqueous solution. Potassic iodate is formed by fusing potassic iodide with potassic chlorate. The argentic and barytic iodates are insoluble in water. Iodic acid is broken up by heat into free iodine and oxygen. 106. The compounds of iodine with most elements have considerable analogy with those of bromine and chlorine ; but there are several elements which are unable to combine with as great a number of atoms of iodine as of bromine or chlorine. Thus phosphorus forms a pentachloride and a pentabromide, but no pentaiodide, and no very distinct compound beyond the biniodide (P 2 ! 4 ). Iron and copper form respectively the compounds Fe 2 Cl 6 and CuCl 2 , but the corresponding iodides decompose immediately into free iodine and a lower salt, in the one case ferrous and in the other cuprous iodide. 107. A Periodate can be formed by the simultaneous 144 PERIOD A TES (H 5 70 5 ). 109 action of sodic iodate and chlorine on a solution of sodic hydrate. The hydrogen salt is liberated from plumbic pe- riodate by sulphuric acid. The hydro -disodic periodate (I O 5 Na 2 H) is almost insoluble in water. There is also a more soluble dihydro-sodic periodate (H 2 Na IO 5 ). 108. Hydriodic Acid (I H = 2 vols.) is formed in small quantities by passing hydrogen and iodine through a red-hot tube. The best way to obtain the acid for use is by decom- posing a mixture of iodine and phosphorous iodide by water. An aqueous solution of the acid is easily made by passing sulphuretted hydrogen through water in which iodine is sus- pended. The solution cannot be kept in contact with air without undergoing decomposition, and becoming red from free iodine dissolved in it. It is also decomposed by many compounds of oxygen (such as nitrous acid), in which that element is feebly combined. It is even more readily decom- posed than hydrobromic acid by strong sulphuric acid. The precipitate which it forms with argentic nitrate is insoluble in ammonia. When added to a solution of mercuric chloride it forms a brilliant scarlet precipitate of mercuric iodide. With soluble salts of lead it forms a yellow precipitate of plumbic iodide, which crystallizes from hot water in beautiful scales. A solution of palladic nitrate forms with hydriodic acid a black precipitate of palladic iodide. This reaction affords the best separation of iodine from bromine, as bro- mine forms a soluble salt with palladium. 109. Nitric Iodide is the name given to a black pow- der, of varying composition, obtained by the action of iodine on a solution of ammonia. It consists of ammonia of which the hydrogen is partly replaced by iodine, atom for atom, and is remarkable for the sharp detonation with which it is decomposed, when rubbed or slightly pressed in the dry state. Iodine combines with olefiant gas under the influence L 14-5 109 CYANIC IODIDE. of sunshine, forming a crystalline compound (C 2 H 4 ! 2 ) cor- responding to Dutch liquid. 110. On hydrocarbons generally iodine has no action, or a very feeble one; but the compounds CHI 3 , C H 2 1 2 , C H 3 1, can be obtained by indirect means. The first (iodoform) is obtained by the action of iodine on spirits of wine in presence of potash. It crystallizes in beautiful yellow scales, which decompose when heated by themselves, but can be slowly volatilized by a current of steam. C H 3 1 is called methylic iodide. It is obtained by the action of phosphorous iodide on the compound C H 4 O (methylic al- cohol). Methylic iodide is a heavy oil of a rather fragrant odour. Its density is 1.9, and boiling-point 44C. When dissolved in alcohol it is decomposed by argentic nitrate ; thus, CH 3 I + NO 3 Ag = CH 3 NO 3 + IAg. Cyanic Iodide (C N I) is a solid compound, which crystal- lizes in beautiful needles. It is easily obtained by mixing mercuric cyanide with iodine and applying gentle heat, when mercuric iodide is formed, and cyanic iodide sublimes out Hg (C N) 2 + 2 I 2 = Hg I 2 + 2 (C N I). Iodine combines with chlorine in two proportions, forming an iodous chloride (I Cl), and an iodic chloride (I Cl 3 ). In presence of an abundance of water each atom of iodine reacts upon five atoms of chlorine, forming hydric iodate and hydrochloric acid. 111. Fluorine (F = 19) is not known in the free state. Hydrofluoric acid decomposes manganic binoxide with evolu- tion of oxygen. Chlorine decomposes argentic fluoride, but if the experiment be performed in a glass vessel the glass is attacked. No compound of fluorine with oxygen is known. 112. Hydrofluoric Acid (H F) is prepared by distilling pure fluorspar in the state of fine powder, or ammonic fluoride, with sulphuric acid. The experiment cannot be performed 146 HYDROFLUORIC ACID (H F). 112 in a glass vessel, as glass is dissolved by hydrofluoric acid. A platinum vessel is best suited for the purpose Ca F 2 + S O 4 H 2 = Ca S O 4 + 2 (H F). The receiver should be surrounded by ice, as the acid is exceedingly volatile. The acid is commonly kept in a dilute state, in bottles composed of gutta-percha. Its most remarkable reaction is that of forming a volatile compound of fluorine and silicon by mere contact with silica, or any silicate, such as glass SiO 2 +4(HF) = SiF 4 +2(H 2 O). A glass plate covered by a varnish of bees'-wax and tur- pentine is not attacked by the acid nor by its vapour, but if the coating be removed in some places, by scratching with a needle, the vapour of hydrofluoric acid will engrave the glass along the lines thus exposed. Hydrofluoric acid appears to be bibasic, for by double decomposition with potash it forms not only a potassium salt but also a double salt, hydro-potassic fluoride, of con- siderable stability (H K F 2 ). With ammonia it forms a similar double salt with great readiness. The element has, moreover, a great resemblance to oxygen in its chemical deportment, for silicic fluoride combines with potassic fluoride, barytic fluoride, and other fluorides, forming salts, which may be compared to the salts formed by the union of silica itself with potash, Vertical Section of Blast Furnace. 22O BLAST FURNACE. 174 stratum of ore thrown in at top has descended sufficiently to be heated by the hot mixture of nitrogen, carbonic oxide, and hydrogen, it becomes reduced to spongy metallic iron, which is mixed with the clay and limestone, &c. which were present with it. The gases take up oxygen from the ore and pass over into carbonic acid and steam, but a considerable proportion of them remains unburnt. The spongy metallic iron, mixed with stones and clay, &c., descends to hotter parts of the furnace, where the iron com- bines with carbon, forming liquid ferrous carburet, while the lime unites with the silica and alumina, &c. forming the liquid slag. The liquid ferrous carburet settles down in the deep hearth at the bottom of the furnace, from which it is let out occasionally by the removal of a plug of clay ; while the slag runs off from the top of the hearth, in proportion as it is formed. While the iron is combining with carbon it also combines with silicon, sulphur, phosphorus, &c., and these substances are present in crude cast-iron (called pig), in various propor- tions, besides occasional admixtures of manganese, aluminium, and other metals, which are not to be regarded as impurities. Liquid iron appears to take up a little more than 5 per cent, of carbon, corresponding to the compound Fe 4 C, and when the molten compound is rapidly cooled a ' white* crystalline mass is obtained of extreme hardness and brittleness. If the molten carburet be allowed to cool slowly, some of the carbon crystallizes out on its surface in scales like plum- bago, while some particles of carbon remain dispersed among the crystals of iron, forming a mass of ' grey' or 'mottled* fracture. The presence of certain foreign bodies such as manganese, sulphur, or phosphorus in the carburet prevents this separation of the carbon in slow cooling. Spiegeleisen is a kind of cast-iron containing 5 per cent, or more of 221 174 IRON (*V = s6). manganese, and no carbon crystallizes out from it even on the slowest cooling. When White Iron is heated with hydrochloric acid it dissolves, with evolution of hydrogen possessing a very foetid odour, and few or no particles of carbon are found in the liquid when the iron has dissolved. The hydrogen owes its smell to the presence in it of volatile compounds of carbon and hydrogen. When Grey Cast-iron is dissolved in the acid, it leaves numerous fragments of carbon, which cannot be driven off by the action of the acid, and the hydrogen which is evolved contains very little of the volatile compounds of carbon and hydrogen. The explanation of these different results is to be found in the fact that the hydrogen which is being evolved from the hydric chloride is able to change places with iron of the com- pound Fe 4 C, and thus to pass off in combination with carbon, but cannot combine with carbon which is present in the state of graphite. The carbon in white iron is held in chemical combination with the iron, and passes off in combination with hydrogen ; whereas the carbon of grey iron is mostly uncombined with iron, and remains unchanged when the iron is dissolved. White iron melts more easily and rapidly than grey iron, as this latter has gradually to combine with the carbon which is mechanically mixed with it, and to reproduce the fusible carburet. The specific gravity of cast-iron varies from 7 to 7.25, and is sometimes even higher. Its tensile strength varies from that which will bear a strain of 6 tons on the square inch, up to more than double that strength. The stiffness of cast-iron is measured by the weight which a straight pillar of it having i square inch thickness can support. It varies from 23 tons to upwards of 50 tons. 222 PUDDLING, & glycollic //-'2TJ3Q\2 C 4 H 4 O 2 acetate v c 2 H4 ' O 2 , glycollic succinate C 2 H 4 O 2 ,acetine ^SsSL^'O 3 , & c . ; an d these bodies, built up entirely of O -H. compound radicals, are most characteristic of organic che- mistry, and entitle that branch of the science to the desig- nation which Liebig gave it. It will be understood from these few examples that the constitution of organic compounds is more complicated than that of mineral compounds, and that organic compounds present greater varieties of property than mineral bodies. Thus alcohol is in organic chemistry the representative of water in mineral chemistry ; but, instead of being the only body of its kind, alcohol is one term of a numerous series, varying in composition from C H 4 O to C 30 H 62 O, and pre- 290 PARTIAL DECOMPOSITIONS. 226 senting properties as different as their composition. Some alcohols are volatile fluids which have not been frozen by the greatest artificial cold to which they have been subjected, whereas others are solid wax-like bodies, fusible only at tem- peratures approaching the boiling-point of water. C 27 H 56 O melts at 97. 226. The formation of most organic compounds such as sugar, woody fibre, quinine, albumen, &c. is effected in the organism of growing plants under the influence of sunshine ; and chemists for some time did nothing more than extract these products from vital organisms, and break them up into the simple products, carbonic acid, ammonia, and water, from the elements of which they were built up, or break them up less completely into products of simpler constitution than themselves, yet more complex than the ultimate products of combustion. Thus by the action of hydric nitrate on sugar (C 6 H 10 O 5 ) carbonic acid and water are obtained by a process of combustion at the expense of the oxygen of the acid But by moderating the action of the acid, and using less of it, oxalate was prepared By using still less of the oxidizing agent, tartrate is obtained, together with a smaller quantity of oxalate C 6 H 10 O 5 + 6 H N O 3 = C 4 H 6 O 6 + C 2 O 4 H 2 + + H 2 O + 6HNO 2 . And by moderating still further the oxidizing action, the hydrate of a substance called saccharic acid is obtained C 6 H io O 5 + 3 H N O 3 = C C H 10 O 8 + 3 H N O 2 . This saccharic acid is easily oxidized to tartaric acid, and thence to oxalic acid ; and oxalic acid in its turn is easily oxidized still further to form carbonic acid C 6 H 10 O 8 + 6 H N O 3 = 3 C 2 O 4 H 2 + 6 H N O 2 + 2 H 2 O ; C 2 O 4 H 2 + H N O 3 = 2 C 2 + H N O 2 + H 2 O. U 2 291 226 SYNTHESIS OF ORGANIC BODIES. Saccharates, tartrates, and oxalates were classed among organic compounds because we had only made them by such processes as the partial decomposition of sugar; and the oxalate was not considered the less entitled to rank among organic compounds from the fact that it was often made from the acid juice of the sorrel. 227. Later researches, however, shewed that oxalates can be built up artificially without the materials of any plants, and from inorganic materials. Thus nitrogen gas passed over a hot mixture of carbon and sodic carbonate forms sodic cyanide (Na C N), while carbonic oxide escapes. From this sodic salt it is easy to prepare mercuric cyanide ; and this when heated gives off cyanogen gas. Cyanogen dis- solves readily in water, and the two compounds gradually decompose one another, forming amongst other products ammonic oxalate 2CN + 4 H 2 = C 2 4 (NH 4 ) 2 ; from which hydric oxalate is liberated by a mineral hydric salt. By the action of sodium on oxalic ether Lowig has obtained a compound, which he calls desoxalate; and a desoxalate breaks up into one kind of tartrate and carbonic acid. Alcohol is another product classed among organic bodies from the fact of its being obtained by a partial breaking up of sugar. For under the influence of growing yeast grape sugar breaks up partly into carbonic acid and alcohol C 6 H 12 O 6 = 2 C 2 H 6 O + 2 C O 2 . But Berthelot has shewn that alcohol can be built up artificially from its elements. He first makes acetylene (C 2 H 2 ) by discharging a galvanic battery in an atmosphere of hydrogen by carbon points. This acetylene he combines with copper, and he then brings it in contact with nascent hydrogen, thereby forming ethylene (C 2 H 4 ); and ethylene he combines with oil of vitriol, forming the compound 292 INFLUENCE OF ORGANISMS. 228 C 2 H 6 SO 4 , from which alcohol is liberated by dilution with water and distillation. Urea is another compound rirst obtained only from an organic source, but subsequently prepared from mineral materials. The number of organic compounds which we have learnt how to build up by inorganic processes is already very great, and additions are constantly being made to it ; so that it is no longer customary to apply the term ' organic' only to those compounds which are derived directly or indirectly from plants or animals. Some com- pounds which were originally considered as organic are now usually studied among mineral compounds, and there seems a tendency in inorganic chemistry to continue this encroachment on the domain of organic chemistry; but the general distinction between the two parts of the science is not the less real nor the less marked. 228. The formation of complex molecules, such as sugar, albumen, &c., together with free oxygen, from carbonic acid, ammonia, and water, are, however, not the only results of the vital processes of plants ; for there are processes of partial breaking up of complex organic molecules into less complex: molecules by the agency of growing plants, analogous to the cases of partial breaking up which are effected by artificial means. Thus the fermentation of sugar is a trans- formation of a complex molecule, into a variety of simpler molecules, of which the best known are alcohol, carbonic acid, glycerine, hydric succinate ; and this process has been shewn by the admirable investigations of Pasteur to be due to the growth of the so-called yeast or ferment, a plant which lives upon sugar and gives off these simpler molecules by decomposition of the sugar. In like manner the for- mation of acetate from alcohol or from sugar in contact with air is effected by another plant, called mycoderma aceti. 293 228 GERMS OF ORGANIC LIFE. Another ferment, called penicillium glaucum, transforms a mixture of chalk and sugar into a lactate ; and the lactate thus formed is in its turn decomposed by another process of fermentation, giving rise to a butyrate, carbonic acid, hy- drogen gas, &c. Under certain conditions sugar is broken up by a process of fermentation into mannite and a kind of gum. As far as researches have gone as yet into this most important class of phenomena, it would appear as if a great variety of elementary plants and infusoriae were capable of effecting transformations of organic bodies by processes of fermentation or putrefaction, and that each little organism has a sphere of action peculiar to itself, being capable of de- composing particular organic compounds only. Thus calcic tartrate in presence of atmospheric oxygen serves as food for monads, bacteriums, &c., which evolve carbonic acid. If, however, oxygen be excluded from the mixture these infusorise die off, and vibrios are developed from germs in the liquid, and grow during the decomposition of the tartrate, and no doubt at its expense. 229. Water containing sugar, ammonic salts, and the ashes of yeast, soon becomes inhabited by various lower forms of living beings if merely exposed to the atmosphere. In like manner other mixtures capable of undergoing fer- mentation are found to contain infusoriae and fungi, &c., after exposure to the air for some time. On the other hand, Pasteur has shewn that all germs of organic life in such a mixture are destroyed at a temperature of about 130, and that the liquid may then be kept for any length of time in a closed vessel without undergoing fermen- tation or putrefaction of any kind. Moreover, no fermentation or putrefaction is started in such a liquid by air which has been passed through a red- hot tube, or which has been strained by passing through a tube filled by a porous plug of cotton wool or of gun-cotton. 294 GERMS OF ORGANIC LIFE. 229 In both of these cases the air is freed from all germs or seeds, &c., and it is found incapable of setting up the process of fermentation or of putrefaction in any liquid previously deprived of all germs of organic beings. On the other hand, it has been shewn by Pasteur that the dust strained off from the air by the cotton is sufficient to set up a process of decomposition of any suitable liquid, and that infusoria and fungi, &c., are found to be in active growth in the liquid during the whole continuance of its fermentation. By examination under the microscope the dust was moreover found to contain, besides the various earthy and woody particles, &c., little cellular masses precisely similar in ap- pearance to the spores of fungi, &c. In the course of these investigations it was found that the germs of animal life contained in milk (an alkaline liquid) are not destroyed by boiling at the ordinary atmo- spheric pressure. They were, however, completely de- stroyed by boiling the milk at a pressure of about 1140 millimetres (1.5 atmospheres), and the milk could then be kept for an indefinite time in a closed vessel without under- going any decomposition. 295 230 VINIC ALCOHOL (C 2 # 6 0). CHAPTER XXXV. 230. Alcohol, sometimes called vinic alcohol (C 2 H 6 O = 2 vols. ; sp. gr. at o is 0.8 1 8, at 15 it is 0.7996 ; boiling-point, 78.4). When mixed with a small quantity of water this compound is called spirits of wine, and the pure alcohol is sometimes distinguished by the name ' absolute alcohol/ By distillation of a fermented liquid a mixture of water and alcohol can be obtained, containing as little as about 10 per cent, of water ; but this mixture cannot be separated by further distillation, as the two liquids go over together in these proportions without any further division. In order to dry the alcohol further, the mixture may be distilled over dry potassic carbonate, but in order to dry it completely it ought finally to be mixed in a retort with its own weight of quick-lime in lumps, allowed to stand on the lime for several days (the retort being closed by a cork), and finally distilled off. The first portions collected contain the moisture of the apparatus, and should accordingly be rejected. Alcohol thus prepared sometimes contains volatile oils, which were contained in the materials from which the alcohol was made, or produced during the fermentation. To purify it from these admixtures it should be shaken up with animal char- coal before it is dried. Alcohol is liable to become aqid by distillation in contact with air, by absorbing oxygen. It is also frequently accompanied by ammonia from the fermented liquid. 231. It mixes with water, in all proportions, and the mixtures occupy a smaller volume than that which the alcohol and water occupied previous to mixing. 296 REACTIONS OF ALCOHOL. 232 Tables have been constructed from careful experiments shewing the density of mixtures of alcohol and water in various proportions, and the usual way of ascertaining how much alcohol is contained in a particular sort of wine or beer, &c., is to distil a known quantity of the liquid, say 500 cubic centimetres, collecting carefully all that comes over until two-thirds of the liquid are distilled off. This distilled liquid (or distillate) is accurately measured, and its specific gravity is then determined at the temperature named in the table of specific gravities, by an araeometer, or better still, by a specific-gravity flask. A reference to the table then shews how much alcohol there is in one hundred parts of a mix- ture of the observed density, and from this the operator cal- culates how much must have been in his measured distillate, and thence how much in the 500 cubic centimetres of wine. The term 'proof spirit' is still in use in this country among those who are not sufficiently aware of the value of the cen- tesimal manner of describing the composition of mixtures in use among scientific persons. The strength of spirits of wine used to be tested by moistening some gunpowder with it, and then setting fire to the spirits. If the spirits of wine fired the gunpowder it was said to be 'over proof/ but if it contained too much water to produce that effect it was called ' under proof/ Proof spirits is now defined by law as containing 49.24 per cent, of alcohol. Every half per cent, of alcohol above this proportion is called one degree ' over proof.' 232. When alcohol is present in small quantity in water, it can be detected by saturating the mixture with potassic carbonate, when the alcohol makes its appearance as an oily stratum floating on the aqueous solution of the carbonate. The separation is the result of the fact that the carbonate is insoluble in alcohol but exceedingly soluble in water. Alcohol does not dissolve any mineral salts which are 297 232 REACTIONS OF ALCOHOL. insoluble in water; and, as Miller has pointed out, it dis- solves nearly all deliquescent salts, such as calcic chloride, nitrate, &c., and very few efflorescent salts, such as sodic carbonate, sulphate, &c. Alcohol dissolves the elementary gases, oxygen, hydrogen, nitrogen ; also nitrous oxide, ammonia, carbonic oxide, car- bonic acid, and the gaseous hydrocarbons, to a considerably ' greater extent than water dissolves them. Caustic potash or soda dissolves to a considerable extent in alcohol, and when exposed to the air such a solution be- comes yellow or brown by absorbing oxygen, and forming a so-called resin of aldehyde. Potassium or sodium also dis- solves in alcohol very rapidly, giving off hydrogen with con- siderable rise of temperature. The solution thus obtained contains a compound called potassic (or sodic) ethylate (K C 2 H 5 O), which remains behind in the solid state when the alcohol is distilled off from it. Potassic ethylate is an intensely alkaline compound, pos- sessing great analogy with potassic hydrate. It is present in the liquid obtained by dissolving potassic hydrate in alcohol, being formed by an interchange of the hydrogen of the hydrate with the group C 2 H 5 , called ethyle, of the alcohol K (H) O + H (C 2 H 5 ) O = K (C 2 H 5 ) O 4- H H O. When alcohol is dropped upon molten potassic hydrate an evolution of hydrogen gas takes place, and potassic acetate is formed Oil of vitriol mixes with alcohol in all proportions, evolving considerable heat. When a mixture of the two liquids is heated, the alcohol breaks up chiefly into ether and water 2 C 2 H 6 = C 4 H 10 0+H 2 0, if the sulphate be present in the proportion of two parts by 298 ACTION OF MONOBASIC ACIDS. 233 weight to one of the alcohol. When as much as four parts of the sulphate are present to one of alcohol, the decom- position which takes place on heating is chiefly into olefiant gas and water; C 2 HO = C 2 H 4 + H 2 O. Alcohol burns in the air with a pale blue flame. Its vapour requires three times its own volume of oxygen for combustion, as can be seen by the equation 2 vols. 6 vols. 4 vols. 6 vols. C 2 H 6 O + O 6 = 2 C O 2 + 3 H 2 O. When its vapour, mixed with an insufficient quantity of air for its complete combustion, is allowed to pass over a warm surface of metallic platinum, it undergoes a partial combustion, forming an acrid and pungent volatile compound. Even in presence of water alcohol is readily oxidized to a limited extent. A red solution of potassic dichromate and hydric sulphate is very speedily changed to an emerald green colour by the addition of alcohol, and a peculiar sickly odour is perceived at the same time, owing to the formation of a body called aldehyde, consisting of C 2 H 4 O, or a mole- cule of alcohol from which two atoms of hydrogen have been burnt away. At the same time with aldehyde there is usually hydric acetate formed (C 2 H 4 O 2 ), by the addition of an atom of oxygen to the elements of the aldehyde. Alcohol is entirely decomposed by passing its vapour slowly through a red-hot tube, a mixture of carbonic oxide, olefiant gas, marsh gas, hydrogen, besides several condensable hydro- carbons, being formed. 233. The action of monobasic hydrogen salts upon alcohol consists in forming water and a salt containing the radical C 2 H 5 in place of the hydrogen of the original hydrogen salt. Thus hydric chloride forms water and ethy- lic chloride 1 = HHO + C 2 H 5 C1. 299 - 233 ANALOGY OF ALCOHOL AND WATER. Hydric iodide, in like manner, forms water and ethylic iodide Hydric nitrate forms water and ethylic nitrate H C 2 H 5 O + H N O 3 = H H O + C 2 H 5 N O 3 . 