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CHEMISTRY 
 
 INORGANIC AND ORGANIC 
 
 WITH EXPERIMENTS 
 
 AND 
 
 A COMPARISON OF EQUIVALENT AND MOLECULAR 
 FORMULA. 
 
 BY 
 
 CHARLES LOUDON BLOXAM, 
 
 PROFESSOR OF PR.VCTICA.L CHEMISTRY IN KINO'S COLLEGE, LONDON; PROFESSOR OF CHEMISTRY IN THE 
 
 LONDON : 
 JOHN CHURCHILL & SONS, NEW BURLINGTON STREET. 
 
 MDCCCLXVII. 
 
NEILL AND COMPANY, PRINTERS EDINBURGH. 
 
PREFACE. 
 
 AT the present time, when there is so much difference of opinion as 
 to the clearest mode of representing the constitution of chemical 
 compounds and the changes in which they are involved, the author 
 of a work on Chemistry is placed in a difficult position. Fully 
 realising this, I should scarcely have ventured to undertake the 
 task, but for the circumstance that, a third edition of "Abel and 
 Bloxarn's Handbook of Chemistry" being required, and my valued 
 coadjutor not having leisure to devote to its preparation, it seemed 
 to me a favourable opportunity for re-writing the handbook in such 
 a form as to render it more useful to the general student. 
 
 The present work, therefore, is designed to give a clear and simple 
 description of the elements and their principal compounds, and of 
 the chemical principles involved in some of the most important 
 branches of manufacture. Keeping this in view, I have employed 
 as few technical terms as possible, especially at the commencement, 
 so that the student may glide into Chemistry without having first to 
 toil through a difficult chapter on the terminology of the science, 
 which he can never appreciate until he has become acquainted with 
 the examples which serve to illustrate its application. 
 
 Convinced, by experience, of the great assistance afforded to the 
 learner by referring him to a simple illustrative experiment, I have 
 introduced, generally in smaller type, a description, and in most 
 cases a wood-engraving,* of the experiments which I have found 
 most useful in illustrating lectures, hoping that these may prove of 
 
 * These were drawn by Mr 'Ceilings and engraved by Mr Hart, to whom I feel much 
 indebted for their patient endeavours to represent faithfully the various forms of apparatus. 
 
iv PREFACE. 
 
 service in fixing the attention of the student, and may assist those 
 who are desirous of performing such experiments for their own 
 instruction, or for that of a class. 
 
 In explaining chemical changes by equations, I have, as a general 
 rule, employed symbols representing combining weights (or equi- 
 valents), and not atoms, of the elements. Had the work been in- 
 tended for advanced students, I should have hesitated- to incur the 
 reproach of obstinate conservatism, or of being behind the chemical 
 spirit of the time, though even then, which of the more advanced 
 systems was to be adopted would have been a very formidable 
 question, for at present the different modes of representing chemical 
 changes are almost as numerous as chemical writers. 
 
 When the atomic or molecular system of notation affords a clearer 
 explanation, I have endeavoured to give the student the benefit of 
 it, and this of course occurs most frequently in the department of 
 Organic Chemistry, where the elements concerned in the formation 
 of compounds are few, and atomic constitution becomes of greater 
 importance. In such cases I have represented the atoms of elements 
 by the barred symbols (6, 6, &c.), and have adopted essentially the 
 same atomic and molecular formulae as have been employed by my 
 colleague, Professor Miller, in the later editions of his " Elements of 
 Chemistry." * 
 
 In general, English weights and measures, and Fahrenheit ther- 
 mometric degrees, have been employed, as conveying more clearly 
 to the beginner the absolute values expressed, since the mental 
 effort of converting what must still be called the continental 
 systems, slight though it be, might have the effect of diverting the 
 attention of the reader from the chemical question under considera- 
 tion. The various calculations have been conducted in the simplest 
 arithmetical form, because the more compendious algebraical expres- 
 sions are not so generally intelligible, and when the principle is 
 once understood, a general algebraical formula for the calculation 
 is easily constructed by the learner. 
 
 The special attention devoted to Metallurgy and some other 
 
 * I must confess myself under heavy obligation to Dr Miller's splendid volume on 
 Organic Chemistry, the luminous summaries which it contains having frequently spared me 
 the trouble of referring to the original memoirs. 
 
PREFACE. . V 
 
 branches of Applied Chemistry, will render the work useful to those 
 who are being educated for employment in manufacture. 
 
 The military student will find more than the usual space allotted 
 to the chemistry of the various substances employed in warlike 
 stores. 
 
 In fine, it has been my endeavour to produce a Treatise on 
 Chemistry sufficiently comprehensive for those studying the science 
 as a branch of general education, and one which a student may 
 peruse with advantage before commencing his chemical studies at 
 one of the colleges or medical schools, where he will abandon it for 
 the more advanced work placed in his hands by the professor. I 
 am not without hope that this book may also be found useful in 
 enabling the student who has acquired his knowledge of Chemistry 
 with the help of the older system of notation in equivalents, to pass, 
 should he deem it advisable, by an easy transition, into the use of 
 atomic symbols and unitary formulae. 
 
 C. L. B. 
 
 WOOLWICH, January 1867. 
 
 *^* In the following pages, the smaller type contains not only 
 the descriptions of experiments, but all such matter as would be of 
 less importance to a student desiring only a general knowledge of 
 the subject without going into details. 
 
TABLE OF CONTENTS. 
 
 Paragraph 
 
 INTRODUCTION. DEFINITIONS, ..... 1 
 Enumeration and classification of elements, with their symbols and 
 
 combining weights, . . . . .2 
 
 Classification of compounds into organic and inorganic, . . 3 
 
 CHEMISTRY OF THE NON-METALLIC ELEMENTS. 
 
 OXYGEN. Its occurrence in nature, ..... 4 
 
 Physical properties of oxygen. Specific gravity of gases defined, . 5 
 
 Chemical properties of oxygen. Combustion, ... 6 
 
 Relations of oxygen to phosphorus ; effects of heat and minute divi- 
 sion upon chemical attraction ; nature of acids, . . 7 
 Relations of oxygen to sulphur, ..... 8 
 
 Relations of oxygen to carbon, . . .,,,'. .9 
 
 Etymology of oxygen, . . . . . .10 
 
 Relations of oxygen to the metals ; sodium and oxygen ; nature of 
 alkalies; meaning of neutralisation; combining weights of com- 
 pounds ; definition of an acid, . . . . .11 
 
 Relations of oxygen to zinc ; definition of base, salt, salt-radical, . 12 
 Relations of oxygen to iron ; naming of oxides to indicate their com- 
 position ; definition of a metal, . . . . .13 
 
 Indifferent oxides ; relation between composition and properties of the 
 
 oxides of a metal, . . . . . .14 
 
 Preparation of oxygen from oxide of mercury, . . .15 
 
 binoxide of manganese, . . .16 
 
 chlorate of potash ; calculation of the 
 
 weight of a given volume of gas, . . . .17 
 
 Ozone. Its production by electric discharge through air or oxygen ; 
 formation by slow oxidation of phosphorus and ether in air ; its 
 presence in the atmosphere ; its reconversion into ordinary oxygen 
 by heat, . . . . . . 18 
 
 Atmospheric air. Its composition; rough demonstration of the pro- 
 portions of oxygen and nitrogen by phosphorus ; exact analysis of 
 air by copper, ....... 19 
 
 Air a mixture, not a chemical compound ; functions of the nitrogen 
 in air ; uniform composition of the atmosphere maintained by 
 diffusion, . . . . . . .20 
 
viii CONTENTS. 
 
 Paragraph 
 
 HYDROGEN. Its occurrence in nature ; analysis of water by the galvanic 
 
 battery ; construction of Grove's battery, . . . .21 
 
 Electrolysis ; electro-positive and electro-negative elements, . . 22 
 
 Relative volumes of hydrogen and oxygen in water ; difference in ap- 
 plication of electricity according to quantity and intensity, . 23 
 Decomposition of steam into detonating gas by electric sparks, .. 24 
 Disengagement of hydrogen from water by metals ; definition of 
 chemical equivalent of a metal; action of potassium and sodium 
 on water ; classification of metals according to their action upon 
 water, . . . . . . . . 25 
 
 Preparation of hydrogen by action of red-hot iron upon steam ; by 
 
 action of zinc or iron upon diluted sulphuric acid, . .26 
 
 Physical properties of hydrogen ; its value as a theoretical unit of 
 
 volume ; illustrations of its extreme lightness, . . . 27 
 
 Diffusibility of gases defined and illustrated ; separation of hydrogen 
 and oxygen by atmolysis; law of the velocities of diffusion. 
 Graham's experiments with air ; mode of doubling the percentage 
 of oxygen, ........ 28 
 
 Chemical properties of hydrogen ; character of its flame, ^. . 29 
 
 Explosive mixtures of hydrogen with air and oxygen, ^ . . . . , . 30 
 
 Synthesis of water in the eudiometer, . ',' . . 31 
 
 Eudiometric analysis of air, . . . ; . 32 
 
 Calculation of the specific gravity of steam, . '; . . 33 
 
 Combining volumes of oxygen and hydrogen, . ' . >,.. 34 
 
 Atomic theory; comparison between the atomic and equivalent formulae 
 
 of water ; atomic heats, .... - *,: '*;.. 35 
 
 Combining volumes of gases and vapours, . . * .*- . 36 
 
 Oxyhydrogen blowpipe ; fusion of platinum ; lime-light, . . 37 
 
 Chemical relations of hydrogen contrasted with those of oxygen, . 38 
 Water from various natural sources; air dissolved in water, . . 39 
 
 Saline components of natural waters ; hardness ; boiler incrustations ; 
 petrifying springs ; stalactites ; processes for softening waters ; 
 temporary and- permanent hardness ; organic matter in waters, . 40 
 Action of water upon leaden cisterns and pipes. Mineral waters, . 41 
 Sea-water, ........ 42 
 
 Purification of water by distillation ; the still and worm ; Liebig's 
 
 condenser, . . . . . . .43 
 
 Physical properties of water ; specific gravity of liquids and solids 
 
 defined ; definition of boiling-point, . . . 44 
 
 Chemical relations of water ; hydrates ; nature of simple solution ; 
 
 crystallisation from, water ; super-saturated solutions, . . 45 
 
 Efflorescence ; water of crystallisation and water of constitution of 
 
 salts ; deliquescence, . . / < ', . . 46 
 
 Hydrated bases ; unitary view of the alkaline hydrates, . . 47 
 
 Hydrated acids ; unitary view of hydrated sulphuric acid, . . .48 
 
 Binoxide of hydrogen. Its preparation and properties ; decomposition 
 by contact ; positive and negative oxygen ; Molecules; molecular 
 formulce ; atom and molecule defined ; nature of ozone ; antozone, 49 
 
 CARBON. Its natural varieties ; demonstration of the nature of diamond ; 
 
 exact synthesis of carbonic acid ; graphite ; its useful applications, . 50 
 Artificial varieties of carbon ; lamp-black, wood-charcoal ; destructive 
 
CONTP;NTS. ix 
 
 Paragraph 
 
 distillation defined ; charcoal-burning ; decolorisation and deodor- 
 isation by charcoal ; animal charcoal ; calorific value of carbon, . 51 
 Coal. Chemistry of its formation ; composition and special uses of lig- 
 nite, bituminous coal and anthracite, . . . .52 
 
 Oxides of carbon ; their composition by weight, . . .53 
 
 Carbonic acid. Sources of atmospheric carbonic acid ; respiration ; fer- 
 mentation ; decomposition of carbonic acid by plants, . . 54 
 Occurrence of carbonic acid in the mineral kingdom ; preparation of 
 
 carbonic acid, ....... 55 
 
 Properties of carbonic acid ; illustrations of its high specific gravity and 
 power of extinguishing flame ; limit to combustion of a taper in 
 confined air ; limit to respiration of animals in confined air ; 
 noxious effects of carbonic acid ; principles of ventilation ; solu- 
 bility of carbonic acid in water ; sparkling drinks ; importance of 
 dissolved carbonic acid to plants, . . . .56 
 
 Liquefaction of carbonic acid in glass tubes, . . . .57 
 
 Separation of carbonic acid from other gases, . . . .58 
 
 Ultimate analysis of organic substances ; calculation of formula exem- 
 plified ; empirical and rational formulae, . . . .59 
 
 Salts formed by carbonic acid. Table of the commonest carbonates, 
 
 with their common names, equivalent and atomic unitary formulae, 60 
 Analytical proof of the composition of carbonic acid, . . .61 
 
 Carbonic oxide. Its formation in fires and furnaces ; its poisonous cha- 
 racter, ........ 62 
 
 Formation of carbonic oxide by passing steam over red-hot carbon ; its 
 
 useful applications, ...... 63 
 
 Carbonic oxide compared with carbonic acid, . . .64 
 
 Preparation of carbonic oxide ; from oxalic acid ; from ferrocyanide of 
 
 potassium, ....... 65 
 
 Reduction of metallic oxides by carbonic oxide ; preparation of pyro- 
 
 phoric iron, ....... 66 
 
 Composition by volume "of carbonic oxide and carbonic acid ; calcula- 
 tion of the specific gravity of carbon vapour, . . .67 
 Combining weight of carbonic acid ; tabular view of the equivalent 
 weight, volume, and composition of carbonic oxide and carbonic 
 acid, ........ 68 
 
 Atomic weight of carbon ; tabular view of the molecular weight, volume, 
 
 and composition of carbonic oxide and carbonic acid, . . 69 
 
 Compounds of carbon and hydrogen ; equivalent and molecular formula) 
 
 of acetylene, marsh-gas, and olefiant gas, . . . .70 
 
 A cetylene. Its production by direct synthesis ; its preparation in quantity 
 by the imperfect combustion of coal-gas ; new radicals derived from 
 acetylene ; cupros-acetyle, argent-acetyle ; fulminating oxide " of 
 argent-acetyle ; remarkable properties of acetylene ; formation of 
 styrole by action of heat upon acetylene, . . . 71 
 
 Olefiant gas. Its preparation and properties ; formation of Dutch liquid ; 
 
 production of acetylene from olefiant gas by the spark-discharge, . 72 
 Marsh-gas. Its occurrence in nature ; fire-damp ; preparation and pro- 
 perties of marsh-gas ; chemistry of explosions in coal-mines ; safety- 
 lamps, ........ 73 
 
 Structure of flame ; cause of luminosity in ordinary flames ; experiments 
 
X CONTENTS. 
 
 Paragraph 
 
 illustrating the structure of flame ; influence of the supply of air 
 upon the character of flames ; smokeless gas-burners ; effect of 
 atmospheric pressure upon the luminosity of flames ; composition 
 of illuminating fuels, . . . . - 74 
 
 The Uowpipe flame. Functions of its different parts ; reduction of metals 
 
 by the blowpipe, on charcoal, . . . ;* 75 
 
 Eudiometric analysis of marsh-gas. Table of the composition by volume 
 
 of acetylene, marsh-gas, and olefiant gas, . . . .76 
 
 Coal-gas. Products of the distillation of coal, . . . .77 
 
 SILICON. Its occurrence as silica in nature ; conversion of silica into a 
 soluble form ; preparation of pure silica by dialysis ; crystallised and 
 amorphous silica, . . . :. .. v J > . 78 
 
 Apparatus for effecting fusions in the laboratory, '. . . . ' 79 
 
 Silicates; bibasic character of silicic acid, .: . .-*.' , 80 
 
 Preparation and properties of silicon ; amorphous, graphitoid, and 
 adamantine silicon ; comparison of silicon with carbon ; hydride of 
 silicon ; combining weight and atomic weight of silicon ; atomic 
 formula of silicic acid, . . . . ." '.> 81 
 
 BORON Boracic acid ; its extraction from the soffioni ; properties of boracic 
 
 acid; borates, . . . . . .' i 82 
 
 Extraction of boron from boracic acid ; amorphous, graphitoid, and 
 diamond boron ; combining weight of boron ; atomic formula of 
 boracic anhydride, . . . . -. * .83 
 
 Review of carbon, boron, and silicon, . . * . . .<*. 84 
 
 NITROGEN. Its occurrence in nature and preparation from air ; inert cha- 
 racter of the element, and activity of its compounds, . V' - . 85 
 Ammonia. An important medium of circulation for nitrogen ; extraction 
 from the ammoniacal liquor of the gas-works ; sublimation ; pre- 
 paration of ammonia gas ; solution of ammonia ; mode of ascer- 
 taining its strength ; liquefaction of ammonia ; Carry's refrigerator ; 
 combination of ammonia with acids ; the ammonium- theory ; for- 
 mation of ammonium-amalgam, . . . .86 
 
 Combining weight and volume of ammonia, . . . .87 
 
 Combining weight and volume of nitrogen ; molecular formula of am- 
 monia ; tabular view of composition of ammonia, . . 88 
 Process for ascertaining the proportion of nitrogen in an organic sub- 
 stance ; calculation of the formula of urea, . . .89 
 Formation of ammonia in the rusting of iron ; nascent state of elements, 90 
 Production of nitrous and nitric acids from ammonia ; nitrification ; 
 
 formation of nitrates in nature, . . . . ; . , 91 
 
 Compounds of nitrogen and oxygen, . . . _ -*.'.' . 92 
 
 Nitric acid. Preparation in the laboratory and on the large scale ; pro- 
 perties of nitric acid ; its action upon metals and organic substances, 93 
 Oxidising effects of nitrates. Combining weight and unitary formula 
 of nitric acid. Table of the chief nitrates with their common 
 names, and equivalent and atomic formulae, . . .94 
 
 Anhydrous nitric acid or nitric anhydride, . . . .95 
 
 Nitrous oxide, . . . . . . . .96 
 
 Nitric oxide ; rough analysis of air by nitric oxide, . . .97 
 
 Nitrous acid ; preparation of nitrite of potash, . . .98 
 
 Nitric peroxide ; commercial nitrous acid, . . .99 
 
CONTENTS. xi 
 
 Paragraph 
 
 General review of the oxides of nitrogen ; combination in multiple pro 
 portions ; determination of the composition of the oxides of 
 nitrogen ; tabular review of their composition by weight and 
 volume ; their atomic constitution and formulae, . . .100 
 
 CHLORINE. Its occurrence in nature and extraction from common salt ; 
 striking physical and chemical properties ; powerful attraction for non- 
 metallic and metallic elements, . . . . .101 
 
 Relations of chlorine to hydrogen ; synthesis of hydrochloric acid 
 effected by natural and artificial light ; displacement of oxygen 
 from water by chlorine ; action of chlorine upon other hydrogen- 
 compounds ; substitution of chlorine for hydrogen in organic sub- 
 stances ; oxidising action of moist chlorine, . . .102 
 Bleaching properties of chlorine ; their application, . . .103 
 Chloride of lime. Mode of using it for bleaching, and for printing white 
 patterns on a coloured ground ; disinfecting properties of chlorine ; 
 application of chloride of lime for disinfecting, . . .104 
 History of the discovery of chlorine ; phlogiston, . . .105 
 Hydrochloric acid. Preparation and properties of the gas ; production 
 of solution of hydrochloric acid in the alkali works. Weak acid 
 properties of liquefied hydrochloric acid, . . -. .106 
 Action of hydrochloric acid upon metals ; demonstration of its com- 
 position by volume, . . . . . .107 
 
 Action of hydrochloric acid upon metallic oxides ; formation of 
 
 chlorides, . . . . . . .108 
 
 Equivalent weights of hydrochloric acid and of chlorine ; molecular 
 
 formula of hydrochloric acid, . . . . .108 
 
 Types of atomic formulae; atomicity of the elements. Molecules of hy- 
 drochloric acid, water, ammonia, and marsh-gas ; monad, dyad, triad, 
 and tetrad elements ; graphical representation of atoms, . . 110 
 
 Compounds of chlorine with oxygen ; tabular view of their composi- 
 tion by weight, . . . . . . .111 
 
 Hypochlorous acid. Its use for erasing ink ; the hypochlorites ; prepara- 
 tion of oxygen from chloride of lime. Chloride of soda, . . 112 
 Chloric acid. Chlorate of potash ; preparation ; from carbonate of 
 potash ; from chloride of potassium. Preparation and properties 
 of hydrated chloric acid. Useful applications of chlorate of potash. 
 Combustion of chlorate of potash in coal-gas. Coloured fire com- 
 positions. Anomalous evolution of heat in the decomposition of 
 chlorate of potash, . . . . . . .113 
 
 Perchloric acid Explosive properties of the hydrated acid, . 1 14 
 
 Chloric peroxide. Its unstable character and powerful oxidising action. 
 
 JBuchlorine, . . . . . . .115 
 
 Chlorous acid, . . . . . . . ~. 116 
 
 General review of the oxides of chlorine ; their composition by volume ; 
 unitary view of the hypochlorites, chlorites, chlorates, and per- 
 chlorates, . . . . . . .117 
 
 Chlorides of carbon. Preparation of the bichloride or tetrachloride. 
 Composition by volume of the chlorides of carbon. Influence of 
 the composition by volume of a compound upon its properties. 
 Molecular formula) of the chlorides of carbon ; table of their 
 equivalent and molecular formula?, weights and volumes, . . 118 
 
xii CONTENTS. 
 
 Paragraph 
 
 Phosgene gas or oxychloride of carbon, . -. . . .119 
 
 Chloride of silicon. Tetsatomic character of silicon. Chloride of 
 
 boron, ... . - 120 
 
 Chloride of nitrogen. Processes for preparing it ; violent explosive 
 
 character, . .... -.-> 121 
 
 Aqua regia.ChloTonitnc and chloronitrous gases, . . .:, 122 
 
 BROMINE. Extraction from the waters of mineral springs ; great chemical 
 
 resemblance to chlorine ; liypobromous and bromic acids, . .123 
 
 Hydrobromic acid. Bromide of nitrogen. Chloride of bromine, . 124 
 
 IODINE. Extraction from ashes of sea- weed. Characteristic properties of 
 
 iodine and the iodides, . V. 6 * - '. . * 125 
 
 lodic acid. Periodic acid, . .-, . > *.> * . 126 
 
 Hydriodic acid. Its powerful reducing properties, 7.>. . ; ~. 127 
 
 Iodide of nitrogen. Explosive character, ;;,.,:, . .-. , . i. 128 
 
 Chlorides and bromides of iodine, . . , , , * , ... 129 
 
 Iodide of potassium. Its preparation. Iodide of iron, ... ; :. 130 
 
 FLUORINE. Fluorspar, . .... . : j-/.*.- '... . 131 
 
 H ydrofluoric acid; etching on glass. Fluorides; kryolite, -.\~ \ . 132 
 Fluoride of silicon', artificial formation of staurolite, . ..i .' : ; 133 
 
 Hydrofluo silicic acid, . . . . . ; . 134 
 
 Fluoride of boron; fluoboric and hydrofluoboric acids, . .- . -. : 135 
 
 General review of chlorine, bromine, iodine, and fluorine, <; <. . 136 
 SULPHUR. Its occurrence in nature; composition of the principal sulphides 
 and sulphates found in the mineral kingdom. Extraction of sulphur 
 in Sicily. Kenning of sulphur. Distillation of sulphur from pyrites. 
 Commercial varieties of sulphur, . . . . o'i. 137 
 
 Properties of sulphur ; remarkable transformation by heat ; electro- 
 positive and electro-negative sulphur ; soluble and insoluble 
 varieties ; octahedral and prismatic sulphur ; table of the chief allo- 
 tropic forms of sulphur, . . . . . .138 
 
 Hydro sulphuric acid. Its preparation for laboratory use ; preparation of 
 sulphide of iron. Properties of sulphuretted hydrogen ; action upon 
 metals and their oxides ; blackening of paint, pictures, &c., by im- 
 pure air ; use of sulphuretted hydrogen in analysis ; sulphur acids, 
 bases and salts ; action of air upon metallic sulphides, . .139 
 
 Composition of hydrosulphuric acid by weight and volume ; its mole- 
 cular formula, . . . . . . .140 
 
 Influence of temperature upon the specific gravity of gases and 
 
 vapours ; anomalous expansion of sulphur vapour, . v :'!.' 141 
 
 Persulphide of hydrogen, . . . . . . . 142 
 
 Compounds of sulphur with oxygen, . . ./, K , ; , 143 
 
 Sulphurous acid. Its bleaching and antiseptic properties. Sulphite of 
 
 soda, . . .144 
 
 Composition of sulphurous acid by weight and volume ; molecular 
 
 formula of sulphurous acid ; sulphurous anhydride, . . 145 
 
 Sulphuric acid. Direct combination of sulphurous acid and oxygen ; 
 Nordhausen oil of vitriol ; preparation of anhydrous sulphuric acid ; 
 gradual development of the English manufacture of oil of vitriol ; 
 experiments illustrating the theory of the process ; preparation of 
 oil of vitriol in the laboratory and on the large scale ; plan for 
 economising nitric oxide ; commercial A-arieties of sulphuric acid. 
 
CONTENTS. xiii 
 
 Paragraph 
 
 Properties of oil of vitriol ; its action upon organic substances and 
 upon metals. Other hydrates of sulphuric acid. Composition of 
 oil of vitriol by weight and volume. Molecular formula of oil of 
 vitriol ; its exceptional molecular volume, . . . .146 
 
 Sulphuric anhydride, . . . . . . .147 
 
 Sulphates. Action of sulphuric acid upon metallic oxides. Neutral, 
 acid, and double sulphates. Decomposition of sulphates by heat 
 and by reducing agents. Table of the chief sulphates, with their 
 common names, and equivalent and atomic formulae. Bibasic 
 character of sulphuric acid, ..... 148 
 
 Hyposulphurous acid. Hyposulphite of soda ; its preparation and use 
 for fixing photographic prints, and for making antimony vermilion. 
 Atomic formula of hyposulphite of soda, . . . .149 
 
 Hypo sulphuric or dithionic acid, . . . . .150 
 
 Trithionic or sulphuretted hyposulphuric acid, . . . .151 
 
 Tetrathionic or bisulphuretted hyposulphuric acid, . . .152 
 
 Pentathionic acid, . . . . . . .153 
 
 Bisulphide of carbon. Its use in spectrum analysis ; its diathermanous 
 character, resistance to congelation, and inflammability ; a starting 
 point for the synthesis of organic compounds. Sulphocarbonates. 
 Removal of bisulphide of carbon from coal-gas. Composition and 
 molecular formula of bisulphide of carbon, . . . .154 
 
 Bisulphide of silicon, .... 155 
 
 Bisulphide of nitrogen. Its explosive character, . . ] 56 
 
 Chlorides of sulphur. Preparation of the subchloride or dichloride of 
 sulphur ; its composition by volume and molecular formula. Iodides 
 of sulphur, ....... 157 
 
 SELENIUM. Its extraction from the deposit in the vitriol chambers. 
 . Selenious and selenic acids. Selenietted hydrogen. Chlorides and 
 . sulphides of selenium, . . . . . .158 
 
 TELLURIUM. Tellurous and telluric acids ; telluretted hydrogen ; chlorides 
 
 and sulphides of tellurium, . . . . . .159 
 
 Review of the sulphur group of elements, comprising sulphur, selenium, 
 
 and tellurium, . . . . . . .160 
 
 PHOSPHORUS. Its distribution in nature ; extraction from bones on the 
 large and small scales ; action of light on phosphorus. Phos- 
 phorescence. Allotropic modifications of phosphorus. Preparation 
 of red phosphorus. Precipitation of metals by phosphorus, . . 161 
 
 Lucifer matches ; silent matches ; safety matches, . . .162 
 
 Armstrong fuze composition, . . . . . .163 
 
 Oxides of phosphorus. Table of their composition, . . .164 
 
 Phosphoric acid. Its natural sources ; preparation from bones. Phos; 
 phoric anhydride. Metaphosphoric, pyrophosphoric, and ortho- 
 phosphoric acids, . . . . . . .165 
 
 Phosphorous acid; phosphites, . . . . . .166 
 
 Hypophosphorous acid, . . . . . .167 
 
 Suboxide of phosphorus. Combustion of phosphorus under water, . 168 
 Phosphides of hydrogen. Preparation and properties of phosphuretted 
 
 hydrogen gas, . . . . . . .169 
 
 Composition of gaseous phosphuretted hydrogen ; its molecular 
 
 formula. Atomic weight of phosphorus, . . .170 
 
xiv CONTENTS. 
 
 Paragraph 
 
 Chlorides of phosphorus. Oxychloride, and sulphochloride of phos- 
 phorus ; sulphoxyphosphate of soda. Action of iodine on phos- 
 phorus, .... ... 171 
 
 Sulphides of phosphorus, . ... 172 
 
 Action of ammonia upon phosphoric anhydride. Phosphamic acid. 
 Phospham. Action of ammonia on oxychloride and penta- 
 chloride of phosphorus. Amides of phosphoric acid, . .173 
 
 ARSEN re. Formulae of natural arsenides and arseniosulphides. Extraction 
 
 of arsenic from mispickel. Properties and chemical relations of arsenic, 174 
 Oxides of arsenic. Arsenious acid. Composition of arsenious and 
 arsenic acids. Molecular formula of arsenious acid. Its basicity. 
 Arsenites. Scheele's green, > . . . . 175 
 
 Arsenic acid. Its hydrates. Arseniate of soda, . . . 176 
 
 Arsenietted hydrogen. Marsh's test for arsenic. Composition and mole- 
 cular formula of arsenietted hydrogen. General review of ammonia, 
 phosphuretted and arsenietted hydrogen, . . v. 177 
 
 Terchloride of arsenic. Terbromide of arsenic, . . . .178 
 
 Teriodide and terfluoride of arsenic, . . . . .179 
 
 Sulphides of arsenic. Eealgar. King's yellow. Sulpharsenious and 
 
 sulpharsenic acids, . . . > . '; , < . 180 
 
 GENERAL REVIEW OF THE NON-METALLIC ELEMENTS. Classification accord- 
 ing to their atomicities. Elucidation of the constitution of compound 
 bodies by the doctrine of atomicity, . . . . .181 
 
 CONSTITUTION OF SALTS. Haloid and oxy-acid Salts. Difference between 
 neutral and normal salts. Criterion of normality. Normal ratios. 
 Binary theory of salts. Water-type theory. Constitution of poly- 
 basic acids and their salts, . . . . .182 
 
 CHEMISTKY OF THE METALS. 
 
 POTASSIUM. Its occurrence in nature. Carbonate of potash. Hydrate of 
 potash. Extraction of potassium. Blowpipe test for potassium. 
 Chloride of potassium. Bicarbonate of potash. Equivalent and 
 atomic weights of potassium, . . . . . .183 
 
 SODIUM. Extraction of salt. Salt-gardens of Marseilles, . .184 
 
 Manufacture of carbonate of soda from common salt. Soda-ash. 
 
 Soda-crystals. Soda- lye. Hydrate of soda, . . .185 
 
 Extraction of sodium from the carbonate. Uses of sodium, . .186 
 
 Borax. Refining of tincal. Crystallisation of borax, . . 187 
 
 Silicate of soda. Soluble glass. Artificial stone. Sulphate of soda. 
 
 Phosphate of soda. Equivalent and atomic weights of sodium, . 188 
 SALTS OF AMMONIA. Sulphate, carbonates, and hydrochlorate of ammonia. 
 Exceptional composition by volume of sal-ammoniac. Hydrosulphate 
 of ammonia. 
 
 Lithium. Lepidolite, petalite, spodumene. Lithia. Carbonate of 
 lithia. Rubidium. Ccesium. Spectrum analysis. Construction 
 of the spectroscope, . . . . . 1 89 
 
 General review of the group of alkali-metals, . . .190 
 
 BARIUM. Preparation of barium-compounds from heavy spar. Nitrate 
 and hydrate of baryta. Binoxide and chloride of barium. Chlorate of 
 baryta, ........ 191 
 
CONTENTS. XV 
 
 Paragraph 
 STRONTIUM. Preparation of nitrate of strontia, . . . .- 192 
 
 CALCIUM. Carbonate of lime ; its various mineral forms. Lime-burning. 
 Sulphate of lime. Preparation of plaster of Paris. Chloride of 
 calcium, ........ 193 
 
 MAGNESIUM. Extraction and properties of the metal. Preparation of 
 
 sulphate and carbonate of magnesia. Chloride of magnesium, . 194 
 
 General review of the metals of the alkaline earths, . . .195 
 
 Equivalent and atomic weights of barium, strontium, calcium, and mag- 
 nesium. Kelation between specific heats and equivalent weights. 
 Atomic heats. Atomic formulae of the oxides and chlorides of the 
 alkaline earth metals, . . . . . .196 
 
 ALUMINUM. Minerals containing alumina. Composition of clay. Manu- 
 facture of alum. Alumina. Chloride of aluminum, . . 197 
 Extraction of aluminum from bauxite. Aluminate of soda. Properties 
 
 and uses of aluminum, . . . . . .198 
 
 Mineral silicates of alumina. Exchange of isomorphous metals in 
 
 minerals. Natural and artificial ultramarine, . . .199 
 
 Equivalent and atomic weights of aluminum. Composition by volume 
 
 of chloride of aluminum. Its molecular formula, . . . 200 
 
 GLUCINUM, THORINUM, YTTRIUM, ERBIUM, TERBIUM, CERIUM, LAN- 
 
 THANIUM, DlDYMIUM, ZlRCONIUM, .... 201-205 
 
 ZINC. Properties upon which its usefulness depends. Galvanised iron. 
 Ores of zinc. Distillation of zinc. English method of extracting the 
 metal from its ores. Belgian and Silesian processes. Oxide, sul- 
 phate, and chloride of zinc, . . . . . 206 
 
 Equivalent and atomic weights of zinc, . . . . '.207 
 
 CADMIUM. Sulphide and iodide of cadmium. INDIUM, . . 208 
 
 URANIUM, ......... 209 
 
 IRON. Its occurrence in nature. Ores of iron. Table of composition of 
 
 British iron ores, . . . . . . .210 
 
 Metallurgy of iron. Its physical properties, . . . .211 
 
 English process of smelting clay iron-stone. Blast-furnace. Chemical 
 changes in the blast-furnace. Composition of gas from blast-fur- 
 nace. The hot blast. Composition of slag from the blast-furnace, 212 
 Cast-iron. Composition of different varieties of cast-iron. Grey, mot- 
 tled, and white iron. Chill -casting, . . . .213 
 
 Conversion of cast-iron into bar-iron. Refining. Puddling. Varieties 
 of bar-iron. Chemical effect of puddling and forging on cast-iron. 
 Composition of tap-cinder. Defects of the puddling process. 
 Bessemer's process. Conditions influencing the strength of bar- 
 iron, . . . . . . . . 214 
 
 Manufacture of steel. The cementation process. Shear steel. Pro- 
 duction of cast-steel. Hardening and tempering steel. Case- 
 hardening. Malleable cast-iron. Bessemer steel. Spiegel-eisen. 
 Homogeneous iron. Parry's steel. Puddled steel. Natural or 
 German steel. Krupp's cast steel, . . . . .215 
 
 Direct extraction of wrought iron from the ore. The Catalan process, . 216 
 Extraction of iron on the small scale. Sefstrom furnace, . .217 
 
 Chemical properties of iron. Passive state of iron, . . .'218 
 
 Oxides of iron. Ferrous oxide. Ferric oxide. Magnetic oxide of iron. 
 
 Ferric acid, ....... 219 
 
 
\ 
 
 xvi CONTENTS. 
 
 Paragraph 
 
 Protosulphate of iron. Persulphate of iron, . . 220 
 
 Perchloride of iron, . 221 
 Equivalent and atomic weights of iron. Varying atomicity of iron. 
 
 Ferrosum and ferricum, . . . . . t - 222 
 
 MANGANESE, . 223 
 Oxides of manganese. Binoxide, protoxide, sesquioxide, red oxide. 
 
 Manganic acid. Permanganic acid. Permanganate of potash, 224 
 
 Chlorides of manganese. Kecovery of waste manganese, . . 225 
 
 Equivalent and atomic weights of manganese, . . . . 226 
 
 COBALT. Protoxide and sesquioxide of cobalt. Chloride and sulphide of 
 
 cobalt, ........ 227 
 
 NICKEL. Oxides, sulphate, and sulphides of nickel, . . . 228 
 
 CHROMIUM. Preparation of bichromate of potash from chrome-iron, . 229 
 Chromic acid. Chromate of potash. Chromate of lead. Sesquioxide 
 
 of chromium. Protoxide of chromium. Perchromic acid, . 230 
 Protochloride and sesquichloride of chromium. Chlorochromic acid. 
 
 Fluoride and sulphide of chromium, .... 231 
 
 Equivalent and atomic weights of chromium, . . . .232 
 
 General review of zinc, iron, cobalt, nickel, manganese, and chromium, 233 
 
 COPPER. Its occurrence in nature, . . . . . 234 
 
 Ores of copper. Copper pyrites. Malachite. Grey copper ore, . 235 
 Smelting of copper-ores. Calcining the ore. Copper smoke. Fusion 
 for coarse metal. Calcining the coarse metal. Fusion for white 
 metal. Pv casting the white metal. Kenning the blister copper. 
 Toughening or poling. Underpoled and overpoled copper. Table 
 
 of products obtained in smelting copper-ores, . . . 236 
 
 Extraction of copper from copper-pyrites in the laboratory, . . 237 
 
 Effect of impurities upon the quality of copper, . . . 238 
 
 Properties of copper, ....... 239 
 
 Effect of sea-water upon copper. Muntz-metal, . . . 240 
 Danger attending the use of copper vessels in cooking food, . .241 
 A Hoys of copper with other metals. Table of their composition. Brass. 
 
 Bronzing. Aich metal. Sterro-metal. .... 242 
 
 Oxides of copper. Cupric and cuprous oxides. Quadrantoxide. 
 
 Cupric acid, ....... 243 
 
 Sulphate of copper. Carbonates and silicates of copper, . . 244 
 Chlorides of copper. Oxychloride ; Brunswick green. Cuprous 
 
 chloride, ........ 245 
 
 Sulphides of copper. Extraction of copper by kernel-roasting. Sub- 
 sulphide of copper. Copper pyrites. Phosphide of copper, . 246 
 Equivalent and atomic weights of copper, .... 247 
 
 LEAD. Its useful qualities. Ores of lead. Galena, . . . 248 
 
 Smelting of galena. Old English process. Economico-furnace, . 249 
 
 Improving process for hard lead, ..... 250 
 
 Extraction of silver from lead. Pattinson's process for concentrating 
 
 silver in lead, ....... 251 
 
 Cupellation of argentiferous lead. Sprouting of silver, . .252 
 
 Extraction and cupellation of lead in the laboratory, . . 253 
 Uses of lead. Type metal. Shot. Solder, . . .254 
 Lead pyrophorus. Oxides of lead. Litharge. Minium. Peroxide 
 
 of lead, . 255 
 
CON-TENTS. XV11 
 
 Paragraph 
 
 Manufacture of white lead. Dutch process. Pattinson's process. Car- 
 bonate, sulphate, and phosphate of lead, .... 256 
 Chloride and oxychloride of lead. Turner's yellow. Iodide of 
 
 lead, .257 
 
 Sulphides, chlorosulphide, and selenide of lead, . . . 258 
 
 Equivalent and atomic weights of lead. Atomic formulae of lead 
 
 compounds, ....... 259 
 
 THALLIUM. Its discovery by the spectroscope. Its position among the 
 
 metals, ........ 260 
 
 SILVER. Extraction of silver from copper by liquation. , Amalgamation 
 of silver-ores. Standard silver. Plating and electro-plating. Silver- 
 ing glass. Preparation of pure silver, . . . . 261 
 
 Properties of silver, . . . . . . .262 
 
 Oxides of silver. Preparation and uses of nitrate of silver. Perma- 
 nent ink, ....... 263 
 
 Chloride of silver. Recovery of silver from photographic baths. 
 
 Subchloride, bromide, iodide, and sulphide of silver, . . 264 
 
 Equivalent and atomic weights of silver. Atomic formulae of silver 
 
 compounds, ....... 265 ' 
 
 MERCURST. Extraction from cinnabar at Idria and Almaden. Purification 
 
 of mercury, ........ 266 
 
 Medicinal preparations of metallic mercury, . . . .267 
 
 Uses of mercury. Silvering looking-glasses. Amalgams, . . 268 
 
 Mercurous and mercuric oxides. Mercuramine, . . . 269 
 
 Mercurous and mercuric nitrates and sulphates, . . .270 
 
 Chlorides of mercury. Corrosive sublimate. White precipitate, . 271 
 
 Calomel. Its preparation and properties. Mercurous and mercuric 
 
 iodides, ........ 272 
 
 Sulphides of mercury. Preparation of vermilion, . . .273 
 
 Equivalent and atomic weights of mercury. Atomic and molecular 
 
 formulae of mercurous and mercuric compounds, . . . 274 
 
 BISMUTH. Extraction and properties. Fusible alloy, . . . 275 
 
 Bismuthous and bismuthic oxides. Bismuthic acid, . . .276 
 
 Trisnitrate of bismuth or flake-white. Pearl-white. Terchloride of 
 
 bismuth. Bismuthous and bismuthic sulphides, . .277 
 
 Equivalent and atomic weights of bismuth. Atomic formulae, of bis- 
 muth compounds, ....... 278 
 
 ANTIMONY. Extraction of regulus of antimony. Amorphous antimony, 279 
 Oxides of Antimony. Antimonic acid. Antimoniate, metanti- 
 
 moniate and bimetantimoniate of potash, .... 280 
 
 Antimonietted hydrogen, . . . . . .281 
 
 Terchloride and pentachloride of antimony, . . . .- -282 
 
 Sulphides of antimony. Mineral kermes. Schlippe's salt, . . 283 
 
 Equivalent and atomic weights of antimony. Atomic formulae of 
 
 antimony compounds, . . . . . . 284 
 
 TIN. Cornish treatment of tin ores. Extraction and purification of tin, 285 
 Physical properties of tin. Manufacture of tin-plate. Tinning of 
 
 copper vessels, ....... 286 
 
 Alloys of tin. Solder. Gun metai. Bronze. Bell-metal, . . 287 
 
 Oxides of tin. Stannous oxide. Stannic acid. Preparation of stannate 
 
 of soda. Metastannic acid, ..... 288 
 
 b 
 
XVlii CONTENTS. 
 
 Paragraph 
 Protochloride of tin or tin-crystals. Bichloride or nitromuriate of 
 
 tin. Pink salt, . . 289 
 
 Sulphides of tin. Preparation of mosaic gold, . . .290 
 
 Equivalent and atomic weights of tin. Atomic formulae of tin com- 
 pounds, . .... 291 
 
 TITANIUM. Titanic acid ; its extraction from iron-sand. Other com- 
 pounds of titanium, ....... 292 
 
 TUNGSTEN. Preparation of tungstate of soda from wolfram. Dialysed 
 
 tungstic acid. Oxides, chlorides, and sulphides of tungsten, . . 293 
 
 MOLYBDENUM. Preparation of molybdate of ammonia, . . . 294 
 
 VANADIUM. Preparation of vanadic acid from vanadiate of lead, . 295 
 
 NIOBIUM. TANTALUM, ....... 296 
 
 PLATINUM. Treatment of platinum ores by the wet and dry processes. 
 
 Spongy platinum. Platinum black, ..... 297 
 
 Platinous and platinic oxides. Preparation of bichloride of platinum. 
 Its double salts with alkaline chlorides. Platinous chloride. Its 
 behaviour with ammonia. Platosamine and platinamine, . . 298 
 
 Equivalent and atomic weights of platinum. Atomic formulas of pla- 
 tinum compounds, ....... 299 
 
 PALLADIUM. Its separation from platinum ores, .... 300 
 
 RHODIUM. Extraction of the metal from rhodio-chloride of sodium, . 301 
 OSMIUM. Osmic acid. Chlorides of osmium, .... 302 
 
 RUTHENIUM. Oxides of ruthenium. Jluthenic acid, . . . 303 
 
 IRIDIUM. Extraction from the native osmiridium alloy, . . . 304 
 
 Tabular view of the analysis of platinum ores. Summary of the group 
 
 of platinoid metals, ...... 305 
 
 GOLD. Washing for gold-dust. Smelting of auriferous ores ; with lead ; 
 with pyrites. Amalgamation of gold ores. Standard gold. Testing 
 and assaying gold, ....... 306 
 
 Physical properties of gold. Gold leaf. Ruby gold. Manufacture of 
 
 goldthread. Gilding, . . . . . .307 
 
 Oxides and chlorides of gold. Fulminating gold. Sd d'or. Purple of 
 
 Cassius, ........ 308 
 
 Equivalent and atomic weights of gold. Atomic formulae of gold com- 
 pounds, ........ 309 
 
 CHEMICAL PRINCIPLES OF THE MANUFACTURE OF GLASS. Window glass. 
 Plate glass. Crown and flint glass. Production of coloured 
 glasses, ........ 310 
 
 CHEMISTRY OF THE MANUFACTURE OF POTTERY AND PORCELAIN. Sevres 
 porcelain. English porcelain. Stone- ware. Earthenware. Bricks. 
 Dinas fire-bricks. Blue bricks, . . . . .311 
 
 CHEMISTRY OF BUILDING MATERIALS. Varieties of building stones. Free- 
 stone. Portland and Bath stones. Magnesian limestones. Test of 
 resistance of building stones to frost, . . . . .312 
 
 Mortar. Hydraulic cements. Concrete, . . . .313 
 
 GUNPOWDER. Nitre or saltpetre. Grough nitre. Conversion of nitrate 
 of soda into nitrate of potash. Artificial production of nitre in the 
 nitre-heaps. Saltpetre-refining, . . . . .314 
 
 Properties of saltpetre. Relation to combustible bodies, . . 315 
 
 Charcoal for gunpowder. Composition of charcoal prepared at different 
 
 temperatures, . . .316 
 
CONTENTS. xix 
 
 Paragraph 
 Sulphur for gunpowder. Tests of its purity. Functions of sulphur in 
 
 gunpowder, . . . . . . .317 
 
 Manufacture of gunpowder. Incorporation. Pressing. Granulating 
 
 or corning. Glazing, . . . . . .318 
 
 Properties of gunpowder. Effects of air, water, and heat upon powder, 319 
 Products of explosion of gunpowder. Difference in results obtained by 
 
 different experimenters. Most recent experiments, . . 320 
 
 Calculation of the force of fired gunpowder. Gas furnished by calcula- 
 tion from a given quantity of powder. Temperature of the gas at 
 instant of explosion. Specific heats of the products of explosion. 
 Expansion of the gas by heat. Mechanical equivalent of gun- 
 powder. Effect of size of grain on the firing of powder. Blasting- 
 powder, ........ 321 
 
 Effect of variations of atmospheric pressure on the combustion of gun- 
 powder. Manufacture of gunpowder in the laboratory, . . 322 
 CHEMISTRY OF FUEL. Calorific value of fuel calculated. Theoretical and 
 actual calorific values. Difference between calorific value and calori- 
 fic intensity. Calculation of the calorific intensity of carbon burning 
 in oxygen and in air. Calculation of the calorific intensity of hydrogen 
 burning in air. Calculation of the calorific intensity of fuel contain- 
 ing carbon, hydrogen, and oxygen. Theoretical and actual calorific 
 intensities. Waste of heat in furnaces. Economy of heat in Siemens' 
 regenerative furnace. Table of composition, calorific values, and in- 
 tensities of ordinary fuels, ...... 323 
 
 ORGANIC^CHEMISTEY. 
 
 Introductory, . . . . . . .324 
 
 CYANOGEN AND ITS COMPOUNDS. History of cyanogen, . . . 325 
 
 Yellow prassiate of potash or ferrocyanide of potassium. Prussian blue. 
 Hydroferrocyanic acid. Hydrocyanic or prussic acid. Cyanide of 
 mercury, . ... . . . . . 326 
 
 Preparation and properties of cyanogen. Cyanide of potassium. Cya- 
 nate of potash. Cyamelide. Hydrated cyanic acid. Sulphocyanide 
 of potassium. Hydrosulphocyanic acid. Liebig's test for prussic 
 acid, . ....... 327 
 
 Red prussiate of potash or ferricyanide of potassium. Turnbull's blue. 
 
 Ferricyanogen and other compound cyanogen radicals, . . 328 
 
 Chlorides of cyanogen. Cyanuric acid. Cyanide of phosphorus, . 329 
 
 Nitroprussides. Hadow's investigation of their constitution. Econo- 
 mical preparation of nitroprusside of sodium, . . . 330 
 The fulminates. Preparation of fulminate of mercury. Its properties. 
 Percussion cap composition. Fulminate of silver. Experiments 
 with the fulminates. Chemical constitution of the fulminates. 
 Fulminurates or isocyanurates, . . . . .331 
 
 PRODUCTS OF THE DESTRUCTIVE DISTILLATION OF COAL. Manufacture of 
 
 coal-gas. Composition of coal-tar, ..... 332 
 
 Coal- naphtha. Separation of its constituents by fractional distillation, . 333 
 Benzole. Chloride of benzole. Trichlorhydrine of phenose. Phenose, 334 
 Aniline. Its preparation from nitrobenzole. Production of colour- 
 ing matters from aniline, ... . . . . 335 
 
XX CONTENTS. 
 
 Paragraph 
 
 Coal-tar dyes. Mauve or aniline-purple. Mauveine. Magenta or ani- 
 line-red. Eosaniline and its salts. Leucaniline. Chrysaniline or 
 aniline-yellow. Triphenylic rosaniline or aniline-blue. Ethyl- 
 iodate of tri-ethyl-rosaniline. Hydrocyan-rosaniline, . . 336 
 
 Chemical constitution of aniline. Formation from phenic acid and 
 
 ammonia. Picoline. Quinoline, .... 337 
 
 Benzole series of homologous hydrocarbons. Their relation to the 
 aromatic acids. Homologous nitro-compounds and bases derived 
 from them, ....... 338 
 
 Carbolic acid. Preparation from the dead-oil of coal-tar. Examina- 
 tion of commercial carbolic acid, ..... 339 
 
 Carbazotic or picric acid. Chloropicrine. The phenyle series. Kresylic 
 
 acid, . . . . . ... 340 
 
 Naphthaline. Substitution products from naphthaline. Phthalic acid. 
 Connection of naphthaline with the phenyle series. Paranaphtha- 
 line. Chrysene. Pyrene, . . . . .341 
 
 PRODUCTS OF THE DESTRUCTIVE DISTILLATION OF WOOD. Proximate con- 
 stituents of wood. Cellulose. Lignine. Composition of different 
 woods. Products of the action of heat upon wood, . . . 342 
 
 Wood-naphtha or methylic alcohol. Purification. Methyle-compounds. 
 Oil of winter green. Metamerism illustrated by formiate of methyle 
 and acetic acid, ....... 343 
 
 Paraffine. Extraction from wood-tar. Paraffine oil. Stockholm tar. 
 
 Petroleum. Rangoon tar. Bitumen or asphaltum, . . 344 
 
 Oil of turpentine and substances allied to it. Colophony. Isomeric 
 
 modifications of turpentine. Artificial camphor, . . . 345 
 
 The turpentine series of hydrocarbons. Essential oils, . . 346 
 
 Camphors. Common camphor. Borneo camphor, . . . 347 
 
 Balsams. Balsam of Peru. Storax. Styrole and metastyrole, . 348 
 Eesins. Copal. Lac. Amber. Varnishes. Benzoin. Benzoic 
 
 acid, ........ 349 
 
 OlL OF BITTER ALMONDS AND ITS DERIVATIVES BENZOYLE SERIES. Forma- 
 tion of bitter almond oil. Amygdaline. Emulsine. Benzoine. Ben- 
 zoyle. Benzoic anhydride, ...... 350 
 
 Oil of cinnamon. Cinnamic acid. Cinnamyle. Cummin oil. Cuminic 
 
 acid, ........ 351 
 
 SALICINE AND ITS DERIVATIVES GLUCOSIDES. Saligenine ; its chlorinated 
 
 derivatives. Salicylic acid. Oil of spircca. Benzoyle-salicyle, . 352 
 Populine or benzoyle-salicine. Phloridzine. Quercitrine. Esculine. 
 
 Paviine. Saponine. Picrotoxine, .... 353 
 
 ESSENTIAL OILS CONTAINING SULPHUR ALLYLE SERIES. Formation of 
 essence of mustard. Myronic acid. Iodide of allyle. Artificial 
 formation of essences of mustard and garlic. Allylic alcohol. Ally- 
 lene, ......... 354 
 
 Gum-resins, Caoutchouc. Vulcanised caoutchouc. Gutta percha, . 355 
 Gums. Arabine. Mucic acid. Gum tragacanth, . . . 356 
 
 STARCH. Manufacture of starch. Composition of the potato ; of wheat ; 
 
 of rice. Properties of Starch. Sago. Tapioca, . . . 357 
 
 Conversion of starch into dextrine and grape-sugar, . . . 358 
 
 Germination of seeds Malting. Action of diastase on starch. Com- 
 position of malted and unmalted barley, and of malt-dust, . 359 
 
CONTENTS. XXI 
 
 Paragraph 
 
 Brewing. Composition of the hop. Nature of yeast. Alcoholic fer- 
 mentation. Composition of beer. Viscous fermentation, . . 360 
 Acetification. Manufacture of vinegar. The quick vinegar process, . 361 
 BREAD. Composition of gluten. Process of bread-making. Aerated 
 
 bread. Leaven. New and stale bread, .... 362 
 THE SUGARS. Production of sugar from cotton, paper, and other varieties 
 of cellulose. Action of sulphuric acid on cellulose. Vegetable parchment. 
 Sugar of fruits or fructose. Conversion of cane-sugar into fructose, . 363 
 Extraction' of cane-sugar. Vacuum pans. Sugar refining, . . 364 
 Beetroot sugar. Maple sugar. Sugar-candy. Barley-sugar. Cara- 
 mel, 365 
 
 Chemical properties of the sugars. Compounds of sugar with bases. 
 Action of solutions of the sugars upon polarised light. Ethyle- 
 glucose, ........ 366 
 
 Mannite. Glycyrrhizine, . . . . . . 367 
 
 GUN-COTTON AND SUBSTANCES ALLIED TO IT. Pyroxyline. Preparation 
 
 of gun-cotton in the laboratory, ..... 368 
 
 Manufacture of gun-cotton. Summary of the processes, . . 369 
 
 Chemical composition of gun-cotton. Trinitro-cellulose. Reconversion 
 
 of gun-cotton into ordinary cotton, . . . .370 
 
 Products of the explosion of gun-cotton. Explosion of loose and con- 
 fined gun-cotton. Karolyi's experiments. Effects of gun-cotton 
 and gunpowder compared, . . . . .371 
 
 Properties of gun-cotton compared with those of gunpowder, . 372 
 
 Behaviour of gun-cotton with solvents, . . . .373 
 
 Collodion-cotton. Action of weak nitro-sulphuric mixtures upon 
 cotton. Preparation of soluble cotton for collodion. Process 
 for making balloons of collodion, . . . . 374 
 
 Xyloidine. Nitromannite, ...... 375 
 
 WINE AND SPIRITS. Preparation and composition of wines. Proportion 
 
 of alcohol in wines, ....... 376 
 
 Distilled spirits. Brandy, whisky, gin, &c. Potato-spirit, . .377 
 
 THE ALCOHOLS AND THEIR DERIVATIVES. General formula of alcohols of 
 the vinic class. Table of the vinic or ethylic class of alcohols, with 
 their sources, common names, and equivalent formulae. Gradation in 
 properties of the homologous alcohols. Table of their boiling points 
 and vapour densities. Chemical definition of an alcohol. General 
 formulae for the derivation of an aldehyde, an acid, and an ether from 
 an alcohol. Table of the acetic series of acids with their sources and 
 equivalent formulae. General description of the acetic series. The 
 defines or olefiant gas series of hydrocarbons. Polymerism, . . 378 
 
 Alcohol as the type of its class. Preparation of absolute alcohol, . 379 
 
 Ether. Continuous etherifying process. Preparation of ethylic iodide, 380 
 The alcohol-radicals. Isolation of ethyle. General formula of alcohol- 
 radicals. Electro-positive and electro-negative hydrocarbon radicals, 381 
 Duplex constitution of the alcohol-radicals. Hydrides of alcohol-radicals, 
 
 or marsh-gas hydrocarbons, ..... 382 
 
 Compound ethers or salts of oxide of ethyle. Oxalic ether. Oxalovinic 
 acid. Acetic ether. Nitrous ether. Nitric ether. Hydroxyla- 
 niine prepared from nitric ether. Perchloric ether. Boracic and 
 silicic ether. Carbonic ether. Formation of subcarbonate of ethyle 
 
XX11 CONTENTS. 
 
 Paragraph 
 
 from chloropicrine. Phosphovinic acid. True sulphuric ether. Oil 
 
 of wine, . ..... 383 
 
 Sulphovinic or sulphethylic acid. Its preparation, . . . 384 
 
 Vinic acids not formed by monobasic acids, . . . . 385 
 
 Theory of etherijication. Formation of double ethers. Ethylene theory 
 
 of alcohol and ether, ...... 386 
 
 Water-type view of alcohols and ethers. Potassium and sodium 
 alcohols. Thallium alcohol. Molecular formulae of alcohol and 
 ether, . . . . . . . . 387 
 
 Sulphuretted derivatives of the alcohols. Mercaptan, . . 388 
 
 Cyanides of alcohol-radicals. Their relation to the acids of the acetic 
 
 series, . . ...-. . . . 389 
 
 KAKODYLE -SERIES ORGANO-METALLIC BODIES. Alcarsin. Chloride of 
 
 kakodyle. Kakodylic acid. Cyanide of kakodyle, . , *,v . 390 
 Preparation and properties of zinc-ethyle. Zinc-methyle. Zinc-amyle. 
 Potassium-ethyle. Sodium-ethyle. Arsenio-dimethyle or kakodyle. 
 Arsenio-diethyle, or ethyle-kakodyle, . . . .391 
 
 Arsenio-trimethyle. Arsenio-triethyle. Stibethyle. Mercuric methide. 
 
 Aluminum ethide. Triborethyle. Boric methide. Silicium-ethyle, 392 
 Table of the compounds of alcohol- radicals with inorganic elements ; 
 with their equivalent formulae and inorganic types. Constitution 
 of the organo- metallic radicals, ..... 393 
 
 ORGANIC ALKALOIDS AMMONIAS. Table of the alkaloids with their 
 sources and equivalent formulae. Theories of the constitution of the 
 alkaloids, . . . . . . . .394 
 
 Ethylated ammonias and their derivatives. Ethylamine. Diethylamine. 
 Triethylamine. Hydrated oxide of tetrethylium. Complex am- 
 monias, ........ 395 
 
 Investigation of the constitution of the alkaloids, . . . 396 
 
 Poly-ammonias ; their constitution, ..... 397 
 
 Diamines. Ethylene- diamine. Aromatic diamines. Paraniline, . 398 
 Triamines. Carbotriamine. Synthesis of guanidine. Melaniline. 
 
 Aniline colours probably triamines, .... 399 
 
 Tetramines. Tetrammoniuin-bases, ..... 400 
 
 Ammonia-bases formed in putrefaction and destructive distillation, . 401 
 Ammonias and ammonium bases containing phosphorus, arsenic and 
 
 antimony, ........ 402 
 
 Platammonium-compounds, ...... 403 
 
 Amides. Oxamide. Oxamic acid, ..... 404 
 
 Nitrites. Imides, ....... 405 
 
 Constitution of the amides, ...... 406 
 
 Metal-amides. Tripotassamide. Zinc- amide. Ziiic-acetimide, . 407 
 
 DERIVATIVES or THE ALCOHOLS. Chloroform. Chloral, . . . 408 
 
 Perfume-ethers. Pine-apple and pear essences. Apple-oil, . . 409 
 
 Aldehydes. Preparation and properties of vinic aldehyde. Constitu- 
 tion and synthesis of the aldehydes. Action of aldehydes on the 
 ammonia-bases, . . . . . . .410 
 
 Acetones or ketones. Synthesis of acetic acetone. Methyle-valeryle 
 
 acetone. Metacetone, . . . . . 41 1 
 
 The essential oils regarded as aldehydes, . . . ; . 412 
 
 Polyatomic alcohols. Glycol. Preparation and properties of glycol. 
 
CONTENTS. xxiii 
 
 Paragraph 
 
 Glycolic acid ; its relation to oxalic acid. Lactic series of acids. 
 Conversion of the oxalic into the lactic series. Synthesis of leucic 
 acid. Conversion of a diatomic into a monatomic alcohol. Water- 
 type view of polyatomic alcohols, . . . . .413 
 
 ACETIC ACID THE FATTY ACID SERIES. Acetates. Acetone. Chlora- 
 
 cetic acids. Synthesis of acetic acid, . . . .414 
 
 Anhydrides of organic acids. Acetic anhydride. Duplex constitution 
 of the anhydrides. Peroxides of organic radicals. Acetic and 
 benzoic peroxides, . . . . . . .415 
 
 Formic acid. Synthesis of formic acid. Furfurole. Butyric acid. 
 Synthetical formation of acids of the acetic series. Ethacetic, 
 dimethacetic, or butyric acid. Diethacetic acid. Ethylated and 
 methylated acetones. Valerianic acid, . . . .416 
 
 Separation of volatile acids by the method of partial saturation, . 417 
 Soap. Composition of the neutral fats. Stearine, oleine, palmitine. 
 
 Action of alkalies upon them. Preparation of the fatty acids, . 418 
 Candles. Decomposition of fats by sulphuric acid. Saponification by 
 
 superheated steam, . . . . . .419 
 
 Synthesis of natural fats. Glycerides. Water-type view of glycerine 
 
 or glyceric alcohol, ...... 420 
 
 Properties of glycerine. Acroleine. The acrylic series of acids. The 
 
 allyle series, ....... 421 
 
 Relation between glycerine and mannite. Mannite-glycerides. Stearic 
 
 glucose. Gluco-tartaric acid, ..... 422 
 
 Nitroglycerine. Its preparation and properties, . . . 423 
 
 OILS AND FATS. Palmitine. Oleine. Margarine. Oleic acid. Sebacic 
 acid. Bibasic fatty acid series. Linseed oil. Drying oils. Castor 
 oil. Butter. Spermaceti. Wax. Table of the neutral fats and 
 fatty acids, with their equivalent formulae, sources, and fusing- 
 points, ........ 424 
 
 VEGETABLE ACIDS. Oxalic acid. Its manufacture from saw-dust. Con- 
 stitution of the oxalates; ...... 425 
 
 Tartaric acid. Preparation from cream of tartar. Tartar-emetic. Con- 
 version of tartaric into succinic and malic acids, . . . 426 
 Eacemicacid. Hemihedrism of the tartrates. Dextrotartaric and laevo- 
 
 tartaric acids. Analysis and synthesis of racemic acid, . .427 
 
 Citric acid. Preparation from lemon-juice. Conversion of citric acid 
 
 into acetic and butyric acids, ..... 428 
 
 Malic acid. Extraction from rhubarb and from mountain ash berries. 
 
 Sorbic and parasorbic acids. Asparagine, . . . 429 
 
 Tannic acid. Preparation of ink. Tanning of hides. Morocco. Kid. 
 
 Wash-leather. Buckskin, . . . . ^. 430 
 
 Gallic acid. Its formation from tannic acid. Pyrogallic acid. Analysis 
 
 of air by potash and pyrogalline, . . . . .431 
 
 VEGETABLE ALKALOIDS. Extraction of the alkaloids from opium. Mor- 
 phine, codeine, narcotine. Meconic acid, .... 432 
 
 Extraction of quinine from Peruvian bark. Quinoidine. Quinic acid. 
 
 Kinone and hydrokinone, ...... 433 
 
 Theine or caffeine. Composition of coffee and tea. Extraction of caffeine 
 from them. Theobromine. Cocoa and chocolate. Methyle-theo- 
 bromine or caffeine, ....'. . . . . 434 
 
CONTENTS. 
 
 Paragraph 
 
 Strychnine. Extraction from nux-vomica. Brucine. Detection of 
 
 small quantities of strychnine. Curarine, ... . . 435 
 
 Nicotine. Extraction from tobacco. Composition of tobacco. Pre- 
 paration of snuff, ....... 436 
 
 VEGETABLE COLOURING MATTERS. Chlorophyll. Phylloxanthine. Phyl- 
 locyanine. Colouring matters of flowers. Cyanine. Saffron. Saf- 
 flower; carthamine. Annatto ; bixine. Weld ; luteoline. Dye-woods. 
 Madder. Rubian. Alizarine. Turmeric, . . . .437 
 
 Colouring matters prepared from lichens. Litmus, archil, cudbear. 
 
 Orcine. Orcelne. Azolitmine. Erythrite, .... 438 
 
 Indigo. Preparation of indigo blue. Indican. White or reduced 
 
 indigo. Dyeing with indigo, *' ' . . . . 439 
 
 Animal colouring matters. Lac. Carmine, .... 440 
 
 Dyeing and calico-printing. Use of mordants. Dyeing red, blue, 
 
 yellow, brown, black, . . . . . .441 
 
 Printing in patterns. Resists and discharges, . . . 442 
 
 ANIMAL CHEMISTRY. Special difficulties attending its study. Chemistry 
 of milk. Cream. Preparation of butter. Coagulation of milk. 
 Preparation of lactic acid. Conversion of lactic into propionic acid. 
 Preparation of cheese. . Caseine. Legumine. Sugar of milk. Com- 
 position of milk from different animals. Adulteration of milk, . 443 
 Chemistry of blood. Composition of blood globules. Colouring matter 
 of blood. Composition of liquor sanguinis. Albumen. Fibrine. 
 Proteine. Eggs, ....... 444 
 
 Composition of flesh. Kreatine. Inosite or sugar of flesh. Cooking 
 
 of meat, ........ 445 
 
 Gelatine. Chondrine. Manufacture of glue. Composition of wool 
 
 and silk, ........ 446 
 
 Chemistry of urine. Urea. Artificial formation of urea, . . 447 
 
 Constitution of urea. Ethyl-urea. Ureides, . . . 448 
 
 Uric acid. Alloxan. Alloxantine. Murexide, . . . 449 
 
 Hippuric acid ; its relation to benzoic acid. Glycocoll. Average 
 
 composition of human urine, . . . . . 450 
 
 CHEMISTRY OF VEGETATION. Components of the food of plants ; their 
 sources. Process of formation of a fertile soil from a barren rock. 
 Action of manures. Fallowing. Rotation of crops. Growth of 
 plants from seeds. Ripening of fruits. Pectose. Pectine. Pectic 
 and pectosic acids. Restoration of the elements of plants to the air. 
 Preservation of wood from decay, . . . . .451 
 
 NUTRITION OF ANIMALS. Chemistry of digestion. Pepsine. Composi- 
 tion of bile. Taurine. Cholesterine. Chemistry of the circulation. 
 Composition of food, ....... 452 
 
 CHANGES IN THE ANIMAL BODY AFTER DEATH. Restoration of its elements 
 
 to the earth and air. Nature of putrefaction, . . . 453 
 
INTRODUCTION. 
 
 1. CHEMISTRY describes the properties of the different particles of which 
 all kinds of matter are composed, and teaches the laws which regulate 
 their union with, or separation from, each other. 
 
 Matter is anything which possesses weight. Matter is chemically 
 divided into two great classes elements and compounds. 
 
 An ELEMENT is that which has not been found divisible into more than 
 one kind of matter. 
 
 A COMPOUND consists of two or more elements held together by chemi- 
 cal attraction. 
 
 CHEMICAL ATTRACTION is the force which causes different kinds of 
 matter to unite, in order to form a new kind of matter. 
 
 Chemical Combination is the operation of chemical attraction. 
 
 Chemical Decomposition is the separation of two or more kinds of 
 matter previously held together by chemical attraction. 
 
 2. The elements known at present are sixty-four in number, and are 
 divided into metallic and non-metallic elements. 
 
 The Non-Metallic Elements are (15) 
 
 Oxygen. 
 
 Sulphur 
 
 Fluorine. 
 
 Hydrogen. 
 
 Selenium. 
 
 Chlorine. 
 
 Nitrogen. 
 
 Tellurium. 
 
 Bromine. 
 
 Carbon. 
 
 Phosphorus. 
 
 Iodine. 
 
 Boron. 
 
 Arsenic.* 
 
 
 Silicon. 
 
 
 
 The Metals are (49) 
 
 Coesium. 
 
 Aluminum. 
 
 Zinc. 
 
 Copper. 
 
 Mercury. 
 
 Rubidium. 
 
 Glucinum. 
 
 Nickel. 
 
 Bismuth. 
 
 Silver. 
 
 Potassium. 
 
 Zirconium. 
 
 Cobalt. 
 
 Lead. 
 
 Gold. 
 
 Sodium. 
 
 Thorinurn. 
 
 Iron. 
 
 Thallium. 
 
 Platinum. 
 
 Lithium. 
 
 Yttrium. 
 
 Manganese. 
 
 Tin 
 
 Palladium. 
 
 Barium. 
 Strontium. 
 Calcium. 
 Magnesium. 
 
 Erbium. 
 Terbium. 
 Cerium. 
 Lanthanum. 
 Didymium. 
 
 Chromium. 
 Cadmium. 
 Uranium. 
 Indium. 
 
 _L in. 
 Titanium. 
 Tantalum. 
 Molybendum. 
 Tungsten. 
 Vanadium. 
 
 Rhodium. 
 Ruthenium. 
 Osmium. 
 Iridium. 
 
 
 Niobium. 
 
 
 Antimony. 
 
 
 The strict definition of a metal will be given hereafter. 
 
 Many of these elements are so rarely met with, that they have not 
 
 * In many English chemical works arsenic is classed among the metals, which it resembles 
 in some of its properties. 
 
INTRODUCTION. 
 
 received any useful application, and are interesting only to the profes- 
 sional chemist. This is the case with selenium and tellurium, among the 
 non-metallic elements, and with a large number of the metals. 
 
 The following list includes those elements with which it is important 
 that the general student should become familiar, together with the 
 symbolic letters by which it is customary to represent- them, for the sake of 
 brevity, in chemical writings. 
 
 Non-Metallic Elements of practical importance (13). 
 
 Oxygen, 
 
 
 
 Sulphur, 
 
 S | 
 
 Fluorine, 
 
 F 
 
 Hydrogen, 
 Nitrogen, 
 
 H 
 
 N 
 
 Phosphorus, 
 Arsenic 
 
 P 
 
 As 
 
 Chlorine, 
 Bromine, 
 
 Cl 
 Br 
 
 Carbon, 
 
 C 
 
 
 
 Iodine, 
 
 I 
 
 Boron, 
 
 B- 
 
 
 
 
 
 Silicon. 
 
 Si 
 
 
 
 
 
 Metallic Elements of practical importance (26). 
 
 Potassium, 
 
 K 
 
 (Kalium.} 
 
 Cadmium, 
 
 Cd 
 
 Sodium, 
 
 Na 
 
 (Natrium.) 
 
 Uranium, 
 
 U 
 
 Barium, 
 
 Ba 
 
 
 Copper, 
 
 Cu (Cuprum.) 
 
 Strontium, 
 
 Sr 
 
 
 Bismuth, 
 
 Bi 
 
 Calcium, 
 
 Ca 
 
 
 Lead, 
 
 Pb (Plumbum.) 
 
 Magnesium, 
 
 Mg 
 
 
 Tin, 
 
 Sn (Stannum.) 
 
 Aluminum, 
 
 Al 
 
 
 Titanium, 
 
 Ti 
 
 Zinc 
 
 Zn 
 
 
 Tungsten, 
 
 W (Wolframium.) 
 
 Nickel, 
 
 Ni 
 
 
 Antimony, 
 
 Sb (Stibium.) 
 
 Cobalt, 
 
 Co 
 
 
 Mercury, 
 
 Hg (Hydrargyrum.) 
 
 Iron, 
 
 Fe 
 
 (Ferrum.) 
 
 Silver, 
 
 Ag (Argentum.) 
 
 Manganese, 
 
 Mn 
 
 
 Gold, 
 
 Au (Aurum.) 
 
 Chromium, 
 
 Cr 
 
 
 Platinum, 
 
 Pt 
 
 The symbols represent definite relative proportions of the elements to 
 which they are attached. 
 
 The values assigned to the symbols in the following list may be regarded 
 as representing the relative weights in which they usually enter into che- 
 mical combination, and may be termed combining weights of the elements. 
 
 Hydrogen is taken as the unit, because its combining weight is less 
 than that of any other known element. 
 
 Combining Weights of the practically important Elements.* 
 
 Aluminum, 
 
 Al 
 
 13-7 
 
 Copper, 
 
 Cu 
 
 31-8 
 
 Phosphorus, 
 
 P 
 
 31-0 
 
 Antimony, 
 
 Sb 
 
 122-0 
 
 Fluorine, 
 
 F 
 
 19-0 
 
 Platinum, 
 
 Pt 
 
 98-6 
 
 Arsenic, 
 
 As 
 
 75-0 
 
 Gold, 
 
 Au 
 
 196-7 
 
 Potassium, 
 
 K 
 
 39-0 
 
 Barium, 
 
 Ba 
 
 68-5 
 
 Hydrogen, 
 
 H 
 
 1-0 
 
 Silicon, 
 
 Si 
 
 14-0 
 
 Bismuth, 
 
 Bi 
 
 210-0 
 
 Iodine, 
 
 I 
 
 127-0 
 
 Silver, 
 
 Ag 
 
 108-0 
 
 Boron, 
 
 B 
 
 11-0 
 
 Iron, 
 
 Fe 
 
 28-0 
 
 Sodium, 
 
 Na 
 
 23-0 
 
 Bromine, 
 
 Br 
 
 80-0 
 
 Lead, 
 
 Pb 
 
 103-5 
 
 Strontium, 
 
 Sr 
 
 43-8 
 
 Cadmium, 
 
 Cd 
 
 56-0 
 
 Magnesium, 
 
 Mg 
 
 12-2 
 
 Sulphur, 
 
 S 
 
 16-0 
 
 Calcium, 
 
 Ca 
 
 20-0 
 
 Manganese, 
 
 Mn 
 
 27-5 
 
 Tin, 
 
 Sn 
 
 59-0 
 
 Carbon, 
 
 C 
 
 6-0 
 
 Mercury, 
 
 Hg 
 
 100-0 
 
 Titanium, 
 
 Ti 
 
 25-0 
 
 Chlorine, 
 
 Cl 
 
 35-5 
 
 Nickel, 
 
 Ni 
 
 29-5 
 
 Tungsten, 
 
 W 
 
 92-0 
 
 Chromium, 
 
 Cr 
 
 26-3 
 
 Nitrogen, 
 
 N 
 
 14-0 
 
 Uranium, 
 
 U 
 
 60-0 
 
 Cobalt, 
 
 Co 
 
 29-5 
 
 Oxygen, 
 
 
 
 8-0 
 
 Zinc, 
 
 Zn 
 
 32-8 
 
 * The combining weights given in this list, though sufficiently correct for all practical 
 purposes, are not in all cases absolutely exact. The small fractions have been omitted, in 
 order that the numbers may be more easily retained in the memory. 
 
INTRODUCTION. 6 
 
 Although the 39 elements here enumerated are of practical importance, 
 many of them derive their importance solely from their having met with 
 useful applications in the arts. The number of elements known to play 
 an important part in the chemical changes concerned in the maintenance 
 of animal and vegetable life is very limited. 
 
 Elements concerned in the Chemical Changes taking place in Life. 
 
 Non-Metallic. 
 
 Oxygen. Sulphur. 
 
 Hydrogen. 
 
 Nitrogen. Phosphorus. 
 
 Carbon. 
 
 Chlorine. 
 
 Silicon. Iodine. 
 
 Metallic. 
 
 Potassium. Aluminum. 
 
 Sodium. 
 
 Iron. 
 
 Calcium. Manganese. 
 
 Magnesium. 
 
 These elements will, of course, possess the greatest importance for those 
 who study Chemistry as a branch of general education, since a knowledge 
 of their properties is essential for the explanation of the simplest chemical 
 changes which are daily witnessed. 
 
 The student who takes an interest in the useful arts will also acquaint 
 himself with the remainder of the 39 elements of practical importance, 
 whilst the mineralogist and professional chemist must extend his studies 
 to every known element. 
 
 By far the greater proportion of the various materials supplied to us by 
 animals and vegetables consists of the four elements oxygen, hydrogen, 
 nitrogen, and carbon ; and if we add to these the two most abundant 
 elements in the mineral world, silicon and aluminum, we have the six 
 elements composing the bulk of all matter. 
 
 3. Compound substances are commonly classified by the chemist into 
 Organic and Inorganic compounds ; and although it is impossible strictly 
 to define the limits of each class, the division is a convenient one for the 
 purposes of study. 
 
 Organic substances may be defined as those for which we are indebted 
 to the operation of animal or vegetable life, such as starch, sugar, &c. 
 
 Inorganic substances are obtained from the mineral world without the 
 intervention of life ; as common salt, alum, &c. 
 
 Organic substances always contain carbon, generally also hydrogen and 
 oxygen, and very frequently nitrogen. 
 
 A2 
 
PROPERTIES OF OXYGEN. 
 
 CHEMISTRY OF THE NON-METALLIC 
 ELEMENTS. 
 
 OXYGEN. 
 
 4. Oxygen is the most abundant of the elementary substances. It con- 
 stitutes about one-fifth (by volume) of atmospheric air, where it is merely 
 mixed, not combined, with the nitrogen, which composes the bulk of the 
 remainder. Water contains eight-ninths (by weight) of oxygen ; whilst 
 silica and alumina, which compose the greater part of the solid earth (as 
 far as we know it), contain about half their weight of oxygen. 
 
 Before inquiring which of these sources will most conveniently furnish 
 pure oxygen, it will be desirable for the student to acquire some know- 
 ledge of the properties of this element, and of the chemical relations 
 which it bears to other elementary bodies, for without such knowledge it 
 will be found very difficult to understand the processes by which oxygen 
 is procured. 
 
 5. Physical properties of Oxygen. From the fact of its occurring in an 
 uncombined state in the atmosphere, it will be inferred that oxygen is 
 perfectly invisible, and without odour. It is a permanent gas, having 
 resisted all attempts to reduce it to a liquid or solid state. Oxygen is a 
 little more than one-tenth heavier than air, which is expressed in the 
 statement that its specific gravity is 1-1057. 
 
 (DEFINITION. The specific gravity of a gas or vapour is its weight as 
 compared with that of an equal volume of dry and pure air at the same 
 temperature and pressure. 
 
 In certain cases it will be found very convenient to express this defini- 
 tion in the following terms : 
 
 DBF. The specific gravity of a gas or vapour is the weight of one volume 
 of that gas or vapour.) 
 
 6. Chemical properties of Oxygen. This element is remarkable for the 
 wide range of its chemical attraction for other elementary bodies, with all 
 of which, except one, it is capable of entering into combination. Fluorine 
 is the only element ivhich is not known to unite with oxygen. 
 
 With nearly all the elements oxygen combines in a direct manner ; 
 that is, without the intervention of any third substance. 
 
 There are only seven elements (among those of practical importance) 
 which do not unite in a direct manner with oxygen, viz., chlorine, bromine, 
 iodine, fluorine, gold, silver, platinum. 
 
COMBUSTION. 5 
 
 (DBF. The compounds of oxygen with, other elements are called 
 Oxides.) 
 
 The act of combination with oxygen, or oxidation, like all other acts of 
 chemical combination, is attended with the development of heat.* When 
 the heat thus produced is sufficient to render the particles of matter 
 luminous, the act of combination is styled combustion. 
 
 (DEF. Combustion is chemical combination attended with heat and 
 light.) 
 
 7. Phosphorus, the only non-metal which combines with oxygen at the 
 ordinary temperature, affords a good illustration of these propositions. 
 This element, a solid at the ordinary temperature, is preserved in bottles 
 filled with water, on account of the readiness with which the oxygen of 
 the air combines with it. If a small piece of phosphorus be dried by 
 gentle pressure between blotting paper, and exposed to the air, its par- 
 ticles begin to combine at once with oxygen, and the heat thus developed 
 slightly raises the temperature of the mass. 
 
 Now, heat generally encourages chemical union, so that the effect of 
 this rise of temperature is to induce a more extensive combination of the 
 phosphorus with the oxygen, causing a greater development of heat in a 
 given time, until the temperature is sufficient to render the particles 
 brilliantly luminous, and a true case of combustion results the combina- 
 tion of the phosphorus with oxygen, attended with production of heat 
 and light. 
 
 (DEF. Combustion in air is the chemical combination of the elements 
 of the combustible with the oxygen of the air, attended with develop- 
 ment of heat and light.) 
 
 If a dry glass (fig. 1) be placed over 
 the burning phosphorus, the thick 
 white smoke which proceeds from it 
 may be collected in the form of snowy 
 flakes. These flakes are commonly 
 termed anhydrous phosphoric acid,+ 
 and are composed of one combining 
 weight of phosphorus (P=31), and 
 five combining weights of oxygen 
 (0 5 = 8 x 5 = 40). This would be re- 
 presented by the formula PCX. 
 
 If the white flakes are exposed to the air for a short time they attract 
 moisture and become little drops, which have a very sour or acid taste. 
 All substances which have such a taste have been found also to be capable 
 of changing the blue colour of litmus J to red, whence the chemist is in 
 the habit of employing paper dyed with blue litmus for the recognition of 
 an acid. It must be remembered, however, that there are some acids 
 which, not being dissolved by water, have neither a sour taste nor the 
 
 * 
 
 * Though this heat is not always perceptible by the thermometer or by the senses. 
 Thus, when chalk is dissolved in an acid, no heat is perceived, because all the heat attend- 
 ing the union of the lime with the acid is consumed in converting the carbonic acid from 
 the solid chalk into a gas. To explain the manifestation of heat in the act of chemi- 
 cal combination falls within the province of the physicist rather than of the chemist. 
 Modern writers attribute it to the motion of the molecules which compose the combining 
 masses. 
 
 t Anhydrous, or without water, from av, negative, and vSwp, water. 
 
 $ A colouring matter prepared from a lichen, Roccella tincioria;. the cause of the 
 Change of colour will be more easily understood hereafter. 
 
OXYGEN. 
 
 power of reddening litmus, so that, in exact research, another mode of de- 
 nning the acid character of a substance is employed. Ordinary sand is 
 known to chemists as silicic acid, but, of course, does not answer to either 
 of the above tests. 
 
 For the exact definition of an acid see page 9. 
 
 During the slow combination of phosphorus with the oxygen of the air, 
 before actual combustion commences, the phosphorus unites with only 
 three combining weights of oxygen, forming the substance called anhy- 
 drous phosphorous acid, which has the formula P0 3 . 
 
 (DBF. The endings -ous and -ic distinguish between two acids formed 
 by oxygen with the same element ; -ous implying the smaller proportion 
 of oxygen.) 
 
 Unless the temperature of the air be rather high, the fragment of 
 phosphorus will not take fire spontaneously, but its combustion may 
 always be ensured by exposing a larger surface to the action of the air. 
 As a general rule, a fine state of division favours chemical combination, 
 because the attractive force inducing combination operates only between 
 substances in actual contact ; and the smaller the size of the particles, the 
 more completely will this condition be fulfilled. 
 
 Thus, if a small fragment of dry phosphorus be placed in a test-tube, and dis- 
 solved in a little bisulphide of carbon, the solution, when poured upon blotting paper 
 
 (fig. 2), will part with the solvent by 
 evaporation, leaving the phosphorus in a 
 very finely divided state upon the sur- 
 face of the paper, where it is so rapidly 
 acted on by the oxygen of the air that it 
 bursts spontaneously into a blaze. 
 
 Though the light emitted by phos- 
 phorus burning in air is very bril- 
 9 liant, it is greatly increased when 
 
 pure oxygen is employed, for since 
 
 the nitrogen with which the oxygen in air is mixed takes no part in the 
 act of combustion, it impedes and moderates the action of the oxygen. 
 Each volume of the latter- gas is mixed, in air, with four volumes of 
 nitrogen, so that we may suppose five times as many particles of oxygen 
 to come into contact in a given time with the particles of the phosphorus 
 immersed in the pure gas, which will account for the great augmentation 
 of the temperature and light of the burning mass. 
 
 To demonstrate the brilliant combustion of phosphorus in oxygen, a piece not 
 larger than a good-sized pea is placed in a little copper or iron cup upon an iron 
 
 stand (fig. 3), and kindled by being touched 
 with a hot wire (for even in pure oxygen spon- 
 taneous combustion cannot be ensured). The 
 globe, having been previously filled with oxy- 
 gen, and kept in a plate containing a little 
 water, is placed over the burning phosphorus.* 
 
 It will be observed that the same white 
 clouds of phosphoric acid are formed, 
 whether phosphorus is burnt in oxygen 
 or in air, exemplifying the fact that a sub- 
 Fig. 3.-Pho^phoras burning in stance will combine with the same pro- 
 portion of oxygen, whether its combustion 
 
 * This globe should be of thin, well-annealed glass, and is sure to be broken if too lame 
 a piece of phosphorus be employed. 
 
OXYGEN WITH NON-METALS. 
 
 be effected in pure oxygen or in atmospheric air. The apparent increase 
 of heat is due to the combustion of a greater weight of phosphorus in a 
 given time. The total heating effect produced by the combustion of a 
 given weight of phosphorus is the same whether air or pure oxygen be 
 employed. 
 
 8. Sulphur (brimstone) affords an example of a non-metallic elements 
 which will not enter into combination with oxygen until its temperature 
 has been raised very considerably. When sulphur is heated in air, it 
 soon melts, and as soon as its temperature reaches 500 F. it takes fire, 
 burning with a pale blue flame. If the burning sulphur be plunged into 
 a jar of oxygen, the blue light will become very brilliant, but the same 
 act of combination takes place, one combining weight (16 1 parts) of sulphur 
 uniting with two combining weights (8 x 2 = 16) of oxygen to form sul- 
 phurous acid gas (S0 2 ), which may be recognised in the jar by the well- 
 known suffocating smell of brimstone matches. 
 
 The experiment is most conveniently performed by heating the sulphur 
 in a deflagrating spoon (A, fig. 4), which is then plunged into the jar of 
 oxygen, its collar (B) resting upon the 
 neck of the jar which stands in a plate 
 containing a little water. The water ab- 
 sorbs a part of the sulphurous acid gas, 
 and will be found capable of strongly red- 
 dening litmus paper. It is possible to 
 produce, though not by simple combustion, 
 a compound of sulphur with three combin- 
 ing weights of oxygen (S0 3 , anhydrous 
 sulphuric acid), showing that a substance 
 'does not always take up its full share of 
 oxygen when burnt. 
 
 The luminosity of the 'flame of sulphur 
 is far inferior to that of phosphorus, be- Fig. 4. -Sulphur burning in oxygen, 
 cause, in the former case, there are no minute solid particles in the flame 
 corresponding to those of the phosphoric acid produced in the combus- 
 tion of phosphorus, and no flame can emit a brilliant light unless it con- 
 tains solid' matter heated to incandescence. 
 
 9. Carbon, also a non-metallic element, requires the application of a 
 higher temperature than sulphur to induce it to enter into direct union 
 with oxygen ; indeed, perfectly pure carbon appears to require a heat ap- 
 proaching whiteness to produce this effect. But charcoal (the carbon in 
 which is associated with not inconsiderable proportions of hydrogen and 
 oxygen) begins to burn in air at a much lower temperature, andlf a piece 
 of wood charcoal, with a single spot heated to redness, be lowered into a 
 jar of oxygen, the adjacent particles will soon be raised to the combining 
 temperature, and the whole mass will glow intensely, each combining 
 weight (6) of carbon uniting with two combining weights (8x2-16) of 
 oxygen to form carbonic acid (C0 2 ) gas, which will redden a piece of 
 moistened blue litmus paper suspended in the jar, though much more 
 feebly than either sulphurous or phosphoric acid, because it is a much 
 weaker acid. It should be remembered that carbon is an essential consti- 
 tuent of all ordinary fuel, and carbonic acid is always produced by its com- 
 bustion. 
 
 It will be noticed that the combustion .of the charcoal is scarcely at- 
 
8 OXYGEN WITH METALS. 
 
 tended with flame, and when pure carbon (diamond, for example) is 
 employed, no flame whatever is produced in its combustion, because car- 
 bon is not convertible into vapour, and all flame is vapour or gas in the 
 act of combustion, hence only those substances burn with flame which are 
 capable of yielding combustible gases or vapours. 
 
 10. The three examples of sulphur, phosphorus, and carbon sufficiently 
 illustrate the tendency of non-metals to form acids by union with oxygen, 
 which originally led to the adoption of its name derived from 6us acid, 
 and yewau, I produce. All the non-metallic elements, except hydrogen 
 and fluorine, are capable of forming acids by their union with oxygen. 
 
 11. The metals, as a class, exhibit a greater disposition to unite directly 
 with oxygen, tho'ugh few of them will do so in their ordinary condition 
 and at the ordinary temperature. Several metals, such as iron and lead, 
 are superficially oxidised when exposed to air under ordinary conditions, 
 but this would not be the case unless the air contained water and car- 
 bonic acid, which favour the oxidation in a very decided manner. Among 
 the metals which are of importance in practice, five only are oxidised by 
 exposure to dry air at the ordinary temperature, viz., potassium, sodium, 
 barium, strontium, and calcium, the attraction of these metals for oxygen 
 being so powerful that they must be kept under petroleum, or some simi- 
 lar liquid free from oxygen. On the other hand, three of the common 
 metals, silver, gold, and platinum, have so little attraction for oxygen that 
 they cannot be induced to unite with it directly, even at high temperatures. 
 
 If a lump of sodium be cut across with a knife, the fresh surfaces will 
 exhibit a splendid lustre, but will very speedily tarnish by combining 
 with oxygen from the air, which gives rise to a coating of oxide of sodium 
 or soda, and this to some extent protects the metal beneath from oxidation. 
 Even when the attraction of the sodium for oxygen is increased by the 
 application of heat, it is long before the mass of sodium is oxidised 
 throughout, unless the temperature be sufficiently high to convert a por- 
 tion of the sodium into vapour, which bursts through the crust of soda, 
 and burns with a yellow flame. If the spoon containing the sodium (see 
 fig. 4) be now plunged into a jar of oxygen, the yellow flame will be far 
 more brilliant. 
 
 One combining weight (23 parts) of sodium here combines with one 
 combining weight (8) of oxygen to form soda (ISTaO), which remains in the 
 spoon in a fused state. When the spoon is cool, it may be placed in 
 water, which will dissolve the soda, acquiring a peculiar soapy feel and 
 taste, as well as the property of restoring the blue colour to litmus paper 
 which has been reddened by an acid. These properties are called alka- 
 line, apparently because they were known to the early alchemists as being 
 possessed by the ashes of plants (potashes) called kali. 
 
 (DEF. A mineral* alkali is a metallic oxide easily soluble in water, and 
 capable of restoring the blue colour to litmus which has been reddened 
 by an acid.) 
 
 If some diluted sulphuric acid be added drop by drop to a portion of 
 the solution of soda, it will be found, after a certain quantity has been 
 added, that the solution no longer feels soapy, and has a saline taste ; if a 
 piece of reddened litmus paper be wetted with it, the colour will remain 
 unchanged, and the solution will not redden blue litmus paper. Such a 
 
 * There are other alkalies, such as ammonia and the vegetable alkalies, which are not 
 metallic oxides. 
 
OXYGEN WITH METALS. 9 
 
 solution is said to be neutral to test-papers, the alkali and the acid 
 having neutralised each other. 
 
 (DEF. Neutralisation is the destruction of the characteristic properties 
 of an acid by an alkali or the converse.) 
 
 The liquid now contains a new substance called a salt (the strict defini- 
 tion of which will be given hereafter), and known as sulphate of soda, 
 which would be represented in symbols by ISTaO . 80 3 .* 
 
 Now, it will be remembered that soda (NaO) is composed of 23 parts 
 by weight of sodium and 8 .parts of oxygen; hence 31 parts by weight 
 would be represented by ISTaO. And sulphuric acid (S0 3 ) is composed of 
 16 parts by weight of sulphur, and (8 x 3) 24 parts of oxygen, so that 
 S0 3 represents 40 parts by weight, and the combining weights of soda 
 and (anhydrous) sulphuric acid are respectively 31 and 40. 
 
 (EuLE. The combining weights of compounds are obtained by adding 
 together the weights represented by their symbols.) 
 
 All acids would not have neutralised the properties of the alkali, in 
 the above experiment, so completely as sulphuric acid ; thus carbonic acid 
 would never entirely destroy the property of the soda to restore the blue 
 colour to reddened litmus, although it would very considerably modify 
 its other properties ; the solution of soda itself is capable of corroding the 
 skin and textile fabrics, whence its old name of caustic soda, but when 
 combined with carbonic acid, to form carbonate of soda, it loses these 
 properties, and becomes what the older chemists called a mild alkali. 
 Even the weakest acids possess this property of partially neutralising the 
 alkalies. 
 
 (DEF. An acid is a compound body which is capable of neutralising 
 an alkali, either partly or entirely.) 
 
 12. Zinc will serve as an example of a metal which has no disposition 
 to enter into combination with oxygen at the ordinary temperature,t but 
 which is induced to unite with it by a very moderate heat. If a little 
 zinc (spelter) be melted in a ladle or crucible, and stirred about with an 
 iron rod, it burns with a beautiful greenish flame produced by the union of 
 the vapour of zinc with the oxygen of the 
 air. But the combustion is far more bril- 
 liant if a piece of zinc-foil be made into a 
 tassel (fig. 5), gently warmed at the end, 
 dipped into a little flowers of sulphur, 
 kindled, and let down into a jar of oxy- 
 gen, when the flame of the burning sul- 
 phur will ignite the zinc, which burns with 
 great brilliancy. On withdrawing what 
 remains of the tassel after the combustion 
 is over, it will be found to consist of a 
 friable J mass, which has a fine yellow Fig. 5. -Zinc burning in oxygen, 
 colour while hot, and becomes white as it cools. This is the oxide of 
 zinc (ZnO), formed by the union of one combining weight (32*8 parts) of 
 zinc with one combining weight (8 parts) of oxygen. 
 
 The oxide of zinc does not possess the properties of an acid or an alkali, 
 but belongs to another class of compounds termed bases, which are not 
 
 * In expressing by symbols a compound of two or more compounds, they are always 
 separated from each other by a full stop. 
 
 'h Unless water and carbonic acid be present, as in common air. 
 Friable, easily crumbled or disintegrated. 
 
10 BASE SALT SALT-RADICAL. 
 
 soluble in water as the alkalies are, but, like them, are capable of neu- 
 tralising, either partly or entirely, the acids. Thus, if the oxide of zinc 
 were added to diluted sulphuric acid as long as the acid would dissolve it, 
 the well-known corrosive properties of the acid would be destroyed, 
 although it would still retain the power of reddening blue litmus, and the 
 solution would now contain a new substance, or salt, called sulphate of 
 oxide of zinc* (ZnO . S0 3 ). 
 
 (DBF. A base is a compound body which is capable of neutralising an 
 acid, either partly or entirely.) 
 
 It will be observed that an alkali is only a particular species of base, 
 and might be defined as a base which is very soluble in water. 
 
 (DEF. A salt is a compound body containing an acid in combination 
 with a base, or a metal in combination with a salt-radical.^ Examples. 
 Mtrate of potash (KO . N0 5 ) composed of (anhydrous) nitric acid (N0 5 ) 
 and potash (KO). Chloride of sodium (NaCl).) 
 
 (DEF. A salt-radical or halogen is a substance which forms an acid 
 when combined with hydrogen. Examples. Chlorine, which forms 
 hydrochloric acid (HC1) ; Cyanogen (C 2 N), which forms hydrocyanic acid 
 (HC.N).) 
 
 13. Iron, in its ordinary form, like zinc, is not oxidised by dry air or 
 oxygen at the ordinary temperature; but if it be heated even to only 
 500 F. a film of oxide of iron forms upon its surface, and as the heat is 
 increased the thickness of the film increases, until eventually it becomes so 
 thick that it can be detached by hammering the surface, as may be seen 
 in a smith's forge. If an iron rod as thick as the little finger be heated 
 to whiteness at the extremity, and held before the nozzle of a powerful 
 
 bellows, it will burn brilliantly, throwing 
 off sparks and dropping melted oxide of 
 iron. If a stream of oxygen be substituted 
 for air, the combustion is of the most bril- 
 liant description. A watch-spring (iron 
 combined with about 1 per cent, of carbon) 
 may be easily made to burn in oxygen by 
 heating it in a flame till its elasticity is 
 destroyed, and coiling it into a spiral (A, 
 fig. 6), one end of which is fixed, by means 
 of a cork, in the deflagrating collar B ; if 
 Fig. 6.-Watch-spring burning the otner end be filed thin and clean? 
 
 dipped into a little sulphur, kindled, and 
 
 immersed in a jar of oxygen (C) standing in a plate of water, the burning 
 sulphur will raise the iron to the point of combustion, and the spring will 
 be converted into molten drops of oxide. 
 
 The black oxide of iron formed in all these cases is really a combina- 
 tion of two distinct oxides of iron, one of which contains one combining 
 weight of iron (28 parts) and one (8 parts) of oxygen, and would be 
 written FeO, whilst the other contains two combining weights (56) of iron 
 and three (24) of oxygen, expressed by the formula Fe 2 3 ." To distinguish 
 them, the former is usually called protoxide of iron (Trpwros, first), and the 
 
 * For the sake of brevity, it is usual to omit oxide of in designating salts. Thus sulphate 
 of copper means sulphate of oxide of copper, nitrate of silter means nitrate of oxide of 
 silver. 
 
 t Salts of this description are termed haloid salts, because they belong to the same class 
 as sea-salt (Nad), from dXs, the sea. 
 
OXIDES. 11 
 
 latter sesquioxide (in allusion to the ratio of one and a-half to one between 
 the oxygen and the metal).* The sesquioxide of iron combined with 
 water constitutes ordinary rust. 
 
 The black oxide usually contains one combining weight of each oxide, 
 so that it would be written FeO . Fe 2 3 , or Fe 3 4 . It is powerfully 
 attracted by the magnet, and is often called magnetic oxide of iron. The 
 abundant magnetic ore of iron, of which the loadstone is a variety, has a 
 similar composition. 
 
 < Iron in a very fine state of division will take fire spontaneously in air 
 as certainly as phosphorus. Pyrophoric iron can be obtained (by a process 
 to be described hereafter) as a black powder, which must be preserved in 
 sealed tubes. When the tube is opened, and its contents thrown into the 
 air, oxidation takes place, and' is attended with a vivid glow. In this 
 case the red sesquioxide of iron is produced instead of the black oxide. 
 
 Both these oxides of iron are capable of neutralising, or partially neu- 
 tralising, acids, and are therefore basic oxides or bases, like the oxides of 
 zinc and sodium obtained in previous experiments. So general is the 
 disposition of metals to form oxides of this class, that it may be regarded 
 as one of the distinguishing features of a metal, for no non-metal ever 
 forms a base with oxygen. 
 
 (DBF. A metal is an element capable of forming a baset by combining 
 with oxygen, or a salt by combining with a salt-radical.) 
 
 Many metals are capable also of forming acids with oxygen ; thus, tin 
 forms stannic acid (Sn0 2 ), antimony forms antimonic acid (Sb0 5 ), and it 
 is always found that the acid oxide of a metal contains a larger proportion of 
 oxygen than any of the other oxides which the metal may happen to form. 
 
 14. There is a third class of oxides, termed the indifferent oxides, be- 
 cause they are neither acids nor bases j such oxides may be formed either 
 by non-metals or metals;. thus water (HO), the oxide of hydrogen, is an 
 indifferent oxide, and the black oxide or binoxide of manganese (Mn0 2 ) 
 is an example of an indifferent metallic oxide. It will be seen hereafter 
 that the oxides of the non-metals are generally acids, and that when 
 a metal combines with oxygen in several proportions, the oxides contain- 
 ing the smallest proportion of oxygen are usually bases, whilst those con- 
 taining the largest proportion are acids, and the indifferent oxides contain 
 an intermediate proportion of oxygen. The following list of the oxides of 
 manganese will exemplify this, and will illustrate the names commonly 
 bestowed upon oxides in order to indicate the proportion of oxygen which 
 they contain : 
 
 Protoxide of Manganese, . . MnO, Strong Base. .. ** 
 Sesquioxide of . Mn 2 3 Weak Base. 
 
 ' 
 
 Manganic Acid, . . . . Mn0 3 
 Permanganic Acid, . . . Mn 2 6 7 
 
 15. Preparation of Oxygen. For almost all the useful arts in which 
 uncombined oxygen is required, the diluted gas contained in atmospheric 
 
 * The terms ferrous and ferric oxide are now very often substituted for protoxide and 
 sesquioxide of iron. 
 
 t The metal tungsten appears at present to be an exception to this rule, no well- 
 defined basic oxide of this metal being known. 
 
 A peroxide is the highest oxide which does not possess acid properties. 
 
12 PREPARATION OF OXYGEN. 
 
 air is sufficient, since the nitrogen mixed with it does not interfere with 
 its action. 
 
 From atmospheric air pure oxygen was first obtained by Lavoisier towards 
 the end of the last century. His process is far too tedious to be employed 
 as a general method of preparing oxygen, but it affords a very good example 
 of the relation of heat to chemical attraction. Some mercury was poured 
 into a glass flask with a long narrow neck, which was placed in a sand- 
 bath, so that its temperature might be constantly maintained at about 
 660 F. for several weeks. The mercury boiled, and a portion of it was 
 converted into vapour, which condensed in the neck of the flask and ran 
 back again. Eventually the mercury was converted into a red powder, 
 having combined with the oxygen of the air (or undergone oxidation) to 
 form the red oxide of mercury. The nitrogen of the air does not enter 
 into combination with the mercury. 
 
 By heating this oxide of mercury to a temperature approaching a red 
 heat (about 1000 F.) it is decomposed into mercury and oxygen gas 
 (HgO = Hg+0). 
 
 It is very generally found, as in this instance, that heat of moderate 
 intensity will favour the operation of chemical attraction, whilst a more 
 intense heat will annul it. 
 
 For the purpose of experimental demonstration, the decomposition of the oxide 
 of mercury may be conveniently effected in the apparatus represented by fig. 7, 
 where the oxide is placed in the German glass tube A, and heated by the Bunsen's 
 
 Fig. 7. Preparation of oxygen from oxide of mercury. 
 
 gas-burner B, the metallic mercury being condensed in the bend C, and the oxygeu 
 gas collected in the gas cylinder D, filled with water, and standing upon the bee- 
 hive shelf of the pneumatic trough E. It may be identified by its property of kindling 
 into flame the spark left at the end of a wooden match. If the heat be continued 
 for a sufficient length of time, the whole of the oxide of mercury \vill disappear, 
 being resolved into its elements. In technical language, the mercury is said to be 
 reduced. 
 
 Upon the first application of heat, the red oxide suffers a physical change, in 
 consequence of which it becomes black ; but its red colour returns again if it be 
 allowed to cool. 
 
 Although processes have lately been devised for obtaining a supply 
 of unmixed oxygen at a cheap rate from the atmosphere, the demand for 
 the gas is as yet so small that they have not been carried out on a large 
 scale. 
 
 1 6. The only other natural source from which it has been found Con- 
 venient to prepare pure oxygen is a black mineral composed of manganese 
 and oxygen. It is found in some parts of England, but much more 
 
PREPARATION OF OXYGEN. 13 
 
 abundantly in Germany and Spain, whence it is imported for the use of 
 the bleacher and glass-maker. Its commercial name is manganese, but it 
 is known to chemists as binoxide of manganese (Mn0 2 ), and to minera- 
 logists by several names designating different varieties. The most signi- 
 ficant of these names is pyrolubite, referring to the facility with which it 
 may be decomposed by heat (imp, fire, and Auto, to loosen). 
 
 One of the cheapest methods of preparing oxygen consists in heating 
 small fragments of this black oxide of manganese in an iron retort, placed 
 in a good fire, the gas being collected in jars filled with water, and stand- 
 ing upon the shelf of the pneumatic trough, or in a gas-holder or gas-bag, 
 if larger quantities are required. 
 
 The attraction existing between manganese and oxygen is too powerful 
 to allow the metal to part with the whole of its oxygen when heated, so 
 that only one-third of the oxygen is given off in the form of gas, a brown 
 oxide of manganese being left in the retort.* 
 
 1 7. By far the most convenient source of oxygen, for general use in the 
 laboratory, is the artificial salt called chlorate of potash, which is largely 
 manufactured for fireworks, percussion- 
 cap composition, &c. If a few crystals 
 of this salt be heated in a test-tube over 
 a spirit-lamp (fig. 8), it soon melts to a 
 clear liquid, which presently begins to 
 boil from the disengagement of bubbles 
 of oxygen, easily recognised by intro- 
 ducing a match with a spark at the end 
 into the upper part of the tube. If the 
 action of heat be continued until no more 
 oxygen is given off, the residue in the 
 tube will be the salt termed chloride of 
 
 . rig. o. 
 
 potassium. 
 
 The chlorate of potash (KO.C10 5 ) is composed of potash (KO) and 
 chloric acid (C10 5 ). If the potash were uncombined with chloric acid, 
 heat would be quite incapable of decomposing it, but chlorine has a more 
 powerful attraction for potassium than even oxygen has at a high tem- 
 perature , and accordingly, when the salt is heated, union takes place 
 between the potassium and the chlorine, whilst the whole of the oxygen 
 is expelled in the form of gas, a result expressed by the equation 
 
 KO.CKX KC1 + 6 . 
 
 Chlorate of potash. Chloride of potassium. 
 
 To ascertain what quantity of oxygen would be furnished by a given* weight of 
 chlorate of potash, the combining weights must be brought into use. Referring to 
 the table of combining weights (p. 2), it is found that K = 39, = 8, and 
 Cl = 35-5 ; hence the combining weight of chlorate of potash is easily calculated. 
 
 One combining weight of potassium, . 
 
 chlorine, . . 35-5 
 
 Six combining weights of oxygen, . . 48 
 
 KO . C10 5 = 122-5 
 So that 122-5 grains of chlorate of potash would yield 48 grains of oxygen. 
 
 * Expressed in the form of an equation : 3 Mn02 = Mn 3 4 + 2 . 
 
 Black oxide of Brown oxide of 
 
 manganese. manganese. 
 
14 
 
 OZONE. 
 
 If it be required to know what would be the measure or volume of this oxygen 
 at the ordinary atmospheric temperature (60 F.) and pressure (30 inches barometer), 
 it must first be known that 31 grains of air under those conditions would occupy 
 100 cubic inches. Then, knowing (5) the specific gravity of oxygen to be 1-1057, 
 the proportion 
 
 1 1-1057 :: 31 x 
 
 Spec. gr. (or 
 
 weight of 1 vol.) 
 
 of air, 
 
 Spec. gr. (or 
 jight of 1 voL) 
 of oxygen, 
 
 Weight of 
 
 100 cub. in. 
 
 of air, 
 
 Weight of 
 100 cub. in. 
 of oxgyen, 
 
 gives us 34-28 grains for the weight of 100 cub. in. of oxygen. 
 
 (KuLE. To find the weight of 100 cub. in. of a gas at 60 F. and 30 in. Bar., multiply 
 its specific gravity by 31). 
 
 Then 34-28 : 100 :: 48 ; 140 
 
 Grs. of Oxygen. Cub. In. Grs. of Oxygen. Cub. In. 
 
 Hence it is found that 122-5 grains of chlorate of potash would give 140 cub. in. 
 of oxygen measured at 60 F. and 30 in. Bar. 
 
 If one gallon (277-276 cub. in.) of oxygen be required, 242-6 grains of chlorate 01 
 potash must be used, or rather more than half an ounce. 
 
 Since the complete decomposition of the chlorate of potash alone re- 
 quires a more intense heat than a glass vessel will, usually endure, it is 
 customary in preparing oxygen for chemical purposes to facilitate the 
 decomposition of the chlorate by mixing it with about one-fifth of its 
 weight of powdered black oxide of manganese, when the whole of the 
 oxygen is given off at a comparatively low temperature, though the oxide 
 of manganese itself suffers no change, and its action has not yet received 
 any explanation which is quite satisfactory. 
 
 Fig. 9 shows a very convenient arrangement for preparing and collecting oxygen 
 for the purpose of demonstrating its relations to combustion. A is a Florence flask, 
 
 Fig. 9. Preparation of oxygen. 
 
 in which the glass tube B is fixed by a perforated cork. C is a tube ol vulcanised 
 india-rubber. The gas-jar is filled with water, and supported upon a bee-hive shelf 
 made of earthenware. If pint gas-jars be employed, 300 grains of the chlorate of 
 potash, mixed with 60 grains of binoxide of manganese, will furnish a sufficient 
 supply of gas for the ordinary experiments. The heat must be moderated according 
 to the rate at which the gas is evolved, and the tube C must be taken out of the 
 water before the lamp is removed, or the contraction of the gas in cooling will suck 
 the water back into the flask. The first jar of gas will contain the air with which 
 the flask was filled at the commencement of the experiment. The oxygen obtained 
 will have a slight smell of chlorine. 
 
 OZONE. 
 
 18. OZONE is the name given to a substance of the true nature of which there is 
 still some doubt, as it has never been obtained in a pure state, but which is pretty 
 generally believed to be oxygen in a peculiar condition, much more disposed to com- 
 
PROPERTIES OF OZONE. 15 
 
 bine directly with other substances at the ordinary temperature than common 
 oxygen, and possessed of a peculiar odour, whence it derives its name (, to smell). 
 Oxygen appears to be capable of assuming this ozonised condition under various 
 circumstances, the principal of which are, the passage of silent electric discharges,* 
 and the contact with substances (such as phosphorus) undergoing slow oxidation in 
 the presence of water. A minute proportion of the oxygen obtained in the decom- 
 position of water by the galvanic current also exists in the ozonised condition, as 
 may be perceived by its odour. 
 
 The use of Siemens' induction tube (fig. 10) affords the readiest method of 
 
 Fig. 10. Tube for ozonising air by induction. 
 
 demonstrating the characteristic properties of ozone. This apparatus consists of a 
 tube (A) coated internally with tin-foil (or silvered on the inside), and surrounded 
 with another tube (B) which is coated with tin-foil on the outside. When the inner 
 and outer coatings are placed in connexion with the wires of an induction coil 
 by means of the screws (C D), and a stream of air or oxygen is passed through (E) 
 between the two tubes, a strong odour is perceived at the orifice (F). 
 
 One of the best chemical tests for ozone is a damp mixture of starch with iodide 
 of potassium. 100 grains of starch are well mixed in a mortar with a measured 
 ounce of cold water, and the mixture is slowly poured into five ounces of boiling 
 water in a porcelain dish, with occasional stirring. The thin starch-paste thus 
 obtained is allowed to cool, and a few drops of solution of pure iodide of potassium 
 are added, the mixture being well stirred with a glass rod. If this mixture be 
 brushed over strips of white cartridge paper, these will remain unchanged in 
 ordinary air ; but when they are exposed to ozonised air (such as that which has 
 passed through the induction tube), they will immediately assume a blue colour. 
 The ozonised oxygen being more active, or endowed with more powerful chemical 
 attractions than ordinary oxygen, abstracts the potassium from the iodide of 
 potassium (KI), and sets free the iodine, which has the specific property of impart- 
 ing a blue colour to starch. The intensity of the blue tint is proportionate to the 
 quantity of iodine liberated, and therefore to that of the ozonised oxygen pre- 
 sent, and hence, by reference to a standard scale of colours previously agreed 
 upon, the ozone may be expressed in degrees. The result, however, is affected 
 by so many trifling circumstances, that it is doubtful whether such determina- 
 tions of the quantity of ozone are to be considered trustworthy. If the ozonised 
 air issuing from F be passed into a solution of indigo (sulphindigotic acid largely 
 diluted) the blue colour will soon disappear, since the ozone oxidises the indigo, 
 and gives rise to products which, in a diluted state, are nearly colourless. Ordi- 
 nary oxygen is incapable of bleaching indigo in this manner. If the ozone is 
 passed through a tube of vulcanised caoutchouc, this ' will soon be perforated by 
 the corrosive effect of the ozone, whilst ordinary oxygen would be without effect 
 upon it. 
 
 If the ozone from F be made to pass slowly through a glass tube heated in the 
 centre by a spirit-lamp, it will be found to lose its power of affecting the iodised 
 starch-paper, the ozone having been reconverted into ordinary oxygen under the 
 influenco of heat. A temperature of 300 F. is sufficient to effect this change. It 
 has been observed that a given volume of oxygen diminishes when a portion of it is 
 converted into ozone by the silent electric discharge, and that it regains its original 
 
 * It is the odour of ozone which is perceived in working an ordinary electrical machine. 
 
16 CHEMISTRY OF THE ATMOSPHERE. 
 
 volume when the ozone is reconverted by heat, proving that the ozonised form of 
 oxygen is denser, or occupies less space than the ordinary form. 
 
 By placing a freshly-scraped stick of phosphorus (scraped under water to avoid 
 inflammation) at the bottom of a quart bottle, with enough water to cover half of it, 
 and loosely covering the bottle with a glass plate, enough ozone may be accumu- 
 lated in a few minutes to be readily recognised by the odour and the iodised starch. 
 A plausible explanation of this production of ozone during the slow oxidation of 
 phosphorus in the presence of water will be found under the head of peroxide of 
 hydrogen. 
 
 If a few drops of ether (C 4 H 5 0) be poured into a quart beaker (fig. 11), taking 
 care to avoid the vicinity of a flame, and pieces of iodised starch-paper and blue 
 
 litmus paper be suspended upon a glass rod laid 
 across the mouth of the beaker, they will be found 
 unaffected by the mixture of ether vapour and 
 air ; but if a hot glass rod be plunged into the 
 beaker, the heated ether vapour will undergo 
 oxidation, producing acid vapours, which redden 
 the blue litmus, whilst the formation of ozone 
 will be indicated by the blue iodised starch (see 
 peroxide of hydrogen) .* 
 
 Ozone has attracted much notice, because a 
 minute proportion of the oxygen in the atmo- 
 sphere appears sometimes to be present in this 
 form, and its active properties have naturally led 
 to the belief that it must exercise some influence 
 upon the sanitary condition of the air. This idea 
 is encouraged by the circumstance that no indica- 
 tions of ozone can be perceived in crowded cities, 
 where there are so many oxidisable substances to consume the active oxygen, whilst 
 the air in the open country and at the sea-side does give evidence of its presence. 
 Some chemists assert that their experiments have demonstrated the very important 
 fact that a portion of the oxygen developed by growing plants is in the ozonised 
 form. 
 
 The investigations into the true nature of ozone have given rise to interesting 
 speculations with respect to the molecular constitution of oxygen, which will be 
 noticed in the article upon peroxide of hydrogen. 
 
 ATMOSPHERIC Am. 
 
 19. Atmospheric air consists chiefly of a mixture of nitrogen with one- 
 fifth of its volume of oxygen, and very small proportions of carbonic 
 acid and ammonia. Vapour of water is of course always present in the 
 atmosphere in varying proportions. Since the atmosphere is the re- 
 ceptacle for all gaseous emanations, other substances may be discovered 
 in it by very minute analysis, but in proportions too small to have 
 any perceptible influence upon its properties. Thus marsh-gas or light 
 carburetted hydrogen, sulphuretted hydrogen, and sulphurous acid, can 
 often be traced in it, the two last especially in or near towns. 
 
 Although the proportion of oxygen in the air at a given spot may be 
 much diminished, and that of carbonic acid increased, by processes of 
 oxidation (such as respiration and combustion) taking place there, the 
 operation of wind and of diffusion so rapidly mixes the altered air with 
 the immensely greater general mass of the atmosphere, that the variations 
 in the composition of air in diiferent places are very slight. Thus it has 
 been found that the proportion of oxygen in the air in the centre of 
 Manchester was, at most, only 0'2 per cent, below the average. 
 
 * The oxygen obtained by the action of warm sulphuric acid on binoxide of barium 
 resembles ozone in its odour and action on the iodised starch-paper. 
 
ATMOSPHERIC AIR. 
 
 17 
 
 The proportions in which the oxygen and nitrogen are generally pre- 
 sent in atmospheric air are 
 
 
 Volumes. 
 
 Weights. 
 
 Mtrogen, . /'.-.. 
 Oxygen, . 
 
 79-19 
 20-81 
 
 76.99 
 23-01 
 
 100-00 
 
 100-00 
 
 The proportion of aqueous vapour may be stated, on the average, as 1 -4 
 per cent, by volume, or 0-87 per cent, by weight of the air. The carbonic 
 acid may be generally estimated at 0*04 per cent, by volume, or 0'06 per 
 cent, by weight of the air. 
 
 The relative proportions of oxygen and nitrogen in air may be exhibited by sus- 
 pending a stick of phosphorus upon a wire stand (A, fig. 12) in a measured volume of 
 air confined over water. The cylinder (B) should 
 have been previously divided into five equal 
 spaces by measuring water into it, and each 
 space marked by a thin line of Brunswick black. 
 After a few hours, the phosphorus will have 
 combined with the whole of the oxygen to form 
 phosphorous acid, which is absorbed by the water, 
 leaving four of the spaces occupied by nitrogen. 
 
 The same result may be arrived at in a much 
 shorter time by burning the phosphorus in the 
 confined portion of air. 
 
 A fragment of phosphorus, dried by careful 
 pressure between blotting paper, is placed upon 
 a convenient stand (A, fig. 13) and covered 
 
 with a tall jar, having an opening at the top -p. ,Q 
 
 for the insertion of a well-fitting stopper 
 
 (which should be greased with a little lard), and divided into seven parts of 
 equal capacity. The jar should be placed over the stand in such a manner 
 that the water may occupy the two lowest 
 spaces into which the jar is divided. The 
 stopper of the jar is furnished with a hook, to 
 which a piece of brass chain (B) is attached, 
 long enough to touch the phosphorus when the 
 stopper is inserted. The end of this chain is 
 heated in the flame of a lamp, and the stopper 
 tightly fixed in its place. On allowing the hot 
 chain to touch the phosphorus, it bursts into 
 vivid combustion, filling the jar with thick 
 white fumes, and covering its sides, for a few 
 moments, with white flakes of phosphoric acid. 
 At the commencement of the experiment, the 
 water in the jar will be depressed, in conse- 
 quence of the expansion of the air, due to the 
 heat produced in the burning of the phosphorus, 
 but, presently, when the combustion begins to 
 decline, the water again rises, and continues 
 to do so until it has ascended to the line (C), so as to occupy the place of one-fifth of the 
 air employed in the experiment. The phosphorus will then have ceased to burn, the 
 white flakes upon the sides of the jar will have acquired the appearance of drops of 
 moisture, and the fumes will have gradually disappeared, until, in the course of half- 
 an-hour, the air remaining in the jar will be as clear and transparent as before, the 
 whole of the phosphoric acid having been absorbed by the water. The jar should 
 now be sunk in water, so that the latter may attain to the same level without as 
 within the jar. On removing the stopper, it will be found that the nitrogen in the 
 jar will no longer support the combustion of a taper. 
 
 In the rigidly accurate determination of the relative proportions of oxygen and 
 
 B 
 
 Fig. 13. 
 
18 ANALYSIS OF AIR. 
 
 nitrogen in the air, it is, of course, necessary to guard against any error arising from 
 the presence of the water, carbonic acid, and ammonia. With this view, Dumas and 
 Boussingault, to whom we are chiefly indebted for our exact knowledge of the com- 
 position of the air, caused it to pass through a series of tubes (A, fig. 14) containing 
 potash, in order to remove the carbonic acid, then through a second series (B), contain- 
 ing sulphuric acid, to absorb the ammonia and water ; the purified air then passed 
 through a glass tube (C) filled with bright copper heated to redness in a charcoal 
 furnace, which removed the whole of the oxygen, and the nitrogen passed into the 
 large globe (N). 
 
 Both the tube (containing the copper) and the globe were carefully exhausted of 
 air and accurately weighed before the experiment ; on connecting the globe and the 
 tube with the purifying apparatus, and slowly opening the stop-cocks, the pressure of 
 the external air caused it to flow through the series of tubes into the globe destined 
 to receive the nitrogen. When a considerable quantity gf air had passed in, the 
 stop-cocks were again closed, and, after cooling, the weight of the globe was accurately 
 determined. The difference between this weight and that of the empty globe before 
 the experiment, gave the weight of the nitrogen which had entered the globe, but 
 this did not represent the whole of the nitrogen contained in the analysed air, for the 
 
 Fig. 14. Exact analysis of air. 
 
 tube containing the copper had, of course, remained full of nitrogen at the close of 
 the experiment. This tube having been weighed, was attached to the air-pump, the 
 nitrogen exhausted from it, and the tube again weighed ; the difference between the 
 two weighings furnished the weight of the nitrogen remaining in the tube, and was 
 added to the weight of that received in the globe. The oxygen was represented by 
 the increase in the weight of the exhausted tube containing the copper, which was 
 partially converted into oxide of copper, by combining with the oxygen of the air 
 passed through it. 
 
 The calculation of the result of the analysis is here exemplified : 
 
 Weight of Grains. 
 
 Globe (N) with nitrogen (at the conclusion) , . . 3076 
 
 Exhausted globe (at the commencement), . . . 3000 
 
 Nitrogen received into the globe, ... 76 
 
 Tube (C) with residual nitrogen (at the conclusion), . 2574 
 Exh austed tube (at the conclusion) 2573 
 
 Nitrogen remaining in the tube, ... 1 
 
 Add nitrogen received into the globe, . . 76 
 
 Total nitrogen in the air analysed, . . 77 
 
 Exhausted tube (C) with oxidised copper (at the conclusion), 2573 
 
 i metallic copper (at the commencement), 2550 
 
 Oxygen in the air analysed, 23 
 
 The ratio of the oxygen to the nitrogen, therefore, is that of 23N : 770, or IN 
 3.3470. 100 parts by weight of the air purified from water, carbonic acid, and am- 
 monia, contain 77 parts of nitrogen and 23 parts of oxygen. 
 
 20. The nitrogen remaining after the removal of the oxygen from air in 
 the above experiments, was so called on account of its presence in nitre 
 (saltpetre KO . N0 5 ). In physical properties it resembles oxygen, but is 
 somewhat lighter than that gas, its specific gravity being 0*9713. 
 
 This difference in the specific gravities of the two gases is well exhibited by 
 the arrangement shown in fig. 16. A jar of oxygen (0) is closed with a glass 
 plate, and placed upon the table. A jar of nitrogen (N), also closed with a glass 
 
HYDROGEN. 
 
 19 
 
 plate, is placed over it, so that the two gases may come in contact when the glass 
 plates are removed. The nitrogen will float for some seconds above the oxygen, 
 and if a lighted taper be quickly introduced through 
 the neck of the upper jar, it will be extinguished in 
 passing through the nitrogen, and will be rekindled 
 brilliantly when it reaches the oxygen in the lower jar. 
 
 It might at first sight appear surprising that 
 oxygen and nitrogen, though of different specific 
 gravities, should exist in uniform proportions in 
 all parts of the atmosphere, unless in a state of 
 chemical combination, but an acquaintance with 
 the property of diffusion (see Hydrogen) pos- 
 sessed by gases teaches us that gases will mix 
 with each other in opposition to gravitation, and 
 when mixed will always remain so. 
 
 That air is simply a mechanical mixture of its 
 component gases is amply proved by the circum- 
 stance that it possesses all the properties which 
 would be predicted for a mixture of these gases 
 in such proportions ; whilst the essential feature 
 of a chemical compound is, that its properties 
 cannot be foreseen from those of its constituents. 
 
 Fig. 15. 
 
 The absence of active chemical properties is a very striking feature of 
 nitrogen, and admirably adapts it for its function of diluting the oxygen 
 in the atmosphere. There is no direct test by which nitrogen gas can be 
 recognised, so that the chemist is obliged to prove that the gas under ex- 
 amination does not possess the characters of any other gas with which he 
 is acquainted before he can pronounce it to be nitrogen. 
 
 The chemical relations of air to animals and plants will be more appro- 
 priately discussed hereafter. (See Carbonic Acid, Ammonia.) 
 
 HYDEOGEK 
 
 21. Unlike oxygen, hydrogen is very rarely found uncombined in nature. 
 In combination it occurs abun- 
 dantly in water and in all ani- 
 mal and vegetable substances. 
 All varieties of fuel contain 
 hydrogen. It is always pro- 
 cured from the first of these 
 sources. 
 
 Water is composed of the 
 two elements, hydrogen and 
 oxygen, held together by che- 
 mical attraction. To separate 
 these elements, that is, to de- 
 compose or analyse water, we 
 have to overcome the chemical 
 attraction between them, which 
 may be effected by causing the 
 particles of water to transmit 
 a current of voltaic electricity. Fi S- 16. -Electrolysis of water. 
 
 An arrangement for decomposing water by the voltaic or galvanic battery 
 is represented in fig. 16. 
 
 B2 
 
20 
 
 ANALYSIS OF WATER. 
 
 The glass vessel A contains water, to which a little sulphuric acid has been added to 
 increase its power of conducting electricity, for pure water conducts so imperfectly tliat 
 it is decomposed with great difficulty. B and C are platinum plates bent into a cylin- 
 drical form, and attached to stout platinum wires, which are passed through corks in 
 the lateral necks of the vessel A, and are connected by binding screws with the copper 
 wires D and E, which proceed from the galvanic battery G. H and are glass cylin- 
 ders with brass caps and stop-cocks, and are enlarged into a bell-shape at their lower 
 ends for the collection of a considerable volume of gas. These cylinders are filled 
 
 Fig. 18. 
 
 Fig. 17. 
 
 with the acidulated water, by sucking out the air through the opened stop-cocks; on 
 closing these, the pressure of the air will of course sustain the column of water in 
 the cylinders. G is a Grove's battery, consisting of five cells or earthenware vessels 
 (A, fig. 17) filled with diluted sulphuric acid (one measure of oil of vitriol to four of 
 water). In each of these cells is placed a bent plate of zinc (B), which has been 
 amalgamated or rubbed with mercury (and diluted sulphuric acid) to protect it from 
 
 corrosion by the acid when the battery is 
 not in use. "Within the curved portion of 
 this plate rests a small flat vessel of un- 
 glazed earthenware (C), filled with strong 
 nitric acid, in which is immersed a sheet of 
 platinum foil (D). The platinum (D) of 
 each cell is in contact, at its upper edge, 
 with the zinc (B) in the adjoining cell (fig. 
 18), so that at one end (P, fig. 16) of the 
 battery there is a free platinum plate, and at 
 the other (Z) a free zinc plate. These plates 
 are connected with the wires D and E by 
 means of the copper plates L and K attached 
 to the ends of the wooden trough in which 
 the cells are arranged. The wire D (fig. 16), which is connected with the last zinc 
 plate of the battery, is often called the " negative pole ;" whilst E, in connexion with 
 the last platinum plate, is called the "positive pole." 
 
 When the connexion is established by means of the wires D and E with the " de- 
 composing cell" (A), the " galvanic current" is commonly said to pass along the 
 wire E to the platinum plate C, through the acidulated water in the decomposing 
 cell, to the platinum plate B, and thence along the wire D back to the battery. 
 
 22. During this "passage of the current" (which is only a figurative mode 
 of expressing the transfer of the electric influence), the water intervening 
 between the plates B and C is decomposed, its hydrogen being attracted 
 to the plate B (negative pole), and the oxygen to the plate C (positive 
 pole). The gases can be seen adhering in minute bubbles to the surface 
 of each plate, and as they increase in size they detach themselves, rising 
 through the acidulated water in the tubes H and 0, in which the two 
 gases are collected. 
 
 Since no transmission of gas is observed between the two plates, it is 
 evident that the H and separated at any given moment from each plate 
 do not result from the decomposition of one particle of water, but from 
 two particles, as represented in fig. 19, where A represents the particles of 
 water lying between the plates P and Z before the " current" is passed, 
 
ELECTROLYSIS OF WATEK. 
 
 21 
 
 and B the state of the particles when the current has been established. 
 P is (the positive pole) in connexion with the last platinum plate of the 
 battery, and Z is (the negative pole) in connexion with the last zinc 
 plate. 
 
 
 o 
 
 
 
 
 
 
 
 O 
 
 
 
 O 
 
 
 
 
 
 H 
 
 H 
 
 H 
 
 H 
 
 H 
 
 H 
 
 H 
 
 H 
 
 H 
 
 
 Fig. 19. 
 
 The signs + and made use of in B refer to a common mode of account- 
 ing for the decomposition of water by the battery, on the supposition that 
 the oxygen is in a negatively electric condition, and therefore attracted by 
 the positive pole P; whilst the hydrogen is in a positively electric condi- 
 tion, and is attracted by the negative pole Z. 
 
 The decomposition of compounds by galvanic electricity is termed elec- 
 trolysis.* When a compound of a metal with a non-metal is decomposed 
 in this manner, the metal is usually attracted to the (negative) pole in 
 connexion with the zinc plate of the battery, whilst the non-metal is 
 attracted to the (positive) pole connected with the platinum plate of the 
 battery. 
 
 Hence the metals are frequently spoken of as electro-positive elements, 
 and the non-metals as electro-negative. 
 
 23. If the passage of the " current" be interrupted when the tube H has 
 become full of gas, the tube will be only half full, since water contains 
 hydrogen and oxygen in the proportion of two volumes of hydrogen to one 
 volume of oxygen. When the wider portions of the tubes (fig. 16) are 
 also filled, the two gases may be distinguished by opening the stop-cocks 
 in succession, and presenting a burning match. The hydrogen will be 
 known by its kindling with a slight detonation, and burning with a very 
 pale flame at the jet ; whilst the oxygen will very much increase the bril- 
 liancy of the burning match, and if a spark left at the extremity of the 
 match be presented to the oxygen, the spark will be kindled into a flame. 
 The oxygen will be found to smell strongly of ozone, and will impart a 
 deep blue tinge to the iodised starch paper (see Ozone). 
 
 Another method of effecting the decomposition of water by electricity 
 consists in passing a succession of electric sparks through steam. It is 
 probable that in this case the decomposition is produced rather by the 
 intense heat of the spark than by its electric influence, t 
 
 For this purpose, however, the galvanic battery does not suffice, since 
 no spark can be passed through any appreciable interval between the wires 
 of the battery, a fact which electricians refer to in the statement that 
 although the quantity of electricity developed by the galvanic battery is 
 large, its intensity is too low to allow it to discharge itself in sparks like 
 the electricity from the machine or from the induction-coil, which pos- 
 sesses a very high intensity, though its quantity is small. 
 
 2L The most convenient instrument for producing a succession of elec- 
 
 (amber root of electricity) ; Xuo>, to loosen. 
 
 That a very intense heat is capable of decomposing water into its elements has long 
 been known. When globules of melted platinum are dropped into water, bubbles of 
 hydrogen and oxygen are disengaged. 
 
22 DECOMPOSITION OF STEAM. 
 
 trie sparks is the induction-coil, by the aid of which the electric influence 
 of even a single cell of the galvanic battery may be so accumulated as to 
 become capable of discharging itself in sparks, such as are obtained from 
 the electrical machine.* 
 
 Fig. 20 represents the arrangement for exhibiting the decomposition of steam by 
 the electric spark. 
 
 A is a half-pint flask furnished with a cork in which three holes are bored ; in one 
 of these is inserted the bent glass tube B, which dips beneath the surface of the water 
 in the trough 0. 
 
 Fig. 20. --Decomposition of steam by electric sparks. 
 
 D and E are glass tubes, in each of which a platinum wire has been sealed so as 
 to project about an inch at both ends of the tube. These tubes are thrust through 
 the holes in the cork, and the wires projecting inside the flask are made to approach 
 to within about T V inch, so that the spark may pass easily between them. 
 
 The flask is somewhat more than half filled with water, the cork inserted, and the 
 tube B allowed to dip beneath the water in the trough ; the wires in D and E being 
 connected with the thin copper wires passing from the induction-coil F, which is 
 connected by stout copper wires with the small battery G. 
 
 The water in the flask is boiled for about fifteen minutes, until all the air con- 
 tained in the flask has been displaced by steam. When this is the case, it will be 
 found that if a glass test-tube (R) filled with water be inverted f over the orifice of 
 the tube B, the bubbles of steam will entirely condense, with the usual sharp rattling 
 sound, and only insignificant bubbles of air will rise to the top of the test-tube. If 
 now, whilst the boiling is still continued, the handle of the coil (F) be turned so 
 as to cause a succession of sparks to pass through the steam in the flask, large 
 bubbles of incondensable gas will accumulate in the tube H. This gas consists of 
 the hydrogen and oxygen gases in a mixed state, having been released from their 
 combined condition in water by the action of the electric sparks. The gas may be 
 tested by closing the mouth of the tube H with the thumb, raising it to an upright 
 position, and applying a lighted match, when a sharp detonation will indicate the 
 recombination of the gases. J 
 
 25. In the preceding experiments, the force of chemical attraction 
 holding the particles of oxygen and hydrogen together in the form of 
 water, has been overcome by the physical forces of heat and electricity. 
 But water may be more easily decomposed by acting upon it with some 
 element which has a sufficiently powerful chemical attraction for the oxygen 
 of water to draw it away from the hydrogen. 
 
 * For a description of the induction-coil, see Miller's " Elements of Chemistry/' Part I. 
 
 f The end of the tube B should be bent upwards and thrust into a perforated cork with 
 notches cut down the sides. By slipping this cork into the neck of the test-tube, the latter 
 will be held firmly. 
 
 J With a powerful coil, a cubic inch of explosive gas may be collected in about fifteen 
 minutes. 
 
ACTION OF METALS ON WATER. 23 
 
 No non-metallic element is capable of abstracting the oxygen from water 
 at the ordinary temperature. 
 
 Among the practically important metals, the five which have been 
 mentioned as undergoing oxidation in dry air at the ordinary temperature, 
 effect the immediate decomposition of water. 
 
 Metals which decompose water at the ordinary temperature. Potassium, 
 Sodium, Barium, Strontium, Calcium. 
 
 When a piece of potassium is thrown upon water it takes fire and burns 
 with a fine violet flame, floating about as a melted globule upon the surface 
 of the water, combining with the oxygen, and producing, in the act of 
 combination, enough heat to kindle the hydrogen as it escapes. The 
 violet colour of the flame is due to the presence of a little potassium in 
 the form of vapour. The water will be found to change red litmus paper 
 to blue, from the presence of the alkali potash (KO) formed by the com- 
 bination of the potassium with the oxygen. The decomposition of the 
 water is expressed by the equation 
 
 HO + K = KO + H 
 
 Water. Potash. 
 
 from which we learn that one combining weight (39 parts) of potassium 
 has been substituted for one combining weight (1 part) of hydrogen. 39 
 parts by weight of potassium, therefore, have the same power as 1 part of 
 hydrogen, to combine with 8 parts (one combining weight) of oxygen. It 
 is found that whenever potassium takes the place of hydrogen in a com- 
 pound, 39 parts of the former are exchanged for one of the latter, and this 
 is generally expressed by stating that 39 is tne chemical equivalent of 
 potassium. 
 
 (DBF. The chemical equivalent of a metal expresses tjie weight which 
 is required to be substituted for one part by weight of hydrogen in its 
 compounds.) 
 
 The action of potassium upon water is an example of the production of 
 compounds by substitution of one element for another, a mode of forma- 
 tion which is far more common than the production of compounds by 
 direct combination of their elements. 
 
 Sodium has a less powerful attraction for oxygen than potassium, and 
 does not usually take fire when thrown into cold water, although it is at 
 once fused by the heat evolved in its combination with the oxygen. By 
 holding a lighted match over the globule as it swims upon the water, the 
 hydrogen may be kindled, when 
 its flame is bright yellow from the 
 presence of the sodium. The solu- 
 tion will be found strongly alkaline 
 from the soda produced. By plac- 
 ing the sodium on a piece of blotting- 
 paper laid on the water, it may be 
 made to ignite the hydrogen spon- 
 taneously, because the paper keeps 
 it stationary, and prevents it from 
 being so rapidly cooled by the water. 
 Several cubic inches of hydrogen 
 may easily be collected by placing 
 a piece of sodium as large as a bean 
 in a small wire-gauze box (A, fig. 21), and holding it under an inverted 
 
24 
 
 ACTION OF METALS ON WATER. 
 
 cylinder (B) filled with water and standing upon a bee-hive shelf. The 
 equation representing the action of sodium upon water, 
 
 HO + ISTa = NaO + H 
 
 Water. Soda. 
 
 shows that one combining weight (23 parts) of sodium is substituted for 
 one combining weight (1 part) of hydrogen, and, in accordance with the 
 definition above given, 23 is the chemical equivalent of sodium. 
 
 Barium, strontium, and calcium decompose water less rapidly than 
 potassium and sodium ; the results of their action upon water are, respec- 
 tively, baryta (BaO), strontia (SrO), and lime (CaO). These substances 
 have strongly alkaline characters, but as they are far less soluble in water 
 than potash and soda, they have been distinguished as alkaline earths. 
 
 The tendency of heat to produce the union of metals with oxygen being 
 known, it might be expected that metals which refuse to decompose water 
 at the ordinary temperature, would be induced to do so if the temperature 
 were raised, and accordingly magnesium and manganese, which are without 
 action upon cold water, decompose it at the boiling point, disengaging 
 hydrogen, and producing magnesia (MgO, a feebly alkaline earth) and 
 oxide of manganese (MnO). 
 
 But the greater number of the common metals must be raised to a much 
 higher temperature than this in order to enable them to decompose water. 
 The following metals will abstract the oxygen from water at high tem- 
 peratures, those at the commencement of the list requiring to be heated to 
 redness (about 1000 F.), and the temperature required progressively in- 
 creasing, until it attains whiteness for those at the end of the list. 
 
 Metals which decompose water at a temperature above a red heat. 
 Zinc, Iron, Chromium, Cobalt, Mckel, Tin, Antimony, Aluminum, Lead, 
 Bismuth, Copper. 
 
 The noble metals, as they are called, which exhibit no tendency to 
 oxidise in air, are incapable of removing the oxygen from water, even at 
 high temperatures. 
 
 Metals which are incapable of decomposing water. Mercury, Silver, 
 Gold, Platinum. 
 
 Fig. 22. Preparation of hydrogen from steam. 
 
 26. Preparation of hydrogen. The simplest process, chemically 
 speaking, for preparing hydrogen in quantity, consists in passing steam 
 over red-hot iron. An iron tube (A, fig. 22) is filled with iron nails and 
 
PKEPAKATION OF HYDEOGEN. 
 
 25 
 
 fixed across a furnace (B), in which it is heated to redness by a charcoal 
 fire. A current of steam is then passed through it by boiling the water in 
 the flask (C), which is connected with the iron tube by a glass tube (D) 
 and perforated corks. The hydrogen is collected from the glass tube (G) 
 in cylinders (E) filled with water, and inverted in the trough (F) upon 
 the bee-hive shelf (H), the first portions being allowed to escape, as con- 
 taining the air in the apparatus. The iron combines with the oxygen of 
 the water to form the black oxide of iron (Fe 3 4 ), which will be found in 
 a crystalline state upon the surface of the metal. The decomposition is 
 represented by the equation 
 
 4HO + Fe 3 - Fe 3 4 + H 4 
 
 Water. 
 
 Fe 3 4 + 
 
 Black oxide of iron. 
 
 from which it would appear that three combining weights (28 x 3 = 84 
 parts) of iron are substituted for four combining weights (4 parts) of 
 hydrogen; and according to the definition given above, the chemical 
 equivalent of iron should be expressed by 21, that being the weight re- 
 quired to be substituted for 1 part of hydrogen. Since, however, this is 
 found to be the only case in which iron displaces hydrogen in this pro- 
 portion, it is better to represent the action of water upon red-hot iron as 
 taking place in two successive stages, of which the first is represented by 
 the equation 
 
 HO + Fe - FeO + H 
 
 Water. Ferrous oxide. 
 
 and the second by 
 
 HO + 3 FeO = Fe 3 4 + H* 
 
 Ferrous oxide. Black oxide of iron. 
 
 According to the first of these equations, one combining weight (28 
 parts) of iron is substituted for one combining weight of hydrogen, and, 
 accordingly, 28 would represent the chemical equivalent of iron. 
 
 The process by which hydrogen is most commonly prepared depends 
 upon the circumstance, that many of those metals which are able to de- 
 compose water, either at ordinary or elevated temperatures, will also 
 decompose it in the presence of an acid without the assistance of heat. 
 
 Metals which decompose water at the ordinary temperature in the pre- 
 sence of an acid. Potassium, Sodium, Barium, Strontium, Calcium, Mag- 
 nesium, Manganese, Zinc, 
 Iron, Chromium, Cobalt, 
 Nickel 
 
 Zinc is the most conve- 
 nient metal to employ for the 
 preparation of hydrogen in 
 this way. It is used either in 
 small fragments or cuttings, 
 or as granulated zinc, pre- 
 pared by melting it in a ladle 
 and pouring it from a height 
 of three or four feet into a 
 pailful of water. The zinc 
 is placed in the bottle 
 (A, fig. 23), covered with 
 water to the depth of two Fi S- 23. Preparation of hydrogen. 
 
 * This view is supported by the fact that FeO (protoxide of iron), when prepared by 
 other processes, is capable of decomposing water in accordance with the second equation. 
 
26 PROPERTIES OF HYDROGEN. 
 
 or three inches, and diluted sulphuric acid slowly poured in through the 
 funnel tube (B) until a pretty brisk effervescence is observed. The 
 hydrogen is unable to escape through the funnel tube, since the end of 
 it is beneath the surface of the water, but it passes off through the bent 
 tube (C), and is collected over water as usual, the first portions being 
 rejected as containing air. The chemical change is expressed in the 
 equation 
 
 HO . SO. + Zn = ZnO . S0 3 + H 
 
 Sulphate of zinc. 
 
 from which it appears that one combining weight (32 '8 parts) of zinc is 
 substituted for one combining weight (1) of hydrogen, and that 3 2 '8 re- 
 presents the chemical equivalent of zinc.* 
 
 By evaporating the larger excess of water from the solution left in the 
 bottle, crystals of sulphate of zinc (white vitriol) may be obtained. It 
 would not be possible to fulfil the above equation without adding a great 
 deal more water than is there represented, in order to dissolve the sul- 
 phate of zinc. 
 
 It will be noticed that the liquid becomes very hot during the action 
 of the acid upon the zinc, the heat being produced by the combination 
 which is taking place. The black flakes which separate during the solu- 
 tion of the zinc consist of metallic lead, which is always present in the 
 zinc of commerce, and much accelerates the evolution of hydrogen by 
 causing galvanic action. Pure zinc placed in contact with diluted sulphuric 
 acid evolves hydrogen very slowly. 
 
 Iron might be used instead of zinc, and the solution when evaporated 
 would then deposit crystals of green vitriol or copperas (sulphate of iron 
 FeO . S0 3 ), the action of iron upon water in the presence of sulphuric 
 acid being represented by the equation 
 
 HO . 80s + Fe = FeO . S0 3 + H 
 
 Su^ate of iron. 
 
 which shows that one combining weight (28) of iron has taken the place 
 of one combining weight of hydrogen. 28 would then be the chemical 
 equivalent of iron. 
 
 27. Physical properties of hydrogen. This gas is permanent, invisible, 
 and inodorous when pure. The hydrogen obtained by the ordinary 
 methods has a very disagreeable smell, caused by the presence of minute 
 quantities of compounds of hydrogen with sulphur, arsenic, and carbon; 
 but the gas prepared with pure zinc and sulphuric acid is quite free from 
 smell. The most remarkable physical property of hydrogen is its light- 
 ness. It is the lightest of all kinds of matter. The specific gravity of 
 hydrogen is 0*0692, so that it is about -fa as heavy as air. This lightness 
 would strongly recommend hydrogen as the unit of comparison for the 
 specific gravities of gases, and theoretical considerations would compel 
 the admission of an elementary standard in place of a somewhat variable 
 mixture like atmospheric air. But since the hydrogen required to fill a 
 pint globe weighs only three quarters of a grain, whilst the same volume 
 
 * Many explanations have been offered to account for the circumstance that the Zn will 
 decompose HO in the presence of S0 3 , although this latter has no attraction for either of 
 the elements of the HO. One of the most satisfactory appears to be that which refers the 
 decomposition to the attraction of the Zn for the group represented by [OS0 3 ], which is 
 greater than the attraction of H for the same group, whilst the attraction of H for alone, 
 at the ordinary temperature, is greater than that of Zn for 0. 
 
DIFFUSION OF GASES. 
 
 of air weighs ten grains and three quarters, it will be seen that no balance 
 of even considerable accuracy could be depended upon for the practical 
 determination of the specific gravities of gases if hydrogen were the 
 standard employed. 
 
 In calculating the weights and volumes of gases, it will be found of great service to 
 remember that one gram of hydrogen measures 46-73 cub. in. at 60 F. and 30 in. Bar. 
 
 The lightness of hydrogen may be demonstrated by many interesting experiments. 
 Soap bubbles or small balloons (of collodion for example) will ascend very rapidly if 
 inflated with hydrogen. A light bea"ker glass may be accurately weighed in a pair 
 of scales ; it may then be held with its mouth downwards, and hydrogen poured up 
 into it from another vessel. If it be then replaced upon the scale-pan with its 
 mouth downwards, it will be found very much lighter than before. Another form 
 of the experiment is represented in fig. 24, where a light glass shade has been sus- 
 pended from the balance and counterpoised, the equilibrium being, of course, at once 
 
 Fig. 24. 
 
 disturbed when hydrogen is poured up into the shade. If a jar full o 
 held with its mouth downwards, and a piece of smouldering brown pap 
 
 hydrogen be 
 er held under 
 
 it, the smoke, which would rise freely in the air, is quite unable to rise through the 
 hydrogen, and remains at the mouth of the jar. 
 
 28. It will be observed, in these experiments, that the glas gradually 
 falls out of the jar, notwithstanding its lightness, and is replaced -by air. 
 This is accounted for by a physical property belonging to all gases (and 
 vapours) called diffusibility, which may be defined as the tendency of the 
 particles of a gas to separate as far as possible from each other. If a jar 
 of hydrogen were placed with its mouth downwards over a jar of air, this 
 mutual repulsion among the particles of each gas would cause it to diffuse 
 itself equally throughout both jars, so that, eventually, as much hydrogen 
 would be found in the lower jar as if it had been completely exhausted of 
 air before the commencement of the experiment. This is often expressed 
 by the statement that one gas acts as a vacuum to another, which is true 
 as far as the ultimate result is concerned, though, of course, the time 
 occupied by the passage of a gas into a vacuum would b far less than 
 that required for its passage into another gas. Even if the two jars be 
 
28 
 
 DIFFUSION OF GASES. 
 
 connected only by a tube with the narrowest passage possible, the same 
 result would be arrived at, but after a longer period. If the two gases 
 were separated by a plate of some material having 
 no visible passages, such as paper, or plaster of 
 Paris, a complete interchange would still take 
 place, and after a time each gas would be found 
 equally distributed through both jars. Ey thus 
 interposing a porous obstacle so as to retard the 
 diffusion of the gas, the rapidity with which the 
 particles of gases separate from each other in con- 
 sequence of this mutual repulsion may be ascer- 
 tained. The diffusion tube (fig. 25) employed for 
 this purpose is a glass tube (A) closed at one 
 end by a plate of plaster of Paris (B). If this 
 tube be filled with hydrogen,* and its open end 
 immersed in coloured water, the water will be ob- 
 served to rise rapidly in the tube, on account of 
 the rapid escape of the hydrogen through the pores of the plaster. The 
 external air, of course, passes into the tube through the pores at the same 
 time, but much less rapidly than the hydrogen passes out, so that the 
 ascent of the column of water (C) marks the difference between the volume 
 of hydrogen which passes out, and that of air which passes into the 
 
 Fig. 25. 
 
 Fig. 26. Separation of hydrogen and oxygen by atmolysis.f 
 
 tube in a given time, and allows a measurement to be made of the rate of 
 diffusion ; that is, of the velocity with which the gas issues on account of 
 the repulsion among its particles, as compared with the velocity with 
 
 * This tube must be filled by displacement (see fig. 30), in order not to wet the plaster. A 
 piece of sheet caoutchouc may be tied over the plaster of Paris, so that dilFusion may not 
 commence until it; is removed. 
 
 t This term has been applied to the separation of gases by diffusion ; OT/UOV, vapnur 
 \vw, to loosen. 
 
DIFFUSION OF GASES. 
 
 29 
 
 which the air enters, this velocity being always taken as unity."' To deter- 
 mine the rate of diffusion, it is of course necessary to maintain the water 
 at the same level within and without the diffusion tube, so as to exclude 
 the influence of pressure. 
 
 Experiment has established the law that 
 the rates of diffusion of gases are inversely 
 as the square roots of their specific gravi- 
 ties ; for example, the specific gravities of 
 oxygen and hydrogen stand to each other 
 in the ratio of 16 : 1 ; the ratio of their 
 square roots will therefore be 4 : 1, and 
 their rates of diffusion will be in the in- 
 verse ratio, or 1 : 4; that is, hydrogen 
 would escape through minute openings with 
 four times the velocity of oxygen; and 
 laboratory experience shows that a cracked 
 jar, or a bottle with a badly fitting stop- 
 per, may often be used to retain oxygen, 
 but not hydrogen. Again, the specific 
 gravities of air and hydrogen, being respec- 
 tively 1 and -069, their rates of diffusion 
 
 will be 1 and . or 3 -8, so that in the 
 v-069 
 
 experiment with the diffusion tube, 3 '8 
 cubic inches of hydrogen would pass out, 
 whilst 1 cubic inch of air passed in ; and 
 if the influence of pressure be excluded, 
 2 '8 cubic inches of water would enter the 
 tube. 
 
 The great difference in the rates of diffusion 
 of hydrogen and oxygen may be easily shown 
 by the arrangement represented in fig. 26. A 
 is a jar filled with a mixture of two volumes of 
 oxygen with one volume of hydrogen, communi- 
 cating through the stop-cock and flexible tube 
 with the glass tube B, which is fitted through 
 a perforated cork in the bowl of the common 
 tobacco pipe C, the sealing-waxed end of which 
 dips under water in the trough D. By opening 
 the stop-cock and pressing the jar down in the water, the mixed gases may be forced 
 rapidly through the pipe, and if a small cylinder (E) be filled with them, the mixture 
 will be found to detonate violently on the approach of a flame. But if the gas be 
 made to pass very slowly through the pipe (at the rate of about a cubic "inch per 
 minute), the hydrogen will diffuse through the pores of the pipe so much faster than 
 the oxygen, that the gas collected in the cylinder will contain so little hydrogen as 
 to be no longer explosive, and to exhibit the property of oxygen to rekindle a partly 
 extinguished match.f 
 
 Another very striking illustration of the high rate of diffusion of hydrogen is 
 arranged as represented in fig. 27. A is a cylinder of porous earthenware (such as 
 
 * Air being a mixture of nitrogen and oxygen, its rate of diffusion is intermediate between 
 the rates of those gases ; however, since the proportions of the gases are very nearly con- 
 stant, no error of any magnitude arises. 
 
 f Caoutchouc and varnished silk, being impervious to air, do not permit ordinary diffu- 
 sion to take place through them. Yet they are capable of transmitting gases by a peculiar 
 mode of action, which may be compared to their power of transmitting ether and other 
 liquids capable of wetting them. In this manner oxygen has been found to be transmitted 
 more rapidly than nitrogen, so that by placing atmospheric air in contact with a film of 
 
 Fig. 27. 
 
30 
 
 PROPERTIES OF HYDROGEN. 
 
 are employed in galvanic batteries) closed at one end, and furnished at the other 
 with a perforated bung, through which passes a glass tube B, about three feet long, 
 and half an inch in diameter. The bung is made air-tight by coating it with seal- 
 ing wax dissolved in spirit of wine. This tube being supported so that its lower 
 end dips about an inch below the surface of water, a jar of hydrogen is held over 
 the porous cylinder, when the self-repulsion of the particles of the gas is mani- 
 fested by their being forced (not only out of the mouth of the jar C, which is open 
 at the bottom, but also) through the pores of the earthenware jar, the air from which 
 is violently driven out, as if by blowing, through the tube, and is seen bubbling up 
 rapidly through the water. When the air has ceased to bubble out, and a large 
 volume of hydrogen has entered the porous jar, the bell-jar C is removed, when 
 the hydrogen escapes so rapidly through the pores, that a column of twenty or 
 thirty inches of water is drawn rapidly up the tube B. If the greatest height 
 to which the water ascends be marked, and when it has returned to its former 
 level, a jar of coal-gas be held over the porous cylinder, 
 it will be found that the above phenomena are mani- 
 fested in a much lower degree, showing that coal-gas, 
 being heavier than hydrogen, does not pass nearly so 
 rapidly through the pores of the earthenware as hydrogen 
 does. 
 
 29. Chemical properties of hydrogen. The 
 most conspicuous chemical property of hydrogen 
 is its disposition to burn in air when raised to 
 a moderately high temperature, entering into 
 combination with the .oxygen of the air to form 
 water. The formation of water during the com- 
 bustion of hydrogen gave rise to its name (vSwp, water). 
 
 Fig 28 
 
 On introducing a taper into an inverted jar of hydrogen (fig. 28), the flame of the 
 taper will be extinguished, but the hydrogen will burn with a pale flame at the 
 mouth of the jar, and the taper may be rekindled at its flame by slowly withdraw- 
 ing it. 
 
 The lightness and combustibility of hydrogen may be illustrated simultaneously 
 by some interesting experiments. If two equal gas cylinders be filled with hydro- 
 gen, and held with their mouths respectively upwards and downwards, it will be 
 
 Fig. 29. 
 
 Fig. 30. 
 
 caoutchouc, on the other side of which a vacuum is maintained, a gaseous mixture may be 
 made to pass through the film, containing 41 '6 per cent, by volume of oxygen, instead of 
 21 per cent., usually present in air. Such a mixture, of course, accelerates combustion in 
 a very high degree. It appears to be in consequence of a similar action that hydrogen is 
 capable of passing through red-hot platinum and iron tubes. (Graham, Proc. Roy. Soc. 
 June 1866.) 
 
PROPERTIES OF HYDROGEN. 
 
 31 
 
 found, on testing each with a taper after the same interval, that the hydrogen has 
 entirely escaped from the cylinder held with its mouth upwards, whilst the other 
 still remains nearly filled with the gas. 
 
 The hydrogen may be scooped out of the jar A (fig. 29) with the small cylinder 
 B attached to a handle. On removing B, and applying a taper to it, the gas will 
 take fire. , 
 
 A cylinder may be filled with hydrogen by displacement of air (fig. 30), if the 
 tube from the hydrogen bottle be passed up into it. 
 
 If such a dry cylinder of hydrogen be kindled whilst held with its mouth down- 
 wards, the formation of water during the combustion of the hydrogen will be indi- 
 cated by the deposition of dew upon the sides of the cylinder. 
 
 By softening a piece of glass tube in the flame of a spirit-lamp, drawing it out, 
 and filing it across in the nar- 
 rowest part (fig. 31), a jet can be 
 made from which the hydrogen 
 may be burnt. This jet may 
 be fitted by a perforated cork to 
 any common bottle for contain- 
 ing the zinc and sulphuric acid Fig. 31. 
 (fig. 32). 
 
 The hydrogen must be allowed to escape for some minutes before applying a 
 light, because it forms an explosive mixture with the air con- 
 tained in the bottle. This may be proved, without risk, by 
 placing a little granulated zinc in a soda-water bottle, pour- 
 ing upon it some diluted sulphuric acid, and quickly insert- 
 ing a perforated cork, carrying a piece of glass tube about 
 three inches long, and one-eighth of an inch wide. If this 
 tube be immediately applied to a flame, the mixture of air 
 and hydrogen will explode, and the cork and tube will be 
 projected to a considerable distance. 
 
 By inverting a small test-tube over the jet in fig. 32, a 
 specimen of the hydrogen may be collected, and may be 
 kindled, to see if it burns quietly, before lighting the jet. 
 
 A dry glass, held over the flame, will collect a considerable 
 quantity of water, formed by the combustion of the hydrogen. Fig. 32. 
 
 The combustion of hydrogen produces a greater heating effect than that 
 of an equal weight of any other combustible body. It has been deter- 
 mined that 1 gr. of hydrogen, in the act of combining with 8 grs. of 
 oxygen, produces enough heat to raise 62,031 grs. of water from 32 F 
 to 33 F. (or 34,462 grs. from C. to 1 C.) 
 
 The temperature of the hydrogen flame has been estimated at 5898 F., 
 which is higher than that of any other 
 single flame with which we are ac- 
 quainted. 
 
 Notwithstanding its high temperature, 
 the flame of hydrogen is almost devoid 
 of illuminating power, on account of the 
 absence of solid particles. 
 
 30. If a taper be held several inches 
 above a cylinder of hydrogen, standing 
 with its mouth upwards, the gas will be 
 kindled with a loud explosion, because 
 an explosive mixture of hydrogen and air 
 is formed in and around the mouth of the 
 cylinder. 
 
 If a stoppered gas jar (fig. 33) be filled with Fig. 33. 
 
 hydrogen, and supported upon three blocks, it 
 will be found, if the hydrogen be kindled at the neck of the jar, that it will burn 
 
32 
 
 EXPLOSION OF HYDROGEN AND AIR. 
 
 quietly until air has entered from below in sufficient proportion to form an explosive 
 
 mixture, which will then explode with a loud report. 
 
 The same experiment may be tried on a smaller scale, with the two-necked copper 
 vessel (fig. 34), the lower aperture being opened some few 
 seconds after the hydrogen has been kindled at the upper 
 one. , 
 
 The explosion of the mixture of hydrogen and 
 air is due to the sudden expansion caused by the 
 heat generated in the combination of the hydrogen 
 with the oxygen throughout the mixture. After 
 the explosion of the mixture of hydrogen and air 
 (oxygen and nitrogen), the substances present are 
 steam (resulting from the combination of the hydro- 
 gen and oxygen) and nitrogen, which are expanded 
 by the heat developed in the combination to a 
 volume far greater than the vessel can contain, so that a portion of it 
 issues very suddenly into the air around, the collision with which pro- 
 duces the report. 
 
 If pure oxygen be substituted for air, the explosion will be more violent, 
 because the mixture is not diluted with the inactive nitrogen. The cal- 
 culated pressure exerted by the mixture of hydrogen and oxygen, when 
 exploded, amounts to 26 atmospheres, or 390 Ibs. upon the square inch, 
 whilst the mixture of hydrogen and air is calculated to exert a pressure 
 of 12 '5 atmospheres, or 187 Ibs. per inch. 
 
 The experiment may be made safely in a soda-water bottle. The bottle is filled 
 with water, and inverted with its mouth beneath the surface of the water ; enough 
 oxygen is then passed up into it to fill one-third of its volume ; if the remainder of 
 the water be then displaced by hydrogen, and the mouth of the bottle be presented 
 to the flame of a spirit-lamp, a very violent explosion will result, attended with a 
 vivid blue flash in the bottle. If the mouth of the bottle be presented towards a disc 
 of paper, previously suspended at a distance of 20 or 30 inches, the paper will be 
 violently torn to pieces, bearing witness to the concussion between the expanded 
 steam issuing from the bottle and the external air. 
 
 Fig. 35. 
 
 If some of the mixture be introduced into a capped jar, provided with a piece of 
 caoutchouc tubing, and a small glass tube, and pressed down in a trough of water, 
 soap-bubbles may be inflated with it, which will ascend rapidly in the air, and ex- 
 plode violently when touched with a flame (fig. 35). 
 
SYNTHESIS OF WATER. 
 
 33 
 
 p 
 
 Fig. 36. 
 
 31. In order to demonstrate the production of water in the explosion, the Caven- 
 dish eudiometer* (fig. 36) is employed. This is a 
 strong glass vessel, with a stopper firmly secured by 
 a clamp (A), and provided with two platinum wires 
 (P), which pass through the stopper, and approach 
 very near to each other within the eudiometer, so 
 that the electric spark may easily be passed between 
 them. By screwing the stop-cock B into the plate of 
 an air-pump, the eudiometer may be exhausted. It 
 is then screwed on to the jar represented in fig. 37, 
 which contains a mixture of two measures of hydro- 
 gen with one measure of oxygen, standing over 
 water. On opening the stop-cocks between the two 
 vessels the eudiometer becomes filled with the mix- 
 ture, and the quantity which has entered is indicated 
 by the rise of the water in the jar. The glass stop- 
 cock C having been closed, to prevent the brass cap 
 from being forced oif by the explosion, the eudio- 
 meter is again screwed on to its foot, and an electric 
 spark passed between the platinum wires, either 
 trom a Leyden jar or an induction coil, when the two gases will combine with a 
 vivid flash of light, attended with a very slight concussion, since there is no col- 
 lision with the external air. For an instant a 
 mist is perceived within the eudiometer, which 
 condenses into fine drops of dew, consisting of 
 the water formed by the combination of the 
 gases, which was here induced by the high tem- 
 perature of the electric spark, as it was in the 
 former experiment by the high temperature of 
 the flame. If the gases have been mixed in 
 the exact proportion of two measures of hydrogen 
 to one measure of oxygen, the eudiometer will 
 now be again vacuous, and if it be screwed on to 
 the capped jar, may be filled a second time with 
 the mixture, which may be exploded in the same 
 manner. 
 
 The entire disappearance of the gases may be 
 rendered obvious to the eye by exploding the 
 mixture over mercury. For this purpose the 
 mixed gases should be collected from water itself, 
 which is strongly acidified with sulphuric acid, 
 and decomposed in the voltameter (A, fig. 
 
 Fig. 37. 
 
 by the aid of five or six cells of Grove's battery. The voltameter contains two 
 platinum plates (B), attached to the platinum wires and D, which are connected 
 with the opposite poles of the battery. The first few bubbles of the mixture of 
 hydrogen and oxygen evolved having been allowed to escape, in order to displace the 
 
 Fig, 38. - -Detonating gas collected from voltameter. 
 
 * So named from ev8io<s, fine or clear, and /mcTpov, a measure, because an instrument 
 upon the same principle has been used to determine the degree of purity of the atmosphere. 
 The particular form of eudiometer here described was employed by Cavendish about the 
 year 1770, for the synthesis of water. 
 
 G 
 
34 
 
 EUDIOMETRIC ANALYSIS OF AIK. 
 
 air, the gas may be collected in the small eudiometer (E), which has been previously 
 filled with water. This eudiometer is a cylinder of very thick glass,* closed at one 
 end, and having two stout platinum wires cemented into holes drilled near the 
 closed end, the wires approaching sufficiently near to each other to allow the passage 
 of the electric spark. Having been filled with the mixture of hydrogen and oxygen 
 from the voltameter, the eudiometer is closed with the finger, and transferred to a 
 basin containing mercury, where it is pressed firmly down upon a stout cushion of 
 india-rubber, and the spark passed through the mixed gases, either from the coil or 
 the Leyden jar. The combustion takes place with violent concussion, but without 
 noise; and since the eudiometer is vacuous after the gases have combined, the 
 cushion will be found to be very firmly pressed against its open end. On loosening 
 the cushion, the mercury will be violently forced up into the eudiometer, which will 
 be completely filled with it, proving that when an electric spark is passed through 
 the mixture of two volumes of hydrogen and one volume of oxygen, no residue of 
 gas remain s.f 
 
 32. The knowledge of the volumes in which hydrogen and oxygen 
 combine, is turned to account in the analysis of gases, to ascertain the 
 proportion of hydrogen or oxygen contained in them. Suppose, for ex- 
 ample, it be required to determine the amount of oxygen in a sample of 
 atmospheric air, the latter is mixed with hydrogen, in more than suffi- 
 cient quantity to combine with the largest proportion of oxygen which 
 could be present, and when the combination has been induced by the 
 electric spark, the volume of gas which has disappeared (2 vols. H + 1 
 vol. 0) has only to be divided by three to give the volume of the 
 oxygen. 
 
 A bent eudiometer (fig. 39) is generally employed for this purpose. Having been 
 completely filled with water, it is inverted in the trough, and the specimen of air is 
 introduced (say 0-5 cubic inch). The open limb is then 
 closed by the thumb, and the eudiometer turned so as to 
 transfer the air to the closed limb. A stout glass rod is 
 thrust down the open limb, so as to displace enough water 
 to equalise the level in both limbs, in order that the 
 volume of the air may not be diminished by the pressure 
 of a higher column of water in the open limb. The 
 volume of the included air having been accurately noted, 
 the open limb of the tube is again filled up with water, 
 inverted in the trough, and a quantity of hydrogen intro- 
 duced, equal to about half the volume of the air. This 
 having been transferred, as before, to the closed limb, the 
 columns of water are again equalised, and the volume of 
 the mixture of air and hydrogen ascertained. The open 
 limb is now firmly closed with the thumb, and the electric 
 spark passed through the mixture, either from the Leyden jar or the induction coil. 
 On removing the thumb, after the explosion, the volume of gas in the closed limb 
 will be found to have diminished very considerably. Enough water is poured into 
 the open limb to equalise the level, and the volume of gas is observed. If this 
 volume be subtracted from the volume before explosion, the volume of gas which 
 has disappeared will be ascertained, and one-third of this will represent the oxygen, 
 which has condensed with twice its volume of hydrogen into the form of water. 
 Thus the numbers recorded will be 
 
 * The bore of this eudiometer should be about half an inch in diameter, and the thick- 
 ness of its sides about three-eighths of an inch ; , its length is 7 inches. 
 
 f This fact may also be demonstrated with the siphon eudiometer, shown in fig. 39, by 
 confining about a cubic inch of the explosive mixture in the closed limb, over water, and 
 stopping the open limb securely with a cork, so as to leave a space filled with air between 
 the cork and the water. The eudiometer must be very firmly fixed on a stand, or it will 
 be broken by the concussion. After it has been proved, it may be held in the hand, as 
 in the figure. By firing mixtures of hydrogen and oxygen, in different proportions, in the 
 same manner, it may be shown that any excess of either gas above the ratio of 2H : 10 will 
 remain ucombined after the explosion. 
 
 Fig. 39. 
 Siphon eudiometer. 
 
COMBINING VOLUMES. 35 
 
 Volume of air analysed, .... 0-50 cub. in. 
 
 Volume of air mixed with hydrogen, . . 0-75 
 
 After explosion, ..... 0*45 
 
 Difference, ) on 
 
 (fHand^O) | 
 
 30, divided by 3 = -10 cub. in. of oxygen. 
 
 It is evident that the volume of hydrogen contained in a gas might be 
 ascertained in a similar manner, by exploding with oxygen, and taking 
 two-thirds of the gas which had disappeared in the form of water to re- 
 present the volume of hydrogen. 
 
 In exact experiments, a correction would be required for any variation 
 of the temperature or barometric pressure during the progress of the 
 analysis. 
 
 33. It will have been observed, in the experiment upon the synthesis 
 of water in the Cavendish eudiometer, that the volume of water obtained 
 is very small in comparison with that of the gases before combination. 
 But it is evident that no comparison can, with propriety, be made between 
 the volume of a compound, in the liquid or solid state, and that of its 
 components in the gaseous state, since the particles of the former are 
 under the influence of the cohesive force from which those of the latter 
 are free. For the purposes of such a comparison the volume of the com- 
 pound body must be taken under precisely the same physical conditions 
 as the volume of its components. 
 
 If the mixture of hydrogen and oxygen be measured and exploded at 
 a temperature above the boiling point of water, it is found that the steam 
 produced occupies two-thirds of the volume of the mixed gases, measured 
 at the same temperature and atmospheric pressure. Hence, two volumes 
 of hydrogen combine with .one volume of oxygen to form two volumes of 
 aqueous vapour, at the same temperature and pressure. 
 
 It very frequently happens, as in this instance, that the volume of a 
 compound gas or vapour is less than the sum of the volumes of its con- 
 stituent gases. 
 
 The relative volumes in which the gases unite could, of course, be in- 
 ferred from a knowledge of their specific gravities and their combining 
 weights. For since oxygen (sp. gr. 1'1057) is sixteen times as heavy as 
 hydrogen (sp. gr. '0692), equal volumes would give us sixteen parts by 
 weight of the former to one of the latter gas ; and we must take twice 
 the volume of hydrogen in order to obtain the ratio of their combining 
 weights (8 : 1). 
 
 The specific gravity of the vapour of water can also be calculated from 
 the above data.. Thus 
 
 Specific gravity (or weight of one volume) of hydrogen, *0692 
 Weight of two volumes of hydrogen, . . 0-1384 
 Specific gravity or weight of one volume of 
 
 oxygen, ....... 1'1057 
 
 Weight of two volumes of the vapour of water, 1'2441 
 Dividing this by two, we obtain for the 
 
 Weight of one volume, or specific gravity, of 
 
 vapour of water, ..... O622 
 
 which agrees with that obtained by actual weighing. 
 
 c2 
 
36 ATOMIC CONSTITUTION OF WATER. 
 
 34. The combining volumes of gases and vapours represent the re- 
 lative volumes occupied by their combining weights. Hence, if one part 
 by weight of hydrogen be represented as occupying one volume, eight 
 parts (the combining weight) of oxygen must be represented as occupy- 
 ing half a volume. In order to avoid the fraction, however, the eight 
 parts of oxygen may be represented as occupying one volume, so that the one 
 part of hydrogen will correspond to two volumes, and the statement will be 
 
 Combining volume of Oxygen = 1 
 Hydrogen - 2 
 
 35. Atomic theory. In seeking for some explanation of the fact that the 
 relative proportions by weight and volume in which the elements unite- 
 are fixed and definite, it occurred to Dalton that these elements are really 
 composed of a collection of indivisible particles or atoms* which pos- 
 sess a fixed weight for each element. Thus, if the weight of each atom 
 of hydrogen be taken as = 1, and that of an atom, of oxygen as = 8, it would 
 follow, as a matter of course, that these elements must bombine with each 
 other, and with the other elements, in proportions represented by these 
 numbers, or by some simple multiples of them, since fractions of atoms 
 would be inconceivable. 
 
 This theory receives very great support from the fact which has been 
 elicited by experiment, that the combining weights of all the elements 
 which have been examined in the state of vapour or gas occupy the same 
 volume as one part by weight of hydrogen, with the exception of oxygen, 
 sulphur, selenium, phosphorus, arsenic, and tellurium, which occupy half 
 that volume. 
 
 If, therefore, it be further assumed, that the atoms of the different ele- 
 ments, in the gaseous state, occupy equal volumes, the atomic theory will 
 afford an adequate explanation of the laws of combination by weight and 
 volume. But, upon this assumption, the numbers representing the atomic 
 weights of oxygen and the other exceptions above mentioned would not 
 be the same as their combining weights (which occupy only half a volume), 
 but would be twice those weights.t Thus, the atomic weight of oxygen 
 would be 16, since that number represents a weight of oxygen occupying 
 the same volume as 1 part by weight of hydrogen, though its equivalent 
 weight would be 8, which represents the weight of oxygen equal in 
 chemical value to 1 part of hydrogen. 
 
 The formula representing the true atomic constitution of water therefore 
 would be H 2 O = 2 volumes of water, where H 2 represents 2 parts by 
 weight, or two volumes, or two atoms of hydrogen, and represents 16 
 parts, or one volume, or one atom of oxygen. A large number of modern 
 chemists employ such formulae, which represent the number of atoms (or 
 volumes) of each element contained in the compound, in place of those 
 expressing merely the number of combining weights or equivalents. The 
 atomic formulce are preferable in speculative chemistry for purposes of 
 research, but the equivalent formulce are more serviceable in the practical 
 applications of chemistry, and will therefore be more generally adopted in 
 these pages. 
 
 The belief in the existence of atoms is supported by the circumstance, 
 
 * "ATO/IOS, indivisible. 
 
 f Since an atom ought to be the smallest conceivable particle of matter, there seems some 
 incongruity in the idea of a combining weight or equivalent representing half the atomic 
 weight. 
 
OXYHYDROGEN BLOWPIPE. 37 
 
 that those weights of the elements which are assumed to represent the 
 relative weights of their atoms require, in most cases, the same amount of 
 heat to raise them through an equal number of degrees of temperature ; in 
 other words, the atomic heats of the elements, like their atomic volumes, 
 are identical, whilst the amounts of heat required to raise equal weights 
 (specific heats) of the elements through an equal number of degrees are 
 expressed by very different numbers. 
 
 Thus, if the specific heat of water (or quantity of heat required to raise 
 one part by weight of water through one degree) be represented by 1, that 
 of oxygen is 0'2175, and that of hydrogen just sixteen times as great, or 
 3 '409. Hence, it follows that a given weight of hydrogen in cooling 
 down through a certain number of degrees, would give out 16 times as 
 much heat as an equal weight of oxygen would give out, and that the 
 atom (or one part by weight) of hydrogen is associated with the same 
 amount of heat as the atom (or sixteen parts by weight) of oxygen ; and 
 since the specific heat represents the amount of heat associated with one 
 part by weight of the element, the atomic heat of oxygen will be 1 6 times 
 its specific heat (0-217 x 16), or 3 '48, which coincides as nearly as can 
 be expected with the atomic heat of hydrogen (3*409 x 1). 
 
 36. It has also been found that the combining weights of all compound 
 substances which have been examined in the state of gas or vapour occupy 
 either twice or four times the volume of one combining weight of oxygen. 
 
 Hence it appears that 
 
 I. The combining volume of an element in the state of gas or vapour is 
 either one volume (0, &c.), or two volumes (H, &c.). 
 
 II. The combining volume of a compound in the state of gas or vapour 
 is either two volumes or four volumes. 
 
 The adoption of atomic formulae (or molecular formulae, see binoxide of 
 hydrogen] in place of equivalent formulae, is attended with great advantage 
 in the study of the combining volumes of gases and vapours, since the 
 atomic symbol for an elementary substance represents one volume of its 
 gas or vapour, and the, molecular formula for a compound substance 
 two volumes of its gas or vapour. 
 
 37. The great energy with which hydrogen combines with oxygen is 
 turned to account for the purpose of producing the highest temperature 
 which can be obtained by any chemical process. 
 
 The oxyhydrogen blowpipe (fig. 40) is an apparatus for burning a jet of hydrogen 
 mixed with half its volume of oxygen. The gases are supplied from separate gas- 
 holders (or bags with pressure-boards and weights) 
 through the tubes H and 0, which conduct them 
 into the brass sphere B. Each of these tubes is 
 provided with a valve of oiled silk opening out- 
 wards, so as to prevent the passage of either gas 
 into the receptacle containing the other. The 
 tube A is stuffed with thin copper wires, which 
 would rapidly conduct away the heat and extin- 
 guish the flame of the mixed gases burning at the 
 jet,, should it tend to pass back and ignite the 
 mixture in B. The stop-cocks D and E allow the 
 flow of the gases to be regulated so that they may 
 mix in the right proportions. If the hydrogen be 
 
 kindled first, it will be found that, as soon as the 
 oxygen is turned on, the flame is reduced to a very 
 
 40. Oxyhydrogen blowpipe. 
 
 much smaller volume, because the undiluted oxygen required to maintain it 
 
38 CHEMISTKY OF WATER. 
 
 pies only one-fifth of the volume of the atmospheric air from which the hydrogen 
 was at first supplied with oxygen. The heat developed by the combustion being 
 therefore distributed over a much smaller area, the temperature at any given point 
 of the flame must be much higher, and very few substances are capable of enduring 
 it without fusion.*' Lime is one of these ; and if a cylinder of lime be supported, 
 as at L, fig. 40, in the focus of the flame, its particles become heated to intense 
 incandescence, and a light is obtained which is visible at night from very great 
 distances, so as to be well adapted for signalling and lighthouses. For such pur- 
 poses coal-gas is often used instead of hydrogen (oxycalcium light). 
 
 If a shallow cavity be scooped in a lump of quicklime, a few scraps of platinum 
 placed in it, and exposed to the oxyhydrogen flame (fig. 41), a fused globule of pla- 
 tinum of very considerable size may be obtained in 
 a few seconds. By employing a little furnace made 
 of lime, Deville has succeeded in fusing platinum 
 in quantities sufficient to cast large ingots, a result 
 unattainable by any other furnace. Pipeclay, which 
 resists the action of all ordinary furnace-heats, may 
 be fused into a glass in this flame, whilst gold and 
 silver are instantaneously melted, and vaporised 
 Fig. 41. into a dense smoke. 
 
 38. In its chemical relations to other elements, hydrogen is diametri- 
 cally opposed to oxygen. Whereas the latter combines directly with the 
 greater number of the elements, hydrogen will enter into direct combina- 
 tion with very few ; oxygen, chlorine, 'bromine, carbon, iodine, and sulphur 
 (the three last with difficulty), are the only elements which unite in a 
 direct manner with hydrogen, and of these only chlorine and bromine 
 combine with hydrogen at the ordinary temperature, though not without 
 exposure to light. Again, whilst fluorine is not known to form any com- 
 pound with oxygen, its combination with hydrogen (hydrofluoric acid) is 
 one of the most stable compounds known, and it may be safely asserted 
 that fluorine in the free state would combine with hydrogen even more 
 readily than chlorine does. All the metals form compounds with oxygen, 
 but very few combinations of metals with hydrogen have been obtained. 
 Indeed, in its relations to other elements, hydrogen closely resembles the 
 metals, though it does not fall within the definition of a metal given 
 above, since it does not form a base with oxygen, and its combinations 
 with the salt-radicals (chlorine, &c.) are acids, and not salts. 
 
 WATER. 
 
 39. Pure water is not found in nature. Rain is the purest form of 
 natural water, but contains certain gases which it collects from the atmo- 
 sphere during its fall. As soon as it reaches the earth, it begins to dissolve 
 small portions of the various solid materials with which it conies in con- 
 tact, and thus becomes charged with salts and other substances to an 
 extent varying, of course, with the nature of the soils and rocks which it 
 has touched, and attaining its highest point in sea water, which contains 
 a larger proportion of saline matters than water from any other natural 
 source. Ice, when melted, affords nearly pure water, since, when water 
 containing salts is partially frozen, these are left dissolved in the uncon- 
 gealed water. 
 
 If a quantity of rain, spring, river, or sea water be boiled in a flask fur- 
 nished with a tube also filled with the water, and passing under a gas 
 cylinder standing in a trough of the same water (fig. 42), it will be found 
 
 * The temperature of this flame has been estimated at above 14,000 F. 
 
WATER OF WELLS, SPRINGS, AND RIVERS. 
 
 39 
 
 to give off a quantity of gas which was previously held in solution by the 
 water, and is now set free because gases are less soluble in hot than in cold 
 water. The quantity of this 
 gas will vary according to 
 the source of the water, but 
 it will always be found to 
 contain the gases existing in 
 atmospheric air, viz., nitro- 
 gen, oxygen, and carbonic 
 acid. One gallon of rain 
 water will generally furnish 
 about 4 cubic inches of nitro- 
 gen, 2 cubic inches of oxygen, 
 and 1 cubic inch of carbonic 
 acid. It is worthy of remark, 
 that the nitrogen and oxygen 
 have been dissolved by the . 
 water, not in the proportions Fig. 42. 
 
 in which they exist in the at- 
 mosphere (4 N : 1 0), but in the proportions in which they ought 
 to be dissolved, if it be true that they exist in the air in the condition 
 of mere mechanical admixture. The oxygen thus carried down from 
 the air by rain appears to be serviceable in maintaining the respiration 
 of aquatic animals, and in conferring upon river waters a self-purifying 
 power, by acting upon certain organic matters which would probably 
 prove hurtful to animals, and converting them into harmless products of 
 oxidation. In the cases of rivers contaminated with the sewage of towns, 
 this action of the dissolved oxygen is probably of great importance. The 
 carbonic acid dissolved in rain water also probably serves some useful pur- 
 poses in the chemical economy of nature. (See Carbonic Acid.) 
 
 40. The waters of wells, springs, and rivers, and especially those of 
 the two first-named sources, differ very much from each other, according 
 to the nature of the layers of rock or earth over or through which they 
 have passed, and from which they dissolve a great variety of substances, 
 some of which are familiar to us in daily life, while others are only met 
 with in chemical collections. Under the former head may be enume- 
 rated Glauber's salt (sulphate of soda), common salt (chloride of sodium), 
 Epsom salt (sulphate of magnesia), gypsum (sulphate of lime), chalk 
 (carbonate of lime), common magnesia (carbonate of magnesia), carbonic 
 acid, and silica. 
 
 Among the substances known only to the chemist may be mentioned 
 sulphuretted hydrogen, sulphate of potash, chloride of potassium, chloride 
 of calcium, chloride of magnesium, phosphate of lime, bromides and 
 iodides of calcium and magnesium (rarely), alumina (probably sulphate 
 of alumina), carbonate of iron, and certain vegetable substances.* 
 
 The well waters of certain localities (as, for example, those of large 
 towns) also frequently contain salts of nitric and nitrous acids, and of 
 ammonia. 
 
 The waters of springs and rivers do not differ very materially from 
 
 * Although it is certainly known that the acids and bases capable of forming the salts 
 here enumerated may be detected in spring and river waters, their exact distribution 
 amongst each other is still a matter of uncertainty. 
 
40 HARD WATERS. 
 
 well waters as to the nature of the substances which they contain, though, 
 in the case of river waters more particularly, the quantity of these sub- 
 stances is materially influenced by the conditions of rapid motion and 
 exposure to air under which such waters are placed. 
 
 Household experience has established a classification of the waters from 
 natural sources into soft and hard waters a division which depends 
 chiefly upon the manner in which they act upon soap. If a piece of 
 soap be gently rubbed in soft water (rain water, for example) it speedily 
 furnishes a froth or lather, and its cleansing powers can be readily 
 brought into action ; but if a hard water (spring water) be substituted for 
 rain water, the soap must be rubbed for a much longer time before a 
 lather can be produced, or its effect in cleansing rendered evident ; a 
 number of white curdy flakes also make their appearance in the hard 
 water, which were not seen when soft water was used. The explana- 
 tion of this difference is a purely chemical one. 
 
 Soap is formed by the combination of a fatty acid with an alkali ; it is 
 manufactured by boiling oil or fat with potash or soda, the former for 
 soft, the latter for hard soaps. In the preparation of ordinary hard soap, 
 the soda takes from the oil or fat two acids, stearic and oleic acids, which 
 exist in abundance in most varieties of fat, and unites with them to form 
 soap, which in chemical language would be spoken of as a mixture of 
 stearate and oleate of soda. 
 
 If soap be rubbed in soft water until a little of it has dissolved, and 
 some Epsom salts (sulphate of magnesia) be dissolved in water, and 
 poured into the soap water, curdy flakes will be produced, as when soap 
 is rubbed in hard water, and the soap water will lose its property of 
 frothing when stirred ; the sulphate of magnesia has decomposed the soap, 
 the soda contained in the latter has combined with the sulphuric acid 
 existing in the sulphate of magnesia, to form a sulphate of soda which 
 remains dissolved in the water, while the magnesia, uniting with the 
 stearic and oleic acids, produces the insoluble curdy flakes which consist 
 of stearate and oleate of magnesia. 
 
 Similar to the effect of the sulphate of magnesia is that of hard waters ; 
 their hardness is attributable to the presence of the different salts of lime 
 and magnesia, all of which decompose the soap in the manner exem- 
 plified above ; the peculiar properties of the soap in forming a lather and 
 dissolving grease can, therefore, be manifested only when a sufficient 
 quantity has been employed to decompose the whole of the salts of lime 
 and magnesia contained in the quantity of water operated on, and thus 
 a considerable amount of soap must be rendered useless when hard water 
 is employed. 
 
 On examining the interior of a kettle in which spring, well, or river 
 water has been boiled, it will be found to be coated more or less thickly 
 with a fur or incrustation, generally of a brown colour, and the harder 
 the water, the more speedily will this incrustation be deposited. A 
 chemical examination shows this deposit to consist chiefly of carbonate of 
 lime, in the form of minute crystals, which may be discovered by the 
 microscope ; it usually contains, in addition, some carbonate of magnesia, 
 sulphate of lime, and small quantities of sesquioxide of iron (rust), and 
 vegetable matter, the last two substances imparting its brown colour. 
 In order to explain the formation of this deposit, it is necessary to be- 
 come acquainted with the particular condition in which the carbonate of 
 lime exists in natural waters. Carbonate of lime is hardly dissolved to 
 
INCRUSTATIONS ON BOILERS. 41 
 
 any perceptible extent by pure water, though it may be dissolved in con- 
 siderable quantity by carbonic acid. This statement, which is of great 
 importance in connexion with natural waters, may be verified in the fol- 
 lowing manner. A little slaked lime is well shaken up in a bottle of dis- 
 tilled or rain water, which is afterwards set aside for an hour or two ; as 
 soon as that portion of the lime which has not been dissolved has sub- 
 sided, the .clear portion is carefully poured into a glass, and a little soda- 
 water or solution of carbonic acid in water is added to it ; the first addi- 
 tion of the carbonic acid to the lime water causes a milkiness, due to the 
 formation of minute particles of carbonate of lime, by the union of the 
 carbonic acid with the lime ; this carbonate of lime, being insoluble in 
 the water, separates from it, ox precipitates, and impairs the*transparency 
 of the liquid ; a further addition of carbonic acid water renders the liquid 
 again transparent, for the carbonic acid dissolves the carbonate of lime 
 which has separated, forming, in the opinion of some chemists, a definite 
 chemical compound, the bicarbonate of lime, which contains twice as 
 much carbonic acid as the carbonate ; since, however, this bicarbonate of 
 lime has not been separated from the water in a pure state, it is safer to 
 regard it merely as a solution of carbonate of lime in free carbonic acid. 
 
 If this clear solution be introduced into a flask, and boiled over the 
 spirit-lamp or gas-flame, it will again become turbid, for the free carbonic 
 acid will be expelled by the heat, and the carbonate of lime will be de- 
 posited, not now, however, in so fine a powder as before, but in small 
 hard grains which have a tendency to fix themselves firmly upon the 
 sides of the flask, and, when examined by the microscope, are seen to con- 
 sist of small crystals. 
 
 In a similar manner, when natural waters are boiled, the free carbonic 
 acid which they contain is expelled in the gaseous state, and the carbon- 
 ates of lime, magnesia, and oxide of iron are precipitated, since they are 
 insoluble in water which - does not contain carbonic acid. But, by the 
 ebullition of the water, a portion of it has been dissipated in vapour, and 
 if there be much sulphate of lime present, the quantity of water left may 
 not be sufficient to retain the whole of that salt in solution ; and this is 
 the more likely to happen, because sulphate of lime requires about 400 
 parts of water to dissolve it;* a quantity of sulphate of lime, then, is 
 liable to be deposited together with the carbonates of lime, magnesia, and 
 oxide of iron, and, should the water contain much vegetable matter, this 
 is also often deposited in an insoluble condition, the whole eventually 
 forming together a hard compact mass, composed of successive thin layers, 
 on the bottom and sides of the vessel in which the water has been boiled. 
 The "furring" of a kettle is objectionable, chiefly in consequence of its 
 retarding the ebullition of the water, since the deposit is a very bad con- 
 ductor of heat, and therefore impedes the transmission of heat from the 
 fire to the water ; hence the common practice of introducing a round stone 
 or marble into the kettle, in order, by its perpetual rolling, to prevent the 
 particles of carbonate of lime from forming a compact layer. In steam 
 boilers, however, even more serious inconvenience than loss of time some- 
 times arises if this deposit be allowed to accumulate, and to form a 
 thick layer of badly conducting material on the bottom of the boiler, since 
 
 * Sulphate of lime has been found nearly insoluble in water having a higher tempera- 
 ture than 212 F., as would be the case in boilers worked under pressure, so that it would 
 readily be deposited. It is said that waters containing little or no sulphate of lime yield 
 a loose and friable deposit. 
 
42 
 
 CALCAREOUS WATERS. 
 
 the latter is then liable to become red hot, and should the incrustation 
 happen to crack, and allow the water to reach the red hot metal, so 
 violent a disengagement of steam follows, that boilers have been known 
 to burst under the sudden pressure. But even though this calamity be 
 escaped, the wear and tear of the boiler is very much increased in conse- 
 quence of the formation of this deposit, since its hardness often renders 
 it necessary to detach it with the hammer, much to the injury .of the iron 
 boiler-plates, which are also subject to increased oxidation and corrosion, 
 in consequence of the high temperature which the incrustation permits 
 them to attain by preventing their contact with the water. The exigency 
 of the case has elicited many propositions for the prevention of these in- 
 crustations ; *some substances have been used of which the action appears 
 to be purely mechanical, in preventing the aggregation of the deposited 
 particles. Clay, saw-dust, and other matters have been employed with 
 this view ; but the action of sal-ammoniac, which has also been found 
 efficacious, must be explained upon purely chemical principles. When 
 this salt is boiled with carbonate of lime, mutual decomposition ensues, 
 resulting in the production of chloride of calcium and carbonate of 
 ammonia, of which salts the former is very soluble in water, while the 
 latter passes off in vapour with the steam.* 
 
 The incrustations formed in cisterns and pipes by hard water are also 
 produced by the carbonates of lime and magnesia deposited in consequence 
 of the escape of the free carbonic acid which held them in solution. Many 
 interesting natural phenomena may be explained upon the same principle. 
 The so-called petrifying springs, in many cases, owe their remarkable 
 properties to the considerable quantity of carbonate of lime dissolved in 
 carbonic acid which they contain; when any object, a basket, for ex- 
 ample, is repeatedly exposed to the action of these waters, it becomes 
 
 coated with a compact 
 layer of carbonate of lime, 
 and thus appears to have 
 suffered conversion into 
 limestone. The celebrated 
 waters of the Sprudel at 
 Carlsbad, of San-Filippo 
 in Tuscany, and of Saint 
 Allyre in Auvergne, are 
 the best instances of this 
 kind. 
 
 The stalactites and sta- 
 lagmites^ which are form- 
 ed in certain caverns or 
 natural grottoes (fig. 43), 
 afford beautiful examples 
 of the gradual separation 
 of the carbonate of lime 
 from water charged with 
 
 Pig. 43. Stalactite Cavern. 
 
 carbonic acid. Each drop of water, as it trickles through the roof of the 
 
 CaO.C0. 2 + NH 3 .HC1 = NH 3 .HO.C0 2 + CaCl 
 
 Carbonate of lime. Sal-ammoniac. Carbonate of ammonia. Chloride of calcium. 
 
 Solutions of the caustic alkalies, of alkaline carbonates, and arsenites, are also occasion- 
 ally employed to prevent the formation of incrustations in boilers, 
 f* From orraXafw, to drop ; tn-aXayua, a drop. 
 
SOFTENING OF WATERS. 43 
 
 cavern, becomes surrounded with a shell of carbonate of lime, the length of 
 which is prolonged by each drop as it falls, till a stalactite is formed, varying 
 in colour according to the nature of the substances which are separated 
 from the water together with the carbonate of lime (such as the oxides of 
 iron and vegetable matter) ; and as each drop falls from the point of the 
 stalactite upon the floor of the cavern, it deposits there another shell of 
 carbonate of lime, which grows, like the upper one, but in the opposite 
 direction, and forms a stalagmite, thus adorning the grotto with conical 
 pillars of carbonate of lime, sometimes, as in the case of the oriental 
 alabaster, variegated with red and yellow, and applicable to ornamental 
 purposes. 
 
 When water which has been boiled for some time is compared with 
 unboiled water from the same source, it will be found to have become 
 much softer, and this can now be easily explained, for, a considerable 
 proportion of the salts of lime and magnesia having separated from the 
 water, the latter is not capable of decomposing so large a quantity of soap. 
 The amount of hardness which is thus destroyed by boiling is generally 
 spoken of as temporary hardness, to distinguish it from the permanent 
 hardness due to the soluble salts of lime and magnesia which still remain 
 in the boiled water. It is customary with analytical chemists, in report- 
 ing upon the quality of natural waters, to express the hardness by a cer- 
 tain number of degrees which indicate the number of grains of chalk or 
 carbonate of lime which would be dissolved in a gallon of water contain- 
 ing carbonic acid, in order to render its hardness equal to that of the 
 water examined, that is, to render it capable of decomposing an equal 
 quantity of soap. Thus, when a water is spoken of as having 16 degrees 
 hardness, it is implied that 16 grs. of carbonate of lime dissolved in a 
 gallon of water, containing carbonic acid, would render that gallon of water 
 capable of decomposing as much soap as a gallon of the water under 
 consideration. 
 
 The utility of a water for household purposes must be estimated, there- 
 fore, not merely according to the total number of degrees of hardness 
 which it exhibits, but also by the proportion of that hardness which may 
 be regarded as temporary, that is, which disappears when the water is 
 boiled. Thus the total hardness of the New River water amounts to 
 nearly 15 degrees, that of the Grand" Junction Company to 14 degrees, and 
 yet these waters are quite applicable to household uses, since their hard- 
 ness is reduced by boiling to about 5 degrees. It has been ascertained 
 that every degree of hardness in water gives rise to a waste of about 10 
 grs. of soap for every gallon of water employed, and hence the use of 100 
 gallons of Thames or New River water in washing will be attended with 
 the loss of about 2 Ibs. of soap ; this loss is reduced, however, to about 
 one third when the temporary hardness has been destroyed by boiling. 
 The addition of washing soda (carbonate of soda) removes not only the 
 temporary, but also the permanent hardness due to the presence of the 
 sulphates of lime and magnesia in the water, for both these salts are de- 
 composed by the carbonate of soda, which separates the lime and mag- 
 nesia as insoluble carbonates, while sulphate of soda remains dissolved in 
 the water.* The household practice of boiling the water, and adding a 
 little washing soda, is therefore very efficacious in removing the hard- 
 ness. Clark's process for softening waters depends upon the neutralisa- 
 
 * CaO.SO., ' + NaO.C0 2 NaO.S0 3 + CaO.C0 2 
 
 Sulphate of lime. Carbonate of soda. Sulphate of soda. Carbonate of lime. 
 
44 ACTION OF WATER ON LEADEN CISTERNS. 
 
 tion of the free carbonic acid contained in the water by the addition of a 
 certain quantity of lime ; the lime thus added combines with the free 
 carbonic acid, and the carbonate of lime so produced separates together 
 with the carbonates of lime and magnesia, which were previously retained 
 in solution by the free carbonic acid ; this process, therefore, affects chiefly 
 the temporary hardness ; moreover, the earthy carbonates which are sepa- 
 rated appear to remove from the water a portion of the vegetable matter 
 which it contains, and thus effect a very important purification. The 
 water under treatment is mixed in large tanks, with a due proportion of 
 lime previously diffused through water (the quantity necessary having 
 been determined by preliminary experiment), and the mixture allowed to 
 settle until perfectly clear, when it is drawn off into reservoirs.* 
 
 Waters which are turbid from the presence of clay in a state of sus- 
 pension, are sometimes purified by the addition of a small quantity of 
 alum or sulphate of alumina, when the alumina is precipitated by the car- 
 bonate of lime, and carries down with it mechanically the suspended clay, 
 leaving the water clear. 
 
 The organic matter contained in waters may be vegetable matter dis- 
 solved from the earth, with which it has come in contact, or resulting 
 from the decomposition of plants, or it may be animal matter derived 
 either from the animalcules and fish naturally existing in it, or from the 
 sewage of towns, and, in the case of well waters, from surface drainage. 
 It is a pretty generally received opinion that such of these organic matters 
 as are very susceptible of chemical change have an injurious effect upon 
 the system of persons drinking the water, and it is now usual, in ex- 
 amining water as to its fitness for consumption, to ascertain how much of 
 the organic matter is in a changeable condition, by determining with the 
 aid of a solution of permanganate of potash the amount of oxygen neces- 
 sary to effect its conversion into more stable forms. 
 
 41. One of the most important points to be taken into account in 
 estimating the qualities of a water is its action upon lead, since this metal 
 is unfortunately so generally employed for the storage and transmission of 
 water, and cases frequently occur in which the health has been seriously 
 injured by repeated small doses of compounds of lead taken in water, 
 which has been kept in a leaden cistern. If a piece of bright, freshly 
 scraped lead be exposed to the air, it speedily becomes tarnished from the 
 formation of a thin film of the oxide of lead, produced by the action of 
 the atmospheric oxygen ; this oxide of lead is soluble in water to some 
 extent, and hence, when lead is kept in contact with water, the oxygen 
 which is dissolved in it acts upon the metal, and the oxide so produced 
 is dissolved by the water ; but, fortunately, different waters act with very 
 different degrees of rapidity upon the metal, according to the nature of 
 the substances which they contain. 
 
 The film of oxide which forms upon the surface of the lead is in- 
 soluble, or nearly so, in water containing much sulphate or carbonate of 
 lime, so that hard waters may generally be kept without danger in leaden 
 cisterns ; but soft waters, and those which contain nitrites or nitrates, 
 should not be drunk after contact with lead. Nearly all waters which 
 have been stored in leaden cisterns contain a trace of the metal, and since 
 the action of this poison, in minute doses, upon the system is so gradual 
 
 * Thames and New River water are softened, in this way, to 3 0< 5, or to a lower point 
 tli an by an hour's boiling. 
 
DISTILLATION. 
 
 45 
 
 that the mischief is often referred to other causes, it is much to be desired 
 that lead should be discarded altogether for the construction of cisterns. 
 
 Mineral ivaters, as they are popularly called, are simply spring waters 
 containing so large a quantity of some ingredient as to have a decided 
 medicinal action. They are differently named according to the nature of 
 their predominating constituent. Thus, a chalybeate water contains a con- 
 siderable quantity of a salt of the oxide of iron (usually the carbonate dis- 
 solved by free carbonic acid) ; an acidulous water is distinguished by a 
 large proportion of carbonic acid, and is well exemplified in the celebrated 
 Seltzer water ; a sulphureous or hepatic water has the nauseous odour due 
 to the presence of sulphuretted hydrogen. The Harrowgate water is emi- 
 nently sulphureous. Saline waters are such as contain a large quantity of 
 some salt ; thus the saline springs of Cheltenham are rich in common salt 
 and sulphate of soda. 
 
 The chalybeate waters, which are by no means uncommon, become 
 brown when exposed to the air, and deposit a rusty sediment which con- 
 sists of the sesquioxide of iron, formed by the union of the oxygen of the 
 air with the oxide of iron existing in the carbonate.* 
 
 42. Sea water contains the same salts as are found in waters from other 
 natural sources, but is distinguished by the very large proportion of chlo- 
 ride of sodium (common salt). A gallon of sea water contains usually 
 about 2500 grains of saline matter, of which 1890 grains consist of common 
 salt. The circumstance that clothes wetted with sea water never become 
 perfectly dry is to be ascribed chiefly to the chloride of magnesium present 
 in the water, which is distinguished by its tendency to deliquesce or become 
 damp in moist air. There are two elements, bromine and iodine, which 
 are found combined with metals in appreciable quantity in sea water, 
 though they are of somewhat rare occurrence in other waters derived from 
 natural sources. 
 
 43. By distillation, pure water may be obtained from most spring and 
 river waters. 
 
 (DBF. Distil- 
 lation is the 
 conversion of a 
 liquid into a va- 
 pour, and its re- 
 condensation in- 
 to the liquid 
 form in another 
 vessel.) 
 
 Fig. 44 repre- 
 sents the ordinary 
 form of still in com- 
 mon use, in which 
 A is a copper boil- 
 er containing the 
 water to be dis- 
 tilled ; B the head 
 of the still, which 
 lifts out at b, and 
 is connected by the 
 
 * 2(FeO . C0 2 ) 
 Carbonate of iron. 
 
 HO = Fe 2 3 -H0 
 Hydrated sesqui- 
 oxide of iron. 
 
 Water. 
 
 2C0 2 
 Carbonic acid. 
 
46 
 
 PROPERTIES OF WATER. 
 
 neck C with the worm D, a pewter pipe coiled round in the tub E, and issuing at F. 
 The steam from the boiler, passing into the worm, is condensed to the liquid state, 
 being cooled by the water in contact with the worm ; this water, becoming heated, 
 passes off through the pipe G, being replaced by cold water, which is allowed to 
 enter through H.* 
 
 Another form of apparatus for distillation of water and other liquids is shown 111 
 fig. 45. A is a stoppered retort, the neck of which fits into the tube of a Liebig's con- 
 denser (B), which consists of a glass tube (G) fitted by means of corks into a glass, 
 copper, or tin tube (D), into which a stream of cold water is passed by the funnel E, 
 the heated water running out through the upper tube F. The water furnished by 
 the condensation of the steam passes through the quilled receiver G, into the flask H. 
 Heat is gradually applied to the retort by a ring gas-burner. 
 
 Fig, 45. Distillation Liebig's condenser. 
 
 Many special precautions are requisite in order to obtain absolutely pure 
 distilled water for refined experiments, but for ordinary purposes the com- 
 mon methods of distillation yield it in a sufficiently pure condition. 
 
 The saline matters present in the water are of course left behind in the 
 still or retort. Sea water is now frequently distilled on board-ship when 
 fresh water is scarce. The vapid and disagreeable taste of distilled water, 
 which is due to its having been deprived of the dissolved air during the 
 distillation, is remedied by the use of Normandy's apparatus, which pro- 
 vides for the restoration of the expelled air. 
 
 44. The physical properties of water are too well known to require any 
 detailed description. Its specific gravity in the liquid state is 1, being 
 taken as the standard to which the specific gravities of liquid and solid 
 bodies are referred. 
 
 (DBF. The specific gravity of a liquid or solid body is its weight as 
 compared with that of an equal volume of pure water at 60 F., 15 '5 C.) 
 
 Water assumes the solid form, under ordinary circumstances, at 32 F. 
 (0 C.), and may be obtained in six-sided prismatic crystals. Snow con- 
 sists of beautiful stellate groupings of these crystals. Ice has the specific 
 gravity 0'9184. In the act of freezing, water expands very considerably, 
 so that 174 volumes of water become 184 volumes of ice. The breakage 
 of vessels, splitting of rocks, &c., by the congelation of water, are due to 
 
 * A rosette gas-burner (K) on Bimsen's principle is very convenient for a small still of 
 .this description. 
 
SOLUTION AND CRYSTALLISATION. 47 
 
 this expansion. Water passes off in vapour at all temperatures, the 
 amount of vapour evolved in a given time of course increasing with the 
 temperature. The boiling-point of water is 212 F. (100 C.) 
 
 (DEF. The boiling-point of a liquid is the constant temperature indi- 
 cated by a thermometer, the bulb of which is immersed in the boiling 
 liquid in the presence of a coil of platinum wire, to facilitate disengage- 
 ment of vapour, and at a pressure of 30 in. (762 Mm.) Bar.) 
 
 At and above 212 F. at the ordinary atmospheric pressure (30 in. Bar.), 
 water is an invisible vapour of specific gravity 0*622 (air = 1). One 
 cubic inch of water at 60 F. becomes 1696 cubic inches of vapour at 
 212 F. 
 
 45. In its chemical relations water presents this very remarkable fea- 
 ture, that, although it is an indifferent oxide, its combining tendencies 
 extend over a wider range than those of any other compound. Its com- 
 binations with other substances are generally called hydrates. Water 
 combines with two of the elementary substances, viz., chlorine and 
 bromine, forming an exception to the general rule that combination does 
 not take place between elementary and compound bodies. No other element 
 is even dissolved by water in any considerable quantity. One part of 
 iodine is dissolved by 7000 parts of cold water, but no chemical combina- 
 tion appears to take place. Oxygen, hydrogen, and nitrogen are dissolved 
 by water in very small quantity, but become only mechanically diffused 
 through it, and do not enter into chemical combination. 
 
 When water acts upon a compound body, it may either effect a simple 
 solution, or may enter into chemical combination with it. 
 
 Simple solution appears to be a purely physical phenomenon, not accom- 
 panied, of necessity, by any chemical action. The dissolved substance, in 
 such cases, is otherwise unchanged in properties, and there is no manifesta- 
 tion of heat, as in cases of chemical combination. On the contrary, there 
 is a reduction of temperature, such as is always noticed in the merely phy- 
 sical change from the solid to the liquid form. For example, common 
 saltpetre (nitre or nitrate of potash, KO.N0 5 ), when shaken with water, 
 is rapidly dissolved, the water becoming sen- 
 sibly colder. If fresh portions of saltpetre be 
 added till the water is unable to dissolve any 
 more, it will be found that 1000 grs. of water 
 (at 60 F.) have dissolved about 300 grs. of 
 saltpetre. Such a solution would be called a 
 cold saturated solution of saltpetre. If the 
 solution be set aside in an open vessel, the ' 
 water will slowly pass off in vapour, and the 
 saltpetre will be gradually deposited, its particles 
 arranging themselves in the regular geometrical 
 shape of the six-sided prism, which is its com- 
 mon crystalline form. The crystals of saltpetre 
 do not contain any water ; they are anhydrous. 
 
 If saltpetre be added to boiling water (in a porcelain evaporating dish, 
 fig. 46), and stirred (with a glass rod) until the water refuses to dissolve 
 any more, 1000 grs. of water will be found to have dissolved about 2000 
 grs. ; this would be called a hot saturated solution. 
 
 As a general rule, solids are dissolved more quickly and in larger quan- 
 tity by hot water than by cold. 
 
48 CRYSTALLISATION. 
 
 One of the commonest methods of crystallising a solid substance con- 
 sists in dissolving it in hot water, and allowing the solution to cool slowly. 
 The more slowly it cools, the larger and more symmetrical are the crystals. 
 A hot saturated solution is not generally the best for crystallising, because 
 it deposits the dissolved body too rapidly. Thus, the hot solution of 
 saltpetre prepared as above would solidify to a mass of minute crystals on 
 cooling; but if 1000 grs. of saltpetre be dissolved in 4 measured ounces of 
 boiling water, it will form crystals of 2 or 3 inches long when slowly cooled 
 (in a covered vessel). If the solution be stirred while cooling, the crystals 
 will be very minute, having the appearance of a white powder. 
 
 Some solids, however, refuse to crystallise, even from a hot saturated 
 solution, if it be kept absolutely undisturbed. 
 
 Sulphate of soda affords a good example of this. If the crystallised sulphate be added 
 to boiling water in a flask, as long as it is dissolved, the water will take into solution 
 more than twice its weight of the salt. If this solution be allowed to cool in the open 
 flask, an abundant crystallisation will take place, for cold water will dissolve only about 
 one-third of its weight of crystallised sulphate. But if the flask (which should be 
 globular) be tightly corked whilst the solution is boiling, it may be kept for several 
 days without crystallising, although moved about from one place to another. In 
 this condition the solution is said to be super- saturated. On withdrawing the cork, 
 the air entering the partly vacuous space above the liquid will be seen to disturb 
 the surface slightly, and from that point beautiful prismatic crystals will shoot 
 through the liquid until the whole has become a nearly solid mass. A consider- 
 able elevation of temperature is observed, consequent upon the passage from the 
 liquid to the solid form. If the solution of sulphate of soda be somewhat weaker, 
 containing exactly two-thirds of its weight of the crystals, it may be cooled with- 
 out crystallising, even in vessels covered with glass plates, but a touch with a glass 
 rod will start the crystallisation immediately.* 
 
 In the laboratory, stirring is always resorted to in order to induce crystallisa- 
 tion, if it does not take place spontaneously. Thus it is usual to test for potash 
 in a solution by adding tartaric acid, which should cause the formation of minute 
 crystals of bitartrate of potash (cream of tartar), but the test seldom succeeds unless 
 the solutions are briskly stirred together with a glass rod. An amusing illustra- 
 tion of this is afforded by pouring a solution of tartaric acid into a solution of 
 saltpetre, and allowing the clear mixture to run over a large plate of glass. 
 Letters traced on the glass with the finger will now be rendered visible by the 
 deposition of the crystals of bitartrate of potash upon the glass. 
 
 46. The crystals of sulphate of soda produced in the above experiments 
 contain, in a state of combination with the salt, more than half their 
 weight of water. Their composition is 
 
 Anhydrous sulphate of soda (NaO . SOg) 71 parts, or one combining weight, 
 Water 90 ,, or ten combining weights, 
 
 as expressed by the formula NaO . S0 3 +10 HO. If some of the crystals 
 be pressed between blotting paper to remove adhering water, and left 
 exposed to the air, they will gradually effloresce, or become covered with a 
 white opaque powder. This powder is the anhydrous sulphate of soda into 
 which the entire crystals would ultimately become converted by exposure 
 to air. Since most crystals containing water have their crystalline form 
 destroyed or modified by the loss of the water, it is commonly spoken of 
 as water of crystallisation. 
 
 Coloured salts, containing water of crystallisation, generally change 
 colour when the water is removed. The sulphate of copper (blue stone) 
 
 * It is very remarkable that, if the glass rod has been recently heated, it will not cause 
 the crystallisation even after it has been cool for some time. 
 
WATER OF CRYSTALLISATION. 49 
 
 affords an excellent example of this. The beautiful blue prismatic crystals 
 of this salt contain 
 
 Anhydrous sulphate of copper (CuO . S0 3 ) 79-8 parts, or one combining weight, 
 Water 45*0 or five combining weights, 
 
 as expressed by the formula CuO . S0 3 + 5HO. 
 
 When these are exposed to the air at the ordinary temperature they 
 remain unchanged; but if heated to the boiling-point of water, they 
 become opaque, and may be easily crumbled down to a white powder. 
 This powder contains 
 
 Anhydrous sulphate of copper (CuO . S0 3 ) 79-8 parts, or one combining weight, 
 Water 9 or one combining weight, 
 
 and would therefore be represented by CuO . S0 3 + HO. The four com- 
 bining weights of water, which have been expelled, constituted the water 
 of crystallisation, upon which the form and colour of the sulphate of 
 copper depend. If the white powder be moistened with water, com- 
 bination takes place, with great evolution of heat, and the blue colour is 
 reproduced. The one combining weight of water which still remains, is 
 not expelled until the salt is heated to 390 F. (199 C.), proving that it 
 is held to the sulphate of copper by a more powerful chemical attraction. 
 On this account it is spoken of as water of constitution, and in order that 
 the formula of the salt may exhibit the difference between the water of 
 constitution and of crystallisation, it is usually written 
 
 CuO . S0 3 . HO + 4Aq.* 
 
 (DEF. Water of crystallisation of salts is that which is generally 
 expelled at 212 F. (100 C.), and is connected with the form and colour 
 of the crystals. Water of constitution is not generally expelled at 212 F., 
 and is in more intimate connexion with the chemical properties of the salt.) 
 
 Several of the so-called sympathetic inks employed for writings which 
 are invisible until heated, depend upon the change of colour which results 
 from the loss of water of crystallisation. Characters written with a weak 
 solution of chloride of cobalt and allowed to dry are very nearly invi- 
 sible, since the pink colour of so small a quantity of the salt is scarcely 
 noticed ; but on warming the paper, the pink hydrated chloride of cobalt 
 (CoCl + 2Aq.) loses its water of crystallisation, and the blue anhydrous 
 chloride of cobalt is produced. On exposure to air this again absorbs 
 water, and the writing fades away. 
 
 Some salts have so great a tendency to combine with water, tha"t they 
 become moist or deliquesce when exposed to air. This deliquescence is 
 exhibited in a marked degree by chloride of calcium, and its great attrac- 
 tion for water is turned to advantage in drying air and other gases by 
 passing them through tubes filled with the salt. 
 
 47. Most bases are capable of combining with water to form hydrates, 
 as exemplified in the slaking of lime. Anhydrous lime or quick-lime 
 (CaO), when wetted with water, combines with it, evolving much heat, 
 and crumbling to a loose bulky powder, which is hydrate of lime or slaked 
 lime (CaO . HO). At a red heat the water is expelled, and anhydrous 
 lime remains. 
 
 * Aqua, water. 
 
50 HYDEATES BINOXIDE OF HYDROGEN. 
 
 The hydrates of potash, soda, and baryta, however, do not lose their 
 water when heated, which has led some chemists to entertain the belief 
 that they do not really contain water as such, but that they have been 
 formed from water by the substitution of a metal for a portion of its 
 hydrogen. Upon this view, the hydrate of potash, instead of being re- 
 presented by the formula KG . HO, would be KH0 2 ,* or two combining 
 weights of water (H 2 2 ), in which potassium has been substituted for half 
 the hydrogen. In representing chemical changes by equations, much 
 convenience often results from the adoption of this formula ; but as the 
 same view would have to be taken of those hydrates which hold their 
 water very loosely, we may question the propriety of insisting upon the 
 above view of the constitution of hydrate of potash, &c., as a fact rather 
 than a convenient hypothesis. 
 
 48. Nearly all the acids are capable of forming hydrates. Indeed, as 
 a general rule, the hydrated form of an acid is that in which it is com- 
 monly obtained and used, the anhydrous acid being usually of very 
 secondary importance. Thus, the liquid used under the name of concen- 
 trated sulphuric acid is the hydrate of that acid (HO . S0 3 ), the anhydrous 
 sulphuric acid (S0 3 ) being a crystalline solid of no use except to the 
 chemist, and not manifesting any acid properties until brought into contact 
 with water, with which it combines with evolution of much heat. The 
 hydrated sulphuric acid (HO . S0 3 ) does not lose its water when heated, 
 but distils unchanged, and some chemists are of opinion that the hydrogen 
 is not contained in it in the form of water, but that the so-called hydrated 
 sulphuric acid should be represented as HS0 4 ,t so as not to indicate that 
 it contains water. The acid is thus represented as a unitary compound 
 (formed of one group), instead of a binary compound of the groups HO 
 and S0 3 . Convenient as this view is sometimes found in notation and in 
 theoretical speculations, the circumstance that S0 3 is known in the separate 
 state, and yields the hydrated sulphuric acid when brought in contact 
 with water, causes the latter view still to find favour among practical 
 chemists. 
 
 The hydrated sulphuric acid (HO . S0 3 ) has a very powerful attraction 
 for more water, which leads to its employment in the laboratory for 
 drying air and gases, as well as for producing many chemical changes 
 which depend upon the abstraction of water or its elements (dehydration). 
 If concentrated sulphuric acid (oil of vitriol) be poured into water, the 
 mixture will become very hot, in consequence of the combination between 
 the two liquids. The water should be stirred whilst the acid is being 
 poured in, as the sudden mixture of considerable quantities might cause 
 danger from the projection of the liquid. 
 
 49. Binoxide or peroxide of hydrogen or oxygenated water, H0 2 .J This compound 
 is not met with in nature, nor has it any important useful application in the arts. 
 It has recently, however, acquired some importance as a medicinal agent, and it 
 possesses very great interest for the student of chemical philosophy, because it helps 
 to throw some light upon the atomic constitution of the elements. 
 
 The easiest and most interesting method of obtaining oxygenated water (though 
 not in the pure state), consists in exposing a few freshly scraped sticks of phos- 
 phorus to the air, at the bottom of a large jar, with enough water to cover one-half 
 
 * Or, ifO=16, byKHO. 
 f Or, if O = 16 and 6 = 32, as H 2 SO 4 . 
 
 J Or, if O = 16, the formula of peroxide of hydrogen will be H 2 O 2 . 
 The phosphorus may be placed upon a porcelain colander, which is supported on the 
 surface of two or three ounces of water in a dish, and freely exposed to the open air. 
 
MOLECULES. 51 
 
 of the sticks. The jar should be loosely covered, and the air renewed by blowing 
 into it occasionally. It should also be placed in a situation where no injury would 
 ensue if the phosphorus were to take fire and crack the jar. Of course ozone will be 
 perceived in abundance in the air of the jar, and in the course of a few days the 
 water will be highly charged with phosphorous and phosphoric acids, and will have 
 absorbed a considerable amount of oxygen from the air. If a test-tube or small 
 cylinder be filled with this water, a little powdered binoxide of manganese thrown 
 into it, and the tube then quickly closed and inverted with its mouth under water, 
 brisk effervescence will ensue from the escape of oxygen which will collect in the 
 tube, and may be recognised by the usual test with a partly extinguished match. 
 Toe binoxide of manganese does not appear to be decomposed in this experiment, 
 the whole of the oxygen being derived from the binoxide of hydrogen dissolved 
 in the water, which is immediately decomposed, by contact with the binoxide of 
 manganese, into water and free oxygen. If a solution of permanganate of potash 
 (KO.Mn 2 7 ), which owes its red colour to the permanganic acid (Mn 2 7 ), be poured 
 into a cylinder partly filled with the liquid, it will cause a rapid evolution of oxygen, 
 derived not only from the binoxide of hydrogen, but from the permanganic acid, 
 the red colour of which disappears, because it becomes reduced to a lower oxide of 
 manganese. 
 
 The usual method of preparing binoxide of hydrogen in a pure state, consists in 
 decomposing the binoxide of barium with diluted hydrochloric acid, under certain 
 precautions to avoid the decomposition of the very unstable binoxide of hydrogen. 
 Its formation is represented by the equation Ba0 2 + HC1 = H0 2 + BaCl. The 
 chloride of barium is removed from the solution by the cautious addition of sulphate 
 of silver, which precipitates the barium as sulphate of baryta, and the silver as 
 chloride of silver, thus, BaCl + AgO . S0 3 = AgCl + BaO . S0 3 . The precipitates 
 are allowed to subside, and the clear liquid evaporated in the exhausted receiver of 
 the air-pump over a dish of oil of vitriol to absorb the water, which evaporates much 
 more rapidly than the binoxide. The pure binoxide of hydrogen is a syrupy liquid 
 of sp. gr. 1-453, with a very slight chlorous odour. Its most remarkable feature is 
 the facility with which it is decomposed into water and oxygen.* Even at 70 F. 
 it begins to evolve bubbles of oxygen, so that it can scarcely be prepared in hot 
 weather. At 212 it decomposes with violence. The mere contact with certain 
 metals, such as gold, platinum, and silver, which have no direct attraction for oxy- 
 gen, will cause the decomposition of the binoxide of hydrogen, without any chemical 
 alteration of the metal itself. | "It was noticed above that the binoxide of manganese 
 decomposes it without undergoing any apparent change. The most surprising 
 effect is that which takes place with oxide of silver. If a drop of binoxide of hydro- 
 gen be allowed to fall upon oxide of silver, which is a brown powder, decomposition 
 takes place with explosive violence and great evolution of heat, the oxide of silver 
 losing its oxygen, and becoming grey metallic silver. The oxides of gold and 
 platinum are acted upon in a similar manner. 
 
 These very extraordinary changes, which were formerly described as catalytic 
 actions, are now generally accounted for by the hypothesis that the oxygen in the 
 oxide of silver, &c., exists in a condition different from that of the second equivalent 
 of oxygen in the binoxide of hydrogen, and that these two conditions of oxygen 
 have a chemical attraction for each other, similar to that which exists between 
 different elements. If the oxygen in the oxide of silver be represented as electro- 
 negative oxygen (see 22), as its relation to the metal would lead us to expect, and 
 the second atom of oxygen in the binoxide of hydrogen be represented as electro- 
 positive oxygen, the mutual decomposition of the two compounds might be repre- 
 sented by the equation, 
 
 AgO + HOO = Ag + HO + 00. 
 
 Molecules Molecular formulce. This would lead to the belief that 
 oxygen in its ordinary condition, as it exists in the atmosphere, is really 
 an oxide of oxygen, consisting of two atoms of oxygen in opposite states, 
 
 * The presence of a little free acid renders it rather more stable, whilst free alkali has 
 the opposite effect. A solution of peroxide of hydrogen, containing a little hydrochloric 
 acid, is now sold for medicinal and photographic uses. 
 
 | Such inexplicable changes as this are sometimes included under the general denomina- 
 tion of catalysis, or decomposition by contact. 
 
 D 2 
 
52 CONSTITUTION OF OZONE. 
 
 and that the smallest particle of oxygen which can exist in the separate 
 state is really composed of two atoms. This smallest particle of free 
 oxygen would be appropriately termed a molecule of oxygen, whilst an 
 atom of oxygen would be defined as the smallest particle which can exist 
 in a state of combination. If the atomic weight of oxygen were taken to 
 be 16, the molecular weight would be 32. It will be seen hereafter that 
 there are reasons for extending this view to the constitution of some other 
 elements, and an opinion has been propounded, somewhat in advance of 
 existing experimental evidence, that direct combination of elements is 
 really a double decomposition where the corresponding atoms are exchanged. 
 According to this view, the formation of water by the combination of 
 hydrogen with oxygen would be expressed by the equation, 
 
 HH + 00 HO + HO 
 
 orH 2 + 2 = H 2 2 
 
 and the molecule of water, or the smallest particle capable of existing in a 
 free state, or of resulting from chemical action, would be represented by 
 H 2 2 , and would weigh 18 parts (H= 1), or if 6 = 16 parts of oxygen, 
 by H 2 0. 
 
 It has been suggested that ozone is really the negative atom of oxygen detached 
 from the positive atom or antozone associated with it in the molecule (9_ +) an( l 
 
 this view is supported by the circumstance, that binoxide of hydrogen appears to be 
 formed in all cases where ozone is produced by slow oxidation in the presence of 
 water, making it appear probable that the latter (HO) combines with the antozone 
 to form binoxide of hydrogen (HOO} whilst the ozone is eliminated in the 
 
 free state. The production of ozone in the electrolysis of water (see 23), appears 
 also to be attended by that of binoxide of hydrogen. Upon this view of the nature 
 of ozone, however, it would not be easy to explain the contraction which pure dry 
 oxygen has been found to suffer during partial conversion into ozone by the action 
 of the electric discharge, or the circumstance, that when a mixture of oxygen and 
 ozone so produced is exposed to the action of mercury, no diminution of volume is 
 observed, although the metal removes the ozone, combining with it to form an oxide 
 of mercury. Both these, however, would be explicable on the theory that ozone is 
 really formed by a coalition of atoms of oxygen, to produce a compound which may 
 be represented as binoxide of hydrogen (HOO), in which the hydrogen is replaced by 
 oxygen, forming (000) ; then, just as two volumes of hydrogen combining with one 
 volume of oxygen contract to two volumes of steam, it might be supposed that two 
 volumes of oxygen combining with one volume of oxygen, would contract to two 
 volumes of ozone, and just as on decomposing two volumes of steam with a metal, 
 two volumes of hydrogen are left, so on decomposing the two volumes of ozone witli 
 a metal two volumes of oxygen would be liberated, and no contraction observed. * 
 Reasoning analogically from the properties of binoxide of hydrogen, this theory 
 would also enable us to explain the easy reconversion of ozone by heat, and by the 
 action of binoxide of manganese.f The occurrence of binoxide of hydrogen in so 
 many cases of the production of ozone would also favour this view. 
 
 * Some recent experiments have indicated that the specific gravity^ ozone is just what 
 this theory would require, that is, half as great again as that of ordinary oxygen, or 1 '66. 
 
 t Finely divided platinum, which causes decomposition of binoxide of hydrogen has 
 also been found to destroy ozone. 
 
53 
 
 CAKBON. 
 
 50. This element is especially remarkable for its uniform presence in 
 organic substances. The ordinary laboratory test by which the chemist 
 decides whether a substance under examination is of organic origin, 
 consists in heating it with limited access of air, and observing whether 
 any blackening from separation of carbon (carbonisation) ensues. 
 
 ^ Few elements are capable of assuming so many different aspects as carbon. 
 It is met with transparent and colourless in the diamond, opaque, black, and 
 quasi-metallic in graphite or black lead, velvety and porous in wood-charcoal, 
 and under new conditions in anthracite, coke, and gas-carbon. 
 
 In nature, free carbon may be said to occur in the forms of diamond, 
 graphite, and anthracite (the other varieties of coal containing considerable 
 proportions of other elements). 
 
 Apart from its great beauty and rarity, the diamond possesses a special 
 interest in chemical eyes, from its having perplexed philosophers up to 
 the middle of the last century, notwithstanding the simplicity of the ex- 
 periments required to demonstrate its true nature. The first inkling of it 
 appears to have been obtained by Newton, when he perceived its great 
 power of refracting light, and thence inferred that, like other bodies 
 possessing that property in a high degree, it would prove to be com- 
 bustible ("an unctuous substance coagulated "). When this prediction 
 was verified, the burning of diamonds was exhibited as a marvellous 
 experiment, but no accurate observations appear to have been made till 
 1772, when Lavoisier ascertained, by burning diamonds suspended in the 
 focus of a burning-glass, in a confined portion of oxygen, that they were en- 
 tirely converted into carbonic acid gas. In more recent times this experi- 
 ment has been repeated with the utmost precaution, and the diamond has 
 been clearly demonstrated to consist of carbon in a crystallised state. 
 
 A still more important result of this experiment was the exact determination of 
 the composition of carbonic acid, without which it would not be possible to ascertain 
 exactly the proportion of carbon in any of its numerous compounds, since it is always 
 weighed in that form. 
 
 The most accurate experiments upon the synthesis of carbonic acid have been 
 conducted with the arrangement represented in fig. 47. 
 
 Within the porcelain tube A, which is heated to redness in a charcoal fire, was 
 placed a little platinum tray, accurately weighed, and containing a weighed quantity 
 of fragments of diamond. One end of the tube was connected with a gas-holder B, 
 containing oxygen which was thoroughly purified by passing through the tube C, 
 containing potash (to absorb any carbonic acid and chlorine which it might contain), 
 and dried by passing over pumice soaked with concentrated sulphuric acid in D and 
 E. To the other end of the porcelain tube, A, there was attached a glass 4ube F, 
 also heated in a furnace, and containing oxide of copper, to convert into carbonic 
 acid any carbonic oxide which might have been formed in the combustion of the 
 diamond. The carbonic acid was then passed over pumice soaked with sulphuric 
 acid in G, to remove any traces of moisture, and afterwards into a weighed bulb- 
 apparatus H, containing solution of potash, and two weighed tubes I K, containing, 
 respectively, solid hydrate of potash and sulphuric acid on pumice, to guard against 
 the escape of aqueous vapour taken up by the excess of oxygen in its passage 
 through the bulbs H. The increase of weight in H, I, K, represented the carbonic 
 acid formed in the combustion of an amount of diamond indicated by the loss of 
 weight suffered by the platinum tray, and the difference between the diamond 
 consumed and the carbonic acid formed would express the amount of oxygen which 
 had combined with the carbon. A large number of experiments conducted in this 
 manner, both with diamond and graphite, showed that 6 parts of carbon furnished 
 22 parts of carbonic acid, and consumed, therefore, 1 6 parts of oxygen. 
 
 The ordinary mode of exhibiting the combustion of the diamond on the lecture 
 
54 
 
 COMBUSTION OF DIAMOND. 
 
 table, consists in suspending it within a double loop of platinum wire attached to an 
 iron wire passing through a deflagrating-collar, and heating it in a jet of oxygen 
 
 Fig. 47. Exact synthesis of carbonic acid. 
 
 sent through a gas or spirit flame (fig. 48). As soon as it has attained a white heat, 
 the diamond is plunged into a globe of oxygen, and after burning for a few seconds, 
 it is withdrawn, and a little lime-water is shaken in the globe to produce the milky 
 
 Fig. 48. 
 
 deposit of carbonate of lime. It not unfrequently happens that the blowpipe flame 
 fuses the platinum wire, and the diamond drops out before it can be immersed in the 
 oxygen. A more convenient arrangement is shown in fig. 49. The diamond is 
 supported in a short helix of platinum wire A, which is attached to the copper wires 
 B B, passing through the cork C, and connected with the terminal wires of a 
 Grove's battery of five or six cells. The globe having been filled with oxygen by 
 passing the gas down into it till a match indicates that the excess of oxygen is 
 
DIAMOND GRAPHITE. 55 
 
 streaming out of the globe, the cork is inserted, and the wires connected with the 
 
 battery. When the heat developed in the platinum coil, by the 
 
 passage of the current, has raised the diamond to a full red 
 
 heat, the connexion with the battery may be interrupted, and 
 
 the diamond will continue to burn with steady and intense 
 
 brilliancy. 
 
 To an observer unacquainted with the satisfactory 
 nature of this demonstration, it would appear incre- 
 dible that the transparent diamond, so resplendent as to 
 have "been reputed to emit light, should be identical in its chemical 
 composition with graphite (plumbago or black lead) from which, in ex- 
 ternal appearance, it differs so widely. For this diiference is not con- 
 fined to their colour; in crystalline form they are not in the least 
 alike, the diamond occurring generally in octahedral crystals, while gra- 
 phite is found either in amorphous masses (that is, having no definite 
 crystalline form), or in six-sided plates which are not geometrically allied 
 with the form assumed by the diamond. Carbon, therefore, is dimorphous, 
 or occurs in two distinct crystalline forms. Even in weight, diamond and 
 graphite are very dissimilar, the former having an average specific gravity 
 of 3 '5, and the latter of 2 '3. Again, a crystal of diamond is the hardest 
 of all substances, whence it is used for cutting and for writing upon glass, 
 but a mass of graphite is soft and easily cut with a knife. The diamond 
 is a non-conductor of electricity, but the conducting power of graphite 
 renders it useful in the electrotype process. 
 
 Diamonds are chiefly obtained from Golconda, Borneo, and the Brazils. 
 They usually occur enveloped in sandstone or quartz pebbles, which ap- 
 pear to have been rounded by attrition in the beds of running streams. 
 The hardness of the diamond renders it necessary to employ diamond- 
 dust for the purpose of cutting and polishing it, which is effected with 
 the aid of a revolving disk of steel, to the surface of which the diamond- 
 dust is applied in the form of a paste made with oil. The crystal in its 
 natural state is best fitted for the purpose of the glazier, for its edges are 
 usually somewhat curved, and the angle formed by these cuts the glass 
 deeply, while the angle formed by straight edges, like those of an ordinary 
 jeweller's diamond, is only adapted for scratching or writing upon glass. 
 The diamond-dust used for polishing, &c., is obtained from a dark amor- 
 phous diamond found at Bahia in the Brazils; 1000 ounces annually are 
 said to have been occasionally obtained from this source. When burnt, 
 the diamond always leaves a minute proportion of ash of a yellowish 
 colour in which silica and oxide of iron have been detected. 
 
 Although the diamond, when preserved from contact with the air, may 
 be heated very strongly in a furnace, without suffering any change, it is 
 not proof against the intense heat of the discharge taking place between 
 two carbon points attached to the terminal wires of a powerful galvanic 
 battery. If the experiment be performed in a vessel exhausted of air, the 
 diamond becomes converted into a black coke-like mass which closely 
 resembles graphite in its properties. 
 
 Graphite always leaves more ash than the diamond, consisting chiefly 
 of the oxides of iron and manganese, with particles of quartz, and some- 
 times titanic acid. The purest specimens are those of compact amor- 
 phous graphite from Borrowdale in Cumberland ; an inferior variety, im- 
 ported from Ceylon, is crystalline, being composed of hexagonal plates. 
 Graphite is obtained artificially in the manufacture of cast iron : in some 
 
56 LAMP BLACK WOOD CHARCOAL. 
 
 cases, a portion of the carbon of the cast iron separates in cooling in the 
 form of crystalline scales of graphite, technically called kish. In the 
 grey variety of cast iron these scales of graphite are diffused through the 
 mass of the metal, and are left undissolved when the iron is dissolved by 
 an acid. 
 
 Graphite is far more useful than the diamond, for, in addition to its 
 application in black lead pencils, and for covering the surface of iron in 
 order to protect it from rust, it is largely employed, in admixture with 
 clay, for the fabrication of the black lead crucibles or Hue pots, as they 
 are commonly called, which are so valuable to the metallurgist, for their 
 power of resisting high temperatures. Graphite is also sometimes em- 
 ployed for lubricating, to diminish friction in machinery, and for facing 
 or imparting a fine glazed surface to gunpowder. 
 
 (Anthracite and the other varieties of coal will be described in a sepa- 
 rate section.) 
 
 51. Several varieties of carbon, obtained by artificial processes, are em- 
 ployed in the arts. The most important of these are lamp black, wood 
 charcoal, and animal charcoal. 
 
 Lamp Hack approaches more nearly in composition to pure carbon than 
 either of the others, and is the soot obtained from the imperfect combus- 
 tion of resinous and tarry matters (or of highly bituminous coal), from 
 which source it derives the small quantities of resin, of nitrogen, and 
 sulphur which it contains. The uses of this substance, as an ingredient 
 of pigments, of printing ink, and of blacking, depend evidently more upon 
 its black colour than upon its chemical properties. 
 
 Wood charcoal presents more features which arrest the attention of the 
 chemist, as well on account of its specific properties, as of the influence 
 exercised by the method adopted for obtaining it, upon its fitness for the 
 particular purpose which it may be destined to serve. 
 
 If a piece of wood be heated in an ordinary fire, it is speedily con- 
 sumed, with the exception of a grey ash consisting of the incombustible 
 mineral substances which it contained ; if the experiment were performed 
 in such a manner that the products of combustion of the wood could be 
 collected, these would be found to consist of carbonic acid and water , 
 woody fibre is composed of carbon, hydrogen, and oxygen (C 12 H 10 Oi ), 
 and when it is burnt, the oxygen, in conjunction with more oxygen de- 
 rived from the air, converts the carbon and hydrogen into carbonic acid 
 and water. But if the wood be heated in a glass tube, closed at one end, 
 it will be found impossible to reduce it, as before, to an ash, for a mass of 
 charcoal will remain, having the same form as that of the piece of wood ; 
 in this case, the oxygen of the air not having been allowed free access to 
 the wood, no true combustion has taken place, but the wood has under- 
 gone destructive distillation, that is, its elements have arranged them- 
 selves, under the influence of the high temperature, into different forms 
 of combination, for the most part simpler in their chemical composition 
 than the wood itself, and capable, unlike the wood, of enduring that 
 temperature without decomposition; thus, it is merely an exchange of an 
 unstable for a stable equilibrium of the particles of matter composing the 
 wood. 
 
 (DBF. Destructive distillation is the resolution of a complex substance 
 
 into simpler forms under the influence of heat, out of contact with air.) 
 
 The vapours issuing from the mouth of the tube will be found acid 
 
PREPARATION OF CHARCOAL. 
 
 57 
 
 to blue litmus paper ; they have a peculiar odour, and readily take fire 
 on contact with name. These will "be more particularly noticed here- 
 after, as they contain some very useful substances. The charcoal which 
 is left is not pure carbon, but contains considerable quantities of oxygen 
 and hydrogen, with a little nitrogen, and the mineral matter or ash of 
 the wood. 
 
 When the charcoal is to be used for fuel, it is generally prepared by 
 a process in which the heat developed by the combustion of a portion 
 of the wood is made to effect the charring of the rest. With this view 
 the billets of wood are built up into a heap (fig. 50) around stakes driven 
 into the ground, a passage 
 being left so that the heap 
 may be kindled in the centre. 
 This mound of wood, which 
 is generally from 30 to 40 feet 
 in diameter, is closely covered 
 with turf and sand, except for 
 a few inches around the base, 
 
 Fig. 50. Charcoal heap. 
 
 where it is left uncovered to 
 give vent to the vapour of 
 water expelled from the wood in the first stage of the process. When 
 the heap has been kindled in the centre, the passage left for this pur- 
 pose is carefully closed up. After the combustion has proceeded for 
 some time, and it is judged that the wood is perfectly dried, the open 
 space at the base is also closed, and the heap left to smoulder for three 
 or four weeks, when the wood is perfectly carbonised. Upon an average, 
 22 parts of charcoal are obtained by this process from 100 of wood. 
 
 A far more economical process for preparing charcoal from wood consists 
 in heating it in an iron case or slip (F, fig. 51) placed in an iron re- 
 tort A, from which the gases and 
 vapours are conducted by the pipe 
 L into the furnace B, where they 
 are consumed. 
 
 On the small scale, the opera- 
 tion may be conducted in a glass 
 retort, as shown in fig. 52, where 
 the water, tar, and naphtha are 
 deposited in the globular receiver, 
 and the inflammable gases are col- 
 lected over water. 
 
 The infusibility of the charcoal 
 left by wood accounts for its very 
 great porosity, upon which some 
 of its most remarkable and useful 
 properties depend. The applica- 
 
 Fig. 51. Charcoal retort. 
 
 tion of charcoal for the purpose of " sweetening" fish and other food in a 
 state of incipient putrefaction has long been practised, and more recently 
 charcoal has been employed for deodorising all kinds of putrefying and 
 offensive animal or vegetable matter. This property of charcoal depends 
 upon its power of absorbing into its pores very considerable quantities of 
 the gases, especially of those which are easily absorbed by water. Thus 
 one cubic inch of charcoal is capable of absorbing about 100 cubic 
 inches of ammonia gas and 50 cubic inches of sulphuretted hydrogen, 
 
58 
 
 ABSORPTION OF GASES BY CHARCOAL. 
 
 Fig. 52. Distillation of wood. 
 
 both which are conspicuous among the offensive results of putrefac- 
 tion. This condensation of gases by charcoal is a mechanical effect, arid 
 
 does not involve a chemical 
 combination of the charcoal 
 with the gas; it is exhibited 
 most powerfully by char- 
 coal which has been re- 
 cently heated to redness in 
 a closed vessel, and cooled 
 out of contact with air by 
 plunging it under mercury. 
 Eventually the offensive 
 gases absorbed by the char- 
 coal are chemically acted on 
 by the oxygen of the air in its pores. A cubic inch of wood charcoal absorbs 
 nearly 10 cubic inches of oxygen, and when the charcoal containing the gas 
 thus condensed is presented to another gas which is capable of undergoing 
 oxidation, this latter gas is oxidised and converted into inodorous pro- 
 ducts. Thus, if charcoal be exposed to the action of air containing sul- 
 phuretted hydrogen gas, it condenses within its pores both this gas and 
 the atmospheric oxygen, which then converts the hydrogen into water 
 (HO) and the sulphur into sulphuric acid (S0 3 ). 
 
 The great porosity of wood charcoal is strikingly exhibited by attaching a piece of 
 lead to a stick of charcoal (fig. 53), so as to sink it in a cylinder of water, which is 
 then placed under the receiver of the air-pump. On exhausting the air, innumerable 
 bubbles will start from the pores of the charcoal, causing brisk effervescence. If a 
 glass tube 10 or 12 inches long be thoroughly filled with ammonia gas (fig. 54), sup- 
 ported in a trough containing mercury, and a small stick of recently calcined char- 
 
 Fig. 53. 
 
 Fig. 54. 
 
 coal introduced through the mercury into the tube, the charcoal will absorb the 
 ammonia so rapidly that the mercury will soon be forced up and fill the tube, carrying 
 the charcoal up with it. On removing the charcoal, and placing it upon the hand, 
 a sensation of cold will be perceived from the rapid escape of ammonia, perceptible 
 by its odour. 
 
 By exposing a fragment of recently calcined wood-charcoal under a jar filled with 
 hydrosulphuric acid gas for a few minutes, so that it may become saturated with 
 the gas, and then covering it with a jar of oxygen, the latter gas will act upon 
 the former with such energy that the charcoal will burst into vivid combustion. 
 The jar must not be closed air-tight at the bottom, or the sudden expansion may 
 burst it. Charcoal in powder exposed in a porcelain crucible may also be em- 
 ployed in the same way. It should be pretty strongly heated in the covered cru- 
 
DECOLORISING POWER OF CHAECOAL. 
 
 59 
 
 cible, and allowed to become nearly cool before being exposed to the hydrosulphuric 
 acid. 
 
 Charcoal prepared from hard woods absorbs the largest volume of gas. Thus 
 logwood charcoal has been found to absorb 111 times its volume of ammoniacal 
 gas. Charcoal made from the shell of the cocoa-nut is even more absorbent, al- 
 though its pores are quite invisible, and its fracture exhibits a semi-metallic lustre. 
 
 As the gases which, are evolved in putrefaction are of a poisonous cha- 
 racter, the power of wood charcoal to remove them acquires great practical 
 importance, and is applied in very many cases ; the charcoal in coarse 
 powder is thickly strewn over matters from which the effluvium proceeds, 
 or is exposed in shallow trays to the air to be sweetened, as in the wards 
 of hospitals, &c. It has even been placed in a flat box of wire gauze to 
 be fixed as a ventilator before a window through which the contaminated 
 air might have access, and respirators constructed on the same principle 
 have been found to afford protection against poisonous gases and vapours. 
 The ventilating openings of sewers in the streets are also fitted with cases 
 containing charcoal for the same purpose. Water is often filtered through 
 charcoal in order to free it from the noxious and disagreeable sulphuretted 
 hydrogen which is sometimes developed in it. For all such uses the char- 
 coal should have been recently heated to redness in a covered vessel in 
 order to expel the moisture which it attracts when exposed to the air, and 
 the charcoal which has lost its power of absorption will be found to regain 
 it in great measure when heated to redness. 
 
 This power of absorption which charcoal possesses is not confined to 
 gases, for many liquid and solid substances are capable of being removed 
 by that agent from their solution in water. 
 This is most readily traced in the case of 
 substances which impart a colour to the 
 solution, such colour being often removed 
 by the charcoal ; if port wine or infusion of 
 logwood be shaken with powdered charcoal 
 (especially if the latter has been recently 
 heated to redness in a closed crucible), the 
 liquid, when filtered (fig. 55), will be found 
 to have lost its colour j the colouring mat- 
 ter, however, seems merely to have adhered 
 to the charcoal, for it may be extracted 
 from the latter by treatment with a weak 
 alkaline liquid. 
 
 The decolorising power of wood charcoal 
 is very feeble in comparison with that pos- 
 sessed by bone-black or animal charcoal, 
 which is obtained by heating bones in ves- 
 sels from which the air is excluded. Bones are composed of about one- 
 third of animal and two-thirds of mineral substances, the latter including 
 phosphate of lime, which amounts to more than half the weight of the bone, 
 and a little carbonate of lime. When bone is heated, as in a retort, so that 
 air is not allowed to have free access to it, the animal matter undergoes 
 destructive distillation, its elements, carbon, hydrogen, nitrogen, and 
 oxygen, assuming other forms, the greater part of the three last elements, 
 together with a portion of the carbon, escaping in different gaseous and 
 vaporous products, while a considerable proportion of the carbon remains 
 behind, intimately mixed with the earthy ingredients of the bone, and 
 constituting the substance known as animal charcoal. The great differ- 
 
 Fig. 55. Filtration. 
 
60 CHEMICAL RELATIONS OF CARBON. 
 
 ence between the products of the destructive distillation of bone and of 
 wood deserves a passing notice. If a fragment of bone or a shaving of 
 horn be heated in a glass tube closed at one end, the vapours which are 
 evolved will be found strongly alkaline to test-papers, while those fur- 
 nished by the wood were acid ; this difference is to be ascribed mainly 
 to the presence of nitrogen in the bone, wood being nearly free, from that 
 element ; it will be found to hold good as a general rule, that the results 
 of the destructive distillation of animal and vegetable matters containing 
 much nitrogen are alkaline, from the presence of ammonia (NH 3 ) and 
 similar compounds, while those furnished by non-nitrogenised substances 
 possess acid characters : the peculiar odour which is emitted by the heated 
 bone is characteristic, and affords us a test by which to distinguish 
 roughly between nitrogenised and non-nitrogenised bodies. 
 
 An examination of the charred mass remaining as the ultimate result 
 of the action of heat upon bone, shows it to contain much less carbon 
 than that furnished by wood, for the bone-charcoal contains nearly nine- 
 tenths of its weight of phosphate (with a little carbonate) of lime ; the 
 consequence of the presence of so large an amount of earthy matter must 
 be to extend the particles of carbon over a larger space, and thus to ex- 
 pose a greater surface for the adhesion of colouring matters, &c. This 
 may partly help to explain the very great superiority of bone-black to 
 wood charcoal as a decolorising agent, and the explanation derives support 
 from the circumstance that when animal charcoal is deprived of its earthy 
 matter, for chemical uses, by washing with hydrochloric acid, its decolor- 
 ising power is very considerably reduced. The application of this variety 
 of charcoal is not confined to the chemical laboratory, but extends to 
 manufacturing processes. The sugar-refiner decolorises his syrup by filter- 
 ing it through a layer of animal charcoal, and the distiller employs char- 
 coal to remove the empyreumatic oils with which distilled spirits are 
 frequently contaminated. 
 
 Carbon is remarkable, among elementary bodies, for its indisposition to 
 enter directly into combination with the other elements, whence it follows 
 that most of the compounds of carbon have to be obtained by indirect 
 processes. This element appears, indeed, to be incapable of uniting with 
 any other at the ordinary temperature, and this circumstance is occasion- 
 ally turned to useful account, as when the ends of wooden stakes are 
 charred before being plunged into the earth, when the action of the 
 atmospheric oxygen, which, in the presence of moisture, would be very 
 active in effecting the decay of the wood, is resisted by the charcoal into 
 which the external layer has been converted. The employment of black 
 lead to protect metallic surfaces from rust is another application of 
 the same principle. At a high temperature, however, carbon combines 
 readily with oxygen, sulphur, and with some of the metals, and, at a 
 very high temperature, even with hydrogen. The tendency of carbon to 
 combine with oxygen under the influence of heat, is shown when a piece 
 of charcoal is strongly heated at one point, when the carbon at this point 
 at once combines with the oxygen of the surrounding air (forming car- 
 bonic acid), and the heat developed by this combustion raises the neigh- 
 bouring particles of carbon to the temperature at which the element unites 
 with oxygen, and thus the combustion is gradually propagated throughout 
 the mass, which is ultimately converted entirely into carbonic acid gas, 
 nothing remaining but the white ash, composed of the mineral substances 
 derived from the wood employed for preparing the charcoal. It is worthy 
 
FORMATION OF COAL. 61 
 
 of remark, that if charcoal had been a better conductor of heat, it would not 
 have been so easily kindled, since the heat applied to any point of the 
 mass would have been rapidly diffused over its whole bulk, and this 
 point could not have attained the high temperature requisite for its igni- 
 tion, until the whole mass had been heated nearly to the same degree ; 
 this is actually found to be the case in charcoal which has been very 
 strongly heated (out of contact with air), when its conducting power is 
 greatly improved, and it kindles with very great difficulty. The calorific 
 value of carbon is represented by the number 8080, that is, 1 gr. of car- 
 bon, when burnt so as to form carbonic acid, is capable of raising 8080 
 grs. of water from C. to 1 C. 
 
 A given weight of charcoal will produce twice as much available heat 
 as an equal weight of wood, since the former contains more actual fuel 
 and less oxygen, and much of the heat evolved by the wood is absorbed 
 or rendered latent in the steam and other vapours which are produced by 
 the action of heat upon it. The attraction possessed by carbon for oxygen 
 at a high temperature is turned to account in metallurgic operations, when 
 coal and charcoal are employed for extracting the metals from their com- 
 pounds with oxygen.* 
 
 The unchangeable solidity of carbon is another remarkable feature. It 
 is stated that some approach has been made, at extremely high tempera- 
 tures, to the fusion and vaporisation of carbon, but it cannot be said to 
 have been fairly established that this element is able to exist in any other 
 than the solid form. Nor can any substance be found by the aid of 
 which carbon may be brought into the liquid form by the process of 
 solution, for although charcoal gradually disappears when boiled with 
 sulphuric and nitric acids, it does not undergo a simple solution, but is 
 converted, as will be seen hereafter, into carbonic acid. 
 
 52. COAL. The various substances which are classed together under the 
 name of coal are characterised by the presence of carbon as a largely pre- 
 dominant constituent, associated with smaller quantities of hydrogen, 
 oxygen, nitrogen, sulphur, and certain mineral matters which compose the 
 ash. Coal appears to have been formed by a peculiar decomposition or 
 fermentation of buried vegetable matter, resulting in the separation of a 
 large proportion of its hydrogen in the form of marsh-gas (C 2 H 4 ), and 
 similar compounds, and of its oxygen in the form of carbonic acid (C0 2 ), 
 the carbon accumulating in the residue. Thus, cellulose (C 12 H I0 10 ), which 
 constitutes the bulk of woody fibre, might be imagined to decompose 
 according to the equation 2C 12 H 10 10 = 5C 2 H 4 + 10C0 2 + C 4 , and the 
 occurrence of marsh-gas, and of the petroleum hydrocarbons o/ similar 
 composition, as well as of carbonic acid, in connexion with deposits of 
 coal, supports this account of its formation. Marsh-gas and carbonic 
 acid are the ordinary products of the fermentation of vegetable matter, 
 and a spontaneous carbonisation is often witnessed in the "heating" of 
 damp hay. But just as the action of heat upon wood produces a charcoal 
 containing small quantities of the other organic elements, so the carbon- 
 ising process by which the plants have been transformed into coal, has 
 left behind some of the hydrogen, oxygen, and nitrogen ; the last, as well 
 probably as a little of the sulphur, having been derived from the vegetable 
 albumen and similar substances which are always present in plants. The 
 
 * Easily reducible oxides, such as oxide of lead, give carb6nic acid when heated with 
 charcoal ; 2PbO + C = Pb 2 + C0 2 , but oxides which are not easily reducible, such as 
 oxide of zinc, give carbonic oxide ; ZnO + C = CO + Zn. 
 
62 COMBUSTION OF COAL. 
 
 chief part of the sulphur is generally present in the form, of iron pyrites, 
 derived from some extraneous source. The examination of a peat-bog is 
 very instructive with reference to the formation of coal, as affording ex- 
 amples of vegetable matter in every stage of decomposition, from that in 
 which the organised structure is still clearly visible, to the black carbon- 
 aceous mass which only requires consolidation by pressure in order to 
 resemble a true coal. 
 
 The three principal varieties of coal lignite, bituminous coal, and an- 
 thracite present us with the material in different stages of carbonisation ; 
 the lignite, or brown coal, presenting indications of organised structure, 
 and containing considerable proportions of hydrogen and oxygen, while 
 anthracite often contains little else than carbon and the mineral matter or 
 ash. The following table shows the progressive diminution in the propor- 
 tions of hydrogen and oxygen in the passage from wood to anthracite : 
 
 Carbon. Hydrogen. Oxygen. 
 
 Wood, . .100 12-18 83-07 
 
 Peat, . 
 Lignite, 
 
 Bituminous coal, 
 Anthracite, 
 
 100 9-85 65-67 
 
 100 8-37 42-42 
 
 100 6-12 21-23 
 
 100 2-84 1-74 
 
 The combustion of coal is a somewhat complex process, in consequence 
 of the re-arrangement which its elements undergo when the coal is sub- 
 jected to the action of heat. 
 
 As soon as a flame is applied to kindle the coal, the heated portion 
 undergoes destructive distillation,, evolving various combustible gases and 
 vapours, which take fire and convey the heat to remoter portions of the 
 coal. Whilst the elements of the exterior portion of coal are undergoing 
 combustion, the heat thus evolved is submitting the interior of the mass 
 to destructive distillation, resulting in the production of various com- 
 pounds of carbon and hydrogen. Some of these products, such as marsh- 
 gas (C 2 H 4 ) and olefiant gas (C 4 H 4 ), burn without smoke; while others, 
 like benzole (C 12 H 6 ) and naphthaline (C^Hg), which contain a very 
 large proportion of carbon, undergo partial combustion, and a consider- 
 able quantity of carbon, not meeting with enough heated oxygen in the 
 vicinity to burn it entirely, escapes in a very finely divided state as 
 smoke or soot, which is deposited in the chimney, mixed with a little 
 carbonate of ammonia, and small quantities of other products of the dis- 
 tillation of coal. When the gas has been expelled from the coal, there 
 remains a mass of coke or cinder, which burns with a steady glow until 
 the whole of its carbon is consumed, and leaves an a-sh, consisting of the 
 mineral substances present in the coal. The final results of the perfect 
 combustion of coal would be carbonic acid (C0 2 ), water (HO), nitrogen, 
 a little sulphurous acid (S0 2 ), and ash. The production of smoke in a 
 furnace supplied with coal may be prevented by charging the coal in 
 small quantities at a time in front of the fire, so that the highly carbon- 
 aceous vapours must come in contact with a large volume of heated air 
 before reaching the chimney. In arrangements for consuming the smoke, 
 hot air is judiciously admitted at the back of the fire, in order to meet 
 and consume the heated carbonaceous particles before they pass into the 
 chimney. 
 
 The difference in the composition of the several varieties of coal gives 
 rise to a great difference in their mode of burning. 
 
VARIETIES OF COAL. 
 
 63 
 
 The following table exhibits the composition of representative speci- 
 mens of the three principal varieties : 
 
 Composition of Coal. 
 
 Carbon, . 
 Hydrogen, 
 Nitrogen, 
 Oxygen, . 
 Sulphur, . 
 Ash,* 
 
 Lignite. 
 
 66-32 
 5-63 
 0-56 
 
 22-86 
 2-36 
 2-27 
 
 100-00 
 
 Bituminous 
 Coal. 
 
 Anthracite. 
 
 78-57 
 
 90-39 
 
 5-29 
 
 3-28 
 
 1-84 
 
 0-83 
 
 12-88 
 
 2-98 
 
 0-39 
 
 0-91 
 
 1-03 
 
 1-61 
 
 100-00 
 
 100-00 
 
 The lignites furnish a much larger quantity of gas under the action of 
 heat, and therefore burn with more flame than the other varieties, 
 leaving a coke which retains the form of the original coal ; while bitumi- 
 nous coal softens and cakes together, a useful property, since it allows 
 even the dust of such coal to be burnt, if the fire be judiciously managed. 
 Anthracite (stone coal or Welsh coal) is much less easily combustible than 
 either of the others, and since it yields but little gas when heated, it usually 
 burns with little flame or smoke. This variety of coal is so compact that it 
 will not usually burn in ordinary grates, but is much employed for furnaces. 
 
 53. Carbon is capable of combining with oxygen in- two proportions, 
 forming the compounds known as carbonic oxide and carbonic acid, the 
 composition of which is shown in the following table : 
 
 Oxides of Carbon. 
 
 Carbonic oxide,. . 
 Carbonic acid, 
 
 . . CO, 
 
 . . C0 2 , 
 
 Parts by weight. 
 
 
 
 6 8 
 6 16 
 
 CARBONIC ACID. 
 
 54. It has been already mentioned that carbonic acid is a component of 
 the atmosphere, which usually contains about four volumes of carbonic acid 
 in 10,000 volumes of air. This carbonic acid is chiefly formed by the opera- 
 tion of the atmospheric oxygen in supporting combustion and respiration. 
 
 All substances used as fuel contain a large proportion of carbon, which, 
 in the act of combustion, combines with the oxygen, and escapes into the 
 atmosphere in the form of carbonic acid. 
 
 In the process of respiration, the carbonic acid is formed from the 
 carbon contained in the different portions of the animal frame to which 
 oxygen is conveyed by the blood, having been taken up by the latter in 
 passing through the lungs, where it gives out, in exchange for the oxygen, 
 a quantity of carbonic acid produced by the union of a former supply of 
 oxygen with the carbon of the different organs to which the blood is 
 supplied, and which, as they are constantly corroded and destroyed by this 
 oxidising action of the blood, are repaired by the supply of food taken 
 into the body. This conversion of the carbon of the organs into carbonic 
 acid will be again referred to ; it will be at once evident that it must be 
 concerned in the maintenance of the animal heat. 
 
 * The ash of coal consists chiefly of silica, alumina, and peroxide of iron. 
 
64 
 
 NATURAL SOURCES OF CARBONIC ACID. 
 
 The leaves of plants, under the influence of light, have the power of 
 decomposing the carbonic acid of the atmosphere, the carbon of which is 
 applied to the production of vegetable compounds forming portions of the 
 organism of the plant, and when this dies, the carbon is restored, after 
 a lapse of time more or less considerable, to the atmosphere, in the same 
 form, namely, that of carbonic acid, in which it originally existed there. 
 If the plant should have been consumed as food by animals, its carbon 
 will have been eventually converted into carbonic acid by respiration ; 
 the use of the plant as fuel, either soon after its death (wood), or after 
 the lapse of time has converted it into coal, will also consign its carbon 
 to the air in the form of carbonic acid. Even if the plant be left to decay, 
 this process involves a slow conversion of its carbon into carbonic acid 
 by the oxygen of the air.* 
 
 Putrefaction and fermentation are also very important processes con- 
 cerned in restoring to the air, in the form of carbonic acid, the carbon 
 contained in dead vegetable and animal matter. Although, in a popular 
 sense, these two processes are distinct, yet their chemical operation is of 
 the same kind, consisting in the resolution of a complex substance into 
 simpler forms, produced by contact with some other substance in a state of 
 chemical change. The discussion of the true nature of the process (which 
 is even now somewhat obscure) would be premature at this stage, and it 
 will suffice for the present to state that carbonic acid is one of the simpler 
 forms into which the carbon is converted by the metamorphosis which 
 ensues so quickly upon the death of animals and vegetables. 
 
 The production of carbonic acid in combustion, respiration, and fermentation may 
 be very easily proved by experiment. If a dry bottle be placed over a burning wax 
 taper standing on the table, the sides of the bottle will 
 be covered with dew from the combustion of the hydrogen 
 in the wax ; and if a little clear lime-water be shaken in 
 the bottle, the milky deposit of carbonate of lime will 
 indicate the formation of carbonic acid. 
 
 By arranging two bottles, as represented in fig. 56, and 
 inspiring through the tube A, air will bubble through tlie 
 lime-water in B. before entering the lungs, and will then 
 be found to contain too little carbonic acid to produce a 
 milkiness, but on expiring the air it will bubble through 
 C, and will render the lime-water in this bottle very dis- 
 tinctly turbid. 
 
 If a little sugar be dissolved in eight or ten times its 
 weight of warm (not hot) water, in the flask A (fig. 57), 
 and a little dried yeast previously rubbed down with water 
 added, fermentation will commence in the course of an hour 
 or less, and carbonic acid may be collected in the jar B. 
 
 55. In the mineral kingdom, free carbonic acid 
 is pretty abundant. The gas issues from the earth 
 
 Fig. 56. 
 
 in some places in considerable quantity, as at Nauheim, where there is 
 said to be a spring exhaling about 1,000,000 Ibs. of the gas annually. 
 Many spring waters, those of Seltzer and Pyrmont, for example, are very 
 highly charged with the gas. 
 
 * In the dark, according to Boussingault, plants evolve carbonic acid. He found that 
 a square metre (39 '37 sq. inches) of oleander leaves decomposed, in sunlight, on an 
 average, 1-108 litre (67 '6 cubic inches) of carbonic acid every hour; whilst the same extent 
 of leaf, in the dark, emitted 0'07 litre (4'27 cubic inches) of carbonic acid in the hour. 
 Even under the influence of light, flowers have been found to absorb oxygen and evolve 
 carbonic acid. 
 
PREPARATION OF CARBONIC ACID. 
 
 65 
 
 But it occurs in far larger quantity in a state of combination with lime, 
 forming the immense deposits of limestone, marble, and chalk, which 
 compose so large a portion 
 of the crust of the globe. 
 Carbonate of lime is also 
 met with in the ani- 
 mal kingdom. Fish shells 
 and pearls contain about 
 two-thirds of their weight 
 of this substance, whilst 
 egg-shells contain as much 
 as nine-tenths of carbonate 
 of lime. 
 
 The expulsion of the 
 carbonic acid from lime- 
 stone (CaO.C0 2 ) forms 
 the object of the process 
 of lime burning, by which 
 
 the large supply of lime Fig. 57. 
 
 (CaO) is obtained for build- 
 ing and other purposes. But if it be required to obtain the carbonic acid 
 without regard to the lime, it is better to decompose the carbonate of 
 lime with an acid. 
 
 Preparation of carbonic acid. The form of the carbonate of lime, and 
 the nature of the acid employed, are by no means matters of indifference. 
 If dilute sulphuric acid be poured upon fragments of marble, the effer- 
 vescence which occurs at first soon ceases, for the surface of the marble 
 becomes coated with the nearly insoluble sulphate of lime, by which it is 
 protected from the further action of the acid 
 
 CaO.C0 2 + HO.S0 3 = CaO.S0 3 
 
 Marble. Sulphuric acid. Sulphate of lime. 
 
 HO 
 
 CO, 
 
 if the marble be finely powdered, or if powdered chalk be employed, each 
 particle of the carbonate of lime will be acted upon. When lumps of 
 carbonate of lime are acted upon by hydrochloric acid, there is no danger 
 that any will escape' the action of the acid, for the chloride of calcium 
 produced is one of the most soluble salts 
 
 CaO. CO, + HCi - CaCl + HO + 
 
 Marble. Hydrochloric acid. 
 
 C0 2 . 
 
 For the ordinary purposes of experiment, 
 carbonic acid is most easily obtained by the 
 action of diluted hydrochloric acid upon 
 small fragments of marble (fig. 58), the lat- 
 ter being covered with water, and hydro- 
 chloric acid poured in through the funnel- 
 tube. The gas may be collected by down- 
 ward displacement. 
 
 56. Properties of carbonic acid. Car- 
 bonic acid gas is invisible, like the gases 
 already examined, but is distinguished by 
 a peculiar pungent odour, as is perceived 
 in soda-water. It is more than half as heavy again as atmospheric air, 
 
 E 
 
 Fig. 58. Preparation of carbonic 
 acid. 
 
66 
 
 HIGH SPECIFIC GRAVITY OF CARBONIC ACID. 
 
 its specific gravity being 1*529, which causes its accumulation near the 
 floor of such confined spaces as the Grotto del Cane, where it issues from 
 fissures in the rock. 
 
 The high specific gravity of carbonic acid may be shown by pouring it into a light 
 jar attached to a balance, and counterpoised by a weight in the opposite scale 
 (fig. 59). 
 
 Fig. 59. 
 
 Another favourite illustration consists in floating a soap-bubble on the surface of a 
 layer of the gas generated in the large jar (fig. 60), by pouring diluted sulphuric 
 acid upon a few ounces of chalk made into a thin cream with water. 
 
 Fig. 60. 
 
 Fig. 61. 
 
 If a small balloon, made of collodion be placed in the jar A (fig. 61), it will ascend 
 on the admission of carbonic acid through the tube B. 
 
EXTINCTION OF FLAME BY CARBONIC ACID. 
 
 67 
 
 The power which carbonic acid possesses of extinguishing flame is 
 very important, and has received practical application in the case of burn- 
 ing mines which must otherwise have 
 been flooded with water.* Many at- 
 tempts have also been made from time 
 to time to employ this gas for subdu- 
 ing ordinary conflagrations, but their 
 success has hitherto been very partial. 
 It will be remembered that pure nitro- 
 gen is also capable of extinguishing 
 the flame of a taper, but a large pro- 
 portion of this gas may be present in 
 air without affecting the flame, whereas 
 a taper is extinguished in air contain- 
 ing one-eighth of its volume of car- 
 bonic acid, and is sensibly diminished 
 in brilliancy by a much smaller pro- 
 portion of the gas. 
 
 The power of extinguishing flame, con- 
 joined with the high density of carbonic 
 
 acid, admit of some very interesting illus- Fig> 
 
 trations. 
 
 Carbonic acid may be poured from some distance upon a candle, and will extin- 
 guish it at once. 
 
 A large torch of blazing tow may be plunged beneath the surface of the carbonic 
 acid in the jar, fig. 60. 
 
 Carbonic acid may be raised in a glass bucket (fig. 62) from a large jar, and 
 poured into another jar the air in which has been 
 previously tested with a taper. 
 
 A wire stand with several tapers fixed at different 
 levels may be placed in the jar- A, fig. 63, and car- 
 bonic acid gradually admitted through a flexible 
 tube connected with the neck of the jar, from the 
 cistern B, a hole in the cover of which allows air 
 to enter it as the gas flows out ; the flame of each 
 taper will gradually expire as the surface of the car- 
 bonic acid rises in the jar. 
 
 A jar of oxygen may be placed over a jar of car- 
 bonic acid, as shown in fig. 15, and a taper let down 
 through the oxygen, in which it will burn bril- 
 liantly, into the carbonic acid, which extinguishes 
 it, and if it be quickly raised again into the oxygen, 
 it will rekindle with a slight detonation. This al- 
 ternate extinction and rekindling may be repeated 
 several times. 
 
 On account of this extinguishing power of 
 carbonic acid, a taper cannot continue to burn Pig. 63. 
 
 in a confined portion of air until it has ex- 
 hausted the oxygen, but only until its combustion has produced a suffi- 
 cient quantity of carbonic acid to extinguish the flame. 
 
 To demonstrate this, advantage may be taken of the circumstance that phos- 
 phorus will continue to burn in spite of the presence of carbonic acid. Upon the 
 stand A (fig. 64) a small piece of phosphorus is placed, and a taper is attached 
 
 * All gases which take no part in combustion may extinguish flame, even in the 
 presence of air, by absorbing heat and reducing the temperature below the burning- 
 point. 
 
 E2 
 
68 
 
 EFFECT OF CARBONIC ACID ON ANIMALS. 
 
 to the stand by a wire. The cork B fits air-tight into the jar, and carries a piepe 
 of copper wire bent so that it may be heated by the flame of the taper. A little 
 water is poured into the plate to prevent the entrance 
 of any fresh air. If the taper be kindled, and the jar 
 placed over it, the flame will soon die out, and on mov- 
 ing the jar so that the hot wire may touch the phos- 
 phorus, its combustion will show that a -considerable 
 amount of oxygen still remains. 
 
 In the same manner, an animal can breathe a 
 confined portion of air only until he has charged 
 it with so much carbonic acid that the hurtful 
 Fi S 64 - effect of this gas begins to be felt, a considerable 
 
 quantity of oxygen still remaining. 
 
 If the air contained in the jar A (fig. 65) standing over water be breathed two 
 or three times through the tube B, a painful sense of oppression will soon be felt in 
 
 consequence of the accumulation of car- 
 bonic acid. By immersing a deflagrating 
 spoon C, containing a piece of burning phos- 
 phorus, and having a lighted taper attached, 
 it may be shown that although there 
 is enough carbonic acid to extinguish the 
 taper, the oxygen is not exhausted, for the 
 phosphorus continues to burn rapidly. 
 
 Carbonic acid is not poisonous when 
 taken into the stomach, but acts most 
 injuriously when breathed, by offering 
 an obstacle to that escape of carbonic 
 acid, by diffusion, from the blood of 
 the venous circulation in the lungs, 
 and its consequent replacement by the 
 oxygen necessary to arterial blood. 
 Any hindrance to this interchange 
 must impede respiration, and such 
 hindrance would, of course, be afforded 
 by carbonic acid present in the air 
 inhaled, in proportion to its quantity. The difference in constitution and 
 temperament in individuals, makes it impossible that any exact general 
 rule should be laid down as to the precise quantity of carbonic acid 
 which may be present in air without injury to respiration, but it may be 
 safely asserted that it is not advisable to breathe for any length of time 
 in air containing more than xoVo^h (O'l P er cen t.) of its volume of car- 
 bonic acid. 
 
 There appears to be no immediate danger, however, until the carbonic 
 acid amounts to ^o-th (0*5 per cent.), when most persons are attacked by 
 the languor and headache attending the action of this gas. A larger pro- 
 portion of carbonic acid produces insensibility, and air containing T Vth of 
 its volume of carbonic acid causes suffocation. The danger in entering old 
 wells, cellars, and other confined places, is due to the accumulation of 
 this gas, either exhaled from the earth or produced by decay of organic 
 matter. The ordinary test applied to such confined air by introducing a 
 candle is only to be depended upon if the candle burns as brightly in the 
 confined space as in the external air ; should the flame become at all dim, 
 it would be unsafe to enter, for experience has shown that combustion 
 may continue for some time in an atmosphere dangerously charged with 
 carbonic acid. 
 
 Fig. 65. 
 
PRINCIPLES OF VENTILATION. 
 
 69 
 
 The accidents from choke damp and after damp in coal mines, and 
 from the accumulation in brewers' and distillers' vats of the carbonic acid 
 resulting from fermentation, are also examples of the fatal effect of this 
 gas. 
 
 The air issuing from the lungs of a man at each expiration contains 
 from 3 '5 to 4 volumes of carbonic acid in 100 volumes of air, and could not, 
 therefore, be breathed again without danger. The total amount of car- 
 bonic acid evolved by the lungs and skin amounts to about 0'7 cubic foot 
 per hour. In order that it may be breathed again without inconvenience 
 this should be distributed through 140 cubic feet of fresh air, or a 
 space measuring 5 *2 feet each way. Hence the necessity for a constant 
 supply of fresh air by ventilation, to dilute the carbonic acid to such an 
 extent that it may cease to impede respiration. This becomes the more 
 necessary where an additional quantity of carbonic acid is supplied by 
 candles or gas-lights. Two ordinary gas-burners, each consuming three 
 cubic feet of gas per hour, will produce as much carbonic acid as one man. 
 Fortunately, a natural provision for ventilation exists in the circumstance 
 that the processes of respiration and combustion, which contaminate the 
 air, also raise its temperature, thus diminishing its specific gravity by 
 expansion, and causing it to ascend 
 and give place to fresh air. Hence 
 the vitiated air always accumulates 
 near the ceiling of an apartment, and 
 it becomes necessary to afford it an 
 outlet by opening the upper sash of 
 the window, since the chimney ven- 
 tilates immediately only the lower 
 part of the room. 
 
 These principles may be illustrated by 
 some very simple experiments. 
 
 Two quart jars (fig. 66) are filled with 
 carbonic acid, and after being tested with 
 
 a taper, a 4 oz. flask is lowered into each, one flask containing cold and the other 
 hot water. After a few minutes, the jar with the cold flask will still contain enough 
 carbonic acid to extinguish the taper, whilst the air in 
 the other jar will support combustion brilliantly. 
 
 A tall stoppered glass jar (fig. 67) is placed over a stand, 
 upon which three lighted tapers are fixed at different 
 heights. The vitiated air, rising to the top of the jar, 
 will extinguish the uppermost taper first, and the others 
 in succession. By quickly removing the stopper and 
 raising the jar a little before the lowest taper has expired, 
 the jar will be ventilated and the taper revived. 
 
 A similar jar (fig. 68), with a glass chimney fixed into 
 the neck through a cork or piece of vulcanised tubing, is 
 placed over a stand with two tapers, one of which is near 
 the top of the jar, and the other beneath the aperture 
 of the chimney ; if a crevice for the entrance of air be 
 left between the jar and the table, the lower taper will 
 continue to burn indefinitely, whilst the upper one will 
 soon be extinguished by the carbonic acid accumulating 
 around it. , 
 
 Fig. 66. 
 
 Fig. 67. 
 
 In ordinary apartments, the incidental crevices of the doors and windows 
 are depended upon for the entrance of fresh air, whilst the contaminated 
 air passes out by the chimney, but in large buildings special provision 
 must be made for the two air currents. -In mines this becomes the more 
 
70 
 
 PRINCIPLES OF VENTILATION. 
 
 necessary, since the air receives much additional contamination by the 
 gases (marsh-gas and carbonic acid) evolved from the workings, and by 
 the smoke occasioned in blasting with gunpowder. 
 Mines are generally provided with two shafts for 
 ventilation, under one of which (the upcast shaft) 
 a fire is maintained to produce the upward current, 
 which carries off the foul air, whilst the fresh air 
 descends by the other (downcast shaft). The cur- 
 rent of fresh air is forced by wooden partitions to 
 divide itself, and pass through every portion of the 
 workings. 
 
 The operation of such provisions for ventilation is easily 
 exhibited. 
 
 A tall jar (fig. 69) is fitted with a ring of cork, carrying 
 a wide glass chimney (A). If this be placed over a taper 
 Fig. 68. standing in a plate of water, the accumulation of vitiated 
 
 air will soon extinguish the taper ; but if a second chimney 
 
 (B), supported in a wire ring, be placed within the wide chimney, fresh air will 
 enter through the interval between the two, and the smoke from a piece of brown 
 paper will demonstrate the existence of the two currents, as shown by the arrows. 
 
 A small box (fig. 70) is provided with a glass chimney 
 at each end. In one of these (B), representing the upcast 
 shaft, a lighted taper is suspended. A piece of smoking 
 brown paper may be held in each chimney to show the 
 direction of the current. On closing A with a glass 
 plate, the taper in B will be extinguished, the entrance 
 of fresh air being prevented. By breathing gently into 
 A the taper will also be extinguished. The experiment 
 may be varied by pouring carbonic acid and oxygen 
 alternately into A, when the taper will be extinguished 
 and rekindled by turns. 
 
 A pint bell-jar (fig. 71) is placed over a taper standing 
 in a tray of water. If a chimney (a common lamp-glass) 
 be placed on the top of the jar, the flame of the taper 
 will gradually die out, because no provision exists for 
 the establishment of the two currents, but on dropping 
 a piece of tin-plate or card-board into the chimney, so 
 as to divide it, the taper will be revived, and the smoke 
 from the brown paper will distinguish the upcast from the 
 F 'g- 69 - downcast shaft. 
 
 If a little water be poured into a wide-mouthed bottle of carbonic 
 acid, and the bottle be then firmly closed by the palm of the hand, it 
 
 will be found, on shaking the bottle 
 violently, that the carbonic acid is 
 absorbed, and the palm of the hand 
 is sucked into the bottle. The pre- 
 sence of carbonic acid in the solution 
 may be proved by pouring it into 
 lime-water, in which it will produce a 
 precipitate of carbonate of lime, re- 
 dissolved by a further addition of the 
 solution of carbonic acid. 
 
 One pint of water shaken in a vessel 
 containing carbonic acid gas, at the 
 ordinary pressure of the atmosphere, will dissolve about one pint of the 
 gas, equal in weight to nearly 1 6 grains. If the carbonic acid be confined 
 in the vessel under a pressure equal to twice or thrice that of the atmo- 
 
 Fig. 70. 
 
SODA-WATER SPARKLING DRINKS. 71 
 
 sphere that is, if twice or thrice the quantity of carbonic acid be com- 
 pressed into the same space, the water will still dissolve one pint of the 
 gas, but the weight of this pint will now be twice 
 or thrice that of the pint of uncompressed gas, so 
 that the water will have dissolved 32 or 48 grains of 
 the gas, accordingly as the pressure had been doubled 
 or trebled. As soon, however, as the pressure is 
 removed, the compressed carbonic acid will resume 
 its former state, with the exception of that portion 
 which the water is capable of retaining in solution 
 under the ordinary pressure of the atmosphere. 
 Thus, if the water had been charged with carbonic 
 acid under a pressure equal to thrice that of the 
 atmosphere, and had therefore absorbed 48 grains 
 of the gas, it would only retain 1 6 grains when the 
 pressure was taken off, allowing 32 grains to escape 
 in minute bubbles, producing the appearance known 
 as effervescence. This affords an explanation of the 
 properties of soda-water, which is prepared by charging water with 
 carbonic acid gas under considerable pressure, and rapidly confining it 
 in strong bottles. As soon as the resistance offered by the cork to the 
 expansion of the gas is removed, the excess of the carbonic acid, above 
 that which it can hold in solution at the ordinary pressure of the air, 
 escapes with effervescence. In a similar manner, the waters of certain 
 springs become charged with carbonic acid, under high pressure, beneath 
 the surface of the earth, and when, upon their rising to the surface, this 
 pressure is removed, the excess of carbonic acid escapes with effervescence, 
 giving rise to the sparkling appearance and sharp flavour which renders 
 spring water so agreeable. On the other hand, the waters of lakes and 
 rivers are usually flat and insipid, because they hold in solution so small 
 a quantity of uncombined carbonic acid. 
 
 The sparkling character of champagne, bottled beer, &c., is due to the 
 presence in these liquids of a quantity of carbonic acid which has been 
 generated by fermentation, subsequent to bottling, and has therefore been 
 retained in the liquid under pressure. In the case of Seidlitz powders 
 and soda-water powders, the effervescence caused by dissolving them 
 in water is due to the disengagement of carbonic acid, caused by 
 the action of the tartaric acid, which composes one of the powders, 
 upon the bicarbonate of soda, producing tartrate of soda and carbonic 
 acid gas. In the dry state these powders may be mixed without any 
 chemical change, but the addition of water immediately causes the effer- 
 vescence. 
 
 The solubility of carbonic acid in water is of great importance in the 
 chemistry of nature; for this acid, brought down from the atmosphere 
 dissolved in rain, is able to act chemically upon rocks, such as granite, 
 which contain alkalies the carbonic acid combining with these, and thus 
 slowly disintegrating or crumbling down the rock, an effect much assisted 
 by the mechanical action of the expansion of freezing water in the inter- 
 stices of the rock. It appears that soils are thus formed by the slow 
 degradation of rocks, and when these soils are capable of supporting 
 plants, the solution of carbonic acid is again of service, not only as a 
 direct food, by providing the plant with carbon through its roots, but as 
 a solvent for certain portions of the mineral food of the plant (such as 
 
72 
 
 LIQUEFACTION OF CARBONIC ACID. 
 
 phosphate of lime), which pure water could not dissolve, and which the 
 plant cannot take up except in the dissolved state. 
 
 57. Although carbonic acid retains its state of gas under all tempera- 
 tures and pressures to which it is commonly exposed, it is capable of 
 assuming the liquid and even the solid state. 
 
 When exposed to a pressure of 38'5 atmospheres (577'5 Ibs, upon the 
 square inch) at 32 F., carbonic acid condenses to a colourless liquid of 
 sp. gr. 0-83 (water = 1), and at a temperature of 70 F. (70 below the 
 zero, or 102 below the freezing point, F.), becomes a transparent mass of 
 solid carbonic acid resembling ice. 
 
 A small specimen of liquid carbonic acid is easily prepared. A strong tube of 
 green glass (A, fig. 72) is selected, about 12 inches long, & inch diameter in the 
 
 bore, and T ^ inch thick in the 
 A walls. With the aid of the 
 
 j. fi blowpipe flame this tube is 
 
 softened and drawn oif at 
 about an inch from one end, 
 
 |T^^>sC' m as at B, which is thus closed 
 
 (C). This operation should 
 be performed slowly, in order 
 
 c! <^ I^^Z^^^I^^II IZl that the closed end may not 
 
 be much thinner than the 
 walls of the tube. When the 
 tube has cooled, between 30 
 and 40 grs. of powdered bi- 
 carbonate of ammonia (ordi- 
 nary sesquicarbonate which 
 has crumbled down) are 
 tightly rammed into it with 
 a glass rod. This part of the 
 tube is then surrounded with 
 a few folds of wet blotting- 
 paper to keep it cool, and the 
 tube is bent, just beyond the 
 carbonate of ammonia, to a 
 somewhat obtuse angle (D). 
 
 Fig. 72. The tube is then softened at 
 
 about an inch from the open 
 
 end, and drawn out to a narrow neck (E), through which a measured drachm of oil 
 of vitriol is poured down a funnel-tube, so as not to soil the neck, which is then 
 carefully drawn out and sealed by the blowpipe flame, as at F. The empty space 
 in the tube should not exceed cubic inch. 
 
 When the tube is thoroughly cold, it is suspended by strings in such a position 
 that the operator, having retired behind a screen at some distance, may reverse the 
 tube, allowing the acid to flow into the limb containing the carbonate of ammonia ; 
 or the tube may be fixed in a box which is shut up, and reversed so as to bring the 
 tube into the required position. 
 
 If the tube be strong enough to resist the pressure, it will be found, after a few 
 hours, that a layer of liquid carbonic acid has been formed upon the surface of the 
 solution of sulphate of ammonia. By cooling the empty limb in a mixture of 
 pounded ice and salt, or of hydrochloric acid and sulphate of soda, the liquid acid 
 can be made to distil itself over intd this limb, leaving the sulphate of ammonia in 
 the other. 
 
 On a larger scale the gas is liquefied in iron vessels. The liquid carbonic acid 
 is employed for illustrating the laws of heat. When a jet of the liquid is allowed 
 to escape into the air, the evaporation of one portion absorbs enough heat to soli- 
 dify the remainder, which becomes a snow-like mass, evaporating rapidly when 
 exposed to air, with production of intense cold. A mixture of the solid carbonic 
 acid with ether forms one of the most powerful frigorific mixtures, and has rendered 
 great service in the liquefaction and solidification of gases. 
 
 58. Carbonic acid may be separated from most other gases by the 
 
ANALYSIS OF ORGANIC SUBSTANCES. 
 
 73 
 
 action of hydrate of potash, which absorbs it, forming carbonate of potash. 
 The proportion of carbonic acid is inferred either from the diminution in 
 volume suffered by the gas when treated with potash, or from the increase 
 of weight of the latter. 
 
 In the former case the gas is carefully measured over mercury (fig. 73). with due 
 attention to temperature and barometric pressure, and a little concentrated solution 
 of potash is thrown up through a curved 
 pipette or syringe, introduced into the 
 orifice of the tuhe beneath the surface of 
 the mercury. The tube is gently shaken 
 for a few seconds to promote the absorp- 
 tion of the gas, and, after a few minutes' 
 rest, the diminution of volume is read 
 off. Instead of solution of potash, damp 
 hydrate of potash in the solid state is 
 sometimes introduced, in the form of 
 small sticks or balls attached to a wire. 
 To determine the weight of carbonic 
 acid in a gaseous mixture, the latter is 
 passed through a bulb-apparatus (C, fig. 
 74), containing a strong solution of po- 
 tash, and weighed before and after the 
 passage of the gas. When the propor- 
 tion of carbonic acid in the gas is small, 
 it is usual to attach to the bulb-appara- 
 tus a little tube, containing solid hydrate 
 of potash, or chloride of calcium, or 
 pumice-stone moistened with sulphuric Fig. 73. 
 
 acid, for the purpose of retaining any 
 
 vapour of water which the large volume of unabsorbed gas might carry away in 
 passing through the solution of potash. 
 
 59. Ultimate organic analysis. It is necessary to determine in this 
 manner the weight of carbonic acid, in order to ascertain the proportion of 
 carbon present in organic substances. For this purpose, an accurately 
 weighed quantity (usually from seven to ten grains) of the organic substance 
 is very carefully mixed with some compound from which it can obtain 
 oxygen at a high temperature, such as oxide of copper (CuO) or chromate 
 of lead (PbO . CrO,,), care being taken to employ a large excess of the 
 oxidising agent. The mixture is introduced into a combustion-tube of 
 German glass (which is free from lead and noted for its infusibility) of the 
 form shown in A, fig. 74. This tube is provided with a small tube B, 
 
 Fig. 74. Apparatus for organic analysis. 
 
 containing chloride of calcium, which is connected by a tube of caoutchouc 
 with the potash-bulbs C. On gradually heating the tube in a charcoal 
 
74 CALCULATION OF FORMULA. 
 
 furnace, or over a properly constructed gas-burner, the hydrogen and carbon 
 contained in the organic substance are converted, respectively, into water 
 and carbonic acid, by the oxygen derived from the chromate of lead or oxide 
 of copper. The water is absorbed by the chloride of calcium in B, and the 
 increase of weight in this tube will indicate the quantity of water formed 
 in the combustion, whilst that of the potash bulbs will show the weight 
 of the carbonic acid. When the whole length of the tube is red hot, and 
 no more gas passes through the bulbs, the sealed point D of the tube is 
 broken off, and air drawn through by applying suction at E, in order to 
 sweep out the last traces of water and carbonic acid into the chloride of 
 calcium and potash. Sometimes the organic substance is heated in a little 
 platinum tray, placed within a glass tube, through which a stream of pure 
 oxygen is passed, the products of combustion being afterwards made to 
 pass over red-hot oxide of copper, to convert any carbonic oxide into car- 
 bonic acid, and collected for weighing as before. 
 
 When the organic substance contains carbon, hydrogen, and oxygen, 
 the weight of this last is inferred by subtracting the weights of the carbon 
 and hydrogen from that of the substance. As an example of the ultimate 
 analysis of an organic substance, the results of an analysis of oxalic acid 
 are here given 
 
 10 grs. of oxalic acid, dried at 212 F., gave 9-78 grs. of carbonic acid 
 and 2 '00 grs of water. 
 
 C0 2 C C0 2 
 
 22 : 6 : : 9'78 : x 
 x = 2'Q7 grs. of carbon in 10 grs. of oxalic acid. 
 
 HO H HO 
 
 9:1:: 2'00 : y 
 
 y - 0*22 gr. of hydrogen in 10 grs. of oxalic acid. 
 
 It having been ascertained by preliminary experiments that oxalic acid 
 contains only carbon, hydrogen, and oxygen, 10 (oxalic acid) minus 2 '89 
 (carbon and hydrogen) = 7*11 grs. of oxygen in 10 grs. of oxalic acid. 
 
 It appears, therefore, that 
 
 10 grs. of oxalic acid contain 
 .2-67 carbon, 
 0'22 hydrogen, and 
 7-11 oxygen. 
 
 Empirical and rational formulae. In order to deduce from these 
 numbers the chemical formula for oxalic acid, that is, the formula express- 
 ing the number of combining weights of each element, it will be necessary, 
 of course, to divide the weight of each element by the number represent- 
 ing its combining weight in the table at p. 2. 
 
 2*67 
 
 Thus = 0*44 of a combining weight of carbon ; 
 
 6 
 
 <^? =0-22 hydrogen; 
 
 7-11 
 
 -- - 0-88 oxygen. 
 
CARBONATES. 75 
 
 And the formula of oxalic acid might be written C44H.220.8s. But as 
 fractions are not admissible in such a formula, it would be written 
 C 44 H2 2 88 . This, however, is only an empirical formula for oxalic acid, 
 that is, a formula which represents its composition only, without reference 
 to its constitution, i.e., to the absolute number of combining weights pre- 
 sent, and to the mode in which they are grouped or arranged within the 
 compound. A formula professing to give such information would be 
 termed a rational formula, and can only be arrived at by the careful study 
 of the relation of the substance under examination to others of which the 
 combining weights are certainly known. Thus, it is found that one com- 
 bining weight (47 parts) of potash requires 45 parts of dry oxalic acid to 
 neutralise it and form the oxalate of potash. Hence it is reasonable to 
 regard 45 as the combining weight of dry oxalic acid. Since the above 
 analysis has proved this quantity of oxalic acid to contain 12 (two com- 
 bining weights) of carbon, 1 (one combining weight) of hydrogen, and 32 
 (four combining weights) of oxygen, the formula would be written 
 C 2 H0 4 . In determining whether this formula represents only one group- 
 ing of the elements, or whether it contains two or more groups in com- 
 bination, the chemist is guided by the results of a more minute study 
 of the decompositions which the compound undergoes under varied con- 
 ditions. 
 
 60. Salts formed by carbonic acid. Although so ready to combine with 
 the alkalies and alkaline earths (as shown in its absorption by solution 
 of potash and by lime-water), carbonic acid must be classed among the 
 weaker acids. It does not neutralise the alkalies completely, and it may 
 be displaced from its combinations with bases by most other acids. Its 
 action upon the colouring matter of litmus is feeble and transient. If a 
 solution of carbonic acid in water be added to blue infusion of litmus, a 
 wine-red liquid is produced, which becomes blue again when boiled, losing 
 its carbonic acid; whilst litmus reddened by sulphuric, hydrochloric, 
 or nitric acid, acquires a brighter red colour, which is permanent on 
 boiling. 
 
 With each of the alkalies carbonic acid forms two well-defined salts, 
 the carbonate and bicarbonate. Thus, the carbonates of potash and soda 
 are represented by the formulae, KO . C0 2 and NaO . C0 2 , whilst the bicar- 
 bonates are KO . HO . 2C0 2 and NaO . HO . 2C0 2 . The existence of the 
 latter salts would favour the belief in the existence of a hydrate of carbonic 
 acid (HO . C0 2 ), when they would become 
 
 KO . C0 2 , HO . C0 2 and NaO . C0 2 , HO . C0 2 , 
 
 although no such combination of water with carbonic acid has yet 
 been obtained in the separate state. Perfectly dry carbonic acid gas 
 is not absorbed by pure quicklime (CaO), but when a little water is added 
 combination at once takes place. This supports the view entertained by 
 some chemists, that C0 2 is not an acid until it is associated with water, 
 and they therefore speak of it as carbonic anhydride, reserving the name 
 carbonic acid for the as yet undiscovered compound HO . C0 2 (or 
 HC0 3 ). 
 
 The following are some of the principal carbonates which are found in 
 nature or employed in the arts : 
 
76 
 
 CARBONIC OXIDE. 
 
 Chemical Name. 
 
 Common Name. 
 
 Equivalent Formula. 
 
 Atomic Unitary 
 Formula. 
 
 Carbonate of pot- 
 ash 
 
 | Potashes, pearl-ash 
 
 KO ; co 2 
 
 K 2 ee s 
 
 Bicarbonate of 
 
 1 
 
 KO . HO . 2C0 2 
 
 T?*TT /11+A 
 IV 11 . V>Wo 
 
 potash 
 
 
 
 a 
 
 Carbonate of 
 soda 
 
 f Alkali V 
 ( Washing soda f 
 
 NaO . C0 2 
 
 Na 2 ee 3 
 
 Bicarbonate of 
 so,da . . . . , 
 
 Carbonate of soda 
 
 NaO . HO . 2C0 2 
 
 NaHe0 3 
 
 '. 
 
 Smelling salts 
 
 
 
 Sesquicarbonate 
 of ammonia 
 
 Preston salts 
 Carbonate of am- 
 
 2NH 3 .2H0.3C0 2 
 
 2[(H 4 N) 2 eo 3 ]ee 2 
 
 
 monia 
 
 
 
 Carbonate of 
 lime ; .<, v 
 
 $ Limestone, chalk 1 
 ( Marble J 
 
 CaO . C0 2 
 
 e a eo 3 
 
 Basic carbonate 
 of magnesia 
 
 | Magnesia alba 
 \ Magnesia 
 
 3'(MgO,C0 2 ), 
 MgO . HO. 
 
 J3Mgee 3 .M g H 2 o 2 
 
 Carbonate cf 
 iron 
 
 > Spathic iron ore 
 
 FeO . C0 2 
 
 Fe0 3 
 
 Carbonate of 
 
 Calamine 
 
 ZnO . C0 2 
 
 ZnOO 
 
 zinc 
 
 
 
 
 I Basic carbonats 
 of copper 
 
 | Malachite 
 
 CuO . C0 2 , 
 CuO . HO 
 
 ) "Gllw . HgO . v7llLO^ 
 
 Basic carbonate 
 of lead 
 
 1 White lead 
 
 2(PbO.C0 2 ), 
 PbO.HO 
 
 }2Pbee 3 .Pbe.H 2 e 
 
 Double carbon- 
 
 f Dolomite } 
 
 
 
 ate of lime 
 and magnesia 
 
 < Magnesian lime- V 
 1 stone J 
 
 CaO . MgO . 2C0 2 
 
 MgOa 2O 3 
 
 61. Analytical proof of the composition of carbonic acid. Lavoisier appears to have 
 been the first to prove that carbonic acid was formed when carbon combined with 
 oxygen, but its composition was first analytically demonstrated by Smithson Ten- 
 nant, who heated carbonate of lime with phosphorus in a sealed glass tube, and 
 obtained phosphate of lime and carbon, the latter having parted with its oxygen to 
 convert the phosphorus into phosphoric acid. 
 
 A far easier method of demonstrating the composition of carbonic acid consists in 
 introducing a pellet of potassium into a bulb tube, through which a current of car- 
 bonic acid (dried by passing through oil of vitriol, or over chloride of calcium) is 
 flowing, and applying the heat of a spirit-lamp to the bulb ; the metal will soon 
 burn in the gas, which it robs of its oxygen, leaving the carbon as a black mass upon 
 the bulb (fig. 75). The potash produced by the oxidation of the potassium enters 
 into combination with another portion of the carbonic acid, forming a white mass of 
 carbonate of potash, 3C0 2 + K 2 = 2(KO . C0 2 ) + C. If slices of sodium be ar- 
 ranged in a test-tube in alternate layers with dried chalk (carbonate of lime), and 
 strongly heated with a spirit-lamp, vivid combustion will ensue, and much carbon 
 will be separated (CaO . C0 2 + Na 2 = CaO + 2NaO + C). 
 
 62. CAEBONIC OXIDE. Other metals, however, which are not endowed 
 with so powerful an attraction for oxygen, do not cany the decomposition 
 of carbonic acid to its final limit ; thus, iron and zinc* at a high tempera- 
 ture will only deprive the gas of one-half of its oxygen, a result which may 
 also be brought about at a red heat by carbon itself. If an iron tube filled 
 with fragments of charcoal be heated to redness in a furnace (fig. 22), and 
 carbonic acid gas be transmitted through it, it will be found, on collecting 
 the gas which issues from the other extremity of the tube, that it has no 
 
 Magnesium also reduces carbonic acid to carbonic oxide. 
 
CAEBONIC OXIDE IN FIRES AND FURNACES. 
 
 77 
 
 longer the properties of carbonic acid, but that, oil the approach of a taper, 
 it takes fire, and burns with a beautiful blue lambent flame, similar to that 
 which is often observed to play over the surface of a clear fire. Both 
 flames, in fact, are due to the same gas, and in both cases this gas results 
 
 Fig. 75 
 
 from the same chemical change, for in the tube the carbonic acid yields 
 half of its oxygen to the charcoal, both becoming converted into carbonic 
 oxide ;C0 2 + C = 2CO. In the fire, the carbonic acid is formed by the 
 combustion of the carbon of the fuel in the oxygen of the air entering at 
 the bottom of the grate ; and this carbonic acid, in passing over the layer 
 of heated carbon in the upper part of the fire, is partly converted into 
 carbonic oxide, which inflames when it meets with the oxygen in the air 
 above the surface of the fuel, and burns with its characteristic blue flame, 
 reproducing carbonic acid. 
 
 The carbonic oxide occupies twice the volume of the carbonic acid from 
 which it was produced. 
 
 This conversion of carbonic acid into carbonic oxide is of great import- 
 ance on account of its extensive application in metallurgic operations. It 
 is often desirable, for instance, that a flame should be made to play over 
 the surface of an ore placed on the bed or hearth of a reverberatory fur- 
 nace (fig. 76). This object is easily attained when the coal affords a large 
 
 Fig. 76. Reverberatory furnace for copper smelting. 
 
 quantity of inflammable gas ; but with anthracite coal, which burns with 
 very little flame, and is frequently employed in such furnaces, it is neces- 
 sary to pile a high column of coal upon the grate, so that the carbonic 
 
78 ILLUMINATING GAS FROM STEAM. 
 
 acid formed beneath may be converted into carbonic oxide in passing over 
 the heated coal above, and when this gas reaches the hearth of the fur- 
 nace, into which air is admitted, it burns with a flame which spreads over 
 the surface of the ore. 
 
 The attraction of carbonic oxide for oxygen is turned to account in 
 removing that element from combination with iron in its ores, as will be 
 seen hereafter. 
 
 Carbonic oxide is a gas of so poisonous a character that, according to 
 Leblanc, one volume of it diffused through 100 volumes of air totally 
 unfits it to sustain life; and it appears that the lamentable accidents 
 which too frequently occur from burning charcoal or coke in braziers and 
 chafing-dishes in close rooms, result from the poisonous effects of the small 
 quantity of carbonic oxide which is produced and escapes combustion, 
 since the amount of carbonic acid thus diffused through the air is not 
 sufficient in many cases to account for the fatal result. 
 
 63. The knowledge of this poisonous character of carbonic oxide gave 
 rise, a few years since, to considerable apprehension when it was proposed 
 to employ this gas in Paris for purposes of illumination. The character 
 of the flame of carbonic oxide would appear to afford little promise of its 
 utility as an illuminating agent ; but that it is possible so to employ it is 
 easily demonstrated, by kindling a jet of the gas which has been passed 
 through a wide tube containing a little cotton moistened with rectified 
 coal naphtha (benzole), when it will be found to burn with a very luminous 
 flame. The carbonic oxide destined to be employed for illuminating pur- 
 poses was prepared by passing steam over red-hot coke or charcoal, when 
 a highly-inflammable gas was obtained, containing carbonic acid, carbonic 
 oxide, and hydrogen 
 
 4HO + C 3 - C0 2 + 2CO + H 4 
 
 Since neither hydrogen nor carbonic oxide burns with a luminous flame, 
 this gas was next passed into a vessel containing red-hot coke, over which 
 melted resin was allowed to trickle. The action of heat upon the resin 
 gave rise to the production of vapours similar to that of the benzole em- 
 ployed in the above experiment, and which, in like manner, conferred 
 considerable illuminating power upon the gas. 
 
 The decomposition of steam by red-hot carbon is also taken advantage 
 of in order to procure a flame from anthracite coal when employed for 
 heating boilers. The coal being burnt on fish-bellied bars, beneath which 
 a quantity of water is placed, the radiated heat converts the water into 
 steam, which is carried by the draught into the fire, where it furnishes 
 carbonic oxide and hydrogen, both capable of burning with flame under 
 the bottom of the boiler. The temperature of the bars is also thus reduced, 
 so that they are not so much injured by the intense heat of the glowing 
 fuel. 
 
 64. Carbonic oxide, unlike carbonic acid, is a permanent gas, and nearly 
 insoluble in water. It is even lighter than air, its specific gravity being 
 0-967. In its chemical relations it is an indifferent oxide, that is, it has 
 neither acid nor basic properties. 
 
 65. A very instructive process for obtaining carbonic oxide, consists in heating 
 crystallised oxalic acid with three times its weight of oil of vitriol. If the gas be 
 collected over water (fig. 77), and one of the jars be shaken with a little lime- 
 
PREPARATION OF CARBONIC OXIDE. 
 
 79 
 
 water, the milkiness imparted to the latter will indicate abundance of car- 
 bonic acid ; whilst, on removing 
 the glass plate, and applying a 
 light, the carbonic oxide will 
 burn with its characteristic blue 
 flame. The gas thus obtained 
 is a mixture of equal volumes 
 of carbonic oxide and carbonic 
 acid gases. Crystallised oxalic 
 acid is represented by the for- 
 mula C 2 H0 4 . 2Aq., and if the 
 water of crystallisation be left 
 out of consideration, its decom- 
 position may be represented by 
 the equation 
 
 C 2 H0 4 = HO + CO + C0 2 , ^^f- *^sr, 
 
 the change being determined by Fi 77 _ 
 
 the attraction of the oil of vitriol 
 
 for water. To obtain pure carbonic oxide, the mixture of gases must be passed 
 
 through a bottle containing solution of potash, to absorb the carbonic acid (fig. 78). 
 
 But pure carbonic oxide is much more easily obtained by the action of four parts 
 
 of oil of vitriol upon one part of crystallised ferrocyanide of potassium (yellow prus- 
 
 Fig. 78. Preparation of carbonic oxide. 
 
 siate ot potash) at a moderate heat, the lamp being removed as soon as the effer- 
 vescence begins to take place. Since the gas contains, especially at the corfimence- 
 ment, small incidental quantities of sulphurous and carbonic acids, it must be passed 
 through solution of potash if it be required perfectly pure. The chemical change 
 which occurs in this process is expressed thus : 
 
 6(HO.S0 3 ) = 6CO 
 
 K 2 C 6 N s Fe + 6HO 
 Fei-rocyanide of potassium. 
 
 + 3(NH 3 . HO . S0 3 ) 
 Sulphate of ammonia. 
 
 2(KO.S0 3 ) 
 Sulphate of potash. 
 
 f FeO.S0 3 
 
 Sulphate of iron. 
 
 66. To demonstrate the production of carbonic acid during the combustion of 
 carbonic oxide, a jar of the gas is closed with a glass plate, and after placing it upon 
 the table, the plate is slipped aside and a little lime-water quickly poured into the 
 jar. On shaking, no milkiness indicative of carbonic acid should be perceived. 
 The plate is then removed, and the gas kindled. On replacing the plate and 
 shaking the jar, an abundant precipitation of carbonate of lime will take place. 
 
80 
 
 HYPOTHETICAL CARBON VAPOUR. 
 
 "When carbonic oxide is passed through a red-hot porcelain tube, a portion of it is 
 decomposed into carbonic acid and carbon ; and when the experiment is conducted 
 without special arrangements, the carbonic oxide is reproduced as the temperature 
 of the gas falls. But by passing through the centre of the porcelain tube a brass 
 tube, through which cold water is kept running, the decomposition has been demon- 
 strated by the deposition of carbon upon the cooled tube, and by collecting the car- 
 bonic acid formed. 
 
 Carbonic acid is also decomposed by intense heat into carbonic oxide and oxygen ; 
 but if these gases be allowed to cool down slowly in contact, they recombine. The 
 gas drawn from the hottest region of a blast-furnace (see IRON), and rapidly cooled, 
 so as to prevent recombination, was found to contain both carbonic oxide and oxygen. 
 
 By passing a pellet of phosphorus up into carbonic acid, over mercury, in a 
 eudiometer, and passing electric sparks for some days, the gas has been entirely 
 decomposed, an equal volume of carbonic oxide being left. 
 
 The reducing action of carbonic oxide upon metallic oxides, at high temperatures, 
 may be illustrated by passing the pure gas from a bag or gas-holder (A, fig. 79), first 
 through a bottle of lime-water (B) to prove the absence of carbonic acid, then over 
 
 Fig. 79. Reduction of oxide of copper by carbonic oxide. 
 
 oxide of copper, contained in the tube C, and afterwards again through lime-water 
 in D. When enough gas has been passed to expel the air, heat may be applied to 
 the tube by the gauze-burner E, when the formation of carbonic acid will be im- 
 mediately shown by the second portion of lime-water, and the black oxide of copper 
 will be reduced to red metallic copper. 
 
 If precipitated peroxide of iron be substituted for oxide of copper, iron in the state 
 of black powder will be left, and if allowed to cool in the stream of gas, will take fire 
 when it is shaken out into the air, becoming reconverted into the peroxide (iron 
 pyrophorus). 
 
 67. Composition by volume of carbonic oxide and carbonic acid. When 
 carbon burns in oxygen, the volume of the carbonic acid produced is 
 exactly equal to that of the oxygen, so that one volume of oxygen fur- 
 nishes one volume of carbonic acid gas. 
 
 If from the weight of one volume (specific gravity] of carbonic acid 
 (1 '529) there be deducted the weight (1 - 105) of one volume of oxygen, the 
 remainder (424) will represent the weight of carbon contained in one 
 volume of carbonic acid ; and if it be assumed that this carbon, were it 
 possible to convert it into vapour, would occupy a volume equal to that of 
 the oxygen (one volume), the number -424 would represent the specific 
 gravity of the hypothetical vapour of carbon, and one volume of carbonic 
 acid would be regarded as containing one volume of carbon vapour, com- 
 bined with one volume of oxygen. 
 
COMBINING WEIGHT OF CARBONIC ACID. 81 
 
 When one volume of carbonic acid (containing one volume of oxygen) 
 is passed over heated carbon, it yields two volumes of carbonic oxide ; 
 hence two volumes of this gas contain one volume of oxygen. 
 The weight of one volume (specific gravity) of carbonic oxide 
 
 is - 967, and the weight of two volumes, therefore, . 1*934 
 Deduct from this the weight of one volume of oxygen, 1*105 
 
 And the remainder, . '829 
 
 represents the weight of carbon contained in two volumes of carbonic 
 oxide. It was calculated above that '424 expressed the weight of one 
 volume of carbon vapour, hence, allowing for errors in determining the 
 specific gravities of the gases, '829 may be taken to represent two volumes 
 of carbon vapour, and carbonic oxide to contain, in two volumes, one 
 volume of oxygen, combined with two volumes of the imaginary vapour 
 of carbon. 
 
 This calculation is much simplified if hydrogen be made the unit of specific 
 gravity, instead of atmospheric air : 
 
 Specific gravity (to H) of C0 ? , i.e., weight of one volume, . 22 
 Specific gravity (to H), or weight of one volume, of 0, . . 16 
 
 Weight of carbon in one volume of C0 2 , or assumed specific 
 gravity (to H) of carbon vapour, 
 
 Specific gravity (to H), or weight of one volume, of CO, 14 
 Weight of two volumes of CO, . '. . . ^J- 28 
 one volume of O, . . ' . . > V . . : . 16 
 
 Weight of carbon in two volumes of CO, or assumed ) -.^ 
 weight of two volumes of carbon vapour, . . J 
 
 68. Combining weight of carbonic acid. It will be remembered that 
 in the decomposition of water by potassium (p. 23), 39 grs. of that metal 
 displaced 1 gr. of hydrogen, combining with the 8 grs. of oxygen to form 
 47 grs. of potash (KO), whence 39 was termed the equivalent (to one of 
 hydrogen) or combining weight of potassium, and 47 would represent the 
 combining weight of potash. These 47 grs. of potash are found by ex- 
 periment to combine with 22 grs. of carbonic acid, so that the number 22 
 may be taken for the combining weight of that acid.* Since it has been 
 ascertained that in 22 parts of carbonic acid there are 6 parts of carbon, 
 united with 16 of oxygen, and that, in carbonic oxide, the 6 parts of 
 carbon are united with 8 parts of oxygen, the number 6 may be taken to 
 represent the combining weight of carbon, or the weight equivalent to 
 one of hydrogen. 
 
 If 8 parts by weight of oxygen be represented as occupying one volume 
 (see p. 36), then the 11 parts of carbonic acid furnished by it would also 
 occupy one volume, and one equivalent (22 parts) of carbonic acid would 
 occupy two volumes, and would contain two volumes of imaginary carbon 
 vapour, and two volumes of oxygen. 
 
 * It is true that 47 grs. of potash may also combine with 44 grs. of carbonic acid (simul- 
 taneously, however, with 9 grs. of water), but the compound (bicarbonate of potash) thus 
 formed so easily loses one-half of its carbonic acid, that it is more natural to regard it as 
 containing two combining weights of the acid. 
 
82 COMPOUNDS OF CARBON AND HYDKOGEN. 
 
 The following table would then represent the equivalents and composi- 
 tion of carbonic oxide and carbonic acid : 
 
 
 4 
 
 Is 
 
 By Weight. 
 
 1 3 
 
 By Volume. 
 
 
 & 
 
 I 
 
 
 P 
 
 
 C 
 
 
 
 F, 
 
 
 
 Carbonic oxide, 
 
 CO 
 
 14 
 
 6 
 
 8 
 
 2 
 
 2 
 
 1 
 
 Carbonic acid, 
 
 C0 2 
 
 22 
 
 6 
 
 16 
 
 2 
 
 2 
 
 2 
 
 69. The atomic weight (see p. 36) of carbon is generally assumed to be 
 1 2, though, in consequence of the impossibility of determining the weight 
 of one volume of carbon vapour by experiment, the chemist is compelled 
 to surrender himself in this matter to the guidance of analogy and purely 
 theoretical considerations. 
 
 The molecular formula? of carbonic oxide and carbonic acid would then 
 become 
 
 
 1| 
 
 N ' 
 
 By Weight 
 
 11 
 
 By Volume. 
 
 
 si 
 
 sg 
 ^ 
 
 C 
 
 
 
 32 - 
 
 C 
 
 
 
 Carbonic oxide, 
 
 60 
 
 28 
 
 12 
 
 16 
 
 2 
 
 1 
 
 1 
 
 Carbonic acid, 
 
 <x> 2 
 
 44 
 
 12 
 
 32 
 
 2 
 
 1 
 
 2 
 
 COMPOUNDS OF CARBON AND HYDROGEN. 
 
 70. No two elements are capable of occurring in so many different 
 forms of combination as carbon and hydrogen. The hydrocarbons, as 
 their compounds are generally designated, include most of the inflammable 
 gases which are commonly met with, and a great number of the essential 
 oils, naphthas, and other useful substances. There is reason to believe 
 that all these bodies, even such as are found in the mineral kingdom, 
 have been originally derived from vegetable sources, and their history 
 belongs, therefore, to the department of organic chemistry. The three 
 simplest examples of such compounds will, however, be brought forward 
 in this place, to afford a general insight into the mutual relations of these 
 two important elements. Their names and composition are 
 
 
 Equivalent 
 Formulae.* 
 
 Parts by Weight. 
 
 C 
 
 H 
 
 Acetylene, . 
 
 C 4 H 2 
 
 24 
 
 2 
 
 Marsh-gas, . 
 
 CA 
 
 12 
 
 4 
 
 Olefiant gas, 
 
 CA 
 
 24 
 
 4 
 
 * The reasons why these formulae should not be written respectively C 2 H, CH 2 , and 
 
PREPARATION OF ACETYLENE. 
 
 83 
 
 71. Acetylene.* When very intensely heated, carbon is capable of 
 combining with hydrogen to form acetylene. The requisite heat is pro- 
 cured by means of a powerful galvanic battery, to the terminal wires of 
 which two pieces of dense carbon are attached, and the voltaic discharge is 
 allowed to take place between them in an atmosphere of hydrogen. The 
 experiment possesses little practical importance, because but little acety- 
 lene is formed in proportion to the force employed, but its theoretical 
 interest is very great, since it is the first step in the production of organic 
 substances by the direct synthesis of mineral elements ; acetylene (C 4 H 2 ) 
 being convertible into olefiant gas (C 4 H 4 ), this last into alcohol (C 4 H 6 2 ), 
 and alcohol into a very large number of organic products. 
 
 Acetylene is constantly found among the products of the incomplete 
 combustion and destructive distilla- 
 tion of substances rich in carbon, 
 hence it is always present in small 
 quantity in coal-gas, and may be pro- 
 duced in abundance by passing the 
 vapour of ether through a red-hot 
 tube. The character by which acety- 
 lene is most easily recognised is that 
 of producing a fine red precipitate in 
 an ammoniacal solution of cuprous 
 chloride (subchloride of copper). 
 
 The most convenient process for pre- 
 paring a quantity of this precipitate, is 
 that in which the acetylene is produced 
 by the imperfect combustion taking place 
 when a jet of atmospheric air is allowed 
 to burn in coal-gas. 
 
 An adapter (A, fig. 80) is connected at 
 its narrow end with the pipe "supply ing 
 coal-gas. The wider opening is closed by a 
 bung with two holes, one of which receives 
 a piece of brass tube (B) about three- 
 quarters of an inch wide and seven inches 
 long, and in the other is inserted a glass 
 tube (C) which conducts the gas to the 
 bottom of a separating funnel (D). The pi g . 80. Preparation of cuprous acetylide. 
 lower opening of the brass tube B is closed 
 
 with a cork, through which passes the glass tube E connected with a gas-holder or bag 
 containing atmospheric air. To commence the operation, the gas is turned on 
 through the tube F, and when all air is supposed to be expelled, the tube E is with- 
 drawn together with its cork, and a light is applied to the lower opening of the 
 brass tube, the supply of coal-gas being so regulated that it shall burn with a small 
 flame at the end of the tube. A feeble current of air is then allowed to issue from 
 the tube E, which is passed up through the flame into the adapter, where the jet 
 of air continues to burn in the coal-gas, t and may be kept burning for hours with 
 
 CH, which would, of course, agree equally well with the results of analysis, will appear 
 hereafter. 
 
 The molecular formulae would be 
 
 Acetylene, e 2 H 2 = 2 vols. 
 
 Marsh-gas, H 4 = 2 vols. 
 
 Olefiant gas, 2 H 4 = 2 vols. 
 
 where = 12. 
 
 * Long known as klumene, having been obtained in 1836 by the action of water upon a 
 compound containing carbon and potassium, produced during the preparation of that 
 metal. The name acetylene is derived from the hypothetical radical acetyle (C 4 H 3 ), to 
 which acetylene bears the same relation as ethylene (C 4 H 4 ) does to ethyle (C 4 H 5 ). 
 
 t It is advisable to attach a piece of thin platinum wire to the mouth of the glass tube, 
 to render the flame of the air more visible. 
 
 T? 9. 
 
84 CUPROS-ACETYLE ARGENT-ACETYLE. 
 
 a little attention to the proportions in which the gas and air are supplied. A solu- 
 tion of subchloride of copper in ammonia is poured into the separating funnel 
 through the lateral opening G, so that the imperfectly burnt gas may pass through 
 it when the cuprous acetylide is precipitated in abundance. When a sufficient 
 quantity has been formed, or the copper solution is exhausted, the liquid is run out 
 through the stop-cock (H) on to a filter, and replaced by a fresh portion. The pre- 
 cipitate may be rinsed into a flask provided with a funnel tube and delivery tube, 
 allowed to subside, the water decanted from it, and some strong hydrochloric acid 
 poured in through the funnel. On heating, the acetylene is evolved, and may be 
 collected, either over water, or more economically in a small gas-bag. To obtain a 
 pint of the gas, as much of the moist copper precipitate is required as will measure 
 about six ounces after settling down. Such a quantity may be prepared in about 
 six hours. 
 
 A solution of cuprous chloride suitable for this experiment is conveniently pre- 
 pared in the following manner : 500 grains of black oxide of copper are dissolved 
 in seven measured ounces of common hydrochloric acid, in a flask, and boiled for 
 about twenty minutes with 400 grains of copper in filings or fine turnings. The 
 brown solution of cuprous chloride in hydrochloric acid thus obtained is poured into 
 about three pints of water contained in a bottle ; the white precipitate (cuprous 
 chloride) is allowed to subside, the water drawn off with a siphon, and the pre- 
 cipitata rinsed into a twenty-ounce bottle, which is then quite filled with water and 
 closed with a stopper. When the precipitate has again subsided, the water is drawn 
 off, and four ounces of powdered chloride of ammonium are introduced, the bottle 
 being again filled up with water, closed and shaken. The cuprous chloride is entirely 
 dissolved by the chloride of ammonium, but would be reprecipitated if more water 
 were added. When required for the precipitation of acetylene, the solution may 
 be mixed with about one-tenth of its bulk of strong ammonia ('880), which maybe 
 poured into the separating funnel (D) before the copper solution is introduced. 
 Four measured ounces of the solution are sufficient for one charge, and yield, in 
 three hours, about three measured ounces of the moist precipitate. The blue solu- 
 tion of ammoniacal cupric chloride filtered from the red precipitate may be ren- 
 dered serviceable again by being shaken, in a stoppered bottle, with precipitated 
 copper, prepared by reducing a solution of sulphate of copper, acidulated with hydro- 
 chloric acid, with a plate of zinc. 
 
 The red precipitate is said to consist chiefly of the oxide of a compound 
 formed from acetylene by the substitution of Cu.^ for H. This compound, 
 C 4 Cu 2 H, has been named by Berthelot cupros-acetyle, and may be regarded 
 as the radical of a series of compounds. If but little free ammonia be 
 present in the solution of cuprous chloride, the precipitate will contain 
 the chloride of cuprous-acetyle, (C 4 Cu 2 H) Cl, as well as the oxide. 
 
 If the acetylene copper precipitate be collected on a filter, washed, and 
 dried either by mere exposure to the air, or over oil of vitriol, it will be 
 found to explode with some violence when gently heated, and it is said 
 that the accidental formation of this compound in copper or brass pipes, 
 through which coal-gas passes, has occasionally given rise to explosions. 
 
 When acetylene is passed through solution of nitrate of silver, a white curdy pre- 
 cipitate is formed, resembling chloride of silver in appearance, but insoluble in 
 ammonia (which turns it yellow) as well as in nitric acid. It may be obtained by 
 allowing the imperfectly burnt gas from the apparatus in fig. 80 to pass through 
 nitrate of silver. 
 
 When this precipitate is washed and allowed to dry, it is violently explosive if 
 heated, though it may be hammered without exploding. A minute fragment of it 
 placed on a glass plate, and touched with a red-hot wire, detonates loudly and 
 shatters the glass like fulminate of silver. The explosive silver compound is said 
 to contain the oxide of argent-acetyle (C 4 Ag 2 H)0, the chloride corresponding to it, 
 (C 4 Ag 2 H) Cl, being precipitated when acetylene is passed through a solution of 
 chloride of silver in ammonia. In a solution of hyposulphite of gold and sodium, 
 acetylene gives a yellowish very explosive precipitate. 
 
 When potassium or sodium is heated in excess of acetylene, it is said that one 
 half of the hydrogen is displaced by the metal, forming acetylide of potassium 
 (C 4 HK) or of sodium (C 4 HNa), a portion of the acetylene being converted into olefi- 
 
PKOPERTIES OF ACETYLENE. 
 
 85 
 
 ant gas (C 4 H 4 ) by combination with the displaced hydrogen. Whenheated to dullred- 
 ness, sodium completely decomposes acetylene, C 4 Na 2 being obtained. Both these 
 sodium compounds are violently decomposed by water, acetylene being reproduced. 
 
 The copious formation of acetylene during the imperfect combustion of ether is 
 very readily shown by introducing a few drops of ether into a test-tube, adding a 
 little ammoniacal solution of cuprous chloride, kindling the ether-vapour at the 
 mouth of the tube, and inclining the latter so as to expose a large surface of the 
 copper solution, when a large quantity of the red cuprous acetylide is produced. If 
 nitrate of silver be substituted for the copper solution, the white precipitate of oxide 
 of argent-acetyle is formed abundantly. 
 
 'Acetylene has been found accompanying the vapour of hydrocyanate of ammonia 
 produced by the action of ammonia on red-hot charcoal. 
 
 Acetylene is a colourless gas having a peculiar odour, recalling that of 
 the geranium, which is always perceived where coal-gas is undergoing 
 imperfect combustion. It burns with a very bright smoky flame. Its 
 most remarkable property is that of inflaming spontaneously when brought 
 in contact with chlorine. If a jet of the gas* be allowed to pass into a 
 bottle of chlorine, it will take fire and burn with a red flame depositing 
 much carbon. When chlorine is decanted up into a cylinder containing 
 acetylene standing over water, a violent explosion immediately takes 
 place, attended with a vivid flash, and separation of a large amount of 
 carbon; C 4 H 2 + 012 = 0, + 2HC1. 
 
 When acetylene is passed into water, it is absorbed in sufficient quan- 
 tity to impart a strong smell to the water, and to yield a decided precipi- 
 tate with ammoniacal cuprous chloride and with nitrate of silver. 
 
 The action of heat upon acetylene is very remarkable and instructive, 
 since it results in the formation of a complex body from one which is less 
 complex in composition. When heated in a glass tube for half an hour 
 to the point at which the glass began to soften, it was found to be re- 
 duced to one-fifth of its original volume, the greater portion of it having 
 been converted into a liquid hydrocarbon sty role, C ]6 H & , hitherto obtained 
 from the vegetable gum-resin known as storax. The remaining gas was 
 chiefly hydrogen (a little carbon having separated) with a little olefiant 
 gas. When heated in contact with coke or iron, the bulk of the acety- 
 lene is decomposed into its elements. 
 
 By suspending the acetylene copper precipitate in solution of ammonia, 
 and heating with a little granulated zinc, Berthelot has induced the acety- 
 lene to combine with the (nas- 
 cent) hydrogen to form olefiant 
 gas (C 4 H 4 ). 
 
 72. Olefiant gas. This gas 
 is found in larger quantity than 
 acetylene, among the products 
 of the action of heat upon coal, 
 and other substances rich in car- 
 bon, and it is one of the most 
 important constituents of the 
 illuminating gases obtained from 
 such materials. 
 
 Olefiant gas may readily be 
 prepared by the action of strong Fi g. 81. Preparation of olefiant gas. 
 
 sulphuric acid (oil of vitriol, 
 HO . S0 3 ) upon alcohol (spirit of wine C 4 H 6 2 ). 
 
 Two measures of oil of vitriol are introduced into a flask (fig. 81), and one measure 
 
OLEFIANT GAS. 
 
 Fig. 82. 
 
 of alcohol is gradually poured in, the flask being agitated after each addition of the 
 acid ; much heat is evolved, and there would bo danger in mixing large volumes 
 suddenly.* On applying a moderate heat, the liquid 
 will darken in colour, effervescence will take place, 
 and the gas may be collected in jars filled with 
 water. When the mixture has become thick, and 
 the evolution of the gas is slow, the end of the tube 
 must be removed from the water and the lamp ex- 
 tinguished. 
 
 The gas will be found to have a very peculiar 
 odour, in which that of ether and of sulphurous acid 
 are perceptible. One of the jars may be closed with 
 a glass plate, and placed upon the table with its 
 mouth upwards ; on the approach of a flame the gas 
 will take fire, burning with a bright white flame char- 
 acteristic of olefiant gas, and seen to best advantage 
 when, after kindling the gas, a stream of water is 
 poured down into the jar in order to displace the gas 
 (fig. 82.) 
 
 Another jar of the gas may be well washed by 
 transferring it repeatedly from one jar to another 
 under water, a little solution of potash may then be 
 poured into it, and the jar violently shaken, its 
 mouth being covered with a glass plate ; the potash 
 will remove all the sulphurous acid, and the gas will 
 now exhibit the peculiar faint odour which belongs 
 to olefiant gas. 
 
 The purified gas may be transferred, under water, to another jar, kindled, and 
 allowed to burn out ; if a little lime-water be then shaken in the jar, its turbidity will 
 indicate the presence of carbonic acid, which is produced, together with water, when 
 olefiant gas burns in air: C 4 H 4 + ]2 = 4C0 2 + 4HO. 
 
 On comparing the composition of olefiant gas (C 4 H 4 ) with that of 
 
 alcohol (C 4 H 6 2 ), it is evident that the 
 former may be supposed to be produced 
 from the latter by the abstraction of two 
 equivalents of water (H 2 2 ) which are re- 
 moved by the sulphuric acid, though other 
 secondary changes take place, resulting 
 in the separation of carbonaceous matter 
 and the production of sulphurous acid. 
 A more complete explanation of the action 
 of sulphuric acid upon alcohol must be re- 
 served for the chemical history of this 
 compound. 
 
 Olefiant gas derives its name from its 
 property of uniting with chlorine and bro- 
 mine to form oily liquids, a circumstance 
 which is applied for the determination of 
 the proportion of this gas present in coal- 
 gas, upon which great part of the illuminat- 
 ing value of coal-gas depends. The com- 
 pound with chlorine (C 4 H 4 C1 ? ) is known 
 as Dutch liquid, having been discovered by 
 Dutch chemists, and is remarkable for its 
 resemblance to chloroform in odour. 
 
 To exhibit the formation of Dutch liquid, a 
 quart cylinder (fig 83) is half filled with olefiant gas, and half with chlorine, which 
 * If methylated spirit be employed, the mixture will have a dark red-brown colour. 
 
ACTION OF HEAT ON OLEFIANT GAS. 
 
 87 
 
 is rapidly passed up into it, from a bottle of the gas, under water. The cylinder is 
 then closed with a glass plate, and supported with its mouth downwards under water 
 in a separating funnel furnished with a glass stop-cock. The volume of the mixed 
 gases begins to diminish immediately, drops of oil being formed upon the side of 
 the cylinder and the surface of the water. As the drops increase, they fall to the 
 bottom of the funnel. Water must be poured into the funnel to replace that which 
 rises into the cylinder, and when the whole of the gas has disappeared, the oil may 
 be drawn out of the funnel through the stop-cock into a test-glass, in which it is 
 shaken with a little potash to absorb any excess of chlorine. The fragrant odour of the 
 Dutch liquid will then be perceived, especially on pouring it out into a shallow dish. 
 
 A very instructive experiment consists in filling a three-pint cylinder one-third 
 full of olefiant gas, then rapidly filling it up, under water, with two pints of chlorine, 
 closing its mouth with a glass plate, shaking it to mix the gases, slipping the plate 
 aside and applying a light, when the mixture burns with a red flame which passes 
 gradually down the cylinder, and is due to the combination of the hydrogen with 
 the chlorine, the whole of the carbon being separated in 
 the solid state 
 
 C 4 H 4 + C1 4 = 4HC1 + C 4 
 
 "When olefiant gas is subjected to the action of 
 high temperatures, as by passing through heated! 
 tubes, one portion is decomposed into marsh-gas 
 (C 2 H 4 ) with separation of carbon, whilst another 
 portion yields acetylene (C 4 H 2 ) and hydrogen ; these 
 decompositions will be found to be of great impor- 
 tance in the manufacture of coal-gas. 
 
 The action of heat upon olefiant gas is most conveniently 
 shown by exposing it to the spark from an induction coil. 
 
 The gas is confined in a tube (A, fig. 84) which is placed 
 in a cylindrical jar (B) containing mercury. Through the 
 mercury passes a copper wire (C) thrust through a glass 
 tube (D) to insulate it from the mercury ; this wire is con- 
 nected with one of the wires (E) from the induction coil, 
 whilst the other (F) is allowed to dip into the mercury contained in the cylinder 
 On putting the coil in action "(with two or three cells of Grove's battery), the spark 
 will pass between the extremity 
 (C) of the insulated copper wire 
 and the surface of the mercury 
 in the tube, decomposing the 
 olefiant gas in its passage, and 
 causing a separation of carbon, 
 which sometimes forms a con- 
 ducting communication, and 
 allows the current to pass with- 
 out a spark. This may be ob- 
 viated by reversing the current, 
 or by gently shaking the tube. 
 
 The olefiant gas will expand to 
 nearly twice its former volume, 
 so that the tube will gradually 
 rise in the mercury, but the 
 same distance may always be 
 maintained for the passage of 
 the spark. 
 
 To show the production of 
 acetylene, another arrangement 
 will be found convenient (fig. 
 85). A globe with four necks 
 is employed ; through two of 
 these necks are passed, air-tight 
 with perforated corks, the cop- 
 per wires connected with the in- Fig. 85. -Preparation of cuprous acetylide from 
 auction coil. A third neck re- olefiant gas. 
 
88 
 
 MARSH-GAS. 
 
 ceives a tube, conveying olefiant gas from a gas-holder, whilst from the fourth 
 proceeds a tube dipping to the bottom of a small cylinder. When the whole of 
 the air has been displaced by olefiant gas, a solution of sub-chloride of copper in 
 ammonia is poured into the cylinder, and the gas allowed to bubble through it, 
 when the absence of acetylene will be shown by there being no red compound 
 formed. As soon, however, as the spark is passed the red precipitate will appear, 
 and, in a very few minutes, a large quantity will be deposited. Coal-gas may be 
 employed instead of olefiant gas, but of course less of the copper-compound will be 
 obtained. 
 
 73. Marsh-gas, or light carburetted hydrogen. Unlike acetylene and 
 olefiant gas, this hydrocarbon is found in nature, being produced wherever 
 vegetable matter is undergoing decomposition in the presence of moisture. 
 The bubbles rising from stagnant pools, when collected and examined, are 
 found to contain marsh-gas mixed with carbonic acid, and there is reason 
 to believe that these two gases represent the principal forms in which the 
 hydrogen and oxygen respectively were separated from wood during the 
 process of its conversion into coal. This would account for the constant 
 presence of this gas in the coal-formations, where it is usually termed fire- 
 damp. It is occasionally found pent up under pressure between the layers 
 of coal, and the pores of the latter are sometimes so full of it that it may 
 be seen rising in bubbles when the freshly hewn coal is thrown into 
 water. Perhaps a similar origin is to be ascribed to the liquid hydro- 
 carbons chemically similar to marsh-gas, which are found so abundantly 
 in Pennsylvania and Canada, and are known by the general name of 
 petroleum. 
 
 Marsh-gas is obtained artificially by the following process : 
 500 grains of dried acetate of soda are finely powdered, and mixed, in a mortar, 
 with 200 grains of solid hydrate of potash, and 300 grains of powdered quicklime 
 (or with 500 grains of the mixture of hydrate of lime and hydrate of soda, which is 
 sold as soda-lime). The mixture is heated in a Florence flask (or better, a copper 
 tube, for the alkali corrodes the glass), and the gas collected over water (fig. 86). 
 
 Fig. 86. Preparation of marsh-gas. 
 
 The decomposition will be evident from the following equation : 
 
 NaO.C 4 H 3 3 + KO.HO = NaO . C0 2 + KO.C0 2 
 
 Acetate of soda. Hydrate of potash. Carb. of soda. Carb. of potash. 
 
 C 2 H 4 
 
 The marsh-gas will be easily recognised by its burning with a pale 
 illuminating flame, far inferior in brilliancy to those of olefiant gas and 
 acetylene, but unattended with smoke. 
 
 The properties of this gas deserve a careful study, on account of the 
 frequent fatal explosions to which it gives rise in coal-mines, where it is 
 
EXPLOSION OF MARSH-GAS WITH AIR. 89 
 
 often found accumulated under pressure, and discharging itself with con- 
 siderable force from the fissures or blowers made in hewing the coal. 
 Marsh-gas has no characteristic smell like coal-gas, and the miner thence 
 receives no timely warning of its presence ; it is much lighter than air 
 (sp. gr. 0*5596), and therefore very readily diffuses* itself (page 29) 
 through the air of the mine, with which it forms an explosive mixture as 
 soon as it amounts to one-eighteenth of the volume of the air. The gas 
 issuing from the blower would burn quietly on the application of a light, 
 since the marsh-gas is not explosive unless mixed with the air, when a 
 large volume of the gas is burnt in an instant, causing a sudden evolution 
 of a great deal of heat, and a consequent sudden expansion or explosion 
 exerting great mechanical force. The most violent explosion takes place 
 when one volume of marsh-gas is mixed with two volumes of oxygen, 
 since this quantity is exactly sufficient to effect the complete combustion 
 of the carbon and hydrogen of the gas, and therefore to evolve the greatest 
 amount of heat : C2H 4 + 8 = 2C0 2 + 4HO. The calculated pressure 
 exerted by the exploding mixture of marsh-gas and oxygen amounts to 
 37 atmospheres, or 555 Ibs. upon the square inch. Since air contains one- 
 fifth of its volume of oxygen, it would be necessary to employ ten 
 volumes of air to one volume of marsh-gas in order to obtain perfect com- 
 bustion, but the explosion will be much less violent on account of the 
 presence of the eight volumes of inert nitrogen, the calculated pressure 
 exerted by the explosion being only 14 atmospheres, or 210 Ibs. on the 
 square inch. Of course, if more air is employed, the explosion will be 
 proportionally weaker, until, when there are more than eighteen volumes 
 of air to each volume of marsh-gas, the mixture will be no longer explosive, 
 but will burn with a pale flame around a taper immersed in it. The car- 
 bonic acid resulting from the explosion is called by miners the after-damp, 
 and its effects are generally fatal to those who may have escaped death 
 from the explosion itself. 
 
 Fortunately, marsh-gas requires a much higher temperature to inflame 
 it than most other inflammable gases ; thus a solid body at an ordinary 
 red heat does not kindle the gas, contact with flame, or with a body 
 heated to whiteness, being required to ignite it. 
 
 If two strong gas-cylinders be filled, respectively, with mixtures of 2 vols. hydrogen 
 with 1 vol. oxygen, and of 1 vol. marsh-gas and 2 vols. oxygen, it will be found, on 
 holding them with their mouths downwards, and inserting a red-hot iron bar, that 
 the marsh-gas mixture will not explode, but if the bar be transferred at once to the 
 hydrogen mixture, explosion will take place. A lighted taper may then be used to 
 explode the marsh-gas and hydrogen. 
 
 Coal-gas, although answering very well for many illustrations of the properties of 
 marsh-gas, cannot be used in this experiment, since some of its constituents inflame 
 at a far lower temperature. 
 
 In consequence of the high temperature required to inflame the mixture 
 of marsh-gas and air, it is necessary that the mixture be allowed to remain 
 for an appreciable time in contact with the flame before its particles are 
 raised to the igniting point. It was on this principle that Stephenson's 
 original safety lamp was constructed, the flame being surrounded with a 
 tall glass chimney, the rapid draught through which caused the explosive 
 mixture to be hurried past the flame without igniting. 
 
 3 Ansell's fire-damp indicator is an apparatus in which the high rate of diflfusion of 
 marsh-gas is taken advantage of in order to detect its presence in the air of mines. The 
 experiment described at page 29 illustrates its principle. 
 
90 
 
 PRINCIPLE OF SAFETY-LAMPS. 
 
 To illustrate this, a copper funnel (fig. 87) holding about two quarts is employed, 
 the neck of which has an opening of about inch in diameter, The funnel being 
 placed mouth downwards in the pneumatic trough, the orifice is closed with the 
 
 Fig. 87. 
 
 finger, and half a pint of coal-gas passed up into the funnel. The latter is now 
 raised from the water, so that it may become entirely filled with air. By depressing 
 the funnel to a considerable depth in the water, the aperture being still closed by 
 the finger, the mixture will be confined under considerable 
 pressure, and if a lighted taper be held to the aperture, and 
 the finger removed, it will be found that the mixture sweeps 
 past the flame without exploding, until the water has reached 
 the same level in the funnel as in the trough, when the gas 
 comes to rest and explodes with great violence. 
 
 Davy's safety lamp (fig. 88) is an application of the 
 principle that ignited gas (flame) is extinguished by 
 contact with a large surface of a good conductor of heat, 
 such as copper or iron. 
 
 If a thin copper wire be coiled round into a helix, and care- 
 Fig. 88. Davy lamp, fully placed over the wick of a burning taper (fig. 89), the flame 
 will be at once extinguished, its heat being so rapidly trans- 
 mitted along the wire that the temperature falls below the point at which the com- 
 bustible gases enter into combination with oxygen, and therefore the combustion 
 ceases. If the coil be heated to redness in a spirit-lamp flame before placing it over 
 the wick, it will not abstract the heat so readily, and will not extinguish the flame. 
 If a copper tube were substituted for the coiled wire, the same result would be ob- 
 tained, and by employing a number of tubes of very small 
 diameter, so that the metallic surface may be very large 
 in proportion to the volume of ignited gas, the most ener- 
 getic combustion may be arrested, as in the case of 
 Hemming 's safety jet, which consists of a brass tube tightly 
 stuffed with thin copper wires so as to leave very narrow 
 passages, thus rendering it impossible for the oxyhydrogen 
 flame at the jet to pass back and ignite the mixture in the 
 reservoir. 
 
 It is evident that the exposure of a large extent ot cool- 
 ing surface to the action of the flame, may be effected 
 either by increasing the length or by diminishing the 
 width of the metallic tubes, so that wire gauze, which may be regarded as a collection 
 of very short tubes, will form an effectual barrier to flame, provided that it has a 
 sufficient number of meshes to the inch. 
 
 If a piece of iron wire gauze, containing about 800 meshes to the square inch, be 
 depressed upon a flame, it will extinguish that portion with which it is in contact, 
 and the combustible gas which escapes through the gauze may be kindled by a 
 lighted match held on the upper side. By holding the gauze two or three inches 
 above a gas jet, the gas may be lighted above it without communicating the flame 
 to the burner itself. 
 
USE OF THE DAVY LAMP. 
 
 91 
 
 Fig. 90. 
 
 When blazing spirit is poured upon a piece of wire gauze (fig. 90) the flame will 
 remain upon the gauze, and the extinguished spirit will pass through. A little 
 benzole or turpentine may be added to the spirit 
 so that its flame may be more visible at a dis- 
 tance. 
 
 The safety lamp is an oil lamp, the flame 
 of which is surrounded by a cage of iron 
 wire gauze, having 700 or 800 meshes in 
 f;he square inch, and made double at the top 
 where the heat of the flame chiefly plays. 
 This cage is protected by stout iron wires 
 attached to a ring for suspending the lamp. 
 A brass tube passes up through the oil 
 reservoir, and in this there slides, with con- 
 siderable friction, a wire bent at the top, so that the wick may be trimmed 
 without taking off the cage. 
 
 If this lamp be suspended in a large jar, closed at the top with a perforated 
 wooden cover (A, fig. 91), and having an aperture (B) below, through which coal- 
 gas may be admitted, the lamp will burn, of course, in 
 the ordinary way ; but if the gas be allowed to pass 
 slowly into the jar, the flame will be seen to waver, to 
 elongate itself very considerably, and will be ultimately 
 extinguished, when the wire cage will be seen to be 
 filled with a mixture of coal-gas and air burning tran- 
 quilly within the gauze, which prevents the flame from 
 passing to ignite the explosive atmosphere surrounding 
 the lamp ; that an explosive mixture really fills the jar 
 may be readily ascertained by introducing, through an 
 aperture (C) in the cover, the unprotected flame of a 
 taper, when an explosion will take place. 
 
 This experiment illustrates the action of the Davy 
 lamp in a mine which contains fire-damp, and makes it 
 evident that this lamp would afford complete protection 
 if carefully used. It would obviously be unsafe to allow 
 the lamp to remain in the explosive mixture when the 
 cage is filled with flame, for the gauze would either 
 
 become sufficiently heated to kindle the surrounding gas, or would be oxidised and 
 eaten into holes, which would allow the passage of the flame. Nor should the lamp 
 be exposed to a very strong current, which might possibly be able to carry the flame 
 through the meshes. 
 
 The great defect of the Davy lamp is that it does not afford more than 
 a glimmering light, so that even if the miners were prohibited from em- 
 ploying any candles, they would (and experience has proved that they do) 
 remove the wire cage at all risks. The lamp has been modified 39 as par- 
 tially to remove this defect, by substituting glass or talc for some portions 
 of the wire gauze. It is now usual, however, to employ the Davy lamp 
 merely in order to test the state of the air in the different parts of the 
 mine; for this purpose the firemen descend before the commencement 
 of work every morning, and examine with their safety lamps every portion 
 of the mine, giving warning to the miners not to approach those parts in 
 which any accumulation of fire-damp (or technically, " sulphur ") is per- 
 ceived. The miners then work with naked candles, and it appears to be 
 not unusual to see a blue flame (or corpse light) playing around the 
 candles, so that the miners may become accustomed to regard with little 
 concern the very indication which shows that the quantity of fire-damp is 
 only a little below that required to form an explosive mixture. When- 
 ever naked flames arc used in the mine there must always be great risk ; 
 
 Fig. 91. 
 
92 ILLUMINATING FLAMES. 
 
 in most seams of coal there are considerable accumulations of fire-damp ; 
 when a fissure is made, the gas escapes very rapidly from the blower, and' 
 the air in its vicinity may soon become converted into an explosive mix- 
 ture. In mines where small quantities of fire-damp are known to be 
 continually escaping from the coal, ventilation is depended upon in order 
 to dilute the gas with so large a volume of air that it is no longer explo- 
 sive, and finally to sweep it out of the mine ; but it has occasionally 
 happened that the ventilation has been interfered with by a door having 
 been left open in one of the galleries, or by a passage having been 
 obstructed through the accidental falling in of a portion of the coal, and 
 an explosive mixture has then been formed. 
 
 STRUCTURE OF FLAME. 
 
 74. The consideration of the structure and properties of ordinary 
 flames is necessarily connected with the history of olefiant gas and marsh- 
 gas. Flame may be defined as gaseous matter, heated to the temperature 
 at which it becomes visible, or emits light. Solid particles begin, for the 
 most part, to emit light when heated to about 1000 F. ; but gases, on 
 account of their greater expansibility, must be raised to a far higher 
 temperature, and hence the point of visibility is seldom attained, except 
 by gases which are themselves combustible, and therefore capable of 
 producing, by their own combination with atmospheric oxygen, the requi- 
 site degree of heat. The presence of a combustible gas (or vapour), 
 therefore, is one of the conditions of the existence of flame ; a diamond, 
 or a piece of thoroughly carbonised charcoal, will burn in oxygen with 
 a steady glow, but without flame, since the carbon is not capable of con- 
 version into vapour, while sulphur burns with a voluminous flame, in 
 consequence of the facility with which it assumes the vaporous condition. 
 It will be observed, moreover, that in the case of a non-volatile combus- 
 tible, the combination with oxygen is confined to the surface of contact, 
 whilst in the flame of a gas or vapour, the combustion extends to a con- 
 siderable depth, the oxygen intermingling with the gaseous fuel. 
 
 Flames may be conveniently spoken of as simple or compound, accord- 
 ingly as they involve one or more phenomena of combustion ; thus, for 
 example, the flames of hydrogen and carbonic oxide are simple, whilst 
 those of marsh-gas and olefiant gas are compound, since they involve both 
 the conversion of hydrogen into water and of carbon into carbonic acid. 
 
 It is obvious that simple flames must be hollow in ordinary cases, such 
 as that of a gas issuing from a tube into the air, the hollow being occu- 
 pied by the combustible gas to which the oxygen does not penetrate. 
 
 All the flames which are ordinarily turned to useful account are com- 
 pound flames, and involve several distinct phenomena. Before examining 
 these more particularly, it will be advantageous to point out the conditions 
 which regulate the luminosity of flames. 
 
 Just as gaseous matter is essential to the existence of flame, the presence 
 of solid particles suspended in the flame is essential to its luminosity. 
 
 It has been seen that, when sulphur burns in oxygen, it emits a pale 
 lurid light, whilst phosphorus, under similar circumstances, yields an 
 intolerable blaze ; this is easily explained, for the product of the combus- 
 tion of sulphur, sulphurous acid, is gaseous at this temperature, but the 
 solid phosphoric acid, formed from the phosphorus, is suspended in the 
 flame, in a state of very minute division, and becomes heated to so high 
 
STRUCTURE OF FLAME. 
 
 a degree as to emit a beautiful white light. That this is a true account 
 of the matter is seen by introducing the phosphorus into a jar of chlorine 
 gas, when it burns with a flame which is even paler than that of sulphur 
 in oxygen, since the chloride of phosphorus which is formed is a vapour 
 at the temperature of the combustion. 
 
 It is not necessary that the suspended solid matter should be a product 
 of the combustion ; any extraneous solid in a finely divided state will 
 confer illuminating power upon a flame. Thus, the flame of hydrogen 
 may be rendered highly luminous by burning a piece of phosphorus in its 
 vicinity, so that the clouds of phosphoric acid may pass 
 through the flame, or by blowing a little very fine char- 
 coal powder into it, from the bottle represented in fig. 92. 
 
 The luminosity of all ordinary flames is due to the 
 presence of highly heated carbon in a state of very 
 minute division, and it remains to consider the changes 
 by which this finely divided carbon is 'separated in the 
 flame. 
 
 A candle, a lamp, and a gas-burner, exhibit contriv- 
 ances for procuring light artifically in different degrees 
 of complexity, the candle being the most complex of 
 the three. When a new candle is lighted, the first portion of the wick is 
 burnt away until the heat reaches that part which is saturated with the 
 wax or tallow of which the candle is composed; this wax or 
 tallow then undergoes destructive distillation, yielding a variety 
 of products, among which olefiant gas is found in abundance. 
 The flame furnished by the combustion of these products melts 
 the fuel around the base of the wick, through which it then 
 mounts by capillary attraction, to be decomposed in its turn, 
 and to furnish fresh gases for the maintenance of the flame. In 
 a lamp, the fuel being liquid at the commencement, the process 
 of fusion is dispensed with ; and in a gas-burner, where the fuel 
 is supplied in a gaseous form, the process of destructive distilla- 
 tion has been already carried on at a distance. It will be seen, 
 however, that the final result is similar in all three cases, the 
 flame being maintained by such gases as acetylene, marsh-gas, 
 and olefiant gas, arising from the destructive distillation of wax, 
 tallow, oil, coal, &c. 
 
 On examining an ordinary flame, that of a candle, for instance, it is 
 seen to consist of three concentric cones (fig. 93), the innermost, around 
 the wick, appearing almost black, the 
 next emitting a bright white light, and 
 the outermost being so pale as to be 
 scarcely visible in broad daylight. 
 
 The dark innermost cone consists merely 
 of the gaseous combustible to which the 
 air does not penetrate, and which is there- 
 fore not in a state of combustion. 
 
 The nature of this cone is easily shown by 
 experiment : a strip of cardboard held across 
 the flame near its base will not burn in the 
 centre where it traverses the innermost cone ; a 
 piece of wire gauze depressed upon the flame 
 near the wick (fig. 94) will allow the passage of 
 the combustible gas, which may be kindled above it. The gas may be conveyed out 
 
94 
 
 EXPERIMENTS ON FLAME. 
 
 of the flame by means of a glass tube inserted into the innermost cone, and may be 
 kindled at the other extremity of the tube, which should be inclined downwards 
 (fig. 95). 
 A piece of phosphorus in a small spoon held in the interior of the flame of a spirit- 
 
 4 
 
 Fjg. 95. 
 
 lamp, will melt and boil, but will not burn unless it be removed from the flame, and 
 
 may then be extinguished by replacing it in the flame. 
 
 The combustible gas from the interior of a flame may be collected in a flask 
 
 (fig. 96) furnished with two tubes, one of which (A) is drawn out to a point for 
 insertion into the flame, whilst the other (B), which passes 
 to the bottom of the flask, is bent over and prolonged by a 
 piece of vulcanised tubing, so that it may act as a siphon. 
 The flask is filled up with water, the jet inserted into the 
 interior of a flame, and the siphon set running by exhaust- 
 ing it with the mouth. As the water flows out through the 
 siphon, the gas is drawn into the flask, and after removing 
 the tube from the flame, the gas may be expelled by 
 blowing down the siphon tube, and may be burnt at the jet. 
 When a candle is used for this experiment, some solid pro- 
 ducts of destructive distillation will be found condensed in 
 Fig. 96. the flask. 
 
 In the second or luminous cone, combustion is taking place, but it is 
 by no means perfect, being attended by the separation of a quantity of 
 carbon, which confers luminosity upon this part of the flame. The 
 presence of free carbon is shown by depressing a piece of porcelain upon 
 this cone, when a black film of soot is deposited. The liberation of the 
 carbon is due to the decomposition of the olefiant gas and similar hydro- 
 carbons by the heat, which separates the carbon from the hydrogen, and 
 this latter, undergoing combustion, evolves sufficient heat to raise the 
 separated carbon to a white heat, the supply of air which penetrates into 
 this portion of the flame being insufficient to effect the combustion of the 
 whole of the carbon. 
 
 Some very simple experiments will illustrate the nature of the luminous portion of 
 flame. 
 
 Over an ordinary candle flame (fig. 97] a tube may be adjusted so as to convey 
 the finely-divided carbon from the luminous part of the flame into the flame of 
 hydrogen, which will thus be rendered as luminous as the candle flame, the dark 
 colour of the carbon being apparent in its passage through the tube. 
 
 A bottle furnished with two straight tubes (fig. 98) is connected with a reservoir 
 of hydrogen. One of the tubes is provided with a small piece of wider tube con- 
 taining a tuft of cotton wool. On kindling the gas at the orifice of each tube, no 
 difference will be seen in the flames until a drop of benzole (C ]2 H 6 ) is placed upon 
 the cotton, when its vapour, mingling with the hydrogen, will furnish enough carbon 
 to render the flame brilliantly luminous. 
 
 The pale outermost cone, or mantle, of the flame, in which the separated 
 carbon is finally consumed, may be termed the cone of perfect combustion, and 
 
EXPERIMENTS ON FLAME. 
 
 95 
 
 is much thinner than the luminous cone, the supply of air to this external 
 shell of flame being unlimited, and the combustion therefore speedily effected. 
 
 Fig. 97. Fig. 98. 
 
 The mantle of the flame may be rendered more visible by burning a little sodium 
 near the flame, when the mantle is tinged strongly yellow. 
 
 By means of a siphon about one-third of an inch in diameter (fig. 99), the nature 
 of the different portions of an ordinary candle flame may be very elegantly shown. 
 If the orifice of the siphon be brought just over the extremity of the wick, the com- 
 bustible gases and vapours will pass through it, and 
 may be collected in a small flask, where they can be 
 kindled by a taper. On raising the orifice into the 
 luminous portion of the flame, voluminous clouds of 
 black smoke will pour over into the flask, and if the 
 siphon be now raised a little above the point of the 
 flame, carbonic acid can be collected in the flask, and 
 may be recognised by shaking with lime-water. 
 
 The reciprocal nature of the relation between the 
 combustible gas and the air which supports its com- 
 bustion may be illustrated in a striking manner by 
 burning a jet of air in an atmosphere of coal-gas. 
 
 A quart glass globe with three necks is connected 
 at A (fig. 100) with the gas-pipe by a vulcanised tube. The second neck (B), at the 
 upper part of the globe, is connected by a short piece of vulcanised tube with a piece 
 of glass tube about inch wide, from which the gas may be burnt. Into the third 
 and lowermost neck is inserted, by means of a cork, a thin brass tube, C (an old 
 cork-borer), about inch in diameter. When the gas is turned on, it may be lighted 
 at the upper neck ; and if a lighted match be then quickly thrust up the tube C, the 
 air which enters it will take fire and burn inside the globe 
 
 Fig. 99. 
 
 Fig. 100. Air burning in Fig. 101. To make a three-necked flask, 
 
 coal-gas. 
 
 A very inexpensive apparatus for this purpose may be constructed from a common 
 Florence oil-flask. By applying a blowpipe flame at A (fig. 101), so as to heat to 
 
96 
 
 GAS-BURNEKS. 
 
 Fig. 102. Argand burner. 
 
 whiteness a spot as large as a threepenny-piece, and quickly blowing into the neck 
 of the flask, the heated portion of the glass may be made to bulge out. A similar 
 protuberance is then to be formed at B. A sharp-pointed flame is directed upon A, 
 and the glass burst by blowing into the flask whilst it is still exposed to the flame. 
 By fusing the edges of the hole thus produced, and turning them outwards with the 
 end of a file, a short neck may be formed capable of receiving a cork. When this 
 is cool it is closed with a cork, and a second similar neck is produced at B. 
 
 From this review of the structure of flame, it is evident that, in order 
 to secure a flame which shall be useful for illumination-, attention must be 
 paid to the supply of oxygen (or air), and to the composition of the fuel 
 employed. The use of the chimney of an Argand burner (fig. 102) affords 
 an instance of the necessity for attention to the 
 proper supply of air. Without the chimney, the 
 flame is red at the edges and smoky, for the 
 supply of air is not sufficient to consume the 
 whole of the carbon which is separated, and 
 the temperature is not competent to raise it to 
 a bright white heat, defects which are remedied 
 as soon as the chimney is placed over it, and 
 the rapidly-ascending heated column of air draws 
 in a liberal supply beneath the burner, as indi- 
 cated by the arrows. 
 
 By using two chimneys, and causing the air 
 to pass down between them, so as to be heated 
 to about 500 F. before reaching the flame, an 
 equal amount of light may be obtained from a 
 much smaller supply of gas. 
 The smokeless gas-burners employed in laboratories and kitchens exhibit 
 the result of mixing the gas with a considerable proportion of air before 
 burning it, the luminous part of the flame then en- 
 tirely disappearing, with great augmentation of the 
 temperature of the flame, since the carbon is burnt 
 simultaneously with the hydrogen. 
 
 The most efficient burner of this kind (Bunsen's burner, 
 fig. 103) is that in which the gas is conveyed into a wide 
 tube, at the base of which there are four large holes for the 
 admission of air. When a good supply of gas is turned 
 on, a quantity of air is drawn in through the lower aper- 
 tures, and the mixture of air and gas may be kindled at 
 the orifice of the wide tube, its rapid motion preventing the 
 flame from passing down within the tube. This tube is sometimes surmounted by 
 a rosette burner to distribute the flame. By closing the air-holes with the fingers 
 a luminous flame is at once produced. 
 
 The principle of this burner has been applied for testing 
 the illuminating value of gas, by measuring the quantity 
 of air which must be supplied to a flame consuming a given 
 quantity of gas, in order to destroy the luminosity, the 
 illuminating value being proportional to the quantity of 
 air which is necessary for this purpose. 
 
 The gauze burner (fig. 104) consists of an open cylinder 
 surmounted by wire gauze. When this is placed over the 
 gas-burner, a supply of air is drawn in at the bottom by 
 the ascending stream of gas, and the mixture burns above 
 the gauze with a very hot smokeless flame, the metallic 
 meshes preventing the flame from passing down to the gas 
 below. 
 
 Fig. 103. Bunsen's 
 burner. 
 
 Fig. 104. Gauze 
 burner. 
 
 The luminosity of a flame is materially affected by the pressure of the 
 
COMPOSITION OF ILLUMINATING FUELS. 
 
 97 
 
 atmosphere in which it burns, a diminution of pressure causing a loss of 
 illuminating power. If the light of a given flame burning in the air when 
 the barometer stands at 30 inches be represented by 100, each diminution 
 of one inch in the height of the barometer will reduce the luminosity 
 by five ; and conversely, when the barometer rises one inch, the lumino- 
 sity will be increased by five. This is not due to any difference in the 
 rate of burning, which remains pretty constant, but to the more complete 
 interpenetration of the rarefied air and the gases composing the flame, 
 gMng rise to the separation of a smaller quantity of incandescent carbon. 
 In air at a pressure of 120 inches of mercury, the flame of alcohol is 
 highly luminous, the high density of the air discouraging the intermixture 
 of the flame-gases with it, and thus allowing the separation of a portion 
 of carbon. 
 
 In considering the influence exerted by the composition of the fuel 
 upon the character of its flame, it will be necessary to bear in mind that 
 some kinds of fuel consist of carbon and hydrogen only, whilst others 
 contain a considerable proportion of oxygen. 
 
 The following table exhibits the composition of some of the principal 
 substances concerned in producing ordinary illuminating flames : 
 
 Fuel. 
 
 Formula. 
 
 Carbon. 
 
 Hydrogen. 
 
 Oxygen. 
 
 Marsh -gas, . 
 
 C 2 H 4 
 
 30 
 
 10 
 
 
 Olefiant gas, 
 
 C 4 H 4 
 
 60 
 
 10 
 
 
 Paraffine, 
 
 CarHa; 
 
 60 
 
 10 
 
 
 Turpentine, . 
 
 C 20 H ]6 
 
 75 
 
 10 
 
 
 Benzole, 
 
 C 12 H 6 
 
 120 
 
 10 
 
 
 Wax 
 
 > C 92 H 92 4 * 
 
 60 
 
 10 
 
 3-5 
 
 Stearine, 
 
 " C 114 H 11012 
 
 62-1 
 
 10 
 
 8-7 
 
 Oleine, 
 
 C 114 H 104 12 
 
 65-8 
 
 10 
 
 9-2 
 
 Alcohol, 
 
 C 4 H 6 2 
 
 40 
 
 10 
 
 27 
 
 Wood naphtha, 
 
 C 2 H 4 2 
 
 30 
 
 10 
 
 40 
 
 It may be stated generally that when the number of equivalents of 
 carbon is less than that of hydrogen, the flame will be free from smoke, 
 as in the case of marsh-gas. When there are as many equivalents of 
 carbon as of hydrogen, as in olefiant gas and parafnne, the flame is very 
 liable to smoke, unless managed with great judgment. Those hydro- 
 carbons whicli contain, like turpentine and benzole, a larger number of 
 equivalents of carbon than of hydrogen, always burn with much smoke, 
 and require special contrivance to render them applicable for illuminating 
 purposes. Thus, camphine (turpentine) must be burnt in lamps with tall 
 narrow chimneys of peculiar construction to afford a strong current of air. 
 Benzole (coal-naphtha) vapour must be mixed with air if it is required to 
 burn with a smokeless flame. 
 
 If a piece of cotton wool, moistened with benzole, be placed in a flask provided 
 with two tubes (fig. 105), it will be found, on gently warming the flask by dipping 
 it into hot water, and blowing through one of the tubes, that the mixture of benzole 
 vapour and air issuing from the other tube will burn with a smokeless bright 
 flame. 
 
 This is the composition of myricine, which forms the greater part of bees' wax. 
 
 G 
 
98 
 
 THE BLOWPIPE FLAME. 
 
 Fig. 105. 
 
 If coal-gas, which is essentially a mixture of hydrogen, marsh-gas, and 
 olefiant gas, and generally contains rather too much hydrogen in propor- 
 tion to its carbon, be enriched with carbon by pass- 
 ing over benzole (light coal naphtha), it burns with 
 a far more luminous flame (napJithalised gas). 
 
 When the fuel contains oxygen, the carbon may 
 exist in larger proportion to the hydrogen without 
 giving rise to the production of smoke, since this 
 oxygen will dispose of a portion of the carbon 
 during the combustion. Thus, wax is much less 
 liable to smoke than paraffine, although containing 
 the same proportions of carbon and hydrogen, 
 whilst stearine (the chief part of tallow) and oleine 
 (forming the bulk of oils) may be burnt in ordi- 
 nary candles and lamps, although still richer in 
 carbon, because they contain more oxygen also. 
 Alcohol yields a flame of no illuminating value, although it contains 
 more carbon in proportion to its hydrogen than is present in marsh-gas, 
 because its oxygen helps to consume the carbon during the combustion, 
 and prevents it from separating in the incandescent state. By adding 
 about one-tenth of its bulk of benzole or turpentine, however, alcohol 
 may be made to burn with a brilliant flame. 
 
 75. The Howpipe flame. The principles already laid down will 
 render the structure of the blowpipe flame easily intelligible. It must 
 be remembered that in using the blowpipe, the stream of air is not pro- 
 pelled from the lungs of the operator (where a great part of its oxygen 
 would have been consumed), but simply from the mouth, by the action 
 of the muscles of the cheeks. The first apparent effect upon the flame 
 is entirely to destroy its luminosity, the free supply of air effecting the 
 immediate combustion of the carbon. The size of the flame, moreover, is 
 much diminished, and the combustion being concentrated into a smaller 
 space, the temperature must be much higher at any given point of the 
 flame. In structure, the blowpipe flame is similar to the ordinary flame, 
 consisting of three distinct cones, the innermost of which (A, fig. 106) is 
 
 filled with the cool mixture of air 
 and combustible gas. The second 
 cone, especially at its point (E), is 
 termed the reducing flame, for the 
 supply of oxygen at that part is not 
 sufficient to convert the carbon into 
 carbonic acid, but leaves it as car- 
 bonic oxide, which speedily reduces 
 
 Fig. 106. Blowpipe flame. almost all metallic oxides placed in 
 
 that part of the flame to the metallic 
 
 state. The outermost cone (0) is called the oxidising flame, for there the 
 supply of oxygen from the surrounding air is unlimited, and any substance 
 prone to combine with oxygen at a high temperature is oxidised when 
 exposed to the action of that portion of the flame ; the hottest point of 
 the blowpipe flame, where neither fuel nor oxygen is in excess, appears 
 to be a very little in advance of the extremity of the second (reducing) 
 cone. The difference in the operation of the two flames is readily shown 
 by placing a little red lead (oxide of lead) in a shallow cavity scooped 
 
EUDIOMETKIC ANALYSIS OF MARSH-GAS. 
 
 99 
 
 Fig. 107. Reduction of metals on charcoal. 
 
 upon the surface of a piece of charcoal (fig. 107), and directing the names 
 
 upon it in succession ; the inner flame will reduce a globule of metallic 
 
 lead, which may be re- 
 
 converted into oxide by 
 
 exposing it to the outer 
 
 flame.* The immense 
 
 service rendered by this 
 
 instrument to the el,,- 
 
 mist and mineralogist is 
 
 well known. 
 
 By forcing a stream 
 of oxygen through a 
 flame from a gas-holder or bag, an intensely hot blowpipe flame is 
 obtained, in which pipe-clay and platinum may be melted, and iron burns 
 with great brilliancy (see tig. 48). 
 
 76. Determination of the composition of gases containing carbon and 
 hydrogen. In order to ascertain the proportions of carbon and hydrogen 
 present in a gas, a measured volume of the gas is mixed with an excess of 
 oxygen, the volume of the mixture carefully noted, and explosion deter- 
 mined by passing the electric spark ; the gas remaining after the explosion 
 is measured and shaken with potash, which absorbs the carbonic acid, 
 from the volume of which the proportion of carbon may be calculated. 
 For example, 
 
 0'4 cubic inch of marsh-gas, mixed with 
 1*0 oxygen, and exploded, left 
 
 0-6 gas j shaken with potash 
 
 it left 0-2 oxygen. 
 
 Showing that 0'4 cubic inch of carbonic acid had been produced. This 
 quantity of carbonic acid would contain 0'4 cubic inch of (imaginary) 
 carbon vapour, and 0'4 cubic inch of oxygen. Deducting this last from 
 the total amount of oxygen consumed (0'8 cubic inch), we have 0*4 
 cubic inch for the volume of oxygen consumed by the hydrogen. Now, 
 0*4 cubic inch of oxygen would combine with 0*8 cubic inch of 
 hydrogen, which represents therefore the amount of hydrogen in the marsh- 
 gas employed. It has thus been ascertained that 
 
 
 
 4 volumes of marsh-gas contain 
 
 4 volumes of (hypothetical) carbon vapour, and 
 
 8 volumes of hydrogen. 
 
 For the purpose of illustration, the analysis of marsh- 
 gas may be effected in a Ure's eudiometer (fig. 108), but 
 a considerable excess of oxygen should be added to 
 moderate the explosion. The eudiometer having been 
 filled with water, O'l cubic inch of marsh-gas is intro- 
 duced into it, as described at p. 34, and having been 
 transferred to the closed limb and accurately measured Fig. 108. 
 
 after equalising the level of the water, the open limb is Siphon eudiometer, 
 
 again filled up with water, the eudiometer inverted in 
 the trough, and 1-2 cubic inch of oxygen added ; this is also transferred to the closed 
 
 * By directing the reducing flame upon the metallic oxide in the cavity, and allowing 
 the oxidising flame to sweep over the surface of the charcoal, as shown in the figure, a 
 yellow incrustation of oxide of lead is formed upon the surface of the charcoal, which 
 affords additional evidence of the nature of the metal. 
 
 G2 
 
100 
 
 PRODUCTS OF DISTILLATION OF COAL. 
 
 limb and carefully measured. The electric spark is then passed through the mixture 
 (see p. 34), the open limb being closed by the thumb. The level of the water in 
 both limbs is then equalised, and the volume of gas measured. The open limb is 
 then filled up with a strong solution of potash, and closed by the thumb, so that 
 the gas may be transferred from the closed to thetopen limb and back, until its 
 volume is no longer diminished by the absorption of carbonic acid. The volume 
 of residual oxygen having been measured, the calculation is effected as above 
 described. 
 
 The results are more exact when the eudiometer is filled with mercury instead of 
 water. 
 
 The following table exhibits the composition by volume of acetylene, 
 marsh-gas, and olefiant gas (8 parts by weight of oxygen being considered 
 to occupy one volume) : 
 
 
 Eqt. Weight. 
 
 Eqt. Volume. 
 
 Carbon Vapour. 
 
 Hydrogen. 
 
 Acetylene, C 4 H 2 
 Marsh-gas, C 2 H 4 
 
 26 
 16 
 
 4 vols. 
 
 * 
 
 8 vols. 1 
 4 ? 
 
 4 vols. 
 
 8 
 
 Olefiant gas, C 4 H 4 
 
 28 
 
 4 
 
 8 ? 
 
 8 ;, 
 
 
 
 
 
 COAL-GAS. 
 
 77. The manufacture of coal-gas is one of the most important appli- 
 cations of the principle of destructive distillation, and affords an ex- 
 cellent example of the tendency of this process to develope new arrange- 
 ments of the elements of a compound body. The action of heat upon 
 coal, in a vessel from which air is excluded, gives rise to the production 
 of a very large number of compounds containing some two or more of 
 the five elements of the coal, in different proportions, or in different 
 forms of arrangement. Although no clue has yet been obtained to indi- 
 cate the true arrangement of these elements in the original coal (or, 
 as it is termed, the constitution of the coal), it is certain that these 
 various compounds do not exist in it before the application of heat, but 
 are really the results of its action, that they are indeed products and 
 not educts. 
 
 The most important forms assumed by the carbon and hydrogen when 
 coal is strongly heated, are, 
 
 f Hydrogen. 
 
 Marsh-gas, C 2 H 4 
 Gases < Olefiant gas, C 4 H 4 
 
 Acetylene, C 4 H 2 
 lOil-gas, C 8 H 8 
 
 T . . , f Benzole, C, y H, 
 
 Liquids | Toluole ; c ;^ H ; 
 
 Solids 
 
 Naphthaline, C 2U H 8 
 Anthracene, C 30 H 12 
 Paraffine, C* H A . 
 Coke, . C 
 
 The nitrogen of the coal reappears in the forms of 
 
 Gases 
 
 f Nitrogen. 
 \ Ammonia, . 
 f Aniline, 
 Liquids < Quinoline, 
 
 { Hydrocyanic acid, 
 
 NH, 
 C 12 H 7 N 
 
 Alkaline. 
 
COMPOSITION OF COAL-GAS. 
 The oxygen contributes to the production of 
 
 101 
 
 p ( Carbonic oxide, CO 
 8 j Carbonic Acid, C0 2 
 
 * 
 
 Sulphur is found among the products as, 
 Sulphuretted hydrogen gas, HS 
 
 /Water, . HO 
 Liquids < Acetic acid, C 4 H 4 4 
 (, Carbolic acid, C 12 H 6 2 
 
 Bisul P llide of car bon, CS 2 
 
 The illuminating gas obtained from coal consists essentially of free hydro- 
 gen, marsh-gas, olefiant gas, and carbonic oxide, with small quantities of 
 acetylene, benzole vapour, and some other substances. 
 
 A fair general idea of its composition is given by the following table : 
 
 Gas from Cannel Coal. 
 
 Hydrogen, 
 Marsh-gas, 
 Carbonic oxide, 
 Olefiant gas, 
 Carbonic acid, 
 Oil-gas, . 
 Nitrogen, 
 Sulphuretted hydrogen, 
 
 . 
 
 
 45-6 voh 
 34-9 
 6-6 
 4-0 
 3-7 
 2-4 
 2-5 
 0-3 
 
 imes. 
 
 en, . 
 
 
 100-0 
 
 The only constituents which contribute directly to the illuminating 
 value of the gas are the marsh-gas, olefiant gas, oil-gas (acetylene, and 
 benzole vapour). 
 
 The most objectionable constituent is the sulphur present as sulphur- 
 etted hydrogen and bisulphide of carbon, for this is converted by com- 
 bustion into sulphuric acid, which seriously injures pictures, furniture, 
 &c. The object of the manufacturer of coal-gas is to remove, as far as 
 possible, everything from it, except the constituents mentioned as essential, 
 and at the same time to obtain as large a volume of gas from a given 
 weight of coal as is consistent with a good illuminating value. 
 
 The mode of purifying the gas, and the general arrangements for its 
 manufacture, will be described in a later part of the work. 
 
 Fig. 109. Destructive distillation of coal. 
 
 The destructive distillation of coal may be exhibited with the arrangement repre- 
 sented in fig. 109. The solid and liquid products (tar, ammoniacal liquor, &c.) are 
 condensed in the globular receiver (A). The first bent tube contains, in one 
 limb (B), a piece of red litmus paper to detect ammonia; and in the other (C) 
 
 V 
 
102 
 
 QUARTZ SAND FLINT. 
 
 Fig. 110. 
 
 a piece of paper impregnated with acetate of lead, which will be blackened by 
 the sulphuretted hydrogen. The second bent 
 tube (D) contains enough lime-water to fill the 
 bend, which will be rendered milky by the car- 
 bonic acid. The ga%is collected over water, in the 
 jar E, which is furnished with a jet from which the 
 gas may be burnt when forced out by depressing 
 the jar in water. 
 
 The presence of acetylene in coal-gas may be 
 shown by passing the gas from the supply-pipe (A, 
 fig. 110), first through a bottle (B) containing a little 
 ammonia, then through a bent tube (C), with enough 
 water to fill the bend, and a piece of bright sheet 
 copper immersed in the water in each limb. After 
 
 a short time the bright red flakes of the acetylide of copper will be seen in the 
 
 water. 
 
 SILICON. 
 
 78. In many of its chemical relations to other bodies this element will 
 be found to bear a great resemblance to carbon; but whilst carbon is 
 remarkable for the great variety of compound forms in which it is met 
 with in nature, silicon is always found in combination with oxygen, as 
 silicic acid, or silica (Si0 2 ), either alone or united with various metallic 
 oxides, with which it forms silicates. 
 
 Silica. The purest natural variety of silica is the transparent and 
 colourless variety of quartz known as rock crystal, the most widely diffused 
 ornament of the mineral world, often seen crystallised in beautiful six- 
 sided prisms, terminated by six-sided pyramids (fig. Ill), which are always 
 
 easily distinguished by 
 their great hardness, 
 scratching glass almost as 
 readily as the diamond. 
 Coloured of a delicate 
 purple, probably by a 
 little organic matter, these 
 
 Fig. lll.-Crystal of quartz. C T stals are J kl J OWn J 
 
 amethyst; and when ol a 
 
 brown colour, as Cairngorm stones or Scotch pebbles. Losing its trans- 
 parency and crystalline structure, we meet with silica in the form of chal- 
 cedony and of carnelian, usually coloured, in the latter, with oxide of iron. 
 
 Hardly any substance has so great a share in the lapidary's art as silica, 
 for in addition to the above instances of its value for ornamental purposes, we 
 find it constituting agate, cat's eye, onyx, so much prized for cameos, opal, 
 and some other precious stones. In opal the silica is combined with water. 
 
 Sand, of which the whiter varieties are nearly pure silica, appears to 
 have been formed by the disintegration of siliceous rocks, and has generally 
 a yellow or brown colour, due to the presence of oxide of iron. 
 
 The resistance offered by silica to all impressions has become proverbial 
 in the case of flint, which consists essentially of that substance coloured 
 with some impurity. Flints are generally found in compact masses, distri- 
 buted in regular beds throughout the chalk formation ; their hardness, 
 which even exceeds that of quartz, formerly rendered them useful for 
 striking sparks with steel, by detaching small particles of the metal, which 
 are so heated by the percussion as to continue to burn (see p. 10) in the 
 air, and to inflame tinder or gunpowder upon which they are allowed to fall. 
 
SILICA RENDERED SOLUBLE. 103 
 
 The part taken by silica in natural operations appears to be chiefly a 
 mechanical one, for which its stability under ordinary influences peculiarly 
 fits it, for it is found to constitute the great bulk of the soil which serves 
 as a support and food-reservoir of land-plants, and enters largely into the 
 composition of the greater number of rocks. 
 
 But that this substance is not altogether excluded from any share in 
 life is shown by its presence in the shining outer sheath of the stems of 
 the grasses and cereals, particularly in the hard external coating of the 
 Dutch rush used for polishing ; and this alone would lead to the inference 
 that silica could not be absolutely insoluble, since the capillary vessels of 
 plants are known to be capable of absorbing only such substances as are in 
 a state of solution. Many natural waters also present us with silica in a 
 dissolved state, and often in considerable quantity, as, for example, in the 
 Geysers of Iceland, which deposit a coating of silica upon the earth around 
 their borders. 
 
 Pure water, however, has no solvent action upon the natural varieties 
 of silica. The action of an alkali is required to bring it into a soluble 
 form. 
 
 To effect this upon the small scale, a few crystals of common washing- 
 soda (carbonate of soda) may be powdered and dried; a little of the dried 
 powder is placed upon a piece of platinum foil slightly bent up (fig. 112), 
 
 Fig. 112. Fusion on platinum foil. 
 
 and is fused by directing the flame of a blowpipe upon the under side of 
 the foil. As soon as the carbonate of soda is perfectly liquefied, a small 
 quantity of very finely powdered white sand is thrown into it, when brisk 
 effervescence will be observed, and the particles of sand will dissolve; 
 fresh portions of sand may now be added as long as they produce effer- 
 vescence, which is due to the escape of the carbonic acid, and since, in 
 general, one acid can only be displaced by another, it is but reasonable to 
 infer that the sand really possesses acid properties, and hence the fitness 
 of its chemical name, silicic acid. 
 
 The piece of platinum foil with the melted mass upon it may now be 
 placed in a little warm water, and allowed to soak for some time, when it 
 will gradually dissolve, forming a solution of silicate of 'soda. This solu- 
 tion will be found decidedly alkaline to test-papers ; for silicic acid, like 
 carbonic, is too feeble an acid to neutralise entirely the alkaline properties 
 of the soda. 
 
 If a portion of the solution of silicate of soda in water be poured into 
 a test-tube, and two or three drops of hydrochloric acid added to it with 
 occasional agitation, effervescence will be produced by the expulsion of 
 any carbonic acid still remaining, and the solution will be converted into 
 
104 DIALYSED SILICA. 
 
 a gelatinous mass by the separation of hydrated silicic acid. But if 
 another portion of the solution of silicate of soda be poured into an excess 
 of dilute hydrochloric acid (i.e., into enough to render the solution dis- 
 tinctly acid), the silicic acid will remain dissolved in the water, together 
 with the chlorde of sodium formed by the action of the hydrochloric acid 
 upon the soda. 
 
 In order to separate the chloride of sodium from the silicic acid, the 
 process of dialysis* must be resorted to. 
 
 Dialysis is the separation of dissolved substances from each other by 
 taking advantage of the different rates at which they pass through moist 
 diaphragms or septa. 
 
 If the mixed solution of chloride of sodium and silicic acid were poured 
 upon an ordinary paper filter, it would pass through without alteration ; 
 but if parchment paper be employed, which is not pervious to water, 
 although readily moistened by it, none of the liquid will pass through. 
 If the cone of parchment paper be supported upon a vessel filled with 
 distilled water (fig. 113), so that the water may be in contact with the 
 outer surface of the cone, the hydrochloric acid and the chloride of sodium 
 will pass through the substance of the parchment paper, and the water 
 charged with them may be seen descending in dense streams 
 from the outside of the cone. After a few hours, especially 
 if the water be changed occasionally, the whole of the 
 hydrochloric acid and chloride of sodium will have passed 
 through, and a pure solution of silicic acid in water will 
 remain in the cone. 
 
 This solution of silicic acid is very feebly acid to blue 
 litmus paper, and not perceptibly sour to the taste. It 
 has a great tendency to set into a jelly in consequence of 
 the sudden separation of hydrated silicic acid. If it be 
 
 slowly evaporated in a dish, it soon solidifies ; but, by con-* 
 
 Fig 113 ducting the evaporation in a flask, so as to prevent any 
 
 drying of the silicic acid at the edges of the liquid, it may 
 be concentrated until it contains 14 per cent, of silicic acid. When this 
 solution is kept, even in a stoppered or corked bottle, it sets into a trans- 
 parent gelatinous mass, which gradually shrinks and separates from the 
 water. When evaporated, in vacuo, over sulphuric acid, it gives a trans- 
 parent lustrous glass which is composed of 22 per cent, of water and 78 per 
 cent of silicic acid (HO . Si0 2 ). 
 
 This hydrate of silica cannot be redissolved in water, and is only soluble 
 to a slight extent in hydrochloric acid. If it be heated to expel the water, 
 the anhydrous silicic acid which remains is insoluble both in water and in 
 hydrochloric acid, but is dissolved when boiled with solution of potash or 
 soda, or their carbonates. 
 
 Silicic acid in the naturally crystallised form, as rock crystal and quartz, 
 is insoluble in boiling solutions of the alkalies, and in all acids except 
 hydrofluoric ; but amorphous silica (such as that found at Farnham) is 
 readily dissolved by boiling alkalies. These represent, in fact, two dis- 
 tinct modifications of silica. A transparent piece of rock crystal may be 
 heated to bright redness without change, but if it be powdered previously 
 to being heated, its specific gravity is diminished from 2 '6 to 24, and it 
 becomes soluble in boiling alkalies, having been converted into the amor- 
 phous modification. 
 
 * From SiaXvw, to part asunder. 
 
ACID CHARACTER OF SILICA. 
 
 105 
 
 Crystals of quartz have been obtained artificially by the prolonged 
 action of water upon glass at a high temperature under pressure. When 
 fused with the oxyhydrogen blowpipe, silica does not crystallise, being 
 thus converted into the amorphous variety of sp. gr. 2 *3. 
 
 To prepare the amorphous modification of silica artificially, white sand in very 
 fine powder may be fused, in a platinum crucible, with six times its weight of a mix- 
 ture of equal weights of carbonate of potash and carbonate of soda, the mixture being 
 more easily fusible than either of the carbonates separately. The crucible may be 
 heated over a gas-burner supplied with a mixture of gas and air, or may be placed in 
 a little calcined magnesia contained in a fire-clay crucible, which may be covered up 
 and introduced into a good fire. The platinum crucible is never heated in direct 
 contact with fuel, since the metal would become brittle by combining with carbon, 
 silicon, and sulphur derived from the fuel. The magnesia is used to protect the pla- 
 tinum from contact with the clay crucible. When the action of the silicic acid upon 
 the alkaline carbonates is completed, which will be indicated by the cessation of the 
 effervescence, the platinum crucible is allowed to cool, placed in an evaporating dish, 
 and soaked for a night in water, when the mass should be 
 entirely dissolved. Hydrochloric acid is then added to 
 the solution, with occasional stirring, until it i distinctly 
 acid to litmus paper. On evaporating the solution, it will, 
 at a certain point, solidify to a gelatinous mass of hydrated 
 silicic acid, which would be spirted out of the dish if 
 evaporation over the flame were continued. To prevent 
 this, the dish is placed over an empty iron saucepan (fig. 
 114), so that the heat from the flame may be equally 
 distributed over the bottom of the dish. When the mass 
 is quite dry the dish is allowed to cool, and some water 
 is poured into it, which dissolves the chlorides of potas- 
 sium and sodium (formed by the action of the hydro- 
 chloric acid upon the silicates of potash and soda), and 
 leaves the silicic acid in white flakes. These may be 
 collected upon a filter (fig. 115), and washed several times with distilled water. 
 The filter is then carefully spread out upon a hot iron plate, or upon a hot brick, and 
 allowed to dry, when the silicic acid is 
 left as a dazzling white powder, which 
 must be strongly heated in a porcelain 
 or platinum crucible to expel the last 
 traces of water. It is remarkable for 
 its extreme lightness, especially when 
 heated, the slightest current of air easily 
 blowing it away. 
 
 79. For effecting such fusions as that 
 just described, an air-gas blow-pipe (A, 
 fig. 116) supplied with air from a double 
 action bellows (B), worked by a treadle (0), 
 will be found most convenient. Where 
 gas is not at hand, the fusion may be 
 effected in a small furnace (fig. 117) sur- 
 mounted with a conical chimney, and fed 
 with charcoal. 
 
 80. Silicates. The acid proper- 
 ties of silicic acid are so feeble that 
 it is a matter of great difficulty to 
 determine the proportion of any 
 base which is required to unite with 
 it in order to form a chemically 
 neutral salt. Like carbonic acid, it does not destroy the action of the alkalies 
 upon test-papers, and we are, therefore, deprived of this method of ascer- 
 taining the proportion of alkali which neutralises it in a chemical sense. In 
 
 Fig. 114. 
 
 Fig. 115. Washing a precipitate. 
 
106 
 
 AMORPHOUS SILICON. 
 
 attempting to ascertain the quantity of alkali with which it combines 
 from that of the carbonic acid which it expels when heated with ah 
 alkaline carbonate, it is found that the proportion of carbonic acid ex- 
 pelled varies considerably, according to the temperature and the proportion 
 of alkaline carbonate employed, probably because the attractions of silicic 
 and carbonic acids for the alkaline bases are pretty evenly balanced. 
 
 By heating silicic acid with hydrate of soda (NaO . HO), it is found that 
 30 parts of silicic acid expel 18 parts of water, however much hydrate of 
 soda is employed, and the same proportion of water is expelled from 
 hydrate of baryta (BaO . HO) when heated with silicic acid. 
 
 According to the table at page 2, the formula Si0 2 represents 30 parts 
 by weight of silicic acid, and 18 parts represent two equivalents of water 
 which were combined in the hydrates with two equivalents of soda and 
 baryta respectively. Hence it would appear that one equivalent of silicic 
 acid is disposed to combine with two equivalents of an alkali, and since it 
 is found that several of the crystallised mineral silicates contain two 
 equivalents of a basic protoxide t (MO) combined with one equivalent of 
 silicic acid, it is usual to repres'ent it as a dibasic acid, that is, an acid 
 requiring two equivalents of an alkali to form a chemically neutral salt. 
 The circumstance that silicic acid is not capable of being converted into 
 
 vapour at a high temperature, 
 enables it to expel from their 
 combinations with bases many 
 other acids which, at ordinary 
 temperatures, are able to displace 
 silicic acid. Thus, sulphuric acid 
 has a far more powerful attrac- 
 tion for bases than silicic acid, at 
 the ordinary temperature, but 
 when a mixture of silicic acid 
 with a sulphate is strongly heated, 
 the tendency of the sulphuric acid 
 to assume the vaporous state at 
 this temperature determines the 
 decomposition of the sulphate 
 and the formation of a silicate. 
 
 The silicates form by far the 
 greatest number of minerals. The 
 
 different varieties of clay consist 
 Fig. 116.-Air.gas blowpipe table. Qf ^^ Q alumina . f elds p ar is 
 
 a silicate of alumina and potash ; meerschaum is a silicate of magnesia. 
 
 The different kinds of glass are composed of silicates of potash, soda, 
 lime, oxide of lead, &c. 
 
 None but the silicates of the alkalies are soluble in water. 
 
 81. Silicon or Silicium. From the remarkably unchangeable character 
 of silica, it is not surprising that it was long regarded as an elementary 
 substance. In 1813, however, Davy succeeded in decomposing it by the 
 action of potassium, and in obtaining an impure specimen of silicon. It 
 has since been produced, far more easily, by converting the silicic acid 
 into silico-fluoride of potassium (KF . SiF 2 ), and decomposing this at a 
 high temperature with potassium or sodium, which combines with the 
 fluorine to form a salt capable of being dissolved out by water, leaving 
 
CHEMICAL RELATIONS OF SILICON. 107 
 
 the silicon in the form of a brown powder (amorphous silicon) which 
 resists the action of all acids, except hydrofluoric, which it decomposes^ 
 forming fluoride of silicon and evolving hydrogen (Si + 2HF = SiF 2 + H 2 ) t 
 It is also dissolved by solution of hydrate of 
 potash, with evolution of hydrogen, and for- 
 mation of silicate of potash. It burns bril- 
 liantly when heated in oxygen, but not com- 
 pletely, for it becomes coated with silica 
 which is fused by the intense heat of the 
 combustion. When heated with the blow- 
 pipe on platinum foil, it eats a hole through 
 the metal, with which it forms the fusible 
 silicide of platinum. 
 
 If silico-fluoride of potassium be fused with 
 aluminum, a portion of the latter combines 
 with the fluorine, and the remainder com- 
 bines with the silicon, forming a silicide of 
 
 aluminum. By boiling this with hydro- 
 
 Ti j T j a -j - Fie*. 11 /. Charcoal furnace, 
 
 chloric and hydrofluoric acids in succession, 
 
 the aluminum is extracted, and crystalline scales of silicon, with a me- 
 tallic lustre resembling black lead, are left (graphitoid silicon). In this 
 form the silicon has a specific gravity of about 2*5, and refuses to burn 
 in oxygen, or to dissolve in hydrofluoric acid. A mixture of nitric and 
 hydrofluoric acids, however, is capable of dissolving it. Like graphite, 
 this variety of silicon conducts electricity, though amorphous silicon is a 
 non-conductor. The amorphous silicon becomes converted into this in- 
 combustible and insoluble form under the action of intense heat. It is 
 worthy of remark that the combustibility of amorphous carbon (charcoal) 
 is also very much diminished by exposure to a high temperature. 
 
 Unlike carbon, however," silicon is capable of being fused at a tempera- 
 ture somewhat above the melting point of cast iron ; on cooling it forms 
 a brilliant metallic-looking mass, which may be obtained, by certain pro- 
 cesses, crystallised in octahedra so hard as to scratch glass like a diamond. 
 
 In their chemical relations to other substances there is much resem- 
 blance between silicon and carbon. They both form feeble acids with 
 oxygen, which correspond in composition. Silicon, however, is capable 
 of displacing carbon from carbonic acid, for if carbonate of potash be 
 fused with silicon, the latter is dissolved, forming silicate of potash, and 
 carbon is separated. Silicon also resembles carbon in its disposition to 
 unite with certain metals to form compounds which still retain their 
 metallic appearance. Thus silicon is found together with carbon in cast 
 iron, and it unites directly with aluminum, zinc, and platinum, to form 
 compounds resembling metallic alloys. Nitrogen enters into direct union 
 with silicon at a high temperature, though it refuses to unite with carbon 
 except in the presence of alkalies. In their relation to hydrogen, these 
 two elements are widely different, for silicon is only known to form one 
 compound with hydrogen, and that of a very unstable character. 
 
 The hydride of silicon has never yet been obtained in a perfectly pure 
 state, but its composition is believed to correspond with the formula SiH 2 . 
 It derives its interest chiefly from the property of taking fire spontaneously 
 in contact with the air, in which it burns with a brilliant white flame, 
 giving off clouds of silica, and depositing a brown film of silicon upon a 
 cold surface. 
 
108 HYDRIDE OF SILICON. 
 
 The impure hydride of silicon is prepared by decomposing silicide of magnesium 
 with dilute hydrochloric acid. The silicide of magnesium is obtained by fusing 
 chloride of magnesium (MgCl) with silico-fluoride of sodium (NaF . SiF 2 ) and 
 metallic sodium, when the latter combines with the chlorine and fluorine, leaving 
 the magnesium free to unite with the silicon. 
 
 The chloride of magnesium may be prepared by dissolving ordinary carbonate of 
 magnesia in hydrochloric acid, adding three parts of chloride of ammonium for each 
 part of carbonate of magnesia, evaporating to dryness in a porcelain dish, fusing the 
 residue, and pouring it out on to a clean stone. Being very deliquescent it must be 
 kept in a well-closed bottle. 
 
 Silico-fluoride of sodium is made by neutralising hydro-fluosilicic acid with car- 
 bonate of soda, and evaporating to dryness. 
 
 To increase the fusibility of the mixture, some fused common salt will be re- 
 quired. Dried salt may be melted in a fire-clay crucible, at a bright red heat, and 
 poured out upon a clean dry stone. 
 