234. These reactions are precisely similar to those which take place between potassic hydrate and the same hydrogen salts, the group C 2 H 5 from alcohol forming a salt as potassium does in its corresponding reactions. Thus writing K for C 2 H 5 in the last equation we have the double decomposition between potassic hydrate and hydric nitrate, forming water and potassic nitrate Throughout all the reactions among its compounds the group C 2 H 5 exhibits this analogy with a monovalent metal, and it is accordingly considered as a monovalent organic radical, that is, as an organic radical of which the atom as represented by the formula C 2 H 5 is capable of replacing one atom of hydrogen in its various salts. According to this view, the constitution of alcohol is explained by comparing it to water. If a molecule of water, H H O, were to lose one of its atoms of hydrogen and to take up an atom of ethyle in the place of that hydrogen, it would be transformed into alcohol. We shall see that alcohol is easily made by this process. It is important, moreover, to observe that inasmuch as the molecule of alcohol and the molecule of water each occupies two volumes in the state of vapour, the atom of ethyle takes exactly the space vacated by the atom of hydrogen which it replaces H H O = 2 vols. H (C 2 H 5 ) O = 2 vols. When alcohol or any other substance is thus represented on the water-type it often becomes necessary to distinguish between the hydrogen of the ethyle and the hydrogen of the original type (water). The term ' typical hydrogen ' is 300 ANALOGY OF ALCOHOL AND WATER. 234 used to denote hydrogen remaining from the water, in any compound belonging to the water-type ; or more generally a ' typical ' element means an element left unreplaced in the typical body from which a compound is formed. Bibasic acids, such as oxalic, sulphuric, &c., form not only salts containing two atoms of ethyle in one molecule of the salt, but they also form double salts containing one atom of ethyle and one atom of hydrogen in each molecule of the salt. Thus we have ethylic oxalate ((C 2 H 5 ) 2 C 2 O 4 ), and hydrethylic oxalate (H (C 2 H 5 ) C 2 O 4 ). So also ethylic sulphate ((C 2 H 5 ; 2 S O 4 ), and also hydrethylic sulphate (H (C 2 H 5 ) SO 4 ), commonly called sulphovinic acid. In like manner there is an ethylic carbonate ((C 2 H 5 ) 2 C O 3 ), and a hydrethylic carbonate (H(C 2 H 5 ) CO 3 ) called carbovinic acid. There are also double phosphates containing ethyle and hydrogen, in proportions corresponding to the sodium and hydrogen in the double phosphates containing those elements. Hydrodiethylic phosphate is H (C 2 H 5 ) 2 P O 4 , dihydroethylic phosphate is H 2 C 2 H 5 PO 4 , and the ethylic phosphate, com- monly called phosphoric ether, is (C 2 H 5 ) 3 PO 4 . 301 235 METHYLIC ALCOHOL (C# 4 O). CHAPTER XXXVI. 235. Methylic Alcohol, or wood -spirits (C H 4 O = 2 vols.; density at c, .82 ; boiling-point, 66). This substance is formed, together with a variety of other liquid com- pounds and several gases, by the destructive distillation of wood. A considerable quantity of tar is deposited from the products which pass off from the retort in which the wood is distilled, and with this tar is water con- taining hydric acetate and wood-spirits. This watery liquid is usually neutralized by lime, and distilled. The crude wood-spirits comes over in the beginning of the distillation accompanied by a little water, and it is usually introduced into commerce, after partial drying by distillation over quick- lime. In this state it is usually a yellowish liquid, of an unpleasant smell. It is often called 'naphtha/ or 'wood- naphtha.' Its chief use is for mixing with spirits of wine to form the so-called methylated spirit, which manufacturers are allowed to use without paying the excise duty which is levied on other spirits of wine. Methylated spirit contains ten per cent, of wood-spirits, and possesses the characteristic smell of that mixture. 236. Common Wood-spirit generally becomes turbid when mixed with water, owing to the precipitation of liquid hydrocarbons which were dissolved in it. For the preparation of methylic alcohol it should be mixed with nearly its own volume of strong caustic soda- solution, and allowed to stand in a closed vessel for several hours. The liquid which in most cases collects on the surface should be removed from the alkaline mixture, and 302 . PROPERTIES OF METHYLIC ALCOHOL. 237 the latter distilled as long as any combustible distillate comes over. The sodic solution which is left behind contains a large quantity of sodic acetate, which was formed simul- taneously with methylic alcohol by the action of the soda on methylic acetate contained in the crude wood-spirit. This distillate usually contains ammonia, and should be distilled with 3 or 4 per cent, of hydric sulphate, which not only keeps back the volatile bases but also a good deal of tarry matter formed from impurities in the wood-spirits. In this manner a mixture of methylic alcohol with water, acetone, and dimethylacetal is obtained ; and to get rid of the two last- named bodies, the mixture should be saturated with dry calcic chloride, and distilled in a water-bath as long as any- thing comes over at that temperature. The distillate consists of acetone, dimethylacetal, and sometimes a part of the methylic alcohol ; and the calcic chloride in the retort retains methylic alcohol in the form of a compound which is not decomposed at the temperature of 100. In order to liberate the alcohol from this compound, water should be added in small quan- tity and the mixture should then be distilled. The alcohol which comes over requires subsequent drying by means similar to those described for drying common vinic alcohol. When required in the purest obtainable state methylic alcohol is made by the action of ammonia on methylic oxalate (C H 3 ) 2 C 2 O 4 + 2 N H 3 = 2 C H 4 O + N 2 H 4 C 2 O 2 ; oxamide being formed at the same time. The filtered liquid is neutralized by sulphate, to take up the excess of ammonia, and distilled. The distillate consists of a mixture of water and pure Methylic Alcohol. 237. This remarkable liquid has great resemblance to vinic alcohol in its properties. It mixes with water in all proportions, and with condensation. Potassium or sodium dissolves in it with evolution of 33 237 HOMOLOGOUS ALCOHOL. hydrogen, forming solutions of the compounds K C H 3 O or Na C H 3 O, called respectively potassic methylate and sodic methylate. Methylic alcohol dissolves caustic potash or soda, forming these same compounds together with water Monobasic hydrogen salts, such as the chloride, iodide, nitrate, &c., react upon methylic alcohol in like manner as upon vinic alcohol, forming water and compounds of me- thyle, such as methylic chloride (CH 3 C1), iodide (CH 3 I), or nitrate (CH 3 NO 3 ). In these reaction's the radical me- thyle changes places with an atom of hydrogen, just as an atom of ethyle does in the corresponding reactions of these salts on vinic alcohol, and a molecule of water is formed in each case from a molecule of methylic alcohol, by the re- placement of its methyle by hydrogen, the vapour-volume being unaltered by the interchange 2 Vols. 2 vols. 2 Vols. 2 vols. H(CH 3 )0 + HCUHHO + (CH 3 )C1. Bibasic acids form both normal salts with methyle, such as (C H 3 ) 2 C 2 O 4 , methylic oxalate ; (C H 3 ) 2 S O 4 , methylic sulphate ; (C H 3 ) 2 C O 3 , methylic carbonate : and also double salts, such as H C H 3 C 2 O 4 , hydromethylic oxalate or oxalomethylic acid ; H C H 3 S O 4 , Jiydromethylic sulphate or sulphomethylic acid ; H C H 3 C O 3 , hydromethylic carbonate or carbomethylic acid. Tribasic acids, such as phosphoric acid, form not only normal methyle salts, containing three atoms of methyle in each molecule of the salt, such as methylic phosphate (CH 3 ) 3 PO 4 ; they also form two classes of double salts: one, in which one-third of the methyle is replaced by hy- drogen or a metal, such as the hydrodimethylic phosphate H (C H 3 ) 2 P O 4 ; another, in which two-thirds of the methyle 34 HOMOLOGOUS ALCOHOLS. 238 are so replaced, as in the case of the dihydromethylic phos- phate H 2 CH 3 PO 4 . Hydric sulphate when heated with one- quarter its weight of methylic alcohol decomposes it into so-called methylic ether (C 2 H 6 O) and water 2 HCH 3 = C 2 H 6 + HHO. Carbonic acid, sulphurous acid, and other products are formed at the same time. All attempts to form from me- thylic alcohol the hydrocarbon C H 2 , as olefiant gas is formed from vinic alcohol, have failed. 238. Methylic alcohol is admitted to be constituted like vinic alcohol, having the radical methyle (C H 3 ) in the place of the ethyle (C 2 H 5 ) of vinic alcohol; and similar argu- ments to those which served to establish that vinic alcohol is a molecule of water (H H O) in which one atom of hydrogen is replaced by an atom of ethyle ((C 2 H 5 ) H O) may be used to prove that methylic alcohol is formed from water by the replacement of one atom of hydrogen by methyle ((C H 3 ) H O). The two alcohols differ empirically in composition by the elements C H 2 ; for if these elements were taken from vinic alcohol without disarranging the remaining elements, methylic alcohol would be formed (C 2 H 6 O - C H 2 = C H 4 O). The term 'homologous* is applied to bodies possessing analogous properties, as shewn by their reactions, and differ- ing from one another by C H 2 , or any multiple of C H 2 . It was stated above that the action of the sulphate upon methylic alcohol gives rise to the formation of a product having a composition represented by the empirical formula C 2 H 6 O. The density of this compound in the state of vapour is identical with that of alcohol vapour C 2 H 6 O= 2 vols,; but this methylic ether is a vapour at the common atmo- spheric temperature, and when condensed to the liquid state x 35 238 DECOMPOSITIONS OF METHYLIC ALCOHOL. is found to have the boiling-point 23.5C, whilst vinic alcohol boils at 78. The study of the reactions of methylic ether shews that its constitution is not analogous to that of methylic alcohol, so that it is not homologous with it. For each mole- cule of methylic ether is found to contain two atoms of methyle ((CH 3 ) 2 O), of which one or both can be removed and replaced by hydrogen, atom for atom ; and in no reac- tions does it shew a behaviour like alcohol, which retains from the water an atom of typical hydrogen replaceable by potassium. 239. Under the action of oxidizing agents, or of molten potassic hydrate, methylic alcohol gives rise to the formation of formiates, such as the hydric formiate HCHO 2 . These formiates are analogous in their constitution to the acetates (such as hydric acetate, HC 2 H 3 O 2 ), and accordingly the two salts afford us a second instance of homology. By limiting the action of oxidizing agents on methylic alcohol there is some reason to believe that a product of the composition CH 2 O, corresponding to aldehyde, has been obtained. Four other alcohols have been found in the fermented ' mark' of the grape. This substance consists of the skins, seeds, and stalks of grapes from which the juice has been expressed for the manufacture of wine. When allowed to ferment, the mass yields vinic alcohol, which is sold as brandy; but with this brandy there is a substance known by the name of fousel oil, which comes over mostly at the end of the distillation. This fousel oil has been found to contain propylic alcohol (HC 3 H 7 O), sometimes called tri- tylic, and amylic alcohol (HC 5 H n O), and caproic alcohol (H C 6 H 13 O), sometimes called hexylic. Different specimens of the fousel oil contain these bodies in different proportions, and they are separated from one another by oft-repeated 306 PROPYLIC ALCOHOLS (C 3 H 8 0). 240 fractional distillations. Butylic alcohol (C 4 H 10 O) has been found in some specimens of fousel oil made from potato spirits, as well as from the fousel oil of beetroot molasses. The most advantageous form of apparatus for the purpose of such fractional distillations is found to be a flask with a very long neck, near the top of which is the bulb of a thermometer. The top of the neck communicates with a condenser, in which the most volatile constituents of the dis- tilling mixture are collected ; whilst the less volatile con- stituents are condensed in the neck of the flask, and run back into the boiling liquid. 240. Propylic alcohol (C 3 H 8 O = 2 vols.; boiling-point, 96). This body is not miscible with water in all propor- tions, although water dissolves a great deal of it. Its reactions are in all respects analogous to those of vinic alcohol, and it is considered to contain the radical propyl (C 3 H 7 ) in the same manner that vinic alcohol contains the radical ethyle. It is therefore homologous with methylic and vinic alcohols, and is the third term of the series of alcohols. Its deriva- tives propylic chloride (C 3 H 7 Cl), propylic iodide (C 3 H 7 I), propylic nitrate (C 3 H 7 N O 3 ), hydropropylic sulphate (H C 3 H 7 S O 4 ), &c. are homologous with the correspond- ing methyle and ethyle compounds. A substance called iso-propylic alcohol of the same com- position as propylic alcohol has been formed by the action of sodium amalgam upon acetone in presence of water. Acetone contains only six atoms of hydrogen in each mole- cule, its formula being C 3 H 6 O, so that the propylic alcohol is formed by the addition of two atoms of hydrogen to acetone. The alcohol thus obtained differs in some respects from that formed from the mark. Its boiling-point is below 90. The same product seems to be formed from acrolein by a similar treatment. Acrolein is composed of C 3 H 4 O, and sodium amalgam in presence of water adds to it hydro- x 2 307 240 PROPYLIC ALCOHOLS (C 3 H* O). gen, forming two liquids of like composition (C 3 H 8 O), but differing from one another by their boiling-points one of them boiling between 87 and 88, while the other boils between 96 and 98. The former of these is supposed to be identical with the product formed from acetone, and the latter identical with propylic alcohol. The hydrocarbon propylene (C 3 H 6 ) is absorbed rapidly by oil of vitrol, and the solution when distilled with water yields a distillate containing an alcohol of the composition C 3 H 8 O, and boiling at 85. It has been found that iso-propylic alcohol breaks up more easily into propylene and water than is the case with the pro- pylic alcohol formed by fermentation, and it is considered probable that the alcohol made from acetone may be identical with this one made from propylene. Propylic alcohol can 'be oxidized like vinic alcohol, yielding propylic aldehyde (C 3 H 6 O), a body isomeric but not identical with acetone ; and by further oxidation it yields so-called propionic acid. 308 BUTYL1C ALCOHOL (C* J/ 10 0). 242 CHAPTER XXXVII. 241. Butylic Alcohol (HC 4 H 9 O = 2 vols.; boiling- point, 1 06 to 109) has been prepared from the fousel oil obtained in the distillation of spirits from fermented beetroot. Its reactions are analogous to those of vinic alcohol, and it is considered to be a molecule of water in which one atom of hydrogen is replaced by the radical butyl C 4 H 9 . A volatile compound of the composition C 4 H 9 1 = 2 vols., boiling at 117 to 118, has been obtained by the action of hydric iodide on erithrite (C 4 H 10 O 4 ), It has been shewn that this compound is isomeric with butylic iodide prepared from butylic alcohol. The alcohol prepared from it boils at 96 to 98. By the action of oxidizing agents, such as fused potash, &c., butylic alcohol yields compounds of an acid homologous with acetic acid, and containing in each of its salts C 2 H 4 more than in the corresponding acetate. The hydrogen salt of this acid has been found in rancid butter, and obtained thence the name butyrate; its formula is H C 4 H 7 O 2 . 242. Amylic Alcohol (H C 5 H 11 O = 2 vols. ; boiling- point, 129 to 132 ). This alcohol is the commonest con- stituent of fousel oil, and is easily obtained in quantity from that source. It has an exceedingly unpleasant odour, and is said to produce headache if much inhaled. Water dissolves it but slightly, and it floats upon water like an oil. Potas- sium displaces one atom of hydrogen in amylic alcohol, forming a solution of potassic amylate (KC 5 H n O) in the alcohol. The common hydric salts decompose amylic 309 242 AMYLIC ALCOHOLS (C 5 # 12 0). alcohol, forming water and compounds of the radical amyle, such as amylic chloride (C 5 H 11 Cl), hydramylic sulphate (H C 5 H 11 S O 4 ), &c.; and there is no doubt that it is analo- gous in its constitution to the true alcohols, and contains the radical amyle C 5 H 11 in the place of one atom of hydrogen of water. When heated with concentrated hydric sulphate amylic alcohol does not, however, yield an ether as vinic alcohol does. The mixture becomes black gives off sulphurous and carbonic acids, together with products of the destruction of the amylic compound* Still less does amylic alcohol yield a gas homologous with olefiant gas when heated with a greater quantity of strong hydric sulphate. When, however, amylic alcohol is mixed with zinc chloride in the proportion of ij times its weight, and after standing two or three days, carefully distilled, a mixture of volatile products is obtained, containing amy- lene (C 5 H 10 = 2 vols.), which boils at 35, and has a specific gravity of .663 at o This body is proved by its reactions to be the olefiant gas of amylic alcohol, and is less volatile than olefiant gas itself in consequence of its greater molecular weight. A mixture of oil of vitriol with one-quarter of its volume of water dissolves amylene, forming sulphamylic acid, and by diluting this liquid with water and distilling, an alcohol is formed, differing from amylic alcohol formed by fermen- tation by its greater tendency to break up into amylene and water. The ether of amylic alcohol (amylic oxide, (C 5 H 11 ) 2 O) has been obtained by another process, and found to boil at 176, a circumstance which sufficiently accounts for its not being obtainable by heating a mixture of the alcohol with strong hydric sulphate, as the ether is burnt by hydric sulphate at a lower temperature than its boiling - point. Pasteur has 310 CAPROIC ALCOHOL (CH 14 0), &Vr. 243 found that in fousel oil there are two isomeric amylic alco- hols ; one of them rotating the ray of polarized light, boiling at 1 2 7 to 128, while the other has no rotating action on the ray, and boils at 129. By combining these two alcohols with hydric sulphate and neutralizing the compound (hydra- mylic sulphate, H C 5 H 11 S O 4 ) by baryta, salts were obtained of like composition (Ba (C 5 H n S O 4 ) 2 ), but differing from one another in their solubility in water ; the salt made from the rotating alcohol being 24 times as soluble as that made from the inactive alcohol. By the action of an aqueous solution of chromic acid mixed with hydric sulphate fousel oil is oxidized, forming a mixture of hydric valerate (C 5 H'O 2 ) and valerianic alde- hyde (C 5 H 10 O); the former a salt homologous with the acetate and boiling at 176, the latter a neutral body which combines with hydrosodic sulphite. The aldehyde boils at 96; in contact with oxygen it is readily transformed into hydric valerate. 243. Caproic Alcohol (H C H 13 O - 2 vols. ; boiling- point, 154 to 1 6 6) has been obtained in small quantities from the mark of the grape. By distilling mannite (C 6 H 14 O 6 ) with an aqueous solution of hydric iodide, Wanklyn has obtained a volatile oil of the composition C G H 13 1 = 2 vols., from which so-called hexylic alcohol (HC C H 13 O) has been obtained isomeric with the alcohol obtained from the mark. A hydric salt of the composition C 6 H 12 O 2 , called caprate, has been found in butter and several other fatty mixtures. It stands to caproic alcohol in the same relation in which the acetate stands to vinic alcohol C 6 H 14 O -H 2 + O = C 6 H 12 O 2 . (Enanthic alcohol (C 7 H 16 O) appears to be formed in many cases by distilling castor-oil soap with potassic hy- drate. 243 CETYLIC ALCOHOL (C lfl # s4 0). Its aldehyde, called oenanthol (C r H 14 O), is found among the products of the dry distillation of castor oil, and is sepa- rated from the oily products accompanying it by distilling the mixture with steam, which carries over the oenanthol accompanied by a little impurity, and a repetition of the dis- tillation with water renders it still purer. By the action of hydric nitrate on castor oil a volatile salt is formed, which distils over with water from the retort in which the oxidation takes place. This oily salt has the composition C 7 H 14 O 2 , and is called hydric cenanthylate. Caprilic alcohol (C 8 H 18 O=2 vols.; boiling-point, 178) was discovered by M. Bouis in the distillation of castor-oil soap with potassic hydrate. Potassic sebate remains behind in the retort Potassic ricinoleate. Potassic sebate. H 2 . Hydric caprilate (C 8 H 18 O 2 ) has been obtained from butter and from cocoa-nut oil. 244. Cetylic Alcohol (C 16 H 34 O) is derived from a beautiful crystalline compound known by the name of sper- maceti, which is found with other fats in the heads of whales. Potassic hydrate melted with a little water decomposes this compound, easily forming potassic palmitate (C 16 H 31 KO 2 ) and cetylic alcohol. The decomposition is effected at a lower temperature by the aid of alcohol. The alcohol can be obtained by precipitating the palmitate by calcic chloride, forming calcic palmitate, which carries down the cetylic alco- hol with it. Ether dissolves the alcohol, leaving the palmitate. Cetylic alcohol melts at 49. By distilling cetylic alcohol with phosphoric acid a hy- drocarbon of the composition C 16 H 32 is obtained. This olefiant gas of cetylic alcohol boils at about 275. 312 CEROTIC ALCOHOL (C 27 H' f < O). 245 Spermaceti has the empirical composition C 32 H 64 O 2 , C 16 H S1 O and its rational formula is ^, lc TTSS O, which represents it as cetylic palmitate. Potassic hydrate puts an atom of potas- sium into this group in lieu of an atom of the radical ce- tyle- H C 16 H 31 H Palmitic acid is the chief solid constituent of so-called palm oil, which is now so largely imported for the manu- facture of soap, &c. 245. Cerotic Alcohol (C 27 H M O) has been prepared by Brodie from Chinese wax, by a decomposition similar to that by which cetylic alcohol was obtained from spermaceti. Potassic cerotate (C 27 H 53 KO 2 ) is obtained at the same time. Cerotic alcohol is a hard and brittle solid, inso- luble in water, but soluble in alcohol and ether. It melts at 97. A solid hydrocarbon has been obtained from Chinese wax, possessing probably the composition C 27 H 54 . It melts between 57 and 58. In its properties this substance has some resemblance to the mixtures now so much used by the name of Paraffine, which are found among the products of dry distillation of boghead, or cannel coal, and various bitu- minous schists. The hydric salt of cerotic acid (C 27 H 54 O 2 ) is found in several varieties of beeswax, and is extracted from that sub- stance by boiling alcohol. It melts at 78. Melissic Alcohol (C 30 H 02 O) is the highest term now known of the alcohol series. It was prepared by Brodie p30 JG1 from melissic palmitate- riGH 31 O^' a const * tuent f beeswax, by the action of potassic hydrate. 313 245 MELISSIC ALCOHOL (C 30 # 62 O). It is partly decomposed by distillation, water being formed, together with a beautiful hydrocarbon (C 30 H 60 ), which melts at 62. Molten potassic hydrate oxidizes melissic alcohol, forming a potash melissate with evolution of hydrogen. P 30 U 01 TJ n 30 U 59 H +K= K ETHER (C 4 # 10 0). 246 CHAPTER XXXVIII. 246. Ether (C 4 H 10 O = 2 vols.; boiling-point, 3 5) is formed by the replacement of two atoms of hydrogen in a molecule of water by two atoms of ethyle. From alcohol it is made by displacing the typical hydrogen by sodium, and acting on the sodic ethylate thus obtained by vinic iodide. The first reaction is this 2 **O + Na = C ^ O + H. The second is this C ^ O + C 2 H 5 1 = * 2 ^ O + Na I. It is commonly prepared by the action of strong hydric sulphate on alcohol. When two volumes of strong spirits of wine are mixed with three volumes of hydric sulphate, considerable heat is evolved, and the mixture contains sul- phovinic acid and water as well as hydric sulphate and alcohol. These products are formed by the exchange of one atom of hydrogen in the sulphate for an atom of ethyle in the alcohol When the mixture of these four compounds is heated to about i35C a second reaction takes place, forming ether and reproducing hydric sulphate. This second reaction con- sists of an interchange between ethyle in the sulphovinic acid and typical hydrogen in alcohol : thus H 4 C 2 H 5 C 2 H 5 H The ether thus formed evaporates, and must be collected by a suitable condenser. The sulphate which is repro- duced at the end of the process is usually employed for 315 246 CONTINUOUS ETHERIFICATION. the transformation of more alcohol into ether and water, and for that purpose it is kept at the same temperature of i35> while alcohol is allowed to flow into it slowly by a tube reaching to the bottom of the vessel containing it. The flow of alcohol should be regulated so as to keep the surface of the mixture in the retort constantly at its initial height. 247. The alcohol which comes in contact with this sul- phate reacts in the same manner as that which was first mixed with it forming water, which distils off, and sul- phovinic acid; and this sulphovinic acid in its turn reacts on another molecule of alcohol, forming ether and the original sulphate. Thus it is that a given quantity of sul- phate transforms an indefinite quantity of alcohol into these two products. The sulphate is renewed occasionally, be- cause it gets contaminated by impurities in the alcohol, and by secondary products, which impair its action. The liquid collected in the receiver consists of two strata ; the lower one being chiefly water, the upper stratum impure ether. Sulphurous acid is usually present in the distillate, and is removed by washing the ether by caustic soda ; alcohol is always carried over with the ether and water, and can be partially removed by washing with salt water, in which it is far more soluble than ether. To obtain the ether pure it should be finally distilled over powdered sodic hydrate, or even metallic sodium, which keep back any water or alcohol. 248. Ether is an exceedingly mobile liquid, of 0.736 density at o. It has an agreeable odour, which is well known under the name ' ethereal/ It produces an anaesthetic effect when inhaled in sufficient quantity, but its use for this purpose has been given up, owing to the unpleasant after- effects which it produces on the patient. It dissolves in about fourteen times its volume of water ; but if there be not PROPERTIES OF ETHER. 249 water enough to dissolve it, the supernatent stratum of ether takes up about -$ of its volume of water, which it holds in solution. When poured on the hand ether produces a strong sensation of cold, owing to the rapidity with which it evaporates, rendering heat latent. Its vapour density is 37, as can be seen from the fact that its molecule (C 4 H 10 O), weighing 74, occupies two volumes in the state of vapour. Being about 2\ times as heavy as air, ether vapour can easily be poured from one vessel to another. It very easily catches fire, and burns with a white flame. A mixture of ether vapour and air explodes with great violence if containing oxygen in about the combining pro- portions, viz. six volumes to every one of ether vapour. Ether ought never to be distilled in the vicinity of fire or flame, but hot water should be brought from a distance to pour into a vessel in which the retort full of ether is contained. Ether dissolves oils, and fats, and resins far more readily than alcohol dissolves them. Sulphur, phosphorus, and iodine dissolve in ether. Metallic salts are as a rule less soluble in ether than in alcohol, and many salts which dissolve readily in alcohol can be precipitated from that solution by the addition of ether. Hydric sulphate dissolves ether readily, doubtless form- ing alcohol and sulphovinic acid C 2 H 5 H w > and probably also water and a second molecule of sulpho- vinic acid. Sulphuric acid combines with ether as with water, forming C 2 H 5 vinic sulphate p 2 TTO S O 4 . 