 Forty parts of the chloride of magnesium, 35 of silico-fluoride of sodium, 10 of 
 fused chloride of sodium, and 20 of sodium in slices, are rapidly weighed, shaken 
 together in a dry bottle, and thrown into a red-hot clay crucible, which is then 
 covered and heated as long as the yellow flame of sodium vapour is perceptible. 
 After cooling, the crucible is broken, when a dark-coloured layer of silicide of mag- 
 nesium will be found beneath a white layer of chloride and fluoride of sodium. The sili- 
 cide of magnesium must be rapidly 'detached, and preserved in a well-stopped bottle. 
 The silicide of magnesium is coarsely powdered, and introduced into a Woulfe's 
 bottle (fig. 118), provided with a funnel tube, and a short wide tube for delivering 
 the gas. The bottle is filled up with water (previously 
 boiled to expel air, and allowed to cool), and placed in 
 the pneumatic trough (containing boiled water), so 
 that both bottle and tubes may remain filled with 
 water. A gas-jar, filled with boiled water, having 
 been placed over the delivery-tube, some strong hydro- 
 chloric acid is added through the funnel, great care 
 being taken that no air shall enter. The hydride of 
 silicon is at once evolved, and must be allowed to 
 stand over water for some little time, to allow the 
 froth, caused by a slight separation of silica, to sub- 
 side. The gas may then be transferred to a capped 
 jar, with a stop-cock, from which it may be allowed to 
 pass into the air for the examination of its flame. 
 Fig. 118. When cast iron, containing silicon, is boiled with 
 
 hydrochloric acid until the whole of the iron is dis- 
 solved, a grey frothy residue is left. If this be collected on a filter, well washed 
 and dried, it is found to consist of black scales of graphite, mixed with a very light 
 white powder. On boiling it with potash, hydrogen is evolved, and the white 
 powder dissolves, forming a solution containing silicate of potash. This white 
 powder appears to be identical with a substance obtained by other processes, and 
 called leucone* which is believed to have the composition Si 3 H 2 5 , and has been 
 regarded as a hydrate of protoxide of silicon, 3SiO . 2HO. Its action upon solution 
 of potash would be explained by the equation 
 
 Si 3 H 2 5 + HO + 6KO = 3(2KO . Si0 2 ) + H 3 . 
 
 Leucone is slowly converted into silicic acid, even by the action of water, hydro- 
 gen being disengaged. 
 
 Another compound, containing silicon, hydrogen, and oxygen, has been named 
 silicone. It is a yellow substance, the general characters of which resemble those of 
 the compound last described. When exposed, under water, to the action of sun- 
 light, hydrogen is evolved, and the yellow body becomes converted into leucone. 
 
 Combining weight of silicon. The experiments of Berzelius proved that 
 8 parts by weight of oxygen combine with 7*4 parte of silicon to form 
 silicic acid. If it be assumed that the composition of silicic acid is analo- 
 gous to that of carbonic acid (C0 2 ), the combining weight of silicon (or 
 
 * Aeu/cos, white. 
 
BORACIC ACID. 109 
 
 the weight combining with C>2=. 16 parts of oxygen) would be 14*8. 
 More exact experiments have recently fixed the number at 14. 
 
 Some chemists represent silicic acid as Si0 3 , when the combining 
 weight of silicon (or the weight combining with 3 = 24 parts of oxygen) 
 would be 2 2 *2 (7*4 x 3), or by the more exact experiments, 21. 
 
 The atomic weight of silicon is generally represented by the number 
 28, though here, as in the case of carbon, theoretical considerations are 
 relied upon, since the specific gravity of vapour of silicon cannot be ascer- 
 tained by experiment. 
 
 The atomic formula of silicic acid would then be SiO 2 , representing 28 
 parts of silicon, combined with 32 parts of oxygen, forming 60 parts of 
 silicic acid. 
 
 BOKON. 
 
 82. Closely allied to silicon is another element, boron, which has at 
 present never been found in animal or vegetable bodies, but appears to 
 be entirely confined to the mineral kingdom. 
 
 Boracic acid. A saline substance called borax (NaO . 2B0 3 + lOAq.), 
 has long been used in medicine, in working metals, and in making imita- 
 tions of precious stones; this substance was originally imported from 
 India and Thibet, where it was obtained in crystals from the waters of cer- 
 tain lakes, and came into this country under the native designation of 
 tincal, consisting of impure borax, surrounded with a peculiar soapy sub- 
 stance, which the refiner of borax makes it his business to remove. 
 
 In 1702, in the course of one of those tentative experiments to which, 
 though empirical in their nature, scientific chemistry is now so deeply 
 indebted, Homberg happened to distil a mixture of borax and green 
 vitriol (sulphate of iron), when he obtained a new substance in pearly 
 plates, which was found useful in medicine, and received the name of 
 sedative salt. A quarter of a century later, Lemery found that this sub- 
 stance might be separated from borax by employing sulphuric acid instead 
 of sulphate of iron ; but another quarter of a century elapsed before it 
 was shown that in borax these pearly crystalline scales were combined 
 with soda, and were possessed of acid properties which entitle them to 
 receive the name boracic acid. 
 
 Much more recently this acid has been obtained in a free state from 
 natural sources, and is now largely imported into this country from the 
 volcanic districts in the north of Italy, where it issues from the earth in 
 the form of vapour, accompanied by violent jets of steam, which are 
 known in the neighbourhood as soffioni. It would appear easy enough, 
 by adopting arrangements for the condensation of this steam, to obtain 
 the boracic acid which accompanies it, but it is found necessary to cause 
 the steam to deposit its boracic acid by passing it through water, for 
 which purpose basins of brickwork (lagunes, fig. 119) are built up around 
 the soffioni, and are kept filled with water from the neighbouring springs 
 or brooks ; this water is allowed to flow successively into the different 
 lagunes, which are built upon a declivity for that purpose, and it thus 
 becomes impregnated with about 1 per cent, of boracic acid. The neces- 
 sity for expelling a large proportion of this water, in order to obtain the 
 boracic acid in crystals, formed for a long time a great obstacle to the 
 success of this branch of industry in a country where fuel is very expen- 
 
110 
 
 BORACIC ACID. 
 
 sive. In 1817, however, Larderello conceived the project of evaporating 
 this water by the steam-heat afforded by the soffioni themselves, and 
 several hundred tons of boracic acid are now annually produced in this 
 manner. The evaporation is conducted in shallow leaden evaporating 
 pans (A, fig. 119), under which the steam from the soffioni is conducted 
 through the flues (F) constructed for that purpose. As the demand for 
 boracic acid increased on account of the immense consumption of borax 
 in the porcelain manufacture, the experiment was made, with success, of 
 boring into the volcanic strata, and thus producing artificial soffioni, yield- 
 ing boracic acid. 
 
 The crystals of boracic acid, as imported from these sources, contain 
 salts of ammonia and other impurities. They dissolve in about three 
 times their weight of boiling water, and crystallise out on cooling, since 
 they require 26 parts of cold water to dissolve them. These crystals are 
 represented by the formula 3HO . B0 3 . If they are sharply heated in a 
 retort, they partly distil over unchanged, together with the water derived 
 from the decomposition of another part ; but if they be heated to 212 F. 
 only, they effloresce, and become converted into HO . B0 3 . When this 
 is further heated, the whole of the water passes off, carrying with it a 
 little boracic acid, and the acid fuses to a glass, which remains perfectly 
 
 Fig. 119. Boracic lagune and evaporating pans. 
 
 transparent on cooling (vitreous boracic acid). This anhydrous boracic 
 acid is slowly volatilised by the continued action of a very high tempera- 
 ture. It dissolves very slowly in water. 
 
 A characteristic property of boracic acid is that of imparting a green 
 colour to flames. Its presence may thus be detected in the steam issuing 
 from a boiling solution of boracic acid in water, for if a spirit-lamp flame, 
 or a piece of burning paper, be held in the steam, the flame will acquire 
 a green tint, especially at the edges. 
 
 The colour is more distinctly seen when the crystallised boracic acid is heated on 
 platinum foil in a spirit-flame or an air-gas flame ; and still better when the crystals 
 are dissolved in boiling alcohol, and the solution burnt on a plate. The presence of 
 boracic acid in borax may be ascertained by mixing the solution of borax with strong 
 sulphuric acid to liberate the boracic acid, and adding enough alcohol to make the 
 mixture burn. Another peculiar property of boracic acid is its action upon turmeric. 
 If a piece of turmeric paper be dipped in solution of boracic acid, and dried at a 
 gentle heat, it assumes a fine brown-red colour, which is changed to green or blue 
 by potash or its carbonate. In applying this test to borax, the solution is slightly 
 acidified with hydrochloric acid, to set free the boracic acid, before dipping the paper. 
 
GRAPHITE AND DIAMOND OF BORON". Ill 
 
 Borates. Eoracic acid, like silicic, must be classed among the feeble 
 acids. It colours litmus violet only, like carbonic acid, and does not 
 neutralise the action of the alkalies upon test-papers. At high tempera- 
 tures fused boracic acid dissolves the metallic oxides to form transparent 
 glassy borates, which have, in many cases, very brilliant colours, and upon 
 this property depend the chief uses of boracic acid in the arts. 
 
 Unlike the silicates, the borates are comparatively rare in the mineral 
 world. No very familiar mineral substance contains boracic acid. A 
 double borate of soda and lime, called boro-natrocalcite, is imported from 
 Peru for the manufacture of borax; and the mineral known as boracite is 
 a borate of magnesia. 
 
 In determining the proportion of base which boracic acid requires to 
 form with it a chemically neutral salt, the same difficulties are met with 
 as in the case of silicic acid (p. 105); but since it is found that 35 parts of 
 boracic acid (the weight represented by B0 3 ) displace 27 parts of water 
 (three equivalents) from hydrate of soda and from hydrate of baryta, both 
 employed in excess, it would appear that the boracic acid requires three 
 equivalents of a basic protoxide (MO) fully to satisfy its acid character, 
 so that it is a tribasic acid, a conclusion which is supported by other 
 evidence. 
 
 83. Boron. It was in the year 1808 that Gay-Lussac and Thenard 
 succeeded, by fusing anhydrous boracic acid with potassium, in extracting 
 from it the element boron as an olive-green powder (amorphous boron), 
 which has a general resemblance to silicon, but, unlike that element, may 
 be oxidised by nitric acid. It also requires a higher temperature to fuse 
 it than is required by silicon. The graphitoid boron, corresponding to the 
 black-lead variety of carbon, is obtained in brilliant copper-coloured scales 
 by a process similar to that which furnishes the graphitoid silicon. 
 
 The most remarkable form of boron is the crystallised variety or diamond 
 of boron, which is obtained by very strongly heating amorphous boron 
 with aluminum, and afterwards extracting the aluminum from the mass 
 with hydrochloric acid. These crystals are brilliant transparent octahedra, 
 which are sometimes nearly colourless, and resemble the diamond in their 
 power of refracting light, and in their hardness, which is so great that 
 they will scratch rubies, and will even wear away the surface of the 
 diamond.* This form of boron cannot be attacked by any acid, but is 
 dissolved by fused hydrates of the alkalies. The flame of the oxyhydrogen 
 blowpipe does not fuse it, and it only undergoes superficial conversion 
 into boracic acid when heated to whiteness in oxygen. When heated to 
 redness in chlorine, however, it burns, forming chloride of boron. ~ Boron 
 closely resembles silicon in its chemical relations to the other elements. 
 It is not known, however, to form a compound with hydrogen, and has a 
 greater disposition to combine with nitrogen than is manifested by silicon. 
 It absorbs nitrogen readily when heated to redness, forming a white 
 infusible insoluble powder, the nitride of boron (BN). 
 
 Combining weight of boron. According to the experiments of Davy, 
 8 parts by weight of oxygen combine with 3*76 parts of boron to form 
 boracic acid. Berzelius found, in borax, that one equivalent of soda (31 
 parts) was combined with 69 '5 parts of boracic acid. This would contain, 
 according to Davy, 47 '3 parts of oxygen, and if it be taken to represent 
 
 * The author has known them to cut through the bottom of the beaker-glass used in 
 separating them from the aluminum. 
 
112 REVIEW OF CARBON, BORON, AND SILICON. 
 
 one equivalent of boracic acid, that of boron would be (69 '5 47'3 = ) v 
 22-2, and the formula of boracic acid would be B0 6 (representing 22 -2 
 parts of boron and 48 parts of oxygen). There are reasons, however, for 
 believing that borax really contains two equivalents of boracic acid, com- 
 bined with one equivalent of soda, so that the equivalent of boron would 
 be the half of 22*2, or ll'l (by more exact experiments, -11), and 
 boracic acid would be B0 3 (11 parts of boron with 24 parts of oxygen). 
 The same number is generally taken for the atomic weight of boron, the 
 atomic formula of boracic anhydride being written B 2 3 , and that of the 
 crystallised acid HBO 2 . H 2 O. 
 
 84. The elements carbon, boron, and silicon form a natural group, pos- 
 sessing many properties in common. They are all capable of existing in 
 the amorphous, the graphitoid, and the crystalline forms ; all incapable of 
 being converted into vapour ; all exhibit a want of disposition to dissolve ; 
 all form feeble acids with oxygen by direct union ; and all unite with 
 several of the metals to form compounds which resemble each other. 
 Boron and silicon are capable of direct union with nitrogen, and so is 
 carbon if an alkali be present. Eecent researches attribute to silicon 
 the power of occupying the place of carbon in some organic compounds, 
 and the formulae of leucone and silicon (Si 3 H 2 5 and Si 6 H 3 4 ) strongly 
 remind us of the organic compounds of carbon with hydrogen and 
 oxygen. In many of its physical and chemical characters, silicon is closely 
 allied with the metals, and it will be found that tin and titanium bear a 
 particular resemblance to it in their chemical relations. 
 
 NITROGEN. 
 
 85. This element, which has already been referred to as forming four- 
 fifths of the volume of air, is elsewhere found in nature in the forms of 
 saltpetre or nitrate of potash (KO . N0 5 ), and Chili saltpetre or nitrate of 
 soda (NaO . N0 5 ). It also occurs as ammonia (NH 3 ) in the atmosphere 
 and in the gaseous emanations from volcanoes. It is contained in the 
 greater number of animal, and in many vegetable substances, and therefore 
 has a most important share in the chemical phenomena of life. 
 
 Nitrogen is generally obtained by burning phosphorus in a portion of 
 air confined over water (fig. 120.) The phosphorus is floated on the water 
 
 in a small porcelain dish, kindled, and 
 covered with a bell-jar. The nitrogen 
 remains mixed with clouds of phosphoric 
 acid (P0 5 ), which may be removed by 
 allowing the gas to stand over water. 
 
 When nitrogen is required in larger 
 quantity, it is more conveniently prepared 
 by passing air from a gas-holder over 
 metallic copper heated to redness in a tube. 
 The negative properties of this gas, how- 
 ever, are so very uninteresting, and render 
 it so useless for most chemical purposes, that 
 
 Fig. 120.-Preparation of nitrogen. j* U be unnecessary to give further de- 
 tails respecting its preparation. The re- 
 markable chemical inactivity of free nitrogen has been alluded to in the 
 article on atmospheric air. It has been seen, however, to be capable of 
 
SOURCES OF AMMONIA. 113 
 
 combining directly with boron and silicon, and magnesium and titanium 
 unite with it even more readily at a high temperature. It is conspicuous 
 among the elements for forming, with hydrogen, a powerful alkali (am- 
 monia, NH 3 ), and with oxygen a powerful acid (nitric acid, NO.), whilst 
 the feeble chemical ties which hold it in combination with other elements, 
 joined to its character of a permanent gas, render many of its compounds 
 very unstable and explosive, as is the case with the so-called chloride 
 and iodide of nitrogen, gun-cotton, the fulminates of silver and mercury, 
 nitroglycerine, &c. 
 
 The discovery of nitrogen was made by Eutherford (Professor of Botany 
 in the University of Edinburgh) in 1772, who was led to it by the obser- 
 vation, that respired air was still unfit to support life when all the carbonic 
 acid had been absorbed from it by a caustic alkali. Hence the name azote 
 (a priv. and aj?) life) formerly bestowed upon this gas. 
 
 AMMONIA. 
 
 86. The proportion of ammonia existing in atmospheric air is so small 
 that it is difficult to determine it with precision ; it appears, however, not 
 to exceed one-hundredth of a grain in a -cubic foot. This scarcity of 
 ammonia in air is not to be accounted for by a scantiness in the supply, 
 but rather by an excess in the demand ; since ammonia is constantly sent 
 forth into the air by the putrefaction of animal and vegetable substances 
 containing nitrogen. Plants do not appear to be capable of absorbing 
 from the atmosphere the nitrogen which it contains so abundantly in the 
 uncombined form, but to derive their chief supply of that element from 
 the ammonia, brought down by rain from the atmosphere, into which it is 
 continually introduced from various sources. During the life of an 
 animal, it restores to the air the nitrogen which formed part of its wasted 
 organs, in part directly as ammonia in the breath and in the exhalation 
 from the skin,* whilst another portion is separated as urea and uric acid 
 in the urine, to be eventually converted into ammonia when the excretion 
 undergoes putrefaction. Dead animal and vegetable matter when putre- 
 fying, restores its nitrogen to the air, chiefly in the forms of ammonia and 
 substances closely allied to it, but partly also, it is said, in the free state. 
 
 The liquor ammonice, or solution of ammonia in water, which is so largely 
 used in medicine and the arts, is obtained chiefly from the ammoniacal 
 liquor resulting from the destructive distillation of coal for the manufac- 
 ture of gas. The ammoniacal liquor of the gas-works contains ammonia 
 in combination with carbonic and hydrosulphuric acids. As the first step 
 towards extracting the ammonia in a pure state, the liquor is neutralised 
 with hydrochloric acid, which combines with the ammonia, expelling the 
 carbonic and hydrosulphuric acid gases. Since the latter has a very bad 
 smell and is injurious to health, the neutralisation is generally effected 
 in covered vats furnished with pipes, which convey the gases into a furnace 
 where the hydrosulphuric acid is burnt, forming water and sulphurous 
 acid. The solution of hydrochlorate of ammonia is evaporated to expel 
 part of the water, and allowed to cool in wooden vessels lined with lead, 
 where the hydrochlorate is deposited in crystals which contain a good 
 
 * Some doubt exists as to the exhalation of ammonia from the lungs .and skin of man 
 under normal conditions. 
 
 II 
 
114 
 
 PROPERTIES OF AMMONIA. 
 
 deal of tarry matter. These crystals are moderately heated in an iron pan 
 to deprive them of tar, and are finally purified by sublimation, that is, by 
 converting them into vapour, and allowing this vapour to condense again 
 into the solid form. For this purpose the crys- 
 tals are heated in a cylindrical iron vessel covered 
 with an iron dome lined with fire-clay. The hydro- 
 chlorate of ammonia rises in vapour below a red 
 heat, and condenses upon the dome in the form of 
 the fibrous cake known as sal-ammoniac in com- 
 merce. 
 
 To obtain ammonia from this salt, an ounce of 
 it is reduced to coarse powder, and rapidly mixed 
 with two ounces of powdered quick-lime. The 
 mixture is gently heated in a dry Florence flask 
 (fig. 121), and the gas, being little more than half 
 as heavy as air (sp. gr. 0'59), may be collected 
 in dry bottles by displacement of air, the bottles 
 being allowed to rest upon a piece of tin plate 
 which is perforated for the passage of the tube. 
 To ascertain when the bottles are filled, a piece of 
 red litmus paper may be held at some little distance above the mouth, 
 when it will at once acquire a blue colour if the ammonia escapes. The 
 bottles should be closed with greased stoppers. 
 
 The action of the lime upon hydrochlorate of ammonia is explained by 
 the following equation : 
 
 Fig. 121. Preparation of 
 ammonia. 
 
 NIL.HC1 + 
 
 + NIL 
 
 CaO - CaCl + HO 
 
 Hydrochlor. amm. Lime. Chloride of calcium. Ammonia. 
 
 The readiest method of obtaining gaseous ammonia for the study of its proper- 
 ties consists in gently heating the strongest liquor ammonice in a retort or flask pro- 
 vided with a bent tube for collecting the gas by displacement (fig. 122). The gas 
 
 is evolved from the solution at a very 
 low heat, and may be collected un- 
 accompanied by steam. 
 
 Ammonia is readily distin- 
 guished by its very characteristic 
 smell, and its powerful alkaline 
 action upon red litmus and tur- 
 meric papers. It is absorbed by 
 water in greater proportion by 
 volume than any other gas, one 
 volume of water absorbing more 
 than 700 volumes of ammonia 
 at the ordinary temperature, and 
 becoming one-and-a-half volumes 
 of solution of ammonia of specific 
 gravity 0*88. No chemical com- 
 bination appears to take place between the water and ammonia, for the 
 gas gradually escapes on exposing the solution to the air, and no definite 
 compound of the two has been noticed. The escape of the gas from 
 the solution is attended with great production of cold, much heat be- 
 coming latent in the conversion of the ammonia from the liquid to the 
 gaseous state. 
 
 The rapid absorption of ammonia by water is well shown by filling a globular 
 
 Fig. 122. 
 
SPECIFIC GRAVITY OF LIQUIDS DETERMINED. 
 
 115 
 
 Fig. 123. 
 
 flask (fig. 123) with the gas, placing it with its mouth downwards in a small capsule 
 
 of mercury which is placed in a large basin. If 
 
 this basin be filled with water, it cannot come into 
 
 contact with the ammonia until the mouth of the 
 
 flask is raised out of the mercury, when the water 
 
 will quickly enter and fill the flask. The water 
 
 should be coloured with reddened litmus to exhibit 
 
 the alkaline reaction of the ammonia. 
 
 To exhibit the easy expulsion of the ammoniacal 
 ga,s from water by heat, a moderately thick glass 
 tube, about 12 inches long and half an inch in dia- 
 meter, may be nearly filled with mercury, and then 
 filled up with strong solution of ammonia ; on closing 
 it with the thumb and inverting it into a vessel of 
 mercury (fig. 124) the solution will, of course, rise 
 above the mercury to the closed end of the tube. By 
 grasping this end of the tube in the hand, a con- 
 siderable quantity of gas may be expelled, and the mercury will be depressed. If 
 a little hot water be poured over the top of the tube, the latter will become filled 
 with ammoniacal gas, which will be absorbed again by the water when the tube is 
 allowed to cool, the mercury re- 
 turning to fill the tube. 
 
 The solution of ammonia, 
 which is an article of com- 
 merce, is prepared by conduct- 
 ing the gas into water con- 
 tained in a two-necked bottle, 
 the second neck being con- 
 nected with a tube passing 
 into another bottle containing 
 water, in which any escaping 
 ammonia may be condensed. 
 The strength of the solutionds 
 inferred from its specific gra- 
 vity, which is lower in propor- 
 tion as the quantity of am- 
 monia in the solution is greater. 
 
 Thus, at 57 F., a solution of 
 sp. gr. 0-8844 contains 36 parts by 
 weight of ammonia in 100 parts 
 of solution ; the sp. gr. 0*8976 in- 
 dicates 30 per cent. ; 0-9106, 25 per cent. ; 0-9251, 20 per cent. ; 0-9414, 15 per 
 cent.; 0-9593, 10 per cent. ; 0-979, 5 per cent. The specific gravity is ascertained by 
 comparing the weights of equal volumes of water and of the 
 solution at the same temperature. For this purpose, a light 
 stoppered bottle is provided, capable of containing about two 
 fluid ounces. This is thoroughly dried, and counterpoised in 
 a balance by placing in the opposite pan a piece of lead, which 
 may be cut down to the proper weight. The bottle is then filled 
 with solution of ammonia, the temperature observed with a ther- 
 mometer and recorded, the stopper inserted, and the bottle weighed. 
 It is then well rinsed out, filled with distilled water, the tempera- 
 ture equalised with that of the ammonia by placing the bottle 
 either in warm or cold water, and the weight ascertained as before. 
 The specific gravity is obtained by dividing the weight of the solu- 
 tion of ammonia by that of the water. The ammonia-meter (fig. 
 125) is a convenient instrument for rapidly ascertaining the specific 
 gravity of liquids lighter than water. It consists of a hollow glass 
 float with a long stem, weighted with a bulb containing shot or mer- 
 cury, so that when placed in distilled water it may sink to 1000 of the 
 
 Fig. 124. 
 
 Fig. 125. 
 
 H 2 
 
116 
 
 LIQUEFACTION OF AMMONIA. 
 
 scale marked on the stem, this number representing the specific gravity of water. 
 When placed in a liquid lighter than water, it must, of course, sink lower in order 
 to displace more liquid (since solids sink until they have displaced their own weight 
 of liquid). By trying it in liquids of known specific gravities, the mark upon the 
 scale to which it sinks may be made to indicate the specific gravity of the liquid. 
 The ammonia-meter generally has a scale so divided that it indicates at once the 
 per-centage weight of ammonia. In this country the specific gravity of a liquid is 
 always supposed to be taken at 62 F. 
 
 The common name for solution of ammonia, spirit of hart's horn, is 
 derived from the circumstance that it was originally obtained for medi- 
 cinal purposes by distilling shavings of that material. 
 
 When ammonia is exposed to a temperature of 40 F. (i.e. 72 below 
 the freezing-point), or to a pressure of 6 J atmospheres at 50, it condenses 
 to a clear liquid, which solidifies at a temperature of - 103 F. to a white 
 
 crystalline mass. The comparative ease 
 with which it may be liquefied has led 
 to its application in Carry's freezing 
 apparatus (fig. 126), in which the gas 
 generated by heating a concentrated 
 solution of ammonia in a strong iron 
 boiler (A) is liquefied by its own pres- 
 sure in an iron receiver (B) placed in 
 cold water. When the boiler is taken 
 off the fire and cooled in water, the 
 liquefied ammonia evaporates very ra- 
 pidly from the receiver back into the 
 boiler, thereby producing so much cold 
 that a vessel of water placed in a cavity 
 (C) in the receiver is at once congealed 
 into ice. A refrigerator constructed 
 upon this principle is employed in the 
 
 salt gardens of the south of France, in order to render their crystallising 
 operations independent of the temperature of the air. 
 
 The liquefaction of ammonia is very easily effected by heating the ammoniated 
 chloride of silver in one limb of a sealed tube, the other limb of which is cooled in a 
 freezing mixture. A piece of stout light green glass tube (A, fig. 127), about 12 
 
 inches long and half an inch in 
 
 A@L . ^ diameter, is drawn out at about an 
 
 inch from one end to a narrow neck. 
 About 300 grains of chloride of silver 
 (dried at 400 F.) are introduced into 
 the tube, so as to lie loosely in it. 
 For this purpose a gutter of stiff 
 paper (B) should be cut so as to slide 
 loosely in the tube, the chloride of 
 silver placed upon it, and when it 
 has been thrust into the tube (held 
 horizontally) the latter should be 
 turned upon its axis, so that the chlo- 
 ride of silver may fall out of the 
 paper, which may then be withdrawn. 
 The tube is now drawn out to a 
 narrow neck at about an inch from 
 the other end, as in 0, and after- 
 wards carefully bent, as in D, care 
 
 being taken that none of the chloride of silver falls into the short limb of the tube, 
 which should be about four inches long. The tube is then supported by a holder, 
 so that the long limb may be horizontal, and is connected, by a tube and cork 
 
 Fig. 126. Carre's freezing apparatus. 
 
COMBUSTION OF AMMONIA IN OXYGEN. 
 
 117 
 
 with an apparatus delivering dry ammonia, prepared by heating 1000 grains of 
 sal-ammoniac with an equal weight of quick-lime in a flask, and passing the gas, 
 first into an empty bottle (A, fig. 128) standing in cold water, and afterwards 
 through a bottle (B) filled with lumps of quick-lime to absorb all aqueous vapour. 
 
 __ 
 
 . Fig. 128. 
 
 Fig. 129. Liquefaction of ammonia. 
 
 The long limb of the tube must be surrounded with filtering paper, which is kept 
 wet with cold water. The current of ammonia should be continued at a moderate 
 rate, until the tube and its contents no longer increase in weight, which will occupy 
 about three hours about 36 grains of ammonia being absorbed. The longer limb 
 is sealed by the blowpipe flame whilst the gas is still passing, and then, as quickly 
 as possible, the shorter limb, keeping that part 
 of the tube which is occupied by the ammoni- 
 ated chloride of silver still carefully surrounded 
 by wet paper. 
 
 When the shorter limb of this tube (fig. 129) 
 is cooled in a mixture of ice and salt (or of 8 
 ounces of sulphate of soda and 4 measured ounces 
 of common hydrochloric acid), whilst the longer 
 limb is gently heated from end to end by waving 
 a spirit flame beneath it, the "ammonia evolved 
 by the heat from the ammoniated chloride 01 
 silver, which partly fuses, will condense into a 
 beautifully clear liquid in the cold limb. When 
 this is withdrawn from the freezing mixture, and the tube allowed to cool, the 
 liquid ammonia will boil and gradually disappear entirely, the gas being again 
 absorbed by the chloride of silver, so that the tube is ready to be used again. 
 
 Ammonia is feebly combustible 
 in atmospheric air, as may be 
 seen by holding a taper just 
 within the mouth of an inverted 
 bottle of the gas, which burns 
 with a peculiar livid flickering 
 light around the flame, but will 
 not continue to burn when the 
 flame is removed. During its 
 combustion the hydrogen is con- 
 verted into water, and the nitro- 
 gen set free. In oxygen, how- 
 ever, ammonia burns with a 
 continuous flame. 
 
 This is very well shown by sur- 
 rounding a tube delivering a stream 
 
 of ammonia (obtained by heating strong solution of ammonia in. a retort) with a 
 much wider tube open at both ends (fig. 130), through which oxygen is passed by 
 
118 
 
 AMMONIUM THEORY. 
 
 holding the flexible tube from a gas-bag or gas-holder underneath it. On kindling 
 the stream of ammonia it will give a steady flame of ten or twelve inches long. x 
 A similar experiment may be made with a smaller supply of oxygen, by lowering 
 
 the tube delivering ammonia into a 
 bottle or jar of oxygen, and apply- 
 ing a light to it just as it enters the 
 mouth of the jar (fig. 131). 
 
 The elements of ammonia are 
 easily separated from each other 
 by passing the gas through a red- 
 hot tube, or still more readily 
 by exposing it to the action of 
 the high temperature of the elec- 
 tric spark, when the volume of 
 the gas rapidly increases until 
 it is exactly doubled, one volume 
 of ammonia being decomposed 
 volume of nitrogen and f volumes of hydrogen. 
 
 Fig. 131. 
 
 into 
 
 For this experiment a measured volume of ammonia gas is confined over mercury 
 (fig. 132), in a tube through which platinum wires are sealed for the passage of the 
 spark from an induction-coil. The volume of the gas 
 is doubled in a few minutes, and if the tube be fur- 
 nished with a stop-cock (A), the presence of free hydrogen 
 may be shown by filling the open limb with mercury and 
 kindling the gas as it issues from the jet.* 
 
 As might be expected from its powerfully alka- 
 line character, ammonia exhibits a strong attrac- 
 tion for acids, which it neutralises perfectly. If 
 a bottle of ammonia gas, closed with a glass plate, 
 be inverted over a similar bottle of hydrochloric 
 acid gas, and the glass plates withdrawn (fig. 133), 
 the gases will combine, with disengagement of 
 much heat, forming a white solid, the hydrochlorate 
 of ammonia (NH 3 . HC1), in which the acid and 
 alkali have neutralised each other. Again, if 
 ammonia be added to diluted sulphuric acid, 
 the latter will be entirely neutralised, and by 
 evaporating the solution, crystals of the sul- 
 phate of ammonia (NH 3 . HO . S0 3 ) may be 
 obtained. 
 
 The substances thus produced by neutralising 
 the acids with solution of ammonia bear a strong 
 
 resemblance to the salts formed by neutralising the same acids with solu- 
 tions of potash and soda, a circumstance which would encourage the 
 idea that the solution of ammonia must contain an alkaline oxide similar 
 to potash or soda. 
 
 Berzelius was the first to make an experiment which appeared strongly 
 to favour this view (commonly spoken of as the ammonium theory of 
 Berzelius). The negative pole of a galvanic battery was placed in con- 
 
 * The eudiometer for passing electric sparks in rapid succession must have the platinum 
 wires passed through the glass as shown in fig. 132, or it will be cracked by the heat of 
 the sparks. The outlet tube B, closed by a small screw clamp C, pinching a caoutchouc 
 connector, allows the mercury to be drawn off when necessary, to equalise the level in the 
 two limbs. 
 
 Fig. 132. 
 
EQUIVALENT OF AMMONIA. 119 
 
 tact with mercury at the bottom of a vessel containing a strong solution of 
 ammonia, in which the positive pole of the battery was immersed. Oxygen 
 was disengaged at this pole, whilst the mer- 
 cury in contact with the negative pole swelled 
 to four or five times its original bulk, and 
 became a soft solid mass, still preserving, 
 however, its metallic appearance. So far, 
 the result of the experiment resembles that 
 obtained when hydrate of potash is decom- 
 posed under similar circumstances, the oxygen 
 separating at the positive pole, and the potas- 
 sium at the negative, where it combines with 
 the mercury. Beyond this, however, the 
 analogy does not hold ; for in the latter case Fi 133 
 
 the metallic potassium can be readily separ- 
 ated from the mercury, whilst in the former, all attempts to isolate the 
 ammonium have failed, for the soft solid mass resolves itself, almost 
 immediately after its preparation, into mercury, ammonia (NH 3 ), and 
 hydrogen, one equivalent of the latter being separated for each equivalent 
 of ammonia. This would also tend to support the conclusion, that a sub- 
 stance having the composition NH 3 + H or NH 4 had united with the 
 mercury ; and since the latter is not known to unite with any non-metallic 
 substance without losing its metallic appearance, it would be fair to con- 
 clude that the soft solid was really an amalgam of ammonium. How- 
 ever, the increase in the weight of the mercury is so slight, and the 
 "amalgam," whether obtained by this or by other methods, is so unstable, 
 that it would appear safer to attribute the swelling of the mercury to a 
 physical change caused by the presence of the ammonia and hydrogen 
 gases. It is difficult to believe that the solution of ammonia does really 
 contain an oxide of ammonium (NH 4 0), when we find it evolving 
 ammonia so easily; but it is equally difficult, upon any other hypo- 
 thesis, to explain the close resemblance between the salts obtained by 
 neutralising acids with this solution, and those furnished by potash and 
 soda. 
 
 The ordinary mode of exhibiting the production of the so-called amalgam of ammo- 
 nium consists in acting upon the hydrochlorate of ammonia (NH 3 . HC1), or chloride of 
 ammonium (NH 4 C1), with the amalgam of sodium. A little pure mercury is heated 
 in a test-tube, and a pellet of sodium thrown into it, when combination takes place 
 with great energy. When. the amalgam is nearly cool it may be poured into a 
 larger tube containing a moderately strong solution of chloride of ammonium ; the 
 amalgam at once swells to many times its former bulk, forming a soft, solid sub- 
 stance lighter than water, which may be shaken out of the tube as a cylindrical 
 mass, decomposing rapidly with effervescence, evolving ammonia and hydrogen, and 
 soon recovering its original volume and liquid condition. 
 
 87. Combining weight and volume of ammonia. It is found by experi- 
 ment that one combining weight (3 6 '5 grains) of hydrochloric acid requires 
 1 7 grains of ammonia to effect complete neutralisation by combining with 
 it to form hydrochlorate of ammonia. This result being confirmed by 
 observations upon other acids, 1 7 is regarded as representing the combin- 
 ing weight (or equivalent) of ammonia. This quantity of the gas occupies 
 four times the volume of 8 parts by weight (one equivalent) of oxygen, so 
 that if this gas be taken as the unit of volume, the combining volume of 
 ammonia will be 4. Since the 1 7 parts by weight of ammonia occupy 
 twice the volume of one part by weight (one equivalent) of hydrogen, if 
 
120 
 
 COMPOSITION OF AMMONIA. 
 
 that gas be taken as the unit of volume, the combining volume of ammonia 
 will be 2. 
 
 88. Combining weight and volume of nitrogen. 17 grains of ammonia 
 have been proved to contain 14 grains of nitrogen combined with 3 
 grains of hydrogen. The latter gas being taken as the unit of combin- 
 ing weights, the 3 grains would represent 3 combining weights* of hydro- 
 gen, and the question arises, How many combining weights of nitrogen 
 are represented by the 14 grains 1 On referring to the composition of 
 ammonia by volume, we find that it furnishes three volumes of hydrogen 
 for one volume of nitrogen when decomposed by the electric spark 
 (p. 118), and hence it seems reasonable to conclude that it contains 
 one combining weight of nitrogen (14) and three combining weights of 
 hydrogen (3), when the combining volume of nitrogen (or the volume 
 occupied by its combining weight) will be equal to that of hydrogen. 
 
 It will also be seen hereafter that the hydrogen in ammonia can be 
 replaced by other bodies in thirds, showing that there must be three 
 atoms of hydrogen present, whilst the 14 parts of nitrogen cannot be 
 replaced in fractions, so that it must represent a single atom. 
 
 The composition of ammonia by weight and volume is exhibited in the 
 following table : 
 
 
 
 = 1 vol. 
 
 H = 1 vol. 
 
 Parts by weight. 
 
 Nitrogen . . . 
 Hydrogen . . . 
 
 Ammonia . . . 
 
 1 equivt. 
 3 equivts. 
 
 2 vols. 
 6 vols. 
 
 1 vol. 
 3 vols. 
 
 14 
 3 
 
 1 equivt. 
 
 4 vols. 
 
 2 vols. 
 
 17 
 
 It will be seen that the atomic or molecular formula of ammonia, based 
 upon the assumption that one volume of an element in the gaseous state 
 represents one atom, coincides with its equivalent formula. 
 
 89. Determination of nitrogen in organic substances. An exact know- 
 ledge of the composition of ammonia is of great importance, because the 
 general method of ascertaining the proportion of nitrogen present in animal 
 and vegetable substances consists in converting that element into ammonia, 
 which, being collected and weighed, furnishes by calculation the weight of 
 nitrogen present. 
 
 To ascertain the proportion of nitrogen present in an organic substance, a weighed 
 
 quantity of it is mixed with a 
 large proportion of soda-lime (a 
 mixture of hydrate of soda and 
 hydrate of lime), and introduced 
 into a tube of German glass (A, 
 fig. 134) to which is attached, by 
 a perforated cork, abulb apparatus 
 (B) containing hydrochloric acid. 
 On heating the tube inch by inch 
 with a charcoal or gas furnace, 
 the nitrogen of the substance is 
 evolved in combination with the hydrogen of the hydrates, in the form of ammonia, 
 which is absorbed by the hydrochloric acid in the bulbs. When the whole length 
 of the tube has been heated, the point (C) is nipped off, and air drawn through by 
 applying suction to the orifice (D) of the bulb apparatus, so that all the ammonia 
 may be carried into the hydrochloric acid. Its weight is then ascertained, either by 
 
 Fig. 134. Estimation of nitrogen. 
 
CALCULATION OF FOEMUL^E. 121 
 
 evaporating the liquid in a weighed dish placed over a steam bath, and weighing the 
 hydrochlorate of ammonia, or more accurately by converting it into the double 
 chloride of platinum and ammonium. Sometimes a solution of sulphuric acid of 
 known strength is substituted for the hydrochloric acid in the bulbs, and the 
 weight of the ammonia is ascertained by determining the quantity of acid which 
 has been neutralised. 
 
 To illustrate the change which takes place when the organic substance is heated 
 with the hydrates of soda and lime, let it be supposed that urea is the substance sub- 
 mitted to analysis. 
 
 'C 2 H 4 N 2 2 + NaO.HO + CaO.HO = NaO.C0 2 + CaO.C0 2 + 2NH 3 
 Urea. 
 
 The hydrate of soda alone would produce the same result, but would corrode the 
 glass too rapidly. 
 
 In the analysis of an organic substance containing carbon, hydrogen, 
 nitrogen, and oxygen, the proportions of carbon and hydrogen having been 
 ascertained by the method described at p. 73, and that of nitrogen by the 
 process given above, the sum of the carbon, hydrogen, and nitrogen is 
 deducted from the entire weight of the substance to obtain the proportion 
 of oxygen. The weights thus found are divided by the combining weights 
 of the several elements to obtain the empirical formula, which is converted 
 into a rational formula on the principle illustrated at p. 75. 
 
 For example, 10 grs. of urea were found to contain 2 grs. of carbon, 0'66 
 gr. of hydrogen, and 4 '6 7 grs. of nitrogen. 
 
 10 grs. of urea minus 7 '33 (carbon, hydrogen, and nitrogen) = 2*67 grs. 
 of oxygen. 
 
 Dividing each of these numbers by the combining weight of the ele- 
 ment to which it refers, we have, 
 
 2-0 -4- 6 = '3 3 of a combining weight of carbon, 
 
 0-66 -4- 1 = 0-66 - hydrogen, 
 
 4-67 - 14 - 0-33 nitrogen, 
 
 2-67 - 8 - 0-33 oxygen, 
 
 leading to the empirical formula C 33 H 66 N 33 33 , or in its simplest form, 
 CH 2 NO, for urea. But urea is an organic base, capable of uniting with 
 acids to form salts, and it is found that to neutralise one combining 
 weight (36 '5 parts) of hydrochloric acid, 60 parts of urea are necessary. 
 This quantity would contain 1 2 parts (two combining weights) of carbon, 
 4 parts (four combining weights) of hydrogen, 28 parts (two combining 
 weights) of nitrogen, and 16 parts (two combining weights) of oxygen, so 
 that the true formula for urea would be C 2 H 4 N 2 2 . 
 
 90. Formation of ammonia in the rusting of iron. Although free 
 nitrogen and hydrogen cannot be made to form ammonia by direct com- 
 bination, this compound is produced when the nitrogen meets with 
 hydrogen in the nascent state; that is, at the instant of its liberation from 
 a combined form. Thus, if a few iron filings be shaken with a little water 
 in a bottle of air, so that they may cling round the sides of the bottle, and 
 a piece of red litmus paper be suspended between the stopper and the neck, 
 it will be found to have assumed a blue colour in the course of a few hours, 
 and ammonia may be distinctly detected in the rust which is produced. 
 It appears that the water is decomposed by the iron, in the presence of the 
 carbonic acid of the air and water, and that the hydrogen liberated enters 
 at once into combination with the nitrogen, held in solution by the water, 
 to form ammonia. 
 
122 
 
 OXIDATION OF AMMONIA. 
 
 91. Production of nitrous and nitric acids from ammonia. If a few drops 
 of a strong solution of ammonia be poured into a pint bottle, and ozonised 
 air (from the tube for ozonising by induction, fig. 10) be passed into the 
 bottle, thick white clouds will speedily be formed, consisting of nitrite of 
 ammonia, the nitrous acid having been produced by the oxidation of the 
 ammonia at the expense of the ozonised oxygen 
 
 2NH 3 
 
 6 = 
 
 ]STH 3 .HO.N0 3 
 
 Nitrite of ammonia. 
 
 2HO 
 
 If copper filings be shaken with solution of ammonia in a bottle of air, 
 white fumes will also be produced, together with a deep blue solution 
 containing oxide of copper and nitrite of ammonia ; 
 the act of oxidation of the copper appearing to have 
 induced a simultaneous oxidation of the ammonia. 
 
 A coil of thin platinum wire made round a pencil, 
 if heated to redness at the lower end and suspended 
 in a flask (fig. 135) with a little strong ammonia at 
 the bottom, will continue to glow for a great length 
 of time, in consequence of the combination of the 
 ammonia with the oxygen of the air taking place at 
 its surface, attended with great evolution of heat. 
 Thick white clouds of nitrite of ammonia are formed, 
 
 Fig. 135. 
 
 and frequently red vapour of nitrous acid (N0 3 ) itself. 
 
 If a tube delivering oxygen gas be passed down to the bottom of the flask (fig. 
 136), the action will be far more energetic, the heat of the platinum rising to white- 
 ness, when an explosion of the mixture of ammonia and 
 oxygen will ensue. After the explosion the action will 
 recommence, so that the explosion will repeat itself as often 
 as may be wished. It is unattended with danger if the 
 mouth of the flask be pretty large. By regulating the 
 stream of oxygen, the bubbles of that gas may be made -to 
 burn as they pass through the ammonia at the bottom of 
 the flask. 
 
 In the presence of strong bases, and of porous 
 materials to favour oxidation, ammonia appears to 
 be capable of suffering further oxidation and conver- 
 sion into nitric acid, which combines with the base 
 
 Fig. 136. 
 
 to form a nitrate, thus 
 
 CaO 
 
 + O 8 - CaO.NO. + 3HO 
 
 Nitrate of lime. 
 
 This formation of nitrates from ammonia is commonly referred to as 
 nitrification, and appears to play an important part in the formation of 
 the natural supplies of saltpetre which are of so great importance to the 
 arts.* 
 
 COMPOUNDS OF NITROGEN AND OXYGEN. 
 
 92. Though these elements in their pure state exhibit no attraction for 
 each other, five compounds, which contain them in different proportions, 
 have been obtained by indirect processes. The relative proportions of 
 
 * The charcoal which has been used in the sewer ventilators (see p. 59) has been found to 
 contain abundance of nitrates. 
 
FORMATION OF NITRIC ACID. 
 
 123 
 
 oxygen in these compounds are exhibited in the following table, where 
 the weight of nitrogen present is supposed to remain constant : 
 
 Oxides of Nitrogen. 
 
 Name. 
 
 Equivalent 
 
 By Weight. 
 
 
 Formula. 
 
 
 
 
 
 N 
 
 
 
 Nitrous oxide . 
 
 NO 
 
 14 
 
 8 
 
 Nitric oxide 
 
 NO, 
 
 14 
 
 16 
 
 Nitrous acid 
 
 N0 3 
 
 14 
 
 24 
 
 Nitric peroxide 
 
 N0 4 
 
 14 
 
 32 
 
 Nitric acid . . 
 
 N0 5 
 
 14 
 
 40 
 
 When a succession of strong electric sparks from the induction coil is 
 passed through atmospheric air in a flask (especially if the air be mixed 
 with oxygen), a red gas is formed in small quantity, which is either nitrous 
 acid (N0 3 ) or nitric peroxide (N0 4 ). 
 
 If the experiment be made in a graduated eudiometer (fig. 137), standing over 
 water coloured with blue litmus, the latter will very soon be reddened by the acid 
 formed, and the air will be found to diminish very considerably in 
 volume, eventually losing its power of supporting combustion, in 
 consequence of the removal of oxygen. 
 
 When hydrogen gas, mixed with a small quantity of 
 nitrogen, is burnt, the water collected from it is found to 
 have an acid taste and reaction, due to the presence of a 
 little nitric acid, resulting from the combination of the 
 nitrogen with the oxygen of the air under the influence of 
 the intense heat of the hydrogen flame. 
 
 Since all the compounds of nitrogen and oxygen are ob- 
 tained, in practice, from hydrated nitric acid (HO . N0 5 ), 
 the chemical history of that substance must precede that 
 of the bodies enumerated in the above table. 
 
 Fig. 137. 
 
 NITRIC ACID. 
 
 93. This most important acid is obtained from saltpetre, which is found 
 as an incrustation upon the sur- 
 face of the soil in hot and dry 
 climates, as in some parts of 
 India and Peru. The salt im- 
 ported into this country from 
 Bengal and Oude consists of 
 nitrate of potash (KO . N0 6 ), 
 whilst the Peruvian or Chilian 
 saltpetre is nitrate of soda 
 (NaO . N0 5 ). Either of these 
 will serve for the preparation 
 of nitric acid. 
 
 Fig. 138. Preparation of nitric acid. 
 
 On the small scale, in the laboratory, nitric acid is prepared by distilling 
 nitrate of potash with an equal weight of concentrated sulphuric acid. 
 
124 
 
 PREPARATION OF NITRIC ACID. 
 
 In order to make the experiment, four ounces of powdered nitre, thoroughly dried, 
 may be introduced into a pint-stoppered retort (fig. 138), and two and a half mea- 
 sured ounces of concentrated sulphuric acid poured upon it. As soon as the acid 
 has soaked into the nitre, a gradually increasing heat may be applied by means of 
 an Argand burner, when the acid will distil over. It must be preserved in a stop- 
 pered bottle. 
 
 When the acid has ceased distilling, the retort should be allowed to cool, and filled 
 with water. On applying a moderate heat for some time, the saline rcs'idue will be 
 dissolved. The solution may then be poured into an evaporating dish, and evapor- 
 ated down to a small bulk. On allowing the concentrated solution to cool, crystals 
 of bisulphate of potash (KO . HO . 2S0 3 ) are deposited, a salt which is very useful in 
 many metallurgic and analytical operations. 
 
 The decomposition of nitrate of potash by an equal weight of concen- 
 trated sulphuric acid is explained by the equation 
 
 KO . NO B + 2 (HO . S0 3 ) . HO . M) 5 + KO . S0 3 , HO . S0 3 
 
 Nitrate of Hydrated Hydrated 
 
 potash. sulphuric acid. nitric acid. 
 
 Bisulphate of potash. 
 
 It would appear at first sight that one-half of the sulphuric acid might 
 be dispensed with, but it is found that when one equivalent only -of sul- 
 phuric acid is employed, so high a temperature is required to effect the 
 complete decomposition of the saltpetre (the above equation then repre- 
 senting only the first stage of the action), that much of the nitric acid is 
 decomposed; and the neutral sulphate of potash (KO . S0 3 ), which would 
 
 be the final result, is not 
 nearly so easily dissolved 
 out of the retort by water 
 as the bisulphate. 
 
 For the preparation of 
 large quantities of nitric 
 acid, the nitrate of soda 
 is substituted for nitrate 
 of potash, being much 
 cheaper, and furnishing a 
 larger proportion of nitric 
 acid. 
 
 The nitrate of soda is intro- 
 duced into an iron cylinder 
 (A, fig. 139), lined with fire- 
 Fig. 139,-Preparation of nitric acid. ^ io f P rotec * ** fn > m , &* ac ~ 
 
 tion of the acid, and half its 
 
 weight ot sulphuric acid (oil of vitriol) is poured upon it. Heat is then applied by 
 a furnace, into which the cylinders are built, in pairs, when the hydrated nitric acid 
 passes off in vapour, and is condensed in a series of stoneware bottles (B) surrounded 
 with cold water. 
 
 NaO.N0 5 
 
 Nitrate of 
 soda. 
 
 HO . S0 3 
 
 Oil of vitriol. 
 
 = NaO . S0 3 
 Sulphate of 
 soda. 
 
 HO . NO B 
 
 Hydrated 
 nitric acid. 
 
 The sulphate of soda left in the retort is useful in the manufacture of glass. 
 
 In the preparation of nitric acid, it will be observed at the beginning 
 and towards the end of the operation, that the retort becomes filled with a 
 red vapour. This is due to the decomposition of a portion of the colour- 
 less vapour of nitric acid by heat into water, oxygen, and nitric peroxide 
 
 HO. NO. = HO + + NO. 
 
PROPERTIES OF NITRIC ACID. 125 
 
 this last forming the red vapour, a portion of which is absorbed by the 
 hydrated nitric acid, and gives it a yellow colour. The pure nitric acid 
 is colourless, but if exposed to sunlight it becomes yellow, a portion 
 suffering this decomposition. In consequence of the accumulation of the 
 oxygen in the upper part of the bottle, the stopper is often forced out 
 suddenly when the bottle is opened, and care must be taken that drops 
 of this very corrosive acid be not spirted into the face. 
 
 The strongest nitric acid (obtained by distilling perfectly dry nitre 
 with an equal weight of pure oil of vitriol, and collecting the middle 
 portion of the acid separately from the first and last portions, which are 
 somewhat weaker) emits very thick grey fumes when exposed to damp 
 air, because its vapour, though itself transparent, absorbs water very 
 readily from the air, and condenses into very minute drops of diluted 
 nitric acid which compose the fumes. The weaker acids commonly sold 
 in the shops do not fume so strongly. An exact criterion of the strength 
 of any sample of the acid is afforded by the specific gravity, which may 
 be ascertained by the methods described at page 115, using a hydro- 
 meter adapted for liquids heavier than water. Thus, the strongest acid 
 (HO . N0 5 ) has the specific gravity 1*52, and contains 85 '72 per cent., by 
 weight, of N0 5 ;* whilst the ordinary aquafortis or diluted nitric acid has 
 the sp. gr. 1 -29, and contains only 40 per cent, of N0 5 . The concentrated 
 nitric acid usually sold by the operative chemist (double aquafortis) has 
 the sp. gr. 1'42, and contains 58 per cent, of N0 5 . 
 
 A very characteristic property of nitric acid is that of staining the skin 
 yellow. It produces the same effect upon most animal and vegetable 
 matters, especially if they contain nitrogen. The application of this in 
 dyeing silk of a fast yellow colour may be seen by dipping a skein of 
 white silk in a warm mixture of concentrated nitric acid with an equal 
 volume of water, and afterwards immersing it in dilute ammonia, which 
 will convert the yellow colour into a brilliant orange. When sulphuric 
 or hydrochloric acid is spilt upon the clothes, a red stain is produced, and 
 a little ammonia restores the original colour ; but nitric acid stains are 
 yellow, and ammonia intensifies instead of removing them, though it pre- 
 vents the cloth from being eaten into holes. 
 
 Nitric acid changes most organic colouring matters to yellow, but, unless 
 very concentrated, it merely reddens litmus. If solutions of indigo and 
 litmus are warmed in separate flasks, and a little nitric acid added to each, 
 the indigo will become yellow and the litmus red, Here the indigo 
 (C 16 H 5 N0 2 ) acquires oxygen from the nitric acid, and is converted into 
 isatine (C 16 H 5 N0 4 ). 
 
 When hydrated nitric acid is heated, it begins to boil at 184 F., but 
 it cannot be distilled unchanged, for a considerable quantity is decom- 
 posed into nitric peroxide, oxygen, and water, the two first passing off in 
 the gaseous form, whilst the water remains in the retort with the nitric 
 acid, which thus becomes gradually more and more diluted, until it con- 
 tains 68 per cent, of HO . NO., when it passes over unchanged at the 
 temperature of 248 F. The specific gravity of this acid is 1 '42. If an 
 acid weaker than this be submitted to distillation, water will pass off' 
 until acid of this strength is obtained, when it distils over unchanged. 
 
 The facility with which hydrated nitric acid parts with a portion of its 
 
 * It is extremely difficult to obtain the HO . NO S free from any extraneous water, as it 
 undergoes decomposition not only when vaporised at the boiling point, but even at ordinary 
 temperatures. 
 
126 ACTION OF NITRIC ACID UPON METALS. 
 
 oxygen, renders it very valuable as an oxidising agent. Comparatively 
 few substances which are capable of forming compounds with oxygen can 
 escape oxidation when treated with nitric acid. 
 
 A small piece of phosphorus dropped into a porcelain dish containing 
 the strongest nitric acid (and placed at some distance to avoid danger), 
 soon begins to act upon the acid, generally with such violence as to burst 
 out into flame, and sometimes to shatter the dish; the result of this action 
 is hydrated phosphoric acid, the same compound which is formed in the 
 anhydrous state, when phosphorus is burnt in oxygen gas. 
 
 When sulphur is heated with nitric acid, it is actually oxidised to a 
 greater extent than when burnt in pure oxygen, for in this case it is con- 
 verted into sulphurous acid (S0 2 ), whilst nitric acid imparts to it three 
 equivalents of oxygen, forming sulphuric acid (S0 3 ). 
 
 Charcoal, which is so unalterable by most chemical agents at the 
 ordinary temperature, is oxidised by nitric acid. If a mixture of the 
 strongest nitric acid with half its volume of fuming (Nordhausen) sul- 
 phuric acid be poured upon finely powdered charcoal, the latter takes fire 
 at once. A stick of charcoal dipped into this mixture will take fire after 
 a few seconds. 
 
 Even iodine, which is not oxidised by free oxygen, is converted into 
 iodic acid (I0 5 ) by nitric acid. 
 
 It not unfrequently happens in this manner that oxygen, in a state of 
 unstable combination, is more prone to unite with other substances than 
 when it is in a free state. It would seem that the disposition to com- 
 bination having been once impressed upon it is retained, so as to facilitate 
 its union with other bodies. 
 
 But it is especially in the case of metals that the oxidising powers of 
 nitric acid are called into useful application. 
 
 Acids are not capable of uniting with metals, but only with their oxides. 
 Hence, when a metal is dissolved by any oxygen-acid, the latter must 
 first convert the metal into an oxide, which then combines with the acid 
 to form a salt. 
 
 If a little black oxide of copper be heated in a test-tube with nitric 
 acid, it dissolves, without evolution of gas, yielding a blue solution, which 
 contains the nitrate of copper, or, to speak correctly, the nitrate of oxide 
 of copper. In this case the oxide of copper has simply displaced the 
 water of the hydrated acid 
 
 CuO + HO . N0 5 = HO + CuO . N0 5 
 
 Oxide of copper. Nitrate of copper. 
 
 But when nitric acid is poured upon metallic copper (copper turnings), 
 a very violent action ensues, red fumes are abundantly evolved, and the 
 metal dissolves in the form of nitrate of copper 
 
 4(HO.N0 5 ) + Cu 3 - 3(CuO.N0 5 ) + 4HO + N0 2 
 
 Nitrate of copper. Nitric oxide. 
 
 The nitric oxide itself is colourless, but as soon as it comes into contact 
 with the oxygen of the air, it is converted into the red nitric peroxide 
 
 T0 2 + 2 - N0 4 
 
 All the metals in common use are acted upon by nitric acid, except 
 gold and platinum, so that this acid is employed to distinguish and 
 separate these metals from others of less value. The ordinary ready 
 method of ascertaining whether a trinket is made of gold consists in 
 
NASCENT STATE OF ELEMENTS. 127 
 
 touching it with, a glass stopper wetted with nitric acid, which leaves 
 gold untouched, but colours base alloys blue, from the formation of 
 nitrate of copper. The touch-stone allows this mode of testing to be 
 applied with greater accuracy. It consists of a species of black basalt, 
 obtained chiefly from Silesia. If a piece of gold be drawn across its sur- 
 face a golden streak is left, which is not affected by moistening with 
 nitric acid; whilst the streak left by brass, or any similar base alloy, 
 would be rapidly dissolved by the acid. Experience enables an operator 
 to determine by means of the touch-stone pretty nearly the amount of 
 gold present in the alloy, comparison being made with the streaks left by 
 alloys of known composition. 
 
 Though all the metals in common use, except gold and platinum, are oxidised by 
 nitric acid, they are not all dissolved; there are two metals, tin and antimony, which 
 are left by the acid in the state of insoluble oxides, which possess acid properties, 
 and do not unite with the nitric acid. 
 
 If some concentrated nitric acid be poured upon tin filings, no action will be 
 observed;* but on adding a little water, red fumes will be evolved in abundance, 
 and the tin will be converted into a white powder, which is the binoxide of tin 
 (Sn0 2 ), putty powder. The gas which is evolved in this case is the nitric peroxide 
 (NOj, and the action of the acid is represented by the equation which follows : 
 
 2(HO . N0 5 ) + Sn = Sn0 2 + 2HO + 2N0 4 
 
 If the white mixture of binoxide of tin with nitric acid be made into a paste with 
 slaked lime, the smell of ammonia will be exhaled ; and experiments with other 
 metals have shown it to be a general principle, that when any metal capable of 
 decomposing water is dissolved in diluted nitric acid, ammonia is always formed, its 
 quantity increasing with the degree of dilution of the nitric acid ; of course, the 
 ammonia combines with the excess of acid present to form nitrate of ammonia, and 
 the lime was added in the above experiment in order to displace the ammonia from 
 its combination, and to exhibit its odour. This conversion of nitric acid into 
 ammonia becomes the more interesting when it is remembered that the ammonia 
 can be reconverted into nitric _acid (p. 122). 
 
 By dissolving zinc in very diluted nitric acid, a very large quantity of ammonia 
 may be obtained. The change is easily followed if we suppose the nascent hydrogen 
 (or hydrogen with the tendency to combination still remaining impressed upon it, 
 see p. 126), produced by the action of the zinc upon the water, to act upon the nitric 
 acid, converting its oxygen into water, and its nitrogen into ammonia, thus 
 N0 5 + H 8 = 5HO + NH 3 . The exalted attractions possessed by substances in 
 the nascent state, that is, at the instant of their passing from a state of combination, 
 are very remarkable, and will be found to receive frequent application.^ 
 
 Action of nitric acid upon organic substances. The oxidising action 
 of nitric acid upon some organic substances is so powerful as to be 
 attended with inflammation; if a little of the strongest nitric acid be 
 placed in a porcelain capsule, and a few drops of oil of turpentine be 
 poured into it from a test-tube fixed to the end of a long stick, the tur- 
 pentine takes fire with a sort of explosion. By boiling some of the 
 strongest acid in a test-tube (fig. 140), the mouth of which is loosely 
 
 * It is a fact which has scarcely been explained in a satisfactory manner, that the con- 
 centrated nitric acid often refuses to act upon metals which are violently attacked by the 
 diluted acid. 
 
 f When a solution of nitrate of potash is mixed with a strong solution of caustic potash, 
 and heated with granulated zinc and clean iron filings, ammonia is abundantly disengaged, 
 being produced from the nitric acid by the nascent hydrogen resulting from the electro- 
 lytic action. 
 
 Recent experiments have indicated the existence of substances intermediate between 
 the nitric acid and the ammonia into which it is finally converted. One of these, named 
 hydroxylamine, NH 3 0,,, has been examined. It is a well-defined base, forming crystalline 
 salts with the acids. 
 
128 EQUIVALENT OF NITRIC ACID. 
 
 stopped with a plug of raw silk or of horse-hair, the latter may be made 
 to take fire and bum brilliantly in the vapour of nitric acid. 
 
 In many cases the products of the action of nitric acid exhibit a most 
 interesting relation to the substances from which they have been pro- 
 duced, one or more equivalents of the hydrogen 
 of the original compound having been removed 
 in the form of water by the oxygen of the nitric 
 acid, whilst the spaces thus left vacant have been 
 filled up by the nitric peroxide resulting from 
 the deoxidation of the nitric acid, producing 
 what is termed a nitro-substitution compound. 
 A very simple example of this displacement of 
 H by N0 4 is afforded by the action, of nitric 
 acid upon benzole. A little concentrated nitric 
 acid is placed in a flask, and benzole cautiously 
 dropped into it ; a violent action ensues, and the 
 acid becomes of a deep red colour ; if the contents of the flask be now 
 poured into a large vessel of water, a heavy yellow oily liquid is separated, 
 having a powerful odour like that of bitter almond oil. This substance, 
 which is used to a considerable extent in perfumery under the name of 
 essence of mirbane, is called nitro-benzole, and its formula, C 12 H 5 (N0 4 ), at 
 once exhibits its relation to benzole, C 12 H 6 .* 
 
 But the change does not stop here, for by continuing the action of the 
 acid, dinitro-benzole C 12 H 4 2(N0 4 ) is obtained, in which two equivalents of 
 hydrogen have been displaced by nitric peroxide. 
 
 It is by an action of this description that nitric acid gives rise to gun- 
 cotton, and other explosive substances of the same class, when acting upon 
 the different varieties of woody fibre, as cotton, paper, sawdust, &c. 
 
 The preparation and composition of gun-cotton will be described here- 
 after. 
 
 94. The oxidising effects of nitric acid are not confined to the free acid, 
 but are shared to some extent by the nitrates. A mixture of nitrate of 
 lead with charcoal explodes when sharply struck, from the sudden evolu- 
 tion of carbonic acid produced by the oxidation of the carbon. If a few 
 crystals of nitrate of copper be sprinkled with water and quickly wrapped 
 up in tin-foil, the latter will, after a time, be so violently oxidised as to 
 emit brilliant sparks. 
 
 But in the case of bases which retain the nitric acid with greater force, 
 such as the alkalies, the oxidation takes place only at a high tempera- 
 ture. If a little nitre be fused in an earthen crucible or an iron ladle, 
 and, when it is at a red heat, some powdered charcoal, and afterwards 
 some flowers of sulphur, be thrown into it, the energy of the combustion 
 will testify to the violence of the oxidation. In this manner the carbon 
 is converted into carbonate of potash (KO . C0 2 ), and the sulphur into 
 sulphate of potash (KO . S0 3 ). See Gunpowder. 
 
 Combining weight of nitric acid. Experiment proves that 47 parts by 
 weight (1 equivalent) of potash are neutralised by 63 parts of hydrated 
 nitric acid, and this quantity of the acid is found to contain 1 part of 
 hydrogen, 14 parts of nitrogen, and 48 parts (6 equivalents) of oxygen. 
 Hence the formula of the acid might be written H . N"0 6 ; but if it be 
 
 * C 12 H 8 + HO . N0 5 = C^H^NOj + 2HO. 
 C 12 H 6 + 2(HO.N0 6 ) = C 12 H,2(N0 4 ) + 4HO. 
 
NITHIC ANHYDRIDE. 
 
 129 
 
 desired to represent in the formula the mode in which the elements are 
 grouped, the acid may be represented as composed of water combined with 
 the anhydrous nitric acid (HO . N0 5 ). 
 
 The unitary (molecular) formula of nitric acid is commonly written 
 HNe 3 (e = 16). 
 
 Nitrates. Its attraction for bases places nitric acid among the strongest 
 of the acids, though the disposition of its elements to assume the gaseous 
 state at high temperatures, conjoined with the feeble attraction existing 
 between nitrogen and oxygen, causes its salts to be decomposed, without 
 exception, by heat. 
 
 The nature of the decomposition varies with the base contained in the 
 nitrate. The nitrates of very powerful bases (such as the alkalies) are 
 first converted into nitrites by the action of heat ; thus KO . N0 5 gives 
 KO . N0 3 and 2 ; the nitrites themselves being eventually decomposed, 
 evolving nitrogen and oxygen, and leaving the uncombined base. The 
 nitrates of feebler bases (such as oxide of copper and oxide of lead) evolve 
 nitric peroxide (N0 4 ) and oxygen, the base being left, unless it be decom- 
 posible by heat, as is the case with the oxides of silver and mercury, when 
 the metal itself will be separated. As a general rule, the nitrates are 
 easily soluble in water. 
 
 Comparatively few of the nitrates are in common use ; the following 
 table contains those most frequently used : 
 
 Chemical Name. 
 
 Common Name. 
 
 Equivalent Formula. 
 
 Atomic Unitary 
 Formula. 
 
 Nitrate of pot- 
 ash 
 
 > Nitre, saltpetre 
 
 KO . N0 5 
 
 KN0 3 
 
 Nitrate of soda 
 
 f Cubic nitre ) 
 1 Peruvian saltpetre \ 
 
 NaO . N0 5 
 
 NaN0 3 
 
 Nitrate of stron- 
 tia 
 
 \ Nitrate of strontian 
 
 SrO . N0 5 
 
 SrNO 3 
 
 Basic nitrate of 
 bismuth 
 
 ( Trisnitrate of bis- \ 
 \ muth 
 I Flake white 
 
 Bi0 3 . N0 5 . HO 
 
 2BiNO 4 , H 2 O 
 
 Nitrate of silver 
 
 Lunar caustic 
 
 AgO.N0 5 
 
 AgN0 3 
 
 95. Anhydrous nitric acid or nitric anhydride is obtained by gently heating nitrate 
 of silver in a slow current of chlorine, great care being taken to exclude every trace 
 of water 
 
 AgO.N0 5 
 
 Cl 
 
 = AgCl + 
 Chloride of silver. 
 
 + N0 6 
 
 Nitric anhydride. 
 
 The anhydride is condensed as a crystalline solid in a receiver cooled with ice and 
 salt. It forms transparent colourless prisms which liquefy at 85 F., and boil at 113. 
 By a slightly higher temperature it is readily decomposed ; and it has been said to 
 decompose, even at the ordinary temperature, in sealed tubes which were shattered 
 by the evolved gas. 
 
 When the anhydride is brought in contact with water, much heat is evolved, and 
 hydrated nitric acid is produced. 
 
 The discovery of the anhydrous nitric acid by Deville in 1848, was welcomed by 
 many chemists as a confirmation of that view of the constitution of nitric acid which 
 had been generally received for thirty years, and which represented the acid as a 
 compound of water with N0 5 . The more modern speculative views, however, discard 
 this substance as the true radical of nitric acid and the nitrates, and represent the 
 latter by formulae which disown all connexion with the anhydride. Thus, the mole- 
 
130 
 
 NITROUS AND NITRIC OXIDES. 
 
 cular formula for the anhydride would be written N 2 O 5 , and its action upon water 
 would be N 2 O 5 + H 2 O = 2HNO 3 . 
 
 96. Nitrous oxide or laughing gas is prepared by heating nitrate of am- 
 monia, when it is resolved into water, and nitrous oxide* 
 
 NH 3 .HO.N0 5 = 4HO + 2NO. 
 
 Nitrate of ammonia is obtained by adding fragments of carbonate of ammonia to 
 nitric acidf diluted with an equal volume of water, until the carbonate no longer 
 effervesces in the liquid, which is then evaporated down until a drop solidifies on a 
 cold surface, when the whole may be poured out upon a clean stone, and the mass 
 broken up and preserved in a well-stoppered bottle, because it is liable to attract 
 moisture from the air. To ob- 
 tain the nitrous oxide, an ounce 
 of the salt may be gently heated 
 in a small retort, when it melts, 
 boils, and gradually disappears 
 entirely in theforms of steam and 
 nitrous oxide. The latter may 
 be collected with slight loss over 
 water. 
 
 Nitrous oxide is perfectly 
 colourless, but has a slight 
 odour and a sweetish taste. 
 Its characteristic intoxicat- 
 ing property is well known. 
 It accelerates the combustion 
 of a taper like oxygen itself, 
 
 Fig. 141. 
 
 and will even kindle into flame a spark at the end of a match. It can 
 readily be distinguished from oxygen, however, by shaking it with water, 
 which absorbs, at the ordinary temperature, about three-fourths of its 
 volume of the nitrous oxide. It is also much heavier than oxygen, its 
 specific gravity being 1'53, and is not a permanent gas, being liquefied 
 by a pressure of 40 atmospheres at 45 F., and solidified at 150 F. 
 The liquid nitrous oxide possesses a special interest, for, by mixing it 
 with bisulphide of carbon, and evaporating in vacuo, the lowest tempera- 
 ture hitherto known has been obtained, viz., 220 F. 
 
 97. Nitric oxide or binoxide of nitrogen is usually obtained by the 
 action of copper upon diluted nitric acid 
 
 4(HO.N0 6 ) + Cu 3 = 3(CuO.N0 5 ) 
 
 4HO. 
 
 300 grains of copper turnings or clippings are introduced into a retort, and three 
 measured ounces of a mixture of concentrated nitric acid with an equal volume of 
 water are poured upon them. A very gentle heat may be applied to assist the 
 action, and the gas may be collected over water (see fig. 141), which absorbs the red 
 fumes (N0 4 ) formed by the union of the N0 2 with the air contained in the retort. 
 
 Nitric oxide is distinguished from all other gases by the production of 
 a red gas, when the colourless nitric oxide is allowed to" come in contact 
 with uncombined oxygen, the presence of which, in mixtures of gases, may 
 be readily detected by adding a little nitric oxide. The red gas consists 
 
 * By passing the mixtiire of nitrous oxide and aqueous vapour over hydrate of potash at 
 a dull red heat, nitric acid and ammonia are reproduced. 
 t Which must remain clear when tested with nitrate of silver showin it to be free from 
 
 chlorine. 
 
 must remain clear when tested with nitrate of silver, showing it to be free from 
 
PROPERTIES OF NITRIC OXIDE. 
 
 131 
 
 chiefly of nitric peroxide (N0 4 ), but it often contains also some 
 nitrous acid. 
 
 The combination of nitric oxide with oxygen may be exhibited by decanting a pint 
 bottle of oxygen, under water, into a tall jar filled with water coloured with blue 
 litmus, and adding to it a pint bottle 
 of nitric oxide (fig. 142). Strong 
 red fumes are immediately produced, 
 and on gently agitating the cylin- 
 der, the fumes are absorbed by the 
 water, reddening the litmus. The 
 oxygen will now have been reduced 
 to half its volume, and if another 
 pint of nitric oxide be added, the 
 remainder of the oxygen will be 
 absorbed, showing that two volumes 
 
 of nitric oxide combine with one volume 
 of oxygen, forming the nitric per- 
 oxide which is absorbed by the 
 water. 
 
 The addition of nitric oxide 
 to atmospheric air was one of 
 
 the earliest methods employed Fig. 142. 
 
 for removing the oxygen in 
 
 order to determine the composition of air ; but important variations were 
 observed in the results, in consequence of the occasional formation of N0 3 
 in addition to the N0 4 . 
 
 The rough analysis of air by this method may be instructively performed with two 
 similar gas cylinders, each divided into ten equal volumes. Into one are introduced 
 five volumes of air, and into the other five volumes of nitric oxide. On decanting 
 the air, under water, into the nitric oxide (fig. 143), the red nitric peroxide will be 
 formed and absorbed by the water, the 
 ten volumes of gas shrinking to seven, 
 showing that three volumes have been 
 absorbed, of which one volume would of 
 course represent the oxygen contained 
 in the five volumes of air. 
 
 The nitric oxide prepared by the action 
 of copper on nitric acid generally con- 
 tains nitrous oxide, and will seldom give 
 correct results in the above experiment. 
 Pure nitric oxide may be obtained by 
 heating in a retort 100 grains of nitrate 
 of potash, 1000 grains of sulphate of iron, 
 and three measured ounces of diluted 
 sulphuric acid (containing one measure 
 of acid to three measures of water), which will yield above two pints of the gas.* 
 
 In all its properties, nitric oxide is very different from nitrous oxide. 
 It is much lighter, having almost exactly the same specific gravity as air, 
 viz., 1*04, has never yet been liquefied, and is not dissolved to any impor- 
 tant extent by water. When a lighted taper is immersed in nitric oxide, 
 it is extinguished, although this gas contains twice as much oxygen as 
 nitrous oxide, which so much accelerates the combustion of a taper, for 
 the elements are held together by a stronger attraction in the nitric oxide, 
 so that its oxygen is not so readily available for the support of combus- 
 tion. (The nitric oxide prepared from copper and nitric acid sometimes 
 contains so much nitrous oxide that a taper burns in it brilliantly.) 
 
 143. 
 
 KO. N0 5 + 6(FeO. S0 3 ) + 4(HO. S0 3 ) = KO. S0 3 + 3(Fe 8 O s - 3S0 3 ) 
 
 N0 2 
 i 2 
 
 4HO. 
 
132 ORIGIN OF NITRITES. 
 
 Even phosphorus, when just kindled, is extinguished in nitric oxide, 
 but when allowed to attain to full combustion in air, it burns with 
 extreme brilliancy in the gas. Indeed, nitric oxide appears to be the least 
 easy of decomposition of the whole series of oxides of nitrogen, which 
 accounts for its being the most common result of the decomposition of 
 the other oxides. Mtrous oxide itself, when passed through a red-hot 
 tube, is partly converted into nitric oxide ; and when a taper burns in a 
 bottle of nitrous oxide, the upper part of the bottle is often filled with a 
 red gas, indicating the formation of nitric oxide, and its oxidation by the 
 air entering the bottle. 
 
 The difference in the stability of the two gases is also shown by their 
 behaviour with hydrogen. A mixture of nitrous oxide with an equal 
 volume of hydrogen explodes when in contact with flame, yielding steam 
 and nitrogen, but a mixture of equal volumes of nitric oxide and hydro- 
 gen burns quietly in air, the hydrogen not decomposing the nitric oxide. 
 An excess of hydrogen, however, is capable of decomposing nitric oxide, 
 ammonia and water being formed. 
 
 If two volumes of nitric oxide be mixed with five volumes of hydrogen, and the 
 gas passed through a tube having a bulb filled with platinised asbestos (fig. 144),* 
 
 the mixture issuing from the orifice 
 of the tube will produce the red va- 
 pours by contact with the air, which 
 will strongly redden blue litmus ; but 
 if the platinised asbestos be heated 
 with a spirit-lamp, the hydrogen, en- 
 couraged by the action of the plati- 
 num (91) will decompose the nitric 
 oxide, and strongly alkaline vapours 
 of ammonia will be produced, restor- 
 ing the blue colour to the reddened 
 litmus: N0 2 + H 5 = NH 3 + 2HO. 
 It will be remembered that when 
 oxygen is in excess, ammonia is con- 
 verted, under the influence of plati- 
 num, into water and nitrous acid (91). 
 
 Fig. 144. Mtric oxide is readily absorbed 
 
 by ferrous salts (salts of protoxide 
 
 of iron) with which it forms dark brown solutions. If a little solution of 
 sulphate of iron be shaken in a cylinder of nitric oxide closed with a glass 
 plate, the gas will be immediately absorbed, and the solution will become 
 dark brown. On applying heat, the brown compound is decomposed. 
 A compound of 4 eqs. of ferrous sulphate and 1 eq. of nitric oxide has 
 been obtained in small brown crystals, which lose all their nitric oxide 
 in vacua. 
 
 98. Nitrous add. This acid is said to exist, as nitrite of ammonia, in 
 minute quantity, in rain water, and is occasionally found in combination 
 with alkalies or alkaline earths, in well-waters, where it has probably been 
 formed by the oxidation of ammonia (91). Small quantities of nitrite of 
 ammonia appear to be formed by the combustion in air of gases contain- 
 ing hydrogen, this element uniting with the atmospheric oxygen and 
 nitrogen. 
 
 Nitrous acid may be obtained by heating starch with nitric acid, but 
 the most convenient process consists in gently heating nitric acid (s.p 
 
 * Asbestos which has been wetted with solution of bichloride of platinum, dried, and 
 heated to redness, to reduce the platinum to the metallic state. 
 
NITROUS ACID. 133 
 
 gr. 1 -35) with an equal weight of arsenious acid, and passing the gas, first 
 through a U-tube (fig. 145) surrounded with cold water, to condense un- 
 
 Fig. 145. Preparation of nitrous acid. 
 
 decomposed nitric acid, then through a similar tube containing chloride 
 of calcium, to absorb aqueous vapour, and afterwards into a U-tube sur- 
 rounded with a freezing mixture of ice and salt. Through a small tube 
 opening into the bend of this U-tube, the condensed nitrous acid drops 
 into a tube drawn out to a narrow neck, so that it may be drawn off, and 
 sealed by the blowpipe. 
 
 HO.M) 5 + As0 3 - HO.As0 5 + NO.. 
 
 Arsenious acid. Arsenic acid. 
 
 The nitrous acid is thus obtained as a blue liquid which boils below 
 32 F., becoming converted into a red vapour. Water at about 32 F. 
 dissolves the acid without decomposing it, yielding a blue solution which 
 is decomposed, as the temperature rises, into nitric acid which remains in 
 the liquid, and nitric oxide which escapes with effervescence 
 3M) 3 + HO - HO.M) 5 + 2N0 2 . 
 
 The salts of nitrous acid, or nitrites, are interesting on account of their 
 production from the nitrates by the action of heat (p. 129). 
 
 If nitrate of potash be fused in a fire-clay crucible and heated to redness, it will 
 evolve bubbles of oxygen, and slowly become converted into nitrite of potash 
 (KO . N0 3 ). The heat should be continued until a portion removed on the end of 
 an iron rod, and dissolved in water, gives a strongly alkaline solution. The fused 
 mass may then be poured upon a dry stone, and when cool, broken into fragments 
 and preserved in a stoppered bottle. On heating a fragment of the nitrite of potash 
 with diluted sulphuric acid, red vapours will be disengaged, but these corftain but 
 little nitrous acid, the greater part of which is decomposed by the water into nitric 
 acid and nitric oxide. 
 
 When nitrous acid acts upon ammonia, both compounds suffer decomposition, 
 water and nitrogen being the results 
 
 NH 3 + N0 3 = N 2 + 3HO. 
 
 This is sometimes taken advantage of in preparing nitrogen gas by boiling mixed 
 solutions of sal-ammoniac and nitrite of potash 
 
 NH 3 .HC1 + KO.N0 3 = N 2 + KC1 + 4HO. 
 
 Sal-ammoniac 
 
 In experiments upon organic compounds, nitrous acid is sometimes employed as 
 a convenient agent for effecting simultaneously the removal of three equivalents of 
 hydrogen from a compound, and the insertion of one equivalent of nitrogen. 
 
 When solutions of nitrites are heated in contact with air, they gradually absorb 
 oxygen, becoming converted into nitrates. 
 
134 PROPERTIES OF NITRIC PEROXIDE. 
 
 99. Nitric peroxide, also called hyponitric acid and peroxide of nitrogen 
 or pernitric oxide : formerly known as nitrous acid. By passing a mix- 
 ture of nitric oxide with half its volume of oxygen, free from every trace 
 of moisture, into a perfectly dry tube cooled in a mixture of ice and salt, 
 the dark red gas is condensed into colourless prismatic crystals, which 
 melt at 10 F. into a nearly colourless liquid. This gradually becomes 
 yellow as the temperature rises, and at the ordinary temperature has a 
 deep orange colour. It is very volatile, boiling at 71 F., and being con- 
 verted into a red-brown vapour, which was long mistaken for a permanent 
 gas, on account of the great difficulty of condensing it when once mixed 
 with air or oxygen. Mtric peroxide is also obtained, mixed with one- 
 fourth of its volume of oxygen, by heating the nitrate of lead (fig. 146) 
 
 - PbO + N0 + 0. 
 
 The vapour of nitric peroxide is much heavier than atmospheric air. 
 Its colour varies with the temperature, becoming 
 very dark at 100 F. The smell of the vapour is 
 very characteristic. It supports the combustion of 
 strongly burning charcoal or phosphorus, and 
 oxidises most of the metals, potassium taking fire 
 in it spontaneously. The nitric peroxide must, 
 therefore, rank as a powerful oxidising agent, and 
 it is the presence of this substance in the red fuming 
 nitric acid that imparts to it higher oxidising 
 Fig. 146. Preparation powers than those of the colourless nitric acid. 
 of nitric peroxide. The so-called nitrous acid of commerce is really 
 
 nitric acid holding in solution a large proportion 
 
 of nitric peroxide, and is prepared by introducing sulphur into the retorts 
 containing the mixture of nitrate of soda and sulphuric acid employed in 
 the preparation of the nitric acid, a portion of which is deoxidised and 
 converted into nitric peroxide. Water immediately decomposes the nitric 
 peroxide into nitric oxide and nitric acid 
 2HO = N0 + 
 
 When water is gradually added to liquid nitric peroxide, it effervesces, 
 from escape of nitric oxide, and becomes green, blue, and ultimately colour- 
 less. The production of the green and blue colours appears to be due to 
 the solution of the unaltered N0 4 in the nitric acid produced, and when 
 this is decomposed by an excess of water, the liquid, of course, becomes 
 colourless. If the red nitric acid of commerce be gradually diluted with 
 water, it will be found to undergo similar changes, always becoming- 
 colourless at last. The nitric acid which has been used in a Grove's battery 
 always has a green colour from the large amount of nitric peroxide which 
 has accumulated in it during the action of the battery, in consequence of 
 the decomposition of the acid by the hydrogen disengaged during the 
 action of the battery; H + HO . N0 5 = 2HO + $T0 4 . If this green 
 acid be diluted with a little water, it becomes blue, and a larger quan- 
 tity of water renders it colourless, causing the evolution of nitric oxide. 
 Similar colours are obtained by passing nitric oxide into nitric acid of 
 different degrees of concentration, apparently because nitric peroxide is 
 formed and dissolved by the acid 
 
 N0 2 + 2(HO.ISr0 5 ) = 3N0 4 4- 2HO. 
 When silver, mercury, and some other metals are dissolved in cold nitric 
 
GENERAL SUMMARY OF OXIDES OF NITROGEN. 135 
 
 acid, a green or blue colour is often produced, leading a novice to suspect 
 the presence of copper, the colour being really caused by the solution in 
 the unaltered nitric acid of the nitric peroxide produced by the deoxida- 
 tion of another portion. 
 
 Nitric peroxide was formerly believed to be an independent acid capable 
 of forming salts. It is true that its vapours have a strongly acid reaction 
 to test-papers, but when brought into contact with bases, it produces a 
 mixture of nitrate and nitrite 
 
 + 2(KO.HO) - KO.N0 5 + KO.N0 3 + 2HO, 
 
 100. General review of the oxides of nitrogen. All the above oxides of 
 nitrogen are directly obtainable from nitric acid by the action of metals ; 
 but since the result of such action varies much with the temperature and 
 state of concentration of the acid, it cannot be depended upon for the 
 preparation of the oxides in a separate state. 
 
 Nitric peroxide is the chief product of the action of tin upon nitric acid 
 
 2(HO.NO a ) 4- Sn - 2HO + 2N0 4 + Sn0 2 . 
 
 Nitrous acid is abundantly formed when silver is acted on by nitric acid 
 
 3(HO.N0 5 ) + Ag 2 - 3HO 4- N0 3 + 2(AgO.N0 5 ). 
 
 Nitric oxide has been shown to be evolved when nitric acid is deoxidised 
 by copper 
 
 4(HO.N0 5 ) + Cu 3 = 4HO + N0 2 + 3(CuO.N0 5 ); 
 
 though, if the acid be concentrated or the temperature high, nitrous oxide 
 and nitrogen are mixed with the nitric oxide. 
 
 Nitrous oxide is given off when zinc is dissolved in nitric acid diluted 
 with ten measures of water 
 
 5(HO.N0 5 ) + Zn 4 = 5HO + NO + 4(ZnO.N0 5 ); 
 
 the nitrous oxide, however, is mixed with nitric oxide. 
 
 Nitric oxide, nitrous acid, and nitric peroxide, are very remarkable for 
 their relations to oxygen. Nitric oxide is one of the very few substances 
 which combine with dry oxygen at the ordinary temperature, and yet the 
 nitric peroxide which is thus produced is very ready to yield its oxygen 
 to other substances. Nitrous acid, as might be expected, is intermediate 
 in this respect, being capable of acting as a reducing agent upon power- 
 fully oxidising substances, and as an oxidising agent upon substances 
 having a great attraction for oxygen. Thus, a solution of nitrite of 
 potash, acidified with sulphuric acid, will bleach permanganate of potash, 
 reducing the permanganic acid (Mn 2 7 ) to manganous oxide (MnO); 
 whilst, if added to sulphate of iron, the nitrite converts the ferrous oxide 
 (FeO) into ferric oxide (Fe 2 O 3 ), and this solution, which was capable of 
 reducing the permanganate of potash before, is now found to be without 
 effect upon it, unless an excess of the nitrite has been added. 
 
 The oxides of nitrogen, as illustrating combination in multiple propor- 
 tions by iceight and volume. In its most general form, the law of multiple 
 proportions may be thus stated. When a substance (A) -combines with 
 another substance (B) in more than one proportion, the quantities of B, 
 which combine with a constant quantity of A, are multiples of the smallest 
 combining quantity of B by some whole number. 
 
 In the oxides of nitrogen this law is exemplified in the simplest form, 
 since the quantities of oxygen which combine with a constant quantity of 
 
136 COMPOSITION BY VOLUME OF OXIDES OF NITROGEN. 
 
 nitrogen, are multiples of the least combining quantity of oxygen by 2, 
 3, 4, and 5 (see table, p. 123). 
 
 It was shown, at p. 120, that there is ground for representing the combining weight 
 of nitrogen as 14, and its combining volume as = 2 (the combining volume of 
 oxygen being = 1). 
 
 When nitrous oxide is passed through a red-hot porcelain tube, its volume is 
 increased by one-half, and the resulting gas is found to be a mixture cf one volume 
 of oxygen and two volumes of nitrogen. Hence it is inferred that, in nitrous oxide, 
 two volumes (representing one combining weight, or 14 parts) of nitrogen are united 
 with one volume (representing one combining weight, or 8 parts) of oxygen, to form 
 two volumes of nitrous oxide (representing 22 parts by weight). But whether this 
 quantity represents one equivalent, or more than one equivalent, of nitrous oxide, 
 cannot be determined by experiment, because this oxide is not known to enter into 
 any sufficiently definite combination with other substances. If the equivalent of 
 nitric acid (N0 5 ) be represented by 54, as deduced from the experiment cited at 
 p. 128, it would appear most convenient to assume the equivalent of nitrous oxide 
 as = 22, since that quantity results from the deoxidation of one equivalent of 
 nitric acid. 
 
 When charcoal is strongly heated in nitric oxide, the volume of the gas remains 
 unchanged ; but it is found, on analysis, to have become converted into a mixture 
 of equal volumes of carbonic acid and nitrogen (N0 2 + C = C0 2 + N). Since 
 one volume of carbonic acid contains one volume of oxygen (page 80), the experiment 
 proves that one volume of oxygen and one volume of nitrogen exist in two volumes 
 of nitric oxide, or that two volumes of nitrogen (representing one combining weight, 
 or 14 parts) are combined with two volumes of oxygen (representing two combining 
 weights, or 16 parts) in four volumes (representing 30 parts by weight) of nitric 
 oxide. The circumstance that this quantity of nitric oxide is capable of forming a 
 definite compound with one equivalent of chlorine, and that it is the quantity 
 resulting from the decomposition of one equivalent of nitric acid, appears to justify 
 the conclusion that the equivalent of nitric oxide is represented by N0 2 = 30 parts 
 by weight = 4 volumes. 
 
 The direct evidence of the composition of nitrous acid is not so satisfactory as 
 that in the two preceding cases. This acid has been obtained, however, by the 
 direct union of one volume of oxygen with four volumes of nitric oxide, leading to 
 the conclusion that it contains N0 3 . Its equivalent has been determined by the 
 analysis of nitrite of silver, which was found to contain, for one equivalent (116 
 parts by weight) of oxide of silver, 38 parts by weight of nitrous acid, representing 
 a compound of 14 parts by weight of nitrogen (or one equivalent = 2 volumes), 
 with 24 parts by weight (or three equivalents = 3 volumes) of oxygen. The 
 volume occupied by the equivalent of nitrous acid in the state of vapour has not 
 yet been ascertained, no accurate determination of the specific gravity of its vapour 
 having been made. 
 
 Nitric peroxide has been analysed by passing the vapour produced from a known 
 weight of the liquid over red-hot metallic copper, which absorbed the oxygen, leaving 
 the nitrogen to be collected and measured. It was thus found that 14 parts by 
 weight (one equivalent rr 2 volumes) of nitrogen were combined with 32 parts by 
 weight (four equivalents = 4 volumes) of oxygen, a result which is confirmed by 
 the direct union of 4 volumes of N0 2 (one equivalent) with 2 volumes of oxygen 
 (two equivalents) to form N0 4 . 
 
 The circumstance that 46 parts by weight of nitric peroxide are capable of dis- 
 placing one equivalent of hydrogen in organic substances (page 128), supports the 
 belief that the formula N0 4 (= 46 by weight) represents the equivalent of nitric 
 peroxide. The results of experiments upon the specific gravity of its vapour have 
 been so unsatisfactory, on account of its variation at different temperatures, that the 
 volume occupied by an equivalent of nitric peroxide can scarcely be said to be 
 satisfactorily established. It is, however, generally believed to represent four 
 volumes (contaiing 2 volumes of nitrogen and 4 volumes of oxygen). 
 
 Nitric anhydride, or anhydrous nitric acid, was analysed by a method similar to 
 that employed for nitric peroxide, and was found to contain 14 parts by weight (one 
 equivalent = 2 volumes) of nitrogen, combined with 40 parts (five equivalents = 5 
 volumes) of oxygen, forming 54 parts of nitric anhydride, the quantity which is 
 united with one equivalent (47 parts) of potasli in nitrate of potash, and which may 
 therefore be taken to represent the equivalent of the anhydride. The volume occu- 
 
ATOMIC FORMULA OF OXIDES OF NITROGEN. 
 
 137 
 
 pied by the equivalent of nitric anhydride in the state of vapour has not been deter- 
 mined, on account of the want of stability of this compound. 
 
 The following table exhibits a general view of the composition and 
 equivalents of the oxides of nitrogen, a note of interrogation (?) being 
 employed to show where the number has been deduced from hypothetical 
 considerations instead of experimental results : 
 
 
 83 
 
 ii 
 
 ii 
 
 g bO 
 
 By Weight. 
 
 li 
 
 By Volume. 
 
 
 II 
 
 
 
 N * 
 
 
 
 1 
 
 N 
 
 
 
 Nitrous oxide, 
 
 NO 
 
 22? 
 
 14 
 
 8 
 
 2? 
 
 2 
 
 1 
 
 Nitric oxide, 
 
 N0 2 
 
 30 
 
 14 
 
 16 
 
 4 
 
 2 
 
 2 
 
 Nitrous acid, 
 
 N0 3 
 
 38 
 
 14 
 
 24 
 
 4? 
 
 2 
 
 3 
 
 Nitric peroxide, 
 
 N0 4 
 
 46 
 
 14 
 
 32 
 
 4? 
 
 2 
 
 4 
 
 Nitric acid, 
 
 N0 5 
 
 54 
 
 14 
 
 40 
 
 4? 
 
 2 
 
 5 
 
 Atomic constitution of the oxides of nitrogen. Assuming that one atom 
 of an elementary substance always occupies one volume, nitrous oxide 
 (containing 2 vols. nitrogen and 1 vol. oxygen) would be represented by 
 the atomic formula N 2 (0 = 16); nitric oxide (containing 1 vol. 
 nitrogen and 1 vol. oxygen), would become NO ; nitrous acid (containing 
 2 vols. nitrogen and three vols. oxygen) would be N 2 3 ; nitric peroxide 
 (containing 1 vol. nitrogen and 2 vols. oxygen), N0 2 ; and anhydrous 
 nitric acid (containing 2 vols. nitrogen and 5 vols oxygen), N 2 5 . These 
 formulae, however, have the disadvantage of wanting that symmetrical re- 
 lation to each other which affords so great assistance in recollecting the 
 composition of such a series of compounds. The symmetry may be pre- 
 served by writing the formula of nitric oxide as a double molecule (4 vols.), 
 and assuming that nitrous acid, nitric peroxide, and nitric acid have really 
 a vapour-density corresponding to a two-volume formula ; thus 
 
 (H = 1 vol.) 
 N 2 = 2 vols. 
 N 2 2 = 4 vols. 
 N 2 
 
 N 2 4 
 
 2 vols.? 
 2 vols.? 
 2 vols.? 
 
 CHLOEINE. 
 
 101. This element is never found in the uncombined state, but is very 
 abundant in the mineral world in the forms of chloride of sodium (common 
 salt) and chloride of potassium. In these forms also it is an important 
 constituent of the fluids of the animal body, but as it is not found in 
 sufficient proportion in vegetable food, or in the solid parts of animal food, 
 a quantity of salt must be added to these in order to form a wholesome 
 diet. Chloride of sodium is indispensable as a raw material for several of 
 the most useful arts, such as the manufactures of soap and glass, bleaching, 
 &c., in fact, it is the source of three of the most generally useful chemical 
 products, viz., chlorine, hydrochloric acid, and soda. 
 
138 
 
 PREPARATION OF CHLORINE. 
 
 About the middle of the seventeenth century, a German chemist named 
 Glauber distilled some common salt with sulphuric acid, and obtained a 
 strongly acid liquid to which he gave the name muriatic acid (from muria, 
 brine) and which was proved to be identical with the acid long known to 
 the alchemists as spirit of salt. The saline mass which was left after the 
 experiment was then termed Glauber's salt, but afterwards received its 
 present name of sulphate of soda. 
 
 It was undoubtedly a natural inference from this experiment that com- 
 mon salt was composed of muriatic acid and soda, and that the sulphuric 
 acid had a greater attraction for the soda than the muriatic acid, which was 
 therefore displaced by it. In accordance with this view, common salt was 
 called muriate of soda, without further question until the year 1810, when 
 the experiments of Davy proved that it was really composed of the two 
 elementary substances, chlorine and sodium, and must therefore be styled, 
 as it now is, chloride of sodium, and represented by the formula Nad. 
 It was further shown by Davy, that the muriatic acid was really composed 
 of chlorine and hydrogen, and that it was, in fact, chloride of sodium 
 (NaCl) in which the sodium had been displaced by hydrogen (HC1). 
 
 Preparation of chlorine. In order to extract chlorine from common 
 salt, it is heated with black oxide of manganese and diluted sulphuric acid ; 
 the acid decomposes the binoxide of manganese, part of the oxygen of 
 which displaces the chlorine from the chloride of sodium, yielding soda 
 which combines with the sulphuric acid, so that the sulphates of soda and 
 manganese are left in solution, and chlorine escapes in the form of gas ; 
 
 NaCl + Mn0 2 + 2(HO. S0 3 ) = KaO. S0 3 
 
 MnO.SO 3 + 
 
 2HO + Cl. 
 
 600 grains of common salt may be mixed with 450 grains of binoxide of manganese, 
 introduced into a retort (fig. 147), and a cold mixture of H oz. by measure of strong 
 sulphuric acid with 4 oz. of water poured upon it. The retort having been well 
 
 Fig. 147. Preparation of chlorine. 
 
 shaken to wet the powder thoroughly with the acid, a very gentle heat is applied, 
 and the gas collected in bottles filled with water and inverted in the pneumatic 
 trough. When the bottles are filled, the stoppers, previously greased, must be in- 
 serted into them under water. The first bottle or two will contain the air from the 
 retort, and will therefore have a paler colour than the pure chlorine afterwards col- 
 lected. It is advisable to keep a jar filled with water standing ready on the shelf of 
 the trough, so that any excess of chlorine may be passed into it instead of being 
 allowed to escape into the air, causing serious inconvenience. The bottles of moist 
 chlorine must always be preserved in the dark. Chlorine may also be conveniently 
 
LIQUEFACTION OF CHLOKINE. 139 
 
 prepared by gently heating 500 grains of binoxide of manganese with 4 oz. (measured) 
 of common hydrochloric acid 
 
 Mn0 2 + 2HC1 = MnCl + 2HO + Cl. 
 Either of the above methods will furnish about five pints of chlorine. 
 
 Properties of chlorine. The physical and chemical properties of chlorine 
 are more striking than those of any element hitherto considered. Its 
 colour, whence it derives its name (xAwpos, pale green) is bright greenish 
 yellow, its odour insupportable. It is twice and a half as heavy as air 
 (sp. gr. 2*4-7), and may be reduced to the liquid state by a pressure of only 
 four atmospheres at 60 F. If a bottle of chlorine be held mouth down- 
 wards in water, its stopper removed, one-third of the 
 chlorine decanted into a jar, and the rest of the gas 
 shaken with the water in the bottle, the mouth of 
 which is closed by the palm of the hand (fig. 148), 
 the water will absorb twice its volume of chlorine, 
 producing a vacuum in the bottle which will be held 
 firmly against the hand by atmospheric pressure. If 
 air be then allowed to enter, and the bottle again 
 shaken as long as any absorption takes place, a satu- 
 rated solution of chlorine (chlorine water) will be Fig< 148 * 
 obtained. By exposing this yellow solution to a temperature approaching 
 32 F., yellow crystals of hydrate of chlorine (Cl + 10 HO) are obtained, 
 the liquid becoming colourless. 
 
 "When the water in the pneumatic trough, over which chlorine is being collected, 
 happens to be very cold, the gas is often so foggy as to be quite opaque, in conse- 
 quence of the deposition of minute crystals of the hydrate. On standing, the gas 
 becomes clear, crystals of the hydrate being deposited like hoar-frost upon the sides 
 of the bottle ; the gas also becomes clear when the bottles are slightly warmed. 
 
 The hydrate of chlorine affords a convenient source of liquid chlorine. A number 
 of bottles of saturated solution of chlorine, prepared as above, are exposed on a cold 
 winter's day until the hydrate has crystallised. The crystals are thrown upon a 
 filter, cooled to nearly 32, allowed to drain, and rammed into a pretty strong tube 
 closed at one end, about twelve inches long, and half an inch in diameter, previously 
 cooled in ice or snow. The tube having been nearly filled with the crystals is kept 
 surrounded with snow, whilst its upper end is gradually softened in the blowpipe flame 
 and drawn off so as to be strongly sealed. When this tube is immersed in warm 
 water, the chlorine separates from the water, and two layers of liquid are formed, the 
 lower one consisting of amber-yellow liquid chlorine (sp. gr. 1-33), and the upper, 
 about three times its volume, of a pale yellow aqueous solution of chlorine. On 
 allowing the tube to cool again, the crystalline hydrate is reproduced, even at common 
 temperatures, being more permanent under pressure. 
 
 Liquid chlorine may also be obtained in a state in which it can be preserved, by 
 disengaging the chlorine in a sealed tube (as in the liquefaction of ammonia) from 
 about 200 grains of bichloride of platinum previously dried at 400 F. The bichloride 
 is heated with a spirit-lamp in one limb of the tube, whilst the other is immersed 
 in a freezing mixture. The face and hands of the operator should be protected 
 against the bursting of the tube. 
 
 The most characteristic chemical feature of chlorine is its powerful 
 attraction for many other elements at the ordinary temperature. Among 
 the non-metals, hydrogen, bromine, iodine, sulphur, selenium, phosphorus, 
 and arsenic, combine spontaneously with chlorine, and nearly all the metals 
 behave in the same way. 
 
 If a piece of dry phosphorus be placed in a deflagrating spoon, and immersed in a 
 bottle of chlorine (fig. 149), it will take fire spontaneously, combining with the chlo- 
 rine to form terchloride of phosphorus (PC1 3 ). A tall glass shade may be placed 
 
140 
 
 EXPERIMENTS WITH CHLORINE. 
 
 over the bottle, which should stand in a plate containing water, so that the fumes 
 
 may not escape into the air. 
 
 If phosphorus be placed in a bottle of oxygen to which a small quantity of chlorine 
 
 has been added, it will burst out after a minute 
 or two into most brilliant combustion. 
 
 Powdered antimony (the metal, not the sul- 
 phide), sprinkled into a bottle of chlorine (fig. 
 150), descends in a brilliant shower of white 
 sparks, the antimony burning in the chlorine to 
 form terchloride of antimony (SbCl 3 ). A little 
 water should be placed at the bottom of the bottle 
 to prevent it from being cracked, and the fumes 
 should be restrained by a shade standing in 
 water. 
 
 If a flask, provided with a stop-cock (fig. 151), be 
 filled with leaves of. Dutch metal (an alloy of copper 
 and zinc, resembling gold leaf), exhausted of air, 
 Fig. 149. and screwed on to a capped jar of chlorine stand- 
 
 ing over water, it will be found, on opening the 
 
 stop-cocks so that the chlorine may enter the flask, that the metal burns with a red 
 
 light, forming thick yellow fumes containing chloride of copper (CuCl) and chloride 
 
 Fig. 150. 
 
 Fig. 151. 
 
 of zinc (ZnCl). If gold leaf be suspended in chlorine, it will not be immediately 
 attacked, but will gradually become converted into terchloride of gold (AuCl 3 ). 
 
 102. The most important useful applications of chlorine depend upon 
 its powerful chemical attraction for hydrogen. The two gases may be 
 mixed without combining, if kept in the dark, but when the mixture is 
 exposed to light, they combine to form hydrochloric acid gas (HC1), with 
 a rapidity proportionate to the intensity of the actinic rays (or rays capable 
 of inducing chemical change) in the light employed. Exposed to gas-light 
 or ordinary diffused daylight, the hydrogen and chlorine combine slowly, 
 but direct sunlight causes sudden combination, attended with explosion, 
 resulting from the expansion which the hydrochloric acid formed suffers 
 by the heat evolved in the act of combination. The light of magnesium 
 burning in air, and some other artificial lights, also cause sudden com- 
 bination. 
 
 Two pint gas-bottles should be ground so that their mouths may be fitted accu- 
 rately to each other, and filled respectively with dry hydrogen and dry chlorine, both 
 gases having been dried by passing through oil of vitriol, and collected, the hydrogen 
 by upward, and the chlorine by downward, displacement of air. The mouths should 
 
SYNTHESIS OF HYDROCHLORIC ACID. 
 
 141 
 
 Fig. 152. 
 
 be slightly greased before the bottles are filled with gas, and afterwards closed with 
 glass plates. On placing the bottles together, and removing the plates so that the 
 gases may come in contact (see fig. 133), the yellow colour of the chlorine will be 
 permanent as long as the mixture is kept in the dark, but on exposure to daylight 
 the colour will gradually disappear, the hydrochloric acid gas being colourless. If 
 the bottles be now closed with glass plates, the small quantity of gas which escapes 
 during the operation will be seen to fume strongly in air, a property not possessed 
 either by hydrogen or chlorine, and when the necks of the bottles are immersed in 
 water and the glass plates withdrawn, the water will rapidly absorb the gas, and be 
 forced into the bottles so as to fill them, with the exception of a small space occupied 
 by the air accidentally admitted, showing that the hydrochloric acid gas possesses 
 the joint volumes of the hydrogen and chlorine. If the water be tinged with blue 
 litmus it will be strongly reddened as it enters the bottles. 
 
 The sudden union of the gases with explosion may be safely exhibited in a Flor- 
 ence flask. The flask is filled with water, which is then poured out into a measure. 
 Exactly half the water is returned 
 to the flask, and its level in the 
 latter carefully marked with a dia- 
 mond or file. The flask having been 
 again filled with water, is closed with 
 the thumb and inverted in the pneu- 
 matic trough, so that hydrogen may 
 be passed up into it to displace one- 
 half of the water. A short-necked 
 funnel is then inserted, under the 
 water, into the neck of the flask, 
 and chlorine rapidly decanted up 
 from a gas-bottle (fig. 152) until the 
 rest of the water has been displaced. 
 The flask is now raised from the 
 water and quickly closed with a cork 
 (fig. 153), through which pass two 
 gutta-percha-covered copper wires, 
 the ends of which have been stripped and brought sufficiently near to each other 
 to allow of the passage of the electric spark within the flask. The ends external to 
 the flask are also stripped "and 
 bent into hooks for convenient 
 connexion with the conducting 
 wires. The flask is placed upon 
 the ground, and covered with a 
 wooden box to prevent the pieces 
 from flying about. On connect- 
 ing the copper wires with the con 
 ducting wires from an induction- 
 coil or an electrical machine, it 
 will be heard, on passing the spark, 
 that the mixture has violently ex- 
 ploded ; on raising the box it will 
 be found filled with strong fumes 
 of hydrochloric acid, and a heap of 
 small fragments of glass will repre- 
 sent the flask. 
 
 A flask filled in the same way with the mixture of hydrogen and chlorine may 
 be attached to the end of a long stick, and thrust out into the sunlight, when it 
 explodes with great violence. 
 
 To illustrate the direct combination of hydrogen and chlorine under the influ- 
 ence of artificial light, it is better to employ the mixture of exactly equal volumes 
 of the two gases obtained by decomposing hydrochloric acid by the galvanic cur- 
 rent. The voltameter (A, fig. 154) is filled with concentrated hydrochloric acid, 
 and its conducting wires (B) connected with the terminals of a Grove's battery 
 of five or six cells. Chlorine is at once evolved at the positive pole (or that con- 
 nected with the platinum in the battery), and hydrogen at the negative pole (at- 
 tached to the zinc of the battery). It is advisable to place the voltameter in a 
 vessel of cold water, to prevent the hydrochloric acid from becoming too hot. The 
 
 Fig. 153. 
 
142 
 
 EXPLOSION OF CHLOKINE AND HYDROGEN. 
 
 gas evolved during the first five minutes should be allowed to pass into a waste-jar, 
 
 because, until the liquid becomes 
 saturated with chlorine, the 
 evolved gas does not contain 
 exactly equal volumes of the 
 constituent elements. A very 
 thin glass bulb (Q), about 2 
 inches in diameter, blown upon 
 a stout piece of tube, the ends of 
 which have been drawn out to 
 narrow open points (fig. 155), is 
 then connected with the volta- 
 meter by means of a caoutchouc 
 tube. A similar caoutchouc tube 
 Fig. 154. is attached to the free end of the 
 
 bulb. When the colour of the 
 
 gas in the bulb (which should be shaded from sunlight) shows that it is completely 
 filled, the caoutchouc tubes are well closed by nipper-taps (fig. 156), and the bulb 
 detached from the voltameter. In this condition it may 
 be kept in the dark for a long time without alteration 
 or escape of gas. The mixture may be most effectively 
 exploded by exposing it to the flash of light evolved by 
 firing a mixture of nitric oxide gas with vapour of bisul- 
 phide of carbon. For this purpose a cylinder may be 
 Fig. 155. filled with nitric oxide (page 130) over water, closed 
 
 with a glass plate, and placed mouth upwards upon the 
 
 table ; the glass plate being lifted for an instant, a few drops of bisulphide of carbon 
 are poured into the cylinder, which is then shaken. The bulb containing the explo- 
 sive mixture is suspended at some 
 distance from the operator, and the 
 gas-cylinder is placed within a few 
 inches of it (fig. 157). On applying 
 a light to the cylinder, the flash will 
 cause the immediate explosion of the 
 mixture in the bulb, with production 
 of strong fumes of hydrochloric acid. 
 If the bulb be thin, no injury will 
 be inflicted by the pieces of glass, or 
 the operator may easily protect his 
 face by a screen. 
 
 The attraction of chlorine for hydrogen enables it to effect the decom- 
 position of water. The solution of chlorine in water may be preserved 
 
 in the dark without change ; but when ex- 
 posed to light it loses the smell of chlorine, 
 and becomes converted into weak hydro- 
 chloric acid, the oxygen being liberated ; 
 HO + Cl = HC1 + 0.* The decomposi- 
 tion takes place much more quickly at a 
 red heat, so that oxygen is obtained in 
 abundance by passing a mixture of chlo- 
 rine and steam through a red-hot tube. 
 
 For this experiment a porcelain tube is em- 
 ployed, which is bound round with sheet copper 
 to prevent it from cracking, and loosely filled 
 with fragments of broken porcelain to expose a 
 large heated surface. This tube is gradually 
 heated to redness in a charcoal furnace (fig. 
 Fig. 157. 158). One end of it receives the mixture of 
 
 chlorine with steam, obtained by passing the 
 
 * A portion of this oxygen combines with chlorine, producing hypochlorous, and, as 
 recently stated, perchloric acids. 
 
 Fig. 156. Nipper-tap. 
 
ACTION OF CHLOEINE UPON HYDROGEN COMPOUNDS. 
 
 143 
 
 chlorine evolved from hydrochloric acid and binoxide of manganese in A (p. 139), 
 through a flask (B) of boiling water. The other end of the tube is connected with 
 a bottle (C) containing solution of potash to absorb any excess of chlorine and the 
 hydrochloric acid formed ; from this bottle the oxygen is collected over the pneu- 
 matic trough. 
 
 Since water is decomposed by chlorine, it is not surprising that most other 
 hydrogen compounds are attacked by it. Ammonia (NH 3 ) is acted upon 
 
 Fig. 158. Steam decomposed by chlorine. 
 
 with great violence. If a stream of ammonia gas issuing from a tube con- 
 nected with a flask in which solution of ammonia is heated (see fig. 131) 
 be passed into a bottle of chlorine, it takes fire immediately, burning 
 with a peculiar flame, and yielding thick white clouds of hydrochlorate of 
 ammonia; 4NH 3 + C1 3 = 3(NH 3 . HC1) + K A piece of folded filter- 
 paper dipped in strong ammonia, and immersed in a bottle of chlorine, 
 will exhibit the same effect. When the chlorine is allowed to act upon 
 hydrochlorate of ammonia, its operation is less violent, and one of the 
 most explosive substances is produced, which was formerly believed to be 
 a chloride of nitrogen, but is probably a compound formed by the removal 
 of a part of the hydrogen from ammonia, and the introduction of chlorine 
 in its stead. 
 
 Many of the compounds of hydrogen with carbon are also decomposed 
 with violence by chlorine. When a piece of folded filter-paper is dipped 
 into oil of turpentine (C 20 H 1G ), and afterwards into a bottle of chlorine, it 
 bursts into a red flame, liberating voluminous clouds of carbon and hydro- 
 chloric acid. Acetylene (C 4 H 2 ) was found to explode spontaneously with 
 chlorine when exposed to light (page 85). The striking decomposition of 
 olefiant gas (C 4 H 4 ) by chlorine on the approach of a flame has already 
 been noticed (page 87). When a lighted taper is immersed in chlorine it 
 continues to burn, but with a small red flame, the hydrogen only of the 
 wax combining with the chlorine, whilst the carbon separates in black 
 smoke, mixed with the hydrochloric fumes. When chlorine is brought 
 in contact with the flame of a spirit-lamp, it renders the flame luminous 
 by causing the separation of solid particles of carbon (page 93). It has 
 been seen, in the case of olefiant gas, that chlorine sometimes combines 
 directly with the hydrocarbons. 
 
144 
 
 BLEACHING BY CHLORINE. 
 
 When marsh-gas (C 2 H 4 ) is diluted with an equal bulk of carbonic acid, 
 to prevent violent action, and four volumes of chlorine added for each 
 volume of marsh-gas, an oily liquid is gradually formed under the influ- 
 ence of daylight. This oily liquid is a mixture of chloroform and bichlo- 
 ride of carbon, the production of which is explained by the following 
 equations : 
 
 C 2 H 4 + C1 6 = 3HC1 + C 2 HC1 3 
 
 Chloroform. 
 
 C 2 H 4 + C1 8 = C 2 C1 4 + 4HC1. 
 
 Bichloride of carbon. 
 
 It is evident from these equations that chlorine is capable, not only of 
 removing hydrogen from a compound, but also of taking its place, 
 equivalent for equivalent a mode of action which gives rise to a very 
 large number of chlorinated products from organic substances. 
 
 The attraction of chlorine for hydrogen enables the moist gas to act as 
 an oxidising agent. Thus, if marsh-gas and chlorine be mixed in the 
 presence of water, and exposed to daylight, the water is decomposed, its 
 hydrogen combining with the chlorine, and its oxygen with the carbon 
 of the marsh-gas; C 2 H 4 + 4HO + C1 8 = 2C0 2 + 8HC1. 
 
 103. The powerful bleaching effect of chlorine upon organic colouring 
 matters is now easily understood. If a solution of chlorine in water be 
 poured into solution of indigo (sulpliindigotic. acid} the blue colour of the 
 indigo is discharged, and gives place to a comparatively light yellow 
 colour. The presence of water is essential to the bleaching of indigo by 
 chlorine, the dry gas not affecting the colour of dry indigo. The indigo 
 is first oxidised at the expense of the water and converted into isatine^ 
 which is then acted upon by the chlorine and converted into cldorisatine^ 
 having a brownish yellow colour 
 
 C 16 H 5 N0 2 + 2HO + 01, = C 16 H 5 N0 4 + 2HC1. 
 
 Indigo. Isatine. 
 
 C 16 H 5 N0 4 + CL, = C 16 H 4 C1N0 4 + HC1. 
 
 Isatine. Chlorisatine. 
 
 Nearly all vegetable and animal colouring matters contain carbon, hydro- 
 gen, nitrogen, and oxygen, and are converted by moist chlorine into pro- 
 ducts of oxidation or chlorination which happen to be colourless, or 
 nearly so. 
 
 That dry chlorine will not bleach, may he shown by 
 shaking some oil of vitriol in a bottle of the gas, and 
 allowing it to stand for an hour or two, so that the acid 
 may remove the whole of the moisture. If a piece of 
 crimson paper be dried at a moderate heat and suspended 
 in the bottle while warm, it will remain unbleached for 
 hours, but a similar piece of paper suspended in a bottle 
 of moist chlorine will be bleached almost immediately. 
 If characters be written on crimson paper with a wet 
 brush, and the paper placed in a jar beside a bottle of 
 chlorine (fig. 159), it will be found, on removing the 
 stopper, that white characters soon make their appear- 
 ance on the red ground. 
 
 If a collection of coloured linen or cotton fabrics, or of 
 artificial flowers, be exposed to the action of moist chlor- 
 ine gas or of chlorine water, those which are dyed with 
 organic colouring matters will be bleached at once, whilst 
 the mineral colours will for the most part remain un- 
 altered. Green leaves, immersed in chlorine, acquire a rich autumnal brown tint, 
 and are eventually bleached. All flowers are very readily bleached by this gas. 
 
 Fig. 159. 
 
CHLORIDE OF LIME. 145 
 
 Chlorine is very extensively employed for bleaching linen and cotton, 
 the gas acting upon the colouring matter without affecting the fibre, but 
 silk and wool present much less resistance to chemical action, and would 
 be much injured by chlorine, so that they are always' bleached by sul- 
 phurous acid. 
 
 Neither chlorine itself nor its solution in water can be very conveniently 
 employed for bleaching on the large scale, on account of the irritating 
 effect of the gas, so that it is usual to employ it in the form of chloride of 
 Ibne, from which it can be easily liberated as it is wanted. 
 
 104. Chloride of lime or bleaching powder is prepared by passing 
 chlorine gas into boxes of lead or stone in which a quantity of slaked 
 lime is spread out upon shelves. The lime absorbs nearly half its weight 
 of chlorine, and forms a white powder which has a very peculiar smell 
 somewhat different from that of chlorine. The chloride of lime thus pro- 
 duced appears to consist of a mixture of liypocMorite of lime (CaO . CIO) 
 with oxychloride of calcium (CaCl . 2CaO), the action of chlorine upon 
 hydrate of lime being represented by the following equation : 
 
 4 (CaO. HO) + 01, = (CaO.CIO + CaCl. 2CaO) + 4HO . 
 
 Hydrate of lime. Chloride of lime. 
 
 When the chloride of lime is treated with water, the hypochlorite of lime 
 (CaO . CIO) and chloride of calcium (CaCl) are dissolved, whilst hydrate 
 of lime is left. If this solution be added to blue litmus, it will be found 
 to exert little bleaching action, but on adding a little acid (sulphuric, for 
 example), the blue colour will be discharged, the acid setting free the 
 chlorine, which acts upon the colouring matter. 
 
 (CaO.CIO + CaCl) + 2(HO.S0 3 ) = 2(CaO.S0 3 ) + 2HO + CL, . 
 
 Solution of Chloride of lime. 
 
 Even carbonic acid will develope the bleaching property of chloride of 
 lime, so that the above mixture may be decolorised by breathing into it 
 through a glass tube. 
 
 When chloride of lime is used for bleaching on the large scale, the stuff 
 to be bleached is first thoroughly cleansed from any grease or weaver's dress- 
 ing, by boiling it in lime-water and in a weak solution of soda, and is then 
 immersed in a weak solution of the chloride of lime. This by itself, how- 
 ever, exerts very little action upon the natural colouring matter of the 
 fibre, and the stuff is therefore next immersed in very dilute sulphuric 
 acid, when the colouring matter is so far altered as to become soluble in 
 the alkaline solution in which it is next immersed, and a repetition of 
 these processes, followed up by a thorough rinsing, generally perfects the 
 bleaching. 
 
 The property possessed by acids of liberating chlorine from the chloride 
 of lime is applied in calico-printing to the production of white patterns 
 upon a red ground. The stuff having been dyed with Turkey red, the 
 pattern is imprinted upon it with a discharge consisting of an acid (tar- 
 taric, phosphoric, or arsenic) thickened with gum. On passing the fabric 
 through a bath of weak chloride of lime, the colour is discharged only at 
 those parts to which the acid has been applied, and where, consequently, 
 chlorine is liberated. 
 
 The explanation above given of the bleaching effect of chlorine may 
 probably be applied also to its so-called disinfecting properties. The 
 
146 DISINFECTION BY CHLORINE. 
 
 atmosphere, in particular localities, is occasionally contaminated with 
 poisonous substances, some of which are known only by their injurious 
 effects upon the health, their quantity being so small that they do not 
 appear in the results of the analysis of such air. Since, however, these 
 substances appear to be acted upon by the same agents which are usually 
 found to decompose organic compounds, they are commonly believed to 
 be bodies of this class, and chlorine has been very commonly employed to 
 combat these insidious enemies to health, since Guyton de Morveau, in> 
 the latter part of the last century, made use of it to destroy the odour 
 arising from the bodies interred in the vaults beneath the cathedral of 
 Dijon. 
 
 Among the offensive and unhealthy products of putrefaction of animal 
 and vegetable matter, sulphuretted hydrogen, ammonia, and bodies simi- 
 larly constituted, are found. That chlorine breaks up these hydrogen 
 compounds is well known, and hence its great value for removing the 
 unwholesome properties of the air in badly drained houses, &c. 
 
 Chloride of lime is one of the most convenient forms in which to apply 
 chlorine for the purposes of fumigating and disinfecting. If a cloth 
 saturated with the solution be suspended in the air, the carbonic acid 
 causes a slow evolution of hypochlorous acid, which is even a more 
 powerful disinfectant than chlorine itself. In extreme cases, where a 
 rapid evolution of chlorine is required, the bleaching powder is placed in 
 a plate, and diluted sulphuric acid is poured over it, or the powder may 
 be mixed with half its weight of powdered alum in a plate, when a pretty 
 rapid and regular escape of chlorine will ensue. 
 
 105. The discovery of chlorine and the discussions which ensued with 
 respect to its real nature, contributed very largely to the advancement of 
 chemical science. About the year 1770, the Swedish chemist Scheele (who 
 afterwards discovered oxygen), first obtained chlorine by heating man- 
 ganese ore with muriatic acid. 
 
 The construction which Scheele put upon the result of this experiment 
 was one which was consistent with the chemistry of that date. He sup- 
 posed the muriatic acid to have been deprived of phlogiston, and hence 
 chlorine was termed by him dephlogisticated muriatic acid. This phlo- 
 giston had long been a subject of contention among philosophers, having 
 been originally assumed to exist in combination with all combustible 
 bodies, and to be separated from them during their combustion. To- 
 wards the decline of the phlogistic theory, attempts were made to prove 
 the identity of this imaginary substance with hydrogen, which shows 
 how very nearly Scheele's reasoning approached to the truth, even with 
 the very imperfect light which he then possessed. Berthollet's move- 
 ment was retrograde when, ten years afterwards, he styled chlorine oxy- 
 genised muriatic or oxymuriatic acid, but the experiments of Gay-Lussac 
 and Thenard, and more particularly those of Davy in 1811, proved de- 
 cisively that hydrochloric acid was composed of chlorine and hydrogen, 
 and that the effect of the black oxide of manganese in Scheele's experi- 
 ment was to remove the hydrogen in the form of water, thus setting the 
 chlorine at liberty. 
 
PREPARATION OF HYDROCHLORIC ACID. 
 
 147 
 
 HYDROCHLORIC ACID. 
 
 106. This acid is found in nature among the gases emanating from 
 active volcanoes, and occasionally in the spring and river waters of vol- 
 canic districts. For use it is always prepared artificially by the action 
 of sulphuric acid upon common salt 
 
 NaCl + HO.S0 3 = HC1 + HaO.SOs 
 
 Common salt. Sulphate of soda. 
 
 the sodium of the common salt 
 changing places with the hydro- 
 gen of the sulphuric acid. 
 
 300 grains of common salt (pre- 
 viously dried in an oven) are intro- 
 duced into a dry Florence flask (fig. 
 160), to which' has been fitted, by 
 means of a perforated cork, a tube 
 bent twice at right angles to allow 
 the gas to be collected by downward 
 displacement. Six fluid drachms of 
 strong sulphuric acid are poured 
 upon the salt, and the cork having 
 been inserted, the flask is very 
 gently heated in order to promote 
 the disengagement of the hydro- 
 chloric acid gas, which is collected 
 in a perfectly dry bottle, the mouth 
 of which, when full, may be covered 
 with a glass plate smeared with a little grease. 
 be closed with a perforated card. 
 
 Common salt in powder sometimes froths to a very inconvenient extent with sul- 
 phuric acid ; it is therefore often preferable to employ fragments of fused salt, pre- 
 pared by fusing the common salt in a clay crucible, and pouring on to a clean dry 
 stone. 
 
 A more regular supply of hydrochloric acid gas is obtained from 1 oz. of sal- 
 ammoniac in lumps, and 1 J oz. (measured) of sulphuric acid. 
 
 The bottle will be known to be filled with gas by the abundant escape 
 of the dense fumes which hydrochloric acid gas, itself transparent, pro- 
 duces by condensing the moisture of the air ; for since the gas is much 
 heavier than air (sp. gr. T247), it will not escape in any quantity from 
 the bottle until the latter is full. The odour of the gas is very suffocat- 
 ing, but not nearly so irritating as that of chlorine. 
 
 The powerful attraction for water is one of 
 the most important properties of hydrochloric 
 acid gas. 
 
 Fig. 160. Preparation of hydrochloric acid gas. 
 While being filled, the bottle may 
 
 If a jar of hydrochloric acid gas be closed with a 
 glass plate and inverted under water, it will be found, 
 on removing the plate, that the gas is absorbed with 
 great rapidity, the water being forced up into the 
 bottle by the pressure of the external air in propor- 
 tion as the gas is absorbed. 
 
 A Florence flask is more convenient than a gas 
 bottle for this experiment. It must be perfectly dry, 
 and thoroughly well filled with the gas, which may be 
 allowed to escape abundantly from the mouth. The 
 tube delivering the hydrochloric acid gas must be 
 slowly withdrawn, so that the vacancy may be filled 
 by gas and not by air. The flask is then closed with the thumb, and opened under 
 
 Fig. 161. 
 
 K 2 
 
148 
 
 HYDROCHLORIC OR MURIATIC ACID. 
 
 water, which will enter it with great violence. The experiment may also be made 
 as in the case of ammonia (fig. 161, see page 115). 
 
 The liquid hydrochloric, or muriatic acid of commerce, is a solution of 
 the gas in water, and may be recognised by the grey fumes, with the 
 peculiar odour of the acid, which it evolves when exposed to the air. One 
 pint of water at a temperature of 40 F. is capable of absorbing 480 pints 
 of hydrochloric acid gas, forming 1 pint of the solution, having the 
 specific gravity 1*21. The strength of the acid purchased in commerce is 
 usually inferred from the specific gravity, by reference to tables indi- 
 cating the weight of hydrochloric acid contained in solutions- of different 
 specific gravities. The strongest hydrochloric acid (sp. gr. 1-21) contains 
 43 per cent, by weight of the gas. The common acid has usually a bright 
 yellow colour, due to the accidental presence of a little perchloride of iron 
 (Fe 2 Cl 3 ), and not unfrequently smells of chlorine. 
 
 This acid is produced in enormous quantities in the alkali works, where 
 common salt is decomposed by sulphuric acid in order to convert it into 
 sulphate of soda, as a preliminary step to the production of carbonate of 
 soda. The alkali manufacturer is compelled to condense the gas, for it 
 is found to wither up the vegetation in the neighbourhood. For this pur- 
 pose the hydrochloric acid gas is drawn up from the furnace through ver- 
 tical cylinders filled with coke, over which streams of water are made 
 to trickle. The water absorbs the acid, and is drawn off from below. 
 
 In preparing a pure solution of the acid for chemical use on a small scale, the gas 
 prepared as above may be passed into a small bottle containing a very little water to 
 wash the gas, or remove any sulphate of soda which may splash over, and then into 
 a bottle about two-thirds filled with distilled water, the tube delivering the gas 
 passing only about ^ inch below the surface, so that the heavy solution of hydro- 
 chloric acid may fall to the bottom, and fresh water may be presented to the gas 
 (fig. 162). For ordinary use, an acid of suitable strength is obtained by passing 
 the gas from C ounces of common salt and 10 ounces of sulphuric acid into 7 (mea- 
 sured) ounces of water until its bulk 
 has increased to 8 ounces. The bottle 
 containing the water should be sur- 
 rounded with cold water, since the ab- 
 sorption of hydrochloric acid by water 
 is attended with evolution of heat. 
 
 When the concentrated solution 
 of hydrochloric acid is heated in a 
 retort, it evolves abundance of hy- 
 drochloric acid gas, rendering it 
 probable that it is not a true che- 
 mical compound of water with the 
 acid. The evolution of gas ceases 
 when the remaining liquid con- 
 tains 20 per cent, of acid (and has 
 a sp. gr. of 1-10). If a weaker 
 acid than this be heated, it loses 
 water until it has attained this strength, when it distils unchanged.* 
 
 The concentrated solution forms a very convenient source from which to procure 
 the gas. It may be heated in a flask, and the gas dried by passing through a bottle 
 filled with fragments of pumice-stone wetted with concentrated sulphuric acid, being 
 collected over the mercurial trough (fig. 163). 
 
 * The proportion of acid thus retained by the water varies directly with the atmospheric 
 pressure to which it is exposed during the distillation. 
 
 Fig. 162. Preparation of solution of hydro- 
 chloric acid. 
 
ACTION OF HYDROCHLORIC ACID ON METALS. 
 
 149 
 
 The avidity with which water absorbs hydrochloric acid is the more 
 remarkable, because this gas can be liquefied only under a very high 
 pressure, amounting at the ordinary temperature to about 40 atmospheres. 
 
 Fig. 163. 
 
 The liquefied hydrochloric acid has comparatively little action even upon 
 those metals which decompose its aqueous solution with great violence ; 
 quick-lime is unaffected by it, and solid litmus dissolves in it with a faint 
 purple colour, instead of the bright red imparted by the aqueous hydro- 
 chloric acid. (These facts answer the objection that anhydrous sulphuric 
 acid (S0 3 ) cannot be considered an acid, because it has none of the power- 
 ful acid characters of oil of vitriol, since it cannot be doubted that hydro- 
 chloric acid is, in a chemical sense, an acid in its anhydrous state, though 
 it manifests its acid properties only when water is present.) 
 
 The injurious action of hydrochloric acid gas upon growing plants is 
 probably connected with its attraction for water. If a spray of fresh 
 leaves is placed in a bottle of hydrochloric acid, it becomes at once brown 
 and shrivelled. 
 
 107. Action of hydrochloric acid upon metals. Those metals which 
 have the strongest attraction for oxygen will also generally have the 
 strongest attraction for chlorine, so that in respect to their capability of 
 decomposing hydrochloric acid, they may be ranked in pretty nearly the 
 same order as in their action upon water (p. 23). Since, however, the 
 attraction of chlorine for the metals is generally superior to that of oxygen, 
 the metals are more easily acted upon by hydrochloric acid than by water, 
 the metal taking the place of the hydrogen, and a chloride of the metal 
 being formed. 
 
 Even silver, which does not decompose water at any temperature, is dis- 
 solved, though very slowly, by boiling concentrated hydrochloric acid, the 
 chloride of silver formed being soluble in the strong acid, though it may 
 be precipitated by adding water. 
 
 Gold and platinum, however, are not attacked by hydrochloric acid, but 
 if a little free chlorine be present, it converts them into chlorides. 
 
 Iron and zinc decompose the acid very rapidly in the cold, forming 
 chlorides of iron and zinc, and liberating hydrogen : Fe + HC1 = FeCl + H. 
 
 When potassium or sodium is exposed to hydrochloric acid gas, it im- 
 mediately becomes coated with a white crust of chloride, which partly 
 protects the metal from the action of the gas, but when these metals are 
 heated to fusion in hydrochloric acid gas, they burn vividly 
 Na + HC1 - NaCl + H. 
 
150 EQUIVALENT OF CHLORINE. 
 
 The composition of hydrochloric acid may be exhibited by confining 
 a measured volume of the gas over mercury (see fig. 73, page 73), 
 and passing up a freshly cut pellet of sodium. On gently agitating the 
 tube, the gas diminishes in volume, and after a time will have contracted 
 to one-half, and will be found to have all the properties of hydrogen. 
 This result confirms that obtained by synthesis, as described above, that 
 one volume of hydrochloric acid contains half a volume of hydrogen and 
 half a volume of chlorine. 
 
 108. Action of hydrochloric acid upon metallic oxides. As a general 
 rule it may be stated, that when hydrochloric acid acts upon the oxide of 
 a metal, the results are water and a chloride of the metal having a com- 
 position which corresponds to that of the oxide. 
 
 Thus, oxide of silver acted on by hydrochloric acid gives water and 
 chloride of silver; AgO + HC1 = HO + AgCl. 
 
 Suboxide of copper (cuprous oxide) yields water and subchloride of 
 copper (cuprous chloride) ; C^O + HC1 = HO + Ci^Cl. 
 
 Sesquioxide of iron gives water and sesquichloride of iron 
 
 Fe 2 3 + 3HC1 = 3HO + Fe 2 Cl 3 . 
 With binoxide of tin, water and bichloride of tin are obtained 
 Sn0 2 + 2HC1 - 2HO + SnCL, . 
 
 Teroxide of antimony is converted into water and terchloride of anti- 
 mony; Sb0 3 + 3HC1 - 3HO + SbCl 3 . 
 
 In cases where the corresponding chloride does not exist, or is not stable 
 under the conditions of the experiment, a chloride is formed containing 
 less chlorine than is equivalent to the oxygen in the oxide, and the bal- 
 ance is evolved in the free state. Thus, when sesquioxide and binoxide 
 of manganese are heated with hydrochloric acid 
 
 Mn 2 3 + 3HC1 - 3HO + 2 MnCl + Cl 
 Mn0 2 + 2HC1 = 2HO + MnCl + Cl 
 
 since the sesquichloride and bichloride of manganese are decomposed by 
 heat into the chloride (MnCl) and free chlorine. 
 
 Chromic acid, a chloride corresponding to which is not known to exist, 
 when heated with hydrochloric acid, yields sesquichloride of chromium 
 and chlorine 
 
 2Cr0 3 + 6HC1 - 6HO + Cr 2 Cl 3 + C1 3 . 
 Every metallic protoxide (containing one equivalent of oxygen with 
 one equivalent of a metal) has a corresponding chloride of a stable cha- 
 racter, but the higher oxides less frequently form corresponding chlorides 
 with any stability. 
 
 109. Equivalent weights of hydrochloric acid and of chlorine. It is 
 ascertained by experiment that 36*5 grains of hydrochloric acid are re- 
 quired to neutralise one equivalent (47 grains) of potash. The number 
 36'5, therefore, represents the equivalent weight of hydrochloric acid. 
 When water is decomposed by chlorine (p. 142) 35 '5 grains of chlorine are 
 required to displace 8 grains (one equivalent) of oxygen, so that 35 '5 is the 
 equivalent weight of chlorine. By measuring 35 "5 grains of chlorine, it 
 is found to occupy twice the volume of 8 grains of oxygen, so that if 1 
 equivalent of oxygen be represented to occupy one volume, 1 equivalent 
 of chlorine will occupy two volumes, like the equivalent of hydrogen. 
 
DOCTRINE OF ATOMICITY. 151 
 
 It appears, then, that two volumes (one equivalent or 1 part by weight) 
 of hydrogen combined with two volumes (one equivalent or 35*5 parts by 
 weight) of chlorine, form four volumes (one equivalent or 3 6 '5 parts by 
 weight) of hydrochloric acid. 
 
 On the assumption that 1 part by weight of hydrogen represents 1 
 volume or 1 atom, 35*5 parts by weight of chlorine will also represent 1 
 volume or 1 atom, and these will unite to form 2 volumes or 1 molecule 
 of hydrochloric acid. The molecular formula of hydrochloric acid is, 
 therefore, identical with its equivalent formula, HC1. 
 
 110. Types of atomic formulae ; atomicity. On examining the composi- 
 tion by volume of hydrochloric acid, water, ammonia, and marsh-gas, it is 
 seen that equal volumes of these compounds, measured in the gaseous 
 state at the same temperature and pressure, contain respectively, 1, 2, 3, 
 and 4 volumes of hydrogen. 
 
 Thus 2 volumes of hydrochloric acid gas contain 1 volume of chlorine and 
 
 1 volume of hydrogen. 
 2 volumes of watery vapour contain 1 volume of oxygen and 2 
 
 volumes of hydrogen. 
 2 volumes of ammonia contain 1 volume of nitrogen and 3 volumes 
 
 of hydrogen. 
 2 volumes of marsh-gas contain 1 volume (?) of imaginary carbon 
 
 vapour and 4 volumes of hydrogen. 
 
 In the case of marsh-gas, it has been already explained that the volume 
 occupied by a given weight of carbon vapour cannot be ascertained by 
 experiment, but there are reasons to justify the assumption that 12 parts 
 by weight of carbon vapour would occupy the same volume as 8 parts by 
 weight of oxygen. In the other cases, the above statements exhibit the 
 direct results of experiments previously described. 
 
 If it be allowed that one atom of each element occupies one volume, 
 then hydrochloric acid, water, ammonia, and marsh-gas will contain, for 
 one atom of chlorine, oxygen, nitrogen, and carbon, respectively, 1, 2, 3, 
 and 4 atoms of hydrogen, or, taking the symbol for each element to re- 
 present one atom 
 
 Vols. Weights. 
 H=l H=l 
 
 Hydrochloric acid = C1H = HC1 = 2 = 36'5 
 
 Water = OHH = H 2 O = 2 = 18 
 
 Ammonia = NHHH = H 3 N = 2 = 17 
 
 Marsh-gas = 6HHHH = H 4 O = 2 = 16 
 
 Since, on the atomic theory, hydrogen is accepted as the unit of atomic 
 weight and volume, it appears reasonable to fix upon it as representing 
 the unit of combining power, and to classify the elements according to the 
 tendency of their atoms to imitate tho combining power of one or more 
 atoms of hydrogen. 
 
 By the atomicity of an element, is meant the number expressing the 
 hydrogen-atoms to which one atom (or volume) of that element is usually 
 equivalent. 
 
 Thus, the atomicity of chlorine is = 1, for one volume (or atom) of this 
 element not only combines with, and neutralises the properties of, one 
 atom (or volume) of hydrogen, but is capable of representing, or occupy- 
 ing the place of, one atom of hydrogen in its compounds (see p. 144). 
 
152 ATOMICITIES OF THE ELEMENTS. 
 
 The atomicity of oxygen is = 2, since one volume (or atom) of oxygen 
 combines with, and neutralises two atoms (or volumes) of hydrogen in 
 water, and is generally capable of occupying the place of two atoms of 
 hydrogen in the compounds of that element. 
 
 The atomicity of nitrogen is = 3, for one volume (or atom) of nitrogen 
 neutralises the properties of three atoms (or volumes) of hydrogen in am- 
 monia, and is often found to occupy the place of three atoms of hydrogen 
 in its compounds. 
 
 The atomicity of carbon is = 4, for one volume (or atom) of imaginary 
 carbon vapour is combined, in marsh-gas, with four atoms (or volumes) of 
 hydrogen, and in its compounds with other elements, one atom of carbon 
 is usually found representing four atoms of hydrogen. 
 
 Since hydrochloric acid, water, ammonia, and marsh-gas are the most 
 conspicuous members of large classes of chemical compounds, they are 
 often referred to as types, and the elements, chlorine, oxygen, nitrogen, 
 and carbon, are taken as the representatives of the various classes into 
 which the elements are divided according to their atomicities. 
 
 Chlorine is the type of one-atom elements (technically called man-atomic, 
 uni-equivalent, monad elements), the atomic weights of which are repre- 
 sented by the same numbers as their equivalent weights. 
 
 Oxygen is the type of two-atom elements (di-atomic, bi-equivalent, dyad 
 elements), of which the number representing the equivalent weight is 
 half of that which represents the atomic weight. 
 
 Equivalent of oxygen = = 8. 
 Atom of oxygen = O = 16. 
 
 Mtrogen is the type of three-atom elements (tri-atomic, ter-equivalent, 
 triad elements), of which the number representing the equivalent weight 
 is commonly taken as identical with that which represents the atomic 
 weight, though if the equivalentic system were rigorously carried out, the 
 equivalent should be one-third of the atomic weight. 
 
 Carbon is the type of four-atom elements (tetratomic, quadr equivalent, 
 tetrad elements), of which the number representing the equivalent weight 
 ought to be one-fourth of that which expresses the atomic weight, whereas 
 it is usually represented as half that number. 
 
 Equivalent of carbon = C = 6. 
 Atom of carbon = @ = 12. 
 
 Such anomalies as these are unavoidable during the present transitional 
 period through which chemistry appears to be passing towards the ulti- 
 mate adoption of atomic (or molecular) formula in the place of equivalent 
 formula, a change which offers dazzling prospects of advantage in specu- 
 lative chemistry, but will probably be of less service in practice than 
 the preservation of equivalent formulae, so corrected as to remove the 
 anomalies presented in some few cases. 
 
 The experience of the last few years seems to warrant the belief, that it 
 will be long before experiment (the only possible final resort for the 
 chemist) has so far removed the exceptions to the atomic formulae which 
 are presented, in some cases, by the gaseous volumes and specific heats of 
 the elements, that these formulas can be said to present us with so true 
 a record of the actual results of experiment as to console us for the loss of 
 the greater simplicity and practical utility of the equivalent formulae. 
 
 It is remarkable that the four elements, hydrogen, oxygen, nitrogen, 
 
GRAPHICAL REPRESENTATION OF ATOMS. 
 
 153 
 
 and carbon, which compose the chief part of living matter, are respectively 
 monatomic, diatomic, triatomic, and tetratomic elements. 
 
 In speculations relating to the atomic structure of compounds, it is 
 now usual to represent graphically the atomicity of each element ; thus a 
 monatomic element, like hydrogen, is represented as affording one point 
 of attachment, which may be indicated by writing the symbol H ; a 
 diatomic element, like oxygen, affords two points of attachment, as shown 
 by writing its atomic symbol ; accordingly, to form water, the dia- 
 tomic oxygen attaches to itself two atoms of hydrogen, as represented by 
 the molecular formula H H, whereas in the peroxide of hydrogen 
 (H 2 2 ) the second atom of oxygen is only held by one point of attach- 
 ment, so that the graphic expression H H accounts at once 
 for its tendency to decompose into water and free oxygen. A triatomic 
 
 element, such as nitrogen, has three points of attachment />N , and 
 
 thus in ammonia, attaches to itself three atoms of hydrogen 
 
 H. 
 
 The tetratomic element, carbon, affords four points of attachment 
 
 and thus marsh-gas (0H 4 ) is represented by 
 
 by 
 
 > an( i carbonic acid 
 
 COMPOUNDS OF CHLOKIXE WITH OXYGEN. 
 
 111. It is worthy of notice that whilst chlorine and hydrogen so readily 
 unite, there is no method by which chlorine can be made to combine in a 
 direct manner with oxygen, all the compounds of these elements having 
 been hitherto obtained only by indirect processes. An excellent illustra- 
 tion is thus afforded of the fact, that the more closely substances resemble 
 each other in their chemical relations, the less will be their tendency to 
 combine, for chlorine and oxygen are both highly electronegative bodies, 
 and therefore, having both a powerful attraction for the electropositive 
 hydrogen, their attraction for each other is of a very low order. 
 
 The following table exhibits the compounds formed by one equivalent 
 of chlorine with different proportions of oxygen. Those distinguished by 
 a note of interrogation have not been obtained in a separate state, though 
 there is good reason for believing them to exist : 
 
 Oxides of CJilorine. 
 
 
 Equivalent 
 
 By Weight. 
 
 
 Formula. 
 
 Cl 
 
 
 
 Hypochlorous acid . 
 
 CIO 
 
 35-5 
 
 8 
 
 Chlorous acid . . . 
 
 cio. 
 
 35-5 
 
 24 
 
 Chloric peroxide . . 
 
 C10 4 
 
 35-5 
 
 32 
 
 Chloric acid ? . . . 
 
 CIO. 
 
 35-5 
 
 40 
 
 Perchloric acid ? . . 
 
 C10 7 
 
 35-5 
 
 66 
 
154 HYPOCHLOROUS ACID. 
 
 112. Hypochlorous acid is of some practical interest as one of the 
 constituents of chloride of lime, chloride of soda, and other bleaching 
 compounds. It is prepared by passing dry chlorine gas over dry preci- 
 pitated oxide of mercury, and condensing the product in a tube sur- 
 rounded with a mixture of ice and salt 
 
 HgO + Cla = HgCl + CIO . 
 
 Oxide of mercury. Chloride of mercury. 
 
 The hypochlorous acid is thus obtained as a deep red liquid, which boils 
 at 19 F., evolving a yellow vapour thrice as heavy as air, and having a 
 very powerful and peculiar odour. This vapour is remarkably explosive, 
 the heat of the hand having been known to cause its separation into its 
 constituents, when two volumes of the vapour yield two volumes of 
 chlorine and one volume of oxygen. As might be expected, most sub- 
 stances which have any attraction for oxygen or chlorine will decompose 
 the gas, sometimes with explosive violence. Even hydrochloric acid de- 
 composes it ; one. volume of hypochlorous acid gas is entirely decom- 
 posed by two volumes of hydrochloric acid, yielding water and chlorine 
 
 CIO + HC1 = HO + C1 2 .. 
 
 Hypochlorous acid is a powerful bleaching agent, both its chlorine and' 
 oxygen acting upon the colouring matter in the manner explained at 
 page 144. 
 
 Hypochlorous acid is absorbed in large quantity by water. The solu- 
 tion may be very readily prepared by shaking the red oxide of mercury 
 with water in a bottle of chlorine as long as the gas is absorbed. The 
 greater part of the chloride of mercury which is produced, combines with 
 the excess of oxide of mercury to form a brown insoluble oxychloride, 
 whilst the hypochlorous acid and a little chloride of mercury remain in 
 solution. This solution is a most powerful oxidising and bleaching agent ; 
 it erases writing ink immediately, and does not corrode the paper if it be 
 carefully washed. Printing ink, which contains lamp-black and grease, is 
 not bleached by hypochlorous acid, so that this solution is very useful 
 for removing ink stains from books, engravings, &c. 
 
 The action of some metals and their oxides upon solution of hypo- 
 chlorous acid is instructive. Iron seizes upon the oxygen, whilst the 
 chlorine is liberated ; copper takes both the oxygen and chlorine, whilst 
 silver combines with the chlorine and liberates oxygen. Oxide of lead 
 (PbO) removes the oxygen, becoming peroxide of lead (Pb02), and libe- 
 rating chlorine, but oxide of silver converts the chlorine into chloride- of 
 silver, and liberates the oxygen ; AgO + CIO = AgCl 4- 2 . 
 
 The salts of hypochlorous acid, or hypochlorites, are not known in a 
 pure state, but are obtained in solution by neutralising the solution of 
 hypochlorous acid with bases. They are decomposed even by carbonic 
 acid, with liberation of hypochlorous acid. 
 
 When the solution of a hypochlorite is boiled, it becomes converted 
 into a mixture of chloride and chlorate ; thus 
 
 3(KO.C10) = KO.C10 5 + 2KC1. 
 
 Hypochlorite of potash. Chl( > rat ' of Chloride of 
 
 potash. potassium. 
 
 This change is turned to practical account in the manufacture of chlorate 
 of potash. It is much hindered by the presence of an excess of alkali. 
 
CHLORATE OF POTASH. 155 
 
 The solution of hypochlorous acid itself, when exposed to light, is decom- 
 posed into chloric acid and free chlorine 
 
 5 CIO + HO = HO.C10 5 + C1 4 
 
 Chloride of lime (see p. 145) is the most important compound 
 containing hypochlorous acid. Its formula has already been given as 
 CaO. CIO + CaCl. 2CaO + 4Aq, showing it to be a mixture of hypo- 
 chlorite of lime with oxy chloride of calcium. When this compound is 
 distilled with a small quantity of diluted sulphuric acid, a solution of 
 hypochlorous acid is obtained ; but if an excess of acid be used, the chlo- 
 ride of calcium is decomposed, furnishing hydrochloric acid, which acts 
 upon the hypochlorous acid, and free chlorine is the result. Alcohol, 
 although capable of dissolving chloride of calcium, does not extract that 
 salt from bleaching powder, because it is combined with lime ; but an 
 excess of water decomposes the compound of chloride of calcium with 
 lime, and dissolves the former. 
 
 Bleaching powder is liable to decomposition when kept, its hypochlorite 
 of lime evolving oxygen, and becoming converted into chloride of calcium, 
 which attracts moisture greedily, and renders the bleaching powder deli- 
 quescent. It has been known to shatter the glass bottle in which it was 
 preserved, in consequence of the accumulation of oxygen. 
 
 When a solution of a salt of manganese or cobalt is added to solution 
 of chloride of lime, a black precipitate of binoxide of manganese or sesqui- 
 oxide of cobalt is obtained, the oxide of manganese or of cobalt acquiring 
 additional oxygen from the hypochlorite of lime, and forming an oxide 
 which is indifferent, and does not remain in combination with the acid. 
 If this precipitate be boiled with an excess of the solution of chloride of 
 lime, it causes a rapid disengagement of oxygen in some manner that has 
 not yet been clearly explained. 
 
 Large quantities of oxygen are easily obtained by adding a few drops of 
 solution of nitrate of cobalt to solution of chloride of lime, and applying a 
 gentle heat. 
 
 Hy pod do rite of soda, which is very useful for removing ink, is prepared 
 in solution by decomposing solution of chloride of lime with solution of 
 carbonate of soda, and separating the carbonate of lime by nitration. The 
 solution is generally called " chloride of soda." 
 
 113. Chloric add. This acid is appropriately studied here, since its 
 compounds are usually obtained by the decomposition of the hypochlorites. 
 The only compound of chloric acid which possesses any great practical 
 importance is the chlorate of potash (KO . CIO.), which is largely em- 
 ployed as a source of oxygen, as an ingredient of several explosive com- 
 positions, and in the manufacture of lucifer matches. 
 
 Chlorate of potash. The simplest method of obtaining this salt con- 
 sists in ' passing an excess of chlorine rapidly into a strong solution of 
 hydrate of potash, when the liquid becomes hot enough to decompose the 
 hypochlorite of potash first formed, into chloride of potassium, which 
 remains in solution, and chlorate of potash, which is deposited in tabular 
 crystals, the ultimate result being expressed by the equation 
 
 6(KO.HO) + C1 6 = KO.CIO, + 5KC1 + 6HO . 
 If carbonate of potash or a weak solution of hydrate of potash be employed, 
 the liquid will require boiling after saturation with chlorine, in order to 
 convert the hypochlorite into chlorate. 
 
156 PREPARATION OF CHLORATE OF POTASH. 
 
 The following proportions will be found convenient for the preparation of chlorate of 
 potash on the small scale as a laboratory experiment. 
 300 grains of carbonate of potash are dissolved, in a 
 beaker, with two measured ounces of water. 600 
 grains of common salt are mixed with 450 grains of 
 binoxide of manganese, and very gently heated in 
 a flask (fig. 164) with a mixture of 1J ounce (mea- 
 sured) of strong sulphuric acid and 4 ounces (mea- 
 sured) of water, the evolved chlorine being passed 
 through a rather wide bent tube into the solution 
 of carbonate of potash. 
 
 At first no action will appear to take place, 
 although the solution absorbs the chlorine ; be- 
 cause the first portion of that gas converts the car- 
 bonate of potash into a mixture of hypochlorite of 
 potash, chloride of potassium, and bicarbonate of 
 potash, some crystals of which will probably be de- 
 Fig. 164. posited 
 
 4(KO.C0 2 ) + C1 2 + 2HO = KC1 + KO.C10 + 2(KO.H0.2C0 2 ) . 
 
 On continuing to pass chlorine, these crystals will redissolve, and brisk effervescence 
 will be caused by the expulsion of the carbonic acid from the bicarbonate of potash 
 
 2(KO.H0.2C0 2 ) + C1 2 = KC1 + KO.C10 + 2HO + 4C0 2 . 
 
 When this effervescence has ceased, and the chlorine is no longer absorbed by the 
 
 liquid, the change is complete, the ultimate result being represented by the equation 
 
 2(KO.C0 2 ) -f C1 2 = KC1 + KO.C10 + 200 2 . 
 
 The solution (which often has a pink colour, due to a little permanganate of 
 potash) is now poured into a dish, boiled for two or three minutes, filtered, if neces- 
 sary, from any impurities (silica, &c.,) derived from the carbonate of potash, and set 
 aside to crystallise. The ebullition has converted the hypochlorite of potash into 
 chlorate of potash and chloride of potassium 
 
 3(KO.C10) = KO.C10 5 + 2KC1. 
 
 The latter being soluble in about three times its weight of cold water, is retained 
 in the solution, whilst the chlorate of potash, which would require about sixteen 
 times its weight of cold water to hold it dissolved, is deposited in brilliant rhom- 
 boidal tables. These crystals may be collected on a filter, and purified from the 
 adhering solution of chloride of potassium by pressure between successive portions 
 of filter-paper. If they be free from chloride of potassium, their solution in water 
 will not be changed by nitrate of silver, which would yield a milky precipitate of 
 chloride of silver if that impurity were present. Should this be the case, the cry- 
 stals must be redissolved in a small quantity of boiling water and recrystallised. 
 
 The above processes for preparing the chlorate of potash are far from 
 economical, since five-sixths of the potash are converted into chloride, 
 being employed merely to furnish oxygen to convert the chlorine into 
 chloric acid. In manufacturing chlorate of potash upon the large scale, a 
 much cheaper material, lime, is used to furnish the oxygen, one equivalent 
 of carbonate of potash being mixed with six equivalents of slaked lime, 
 and the damp mixture saturated with chlorine. On treating the mass 
 with boiling water, a solution is obtained which contains chlorate of 
 potash and chloride of calcium, the latter, being very soluble, remains in 
 the liquor from which the chlorate. of potash crystallises on cooling. The 
 ultimate result of the action of chlorine upon the mixture of carbonate of 
 potash and lime is thus expressed 
 
 KO . C0 2 + 6CaO + C1 6 - KO . C10 5 + 5CaCl + CaO . C0 2 . 
 
 A still cheaper salt of potassium, the chloride, has recently been em- 
 ployed with great economy as a substitute for the carbonate of potash. 
 
DETONATING COMPOSITIONS. 
 
 157 
 
 The solution of chloride of potassium is mixed with lime, and saturated 
 with chlorine in close leaden tanks. The solution is filtered, evaporated 
 nearly to dryness, and redissolved in hot water, when the chlorate of 
 potash crystallises out on cooling. The chloride of calcium is precipi- 
 tated by carbonate of soda to obtain precipitated chalk. 
 
 Anhydrous chloric acid (C10 5 ) has never been obtained in the separate 
 state ; but its hydrate (HO . C10 5 ) may be procured by decomposing a 
 solution of chlorate of potash with hydrofluosilicic acid, when the potas- 
 sium is deposited as an insoluble silico-fluoride, and hydrated chloric acid 
 is found in the solution* 
 
 KO.C10, 
 
 HO . CIO, 
 
 KF.SiF, 
 
 - HF.SiF 2 = 
 
 Hydrofluosilicic acid. 
 
 On evaporating the solution at a temperature not exceeding 100 F., 
 the hydrated chloric acid is obtained as a yellow liquid with a peculiar 
 pungent smell. 
 
 In its chemical characters, hydrated chloric acid bears a very strong 
 resemblance to hydrated nitric acid, but is far more easily decomposed. 
 It cannot even be kept unchanged for any length of time, and at tem- 
 peratures above 104 F. it is decomposed into perchloric acid, chlorine, 
 and oxygen 
 
 2(HO.C10 5 ) = HO.C10 7 + HO + Cl + 3 . 
 
 Hydrated chloric acid is one of the most powerful oxidising agents. 
 A drop of it will set fire to paper, and oxidises phosphorus (even the 
 amorphous variety) with explosive violence. 
 
 Clilorates. Chloric acid, like nitric, is monobasic, one equivalent (47 
 parts) of potash forming a neutral salt with 75*5 parts of imaginary 
 anhydrous chloric acid (C10 5 ). The chlorates resemble the nitrates in 
 their oxidising power, but generally act at lower tem- 
 peratures, in consequence" of the greater facility with 
 which the chlorates part with their oxygen. 
 
 A grain or two of chlorate of potash, rubbed in a mortar with 
 a little sulphur, for example, detonates violently, evolving a 
 powerful odour of chloride of sulphur. Chlorate of potash and 
 sulphur were used in some of the first percussion caps, but being 
 found to corrode the nipple of the gun, they gave place to the 
 anticorrosive caps containing fulminate of mercury. 
 
 If a little powdered chlorate of potash be mixed, on a card, 
 with some black sulphide of antimony, and wrapped up in paper, 
 the mixture will detonate when struck with a hammer. 
 
 A mixture of this description is employed in the friction tubes 
 used for firing cannon. These are small tubes (A, fig. 165) of 
 sheet copper (for military) or of quill (for naval use), filled 
 with gunpowder ; in the upper part of the tube a small copper 
 rasp (B) is tightly fixed across it, and on each side of the rasp 
 a pellet is placed containing 12 parts of chlorate of potash, 
 12 of sulphide of antimony, and 1 of sulphur, these ingredients 
 being worked up into a paste with a solution of an ounce of 
 shellac in a pint of spirit of wine. The friction tube is fixed in 
 the vent of the gun, and the copper rasp quickly withdrawn by 
 a cord in the hands of the gunner, when the detonating pellets 
 explode and fire the powder. 
 
 The earliest lucifer matches were tipped with a mixture of chlorate of potash, 
 sulphide of antimony and starch, and were kindled by drawing them briskly through 
 a doubled piece of sand-paper. 
 
 * 440 grain measures of hydrofluosilicic acid of sp. gr. 1078 will decompose 100 grains 
 of chlorate of potash. 
 
 Fig. 165. 
 
158 COLOURED FIKES. 
 
 At high temperatures the chlorates act violently upon combustible 
 bodies. A little chlorate of potash sprinkled upon red-hot coals causes a 
 very violent deflagration. If a little chlorate of pot- 
 ash be melted in a deflagrating spoon, and plunged 
 into a bottle or flask containing coal-gas (fig. 166), 
 the salt burns with great brilliancy, its oxygen com- 
 bining with the carbon and hydrogen in the gas, 
 which becomes, in this case, the supporter of com- 
 bustion. The flask may be conveniently filled with 
 coal-gas by inverting it, and passing a flexible tube 
 from the gas pipe up into it. 
 
 Chlorate of potash is much used in the manufac- 
 ture of fireworks, especially as an ingredient of 
 coloured fire compositions, which generally consist 
 of chlorate of potash mixed with sulphur, and with 
 Fig 166 some metallic compound to produce the desired 
 
 colour in the flame. They are not generally made 
 of the best quality on the small scale, from want of attention to the very 
 finely powdered state of the ingredients, the absence of all moisture, and 
 the most intimate mixture. 
 
 If these precautions be attended to, the following prescriptions will give very good 
 coloured fires : 
 
 Red fire. 40 grains of nitrate of strontia, thoroughly dried over a lamp, are mixed 
 with 10 grains of chlorate of potash, and reduced to the finest possible powder. In 
 another mortar 13 grains of sulphur are mixed with 4 grains of black sulphide of 
 antimony (crude antimony). The two powders are then placed upon a sheet of 
 paper, and very intimately mixed with a bone knife, avoiding any great pressure. 
 A little heap of the mixture touched with a red-hot iron ought to burn with a 
 uniform red flame, the colour being due to the strontium. 
 
 Blue fire. 15 grains of chlorate of potash are mixed with 10 grains of nitrate of 
 potash and 30 grains of oxide of copper in a mortar. The finely-powdered mixture 
 is transferred to a sheet of paper, and mixed, by a bone knife, with 15 grains of 
 sulphur. The colour of the fire is given chiefly by the copper. 
 
 Green fire. 10 grains of chlorate of baryta are mixed with 10 grains of nitrate of 
 baryta in a mortar, and afterwards, on paper, with 12 grains of sulphur. The barium 
 is the cause of the bright green colour of the flame. 
 
 These compositions are rather dangerous to keep, since they are liable to spon- 
 taneous combustion. 
 
 White gunpowder is a mixture of two parts of chlorate of potash with one part of 
 dried yellow prussiate of potash, and one part of sugar, which explodes very easily 
 under friction or percussion. 
 
 The decomposition of chlorate of potash by heat into oxygen and chlo- 
 ride of potassium is attended with evolution of heat, unlike most cases of 
 chemical decomposition, in which heat is generally absorbed. If chlorate 
 of potash be heated to the point at which it begins to decompose, and a 
 little peroxide of iron be thrown into it, enough heat will be evolved to 
 bring the mass to a red heat, although the peroxide of iron is not oxidised. 
 Experiment has shown that one part of chlorate of potash evolves, during 
 decomposition, nearly 39 units of heat, or enough heat to' raise 39 parts of 
 water through 1 C. This anomalous evolution of heat must of course 
 contribute to increase the energy of explosive mixtures containing the 
 chlorate, and may be accounted for on the supposition, that the heat evolved 
 by the combination of the potassium with the chlorine to form chloride of 
 potassium exceeds that which is absorbed in effecting the chemical disin- 
 tegration of the chlorate. 
 
CHLORIC PEROXIDE. 159 
 
 114. Anhydrous perchloric acid (C10 7 ) is not known. The hydrated 
 acid is obtained by evaporating down, at a boiling heat, the solution of 
 chloric acid obtained by decomposing chlorate of potash with hydrofluo- 
 silicic acid (see p. 157), when the chloric acid is decomposed into per- 
 chloric acid, chlorine, and oxygen 
 
 2(HO.C10 5 ) = HO.C10 7 + HO + Cl + 3 . 
 
 When the greater part of the water has been boiled off, the liquid may be intro- 
 duced into a retort and distilled. After the remainder of the water has passed over, 
 it is followed by a heavy oily liquid which is HO . C10 7 + 4HO. If this be mixed 
 with four times its volume of strong sulphuric acid and again distilled, the pure 
 hydrated perchloric acid (HO.C10 7 ) first passes over as a yellow watery liquid. 
 If the distillation be continued, the oily HO . C10 7 + 4HO distils over, and if 
 this be mixed with the former and cooled, it yields silky crystals containing 
 HO.C10 7 + 2HO, which are decomposed at 230 F. into HO.C10 7 , which may be 
 distilled off, and HO . C10 7 + 4HO, which is left in the retort 
 
 2(HO . C10 7 + 2HO) = HO . C10 7 + (HO . C10 7 + 4HO) . 
 
 The pure hydrated perchloric acid is a colourless, very heavy liquid 
 (sp. gr. 1*782), which soon becomes yellow from decomposition. It 
 cannot be kept for any length of time. When heated it undergoes de- 
 composition, often with explosion. In its oxidising properties it is more 
 powerful than chloric acid. It burns the skin in a very serious manner, 
 and sets fire to paper, charcoal, &c., with explosive violence. This want 
 of stability, however, belongs only to the pure hydrate. If water be 
 added to it heat is evolved, and a diluted acid of far greater permanence 
 is obtained. Diluted perchloric acid does not even bleach, but reddens 
 litmus in the ordinary way. 
 
 Perchloric acid is monobasic. The percklorates are decomposed by 
 heat, evolving oxygen, and leaving chlorides ; thus 
 
 KO.C10 7 = KC1 + 8 . 
 
 Perchlofate of potash. 
 
 The perchlorate of potash is always formed in the first stage of the decom- 
 position of chlorate of potash by heat 
 
 2(KO . C10 5 ) = KO . C10 7 + KC1 + 4 . 
 
 If a few crystals of chlorate of potash be heated in a test-tube, they first melt to 
 a perfectly clear liquid, which soon evolves bubbles of oxygen. After a time the 
 liquid becomes pasty, and if the contents of the tube, after cooling, be dissolved by 
 boiling with water, the latter will deposit, as it cools, crystals of perchlorate of 
 potash. These are readily distinguished from chlorate of potash by their not yield- 
 ing a yellow gas (C10 4 ) when treated with strong sulphuric acid. The perchlorate 
 of potash is remarkable as one of the least soluble of the salts of potash, requiring 
 150 times its weight of cold water to dissolve it. Neither perchloric acid nor any 
 of its salts is applied to any useful purpose. 
 
 115. Chloric peroxide or peroxide of chlorine is dangerous to prepare and examine' 
 on account of its great instability and violently explosive character. It is obtained 
 by the action of strong sulphuric acid upon chlorate of potash 
 
 3(KO . C10 5 ) + 2(HO . S0 3 ) = KO . C10 7 + KO . S0 3 , HO . S0 3 + 2C10 4 + HO . 
 Sulphuric acid. ? ~ < Bisulphate of potash. 
 
 It is a bright yellow gas, with a chlorous and somewhat aromatic smell, and sp. gr. 
 2-32 ; condensible at 4 F. to a red, very explosive liquid. The gas is gradually 
 decomposed into its elements by exposure to light, and a temperature of 140 F. 
 causes it to decompose with violent explosion into a mixture of chlorine and oxygen, 
 the volume of which is one-third greater than that of the compound. 
 
 On a small scale chloric peroxide may be prepared with safety by pouring a little 
 
160 
 
 CHLOROUS ACID. 
 
 Fig. 167. 
 
 strong sulphuric acid upon one or two crystals of chlorate of potash in a test-tube 
 supported in a holder. The crystals at once acquire a red colour, which gradually 
 diffuses itself through the liquid, and the bright yellow gas collects in the tube. If 
 heat be applied, the gas will explode, and the colour and odour of chloric peroxide 
 will be exchanged for those of chlorine. If the chlorate of 
 potash employed in this experiment contains chloride of 
 potassium, explosion often takes place in the cold, since the 
 hydrochloric acid evolved by the action of the acid upon that 
 salt decomposes a part of the chloric peroxide, and thus pro- 
 vokes the decomposition of the remainder. 
 
 Chloric peroxide is easily absorbed by water, and 
 the solution has powerful bleaching properties. Com- 
 bustible bodies, such as sulphur and phosphorus, de- 
 compose the gas, as might be expected, with great vio- 
 lence. This powerful oxidising action of chloric per- 
 oxide upon combustible substances, appears to be the 
 cause of the property possessed by mixtures of such 
 substances with chlorate of potash to inflame when 
 touched with strong sulphuric acid. 
 
 If a few crystals of chlorate of potash be thrown into a glass of water (fig. 167). 
 one or two small fragments of phosphorus dropped upon them, and some strong 
 sulphuric acid poured down a funnel tube to the bottom of the glass, the chloric 
 peroxide will inflame the phosphorus with bright flashes of light and slight detona- 
 tions. 
 
 Powdered sugar, mixed with chlorate of potash, on paper, will burn brilliantly 
 when touched with a glass rod dipped in strong sulphuric acid. Matches, may be 
 prepared which inflame when moistened with sulphuric acid, by dipping the ends of 
 splinters of wood in melted sulphur, and when cool, tipping them with a mixture of 
 5 grains of sugar and 15 grs. of chlorate of potash made into a paste with 4 drops 
 of water. When dry they may be fired by dipping them into a bottle containing 
 asbestos moistened with strong sulphuric acid. These matches, under the names of 
 Eupyrion and Vesta matches, were used before the introduction of phosphorus into 
 general use. The Promethean light was an ornamental scented paper spill, one end 
 of which contained a small glass bulb of sulphuric acid surrounded with a mixture 
 of chlorate of potash and sugar, which inflamed when the end of the spill was 
 struck or squeezed, so as to break the bulb containing the sulphuric acid. The paper 
 was waxed in order to make it inflame more easily. Percussion fuzes, &c., have 
 been often constructed upon a similar principle. 
 
 Chloric peroxide used to be called hypochloric acid, but, like nitric per- 
 oxide, it appears to have no claim to be considered a true acid, since, in con- 
 tact with the alkalies, it yields mixtures of chlorites and chlorates ; thus 
 
 2C10 4 + 2KO = KO.C10 3 + KO . C10 5 . 
 Euchlorine, the deep yellow, dangerously explosive gas evolved by the 
 action of strong hydrochloric acid upon chlorate of potash, appears to be 
 a compound of chloric and chlorous acids (2C10 5 . C10 3 ) mixed with free 
 chlorine. 
 
 116. Chlorous acid is another unstable and dangerously explosive gas, 
 obtained by the action of a very gentle heat upon a mixture of three parts 
 of arsenious acid, four of chlorate of potash, and sixteen of diluted nitric 
 acid (sp. gr. T24) 
 
 KO . CIO, + HO . NO, + AsO Q + 2HO = 
 
 Chlorate of potash. Nitric acid. 
 
 KO . N0 5 + 3HO . As0 5 
 
 Nitrate of potash. Arsenic acid. 
 
 Chlorous acid is a deep yellowish green heavy gas (sp. gr. 2-65) which 
 
 Arsenious acid. 
 
 r- C10 3 
 Chlorous acid. 
 
REVIEW OF OXIDES OF CHLORINE, 
 
 161 
 
 is absorbed by water, and decomposed even more easily than the chloric 
 peroxide. It is a weak acid, its salts, the chlorites, being decomposed 
 even by carbonic acid. A mixture of ice and salt does not liquefy chlorous 
 acid, but an intense cold condenses it to a red liquid. 
 
 117. General review of the oxides of chlorine. Several points of resem- 
 blance will have been noticed between the series of oxides of chlorine and 
 those of nitrogen, but the former are much less stable than the latter. 
 Chlorous acid (C10 3 ), like nitrous acid (N0 3 ), is a weak acid; chloric per- 
 oxide (ClO^ is easily resolved by bases into chlorous and chloric acids, 
 just as nitric peroxide (N0 4 ) is resolved into nitrous and nitric acids. 
 The hydrated chloric acid (HO . C10 5 ) is a powerful oxidising agent like 
 hydrated nitric acid (HO . N0 5 ), and the chlorates resemble the nitrates 
 in their solubility in water and their oxidising power. The composition 
 by volume of those oxides of chlorine which are known in the separate 
 state, is exhibited in the following table : 
 
 
 Equivt. 
 Formula. 
 
 Equivt. 
 Weight. 
 
 Equivt. 
 Volume. 
 
 By Volume. 
 
 Cl 
 
 
 
 Hypochlorous acid . 
 
 CIO 
 
 43-5 
 
 2 
 
 2 
 
 1 
 
 Chlorous acid . . 
 
 C10 3 
 
 59-5 
 
 3 
 
 2 
 
 3 
 
 Chloric peroxide . 
 
 C10 4 
 
 67'5 
 
 4 
 
 2 
 
 4 
 
 The relative volumes in which the chlorine and oxygen are united are 
 the same, therefore, as in the corresponding oxides of nitrogen, but the 
 equivalent volume of chlorous acid differs from that which is usually 
 assumed for nitrous acid (see the table at p. 137). 
 
 On the hypothesis that each atom of an element occupies one volume, 
 the molecular (atomic) formula of hypochlorous acid would be C1 2 0, that 
 of chlorous acid C1 2 O 3 , and that of chloric peroxide C1 2 O 4 , or, on the as- 
 sumption that the compound molecule occupies only two volumes, C1O 2 . 
 
 Some chemists refuse to regard the hypochlorites, chlorites, chlorates, 
 and perchlorates as composed of basic oxides united with hypochlorous, 
 chlorous, (hypothetical) chloric, and (hypothetical) perchloric acids respec- 
 tively, but consider them as derived from (hypothetical) hydrated hypo- 
 chlorous acid (HO . CIO or HC10 2 ), (hypothetical) hydrated chlorous acid 
 (HO . C10 3 or HC10 4 ), hydrated chloric acid (HO . C10 5 or HC10 6 )5 and 
 hydrated perchloric acid (HO . C10 7 or HC10 8 ), by the substitution of 
 metals for the hydrogen contained in those compounds. Thus hypo- 
 chlorite of lime (CaO . CIO) would become CaC10 2 , chlorate of potash 
 (KO . C10 5 ) would be KC10 6 , &c. 
 
 Against the first view it may be plausibly advanced, that we are unac- 
 quainted with the compounds C10 5 and C10 7 , and against the second, that 
 HC10 2 and HC10 4 are at present unknown. Moreover, if these formula) 
 represented the true constitution of the acids, it would be expected that 
 their solutions in water should tend to decompose into hydrochloric acid 
 and free oxygen, which is not the case. 
 
162 
 
 BICHLOKIDE OR TETRACHLORIDE OF CARBON. 
 
 CHLORIDES OF CARBON. 
 
 118. It has already been seen that chlorine has no direct attraction for 
 carbon, the two elements not being known to enter into direct combina- 
 tion, but several chlorides of carbon may be obtained by the action of 
 chlorine upon other compounds of carbon. Thus, if Dutch liquid 
 (C 4 H 4 C1 2 ), produced by the combination of olefiant gas with chlorine 
 (p. 86), be acted upon with an excess of chlorine in sunlight, the whole 
 of its hydrogen is removed in the form of hydrochloric acid, and an equi- 
 valent amount of chlorine is substituted for it, yielding the sesquichloride 
 of carbon (Cfl,) 
 
 C 4 H 4 C1 2 + C1 8 = C 4 C1 6 + 4HC1 . 
 
 Sesquichloride of carbon is a white crystalline solid, with an aromatic 
 odour rather like that of camphor. It fuses at 320 F., and boils at 360, 
 subliming unchanged. It is not dissolved by water, but is soluble in 
 alcohol and ether. 
 
 When the vapour of sesquichloride of carbon is passed through a tube 
 containing fragments of glass heated to redness, it is decomposed into 
 chlorine and a colourless liquid, which is the protochloride of carbon 
 (C 4 C1 4 ). It has an aromatic odour, and boils at 248 F. ; is heavier than 
 water (sp. gr. 1*5), which does not dissolve it, and is soluble in alcohol 
 and ether. 
 
 By passing the vapour of this protochloride of carbon through tubes 
 heated to bright; redness, it is decomposed into chlorine and subcldoride of 
 carbon (C 4 C1 2 ), which forms silky crystals almost free from odour, insoluble 
 in water, but soluble in ether, and capable of being sublimed unchanged 
 at a high temperature. It burns in air with a red smoky flame. 
 
 Bichloride of carbon (C 2 C1 4 ) has been mentioned (p. 144) as the 
 
 Fig. 168. Preparation of bichloride of carbon. 
 
 final result of the action of chlorine upon marsh-gas (C 2 H 4 ) and upon 
 chloroform (C 2 HC1 3 ), It is easily obtained in large quantity, by passing 
 chlorine (dried by passing through a tube containing pumice wetted with 
 strong sulphuric acid) (fig. 168) through a bottle containing bisulphide of 
 carbon, and afterwards through a porcelain tube wrapped in sheet copper, 
 
CHLORIDES OF CARBON. 163 
 
 and filled with fragments of broken porcelain, maintained at a red heat 
 by a charcoal or gas furnace, and condensing the products in a bottle sur- 
 rounded by ice. A mixture of bichloride of carbon and subchloride of 
 sulphur is thus obtained 
 
 2CS 2 + C1 6 = C 2 C1 4 + 2S 2 C1. 
 
 By shaking this mixture with solution of potash, the subchloride of sul- 
 phur is decomposed and dissolved, whilst the bichloride of carbon separates 
 and falls to the bottom. The upper layer having been poured off, the 
 bichloride may be purified by distillation. 
 
 Bichloride of carbon is a colourless liquid much heavier than water 
 (sp. gr. 1'6), having a peculiar odour, and boiling at 172 F. It may be 
 solidified at 9 F. The bichloride is insoluble in water, but dissolves 
 in alcohol and ether. 
 
 By the action of chlorine on naphthaline (C 20 H 8 ) Laurent obtained, as 
 the ultimate result, a crystalline chloride of carbon containing C 20 C1 8 , to 
 which he gave the name chlonaplithalise. 
 
 It will be noticed that each of the compounds of chlorine with carbon, 
 except the sesquichloride, has its parallel in the compounds of hydrogen 
 with carbon;* thus 
 
 Acetylene C 4 H 2 corresponds to subchloride of carbon C 4 C1 2 
 Olefiant gas C 4 H 4 protochloride ,, C 4 C1 4 
 
 Marsh-gas C 2 H 4 bichloride C 2 C1 4 
 
 Indeed the principal reason for preferring these formulae to the formulae 
 C 2 C1, CC1, and CC1 2 , is that this correspondence may be exhibited, for 
 since the chlorides of carbon are indifferent substances, it is not possible 
 to obtain their equivalent weights by direct experiment, as in the case of 
 bases or acids. 
 
 Composition by volume of the chlorides of carbon. The composition 
 of the chlorides of carbon, as determined by analysis, has been confirmed 
 by the observation of their vapour densities (or specific gravities of their 
 vapours), except in the case of the subchloride, of which the vapour 
 density does not appear to have been correctly ascertained. 
 
 If it be assumed (see p. 81) that 6 parts by weight (1 eq.) of carbon, 
 if converted into vapour, would occupy 2 vols. (0 = 1 vol.), then the 
 protochloride of carbon would contain 2 vols. of imaginary carbon vapour 
 and 2 vols. of chlorine. 
 
 The specific gravity (or weight of 1 vol.) of imaginary carbon vapour 
 being '424, and that of chlorine 2 '4 7 
 
 2 vols. carbon vapour would weigh '848 
 2 vols. chlorine 4 "940 
 
 5-788 
 
 The weight of 1 vol. (sp. gr.) of protochloride of carbon vapour has 
 been found to be 5 '82, which (allowing for experimental errors) is 
 clearly the sum of these weights. Hence the weight of protochloride of 
 carbon represented by the formula CC1 occupies 1 vol., and contains 2 
 vols. of imaginary carbon vapour and 2 vols. of chlorine. But if the 
 formula of olefiant gas be represented as C 4 H 4 (28 parts by weight, occu- 
 
 * When vapour of protochloride of carbon is mixed with hydrogen, and passed through 
 a red-hot tube, olefiant gas and hydrochloric acid are produced. The bichloride, under 
 similar circumstances, yields marsh-gas. 
 
 L2 
 
164 
 
 MOLECULAR FORMULA OF CHLORIDES OF CARBOX. 
 
 pying 4 vols. ; = 1 vol.), then the formula of protochloride of carbon 
 must be C 4 C1 4 (166'0 parts by weight, occupying 4 vols. ; = 1 vol.) 
 
 It has also been found that the weight of 1 volume (sp. gr.) of the 
 vapour of sesquichloride of carbon is 8 '157. But the sum of the weights 
 of 4 vols. (2 eqs.) imaginary carbon vapour, and 6 vols. (3 eqs.) chlorine, 
 would be 16*516, representing 2 vols. of C 2 C1 3 . The formula G 4 C1 6 , there- 
 fore, would represent 8 vols. of carbon vapour and 12 vols. of chlorine 
 condensed into 4 vols. of sesquichloride of carbon. 
 
 The history of sesquichloride of carbon affords an instructive instance 
 of the influence of the composition by volume of a compound upon its 
 properties. By passing the vapour of bichloride of carbon through a 
 tube heated to dull redness, a liquid is obtained which is found by 
 analysis to contain precisely the same proportions of carbon and chlorine 
 as the solid sesquichloride above described, but the specific gravity of its 
 vapour is only 4 '082, which is half that of the vapour of solid sesqui- 
 chloride of carbon, showing that in the liquid compound the same propor- 
 tions of carbon vapour and chlorine are condensed into a volume twice as 
 large as in the solid sesquichloride, 4 vols. of the vapour of the liquid 
 containing 4 vols. imaginary carbon vapour, and 6 vols. chlorine, and 
 being represented by the formula C 2 C1 3 . 
 
 The weight of 1 volume (sp. gr.) of vapour of bichloride of carbon is 
 5 '3, which is the sum of 1 vol. imaginary carbon vapour and 2 vols. chlo- 
 rine. The formula CC1 2 , therefore, would represent (1 eq.) 2 vols. of 
 carbon vapour and (2 eqs.) 4 vols. of chlorine condensed into 2 vols. of 
 bichloride of carbon ; whilst C 2 C1 4 represents 4 vols. carbon and 8 vols. 
 chlorine condensed into 4 vols. of bichloride of carbon. 
 
 Molecular formula? of the chlorides of carbon. If the atom of carbon 
 (O) be assumed to represent 12 parts by weight, and to occupy the same 
 volume in the form of vapour as 1 part by weight of hydrogen ( = 1 vol. 
 or 1 atom), and 35 '5 parts by weight of chlorine, which occupy the same 
 volume as 1 part of hydrogen, be taken to represent one atom, the mole- 
 cular formulce of the chlorides of carbon would be 
 Subchloride of carbon ^0^ corresponding to O 2 H 2 acetylene. 
 
 Protochloride of carbon @ 2 d.i ^ft olefiant gas. 
 
 Sesquichloride of carbon (solid) O 2 C1 6 
 
 (liquid) eci 3 
 
 Bichloride of carbon C1 4 OH 4 marsh-gas. 
 
 And each of these formulae would represent twice the volume occupied by 
 one atom of hydrogen, that is, would represent two volumes. 
 
 The following table exhibits the relations between the equivalent for- 
 mulae and the molecular formulae of the chlorides of carbon : 
 
 Chlorides of Carbon. 
 
 
 Equivt. 
 Formulae. 
 
 Equivt. 
 Volume. 
 
 Equivt. 
 Weight. 
 
 Molecular 
 Formulae. 
 
 Molecular 
 Volume. 
 
 Molecular 
 Weight. 
 
 Sufochloride 
 
 C,CL 
 
 49 
 
 95-0 
 
 Cl 
 
 2? 
 
 95-0 
 
 Protochloride, .... 
 
 
 4 
 
 166-0 
 
 
 2 
 
 166-0 
 
 Sesquichloride (solid), 
 
 C 4 C1 6 
 
 4 
 
 237-0 
 
 e 2 ci 6 
 
 2 
 
 237-0 
 
 (liquid), . 
 
 C 2 C1 3 
 
 4 
 
 118-5 
 
 e 2 ci 3 
 
 2 
 
 118-5 
 
 Bichloride, . . . . . 
 
 C 2 C1 4 
 
 4 
 
 154-0 
 
 e 2 ci 4 
 
 2 
 
 154-0 
 
CHLORIDE OF SILICON. 165 
 
 119. Oxycldoride of carbon, chlorocarbonic acid, or phosgene gas, is pro- 
 duced by the direct combination of equal volumes of carbonic oxide and 
 chlorine gases under the influence of sunlight (whence its last name), 
 when the mixture condenses to half its volume of a colourless gas, having 
 a very t peculiar pungent smell, and fuming strongly when exposed to 
 moist air, decomposing the moisture and producing hydrochloric acid; 
 CO . Cl + HO = C0 2 + HC1. It is not a true acid, for it is de- 
 composed by bases, producing chlorides and carbonates. It is sometimes 
 fdund useful in chemical research for removing hydrogen from organic 
 compounds, and introducing carbonic oxide, or its elements, into its place. 
 Its action on ammonia affords an example of this 
 
 4(NH 3 ) + C 2 2 .C1 2 = C 2 2 H 4 N 2 + 2(NH 3 .HC1) 
 
 Urea. Hydroclilorate of 
 
 ammonia. 
 
 in which two equivalents of NH 3 have been decomposed, two equivalents 
 of the hydrogen having been removed in the form of hydrochloric acid, 
 and replaced by two equivalents of carbonic oxide. 
 
 From this and similar reactions, it is inferred that the true equivalent 
 formula of the oxychloride of carbon is C 2 2 C1 2 . 
 
 120. Chloride of silicon, unlike the chlorides of carbon, may be formed 
 by the direct union of silicon with chlorine at a high temperature, but it 
 is best prepared by passing dry chlorine over a mixture of artificial silica 
 and charcoal, heated to redness in a porcelain tube connected with a 
 receiver kept cool by a freezing-mixture. Neither carbon nor chlorine 
 separately will act upon the silica, but when they are employed to- 
 gether, the carbon removes the oxygen and the chlorine combines with 
 the silicon 
 
 Si0 2 + C 2 + C1 2 = SiCl 2 + 2CO . 
 
 The chloride of silicon is a colourless heavy liquid (sp. gr. 1 -52) which 
 is volatile (boiling point, 138 F.), and fumes when exposed to air, the 
 moisture of which decomposes it, yielding hydrochloric and silicic acids 
 
 SiCl 2 + 2HO = Si0 2 + 2HC1 . 
 
 Athough it has received no practical application on a large scale, the 
 chloride of silicon is valuable to the chemist as a convenient source of 
 compounds of silicon, which could not easily be procured from the very- 
 unchangeable silicic acid. 
 
 The specific gravity (or weight of one volume) of vapour of chloride of 
 silicon is 5*87. Supposing it to be similarly constituted to the bichloride 
 of carbon, this would contain 2 vols. of chlorine, and 1 vol. of imaginary 
 vapour of silicon. Deducting the weight of 2 vols. chlorine (4'94) from 
 that of 1 vol. of the chloride of silicon (5-87), there remains 0'93 for the 
 weight of 1 vol. or sp. gr. of hypothetical vapour of silicon. 
 
 The formula SiCl^ would represent 4 vols. of chlorine (2 eqs.) com- 
 bined with 2 vols. (1 eq.) of imaginary vapour of silicon, and condensed 
 into a space of two volumes. 
 
 Since SiCl 2 represents 14 parts by weight (1 eq.) of silicon combined 
 with 71 parts (2 eqs.) of chlorine, if the atom of silicon be assumed to 
 weigh 28 (see p. 109), it would be combined with 142 (4 atoms) of chlo- 
 rine, and the atomic (molecular) formula of the chloride of silicon would 
 be SiCl^ (Si = 28.) The silicon, here occupying the place of four atoms 
 of hydrogen in hydrochloric acid, is often designated a tetmtomic element 
 
1G6 PREPARATION OF CHLORIDE OF NITROGEN. 
 
 (see p. 151). Those chemists who regard silicic acid as Si0 3 of course 
 represent the chloride of silicon as SiCl 3 . 
 
 By passing hydrochloric acid over silicon heated to redness, a very remarkable 
 liquid is obtained, which is much more volatile than the chloride of silicon (boiling 
 point, 108 F.), and, unlike most chlorine compounds, is inflammable, burning with a 
 .greenish flame, and producing silica and hydrochloric acid. It fumes strongly in air, 
 and is decomposed by water, yielding hydrochloric acid, and the substance termed 
 leukone. The composition of this liquid appears to be Si 3 H 2 Cl., and its production 
 would be represented by the equation Si 3 + 5HC1 =: Si 3 H 2 Cl 5 + H 3 . Its decom- 
 position by water would be explained by the equation 
 
 Si 3 H 2 01 5 + 5HO = Si 3 H 2 5 + 5HC1. 
 * Leukone. 
 
 The chloride of boron (BC1 3 ) is similar in its general character to the 
 chloride of silicon, and is prepared by a similar process, but it is a gas 
 instead of a liquid at ordinary temperatures. 
 
 121. Chloride of nitrogen is the name usually given to the very explo- 
 sive compound before referred to as being produced by the action of 
 chlorine on sal-ammoniac. Its composition is somewhat uncertain; its 
 explosive character rendering its exact analysis very difficult. Some 
 chemists regard it as NC1 3 , that is, ammonia in which all the hydrogen 
 has been displaced by chlorine, whilst others believe it to contain hydrogen, 
 regarding it as derived from two equivalents of ammonia (NH 3 . NH 3 ), 
 by the substitution of five equivalents of chlorine for five of hydrogen 
 
 It is a yellow, heavy, oily liquid (sp. gr. 1*65), which volatilises easily, 
 yielding a vapour of very characteristic odour, which affects the eyes. 
 When heated to about 200 F. it explodes with great violence, emitting a 
 loud report and a flash of light. Its instability is, of course, attributable 
 to the feeble attraction which holds its elements together; and the violence 
 of the explosion, to the sudden expansion of a small volume of the liquid 
 into a large volume of nitrogen, chlorine, and perhaps hydrochloric acid. 
 As might be expected, its explosion is at once brought about by contact 
 with substances which have an attraction for chlorine, such as phosphorus 
 and arsenic ; the oils and fats cause its explosion, probably by virtue of 
 their hydrogen ; oil of turpentine explodes it with greater certainty than 
 the fixed oils. Alkalies also decompose it violently ; whilst acids, having 
 no action upon the chlorine^ are not so liable to explode it. At 160 F. 
 this substance has actually been distilled without explosion. 
 
 Although practically unimportant, the violent explosive properties of 
 this substance render it so interesting that it may be well to give some 
 directions for its safe preparation. 
 
 Preparation of chloride of nitrogen. 'Dissolve 4 oz. of sal-ammoniac in 48 oz. 
 (measured) of water, in a porcelain dish, at a gentle heat. Filter the solution, and 
 pour it into a shallow leaden dish (A. fig. 169), previously cleaned from all grease by 
 
 ooiling a little solution of potash in it. Place in 
 the solution a smaller leaden dish (B) (capacity, 
 1| oz.), cleaned in the same way, and furnished 
 with a copper wire handle. 
 
 Cut off the neck of a Florence flask (by scratch- 
 ing with a file, and leading the crack round with 
 a red-hot iron), clean it by boiling a little potash 
 in it, rinse it in water, and attach it to a string, so 
 Fig. 169. that it may be suspended, in an inverted position, 
 
 upon a stand. 
 
 When the temperature of the solution of sal-ammoniac has fallen to nearly 90 F., 
 fill the Florence flask with water in the pneumatic trough, and displace the water 
 
NITROMURIATIC ACID AQUA REGIA. 
 
 167 
 
 by chlorine, passed up from a gas bottle free from grease. Close the flask with a 
 watch-glass placed under the orifice, and suspend it by the string from a stand (fig, 
 170), so that its mouth may be about an inch below the surface of the solution of 
 sal-ammoniac, and immediately over the 
 centre of the small leaden dish. Remove 
 the watch-glass, and let the whole arrange- 
 ment be placed where the explosion can 
 do no harm. The solution will soon begin 
 to absorb the chlorine and to rise in the 
 flask, whilst yellow oily globules form upon 
 Us surface, occasionally collecting into a 
 larger one, which falls through the solution 
 into the small leaden dish. When the 
 flask is nearly filled with the solution, which 
 will require about twenty minutes, gently 
 raise the flask, from a distance, by hooking 
 the string with a wire at the end of a long 
 
 Fig. 170. 
 
 stick, and allow the solution to flow gently out of it into the leaden dish. Place 
 the flask at a safe distance, lest there should be any chloride of nitrogen still clinging 
 to it. Examine the leaden dishes to see where the oily globules have fallen, 
 lifting out the smaller dish by hooking its wire handle with a long stick. Explode 
 the globules from a safe distance with a stick dipped in turpentine. A good explo- 
 sion will throw the solution up several feet, and will raise a large leaden dish several 
 inches into the air, indenting it deeply at the seat of the explosion. 
 
 Another method of preparing the chloride, when it is not desired to examine it 
 closely, but merely to witness the explosion, consists in acting upon sal-ammoniac 
 with solution of hypochlorous acid ; but as this does not succeed in a leaden vessel, 
 and must be performed in glass or porcelain, the action should be conducted at a 
 distance from the operator, lest he be wounded by the fragments of the vessel. 
 
 Fifty grains of red oxide of mercury are very finely powdered, and thrown into a 
 pint bottle of chlorine together with ^ oz. (measured) of water. The stopper is 
 replaced, and the bottle well shaken, loosening the stopper occasionally as long as the 
 chlorine is absorbed. The solution of hypochlorous acid thus produced is filtered 
 from the residual oxychloride of mercury, and poured into a clean thumb-glass (fig. 
 171). A lump of sal-ammoniac weighing 20 grains is then dropped 
 into the solution, and the glass is placed in a safe situation where 
 the explosion will do no harm. After the lapse of twenty minutes, the 
 chloride of nitrogen may be exploded from a safe distance (9 feet) 
 by touching it with a stick dipped in turpentine. The glass will be 
 shattered into very small fragments, and the operator will be safer 
 behind a screen, unless protected by a fencing-mask and leather gloves. Fig. 171. 
 
 122. Aqua regia. This name has been bestowed upon the mixture of 
 (1 measure of) nitric, and (3 measures of) hydrochloric acid (nitromuriatir, 
 acid) which is employed for dissolving gold, platinum, and other metals 
 which are not soluble in the separate acids. If a little gold leaf be placed 
 in hydrochloric and nitric acids contained in separate glasses, the metal 
 will remain unaffected even on warming the acids, but if the contents of 
 the glasses be mixed, the gold will be immediately dissolved' by the 
 chlorine which is liberated in the action of the acids upon each other 
 
 3HC1 = 4110 
 
 Cl 
 
 Chloronitric gas. 
 
 The cliloronitric gas which is formed does not act upon the gold, but is 
 evolved as a red gas, condensable in a freezing mixture to a dark red liquid. 
 It has a very peculiar odour, and is decomposed by contact with water 
 into hydrochloric acid and nitric peroxide 
 
 NO.CL, + 2HO = 2HC1 + N0 4 . 
 
 A similar, though somewhat less volatile substance, called cldoronitrous gas, 
 and having the formula N0 2 C1, is produced by mixing 2 volumes of nitric 
 
168 EXTRACTION OF BROMINE. 
 
 oxide with 1 volume of chlorine ; it condenses to a red liquid at F. ; it 
 is also produced in small quantity by the action of hydrochloric acid on 
 nitric acid; HO.M), + 3HC1 = 4HO + NOfl + Ci,. 
 
 BKOMINE. 
 
 123. It generally happens that elements between which any strong 
 family likeness exists are found associated in nature. This remark par- 
 ticularly applies to the three elements chlorine, bromine, and iodine, 
 all of which are found in sea water, though the first predominates to such 
 an extent that the others for a long time escaped notice. Bromine was 
 brought to light in the year 1826 by Balard in the examination of bittern, 
 which is the liquid remaining after the chloride of sodium and some 
 other salts have been made to crystallise by evaporating sea water, which 
 contains only about one grain of bromine per gallon, in the forms of bro- 
 mide of magnesium and bromide of sodium. It is also extracted from the 
 waters of certain mineral springs, as those of Kreuznach and Kissingen, 
 which contain much larger quantities of bromine, either as bromide of 
 potassium or of sodium or magnesium. 
 
 In extracting the bromine from these waters, advantage is taken of the 
 circumstance that chlorine is capable of displacing bromine from its com- 
 binations with the metals. After most of the other salts, such as chloride of 
 sodium, sulphate of soda, and sulphate of magnesia, which are less soluble 
 than the bromides, have been separated from the water by evaporation 
 and crystallisation, the remaining liquid is subjected to the action of 
 chlorine gas, when it acquires an orange colour, due to the liberation of 
 the bromine; KBr + Cl = KC1 + Br. The bromine thus set free 
 exists now diffused through a large volume of water, which cannot be 
 separated from it in the usual way by evaporation, because bromine is 
 itself very volatile. An ingenious expedient is therefore resorted to of 
 shaking the orange liquid briskly with ether, which has a greater solvent 
 power for bromine than is possessed by water, and therefore abstracts it 
 from the aqueous solution ; since ether does not mix to any great extent 
 with water, it now rises to the surface of the liquid, forming a layer of a 
 beautiful orange colour, due to the bromine which it holds in solution. 
 This orange layer is carefully separated, and shaken with solution of 
 potash, which immediately destroys the colour by removing the bromine, 
 leaving the ether to rise to the surface in a pure state, and fit to be 
 employed for abstracting the bromine from a fresh portion of the water. 
 The action of the bromine upon potash is precisely similar to that of 
 chlorine 
 
 6KO + Br 6 = 5KBr + KO.Br0 5 . 
 
 Bromide of potassium. B J*h f 
 
 After the solution of potash has been several times shaken with the 
 ethereal solution of bromine, and has become highly charged with this 
 element, it is evaporated so as to expel the water, leaving a solid residue 
 containing the bromide of potassium and bromate of potash. This saline 
 mass is strongly heated to decompose the bromate of potash, and convert 
 it into bromide of potassium 
 
 KO . Br0 5 = KBr + 6 . 
 From this salt the bromine is extracted by distilling it with binoxide of 
 
HYDROBROMIC ACID. 169 
 
 manganese and sulphuric acid, when the potassium is oxidised at the 
 expense of the binoxide of manganese, and the bromine is liberated and 
 condensed in a receiver kept cool by iced water 
 
 KBr + Mn0 2 + 2(HO. S0 3 ) = KO. S0 3 + MnO. S0 3 + 2HO + Br. 
 
 The aspect of the bromine so produced is totally different from that of 
 any other element, for it distils over in the liquid condition, and pre- 
 serves that form at ordinary temperatures, being the only liquid non- 
 nietallic element. Its dark red-brown colour, and the peculiar orange 
 colour of the vapour which it exhales continually, are also characteristic ; 
 but, above all, its extraordinary and disagreeable odour, from which it 
 derives its name (/3po>/>ios, a stench], leaves no doubt of its identity. The 
 odour has some slight resemblance to that of chlorine, but is far more 
 intolerable, often giving rise to great pain, and sometimes even to bleed- 
 ing at the nose. 
 
 Liquid bromine is thrice as heavy as water (sp. gr. 2 '9 6), and boils at 
 145 F., yielding a vapour 5J times as heavy as air (sp. gr. 5*54). It 
 may be frozen at 9 '5 F. to a brown crystalline solid. It requires 33 
 times its weight of cold water to dissolve it, and is capable of forming a 
 crystalline hydrate (Br + 10HO) corresponding to hydrate of chlorine. 
 
 In its bleaching power, its aptitude for direct combination, and its 
 other chemical characters, it very closely resembles chlorine so closely, 
 indeed, that it is difficult to distinguish, in many cases, between the com- 
 pounds of chlorine and bromine with other substances, unless the elements 
 themselves be isolated. A necessary consequence of so great a similarity 
 is, that very little use has been made of bromine, since the far more abun- 
 dant chlorine fulfils nearly all the purposes to which bromine might 
 otherwise be applied. In the daguerreotype and photographic arts, how- 
 ever, some special applications of bromine have been discovered, and for 
 some chemical operations,, such as the determination of the illuminating 
 hydrocarbons in coal-gas, bromine is sometimes preferred to chlorine. In 
 the composition of their compounds, chlorine and bromine also exhibit 
 great analogy. 
 
 Hypobromous acid (BrO) has not been obtained in the anhydrous state, 
 but its solution in water may be obtained by shaking oxide of mercury 
 with water and bromine. The solution is very unstable, decomposing, 
 especially when heated, with liberation of bromine and formation of 
 bromic acid. The action of bromine upon diluted solutions of the alka- 
 lies, and upon the alkaline earths, produces bleaching liquids similar to 
 those formed by chlorine. 
 
 Anhydrous bromic acid (Br0 5 ) has never been obtained, but hydrated 
 bromic acid (HO . Br0 5 ) can be prepared in a similar manner to hydrated 
 chloric acid, to which it has a great general resemblance, the bromates 
 being also similar to the chlorates. 
 
 124. Hydrobromic acid. The inferiority of bromine to chlorine ix 
 chemical energy is well exemplified in its relations to hydrogen, for the 
 vapour of bromine mixed with hydrogen will not explode under the action 
 of flame or of the electric spark, like the mixture of chlorine and hydrogen. 
 Direct combination may, however, be slowly induced by contact with 
 heated platinum. 
 
 When it is attempted to prepare this acid by distilling bromide of 
 sodium or potassium with sulphuric acid (as in the preparation of hydro- 
 chloric acid), the inferior stability of hydrobromic acid is shown by the 
 
 x 
 
170 
 
 DISCOVERY OF IODINE. 
 
 decomposition of a part of it, the hydrogen being oxidised by the sulphuric 
 acid, and the bromine set free ; HBr + HO . S0 3 - 2HO + S0 2 + Br. 
 
 If a strong solution of phosphoric acid be employed instead of the 
 sulphuric, pure hydrobromic acid may be obtained. 
 
 But the most instructive method of obtaining hydrobromic acid consists 
 in attacking water with bromine and phosphorus simultaneously, when 
 the phosphorus takes the oxygen of the water, forming phosphorous acid, 
 and the bromine combines with the hydrogen to form hydrobromic acid 
 
 6HO + Br 3 + P = 3HO.P0 3 
 
 Hydrated 
 phosphorous acid. 
 
 3HBr 
 
 f 
 
 Probably bromide of phosphorus (PBr 3 ) is formed as an intermediate stage. 
 
 The experiment may be made in a W-formed tube (fig. 172), one bend of which 
 contains 40 grains of phosphorus in fragments inter- 
 mingled with glass moistened with water, whilst the 
 other bend contains 240 grains of bromine ( about one 
 drachm). This limb of the tube is corked, and the 
 other furnished with a delivery tube, so that the gas 
 may be collected either by downward displacement 
 or over mercury. The bromine is slightly heated, 
 when it distils over to the moist phosphorus, and 
 hydrobromic acid is evolved. A moderate heat should 
 afterwards be applied to the moist glass, to expel part 
 of the hydrobromic acid from the water. 
 
 Hydrobromic acid is very similar to hydrochlo- 
 ric acid ; it liquefies at - 92 F., and has been 
 solidified by a still lower temperature, which is 
 not the case with hydrochloric acid. Like that gas it is very soluble in 
 water, and the solution acts upon metals and their oxides in the same 
 manner as hydrochloric acid. Chlorine removes the hydrogen from 
 hydrobromic acid, liberating bromine, which it converts into chloride of 
 bromine if employed in excess. 
 
 The composition of hydrobromic acid corresponds to that of hydro- 
 chloric. It contains 80 parts by weight (1 eq.) of bromine, combined 
 with 1 part (1 eq.) of hydrogen, or 2 vols. of bromine vapour, combined 
 with 2 vols. of hydrogen to form 4 vols. of hydrobromic acid. 
 
 Bromide of nitrogen has been obtained by the action of bromide of 
 potassium upon chloride of nitrogen, which it resembles in general 
 character and explosive properties. 
 
 Chloride of bromine is a very volatile yellow liquid of pungent odour. 
 Its composition is not certainly known. That chlorine should unite 
 directly with bromine, which it so much resembles in chemical character, 
 illustrates its great tendency to direct chemical combination. 
 
 IODINE. 
 
 125. Iodine is contained in sea water in even smaller quantity than 
 bromine, but the iodide of sodium appears to constitute a portion of the 
 necessary food of certain varieties of sea-weed, which extract it from the 
 sea water, and concentrate it in their tissues. The ash remaining after 
 sea-weed has been burnt was long used, under the name of kelp, in soap- 
 making, because it contains a considerable quantity of carbonate of soda ; 
 and in the year 1811, Courtois, a soap-boiler of Paris, being engaged in 
 the manufacture of soda from kelp, obtained from the waste liquors a 
 
EXTRACTION OF IODINE FROM SEA- WEED. 171 
 
 substance which possessed properties different from those of any form of 
 matter with which he was acquainted. He transferred it to a French 
 chemist, 'Clement, who satisfied himself that it was really a new substance, 
 and Gay-Lussac and Davy having examined it still more closely, it took 
 its rank among the non-metallic elementary substances, under the name 
 of iodine (10)8779, violet colotired), conferred upon it in allusion to the 
 magnificent violet colour of its vapour. 
 
 This history of the discovery of iodine affords a very instructive example 
 of the advantage of training persons engaged in manufactures to habits of 
 accurate observation, and, if possible, of accurate chemical observation ; for 
 had Courtois passed over this new substance as accidental, or of no con- 
 sequence, the community would have lost, at least for some time, the 
 benefits derived from the discovery of iodine. 
 
 For some years the new element was only known as a chemical 
 curiosity, but an unexpected demand for it at length arose on the part of 
 the physician, for it had been found that the efficacy of the ashes of 
 sponge, which had long been used in some particular maladies, was due to 
 the small quantity of iodine which they contained, and it was, of course, 
 thought desirable to place this remedy in the hands of the medical pro- 
 fession in a purer form than the ash of sponge, where it is associated with 
 very large quantities of various saline substances. Much more recently 
 the demand for this element has greatly increased, on account of its employ- 
 ment in photography, and large quantities of it are annually produced 
 from kelp, the collection and burning of which affords occupation to the 
 very poor inhabitants of some parts of the coasts of Ireland and Scotland, 
 who would otherwise have been thrown out of work when soda began to 
 be manufactured from common salt, and the demand for kelp as the source 
 of that alkali had ceased. The sea-weed is spread out to dry, and burnt 
 in shallow pits at as low a temperature as possible, for the iodide of sodium 
 is converted into vapour and lost if the temperature be very high.* The 
 ash, which is left in a half-fused state, is broken into fragments and 
 treated with hot water, which dissolves about half of it, leaving a residue, 
 consisting of carbonate and sulphate of lime, sand, &c. The whole of the 
 iodide of sodium is contained in the portion dissolved by the water, but is 
 mixed with much larger quantities of sulphate of soda, carbonate of soda, 
 chloride of potassium, hyposulphite of soda, and sulphide of sodium. A 
 portion of the water is expelled by evaporation, when the sulphate of 
 soda, carbonate of soda, and chloride of potassium, being far less soluble 
 than the iodide of sodium, crystallise out. In order to decompose the 
 hyposulphite of soda and the sulphide of sodium, the liquid is mixed 
 with an eighth of its bulk of oil of vitriol, which decomposes these salts, 
 evolving sulphurous and hydrosulphuric acid, with deposition of sulphur, 
 and forming sulphate of soda, which is deposited in crystals. The liquor 
 thus prepared is next mixed with binoxide of manganese, and heated in a 
 leaden retort (fig. 173), placed in a sand-bath, when the iodine is evolved 
 as a magnificent purple vapour, which condenses in the globular glass 
 receivers in the form of dark grey scales with metallic lustre, and having 
 considerable resemblance to black lead. The liberation of the iodine is 
 explained by the following equation 
 
 Nal + Mn0 2 + 2(HO . S0 3 ) = STaO . S0 3 + MnO . S0 3 + 2HO + I . 
 
 % 
 
 * The sea-weed is often only charred and not incinerated, so as to avoid loss of iodine. 
 
172 PROPERTIES OF IODINE. 
 
 The distillation is conducted at a temperature below 212, to avoid the 
 liberation of chlorine from the chloride of sodium, and the consequent 
 formation of chloride of iodine. 
 
 Several processes have been devised to render the extraction of the iodine from 
 the concentrated solution of kelp easier and more economical. The most promising 
 is very similar to that employed for separating bromine (p. 168). The iodine is 
 liberated by chlorine, and extracted from the liquid by shaking it with benzole ; by 
 treating the benzole with solution of potash, the iodine is converted into a mixture 
 of iodide of potassium and iodate of potash, from which the iodine may be preci- 
 pitated by acidifying with hydrochloric acid. 
 
 6KO + I 6 = SKI + KO.I0 5 
 SKI + KO.I0 5 + 6HC1 = 6KC1 + 6HO + I 6 . 
 
 The features of this element are extremely well marked ; its metallic 
 lustre and peculiar odour sufficiently distinguish it from all others, and 
 
 the effect of heat upon it is 
 very striking, in first easily 
 fusing it (at 225 F.), and 
 afterwards converting it 
 (boiling point, 347 F.) 
 into the most exquisitely 
 purple vapour, which is 
 nearly nine times as heavy 
 as air (sp. gr. 8 '72), and 
 condenses upon a cool sur- 
 face in shining scales. It 
 stains the skin intensely 
 brown if handled. The 
 specific gravity of solid 
 iodine is 4*95. 
 
 When iodine is shaken 
 with cold water a very 
 small quantity is dissolved, 
 
 forming a light brown solution. Hot water dissolves a larger quantity, 
 but alcohol is one of the best solvents for iodine, producing a dark red- 
 brown solution (tincture of iodine) from which part of the iodine may 
 be precipitated by adding water. A solution of iodide of potassium 
 also dissolves iodine freely. Benzole and bisulphide of carbon dissolve it 
 abundantly, producing fine violet-red solutions, which deposit the iodine, 
 if allowed to evaporate spontaneously, in minute rhombic octahedral cry- 
 stals aggregated into very beautiful fern-like forms. If an extremely 
 weak aqueous solution of iodine be shaken with a little bisulphide of car- 
 bon, the latter will remove the iodine from the solution, and on standing, 
 will fall to the bottom of the liquid, having a beautiful violet colour. By 
 dissolving a large quantity of iodine in bisulphide of carbon, a solution is 
 obtained which is perfectly opaque to rays of light, though it allows heat- 
 rays to pass freely, and is, therefore, of great value in physical experi- 
 ments. A solution of iodine in bichloride of carbon is also used for the 
 same purpose. 
 
 Existing, as iodine does, in very minute quantity in the water from 
 various natural sources, it would often be overlooked if the chemical 
 analyst did not happen to possess a test of the most delicate description 
 for it. 
 
 Iodine, in the uncombined state, dyes starch of a beautiful blue colour, 
 
IODIC ACID. 173 
 
 as may be proved by heating a grain or two of the element with water, 
 and adding to the solution a little thin starch (see p. 15), or by placing a 
 minute fragment of iodine in a stoppered bottle, and suspending in it a 
 piece of paper dipped in thin starch. This test, however, though sensi- 
 tive to the smallest quantity of free iodine, gives no indication whatever 
 with iodine in combination, as it always exists in nature ; in order, there- 
 fore, to test for iodine, a little starch-paste is added to the suspected 
 liquid, and then a drop of a weak solution of chlorine, which will set free 
 the iodine, and cause the production of the blue colour. Characters 
 written on paper with a brush dipped in a mixture of iodide of potassium 
 and starch, are brought out in blue by pouring a little chlorine-gas upon 
 them. It is necessary, however, carefully to avoid adding too much chlo- 
 rine, since it would immediately destroy the colour of the iodised starch. 
 Alkalies also bleach it, and the colour of a mixture of the iodised starch 
 with water is removed by heating, but returns in great measure when the 
 solution cools. 
 
 Though very closely connected with chlorine and bromine in its gene- 
 ral chemical relations, there are several points in the history of iodine which 
 cause it to stand out in marked contrast by the side of these elements. The 
 attraction which binds it to hydrogen and the metals is certainly weaker 
 than that exerted by chlorine and bromine, so that either of these is cap- 
 able of displacing it from its compounds, and its bleaching properties are 
 very feeble. On the other hand, it exhibits a more powerful tendency to 
 unite with oxygen, for boiling nitric acid converts it into iodic acid (I0 5 ), 
 though this oxidising agent would not affect chlorine or bromine. 
 
 Some of the compounds of iodine with the metals are remarkable for their beauti- 
 ful colours. The iodide of mercury, produced by mixing solutions of iodide of potas- 
 sium and chloride of mercury, forms a fine scarlet precipitate, which dissolves in an 
 excess of iodide of potassium to a colourless solution. 
 
 If this iodide of mercury be collected on a filter, washed and dried, it will be 
 found, on heating a portion of it in a test-tube, that it acquires a fine yellow colour 
 and sublimes in golden yellow crystals, which resume the original red colour when 
 rubbed with a glass rod. If it be spread upon paper and gently heated, the scarlet 
 iodide becomes yellow, but the red colour returns on rubbing it with the thumb- 
 nail. These changes of colour are attended by an alteration in crystalline form, but 
 not in the chemical composition of the iodide of mercury. 
 
 Iodide of lead has a bright yellow colour, as may be seen by precipitating iodide 
 of potassium with a solution of acetate of lead. The precipitate is dissolved by 
 boiling with water (especially on adding a little hydrochloric acid), forming a colour- 
 less solution, from which the iodide of lead crystallises in very brilliant golden scales 
 on cooling. Iodide of silver is produced as a yellow precipitate when nitrate of silver 
 is added to iodide of potassium. The bromide and chloride of silver would form 
 white precipitates. *. 
 
 126. Oxides of iodine. Although the compound 10, corresponding to 
 hypochlorous acid, is believed to exist, it has never yet been obtained in a 
 separate state, the only known oxides of iodine being iodic acid (I0 5 ) and 
 periodic acid (I0 7 ?) which has only been obtained in the hydrated state. 
 
 Iodic acid, like the corresponding chloric and bromic acids, is formed 
 when iodine is dissolved in solution of potash or soda 
 
 6KO + I 6 = KO.I0 5 + 5KI. 
 
 It is most easily prepared by boiling iodine with the strongest nitric acid 
 in a long-necked flask, when it is dissolved in the form of iodic acid which 
 is left on evaporating the nitric acid, as a white mass. This may be puri- 
 fied by dissolving in water and crystallising, when the iodic acid forms 
 
174 PERIODIC ACID. 
 
 white hexagonal tables, which have the composition HO . I0 5 + 2Aq. 
 Heated to 266 F., they become HO . I0 5 , and at 360 F. the whole of. the 
 water is expelled, leaving anhydrous iodic acid, which is decomposed at 
 about 700 F. into iodine and oxygen. The anhydrous iodic acid oxidises 
 combustible bodies, but not with any great violence. The hydrate is far 
 more stable than the hydrated chloric and bromic acids. Its solution 
 first reddens litmus paper, and afterwards bleaches it by oxidation. Its 
 salts, the iodates, are less easily soluble in water than the chlorates and 
 bromates, which they resemble in their oxidising action upon combustible 
 bodies. They are all decomposed by heat, evolving oxygen, and sometimes 
 even iodine, showing how much inferior this element is to chlorine and 
 bromine in its attraction for metals. 
 
 It is a remarkable feature of the iodates, that some of them contain two 
 or even three equivalents of iodic acid to one of base. Thus there are 
 three iodates of potash, KO. I0 5 , KO. 2I0 5 , and KO . 3I0 5 . No such 
 compounds are known in the cases of chloric and bromic acids. 
 
 Periodic acid has not been satisfactorily obtained in the anhydrous 
 state. The hydrated periodic acid is obtained from the basic periodate of 
 soda formed by passing chlorine through a mixture of iodate of soda and 
 free soda, when the latter is decomposed, its sodium being abstracted by 
 the chlorine, whilst its oxygen converts the iodic acid into periodic acid 
 
 . I0 5 + 3NaO + C1 2 = 2NaO . I0 7 
 
 Basic periodate of 
 soda. 
 
 This periodate of soda is deposited, being sparingly soluble in water, a 
 most unusual circumstance with salts of soda. By dissolving it in nitric 
 acid, and adding nitrate of silver, a basic periodate of silver is obtained, 
 which is yellow when precipitated from cold, and red from hot solutions 
 
 2NaO.I0 7 4- 2(AgO.N0 5 ) = 2AgO.I0 7 + 2(NaO.M) 5 ) . 
 
 Basic periodate of 
 
 Nitrate of soda. 
 
 silver. 
 
 When the silver salt is dissolved in nitric acid, it is decomposed into 
 nitrate of silver, which remains in solution, and neutral periodate of 
 silver, which is deposited in crystals 
 
 2AgO.I0 7 + HO.N0 5 = AgO.I0 7 + AgO.N0 5 + HO. 
 
 When neutral periodate of silver is boiled with water, it again yields 
 the insoluble basic periodate of silver, and hydrated periodic acid is 
 found in the solution 
 
 2(AgO.I0 7 ) + HO = 2AgO.I0 7 + HO.I0 7 . 
 
 On evaporating the solution, the hydrated periodic acid is deposited in 
 prismatic crystals having the composition HO . I0 7 + 4Aq, which lose 
 their water at about 320 F., and are decomposed into iodic acid and 
 oxygen at 400 F. The solution of periodic acid, of course, exhibits 
 oxidising properties. 
 
 The periodates are remarkable for their sparing solubility in water ; 
 they are easily decomposed by heat, like the iodates. It will have been 
 remarked, in the above account of the preparation of periodic acid, that 
 this acid exhibits a great tendency to the formation of basic salts, whilst 
 iodic acid is remarkable for its acid salts. 
 
 127. Hydriodic acid. Iodine vapour combines with hydrogen, under 
 
HYDRIODIC ACID. 175 
 
 the influence of heated platinum, to form hydriodic acid gas. The gas is 
 best prepared by decomposing water with iodine in the presence of phos- 
 phorus, so as to produce hydriodic acid and phosphoric acid, which is 
 allowed to act upon iodide of potassium in order to produce more hydriodic 
 acid 
 
 8HO + I 3 + P = SHI + 3HO.P0 5 and 
 2KI + 3HO.P0 5 = 2HI + 2KO.HO.P0 5 . 
 
 Phosphate of potash. 
 
 100 grains of iodide of potassium are dissolved in 50 grains of water in a retort 
 (fig. 174), and 200 grains of iodine are added; when this has dissolved, 10 grains 
 of phosphorus are introduced, and the mixture 
 heated very gradually, the gas being collected 
 by downward displacement in stoppered bottles, 
 which must be placed in readiness, as the gas 
 comes off very rapidly. A loose roll of dry 
 filter paper in the neck of the retort will be 
 useful to retain drops of liquid. These quan- 
 tities will fill four pint bottles with the gas. 
 
 Hydriodic acid gas is very similar in 
 its properties to hydrochloric and hydro- 
 bromic acids, fuming strongly in moist 
 air, very readily absorbed by water, lique- Flg ' ^4. -Preparation of hydnodic 
 fied only under strong pressure, and soli- 
 dified by extreme cold. It is much heavier, its specific gravity being 
 4*44. If a bottle of hydriodic acid gas be placed in contact with a 
 bottle containing chlorine or bromine vapour diluted with air (fig. 133), 
 it will be instantly decomposed, with separation of the beautiful violet 
 vapour of iodine. 
 
 The aqueous solution of hydriodic acid is most conveniently prepared 
 by passing hydrosulphuric acid gas through water in which iodine is sus- 
 pended, HS + I = HI "+ S, the separated sulphur being filtered off, 
 and the solution boiled to expel the excess of hydrosulphuric acid. 
 Solution of hydriodic acid differs greatly from hydrochloric and hydro- 
 bromic acids, in being decomposed by exposure to air, its hydrogen being 
 oxidised and iodine separated, which dissolves in the liquid and renders 
 it brown. 
 
 This tendency of the hydrogen of hydriodic acid to combine with 
 oxygen renders that acid a powerful reducing agent. It is even capable 
 of converting hydrated sulphuric acid into hydrosulphuric acid 
 
 HO.S0 3 + 4HI := HS + 4HO + I 4 
 
 so that when iodide of potassium is heated with concentrated Sulphuric 
 acid, hydrosulphuric acid is evolved in considerable quantity. 
 
 The action of hydriodic acid upon the metals and their oxides is gene- 
 rally similar to that of the other hydrogen acids. 
 
 When potassium is heated in a measured volume of hydriodic acid, the 
 iodine is removed, and the hydrogen occupies half the original volume. 
 Hence 1 volume of hydrogen is combined with 1 volume of iodine vapour 
 in 2 volumes of hydriodic acid. One equivalent (47 grains) of potash 
 is neutralised by 128 grains of hydriodic acid. This quantity occupies 
 4 volumes (8 grains = 1 volume), so that 1 eq. or 4 volumes or 128 
 parts by weight of hydriodic acid, will contain 1 eq. or 2 volumes or 1 
 part by weight of hydrogen, and 1 eq. or 2 volumes or 127 parts by weight 
 of iodine vapour. 
 
176 IODIDE OF POTASSIUM. 
 
 Like chlorine and bromine, iodine is capable of displacing hydrogen 
 from many organic compounds, and of taking its place, but its action in 
 this respect is much feebler. The circumstance that the organic com- 
 pounds containing iodine are generally much less volatile, and therefore 
 more manageable than those of chlorine and bromine, leads to the exten- 
 sive employment of this element in researches upon organic substances. 
 
 With olefiant gas, iodine forms a crystalline solid compound (C 4 HJ 2 ) 
 corresponding to Dutch liquid (p. 86), and from this compound a yellow 
 unstable aromatic liquid has been obtained, which is believed to be an 
 iodide of carbon. 
 
 128. Iodide of nitrogen. The action of chlorine, bromine, and iodine 
 upon ammonia, exemplifies the difference in their attraction for hydrogen ; 
 for whilst chlorine and bromine, acting upon ammonia, cause the libera- 
 tion of a certain amount of nitrogen, iodine simply removes two-thirds of 
 the hydrogen, and itself fills up the vacancies thus occasioned, no nitrogen 
 being liberated 
 
 2HI 
 
 the hydriodic acid thus formed combining with more ammonia to form 
 hydriodate of ammonia. 
 
 To prepare the iodide of nitrogen, 20 grains of iodine are rubbed to powder in a 
 mortar and mixed with half an ounce (measured) of strong ammonia ; the mortar 
 is covered with a glass plate, and after about half an hour the iodide of nitrogen is 
 collected in separate portions upon four filters, which are allowed to drain and 
 spread out to dry. The brown solution contains iodine dissolved in hydriodate of 
 ammonia. 
 
 The iodide is a black powder, which explodes with a loud report even 
 when touched with a feather, emitting fumes of hydriodic acid and purple 
 vapour of iodine ; its explosion is probably represented by the equation 
 
 NHI 2 = N + HI + I 
 
 its violence being accounted for by the sudden evolution of a large volume 
 of gas and vapour from a small volume of solid. Even when allowed to 
 fall from the height of a few feet upon the surface of water, it explodes if 
 perfectly dry. In the moist state it slowly undergoes decomposition. 
 
 129. Iodine forms two compounds with chlorine, the protochloride of 
 iodine (IC1) and the terchloride (IC1 3 ). The former is a brown volatile 
 liquid of irritating odour, obtained by distilling 1 part of iodine with 4 
 parts of chlorate of potash. 
 
 The terchloride forms fine red needle-like crystals, and is produced when 
 iodine is acted upon with an excess of chlorine. Bromides of iodine have 
 also been obtained, but their composition is not well known. 
 
 130. Iodide of potassium. This salt is the most useful compound of 
 iodine, being largely employed in medicine and in photography. It is 
 generally prepared by decomposing iodide of iron with carbonate of 
 potash. 
 
 The iodide of iron (also a useful medicine) is made by placing two 
 parts of iodine in contact with one part of iron filings and ten parts of 
 water. The iodine combines with part of the iron, evolving considerable 
 heat, and producing the iodide of iron (Fel). 
 
 The liquid is decanted from the excess of iron, and one-third of the 
 weight of iodine previously employed is dissolved in it. In this way, two- 
 
FLUORINE HYDROFLUORIC ACID. 177 
 
 thirds of the iodide of iron are converted into sesqui-iodide (Fe 2 I 3 ), so that 
 the solution contains a mixture of one equivalent of the iodide (Fel) and 
 one of the sesqui-iodide (Fe 2 I 3 ). It is now boiled, and carbonate of 
 potash is gradually added as long as it causes a dark green precipitate of 
 magnetic oxide of iron 
 
 Fel + Fe 2 I 3 + 4(KO . C0 2 ) = 4 KI + FeO . Fe 2 3 + 4C0 2 
 
 the carbonic acid is evolved with effervescence, and if the solution be 
 filtered and evaporated, it deposits beautiful cubical (or sometimes octa- 
 hedral) crystals, which are generally milk-white and opaque, but occa- 
 sionally quite transparent. Pure iodide of potassium remains dry in 
 ordinary air, but if an excess of carbonate of potash is employed in its 
 preparation, the crystals retain some of that salt and become damp when 
 exposed to air. The iodide of potassium dissolves easily in water and 
 alcohol. If the solution be pure, it does not become coloured when mixed 
 with pure hydrochloric acid ; but if any iodate of potash be present in it, a 
 brownish colour will be produced, due to iodine liberated in the action 
 of the iodic acid upon the hydriodic acid ; I0 5 + 5HI = I 6 + 5HO. 
 The iodate of potash is liable to be present in those specimens which are 
 prepared by dissolving iodine in potash, to obtain a mixture of iodide of 
 potassium and iodate of potash (see p. 173), the latter salt being after- 
 wards decomposed by heat. 
 
 ELUOEDTE. 
 
 131. The most ornamental mineral substance occurring in any abun- 
 dance in this country is known as fluor spar or Derbyshire spar (fluoride 
 of calcium), and is found with several beautiful shades of colour blue, 
 purple, violet, or green, and sometimes perfectly colourless, either in large 
 masses, or in crystals, which have the form of a cube or of some solid 
 derived from it. The use of this mineral as a flux in smelting ores dates 
 from a very remote period, and from this use the name fluor appears to 
 have been originally derived, but we have no record of its chemical ex- 
 amination till about a century since, when Margraf found his glass retort 
 powerfully corroded in distilling this mineral with sulphuric acid, and 
 Scheele soon after announced that it contained lime said, fluoric acid; but 
 though this chemist had fallen into the 
 
 error to which analysts are continually 
 liable, of mistaking products for educts, 
 his experiments, as they were afterwards 
 perfected by Gay-Lussac and The'nard, 
 deserve particular consideration. 
 
 132. Hydrofluoric acid. If powdered 
 fluor spar be mixed with twice its weight 
 of oil of vitriol, and heated in a leaden 
 
 retort (fig. 175), the neck of which fits Fig. 175. 
 
 tightly into a leaden condensing-tube, 
 
 cooled in a mixture of ice and salt, a colourless liquid distils over, and the 
 residue in the retort is found to consist of sulphate of lime 
 
 CaF + HO.S0 = CaO.SOs + HF . 
 
 Sulphate of mne. 
 
 The colourless liquid (hydrofluoric acid) possesses most remarkable pro- 
 
178 ETCHING ON GLASS. 
 
 perties ; it is powerfully acid, fumes strongly in the air, and has a most 
 pungent irritating odour. If the air is at all warm the liquid "begins to 
 boil when taken out of the freezing mixture, and is soon entirely dissi- 
 pated in vapour (boiling point, 60 F.) Should the operator have the mis- 
 fortune to allow a drop to fall upon his hand, it will produce a very 
 painful sore, even its vapour producing pain under the finger-nails. Its 
 attraction for water is so great, that the acid hisses like red-hot iron when 
 brought in contact with it. But its most surprising property is that of 
 rapidly corroding glass, which has already been alluded to as noticed by 
 Margraf. Experiment soon proved that great analogy existed between 
 the properties of this new acid and those of hydrochloric acid; and 
 Ampere was led to institute a comparison between them, which caused 
 him to adopt the opinion that the acid was a hydrogen acid, containing a 
 new salt radical which he named fluorine ; the name of the acid was then 
 changed from fluoric to hydrofluoric acid. 
 
 This liquid has since been proved to be a solution of hydrofluoric acid 
 in water, for if it be distilled with anhydrous phosphoric acid, which 
 retains the water, it evolves hydrofluoric acid gas, which resembles hydro- 
 chloric acid gas in fuming strongly on contact with moist air, and being 
 eagerly absorbed by water, but has a far more pungent odour. The per- 
 fectly dry gas has very little action upon glass. 
 
 It is remarkable that the solution of hydrofluoric acid, in its concen- 
 trated form, is not so heavy as a somewhat weaker acid. . Thus, the acid 
 of sp. gr. 1/06 acquires the sp. gr. 1-15 on addition of a little water, but 
 on adding more water its sp. gr. is again reduced. It would hence appear 
 that the acid of 1/15 is a definite hydrate of hydrofluoric acid ; its com- 
 position corresponds to HF . 4HO. It distils unchanged at 248 F. The 
 .solution is generally kept in bottles made of gutta-percha. 
 
 The action of hydrofluoric acid upon metals and their oxides resembles 
 that of hydrochloric acid. It dissolves all ordinary metals except gold, 
 platinum, silver, mercury, and lead. 
 
 The property which renders this acid so useful to the chemist is its 
 power of dissolving silica even in its most refractory form. When sand 
 or flint reduced to powder is digested in a leaden or platinum vessel with 
 hydrofluoric acid, it is gradually dissolved, and if the solution be evapo- 
 rated, the whole of the silica will be found to have disappeared in the 
 form of gaseous fluoride of silicon ; Si0 2 + 2HF = SiF 2 + 2HO. If 
 the silicic acid be combined with a base, the metal will be left as a fluo- 
 ride, decomposable by sulphuric or hydrochloric acid. This renders 
 hydrofluoric acid a most valuable agent in the analysis of the numerous 
 mineral silicates which resist the action of other acids. 
 
 The corrosion of glass by hydrofluoric acid is now easily explained. 
 Ordinary glass consists of silicate of soda or potash combined with silicate 
 of lime or oxide of lead. The hydrofluoric acid attacks and removes the 
 silica, and thus eats its way into the glass. 
 
 In order to demonstrate the action of this acid upon glass, a glass plate is warmed 
 sufficiently to melt wax, a piece of which is then rubbed over it, until the glass is 
 covered with a thin and pretty uniform coating. Upon this a word or drawing may 
 be engraved with a shurp point so that the lines shall expose the glass. A mixture 
 of powdered fluor spar with concentrated sulphuric acid is then poured over it, and 
 allowed to remain for a quarter of an hour ; the acid mixture is washed off, and the 
 plate gently warmed to melt the wax, which may be wiped off with a little tow, 
 when it will be found that the hydrofluoric acid evolved from the mixture has cor- 
 roded those portions of the glass from which the graver had removed the wax. It 
 
FLUORIDES FLUORIDE OF SILICON. 179 
 
 lias been attempted to apply this process to the production of engravings, but the 
 brittleness of the plate has formed a very serious obstacle. 
 
 If a leaden or platinum dish be at hand, it is better to place the glass to be etched 
 over the dish containing the mixture of fluor spar and sulphuric acid exposed to a 
 very gentle heat. 
 
 Many ingenious experiments have been made in order to obtain fluorine 
 in the separate state, but it was found that it invariably combined with 
 some portion of the material of the vessel in which the operation was 
 conducted. The most successful of the early attempts to isolate fluorine 
 appears to have been made, at the suggestion of Davy, in a vessel of 
 fluor spar itself, which could not, of course, be supposed to be in any way 
 affected by it. A greenish gas was obtained, possessing chemical proper- 
 ties similar to those of chlorine, but of much higher intensity. The diffi- 
 culty, however, of obtaining vessels of fluor spar adapted to these experi- 
 ments appears to have prevented any complete investigation of this most 
 interesting element. 
 
 The most recent experiments, in which fluoride of silver was decom- 
 posed by iodine, lead to the conclusion that fluorine - is a colourless gas 
 which is without action upon dry glass or upon mercury, but they require 
 extension and confirmation. 
 
 The composition of hydrofluoric acid has been inferred from that of 
 fluoride of calcium, which has been shown by analysis to contain one 
 equivalent (20 parts by weight) of calcium combined with 19 parts by 
 weight of fluorine. Assuming that hydrofluoric acid resembles hydro- 
 chloric acid in composition as well as in general character, and that 1 9 re- 
 presents the equivalent of fluorine, this acid would contain 1 equivalent 
 (or 2 volumes) of hydrogen combined with 1 equivalent of fluorine, and 
 if it be supposed that the 20 parts (1 equivalent) of hydrofluoric acid 
 occupy 4 volumes (0 = 1 volume), the hypothetical specific gravity of 
 hydrofluoric acid gas would be 0'69, and that of fluorine 1'31. 
 
 Solutions of the fluorides of potassium and the other alkali metals cor- 
 rode glass slowly like hydrofluoric acid. These fluorides are capable of 
 combining with the acid ; thus fluoride of potassium forms KF . HF, which, 
 when dry, is a convenient source of hydrofluoric acid gas when moder- 
 ately heated. The only fluoride possessed of much practical interest beside 
 the fluoride of calcium is the mineral kryolite (*pvos, frost), which is a 
 double fluoride of aluminum and sodium (3NaF . A1 2 F 3 ) found abundantly 
 in Greenland, and valuable as a source of aluminum and soda. The topaz 
 contains fluorine, but in what form of combination is not well known j its 
 other constituents are alumina and silica. 
 
 Fluorides are also found, though in very small quantity, in sea 'water, 
 and they have been discovered in plants and animals. Human bone con- 
 tains about 2 per cent, of fluoride of calcium. 
 
 It will be remembered that fluorine is the only element which is not 
 known to form any compound with "oxygen. 
 
 133. Fluoride of silicon,. If a mixture of powdered fluor spar and 
 glass be heated, in a test-tube or small flask, with concentrated sulphuric 
 acid, a gas is evolved which has a very pungent odour, and produces thick 
 white fumes in contact with the air ; it might at first be mistaken for 
 hydrofluoric acid, but if a glass rod or tube be moistened with water and 
 exposed to the gas, the wet surface becomes coated with a white film, 
 which proves, on examination, to be silicic acid. This result originated 
 the belief that the gas consisted of fluoric (now hydrofluoric) acid and 
 
 M2 
 
180 FOKMATION OF ARTIFICIAL MINEBALS. 
 
 silica, but Davy corrected this view by showing that it really contained 
 no oxygen, and consisted solely of silicon and fluorine. The gas is now 
 called the fluoride of silicon, and represents silicic acid in which the oxygen 
 has been displaced by the fluorine ; the change of places between these two 
 elements in the above experiment is represented by the subjoined equa- 
 tion 
 
 2CaF + Si0 2 + 2(HO.S0 3 ) - 2(CaO.S0 3 ) + SiF 2 + 2HO . 
 
 Silica. Sulphuric acid. Sulphate of lime. 
 
 The formation of the crust of silica upon the wetted surface of the glass 
 is due to a decomposition which takes place between the fluoride of silicon 
 and the water, in which the oxygen and fluorine again change places 
 
 SiF 2 + 2HO = Si0 2 + 2HF . 
 
 Since this latter equation shows that hydrofluoric acid is again formed, 
 it would be expected that the glass beneath the deposit of silica would be 
 found corroded by the acid ; this, however, is not the case, and when the 
 experiment is repeated upon a somewhat larger scale, so that the water 
 which has acted upon the gas may be examined, it will be found to hold 
 in solution, not hydrofluoric acid, but an acid which does not act upon 
 glass, and is composed of hydrofluoric acid and fluoride of silicon ; so that 
 the hydrofluoric acid produced when water acts upon the fluoride com- 
 bines with a portion of the latter to produce the new acid (HF . SiF 2 ) 
 hydrofluo-silicic acid. 
 
 For the preparation of fluoride of silicon, 1 oz. of fluor spar and 1 oz. of powdered 
 glass are mixed together, and heated, in a Florence flask, with 7 oz. (measured) of 
 oil of vitriol, the gas being collected in dry bottles by downward displacement (see 
 fig. 160, p. 147). If a little of the gas be poured from one of the bottles into a flask 
 filled up to the neck with water, the surface of the latter will become covered with 
 a layer of silica, so that if the flask be quickly inverted, the water will not pour from 
 it, and will seem to have been frozen. In a similar manner, a small tube filled 
 with water and lowered into a bottle of the gas, will appear to have been frozen 
 when withdrawn. A stalactite of silica some inches in length may be obtained by 
 allowing water to drip gently from a pointed tube into a bottle of the gas. Characters 
 written on glass with a wet brush are rendered opaque by pouring some fluoride 
 of silicon upon them. 
 
 Fluoride of silicon is a substance of some importance in mineralogical 
 chemistry, since, by its aid, certain crystallised minerals may be artifi- 
 cially obtained under conditions which are not unlikely to have attended 
 the production of the natural crystals. Thus, the mineral staurotide or 
 staurolite (oravpos, a cross), or granatite or cross-stone, a naturally crystal- 
 lised compound of alumina and silicic acid, may be obtained by the action 
 of fluoride of silicon upon alternate layers of alumina and silica, heated to 
 whiteness in a porcelain tube. The fluoride of silicon, acting upon the 
 heated alumina, gives silicate of alumina and fluoride of aluminum 
 
 3A1 2 3 + 3SiF 2 = Al 2 3 .3Si0 2 + 2A1 2 F 3 
 
 the newly-formed fluoride of aluminum, passing over a heated layer of 
 silica, produces more silicate of alumina, regenerating fluoride of silicon 
 
 5Si0 2 + 2A1 2 F 3 = 2(Al 2 3 .Si0 2 ) + 3SiF 2 
 
 so that a given quantity of the fluoride of silicon will convert an indefinite 
 quantity of silica and alumina into the crystallised staurolite. It appears 
 probable that other crystallised minerals have been formed in a similar 
 
HYDKOFLUO-SILICIC ACID. 
 
 181 
 
 manner, by the action of minute quantities of such agents of transforma- 
 tion. The frequent occurrence of minute quantities of fluorides in various 
 minerals may thus have great significance. 
 
 The specific gravity of fluoride of silicon is 3 '60. Assuming 0*93 to re- 
 present the sp. gr. (weight of 1 vol.) of imaginary silicon vapour (seep. 165), 
 and 1'31 to represent the sp. gr. of fluorine, the number 3 '55 would be the 
 sum of the weights of 1 vol. of silicon vapour and 2 vols. of fluorine ; so 
 that 2 vols. (1 eq.) of silicon vapour are combined with 4 vols. (2 eqs.) 
 of fluorine, to form 2 vols. of fluoride of silicon. 
 
 134. Hydrofluo-silicic acid or silico-fluoric acid. This acid is only 
 known in the form of a solution, which is obtained by passing fluoride of 
 silicon into water 
 
 3SiF 2 + 2HO 2(HF.SiF 2 ) + Si0 2 . 
 
 Hydrofluo-silicic acid. 
 
 The gas must not be passed directly into the water, lest the separated 
 silica should stop the orifice of the tube, to prevent which, the latter 
 should dip into a little mercury at the bottom of the water, when each 
 bubble, as it rises through the mercury into the water, will become sur- 
 rounded with an envelope of gelatinous silica, and if the bubbles be very 
 regular, they may even form tubes of silica extending through the whole 
 height of the water. 
 
 For preparing hydrofluo-silicic acid 
 it will be found convenient to employ 
 a gallon stoneware bottle (fig. 176), 
 furnished with a wide tube dipping 
 into a cup of mercury placed at the 
 bottom of the water. 1 Ib. of finely 
 powdered fluor spar, 1 Ib. of fine sand, 
 and 64 measured ounces of oil of vi- 
 triol, are introduced into the bottle, 
 which is gently heated upon a sand- 
 bath, the gas being passed into about 
 5 pints of water. After 6 or 7 hours 
 the water will have become pasty, 
 from the separation of gelatinous 
 silica. It is poured upon a filter, and 
 when the liquid has drained through 
 as far as possible, the filter is wrung 
 in a cloth to extract the remainder 
 of the acid solution, which will have 
 a sp. gr. of about 1-078. 
 
 Fig. 176. Preparation of hydrofluo-silicic 
 acid. 
 
 A dilute solution of hydrofluo- 
 silicic acid may be concentrated 
 by evaporation up to a certain point, when it begins to decompose, evolving 
 fumes of fluoride of silicon, hydrofluoric acid remaining in solution and 
 volatilising in its turn if the heat be continued. Of course the solution 
 corrodes glass and porcelain when evaporated in them. If the solution of 
 hydrofluo-silicic acid be neutralised with potash, and stirred, a very cha- 
 racteristic crystalline precipitate of silico-fluoride of potassium is formed 
 HF.SiF 2 + KO = KF.SiF 2 + HO. 
 
 Silico-fluoride 
 of potassium. 
 
 But if an excess of potash be employed, a precipitate of gelatinous silica 
 will be separated, fluoride of potassium remaining in the solution 
 HF.SiF 2 + 3KO = 3KF + HO + - SiO, . 
 
182 GENERAL REVIEW OF THE HALOGENS. 
 
 One of the chief uses of hyclrofluo-silicic acid is to separate the potash 
 from its combination with certain acids, in order to obtain these in the 
 separate state. 
 
 1 35. Fluoride of boron may be prepared by a process similar to that 
 employed for fluoride of silicon, but it is also obtained by strongly heat- 
 ing a mixture of powdered anhydrous boracic acid with twics its weight 
 of fluor spar in an iron tube 
 
 3CaF + B0 3 = 3CaO + BF 8 . 
 
 Fluoride of boron. 
 
 The fluoride of boron is a gas which fumes strongly in moist air like 
 the fluoride of silicon. It is absorbed eagerly by water, with evolution of 
 heat. One volume of water is capable of dissolving 700 volumes of 
 fluoride of boron, producing a corrosive heavy liquid (sp. gr. 1*77) which 
 fumes in air, and chars organic substances on account of its attraction for 
 water. This solution is known as fluoboric or borofluoric acid, and its 
 formation is explained by the equation 
 
 BF 3 ' + 3HO = B0 3 .3HF . 
 
 Fluoboric acid. 
 
 When the solution is heated, it evolves fluoride of boron until its 
 specific gravity is reduced to 1'58, when it distils unchanged. 
 
 Hydrofluoboric acid is obtained in solution by adding a large quantity 
 of water to fluoboric acid 
 
 3(B0 3 .3HF) - B0 3 + 6HO + 3HF.2BF 3 . 
 
 Hydrofluoboric 
 acid. 
 
 This acid resembles the hydrofluo-silicic ; its hydrogen may be ex- 
 changed for metals to form bore fluorides. 
 
 136. General review of chlorine, bromine, iodine, and fluorine. These 
 four elements compose a natural group, the members of which are con- 
 nected by the similarity of their chemical properties, far more closely than 
 those of any other group of elements. They are usually styled the 
 halogens, from their tendency to produce salts resembling sea-salt in their 
 composition (oA.?, the sea), and such salts are called haloid salts. These ele- 
 ments are also called salt-radicals, from their property of forming salts by 
 direct union with the metals. 
 
 The equivalent weights of chlorine, bromine, iodine, and probably of 
 fluorine, in the state of vapour, occupy the same volume as an equivalent 
 of hydrogen, and each of these elements combines with an equal volume 
 of hydrogen to form an acid which occupies the joint volumes of its con- 
 stituents. 
 
 If one volume of hydrogen represents one atom, then the equivalent 
 weights of these elements (occupying the same volume as hydrogen) will 
 also represent their atomic weights, and they are decidedly mon-atomic 
 elements. 
 
 The halogens also supply the most prominent example of the gradation 
 in properties sometimes observed among the members of the same natural 
 group of elements. 
 
 In the order of their chemical energy, that is, of the force with which 
 they hold other elements in chemical combination with them, fluorine 
 should stand first, its combining energy being so great as to cause a serious 
 difficulty in isolating it at all ; chlorine would rank next, then bromine, 
 and iodine last. 
 
ORES AND MINERALS CONTAINING SULPHUR. 183 
 
 Their equivalent weights follow the inverse order of their chemical 
 energies: fluorine, 19; chlorine, 35 -5 ; bromine, 80; iodine, 127; num- 
 bers which, of course, also represent their relative specific gravities in the 
 state of vapour. 
 
 A similar gradation is observed in the physical state and colour of those 
 three which are well known ; chlorine being a yellow gas, bromine a red 
 liquid, boiling at 145 E., and iodine a black solid, boiling at 347 E. 
 
 Even in the exceptions which occur to the order of chemical energy 
 above alluded to, the same progression is noticed ; thus fluorine has so 
 little attraction for oxygen that no oxide is known, chlorine has less 
 attraction for oxygen than bromine (chloric acid being less stable than 
 bromic), whilst bromine has less than iodine, which is said to be capable 
 even of uniting directly with ozonised oxygen to form iodic acid. 
 
 The compounds of these elements with hydrogen are all gases distin- 
 guished by a powerful attraction for moisture and great similarity of 
 odour. 
 
 Their potassium-salts all crystallise in the same (cubical) form. 
 
 The fluoride of silver is soluble in water ; the chloride is insoluble in 
 water, but dissolves very easily in ammonia ; the bromide dissolves with 
 some difficulty in ammonia ; and the iodide is insoluble. 
 
 SULPHUR 
 
 137. Sulphur is remarkable for its abundant occurrence in nature in 
 the uncombined state, in many volcanic districts. It is also found, as 
 sulphuretted hydrogen, in many mineral waters, and very abundantly in 
 combination with metals, forming the numerous ores known as sulphurets 
 or sulphides, of which the following are the most abundant : 
 
 Iron pyrites, Bisulphide of iron, FeS 2 
 
 Copper pyrites, Sulphide of iron and copper, Cu 2 S . Fe 2 So 
 
 Galena, Sulphide of lead, PbS 
 
 Blende, Sulphide of zinc, ZnS 
 
 Crude antimony, Sulphide of antimony, SbS 3 
 
 Cinnabar, Sulphide of mercury, HgS . 
 
 Sulphur is plentifully distributed also, in combination with oxygen and 
 a metal, in the form of sulphates, of which the most conspicuous are : 
 
 Gypsum, Sulphate of lime, CaO . S0 3 + 2HO 
 
 Heavy spar, Sulphate of baryta, BaO . S0 3 
 
 Celestine, Sulphate of strontia, SrO . S0 3 
 
 Epsom salts, Sulphate of magnesia, MgO.SOo+ 7HO 
 
 Glauber's salt, Sulphate of soda, NaO . S0 3 + 10HO . 
 
 In plants, sulphur is also found in the form of sulphates, and as a con- 
 stituent of the vegetable albumen (of which it forms about 1'5 per cent.) 
 present in the sap. It is also contained in certain of the essential oils 
 remarkable for their peculiar pungent odour, such as 
 
 Essence of garlic, Sulphide of allyle,* C 6 H 5 S 
 
 Essence of mustard, Sulphocyanide of allyle, C 6 H 5 . C 2 NS 2 . 
 
 In animals, sulphur occurs as sulphates, as a constituent of albumen, 
 fibrine, and caseine (in neither of which does it exceed 2 per cent. ) ; and 
 
 * Allium, garlic. 
 
184 
 
 EXTRACTION OF SULPHUR. 
 
 in bile, one of the products from which (taurine, C 4 H 7 N0 6 S 2 ) contains 25 
 per cent, of sulphur. 
 
 For our supplies of sulphur we are chiefly indebted to Sicily, where 
 large quantities of it are found in an uncombined state in beds of blue 
 clay. Magnificent crystalline masses of sulphate of strontia are often 
 found associated with it; the sulphur itself sometimes occurs in the 
 form of transparent yellow octahedra, but more frequently in opaque 
 amorphous masses. The districts in which sulphur is found are usually 
 volcanic, and those which border the Mediterranean are particularly rich 
 in it. Sulphur has also been found in Iceland and California. 
 
 The native sulphur being commonly distributed in veins through masses 
 of gypsum and celestine, has to be separated from these by the action of 
 heat. When the ores contain more than 1 2 per cent, of sulphur, the bulk 
 of it is melted out, the ore being thrown into rough furnaces or cauldrons 
 with a little fuel, and smothered up with earth, so as to prevent the corn- 
 
 Fig. 177. Distillation of sulphur. 
 
 bustion of the sulphur, which runs down in the liquid state to the bottom of 
 the cauldron, and is drawn out into wooden moulds. But when the propor- 
 tion of sulphur is small, the ore is heated so as to convert the sulphur into 
 vapour, which is condensed in another vessel. The operation is conducted 
 in Sicily in rows of earthen jars (A, fig. 177), heated in a long furnace, 
 
 Fig. 178. Sulphur refinery. 
 
 and provided with short lateral pipes, which convey the sulphur into 
 similar jars (B) standing outside the furnace, in which the vapour of sul- 
 phur condenses in the liquid state, and flows out into pails of water. The 
 
SULPHUR DISTILLED FROM PYRITES. 
 
 185 
 
 sulphur obtained by this process is imported as rough sulphur, and con- 
 tains 3 or 4 per cent, of earthy impurities. In order to separate these it 
 is redistilled, in this country, in an iron retort (A, fig. 178), from which 
 the vapour is conducted into a large brick chamber (B), upon the sides of 
 which it is deposited in the form of a pale yellow powder (flowers of sul- 
 phur, or sublimed sulphur). When the operation has been continued for 
 some time the walls of the chamber become sufficiently hot to melt the 
 sulphur, which is allowed to collect, and afterwards cast in wooden 
 moulds, forming roll sulphur or brimstone. Distilled sulphur is obtained 
 by allowing the vapour to pass from the retort into a small receiving- 
 vessel (C) cooled by water, where it condenses in the liquid state ; this 
 variety of sulphur is preferred for the manufacture of gunpowder, for 
 reasons which will be stated hereafter. 
 
 Sulphur is readily distilled on a small scale in a Florence flask (fig. 179), another 
 flask cut off at the neck (see p. 166) being employed 
 as a receiver. The flask containing the sulphur 
 should be supported upon a thin iron wire triangle, 
 and heated by a gauze-burner, at first gently, and 
 afterwards to the full heat. Flowers of sulphur 
 will at first condense in the receiver, and will be 
 followed by distilled sulphur when the temperature 
 increases. A slight explosion of the mixture of 
 sulphur vapour and air may take place at the com- 
 mencement of the distillation. An ounce of sulphur 
 may be distilled in a few minutes. 
 
 We are by no means entirely dependent 
 upon Sicily for sulphur, for this element can 
 be easily extracted from iron and copper pyrites, both which are found 
 abundantly in this country. 
 
 Iron pyrites forms the yellow metallic-looking substance which is often 
 met with in masses of coal, sometimes in distinct cubical crystals, and 
 which is to be picked up in large quantities on some sea-beaches, where it 
 occurs in rounded nodules, rusty outside, but having a fine radiated 
 metallic fracture. When this mineral is strongly heated it gives up part 
 of its sulphur ; at a very 
 high temperature one 
 half of the sulphur may 
 be separated 
 
 FeS 2 = FeS + S 
 
 but by an ordinary fur- 
 nace heat only about 
 one-fourth can be ob- 
 tained. The distillation 
 of iron pyrites is some- 
 times effected in conical 
 fire-clay vessels (fig. 
 180) closed at the wider 
 end, and stopped to- 
 wards the other with a 
 perforated plate to allow 
 the passage of the sul- 
 phur vapour. Each vessel contains 100 Ibs. of pyrites, and yields 14 Ibs. 
 of sulphur. 
 
 Fig. 180. Furnace for distillation of sulphur 
 from pyrites. 
 
186 ACTION OF HEAT UPON SULPHUR. 
 
 The sulphur obtained in this way has a green colour, due to the pre- 
 sence of a little sulphide of iron carried over mechanically during the 
 distillation ; in order to purify it, it is melted and allowed to cool slowly, 
 when the sulphide of iron subsides ; the upper portion of the mass is then 
 further purified by distillation. 
 
 Sulphur may also be obtained from copper pyrites (Cu^S . FejS 3 ) in the 
 process of roasting the ore previously to the extraction of the copper. 
 The ore is heaped up into a pyramid, the base of which is about 30 feet 
 square ; a layer of powdered ore is placed at the bottom to prevent too 
 rapid access of air ; above this there is a layer of brushwood ; a wooden 
 chimney is placed in the centre, and is made to communicate with air- 
 passages left between the faggots; around this chimney the large frag- 
 ments of the ore are piled to a height of about 8 feet, and a layer of 
 powdered ore, about 12 inches deep, is strewn over the whole. The heap 
 contains about 2000 tons of pyrites, and will yield 20 tons of sulphur. 
 The fire, being kindled by dropping lighted faggots down the chimney, 
 burns very slowly because of the limited access of air, and after a few 
 days sulphur is seen to exude from the surface, and is received in cavities 
 made for the purpose in different parts of the heap ; the roasting requires 
 five or six months for its completion. In this operation a part of the 
 sulphur has been separated by the mere action of heat, and another part 
 has been displaced by the oxygen of the air, which has converted a portion 
 of the iron into an oxide ; a part of the separated sulphur has been burnt, 
 the rest having escaped combustion on account of the limited access of air. 
 
 The sulphur extracted from pyrites is generally found to contain a little 
 arsenic, which is frequently associated with those minerals. Immense 
 quantities of sulphur are consumed in this country for the manufacture of 
 sulphuric acid, gunpowder, lucifer matches, vulcanised caoutchouc, and 
 for making the sulphurous acid employed in bleaching processes. 
 
 138. Properties of sulphur. In its ordinary forms sulphur has a 
 characteristic yellow colour, though milk of sulphur, or precipitated sul- 
 phur (obtained by adding an acid to the solution of sulphur in an alkali), 
 is white. It suffers electrical disturbance with remarkable facility, so 
 that when powdered in a dry mortar it clings to it with great pertinacity. 
 One of the most remarkable features of sulphur is its inflammability, 
 due to its tendency to combine with oxygen at a moderately elevated 
 temperature. It melts at a heat not much above the boiling point of 
 water (239 F.), and inflames at about 500 F., 
 burning with a pale blue flame, and emitting the 
 well-known suffocating odour of sulphurous acid 
 
 The changes in the physical condition of this 
 element under the influence of heat are very extra- 
 ordinary. If a quantity of sulphur be introduced 
 into a Florence flask and subjected to a gradually 
 increasing heat (fig. 181), it is soon converted into 
 a pale yellow limpid liquid (250 F.), the colour 
 of which becomes gradually brown as the heat 
 rises, until, at about 350 F., it is nearly black and 
 Fig 181 opaque, and is so viscid that the flask may be 
 
 inverted without spilling it; at this point the 
 temperature of the sulphur remains stationary for a time, notwithstand- 
 
ELECTROPOSITIVE AND ELECTRONEGATIVE SULPHUR. 187 
 
 ing that it is still over the flame, showing that heat is becoming latent in 
 converting the sulphur into the new modification. On continuing the 
 heat, the sulphur once more becomes liquid (500), though not so mobile 
 as at first, and at a much higher temperature (836 F.) it boils, and is 
 converted into a brownish red very heavy vapour ; at this point of the 
 experiment, an explosion of the mixture of sulphur vapour with air 
 often takes place. The flask may now be removed from the flame, and 
 a little of the sulphur poured into a vessel of water, through which 
 it will descend in a continuous stream, forming a soft elastic string like 
 india-rubber ; the portion remaining in the flask will be observed, as 
 it cools, to pass again through 'the same states, becoming viscid at 350 
 and very liquid at 250 ; another portion may now be poured into water, 
 through which it will fall in isolated drops, solidifying into yellow brittle 
 crystalline buttons of ordinary sulphur. As the portion of sulphur left 
 in the flask cools, it will be found to deposit small tufts of crystals, and 
 ultimately to solidify altogether to a yellow crystalline mass. 
 
 The brown ductile sulphur, when kept for a few hours, w T ill become yel- 
 low and brittle, passing, in great measure, spontaneously into the crystalline 
 sulphur. The change is accelerated by a gentle heat, and is attended with 
 evolution of the heat which the sulphur was found to absorb at 350 F. 
 Both these varieties of sulphur are, of course, insoluble in water, and they 
 are not dissolved to any great extent by alcohol and ether. If the crystal- 
 line variety be shaken with a little bisulphide of carbon it rapidly dis- 
 solves, and on allowing the solution to evaporate spontaneously, it deposits 
 beautiful octahedral crystals, resembling those of native sulphur (fig. 182). 
 Ductile sulphur, however, is insoluble in bisulphide of carbon. 
 
 When flowers of sulphur are shaken with bisulphide of carbon, a con- 
 siderable quantity passes into solution, the remainder consisting of the 
 amorphous, or insoluble sulphur. Eoll sulphur dissolves to a greater 
 extent, and sometimes entirely, in the bisulphide, and distilled sulphur 
 is always easily soluble. 
 
 The soluble and insoluble forms of sulphur appear to represent distinct 
 chemical varieties of the element. When a solution of sulphuretted hydro- 
 gen (HS) is decomposed by the galvanic battery, the hydrogen, as would 
 be expected, is separated at the negative pole, and the sulphur at the 
 positive pole (p. 21). The sulphur, therefore, was the electronegative 
 element of the compound. This sulphur is soluble in bisulphide of car- 
 bon. When an acid is added to a solution of an alkaline sulphide con- 
 taining more than one equivalent of sulphur, the excess of the latter is 
 precipitated, and is then also found to be soluble in bisulphide of carbon, 
 for it played an electronegative part towards the metal with whicn it was 
 in combination. 
 
 When sulphurous acid (S0 2 ) is decomposed by the battery, the sulphur 
 is separated at the negative pole, showing that it played an electropositive 
 part in the sulphurous acid. This electropositive sulphur is insoluble in 
 bisulphide of carbon. The sulphur in the chloride of sulphur (S 2 C1) also 
 plays an electropositive part, and accordingly, when this compound is 
 decomposed by water, the sulphur which separates is insoluble in bisul- 
 phide of carbon. The existence of these two forms of sulphur affords 
 some support to the theory of the dual constitution of the elements noticed 
 at p. 51. 
 
 The electropositive sulphur would be expected to manifest a greater 
 attraction, for oxygen than the electronegative variety, and accordingly, it 
 
188 
 
 ALLOTROPIC FORMS OF SULPHUR. 
 
 is found to be far more easily oxidised by nitric acid. Electropositive or 
 insoluble sulphur is converted into electronegative or soluble sulphur by 
 the action of a moderate heat, itself evolving heat during the process of 
 conversion. When melted in contact with sulphurous acid, 
 the soluble sulphur is converted externally into the insoluble 
 form. 
 
 Crystalline or soluble sulphur is capable of existing in 
 two distinct forms. The natural form of crystallised sul- 
 phur is the octahedron with a rhombic base (fig. 182), and 
 this is the usual form which sulphur assumes when crystal- 
 lised from its solutions. But if sulphur be melted in a 
 Fig. 182. covered crucible, allowed to cool until the surface has con- 
 gealed, and the remaining liquid portion poured out after 
 piercing the crust (with two holes, one for admission of air), the crucible 
 will be lined with beautiful needles which are oblique prisms (fig. 183). 
 These crystals are brownish yellow, and transparent when freshly made ; 
 but they soon become opaque yellow, and although they retain their 
 prismatic appearance, they have now changed into minute 
 rhombic octahedra, the change being attended with evolu- 
 tion of heat. On the other hand, if a crystal of octahedral 
 sulphur be exposed for a short time to a temperature of 
 about 230 F. (in a boiling saturated solution of common 
 salt, for example), it becomes opaque, in consequence of 
 the formation of a number of minute prismatic crystals in 
 the mass. 
 
 The difference between these two forms of crystalline 
 sulphur extends to their fusing-points and specific gravities ; 
 the prismatic sulphur fusing at 248 F., and the octahedral 
 sulphur at 239 F. ; the specific gravity of the prisms being 1'98, and 
 that of the octahedra 2*05. 
 
 Roll sulphur, when freshly made, consists of a mass of oblique prismatic 
 crystals, but after being kept for some time, it consists of octahedra, although 
 the mass generally retains the specific gravity proper to the prismatic form. 
 This change in the structure of the mass, taking place when its solid 
 condition prevented the free movement of the particles, gives rise to a 
 state of tension which may account for the extreme brittleness of roll sul- 
 phur. If a stick of sulphur be held in the warm hand, it often splits, 
 from unequal expansion. These peculiarities of sulphur deserve careful 
 study, as helping to elucidate the spontaneous alterations in the structure 
 of glass, iron, &c., under certain conditions. 
 
 Flowers of sulphur do not present a crystalline structure, but consist of 
 spherical granules composed of insoluble sulphur enclosing soluble sulphur. 
 Hot oil of turpentine dissolves sulphur freely, and when the solution is 
 allowed to stand, the crystals which are deposited whilst the solution is 
 hot have the prismatic form, but as it cools, octahedra are separated. 
 The following table exhibits the chief allotropic forms of sulphur : 
 
 Fig. 183. 
 
 Octahedral . . 
 Electro negative 
 
 Prismatic . . 
 
 Ductile . . 
 
 Amorphous 
 
 Electropositive 
 
 Sp. gr. 
 2-05 
 
 1-98 
 1-96 
 
 Fusing point. 
 239 
 
 248 
 
 Becomes 
 octahedral. 
 
 Soluble in bisulphide of 
 
 carbon. 
 Soluble in bisulphide of 
 
 carbon. 
 
 Insoluble in bisulphide 
 of carbon. 
 
SOURCES OF SULPHURETTED HYDROGEN. 189 
 
 The octahedral is by far the most stable of the three, and is the ultimate 
 condition which the others assume. 
 
 Other varieties of sulphur, such as a black and a red modification, have 
 been described, but they are of minor importance. 
 
 Sulphur is capable of entering into direct combination with several other 
 elements. It unites with chlorine and with some of the metals, if finely 
 divided, even at the ordinary temperature, and it is capable of combining 
 at a high temperature with all the non-metals except nitrogen, and with 
 nearly all the metals. 
 
 If a mixture of 2 parts of copper filings and I part of sulphur, or of equal weights of 
 iron filings and sulphur, be heated in a Florence flask or a test-tube, the combination 
 will be attended with vivid combustion. 
 
 The so-called Lemery's volcano was made by mixing iron filings with two-thirds of 
 their weight of powdered sulphur, and burying several pounds of the moist mixture 
 in the earth, when the heat evolved by the rusting of part of the iron provoked the 
 energetic combination of the remainder with the sulphur, and the consequent develop- 
 ment of much steam.* 
 
 Several metals may be made to burn in sulphur vapour, as in oxygen, by heating 
 the sulphur in a Florence flask with a gauze burner, so 
 as to keep the flask constantly filled with the brown 
 vapour. Potassium and sodium, introduced in deflagrat- 
 ing spoons, take fire spontaneously in the vapour (fig. 
 184). 
 
 A coil of copper wire glows vividly in sulphur vapour, 
 and becomes converted into a brittle mass of sulphide of 
 copper. 
 
 Sulphur dissolves, though slowly, in boiling 
 concentrated nitric and sulphuric acids, being 
 oxidised by the former into sulphuric, and by 
 the latter into sulphurous acid. It is far more 
 rapidly converted into sulphuric acid by a mix- 
 ture of nitric acid and chlorate of potash. The 
 alkalies dissolve sulphur when heated, yielding 
 yellow or red solutions which contain hyposulphites of the alkalies and 
 sulphides of their metals. 
 
 There is a very general resemblance in composition between the com- 
 pounds of sulphur and those of oxygen with the same elements. 
 
 HYDROSULPHURIC ACID. 
 
 139. Sulphuretted hydrogen, or hydrosulphuric acid, has been already 
 mentioned as occurring in some mineral waters, as at Harrowgate. It is 
 also found in the gases emanating from volcanoes, sometimes amounting 
 to one-fourth of their volume. It is a product of the putrefaction of 
 organic substances containing sulphur, and is one of the causes of the 
 sickening smell of drains, &c. Eggs, which contain a considerable pro- 
 portion of sulphur, evolve sulphuretted hydrogen as soon as they begin 
 to change, and hence the association between this gas and the " smell of 
 rotten eggs." The same smell is observed when a kettle boils over upon 
 a coke or coal fire, the hydrogen liberated from the water combining with 
 the sulphur present in the fuel. 
 
 * A mixture of 60 parts of fine iron filings, 2 of sal-ammoniac, and 1 of sulphur, made 
 into a paste with water, is very useful for making the joints of iron tubes air-tight, for 
 it sets into a hard cement, the iron combining with the sulphur. 
 
190 
 
 PREPARATION OF SULPHURETTED HYDROGEN. 
 
 Hydrosulphuric acid is also found among the products of destructive 
 distillation of organic substances containing sulphur ; it was mentioned 
 among the products from coal, in which it is for the most part combined 
 with the ammonia formed at the same time, producing hydrosulphate of 
 ammonia. 
 
 It may be produced, though not in large quantity, by the direct union 
 of hydrogen with sulphur vapour at a high temperature, or by passing a 
 mixture of sulphur vapour and steam through a tube filled with red-hot 
 pumice stone (the latter encouraging the action by its porosity). Hydro- 
 sulphuric acid is more readily formed by heating a damp mixture of sul- 
 phur and wood charcoal, and may be obtained in large quantity by heating 
 a mixture of equal weights of sulphur and tallow, the latter furnishing 
 the hydrogen. 
 
 Preparation of hydrosulpliuric acid. For use in the laboratory, where 
 it is very largely employed in testing for and separating metals, hydro- 
 sulphuric acid is generally prepared by decomposing sulphide of iron with 
 diluted sulphuric acid 
 
 FeS + HO.SO a = HS + FeO . S0 3 . 
 
 Sulphide Hydrosulphuric Sulphate of 
 
 of iron. acid. iron. 
 
 To obtain sulphide of iron, a mixture of 3 parts of iron filings with 2 parts of 
 flowers of sulphur is thrown, by small portions at a time, into an earthen crucible 
 
 [A, fig. 185), heated to redness 
 in a charcoal fire, the crucible 
 being covered after each por- 
 tion has been added. The iron 
 and sulphur combine with 
 combustion, and when the 
 whole of the mixture has been 
 introduced, the crucible is al- 
 lowed to cool, the mass of sul- 
 phide of iron broken out, and 
 a few fragments of it are intro- 
 duced into a bottle (fig. 186) 
 provided with a funnel tube 
 for the addition of the acid, 
 and a bent tube for conduct- 
 ing the gas through a small 
 quantity of water, to remove 
 any splashes of sulphate of 
 iron. From the second bottle 
 the gas is conducted by a glass 
 tube* with a caoutchouc joint, 
 either down into a gas-bottle, 
 
 or into water, or any other liquid upon which the gas is intended to act. The frag- 
 ments of sulphide of iron should be covered with enough water to fill the gas-bottle 
 
 to about one-third, and strong sulphuric acid added 
 by degrees through the funnel, the bottle being 
 shaken, until effervescence is observed. An excess 
 of strong sulphuric acid stops the evolution of gas 
 by precipitating a quantity of white anhydrous sul- 
 phate of iron, which coats the sulphide and defends 
 it from the action of the acid. When no more gas 
 is required, the acid liquid should be at once 
 poured away, leaving the fragments of sulphide of 
 iron at the bottom of the bottle for a fresh opera- 
 tion. The liquid, if set aside, will deposit beauti- 
 ful green crystals of copperas or sulphate of iron 
 (FeO.S0 3 + 7HO). 
 Since the sulphide of iron prepared as above generally contains a little metallic 
 
 Fig. 185. 
 
 Fig. 186. Preparation of 
 hydrosulpliuric acid. 
 
SOLUTION OF HYDROSULPHURIC ACID. 191 
 
 iron, the sulphuretted hydrogen is mixed with free hydrogen, which does not gene- 
 rally interfere with its uses. The pure gas may he prepared by heating sulphide of 
 antimony (crude antimony) in a flask with hydrochloric acid 
 
 SbS 3 + 3HC1 3HS + SbCl 3 . 
 
 Properties of liydrosulphuric add. This gas is at once distinguished 
 from all others by its disgusting odour. It is one-fifth heavier than air 
 (sp. gr. 1-1912). Its gaseous state is not permanent, but a pressure of 17 
 atmospheres is required to reduce it to a colourless liquid, which congeals 
 to a transparent solid at 122 F. "Water absorbs about three times its 
 volume of sulphuretted hydrogen at the ordinary temperature ; both the 
 gas and its solution are feebly acid to red litmus paper. The gas is very 
 combustible, burning with a blue flame like that of sulphur, and yielding, 
 as the chief products, water and sulphurous acid 
 
 HS + 3 HO + S0 2 
 
 a little hydrated sulphuric acid (HO . S0 3 ) is also formed, and unless the 
 supply of air is very good, some of the sulphur will be separated ; thus, if 
 a taper be applied to a bottle filled with sulphuretted hydrogen, a good 
 deal of sulphur will be deposited upon the sides. This combustibility of 
 sulphuretted hydrogen is of the greatest importance in those processes of 
 chemical manufacture in which this gas is evolved (as in the preparation 
 of ammoniacal salts from gas liquors), enabling it to be disposed of in the 
 furnace instead of becoming a nuisance to the neighbourhood. The gas 
 causes fainting when inhaled in large quantity, and appears much to de- 
 press the vital energy when breathed for any length of time even in a 
 diluted state. 
 
 When dissolved in water, hydrosulphuric acid is slowly acted upon by 
 the oxygen of the air, which converts its hydrogen into water, and causes 
 a white deposit of (electronegative Or soluble) sulphur. 
 
 This is a great drawback 'to the use of this indispensable chemical in the labor- 
 atory, since the solution of hydrosulphuric acid is so soon rendered useless. To 
 diminish it as far as possible, the solution should be made either with boiled water (free 
 from dissolved air), or with water which has already been once charged with the gas 
 and spoilt by keeping, for all the oxygen dissolved in this water will have been con- 
 sumed by the former portion of gas. The gas should be passed through the water 
 until, on closing the bottle with the hand and shaking violently, the pressure is 
 found to act outwards, showing the water to be saturated with the gas. By closing 
 the bottle with a greased stopper, and inverting it, the solution may be preserved 
 for some weeks, even though occasionally opened for use. 
 
 In preparing the solution of hydrosulphuric acid, a certain quantity of the gas 
 always escapes absorption. To prevent this from becoming a nuisance, the bottle 
 containing the water to be charged with gas may be covered with an air-tight 
 caoutchouc cap having two tubes, through one of which passes the glass-tube con- 
 veying the gas down into the water, and through the other, a tube conducting the 
 excess of gas either into a gas-burner, where it may be consumed, or into a solution 
 of ammonia which will absorb it, forming the very useful hydrosulphate of am- 
 monia. 
 
 The hydrogen of the hydrosulphuric acid is oxidised immediately by 
 nitrous acid (N0 3 ), the sulphur being separated, and a considerable quan- 
 tity of nitrite of ammonia produced 
 
 N0 3 + 6HS = NH 3 + 3HO + S 6 . 
 Concentrated nitric acid also oxidises the hydrogen and a part of the 
 sulphur, sulphate of ammonia (NH 3 . HO . S0 3 ) being found in the solu- 
 tion, and a pasty mass of sulphur separated. Chlorine, bromine, and 
 iodine at once appropriate its hydrogen and separate the sulphur. 
 
192 PAINTS BLACKENED BY SULPHURETTED HYDROGEN. 
 
 In its action upon the metals and their oxides, hydrosulphuric acid 
 resembles hydrochloric and the other hydrogen acids. Many of the metals 
 displace the hydrogen and form metallic sulphides. This usually requires 
 the assistance of heat, but mercury and silver act upon the gas at the 
 ordinary temperature. Thus, if sulphuretted hydrogen be collected over 
 mercury, the surface of the latter becomes coated with a black film of sub-- 
 sulphide of mercury ; HS + Hg 2 = H + Hg 2 S. In a similar way the 
 surface of silver is slowly tarnished when exposed to sulphuretted hydro- 
 gen, its surface being covered with a black film of sulphide of silver. It 
 is on this account that silver plate is so easily blackened by the air of 
 towns, which is contaminated with sulphuretted hydrogen. An egg spoon 
 is always blackened by the sulphur from the egg. Silver coins kept in 
 the pocket with lucifer matches are blackened, from the formation of a 
 little sulphide of silver. The original brightness of the coin may be 
 restored by rubbing it with a solution of cyanide of potassium, which dis- 
 solves the sulphide of silver. 
 
 When heated in the gas, several metals displace the hydrogen from it. 
 Thus, potassium acts upon it in a corresponding manner to that in which 
 it acts upon water 
 
 2HO + K = KO.HO + H 
 2HS + K = KS . HS + H 
 
 forming liydrosulphate of (sulphide of) potassium (KS . HS). 
 
 Tin removes the whole of the sulphur from hydrosulphuric acid at a 
 moderate heat ; Sn + HS = H + SnS. 
 
 When hydrosulphuric acid acts upon a metallic oxide, it generally con- 
 verts it into a sulphide corresponding to the oxide, whilst the hydrogen 
 and oxygen unite to form water. Oxide of lead in contact with the gas 
 yields black sulphide of lead and water ; PbO + HS = PbS + HO. Even 
 if the oxide of lead be combined with an acid, the same change is produced 
 by hydrosulphuric acid ; and hence paper impregnated with a salt of lead 
 is used as a test for the presence of this gas. Thus, if paper be spotted 
 with a solution of nitrate (or acetate) of lead, it will indicate the presence 
 of even minute quantities of sulphuretted hydrogen (in impure coal-gas, 
 for example) by the brown colour imparted to the spots, the nitrate of 
 lead being decomposed by the hydrosulphuric acid 
 
 PbO.N0 5 + HS - H0.tf0 5 + PbS. 
 
 Nitrate of lead. Nitric acid. 
 
 It is in this manner that paints containing white lead (carbonate of 
 lead) are darkened by exposure to the air of towns, Cards glazed with 
 white lead, and engravings on paper whitened with that substance, suffer 
 a similar change. Paintings, whether in oil or water colours, in which 
 lead is an ingredient, are also injured by air containing sulphuretted 
 hydrogen. The interesting observation has recently been made that such 
 colours, damaged by the formation of sulphide of lead, are restored by 
 the continued action of light and air, the black sulphide of lead becoming 
 oxidised and converted into the white sulphate of lead 
 
 PbS + 4 = PbO.S0 3 . 
 
 In the dark this restoration does not take place, so that it is often a mis- 
 take to screen pictures from the light by a curtain. 
 
 In cases where the sulphide corresponding to the oxide is of an unstable 
 
SULPHUR ACIDS, BASES, AND SALTS. 193 
 
 character, the action of hydrosulphuric acid upon the oxide will be attended 
 with separation of sulphur. This is the case with peroxide of iron 
 
 Fe 2 3 + 3HS = 2FeS + 3HO + S 
 
 as is seen in the purifiers in which that substance is employed for remov- 
 ing the sulphuretted hydrogen from coal-gas. 
 
 The action of hydrosulphuric acid upon the chlorides and other haloid 
 salts of the metals generally resembles its action upon the oxides of the 
 same metals. 
 
 Most of the sulphides of the metals, like the corresponding oxides, are 
 insoluble in water, but many of the sulphides are also insoluble in diluted 
 acids and in alkalies, so that when hydrosulphuric acid is brought into 
 contact with the solutions of metals, it will often precipitate the metal in 
 the form of a sulphide having some characteristic colour or other property 
 by which the metal may be identified. 
 
 Any solution of lead will give a black precipitate with solution of hydrosulphuric 
 acid, the sulphide of lead being insoluble in diluted acids and in alkalies. 
 
 A solution of antimony (tartar-emetic, for example, the tartrate of antimony and 
 potash) mixed with an excess of hydrochloric acid, gives an orange-coloured preci- 
 pitate (SbS 3 ) on adding hydrosulphuric acid ; but if another portion be mixed with 
 an excess of potash before adding the hydrosulphuric acid, there will be no precipi- 
 tate, for the sulphide of antimony is soluble in alkalies. 
 
 Chloride of cadmium gives a brilliant yellow precipitate of sulphide of cadmium 
 on adding hydrosulphuric acid. 
 
 Sulphate of zinc yields a white precipitate of sulphide of zinc (ZnS), but if a little 
 hydrochloric acid be previously added, no precipitate is formed, the sulphide of zinc 
 being soluble in acids. On neutralising the hydrochloric acid with ammonia, the 
 sulphide of zinc is at once precipitated. 
 
 It is evident that, in a solution containing cadmium and zinc, the metals may be 
 separated by acidifying the liquid with hydrochloric acid, and adding excess of 
 hydrosulphuric acid, which precipitates the sulphide of cadmium only. On filtering 
 the solution, and adding ammonia, the sulphide of zinc is precipitated. 
 
 Sulphur-acids and sulphur-bases. Those sulphides which are soluble 
 in the alkalies are often designated sulphur-acids, whilst the sulphides of 
 the alkali-metals are sulphur-bases. These two classes of sulphides com- 
 bine to form sulphur-salts analogous in composition to the oxygen-salts of 
 the same metals. Thus, there have been crystallised, the salts 
 
 Sulphostannate of (sulphide of) sodium, 2NaS . SnS 2 
 Sulphantimoniate 3NaS . SbS 5 
 
 Sulpharseniate 3NaS . AsS 5 . 
 
 The sulphostannic (SnS 2 ), sulphantimonic (SbS 5 ), and sulpharsenic 
 (AsS 5 ) acids respectively, corresponding to stannic (Sn0 2 ), an^imonic 
 (Sb0 5 ), and arsenic (As0 5 ) acids. 
 
 The action of air upon the sulphides of the metals is often turned to 
 account in chemical manufactures. At the ordinary temperature, the sul- 
 phides of those metals which form alkaline oxides (such as sodium and 
 calcium), when exposed to the air in the presence of water, yield, first, 
 mixtures of the oxide and bisulphide, 2NaS + = NaO + NaS 2 ; and 
 afterwards the hyposulphite, NaS 2 + 3 = NaO . S 2 2 . This change is 
 sometimes turned to account for the manufacture of hyposulphite of 
 soda. When the metal forms a less powerful base with oxygen, the sul- 
 phide is often converted into sulphate by exposure to moist air ; thus, 
 CuS + 4 = CuO . S0 3 , which is taken advantage of for the separation 
 of copper from tin ores. 
 
 N 
 
194 ANOMALOUS EXPANSION OF SULPHUR VAPOUR. 
 
 The black sulphide of iron (FeS), when exposed to moist air, becomes 
 converted into red peroxide of iron, with separation of sulphur 
 
 2FeS + 3 = Fe 2 3 + S 2 
 
 a change which enables the gas manufacturer to revive, by the action of 
 air, the peroxide of iron employed for removing the sulphuretted hydrogen 
 from coal-gas (see p. 193). 
 
 When roasted in air at a high temperature, the sulphides correspond- 
 ing to the more powerful bases are converted into sulphates ; thus 
 ZnS + 4 = ZnO . S0 3 , which explains the production of sulphate of 
 zinc by roasting blende. But in most cases part of the sulphur is 
 converted into sulphurous acid at the same time. Subsulphide of 
 copper, for instance, is partly converted into oxide of copper by roasting, 
 Cu 2 S + 4 = 2CuO + S0 2 , a change of great importance in the extrac- 
 tion of copper from its ores. 
 
 140. Composition of hydrosulphuric acid. When this acid acts upon 
 a metallic oxide, the oxide, as a general rule, is found to exchange 8 parts 
 by weight of oxygen for 1 6 parts of sulphur ; therefore, if 8 be taken as 
 the equivalent of oxygen (H = 1), 16 will represent that of sulphur, and 
 the equivalent weight of hydrosulphuric acid will be 17 (containing 1 eq. 
 of hydrogen and 1 eq. of sulphur). If metallic tin be heated in a measured 
 volume of hydrosulphuric acid gas, it removes the whole of the sulphur, 
 whilst the hydrogen which is left occupies the same volume as the original 
 hydrosulphuric acid. Hence, 1 vol. of this gas contains 1 vol. of hydro- 
 gen. 
 
 The weight of 1 vol. (sp. gr.) of HS . . = M912 
 Deducting the weight of 1 vol. (sp. gr.) of H = 0-0692 
 
 There remains . . . . 1-1220 
 
 for the weight of the sulphur vapour contained in 1 vol. of hydrosulphuric 
 acid. The specific gravity (or weight of 1 vol.) of sulphur vapour (at 
 1900 F.) is 2 '23, so that the weight of sulphur vapour in 1 vol. of hydro- 
 sulphuric acid represents half a volume ; accordingly, there are, in 1 vol. 
 of HS, 1 vol. of hydrogen and J vol. of sulphur vapour. But 1 eq. (17 
 parts by weight) of hydrosulphuric acid occupies 2 vols. (8 parts of oxygen 
 representing 1 vol.), and would contain 1 eq. of hydrogen (occupying 2 
 vols.) and 1 eq. of sulphur (occupying 1 vol.). 
 
 The composition of hydrosulphuric acid by volume, therefore, is precisely 
 similar to that of water, and its molecular formula (1 vol. 1 atom of H) 
 would be H 2 S ( = 2 vols.), the atomic weight of sulphur being 32, and 
 occupying, in the state of vapour at 1900 F., the same volume as 1 part 
 by weight of hydrogen. 
 
 141. Influence of temperature upon the specific gravity of gases and 
 vapours. The specific gravity of a gas or vapour being defined as its 
 weight, compared with that of an equal volume of dry and pure air at the 
 same temperature and pressure, it might be supposed that so long as the 
 temperatures were equal, their actual thermometric value would not influ- 
 ence the specific gravity. Indeed, with those gases and vapours which 
 are condensible with difficulty, this is actually the case. Thus, if equal 
 volumes of oxygen and air be weighed, either at a low or a high tempera- 
 ture, provided their temperatures are the same, their weights will always 
 stand to each other in the ratio of 1 '105 7 : 1 
 
PERSULPHIDE OF HYDROGEN. 195 
 
 But with many vapours it is found that if they be weighed at tempera- 
 tures too nearly approaching to their condensing points, their specific 
 gravities are much higher than they are found to he at higher tempera- 
 tures. Sulphur affords a very well-marked instance of this. It boils at 
 836 F., and if its vapour be weighed at a temperature of 900 F., it is 
 found to weigh 6*617 times as much as an equal volume of air at 900 F., 
 so that its specific gravity would be 6-617, or 1 eq. of sulphur would 
 occupy l vol. (0 = 1 vol.). But if the vapour of sulphur be weighed at 
 1900 F., it is found to weigh only 2 '2 3 times as much as an equal volume 
 of air at the same temperature and pressure, so that its specific gravity is 
 only one-third of that formerly given, and 1 eqt. of sulphur occupies 1 vol. 
 
 142. Persulphide of hydrogen. The composition of this substance is not yet satis- 
 factorily ascertained. The similarity of its chemical properties to those of binoxide 
 of hydrogen prompts the wish that its formula may be HS 2 . Some analyses, how- 
 ever, seem to lead to the formula HS 5 , but since the persulphide is a liquid capable 
 of dissolving free sulphur, which is not easily separated from it, there is much diffi- 
 culty in determining the exact proportion of this element with which the hydrogen 
 is combined. 
 
 When equal weights of slaked lime and sulphur are boiled with water, an orange- 
 coloured liquid is formed, which contains hyposulphite of lime, bisulphide of calcium, 
 and pentasulphide of calcium (CaS 5 ) 
 
 3CaO + S 6 = CaO . S 2 2 + 2CaS 2 . 
 
 Hyposulphite Bisulphide 
 
 of lime. of calcium. 
 
 When hydrochloric acid is added to the filtered solution, an abundant precipitation 
 of sulphur occurs, and much hydrosulphuric acid is evolved 
 
 CaS 2 + HC1 = CaCl + HS + S. 
 
 But if the solution be poured by degrees into a slightly warm mixture of hydro- 
 chloric acid with twice its bulk of water, and constantly stirred, a yellow heavy oily 
 liquid collects at the bottom, which is the persulphide of hydrogen 
 
 CaS 2 + HC1 = HS 2 (?) + CaCl . 
 
 The acid having been kept in excess, the persulphide has been preserved from the 
 decomposition which it suffered in the presence of the alkaline solution in the 
 former experiment. For the persulphide of hydrogen very closely resembles the bin- 
 oxide in the facility with which it may be decomposed into hydrosulphuric acid and 
 sulphur ; it undergoes spontaneous decomposition even in sealed tubes, and the hydro- 
 sulphuric acid then becomes liquefied by its own pressure. Most of the substances, 
 the contact of which promotes the decomposition of the binoxide of hydrogen, have 
 the same effect upon the persulphide. This compound has a peculiar odour which 
 appears to affect the eyes ; of course, its vapour is mixed with that of hydrosul- 
 phuric acid. 
 
 OXIDES OF SULPHUR. 
 
 143. Only two compounds of sulphur with oxygen have been obtained 
 in the separate state, viz., sulphurous acid (S0 2 ) and sulphuric acid (S0 3 ). 
 Four more have been obtained in combination with water, viz., dithionic 
 (Otiov, sulphur) or hyposulphuric (S 2 0.), irithionic (S 3 5 ), tetrathionic 
 (S 4 5 ), and pentathionic (S 5 5 ) acids. One of the oxides has only been 
 obtained in the form of salts, viz., hyposulphurous acid (S 2 2 ). 
 
 The following table exhibits their composition, the imaginary oxides 
 being distinguished by (?) : 
 
 N 2 
 
196 
 
 PKEPAKATION OF SULPHUROUS ACID. 
 
 Oxides of Sulphur. 
 
 
 Equivalent 
 
 By Weight. 
 
 Name. 
 
 Foimula. 
 
 Sulphur. 
 
 Oxygen. 
 
 Hyposulphurous acid, . . ? 
 
 8,0, 
 
 32 
 
 16 
 
 Sulphurous 
 
 S0 2 
 
 16 
 
 16 
 
 Sulphuric 
 
 S0 3 
 
 16 
 
 24 
 
 Dithionic ,, . . ? 
 
 S 2 5 
 
 32 
 
 40 
 
 Trithionic . . ? 
 
 S 3 5 
 
 48 
 
 40 
 
 Tetrathionic . . ? 
 
 S 4 0- 
 
 04 
 
 40 
 
 Pentathionic . . ? 
 
 S 5 5 
 
 80 
 
 40 
 
 SULPHUROUS Acm. 
 
 144. In nature, sulphurous acid is but rarely met with ; it exists in the 
 gases issuing from volcanoes. Although constantly discharged into the 
 air of towns by the combustion of coal (containing sulphur), it is so easily 
 oxidised and converted into sulphuric acid, that no considerable quantity 
 is ever found in the atmosphere. Sulphurous acid has been already men- 
 tioned as the sole product of the combustion of sulphur in dry air and 
 oxygen, but it is generally prepared for chemical purposes by removing 
 part of the oxygen from sulphuric acid, which is easily effected by heating 
 it with metallic copper 
 
 2(HO.S0 3 ) 
 
 Hydrated sulphuric 
 acid. 
 
 Cu 
 
 CuO.S0 3 
 
 Sulphate of copper. 
 
 2HO 
 
 S0 2 . 
 
 300 grains of copper clippings are heated in a Florence flask with 4 oz. (measured) 
 of strong sulphuric acid, the gas being conducted by a bent tube down to the bottom 
 of a dry bottle closed with a perforated card (see fig. 160, p. 147). Some time will 
 elapse before the gas is evolved, for sulphuric acid acts upon copper only at a high 
 temperature ; but when the evolution of gas fairly commences, it will proceed very 
 rapidly, so that it is necessary to remove the flame from under the flask. The 
 gas will contain a little suspended vapour of sulphuric acid, which renders it 
 turbid. 
 
 When the operation is finished, and the flask has been allowed to cool, it will be 
 found to contain a grey crystalline powder at the bottom of a brown liquid. The 
 latter is the excess of sulphuric acid employed, and retains very little copper, since 
 sulphate of copper is insoluble in strong sulphuric acid. If the liquid be poured off, 
 and the flask filled up with water, and set aside for some time, the crystalline powder 
 will dissolve, forming a blue solution of sulphate of copper, yielding that salt in fine 
 prismatic crystals by evaporation and cooling. The dark powder remaining un- 
 dissolved after extracting the whole of the sulphate of copper consists chiefly of sul- 
 phide of copper, the production of which is interesting, as showing how far the 
 deoxidising effect of the copper may be carried in this experiment. 
 
 Sulphurous acid is a very heavy (sp. gr. 2 -25) colourless gas, character- 
 ised by its odour of burning brimstone. It condenses to a clear liquid at 
 F. (the temperature of a mixture of ice and salt) even at the ordinary 
 pressure of the air, and has been frozen to a colourless crystalline solid at 
 -105F. 
 
 The liquefaction of the gas is easily exhibited by passing it down to the bottom of 
 

 BLEACHING BY SULPHUROUS ACID. 
 
 197 
 
 Fig. 187. 
 
 a tube (A. fig. 187) closed at one end, and surrounded with a mixture of pounded 
 ice with half its weight of salt. The tube should have been previously drawn out 
 to a narrow neck at B, which may afterwards be sealed 
 by the blowpipe, the lower part of the tube being still 
 surrounded by the freezing mixture, since the liquid 
 sulphurous acid boils at 14 F. The tube need not be 
 very strong, for at the ordinary temperature the vapour 
 of sulphurous acid exerts a pressure of only 2'5 atmo- 
 spheres. Liquid sulphurous acid is a convenient agent 
 for producing (by its rapid evaporation) the low tempe- 
 rature ( - 39 F.) required to effect the solidification of 
 mercury. A small globule of this metal may readily 
 be frozen by dropping some liquid sulphurous acid 
 upon it in a watch-glass placed in a strong draught of 
 air. The tube containing the sulphurous acid should 
 be held in a woollen cloth or glove. The attractive ex- 
 periment of freezing water in a red-hot crucible may 
 also be made with the liquid acid. A platinum crucible 
 being heated to redness, and some liquid sulphurous 
 acid poured into it, the liquid becomes surrounded with an atmosphere of sulphurous 
 acid gas, which prevents its contact with the metal (assumes the spheroidal state), 
 and its temperature is reduced by its own evaporation to so low a degree that a few 
 drops of water allowed to flow into it will at once become converted into ice. 
 
 Sulphurous acid gas is very easily absorbed by water, as may be shown 
 by pouring a little water into a bottle of the gas, closing the bottle with 
 the palm of the hand, and shaking it violently (see fig. 148, p. 139), 
 when the diminished pressure due to the absorption of the gas will cause 
 the bottle to be sustained against the hand by the pressure of the 
 atmosphere. Water absorbs 4 3 '5 times its bulk of the gas at the ordi- 
 nary temperature. If the solution be exposed to a low temperature, a 
 crystallised hydrate of sulphurous acid is obtained, the composition of 
 which does not appear to be accurately settled. When the solution of 
 sulphurous acid is kept for' some time in a bottle containing air, its smell 
 gradually disappears, the acid absorbing oxygen and becoming converted 
 into sulphuric acid. 
 
 Sulphurous acid, like carbonic acid, possesses in a high degree the 
 power of extinguishing flame. A taper is at once extinguished in a 
 bottle of the gas, even when containing a considerable proportion of air. 
 One of the best methods of extinguishing burning soot in a chimney 
 consists in passing up sulphurous acid by burning a few ounces of sul- 
 phur in a pan placed over the fire. 
 
 The principal uses of sulphurous acid depend upon its property of 
 bleaching many animal and vegetable colouring matters. Although a 
 far less powerful bleaching agent than chlorine, it is preferred for bleach- 
 ing silk, straw, wool, sponge, isinglass, baskets, &c., which would be 
 injured by the great chemical energy of chlorine. The articles to be 
 bleached are moistened with water and suspended in a chamber in which 
 sulphurous acid is produced by the combustion of sulphur. The colour- 
 ing matters do not appear in general to be decomposed by the acid, but 
 rather to form colourless combinations with it, for, in course of time, 
 the original colour often reappears, as is seen in straw, flannel, &c., which 
 become yellow from age, the sulphurous acid probably being oxidised 
 into sulphuric acid. Stains of fruit and port wine on linen are conve- 
 niently removed by solution of sulphurous acid. 
 
 The red solution obtained by boiling a few chips of logwood with river water (dis- 
 tilled water does not give so fine a colour), serves to illustrate the bleaching proper- 
 
198 
 
 ANTISEPTIC PROPERTIES OF SULPHUROUS ACID. 
 
 ties of sulphurous acid. A few drops of the solution of the acid will at once change 
 the red colour of the solution to a light yellow, but that the colouring power is sus- 
 pended and not destroyed, may be shown by dividing the yellow liquid into two 
 parts, and adding to them, respectively, potash and diluted sulphuric acid, which 
 will restore the colour in a modified form. To contrast 
 this with the complete decomposition of the colouring 
 matter, a little sulphurous acid may be added to a weak 
 solution of the permanganate of potash, when the splendid 
 red solution at once becomes perfectly colourless, and nei- 
 ther acid nor alkali can effect its restoration, for in this 
 case the red permanganic acid (Mn 2 7 ), supposed to exist 
 in the permanganate of potash, is reduced to the state of 
 protoxide of manganese. 
 
 If a bunch of damp coloured flowers be suspended in a 
 bell-jar over a crucible containing a little burning sulphur 
 (fig. 188), many of the flowers will be completely bleached 
 by the sulphurous acid, and by plunging them afterwards 
 into diluted sulphuric acid and ammonia, their colours 
 may be partly restored, with some very curious modifica- 
 tions. 
 
 Fig. 188. 
 
 Fig. 189, 
 
 Another very useful property of sulphurous acid is that of arresting 
 fermentation (or putrefaction), apparently by killing the vegetable or ani- 
 mal growth which is the cause of the fermentation. This is commonly 
 designated the antiseptic property of sulphurous acid, and is turned to 
 
 account when casks for wine or beer 
 are sulphured in order to prevent the 
 action of any substance contained in the 
 pores of the wood, and capable of ex- 
 citing fermentation, upon the fresh liquor 
 to be introduced. If a little solution of 
 sugar be fermented with yeast in a flask 
 provided with a funnel tube (fig. 189), 
 a solution of sulphurous acid poured in 
 through the latter will at once arrest the fer- 
 mentation. The salts of sulphurous acid 
 (sulphites) are also occasionally used to 
 arrest fermentation, in the manufacture of 
 sugar, for instance. Clothes are sometimes fumigated with sulphurous 
 acid to destroy vermin. 
 
 The disposition of sulphurous acid to absorb oxygen and pass into sul- 
 phuric acid, renders it a powerful deoxidising or reducing agent. Solu- 
 tions of silver and gold are reduced to the metallic state by sulphurous 
 acid if a very little ammonia be added, and a gentle heat applied. 
 
 If a solution of sulphurous acid be heated for some time in a sealed tube to 340 F. 
 one portion of the acid deoxidises another, sulphur is separated, and sulphuric acid 
 formed; 3S0 2 + 2HO = 2(HO.SO S ) + S. 
 
 Sulphurous acid gas combines with ammonia gas to form two solid compounds 
 (NH 3 .S0 2 , and NH 3 .2S0 2 ) which are quite different in their properties from the 
 sulphite and bisulphite of ammonia (NH V HO.S0 2 , and NH V H0.2S0 2 ), which are 
 formed when sulphurous acid acts upon solution of ammonial 
 
 Chlorine combines with an equal volume of sulphurous acid, under the influence 
 of bright sunshine, to produce a colourless liquid, the vapour of which is very acrid 
 and irritating to the eyes. Its composition is represented by S0 2 C1, and it is some- 
 times called chlorosulphuric acid, though it does not combine with bases, and is de- 
 composed by water, yielding hydrochloric and sulphuric acids. It is also known as 
 chloride of sulphuryle, S0 2 being looked upon as the radical of sulphuric acid. The 
 chloride of thionyle, SOC1, is a colourless volatile liquid obtained by the action of 
 
SULPHITES COMPOSITION OF SULPHUROUS ACID. 199 
 
 hypochlorous acid gas on sulphur dissolved in the subchloride of sulphur. It is 
 decomposed by water, yielding hydrochloric and sulphurous acids. 
 
 Potassium and sodium, when heated in sulphurous acid, burn vividly, producing 
 the oxides and sulphides of the metals. 
 
 Iron, lead, tin, and zinc are also converted into oxides and sulphides when heated 
 in sulphurous acid ; S0 2 + Zn 3 = ZnS + 2ZnO . 
 
 Sulphites. The acid character of sulphurous acid is rather feeble, al- 
 though stronger than that of carbonic acid. There is much general 
 resemblance between the sulphites and carbonates, in point of solubility, 
 the sulphites of the alkali-metals being the only salts of sulphurous acid 
 which are freely soluble in water. Sulphurous acid, like carbonic, forms 
 two classes of salts, the sulphites (for example, sulphite of soda, NaO . 862) 
 and bisulphites (as bisulphite of potash, KO . HO . 2S0 2 ). 
 
 The sulphite of soda is extensively manufactured for the use of the 
 paper-maker, who employs it as an antichlore for killing the bleach, that 
 is, neutralising the excess of chlorine after bleaching the rags with chlo- 
 ride of lime and sulphuric acid (see p. 145) 
 
 NaO . S0 a + HO + Cl = NaO . S0 3 + HC1 . 
 
 It is prepared by passing sulphurous acid over damp crystals of car- 
 bonate of soda, when the carbonic acid is expelled, and sulphite of soda 
 formed, which is dissolved in water and crystallised. It forms oblique 
 prisms having the composition NaO . S0 2 + 7Aq, which effloresce in the 
 air, becoming opaque, and slowly absorbing oxygen, passing into sulphate 
 of soda (NaO . S0 3 ). Its solution is slightly alkaline to test-papers. 
 
 For the manufacture of sulphite of soda, the sulphurous acid is obtained 
 either by the combustion of sulphur or by heating sulphuric acid with 
 charcoal 
 
 2(HO.SO S ) + C - 2HO + C0 2 + 2S0 2 . 
 
 The carbonic acid, of course, will not interfere with this application of 
 the sulphurous acid. 
 
 145. Composition of sulphurous acid. When sulphur is burnt in 
 oxygen, the volume of the sulphurous acid produced is equal to that of 
 the oxygen, so that 1 vol. of sulphurous acid contains 1 vol. of oxygen. 
 
 The weight of 1 vol. (sp. gr.) of sulphurous acid is, . 2*2470 
 Deducting the weight of 1 vol. (sp. gr.) of oxygen, . 1*1056 
 
 1*1414 
 
 The remainder represents the weight of sulphur vapour contained in 
 one volume of sulphurous acid. But it has been seen (p. 195) that the 
 weight of one volume of sulphur vapour (at 1900 F.) is 2*23, so that the 
 above weight represents half a volume of sulphur vapour ; and 2 vols. of 
 sulphurous acid contain 2 vols. of oxygen and 1 vol. of sulphur vapour. 
 
 The quantity of sulphurous acid which generally combines with one 
 equivalent of a base amounts to 32 parts by weight, which may, there- 
 fore, be taken as the equivalent weight of sulphurous acid. This weight 
 would occupy twice the volume of 8 parts by weight of oxygen. 
 
 One equivalent of sulphurous acid, therefore, representing 32 parts by 
 weight or 2 vols., contains 1 eq. (16 parts by weight) or 1 vol. of sulphur 
 vapour, and 2 eqs. (16 parts by weight) or 2 vols. of oxygen. 
 
 The molecular formula of sulphurous acid would be S0 2 (8 = 32, 6 = 16) 
 
200 
 
 NORDHAUSEN SULPHURIC ACID. 
 
 representing 2 vols. of the gas (H = 1 vol.), containing 1 vol. (or 1 atom) 
 of sulphur vapour and 2 vols. (or 2 atoms) of oxygen. 
 
 Just as in the case of carbonic acid (see p. 75), many chemists deny the 
 acid nature of the compound S0 2 altogether, and term it sulphurous 
 anhydride, reserving the name of sulphurous acid for the hydrated sul- 
 phurous acid, HO . S0 2 or HS0 3 (or H 2 S0 3 ), obtained by exposing the 
 aqueous solution of sulphurous acid to a very low temperature. 
 
 SULPHURIC ACID. 
 
 146. It has been already noticed that one of the most abundant forms 
 in which sulphur occurs in nature is that of sulphuric acid in combina- 
 tion with certain bases. Hydrated sulphuric acid has also been found in 
 certain springs and rivers in volcanic regions. Sulphurous acid and 
 oxygen gases combine to form sulphuric acid (SOs) when passed through 
 a tube containing heated platinum or certain metallic oxides, such as those 
 of copper and chromium, the action of which in promoting the combina- 
 tion is not thoroughly understood. 
 
 The combination may be shown by passing oxygen from the tube A (fig. 190) 
 connected with a gas-holder, through a strong solution of sulphurous acid (B), so 
 
 that it may take up a quantity of that gas, 
 afterwards through a tube (0) containing 
 pumice stone soaked with oil of vitriol, to 
 remove the water, and then through a 
 bulb (D) containing platinised asbestos 
 (see p. 132). The mixture of the gases 
 issuing into the air is quite invisible, but 
 when the bulb is gently heated, combina- 
 tion takes place, and dense white clouds 
 are formed in the air, from the combina- 
 tion of the anhydrous sulphuric acid (S0 3 ) 
 produced, with the atmospheric moisture. 
 
 Fig. 190. An easier method of obtaining the 
 
 anhydrous sulphuric acid will be 
 
 noticed hereafter, but the hydrated acid is of so much more importance 
 that its preparation and properties should be studied before those of the 
 anhydrous acid. 
 
 Hydrated sulphuric acid. More than four centuries ago, the alchemist 
 Basil Valentine subjected green vitriol, as it was then called (sulphate of 
 iron), to distillation, and obtained an acid liquid which he named oil 
 of vitriol. The process discovered by this laborious monk is even 
 now in use at Nordhausen in Saxony, and the Nordhausen oil of vitriol 
 is an important article of commerce. The crystals of sulphate of iron 
 (FeO . S0 3 + 7HO) .are exposed to the air so that they may absorb 
 oxygen, and become converted into the basic persulphate of iron 
 
 2(FeO.S0 3 ) + = FegOj.280,,. 
 
 Bas'c persulphate 
 of iron. 
 
 This salt is dried, and distilled in earthen retorts, the oil of vitriol 
 being condensed in receivers of glass or stoneware. The action of heat 
 upon the basic persulphate of iron separates the acid from the base, and 
 if the salt were absolutely dry, the anhydrous sulphuric acid would be 
 expected to distil over. There is always enough water, however, left in 
 
MANUFACTURE OF OIL OF VITRIOL. 201 
 
 the persulphate, to combine with the anhydrous acid to form the Nord- 
 hausen oil of vitriol, the composition of which is pretty correctly ex- 
 pressed by the formula HO . 2S0 3 . The peroxide of iron (Fe 2 3 ) which is 
 left in the retorts, is the red powder known as colcothar, which is used for 
 polishing plate glass and metals. 
 
 The green vitriol employed for preparing the Nordhausen acid is obtained from 
 iron pyrites (FeS 2 ). A particular variety of this mineral, white pyrites (or efflores- 
 cent pyrites), when exposed to moist air, undergoes oxidation, yielding sulphate of 
 iron and sulphuric acid 
 
 FeS 2 + HO + 7 = FeO.S0 3 + HO.S0 3 . 
 
 Large masses of this variety of pyrites in mineralogical cabinets may often be 
 seen broken up into small fragments, and covered with an acid efflorescence of sul- 
 phate of iron from this cause. Ordinary iron pyrites is not oxidised by exposure to 
 the air unless it be first subjected to distillation in order to separate a portion of the 
 sulphur which it contains. 
 
 The Nordhausen acid is readily distinguished from English sulphuric 
 acid by its fuming in the air, when the bottle is opened. This is due to 
 the escape of a little vapour of anhydrous sulphuric acid. It is heavier 
 than the English acid, its specific gravity being 1 '9. It is chiefly used 
 for dissolving indigo in preparing the Saxony blue dye, and is a con- 
 venient source of the anhydrous sulphuric acid; for if it be gently heated 
 in a retort, the anhydrous acid is disengaged, and may be condensed in 
 silky crystals in a receiver kept cool by ice, whilst ordinary hydrated sul- 
 phuric acid (HO . S0 3 ) is left in the retort. 
 
 The process adopted at Nordhausen, though simple in theory, is expen- 
 sive on account of the consumption of fuel and the breaking of the retorts, 
 so that the price of the acid, compared with that of English manufacture, 
 is very high. 
 
 The first step towards the discovery of our present process was also 
 made by Valentine, when he prepared his oleum sulpliuns per campanum, 
 by burning sulphur under a bell-glass over water, and evaporating the acid 
 liquid thus obtained. The same experimenter also made a very important 
 advance when he burnt a mixture of sulphur, sulphide of antimony, and 
 nitre, under a bell-glass placed over water ; but it was not until the middle of 
 the eighteenth century that it was suggested by some Erench chemists to 
 burn the sulphur and nitre alone over water, a process by which the acid ap- 
 pears actually to have been manufactured upon a pretty large scale. The 
 substitution of large chambers of lead for glass vessels by Dr Eoebuck was 
 a great improvement in the process, and about the year 1770 the prepara- 
 tion of the acid formed an important branch of manufacture ; since then 
 the process has been steadily improving, until, at the present time, up- 
 wards of 100,000 tons are annually consumed in Great Britain, and a very 
 large quantity is exported. The diminution in the price of oil of vitriol 
 well exhibits the progress of improvemeut in its production, for the 
 original oil of sulphur appears to have been sold for about half-a-crown an 
 ounce, and that prepared by burning sulphur with nitre in glass vessels at 
 the same price per pound ; but when leaden chambers were introduced, 
 the price fell to a shilling per pound, and at present oil of vitriol can be 
 purchased at the rate of five farthings per pound. 
 
 The description of the present process of manufacture will be best 
 understood after a consideration of the chemical changes upon which it 
 depends. 
 
 It has been seen that when sulphur is burnt in air, sulphurous acid is 
 
202 
 
 THEORY OF PRODUCTION OF OIL OF VITRIOL. 
 
 the chief product. When sulphurous acid acts upon hydrated nitric acid, 
 in the presence of water, sulphuric acid and nitric oxide are formed 
 
 3S0 2 + HO.N0 5 + 2HO = 3(HO.SOj) + N0 2 . 
 JSTitric oxide, in contact with air, combines with its oxygen to form 
 nitric peroxide (N0 4 ). 
 
 If nitric peroxide is brought into contact with sulphurous acid and 
 water, it is again converted into nitric oxide with formation of sulphuric 
 acid 
 
 N0 4 + 2S0 2 + 2HO = N0 2 + 2(HO.S0 3 ). 
 
 It appears, therefore, that nitric oxide may be employed to absorb 
 oxygen from the air, and to convey it to the sulphurous acid, so that, 
 theoretically, an unlimited quantity of sulphurous acid, supplied with air 
 and water, might be converted into sulphuric acid by a given quantity of 
 nitric oxide. 
 
 To illustrate these important chemical principles of the manufacture of sulphuric 
 
 acid, the following experiments may be performed : 
 
 I. A quart bottle of nitric oxide (p. 130) is placed mouth to mouth with a pint 
 
 bottle of oxygen, when both bottles will be filled with the red nitric peroxide. 
 
 , II. The quart bottle of this red gas is placed mouth to mouth with a quart bottle 
 
 of sulphurous acid gas (fig. 191), when the red colour will soon disappear, and the 
 
 sides of the bottles will be covered with a crystalline 
 substance formed by the reaction between the nitric 
 peroxide, the sulphurous acid, and the small quantity 
 of water present in the gases. The true composi- 
 tion of this crystalline body is doubtful, but if, 
 for the purpose of the present reasoning, it be re- 
 garded as N0 2 . 2S0 3 . HO, its formation would be 
 represented by the equation 
 
 N0 4 + 2S0 2 + HO = N0 2 .2S0 3 .HO. 
 
 III. A little water is shaken round the insides of 
 the bottles, when the crystalline compound will be 
 decomposed with effervescence, evolving nitric oxide, 
 and producing hydrated sulphuric acid 
 
 N0 2 .2S0 3 .HO + HO = N0 2 + 2(HO.S0 3 ). 
 
 Fig. 191. 
 
 IV. Air is blown into the bottles through a glass tube, when the presence of the 
 nitric oxide will be proved by the formation of the red nitric peroxide. 
 
 In the presence of abundance 
 of water this crystalline com- 
 pound is not produced, as may 
 be shown by the following modi- 
 fication of the experiment. 
 
 V. A large glass flask or 
 globe (A, fig. 192) is fitted with 
 a cork, through which are 
 
 (a) a tube connected with a 
 flask (D) containing copper and 
 strong sulphuric acid, for evolv- 
 ing sulphurous acid ; 
 
 (b) a tube connected with a 
 flask (B) containing copper and 
 diluted nitric acid (sp. gr. 1-2) 
 for supplying nitric oxide ; 
 
 (c) a tube proceeding from 
 a small flask (E) containing 
 water. 
 
 a gentle heat to the flask containing nitric acid and copper, the nitric 
 
 Fig. 192. Preparation of sulphuric acid. 
 
 On applyin 
 
REACTIONS IN THE VITRIOL CHAMBERS. 203 
 
 oxide passes into the globe and combines with the oxygen of the air, filling the 
 globe with red nitric peroxide. The nitric oxide flask may then be removed. Sul- 
 phurous acid is then generated by heating the flask containing sulphuric acid and 
 copper ; the sulphurous acid will soon decolorise the red nitric peroxide, the con- 
 tents of the globe becoming colourless, and the crystalline compound forming 
 abundantly on the sides : the sulphurous acid flask may then be removed. Steam 
 is sent into the globe from the flask containing water, when the crystalline compound 
 will be dissolved, and sulphuric acid will collect at the bottom of the globe. If air 
 be now blown into the globe, the nitric oxide will again acquire the red colour of 
 nitric peroxide. 
 
 If the experiment be repeated, the steam being introduced simultaneously with 
 the sulphurous acid, no crystalline compound whatever will be formed, the sulphurous 
 acid being at once converted into hydrated sulphuric acid. 
 
 Since the cork is somewhat corroded in this experiment, it is preferable to have 
 the mouth of the flask ground and closed by a ground glass plate, perforated with 
 holes for the passage of the tubes. The perforations are easily made by placing the 
 glass plate flat against the wall and piercing it with the point of a revolving rat's- 
 tail file dipped in turpentine ; the file is then gradually worked through the hole 
 until the latter is of the required size. 
 
 The process employed for the manufacture of English oil of vitriol will 
 now be easily understood. 
 
 A series of chambers is constructed of leaden plates, the edges of 
 which are united by autogenous soldering (that is, by fusing their edges, 
 without solder, which would be rapidly corroded by the acid vapours) ; 
 the leaden chambers are supported and strengthened by a framework of 
 timber (fig. 193). 
 
 The sulphurous acid is generated by burning sulphur or iron pyrites in 
 a suitable furnace (A) adjoining the chambers, and so arranged that the 
 sulphurous acid produced may be mixed with about the proper quantity 
 of air to furnish the oxygen required for its conversion into sulphuric 
 acid. 
 
 Nitric acid vapour is evolved from a mixture of nitrate of soda and oil 
 of vitriol (see p. 124) contained in an iron pan which is heated by the com- 
 bustion of the sulphur, so that the nitric acid is carried into the chambers 
 with the current of sulphurous acid and air. 
 
 Water covers the floor of the chambers to the depth of about two inches, 
 and jets of steam are introduced at different parts from an adjacent 
 boiler (B). 
 
 The sulphurous acid acts upon the nitric acid vapour, in the presence 
 of the water, forming nitric oxide and hydrated sulphuric acid, which 
 rains down into the water on the floor of the chambers 
 
 3S0 3 + HO.]TO 5 + 2HO - N0 2 + 3(HO.S0 3 ) . 
 
 If this nitric oxide were permitted to escape from the chambers, and a 
 fresh quantity of nitric acid vapour introduced to oxidise another portion 
 of sulphurous acid, it is evident that 1 eq. (85 parts by weight) of nitrate 
 of soda would be required to furnish the nitric acid for the conversion of 
 3 eqs. (48 parts by weight) of sulphur, whereas, in practice, 3 parts by 
 weight only of nitrate of soda are employed for 48 parts of sulphur. 
 
 For the nitric oxide (N0 2 ) at once acquires oxygen from the air ad- 
 mitted together with the sulphurous acid, and becomes nitric peroxide 
 (N0 4 ), which oxidises more sulphurous acid in the presence of water, 
 converting it into hydrated sulphuric acid 
 
 2S0 2 + N0 4 + 2HO = 2(HO . S0 3 ) + N0 2 . 
 
 A great reduction in the volume of the gas in the chamber thus takes 
 place (4 vols. S0 2 and 4 vols. N0 4 yielding 4 vols. N0 2 ), so that there 
 
204 
 
 PLAN FOR ECONOMISING NITRIC OXIDE. 
 
 is room for the introduction of a fresh quantity of the mixture of sul- 
 phurous acid and air from the furnace, upon which the nitric oxide acts 
 as before, taking up the oxygen from the air and handing it over to the 
 sulphurous acid, in the presence of water, to produce a fresh supply of 
 hydrated sulphuric acid. 
 
 But the nitrogen of the air takes no part in these changes, and since 
 
 Fig. 193. Sulphuric acid chambers. 
 
 the oxygen consumed in converting the sulphur into sulphuric acid is 
 accompanied by four times its volume of nitrogen, a very large accumula- 
 tion of this gas takes place in the chambers, and provision must be made 
 for its removal in order to allow space for those gases which take part in 
 the change. The obvious plan would appear to be the erection of a simple 
 chimney for the escape of the nitrogen at the opposite end of the chamber 
 to that at which the sulphurous acid and air enter it \ and this plan was 
 formerly adopted, but the nitrogen carries off with it a portion of the 
 nitric oxide which is so valuable in the chamber, and to save this the 
 escaping nitrogen is now generally passed through a leaden chamber (C) 
 filled with coke, over which oil of vitriol is allowed to trickle ; the oil of 
 vitriol absorbs the nitric oxide, and flows into a cistern (D), from which 
 it is pumped up to the top of another chamber (E) filled with coke, or 
 arranged with shelves in cascade, through which the hot sulphurous acid 
 
COMMERCIAL VARIETIES OF SULPHURIC ACID. 205 
 
 and air are made to pass as they enter, when they take up the nitric oxide 
 from the oil of vitriol, and carry it with them into the chamber. 
 
 Before the introduction of this plan of retaining the nitric oxide by oil 
 of vitriol, it required a quantity of nitrate of soda amounting to |th or 
 T Vth of the weight of the sulphur to convert it into sulphuric acid, whereas 
 about ^Q-th or even less is now often made to suffice. 
 
 The sulphuric acid is allowed to collect on the floor of the chamber 
 until it has a specific gravity of about 1 -6, and contains 70 per cent, of oil 
 of vitriol (HO . 80s). If it were allowed to become more concentrated 
 than this, it would absorb some of the nitric oxide in the chamber, so 
 that it is now drawn off. 
 
 This acid is quite strong enough for some of the applications of sul- 
 phuric acid, particularly for that which consumes the largest quantity in 
 this country, viz., the conversion of common salt into sulphate of soda as 
 a preliminary step* in the manufacture of carbonate of soda. To save the 
 expense of transporting the acid for this purpose, the vitriol chambers 
 form part of the plant of the alkali works. 
 
 To convert this weak acid into the ordinary oil of vitriol of commerce, 
 it is run off into shallow leaden pans set in brickwork, and supported on 
 iron bars over the flue of a furnace, where it is heated until so much 
 water has evaporated that the specific gravity of the acid has increased to 
 1 '72. The concentration cannot be carried further in leaden pans, be- 
 cause the strong acid acts upon the lead, and converts it into sulphate 
 
 2(HO . S0 3 ) + Pb = PbO . S0 3 + 2HO + S0 2 . 
 
 The acid of 1 *72 sp. gr. contains about 80 per cent, of true oil of vitrioi 
 (HO . S0 3 ), and is largely employed for making superphosphate of lime^ 
 and in other rough chemical manufactures. It is technically called brown 
 acid, having acquired a brown colour from organic matter accidentally 
 present in it. 
 
 To convert this brown acid into commercial oil of vitriol, it is boiled 
 down, either in glass retorts or platinum stills, when water distils over, 
 accompanied by a little sulphuric acid, and the acid in the retort becomes 
 colourless, the brown carbonaceous matter being oxidised by the strong 
 sulphuric acid, with formation of carbonic and sulphurous acids. When 
 dense white fumes of oil of vitriol begin to pass over, showing that all the 
 superfluous water has been expelled, the acid is drawn off by a siphon. 
 
 The very diluted acid which distils off is employed instead of water on 
 the floor of the leaden chamber. 
 
 The cost of the acid is very much increased by this concentration. It cannot be 
 conducted in open vessels, partly on account of the loss of sulphuric acid, partly be- 
 cause concentrated sulphuric acid absorbs moisture from the open air even at the 
 boiling point. The loss by breakage of the glass retorts is very considerable, al- 
 though it is reduced as far as possible by heating them in sand, and keeping them 
 always at about the same temperature by supplying them with hot acid. But the 
 boiling point of the concentrated acid is very high (640 F.), and the retorts conse- 
 quently become so hot that a current of cold air or an accidental splash of acid will 
 frequently crack them at once. Moreover, the acid boils with succussion or violent 
 bumping, caused by sudden bursts of vapour, which endanger the safety of the retort. 
 
 With platinum stills the risk of fracture is avoided, and the distillation may be 
 conducted more rapidly, the brown acid (sp. gr. 1-72) being admitted at the top, 
 and the oil of vitriol (sp. gr. 1-84) drawn off by a platinum siphon from the bottom 
 of the still, which is protected from the open fire by an iron jacket. But since a 
 platinum still will cost 2000 or 3000, the interest upon its value increases the 
 cost of production of the acid. 
 
206 ACTION OF SULPHURIC ACID ON OKGANIC MATTEKS. 
 
 When the perfectly pure acid is required, it is actually distilled over so as to 
 leave the solid impurities (sulphate of lead, &c.,) behind in the retort. Some 
 fragments of rock crystal should be introduced into the retort to moderate the 
 bursts of vapour, and heat applied by a ring gas-burner with somewhat divergent 
 jets. 
 
 Divested of working details, this most important chemical manufacture 
 may be thus described : 
 
 A mixture of sulphurous acid, air. steam, and a little vapour of nitric 
 acid, is introduced into a leaden chamber containing a layer of water. The 
 nitric acid is reduced by the sulphurous acid to the state of nitric oxide 
 (N0 2 ), which takes up oxygen from the air (forming N0 4 ), and gives it to 
 the sulphurous acid, which it converts into sulphuric acid. This is ab- 
 sorbed by the water, forming diluted sulphuric acid, which is concentrated 
 by evaporation, first in leaden pans, and afterwards in glass retorts or 
 platinum stills. 
 
 Properties of oil of vitriol. The properties of concentrated sulphuric 
 acid are very characteristic. Its great weight (sp. gr. 1*842), freedom from 
 odour, and oily appearance, distinguish it from any other liquid commonly 
 met with, which is fortunate, because it is difficult to preserve a label upon 
 the bottles of this powerfully corrosive acid. Although, if absolutely pure, 
 it is perfectly colourless, the ordinary acid used in the laboratory has a 
 peculiar grey colour, due to traces of organic matter. Its high boiling- 
 point (640 F.) has been already noticed ; and although its. vapour is per- 
 fectly transparent in the vessel in which the acid is boiled, as soon as it 
 issues into the air it condenses into voluminous dense clouds of a most 
 irritating description. Even a drop of the acid evaporated in an open dish 
 will fill a large space with these clouds. Oil of vitriol solidifies when 
 cooled to about 30 F., but the acid once solidified requires a much 
 higher temperature to liquefy it again. Oil of vitriol rapidly corrodes the 
 skin and other organic textures upon which it falls, usually charring or 
 blackening them at the same time. Poured upon a piece of wood, the 
 latter speedily assumes a dark brown colour ; and if a few lumps of sugar 
 be dissolved in a very little water, and stirred with oil of vitriol, a violent 
 action takes place, and a semi-solid black mass is produced. This pro- 
 perty of sulphuric acid is turned to account in the manufacture of black- 
 ing, in which treacle and oil of vitriol are employed. These effects are to 
 be ascribed to the powerful attraction of oil of vitriol for water. Woody 
 fibre (C 12 H !0 JO ) (which composes the bulk of wood, paper, and linen), 
 and sugar (C 12 H n O H ), may be regarded, for the purpose of this explana- 
 tion, as composed of carbon associated with 10 and 11 equivalents of 
 water, and any cause tending to remove the water would tend to eliminate 
 the carbon. 
 
 The great attraction of this acid for water is shown by the high tempe- 
 rature (often exceeding the boiling point of water) produced on mixing 
 oil of vitriol with water, which renders it necessary to be careful in dilut- 
 ing the acid. 
 
 The water should be placed in a jug, and the oil of vitriol poured into it in a 
 thin stream, a glass rod being used to mix the acid with the water as it flows in. 
 Ordinary oil of vitriol becomes turbid when mixed with water, from the separa- 
 tion of sulphate of lead (formed from the evaporating pans), which is soluble in 
 the concentrated but not in the diluted acid, so that if the latter be allowed to 
 stand for a few hours, the sulphate of lead settles to the bottom, and the clear acid 
 may be poured off free from lead. Diluted sulphuric acid has a smaller bulk than 
 is occupied by the acid and water before mixing. 
 
ACTION OF SULPHURIC ACID ON METALS. 207 
 
 Even when largely diluted, sulphuric acid corrodes textile fabrics very 
 rapidly, and though the acid be too dilute to appear to injure them at 
 first, it will be found that the water evaporates by degrees, leaving the 
 acid in a more concentrated state, and the fibre is then perfectly rotten. 
 The same result ensues at once on the application of heat ; thus, if charac- 
 ters be written on paper with the diluted acid, they will remain invisible 
 until -the paper is held to the fire, when the acid will char the paper, and 
 the writing will appear intensely black. 
 
 " If oil of vitriol be left exposed to the air in an open vessel, it very soon 
 increases largely in bulk from the absorption of water, and a flat dish of 
 oil of vitriol under a glass shade (fig. 194) is frequently employed in the 
 laboratory for drying substances with- 
 out the assistance of heat. The drying- 
 is of course much accelerated by plac- 
 ing the dish on the plate of an air- 
 pump, and exhausting the air from 
 the shade, so as to effect the drying 
 in vacuo. It will be remembered 
 also that oil of vitriol is in constant 
 use for drying gases. 
 
 At a red heat, the vapour of oil 
 
 of vitriol is decomposed into water, Fig. 194. Drying over oil of vitriol, 
 sulphurous acid, and oxygen 
 
 HO . SO S = HO + S0 2 + . 
 
 This decomposition takes place most easily when the vapour is passed 
 through a strongly-heated tube of platinum, and it has been taken advan- 
 tage of for the preparation of oxygen, the sulphurous acid being absorbed 
 by passing the mixed gases through lime. ^Reflecting upon the manufac- 
 ture of oil of vitriol, it will be perceived that the oxygen thus obtained 
 was originally derived from the air. 
 
 "When sulphur is boiled with oil of vitriol, the latter gradually dissolves 
 the melted sulphur, converting it into sulphurous acid 
 
 S + 2(HO.SO S ) = 3S0 2 + 2HO . 
 
 All ordinary metals are acted upon by concentrated sulphuric acid when 
 heated, except gold and platinum (this last even does not quite escape 
 when long boiled with the acid), the metal being oxidised by one portion 
 of the acid, which is thus converted into sulphurous acid, the oxide com- 
 bining with another part of the sulphuric acid to form a sulphate. Thus, 
 when silver is boiled with strong sulphuric acid, it is converted into sul- 
 phate of silver, which is soluble in hot water 
 
 Ag + 2(HO.S0 3 ) = AgO.S0 3 + 2HO + S0 2 . 
 
 Should the silver contain any gold, it is left behind in the form of a dark 
 powder. Sulphuric acid is extensively employed for the separation or 
 parting of silver and gold. This acid is also employed for extracting gold 
 from copper ; and when sulphate of copper is manufactured by dissolving 
 that metal in sulphuric acid (see p. 196), large quantities of gold are 
 sometimes extracted from the accumulated residue left undissolved by the 
 acid. 
 
 If the sulphuric acid contains nitric acid, it dissolves a considerable 
 quantity of gold, which separates again in the form of a purple powder 
 when the acid is diluted with water. 
 
208 COMPOSITION OF OIL OF VITRIOL. 
 
 Some of the uses of sulphuric acid depend upon its specific action on 
 certain organic substances, the nature of which has not yet been clearly 
 explained. Of this kind is the conversion of paper into vegetable parch- 
 ment by immersion in a cool mixture of two measures of oil of vitriol and 
 one measure of water, and subsequent washing. The conversion is not 
 attended by any change in the weight of the paper. 
 
 Beside oil of vitriol, sulphuric acid forms other definite combinations 
 with water. By evaporating diluted sulphuric acid in vacuo at 212 F., 
 an acid is left which has the composition HO . S0 3 + 2HO (sp. gr. 1*63). 
 If this acid be evaporated in air at 400 F., as long as steam escapes, the 
 remaining acid has the composition HO. S0 3 + HO (sp. gr. 1-78). This 
 acid is called glacial sulphuric acid, because it solidifies to a mass of ice- 
 like crystals at 47 F. 
 
 Composition of oil of vitriol* It is found by experiment that in order 
 to neutralise 1 equivalent (47 parts by weight) of potash (KO) there 
 are required 49 parts by weight of oil of vitriol. If 49 parts of oil of 
 vitriol be heated with a weighed quantity of pure oxide of lead, more 
 than sufficient to combine with the acid, 9 parts of water are expelled, 
 and the weight of the oxide of lead is increased by 40. One equivalent 
 (49 parts by weight) of oil of vitriol, therefore, contains 40 parts (1 
 equivalent =16 sulphur + 24 oxygen) of anhydrous sulphuric acid, and 
 9 parts (1 equivalent) of water. The specific gravity (or weight of 1 
 volume) of vapour of oil of vitriol (at 880) is stated to be .1 '6 9 2, so that 
 1 equivalent (49 parts) would occupy 4 volumes (8 parts = 1 volume) 
 
 Weight of 4 volumes HO. S0 3 (1'692 x 4) = 6-768 
 Weight of 2 volumes HO ( -622 x 2) = 1-244 
 
 5-524 
 
 The difference (5-524) represents the weight of the vapour of anhydrous 
 sulphuric acid contained in 4 volumes of vapour of oil of vitriol. 
 
 Experiment has proved that when the vapour of anhydrous sulphuric 
 acid is passed through red-hot porcelain tubes, it yields a mixture of 2 
 volumes of sulphurous acid and 1 volume of oxygen, showing it to con- 
 tain 1 equivalent of S0 2 ( = 1 equivalent or 1 volume of sulphur and 
 2 equivalents or 2 volumes of oxygen) and 1 equivalent of oxygen; 
 hence the anhydrous sulphuric acid contains 
 
 1 volume sulphur vapour, weighing 2-2300 
 3 volumes oxygen 3-3168 
 
 5-5468 
 
 Now the weight of 1 volume (sp. gr.) of vapour of anhydrous sulphuric 
 acid has been found by experiment to be 3'01, so that it would appear 
 that the above number (5 -5 4) really represents 2 volumes of the vapour, 
 though the difference is somewhat greater than usual, between the results 
 of experiment and calculation. 
 
 The number 5 -546, however, closely approximates to that above given 
 (5-524), as representing the weight of the vapour of the anhydrous acid 
 contained in 4 volumes of vapour of oil of vitriol. 
 
 * Pure oil of vitriol (HO . S0 3 ) can only be obtained by crystallisation, for when concen- 
 trated by boiling, a portion of the hydrate is decomposed, anhydrous sulphuric acid passing 
 off, until the residual acid in the retort contains 98*7 per cent, of HO. S0 3 . 
 
SULPHURIC ANHYDRIDE SULPHATES. 209 
 
 It would appear, therefore, that 4 volumes (1 equivalent) of vapour 
 of oil of vitriol contain 2 volumes (1 equivalent) of vapour of water, 
 and 2 volumes (1 equivalent) of vapour of anhydrous sulphuric acid, or 
 2 volumes of hydrogen (contained in 2 volumes HO), 1 volume of sulphur, 
 and 4 volumes of oxygen (3 volumes belonging to the S0 3 , and 1 volume 
 to the HO). 
 
 The molecular formula of oil of vitriol would therefore be written 
 H 2 O. SO 3 or H 2 SO 4 (S = 32, O = 16). This formula would represent 
 a'molecule of the acid to occupy 4 volumes (H = 1 volume) instead of 
 2, the ordinary molecular volume of compound vapours. Some chemists 
 explain this by assuming that the oil of vitriol vapour is decomposed into 
 water and anhydrous sulphuric acid at the temperature (880 F.) at which 
 its specific gravity is determined. 
 
 147. Anhydrous sulphuric acid or sulphuric anhydride. The mode of 
 preparing this substance from the fuming sulphuric acid has already been 
 noticed. It is more commonly obtained by expelling the water from bi- 
 sulphate of soda (NaO . HO . 2S0 3 ) by fusing it at a dull red heat, and 
 afterwards distilling the anhydrous bisulphate (NaO . 2S0 3 ) in an earthen 
 retort, when neutral sulphate of soda (NaO . S0 3 ) is left, and the anhydrous 
 sulphuric acid passing off as vapour may be condensed in a receiver cooled 
 by ice. 
 
 Anhydrous sulphuric acid forms a white mass of crystals resembling 
 asbestos ; it fumes when exposed to air, since it emits vapour which con- 
 denses the moisture of the air, and it soon deliquesces from absorption of 
 water, becoming hydrated sulphuric acid. When thrown into water it 
 hisses like red-hot iron from the sudden formation of steam. It fuses at 
 65 F., and boils at 110 F. The vapour is decomposed, as mentioned 
 above, into sulphurous acid and oxygen when passed through a red-hot 
 tube. Phosphorus burns in its vapour, combining with the oxygen arid 
 liberating sulphur. Baryta glows when heated in the vapour of anhydrous 
 sulphuric acid, and combines with it to form sulphate of baryta. 
 
 Anhydrous sulphuric acid is capable of combining with olefiant gas 
 (C 4 H 4 ) and oil-gas (C 8 H 8 ), and absorbs these from mixtures of gases. 
 In the analysis of coal-gas, a fragment of coke wetted with Nordhausen 
 sulphuric acid is passed up into a measured volume of the gas standing 
 over mercury, to absorb these illuminating hydrocarbons. 
 
 An interesting method of obtaining the anhydrous sulphuric acid con- 
 sists in pouring 2 parts by weight of oil of vitriol over 3 parts of anhydrous 
 phosphoric acid, contained in a retort cooled in ice and salt, and after- 
 wards distilling at a gentle heat, when the phosphoric acid retains the 
 water, and the anhydrous sulphuric acid may be condensed in a cooled 
 receiver. 
 
 148. Sulphates. Action, of sulphuric acid upon metallic oxides. At 
 common temperatures sulphuric acid has a more powerful attraction for 
 bases than any other acid, and is therefore capable of displacing all other 
 acids from their salts ; many cases will be remembered in which this power 
 of sulphuric acid is turned to account. . 
 
 So great is the acid energy of sulphuric acid, that when it is allowed 
 to act upon an indifferent or acid metallic oxide, it causes the separation 
 of a part of the oxygen, and combines with the basic oxide so produced. 
 Advantage is sometimes taken of this circumstance for the preparation of 
 
 o 
 
210 ACID AND DOUBLE SULPHATES. 
 
 oxygen ; for instance, when binoxide of manganese is heated with sul- 
 phuric acid, sulphate of manganese is produced, and oxygen disengaged 
 
 Mn0 2 + HO . S0 3 = MnO . S0 3 + + HO . 
 
 Again, if chromic acid be treated in the same way, sulphate of sesquioxide 
 of chromium will be produced, with liberation of oxygen 
 
 2Cr0 3 + 3(HO.S0 3 ) = Cr 2 3 .3S0 3 + 3 + 3HO . 
 
 A mixture of bichromate of potash (KO . 2Cr0 3 ) and sulphuric acid is 
 sometimes used as a source of oxygen. 
 
 Many bases are capable of forming two salts with sulphuric acid, a 
 neutral sulphate and an acid sulphate. The acid sulphates may be repre- 
 sented as compounds of the neutral sulphates with hydrated sulphuric 
 acid ; thus, the neutral sulphate of potash is KO . S0 3 , and the bisulphate 
 is KO . S0 3 , HO . S0 3 . The latter, being a solid salt which possesses, at 
 high temperatures, almost all the acid energy of sulphuric acid, is most 
 useful in blowpipe and metallurgic experiments. When strongly heated, 
 this salt parts with hydrated sulphuric acid, and neutral sulphate of pot- 
 ash is left. It has been seen that bisulphate of soda (Na.0 . S0 3 , HO . S0 3 ) 
 parts with its water when heated, and becomes NaO . 2S0 3 . Crystals 
 of anhydrous bisulphate of potash KO . 2S0 3 have also been obtained. 
 
 Sulphuric acid forms a large number of double salts in which two sul- 
 phates are combined together. The large class of alums yields examples 
 of these, in which one of the sulphates contains an alkaline base, and the 
 other a basic sesquioxide. Potash-alum, for example, is represented by 
 the formula KO . S0 3 , A1 2 3 . 3S0 3 + 24Aq, being a double sulphate 
 of alumina and potash. 
 
 In consequence of the tendency of sulphuric acid to break up into sul- 
 phurous acid and oxygen at a high temperature, most of the sulphates are 
 decomposed by heat ; sulphate of copper, for example, when very strongly 
 heated, leaves oxide of copper, whilst sulphurous acid and oxygen escape ; 
 CuO . S0 3 = CuO + S0 2 + . Sulphate of iron is more easily 
 decomposed, because of the attraction of the protoxide of iron for the 
 oxygen, with which it combines to form sesquioxide 
 
 2(FeO.S0 3 ) = Fe 2 3 + S0 2 + SO 
 
 part of the acid escaping in the anhydrous state. 
 
 Sulphate of zinc (ZnO . S0 3 ) has been proposed as a source of oxygen 
 upon the large scale, since it is a very cheap salt, and when strongly 
 heated, yields a residue of oxide of zinc which is useful as a white paint, 
 whilst sulphurous acid and oxygen gases escape, the former of which may 
 be absorbed by lime or soda, yielding sulphites which are useful in the 
 arts. 
 
 The neutral sulphates of potash, soda, baryta, strontia, lime, and oxide 
 of lead are not decomposed by heat, and sulphate of magnesia is only 
 partly decomposed at a very high temperature. 
 
 When a sulphate is heated with charcoal, the carbon removes the whole 
 of the oxygen, and a sulphide of the metal remains, thus 
 
 KO . S0 3 + C 4 = KS + 4CO . 
 
 Sulphate of Sulphide of 
 
 potash. potassium. 
 
 Hydrogen, at a high temperature, effects a similar decomposition. 
 
TABLE OF THE P1UNCIPAL SULPHATES. 
 
 211 
 
 Even at the ordinary temperature, sulphate of lime in solution is some- 
 times deoxidised by organic matter ; this may occasionally be noticed in 
 well and river waters when kept in closed vessels; they acquire a strong 
 smell of hydrosulphuric acid, in consequence of the conversion of a part 
 of the sulphate of lime into sulphide of calcium by the organic constitu- 
 ents of the water, and the subsequent decomposition of the sulphide of 
 calcium by the carbonic acid present in the water. 
 
 The following table exhibits the composition of the sulphates most 
 frequently met with : 
 
 Chemical Name. 
 
 Common Name. 
 
 Equivalent Formula. 
 
 Atomic 
 Unitary Formula. 
 
 Sulphate of potash 
 Sulphate of soda 
 Bisulphate of potash 
 
 Sal polychrest 
 Glauber's salt 
 
 KO . S0 3 
 NaO . S0 3 + 10HO 
 KO . S0 3 , HO . S0 3 
 
 K 2 SO 
 Na 2 S0 4 . 10H 2 
 KHSO* 
 
 Sulphate of am- \ 
 monia j 
 
 
 NH 3 . HO . S0 3 
 
 (NH 4 ) 2 S0 4 
 
 Sulphate of baryta 
 
 Heavy spar 
 
 BaO . S0 3 
 
 fiaSO 4 
 
 Sulphate of lime 
 
 Gypsum 
 
 CaO . S0 3 + 2HO 
 
 OaSO 4 . 2H 2 O 
 
 Sulphate of mag- 1 
 nesia J 
 
 Epsom salts 
 
 MgO . S0 3 + 7HO 
 
 Mg . S0 4 . 7H 2 
 
 Double sulphate \ 
 of alumina and I 
 potash J 
 
 Potash-alum j 
 
 KO . S0 3 , 1 
 A1 2 3 . 3S0 3 + 24HO J 
 
 KA-1 2S0 4 . 12H 2 
 
 Double sulphate \ 
 of alumina and V 
 
 Ammonia- 1 
 alum l 
 
 NH 3 . HO . S0 3 , \ 
 AL0 3 . 3S0 3 + 24HO J 
 
 NH 4 A-12SO 4 .12H 2 O 
 
 ammonia J 
 
 
 Z 3 o J 
 
 
 Double sulphate \ 
 of chromium I 
 and potash J 
 
 Chrome- f 
 alum \ 
 
 KO . S0 3 , 1 
 Cr 2 3 . 3S0 3 + 24HO j 
 
 KOr 2S0 4 . 12H 2 
 
 Sulphate of iron j 
 
 Green vitriol "> 
 Copperas J 
 
 FeO . S0 3 + 7HO 
 
 FeS0 4 . 7H 2 
 
 Sulphate of man- j 
 ganese j 
 
 
 MnO . S0 3 + 5HO 
 
 MnSO 4 . 5H 2 O 
 
 Sulphate of zinc 
 
 White vitriol 
 
 ZnO . S0 3 + 7HO 
 
 ZnSO 4 . 7H 2 
 
 Sulphate of lead 
 
 
 PbO . S0 3 
 
 PbS0 4 
 
 Sulphate of copper j 
 
 Blue vitriol 1 
 Blue stone J 
 
 CuO . S0 3 + 5HO 
 
 OuS0 4 . 5H 2 
 
 The disposition of sulphuric acid to form acid salts and double salts, 
 into the composition of which the acid enters as 2S0 3 or 4S0 3 , has 
 induced some chemists to regard the true formula of this acid as 
 H 2 2 .S 2 6 or H 2 S 2 8 (or, if S = 32 and 6 = 16, as H 2 SO 4 ), which 
 would require two equivalents of potash to form a neutral salt, making 
 sulphuric acid a bibasic acid. 
 
 149. Hyposulpliurous acid* This acid has not been obtained either 
 in the anhydrous state or in combination with water, but as many salts 
 are known which contain, in addition to a metallic oxide, sulphur and 
 oxygen in the proportions expressed by the formula S 2 2 , many chemists 
 assume the existence of hyposulphurous acid, having that composition, 
 in such salts, which are therefore called hyposulphites. 
 
 The hyposulphite of soda is by far the most important of these salts, 
 being very largely employed in photography, and as a substitute for 
 
 * TTTO, under, containing less oxygen than sulphurous acid. 
 
 O 2 
 
212 HYPOSULPHITE OF SODA. 
 
 sulphite of soda as an anticlilore. The simplest method of preparing 
 it consists in digesting powdered roll sulphur with solution of sul- 
 phite of soda (NaO . S0 2 ), when the latter dissolves an equivalent of 
 sulphur and becomes hyposulphite of soda (NaO . S 2 2 ), which crystallises 
 from the solution, when sufficiently evaporated, in fine prismatic crystals, 
 having the formula NaO . S 2 2 + 5 HO. 
 
 On a large scale, the hyposulphite of soda is more economically prepared 
 from the hyposulphite of lime obtained by exposing the refuse (tank-waste 
 or soda-waste) of the alkali-works to the air for some days. This refuse 
 contains a large proportion of sulphide of calcium, which becomes con- 
 verted into hyposulphite of lime by oxidation 
 
 2CaS + 4 = CaO . S 2 2 + CaO . 
 
 The hyposulphite of lime is dissolved out by water, and the solution 
 mixed with carbonate of soda, when carbonate of lime is precipitated, 
 and hyposulphite of soda remains in solution 
 
 CaO . S 2 2 + NaO . C0 2 = CaO . C0 2 + ]*TaO . S 2 2 . 
 
 The most remarkable and useful property of the hyposulphite of soda is 
 that of dissolving the chloride and iodide of silver, which are insoluble in 
 water and most other liquids. 
 
 On mixing a solution of nitrate of silver with one of chloride of sodium, a white 
 precipitate of chloride of silver is obtained, the separation of which is much promoted 
 by stirring the liquid ; AgO . N0 5 + NaCl = AgCl + NaO . N0 5 . The precipitate 
 may be allowed to settle and washed twice or thrice by decantation. One portion of 
 the chloride of silver is transferred to another glass, mixed with water, and solution 
 of hyposulphite of soda added by degrees. The chloride of silver is very easily 
 dissolved, yielding an intensely sweet solution, which contains the hyposulphite of 
 silver, produced by double decomposition between the chloride of silver and hypo- 
 sulphite of soda 
 
 AgCl + NaO.S 2 2 = NaCl + AgO.S 2 2 . 
 Chloride of Hyposulphite of Chloride of Hyposulphite of 
 
 silver. soda. sodium. silver. 
 
 The hyposulphite of silver combines with the excess of hyposulphite of soda to 
 form the double salt AgO . S 2 2 . 2(NaO . S 2 2 ), which may be obtained in extremely 
 sweet crystals from the solution. 
 
 If the other portion of the chloride of silver be exposed to the action of light, and 
 especially of direct sunlight, it assumes by degrees a dark slate colour, from the for- 
 mation of subchloride of silver, chlorine being set free ; 2AgCl = Ag 2 Cl + 01. 
 By treating this darkened chloride of silver with hyposulphite of soda, as before, the un- 
 altered chloride of silver will be entirely dissolved, but the subchloride will be decom- 
 posed into chloride of silver, which dissolves in the hyposulphite, and metallic silver, 
 which is left in a very finely divided state as a black powder; Ag 2 Cl = AgCl + Ag. 
 The application of these facts in photography is well illustrated by the following 
 experiments. A sheet of paper is soaked for a minute or two in a solution of 10 
 grains of common salt in an ounce of water contained in a flat dish. It is then 
 dried, and soaked for three minutes in a solution of 50 grains of nitrate of silver in 
 an ounce of water. The paper thus becomes impregnated with chloride of silver 
 formed by the decomposition between the chloride of sodium and the nitrate of 
 silver. It is now hung up in a dark place to dry. If a piece of lace, or a fern leaf, 
 or an engraving on thin paper, with well-marked contrast of light and shade, be 
 laid upon a sheet of the prepared paper, pressed down upon it by a plate of glass, 
 and exposed for a short time to sunlight, a perfect representation of the object will 
 be obtained, those parts of the sensitive paper to which the light had access having 
 been darkened by the formation of subchloride of silver, whilst those parts which 
 were protected from the light remain unchanged. 
 
 But if this photographic print were again exposed to the action of light, it would 
 soon be obliterated, the unaltered chloride of silver in the white parts being acted 
 on by light in its turn. The print is therefore fixed by soaking it for a short time 
 
HYPOSULPHITE OF SODA. 213 
 
 in a saturated solution of hyposulphite of soda, which dissolves the white unaltered 
 chloride of silver entirely, and decomposes the subchloride formed by the action of 
 light, leaving the black finely-divided metallic silver in the paper. The print 
 should now be washed for two or three hours in a gentle stream of water, to remove 
 all the hyposulphite of silver, when it will be quite permanent. 
 
 The power of hyposulphite of soda to dissolve chloride of silver has 
 also been turned to account for extracting that metal from its ores, in 
 which it is occasionally present in the form of chloride. 
 
 x The behaviour of solution of hyposulphite of soda with powerful acids 
 explains the circumstance that the hyposulphurous acid has not been 
 isolated, for if the solution be mixed with a little diluted sulphuric or 
 hydrochloric acid, it remains clear for a few seconds, and then becomes 
 suddenly turbid from the separation of sulphur, at the same time evolving 
 a powerful odour of sulphurous acid ; S 2 2 = S + S0 9 . This disposi- 
 tion of the hyposulphurous acid to break up into sulphurous acid and 
 sulphur also explains the precipitation of metallic sulphides, which often 
 takes place when hyposulphite of soda is added to the acid solutions of 
 the metals. Thus if an acid solution of chloride of antimony (obtained 
 by boiling crude antimony ore (SbS 3 ) with hydrochloric acid) be added to 
 a boiling solution of hyposulphite of soda, the sulphur separated from the 
 hyposulphurous acid combines with the antimony to form a fine orange- 
 red precipitate of sulphide of antimony (SbS 3 ), which is used in painting 
 under the name of antimony vermilion. On the large scale the solution 
 of hyposulphite of lime obtained from the alkali waste is employed in the 
 preparation of antimony vermilion, as being less expensive than the soda-salt. 
 
 Instead of adding sulphur to sulphurous acid, hyposulphurous acid in 
 combination may be obtained by removing oxygen from the former acid. 
 Thus if an aqueous solution of sulphurous acid be acted on by zinc, one 
 portion of the acid is deoxidised and converted into hyposulphurous acid, 
 which combines with the oxide of zinc 
 
 3S0 2 + Zn 2 = ZnO.S0 2 + ZnO . S 2 2 . 
 
 The presence of hyposulphite in the solution may be proved by adding 
 hydrochloric acid. 
 
 When crystals of hyposulphite of soda are heated in the air, they first 
 fuse in their water of crystallisation, then dry up to a white mass, which 
 burns with a blue flame, leaving a residue of sulphate of soda. If heated 
 out of contact with air, pentasulphide of sodium will be left with the sul- 
 phate of soda 
 
 4(NaO.S 2 2 + 5HO) = 20HO + 3(NaO . S0 3 ) + NaS 5 . 
 
 None of the hyposulphites appear as yet to have been obtained in the 
 perfectly anhydrous state, all of them retaining 1 eq. of water of constitu- 
 tion, which cannot be expelled without decomposition of the salt. Hence 
 there -is reason for believing that the elements of the water are really con- 
 stituents of the hyposulphurous acid itself, and that instead of being 
 expressed by the formula S 2 2 , it should be written HS 2 O 3 ( = S 2 . HO), 
 the hyposulphite of soda being NaO . HS 2 3 + 4HO, or NaHS 2 0~ + 4HO, 
 instead of ISTaO . S 2 2 + 5HO. 
 
 The atomic formula of the hyposulphite of soda would then be 
 Na 2 H 2 S 2 e 4 + 4H 2 (9 == 32, O = 16). 
 
 150. Hyposulphuric acid or dithionic acid has not at present acquired any practical 
 importance, and has not been obtained in the anhydrous state. To prepare a solu- 
 tion of the acid, binoxide of manganese in a state of fine division is suspended in 
 
214 THIONIC ACIDS. 
 
 water and exposed to a current of sulphurous acid gas, the water being kept very 
 cold whilst the gas is passing. A solution of hyposulphate of manganese is thus 
 obtained ; 2S0 2 + Mn0 2 MnO . S 2 5 . Some sulphate of manganese is always 
 formed at the same time ; S0 2 + Mn0 2 = MnO . S0 3 , and if the temperature be 
 allowed to rise, this will be produced in large quantity. 
 
 The solution containing sulphate and hyposulphate of manganese is decomposed 
 by solution of baryta (baryta- water), when the oxide of manganese is precipitated, 
 together with sulphate of baryta, and hyposulphate of baryta is left in solution. To 
 the filtered solution diluted sulphuric acid is carefully added until all the baryta is 
 precipitated as sulphate of baryta, when the solution of hyposulphuric acid is filtered 
 off and evaporated in vacuo over oil of vitriol. It forms a colourless inodorous 
 liquid, which is decomposed when heated into hydrated sulphuric and sulphurous 
 acids ; HO . S 2 5 = HO . S0 3 + S0 2 . Oxidising agents (nitric acid, chlorine, &c.) 
 convert it into sulphuric acid. 
 
 The hyposulphates are not of any practical importance ; they are all soluble, and 
 are decomposed by heat, leaving sulphates, and evolving sulphurous acid. 
 
 151. Trithionic acid, or sulphuretted hyposulphuric acid, is also a practically unim- 
 portant acid, not known in the anhydrous state. Its hydrate is prepared from the 
 trithionate of potash, which is formed by boiling a strong solution of bisulphite of 
 potash with sulphur until the solution becomes colourless, and filtering the hot 
 solution from any undissolved sulphur 
 
 3(KO.H0.2S0 2 ) + S = 2(KO.S 3 5 ) + KO.S0 2 + 3HO . 
 
 Bisulphite of potash. Trithionate of potash. 
 
 The solution deposits trithionate of potash in prismatic crystals. By dissolving 
 these in water, and decomposing the solution with perchloric acid, the potash is 
 precipitated as perchlorate, and a solution of trithionic acid is produced, from which 
 the hydrated acid has been obtained in crystals. It is, however, very unstable, 
 being easily resolved into sulphurous acid, sulphuric acid, and free sulphur 
 
 HO.S 3 5 = HO.S0 3 + S0 2 + S. 
 
 152. Tetrathionic acid, or bisulphuretted hyposulphuric acid, is rather more stable 
 than the preceding acid, though equally devoid of practical importance. It is formed 
 when hyposulphite of baryta, suspended in a little water, is treated with iodine, 
 when tetrathionate of baryta is obtained in crystals 
 
 2(BaO.S 2 2 ) + I = Bal + 
 
 Hyposulphite of** 
 
 By exactly precipitating the baryta from a solution of the tetrathionato by addi- 
 tion of diluted sulphuric acid, the solution of tetrathionic acid may be obtained. 
 When the solution is boiled, it is decomposed into sulphuric and sulphurous acids 
 and free sulphur ; HO . S 4 5 = HO . S0 3 + S0 2 + S 2 . 
 
 When solution of perchloride of iron is added to hyposulphite of soda, a fine 
 purple colour is at first produced, which speedily vanishes, leaving a colourless solu- 
 tion. The purple colour appears to be due to the formation of the hyposulphite of 
 sesquioxide of iron, which speedily decomposes, the ultimate result being expressed 
 by the equation 
 
 Fe 2 Cl 3 + 2(NaO . S 2 2 ) = . NaO . S 4 5 + 2FeCl + NaCl . 
 Perchloride of Hyposulphite of Tetrathionate of Chloride of Chloride of 
 
 iron. soda. soda. iron. sodium. 
 
 153. Pentathionic acid possesses some interest as resulting from the action of sul- 
 phuretted hydrogen upon sulphurous acid, when much sulphur is deposited, and 
 pentathionic acid remains in solution / 
 
 5HS + 5S0 2 = HO.S 5 5 + 4HO + S fi . 
 
 Hydrated pentathionic 
 
 To obtain a concentrated solution of the acid, sulphuretted hydrogen and sul- 
 phurous acid are passed alternately through the same portion of water until a largo 
 deposition of sulphur has taken place. This is allowed some hours to settle ; the 
 clear liquid poured off and the solution concentrated by evaporation, first over a 
 water-bath, and, finally, in vacuo, over oil of vitriol, for a concentrated solution of 
 pentathionic acid is decomposed by heat into sulphuric and sulphurous acids, with 
 separation of sulphur ; HO . S S 5 = HO . S0 3 + S0 2 + S 3 . 
 
PREPARATION OF BISULPHIDE OF CARBON. 
 
 215 
 
 BISULPHIDE OF CARBON. 
 
 154. This very important compound (also called bisulplmret of carbon) 
 is found in small quantity among the products of destructive distillation 
 of coal, and is very largely manufactured for use as a solvent for sulphur, 
 phosphorous, caoutchouc, fatty matters, &c. It is one of the few com- 
 pounds of carbon which can be obtained by the direct union of their 
 elements, and is prepared by passing vapour of sulphur over charcoal 
 heated to redness. 
 
 In small quantity bisulphide of carbon is easily prepared in a tube of German 
 glass (combustion-tube) about two feet long and half-an-inch in diameter (fig. 195). 
 This tube is closed at one end, and a few fragments of sulphur dropped into it, so 
 as to occupy two or three inches. The rest of the tube is filled up with small frag- 
 
 Fig. 195. 
 
 inents of recently calcined wood charcoal. The tube is placed in a combustion- 
 furnace, and its open end connected by a perforated cork with a glass tube, which 
 dips just below the surface of water contained in a bottle placed in a vessel of very 
 cold water. That part of the tube which contains the charcoal is first surrounded 
 with red-hot charcoal, and when it is heated to redness, a little red-hot charcoal is 
 placed near the end containing.the sulphur (hitherto protected by a sheet-iron screen), 
 so that the vapour of sulphur may be slowly passed over the red-hot charcoal. The 
 bisulphide of carbon being insoluble in water, and much heavier (sp. gr. T27), is 
 deposited beneath the water in the receiver. To purify the bisulphide of carbon 
 from the water and the excess of sulphur which is deposited with it, the water is 
 carefully drawn off with a small syphon, the bisulphide of carbon transferred to a 
 flask, and a few fragments of chloride of calcium dropped into it to absorb the water. 
 A bent tube connected with a Liebig's con- 
 denser, or with a worm, is attached to the 
 flask (fig. 196) by a perforated cork, and the 
 flask is gently heated in a water bath, when 
 the bisulphide of carbon is distilled over as a 
 perfectly colourless liquid. The inflammability 
 of the bisulphide of carbon renders great care 
 necessary. 
 
 On a large scale, a fire-clay retort is filled 
 with fragments of charcoal and heated to 
 redness, pieces of sulphur being occa- 
 sionally dropped in through an earthen- 
 ware tube passing to the bottom of the 
 retort. When very large quantities are 
 made, coke is employed, and the vapour 
 of sulphur is obtained from iron pyrites. 
 The bisulphide of carbon is possessed of some very remarkable properties : 
 it is a very brilliant liquid, the light passing through which is partly de- 
 composed into its component coloured rays before it reaches the eye. 
 These properties are dependent upon its high refractive and dispersive 
 
 Fig. 196. 
 
216 PROPERTIES OF BISULPHIDE OF CARBON. 
 
 powers, which, are turned to great advantage in optical experiments, espe- 
 cially in spectrum analysis, where the rays emanating from a coloured 
 flame are analysed by passing them through a prismatic bottle filled with 
 bisulphide of carbon. It is also highly diathermanous, that is, it allows 
 rays of heat to pass through it with comparatively little loss, so that if it 
 be rendered opaque to light by dissolving iodine in it, the rays of light 
 emanating from a luminous object may be arrested, whilst the calorific 
 rays are allowed to pass. It has never been frozen, and is therefore 
 employed in thermometers for measuring very low temperatures. Bisul- 
 phide of carbon is a very volatile liquid, readily assuming the form of 
 vapour at the ordinary temperature, and boiling at 118'5 F. Its vapour, 
 when diluted with air, has a very disgusting and exaggerated odour of 
 sulphuretted hydrogen, but the smell at the mouth of the bottle is ethereal 
 and not unpleasant. 
 
 The rapid evaporation of bisulphide of carbon is, of course, productive of great 
 cold. If a few drops be placed in a watch-glass and blown upon, they soon pass off 
 in vapour, and the temperature of the glass is so reduced that the moisture of the 
 breath condenses upon it in hoar-frost, which melts when the glass is placed in the 
 palm of the hand. If a glass plate be covered with water, a watch-glass containing 
 bisulphide of carbon placed on it, and evaporation promoted by blowing through a 
 tube, the watch-glass will be frozen on to the plate, so that the latter may be lifted 
 up by it. 
 
 The bisulphide of carbon is exceedingly inflammable ; it takes fire at a 
 temperature far below that required to inflame ordinary combustible 
 bodies, and burns with a bright blue flame, producing carbonic and sul- 
 phurous acids (CS 2 + 6 = C0 2 + 2S0 2 ), and having a great tendency to 
 deposit sulphur unless the supply of air is very good. 
 
 If a little bisulphide of carbon be dropped into a small beaker, it may be inflamed 
 by holding in its vapour a test-tube containing oil heated to about 300 F., which 
 will be found incapable of firing gunpowder or of inflaming any ordinary com- 
 bustible substance. An iron rod heated below redness will be found quite incap- 
 able of firing the explosive mixture of hydrogen or coal-gas with oxygen (fig. 197), 
 
 but if the cylinder be placed upon a glass 
 plate, on which is laid a piece of paper soaked 
 in bisulphide of carbon, and allowed to stand 
 for a few moments, it will be found that the 
 same rod will afterwards inflame the mixture, 
 even although a little cooler than before. If 
 a little bisulphide of carbon be dropped into a 
 strong cylinder of oxygen, a mixture will be 
 formed which explodes with great noise on the 
 approach of a flame. 
 
 Since vapour of bisulphide of carbon is liable 
 to be present in coal-gas, its great inflamma- 
 bility has/been cited to account for explosions 
 
 Fig. 197. produced/ by sparks from workmen's tools 
 
 against the pavement, which would be incap- 
 able of inflaming pure coal-gas. 
 
 The abundance of sulphur separated in the flame of bisulphide of carbon enables 
 it to burn iron by converting it into sulphide. If some bisulphide of carbon be 
 boiled in a test-tube provided with a piece of glass tube from which the vapour may 
 be burnt, and a piece of thin iron wire be held in the flame (fig. 198), it will burn 
 with vivid scintillation, the fusible sulphide of iron dropping off. 
 
 The vapour of bisulphide of carbon acts very injuriously if breathed for 
 any length of time, producing symptoms somewhat resembling those 
 caused by sulphuretted hydrogen. Its poisonous properties have been 
 turned to account for killing insects in grain without injuring it. 
 
BISULPHIDE OF CARBON IN COAL-GAS. 
 
 217 
 
 The chief applications of bisulphide of carbon depend upon its power of 
 dissolving the oils and fats. After as much oil as possible has been ex- 
 tracted from seeds and fruits by pressure, 
 a fresh quantity is obtained by treating the 
 pressed cake with bisulphide of carbon, 
 which is afterwards recovered by distilla- 
 tion from the oil. In Algiers bisulphide 
 of carbon is employed for extracting the 
 essential oils in which reside the perfumes 
 of roses, jasmine, lavender, &c. 
 
 Bisulphide of carbon has often been 
 made a starting point in the attempts to 
 produce organic compounds by synthesis. 
 It may be employed in the formation of 
 the hydrocarbons which are usually derived 
 from organic sources, for if it be mixed 
 with sulphuretted hydrogen (by passing 
 that gas through a bottle containing bi- 
 sulphide of carbon gently warmed), and 
 passed over copper-turnings heated to red- 
 ness in a porcelain tube, olefiant gas will be produced 
 
 Fig. 198. 
 
 4CS 2 
 
 4HS 
 
 Cu 12 = 12CuS 
 
 C 4 H 4 . 
 
 The action of bisulphide of carbon upon ammonia is practically im- 
 portant for the easy production of sulpliocyanide of ammonium, which is 
 formed when the bisulphide of carbon is dissolved in alcohol, and acted on 
 by ammonia with the aid of heat 
 
 2CS 2 + 
 
 Bisulphide of carbon. 
 
 - 2HS 
 
 Sulphocyanide of ammonium. 
 
 Bisulphide of carbon is the sulphur-acid corresponding to carbonic acid, 
 and is often called sulphocarbonic acid; it combines with some of the 
 sulphur-bases to form sulphocarbonates, which correspond to the carbonates, 
 containing sulphur in place of oxygen. Thus, when a solution of sulphide 
 of potassium in alcohol is mixed with bisulphide of carbon, the sulpho- 
 carbonate of (sulphide of) potassium is deposited in orange-yellow crys- 
 tals. Even the hydrogen compound corresponding in composition to the 
 unknown hydrate of carbonic acid may be obtained as a yellow oily liquid 
 by decomposing sulphocarbonate of potassium with hydrochloric acid 
 
 KS.CS 2 + HC1 = 
 
 Sulphocarbonate 
 of potassium. 
 
 HS.CS 2 ' 
 
 Hydrosulphocafbonic 
 acid. 
 
 KC1. 
 
 As would be expected, the sulphocarbonates, when boiled with water, 
 exchange their sulphur for oxygen, becoming carbonates 
 
 KS.CS 2 + 3HO - KO.C0 2 + 3HS . 
 
 The bisulphide of carbon vapour in coal-gas is one of the most injuri- 
 ous of the impurities, and one of the most difficult to remove with economy. 
 It is especially injurious, because when burning in the presence of aque- 
 ous vapour, a part of its sulphur is converted into sulphuric acid, the cor- 
 rosive effects of which are so damaging. Several processes have been 
 devised for its removal. The gas has been washed with the ammoniacal 
 liquor (containing hydrosulphate of ammonia) which absorbs the bisul- 
 
218 CHLORIDES OF SULPHUR. 
 
 phide. Steam, at a high temperature, has been employed to convert it 
 into hydrosulphuric and carbonic acids, which are both easily removed 
 from the gas ; CS 2 -f 2HO = C0 2 + 2HS. Lime at a red heat decom- 
 poses it in a similar way ; CS 2 + 3CaO = CaO . C0 2 + 2CaS. Oxide of 
 lead dissolved in caustic soda has been used to convert it into sulphide of 
 lead; CS 2 + 2PbO + NaO - 2PbS + I^aO. C0 2 . Its removal as sul- 
 phocarbonate by an alcoholic solution of potash or soda has also been 
 proposed. At present, however, it retains its character as one of the most 
 troublesome impurities with which the gas manufacturer has to deal. 
 
 Composition of bisulphide of carbon. Analysis proves that 6 parts by 
 weight (1 eq.) of carbon are combined with 32 parts (2 eqs.) of sulphur 
 in the bisulphide, and since 1 equivalent of sulphide of potassium (55 parts) 
 is combined with 38 parts of bisulphide in the sulphocarbonate, the formula 
 CS 2 is taken to represent 1 equivalent of the bisulphide of carbon. The 
 specific gravity, or weight of 1 volume of bisulphide of carbon vapour, is 
 2 '6447. Supposing, then, 1 equivalent (8 parts) of oxygen to occupy 1 
 volume, 1 equivalent (38 parts) of bisulphide would occupy 2 volumes 
 
 Specific gravity. 
 
 2 volumes of CS 2 vapour weigh (2 '6447 x 2) 5 '2894 
 
 2 volumes (2 equivalents) of sulphur vapour (2'23 x 2) 4*4600 
 
 8294 
 
 The difference represents the weight of imaginary carbon vapour con- 
 tained in 2 volumes of vapour of bisulphide of carbon ; this weight of 
 imaginary carbon vapour was assumed, on the grounds set forth at p. 81, 
 to occupy 2 volumes. 
 
 Hence, 1 equivalent, or 2 volumes of bisulphide of carbon vapour, con- 
 tains 1 equivalent or 2 volumes of imaginary carbon vapour, combined 
 with 2 equivalents or 2 volumes of sulphur vapour, its composition by 
 volume being precisely analogous to that of carbonic acid. The molecular 
 formula of bisulphide of carbon would be OS 2 (O = 12, & = 32), repre- 
 senting 2 volumes (H = 1 volume). 
 
 155. Bisulphide of silicon (SiS 2 ), corresponding in composition to bisulphide of 
 carbon, is obtained by burning silicon in sulphur vapour, or by passing vapour of bisul- 
 phide of carbon over a mixture of silica and charcoal. Unlike the carbon compound, 
 it is a white amorphous solid, absorbing moisture when exposed to air, and soluble 
 in water, which gradually decomposes it into silicic and hydrosulphuric acids 
 
 SiS 2 + 2HO = Si0 2 + 2HS . 
 When heated in air, it burns slowly, yielding silicic and sulphurous acids. 
 
 156. Bisulphide of nitrogen (NS 2 ) is a yellow crystalline explosive substance, pro- 
 duced by a complicated reaction whicti takes place when chloride of sulphur, dis- 
 solved in bisulphide of carbon, is acted on by gaseous ammonia, when hydrochlorate 
 of ammonia is deposited, and the filtered liquid, allowed to evaporate, deposits bisul- 
 phide of nitrogen mixed with sulphur, which may be dissolved out by bisulphide of 
 carbon, in which the nitrogen compound is nearly insoluble ; this substance is re- 
 markable for its sparing solubility, its irritating odour, and its explosibility when 
 struck or moderately heated, its elements being held together by a very feeble 
 attraction. 
 
 157. CHLORIDES OF SULPHUR. The subchloride, or dichloride of sulphur 
 (S 2 C1), is the most important of these, since it is employed in the process 
 of vulcanising caoutchouc. It is very easily prepared by passing dry 
 chlorine over sulphur very gently heated in a retort (fig. 199) ; the sul- 
 phur quickly melts, and the dichloride of sulphur distils over into the 
 
EXTKACTION OF SELENIUM. 219 
 
 receiver as a yellow volatile liquid (boiling point, 280 F.), which has a 
 most peculiar odour. It fumes strongly in air, the moisture decomposing 
 
 Fig. 199. Preparation of subchloride of sulphur. 
 
 it, forming hydrochloric and sulphurous acids, and causing a deposit of 
 sulphur upon the neck of the bottle 
 
 2S 2 C1 + 2HO = 2HC1 + S0 2 '+ S 3 . 
 
 When poured into water, it sinks (sp. gr. 1 *68) and slowly undergoes de- 
 composition ; the separated sulphur, of course, belongs to the electroposi- 
 tive variety (see p. 187), and the solution contains, beside hydrochloric 
 and sulphurous acids, some of the acids containing a larger proportion of 
 sulphur. The specific gravity of the vapour of dichloride of sulphur is 
 4-7, showing that it contains 2 vols. Cl (4 -94) and 2 vols. S (4 -46), con- 
 densed into 2 vols. (9*40) of vapour of dichloride of sulphur. Its mole- 
 cular formula would therefore be S.Cls(S = 32), representing 2 vols. 
 (H = 1 vol.) 
 
 Chloride of sulphur (SCI) is a far less stable compound than the dichloride, from 
 which it is obtained by the action of an excess of chlorine. It is a dark red fuming 
 liquid, easily resolved, even by sunlight, into free chlorine and dichloride of sulphur. 
 
 Iodide of sulphur (SI) is a crystalline unstable substance, produced by the direct 
 union of its elements, and occasionally employed in medicine. 
 
 Subiodide of sulphur, or bisulphide of iodine (S 2 I), is obtained in large tabular 
 crystals resembling iodine, by decomposing the subchloride of sulphur with iodide 
 of ethyle ; S 2 C1 + C 4 H 5 I = S 2 I + C 4 H 5 G1 . 
 
 SELENIUM. Eq. 39 -75. 
 
 158. Selenium (SiXijvjj, the moon) is a rare element, very closely allied to sulphur 
 in its natural history, physical characters, and chemical relations to other bodies. 
 It is found sparingly in the free state associated with some varieties of native sul- 
 phur, but more commonly in combination with metals, forming selenides, which are 
 found together with the sulphides. The iron pyrites of Fahlun, in Sweden, is 
 especially remarkable for the presence of selenium, and was the source whence this 
 element was first obtained. The Fahlun pyrites is employed for the manufacture 
 of oil of vitriol, and in the leaden chambers a reddish brown deposit is found, which 
 was analysed by Berzelius in 1817, and found to contain the new element. 
 
 In order to extract selenium from the seleniferous deposit of the vitriol works, it 
 may be boiled with sulphuric acid diluted with an equal volume of water, and nitric 
 acid added in small portions until the oxidation is completed, when no more red 
 fumes will escape. The solution, containing selenious (Se0 2 ) and selenic (Se0 3 ) 
 acids, is largely diluted with water, filtered off from the undissolved matters, mixed 
 
220 EXTRACTION OF TELLURIUM. 
 
 with about one-fourth of its bulk of hydrochloric acid, and somewhat concentrated 
 by evaporation, when the hydrochloric acid reduces the selenic to selenious acid 
 
 HO.Se0 3 + HC1 = HO.Se0 2 + HO + Cl . 
 
 A current of sulphurous acid gas is now passed through the solution, when the 
 selenium is precipitated in fine red flakes, which collect into a dense black mass 
 when the liquid is gently heated 
 
 HO.Se0 2 + HO + 2S0 2 = 2(HO . S0 3 ) + Se . 
 The proportion of selenium in the deposit from the leaden chambers is variable. 
 The author has obtained above 3 per cent, by this process. 
 
 Selenium, like sulphur, is capable of existing in three allotropic states : the red 
 amorphous variety precipitated from its solutions, or sublimed like flowers of sul- 
 phur; the black vitreous form ; and the crystalline form deposited from its solution 
 in bisulphide of carbon, in which it is far less easily dissolved than sulphur. When 
 heated, it fuses easily, boils below a red heat, and is converted into a deep yellow 
 vapour, which expands when heated in the same anomalous manner as vapour of 
 sulphur. 
 
 Selenium is less combustible than sulphur ; when heated in air it burns with a 
 blue flame, and emits a peculiar odour like that of putrid horse-radish, which ap- 
 pears to be due to the formation of a little selenietted hydrogen from the moisture 
 of the air. When heated with oil of vitriol, selenium forms a green solution which 
 deposits the selenium again when poured into water. 
 
 Selenious acid (Se0 2 ), corresponding to sulphurous acid, is the product of combus- 
 tion of selenium in oxygen. It is best obtained by dissolving selenium in boiling 
 nitric acid (which would convert sulphur into sulphun'c acid), and evaporating to 
 dryness, when the selenious acid remains as a white solid which sublimes in needle- 
 like crystals when heated. When dissolved in boiling water, it yields a crystalline 
 hydrate of selenious acid. 
 
 Selenic acid (Se0 3 ) is not known in the anhydrous state. It is formed when 
 selenium is oxidised by fused nitre ; KO . N0 5 +*Se = KO . Se0 3 + N0 2 . By dis- 
 solving the seleniate of potash in water, and adding nitrate of lead, a precipitate of 
 seleniate of lead (PbO . Se0 3 ) is obtained, and if this be suspended in water and 
 decomposed by passing hydrosulphuric acid gas, lead will be removed as insoluble 
 sulphide, and a solution of hydrated selenic acid will be obtained 
 
 PbO.Se0 3 + HS = HO.Se0 3 + PbS . 
 
 This solution may be evaporated till it has a sp. gr. of 2-6, when it very closely 
 resembles oil of vitriol. It is decomposed, however, at about 550 F., evolving 
 oxygen, and becoming selenious acid. It oxidises the metals like oil of vitriol, and 
 even dissolves gold. The seleniates closely resemble the sulphates, but they are 
 decomposed when heated with hydrochloric acid, chlorine being evolved, and seleni- 
 ous acid produced. 
 
 Hydroselenic acid, or selenietted hydrogen (HSe), is the exact parallel of sulphuretted 
 hydrogen, and is produced by a similar process. It is even more offensive and 
 poisonous than that gas, and acts in a similar way upon metallic solutions, preci- 
 pitating the selenides. 
 
 There are two chlorides of selenium : the dichloride, Se 2 Cl, a brown volatile liquid 
 corresponding to dichloride of sulphur ; and the bichloride, SeCl 2 , a white crystalline 
 solid, without any well-established analogue in the sulphur series. 
 
 Notwithstanding the resemblance between the two elements, there are two sul- 
 phides of selenium, a bisulphide (SeS 2 ) and a tersulphide (SeS 3 ). The former is 
 obtained as a yellow precipitate when hydrosulphuric acid is passed into solution of 
 selenious acid. 
 
 TELLURIUM. Eq. 64-5. 
 
 159. Tellurium (from tellus, the earth] is connected with selenium by analogies 
 stronger than those which connect that element with sulphur. It is even less fre- 
 quently met with than selenium, being found chiefly in certain Transylvanian gold 
 ores. It occasionally occurs in an uncombined form, but more frequently in com- 
 bination with metals. Foliated or graphic tellurium is a black mineral containing 
 the tellurides of lead, silver, and gold. Telluride of bismuth is also found in 
 nature. 
 
REVIEW OF THE SULPHUR GROUP. 221 
 
 Tellurium is extracted from the foliated ore by a process similar to that for ob- 
 taining selenium. From telluride of bismuth it is procured by strongly heating the 
 ore with a mixture of carbonate of potash and charcoal, when telluride of potassium 
 is formed, which dissolves in water to a purple-red solution, from which tellurium is 
 deposited on exposure to air. 
 
 Tellurium much more nearly resembles the metals than the non-metals in its 
 physical properties, and is on that account often classed among the former, but it is 
 not capable of forming a basic oxide. In appearance it is very similar to bismuth 
 (with which it is so frequently found), having a pinkish metallic lustre, and being, 
 like that metal, crystalline and brittle. It fuses below a red heat, and is converted 
 into a yellow vapour at a higher temperature. When heated in air it burns with a 
 blue flame edged with green, and emits fumes of tellurous acid (Te0 2 ) and a peculiar 
 odour. 
 
 Like selenium, tellurium is dissolved by strong sulphuric acid, yielding a purple- 
 red solution, from which water precipitates it unchanged. 
 
 The oxides of tellurium correspond in composition to those of selenium. Tellurous 
 acid (Te0 2 ) is precipitated in the hydrated state when a solution of tellurium in 
 diluted nitric acid is poured into water. If the nitric solution is boiled, a crystal- 
 line precipitate of anhydrous tellurous acid is obtained. Unlike selenious acid, 
 tellurous acid is sparingly soluble in water. It is easily fusible, forming a yellow 
 glass, which becomes white on cooling, and it may be sublimed unchanged. Its acid 
 character is rather feeble, and with some of the stronger acids, it forms soluble 
 compounds in which it takes the part of a very feeble base. 
 
 Telluric acid (Te0 3 ) is also a weak acid obtained by oxidising tellurium with nitre, 
 precipitating the tellurate of potash with chloride of barium, and decomposing the 
 tellurate of baryta with sulphuric acid. On evaporating the solution, crystals of 
 hydrated telluric acid (HO . Te0 3 + 2HO) are obtained, which become HO . Te0 3 at 
 a moderate heat, and when heated nearly to redness, are converted into an orange- 
 yellow powder, which is the anhydrous acid. In this state it is insoluble in acids and 
 alkalies. When strongly heated, it evolves oxygen, and becomes tellurous acid. 
 The tellurates are unstable salts which are converted into tellurites when heated. 
 
 Telluretted hydrogen, or hydrotelluric acid (HTe), exhibits in the strongest manner 
 the chemical analogy of tellurium with selenium and sulphur. It is a gas very 
 similar to sulphuretted hydrogen in smell, and in most of its other properties. 
 When its aqueous solution is exposed to the air, it yields a brown deposit of tellu- 
 rium. When passed into metallic solutions it precipitates the tellurides. 
 
 The gas is prepared by decomposing telluride of zinc with hydrochloric acid. 
 
 The most characteristic property of tellurium compounds, is that of furnishing 
 the purple solution of telluride of potassium, when fused with carbonate of potash 
 and charcoal, and treated with water. Two solid chlorides of tellurium have been 
 obtained ; TeCl is a black solid with a violet coloured vapour, and is decomposed by 
 water into tellurium and TeCl 2 . The latter may be obtained as a white crystalline 
 volatile solid, decomposed by much water into hydrochloric and tellurous acids. 
 There are also two sulphides of tellurium corresponding to the oxides, from which 
 they may be obtained as dark brown precipitates, by the action of hydrosulphuric 
 acid. They are both sulphur-acids, and, therefore, soluble in alkaline sulphides. 
 
 160. Review of the sulphur group of elements. The three elements 
 sulphur, selenium, and tellurium exhibit a relation of a similar Character 
 to that observed between the members of the chlorine group, both in their 
 physical arid chemical properties. 
 
 Sulphur is a pale yellow solid, easily fusible and volatile, without any 
 trace of metallic lustre, and of specific gravity 2*05 (sp. gr. of vapour, 
 2 - 23). Selenium is either a red powder or a lustrous mass appearing 
 black, but transmitting red light through thin layers, much less fusible 
 and volatile than sulphur, and of specific gravity 4*8 (sp. gr. of vapour, 
 5 '68). Tellurium has a brilliant metallic lustre, is much less fusible and 
 volatile than selenium, and of specific gravity 6-65 (sp. gr. of vapour, 9*0). 
 
 Sulphur (eq. 16) has the most powerful attraction for oxygen, hydro- 
 gen, and the metals. Selenium (eq. 39 '75) ranks next in the order of 
 chemical energy. Tellurium (eq. 64 -5) has a less powerful attraction for 
 
222 EXTRACTION OF PHOSPHORUS FROM BONES. 
 
 oxygen, hydrogen, and the metals, than either sulphur or selenium. This 
 element appears to stand on neutral ground between the non-metallic 
 bodies and the less electropositive metals. 
 
 PHOSPHOKUS. 
 
 161. This is the only element for the ordinary preparation of which 
 animal substances are employed. It is never known to occur uncombined 
 in nature, but is found abundantly in the form of phospJiate of lime 
 (3CaO . P0 5 ), which is contained in the minerals cqprolite, phosphorite, 
 and apatite, and occurs diffused, though generally in small proportion, 
 through all soils upon which plants will grow, for this substance is an 
 essential constituent of the food of most plants, and especially of the 
 cereal plants which form so large a proportion of the food of animals. 
 The seeds of such plants are especially rich in the phosphates of lime and 
 magnesia. 
 
 Animals feeding upon these plants still further accumulate the phos- 
 phoric acid, for it enters, chiefly in the form of phosphate of lime, into the 
 composition of almost every solid and liquid in the animal body, and is 
 especially abundant in the bones, which contain about three-fifths of 
 their weight of phosphate of lime. It is from this source that our supply 
 of phosphorus is chiefly derived. 
 
 Composition of the Bones of Oxen. 
 
 Animal matter, . 
 Phosphate of lime, 
 Fluoride of calcium, . 
 Carbonate of lime, 
 Phosphate of magnesia, 
 
 30-58 
 
 57-67 
 
 2-69 
 
 6-99 
 
 2-07 
 
 100-00 
 
 What is here termed animal matter is a cartilaginous substance, con- 
 verted into gelatine when the bones are heated with water under pressure, 
 and containing carbon, hydrogen, nitrogen, and oxygen. It was formerly 
 the custom to get rid of this by burning the bones in an open fire, but 
 the increased demand for chemical products, and the diminished supply 
 of bones, have taught economy, so that the cartilaginous matter is now 
 dissolved out by heating the bones with water at a high pressure for the 
 manufacture of glue ; or the bones* are subjected to destructive distilla- 
 tion, so as to save the ammonia which they evolve, and the bone charcoal 
 thus produced is used by the sugar-refiner until its decolorising powers 
 are exhausted, when it is heated in contact with air to burn away the 
 charcoal, and leave the bone-ash, consisting chiefly of phosphate of lime 
 (3CaO . P0 5 ). In order to extract the phosphorus, the bone-ash is heated 
 for some time with diluted sulphuric acid, which removes the greater part 
 of the lime in the form of the sparingly soluble sulphate of lime, leaving 
 the phosphoric acid in the solution, which is strained from the deposit, 
 evaporated to a syrup, mixed with charcoal, thoroughly dried in an iron 
 pot, and distilled in an earthen retort (fig. 200), when the carbon removes 
 the oxygen from the phosphoric acid, and the phosphorus distils over, 
 and is condensed in a receiver containing water to protect it from the 
 
PROPERTIES OF PHOSPHORUS. 223 
 
 action of the air. The decomposition of the dried phosphoric acid by the 
 carbon of the charcoal is expressed by the equation 
 
 HO.P0 5 + C 6 = 600 + H + P. 
 
 Hydrated phosphoric Carbonic oxide, 
 
 acid. 
 
 This is the simplest account that can be given of the preparation of phosphorus 
 from bone-ash, but it is not strictly correct, for the sulphuric acid does not remove 
 
 Fig. 200. Extraction of phosphorus. 
 
 the whole of the lime from the phosphate, a portion remaining in the solution con- 
 taining the phosphoric acid, so that this solution is generally said to contain super- 
 phosphate of lime, and the action of the sulphuric acid is thus represented 
 
 3CaO . P0 5 + 2(HO . S0 3 ) = CaO . 2HO . P0 5 + 2(CaO . S0 3 ) . 
 Bone phosphate Supei-phosphate 
 
 of lime. of lime. 
 
 When the superphosphate of lime is dried, it becomes converted into metaphos- 
 phate of lime (CaO . P0 5 ), and on distilling this with charcoal 
 
 3(CaO.P0 5 ) + C 10 = 3CaO.P0 5 + 10CO + P 2 . 
 Metaphosphate Bone phosphate 
 
 of lime. of lime. 
 
 Silicic acid (sand) is sometimes added to combine with the lime, and liberate the 
 remainder of the phosphoric acid, so that it may be decomposed by the charcoal. 
 
 On the small scale, for the sake of illustration, phosphorus may be prepared by a 
 process which has also been successfully employed for its manufacture in quantity, 
 and consists in heating a mixture of bone-ash and charcoal in a stream of hydro- 
 chloric acid gas 
 
 3CaO.P0 5 + 3HC1 + C 8 = 3CaCl + SCO + H 3 +^ P . 
 
 A mixture of equal weights of well-dried charcoal and bone-ash, both in fine 
 powder, is introduced into a porcelain tube sheathed with copper, and placed in a 
 charcoal furnace (fig. 201). One end of the tube is connected with a flask (A), con- 
 taining fused salt and sulphuric acid for evolving hydrochloric acid, and the other is 
 cemented with putty into a bent retort-neck (B), for conveying the phosphorus 
 into a vessel of water (C). On heating the porcelain tube to bright redness, phos- 
 phorus distils over in abundance. The hydrogen and carbonic oxide inflame as 
 they escape into the air, from their containing phosphorus vapour. 
 
 When first prepared the phosphorus is red and opaque, from the pre- 
 sence, of some suboxide of phosphorus and mechanical impurities ; the 
 latter are removed by melting the phosphorus under warm water, and 
 squeezing it through wash leather. The phosphorus is then fused under 
 ammonia to remove any acid impurity, and afterwards under bichromate 
 
224 INFLAMMABILITY OF PHOSPHORUS PHOSPHORESCENCE. 
 
 of potash acidified with sulphuric acid, when the chromic acid oxidises 
 the suboxide of phosphorus, and converts it into phosphoric acid which 
 dissolves. The phosphorus is then thoroughly washed, melted under 
 
 water, and drawn up into 
 glass tubes, where it soli- 
 difies into the, sticks in 
 which it is sold. These 
 are always preserved un- 
 der water from the action 
 of oxygen, and in tin cases 
 from that of light. 
 
 Pure ordinary phospho- 
 rus is almost colourless 
 and transparent, but when 
 exposed to light, and espe- 
 cially to direct sun-light, 
 it gradually acquires an 
 opaque red colour, from 
 its partial conversion into 
 the allotropic variety 
 known as red or amor- 
 phous phosphorus. By 
 tying bands of black cloth 
 round a stick of phos- 
 phorus and exposing it, 
 under water, to the action 
 of sun-light, alternate 
 zones of red may be pro- 
 duced. 
 
 Even though the phosphorus be screened from light, it will not remain 
 unchanged unless the water be kept quite free from air, which irregularly 
 corrodes the surface of the phosphorus, rendering it white and opaque. 
 This action is accelerated by exposure to light. 
 
 The most remarkable character of ordinary phosphorus is its easy in- 
 flammability. It inevitably takes fire in air when heated a little above 
 its melting point (111 0< 5 F.), burning with a brilliant white flame, which 
 becomes insupportable when the combustion takes place in oxygen (p. 6), 
 and evolving dense white clouds of solid phosphoric acid. When a piece 
 of dry phosphorus is exposed to the air, it combines slowly with oxygen, 
 forming .phosphorous acid,* and its temperature often becomes so much 
 elevated during this slow combustion, that it melts and takes fire, espe- 
 cially if the combination be encouraged by the warmth of the hand or by 
 friction. Hence, ordinary phosphorus must never be handled or cut in 
 the dry state, but always under water, for it causes most painful burns. 
 
 The slow oxidation of phosphorus is attended with that peculiar lumi- 
 nous appearance which is termed phosphorescence (</>ws, light, ^>ep<o, to bear), 
 but this glow is not seen in pure oxygen or in air containing a minute 
 proportion of olefiant gas or oil of turpentine. It will be remembered 
 that the slow oxidation of phosphorus is attended with the formation of 
 ozone. ^ t 
 
 * The white fumes evolved by phosphorus in mpist air are said to consist partly of 
 nitrite of ammonia, formed by the action of the ozonised oxygen upon the air and aqueous 
 vapour. 
 
 Fig. 201. 
 
EXPERIMENTS WITH PHOSPHORUS. 
 
 225 
 
 The characteristic behaviour of phosphorus in air is best observed when the phos- 
 phorus is in a finely-divided state. When a fragment of phosphorus is shaken with 
 a little bisulphide of carbon, it is quickly dissolved, and if the solution be poured 
 upon a piece of filtering-paper (fig. 202), and allowed to evaporate in a darkened 
 room, the very thin film of phosphorus 
 which is left will exhibit a glow increas- 
 ing in brilliancy till the phosphorus bursts 
 out into spontaneous combustion. 
 
 If . phosphorus be dissolved in olive oil, 
 a^ a gentle heat, the solution is strongly 
 phosphorescent when shaken in a bottle 
 containing air, or when rubbed upon the 
 hands. 
 
 Characters may be written on paper 
 with a stick of phosphorus held in a Fig. 202. 
 
 thickly-folded piece of damp paper (hav- 
 ing a vessel of water at hand into which to plunge the phosphorus if it should 
 take fire). When the paper is held with its back to the fire, or to a hot iron, 
 in a darkened room, a twinkling combustion of the finely-divided phosphorus will 
 ensue, and the letters will be burnt into the paper. Phosphorus, which has been 
 partly oxidised, is even more easily inflamed than pure phosphorus. If a few small 
 pieces of phosphorus be placed in a dry stoppered bottle, gently warmed till they 
 melt, and then shaken round the sides of the bottle so as to become partly converted 
 into red oxide of phosphorus, it will be found, long after the bottle is cold, to be 
 spontaneously inflammable, so that if a wooden match tipped with sulphur be rubbed 
 against it, the phosphorus which it takes up will ignite when the match is brought 
 into the air, kindling the sulphur, which will inflame the wood. This was one of 
 the earliest forms in which phosphorus was employed for the purpose of procuring 
 an instantaneous light. If the stopper be greased, the phosphorus may be preserved 
 unchanged for a long time. 
 
 In the last experiment, if the wood had not been tipped with sulphur, the phos 
 phorus would not have kindled it, the flame of phosphorus generally being unable 
 to ignite solid combustibles, because it deposits upon them a coating of phosphoric 
 acid, which protects them from the action of air. Hence, in the manufacture of 
 lucifer matches, the wood is first tipped with sulphur, or wax, or paraffine, which 
 easily give off combustible vapours to be kindled by the flame of the phosphorus 
 composition, and thus to inflame the wood. 
 
 If a small stick of phosphorus be carefully dried with filtering paper, and dropped 
 into a cylinder of oxygen, which is afterwards covered with a glass plate, no luminosity 
 will be observed in a darkened room until the cylin- 
 der is placed under the air-pump receiver, and the 
 air slowly exhausted. When the oxygen has thus been 
 rarefied to about one-fifth of its former density, the 
 phosphorescence will be seen. A similar effect may 
 be produced by covering the cylinder of oxygen con- 
 taining the phosphorus (having removed the glass 
 plate) with another cylinder, about four times its 
 size (fig. 203), filled with carbonic acid, which will 
 gradually dilute the oxygen and produce phosphor- 
 escence. By suspending in a bottle of air contain- 
 ing a strongly luminous piece of phosphorus a piece 
 of paper with a drop of oil of turpentine upon it, the 
 glow may be almost instantaneously destroyed. A 
 small tube of olefiant gas or coal-gas dropped into 
 the bottle will also extinguish the luminosity. 
 
 Ordinary phosphorus is slowly converted into vapour at the ordinary 
 temperature, and emits in the air white fumes with a peculiar alliaceous 
 smell, which appear phosphorescent in the dark. When heated out of 
 contact with air, it boils at 550 F., and is converted into a colourless 
 vapour. 
 
 The luminosity of phosphorus vapour is seen to advantage when a piece of phos- 
 phorus is boiled with water in a narrow-necked flask, or a test-tube with a cork and 
 
 P 
 
 Fig. 203. 
 
226 
 
 PREPAKATION OF AMORPHOUS PHOSPHORUS. 
 
 narrow tube. The steam charged with vapour of phosphorus has all the appearance 
 of a blue flame in a darkened room, but of course combustibles are not inflamed by 
 it, since its temperature is not higher than 212 F. Phosphorus may be distilled 
 with perfect safety in an atmosphere of carbonic acid, the neck of the retort being 
 allowed to dip under water in the receiver. 
 
 Although, ordinary phosphorus is of a decidedly glassy or vitreous struc- 
 ture, and not at all crystalline, it may be obtained in dodecahedral 
 crystals, by allowing its solution in bisulphide of carbon to evaporate in 
 an atmosphere of carbonic acid. 
 