249. Methylic Ether (C 2 H G O - 2 vols.; boiling-point, 23.6). This gas is obtained from inethylic alcohol by 249 METHYLIC ETHER (C 2 H G 0). processes similar to those described for the preparation of vinic ether from its alcohol. Water dissolves between 30 and 40 times its volume of methylic ether at the ordinary temperature. /r>2 TJ5 Vinomethylic Ether ^ H3 O - 2 vols.; boiling-point, n) is formed by the action of methylic iodide on potassic ethylate p 2 TJ 5 p 2 TIT 5 CH'I + ^j* 1 0-KI + j*J O; or by the equivalent reaction of vinic iodide on potassic methylate C2HSI + CH' = KI + C 2 H3- It is also formed by the action of methylic alcohol on a mixture of hydric sulphate with vinic alcohol. The sulpho- vinic acid contained in this mixture replaces the typical hydrogen of the methylic alcohol by ethyle, just as it replaces the typical hydrogen of vinic alcohol by ethyle in the forma- tion of vinic ether Hp2 us pa us TJ n_i_ <>o 4 ^ n n _i_ Q n 4 CH' H k = C H 3 f H b This ether has an agreeable odour, easily distinguishable from that of common ether. /p3TJ7 \ /p4TJ9 \ Propylic ether (^ 3 g 7 OJ and butylic ether (^ 4 j^ 9 OJ are but little known. Amylic ether (C 10 H 22 O = 2 vols.; boiling-point, 176) cannot be obtained by distilling hydric sulphate with amylic alcohol, but it has been prepared by the action of amylic iodide on potassic amylate And this mode of formation leaves no doubt as to the fact that its constitution is analogous to that of the lower ethers. AMYLGMETHYLIC ETHER (C 6 H }2 0). 251 (Q5TT11 \ r us O; boiling-point, 92 j is obtained by the action of methylic iodide on potassic amy- late, or by distilling a mixture of equivalent weights of amylic and methylic alcohols with hydric sulphate, allowing the mixed alcohols to flow gradually into the boiling mixture, as vinic alcohol is allowed to flow in during the common continuous process of etherification. /C 5 H n Amylovinic ether ^p 2 TT5 O = 2 vols. ; boiling-point, 112) has been obtained by perfectly similar processes, from the vinic and amylic alcohols. 251. The higher ethers of the alcohol series are but little known. The formation and constitution of ethers have taught us the important fact that the oxide of a mono- valent element or radical contains in each molecule two monads, and that the compound of water with the oxide of a monad does not contain in each molecule the elements of one molecule of the oxide in addition to the elements of one molecule of water, but only half of that quantity. Thus alcohol, which is truly the compound of water with ethylic oxide, (C 2 H 5 ) 2 O, does not contain a complete molecule of ether plus a complete molecule of water in each of its own molecules, for two molecules of alcohol must concur to form one of ether and one of water. It is not long since chemists believed that ether and water were formed by the mere cutting in two of a molecule of alcohol ; and while so representing the process, they consistenly assumed that the oxygen in each molecule (weighing 16) was not one atom, but two atoms, each weighing 8. Thus using the symbol f = 8, we should represent ether as C 2 H 5 f, C 2 H 5 water as Hf, and alcohol as -^- methylic alcohol would be jWS an d methylic oxide CH 3 f: and according to 319 251 AMYLOMETHYLIC ETHER this system each molecule of water, methylic oxide, or vinic oxide would occupy one volume, while each molecule of the alcohols would occupy two volumes, like a molecule of vinic or methylic iodide. The formation of common ether by the action of vinic iodide on potassic ethylate would be represented as an interchange between potassium in the one and ethyle in the other molecule; such exchange being accompanied by a breaking up of the molecule C 2 H 5 p 2TT5.| m to two molecules of the composition C 2 H 5 f. But this explanation would assume the occurrence of a pro- cess of breaking up, which is proved not to occur in the closely analogous case of the formation of methylovinic ether, by the action of methylic iodide on potassic ethylate. C 2 H 5 In this case the compound r TT 3 5 does not break up into L> .ti Tj" C 2 H 5 f andCH 3 f. In like manner, when sulphovinic acid reacts upon alco- hol, forming sulphuric acid and ether, the process would have to be represented as an interchange of ethyle in the acid with hydrogen in the alcohol, and as a breaking up of the ether into two molecules. It is found in every case in which the radical contained in the acid can be distinguished from the radical contained in the alcohol, that the two go into the composition of one molecule of ether. When sulphovinic acid is boiled with water an interchange of ethyle in the acid and hydrogen in the water takes place, forming hydric sulphate and alcohol ; and if the molecule of water were Hf, the process could not be explained without assuming that the ether C 2 H 5 combines at the moment of its formation with a molecule of water to form a molecule of alcohol. Not only would the analogous bodies water, alcohols, ethers, &c. be represented in this manner by dissimilar 320 AMYLOMETHYLIC ETHER (C*H0\ 251 formulae, some containing f in one molecule, others two small atoms of oxygen in each molecule Hf, C H 3 f, C 2 H 5 f , C 2 H 5 Hf f , C H 3 Hf f, &c. ; C H 3 C 2 H 5 f f , C 2 H 5 C 5 H n ff , &c. ; but it would be necessary to assume, besides the inter- changes which are known to take place, a number of separations and combinations among the products of these interchanges, combinations and separations which are proved to have no existence in closely analogous cases. 121 252 EVIDENCE THAT SULPHUR IS DIVALENT. CHAPTER XXXIX. 252. The analogy between oxygen and sulphur, between sulphur and selenium, and between selenium and tellurium, naturally suggests the probability of these elements being able to replace oxygen, atom for atom, in the alcohols and ethers forming sulphides, selenides, tellurides, &c. analogous to these oxides. As far as experiments have gone as yet these anticipations have been confirmed. Hydromethylic Sulphide, or methylic mercaptan / S = 2 vols. ; boiling-point, 2iV is formed by distilling a mixture of methylcalcic sulphate and hydropotassic sulphide (C ^3 )2 (S0 4 ) 2 + K 2 S 2 = 2 C g 3 S + K 2 S0 4 + CaS0 4 . It is more easily formed by the action of methylic iodide upon an alcoholic solution of potassic sulphydrate When potassic sulphide is used instead of hydropotassic sul- phide, the product is methylic sulphide ((C H 3 ) 2 S = 2 vols.) Methylic sulphide boils at 41. Its density is 0.845. It stands to methylic mercaptan in the same relation in which potassic sulphide (K 2 S) stands to hydropotassic sulphide (HKS). The addition of mercuric oxide precipitates the sulphur alcohol in combination with mercury in the form of the 322 AMYLIC MERCAPTAN. 253 (C H 3 Y compound ^ u- ' S 2 , a white crystalline mass, which sul- phuretted hydrogen decomposes H 2 S + (CH 3 ) 2 HgS 2 = Hg S + 2 C ^S. The compound CH 4 S is sometimes called methylic mer- captan, the name 'mercaptan' being given to the sulphur alcohols, from the force with which they react on mercuric oxide. They are remarkable for their peculiarly disagree- able smell. (C 2 H 5 H S = 2 vols. ; boiling-point, 62; sp. gr. 0.835) is obtained by processes similar to those for obtaining the methylic compound. Mercaptan floats upon water, and is almost insoluble in it. At a low temperature it crystal- lizes. Hydric nitrate oxidizes it, forming hydrovinic sulphite Vinic sulphide ((C 2 H 5 ) 2 S = 2 vols.; boiling-point, 73; sp. gr. 0.825). When prepared by the action of vinic iodide on an alcoholic solution of potassic sulphide this compound can be precipitated from the alcoholic solution by the addition of water. It has an odour resembling that of garlic. There is also a vinic disulphide, (C 2 H 5 ) 2 S 2 . /C 5 H U 253. Amylic Mercaptan (^ -^ S = 2 vols. ; boiling- point, 1 25) and amylic sulphide ((C 5 H 11 ) 2 8 = 2 vols.; boiling- point, 2 1 6) are made by processes similar to those adopted in the preparation of the methyle and ethyle compounds. These compounds are analogous to the alcohols and ethers, and they are to be considered as derived from them by the substitution of an atom of sulphur for an atom of oxygen; the resulting sulphur compound occupying the same vapour-volume as the original oxygen compound. Vinic alcohol is decomposed by phosphoric sulphide, form- Y 2 323 253 MARSH GAS SERIES. ing mercaptan, an atom of sulphur going into the place of the atom of oxygen in the alcohol ; whereas when it is de- composed by phosphoric chloride, the atom of oxygen being replaced by two atoms of chlorine, the result is the formation of a molecule of vinic chloride plus a molecule of hydric chloride If sulphur were monovalent, like chlorine, the phosphoric sulphide would form vinic sulphide and hydric sulphide in C 2 H 5 separate molecules, instead of the compound -- S. The compounds containing ethyle, which are formed by the action of hydrogen salts upon alcohol, are commonly called 'compound ethers/ and they are best classified according to the equivalence of the atoms from which they are formed. The simplest are those formed on the type of hydric chloride, each molecule occupying two volumes and containing one atom of ethyle, combined with one atom of an element analogous to chlorine, or one atom of a mono- valent compound radical, such as N O 3 , C N. 254. A considerable number of hydrocarbons are known which contain more than twice as many atoms of hydrogen as of carbon. In composition they stand in the relation of homologues of marsh gas, and it was supposed some time ago that they ought to be ranged in two series differing from one another, as the alcohol series differs from the ether series : one series being composed of hydrides, such as HCH 3 , HC 2 H 5 , HC 3 H r , &c. ; the other series consist- ing of compounds each molecule of which contains two alcohol radicals, as C H 3 C H 3 , C 2 H 5 C 2 H 5 , C 3 H 7 C 3 H 7 , &c. Thus a hydrocarbon consisting of C 2 H 6 = 2 vols. has been obtained by the electrolysis of potassic acetate, in which process carbonic acid and a gas of this composition are 324 CONSTITUTION OF MARSH GAS SERIES. 255 given off at the positive pole, whilst hydrogen is evolved at the negative pole. When made in this manner the gas was called methyle, and its molecule was written thus (CH 3 ) 2 , while the systematic name 'methylic methide' is given to it. By the action of water on zinc ethyie a compound of identical composition is obtained, by the combination of hydrogen with ethyie; and when the gas is prepared in this way chemists called it ethylic hydride, and wrote its formula accordingly C 2 H 5 H. A slight difference of solubility has been stated to distinguish the gas from the acetate from the gas made from zinc ethyie, and a difference in the products of the action of chlorine upon them; but there seems good reason to believe that the gases obtained by the two processes are identical and not isomeric, and that methyle yields ethylic chloride among the products of the action of chlorine gas upon it. The gas (C 4 H 10 = 2 vols.) formed by the action of ethylic iodide on zinc ethide yielded by the action of chlorine a liquid of the composition C 4 H 9 C1, which behaved like butylic chloride. These re- actions were not expected upon the view that 'methyle' had a different constitution from 'hydride of ethyie/ or that ' ethyie' was different from ' hydride of butyl.' 255. A hydrocarbon (C 7 H 16 = 2 vols.) was obtained by the action of sodium on a mixture of amylic iodide and ethylic iodide, and from the mode of its formation it was considered as built up of an atom of ethyie and an atom of amyle (C 2 H 6 C 5 H n ). By the action of chlorine upon this compound two products were obtained besides hydro- chloric acid. One of these compounds boiled at 150, and was found to possess the composition and, at least, some of the properties of the chloride of the radical heptyl C 7 H 15 C1. 325 255 SrNTHESrs OF MARSH GASES. The formation of marsh gas and its chief properties were described among the inorganic compounds of carbon, to which it may in some measure be considered as belonging from the fact that it is one of the most general products of the destructive distillation of organic bodies. Berthelot has shewn that by the action of chlorine, marsh gas yields methylic chloride CH 4 + Cl 2 = CH 3 C1 + HC1; and that when heated with potassic hydrate this product forms potassic chloride and methylic alcohol . rl Marsh gas is obtained by the action of water on zinc methide The next term of the series (C 2 H 6 = 2 vols.) is not only obtained by this process, as above mentioned, but also by the action of methylic iodide on zinc methide 2 CH 3 I + Zn(CH 3 ) 2 = 2 C 2 H 6 + Znl 2 . It has also been prepared by the action of potassium on vinic cyanide (C 2 H 5 C N), in which reaction it is accompanied by olefiant gas (C 2 H 4 ) and so-called ethyle (C 4 H 10 ). The third term of the series is C 3 H 8 = 2 vols. It may be formed by uniting the radicals ethyle and methyle into one molecule (CH 3 C 2 H 5 ), or by combining the radical propyl with hydrogen. The fourth term (C 4 H 10 =2 vols.) is the gas usually called ethyle, and represented as containing in one molecule two atoms of that radical. It is identical with butylic hy- dride (C 4 H 9 H) and with propylic methide (C 3 H 7 C H 3 ). At a pressure of 2.5 atmospheres ethyle condenses to a liquid at 3C, and at the ordinary atmospheric pressure it requires a cold of 23 for its liquefaction. Some hydrocarbons have been built up partly from 326 SYNTHESIS OF MARSH GASES. 255 elements supplied by one compound, partly from those supplied by another. Thus a hydrocarbon consisting of C 7 H 16 = 2 vols., and considered as formed by the union of an atom of methyle with an atom of caproyl (p 6 rrisjj has been obtained by the electrolysis of a solution containing both potassic acetate (KC 2 H 3 O 2 ) and potassic caproate (KC 7 H 13 O 2 ). 327 256 ALCOHOLIC CHLORIDES AND BROMIDES. CHAPTER XL. 256. The chlorides of the alcohol radicals are obtained together with water by the action of hydric chloride on the alcohols Also by the action of an excess of phosphoric chloride on the alcohols, thus p2 TJ5 g O + P Cl 5 = C 2 H 6 Cl + H Cl + P O Cl 3 . Methylic chloride is also obtained by the action of iodic chloride on sodic acetate NaC 2 H 3 2 +2lCUNaCl+CH 3 Cl + I 2 + C0 2 . The molecule of each of them occupies two volumes in the state of vapour. For the most part these chlorides are insoluble in water, but readily soluble in alcohol, ether, &c. Methylic chloride dissolves however in water to a con- siderable extent, and forms with it a crystalline compound at 6C. Vinic Chloride boils at i iC. It floats upon water, and dissolves very slightly in it. Its density at 5 is .874. Its vapour has an agreeable odour, and burns with a bright flame, of which the borders are tinged with green. Amylic chloride boils at 100. The bromides of the alcohol radicals present great analogy with the chlorides both in their mode of formation, and in their properties and decompositions. One molecule of each of them occupies two volumes in the state of vapour. In the liquid state, as in the gaseous state, each of these bromides is heavier 328 ALCOHOLIC IODIDES. 257 than the corresponding chloride. Thus ethylic bromide has a density of 1.4. Its vapour has a density of 54.5 (half its molecular weight), while the vapour-density of the chloride (C 2 H 5 C1 = 2 vols.) is 32.25. The bromides boil at higher temperatures than the corresponding chlorides : thus vinic bromide (C 2 H 5 Br) boils at 4 iC. Under the action of decomposing agents the bromides undergo double decom- positions more easily than the chlorides. 257. Iodine forms a series of compounds with the alcohol radicals which are of great interest and value as reagents. They are perfectly analogous to the bromides and chlorides, but are far more easily decomposed, and are consequently more serviceable as affording means of replacing hydrogen or metals by the alcohol radicals. Their density and vapour- density are greater than those of the corresponding bromides. For instance, vinic iodide (C 2 H 5 I = 2 vols.) has a density of 1.92 and a vapour-density of 78. Methylic iodide (CH 3 I = 2 vols. ; boiling-point, 43; sp. gr. 2.2). This ether is easily obtained by the action of iodine and red phosphorus on methylic alcohol. It is also formed in considerable quantities by the action of hydric iodide on narcotine. It has an agreeable, ethereal, and sweet odour. When exposed even to diffused sunlight it becomes red from liberation of iodine. Its alcoholic solution precipi- tates silver nitrate rapidly CH 3 I + AgNO 3 = CH 3 NO 3 + AgL Ethylic iodide (C 2 H 5 1=2 vols. ; boiling-point 72 ; sp. gr. 1.92) is obtained by the action of a mixture of iodine and phosphorous iodide on alcohol. It is decomposed by sun- light, though less rapidly than the methylic iodide. A mix- ture of the three hydrocarbons C 2 H 4 , C 2 H 6 , and C 4 H 10 is given off, while iodine dissolves in the liquid. Amylic iodide (C 5 H 11 1 = 2 vols.) boils at 146. Its density is only 1.51. In all its reactions this iodide mani- 329 257 ALCOHOLIC CYANIDES. fests greater sluggishness than the ethyle compound; and the contrast is still greater with the methyle compound, which is the most decomposable of the whole series, short of hydric iodide. 258. Side by side with these ethers should be studied the cyanides, such as methylic cyanide, vinic cyanide, &c. (C H 3 CN, C 2 H 5 CN). These remarkable compounds have been made by two perfectly distinct processes : i . By double decomposition between a methyle salt or double salt, and potassic cyanide. Thus methpotassic sulphate undergoes double decomposition with potassic cyanide, forming po- tassic sulphate and methylic cyanide C ^ S O 4 + K C N = K 2 S O 4 + C H 3 C N ; or better still, methylic iodide in presence of alcohol decom- poses potassic cyanide 2. By the action of anhydrous phosphoric acid on ammonic acetate the elements of water are abstracted from the salt, and a volatile compound, originally called acetonitrile but found to be identical with methylic cyanide, is formed P2 us n ^ g 4 u O 2 H 2 = CH 3 CN. Similar reactions occur with the higher terms of the acetic series ; so that each cyanide can be made by unit- ing cyanogen with the alcohol radical or by deshydrating an ammonic salt of the acetic series. Thus valeronitrile (C 5 H 11 C N) is made either from fousel oil or from ammonic caproate Under the action of a boiling solution of caustic potash these cyanides are decomposed, ammonia going off and a potassic salt of the acetic series remaining behind. The acid 330 ALCOHOLIC CYANATES AND SULPHO CYANATES. 259 of this salt contains the carbon of the alcohol radical added to the carbon of the cyanogen. Thus methylic cyanide yields potassic acetate C 2 H 3 N + H 3 KO 2 = C 2 H 3 KO 2 + NH 3 . Ethylic cyanide gives rise in this manner to potassic pro- pionate C 3 H 5 N + H 3 KO 2 = C 3 H 5 KO 2 -f N H 3 . Methylic cyanide is a fragrant liquid, which floats upon water and boils at 77. By the action of nascent hydrogen evolved by the action of zinc on hydric chloride, methylic cyanide is converted into ethylia C 2 H 3 N + 2 H 2 = C 2 H 7 N. This reaction is analogous to the conversion of prussic acid (hydric cyanide) into methylia, described in 87. The mole- cule of every term of this series occupies two volumes in the state of vapour. 259. The cyanates such as Methylic Cyanate (CH 3 CNO), Vinic Cyanate (C 2 H 5 CNO), are formed by heating an intimate mixture of potassic cyanate with a double sulphate containing an alcohol radical and potassium. Thus methylic cyanate is obtained by distilling a mixture of potassic cyanate and methpotassic sulphate KCNO + C i? S SO 4 = CH 3 CNO + K 2 SO 4 . j\. Vinic cyanate is obtained by a similar process, using ethyl- potassic sulphate. This cyanate is a liquid of exceedingly pungent odour. It boils at 6oC. Ethylic cyanurate is formed at the same time and crystallizes out from the cya- nate. Its composition corresponds to that of metallic cyanu- rates, being (C 2 H 5 ) 3 C 3 N 3 O 3 .. When either of these ethers is boiled with caustic potash a decomposition occurs, forming potassic carbonate and a kind of ammonia containing an atom of ethyle (or methyle) 259 NITROUS AND NITRIC ETHERS. and two atoms of hydrogen united with an atom of ni- trogen C 2 H 5 N C O + H 2 K 2 O 2 = K 2 C O 3 + C 2 H 5 H 2 N. This remarkable base was called ethylamine by Wurtz, its discoverer, and is now more commonly called ethylia. Me- thylia and ethylia were the first discovered members of an immense family of ammonias containing organic radicals in the place of some of the hydrogen of common ammonia. Methylic cyanate yields, when acted upon by potassic hydrate, a volatile base, called methylia, and containing C H 5 N. In like manner amylia is obtained from amylic cyanate. Ethylic cyanate combines with ammonia, forming a compound called ethylurea, being a molecule of urea in which an atom of hydrogen is replaced by ethyle C 2 H 5 CNO + NH 3 = CN 2 H 3 (C 2 H 5 )O. Common urea is CN 2 H 4 O. The sulphocyanates of the alcohol radicals correspond in their mode of formation and in their composition to the cya- nates, containing an atom of sulphur in lieu of the atom of oxygen. Thus ethylic sulphocyanate (C 2 H 5 C N S = 2 vols.) is obtained by distilling a mixture of potassic sulphocyanate and ethylpotassic sulphate in concentrated aqueous solu- tion KCNS + C 2 H 5 KSO 4 = C 2 H 5 CNS + K 2 SO 4 ; it sinks to the bottom of water, and boils at 146. By the action of potassic hydrate it has not been found to yield ethylia. 260. There are ethers corresponding to monovalent nitrites and nitrates. By the action of hydric nitrate on an alcohol a mixture of products of oxidation of the alcohol with a nitrite is usually obtained, and for the preparation of the pure ni- trites it is found most advantageous to mix the alcohol with hydric nitrate in the cold and to add copper turnings to the mixture. 332 CARBONIC ETHERS. 261 Methylic nitrite (C H 3 N O 2 ), obtained in this manner from methylic alcohol, is a liquid which boils below o. It is also formed by the action of hydric nitrate on brucia. Vinic nitrite (C 2 H 5 NO 2 = 2 vols.), or nitrous ether, should be made to pass from the flask in which it is generated, through a bottle of water, and then through a tube full of calcic chloride. It condenses to a liquid which boils at about 21, and has an exceedingly fragrant agreeable odour. It was discovered by Millon that the presence of urea in a mixture of alcohol and hydric nitrate prevents the oxidizing action which otherwise takes place upon the alcohol, and consequently prevents the formation of a nitrite. Ethylic nitrate (C 2 H 5 N O 3 ), obtained in this manner, is a liquid heavier than water and quite insoluble in it. It boils at 85, and its vapour explodes with violence when much superheated. 261. The Alcoholic Carbonates are of two classes, i. Normal carbonates, such as vinic carbonate ((C 2 H 5 ) 2 CO 3 = 2 vols.) These salts are most easily obtained by the action of metallic sodium on a corresponding oxalate. Each mole- cule of these ethers contains two atoms of the alcohol radical and occupies the same vapour-volume as one molecule of chloride, bromide, &c. 2. Double carbonates, such as hydro- vinic carbonate (HC 2 H 5 CO 3 ), called carbovinic acid from the facility with which its typical hydrogen can be replaced by potassium, sodium, &c., forming salts, such as ethylpo- tassic carbonate (C 2 H 5 KCO 3 ), &c., or by an alcohol radi- cal, as in the case of vinomethylic carbonate C 2 H 5 CH 3 CO 3 . Strong alcohol, in which potassic hydrate has been dis- solved, contains potassic ethylate (KC 2 H 5 O), and accord- ingly carbonic acid passed into the liquid forms vinopotassic carbonate by uniting with the ethylate. A good deal of potassic carbonate is formed at the same time, but being 333 261 CARBONIC ETHERS. insoluble in alcohol, this salt goes down, whilst the double salt remains in part at least in the liquid, from which it can be precipitated by the addition of ether. It can be purified by solution in dry alcohol and re -precipitation by ether. The sulphur salts corresponding to these carbonates are easily obtained by corresponding processes. Thusvinic sulphocarbonate ((C 2 H 5 ) 2 C S 3 ) is formed by the action of vinic chloride on the double salt C 2 H 5 K C S 3 , and this double salt is obtained by pouring carbonic sulphide into an alcoholic solution of potassic sulphide, which no doubt contains ethylpotassic sulphide (C 2 H 5 K S). 262. The Alcoholic Oxalates are, like the carbonates, of two classes viz. normal oxalates, such as vinic oxalate ((C 2 H 5 ) 2 C 2 O 4 ), which contain two atoms of the alcohol radical in each volume while occupying the normal molecular volume. There are also double oxalates, such as hydrovinic oxalate (H C 2 H 5 C 2 O 4 ), vinopotassic oxalate (C 2 H 5 KG 2 O 4 ), ethmethylic oxalate (C 2 H 5 C H 3 C 2 O 4 ). Vinic Oxalate ((C 2 H 5 ) 2 C 2 O 4 =2 vols.; boiling-point, 182; sp. gr. i.i) is formed by passing hydric chloride gas into a mixture of dry alcohol and hydric oxalate, or by heat- ing the mixture with hydric sulphate. In either case the mineral hydric salt accelerates a process which takes place more slowly without its intervention. The ether is almost insoluble in water. Its solution in alcohol is decomposed by the cautious addi- tion of potash, with formation of a precipitate of vinopotassic oxalate (C 2 H 5 K C 2 O 4 ), whilst alcohol is formed. Ammonia decomposes the ether rapidly, forming oxamide and alcohol By the cautious addition of an alcoholic solution of am- monia to a similar solution of the ether, an intermediate compound is formed, consisting of crystalline plates pos- sessing the composition, 334 CARBONIC ETHERS. 262 C 2 H 5 NH 2 C 2 O 3 = (C 2 H 5 ) 2 C 2 O 4 + NH 3 HC 2 H 5 O. This compound is considered as an oxamate. Oxalic ether is gradually decomposed by cold water, but more rapidly by boiling water, the ultimate products being alcohol and water. Its formation and subsequent decom- position afford the best means of obtaining hydric oxalate free from mineral impurity, as the ether is easily purified by distillation. 335 263 SULPHUROUS ETHERS. CHAPTER XLI. 263. Sulphurous acid forms a normal ethyle salt, which is obtainable by the action of hyposulphurous chloride on absolute alcohol. It is a colourless liquid, somewhat heavier than water, and nearly insoluble in it. Its molecule oc- cupies the normal volume, and contains two atoms of ethyle ((C 2 H 5 ) 2 S O 3 = 2 vols.) It boils at i6oC. Hydrovinic sulphite (HC 2 H 5 SO 3 ) is formed by the action of hydric nitrate on mercaptan. It can be obtained in the form of crystals from a concentrated aqueous solution. Its salts, even with barium and lead, are soluble in water. 