 The conversion of ordinary phosphorus into the red or amorphous phos- 
 phorus is one of the most striking instances of allotropic modification. 
 When phosphorus is heated for a considerable length of time to about 
 450 F. in vacua, or in an atmosphere in which it cannot burn, it becomes 
 converted into a red infusible mass of amorphous phosphorus. This form 
 of phosphorus differs as widely from the vitreous form as graphite differs 
 from diamond. It is almost unchangeable in the air, evolves no vapour, 
 is not luminous, cannot be inflamed by friction, or even by any heat short 
 of 500 F., when it actually becomes reconverted into ordinary phosphorus.* 
 Amorphous phosphorus is insoluble in the solvents for ordinary phosphorus. 
 The two varieties also differ greatly in specific gravity, that of the ordinary 
 phosphorus being 1'83, and of the amorphous variety 2*14. 
 
 The conversion of vitreous into amorphous phosphorus may be effected by heating 
 it in a flask (A, fig. 204) placed in an oil-bath (B), maintained at a temperature 
 ranging from 450 to 460 F., the flask being furnished with a bent tube (C) dipping 
 
 into mercury, and with another tube 
 (D) for supplying carbonic acid gas, 
 dried by passing over chloride of cal- 
 cium. The flask should be thoroughly 
 filled with carbonic acid before apply- 
 ing heat, and the tube delivering it 
 may then be closed with a small clamp 
 (E). After exposure to heat for about 
 forty hours, but little ordinary phos- 
 phorus will remain, and this may be 
 removed by allowing the mass to 
 remain in contact with bisulphide of 
 carbon for some hours, and subse- 
 quently washing it with fresh bisul- 
 phide of carbon till the latter leaves 
 no phosphorus when evaporated. 
 
 On the large scale, the red phos- 
 Fig. 204. phorus is prepared by heating about 
 
 200 Ibs. of vitreous phosphorus to 
 
 450 F. in an iron boiler. After three or four weeks the phosphorus is found to be 
 converted into a hard red brittle mass, which is ground by mill-stones under water, 
 and separated from the ordinary phosphorus either by bisulphide of carbon or caustic 
 soda, in which the latter is soluble. The temperature requires careful regula- 
 tion, for if it be allowed to rise to 500, the red phosphorus quickly resumes the 
 vitreous condition, evolving the heat which it had absorbed during its conversion, 
 and thus converting much of the phosphorus into vapour. This reconversion may 
 be shown by heating a little red phosphorus in a narrow test-tube, when drops of 
 vitreous phosphorus condense on the cool part of the tube. The colour of different 
 specimens of amorphous phosphorus varies considerably ; that prepared on the 
 large scale is usually of a dark purplish colour, but it may be obtained of a bright 
 scarlet colour. Rhombohedral crystals of phosphorus, resembling crystals of arsenic 
 in form and metallic appearance, have been obtained by fusing phosphorus with 
 lead, and dissolving out the latter with diluted nitric acid (sp. gr. !!). 
 
 * According to Hittorf, the reconversion does not take place till 800 F., the red phos- 
 phorus being convertible into vapour below that temperature, without fusion. 
 
PRECIPITATION OF METALS BY PHOSPHORUS. 227 
 
 Ordinary phosphorus is very poisonous, whilst amorphous phosphorus 
 appears to be harmless. The former is employed, mixed with fatty sub- 
 stances, for poisoning rats and beetles. Cases are, unhappily, not very 
 rare, of children being poisoned by sucking the phosphorus composition 
 on lucifer matches. The vapour of phosphorus also produces a very 
 injurious effect upon the persons engaged in the manufacture of lucifer 
 matches, resulting in the decay of the lower jaw-bone. This evil is much 
 mitigated by good ventilation, or by diffusing turpentine vapour through 
 th'e air of the work-room, and attempts have been made to obviate it 
 entirely by substituting amorphous phosphorus for the ordinary variety, 
 but, as might be expected, the matches thus made are not so sensitive to 
 friction as those in which the vitreous phosphorus is used. 
 
 The difference between the two varieties of phosphorus, in respect to 
 chemical energy, is seen when they are placed in contact with a little 
 iodine on a plate, when the ordinary phosphorus undergoes combustion, 
 and the red phosphorus remains unaltered. 
 
 Black phosphorus has been obtained by heating vitreous phosphorus to 
 a little above its melting point and suddenly cooling it. It is reconverted 
 by fusion and slow cooling. Viscous phosphorus results from the sudden 
 cooling of phosphorus heated nearly to its boiling point. 
 
 Ordinary phosphorus is capable of direct union with oxygen, chlorine, 
 bromine, iodine, sulphur, and most of the metals, with which it forms 
 phosphides or phosphurets. Even gold and platinum unite with this 
 element when heated, so that crucibles of these metals are liable to cor- 
 rosion when heated in contact with a phosphate in the presence of a 
 reducing agent, such as carbon. Thus the inside of a platinum dish or 
 crucible is roughened when vegetable or animal substances containing 
 phosphates are incinerated in it. The presence even of small quantities 
 of phosphorus in metallic iron or copper produces considerable effect upon 
 their physical qualities. 
 
 Phosphorus has the property, a very remarkable one in a non-metal, of 
 precipitating some metals from their solutions in the metallic state. If a 
 stick of phosphorus be placed in a solution of sulphate of copper, it 
 becomes coated with metallic copper, the phosphorus appropriating the 
 oxygen. This has been turned to advantage in copying very delicate 
 objects by the electrotype process, for by exposing them to the action of a 
 solution of phosphorus in ether or bisulphide of carbon, and afterwards to 
 that of a solution of copper, they acquire the requisite conducting metallic 
 film, even on their finest filaments. Solutions of silver and gold are 
 reduced in a similar manner by phosphorus. 
 
 By floating very minute scales of ordinary phosphorus upon a dilute solution of 
 chloride of gold, the metal will be reduced in the form of an extremely thin film, 
 which may be raised upon a glass plate, and will be found to have various shades 
 of green and violet by transmitted light, dependent upon its thickness, whilst its 
 thickest part exhibits the ordinary colour of the metal to reflected light. By heat- 
 ing the films on the plate, various shades of amethyst and ruby are developed. If 
 a very dilute solution of chloride of gold in distilled water be placed in a perfectly clean 
 bottle, and a few drops of ether, in which phosphorus has been dissolved, poured 
 into it, a beautiful ruby-coloured liquid is obtained, the colour of which is due to 
 metallic gold in an extremely finely divided state, and on allowing it to stand for 
 some months, the metal subsides as a purple powder, leaving the liquid colourless. 
 If any saline impurity be present in the gold solution, the colour of the reduced gold 
 will be amethyst or blue. These experiments (Faraday) illustrate very strikingly 
 the use of gold for imparting ruby and purple tints to glass and the glaze of 
 porcelain. 
 
228 MANUFACTURE OF LUCIFER MATCHES. 
 
 162. Lucifer matches are made by tipping the wood with sulphur or 
 wax or paraffine to convey the flame, and afterwards with the match com- 
 position, which is generally composed of saltpetre or chlorate of potash, 
 phosphorus, red lead, and glue, and depends for its action on the easy 
 inflammation, by friction, of phosphorus when mixed with oxidising agents 
 like saltpetre (KO . N0 5 ), chlorate of potash (KO . C10 6 ), Or red lead 
 (Pb 3 4 ), the glue only serving to bind the composition together and 
 attach it to the wood. The composition used by different makers varies 
 much in the nature and proportions of the ingredients. In this country, 
 chlorate of potash is most commonly employed as the oxidising agent, 
 such matches usually kindling with a slight detonation ; but the German 
 manufacturers prefer either nitrate of potash or nitrate of lead, together 
 with binoxide of lead or with red lead, which produce silent matches. 
 
 Sulphide of antimony (which is inflamed by friction with chlorate of 
 potash, see p. 157) is also used in those compositions in which a part of 
 the phosphorus is employed in the amorphous form, and fine sand or 
 powdered glass is very commonly added to increase the susceptibility 
 of the mixture to inflammation by friction. 
 
 The match composition is coloured either with ultramarine blue, Prus- 
 sian blue, or vermilion. In preparing the composition, the glue and the 
 nitre or chlorate of potash are dissolved in hot water, the phosphorus then 
 added and carefully stirred in until intimately mixed, the whole being 
 kept at a temperature of about 90 F. The fine sand and colouring 
 matter are then added, and when the mixture is complete, it is spread out 
 upon a stone slab heated by steam, and the sulphured ends of the matches 
 are dipped into it. 
 
 The safety matches, which refuse to ignite unless rubbed upon the bot- 
 tom of the box, are tipped with a mixture of sulphide of antimony, 
 chlorate of potash, and powdered glass, which is not sufficiently sensitive 
 to be ignited by any ordinary friction, but inflames at once when rubbed 
 upon the amorphous phosphorus mixed with glass which coats the rubber 
 beneath the box. On this principle some French matches have been made 
 which can be ignited only by breaking the match and rubbing the two 
 ends together. 
 
 It would be very desirable to dispense entirely with the use of phos- 
 phorus in lucifer matches, not only because of the danger from accident 
 and disease in the manufacture, but because a very large quantity of 
 phosphate of lime which ought to be employed for agricultural purposes 
 is now devoted to the preparation of phosphorus, of which six tons are 
 said to be consumed annually in this country for the manufacture of 
 matches. The most successful attempt in this direction appears to be the 
 employment of a mixture of chlorate of potash and hyposulphite of lead, 
 in place of the ordinary phosphorus composition. 
 
 For illustration, very excellent matches may be made upon the small scale in the 
 following manner. The slips of wood are dipped in melted sulphur so as to acquire 
 a slight coating. 30 grains of gelatine or isinglass are dissolved in 2 drachms of 
 water in a porcelain dish placed upon a steam-bath ; 20 grains of ordinary phos- 
 phorus are then added, and well mixed in with a piece of stick ; to this mixture are 
 added, in succession, 15 grains of red lead and 50 grains of powdered chlorate of 
 potash. The sulphured matches are dipped into this paste, and left to dry in the air. 
 
 To make the safety matches : 10 grains of powdered chlorate of potash and 10 
 grains of sulphide of antimony are made into a paste with a few drops of a warm 
 solution of 20 grains gelatine in 2 drachms water, the sulphured matches being 
 tipped with this composition. The rubber is prepared with 20 grains of amorphous 
 
COMPOUNDS OF PHOSPHOKUS AND OXYGEN. 
 
 229 
 
 phosphorus, and 10 grains of finely-powdered glass, mixed with the solution of 
 gelatine, and painted on paper or card-board with a brush. 
 
 163. Phosphorus-fuze composition. To ignite the Armstrong percus- 
 sion shells, a very sensitive detonating composition is employed, which is 
 composed of amorphous phosphorus, chlorate of potash, shellac,- and pow- 
 dered glass made into a paste with spirit of wine. This is placed in the 
 little cap designed for it, and when dry is waterproofed with a little 
 shellac dissolved in spirit. 
 
 Such a composition may be prepared with care in the following manner: 4 grains 
 of powdered chlorate of potash are moistened on a plate with 6 drops of spirit of 
 wine, 4 grains of powdered amorphous phosphorus are added, and the whole mixed 
 at arm's-length with a bone knife, avoiding great pressure. The mixture, which 
 should still be quite moist, is spread in small portions upon ten or twelve pieces 
 of filtering paper, and left in a safe place to dry. If one of these be gently 
 pressed with a stick, it explodes with great violence. It is dangerous to press it 
 with the blade of a knife, as the latter is commonly broken, and the pieces pro- 
 jected with considerable force. A stick dipped in oil of vitriol of course explodes 
 it immediately. If a bullet be placed very lightly upon one of the pellets, and 
 the paper tenderly wrapped round it, a percussion shell may be extemporised, which 
 explodes with a loud report when dropped upon the floor. 
 
 OXIDES OF PHOSPHORUS. 
 
 164. There are only two compounds of phosphorus with oxygen which 
 have been obtained and satisfactorily examined in the separate state, viz. , 
 phosphorous acid (P0 3 ), and phosphoric acid (P0 5 ). The sub-oxide of 
 phosphorus (P 2 0) is said to have been obtained, but very little is known 
 of it, and hypophosphorous acid (PO) has only been obtained in combina- 
 tion with water. 
 
 Oxides of Phosphorus. 
 
 Name. 
 
 Equivalent Formula, 
 
 By Weight. 
 
 Phosphorus. 
 
 Oxygen. 
 
 Suboxide of phosphorus ? . . . . 
 Hypophosphorous acid? .... 
 Phosphorous acid 
 Phosphoric acid ... . 
 
 P 2 
 PO 
 
 POo 
 
 P5 
 
 62 
 31 
 31 
 31 
 
 8 
 8 
 24 
 40 
 
 
 PHOSPHORIC ACID. 
 
 165. Phosphoric acid is by far the most important of the compounds 
 of phosphorus. It has been already noticed as almost the only form of 
 combination in which that element is met with in nature, and as an indis- 
 pensable ingredient in the food of plants and animals. No other mineral 
 substance can bear comparison with it as a measure of the capability of a 
 country to support animal life. The acid itself is very useful in calico- 
 printing and some other arts. 
 
 The mineral sources of this acid appear to be phosphorite, coprolite, and 
 apatite, all consisting essentially of phosphate of lime (3CaO . P0 5 ), but 
 associated in each case with fluoride of calcium, which is also contained, 
 with phosphate of lime, in bones, and would appear to indicate an organic 
 origin for these minerals. Phosphorite is an earthy -looking substance, 
 
230 
 
 TREPAKATION OF PHOSPHOKIC ACID. 
 
 forming large deposits in Estremadura. Apatite (from a^ardta, to cheat, 
 in allusion to mistakes in its early analysis) occurs in prismatic crystals, 
 and is met with in the Cornish tin-veins. Both these minerals are 
 largely imported from Spain, Norway, and America, for use in this 
 country as a manure. 
 
 Coprolites (/compos, dung, Ai'0os, a stone, from the idea that they were 
 petrified dung) are rounded nodules of phosphate of lime, which are 
 found abundantly in this country. 
 
 Large quantities of phosphoric acid, combined with lime and magnesia, 
 are imported in the form of guano, the partially decomposed excrement of 
 sea-fowl, which sometimes contains one-fourth of its weight of phosphoric 
 acid. 
 
 Bones, however, must be regarded as the chief immediate source whence 
 the phosphate of lime for agricultural purposes is derived. 
 
 Hydrated phosphoric acid is obtained from bone-ash by decomposing it 
 with sulphuric acid, so as to remove as much of the lime as possible in 
 the form of sulphate, which is strained off, and the acid liquid neutralised 
 with carbonate of ammonia, which precipitates any unchanged phosphate 
 of lime, and converts the phosphoric acid into phosphate of ammonia, 
 consisting of phosphoric acid, water, and ammonia. On evaporating the 
 solution, and heating the phosphate of ammonia, the ammonia is expelled, 
 and hydrated phosphoric acid (HO . P0 5 ) is left in a fused state, solidifying 
 to a glass on cooling. Thus prepared, however, it always retains some 
 ammonia, and is contaminated with soda derived from the bones. 
 
 The pure hydrated acid is prepared by oxidising phosphorus with 
 diluted nitric acid (sp. gr. 1'2), and evaporating the solution in a platinum 
 dish, until the hydrated phosphoric acid begins to volatilise in white 
 fumes 
 
 5(HO . 
 
 Fig. 205. 
 
 Some phosphorous acid is formed at an intermediate stage. A transparent 
 glass (glacial phosphoric acid) is thus obtained, which eagerly absorbs 
 moisture from the air, and becomes liquid. 
 
PHOSPHOKIC ANHYDRIDE. 
 
 231 
 
 The water cannot be separated from the hydrated phosphoric acid by 
 the action of heat, so that the anhydrous phosphoric acid must be pre- 
 pared by burning phosphorus in dry air. 
 
 When required in considerable quantity, the anhydrous phosphoric acid (phos- 
 phoric anhydride) is prepared by burning the phosphorus in a small porcelain dish 
 (A, fig. 205) attached to a wide glass tube (B) for introducing the phosphorus, and 
 suspended in a glass flask with two lateral necks, one of which is connected with a 
 tube containing pumice-stone and oil of vitriol for drying the air as it enters, whilst 
 the other neck is provided with a wide tube conveying the anhydrous phosphoric 
 acid into a bottle connected, at C, with an aspirator, or cistern of water, for drawing 
 air through the apparatus. The first piece of phosphorus is kindled by passing a 
 hot wire down the wide tube, but afterwards the heat of the dish will always ignite 
 the fresh piece as it is dropped in. The wide tube must be closed with a cork whilst 
 the phosphorus is burning. 
 
 A small quantity of anhydrous phos- 
 phoric acid is more conveniently prepared 
 by burning phosphorus under a large bell- 
 jar of air, under which a shallow dish of 
 oil of vitriol has been standing for an hour 
 or two to dry the air. This dish is care- 
 fully removed without disturbing the air 
 within the jar, and the well-dried phos- 
 phorus is introduced in a small porcelain 
 crucible standing upon a large glass plate. 
 The phosphorus having been kindled with 
 a hot wire, the flakes of phosphoric acid 
 will be seen falling like snow on to the glass 
 plate, where they accumulate in a layer of 
 considerable thickness. To preserve it, 
 
 Fig. 206. 
 
 the phosphoric acid must be immediately scraped up with a bone or platinum knife 
 and thrown into a thoroughly dry stoppered bottle. 
 
 Anhydrous phosphoric acid may be fused at a very high temperature, 
 and even sublimed. Its -great feature is its attraction for water ; left 
 exposed to the air for a very short time, it deliquesces entirely, becoming 
 converted into" hydrated phosphoric acid. It is often used by chemists as 
 a dehydrating agent, and will even remove the water from oil of vitriol. 
 When thrown into water, it hisses like a red-hot iron, but does not entirely 
 dissolve at once, a few flakes of hydrated phosphoric acid remaining 
 suspended in the liquid for some time. Phosphoric acid, like sulphuric 
 acid, forms three definite combinations with water, but in the case of 
 phosphoric acid, each of these three hydrates is a different acid, capable 
 of producing diiferent salts, whereas the sulphuric acid generates the same 
 salts in whateyer degree of hydration it is employed. 
 
 The solution obtained by dissolving anhydrous phosphoric acid in 
 water contains monohydrated phosphoric acid or metaphosphoric acid 
 (HO . P0 5 ). If a little nitrate of silver be added to a portion of it, a 
 transparent gelatinous precipitate is formed, which is the metaphosphate 
 of silver (AgO . N0 5 + HO . P0 5 = HO . N0 5 + AgO . P0 5 ). 
 
 If the solution of metaphosphoric acid be heated in a flask for, a short 
 time, it will lose the property of yielding a precipitate with nitrate of 
 silver, unless one or two drops of ammonia be added to neutralise it, when 
 an opaque white precipitate of pyrophosphate of silver (2AgO . P0 5 ) is 
 obtained, for the phosphoric acid has now been converted into the 
 dihydmted or pyrophosphoric acid (2HO . P0 5 ). The formation of the 
 precipitate is thus expressed 
 
 2110 . P0 5 + 2(AgO . 1S T 5 ) + 2NH, - 2AgO . P0 5 + 2(NH 3 . HO . 
 
232 PYROPHOSPHORIC AND ORTHO-PHOSPHORIC ACIDS. 
 
 When the solution of pyrophosphoric acid is mixed with more water 
 and boiled for a long time, it gives, when tested with nitrate of silver 
 and a little ammonia, a yellow precipitate of triphosphate of silver 
 (3AgO . PO 5 ) ; the phosphoric acid having "become converted into tri- 
 hydrated phosphoric acid (3HO . P0 5 ), and acting upon the nitrate of silver 
 in the presence of ammonia, thus 
 
 3HO . P0 5 + 3(AgO . N0 5 ) + 3^H = 3AgO . P0 5 + 3(NH 3 . HO . 
 
 The pyrophosphoric acid (2HO . P0 5 ) cannot be obtained by the above 
 process without an admixture of one of the other hydrates, but it has 
 been obtained in crystals by decomposing the pyrophosphate of lead 
 (2PbO.P0 5 ) with hydrosulphuric acid, and evaporating the filtered 
 solution in vacua over oil of vitriol. 
 
 Trihydrated phosphoric acid may also be obtained in prismatic crystals, 
 by evaporating its solution in a similar way. This acid is also called 
 ortho-phosphoric acid (6p0b<s, true), and common phosphoric acid, in allusion 
 to the circumstance that the phosphates commonly met with and employed 
 in the arts are the salts of this acid. 
 
 For it will be perceived that each of these acids is able to combine with 
 a quantity of base equivalent to the water present in the hydrate. Thus 
 the rnetaphosphoric acid (HO . P0 5 ) is monobasic, or forms salts with one 
 equivalent of a base having the general formula MO, as in metaphosphate 
 of soda, NaO . P0 5 . Pyrophosphoric acid (2HO . P0 6 ) is dibasic (or 
 bibasic), forming salts with two equivalents of a basic protoxide, as in 
 pyrophosphate of soda, 2NaO . P0 3 . Common phosphoric acid (3HO . P0 5 ) 
 is tribasic, forming salts with three equivalents of a basic protoxide, as in 
 triphosphate (or subphosphate) of soda, 3NaO . P0 5 . 
 
 In the cases of pyrophosphoric and common phosphoric acids, it is not 
 necessary that the two or three equivalents of water should be displaced by 
 the same base, for it is found that salts of these acids may be formed which 
 contain two bases, and some in which part of the water does duty as a base. 
 Examples of this kind are, the common phosphate of soda, 2ISraO . HO . P0 5 , 
 which is derived from the tribasic acid, 3HO . P0 5 , by the displacement 
 of two equivalents of water by soda ; microcosmic salt, or phosphate of 
 soda and ammonia, NaO . NH 4 . HO . P0 5 , where two equivalents of 
 the water % in the tribasic acid are displaced respectively by soda and by 
 the imaginary oxide of ammonium (NH 4 0). A 
 pyrophosphate of soda having the composition 
 JS"aO . HO . P0 5 may be prepared, and is obviously 
 derived from the dibasic acid, 2HO . P0 5 , by 
 the displacement of one equivalent of water by 
 soda. 
 
 It is evident that when water or ammonia enters 
 into the composition of the salt, the action of heat 
 may convert a tribasic phosphate into a pyrophos- 
 phate, or even into a metaphosphate. 
 
 Thus, if a crystal of the common rhombic phosphate 
 of soda (2NaO . HO . P0 5 + 24Aq.) be heated gently in a 
 Fig. 207. crucible (fig. 207), it melts in its water of crystallisation, 
 
 and gradually dries up to a white mass, the composition of 
 
 which, if not heated beyond 300 F., will be 2NaO . HO . P0 5 . If a little of this 
 white mass be dissolved in water, the solution will be alkaline to red litmus paper ; 
 and if nitrate of silver (itself neutral to test-papers) be added to it, a yellow 
 
PHOSPHOROUS ACID. 233 
 
 precipitate of triphosphate of silver will be obtained, and the solution will become 
 strongly acid 
 
 2NaO.HO.P0 5 + 3(AgO.N0 5 ) = 3AgO.P0 5 + 2(NaO.N0 5 ) + HO.N0 5 . 
 
 If the dried phosphate of soda be now strongly heated over a lamp, it will lose its 
 basic water, and become pyrophosphate of soda ( fire). On dissolving this in 
 water, the solution will be alkaline, and will give with nitrate of silver a white preci- 
 pitate and a neutral solution 
 
 2NaO . P0 5 + 2(AgO . N0 5 ) = 2AgO . P0 5 + 2(NaO . N0 5 ) . 
 
 Microcosmic salt (NaO . NH 4 . HO . P0 5 + 8Aq), when dissolved in water, yields 
 an alkaline solution which gives a yellow precipitate with nitrate of silver, the liquid 
 becoming acid 
 
 NaO.NH 4 O.HO.P0 5 + 3(AgO.N0 5 ) = 3AgO.P0 5 + NaO.N0 5 + NH 4 O.N0 6 + HO.NO. 
 
 But if the salt be heated in a crucible, it fuses, evolving water and ammonia, and 
 leaving a transparent glass of metaphosphate of soda (NaO . P0 5 ), which may be dis- 
 solved by soaking in water, yielding a slightly acid solution, which gives a white 
 gelatinous precipitate with nitrate of silver, the liquid being neutral 
 
 NaO . P0 5 + AgO . N0 5 = AgO . P0 5 + NaO . N0 5 . 
 
 The crystallised metaphosphate of soda retains 1 eq. of water when dried at 
 212 F., becoming NaO . P0 5 + HO. On heating this to 300 F., the salt is con- 
 verted into the acid pyrophosphate of soda, NaO . HO . P0 3 , the water having 
 assumed a basic character in the salt. 
 
 All the phosphates may be converted into tribasic phosphates, by fusing them 
 with an alkaline hydrate or carbonate.* 
 
 Composition of phosphoric acid. When anhydrous phosphoric acid is 
 dissolved in water, forming metaphosphoric acid, a quantity of the solu- 
 tion containing 71 parts by weight of the anhydrous acid is required to 
 neutralise 1 eq. (31 parts) of soda (NaO), forming metaphosphate of soda. 
 71 parts of phosphoric acid have been found to be produced by burning 
 31 parts of pure phosphorus in dry air; hence (71 minus 31) 40 parts of 
 oxygen or 5 eqs. are combined with 31 parts of phosphorus to form 71 
 parts (1 eq.) of phosphoric acid. 
 
 166. Phosphorous acid (P0 3 ) is the product of the slow combustion of phosphorus. 
 If a piece of phosphorus be heated in a long glass tube, into which a very slow cur- 
 rent of dry air is drawn through a very narrow tube, it burns with a pale blue flame, 
 and white flakes of anhydrous phosphorous acid are deposited. Phosphorous acid 
 is more easily converted into vapour than phosphoric acid. It eagerly absorbs mois- 
 ture from the air, and is decomposed when strongly heated in a sealed tube, yielding 
 free phosphorus and phosphoric acid ; 5P0 3 = 3P0 5 + P 2 . 
 
 Hydrated phosphorous acid is obtained in solution, mixed with phosphoric acid, 
 when sticks of phosphorus arranged in separate tubes, open at both ends, and 
 placed in a funnel over a bottle, are exposed under a bell-jar, open at the top, to air 
 saturated with aqueous vapour. To obtain the pure acid, chlorine is very slowly 
 passed through phosphorus fused under water, when the terchloride of phosphorus 
 first formed is decomposed by the water into phosphorous and hydrochloric acids ; 
 PC1 3 + 6HO = 3HO . P0 3 + 3HC1. The hydrochloric acid is expelled by a mode- 
 rate heat, when the hydrated phosphorous acid is deposited in prismatic crystals. 
 The water cannot be separated from phosphorous acid by heat ; when the hydrate 
 is heated, it is decomposed into hydrated phosphoric acid and gaseous phosphuretted 
 hydrogen ; 4(3HO . P0 3 ) = 3(3HO . P0 5 ) + PH 3 . 
 
 Solution of phosphorous acid gradually absorbs oxygen from the air, becoming 
 phosphoric acid. This tendency to absorb oxygen causes it to act as a reducing 
 agent upon many solutions ; thus it precipitates finely-divided metallic silver from 
 
 * It has been remarked that the pliancy of the acid character of phosphoric acid parti- 
 cularly fits it to take part in the vital phenomena. It may be regarded as three acids 
 
234 HYPOPHOSPHOKOUS ACID. 
 
 a solution of the nitrate, by which its presence may be recognised in the water in 
 which ordinary phosphorus has been kept. The solution of phosphorous acid even 
 reduces sulphurous acid, producing sulphuretted hydrogen and sulphur, the latter 
 being formed by the action of the sulphuretted hydrogen upon the sulphurous acid ; 
 2S0 2 + 2HO + 3(3HO . P0 3 ) = 2HS + 3(3HO . P0 6 ). 
 
 Phosphorous acid was formerly supposed to be a tribasic acid like common phos- 
 phoric acid, but it has not been found possible to combine it with more than two 
 equivalents of a basic protoxide. Thus, when solution of phosphorous acid is mixed 
 with a slight excess of solution of soda, and carefully evaporated, crystals are depo- 
 sited which have the composition 2NaO . P0 3 + 11HO. From these crystals, how- 
 ever, only 10 eqs. of water can be separated, even at 570 F., leading to the belief 
 that the elements of the last equivalent of water really belong to the acid itself, 
 and that the true formula of the phosphite of soda dried at that temperature is 
 2NaO . HO . P0 3 , or 2NaO . PH0 4 . In support of this view, it is to be desired that 
 the compound PH0 4 or HO . P0 3 should be obtained in a separate state. Granting 
 that phosphorous acid is dibasic, it should form, like dibasic phosphoric acid, two 
 classes of salts ; accordingly, we find the acid phosphites containing only one equi- 
 valent of base, the absent equivalent being represented by water. Thus, acid phos- 
 phite of baryta dried at 212 F. has the composition BaO . 2HO . P0 3 , or (allowing 
 the existence of PH0 4 ) BaO . HO . PH0 4 . When heated, the phosphites are con- 
 verted into phosphates at the expense of the oxygen of the water contained in them, 
 the hydrogen being evolved, often accompanied by phosphuretted hydrogen. 
 
 167. Eypophosphorous acid. The anhydrous hypophosphorous acid is at present 
 entirely imaginary. When phosphorus is boiled with hydrate of baryta and water, 
 the latter is decomposed, its hydrogen combining with part of the phosphorus to 
 form phosphuretted hydrogen (spontaneously inflammable), which escapes, whilst 
 the oxygen of the water unites with another part of the phosphorus, forming hypo- 
 phosphorous acid, which combines with baryta and water to form hypophosphite of 
 baryta ; this may be obtained by evaporating the solution, in crystals having the 
 composition BaO . 2HO . PO. The action of phosphorus upon hydrate of baryta may 
 be represented by the equation 
 
 3(BaO.HO) + 6HO + P 4 = 3(BaO . 2HO . PO) + PH 3 . 
 Hydrate of Hypophosphite of Phosphuretted 
 
 baryta. baryta. hydrogen. 
 
 Some phosphate of baryta (3BaO.P0 5 ) is also formed at the same time, as tbe 
 result of a secondary action. 
 
 By dissolving the hypophosphite of baryta in water, and decomposing it with the 
 requisite quantity of sulphuric acid, so as to precipitate the baryta as sulphate, a 
 solution is obtained which may be concentrated by careful evaporation till it has 
 the composition represented by the formula 3HO . PO. If this hydrated hypophos- 
 phorous acid be heated, it evolves phosphuretted hydrogen, and becomes converted 
 into hydrated phosphoric acid ; 2(3HO . PO) = 3HO . P0 5 + PH 3 . When exposed 
 to the air it absorbs oxygen, and becomes converted into phosphorous and phos- 
 phoric acids. It is a more powerful reducing agent than phosphorous acid. The 
 latter acid does not reduce a solution of sulphate of copper, but hypophosphorous 
 acid, when gently warmed with it, gives a black precipitate of subhydride of copper 
 (Cu 2 H), which is decomposed by boiling, evolving hydrogen and leaving metallic 
 copper. 
 
 The composition of the hydrated hypophosphorous acid (3HO . PO) formerly led 
 to the belief that this acid was tribasic, but it is found incapable of generating salts 
 which contain more than 1 eq. of basic protoxide. These always retain the elements 
 of 2 eqs. of water, even though exposed to a high temperature. Thus the dried 
 hypophosphite of baryta contains BaO . 2HO . PO. Hence it is often represented as 
 BaO . PH 2 3 ,when the hydrated acid would be HO . PH 2 3 (= 3HO . PO), and would 
 be a monobasic acid like metaphosphoric acid. When heated, the hypophosphites 
 evolve phosphuretted hydrogen, and are converted into phosphates. The hypophos- 
 phite of soda (NaO . PH 2 3 ) is sometimes used in medicine ; its solution has been 
 known to explode with great violence during evaporation, probably from a sudden 
 disengagement of phosphuretted hydrogen. 
 
 It will be noticed that the phosphites may be represented as pyrophosphates, in 
 which 1 eq. of oxygen in the phosphoric acid has been displaced by hydrogen. Thus, 
 if in pyrophosphate of soda (2NaO . P0 5 ) one equivalent of oxygen in the acid be dis- 
 placed by hydrogen, it would give phosphite of soda (2NaO . PH0 4 ), and in a similar 
 
COMPOUNDS OF PHOSPHOKUS WITH HYDROGEN. 
 
 235 
 
 manner, hypophosphite of soda (NaO .PH 2 3 ) may be represented as derived from 
 metaphosphate of soda (NaO . P0 5 ) by the displacement of two equivalents of oxygen 
 in the acid by hydrogen. 
 
 168. Suboxide of phosphorus is supposed to constitute the yellow or red residue 
 which is left in the dish when phosphorus 
 burns in air, but it is always mixed with much 
 phosphoric acid. If phosphorus be melted 
 under water in a flask (fig. 208), and oxygen 
 gas be allowed to bubble through it (a brass 
 tube being employed to convey the oxygen), 
 each bubble of the gas produces a brilliant 
 flash, and the phosphorus is converted into 
 red flakes, which were believed to be suboxide 
 of phosphorus, but are probably amorphous 
 phosphorus. The true suboxide of phosphorus 
 (P 2 0) appears to be formed when small pieces 
 of phosphorus are covered with terchloride of 
 phosphorus, exposed to the air, and afterwards 
 heated with water, when the suboxide is deposited as a yellow powder, becoming 
 red at high temperatures, and inflaming when heated in air. 
 
 Fig. 208. 
 
 PHOSPHIDES OF HYDROGEN. 
 
 169. Although, phosphorus and hydrogen do not combine directly, 
 there are three compounds of these elements producible by processes of 
 substitution, the composition of which is shown in the following table : 
 
 Name. 
 
 Equivalent Formula. 
 
 By Weight. 
 
 Phosphorus. 
 
 Hydrogen. 
 
 Phosphuretted hydrogen gas . . . 
 Liquid phosphide of hydrogen . . 
 Solid phosphide 
 
 PH 3 
 PH a 
 P 2 H? 
 
 31 
 31 
 
 62 
 
 3 
 2 
 1 
 
 Phosphuretted hydrogen gas is by far the most important of these, 
 has been mentioned above as re- 
 sulting from the action of heat upon 
 hydrated phosphorous acid, and when 
 prepared by this process it is ob- 
 tained as a colourless gas, with a 
 most powerful odour of putrid fish, 
 inflaming on the approach of a light, 
 and burning with a brilliant white 
 flame, producing thick clouds of 
 phosphoric acid. It is slightly 
 heavier than air (sp. gr. 1*19), and 
 has been liquefied under high pres- 
 sure. 
 
 The ordinary method of preparing this JT=^^ 
 
 gas for experimental purposes consists in ". ."^^ r ^ 
 
 boiling phosphorus with a strong solution ^ 209 
 of potash, when water is decomposed, its 
 hydrogen combining with one part of the 
 
 It 
 
 Preparation of phosphuretted 
 hydrogen. 
 
 11 J ^AU^r/lJ. UUliJ.IL/lAAJ.JJ.j " * -^^ ^*~~ 
 
 phosphorus, and its oxygen with another part forming hypophosphorous acid, which 
 unites with the potash. 
 
236 GASEOUS PHOSPHURETTED HYDROGEN. 
 
 A few fragments of phosphorus are introduced into a small retort (fig. 209), 
 which is then nearly filled with a strong solution of potash (sp. gr. 1-3*), and 
 heated. The extremity of the neck of the retort should not be plunged under 
 water until the spontaneously inflammable gas is seen burning at the orifice, 
 and the retort must not be placed close to the face of the operator, since explo- 
 sions sometimes take place in preparing the gas, and the boiling potash produces 
 dangerous effects. The gas may be collected in small jars filled, with water, 
 taking care that no bubble of air is left in them. It contains phosphuretted 
 hydrogen, mixed with free hydrogen, the latter being formed from the deoxidation 
 of water by the hypophosphite of potash. As each bubble of this gas escapes into 
 the air through the water of the pneumatic trough, it burns with a vivid white 
 flame, producing beautiful wreaths of smoke (phosphoric acid), resembling the 
 gunner's rings sometimes seen in firing cannon. Small bubbles sometimes escape 
 without spontaneously inflaming. If a bubble be sent up into a jar of oxygen, the 
 flash of light is extremely vivid, and the jar must be a strong one to resist the con- 
 cussion. It is advisable to add a trace of chlorine to the oxygen to insure the 
 inflammation of each bubble, for an accumulation of the gas would shatter the jar. 
 
 If this gas be passed through a tube cooled in a freezing mixture of ice and salt, 
 the gas escaping from the tube is found to have lost its spontaneous inflammability, 
 although it takes fire on contact with flame. The cold tube contains the liquid 
 phosphide of hydrogen (PH 2 ), which was present in the gas in the state of vapour, and 
 caused its spontaneous inflammability, for as soon as this liquid comes in contact 
 with air it takes fire. "When exposed to light, the liquid phosphide is decomposed 
 into phosphuretted hydrogen gas and a yellow solid phosphide (P 2 H), which is not 
 spontaneously inflammable ; 5PH 2 = P 2 H + 3PH 3 . It is for this reason that the 
 spontaneously inflammable gas loses that property when kept (unless in the dark), 
 depositing the solid phosphide upon the sides of the jar. 
 
 By passing a few drops of oil of turpentine up through the water into a jar of the 
 spontaneously inflammable gas, this property will be entirely destroyed, whereas 
 the addition of a trace of nitrous acid imparts spontaneous inflammability. 
 
 Phosphuretted hydrogen, when passed through solutions of some of the metals, 
 precipitates their phosphides. For example, with sulphate of copper it gives a 
 black precipitate of phosphide of copper 
 
 3(CuO.S0 3 ) + PH a = 3(HO.S0 3 ) + PCu 3 . 
 
 When this black precipitate is heated with solution of cyanide of potassium, it 
 evolves self-lighting phosphuretted hydrogen, t In fact this is one of the easiest 
 and safest methods of preparing this gas ; for the phosphide of copper is readily ob- 
 tained by simply boiling phosphorus in a solution of sulphate of copper. 
 
 Phosphuretted hydrogen has great pretensions to rank as the chemical analogue 
 of ammonia, for although it has no alkaline properties, it is capable of combining 
 with hydrobromic and hydriodic acids to form crystalline compounds analogous to 
 the hydrobromate and hydriodate of ammonia ; these compounds, however, are de- 
 composed by water. It will be seen hereafter, that when the hydrogen of phos- 
 phuretted hydrogen is displaced by certain compound radicals, such as ethyle, power- 
 ful organic bases are produced. 
 
 The spontaneously inflammable phosphuretted hydrogen may also be obtained 
 by throwing fragments of phosphide of calcium into water ; this substance is pre- 
 pared by passing vapour of phosphorus over red-hot quick-lime, or simply by heat- 
 ing small lumps of quick-lime to redness in a crucible and throwing in fragments 
 of phosphorus, closing the crucible immediately. The dark brown mass thus 
 obtained is a mixture of pyrophosphate of lime and phosphide of calcium of some- 
 what variable composition. 
 
 1 70. Composition of phosphuretted hydrogen gas. Analysis has shown 
 this gas to contain 31 parts by weight of phosphorus combined with 3 
 parts by weight of hydrogen, or 1 eq. of phosphorus and 3 eqs. of hydro- 
 gen. It combines with an equal volume of hydriodic acid gas, and the 
 compound is found to contain 34 parts by weight of phosphuretted hydro- 
 
 * 450 grains of common stick potash dissolved in 1000 grains of water, 
 t Cyanide of copper and phosphide of potassium being formed, and the latter de- 
 composed by water, giving phosphuretted hydrogen, and hypophosphite of potash. 
 

 COMPOUNDS OF PHOSPHORUS WITH CHLORINE. 237 
 
 gen, and 128 parts (1 eq.) of hydriodic acid. But 1 eq. of hydriodic acid 
 occupies 4 vols. (0 = 1 vol.), therefore 1 eq. of phosphuretted hydrogen 
 occupies 4 vols. The specific gravity of the gas (or weight of 1 vol.) 
 being M85, the weight of 4 vols. will be 4'740. But 3 eqs. of hydrogen 
 occupy 6 vols. 
 
 4 vols. PH 3 weigh, ..... 4'740 
 6 vols. H (.069 x 6) .... -414 
 
 Weight of phosphorus vapour, . . . 4 '32 6 
 
 contained in 4 vols. PH 3 . The specific gravity of phosphorus vapour is 
 4 '50, so that, allowing for errors of experiment, the above number repre- 
 sents 1 vol. of the vapour. 
 
 1 eq. or 4 vols. of PH 3 , therefore, contain 1 eq. or 1 vol. of phosphorus 
 vapour, and 3 eqs. or 6 vols. of hydrogen. "Unfortunately this is not 
 analogous to the composition of ammonia (NH 3 ), in which the 1 eq. of 
 nitrogen occupies 2 vols. The molecular formula of phosphuretted 
 hydrogen, on the assumption that 1 vol. of vapour of phosphorus repre- 
 sents one atom, would, of course, be PH 6 , but the chemical resemblance 
 between that substance and ammonia is so great,* that preference is given 
 to the molecular formula PH 3 (=2 vols.), when P represents only J vol. 
 of vapour (H = 1 vol.), it being hoped that future investigation may re- 
 move the anomaly. When phosphuretted hydrogen is decomposed by a 
 succession of electric sparks, 2 vols. of the gas yield 3 vols. of hydrogen, 
 red phosphorus being deposited. Assuming 31 to represent the atomic 
 weight of phosphorus, the atomic formula of anhydrous phosphoric acid 
 would be P 2 O 5 (0 = 16), and that of the trihydrated or common phos- 
 phoric acid H 3 PO 4 . 
 
 171. The chlorides of phosphorus correspond in composition to phosphorous and 
 phosphoric acids. The terchlnride (PC1 3 ) is prepared by acting upon phosphorus 
 with perfectly dry chlorine in the apparatus employed (p. 219) for preparing the 
 dichloride of sulphur. Terchloride of phosphorus distils over very easily (boiling 
 point, 173-4 F.), as a colourless pungent liquid (sp. gr. 1'62), which fumes strongly 
 in air, its vapour decomposing the moisture of the air and producing hydrochloric 
 
 acid fumes. In contact with water the liquid is immediately decomposed, yielding 
 
 described for the p 
 acid (p. 233). Its analogy to anhydrous phosphorous acid is shown by its absorb- 
 
 hydrochloric and phosphorous acids, as described for the preparation of the latter 
 
 ing oxygen when boiled in the presence of that gas, and forming the oxychloride of 
 phosphorus (PC1 3 2 ), corresponding in composition to anhydrous phosphoric acid. It 
 also absorbs chlorine with avidity, becoming converted into pentachloride of phosphorus 
 (PC1 5 ). This compound, however, is more conveniently prepared by passing 
 chlorine through a solution of phosphorus in bisulphide of carbon, carefully cooled. 
 On evaporation, the pentachloride of phosphorus is deposited in white pjrismatic 
 crystals, which volatilise below 212 F., and fume when exposed to air, from the pro- 
 duction of hydrochloric acid. When thrown into water it is decomposed into phos- 
 phoric and hydrochloric acids ; PC1 5 + 8HO = 3HO . P0 5 + 5HC1. But if it be 
 allowed to deliquesce in air, only a partial decomposition takes place, and the 
 oxychloride of phosphorus is formed ; PC1 5 + 2HO = PC1 3 2 + 2HC1. 
 
 This oxychloride of phosphorus may also be produced by heating pentachloride 
 of phosphorus with anhydrous phosphoric acid ; 2P0 5 + 3PC1 5 = 5PC1 3 O 2 . A 
 more instructive method of preparing it consists in distilling the pentachloride of 
 phosphorus with crystallised boracic acid 
 
 3PC1 5 + 2(3HO.B0 3 ) = 3PC1 3 2 + 6HC1 + 2B0 3 . 
 Some of the hydrated organic acids (succinic, for example) may be obtained in 
 
 wei 
 
 Moreover, the specific heat of phosphorus agrees much more closely with an atomic 
 *ht of 31 (= vol.) than with 62 (= 1 vol.) 
 
238 ACTION OF IODINE ON PHOSPHORUS. 
 
 the anhydrous state, as the boracic acid is in this case, by distillation with penta- 
 chloride of phosphorus. The oxychloride of phosphorus distils over (boiling-point, 
 230 F.) as a heavy (sp. gr. 1-7) colourless fuming liquid of pungent odour. Of 
 course it is decomposed by water, yielding hydrochloric and phosphoric acids. It 
 will be found of the greatest use in effecting certain transformations in organic sub- 
 stances. 
 
 The analogy between water and hydrosulphuric acid would lead to the expecta- 
 tion that a sulphochloride of phosphorus (PC1 3 S 2 ), corresponding to the oxychloride, 
 would be formed by the action of hydrosulphuric acid upon pentachloride of phos- 
 phorus ; P01 5 + 2HS = PC1 3 S 2 + 2HC1. It is a colourless fuming liquid, which 
 is slowly decomposed by water, giving phosphoric, hydrochloric, and hydrosulphuric 
 acids; PC1 3 S 2 + 8HO = 3HO.P0 6 + 3HC1 + 2HS. When acted on by solu- 
 tion of soda, the sulphochloride of phosphorus loses its chlorine to the so'dium, 
 and acquires an equivalent quantity of oxygen, a sulphoxy -phosphate of soda 
 (3NaO . P0 3 S 2 + 24HO) being deposited in crystals. This salt evidently corre- 
 sponds in composition to the triphosphate of soda (3NaO . P0 5 + 24HO), and its pro- 
 duction is expressed by the equation ; PC1 3 S 2 + 6NaO = 3NaCl + 3NaO . P0 3 S 2 . 
 Since salts of similar composition may be obtained with other metallic oxides, there 
 probably exists a sulphoxy-phosphoric acid (P0 3 S 2 ) corresponding to phosphoric 
 acid. 
 
 The terchloride of phosphorus (PC1 3 ) contains 1 vol. of phosphorus vapour and 
 6 vols. of chlorine, condensed into the space of 4 vols. (0 = ] vol.), its vapour 
 density being 4-875. 
 
 The pentachloride (PC1 5 ) having a vapour density of 3-654, contains 1 vol. of 
 phosphorus vapour and 10 vols. of chlorine condensed into 8 vols. of pentachloride 
 of phosphorus vapour.* 
 
 In the oxychloride of phosphorus (PC1 3 2 ), however, 1 vol. of phosphorus vapour, 
 6 vols. of chlorine, and 2 vols. of oxygen, are condensed into 4 vols., the specific 
 gravity of its vapour being 5-29. 
 
 The composition by volume of the sulphochloride (PC1 3 S 2 ) corresponds to that of 
 the oxychloride, 2 vols. of sulphur vapour (at 1900 F.) occupying the place of the 
 2 vols. of oxygen, so that the specific gravity of the vapour of sulphochloride of phos- 
 phorus is 5-878. 
 
 The bromides and oxybromide of phosphorus correspond to the chlorine compounds. 
 
 Iodine in the solid state combines very energetically with phosphorus, but if the 
 two elements be brought together in a state of solution in bisulphide of carbon, a 
 more moderate action ensues, and two iodides of phosphorus may be obtained in crys- 
 tals ; a teriodide (PI 3 ) corresponding to the terchloride, and a biniodide (PI 2 ), 
 which has no analogue either among the oxygen, chlorine, or bromine compounds 
 of phosphorus. 
 
 The addition of a very small quantity of iodine to ordinary phosphorus, fused in a 
 flask filled with carbonic acid gas, materially accelerates its conversion into the red 
 modification, and allows the change to be effected at a much lower temperature 
 than that required when the phosphorus is heated alone. This has been ascribed 
 to the disposition of the electro -negative iodine to cause the phosphorus to assume 
 the positive or amorphous state when entering into combination with it ; this com- 
 pound being decomposed by heat with separation of amorphous phosphorus, the 
 iodine combines with a fresh portion of the phosphorus, which is converted in the 
 same way. 
 
 172. The sulphides of phosphorus may be formed by the direct combination of their 
 elements. If ordinary phosphorus be used, the experiment is not unattended with 
 danger, and should be performed under water. It is safer to combine the amor- 
 phous phosphorus with sulphur, at a moderate heat, in an atmosphere of carbonic 
 acid. 
 
 There appear to be at least three sulphides of phosphorus corresponding to the 
 oxides, viz., the protosulphide (PS) corresponding to the imaginary anhydrous hypo- 
 phosphorous acid (PO), the tersulphide (PS 3 ), representing phosphorous acid (P0 3 ), 
 and the pentasulphide (PS 5 ), analogous to phosphoric acid (P0 5 ). 
 
 * This is an exception to the rule, that the equivalents of compound vapours usually 
 occupy 4 vols. (0 = 1 vol.) But it appears that, at the temperature (572 F.) at which 
 the vapour density of pentachloride of phosphorus is determined, it undergoes dissocia- 
 tion, giving a mixture of 4 vols. of terchloride of phosphorus and 4 vols. of chlorine, the 
 colour of which is visible in the tube in which the vapour is heated. 
 
PHOfcPHORlSED DERIVATIVES OF AMMONIA. 239 
 
 PS is a yellow oily liquid which may be distilled out of contact with air. 
 
 PS 3 is a yellow solid, easily fusible, and capable of subliming in a crystalline 
 form if air be excluded. It may be produced by the action of hydrosulphuric acid 
 upon terchloride of phosphorus ; PC1 3 + 3HS = PS 3 + 3HC1. 
 
 PS 3 crystallises more readily in a fused state than PS 3 . Both these sulphides, 
 unlike the protosulphide, are easily decomposed by water. All the sulphides are 
 sulphur-acids like their prototypes among the oxides of phosphorus. 
 
 173. Action of ammonia upon anhydrous phosphoric acid. Some remarkably stable 
 and definite compounds, containing nitrogen and phosphorus, are derived from the 
 action of ammonia on anhydrous phosphoric acid, and the study of their mode of 
 formation will be found to throw some light upon the history of a very large and 
 important class of organic substances known as the amides. Anhydrous phosphoric 
 acid absorbs ammoniacal gas with great evolution of heat, and produces, not phos- 
 phate of ammonia, for that cannot be formed unless water is present, but the 
 ammoniacal salt of a new acid, phosphamic acid, which contains the elements of acid 
 phosphate of ammonia (NH 4 . 2HO . P0 5 ) minus four equivalents of water 
 
 NH 3 + P0 5 = HO + NH 2 P0 4 . 
 
 Phosphamic acid. 
 
 When gently heated with water, phosphamic acid is converted into acid phosphate 
 of ammonia. 
 
 When the phosphamate of ammonia is heated in a current of dry ammonia, it 
 gives off water, and leaves a yellow insoluble substance formerly supposed to be 
 phosphide of nitrogen, but now known as phospham 
 
 NH 3 .HO.NH 2 P0 4 = 5HO + N 2 HP . 
 
 Phosphamate of ammonia. Phospham. 
 
 It is not surprising that the presence of hydrogen in this substance should have 
 been overlooked, for it may be heated to redness (out of contact with air) without 
 alteration, is unaffected by chlorine, and is very slowly acted upon by nitric acid. 
 
 Action of ammonia on oxy chloride of phosphorus. 
 
 PC1 3 2 + 8NH S = 3HC1 + N 3 H 6 P0 2 . 
 Oxychloride of Phosphotriamide. 
 
 phosphorus. 
 
 Of course the hydrochloric acid combines with the excess of ammonia to form 
 hydrochlorate of ammonia, which may be washed out with water, leaving the phos- 
 photriamide as a white insoluble solid, not easily attacked by acids or alkalies. It 
 may be regarded as triphosphate of ammonia (3NH 4 . P0 5 ) minus six equivalents 
 of water. 
 
 If sulphochloride of phosphorus be submitted to the action of ammonia, sulphos- 
 photriamide is obtained 
 
 PC1 S S 2 + 3NH 3 = 3HC1 + N 8 H 6 PS 2 . 
 
 Sulphochloride of Sulphosphotriamide. 
 
 phosphorus. 
 
 This compound may evidently be regarded as sulphophosphate of (sulphide of) 
 ammonium (3NH 4 S . PS 5 ) minus six equivalents of hydrosulphuric acid. 
 
 Action of ammonia on pentachloride of phosphorus. 
 
 PC1 5 + 2NH 3 = 2HC1 + N 2 H 4 PC1 3 . 
 
 Chlorophosphamide. 
 
 The hydrochloric acid combines with the excess of ammonia, forming hydrochlorate 
 of ammonia. By boiling chlorophosphamide with water, a very stable insoluble sub- 
 stance is obtained, known as phosphodiamide 
 
 N 2 H 4 PC1 3 + 2HO = N 2 H 3 P0 2 + 3HC1 . 
 
 Chlorophosphamide. Phosphodiamide. 
 
 This substance may be represented as derived from the phosphate of ammonia 
 (2NH 4 . HO . P0 5 ), by the abstraction of six equivalents of water. 
 
 When phosphodiamide is heated it loses ammonia and becomes monophosphamide 
 
 N 2 H 3 P0 2 = NH 3 + NP0 2 . 
 Phosphodiamide. Monophosphamide. 
 
240 OCCURRENCE OF ARSENIC IN NATURE. 
 
 which may be regarded as acid phosphate of ammonia (NH 4 . 2HO . P0 5 ) minus 
 six equivalents of water. 
 
 The phrase amides of phosphoric acid refers to those substances which may be 
 represented as derived from the phosphates of ammonia by the loss of a certain 
 number of equivalents of water ; thus 
 
 NH 4 . 2HO . P0 5 6HO = NP0 2 Monophosphamide. 
 2NH 4 . HO . P0 5 6HO = N 2 H 3 P0 2 Phosphodiamide. 
 3NH 4 O.P0 6 6HO = N 8 H 6 P0 2 Phosphotriamide. 
 
 All these substances yield ammonia and phosphate of potash when heated with 
 hydrate of potash, when they acquire the elements of water. 
 
 AKSENIC. 
 
 1 74. This element is often classed among the metals, because it has a 
 metallic lustre and conducts electricity, but it is not capable of forming a 
 base with oxygen, and the chemical character and composition of its 
 compounds connect it in the closest manner with phosphorus. 
 
 In its mode of occurrence in nature it more nearly resembles the 
 sulphur group of elements, for it is occasionally found in the uncombined 
 state (native arsenic}, but far more abundantly in combination with 
 various metals, forming arsenides, which frequently accompany the sul- 
 phides of the same metals. The following are some of the chief arsenides 
 and arsenio-sulphides found in the mineral kingdom : 
 
 Kupfernickel, Ni 2 As. 
 
 Arsenical nickel, NiAs. 
 
 Tin-white cobalt, CoAs. 
 
 Mispickel or arsenical pyrites, FeS 2 . FeAs. 
 
 Cobalt-glance, CoS 2 . CoAs. 
 
 Nickel-glance, NiS 2 . NiAs. 
 
 But arsenic also occurs, like the metals, in combination with sulphur, thus 
 we have 
 
 Red orpiment or realgar, AsS 2 . 
 Yellow orpiment, AsS 3 . 
 
 It is from these minerals that arsenic derives its name (dpo-eviKov, orpiment), 
 and the sulphides of arsenic being sulphur-acids, are found in combination 
 with other sulphides ; thus, red silver ore is a compound of the sulphides 
 of silver and arsenic (3AgS . AsS 3 ) ; Tennantite contains sulphide of 
 arsenic combined with the sulphides of iron and copper ; and grey copper 
 ore is composed of sulphide of arsenic with the sulphides of copper, silver, 
 zinc, iron, and antimony. In an oxidised form arsenic is found in condur- 
 rite, which contains arsenious acid (As0 3 ) and suboxide of copper. 
 Cobalt-bloom consists of arseniate of cobalt (3CoO . As0 5 ). 
 
 Arsenical pyrites is one of the principal sources of arsenic and its com- 
 pounds, though a considerable quantity is also obtained in the form of 
 arsenious acid as a secondary product in the working of certain ores, 
 especially those of copper, tin, cobalt, and nickel. 
 
 The substance used in the arts under the name of arsenic is really the 
 oxide of arsenic or arsenious acid (As0 3 ) ; pure arsenic itself has very few 
 useful applications, so that it is not the subject of an extensive manufac- 
 ture. It can be extracted from arsenical pyrites (FeS 2 . FeAs) by heating 
 it in earthen cylinders fitted with iron receivers, in which the arsenic con- 
 denses as a metallic-looking crust, the heat expelling it from the pyrites 
 in the form of vapour. 
 
PROPERTIES OF ARSENIC. 
 
 241 
 
 On a small scale it may be obtained by heating a mixture of arsenious acid with 
 half its weight of recently calcined charcoal in a crucible (fig. 210), the* mixture 
 being covered with two or three inches of char- 
 coal in very small fragments, and the crucible so 
 placed that this charcoal may be heated to red- 
 ness first, in order to ensure the reduction of any 
 arsenious acid which might escape from below. 
 In order to collect the arsenic, another crucible, 
 having a small hole drilled through the bottom 
 for the escape of gas, is cemented on to the first, 
 in an inverted position, with fire-clay, and pro- 
 tected from the fire by an iron plate with a hole 
 in it for the crucible. The reduction of arseni- 
 ous acid by charcoal is thus represented 
 
 As0 3 + C 8 = As + SCO . 
 
 For the sake of illustration, a small quantity 
 of arsenic may be prepared from arsenious acid 
 by a method commonly employed in testing for 
 that substance. A small tube of German glass 
 
 Fig. 210. Extraction of arsenic. 
 
 Fig. 211. Eeduction of arsenious acid. 
 
 is drawn out to a narrow point (A. fig. 211), and sealed with the aid of the blow- 
 pipe. A very minute quantity of arsenious acid is introduced into the point of the 
 tube, and a few fragments of 
 charcoal are placed in the tube 
 itself at B. The charcoal is 
 heated to redness with a blow- 
 pipe flame, and the point is 
 then heated so as to drive the 
 arsenious acid in vapour over 
 the red-hot charcoal, when a 
 shining black ring of arsenic 
 (C) will be deposited upon the 
 cooler portion of the tube. 
 
 The arsenic thus obtained 
 is a brittle mass of a dark 
 steel-grey colour and bril- 
 liant metallic lustre (sp. 
 
 gr. 5*7). It does not fuse when heated, unless in a sealed tube, since it 
 is converted into vapour at 356 F. It is not changed by exposure to air, 
 unless powdered and moistened, when it is slowly converted into arsenious 
 acid. When heated in air, it oxidises rapidly at about 160 F., giving off 
 white fumes of arsenious acid and a characteristic garlic odour (recalling 
 that of phosphorus). At a red heat it burns in air with a bluish white 
 flame, and in oxygen with great brilliancy. It is not dissolved by water 
 or any simple solvent (herein resembling the metals), but is oxidised and 
 dissolved by nitric acid. 
 
 In its chemical relations to other elements, arsenic much resembles 
 phosphorus, undergoing spontaneous combustion in chlorine, and easily 
 combining with sulphur. Like phosphorus also, it combines with many 
 metals, even with platinum, to form arsenides, and its presence often 
 affects materially the properties of the useful metals. There are some 
 reasons for believing in the existence of two allotropic forms of arsenic 
 differing in chemical activity like those of phosphorus. 
 
 Pure arsenic does not produce symptoms of poisoning till a considerable 
 period after its administration, being probably first oxidised in the stomach 
 and intestines, and converted into arsenious acid. 
 
242 AKSENIOUS ACID. 
 
 OXIDES OF ARSENIC. 
 
 175. Arsenic forms two well-defined acids with oxygen, corresponding 
 to phosphorous and phosphoric acids. 
 
 
 Equivalent 
 
 By Weight. 
 
 
 
 Arsenic. 
 
 Oxygen. 
 
 Arsenious acid, 
 
 As0 3 
 
 75 
 
 24 
 
 Arsenic acid, 
 
 As0 5 
 
 75 
 
 40 
 
 ARSENIOUS ACID. Unlike phosphorus, arsenic, when burning in air, 
 only combines with three equivalents of oxygen. Arsenious acid, or 
 white arsenic, is a very useful substance in many branches of industry. 
 It is employed in the manufacture of glass, of several colouring-matters, 
 and of shot. A large quantity is also consumed for the preparation of 
 arsenic acid and arseniate of soda ; it is, indeed, the source from which 
 nearly all the compounds of arsenic are procured. Small quantities of 
 crystalline arsenious acid are occasionally found associated with the ores 
 of nickel and cobalt. 
 
 Arsenious acid is manufactured by roasting the arsenical pyrites, chiefly 
 obtained from the mines of Silesia, in muffles or ovens, through which 
 air is allowed to pass, when the arsenic is converted into arsenious acid, 
 and the sulphur into sulphurous acid, which are conducted into large 
 chambers, in which the arsenious acid is deposited as a very fine powder. 
 The iron of the pyrites is left partly as oxide, and partly as sulphate of 
 iron. The removal of the arsenious acid from the condensing chambers 
 is a very unwholesome operation, owing to its dusty and very poisonous 
 character. The workmen are cased in leather, and protect their mouths 
 and noses with damp cloths, so as to avoid inhaling the fine powder. 
 
 This rough arsenious acid is subjected to a second sublimation on a 
 smaller scale in iron vessels, when it is obtained in the form of a semi- 
 transparent glassy mass known as vitreous arsenious acid, which gradually 
 becomes opaque when kept, and ultimately resembles porcelain. The 
 white arsenic sold in the shops is a fine powder, dangerously resembling 
 flour in appearance, but so much heavier (sp. gr. 3' 7) that it ought not to 
 be mistaken for it. When examined under the microscope, it appears in 
 the form of irregular glassy fragments, mixed with octahedral crystals. 
 Arsenious acid softens when gently heated, but does not fuse (unless in a 
 sealed tube), being converted into vapour at 380 F., and depositing in 
 brilliant octahedral crystals upon a cool surface. The experiment may be 
 made in a small tube sealed at one end, the upper part of which should 
 be slightly warmed before heating the arsenious acid, so as to prevent too 
 rapid condensation, which is unfavourable to the formation of distinct 
 crystals.* The octahedra are best examined with a binocular microscope. 
 This common poison may fortunately be still more easily recognised by 
 sprinkling it upon a red-hot coal, when a strong odour of garlic is percep- 
 tible, due to the reduction of the acid by the heated carbon ; the vapour 
 of arsenious acid itself is inodorous. The sparing solubility of arsenious 
 
 * When arsenious acid is fused in a long tube, sealed at both ends, and buried in hot 
 sand, the mass, after Cooling, is found to contain some prismatic crystals, which are also 
 sublimed on those parts of the tube which have been heated above 390 F. 
 
SOLUBILITY OF ARSENIOUS ACID. 243 
 
 acid in water is very unfavourable to its action as a poison, for, when 
 thrown into ordinary liquids, it is dissolved in very small quantity, the 
 greater part of it collecting at the bottom. Even when arsenious acid is 
 taken into the stomach in a solid state, its want of solubility delays its 
 passage into the blood sufficiently to give a better chance of antidotal 
 treatment than in the case of most other common poisons. Its compara- 
 tive insolubility is shown by its being almost tasteless. 
 
 When thrown into water, arsenious acid exhibits great repulsion for 
 the particles of that liquid, and collects in a characteristic manner round 
 little bubbles of air, forming small white globes which are not wetted by 
 the water. Even if the acid be stirred with the water, and allowed to 
 remain in contact with it for some hours, a pint of water (20 oz.) would 
 not take up more than 20 grs. of arsenious acid. The smallest dose which 
 has been known to prove fatal is 2*5 grs. If boiling water be poured 
 upon powdered arsenious acid, and allowed to remain in contact with it 
 till cold, it will dissolve about ^ of its weight (22 grs. in a pint). 
 
 When powdered arsenious acid is boiled with water for two or three 
 hours, 100 parts by weight of water may be*., made to dissolve 11 '5 parts 
 of the acid, and when the solution is allowed|fco cool, about 9 parts of the 
 acid will be deposited in octahedral crystals, feaving 2*5 parts dissolved 
 in 100 of water (219 grs. in a pint). 
 
 This great increase in the solubility of the arsenious acid by long boiling 
 with water is usually attributed to the conversion of the opaque or crys- 
 talline variety of the acid, which always composes the powder, into the 
 vitreous modification, which is the more soluble in water. Water, heated 
 with arsenious acid in a sealed tube, may be made to dissolve its own 
 weight of the acid ; as the solution cools, it first deposits prismatic crystals, 
 and afterwards the ordinary octahedral form. The solution of arsenious 
 acid is very feebly acid to blue litmus paper. 
 
 Arsenious acid dissolves abundantly in hot hydrochloric acid (a part of 
 it being converted into terchloride of arsenic), and as the solution cools, 
 part of the acid is deposited in large octahedral crystals. It is said that 
 if the vitreous acid be dissolved in hydrochloric acid, the formation of 
 these crystals will be attended by flashes of light, visible in a darkened 
 room ; but the opaque variety does not exhibit this phenomenon. 
 
 The vitreous arsenious acid has a slightly higher specific gravity than 
 the opaque form, and fuses rather more easily. The opaque variety appears 
 to be identical in its properties with crystallised arsenious acid. 
 
 Solutions of the alkalies readily dissolve arsenious acid, forming alkaline 
 arsenites, the solutions of which are capable of dissolving arsenious' acid 
 more easily than water, and deposit it in crystals on cooling. Arsenious 
 acid is sometimes deposited in prismatic crystals from its solution in 
 potash, and the same form of crystallised arsenious acid has been found 
 native. On adding a small quantity of hydrochloric acid to the solution 
 of the alkaline arsenite, a white precipitate of arsenious acid is formed. 
 
 Arsenious acid has the property of preventing the putrefaction of skin 
 and similar substances, and is occasionally employed for the preservation 
 of objects of natural history, &c. 
 
 Composition of arsenic acid and arsenious acid. The chemical resem- 
 blance between arsem'c acid and phosphoric acid is so strong as to lead to 
 the belief that they resemble each other in composition, and that, as 
 phosphoric acid is PO., so arsenic acid must be represented by As0 5 . 
 Analyses have shown that in arsenic acid the 5 equivalents (40 parts by 
 
 Q 2 
 
244 BASICITY OF ARSENIOUS ACID. ARSENITES. 
 
 weight) of oxygen are combined with 75 parts by weight of arsenic, and 
 this number may be assumed to represent the equivalent of arsenic. In 
 arsenious acid it is found that 75 parts of arsenic are combined with 24 
 parts of oxygen, or 3 equivalents, and hence that acid may be represented by 
 the formula As0 3 , rendering it the analogue of anhydrous phosphorous acid. 
 
 The specific gravity, or weight of 1 volume of As0 3 vapour '= 13-85 
 Deducting that of vapour of arsenic, = 10-60 
 
 3-25 
 
 the difference represents nearly the weight of 3 volumes (1-1057 x 3) 
 of oxygen. Hence, 1 volume of arsenious acid vapour contains 1 volume 
 of vapour of arsenic and 3 volumes of oxygen, and the equivalent volume 
 of arsenic is 1, like that of phosphorus. The molecular formula of 
 arsenious acid should be (A:s0 3 ) 2 , according to the experimental results 
 stated above, representing 2 volumes of its vapour, the symbol As standing 
 for 1 volume or 1 atom of arsenic (150 parts by weight), and O 3 for 3 
 volumes of oxygen (48 parts by weight) ; but since the specific heat of 
 arsenic indicates 75 as its atomic weight, the molecular formula of arsenious 
 acid is generally written (As 2 3 ) 2 , 1 atom of arsenic vapour being taken 
 to occupy J volume. 
 
 The atomic formula of arsenic acid would then be written As 2 5 . 
 
 Arsenites. Arsenious acid does not destroy the alkaline reaction of the 
 alkalies, and it does not decompose the alkaline carbonates unless heat is 
 applied, proving it to be a feeble acid. The arsenite of ammonia is very 
 unstable, evolving ammonia freely when exposed to the air. When 
 arsenious acid is dissolved in a hot solution of ammonia, octahedral crys- 
 tals of the acid are deposited on cooling, notwithstanding the presence of 
 ammonia in large excess. 
 
 When the carbonates of potash and soda are fused with an excess of 
 arsenious acid, brilliant transparent glasses are obtained which are similar 
 in composition to glass of borax (KO . 2 As0 3 and NaO . 2As0 3 ). 
 
 If an alkaline arsenite be fused in contact with platinum, the latter is 
 easily melted, combining with a small proportion of arsenic to form a 
 fusible arsenide of platinum, a portion of the arsenious acid being con- 
 verted into arsenic acid ; 5 As0 3 = 3As0 5 + As 2 . The alkaline arseniates 
 are so much more stable than the arsenites, that the latter exhibit a great 
 tendency to pass into the former, with separation of arsenic. 
 
 In consequence of the feeble acid character of arsenious acid, and the 
 want of stability of the alkaline arsenites, there is some difficulty in ascer- 
 taining whether it is a monobasic acid or otherwise. The arsenite of 
 silver (3AgO . As0 3 ), however, contains 3 eqs. of oxide of silver (348 
 parts) combined with 1 eq. (99 parts) of arsenious acid ; and arsenite of 
 zinc (3ZnO. AsOa) contains 3 eqs. of oxide of zinc (122 -1 parts) com- 
 bined with 1 eq. of arsenious acid. Moreover, the arsenite of magnesia, 
 dried at 400 F., has the composition 2MgO . HO . As0 3 , so that arsenious 
 acid would appear to be a tribasic acid, though there are not wanting 
 arsenites, the composition of which would support the view that arsenious 
 acid ought to be represented, like phosphorous acid, as a bibasic acid of 
 the formula 2HO . AsH0 4 . No compound of the anhydrous acid with 
 water or its elements has yet, however, been obtained. 
 
 The arsenites of potash and soda in solution are sometimes employed 
 as sheep-dipping compositions; and an arsenical soap, composed of arsenite 
 
ARSENIC ACID. 245 
 
 of potash, soap, and camphor, is used by naturalists to preserve the skins 
 of animals. Arsenite of soda is also occasionally employed for preventing 
 incrustations in steam-boilers, being prepared for that purpose by dissolving 
 2 eqs. of arsenious acid in 1 eq. of carbonate of soda. 
 
 Sclieele's green is an arsenite of copper (2CuO . HO . As0 3 ) prepared by 
 dissolving arsenious acid in a solution of carbonate of potash, and decom- 
 posing the arsenite of potash thus produced by adding sulphate of copper, 
 when the arsenite of copper is precipitated. This poisonous colour is used 
 to impart a bright green tint to paper-hangings, and is sometimes injurious 
 to the health of the occupants of rooms thus decorated, since the arsenite 
 of copper is often easily rubbed off the paper, and diffused through the 
 air in the form of a fine dust, a small portion of which is inhaled with 
 every breath. 
 
 The presence of the arsenite of copper in a sample of such paper is readily proved 
 by soaking it in a little ammonia, which 
 will dissolve the arsenite of copper to a 
 blue liquid, the presence of arsenic in 
 which may be shown by acidifying it 
 with a little pure hydrochloric acid, and 
 boiling with one or two strips of pure 
 copper, which will become covered with 
 a steel-grey coating of arsenide of cop- 
 per. On washing the copper, drying it 
 on filter-paper, and heating it in a small 
 tube (fig. 212), the arsenic will be con- 
 verted into arsenious acid, which will 
 deposit in brilliant octahedral crystals on 
 
 the cool part of the tube. It is obvious Fig. 212. 
 
 that, to avoid mistakes, the ammonia, hy- 
 drochloric acid, and copper should be examined in precisely the same way, without 
 the suspected paper, so as to render it certain that the arsenic is not derived from them. 
 
 The effective green colour of the arsenite of copper also leads to its 
 employment as a colour for feathers, muslin, &c., where it is very inju- 
 rious to the health of the work-people. It has even been ignorantly or 
 recklessly used for colouring twelfth-cake ornaments, &c. 
 
 In quantities short of poisonous doses, arsenious acid appears to have a 
 remarkable effect upon the animal body. Grooms occasionally employ it 
 to improve the appearance of horses, and in Styria it seems to be taken 
 by men and women for the same purpose, apparently favouring the secre- 
 tion of fat. It is said that a continuance of the custom developes a 
 craving for this drug, and enables large doses to be taken without imme- 
 diate danger, though the ultimate consequences are very serious. 
 
 Solution of arsenite of potash (Fowler's solution) has long been used in 
 medicine. 
 
 176. Arsenic acid. This acid has acquired great importance in the 
 chemical arts during the last few years, having been employed to replace 
 the expensive tartaric acid used in calico-printing, and to furnish, by its 
 action upon aniline, the magnificent dye known as Magenta. 
 
 Arsenic acid is prepared by oxidising arsenious acid with three-fourths 
 of its weight of nitric acid of sp. gr. 1'35, when it dissolves with evolution 
 of much heat and abundant red fumes of nitrous acid 
 
 As0 3 + HO.N0 5 + 2HO = N0 3 + 3HO.As0 5 . 
 After cooling, the solution deposits very deliquescent prismatic crystals 
 containing 3HO. As0 5 + Aq. When these are heated to 212 F. they 
 
246 AKSENIETTED HYDKOGEN. 
 
 melt, and the liquid gradually deposits needle-like crystals of trihydrated 
 arsenic acid, 3HO . As0 5 , corresponding to common or tribasic phosphoric 
 acid. At 300 F. the hydrate 2HO.As0 5 may be obtained, and at a 
 temperature of 500 F. a white mass of anhydrous arsenic acid (AsO ft ) is 
 left. If this be heated to redness, it fuses and is decomposed into arsenious 
 acid and oxygen. 
 
 The hydrates of arsenic acid have acquired unusual importance, in con- 
 sequence of a costly trial, in the law courts, of the question, whether the 
 patent for Magenta dye could be pronounced invalid because the patentee 
 had described it as being producible by the action of dry arsenic acid 
 upon aniline ; whereas the anhydrous acid, acting upon aniline, will not 
 furnish the colour, though either of the solid (and therefore dry in popular 
 language) hydrates will do so. The patent was eventually invalidated, 
 though not merely upon this question. 
 
 Anhydrous arsenic acid has very much less attraction for water than 
 the anhydrous phosphoric acid to which it corresponds ; it deliquesces 
 slowly in air, and dissolves rather reluctantly in water. Neither does it 
 appear that its combinations with water differ from each other, like the 
 phosphoric acids, in the salts to which they give rise, arsenic acid forming 
 tribasic salts only, like common phosphoric acid. The arseniates cor- 
 respond very closely to the tribasic phosphates with which they are 
 isomorphous (i. e., identical in crystalline form). Thus the three arseniates 
 of soda are similar in composition to the three tribasic phosphates of soda, 
 their formulae being 
 
 3NaO.As0 5 + 24Aq. 
 
 2NaO . HO . AsO. + 24Aq. 
 NaO . 2HO . As0 5 + Aq. 
 
 But if the two last salts be heated, they lose their basic water without 
 giving rise to new salts corresponding to the pyrophosphate and meta- 
 phosphate of soda, and resume their former condition when placed in 
 contact with water. 
 
 The common arseniate of soda (2NaO. HO . As0 5 -f 14Aq.) is largely 
 used by calico-printers as a substitute for the dung-baths formerly em- 
 ployed, since, like the common phosphate of soda, it possesses the feebly 
 alkaline properties required in that particular part of the process. It is 
 manufactured by combining arsenious acid with soda, and heating the 
 resulting arsenite of soda with nitrate of soda, from which it acquires 
 oxygen, becoming converted into arseniate of soda. 
 
 Arsenic acid is a much more powerful acid than arsenious acid, being 
 comparable, in this respect, with phosphoric acid. It appears to be less 
 poisonous than arsenious acid. 
 
 177. Arsenietted hydrogen. The only compound of arsenic and hydro- 
 gen, the existence of which has been satisfactorily established, is that 
 which corresponds to ammonia and phosphuretted hydrogen gas, and is 
 represented by the formula, AsH 3 . It is prepared by the action of sul- 
 phuric acid diluted with three parts of water upon the arsenide of zinc, 
 obtained by heating equal weights of zinc and arsenic in an earthen 
 retort ; Zn 3 As + 3(HO . S0 3 ) = AsH 3 + 3(ZnO . S0 3 ). The gas is so 
 poisonous in its character that its preparation in the pure state is attended 
 with danger. It has a sickly alliaceous odour, and may be liquefied at 
 40 F. It is inflammable, burning with a peculiar livid flame, pro- 
 
MARSH'S TEST FOR ARSENIC. 
 
 247 
 
 ducing water and fumes of arsenious acid ; AsH 3 -f 6 = AsO 3 + 3HO. 
 The chief interest attaching to this gas depends upon the circumstance 
 that its production allows of the detection of very minute quantities of 
 arsenic in cases of poisoning. 
 
 The application of this test, known as Marsh's test, is the safest method of prepar- 
 ing arsenietted hydrogen in order to study its properties, for it is obtained so largely 
 diluted with free hydrogen that it ceases to be so very dangerous. Some fragments 
 of granulated zinc are introduced into a half-pint bottle 
 (fig. 213), provided with a funnel -tube (A), and a narrow tube 
 (B) bent at right angles and drawn out to a jet at the extremity ; 
 this tube should be made of German glass, so that it may not 
 fuse easily. The bottle having been about one-third filled 
 with water, a little diluted sulphuric acid is poured down the 
 funnel-tube so as to cause a moderate evolution of hydrogen, 
 and after about five minutes (to allow the escape of the air) 
 the hydrogen is kindled at the jet. If a few drops of a solu- 
 tion obtained by boiling arsenious acid with water be now 
 poured down the funnel, arsenietted hydrogen will be evolved 
 together with the hydrogen - j^ 213 
 
 As0 3 + Zn 6 + 6(HO . S0 3 ) = AsH s + 6(ZnO . S0 3 ) + 3HO . 
 
 The hydrogen flame will now acquire the livid hue above referred to, and a white 
 smoke of arsenious acid will rise from it. If a piece of glass or 
 porcelain be depressed upon the flame (fig. 214), it will acquire 
 a metallic-looking coating of arsenic, just as carbon would be 
 deposited from an ordinary gas-flame. Arsenietted hydrogen 
 is easily decomposed by heat, so that if the glass tube Fig. 214. 
 
 through which it passes be heated with a spirit-lamp (fig. 215), 
 a dark mirror of arsenic will be deposited a little in front of the heated part, and 
 the flame of the gas will lose its livid hue. These 
 deposits of arsenic are extremely thin, so that a 
 very minute quantity of arsenic is required to 
 form them, thus rendering the test one of extra- 
 ordinary delicacy. It must be remembered, how- 
 ever, that both sulphuric acid" and zinc are liable 
 to contain arsenic, so that erroneous results may 
 be very easily arrived at by this test in the hands 
 of any but those specially devoted to such investi- 
 gations. 
 
 Arsenietted hydrogen, like sulphuretted hydro- 
 gen, causes dark precipitates in many metallic 
 solutions. 
 
 Composition of arsenietted Jiydrogen. 
 The specific gravity of this gas has been 
 found to be 2-695. The formula AsH 3 
 would represent 1 vol. of arsenic vapour and 6 vols. of hydrogen (0 = 1 vol.) 
 
 Weight of 1 vol. (sp. gr.) of arsenic vapour, 10-600 
 6 vols. of hydrogen (-069 x 6), -414 
 
 11-014 
 
 But the sum of these is evidently four times the weight of 1 vol. of 
 arsenietted hydrogen, hence the formula AsH 3 represents 4 vols. of this 
 gas, containing 1 vol. of arsenic vapour and 6 vols. of hydrogen. 
 
 Its molecular formula ought strictly to be written AsH fi , but, as in the 
 case of phosphuretted hydrogen, the formula AsH. { is preferred, in order 
 to exhibit a correspondence in composition to ammonia (see also p. 244). 
 
 Phosphuretted hydrogen, arsenietted hydrogen, and ammonia, constitute 
 a group of hydrogen compounds having certain properties in common, 
 
 215. 
 
248 
 
 CHLORIDE OF ARSENIC. 
 
 which distinguish them from the compounds of hydrogen with other 
 elements. 
 
 Two volumes of each of these gases contain three volumes of hydrogen. 
 
 They are all possessed of peculiar odours, that of ammonia being the 
 most powerful, and that of arsenietted hydrogen the least. 
 
 Ammonia is powerfully alkaline, phosphuretted hydrogen -exhibits 
 some tendency to play an alkaline part, whilst arsenietted hydrogen seems 
 devoid of alkaline disposition. 
 
 All these are inflammable, ammonia being the least so of the group ; 
 and all are decomposed by heat, ammonia least easily and arsenietted 
 hydrogen most easily. 
 
 They are all producible from their corresponding oxygen compounds, 
 viz., NO 3 , P0 3 , and As0 3 , by the action of nascent hydrogen (e.g., by 
 contact with zinc and diluted sulphuric acid). 
 
 All three are the prototypes of various organic bases which contain 
 some compound radical in place of the hydrogen, thus 
 
 NH 3 is the prototype of triethylamine, N(C 4 H 5 ) 3 
 
 PH 3 triethylphosphine, P(C 4 H 5 ) 3 
 
 AsH 3 triethylarsine, As(C 4 H 5 ) 3 . 
 
 178. Terchloride of arsenic. Only one compound of chlorine with arsenic (AsCl 3 ) has 
 yet been obtained ; the chloride corresponding to pentachloride of phosphorus remains 
 
 to be discovered.* The terchloride 
 may be formed by the direct union of 
 its elements, but the simplest laboratory 
 process for procuring it consists in heat- 
 ing arsenious acid in dry chlorine gas, in 
 a tubulated retort (A, fig. 216), extem- 
 porised from a Florence flask (see p. 
 95.) The arsenious acid soon melts, and 
 the terchloride of arsenic distils over, 
 leaving a melted mass in the flask, 
 which forms a brilliantly transparent 
 glass on cooling, the composition of 
 which varies somewhat with the tem- 
 perature employed, but appears to be 
 essentially 2As0 3 .As0 5 . The same 
 vitreous compound may be obtained 
 by fusing arsenious and arsenic acids 
 together. The formation of the terchloride of arsenic may be represented by the 
 equation, llAs0 3 + C1 6 = 2As01 3 + 3(2As0 3 . As0 5 ). 
 
 Terchloride of arsenic bears a great general resemblance to terchloride of phos- 
 phorus; it is a heavy (sp. gr. 2-2), pungent, fuming liquid, decomposed by the 
 moisture of the air, its vapours depositing a white coating of arsenious acid upon 
 the objects in its immediate neighbourhood. When poured into water it deposits 
 arsenious acid ; AsCl 3 + 3HO = As0 3 + 3HC1 ; but when dissolved in the smallest 
 possible quantity of water, it deposits crystals of the formula As0 2 Cl . 2HO. 
 
 When arsenious acid is dissolved in hydrochloric acid, terchloride of arsenic is 
 formed, As0 3 + 3HC1 = AsCl 3 + 3HO, and remains undecomposed by the water in 
 the presence of strong hydrochloric acid, but if water be added, arsenious acid is 
 precipitated. When the solution of arsenious acid in hydrochloric acid is distilled, 
 the terchloride of arsenic distils over, and this is sometimes a convenient method of 
 separating arsenic from articles of food, &c., in testing for that poison. When 
 heated in dry hydrochloric acid gas, arsenious acid yields a glassy compound, which 
 contains 2As0 3 . AsC10 2 ; 3As0 3 + HC1 = 2As0 3 . AsClO 2 + HO. 
 
 In composition by volume, the terchloride of arsenic resembles terchloride of 
 
 * Nickles appears to have succeeded in forming the pentachloride by the action of hydro- 
 chloric acid gas on arsenic acid in presence of ether ; he describes it as very unstable, and 
 easily converted into the terchloride. 
 
 Fig. 216. 
 
REALGAR OKPIMENT. 249 
 
 phosphorus, containing 1 vol. of arsenic vapour, and 6 vols. of chlorine condensed 
 into 4 vols., the specific gravity of its vapour being 6-3. 
 
 Terbromide of arsenic much resembles the terchloride in its chemical characters, 
 but is a solid crystalline substance, easily fusible. 
 
 179. Teriodide of arsenic (AsT 3 ) is remarkable for not being decomposed fay water, 
 like the corresponding phosphorus compound. When obtained by heating arsenic 
 and iodine together, it sublimes in brick-red flakes, which, if prepared on a large scale, 
 hang in long laminae like sea-weed. It may be dissolved in boiling water, and 
 crystallises out unchanged. It may even be prepared by heating 3 parts of arsenic 
 with 10 of iodine and 100 of water, when the solution deposits red crystals of the 
 hydrated teriodide, from which the water may be expelled by a gentle heat. 
 
 The terfluoride of arsenic (AsF 3 ) resembles the terchloride, but is much more 
 volatile. It may be obtained by distilling 4 parts of arsenious acid with 5 of fluor- 
 spar and 10 of strong sulphuric acid in a leaden retort (see p. 177). It does not 
 attack glass unless water be present, which decomposes it into arsenious and hydro- 
 fluoric acids. 
 
 180. SULPHIDES OF ARSENIC. There are three well-known sulphides of 
 arsenic, having the composition AsS 2 , AsS 3 , and AsS 5 , the two former 
 being found in nature. 
 
 Realgar, or bisulphide of arsenic (AsS 2 ), is a beautiful mineral, crystal- 
 lised in orange-red prisms ; but the red orpiment used in the arts is gene- 
 rally prepared by heating a mixture of arsenious acid and sulphur, when 
 sulphurous acid escapes, and an opaque mass of realgar is left 
 
 2As0 3 + S 7 - 2AsS 2 + 3S0 2 . 
 
 Another process for preparing it consists in distilling arsenical pyrites 
 with iron pyrites 
 
 FeS 2 . FeAs + 2FeS 2 = 4FeS + AsS 2 . 
 
 Arsenical pyrites. Iron pyrites. ^^JS?** Realgar. 
 
 The realgar distils over, and condenses to a red transparent solid. 
 Realgar burns in air with a blue flame, yielding arsenious acid and sul- 
 phurous acid. If it be thrown into melted saltpetre, it burns with a 
 brilliant white flame, being converted into arseniate and sulphate of 
 potash. This brilliant flame renders realgar an important ingredient in 
 Indian fire and similar compositions for fire- works and signal- lights. A 
 mixture of one part of red orpiment with 3 '5 parts of sublimed sulphur 
 and 14 parts of nitre is used for signal-light composition. 
 
 Kealgar is not easily attacked by acids ; nitric acid, however, dissolves it, with 
 the aid of heat, forming arsenic acid and sulphuric acid, with separation of part of 
 the sulphur in the free state. Alkalies (potash, for example) partly dissolve it, 
 leaving a brown substance, which appears to be a subsulphide of arsenic (As^S). 
 
 Fellow orpiment, or ter sulphide of arsenic (AsS 3 ), is found native in 
 yellow prismatic crystals. The paint known as King's yellow is a mix- 
 ture of tersulphide of arsenic and arsenious acid, prepared by subliming a 
 mixture of sulphur with arsenious acid 
 
 S 9 + 2As0 3 = 2AsS 3 + 3S0 2 . 
 It is, of course, very poisonous. 
 
 This substance, like realgar, is not much affected by acids, excepting nitric acid ; 
 but it dissolves entirely in potash, forming arsenite of potash and sulpharsenite of 
 (sulphide of) potassium ; 6KO + 2AsS 3 = 3KS . AsS 3 + 3KO . As0 3 . Ammonia 
 also dissolves it easily, forming a colourless solution which is employed for dyeing 
 yellow, since if a piece of stuff be dipped into it and exposed to air, the ammonia 
 will volatilise, leaving the yellow orpiment behind. 
 
250 REVIEW OF THE NON-METALLIC ELEMENTS. 
 
 The formation of the characteristic yellow tersulphide is turned to account in 
 testing for arsenic ; if a solution prepared by boiling arsenious acid with distilled 
 water be mixed with a solution of hydrosulphuric acid, a bright yellow liquid is 
 produced, which looks opaque by reflected, but transparent by transmitted light, 
 and may,be passed through a filter without leaving any solid matter behind. This 
 solution probably contains a soluble compound of tersulphide of arsenic with hydro- 
 sulphuric acid (3HS . AsS 3 ) ; it is, however, very unstable, being decomposed by 
 evaporation, with precipitation of the tersulphide. The addition of a little hydro- 
 chloric acid, or of sal-ammoniac, and many other neutral salts, will also cause a 
 separation of the tersulphide from this solution ; even the addition of a hard water 
 will have that effect. If the solution of arsenious acid be acidified with hydro- 
 chloric acid before adding the hydrosulphuric acid, the bright yellow tersulphide of 
 arsenic is precipitated at once, and may be distinguished from any other similar 
 precipitate by its ready solubility in solution of carbonate of ammonia. 
 
 From its combining readily with the alkaline sulphides to form soluble com- 
 pounds, the tersulphide of arsenic is often called sulpharsenious acid. 
 
 Pentasulphide of arsenic (AsS ft ), or sulpharsenic acid, possesses far less practical im- 
 portance than the preceding sulphides ; it may be obtained by fusing the tersulphide 
 with sulphur, when it forms an orange-coloured glass, easily fusible, and capable of 
 being sublimed without change. When hydrosulphuric acid gas is passed through 
 solution of arsenic acid, a white precipitate of sulphur is first obtained, the hydrogen 
 reducing the arsenic acid to arsenious acid ; As0 5 + 2HS = As() 3 4- 2HO + S 2 ; 
 and if the passage of the gas be continued, the arsenious acid is decomposed, and 
 tersulphide of arsenic is precipitated ; these changes are much accelerated by heat. 
 But if a solution of arseniate of soda be saturated with hydrosulphuric acid, it is 
 converted into sulpharseniate of (sulphide of) sodium 
 
 2NaO . HO . As0 5 -h 7HS = 8HO + 2NaS . AsS 6 . 
 
 On adding hydrochloric acid to this solution, a bright yellow precipitate of penta- 
 sulphide of arsenic is obtained 
 
 2NaS.AsS 5 + 2HC1 = 2NaCl + 2HS + AsS 5 . 
 
 Pentasulphide of arsenic is one of the most powerful of the sulphur acids ; it 
 expels hydrosulphuric acid from its combinations with the alkaline sulphides, and 
 is capable of forming with these, sulpho-salts, containing respectively one, two, and 
 three equivalents of the alkaline sulphide, which may be obtained by the action of 
 hydrosulphuric acid upon the corresponding arseniates. 
 
 GENEKAL EEVIEW OF THE NON-METALLIC ELEMENTS. 
 
 181. At the conclusion of the history of the non-metals, it may be 
 well to call attention to the points of resemblance which classify them 
 into separate groups or families, most of which are connected, by some 
 analogies, with one or more members of the class of metals. 
 
 Hydrogen stands alone among the non-metals, its chemical properties 
 and functions being widely different from those of any other non-metal, 
 but connecting it very closely with the most highly electropositive (or 
 basylous) metals, such as potassium and sodium. 
 
 Oxygen, Sulphur, Selenium, and Tellurium compose a group, the mem- 
 bers of which (in the state of vapour) combine with twice their volume 
 of hydrogen to form compounds which (in the state of vapour) occupy 
 the same volume as the hydrogen occupied before combination. All these 
 hydrogen compounds are capable of playing a feebly acid part, and their 
 hydrogen may be displaced by an equivalent weight of a metal to produce 
 compounds exhibiting a general agreement in chemical properties. This 
 group is connected with the metals through tellurium, not only by its 
 physical properties, but by its forming an oxide (Te0 2 ), which occasion- 
 ally acts as a weak base. 
 
CLASSIFICATION ACCORDING TO ATOMICITY. 251 
 
 Nitrogen, Phosphorus, and Arsenic are connected together by the gene- 
 ral analogy of their hydrogen and oxygen compounds, the two last mem- 
 bers of the group being far more closely connected with each other than 
 with nitrogen. With the metals, they are connected through arsenic, the 
 hydrogen compound of which is very similar in properties, and probably in 
 composition, to antimonietted hydrogen ; arsenious acid (As0 3 ) is also cap- 
 able of occupying the place of teroxide of antimony (Sb0 3 ) in certain salts 
 of that oxide; and the sulphides of antimony correspond in composition, and 
 in some of their properties, to those of arsenic. One form of arsenious 
 acid (the prismatic) is isomorphous with native oxide of antimony, and 
 this oxide may be obtained in octahedra, the ordinary form of arsenious 
 acid, so that these oxides are isodimorphous. 
 
 These elements are also connected with the oxygen group through 
 sulphur, selenium, and tellurium, the relations of which to hydrogen and 
 the metals are somewhat similar to those of phosphorus and arsenic. 
 
 Carbon, Boron, and Silicon resemble each other in their allotropic 
 forms, their resistance to fusion and volatilisation, and their forming 
 feeble acids with oxygen. To the metals they are allied through silicon, 
 which resembles tin in the composition and character of its oxide and 
 chloride. 
 
 This group is connected with the nitrogen group through boron, for 
 boracic acid resembles arsenious acid in its tribasic character, and its 
 forming vitreous compounds with the alkalies. In certain compounds 
 boracic and arsenious acids are interchangeable. 
 
 Chlorine, Bromine, Iodine, and Fluorine are intimately connected by 
 numerous analogies, which have been already pointed out (p. 182). Some 
 of the properties of iodine, as its relations to oxygen, and the solubility 
 of its terchloride in water, connect it slightly with the metals, whilst the 
 general correspondence in composition between the chlorides and the 
 oxides, allies this group to the oxygen group of non-metallic elements. 
 
 If the non-metals be classified according to their atomicities (see p. 151), 
 it will be found that, with only few exceptions, the classification will 
 coincide with that founded upon their chemical analogies in other respects. 
 Thus, the members of the oxygen group are all diatomic, or capable of 
 combining with two atoms of hydrogen, as shown by the molecular for- 
 mulae of their hydrogen compounds, H 2 0, H 2 S, H 2 Se, H 2 e. The 
 nitrogen group is generally represented as triatomic (though, from our 
 present knowledge of the vapour densities of phosphorus and arsenic, 
 these elements are strictly hexatomic), their hydrogen compounds being 
 NH S , PH 3 , and AsH 3 . Boron is also a triatomic element, for, in BC1 3 , 
 the boron occupies the place of three atoms of hydrogen. 
 
 Carbon and silicon, however, are tetratomic elements, as shown in 
 marsh-gas, 6H 4 , and in chloride of silicon, SiCl 4 . 
 
 Chlorine, bromine, iodine, and fluorine are monatomic, their hydrogen 
 compounds having the molecular formula, HC1, HBr, HI, and HF. 
 
 The atomicity of an element is sometimes expressed in a formula by a 
 dash, or dashes, placed above and to the right of the element ; thus the 
 symbols, CF, 0", 1ST"', Q"", indicate the respective atomicities of those 
 elements. When the atomicity of an element is taken into account, it 
 helps to explain the constitution of compounds which would otherwise 
 appear quite anomalous. For example, there is a compound of the mole- 
 cular formula, N 3 H 6 P, obtained by the action of terchloride of phos- 
 phorus upon ammonia ; recollecting the triatomic character of phosphorus, 
 
252 CONSTITUTION OF SALTS. 
 
 we perceive this compound to represent three molecules of ammonia 
 (.N~ 3 H 9 ), in which phosphorus is the substitute for three atoms of hydro- 
 gen, which is at once expressed if the formula be written, N 3 H 6 P"'. 
 Again, chlorocarbonic acid, 60C1 2 , appears an inexplicable association of 
 elements, until the tetratomic character of carbon and diatomic character 
 of oxygen are taken into account, as in the formula 6-""O"Cl' g , when it 
 appears that the diatomic oxygen and the two atoms of monatomic 
 chlorine are the substitutes for four atoms of hydrogen in marsh-gas, 
 0H 4 , and it might plausibly be given as a reason why the apparently in- 
 different carbonic oxide should combine with chlorine, that the atomicity 
 of the carbon is only partly satisfied in carbonic oxide, which contains 
 only oxygen equal in value to two atoms of hydrogen, the tetratomic 
 carbon requiring the value of two more atoms of hydrogen to complete 
 the compound atom. In carbonic acid, 6""0" 2 , the two atoms of dia- 
 tomic oxygen fully complete the compound. 
 
 In a similar manner the absorption of carbonic oxide by subchloride of 
 copper may be explained ; for the atomic formula of that salt is Gu'Cl', 
 and hence it is capable of supplying the two absent atoms in G""W. 
 
 Many more examples of the same kind might be gathered from the 
 preceding pages, but these will probably be sufficient to mark the import- 
 ance of remembering the atomicities of the elements in speculative che- 
 mistry ; indeed, without this clue it is impossible to find any meaning 
 whatever in a very large number of the formulae of organic substances, 
 whilst with it, not only their constitution, but in many cases their mode 
 of formation, becomes as intelligible as that of the simplest mineral com- 
 pounds. 
 
 CONSTITUTION OF SALTS. 
 
 182. The term salt, like acid and alkali, was, of course, purely em- 
 pirical in its origin, being conferred upon every solid substance which 
 exhibited any of the prominent characters of sea-salt (sal, brine, o-aAos, the 
 sea), such as solubility in water and tendency to crystallisation. 
 
 When the great mass of chemical facts accumulated by the alchemists, 
 metallurgists, and apothecaries, came to be classified, and the distinction 
 between acids and bases was recognised, the term salt was extended to all 
 those substances, such as muriate of soda, nitrate of potash, carbonate of 
 lime, &c., from which a base and an acid could be obtained, without re- 
 gard to their solubility or tendency to crystallise. When the analytical 
 powers of the chemist were more fully developed, it was found that 
 muriate of soda and a large class of similar salts did not contain an acid 
 and a base, but that these substances were produced and not educed from 
 the salts by the chemical operations to which they were subjected. Thus 
 muriate of soda, from which muriatic acid had been so easily produced by 
 the action of sulphuric acid, was shown to contain only sodium and 
 chlorine. 
 
 This led to a classification of salts into haloid salts (aA.<?, th-e sea), or 
 those composed, like chloride of sodium, of a metal combined with a salt- 
 radical or halogen, and oxy-acid salts, or those composed of a metallic 
 oxide combined with an oxygen acid. (It will have been remarked that 
 the tendency of modern chemistry is to represent this second class of salts 
 by formulae which do not admit the existence of the metal as an oxide in 
 the salt.) 
 
NEUTRAL AND NORMAL SALTS. 253 
 
 Independently of all differences of opinion with respect to the actual 
 constitution of salts, the criterion by which the claims of a substance to 
 this title can be estimated is this : a salt is a compound which may be 
 formed by the action of an acid upon a base, water, which is a very general 
 result of such action, being excepted. 
 
 The oxy-acid salts soon came to be divided into neutral and acid salts, 
 according to their effect upon vegetable colours and the organ of taste, 
 and a class of basic salts was afterwards added when it was found that a 
 neutral soluble salt sometimes became insoluble by combining with an 
 additional quantity of base. 
 
 Further investigation has shown that the neutral taste of a salt, and its 
 neutrality to test-papers, depend less upon the proportions of the acid and 
 base which are contained in it, than upon the chemical energy of these 
 substances. 
 
 Thus, potash combined with 1 eq. of sulphuric acid forms a salt which 
 is perfectly neutral to taste and to litmus-papers, whilst with 1 eq. of 
 carbonic acid it forms a strongly alkaline salt; and 1 eq. of sulphuric 
 acid combined with 1 eq. of oxide of zinc forms a salt which is strongly 
 acid to test-papers. 
 
 A salt may. therefore, be neutral in chemical constitution, and acid or 
 alkaline in reaction to test-papers, and it has been proposed to employ the 
 term normal to designate those salts which are neutral in chemical con- 
 stitution, and to restrict the term neutral to those salts which are neither 
 acid nor alkaline to test-papers. Thus, sulphate of potash would be both 
 a neutral and a normal salt, whilst sulphate of zinc and carbonate of 
 potash are normal, but not neutral salts. 
 
 A normal salt is one in which the oxygen contained in the base bears 
 a certain proportion to the oxygen contained in the acid, this proportion 
 being fixed for each acid. 
 
 Thus, a normal carbonate is one in which the oxygen of the base bears 
 to the oxygen of the acid the ratio of 1 : 2, as in normal carbonate of 
 potash, KO . C0 2 . 
 
 A normal sulphate is one in which the oxygen of the base bears to the 
 oxygen of the acid the ratio of 1 : 3, as in normal sulphate of zinc 
 ZnO . S0 3 . 
 
 To form a normajl salt with a sesquioxide, 3 eqs. of sulphuric acid are 
 required. Thus the sulphate of alumina, A1 2 3 . 3S0 3 , although powerfully 
 acid to test-papers, is a normal sulphate, for the oxygen of the base bears 
 to the oxygen of the acid the ratio of 1 : 3. 
 
 "~j An acid salt is one in which the oxygen in the acid is in greater proportion 
 than in the normal ratio. Thus bicarbonate of potash, KO . HO . 2C0 2 , 
 is acid in chemical constitution, though alkaline to test-papers, for the 
 oxygen of the base is to the oxygen of the acid as 1 : 4, whilst the normal 
 ratio for carbonates is 1 : 2. Acid salts usually have the deficiency of 
 base supplied by water, but not invariably, as in fused borax, NaO . 2B0 3y 
 bichromate of potash, KO . 2Cr0 3 , dried bisulphate of soda, NaO . 2S0 3 . 
 y'A basic salt is one in which the oxygen in the base is in greater propor : 
 on than in the normal ratio. Thus, white lead, 2(PbO . C0 2 ), PbO . HO, 
 is a basic carbonate, for the oxygen of the base is to the oxygen of the 
 acid as 3 : 4, whereas the normal ratio is 2 : 4 or 1 : 2. 
 
 Aluminite, A1 2 3 . S0 3 + 9HO, is a basic salt, for the oxygen in 
 the base is to the oxygen in the acid as 3 : 3, whilst the normal ratio is 
 1 :3. 
 
254 
 
 BINARY AND WATER-TYPE THEORIES. 
 
 The following are the normal ratios for some of the most important 
 classes of salts : 
 
 Salts. 
 
 Normal Ratio. 
 
 Examples. 
 
 Carbonates, 
 
 
 
 
 1 
 
 2 
 
 NaO . C0 2 Carbonate of soda. 
 
 Borates, 
 
 
 
 
 3 
 
 3? 
 
 3MgO . BO 3 Borate of magnesia. 
 
 Silicates, 
 
 
 
 
 2 
 
 2 
 
 2FeO . Si0 2 Forge cinder. 
 
 Nitrates, 
 
 
 
 
 I 
 
 5 
 
 KO . NO 5 Saltpetre. 
 
 Chlorates, 
 
 
 
 
 1 
 
 5 
 
 KO . CIO Chlorate of potash. 
 
 Sulphites, 
 
 
 
 
 -I 
 
 2 
 
 NaO . S0 2 Sulphite of soda. 
 
 Sulphates, 
 
 
 
 
 i 
 
 3 
 
 CaO . S0 3 Sulphate of liine. 
 
 Metaphosphates, 
 
 
 
 1 
 
 5 
 
 NaO . P0 5 Metaphosphate of soda. 
 
 Pyrophosph ates, 
 
 
 
 '2 
 
 5 
 
 2NaO . P0 5 Pyrophosphate of soda. 
 
 Orthophosphates 
 
 
 
 3 
 
 5 
 
 3CaO . P0 5 Bone phosphate of lime. 
 
 Arsenites, 
 
 
 
 3 
 
 3? 
 
 3AgO . As(> 3 Arsenite of silver. 
 
 Arseniates, . 
 
 
 
 3 
 
 5 
 
 3CoO . AsO 5 Cobalt bloom. 
 
 Chromates, . 
 
 
 
 1 
 
 3 
 
 KO . Cr0 3 Chromate of potash. 
 
 Permanganates, 
 
 
 
 1 
 
 7 
 
 KO . Mn 2 O 7 Permanganate of potash. 
 
 In order to explain the above results obtained by the actual analysis of 
 salts, it may be supposed that the salts are formed upon the type of the 
 hydrated acid, and that a normal salt is one in which the water in the 
 hydrated acid is displaced by an equivalent quantity of base ; thus, the 
 sulphates are formed upon the type of oil of vitriol, HO . S0 3 , and the HO 
 must be displaced by KO to form the normal sulphate of potash ; but 
 when alumina (A1 2 3 ) is employed to displace the water, one-third of the 
 quantity represented by that formula would be equivalent to the HO (for 
 A1 2 is equivalent to H 3 ), and therefore the normal sulphate of alumina 
 
 would be 
 
 S0 3 , or avoiding the fraction, A1 2 3 . 3S0 3 . 
 
 Binary theory of the constitution of salts. The circumstance that it is 
 only the hydrogen of the hydrated acid that is displaced by the metal, 
 has given rise to the binary theory of salts, according to which all acids 
 and salts are constituted after the type of hydrochloric acid and chloride 
 of sodium ; the acid being composed of hydrogen combined with a com- 
 pound salt-radical made up of the other elements present in the acid. 
 Thus, sulphuric acid (HO . S0 3 ) would become H,S0 4 nitric acid, 
 H,N0 6 ; metaphosphoric acid, H,P0 6 ; pyrophosphoric, H 2 ,P0 7 ; tri- 
 basic phosphoric, H 3 ,P0 8 , and their normal salts are formed by the sub- 
 stitution of an equivalent quantity of a metal for the hydrogen ; neu- 
 tral sulphate of potassium would be K, S0 4 ; pyrophosphate of sodium, 
 Na 2 , P0 7 ; triphosphate of calcium, Ca 3 , PO S . The acid salts would be 
 those in which only part of the hydrogen is displaced by a metal ; bisul- 
 phate of potassium would become K, H, 2S0 4 , acid pyrophosphate of 
 sodium, Na, H, P0 7 . Double salts would be those in which the hydrogen 
 is displaced by different metals ; thus, alum (KO . SO 3 , A1 2 3 . 3S0 3 ) 
 would become K, A1 2 , 4S0 4 ; acid phosphate of potassium and sodium 
 (KO, NaO, HO, P0 5 ) K, ISTa, H, P0 8 . The serious objection to this 
 view, that it overlooks radicals now existing (as S0 3 , P0 5 , C0 2 ), and 
 substitutes others which are not known to exist (as S0 4 , PO 8 , C0 3 ) has 
 been already pointed out. 
 
 Water-type theory of the constitution of salts. Another ingenious 
 theory of the constitution of salts is that known as the water-type theory, 
 according to which all oxygen acids are fashioned after the type of water, 
 
WATER-TYPE THEORY OF ACIDS AND SALTS. 255 
 
 by the displacement of its hydrogen by a compound radical, such displace- 
 ment being total in the anhydrous acids, and partial in the hydrated acids. 
 To render it possible to show the partial displacement of the hydrogen, 
 
 H ) 
 the molecular formula for water, H 2 or-^ V 0, must be employed. Then, 
 
 a monobasic acid is formed upon the type of one molecule of water, by 
 the displacement of one atom of hydrogen to form the (hydrated) acid, and 
 of both atoms to form the (anhydrous acid or) anhydride. Thus nitric 
 
 TT \ 
 
 acid (HO. IST0 5 ) would be written -^ V0, and nitric anhydride (N0 5 ) 
 would become ^^ 2 > ; and nitrate of potassium (KO . N0 5 ) would 
 
 -rr % 
 
 "b e N0 V 0, and a glance at these formulae shows why a monobasic acid 
 
 like nitric acid does not form either acid salts or double salts, because it 
 contains only one atom of hydrogen, and therefore can only form a single 
 salt with each metal by displacement of that hydrogen. This view does 
 not ignore the existence of the anhydrous nitric acid, and assumes, as the 
 radical of the acid, the substance N0 2 , which has the composition of nitric 
 peroxide. The formation of nitric acid by the action of water upon nitric 
 anhydride would be thus expressed 
 
 H 
 
 H l 
 
 HJ 
 
 f> 
 
 H 
 
 In a similar manner, phosphoric anhydride (P0 5 ) would be represented 
 
 P0 ) TT ) 
 
 by p0 2 > 0, metaphosphoric acid (HO. P0 5 ) bypri >0, and the meta- 
 
 phosphate of sodium by p^ I 0. In this case, however, the radical P0 2 
 is, so far as we know, imaginary. 
 
 A bibasic acid is one which is composed after the type of a double 
 
 TT \ 
 
 molecule of water, j 2 V 2 and therefore contains two atoms of hydro- 
 
 gen which may be displaced either entirely by a metal, yielding a normal 
 salt, or partly by a metal, yielding an acid salt, or by two metals, yielding 
 a double salt. For example, sulphuric acid (HO . S0 3 ) would be 
 
 S0 '' | ^ 2 ' or two mo ^ ecu ^ es f wa ter, in which two atoms of hydrogen 
 are displaced by the diatomic radical S0 2 ; normal sulphate of potassium 
 jr \ KT-I' ) 
 
 S0 " | ' 2 ' ac ^ su lp nate f potassium (bisulphate of potash) S^// [ 2 
 
 &r\ it \ 
 
 and sulphuric anhydride, ~ 2 ,, 1 2 . 
 
 Here again the radical S0 2 has the same composition as sulphurous 
 acid, which might well be accepted as the radical of sulphuric acid. 
 
 ri r\/f \ 
 
 Again, carbonic anhydride would be ^,, V 0,, the imaginary carbonic 
 acid, ^,, i 2 , carbonate of potassium, ^,, 1 0,, acid carbonate of potas- 
 [ ^ carbonate of potassium and sodium, ^^f 1 1 . 
 
 K TT 
 
 sium, ^^., 
 
256 CONSTITUTION OF POLYBASIC ACIDS. 
 
 The radical of carbonic acid, therefore (@0), would have the same com- 
 position as carbonic oxide, which is seen to have a diatomic character in 
 its compound with chlorine, 60"C1 2 , where it occupies the place of two 
 atoms of hydrogen. 
 
 In applying this view to pyrophosphoric acid (2HO . P0 5 = H 2 P0 7 ), some 
 difficulty arises because its molecular formula cannot be written on the 
 type of two molecules of water (H 4 2 ) on account of the indivisibility of 
 the 7 into two whole numbers ; it is therefore necessary to take four 
 molecules of water as the type, when we have 
 
 TT \ TT \ 
 
 T JP e > jj 4 [& pyrophosphoric acid, /p^y/// >O 4 , pyrophosphate of 
 sodium, ,p a ^ y fff I 4 , acid pyrophosphate of sodium, , p a ^ I,,, i 4 . 
 
 Here the increased complexity of the formulae appears objectionable. 
 
 A few salts are known in which two acids are combined with the same base, such 
 as the acetonitrate of baryta (BaO . N0 5 , BaO.C 4 H 3 3 ), composed of nitrate and 
 acetate of baryta. 
 
 It is obvious that the same reasoning which leads to the conclusion that an acid 
 capable of forming a double salt with two different bases is dibasic, or contains a 
 diatomic acid radical, would also support the inference that a base capable of form- 
 ing a double salt with two different acids is di-acid, or contains a diatomic basic 
 radical. Hence the existence of the above acetonitrate of baryta countenances the 
 belief that barium is a diatomic metal. The formula of the salt would then be 
 
 Ba" i 
 
 written, on the type of two molecules of water, thus (6 2 H 3 0)' 1 
 
 (N0 2 )'J 
 
 A tribasic acid is formed upon the type of a treble molecule of water, 
 thus 
 
 TT \ TT \ 
 
 Type, TT 3 > 6 3 , tribasic phosphoric acid, pA/// f &3> triphosphate of 
 
 ~N& } !N"a H ) 
 
 sodium, pry,,/ > O 3 , common phosphate of sodium, -prytt >O 3 , microcos- 
 
 mic salt (phosphate of sodium and ammonium), a p/y// \ 3 . 
 
 But in this case also an unknown radical, PO, is assumed. 
 
 Many chemists now represent the acids and salts by their molecular 
 formulae, without insisting upon their containing any definite compound 
 radical, or being composed upon any particular type. Thus nitric acid is 
 written HN0 3 , without expressing an opinion as to the existence of 
 N0 3 as an actual entity. 
 
 The following definitions are relied upon by those who adopt this 
 course : 
 
 An acid is a compound containing hydrogen, the whole or part of 
 which is displaceable by a metal. 
 
 A salt is a compound derived from an acid by the displacement of its 
 hydrogen by a metal. 
 
 A monobasic acid contains but one atom of displaceable hydrogen, and 
 therefore can only form one series of salts. 
 
 A dibasic acid contains two atoms of displaceable hydrogen, and there- 
 fore can form two series of salts (normal and acid salts). 
 
 A tribasic acid contains three atoms of displaceable hydrogen, and 
 
CONSTITUTION OF ACIDS AND SALTS. 
 
 257 
 
 therefore can form three series of salts (normal salts, and two series of 
 acid salts). 
 
 A normal salt is one in which the whole of the displaceable hydrogen 
 has been displaced by a metal. 
 
 An -add salt is one in which only part of the displaceable hydrogen 
 has been displaced by a metal. 
 
 A double salt is one in which the displaceable hydrogen has been dis- 
 placed by different metals. 
 
 'A basic salt is a combination of a salt with a basic oxide. 
 
 A few examples may be collected here to illustrate these definitions : 
 
 Monobasic Acids and Salts. 
 
 Nitric acid, ..... HN0 3 
 
 Nitrate of potassium, .... KN0 3 
 
 Metaphosphoric acid, . . . . HP0 3 
 
 Metaphosphate of sodium, . . . NaP0 3 
 
 Hypophosphorous acid, . HPH 2 2 
 
 Hypophosphite of sodium, . . . NaPH 2 2 
 
 Dibasic Acids and Salts. 
 
 Sulphuric acid, .... H 2 S0 4 
 
 Normal sulphate of potassium, . . K 2 S6 t 
 
 Acid . . KHS0 4 
 
 Phosphorous acid, .... H 2 PH0 3 
 
 Normal phosphite of sodium, . . . Na 2 PH0 3 
 
 Acid phosphite of barium, . . . BaHPH0 3 
 
 Tribasic Acids and Salts. 
 
 Orthophosphoric acid," . . . H 3 PO 4 
 
 Normal orthophosphate of sodium, . . Na 3 P0 4 
 
 Monacid orthophosphate (or common phosphate), Na 2 HP0 4 
 
 Diacid orthophosphate, . . . NaH 2 P0 4 
 
 Microcosmic salt, . . Na(NH 4 )HPO 4 
 
 Arsenic acid, ..... H 3 As0 4 
 
 Normal arseniate of sodium, . . . Na 3 As0 4 
 
 Monacid arseniate ,, . . . Na 2 HAs0 4 
 
 Diacid arseniate . . . NaH 2 As0 4 
 
 To this view of the constitution of acids and salts, it may be objected 
 that it presupposes the existence of a hydrogen compound corresponding 
 in composition to the normal salt. Thus the carbonates would be derived 
 from an imaginary carbonic acid of the formula H 2 OO 3 ; the arsenites 
 from an imaginary arsenious acid, H 3 As0 3 , &c. It must, however, be 
 acknowledged that no theory of the constitution of acids and salts has 
 yet been advanced which is thoroughly supported on all sides by experi- 
 mental evidence. 
 
 From what has been stated above, it will have been seen that an 
 examination of the acid itself is by no means necessary in order to ascer- 
 tain what its basicity is. If only one series of its salts can be discovered, 
 it is a monobasic acid. If a normal and an acid salt (or a double salt) 
 can be obtained, the acid is dibasic. When, beside the normal salt, there 
 are two series of acid salts, the acid is tribasic. 
 
 R 
 
CHEMISTRY OF THE METALS. 
 
 183. The general principles of chemistry having been explained and 
 illustrated in the history of the non-metallic elements, the chemistry of 
 the metals will be discussed with less attention to details, which, 
 however interesting in a strictly chemical sense, are not, at present, of 
 immediate practical importance. 
 
 The definition of a metal has been already given at p. 11, as an element 
 capable of forming a base by union with oxygen. 
 
 POTASSIUM. 
 
 The indispensable alkali, potash, appears to have been originally derived 
 from the granitic rocks, where it exists in combination with silicic acid 
 and alumina, in the well-known minerals, feldspar and mica. These rocks 
 having, in course of time, disintegrated to form soils for the support of 
 plants, the potash has been converted into a soluble state, and has passed 
 into the plants as a necessary portion of their food. 
 
 In the plant, the potash is found to have entered into various forms of 
 combination ; thus, most plants contain sulphate of potash and chloride 
 of potassium ; but the greater portion of the potash exists in combination 
 with certain vegetable acids formed in the plant, and when the latter is 
 burnt, the salts of potash with the vegetable acids are decomposed by 
 the heat, leaving the potash in combination with carbonic acid, forming 
 carbonate of potash (KO . C0 2 ). 
 
 Carbonate of potash. When the ashes of plants are treated with water, 
 the salts of potash are dissolved, those of lime and magnesia being left. 
 On separating the aqueous solution and evaporating it to a certain point, 
 a great deal of the sulphate of potash, being much less soluble, is deposited, 
 and the carbonate of potash remains in the solution ; this is evaporated to 
 dryness, when the carbonate of potash is left, mixed with much chloride 
 of potassium, and some sulphate of potash ; this mixture constitutes the 
 substances imported from America and other countries where wood is 
 abundant, under the name of potashes, which are much in demand for the 
 manufacture of soap and glass. When further purified, these are sold 
 under the name ofpearlash, but this is still far from being pure carbonate 
 of potash. 
 
 During the fermentation of the grape-juice, in the preparation of wine, 
 a hard crystalline substance is deposited, which is known in commerce by 
 the name of argol, or when purified, as cream of tartar. The chemical 
 
CAUSTIC POTASH. 259 
 
 name of this salt is bitartrate of potash, for it is derived from potash and 
 tartaric acid, a vegetable acid having the composition 2HO . C 8 H 4 10 . 
 When this salt (KO . HO . C 8 H 4 10 ) is heated, the tartaric acid is decom- 
 posed into a variety of products, among which are found carbonic acid, 
 which remains in combination with the potash, and carbon, which is 
 left mixed with the carbonate of potash ; but if the heat be continued, 
 and free access of air permitted, the carbon will be entirely burnt away, 
 and carbonate of potash will be left (salt of tartar). 
 
 'In wine-producing countries, carbonate of potash is prepared from the 
 refuse yeast which rises during the fermentation, and is dried in the sun 
 in order to be subsequently incinerated. 
 
 The fleeces of sheep contain a considerable proportion of potash com- 
 bined with an animal acid ; when the fleece is washed with water, the 
 salt of potash is dissolved out, and on evaporating the liquid and burning 
 the residue, it is converted into carbonate of potash. 
 
 Hydrate of potash. Carbonate of potash was formerly called potash, 
 and was supposed to be an elementary substance. It was known that its 
 alkaline qualities were rendered far more powerful by treating it with 
 lime, which caused it to be termed mild alkali, in order to distinguish it 
 from the caustic* alkali obtained by means of lime, and possessed of very 
 powerful corrosive properties. Lime, it was said, is derived from lime- 
 stone by the action of fire, and therefore owes its peculiar properties to 
 the acquisition of a certain amount of the matter of fire, which, in turn, it 
 imparts to the mild alkali, and thus confers upon it a caustic or burning 
 power. 
 
 Black's researches in the middle of the eighteenth century, which are 
 often referred to as models of inductive reasoning, exposed the fallacy of 
 this explanation, and proved that instead of acquiring anything from the 
 fire, the limestone actually lost carbonic acid, and instead of imparting 
 anything to the mild alkali," the lime really gained as much carbonic acid 
 as it had previously lost. 
 
 The caustic potash, so largely employed by the soap-maker, is obtained 
 by adding slaked lime to a boiling diluted solution of the carbonate 
 of potash, when the water of the hydrate of lime is exchanged for the 
 carbonic acid, and the carbonate of lime is deposited at the bottom of the 
 vessel, whilst hydrate of potash remains in the clear solution 
 
 KO.C0 2 + CaO.HO = CaO.C0 2 + ^O.HO. 
 
 Carbonate of potash. Hydrate of lime. Carbonate of lime. Hydrate of potash. 
 
 If the solution of carbonate of potash be too strong, the lime will not 
 remove the whole of the carbonic acid. 
 
 When the solution is evaporated, the hydrate of potash remains as a 
 clear oily liquid, which solidifies to a white mass as it cools, and forms 
 the fused potash of commerce, which is often cast into cylindrical sticks 
 for more convenient use.t The hydrate of potash is the most powerful 
 alkaline substance in ordinary use, and is very frequently employed by the 
 chemist on account of its energetic attraction for the different acids. It 
 is generally used in the state of solution, the strength of which is inferred 
 from its specific gravity, this being higher in proportion to the amount of 
 potash contained in the solution. 
 
 * From Kcaa>, to burn. 
 
 t These have sometimes a greenish colour, due to the presence of some manganate of 
 potash. 
 
 R2 
 
260 
 
 POTASSIUM. 
 
 Potassium. Of the composition of hydrate of potash nothing was known 
 till the year 1807, when Davy succeeded in decomposing it by the gal- 
 vanic battery ; this experiment, which deserves particular notice, as being 
 the first of a series resulting in the discovery of so many important metals, 
 was made in the following manner : A fragment of hydrate of potash, 
 which, in its dry state, does not conduct electricity, was allowed to become 
 slightly moist by exposure to the air, and placed upon a plate of platinum 
 attached to the positive (copper) end of a very powerful galvanic battery ; 
 when the wire connected with the negative (zinc) end was made to touch 
 the surface of the hydrate of potash, some small metallic globules resem- 
 bling mercury made their appearance at the extremity of this (negative) 
 wire, at which the hydrogen contained in the hydrate of potash was also 
 eliminated, whilst bubbles of oxygen were separated on the surface of the 
 platinum plate connected with the positive wire (see p. 21). By allow- 
 ing the negative wire to dip into a little mercury contained in a cavity 
 upon the surface of the potash, a combination of potassium with mercury 
 was obtained, and the mercury was afterwards separated by distillation. 
 This process, however, furnished the metal in very small quantities, and, 
 
 though it was obtained with 
 greater facility a year or two 
 afterwards by decomposing 
 hydrate of potash with 
 white-hot iron, some years 
 elapsed before any consider- 
 able quantity of potassium 
 was prepared by the present 
 method of distilling in an 
 iron retort an intimate 
 mixture of carbonate of pot- 
 ash and carbon, obtained 
 by calcining cream of tar- 
 tar; in this process the 
 oxygen of the potash is re- 
 moved by the carbon in 
 the form of carbonic oxide 
 (KO.C0 2 +C 2 = K 
 
 The annexed figure repre- 
 sents the iron retort connected 
 Fig. 217. Preparation of potassium. with its copper receiver, sur- 
 
 rounded with cold water, and 
 
 containing petroleum to protect the distilled potassium from oxidation. The lateral 
 tube of the receiver permits the tube of the retort to be cleared, if necessary, during 
 the distillation, by the passage of an iron rod. 
 
 Some of the most striking properties of this metal have already been 
 referred to (p. 23) ; its softness, causing it to be easily cut like wax, the 
 rapidity with which its silvery surface tarnishes when exposed to the air, 
 its great lightness (sp. gr. 0'865), causing it to float upon water, and its 
 taking fire when in contact with that liquid, sufficiently distinguish it 
 from other metals. It fuses easily when heated, and is converted, at a 
 higher temperature, into a green vapour; if air be present, it burns with 
 a violet-coloured flame, and is converted into anhydrous potash, the oxide 
 of potassium (KO). 
 
 The property of burning with this peculiar violet-coloured flame is 
 
COMPOUNDS OF POTASSIUM. 2G1 
 
 characteristic of potassium, and allows it to be recognised in its com- 
 pounds. 
 
 If a solution of nitrate of potash (saltpetre) in water be mixed with enough spirit 
 of wine to allow of its being inflamed, the flame will have a peculiar lilac colour. 
 This colour may also be developed by exposing a very minute particle of saltpetre, 
 taken on the end of a heated platinum wire, to the reducing (inner) blowpipe flame 
 (fig. 218), when the potassium, being reduced to the metallic state, and passing 
 
 Fig. 218. Coloured flame test. 
 
 into the oxidising (outer) flame in the state of vapour, imparts to that flame a lilac 
 tinge. 
 
 The difficulty and expense attending the preparation of potassium have 
 prevented its receiving any application except in purely chemical opera- 
 tions, where its attraction for oxygen, chlorine, and other electronegative 
 elements, is often turned to account. 
 
 The chloride of potassium (KC1) is an important natural source of this 
 metal, being extracted from sea-water, from kelp (the ash of sea-weed), and 
 from the refuse of the manufacture of sugar from beet-root. It also occurs 
 in combination with chloride of magnesium, forming the mineral known 
 as carnallite (KC1 . 2MgCl . 12HO), an immense saline deposit overlying 
 the rock-salt in the salt-mines of Stassfurth in Saxony. Carnallite re- 
 sembles rock-salt in appearance, but is very deliquescent ; it promises to 
 become the most important source of potassium hitherto discovered. 
 
 Bicarbonate of potash (KO . HO . 2C0 2 ), which is much used in medi- 
 cine, is obtained by passing carbonic acid through a strong solution of 
 carbonate of potash, when it is deposited in crystals, being much less 
 soluble in water than the normal carbonate. 
 
 Nitrate of potash (KO . N0 5 ), or saltpetre, will be specially considered 
 in the section on gunpowder. 
 
 Equivalent and atomic weights of potassium. The chloride of potassium 
 has been found to contain 35 '5 parts by weight (1 eq.) of chlorine and 39 
 parts of potassium ; 39 is therefore regarded as the equivalent weight of this 
 metal. Since this represents the quantity required to displace one atom 
 of hydrogen from its compounds, it is also taken as the atomic weight of 
 potassium. Since potash contains 39 potassium combined with 8 oxygen, 
 its atomic formula would be K 2 (0 = 16) j and hydrate of potash would 
 be KHO. Chloride of potassium, however, has the atomic formula KC1 
 corresponding with its equivalent formula, because the atomic weights of 
 both its elements are the same as their equivalent weights. 
 
 The following less important compounds of potassium have not been noticed else- 
 
262 EXTRACTION OF COMMON SALT. 
 
 where, and are not of sufficient practical importance to require particular description 
 in this work : 
 
 Binoxide of potassium, KO 2 
 
 Peroxide ,. KO 4 
 
 Sulphide KS 
 
 Bisulphide KS 2 
 
 Tersulphide of potassium, KS 3 
 Tetrasulphide KS 4 
 
 Pentasulphide KS 5 
 
 SODIUM. 
 
 184. Sodium is often found, in place of potassium, in the feldspars and 
 other minerals, but we are far more abundantly supplied with it in the 
 form of common salt (chloride of sodium, NaCl), occurring not only in the 
 solid state, but dissolved in sea-water, and in smaller quantity in the 
 waters derived from most lakes, rivers, and springs. 
 
 Rock-salt forms very considerable deposits in many regions; in this 
 country the most important is situated at Northwich in Cheshire, where very 
 large quantities are extracted by mining. Wielitzka, in Poland, is cele- 
 brated for an extensive salt mine, in which there are a chapel and dwell- 
 ing-rooms, the furniture of which is made of this rock. Extensive beds 
 of rock-salt also occur in France, Germany, Hungary, Spain, Abyssinia, 
 and Mexico. Perfectly pure specimens form beautiful colourless cubes, 
 and are styled sal gem; but ordinary rock-salt is only partially transpar- 
 ent, and exhibits a rusty colour, due to the presence of iron. In some 
 places the salt is extracted by boring a hole into the rock and filling 
 it with water, which is pumped up when saturated with salt, and evapo- 
 rated in boilers, the minute crystals of salt being removed as they are 
 deposited. 
 
 At Droitwich, in Worcestershire, the salt is obtained by evaporation from 
 the waters of certain salt springs. In some parts of France and Germany 
 the water from the salt springs contains so little salt that it would not 
 pay for the fuel necessary to evaporate the w r ater, and a very ingenious 
 plan is adopted, by which the proportion of water is greatly reduced with- 
 out the application of artificial heat. For this purpose a lofty scaffolding is 
 erected and filled with bundles of brushwood, over which the salt water 
 is allowed to flow, having been raised to the top of the scaffolding by 
 pumps. In trickling over the brushwood this water exposes a large sur- 
 face to the action of the wind, and a considerable evaporation takes place, 
 so that a much stronger brine is collected in the reservoir beneath the 
 scaffolding ; by several repetitions of the operation, the proportion of water 
 is so far diminished that the rest may be economically evaporated by arti- 
 ficial heat. The brine is run into boilers and rapidly boiled for about 
 thirty hours, fresh brine being allowed to flow in continually, so as to 
 maintain the liquid at the same level in the boiler. During this ebullition 
 a considerable deposit, composed of the sulphates of lime and soda, is 
 formed, and raked out by the workmen. When a film of crystals of salt 
 begins to form upon the surface, the fire is lowered and the temperature of 
 the brine allowed to fall to about 180 F., at which temperature it is 
 maintained for several days whilst the salt is crystallising. The crystals 
 are afterwards drained and dried by exposure to air. The grain of the 
 salt is regulated by the temperature at which it crystallises, the size of the 
 crystals increasing as the temperature falls. It is not possible to extract 
 the whole of the salt in this way, since the last portions which crystallise 
 will always be contaminated with other salts present in the brine, but the 
 
EXTKACTION OF COMMON SALT. 263 
 
 mother-liquor is not wasted, for after as much salt as possible has been 
 obtained, it is made to yield sulphate of soda (Glauber's salt), sulphate of 
 magnesia (Epsom salts), bromine and iodine. 
 
 The process adopted for extracting the salt from sea-water depends 
 upon the climate. In Eussia, shallow pits are dug upon the shore, in 
 which the sea-water is allowed to freeze, when a great portion of the 
 water separates in the form of pure ice, leaving a solution of salt suffi- 
 ciently strong to pay for evaporation. 
 
 , Where the climate is sufficiently warm, the sea-water is allowed to run 
 very slowly through a series of shallow pits upon the shore, where it be- 
 comes concentrated by spontaneous evaporation, and is afterwards allowed 
 to remain for some time in reservoirs in which the salt is deposited. The 
 coarse crystals thus obtained are known in commerce as bay-salt. Before 
 they are sent into the market they are allowed to drain for a long time, 
 in a sheltered situation, when the chloride of magnesium with which they 
 are contaminated deliquesces in the moisture of the air and drains off. 
 The bittern or liquor remaining after the salt has been extracted is em- 
 ployed to furnish magnesia and bromine. 
 
 Great improvements have been made during the last few years in the economical 
 extraction of the salts from sea-water. It will be remembered that 1000 parts of 
 sea-water contain about 
 
 29-0 parts of chloride of sodium, 
 0'5 ,, chloride of potassium, 
 3-0 ,, chloride of magnesium, 
 25 ,, sulphate of magnesia, 
 1-5 ,, sulphate of lime, &c. 
 
 In a warm climate, that of Marseilles, for example, the water is allowed to evapo- 
 rate spontaneously until it has a specific gravity of 1-24. During this evaporation 
 it deposits about four-fifths of its chloride of sodium. It is then mixed with one 
 tenth of its volume of water and artificially cooled to F. (see p. 116), when it de- 
 posits a quantity of sulphate of soda, resulting from the decomposition of part of the 
 remaining chloride of sodium by the sulphate of magnesia. The mother-liquor is 
 evaporated down till its specific gravity is 1-33, a fresh quantity of chloride of 
 sodium being deposited during the evaporation. When the liquid cools it deposits 
 a double salt composed of chloride of potassium and chloride of magnesium, from 
 which the latter may be extracted by washing with a very little water, leaving the 
 chloride of potassium fit for the market. 
 
 This process is instructive as illustrating the influence exerted upon the arrange- 
 ment of the various acids and bases in a saline solution by the temperature to which 
 the solution is exposed, the general rule being that a salt is formed which is in- 
 soluble in the liquid at that particular temperature. 
 
 The great tendency observed in ordinary table salt to become damp 
 when exposed to the air is due chiefly to the presence of small quantities 
 of chloride of magnesium and chloride of calcium, for pure chloride of 
 sodium has very much less disposition to attract atmospheric moisture, 
 although it is very easily dissolved by water, 2 J parts of this liquid being 
 able to dissolve one part (by weight) of salt. 
 
 In the history of the useful applications of common salt is to be found 
 one of the best illustrations of the influence of chemical research upon 
 the development of the resources of a country, and a capital example of a 
 manufacturing process not based, as such processes usually are, upon mere 
 experience, independent of any knowledge of chemical principles, but 
 upon a direct and intentional application of these to the attainment of a 
 particular object. 
 
264 
 
 MANUFACTURE OF ALKALI. 
 
 Until the last quarter of the eighteenth century the uses of common 
 salt were limited to culinary and agricultural purposes, and to the glazing 
 of the coarser kinds of earthenware, whilst a substance far more useful in 
 the arts, carbonate of soda, was imported chiefly from Spain under the 
 name of barilla, which was the ash obtained by burning a marine plant 
 known as the salsola soda. But this ash only contained about one-fourth 
 of its weight of carbonate of soda, so that this latter substance was thus 
 imported at a great expense, and the manufactures of soap and glass to 
 which it is indispensable were proportionally fettered. 
 
 During the wars of the French Devolution the price of barilla had risen 
 so considerably, that it was deemed advisable by Napoleon to offer a 
 premium for the discovery of a process by which the carbonate of soda 
 could be manufactured at home, and to this circumstance we are indebted 
 for the discovery, by Leblanc, of the process at present in use for the 
 manufacture of carbonate of soda from common salt, a discovery which 
 placed this substance at once among the most important raw materials 
 with which a country could be furnished. 
 
 185. Manufacture of carbonate of soda from common salt. The salt is 
 spread upon the hearth of a reverberatory furnace (fig. 219),* and mixed 
 
 Fig. 219. Furnace for converting common salt into sulphate of soda. 
 
 with an equal weight of sulphuric acid, which converts it into the sul- 
 phate of soda (p. 147), expelling the hydrochloric acid in the form of 
 gas, which would prove highly injurious to the vegetation in the neigh- 
 bourhood, and is therefore -usually condensed by being brought into con- 
 tact with water (see p. 148). The flame of the fire is allowed to play 
 over the surface of the mixture of salt and sulphuric acid until it has 
 become perfectly dry ; in this state it is technically known as salt-cake, 
 and is next mixed with about an equal weight of limestone and rather 
 more than half its weight of small coal; this mixture is again heated 
 upon the hearth of a reverberatory furnace, when it evolves an abun- 
 dance of carbonic oxide, and yields a mixture of carbonate of soda with 
 
 * The hearth of this furnace is usually divided, as seen in the figure, into two compart- 
 ments, in one of which (lined with lead), more remote from the grate, the decomposition is 
 effected, the acid being poured in through the funnel, while in that nearest to the grate, 
 lined with fire-brick, the whole of the hydrochloric acid is expelled, and the sulphate of 
 soda fused. 
 
SODA-ASH SODA-CRYSTALS. 265 
 
 lime and sulphide of calcium ; this mixture is technically known as 
 Hack ash. 
 
 The change which has been effected in the sulphate of soda will be 
 easily understood ; for when this salt is heated in contact with carbon 
 (from the small coal) it loses its oxygen, and becomes sulphide of sodium, 
 whilst carbonic acid is evolved ; thus 
 
 NaO . S0 3 + C 2 = NaS + 2C0 2 . 
 
 Again, when carbonate of lime is heated in contact with carbon, carbonic 
 oxide is given off, and lime remains 
 
 CaO . C0 2 + C = 2CO + CaO . 
 
 Finally, when sulphide of sodium and lime are heated together in the 
 presence of carbonic acid, carbonate of soda and sulphide of calcium are 
 produced 
 
 NaS + CaO + C0 2 = JS"aO . C0 2 + CaS . 
 
 When the black ash is treated with water, the carbonate of soda is dis- 
 solved, leaving the sulphide of calcium, and by evaporating the solution, 
 ordinary soda ash is obtained. But this is by no means pure carbonate of 
 soda, for it contains, in addition to a considerable quantity of common 
 salt and sulphate of soda, a certain amount of caustic soda or hydrate of 
 soda formed by the action of the lime upon the carbonate of soda. In 
 order to purify it, the crude soda-ash is mixed with small coal or saw-dust 
 and again heated, when the carbonic acid formed from the carbonaceous mat- 
 ter converts the hydrate of soda into carbonate, and on dissolving the mass 
 in water and evaporating the solution, it deposits oblique rhombic prisms 
 of common washing soda, having the composition, NaO . C0 2 + lOAq. 
 (soda-crystals) . 
 
 A little reflection will show the important influence which this process 
 has exerted upon the progress of the useful arts in this country. The 
 three raw materials, salt, coal, and limestone, we possess in abundance. 
 The sulphuric acid, when the process was first introduced, bore a high 
 price, but the resulting demand for this acid gave rise to so many improve- 
 ments in its manufacture that its price has been very greatly diminished, 
 a circumstance which has, of course, produced a most beneficial effect upon 
 all branches of manufacture in which the acid is employed. 
 
 The large quantity of hydrochloric acid obtained as a secondary product 
 has been employed for the preparation of bleaching powder, and the 
 important arts of bleaching and calico-printing have thence received a 
 considerable impulse. These arts have also derived a more direct, benefit 
 from the increased supply of carbonate of soda, which is so largely used 
 for cleansing all kinds of textile fabrics. The manufactures of soap and 
 glass, which probably create the greatest demand for carbonate of soda, 
 have been increased and improved beyond all precedent by the production 
 of this salt from native sources. 
 
 The crystals of carbonate of soda are easily distinguished by their pro- 
 perty of efflorescing in dry air (p. 48), and by their alkaline taste, which is 
 much milder than that of carbonate of potash, this being, moreover, a 
 deliquescent salt. The crystals are very soluble in water, requiring only 2 
 parts of cold and less than their own weight of boiling water ; the solution 
 is strongly alkaline to test papers. 
 
 The substance commonly used in medicine under the name of carbonate 
 
266 SODIUM. 
 
 of soda, is really the bicarbonate (NaO . C0 2 . HO . CO^), and is prepared 
 by saturating the carbonate of soda with carbonic acid gas. It is readily 
 distinguished from the carbonate, as it is but slightly alkaline, and is very 
 much less easily dissolved by water. 
 
 Soda lye, employed in the manufacture of hard soap, is a solution of 
 hydrate of soda (NaO. HO), obtained by decomposing the carbonate of 
 soda with hydrate of lime (slaked lime, CaO . HO), when the v/ater of this 
 latter compound is exchanged for the carbonic acid of the carbonate. 
 
 The solid hydrate of soda of commerce is generally obtained in the pro- 
 cess for manufacturing carbonate of soda, just described; the solution 
 obtained by treating the black ash with water is concentrated by evapo- 
 ration, so that the carbonate and sulphate of soda and chloride of sodium 
 may crystallise out, leaving the hydrate of soda, which is far more soluble, 
 in the liquid. The latter, which still contains a compound of sulphide of 
 sodium and sulphide of iron, which gives it a red colour, is mixed with 
 some nitrate of soda to oxidise the sulphides, and evaporated down until 
 a fused mass of hydrate of soda is left, which is poured out into iron 
 moulds.* 
 
 Kryolite (3NaF . A1 2 F 3 ) is sometimes employed as a source of the 
 sodium for hydrate of soda, which may be obtained by decomposing it 
 with hydrate of lime. ;..; 
 
 186. Sodium. Potash and soda exhibit so much similarity in their 
 properties, that we cannot be surprised at their having been confounded 
 together by the earlier chemists, and it was not till 1736 that Du Hamel 
 pointed out the difference between them. The discovery of potassium 
 naturally led Davy to that of sodium, which can be obtained by processes 
 exactly similar to those adopted for procuring potassium, to which it will 
 be remembered sodium presents very great similarity in properties (p. 23). 
 Sodium, however, is readily distinguished from potassium by its burning 
 with a yellow flame, which serves even to characterise it when in com- 
 bination. 
 
 This yellow flame is well seen by dissolving salt in water in a plate, and adding 
 enough spirit of wine to render it inflammable, the mixture being well stirred while 
 burning. If a little piece of sodium be burnt in an iron spoon held in a flame, all 
 the flames in the room, even at a remote distance, will be tinged yellow. The 
 blowpipe flame may also be employed to detect sodium by this colour, as in the 
 case of potassium (p. 261). In fireworks, nitrate of soda is employed for producing 
 yellow flames. A very good yellow fire may be made by intimately mixing, in a 
 mortar, 74 grs. of nitrate of soda, 20 grs. of sulphur, 6 grs. of sulphide of antimony, 
 and 2 grs. of charcoal, all carefully dried, and very finely powdered. 
 
 The preparation of sodium, by distilling a mixture of carbonate of soda 
 and charcoal, is much easier than that of potassium, for which reason 
 sodium is far less costly than that metal, and has received applications, on 
 the large scale, during the last few years, for the extraction of the metals 
 aluminum and magnesium. An amalgam of sodium (p. 119) is also 
 employed with advantage in extracting gold and silver from their ores. 
 
 * Another plan of treating the black ash liquor consists in allowing it to trickle through 
 a column of coke against a current of air, when the sulphid e of sodium (NaS) is oxidised and 
 converted into soda (NaO) and hyposulphite of soda (NaO . S 2 O 2 ), whilst the sulphide of 
 iron is deposited. The liquor is mixed with a little chloride of lime to oxidise any remain- 
 ing sulphides, and concentrated by evaporation, when carbonate of soda and ferrocyanide 
 of sodium are deposited in crystals. The liquor separated from these contains the hydrate 
 of soda, and is evaporated till it solidifies on cooling. 
 
MANUFACTURE OF BOliAX. 267 
 
 To obtain sodium, in large quantity, a mixture of dried carbonate of soda, 
 powdered coal, and chalk, is distilled in iron cylinders, when the oxygen 
 of the soda is abstracted by the carbon, which it converts into carbonic 
 oxide, and the sodium passes over in the form of vapour. 
 
 NaO.COj + C 2 - Na + SCO. 
 The chalk is employed to prevent the fusion of the mixture. 
 
 187. Borax, or biborate of soda. A very important compound of soda 
 is used in the arts under the name of borax, in which the soda is combined 
 with boracic acid. It has already been stated that this substance is 
 deposited during the evaporation of the waters of certain lakes in Thibet, 
 whence it is imported into this country in impure crystals, which are 
 covered with a peculiar greasy coating. The refiner of tincal powders the 
 crystals and washes them, upon a strainer, with a weak solution of soda, 
 which converts the greasy matter into a soap and dissolves it. The borax 
 is then dissolved in water, a quantity of carbonate of soda is added to 
 separate some lime which the borax usually contains, and, after filtering 
 off the carbonate of lime, the solution is evaporated to the crystallising 
 point and allowed to cool, in order that it may deposit the pure crystals 
 of borax. 
 
 It appears, however, that the greater part of the borax employed in the 
 arts is manufactured in this country by heating carbonate of soda with 
 boracic acid, when the latter expels the carbonic acid and combines with 
 the soda.* The mass is then dissolved in water, and the borax crystal- 
 lised, an operation upon which much care is bestowed, since the product 
 does not meet with a ready sale unless in large crystals. 
 
 The solution of borax, having been evaporated to the requisite degree of 
 concentration, is allowed to crystallise in covered wooden boxes, which are 
 lined with lead and enclosed in an outer case of wood, the space between 
 the sides of the case and -the box being stuffed with some bad conductor 
 of heat, so that the solution of borax may cool very slowly, and large 
 crystals may be deposited. In about thirty hours the crystallisation is com- 
 pleted, when the liquid is drawn off as rapidly as possible, the last portion 
 being carefully soaked up with sponges, so that no small crystals may be 
 afterwards formed upon the surface of the large ones ; the case is then 
 again covered up, so that the crystals may cool slowly without cracking. 
 
 Borax is chemically known as biborate of soda, and is represented, in 
 the dry state, by the formula NaO . 2B0 3 . The ordinary prismatic crys- 
 tals, however, contain ten equivalents of water of crystallisation, and are, 
 therefore, represented by the formula NaO . 2B0 3 + lOAq. They soon 
 effloresce and become opaque when exposed to air, and may readily be 
 distinguished by their alkaline taste and action upon test-papers, and 
 especially by their behaviour when heated, for they fuse easily and intu- 
 mesce most violently, swelling up to a white spongy mass of many times 
 their original bulk; this mass afterwards fuses down to a clear liquid 
 which forms a transparent glassy mass on cooling (wtrefied borax), and 
 since this glass is capable of dissolving many metallic oxides with great 
 readiness (borax being, by constitution, an acid salt, and therefore ready 
 to combine with more base), it is much used in the metallurgic arts. 
 Large quantities of borax are also employed in glazing stoneware. 
 
 * The ammonia which is evolved from the Tuscan boracic acid employed in this process 
 is known in commerce as Volcanic ammonia, and is free from the empyreumatic odour which 
 generally accompanies that from coal and bones. 
 
268 SALTS OF SODA. 
 
 188. Silicate of soda. A combination of soda with silicic acid has long 
 been used, under the name of soluble glass, for imparting a lire-proof cha- 
 racter to wood and other materials, and, more recently, for producing 
 artificial stone for building purposes, and for a peculiar kind of permanent 
 fresco-painting (stereochromy), the results of which are intended to with- 
 stand exposure to the weather. 
 
 Soluble glass is usually prepared by fusing 15 parts of sand with 8 
 parts of carbonate of soda and 1 part of charcoal. The silicic acid, com- 
 bining with the soda, disengages the carbonic acid, the expulsion of which 
 is facilitated by the presence of charcoal, which converts it into carbonic 
 oxide. The mass thus formed is scarcely affected by cold water, but dis- 
 solves when boiled with water, yielding a strongly alkaline liquid. 
 
 In using this substance for rendering wood fire-proof, a rather weak 
 solution is first applied to the wood, and over this a coating of lime-wash 
 is laid, a second coating of soluble glass (in a more concentrated solu- 
 tion) is then applied. The wood so prepared is, of course, charred, as 
 usual, by the application of heat, but its inflammability is remarkably 
 diminished. 
 
 For the manufacture of Ransome's artificial stone, the soluble glass is 
 prepared by heating flints, under pressure, with a strong solution of hydrate 
 of soda, to a temperature between 300 and 400 F., when the silicic acid 
 constituting the flint enters into combination with the soda. Finely 
 divided sand is moistened with this solution, pressed into moulds, dried, 
 and exposed to a high temperature, when the silicate of soda fuses and 
 cements the grains of sand together into a mass of artificial sandstone, to 
 which any required colour may be imparted by mixing metallic oxides 
 with the sand before it is moulded. 
 
 Silicate of soda is also sometimes used as a dung substitute (p. 246) in 
 calico-printing. 
 
 Sulphate of soda forms the very common saline efflorescence upon the 
 surface of brick walls, and has been found covering the sandy soil of the 
 Desert of Atacama, over a considerable area. The mineral known as 
 Thenardite also consists of sulphate of soda, and Glauberite is a double 
 sulphate of soda and lime (NaO . S0 3 , CaO . SO.) which is nearly insoluble 
 in water. 
 
 Phosphate of soda (2NaO . HO . P0 5 + 24Aq.) is obtained by neutra- 
 lising, with carbonate of soda, the impure phosphoric acid obtained by 
 decomposing bone-ash with sulphuric acid (p. 230). On evaporation 
 the phosphate is deposited in oblique rhombic prisms which effloresce 
 in air. 
 
 Nitrate of soda will be more particularly noticed in the section on gun- 
 powder. It is imported from Peru, and used in considerable quantity as 
 a manure, and for the manufacture of nitrate of potash. 
 
 Equivalent and. atomic weights of sodium. The analysis of pure chlo- 
 ride of sodium has shown it to contain one equivalent, or 35*5 parts by 
 weight of chlorine combined with 23 parts of sodium; hence 23 is taken 
 to represent the equivalent of sodium. As in the case of potassium, the 
 atomic weight of sodium coincides with the equivalent, the atomic formula 
 of chloride of sodium being NaCl ; that of soda would be Na 2 O (0 = 16), 
 and that of hydrate of soda NaHO. 
 
SALTS OF AMMONIA. 269 
 
 SALTS OF AMMONIA. 
 
 The great chemical resemblance between some of the salts of ammonia 
 and those of potash and soda has been already pointed out as affording 
 a reason for the hypothesis of the existence of a compound metal 
 ammonium (NH 4 ) equivalent in its functions to potassium and sodium. 
 However convenient this assumption may be for the purpose of repre- 
 senting by equations the chemical changes in which the salts of ammonia 
 take part, it is evidently necessary to place these salts on a different 
 footing from those of potash and soda, until either the metal itself or 
 its oxide (NH 4 0), which is at present equally hypothetical, shall be 
 obtained. This has become the more necessary since modern chemistry 
 has brought to light certain organic bases which exhibit a stronger resem- 
 blance to potash and soda than that evinced by ammonia, rendering it 
 necessary to extend to these also the hypothesis of the existence of com- 
 pound metals, and thus to encumber chemical pages with the names ofk, large 
 class of substances of the existence of which there is no direct evidence. 
 
 Much encouragement has been afforded to the belief in the existence of 
 oxide of ammonium (NH 4 0), by the circumstance that the compounds which 
 are formed when ammonia (NH 3 ) combines with the anhydrous acids, 
 such as carbonic (C0 2 ) and sulphuric (S0 3 ), do not exhibit the resem- 
 blance to the salts of potash and soda until water is added, the elements 
 of which are required to convert the NH 3 into NH 4 O. Thus, by the 
 action of dry ammonia gas upon anhydrous sulphuric acid, a compQund 
 called sulphuric ammonide is formed, having the composition NH 3 . S0 a . 
 This substance dissolves in water and crystallises in octahedra, but its 
 solution is not precipitated by chloride of barium, which always precipi- 
 tates the true sulphates, nor by chloride of platinum which precipitates 
 the true salts of ammonia. By long boiling with water, however,, it 
 becomes converted into tHe sulphate of ammonia, NH 3 . HO . S0 3 (or sul- 
 phate of oxide of ammonium, NH 4 . S0 3 ), which yields precipitates with 
 both the above tests. The anhydrous phosphoric, carbonic, and sulphurous 
 acids also combine with dry ammonia to form ammonides, which do not 
 respond to the ordinary tests for the corresponding salts of ammonia until 
 after water has been assimilated. The true salts of ammonia are pro- 
 duced either by the combination of a hydrated acid with ammonia, or by 
 double decomposition. 
 
 Sulphate of ammonia (NH 3 . HO . S0 3 ) is largely employed in the pre- 
 paration of ammonia-alum, and of artificial manures, for which purposes it 
 is generally obtained from the ammoniacal liquor of the gas-works by 
 neutralising with sulphuric acid and evaporating. The rough crystals are 
 gently heated to expel tarry substances, and purified by recrystallisation. 
 The crystals have the same shape as those of sulphate of potash, and are 
 easily soluble in water. When heated to about 500 F. the sulphate 
 of ammonia is decomposed, yielding vapour of sulphite of ammonia 
 (NH 3 . HO . S0 2 ), water, ammonia, nitrogen, and sulphurous acid. If 
 muslin be dipped into a solution of sulphate of ammonia in ten parts of 
 water, and dried, it will no longer burn with flame when ignited. The 
 mineral mascagnine consists of sulphate of ammonia. This salt is occa- 
 sionally found in needle-like crystals upon the windows of rooms in which 
 coal-gas is burnt. The bisulphate of ammonia contains NH 3 . 2 (HO . S0 3 ). 
 
 Sesquicarbonate of ammonia, 2KH 3 . 2HO. 3C0 2 (or 2NH 4 O. 3C0 2 ), is 
 
270 SAL-AMMONIAC. 
 
 the common carbonate of ammonia of the shops, also called smelling salts 
 or Preston salts, largely used in medicine, and by bakers and confec- 
 tioners, for imparting lightness or porosity to cakes, &c. It is com- 
 monly prepared by mixing sal-ammoniac (hydrochlorate of ammonia) 
 with twice its weight of chalk, and distilling the mixture in an earthen 
 or iron retort communicating, through an iron pipe, with a leaden chamber 
 or receiver, in which the sesquicarbonate of ammonia collects as a trans- 
 parent fibrous mass, which is extracted by taking the receiver to pieces, 
 and purified by re-subliming it at about 130 F., in iron vessels sur- 
 mounted by leaden domes. The action of carbonate of lime upon hydro- 
 chlorate of ammonia would be expected to furnish the neutral carbonate 
 (NH 3 . HO . C0 2 ), but this salt (even if produced) is decomposed by the heat 
 employed in the process, with loss of ammonia and water, and formation 
 of sesquicarbonate of ammonia 
 
 3(NH 3 .HC1) + 3(CaO.C0 2 ) = 
 2NH 3 .2H0.3C0 2 + ]STH 3 + HO + 3CaCl. 
 
 When a mass of freshly prepared sesquicarbonate of ammonia is ex- 
 posed to air, it evolves ammonia and carbonic acid, and becomes gradually 
 converted into an opaque crumbly mass of bicarbonate of ammonia 
 
 2NH 3 .2H0.3C0 2 = JSTH 3 + C0 2 + NH 3 . 2HO . 2C0 2 . 
 
 Water effects this decomposition more rapidly ; if the powdered sesqui- 
 carbonate of ammonia be washed with a little water, bicarbonate of 
 ammonia is left, and the solution contains the elements of neutral car- 
 bonate of ammonia (NH 3 . HO . C0 2 ), but this salt has not been obtained 
 in the solid form. The sesquicarbonate dissolves in about three times its 
 weight of cold water. Boiling water decomposes it, and the solution, on 
 cooling, deposits large prismatic crystals of bicarbonate of ammonia 
 (NH 3 . 2HO . 2C0 2 ) which is much less soluble in water. This salt has 
 been found in considerable quantity, forming crystalline masses in a bed 
 of guano on the western coast of Patagonia. Sal volatile is an alcoholic 
 solution of carbonate of ammonia obtained by distilling sal-ammoniac 
 with carbonate of potash and rectified spirit of wine, or by treating the 
 sesquicarbonate of ammonia with hot spirit. 
 
 By dissolving sesquicarbonate of ammonia in strong solution of am- 
 monia, and adding alcohol, prismatic crystals of the sesquicarbonate, of 
 the formula 2NH 3 . 2HO . 3C0 2 + 2Aq., may be obtained. 
 
 Hydrochlorate of ammonia (NH 3 .HC1), or chloride of ammonium 
 (NH 4 C1), also called muriate of ammonia and sal-ammoniac. When dry 
 ammonia gas is brought in contact with an equal volume of dry hydro- 
 chloric acid gas, it has been seen (p. 119) that they combine directly to 
 produce the hydrochlorate of ammonia, the preparation of which on the 
 large scale has been noticed at p. 1 1 3. It is also sometimes made by 
 subliming a mixture of sulphate of ammonia with common salt 
 
 NH 3 .HO.S0 3 + NaCl = NH 3 .HC1 + NaO.SO, . 
 
 Its commercial form is that of a very tough translucent fibrous mass, 
 generally of the dome-like shape of the receivers, and often striped with 
 brown, from the presence of a little iron. It has not the least smell of 
 ammonia, and is very soluble in water, requiring about three parts of cold 
 water, and little more than its own weight of boiling water. As the hot 
 solution cools, it deposits beautiful fern-like crystallisations composed of 
 minute cubes and octahedra. The liquefaction of sal-ammoniac in water 
 
DISSOCIATION OF VAPOUR OF SAL-AMMONIAC. 271 
 
 lowers the temperature very considerably, which renders the salt very 
 useful in freezing mixtures. A mixture of equal weights of sal-ammoniac 
 and nitre, dissolved in its own weight of water, lowers the temperature 
 of the latter from 50 F. to 10. In this case partial decomposition takes 
 place, resulting in the production of chloride of potassium and nitrate of 
 ammonia, both of which absorb much heat whilst being dissolved by 
 water. The solution of hydrochlorate of ammonia in water is slightly 
 acid to blue litmus paper. When sal-ammoniac is heated, it passes off in 
 vapour, at a temperature below redness, without previously fusing ; the 
 vapour forms thick white clouds in the air, and may be recondensed as a 
 white crust upon a cold surface; but it cannot be sublimed without some loss, 
 a portion being decomposed into hydrochloric acid, hydrogen, and nitrogen. 
 The specific gravity (weight of 1 vol.) of the vapour of sal-ammoniac is 
 0'89. The formula NH 3 . HC1 represents a compound of 1 eq. or 4 vols. 
 of ammonia (0 = 1 vol.), and 1 eq. or 4 vols. of hydrochloric acid. 
 
 sp. gr. 
 
 Weight of 4 vols. of NH, (059 x 4) = 2 -36 
 4 vols. of HC1 (1-25 x 4) = 5'00 
 
 7-36 
 
 This number obviously represents the weight of 8 vols. of hydrochlorate 
 of ammonia vapour, or one equivalent of this vapour occupies eight times 
 the volume of an equivalent (8 parts by weight) of oxygen, or four 
 times that of an equivalent (1 part by weight) of hydrogen. On the 
 atomic system, according to which one atom of an element occupies one 
 volume, and one molecule of a compound occupies two volumes, hydro- 
 chlorate of ammonia vapour should occupy twice the volume of one part 
 by weight of hydrogen, whereas its specific gravity shows it to occupy 
 four times that volume. This anomaly might be explained by supposing 
 a temporary dissociation of the hydrochloric acid and ammonia when the 
 salt is converted into vapour, so that the observed specific gravity is really 
 that of a mixture of equal volumes of these constituent gases. Some 
 experimental evidence has been obtained in support of this view, for it 
 has been found that free ammonia and hydrochloric acid may be separated 
 by diffusion from the vapour obtained on heating hydrochlorate of 
 ammonia. When this salt is heated with metallic oxides, its hydro- 
 chloric acid often converts the oxide into a chloride which is either 
 fusible or volatile, so that sal-ammoniac is often employed for cleansing 
 the surfaces of metals previously to soldering them. Even those metallic 
 oxides which are destitute of basic properties, such as antimonic and 
 stannic acids, are convertible into chlorides by the action of sal-ammoniac 
 at a high temperature. 
 
 Hydrochlorate of ammonia is found in volcanic districts, and is present 
 in very small quantity in sea-water. 
 
 Hydrosulpliate of ammonia (NH 3 .HS), or sulphide of ammonium 
 (NH 4 S), has been obtained in colourless crystals by mixing hydrosulphuric 
 acid gas with twice its volume of ammonia gas in a vessel cooled by a 
 mixture of ice and salt. It is a very unstable compound, decomposing at 
 the ordinary temperature of the air into free ammonia and bi-hydrosulphate 
 of ammonia, NH 3 . 2HS, which may be obtained in very volatile colour- 
 less needles by passing equal volumes of its constituent gases into a vessel 
 cooled in ice. When a solution of ammonia is saturated with hydrosul- 
 
272 LITHIUM. 
 
 phuric acid gas, the ammonia is found to have combined with two 
 equivalents of hydrosulphuric acid, forming a solution of the bi-hydrosul- 
 phate or hydrosulphate of sulphide of ammonium (NH 4 S . HS). The 
 solution is colourless when freshly prepared, but it soon becomes yellow in 
 contact with the air, from the formation of the bisulphide of ammonium 
 (NH 4 S 2 ), hyposulphite of ammonia being formed at the same time 
 
 2(m 4 S.HS) + 5 - NH 4 S 2 + NH 4 O.S 2 2 + 2HO . 
 
 Eventually, the solution deposits sulphur and becomes colourless, hypo- 
 sulphite, sulphite, and sulphate of ammonia being formed. When the 
 freshly prepared colourless solution of the bi-hydrosulphate of ammonia is 
 mixed with an acid, the solution remains clear, hydrosulphuric acid being 
 evolved with effervescence ; NH ? .2HS + HC1 = NH 3 .HC1 + 2HS ; 
 but if the solution be yellow, a milky precipitate of sulphur is produced, 
 from the decomposition of the bisulphide of ammonium 
 
 NH 4 S 2 + HC1 - NH 4 C1 + HS + S . 
 
 The fresh solution gives a black precipitate of sulphide of lead when 
 solution of acetate of lead is added to it, but after it has been kept till it 
 is of a dark yellow or red colour, it gives a red precipitate of the per- 
 sulphide of lead. Solution of hydrosulphate of ammonia, prepared by 
 mixing the bi-hydrosulphate with an equal volume of solution of ammonia, 
 is largely employed in analytical chemistry. The solution has a very 
 disagreeable odour. 
 
 Bisulphide of ammonium is obtained in deliquescent yellow crystals, when a mixture 
 of ammonia gas with vapour of sulphur is passed through a red-hot porcelain tube. 
 It is the chief constituent of Boyle's fuming liquor, a fetid yellow liquid obtained by 
 distilling sal-ammoniac with sulphur and lime. The bisulphide of ammonium is 
 sometimes deposited in yellow crystals from this liquid. By dissolving sulphur in 
 the bisulphide of ammonium, orange-yellow prismatic crystals of pentasulphide of 
 ammonium (NH 4 S 5 ) may be obtained. Even a heptasulphide of ammonium (NH 4 S 7 ) 
 has been crystallised. 
 
 Compounds may be obtained in which the sulphide of ammonium (NH 4 S) plays 
 the part of a sulphur-base towards the sulphides of arsenic, antimony, and other 
 sulphur-acids. 
 
 It is scarcely possible to represent the constitution of the higher sulphides of 
 ammonium except on the ammonium hypothesis. 
 
 The hydrobromate of ammonia (NH 3 . HBr), or bromide of ammonium (NH 4 Br), and 
 the hydriodate of ammonia (NH 3 . HI), or iodide of ammonium (NH 4 I), are useful in 
 photography. They are both colourless crystalline salts, but the iodide is very liable 
 to become yellow or brown, from the separation of iodine, unless kept dry and in 
 the dark. Both salts are extremely soluble in water. 
 
 LITHIUM is a comparatively rare metal, obtained chiefly from the minerals lepido- 
 lite (x**r/j, a scale) or lithia-mica, containing silicate of alumina with fluorides of 
 potassium and lithium ; petalite (ffiru.Xav, a leaf), silicate of soda, lithia, and alumina, 
 and triphane or spodumene (<rv<dos, ashes), which has a similar composition. Its name 
 (from x'dos, a stone) was bestowed in the belief that it existed only in the mineral 
 kingdom, but recent investigation has detected it in minute proportion in the ashes 
 of tobacco and other plants. 
 
 Metallic lithium is obtained by decomposing fused chloride of lithium by a gal- 
 vanic current. It is remarkable as the lightest of the solid elements (sp. gr. 0-69). 
 It bears a general resemblance to potassium and sodium, but is harder and less 
 easily oxidised than those metals. It decomposes water rapidly at the ordinary 
 temperature, but does not inflame upon it. 
 
 The alkali lithia (LO) powerfully corrodes platinum when heated upon it, and also 
 differs from potash and soda by forming a sparingly soluble phosphate (3LO . P0 5 ) 
 and carbonate (LO.C0 2 ). The compounds of lithium impart a red colour to the 
 flame of the blowpipe (p. 261). 
 
 Carbonate of lithia is occasionally employed medicinally. 
 
SPECTKUM ANALYSIS. 273 
 
 RUBIDIUM and CCESIUM were discovered so lately as in 1860, by Bunsen and 
 Kirchhoff, during the analysis of a certain spring water which contained these 
 metals in so minute quantity (2 or 3 grs. in a ton) that they would certainly have 
 escaped observation if the analysis had been conducted in the ordinary way. The 
 discovery of these metals, as well as of two others (thallium and indium) to be 
 mentioned hereafter, was the result of the application of the method of spectrum 
 analysis, of which a brief description is here given, although the discussion of the 
 optical principles upon which it depends would be misplaced in a chemical work. 
 
 189. Spectrum analysis. It has been mentioned above that compounds 
 of potassium, sodium, and lithium impart, respectively, lilac, yellow, and 
 red colours to the blowpipe- flame (or air-gas flame, see p. 96), or, in 
 other words, that the highly heated vapours of the metals evolve luminous 
 rays of these particular colours. When the quantity of the metal is 
 extremely minute, and its peculiar luminous rays proportionally scanty, 
 their colour may very easily escape notice, especially if two or three metals 
 are present in the flame at the same time. But if the light emanating 
 from the flame be collected by a lens (at A, fig. 220), and transmitted 
 through a prism of flint glass, or through a hollow prism filled with 
 bisulphide of carbon (B), all 
 the rays of one colour will 
 be refracted in a definite 
 direction, so that the spec- 
 trum, or image of the flame, 
 when thrown upon a screen, 
 instead of exhibiting colours 
 uniformly distributed like 
 the flame itself, will show 
 stripes or bands of the vari- 
 ous coloured rays existing in 
 the flame. Thus, when va- 
 pour of sodium is present in Fig. 220. Spectroscope, 
 the flame, the whole of the 
 
 yellow light emitted by it will be collected in the spectrum into a narrow 
 yellow stripe of great intensity, and so extremely delicate is this test that 
 it is scarcely possible to obtain a flame which does not exhibit this sodium 
 line. The heated vapour of lithium emits a mixture of red with a few 
 yellow rays, and accordingly, the spectrum of a flame containing lithium 
 exhibits a very bright band of red light, and a comparatively dull band 
 of yellow light, the red band being characteristic of lithium. The potas- 
 sium flame emits a mixture of blue and red rays, so that its spectrum 
 exhibits a distinct red band of a darker colour than the lithium band, and 
 a feeble violet band. Instead of throwing the spectrum upon a screen, it 
 is generally passed through a telescope (C) to the eye of the observer, 
 and the spectroscope so constructed has now taken its place among the 
 apparatus indispensable to the analytical chemist. The prism B may be 
 slowly moved round by a handle attached to the stage on which it rests, 
 in order that the different parts of the spectrum may be successively 
 brought into sight. By comparing the spectra of the flames containing 
 vapours of the metals with a picture or map of the solar spectrum (fig. 
 221), the exact position of the various coloured bands may be noted, and 
 thus, if several metals are present in the same flame, they may still be dis- 
 tinguished by the colours and positions of their bands. Thus, if a mixture 
 of the chlorides of potassium, sodium, and lithium be taken upon a loop 
 of platinum wire and held in the flame, the dull red line of potassium 
 
274 
 
 RUBIDIUM CCE SIUM. 
 
 (K, fig. 221) is seen close to one end of the spectrum, at some distance 
 from it the bright red band (L) of lithium ; at about the same distance 
 
 Violet. Indigo. -Blue 
 
 Green. Yellnw. Orcnine. Red. 
 
 Spectrum furnished by solar light decomposed by a prism. 
 
 g 
 
 B 
 ' g 
 
 I H 
 
 3 " 8 
 
 ^Q yj u 
 
 83 
 
 Coloured bands in the spectrum. 
 Fig. 221. 
 
 from this, the pale yellow lithium line ; and close to this, the bright yel- 
 low band of sodium (Na) ; whilst near to the other end of the spectrum 
 is the feeble violet band of potassium (k). The chlorides of the metals 
 are most suitable for this experiment, on account of their easy conversion 
 into vapour. 
 
 When examining, with the spectroscope, the alkaline chlorides extracted from the 
 spring water above alluded to, Bunsen and Kirchhoff observed two red and two blue 
 bands in the spectrum, which they could not ascribe to any known substance, and 
 which they ultimately traced to the two new metals, rubidium (rubidus, dark-red) 
 and ccesium (coesius, sky-blue). 
 
 Kubidium has since been found in small quantity in other mineral waters, in 
 lepidolite, and in the ashes of many plants. This metal is closely related, in pro- 
 perties, to potassium, but is more easily fusible and convertible into vapour, and 
 actually surpasses that metal in its attraction for oxygen, rubidium taking fire 
 spontaneously in air. It burns on water with exactly the same flame as potassium. 
 Its oxide, rubidia (RbO), is a powerful alkali, like potash, and its salts are isomor- 
 phous with those of potash. The double chloride of platinum and potassium, how- 
 ever, is eight times as soluble in boiling water as the corresponding salt of rubidium, 
 which is taken advantage of in separating these two allied metals. 
 
 Ccesium appears to be even more highly electropositive than rubidium, forming a 
 strong alkali, coesia (CsO), with oxygen, and salts which are isomorphous with those 
 of potassium. Carbonate of ccesia, however, is soluble in alcohol, which does not 
 dissolve the carbonates of potash and rubidia. Moreover, the bitartrate of ccesium 
 is nine times as soluble in water as the bitartrate of rubidium. 
 
 Ccesium has been found in lepidolite ; and the rare mineral pollux, found in Elba, 
 and resembling feldspar in composition, is said to contain a very large quantity of 
 this metal. 
 
 190. General review of the group of alkali-metals. Coesium, rubidium, 
 potassium, sodium, and lithium, constitute a group of elements conspicuous 
 for their highly electropositive character, the powerfully alkaline nature of 
 their oxides, and the general solubility of their salts. Their chemical cha- 
 racters and functions are directly opposite to those of the electronegative 
 group containing fluorine, chlorine, bromine, and iodine, and, like those ele- 
 
BARIUM AND ITS COMPOUNDS. 275 
 
 merits, they exhibit a gradation of properties. Thus, coesiutii appears to be 
 the most highly electropositive member, rubidium the next, then potassium 
 and sodium, whilst lithium is the least electropositive ; and just as iodine, 
 the least electronegative of the halogens, possesses the highest equivalent 
 number, so ccesium, the least electronegative (or most electropositive) of 
 the alkali-metals, has a higher equivalent than any other member of this 
 group, their equivalent weights being represented by the numbers, 
 coesium, 133: rubidium, 85*3; potassium, 39; sodium, 23; lithium, 7. 
 As in the case of the halogens, also, there is no reason to believe that the 
 atomic weights of this group differ from their equivalent weights, so that 
 they are all uni-equivalent elements. Just as chlorine is accepted as the 
 representative of chlorous radicals, so potassium is commonly regarded as 
 the type of basylous radicals, the term radical being applied to all sub- 
 stances, whether elementary or compound, which are capable of being 
 transferred, like chlorine or potassium, from one compound to another 
 without suffering decomposition. 
 
 Some of the physical properties of these elements exhibit a gradation 
 in the same order as their equivalent weights; thus rubidium fuses at 
 101 F., potassium at 144'5, sodium at 207'7, and lithium at 356, so 
 that, at ordinary temperatures, rubidium is the softest, and lithium the 
 hardest of these metals. 
 
 In some of their salts a similar gradational relation is observed; the 
 carbonates, for example, of coesia, rubidia, and potassa, are highly deli- 
 quescent, absorbing water greedily from the air, whilst carbonate of soda 
 is not deliquescent, and carbonate of lithia is sparingly soluble in water. 
 The difficult solubility of the carbonate and phosphate of lithia consti- 
 tutes the connecting link between this and the succeeding group of metals, 
 the carbonates and phosphates of which are insoluble in water. 
 
 BAKIUM. 
 
 191. Barium, so named from the great weight of its compounds (ftapvs, 
 heavy) is found in considerable abundance in the north of England, in 
 two minerals known as Witherite (carbonate of baryta, BaO . C0 2 ) and 
 heavy spar (sulphate of baryta, BaO. S0 3 ). Witherite is found in large 
 masses in the lead mines at Alston Moor, and at Anglesark in Lancashire. 
 It is said to be used for poisoning rats, and was originally mistaken, on 
 account of its great weight, for an ore of lead. 
 
 The metal itself is obtained by decomposing fused chloride of barium 
 by the galvanic current. It is a pale yellow, fusible, malleable in,etal of 
 sp. gr. about 4, which is easily oxidised by air, and rapidly decomposes 
 water at common temperatures. 
 
 Such compounds of baryta as are used in the arts are chiefly prepared 
 from heavy spar or sulphate of baryta, which is remarkable for its insolu- 
 bility in water and acids. In order to prepare other compounds of baryta 
 from this refractory mineral, it is ground to powder and strongly heated 
 in contact with charcoal or some other carbonaceous substance, which 
 removes the oxygen from the mineral in the form of carbonic oxide, and 
 converts it into sulphide of barium ; BaO . S0 3 + C 4 = 4CO + BaS. 
 This latter compound, being soluble in water, can be readily converted into 
 other barytic compounds. 
 
 The artificial sulphate of baryta which is used by painters, instead of 
 white lead, under the name of permanent white, and is employed for 
 
276 CHLORIDE OF BARIUM. 
 
 glazing cards, is prepared by mixing the solution of sulphide of barium 
 with dilute sulphuric acid, when the sulphate of baryta separates as a 
 white precipitate, which is collected, washed, and dried 
 
 BaS 4- HO . S0 3 = HS + BaO . S0 8 . 
 
 The artificial carbonate of baryta, which is used in the manufacture of 
 some kinds of glass, is prepared by passing carbonic acid gas through a 
 solution of .sulphide of barium, when the carbonate of baryta is precipi- 
 tated ; BaS + HO + C0 2 = HS + BaO . C0 2 . 
 
 In preparing -compounds of barium from heavy spar on the small scale, it is 
 better to convert the sulphate of baryta into carbonate of baryta. 50 grs. of the 
 finely powdered .sulphate are mixed with 100 grs. of dried carbonate of soda, 600 
 grs. of powdered nitre, and 100 grs. of very finely powdered charcoal. The mixture 
 is placed in a heap upon a brick or iron plate, and kindled with a match, when the 
 heat evolved by the combustion of the charcoal in the oxygen of the nitre, fuses the 
 sulphate of baryta with the carbonate of soda, when they are decomposed into car- 
 bonate of baryta and sulphate of soda 
 
 BaO . S0 3 + NaO . C0 2 = NaO . S0 3 + BaO . C0 2 . 
 The fused mass is thrown into boiling water, which dissolves the sulphate of soda 
 and leaves the carbonate of baryta. The latter may be allowed to settle, and 
 washed several times, by decantation, with distilled water, until the washings no 
 longer yield a precipitate with chloride of barium, showing that the whole of the 
 sulphate of soda has been washed away, and pure carbonate of baryta remains. 
 
 Nitrate of baryta (BaO . N0 5 ) is obtained by dissolving carbonate of 
 baryta in diluted nitric acid, and evaporating the solution, when octa- 
 hedral crystals of the nitrate are deposited. It is an ingredient in some 
 kinds of blasting powder used by miners. If nitrate of baryta be heated 
 in a porcelain crucible, it fuses and is decomposed, leaving a grey porous 
 mass of baryta ; BaO.N0 5 = BaO + M) 4 + 0. 
 
 Hydrate of baryta may be procured by adding 4 oz. of the powdered 
 nitrate of baryta to 12 oz. of a boiling solution of hydrate of soda, of sp. 
 gr. 1*13 (prepared by dissolving 3 oz. of commercial hydrate of soda in 
 20 measured ounces of water) ; the solution becomes turbid from the 
 separation of carbonate of baryta produced from the carbonate of soda in 
 the hydrate ; it is boiled for some minutes and then filtered ; on partial 
 cooling, some crystals of undecomposed nitrate of baryta are deposited, 
 and if the clear liquid be poured off into another vessel and stirred, it 
 deposits abundant crystals of hydrate of baryta, having the composition 
 BaO . HO + 8Aq. ; these effloresce and become opaque when exposed to 
 air, becoming BaO . HO + Aq. ; when heated to redness, they become 
 pure hydrate of baryta, BaO . HO, which fuses, but is not decomposed 
 when further heated. The hydrate of baryta is moderately soluble in 
 water, the solution being strongly alkaline, and absorbing carbonic acid 
 from the air, depositing carbonate of baryta. 
 
 When baryta is heated in a tube through which oxygen or air is passed, 
 it absorbs the oxygen and is converted into binoxide of barium (Ba0 2 ), 
 which is employed for the preparation of binoxide of hydrogen (see p. 51). 
 
 Chloride of barium, which is the barium compound most commonly 
 employed in the laboratory, may be obtained by dissolving the carbonate 
 of baryta in diluted hydrochloric acid, and evaporating the solution ; on 
 cooling, the chloride is deposited in tabular crystals, BaCl + 2Aq. 
 
 On the large scale it is generally manufactured by fusing heavy spar 
 (sulphate of baryta) with chloride of calcium (the residue from the pre- 
 paration of ammonia, see p. 114), in a reverberatory furnace 
 BaO.S0 3 + CaCl = CaO.S0 3 + BaCl . 
 
STRONTIUM CALCIUM. 277 
 
 The mass is rapidly extracted with hot water, which leaves the sulphate 
 of lime undissolved, and the clear solution of chloride of barium is de- 
 canted and evaporated. If the sulphate of lime and chloride of barium 
 were allowed to remain long together in contact with the water, sulphate 
 of baryta and chloride of calcium would be reproduced. 
 
 Chlorate of baryta (BaO . C10 5 ) is employed in the manufacture of fire- 
 works, being prepared for that purpose by dissolving the artificial car- 
 bonate of baryta in solution of chloric acid ; it forms beautiful shining 
 tabular crystals. When mixed with combustible substances, such as 
 charcoal and sulphur, it imparts a brilliant green colour to the flame of 
 the burning mixture (see p. 158). 
 
 All the soluble salts of barium are very poisonous. 
 
 STRONTIUM. 
 
 192. Strontium is less abundant than barium, and occurs in nature in 
 similar forms of combination. Strontianite, the carbonate of strontia 
 (SrO . C0 2 ), was first discovered in the lead mines of Strontian in Argyle- 
 shire, and has since been found in small quantity in some mineral waters. 
 
 Celestine (so called from the blue tint of many specimens) is the sul- 
 phate of strontia (SrO . S0 3 ), and is found in beautiful crystals associated 
 with the native sulphur in Sicily. It is also met with in this country, 
 and is the source from which the nitrate of strontia employed in firework 
 compositions is derived. The sulphate of strontia resembles that of 
 baryta with respect to its insolubility, and is converted into the soluble 
 sulphide of strontium (SrS) by calcination with carbonaceous matter. 
 The solution of sulphide of strontium so obtained is decomposed by nitric 
 acid, and the nitrate of strontia crystallised from the solutions. This salt 
 forms prismatic crystals which have the formula SrO . N0 5 + 5Aq. It 
 has the property of imparting a magnificent crimson colour to flames, and 
 is hence largely used for the preparation of red theatrical fires. (See 
 p. 158). The other compounds of strontium possess too little practical 
 importance, and too nearly resemble those of barium, to require particular 
 description here. No peroxide of strontium, however, has been obtained. 
 
 The metal itself is prepared in a similar manner to metallic barium, 
 which it much resembles, though it is lighter (sp. gr. 2*54) and less 
 fusible. It burns, when heated in air, with a crimson flame. 
 
 CALCIUM. 
 
 193. !Nb other metal is so largely employed in a state of combination 
 as calcium, for its oxide, lime (CaO), occupies among bases much the 
 same position as that which sulphuric acid holds among the acids, and is 
 used, directly or indirectly, in most of the arts and manufactures. 
 
 Like barium and strontium, it is found, though far more abundantly 
 than these, in the mineral kingdom, in the forms of carbonate and sul- 
 phate, but it also occurs in large quantity as fluoride of calcium (p. 177), 
 and less frequently in the form of phosphate of lime (p. 222). Calcium, 
 moreover, is found in all animals and vegetables, and its presence in their 
 food, in one form or other, is an essential condition of their existence. 
 
 Metallic calcium may be obtained by decomposing fused iodide of cal- 
 cium with metallic sodium. It has a light golden-yellow colour, is harder 
 
278 LIME-BURNING. 
 
 than lead, and very malleable ; it oxidises slowly in air at the ordinary 
 temperature, but when heated to redness, it fuses and burns with a very 
 brilliant white light, being converted into lime (calx). It decomposes 
 water at the ordinary temperature. It is lighter than barium and stron- 
 tium, its specific gravity being 1 -58. 
 
 CARBONATE OF LIME, from which all the manufactured compounds of 
 lime are derived, constitutes the different varieties of limestone which are 
 met with in such abundance. 
 
 Limestones and chalk are simply carbonate of lime in an amorphous or 
 uncrystallised state. The oolite limestone, of which the Bath and Port- 
 land building-stones are composed, is so called from its resemblance to the 
 roe of a fish (wov, an egg.) Marble, in its different varieties, is an assem- 
 blage of minute crystalline grains of carbonate of lime, sometimes varie- 
 gated by the presence of oxides of iron and manganese, or of bituminous 
 matter. This last constituent gives the colour to black marble. Car- 
 bonate of lime is also found in large transparent rhombohedral crystals, 
 which are known to mineralogists as calcareous spar, cole spar, or Iceland 
 spar. When the crystals have the form of a six-sided prism, the mineral 
 is termed Arragonite. The attention of the crystallographer has long 
 been directed to these two crystalline forms of carbonate of lime, on ac- 
 count of the circumstance, that if a prism of arragonite be heated, it breaks 
 up into a number of minute rhombohedra of calc spar. 
 
 Carbonate of lime is a chief constituent of the shells of fishes and of 
 egg shells, so that, except phosphate of lime, no mineral compound has 
 so large a share in the composition of animal frames. Corals also con- 
 sist chiefly of carbonate of lime derived from the skeletons of innumer- 
 able minute insects. The mineral gaylussite is a double carbonate of 
 lime and soda (CaO . C0 2 , NaO . C0 2 + 5Aq.), and is scarcely affected 
 by water unless previously heated, when water dissolves out the car- 
 bonate ot soda. Baryto-calcite is a double carbonate of baryta and lime 
 (BaO . C0 2 , CaO . C0 2 ). 
 
 LIME. The process by which lime is obtained from the carbonate has 
 been already alluded to under the name of lime-burning. In order that 
 the carbonic acid may be completely expelled from the carbonate of lime, 
 it is necessary that the products of combustion of the fuel should be 
 allowed to pass over the limestone, since although a very intense heat 
 is insufficient to decompose carbonate of lime when shut up in a crucible, 
 the decomposition is easily effected if the carbonate be heated in a cur- 
 rent of atmospheric air or of any other gas, especially if aqueous vapour 
 be present, as is the case in the products of combustion of the fuel. 
 
 Accordingly, a kiln is commonly employed of the form of an inverted 
 cone of brickwork (fig. 222), and into this the limestone and fuel are 
 thrown in alternate layers. The former losing its carbonic acid before 
 it reaches the bottom of the furnace, is raked out in the form of burnt 
 or quick lime (CaO), whilst its place is supplied by a fresh layer of lime- 
 stone thrown in at the top of the kiln. Fig. 223 represents another form 
 of kiln, in which the limestone is supported upon an arch built with 
 large lumps of the stone above the fire, which is kept burning for about 
 three days and nights, until the whole of the limestone is decomposed. 
 
 The usual test of the quality of the lime thus obtained consists in 
 sprinkling it with water, with which it should eagerly combine, evolv- 
 ing much heat, swelling greatly, and crumbling to a light white powder 
 of hydrate of lime (slaked lime}. Lime which behaves in this manner is 
 
PLASTER OF PARIS. 
 
 279 
 
 termed fat lime ; whereas, if it be found to slake feebly, it is pronounced 
 a poor lime, and is known to contain considerable quantities of foreign 
 substances, such as silica, alumina, magnesia, &c. Lime is said to be 
 overburnt when it contains hard cinder-like masses of silicate of lime, 
 
 Fig. 222. Lime-kiln. 
 
 Fig. 223. Lime-kiln. 
 
 formed by the combination of the silica, which is generally found in lime- 
 stone, with a portion of the lime, under the influence of excessive heat in 
 the kiln. 
 
 The hydrate of lime is about twice as soluble in cold as it is in hot 
 water, so that lime-water should always be made by shaking slaked 
 lime with cold distilled water, which dissolves about 1 -700th of its weight ; 
 the solution is allowed to settle in a closed bottle, for it absorbs carbonic 
 acid rapidly from the air. Crystals of hydrate of lime have been obtained 
 by evaporating lime-water in vacuo. 
 
 SULPHATE OF LIME in combination with water (CaO . S0 3 . HO + Aq.) 
 is met with in nature, both in the form of transparent prisms of selenite, 
 and in opaque and semi-opaque masses known as alabaster and yypsum. 
 It is this latter form which yields plaster of Paris, for when heated to 
 between 300 and 400 F., it loses its water, and if the mass be then 
 powdered, and again mixed with water, the powder recombines with it 
 to form a mass of hydrated sulphate of lime, the hardness of which nearly 
 equals that of the original gypsum. 
 
 In the preparation of plaster of Paris, a number of large lumps of 
 gypsum are built up into a series of arches, upon which the rest of the 
 gypsum is supported ; under these arches the fuel is burnt, and its flame 
 is allowed to traverse the gypsum, care being taken that the temperature 
 does not rise too high, or the gypsum is over-burnt and does not exhibit 
 the property of recombining with water. When the operation is supposed 
 to be completed, the lumps are carefully sorted, and those which appear 
 to have been properly calcined are ground to a very fine powder. When 
 this powder is mixed with water to a cream, and poured into a mould, the 
 minute particles of anhydrous sulphate of lime (CaO . S0 3 ) combine with 
 2 eqs. of water to reproduce the original gypsum (CaO . S0 3 . HO + Aq.), 
 and this act of combination is attended with a slight expansion which 
 forces the plaster into the finest lines of the mould. 
 
280 MAGNESIAN MINERALS. 
 
 Stucco consists of plaster of Paris (occasionally coloured) mixed with a 
 solution of size ; certain cements used for building purposes (Keene's and 
 Keating's cements) are prepared from burnt gypsum, which has been 
 soaked in a solution of alum and again burnt ; and although the plaster 
 thus obtained takes much longer to set than the ordinary kind, it is much 
 harder, and therefore takes a good polish. 
 
 Plaster of Paris is much damaged by long exposure to moist air, from 
 which it regains a portion of its water, and its property of setting is so far 
 diminished. 
 
 Precipitated sulphate of lime is used by paper-makers under the name 
 of pearl hardener. 
 
 Chloride of calcium has been mentioned as the residue left in the 
 preparation of ammonia. The pure salt may be obtained by dissolving 
 pure carbonate of lime (white marble) in hydrochloric acid, and evaporating 
 the solution, when prismatic crystals of the composition CaCl + 6Aq. 
 are obtained. When these are heated they melt, and at about 390 F. are 
 converted into a white porous mass of CaCl + 2Aq.. which is much 
 used for drying gases. At a higher temperature, fused chloride of calcium, 
 free from water, is left j this is very useful for removing water from some 
 liquids. 
 
 When hydrate of lime is boiled with a strong solution of chloride of 
 calcium, it is dissolved, and the filtered solution deposits prismatic crystals 
 of oxy chloride of calcium, CaCl. 3CaO + 15Aq., which are decomposed 
 by pure water. 
 
 Less important compounds of calcium not previously noticed. 
 
 Sulphide of calcium, CaS I Pentasulphide of calcium, CaS 5 
 
 Bisulphide CaS 2 | Silicide CaSi 2 
 
 MAGNESIUM. 
 
 194. Magnesium is found, like calcium, though less abundantly, in 
 each of the three natural kingdoms. Among minerals containing this 
 metal, those with which we are most familiar are certain combinations of 
 silica and magnesia (silicates of magnesia) known by the names of talc, 
 steatite or French chalk, asbestos, and meerschaum, which always contains 
 water. Magnesite is a carbonate of magnesia. Most of the minerals 
 containing magnesium have a remarkably soapy feel. The compounds of 
 magnesium, which are employed in medicine, are derived either from the 
 mineral dolomite or magnesian limestone, which contains the carbonate 
 of magnesia and carbonate of lime, or from the sulphate of magnesia, 
 which is obtained from sea-water and from the waters of many mineral 
 springs. 
 
 Metallic magnesium has acquired some importance during the last few 
 years as a source of light. When the extremity of a wire of this metal 
 is heated in a flame, it takes fire, and burns with a dazzling white light, 
 becoming converted into magnesia (MgO). If the burning wire be plunged 
 into a bottle of oxygen, the combustion is still more brilliant. The light 
 emitted by burning magnesium is capable of inducing chemical changes 
 similar to those caused by sun-light, a circumstance turned to advantage 
 for the production of photographic pictures by night. Attempts have 
 been made to introduce magnesium as an illuminating agent for general 
 purposes, but the large quantity of solid magnesia produced in its com- 
 
SULPHATE OF MAGNESIA. 281 
 
 bustion forms a very serious obstacle to its use. The metal is extracted 
 from the chloride of magnesium (see p. 108) by fusing it with sodium, using 
 chloride of sodium and fluoride of calcium to promote the fusibility of the 
 mass. 
 
 On a small scale magnesium may be prepared by mixing 900 grs. of chloride of 
 magnesium with 150 grs. of fluoride of calcium, 150 of fused chloride of sodium, 
 and 150 of sodium cut into slices (see p. 108). The mixture is thrown into a red- 
 hot earthen crucible, which is then covered and again heated. When the action 
 appears to have terminated, the fused mass is stirred with an iron rod to promote 
 the union of the globules of magnesium. It is then poured upon an iron tray, 
 allowed to solidify, broken up, and the globules of magnesium separated from the 
 slag; they may be collected into one globule by throwing them into a melted mix- 
 ture of chlorides of magnesium and sodium and fluoride of calcium. 
 
 In most of its physical and chemical characters magnesium resembles 
 zinc, though its colour more nearly approaches that of silver ; in ductility 
 and malleability it also surpasses zinc. It is nearly as light, however, as 
 calcium, its specific gravity being 1/74. It fuses below a red heat, and 
 may be distilled like zinc. Cold water has scarcely any action upon 
 magnesium ; even when boiled it oxidises the metal very slowly. In the 
 presence of acids, however, it is rapidly oxidised by water. Solution of 
 hydrochlorate of ammonia also dissolves it, owing to the tendency of the 
 magnesium salts to form double salts with those of ammonia 
 
 2(NH 3 . HC1) + Mg = NH 3 . HC1, MgCl + H + NH 3 . 
 
 Magnesium is one of the few elements which unite directly with nitrogen 
 at a high temperature. The nitride of magnesium, NMg 3 , has been obtained 
 in transparent crystals, and is evidently composed after the type NH 3 , so 
 that it is not surprising that the action of water upon it gives rise to 
 magnesia and ammonia, NMg 3 + 3HO = NH 3 + 3MgO. 
 
 The sulphate of magnesia, so well known as Epsom salts, is sometimes 
 prepared by calcining dolomite to expel the carbonic acid, washing the 
 residual mixture of lime and magnesia with water to remove part of the 
 lime, and treating it with sulphuric acid which converts the lime and 
 magnesia into sulphates ; and since the sulphate of lime is almost in- 
 soluble in water, it is readily separated from the sulphate of magnesia 
 which passes into the solution, and is obtained by evaporation in pris- 
 matic crystals having the composition MgO . S0 3 . HO + 6Aq. The 
 preparation of Epsom salts from sea-water has already been alluded to 
 (p. 263). In some parts of Spain, sulphate of magnesia is found in large 
 quantities (like nitre in hot climates) as an efflorescence upon the surface 
 of the soil. This sulphate of magnesia, as well as that contained^ well- 
 waters, appears to have been produced by the action of sulphate of 
 lime, originally present in the water, upon magnesian limestone rocks ; 
 MgO . C0 2 + CaO . S0 3 = MgO . S0 3 + CaO . C0 2 . ^ 
 
 The water of constitution in the sulphate of magnesia may be displaced 
 by the sulphate of an alkali without alteration in its crystalline form ; 
 a double sulphate of magnesia and potash (MgO . S0 3 , KO . S0 3 + 6Aq.), 
 and a similar salt of ammonia (MgO . S0 3 , NH 3 . HO . S0 3 + 6Aq.) may 
 be thus obtained. The mineral polyhalite (TTO\V<S, many, aX<s, salt) is a 
 remarkable salt, containing MgO . S0 3 , KO . S0 3 , 2(CaO . S0 3 ) + 2HO. 
 Water decomposes it into its constituent salts. 
 
 The preparation commonly used in medicine under the name of mag- 
 nesia, is really a basic carbonate of magnesia, or a compound of carbonate 
 
282 REVIEW OF THE ALKALINE EARTH METALS. 
 
 of magnesia with hydrate of magnesia and water in the proportions 
 expressed by the formula, 3(MgO . C0 2 ) . MgO . HO . 3Aq. It is obtained 
 by mixing boiling solutions of sulphate of magnesia and carbonate of soda, 
 when one-fourth of the carbonic acid is expelled in the state of gas ; the 
 white precipitate is thrown upon a cloth strainer, well washed, and dried 
 in rectangular moulds. 
 
 Another process for preparing carbonate of magnesia consists in heating 
 magnesian limestone to low redness, so as to decompose the carbonate of 
 magnesia which it contains, and exposing it, under pressure, to the action 
 of water and carbonic acid, which dissolves the magnesia and leaves the 
 carbonate of lime. On boiling the solution, to expel the excess of car- 
 bonic acid, the carbonate of magnesia is precipitated. 
 
 By moderately heating the carbonate of magnesia, its water and carbonic 
 acid are expelled, and pure or calcined magnesia (MgO) is left, which is 
 very slightly soluble in water and feebly alkaline. 
 
 The mineral periclase consists of magnesia in a crystallised form. 
 Magnesia combines with water to form a hydrate (MgO . HO), but not 
 with evolution of heat, as in the cases of baryta, strontia, and lime. 
 Crystallised hydrate of magnesia constitutes the mineral brucite. Mag- 
 nesia, like lime, is remarkable for its infusibility. 
 