264. Vinic Sulphate ((C 2 H 5 ) 2 S O 4 ) is formed by slowly passing the vapour of anhydrous sulphuric acid into ether cooled by immersion in a frigorific mixture. The product is shaken up with a mixture of ether and water, the sulphate being dissolved by the former, while various foreign bodies are dissolved by the water. The sulphate is obtained by evaporation of its ethereal solution. It cannot be distilled without decomposition. Far more important are the double sulphates containing ethyle and metals, the so-called sulphovinates. Sulphovinic acid is formed simultaneously with water by mixing alcohol and hydric sulphate H C 2 !! _ ^ r\4 , Q H H H b +H U The mixture after standing for some days, or after heating, should be poured in a fine stream in an excess of slaked lime suspended in water with lumps of ice, and the mass should be constantly agitated while the acid mixture flows 336 VINIC SULPHATES. 265 into it. Calcic sulphate and sulphovinate are formed, and the latter being readily soluble in water is separated by fil- tration, and crystallized from its solution by evaporation. The salt crystallizes in plates, which contain two molecules of water of crystallization Ca(C 2 H 5 ) 2 (S0 4 ) 2 (H 2 0) 2 . The solution of this or of any neutral sulphovinate can be heated in presence of water without undergoing decom- position ; but when the basic metal is replaced by hydrogen, by the addition of hydric chloride or sulphate, the double sulphate decomposes easily, alcohol and a sulphate being formed. Thus an aqueous solution of barytic sulphovinate deposits barytic sulphate when boiled with hydric chloride /P2TLT5N2 f<2U5 I. ^ a ' (S0 4 ) 2 + 2 HCU2 U g S0 4 + BaCl 2 ; r<2TLT5 TJ TLT /^2TJ5 II. ' g S0 4 fg0^gS0 4 -f U g O; III. H 2 SO 4 + BaCl 2 = BaSO 4 +2HCl. The other alcohol radicals form similar double sulphates. Thus we have the sulphomethylates, such as potassic sulphomethylate (KCH 3 SO 4 ), barytic sulphomethylate (Ba (CH 3 ) 2 (SO 4 ) 2 ), &c. Also the corresponding sulph- amylates (K C 5 H 11 S O 4 , Ba (C 5 H 11 ) 2 (S O 4 ) 2 ), &c. The same difference which was pointed out between the iodides of these radicals, in respect to the rapidity with which they exchange their radicals for metals, in processes of double decomposition, holds good with regard to these double sulphates. The sulphomethylates are far more rapidly decomposed than the sulphovinates, and the sulphamylates far less rapidly. 265. Side by side with these salts, containing divalent radicals, may be considered compounds of the dyads zinc and mercury with the radicals. These compounds are of two classes : one class consisting of compounds of an atom z 337 265 ZINC METHYLE ( of metal with two atoms of alcohol radical, such as Zn (C H 3 ) 2 , Hg(C 2 H 5 ) 2 , &c. ; the other class consisting of compounds of one atom of metal and one atom of chlorine or iodine, &c., such as ZnCH 3 !, HgCH 3 !, &c. The latter class must be considered as double salts, in which the alcohol radical has chlorous functions. The compounds belonging to it may be compared to the inorganic salts of the cor- responding metals, such as ZnCl 2 , Hgl 2 , &c., one atom of the chlorous constituent of these being replaced by an atom of alcohol radical. They are formed by the action of the metals on the corresponding ethers. Thus zinc combines with methylic iodide at the ordinary temperature, forming zinc methiodide (Zn Me I), (Me = C H 3 ). The best way to obtain the compound is to use zinc amalgam, containing 12 to 15 per cent, of mercury, and in the state of fine powder. In a glass bottle the combination is complete after contact of two or three weeks at the ordinary temperature, when enough amalgam is used to fill the liquid ; but it is complete in a few hours if the same mixture be heated to 1 00 in an iron digester. The compound consists of scaly crystals, which are easily decomposed by distillation, 'even in vacuo. The products are zinc methide, which distils over, and zinc iodide, which remains behind Zinc methiodide emits dense white fumes in contact with moist air. It is decomposed with great violence by water, marsh gas being evolved. Zinc ethiodide (ZnC 2 H 5 I) is formed in the same way as the methyle compound, but it requires longer contact of the metal and iodide. It is also decomposed by distillation into zinc iodide and zinc ethide.* Zinc ethide and zinc methide are liquids heavier than water. They catch fire spontaneously in contact with air, 338 MERCURIC METHIODIDE (Hg C H 3 7). 266 but when oxygen is brought gradually in contact with the ethide, zinc alcohol is formed ^^ O 2 ). Zinc ethide occupies two volumes in the state of vapour (Zn (C 2 H 5 ) 2 = 2 vols.), the two atoms of ethyle being held together by one atom of zinc. The compound boils at 1 10. Ammonia gas decomposes it, forming zinc amide andethylic hydride; Zn (C 2 H 5 ) 2 + 2 N H 3 = Zn (N H 2 ) 2 -f 2 C 4 H 6 . Potassium decomposes zinc ethide, forming a solution of potassic ethide in the zinc compound Zn (C 2 H 5 ) 2 + K 2 = 2 K C 2 H 5 + Zn. By the action of carbonic acid in potassic ethide Wanklyn obtained potassic propionate By heating zinc ethide with ethylic iodide Frankland obtained the so-called ethyle or ethylic ethide Zn (C 2 H 5 ) 2 + 2 C 2 H 5 1 = Zn I 2 + 2 C 4 H 10 ; and in like manner ethylic methide is formed by the action of zinc ethide on methylic iodide Zn (C 2 H 5 ) 2 + 2 C H 3 1 = Zn I 2 + 2 C 3 H 8 . 266. Mercuric Methiodide (Hg C H 3 1) is formed by exposing metallic mercury and methylic iodide to the sun- shine, with frequent agitation. It crystallizes in scales, which can easily be volatilized without decomposition. The iodine can be replaced in this compound by an equivalent quantity of a monovalent radical, or even of a divalent or trivalent radical, forming salts such as H ' They are monobasic, like the acetate itself, though no doubt stronger. A Thiacetate is a compound formed by the action of phosphoric sulphide on the acetate, probably thus first =: It boils at 93. A sulphacetate is formed by the action of anhydrous sulphuric acid on the acetate. Its formation is analogous to that of sulphovinic acid, for it contains the elements of a molecule of hydrated acetic acid in addition to those of a molecule of anhydrous sulphuric acid It forms a potash salt of the empirical formula C 2 H 2 K 2 SO 5 , and a baryta salt (C 2 H 2 BaS O 5 ), which is slightly soluble in water. 288. Propionic Acid has obtained its name from the circumstance of its being the first acid of the series which can be precipitated, like an oily compound, from its aqueous solution by calcic chloride or glacial phosphoric acid. A 367 288 ACETIC SERIES. propionate is best obtained by the action of potash on vinic cyanide Butyrates were first obtained by Chevreul from the con- stituents of butter. They are most advantageously prepared by leaving calcic lactate with water and old cheese at a temperature of 35. Hydrogen and carbonic acid are given off during the process of fermentation which takes place, and the lactate is entirely destroyed, a butyrate being formed in its place. Acetates and valerates are frequently formed in smaller quantity at the same time. Hydric butyrate boils at 159. Its density is 0.9886 at oC. It dissolves in water in all proportions. Its metallic deriva- tives are in general soluble in water. It forms ethers, each of them boiling at a higher temperature than the correspond- ing acetate. They are also less soluble in water than the acetic ethers. 289. Hydric Valerate (C 5 H 10 O 2 ; boiling-point, 175- 180; sp. gr. 0.937). This acid salt has obtained its name from the valerian root from w r hich it was extracted. It is present in rancid cheese and in many other decomposed organic mixtures. It is best obtained by the action of amylic alcohol on a solution of potassic dichromate acidulated by hydric sulphate. On distilling the mixture an acid distillate is obtained containing valerianic aldehyde and the valerate, which can easily be separated by potash. The valerate requires about thirty volumes of water for its solution ; and when added in greater quantity the salt floats as an oily stratum upon the aqueous solution. The oily stratum is a compound of valerate with a molecule of water (C 5 H ]0 O 2 H 2 O), having a density greater than that of the salt itself, viz. 0.95. Valerates have an exceedingly persistent and unpleasant odour. 368 VALERIANIC ACID (C 5 H 10 O 2 ), &c. 289 The Caproate (C G H 12 O 2 ) was obtained from the liquid part of cow's butter. Butter was melted, and pressed after cooling. The solid crystalline residue, consisting of the glycerine derivatives of margaric and other solid acids, was put aside, and the liquid portion was dissolved in potash by the aid of heat, or, as it is called, saponified. The aqueous solution of the soap was precipitated by salt, and the soap thus obtained was decomposed by dilute hydric sul- phate, and distilled. In this manner an acid distillate was obtained, consisting of water holding several hydric salts in solution, and having oily drops of acid floating upon it. The mixture was neutralized by baryta-water, and the barytic salts thus obtained were separated by crystallization. In this man- ner a butyrate, caproate, caprilate, and caprate were obtained, the butyrate being the most soluble in water, and the solu- bility of the others diminishing with the increase of their molecular weight. Hydric caproate boils at about 198. It is most easily obtained by the decomposition of amylic cyanide. The next term of the series, viz. the cenanthylate (C r H 14 O 2 ), is obtained by distilling castor oil with hydric nitrate. The cenanthylate comes over with the vapour of water and is collected in the receiver. Hydric Caprilate (C 8 H 1C O 2 ; boiling-point, 236-24o) is most conveniently prepared from cocoa-nut oil. Hydric Pelargonate (C 9 H 18 O 2 ; boiling-point, 260) was first prepared from geranium-leaves. Gerhardt recom- mends oil of rue for its preparation. This oil is distilled with dilute hydric nitrate, and the distillate neutralized by ba- ryta and crystallized. Ethylic pelargonate appears to be the chief constituent of the so-called oil of wine a fragrant oil which is used for flavouring purposes. The hydrogen salt of capric or rutic acid (C 10 H 20 O 2 ) has been found in the fousel oil of whiskey. Its barytic salt (Ba (C 10 H 19 O 2 ) 2 ) is B b 369 289 PALMITATE (C 16 # 32 2 ). purified by repeated crystallizations and then decomposed by sodic carbonate. The addition of dilute hydric sulphate to the sodic salt precipitates the hydrogen salt in the solid form. Laurate (C 12 H 24 O 2 ) melts at 42 or 43. Cocinate (C 13 H 26 O 2 ) is said to have been obtained by saponifying cocoa-nut oil and decomposing the soap by hydric chloride. In this manner an oily mixture of hydric salts is obtained, from which cocinate crystallizes out. The liquid constituents are pressed out from the mass by a hy- draulic press. The impure cocinate thus obtained is dis- solved in hot alcohol, and purified by repeated crystallizations. It is ultimately obtained with a melting-point of 42 to 43. There seems some reason to believe that the acid sub- stance thus obtained was a mixture. Myristate (C 14 H 28 O 2 ) melts at 49. The next term of the series is called benic acid. The hydrate is represented by the formula C 15 H 30 O 2 . 290. Hydric Palmitate or Cetylate (C 16 H 32 O 2 ) melts at 62. It is obtained from palm oil in the same way as the cocinate from cocoa-nut oil, or from spermaceti after decomposition by alcoholic potash. The palmitate is fre- quently used for the manufacture of so-called composition candles. For this purpose palm oil can be decomposed by the action of hydric sulphate, and purified by distillation in superheated steam. It has, however, been found that the palm oil itself is decomposed by the action of superheated steam into hydrated acids and glycerine. These products are condensed from the steam, and the liquid hydrates removed by the action of a powerful hydraulic press from the palmitic and other solid hydrates. Water heated to a high temperature in a Papin's digester likewise decomposes palm oil and most other fats. Hydric Margarate (C 17 H 34 O 2 ) was supposed to be obtained from many common oils and fats, such as olive 370 STEARATE (C 18 # S3 2 ). 201 oil, butter, goose fat, human fat, &c., by decomposition of its glycerine derivative. Its melting-point is given at 60, but according to analogy it ought to be higher than 62, the melting-point of the palmi~ tate, instead of lower. There seems some reason to suspect that what has passed for margarate is a mixture of palmitate with stearate. The former of these melts at 62 and the latter at 69 or 70, but a mixture of the two has been found to melt at as low a temperature as 54, and mixtures con- taining greater proportions of the stearate melt at higher temperatures. A substance possessing the composition of the margarate has been made by the action of potassic hydrate on cetylic cyanide C i6 H 33 c N + H 3 K O 2 = C 17 H 33 K O 2 + N H 3 . The hydrogen salt made from this melts below 60. 291. Hydric Stearate (C 18 H 36 O 2 ) is obtained from beef and mutton suet, together with glycerine. To obtain a stearate in a state of purity from a mixture in which it is accompanied by homologues of lower atomic weight, Heintz's process of partial precipitation should be resorted to. This process consists in dissolving in alcohol the soap containing the stearate, and adding to the solution at the temperature of ebullition an alcoholic solution of barytic or magnesic acetate in very small quantity. A stearate is under these circum- stances precipitated before a palmitate or other satt contain- ing less carbon in its molecule, and if the quantity of acetate employed be small enough, no palmitate or lower term of the series goes down with the stearate. The stearate crystallizes in shining needles. It decom- poses alkaline carbonates with effervescence, forming a so- called soap. Potassic and sodic stearates are very soluble in water, and are alkaline to test-paper. Water saturated with sodic chloride does not dissolve soaps, and the Bb2 371 291 STEARATE (C u fl O 2 ). addition of salt precipitates soap from its solution. Solutions of alkaline stearates are decomposed on dilution into alkali, and hydric salt, which is precipitated together with an equivalent of the soap. The compounds with the alkaline earths and heavy metallic oxides are insoluble in \vater. The potash and soda salts dissolve in alcohol, but not in ether. Hydric stearate is insoluble in water, but dissolves in alcohol, and the solution has an acid reaction to test-paper. THE OLE ATE (C ls H zl O 2 ). 292 CHAPTER XLVII. 292. Oleates are an exceedingly common accompaniment of the compounds of this series. The glycerine derivative of oleic acid, called oleine, is liquid and uncrystallizable, whereas stearic and palmitic acid, &c. form with glycerine compounds called stearine and palmitine, and which are solid at the ordinary atmospheric temperature, and which crystallize out from their solution in oleine on cooling. Thus olive oil in cold weather deposits crystals of palmitine, &c., while oleine remains fluid and can be pressed out from the crystals. Alkaline oleates are not decomposed by dilu- tion with water, as stearates, &c. are; and by neutralizing the alkali liberated by the dilution of a concentrated solution of a stearate, and then diluting again, some more stearate is decomposed, and it is stated that the whole of the alkaline stearate can be decomposed in a mixture with an oleate, by a frequent repetition of this process. Oleine is more soluble in ether than stearine or palmitine, and can in great part be separated from the solid fats by washing with ether. Plumbic oleate is readily soluble in ether, whereas plumbic palmitate or stearate, &c. are nearly insoluble. Hydric oleate is represented by the formula C 18 H 34 O 2 . A mixture of lead salts of the fatty acids is used, it is named plaster. Olive oil is frequently used for the pre- paration of plaster. Litharge jn presence of water gradually decomposes it at 100, forming glycerine. Many oils such as those expressed from the seeds of lint, .poppy, walnut, hemp, ricinus, or castor-oil plant possess the 373 292 CONSTITUTION OF ACETIC SERIES. property of becoming thick, and ultimately hard and resinous, by exposure to the air. This process takes place still more rapidly if the oil has been heated with litharge. These so- called ' drying' oils are used by painters to fix their colours. Linseed oil 'and poppy oil appear to be derivatives of a salt of the composition C 16 H 28 O 2 , to the oxidation of which this ' drying' process is due. The acid containing C 20 H 40 O 2 is called arachidic acid, and the one containing C 22 H 44 O 2 is behenic acid. Hyenic acid (C 25 H 50 O 2 ; melting-point, 77 to 78) has been found in the fat of the hysena. 293. Derivatives of Cerotic Acid (C 27 H 54 O 2 ) are con- tained in bees'-wax, and the hydrate can be dissolved out from it by alcohol. Its melting-point is given at 78. Hydric melissate (C 30 H 60 O 2 ) has been obtained from melissic alcohol by fusion with potassic hydrate. It melts at 88 to 89. All the salts of this series, frequently called the adipic series, are oxidized by boiling hydric nitrate. Two classes of products are formed in the process viz. lower hydric salts of the same series, such as caproate, cenanthate, caprilate, &c., which pass over into the receiver, and salts homologous with the oxalate, which remain in the retort. 294. Phosphoric chloride decomposes hydric acetate* exactly in the same manner as it decomposes alcohol, forming chlorophosphoric acid, hydric chloride, and the chloride of the radical acetyl rl The action is exceedingly energetic, and the acetic chloride can be distilled over at a gentle heat, leaving the greater part of the chlorophosphoric acid behind. Acetic chloride is a liquid heavier than water, and boiling at 55. It has a 374 OLE A TE (C 18 H 5i 2 ). 295 very pungent odour; and in contact with moisture it is rapidly decomposed, forming hydric chloride and acetate C 2 H 3 O Cl + O = H Cl + C2 3 O. n. Jfj. In this decomposition the acetate is formed by replacing one atom of hydrogen in water by an atom of acetyl. Acetic chloride reacts very violently on ammonia, removing one atom of hydrogen from a molecule of the volatile alkali and replacing it by an atom of acetyl C 2 H 3 O Cl + 2 N H 3 = N H 2 C 2 H 3 O + N H 4 Cl. This ammonia, containing acetyl in the place of one atom of hydrogen, is called Acetamide. It is obtained by heating ammonic acetate, so as to remove half the oxygen of that salt in combination with hydrogen C 2 H 3 O n _ C 2 H 3 O ^ 2C . NH 2 H 2U NH 2 In contact with alcohol, acetic chloride forms hydric chlo- ride and acetic ether C iP + 2 R3 C1 = C 2 H 3 O + H CL 295. With potassic acetate it forms anhydrous acetic acid by replacing the potassium in the salt by acetyle C 2 H 3 OCl-f TT O = p2TT3 r) O + K Cl. According to this reaction anhydrous acetic acid is a molecule of water in which the two atoms of hydrogen are replaced by two atoms of acetyl ; the hydrate being a molecule of water in which one atom of hydrogen is replaced by one of acetyl. Anhydrous acetic acid boils at 138. It sinks in water, and does not appear to dissolve in it as such. It, however, gradually decomposes the water, forming two molecules of hydrated acid C 2 H 3 0^ , H n _C 2 H 3 , H n : u H " h c 2 H 3 o u - 375 295 ANHYDROUS ACETIC ACID (C i H 6 O 3 ). Its reactions are in general similar to those of acetic chloride, the group C 2 H 3 O 2 acting like chlorine. Thus with am- monia it forms ammonic acetate and acetamide Phosphoric chloride decomposes anhydrous acetic acid, forming phosphoric oxychloride and acetic chloride Formiates do not yield similar products to acetates. When acted upon by phosphoric chloride the formic chloride breaks up into carbonic oxide and hydric chloride Anhydrous formic acid has not as yet been obtained. Propionates, butyrates, valerates, and the higher terms of the adipic series, all yield chlorides homologous with acetic chloride (C 3 H 5 O Cl, C 4 H 7 O Cl, C 5 H 9 O Cl, &c.), and these chlorides, in their turn, react like acetic chloride on the corresponding potassium salts, forming anhydrous propionic /p3TJ5f) \ /r>4TT7n \ acid (c3H 5 0/' anh ^ drous but y ric acid (c 4 H 7 0/' /C 5 H 9 O \ anhydrous valerianic acid (QS JJOQ Oy, &c. 296. Several terms of a series of monatomic salts have been discovered containing in each molecule two atoms of hydrogen less than the corresponding salts of this series. .The first of these, hydric acrylate (C 3 H 4 O 2 ), is formed from acrolein by absorption of -oxygen. The crotonate (C 4 H 6 O 2 ) has been extracted from the croton-seed oil. Hydrated angelic acid (C 5 H 8 O 2 ) is obtained from an- gelica root. 376 ACRYLIC SERIES (C 3 H* O 2 ). 296 The other hydric salts considered to belong to this series are Of Pyroterebic acid (C G H 10 O 2 ). Damaluric acid (C 7 H 12 O 2 ). - Campholic acid (C 10 H 18 O 2 ). Moringic acid (C 15 H 28 O 2 ). Of Hypogeic acid (C 16 H 30 O 2 ). Oleic acid (C 18 H 3 *O 2 ). Brassic acid (C 22 H 42 O 2 ). Oleate of glycerine is the liquid constituent of a great many non-drying oils. 377 297 AROMATIC SERIES. CHAPTER XLVIII. 297. A series of monatomic salts homologous with the benzoates is called the aromatic series. Hydric Benzoate (C 7 H 6 O 2 ) is the first and most im- portant term of the series. It is contained in gum benzoin, and is best extracted by boiling the powdered gum resin with milk of lime, filtering off the solution of calcic benzoate thus obtained, and precipitating the hydric salt from it by hydric chloride. Benzoates are present in large quantities in the putrid urine of horses and cows, and can be obtained by evaporating the decomposed urine. Fresh urine of these herbivorous animals contains no benzoate, but in its place the hippurate (C 9 H 9 NO 3 ). Hippurates break up under the influence of ferments, or of hot hydric chloride. They take up the elements of a molecule of water, forming ben- zoate and an amide called glycocoll . C 9 H 9 NO 3 + H 2 O = C 7 H 6 O 2 + C 2 H 5 NO 2 . The glycocoll decomposes further in the putrifying urine. The benzoate is a solid compound of very crystalline structure. It melts easily, and can be sublimed with very slight decomposition. It is very slightly soluble in cold water, but sufficiently so to impart to it a decidedly acid reaction. Its salts with the alkalies and alkaline earths are readily soluble in water. The study of the composition and derivatives of the benzoates has shewn that the molecule of the hydric salt (HC 7 H 5 O) contains only one stem of hydrogen replaceable by metals. Barytic benzoate, Ba (C 7 H 5 O 2 ) 2 , is not precipitated from 378 AROMATIC SERIES. 298 its aqueous solution by alcohol in the presence of ammonic chloride. Potassic benzoate distilled with potassic formiate yields benzoic aldehyde, the essential oil of bitter almonds pt us n p TT n ' j U O + U O = C 7 H 5 OH + CO 3 K 2 . The oil is thus formed by the combination of hydrogen with the radical benzoile (C 7 H 5 O). 298. When potassic benzoate is distilled by itself, a per- fectly similar reaction takes place between two molecules of the salt ; one molecule furnishing phenyl, and the other furnishing benzoile The analogy between benzoic hydride and benzoic phenylide is moreover not confined to the circumstances of their formation ; for when they are heated with potassic hydrate both compounds form potassic benzoate, by replacing the hydrogen of the hydrate by benzoile, while in each case this expelled hydrogen takes the place of the benzoile, forming in one case a molecule of free hydrogen (hydric hydride), in the other case phenylic hydride tj5 r\ Chlorine decomposes benzoic hydride, forming benzoic chloride and hydric chloride C 7 H 5 OH + C1CUC 7 H 5 OC1 + HC1. Phosphoric chloride decomposes the benzoate, forming this same benzoic chloride = C 7 H 5 OC1 -fHCl + POC1 3 . 379 298 ' EENZONE (C 13 H w 0). Benzole Chloride corresponds in its general reactions to acetic chloride, and other compounds of chlorous radicals with chlorine. It reacts on potassic benzoate, forming an- hydrous benzoic acid r<7 us n C 7 H 5 OCl-f L ' U O With potassic acetate it forms an anhydrous acid, containing acetyl and benzoile in one molecule f2TT3n p2TT3o C 7 H 5 OC14> U = ^H 5 + KCL Benzoic ether is a fragrant oil somewhat heavier than water. It boils at 209. Hydrated toluilic acid (C 8 H 8 O 2 ) is obtained by the action of very dilute hydric nitrate on a hydrocarbon called cymene, or cymol. Its reactions and decompositions correspond to those of the benzoates. The cuminate (C 10 H 12 O 2 ) is obtained by the oxidation of its aldehyde, which occurs in the volatile oil of cummin- seed. 299. The lower terms of the adipic series form com- pounds with ammonia in one proportion, similar to those which other monobasic hydric salts form with it. Thus ammonic formiate and acetate have the formulae NH 4 CHO 2 ; NH 4 C 2 H 3 O 2 . When ammonia reacts on an ether of one of these acids, alcohol is formed together with an amide. Thus acetic ether O with ammonia forms acetamide (C 2 H 3 O N H 2 ) and alcohol. Acetamide is also formed by the dry distillation of am- monic acetate. It is a crystalline solid, having very nearly neutral properties ; for on the one hand it combines freely with hydric nitrate or chloride, on the other hand it is decomposed by potassium, with evolution of hydrogen and 380 ACETAMIDE (C 2 H 5 ON). 300 formation of a weak salt. Products formed like acetamide by the replacement of hydrogen in ammonia by a radical of chlorous properties are called amides. Acetamide is a primary amide. When two atoms of hydrogen are so replaced as in the diacetamide (C 2 H 3 O) 2 NH, the com- pound is termed a secondary amide, and tertiary amides are single molecules of ammonia in which all the typical hy- drogen is replaced by chlorous radicals. There are also ammonias in which the typical hydrogen is replaced partly by basylous radicals such as the alcohol radicals, partly by chlorous radicals. Thus by the action of anhydrous acetic acid on cyanic ether may be prepared an ammonia containing two atoms of acelyle and one of ethyl N CO C 2 H 3 Q N (C 2 H 3 0) 2 N25 + 2U C 2 H 5 300. Diatomic Alcohols are compounds formed on the type of two molecules of water; an atom of a hydro- carbon replacing two atoms of hydrogen in them, one in one molecule of water, the other in the other molecule. Ethylene (C 2 H 4 ) is a hydrocarbon, of which one atom is capable of replacing two atoms of hydrogen, or of com- bining with two atoms of chlorine. A molecule of ethy- lenic bromide (C 2 H 4 Br 2 ) reacts on two molecules of argentic acetate, forming argentic bromide and ethylenic acetate r<2 rr3 r\ O C 2 H 3 O o n c 2 TT 3 o C 2 H 3 U The reaction is parallel to that of zinc bromide (Zn Br 2 ) on argentic acetate, an atom of zinc forming the acetate Zn(C 2 H 3 O 2 ) 2 , just as an atom of ethylene forms ethy- lenic acetate (C 2 H 4 (C 2 H 3 O 2 ) 2 ). By the action of potash on this acetate the ethylenic 381 300 GLYCOL (C 2 # 6 2 ). hydrate is obtained C 2 H 4 (HO) 2 , in the form of a liquid, soluble in water in all proportions, and having a sweet taste. It distils without decomposition at 197.5. This remarkable body was named Glycol by its dis- coverer, Wurtz. With monobasic hydric salts it forms two classes of salts. Thus hydric chloride forms ethylenic hydrochloride, Cl C 2 H 4 TT~, and by the action of phosphoric chloride on this body the normal chloride C 2 H 4 C1 2 is obtained, just as the divalent radical S O 2 of the sulphates forms not only the normal hydrate S O 2 (H O) 2 , but also by the action of phos- Cl phoric chloride the hydrochloride S O Vr Q, and the normal chloride SO 2 C1 2 . With acetic acid, glycol forms the normal ethylenic acetate C 2 H 3 O 2 C 2 H 4 p 2 jj 3 Q 2j and also ethylenic hydroacetate P2TT4HO 1 C 2 H 3 2 . Sodium decomposes glycol, with evolution of hydrogen, C 2 H 4 forming in the first instance the compound -vr TT O 2 . By prolonged heating with sodium the second atom of typical hydrogen is with difficulty expelled, forming the C 2 H 4 compound ^ 2 O 2 . 301. Ethylenic Oxide (C 2 H 4 O) has not been obtained by processes similar to those by which ethylic oxide is ob- tained from alcohol. Zinc chloride decomposes glycol with the aid of heat, forming vinic aldehyde, isomeric with ethy- lenic oxide. The oxide has been prepared by the action of potash on the ethylenic hydrochloride. This compound breaks up into hydric chloride and ethylenic oxide 382 ETHYLENIC OXIDE (C 2 tf*0). 302 In this respect it differs from its prototype, sulphuric hydro- chloride, which breaks up into sulphuric hydrate and sul- phuric chloride. Ethylenic oxide boils at 13.5. By heating in a closed vessel with water it reproduces glycol. Some of the oxide combines in the process with water in the proportion of two molecules of ethylenic oxide to one of water, forming the /Q2 W4\2 compound v jW O 3 > called diethylenic glycol. 302. When ethylenic bromide is heated with glycol this same compound is obtained together with triethylenic glycol, /p2TJ4\3 /r<2Tqr4\4 J 2 ' O 4 , tetrethylenic glycol, A g/ O 5 , pentethylenic glycol, ( C2 ^7o 6 , and hexethylenic glycol, ^'^O 7 . These Polyethylenic Glycols are analogous to gly- col itself in their reactions. But the addition of each molecule of ethylenic oxide raises the boiling-point of the glycol. Propylenic bromide forms a glycol by the same processes which serve to prepare ethylenic glycol. Propylenic hydrate (C 3 H 6 TT Q) boils however at a lower temperature than ethylenic hydrate viz. at 188. Butylenic glycol (C 4 H 10 O 2 ) boils still lower viz. at 183 to 184. Amylenic glycol (C 5 H 12 O 2 ) boils lowest of the four viz. at 177. Methylenic glycol (CH 4 O 2 ) has not been obtained. / O H 2 \ Methylenic acetate ( jpOY 2 ^ / * S ^ ta ^ ne( ^ ^y the action of methylenic iodide on argentic acetate. It is 383 302 POLYETHYLENIC GLYCOLS. decomposed by water into hydric acetate and a solid body melting at 152 and isomeric with methylenic oxide CH2 n_i u'n2 CH 2 n2 . C 2 H 3 O n 2 (C 2 H 3 0) 0+2H ~ ( = CH 2 +2 H C 2 H 4 \ Ethylenic sulphhydrate / -^ 2 S 2 J was obtained many years ago by Lowig, by decomposing ethylenic bromide by an alcoholic solution of potassic sulphhydrate C 2 H 4 Br 2 +2 l ftl$ = C ^Ts 2 +2KBr. It combines readily with mercuric oxide, as the monatomic mercaptans do. 384 GLYCOLLIC ACID (C 2 #*0 3 ). 303 CHAPTER XLIX. 303. When cautiously oxidized, glycol gives rise to the formation of an acid called Hydric glycollate. The re- action is perfectly similar to the formation of acetate by the oxidation of alcohol A glycollate is also obtained by the action of potassic hydrate at a high temperature on potassic chloracetate = When potassic chloracetate is heated by itself, anhydrous glycollic acid is formed C 2 H 2 C1KO 2 = C1K + C 2 H 2 O 2 . The gly collates are monobasic, forming only normal salts, such as K C 2 H 3 O 3 , Ba (C 2 H 3 O 3 ) 2 , &c. When further oxidized glycol yields oxalate 2 + 2 O 2 = 2 2 + 2 H 2 O; and glycollates are easily oxidized, forming oxalates. It is worthy of note that the oxalate, having two atoms of oxygen in its radical (C 2 O 2 ), is bibasic, whereas the glycol- late, having one atom of oxygen in its radical (C 2 H 2 O), is monobasic. Under the influence of nascent hydrogen an oxalate has been reduced to a glycollate. The two salts which stand to propylic glycol in the same relation as glycollate and oxalate stand to glycol, are lactate c c 385 303 HYDRIC LACTATE (C 3 H 6 O 3 ), &c. (C 3 H 6 O 3 ), homologous with glycollate, and malonate (C 3 H 4 O 4 ), homologous with oxalate. 304. Lactates, such as the hydric lactate (C 3 H 6 O 3 ), have obtained their name from the circumstance of being formed from the sugar of milk, by the spontaneous decom- position of milk when exposed to the air. Milk is well known to 'turn sour' on keeping, and at the same time to become thick by the formation of a solid precipitate of caseine. Salts isomeric with the lactates are present in many animal fluids. They are called sarkolactates. Lactates are most easily obtained in quantity by the lactic fermentation of sugar. This change takes place when sugar is dissolved in water and mixed with powdered cheese, the mixture being kept at a temperature of about 30, and the free hydric salt neutralized in proportion as it is formed. The best way to keep the liquid neutral is to put into it calcic carbonate, when calcic lactate is formed, and can be purified by recrystallization. When carefully heated to 130 or 140, hydric lactate de- composes in part into water and anhydrous lactic acid (C 3 H 4 O 2 ). Some of this anhydrous acid decomposes into aldehyde and carbonic oxide (C 3 H 4 O 2 = C 2 H 4 O + CO). Phosphoric chloride forms with lactates the lactic chloride C 3 H 4 OC1 2 , and when partially decomposed by an alkaline hydrate this chloride forms a chloro-propionate C 3 H 4 OC1 2 + HKO = C 3 H 4 C1KO 2 + HC1. By the action of nascent hydrogen the chlorine can be removed from this salt and replaced by hydrogen, forming a common propionate. Lactate is easily reduced to pro- pionate by the action of strong hydriodic acid C 3 H O 3 + 2 H I = C 3 H 6 O 2 + H 2 O 4- I 2 . Acetonate (C 4 H 8 O 3 ) is in its composition homologous with lactate, but has not as yet been much studied. It is made by adding to acetone the elements of the formiate, by 386 OXALIC SERIES. 305 the action of hydric chloride on prussic acid in presence of water C 3 H 6 O + CNH + 2 H 2 O + HC1 = C*H 8 O 3 + C1NH 4 . Butylactic and oxybutyric acids are names given to acids of the same composition as acetonic acid. Hydrated leucic acid (C 6 H 12 O 3 ) has been obtained from a crystalline amide called leucine by the action of nitrous acid. A body of the same composition has been obtained by Frankland and Duppa from vinic oxalate. One atom of oxygen in the radical of the oxalate is replaced by two atoms of ethyle 2 - (C 2 H 5 ) 2 (C 2 H 5 ) 2 From this leucic ether other salts of the acid are prepared. A similar process has been applied by the same chemists to the preparation of other terms of the series, such as _ The substitutions are effected by the action of metallic zinc on oxalic ether mixed with vinic iodide or methylic iodide, &c., or a mixture of iodides. There are also some salts which differ from those of the aromatic series by containing one atom of oxygen in each molecule beyond the elements of the aromatic acids. These are Hydrated oxybenzoic acid (C 7 H 6 O 3 ). Hydrated oxytolulic acid (C 8 H 8 O 3 ). Hydrated phloretic acid (C 9 H 10 O 3 ). Hydrated oxycuminic acid (C 10 H 12 O 3 ). 305. Another series of diatomic salts is the oxalic series. Each molecule of these hydrogen salts forms a neutral salt with potassium, containing two atoms of the metal, and a double salt containing an atom of hydrogen and an atom of potassium, having a decidedly acid reaction. The salts are c c 2 387 305 OXALIC SERIES. accordingly considered as dibasic. These hydrogen salts are Hydrated oxalic acid (H 2 C 2 O 4 ). Hydrated malonic acid (H 2 C 3 H 2 O 4 ). Hydrated succinic acid (H 2 C 4 H 4 O 4 ). Hydrated lipic acid (H 2 C 5 H 6 O 4 ). Hydrated adipic acid (H 2 C 6 H 8 O 4 ). Hydrated pimelic acid (H 2 C 7 H 10 O 4 ). Hydrated suberic acid (H 2 C 8 H 12 O*). Hydrated anchoic acid (H 2 C 9 H 14 O 4 ). Hydrated sebacic acid (H 2 C 10 H 16 O 1 ). The oxalate has been described among the simplest com- pounds of carbon. Malonic acid is but little known as yet. It has been obtained by the oxidation of malic acid, and by the action of caustic potash on cyanacetic acid 8 Also by the oxidation of a sarkolactate. Hydric Succinate (C 4 H 6 O 4 ) is among the products of the dry distillation of amber. It is formed by the action of the nitrate on salts of the adipic series, such as buty- rates C 4 H 8 O 2 + 3 O = C 4 H 6 O 4 + H 2 O. In many processes of fermentation it is one of the secondary products, and in the fermentation of a malate it is one of the chief products. It is formed by the action of hydric iodide on a tartarate C 4 H 6 O 6 + 4 HI = C 4 H 6 O 4 + 2H 2 O + 4! Also by the same treatment of a malate C 4 H 6 O 5 + 2 H I = C 4 H 6 O 4 + (H 2 O) + I 2 . Succinates have been built up from ethylene and cyano- gen. Ethylenic cyanide is decomposed by potash, forming succinate C 2 H 4 (CN) 2 + 2 H 3 KO 2 = C 4 H 4 K 2 O 4 + 2 NH 3 . Hydric succinate dissolves readily in water with a 388 OXALIC SERIES. 305 decidedly acid reaction. When subjected to dry distillation it decomposes into water and anhydrous succinic acid C 4 H 6 O 4 =C 4 H 4 O 3 + H 2 O. Phosphoric chloride decomposes the succinate, forming the anhydrous acid, hydrochloric acid, and phosphoric oxy- chloride. A further action of phosphoric chloride decomposes the anhydrous acid, forming succinic chloride C 4 H 4 O 3 + P Cl 5 = C 4 H 4 O 2 Cl 2 + P O Cl 3 . Calcic succinate (C 4 H 4 Ca O 4 ) is soluble in water. The hydrocalcic succinate (Ca H 2 (C 4 H 4 O 4 ) 2 ) is a crystallizable salt. Barytic succinate (C 4 H 4 BaO 4 ) is but slightly soluble in water, and it is insoluble in a mixture of ammonia and alcohol. Ferric succinate is insoluble in water but soluble in hydric salts. Succinic ether is decomposed by ammonia, forming suc- cinamide C 4 H 4 (C 2 H J O 4 + 2 N H 3 = C 4 H 4 O 2 (N H 2 ) 2 + + 2 C 2 H 6 0. There is also a class of salts called succinates, derivable by a similar reaction from hydrovinic succinate C 4 H 4 O 2 C 2 i y? + 2 N R3 = C4 R4 2 NH 2 + 2 R6 ' Anhydrous succinic acid combines w r ith ammonia, forming a compound in which the radical succinyle (C 4 H 4 O 2 ) re- places two atoms of hydrogen of the ammonia This compound is called succinimide. It dissolves readily in water and forms beautiful crystals. Most of the higher terms of the oxalic series are made by the action of dilute nitrate on salts of the adipic series or on oleates. 389 305 FORMATION OF THE OXALIC SERIES. Hydric sebate is formed by the dry distillation of oleate, but the most ready way of obtaining a sebate in quantity is by heating castor-oil soap with potassic hydrate. The soap contains a salt called ricinoleate, and this breaks up with the hydrate into sebate and a volatile alcohol. Hydrated sebacic acid is very slightly soluble in water, and can easily be obtained in crystals. 306. All these salts contain diatomic radicals oxalyl (C 2 O 2 ), malonyl (C 3 H 2 O 2 ), succinyl (C 4 H 4 O 2 ), &c. These radicals form chlorides corresponding to the hy- drates. Thus succinic chloride is C 4 H 4 O 2 C1 2 . Oxalates form, however, an exception in this respect, for by the action of phosphoric oxychloride they are broken up into a mixture of carbonic acid and carbonic oxide, whilst hydric chloride and phosphoric hydrate are formed. These salts are formed on the type of two molecules of /H 2 \ water (jjs Oy, the radical replacing two atoms of hydrogen, one in each molecule, whilst imparting to the compounds sufficient acid power to react on two molecules of potassic hydrate, and to neutralize the two atoms of alkali metal in C 4 H 4 O 2 the normal succinates, such as -^ 2 O 2 - In this respect the salts of the oxalic series differ from those of the lactic series. For although a lactate contains the diatomic radical lactyl (C 3 H 4 O) in the place of two (H 2 \ TT 2 O 2 ) thus, C 3 H 4 O TT 2 O 2 , it is only capable of reacting on one atom of potassic hydrate, forming the so-called normal potassic lactate C 3 H 4 H K ( 39 DI AMINES. 307 and if the second atom of typical hydrogen be expelled by C 3 H 4 O the action of metallic potassium, the compound -^ 2 O 2 /C 2 H 5 \ is as alkaline as potassium alcohol I TT- O), and is decom- posed even by water like potassium alcohol. The two atoms of typical hydrogen in each molecule of the hydrogen salts of the lactic series are distinguished by the terms ' metallic hydrogen' and 'alcoholic hydrogen/ Metallic hydrogen is that which is easily replaced by metals, and alcoholic hy- drogen is that which can only be replaced with difficulty by metals like the typical hydrogen of vinic alcohol. This difference of acid power in the two series is con- nected with the fact that each salt of the oxalic series has two atoms of oxygen in its radical, whereas each salt of the lactic series has only one atom of oxygen in its radical. Glycols, and homologues which have no oxygen in their radicals, cannot neutralize even one atom of potassium when it replaces one of their atoms of typical hydrogen, as in the C 2 H 4 compound ^ -^ O 2 . 307. The chlorides or bromides of divalent radicals react normally upon two molecules of ammonia as upon two molecules of water. Thus ethylenic bromide, heated with ammonia, forms compounds called diamines, derived from two molecules of ammonia (N 2 H 2 H 2 H 2 ), by the re- placement of two atoms of hydrogen by one atom of ethylene, forming N 2 H 2 H 2 (C 2 H 4 ); or by the replace- ment of four atoms of hydrogen by two atoms of ethylene, forming N 2 H 2 (C 2 H 4 )(C 2 H 4 ); or by the replacement of the six atoms of hydrogen by three atoms of ethylene, forming N 2 (C 2 H 4 ) (C 2 H 4 ) (C 2 H 4 ), called triethylene diamine. Each molecule of these diamines 39 1 307 DI AMINES. combines with two molecules of hydric chloride, forming salts such as N 2 H 4 C 2 H 4 H 2 Cl 2 , and these chlorides, in their turn, unite with platinic chloride, forming double chlorides, 392 GLYCERINE (C 3 H S 0*). 308 CHAPTER L. 308. Glycerine has been shewn by the classical investi- gations of Berthelot to be a triatomic alcohol; and its empirical formula (C 3 H 8 O 3 ) is written on the water-type as containing the trivalent radical glycerile (C 3 H 5 ) in the place of three atoms of hydrogen. Glycerine is now prepared on a large scale by the distilla- tion of palm-oil and other fats in superheated steam. The fat is decomposed, by the action of the steam, into glycerine and hydric palmitate, &c. Thus palmitine, in an excess of steam, takes up three molecules of water C 3 H 5 C 3 H 5 H The products are condensed above iooC; so that the excess of steam passes on, leaving the hydric salts and the glycerine in the condenser. Glycerine is also prepared by the action of litharge in presence of water upon fat. The glycerine can easily be washed away from the plaster which is formed, purified by sulphuretted hydrogen, and evaporated in a water- bath, to drive off the excess of water which is present. In this manner glycerine is obtained, in the form of a thick liquid of sweet but peculiar taste, soluble in water in all proportions, also soluble in alcohol, but insoluble in ether. Glycerine is decomposed at a high temperature, and one of the products formed is acroleine (C 3 H 4 O), a volatile liquid of most penetrating odour. Some of the glycerine evaporates in the products of decomposition of the remainder. Redtenbacher recommends heating glycerine, or a compound 393 308 GLYCERINE (C 3 # 8 3 ). of glycerine, with hydropotassic sulphate, in order to detect it by the odour of acroleine which is formed. Hydric chloride decomposes glycerine in three succes- sive stages C 3 H 8 3 + HCUC 3 H 7 2 C1 + H 2 0. This first compound is called monochlorhydrine. It is in its turn decomposed by hydric chloride, forming dichlor- hydrine C 3 H 7 O 2 C1 + HCUC 3 H 6 OC1 2 + H 2 O. The further action of hydric chloride causes the dichlor- hydrine to break up into hydric chloride and so-called epichlorhydrine C 3 H 6 OC1 2 = HC1 + C 3 H 5 OC1. Phosphoric chloride, however, forms the normal chlor- hydrine C 3 H 6 O C1 2 + P Cl 5 = C 3 H 5 C1 3 + P O C1 3 + H Cl. This chlorhydrine is the normal chloride of the trivalent radical glycerile. A corresponding bromide has been ob- tained ; and from the bromhydrine Wurtz has reproduced glycerine by the action of argentic acetate, and the subse- quent decomposition of the ' acetine ' thus obtained. Other monobasic hydrogen salts act in a similar manner to the chloride. Thus a mixture of hydric sulphate and nitrate transforms glycerine into a heavy oil glyceric nitrate, (C 3 H 5 \ (NO 2 ) 30 /' By acting upon glycerine by potassium, its typical hy- drogen can be partially replaced by the metal, and ethylic iodide replaces this potassium by ethyle. 309. By heating glycerine with hydrogen salt of the acetic series Berthelot has prepared artificially a considerable 394 CONSTITUTION OF FATS. 310 number of fats. Thus on the acetate glycerine reacts in three successive proportions C 3 H 8 O 3 + C 2 H 4 O 2 = C 3 H 7 O 2 C 2 H 3 O 2 + H 2 O; C 3 H 8 3 + 2 C 2 H 4 2 = C 3 H 6 O(C 2 H 3 2 ) 2 + 2 H 2 O; C 3 H 8 O 3 -H 3C 2 H 4 O 2 = C 3 H 5 (C 2 H 3 O 2 ) 3 + sH 2 O. These compounds are called monacetine, diacetine, and triacetine. The compounds formed by the action of the higher salts of the series are perfectly analogous to them. In order to separate the fat from the excess of hydrogen salt which was used in the operation, Berthelot acted upon the mixture by sodic carbonate, thereby dissolving out all the salt without decomposing the glycerine compound ; and by dissolving the fat in ether he separated it from the free glycerine. By the action of monochlorhydrine on sodic ethylate monethyl glycerine has been prepared C 3 H 7 O 2 Cl + Na C 2 H 5 O = Na Cl + H ?c?^ 5 3 ' And in like manner dichlorhydrine reacts on two molecules of sodic ethylate, forming diethylic glycerine ; and the tri- ethyline has been obtained by the action of ethylic iodide on diethylsodic glycerine nsj-r^TT 5 ! NT a T -i_ Na(C 2 H 5 ) 2 f (C 2 H 5 ) 3 - 310. By the oxidation of glycerine a hydrogen salt called glycerate, of the composition C 3 H 6 O 4 , has been obtained. Glycerate contains the trivalent radical C 3 H 3 O; but it appears to be monobasic, so that two of the typical atoms of hydrogen in it are considered as alcoholic hydrogen, /C 3 H 3 O \ while one only is metallic f TT2TT O 3 ). 395 310 HYDRIC MALATE (C 4 # 6 5 ). A hydrogen salt called tartronate has been obtained by the decomposition of nitrotartrate. The tartronate has the composition C 3 H 4 O 5 ; and Kekule' suggests that it may be the next product of the oxidation of glycerine, so that its rational formula would then be T/TJ? O 3 . Jbi rl Another class of salts, nearly related to these, are the malates such as (C 4 H 6 O 5 ); these salts occur in goose- berries, rhubarb, sour apples, barberries, and many other vegetables; but they are most conveniently prepared from the juice of unripe mountain-ash berries. Malates are dibasic ; but, as Kekule suggests, its radical C 4 H 3 O 2 is probably trivalent, according to the formula TT rp O 3 5 according to which it is represented as homologous with /C 4 H 7 \ tartronate, and is derived from butylic glycerine ( TTS O 3 ). Calcic malate (Ca C 4 H 4 O 5 ) is insoluble in water. It dissolves in dilute hydric nitrate ; and the double salt H 2 Ca(C 4 H 4 O 5 ) 2 crystallizes out easily from this solution. Plumbic malate becomes semi-fluid and crystalline by heating in a solution of plumbic acetate. Hydric iodide reduces malate to succinate C 4 H 6 O 5 + 2 H I = C 4 H 6 O 4 + H 2 O 2 + I 2 . Malates rotate a polarized ray of light. By the action of heat the malate yields two hydrogen salts isomeric with one another, and differing from it by contain- ing the elements H 2 O less than the malate in each mole- cule C 4 H 6 O 5 H 2 O = C 4 H 4 O 4 . These salts are called maleate and fumarate. They com- bine with nascent hydrogen, forming succinate C 4 H 4 O 4 + H 2 = C 4 H 6 O 4 . 396 ROSANILINE (C 20 H 19 N 5 }. 311 Many vegetables contain a nitrogenized crystallizable compound called asparagine, which is represented by the formula C 4 H 4 O 3 (N H 2 ) 2 . Asparagine behaves as the malic amide. By prolonged contact with hot water it is converted into ammonic malamate C 4 H 4 O 3 (N H 2 ) 2 + H 2 O = N H 4 C 4 H 4 O 4 N H 2 . By the action of nitrous acid it is decomposed, yielding a kind of malate, which does not rotate light 311. Amongst trivalent compounds Kekule classes the so-called nitriles bodies such as acetonitrile, &c., which are formed either by the combination of cyanogen with a monovalent alcohol radical or by the action of anhy- drous phosphoric acid on the ammonia -salt of the acetic series. It is not impossible that Aniline-red or Rosaniline may contain a trivalent radical. This beautiful base is usually made by the action of hydric arseniate on a mixture of toluidine and aniline. Its formula (C 20 H 19 N 3 ) shews it to be a triamine. Its acetate (C 20 H 19 N 3 C 2 H 4 O 2 ) crystal- lizes in magnificent crystals, shewing a greenish metallic lustre by reflected light. Its hydrochlorate (C 20 H 19 N 3 H Cl) crystallizes in needles. Aniline blue (C 20 H 16 (C 6 H 5 ) 3 N 3 H Cl) is made by the action of aniline on the acetate of rosaniline. Ammonia is given off in the process, and three atoms of hydrogen are replaced in the red compound by three atoms of phenyl. The product acquires its characteristic blue colour by com- bination with hydric chloride. Chrysaniline is the name given to a yellow compound, formed simultaneously with rosaniline by the action of the arseniate on commercial aniline. It is extracted from the residues from which the rosaniline has been sepa- 397 311 ROSANILINE (C 20 H N s ). rated out. Its composition is represented by the formula C 20 H 17 N 3 . Another beautiful dye is the so-called mauveine (C 27 H 24 N 4 ), which was discovered by Mr. Perkin, and opened the field of investigation of these coloured derivatives of aniline and toluidine. 39S ERITHRITE AND TARTARIC ACID. 312 CHAPTER LI. 312. Tetratomic compounds are chiefly known among acids, but a crystallizable body called erithrite has been extracted from various lichens, and Berthelot has proved that it reacts upon hydric salts under similar circum- stances to glycerine. The formula of erithrite is C 4 H 10 O 4 , and it is considered as a tetratomic alcohol of the formula C*H' 4 H 4 ' Hydric iodide decomposes it, with formation of a com- pound isomeric with butylic iodide (C 4 H 9 I). Hydric Tartrate (C 4 H 6 O 6 ) is classed by Kekule' as a tetratomic compound, and thus related to erithrite by re- placement of four atoms of hydrogen in the radical C 4 H 6 C 4 H 2 O 2 \ by two atoms of oxygen ( Tj 4 O 4 ). Tartrates are contained in many vegetable juices. The hydrogen salt is usually prepared from argol, the crude hydropotassic tartrate which collects from acid continental wines in the form of a reddish crust. The salt is decom- posed by boiling with chalk, forming a precipitate of calcic tartrate and a solution of potassic tartrate 2 C 4 H 5 KO 6 + CaCO 3 = C 4 H 4 CaO 6 + + C 4 H 4 K 2 O 6 + CO 2 + H 2 O. The solution of the potassic salt is transformed into calcic tartrate by the action of calcic chloride C 4 H 4 K 2 O 6 + Ca Cl 2 = C 4 H 4 Ca O 6 + 2 K Cl. The two portions of calcic salt obtained by these operations 399 312 DERIVATIVES OF THE TARTRATES. are decomposed by dilute hydric sulphate, and the tartrate is usually evaporated in vacuum pans. It is thus obtained in the form of clear crystals, which contain no water of crystallization. When heated these crystals become electrical, shewing two opposite electrical charges at two opposite corners. These polarities are re- versed during the process of cooling. The tartrate dissolves readily in water, and its solution has a powerful acid reaction. It is very liable to become mouldy, and to decompose on keeping. The aqueous solution of tartrates is dextrorotatory. If present in sufficient quantity with a salt of a heavy metal, a tartrate prevents the precipitation of the metallic oxide by potash. Alkaline solutions thus formed allow the heavy metal to be precipitated by sulphuretted hydrogen. This property is however not by any means characteristic of tartrates, as it belongs equally to many other polybasic salts. 313. Tartrates are decomposed by heat, and the odour of the products of their destructive distillation possesses some resemblance to that of burnt sugar, and is employed occa- sionally as a means of recognizing the hydrogen salt. When the salt is cautiously heated it loses a molecule of water, forming anhydrous tartaric acid C 4 H 6 6 -H 2 = C 4 H 4 5 ; and this anhydrous acid is capable of combining with the hydrate, forming the so-called ditartrate. Among the pro- ducts of the dry distillation of tartrate are pyruvate (C 4 H 4 O 3 ), and pyrotartrate (C 5 H 8 O 4 ). It is easy to account for the formation of these salts. Thus : C 4 H 6 O 6 -CO 2 -H 2 O = C 3 H 4 O 3 , and Acetate accompanies these products. 400 DERIVATIVES OF THE TARTRATES. 314 When fused with potassic hydrate tartrates break up into an acetate and an oxalate Tartrates are amongst the best characterized bibasic salts. When half neutralized by potash the hydric salt forms the slightly soluble hydropotassic tartrate commonly called cream- of-tartar. But when twice as much potash is added, the salt is dissolved, with formation of the readily soluble normal tartrate C 4 H 4 K 2 O 6 . When lime-water is added gradually to a solution of the hydrogen salt, no precipitate is produced so long as the liquid is acid, but as soon as it becomes neutral a white precipitate of normal calcic tartrate is formed. This salt dissolves in cold potash, but is precipitated by boiling. It dissolves also in ammonic chloride. Sodium forms a normal tartrate and a double tartrate with hydrogen. This hydrosodic tartrate is an exceedingly con- venient reagent for the distinction of potassium and sodium in their salts, as it precipitates concentrated solutions of potassic salts and has no action on sodic salts. Rochelle salt is the name given to sodiopotassic tartrate, a salt which crystallizes in singularly well-formed crystals. Tartrates are readily oxidized by hydric nitrate. They reduce metallic silver from solutions of its salts. One of the commonest tartrates is the so-called tartar-emetic, potassio- antimonic oxytartrate (C 4 H 4 KSbO 7 ). This salt is usually prepared by boiling pure antimonic oxide with hydropotassic tartrate. It may be considered as containing the monovalent radical Sb O in place of one atom of potassium of the normal tartrate C 4 H 4 K (Sb O) O 6 . 