 It has recently been noticed that calcined magnesia, when mixed with 
 water, solidifies after a time into a very hard compact mass of hydrate of 
 magnesia (MgO . HO), and may serve, like plaster of Paris, for taking casts. 
 Dolomite calcined below redness also sets to a very hard mass with water. 
 This hydraulicity of magnesia is likely to meet with useful applications. 
 
 The phosphate of magnesia (3MgO . P0 5 ) enters into the composition of 
 bones, and \h& phosphate, of 'magnesia and ammonia (2MgO . NH 3 . HO. PO 5 ), 
 or triple phosphate, is found in calculi and in the minerals guanite and 
 struvite. 
 
 Borate of magnesia composes the mineral boracite; hydroboracite is a 
 hydrated borate of lime and magnesia. 
 
 Serpentine and olivine are silicates of magnesia and protoxide of iron. 
 Some of the varieties of serpentine are employed for preparing the com- 
 pounds of magnesia, for they are easily decomposed by acids with separa- 
 tion of silica. 
 
 Pearl-spar is a crystallised carbonate of lime and magnesia. 
 
 Chloride of magnesium is important as the source of metallic mag- 
 nesium. It is easily obtained in solution by neutralising hydrochloric 
 acid with magnesia or its carbonate, but if this solution be evaporated in 
 order to obtain the dry chloride, a considerable quantity of the salt is 
 decomposed by the water at the close of the evaporation, leaving much 
 magnesia mixed with the chloride (MgCl + HO = HC1 + MgO). This 
 decomposition may be prevented by mixing the solution with three parts 
 of hydrochlorate of ammonia for every part of magnesia, when a double 
 salt (MgCl, NH 3 . HC1) is formed, which may be evaporated to dryness 
 without decomposition, and leaves fused chloride of magnesium when 
 further heated, the hydrochlorate of ammonia being volatilised. The 
 chloride of magnesium absorbs moisture very rapidly from the air, and is 
 very soluble in water. Like all the soluble salts of magnesium, it has a 
 decidedly bitter taste. 
 
 195. General review of the metals of the alkaline earths. Barium, 
 strontium, calcium, and magnesium form a highly interesting natural 
 
ATOMIC HEATS. 283 
 
 group of metals related to each, other in a most remarkable manner. 
 They exhibit a marked gradation in their attraction for oxygen ; barium is 
 more readily tarnished or oxidised, even in dry air, than strontium, and 
 strontium more readily than calcium ; whilst magnesium is not at all 
 affected by dry air, and is comparatively slowly tarnished even in moist 
 air. Again, the three first metals decompose water at the ordinary tempera- 
 ture, combining with its oxygen and liberating the hydrogen, but mag- 
 nesium requires the aid of heat to effect this decomposition. The oxides 
 of the metals exhibit a similar gradation in properties ; baryta, strontia, 
 and lime combine with water very energetically with great evolution of 
 heat, whilst in the case of magnesia no rise of temperature is observed ; 
 the hydrate of baryta does not lose its water, however strongly it may be 
 heated, whereas the hydrates of strontia and lime are decomposed at a red 
 heat, and hydrate of magnesia even at a lower temperature. Then hydrate 
 of baryta and hydrate of strontia are far more soluble in water than hydrate 
 of lime (which requires about 700 parts of water to dissolve it), and all 
 these three exhibit a very decided alkaline reaction which entitles them 
 to the name of alkaline earths, but hydrate of magnesia requires about 
 3000 parts of water to dissolve it, and is so feebly alkaline, that it might 
 even be fairly classed among the earths proper. Among the other com- 
 pounds of these metals, the sulphates may be named as presenting a 
 gradation of a similar description ; for sulphate of baryta may be said to 
 be insoluble in water, sulphate of strontia dissolves to a very slight extent, 
 sulphate of lime is rather more soluble, and the sulphate of magnesia is 
 very readily dissolved by water. 
 
 It will be seen hereafter that the sulphates of the earths proper are 
 remarkable for their solubility in water, so that, in this respect also, mag- 
 nesia appears to stand on the border line between the two classes. The 
 manner in which these metals are associated in nature is also not without 
 its significance, for if two of them are found in the same mineral, they 
 will usually be those which stand next to each other in the group ; thus 
 carbonate of strontia is found together with carbonate of baryta in 
 witherite, whilst carbonate of lime is associated with the sulphate of 
 strontia in celestine. Again, carbonate of strontia is often found with 
 carbonate of lime in arragonite, and the carbonate of magnesia occurs with 
 carbonate of lime in dolomite. 
 
 196. Equivalent and atomic weights of barium, strontium, calcium, 
 and magnesium. The analysis of chloride of barium has proved it to con- 
 tain 68'5 parts by weight of barium, combined with 1 eq. (35*5 parts) of 
 chlorine ; whence the equivalent of barium is accepted as 68 '5. In a 
 similar manner, that of strontium has been fixed at 43 '8, that of calcium 
 at 20, and that of magnesium at 12 ; so that here, as in the group of 
 alkali-metals, the equivalent numbers decrease with the diminution of the 
 electropositive character in the metals. 
 
 Relation between specific heats and equivalent weights. Atomic heats. 
 Since the specific volumes of the vapours of these metals have not been 
 ascertained, recourse is*had to their specific heats in order to ascertain 
 their atomic weights. It will be remembered that the specific heat of a 
 substance is the quantity of heat required to raise it 1 in temperature, as 
 compared with the quantity of heat required to raise an equal weight of 
 water 1 ; or, more concisely, the quantity of heat required to raise one 
 part by weight of the substance 1 (referred to water as the unit). 
 
284 ATOMIC HEATS. 
 
 Thus, the specific heats of potassium, sodium, and lithium are, respec- 
 tively, 0-1696, 0-2934, and 0-9408; these numbers representing the 
 relative quantities of heat required to raise one part by weight of each of 
 these metals 1 in temperature, supposing that an equal weight of water 
 would be raised 1 by a quantity of heat expressed by one. No simple 
 relation can be traced between these numbers, but if the quantities of heat 
 be calculated which are required to raise equivalent weights of these ele- 
 ments 1, the case will be different. 
 
 If '1696 be the quantity of heat required to raise one part by weight 
 of potassium 1, 0-1696 x 39, or 6'61, will represent the quantity of heat 
 required to raise 39 parts (1 eq.) of potassium 1. In the same way, 
 0*2934 x 23, or 6*75, is the quantity of heat required to raise 23 parts 
 (1 eq.) of sodium 1 ; and 0'9408 x 7, or 6'59, is the quantity required 
 to raise 7 parts (1 eq.) of lithium 1. Allowing for experimental error in 
 the determination of the specific heats, these numbers, 6 -61, 6*75, and 
 6*59, may be regarded as representing the same quantities of heat. Since 
 the atomic weights of potassium, sodium, and lithium are expressed by 
 the same numbers as their equivalent weights (see p. 275), the numbers, 
 6*61, 6*75, and 6*59, would represent the atomic heats of these metals, 
 that is, the relative quantities of heat required to raise an atom of each 1 
 in temperature. 
 
 (DBF. The atomic heat of a substance is the number obtained by 
 multiplying its specific heat by its atomic weight.) 
 
 The atomic heat, therefore, which is common to these three metals, may 
 be represented by the mean of the three numbers, or 6*65. 
 
 The experiments which have been made to determine the specific heats 
 of those elements which can be obtained in a similar physical condition, 
 lend strong support to the belief that the atomic heats of all elements 
 belonging to the same group are identical, and even hold out a prospect of 
 the identity of the atomic heats of a great majority of the elementary bodies. 
 The atomic heats of oxygen, hydrogen, and nitrogen are, respectively, 
 3*48, 3-41, and 3'41, and may therefore be considered to be identical. 
 
 A similar relation has been observed between the atomic heats of com- 
 pound bodies belonging to the same group ; thus, if the specific heats of 
 the chlorides of potassium, sodium, and lithium be multiplied by the 
 atomic weights of those chlorides, the product in each case will approach 
 very nearly to the number 12 -69. If these chlorides be allowed to con- 
 tain one atom of each of their constituents, and it be supposed that the 
 atomic heats of these constituents are identical, the half of this number 
 (or 6 -34) should represent the atomic heat of the alkali-metals, and, in 
 fact, it does nearly coincide with that number (6-65). 
 
 The specific heats of barium, strontium, and calcium have not been 
 determined, and therefore their atomic heats cannot be directly ascertained. 
 The specific heat of magnesium, however, is 0-2499, and if the atomic 
 weight of this metal were identical with its equivalent (12), its atomic 
 heat would be represented by the number 3 ; but if the atomic weight be 
 regarded as double the equivalent, or 24, the atomic heat will be 
 (0-2499 x 24) 6, a number more nearly approaching to the atomic heats 
 of the alkali-metals. This is one reason for supposing that the atomic 
 weight of magnesium is really represented by 24 (-Mg). 
 
 The specific heats of the chlorides of barium, strontium, calcium, and 
 magnesium have been ascertained to be represented by the numbers 
 0-0900, 0-1180, 0-1686, and 0*1970, respectively. Now, if the atomic 
 
GRANITE FELDSPAR MICA. 285 
 
 weights of these metals be regarded as identical with their equivalent 
 weights, the atomic heats of the chlorides, obtained by multiplying their 
 atomic weights into their specific heats, would be expressed by the mean 
 number 9 '36, and if this be divided by 2 (the presumed number of atoms in 
 each chloride), it would give 4*68 for the atomic heat of each of the ele- 
 ments of the compound, a number which exhibits no simple relation to the 
 atomic heat of magnesium, or to those of the alkali-metals. If it be sup- 
 posed, however, that the atom of barium, strontium, calcium, or mag- 
 nesium really represents two equivalents, so that each chloride contains 
 three elementary atoms (two of chlorine and one of metal), the atomic 
 weight of each of the chlorides would be doubled, and, consequently, the 
 atomic heat would be twice that given above, or 18 '72. Dividing this by 
 3, the presumed number of atoms in the chloride, we obtain the number 
 6-24 for the atomic heat of each of the elements, which agrees very well 
 with that directly obtained for magnesium and the alkali-metals. 
 
 The metals barium, strontium, calcium, and- magnesium, therefore, are 
 generally regarded as bi-equivalent or diatomic elements, one atom of each 
 occupying the place of two atoms of hydrogen, their atomic weights being 
 Ba 137, Sr 87 '5, Oa 40, Mg 24. The atomic formulae of their oxides 
 would be BaO, Sr0, 6a0, and MgO, and that of their chlorides fiaCl^, 
 SrCLj, -BaC^ and MgCL,* 
 
 If the atomic formulae were generally adopted, the absence of the 
 analogy between the formulae of the oxides and those of the chlorides 
 would be found to detract from the simplicity of many of the equations 
 explanatory of chemical changes in which these metals are concerned. 
 
 ALUMINUM. 
 
 197. Aluminum is the representative of the class of metals usually 
 styled metals of the earths proper, and including also glucinum, thorinum, 
 yttrium, zirconium, erbium, terbium, cerium, lanthanum, and didymium, 
 but of these, aluminum is the only metal having any claim to our attention 
 on the ground of its practical importance. 
 
 Aluminum is distinguished among metals, as silicon is among non- 
 metallic bodies, for its immense abundance in the solid mineral portion of 
 the earth, to which, indeed, it is almost entirely confined, for it is present 
 in vegetables and animals in so small quantity that it can scarcely be re- 
 garded as forming one of their necessary components. 
 
 One of the oldest rocks, which appear to have originally formed the 
 basis of the solid structure of the globe, is that known as granite. This 
 mineral, which derives its name from its conspicuous granular structure, 
 is a mixture, in variable proportions, of quartz, feldspar, and mica, tinged 
 of various colours by the presence of small quantities of the oxides of 
 iron and manganese. 
 
 Quartz, which forms the translucent or transparent grains in the granite, 
 consists simply of silicic acid ; feldspar, the dull cream-coloured opaque 
 part, is a combination of that acid with alumina and potash, and is 
 generally spoken of as a double silicate of alumina and potash, its com- 
 position being represented by the formula KO . 3Si0 2 , A1 2 O 3 . 3Si0 2 . 
 
 Mica, so named from the glittering scales which it forms in the granite, 
 is also a double silicate of alumina and potash, but the alumina is very 
 frequently displaced by sesquioxide of iron, and the potash by magnesia. 
 * Another argument for the diatomic character of barium will be found at p. 256. 
 
286 
 
 CLAY ALUM. 
 
 By the long-continued action of air and water, the granite rock is 
 gradually crumbled down or disintegrated, an effect which must be as- 
 cribed to a concurrence of mechanical and chemical causes. Mechani- 
 cally, the rock is continually worn down by variations of temperature, 
 by the congelation of water within its minute pores, the rock being gra- 
 dually split by the expansion attendant upon such congelation. Chemi- 
 cally, the action of water containing carbonic acid would tend to remove 
 the potash from the feldspar and mica in the form of carbonate of potash, 
 whilst the silicate of alumina and the quartz would subsequently be sepa- 
 rated by the action of water ; the former, being so much lighter, would 
 be soon washed away from the heavy quartz, and, when again deposited, 
 would constitute clay. 
 
 Although clay, therefore, always consists mainly of silicate of alumina, 
 it generally contains some uncombined silicic acid, together with variable 
 quantities of lime, of oxide of iron, &c., which give rise to the numerous 
 varieties of clay. 
 
 Composition of Clay. 
 
 
 Chinese Kaolin. 
 
 Fire-clay. 
 (Stourbridge) 
 
 Pipe-clay. 
 
 Silica . 
 
 50-5 
 
 64-1 
 
 53-7 
 
 Alumina 
 
 33-7 
 
 23-1 
 
 32-0 
 
 Water . 
 
 11-2 
 
 10-0 
 
 12-1 
 
 Oxide of iron 
 
 1-8 
 
 1-8 
 
 1-4 
 
 Lime 
 
 
 ... 
 
 0-4 
 
 Magnesia 
 
 0-8 
 
 0-9 
 
 
 Potash \ 
 
 1 Q 
 
 
 
 Soda J 
 
 
 
 
 
 99-9 
 
 99-9 
 
 99-6 
 
 The silicate of alumina also constitutes the chief portion of several other 
 very important mineral substances, among which may be mentioned slate, 
 fuller's earth, and pumice-stone. Marl is clay containing a considerable 
 quantity of carbonate of lime. Loam is also an impure variety of clay. 
 The different varieties of ochre, as well as umber and sienna, are simply 
 clays coloured by the oxides of iron and manganese. 
 
 ALUM, which is the chief compound of aluminum employed in the arts, 
 is always obtained either from clay or slate, but there are several processes 
 by which it may be manufactured. 
 
 The simplest process is that in which pipe-clay, or some other clay con- 
 taining very little iron, is calcined, ground to powder, and heated on the 
 hearth of a reverberatory furnace with half its weight of sulphuric acid, 
 until it becomes a stiff paste, which is then exposed to air for several 
 weeks. During this time the alumina of the clay enters into combination 
 with the sulphuric acid to form sulphate of alumina, which may be ob- 
 tained by washing the mass with water, when the sulphate of alumina 
 dissolves, and the undissolved silicic acid (still retaining a portion of the 
 alumina) is left. When the solution containing the sulphate of alumina 
 is evaporated to a syrupy consistence and allowed to cool, it solidifies into 
 a white crystalline mass, which is used by dyers under the erroneous name 
 of concentrated alum. The sulphate of alumina can be obtained in crys- 
 
MANUFACTURE OF ALUM. 287 
 
 tals containing A1 2 3 . 3SO 3 + 18Aq., but there is considerable difficulty 
 in obtaining these crystals on account of the extreme solubility of the 
 salt. It is on account of this circumstance that the sulphate of alumina 
 is usually converted into alum, which admits of very easy crystallisation 
 and purification. In order to transform the sulphate of alumina into 
 alum, its solution is mixed with sulphate of potash, when, by suitable 
 evaporation, beautiful octahedral crystals are obtained, having the compo- 
 sition Al ? 3 . 3S0 3 , KO . S0 3 + 24: Aq. 
 
 ' Alum is more commonly prepared from the mineral termed alum-shale, 
 which contains silicate of alumina, together with a considerable quantity 
 of finely-divided iron pyrites and some bituminous matter. This shale 
 is coarsely broken up, and built into long pyramidal heaps, together with 
 alternate layers of coal, unless the shale should happen to contain a suffi- 
 cient amount of bitumen. These heaps are set fire to in several places, 
 and are partly smothered with spent ore in order to prevent too great a 
 rise of temperature. During this slow roasting of the heap, the iron 
 pyrites (FeS 2 ) loses half its sulphur, which is converted by burning into 
 sulphurous acid (S0 2 ), and this, in contact with the porous shale and the 
 atmospheric oxygen, becomes converted into sulphuric acid (p. 200). 
 This latter acid combines with the alumina to produce sulphate of alumina. 
 The roasted heap is then allowed to remain for some months exposed to 
 the air, and moistened from time to time, in order to promote the absorp- 
 tion of oxygen by the sulphide of iron (FeS), and its conversion into sul- 
 phate of iron (FeO . S0 3 ). The heap is afterwards lixiviated with water, 
 which dissolves out the sulphates of alumina and iron, together with some 
 sulphate of magnesia, which has also been formed in the process. When 
 this crude alum liquor is evaporated to a certain extent, a large quantity 
 of sulphate of iron (green vitriol) crystallises out, and the liquid from 
 which these crystals have separated is then mixed with so much solu- 
 tion of chloride of potassium as a preliminary experiment has shown to 
 be necessary to yield the largest amount of alum. The chloride of potas- 
 sium is obtained as soap-boiler's waste, and as the refuse from saltpetre 
 refineries and glass-houses. The sulphate of iron still left in the solu- 
 tion is decomposed by the chloride of potassium, yielding chloride of 
 iron and sulphate of potash, which combines with the sulphate of alumina 
 to form alum. If there be much sulphate of magnesia in the liquor, it is 
 subsequently obtained in crystals and sent into the market. 
 
 Where sulphate of ammonia can be obtained at a cheap rate (as in the 
 neighbourhood of the gas-works), it is very commonly substituted for the 
 chloride of potassium, w r hen ammonia-alum is obtained instead of potash- 
 alum. The former is similar in all respects to the latter salt, exeept that 
 it contains the hypothetical metal ammonium (NH 4 ) in place of potassium, 
 and its formula is, therefore, A1 2 3 . 3S0 3 , NH 4 . S0 3 + 24 Aq. 
 
 For all the uses of alum, in dyeing and calico-printing, in paper-making 
 and in the manufacture of colours, ammonia-alum answers quite as well 
 as potash-alum, and hence both these salts are sold under the common 
 name of alum. 
 
 These alums are the representatives of an important class of double 
 sulphates, composed of a sulphate of one of the alkalies combined with 
 the normal sulphate of a sesquioxide. They all contain 24 eqs. of water 
 of crystallisation, and their crystalline form is that of the cube or octa- 
 hedron. 
 
 When a solution of alum is mixed with a little solution of carbonate of 
 
288 ALUMINA CHLORIDE OF ALUMINUM. 
 
 soda, a precipitate of alumina is formed, which redissolves when the solu- 
 tion is stirred. If the addition of carbonate of soda be continued as long 
 as the precipitate redissolves when stirred, the salt A1 2 3 . SO 3 will remain 
 in the solution 
 
 A1 2 3 .3S0 3 ,KO.S0 3 + 2(ffaO.C0 2 ) = 
 A1 2 3 . S0 3 + 2(NaO . S0 3 ) + KO . S0 3 + 2C0 2 . 
 
 This solution of basic alum, as it is called, is decomposed by boiling, 
 alumina being deposited and ordinary alum remaining in solution 
 
 3(A1 2 3 .S0 3 ) + KO.S0 3 = 2A1 2 3 + A1 2 3 . 3S0 3 , KO . S0 3 . 
 
 When stuffs are immersed in the solution of basic alum they also with- 
 draw a portion of alumina, which becomes fixed in their fibre, and serves 
 as a mordant to attract and fix the colouring matter when the stuff is 
 transferred to a dye-bath. 
 
 Alumina. When ammonia-alum is strongly heated, it loses the whole 
 of its water, ammonia,* and sulphuric acid, leaving merely a white in- 
 soluble earthy substance which is alumina itself (A1 2 3 ), and differs 
 widely from the metallic oxides which have been hitherto considered, by 
 the feebly basic character which it exhibits. Not only is alumina des- 
 titute of alkaline properties, but it is not even capable of entirely neu- 
 tralising the acids, and hence both sulphate of alumina and alum are 
 exceedingly acid salts. 
 
 Pure crystallised alumina is found in nature as the mineral corundum, 
 distinguished by its extreme hardness, in which it ranks next to the 
 diamond. An opaque and impure variety of corundum constitutes the 
 very useful substance emery. The ruby and sapphire^ consist of nearly 
 pure alumina; spinelle is a compound of magnesia with alumina, 
 MgO . A1 2 3 ; whilst in the topaz the alumina is associated with silica 
 and fluoride of aluminum. The mineral diaspore is a hydrate of alumina 
 (A1 2 3 . 2 HO), so named from its falling to powder when heated (Suunropd, 
 dispersion). 
 
 The artificially prepared hydrate of alumina is characterised by its gelatinous ap- 
 pearance. If a little alum be dissolved in warm water, and some ammonia added 
 to the solution, the ammonia will combine with the sulphuric acid, whilst the 
 alumina will unite with water to form a semi-transparent gelatinous mass of hydrate 
 of alumina (A1 2 3 .3HO). When washed and dried, it shrinks very much and 
 forms a mass resembling gum. The hydrate of alumina has a great attraction for 
 most colouring matters, with which it forms insoluble compounds called lakes. 
 Thus, if a solution of alum be mixed with infusion of logwood, and a little ammonia 
 added, the hydrate of alumina will form, with the colouring matter, a purplish-red 
 lake, which may be filtered off, leaving the solution colourless. This property is 
 turned to advantage in calico-printing, where the compounds of alumina are largely 
 used as mordants. 
 
 Chloride of aluminum. If the alumina obtained by calcining ammonia- 
 alum be intimately mixed^with charcoal, and strongly heated in an earthen 
 tube or retort through which a stream of well-dried chlorine is passed, 
 the oxygen of the alumina is abstracted by the charcoal, to form carbonic 
 
 * The great absorption and disappearance of heat during the evaporation of the water 
 and ammonia from this alum, has led to its employment for filling the space between the 
 double walls of fire-proof safes, which may become red-hot outside, whilst the inside is 
 kept below the scorching-point of paper. 
 
 t Small crystals of alumina resembling natural sapphire have been obtained by the 
 action of vapour of fluoride of aluminum upon boracic acid at a high temperature. By 
 adding a little fluoride of chromium, crystals similar to rubies and emeralds have been 
 produced. 
 
EXTRACTION OF ALUMINUM FROM BAUXITE. 289 
 
 oxide, whilst the chlorine combines with the aluminum yielding chloride 
 of aluminum (A1 2 C1 3 ) which passes off in vapour and may be condensed, 
 in an appropriate receiver, as a white crystalline solid 
 
 A1 2 3 + C 3 + C1 3 = A1 2 C1 3 + SCO . 
 
 This formation of the chloride of aluminum is possessed of some in- 
 terest, as an example of the decomposition of a compound body by the 
 cp-operation of two elements, neither of which alone would be able to 
 decompose the compound ; neither carbon nor chlorine would, alone, de- 
 compose alumina, however high the temperature, but when the attraction 
 of the carbon for the oxygen is added to that of the chlorine for the 
 aluminum, the decomposition is easily effected. 
 
 But this chloride of aluminum also deserves attention as being the 
 source from which the metal aluminum may be prepared in large quan- 
 tities. 
 
 198. Aluminum. In order to obtain this interesting metal, it is only 
 necessary to pass the chloride of aluminum in the state of vapour over heated 
 sodium, which removes the chlorine in the form of chloride of sodium, 
 leaving the aluminum as a white malleable metal about as hard as zinc, 
 and fusing at a somewhat lower temperature than silver. For the extrac- 
 tion of aluminum upon the large scale, the alumina is not prepared from 
 alum, but from the mineral known as Bauxite, which contains about 67 per 
 cent, of alumina, together with peroxide of iron and silica. This mineral 
 is heated with soda-ash (see p. 265), when carbonic acid escapes, and the 
 silica and alumina combine with soda to form silicate of soda, and a 
 soluble compound of alumina with soda, which is generally called alumi- 
 nate of soda, and has the composition 3NaO . A1 2 3 . On treating the 
 mass with water, an insoluble silicate of alumina and soda is left, whilst 
 the aluminate of soda is dissolved, and is obtained as an infusible mass 
 when the solution is evaporated. This aluminate of soda is largely used 
 by calico-printers as a mordant. To obtain alumina from it, the solution 
 is neutralised with hydrochloric acid, which converts the sodium into 
 chloride, and precipitates the alumina as hydrate of alumina (A1 2 3 . 3HO). 
 As the next step towards the preparation of aluminum, the hydrate of 
 alumina is mixed with charcoal and common salt, made up into balls, 
 dried, and strongly heated in earthen cylinders through which dry 
 chlorine is passed. The carbon abstracts the oxygen from the alumina, 
 forming carbonic oxide, whilst the aluminum combines with the chlorine, 
 and the chloride of aluminum so formed combines with the chloride of 
 sodium, and distils over as the double chloride of aluminum and'sodium 
 (A1 2 C1 3 . NaCl). This salt is then mixed with a proper proportion of 
 metallic sodium, and heated in a reverberatory furnace, when the sodium 
 combines with the chlorine of the chloride of aluminum, leaving the latter 
 metal to separate in a fused state beneath the melted chloride of sodium, 
 which protects it from oxidation. The aluminum may be rolled into 
 sheets or drawn into wire. 
 
 Aluminum is much more sonorous than most other metals. A bar of 
 it suspended from a string, and struck with a hammer, emits a clear 
 musical sound. It is remarkable as being the lightest metal capable of 
 resisting the action of air even in the presence of moisture. Its specific 
 gravity is 2 '5. This lightness renders it valuable for the manufacture of 
 small weights, such as the grain and its fractions, since these, when made 
 
290 MINERALS CONTAINING ALUMINA AND SILICA. 
 
 of aluminum, are more than three times as large as when made of brass, 
 and nearly nine times as large as platinum weights of the same denomina- 
 tion. It is also employed for ornamental purposes, for though not so 
 brilliant as silver, it is not blackened by sulphuretted hydrogen, which so 
 easily affects that metal (p. 192). 
 
 Another characteristic feature of aluminum is its comparative resistance 
 to the action of nitric acid even at a boiling heat. No other metal com- 
 monly met with, except platinum and gold, is capable of resisting the 
 action of nitric acid to the same extent. Hydrochloric acid, however, 
 which will not attack gold and platinum, dissolves aluminum with faci- 
 lity, converting it into chloride of aluminum, with disengagement of 
 hydrogen ; A1 2 + 3HC1 = A1 2 C1 3 + H 3 . Solutions of potash and soda 
 also easily dissolve it, forming the so-called aluminates of those alkalies ; 
 thus 3(NaO.HO) + AL, = SNaO.AJ/)., + H 3 . Even when very 
 strongly heated in air, aluminum is oxidised to a very slight extent, pro- 
 bably because the coating of alumina which is formed remains infusible 
 and protects the metal beneath it. For a similar reason, apparently, 
 aluminum decomposes steam slowly, even at a high temperature. 
 
 When aluminum is fused with nine times its weight of copper, it forms 
 an alloy very similar to gold in appearance, but almost as strong as iron. 
 This alloy was strongly recommended to replace gold for ornamental pur- 
 poses, but it does not retain its brilliancy so completely as that metal. 
 Aluminum does not unite with mercury or with melted lead, both of 
 which are capable of dissolving nearly all other metals. 
 
 199. Mineral silicates of alumina. Many of the chemical formulae of 
 minerals which contain silicates of alumina associated with the silicates 
 of other metallic oxides are complicated, from the circumstance that a part 
 of the aluminum is often replaced by iron, which, in the form of sesqui- 
 oxide (Fe 2 3 ), is isomorphous with it, and therefore capable of replacing 
 it without altering the crystalline form and general character of the 
 mineral. In a similar manner, the other metals present in the mineral 
 may be exchanged for isomorphous representatives ; thus there are two 
 well-known feldspars, potash-feldspar (orthodase) and soda-feldspar (albite), 
 having the formulas KO. Al/),. 6Si0 2 , and NaO. ALft. 6Si0 2 . These mine- 
 rals are sometimes mingled in one and the same crystal (potash-ollnte or peri- 
 dine) without bearing any definite equivalent proportion to each other ; 
 the formula of such a mineral would be written (KNa)0. Alf> a . 6Si0 2 . 
 
 Porphyry has the same chemical composition as feldspar. 
 
 Mica, again, is composed essentially of magnesia, alumina, and silica 
 (4MgO . A1 2 3 . 4Si0 2 ), but part of the magnesium is so constantly re- 
 placed by potassium and iron (as protoxide), and part of the aluminum 
 by iron (as sesquioxide), that the general formula for mica must be written 
 4(KMgFe) . (AlFe) 2 3 . 4Si0 2 . 
 
 Garnet is essentially a double silicate of alumina and lime, but often 
 contains magnesium, iron, or manganese, replacing part of the calcium, 
 and iron replacing part of the aluminum, being written 
 
 3(CaMgFeMn) . (AlFe) 2 3 . 3Si0 2 . 
 
 This mineral is sometimes formed artificially in the slag of the iron blast- 
 furnaces. 
 
 Chlorite, a very important variety of rock, is a double silicate of alumina, 
 and magnesia, with variations as expressed by the formula 
 4(MgFe) 0. (AlFe) 2 3 . 2Si0 2 . 3HO . 
 
NATURAL AND ARTIFICIAL ULTRAMARINE. 291 
 
 Basalt is a feldspathic rock containing crystals of augite 
 4(CaMgFe)0.5Si0 2 . 
 
 Gneiss is chemically composed like granite, but the mica is arranged in 
 regular layers. Trap rock contains feldspar, together with hornblende, 
 which consists of silicates of alumina, lime, magnesia, and oxide of iron. 
 Hornblende is sometimes found replacing the mica in granite, forming the 
 rock called syenite. 
 
 v Lapis lazuli, the valuable mineral which furnishes the natural ultra- 
 marine used in painting, consists chiefly of silica and alumina, which con- 
 stitute respectively 45 and 32 per cent, of it, but there are also present 
 9 per cent, of soda, 6 per cent, of sulphuric acid, about 1 per cent, of sul- 
 phur, and a somewhat smaller quantity of iron, together with a variable 
 proportion of lime. The cause of its blue colour is not understood, since 
 neither of its predominant constituents is concerned in the production of 
 such a colour in other cases. In consequence of the rarity of the mineral, 
 the natural ultramarine bears a very high price, but the artificial ultramarine 
 is manufactured in very large quantities at a low cost, and forms a very 
 good imitation. One of the processes for preparing it consists in heating 
 to bright redness in a covered crucible, for three or four hours,, an inti- 
 mate mixture of 100 parts of pure white clay (kaolin), 100 of dried car- 
 bonate of soda, 60 of sulphur, and. 12 of charcoal. This would be expected 
 to yield a mixture of silicate of soda, aluminate of soda, and sulphide of 
 sodium, the two first being white, and the latter yellow or brown, but the 
 mass is found to have a green colour (green ultramarine). It is finely 
 powdered, washed with water, dried, mixed with a fifth of its weight of 
 sulphur, and gently roasted in a thin layer till the sulphur has burnt off, 
 this operation being repeated, with fresh additions of sulphur, until the 
 residue has a fine blue colour. In the opinion of some chemists, the pro 
 sence of a small proportion of iron is essential to the blue colour, while 
 others believe the colour to be due to sulphide of sodium or hyposul- 
 phite of soda, or both. Ultramarine is a very permanent colour under 
 ordinary conditions of exposure to air and light, but acids bleach it at 
 once, with separation of gelatinous silica and evolution of sulphuretted 
 hydrogen. Blue writing-paper is often coloured with ultramarine, so that 
 its colour is discharged by acids falling upon it in the laboratory. Chlo- 
 rine also bleaches ultramarine. Starch is often coloured blue with this 
 substance. 
 
 Phosphates of alumina are found naturally in several forms. Targuoise 
 is a hydrated phosphate of alumina (A1 2 3 . P0 5 ), owing its colour to the 
 presence of oxide of copper. Wavellite has the composition 3A1 2 3 ". 2P0 6 . 
 None of the earlier analysts detected the phosphoric acid in this mineral, 
 on account of the difficulty in separating it from the alumina, so that 
 even in comparatively modern chemical works it is described as a hydrate 
 of alumina. 
 
 200. Equivalent and] atomic loeights of aluminum. The chloride of 
 aluminum has been found by analysis to contain 35*5 parts by weight 
 (1 eq.) of chlorine, combined with 9 '16 parts of aluminum, and if the 
 chloride of aluminum be represented as a protochloride (A1C1), the equi- 
 valent of this metal would be 9*16. But when the chloride of aluminum 
 is decomposed by an alkali, it furnishes alumina and a chloride of the 
 alkali-metal. If the formula of chloride of aluminum were really A1C1, 
 the action of potash, for example, upon it must be represented by tho 
 
 T2 
 
292 ATOMIC WEIGHT OF ALUMINUM. 
 
 equation AJC1 + KO = KC1 + A10 ; so that A10 would represent the 
 formula of alumina. The very strong chemical resemblance of alumina 
 and its salts to sesquioxide of iron (Fe 2 O 3 ) and its salts, as well as the 
 isomorphism of these oxides observed in the alums and in many minerals 
 (p. 290), compels the belief that alumina is also a sesquioxide, and that 
 its formula is A1 2 3 . Its formation from the chloride of aluminum by 
 the action of potash must then be represented by 
 
 A1,C1 3 + 3KO - 3KC1 + A1 2 3 
 
 so that the chloride of aluminum is a sesquichloride (A1 2 C1 3 ). 
 
 Again, referring to the results of experiment, 3 eqs. (35*5 x 3) of 
 chlorine were found to be combined with 2 7 '48 parts of aluminum, and 
 if this represents 2 eqs., the equivalent of aluminum will be 1374, though 
 this does not represent correctly the weight of aluminum which displaces 
 1 part by weight of hydrogen from its compounds (see p. 23). 
 
 The volume occupied by a definite weight of vapour of aluminum being 
 unknown, the atomic weight of this metal must be deduced from other 
 considerations. The specific gravity (or weight of one volume) of vapour 
 of chloride of aluminum is 9*34. It has been seen that this weight of 
 chloride of aluminum contains 1 -92 of aluminum. Hence, 
 
 "Weight of 1 vol. of chloride of aluminum, 9 '34 
 aluminum contained in it, 1 '92 
 
 ,, chlorine 7*42 
 
 Now, 1 vol. of chlorine weighs 2*47, so that 7 '42 represents 3 vols. of 
 chlorine ; and if it be assumed that 1 '92 represents the weight of 1 vol. of 
 aluminum, there are contained, in 1 vol. of chloride of aluminum vapour, 
 1 vol. or 1 atom of aluminum, and 3 vols. or 3 atoms of chlorine. But it 
 will be remembered that the molecule of a compound body is generally 
 taken to represent 2 vols. (H= 1 vol.), and therefore 1 molecule or 2 vols. 
 of chloride of aluminum vapour would contain 2 vols. or 2 atoms of 
 aluminum, and 6 vols. or 6 atoms of chlorine. These 6 atoms of chlorine re- 
 present (35*5 x 6) 213 parts by weight, and are combined, in the chloride, 
 as shown by analysis, with 55 ! parts by weight of aluminum j so 
 that the 2 atoms of aluminum in the chloride represent 55 '1 parts by 
 weight, or each atom of aluminum (Al) weighs 27*5, or twice as much 
 as the equivalent accepted above, and the molecular formula of the chloride 
 of aluminum must be written A1 2 C1 6 . The atomic heat of aluminum sup- 
 ports the assumption of the number 27*5 for its atomic weight. Since, in 
 the chloride of aluminum, the 2 atoms of metal stand to the 6 atoms of 
 chlorine in the place of 6 atoms of hydrogen, 1 atom of aluminum would 
 represent 3 atoms of hydrogen, and the metal would be tri-atomic or ter- 
 equivalent. The atomic formula of alumina would be A^O^O = 16). 
 
 GLUCINUM. 
 
 201. This comparatively rare metal (which derives its name from the sweet taste of 
 its salts, -y^tfxvs, sweet) is found associated with silica and alumina in the emerald, 
 which is a double silicate of alumina and glucina, A1 2 3 . 3SiO 2 , 3(G10 . Si0 2 ), and 
 appears to owe its colour to the presence of a minute quantity of oxide of chromium. 
 The more common mineral beryl has a similar composition, but is of a paler green 
 colour, apparently caused by protoxide of iron. Chrysoberyl consists of glucina and 
 
THORINUM CERIUM ZIRCONIUM. 293 
 
 alumina, also coloured by iron. The earlier analysts of these minerals mistook the 
 glucina for alumina, which it resembles in forming a gelatinous precipitate on add- 
 ing ammonia to its solutions, but it is a stronger base than alumina, and is there- 
 fore capable of displacing ammonia from its salts, and of being dissolved by them. 
 Carbonate of ammonia is employed to separate the glucina from alumina, since it dis- 
 solves the glucina in the cold, forming a double carbonate of glucina and ammonia, 
 from which the carbonate of glucina is precipitated on boiling. Glucina (G10) is 
 intermediate in properties between alumina and magnesia, resembling the latter in 
 its tendency to absorb carbonic acid from the air, and to form soluble double salts 
 with the salts of ammonia, and so much resembling alumina in the gelatinous form 
 of its hydrate, its solubility in alkalies, and the sweet astringent taste of its salts , 
 that it was formerly regarded as a sesquioxide like alumina. 
 The metal itself is very similar to aluminum. 
 
 202. THORINUM is present in a rare Norwegian mineral, thorite, where it is asso- 
 ciated with silica, lime, magnesia, and other metallic oxides. The metal itself is 
 similar to aluminum, but its oxide thorina appears to be a protoxide (ThO), and 
 differs from alumina and glucina in being insoluble in the alkalies (potash, for ex- 
 ample), though it dissolves in carbonate of potash. Moreover, the sulphate of thorina, 
 is sparingly soluble in hot water, so that it is precipitated on boiling its solution. 
 
 203. YTTRIUM, ERBIUM, and TERBIUM, are very rare metals found in gadolinite, a 
 mineral silicate occurring at Ytterby in Sweden, and containing beside these, glu- 
 cinum, cerium, and iron. Their oxides, yttria (YO), erbia, and terbia, resemble 
 thorina in being insoluble in the alkalies, but soluble in their carbonates ; yttria is 
 white, but erbia has a yellow colour. The salts of yttria and erbia are colourless, 
 but those of terbia are pinkish. 
 
 204. CERIUM is also found in gadolinite, but more abundantly in cerite, which is 
 essentially a silicate of cerium. This metal has been employed medicinally, in the 
 form of oxalate of cerium (CeO . C 2 3 . 3HO). It forms two basic oxides, CeO, which 
 is white, and forms colourless salts, and Ce 2 3 , which is yellow, and gives yellow 
 or red salts. In this respect, cerium more nearly resembles iron than aluminum. 
 These oxides of cerium are insoluble in the alkalies ; the protoxide is easily preci- 
 pitated from its salts by oxalic acid in the form of the oxalate mentioned above. 
 Sesquioxide of cerium does not appear to form a corresponding chloride, but 
 yields protochloride of cerium and free chlorine when heated with hydrochloric 
 acid. 
 
 LANTHANIUM (from Xavfeivu, to escape notice) is also found in cerite, but it differs 
 from cerium in forming only one oxide (LaO), which is white in the hydrated, but 
 buff in the anhydrous state. When a mixture of nitrates of cerium and lanthanium 
 is calcined, sesquioxide of cerium and oxide of lanthanium are left, and may be 
 separated by treatment with nitric acid, diluted with 100 parts of water, which dis- 
 solves only the latter, 
 
 DIDYMIUM C&ftvpos, twin) is very similar to lanthanium, which is associated with it 
 in cerite. It also forms but one oxide (DiO), which is violet when hydrated, and 
 brown when anhydrous. It is insoluble in potash. The salts of didymium are 
 either pink or violet. 
 
 205. ZIRCONIUM exists in the rare minerals zircon and hyacinth, in which its oxide 
 zirconia (Zr0 2 ) is combined with silicic acid. Zirconia is somewhat similar to 
 alumina, but is insoluble in potash, and dissolves in carbonate of potash. Its sul- 
 phate, moreover, is decomposed by boiling with sulphate of potash, which removes 
 part of the sulphuric acid, forming bisulphate of potash, and precipitates basic 
 sulphate of zirconia. Metallic zirconium somewhat resembles amorphous silicon, 
 but it decomposes water slowly at the boiling point, and has not been fused. 
 
294 ORES OF ZINC. 
 
 ZINC. 
 
 206. Zinc occupies a high position among useful metals, being peculiarly 
 fitted, on account of its lightness, for the construction of gutters, water- 
 pipes, and roofs of buildings, and possessing for these purposes a great 
 advantage over lead, since the specific gravity of the latter metal is about 
 1.1 *5, whilst that of zinc is only 6 '9. For such applications as these, where 
 great strength is not required, zinc is preferable to iron, on account of its 
 superior malleability j for although a bar of zinc breaks under the ham- 
 mer at the ordinary temperature, it becomes so malleable at 250 F. as to 
 admit of being rolled into thin sheets. This malleability of zinc when 
 heated was discovered only in the commencement of this century, until 
 which time the only use of the metal was in the manufacture of brass. 
 When zinc is heated to 400 F., it again becomes brittle. The easy 
 fusibility of zinc also gives it a great advantage over iron, as rendering it 
 easy to be cast into any desired form ; indeed, zinc is surpassed in 
 fusibility (among the metals in ordinary use) only by tin and lead, its 
 melting point being below a red heat, and usually estimated at 770 F. 
 Zinc is also less liable than iron to corrosion under the influence of moist 
 air, for although a bright surface of zinc soon tarnishes when exposed to 
 the air, it merely becomes covered with a thin film of oxide of zinc (pass- 
 ing gradually into basic carbonate, by absorption of carbonic acid from the 
 air) which protects the metal from further action. 
 
 The great strength of iron has been ingeniously combined with the 
 durability of zinc, in the so-called galvanised iron, which is made by coat- 
 ing clean iron with melted zinc, thus affording a protection much needed 
 in and around large towns, where the sulphurous and sulphuric acids 
 arising from the combustion of coal, and the acid emanations from various 
 factories, greatly accelerate the corrosion of unprotected iron. The iron 
 plates to be coated are first thoroughly cleansed by a process which will be 
 more particularly noticed in the manufacture of tin-plate, and are then 
 dipped into a vessel of melted zinc, the surface of which is coated with 
 sal-ammoniac (hydrochlorate of ammonia) in order to dissolve the oxide of 
 zinc which forms upon the surface of the melted metal, and might adhere 
 to the iron plate so as to prevent its becoming uniformly coated with the 
 zinc (ZnO + NH 3 . HC1 = ZnCl + NH 3 + HO). A more firmly ad- 
 herent coating of zinc is obtained by first depositing a thin film of tin 
 upon the surface of the iron plate by galvanic action, and hence the name 
 of galvanised iron. 
 
 The ores of zinc are found pretty abundantly in England, chiefly in the 
 Mendip Hills in Somersetshire, at Alston Moor in Cumberland, in Corn- 
 wall and Derbyshire, but the greater part of the zinc used in this country 
 is imported from Belgium and Germany, being derived from the ores of 
 Transylvania, Hungary, and Silesia. 
 
 Metallic zinc is never met with in nature. Its chief ores are calamine 
 or carbonate of zinc (ZnO . C0 2 ), blende or sulphide of zinc (ZnS), and 
 red zinc ore, in which oxide of zinc (ZnO) is associated with the oxides of 
 iron and manganese. 
 
 Calamine is so called from its tendency to form masses resembling a 
 bundle of reeds (calamus, a reed). It is found in considerable quantities 
 in Somersetshire, Cumberland, and Derbyshire. The mineral known as 
 electric calamine is a silicate of zinc (2ZnO . SiO 2 . HO). Blende derives 
 
METALLURGY OF ZINC. 295 
 
 its name from the German Uenden, to dazzle, in allusion to the brilliancy 
 of its crystals, which are generally almost black from the presence of sul- 
 phide of iron, the true colour of pure sulphide of zinc being white. 
 Blende is found in Cornwall, Cumberland, Derbyshire, Wales, and the 
 Isle of Man, and is generally associated with galena or sulphide of lead, 
 which is always carefully picked out of the ore before smelting it, since it 
 would become converted into oxide of lead, which corrodes the earthen 
 crucibles employed in the process. 
 
 , In England, the extraction of zinc from its ores is carried on chiefly at 
 Bristol, Birmingham, and Sheffield. Before extracting the metal from 
 these ores, they are subjected to a preliminary treatment which brings 
 them both to the condition of oxide of zinc. For this purpose the cala- 
 mine is simply calcined in a reverberatory furnace, in order to expel the 
 carbonic acid ; but the blende is roasted for ten or twelve hours with con- 
 stant stirring, so as to expose fresh surfaces to the air, when the sulphur 
 passes off in the form of sulphurous acid, and its place is taken by the 
 oxygen, the ZnS becoming ZnO. The extraction of the metal from this 
 oxide of zinc depends upon the circumstance that zinc is capable of being 
 distilled at a bright red heat, its boiling point being 1904 F. 
 
 The facility with which this metal passes off in the form of vapour is 
 seen when it is melted in a ladle over a brisk fire, for at a bright red 
 heat abundance of vapour rises from it, which, taking fire in the air, burns 
 with a brilliant greenish white light, throwing off into the air numerous 
 white flakes of light oxide of zinc (the philosopher's wool, or nil album 
 of the old chemists). 
 
 The distillation of zinc may be effected on the small scale in a black-lead crucible 
 (A, fig. 224) about 5 inches high and 3 in diameter. A hole is drilled through the 
 bottom with a round file, and into this is fitted a piece 
 of wrought-iron gas-pipe (B) about 9 inches long and 1 
 inch wide, so as to reach nearly to the top of the inside 
 of the crucible. Any crevices- between the pipe and the 
 sides of the hole are carefully stopped up with fire-clay 
 moistened with solution of borax. A few ounces of zinc 
 are introduced into the crucible, the cover of which is 
 then carefully cemented on with fire-clay (a little borax 
 being added to bind it together at a high temperature), 
 and the hole in the cover is stopped up with fire-clay. 
 The crucible having been kept for several hours in a 
 warm place, so that the clay may dry, it is placed in a 
 cylindrical furnace with a hole at the bottom, through 
 which the iron pipe may pass, and a lateral opening 
 into which is inserted an iron tube (C) connected with 
 a forge bellows. Some lighted charcoal is thrown into 
 the furnace, and when this has been blown into a blaze, 
 the furnace is filled up with coke broken into small 
 pieces. The fire is then blown till the zinc distils freely Fig. 224. Distillation of 
 into a vessel of water placed for its reception. Four zmc - 
 
 ounces of zinc may be easily distilled in half-an-hour. 
 
 English method of extracting zinc. The oxide of zinc, obtained as above 
 from calamine or blende, is mixed with about half its weight of coke or an- 
 thracite coal. This mixture is introduced into large crucibles (fig. 225) with 
 a hole in the bottom, through which passes a short wide iron pipe destined 
 for the passage of the vapour of zinc. These crucibles are about 4 feet high 
 by 2 J feet wide. Some large pieces of coke are first introduced into them 
 to prevent the charge from passing into the iron pipes, and when they have 
 been charged with the above mixture, their covers are cemented on, and 
 
296 
 
 EXTRACTION OF ZINC FROM ITS ORES. 
 
 they are heated in furnaces somewhat resembling those of a glass-house, 
 each furnace receiving six crucibles, which generally contain, in all, one 
 ton of roasted ore. When the mixture in the crucibles is heated to red- 
 ness, it begins to evolve carbonic oxide, produced by the combination of 
 the carbon with the oxygen from the oxide of zinc. This gas burns with 
 a blue flame at the mouth of the iron pipe ; but at a bright red heat the 
 metallic zinc which has been thus liberated is converted into vapour, and 
 the greenish-white flame of burning zinc is perceived at the orifice. 
 
 When this is the case, about 8 feet of 
 iron pipe are joined on to the short 
 piece, in order to condense the vapour 
 of zinc, which falls into a vessel placed 
 for its reception. The distillation occu- 
 pies about sixty hours, and the average 
 yield is about 35 parts of zinc from 100 
 of ore, a considerable quantity of zinc 
 being left behind in the form of silicate 
 of zinc (electric calamine), which is not 
 reduced by distillation with carbon. 
 
 The zinc thus obtained, however, is 
 mixed with a considerable quantity of 
 oxide of zinc, and with other foreign 
 matters carried over from the crucibles. 
 It is, therefore, again melted in a large 
 iron pan, and allowed to rest, in order 
 that the dross may rise to the surface ; 
 this is skimmed off, to be worked over 
 again in a fresh operation, and the metal 
 is cast into ingots, which are sent into commerce under the name of 
 spelter. 
 
 Belgian process for the extraction of zinc.^-At the Vieille-Montagne 
 works, near Liege, calamine is exposed to the rain for several months in 
 order to wash out the clay; it is then calcined to expel 
 the water and carbonic acid, the oxide of zinc so ob- 
 tained being mixed with half its weight of coal dust, 
 and distilled in fire-clay cylinders (C, fig. 226), hold- 
 ing about 40 Ibs. each, and set in seven tiers of six 
 each in the same furnace, the vapour of zinc being 
 conveyed by a short conical iron pipe (B) into a 
 conical iron receiver (D), which is emptied every two 
 hours into a large ladle, from which the zinc is poured 
 into ingot-moulds. Each distillation occupies about 
 twelve hours. The advantage of this particular mode 
 of arranging the cylinders is, that it economises fuel 
 by allowing the poorer ores, which require less heat 
 to distil all the zinc from them, to be introduced into 
 the upper rows of cylinders farthest from the fire (A). 
 There are two varieties of Belgian ore, one containing 
 33 and the other 46 per cent, of zinc, but a large proportion of this is in 
 the form of silicate, which is not extracted by the distillation. 
 
 Silesian process for extracting zinc. In Silesia, the oxide of zinc ob- 
 tained by the calcination of calamine is mixed with fine cinders, and dis- 
 tilled in arched earthen retorts (A, fig. 227), into which the charge is 
 
 Fig. 225. English zinc furnace. 
 
 Fig. 226. Belgian 
 zinc furnace. 
 
PROPERTIES OF ZINC. 
 
 297 
 
 Fig. 228. Silesian zinc furnace. 
 
 introduced through a small door (B), which is then cemented up. These 
 retorts are arranged in a double row in the same furnace (fig. 228), and 
 the vapour of zinc is con- 
 densed in a bent earthen- 
 ware pipe attached to each 
 retort, and having an 
 opening (C) near the bend, 
 which is kept closed, un- 
 less it is necessary to clear Fi g- 227. 
 out the pipe. In regard 
 
 to the consumption of fuel, this process is far more economical than that 
 followed in this country. The Silesian zinc is remelted, before casting 
 into ingots, in clay in- 
 stead of iron pots, since 
 melted zinc always dis- 
 solves iron, and a very 
 small quantity of that 
 metal is found to injure 
 zinc when required for 
 rolling into sheets. 
 
 A small quantity of 
 lead always distils over 
 together with the zinc, 
 and since this metal also 
 interferes with the roll- 
 ing of zinc into sheets, 
 
 a portion of it is separated from zinc intended for this purpose, by melting 
 the spelter, in large quantity, upon the hearth of a reverberatory furnace, 
 the bed of which is inclined so as to form a deep cavity at the end nearest 
 the chimney. The specific gravity of lead being 1 1 '4, whilst that of zinc 
 is 6*9, the former accumulates chiefly at the bottom of the cavity, and 
 the ingots cast from the upper part of the melted zinc will contain but 
 little lead. 
 
 Ingots of zinc, when broken across, exhibit a beautiful crystalline frac- 
 ture, which, taken in conjunction with the bluish colour of the metal, 
 enables it to be easily identified. 
 
 The spelter of commerce is liable to contain lead, iron, tin, antimony, 
 arsenic, copper, and cadmium. 
 
 Zinc being easily dissolved by diluted acids, it is necessary to be care- 
 ful in employing this metal for culinary purposes, since its soluble salts 
 are poisonous. 
 
 It will be remembered that the action of diluted sulphuric acid upon 
 zinc is employed for the preparation of hydrogen. Pure zinc, however, 
 evolves hydrogen very slowly, since it becomes covered with a number of 
 hydrogen bubbles which protect it from further action; but if a piece of 
 copper or platinum be made to touch the zinc beneath the acid, these 
 metals, being electronegative towards the zinc, will attract the electroposi- 
 tive hydrogen, leaving the zinc free from bubbles and exposed on all 
 points to the action of the acid, so that a continuous disengagement of 
 hydrogen is maintained. As a curious illustration of this, a thin sheet of 
 platinum or silver foil may be shown to sink in diluted sulphuric acid, 
 until it conies in contact with a piece of zinc, when the bubbles of hydro- 
 
298 CADMIUM. 
 
 gen bring it up to the surface. The lead, iron, &c., met with in commer- 
 cial zinc are electronegative to the zinc, and thus serve to maintain a con- 
 stant evolution of hydrogen. 
 
 A coating of metallic zinc may be deposited upon copper by slow gal- 
 vanic action, if the copper be immersed in a concentrated solution of 
 potash, at the boiling point of water, in contact with metallic zinc, when 
 a portion of the latter is dissolved in the form of oxide, with evolution of 
 hydrogen, and is afterwards precipitated on the surface of the electro- 
 negative copper. 
 
 Oxide of zinc. Zinc forms but one oxide, which is known in commerce 
 as zinc-white, and is prepared by allowing the vapour of the metal to burn 
 in earthen chambers through which a current of air is maintained. This 
 zinc- white is sometimes used for painting in place of white lead (carbonate 
 of lead), over which it has the advantages of not injuring the health of 
 the persons using it, and of being unaffected by sulphuretted hydrogen, 
 an important consideration in manufacturing towns where that substance 
 is so abundantly supplied to the atmosphere. Unfortunately, however, 
 the oxide of zinc does not combine with the oil of the paint, as oxide of 
 lead does, and the paint is consequently more liable to peel off. The 
 oxide of zinc has the characteristic property of becoming yellow when 
 heated, and white again as it cools. It is sometimes used in the manu- 
 facture of glass for optical purposes. 
 
 Oxide of zinc forms a soluble compound with potash, in this respect 
 resembling alumina, and therefore metallic zinc, like aluminum, is dis- 
 solved by boiling with solution of potash, hydrogen being disengaged 
 from the water, the oxygen of which combines with the zinc. 
 
 The sulphate of zinc or 'white vitriol, which is employed in medicine, 
 and more extensively in calico-printing, is prepared by roasting blende 
 (sulphide of zinc, ZnS) at a low temperature, when both its elements com- 
 bine with oxygen, the oxide of zinc and sulphuric acid thus produced 
 remaining in combination as sulphate of oxide of zinc (ZnO . S0 3 ). After 
 roasting, the mass is treated with water, which dissolves the sulphate, and 
 yields it again, on evaporation, in prismatic crystals having the formula 
 ZnO.S0 3 .HO + 6Aq. 
 
 Chloride of zinc (ZnCl), prepared by dissolving zinc in hydrochloric 
 acid, is known in commerce as Burnett's disinfecting fluid, since it is cap- 
 able of absorbing hydrosulphuric acid, ammonia, and other offensive pro- 
 ducts of putrefaction, and arrests the decomposition of wood and animal 
 substances. By evaporating its solution, the chloride of zinc is obtained 
 in a fused state, and solidifies on cooling into white deliquescent masses. 
 It has a very powerful attraction for water. 
 
 207. Equivalent and atomic weights of zinc. When zinc is dissolved 
 in hydrochloric acid, 3 2 -5 parts by weight of zinc displace 1 part of 
 hydrogen; hence 32*5 represents the equivalent of zinc. Considerations 
 similar to those referred to in the case of magnesium (p. 284) have induced 
 most chemists to regard the atomic weight of zinc as 65, or double its 
 equivalent, so that zinc is a bi-equivalent or di-atomic metal, and the 
 atomic formula of its oxide is ihiO, (in = 65, = 16), and that of its 
 chloride 
 
INDIUM URANIUM. 299 
 
 CADMIUM. 
 
 208. This metal is found in small quantities in the ores of zinc, its 
 presence being indicated during the extraction of that metal (p. 296) by 
 the appearance of a brown flame (/brown blaze) at the commencement of 
 the distillation, before the characteristic zinc-flame (blue blaze) is seen at 
 the orifice of the iron tube. Cadmium is more easily vaporised than zinc 
 (boiling at 1580 F.), so that the bulk of it is found in the first portions 
 of "the distilled metal. If the mixture of cadmium and zinc be dissolved 
 in diluted sulphuric acid, and the solution treated with hydrosulphuric 
 acid gas, a bright yellow precipitate of sulphide of cadmium (CdS) is ob- 
 tained, which is employed in painting under the name of cadmia. By 
 dissolving this in strong hydrochloric acid and adding carbonate of am- 
 monia, the carbonate of cadmium (CdO . C0 2 ) is precipitated, from which 
 metallic cadmium may be extracted by distillation with charcoal. 
 
 Although resembling zinc in its volatility and its chemical relations, in 
 appearance it is much more similar to tin, and emits a crackling sound 
 like that metal when bent. Like tin, also, it is malleable and ductile at 
 the ordinary temperature, and becomes brittle at about 180 F. It is 
 even more fusible than tin, becoming liquid at 242 F., so that it is useful 
 for making fusible alloys. An alloy of 3 parts of cadmium with 15 of 
 bismuth, 8 of lead, and 4 of tin, fuses at 140 F. In its behaviour with 
 acids and alkalies cadmium is similar to zinc, but the metal is easily dis- 
 tinguished from all others by its yielding a characteristic chestnut-brown 
 oxide when heated in air. This oxide (CdO) is the only oxide of cadmium. 
 
 The iodide of cadmium (Cdl), obtained by the action of iodine upon 
 the metal in the presence of water, is employed in photography. 
 
 The equivalent weight of cadmium, deduced from the analysis of its 
 chloride, is 56. The specific gravity (or weight of one volume) of vapour 
 of cadmium is 3*94, or 57 times that of hydrogen. If one vol. of hydro- 
 gen be represented as 1 atom, weighing 1, then 1 vol. of cadmium vapour 
 (or one atom) would weigh 57 ; or allowing for error in the troublesome 
 experiment of determining the specific gravity of its vapour, the atom of 
 cadmium would be represented by a number identical with its equivalent 
 weight. The specific heat of cadmium, however, as well as its general 
 chemical relations, favour the view that it is a di-atomic metal like zinc, 
 its atomic weight being 112. 
 
 INDIUM is the name of a metal which has recently been discovered, with the help 
 of the spectroscope, in a specimen of blende from Freiberg. Its name refers to an 
 indigo blue line in the spectrum. The examination of the metal is as yet imper- 
 fect, but it is white, malleable, and dissolves, like zinc and cadmium, in'hydro- 
 chloric acid. Its specific gravity is 7'36. To extract indium from the Freiberg 
 zinc, the metal is boiled with dilute sulphuric acid, employed in such quantity as to 
 leave part of the zinc undissolved, together with indium and lead. The residue is 
 dissolved in nitric acid, the lead and cadmium precipitated by hydrosulphuric acid, 
 the latter expelled by boiling, and the oxide of indium precipitated from the 
 solution by carbonate of baryta. When this precipitate is dissolved in hydrochloric 
 acid, and excess of ammonia added, the white hydrated oxide of indium is precipi- 
 tated, and may be reduced by heating in hydrogen. 
 
 At a bright red heat it burns with a violet blue flame, yielding a yellow oxide of 
 indium, InO. 
 
 The equivalent of indium appears to be about 36. 
 
 209. UKANIUM. This is a rare metal, never employed in the metallic state, but 
 in the form of sesquioxide (U 2 3 ) and black oxide (2UO . U 2 j!} ) , for imparting 
 
300 
 
 OCCURRENCE OF IRON IN NATURE. 
 
 yellow and black colours respectively to glass and porcelain. The chief source of 
 these compounds is the mineral pitch-blende, which contains a large proportion of 
 black oxide of uranium, together with silica, iron, copper, lead, and arsenic. In its 
 chemical relations uranium presents some similarity to iron and manganese. It 
 forms two distinct oxides, UO and U 2 S , of which the former is decidedly basic, 
 whilst the latter is capable of acting both as an acid and a base. The bright 
 greenish-yellow colour of the salts of the sesquioxide of uranium is characteristic of 
 the metal, and glass coloured with this oxide exhibits the remarkable optical effect 
 of fluorescence in a very high degree. 
 
 IKON. 
 
 210. This most useful of all metals is one of those most widely and 
 abundantly diffused in nature. It is to be found in nearly all forms of 
 rock, clay, sand, and earth, its presence in these being commonly indi- 
 cated by their colours, for iron is the commonest of natural mineral 
 colouring ingredients. It is also found, though in small proportion, in 
 plants, and in larger quantity in the bodies of animals, especially in the 
 blood, which contains about 0'5 per cent, of iron in very intimate associ- 
 ation with its colouring matter. 
 
 But iron is very rarely found in the metallic state in nature, being 
 almost invariably combined either with oxygen or sulphur. 
 
 Metallic iron is met with, however, in the meteorites or metallic masses, 
 sometimes of enormous size, and of unknown origin, which occasionally 
 fall upon the earth. Of these iron is the chief component, but there are 
 also generally present, cobalt, nickel, chromium, manganese, copper, tin, 
 magnesium, carbon, phosphorus, and sulphur. 
 
 The chief forms of combination in which iron is found in sufficient 
 abundance to render them available as sources of the metal, are shown in 
 the following table : - 
 
 Ores of Iron. 
 
 Common Name. 
 
 Chemical Name. 
 
 Composition. 
 
 Magnetic iron ore 
 
 Protosesquioxide of iron 
 
 Fe 3 4 
 
 Ked haematite 
 
 Sesquioxide of iron 
 
 Fe 2 3 
 
 Specular iron 
 
 
 
 
 Brown haematite 
 
 Hydrated sesquioxide 
 
 2Fe 2 3 .3HO 
 
 Spathic iron ore 
 
 Carbonate of iron 
 
 FeO . C0 2 
 
 Clay iron-stone 
 
 ( Carbonate of iron with 
 
 
 
 I clay 
 
 
 
 ( Carbonate of iron with 
 
 
 Blackband 
 
 < clay and bituminous 
 
 
 
 \ matter 
 
 
 Iron pyrites 
 
 Bisulphide of iron. 
 
 FeS 2 
 
 These ores are frequently associated with extraneous minerals, some of 
 the constituents of which are productive of injury to the quality of the 
 iron. It is worthy of notice that scarcely one of the ores of iron is 
 entirely free from sulphur and phosphorus, substances which will be seen 
 to have a very serious influence on the quality of the iron extracted from 
 them, and the presence of which increases the difficulty of obtaining the 
 metal in a marketable condition. 
 
 The following table illustrates the general composition of the most im- 
 portant English ores of iron, with reference to the proportions of iron, and 
 of those substances which materially influence the character of the iron 
 
OKES OF IRON. 
 
 301 
 
 extracted from the ore, viz., manganese (present as oxide or carbonate), 
 phosphorus (present as phosphoric acid), and sulphur (present as bisul- 
 phide of iron). The maximum and minimum quantities found in each 
 ore are specified. 
 
 British Iron Ores* 
 
 
 Iron. 
 
 Oxide of 
 Manganese. 
 
 Phosphoric 
 Acid. 
 
 Bisulphide 
 of Iron. 
 
 (Pyrites.) 
 
 No. of 
 Samples 
 Analysed. 
 
 In 100 parts. 
 
 
 
 
 
 
 
 Max. 
 
 Mhu 
 
 Max. 
 
 Min. 
 
 Max. 
 
 Min. 
 
 Max. 
 
 Min. 
 
 
 Clay iron-stone from coal-measures, 
 
 43-30 
 
 L'0-#> 
 
 3-30 
 
 0-46 
 
 1-42 
 
 0-07 
 
 1-21 
 
 
 
 77 
 
 Clay iron-stone from the lias, 
 
 49-17 
 
 17-34 
 
 1-30 
 
 
 
 5-05 
 
 
 
 1-60 
 
 
 
 12 
 
 Brown haematite, .... 
 
 63-04 
 
 11-98 
 
 1-60 
 
 trace 
 
 3-17 
 
 
 
 0-30 
 
 
 
 23 
 
 Red haematite, .... 
 
 69-10 
 
 47-47 
 
 1-13 
 
 trace 
 
 trace 
 
 trace 
 
 0-06 
 
 
 
 5 
 
 Spathic ore, 
 
 4S-78 
 
 13-98 
 
 12-64 
 
 1-93 
 
 0-22 
 
 
 
 Oil 
 
 
 
 6 
 
 Magnetic ore, 
 
 67-01 
 
 0-14 
 
 o-io 
 
 0-07 
 
 I 
 
 From this table it will be gathered that, among the most abundant of 
 the iron ores of this country, red haematite is the richest and purest, 
 whilst the brown haematite often contains considerable proportions of 
 sulphur and phosphorus, and the spathic ore, though containing little 
 sulphur and phosphorus, often contains much manganese. 
 
 The argillaceous ores, or clay iron-stones, found in the lias contain more 
 phosphoric acid than those from the coal-measures ; and these latter, as a 
 general rule, contain more sulphur (pyrites) than the former, although the 
 maximum in the table does not show this. 
 
 Clay iron-stone is the ore from which the largest quantity of iron is 
 extracted in England, since it is found abundantly in the coal-measures 
 of Staffordshire, Shropshire, and South Wales, and it is a circumstance 
 of great importance in the economy of English iron-smelting, that the 
 coal and limestone required in the smelting process, and even the fire-clay 
 employed in the construction of the furnace, are found in the immediate 
 vicinity of the ore. 
 
 Blackband is the clay iron-stone found in the coal-fields of Scotland, 
 and often contains between 20 and 30 per cent, of bituminous matter, 
 which contributes to the economy of fuel in smelting it. 
 
 Bed hcematite (Fe 2 3 ) is the most characteristic of the ores of iron, 
 occurring in hard shining rounded masses, with a peculiar fibrous structure 
 and a dark red-brown colour, whence the ore derives its name (ai/xa, blood). 
 It is found in considerable quantities in Lancashire and Cornwall, but un- 
 fortunately its very compact structure is an obstacle to its being smelted 
 alone, so that it is generally mixed with some clay iron-stone, and hence 
 the iron obtained is not so free from sulphur and phosphorus as if it were 
 extracted from haematite alone. 
 
 Red oclire is a soft variety of this ore, containing a little clay. 
 
 Brown hcematite (2Fe 2 3 . 3HO) is found at Alston Moor (Cumber- 
 land) and in Durham, but it is more abundant on the Continent, and is 
 the source of most of the Belgian and French irons. Pea iron, ore and 
 yellow ochre are varieties of brown haematite. The Scotch ore which is 
 called kidney-form clay iron-stone is really a hydrated sesquioxide of iron. 
 
 * This table has been compiled from the analyses given in " Percy on Iron and Steel." 
 
302 METALLURGY OF IRON. 
 
 Specular iron ore (Fe 2 3 ) (oligist ore or iron-glance), although of the 
 same composition as red haematite, is very different from it in appearance, 
 having a steel-grey colour and a brilliant metallic lustre. The island of 
 Elba is the chief locality where this ore is found, but it also occurs in 
 Germany, France, and Eussia. The excellent quality of the iron smelted 
 from this ore is due partly to the purity of the ore, and partly to the cir- 
 cumstance that charcoal, and not coal, is employed in smelting it. 
 
 Magnetic iron ore (Fe 3 4 ), of which the loadstone is a variety, has a 
 more granular structure, and a dark iron-grey colour. It forms moun- 
 tainous masses in Sweden, and is also found in Russia and North America. 
 It is generally smelted with charcoal, and yields an excellent iron. Iron 
 sand, a peculiar heavy black sand, of metallic lustre, consists in great 
 measure of the magnetic ore, but contains a very large proportion of titanic 
 acid. It is found abundantly in India, Nova Scotia, and New Zealand ; 
 but its fine state of division prevents it from being largely available as a 
 source of iron. 
 
 Spathic iron ore (FeO . C0 2 ) is found in abundance in Saxony, and 
 often contains a considerable quantity of carbonate of manganese, which 
 influences the character of the metal extracted from it. 
 
 The oolitic iron ore, occurring in the Northampton oolite, contains both 
 hydrated sesquioxide and carbonate of iron, together with clay. 
 
 Iron pyrites (FeS 2 ) is remarkable for its yellow colour, its brilliant 
 metallic lustre, and crystalline structure, being generally found either in 
 distinct cubical or dodecahedral crystals, or in rounded nodules of 
 radiated structure. It was formerly disregarded as a source of iron, on 
 account of the difficulty of separating the sulphur ; but since the demand 
 for iron has so largely increased, an inferior quality of the metal has been 
 extracted from the residue left after burning the pyrites in the manufac- 
 ture of oil of vitriol (p. 203), the residue being first well roasted in a 
 lime-kiln to remove as much as possible of the sulphur. 
 
 211. Metallurgy of iron. Iron owes the high position which it occupies 
 among useful metals to a combination of valuable qualities not met with 
 in any other. Although possessing nearly twice as great tenacity or strength 
 as the strongest of the other metals commonly used in the metallic state, 
 it is yet one of the lightest, its specific gravity being only 7. 7, and is 
 therefore particularly well adapted for the construction of bridges and 
 large edifices, as well as for ships and carriages. It is the least yield- 
 ing or malleable of the metals in common use, and can therefore be relied 
 upon for affording a rigid support ; and yet its ductility, when heated, is 
 such that it admits of being rolled into the thinnest sheets and drawn 
 into the finest wire, the strength of which is so great that a wire of y^th 
 inch in diameter is able to sustain 705 pounds, while a similar wire of 
 copper, which stands next in order of tenacity, will not support more than 
 385 pounds. 
 
 Being, with the exception of platinum, the least fusible of useful metals, 
 iron is applicable to the construction of fire-grates and furnaces. Nor are 
 its qualifications all dependent upon its physical properties, for it not only 
 enters into a great number of compounds which are of the utmost use in 
 the arts, but its chemical relations to one of the non-metallic elements, 
 carbon, are such, that the addition of a small quantity of this element 
 converts it into steel, far surpassing iron in the valuable properties of hard- 
 ness and elasticity; whilst a larger quantity of carbon gives rise to cast- 
 
EXTRACTION OF IRON FROM CLAY IRON-STONE. 
 
 303 
 
 mm, the greater fusibility of which permits it to be moulded into vessels 
 and shapes which could not be produced by forging. 
 
 212. English process of smelting clay iron-stone. The first step 
 towards the extraction of the metal consists in calcining (or roasting) the 
 ore in order to expel the water and carbonic acid which it contains. To 
 effect this the ore is built up, together with a certain amount of small 
 coal, into long pyramidal heaps, resting upon a foundation of large lumps 
 of coal ; blackband often contains so much coal that any further addition 
 is unnecessary. These heaps are kindled in several places, and allowed to 
 burn slowly until all the fuel is consumed. This calcination has the effect 
 of rendering the ore more porous, and better fitted for the smelting pro- 
 cess. If the ore contained much sulphur, a part of it would be expelled 
 by the roasting, in the form of sulphurous acid. 
 
 Sometimes the calcination is effected in kilns resembling lime-kilns, 
 and it is often altogether omitted as a separate process, the expulsion of 
 the water and carbonic acid being then effected in the smelting-furnace 
 itself as the ore descends. 
 
 The calcined ore is smelted in a huge blast-furnace (fig. 229) about fifty or 
 sixty feet high, built of massive masonry, and lined internally with fire-brick. 
 
 Fig. 229. Blast-furnace for smelting iron ores. 
 
 Since it would be impossible to obtain a sufficiently high temperature with 
 the natural draught of this furnace, air is forced into it at the bottom, 
 under a pressure of three or four pounds upon the inch, through three 
 
304 CHEMICAL CHANGES IN THE BLAST-FURNACE. 
 
 tuyere pipes, the nozzles of which pass through apertures in three sides 
 of the furnace. It would be very easy to reduce to the metallic state the 
 oxide of iron contained in the calcined ore, by simply throwing it into this 
 furnace, together with a proper quantity of coal, coke, or charcoal j but 
 the metallic iron fuses with so great difficulty, that it is impossible to sepa- 
 rate it from the clay unless this latter is brought into a liquid state ; and 
 even then the fusion of the iron, which is necessary for complete separa- 
 tion, is only effected after it has formed a more easily fusible compound 
 with a small proportion of carbon derived from the fuel. 
 
 fow, clay is even more difficult to fuse than iron, so that it is neces- 
 sary to add, in the smelting of the ore, some substance capable of forming 
 with the clay a combination which is fusible at the temperature of the 
 furnace. If clay (silicate of alumina) be mixed with limestone (carbonate 
 of lime), and exposed to a high temperature, the carbonic acid is expelled 
 from the limestone, and the lime unites with the clay, forming a double 
 silicate of alumina and lime, which becomes perfectly liquid, and when 
 cool, solidifies to a glass or slag. The limestone is here said to act as a 
 flux, because it induces the clay to flow in the liquid state. In order, 
 therefore, that the clay may be readily separated from the metallic iron, 
 the calcined ore is mixed with a certain proportion of limestone before 
 being introduced into the furnace. 
 
 Great care is necessary in first lighting the blast-furnace lest the new 
 masonry should be cracked by too sudden a rise of temperature, and when 
 once lighted, the furnace is kept in constant work for years until in want of 
 repair. When the fire has been lighted, the furnace is filled up with coke, 
 and as soon as this has burnt down to some distance below the chimney, a 
 layer of the mixture of calcined ore with the requisite proportion of lime- 
 stone is thrown upon it ; over this there is placed another layer of coke, then 
 a second layer of the mixture of ore and flux, and so on, in alternate layers, 
 until the furnace has been filled up ; when the layers sink down, fresh 
 quantities of fuel, ore, and flux are added, so that the furnace is kept con- 
 stantly full. As the air passes from the tuyere pipes into the bottom of 
 the furnace, it parts with its oxygen to the carbon of the fuel, which it 
 converts into carbonic acid (C0 2 ) ; the latter, passing over the red-hot 
 fuel as it ascends in the furnace, is converted into carbonic oxide (CO) by 
 combining with an additional quantity of carbon. It is this carbonic 
 oxide which reduces the calcined ore to the metallic state, when it comes 
 in contact with it, at a red heat, in the upper part of the furnace, for 
 carbonic oxide removes the oxygen, at a high temperature, from the oxides 
 of iron, and becomes carbonic acid, the iron being left in the metallic state. 
 But the iron so reduced remains disseminated through the mass of ore 
 until it has passed down to a part of the furnace which is more strongly 
 heated, where the iron enters into combination with a small proportion of 
 carbon to form cast-iron, which fuses and runs down into the crucible or 
 cavity for its reception at the bottom of the furnace. At the same time, 
 the clay contained in the ore is acted upon by the lime of the flux, pro- 
 ducing a double silicate of alumina and lime, which also falls in the liquid 
 state into the crucible, where it forms a layer of " slag " above the heavier 
 metal. This slag, which has five or six times the bulk of the iron, is 
 allowed to accumulate in the crucible, and to run over its edge down the 
 incline (or cinder-fall) upon which the blast-furnace is built ; but when 
 a sufficient quantity of cast-iron has collected at the bottom of the crucible, 
 it is run out through a hole provided for the purpose, either into channels 
 
HOT-BLAST IRON. 305 
 
 made in a bed of sand or into iron moulds, where it is cast into rough 
 semi-cylindrical masses called pigs, whence cast-iron is also spoken of as 
 pig-iron. The temperature of the furnace is, of course, highest in the 
 immediate neighbourhood of the tuyeres ; the reduction of the iron to the 
 metallic state appears to commence at about two-thirds of the way down 
 the furnace, the volatile matters of the ore, fuel, and flux being driven oif 
 before this point is reached. 
 
 Some idea may be formed of the immense scale upon which the smelt- 
 ing of iron ores is carried out, when it is stated that each furnace con- 
 sumes, in the course of twenty-four hours, about 50 tons of coal, 30 tons 
 of ore, 6 tons of limestone, and 100 tons of air. The cast-iron is run off 
 from the crucible once or twice in twelve hours, in quantities of five 
 or six tons at a time. The average yield of calcined clay iron-stone is 35 
 per cent, of iron. 
 
 The gases escaping from the chimney of the blast-furnace are highly 
 inflammable, for they contain, beside the nitrogen of the air blown into the 
 furnace, a considerable quantity of carbonic oxide and some hydrogen, 
 together with the carbonic acid formed by the action of the carbonic oxide 
 upon the ore. Since the carbonic oxide and hydrogen confer considerable 
 heating power upon these gases, they are employed in some iron-works for 
 heating steam boilers, or for calcining the ore, or for raising the temperature 
 of the blast. 
 
 The composition of the gas issuing from a hot-blast furnace (fed with uncoked 
 coal) may be judged of from the following table : 
 
 Gas from Blast- Furnace. 
 Nitrogen, . 55-35 vols. 
 
 Carbonic oxide, 
 Hydrogen, . 
 Carbonic acid, 
 Marsh-gas, 
 Olefiant-gas, 
 
 25-97 
 6-73 
 7-77 
 3-75 
 0-43 
 
 100-00 
 
 The carbonic oxide, of course, renders these gases highly poisonous, and fatal acci- 
 dents occasionally happen from this cause. 
 
 Although the bulk of the nitrogen present in the air escapes unchanged from the 
 furnace, it is not improbable that a portion of it contributes to the formation of the 
 cyanide of potassium (KC 2 N), which is produced in the lower part of the furnace, 
 the potassium being furnished by the ashes of the fuel. 
 
 The hot-blast. On considering the enormous quantity of air which 
 passes through the blast furnace, it will be seen that it occasions the ioss of 
 a considerable amount of heat. In order to economise the fuel, hot-blast 
 furnaces are fed with air of which the temperature is raised to about 
 600 F., by passing it through heated iron pipes before allowing it to 
 enter the blast furnace. The higher temperature which is thus attained 
 permits the use of uncoked coal, which would not have given enough heat 
 in a cold-blast furnace, and the same quantity of ore may be smelted with 
 less than half the coal formerly employed. It appears, however, that the 
 hot-blast iron is inferior in quality to that obtained from the same ore in a 
 cold- blast furnace, and this is generally explained by referring to the larger 
 quantity of sulphur contained in the raw coal; to the circumstance, that the 
 cast-iron being exposed to a much higher temperature in the hot-blast 
 furnace is more liable to receive and retain a larger amount of foreign sub- 
 
 u 
 
306 BLAST FUKNACE CINDER. 
 
 stances; and (most important of all) to the custom of extracting iron in a 
 hot-blast furnace from slags obtained in the subsequent processes of the 
 iron-manufacture, which could not be smelted in a cold-blast furnace. 
 These slags always contain sulphur and phosphorus, and therefore yield an 
 inferior quality of iron. Hence the distinction commonly drawn between 
 mine-iron extracted from the ore without admixture of slags, and cinder- 
 iron in the preparation of which slag or cinder has been employed. 
 
 The slag from the blastfurnace is essentially a glass composed of a 
 double silicate of alumina and lime, the composition of which varies much 
 according to the nature of the earthy matters in the ore, and the com- 
 position of the flux. Its colour is generally opaque white, streaked with 
 blue, green, or brown. 
 
 The nature of the flux employed must, of course, be modified according 
 to the composition of the earthy substances (or gangue) present in the ore. 
 Where this consists of clay (silicate of alumina) the addition of lime 
 (which is sometimes added in the form of limestone and sometimes as 
 quick-lime) will provide for the formation of the double silicate of alumina 
 and lime. But if the iron-ore happened already to contain limestone, an 
 addition of clay would be necessary, or if quartz were present, consisting 
 of silica only, both lime and alumina (in the form of clay) will be neces- 
 sary as a flux. It is sometimes found economical to employ a mixture of 
 ores containing different kinds of gangue, so that one may serve as a flux 
 to the other. If a proper proportion of lime were not added, a portion of 
 the oxide of iron would combine with the silica and be carried off in the 
 slag, but if too large a quantity of lime be employed, it will diminish the 
 fusibility of the slag, and prevent the complete separation of the iron from 
 the earthy matter. The most easily fusible slag which can be formed by 
 the action of lime upon clay has the composition 6CaO . AL 2 3 . 9Si0 2 ; but, 
 in English furnaces, where coal and coke are employed, it is found neces- 
 sary to employ a larger proportion of lime to convert the sulphur of the 
 fuel into sulphide of calcium, so that the slag commonly has a composi- 
 tion more nearly represented by the formula, 12CaO . 2A1 2 3 . 9Si0 2 , 
 which would express a compound of 6 eqs. of normal silicate of lime with 
 1 eq. of normal silicate of alumina, 6(2CaO . Si0 2 ) , 2A1) 3 , 3Si0 2 , silicic 
 acid being considered a bibasic acid. 
 
 Since iron, manganese, and magnesium are commonly found occupying 
 the place of a portion of the calcium, a more general formula for the 
 slag from English blast furnaces would be 
 
 6(2[CaFeMnMg]0 . Si0 2 ) , 2A1 2 3 . 3Si0 2 . 
 
 A fair impression of the ordinary composition of the slag from blast 
 furnaces is conveyed by the following table : 
 
 Slag from Blast Furnace. 
 Silica, 43-07 
 
 Alumina, . 
 
 Lime, 
 
 Magnesia, 
 
 Oxide of iron (FeO) 
 
 Oxide of manganese (MnO). 
 
 Potash, . 
 
 Sulphide of calcium, 
 
 Phosphoric acid, 
 
 14-85 
 
 28-92 
 
 5-87 
 
 2-53 
 
 1-37 
 
 1-84 
 
 1-90 
 
 trace 
 
 100-35 
 
COMPOSITION OF CAST-IRON. 307. 
 
 These slags are sometimes run from the blast furnace into iron moulds, 
 in which they are cast into blocks for rough building purposes. The 
 presence of a considerable proportion of potash has led to experiments 
 upon their employment as a manure, for which purpose they have been 
 blown out, when liquid, into a finely divided frothy condition lit for grind- 
 ing and applying to the soil. 
 
 213. CAST-IRON is, essentially, composed of iron with from 2 to 5 per 
 cent, of carbon, but always contains other substances derived either from 
 tHe ore or from the fuel employed in smelting it. On taking into con- 
 sideration the energetic deoxidising action in the blast furnace, it is not 
 surprising that portions of the various oxygen compounds exposed to it 
 should part with their oxygen, and that the elements thus liberated 
 should find their way into the cast-iron. In this way the silicic acid is 
 reduced, and its silicon is found in cast-iron in quantity sometimes amount- 
 ing to 3 or 4 per cent. Sulphur and phosphorus are also generally pre- 
 sent in cast-iron, but in very much smaller quantity; their presence 
 diminishes its tenacity, and the smelter endeavours to exclude them as far 
 as possible, though a small quantity of phosphorus appears to be rather 
 advantageous for some castings, since it augments the fusibility and 
 fluidity of the cast-iron. The sulphur is chiefly derived from the coal or 
 coke employed in smelting, and for this reason charcoal would be pre- 
 ferable to any other fuel if it could be obtained at a sufficiently cheap 
 rate. The iron-works of America and those of the European continent 
 enjoy a great advantage in this respect over those of England. The 
 phosphorus is obtained from the phosphoric acid existing in the ore or in 
 the flux. Manganese, amounting to 1 or 2 per cent., is often met with in 
 cast iron, having been reduced from the oxide of manganese, which is 
 generally found in iron ores. Other metals, such as chromium, cobalt, 
 &c., are also occasionally present, though in so small quantities as to be 
 of no importance in practice. 
 
 The following table exhibits the largest and smallest proportions of the 
 various elements determined in the analysis of upwards of a hundred 
 specimens of cast-iron : 
 
 Composition of Cast-iron* 
 
 Max. Min. 
 
 Carbon, 4-81 1-04 per cent. 
 
 Silicon, 4-77 0-08 
 
 Sulphur, 1-06 0-00 
 
 Phosphorus, 1-87 trace 
 
 Manganese, 6-08 trace 
 Iron, 
 
 In order to understand the differences observed in the several varieties 
 of cast-iron, it is necessary to consider the peculiar relations between iron 
 and carbon. Iron fused in contact with carbon is capable of combining 
 with nearly 6 per cent, of that element, to form a white, brilliant, and 
 brittle compound which may be represented pretty nearly as composed 
 of Fe 4 C. Under certain circumstances, as this compound of iron and 
 carbon cools, a portion of the carbon separates from the iron, and remains 
 disseminated throughout the mass in the form of minute crystalline par- 
 ticles very much resembling natural graphite. If a broken piece of iron 
 containing these scales 'be examined, the fracture will be found to exhibit 
 
 * Compiled from " Percy on Iron and Steel." 
 
 U2 
 
308 
 
 GIIEY, MOTTLED, AND WHITE IRON. 
 
 a more or less dark grey colour, due to the presence of the uncombined 
 carbon, and for this reason a cast-iron in which a portion of the carbon 
 has thus separated is commonly spoken of as grey iron, whilst that in 
 which the whole of -the carbon has remained in combination with the 
 metal exhibits a white fracture, and is termed white iron or bright iron. 
 Intermediate between these is the variety known as mottled iron, which 
 has the appearance of a mixture of the grey and w r hite varieties. 
 
 The different condition of the carbon in the two varieties of cast-iron is 
 rendered apparent when the metal is dissolved in diluted sulphuric or 
 hydrochloric acid, for any carbon which exists in the uncombined state 
 will then be left, whilst that which had been in combination with the 
 iron passes off in the form of peculiar compounds of carbon and hydrogen, 
 which impart the disagreeable odour perceived in the gas evolved when 
 the metal is dissolved in an acid. 
 
 The properties of these two varieties of cast-iron are widely different, 
 grey iron being so soft that it may be turned in a lathe, whilst the white 
 iron is extremely hard and brittle. Again, although white iron fuses at 
 a lower temperature than grey-iron, the latter is far more liquid when 
 fused, and is therefore much better fitted for casting. 
 
 Although the presence of uncombined carbon is the chief point which 
 distinguishes grey from white iron, other differences are commonly observed 
 in the composition of the two varieties. Thus white iron usually contains 
 less silicon than grey iron, but a larger proportion of sulphur. White 
 iron also usually contains a much larger quantity of manganese. 
 
 The difference in the composition of these three varieties of cast-iron is 
 shown in the following table : 
 
 
 Grey. 
 
 Mottled. 
 
 White. 
 
 Iron . . . 
 
 9024 
 
 89-31 
 
 89-86 
 
 Combined carbon 
 
 1-02 
 
 1-79 
 
 2-46 
 
 Graphite 
 Silicon . 
 
 2-64 
 306 
 
 1-11 
 2-17 
 
 0-87 
 1-12 
 
 Sulphur . 
 Phosphorus 
 Manganese 
 
 1-14 
 
 0-93 
 0-83 
 
 1-48 
 1-17 
 1-60 
 
 2-52 
 0-91 
 
 2-72 
 
 
 99-86 
 
 98-63 
 
 100-46 
 
 As might be expected, it is not easy to tell where a cast-iron ceases to 
 be grey and begins to be mottled, or where the mottled iron ends and 
 white iron begins. There are, in fact, eight varieties of cast-iron in com- 
 merce distinguished by the numbers one to eight, of which No. 1 is dark 
 grey, and contains the largest proportion of graphite, which diminishes in 
 the succeeding numbers up to No. 8, which is the whitest iron, the inter- 
 mediate numbers being more or less mottled. 
 
 The particular variety of cast-iron produced is to some extent under 
 the control of the smelter, a furnace in good order appearing usually to 
 yield grey iron, whilst a defective furnace, or one supplied with too small 
 a proportion of fuel, will commonly give a white iron. But the metal 
 sometimes varies considerably at different levels in the crucible of the 
 furnace, so that pigs of different degrees of greyness are obtained at the 
 same tapping. 
 
 Mottled cast-iron surpasses both the other varieties in tenacity, and 
 
REFINING CAST-IRON. 
 
 309 
 
 is therefore preferred for such purposes as casting ordnance, where this 
 quality is particularly desirable. 
 
 The dark grey iron used for casting, known as foundry-iron, is produced 
 by supplying the blast furnace with a larger proportion of fuel than is 
 employed in making the lighter forge-iron destined for conversion into 
 wrought-iron. The extra consumption of fuel, of course, renders the 
 foundry-iron more expensive. When a furnace is worked with a low 
 charge of fuel to produce a white iron, a larger quantity of iron is lost 
 in the slag, sometimes amounting to 5 per cent, of the metal, whilst 
 the average loss in producing grey iron does not exceed 2 per cent. 
 Ores containing a large proportion of manganese are generally found to 
 yield a white iron. 
 
 When grey iron is melted, the particles of graphite to which its grey 
 colour is due are dissolved by the liquid iron, and if it be poured into 
 a cold iron mould so as to solidify it as rapidly as possible, the external 
 portion of the casting will present much of the hardness and appear- 
 ance of white iron, the sudden cooling having prevented the separation 
 of the graphite. This affords the explanation of the process of chill- 
 casting, by which shot, &c., made of the soft fusible grey iron, are made 
 to acquire externally a hardness approaching that of steel. 
 
 The specific gravity of cast-iron varies between 6 - 92 and 7 '53, and its 
 fusing point is somewhat below 3000 F. 
 
 CONVERSION OF CAST-IRON INTO BAR OR WROUGHT IRON. 
 
 214. In order to convert cast-iron into bar-iron, it is necessary to reduce 
 it as far as possible to the condition of pure iron by removing the carbon, 
 silicon, and other substances associated with it. This purification is 
 effected upon the principle, that when cast-iron is strongly heated in con- 
 tact with oxide of iron, its carbon is evolved in the form of carbonic oxide, 
 whilst the silicon, also combining with the oxygen from a part of the 
 oxide of iron, is con- 
 verted into silicic acid, 
 which unites with an- 
 other portion of oxide 
 to form a fusible slag 
 easily separated from the 
 metal. 
 
 The most important 
 of the processes em- 
 ployed for the conver- 
 sion of pig-iron into bar- 
 iron, is that known as 
 the puddling process, 
 but this is sometimes 
 preceded by the process 
 of refining, which will 
 therefore be first de- 
 scribed. 
 
 Refining of cast-iron. 
 
 Fig. 230. Hearth for refining pig-iron. 
 
 This process consists essentially in exposing the 
 metal, in a fused state, to the action of a blast of air. The refinery (figs. 
 230, 231) is a rectangular trough with double walls of cast-iron, between 
 
310 
 
 REFINING CAST-IKON. 
 
 which cold water is kept circulating to prevent their fusion. This trough 
 is about 3 J feet long by 2J wide, and usually lined with fire-clay ; on each 
 
 side of it are arranged 
 three tuyere pipes for the 
 supply of air, inclined at 
 an angle of 25 to 30 to 
 the bottom of the fur- 
 nace, which is fed with 
 coke, unless the very best 
 iron is required, as for 
 the manufacture of tin- 
 plate, when charcoal is 
 generally used in the 
 refinery. 
 
 This furnace having 
 been filled to a certain 
 height with fuel, five or 
 six pigs of iron (from 
 20 to 30 cwt.) are ar- 
 ranged symmetrically upon it, a blast of air being forced in through the 
 tuyeres, under a pressure of about 3 Ibs. upon the inch. In about a 
 quarter of an hour the metal begins to fuse gradually, and to trickle down 
 through the fuel to the bottom of the refinery, a portion of the iron 
 being converted into oxide in its descent, by the air issuing from the 
 tuyere pipes. When the whole of the metal has been fused, the air is still 
 allowed to play for some time upon its surface, when the fused metal 
 appears to boil in consequence of the escape of bubbles of carbonic oxide. 
 After about two hours the tap hole is opened, and the molten metal 
 run out into a flat mould ; when it begins to solidify, water is thrown 
 upon its surface in order to chill it and render it brittle. The plate of 
 refined iron thus obtained is usually about 2 inches thick. The slag (or 
 finery cinder) is generally received in a separate mould ; its composition 
 may be generally expressed by the formula 2FeO . Si0 2 , the silicic acid 
 having been derived from the silicon contained in the cast-iron. 
 
 The change effected in the composition of the iron by the process of 
 refining will be apparent from the following table : 
 
 Fig. 231. Hearth for refining pig-iron. 
 
 Refined Iron. 
 
 Iron, 
 
 Carbon, . 
 Silicon, . 
 Sulphur, 
 Phosphorus, 
 Manganese, 
 Slag, . 
 
 95-14 
 3-07 
 0-63 
 0-16 
 0-73 
 
 trace 
 044 
 
 100-17 
 
 The carbon, therefore, is not nearly so much diminished as the silicon, 
 which is in some cases reduced to -^th of its former proportion by the 
 refining process. Half of the sulphur is also sometimes removed, being 
 found in the slag as sulphide of iron. The phosphorus is not removed to 
 the same extent in the refining process, though some of it is converted 
 into phosphoric acid, which may be found in the finery cinder. 
 
PUDDLING. 
 
 311 
 
 The further purification of the metal could not be effected in the 
 refinery, since the fusibility of the iron is so greatly diminished as it 
 approaches to a pure state, that it could not be retained in a fluid condi- 
 tion at the temperature attainable in this furnace, and a more spacious 
 hearth is required upon which the pasty metal may be kneaded into close 
 contact with the oxide of iron which is to complete the oxidation and 
 separation of the carbon. For this reason the metal is transferred to the 
 puddling furnace. 
 
 x The puddling process is carried out in a reverberatory furnace (figs. 232, 
 233) connected with a tall chimney provided with a damper, so as to admit 
 of a very perfect regulation of the draught. A bridge of fire-brick between 
 
 Fig. 232. Puddling furnace. 
 
 the grate and the hearth prevents the contact of the coal with the iron to 
 be puddled. The hearth "is composed either of fire-brick or of cast-iron 
 plates, covered with a layer of a very infusible slag, and cooled by a free 
 
 Fig. 233. Puddling furnace. 
 
 circulation of air beneath them. This hearth is about 6 feet in length, by 
 4 feet in the widest part near the grate, and 2 feet at the opposite end ; 
 
312 VARIETIES OF BAR-IRON. 
 
 it is slightly inclined towards the end farthest from the grate, and finishes 
 in a very considerable slope, at the lowest point of which is the /loss-hole 
 for the removal of the slag. Since the metal is to attain a very high 
 temperature in this furnace (estimated at 3000 F.), it is usually covered 
 with an iron casing, so as to prevent any entrance of cold air through 
 chinks in the brick work. 
 
 About 5 cwt. of the fine metal is broken up and heaped upon the 
 hearth of this furnace, together with about 1 cwt. of iron scales (black 
 oxide of iron, Fe 3 4 ), and of hammer-slag (basic silicate of iron, obtained 
 in subsequent operations), which are added in order to assist in oxidising 
 the impurities. When the metal has fused, the mass is well stirred or 
 puddled, so that the oxide of iron may be brought into contact with 
 every part of the metal, to effect the oxidation of the impurities. The 
 metal now appears to boil, in consequence of the escape of carbonic oxide, 
 and in about an hour from the commencement of the puddling, so much 
 of the carbon has been removed that the fusibility of the metal is con- 
 siderably diminished, and instead of retaining a fused condition at the 
 temperature prevailing in the furnace, it assumes a granular, sandy, or dry 
 state, spongy masses of pure iron separating or coming to nature in the 
 fused mass. The puddling of the iron is continued until the whole has 
 assumed this granular appearance, when the evolution of carbonic oxide 
 ceases almost entirely, showing that the removal of the carbon is nearly 
 completed. The damper is now gradually raised, so as to increase the 
 temperature and soften the particles of iron, in order that they may be 
 collected into a mass ; and the more easily to effect this, a part of the 
 slag is run off through the floss-hole. The workman then collects some 
 of the iron upon the end of the paddle, and rolls it about on the hearth 
 until he has collected a sort of rough ball of iron, weighing about half-a- 
 hundred weight. When all the iron has been collected into balls in this 
 way, they are placed in the hottest part of the furnace, and pressed occa- 
 sionally with the paddle, so as to squeeze out a portion of the slag with 
 which their interstices are filled. The doors are then closed to raise the 
 interior of the furnace to a very high temperature, and after a short time, 
 when the balls are sufficiently heated, they are removed from the furnace, 
 and placed under a steam hammer, which squeezes out the liquid slag, 
 and forces the softened particles of iron to cohere into a continuous oblong 
 mass or bloom, which is then passed between rollers by which it is ex- 
 tended into bars. These bars, however (Hough or Puddled, or No. 1 Bar), 
 are always hard and brittle, and are only fit for such constructions as rail- 
 way bars, where hardness is required rather than great tenacity. In order 
 to improve this latter quality, the rough bars are cut up into short lengths, 
 which are made into bundles, and after being raised to a high tempera- 
 ture in the mill-furnace, are passed through rollers, which weld the 
 several bars into one compound bar, to be subsequently passed through 
 other rollers until it has acquired the desired dimensions. By thus fagot- 
 ting the bars, their texture is rendered far more uniform, and they are 
 made to assume a fibrous structure, which appears greatly to increase 
 their strength (Merchant Bar, or No. 2 Bar). To obtain the best, or No. 
 3 Bar, or wire-iron, these bars are doubled upon themselves, raised to a 
 welding heat, and again passed between rollers. These repeated rollings 
 have the effect of thoroughly squeezing out the slag which is mechanically 
 entangled among the particles of iron in the rough bars, and would pro- 
 duce flaws if allowed to remain in the metal. A slight improvement 
 
DEFECTS OF THE PUDDLING PKOCESS. 
 
 313 
 
 appears also to "be effected in the chemical composition of the iron during 
 the rolling, some of the carbon, silicon, phosphorus, and sulphur, still 
 retained by the puddled iron, becoming oxidised, and passing away as 
 carbonic oxide and slag. 
 
 The following table exhibits the change in chemical composition which 
 takes place in pig-iron when puddled (without previous refining) and 
 rolled into wire-iron : 
 
 Effect of Puddling and Forging on Cast-iron. 
 
 In 100 parts. 
 
 Carbon. 
 
 Silicon. 
 
 Sulphur. 
 
 Phosphorus. 
 
 Grey pig-iron, . . 
 Puddled bar, . . . 
 Wire-iron, .... 
 
 2-275 
 0-296 
 0-111 
 
 2-720 
 0-120 
 0-088 
 
 0-301 
 0-134 
 0-094 
 
 0-645 
 0-139 
 0-117 
 
 About 90 parts of bar-iron are obtained from 100 of pig-iron by the 
 puddling process, the difference representing the carbon which has passed 
 off as carbonic oxide, and the silicon, sulphur, phosphorus, and iron, 
 which have been removed in the slag or tap-cinder, this being essentially 
 a silicate of protoxide and sesquioxide of iron, varying much in composi- 
 tion according to the character of the iron employed for puddling, and 
 the proportions of iron-scale and hammer-slag introduced into the furnace. 
 Of course, also, the material of which the hearth is composed will in- 
 fluence the composition of the slag. The following table affords an illus- 
 tration of its composition : 
 
 Tap- Cinder from Puddling Furnace. 
 
 Protoxide of iron (FeO), . 
 Peroxide of iron (Fe 2 3 ), 
 Silicic acid, 
 Phosphoric acid, 
 Sulphide of iron, 
 Lime, .... 
 Oxide of manganese, 
 Magnesia, 
 
 99-62 
 
 The lime in the above cinder was probably derived from the hearth of 
 the furnace, which is sometimes lined with that material to assist in 
 removing the sulphur. 
 
 When pig-iron is puddled without undergoing the refining process, it 
 becomes much more liquid than refined iron, and the process is some- 
 times described as the boiling process, whilst refined iron undergoes dry 
 puddling. 
 
 It will be observed that this process of puddling is attended with some 
 important disadvantages ; it involves a great expenditure of manual 
 labour, and of a most exhausting kind; the very high temperature to 
 which the puddler is exposed renders him liable to lung disease, and 
 cataract is not uncommonly caused by the intense light from the glowing 
 iron ; the wear and tear of the puddling furnace is very considerable, and 
 since it receives only ten or eleven charges of about five cwts. each in the 
 course of twenty-four hours, it is necessary to work five or six puddling 
 furnaces at once, in order to convert into bar-iron the whole of the cast- 
 
314 
 
 BESSEMER IRON. 
 
 Fig. 234. Bessemer's converting vessel. 
 
 iron turned out from a single blast furnace. These considerations have 
 led to several attempts to improve the puddling process by employing 
 revolving furnaces and other mechanical arrangements to supersede the 
 heavy manual labour, and even to dispense with it , altogether by forcing 
 the air into the molten iron. The most generally known of the processes 
 devised for this purpose is that of Bessemer, which consists in running 
 the melted cast-iron into a huge crucible, and forcing air up through it 
 under considerable pressure, thus combining the purifying influence of the 
 blast of air in the refinery with the mechanical agitation effected in the 
 puddling furnace. Bessemer's converting vessel (fig. 234) is a large, nearly 
 
 cylindrical crucible of wrought iron, 
 lined with fire-clay, having apertures 
 (A) at the bottom, through which air 
 is blown at a pressure of fifteen or 
 twenty pounds upon the inch. This 
 vessel is sometimes large enough to 
 receive ten tons of cast-iron for a charge. 
 The metal having been melted in a 
 separate furnace, is run into the con- 
 verting vessel, the blast being already 
 turned on so that the liquid iron may 
 not run into the air tubes. The iron 
 burns vividly in the current of air, and the oxide of iron .produced is dif- 
 fused in a melted state through the mass of metal by the rapid current of 
 air. This oxide of iron acts upon the silicon and carbon in the cast-iron, 
 converting the latter into carbonic oxide, which burns with flame at the 
 mouth of the converter, and the former into silicic acid, which enters into 
 the slag, and is carried up as a froth to the surface of the liquid iron. 
 The blast of air is continued for about twenty minutes, when the disap- 
 pearance of the flame of carbonic oxide indicates the completion of the 
 process ; but the remaining purified iron is not pasty, as in the puddling 
 furnace, being retained in a perfectly liquid condition by the high tem- 
 perature resulting from the combustion of part of the iron, so that the 
 metal may be run out into moulds by tilting the converting vessel. In 
 this way about 85 parts of bar-iron are obtained from 100 of pig-iron. 
 
 Although so great an economy of time and labour would result from 
 the application of Bessemer's process, it has not superseded the puddling 
 process, because it does not remove the sulphur and phosphorus from the 
 pig-iron, so that only the best varieties of that material, extracted from 
 hematite or magnetic ore, yield a bar-iron of good quality when purified 
 in this way. Its application to the manufacture of steel will be noticed 
 hereafter. The effect of the Bessemer process upon a particular specimen 
 of pig-iron is shown in the table. 
 
 In 100 parts of Pig-iron. 
 
 Before. 
 
 After. 
 
 Carbon, .... 
 
 3-309 
 
 0-218 
 
 Silicon . 
 
 0-595 
 
 
 Sulphur, 
 
 0-485 
 
 0-402 
 
 Phosphorus, 
 
 1-012 
 
 1-102 
 
 Composition of bar-iron. Even the best bar-iron contains from O'l to 
 
CHARACTERS OF STEEL. 315 
 
 0'5 per cent, of carbon, together with minute proportions of silicon, sul- 
 phur, and phosphorus. Perfectly pure iron is inferior in hardness and 
 tenacity to that which contains a small proportion of carbon. 
 
 Bar-iron is liable to two important defects, which are technically known 
 as cold-shortness and red-shortness. Cold-short iron is brittle at ordinary 
 temperatures, and appears to owe this to the presence of phosphorus, 
 of which element 0*5 per cent, is sufficient materially to diminish the 
 tenacity of the iron. When the iron is liable to brittleness at a red heat, 
 it is termed red-short iron, and a very little sulphur is sufficient to affect 
 the quality of the iron in this respect. 
 
 There is much difference of opinion as to the true causes of the varia- 
 tion in the strength of wrought-iron, and this is not surprising when 
 we reflect upon the number of circumstances which may be reasonably 
 expected to exert some influence upon it. Not only the proportions of 
 carbon, silicon, sulphur, phosphorus, and manganese may be supposed to 
 affect the quality of the iron, but the state of combination in which these 
 elements exist in the mass is not unlikely to cause a difference. It also 
 appears certain that the mechanical structure, dependent upon the arrange- 
 ment of the particles composing the mass of metal, has at least as much 
 influence upon the tenacity of the iron as its chemical composition. 
 
 The best bar-iron, if broken slowly, always exhibits a fibrous structure, 
 the particles of iron being arranged in parallel lines. This appears to con- 
 tribute greatly to the strength of the iron, for when it is wanting, and the 
 bar is composed of a confused mass of crystals, it is weaker in proportion 
 to the size of the crystals. The presence of phosphorus is said to favour 
 the formation of large crystals, and hence to produce cold-shortness. There 
 is some reason to believe that the fibrous is sometimes exchanged for the 
 crystalline texture under the influence of frequent vibrations, as in the 
 case of railway axles, girders of suspension-bridges, &c. 
 
 Considering the difficult fusibility of bar-iron, it is fortunate that it 
 possesses the property of being ivelded, that is, of being united by ham- 
 mering when softened by heat. It is customary first to sprinkle the 
 heated bars with sand or clay in order to convert the superficial oxide of 
 iron into a liquid silicate, which will be forced out from between them by 
 hammering, leaving the clean metallic surfaces to adhere. Burnt iron 
 does not weld, and is largely crystalline in structure. 
 
 MANUFACTURE OF STEEL. 
 
 215. Steel differs from bar-iron in possessing the property of becoming 
 very hard and brittle when heated to redness and then suddenly cooled 
 by being plunged into water. Perfectly pure iron, obtained by the elec- 
 trotype process, is not hardened by sudden cooling; but all bar-iron 
 which contains carbon does exhibit this property in a greater or less 
 degree according to the proportion of carbon present. It does not become 
 decidedly steely, however, until the carbon amounts to O5 per cent. The 
 best steel contains about 1 -5 per cent, of carbon, and when the proportion 
 reaches 1'7 per cent, it begins to assume the properties of cast-iron. Bar- 
 iron may, therefore, be converted into steel by the addition of about 1'5 
 per cent, of carbon, and, conversely, cast-iron is converted into steel when 
 the quantity of carbon contained in it is reduced to about 1 '5 per cent. 
 There are thus two processes by which steel may be produced ; but that 
 
316 PRODUCTION OF STEEL BY CEMENTATION. 
 
 which is employed almost exclusively in this country consists in combin- 
 ing bar-iron with the requisite amount of carbon by what is technically 
 known as cementation, the bars being imbedded in charcoal and exposed 
 for several days to a high temperature. 
 
 The operation is effected in large chests of fire-brick or stone, about 10 
 or 12 feet long by 3 feet wide and 3 feet deep. 
 
 IHIIII ' llllllrllll'lMlllllNIIHIiri 1 
 
 Fig. 235. Furnace for converting bar-iron into steel. 
 
 Two of these chests are built into a dome-shaped furnace (converting 
 furnace, fig. 235), so that the flame may circulate round them, and the 
 furnace is surrounded with a conical jacket of brick- work in order to allow 
 a steady temperature to be maintained in it for some days. The charcoal 
 is ground so as to pass through a sieve of J inch mesh, and spread in an 
 even layer upon the bottom of the chests. Upon this the bars of iron, 
 which must be of the best quality, are laid in regular order, a small in- 
 terval being left between them, which is afterwards filled in with the 
 charcoal powder, with a layer of which the bars are now covered ; over 
 this more bars are laid, then another layer of charcoal, and so on until the 
 chest is filled. Each chest holds 5 or 6 tons of bars. One of the bars is 
 allowed to project through an opening in the end of the chest, so that 
 the workmen may withdraw it from time to time and judge of the progress 
 of the operation. The whole is covered in with a layer of about 6 inches 
 of damp clay or sand. 
 
 The fire is carefully and gradually lighted, lest the chests should be 
 split by too sudden application of heat, and the temperature is eventually 
 raised to about the fusing point of copper (2000 F.), at which it is main- 
 tained for a period varying with the quality of steel which it is desired to 
 obtain. Six or eight days suffice to produce steel of moderate hardness ; 
 but the process is continued for three or four days longer if very hard 
 steel be required. The fire is gradually extinguished, so that the chests 
 are about ten days in cooling down. 
 
 On opening the chests, the bars are found to have suffered a remarkable 
 change both in their external appearance and internal structure. They 
 are covered with large blisters, obviously produced by some gaseous sub- 
 stance raising the softened surface of the metal in its attempt to escape. 
 It is conjectured either that the small quantity of sulphur present in the 
 bar-iron is converted into bisulphide of carbon during the cementation 
 process, and that the vapour of this substance swells the softened metal 
 
SHEAR STEEL CAST STEEL. 317 
 
 into bubbles as it passes off; or that the blisters are caused by carbonic 
 oxide produced by the action of the carbon upon particles of slag acci- 
 dentally present in the bar. On breaking the bars across, the fracture is; 
 found to have a finely granular structure, instead of the fibrous appearance 
 exhibited by bar-iron. Chemical analysis shows that the iron has com- 
 bined with about 1 '5 per cent, of carbon, and the most remarkable part 
 of the result is that this carbon is not only found in the external layer of 
 iron, which has been in direct contact with the heated charcoal, but is 
 also present in the very centre of the bar. It is this transmission of the 
 solid carbon through the solid mass of iron which is implied by the term 
 cementation. The chemistry of the process probably consists in the forma- 
 tion of carbonic oxide from the small quantity of atmospheric oxygen in 
 the chest, and the removal of one-half of the carbon from this carbonic 
 oxide, by the iron, which it converts into steel, leaving carbonic acid 
 (2CO C = C0 2 ) to be reconverted into carbonic oxide by taking up 
 more carbon from the charcoal (C0 2 + C = CO), which it transfers again 
 to the iron. Experiment has recently shown that soft iron is capable of 
 absorbing, mechanically, 4*15 volumes of carbonic oxide at a low red heat, 
 so that the action of the gas upon the metal may occur throughout the 
 substance of the bar. The carbonic oxide is retained unaltered by the 
 iron, after cooling, unless the bar is raised to the temperature required for 
 the production of steel. 
 
 The blistered steel obtained by this process is, as would be expected, 
 far from uniform either in composition or in texture ; some portions of 
 the bar contain more carbon than others, and the interior contains nume- 
 rous cavities. In order to improve its quality, it is subjected to a process 
 of fagotting similar to that mentioned in the case of bar-iron ; the bars 
 of blistered steel, being cut into short lengths, are made up into bundles, 
 which are raised to a welding heat, and placed under a tilt-hammer 
 weighing about 2 cwt., which strikes two or three hundred blows in a 
 minute ; in this way, the several bars are consolidated into one compound 
 bar, which is then extended under the hammer till of the required 
 dimensions. The bars, before being hammered, are sprinkled with sand, 
 which combines with the oxide of iron upon the surface, and forms 
 a vitreous layer which protects the bar from further oxidation. The 
 steel w r hich has been thus hammered is much denser and more uniform 
 in composition ; its tenacity, malleability, and ductility are greatly in- 
 creased, and it is fitted for the manufacture of shears, files, and other 
 tools. It is commonly known as shear steel. Double shear steel is 
 obtained by breaking the tilted bars in two, and welding these into a 
 compound bar. 
 
 The best variety of steel, however, which is perfectly homogeneous in 
 composition, is that known as cast steel, to obtain which, about 30 Ibs. of 
 blistered steel are broken into fragments, and fused in a fire-clay crucible, 
 heated in a wind-furnace, the surface of the metal being protected from 
 oxidation by a little glass melted upon it. The fused steel is cast into 
 ingots, several crucibles being emptied simultaneously into the same 
 mould. Cast steel is far superior in density and hardness to shear steel, 
 but since it is exceedingly brittle at a red heat, great care is necessary in 
 forging it. It has been found that the addition, to 100 parts of the cast 
 steel, of one part of a mixture of charcoal and oxide of manganese, pro- 
 duces a very fine grained steel which admits of being cast on to a bar of 
 wrought-iron in the ingot-mould, so that the tenacity of the latter may 
 
318 TEMPERING OF STEEL. 
 
 compensate for the brittleness of the steel when the compound bar is 
 forged, the wrought-iron forming the back of the implement, and the 
 steel its cutting edge. 
 
 This addition of manganese to the cast steel (Heath's patent) has effected 
 a great reduction in its cost, allowing the use of blister steel made from 
 British bar-iron, whereas, before its introduction, only the expensive iron 
 of Swedish or Eussian make could be employed. 
 
 After the steel has been forged into the shape of any implement, it is 
 hardened by being heated to redness, and suddenly chilled in cold water, 
 or oil, or mercury. It is thus rendered nearly as hard as diamond, at the 
 same time increasing slightly in volume (sp. gr. of cast steel 7 - 93, after 
 hardening, 7 '6 6). The chemical difference between hard and soft steel 
 appears to be of the same kind as that between grey and white cast-iron 
 (p. 307), the great proportion of the carbon in hard steel being in combina- 
 ation with the metal, while in soft steel the greater part seems to be in 
 intimate mechanical admixture with the iron, for it is left undissolved on 
 treating the steel with an acid. If the hardened steel be heated to red- 
 ness,, and allowed to cool slowly, it is again converted into soft steel, but 
 by heating it to a temperature short of a red heat, its hardness may be 
 proportionally reduced. This is taken advantage of in annealing the 
 steel or " letting it down" to the proper temper. The very hardest steel 
 is almost as brittle as glass, and totally unfit for any ordinary use, but 
 by heating it to a given temperature and allowing it to cool, its elasti- 
 city may be increased to the desired extent, without reducing its hard- 
 ness below that required for the implement in hand. On heating a steel 
 blade gradually over a flame, it will acquire a light yellow colour when 
 its temperature reaches 430 F., from the formation of a thin film of 
 oxide ; as the temperature rises, the thickness of the film increases, and 
 at 470 a decided yellow colour is seen, which assumes a brown shade 
 at 490, becomes purple at 520, and blue at 550. At a still higher 
 temperature the film of oxide becomes so thick as to be black and 
 opaque. Steel which has been heated to 430, and allowed to cool slowly, 
 is said to be tempered to the yellow, and is hard enough to take a very 
 fine cutting edge, whilst, if tempered to the blue, at 550, it is too soft to 
 take a very keen edge, but has a very high degree of elasticity. The fol- 
 lowing table indicates the tempering heats for various implements : 
 
 Tempering of Steel. 
 
 Temperature, F. 
 
 Colour. 
 
 Implements thus tempered. 
 
 430 to 450. 
 470 
 490 
 510 
 520 
 530 to 570. 
 
 Straw-yellow. 
 Yellow. 
 Brown-yellow. 
 Brown-purple. 
 Purple. 
 Blue. 
 
 Eazors, lancets. 
 Pen-knives. 
 Large shears for cutting metal. 
 Clasp-knives. 
 Table-knives. 
 Watch-springs, sword-blades. 
 
 If a knife blade be heated to redness, its temper is spoilt, for it is 
 converted into soft steel. 
 
 In general, the steel implements are ground after being tempered, so 
 that they are not seen of the colours mentioned above, except in the case 
 of watch-springs. 
 
BESSEMEK STEEL SPIEGEL-EISEN. 319 
 
 A steel blade may be easily distinguished from iron by placing a drop 
 of diluted nitric acid upon it, when a dark stain is produced upon the 
 steel, from the separation of the carbon. 
 
 Some small instruments, such as keys, gun-locks, &c., which are ex- 
 posed to considerable wear and tear by friction, and require the external 
 hardness of steel without its brittleness, are forged from bar-iron, and 
 converted externally into steel by the process of case-hardening, which 
 consists in heating them in contact with some substance containing carbon 
 (such as bone-dust, yellow prussiate of potash, &c.) A process which is 
 the reverse of this is adopted in order to increase the tenacity of stirrups, 
 bits, and similar articles made of cast-iron; by heating them for some 
 hours, in contact with oxide of iron or manganese, their carbon and silicon 
 are removed in the forms of carbonic oxide and silicic acid, and they be- 
 come converted into malleable cast-iron. 
 
 The opinion that steel owes its properties entirely to the presence of 
 carbon is not universally entertained. Some chemists believe that nitrogen 
 (or some analogous element) is an indispensable constituent, but the pro- 
 portion of nitrogen found in steel is too minute to warrant this supposi- 
 tion. Titanium is alleged by some authorities to have an important 
 influence upon the quality of steel, but this also appears to be a doubtful 
 matter. Bar-iron may be converted into steel by being kept at a high 
 temperature in an atmosphere of coal-gas, from which it abstracts carbon. 
 
 Bessemer steel was originally produced by arresting the purification of 
 cast-iron in Bessemer's process (page 314), as soon as the carbon had dimi- 
 nished to about 1'5 per cent., when the steel was poured out in the fused 
 state, i.e., in the form of cast steel. A steel of better quality, however, 
 has been obtained by continuing the purification until liquid bar-iron 
 remains in the converter, and introducing the proper proportion of carbon 
 in the form of a peculiar description of white cast-iron known as Spiegel- 
 eisen (mirror iron), which crystallises in lustrous tabular crystals, and 
 contains large proportions of carbon and manganese, being obtained by 
 smelting spathic iron ore rich in manganese, with charcoal as fuel. The 
 Spiegel-eisen is added, in a melted state, to the Bessemer iron before pour- 
 ing from the converter. 
 
 The composition of a sample of Spiegel-eisen smelted from a spathic ore, 
 found near Miisen in Prussia, is here given : 
 
 Iron, . . . 82-86 
 
 Manganese, . . 10-71 
 
 Silicon, . . . 1-00 
 
 Carbon, . . . 4-32 
 
 98-89 
 
 Homogeneous iron, as it is called, is really a mild steel containing a low 
 percentage of carbon, and obtained by fusing the best Swedish bar-iron 
 with carbonaceous matters. It is remarkable for its malleability and 
 toughness, and, having undergone complete fusion, it is more likely to be 
 homogeneous in composition and structure than wrought-iron produced 
 by puddling. 
 
 Parry's steel is manufactured by melting bar-iron with fuel free from 
 sulphur and phosphorus, so as to obtain a very pure cast-iron, which is 
 
320 EXTRACTION OF WROUGHT IRON FROM THE ORE. 
 
 then partly decarbonised by a process similar to Bessemer's. The addi- 
 tion of manganese improves its quality. 
 
 Puddled steel is obtained by arresting the puddling process at an earlier 
 stage than usual, so as to leave a proportion of carbon varying from 0'5 
 to 1 "0 per cent. 
 
 Natural steel or German steel results in a similar way, from the incom- 
 plete purification of cast-iron in the refinery. The presence of manganese 
 in the iron is favourable to its production. 
 
 Krupp's cast steel, manufactured at Essen near Cologne, and employed 
 for ordnance, shells, &c., is a puddled steel made from hsematite and spathic 
 ore, smelted with coke. The iron thus obtained contains much manganese, 
 which is removed in the puddling process. Krupp's steel contains about 
 1 '2 per cent of combined carbon, and is fused with a little bar-iron for 
 casting ordnance. The fusion is effected in black lead crucibles holding 
 30 Ibs. each, of which as many as 1200 are emptied simultaneously into 
 the mould for the largest castings. A casting of 1 6 tons requires about 
 400 men, who act together in well-disciplined gangs, so that the stream 
 of molten metal shall flow continuously along the gutters into the mould. 
 Such large castings must be allowed to cool very gradually, so that they 
 are kept surrounded with hot cinders, sometimes for two or three months, 
 till required for forging. 
 
 216. Direct extraction of wrought-iron from the ore. Where very rich 
 and pure ores of iron, such as haematite and magnetic iron ore, are obtain- 
 able, and fuel is abundant, the metal is sometimes extracted without being 
 
 Fig. 236. Catalan forge for smelting iron ores. 
 
 converted into cast-iron. It is probable that the iron of antiquity was 
 extracted in this way, for it is doubtful whether cast-iron was known to 
 
EXTRACTION OF IRON IN THE LABORATORY. 321 
 
 the ancients, and the slag left from old iron- works does not indicate the 
 use of any flux. Some works of this Description are still in operation in 
 the Pyrenees, where the Catalan process is employed. The crucible is 
 lined at the sides with thick iron plates, and at the bottom with a refrac- 
 tory stone. A quantity of red-hot charcoal is thrown into it, and the space 
 above this is temporarily divided into two compartments by a shovel. 
 The compartment nearest to the pipe through which the blast enters is 
 charged with charcoal, and the other compartment with the calcined ore 
 in small pieces. The shovel is then withdrawn, and a gradually increasing 
 current of air supplied, fresh ore and fuel being added as they sink down. 
 One part of the oxide of iron is reduced to the metallic state by the 
 carbonic oxide, and the rest combines with the silica present in the ore to 
 form a slag. After about five hours the spongy masses of bar-iron are 
 collected into a ball upon the end of an iron rod, and hammered into a 
 compact mass like the metal obtained in the puddling furnace. The 
 blowing machine employed in the Pyrenees is one in which the fall of 
 water from a cistern down a long wooden pipe, sucks in, through lateral 
 apertures, a supply of air which it carries down with it into a box, from 
 which the pressure of the column of water projects it with some force 
 through the blast-pipe, the water escaping from the box through another 
 aperture. 
 
 In the North American Uoomery forges a modernised form of the same 
 process is adopted. 
 
 The wrought-iron produced by this process always contains a larger 
 proportion of carbon than puddled iron, and is therefore somewhat steely 
 in character. 
 
 217. Extraction of iron on the small scale. In the laboratory, iron may be extracted 
 from haematite in the following manner: A fire-clay crucible (A, fig. 237), about 3 
 inches high, is filled with damp charcoal powder, rammed down in successive layers ; 
 a smooth conical cavity is scooped in the 
 charcoal, and a mixture of 100 grs. red hae- 
 matite, 25 grs. chalk, and 25 grs. pipe-clay, 
 is introduced into it ; the mixture is covered 
 with a layer of charcoal, and a lid placed on 
 the crucible, which is heated in a Sefstrom 
 blast furnace,* fed with coke in small pieces, 
 for about half an hour. On breaking the 
 cold crucible, a button of cast-iron will be 
 obtained. Chemically pure iron may be 
 prepared by fusing the best wire-iron with 
 about one-fifth of its weight of pure peroxide Fig. 237. Sefstrom furnace, 
 
 of iron, to oxidise the carbon and silicon 
 
 which it contains. Some powdered green glass, perfectly free from lead<must be 
 employed as a flux, and the crucible (with its cover well cemented on with fire-clay) 
 exposed for an hour to a very high temperature. A silvery button of pure iron will 
 then be obtained. 
 
 218. Chemical properties of iron. In its ordinary condition, iron is 
 unaffected by perfectly dry air, but in the presence of moisture it is 
 gradually converted into hydrated sesquioxide of iron (2Fe 2 8 . 3HO), or 
 rust. This conversion takes place more rapidly when carbonic acid is 
 present, water being then decomposed, and carbonate of iron formed 
 (Fe + HO + C0 2 = FeO . C0 2 + H) ; this is dissolved by the carbonic 
 
 * This very useful furnace, shown in section in fig. 237, consists of two iron cylinders 
 with a space (B) between them, into which air is forced through the tube C by a double- 
 action bellows. The inner cylinder has a fire clay lining (D), through which four or six 
 copper tubes (E) admit the blast into the fuel. 
 
322 FERROUS AND FERRIC OXIDES. 
 
 acid present, and the solution rapidly absorbs oxygen from the air, depo- 
 siting the sesquioxide of iron in a hydrated state 
 
 2(FeO.C0 2 ) + = Fe 2 3 + 2C0 2 . 
 
 When iron nails are driven into a new oaken fence, a black streak will 
 soon be observed descending from each nail, caused by the formation of 
 tannate of iron (ink) by the action of the tannic acid in the wood upon 
 the solution of carbonate of iron formed from the nails. The diffusion of 
 iron-mould stains through the fibre of wet linen by contact with a nail is 
 also caused by the formation of solution of carbonate of iron. The iron 
 in chalybeate waters is also generally present in the form of carbonate 
 dissolved in carbonic acid, and hence the rusty deposit which is formed 
 when they are exposed to the air. Iron does not rust in water containing 
 a free alkali, or alkaline earth, or an alkaline carbonate. 
 
 Concentrated sulphuric and nitric acids do not act upon iron at the 
 ordinary temperature, though they dissolve it rapidly when diluted. 
 Even when boiling, strong sulphuric acid acts upon it but slowly. 
 When iron has been immersed in strong nitric acid (sp. gr. 1'45), it is 
 found to be unacted upon when subsequently placed in diluted nitric 
 a.cid, unless previously wiped ; it is then said to have assumed the passive 
 state. If iron wire be placed in nitric acid of sp. gr. 1 "35, it is acted 
 upon immediately, but if a piece of gold or platinum be made to touch it 
 beneath the acid, the iron assumes the passive state, and the action ceases 
 at once. A state similar to this, the cause of which has not yet been 
 satisfactorily explained, is sometimes assumed by other metals, though in 
 a less marked degree. 
 
 219. Oxides of iron. Three compounds of iron with oxygen are known 
 in the separate state, and one is believed to exist in certain compounds 
 
 Protoxide of iron, or ferrous oxide, FeO 
 
 Sesquioxide or peroxide of iron, or ferric oxide, Fe 2 3 
 
 Magnetic oxide, or ferroso-ferric oxide, Fe 3 4 
 
 Ferric acid (?), Fe0 3 . 
 
 The protoxide of iron is little known in the separate state on account of 
 the readiness with which it absorbs oxygen and forms sesquioxide of iron. 
 If a little potash or ammonia be added to a solution of the green sulphate 
 of iron (FeO . S0 3 ), a whitish precipitate of hydrated protoxide of iron is 
 formed, which immediately absorbs oxygen, and is converted into the 
 dingy green hydrate of the magnetic oxide ; on exposing this to the air, 
 it absorbs more oxygen and becomes brown hydrated peroxide. This 
 disposition of the hydrated protoxide to absorb oxygen is turned to 
 advantage when a mixture of sulphate of iron with lime or potash is 
 employed for converting blue into white indigo. The protoxide of iron 
 is a strong base. 
 
 Peroxide or red oxide of iron has been already noticed among the ores 
 of iron, and has also been referred to as occurring in commerce under the 
 names of colcothar, jeweller's rouge, and Venetian red, which are obtained 
 by the calcination of the green sulphate of iron 
 
 2(FeO.S0 3 ) = Fe 2 ;J + SO 2 + S0 3 . 
 
 The hydrated peroxide (2Fe 2 ;J . 3HO), obtained by decomposing a solu- 
 tion of perchloride of iron with an alkali, forms a brown gelatinous 
 precipitate, which is easily dissolved by acids; but if it be dried and 
 
FEKROUS SULPHATE. 323 
 
 heated to dull redness it exhibits a sudden glow, and is converted into a 
 modification which is dissolved with great difficulty ]by acids, although 
 it has the same composition as the soluble form which has not been 
 strongly heated. When the peroxide of iron is heated to whiteness it 
 loses oxygen, and is converted into magnetic oxide of iron 
 
 3Fe 2 3 = 2Fe,0 4 + . 
 
 Existing as it does in all soils, sesquioxide of iron is believed to fulfil the 
 purpose of oxidising the organic matter in the soil, and converting its carbon 
 into carbonic acid, to be absorbed by the plant ; the sesquioxide being thus 
 reduced to protoxide, which is oxidised by the air, and fitted to perform 
 again the same office. The sesquioxide of iron, like alumina, is a weak 
 base, and even exhibits some tendency to play the part of an acid towards 
 strong bases, though not in so marked a degree as alumina. 
 
 Magnetic or black oxide of iron is generally regarded as a compound 
 of the protoxide with the sesquioxide of iron (FeO . Fe >2 3 ), a view which 
 is confirmed by the occurrence of a number of minerals having the same 
 crystalline form as the native magnetic oxide of iron, in which the iron, 
 or part of it, is displaced by other metals. Thus, spinelle is MgO . ALfiz ; 
 Franklinite, ZnO . Fe 2 3 ; chrome-iron ore, FeO . Cr 2 3 . The natural 
 magnetic oxide was mentioned among the ores of iron, and this oxide has 
 been seen to be the result of the action of air or steam upon iron at a 
 high temperature. The hydrated magnetic oxide of iron (Fe 3 4 . HO) is 
 obtained as a black crystalline powder by mixing one equivalent of proto- 
 sulphate with one equivalent of persulphate of iron, and pouring the 
 mixture into a slight excess of solution of ammonia, which is afterwards 
 boiled with it. Magnetic oxide of iron, when acted upon by acids, yields 
 mixtures of protosalts and persalts of iron, so that it is not an independent 
 basic oxide. 
 
 Ferric acid is only known in combination with bases as ferrates. When iron filings 
 are strongly heated with nitre, and the mass treated with a little water, a fine purple 
 solution of ferrate of potash is obtained. A better method of preparing this salt 
 consists in suspending 1 part of freshly precipitated sesquioxide of iron in 50 parts 
 of water, adding 30 parts of solid hydrate of potash, and saturating the mixture 
 with chlorine (Fe 2 3 + C1 3 + 5KO = 3KC1 + 2(KO . FeO ? ) ; the ferrate of potash 
 forms a black precipitate, being insoluble in the strongly alkaline solution, though 
 it dissolves in pure water to form a purple solution, which is decomposed even by 
 dilution, oxygen escaping, and hydrated peroxide of iron being precipitated ; 
 2(KO . Fe0 3 ) = 2KO + Fe 2 3 + 3 . A similar decomposition takes place on 
 boiling a strong solution, or on adding an acid with a view to liberate the ferric 
 acid. The ferrates of baryta, strontia, and lime are obtained as fine red precipitates 
 when solutions of their salts are mixed with ferrate of potash. 
 
 220. Protosulphate of iron, copperas, green vitriol, or ferrous sulphate, 
 is easily obtained by heating 1 part of iron wire with 1J parts of strong 
 sulphuric acid, mixed with 4 times its weight of water, until the whole of 
 the metal is dissolved, when the solution is allowed to crystallise. Its 
 manufacture on the large scale by the oxidation of iron pyrites has been 
 already referred to. 
 
 It forms fine green rhomboidal crystals, having the composition 
 
 FeO.S0 3 .HO + 6Aq. 
 
 The colour of the crystals varies somewhat, from the occasional presence 
 of small quantities of the sulphate of sesquioxide of iron (Fe 2 3 . 3S0 3 ). It 
 dissolves very easily in twice its weight of cold water, yielding a pale green 
 solution. When the commercial sulphate of iron is boiled with water, it 
 
 x2 
 
324 EQUIVALENT AND ATOMIC WEIGHTS OF IRON. 
 
 yields a brown muddy solution, in consequence of the decomposition of the 
 sulphate of sesquioxide of iron contained in it, with precipitation of a basic 
 sulphate. The sulphate of iron has a great tendency to absorb oxygen, 
 and to become converted into the sulphate of sesquioxide. Thus, the 
 ordinary crystals when exposed to air gradually become brown, and are 
 converted into a mixture of the neutral and basic sulphates of the 
 sesquioxide of iron 
 
 10(FeO.S0 3 ) + 5 - 3(Fe 2 3 . 3S0 3 ) + 2Fe 2 3 .S0 3 . 
 
 This disposition to absorb oxygen renders the sulphate of iron useful as a 
 reducing agent ; thus, it is employed for precipitating gold in the metallic 
 state from its solutions. But its chief use is for the manufacture of ink 
 and black dyes, by its action upon vegetable infusions containing tannic 
 acid, such as that of nut-galls. This application will be more particularly 
 noticed hereafter. 
 
 Sulphate of sesquioxide of iron, or persulphate of iron, or ferric sulphate, 
 is found in Chile as a white silky crystalline mineral, coquimbite, having 
 the composition, Fe 2 3 . 3S0 3 + 9 Aq. 
 
 The phosphates of protoxide and sesquioxide of iron are found associated 
 in the mineral known as vivianite or native Prussian blue. 
 
 221. Sesquichloride, or perchloride of iron or ferric chloride (Fe 2 Cl 3 ), 
 is obtained in beautiful dark green crystalline scales when iron wire is 
 heated in a glass tube through which a current of dry chlorine is passed, 
 the sesquichloride passing off in vapour, and condensing in the cool part of 
 the tube. The crystals almost instantly become wet when exposed to air, 
 on account of their great attraction for water. The perchloride of iron 
 may be obtained in solution by dissolving iron in hydrochloric acid, and 
 converting the protochloride of iron (FeCl) thus formed into perchloride by 
 the action of nitric and hydrochloric acids (p. 167). The solution of per- 
 chloride of iron has been recommended in some cases as a disinfectant, 
 being easily reduced to protochloride, and thus affording chlorine to 
 unstable organic matters in contact with it (p. 146). A solution of per- 
 chloride of iron in alcohol is used in medicine under the name of tincture 
 of iron. 
 
 222. Equivalent and atomic weights of iron. When iron is dissolved 
 in hydrochloric acid, 28 parts by weight of iron combine with 1 eq. 
 (35*5 parts) of chlorine, displacing 1 part of hydrogen; hence 28 is the 
 equivalent weight of iron. 
 
 The specific heat of iron and its isomorphism with magnesium, zinc, and 
 cadmium, show that its atomic weight must be represented by double the 
 equivalent, or 56, so that iron is a diatomic or biequivalent element. 
 
 The atomic formula? of the oxides and chlorides of iron would then be 
 written thus (Fe = 56) 
 
 Ferrous chloride, :PeCl 2 
 Ferric chloride, :Pe (2 Cl 6 . 
 
 The molecular formula of ferric chloride has been confirmed by the 
 determination of the specific gravity of its vapour, which has been found 
 to be 1 65 times that of hydrogen. If, therefore, one volume (or one 
 atom) of hydrogen be represented as having a weight = 1, two volumes 
 (or one molecule) of ferric chloride vapour would weigh (165 x 2) 330, 
 
 Ferrous oxide, 
 Ferric oxide, :Pe 2 3 
 
PEROXIDE, OF MANGANESE. 325 
 
 a number nearly agreeing with the sum of two atoms of iron (112) and six 
 atoms of chlorine (21 3*0). 
 
 It will be remarked that iron possesses a different atomicity accordingly 
 as it exists in ferrous or ferric compounds. Thus, in ferrous oxide (FeO) 
 and ferrous chloride (PeCl 2 ), it occupies the place of two atoms of hydrogen, 
 and is diatomic ; but in ferric oxide (Fe^OJ and ferric chloride (Fe 2 Cl 6 ) each 
 atom of iron occupies the place of three atoms of hydrogen, and is tri- 
 atomic. Some chemists designate the diatomic iron existing in ferrous 
 compounds by the name ferrosum (W), and the triatomic iron of the 
 ferric compounds by ferricum (IV"). 
 
 MANGANESE. 
 
 223. Manganese much resembles iron in several particulars relating both 
 to its physical and chemical characters, and is often found in nature, asso- 
 ciated, in small quantities, with the compounds of that metal. The metal 
 itself has not been applied to any useful purpose. 
 
 It is obtained by reducing carbonate of manganese (MnO . G0 2 ) with 
 charcoal, at a very high temperature, when a fused mass, composed of man- 
 ganese combined with a little carbon (corresponding to cast-iron), is ob- 
 tained, which is freed from carbon by a second fusion in contact with car- 
 bonate of manganese. 
 
 Metallic manganese is darker in colour than (wrought) iron, and very 
 much harder ; it is brittle, and only feebly attracted by the magnet. It 
 is somewhat more easily oxidised than iron. 
 
 224. Oxides of manganese. Three distinct compounds of manganese 
 with oxygen have been obtained in the separate state, and two others are 
 believed to exist in combination, but have not been satisfactorily made 
 out in the anhydrous state 
 
 Protoxide of manganese, MnO 
 
 Sesquioxide ,, Mn 2 3 
 
 Binoxide or peroxide of manganese, Mn0 2 
 Manganic acid (?) MnO 3 
 
 Permanganic acid (?) Mn 2 7 . 
 
 The binoxide of manganese is the chief form in which this metal is found 
 in nature, and is the source from which all other compounds of manganese 
 are obtained. Its chief mineral form is pyrolusite, which forms steel-grey 
 prismatic crystals ; but it is also found amorphous, as psilomelane, and in 
 the hydrated state as wad. In commerce pyrolusite is known as black 
 manganese, or simply manganese, and is largely imported from Germany, 
 Spain, &c., for the use of the manufacturer of bleaching-powder, the glass- 
 maker, &c. It is also used as a cheap source of oxygen, which it evolves 
 when heated to redness, leaving the red oxide of manganese, Mn 3 4 . 
 The binoxide of manganese is an indifferent oxide, and does not combine 
 with acids ; when heated with strong sulphuric acid, it loses half its 
 oxygen, and forms the protoxide of manganese, which is a*powerful base, 
 and combines with the sulphuric acid to form sulphate of manganese 
 
 Mn0 2 + HO . S0 3 = MnO . S0 3 + HO + O . 
 
 Since the natural binoxide contains peroxide of iron, some persulphate of 
 iron is formed at the same time ; but if the mixture be dried and heated to 
 redness, the iron-salt is decomposed, evolving sulphuric acid, and leaving 
 
3.26 OXIDES OF MANGANESE. 
 
 peroxide of iron ; while the protoxide of manganese, being a stronger base, 
 does not abandon its sulphuric acid ; and the sulphate of manganese may 
 be dissolved out of the mass by treatment with water. On evaporating 
 the solution, and allowing it to cool, it deposits light pink crystals of sul- 
 phate of manganese, MnO . S0 3 . HO + 4Aq. 
 
 This salt is employed by the dyer and calico-printer in the production 
 of black and brown colours. When a solution of sulphate of manganese 
 is mixed with solution of chloride of lime (p. 145), it gives a black pre- 
 cipitate of hydrated peroxide of manganese 
 
 2(MnO.S0 3 ) + CaO.C10 + 2CaO = 2Mn0 2 + 2(CaO.S0 3 ) + CaCl. 
 
 By decomposing a solution of sulphate of manganese with potash or soda, 
 a white precipitate of hydrated protoxide of manganese is obtained, which 
 becomes brown when exposed to the air, absorbing oxygen, and becoming 
 converted into the hydrated sesquioxide of manganese. 
 
 If solution of sulphate of manganese be mixed with carbonate of soda, 
 a white precipitate of carbonate of manganese, 2(MnO . C0 2 ) . HO, is 
 obtained. The pink crystallised mineral manganese spar consists of 
 carbonate of manganese (MnO . C0 2 ). 
 
 Protoxide of manganese (MnO) itself is obtained as a green powder 
 by heating carbonate of manganese in a tube through which hydrogen is 
 passed to exclude the air, which would convert the protoxide into red 
 oxide (Mn 3 4 ). The protoxide has been obtained in transparent emerald- 
 green crystals. 
 
 Sesquioxide of manganese, crystallised in octahedra, forms the mineral 
 braunite, and, in combination with water, the prismatic crystals of man- 
 ganite (Mn 2 3 . HO), which often occurs in the commercial ores of man- 
 ganese. The sesquioxide is a weak base, dissolving in acids to form deep 
 red solutions, which evolve oxygen when heated, leaving salts of the 
 protoxide of manganese. The sulphate of sesquioxide of manganese 
 combines with sulphate of potash to form manganese-alum 
 
 KO . S0 3 , Mn 2 3 . 3S0 3 + 24Aq. 
 
 corresponding in crystalline form, as in composition, to alumina-alum. 
 When binoxide of manganese in minute quantity is added to melted glass, 
 it imparts a purple colour, which is probably due to the formation of a 
 silicate of sesquioxide of manganese. The amethyst is believed by some to 
 owe its colour to the same cause. 
 
 Red oxide of manganese (Mn 3 4 ) is the most stable of the oxides 
 of this metal, and is formed when either of the others is heated in air. 
 Thus obtained, it has a brown or reddish colour; but it is found in 
 nature as the black mineral hausmannite. In composition it resembles 
 the magnetic oxide of iron, but it seems probable that its true formula is 
 2MnO . Mn0 2 , for when treated with diluted nitric acid it leaves the 
 black hydrated binoxide. 
 
 When a compound containing manganese, in however small a quantity, is fused 
 on a piece of platinum foil with carbonate of soda (fig. 112), a mass of manganate 
 of soda (NaO . Mn0 3 ) is formed, which is green while hot, and becomes blue on 
 cooling. The oxygen required to convert the lower oxides of manganese into man- 
 ganic acid has been absorbed from the air. 
 
 Manganic acid is obtained in combination with potash, by mixing 
 finely powdered binoxide of manganese into a paste with an equal weight 
 
PERMANGANATE OF POTASH. 327 
 
 of hydrate of potash dissolved in a little water, drying the paste, and 
 heating it to dull redness in a glass tube, through which oxygen is passed 
 as long as it is absorbed. When the mass is treated with a little cold 
 water, it gives a dark emerald-green solution, and by evaporating this 
 over oil of vitriol, in vacuo, dark-green crystals of manganate of potash 
 (KO . Mn0 3 ) are formed, which have the same crystalline form as 
 those of sulphate of potash. These crystals dissolve unchanged in water 
 containing potash; but when dissolved in pure water, they yield a red 
 solution of permanganate of potash, and a precipitate of binoxide of 
 manganese 
 
 3(KO.Mn0 3 ) + 2HO = KO . Mii/) 7 + Mn0 2 + 2(KO.HO). 
 
 The change is more completely effected by adding a little free acid, even 
 carbonic acid. The changes of colour thus produced have acquired for 
 the manganate of potash the name chameleon mineral. The solution of 
 manganate of potash (containing free potash) is very easily decomposed by 
 substances having an attraction for oxygen. Thus, most organic sub- 
 stances abstract oxygen from it, and cause the separation of brown sesqui- 
 oxide of manganese ; filtering its solution through paper will even effect 
 this change. The offensive emanations from putrefying organic matters 
 are at once oxidised and rendered inodorous by manganate of potash or 
 soda. 
 
 Manganate of soda (N&O . Mn(X) obtained by heating binoxide of 
 manganese with hydrate of soda, under free exposure to air, is employed in 
 a state of solution in water, as Candy's green disinfectant fluid. 
 
 The temporary formation of manganic acid affords a probable explana- 
 tion of the effect of binoxide of manganese in facilitating the disengage- 
 ment of oxygen from chlorate of potash (p. 14). 
 
 Permanganic acid has been obtained in a hydrated crystalline state by 
 decomposing the permanganate of baryta with sulphuric acid, and evapo- 
 rating the solution in vacuo. It is a brown substance, easily dissolving 
 in water to a red liquid, which is decomposed at about 90 F., evolving 
 oxygen, and depositing binoxide of manganese. 
 
 Permanganate of potash is largely used in many chemical operations. 
 In order to prepare it, 4 parts of finely powdered binoxide of manganese 
 are intimately mixed with 3J parts of chlorate of potash, and 5 parts of 
 hydrate of potash dissolved in a very little water. The pasty mass is 
 dried, and heated to dull redness for some time in an iron tray or earthen 
 crucible. The oxygen derived from the chlorate of potash converts the 
 binoxide of manganese into manganic acid, which combines with the 
 potash of the hydrate. On treating the cold mass with water, the man- 
 ganate of potash is dissolved, forming a dark-green solution. " This is 
 diluted with water, and a stream of carbonic acid gas passed through it as 
 long as any change of colour is observed ; the carbonic acid combines with 
 the excess of potash, the presence of which conferred stability upon the 
 manganate, which is then decomposed into permanganate of potash and 
 binoxide of manganese. The latter is allowed to settle, and the clear red 
 solution poured off and evaporated to a small bulk. On cooling, it de- 
 posits prismatic crystals of the permanganate of potash (KO . Mn 2 7 ), 
 which are red by transmitted light, but reflect a dark-green colour. The 
 carbonate of potash, being much more soluble in water, is left in the 
 solution. Permanganate of potash is remarkable for its great colouring 
 power, a very small quantity of the salt producing an intense purplish- 
 
328 EQUIVALENT AND ATOMIC WEIGHTS OF MANGANESE. 
 
 red colour in a large quantity of water. Its solution in water is very 
 easily decomposed by substances having an attraction for oxygen, such as 
 sulphurous acid or a ferrous salt, the permanganic acid being reduced to 
 protoxide of manganese, so that the solution becomes colourless. If a very 
 small piece of iron wire be dissolved in diluted sulphuric acid, the solu- 
 tion of ferrous sulphate so produced will decolorise a large volume of 
 weak solution of the permanganate, being converted into ferric sulphate 
 
 KO.MiXjO, + 10(FeO.S0 3 ) + 8(HO . S0 3 ) = 
 KO.S0 3 + 2(MnO.S0 3 ) + 5(Fe 2 3 . 3S0 3 ) + 8HO. 
 
 This decomposition forms the basis of a valuable method for determining 
 the proportion of iron in its ores. 
 
 Many organic substances are easily oxidised by permanganate of potash, 
 and this is the case especially with the offensive emanations from putrescent 
 organic matter. Hence it is extensively used, under the name of Condy's 
 red disinfecting fluid, in cases where a solid or liquid substance is to be 
 deodorised. 
 
 225. Chlorides of manganese. There appear to be three compounds 
 of manganese with chlorine, corresponding to three of the oxides, viz., 
 MnCl, Mn 2 Cl 3 , and MnCl 2 ; but only the first is obtainable in the pure 
 state, the others forming solutions, which are easily decomposed with 
 evolution of chlorine. 
 
 The prolochloride of manganese (MnCl) is obtained in large quantity, as a waste 
 product in the preparation of chlorine, for the manufacture of bleaching-powder. 
 Since there is no useful application for it, the manufacturer sometimes reconverts 
 it into the black oxide. As the native binoxide always contains iron, the liquor 
 obtained by treating it with hydrochloric acid contains sesquichloride of iron 
 (Fe 2 Cl 3 ) mixed with chloride of manganese (MnCl). In order to separate the iron, 
 advantage is taken of the circumstance that sesquioxides are weaker bases than the 
 protoxides, so that if a small proportion of lime be added to the solution, the iron may 
 be precipitated as sesquioxide, without decomposing the chloride of manganese 
 
 Fe 2 Cl 3 + 3CaO = Fe 2 3 + 3CaCl . 
 
 The solution of chloride of manganese is then mixed with chalk, and subjected to 
 the action of steam at a pressure of about two atmospheres. Carbonate of manganese 
 .is precipitated (MnCl + CaO . C0 2 CaCl + MnO . C0 2 ), and when this is dried 
 and heated to about 600 in a current of moist air, the carbonic acid is expelled, 
 and a large proportion of the oxide of manganese is converted into binoxide, which 
 may be employed again for the preparation of chlorine. 
 
 By dissolving permanganate of potash in oil of vitriol, and adding fragments of 
 fused chloride of sodium, a remarkable greenish-yellow gas is obtained, which gives 
 purple fumes with moist air, and is decomposed by water, yielding a red solution 
 which contains hydrochloric and permanganic acids. It, therefore, must contain 
 manganese and chlorine, and is sometimes regarded as the perchloride (Mn 2 Cl ? ) 
 corresponding to permanganic acid ; but it is more probably an oxychloride of man- 
 ganese (see chlorochromic acid). 
 
 226. Equivalent and atomic weights of manganese. The chloride of 
 manganese has been found to contain 35*5 parts (one equivalent) by 
 weight of chlorine, and 27*5 parts of manganese ; hence the equivalent of 
 manganese is represented by 27*5. 
 
 The specific heat of manganese and its isomorphism with iron and zinc, 
 lead to the conclusion that its atomic weight is 55 (Mn), so that it is 
 a diatomic metal. The atomic formula of protoxide of manganese is 
 MnO (0 = 16), of the binoxide MnO 2 , of protochloride of manganese 
 
 The permanganates are isomorphous with the perchlorates j the atomic 
 
OXIDES OF COBALT. 329 
 
 formula of perchlorate of potash is KC10 4 , and, taking the atomic 
 weight of manganese to be 55, the atomic formula of permanganate of 
 potash would be KMnO 4 , whereas if 2 7 '5 were taken for the atomic 
 weight of the metal, the formula of this salt would be KMn 2 4 , and its 
 analogy to the perchlorate would disappear. 
 
 COBALT. 
 
 227. Some of the compounds of cobalt are of considerable importance 
 in the arts, on account of their brilliant and permanent colours. It is 
 generally found in combination with arsenic and sulphur, forming tin- 
 white cobalt, CoAs, and cobalt glance, CoAs, CoS 2 , but its ores also gene- 
 rally contain nickel, copper, iron, manganese, and bismuth. 
 
 The metal itself is obtained by strongly heating the oxalate of cobalt 
 (CoO . C 2 3 ) in a covered porcelain crucible. In its properties it closely 
 resembles iron, but is said to surpass it in tenacity. 
 
 Two oxides of cobalt are known the protoxide, CoO, which is decidedly 
 basic, and the sesquioxide, Co 2 O 3 , which is a very feeble base. The protoxide 
 of cobalt, like those of iron and manganese, tends to absorb oxygen from 
 the air, and when heated in air, becomes converted into CoO . Co 2 3 , 
 corresponding to the magnetic oxide of iron. The commercial oxide of 
 cobalt, which is employed for painting on porcelain, is obtained by roast- 
 ing the ore, in order to expel part of the sulphur and arsenic, dissolving 
 it in hydrochloric acid, and precipitating the sesquioxide of iron by the 
 careful addition of lime, when the remaining arsenic is also precipi- 
 tated as arseniate of iron. Hydrosulphuric acid is passed through the 
 acid solution to precipitate the bismuth and copper, leaving the cobalt 
 and nickel in solution. The latter having been boiled to expel the excess 
 of hydrosulphuric acid, is neutralised with lime and mixed with solution 
 of chloride of lime (CaO . CIO + CaCl), which precipitates the sesqui- 
 oxide of cobalt as a black powder, leaving the oxide of nickel in solution, 
 from which it may be precipitated by the addition of lime. 
 
 The salts of oxide of cobalt have a fine red colour in the hydrated state, or 
 in solution, but are generally blue when anhydrous. The silicate of cobalt 
 associated with silicate of potash forms the blue colour known as smalt, 
 which is prepared by roasting the cobalt-ore, so as to convert the bulk of 
 the cobalt into oxide, leaving, however, a considerable quantity of arsenic 
 and sulphur still in the ore. The residue is then fused in a crucible with 
 ground quartz and carbonate of potash, when a blue glass is formed con- 
 taining silicate of cobalt and silicate of potash, whilst the iron, nickel, and 
 copper, combined with arsenic and sulphur, collect at the bottom of the 
 crucible and form a fused mass of metallic appearance known as speiss, 
 which is employed as a source of nickel. The blue glass is poured into 
 cold water, so that it may be more easily reduced to the fine powder in 
 which the smalt is sold. If the cobalt-ore destined for smalt be over 
 roasted, so as to convert the iron into oxide, this will pass into the smalt 
 as a silicate, injuring its colour. 
 
 Zaffre is prepared by roasting a mixture of cobalt-ore with two or three 
 parts of sand. 
 
 Thenard's blue consists of phosphate of cobalt and phosphate of alumina, 
 and is prepared by mixing precipitated alumina with phosphate of cobalt 
 and calcining in a covered crucible. The phosphate is obtained by preci- 
 pitating a solution of nitrate of cobalt with phosphate of potash or soda. 
 
330 COMPOUNDS OF NICKEL. 
 
 Rinmaris green is prepared by calcining the precipitate produced by 
 carbonate of soda in a mixture of sulphate of cobalt with sulphate of zinc. 
 It is a compound of the oxides of cobalt and zinc. 
 
 Chloride of cobalt (CoCl), obtained by dissolving oxide of cobalt in 
 hydrochloric acid, forms red hydrated crystals, which become blue when 
 their water is expelled. If strong hydrochloric acid be added to a red 
 solution of this salt, it becomes blue ; if enough water be now added to 
 render it pink, the blue colour may be produced at pleasure by boiling, 
 the solution first passing through a neutral tint. Chloride of cobalt is 
 employed as a sympathetic ink, for characters written with its pink solu- 
 tion are nearly invisible till they are held before the fire, when they 
 become blue, and resume their original pink colour if exposed to the air ; 
 a little chloride of iron causes a green colour. 
 
 The sulphide of cobalt (CoS) is obtained as a black precipitate when 
 an alkaline sulphide is added to a solution of a salt of cobalt. A sesqui- 
 sulphide (Co 2 S 3 ) is found in grey octahedra, cobalt pyrites. The bisul- 
 phide (CoS 2 ) has been obtained artificially. 
 
 When ammonia in excess is added to a solution of a salt of cobalt, a 
 deep red liquid is produced, which rapidly absorbs oxygen from the air, 
 especially if hydrochlorate of ammonia be present, giving rise to the pro- 
 duction of some remarkable and complex bases which contain the elements 
 of ammonia and of different oxides of cobalt. 
 
 NICKEL. 
 
 228. Nickel owes its value in the useful arts chiefly to its property of 
 imparting a white colour to the alloys of copper and zinc, with which it 
 forms the alloy known as German silver. Nickel is very nearly allied 
 to cobalt, and generally occurs associated with that metal in its ores. 
 One of the principal ores of nickel is the Kupfernickel or copper-nickel, 
 so called by the German miners because they frequently mistook it for an 
 ore of copper; it has a reddish metallic appearance, and the formula 
 Ni 2 As. Grey nickel ore or nickel glance is an arseniosulphide of nickel, 
 NiAs, NiSg. Arsenical nickel, NiAs, corresponds to tin-white cobalt. 
 The metal is commonly extracted from the speiss separated during the 
 preparation of smalt from cobalt-ores (p. 329) ; the oxide of nickel pre- 
 pared by the method described above, when strongly heated in contact 
 with charcoal, yields metallic nickel containing carbon. 
 
 The pure metal is obtained by igniting the oxalate, as in the case of 
 cobalt, which it much resembles in properties. 
 
 The oxides of nickel correspond in composition to those of cobalt. The 
 salts formed by the oxide of nickel (MO) are usually green, and give 
 bright green solutions. The hydrated oxide has a characteristic apple- 
 green colour, and does not absorb oxygen from the air like the hydrated 
 oxide of cobalt. The greater facility with which the latter is converted 
 into sesquioxide has been applied (as above described) to effect the separa- 
 tion of the two metals. Oxide of nickel has been found native in octa- 
 hedral crystals, which have also been obtained accidentally in a copper- 
 smelting furnace. 
 
 Sulphate of nickel (NiO . S0 3 . HO + 6Aq.) forms fine green prismatic 
 crystals, the water of constitution in which may be displaced by sulphate 
 of potash, forming the double sulphate of nickel and potash 
 
 (NiO . 80, , KO . S0 3 + 6Aq.) 
 
CHROMIC ACID. 331 
 
 which crystallises so readily that it was at one -time the form in which 
 nickel was separated from the other metals present in its ores. 
 
 Three sulphides of nickel are known a subsulphide, M 2 S ; a proto- 
 sulphide, NiS, found native as capillary pyrites, and obtained as a black 
 precipitate by the action of an alkaline sulphide upon a salt of nickel ; and 
 a bisulphide, NiS*. 
 
 CHROMIUM. 
 
 229. This metal derives its name from XP^^ colour, in allusion to the 
 varied colours of its compounds, upon which their uses in the arts chiefly 
 depend. It is comparatively seldom met with, its principal ore being the 
 chrome-iron ore (FeO . Cr 2 3 ), which is remarkable for its resistance to the 
 action of acids and other chemical agents. It is chiefly found in Sweden, 
 Russia, and the United States, and is imported for the manufacture of 
 bichromate of potash (KO. 2Cr0 3 ), which is one of the chief commercial 
 compounds of chromium. The ore is first heated to redness and thrown 
 into water, in order that it may be easily ground to a fine powder, which 
 is mixed with carbonate of potash, chalk being added to prevent the fusion 
 of the mass, and strongly heated in a current of air on the hearth of a 
 reverberatory furnace, the mass being occasionally stirred to expose a 
 fresh surface to the air. The oxide of iron is thus converted into sesqui- 
 oxide, and the sesquioxide of chromium (Cr 2 3 ) also absorbs oxygen from 
 the air, becoming chromic acid (Cr0 3 ), which combines with the potash 
 to form chromate of potash (KO . Cr0 3 ). Nitre is sometimes added to 
 hasten the oxidation. On treating the mass with water, a yellow solu- 
 tion of chromate of potash is obtained, which is drawn off from the 
 insoluble residue of sesquioxide of iron and lime, and mixed with a 
 slight excess of nitric acid 
 
 2(KO . Cr0 3 ) + HO , N0 5 - KO . 2Cr0 3 + KO . N0 5 + HO . 
 
 Chromate of Bichromate of 
 
 potash. potash. 
 
 The solution, when evaporated, deposits beautiful red tabular crystals of 
 bichromate of potash, which dissolve in 10 parts of cold water, forming 
 an acid solution. It is from this salt that the other compounds of 
 chromium are immediately derived. 
 
 Metallic, chromium has received no useful application. It has been 
 obtained in octahedral crystals by the action of sodium on sesquichloride 
 of chromium, and in a pulverulent state by the action of potassium. In 
 the latter condition it is easily acted on by acids, but the crystallised 
 chromium is insoluble even in nitro-hydrochloric acid. Like aluminum, 
 it is more easily attacked by hydrated alkalies at a high temperature, 
 evolving hydrogen and producing chromates. It is remarkably infusible. 
 
 230. OXIDES OF CHROMIUM. Two oxides of chromium are known in 
 the separate state the sesquioxide, Cr 2 3 , and chromic acid, Cr0 3 . Pro- 
 toxide of chromium (CrO) is known in the hydrated state, and perchromic 
 acid (Cr 2 7 ) is believed to exist in solution. 
 
 Chromic acid, the most important of these, is obtained by adding to 
 one measure of a solution of bichromate of potash, saturated at 130 F., 
 one measure and a-half of concentrated sulphuric acid, by small portions 
 at a time, and allowing the solution to cool, when chromic acid crystallises 
 out in fine crimson needles, which are deliquescent, very soluble in water, 
 
332 SESQUIOXIDE OF CHROMIUM. 
 
 and decomposed by a moderate heat into oxygen and sesquioxide of 
 chromium. Chromic acid is a powerful oxidising agent; most organic 
 substances, even paper, will reduce it to the green sesquioxide of chromium. 
 A mixture of bichromate of potash and sulphuric acid is employed for 
 bleaching some oils, the colouring matter being oxidised at the expense of 
 the chromic acid, and sulphate of sesquioxide of chromium produced 
 KO. 2Cr0 3 + 4(HO. S0 3 ) = KO. S0 3 + O 2 3 . 3S0 3 + 3 '+ 4HO . 
 
 The bichromate itself evolves oxygen when heated to bright redness, being 
 first fused, and afterwards decomposed 
 
 2(K0.2Cr0 3 ) - 2(KO.Cr0 3 ) + Cr 2 3 + 3 . 
 
 Neutral chromate of potash (KO . Cr0 3 ) is formed by adding carbonate 
 of potash to the red solution of bichromate of potash until its red colour 
 is changed to a fine yellow, when it is evaporated and allowed to 
 crystallise. It forms yellow prismatic crystals having the same form as 
 those of sulphate of potash, and is far more soluble in water than the 
 bichromate, yielding an alkaline solution. It becomes red when heated, 
 and fuses without decomposition. 
 
 Terchromate of potash (KO . 3Cr0 3 ) has been obtained in red crystals 
 by adding nitric acid to the bichromate. 
 
 Chrome-yellow is the chromate of lead (PbO . Cr0 3 ), prepared by mix- 
 ing dilute solutions of acetate of lead and chromate of potash. It is 
 largely used in painting and calico-printing, and by the chemist as a 
 source of oxygen for the analysis of organic substances, since, when heated, 
 it fuses to a brown mass, which evolves oxygen at a red heat. Chrome- 
 yellow being a poisonous salt, its occasional use for colouring confectionery 
 is very objectionable. Chromate of lead in prismatic crystals forms the 
 rather rare red lead ore of Siberia, in which chromium was first discovered. 
 
 Orange chrome is a basic chromate of lead (2PbO . Cr0 3 ), and may be 
 obtained by boiling the yellow chromate with lime 
 
 2(PbO.Cr0 3 ) + CaO - 2PbO.Cr0 3 + CaO.Cr0 3 . 
 
 The calico-printer dyes the stuff with yellow chromate of lead, and con- 
 verts it into orange chromate by a bath of lime-water. 
 
 The colour of the ruby (crystallised alumina) appears to be due to the 
 presence of a small proportion of chromic acid. 
 
 Sesquioxide of chromium (Cr 2 3 ) is valuable as a green colour, especially 
 for glass and porcelain, since it is not decomposed by heat. It is prepared 
 by heating bichromate of potash with one-fourth of its weight of starch, 
 the carbon of which deprives the chromic acid of half its oxygen, leaving 
 a mixture of sesquioxide of chromium with carbonate of potash, which may 
 be removed by washing with water. If sulphur be substituted for 
 the starch, sulphate of potash will be formed, which may also be 
 removed by water. When the sesquioxide of chromium is strongly 
 heated, it exhibits a sudden glow, becomes darker in colour, and in- 
 soluble in acids which previously dissolved it easily; in this respect 
 it resembles alumina and sesquioxide of iron. Like these oxides, the 
 sesquioxide of chromium is a feeble base ; it is remarkable for forming 
 two classes of salts containing the same proportions of acid and base, but 
 differing in the colour of their solutions, and in some other properties. 
 Thus, there are two modifications of the sulphate of sesquioxide of 
 chromium the green sulphate, Cr 2 3 . 3S0 3 4- 5Aq., and the violet sul- 
 phate, Cr 2 3 . 3S0 3 + 1 5 Aq, The solution of the latter becomes green 
 
CHLORIDES OF CHROMIUM. 333 
 
 when boiled, being converted into the former. Chrome-alum forms dark 
 purple octahedra (KO . S0 3 , Cr 2 3 . 3S0 3 + 24 Aq.) which contain the 
 violet modification of the sulphate; and if its solution in water be boiled, 
 its purple colour changes to green, and the solution refuses to crystallise.* 
 The anhydrous sulphate of chromium forms red crystals, which are in- 
 soluble in water and acids. A green basic borate of sesquioxide of chromium 
 is used in painting and calico-printing, under the name of vert de Guignet, 
 and is prepared by strongly heating bichromate of potash with 3 parts of 
 Crystallised boracic acid, when borate of potash and borate of chromium 
 are formed, half the oxygen of the chromic acid being expelled. The borate 
 of potash and the excess of boracic acid are afterwards washed out by 
 water. By reducing an alkaline chromate with hyposulphite of soda, the 
 compound Cr 2 3 . Cr0 3 has been obtained as a brown precipitate. 
 
 Protoxide of chromium (CrO) is not known in the pure state, but is 
 precipitated as a brown hydrate when protochloride of chromium is de- 
 composed by potash. It absorbs oxygen even more readily than protoxide 
 of iron, becoming converted into a hydrated proto-sesquioxide of chromium 
 (CrO . Cr 2 3 ), corresponding in composition to the magnetic oxide of iron. 
 The protoxide of chromium is a feeble base ; a double sulphate of protoxide 
 of chromium and potash (CrO . S0 3 , KO . S0 3 + 6Aq.) is known, which 
 has the same crystalline form as the corresponding iron salt 
 
 (FeO . S0 3 , KO . S0 3 + 6Aq.) 
 
 it has a blue colour, and gives a blue solution, which becomes green when 
 exposed to air, from the formation of sesquioxide of chromium. 
 
 Perchromic acid {&? 3 Q 7 1) is believed to exist in the blue solution 
 obtained by the action of binoxide of hydrogen upon solution of chromic 
 acid, but neither the acid nor its salts have been obtained in a separate 
 state. 
 
 231. Chlorides of chromium. The sesquichloride of chromium (Cr 2 Cl 3 ), obtained by 
 passing dry chlorine over a mixture of sesquioxide of chromium with charcoal, 
 heated to redness in a glass tube, is converted into vapour, and condenses upon 
 the cooler part of the tube in shining leaflets, having a fine violet colour. Cold 
 water does not affect them, but boiling water slowly dissolves them to a green solu- 
 tion resembling that obtained by dissolving sesquioxide of chromium in hydrochloric 
 acid. 
 
 Protochloride of chromium (CrCl) results from the action of hydrogen, at a red heat, 
 upon the sesquichloride. Strange to say, it is white, and dissolves in water to form 
 a blue solution which absorbs oxygen from the air, becoming green. It is remark- 
 able that if the violet sesquichloride of chromium is suspended in water, and a 
 minute quantity of the protochloride added, the sesquichloride immediately dis- 
 solves to a green solution, evolving heat. 
 
 Chlorochromic acid (Cr0 2 Cl) is a very remarkable brown-red liquid, obtained by 
 distilling 10 parts of common salt and 17 of bichromate of potash, previously fused 
 together and broken into fragments, with 40 parts of oil of vitriol 
 
 KO . 2Cr0 3 + 2NaCl + 3 (HO . S0 3 ) rr KO . S0 3 + 2(NaO . S0 3 ) + 3HO + 2Cr0 2 Cl. 
 
 It much resembles bromine in appearance, and fumes very strongly in air, the mois- 
 ture of which decomposes its red vapour, forming chromic and hydrocbloric acids ; 
 Cr0 2 Cl + HO = Cr0 3 + HC1. It is a very powerful oxidising and chlorinating 
 agent, and inflames ammonia and alcohol when brought in contact with them. 
 
 It is occasionally used to illustrate the nature of illuminating flames ; for if 
 hydrogen be passed through a bottle containing a few drops of chlorochromic acid, 
 the gas becomes charged with its vapour, and, if kindled, burns with a brilliant 
 white flame, which deposits a beautiful green film of sesquioxide of chromium upon 
 
 * Exposure to cold, it is said, again converts it into the crystallisable violet form. 
 
334 GENERAL REVIEW OF THE IRON GROUP. 
 
 a cold surface. The name oxychloride of chromium, applied to this compound, is more 
 correct than chlorochromic acid, for it is not known to form salts. 
 
 Terfluoride of chromium (CrF 3 ) is another volatile compound of chromium, obtained 
 by distilling chromate of lead with fluor spar and sulphuric acid ; it is a red gas, con- 
 densible to a red liquid at a low temperature. Water decomposes it, yielding chromic 
 and hydrofluoric acids. 
 
 Sesquisulphide of chromium (Cr 2 S 3 ) is formed when vapour of bisulphide of carbon 
 is passed over sesquioxide of chromium heated to redness. It forms black lustrous 
 scales resembling graphite. 
 
 232. Equivalent and atomic weights of chromium. The analysis of the 
 chromate of silver has proved it to contain 2 6 '3 parts by weight of 
 chromium for 108 parts (1 eq.) of silver. The isomorphism (identity of 
 crystalline form) existing between the chromates and the sulphates, leads 
 to the belief that they correspond in composition, so that the chromate 
 of silver would be represented by the formula AgO . Cr0 3 , and since 
 Ag= 108, Cr, or the equivalent of chromium, is 2 6 '3. 
 
 The close analogy between chromium and iron renders it necessary to 
 double the equivalent number of chromium in order to obtain its atomic 
 weight, so that the atom of chromium would be 6r = 52*6, the metal being 
 diatomic; and the atomic formula of chromic oxide would be Gr 2 O 3 , of 
 chromic acid Or0 3 , of chromous chloride 6rCl 2 , and of chromic chloride 
 
 er 2 ci 6 . 
 
 The molecular formula of chlorochromic acid would be 6rCl 2 2 , repre- 
 senting 155*6 parts by weight. Now, the specific gravity (or weight 
 of 1 volume) of the vapour of chlorochromic acid is 5 '52, or 80 times 
 that of hydrogen; if 1 atom (or 1 vol.) of hydrogen be taken to weigh 1, 
 one molecule (or 2 vols.) of chlorochromic acid should weigh 160, which is 
 sufficiently near to the weight (155 -6) represented by the above formula, 
 allowing for unavoidable experimental errors, 
 
 233. General review of zinc, iron, cobalt, nickel, manganese, and chro- 
 mium. Many points of resemblance will have been noticed in the chemical 
 history of these metals to justify their being classed in the same group. 
 They are all capable of decomposing water at a red heat, and easily dis- 
 place hydrogen from hydrochloric acid. Each of them forms a base by 
 combining with one equivalent of oxygen, and these oxides produce salts 
 which have the same crystalline form. All these oxides, except those of 
 zinc and nickel, easily absorb oxygen from the air, and are converted into 
 sesquioxides. Zinc does not form a sesquioxide, and the sesquioxide of 
 nickel is an indifferent oxide, while that of cobalt is very feebly basic ; 
 the sesquioxide of manganese is a stronger base, and the basic properties 
 of the sesquioxides of chromium and iron are very decided. Zinc and 
 nickel do not exhibit any tendency to form a well-marked acid oxide, 
 but the existence of an acid oxide of cobalt is suspected ; and iron, man- 
 ganese, and chromium form undoubted acids with three equivalents of 
 oxygen. Zinc and nickel are only known to form one compound with a 
 single equivalent of chlorine ; cobalt and manganese form, in addition to 
 their protochlorides, very unstable sesquichlorides known only in solution, 
 but iron and chromium form very stable volatile sesquichlorides. The 
 metals composing this group are all bi-equivalent or diatomic, and are 
 found associated in natural minerals; this is especially the case with iron, 
 manganese, cobalt, and nickel. They are all attracted by the magnet, with 
 the exception of zinc, and, with the same exception, require a very high 
 temperature for their fusion. Through zinc, the metals of this group are 
 
METALLURGY OF COPPER. 335 
 
 connected with magnesium, which resembles it in volatility, in combusti- 
 bility, and in the crystalline form of its ' salts. Iron and chromium con- 
 nect this group with aluminum, their sesquioxides being isomorphous with 
 alumina, and their sesquichlorides volatile like that of aluminum. 
 
 COPPEE. 
 
 , 234. Metallic copper is met with in nature more abundantly than 
 metallic iron, though the compounds of the latter metal are of more fre- 
 quent occurrence than those of the former. A very important vein of 
 metallic copper, of excellent quality, occurs near Lake Superior in North 
 America, from which 6000 tons were extracted in 1858. Metallic copper 
 is also sometimes found in Cornwall; and copper sand, containing metallic 
 copper and quartz, is imported from Chile. 
 
 235. Ores of copper. The most important English ore of copper is 
 copper pyrites, which is a double sulphide, containing copper, iron, and 
 sulphur in the proportions indicated by the formula CuFe$2. It may be 
 known by its beautiful brass yellow colour and metallic lustre. Copper 
 pyrites is found in Cornwall and Devonshire, and is generally associated 
 with arsenical pyrites (FeS 2 . EeAs), tinstone (Sn0 2 ), quartz, fluor-spar, and 
 clay. A very attractive variety of copper pyrites is called variegated 
 copper ore or peacock copper, in allusion to its rainbow colours ; its simplest 
 formula is CugFeS^ This variety is found in Cornwall and Killarney. 
 
 Copper glance (Cu 2 S) is another Cornish ore of copper, of a dark grey 
 colour and feeble metallic lustre. 
 
 Grey copper ore, also abundant in Cornwall, is essentially a compound 
 of the sulphides of copper and iron with those of antimony and arsenic, 
 but it often contains silver, lead, zinc, and sometimes mercury. 
 
 Malachite, a basic carbonate of copper, is imported from Australia 
 (Burra Burra), and is also found abundantly in Siberia. Green malachite, 
 the most beautifully veined ornamental variety, has the composition 
 CuO . C0 2 , CuO . HO, and blue malachite is 2(CuO . C0 2 ) . CuO . HO. 
 
 Red copper ore (Cu 2 0) is found in West Cornwall, and the black oxide 
 (CuO) is abundant in the north of Chile. 
 
 236. The seat of English copper-smelting is at Swansea, which is 
 situated in convenient proximity to the anthracite coal employed in the 
 furnaces. The chemical process by which copper is extracted from the 
 ore includes three distinct operations : (1), the roasting, to expel the 
 arsenic and part of the sulphur, and to convert the sulphide of irpn into 
 oxide of iron ; (2), fo& fusion ivith silica, to remove the oxide of iron as 
 silicate, and to obtain the copper in combination with sulphur only ; and 
 (3), the roasting of this combination of copper with sulphur, in order to 
 expel the latter and obtain metallic copper. 
 
 The details of the smelting process appear somewhat complicated, 
 because it is divided into several stages to allow of the introduction of 
 the different varieties of ore to be treated. Thus, the first roasting pro- 
 cess is unnecessary for the oxides and carbonates of copper, and the fusion 
 with silica is not needed for those ores which are free from iron, so that 
 they may be introduced at a later stage in the operations. 
 
 (1.) Calcining or roasting the ore, to expel arsenic and part of the sulphur. 
 The ores having been sorted, and broken into small pieces, are mixed 
 
336 
 
 WELSH COPPER-SMELTING PROCESS. 
 
 so as to contain from 8 to 10 per cent, of copper, and roasted, in quanti- 
 ties of about three tons, for at least twelve hours, on the spacious hearth 
 
 Fig. 239. 
 
 Fig. 238. 
 
 (H, fig. 239) of a reverberatory furnace (fig. 238), at a temperature insufficient 
 for fusion, being occasionally stirred to expose them freely to the action of 
 
 the air, which is admitted into the fur- 
 nace through an opening (0) in the side of 
 the hearth upon which the ore is spread. 
 The oxygen of the air converts a part of 
 the sulphur into sulphurous acid gas, 
 and the bulk of the arsenic into arsenious 
 acid, which passes off in the form of 
 vapour. A part of the sulphide of iron 
 is converted into sulphate of iron by 
 absorbing oxygen at an early stage of the 
 process, and this sulphate is afterwards 
 decomposed at a higher temperature, 
 evolving sulphurous and sulphuric acids, and leaving oxide of iron (see 
 p. 322). A portion of the sulphide of copper is also converted into 
 oxide of copper during the roasting, so that the roasted ore consists essen- 
 tially of a mixture of oxide and sulphide of copper with oxide and 
 sulphide of iron. Since the sulphide of iron is more easily oxidised than 
 sulphide of copper, the greater part of the latter remains unaltered in the 
 roasted ore. 
 
 During the roasting of copper ore dense white fumes escape from the 
 furnaces. This copper-smoke, as it is termed, contains arsenious, sulphur- 
 ous, sulphuric, and hydrofluoric acids, the latter being derived from the 
 fluor spar associated with the ore; if allowed to escape, these fumes 
 seriously contaminate the air in the neighbourhood, and copper-smelters 
 are endeavouring to apply some method of condensing, and perhaps turn- 
 ing them to profitable account. 
 
 (2.) Fusion for coarse metal, to remove the oxide of iron by dissolving 
 it with silicic acid at a high temperature. The roasted ore is now 
 mixed with metal-slag from process 4, and with ores containing silicic acid 
 and oxides of copper, but no sulphur; the mixture is introduced into 
 the ore-furnace (fig. 240), and fused for five hours at a higher tempera- 
 ture than that employed in the previous operation. In this process fluor 
 spar is sometimes added in order to increase the fluidity of the slag. 
 
 The oxide of copper acts upon the sulphide of iron still contained in 
 the roasted ore, with formation of sulphide of copper and oxide of iron ; 
 
WELSH COPPER-SMELTING PROCESS. 
 
 337 
 
 but since there is more sulphide of iron present than the oxide of copper 
 can decompose, the excess of sulphide of iron combines with the 
 sulphide of copper to form a 
 fusible compound, which sepa- 
 rates from the slag, and col- 
 lects in the form of a matt or 
 regulus of coarse metal, in a 
 cavity (C) on the hearth of the 
 furnace; it is run out into a 
 tank of water (T) in order to 
 granulate it, so that it may be 
 better fitted to undergo the next 
 operation. 
 
 The oxide of iron combines 
 with the silicic acid contained 
 in the charge to form a fusible 
 silicate of iron (ore-furnace 
 slag), which is raked out into 
 moulds of sand, and cast into 
 blocks used for rough building 
 purposes in the neighbourhood. 
 
 The composition of the coarse 
 metal corresponds pretty closely Fig. 240. 
 
 with the formula CuFeS 2 . It 
 
 contains from 33 to 35 per cent, of copper ; whilst the original ore, before 
 roasting, is usually sorted so that it may contain about 8 '5 per cent. 
 
 The ore-furnace slag is approximately represented by the formula 
 FeO . Si0 2 ; but it contains a minute proportion of copper, as is shown by 
 the green efflorescence on the walls in which it is used around Swansea. 
 Fragments of quartz are seen disseminated through this slag. 
 
 (3.) Calcination of the coarse metal, to convert the greater part of the 
 sulphide of iron into oxide. The granulated coarse metal is roasted at a 
 moderate heat for twenty-four hours, as in the first operation, so that the 
 oxygen of the air may decompose the sulphide of iron, removing the sul- 
 phur as sulphurous acid gas, and leaving the iron in the form of oxide. 
 
 (4.) Fusion for white metal, to remove the whole of the iron as silicate. 
 The roasted coarse metal is mixed with roaster and refinery slags from 
 processes 5 and 6, and with ores containing carbonates and oxides of 
 copper, and fused for six hours, as in the second operation. Any suiphide 
 of iron which was left unchanged in the roasting is now converted into 
 oxide of iron by the oxide of copper, the latter metal taking the sulphur. 
 The whole of the oxide of iron combines with the silicic acid to form a 
 fusible slag, the composition of which is approximately represented by the 
 formula 3FeO . 2Si0 2 . 
 
 The matt or regulus of white metal which collects beneath the slag is 
 nearly pure subsulphide of copper (Cu 2 S), half the sulphur existing in the 
 protosulphide (CuS) having been removed by oxidation in the furnace. The 
 white metal is run into sand-moulds and cast into ingots. The tin and 
 other foreign metals usually collect in the lower part of the ingot, so that, 
 for making best selected copper, the upper part is broken off and worked 
 separately, the inferior copper obtained from the lower part of the ingot 
 
338 POLING OF COPPER. 
 
 being termed tile-copper. The ingots of white metal often contain "beautiful 
 tufts of metallic copper in the form of copper moss. 
 
 The slag separated from the white metal (metal-slag) is much more fluid 
 than the ore-furnace slag, and contains so much silicate of copper that it 
 is preserved for use in the melting for coarse metal. 
 
 (5.) Roasting the white metal, to remove tiie sulphur and obtain blistered 
 copper. The ingots of white metal (to the amount of about 3 tons) are 
 placed upon the hearth of a reverberatory furnace, and heated for four 
 hours to a temperature just below fusion, so that they may be oxidised at 
 the surface, the sulphur passing off as sulphurous acid, and the copper 
 being converted into oxide. During this roasting the greater part of the 
 arsenic, generally present in the fine metal, is expelled as arsenious acid. 
 The temperature is then raised, so that the charge may be completely 
 fused, after which it is lowered again till the 12th hour. The oxide of 
 copper now acts upon the sulphide of copper to form metallic copper and 
 sulphurous acid gas, which escapes with violent ebullition from the 
 melted mass ; Cu^S + 2CuO = S0 2 *- Cu 4 . When this ebullition ceases, 
 the temperature is again raised so as to cause the complete separation of 
 the copper from the slag, and the metal is run out into moulds of sand. 
 Its name of blister copper is derived from the appearance caused by the 
 escape of the last portions of sulphurous acid from the metal when solidi- 
 fying in the mould. 
 
 The slag (roaster slag) is formed in this operation by the combination 
 of a part of the oxide of copper with silicic acid derived from the sand 
 adhering to the ingots, and from the hearth of the furnace. The slag 
 also contains the silicates of iron and of other metals, such as tin and lead, 
 which might have been contained in the white metal. This slag is used 
 again in the melting for white metal. 
 
 (6.) Refining, to remove foreign metals. This process consists in slowly 
 fusing 7 or 8 tons of the blistered copper in a reverberatory furnace, so 
 that the air passing through the furnace may remove any remaining sul- 
 phur as sulphurous acid, and may oxidise the small quantities of iron, tin, 
 lead, &c., present in the metal. Of course, a large proportion of the 
 copper is oxidised at the same time, and the suboxide of copper, together 
 with the oxides of the foreign metals, combines with silicic acid (from the 
 hearth or from adhering sand) to form a slag which collects upon the sur- 
 face of the melted copper. A portion of the suboxide of copper is dis- 
 solved by the metallic copper, rendering it brittle or- dry copper. 
 
 (7.) Toughening or poling, to remove apart of the oxygen and bring the 
 copper to tough-pitch. After about twenty hours, the slag is skimmed 
 from the metal, a quantity of anthracite is thrown over the surface to pre- 
 vent further oxidation, and the metal is poled, i.e., stirred with a pole of 
 young wood until a small sample, removed for examination, presents a 
 peculiar silky fracture, indicating it to be at tough-pitch, when it is cast 
 into ingots. 
 
 The chemical change during the poling appears to consist in the re- 
 moval of the oxygen contained in the suboxide present in the metal, by 
 the reducing action of the combustible gases disengaged from the wood. 
 The presence of a small proportion of suboxide of copper is said to confer 
 greater toughness upon the metal, so that if the poling be continued until 
 the whole of the oxygen is removed, overpoled copper of lower tenacity is 
 
EXTRACTION OF COPPER IN THE LABORATORY. 
 
 339 
 
 obtained. On the other hand, the brittleness of underpoled copper is due 
 to the presence of suboxide of copper in too large proportion. Tough-cake 
 copper is that which has been poled to the proper extent. 
 
 When the copper is intended for rolling, a small quantity (not exceed- 
 ing \ per cent.) of lead is generally added to it before it is ladled into the 
 ingot moulds. 
 
 The chemical changes which take place during the above processes will 
 be more clearly understood after inspecting the subjoined table, which 
 exhibits the composition of the products obtained at different stages of the 
 process, these being distinguished by the same numerals as were employed 
 in the above description. 
 
 Products obtained in smelting Ores of Copper. 
 
 In 100 parts. 
 
 Ore. 
 
 Roasted 
 Ore. 
 
 Coarse 
 Metal. 
 
 Roasted 
 Coarse 
 Metal. 
 
 White 
 Metal. 
 
 Blister 
 Copper. 
 
 Refined 
 Copper. 
 
 Tough- 
 pitch 
 Copper. 
 
 Copper 
 
 8-2 
 17-9 
 19-9 
 1-0 
 34-3 
 
 (!) 
 8-6 
 17-6 
 12-5 
 4-5 
 34-3 
 1-1 
 
 (2.) 
 33-7 
 33-6 
 29-2 
 
 (3.) 
 33-7 
 33-6 
 13-0 
 11-0 
 
 (4.)' 
 77-4 
 0-7 
 21-0 
 
 (5.) 
 98*0 
 0-6 
 0-2 
 
 (6.) 
 99-4 
 trace 
 trace 
 0-4 
 
 (7.) 
 99-6 
 trace 
 trace 
 0-03 
 
 Iron . . 
 
 Sulphur, .... 
 Oxygen, .... 
 Silicic acid, . . . 
 Sulphuric acid, . . 
 
 
 Ore 
 Furnace 
 
 Slag. 
 
 
 Metal 
 
 Slag. 
 
 Roaster 
 
 Slag. 
 
 Refinery 
 
 Slag. 
 
 
 Oxide of iron (FeO), 
 Suboxide of copper (Cu 2 0), . . . 
 Silicic acid, 
 
 (2.) 
 28-5 
 0-5 
 30-0 
 
 ... 
 
 (4.) 
 56-0 
 0-9 
 33-8 
 
 (5.) 
 28-0 
 16-9 
 47-5 
 
 (6.) 
 3-1 
 36-2 
 47-4 
 
 
 Slue metal is the term applied to the regulus of white metal (from process 4), 
 when it still contains a considerable proportion of sulphide of iron, in consequence 
 of a deficient supply of oxide of copper in the furnace. Pimple metal is obtained in 
 the same operation when the oxide of copper is in excess, so that a portion of the 
 copper is reduced, as in process 5, with evolution of sulphurous acid, which produces 
 the pimply appearance in escaping. The reduced copper gives a reddish colour to 
 the pimple copper. Coarse copper is a similar intermediate stage between white 
 metal and blistered copper. Tile copper is that extracted from the bottoms of the 
 ingots of white metal, when the tops have been detached for making best select 
 copper. Rosette or rose copper is obtained by running water upon the toughened 
 metal, so as to enable the metal to be removed in films. Anglesea or Mono, copper is 
 a very tough copper, reduced by metallic iron from the blue water of ther copper 
 mines, which contains sulphate of copper. 
 
 237. For the purpose of illustration, copper may be extracted from copper pyrites 
 on the small scale in the following manner : 
 
 200 grains of the powdered ore are mixed with an equal weight ot dried borax, 
 and fused in a covered earthen crucible (of about 8 oz. capacity), at a full red heat, 
 for about half an hour. The earthy matters associated with the ore are dissolved 
 by the borax, and the pure copper pyrites collects at the bottom of the crucible. The 
 contents of the latter are poured into an iron mould (scorifying mould, fig. 241), 
 and when the mass has set, it is dipped into water. The semi-metallic button is 
 then easily detached from the slag by a gentle blow ; it is weighed, finely powdered 
 in an iron mortar, and introduced into an earthen crucible, which is placed obliquely 
 over a dull fire, so that it may not become hot enough to fuse the ore, which should 
 be stirred occasionally with an iron rod to promote the oxidation of the sulphur by 
 the air. When the odour of sulphurous acid is no longer perceptible, the crucible is 
 
 Y 2 
 
340 IMPURITIES IN COMMERCIAL COPPER. 
 
 placed in a Sefstrom's blast-furnace (fig. 237), and exposed for a few minutes to a white 
 heat, in order to decompose the sulphates of iron and copper. When no more fumes of 
 
 sulphuric acid are perceived, the cru- 
 cible is lifted from the fire, held over 
 the iron mortar, and the roasted ore 
 quickly scraped out of it with a steel 
 spatula. This mixture of the oxides 
 of copper and iron is reduced to a 
 fine powder, mixed with 600 grains 
 of dried carbonate of soda and 60 
 grains of powdered charcoal, re- 
 Fig. 241. turned to the same crucible, covered 
 with 200 grains of dried borax, 
 
 and heated in a Sefstrom's furnace for twenty minutes. The crucible is then 
 allowed to cool partly, plunged into water to render it brittle, and carefully broken 
 to extract the button of metallic copper, which is weighed to ascertain the amount 
 contained in the original ore. 
 
 238. Effect of impurities upon the quality of copper. The information 
 possessed by chemists upon this subject is still very limited. It has been 
 already mentioned that the presence of a small proportion of suboxide of 
 copper in commercial copper is found to increase its toughness. It is 
 believed that copper, perfectly free from metallic impurities, is not im- 
 proved in quality by the presence of the suboxide, but that this substance 
 has the effect of counteracting the red-shortness (see p. 315) of commercial 
 copper, caused by the presence of foreign metals. 
 
 Sulphur, even in minute proportion, appears seriously to injure the 
 malleability of copper. 
 
 Arsenic is almost invariably present in copper, very frequently amount- 
 ing to O'l per cent., and does not appear to exercise any injurious influence 
 in this proportion ; indeed, its presence is sometimes stated to increase 
 the malleability and tenacity of the metal. 
 
 Phosphorus is not usually found in the copper of commerce. When 
 purposely added in quantity varying from 0*12 to 0*5 per cent, it is found 
 to increase the hardness and tenacity of the copper, though rendering it 
 somewhat red-short. 
 
 Tin, in minute proportion, is also said to increase the toughness of 
 copper, though any considerable proportion renders it brittle. 
 
 Antimony is a very objectionable impurity, and is by no means uncom- 
 mon in samples of copper. 
 
 Nickel is believed to injure the quality of copper in which it occurs. 
 
 Bismuth and silver are very generally found in marketable copper, but 
 their effect upon its quality has not been clearly determined. 
 
 All impurities appear to affect the malleability and tenacity of copper, 
 more perceptibly at high than at low temperatures. 
 
 The conducting power of copper for electricity is affected in an ex- 
 traordinary degree by the presence of impurities. Thus, if the conducting 
 power of chemically pure copper be represented by 100, that of the very 
 pure native copper from Lake Superior has been found to be 93, that of 
 the copper extracted from the malachite of the Burra Burra mines in 
 South Australia was 89, whilst that of Spanish copper, remarkable for 
 containing much arsenic, was only 14. 
 
 Pure copper is obtained by decomposing a solution of pure sulphate of 
 copper by the galvanic current, as in the electrotype process. If the 
 negative wire be attached to a copper plate immersed in the solution, the 
 pure copper may be striped off this plate in a sheet. 
 
EFFECT OF SEA- WATER UPON COPPER. 341 
 
 239. Properties of copper. The most prominent character which 
 confers upon copper so high a rank among the useful metals is its mal- 
 leability, which allows it to be readily fashioned under the hammer, and to 
 be beaten or rolled out into thin sheets ; among the metals in ordinary 
 use, only gold and silver exceed copper in malleability, and the com- 
 parative scarcity of those metals leads to the application of copper for 
 most purposes where great malleability is requisite. 
 
 Although, in tenacity or strength, copper ranks next to iron, it is still 
 very far inferior to it, for a copper wire of -^ inch in diameter will support 
 only 385 Ibs., while a similar iron wire will carry 705 Ibs. without breaking; 
 and in consequence of its inferior tenacity, copper is less ductile than iron, 
 and does not admit of being so readily drawn into exceedingly thin wires. 
 
 The comparative ease with which copper may be fused, allows it to be 
 cast much more readily than iron ; for it will be remembered that the 
 latter metal can be liquefied only by the highest attainable furnace heat, 
 whereas copper can be fused at about 2000 F., a temperature generally 
 spoken of as a bright red heat. 
 
 As being the most sonorous of metals, copper has been, from time 
 immemorial, employed in the construction of bells and musical instru- 
 ments. The readiness with which it transmits electricity is turned to 
 account in telegraphic communication, its conducting power being almost 
 equal to that of silver, which is the best of electric conductors. In con- 
 ducting power for heat, copper is surpassed only by silver and gold. 
 
 Copper is not so hard as iron, and is somewhat heavier, the specific 
 gravity of cast copper being 8 '92, and that of hammered or drawn copper 
 8-95. 
 
 The resistance of copper to the chemical action of moist air gives it a 
 great advantage over iron for many uses, and the circumstance that it does 
 not decompose water in presence of acids, enables it to be employed as 
 the negative plate in galvanic couples. 
 
 240. Effect of sea-water upon copper. When copper is placed in a 
 solution of salt in water, no perceptible action takes place ; but in the 
 course of time, if air be allowed access, it becomes covered with a green 
 coating of oxy chloride of copper (CuCl . 3GuO . 4HO), the action probably 
 consisting, first, in the conversion of the copper into oxide by the air, 
 and afterwards in the decomposition of the oxide by the chloride of 
 sodium ; 4CuO + NaCl = CuCl . 3CuO + NaO. The surface of the 
 copper is thus corroded, and in the case of a copper-bottomed ship, the 
 action of sea-water not only occasions a great waste of copper, but roughens 
 the surface of the sheathing, and affords points of attachment to barnacles, 
 &c., which injure the speed of the vessel. Many attempts have been made 
 to obviate this inconvenience. Zinc has been fastened here and there to 
 the outside of the copper, placing the latter in an electronegative con- 
 dition ; the copper has been coated with various compositions, but with 
 very indifferent success. Muntz metal, an alloy of 3 parts of copper and 
 2 parts of zinc, has been employed with some advantage in place of 
 copper, for it is very much cheaper and somewhat less easily corroded ; 
 but the difficulty is by no means overcome. Copper containing about 0'5 
 per cent, of phosphorus is said to be corroded by sea- water much less 
 easily than pure copper. 
 
 241. Danger attending the use of copper vessels in cooking food. The 
 use of copper for culinary vessels has occasionally led to serious conse- 
 
342 
 
 ALLOYS OF COPPER. 
 
 quences, from the poisonous nature of its compounds, and from ignorance 
 of the conditions under which these compounds are formed. A perfectly 
 clean surface of metallic copper is not affected by any of the substances 
 employed in the preparation of food, but if the metal has been allowed to 
 remain exposed to the action of the air, it becomes covered with a film of 
 oxide of copper, and this subsequently combines with water and carbonic 
 acid derived from the air, to produce a basic carbonate of copper,* which, 
 becoming dissolved, or mixed with the food prepared in these vessels, 
 confers upon it a poisonous character. This danger may be avoided by 
 the use of vessels which are perfectly clean and bright, but even from 
 these, certain articles of food may become contaminated with copper, for 
 this metal is much more likely to be oxidised by the air when in con- 
 tact with acids (vinegar, juices of fruits, &c.), or with fatty matters, or 
 even with common salt, and if oxide of copper be once formed, it will be 
 readily dissolved by such substances. Hence it is usual to coat the in- 
 terior of copper vessels with tin, which is able to resist the action of the 
 air, even in the presence of acids and saline matters. 
 