314. The racemate is isomeric with common tartrate. It has no rotating action on a polarized ray of light. Its solu- tion causes a precipitate when added to a solution of calcic D d 401 314 RACEMATES. chloride, and the racemate is thus distinguished from the tartrate. Pasteur has shewn that the racemate is a com- pound of tartrate (dextrorotatory) with an isomeric body which he calls levorotatory tartrate. The two are separated by crystallizing a solution of ammonio-sodic racemate. Two varieties of crystals are formed, each of them hemihedral, but one having the opposite modifications to the other; so that if a model of one of the crystals were made of cardboard it would represent the other variety when turned inside out. Tartrate and racemate are formed by the cautious oxida- tion of saccharate and mucate by hydric nitrate. They are, in their turn, easily oxidized by the nitrate, forming oxalate and ultimately carbonic acid. Tartrates also reduce metallic silver from solutions of its salts. The tartrate has been made from succinate. The first step of the process is to form the so-called dibromo-succinate C 4 H 4 Br 2 O 4 . The silver-salt of this body is next prepared by precipitation. When boiled for some time in contact with water this silver-salt takes up the elements of two mole- cules of water, giving up in their place its bromine and silver together as argentic bromide Homotartrate is the name given by its discoverer, Kekule', to a salt of the composition C 5 H 8 O 6 , formed by the action of argentic hydrate on the compound of bromine with itaconate. This compound is homologous with dibromo- succinate, and is called dibromopyro-tartrate C 5 H 6 Br 2 O 4 + 2 Ag H O = 2 Ag Br + C 5 H 8 O 6 . 315. The Citrate (C 6 H 8 O 7 ) is usually prepared from lemon-juice. It is also contained in tamarinds, and in many other acid fruits. The expressed juice is neutralized by lime, and the dry calcic citrate is imported into this country for the preparation 402 HYDRIC CITRATE (C 6 fi0 7 ). 315 of the hydric salt. The salt is prepared from this calcic salt by the action of hydric sulphate, very much in the same way as the tartrate. The salt crystallizes readily from water, and the crystals contain a molecule of water of crystallization. Citrates are tribasic, and the formula of the hydric salt is written on the water-type as containing the trivalent radical pe U4 r^s C 6 H 4 O 3 : thus, j^ H s O 4 . It is thus considered to con- tain four atoms of typical hydrogen, three of which are metallic and replaceable by potassium, sodium, &c., while the fourth is called alcoholic hydrogen. Potassic Citrate (K 3 C 6 H 5 O 7 ), as well as hydrodi- potassic citrate (HK 2 C 6 H 5 O 7 ) and dihydropotassic citrate (H 2 K C 6 H 5 O 7 ), are readily soluble in water ; and the citrate can be distinguished from tartrate by the non-precipitation of potash by an excess of hydric citrate. When lime-water is added gradually to an aqueous solution of hydric citrate a double salt is at first formed, but even \vhen the salt is neutralized by the formation of the normal salt Ca 3 (C 6 H 5 O 7 ) 2 no precipitate is formed in the cold. On boiling an alkaline mixture of citrate and lime-water, the salt is precipitated, When the citrate is cautiously heated it loses the elements of a molecule of water, forming aconitate (C 6 H 6 O 6 ); and when aconitate is heated to a still higher temperature than that at which it was formed, carbonic acid is given off, and a salt of the composition C 5 H 6 O 4 is formed. This salt is called itaconate. The citraconate, ispmeric with itaconate, is formed at the same time, and a third isomeric is called mesaconate. Pentatomic compounds are as yet but little known. Kekule places, however, in this group two hydric salts aposorbate (C 5 H 8 O 7 ), a dibasic salt supposed to contain D d 2 403 315 MANNITE the pentavalent radical C 5 H 3 O 2 . It was made by Des- saignes, by the action of hydric nitrate on sorbin. The other pentatomic salt is desoxalate (C 5 H 6 O 8 ), obtained by Lowig among the products of the action of sodium on oxalic ether. Desoxalates are supposed to contain the radical C 5 HO 3 , and they are tribasic. The hydric desoxalate breaks up when heated into carbonic acid and racemate C 5 H 6 O 8 = C 4 H 6 O 6 + CO 2 . 316. Mannite (C 6 H 14 O 6 ) is a hexatomic alcohol, con- taining the radical C 6 H 8 in the place of six atoms of hydro- /C 6 H 8 \ gen in six molecules of water ( Tt 6 O). It is contained in manna, and is frequently formed from sugar by a process of fermentation. It has been made by the action of nascent hydrogen, evolved by sodium amalgam, on uncrystallizable sugar. It is readily soluble in water, but far less soluble in alcohol. It melts between 160 and 165, and boils, with partial decomposition, at 200. Mannite reduces gold and silver from aqueous solutions of their salts, but it does not reduce copper from cupric oxide in presence of free potash. It reacts with hydric stearate, &c. in the same sort of way as glycerine, and Berthelot has obtained mannitic tetrahydric distearate and mannitic dihydric tetrastearate. / C 6 H 8 \ Mannitic nitrate L^ Q2\eO ( y is formed by the action of a mixture of strong nitrate and sulphate upon mannite. Sulphuretted hydrogen in presence of alcohol and ammonia reduces it to mannite. Hydriodic acid decomposes mannite, forming a compound isomeric with caproic iodide (C 6 H 13 I). Mannitan (C 6 H 12 O 5 ) is formed by the removal of a mole- cule of water from mannite, by the action of heat. Mannide (C 6 H 10 O 4 ) has been obtained by Berthelot by heating mannite to 200 or 250 with hydric butyrate. 404 HYDRIC SA CCHARA TE (C 6 H w 8 ). 317 /C 6 H 6 O \ Hydric mannitate f TTG O 6 ) is formed by the action of air on a mixture of platinum black and moist mannite. It is probably monobasic. 317. Hydric Saccharate and Mucate ( C ^g^O 6 ,) are formed by the action of dilute nitrate on mannite. Sac- charate is also formed by the first action of nitrate on several kinds of sugar. It is most easily prepared from common cane-sugar. One part by weight of sugar is heated with three parts by weight of nitrate, of density 1.25, and removed from the fire as soon as the action is fairly started. After the liquid has cooled down to about 50 it is kept at this temperature as long as any fumes are evolved. It is then diluted with half its volume of water, and half neutra- lized by potash. When allowed to stand for some days the liquid deposits crystals of hydropotassic saccharate C 6 H 4 2 H 4 HK U ' C 6 H 4 O 2 Its normal potassic salt has the composition TT 4-17-2 O G . Hydric saccharate has not been obtained in the crystalline state. When made from cane-sugar it is dextrorotary. By the gentle action of nitrate it forms dextrotartrate. There are two saccharic ethers corresponding to the po- tassium salts above-named, and an amide corresponding to the normal ether and obtained from it by the action of ammonia C 6 H 4 O 2 f\t, AT TT3 _ C 6 H 4 O n 4 _Lo ^ n H 4 (C 2 H 5 ) 2U ~H 4 (NH 2 ) 2U 2 C 2 H 5U> Mucate, isomeric with saccharate, is formed by the action of nitrate on milk-sugar, or gum-arabic. According to Pasteur it is best made from galactose. Hydric mucate is easily deposited in the crystalline form 405 317 HYDRIC MUCATE. from its aqueous solution, for it is very slightly soluble in cold water. Like saccharates it is dibasic. On dry distil- lation it yields pyromucate C 6 H 10 O 8 = C 5 H 4 O 3 + 3 H 2 O + C O 2 . Hydric iodide reduces mucates, and, according to Crum- Brown, it appears that adipate is formed by the reduction Hydric nitrate oxidizes a mucate, with formation of race- mate; and this, in its turn, is subsequently oxidized to oxalate. CARBONIC HYDRATES. 318 CHAPTER LII. 318. One of the most important families of organic bodies are the so-called carbonic hydrates ; including sugars, gums, starch, woody fibre, &c. These bodies contain oxy- gen and hydrogen in the proportions in which those ele- ments form water ; or, in other words, they contain twice as many atoms of hydrogen as of oxygen, but it is by no means probable that these elements are combined with one another in the form of water. They are probably related to alcohols in their composition, containing polyvalent radicals, such as C R H 6 , in lieu of the hydrogen of water. These compounds are classified by Kekule under the three following formulae, viz. C 6 H 12 O 8 ; C 12 H 22 O 11. C 6 H 10 O 5 . It may be, however, that some of them ought to be re- presented by multiples of these formulae. Grape-sugar, or dextrose, and uncrystallizable sugar are two of the most important compounds, having the formula C 6 H 12 O 6 . Galactose is also isomeric with them, and, like them, is capable of undergoing alcoholic fermentation under the action of yeast. These fermentable sugars are formed by the action of hydric salts on compounds belonging to the other families of carbonic hydrates. Thus dextrose is formed by boiling starch or dextrine with dilute sulphate. It is also formed together with levulose by the action of dilute sul- phate on cane-sugar. Levulose is alone formed from inulin. And galactose is formed from milk-sugar by the action of 407 318 CARBONIC HYDRATES. dilute hydric salts. These sugars are also formed from the same materials by the action of yeast. Thus cane-sugar in a fermenting fluid takes up the elements of water and forms a molecule of dextrose and a molecule of levulose. Dextrose is best obtained from so-called candied honey, i. e. honey which has deposited crystals by long standing. The syrup is drained from these crystals by allowing them to lie on a porous tile. They are then dissolved by the aid of heat in spirits of wine, and crystallized. Dextrose dissolves in about an equal weight of water, and its solution is not decomposed by dilute sulphate. It reduces ferric salts to ferrous salts, and reduces metallic silver from many of its solutions. It dissolves cupric hydrate in presence of caustic potash, and the solution deposits cuprous hydrate when gently heated. A lime compound is obtained by dissolving calcic hydrate in a solution of dextrose, and then adding alcohol. Its composition is represented by the formula C fi H 10 Ca0 6 H 2 0. Dextrose also combines with common salt. There are three crystallizable compounds, but the one most easily obtained consists of two molecules of dextrose combined with one molecule of salt and one of water (C 6 H 12 O 6 ) 2 NaClH 2 O. 319. Compounds of glucose with acids are called Glti- cosates. Many of them, such as tannin, amygdalin, salicin, &c. occur in the vegetable kingdom. These bodies are decomposed in a manner which may be compared to the decomposition of fats by water. Thus, when boiled with a dilute mineral hydric salt tannin takes up the elements of water, and decomposes into glucose and hydric gallate C 27 H 22 o 17 + 4 H 2 O = 3 C 7 H 6 O 5 + C 6 H :2 O 6 . V / V / ( y ; Tannin. Gallate. Glucose. 408 GLUCOSATES. 319 In like manner salicin breaks up into saligenine and glucose C i3 H is o r + H 2 O = C 7 H 8 O 2 + C 6 H 12 O 6 . Salicin. Saligenine. Glucose. The decomposition of amygdaline is more complicated. It takes place in presence of certain ferments, forming benzoic aldehyde, prussic acid, and glucose Berthelot has prepared several glucosates by heating glu- cose with hydrated organic hydric salts. Acetic glucosate was obtained by heating glucose for about 50 hours to 100 with the acetate. It contains six atoms of acetyl, thus (C 6 H 4 (C 2 H 3 O; 6 O 5 ), and the glucose lost a molecule of water at the same time, forming glucosan (C 6 H 10 O 5 ), of which, properly speaking, this compound is the acetate. Similar compounds have been obtained with butyrate and stearate, containing in one molecule two atoms of the radicals of these salts. Levulose is not easily obtained in a state of purity, as dextrose, which usually accompanies it in sweet fruits, can only be separated approximatively from it by alcohol. In contact with nascent hydrogen, evolved by sodium, levulose takes up hydrogen and is converted into mannite, a property which dextrose does not seem to possess C 6 H 12 O 6 + H 2 = C 6 H 14 O 6 . Levulose. Mannite. It is less rapidly decomposed by yeast than dextrose ; and accordingly a mixture of the two, such as is formed by boiling common sugar with dilute sulphate, becomes more and more levorotatory up to a certain point, in proportion as the dex- trose is broken up. Its compound with lime is less soluble in water than the compound containing dextrose. 409 319 CANE-SUGAR ( In order to separate levulose from dextrose Dubrunfaut recommends that 10 parts of so-called inverted sugar be mixed with 6 parts of calcic hydrate and 100 of water. After the mixture has been shaken for some time a deposit is formed, containing levulose combined with lime. Hydric oxalate liberates the levulose from this compound. Galactose is obtained by boiling milk sugar with very dilute sulphate. It has much resemblance to glucose, but, unlike glucose, it does not combine with salt. 320. Sugar (C 12 H 22 O n ), called by way of distinction cane-sugar, is found in the juices of many plants. It is mostly prepared from the juice of the sugar-cane, but in many parts of the continent of Europe it is prepared from beet-root. The manufacture of sugar from the sugar-cane is divided into two distinct operations : first, the preparation of a crude sugar in the neighbourhood in which the sugar is grown ; and, secondly, the purification of the crude sugar by the so-called process of refining an operation which is only performed with advantage in or near some large town, where skilled labour is abundant. The freshly-cut sugar-canes are first passed through rollers, which press out the greater part of the juice ; and this juice is rapidly evaporated down after the neutralization of its acidity by lime. The mother-liquid drained off from the crystals of sugar is known by the name of molasses, or treacle. The refining of sugar is effected by dissolving it in water and depriving it of its colouring matter by animal charcoal and albumen (from ox blood). The solution is evaporated in a so-called vacuum pan a large boiler in which the syrup is boiled down by the aid of a partial vacuum maintained by a powerful air-pump and condenser. The lower tem- perature at which ebullition thus takes place, saves the sugar from the partial decomposition which it would undergo if 410 REACTIONS OF CANE-SUGAR. 321 boiled for an equal length of time under the atmospheric pressure. When allowed to crystallize slowly, sugar is obtained in the form of very hard and regular crystals, which are known by the name of sugar-candy. For most purposes the con- sumers prefer to use sugar in very small crystals, and to obtain it in that form. The concentrated syrup is agitated artificially during the process of crystallization. A thick magma is thus obtained, which is poured into moulds, where the little crystals are cemented together by the de- position of more sugar between them, and assume the form of a sugar-loaf. Sugar has a density of 1.6. It dissolves in about one- third of its weight of cold water, and in still less hot water, and the solution is dextrorotatory. It is not soluble in ether or in cold alcohol. It melts at 160, and becomes coloured when heated to a higher temperature. It is completely de- stroyed by dry distillation. 321. Dilute mineral hydric salts transform sugar, with assimilation of water, into a mixture of dextrose and levulose. This mixture is called inverted sugar. Yeast effects the same transformation, and these products necessarily precede the formation of alcohol and the other products of vinous fermentation. Sugar holds cupric oxide in solution in presence of caustic potash, and cuprous oxide is deposited very slowly indeed from this solution on the application of heat. When heated with dilute hydric nitrate it forms saccharate, tartrate, and oxa- late. Caustic potash has very little action on sugar even at 100, and serves to distinguish it from dextrose and levulose. A solution of sugar is precipitated by baryta, the com- pound C 12 H 22 O 11 Ba O being formed. Lime dissolves very freely in syrup, forming various com- pounds. 321 MILK-SUGAR (C M H* O u ). The compound C 12 H 22 O n CaO is obtained by dissolving lime in aqueous solutions of sugar, taking care to keep the sugar in slight excess, and then adding alcohol to the solution. The compound is thus precipitated. C 12 H 22 O 1; Ca 2 O 2 is obtained by saturating a solution of sugar and lime, by digesting it with an excess of the base, and then precipitating the filtered liquid by alcohol. C 12 H 22 O n Ca 3 O 3 is precipitated by boiling an aqueous solution of sugar previously saturated with lime. Milk-sugar (C 12 H 22 O n ) is obtained by evaporating to crystallization the clear liquid called whey, obtained by allow- ing skimmed milk to remain in contact with rennet until all the casein is deposited from it. The crystals first obtained can be purified by the action of animal charcoal, and re- crystallization. When dried at 100 milk-sugar contains a molecule of water of crystallization, which can be expelled at i40C. The crystals C 12 H 22 O 11 H 2 O require about six times their weight of cold water for their solution ; but they dissolve in twice their weight of boiling water. They are remarkably insipid; but the aqueous solution has a very sweet taste. It is dextrorotatory. Dilute mineral hydric salts convert milk-sugar into galac- tose, and yeast probably effects the same transformation before alcoholic fermentation sets in. Cheese transforms milk-sugar into a lactate, alcohol and carbonic acid being formed in small quantity at the same time. Milk-sugar holds cupric oxide in solution in presence of potash ; and the solution readily deposits cuprous oxide even in the cold. Dilute hydric nitrate oxidizes milk-sugar, with formation of mucate. 412 DEXTRINE ((C fl H s )"}. 322 CHAPTER LIII. 322. Dextrine ((C 6 H 10 O 5 )) is a neutral and insipid body, used in the impure state under the name of British gum. It is obtained by heating starch to about 160. The starch is sometimes moistened with exceedingly dilute nitrate before heating. Dextrine is also formed from starch by the action of certain ferments. It is named from its powerfully dextrorotatory action on light. It dissolves in water, but not in alcohol or ether. It does not reduce cupric oxide when boiled with it in an alkaline liquid. Dilute hydric salts transform dextrine into dextrose. The nitrate does not form mucate on oxidizing it. Gum- Arabic, or tree-gum, has the same empirical com- position as dextrine. Its aqueous solution is levorotatory. Moderately strong nitrate oxidizes gum-arabic, with forma- tion of the mucate. Other members of this same natural family are Lichenine, which is extracted by boiling water from Iceland moss. Its solution gelatinizes on cooling. Inuline, prepared from dahlia-roots. Glycogen, discovered by Bernard in the liver. Starch ((C 6 H 10 O 5 ) n ) is contained in many vegetables, in the form of granules varying in size according to the vegetable from which it is obtained. Thus the granules of potato -starch have a diameter of nearly 0.2 millimetre, whilst those from Indian-corn have only a diameter of 0.03, and those from the seed of chenopodium quinoa have a diameter of about 0.002. Starch is usually prepared from potatoes or rice. The granules are washed out from the fibrous substances in 322 CELLULOSE ((C 6 fl 10 5 ) n ). which they are interspersed, and they collect at the bottom of vessels in which the water is allowed to stand. Dilute caustic soda is used to dissolve out from the starch the albuminous matter' with which it is at first mixed, and which would cause its decomposition if left in it. Starch is not, properly speaking, soluble in water; but when it is heated to about 80 with water, the granules swell up and burst, forming a paste. When long boiled in water starch passes over into a soluble substance usually called soluble starch. This soluble compound is exceedingly dextrorotatory. It is precipitated by alcohol in the form of a white powder, but retains its solubility in water. Granulous starch and soluble starch are characterized by the deep blue colour of the compound which each of them forms with iodine. Starch granules are dissolved by caustic potash, forming a liquid which has no rotatory action on a ray of light. Dilute hydric salts, as well as diastase, and some other ferments, dissolve starch by transforming it into a mixture of dextrine and dextrose. Starch is not dissolved by ammonic cuprate. 323. Cellulose, or Woody fibre ((C 6 H 10 O 5 )*), is the name usually given to the most insoluble bodies of this class. They are not soluble in water, nor in dilute caustic potash. Ammonic cuprate dissolves woody fibre. The material is most easily obtained in a state of purity from fresh and picked cotton-fibre. Caustic potash, alcohol, and ether are used successively to dissolve out foreign substances adhering to the fibres; and they are then very carefully washed and dried. Woody fibre immersed for some time in a con- centrated solution of potash appears to combine with the alkali, and to form a compound containing two atoms of potassium to twenty-four atoms of carbon 414 CELLULOSE ((C 6 H w 5 )"). 323 Water dissolves out all the potash from this compound, reproducing woody fibre. Strong hydric sulphate reacts on cellulose, forming a conjugated compound, analogous to sulphovinic acid. When paper is immersed for a short time in a mixture of two volumes oil of vitriol and one of water, and thoroughly cleansed by repeated washings with water, and ultimately with ammonia, it is changed into a substance possessing considerable resemblance to parchment, and usually called * vegetable parchment.' Strong hydric nitrate reacts on woody fibre, forming products of substitution of N O 2 for hydrogen in the cotton. A mixture of strong nitrate and sulphate replaces three atoms of hydrogen by (NO 2 ) 3 in the group C 6 H 10 O 5 , and the compound C 6 H 7 (NO 2 ) 3 O 5 is the valuable explosive material called gun-cotton. A variety of nitrocellulose containing a smaller proportion of the radical N O 2 is used for the preparation of collodion, which is a solution of it in ether and a little alcohol. The gun- cotton (C 6 H 7 (NO 2 ) 3 O 5 ) does not dissolve in ether and alcohol, but it dissolves in acetic ether. An alcoholic solu- tion of potassic sulph-hydrate decomposes these bodies, reproducing woody fibre from all of them. Strong hydric sulphate dissolves cellulose, transforming it into a substance analogous to starch, insoluble in water, but swelling up by contact with it, and becoming blue \vhen placed in contact with iodine. By longer action of the sulphate a substance very much like dextrine is formed. When this dextrine from woody fibre is boiled with dilute sulphate it is converted into dextrose. 324 HYDRIC UFA TE (C 5 H* N* O 3 ). CHAPTER LIV. 324. Hydric Urate (C 5 H 4 N 4 O 3 ) is in its constitution related to urea. It occurs sometimes in human urine, and if present in considerable quantity gives rise to the formation of concretions in the bladder and in other organs. It is most easily obtained in a pure state from the urine of the boa-constrictor or other large serpents. This sub- stance resembles chalk in its appearance, and consists chiefly of ammonic urate. Dilute caustic potash dissolves it at a boiling heat, evolving ammonia. The solution contains H 2 potassic urate, C 5 -ggN 4 O a a salt of exceedingly alkaline properties. There is in the solution some colouring matter, which is most easily separated from the compound by pass- ing carbonic acid through the impure solution of the potash salt. A double salt is thus precipitated (hydropotassic urate, TT3 C 5 K N 4 O 3 ), while the colouring matter remains mostly dissolved in the alkaline carbonate. By repeatedly dis- solving in potash and reprecipitating by carbonic acid a colourless urate is at last obtained, from which the urale is precipitated in the form of a white crystalline powder by dilute hydric chloride or sulphate. Hydric urate requires about 18,000 parts of cold water for its solution. It is insoluble in alcohol and ether. On dry distillation it is entirely decomposed, forming amongst other products cyanurate, urea, ammonic cyanide, &c. 416 DERIVATIVES OF URIC ACID. 325 Its potassic salts are more soluble in water than its sodic salts, and lithia dissolves it even more freely than potash. Its derivatives with the alkaline earths and the heavy metallic oxides are nearly insoluble in water. Urates are detected by the bright red colour which is formed when crystals of hydric urate are moistened with the nitrate, dried by the aid of gentle heat, and then moistened with ammonia. The re- action is due to the formation of murexide. Another way of dectecting urates, described by Schiff, is to dissolve the urates in sodic carbonate and drop the solu- tion on to paper moistened by silver nitrate. A brown colour is produced, owing to the reduction of silver. 325. The derivatives obtained from the urates by the action of various reagents are exceedingly numerous. A few only of them can be here mentioned. Alloxan (C 4 H 2 N 2 O 4 ) is formed by the action of various oxidizing agents, such as hydric nitrate or chlorate. Urea is formed at the same time thus C 5 H 4 N 4 O 3 + O + H 2 O = C 4 H 2 N 2 O 4 + CH 4 N 2 O. Hydric urate. Alloxan. Urea. AUoxantin (C 8 H 4 N 4 O 7 ) is formed by the action of re- ducing agents, such as sulphuretted hydrogen, sulphurous acid, &c. on alloxan (C 4 H 2 N 2 O 4 ) 2 + H 2 = C 8 H 4 N 4 O 7 + H 2 O. Alloxan. AUoxantin. Hydric Dialurate (C 4 H 4 N 2 O 4 ) is formed by the further action of reducing agents with the aid of heat C 4 H 2 N 2 O 4 + H 2 = C 4 H 4 N 2 O 4 . Alloxan. Dialurate. Hydric Parabanate (C 3 H 2 N 2 O 3 ) is formed by the action of oxidizing agents, such as nitrate, on alloxan E e 417 325 DERIVATIVES OF URIC ACID. 4 + o = C 3 H 2 N 2 O 3 + CO 2 . Alloxan. Parabanate. AUoxanates (C 4 H 4 N 2 O 5 ), such as the hydric salt, are formed by the action of bases on alloxan. The barytic salt (C 4 H 2 BaN 2 O 5 ) is decomposed by boiling into urea and the barytic mesoxalic acid C 4 H 2 BaN 2 5 + H 2 = Barytic alloxanate. Barytic Urea, mesoxalate. Parabanates undergo decompositions analogous to those of alloxan, and hydric parabanate may be considered as a kind of alloxan containing the elements C O less than alloxan itself. Thus Ammonic Oxalurate (C 3 H 4 N 2 O 4 ) is obtained by the action of that base on the parabanate. And oxalurates decompose when boiled into urea and corresponding oxalates. The formation of oxalurates from parabanates is similar to that of alloxanates from alloxan. Oxalurate differs from alloxanate in composition by the elements C O. When boiled with a hydric salt a solution of parabanic acid decom- poses into oxalate and urea C 3 H 2 N 2 O 3 + 2 H 2 O-C 2 H 2 O 4 + CH 4 N 2 O; oxalurate being no doubt first formed. The two salts yield urea, while alloxanate yields a mes- oxalate (C 3 O 5 Ba), and oxalurate yields an oxalate (C 2 O 4 Ba); and the mesoxalate has the same C O beyond the elements of the oxalate which alloxanate has beyond the elements of the oxalurate. 