 242. Useful alloys of copper with other metals. The most important 
 alloys of which copper is a predominant constituent are included in the 
 following table : 
 
 Composition of 100 parts. 
 
 
 Copper. 
 
 Zinc. 
 
 Tin. 
 
 Iron. 
 
 Nickel. 
 
 Aluminum. 
 
 
 64 
 
 36 
 
 
 
 
 
 Muntz metal, .... 
 German silver, . . . 
 Aich (or Gedge's) metal, 
 Sterro-metal, .... 
 Bell metal, 
 
 60 to 70 
 51 
 
 60 
 55 
 78 
 
 40 to 30 
 30-5 
 38-2 
 424 
 
 0-8 
 22 
 
 i : 8 
 
 1-8 
 
 18-5 
 
 
 Speculum metal, . . . 
 Bronze 
 
 66-6 
 80 
 
 4 
 
 33-4 
 16 
 
 
 
 
 Gun metal, .... 
 Bronze coinage, . . . 
 Aluminum bronze, . . 
 
 90-5 
 
 95 
 90 
 
 l'" 
 
 9-5 
 4 
 
 ... 
 
 ... 
 
 10 
 
 Brass is made by melting copper in a crucible, and adding rather more 
 than half its weight of zinc. It is difficult to decide whether brass is a 
 true chemical compound, or a mere mechanical mixture of copper and 
 zinc, because it is capable of dissolving either of those metals when in a 
 state of fusion. The circumstance that it can be deposited by decom- 
 posing a solution containing copper and zinc by the galvanic current, would 
 appear to indicate that it is a chemical compound, and its physical pro- 
 perties are not such as would be expected from a mere mixture of its 
 constituents. A small quantity of tin is added to brass intended for 
 door-plates, which renders the engraving much easier. When it has to 
 be turned or filed, about 2 per cent, of lead is usually added to it, in 
 order to prevent it from adhering to the tools employed. Brass cannot 
 be melted without losing a portion of its zinc in the form of vapour. 
 When exposed to frequent vibration (as in the suspending chains of chan- 
 deliers) it suffers an alteration in structure and becomes extremely brittle. 
 
 * Often erroneously called verdigris, which is really a basic acetate of copper. 
 
CUPRIC OXIDE. 343 
 
 The solder used by braziers consists of equal weights of copper and zinc. 
 In order to prevent ornamental brass-work from being tarnished by the 
 action of air, it is either lacquered or bronzed. Lacquering consists 
 simply in varnishing the brass with a solution of shell-lac in spirit, 
 coloured with dragon's blood. Bronzing is effected by applying a solution 
 of arsenic or mercury, or platinum, to the surface of the brass. By the 
 action of arsenious acid dissolved in hydrochloric acid, upon brass, the 
 latter acquires a coating composed of arsenic and copper, which imparts a 
 bronzed appearance, the zinc being dissolved in place of the arsenic, 
 which combines with the copper at the surface 
 
 AsO a 4- 3HC1 + Zn 3 = As + 3ZnCl + 3HO . 
 A mixture of corrosive sublimate (chloride of mercury, HgCl) and acetic 
 acid is also sometimes employed, when the mercury is displaced by the 
 zinc, and precipitated upon the surface of the brass, with which it forms, 
 a bronze-like amalgam. For bronzing brass instruments, such as 
 theodolites, levels, &c., a solution of bichloride of platinum is employed, 
 the zinc of the brass precipitating a very durable film of metallic platinum 
 upon its surface (PtClj + Zn 2 = Pt + 2ZnCl). Aich-metal is a kind of 
 brass containing iron, and has been employed for cannon, on account 
 of its great strength. At a red heat it is very malleable. 
 
 Sterro-metal (oreppos, strong) is another variety of brass containing iron 
 and tin, said to have been discovered accidentally in making brass with 
 the alloy of zinc and iron obtained during the process of making gal- 
 vanised iron (p. 294). It possesses great strength and elasticity, and is 
 used by engineers for the pumps of hydraulic presses. 
 
 Aluminum bronze has been already noticed, and $he alloys of copper 
 and tin will be described under the latter metal. 
 
 A very hard white alloy of 77 parts of zinc, 17 of tin, and 6 of copper, 
 is sometimes employed for the bearings of the driving-wheels of loco- 
 motives. 
 
 Iron and steel are coated with a closely adherent film of copper, by 
 placing them in contact with metallic zinc in an alkaline solution of oxide 
 of copper, prepared by mixing sulphate of copper with tartrate of potash 
 and soda, and caustic soda. The copper is thus precipitated upon the iron 
 by slow voltaic action, the zinc being the attacked metal. By adding a 
 solution of stannate of soda to the alkaline copper solution, a deposit of 
 bronze may be obtained. 
 
 243. OXIDES OF COPPER. Two oxides of copper are well known in the 
 separate state, viz., the suboxide CugO, and the oxide CuO. Another 
 oxide, Cu 4 0, has been obtained in a hydrated state, and there is some 
 evidence of the existence of an acid oxide. 
 
 The black oxide of copper (cupric oxide), CuO, is the black layer which 
 is formed upon the surface of the metal when heated in air. It is em- 
 ployed by the chemist in the ultimate analysis of organic substances by 
 combustion (p. 73), being prepared for this purpose by acting upon 
 copper with nitric acid to convert it into nitrate of copper (p. 126), and 
 heating this to dull redness in a rough vessel made of sheet copper, when 
 it leaves the black oxide ; CuO . JST0 5 = N0 4 + + CuO. At a higher 
 temperature the oxide fuses into a very hard mass ; but it cannot be de- 
 composed by heat. Oxide of copper absorbs water easily from the air, 
 but it is not dissolved by water ; acids, however, dissolve it, forming the 
 
344 SULPHATE OF COPPER. 
 
 salts of copper, whence the use of oil of vitriol and nitric acid for cleans- 
 ing the tarnished surface of copper ; a blackened coin, for example, im- 
 mersed in strong nitric acid, and thoroughly washed, becomes as bright as 
 when freshly coined. Silicic acid dissolves oxide of copper at a high tem- 
 perature, forming silicate of copper, which is taken advantage of in pro- 
 ducing a fine green colour in glass. 
 
 Red oxide or suboxide of copper (cuprous oxide), Cu/), is formed when 
 a mixture of 5 parts of the black oxide with 4 parts of copper filings is 
 heated in a closed crucible. It may also be prepared by boiling a solution 
 of sulphate of copper with a solution containing sulphite of soda and car- 
 bonate of soda, in equal quantities, when the suboxide of copper is preci- 
 pitated as a reddish yellow powder, which should be washed, by decanta- 
 tion, with boiled water 
 
 2(CuO.S0 3 ) + 2(NaO.C0 2 ) + NaO . S0 2 = 
 Cu 2 + 3(NaO.S0 3 ) + 2C0 2 . 
 
 The suboxide of copper is a feeble base, but its salts are not easily ob- 
 tained by direct union with acids, for these generally decompose it into 
 metallic copper and oxide of copper, which combines with the acid. In 
 the moist state it is slowly oxidised by the air. Ammonia dissolves the 
 suboxide, forming a solution which is perfectly colourless until it is 
 allowed to come into contact with air, when it assumes a fine blue colour, 
 becoming converted into an ammoniacal solution of the oxide. If the 
 blue solution be placed in a stoppered bottle (quite filled with it) with a 
 strip of clean copper, it will gradually become colourless, the oxide being 
 again reduced to suboxide, a portion of the copper being dissolved. When 
 copper filings are shaken with ammonia in a bottle of air, the same blue 
 solution is obtained, the oxidation of the copper being attended with a 
 simultaneous oxidation of a portion of the ammonia, and its conversion 
 into nitrous acid, so that white fumes of nitrite of ammonia are formed 
 in the upper part of the bottle. If the blue solution be poured into a 
 large quantity of water, a light blue precipitate of hydrated oxide of 
 copper is obtained. The ammoniacal solution of oxide of copper has the 
 unusual property of dissolving paper, cotton, tow, and other varieties of 
 cellulose, this substance being reprecipitated from the solution on adding 
 an acid. 
 
 Suboxide of copper, added to glass, imparts to it a fine red colour, 
 which is turned to account by the glass-maker. 
 
 Quadrant-oxide of copper, Cu 4 0, has been obtained in combination 
 with water by the action of protochloride of tin and potash upon a salt of 
 copper. 
 
 Cupric acid is believed to be formed when metallic copper is fused with 
 nitre and caustic potash. The mass yields a blue solution in water, which 
 is very easily decomposed, with evolution of oxygen and precipitation of 
 oxide of copper. The existence of an unstable oxide of copper, containing 
 more than one equivalent of oxygen, is also rendered probable by the cir- 
 cumstance, that oxide of copper acts like binoxide of manganese in facili- 
 tating the disengagement of oxygen from chlorate of potash by heat 
 (page 14). 
 
 244. Sulphate of copper. The beautiful prismatic crystals known as 
 blue vitriol, blue stone, blue copperas, or sulphate of copper, have been 
 already mentioned as formed in the preparation of sulphurous acid (p. 196), 
 
SULPHATE OF COPPER. 345 
 
 by dissolving copper in oil of vitriol, a process which is occasionally em- 
 ployed for the manufacture of .this salt. A considerable supply of the 
 sulphate is obtained as a secondary product in the process of silver-refin- 
 ing (p. 207). 
 
 The sulphate of copper is also manufactured by roasting copper pyrites 
 (FeCuS 2 ) with free access of air, when it becomes partly converted into a 
 mixture of sulphate of copper with sulphate of iron 
 
 FeCuS 2 + 8 = FeO.S0 3 + CuO . S0 3 . 
 
 The sulphate of iron, however, is decomposed by the heat, losing its 
 sulphuric acid, and leaving simply peroxide of iron (see p. 322). When 
 the roasted mass is treated with water, the oxide of iron is left undis- 
 solved, but the sulphate of copper enters into solution, and may be ob- 
 tained in crystals by evaporation. 
 
 These crystals, as they are found in commerce, are usually opaque, 
 but if they are dissolved in hot water and allowed to crystallise slowly, 
 they become perfectly transparent, and have then the composition ex- 
 pressed by the formula CuO . S0 3 + 5HO. If the crystals be heated to 
 the temperature of boiling water, they lose four-fifths of their water, and 
 crumble down to a greyish white powder, which has the composition 
 CuO . S0 3 + HO, and if this be moistened with water, it becomes very 
 hot and resumes its original blue colour. The whitish opacity of the 
 ordinary crystals of blue stone is due to the absence of a portion of the 
 water of crystallisation. 
 
 The fifth equivalent of water can be expelled only at a temperature of 
 nearly 400 F., and is therefore generally called water of constitution (see 
 p. 49), the formula of the crystals being then written CuO . S0 3 . HO + 4Aq. 
 The crystals dissolve in four parts of cold and two parts of boiling water. 
 The solution reddens litmus. 
 
 The sulphate of copper- is largely employed by the dyer and calico- 
 printer, and in the manufacture of pigments. It is also occasionally used 
 in medicine, in the electrotype process, and in galvanic batteries. 
 
 If a solution of sulphate of copper be mixed with an excess of solution 
 of potash, a blue precipitate of hydrated oxide of copper (CuO . HO) is 
 produced. On boiling this in the liquid, it loses its water and becomes 
 black oxide. The paint known as blue verditer is hydrated oxide of 
 copper obtained by decomposing nitrate of copper with hydrate of lime. 
 
 When ammonia is added to solution of sulphate of copper, a basic 
 sulphate is first precipitated, which is dissolved by an excess of ammonia 
 to a dark blue fluid. On allowing this to evaporate, dark blue crystals of 
 ammonia-sulphate of copper, CuO . S0 3 , 2NH 3 , HO, are deposited. - They 
 lose their ammonia when exposed to the air. 
 
 A basic sulphate of copper, CuO . S0 3 , 4(CuO . HO), constitutes the 
 mineral brochantite. 
 
 Sulphate of copper cannot easily be separated by crystallisation from the 
 sulphates of iron, zinc, and magnesia, because it forms double salts with 
 them, which contain, like those sulphates, 7 equivalents of water. An in- 
 stance of this is seen in the black vitriol obtained from the mother-liquor 
 of the sulphate of copper at Mansfeld, and forming bluish black crystals 
 isomorphous with green vitriol, FeO . S0 3 . 7HO. The formula of black 
 vitriol may be written 
 
 (CuMgFeMnCoNi)O . S0 3 . 7IIO 
 
346 CUPROUS CHLORIDE. 
 
 the six isomorphous metals being interchangeable without altering the 
 general character of the salt. 
 
 Arsenite of copper or Scheele's green has been mentioned at p. 245. 
 
 The basic phosphates of copper compose the minerals tagalite and 
 libethenite. 
 
 The basic carbonates of copper have been noticed as forming the very 
 beautiful minerals blue malachite, or chessylite, and green mal'achite. 
 
 Mineral green (CuO . C0 2 , CuO . HO) has the same composition as 
 green malachite, and is prepared by mixing hot solutions of carbonate of 
 soda and sulphate of copper. When boiled in the liquid, it is gradually 
 converted into black oxide of copper. 
 
 Silicates of copper are found in the minerals dioptase, or emerald copper, 
 and chrysocolla. 
 
 245. Chlorides of copper. The chloride of copper (cupric chloride) 
 (CuCl) is produced by the direct union of its elements, when it forms a 
 brown mass, which fuses easily, and is decomposed into chlorine and sub- 
 chloride of copper, the latter being afterwards converted into vapour. 
 When dissolved in water, it gives a solution which is green when concen 
 trated, and becomes blue on dilution. The hydrated chloride of copper 
 is readily prepared by dissolving the black oxide in hot hydrochloric 
 acid, and allowing the solution to crystallise ; it forms green needle-like 
 crystals (CuCl. 2HO). A solution of chloride of copper in alcohol burns 
 with a splendid green flame, and the chloride imparts a similar colour to 
 a gas flame. 
 
 Oxychloride of coppei" (CuCl . 3CuO . 4HO) is found at Atacama in 
 prismatic crystals, and is called atacamite. The paint Brunswick green 
 has the same composition, and is made by moistening copper with solu- 
 tion of hydrochloric acid or of sal-ammoniac, and exposing it to the air in 
 order that it may absorb oxygen 
 
 Cu 4 + HC1 + 3HO + 4 = CuCl.3CuO.4HO. 
 
 The Brunswick green of the shops frequently consists of a mixture of 
 Prussian blue, chromate of lead, and sulphate of baryta. 
 
 Subchloride of copper (cuprous chloride}, Ci^Cl, is formed when fine 
 copper turnings are shaken with strong hydrochloric acid in a bottle of 
 air (Cu 2 + HC1 + = Cu 2 Cl + HO). The subchloride dissolves in the 
 excess of hydrochloric acid, forming a brown solution, from which water 
 precipitates the white subchloride of copper, for this is one of the few 
 chlorides insoluble in water. When exposed to light, it assumes a purplish 
 grey tint. It may be obtained in larger quantity by dissolving 5 parts 
 of black oxide of copper in hydrochloric acid, and boiling with 4 parts 
 of fine copper turnings, the brown solution being afterwards precipitated 
 by water. If the solution be moderately diluted and set aside, it deposits 
 tetrahedral crystals of the subchloride. Ammonia (free from air) dissolves 
 the subchloride to a colourless liquid, which becomes dark-blue by 
 contact with air, absorbing oxygen. The ammoniacal solution of sub- 
 chloride of copper is employed as a test for acetylene (p. 84), which 
 gives a red precipitate with it. The solution may be preserved in a 
 colourless state by keeping it in a well-stoppered bottle, quite full, with 
 strips of clean copper. When copper, in a finely divided state, is 
 boiled with solution of hydrochlorate of ammonia, the solution deposits 
 
COPPER AND SULPHUR. 347 
 
 colourless crystals of the salt Cu 2 Cl . NHg. If the solution of this salt 
 be exposed to the air, blue crystals are deposited, having the formula 
 Cu 2 Cl . NH 3 + CuCl . NH 3 + HO, and on further exposure, a compound 
 of this last salt with hydrochlorate of ammonia is deposited. The solu- 
 tion of subchloride of copper in hydrochloric acid is employed for 
 absorbing carbonic oxide in the analysis of gaseous mixtures (p. 252). 
 When this solution is exposed to air it absorbs oxygen, and deposits the 
 oxychloride of copper. A strong solution of hydrochlorate of ammonia 
 or of chloride of potassium readily dissolves the cuprous chloride, even 
 in the cold, forming soluble double chlorides. The solution in chloride 
 of potassium does not absorb oxygen quite so easily as that in hydro- 
 chlorate of ammonia. 
 
 246. Sulphides of copper. Copper has a very marked attraction for 
 sulphur, even at the ordinary temperature. A bright surface of copper 
 soon becomes tarnished by contact with sulphur, and hydrosulphuric acid 
 blackens the metal. Finely divided copper and sulphur combine slowly 
 at the ordinary temperature, and when heated together, they combine with 
 combustion. A thick copper wire burns easily in vapour of sulphur 
 (p. 189). Copper is even partly converted into sulphide when boiled 
 with sulphuric acid, as in the preparation of sulphurous acid gas. This 
 great attraction of copper for sulphur is taken advantage of in the process 
 of kernel-roasting for extracting the copper from pyrites containing as 
 little as 1 per cent, of the metal. The pyrites is roasted in large heaps 
 (p. 186) for several weeks, when a great part of the iron is converted 
 into peroxide, and the copper remains combined with sulphur, forming 
 a hard kernel in the centre of the lumps of ore. This kernel contains 
 about 5 per cent, of copper, and can be smelted with economy. Children 
 are employed to detach the kernel from the shell, which consists of 
 peroxide of iron and a little sulphate of copper, which is washed out with 
 water. 
 
 The subsulphide of copper (Cu 2 S) has been mentioned among the ores 
 of copper, and among the furnace products in smelting, when it is some- 
 times obtained in octahedral crystals. It is not attacked by hydrochloric 
 acid, but nitric acid dissolves it readily. Copper pyrites, is believed to 
 contain the copper in the form of subsulphide, its true formula being 
 Cu 2 S . Fe 2 S 3 ; for if the copper be present as sulphide, CuS, the iron must 
 be present as protosulphide, and the mineral would have the formula 
 CuS . FeS. Now, FeS is easily attacked by dilute sulphuric or hydro- 
 chloric acid, which is not the case with copper pyrites. Nitric acid, how- 
 ever, attacks it violently. 
 
 Sulphide of copper (CuS) occurs in nature as indigo-copper or blue 
 copper, and may be obtained as a black precipitate by the action of 
 hydrosulphuric acid upon solution of sulphate of copper. When this 
 precipitate is boiled with sulphur and hydrosulphate of ammonia > it is 
 dissolved in small quantity, and the solution on cooling deposits fine 
 scarlet needles containing a higher sulphide of copper combined with 
 hydrosulphate of ammonia. 
 
 A pentasulphide of copper (CuS 5 ) is obtained by decomposing sulphate 
 of copper with pentasulphide of potassium ; it forms a black precipitate, 
 distinguished from the other sulphides of copper by its solubility in car- 
 bonate of potash. 
 
 The sulphides of copper, when exposed to air in the presence of water, 
 
348 CHARACTERS OF LEAD. 
 
 are slowly oxidised and converted into sulphate of copper, which is dis- 
 solved by the water. It appears to be in this way that the Hue water of 
 the copper mines is formed. - 
 
 Phosphide of copper (Cu 3 P), obtained as a black powder by boiling 
 solution of sulphate of copper with phosphorus, has been already men- 
 tioned as a convenient source of phosphuretted hydrogen. Another phos- 
 phide, obtained by passing vapour of phosphorus over finely divided 
 copper at a high temperature, is employed in Abel's composition for 
 magneto-electric fuzes, in conjunction with subsulphide of copper and 
 chlorate of potash. 
 
 Silicon may be made to unite with copper by strongly heating finely 
 divided copper with silicic acid and charcoal. A bronze-like mass is thus 
 obtained, containing about 5 per cent, of silicon. It is said to rival iron 
 in ductility and tenacity, and fuses at about the same temperature as 
 bronze. 
 
 247. Equivalent and atomic weights of copper. When pure black oxide 
 of copper is heated in hydrogen, 39*5 parts by weight of the oxide give 
 up 8 parts (one equivalent) of oxygen, to form water with the hydrogen, 
 leaving 31 '5 parts of copper. If the black oxide, then, be regarded as 
 containing single equivalents of its elements, the equivalent of copper 
 will be 31*5 ; but if the red oxide (which contains twice as much copper 
 in proportion to the oxygen) be supposed to contain single equivalents, 
 that of copper would be 63. The isomorphism of the black oxide of 
 copper with the protoxide of iron (FeO) and the oxide of zinc (ZnO), 
 which it replaces in their sulphates without alteration of crystalline form, 
 leads to the belief that it resembles them in composition, and that the 
 equivalent weight of copper is 31*5. 
 
 That copper is a diatomic element, i.e., that its atomic weight is twice 
 its equivalent weight (or ru = 63), is shown by its specific heat, and by 
 the constitution of its compounds. Thus, the nitride of copper, N6u 3 , 
 obtained by the action of ammonia gas upon heated oxide of copper, re- 
 presents ammonia (NH 3 ), in which three atoms of copper occupy the place 
 of three atoms of hydrogen. The atomic formulae for some of the more 
 important compounds of copper would be red oxide Ou. 2 O, black oxide 
 6uO, subsulphide 6u 2 S, sulphide hi&, cuprous chloride (subchloride) 
 <juCl, cupric chloride 6uCl 2 . 
 
 LEAD. 
 
 248. Lead owes its usefulness in the metallic state chiefly to its soft- 
 ness and fusibility. The former quality allows it to be easily rolled into 
 thin sheets, and to be drawn into the form of tubes or pipes ; it is indeed 
 the softest of the metals in common use, and, at the same time, the least 
 tenacious, so that it can only be drawn with difficulty into thin wire, and 
 is then very easily broken. The ease with which it makes a dark streak 
 upon paper shows how readily minute particles of the metal may be 
 abraded. 
 
 In fusibility it surpasses all the other metals commonly employed in 
 the metallic state, except tin, for it melts at 617 F., and this circum- 
 stance, taken in conjunction with its high specific gravity (H'4), parti- 
 cularly adapts it for the manufacture of shot and bullets. For one of its 
 extensive uses, however, as a covering for roofs, it would be better suited 
 
SMELTING OF GALENA. 349 
 
 if it were lighter and less fusible, for in case of fire in houses so roofed, 
 the fall of the molten lead frequently aggravates the calamity. 
 
 With the exception, perhaps, of the ores of iron, none is more abundant 
 in this country than the chief ore of lead, galena, a sulphide of lead 
 (PbS). This ore might at the first glance be mistaken for the metal 
 itself, from its high specific gravity and metallic lustre. It is found 
 forming extensive veins in Cumberland, Derbyshire, and Cornwall, 
 traversing a limestone rock in the two first counties, and a clay slate in 
 the last. Spain also furnishes large supplies of this important ore. 
 
 Galena presents a beautiful crystalline appearance, being often found 
 in large isolated cubes, which readily cleave or split up in directions 
 parallel to their faces. Blende (sulphide of zinc) and copper pyrites 
 (sulphide of copper and iron) are frequently found in the same vein with 
 galena, and it is usually associated with quartz (silica), heavy-spar (sul- 
 phate of baryta), or fluor spar (fluoride of calcium). Considerable 
 quantities of sulphide of silver are often present in galena, and in many 
 specimens the sulphides of bismuth and antimony are found. 
 
 Though the sulphide is the most abundant natural combination of lead, 
 it is by no means the only form in which this metal is found. The metal 
 itself is occasionally met with, though in very small quantity, and the 
 carbonate of lead (PbO . C0 2 ), white lead ore, forms an important ore in 
 the United States and in Spain. The sulphate of lead (PbO . S0 3 ) is also 
 found in Australia, and is largely imported into this country to be smelted. 
 
 249. The extraction of lead from galena is effected by taking advantage 
 of the circumstance, that when a combination of a metal with oxygen is 
 raised to a high temperature in contact with a sulphide of the same metal, 
 the oxygen and sulphur unite, and the metal is liberated. 
 
 The ore having been separated by mechanical treatment as far as 
 possible from the foreign matters associated with it, is mixed with a small 
 proportion of lime, and spread over the hearth of a reverberatory furnace 
 (fig. 242), the sides of which are considerably inclined towards the centre, 
 so as to form a hollow for the reception of the molten lead. 
 
 During the first stage of the smelting process, the object is to roast the 
 ore with free access of air, exposing as large a surface as possible, on 
 
 Fig. 242. Furnace for smelting lead-ores. 
 
 which account the heat is kept below that at which galena fuses ; indeed, 
 during the first two hours, no fuel is thrown into the grate, sufficient heat 
 
350 SMELTING OF GALENA. 
 
 being radiated from the sides of the furnace, which have become red hot 
 during the smelting of the previous charge of ore. The ore is stirred from 
 time to time, to expose fresh surfaces to the action of the atmospheric oxygen. 
 The effect of this roasting is to convert a portion of the sulphide of lead 
 (PbS) into sulphate of lead (PbO . S0 3 ), whilst another portion loses its sul- 
 phur, which is evolved as sulphurous acid (S0 2 ), and acquires oxygen in its 
 stead, becoming converted into oxide of lead (PbO). A large proportion of the 
 galena, however, remains unoxidised. When the roasting is sufficiently 
 advanced, some fuel is thrown into the grate, some rich slags from previous 
 smeltings are thrown on to the hearth, the damper is slightly raised, and 
 the doors of the furnace are closed, so that the charge may be heated to 
 the temperature at which the oxide and sulphate of lead act upon the 
 unaltered sulphide, furnishing metallic lead, whilst the sulphur is ex- 
 pelled in the form of sulphurous acid. 
 
 Thus, PbS + 2PbO = Pb 3 + S0 2 , and 
 
 PbO.S0 3 + PbS = Pb a + 2S0 2 . 
 
 During this part of the operation, the contents of the hearth are con- 
 stantly raked up towards the fire-bridge, so as to facilitate the separa- 
 tion of the lead, and to cause it to run down into the hollow provided for 
 its reception. It is also found that the separation of the lead from the 
 slags is much assisted by occasionally throwing open the doors to chill the 
 furnace. After about four hours, the charge is reduced to a pretty fluid 
 condition, the lead having accumulated at the bottom of the depressed 
 portion of the hearth with the slag above it ; this slag consists chiefly of 
 the silicates of lime and oxide of lead, and would have contained a larger 
 proportion of the latter, if the lime had not been added as a flux at the 
 commencement of the operation. In order still further ,to reduce the 
 quantity of lead in the slag, a few more shovelfuls of lime are now thrown 
 into the hearth, together with a little small coal, the latter serving to 
 reduce to the metallic state the oxide of lead displaced by the lime from its 
 combination with the silicic acid. 
 
 But since silicate of lime is far less fusible than silicate of oxide of lead, 
 the effect of this addition of lime is to " dry up " the slags to a semi-solid 
 mass, and it will now be seen that if the whole of the lime had been added 
 at the commencement of the smelting, the diminished fusibility of the slag 
 would have opposed an obstacle to the separation of the metallic lead. 
 
 During the last hour or so, the temperature is very considerably raised, 
 and at the expiration of about six hours, when the greater portion of the 
 lead is thought to have separated, the slag is raked out through one of the 
 doors of the furnace, and the melted metal allowed to run out through a 
 tap-hole in front of the lowest portion of the hearth, into an iron basin, 
 from which it is ladled into pig-moulds. 
 
 The rich slags, together with the layer of subsulphide of lead (Pb 2 S) 
 which forms over the surface of the metal, are worked up again with a 
 fresh charge of ore. 
 
 In the smelting of galena a very considerable quantity of lead is carried 
 off in the form of vapour ; and in order to condense this, the gases from 
 the furnace are made to pass through flues, the aggregate length of which 
 is sometimes three or four miles, before being allowed to escape up the 
 chimney. When these flues are swept, many tons of lead are recovered 
 in the forms of oxide and sulphide. 
 
 In the north of England, the smelting of lead ores is now generally con- 
 
TKEATMENT OF HARD LEAD. 
 
 351 
 
 ducted in an economico-furnace (fig. 243), or small blast-furnace, instead of 
 m the reverberatory furnace described 
 above. Air is supplied to the furnace 
 through three blast-pipes (A), and the 
 lead-ore and fuel being charged in at B, 
 the lead runs into a cavity (C) at the 
 bottom of the furnace, whilst the slag 
 flows over into a reservoir (D) outside 
 the furnace. The charge is sprinkled 
 with water through the rose (E) fixed 
 just above the opening into the chim- 
 ney (F), to prevent it from being blown 
 away by the current of air. 
 
 250. Some varieties of lead, particu- 
 larly those smelted from Spanish ores, 
 are known as hard lead, their hardness 
 being chiefly due to the presence of 
 antimony,* and since this hardness in- 
 terferes materially with some of the 
 uses of the metal, such lead is generally 
 subjected to an improving or calcining 
 process, in which the impurities are 
 oxidised and removed, together with 
 a portion of the lead, in the dross. To 
 effect this, six or eight tons of the hard lead are fused in an iron pot 
 (P, fig. 244), and trans- 
 ferred to a shallow cast- 
 iron pan (C) measuring 
 about ten feet by five. 
 In this pan, which is set 
 in the hearth of a rever- 
 beratory furnace, and is 
 about eight inches deep 
 nearest the grate, and 
 nine inches at the other 
 end, the lead is kept in 
 fusion by the flame which 
 traverses it from the grate 
 G to the flue F, for a 
 period varying with the 
 degree of impurity, some 
 specimens being found 
 sufficiently soft after a 
 single day's calcination, 
 
 Fig. 243. 
 
 Fig. 244. 
 
 The following analyses illustrate the composition of hard lead : 
 
 
 English. 
 
 Spanish. 
 
 Lead, 
 
 99*27 
 
 95-8! 
 
 Antimony, . 
 Copper, .... 
 
 0-57 
 0-12 
 0-04 
 
 3-66 
 0-32 
 0-21 
 
 
 
 
 
 100.00 
 
 100-00 
 
352 
 
 PATTINSON'S DESILVEJJISING PKOCESS. 
 
 whilst others must be kept in a state of fusion for three or four weeks. 
 The workman judges of the progress of the operation by a peculiar flak^r 
 crystalline appearance assumed by a small sample on cooling. When 
 sufficiently purified, the metal is run off and cast into pigs. 
 
 At first sight, it is not intelligible how antimony should be removed 
 from lead by calcination, since lead is the more easily oxidised metal. 
 The result must be ascribed to the tendency of antimony to form antimonic 
 acid (Sb0 5 ) which combines with the oxide of lead. The dross (antimoniatc 
 of lead) formed in this process, when reduced to the metallic state, yields 
 an alloy of lead with 30 or 40 per cent, of antimony, which is much used 
 for casting type-furniture for printers. 
 
 251. Extraction of silver from lead. The lead extracted from galena 
 often contains a sufficient quantity of silver to allow of its being profitably 
 extracted. Previously to the year 1829 this was practicable only when 
 the lead contained more than 1 1 oz. of silver per ton, for the only process 
 then known for effecting the separation of the two metals, was that of 
 cupellation, which necessitates the conversion of the whole of the lead into 
 oxide, which has then to be separated from the silver and again reduced 
 to the metallic state, thus consuming so large an amount of labour, that a 
 considerable yield of silver must be obtained to pay for it. 
 
 By the simple and ingenious operation known as Pattinsorfs desilverising 
 process, a very large amount of the lead can be at once separated in the 
 metallic state with little expenditure of labour, thus leaving the remainder 
 
 Fig. 245. Pattinson's desilverising process. 
 
 sufficiently rich in the more precious metal to defray the cost of the far 
 more expensive process of cupellation, so that 3 or 4 oz. of silver per ton 
 can be extracted with profit. Pattinson founded his process upon the 
 
CUPELLATION OF ARGENTIFEROUS LEAD. 
 
 353 
 
 observation that when lead containing a small proportion of silver is 
 melted and allowed to cool, being constantly stirred, a considerable quantity 
 of the lead separates in the form of crystals containing a very minute pro- 
 portion of silver, almost the whole of this metal being left behind in the 
 portion still remaining liquid. 
 
 Eight or ten cast-iron pots, set in brickwork, each capable of holding 
 about 6 tons of lead, are placed in a row, with a fire-place underneath each 
 of them (fig. 245). Suppose that there are ten pots numbered consecutively, 
 tjiat on the extreme left of the workman being No. 1, and that on his 
 extreme right No. 10. About 6 tons of the lead containing silver are 
 melted in pot No. 5, the metal skimmed, and the fire raked out from 
 beneath so that the pot may gradually cool, its liquid contents being con- 
 stantly agitated with a long iron stirrer. As the crystals of lead form, 
 they are well drained in a perforated ladle (about 10 inches wide and 5 
 inches deep) and transferred to pot No. 4. When about ths of the 
 metal have thus been removed in the crystals, the portion still remaining 
 liquid, which retains the silver, is ladled into pot No. 6, and the pot No. 
 5, which is now empty, is charged with fresh argentiferous lead to be 
 treated in the same manner. 
 
 When pots Nos. 4 and 6 have received, respectively, a sufficient quantity 
 of the crystals of lead and of the liquid part rich in silver, their contents 
 are subjected to a perfectly similar process, the crystals of lead being 
 always passed to the left, and the rich argentiferous alloy to the right. 
 As the final result of these operations, the pot No. 10, to the extreme 
 right, becomes filled with a rich alloy of lead and silver, sometimes con- 
 taining 300 ounces of silver to the ton, whilst pot No. 1, to the extreme 
 left, contains lead in which there 
 is not more than % ounce of silver 
 to the ton. This lead is cast into 
 pigs for the market. The. ladle 
 used in the above operation is 
 kept hot by a small temper pot 
 containing melted lead. A ful- 
 crum is provided at the edge of 
 each pot, for resting the ladle 
 during the shaking of the crystals 
 to drain off the liquid metal. 
 Any copper present in the lead is 
 also left with the silver in the 
 liquid portion. 
 
 252. In order to extract the 
 silver from the rich alloy, it is 
 subjected to a process of refining, 
 ''or cupellation, which is founded 
 upon the oxidation suffered by 
 lead when heated in air, and upon 
 the absence of any tendency on 
 the part of silver to combine 
 directly with oxygen. 
 
 The refinery, or cupelling fur- 
 nace (fig. 246), in which this 
 operation is performed, is a reverberatory furnace, the hearth of which con- 
 
 Fig. 246. Cupellation furnace. 
 
354 EXTRACTION OF LEAD IN THE LABORATORY. 
 
 sists of a cupel (C), made by ramming moist powdered bone ashes mixed with 
 a little wood-ash into an oval iron frame about 4 inches deep, and provided 
 with four cross-bars at the bottom, each about 4 inches wide. When this 
 frame has been well filled with bone ash, part of it is scooped out, so as 
 to leave the sides about two inches thick at the top, and three inches at 
 the bottom, the bone-ash being left about one inch thick above the iron 
 cross-bars. 
 
 The cupel, which is about 4 feet long by 2 \ feet wide, is fixed so that 
 the flame from the grate (G) passes across it into the chimney (B), and at 
 one end, the nozzle (N) of a blowing apparatus directs a blast of air over the 
 surface of the contents of the cupel. The latter is carefully dried by a 
 gradually increasing heat, and is then heated to redness; the alloy of 
 lead and silver, having been previously melted in an iron pot (P) fixed 
 by the side of the furnace, is ladled in through a gutter until the cupel is 
 nearly filled with it ; a film of oxide soon makes its appearance upon 
 the surface of the lead, and is fused by the high temperature. When 
 the blast is directed upon the surface, it blows off this film of oxide, and 
 supplies the oxygen for the formation of another film upon the clean 
 metallic surface thus exposed. A part of the oxide of lead or litharge 
 thus formed is at first absorbed by the porous material of the cupel, but 
 the chief part of it is forced by the blast through a channel cut for the 
 purpose in the opposite end to that at which the blast enters, and is re- 
 ceived, as it issues from A, in an iron vessel placed beneath the furnace. 
 
 In proportion as the lead is in this manner removed from the cupel, 
 fresh portions are supplied from the adjoining melting-pot, and the pro- 
 cess is continued until about 5 tons of the alloy have been added. 
 
 The cupellation is not continued until the whole of the lead has been 
 removed, but until only 2 or 3 cwts. of that metal are left in combination 
 with the whole of the silver (say 1000 ounces) contained in the 5 tons of 
 alloy. The metal is run out through a hole made in the bottom of the 
 cupel, which is then again stopped up so that a fresh charge may be in- 
 troduced. 
 
 The fumes of oxide of lead which are freely evolved during this pro- 
 cess are carried oif by a hood and chimney (H) situated opposite to the 
 blast of air. 
 
 When three or four charges have been cupelled, so as to yield from 
 3000 to 5000 ounces of silver, alloyed with 6 or 8 cwts. of lead, the removal 
 of the latter metal is completed in another cupel, since some of the silver 
 is carried off with the last portions of litharge. 
 
 The appearances indicating the removal of the last portion of lead are 
 very striking ; the surface of the molten metal, which has been hitherto 
 tarnished, becomes iridescent as the film of oxide of lead thins off, and 
 afterwards resplendently bright, and when the cake of refined silver is 
 allowed to cool, it throws up from its surface a variety of fantastic arbores- 
 cent excrescences, caused by the escape of oxygen which has been mechan- 
 cally absorbed by the fused silver, and is given off during solidification. 
 
 The litharge obtained from the cupelling furnaces is reduced to the 
 metallic state by mixing it with small coal, and heating it in a furnace 
 similar to that employed in smelting galena. 
 
 253. On the small scale, lead may easily be extracted from galena by mixing 300 
 grains with 450 grains of dried carbonate of soda and 20 grains of charcoal, intro- 
 ducing the mixture into a crucible, and placing in it two tenpenny nails, heads down- 
 wards. The crucible is covered and heated in a moderate fire for about half an hour. 
 
USES OF LEAD. 
 
 355 
 
 (A charcoal fire in the small furnace, fig. 117, p. 107, will suffice.) The remainder 
 of the nails is carefully removed from the liquid mass, which is then allowed to cool, 
 the crucible broken, and the lead extracted and weighed. To ascertain if it contains 
 silver, the button is placed in a small bone-ash cupel (fig. 247), heated m a muffle 
 (fig. 248) until the whole of the lead is oxidised, and 
 absorbed by the bone-ash of the cupel, leaving the 
 minute globule of silver. 
 
 Small globules of lead may be conveniently cupelled 
 on charcoal before the blowpipe, by pressing some bone- 
 ash into a cavity scooped in the charcoal, placing the Fig. 247. 
 lead upon its surface, and exposing it to a good oxidising 
 
 flame (p. 98) as long as it decreases in size. If any copper be present, the bone- 
 ash will show a green stain after cooling. Pure lead gives a yellow stain. In the 
 above process the sulphur of the galena is removed, 
 partly by the sodium of the carbonate, and partly 
 by the iron of the nails, the excess of carbonate of 
 soda serving to flux any silica with which the 
 galena may be mixed. 
 
 254. Uses of lead. The employment of 
 this metal for roofing, &c., has been already 
 noticed. Its fusibility adapts it for casting 
 type for printing, but it would be far too soft 
 for this purpose; accordingly, type-metal con- 
 sists of an alloy of 4 parts of lead with 1 of 
 antimony. A similar alloy is used for the 
 bullets contained in shrapnel shells, since 
 bullets of soft lead would be liable to be 
 jammed together, and would not scatter so 
 well on the explosion of the shell. On the 
 other hand, rifle-bullets are made of very pure 
 soft lead, in order that they may more easily 
 take the grooves of the rifle. 
 
 Small shot are made of lead to which about 
 40 Ibs. of arsenic per ton has been added. 
 The arsenic dissolves in the lead, hardening 
 it and causing it to form spherical drops 
 when chilled. The fluid metal is poured 
 through a sort of colander fixed at the top of a lofty tower (or at the mouth 
 of a deserted coal-shaft), and the minute drops into which it is thus divided 
 are allowed to fall into a vessel of water, after fiaving been chilled by the 
 air in their descent. They are afterwards sorted, and polished in revolving 
 barrels containing plumbago. If too little arsenic is employed, the shot 
 are elongated or pyriform ; and if the due proportion has been exceeded, 
 their form is flattened or lenticular. 
 
 Common solder is an alloy of equal weights of lead and tin, which is 
 more fusible than either metal separately. Other alloys containing lead 
 will be noticed in their proper places. 
 
 Leaden vessels are much used in manufacturing chemistry, on account 
 of the resistance of this metal to the action of acids. Neither concen- 
 trated sulphuric, hydrochloric, nitric, or hydrofluoric acid, will act upon 
 lead at the ordinary temperature. The best solvent for the metal is nitric 
 acid of sp. gr. 1'2, since the nitrate of lead, being insoluble in an acid of 
 greater strength, would be deposited upon the metal, which it would pro- 
 tect from further action. 
 
 Lead is easily corroded in situations where it is brought in contact with 
 air highly charged with carbonic acid, when it absorbs oxygen, forming 
 
 z2 
 
 Fig. 248. 
 
356 OXIDES OF LEAD LITHARGE. 
 
 oxide of lead, which combines with carbonic acid and water to produce the 
 basic carbonate of lead (PbO . C0 2 , PbO . HO). The lead of old coffins 
 is often found converted into a white earthy-looking brittle mass of basic 
 carbonate, with a very thin film of metallic lead inside it. 
 
 When lead is exposed to the joint action of air and the acetic acid con- 
 tained in beer, wine, cider, &c., it becomes converted into acetate of lead 
 or sugar of lead, which is very poisonous. Hence the accidents arising 
 from the reprehensible practice of sweetening cider by keeping it in con- 
 tact with lead, and from the accidental presence, in beer and wine bottles, 
 of shot which have been employed in cleaning them. The action of water 
 upon leaden cisterns has been already noticed. Contact with air and sea- 
 water soon converts lead into oxide and chloride. 
 
 255. OXIDES OP LEAD. Four compounds of lead with oxygen are 
 known 
 
 Suboxide of lead, Pb 2 
 Oxide PbO 
 
 Eed oxide Pb 3 4 
 
 Peroxide Pb0 2 . 
 
 The bright surface of lead soon tarnishes when exposed to the air, 
 becoming coated with a dark film, which is believed to consist of suboxide 
 of lead. In a very finely divided state, lead takes fire when thrown into 
 the air, and is converted into oxide of lead. 
 
 The lead pyrophorus, for exhibiting the spontaneous combustion of lead, is prepared 
 by placing some tartrate of lead in a glass tube closed at one end (fig. 249), drawing 
 the tube out to a narrow neck near the open end, and 
 holding it nearly horizontally, whilst the iprtrate of lead 
 is heated with a gas or spirit flame as long as any fumes 
 are evolved ; the neck is then fused with a blowpipe flame 
 and drawn off. The tartrate of lead (2PbO . C 8 H 4 10 ), 
 when heated, leaves a mixture of metallic lead with char- 
 coal, which prevents it from fusing into a compact mass. 
 This mixture may be preserved unchanged in the tube 
 for any length of time ; but when the neck is broken off 
 and the contents scattered into the air, they inflame at 
 once, producing thick fumes of oxide of lead. Tartrate 
 of lead is prepared by adding ammonia to solution of 
 Fig. 249. tarfciric acid constantly stirred, until the precipitate of 
 
 bitartrate of ammonia at first formed is just redissolved, 
 
 and precipitating the liquid with solution of acetate of lead. The precipitated tar- 
 trate of lead is collected upon a filter, washed several times, and dried at a gentle 
 heat. 
 
 Oxide or protoxide of lead is prepared on a large scale by heating lead 
 in air. When the metal is only moderately heated, the oxide forms a 
 yellow powder, which is known in commerce as massicot, but at a higher 
 temperature the oxide melts, and on cooling forms a brownish scaly mass 
 which is called litharge (Ai'0os, stone ; apyvpos, silver), probably because 
 that obtained by the alchemists would always furnish a considerable pro- 
 portion of silver, which was present in most samples of lead before the 
 introduction of Pattinson's process. The litharge of commerce often has 
 a red colour, caused by the presence of some red oxide of lead. When 
 heated to dull redness, litharge assumes a dark brown colour, and becomes 
 .yellow on cooling. At a bright red heat it fuses, and readily attacks clay 
 crucibles, forming a fusible silicate of lead, and soon perforating the sides. 
 

 MANUFACTURE OF RED LEAD. 357 
 
 When boiled with distilled water, litharge is dissolved in small quantity, 
 yielding a solution which is decidedly alkaline, and becomes turbid when 
 exposed to the air, absorbing carbonic acid, and depositing carbonate of 
 lead. The presence of a small quantity of saline matter in the water 
 hinders the solution of the oxide, but organic matter, and especially sugar, 
 favours it. Two definite white hydrates of oxide of lead, HO . 2PbO and 
 HO . 3PbO, may be obtained by precipitating solutions of lead with the 
 alkalies. Oxide of lead is a powerful base, and has a strong tendency to 
 form basic salts. Hot solutions of potash and soda dissolve it readily, 
 and deposit it in pink crystals on cooling. 
 
 Litharge, from its easy combination with silicic acid at a high tempera- 
 ture, is much used in the manufacture of glass, and in glazing earthenware. 
 The assayer also employs it as a flux. A mixture of litharge with lime 
 is sometimes applied to the hair, which it dyes of a purplish-black colour, 
 due to the formation of sulphide of lead from the sulphur existing in hair. 
 Dhil mastic, used by builders in repairing stone, is a mixture of 1 part of 
 massicot with 10 parts of brickdust, and enough linseed oil to form a 
 paste ; it sets into a very hard mass, which is probably due partly to the 
 formation of silicate of lead, and partly to the drying of the linseed oil by 
 oxidation favoured by the oxide of lead. 
 
 Red lead or minium is prepared by heating massicot in air to about 
 600 F., when it absorbs oxygen, and becomes converted into red lead. 
 The massicot for this purpose is prepared by heating lead in a reverberatory 
 furnace to a temperature insufficient to fuse the oxide which is formed, 
 and rejecting the first portions, which contain iron and other metals more 
 easily oxidisable than lead (as cobalt), as well as the last, which contain 
 copper and silver, less easily oxidised than lead. The intermediate pro- 
 duct is ground to a fine powder and suspended in water; the coarser 
 particles are thus separated from the finer, which are dried, and heated 
 on iron trays placed in a reverberatory furnace till the requisite colour 
 has been obtained. Minium is largely used in the manufacture of 
 glass, whence it is necessary that it should be free from the oxides 
 of iron, copper, cobalt, &c., which would colour the glass. It is also em- 
 ployed as a common red mineral colour, and in the manufacture of lucifer- 
 inatches. 
 
 When minium is treated with dilute nitric acid, nitrate of lead 
 (PbO . IsT0 5 ) is obtained in solution, and peroxide of lead (Pb0 2 ) is left 
 as a brown powder, showing that minium is probably a compound of the 
 oxide and peroxide of lead. The minium obtained by heating massicot 
 in air till no further increase of weight is observed, has the composition 
 2PbO . Pb0 2 or Pb 3 4 , which would appear to represent pure minium ; 
 commercial minium, however, has more frequently a composition corre- 
 sponding to 3PbO . Pb0 2 , but when this is treated with potash, PbO is 
 dissolved out, and 2PbO . Pb0 2 remains. Minium evolves oxygen at a 
 red heat, becoming PbO, hence the necessity for keeping the temperature 
 below 600 F. during its preparation. 
 
 Peroxide, or Unoxide, or puce oxide of lead, is found in the mineral 
 kingdom as heavy lead ore, forming black, lustrous, six-sided prisms. It 
 may be prepared from red lead by boiling it, in fine powder, with nitric 
 acid, diluted with five measures of water, washing and drying. The bin- 
 oxide of lead easily imparts oxygen to other substances ; sulphur, mixed 
 with it, may be ignited by friction, hence this oxide is a common ingre- 
 dient in lucifer-match compositions. Its oxidising property is frequently 
 
358 MANUFACTURE OF WHITE LEAD. 
 
 turned to account in the laboratory, for example, in absorbing sulphurous 
 acid from gaseous mixtures by converting it into sulphate of lead; 
 Pb0 2 + S0 2 = PbO . S0 3 . Binoxide of lead is not dissolved by dilute 
 acids and has no basic properties ; indeed, it is sometimes called plumbic 
 acid, for it combines with potash and soda when fused with their hydrates. 
 Plumbate of potash (KO . Pb0 2 . 3HO) has been crystallised from an 
 alkaline solution, but is decomposed by pure water. 
 
 256. White lead or ceruse is a carbonate of oxide of lead, or, strictly 
 speaking, a basic carbonate, a combination of carbonate of oxide of 
 lead (PbO . C0 2 ) with variable proportions of hydrated oxide of lead 
 (PbO . HO). This substance is a constant product of the corrosive action 
 of air and water upon the metal. Its formation is, of course, very much 
 encouraged by the presence of organic matters in a state of decay, which 
 evolve carbonic acid. 
 
 White lead is manufactured on the large scale by two processes, which 
 depend, however, upon the same principle; this may be stated as follows : 
 when oxide of lead is brought in contact with acetic acid (HO . C 4 H 3 3 ), 
 it displaces the water from the latter to form the acetate of lead (sugar of 
 lead, PbO . C 4 H 3 3 ). This salt is capable of combining with twice as 
 much oxide of lead as it at present contains, forming the tribasic acetate 
 of lead (3PbO . C 4 H 3 3 ), and if this be acted upon by carbonic acid, two- 
 thirds of the oxide of lead are converted into carbonate, whilst the neutral 
 acetate of lead (PbO . C 4 H 3 3 ) is left. 
 
 In the older of the two processes, commonly known as the Dutch pro- 
 cess, metallic lead, in the form of square gratings cast from the purest 
 lead, is placed over earthen pots containing a small quantity of common 
 vinegar ; a number of these pots being built up into heaps, together with 
 alternate layers of dung or spent tan, the heaps are entirely covered up 
 with the same material. The metal is thus exposed to conditions most 
 favourable to its oxidation, viz., a very warm and moist atmosphere pro- 
 duced by the fermentation of the organic matters composing the heap, 
 and the presence of a large quantity of acid vapour generated from the 
 acetic acid of the vinegar. The lead is therefore soon converted into 
 oxide, a portion of which unites with the acetic acid to form the tribasic 
 acetate of lead, which is then decomposed by the carbonic acid evolved 
 from the fermenting dung or tan, yielding carbonate of lead, which com- 
 bines with another portion of the oxide of lead and of water to form the 
 white lead. The neutral acetate of lead left after the removal of the oxide 
 of lead from the tribasic acetate, is now ready to take up an additional 
 quantity of the oxide, and the process is thus continued until, in the 
 course of a few weeks, the lead has become coated with a very thick crust 
 of white lead ; the heaps are then destroyed, the crust detached, washed, 
 to remove adhering acetate of lead, ground to a paste with water, and 
 dried. Eolled lead is not so easily converted as cast lead. 
 
 The newer process is a more direct application of the same principle, 
 for it consists in boiling acetic acid with an excess of litharge in order 
 to produce the tribasic acetate of lead, which is afterwards decomposed 
 by passing through it a current of carbonic acid obtained by combustion 
 or fermentation, or even by exhalation from the earth. The solution of 
 neutral acetate of lead is then again boiled with litharge, when tribasic 
 acetate is produced, and is again precipitated by the carbonic acid. The 
 precipitated carbonate of lead al\va} r s carries down with it a variable pro- 
 
CHLORIDE OF LEAD. 359 
 
 portion of the hydrated oxide of lead. This process is, of course, much 
 more rapid than the old one, and dispenses with the grinding which is so 
 injurious to the workmen ; but the white lead so produced, being crystal- 
 line, has less opacity or covering-power (body) than that obtained by the 
 Dutch method. 
 
 The usual composition of white lead is expressed by the formula 
 PbO . HO, 2(PbO . C0 2 ), though other basic carbonates of lead are often 
 mixed with it. 
 
 x White lead being very poisonous, its use by painters and others is gene- 
 rally attended with symptoms of lead-poisoning, arising in many cases 
 probably, from neglecting to wash the hands before eating, the effect of 
 lead being cumulative, so that minute doses may show their combined 
 action after many days. Diluted sulphuric acid and solutions of the sul- 
 phates of magnesia and the alkalies are sometimes taken internally to 
 counteract its effect, since the sulphate of lead is not poisonous. 
 
 All paints containing lead, and cards glazed with white lead, are 
 blackened even by minute quantities of sulphuretted hydrogen, from the 
 production of black sulphide of lead. If the blackened surface remain 
 exposed to the light and air, it is bleached again, the sulphide of lead 
 (PbS) being oxidised and converted into white sulphate of lead 
 (PbO . S0 3 ), but this does not take place in the dark. A little sulphide 
 of lead or powdered charcoal is sometimes mixed with commercial white 
 lead to give it a bluish tint. 
 
 The pure carbonate of lead is found in white crystals associated with 
 galena. 
 
 Sulphate of lead is found in nature in prismatic and octahedral crystals 
 of anglesite or lead-vitriol. It is nearly insoluble in diluted acids, 
 and is one of the chief forms in which lead is precipitated from its 
 solutions in analytical operations. The minerals lanarkite and leadliillite 
 are compounds of sulphate and carbonate of lead. The chromates of 
 lead have been already noticed. 
 
 Phosphate of lead (3PbO . P0 5 ) is occasionally associated with the car- 
 bonate in the ores of lead. 
 
 257. Chloride of lead (PbCl) forms the mineral termed horn-lead. It 
 is one of the few chlorides which are not readily soluble in water, and is 
 precipitated when hydrochloric acid or a soluble chloride is added to a 
 solution of lead. Boiling water dissolves about 3^ of its weight of chloride 
 of lead, and deposits it in beautiful shining white needles on cooling. It 
 fuses easily, and is converted into vapour at a high temperature. 
 
 The oxychloride of lead (PbCl . PbO) is formed when chloride of lead 
 is heated in air. It is sometimes employed as a substitute for white lead 
 in painting, being prepared for this purpose by decomposing finely 
 powdered galena with concentrated hydrochloric acid (PbS + HC1 = 
 PbCl + HS) washing the resulting chloride of lead with cold water, dis- 
 solving it in hot water, and adding lime-water, which precipitates the 
 oxychloride 
 
 2PbCl + CaO = PbCl. PbO * CaCl . 
 
 Turner's yellow (Paris yellow, patent yellow, mineral yellow) is another 
 oxychloride of lead (PbCl . 7PbO), prepared by heating a mixture of 
 litharge and sal-ammoniac. It has a fine golden yellow colour, is easily 
 fused, and crystallises in octahedra on cooling. The mineral mendipite 
 
360 THALLIUM. 
 
 is an oxychloride of lead (PbCl . 2PbO) which occurs in colourless pris- 
 matic crystals. 
 
 Iodide of lead (Pbl) is obtained as a bright yellow precipitate on mix- 
 ing solutions of nitrate or acetate of lead and iodide of potassium. If it 
 be allowed to settle, the liquid poured off, and the precipitate dissolved 
 in boiling water (with one or two drops of hydrochloric acid), it forms a 
 colourless solution, depositing golden scales as it cools. 
 
 258. Sulphides of lead. The subsulphide (Pb 2 S) has been mentioned 
 as produced in smelting galena. Sulphide of lead, or galena, has been 
 described among the ores of lead. It is always obtained as a black pre- 
 cipitate when hydrosulphuric acid or a soluble sulphide acts upon a solu- 
 tion containing lead, even in minute proportion. 
 
 A persulphide of lead, the composition of which has not been ascer- 
 tained, is formed as a red precipitate when a solution of lead is mixed 
 with a solution of an alkaline sulphide saturated with sulphur (or with 
 solution of hydrosulphate of ammonia which has been kept till it has 
 acquired a red colour). 
 
 Chlorosulphide of lead (3PbS . 2PbCl) is obtained as a bright red pre- 
 cipitate when hydrosulphuric acid is added in small quantity to a solution 
 of chloride of lead in hydrochloric acid. 
 
 Selenide of lead (PbSe) occurs associated with the sulphide in some 
 lead ores ; it much resembles galena, and has the same crystalline form. 
 
 259. Equivalent and atomic weights of lead. The analysis of the oxide 
 and chloride of lead has shown that 8 parts by weight (1 eq.) of oxygen 
 and 35 '5 parts (1 eq.) of chlorine, are respectively combined with 103'5 
 parts of lead; the equivalent of lead, therefore, is 103*5. The specific 
 heat of lead, and its isomorphism with other diatomic metals, show its 
 atomic weight to be twice its equivalent weight, or 207. The atomic 
 formulae of some of its chief compounds would be litharge Pb0, minium 
 2Pb0 . Pb0 2 , peroxide of lead Pb0 2 , galena PbS, chloride of lead #bC! 2 . 
 
 260. THALLIUM, The discovery of this metal in 1861 was one of the first results 
 of the application of the new method of testing by observation of coloured lines in 
 the spectrum of a flame, described at p. 273. Crookes was examining the spectrum 
 obtained by holding in the flame of a Bun sen burner the deposit formed in the 
 flues of a sulphuric acid chamber, in which pyrites was employed as the source of 
 sulphur. A green line made its appearance in the spectrum, which a less acute and 
 practised observer might have mistaken for one of the lines caused by barium 
 (see fig. 221), with which it nearly coincides in position; but the line was much 
 brighter than that produced by barium, and on instituting a searching analysis of 
 the deposit, a metal was obtained which did not agree in properties with any hitherto 
 described, and was named thallium, from 6.*xxo?, a young shoot, in allusion to the 
 vernal green colour of its spectrum line. It has since been detected in several 
 mineral waters; but the pyrites obtained from Spain and Belgium appear to be its 
 best source. From the flue-dust of the sulphuric acid chambers, the metal is extracted 
 by a simple process, but large quantities must be operated on to obtain any consider- 
 able amount. The deposit is treated with boiling water, and the solution mixed 
 with much strong hydrochloric acid, which precipitates the thallium as chloride ; 
 this is converted into acid sulphate of thallium by treatment with sulphuric acid, 
 and this salt having been purified by recrystallisation, is decomposed by zinc, which 
 precipitates metallic thallium in a spongy form, fusible into a compact mass in an 
 atmosphere of coal-gas. 
 
 In external characters thallium is very similar to lead ; but it tarnishes much 
 more rapidly when exposed to air, and the streak which it makes on paper soon be- 
 comes yellowish, being converted into oxide of thallium. If a tarnished piece of the 
 metal be allowed to touch the tongue, a strongly alkaline taste is perceived, for the 
 oxide of thallium or thallous oxide (T10) is very soluble in water, so that the tarnished 
 
OCCURRENCE OF SILVER IN NATURE. 361 
 
 metal becomes bright when immersed in water. The ready solubility of the oxide 
 seemed to require thallium to be classed among the alkali-metals, a view which was 
 encouraged by the circumstance that its specific heat proved it to be monatomic like 
 potassium and sodium. But thallium appears to be more nearly related to another 
 monatomic metal, silver, by the sparing solubility of its chloride and the insolubility 
 of its sulphide. The circumstance that it may be kept unaltered in water, and may 
 be precipitated from its salts by zinc, at once removes it from the group of alkali- 
 metals. The ready solubility of its oxide in water is only an exaggeration of the 
 behaviour of the oxides of lead and silver, both of which dissolve slightly in water, 
 yielding alkaline solutions. Diluted sulphuric acid acts upon thallium as upon 
 zinc, evolving hydrogen. Thallium burns in oxygen with a beautiful green flame, 
 and the chlorate of thallium has been recommended for the manufacture of green 
 fires in place of chlorate of baryta (see p. 158). The sulphate of thallium, unlike 
 that of lead, is easily soluble in water ; the carbonate is rather sparingly soluble, 
 but far more soluble than carbonate of lead. f 
 
 Thallic oxide, T10 3 , is obtained by adding hypochlorite of soda to thallous chloride 
 mixed with excess of carbonate of soda. It is also a basic oxide, its sulphate having 
 the composition T10 3 . 3S0 3 . HO + 6Aq. 
 
 Salts of thallium, like those of lead, are poisonous. 
 
 The equivalent and atomic weights of thallium appear to be identical, and are ex- 
 pressed by the number 204. 
 
 SILVER 
 
 261. In silver, we meet with the first metal hitherto considered which 
 is not capable of undergoing oxidation in the air, under any circumstances, 
 and this, in conjunction with its beautiful appearance, occasions its mani- 
 fold ornamental uses, which are much favoured also by the great mal- 
 leability and ductility of this metal (in which it ranks only second to 
 gold), for the former property enables it to be rolled out into thin plates 
 or leaves, so that a small quantity of silver suffices to cover a large surface, 
 whilst its ductility permits the wire-drawer to produce that extremely thin 
 silver wire which is employed in the manufacture of silver lace. 
 
 Silver, although pretty -widely diffused, is found in comparatively small 
 quantity, and hence it bears a high value, which adapts it for a medium 
 of currency. 
 
 As might be expected from its want of direct attraction for oxygen, 
 silver is found frequently in the metallic or native state, crystallised in 
 cubes or octahedra, which are sometimes aggregated together, as in the 
 silver-mines of Potosi, into arborescent or dendritic forms. Silver is more 
 frequently met with, however, in combination with sulphur, forming the 
 sulphide of silver (AgS), which is generally associated with large quantities 
 of the sulphides of lead, antimony, and iron. The largest supplies of silver 
 are obtained from the Mexican and Peruvian mines, but the quantity 
 furnished by Saxony and Hungary is by no means insignificant. - 
 
 The process by which silver is extracted from galena has been already 
 described under the history of lead. 
 
 The ores of copper (particularly the grey copper-ore) often contain so 
 much silver as to be worth working for that metal, in which case they 
 are smelted in the usual way, when the copper obtained is found to con- 
 tain the whole of the silver present in the ore. This silver is separated 
 from the copper by taking advantage of the facility with which the 
 former metal is dissolved by melted lead. The process of liquation, as 
 it is termed, consists in fusing the argentiferous copper with about thrice 
 its weight of lead, and casting the alloy thus obtained into cakes or disks, 
 which are afterwards gradually heated upon a hearth (fig. 250), so con- 
 trived that the lead, which melts much more easily than the copper, may 
 
362 
 
 AMALGAMATION OF SILVER ORES. 
 
 Fig. 250. Liquation hearth. 
 
 flow off in the liquid state, carrying with it, in the form of an alloy, the 
 silver which was associated with the copper, leaving this last metal in 
 porous masses, having the form of the 
 original disks, upon the hearth. The 
 lead and silver are separated by the 
 process of cupellation (p. 353). 
 
 When the extraction of the silver 
 is the main object with which a par- 
 ticular ore is treated, the process of 
 amalgamation is adopted, in which 
 the silver is dissolved out by means 
 of mercury. At Freiberg, the silver 
 is extracted by this method from an 
 ore which contains sulphide of silver 
 together with much iron pyrites and 
 other metallic sulphides. The ore is 
 mixed with a small proportion of common salt, and roasted in a rever- 
 beratory furnace, when the sulphide of silver is converted into chloride of 
 silver. It is then ground to a very fine powder, which is agitated, in re- 
 volving casks, with water and metallic iron, when the latter appropriates 
 the chlorine and reduces the silver to the metallic state. A quantity of 
 mercury is then introduced into the casks, and the revolution continued 
 for several hours ; the mercury dissolves the silver, copper, and lead, and 
 is run out of the barrels into stout linen strainers, which allow the excess 
 of fluid mercury to pass through, but retain the soft solid amalgam con- 
 taining the silver. In order to recover the silver, this amalgam is placed 
 in iron trays arranged one above the other (fig. 251), and covered with an 
 iron bell-shaped receiver standing over water. 
 By heaping burning fuel round the upper part 
 of this dome, its temperature is raised suffi- 
 ciently to convert the mercury into vapour, 
 which condenses again in the water, leaving 
 the silver, together with the copper and lead, 
 upon the iron trays. Finally, the silver is re- 
 fined by fusing it with an additional quantity 
 of lead and subjecting the alloy to cupellation 
 (p. 353), when the fused oxide of lead which 
 is formed carries with it the copper, also in the 
 form of oxide, leaving the silver in a state of 
 purity. 
 
 Various methods have been devised to 
 supersede the amalgamation process. For 
 example, the ores have been roasted with corn- 
 
 Fig. 251. 
 
 inon salt to convert the silver into chloride, which is dissolved out of the 
 mass by means of a strong solution of common salt, from which the silver 
 is afterwards precipitated in the metallic state by copper. Hyposulphite 
 of soda has also been employed to dissolve out the chloride of silver, and 
 the solution precipitated by sulphide of sodium, the resulting sulphide of 
 silver being roasted to remove the sulphur and leave metallic silver. 
 
 Although silver is capable of resisting the oxidising action of the atmo- 
 sphere, it is liable to considerable loss by wear and jtear in consequence of 
 its softness, and is therefore always hardened, for useful purposes, by the 
 addition of a small proportion of copper. The standard silver employed 
 
PLATING AND SILVERING. 363 
 
 for coinage and for most articles of silver plate, in this country, contains, 
 in 1000 parts, 925 of silver and 75 of copper, whilst that used in France 
 contains 900 of silver and 100 of copper. 
 
 Standard silver, for coining and other purposes, is whitened by being 
 heated in air and immersed in diluted sulphuric acid, which dissolves out 
 the oxide of copper, leaving a superficial film of nearly pure silver. Dead 
 or frosted silver is produced in this manner. Oxidised silver is covered 
 with a thin film of sulphide by immersion in a solution obtained by boiling- 
 sulphur with potash. 
 
 The solder employed in working silver consists of 5 parts of silver, 2 of 
 zinc, and 6 of brass. 
 
 Plated articles are manufactured from copper or one of its alloys, which 
 has been united by rolling with a thin plate of silver, the adhesion of the 
 latter being promoted by first washing the surface of the copper with a 
 solution of nitrate of silver, when a film of this metal is deposited upon 
 its surface, the copper taking the place of the silver in the solution. 
 
 Electro-plating consists in covering the surface of baser metals with a 
 coating of silver, by connecting them with the negative (or zinc) pole of 
 the galvanic battery, and immersing them in a solution made by dissolv- 
 ing cyanide of silver in cyanide of potassium ;* the current gradually de- 
 composes the cyanide of silver, and this metal is of course (see p. 21) 
 deposited upon the object connected with the negative pole, whilst the 
 cyanogen liberated at the positive (copper or platinum) pole is allowed to 
 act upon a silver-plate with which this pole is connected, so that the 
 silvering solution is always maintained at the same strength, the quantity 
 of silver dissolved at this pole being precisely equal to that deposited at 
 the opposite pole. 
 
 Brass and copper are sometimes silvered by rubbing them with a mix- 
 ture of 10 parts of chloride of silver with 1 of corrosive sublimate (chlo- 
 ride of mercury) and 100 of bitartrate of potash. The silver and mercury 
 are both reduced to the metallic state by the baser metal, and an amalgam 
 of silver is formed, which readily coats the surface. The acidity of the 
 bitartrate of potash promotes the reduction. The surface to be silvered 
 should always be cleansed from oxide by momentary immersion in nitric 
 acid, and washed with water. For dry silvering, an amalgam of silver and 
 mercury is applied to the clean surface, and the mercury is afterwards ex- 
 pelled by heat. 
 
 Silvering upon glass is effected by means of certain organic substances 
 which are capable of precipitating metallic silver from its solutions. Look- 
 ing glasses have been made by pouring upon the surface of plates of glass 
 a solution containing tartrate of silver and tartrate of ammonia. On heat- 
 ing the glass plates to a certain temperature, the oxide of silver contained 
 in the tartrate parts with its oxygen to the tartaric acid, and the metallic 
 silver is deposited in a closely adhering film. Glass globes and vases are 
 silvered internally by a process which is exactly similar in principle. 
 
 Pure silver is easily obtained from standard silver by dissolving it in 
 nitric acid, with the aid of heat, diluting the solution with water, adding 
 solution of common salt as long as it produces any fresh precipitate of 
 chloride of silver, washing the precipitate by decantation as long as the 
 washings give a blue tinge with ammonia, and fusing the dried precipitate 
 
 * A solution of cyanide of potassium in 10 parts of water, with 50 grains of chloride 
 of silver dissolved in each pint of the liquid, will answer the purpose. 
 
364 NITRATE OF SILVER. 
 
 with, an equal weight of dried carbonate of soda in a brisk fire, when a 
 button of silver will be found on breaking the crucible 
 
 AgCl + NaO.C0 2 - Ag + NaCl + + C0 2 . 
 
 262. Properties of silver. The brilliant whiteness of silver distin- 
 guishes it from all other metals. It is lighter than lead,- its specific 
 gravity being 10*53 ; harder than gold, but not so hard as copper; more 
 malleable and ductile than any other metal except gold, which it sur- 
 passes in tenacity. It fuses at a somewhat lower temperature than gold or 
 copper (about 1870 F.), and is the best conductor of heat and electricity. 
 It is not oxidised by dry or moist air, either at the ordinary or at high 
 temperatures, but is oxidised by ozone, and tarnished by air containing 
 sulphuretted hydrogen, from the production of sulphide of silver, which is 
 easily removed by solution of cyanide of potassium. It is unaffected by 
 dilute acids, with the exception of nitric ; but hot concentrated sulphuric 
 acid converts it into sulphate of silver, and when boiled with strong 
 hydrochloric acid, it dissolves to a slight extent in the form of chloride of 
 silver, which is precipitated on adding water. The hydrates of potash 
 and soda do not act on silver to the same extent as on platinum when 
 fused with it; hence silver basins and crucibles are much used in the 
 laboratory. 
 
 263. Oxides of silver. There are three compounds, of silver with 
 oxygen : the suboxide, Ag 2 ; the oxide, AgO ; and the peroxide, probably 
 Ag0 2 , which is not known in the pure state. The oxide alone has any 
 practical interest, as being the base contained in the salts of silver with 
 oxygen-acids. 
 
 Oxide of silver (AgO) is obtained as a brown precipitate when solution 
 of nitrate of silver is decomposed by potash. It is a powerful base, 
 slightly soluble in water, to which it imparts a weak alkaline reaction. A 
 moderate heat decomposes it into its elements. When moist freshly pre- 
 cipitated oxide of silver is covered with a strong solution of ammonia, and 
 allowed to stand for some hours, it becomes black, and acquires danger- 
 ously explosive properties. The composition of this fulminating silver is 
 not accurately known, but it is supposed to be a nitride of silver, NAg 3 , 
 corresponding in composition to ammonia. 
 
 Nitrate of silver (AgO . NO.), or lunar caustic (silver being distinguished 
 as luna by the alchemists), is procured by dissolving silver in nitric acid, 
 with the aid of a gentle heat, evaporating the solution to dryness, and 
 heating the residue till it fuses, in order to expel the excess of acid. For 
 use in surgery, the fused nitrate is poured into cylindrical moulds, so as 
 to cast it into thin sticks ; but for chemical purposes it is dissolved in 
 water and crystallised, when it forms colourless square tables. The action 
 of nitrate of silver as a caustic depends upon the facility with which it 
 parts with oxygen, the silver being reduced to the metallic state, and the 
 oxygen combining with the elements of the organic matter. This effect 
 is very much promoted by exposure to sunlight or diffused daylight. Pure 
 nitrate of silver is not changed by exposure to light, but if organic matter 
 be present, a black deposit, containing finely divided silver, is produced. 
 Thus, the solution of nitrate of silver stains the fingers black when ex- 
 posed to light, but the stain may be removed by cyanide of potassium. If 
 solution of nitrate of silver be dropped upon paper, and exposed to light, 
 black stains will be produced, and the paper corroded. Nitrate of silver 
 
CHLOKIDE OF SILVER. 365 
 
 is a frequent constituent of marking inks, since the deposit of metallic 
 silver formed on exposure to light is not removable by washing. The 
 linen is sometimes mordanted by applying a solution of carbonate of soda 
 before the marking ink, when the insoluble carbonate of silver is preci- 
 pitated in the fibre, and is more easily blackened than the nitrate, espe- 
 cially if a hot iron is applied. Marking inks without preparation are 
 made with nitrate of silver containing an excess of ammonia, which 
 appropriates the nitric acid, and hastens the blackening on exposure to 
 light or heat. Hair dyes often contain nitrate of silver. The important 
 use of this salt in photography has been noticed already (p. 212). 
 
 In order to prepare nitrate of silver from standard silver (containing copper), the 
 metal is dissolved in moderately strong nitric acid, and the solution evaporated to 
 dry ness in a porcelain dish, when a blue residue containing the nitrates of silver 
 and copper is obtained. The dish is now moderately heated until the residue has 
 fused, and become uniformly black, the blue nitrate of copper being decomposed, 
 and leaving black oxide of copper, at a temperature which is insufficient to decom- 
 pose the nitrate of silver. To ascertain when all the nitrate of copper is decom- 
 posed, a small sample is removed on the end of a glass rod, dissolved in water, 
 filtered, and tested with ammonia, which will produce a blue colour if any nitrate 
 of copper is left. The residue is treated with hot water, the solution filtered from 
 the oxide of copper, and evaporated to crystallisation. 
 
 264. Chloride of silver (AgCl) is an important compound, as being 
 the form into which silver is commonly converted in extracting it from 
 its ores, and in separating it from other metals. It separates as a white 
 curdy precipitate, when solution of hydrochloric acid or a chloride is 
 mixed with a solution containing silver. The precipitate is brilliantly 
 white at first, but soon becomes violet, and eventually black, if exposed 
 to daylight, or more rapidly in sunlight, the chloride of silver being 
 reduced to subchloride (Ag 2 Cl), with separation of chlorine (see p. 212). 
 The blackening takes place more rapidly in the presence of an excess of 
 nitrate of silver or of organic matter, upon which the liberated chlorine is 
 capable of acting. The chloride of silver formed by suspending silver 
 leaf in a bottle of chlorine gas is not blackened by light. If the white 
 chloride of silver be dried in the dark, and heated in a crucible, it fuses 
 at about 500 F. to a brownish liquid, which solidifies, on cooling, to a 
 transparent, nearly colourless mass, much resembling horn in external 
 characters (horn silver) ; a strong heat converts it into vapour, but does 
 not decompose it. If fused chloride of silver be covered with hydro- 
 chloric acid, and a piece of zinc placed upon it, it will be found entirely 
 reduced, after a few hours, to a cake of metallic silver ; the first portion of 
 silver having been reduced in contact with the zinc, and -the remainder by 
 the galvanic action set up by the contact of the two metals beneath the 
 acid. Ammonia readily dissolves chloride of silver, and the solution 
 deposits colourless crystals of the chloride when evaporated. If the 
 ammonia be very strong, the solution deposits a crystalline compound of 
 chloride of silver with ammonia. The absorption of ammoniacal gas by 
 chloride of silver has been noticed at p. 116, and the photographic appli- 
 cation of the chloride at p. 212. 
 
 Recovery of silver from old photographic baths. One of the simplest methods of 
 effecting this consists in mixing the liquid with solution of common salt as long as 
 it causes a fresh precipitate of chloride of silver, which is allowed to subside, washed 
 once or twice by decantation, mixed with a little sulphuric acid, a lump of zinc 
 (spelter) placed in it, and left for a day or two to reduce the silver to the metallic 
 state. The zinc is then taken out, and the metallic silver well washed by decanta- 
 
366 EQUIVALENT AND ATOM OF SILVER. 
 
 tion, till the washings are quite tasteless. It may either be reconverted into nitrate 
 by dissolving in nitric acid (p. 364), or fused in an earthen crucible with a little 
 borax. 
 
 From the fixing solutions containing hyposulphite of soda, the silver cannot be 
 precipitated by salt, because the chloride of silver is soluble in the hyposulphite. A 
 piece of sheet copper left in this for a day or two will precipitate the silver at once 
 in the metallic state. 
 
 Subchloride of silver (j^g 2 Cl) has been obtained by the action of per- 
 chloride of iron upon metallic silver (Ag 2 + Fe 2 Cl 3 = Ag 2 Cl + 2FeCl). 
 It is black and insoluble in nitric acid. Ammonia decomposes it, dis- 
 solving out chloride of silver, and leaving metallic silver. 
 
 Bromide of silver (AgBr) is a rare Chilian mineral. Associated with 
 chloride of silver, it forms the mineral embolite. It much resembles the 
 chloride, but is somewhat less easily dissolved by ammonia. 
 
 Iodide of silver (Agl) is also found in the mineral kingdom. It is worthy 
 of remark that silver decomposes hydriodic acid much more easily than 
 hydrochloric acid, forming iodide of silver, and evolving hydrogen. The 
 iodide of silver dissolves in hot hydriodic acid, and is deposited in crys- 
 tals on cooling. By adding nitrate of silver to iodide of potassium, the 
 iodide of silver is obtained as a yellow precipitate which, unlike the 
 chloride, does not dissolve in ammonia. Iodide of silver dissolves in a 
 boiling saturated solution of nitrate of silver, and the solution, on cooling, 
 deposits crystals having the composition Agl . AgO . NO., which are far 
 more sensitive to the action of light than iodide of silver itself, a circum- 
 stance which is taken advantage of by photographers. The crystals are 
 decomposed by water, with separation of iodide of silver. 
 
 Sulphide of silver (AgS) is found as silver glance, which may be re- 
 garded as the chief ore of silver ; it has a metallic lustre, and is some- 
 times found in cubical or octahedral crystals. The minerals known as 
 rosiclers or red silver ores contain sulphide of silver combined with the 
 sulphides of arsenic and antimony. The black precipitate obtained by 
 the action of hydrosulphuric acid upon a solution of silver is the sulphide 
 of silver. It may also be formed by heating silver with sulphur in a 
 covered crucible. Sulphide of silver is remarkable for being soft and 
 malleable, so that medals may even be struck from it. It is not dis- 
 solved by diluted sulphuric or hydrochloric acid, but nitric acid readily 
 dissolves it. Metallic silver dissolves sulphide of silver when fused with 
 it, and becomes brittle even when containing only 1 per cent, of the 
 sulphide. 
 
 265. Equivalent and atomic weights of silver. When finely divided 
 silver is heated in a current of chlorine gas, 108 parts by weight of silver 
 combine with 35*5 parts (1 eq.) of chlorine; hence 108 is taken to re- 
 present the equivalent of silver. The specific heat of silver shows its 
 atomic weight to be represented by the same number as its equivalent, so 
 that it is a monatomic element, and the atomic formulae of its principal 
 compounds are written thus : Oxide of silver, Ag.,0 ; chloride of silver, 
 AgCl ; sulphide of silver, Ag 2 S. 
 
EXTRACTION OF MERCURY FROM CINNABAR. 
 
 367 
 
 MERCUEY. 
 
 266. Mercury (quicksilver) is the only metal which is liquid at the 
 ordinary temperature, and since it requires a temperature of 39 below 
 zero F. to solidify it, this metal is particularly adapted for the construc- 
 tion of thermometers and "barometers. Its high boiling point (662 F.) 
 also recommends it for the former purpose, as does its high specific gravity 
 (13-54) for the latter, a column of about 30 inches in height being able 
 to counterpoise a column of atmospheric air having the same sectional 
 area, and a height equal to that of the atmosphere above the level of the sea. 
 The symbol for mercury (Hg) is derived from the Latin name for this ele- 
 ment, hydrargyi-um (vSoy>, water, referring to its fluidity, apyvpov, silver). 
 
 Mercury is not met with in this country, but is obtained from Idria 
 (Austria), Almaden (Spain), China, and New Almaden (California). It 
 occurs in these mines partly in the metallic state, diffused in minute 
 globules or collected in cavities, but chiefly in the state of cinnabar, which 
 is a sulphide of mercury (HgS). 
 
 The metal is extracted from the sulphide at Idria by roasting the ore 
 in a kiln (fig. 252), which is connected with an extensive series of con- 
 
 Fig. 252. Extraction of mercury at Idria. 
 
 densing chambers built of brick-work. The sulphur is converted, by the 
 air in the kiln, into sulphurous acid gas, whilst the mercury passes off in 
 vapour and condenses in the chambers. 
 
 At Almaden the extraction is conducted upon the same principle, but 
 the condensation of the mercury is effected in earthen receivers (called 
 aludels) opening into each other, and delivering the mercury into a gutter 
 which conveys it to the receptacles. 
 
 The cinnabar is placed upon the arch (A, fig. 253) of brick-work, in 
 which there are several open- 
 ings for the passage of the flame 
 of the wood fire kindled at B ; 
 this flame ignites the sulphide 
 of mercury, which burns in 
 the air passing up from be- 
 low, forming sulphurous acid 
 gas and vapour of mercury 
 (HgS + 2 = Hg + S0 2 ), 
 which escape through the flue 
 (F) into the aludels (C), where Fig. 253. 
 
 the chief part of the mercury 
 condenses, and runs down into the gutter (G). The sulphurous acid gas 
 
368 USES OF MERCURY. 
 
 escapes through the flue (H), and any mercury which may have escaped 
 condensation is collected in the trough (D), the gas finally passing out 
 through the chimney (E), which provides for the requisite draught. 
 
 In the Palatinate, the cinnabar is distilled in cast-iron retorts with 
 lime, when the sulphur is left in the residue as sulphide of calcium, and 
 sulphate of lime, whilst the mercury distils over 
 
 4HgS + 4CaO = 3CaS + CaO . S0 3 + Hg 4 . 
 
 The mercury found in commerce is never perfectly pure, as may be shown by 
 scattering a little upon a clean glass plate, when it tails or leaves a track upon the 
 glass, which is not the case with pure mercury. Its chief impurity is lead, which 
 may be removed by exposing it in a thin layer to the action of nitric acid diluted 
 with two measures of water, which should cover its surface, and be allowed to re- 
 main in contact with it for a day or two, with occasional stirring. The lead is far 
 more easily oxidised and dissolved than the mercury, though a little of this also 
 passes into solution. The mercury is afterwards well washed with water and dried, 
 first with blotting-paper, and then by a gentle heat. Mercury is easily freed from 
 mechanical impurities by filtering it through a cone of paper, round the apex of 
 which a few pin-holes have been made. 
 
 267. Although mercury in its ordinary condition is not oxidised by air 
 at the ordinary temperature, it appears to undergo a partial oxidation 
 when reduced to a fine state of division, as in those medicinal prepara- 
 tions of the metal which are made by triturating it with various sub- 
 stances which have no chemical action upon it, until globules of the metal 
 are no longer visible. Blue pill and grey powder, or hydrargyrum cum 
 cretd, afford examples of this, and probably owe much of their medicinal 
 activity to the presence of one of the oxides of mercury. 
 
 268. Uses of mercury. One of the chief uses to which mercury is 
 devoted is the silvering of looking-glasses, which is effected by means of an 
 amalgam of tin in the following manner : a sheet of tin-foil of the same size 
 as the glass to be silvered is laid perfectly level upon a table, and rubbed 
 over with metallic mercury, a thin layer of which is afterwards poured 
 upon it. The glass is then carefully slid on to the table, so that its edge 
 may carry before it part of the superfluous mercury with the impurities upon 
 its surface ; heavy weights are laid upon the glass so as to squeeze out the 
 excess of mercury, and in a few days the combination of tin and mercury 
 is found to have adhered firmly to the glass ; this coating usually contains 
 about 1 part of mercury and 4 parts of tin. In this and all other arts in 
 which mercury is used (such as barometer-making) much suffering is expe- 
 rienced by the operatives, from the poisonous action of the mercury. 
 
 The readiness with which mercury unites with most other metals to 
 form amalgams is one of its most striking properties, and is turned to 
 account for the extraction of silver and gold from their ores. The attrac- 
 tion of the latter metal for mercury is seen in the readiness with which it 
 becomes coated with a silvery layer of mercury, whenever it is brought in 
 contact with that metal, and if a piece of gold leaf be suspended at a little 
 distance above the surface of mercury, it will be found, after a time, sil- 
 vered by the vapour of the metal which rises slowly even at the ordinary 
 temperature. From the surface of rings which have been accidentally 
 whitened by mercury, it may be removed by a moderate heat, or by warm 
 dilute nitric acid, but the gold will afterwards require burnishing. 
 
 Zinc plates are amalgamated, as it is termed, for use in the galvanic 
 battery, by rubbing the liquid metal over them under the surface of dilute 
 sulphuric acid, which removes the coating of oxide from the surface of the 
 zinc. The amalgam of zinc is not acted on by the diluted sulphuric acid used 
 
MERCUROUS AND MERCURIC OXIDES. 369 
 
 in the battery (see p. 20) until the circuit is completed, so that no zinc is 
 wasted when the battery is not in use. A combination of 5 parts of mercury 
 and 2 parts of zinc is also used to promote the action of electrical machines. 
 The addition of a little amalgam of sodium to metallic mercury gives it 
 the power of adhering much more readily to other metals, even to iron. 
 Such an addition has been recommended in all cases where metallic sur- 
 faces have to be amalgamated, and especially in the extraction of silver 
 and gold from their ores by means of mercury. 
 
 < Iron and platinum are the only metals in ordinary use which can be 
 employed in contact with mercury without being corroded by it. Mer- 
 cury, however, adheres to platinum. 
 
 The following definite compounds of mercury with other metals have been ob- 
 tained by combining them with excess of mercury, and squeezing out the fluid metal 
 by hydraulic pressure, amounting to 60 tons upon the inch: 
 
 Amalgam of lead, Pb 2 Hg 
 
 b 2 H 
 H 
 
 silver, 
 
 iron, FeHg " 
 
 Amalgam of zinc, Zn 2 Hg 
 
 copper, CuHg 
 
 platinum, PtHg 2 
 
 The amalgam of silver (AgHg 2 ) has been found in nature, in dodecahedral crystals. 
 A very beautiful crystallisation of the amalgam of silver (Arbor Diance) may be 
 obtained in long prisms having the composition AgHg 3 , by dissolving 400 grains of 
 nitrate of silver in 40 measured ounces of water, adding 160 minims of concentrated 
 nitric acid, and 1840 grains of mercury ; in the course of a day or two crystals of 
 2 or 3 inches in length will be deposited. 
 
 269. Oxides of mercury. Two oxides of mercury are known, the sub- 
 oxide Hg.,0, and the oxide HgO ; both combine with acids to form salts. 
 
 Suboxide of mercury, black oxide or mercurous oxide (Hg^O), is obtained 
 by decomposing calomel with solution of potash, and washing with water 
 (HgjCl + KO = Hg. 2 + KC1). It is very easily decomposed by exposure 
 to light or to a gentle heat, into oxide of mercury and metallic mercury. 
 
 Red oxide of mercury, or mercuric oxide (HgO), is formed upon the 
 surface of mercury, when heated for some time to its boiling point in con- 
 tact with air. The oxide is black while hot, but becomes red on cooling. 
 It is used under the name of red precipitate in ointments, and is prepared 
 for this purpose by dissolving mercury in nitric acid, evaporating the 
 solution to dryness, and gently calcining the nitrate of mercury (HgO . N0 5 ) 
 until the nitric acid is expelled. The name nitric oxide of mercury refers 
 to this process. It is thus obtained, after cooling, as a brilliant red crystal- 
 line powder, which becomes nearly black when heated, and is resolved 
 into its elements at a red heat. It dissolves slightly in water, and the 
 solution has a very feeble alkaline reaction. A bright yellow modification 
 of the oxide is precipitated when a solution of corrosive sublimate is 
 decomposed by potash (HgCl + KO = HgO + KC1) ; the yellow varfety is 
 chemically more active than the red. 
 
 When oxide of mercury is acted on by strong ammonia, it becomes converted into 
 a yellowish white powder which possesses the properties of a strong base, absorbing 
 carbonic acid eagerly from the air, and combining readily with other acids. It is 
 easily decomposed by exposure to light, and, if rubbed in a mortar when dry, is 
 decomposed with slight detonations, a property in which it feebly resembles fulmi- 
 nating silver (p. 364). The composition of this substance is represented by the 
 formula 4HgO . NH 3 . 2HO, and it is sometimes called ammoniated oxide of mercury. 
 When exposed in vacuo over oil of vitriol, it loses 2HO, becoming 4HgO . NH S , but if 
 heated to about 260 F., it evolves another equivalent of water and becomes brown.* 
 
 * It has been stated that by heating it for some time in a current of dry ammonia, the 
 whole of the hydrogen may be expelled as water, leaving the oxide of tetra-mercurammo- 
 niuni, NHg 4 0, which is very explosive, and combines with water to form a hydrate which 
 produces salts with the acids. 
 
 2 A 
 
370 MERCURIC CHLORIDE OR CORROSIVE SUBLIMATE. 
 
 It now contains Hg 4 3 NH2, and may be regarded as a compound of oxide of mer- 
 cury with ammonia in which one equivalent of hydrogen is displaced by mercury 
 (NH 2 Hg , 3HgO), a view which would explain, in a simple manner, the evolution 
 of ammonia when the substance is fused with hydrate of potash 
 
 NH 2 Hg,3HgO + KO.HO = NH 3 + 4HgO + KO. 
 
 This substance is sometimes called mercuramine; it forms salts with the acids ; the 
 sulphate of mercuramine has the composition (NH 2 Hg, 3HgO)S0 3 . 
 
 By passing ammonia gas over the yellow oxide of mercury as long as it is absorbed, 
 and heating the compound to about 260 F. in a current of ammonia as long as any 
 water is evolved, a brown explosive powder is obtained, which is believed to be a 
 nitride of mercury, NHg 3 , representing ammonia in which the hydrogen has been 
 displaced by mercury. It yields salts of ammonia when decomposed by hydrated 
 acids. 
 
 270. The salts formed by the oxides of mercury with the oxygen-acids are not of 
 great practical importance. Protonitrate of mercury or mercurous nitrate is obtained 
 when mercury is dissolved in nitric acid diluted with five volumes of water ; it may 
 be procured in crystals having the composition Hg 2 . NO 5 , 2Aq. The prismatic 
 crystals which are sometimes sold as protonitrate of mercury consist of a basic nitrate, 
 3(Hg 2 . N0 5 ), Hg 2 . HO, prepared by acting with diluted nitric acid upon mercury 
 in excess. When this salt is powdered in a mortar with a little common salt, it 
 becomes black from the separation of suboxide of mercury 
 
 8(Hg a O . N0 6 ), Hg 2 . HO + 3NaCl = 3Hg 2 Cl + 3(NaO . N0 5 ) + Hg 2 + HO ; 
 
 but the neutral nitrate is not blackened (Hg 2 . N0 5 + NaCl = Hg 2 Cl + NaO . NO S ). 
 These nitrates cannot be dissolved in water without partial decomposition and pre- 
 cipitation of yellow basic nitrates. 
 
 Nitrate of mercury or mercuric nitrate is formed when mercury is dissolved with an 
 excess of strong nitric acid, and the solution boiled. It is better to prepare it by 
 saturating strong nitric acid, diluted with an equal measure of water, with oxide of 
 mercury. It may be obtained in crystals of the formula 2(HgO . NO,), Aq. Water 
 decomposes it, precipitating a yellow basic nitrate, which leaves oxide of mercury 
 when long washed with water. 
 
 Sulphate of suboxide of mercury or mercurous sulphate (Hg 2 . S0 3 ) is precipitated as 
 a white crystalline powder when dilute sulphuric acid is added to a solution of proto- 
 nitrate of mercury. 
 
 Sulphate of mercury or mercuric sulphate (HgO . S0 3 ) is obtained by heating 2 parts 
 by weight of mercury with 3 parts of oil of vitriol, and evaporating to dryness. Mer- 
 curous sulphate is first produced, and is oxidised by the excess of sulphuric acid. It 
 forms a white crystalline powder, which is decomposed by water into a soluble acid 
 sulphate, and an insoluble yellow basic sulphate of mercury, HgO . S0 3 . 2HgO, 
 known as turbith or turpeth mineral, said to have been so named from its resembling in 
 its medicinal effects the root of the Convolvulus turpethum. 
 
 271. CHLORIDES OF MERCURY. The chlorides are the most important 
 .of the compounds of mercury, the subchloride "being calomel (Hg 2 Cl) and 
 the chloride, corrosive sublimate (HgCl). Vapour of mercury burns in 
 chlorine gas, corrosive sublimate being produced. 
 
 Corrosive sublimate, chloride of mercury, bichloride or -perchloride of 
 mercury, or mercuric chloride, is manufactured by heating 2 parts by 
 weight of mercury with 3 parts of strong sulphuric acid, and evaporat- 
 ing to dryness, to obtain mercuric sulphate (Hg + 2(HO.S0 3 ) 
 HgO. S0 3 + 2HO + S0 2 ), which is mixed with 1J part of common 
 salt and heated in glass vessels (HgO . S0 3 + NaCl = NaO . S0 3 + HgCl), 
 when sulphate of soda is left, and the corrosive sublimate is converted 
 into vapour, condensing on the cooler part of the vessel in lustrous 
 colourless masses, which are very heavy (sp. gr. 5*4), and have a crys- 
 talline fracture. It fuses very easily (at 509 F.) to a perfectly colour- 
 less liquid, which boils at 563 F., emitting an extremely acrid vapour, 
 which destroys the sense of smell for some time. This vapour condenses 
 
WHITE PRECIPITATE. 371 
 
 in fine needles, or sometimes in octahedra. Corrosive sublimate dis- 
 solves in three times its weight of boiling water, but requires 16 parts 
 of cold water, so that the hot solution readily deposits long four-sided 
 prismatic crystals of the salt. It is remarkable that alcohol and ether 
 dissolve corrosive sublimate much more easily than water, boiling alcohol 
 dissolving about an equal weight of the chloride, and cold ether taking 
 up one-third of its weight. By shaking the aqueous solution with ether, 
 the greater part of the corrosive sublimate will be removed, and will 
 remain dissolved in the ether which rises to the surface. Water in which 
 sal-ammoniac has been dissolved will take up corrosive sublimate more 
 easily than pure water, a soluble double chloride (sal alembroth) being 
 formed, which may be obtained in tabular crystals of the composition 
 HgCl, 3JS"H 4 C1, HO. A solution of corrosive sublimate in water con- 
 taining sal-ammoniac is a very efficacious bug-potion. 
 
 The poisonous properties of corrosive sublimate are very marked, so 
 little as three grains having been known to cause death in the case of a 
 child. The white of egg is commonly administered as an antidote, because 
 it is known to form an insoluble compound with corrosive sublimate, so 
 as to render the poison inert in the stomach. The compound of albumen 
 with corrosive sublimate is also much less liable to putrefaction than 
 albumen itself, and hence corrosive sublimate is sometimes employed for 
 preserving anatomical preparations and for preventing the decay of wood 
 (by combining with the vegetable albumen of the sap). 
 
 Chloride of mercury unites with many other chlorides to form soluble 
 double salts, and with oxide of mercury, forming several oxychlorides of 
 mercury, which have no useful applications. 
 
 White precipitate, employed for destroying vermin, is deposited when 
 a solution of corrosive sublimate is poured into an excess of solution of 
 ammonia; 2HgCl + 2NH 3 = NH 3 .HC1 4- NH 2 Hg.HgCl. 
 
 White precipitate. 
 
 The true constitution of white precipitate has been the subject of much discus- 
 sion, but the changes which it undergoes, under various circumstances, appear to 
 lead to the conclusion that it represents the hydrochlorate of ammonia, NH 3 . HC1, 
 in which the hydrogen of the hydrochloric acid, and one-third of that of the 
 ammonia, have been displaced by mercury. When boiled with potash, it yields 
 ammonia and oxide of mercury 
 
 NH 2 Hg.HgCl + KO.HO = NH 3 + 2HgO + KC1. 
 
 If it be boiled with water, it is only partly decomposed in a similar manner, leaving 
 a yellow powder having the composition (NH 2 Hg . HgCl) . 2HgO, produced accord- 
 ing to the equation 
 
 2(NH 2 Hg.HgCl) + 2HO = NH 3 .HC1 + (NH 2 Hg . HgCl) . 2HgO. 
 
 White precipitate. Yellow precipitate. 
 
 A compound corresponding to this yellow precipitate, but containing chloride of 
 mercury in place of the oxide, is precipitated when ammonia is gradually added to 
 solution of corrosive sublimate in large excess, the result being a compound of white 
 precipitate with two equivalents of undecomposed chloride of mercury, 
 
 (NH 2 Hg.H g Cl).2HgCl. 
 
 If white precipitate be heated to about 600 F., it evolves ammonia, and yields a 
 sublimate of ammoniated subchloride of mercury, 2HgoCl . NH 3 , leaving a red 
 crystalline powder which is insoluble in water and in diluted acids, and is un- 
 changed by boiling with potash ; it may be represented as a compound of chloride 
 of mercury with hydrochlorate of ammonia in which the whole of the hydrogen has 
 been displaced by mercury (NHg 3 . HgCl) .HgCl. 
 
 When solution of corrosive sublimate is added to a hot solution of sal-ammoniac, 
 
 2 A2 
 
372 CALOMEL OR MERCUROUS CHLORIDE. 
 
 mixed with ammonia, a crystalline deposit is obtained on cooling the liquid, which 
 is known as fusible white precipitate, and represents hydrochlorate of ammonia, in 
 which one-fourth of the hydrogen has been displaced by mercury, its composition 
 being NH 2 Hg.HCl. The same compound is formed when white precipitate is 
 boiled with a solution of sal-ammoniac 
 
 NH 2 Hg.HgCl + NH 3 .HC1 == 2(NH 2 Hg.HCl). 
 
 The above compounds possess a special interest for the chemist, as they were 
 nmong the first to attract attention to the mobility of the hydrogen in ammonia, 
 which has since been so well exemplified in the artificial production of organic 
 bases by the action of ammonia upon the iodides of the alcohol-radicals. The relation 
 of these compounds to each other is here exhibited : 
 
 "White precipitate, .... 
 Produced with corrosive sublimate in excess, 
 by boiling with water, 
 
 by heating to 600 
 
 sal-ammoniac, 
 
 NH 2 Hg.HgCl 
 (NH 2 Hg.HgCl).2HgCl 
 (NH 2 Hg.HgCl).2HgO 
 NH 2 Hg.HCl 
 (NHg 3 . HgCl). HgCl. 
 
 272. Calomel, subchloride or protochloride of mercury, or mercurous 
 chloride (Hg 2 Cl), unlike corrosive sublimate, is insoluble in water, so that 
 it is precipitated when hydrochloric acid or a soluble chloride is added to 
 mercurous nitrate. The simplest mode of manufacturing it consists in 
 intimately mixing corrosive sublimate with 1 eq. of metallic mercury, a 
 little water being added to prevent dust, drying the mixture thoroughly, 
 and subliming it; HgCl + Hg = Hg 2 Cl. But it is more commonly 
 made by adding another equivalent of mercury to the materials employed 
 in the preparation of corrosive sublimate. 2 parts by weight of mercury 
 are dissolved, with the aid of heat, in 3 parts of oil of vitriol, and eva- 
 porated to dryness; Hg + 2(HO.SO 3 ) = HgO . S0 3 + S0 2 + 2HO. 
 The residue of mercuric sulphate is intimately mixed with 2 more parts of 
 mercury, and the mixture afterwards triturated with 1 J parts of common 
 salt, until globules are no longer visible. The mixture is then heated, so 
 that the calomel may pass off in^vapour, which condenses as a translucent 
 fibrous cake on the cool part of the subliming vessel, leaving sulphate of 
 soda behind; HgO.S0 3 + Hg + NaCl = Hg 2 Cl + NaO.SO,. For 
 medicinal purposes the calomel is obtained in a very fine state of division 
 by conducting the vapour into a large chamber, so as to precipitate it in 
 a fine powder by contact with a large volume of cold air. Steam is some- 
 times introduced to promote its fine division. Sublimed calomel always 
 contains some corrosive sublimate, so that it must be thoroughly washed 
 with water before being employed in medicine. When perfectly pure 
 calomel is sublimed, a little is always decomposed during the process into 
 metallic mercury and corrosive sublimate. 
 
 Calomel is met with either as a semitransparent fibrous mass, or an 
 amorphous powder, with a slightly yellow tinge. It is heavier than cor- 
 rosive sublimate (sp. gr. 7*18), and does not fuse before subliming; it 
 may be obtained in four-sided prisms by slow sublimation. Diluted acids 
 will not dissolve it, but boiling nitric acid gradually converts it into mer- 
 curic chloride and nitrate, which pass into solution. Alkaline solutions 
 convert it into black suboxide of mercury, as is seen in black-wash, made 
 by treating calomel with lime-water (Hg 2 Cl + CaO = Hg 2 + CaCl). 
 Solution of ammonia converts it into a grey compound (NH 2 Hg 2 . Hg 2 Cl), 
 which is the analogue of white precipitate (NH 2 Hg. HgCl), containing 
 Hg 2 in place of Hg. 
 
 Mercurous iodide (Hg 2 I) is a green unstable substance, formed when iodine is tri- 
 turated with an excess of mercury and a little alcohol. The beautiful scarlet 
 
VERMILION OR MERCURIC SULPHIDE. 373 
 
 mercuric iodide (Hgl) has been noticed at p. 173. Its vapour has the remarkably 
 high specific gravity 15-68. 
 
 If mercuric iodide be dissolved in iodide of potassium, the solution mixed with 
 potash, and some ammonia added, a brown precipitate is formed, which may be repre- 
 sented by the formula NHg 3 . Hgl . 2HO ; its formation can be explained by the 
 equation, 4HgI + 3KO + NH 3 = NHg 3 . Hgl . 2HO + 3KI + HO. 
 
 A solution of mercuric iodide in iodide of potassium, mixed with potash, is 
 employed as one of the most delicate tests (Nessler's test) for ammonia in waters ; 
 T T gr. of ammonia in half a pint of water is distinctly recognised by the brown 
 yellow tinge caused by this test. 
 
 ' 273. Sulphides of mercury. When mercury is triturated with, sulphur, 
 the black subsulphide of mercury or mercurous sulphide (Hg 2 S) is formed ; 
 it was termed by old writers Ethiop's mineral, and is an unstable com- 
 pound easily resolvable into metallic mercury and mercuric sulphide (HgS). 
 The latter has been mentioned as the principal ore of mercury, and is 
 important as composing vermilion. The native sulphide of mercury, or 
 cinnabar, is found sometimes in amorphous masses, sometimes crystallised 
 in six-sided prisms varying in colour from dark brown to bright red. It 
 may be distinguished from most other minerals by its great weight (sp. gr. 
 8*2), and by its red colour when scraped with a knife. Neither hydrochloric 
 or nitric acid, separately, will dissolve it, but a mixture of the two dis- 
 solves it as mercuric chloride, with separation of sulphur. Some speci- 
 mens of cinnabar have a bright red colour, so that they only require 
 grinding and levigating to be used as vermilion ; and if the brown cinna- 
 bar in powder be heated for some time to 120 F. with a solution of sul- 
 phur in potash, it is converted into vermilion. 
 
 Of the artificial sulphide of mercury there are two varieties, the black, 
 which is precipitated when corrosive sublimate is added to hydrosulphuric 
 acid or a soluble sulphide, and the red (vermilion), into which the black 
 variety is converted by sublimation, or by prolonged contact with solutions 
 of alkaline sulphides containing excess of sulphur, though, so far as is 
 known, the conversion is effected without chemical change, the red sul- 
 phide having the same composition as the black. In Idria and Holland, 
 6 parts of mercury and 1 of sulphur are well agitated together in revolving 
 casks for several hours, and the black sulphide thus obtained is sublimed 
 in tall earthen pots closed with iron plates, when the vermilion is de- 
 posited in the upper part of the pots, and is afterwards ground and 
 levigated. The sublimed vermilion, however, is generally inferior to that 
 obtained by the wet process, of which there are several modifications. 
 One of the processes consists in triturating 300 parts of mercury with 
 114 parts of sulphur for two or three hours, and digesting the black 
 product, at about 120 F., with 75 parts of hydrate of potash andJtOO of 
 water until it has acquired a fine red colour. The permanence of vermilion 
 paint is, of course, attributable to the circumstance that it resists the 
 action of light, of oxygen, carbonic acid, aqueous vapour, and even of the 
 sulphuretted hydrogen and sulphurous or sulphuric acid which contaminate 
 the air of towns, whereas the red paints containing lead are blackened by 
 sulphuretted hydrogen, and all vegetable and animal reds are liable to be 
 bleached by atmospheric oxygen and by sulphurous acid. 
 
 When the black precipitated mercuric sulphide is boiled with solution 
 of corrosive sublimate, it is converted into a white chlorosulphide of 
 mercury, HgCl . 2HgS, which is also formed when a small quantity of 
 hydrosulphuric acid is added to corrosive sublimate. 
 
 274. Equivalent and atomic weights of mercury. The analysis of the 
 
374 ATOMIC WEIGHT OF MERCURY. 
 
 red oxide of mercury proves it to contain 1 equivalent (8 parts by weight) of 
 oxygen combined with 100 parts of mercury ; therefore, assuming it to be 
 composed of one equivalent of each element, the equivalent of mercury 
 would be 100. But if the black oxide, which contains 200 of mercury 
 combined with 8 of oxygen, be regarded as composed of single equivalents, 
 that of mercury will be 200. The greater stability of the red oxide, how- 
 ever, encourages the belief that it contains one equivalent 'of mercury 
 and one of oxygen, for the black oxide is easily resolved into metallic 
 mercury and the red oxide. This argument also applies to other mer- 
 curic compounds, which are decidedly more stable than the mercurous 
 compounds. Thus, calomel (mercurous chloride) exhibits a disposition 
 to separate into metallic mercury and mercuric chloride, leading to the 
 belief that the equivalent of chlorine (3 5 '5) is combined with one 
 equivalent (100) of mercury in the latter, and with two equivalents (200) 
 in calomel. Moreover, the strongly basic character of the red oxide of 
 mercury classes it with the oxides of silver and lead, which were allowed 
 to contain single equivalents, whilst the feebly basic character and 
 instability of the mercurous oxide places it on a par with the suboxide 
 of copper. 
 
 In determining the atomic weight of mercury, we are able to compare it 
 with hydrogen, under similar physical conditions, for the specific gravity 
 of the vapour of mercury has been found to be 6 '9 7 6, or 100 times that of 
 hydrogen. If 1 vol. or 1 atom of hydrogen, therefore, be taken to weigh 
 1, 1 vol. or 1 atom of mercury should weigh 100. 
 
 The specific gravity, or weight of 1 vol. of calomel vapour, is 8*35. If 
 the atom of mercury = 100, calomel will contain 2 atoms of mercury and 
 1 atom of chlorine 
 
 Weight of 2 vols. of mercury vapour, . 13*952 
 1 vol. of chlorine, . . . 2-470 
 
 16-422 
 
 which represents, as nearly as can be expected, the weight of 2 vols. of 
 calomel vapour. Hence, 1 molecule (or 2 vols.) of calomel vapour con- 
 tains 2 vols. of mercury vapour (or 2 atoms) and 1 vol. (1 atom) of 
 chlorine, and its molecular formula should be Hg 2 Cl, or the same as its 
 equivalent formula. 
 
 The specific gravity of the vapour of corrosive sublimate is 9 '8 
 
 Weight of 1 vol. of mercury vapour, . 6 '9 7 6 
 1 vol. of chlorine, . . . 2*470 
 
 9-446 
 
 so that 1 volume of corrosive sublimate vapour contains 1 vol. of mercury 
 and 1 vol. of chlorine, thus presenting a deviation from the hydrochloric 
 acid type, in which 1 vol. of each of the elements form 2 vols. of the com- 
 pound. In order to bring corrosive sublimate under the general rule that one 
 molecule of a compound body occupies two volumes, its molecular formula 
 must be written Hg 2 Cl g , representing 2 vols. Similar reasoning leads to 
 the conclusion that the bromides of mercury have the molecular formulae 
 Hg 2 Br and Hg 2 Br 2 , and the red iodide of mercury Hg 2 I 2 . 
 
 The vapour of vermilion has the specific gravity 5 -51. Since 1 vol. of 
 sulphur vapour (at 1900 F.) weighs 2*23, and is combined with mercury 
 
ATOMIC FORMULAE OF MERCURIAL COMPOUNDS. 
 
 375 
 
 in the proportion of 16 to 100, the weight of mercury combined with it 
 iii vermilion is 13*952 
 
 2 vols. of mercury vapour weigh 
 1 vol. of sulphur vapour weighs 
 
 13-952 
 2-230 
 
 16-182 
 
 amounting as nearly as possible to three times the specific gravity of the 
 vapour of vermilion. Hence, 3 vols. of vermilion vapour contain 2 vols. 
 o* 2 atoms of mercury vapour, and 1 vol. or 1 atom of sulphur vapour ; 
 whereas, in accordance with the composition of hydrosulphuric acid, the 
 2 vols. of mercury and 1 vol. of sulphur should be condensed into 2 vols. 
 The anomaly might be explained on the supposition that the high tem- 
 perature requisite to convert the vermilion into vapour suffices to suspend 
 the attraction between its elements, so that the vapour of which the 
 specific gravity is taken is not really that of the compound of mercury 
 and sulphur (which should occupy two vols.), but a mixture of the 2 vols. 
 of mercury vapour and 1 vol. of sulphur vapour, occupying 3 vols. This 
 view of the temporary decomposition of the vapour receives some slight 
 support from the convertibility of the black into the red sulphide by sub- 
 limation. 
 
 The above considerations would lead to the adoption for vermilion of 
 the molecular formula, Hg a S ( = 2 vols. ?) 
 
 The specific heat of mercury is twice as great as it should be if its 
 atomic weight be = 100, and this, conjoined with some other considera- 
 tions, has led many chemists to adopt 200 as the atomic weight of mer- 
 cury, thus making it a diatomic metal. It is evident that in calomel the 
 200 parts of mercury, which are combined with 35-5 parts ,of chlorine, 
 occupy the place of 1 part of hydrogen in hydrochloric acid, so that 
 mercurosum, Hg' (or the mercury in mercurous salts), is monatomic ; 
 whilst in corrosive sublimate the 200 parts of mercury are combined with 
 71 parts of chlorine, and occupy the place of 2 parts of hydrogen in 
 hydrochloric acid ; hence mercuricum, Hg" (or the mercury in mercuric 
 salts), is diatomic. 
 
 The following table exhibits the formula? of some of the chief com- 
 pounds of mercury on the three views : 
 
 
 Equiv. Formula. 
 Hg = 100. 
 
 Atomic Formula, 
 Hg = 100 = 1 vol. 
 
 Atomic Formula, 
 Hg = 200 = 2 vols. 
 
 Mercurous oxide, 
 
 Hg 2 = 208 
 
 Hg 4 O =416 
 
 Hg 2 O = 416 ^ 
 
 Mercuric oxide, 
 
 HgO = 108 
 
 Hg 2 O = 216 
 
 HgO = 216 
 
 Calomel, 
 
 Hg 2 Cl == 235-5 { 
 
 Hg 9 Cl = 235-5 
 
 = 2 vols. 
 
 HgCl = 235-5 
 = 2 vols. 
 
 Corrosive sub- ) 
 liraate, j 
 
 HgCl = 135-5 | 
 
 Hg 2 Cl 2 = 271 
 = 2 vols. 
 
 HgCI 2 = 271 
 = 2 vols. 
 
 Mercurous sul- ) 
 pliide, . . \ 
 
 Hg 2 S = 216 
 
 Hg 4 S = 432 
 
 Hg 2 S = 432 
 
 Vermilion, . 
 
 HgS = 116 { 
 
 Hg 2 S = 232 
 = 3 vols. 
 
 HgS = 232 
 = 3 vols. 
 
 White preci- 1 
 pitate, . . j 
 
 NH 2 Hg . HgCl 
 = 251-5 
 
 NH 2 Hg.HgCl 
 = 251-5 
 
 NH 2 Hg"Cl 
 = 261-5 
 
376 
 
 USES OF BISMUTH. 
 
 BISMUTH. 
 
 275. Bismuth, though useful in various forms of combination, is too 
 brittle to be employed in the pure metallic state. It is readily distin- 
 guished from other metals by its peculiar reddish lustre and its highly 
 crystalline structure, which is very perceptible upon a freshly broken 
 surface; large cubical (or, strictly speaking, rhombohedral) - crystals of 
 bismuth are easily obtained by melting a few ounces in a crucible, allow- 
 ing it to cool till a crust has formed upon the surface, and pouring out 
 the portion which has not yet solidified, when the crystals are found lining 
 the interior of the crucible. It is somewhat lighter than lead (sp. gr. 9-8), 
 and volatilises more readily at high temperatures. 
 
 Unlike most other metals, bismuth is found chiefly in the metallic state, 
 disseminated, in veins, through gneiss and clay-slate, The chief supply 
 is derived from the mines of Schneeberg, in Saxony, where it is associated 
 with the ores of cobalt. 
 
 In order to extract the metal from the masses of earthy matter through 
 which it is distributed, advantage is taken of its very low fusing point 
 
 (507 F.) The ore is broken 
 into small pieces, and in- 
 troduced into iron cylinders 
 which are fixed in an in- 
 clined position over a fur- 
 nace (fig. 254). The upper 
 opening of the cylinders, 
 through which the ore is in- 
 troduced, is provided with 
 an iron door, and the lower 
 opening is closed with a 
 plate of fire-brick perforated 
 
 Fig. 254. Extraction of bismuth. for the escape of the metal, 
 
 which flows out when the 
 
 cylinders are heated, into iron receiving pots, which are kept hot by a 
 charcoal fire. 
 
 Commercial bismuth generally contains considerable quantities of arsenic, 
 sulphur, and silver ; it is sometimes cupelled in the same manner as lead, 
 in order to extract the silver, the oxide of bismuth being afterwards again 
 reduced to the metallic state by heating it with charcoal. Pure bismuth 
 dissolves entirely and easily in diluted nitric acid (sp. gr. 1 -2) ; but if it 
 contains arsenic, a white deposit of arseniate of bismuth is obtained. Hydro- 
 chloric and diluted sulphuric acids will not act upon bismuth. 
 
 The chief use of bismuth is in the preparation of certain alloys with 
 other metals. Some kinds of type metal and stereotype metal contain 
 bismuth, which confers upon them the property of expanding in the 
 mould during solidification, so that they are forced into the finest lines of 
 the impression. 
 
 This metal is also remarkable for its tendency to lower the fusing point 
 of alloys, which cannot be accounted for merely by referring to the low 
 fusing point of the metal itself. Thus, an alloy of 2 parts bismuth, 
 1 part lead, and 1 part tin, fuses below the temperature of boiling water, 
 although the most fusible of the three metals, tin, requires a temperature 
 of 442 F. Bismuth is also employed, together with antimony, in the con- 
 struction of thermo-electric piles. 
 
EQUIVALENT AND ATOMIC WEIGHTS OF BISMUTH. 377 
 
 276. Oxides of bismuth. Three compounds of bismuth with oxygen have been pre- 
 pared; bismuthous oxide Bi0 2 , bismuthic oxide Bi0 3 , and bismuthic acid Bi0 5 . 
 
 Bismuthous oxide (Bi0 2 ) is obtained as a black precipitate by reducing terchloride 
 of bismuth with protochloride of tin in the presence of an excess of potash. It is 
 easily converted into bismuthic oxide when heated in contact with air. 
 
 Bismuthic oxide, or teroxide of bismuth (Bi0 3 ), is the basic and most important 
 oxide of the metal. It is formed when bismuth is heated in air, or when nitrate 
 of bismuth is decomposed by heat, and is a yellow powder which becomes brown 
 when heated, and fuses easily. Bismuthic oxide forms the rare mineral bismuth- 
 ochre. 
 
 Bismuthic acid (Bi0 5 ) is formed when teroxide of bismuth is suspended in a strong 
 solution of potash through which chlorine is passed, when a red solution of bis- 
 muthate of potash is obtained, and hydrated bismuthic acid (HO . Bi0 5 ) is precipi- 
 tated as a red powder, which becomes brown and anhydrous at 270 F. It is easily 
 decomposed by heat, evolving oxygen and leaving Bi0 3 . BiO 5 . "When heated with 
 acids it also evolves oxygen, and forms salts of bismuthic oxide. The bismuthates 
 of the alkalies are very unstable, being decomposed by water. 
 
 277. The only two salts of bismuth which are known in the arts are the 
 basic nitrate (trisnitrate of bismuth or flake-white) and the oxy chloride of 
 bismuth (pearl-white). The preparation of these compdunds illustrates one 
 of the characteristic properties of the salts of bismuth, viz., the facility 
 with which they are decomposed by water with the production of in- 
 soluble basic salts. 
 
 If bismuth be dissolved in nitric acid, it acquires oxygen from the latter, 
 and becomes teroxide of bismuth, which combines with nitric acid to 
 form the nitrate of bismuth (Bi0 3 . 3N0 5 ), and this may be obtained in 
 prismatic crystals of the composition Bi0 3 . 3N0 5 + lOAq. If the solu- 
 tion be mixed with a large quantity of water, it deposits a precipitate of 
 flake-white (Bi0 3 . N0 5 + HO), or basic nitrate of bismuth, the remainder 
 of the nitric acid being left in the solution. 
 
 Pearl-white has the composition BiCl 3 . 2Bi0 3 + HO, and is obtained by 
 dissolving bismuth in nitric acid, and pouring the solution into water in 
 which common salt has been dissolved. 
 
 Terchloride of bismuth (Bi01 3 ) may be distilled over when bismuth is heated in a 
 current of dry chlorine ; it is a deliquescent fusible solid, easily dissolved by hydro- 
 chloric acid, but decomposed by water, with formation of the above-mentioned 
 oxychloride of bismuth; 3BiCl 3 + 6HO = BiCl 3 .2Bi0 3 -f- 6HC1. This compound is 
 so insoluble in water that nearly every trace of bismuth may be precipitated from a 
 moderately acid solution of the terchloride by adding much water. 
 
 Bismuthous sulphide (BiS 2 ) is- sometimes found in nature, but more frequently 
 bismuthic sulphide (BiS 3 ) or bismuth glance, which occurs in dark-grey lustrous prisms 
 isomorphous with native sulphide of antimony. It is also obtained as a black pre- 
 cipitate by the action of hydrosulphuric acid upon bismuthic salts. Bismuthic sul- 
 phide is not soluble in diluted sulphuric or hydrochloric acid, but dissolves easily in 
 nitric acid. 
 
 278. Equivalent and atomic weights of bismuth. The analysis of the chloride of bis- 
 muth has shown it to contain 35-5 parts by weight (1 equivalent) of chlorine com- 
 bined with 70 parts of bismuth ; but the very marked analogy which exists between 
 this chloride and the terchloride of antimony has led to the belief that it is also a 
 terchloride, containing 3 equivalents of chlorine combined with one equivalent (210 
 parts) of bismuth, and the assumption of the number 210 for the equivalent of bis- 
 muth, will be found to receive confirmation from the general analogies of this metal 
 with antimony and arsenic. The specific heat of bismuth confirms the conclusion 
 drawn from the composition of the chloride, that the atomic weight of bismuth is 
 identical with its equivalent, or 210, and that this element is triatomic, like 
 nitrogen, phosphorus, and arsenic among the non-metals. The atomic formula 
 for bismuthic oxide is Bi 2 ^ 3 ; bismuthic chloride, BiCl 3 ; bismuthic sulphide, 
 Bi 2 S 3 . 
 
378 CKUDE ANTIMONY REGULUS OF ANTIMONY. 
 
 ANTIMONY. 
 
 279. Antimony is nearly allied to bismuth in "both its physical and 
 chemical characters. It is even harder and more brittle than that metal, 
 being easily reduced to a black powder. Its highly crystalline structure 
 is another very well-marked feature, and is at once perceived upon the 
 surface of an ingot of antimony, where it is exhibited in beautiful fern-like 
 markings (star antimony). Its crystals belong to the same system (the 
 rhombohedral) as those of bismuth and arsenic. It is much lighter than 
 bismuth (sp. gr. 6*715), and requires a higher temperature (800 F.) to 
 fuse it, though it is more easily converted into vapour, so that, when 
 strongly heated in air, it emits a thick white smoke, the vapour being 
 oxidised. like bismuth, it is but little affected by hydrochloric or dilute 
 sulphuric acid, but nitric acid oxidises it, though it dissolves very little of 
 the metal, the greater part being left in the form of antimonic acid. The 
 best mode of dissolving antimony is to boil it with hydrochloric acid and 
 to add nitric acid by degrees. 
 
 Antimony is chiefly found in nature as grey antimony ore or sulphide 
 of antimony (SbS 3 ), which occurs in Cornwall, but much more abundantly 
 in Hungary. It is found in veins associated with galena, iron pyrites, 
 quartz, and heavy spar. In order to purify it from these, advantage is 
 taken of its easy fusibility, the ore being heated upon the hearth of a re- 
 verberatory furnace, with some charcoal to prevent oxidation, when the 
 sulphide of antimony melts and collects below the impurities, whence it 
 is run off and cast into moulds. The product thus obtained is known in com- 
 merce as crude antimony, and contains sulphides of arsenic, iron, and lead. 
 
 To obtain regulus of antimony or metallic antimony, the sulphide of 
 antimony is sometimes fused in contact with refuse metallic iron (such as 
 the clippings of tin-plate), when sulphide of iron is formed, and collects 
 as a fused slag upon the surface of the melted antimony 
 
 SbS 3 + Fe 3 - 3FeS + Sb . 
 
 The antimony thus obtained always contains a considerable proportion of 
 iron. 
 
 A purer product is procured by another process, which consists in 
 roasting the sulphide in a reverberatory furnace at a temperature insuffi- 
 cient to fuse it, for about twelve hours, when most of the sulphur and 
 arsenic are expelled as sulphurous and arsenious acids, carrying with them 
 a considerable quantity of oxide of antimony. The roasted ore has a 
 brown-red colour, and contains both oxide and sulphide of antimony : it 
 is mixed into a paste with % its weight of charcoal saturated with a strong 
 solution of carbonate of soda. The mixture is strongly heated in crucibles, 
 when the oxide of antimony is reduced by the charcoal, and a portion of 
 the sulphide, having been converted into oxide by double decomposition 
 with the soda (SbS 3 + 3NaO = Sb0 3 + 3NaS), is also reduced, the re- 
 mainder of the sulphide combining with the sulphide of sodium to form a 
 slag which floats above the metallic antimony; the latter is cast into 
 ingots for the market, and the slag, known as crocus of antimony (chiefly 
 3NaS . SbS 3 ), is employed for the preparation of some of the compounds- 
 of the metal. 
 
 On the small scale, antimony may be extracted from the sulphide by fusing it in 
 an earthen crucible with 4 parts of commercial cyanide of potassium, at a moderate 
 heat; or by mixing 4 parts of the sulphide with 3 of bitartrate of potash and \\ of 
 
OXIDES OF ANTIMONY. 879 
 
 nitre, and throwing the mixture, by small portions, into a red-hot crucible, when 
 the sulphur is oxidised and converted into sulphate of potash by the nitre, which is 
 not present in sufficient quantity to oxidise the antimony, so that the metal collects 
 at the bottom of the crucible. 
 
 The brittleness of antimony renders it useless in the metallic state ex- 
 cept for the construction of thermo-electric piles, where it is employed in 
 conjunction with bismuth. Antimony is employed, however, to harden 
 several useful alloys, such as type-metal, shrapnel-shell bullets, Britannia 
 metal, and pewter. 
 
 Amorphous antimony. The ordinary crystalline form of antimony maybe obtained, 
 like copper and other metals, by decomposing solutions containing the metal by 
 transmitting the galvanic current ; but in some cases the antimony is deposited from 
 very strong solutions in an amorphous condition, having properties very different 
 from those of ordinary antimony. The best mode of obtaining it in this form is to 
 decompose a solution of 1 part of tartar emetic (tartrate of antimony and potash) in 
 4 parts of a strong solution of terchloride of antimony (obtained by heating hydro- 
 chloric acid with sulphide of antimony till it refuses to dissolve any more), by the 
 aid of three cells of Smee's battery, the zinc of which is connected by a copper wire 
 with a plate of copper immersed in the antimonial solution, whilst the platinised 
 silver of the battery is connected with a plate of antimony in the same solution, at 
 some little distance from the copper plate. The deposit of antimony which forms 
 upon the copper has a brilliant metallic appearance, but is amorphous, and not crys- 
 talline, like the ordinary metal. If it be gently heated or sharply struck, its tem- 
 perature suddenly rises to about 400, and it becomes converted into a form more 
 nearly resembling crystalline antimony. At the same time, however, thick fumes of 
 terchloride of antimony are evolved, for this substance is always present in the amor- 
 phous antimony to the amount of 5 or 6 per cent.,* so that, as yet, there is not suffi- 
 cient evidence to establish beyond a doubt the existence of a pure amorphous form 
 of antimony corresponding to amorphous phosphorous, however probable this may 
 appear from the chemical resemblance between these elements. 
 
 280. Oxides of antimony. There are two well-known oxides of anti- 
 mony, the teroxide (Sb0 3 ) and antimonic acid (Sb0 5 ). Teroxide or sesgui- 
 oxide of antimony, or antimonic oxide, is formed when antimony burns in 
 air, and is prepared on a large scale by roasting either the metal or the 
 sulphide in air, for use in painting as a substitute for white lead. It is 
 also found in nature as white antimony ore or valentinite. Antimonic 
 oxide forms a crystalline powder usually composed of minute prisms having 
 the shape of the rarer form of arsenious acid (p. 251), whilst occasionally 
 it is obtained in crystals similar to those of the common octahedral 
 arsenious acid, with which, therefore, antimonic oxide is isodimorpJwus.^ 
 When heated in air it assumes a yellow colour, afterwards takes fire, 
 smoulders, and becomes converted into the antimoniate of teroxide of 
 antimony (Sb0 3 . Sb0 5 = Sb0 4 ), which was formerly regarded as an inde- 
 pendent oxide. The teroxide is insoluble in water, but acids dissolve it, 
 forming salts, though its basic properties are weak, and its salts rather ill 
 defined. Potash and soda are also capable of dissolving it, whence it is 
 sometimes called antimonious acid.% 
 
 Antimonic acid (Sb0 5 ) is formed when antimony is oxidised with nitric 
 acid ; it then forms a white powder, which should be well washed and 
 dried. When heated it becomes pale yellow, and is decomposed at a high 
 
 * It has been plausibly suggested that the sudden rise of temperature may be due to 
 the presence of an antimony compound analogous to the so-called chloride of nitrogen, the 
 latter element being connected with antimony by several chemical analogies. 
 
 f The octahedral form appears to be produced only when the prismatic form is slowly 
 sublimed in a non-oxidising atmosphere. The mineral exitele is prismatic oxide of anti- 
 mony, and senarmontite is the octahedral form of that oxide. 
 
 J Two crystallised antimonites of soda have been obtained, the neutral antimonite 
 NaO. Sb0 3 + 6Aq., and the terantimonite NaO. 3Sb0 3 + 2Aq. ; the former is sparingly 
 soluble, the latter almost insoluble in water. 
 
380 CHLORIDES OF ANTIMONY. 
 
 temperature, leaving Sb0 3 . Sb0 6 . It is dissolved by solution of potash, 
 forming antimoniate of potash. 
 
 A better method of obtaining the antimoniate of potash consists in 
 gradually adding 1 part of powdered antimony to 4 parts of nitre fused in 
 a clay crucible, when the oxygen of the nitre converts the antimony into 
 antimonic acid, which combines with the potash. The mass is powdered 
 and washed with warm water to remove the excess of nitre aiid the nitrate 
 of potash, when the insoluble anhydrous antimoniate of potash is left ; 
 and on boiling this for an hour or two with water, it becomes hydrated 
 and dissolves. The solution, when evaporated, leaves a gummy mass of 
 antimoniate of potash, having the composition KO. Sb0 5 + 5Aq. 
 
 When the solution of antimoniate of potash is treated with carbonic 
 acid, a crystalline precipitate of biantimoniate of potash (KO . 2Sb0 5 ) is 
 obtained. If antimoniate of potash be fused (in a silver crucible) with 
 hydrate of potash, it becomes converted into metantimoniate of potash 
 (2KO . Sb0 5 ), which is decomposed by water into potash and bimetan- 
 timoniate of potash (KO . HO . Sb0 5 ), which may be crystallised from the 
 solution. This latter salt is valuable as a test for soda, since the bimetan- 
 timoniate of soda, NaO . HO . Sb0 5 , is one of the very few salts of soda 
 which are insoluble in water, and is therefore obtained as a crystalline 
 precipitate when the bimetantimoniate of potash is added to a solution 
 containing soda. The solution of bimetantimoniate of potash is gradually 
 changed by keeping, into antimoniate of potash (KO . Sb0 5 ), which does 
 not so readily precipitate soda. 
 
 It will be remarked that the aiitinioniates correspond in composition 
 with the ' monobasic (or meta) phosphates, whilst the metantimoniates 
 represent the bibasic (or pyro) phosphates. 
 
 Naples yellow is a compound of antimonic acid with oxide of lead. 
 
 281. Antimonietted hydrogen (SbH 3 ?) is obtained, mixed with free hydro- 
 gen, when an alloy of zinc and antimony is acted on by diluted sulphuric 
 acid, or when a solution of a salt of antimony (tartar emetic, for example) 
 is poured into a hydrogen apparatus containing zinc and dilute sulphuric 
 acid (fig. 255). If the gas be inflamed as it issues into the air, it burns 
 with a livid flame, emitting fumes of antimonic oxide, 
 and when a piece of glass or porcelain is depressed in 
 the flame (fig. 256) it becomes coated with a black 
 film of metallic antimony. A red heat decomposes the 
 gas into its elements, so that if the tube through which 
 it is passing be heated with a spirit lamp (fig. 257) a 
 lustrous black deposit of antimony will be formed just 
 beyond the heated part. The composition of anti- 
 
 __ monietted hydrogen is not certainly established, since 
 
 Fig. 255. it has never been obtained unmixed with hydrogen ; 
 
 but it is believed to contain SbH 3 , because, when 
 passed into nitrate of silver, it gives a black precipitate containing SbAg 3 . 
 It would then be analogous to ammonia (NH 3 ), phosphuretted hydrogen 
 (PH 3 ), and arsenietted hydrogen (AsH 3 ). Very minute 
 quantities of antimony are detected in chemical analysis 
 by converting it into this form. 
 
 Fig. 256. 282. CHLORIDES OF ANTIMONY. Chlorine and anti- 
 
 mony combine readily, with evolution of heat and light ; 
 the chlorides are among the most important compounds of this metal. 
 
SULPHIDES OF ANTIMONY. 381 
 
 Tercliloride or sesquichloride of antimony (SbCl 3 ) may be prepared by 
 distilling 3 parts of powdered antimony with 
 8 parts of corrosive sublimate, when calomel 
 and an amalgam of antimony are left, and 
 the terchloride of antimony (boiling at 433 
 F.) distils over 
 
 Sb 2 + 4HgCl = SbCl 3 + SbHg 2 + Hg a Cl . 
 
 It can also be obtained by boiling powdered 
 antimony or sulphide of antimony to dry- 
 ness with strong sulphuric acid, and distil- 
 ling the sulphate of teroxide of antimony 
 thus obtained, with common salt. The ter- 
 chloride is a soft grey crystalline fusible P itr 257 
 solid, whence its old name of butter of anti- 
 mony. It may be dissolved in a small quantity of water, but a large 
 quantity of water decomposes it, forming a bulky white precipitate, which 
 is an oxychloride of antimony (3SbCl 3 + 6HO = SbCl ? . 2Sb0 3 + 6HC1). 
 When hot water is added to a hot solution of terchloride of antimony in 
 hydrochloric acid, minute prismatic needles are deposited, containing 
 SbCl 3 . 5Sb0 3 , and formerly called powder of Algarotli. The terchloride 
 of antimony, in its behaviour with water, much resembles that of bismuth. 
 Terchloride of antimony is occasionally used in surgery as a caustic ; it also 
 serves as a bronze for gun-barrels, upon which it deposits a film of 
 antimony. 
 
 Pentachloride of antimony (SbCl 5 ) is prepared by heating coarsely 
 powdered antimony in a retort, through which a stream of dry chlorine is 
 passed (fig. 199), the neck of the retort being fitted into an adapter, which 
 serves to condense the pentachloride. One ounce of antimony will require 
 the chlorine from about 6 oz. of common manganese and 18 oz. (measured) 
 of hydrochloric acid. The pure pentachloride is a colourless fuming 
 liquid of a very suffocating odour ; it combines energetically with a small 
 quantity of water, forming a crystalline hydrate, but an excess of water 
 decomposes it into hydrochloric and hydrated metantimonic acids, the 
 latter forming a white precipitate 
 
 SbCl 5 + 7HO = 5HC1 + 2HO . SbO 
 
 Pentachloride of antimony is employed by the chemist as a chlorinating 
 agent ; thus, olefiant gas (C 4 H 4 ) when passed through it, is converted into 
 Dutch liquid (C 4 H 4 C1. 2 ), and carbonic oxide into phosgene gas, the penta- 
 chloride of antimony being converted into terchloride. 
 
 The pentachloride of antimony is the analogue of pentachloride of 
 phosphorus, and a chlorosulphide of antimony (SbCl 8 S 2 ), corresponding to 
 chlorosulphide of phosphorus, is obtained as a white crystalline solid by 
 the action of hydrosulphuric acid upon pentachloride of antimony. 
 
 283. Sulphides of antimony. The tersulphide or sesquisulphide of 
 antimony (SbS 3 ) has been noticed as the chief ore of antimony. It is a 
 heavy mineral (sp. gr. 4 -63) of a dark-grey colour and metallic lustre, 
 occurring in masses which are made up of long prismatic needles. It fuses 
 easily, and may be sublimed unchanged out of contact with air. It is 
 easily recognised by heating it, in powder, with hydrochloric acid, when 
 it evolves the odour of hydrosulphuric acid, and if the solution be poured 
 
382 ATOMIC WEIGHT OF ANTIMONY. 
 
 into water, it deposits an orange precipitate. This orange sulphide, which 
 has the same composition as the grey sulphide, is also obtained by adding 
 hydrosulphuric acid to a solution of a salt of antimony (for example, tartar- 
 emetic) acidulated with hydrochloric acid. It may be converted into the 
 grey sulphide by the action of heat. The orange variety constitutes the 
 antimony vermilion, the preparation of which has been described at p. 213. 
 Native tersulphide of antimony is employed, in conjunction with chlorate 
 of potash, in the friction-tube for firing cannon ; it is also used in per- 
 cussion caps, together with chlorate of potash and fulminate of mercury. 
 Its property of deflagrating with a bluish- white flame when heated with 
 nitre renders it useful in compositions for coloured fires. 
 
 Glass of antimony is a transparent red mass obtained by roasting the 
 tersulphide of antimony in air, and fusing the product ; it contains about 
 8 parts of teroxide and 1 part of tersulphide of antimony. 
 
 Red antimony ore is an oxysulphide of antimony, Sb0 3 . 2SbS 3 . 
 
 Pentasulphide of antimony (SbS 3 ) is obtained as a bright orange-red 
 precipitate by the action of hydrosulphuric acid upon a solution of penta- 
 chloride of antimony in hydrochloric acid. 
 
 Both the sulphides of antimony are sulphur-acids, capable of combining 
 with the alkaline sulphides to form sulpliantimonites and sulphantimoniates 
 respectively. Hence they are easily dissolved by alkalies and alkaline 
 sulphides. Even metallic antimony, in powder, is dissolved when gently 
 heated with solution of sulphide of potassium, in which sulphur has been 
 dissolved, any lead or iron which may be present being left in the residue, 
 so that the antimony may be tested by this process as to its freedom from 
 those metals. 
 
 Mineral kermes is a variable mixture of teroxide and tersulphide of 
 antimony, which is deposited as a reddish-brown powder from the solution 
 obtained by boiling tersulphide of antimony with potash or soda. It was 
 formerly much valued for medicinal purposes. 
 
 Schlippe's salt is the sulphantimoniate of sulphide of sodium 
 (3NaS , SbS 5 , 1 8HO) and may be obtained in fine transparent tetrahedral 
 crystals. 
 
 284. Equivalent and atomic weights of antimony. The solid chloride of 
 antimony (terchloride) has been found to contain 35*5 parts by weight 
 (1 eq.) of chlorine, combined with 40'66 parts of antimony, so that if this 
 chloride be assumed to contain 1 equivalent of antimony, combined with 
 one of chlorine, the equivalent weight of the metal would be 40*66. But, 
 upon this supposition, the liquid (penta-) chloride would contain 1 eq. 
 of antimony and If eq. of chlorine, whilst the analogy of this chloride 
 with pentachloride of phosphorus shows that it must contain 5 eqs. of 
 chlorine, and that the solid chloride must contain 3 eqs. of chlorine com- 
 bined with 1 eq. of antimony ; hence, the equivalent weight of antimony 
 is 122. 
 
 The specific heat of antimony, and its isomorphism with arsenic, show 
 that its atomic weight is identical with its equivalent, so that it usually 
 acts the part of a triatomic element, occupying the place of three atoms 
 of hydrogen. 
 
 The weight of 1 volume, or specific gravity, of the vapour of terchloride 
 of antimony, has been found to be 8*1. Assuming it to have a normal 
 constitution, and to contain, in 2 volumes, 1 vol. of antimony vapour and 
 3 vols. of chlorine, the specific gravity of vapour of antimony would = 8*79. 
 
EXTRACTION OF TIN FKOM TIN-STONE. 383 
 
 Weight of 2 vols. vapour of SbCL, . . 16-20 
 3 vols. chlorine, . . . 7 '41 
 
 1 vol. of antimony vapour, . 8 -7 9 
 
 The weight of 1 voL of antimony vapour, therefore, would be rather more 
 than 122 times that of 1 vol. of hydrogen, so that this number may be 
 accepted as the atomic weight of the metal. The atomic formulce of 
 some of the chief compounds of antimony are antimonic oxide, Sb.,0 3 ; 
 antimonic acid, Sb 2 O 5 ; sulphantimonious acid, Sb a & 3 ; sulphantimonic 
 acid, Sb 2 S 5 ; terchloride of antimony, SbCl 3 ; pentachloride, SbCl 5 . 
 
 The equivalent of antimony was formerly taken at half its present value, 
 whence the names of sesquichloride, &c., instead of terchloride, &c. 
 
 TIN. 
 
 285. Tin is by no means so widely diffused as most of the other metals 
 which are largely used, and is scarcely ever found in the metallic state in 
 nature. Its only important ore is that known as tin-stone, which is a 
 binoxide of tin (SnO.,), and is generally found in veins traversing quartz, 
 granite, or slate. It is generally associated with arsenical iron pyrites, 
 and with a mineral called wolfram, which is a compound of tungstic acid 
 (W0 3 ) with the oxides of iron and manganese. 
 
 Tin-stone is sometimes found in alluvial soils in the form of detached 
 rounded masses ; it is then called stream tin ore, and is much purer than 
 that found in veins, for it has undergone a natural process of oxidation 
 and levigation exactly similar to the artificial treatment of the impure ore. 
 These detached masses of stream tin ore are not unfrequently rectangular 
 prisms with pyramidal terminations. 
 
 The Cornish mines furnish the largest supplies of tin, and "those of 
 Malacca and Banca stand next. At the Cornish tin-works the purer 
 portions of the ore are picked out by hand, and the residue, which contains 
 quartz and other earthy impurities, together with copper pyrites and 
 arsenical iron pyrites, is reduced to a coarse powder in the stamping-mills, 
 and washed in a stream of water. The tin-stone, being extremely hard, 
 is not reduced to so fine a powder as the pyritous minerals associated with 
 it, and these latter are therefore more readily carried away by the stream 
 of water than the tin-stone. The removal of the foreign matters from the 
 ore is also much favoured by the high specific gravity of the binoxide of 
 tin, which is 6*5, whilst that of sand or quartz is only 2 '7, so that the 
 latter would be carried off by a stream which would not disturb the former. 
 So easily and completely can this separation be effected, that a sand con- 
 taining less than one per cent, of tin-stone is found capable of being 
 economically treated. 
 
 In order to expel any arsenic and sulphur which may still remain in 
 the washed ore, it is roasted in quantities of, 8 or 10 cwts. in a reverbera- 
 tory furnace, when the sulphur is disengaged in the form of sulphurous 
 acid, and the arsenic in that of arsenious acid, the iron being left in the 
 state of sesquioxide, and the copper partly as sulphate of copper, partly 
 as unaltered sulphide. To complete the oxidation of the insoluble sulphide 
 of copper, and its conversion into the soluble sulphate, the roasted ore is 
 moistened with water and exposed to the air for some days, after which 
 the whole of the copper may be removed by again washing with water. 
 
384 
 
 PURIFICATION OF TIN. 
 
 A second washing in a stream of water also removes the sesquioxide of 
 iron in a state of suspension, and this is much more easily effected than 
 when the iron was in the form of pyrites, since the difference between the 
 specific gravity of this mineral (5*0) and that of the tin-stone (6 -5) is far 
 less than that between sesquioxide of iron and tin-stone. 
 
 The ore thus purified contains between 60 and 70 per cent, of tin ; it 
 is mixed very intimately with about J of powdered coal, and a little lime 
 or fluor spar to form a fusible slag with the earthy impurities ; the mixture 
 is sprinkled with water to prevent its dispersion by the draught of air, 
 and thrown on the hearth (A, fig. 258) of a reverberatory furnace, in 
 charges of between 20 and 25 cwts. 
 
 The temperature is not permitted 
 to rise too high at first, lest a portion 
 of the oxide of tin should combine 
 with the silicic acid to form a sili- 
 cate, from which the metal would 
 be reduced with difficulty. 
 
 During the first 6 or 8 hours the 
 doors of the furnace are kept shut, 
 so as to exclude the air and favour 
 the reducing action of the carbon 
 upon the binoxide of tin, the oxy- 
 gen of which it converts into car- 
 bonic oxide, leaving the tin in the 
 metallic state to accumulate upon 
 the hearth beneath the layer of slag. 
 When the reduction is deemed com- 
 plete, the mass is well stirred with 
 an iron paddle to separate the metal 
 from the slag ; the latter is run out 
 first, and the tin is then drawn off 
 into an iron pan (B), where it is 
 allowed to remain at rest for the 
 dross to rise to the surface, and is ladled out into ingot-moulds. 
 
 The slags drawn out of the smelting-furnace are carefully sorted, those 
 which contain much oxide of tin being worked up with the next charge of 
 ore, whilst those in which globules of metallic tin are disseminated are 
 crushed, so that the metal may be separated by washing in a stream of 
 water. 
 
 The tin, when first extracted from the ore, is far from pure, being con- 
 taminated with small quantities of iron, arsenic, copper, and tungsten. 
 In order to purify it from these, the ingots are piled into a hollow heap 
 near the fire-bridge of a reverberatory furnace, and gradually heated to the 
 fusing point, when the greater portion of the tin flows into an outer basin, 
 whilst the remainder is converted into the binoxide, which remains as 
 dross upon the hearth, together with the oxides of iron, copper, and tung- 
 sten, the arsenic having passed off in the form of arsenious acid. Fresh 
 ingots of inn are introduced at intervals, until about 5 tons of the metal 
 have collected in the basin, which is commonly the case in about an hour 
 after the commencement of the operation. 
 
 The specific gravity of tin being very low (7 -285), any dross which 
 may still remain mingled with it does not separate very readily ; to 
 obviate this, the molten metal is well agitated by stirring with wet 
 
 Fig. 258. 
 
MANUFACTURE OF TIN-PLATE. 385 
 
 wooden poles, or lowering billets of wet wood into it, when the evolved 
 bubbles of steam carry the impurities up to the surface in a kind of froth ; 
 the stirring is continued for about three hours, and the metal is allowed to 
 remain at rest for two hours, when it is skimmed and ladled into ingot- 
 moulds. It is found that, in consequence of the lightness of the metal, 
 and its tendency to separate from the other metals with which it is con- 
 taminated, the ingots which are cast from the metal first ladled out of the 
 pot are purer than those from the bottom ; this is shown by striking the 
 hot ingots with a hammer, when they break up into the irregular prismatic 
 fragments known as dropped or grain-tin, the impure metal not exhibiting 
 this extreme brittleness at a high temperature. The tin imported from 
 Banca is celebrated for its purity (Straits tin). 
 
 When the tin ore contains wolfram, it is usual to purify it before smelt- 
 ing, by fusion with carbonate of soda in a reverberatory furnace, when 
 the tungstic acid is converted into tungstate of soda, which is dissolved 
 out by water and crystallised. This salt finds an application in calico- 
 printing. 
 
 On the small scale, tin may be extracted from tin-stone, by fusing 100 
 grains with 20 grains of dried carbonate of soda, and 20 of dried borax, 
 in a crucible lined with charcoal, exactly as in the extraction of iron 
 (see p. 321). 
 
 286. By its physical characters, tin is very readily distinguished from 
 other metals. If a bar of tin be bent, it emits a peculiar crackling sound. 
 With the exception of lead and zinc, it is the least tenacious' of all the 
 metals in common use ; its ductility is therefore very low, and lead is the 
 only common metal which is more difficult to draw into wire at the 
 ordinary temperature. Tin may, however, be drawn at 212 F. 
 
 In fusibility, tin surpasses all the other common metals, becoming liquid 
 at 442 F., but it is not easily vaporised. Its malleability is also very 
 great, only gold, silver, and copper exhibiting this quality in a higher 
 degree. This malleability is shown in the manufacture of tin-foil, where 
 plates of the best tin are hammered down to a certain thinness, then cut 
 up, laid upon each other, and again beaten till extended to the required 
 degree. 
 
 Tin-plate, it must be remembered, is made in a very different way, by 
 coating sheets of iron with a layer of tin ; the best kind, known as Hock 
 tin, being that which is covered with the thickest layer of tin, and after- 
 wards hammered upon a polished anvil in order to consolidate the coating 
 and make it adhere more firmly. Tin, being unaltered by exposure to air 
 at the ordinary temperature, will effectually protect the iron from rust as 
 long as the coating of tin is perfect, but as soon as a portion of the tin is 
 removed so as to leave the iron exposed, corrosion will take place very 
 rapidly, because the two metals form a galvanic couple, w r hich will decom- 
 pose the water (charged with carbonic acid) deposited upon them from 
 the air, and the iron, having the greater attraction for oxygen, will be the 
 metal attacked. In the case of galvanised iron (coated with zinc), on the 
 contrary, the zinc would be the metal attacked, and hence the greater 
 durability of this material under certain conditions. 
 
 For the manufacture of tin-plate, the very best iron refined with char- 
 coal (see p. 310) is employed, and the most important part of the process 
 consists in cleansing the iron plates from every trace of oxide which would 
 prevent the adhesion of the tin. To effect this they are made to undergo 
 
 2s 
 
386 GUN METAL. 
 
 several processes, of which the most important are (1), immersion in 
 diluted sulphuric acid; (2), heating to redness; (3), hammering and roll- 
 ing to scale off the oxide ; (4), steeping in sour bran ; (5), immersion in 
 mixed diluted sulphuric and hydrochloric acids ; (6), scouring with "bran ; 
 (7), washing with water ; they are then dried for an hour in a vessel of 
 melted tallow which prevents contact of air, and immersed for an hour 
 and a half in melted tin, the surface of which is protected from oxidation 
 by tallow ; after draining, they are dipped a second time into the tin to 
 thicken the layer ; then transferred to a bath of hot tallow to allow the 
 superfluous tin to run down to the lower edge, whence it is afterwards 
 removed by liquefying it in a vessel of melted tin, and shaking it off by a 
 sharp blow. About 8 Ibs. of tin are required to cover 225 plates, weigh- 
 ing 112 Ibs. 
 
 T erne-plate is iron coated with an alloy of tin and lead. In tinning 
 the interior of copper vessels, in order to prevent the contamination of 
 food with the metal, the surface is first thoroughly cleaned from oxide 
 by heating it and rubbing over it a little sal-ammoniac (hydrochlorate 
 of ammonia, NH 3 . HC1), which decomposes any oxide of copper, con- 
 verting it into the volatile chloride of copper (CuO + NH 3 . HC1 = 
 CuCl + HO + NH 3 ). A little resin is then sprinkled upon the metallic 
 surface, to protect it from oxidation, and the melted tin is spread over 
 it with tow. 
 
 Pins (made of brass wire) are coated with tin by boiling them with 
 cream of tartar (bitartrate of potash), common salt, alum, granulated tin, 
 and water ; the tin is oxidised at the expense of the water, and is then 
 dissolved by the acid liquid, from which solution it is reduced by the 
 action of the zinc in the brass, for zinc is more highly electro-positive than 
 tin, and is therefore capable of precipitating the metal from its solutions. 
 
 287. Alloys of tin. The solder employed for tin wares is an alloy of 
 tin and lead in various proportions, sometimes containing 2 parts of tin 
 to 1 of lead (fine solder), sometimes equal weights of the two metals 
 (common solder), and sometimes 2 parts of lead to 1 of tin (coarse solder). 
 All these alloys melt at a lower temperature than tin, and, therefore, than 
 lead. In applying solder, it is essential that the surfaces to be united be 
 quite free from oxide, which would prevent the adhesion of the solder ; 
 this is insured by the application of sal-ammoniac, or of hydrochloric 
 acid,* or sometimes of powdered borax, remarkable for its ready fusibility 
 and its solvent power for the metallic oxides. 
 
 Tin forms the chief part of the alloys known as pewter and Britannia 
 metal, the former being composed of about 4 parts of tin and 1 of lead, 
 whilst the latter contains, in addition to the tin, comparatively small 
 quantities of antimony, copper, and lead. Another similar alloy is com- 
 posed of 12 parts of tin, 1 of antimony, and a little copper. 
 
 Gun metal is an alloy of 90-5 parts of copper with 9'5 of tin, especially 
 valuable for its tenacity, hardness, and fusibility. In preparing this 
 alloy, it is usual to melt the tin, in the first place, with twice its weight 
 of copper, when a white, hard, and extremely brittle alloy (hard metal) is 
 obtained. The remainder of the copper is fused in a deoxidising flame 
 on the hearth of a reverberatory furnace, and the hard metal thoroughly 
 mixed with it, long wooden stirrers being employed. A quantity of old 
 
 * It is customary to kill the hydrochloric acid by dissolving some zinc in it. The 
 chloride of zinc is probably useful in protecting the work from oxidation. 
 
PROPERTIES OF TIN. 387 
 
 gun metal is usually melted with the copper, and facilitates the mixing of 
 the metals. When the metals are thoroughly mixed, the oxide is re- 
 moved from the surface, and the gun metal is run into moulds made of 
 loam, the stirring being continued during the running, in order to prevent 
 the separation, to which this alloy is very liable, of a white alloy contain- 
 ing a larger proportion of tin, which has a lower specific gravity, and 
 would chiefly collect in the upper part of the casting. In casting cannon 
 (erroneously called brass guns), the mould is placed perpendicularly with 
 the muzzle upwards, the upper part of the mould being about 3 feet 
 longer than is required for the gun, so that a superfluous cylinder of metal 
 or dead-head is formed, in which the separated alloy collects, together 
 with any oxide or dross which may have run out with the metal ; pro- 
 bably, also, the weight of this column of metal hastens the solidification 
 and hinders the separation of the metals, at the same time increasing the 
 density and consequent tenacity of the metal at the breech of the gun; 
 this dead-head is cut off before the gun is turned and bored. The metal 
 is run into the mould at a temperature as near its point of solidification as 
 possible, so as to diminish the chance of separation. The purest commer- 
 cial qualities of copper and tin are always employed in gun metal. 
 
 Bronze is essentially an alloy of copper and tin, containing more tin 
 than gun metal; its composition is varied according to its application, 
 small quantities of zinc and lead being often added to it. Bronze is 
 affected by changes of temperature, in a manner precisely the reverse 
 of that in which steel is influenced, for it becomes hard and brittle 
 when allowed to cool slowly, but soft and malleable when quickly cooled. 
 The art of making bronze was practised before any progress had been 
 made in working iron, and ancient weapons were very commonly of this 
 material. 
 
 Bronze coin (substituted for the copper coinage) is composed of 95' 
 copper, 4 tin, and 1 zinc. 
 
 Bell metal is an alloy of about 4 parts of copper and 1 of tin, to which 
 lead and zinc are sometimes added. The metal of which musical instru- 
 ments are made generally contains the same proportions of copper and tin 
 as bell metal. 
 
 Speculum metal, employed for reflectors in optical instruments, consists 
 of 2 parts of copper and 1 of tin, to which a little zinc, arsenic, and 
 silver are sometimes added to harden it and render it susceptible of a high 
 polish. 
 
 A superior kind of type metal is composed of 1 part of tin, 1 of anti- 
 mony, and 2 of lead. 
 
 Tin is not dissolved by nitric acid, but is converted into a white 
 powder, the binoxide of tin ; hydrochloric acid dissolves it with the aid 
 of heat, evolving hydrogen ; but the best solvent for tin is a mixture of 
 hydrochloric with a little nitric acid. When the metal is acted upon by 
 hydrochloric acid, it assumes a crystalline appearance, which has been 
 turned to account for ornamenting tin-plate. If a piece of common tin- 
 plate be rubbed over with tow dipped in a warm mixture of hydrochloric 
 and nitric acids, its surface is very prettily diversified (moire metallique) ; 
 it is usual to cover the surface with a coloured transparent varnish. 
 
 Commercial tin is liable to contain minute quantities of lead, iron, 
 copper, arsenic, antimony, bismuth, gold, molybdenum, and tungsten. 
 Pure tin may be precipitated in crystals by the feeble galvanic current 
 
 2 B 2 
 
388 STANNIC AND METASTANNIC ACIDS. 
 
 excited by immersing a plate of tin in a strong solution of stannous 
 chloride, covered with a layer of water, so that the metal may be in con- 
 tact with both layers of liquid. 
 
 288. OXIDES OF TIN. Two oxides of this metal are known the prot- 
 oxide, SnO, and the binoxide, Sn0 2 . 
 
 Protoxide of tin (SnO), or stannous oxide, is a substance of little prac- 
 tical importance, obtained by decomposing stannous chloride with an 
 alkali. Its colour varies, according to the mode of preparing it, from 
 black or olive-coloured to red. It is a feebly basic oxide, and therefore 
 dissolves in the acids ; it may also be dissolved by a strong solution of 
 potash, but is then easily decomposed into metallic tin and the binoxide 
 which combines with the potash. 
 
 Binoxide of tin (Sn0 2 ), or stannic oxide, has been mentioned as the 
 chief ore of tin, and is formed when tin is heated in air. Tin-stone or 
 cassiterite, as the natural form of this oxide is called, occurs in very hard, 
 square prisms, usually coloured brown by peroxide of iron. In its insolu- 
 bility in acids it resembles crystallised silica, and, like that substance, it 
 forms, when fused with alkalies or their carbonates, compounds which are 
 soluble in water ; these compounds are termed stannates, the binoxide of 
 tin being known as stannic acid. 
 
 Stannate of soda is prepared, on the large scale, for use as a mordant 
 by calico-printers. The prepared tin ore (p. 384) is heated with solution 
 of hydrate of soda, and boiled down till the temperature rises to 500 or 
 600 F. ; or the tin ore is fused with nitrate of soda, when the nitric acid 
 is expelled. It crystallises easily in hexagonal tables having the compo- 
 sition NaO. Sn0 2 , 4Aq., which dissolve easily in cold water, and are 
 partly deposited again when the solution is heated. Most neutral salts of 
 the alkalies also cause a separation of stannate of soda from its aqueous 
 solution. The solution of stannate of soda has, like the silicate, a strong 
 alkaline reaction, and when neutralised by an acid, yields a precipitate of 
 hydrated stannic acid, HO . Sn0 2 . If the solution of stannate of soda be 
 added to an excess of hydrochloric acid, the stannic acid remains in solu- 
 tion, and if the liquid be dialysed (see p. 104), a jelly is first formed, which 
 gradually liquefies as the chloride of sodium diffuses away, and eventually 
 a pure aqueous solution of stannic acid is obtained, which is very easily 
 gelatinised by the addition of a minute quantity of hydrochloric acid, or 
 of some neutral salt. The great similarity between stannic and silicic 
 acids is here very remarkable. When heated, stannic acid is converted into 
 metastannic acid. 
 
 Metastannic acid (Sn 5 IO ) is obtained as a white crystalline hydrate when tin is 
 oxidised by nitric acid ; when washed with water and dried by exposure to air, it has 
 the composition Sn 5 10 . 10HO, but when dried at 212 F. it becomes Sn 5 10 . 5HO. 
 If more strongly heated, it assumes a yellowish colour, and a hardness resembling 
 that of powdered tin-stone. Putty powder, used for polishing, consists of meta- 
 stannic acid ; as found in commerce it generally contains much oxide of lead. Meta- 
 stannic acid is insoluble in water and diluted acids, and when fused with hydrated 
 alkalies, is converted into a soluble stannate ; but if boiled with solution of potash it 
 is dissolved in the form of metastannate of potash, which will not crystallise, like 
 the stannate, but is obtained as a granular precipitate by dissolving hydrate of 
 potash in its solution. This precipitate has the composition KO . Sn 5 10 . 4Aq. ; it 
 is very soluble in water, and is strongly alkaline. When it is heated to expel the 
 water, it is decomposed, and the potash may be washed out with water, leaving meta- 
 stannic acid. The hydrated metastannic acid may be distinguished from hydrated 
 
STANNOUS AND STANNIC CHLORIDES. 389 
 
 stannic acid by the action of protochloride of tin, which converts it into the yellow 
 inetastannate of tin (SnO . Sn 5 10 . 4Aq.) 
 
 Stannate of tin is obtained as a yellowish hydrate by boiling protochloride of tin 
 with hydrated sesqtiioxide of iron ; Fe 2 3 + 2SnCl = SnO . Sn0 2 + 2FeCl. It is 
 sometimes written Sn 2 3 , and called sesquioxide of tin. 
 
 289. CHLORIDES OP TIN. The two chlorides of tin correspond in com- 
 position to the oxides. 
 
 Stannous chloride, or protochloride of tin (SnCl), is much used by dyers 
 and calico-printers, and is prepared by dissolving tin in hydrochloric acid, 
 when it is deposited, on cooling, in lustrous prismatic needles (SnCl . 2Aq.), 
 known as tin crystals or salts of tin. The solution of the tin is generally 
 effected in a copper vessel, in order to accelerate the action by forming 
 a voltaic couple, of which the tin is the attacked metal. When gently 
 heated, the crystals lose their water, and are partly decomposed, some 
 hydrochloric acid being evolved (SnCl -f HO = SnO + HC1) ; but, at a 
 higher temperature, a great part of the chloride may be distilled in the 
 anhydrous state ; the anhydrous chloride is generally prepared by distill- 
 ing powdered tin with corrosive sublimate, when it remains in the retort 
 as a brilliant grey solid, which requires a bright red heat to convert it into 
 vapour. When water is poured upon the crystals of stannous chloride, they 
 are only partially dissolved, a white oxy chloride of tin (SnCl . SnO . 2Aq.) 
 being separated. A moderately dilute solution of stannous chloride absorbs 
 oxygen from the air, and deposits a white compound of bichloride and 
 binoxide of tin; 2SnCl -f 2 = SnCl 2 . Sn0 2 . If the solution contains 
 much free hydrochloric acid it remains clear, being entirely converted into 
 bichloride of tin. A strong solution of the chloride is not oxidised by 
 the air, and the weak solution may be longer preserved in contact with 
 metallic tin. Stannous chloride has a great attraction for chlorine as well 
 as for oxygen, and is frequently employed as a deoxidising or dechlorinat- 
 ing agent. Tin may be precipitated from stannous chloride by the action 
 of zinc, in the form of minute crystals. A very beautiful tin tree is 
 obtained by dissolving granulated tin in strong hydrochloric acid, with 
 the aid of heat, in the proportion of 8 measured oz. of acid to 1000 grs. 
 of tin, diluting the solution with four times its bulk of water, and intro- 
 ducing a piece of zinc. 
 
 Stannic chloride, or bichloride of tin (SnCl 2 ), is obtained in solution 
 when tin is heated with hydrochloric and nitric acids ; for the use of the 
 dyer, the solution is generally made with hydrochlorate of ammonia (sal- 
 ammoniac) and nitric acid (nitromuriate of tin). The anhydrous bichloride 
 is obtained by heating tin in a current of dry chlorine, when combination 
 takes place with combustion, and the bichloride distils over as a heavy 
 (sp. gr. 2 -28) colourless liquid, volatile (boiling point, 240 F.), and^giving 
 suffocating white fumes in the air. When mixed with a little water, 
 energetic combination takes place, and a crystalline hydrate (SnClj . 5Aq.) 
 is formed, which is decomposed by an excess of water, with separation of 
 hydrated stannic acid. Stannic chloride forms crystallisable double salts 
 with the alkaline chlorides. Pink salt, used by dyers, is a compound of 
 stannic chloride with hydrochlorate of ammonia (NH 3 . HC1 . SnCl 2 ). 
 
 290. Sulphides of tin. The protosulphide, or stannous sulphide (SnS), 
 is found in Cornwall as tin pyrites, and may be easily prepared by heating 
 tin with sulphur, when it forms a grey crystalline mass. It is also 
 obtained as a dark brown precipitate by the action of hydrosulphuric aeid 
 upon a solution of stannous chloride. Protosulphide of tin is a sulphur- 
 
390 EQUIVALENT AND ATOMIC WEIGHTS OF TIN. 
 
 base, but it may be dissolved by alkalies if some sulphur be added, which 
 converts it into the bisulphide, a decided sulphur acid. 
 
 Bisulphide of tin, or stannic sulphide (SnS 2 ), is commonly known as 
 mosaic gold or bronze powder, and is used for decorative purposes. It is 
 prepared by a curious process, which was devised in 1771, and must have 
 been the result of a number of trials. 12 parts by weight of tin are dis- 
 solved in 6 parts of mercury; the brittle amalgam thus' obtained is 
 powdered and mixed with 7 parts of sulphur and 6 of sal-ammoniac. 
 The mixture is introduced into a Florence flask, which is gently heated 
 in a sand-bath as long as any smell of hydrosulphuric acid is evolved ; 
 the temperature is then raised to dull redness until no more fumes are 
 disengaged. The mosaic gold is found in beautiful yellow scales at the 
 bottom of the flask, and sulphide of mercury and calomel are deposited in 
 the neck. The mercury appears to be used for effecting the fine division 
 of the tin, and the sal-ammoniac to keep down the temperature (by its 
 volatilisation) below the point at which the bisulphide of tin is converted 
 into protosulphide. 
 
 Mosaic gold, like the metal itself, is not dissolved by hydrochloric or 
 nitric acid, but easily by aqua regia. Alkalies also dissolve it when 
 heated, since the bisulphide of tin is a sulphur acid. On adding hydro- 
 sulphuric acid to a solution of stannic chloride, the stannic sulphide is 
 obtained as a yellow precipitate. 
 
 291. Equivalent and atomic weights of tin. When tin is oxidised by 
 nitric acid, 8 parts by weight (1 eq.) of oxygen are taken up by 29*5 parts 
 of the metal, and if the oxide thus formed be composed of single equivalents, 
 2 9 '5 must be the equivalent weight of tin; but the existence of another 
 oxide, containing only half as much oxygen, and the analogies between 
 the first mentioned oxide and silicic acid (Si0 2 ), lead to the conclusion 
 that the oxide obtained by the action of nitric acid is a binoxide, contain- 
 ing 16 parts by weight of oxygen, combined with 1 eq. of tin, when the 
 equivalent weight of the metal would be 59. 
 
 But the specific heat of tin shows that its atomic weight must be repre- 
 sented by the number 118, and this receives confirmation from the specific 
 gravity of the vapour of stannic chloride. 
 
 Weight of 1 vol. of stannic chloride vapour, . 9*20 
 
 2 vols. (1 molecule), . ' . .18-40 
 
 tin contained in it, ... 8 '35 
 
 chlorine contained in 2 vols. of 
 
 stannic chloride, . ' + ,. .10*05 
 
 Since 2 '47 is the specific gravity or weight of 1 vol. of chlorine, the 
 number 10 '05 represents 4 vols. of that gas; and if it be allowed that 2 
 vols. of stannic chloride represent, as usual, 1 molecule, it will contain 1 
 atom of tin and 4 atoms (or vols.) of chlorine, and its molecular formula 
 will be BnCl 4 (Sn = 118). Tin, therefore, would be a tetratomic element 
 like carbon and silicon, one atom being capable of occupying the place of 
 four atoms of hydrogen, and the atomic formulce for some of its chief 
 compounds would be stannous oxide, SnG ; stannic acid, SiiO 2 ; stannous 
 chloride, SnCl 2 ; stannic chloride, BnCl 4 ; stannous sulphide, BnS; stannic 
 sulphide, 
 
TITANIUM TITANIC ACID. 391 
 
 292. TITANIUM, which stands in close chemical relationship to tin, used to be 
 described as a very rare metal, but it has lately been found to exist in considerable 
 quantity in iron ores and clays, although no very important practical application 
 lias hitherto been found for it. The form in which it is generally found is titanic 
 acid (Ti0 2 ), which occurs uncombined in the minerals rutile, anatase, and brookite, 
 the first of which is isomorphous with tin-stone, and is extremely hard like that 
 mineral. In combination with oxide of iron, titanic acid is found in iron-sand, 
 iserine, or menachanite (found originally at Menachan in Cornwall), which resembles 
 gunpowder in appearance, and is now imported in abundance from Nova Scotia and 
 New Zealand. Some specimens of this mineral contain 40 per cent, of titanic acid, 
 combined with protoxide of iron. To extract titanic acid from it, the finely ground 
 mineral is fused with three parts of carbonate of potash, when carbonic acid is 
 expelled and titanate of potash formed ; on washing the mass with hot water, this 
 salt is decomposed, a part of its alkali being removed by the water, and an acid 
 titanate of potash left, mixed with the oxide of iron. This is dissolved in hydro- 
 chloric acid, and the solution evaporated to dryness, when the titanic acid, and any 
 silicic acid which may be present, are converted into the insoluble modifications, 
 and are left on digesting the residue again with dilute hydrochloric acid ; the residue 
 is washed with water (by decantation, for titanic acid easily passes through the 
 filter), dried, and fused at a gentle heat with bisulphate of potash. The sulphuric 
 acid forms a soluble compound with the titanic acid (Ti0 2 .S0 3 ), which maybe 
 extracted by cold water, leaving the silicic acid undissolved. The solution contain- 
 ing the titanic acid is mixed with about twenty times its volume of water, and 
 boiled for some time, when the titanic acid is separated as a white precipitate, 
 exhibiting a great disposition to cling as a film to the surface of the flask in which 
 the solution is boiled, and giving it the appearance of being corroded. The titanic 
 acid becomes yellow when strongly heated, and white again on cooling ; it does not 
 dissolve in solution of potash like silica, but when fused with potash it forms 
 a titanate, which is decomposed by water; the acid titanate of potash which is 
 left may be dissolved in hydrochloric acid, and if the solution be neutralised 
 with carbonate of ammonia, hydrated titanic acid is precipitated, very much 
 resembling alumina in appearance. By dissolving the gelatinous hydrate in cold 
 hydrochloric acid, and dialysing, a solution of titanic acid in water is obtained, 
 which is liable to gelatinise spontaneously if it contain more than one per cent, of 
 the acid. 
 
 Titanic acid is employed in the manufacture of artificial teeth, and for imparting 
 a straw-yellow tint to the glaze of porcelain. 
 
 If a mixture of titanic acid and charcoal be heated to redness in a porcelain tube, 
 through which dry chlorine is passed, bichloride of titanium (TiCl 2 ) is obtained 
 as a colourless volatile liquid, very similar to bichloride of tin. By passing the 
 vapour of the bichloride of titanium over heated sodium, the metallic titanium is 
 obtained in prismatic crystals resembling specular iron ore in appearance. Like 
 tin, it is said to dissolve in hydrochloric acid with liberation of hydrogen. The 
 most remarkable chemical feature of titanium is its direct attraction for nitrogen, 
 with which it combines when strongly heated in air. By passing ammonia gas over 
 titanic acid heated to redness, a violet powder is formed, which is a nitride of titanium 
 (TiN). Beautiful cubes of a copper colour and great hardness, formerly believed 
 to be metallic titanium, are found adhering to the slags of blast-furnaces in which 
 titaniferous iron ores are smelted ; these contain about 77 per cent, of titanium, 18 of 
 nitrogen, and rather less than 4 of carbon, and are believed to consist of a compound 
 of cyanide with nitride of titanium, TiCy, 3Ti 3 N. A similar compound is obtained 
 by passing nitrogen over a mixture of titanic acid and charcoal heated to whiteness. 
 
 Violet-coloured crystals of sesquichloride of titanium (Ti 2 Cl 3 ) are obtained by pass- 
 ing hydrogen charged with vapour of bichloride of titanium through a red-hot por- 
 celain tube ; it forms a violet solution in water, which resembles stannous chloride 
 in its reducing properties. 
 
 When a solution of titanic acid (or acid titanate of potash) in hydrochloric acid 
 is acted on by zinc, a violet solution is formed, which deposits, after a time, a blue 
 (or green) precipitate, which appears to be a sesquioxide of titanium (Ti 2 3 ), and 
 rapidly absorbs oxygen from the air, being converted into titanic acid. A. protoxide 
 of titanium (TiO) is said to be obtained as a black powder when titanic acid is 
 strongly heated in a crucible lined with charcoal. 
 
 Bisulphide of titanium is not precipitated, like bisulphide of tin, when hydrosul- 
 phuric acid acts upon the bichloride ; but if a mixture of the vapour of bichloride 
 
392 TUNGSTEN TUNGSTIC ACID. 
 
 of titanium with hydrosulphuric acid is passed through a red-hot tube, greenish- 
 yellow scales of the' bisulphide, resembling mosaic gold, are deposited. 
 
 Titanium, like tin, is classed among the tetratomic elements ; its equivalent is 25, 
 and its atomic weight 50. 
 
 293. TUNGSTEN is chiefly found in the mineral wolfram, which occurs, often 
 associated with tin-stone, in large brown shining prismatic crystals, which are even 
 heavier than tin-stone (sp. gr. 7'3), from which circumstance the metal derives its 
 name, tungsten, in Swedish, meaning heavy stone. The symbol -(W) used for 
 tungsten is derived from the Latin name wolframium. Wolfram contains the 
 tungstates of iron and manganese in somewhat variable proportions, but its general 
 composition is expressed by the formula MnO. W0 3 , 3(FeO . W0 3 ). Scheelite, 
 tungstate of lime (CaO . W0 3 ), is another mineral in which tungsten is found. 
 
 Tungstate of soda is employed by calico-printers as a mordant, and is sometimes applied 
 to muslin, in order to render it inflammable. It is obtained by fusing wolfram with 
 carbonate of soda, an operation to which tin ores containing this mineral in large 
 quantity are sometimes submitted previously to smelting them. Water extracts the 
 tungstate of soda, which may be crystallised in rhomboidal plates having the composi- 
 tion NaO . W0 3 , 2Aq. When a solution of this salt is mixed with an excess of hydro- 
 chloric acid, white hydrated tungstic add (HO.W0 3 + Aq.) is precipitated; but if 
 dilute hydrochloric acid be carefully added to a 5 per cent, solution of tungstate of soda, 
 in sufficient proportion to neutralise the alkali, and the solution be then dialysed 
 (p. 104), the chloride of sodium passes through, and a pure aqueous solution of 
 tungstio acid is left in the dialyser. This solution is unchanged by boiling, and 
 when evaporated to dryness, it forms vitreous scales, like gelatine, which adhere 
 very strongly to the dish. It redissolves in one-fourth of its weight of water, form- 
 ing a solution of the very high specific gravity 3-2, which is, therefore, able to float 
 glass. The solution has a bitter and astringent taste, and decomposes carbonate of 
 soda with effervescence. It becomes green when exposed to air, from the deoxidis- 
 ing action of organic dust. When the hydrated tungstic acid is heated, it loses 
 water, and becomes of a straw-yellow colour and insoluble in acids. There are at 
 least two modifications of tungstic acid, which bear to each other a relation similar 
 to that between stannic and metastannic acids. 
 
 The most characteristic property of tungstic acid is that of yielding a blue oxide 
 (W0 2 , W0 3 ) when placed in contact with hydrochloric acid and metallic zinc. 
 
 A very remarkable compound containing tungstic acid and soda is obtained when 
 bitungstate of soda (NaO . 2W0 3 . 4HO) is fused with tin. If the fused mass be 
 treated with strong potash, to remove free tungstic acid, washed with water, and 
 treated with hydrochloric acid, yellow lustrous cubical crystals are obtained, which 
 are remarkable, among sodium compounds, for their resistance to the action of water, 
 of alkalies, and of all acids except hydrofluoric. The composition of these crystals 
 appears to be NaO . W0 2 . 2 W0 3 . 
 
 The binoxide of tungsten (W0 2 ) appears to be an indifferent oxide, and is obtained 
 by reducing tungstic acid with hydrogen at a low red heat, when it forms a brown 
 powder which is dissolved by boiling in solution of potash, hydrogen being evolved, 
 and tungstate of potash formed. 
 
 Metallic tungsten is obtained by reducing tungstic acid with charcoal at a white 
 heat, as an iron-grey infusible metal of sp. gr. 17-6, very hard, not affected by hydro- 
 chloric or diluted sulphuric acid, but converted into tungstic acid by the action of 
 nitric acid. When tungsten is dissolved in about ten times its weight of fused steel, 
 it forms an extremely hard alloy. 
 
 When tungsten is heated in chlorine, the terchloride of tungsten (WC1 3 ) sublimes 
 in bronze coloured needles, which are decomposed by water. When gently heated in 
 hydrogen, it is converted into the bichloride (WC1 2 ), but if its vapour be mixed with 
 hydrogen and passed through a glass tube heated to redness, metallic tungsten is ob- 
 tained in a form in which it is not dissolved even by aqua regia, though it may be con- 
 verted into tungstate of potash by hypochlorite of potash mixed with potash in excess. 
 
 Bisulphide of tungsten (WS 2 ) is a black crystalline substance resembling plumbago, 
 obtained by heating a mixture of bitungstate of potash with sulphur, and washing 
 with hot water. Tersulphide of tungsten (WS 3 ) is a sulphur-acid, obtainable as a 
 brown precipitate by dissolving tungstic acid in an alkaline sulphide, and precipitat- 
 ing by an acid, 
 
 294. MOLYBDENUM derives its name from ptiufaam, lead, on account of the re- 
 semblance of its chief ore, molybdena, to black lead. Molybdena is the bisulphide of 
 molybdenum (MoS 2 ), and is found chiefly in Bohemia and Sweden ; it may be recog- 
 
MOLYBDENUM VANADIUM. 893 
 
 nised by its remarkable similarity to plumbago, and by its giving a blue solution 
 when boiled with strong sulphuric acid. It is chiefly employed for the preparation 
 of molybdate of ammonia, which is used in testing for phosphoric acid. For this 
 purpose the bisulphide of molybdenum is roasted in air at a dull red heat, when 
 sulphurous acid is evolved, and molybdic acid (Mo0 8 ) mixed with oxide of iron is left. 
 The residue is digested with strong ammonia, which dissolves the molybdic acid in 
 the form of molybdate of ammonia, obtainable in prismatic crystals on evaporation. 
 When a solution of molybdate of ammonia is added to a phosphate dissolved in 
 diluted nitric acid, a yellow precipitate of phosphomolybdate of ammonia is produced, 
 which contains molybdic and phosphoric acids combined with ammonia, by the for- 
 majtion of which very minute quantities of phosphoric acid can be detected. If 
 hydrochloric acid be added in small quantity to a strong solution of molybdate of 
 ammonia, the molybdic acid is precipitated, but it is dissolved by an excess of 
 hydrochloric acid, and if the solution be dialysed, the molybdic acid is obtained in 
 the form of an aqueous solution which reddens blue litmus, has an astringent taste, 
 and leaves a soluble gum-like residue when evaporated. Molybdic acid fuses at a 
 red heat to a yellow glass, and may be sublimed in a current of air in shining 
 needles. In contact with diluted hydrochloric acid and metallic zinc, it is con- 
 verted into a blue compound of molybdic acid with binoxide of molybdenum 
 (Mo0 2 . 4Mo0 3 ) which is soluble in water, but is precipitated on adding a saline 
 solution. Molybdate of lead (PbO . Mo0 3 ) is found as a yellow crystalline mineral. 
 The binoxide of molybdenum (Mo0 2 ) is basic, and forms dark red-brown salts. Prot- 
 oxide of molybdenum (MoO) is obtained by adding an alkali to the solution resulting 
 from the prolonged action of zinc upon a hydrochloric solution of molybdic acid. It 
 is a basic oxide which absorbs oxygen from the air. 
 
 Metallic molybdenum is obtained by reducing molybdic acid with charcoal at a white 
 heat, as a white metal, fusible with difficulty, unacted upon by hydrochloric and 
 diluted sulphuric acids, but converted into molybdic acid by boiling with nitric 
 acid. It is rather a light metal, its specific gravity being 8*62. When heated in 
 chlorine it yields bichloride of molybdenum (MoCl 2 ), which forms a red vapour, and 
 condenses in crystals resembling iodine, soluble in water. A protochloride (MoCl) is 
 also known. The tersulphide (MoS 3 ) and tetrasulphide (MoS 4 ) of molybdenum are 
 sulphur-acids. 
 
 In addition to the natural sources of molybdenum above mentioned, there may 
 be noticed molybdic ochre (an impure molybdic acid), and the difficultly fusible 
 masses called bear, from the copper works in Saxony, which contain a large amount 
 of molybdenum combined with iron, copper, cobalt, and nickel. 
 
 295. VANADIUM (Vanadis, a Scandinavian deity) was originally obtained from 
 certain Swedish iron ores, but its chief ore is the vanadiate of lead, which is found in 
 Scotland, Mexico, and Chile. Vanadic acid has also been found in some clays, and 
 in the cupriferous sandstone at Perm in Kussia. By treating the vanadiate of lead 
 with nitric acid, expelling the excess of acid by evaporation, and washing out the 
 nitrate of lead with water, impure vanadic acid(VO s )is obtained, which may be 
 purified by dissolving in ammonia, crystallising the vanadiate of ammonia, and 
 decomposing it by heat, when vanadic acid is left as a reddish-yellow fusible solid, 
 which crystallises on cooling, and dissolves sparingly in water, giving a yellow solu- 
 tion. It dissolves in hydrochloric acid, and if the solution be treated with a redu- 
 cing agent (such as hydrosulphuric acid) it assumes a fine blue colour, from the pro- 
 duction of bichloride of vanadium (VC1 2 ). If a solution of vanadiate of amcaonia 
 be mixed with tincture of galls, it gives an intensely black fluid, which forms an 
 excellent ink, for it is not bleached by acids, alkalies, or chlorine. By heating 
 vanadic acid with potassium, metallic vanadium is obtained as a white metallic powder, 
 which is not attacked by sulphuric or hydrochloric acid, but dissolves in nitric acid, 
 forming a blue solution of nitrate of binoxide of vanadium. 
 
 The protoxide of vanadium (VO) appears to be an indifferent oxide. Terchloride of 
 vanadium (VC1 3 ) is a volatile yellow fuming liquid. 
 
 Bisulphide of vanadium (VS 2 ) is obtained as a black precipitate by the action of an 
 alkaline sulphide upon the bichloride of vanadium ; it appears to be a sulphur-acid, 
 for it dissolves in an excess of the alkaline sulphide, fuming a purple solution. 
 
 296. Niobium (formerly called columbium} has been obtained from a rare dark grey 
 hard crystalline mineral known as columbite, occurring in Massachusetts. This 
 mineral contains niobic acid (Nb0 2 ) combined with the oxides of iron and manganese. 
 
 The niobic acid is extracted by a laborious process, and forms a white powder 
 
394 METALLURGY OF PLATINUM. 
 
 sparingly soluble in hydrochloric acid. Niobium itself has been obtained as a black 
 powder insoluble in nitric acid and in aqua regia, but dissolved by a mixture of 
 nitric and hydrofluoric acids. 
 
 Tantalum, formerly believed to be identical with niobium, occurs in the tantalite 
 and yttrotantalite of Sweden, which contain tantalic acid (Ta0 2 ) * resembling niobic 
 acid. 
 
 Niobium and tantalum have recently been found to the amount of 2 or 3 per 
 cent, in the tin ore of Montebras. 
 
 PLATINUM. 
 
 297. Platinum (jplatina, Spanish diminutive of silver) is always found 
 in the metallic state, distributed in flattened grains through alluvial 
 deposits similar to those in which gold is found ; indeed, these grains are 
 generally accompanied by grains of gold, and of a group of very rare 
 metals only found in platinum ores, viz., palladium, iridium, osmium, 
 rhodium, and ruthenium. Eussia furnishes the largest supply of platinum 
 from the Ural Mountains, but smaller quantities are obtained from Brazil, 
 Peru, Borneo, Australia, and California. 
 
 The process for obtaining the platinum in a marketable form is rather 
 a chemical than a metallurgic operation. The ore containing the grains 
 of platinum and the associated metals is heated with a dilute mixture of 
 hydrochloric and nitric acids, by which the platinum is converted into 
 bichloride of platinum (PtClJ and dissolved, whilst . the iridium and 
 osmium are left in the residue. The solution is then mixed with some chlo- 
 ride of ammonium, which combines with the bichloride of platinum to form 
 a yellow insoluble salt (ammonio-chloride of platinum, NH 3 . HC1 . PtCl 2 ) . 
 This precipitate is collected, washed, and heated to redness, when all its 
 constituents, except the platinum, are expelled in the form of gas, that 
 metal being left in the peculiar porous condition in which it is known as 
 spongy platinum. To convert this into compact platinum is by no means 
 an easy task, on account of the infusibility of the metal, for it remains 
 solid at the very highest temperatures of our furnaces. The spongy 
 platinum is finely powdered in a wooden mortar (as it would cohere into 
 metallic spangles in one of a harder material) and rubbed to a paste with 
 water ; this paste is then rubbed through a sieve to render it perfectly 
 smooth and uniform, and introduced into a cylinder of brass, in which it 
 is subjected to pressure so as to squeeze out the water and cause the 
 minute particles of platinum to cohere into a somewhat compact disk ; 
 this disk is then heated to whiteness and beaten into a compact metallic 
 ingot by a heavy hammer ; it is then ready for forging. 
 
 A more modern process for obtaining platinum from its ores is based 
 upon the tendency of this metal to dissolve in melted lead. The platinum 
 ore is fused in a small reverberatory furnace, with an equal weight of sul- 
 phide of lead and the same quantity of oxide of lead, when the sulphur 
 and oxygen escape as sulphurous acid, and the reduced lead dissolves the 
 platinum, leaving undissolved a very heavy alloy of osmium and iridium 
 which sinks to the bottom. The upper part of the alloy of lead and 
 platinum is then ladled out and cupelled (page 353), when the latter metal 
 is left in a spongy condition, the lead being removed in the form of 
 oxide. The platinum is then fused by the aid of the oxyhydrogen blow- 
 pipe in a furnace made of lime (fig. 259), whence it is poured into an 
 
 * Ta0 5 according to more recent experiments. 
 
PROPERTIES OF PLATINUM. 
 
 395 
 
 Fig. 259. 
 
 ingot mould made of gas-carbon. The melted platinum absorbs oxygen 
 mechanically like melted silver, and evolves it again on cooling (see 
 page 354). Platinum articles are now frequently made from the fused 
 metal, instead of from that which has been welded. 
 
 Its resistance to the action of high temperatures and of most chemical 
 agents, renders platinum of the greatest service in chemical operations. 
 It will be remembered that platinum stills 
 are employed, even on the large scale, for the 
 concentration of sulphuric acid. In the form 
 of basins, small crucibles, foil, and wire, 
 this metal is indispensable to the analytical 
 chemist. Unfortunately, it is softer than 
 silver, and therefore ill adapted for wear, 
 and is so heavy (sp. gr. 21*5) that even 
 small vessels must be made very thin in 
 order not to be too heavy for a delicate bal- 
 ance. Since it expands less than any other 
 metal when heated, wires of platinum may be 
 sealed into glass without danger of splitting it 
 by unequal expansion. Its malleability and 
 ductility are very considerable, so that it is easily rolled into thin foil and 
 drawn into fine wires ; in ductility it is surpassed only by gold and silver, 
 and it has been drawn, by an ingenious contrivance of Wollaston's, into 
 wire of only -5 o-|o~oth of an inch in diameter, a mile of which (notwith- 
 standing the high specific gravity of the metal) would only weigh a single 
 grain. This remarkable extension of the metal was effected by casting a 
 cylinder of silver around a very thin platinum wire obtained by the ordinary 
 process of wire-drawing. When the cylinder of silver, with the platinum 
 wire in its centre, was itself drawn out into an extremely thin wire, of 
 course the platinum core would have become inconceivably thin, and when 
 the silver casing was dissolved off by nitric acid, this minute filament of 
 platinum was left. Platinum is sometimes employed for the touch-holes 
 of fowling-pieces on account of its resistance to corrosion. A little iridium 
 is sometimes added to platinum in order to increase its elasticity. 
 
 The remarkable power possessed by platinum, of inducing chemical 
 combination between oxygen and other gases, has already been noticed. 
 Even the compact metal possesses this property, as may be seen by heat- 
 ing a piece of platinum foil to redness in the flame of a gauze gas-burner, 
 rapidly extinguishing the gas, and turning it on again, when the cold 
 stream of gas will still maintain the metal at a red heat, in consequence of 
 the combination with atmospheric oxygen at the surface of the platinum. 
 
 A similar experiment may be made by suspending a coil of platinum 
 wire in the flame of a spirit-lamp (fig. 260), and suddenly 
 blowing out the flame when the metal is intensely heated ; 
 the wire will continue to glow by inducing the combina- 
 tion of the spirit vapour with oxygen on its surface. By 
 substituting a little ball of spongy platinum for the coil 
 of platinum wire, and mixing some fragrant essential oil 
 with the spirit, an elegant perfuming lamp has been con- 
 trived. Upon the same principle an instantaneous light 
 apparatus has been made, in which a jet of hydrogen gas 
 is kindled by falling upon a fragment of cold spongy 
 platinum, which at once ignites it by inducing its combination with the 
 
396 PLAT1NOUS AND PLATINIC OXIDES. 
 
 oxygen condensed within the pores of the metal. Spongy platinum is 
 obtained in a very active form by heating the ammonio-chloride of pla- 
 tinum very gently in a stream of coal-gas or hydrogen as long as any 
 fumes of hydrochloric acid are evolved. 
 
 If platinum be precipitated in the metallic state from a solution, it is 
 obtained in the form of a sooty powder, called platinum-black, which 
 possesses this power of promoting combination with oxygen in the highest 
 perfection. This form of platinum may be obtained by dissolving the 
 metal in aqua regia, which converts it into bichloride of platinum (PtCl 2 ), 
 evaporating the solution to dryness, and heating the residue on a sand-bath 
 as long as it smells of chlorine. The chloride of platinum (PtCl) thus 
 obtained is dissolved in a strong solution of potash and heated with 
 alcohol, when the platinum-black is precipitated, and must be filtered off, 
 washed, and dried at a gentle heat. 
 
 Platinum in this form is capable of absorbing 800 times its volume of 
 oxygen, which does not enter into combination with it, but is simply con- 
 densed into its pores, and is available for combination with other bodies. 
 A jet of hydrogen allowed to pass on to a grain or two of this powder is 
 kindled at once, and if a few particles of it be thrown into a mixture of 
 hydrogen and oxygen, explosion immediately follows. A drop of alcohol 
 is also inflamed when allowed to fall upon a little of the powder. Pla- 
 tinum-black loses its activity after having been heated to redness. 
 
 Although platinum resists the action of hydrochloric and nitric acids, 
 unless they are mixed, and is unaffected at the ordinary temperature by 
 other chemical agents, it is easily attacked at high temperatures by phos- 
 phorus, arsenic, carbon, boron, silicon, and by a large number of the 
 metals ; the caustic alkalies and alkaline earths also corrode it, so that 
 some discretion is necessary in the use of vessels made of this costly 
 metal. When platinum is alloyed with 10 parts of silver, both metals 
 may be dissolved by nitric acid. 
 
 298. Oxides of platinum. Only one compound of platinum with 
 oxygen is known in the separate state, the other having been obtained 
 in combination with water. The protoxide, PtO (platinous oxide), 
 is precipitated as a black hydrate by decomposing the protochloride 
 with potash, and neutralising the solution with dilute sulphuric acid. It 
 is a feeble base, and decomposes when heated, leaving metallic platinum. 
 Binoxide of platinum, Pt0 2 (platinic oxide), is also a weak base, but 
 occasionally plays the part of an acid, whence it is sometimes termed 
 platinic acid. The hydrated binoxide (Pt0 2 . 2HO) is obtained by mixing- 
 solution of bichloride of platinum with excess of potash, heating until the 
 precipitate of platino-chloride of potassium (KC1, PtCl 2 ) is redissolved, 
 and adding acetic acid, which gives a brown precipitate of the hydrated 
 binoxide ; this may be freed from water by a moderate heat, and at a 
 higher temperature loses its oxygen. Platinate of soda (NaO . 3Pt0 2 . 6Aq. ) 
 may be crystallised from a solution of the hydrated binoxide in soda. 
 Platinate of lime is convenient for the separation of platinum from iridium, 
 which is generally contained in the commercial metal ; for this purpose 
 the platinum is dissolved in nitro-hydrochloric acid, the solution evapo- 
 rated till it solidifies on cooling, the mixed chlorides of iridium and 
 platinum dissolved in water, and decomposed with an excess of lime with- 
 out exposure to liyht ; the platinum then passes into solution as platinate 
 of lime, and the platinic acid may be separated from the filtered solution 
 
BICHLORIDE OF PLATINUM. 397 
 
 by exposure to light. Acids dissolve binoxide of platinum, forming salts 
 of a brown colour which have not been crystallised. If binoxide of pla- 
 tinum be dissolved in diluted sulphuric acid and the solution mixed with 
 excess of ammonia, a black precipitate of fulminating platinum is obtained, 
 which detonates violently at about 400 F. This compound is said to 
 have a composition corresponding to the formula NH 3 , HO, Pt0 2 + HO 
 (hydrated platinate of ammonia) ; and might also be represented as 
 NHPt . 4HO, or a combination of water with ammonia (NH 3 ), in which 
 two equivalents of hydrogen are replaced by one equivalent of platinum 
 (which, in the binoxide, Pt0 2 , represents H 2 ). 
 
 Chlorides of platinum. The bichloride, or platinic chloride (PtCl 2 ), is 
 the most useful salt of the metal, and may be prepared by dissolving- 
 scraps of platinum foil in a mixture of four measures of hydrochloric acid 
 with one of nitric acid (100 grains of platinum require 3 measured ounces 
 of hydrochloric acid), evaporating the liquid at a gentle heat to the con- 
 sistence of a syrup, redissolving in dilute hydrochloric acid, and again 
 evaporating to expel excess of nitric acid. The syrupy liquid solidifies 
 on cooling to a red-brown mass, which is very deliquescent, and dissolves 
 easily in water or alcohol to a red-brown solution. If the concentrated 
 solution be allowed to cool before all the free hydrochloric acid has been 
 expelled, long brown prismatic crystals of a combination of the bichloride 
 with hydrochloric acid are obtained. The bichloride of platinum is re- 
 markable for its disposition to form sparingly soluble double chlorides with 
 the chlorides of the alkali metals and the hydrochlorates of organic bases, 
 a property of great value to the chemist in effecting the detection and sepa- 
 ration of these bodies. 
 
 A good example of this has lately been afforded in the separation 
 of potassium, rubidium, and coesium. The chlorides of these three 
 metals having been separated from the various other salts contained in 
 the mineral water in whieh they occur, are precipitated with bichlo- 
 ride of platinum, which forms combinations with all the three chlorides. 
 The platino-chloride of potassium is more easily dissolved by boiling 
 water than those of rubidium and coesium, and is removed by boiling the 
 mixed precipitate with small portions of water as long as the latter 
 acquires a yellow colour. The remaining platino-chlorides of rubidium 
 and coesium. are then heated in a current of hydrogen, which reduces the 
 platinum to the metallic state, and the chlorides may then be extracted 
 by water, in which they are very soluble. 
 
 Platino-chloride of potassium (KC1, PtCl 2 ) forms minute yellow octa- 
 hedral crystals ; those of rubidium and coesium have a similar composition 
 and crystalline form. 
 
 Platino-chloride of sodium differs from these in being very soluble in 
 water and alcohol ; it may be crystallised in long red prisms, having the 
 composition (NaCl, PtCl 2 , 6Aq.) 
 
 Ammonio-cMoride of platinum (NH 3 .HC1, PtCl 2 ) has been already 
 noticed as the form in which platinum is precipitated in order to separate 
 it from other metals. It crystallises, like the potassium-salt, in yellow 
 octahedra, which are very sparingly soluble in water and insoluble in 
 alcohol. It is the form into which nitrogen is finally converted in 
 analysis in order to determine its weight. When heated to redness, this 
 salt leaves a residue of spongy platinum. The bichloride of platinum is 
 sometimes used for browning gun-barrels, &c., under the name of muriate 
 of platina. 
 