326. Mesoxlates and Oxalates may with advantage be compared to carbonates, as an oxalate contains C O in addi- tion to the elements of a carbonate. Thus 418 MESOXALATE (C 3 5 # 2 ). 327 CO 3 H 2 C 2 O 4 H 2 C 3 O 5 H 2 Carbonate. Oxalate. Mesoxalate. If we represent these salts on the type of two molecules of water (r^O 2 ) we have the series TT2 O 2 ? jT2 O 2 ? H 2; containin g the radicals CO (carbonyl), C 2 O 2 (oxalyl), and C 3 O 3 (mesoxalyl). If, as Kekule has sug- gested, the carbonate be represented as derived from methy- lenic glycol (^'o 2 ) by the replacement of H 2 by O, while glycollate in like manner is derived from ethylenic glycol ( TT2O 2 ) by the same substitution, and oxalate by the replacement of the four atoms of hydrogen in the glycol by two atoms of oxygen, then the mesoxalote will be /C 3 H 6 \ derived from propylenic glycol ^ T O 2 ) by the re- placement of the six atoms of hydrogen in the radical by (C 3 H 4 O \ j^-2 O 2 / an d malonate /C 3 H 2 O 2 \ ( u2 O 2 ) being the first two products of the oxidation. 327. An aqueous solution of alloxan decomposes on keeping, but more rapidly on boiling, into alloxantin, para- banate, and carbonic acid (C 4 H 2 N 2 O 4 ) 3 = C 8 H 4 N 4 O 7 + C 3 H 2 N 2 O 3 + CO 2 . Alloxan. Alloxantin. Parabanate. Alloxantin can also be obtained by the action of sul- phuretted hydrogen in the cold on an aqueous solution of alloxan 2 C 4 H 2 N 2 O 4 + H 2 S = C 8 H*M 4 O 7 + H 2 O + S. Hydric nitrate easily reverses this action and oxidizes alloxantin, with formation of alloxan. A dialurate (C 4 H 4 N 2 O 4 ) is formed by the reduction of E e 2 419 327 ALL OX A NTIN (C 8 & A' 4 O 7 ) . alloxantin by sulphuretted hydrogen, or by sodium-amalgam. It can also be obtained by adding baryta-water to a so- lution of alloxantin, and boiling the violet precipitate which is first formed. The barytic alloxanate and dialurate are thus formed 2 C 8 H 4 N 4 O 7 + H 2 Ba 3 O 4 = 2C 4 H 2 BaN 2 O 5 + Ba(C 4 H 3 N 2 O 4 ) 2 . Alloxanate. Alloxantin is accordingly built up of alloxan and dialurate with elimination of water C 4 H 2 N 2 O 4 + C 4 H 4 N 2 O 4 = C 8 H 4 N 4 O 7 + H 2 O. Alloxan. Dialurate. Alloxantin. By the action of oxidizing agents hydric dialurate is trans- formed into alloxan. Murexide (G 8 H 8 N 6 O 6 ) is the name given to a beautiful compound, of red colour by transmitted light, and of which the crystals have a green colour and metallic lustre when seen by reflected light. Murexide is considered as ammonic purpurate, and is re- presented by the rational formula C 8 H 4 (N H 4 ) N 5 O 6 . It is formed by the action of ammonia or its carbonate on a hot solution of alloxantin or of alloxan. It is also said to be formed by the action of ammonia upon dry alloxantin heated to iooC. Several other purpurates have been prepared, such as C 8 H 4 K N 5 O 6 , a deep red powder, and Ba(C 8 H 4 N 5 O 6 ) 2 . 328. It appears from the elaborate investigations of Baeyer that the dialurate and alloxanate are products of oxida- tion of a hydric salt of the composition C 4 H 4 N 2 O 3 , which he calls barbiturate. That able chemist represents dialurate as barbiturate, in which an atom of hydrogen is replaced by (H O), as seen by the formula 420 BARBITURIC ACID (C 4 tf 4 JV 2 3 ). 328 C 4 H 3 (HO)N 2 3 ; and the alloxanate will then be C 4 H 2 (H O) 2 N 2 O 3 . The amide of ammonic cyanate ((C N) N H 2 ) may be re- presented as the hydride of a radical ((CN 2 H)H), and if this radical replace one atom of hydrogen in a molecule of barbiturate, we have the formula C 4 H 3 (CN 2 H)N 2 O 3 = C 5 H 4 N 4 O 3 , containing the elements of the urate. Allantoine (C 4 H 6 N 4 O 3 ) is a compound which crystallizes in transparent prisms, and was named from its occurrence in the allantoic fluid of cows. It is formed by the action of plumbic peroxide on hydric urate. Water containing the urate in suspension is heated to the boiling-point, and the peroxide is thrown into the mixture in small quantities as long as it continues to lose its brown colour. The liquid thus obtained is filtered, treated with sulphuretted hydrogen, and evaporated to crystallization. Allantoine combines with silver, forming the compound C 4 H 5 Ag N 4 O 3 . 421 329 GUANIN (C 5 H S N*0). CHAPTER LV. 329. Guanin (C 5 H 5 N 5 O) is a feeble base found in guano. For its preparation guano should be boiled with milk of lime, and the solution filtered off from the residual solid matter, as often as a repetition of the process serves to dissolve out any colouring matter. Urate and guanin are thus left undissolved, while most of the other substances which accompany them in the guano are dissolved out. Guanin dissolves in boiling hydric chloride, and can thus 'be separated from the greater part of the urate. It can be precipitated by ammonia from a solution of its hydro- chlorate (C 5 H 5 N 5 O H Cl), and is insoluble in water. By the action of a mixture of hydric chloride and potassic chlorate it is oxidized, with formation of parabanate and guanidin Guanin. Parabanate. Guanidin. Guanidin (CH 5 N 3 ) is a strong base which dissolves readily in water and absorbs carbonic acid from the air. Its carbonate (CO 3 H 2 (CH 5 N 3 ) 2 ) crystallizes from water, but is insoluble in alcohol. Its platinum-salt has the com- position Pt Cl 6 (C H 5 N 3 ) 2 H 2 . 330. Xanthin, or xanthic oxide (C 5 H 4 N 4 O 2 ), was found in an urinary calculus. It has since been found in flesh. It is also formed by the action of the nitrite on guanin Guanin. Xanthin. 4 22 GLYCOCYAMINE (C 3 ^ 7 ^ 3 O 2 ). 331 It is almost insoluble in cold water, and very slightly soluble in boiling water. It combines both with hydric salts and bases, forming crystalline salts. Another compound intimately related to xanthin in com- position is Sarkine (C 5 H 4 N 4 O). It is a weak base, which has been found in flesh, also in blood, the liver, &c. It requires about 300 times its weight of cold water for its solution, but only 78 times its weight of boiling water. It differs in compo- sition from hydric urate by containing two atoms of oxygen less than the urate contains, while xanthin stands between the two in composition. A group of compounds related to the urate and to gua- nin by their decompositions is formed of creatine and crea- tinine, together with their homologues glycocyamine and glycocyamidine. 331. Glycocyamine (C 3 H 7 N 3 O 2 ) is formed by the action of glycocoll on an aqueous solution of cyanamide C 2 H 5 NO 2 +CN 2 H 2 = C 3 H 7 N 3 O 2 . Glycocoil. Cyanamide. Glycocyamine. The compound crystallizes out from the mixture after a few days' standing. It requires 126 times its weight of cold water for its solution, but dissolves much more readily in hot water. Alcohol does not dissolve it. It forms a crystal- line hydrochlorate (C 3 H 7 N 3 O 2 II Cl) and a platinum-salt of the composition Pt Cl 6 H 2 (C 3 H 7 N 3 O 2 ) 2 . When heated to i6oC in a current of hydric chloride gas, glycocyamine loses the elements of water and takes up those of the chloride. The compound thus obtained is the hydro- chlorate of glycocyamidine C 3 H 7 N 3 O 2 + HC1-H 2 O = C 3 H 5 N 3 OHC1. From this hydrochlorate the base glycocyamidine (C 3 H 5 N 3 O) can be liberated by plumbic oxide. 423 331 CREATINE (C*H 9 N 3 2 ). Glycocyamidine forms with zinc chloride a compound which crystallizes in needles, and is but slightly soluble in water. 332. Creatine (C 4 H 2 N 3 O 2 ) is contained in the juices of flesh. It has also been found in the brain and in urine. For its preparation lean meat should be finely minced and the soluble constituents extracted by cold water, pressure being applied to complete the separation of the fluid from the insoluble fibres. The solution thus obtained is heated to the boiling-point to coagulate the albumen contained in it, and baryta-water is subsequently added to it as long as it continues to throw down any phosphate. After filtration, the liquid is evaporated in a water-bath, and the crystals first obtained are purified by animal char- coal. Creatine crystallizes in clear prisms, which contain a molecule of water of crystallization. They require 74 parts of cold water to dissolve them. In absolute alcohol and in ether creatine is almost insoluble. It combines at tem- peratures below 33 with hydric salts, forming salts, from which it can be recovered again. But when heated to a temperature above 30, the creatine in one of these salts gradually loses water and passes over into creatinine C 4 H 9 N 3 O 2 -H 2 O = Creatine. Creatinine. When heated with soda-lime creatine evolves methylia. The same product is formed together with ammonia by the oxidizing action of nitrate upon it. These reactions shew that the radical methyle is contained in the molecule of creatine. When boiled with baryta-water creatine takes up the elements of water, and decomposes into sarkosine and urea 424 CREATININE (C*H 7 N 3 O). 333 Creatine. Sarkosine. And sarkosine is proved to be a methylated glycocoll (C 2 H 4 (C H 3 ) NO 2 ); for it has been made by the action of hydric monochloracetate on methylia When an aqueous solution of creatine is boiled with mer- curic oxide a compound called methyluramine, but which might with advantage be termed methylated guanidin, is formed, together with oxalate C 4 H 9 N 3 O 2 + O 2 = C H 4 (C H 3 ) N 3 + C 2 H 2 O 4 . Some carbonic acid is given off at the same time. 333. Creatinine (C 4 H 7 N 3 O) is found in the juice of flesh, and also in the human urine, as well as in the urine of horses and dogs, and especially in calves' urine. It is also formed by the action of hot hydric salts on creatine. To prepare it from urine, calcic chloride should be added in sufficient quantity to precipitate the phosphates, &c. from the liquid previously neutralized by lime-water. The filtrate should be evaporated to crystallization, and the mother liquid from which the salts have been deposited should be mixed with a very strong solution of zinc chloride. Crystals containing creatinine combined with zinc chloride are deposited from this mixture after a few days' standing. These crystals can be dissolved in hot water and decom- posed by plumbic oxide. The solution of creatinine is finally purified by animal charcoal. Creatinine is much more soluble than creatine in water, for at i6C it only requires 11.5 parts of water for its solu- tion. It dissolves still more readily in hot water, and crystal- lizes from a hot saturated solution in needles. Its aqueous solution has an alkaline reaction to litmus-paper, and expels ammonia from its salts. 425 333 CREA TININE ( C 4 H 7 N 3 0). The platinum -salt (Pt Cl 6 H 2 (C 4 H 7 N 3 O) 2 ) is soluble. The compound with zinc chloride has a composition repre- sented by the formula Zn Cl 2 (C 4 H 7 N 3 O 2 ). It is slightly soluble in water, and insoluble in alcohol. Creatinine is converted into creatine by boiling with an aqueous alkali. Even plumbic oxide, in a boiling solution of creatinine, slowly produces the same change. 426 THEINE ^C* H w N* O 2 ). 334 CHAPTER LVI. 334. Theine (C 8 H 10 N 4 O 2 ) and theobromine (C 7 H 8 N 4 O 2 ) are bodies of great importance as aliments. Their trans- formations prove that they are nearly related to the urate in constitution. Theine is contained in tea, coffee, and in matd, or Para- guay tea, and also in a substance called guarana. It was called caffeine when first obtained from coffee, but its pro- perties are in all respects the same, from whichever of the above-named vegetable bodies it may have been extracted. Tea-leaves contain from two to four per cent, of theine ; coffee-berries rather less than one per cent. Paraguay tea contains rather more than one per cent, of it. To prepare theine a cold alcoholic infusion of tea-leaves is precipitated by plumbic acetate, for the removal of the tannin which is present. The excess of lead is precipitated from the filtrate by sulphuretted hydrogen ; and the liquid is evaporated to crystallization. The crude product is purified by subli- mation. Theine crystallizes in long silky needles, which contain a molecule of water. It dissolves in water, alcohol, or ether. When gradually heated it sublimes without decomposition. It combines with hydric salts, forming salts (such as the hydrochlorate C 8 H 10 N 4 O 2 H Cl). Water decomposes this compound easily, and hydric chloride evaporates from it in warm air so weak a base is the theine. The platinum-salt (PtCl 6 H 2 (C 8 H 10 N 4 O 2 ) 2 ) is but slightly soluble in water, but the gold-salt (Au Cl 4 H C 8 H 10 N 4 O 2 ) is more soluble. 427 334 THEOBROMINE (C 7 H s N 1 2 ). Oxidizing agents, such as the nitrate or chlorine, form in presence of water a compound called amalate, which is alloxantin, in which four atoms of hydrogen are replaced by four atoms of methyle: thus, C 8 (C H 3 ) 4 N 4 O 7 . The further action of the same oxidizing agents forms cho- lestrophane, which is in constitution dimethyl-parabanate (C 3 (CH 3 ) 2 N 2 O 3 ). When acted upon by the nitrate and subsequently by ammonia, theine yields a purple-coloured product, similar to that obtained from the urate. When boiled with potash theine is decomposed, with evolution of methylia. 335. Theobromine (C 7 H 8 N 4 O 2 ) is contained in choco- late, and is prepared from the cacao-nuts. It resembles theine in its chemical properties, and no doubt also in its action upon the human system. An aqueous solution of theobromine mixed with ammonia is precipitated by argentic nitrate. The precipitate is a silver- salt of the composition C 7 H 7 AgN 4 O 2 . By the action of methylic iodide upon this compound at 100, Strecker has prepared theine This reaction proves theine to be methylated theobromine. But theobromine yields methylia by the action of various destructive reagents, and must therefore be admitted to con- tain the radical methyle in its molecule. The body xanthin (C 5 H 4 N 4 O 2 ), described above, differs from theobromine empirically by 2 C H 2 , and Strecker was led by this circum- stance to prepare and examine dimethylexanthin C 5 H 2 (CH 3 ) 2 N 4 O 2 . He found it to be isomeric, and not identical with theo- bromine. From these facts it is inferred that theobromine is derived 428 BILE. 336 from a body of the composition C 6 H 6 N 4 O 2 , by the sub- stitution of methyle for one atom of hydrogen (C 6 H 5 (CH 3 )N 4 2 ); and that theine is similarly formed by the replacement of two atoms of hydrogen in that same body by two atoms of methyle (C 6 H 4 (CH 3 ) 2 N 4 O 2 ). 336. In the bile of man, of oxen, sheep, pigs, and other animals, compounds analogous to soap in their properties and constitution have been discovered. Some remarkable transformations of these compounds have been explained by Strecker's able investigations. Ox bile is the material most easily obtained in abundance for the preparation of these compounds. The liquid is usually of a brown colour, and must be used quite fresh, as it very soon undergoes putre- faction. The liquid is alkaline to test-paper from the pre- sence of sodic salts of the acids of the bile. Dry sodic sulphate dissolves in large quantities in bile, especially with the aid of heat, and if the liquid be saturated by this salt, the original salts of the bile are precipitated in the form of a brown resinous mass, very much in the same way as a soap is precipitated from aqueous solution by the action of salt. The solid matter obtained in this way, or by evaporating the bile to dry ness in a water-bath, should be treated with alcohol, which takes up the salts of the bile and the colouring matter, leaving mucus and some mineral salts undissolved. The addition of ether to the alcoholic solution of the salts of the bile causes a precipitate ; and if the precipitation of a large quantity of the solution be effected in successive steps, and each successive precipitate kept separate, it is found that all the colouring matter is carried down by the first portions precipitated, and the later portions are colour- less. By redissolving these colourless precipitates in alcohol, pouring ether on to the top of the solution, and leaving 429 336 HYDRIC CHOLA TE it in a closed flask, the salts of the bile can be obtained in crystals. These crystals consist of two sodic salts which have been called by Strecker cholate and taurocholate. Each of these salts contains carbon, hydrogen, nitrogen, and oxygen; but the taurocholate contains sulphur in addition to those four elements. The proportion between these two salts varies in different sorts of bile, that from fishes being particularly rich in taurocholate. The name ' glycocholate ' is applied by some chemists to Strecker' s cholate, but the shorter name is preferable. 337. Sodic cholate (C 26 H 42 NaN O 6 ) and sodic tauro- cholate (C 26 H 44 NaNO 7 S) dissolve readily in water, and mineral hydric salts precipitate their respective hydrogen salts. Strong hydric sulphate added in excess dissolves the pre- cipitate first formed in a solution of bile; and the addition of a strong syrup of cane-sugar to this hot mixture causes the appearance of a beautiful purple colour, which dis- appears on the subsequent addition of water. This reaction is even known as Pettenkofer's test for the salts of the bile. It belongs also to cholalates. Both cholates and taurocholates are decomposed by con- tinued ebullition, in presence of an excess of baryta. The cholate takes up a molecule of water, and forms a cholalate and glycocoll Ba(C 26 H 42 NO 6 ) 2 + 2H 2 O = Ba(C 24 H 39 O 5 ) 2 +2C 2 H 5 NO 2 . Cholate. Cholalate. Glycocoll. 338. Taurocholates also yields cholalate, but the other product is taurine Ba(C 26 H 42 NS0 7 ) 2 + 2 H 2 O = Ba(C 2 * H 39 O 5 ) 2 -f C 2 H 7 O 3 N S. Taurocholate. Cholalate. 430 TAUROCHOLATE (C^H^NSO 7 ). 338 Taurine had been discovered for many years, and was represented by a formula containing no sulphur, but two atoms of oxygen instead of one of sulphur. Strecker has shewn that it is the amide of ammonic isethionate, a com- pound formed by the combination of olefiant gas with anhydrous sulphuric acid and neutralization by ammonia C 2 H 5 (N H 4 ) S O 4 - H 2 O = C 2 H 7 N S O 3 . Ammonic isethionate. Taurine. The bile of hogs contains in place of cholate a salt homo- logous with it, which Strecker has named, from its source, hyocholate. Hyocholate is decomposed like cholate, by boiling with alkalies, and instead of cholalate it yields a salt containing CH 2 in addition to the elements of cholalate, and is called hyocholalate. Cholesterine (C^H^O) is a beautiful crystalline body, which has been usually classed among fats, but which more recent investigations have proved to possess an alcoholic constitution. It combines with hydric stearate or benzoate like a monatomic alcohol. 431 339 CHININE (C 20 H 2i N* 2 ). CHAPTER LVII. 339. One of the most important groups of organic com- pounds are the so-called alkaloids ; organic bases possess- ing powerful medical properties, and very complex molecules, of which the arrangements are for the most part unknown to us. The most valuable alkaloid of cinchona bark is Chinine (C 20 H 24 N 2 O 2 ). This bark contains this base together with cinchonine, combined as chinates. For the preparation of chinine the bark is ground and boiled with dilute hydric sulphate or chloride. The strained liquid is precipitated by sodic carbonate, and the precipitate, consisting of chinine and cinchonine, is dissolved in dilute sulphate and crystallized, the chinine salt being first de- posited. If the mixed bases be dissolved in spirits of wine, after precipitation of the original extract and desiccation of the precipitate, and cinchonine can in great part be crystal- lized out from the alcoholic solution, while the chinine remains in the mother liquid. Chinine is slightly soluble in water, but it dissolves readily in alcohol or in ether. It forms crystallizable salts, of which an aqueous solution has an intensely bitter taste. Solutions of salts of chinine, containing free hydric salts, are exceedingly fluorescent. In light containing ultraviolet rays an acid solution of the sulphate presents on its surface a beautiful blue opalescent appearance. Ammonia and potash precipitate chinine from an aqueous solution of one of its salts, and the precipitate is scarcely at all soluble in an excess of the precipitant. 432 CHININE (C 20 H N- O 2 ). 339 Chlorine water acts on a solution of the sulphate in such a manner that the subsequent addition of ammonia forms a deep emerald-green solution. Chinine combines with hydric chloride in two proportions, forming the compounds C 20 H 24 N 2 O 2 H Cl and C 20 H 24 N 2 O 2 (H Cl) 2 . Its platinum-salt corresponds to the latter of these com- pounds, for it contains its elements in the following propor- tions Ft Cl H 2 C 20 H 24 N 2 O 2 . It is but slightly soluble in water. There are two chinine sulphates. That which usually occurs in commerce has a composition represented by the formula S O 4 H 2 (C 20 H 24 N 2 O 2 ) 2 (H 2 O) 7 . It consists of needle-shaped crystals, which dissolve very slightly in water. The crystals are gradually decomposed, and become brown, by exposure to sunshine. Dilute hydric sulphate dissolves these crystals readily, forming the hydrochinic sulphate S O 4 H 2 C 20 H 24 N 2 O 2 (H 2 O) 7 . When this salt is dissolved in strong acetate, and an alcoholic solution of iodine is gradually added to it, a com- pound is formed which crystallizes out from the solution in flat plates. These plates are called the sulphate of iodo- chinine, and are represented by the formula S O 4 H 2 C 20 H 24 N 2 O 2 1 2 (H 2 O) 5 . They exhibit a green colour by reflected light, and are particularly interesting from the polarizing action which they exert upon transmitted light. Chinic Sulphate has in solution a powerful levorotatory action on polarized light. When heated to iooC the salt is phosphorescent. The commercial salt sometimes contains cinchonine, and this admixture can be discovered by adding ammonia in slight excess to a concentrated solution of acid sulphate Ff 433 339 CINCHONINE (C 20 H* N* 0) . and then agitating the mixture with ether. Cinchonine re- mains undissolved. There are two alkaloids isomeric with chinine, and formed from it. These bases are called chinidine and chinicine. They are obtained from a resinous substance called quin- oidine. 340. Cinchonine (C 20 H 24 N 2 O) crystallizes from an alcholic solution in the form of needles. Its solution has an alkaline reaction to test-paper. In cold water it is almost insoluble, and in boiling water very slightly soluble. The alkaloid melts at 105, and can be partially sublimed. Its salts exert a powerful dextrorotatory action on light. They do not give a green product when treated by chlorine and subsequently by ammonia. There are two hydrochlorates (C 20 H 24 N 2 OHC1 and C 20 H 24 N 2 O (H Cl) 2 ). The platinum-salt is represented by the formula C 2 H 24 N 2 OPtCl 6 H 2 . There are two sul- phates, viz. S O 4 H 2 (C 20 H 24 N 2 O) 2 and S O 4 H 2 C 20 H 24 N 2 O. Both chinine and cinchonine are decomposed by fusion with potash, yielding an oily product of alkaline properties, called quinoleine. Both alkaloids unite with methylic iodide or ethylic iodide, forming the compounds C 20 H 24 N 2 O 2 C H 3 1 and C 20 H 24 N 2 O C H 3 1. The methyle thus added to the composition of the base is not in the place of any typical hydrogen of ammonia, but in the place of the fourth atom of hydrogen which is added to an ammonia when an ammonium salt is formed. Freshly- precipitated argentic hydrate, added to the solution of one of these iodides, removes the iodine and replaces it by H O C 20 H 24 N 2 O 2 CH 3 I + HOAg = = C 20 H 24 N 2 O 2 CH 3 HO + Agl. The hydrates thus obtained are very strong bases. 434 OPIUM. 342 341. Opium is the name given to a mixture of a number of alkaloids with resins, mucilage, caoutchouc, &c., some of which occur as meconates. The substance is obtained by scratching unripe poppy capsules, and collecting, after it has dried, the milky juice which exudes. The opium undergoes a process of fermentation before it is exported for use. The proportions in which the various constituents are present vary in different specimens of opium. The best varieties, such as Smyrna opium, sometimes contain as much as fifteen per cent, of morphia, while the inferior sorts sometimes con- tain as little as three per cent, of morphia, or even less. Narcotine and hydric meconate can be extracted in quantities varying from six to eight per cent., and codeia, thebaia, papaverine, opianine, narceia, and meconine are present in far smaller quantities. 342. Morphia (C 17 H 19 NO 3 ) is usually prepared by dissolving in water the soluble constituents of the opium, neutralizing the solution by chalk, and adding calcic chloride in quantity sufficient for the precipitation of the meconate. The alkaloids are thus left in solution as hydrochlorates, and. are filtered off from the precipitate of calcic meconate, and evaporated to crystallization. The morphic hydrochlorate crystallizes out first, while the mother liquid retains a quantity of colouring matter with a little morphia and other bases. A second crystallization yields a mixture of the hydro- chlorates of codeia and morphia. Morphia can be pre- cipitated with facility by ammonia from a solution of its hydrochlorate. Another method of preparing morphia from opium con- sists in boiling the aqueous extract of the drug with milk of lime, and filtering off the alkaline solution thus obtained from the undissolved matter. The morphia is combined with lime in the solution, and can be precipitated from it by the action of sal ammoniac with the aid of heat. Ammonia F f 2 435 342 MORPHIA (C ]7 H i9 NO^. evaporates, while morphia falls down and calcic chloride remains in solution. Morphia requires about icoo times its weight of cold water for its solution, and about 400 times its weight of boiling water. The solution has an alkaline reaction to turmeric paper. "Morphia dissolves readily in alcohol, but is insoluble in ether and in chloroform. The alkaloid is readily oxidized by iodic acid or by ferric salts. Neutral ferric chloride forms with morphia a dark blue compound not very unlike ink, and this property serves as a test for morphia. Although readily soluble in fixed alkalies, morphia is but slightly soluble in ammonia. Morphic hydrochlorate (C 17 H 19 N O 3 H Cl (H 2 O) 3 ) dis- solves in sixteen parts of cold water, or in one part of boiling water. Its platinum -salt is represented by the formula (C 17 H 19 N0 3 ) 2 PtCl 6 H 2 . Narcotine (C 22 H 23 NO 7 ) is a much weaker base than morphia, as might be inferred from the larger quantity of oxygen contained in it. It is readily soluble in ether or chloroform, and can thus be separated from morphia. Nar- cotine is readily oxidizable, and undergoes numerous in- teresting decompositions, which have been ably investigated by Matthiessen and Foster. When acted on by hydric iodide in aqueous solution a molecule of narcotine forms three molecules of methylic iodide. 343. The chief alkaloids of the Strychnos tribe of plants are Strychnia and Brucia. These alkaloids can be prepared from the nux vomica, by rasping the seeds and boiling them with alcohol containing one or two per cent, of sulphate. The solution thus obtained is neutralized by lime, and the alcoholic solution of the two alkaloids is evaporated to dryness. The alkaloids are sub- sequently dissolved in dilute nitrate, and separated by crystal- 436 STRYCHNIA (C^-H^-ZV'O 2 ). 343 lization of their nitrates, the strychnia nitrate being less soluble than brucic nitrate. Strychnia (C 21 H 22 N 2 O 2 ) is easily precipitated by am- monia or potash from a solution of one of its salts, and is> not soluble in an excess of potash. It is almost insoluble in water, or in absolutely dry alcohol. The very small quantity of it which dissolves in water, is however sufficient to impart a bitter taste to the liquid. Animal charcoal removes strych- nia from an aqueous solution. It is readily soluble in spirits of wine, and it dissolves also in chloroform, but not in ether. Strychnia is not reddened by the action of strong hydric nitrate, and its freedom from brucia is thus tested. When mixed with plumbic peroxide, and then moistened by strong hydric sulphate, strychnia forms a blue compound, which soon changes to a violet one, and ultimately becomes red and brown. This colour-test is used for the detection of strychnia. The platinum-salt of strychnia is almost insoluble in. water. It is represented by the formula PtCl 6 H 2 (C 21 H 22 N 2 2 ) 2 . There is a normal sulphate of the composition SO 4 H 2 (C 21 H 22 N 2 O 2 ) 2 and an acid salt SO 4 H 2 C 21 H 22 N 2 O 2 . Strychnia and its salts produce lockjaw, or 'tetanus/ and the alkaloid can be detected by its action on a frog, even when given in an exceedingly small quantity. Brucia (C 23 H 26 N 2 O 4 ) is soluble in about 850 parts of boiling water, and in a far smaller quantity of spirits of wine. It forms large crystals containing four molecules of water. For the preparation of the pure alkaloid its oxalate is washed with dry alcohol at oC. The salt is then dissolved in water, decomposed by lime, evaporated to dryness, and then crystal- lized from alcohol. 437 343 NICOTINE (C 10 ^ 14 ^). Strong hydric nitrate in contact with brucia produces a deep red colour, whilst methylic nitrite is evolved. 344. Nicotine (C 10 H 14 N 2 ) is a volatile and liquid alka- loid contained in tobacco, and imparting to that plant the narcotic properties for which its leaves are used. Nicotine is a very strong base, belonging to the class of tertiary diamines. It boils at about 250, is readily soluble in water, and forms crystallizable salts. Its hydrochlorate is repre- sented by the formula C 10 H 14 N 2 Cl 2 H 2 . Nicotine is exceedingly poisonous ; 5 milligrammes of it placed on the tongue of a middle-sized dog having been found sufficient to kill the animal in three minutes. 438 INDIGO (C 8 H 5 N 0). 345 CHAPTER LVIII. 345. Amongst organic compounds of which the molecular arrangement is but little known there are two important colouring bodies which deserve some study, viz. indigo and alizarine. Indigo (C 8 H 5 NO) is manufactured in India by mace- rating the indigo plants with water in large vats. A process of fermentation takes place, by which indigo-white is formed and dissolved by the water. As soon as the process is judged to be complete, the water is pressed out from the plants and led into vats, in which air has access to it, and precipitates indigo-blue from the solution. The process is aided by beating the surface of the liquid with flat shovels, whereby more of the liquid is brought into contact with air, and the precipitate is rendered more dense. The indigo-blue which is collected in this manner con- tains various earthy and other impurities, sometimes in large quantity. Good specimens contain 50 to 60 per cent, of indigo, besides substances called indigo-gluten, indigo-red, indigo-brown, and other resinous bodies. Some of these foreign bodies can be dissolved out by the successive action of dilute sulphate, boiling water, and alcohol; but the indigo-vat affords the best means of purifying the colouring- matter. There are various sorts of so-called indigo-vat, but the operation in all of them consists in transforming the indigo-blue, by the action of a reducing agent, into indigo- white, and dissolving this indigo-white. Water with lime and ferrous sulphate is a mixture which forms a 'vat' of 439 345 ALIZARINE (C lo # 6 3 ). frequent use. The ferrous oxide becomes converted into ferric oxide, whilst the indigo is reduced and dissolved. Air should be excluded during the operation. From the solution formed in the vat indigo-white can be precipitated by hydric chloride ; or indigo -blue by the absorption of oxygen from the air. Indigo-blue (C 8 H 5 N O) is a neutral solid, presenting a coppery lustre by reflected light. When heated it melts, and a small quantity can be sublimed in the form of crystals. Several oxidizing agents such as chromic acid are capable of converting indigo into isatine (C 8 H 5 NO 2 ). By further oxidation by strong nitrate this is in its turn converted into Nitrosalycylate (C 7 H 5 (NO 2 ) O 3 ), and ultimately into carbazotate (C 6 H 3 (N O 2 ) 3 O). Indigo is decomposed by strong aqueous potash, with the aid of heat, forming, according to Gerhardt, a product of oxidation, isatate ; and by simultaneous reduction of another portion, indigo-white Potassic isatate. Indigo-white. When melted with potash it evolves hydrogen, and potassic anthranilate (C 7 H 6 K N O 2 ) is formed. When distilled with potash, indigo yields aniline. 346. Alizarine (C 10 H 6 O 3 ) is a valuable dye obtained from madder-root. Some alizarine is found ready formed in the roots, but more of it is obtained by the decomposition of a yellowish compound which is present in the root. This yellowish compound can be extracted by cold water (alizarine is not soluble in it), and the solution can be used for dyeing with alizarine colours. Alizarine dissolves in alkalies, or alkaline carbonates, forming purple solutions, from which it is precipitated on the addition of a hydric salt. 440 ORCEINE (C 7 ^ 7 A r 3 ). 348 It dissolves in alcohol or ether, and also in strong sul- phate, from which it is thrown down again by water. By ebullition with nitrate it is oxidized, forming naphthalate and oxalate. Alizarine. Naphthalate. Alizarine crystallizes in red prisms, which can be volatilized at 215. 347. Orceine (C 7 H 7 NO 3 ) is a red colouring-matter which is obtained from litmus. It is made by exposing orcine to the simultaneous action of ammonia and air. Orceine is very slightly soluble in water or ether, but alcohol dissolves it readily. It dissolves in aqueous potash or ammonia. Orcine (C 7 H 8 O 2 ) is made by boiling erithrine with milk of lime for several hours. The liquid is filtered, de- prived of the lime in it by hydric oxalate, and reduced to a small bulk. The orcine is dissolved in alcohol, and crystal- lized from that solution, and subsequently from, solution in ether. The reaction gives rise to the formation of orsellate and erithrite C 2o H 22 O io + (H 2 O) 2 = (C 8 H 8 O 4 ) 2 + G 4 H 10 O 4 . Erithrine. Orsellate. Erithrite. Orsellate breaks up subsequently into carbonic acid and orcine. Orcine crystallizes with a molecule of water, which is given off at 100. At a high temperature it can be sublimed without decomposition. 348. Turpentine (C : H ]6 ) is a member of a very numerous family of hydrocarbons which occur in plants, and often impart to them their peculiar smell. They are 441 348 TURPENTINE (C 10 # 16 ). classed among essential oils ; of which several (such as gaultheria oil, oil of cinnamon, &c.) have already been de- scribed. Many plants supply hydrocarbons isomeric with oil of turpentine. Among the most important of these isomeric hydrocarbons may be mentioned oil of lemons, oil of bergamot, oil of birch, oil of camomile, oil of carraway, oil of juniper, oil of ginger, oil of hops, oil of parsley, oil of pepper, and oil of thyme. These essential oils are frequently prepared by distilling the plants or parts of plants containing them, with water. The oils are carried over into a receiver by the steam, at a temperature far below their own boiling-points. Many of them are, however, altered by exposure to the temperature of 1 00, and deteriorated as perfumes. These are accordingly collected at the atmospheric temperature by placing a con- siderable surface of some inodorous fat in a suitable box near to the flowers which are exhaling the fragrant oil. The fat absorbs and dissolves it with its original properties. Commercial turpentine varies considerably in its proper- ties, according to the plant from which it was collected ; but in addition to a hydrocarbon of the composition C 10 H 16 it always contains a resinous body formed by the oxidation of that hydrocarbon. It is usually purified by rectification, the resin being left in the still. Its specific gravity is about 0.86, and it boils at 160. Some varieties of it are dextro- rotatory, some levorotatory. It dissolves sulphur or phosphorus. It is also a good solvent for grease. It is almost insoluble in water, but dissolves in alcohol or ether. It absorbs oxygen rapidly from the air, especially when mixed with litharge or ceruse. It combines with hydric chloride, forming crystalline compounds. It also combines with water under favourable circumstances, forming crystalline hydrates. 442 CAMPHOR (C 10 .ff 16 0). 349 These compounds are sometimes called artificial camphors. Turpentine is readily oxidized by hydric nitrate, forming terebate, oxalate, and resinous bodies. 349. Camphor (C 10 H 16 O) is the common camphor of commerce. It is made from a laurel-tree, and is often called laurel-camphor. It has a density of 0.996, and it boils at 204. It dissolves to a very small extent in water, and undergoes during the process of solution a rotatory motion. In alcohol or ether it is readily soluble, also in fixed and volatile oils. When heated under pressure with potassic hydrate it unites with the alkali, forming a campholate C 10 H 16 O + H K O = C 10 H 17 K O 2 . Anhydrous phosphoric acid deprives it of water, liberating a hydrocarbon called cymene, or, by some authors, cymol C 10 H 16 O-H 2 O = C 10 H 14 . When boiled with strong hydric nitrate camphor is oxidized, forming camphorate C io H i6 O + 3 O=C 10 H 16 O 4 . Borneo camphor (C 30 H 18 O) is another compound which is sometimes found in commerce. It is deprived of two atoms of hydrogen by the action of nitrate, and converted into laurel-camphor. Anhydrous phosphoric acid liberates from it a hydrocarbon isomeric with turpentine, 443 TABLE I. Units of heat evolved by complete oxidation of one gramme of Hydrogen - - - - 34462 Charcoal 8080 Carbonic oxide - - - 2403 Sulphur (forming So 2 ) - 2220 Phosphorus - - - - 5747 Zinc 1330" Iron (forming Fe 2 O 3 ) - 1582 Tin 1147" Copper 603 TABLE II. Specific gravity, at i4C, of ammonia solutions of various strengths, from Carius' determinations. Sp.gr. Percent ". of r ammonia. Sp.gr. Percent '. of ammonia. Sp.gr. Percent '. of r ammonia. 0.8844 36.0 0.8885 34-0 0.8929 32.0 0-8953 3- 0.9026 28.0 0.9078 26.0 0.9133 24.0 0.9191 22.0 0.9251 -2O.O 0.9314 18.0 0.9380 16.0 0.9449 14.0 0.9520 12.O 0.9556 10.0 0.9670 8.0 0.9749 6.0 0.9831 40 0.9915 2.0 0.9959 i-o TABLE III. Percentage of sulphuric acid in hydrates of various densities at 15.5. (URE.) Sp. gr. Percent, of S O 3 . Sp gr. Percent. ofSO: Sp.gr. Percent. ofSO ; . 1.8460 81.54 1.6624 61.97 .4265 44-3 1.8415 79 9 1.6415 60.34 .4073 42.40 1.8366 78.28 1.6204 58.71 . 3 S8 4 40-77 1.8288 7665 T-5957 57.08 3697 39 J 4 1.8181 75-02 1.5760 55-45 3530 37-51 .8070 73-39 1.5503 53-82 3345 35-88 .7901 71.75 1.5280 52.18 .3165 34-25 .7728 70.12 i 5066 50.55 .2999 32.61 754 68.49 1.4860 48.92 .2826 30.98 i73*5 66.86 1.4660 47.29 .2654 29-35 .7080 65.23 1.4460 45.66 2490 27.22 .6860 63.60 444 SOLUTIONS TO THE PROBLEMS. 1. A kilogramme is equal to 1000 grammes, and inasmuch as 100 parts of chlorate contain 39.183 of oxygen, 1000 grammes must contain 391.83 of the gas. The proportion of oxygen evolved from potassic chlorate may be found by the equation which represents the decom- position, viz. KC1O 3 = K Cl + O 3 ; and by replacing these symbols by the weights which they respectively represent, we have 39 + 35.5-1-48, or 122.5, parts by weight of potassic chlorate yielding 74.5 parts by weight of potassic chloride and 48 parts by weight of oxygen, whence the proportion 122.5 : 48 : : 1000 : x = 391-83. 2. In order to calculate the weight of 100 litres of oxygen we have to recollect that one volume of the gas (or 11.2 litres) weighs 1 6 grammes, whence the proportion ii. 2 16 : : ioo : x weight of one volume number of litres weight re- of oxygen. given. quired. 1600 .-. # = -=: 142.85 grammes. 1 1.2 445 THE SOLUTIONS The remaining calculation is then similar to that in the last problem, viz. 39.183 : 100 : : 142.85 : x per-centage of oxygen weight of I oo litres weight of chlorate in chlorate. of oxygen. required. whence * = = 364.5; 122.5 x 142.85 or 48 : 122.5: : 142.85 : x; x=- -= 364.5 grms. 48 3. One litre of oxygen measured off at o becomes 1 + 15x0.003665= 1.054975 at 15, and inasmuch as the contraction on cooling is equal to the expansion on heating we have the proportion 1.054975 : i : : 30 : x bulk at 1 1; of a litre of c oxygen measured one litre. meai ! ure <* ox ^ en meas , ure re ' o ff at O o. g lven at I5- q^red at o". 3O /. x = - = 28.437. 1-054975 Using the vulgar fraction , we should have the proportion 288 : 273 : : 30 : x bulk at 15 of 273 parts ., of oxygen measured measured at o. bu ? ox 7g en bulk required, off at oo. g' ven " The 30 litres (30,000 cubic centimetres) therefore contract to 28437 cubic centimetres. 4. Inasmuch as the globe is to be filled with oxygen at the temperature of 1 2, it will require a smaller weight of gas than if filled at o. The weight of a volume of oxygen at 12 can be found from the proportion i + 12 x 0.003665 : i : : 16 : x\ /. x = -=15.326. 446 TO THE PROBLEMS. If n.2 litres of oxygen at 12 weigh 15.326 grammes, the weight of 1 3 litres of the gas is given by the proportion ii. 2 : 15.326 : : 13 : x; whence x = -^ = I 7-7 8 9 grammes. Another way of finding the required weight is to calculate first what sized globe full of oxygen at o would contain the same weight of gas as the globe of 13 litres capacity full of oxygen at 12. The capacity of this imaginary globe must be to that of the given globe in the same proportion as the volume of a given quantity of gas at o is to its volume at i2C. i + 12 x 0.003665 : i : : 13 : x\ 1 3 whence x= ' -- = 12.452 litres. 1.04398 The remaining calculation is the same as if the problem had been to calculate the weight of oxygen at oC needed to fill a globe of 12.452 litres capacity ii. 2 : 16 : : 12.452 : x\ 16 x 12.4^2 whence x = I ^-= 17.78. II. 2 5. The first operation must be to reduce the temperature quoted in Fahrenheit's degrees, to an equivalent value on the Centigrade scale. 14? is 18 degrees below 32F, the freezing-point of water ; and a range of 9 degrees on the Fahrenheit scale is equal to a range of 5 degrees on the Centigrade scale, so that the temperature at which the oxygen is measured off is ioC. The rise of temperature up to o expands the gas in such proportion that its volume at o is to its volume at 10 as i is to 1 0.03665; i.e. as i to 0.96335. The further rise of temperature from oC to 15 expands the gas in the proportion of i to 447 THE SOLUTIONS 1 + 15x0.003665; i.e. i to 1.054975. The total rise of temperature therefore expands the gas in the proportion of 0-96335 to 1.054975. o-9 6 335 : 1-054975 : : 10 : x; 10x1.054975 X - - = lO.Qfs. 0.96335 6. Let the reduction for change of temperature be made first. The proportion i + 14 x 0.003665 : i : : 230 : x 230 gives x = ~ --218.774. To reduce this volume at 740 millimetres pressure to the volume corresponding to the pressure of 760 millimetres, we have the proportion 38 : 37 : : 218.77 : x \ whence x = - = 213.02. 3 b 7. The volume of 43 grammes of oxygen at the normal temperature is found by the proportion 1 6 : 1 1. 2 : : 43 : x ; whence x = ^ --- = 30.1 litres. In order to find the volume which the gas occupies when cooled sufficiently to acquire a density of 18, we have the proportion 8 x 30.1 9:8:: 30.1 : x] .'. x= - = 26.75 litres. The temperature at which the gas will occupy this bulk is found by the proportion 30.1 : 26.75 : : i : i x 0.003665; 26.75-30.1, _ o .1103165 448 TO THE PROBLEMS. 8. . The required temperature is the same as if the oxygen had to be expanded in such proportion that 76 volumes be- came 150. The temperature necessary to do this is found by the proportion i : 1 + ^x0.003665 : : 76 : 150; whence x = = 265.6. 9. The oxygen is given at ioC and 820 millimetres pressure. If the pressure remained constant the rise of temperature from ioCto 3ooC would expand the gas in such proportion that 1.03665 volumes would expand to 2.0995 volumes. In order to prevent any expansion the pressure must be in- creased in the same proportion whence 1.03665 : 2.0995 : ' 82 : x '> 820x2.0995 .-. x = - - = 1660.6. 1.03665 From this total pressure the atmospheric pressure of 760 millimetres has to be deducted, leaving 900.6 millimetres as the height of the required mercurial column. 10. The pressure required to compress oxygen from the density of 1 6 to that of 100 is found by the proportion 76000 16 : 100 : : 760 : x\ .-. x = = 4750. At the pressure of 4750 millimetres of mercury the weight of a litre of oxygen is found by the proportion 16 760: 4750 : : \x\ 16 x 4750 whence x = '~- =8.93 grammes. ii. 2 x76o Gg 449 THE SOLUTIONS The weight of chlorate required for the evolution of 8.93 grammes of oxygen is found from the proportion 48 : 122.5 :: 8 -93 : *', ' x= 22.8 grammes. 11. One gramme of hydrogen measures 11.2 litres at oC, therefore 12 grammes measure 12 x 11.2 = 134.4 litres at o. To find their volume at i5C we have the proportion i : i + 15 x 0.003665 : : 134.4 : x\ whence x = 134.4 x 1.054975 - 141.788 litres. 12. Assuming 11.2 litres as the volume of one gramme of hydrogen at oC, the volume at i2C is 11.69 litres, and the number of grammes is found by dividing 100,000 litres by 11.69. We thus find 8554.4 grammes as the weight of the hydrogen. The volume occupied by the silk of the balloon is so small that it may be neglected, and the volume of air displaced may be taken as 100,000 litres, weighing 14.45 times as much as the hydrogen, or having 13-45x8554.4= 11505.868 grammes excess of weight over the hydrogen. If the balloon weigh 20 grammes less than this, or 115.056 kilogrammes, it will satisfy the requirements of the problem. 13. To expand air so that it may occupy the same volume as an equal weight of hydrogen, it must be heated according to the proportion i :i+ x 0.003665:: i:i445; * 14. Hydrogen combines with eight times its weight of oxygen ; therefore 2 grammes of hydrogen will take 16 grammes of oxygen from the cupric oxide, forming 18 grammes of water. TO THE PROBLEMS. 15. If 1 1. 2 litres of hydrogen weigh one gramme, 4 litres weigh 0.357. The loss of weight in the cupric oxide is eight times as great as the weight of hydrogen 8 x -357 = 2.856 grammes. The volume of oxygen needed is equal to that with which the hydrogen combines, viz. 2 litres. 16. 10 grammes of hydrogen measure 112 litres, and combine with 56 litres of oxygen. Assuming that air contains 20 per cent, of its volume of oxygen, 280 litres of air would be needed. 17. Assuming that air contains 20 per cent, of oxygen (less than the truth), there will be 20 cubic centimetres of oxygen in the air employed, and these combine with 40 cubic centi- metres of hydrogen, leaving 10 cubic centimetres of hydrogen mixed with 80 of nitrogen, or 90 cubic centimetres in all. 18. 10 litres of hydrogen combine with 5 litres of oxygen, and the weight of these at the normal temperature and pressure is found by the proportion 1 1. 2 : 16 : : 5 : x\ whence x = 7.143 grms. of oxygen. The weight of chlorate requisite for the evolution of 7.143 grammes of oxygen is found by a calculation similar to those in solutions 1 and 2 to be 18.226 grammes. 19. The heat of combustion of hydrogen is 34462, or in other words, one gramme of hydrogen evolves in burning enough heat to warm 34,462 grammes of water from oC to iC. 20,000 grammes only have to be so warmed 20000 34462 : i : : 20000 : x; .'. x = ^- = .580 grammes. 34402 Gg2 4 5I THE SOLUTIONS 20. Two-thirds of the volume of the oxy-hydrogen gas, or litres, consists of hydrogen. The weight of this is found (as in 15) to be nearly n.8 grammes. Multiplying this number by 34462 we obtain 406651.6 as the number of grammes of water required, or 406.6516 kilogrammes. 21. For every 102.7 volumes of ice floating in water 94 volumes of water are displaced. There are therefore 8.7 volumes of ice above water for every 94 immersed; so that the volume of ice above water is to the total bulk of the iceberg in the proportion of 8.7 to 102.7 whence 8.7 : 102.7 : : 30000 : x' y and x = 3541379.3 cubic metres. 22. 94 kilogrammes of ice measure 100 cubic decimetres, so that the bulk of 280 kilogrammes is found by the proportion 94 : 100 : : 280 : X] .'. x = 297.8. 23. At 7oC the tension of steam is found to be equal to a column of mercury 233.093 millimetres high. Its density is 9 at the atmospheric pressure of 760 millimetres, and: at the given pressure its density is found by the proportion 760 : 233.093 :: 9 : x; :. ^ = 2.76. It is, however, expanded by heating up to 70, and its density at this temperature is found by the proportion 1 + 70x0.003665 : i : : 2.892 : x\ .. x = 2.2 at 7oC. Similar calculations shew that 12.27 is tne theoretical density at i2OC. At i4oC it is 21.26; At i8oC it is 53.840. 452 TO THE PROBLEMS. 24. At 2OOC the volume of steam is found by the same cal- culation which is employed for permanent gases, and to find its density at that temperature the proportion must be reversed ; standing thus 1.7330 : i : : 9 \x\ .'. x = 5.20. 25. The tension of steam at i2C is not given in our table, but from the tensions at ioC and i5C it may be estimated at a little over 10 millimetres. The mixture of steam and air in the room has a total tension of 760 millimetres, and the volume of the mixture would by the removal of the steam be reduced in the proportion of 76 volumes for every 77 ; whence the pro- portion 77 : 76 : : 80 : x ; /. x = 78.956 cubic metres. 26. The tension of steam at 100 is 760, and this added to the tension of the air with which it mixes gives us 1520 milli- metres as the measure of the tension of the moist air. 27. In order to get one volume of steam to every two volumes of air we must have the water at the temperature at which it exerts a tension half as great as the atmospheric pressure ; i. e. equal to 380 millimetres. The table shews that the tem- perature must be between 8oC and 85C, and near to 82C. 28. TOO volumes of water dissolve 1.93 volumes of hydrogen, so that 30 cubic metres dissolve 0.579 cubic metres, or 579 litres. At the normal pressure and temperature 11.2 litres of hydrogen weigh one gramme, and accordingly at 7600 they weigh 10 grammes. n.2 : 10 : : 579 : .r; /. x = 517 grammes, 453 THE SOLUTIONS and this weight corrected for temperature gives us 498.7 grammes. 29. We must first ascertain the weight of oxygen given by the proportion 1 1. 2 : 1 6 : : 4000 : x\ :. x = 5714 grammes. Each kilogramme absorbs .2182 when heated iC, or 21.82 when heated 100; and accordingly the four cubic metres absorb 21.82x5.714 = 124.67948. 30. The requisite quantity of heat must first be calculated by multiplying the rise of temperature reckoned in degrees (80) given by .4805, and the product by the number (100) of kilogrammes of steam. 3844 is the quantity of heat to be evolved by combustion of hydrogen : 34462 : i : : 384.4 : x\ 0.0115 kilos, is 111.5 grms. 31. One kilogramme gives off 300 x 3.4046, or 1021.38, on cooling from 300 to o : 90 grammes therefore give off 91.9242. 32. The increase of volume which the 11,190 litres of hydrogen undergo must first be calculated. Their volume at 100 is found by the usual calculation to be 15291.135 litres; so that the increase of volume amounts to 4101.135 litres. This increase of volume may be represented as due to the raising of a weight of 103.3 kilogrammes to a height of 4101.135 decimetres, or 410.1135 metres. The product of these two numbers, viz. 42364.72455, represents in metre kilogrammes the work done. 33. I OOOO Ten thousand metre kilogrammes of work evolve - 423.6 = 23.6 degrees of heat. TO THE PROBLEMS. 34. The quantity of heat described is 17231, and this number has to be multiplied by 423.6 in order to find the work equivalent to it, viz. 7299051.6 metre kilogrammes. 35. For 1 50 Regnault's formula gives us 606.5+ 150 x. 305, or 652.25; for 250, in like manner, 682.750; and for 50, in like manner, 621.75. 36. A litre of ice weighs only 940 grammes ; so that 1,100,000 Itres weigh 1,034,000 kilogrammes. Each kilogramme ab- SDrbsSo in melting; so that 82,720,000 of heat are needed. 37. The question requires us to find the weight of saturated steam which will give off 80 on cooling to o. A kilo- gramme of the steam evolves 637 on cooling to oC : 125.6 jrammes are therefore needed. 38. Each kilogramme of oxygen gives off 2i.82. 10 kilo- g-ammes therefore give off 2i8.2. By dividing this number b 7 80 we find the number of kilogrammes of ice which this qiantity of heat can melt; viz. 2.7275. 39. In an extensible vessel at constant pressure the gas would aborb 21.82; but if heated at constant volume it will , 21.82 aborb 15.4 40. I we neglect the volume of the water, the work may be represented by the movement of a piston of a square area throigh a length of 100 metres against the atmospheric presure, or 1,033,000 metre kilogrammes. To allow for the 455 THE SOLUTIONS volume of the water formed by condensation of the steam, we may ascertain the relative densities of water and steam at 100 from their relative densities at o: viz. 11.19 litres of steam at o^ weigh 9 grammes, and 11.19 litres of water at o weigh nearly 11.19 kilogrammes, or 11,190 grammes. The expansion of water and of steam between o and IOCT are also given. In round numbers we may however assume that the water occupies - - the volume of the steam formed from it. This correction would give for our work the value 1749 x 1033000 41. (1) Two atoms of chlorine (weighing together 71) decom- pose a molecule of water (weighing 18), forming a molecule of a compound (weighing 36.1), and containing one atom of chlorine combined with one atom of hydrogen ; and at the same time a molecule of a compound weighing 52.5 and containing one atom of chlorine combined with one of hydrogen and one of oxygen. (2) A molecule (weighing 208) containing an atom d barium combined with two atoms of chlorine, when addei to a molecule (weighing 98) containing two atoms