398 PLATOSAMINE AND PLATINAMINE COMPOUNDS. 
 
 Protochloride of platinum or platinous chloride (PtCl). The bichloride of platinum 
 may be heated to 450 F. without decomposition, but above that temperature it 
 evolves chlorine, and is slowly converted into the protochloride, which is reduced, at 
 a much higher temperature, to the metallic state. Platinous chloride forms a dingy 
 green powder, which is insoluble in water and in nitric and sulphuric acids, but 
 dissolves in hot hydrochloric acid, and in solution of platinic chloride, yielding in 
 the former a bright red, in the latter a very dark brown-red solution. Its solution 
 in hydrochloric acid is not precipitated by chloride of potassium, 'but a soluble 
 double chloride (KC1, PtCl) may be crystallised from the liquid. If hydrochlorate 
 of ammonia be added to the hydrochloric solution, a double salt of hydrochlorate of 
 ammonia with protochloride of platinum (NH 3 . HC1 . PtCl) may be obtained in 
 yellow crystals by evaporation. If, instead of hydrochlorate of ammonia, free 
 ammonia be added in excess to the boiling solution of protochloride of platinum in 
 hydrochloric acid, brilliant green needles (green salt of Magnus) are deposited on 
 cooling, which contain the elements of platinous chloride and ammonia (PtCl . NH 3 ) ; 
 but from the behaviour of this compound with chemical agents, its true formula 
 would appear to be N 2 H 5 Pt . HC1, PtCl, in which the place of 1 equivalent of 
 hydrogen in two of ammonia is occupied by platinum. By heating this salt 
 with an excess of ammonia, the platinous chloride which it contains may be decom- 
 posed, and when the solution is allowed to cool, it deposits yellowish-white prismatic 
 crystals of hydrochlorate of diplatosamine; N 2 H 5 Pt.HCl + Aq., the production of 
 which may be represented by the equation 
 
 N 2 H 5 Pt . HC1, PtCl + 2NH 3 = 2(N 2 H 5 Pt . HC1) . 
 
 By decomposing a solution of this salt with sulphate of silver, the sulphate of dipla- 
 tosamine is obtained ; N 2 H 5 Pt . HC1 + AgO . S0 3 = N 2 H 5 Pt . HO . S0 8 + AgCl. 
 
 When the solution of sulphate of diplatosamine is treated with hydrate of baryta, 
 sulphate of baryta is precipitated, and a powerfully alkaline solution is obtained, 
 which yields crystals of hydrate of diplatosamine N 2 H 5 Pt . 2HO, a strong alkali which 
 may be regarded as a compound of water with 2 equivalents of ammonia (N 2 H 6 ) in 
 which 1 equivalent of hydrogen is replaced by platinum. The hydrate of diplatosa- 
 mine has a strong resemblance to the hydrated mineral alkalies, eagerly absorbing 
 carbonic acid from the air, and expelling ammonia from its salts. When the 
 hydrate of diplatosamine is heated to 230 F. it gives oif water and ammonia, and 
 becomes converted into a grey insoluble substance, which is hydrate of platosamine, 
 NH 2 Pt.HO, and may be regarded as a compound of water with a single equivalent 
 of. ammonia (NH 3 ), in which one-third of the hydrogen is replaced by platinum. 
 This substance is also a base, and forms salts, most of which are insoluble ; the 
 sulphate of platosamine, NH 2 Pt . HO . S0 3 + HO, may be regarded as sulphate of 
 ammonia (NH 3 . HO . S0 3 ), in which 1 equivalent of the hydrogen is replaced by 
 platinum. The hydrochlorate of platosamine (NH 2 Pt . HC1) is isomeric with the 
 green salt of Magnus, and may be obtained from that compound by dissolving it in 
 a, hot solution of sulphate of ammonia, from which it crystallises on cooling."* 
 
 If the hydrochlorate of platosamine, suspended in boiling water, be treated witli 
 chlorine, it is converted into hydrochlorate of platinamine, NHPt . 2HC1, which may 
 be represented as the hydrochlorate of an ammonia, in which 2 equivalents of 
 hydrogen have been replaced by 1 equivalent of platinum in the condition in which 
 it exists in the bichloride (PtCl 2 ), where it is equivalent to H 2 . The conversion of 
 the hydrochlorate of platosamine into hydrochlorate of platinamine may be repre- 
 sented by the equation, NH 2 Pt . HC1 + 01 = NHPt . 2HC1. By boiling the hydro- 
 chlorate of platinamine with nitrate of silver, it is converted into nitrate of platina- 
 mine (NHPt . HO . N0 5 ), and when this is dissolved in boiling water and decomposed 
 by ammonia, the hydrate of platinamine (NHPt, 4HO) is obtained in yellow prismatic 
 crystals, having the same composition as that assigned to fulminating platinum. 
 
 Several other platinum compounds derived from ammonia have been obtained, 
 but cannot at present be so conveniently classified. The following table exhibits 
 
 * The salts of diplatosamine are distinguished from those of platosamine by the action 
 of nitrous acid, which gives a fine blue or green precipitate or coloration with the former. 
 
 For the cause of this change, and for many other interesting points in the history of 
 these platinum compounds, the author sorrowfully refers to the elaborate and accurate 
 memoir by his lamented colleague, the late Mr Hadow, written during his last illness, and 
 published in the Journal of the Chemical Society for August 1860, in which month he died, 
 having there given a summary of the results of persevering and sagacious experimental 
 work, extending over several years. He too truly wrote, that he was " prevented from 
 making any further experiments for some time to come. " He died August 11, 1866, aged 35. 
 
PALLADIUM. 399 
 
 the composition of those here enumerated, the platinum, as it exists in platinous 
 chloride (PtCl), occupying the place of 1 equivalent of hydrogen, being represented 
 by Pt', and the platinum, as it exists in platiuic chloride (PtCl 2 ), occupying the 
 place of 2 equivalents of hydrogen, by Pt". 
 
 Hydrate of platosamine, . . . NH 2 Pt' . HO 
 Hydrochlorate of platosamine, . . NH 2 Pt' . HC1 
 Sulphate of platosamine, . . , NH 2 Pt' . HO . S0 8 + HO 
 
 'Hydrate of platinamine, , . . NHPt".4HO 
 Hydrochlorate of platinamine, . . NHPt" . 2HC1 
 
 Hydrate of diplatosamine, . . . N 2 H 5 Pt' . 2HO 
 Hydrochlorate of diplatosamine, . . N 2 H 5 Pt' . HC1 
 Sulphate of diplatosamine, . . . N 2 H 5 Pt' . HO . S0 8 
 
 Some of tlfe salts of diplatinamine (N 2 H 4 Pt") have been obtained, this base being 
 derived from two equivalents of ammonia in which H 2 have been replaced by Pt". 
 
 The sulphides of platinum correspond in composition to the oxides and chlorides, 
 and may be obtained by the action of hydrosulphuric acid upon the respective chlo- 
 rides, as black precipitates. 
 
 299. Equivalent and atomic weights of platinum. Platinic chloride, 
 analysed in its pure combination with chloride of potassium, is found to 
 contain 35 '5 parts by weight (1 eq.) of chlorine combined with 49 '3 parts 
 of platinum, and this latter number would represent the equivalent weight 
 of platinum if the platinic chloride contained a single equivalent of chlo- 
 rine ; but since the platinous chloride contains only half as much chlorine 
 as the platinic chloride, it is usual to represent the former as containing 
 1 eq. and the latter 2 eqs. of chlorine combined with 1 eq. of platinum, 
 so that the equivalent weight . of platinum (the quantity combined with 
 71 parts or 2 eqs. of chlorine) would be 98 '6, a view which is confirmed 
 by the composition of the ammonia derivatives containing platinum. 
 The specific heat of platinum shows that its atomic iveight must be twice its 
 equivalent weight, or 197 '2, and since, in the platinic compounds, which 
 may be regarded as the normal compounds of platinum, this weight of 
 the metal occupies the place of 4 atoms of hydrogen, platinum is gene- 
 rally regarded as a tetratomic element (Pt iv = 197*2), and the atomic 
 formula! of its chief compounds are written thus : platinous oxide, 
 PtO ; platinic oxide, PtO. 2 ; platinous chloride, PtCl ; platinic chloride, 
 PtCl 4 ; hydrate of platosamine, N 2 H 4 Pt" . H 2 ; hydrate of platinamine, 
 N 2 H 2 Pt iv , 4H 2 j hydrate of diplatosamine, N 4 H 10 Pt". 2H 2 0. 
 
 300. PALLADIUM is found in small quantity associated with native gold and pla- 
 tinum. It presents a great general resemblance to platinum, but is distinguished 
 from it by being far more easily oxidised, and by its special attraction for cyanogen, 
 with which it forms an insoluble compound. This circumstance is taken advantage 
 of in separating palladium from the platinum ores, for which purpose thelsolution 
 from which the greater part of the platinum has been precipitated by hydrochlorate 
 of ammonia (p. 394) is neutralised with carbonate of soda, and mixed with solution 
 of cyanide of mercury (Hg, C 2 N), when a yellowish precipitate of cyanide of pal- 
 ladium is obtained, yielding spongy palladium when heated, which may be welded 
 into a compact form in the same manner as platinum. When alloyed with native 
 gold, palladium is separated by fusing the alloy with silver, and boiling it with 
 nitric acid, which leaves the gold undissolved. The silver is precipitated from the 
 solution as chloride by adding chloride of sodium, and metallic zinc is placed in the 
 liquid, which precipitates the palladium, lead, and copper, as a black powder. This 
 is dissolved in nitric acid, and the solution mixed with an excess of ammonia, which 
 precipitates the oxide of lead, leaving the copper and palladium in solution. On 
 adding hydrochloric acid in slight excess, a yellow precipitate of hydrochlorate of pal- 
 ladamine (NH 2 Pd . HC1) is obtained, which leaves metallic palladium when heated. 
 
 Palladium is harder than platinum and much lighter (sp. gr. 11-6); it is malle- 
 
400 KHODIUM OSMIUM. 
 
 able and ductile like that metal, and somewhat more fusible, though it cannot be 
 melted in an ordinary furnace.* It is unchangeable in air unless heated, when it 
 becomes blue from superficial oxidation, but regains its whiteness when further 
 heated, the oxide being decomposed. Unlike platinum, it may be dissolved by 
 nitric acid, forming nitrate of palladium (PdO . N0 5 ), which is sometimes employed 
 in analysis for precipitating iodine from the iodides, in the form of black iodide of 
 palladium (Pdl). Palladium is useful, on account of its hardness, lightness, and 
 resistance to tarnish, in the construction of philosophical instruments ; alloyed with 
 twice its weight of silver, it is used for small weights. 
 
 Of the oxides of palladium, two correspond with those of platinum, and a basic sub- 
 oxide (Pd 2 0) has been obtained by gently heating the protoxide. Bichloride of pal- 
 ladium (PdCl 2 ) is very unstable, being easily decomposed, even in solution, into the 
 protochloride (PdCl) and free chlorine. Both the chlorides form double salts with 
 the alkaline chlorides, those containing the palladious chloride (PdCl) having a 
 dark green colour. A pulverulent carbide of palladium is formed when the metal is 
 heated in the flame of a spirit-lamp. 
 
 301. RHODIUM, another of the metals associated with the ores of platinum, has 
 acquired its name from the red colour of many of its salts (p'olov, a rose). It is ob- 
 tained from the solution of the ore in aqua regia by precipitating the platinum with 
 hydrochlorate of ammonia, neutralising with carbonate of soda, adding cyanide of 
 mercury to separate the palladium, and evaporating the filtered solution to dryness 
 with excess of hydrochloric acid. On treating the residue with alcohol, the double 
 chloride of rhodium and sodium is left undissolved as a red powder. By heating 
 this in a tube through which hydrogen is passed, the rhodium is reduced to the 
 metallic state, and the chloride of sodium may be washed out with water, leaving 
 a grey powder of metallic rhodium, which is fused by the oxyhydrogen blowpipe 
 with greater difficulty than platinum, and forms a very hard malleable metal not 
 dissolved even by aqua regia, although this acid dissolves it in the ores of platinum, 
 because it is alloyed with other metals. If platinum be alloyed with 30 per cent, 
 of rhodium, however, it is not aifected by aqua regia, which will probably render the 
 alloy useful for chemical vessels. Rhodium may be brought into solution by fusing 
 it with bisulphate of potash, when sulphurous acid escapes, and a double sulphate 
 of rhodium and potash is formed, which gives a pink solution with water. Finely 
 divided rhodium is oxidised when heated in air. It appears to form two oxides, the 
 protoxide (RoO), which is very little known, and the sesquioxide (Ro 2 3 ), obtained by 
 fusing rhodium with carbonate of potash and nitre, and washing the fused mass 
 with water, which leaves an insoluble compound of the sesquioxide with potash ; on 
 treating this with hydrochloric acid, the sesquioxide of rhodium is left. It is not 
 decomposed by heat, and is insoluble in acids, though it is a basic oxide, and its 
 salts, which have a red colour, are obtained by indirect methods. 
 
 Sesquichloride of rhodium (Ro 2 Cl 3 ) has a brownish black colour, and does not 
 crystallise. Its aqueous solution is red, and it forms crystallisable double salts with 
 the alkaline chlorides, which have a fine red colour. The double chloride of rhodium 
 and sodium, (3NaCl . Ro 2 Cl 3 ) .18Aq., is prepared by heating a mixture of pulveru- 
 lent rhodium and chloride of sodium in a current of chlorine. It crystallises in red 
 octahedra. On boiling a solution of sesquichloride of rhodium with ammonia in 
 excess, a yellow ammoniated salt (Ro 2 Cl 3 . 5NH 3 ) may be crystallised out, from 
 which metallic rhodium may be obtained by ignition. 
 
 With sulphur, rhodium combines energetically at a high temperature ; a proto- 
 sulphide and a sesquisulphide have been obtained. 
 
 302. OSMIUM is characterised by its yielding a very volatile acid oxide (osmic 
 acid, Os0 4 ), the vapours of which have a very irritating odour (6ffft*i, odour). It 
 occurs in the ores of platinum in flat scales, consisting of an alloy of osmium, 
 iridium, ruthenium, and rhodium. This alloy is also found associated with native 
 gold, and being very heavy, it accumulates at the bottom of the crucible in which 
 the gold is melted. The osmium alloy is extremely hard, and has been used to tip 
 the points of gold pens. When a grain of it happens to be present in the gold 
 which is being coined, it often seriously injures the die. When the platinum ore 
 
 * Palladium, at a slightly elevated temperature, absorbs, mechanically, many times its 
 volume of hydrogen. Hammered palladium foil condenses 640 times its volume of hydrogen, 
 below 212 F., though it has not the power of absorbing oxygen or nitrogen. Foil made 
 from fused palladium only absorbs 68 times its volume of hydrogen. (Graham, Proc. Roy. 
 Soc., June 1866). 
 
RUTHENIUM IRIDIUM. 401 
 
 is treated with aqua regia, this alloy is left undissolved, together with grains of 
 chrome-iron ore and titanic iron. To extract the osmium from this residue, it is 
 heated in a porcelain tube through which a current of dry air is passed, when the 
 osmium is converted into osmic acid, the vapour of which is carried forward by the 
 current of air and condensed in bottles provided to receive it. The osmic acid forms 
 colourless prismatic crystals which fuse and volatilise below the boiling-point of 
 water, yielding a most irritating vapour resembling chlorine. It is very soluble in 
 water, giving a solution which exhales the odour of the acid and stains the skin 
 black ; tincture of galls gives a blue precipitate with the solution. Its acid pro- 
 perties are feeble, for it neither reddens litmus nor decomposes the carbonates, and 
 its-salts are decomposed by boiling their solutions. By adding hydrosulphuric acid 
 to a solution of osmic acid, the tetrasulphide of osmium (OsS 4 ) is obtained as a black 
 precipitate, and if this be carefully dried and heated in a crucible made of gas-carbon, 
 metallic osmium is obtained as a brittle mass (sp. gr. 21-4;, which is not fused even 
 by the oxyhydrogen blowpipe, and is not soluble in acids. When obtained by other 
 processes in a finely divided state, osmium oxidises even at the ordinary temperature, 
 and emits the odour of osmic acid. In this state, also, it may be dissolved by nitric 
 acid, which converts it into.osmic acid. 
 
 By dissolving osmic acid in potash and adding alcohol, the latter is oxidised at 
 the expense of the osmic acid, and rose-coloured octahedral crystals of osmite of 
 potash (KO . Os0 3 , 2Aq.) are obtained; the osmious acid has not been isolated. A 
 protoxide and a binoxide of osmium have been obtained. 
 
 Osmium appears to form four chlorides protochloride (OsCl), sesquichloride 
 (Os 2 Cl 3 ), bichloride (OsCl 2 ), and terchloride (OsCl 3 ). The protochloride and bichloride 
 are formed by the direct combination of chlorine with osmium ; the former sublimes 
 in green needles, which yield a blue solution in water, soon absorbing oxygen from 
 the air and becoming converted into bichloride. By heating a mixture of pulverulent 
 osmium with chloride of potassium in a current of chlorine, a double chloride of 
 osmium and potassium (KC1, OsCl 2 ), is obtained which is sparingly soluble, and 
 crystallises in octahedra like the corresponding salt of platinum. When decom- 
 posed with nitrate of silver, it gives a dark green precipitate (AgCL, OsCl 2 ). 
 
 303. RUTHENIUM.* In the process for extracting osmium from the residue left 
 on treating the platinum ore with aqua regia, by heating in a current of air, square 
 prismatic crystals of binoxide of ruthenium (Ku0 2 ) are deposited, nearer to the heated 
 portion of the tube than the osmic acid, for the binoxide is not itself volatile, being 
 only carried forward mechanically in company with the osmic acid. When binoxide 
 of ruthenium is heated in hydrogen, metallic ruthenium is obtained as a hard, brittle, 
 almost infusible metal, which is scarcely affected even by aqua regia. The pro- 
 toxide of ruthenium (RuO) is a dark grey powder insoluble in acids. The sesquioxide 
 (Ru 2 3 ) and the binoxide (Ru0 2 ) have feebly basic properties. The sesquioxide 
 is not decomposed by heat. The anhydrous binoxide is a greenish blue powder. 
 Ruthenic acid (Ru0 3 ) is known only in combination with bases. 
 
 304. IRIDIUM, named from Iris, the rainbow, in allusion to the varied colours of its 
 compounds, has been mentioned above as occurring in the insoluble alloy from the 
 platinum ores. It is also sometimes found separately, and occasionally alloyed with 
 platinum, the alloy crystallising in octahedra, which are even heavier than platinum 
 (sp. gr. 22-3). If the insoluble osmiridium alloy left by aqua regia be mixed with 
 common salt and heated in a current of chlorine, a mixture of the sodio-chlqjides of 
 the metals is obtained, and may be extracted by boiling water. If the solution be 
 evaporated and distilled with nitric acid, the osmium is distilled off as osmic acid, 
 and by adding chloride of ammonium to the residual solution, the iridium is pre- 
 cipitated as a dark red-brown ammonio-chloride (NH 3 , HC1, IrCl 2 ) which leaves 
 metallic iridium when heated. Like platinum, it then forms a grey spongy mass, 
 but is oxidised when heated in air, and may be fused with the oxyhydrogen 
 blowpipe to a hard brittle mass (sp. gr. 21-2), which does not oxidise in air. Like 
 rhodium it is not attacked by aqua regia, unless alloyed with platinum. The pro- 
 duct of the oxidation of finely divided iridium in air is the sesquioxide (Ir 2 3 ), which 
 is a black powder used for imparting an intense black to porcelain ; it is insoluble 
 in acids. The protoxide (IrO) is also more easily acted upon by alkalies than by 
 acids ; its solution in potash becomes blue when exposed to air, from the formation 
 
 * A new mineral found in Borneo, and named laurite, contains sulphides of ruthenium 
 and osmium. It forms small lustrous granules. 
 
 2 c 
 
402 
 
 OCCURRENCE OF GOLD IN NATURE. 
 
 of the binoxide (IrO^). The teroxide (Ir0 3 ) is green. The protochloride (IrCl) and 
 bichloride (IrCl 2 )of iridium resemble the corresponding chlorides of platinum in 
 forming double salts with the alkaline chlorides. There is also a sesquichloride 
 (Ir 2 Cl 3 ), the solution of which has a green colour, and gives a yellow precipitate 
 with mercurous nitrate, and a blue precipitate, soon becoming white, with nitrate 
 of silver. Iridium resembles palladium in its disposition to combine with carbon 
 when heated in the flame of a spirit-lamp. 
 
 305. The following table exibits a general view of the analytical process by which 
 the remarkable metals associated in the ores of platinum may be separated from 
 each other, omitting the minor details which are requisite to ensure the purity of 
 each metal. 
 
 Analysis of the Ore of Platinum. 
 Boil with aqua regia. 
 
 Dissolved. 
 PLATINUM, PALLADIUM, RHODIUM. 
 
 Add chloride of ammonium. 
 
 Undissolved. 
 IRIDIUM, OSMIUM, RUTHENIUM. 
 Chrome iron, Titanic iron, &c. 
 Heat in current of dry air. 
 
 Precipitated ; 
 PLATINUM 
 asNH 4 CL,PtCl 2 
 
 Solution ; 
 Neutralise with carbonate of soda; 
 add cyanide of mercury. 
 
 Volatilised 
 OSMIUM 
 as Os0 4 . 
 
 Carried 
 forward by 
 the current ; 
 RUTHENIUM 
 as Ru0 2 . 
 
 Residue ; 
 Mix with chloride of 
 sodium, and heat in 
 current of chlorine. 
 Treat with boiling water. 
 
 Precipitated ; 
 PALLADIUM 
 as PdCy. 
 
 Solution ; 
 Evaporate with 
 hydrochloric acid. 
 Treat with alcohol. 
 Insoluble. 
 RHODIUM 
 as3NaCl.Ro 2 Cl 3 . 
 
 Dissolved 
 IRIDIUM 
 as NaCl.IrCl 2 
 
 Residue. 
 Titanic iron, 
 Chrome iron, 
 &c. 
 
 The group of platinoid metals exhibits some very remarkable features, and it is to 
 be regretted that it is comparatively imperfectly known in consequence of the diffi- 
 culty and expense attendant upon the purification of the metals. Its members may 
 be arranged in two divisions, the metals in each agreeing closely in their equivalent 
 weights and specific gravities. 
 
 Platinum, 
 Osmium, , 
 Iridium, 
 
 Eq. 
 98-56 
 99-41 
 98-56 
 
 Sp. gr. 
 21-5 
 21-4 
 21-2 
 
 Palladium, 
 
 Khodium, 
 
 Ruthenium, 
 
 Eq. 
 
 63-24 
 52-16 
 52-11 
 
 Sp. gr. 
 11-4 
 12-1 
 11-4 
 
 Through osmium, this group of elements is connected with the group containing 
 antimony, arsenic, and phosphorus, which osmium resembles in the facility with 
 which it is oxidised, and in the volatility of the oxide formed. Palladium connects 
 it with mercury and silver by its solubility in nitric acid, and its special attraction 
 for cyanogen and iodine. 
 
 GOLD. 
 
 306. Gold is one of those few metals which are always found in the 
 metallic state, and is remarkable for the extent to which it is distributed, 
 though in small quantities, over the surface of the earth. The principal 
 supplies of this metal are derived from Australia, California, Mexico, 
 Brazil, Peru, and the Uralian Mountains. Small quantities have been 
 occasionally met with in our own islands, particularly at Wicklow, at 
 Cader Idris in Wales, Leadhills in Scotland, and in Cornwall. 
 
 The mode of the occurrence of gold in the mineral kingdom resembles 
 that of the ore of tin, for it is either found disseminated in the primitive 
 rocks, or in alluvial deposits of sand, which appear to have been formed 
 by the disintegration of those rocks under the continued action of torrents. 
 In the former case, the gold is often found crystallised in cubes and octa- 
 hedra, or in forms derived from these, and sometimes aggregated together 
 
SMELTING OF GOLD OKES. 403 
 
 in dendritic or branch-like forms. In the alluvial deposits, the gold is 
 usually found in small scales (gold dust), but sometimes in masses of con- 
 siderable size (nuggets), the rounded appearance of which indicates that 
 they have been subjected to attrition. 
 
 The extraction of the particles of gold from the alluvial sands is effected 
 by taking advantage of the high specific gravity of the metal (19 '3), which 
 causes it to remain behind, whilst the sand, which is very much lighter 
 (sp. gr. 2 '6), is carried away by water. This washing is commonly 
 performed by hand, in wooden or metal bowls, in which the sand is 
 shaken up with water, and the lighter portions dexterously poured off, so 
 as to leave the grains of gold at the bottom of the vessel. On a somewhat 
 larger scale, the auriferous sand is washed in a cradle or inclined wooden 
 trough, furnished with rockers, and with an opening at the lower end for the 
 escape of the water. The sand is thrown on to a grating at the head of the 
 cradle, which retains the large pebbles, whilst the sand and gold pass 
 through, the former being washed away by a stream of water which is kept 
 flowing through the trough. 
 
 When the gold is disseminated through masses of quartz or other rock, 
 much labour is expended in crushing the latter before the gold can be 
 separated. This is effected either by passing the coarse fragments between 
 heavy rollers of hard cast-iron, or by stamping them, with wooden beams 
 shod with iron, in troughs through which water is kept continually 
 flowing. 
 
 In some cases it is found advantageous to smelt the ore by fusing it 
 with some substance capable of uniting with the gold, and of being after- 
 wards readily separated from it. Lead is peculiarly adapted for this pur- 
 pose ; the crushed ore, being mixed with a suitable proportion, either of 
 metallic lead, or of litharge (oxide of lead) and charcoal, or even of galena 
 (sulphide of lead), together with some lime and oxide of iron or clay, to 
 flux the silica, is fused on the hearth of a reverberatory furnace, when the 
 fused lead dissolves the particles of gold, and collects beneath the lighter 
 slag. The lead is afterwards separated from the gold by cupellation (see 
 p. 353). 
 
 In smelting the ores of gold in Hungary, the metal is concentrated by 
 means of sulphide of iron. The ore consists of quartz and iron pyrites 
 (bisulphide of iron) containing a little gold. On fusing the crushed ore 
 with lime, to flux the quartz, the pyrites loses half its sulphur, and becomes 
 sulphide of iron (FeS), which fuses and sinks below the slag, carrying with 
 it the whole of the gold. If this product be roasted so as to convert the 
 iron into oxide, and be then again fused with a fresh portion of the ore, 
 the oxide of iron will flux the quartz, whilst the fresh portion o sul- 
 phide of iron will carry down the whole of the gold contained in both 
 quantities of ore. This operation having been repeated until the sulphide 
 of iron is rich in gold, it is fused with a certain quantity of lead, which 
 extracts the gold and falls to the bottom. The lead is then cupelled in 
 order to obtain the gold. 
 
 When the ores of lead, silver, or copper contain gold, it is always found 
 to have accompanied the silver extracted from them, and is separated from 
 it by a process to be presently noticed. 
 
 Gold is sometimes separated from the impurities remaining with it after 
 extraction by washing, by the process of amalgamation, which consists in 
 shaking the mixture with mercury in order to dissolve the gold-dust, and 
 straining the liquid amalgam through a chamois leather, which allows the 
 
 '2c2 
 
404 REFINING GOLD, 
 
 excess of mercury to pass through, but retains the solid portion containing 
 the gold, from which the mercury is then separated by distillation.* 
 
 In the Tyrol, this process is adopted for separating the gold from an 
 auriferous iron pyrites by grinding it in a mill of peculiar construction, 
 with water and a little mercury, the latter being allowed to act upon suc- 
 cessive portions of ore until it becomes sufficiently rich to be strained and 
 distilled. 
 
 Gold, as found in nature, is generally alloyed with variable proportions 
 of silver and copper, the separation of which is the object of the gold 
 refiner. It may be effected by means of nitric acid, which will dissolve 
 the silver and copper, provided that they do not bear too small a propor- 
 tion to the gold. Sulphuric acid, however, being very much cheaper, is 
 generally employed. The alloy is fused and poured into water, so as to 
 granulate it and expose a larger surface to the action of the acid ; it is 
 then boiled with concentrated sulphuric acid (oil of vitriol), which dis- 
 solves the silver and the copper in the form of sulphates, with evolution 
 of sulphurous acid gas, whilst the gold is left untouched. In order to 
 recover the silver from the solution, scraps of copper are introduced into 
 it, when that metal decomposes the sulphate of silver, producing sulphate 
 of copper, and causing the deposition of the silver in the metallic state. 
 Finally, the sulphate of copper may be obtained from the solution by 
 evaporation and crystallisation. This process is so effectual when the 
 proportion of gold in an alloy is very small, that even ^V^ n P ar ^ f ^is 
 metal may be profitably extracted from 100 parts of an alloy, and much 
 gold has been obtained in this way from old silver-plate, coins, &c., which 
 were manufactured before so perfect a process for the separation of these 
 metals was known. On boiling old silver coins or ornaments with nitric 
 acid, they are generally found to yield a minute proportion of gold in the 
 form of a purple powder. But this plan of separation is not so successful 
 when the alloy contains a very large quantity of gold, for the latter metal 
 seems to protect the copper and silver from the solvent action of the acid. 
 Thus, if the alloy contains more than th of its weight of gold, it is 
 customary to fuse it with a quantity of silver, so as to reduce the propor- 
 tion of gold below that point, before boiling it with the acid. Again, if 
 the alloy contains a large quantity of copper, it is found expedient to 
 remove a great deal of this metal in the form of oxide by heating the alloy 
 in a current of air. 
 
 Pure gold, like pure silver, is too soft to resist the wear to which it is 
 subjected in its ordinary uses, and it is therefore alloyed for coinage in 
 this country with T J T th of its weight of copper, so that gold coin contains 
 1 part of copper and 11 parts of gold. The gold used for articles of 
 jewellery is alloyed with variable proportions of copper and silver. The 
 alloy of copper and gold is much redder than pure gold. 
 
 The degree of purity of gold is generally expressed by quoting it as of 
 so many carats fine. Thus, pure gold is said to be 24 carats fine ; English 
 standard gold is 22 carats fine, that is, contains 22 carats of gold out of 
 the 24. Gold of 18 carats fine would contain 18 parts of gold out of the 
 24, or f-ths of its weight of gold. 
 
 Pure gold is easily prepared from standard or jeweller's gold, by dissolving it in 
 hydrochloric acid mixed with one-fourth of its volume of nitric acid, evaporating 
 the solution to a small bulk to expel excess of acid, diluting with a considerable 
 
 * A small quantity of sodium dissolved in the mercury lias been found very materially 
 to facilitate the amalgamation of gold and silver ores. 
 
PROPERTIES OF GOLD. 405 
 
 quantity of water, filtering from the separated chloride of silver, and adding a solu- 
 tion of sulphate of iron, when the gold is precipitated as a dark purple powder, 
 which may be collected on a filter, well washed, dried, and fused in a small crucible 
 with a little borax, the crucible having been previously glazed with borax to prevent 
 adhesion of the globules of gold. The action of the sulphate of iron upon the ter- 
 chloride of gold is explained by the equation 
 
 AuCl 3 + 6(FeO . S0 3 ) = Au + Fe 2 01 3 + 2(Fe 2 3 . 3S0 3 ) . 
 
 By employing oxalic acid instead of sulphate of iron, and heating the solution, 
 the gold is precipitated in a spongy state, and becomes a coherent lustrous mass 
 under pressure. The metal is employed in this form by dentists. 
 
 When standard gold is being dissolved in aqua regia, it sometimes becomes coated 
 with a film of chloride of silver which stops the action of the acid ; the liquid must 
 then be poured off, the metal washed, and treated with ammonia, which dissolves 
 the chloride of silver ; the ammonia must be washed away before the metal is re- 
 placed in the acid. In the case of jeweller's gold, it is advisable to extract as much 
 silver and copper as possible by boiling it with nitric acid, before attempting to dis- 
 solve the gold. Gold lace should be incinerated to get rid of the cotton before being 
 treated with acid. 
 
 The genuineness of gold trinkets, &c., is generally tested by touching them with 
 nitric acid, which attacks them if they contain a very considerable proportion of 
 copper, producing a green stain, but this test is evidently useless if the surface be 
 gilt. The weight is, of course, a good criterion in practised hands, but even these 
 have been deceived by bars of platinum covered with gold. The specific gravity 
 may be taken in doubtful cases ; that of sovereign gold is 17-157. 
 
 In assaying gold, the metal is wrapped in a piece of thin paper together with about 
 three times its weight of pure silver, and added to twelve times its weight of pure 
 lead fused in a bone-ash cupel (see page 355) placed in a muffle (or exposed to a 
 strong oxidising blowpipe flame), when the lead and copper are oxidised, and the 
 fused oxide of lead dissolves that of copper, both being absorbed by the cupel. 
 When the metallic button no longer diminishes in size, it is allowed to cool, ham- 
 mered into a flat disk, which is annealed by being heated to redness, and rolled out 
 to a thin plate, so that it may be rolled up by the thumb and finger into a cornet, 
 which is boiled with nitric acid (sp. gr. 1-18) to extract the silver; the remaining 
 gold is washed with distilled water, and boiled with nitric acid of sp. gr. 1-28 to 
 extract the last traces of silver, after which it is again washed, heated to redness in 
 a small crucible, and weighed.- 
 
 The stronger nitric acid could not be used at first, since it would be likely to 
 break the cornet into fragments which could not be so readily washed without loss. 
 The addition of the three parts of silver (quartatiori) is made in order to divide the 
 alloy, and permit the easy extraction of the silver by nitric acid, which cannot be 
 effected when the gold predominates. 
 
 307. The physical characters of gold render it very conspicuous among the 
 metals ; it is the heaviest of the metals in common use, with the exception 
 of platinum, its specific gravity being 19 '3. In malleability and ductility 
 it surpasses all other metals ; the former property is turned to advantage 
 for the manufacture of gold leaf, for which purpose a bar of gold is passed 
 between rollers which extend it into the form of a riband ; this is cut up 
 into squares, which are packed between layers of fine vellum, and"beaten 
 with a heavy hammer ; these thinner squares are then again cut up and 
 beaten between layers of 'gold-beater's skin until they are sufficiently thin. 
 An ounce of gold may thus be spread over 100 square feet; 282,000 of 
 such leaves placed upon each other form a pile of only one inch high. 
 These leaves will allow light to pass through them, and always appear 
 green or blue when held up to the light, though they exhibit the ordinary 
 colour of gold by reflected light ; extremely thin leaves of gold, obtained 
 by partially dissolving ordinary gold leaf by floating it on solution of 
 cyanide of potassium, transmit a violet or a red light, according to their 
 thickness, though they still appear yellow by reflected light, and if taken 
 up on a glass plate and heated to about 600 F. they lose their 
 
406 OXIDES OF GOLD. 
 
 golden reflection and become ruby red, changing to green if pressed with 
 a hard substance. If very finely divided gold be suspended in water, it 
 imparts a violet or red colour to it. Such coloured fluids containing very 
 minute particles of gold in a state of suspension, may be obtained by the 
 action of phosphorus dissolved in ether upon a very weak solution of 
 gold in aqua regia ; on standing for a long time, the particles of finely 
 divided gold are deposited, having the same tint as that, which they 
 previously exhibited when suspended in the liquid; the blue particles 
 being less minute are soonest deposited, but the red particles require many 
 months to settle down. These divers colours of finely divided gold are 
 taken advantage of in painting upon porcelain, and the well-known 
 magnificent ruby red glass owes its colour to the same cause. T -foj-th of a 
 grain of gold is capable of imparting a deep rose colour to a cubic inch 
 of fluid. 
 
 The extreme ductility of gold is exemplified in the manufacture of gold 
 thread for embroidery, in which a cylinder of silver having been covered 
 with gold leaf, it is drawn through a wire-drawing plate and reduced to 
 the thinness of a hair ; in this way six ounces of gold are drawn into a 
 cylinder two hundred miles in length. Although fusing at about the 
 same temperature as copper, gold is seldom cast, on account of its great 
 contraction during solidification. 
 
 Gold is not even affected to the same extent as silver by exposure to the 
 atmosphere, for sulphuretted hydrogen has no action upon it, and hence 
 no metal is so well adapted for coating surfaces which are required to 
 preserve their lustre. 
 
 The gold is sometimes applied to the surfaces of metals in the form of 
 an amalgam, the mercury being afterwards driven off by heat. Metals 
 may also be gilt by means of a boiling solution prepared by dissolving 
 gold in aqua regia, and adding an excess of bicarbonate of potash or of 
 soda. But the most elegant process of gilding is that of electro-gilding, 
 in which the object to be gilt is connected with the negative (zinc) end 
 of the galvanic battery, and immersed in a solution of cyanide of gold in 
 cyanide of potassium, in which is also placed a gold plate connected with 
 the positive (copper) end of the battery, and intended, by gradually dis- 
 solving, to replace the gold abstracted from the solution at the negative 
 pole. 
 
 A gold crucible is very useful in the laboratory for effecting the fusion 
 of substances with caustic alkalies, which would corrode a platinum crucible. 
 
 308. Oxides of gold. Two compounds of gold with oxygen have been 
 obtained, AuO and Au0 3 , but neither of them is of any great practical 
 importance. 
 
 Teroxide of gold or auric add (Au0 3 ) is prepared from the solution of 
 gold in aqua regia, by boiling it with excess of potash, decomposing the 
 aurate of potash with sulphuric acid, and purifying the auric acid by 
 dissolving it in nitric acid and precipitating by water. It forms a yellow 
 precipitate, which is easily decomposed by exposure to light or to a tem- 
 perature of 500 F. By dissolving it in potash and evaporating in vacuo, 
 the aurate of potash is obtained in yellow needles (KO.Au0 3 , 6Aq.) 
 Protoxide of gold (AuO) forms a dark precipitate when protochloride of 
 gold is decomposed by potash. 
 
 The chlorides of gold correspond in composition to the oxides. The 
 terchloride of gold ( AuCl 3 ) is obtained by dissolving gold in hydrochloric 
 
PURPLE PRECIPITATE OF CASSIUS. 407 
 
 acid with one-fourth of its volume of nitric acid, and evaporating on a 
 water-bath to a small bulk ; on cooling, yellow prismatic crystals of a 
 compound of the terchloride with hydrochloric acid are deposited, from 
 which the hydrochloric acid may be expelled by a gentle heat (not 
 exceeding 250 F.), when the terchloride forms a red brown deliquescent 
 mass, dissolving very readily in water, giving a bright yellow solution 
 which stains the skin and other organic matter purple when exposed to 
 light, depositing finely divided gold. Almost every substance capable of 
 combining with oxygen reduces the gold to the metallic state. The inside 
 of a perfectly clean flask or tube may be covered with a film of metallic 
 gold by a dilute solution of the terchloride mixed with citric acid and 
 ammonia, and gently heated. The facility with which it deposits metallic 
 gold, and the resistance of the deposited metal to atmospheric action, has 
 rendered terchloride of gold very useful in photography. Alcohol and 
 ether readily dissolve the terchloride, the latter being able to extract it 
 from its aqueous solution. Terchloride of gold (like bichloride of platinum) 
 forms crystallisable compounds with the alkaline chlorides and with the 
 hydrochlorates of organic bases, and affords great help to the chemist in 
 defining these last. Aurochloride of sodium forms reddish yellow pris- 
 matic crystals (Nad. AuCl 3 , 4Aq.) which are sometimes sold for photo- 
 graphic purposes. 
 
 ProtoMoride of gold (AuCl) is obtained by gently heating the terchlo- 
 ride, when it fuses and is decomposed at 350 F., leaving the protochloride, 
 which is reduced to metallic gold at about 400 F. The protochloride is 
 sparingly soluble in water and of a pale-yellow colour. Boiling water 
 decomposes it into metallic gold and terchloride. 
 
 Fulminating gold is obtained as a buff precipitate when ammonia is 
 added to solution of terchloride of gold; its composition is not well estab- 
 lished , but appears to be Au0 3 . 2KE 3 . HO. It explodes violently when 
 gently heated. 
 
 The Sel d'or of the photographer is a hyposulphite of gold and soda 
 (AuO . S 2 0. 2 , 3(NaO . S 2 2 ), 4Aq.), which is obtained in fine white needles 
 by pouring a solution of one part of terchloride of gold into a solution of 
 three parts of hyposulphite of soda, and adding alcohol, in which the 
 double salt is insoluble. Its formation may be explained by the equation 
 
 8(NaO . S 2 2 ) + AuCl 3 - 
 
 AuO . S 2 2 , 3(NaO . S/) 2 ) + SNaCl + 2(NaO . S 4 5 ). 
 It is doubtful whether the above formula represents the true constitution 
 of this salt, for it is not decomposed by acids in the same manner as ordi- 
 nary hyposulphites. Nitric acid causes the whole of the gold to separate 
 in the metallic state. 
 
 Purple of Cas&ius, which is employed for imparting a rich red colour to 
 glass and porcelain,- is a compound of gold, tin, and oxygen, which are be- 
 lieved to be grouped according to the formula AuO. Sn0 2 , SnO. Sn0 2 + 4Aq. 
 It may be prepared by adding protochloride of tin to a mixture of bi- 
 chloride of tin and terchloride of gold ; 7 parts of gold are dissolved in 
 aqua regia and mixed with 2 parts of tin also dissolved in aqua regia ; 
 this solution is largely diluted with water, and a weak solution of 1 part 
 of tin in hydrochloric acid is added, drop by drop, till a fine purple colour 
 is produced. The purple of Cassius remains suspended in water in a very 
 fine state of division, but subsides gradually, especially if some saline 
 solution be added, as a purple powder. The fresh precipitate dissolves in 
 
408 EQUIVALENT AND ATOM OF GOLD. 
 
 ammonia, but the purple solution is decomposed by exposure to light, 
 becoming blue, and finally colourless, metallic gold being precipitated, 
 and binoxide of tin left in solution. 
 
 The sulphides of gold are not thoro uglily known. When hydrosul- 
 phuric acid acts on solution of terchloride of gold, a black precipitate of 
 AuS, AuS 3 is obtained, which dissolves in alkaline sulphides. The salt 
 NaS, AuS, 8Aq. has been obtained, in colourless prisms soluble in alcohol. 
 The precipitated sulphide of gold is not dissolved by the acids, with the 
 exception of aqua regia. Nitric acid oxidises the sulphur, leaving metallic 
 gold. When hydrosulphuric acid is added to a boiling solution of ter- 
 chloride of gold, the metal itself is precipitated 
 
 4AuCl 3 + 3HS + 12HO - Au 4 + 12HC1 + 3(HO . S0 3 ). 
 
 309. Equivalent and atomic weights of gold. Terchloride of gold, 
 analysed in its crystalline compound with chloride of 'potassium, was 
 found to contain 35 - 5 parts by weight (1 eq.) of chlorine in combination 
 with 65 '53 parts of gold. The existence of a chloride containing three 
 times as much gold in combination with the above weight of chlorine leads 
 to the belief that the equivalent of gold should be represented by 65 -53 x 3, 
 or 196 '6. The specific heat of gold shows that its atomic weight is also 
 196 '6, so that the atomic formula? of its chief compounds are protoxide, 
 Au 2 O ; auric acid, Au 2 O 3 ; aurous chloride, AuCl ; auric chloride, AuCl 3 . 
 Gold is usually considered a triatomic element, occupying the place of 
 three atoms of hydrogen. 
 
409 
 
 ON SOME OF THE 
 
 USEFUL APPLICATIONS OF CHEMICAL PBINCIPLES 
 NOT HITHEKTO MENTIONED, 
 
 CHEMICAL PRINCIPLES OF THE MANUFACTURE 
 OF GLASS. 
 
 310. Glass is defined chemically to be a mixture of two or more silicates, 
 one of which is a silicate of an alkali, the other being a silicate of lime, 
 baryta, oxide of iron, oxide of lead, or oxide of zinc. 
 
 If silicic acid be fused with an equal weight of carbonate of potash or 
 soda, a transparent glassy mass is obtained, but this is slowly dissolved by 
 water, and would therefore be incapable of resisting the action of the 
 weather ; if a small proportion of lime or baryta, or of the oxides of iron, 
 lead, or zinc, be added, the glass becomes far less easily affected by atmo- 
 spheric influences. 
 
 The most valuable property of glass, after its transparency and per- 
 manence, is that of assuming a viscid or plastic consistency when fused, 
 which allows it to be so easily fashioned into the various shapes required 
 for use or ornament. 
 
 The composition of glass is varied according to the particular purpose 
 for which it is intended, the materials selected being fused in large clay 
 crucibles placed in reverberatory furnaces, and heated by a coal-fire or in 
 a gas-furnace. 
 
 Ordinary window glass is essentially composed of silicate of soda and 
 silicate of lime, containing one equivalent (13*3 per cent.) of soda, one 
 equivalent (12'9 per cent.) of lime, and five equivalents (69*1 per cent.) of 
 silicic acid ; it also usually contains a little alumina. This variety, of glass 
 is manufactured by fusing 100 parts of sand with about 35 parts of chalk 
 and 35 parts of soda-ash : a considerable quantity of broken window glass 
 is always fused up at the same time. Of course, the carbonic acid of the 
 chalk and of the carbonate of soda is expelled in the gaseous state, and in 
 order that this may not cause the contents of the crucible to froth over 
 during the fusion, the materials are first fritted together, as it is termed, 
 at a temperature insufficient to liquefy them, when the carbonic acid 
 is evolved gradually, and the fusion afterwards takes place without 
 effervescence. 
 
 Occasionally sulphate of soda is employed instead of the carbonate, 
 when it is usual to add a small proportion of charcoal, in order to reduce 
 the sulphuric to the state of sulphurous acid, which is far more easily 
 
410 FLINT GLASS COLOURED GLASS. 
 
 expelled. Before the glass is worked into sheets, it is allowed to remain 
 at rest for some time in the fused state, so that the air-bubbles may 
 escape, and the glass-gall or scum (consisting chiefly of sulphate of soda 
 and chloride of sodium), which rises to the surface, is removed. 
 
 Plate glass is also chiefly a silicate of soda and lime, but it contains, in 
 addition, a considerable quantity of silicate of potash (74 per cent, of 
 silicic acid, 12 of soda, 5*5 of potash, and 5*5 of lime). The purest white 
 sand is selected, and great care is taken to exclude impurities. 
 
 Crown glass, used for optical purposes, contains no soda, since that 
 alkali has the property of imparting a greenish tint to glass, which is not 
 the case with potash. This variety of glass, therefore, is prepared by fus- 
 ing sand with carbonate of potash and chalk in such proportions that the 
 glass may contain one equivalent (22 per cent.) of potash, one equiva- 
 lent (12 '5 per cent.) of lime, and four equivalents (62 per cent.) of 
 silicic acid. 
 
 The glass 01 which wine bottles are made is of a much cheaper and com- 
 moner description, consisting chiefly of silicate of lime, but containing, in 
 addition, small quantities of the silicates of the alkalies, of alumina, and of 
 oxide of iron, to the last of which it owes its dark colour. It is made of the 
 coarsest materials, such as common red sand (containing iron and alumina), 
 soap-makers' waste (containing lime and small quantities of alkali), refuse 
 lime from the gas-works, clay, and a very small proportion of rock-salt. 
 
 Flint glass, which is used for table glass and for ornamental purposes, 
 is a double silicate of potash and oxide of lead, containing one equivalent 
 (13 '67 per cent.) of potash, one equivalent (33*28 per cent.) of oxide of 
 lead, and six equivalents (51*93 per cent.) of silicic acid. It is prepared 
 by fusing 300 parts of the purest white sand with 200 parts of minium 
 (red oxide of lead), 100 parts of refined pearl-ash, and 30 parts of nitre. 
 The fusion is effected in crucibles covered in at the top to prevent the 
 access of the flame, which would reduce a portion of the lead to the metallic 
 state. The nitre is added in order to oxidise any accidental impurities 
 which might reduce the lead. 
 
 The presence of the oxide of lead in glass very much increases its 
 fusibility, and renders it much softer, so that it may be more easily cut 
 into ornamental forms ; it also greatly increases its lustre and beauty. 
 
 Baryta has also the effect of increasing the fusibilty of glass, and oxide 
 of zinc, like oxide of lead, increases its brilliancy and refracting power, on 
 which account it is employed in some kinds of glass for optical purposes. 
 Glass of this description is also made by substituting boracic acid for a 
 portion of the silicic acid. 
 
 Some varieties of glass, if heated nearly to their melting point, and 
 allowed to cool slowly, become converted into an opaque very hard mass 
 resembling porcelain (Reaumur's porcelain). This change, which is known 
 as devitrification, is due to the crystallisation of the silicates contained in 
 the mass, and by again fusing it the glass may be restored to its original 
 transparent condition. 
 
 In producing coloured glass, advantage is taken of its property of dis- 
 solving many metallic oxides with production of peculiar colours. It has 
 been mentioned above that bottle glass owes its green colour to the pre- 
 sence of oxide of iron ; and since this oxide is generally found in small 
 quantity in sand, and even in chalk, it occasionally happens that a glass 
 which is required to be perfectly colourless turns out to have a slight green 
 tinge. In order to remove this, a small quantity of some oxidising agent 
 
POTTERY AND PORCELAIN. 411 
 
 is usually added, in order to convert the oxide of iron into the sesquioxide, 
 which does not impart any colour when present in minute proportion. A 
 little nitre is sometimes added for this purpose, or some arsenious acid, 
 which yields its oxygen to the oxide of iron, and escapes in the form of 
 vapour of arsenic ; red oxide of lead (Pb 3 4 ) may also be employed, and is 
 reduced to oxide of lead (PbO), which remains in the glass. Bin- 
 oxide of manganese is often added as an oxidising agent, being reduced to 
 the state of oxide of manganese (MnO), which does not colour the glass ; 
 but care is then taken not to add too much of the binoxide, for a very 
 minute quantity of this substance imparts a beautiful amethyst purple 
 colour to glass. 
 
 Suboxide of copper is used to produce a red glass, and the finest ruby 
 glass is obtained (as already mentioned at p. 406) by the addition of a 
 little gold. The oxides of antimony impart a yellow colour to glass ; a 
 peculiar brown-yellow shade is given by charcoal in a fine state of division, 
 and sesquioxide of uranium produces a fine greenish-yellow glass. Green 
 glass is coloured either by oxide of copper or sesquioxide of chromium, 
 whilst oxide of cobalt gives a magnificent blue colour. For black glass, 
 a mixture of the oxides of cobalt and manganese is employed. The white 
 enamel glass is a flint glass, containing about 10 per cent, of binoxide of 
 tin. Bone ash is also used to impart this appearance to glass. 
 
 CHEMISTEY OF THE MANUFACTURE OF POTTEEY 
 AND POKCELAIN. 
 
 311. The manufacture of pottery obviously belongs to an earlier period 
 of civilisation than that of glass, since the raw material, clay, would at 
 once suggest, by its plastic properties, the possibility of working it into 
 useful vessels, and the application of heat would naturally be had recourse 
 to in order to dry and harden it. Indeed, at the first glance, it would 
 appear that this manufacture, unlike that of glass, did not involve the 
 application of chemical principles, but consisted simply in fashioning the 
 clay by mere mechanical dexterity into the required form. It is found, 
 however, at the outset, that the name of clay is applied to a large class of 
 minerals, differing very considerably in composition, and possessing in 
 common the two characteristic features of plasticity and a predominance 
 of silicate of alumina. 
 
 It has already been stated (p. 286) that kaolin is a hydrated silicate 
 of alumina, and it is from this material that the best variety of porcelain 
 is made. This clay is eminently plastic, and can therefore be readily 
 moulded, but when baked, it shrinks very much, so that the vessels made 
 from it lose their shape and often crack in the kiln. In order to prevent 
 this, the clay is mixed with a certain proportion of sand, chalk, bone-ash, 
 or heaVy-spar ; but another difficulty is thus introduced, for these sub- 
 stances diminish the tenacity of the clay, and would thus render the 
 vessels brittle, A further addition must therefore be made, of some sub- 
 stance which fuses at the temperature employed in baking the ware, and 
 thus serves as a cement to bind the unfused particles of clay, &c., into 
 a compact mass. Feldspar (silicate of alumina and potash) answers this 
 purpose ; or carbonate of potash or of soda is sometimes added, to convert 
 a portion of the silica into a fusible alkaline silicate. With a mixture of 
 clay with sand and feldspar (or some substitutes), a vessel may be moulded 
 which will preserve its shape and tenacity when baked, but it will be 
 
412 ENGLISH PORCELAIN STONE- WAKE. 
 
 easily pervious to water, and thus quite unfit for ordinary use. It has, there- 
 fore, to be water-proofed by the application of some easily fusible material, 
 which shall either form a glaze over the surface, or shall become incor- 
 porated with the body of the ware, and the vessel is then fit for all its 
 uses. Handles and ornaments in relief are moulded separately, and fixed 
 on the ware before baking, and coloured designs are transferred from 
 paper to the porous ware before glazing. 
 
 The manufacture of Scores porcelain is one of the most perfect examples 
 of this art. The purest materials are selected in the following propor- 
 tions : Kaolin (porcelain clay), 62 parts ; chalk, 4 parts ; sand, 17 parts ; 
 feldspar, 17 parts. These materials are ground up with water before 
 being mixed, and the coarser particles allowed to subside; the creamy 
 fluids containing the finer particles in suspension are then mixed in 
 the proper proportions, and allowed to settle ; the paste deposited at the 
 bottom is drained, thoroughly kneaded, and stored away for some months 
 in a damp place, by which its texture is considerably improved, and any 
 organic matter which it contains becomes oxidised and removed; the 
 oxidation being effected partly by the sulphates present, which become 
 reduced to sulphides. It is then moulded into the required forms, and 
 dried by simple exposure to the air. The vessels are packed in cylindrical 
 cases of very refractory clay, which are arranged in a furnace or kiln of 
 peculiar construction, and very gradually but strongly heated by the 
 flame of a wood fire. When sufficiently baked, the biscuit porcelain has 
 to be glazed, and great care is taken that the glaze may possess the same 
 expansibility by heat as the ware itself, for otherwise it would crack in all 
 directions as the glazed ware cooled. The glaze employed at Sevres is a 
 mixture of feldspar and quartz very finely ground, and suspended in 
 water, to which a little vinegar is added to prevent the glaze from subsid- 
 ing too rapidly. When the porous ware is dipped into this mixture, it 
 absorbs the water, and retains a thin coating of the mixture of quartz and 
 feldspar upon its surface. It is now baked a second time, when the glaze 
 fuses, partly penetrating the ware, partly remaining as a varnish upon 
 the surface. 
 
 When the ware is required to have some uniform colour, a mineral 
 pigment capable of resisting very high temperatures is mixed with the 
 glaze ; but coloured designs are painted upon the ware after glazing, the 
 ware being then baked a third time, in order to fix the colours. These 
 colours are glasses coloured with metallic oxides, and ground up with oil 
 of turpentine, so that they may be painted in the ordinary way upon the 
 surface of the ware ; when the latter is again heated in the kiln, the 
 coloured glass fuses, and thus contracts a firm adhesion with the ware. 
 
 Gold is applied either in the form of precipitated metallic gold, or of 
 fulminating gold, being ground up in either case with oil of turpentine, 
 burnt in, and burnished. 
 
 English porcelain is made from Cornish clay mixed with ground flints, 
 burnt bones, and sometimes a little carbonate of soda, borax, and binoxide 
 of tin, the last improving the colour of the ware. It is glazed with a 
 mixture of Cornish stone (consisting of quartz and feldspar), flint, chalk, 
 borax, and sometimes white lead to increase its fusibility. 
 
 Stone-ware is made from less pure materials, and is covered with a glaze 
 of silicate of soda, in a very simple manner, by a process known as salt- 
 glazing. The ware is coated with a thin film of sand by dipping it in a 
 mixture of fine sand and water, and is then intensely heated in a kiln into 
 
BUILDING MATERIALS. 413 
 
 which a quantity of damp salt is presently thrown. The joint action of 
 the aqueous vapour and the salt converts the sand into silicate of soda, 
 which fuses into a glass upon the surface of the ware 
 
 XaCl + HO + Si0 2 - NaO.SiO, + HC1 . 
 
 Pipkins, and similar earthenware vessels are made of common clay 
 mixed with a certain proportion of marl and of sand. They are glazed 
 with a mixture of 4 or 5 parts of clay, with 6 or 7 parts of litharge. 
 The colour of this ware is due to the presence of peroxide of iron. 
 Bricks and tiles are also made from common clay mixed, if necessary, 
 with sand. These are very often grey, or blue, or yellow, before baking, 
 and become red under the action of heat, since the iron, which is origin- 
 ally present as carbonate (FeO . C0 2 ), becomes converted into the red 
 peroxide (Fe 2 3 ) by the atmospheric oxygen. 
 
 The impure varieties of clay fuse much more easily than pure clay, so 
 that, for the manufacture of the refractory bricks for lining furnaces, of 
 glass-pots, crucibles for making cast steel, &c., a pure clay is employed, to 
 which a certain quantity of broken pots of the same material is added, to 
 prevent the articles from shrinking whilst being dried. 
 
 Dinas fire-bricks are made from a peculiar siliceous material found in 
 the Vale of Neath, and containing alumina with about 98 per cent, of 
 silica. The ground rock is mixed with 1 per cent, of lime and a little 
 Water before moulding. These bricks are expanded by heat, whilst or- 
 dinary fire-bricks contract. 
 
 Blue bricks are glazed by sprinkling with iron scurf, a mixture of par- 
 ticles of stone and iron produced by the wear of the siliceous grindstones 
 employed in grinding gun-barrels, &c. When the bricks are fired, a glaze 
 of silicate of iron is formed upon them. 
 
 CHEMISTEY OF BUILDING MATERIALS. 
 
 312. Chemical principles would lead to the selection of pure silica 
 (quartz, rock-crystal) as the most durable of building materials, since it is 
 not acted on by any of the substances likely to be present in the atmo- 
 sphere ; but even if it could be obtained in sufficiently large masses for 
 the purpose, its great hardness presents an obstacle to its being hewn into 
 the required forms. Of the building stones actually employed granite, 
 basalt, and porphyry are the most lasting, on account of their capability 
 of resisting for a great length of time the action of water and of atmo- 
 spheric carbonic acid ; but their hardness makes them so difficult to work, 
 as to prevent their employment except for the construction of pavements, 
 bridges, &c., where the work is massive and straightforward, and much 
 resistance to wear and tear is required. The millstone grit is also a very 
 durable stone, consisting chiefly of silica, and employed for the foundations 
 of houses. Freestone is a term applied to any stone which is soft enough 
 to be wrought with hammer and chisel, or cut with a saw; it includes the 
 different varieties of sandstone and limestone. The sandstones consist of 
 grains of sand cemented together by clay or limestone. The Yorkshire flags 
 employed for paving are siliceous stones of this description. The Craig- 
 leith sandstone, which is one of the freestones used in London, contains 
 about 98 per cent, of silica, together with some carbonate of lime. 
 
 The building stones in most general use are the different varieties of 
 carbonate of lime. The durability of these is in proportion to their com- 
 pact structure ; thus marble, being the most compact, has been found to 
 
414 MORTAR CEMENT. 
 
 resist for many centuries the action of the atmosphere, whilst the more 
 porous limestones are corroded at the surface in a very short time. Port- 
 land stone, of which St Paul's and Somerset House are built, and Bath 
 stone, are among the most durable of these ; but they are all slowly cor- 
 roded by exposure to the atmosphere. The chief cause of this corrosion 
 appears to be the mechanical disintegration caused by the expansion, in 
 freezing, of the water absorbed in the pores of the stone. In order to 
 determine the relative extent to which different stones are liable to be dis- 
 integrated by frost, a test has been devised, which consists in soaking the 
 stone repeatedly in a saturated solution of sulphate of soda and allowing 
 it to dry, when the crystallisation of the salt disintegrates the stone, as 
 freezing water would, so that if the particles detached from the surface be 
 collected and weighed, a numerical expression for the resistance of the 
 material will be obtained. Magnesian limestones (carbonate of lime with 
 carbonate of magnesia) are much valued for ornamental architecture, on 
 account of the ease with which they may be carved, and are said to be 
 more durable in proportion as they approach the composition expressed by 
 the formula CaO . C0 2 , MgO . C0 2 .* The magnesian limestone from Bol- 
 sover Moor, of which the Houses of Parliament are built, contains 50 per 
 cent, of carbonate of lime, 40 of carbonate of magnesia, with some silica 
 and alumina. 
 
 It is probable that a slow corrosion of the surface of limestone is effected 
 by the carbonic acid continually deposited in aqueous solution from the 
 air ; and it is certain that in the atmosphere of towns the limestone is 
 attacked by the sulphuric acid which results from the combustion of coal 
 and the operations of chemical works. The Houses of Parliament have 
 suffered severely, probably from this cause. Many processes have been 
 recommended for the preservation of building stones, such as waterproofing 
 them by the application of oily and resinous substances, and coating or 
 impregnating them with solution of soluble glass and similar matters; but 
 none seems yet to have been thoroughly tested by practical experience. 
 
 Purbeck, Ancaster, and Caen stones are well-known limestones employed 
 for building. 
 
 313. The mortar employed for building is composed of 1 part of 
 freshly slaked lime and 2 or 3 parts of sand intimately mixed with enough 
 water to form an uniform paste. The hardening of such a composition 
 appears to be due, in the first instance, to the absorption of carbonic acid 
 from the air, by which a portion of the lime is converted into carbonate, 
 and this, uniting with the unaltered hydrate of lime, forms a solid layer 
 adhering closely to the two surfaces of brick or stone, which it cements 
 together. In the course of time, the lime would act upon the silica, pro- 
 ducing silicate of lime, and this chemical action would render the adhesion 
 more perfect. The chief use of the sand here, as in the manufacture of 
 pottery (p. 411), is to prevent excessive shrinking during the drying of 
 the mortar. 
 
 In constructions which are exposed to the action of water, mortars of 
 peculiar composition are employed. These hydraulic mortars or cements, 
 as they are termed, are prepared by calcining mixtures of carbonate of 
 lime with from 10 to 30 per cent, of clay, when the carbonic acid is 
 expelled, and the lime combines with a portion of the silicic acid from the 
 
 * Any excess of carbonate of lime above that required by this formula may be dissolved 
 out by treating the powdered magnesian limestone with weak acetic acid. 
 
NITRE OR SALTPETRE. 415 
 
 clay, producing a silicate of lime, and probably also, with the alumina, to 
 form aluminate of lime. When the calcined mass is ground to powder 
 and mixed with water, the silicates of alumina and lime, and the aluminate 
 of lime, unite to form hydrated double silicates and aluminates, upon which, 
 water has no action. Roman cement is prepared by calcining a limestone 
 containing about 20 per cent, of clay, and hardens in a very short time 
 after mixing with water. 
 
 For Portland cement (so called from its resembling Portland stone) 
 a mixture of river-mud (chiefly clay) and limestone is calcined at a very 
 high temperature. 
 
 Concrete is a mixture of hydraulic cement with small gravel. A speci- 
 men of this material from a very ancient Phoenician temple was as hard 
 as a rock, and contained nearly 30 per cent, of pebbles. 
 
 Scott's cement is prepared by passing air containing a small quantity of 
 sulphurous acid, evolved from burning sulphur, over quick-lime heated to 
 dull redness. The setting of this cement appears due to the presence of 
 a small proportion of sulphate of lime very intimately mixed with the 
 quick-lime. 
 
 GUNPOWDER 
 
 314. Gunpowder is a very intimate mixture of saltpetre (nitre or 
 nitrate of potash), sulphur, and charcoal, which do not act upon each 
 other at the ordinary temperature, but when heated together arrange 
 themselves into new forms, evolving a very large amount of gas. 
 
 In order to manufacture gunpowder capable of producing the greatest 
 possible eifect, great attention is requisite to the purity of the ingredients, 
 the process of mixing, and the form ultimately given to the finished 
 powder. 
 
 CHEMISTRY OF THE INGREDIENTS OF GUNPOWDER SALTPETRE. Nitrate 
 of potash (KO . N0 5 ), nitre or saltpetre, is found in some parts of India, 
 especially in Bengal and Oude, where it sometimes appears as a white in- 
 crustation on the surface of the soil, and is sometimes mixed with it to 
 some depth. The nitre is extracted from the earth by treating it with 
 water, and the solution is evaporated, at first by the heat of the sun, and 
 afterwards by artificial heat, when the impure crystals are obtained, which 
 are packed in bags and sent to this country as grough (or impure) salt- 
 petre. It contains a quantity of extraneous matter varying from 1 to 10 
 per cent., and consisting of the chlorides of potassium and sodium, sul- 
 phates of potash, soda, and lime, vegetable matter from the soil, sand, and 
 moisture. The number representing the weight of impurity present is 
 usually termed the refraction of the nitre, in allusion to the old method 
 of estimating it by casting the melted nitre into a cake and examining its 
 fracture, the appearance of which varies according to the amount of 
 foreign matter present. 
 
 Peruvian or Chili saltpetre is the nitrate of soda (NaO . N0 5 ) found in 
 Peru and Chili in beds beneath the surface soil. It is often spoken of as 
 cubical saltpetre, since it crystallises in rhombohedra, easily mistaken for 
 cubes, whilst prismatic saltpetre, nitrate of potash, crystallises in six-sided 
 prisms. Nitrate of soda cannot be substituted for nitrate of potash as an 
 ingredient of gunpowder, since it attracts moisture from the air, becoming 
 damp, and appears to be less powerful in its oxidising action upon com- 
 bustible bodies at a high temperature. The Peruvian saltpetre, however, 
 
416 
 
 ARTIFICIAL PRODUCTION OF NITRE. 
 
 forms a very important source from which to prepare the nitrate of potash 
 for gunpowder, since it is easily converted into this salt by double decom- 
 position with chloride of potassium. The latter salt is now imported in so 
 large a quantity from the salt mines of Stassfurth (p. 261), that it enables 
 nitrate of soda to be very cheaply converted into nitrate of potash, and 
 renders Indian saltpetre of less importance to the manufacturer of gun- 
 powder. 
 
 In order to understand the production of saltpetre by the decomposition 
 of nitrate of soda with chloride of potassium, it is necessary to be ac- 
 quainted with the solubility of those salts and of the salts produced by 
 their mutual decomposition. 
 
 100 parts of boiling water dissolve 
 218 parts of nitrate of soda, 
 
 53 ,, chloride of potassium, 
 200 nitrate of potash, 
 
 37 ,. chloride of sodium. 
 
 100 parts of cold water dissolve 
 50 parts of nitrate of soda, 
 33 ,, chloride of potassium, 
 30 ,, nitrate of potash, 
 36 chloride of sodium. 
 
 It is a general rule that when two salts in solution are mixed, which 
 are capable of forming, by exchange of their metals, a salt which is less 
 soluble in the liquid, that salt will be produced and separated. 
 
 Thus when nitrate of soda and chloride of potassium are mixed, and 
 the solution boiled down, chloride of sodium is deposited, and nitrate of 
 potash remains in the boiling liquid 
 
 + KC1 = KO . N0 + 
 
 When this is allowed to cool, the greater part of the nitrate of potash 
 crystallises out, leaving the remainder of the chloride of sodium in solu- 
 tion. 
 
 The method usually adopted is to add the chloride of potassium by 
 degrees to the boiling solution of nitrate of soda, to remove the chloride 
 of sodium with a perforated ladle in proportion as it is deposited, and, 
 after allowing the liquid to rest for some time to deposit suspended 
 impurities, to run it out into the crystallising pans. 
 
 The potash-salt required for the conversion of nitrate of soda into nitrate 
 of potash is sometimes obtained from the refuse of the beet root employed 
 in the manufacture of sugar. 
 
 Nitrate of potash is sometimes prepared from the nitrates obtained in 
 the nitre-heaps, which consist of accumulations of vegetable and animal 
 refuse with limestone, old mortar, ashes, &c. These heaps are constructed 
 upon an impermeable clay floor under a shed to protect them from rain. 
 One side of the heap is usually vertical and exposed to the prevailing- 
 wind, the other side being cut into steps or terraces. They are occasionally 
 moistened with stable drainings, which are allowed to run into grooves 
 cut in the steps at the back of the heap. In such a mass, at an atmo- 
 spheric temperature between 60 and 70 F., nitrates of the various bases 
 present in the heap are slowly formed, and being dissolved by the 
 moisture, are left by it, as it evaporates on the vertical side, in the form 
 of an efflorescence. When this has accumulated in sufficient quantity, it 
 is scraped off, together with a few inches of the nitrified earth, and 
 extracted with water, which dissolves the nitrates, whilst the undissolved 
 earth is built up again on the terraced back of the heap. After two or 
 three years the heap is entirely broken up and reconstructed. The prin- 
 cipal nitrates which are found dissolved in the water are those of potash, 
 
SALTPETRE REFINING. 
 
 417 
 
 lime, magnesia, and ammonia, the three last of which may be converted 
 into nitrate of potash by decomposing them with carbonate of potash. 
 
 The formation of nitric acid in these heaps probably results from che- 
 mical changes similar to those which occur in the soils in which nitre 
 is naturally formed, but, at present, these changes are not thoroughly 
 explained. Some chemists are of opinion that the nitric acid is formed 
 by the union of atmospheric nitrogen and oxygen, encouraged by the 
 presence of porous solids, and of matters undergoing oxidation. The 
 explanation which is best supported by experimental evidence is that 
 which refers the formation of nitric acid to the oxidation of ammonia 
 (p. 122), evolved by the putrefaction of the nitrogenised matters which 
 the heaps contain, this oxidation also being much promoted by the 
 presence of the strongly alkaline lime, and of the porous materials capable 
 of absorbing ammonia and presenting it under circumstances favourable 
 to oxidation. 
 
 In refining saltpetre, for the manufacture of gunpowder, the impure salt 
 is dissolved in about an equal weight of boiling water in a copper boiler, 
 the solution run through cloth niters to remove insoluble matter, and 
 allowed to crystallise in a shallow wooden trough lined with copper, the 
 bottom of which is formed of two inclined planes (fig. 261). Whilst 
 cooling, the solution is kept in continual agitation with wooden stirrers, 
 in order that the saltpetre may be deposited in the 
 minute crystals known as saltpetre flour, and not in 
 the large prisms which are formed when the solution 
 is allowed to crystallise tranquilly, and which con- 
 tain within them cavities enclosing some of the 
 impure liquor from which the saltpetre has been 
 crystallised. The saltpetre, being so much less 
 soluble in cold than in hot water, is, in great part, 
 deposited as the liquid cools, whilst the chlorides 
 and other impurities being" present in small propor- 
 tion, and not presenting the same disparity in their 
 solubility at different temperatures, are retained in 
 the liquid. The saltpetre flour is drained in a 
 wooden trough with a perforated bottom, and trans- 
 ferred to a washing-cistern, where it is allowed to 
 remain for half an hour in contact with two or three successive small 
 quantities of water to wash away the adhering impure liquor ; it is then 
 allowed to drain thoroughly, and in that state, containing from three to 
 six per cent, of water, according to the season, is ready to be transferred 
 to the incorporating mill or to a hot-air oven, where it is dried if not 
 required for immediate use. 
 
 The mother-liquor, from which the saltpetre flour has been deposited, 
 is boiled down and crystallised, the crystals being worked up with the 
 next batch of grough nitre. The final washings of the flour are returned 
 to the boiler in which the grough nitre is originally dissolved. When 
 the saltpetre contains very much colouring matter, a little glue or animal 
 charcoal is employed by the refiner to assist in its removal. 
 
 The old method of refining saltpetre consisted in crystallising it three 
 times in large crystals, which were afterwards melted into cakes or cheeses. 
 It not unfrequently happened that the fusion was effected at too high a 
 temperature, when a portion of the nitrate of potash became converted 
 into nitrite of potash (KO . N0 3 ). The test for overfused nitre was solu- 
 
 2D 
 
 Fig. 261. 
 
418 TESTS FOR PURITY OF SALTPETRE. 
 
 tion of sulphate of copper, which gave a green colour, due to the production 
 of nitrite of copper. 
 
 The impurities most objectionable in the saltpetre employed for gun- 
 powder would be the chlorides of potassium and sodium, which cause it 
 to absorb moisture easily from the air ; the chief test, therefore, to which 
 the refiner subjects it, is the addition, to its solution in distilled water, of 
 a few drops of solution of nitrate of silver, which causes a mjlkiness, due 
 to the separation of a precipitate of chloride of silver, if the chlorides have 
 not been entirely removed. Moreover, the sample should dissolve entirely 
 in water, to a perfectly clear colourless solution, which should have no 
 effect on blue or red litmus paper, and should give no cloudiness with 
 chloride of barium (indicating the presence of sulphates), or with oxalate 
 of ammonia (indicating lime), when these are added to separate portions 
 of it. Very minute quantities of sulphates and of lime, such as may have 
 been derived from the use of river water in washing the flour, are gene- 
 rally disregarded. 
 
 315. Properties of saltpetre. Nitrate of potash is usually distinguish- 
 able by the long striated or grooved six-sided prismatic form in which it 
 crystallises (though it may also be obtained in rhombohedral crystals like 
 those of nitrate of soda), and by the deflagration which it produces when 
 thrown on red-hot coals. It fuses at about 660 F. to a colourless liquid, 
 which solidifies on cooling to a translucent brittle crystalline mass. The 
 sal prunelle of the shops consists of nitre which has been fused and cast 
 into balls. At a red heat it effervesces from the escape of bubbles of 
 oxygen, and is converted into nitrite of potash (KO . N0 3 ), which is 
 itself decomposed by a higher temperature, evolving nitrogen and oxygen, 
 and leaving a mixture of potash and peroxide of potassium. In contact 
 with any combustible body, it undergoes decomposition with great rapidity, 
 the five equivalents of oxygen in the nitric acid (N0 5 ) being available for 
 the oxidation of the combustible substance, and the nitrogen being evolved 
 in the free state ; thus, in contact with carbon, the decomposition of the 
 nitre may be represented by the equation 
 
 2(KO.M) 5 ) + C 5 = 2(KO.CCg + 3C0 2 + N 2 . 
 
 Since .the combustion of a large quantity of material may be thus effected 
 in a very small space and in a short time, the temperature produced is 
 much higher than that obtained by burning the combustible in the ordi- 
 nary way. The specific gravity of saltpetre is 2*07, so that one cubic 
 inch weighs 523 grains (obtained by multiplying the weight of a cubic 
 inch of water, 252'5 grains by 2 '07). Since 101 grains (1 eq.) of nitre 
 contain 40 grains (5 eqs.) of oxygen available for the oxidation of com- 
 bustible bodies, 523 grains, or one cubic inch, of nitre, would contain 207 
 grains or 605 cubic inches of available oxygen, a volume which would be 
 contained in about 3000 cubic inches of air ; hence, one volume of saltpetre 
 represents, in its' power of supporting combustion, 3000 volumes of 
 atmospheric air. It also enables some combustible substances to burn 
 without actual flame, as is exemplified by its use in touch-paper or slow 
 port-fire, which consists of paper soaked in a weak solution of saltpetre 
 and dried. 
 
 If a continuous design be traced on foolscap paper with a brush dipped in a solu- 
 tion of 30 grains of saltpetre in 100 grains of water, and allowed to dry, it will be 
 found that when one part of the pattern is touched with a red-hot iron, it will 
 gradually burn its way out, the other portion of the paper remaining unaffected. 
 
COMPOSITION OF CHARCOAL. 
 
 419 
 
 A mixture of 90 grains of saltpetre, 30 of sulphur, and 30 of moderately fine saw- 
 dust (Baume's flux), will deflagrate with sufficient intensity to fuse a small silver 
 coin into a globule ; the mixture may be pressed down in a walnut shell or a small 
 porcelain crucible, and the coin buried in it, the flame of a lamp being applied out- 
 side until deflagration commences. 
 
 Pulvis fulminans is a mixture of 3 parts of saltpetre, 1 part of sulphur, and 2 of 
 carbonate of potash, all carefully dried ; when it is heated on an iron plate, no action 
 takes place till it begins to melt, when it explodes very violently. 
 
 316. CHARCOAL FOR GUNPOWDER. Charcoal has been already described 
 a the residue of the destructive distillation of wood, in which process the 
 hydrogen and oxygen of the wood are for the most part expelled in the 
 forms of wood naphtha (C 2 H 4 2 ), pyroligneous acid (C 4 H 4 4 ), carbonic 
 acid, carbonic oxide, water, &c., leaving a residue containing a much 
 larger proportion of carbon than the original wood, and therefore capable 
 of producing a much higher temperature (p. 61) by its combustion with 
 the saltpetre. The higher the temperature to which the charcoal is 
 exposed in its preparation, the larger the proportion of hydrogen and 
 oxygen expelled, and the more nearly does the charcoal approach in com- 
 position to pure carbon ; but it is not found advantageous in practice to 
 employ so high a temperature, since it yields a dense charcoal of difficult 
 combustibility, and therefore less fitted for the manufacture of powder. 
 
 The following table exhibits the composition of dried alder-wood and 
 of the charcoal obtained at different temperatures. The incombustible 
 matter or ash of the wood and charcoal is here omitted. 
 
 In 100 parts. 
 
 Temperature 
 of charring. 
 
 Carbon. 
 
 Hydrogen. 
 
 Oxygen. 
 
 Nitrogen. 
 
 Alder-wood, . . 
 
 ... 
 
 48-63 
 
 6-94 
 
 44-75 
 
 0-68 
 
 Charcoal, . . . 
 
 518 F. 
 
 71-0 
 
 4-6 
 
 24-4 
 
 
 662 
 
 77-2 
 
 4-1 
 
 18-7 
 
 
 800 
 
 82-6 
 
 1-9 
 
 15-5 
 
 
 2000 
 
 83-3 
 
 2-3 
 
 14-4 
 
 5 
 
 2300 
 
 89-2 
 
 1-4 
 
 9-4 
 
 j 
 
 2700 
 
 95-4 
 
 0-7 
 
 3-9 
 
 5> 
 
 Above 3000 
 
 98-8 
 
 0-6 
 
 0-6 
 
 This table shows that at temperatures between 800 and 2000 F., there 
 is very little alteration in the composition of the charcoal, and it is within 
 these limits that the charcoal employed for the manufacture of gunpowder 
 in this country is prepared. Between these limits, however, the density 
 and consequent inflammability of the charcoal vary considerably, that 
 prepared at the lower temperatures igniting most readily. Hence it is 
 desirable that the temperature of carbonisation should noli exceed an 
 ordinary low red heat (about 1000 F.) 
 
 The charcoal prepared between 500 and 600 F. has a brown colour 
 (charlon roux), and although it is more easily inflamed than the black 
 charcoal obtained at higher temperatures, the presence of so large a pro- 
 portion of oxygen so much diminishes its calorific value, that its employ- 
 ment in gunpowder is not advantageous. It is used on the Continent in 
 the manufacture of sporting-powder, and is prepared by exposing the 
 wood, in an iron cylinder, to the action of high-pressure steam heated to 
 about 540 F. The charbon roux is very hygroscopic. 
 
 Light woods, such as alder, willow, and dogwood (cornel tree), are 
 
420 
 
 SULPHUR FOR GUNPOWDER. 
 
 Fig. 262. Charcoal retort. 
 
 selected for the preparation of charcoal for gunpowder, because they yield 
 a lighter and more easily combustible charcoal, dogwood being employed 
 for the best quality of powder. This wood is chiefly imported, since it 
 has not been successfully grown in this country. The wood is stripped of 
 its bark, and either exposed for a length of time to the air or dried in a hot 
 chamber. Considerable loss of charcoal takes place if damp wood be charred, 
 a portion of the carbon being oxidised by the steam at a high temperature. 
 In order to convert the wood into charcoal, 1 J cwt. of wood is packed 
 into a sheet iron cylinder or slip (fig. 262), one end of which is closed 
 
 by a tightly fitting cover, and the 
 other by a perforated plate, to 
 allow of the escape of the gases and 
 vapours expelled during the car- 
 bonisation. This cylinder is then 
 introduced into a cylindrical iron 
 retort built into a brick furnace, 
 and provided with a pipe (L) for the 
 escape of the products, which are 
 usually carried back into the fur- 
 nace (B) to be consumed. The pro- 
 cess of charring occupies from 3 J 
 to 4 hours, and as soon as it is 
 completed, the slip is transferred 
 to an iron box or extinguisher, 
 where the charcoal is allowed to 
 cool. About 40 Ibs. of charcoal 
 
 are obtained from the above quantity of wood. Charcoal prepared by this 
 process is spoken of as cylinder charcoal, to distinguish it from pit char- 
 coal, prepared by the ordinary process of charcoal-burning described at 
 (p. 57), and which is employed for fuze compositions, &c., but not for 
 the best gunpowder. The fitness of the charcoal for the manufacture of 
 powder is generally judged of by its physical characters. It is of course 
 desirable that the charcoal should be as free from incombustible matter as 
 possible. The proportion of the ash left by different charcoals varies con- 
 siderably, but it seldom exceeds two per cent. This ash consists chiefly 
 of the carbonates of potash and lime ; it also contains phosphate of lime, 
 carbonate of magnesia, silicate and sulphate of potash, chloride of sodium, 
 and the oxides of iron and manganese. 
 
 The properties of charcoal have been already described ; its great ten- 
 dency to absorb moisture from the air is of some importance in the manu- 
 facture of gunpowder, from its causing a false estimate to be made of the 
 proportion employed, unless the actual amount of water present in the 
 charcoal is known. 
 
 Tar charcoal is the name given to sticks of charcoal which have acci- 
 dentally become coated with a shining film of carbon left behind by tar 
 which has condensed upon it in the retorts ; it is sometimes rejected by 
 the powder manufacturer. 
 
 317. SULPHUR FOR GUNPOWDER. Distilled sulphur (p. 185) is the 
 variety always employed for the manufacture of gunpowder, the sub- 
 limed sulphur being employed for fuze compositions, &c. The alleged 
 reason for the preference is that the sublimed sulphur, having been 
 deposited in a chamber containing much sulphurous and sulphuric acid 
 
MANUFACTURE OF GUNPOWDER. 421 
 
 vapours, its pores have become charged with acid which would be injurious 
 in the powder; but it has been pointed out (p. 187) that distilled sul- 
 phur consists entirely of the soluble or electro-negative variety of sulphur, 
 whilst sublimed sulphur contains a large proportion of the insoluble or 
 positive sulphur, which would probably influence its action in gunpowder. 
 The sulphur should leave scarcely a trace of incombustible matter when 
 burnt, and after stirring the powdered sulphur for some time with warm 
 distilled water, the latter should only very feebly redden blue litmus. 
 As an ingredient of gunpowder, sulphur is valuable on account of the low 
 temperature (560 F.) at which it inflames, thus facilitating the ignition 
 of the powder. Its oxidation by saltpetre appears also to be attended with 
 the production of a higher temperature than is obtained with charcoal, 
 which would have the effect of accelerating the combustion and of increas- 
 ing, by expansion, the volume of gas evolved. 
 
 The difference in the inflammability of sulphur and charcoal is strikingly shown 
 by heating a square of coarse wire gauze over a flame till it is red hot in the centre, 
 placing it over a jar of oxygen, allowing it to cool till it no longer kindles charcoal- 
 powder sprinkled through it from a pepper-box, and whilst the cloud of charcoal is 
 still floating in the gas, throwing in sulphur from a second box ; the hot gauze will 
 inflame the sulphur, and this will kindle the charcoal. 
 
 An iron rod allowed to cool below redness may be used to stir a mixture of char- 
 coal with (3 parts of) nitre ; but if it be dipped into powdered sulphur, at once 
 inflames it, and the flame of the sulphur will kindle the mixture. The effect of the 
 same rod upon mixtures of nitre with charcoal alone, and with charcoal and sulphur, 
 is instructive. 
 
 The acceleration of the combustion of gunpowder by the sulphur is well shown by 
 laying a train, of which one-half consists of a mixture of 75 nitre and 25 charcoal, 
 and the other of 75 nitre, 15 charcoal, and 10 sulphur, a red-hot iron being applied 
 at the junction of the two trains to start them together. 
 
 318. MANUFACTURE OP GUNPOWDER. The proportions of the ingredients 
 of gunpowder have been varied somewhat in different countries, the salt- 
 petre ranging from 74 to 77 per cent., the charcoal from 12 to 16, and 
 the sulphur from 9 to 12*5 per cent. English Government powder con- 
 tains 
 
 75 per cent, of nitre. 
 
 15 ,, charcoal. 
 
 10 sulphur. 
 
 The powdered ingredients are first roughly mixed in a revolving copper 
 drum, with mixing arms turning in 
 an opposite direction, and the mixture 
 is subjected, in quantities of about 50 
 Ibs. at a time, to the action of the 
 incorporating mill (fig. 263), where 
 it is sprinkled with water, poured 
 through the funnel (F), or from a 
 can with a fine rose, and exposed to 
 trituration and pressure under two 
 cast-iron edge-runners (B), rolling 
 round in different paths upon a cast- 
 iron bed, a very intimate mixture 
 being thus effected by the same kind 
 of movement as in a common pestle i 
 and mortar, the distribution of the pig. 263. Incorporating mill, 
 
 nitre through the mass being also 
 assisted by its solubility in water. A wooden scraper (C) tipped with 
 
422 PROPERTIES OF GUNPOWDER. 
 
 copper, prevents the roller from getting clogged, and a plough (D) keeps the 
 mixture in the path. Of course, the water employed to moisten the powder 
 must be as free from deliquescent salts (especially chlorides, see p. 418) as 
 possible ; the quantity required varies with the state of the atmosphere. 
 The duration of the incorporating process is varied according to the kind 
 of powder required, the slow-burning powder employed for cannon being 
 sufficiently incorporated in about 3 hours, whilst rifle-powder requires 5 
 hours. 
 
 The dark-grey slaty mass of mill-cake, which is thus produced, is broken 
 up by passing between grooved rollers of gun metal, and is then placed, 
 in layers of about an inch thick, between copper plates packed in a stout 
 box, in which it is subjected for a quarter of an hour to a pressure of 
 about 70 tons on the square foot, in a hydraulic press, which has the eifect 
 of condensing a larger quantity of explosive material into a given volume, 
 and of diminishing the tendency of the powder to absorb moisture from 
 the air and to disintegrate or dust after granulation. The press-cake thus 
 obtained is very hard and compact, resembling slate in appearance. As far 
 as its chemical nature is concerned, it is finished gunpowder, but if it be 
 reduced to powder and a gun loaded with it, the combustion of the charge 
 is found to take place too slowly to produce its full effect, since the pulve- 
 rulent form offers so great an obstacle to the passage of the flame by which 
 the combustion is communicated from one end of the charge to the other. 
 The press-cake must, therefore, be granulated (corned} or ( broken up into 
 grains of sufficient size to allow the rapid passage of the flame between them, 
 and the consequent immediate firing of the whole charge. The granulation 
 is effected by crushing the press cake between successive pairs of toothed gun 
 metal rollers, from which it falls on to sieves, which separate it into grains 
 of different sizes, the dust, or meal poivder, passing through the last sieve. 
 The granulated powders are freed from dust by passing them through 
 revolving cylinders of wooden frame-work covered with canvas, and the 
 fine grain powder is glazed by the friction of its own grains against each 
 other in revolving barrels. The large grain powders are sometimes glazed 
 or faced with graphite, by introducing a little of that substance into the 
 glazing-barrels with the powder. The powder is dried in a hot-air cham- 
 ber very gradually, so as not to injure the grain, and is once more dusted 
 in canvas cylinders before being packed. 
 
 Various modifications are introduced into the above processes in different 
 places, but the principles upon which the manufacture is conducted are 
 always the same. 
 
 319. PROPERTIES OF GUNPOWDER. Good gunpowder is composed of 
 hard angular grains, which do not soil the fingers, and have a perfectly 
 uniform dark-grey colour. Its specific gravity (absolute density) appears to 
 vary between 1'84 and 1'97, and its apparent density (obtained by weigh- 
 ing a given measure of the grain against an equal measure of water) varies 
 from 0'89 to 0'94, so that a cubic foot will weigh from 55 to 58 Ibs. 
 When exposed to air of average dryness, gunpowder absorbs about 0'5 per 
 cent, of water. In damp air it absorbs a much larger proportion, and 
 becomes deteriorated in consequence of the saltpetre being dissolved, and 
 crystallising upon the surface of the grains. Actual contact with water 
 dissolves the saltpetre and disintegrates the grains. When very gradually 
 heated in air, gunpowder begins to lose sulphur, even at 212 F., this 
 ingredient passing off rapidly as the temperature rises, so that the greater 
 
CHEMISTRY OF THE EXPLOSION OF GUNPOWDER. 423 
 
 part of it may be expelled without inflaming the powder, especially if the 
 powder is heated in carbonic acid or hydrogen, to prevent contact with 
 air. If gunpowder be suddenly heated to 600 F. in air, it explodes, the 
 sulphur probably inflaming first ; but out of contact with air a higher 
 temperature is required to inflame it. The ignition of gunpowder by 
 flame is not ensured unless the flame be flashed among the grains of powder ; 
 it often takes some time to ignite powder with the flame of a piece of burning 
 paper or stick, but contact with a red-hot solid body inflames it at once. A 
 heap of good powder, when fired on a sheet of white paper, burns without 
 .sparks and without scorching or kindling the paper, which should exhibit 
 only scanty black marks of charcoal after the explosion. If the powder 
 has not been thoroughly incorporated, it will leave minute globules of 
 fused nitre upon the paper. Two ounces of the powder should be capable 
 of throwing a 68-lb. shot to a distance of 260 to 300 feet from an 8-inch 
 mortar at 45 elevation. 
 
 Very fortunately, it is difficult to explode gunpowder by concussion, 
 though it has been found possible to do so, especially on iron, and acci- 
 dents appear to have been caused in this way by the iron edge-runners in 
 the incorporating mill, when the workmen have neglected the special pre- 
 cautions which are laid down for them. The use of stone upon iron in 
 the incorporation is avoided, because of the great risk of producing sparks, 
 and copper is employed in the various fittings of a powder mill wherever it 
 is possible. 
 
 The electric spark is, of course, capable of firing gunpowder. 
 
 320. PRODUCTS OF EXPLOSION OF GUNPOWDER. In the explosion of gun- 
 powder, the oxygen of the nitre converts the carbon of the charcoal chiefly 
 into carbonic acid (C0 2 ), part of which assumes the gaseous state, whilst 
 the remainder combines with the potash of the nitre to form carbonate of 
 potash (KO . C0 2 ). The greater part of the sulphur is converted into 
 sulphuric acid (S0 3 ), which forms sulphate of potash (KO . S0 3 ). The 
 chief part of the nitrogen contained in the nitre is evolved in the uncom- 
 bined state. The rough chemical account of the explosion of gunpowder, 
 therefore, is that the mixture of nitre, sulphur, and charcoal is resolved 
 into a mixture of carbonate of potash, sulphate of potash, carbonic acid, 
 and nitrogen, the two last being gases, the elastic force of which, when 
 expanded by the heat of the combustion, accounts for the mechanical 
 effect of the explosion. 
 
 But in addition to these, several other substances are found among the 
 products of the explosion. Thus, the presence of sulphide of potassium 
 (KS) may be recognised by the smell of hydrosulphuric acid produced on 
 moistening the solid residue in the barrel of a gun, and hydrostflphuric 
 acid (HS) itself may often be perceived in the gases produced by the 
 explosion, the hydrogen being derived from the charcoal. A little marsh- 
 gas (C 2 H 4 ) is also found among the gases, being produced by the decom- 
 position of the charcoal, a portion of the hydrogen of which is also 
 disengaged in the free state. Carbonic oxide (CO) is always detected 
 among the products. It is evident that the collection for analysis of the 
 products of explosion must be attended with some trouble, and that con- 
 siderable differences are to be expected between the results obtained by 
 different operators, from the variation of the circumstances under which 
 the powder is fired and the products collected. When the powder is 
 slowly burnt, a considerable proportion of the nitrogen in the saltpetre is 
 
424 
 
 PRODUCTS OF EXPLOSION OF GUNPOWDER. 
 
 evolved in the form of nitric oxide gas (N0 2 ), which, is not found among 
 the products of the rapid explosion of powder. 
 
 Some of the most recent experiments upon the explosion of 'gunpowder 
 have been made under conditions very similar to those which occur in 
 practice, the powder having been confined in a thin iron case and sus- 
 pended in the centre of a strong iron globe exhausted of air, in which the 
 powder was fired by electricity, so that the gaseous and solid ^products of 
 the explosion remained within the globe, and could be submitted to 
 analysis. Two samples of powder were thus examined, but their c6m- 
 position differed from that of English Government powder stated above, 
 as will be seen by the following table : 
 
 I. II. 
 
 Nitre, . ;: . ' . . 
 Sulphur, . . :; 
 Charcoal, viz., Carbon, 
 
 Hydrogen, 
 
 Oxygen, 
 
 Ash, . 
 
 99-97 
 
 100-05 
 
 About 570 grs. of powder were exploded in each experiment. The gas 
 collected was found to be inflammable, as would be expected from the 
 flash which is always perceived at the muzzle when a gun is discharged. 
 
 100 grs. of sample I. gave 1074 cub. in. of gas at 32 F. and 30 in. Bar. 
 
 >J II' 5? 1*1*0 
 
 The gases contained, in 100 cubic inches 
 
 I. II. 
 
 Nitrogen,. . .' ,' . 37-58 .. 35-33 
 
 Carbonic acid (C0 2 ), . 42-74 .. 48-90 
 
 Carbonic oxide (CO), ' : 10-19 .. 5-18 
 
 Hydrogen, . . . 6-93 .. 6-90 
 
 Sulphuretted hydrogen (HS), 0-86 .. 0-67 
 
 Marsh-gas (C 2 H 4 ), . . 2-70 .. 3-02 
 
 100-00 
 
 100-00 
 
 The products of explosion furnished by 100 grains of each powder. 
 
 were 
 
 Sulphate of potash (KO . S0 3 ), . 
 Carbonate of potash (KO . C0 2 ), . 
 Hyposulphite of potash (KO . S 2 2 ), 
 Sulphide of potassium (KS), 
 Sesquicarbonate of ammonia, 
 Charcoal, . . . . ,-.. 
 Sulphur, 
 
 Nitrogen, . . . . . 
 Carbonic acid (C0 2 ), . 
 Carbonic oxide (CO), . 
 
 Hydrogen, 
 
 Sulphuretted hydrogen (HS), 
 Marsh-gas (C 2 H 4 ), 
 
 99-83 
 
 II. 
 
 36-17 
 20-78 
 
 1-77 
 
 o-oo 
 
 2-66 
 
 2-60 
 
 1-16 
 
 10-06 
 
 21-79 
 
 1-47 
 
 0-14 
 
 0-23 
 
 0-49 
 
 99-32 
 
 In both these cases it will be seen that if the charcoal and sulphur 
 which took no part in the combustion be left out of consideration, the 
 
CALCULATION OF THE FOECE OF FIRED GUNPOWDER. 425 
 
 sulphate and carbonate of potash formed together more than f of the 
 solid products of explosion; and that the carbonic acid and nitrogen 
 taken together amounted, in the one case to T 9 Q-, and in the other to ^ of 
 the gaseous products. If only the chief products of the explosion be 
 taken into consideration, viz., sulphate and carbonate of potash, carbonic 
 acid, carbonic oxide, and nitrogen, the following equation is the simplest 
 which can be constructed from the above numerical data : 
 
 7(KO.N0 5 ) + S 4 + C 12 = 
 4(KO.S0 3 ) + 3(KO.C0 2 ) + 8CO, + N 7 + CO . 
 
 This equation, however, would represent a gunpowder composed of 
 
 Nitre, . . . 83-8 
 Sulphur, . . 7 '6 
 
 Charcoal, . . 8-5 
 
 99-8 
 and would require the products of decomposition to be 
 
 Sulphate of potash, 
 Carbonate of potash, 
 Carbonic acid, 
 Nitrogen, . 
 Carbonic oxide, . 
 
 41-2 
 24-5 
 20-8 
 11-6 
 1-6 
 
 997 
 
 Seasoning from analogy with other chemical operations, it seems pro- 
 bable that the explosion of gunpowder really includes a number of 
 chemical changes which cannot be simply represented in one equation, 
 and that whilst the above equation, or some similar one, represents the 
 principal reaction which takes place during the explosion, there are other 
 minor reactions in progress, the products of which are found in smaller 
 quantity. 
 
 321. CALCULATION OF THE FORCE OF FIRED GUNPOWDER. The mechani- 
 cal force exerted in the explosion of gunpowder depends upon the pro- 
 duction of a large volume of gas from a small volume of solid, the volume 
 of the gas being increased by the expansive effect of the heat generated 
 in the combustion of the charcoal and sulphur. To calculate the amount 
 of this mechanical force, it is necessary to ascertain the volume of gas 
 which would be evolved by a given volume of powder, and the extent to 
 which this gas would be expanded by the heat at the instant of explosion. 
 
 In order to illustrate this calculation, let it be assumed that the equa- 
 tion given above correctly represents the explosion of the powder, viz. 
 
 7(KO.N0 5 ) + S 4 + C 12 = 
 4(KO.S0 3 ) + 3(KO.C0 2 ) + 8C0 2 + N 7 + CO. 
 
 Now, it is known, as a result of experimental determination, that 
 
 7 eqs. nitrate of potash (101 x 7) = 707 grains. 
 4 eqs. sulphur ( 16 x 4h = 64 
 
 12 eqs. carbon ( 6 x 12) = 72 
 
 Gunpowder, . . 843 
 
426 CALCULATION OF THE FORCE OF FIRED GUNPOWDER. 
 
 At 60 F., and 30 in. Bar. 
 
 8 eqs. carbonic acid (22 x 8) = 176 grains = 372-0 cub. inches. 
 7 eqs. nitrogen (14 x 7) = 98 = 325-4 
 
 1 eq. carbonic oxide = 14 = 46-5 
 
 743-9 
 
 Hence it appears that 843 grains of gunpowder would yield 743 -9 
 cubic inches of gas measured at 60 F. and 30 in. barometric pressure. 
 
 If one cubic foot of the powder weighs 58 Ibs., one cubic inch will 
 weigh 234-9 grains, and will evolve 207 cubic inches of gas measured at 
 60 F. and 30 in. Bar. 
 
 But the mechanical force exerted by the powder depends upon the 
 volume of this gas at the period of explosion, and in order to calculate 
 this, we must ascertain what would be its temperature at that period. 
 
 A carefully conducted experiment has shown that the explosion of one 
 part by weight of gunpowder is able to raise the temperature of 61 9 '5 
 parts by weight of water from C. to 1 C., or to raise the temperature of 
 one part by weight of water from C. to 6 19 '5 C., supposing the water 
 to be capable of bearing so great an elevation of temperature without 
 change of state. 
 
 This result is generally expressed by saying that the combustion of the 
 powder evolves 619 '5 units of heat (the unit of heat being the quantity 
 required to raise 1 part by weight of water from C. to 1 C.) 
 
 But the products of the explosion of powder will be raised to a higher 
 temperature than 619'5 C., because their specific heat is lower than that 
 of water. 
 
 For the purpose of this calculation, the specific heat of a substance may 
 be defined as the quantity of heat required to raise 1 gr. of the substance 
 through 1 of the thermometer, water being taken as the unit. 
 
 It is evident that if the specific heat of each product of the explosion 
 be multiplied by the actual weight of that product, the result will be the 
 quantity of heat required to raise that product 1 in temperature. 
 
 The specific heats of the products have been ascertained by experiment, 
 and are contained in the first column of figures in the following table. 
 The actual weight of each product from the explosion of 1 gr. of powder 
 is contained in the second column, and the third column shows the 
 quantity of heat required to raise each product 1 C. (representing as 
 unity the quantity of heat required to raise 1 gr. of water from C. 
 to 1 C.) 
 
 Sulphate of potash, . 
 Carbonate of potash, 
 Carbonic acid, , .- 
 Nitrogen, u 1'' 
 Carbonic oxide, 
 
 SpeaHeat. 
 
 0-1901 x 0-412 = 0-07832 
 
 0-2162 x 0-246 = 0-05319 
 
 0-2164 x 0-209 = 0-04523 
 
 0-2440 x 0-116 = 0-02830 
 
 0-2479 x 0-017 = 0-00421 
 
 0-20925 
 
 The quantity of heat, therefore, which is required to raise, through 
 1 C., the joint products of the explosion of one grain of gunpowder is 
 0-20925 of the above-mentioned unit. 
 
 Dividing the 619*5 units of heat generated in the explosion, by the 
 quantity of heat required to raise the joint products through one degree, 
 viz., 0-20925, we obtain 2960 C. ( = 5328 F.) for the number of 
 
EFFECT OF SIZE OF GRAIN IN GUNPOWDER. 427 
 
 degrees through which the products will be raised by the explosion, i.e., 
 for the temperature of the products at the moment of explosion.* 
 
 It remains to be ascertained what volume would be occupied, at 5328 
 F., by the 207 cubic inches of gas at 60 F. evolved from one cubic inch 
 of powder. 
 
 The expansion which gases suffer when heated amounts to T of then- 
 volume at 32 F. for each degree Fahrenheit. 
 
 Thus 491 volumes of gas at 32 F. become 
 492 33 F, 
 
 and, if heated 28 above 32, i.e., to 60 F., they would become 491 + 28, 
 or 519 volumes. If the 491 volumes be heated to 5328 F., or 5296 
 above 32, they will expand to 491 + 5296, or 5787 volumes. 
 
 The volume of the gas at the moment of explosion, therefore, will be 
 ascertained from the following proportion 
 
 Vols. at 60 F. Vols. at 5328 F. Cub. in. at 60 F. Cub. in. at 5328 F. 
 519 : 5787 : : 207 : 2308 
 
 from which it appears that one cubic inch of powder would evolve a 
 quantity of gas measuring 2308 cubic inches at the moment of ex- 
 plosion. 
 
 Since the pressure exerted by gases upon the sides of a containing 
 space is inversely as their volume, the gas evolved from a cubic inch of 
 powder, if developed in a space exactly filled by the powder, would exert 
 a pressure of 2308 atmospheres, or 34,620 Ibs., or 15 tons upon the 
 square inch. 
 
 It is here supposed, of course, that the whole of the gas is evolved at 
 once, and is immediately raised to the same temperature, conditions never 
 fulfilled in the use of gunpowder in small arms or in cannon, where the 
 combustion of the charge is not instantaneous but rapidly progressive, 
 where the confining space is rapidly enlarged by the movement of the 
 projectile long before the whole of the charge has exploded, and where 
 the heated gas is cooled by contact with the metal of the piece. 
 
 The period over which the combustion of a given weight of powder ex- 
 tends will, of course, depend upon the extent of surface over which it 
 can be kindled ; thus a single fragment of powder weighing 10 grains, 
 even if it were instantaneously kindled over its entire surface, could not 
 evolve so much gas in a given time as if it had been broken into ten 
 separate grains, each of which was kindled at the same instant, since the 
 inside of the large fragment can only be kindled from the outside. Upon 
 this principle a given weight of powder in large grains will occupy a 
 longer period in its explosion than the same weight in small grains, so 
 that the large grain powder is best fitted for ordnance, where the ball is 
 very heavy, and the time occupied in moving it will permit the whole of 
 the charge to be fired before the ball has left the muzzle, whilst in small 
 arms with light projectiles, a finer grained and more quickly burning 
 charge is required. If the fine grain powder were used in cannon, the 
 whole of the gas might be evolved before the containing space had been 
 sensibly enlarged by the movement of the heavy projectile, and the gun 
 would be subjected to an unnecessary strain ; on the other hand, a large 
 
 * Strictly speaking 32 F. should be added, on account of the different positions of the 
 zero in the two scales, but it would not materially affect the result. 
 
428 EFFECT OF ATMOSPHERIC PRESSURE ON FIRED GUNPOWDER. 
 
 grain powder, in a musket, would evolve its gas so slowly that the ball 
 might be expelled with little velocity by the first half of it, and the re- 
 mainder would be wasted. There is good reason to believe that even 
 under the most favourable circumstances, a large proportion of every charge 
 of powder is discharged unexploded from the muzzle of the gun, and is 
 therefore wasted. In blasting rocks and other mining operations, the 
 space within which the powder is confined is absolutely incapable of en- 
 largement until the gas evolved by the combustion has attained sufficient 
 pressure to do the whole work, that is, to rend the rock, for example, 
 asunder. Accordingly, a slowly burning charge will produce the effect, 
 since the rock must give way when the gas attains a certain pressure, 
 whether that happens in one second or in ten. Indeed, a slowly burning 
 charge is advantageous, as being less liable to shatter the rock or coal, and 
 bringing it away in larger masses with less danger. Nitrate of baryta and 
 nitrate of soda are sometimes substituted for a part of the nitrate of 
 potash in mining powder, its combustion being thus retarded.* 
 
 When gunpowder is slowly burnt, the products of its decomposition are 
 different from those mentioned above ; thus, nitric oxide (N0 2 ), arising 
 from incomplete decomposition of the nitre, is, perceived in considerable 
 quantity, and may be recognised by the red colour produced when it is 
 brought in contact with air. 
 
 The white smoke resulting from the explosion of gunpowder consists 
 chiefly of the sulphate and carbonate of potash in a very finely divided 
 state ; it seems probable that at the instant of explosion they are con- 
 verted into vapour, and are afterwards deposited in a state of minute 
 division as the temperature falls. The fouling or actual solid residue in 
 the gun is very trifling when the powder is dry and has been well incor- 
 porated ; a damp or slowly burning powder leaves, as might be expected, 
 the larger residue. The residue always becomes wet on exposure to air, 
 from the great attraction for moisture possessed by the carbonate of potash 
 and sulphide of potassium. 
 
 322. Effect of variations of atmospheric pressure on the combustion of 
 gunpowder. From the circumstance that the combustion of gunpowder is 
 independent of any supply of oxygen from the air, it might be supposed 
 that it would be as easily inflamed in vacua as under ordinary atmo- 
 spheric pressure. This is not found to be the case, however, for a 
 mechanical reason, viz., that the flame from the particles which are first 
 ignited escapes so rapidly into the vacuous space, that it does not inflame 
 the more remote particles. For a similar reason, charges of powder in 
 fuzes are found to burn more slowly under diminished atmospheric 
 pressure, the flame (or heated gas) escaping more rapidly and igniting less 
 of the remaining charge in a given time. It has been determined that if 
 a fuze be charged so as to burn for thirty seconds under ordinary atmo- 
 pheric pressure (30 inches barometer), each diminution of one inch in 
 barometric pressure will cause a delay of one second in the combustion of 
 the charge, so that the fuze will burn for thirty-one seconds when the 
 barometer stands at 29 inches. 
 
 The manufacture of gunpowder may be illustrated by the following experiments 
 on a small scale : 
 
 * Some doubt appears to be thrown upon these principles by the efficiency of nitrogly- 
 cerine in blasting (see that compound). 
 
CHEMISTRY OF FUEL. 
 
 429 
 
 Fig. 264. Distillation of 
 sulphur. 
 
 Preparation of the ingredients Charcoal. A few small pieces of wood are placed 
 in a clay crucible, which is then filled up with dry 
 sand and heated in a moderate fire as long as any 
 vapours are evolved, when it may be set aside to 
 cool. 
 
 Sulphur. 500 grains of roll sulphur may be dis- 
 tilled in a Florence flask, using another flask, the 
 neck of which has been cut off (fig. 264), for a 
 receiver, from which the sulphur is afterwards 
 poured, in a melted state, upon a piece of tin-plate. 
 
 N$tre. 1000 grains of impure nitre are dissolved, 
 at a moderate heat, in four measured ounces of 
 distilled water, in an evaporating dish (fig. 265) ; 
 the solution is filtered into a beaker which is placed 
 in cold water, and stirred with a glass rod until it 
 is quite cold. The saltpetre flour thus obtained is collected upon a filter, thoroughly 
 drained, the filter removed from the funnel, spread out, the saltpetre transferred to 
 another piece of filter paper, and pressed between 
 the paper to remove as much of the liquid as pos- 
 sible ; it is then spread out on paper and dried on a 
 hot brick. (For the mode of testing its purity see 
 p. 418). 
 
 Mixture of the ingredients. 60 grains of the char- 
 coal, reduced to a very fine powder, 40 grains of the 
 sulphur, also previously powdered, and 300 grains of 
 the dried nitre, are very intimately mixed in a mortar ; 
 50 grains of the mixture are set aside for comparison. 
 To the remainder enough water is added to make 
 it into a stiff cake, which is well incorporated under 
 the pestle for some time. It is then scraped out of 
 the mortar and allowed to dry slowly at a very gentle 
 heat. When perfectly dry it is crumbled to a coarse 
 powder, and the dust sifted out through a piece of 
 wire gauze. It will be found instructive to compare, 
 in trains and otherwise, the firing of the powder in grains, of the dust, and of the 
 mixed ingredients without incorporation, observing especially the difference in 
 rapidity of burning and in the amount of residue. 
 
 Fig. 265. 
 
 CHEMISTRY OF FUEL. 
 
 323. Several of the applications of chemical principles in the combus- 
 tion of fuel have been already explained and illustrated. The object of 
 this chapter is to compare the chemical composition of the most important 
 varieties of fuel, and to exemplify the principles upon which their heating 
 power may be calculated from the results furnished by the analysis of the 
 fuel. 
 
 All the varieties of ordinary fuel, of course, contain a large proportion 
 of carbon, always accompanied by hydrogen and oxygen, and sometimes 
 by small proportions of nitrogen and sulphur. Certain mineral substances 
 are also contained in all solid fuels, and compose the ash when the fuel is 
 burnt. 
 
 For all practical purposes it may be stated, that the amount of heat 
 generated by the combustion of a given weight of fuel depends upon the 
 weights of carbon and hydrogen, respectively, which enter into combina- 
 tion with the oxygen of the air in the act of combustion of the fuel. 
 
 It has been ascertained by experiment that 1 grain of carbon (in the 
 form in which it exists in wood charcoal), when combining with oxygen to 
 form carbonic acid, produces a quantity of heat which is capable of raising 
 8080 grains of water from to 1 of the Centigrade thermometer. This 
 is usually expressed by saying that the calorific value of carbon is 8080, 
 
430 CALCULATION OF CALORIFIC VALUE OF FUEL. 
 
 or that carbon produces 8080 units of lieat during its combustion to 
 carbonic acid. If the fuel, therefore, consisted of pure carbon, it would 
 merely be necessary to multiply its weight by 8080 to ascertain its calorific 
 value. 
 
 1 grain of hydrogen, during its conversion into water by combustion, 
 evolves enough heat to raise 34,400 grains of water from C. to 1 C., so 
 that the calorific value of hydrogen is 34,400. 
 
 If the fuel consisted of carbon and hydrogen only, its calorific value 
 would be calculated by multiplying the weight of the carbon in one grain 
 of the fuel by 8080, and that of the hydrogen by 34,400, when the sum 
 of the products would represent the calorific value. But if the fuel 
 contains oxygen already combined with it, the calorific value will be 
 diminished, since this oxygen will consume a part of the combustible 
 without generating heat, because it already exists in a state of combina- 
 tion with the carbon and hydrogen of the fuel. For example, 1 grain of 
 wood contains 0'5 grain of carbon, 0'06 of hydrogen, and 0'44 of oxygen. 
 Now, oxygen combines with one-eighth of its weight of hydrogen to 
 
 44 
 form water, so that the 0*44 grain of oxygen will convert -Q- = '055 
 
 of the hydrogen into water, without evolution of available heat, leaving 
 only - 005 available for the production of heat. The calorific value of 
 the wood, therefore, would be represented by the sum of 0*005 x 34,400 
 (= 172) and 0'5 x 8080 (= 4040), which would amount to 4212; or 1 
 grain of wood should raise 4212 grains of water from C. to 1 C. 
 
 These considerations lead to the following general formula for calculat- 
 ing the calorific value of a fuel containing carbon, hydrogen, and oxygen, 
 where c, h, and o respectively represent the carbon, hydrogen, and oxygen 
 in one grain of fuel. 
 
 The calorific value (or number of grains of water which might be heated 
 
 by the fuel from C. to 1 C.) = 8080 c + 34,400 (h - -|) or 
 
 8080 c + 34,400 h - 4300 o. 
 
 The calorific value of a fuel, as determined by experiment, is generally 
 less than would be calculated from its chemical composition, in consequence 
 of the absorption of a certain amount of heat attending the chemical 
 decomposition of the fuel. In the case of compounds of carbon and hydro- 
 gen, it has been observed that even when they have the same composition 
 in 100 parts, they have not of necessity the same calorific value, the latter 
 being affected by the difference in the arrangement of the component par- 
 ticles of the compound, which causes a difference in the quantity of heat 
 absorbed during its decomposition. Thus olefiant gas (C 4 H 4 ) and cetylene 
 (CjjjHgjj) have the same percentage composition, and their calculated calorific 
 values would be identical, but the former is found to produce 11,858 units 
 of heat, and the latter only 1 1,055. As a general rule, however, it is found 
 that the calorific values of the hydrocarbons which contain an equal 
 number of equivalents of each element, agree more nearly with the calcu- 
 lated numbers than do those of hydrocarbons which contain an unequal 
 number of equivalents, like marsh-gas (C 2 H 4 ). 
 
 It must be remembered that the calorific value of a fuel represents the 
 actual amount of heat which a given weight of it is capable of producing, 
 and is quite independent of the manner in which the fuel is burnt. Thus, 
 a hundredweight of coal will produce precisely the same amount of heat in 
 an ordinary grate as in a wind-furnace, though in the former case the fire 
 
CALCULATION OF CALORIFIC INTENSITY OF FUEL. 431 
 
 will scarcely be capable of melting copper, and in the latter it will melt 
 steel. The difference resides in the temperature or calorific intensity of 
 the two fires ; in the wind-furnace, through which a rapid draught of air 
 is maintained by a chimney, a much greater weight of atmospheric oxygen 
 is brought into contact with the fuel in a given time, so that, in that 
 time, a greater weight of fuel will be consumed and more heat will be 
 produced; hence the fire will have a higher temperature, for the tem- 
 perature represents, not the quantity of heat present in a given mass of 
 matter, but the intensity, or extent to which that heat is accumulated at 
 any particular point. In the case of the wind-furnace here cited, a further 
 advantage is gained from the circumstance, that the rapid draught of air 
 allows a given weight of fuel to be consumed in a smaller space, and, of 
 course, the smaller the area over which a given quantity of heat is distri- 
 buted, the higher the temperature within that area (as exemplified in the 
 use of the common burning-glass). In some of the practical applications 
 of fuel, such as heating steam-boilers and warming buildings, it is the 
 calorific value of the fuel which chiefly concerns us, but the case is different 
 where metals are to be melted, or chemical changes to be brought about 
 by the application of a very high temperature, for it is then the calorific 
 intensity, or actual temperature of the burning mass, which has to be con- 
 sidered. No trustworthy method has yet been devised for determining 
 by direct experiment the calorific intensity of fuel, and it is therefore 
 ascertained by calculation from the calorific value. 
 
 Let it be required to calculate the calorific intensity, or actual tempera- 
 ture, of carbon burning in pure oxygen gas. 
 
 6 grains (1 eq.) of carbon combine with 16 grains (2 eqs.) of oxygen, 
 producing 22 grains of carbonic acid ; hence 1 grain of carbon combines 
 with 2-67 grains of oxygen, producing 3'67 grains of carbonic acid. It 
 has been seen above that 1 grain of carbon evolves 8080 units of heat, or 
 is capable of raising 8080 grains of water from to 1C., or, on the sup- 
 position that the water would bear such an elevation of temperature, the 
 1 grain of carbon would raise 1 grain of water from to 8080 C. If 
 the specific heat (or heat required to raise 1 grain through 1, see p. 426) of 
 carbonic acid were the same as that of water, 8080 divided by 3 '6 7 
 would represent the temperature to which the 3*67 grains of carbonic acid 
 would be raised, and therefore the temperature to which the solid carbon 
 producing it would be raised in the act of combustion. But the specific 
 heat of carbonic acid gas is only 0*2163, so that a given amount of heat 
 would raise 1 grain of carbonic acid to nearly five times as high a tem- 
 perature as that to which it would raise 1 grain of water. 
 
 Dividing the 8080 units of heat (available for raising the temperature 
 of the carbonic acid) by 0'2163, the quantity of heat required to r&ise 1 
 grain of carbonic acid 1, we obtain 37,355 for the number of degrees 
 through which 1 grain of carbonic acid might be raised by the combustion 
 of 1 grain of carbon. But there are 3 '6 7 grains of carbonic acid formed 
 in the combustion, so that the above number of degrees must be divided 
 by 3 '6 7 in order to obtain the actual temperature of the carbonic acid at 
 the instant of its production, that is, the temperature of the burning mass. 
 The calorific intensity of carbon burning in pure oxygen is, therefore, 
 (37,355 C. -r- 3-67 =) 10,178 C. or 18,352 F. But if the carbon be 
 burnt in air, the temperature will be far lower, because the nitrogen of 
 the air will absorb a part of the heat, to which it contributes nothing. 
 The 2-67 grains of oxygen required to burn 1 grain of carbon would be 
 
432 CALCULATION OF CALORIFIC INTENSITY OF FUEL. 
 
 mixed, in air, with 8 '9 3 grains of nitrogen, so that the 8080 units of 
 heat would be distributed over 3 '6 7 grains of carbonic acid and 8 '9 3 
 grains of nitrogen. Since the specific heat of carbonic acid is 0*2163, 
 the product of 3'67 x 0*2163 (or 0'794) represents the quantity of 
 heat required to raise the 3 '6 7 grains of carbonic acid from to 
 1C. 
 
 The specific heat of nitrogen is 0-2438; hence 8-93 x 0-2438 (or 
 2*177) represents the quantity of heat required to raise the 8-93 grains of 
 atmospheric nitrogen from to 1 C. 
 
 Adding together these products, we find that 0-794 + 2'177 = 2-971 
 represents the quantity of heat required to raise both the nitrogen and 
 carbonic acid from to 1 C. 
 
 Dividing the 8080 by 2-971, we obtain 2720 C. (4928 F.) for the 
 number of degrees through which these gases would be raised in the com- 
 bustion, i.e., for the calorific intensity of carbon burning in air. By heat- 
 ing the air before it enters the furnace (as in the hot blast iron furnace), 
 of course the calorific intensity would be increased ; thus if the air be in- 
 troduced into the furnace at a temperature of 600 F., it might be stated, 
 without serious error, that the temperature producible in the furnace 
 would be 5528 F. (4928 + 600). The temperature might be further 
 increased by diminishing the area of combustion, as by employing very 
 compact fuel and increasing the pressure of the blast. 
 
 In calculating the calorific intensity of hydrogen burning in air, from 
 its calorific value, it must be remembered that in the experimental deter- 
 mination of the latter number the steam produced in the combustion was 
 condensed to the liquid form, so that its latent heat was added to the 
 number representing the calorific value of the hydrogen ; but the latent 
 heat of the steam must be deducted in calculating the calorific intensity, 
 because the steam goes off from the burning mass and carries its latent 
 heat with it. 
 
 1 grain of hydrogen, burning in air, combines with 8 grains of oxygen, 
 producing 9 grains of steam, leaving 26'77 grains of atmospheric nitrogen, 
 and evolving 34,400 units of heat. 
 
 It has been experimentally determined that the latent heat of steam is 
 537 C., that is, 1 grain of water, in becoming steam, absorbs 537 units 
 of heat (or as much heat as would raise 537 grains of water from to 1 
 C.) without rising in temperature as indicated by the thermometer. The 
 9 grains of water produced by the combustion of 1 grain of hydrogen will 
 absorb, or render latent, 537 x 9 =. 4833 units of heat. Deducting this 
 quantity from the 34,400 units evolved in the combustion of 1 grain of 
 hydrogen, there remain 29,567 units of heat available for raising the tem- 
 perature of the 9 grains of steam and 26*77 grains of atmospheric nitrogen. 
 The specific heat of steam being 0-480, the number (0*480 x 9 =) 4'32 
 represents the quantity of heat required to raise the 9 grains of steam 
 through 1 C. and the specific heat of nitrogen (0-2438) multiplied by 
 its weight (26*77 grains), gives 6'53 units of heat required to raise the 
 26'77 grains of nitrogen through 1 C. By dividing the available heat 
 (29,567 units) by the joint quantities required to raise the steam and nitro- 
 gen through 1 C. (4-32 + 6*53 = 10-85), we obtain the number 2725 C. 
 (4937 F.) for the calorific intensity of hydrogen burning in air. 
 
 The method of calculating the calorific intensity of a fuel composed of carbon, 
 hydrogen, and oxygen, will now be easily followed. 
 Let c and h respectively represent the weights of carbon and hydrogen in 1 gr. 
 
WASTE OF HEAT IN FURNACES. 433 
 
 of fuel, and o that of the oxygen. Then = weight of hydrogen required to convert 
 
 the oxygen into water, and h ~ represents the hydrogen which is available for the 
 production of heat. 
 
 8080 c + 34,400 U, - ~ ) represents the 
 
 calorific value in C., = 8080 c + 34,400 h - 4300 o. 
 2-67 c = atmospheric oxygen consumed by the carbon ; 
 8 ^ _ J? j or 8 A o = atmospheric oxygen consumed by the hydrogen available 
 
 as fuel. 
 
 3-34 (2-67 c + 8 h - o) = atmospheric nitrogen = 8-92 c + 26-72 h - 3-34 o. 
 
 Multiplying this by the specific heat of nitrogen 0-2438, we obtain 
 2-17 c + 6-61 h 0-81 o for the heat required to raise the nitrogen through 1 C. 
 
 0-794 c represents the quantity of heat required to raise the carbonic acid through 
 1 C., and 4-32 h is the heat required to raise the steam through 1. Accordingly, 
 the available heat, 8080 c + 34,400 h 4300 o, must be divided by 0-794 c + 4-32 h 
 + (2-17 c + 6-51 h - 0-81 o), or 2-96 c + 10-83 h - 0-81 o in order to obtain the 
 calorific intensity. 
 
 Hence, the calorific intensity, in Centigrade degrees, of a fuel composed of carbon, 
 hydrogen, and oxygen, is represented by the formula 
 
 8080 c + 34,400 h - 4300 o 
 2-96 c + 10-83 h - 0-81 o. 
 
 The actual calorific intensity of the fuel is not so high as it should be 
 according to theory, because a part of the carbon and hydrogen is con- 
 verted into gas by destructive distillation of the fuel, and this gas is not 
 actually burnt in the fire, so that its calorific intensity is not added to 
 that of the burning solid mass. Again, a portion of the carbon is con- 
 verted into carbonic oxide (CO), especially if the supply of air be imperfect, 
 and much less heat is produced than if the carbon were converted into 
 carbonic acid ; although it is true that this carbonic oxide may be con- 
 sumed above the fire by supplying air to it, the heat thus produced does 
 not increase the calorific intensity or temperature of the fire itself. 
 
 One grain of carbon furnishes 2*33 grains of carbonic oxide. These 2*33 
 grains of carbonic oxide evolve, in their combustion, 5599 units of heat. 
 But if the 1 grain of carbon had been converted at once into carbonic 
 acid, it would have evolved 8080 units of heat, so that 8080 - 5599, or 
 2481, represents the heat evolved during the conversion of 1 grain of 
 carbon into carbonic oxide, showing that a considerable loss of heat in the 
 fire is caused by an imperfect supply of air. It has been already pointed 
 out, in the section relating to Coal, that the formation of carbonic oxide is 
 sometimes encouraged with a view to the production of a flame from non- 
 flaming coal, such as anthracite. 
 
 The table (p. 434) exhibits the average percentage composition of the 
 principal varieties of fuel (exclusive of ash), together with their calculated 
 calorific values and intensities. 
 
 In all ordinary fires and furnaces, a large amount of heat is wasted in 
 the current of heated products of combustion escaping from the chimney. 
 Of course, a portion of this heat is necessary in order to produce the 
 draught of the chimney. In boiler furnaces it is found that, for this pur- 
 pose, the temperature of the air escaping from the chimney must not be 
 lower than from 500 to 600 F. If the fuel could be consumed by sup- 
 
 2 E 
 
434 
 
 COMPOSITION AND VALUE OF FUELS. 
 
 plying only so much air as contains the requisite quantity of oxygen, a 
 great saving might be effected, but in practice, about twice the calculated 
 quantity of air must be supplied, in order to effect the removal of the 
 products of combustion with sufficient rapidity. 
 
 Much economy of fuel may be expected from the use of furnaces con- 
 structed on the principle of Siemens' regenerative furnace, in which the 
 waste heat of the products of combustion is absorbed by a- quantity of 
 fire-bricks, and employed to heat the air before it enters the furnace, two 
 chambers of fire-bricks doing duty alternately, for absorbing the heat from 
 the issuing gas, and for imparting heat to the entering air, the current 
 being reversed by a valve as soon as the fire-bricks are strongly heated. 
 
 
 Carbon. 
 
 Hydrogen. 
 
 Oxygen. 
 
 Nitrogen. 
 
 Sulphur. 
 
 Calorific 
 Value. Intensity. 
 
 Wood (Oak), 
 Peat, .... 
 
 50-18 
 61-53 
 
 6-08 
 5-64 
 
 43-74 
 32-82 
 
 ... 
 
 ... 
 
 4212 C. 
 5654 
 
 2380C. 
 2547 
 
 Lignite (Bovey) 
 Bituminous coal, 
 
 67-86 
 79-38 
 
 575 
 5-34 
 
 23-39 
 13-01 
 
 0-57 
 1-85 
 
 2-41 
 0-39 
 
 6569 
 7544 
 
 2628 
 2694 
 
 Charcoal, . . . 
 
 90-44 
 
 2-91 
 
 6-63 
 
 
 
 8003 
 
 2760 
 
 Anthracite, . . 
 
 91-86 
 
 3-33 
 
 3-02 
 
 0-84 
 
 092 
 
 8337 
 
 2779 
 
 Coke, .... 
 
 97-32 
 
 0-49 
 
 ^- ^ . 
 2-17 
 
 8009 
 
 2761 
 
 (For the principles of smoke prevention, and other particulars of the 
 chemistry of fuel, see Coal.) 
 
435 
 
 ORGANIC CHEMISTRY. 
 
 324. Although it is impossible to propose a definition of the term 
 organic substance which shall not be applicable to some of the substances 
 commonly regarded as inorganic, it is found advantageous for the purposes 
 of study to treat organic chemistry as a separate division of the science, 
 dealing especially with those substances which are usually obtained, 
 either directly or indirectly, from animals and vegetables. 
 
 One very important distinction between organic and inorganic substances 
 is, that thj former are for the most part composed of carbon, hydrogen, 
 nitrogen, and oxygen, in different proportions and in various modes of 
 arrangement, and that they are, therefore, much more frequently con- 
 vertible into each other by metamorphosis, without extraneous addition 
 of matter, than inorganic substances are. 
 
 It has been already pointed out (p. 83) that the chemist is gradually 
 learning to produce, though by somewhat clumsy and circuitous processes, 
 many of the substances which were formerly believed incapable of being 
 formed, except through the intervention of life ; but no substance possess- 
 ing an organised structure, such as woody fibre or muscular fibre, and no 
 absolutely indispensable cons'tituent of animal or vegetable frames, if we 
 except water, has yet been artificially procured. 
 
 It will not escape notice that the four elements which compose the 
 greater number of organic substances, viz., hydrogen, oxygen, nitrogen, 
 and carbon, are, respectively, monatomic, diatomic, triatomic, and tetratomic 
 elements (p. 151), and are, therefore, capable of forming a greater variety 
 of compounds than would be the case if they were elements of equal 
 atomicities. 
 
 In the following pages, no strictly scientific classification of organic 
 substances has been adopted, since it would often render it necessary to 
 describe, in separate sections, substances which are, in nature, closely^con- 
 nected with each other, but an empirical arrangement has been followed, 
 so that the reader may find his memory assisted and the interest of the 
 subject sustained, by being enabled to bring the facts and explanations 
 into immediate connection with familiar processes of ordinary life.* 
 
 One of the most conspicuous substances standing upon the boundary 
 between organic and inorganic chemistry is the compound of carbon and 
 nitrogen known as cyanogen, which is intimately connected with inorganic 
 substances through some of the processes for its production, and through 
 its similarity to the chlorine group of elements, whilst the origin and 
 
 * The number of organic substances known to the chemist is so great that a mere list of 
 them would occupy a volume. In the present work a selection has been made of those 
 which are interesting for their practical applications or instructive from theoretical con- 
 siderations. 
 
 2E 2 
 
436 HISTORY OF CYANOGEN. 
 
 chemical properties of a large number of its compounds give them a 
 claim to be ranked among organic substances. The study of this sub- 
 stance, therefore, will form a fit introduction to organic chemistry. 
 
 CYANOGEN AND ITS COMPOUNDS. 
 
 325. In the beginning of the last century, a manufacturer of colours at 
 Berlin accidentally obtained a blue powder when precipitating sulphate of 
 iron with potash. This substance was used as a colour, under the name 
 of Prussian blue, for several years, before any explanation of its production 
 was attempted, or even before the conditions under which it was formed 
 were exactly determined. In 1824 it was shown that Prussian blue could 
 be prepared by calcining dried animal matters with carbonate of potash, 
 and mixing the aqueous solution of the calcined mass, first with sulphate 
 of iron and afterwards with hydrochloric acid; but the most important step 
 towards the determination of its composition was made by Macquer, who 
 found that by boiling it with an alkali, Prussian blue was decomposed, 
 yielding a residue of red oxide of iron, and a solution which reproduced 
 the blue when mixed with a salt of iron, from which he inferred that the 
 colour was a compound of the oxide of iron with an acid for which the 
 alkali had a more powerful attraction, a belief confirmed, in 1782, by 
 Scheele's observation, that when an alkaline solution prepared for mak- 
 ing the blue was exposed to the air, or to the action of carbonic acid, it 
 lost the power of furnishing the colour, but the escaping vapour struck a 
 blue on paper impregnated with oxide of iron. Scheele also prepared this 
 acid in a pure state, and it soon after obtained the name ofpntssic acid. 
 
 In 1787 Berthollet found prussic acid to be composed of carbon, 
 hydrogen, and nitrogen, but he also showed that the power of the alka- 
 line liquor to produce Prussian blue depended upon the presence of a 
 yellow salt crystallising in octahedra, and containing prussic acid, potash, 
 and oxide of iron, though the latter was so intimately bound up with the 
 other constituents, that it could not be separated by those substances 
 which are usually employed to precipitate iron. 
 
 Porrett, in 1814, applying the greatly increased resources of chemistry 
 to the investigation of this subject, decomposed Prussian blue with baryta, 
 and subsequently removed the baryta from the salt thus obtained by 
 means of sulphuric acid, when he obtained a solution of the acid, which 
 he named ferruretted chyazic acid, 
 
 In 1815, Gay-Lussac, having boiled Prussian blue (or prussiate of iron, 
 as it was then called) with red oxide of mercury and water, and crystal- 
 lised the so-called prussiate of mercury, exposed it, in the dry state, to the 
 action of heat, and obtained a gas, having the composition C 2 N, which 
 was called cyanogen* in allusion to its connection with Prussian blue. It 
 was then seen that the substance which had been called ferruretted chyazic 
 acid contained iron and the elements of cyanogen, whence it was called 
 ferrocyanic acid, and its salts were spoken of as ferrocyanates. Robiquet 
 first obtained this acid in the crystallised state, having the composition 
 C 6 H 2 N 3 Fe ; and since it was found that, when brought in contact with 
 metallic oxides, it exchanged the H 2 for two equivalents of the metal, 
 according to the equation 
 
 H 2 .C 6 N 3 Fe + 2MO = M 2 .C 6 N 3 Fe + 2HO 
 
 * From Kuaveos, blue. 
 
YELLOW PKUSSIATE OF POTASH. 437 
 
 it was concluded that the C 6 N 3 Fe composed a distinct group or radical, 
 which was named ferrocyanogen, the acid being called Jiydroferrocyanic 
 acid, and the salts ferrocyanides. 
 
 326. Prussiate of potash. The yellow prussiate of potash or fer- 
 rocyanide of potassium (K. 2 .C 6 N 3 Fe + 3Aq.), is manufactured upon a 
 large scale by a process which is the more interesting because it turns to 
 account some of the commonest kinds of refuse, such as old leather, hoof 
 parings, blood, and, in short, any animal matter rich in nitrogen, and not 
 applicable to any more economical purpose. Sometimes these substances 
 are first subjected to destructive distillation for the carbonate of ammonia 
 which they are capable of yielding, and the residual highly nitrogenised 
 charcoal is then used for the production of the ferrocyanide of potassium. 
 Such matters are fused in an iron vessel with carbonate of potash and iron 
 filings, and the fused mass is heated with water in open boilers, when a 
 yellow solution is obtained, which, after evaporation, deposits truncated 
 pyramidal crystals of ferrocyanide of potassium, containing 3 equivalents 
 of water. 
 
 The theory of this process has been elucidated by the researches of 
 Liebig. If carbonate of potash be strongly heated in contact with 
 pure carbon, there result (page 260) carbonic oxide and potassium, 
 KO.C0 2 + C 2 = 3CO + K; but if the carbon be associated with nitrogen, 
 the reduction will be effected at a much lower temperature, and the potas- 
 sium will combine with 2 equivalents of carbon and 1 equivalent of 
 nitrogen, to form the cyanide of potassium (KC 2 N). When this salt, dis- 
 solved in water, is heated with metallic iron in the presence of air, oxygen 
 is absorbed, and the iron dissolved to form ferrocyanide of potassium 
 
 3KC 2 N + Fe + - K 2 .C 6 N 3 Fe + KO. 
 
 The oxygen may also be acquired from the water, an equivalent quantity 
 of hydrogen being evolved: 
 
 Prussian blue. For the preparation of Prussian blue it is usual to 
 mix solutions of ferrocyanide of potassium and persulphate of iron, when 
 the blue is precipitated, having been produced according to the equation 
 
 3K 2 Fcy + 2(Fe 2 3 .3S0 3 ) - 6(KO.S0 3 ) + Fe 4 Fcy 3 
 
 Prussian Mu, 
 
 in which the symbol Fey represents the group C 6 N 3 Fe (ferrocyanogen), 
 which is capable of playing the same part in many decompositions as if 
 it were an elementary substance. This compound radical has never yet 
 been obtained in the separate state, but it can be traced through a com- 
 plete series of compounds, in which it exactly resembles chlorine' in its 
 chemical relations ; thus the hydroferrocyanic acid (H 2 Fcy), and the fer- 
 rocyanides of the metals (M 2 Fcy), are perfectly analogous to hydrochloric 
 acid and the chlorides, though containing a compound radical instead of a 
 simple one ; but whereas chlorine is a monobasic or monatomic radical, 
 combining only with 1 equivalent of hydrogen or a metal, ferrocyanogen 
 is bibasic or di-atomic ; and hence Prussian blue, the sesquiferrocyanide of 
 iron, corresponding to the sesquioxide (Fe.,0 3 ), has the composition 
 Fe 4 Fcy 3 , whilst the sesquichloride is Fe 2 CL 3 . When Prussian blue is pre- 
 pared by pouring solution of persulphate of iron into an excess of ferro- 
 cyanide of potassium, it is found that, as soon as the excess of the latter 
 salt has been washed away, the precipitate dissolves in pure water, form- 
 
438 PRUSSIAN BLUE. 
 
 ing what is used by dyers under the name of soluble, Prussian blue. Oxalic 
 acid is capable of dissolving the blue, and this solution forms the basis of 
 ordinary blue ink. 
 
 Prussian blue is sometimes prepared with the green protosulphate of 
 iron (FeO . S0 3 ), but in that case it is necessary to expose the precipitate 
 for some time to the air, since the first result is a nearly white precipitate, 
 which may be regarded as a double ferrocyanide of iron and potassium 
 (K. 2 Fcy,Fe 2 Fcy). 
 
 2(K 2 Fcy) + 2(FeO.S0 3 ) = 2(KO.S0 3 ) + K 2 Fcy, Fe.Fcy . 
 
 When this precipitate is exposed to the air, it gradually acquires a dark-blue 
 colour, becoming eventually converted into Prussian blue by oxidation 
 
 3(K 2 Fcy.Fe 2 Fcy) + 3 = 3K 2 Fcy + Fe 2 3 + Fe 4 Fcy 3 . 
 
 Prussian blue is easily decomposed by alkalies, a brown residue of 
 sesquioxide of iron being left, Fe 4 Fcy 3 + 6KO = 3K 2 Fcy + 2Fe 2 3 . 
 This decomposition is turned to account by the calico-printer for pro- 
 ducing a buff or white pattern upon a blue ground. The stuff having 
 been dyed blue by passing, first through a solution of a per-salt of iron, 
 and afterwards through one of ferrocyanide of potassium, the pattern is 
 discharged by an alkali, which leaves the brown peroxide of iron capable 
 of being removed by a dilute acid, when the stuff has been rinsed, so as to 
 leave the design white. 
 
 Hydroferrocyanic acid. By decomposing a cold saturated solution of the 
 ferrocyanide of potassium with about an equal volume of hydrochloric acid, 
 colourless crystals of hydroferrocyanic acid (H 2 Fcy) are obtained, which 
 are insoluble in hydrochloric acid, but readily soluble in water. When a 
 solution of this acid is heated, it evolves hydrocyanic acid (HC 2 N), and 
 deposits a white precipitate of cyanide of iron (FeC2N), which becomes 
 blue on exposure to the air, being converted into Prussian blue ; the 
 simplest way of explaining this, as well as many other decompositions of 
 hydroferrocyanic acid and the ferrocyanides, is to view the radical fer- 
 rocyanogen as formed by the union of three equivalents of cyanogen 
 (C 2 N) and one equivalent of iron, when hydroferrocyanic acid becomes 
 H 2 . Cy 3 Fe, and Prussian blue Fe 4 . 3Cy 3 Fe.* 
 
 The decomposition of the hydroferrocyanic acid by heat would then be 
 represented by the equation 
 
 H 2 . Cy 3 Fe = 2HCy + FeCy 
 
 Hydroferrocyanic Hydrocyanic Protocyanide 
 
 acid. acid. of iron. 
 
 and the formation of Prussian blue from this last compound on exposure 
 to air 
 
 9FeCy + 3 - Fe 4 . 3Cy 3 Fe + Fe 2 3 . 
 
 Prussian blue. 
 
 Hydrocyanic or prussic acid. Advantage is taken of the decomposition 
 of the ferrocyanide of potassium by acids, in the preparation of solution 
 of hydrocyanic acid for medicinal use. For this purpose, 2 parts of the 
 ferrocyanide of potassium in powder are distilled with 1 J parts of oil of 
 vitriol diluted with 2 parts of water, the vapour of hydrocyanic acid 
 
 * Since Cy requires one equivalent of hydrogen or a metal to saturate its combining 
 power, Cy 3 would require three equivalents, so that Cy 3 Fe would still be capable of receiving 
 two equivalents of a metal, and hence the ferrocyanide of potassium is Cy 3 Fe . K 2 . In 
 Prussian blue the four equivalents of iron represent six equivalents of hydrogen or potas- 
 sium, exactly as in 2Fe 2 Cl ? or Fe 4 Cl fi . 
 
HYDROCYANIC OR PRUSSIC ACID. 439 
 
 being carefully condensed (see fig. 45). The change is represented by 
 the equation 
 
 2K 2 (Cy 3 Fe) + 3(HO . S0 3 ) = 3(KO . SO.) + KFe(Cy 3 Fe) + 3HCy. 
 
 FeiTocyanide of Ferrocyanide of Hydrocyanic 
 
 potassium. iron and potassium. acid. 
 
 There is left in the retort a pale greenish salt, which rapidly becomes blue 
 when exposed to the air, and is probably identical with the double fer- 
 rocyanide of potassium and iron produced when protosulphate of iron is 
 decomposed by ferrocyanide of potassium (p. 438). 
 
 The solution of hydrocyanic acid thus obtained is colourless, and 
 exhales the remarkable odour of the acid; its acid characters are very 
 feeble indeed, even more so than those of carbonic acid, but it is extremely 
 poisonous, a very small dose destroying life almost immediately. Hydro- 
 cyanic acid is found in laurel-water, and in water distilled from the kernels 
 of many stone-fruits, such as the peach, apricot, plum. In minute closes 
 hydrocyanic acid is a very valuable remedy, and is employed in medicine 
 in solutions of different strengths. One of these, which is known as the 
 acid of the London Pharmacopoeia, contains 2 per cent, of hydrocyanic 
 acid, and is prepared by the process mentioned above. Scheele's acid 
 varies in strength, but usually contains between 4 and 5 per cent, of true 
 hydrocyanic acid. This acid is prepared from Prussian blue, by the 
 process originally employed by Scheele when the acid was discovered. 
 It consists in boiling Prussian blue with water and red oxide of mercury, 
 until the blue colour disappears; peroxide of iron is separated, and 
 cyanide of mercury (HgCy) passes into solution; the latter is filtered, 
 mixed with diluted sulphuric acid, and shaken with iron-filings, which 
 precipitate the mercury in the metallic state, leaving free hydrocyanic 
 acid in the liquid, which is then distilled 
 
 HgCy + Fe + HO.S0 3 = HCy + FeO . SO S + Hg. 
 
 In order clearly to understand this process, it must be known that the 
 mercury exhibits a special tendency to combine with cyanogen, which is 
 sufficiently powerful, in this instance, to bring about the decomposition 
 of the ferrocyanogen existing in the Prussian blue, a part of the cyanogen 
 being exchanged for the oxygen of the oxide of mercury. 
 
 It is from the cyanide of mercury that the pure anhydrous hydrocyanic 
 acid and cyanogen itself are prepared. For these purposes, it may be ob- 
 tained by dissolving the red oxide of mercury in hydrocyanic acid, when 
 a double decomposition takes place, exactly as with hydrochloric acid, 
 HgO + HCy = HgCy + HO, and the cyanide of mercury is ob- 
 tained in square prismatic crystals on evaporating the solution. If 
 these crystals be dried and gently warmed with strong hydrochloric 
 acid, chloride of mercury will be formed, and hydrocyanic acid evolved, 
 HgCy + HC1 = HgCl + HCy. The mixed vapours of hydrochloric and 
 hydrocyanic acid are passed over fragments of marble (CaO . C0 ), which 
 absorb the hydrochloric acid (CaO . C0 2 + HC1 = CaCl + HO "+ C0 2 ), 
 but not the hydrocyanic, since the latter is too weak an acid even to 
 displace carbonic acid. The mixture of hydrocyanic and carbonic acids 
 is passed over chloride of calcium to remove aqueous vapour, and after- 
 wards through a tube cooled in a mixture of ice and salt, when the 
 hydrocyanic acid is condensed to a colourless liquid, which evaporates 
 so rapidly when exposed to the air that it lowers the temperature to 
 the freezing point of the acid, which is about F. ; at a little 
 
440 PREPARATION OF CYANOGEN. 
 
 above the ordinary temperature (79 F.) it boils, and emits a vapour 
 which burns with a blue flame. When kept for some time it is liable 
 to undergo a spontaneous decomposition, evolving ammonia, and being- 
 converted into a brown mass of uncertain composition. The aqueous 
 solution of the acid suffers a similar change, and since exposure to light 
 favours the decomposition, the medicinal acid is usually kept in bottles 
 covered with paper. The presence of a very small quantity of sulphuric 
 acid prevents this change, and hence the acid prepared by distilling 
 ferrocyanide of potassium with sulphuric acid, which usually contains 
 traces of the latter, can be preserved much better than that prepared by 
 other methods. 
 
 When hydriodic acid gas is passed into anhydrous hydrocyanic acid cooled by ice, 
 a crystalline body is formed, which has the composition HC ? N . HI. It is readily 
 soluble in water and alcohol, but not in ether, and may be sublimed with little decom- 
 position. This substance is not acid, and does not answer to the tests for hydrocyanic 
 acid. When decomposed by potash, it gives ammonia, formiate of potash, and iodide 
 of potassium, so that it may be regarded as the hydriodate of an ammonia formed 
 by the substitution of one equivalent of the triatomic radical formyle (C 2 H) for the 
 three equivalents of hydrogen ; or hydriodate of formylamine N(C 2 H/ // . HI. 
 
 327. Cyanogen itself (C 2 N) can be prepared by the mere action of heat 
 upon the cyanide of mercury (in a test-tube provided with a glass jet for 
 burning the gas, fig. 266). This salt resolves itself into metallic mercury, 
 cyanogen, and a brown substance which has been 
 called paracyanogen (C 6 N 3 ), and appears to have 
 been formed by the union of three equivalents 
 of cyanogen. Cyanogen gas is easily distin- 
 guished from all others by its peculiar odour and 
 its property of burning with a fine peach-coloured 
 flame. Being nearly twice as heavy as air (sp. gr. 
 1 -8), it may be collected by downward displace- 
 ment, for water dissolves about four times its 
 volume of the gas, yielding a solution which is 
 prone to undergo a spontaneous decomposition 
 Fig. 266. remarkable for the comparatively complex pro- 
 
 ducts which it furnishes, amongst which we trace 
 
 the oxalate (NH 4 . C 2 3 ) and formiate (NH 4 . C 2 H0 3 ) of ammonia, and 
 urea (C 2 H 4 N. 2 2 ), all derived, be it remembered, from the elements of 
 cyanogen and water. In its chemical relations cyanogen presents a striking 
 resemblance to chlorine. Thus, at a slightly elevated temperature, potas- 
 sium and sodium take fire in it, forming the cyanides of those metals 
 precisely as the chlorides would be formed. Again, when cyanogen is 
 absorbed by a solution of potash, the cyanide of potassium and cyanate of 
 potash are formed 
 
 2KO + Cy 2 - KO.CyO + KCy 
 
 Cyanate of potash. ^yamdeof 
 
 just as the chloride of potassium and hypochlorite of potash result from the 
 action of chlorine upon potash, 2KO + CLj = KO . CIO + KC1 . A pres- 
 sure of about 4 atmospheres is required to liquefy cyanogen, when it forms 
 a colourless liquid of sp. gr. 0'87, freezing to a crystalline mass at 30 F. 
 
 Cyanide of potassium. The most useful of the cyanides is the cyanide 
 of potassium, which is extensively employed in electro-plating and gilding. 
 
 This salt may be formed by a very interesting process, which is one of 
 
CYANIDE OF POTASSIUM. 441 
 
 the few in which the atmospheric nitrogen takes part, and consists in 
 passing air over red-hot charcoal which has been previously soaked in a 
 strong solution of carbonate of potash and dried, when the nitrogen requi- 
 site for the formation of the cyanide is absorbed from the air, and carbonic 
 oxide is disengaged 
 
 KO.C0 2 + C 4 + N - KC 2 N + SCO. 
 
 Cyanide of potassium. 
 
 It is probably by a similar change that the cyanide of potassium is pro- 
 duced in the blast-furnaces (page 305) in which iron ores are reduced, 
 the potash being derived from the ash of the fuel. The cyanide is always 
 prepared for use from the ferrocyanide, which is resolved by a very high 
 temperature into cyanide of potassium and carbide of iron, with evolution 
 of nitrogen 
 
 K 2 Cy 3 Fe = 2KCy + PeC 2 + N. 
 
 Ferrocyanide Cyanide of 
 
 of potassium. potassium. 
 
 In order to avoid the loss of the third equivalent of cyanogen, it is usual 
 to fuse the ferrocyanide with carbonate of potash in the proportion of 3 
 parts of the dry carbonate to 7 parts of the dried ferrocyanide ; the mixture 
 is fused in a covered earthen crucible, and occasionally stirred until gas 
 ceases to be evolved ; the crucible is then removed from the fire, allowed 
 to stand for a minute or two that the metallic iron may subside, and the 
 clear fused cyanide poured out on to a stone. The change involved in this 
 process is represented by the following equation 
 
 2K 2 Cy 3 Fe + 2(KO.C0 2 ) = 5KCy + KO.CyO + Fe 2 + 2CO, 
 
 Cyanate of potash. 
 
 whence it will be seen that the commercial cyanide of potassium is con- 
 taminated withcyanate of potash. It also contains a considerable quan- 
 tity of carbonate of potash,' so that the proportion of cyanide is often only 
 60 per cent. The white porcelain-like masses of cyanide of potassium 
 deliquesce when exposed to the air, and emit the odour of hydrocyanic acid 
 as well as that of ammonia ; the former is disengaged from the cyanide by 
 the action of the atmospheric carbonic acid, whilst the ammoniacal odour 
 is due to the carbonate of ammonia produced by the action of moisture 
 upon the cyanate of potash 
 
 KO.C 2 NO + 4HO = KO.C0 2 + NH 4 O.C0 2 . 
 
 Cyanate of potash. 
 
 Pure cyanide of potassium is deposited in colourless cubical crystals 
 when vapour of hydrocyanic acid is passed into an alcoholic solution of 
 potash, or it may be obtained by boiling the commercial cyanicfe with 
 alcohol and filtering while hot, when the cyanide crystallises out as the 
 solution cools. 
 
 The use of cyanide of potassium in electroplating and gilding" depends 
 upon the power of a solution of the salt to dissolve the cyanides of gold 
 and silver, forming compounds which are easily decomposed by the gal- 
 vanic current, with deposition of metallic gold or silver upon any object 
 capable of conducting the current, which may be attached to the negative 
 pole (p. 363). Solution of cyanide of potassium is also able to dissolve 
 metallic silver and sulphide of silver, which is taken advantage of in 
 removing photographic stains from the hands and in cleaning silver or 
 gold lace. 
 
442 SULPHOCYANIDE OF POTASSIUM. 
 
 At a high temperature, cyanide of potassium is a very powerful reducing 
 agent, abstracting two equivalents of oxygen from most of the metallic 
 oxides, so as to liberate the metals, being itself converted into cyanate of 
 potash. Thus, when the binoxide of tin is fused with cyanide of potas- 
 sium, Sn0 2 + KCy = Sn + KO . CyO. This property of the cyanide 
 is often applied in chemical experiments. The cyanate of potash is readily 
 distinguished by the peculiar pungent odour of cyanic acid, which it emits 
 when treated with dilute sulphuric acid, though the greater part of the 
 cyanic acid is decomposed with effervescence, yielding sulphate of ammonia 
 and carbonic acid 
 
 KO . C 2 NO + 2(HO . S0 3 ) + 2HO = KO . S0 3 + NH 4 . S0 3 + 2C0 2 . 
 
 When fused cyanate of potash is triturated with dried oxalic acid, and 
 the mass treated with water, a white insoluble substance is left, which has 
 been called cyamelide, and has the composition C.jHN0 2 , being metameric 
 with hydrated cyanic acid, HO . C 2 NO ; when this substance is distilled, 
 hydrated cyanic acid passes over as a colourless liquid, which can only be 
 preserved at a very low temperature, for if the receiver containing it be 
 removed from the freezing mixture employed to condense the cyanic acid, 
 the latter becomes hot and turbid, soon begins to boil violently, and is 
 converted into a white mass of cyamelide resembling porcelain. 
 
 Cyanide of potassium when fused with sulphur, forms a compound cor- 
 responding to cyanate of potash, but containing sulphur in place of 
 oxygen, and having the formula KS, CyS, which is commonly spoken of 
 as sulphocyanide of potassium, being represented as containing a com- 
 pound radical, sulphocyanogen CyS 2 = Scy. The sulphocyanide of potas- 
 sium is generally prepared by fusing 3 parts of dried ferrocyanide of 
 potassium and 1 part of carbonate of potash (the materials for making 
 cyanide of potassium) with 2 parts of sulphur, in a covered crucible. By 
 washing the cooled mass with boiling water, the sulphocyanide is ex- 
 tracted, and may be obtained by evaporating the solution, in prismatic 
 crystals resembling nitre. By decomposing the sulphocyanide of potas- 
 sium with acetate of lead, the sulphocyanide of lead (PbCyS 2 ) is obtained, 
 and this, when acted upon with sulphuretted hydrogen, yields sulphide 
 of lead and hydrosulphocyanic acid, HCySo, the latter being a colourless 
 oily liquid which may be crystallised by cold. This acid is remarkable 
 for the dark red colour (due to sulphocyanide of iron) which it gives with 
 the per-salts of iron, for which sulphocyanide of potassium is frequently 
 employed as a test. A very delicate test (Liebig's test) for hydrocyanic 
 acid in cases of poisoning is also founded upon that circumstance, for if a 
 watch-glass moistened with yellow sulphide of ammonium (p. 272) be 
 exposed to the action of vapour of hydrocyanic acid, the latter is absorbed 
 and converted into sulphocyanide of ammonium 
 
 + S 2 + HCy = NH 4 CyS 2 + HS 
 
 Yellow sulphide Sulphocyanide 
 
 of ammonium. of ammonium. 
 
 by applying a gentle heat to the watch-glass, any excess of sulphide of 
 ammonium is volatilised, and a drop of perchloride of iron will then give 
 the blood-red colour with the sulphocyanide. 
 
 328. Ferricyanide of potassium. When chlorine is passed into a solu- 
 tion of ferrocyanide of potassium, the liquid assumes a brown colour, and, 
 when evaporated, deposits beautiful red rhombic prisms, which are found, 
 
RED PRUSSIATE OF POTASH. 443 
 
 on analysis, to have the composition K 3 Cy 6 Fe 2 , having been formed from 
 the ferrocyanide according to the equation 
 
 2K 2 Cy 3 Fe + Cl = KjCyJFe, + KC1 . 
 
 FeiTocyanide Ferricyanide 
 
 of potassium. of potassium. 
 
 This salt is known as red prussiate of potash, or ferricyanide of potas- 
 sium, and is used in dyeing; for if a piece of stuff be heated in a solution 
 of the ferricyanide acidulated with acetic acid, a blue compound similar 
 to Prussian blue is deposited in the fibre. 
 
 Ferricyanide of potassium is also employed for the preparation of Turn- 
 b nil's blue (ferricyanide of iron), which is precipitated when a solution of 
 that salt is mixed with one of sulphate of iron. 
 3(FeO.S0 3 ) + K 3 (Cy 6 Fe 2 ) = 3(KO . S0 3 ) + Fe 3 (Cy 6 Fe. 2 ) . 
 
 Ferricyanide Ferricyanide 
 
 of potassium. of iron. 
 
 In calico-printing, a mixture of the ferricyanide of potassium with potash 
 is employed as a discharge for indigo, such a mixture acting as a powerful 
 bleaching agent, in consequence of its tendency to impart oxygen to any 
 substance in need of that element, the ferricyanide being converted into 
 the ferrocyanide ; thus 
 
 K 3 (Cy 6 Fe 2 ) + KO = 2K 2 Cy 3 Fe + . 
 
 Ferricyanide Ferrocyanide 
 
 of potassium. of potassium. 
 
 The ferricyanide of potassium is assumed to contain a compound radical, 
 ferricyanogen (Cy 6 Fe 2 ), which represents a double equivalent of ferro- 
 cyanogen (Cy 3 Fe).* The hydroferricyanic acid (H 3 Cy 6 Fe 2 ) can be obtained 
 in a crystallised state, and many of the corresponding ferricyanides have 
 been examined. 
 
 Ferrocyanogen and ferricyanogen are not the only compound radicals of 
 this description ; there are cobalticyanogen (Cy 6 Co 2 ), manganicyanogen 
 (Cy 6 Mn 2 ), chromicyanogen . (Cy 6 Cr. 2 ), platinocyanogen (Cy 2 Pt), palladia- 
 cyanogen (Cy 2 Pd), and iridiocyanogen (Cy 3 Ir), but none of these have 
 received any useful applications. The platinocyanides are remarkable for 
 their brilliant colours. 
 
 329. Chlorides of cyanogen. When moist cyanide of mercury is shaken 
 up in a bottle of chlorine gas, and set aside for some time in a dark place, 
 the yellow colour of the chlorine disappears, and the bottle is filled with 
 a colourless gas having a remarkably pungent and tear-exciting odour ; this 
 is the gaseous chloride of cyanogen (CyCl) ; HgCy + C1 2 = HgCl + CyCl. 
 If light have access during this experiment, an oily liquid chloride of 
 cyanogen, Cy 2 Cl 2 , is produced. 
 
 The chloride of cyanogen gas may be liquefied by a pressure of four 
 atmospheres, and if the liquid is kept for some days in a sealed tube, it is 
 converted into a white mass of solid chloride of cyanogen, Cy 3 Cl 3 . When 
 this is acted on by water, it yields cyanuric acid, 3HO . Cy 3 O 3 , according 
 to the equation Cy 3 Cl 3 + 6HO ---- 3HC1 + 3HO . Cy 3 3 . This acid 
 is very interesting on account of its polymeric relation to cyanic acid 
 (HO . CyO), which may be obtained from it by distillation. It is a 
 tribasic acid, and forms, like tribasic phosphoric acid (p. 232), three 
 series of salts, having the formulae, respectively 
 
 3MO . Cy 3 8 , 2MO . HO . Cy 3 3 , and MO . 2HO . Cy 3 3 . 
 
 * The Fe 2 contained in ferricyanogen are equivalent to H 3 or K 3 , as in Fe 2 Cl 3 , hence 
 the Cy s Fe a requires only H 8 or K 3 to complete the saturation of the Cy e . 
 
444 PREPARATION OF FULMINATE OF MERCURY. 
 
 The cyanide of phosphorus, PCy 3 , has been sublimed in tabular crystals 
 from a mixture of cyanide of silver and terchloride of phosphorus heated 
 in a sealed tube to 280 F. for some hours, and afterwards distilled in a 
 current of dry carbonic acid. Cyanide of phosphorus inflames at a very 
 low temperature, and is decomposed by water, yielding cyanic and phos- 
 phorous acids. 
 
 330. Nitroprussides. When ferrocyanide of potassium is boiled with 
 dilute nitric acid, a point is attained at which the solution gives a slate- 
 coloured precipitate with a per-salt of iron ; if it be then boiled with an 
 excess of carbonate of soda, filtered, and evaporated, it deposits ruby-red 
 prismatic crystals of nitroprusside of sodium (Na 2 , Cy 5 N0 3 Fe 2 + 4Aq.), 
 from which the nitroprussides of other metals may be obtained. 
 
 The hydronitroprussic acid (H 2 , Cy 5 N0 3 Fe 2 + 2Aq.) has also been pre- 
 pared and crystallised. 
 
 The nitroprussides have been recently proved by the late Mr Hadow to be 
 formed from the ferricyanides by the exchange of one equivalent of cyanogen 
 for an equivalent of nitrous acid (N"0 3 ), and the simultaneous removal of 
 an equivalent of the metal with which the ferricyanogen was combined. 
 Thus ferricyanide of potassium, Kg . Cy 6 Fe 2 , becomes nitroprusside of potas- 
 sium, K 2 . Cy 5 N0 3 Fe 2 , when boiled with nitric acid, other products being 
 formed at the same time by the oxidising action of the nitric acid. 
 
 Based upon this view of its constitution, a more certain and economical 
 process for the production of nitroprusside of sodium, was devised by 
 Hadow, which consists in acting upon the ferricyanide of potassium with 
 nitrite of soda, acetic acid, and chloride of mercury (corrosive sublimate), 
 when the mercury removes an equivalent of cyanogen, and the chlorine an 
 equivalent of potassium, the nitrous acid of the nitrite of soda entering 
 into the residue of the ferricyanide, and converting it into nitroprusside of 
 potassium, which, by double decomposition with the acetate of soda, yields 
 acetate of potash and nitroprusside of sodium. The cyanide of mercury 
 crystallises out first, and the nitroprusside of sodium may be obtained in 
 crystals from the evaporated solution. 
 
 The nitroprusside of sodium is used as a test for the alkaline sulphides, 
 with a very slight trace of which it gives a magnificent purple colour. 
 Thus, an inch or two of human hair, fused with carbonate of soda before 
 the blowpipe, will yield sufficient sulphide of sodium to strike a purple 
 tint with the nitroprusside. 
 
 331. THE FULMINATES. The violently explosive compound known as 
 fulminate of mercury, which is so largely employed for the manufacture of 
 percussion caps, is connected with the series of cyanogen compounds. 
 
 Preparation of fulminate of mercury. This substance is prepared by 
 the action of alcohol upon a solution of mercury in excess of nitric acid ; 
 and as this action is of a violent character, some care is necessary in order 
 to avoid an explosion. On a small scale, the fulminate may be obtained 
 without any risk by strictly attending to the following prescription : 
 
 Weigh out, in a watch-glass, 25 grains of mercury, transfer it to a half-pint 
 beaker, add half an ounce (measured) of ordinary concentrated nitric acid (sp. gr. 
 1-42), and apply a gentle heat. As soon as the last particle of mercury is dis- 
 solved, place the beaker upon the table, away from any flame, and pour into it, 
 pretty quickly, at arm's length, 5 measured drachms of alcohol (sp. gr. 0-87). Very 
 brisk action will ensue, and the solution will become turbid from the separation of 
 crystals of the fulminate, at the same time evolving very dense white clouds, which 
 have an agreeable odour, due to the presence of nitrous ether, aldehyde, and other 
 
PROPERTIES OF FULMINATE OF MERCURY. 445 
 
 products of the action of nitric acid upon alcohol. The heavy character of these 
 clouds is caused by the presence of mercury, though in what form has not been 
 ascertained ; much nitrous oxide and hydrocyanic acid are evolved at the same 
 time. When the action has subsided, the beaker may be filled with water, the ful- 
 minate allowed to settle, and the acid liquid poured oif. The fulminate is then 
 collected on a filter, washed with water as long as the washings taste acid, and dried 
 by exposure to air. 
 
 The chemical change involved in the preparation of the fulminate is 
 complicated by the formation of the secondary products of the action of 
 nitric acid upon alcohol, but if these be left out of consideration, a clear 
 idea of the reaction may be obtained. 
 
 The fulminate of mercury is found, on analysis, to contain mercury, 
 carbon, nitrogen, and oxygen in proportions corresponding to the formula 
 HgC 2 N0 2 ; if the mercury be supposed to exist in the state of oxide, into ' 
 which it would have been converted by the nitric acid, this formula might 
 be written HgO . C 2 NO. The formula for alcohol is C 4 H 6 2 , and if 
 the above expression for fulminate of mercury be doubled, it becomes 
 2 HgO . C 4 N 2 2 , and appears to be derivable from alcohol by the exchange 
 of H 6 for !N" 2 , and the addition of 2HgO. It has been remarked (p. 133) 
 that the action of nitrous acid (N0 3 ) upon organic substances frequently 
 results in the removal of H 3 from the substance in the form of 3HO ; and 
 it may be supposed that this acid, resulting from the de-oxidation of the 
 nitric acid by one portion of the alcohol, has acted upon another portion 
 so as to eliminate the whole of its hydrogen, and to leave, in exchange, 
 2 eqs. of nitrogen; thus, C 4 H 6 2 + 2N0 3 = C 4 N S 8 + 6HO. It is 
 evident that the combining value of the two atoms of triatomic nitrogen 
 is equal to that of six atoms of hydrogen.* The substance C 4 N 2 2 , sup- 
 posed to be combined with the oxide of mercury (though never obtained 
 in the separate state), has been named fulminic acid. The chemical con- 
 stitution of the fulminate will be more advantageously discussed when 
 its properties have been considered. 
 
 Properties of fulminate of mercury. This substance is deposited in 
 the above process in fine needle-like crystals, which often have a grey 
 colour from the accidental presence of a little metallic mercury. It may 
 be purified by boiling it with water, in which it is sparingly soluble, and 
 allowing the fulminate to crystallise from the filtered solution. Very 
 moderate friction or percussion will cause it to detonate violently, so that 
 it must be kept in a corked bottle lest it should be exploded between the 
 neck and the stopper. Its explosion is attended with a bright flash, and 
 with grey fumes of metallic mercury. The simplest equation to represent 
 the decomposition would be Hg 2 C 4 N 2 4 = Hg 2 + 4CO + N ; and its 
 violence must be attributed to the sudden evolution of a large valume of 
 gas and vapour from a small volume of solid, for the fulminate of mercury, 
 being exceedingly heavy (sp. gr. 4*4), occupies a very small space when 
 compared with the gaseous products of its decomposition, especially when 
 the latter are expanded by the heat. The evolution of heat during the 
 explosion, apparently in contradiction to the rule that heat is absorbed in 
 decomposition, must be ascribed to the circumstance that the heat evolved 
 by the oxidation of the carbon exceeds that absorbed in the decomposition 
 of the fulminate. A temperature of 360 F. explodes fulminate of mer- 
 cury, and the same result is brought about by touching it with a glass- rod 
 
 * This view is supported by the circumstance that fulminate of silver is abundantly 
 formed when nitrous acid is passed into an alcoholic solution of nitrate of silver. 
 
446 PREPARATION OF FULMINATE OF SILVER. 
 
 dipped in concentrated sulphuric or nitric acid. The electric spark of 
 course explodes it. 
 
 Cap composition. The explosion of the fulminate of mercury is so 
 violent and rapid that it is necessary to moderate it for percussion-caps. 
 For this purpose it is mixed with nitrate or chlorate of potash, the 
 oxidising property of these salts possibly causing them to be preferred to 
 any merely inactive substances, since it would tend to increase the tem- 
 perature of the flash by burning the carbonic oxide into carbonic acid, 
 and would thus ensure the ignition of the cartridge. For military caps, 
 in this country, chlorate of potash is always mixed with the fulminate, 
 and powdered glass is sometimes added to increase the sensibility of the 
 mixture to explosion by percussion. Sulphide of antimony is sometimes 
 substituted for powdered glass, apparently for the purpose of lengthening 
 the flash by taking advantage of the powerful oxidising action of chlorate 
 of potash upon that compound (p. 157). Since the composition is very 
 liable to explode under friction, it is made in small quantities at a time, 
 and without contact with any hard substance. After a little of the com- 
 position has been introduced into the cap, it is made to adhere and water- 
 proofed by a drop of solution of shell-lac in spirit of wine. 
 
 If a thin train of fulminate of mercury be laid upon a plate, and covered, except 
 a little at one end, with gunpowder, it will be found on touching the fulminate with 
 a hot wire, that its explosion scatters the gunpowder, but does not inflame it. On 
 repeating the experiment with a mixture of 10 grains of the fulminate and 15 grains 
 of chlorate of potash, made upon paper with a card, the explosion will be found to 
 inflame the gunpowder. 
 
 By sprinkling a thin layer of the fulminate upon a glass plate, and firing it with 
 a hot wire, the separated mercury may be made to coat the glass, so as to give it 
 all the appearance of a looking-glass. 
 
 Although the effect produced by the explosion of fulminate of mercury 
 is very violent in its immediate neighbourhood, it is very slightly felt at 
 a distance, and the sudden expansion of the gas will burst fire-arms, 
 because it does not allow time for overcoming the inertia of the ball, 
 though, if the barrel escape destruction, the projectile effect of the fulmi- 
 nate is found inferior to that of powder. 
 
 The fulminate of mercury is generally contaminated with oxalate of 
 mercury (HgO . C. 2 { ), which is one of the secondary products formed 
 during its preparation. 
 
 Fidminate of silver is prepared by a process very similar to that for 
 fulminate of mercury, but since its explosive properties are far more 
 violent, it is not advisable to prepare so large a quantity. 10 grains of 
 pure silver are dissolved, at a gentle heat, in 70 minims of ordinary con- 
 centrated nitric acid (sp. gr. 1 -42) and 50 minims of water. As soon as 
 the silver is dissolved, the heat is removed, and 200 minims of alcohol 
 (sp. gr. 0'87) are added. If the action does not commence after a short 
 time, a very gentle heat may be applied until effervescence begins, when 
 the fulminate of silver will be deposited in minute needles, and may be 
 further treated as in the case of fulminate of mercury.* When dry, the 
 fulminate of silver must be handled with the greatest caution, since it is 
 exploded far more easily than the mercury salt; it should be kept in small 
 quantities wrapped up separately in paper, and placed in a card-board box. 
 
 * If the nitric acid and alcohol are not of the exact strength here prescribed, it may be 
 somewhat difficult to start the action unless two or three drops of red nitric acid (contain- 
 ing nitrous acid) are added. Standard silver (containing copper) may be used for prepar- 
 ing the fulminate. 
 
CHEMICAL CONSTITUTION OF THE FULMINATES. 447 
 
 Nothing harder than paper should be employed in manipulating it. The 
 violence of its explosion renders it useless for percussion caps, but it is 
 employed in detonating crackers. Fulminate of silver is sparingly soluble 
 in cold water, but dissolves in 36 parts of boiling water. 
 
 If a minute particle of fulminate of silver be placed upon a piece of quartz, and 
 gently pressed with the angle of another piece, it will explode with a flash and 
 smart report. 
 
 A throw-down detonating cracker may be made by screwing up a particle of the 
 fulminate of silver in a piece of thin paper, with some fragments obtained by crush- 
 ing >a common quartz pebble. 
 
 The explosion of fulminate of silver may be compared with that of the mercury 
 salt by heating equal quantities upon thin copper or platinum foil, when the ful- 
 minate of mercury will explode with a slight puff, and will not injure the foil, but 
 that of silver will give a loud crack and rend a hole in the metal. 
 
 If a particle of fulminate of silver be placed upon a glass plate and touched with 
 a glass rod dipped in oil of vitriol, it will detonate and leave a deposit of silver upon 
 the glass. 
 
 When fulminate of silver is dissolved in warm ammonia, the solution 
 deposits, on cooling, crystals of a double fulminate of silver and ammonia, 
 AgO . NH 3 . HO . C 4 N 2 2 , which is even more violently explosive, and is 
 dangerous while still moist. 
 
 On adding chloride of potassium in excess to fulminate of silver, only 
 half the silver is removed as chloride, and the double fulminate of silver 
 and potassium, AgO, KO, C 4 N 2 2 , may be crystallised from the solution. 
 By the careful addition of nitric acid, the KO may be removed from this 
 salt, and the acid fulminate of silver, AgO . HO . C 4 N" 2 2 , obtained, which 
 is easily soluble in boiling water, and crystallises out on cooling ; by boil- 
 ing with oxide of silver, it is converted into the neutral fulminate. 
 
 Various other fulminates and double fulminates have been obtained. 
 They are all more or less explosive. 
 
 Chemical constitution of the fulminates. The fact of the existence of 
 double fulminates and acid" fulminates renders it necessary to write the 
 empirical formula of fulminate of silver, for example, Ag 2 C 4 N 2 4 , instead 
 of AgC 2 N0 2 , in order to show that half of the silver is capable of being 
 exchanged for another metal or for hydrogen. It will be seen that 
 this formula would also represent two equivalents of cyanate of silver 
 (AgO . C 2 NO), but the properties of this salt are entirely different from 
 those of the fulminate. That a strong connection exists, however, between 
 the fulminates and the cyanogen-compounds, is shown by several reactions. 
 Thus, if fulminate of mercury be heated with hydrochloric acid, it is dis- 
 solved with evolution of a powerful odour of hydrocyanic acid, whilst mer- 
 curic chloride and oxalate, with hydrochlorate of ammonia, remain in the 
 solution. Again, if an excess of fulminate of silver be acted on by Hydro- 
 sulphuric acid, cyanic acid may be obtained in solution, and becomes 
 converted into hydrosulphocyanic acid, when the hydrosulphuric acid is 
 in excess. By decomposing the double fulminate of copper and ammonia 
 (CuO . NH 3 . HO . C 4 1N~ 2 2 ) with hydrosulphuric acid, there are produced 
 hydrosulphocyanic acid and urea, the latter having the same composition 
 as cyanate of ammonia 
 
 CuO.NH 3 .HO.C 4 N 2 2 + 3HS = CuS + 2HO + H. C.;X T S 2 + C 2 H 4 N 2 2 . 
 
 Hydrosulphocyanic TT 
 acid. 
 
 These reactions have induced many chemists to regard the fulminates 
 as compounds of the metallic oxides with an acid having the composition 
 
448 PRODUCTS FROM COAL. 
 
 Cy 2 2 , intermediate in composition between the hypothetical anhydrous 
 cyanic acid (CyO) and the hypothetical anhydrous cyanuric acid (Cy 3 3 ), 
 but neither the anhydrous nor the -hydrated fulminic acid has yet been 
 obtained in a separate form. This view of the constitution of the ful- 
 minates, however, has the recommendation of simplicity, and enables the 
 greater number of their reactions to be easily explained. 
 
 Fulminate of mercury dissolves when boiled with solution of chloride of potas- 
 sium, and the solution, when evaporated, yields crystals of fulminurate or isocyanu- 
 rate of potash, KG . C 6 N 8 H 2 5 , which has the same percentage composition as acid 
 cyanurate of potash, KG . 2HO . Cy 3 G 3 , but the acid contained in fulminurate of 
 potash forms only one series of salts, and is therefore monobasic. The fulminurates 
 are feebly explosive. The production of fulminuric acid from the hypothetical 
 hydrate of fulminic acid may be represented by the equation 
 
 2(2HO . C 4 N 2 2 ) + 2HO = 2C0 2 + NH 3 + HO . C fl N 3 H 2 5 . 
 
 PRODUCTS OF THE DESTRUCTIVE DISTILLATION OJF COAL. 
 
 332. Much of the extraordinary progress made by chemistry during 
 the last half century must be attributed to the introduction and great ex- 
 tension of the manufacture of coal-gas. No other branch of manufacture 
 has brought into notice so many compounds not previously obtained from 
 any other source; and, above all, offering, at first sight, so very little 
 promise of utility, as to press urgently upon the chemist the necessity for 
 submitting them to investigation. 
 
 Although many important additions to chemical knowledge have re- 
 sulted from the labours of those who have engaged in devising the best 
 methods of obtaining the coal-gas itself in the state best fitted for con- 
 sumption, far more benefit has accrued to the science from investigations 
 into the nature of the secondary products of the manufacture, the removal 
 of which Avas the object to be attained in the purification of the gas. 
 
 Of the compounds of carbon and hydrogen, very little was known pre 
 viously to the introduction of coal-gas ; and although the liquid hydro- 
 carbons composing coal-naphtha were originally obtained from other 
 sources, the investigation of their chemical properties has been greatly pro- 
 moted by the facility with which they may be obtained in large quantities 
 from that liquid. The most important of these hydrocarbons, benzole or 
 benzine, was originally procured from benzoic acid j but it would have 
 been impossible for it to have fulfilled its present useful purposes but for 
 the circumstance that it is obtained in abundance as a secondary product 
 in the manufacture of coal-gas ; for, leaving out of consideration the 
 various uses to which benzole itself is devoted, it yields the nitrobenzole, 
 so much used in perfumery, and from this we obtain aniline, from which 
 many of the most beautiful dyes are now prepared. 
 
 The naphthaline found so abundantly in coal-tar possesses a peculiar 
 interest, as having formed the subject of the beautiful researches by which 
 Laurent was led to propose the doctrine of substitution, which has since 
 thrown so much light upon the constitution of organic substances. 
 
 We are also especially indebted to coal-tar for our acquaintance with 
 the very interesting and rapidly-extending class of volatile alkalies, of 
 which the above-mentioned aniline is the chief representative, and for 
 phenic or carbolic acid, from which are derived the large number of sub- 
 stances composing the phenyle-series. 
 
MANUFACTUKE OF COAL-GAS. 
 
 449 
 
 The retorts in which the distillation of coal is effected are made either of 
 cast-iron or stoneware, generally having the form of a flattened cylinder, and 
 arranged in sets of three or five, heated by the same coal fire (fig. 267). The 
 charge for each retort is about two bushels, and is thrown on to the red-hot 
 
 Fig. 267. Manufacture of coal-gas. 
 
 floor of the retort, as soon as the coke from the previous distillation has been 
 raked out ; the mouth of the retort is then closed with an iron plate luted 
 with clay. An iron pipe rises from the upper side of the front of the retort 
 projecting from the furnace, and is curved round at the upper extremity, 
 which passes into the side of a much wider tube, called the hydraulic 
 main, running above the furnaces, at right angles to the retorts, and re- 
 ceiving the tubes from all of them. This tube is always kept half full of 
 the tar and water which condense from the gas, and below the surface of 
 this liquid the delivery tubes from the retorts are allowed to dip, so that 
 although the gas can bubble freely through the liquid as it issues from 
 the retort, none can return through the tube whilst the retort is open for 
 the introduction of a fresh charge. 
 
 The aqueous portion of the liquid deposited in the hydraulic main is 
 known as the ammoniacal liquor, from its consisting chiefly of a solution 
 of various salts of ammonia, the chief of which is the sesquicarbonate ; 
 sulphide, cyanide, and sulphocyanide of ammonium are also found in it. 
 
 From the hydraulic main the gas passes into the condenser, which is 
 composed of a series of bent iron tubes kept cool either by the large sur- 
 face which they expose to the air, or sometimes by a stream of cold 
 water. In these are deposited, in addition to water, any of the volatile 
 hydrocarbons and salts of ammonia which may have escaped condensation 
 in the hydraulic main. Even in the condenser the removal of the am- 
 moniacal salts is not complete, so that it is usually necessary to pass the 
 gas through a scrubber or case containing fragments of coke, over which a 
 stream of water is allowed to trickle in order to absorb the remaining 
 ammoniacal vapours. 
 
 SF 
 
450 
 
 PURIFICATION OF COAL-GAS. 
 
 The tar which condenses in the hydraulic main is a very complex 
 mixture, of which the following are some of the leading components 
 
 
 Boiling Point, 
 
 Equivalent 
 Formula. 
 
 Sp. Gr. 
 
 NEUTRAL HYDROCARBONS. 
 Liquid. 
 Benzole, 
 Toluole, 
 
 176 F. 
 230 
 
 C 12 H 6 
 C u H fl 
 
 0-88 
 0-87 
 
 Xylole . 
 
 284 
 
 
 0-87 
 
 Isocumole* .... 
 Solid. 
 Naphthaline 
 Paranaphthaline, . . 
 Chrysene . 
 
 338 
 
 428 
 680 
 
 Ci 8 H 12 
 
 C 2 H 8 
 ^30^12 
 
 C 9 ,H 8 
 
 0-85 
 
 Pyrene 
 ALKALINE PRODUCTS. 
 Ammonia, ... 
 Aniline, 
 
 360 J 
 
 C'30-^-12 
 
 NH, 
 
 C 12 H 7 N 
 
 1-02 
 
 Picoline 
 
 271 
 
 C oH*N 
 
 0-96 
 
 Quinoline, .... 
 Pyridine 
 
 462 
 240 
 
 C 18 H 7 N 
 C, H N 
 
 1-08 
 
 ACIDS. 
 Carbolic acid, . . . 
 Kresylic . . . . 
 Kosolic . . . . 
 
 370 
 397 
 
 '-'ID 6 
 
 C 12 H 6 2 
 C U H 8 2 
 
 C 46 H 228 
 
 1-07 
 
 Acetic . . 
 
 243 
 
 C 4 H 4 4 
 
 1-06 
 
 The gas is now passed through the lime-purifier, which is an iron box 
 with shelves, on which dry slaked lime is placed in order to absorb the 
 carbonic acid and. sulphuretted hydrogen, and the last portions of ammonia 
 are removed by passing the gas through dilute sulphuric acid. 
 
 A great many other methods have been devised for the purification of 
 the gas from sulphuretted hydrogen, but none appears to be so efficacious 
 and economical as that which consists in passing the gas over a mixture 
 of sulphate of iron (green vitriol or copperas), slaked lime, and sawdust 
 (which is employed to prevent the other materials from caking together). 
 The lime decomposes the sulphate of iron, forming sulphate of lime and 
 hydrated oxide of iron 
 
 FeO.S0 3 + CaO.HO = FeO.HO + CaO.S0 3 . 
 
 The action of air upon the mixture soon converts the oxide into sesqui- 
 oxide of iron, which absorbs the sulphuretted hydrogen and the hydro- 
 cyanic acid, producing with the former sulphide of iron, and with the 
 latter Prussian blue, or some similar compound. The sulphate of lime 
 existing in this purifying mixture is useful in absorbing any vapour of 
 carbonate of ammonia from the gas, forming sulphate of ammonia and 
 carbonate of lime.t 
 
 * Benzole, originally derived from benzoic acid; toluole, from balsam of tolu ; 'xyloU, 
 found among the products from wood (v\ov) ; isocumole, isomeric with cumole, obtained 
 from oil of cummin. , 
 
 f Sesquioxide of iron itself, derived from various natural and artificial sources, is also 
 employed for the purification of coal-gas. 
 
COAL-TAR. 
 
 451 
 
 The action of the sulphuretted hydrogen on the sesquioxide of iron may 
 be thus represented, Fe 2 3 + 3HS = 2FeS + S + 3HO ; and the cir- 
 cumstance which especially conduces to the economy of the process, is the 
 facility with which the sulphide of iron may be reconverted into the 
 sesquioxide by mere exposure to the action of atmospheric oxygen, for 
 2FeS + 3 = Fe 2 3 + S 2 , thus reviving the power of the mixture to absorb 
 sulphuretted hydrogen. Accordingly, if a small quantity of air be ad- 
 mitted into the purifier together with the gas, it reconverts the sulphide of 
 iron into sesquioxide, and the oxidation is attended with enough heat to 
 convert into vapour any benzole which may have condensed in the purify- 
 ing mixture, and of which the illuminating value would otherwise be lost. 
 The same purifying mixture may thus be employed to purify a very large 
 quantity of gas, until the separated sulphur has increased its bulk to an 
 inconvenient extent, when it is distilled off in iron retorts. The various 
 processes which have been devised for the removal of the bisulphide of 
 carbon vapour are mentioned at p. 217. 
 
 The purified gas is passed into the gasometers, from which it is sup- 
 plied for consumption. 
 
 In the manufacture of coal-gas, attention is requisite to the temperature 
 at which the distillation is effected, for if it be too low, the solid and 
 liquid hydrocarbons will be formed in too great abundance, not only 
 diminishing the volume of the gas, but causing much inconvenience by 
 obstructing the pipes. On the other hand, if the retort be too strongly 
 heated, the vapours of volatile hydrocarbons, as well as the olefiant gas 
 and marsh-gas, may undergo decomposition, depositing their carbon upon- 
 the sides of the retort, in the form of gas-carbon, and leaving their hydro- 
 gen to increase the volume and dilute the illuminating power of the gas. 
 
 These effects are well exemplified in the following analyses of the gas 
 collected from Wigan cannel coal at different periods of the distillation : 
 
 In 100 volumes. 
 
 1st hour. 
 
 5th hour. 
 
 10th hour. 
 
 Olefiant gas and volatile hydrocarbons, 
 Marsh-gas 
 
 13-0 
 
 82-5 
 
 7-0 
 66-0 
 
 o-o 
 
 20-0 
 
 Carbonic oxide, 
 
 3-2 
 
 11-0 
 
 10-0 
 
 Hvdroaren, . 
 
 0-0 
 
 21-3 
 
 60-0 
 
 Nitrogen, 
 
 1-3 
 
 4-7 
 
 10-0 
 
 
 
 
 
 The increase of the carbonic oxide after the first hour must be attri- 
 buted to the decomposition of the aqueous vapour by the carbon as the 
 temperature rises, and the increase of the nitrogen may probaljly be 
 ascribed to the decomposition of the ammonia into its elements at a high 
 temperature. 
 
 333. One of the most useful of the secondary products of the coal-gas 
 manufacture is the ammonia, and this process has been already noticed as 
 a principal source of the ammoniacal salts found in commerce. 
 
 Next in the order of usefulness stands the coal-tar, which deserves 
 attentive consideration not only on that account, but because the extrac- 
 tion of the various useful substances from this complex mixture affords an 
 excellent example of proximate organic analysis, that is, of the separa- 
 tion of an organic mixture into its immediate components. 
 
 For the separation of the numerous volatile substances contained in 
 
 2 F2 
 
452 COAL-NAPHTHA. 
 
 coal-tar, advantage is taken of the difference in their boiling points, which 
 will he observed on examining the table at p. 450. 
 
 A large quantity of the tar is distilled in an iron retort, when water 
 passes over, holding salts of ammonia in solution, and accompanied by a 
 brown oily offensive liquid which collects upon the surface of the water. 
 This is a mixture of the hydrocarbons which are lighter than water, viz., 
 benzole, toluole, xylole, and isocumole, all having, as represented in the 
 table at p. 450, a specific gravity of about 0'85. 100 parts of the tar 
 yield, at most, 10 parts of this light oil. 
 
 As the distillation proceeds, and the temperature rises, a yellow oil dis- 
 tils over, which is heavier than water, and sinks in the receiver. This 
 oil, commonly called dead oil, is much more abundant than the light oil, 
 amounting to about one-fourth of the weight of the tar, and contains those 
 constituents of the tar which have a high specific gravity and boiling point, 
 particularly naphthaline, aniline, quinoline, and carbolic acid. The pro- 
 portion of naphthaline in this oil augments with the progress of the dis- 
 tillation, as would be expected from its high boiling point, so that the 
 last portions of the oil which distil over become nearly solid on cooling. 
 When this is the case, the distillation is generally stopped, and a black 
 viscous residue is found in the retort, which constitutes pitch, and is 
 employed for the preparation of Brunswick black and of asphalt for 
 paving. 
 
 The light oil which first passed over is rectified by a second distillation, 
 and is then sent into commerce under the name of coal naphtha, a quan- 
 tity of the heavy oil being left in the retort, the lighter oils having lower 
 boiling points. 
 
 This coal naphtha may be further purified by shaking it with sulphuric 
 acid, which removes several of the impurities, whilst the pure naphtha 
 collects on the surface when the mixture is allowed to stand. When this 
 is again distilled it yields the rectified coal naphtha. 
 
 This light oil, especially when distilled from cannel coal at a low temperature, 
 contains, in addition to the hydrocarbons above enumerated, somq. belonging to the 
 marsh-gas series (C TC H 2n ), and others more recently brought to light, belonging to a 
 series the general formula of which is C n H n _ 2 ; but these last appear to be acted 
 on by the sulphuric acid, employed to remove the basic substances from the light oil, 
 in such a manner that they are converted into polymeric hydrocarbons, having the 
 general formula C 2n H 2n _ 4 , of which the three following have been particularly 
 examined : 
 
 Equivalent formula. 
 C 24 H 20 
 C 28 H 
 
 ^32 H 28 
 
 The hydrocarbons, C 12 H 10 , C> 14 H 12 , and C 1( 
 formed by the action of sulphuric acid, w 
 
 Boiling point. 
 4JOF. 
 464 
 536 
 
 H 14 , from which these appear to have been 
 Duld evidently be the higher homologues 
 
 of acetylene, C 4 H 2 . 
 
 The distillation of cannel coal, and of various minerals nearly allied to coal, at 
 low temperatures, is now extensively carried on for the manufacture of paraffine and 
 paraffine oil. (See Paraffine.) 
 
 The separation of the hydrocarbons composing this naphtha is effected 
 by a process in constant use for similar purposes, and known as fractional 
 distillation. 
 
 This consists in distilling the liquid in a retort (A, fig. 268) through 
 the tubulure of which a thermometer (T) passes, to indicate the tempera- 
 ture at which it boils. The first portion which distils over will, of course, 
 
SEPARATION OF THE HYDROCARBONS IN COAL-NAPHTHA. 453 
 
 consist chiefly of that liquid which has the lowest boiling point ; and if 
 the receiver (E) be changed at stated intervals corresponding to a certain 
 
 Fig. 268. Fractional distillation. 
 
 rise in the temperature, a series of liquids will be obtained, containing 
 substances the boiling points of which lie within the limits of tempera- 
 ture between which such liquids were collected. 
 
 When these liquids are again distilled separately in the same way, a 
 great part of each is generally found to distil over within a few degrees 
 on either side of some particular temperature, which represents the boil- 
 ing point of the substance of which that liquid chiefly consists ; and if the 
 receivers be again changed at stated intervals, a second series of distillates 
 will be obtained, the boiling points of which are comprised within a 
 narrower range of temperature. It will be evident that, by repeated dis- 
 tillations of this description, the mixture will eventually be resolved into 
 a number of substances, each distilling over entirely at or about one par- 
 ticular degree, viz., the boiling point of that substance. 
 
 To apply this to the separation of the constituents of light coal naphtha. 
 
 The crude light oil is first agitated with dilute sulphuric acid, which removes any 
 basic substances present in it, and afterwards with a dilute solution of potash, to 
 separate carbolic acid. The adhering potash is removed by shaking with water, 
 and the naphtha is allowed to remain at rest, so that all the water may settle down, 
 and the naphtha may be drawn off for distillation. 
 
 The naphtha begins to boil at about 160 F., but a small quantity distils over 
 before the temperature has risen to 180, when the receiver may be changed ; 
 between 180 and 200 a considerable quantity of the naphtha distils over, and at 
 the latter degree the receiver is changed a second time. The receiver is changed at 
 every 20 throughout the distillation, until nearly the whole of the naphtha has 
 passed over, which will be the case at about 360.* 
 
 Ten unequal quantities of liquid will have been thus obtained, diminishing as the 
 temperature rises. 
 
 Each of these must then be distilled in a smaller retort than the first, also pro- 
 vided with a thermometer. 
 
 The first portion (160 to 180) will probably begin to boil at 150, and will distil 
 in great part before 160, when the receiver may be changed. When the tempera- 
 ture reaches 170 it will probably be found that nothing remains worth distilling. 
 The liquid passing over in this distillation between 160 and 170 may be added to 
 that which is next to be distilled (180 to 200). 
 
 * On the large scale, that portion of the naphtha which is distilled over between 180 and 
 250 F. is sold as benzole, and employed for the preparation of aniline. 
 
454 
 
 BENZOLE OR BENZINE. 
 
 The second portion (180 to 200) will begin to boil at about 175, and will distil 
 over chiefly between that temperature and 185, when the receiver may be changed. 
 Nearly the whole will have passed over before 195, and this last fraction may be 
 added to that previously obtained from 200 to 220. 
 
 When all the first series of liquids have been thus distilled, it will be found that 
 the second series consists chiefly of six portions distilling between the following 
 degrees of temperature, viz., 150-160, 175-185, 180-190, 240-250, 300-310, 
 340-350. 
 
 By another distillation of each of these portions, a third series of liquids will be 
 formed, consisting chiefly of five portions distilling between the following points, viz., 
 145-150, 175-180, 230-235, 288-293, 336-342. 
 
 The portion distilling between 145 and 150 is comparatively small in quantity, 
 and has not yet been fully examined. 
 
 That obtained between 175 and 180 is more abundant than either of the others, 
 and is nearly pure benzole (C 12 H 6 ). 
 
 The portion boiling between 230 and 235 is chiefly toluole (C U H 8 ), whilst 288 
 to 293 gives xylole (0 16 H 10 ), and 366 to 342 isocumole (C 18 H la ). 
 
 In order to separate the benzole completely from the hydrocarbons which still 
 adhere to it, the portion boiling between 175 and 180 is exposed to a temperature 
 of 32, when the benzole alone freezes, the other hydrocarbons remaining liquid, and 
 being easily extracted by pressure. 
 
 A simpler method of separating liquids which have different boiling points con- 
 sists in distilling them in a flask (F, fig. 269) connected with a spiral worm (W) of 
 
 Fig. 269. Fractional distillation. 
 
 pewter or copper, surrounded by water, or some other liquid, maintained at a tem- 
 perature just above the boiling point of the particular liquid which is required to 
 distil over. The greater part of the less volatile liquids will condense in the worm 
 and run back into the flask. Thus, in extracting benzole from the light oil, the liquid 
 in A might be kept at 180 F., when the toluole, &c., would be partly condensed in 
 the worm, and the portion which passed into the receiver would consist chiefly of 
 benzole. When little more distilled over, the temperature of A might be raised to 
 230 and the receiver changed, when the distillate would contain toluole as its 
 predominant constituent, and so on. 
 
 334. .Benzole. The pure benzole or benzine is a brilliant colourless 
 liquid, exhaling a powerful odour of coal-gas; it boils at 176 F., and is 
 very inflammable, burning with a smoky flame. It mixes readily with 
 alcohol and wood-spirit, but not with water. Its property of dissolving 
 caoutchouc and gutta percha renders it very useful in the arts, and it is an 
 excellent solvent for the removal of grease, paint, &c., from clothes and 
 furniture. 
 
ANILINE OR PHENYIAMINE. 455 
 
 Benzole combines directly with chlorine to form a solid chloride of benzole, 12 H 6 C1 6 , 
 which is decomposed by an alcoholic solution of potash, yielding chlorobenzole. 
 C 12 H 3 C1 3 . 
 
 -By the action of an aqueous solution of hypochlorous acid upon benzole, a crys- 
 talline body has been obtained, having the composition C 12 H 9 C1 3 O 6 , and called 
 trichlorhydrine of phenose. When acted on by alkalies, this substance yields a sweet 
 substance called phenose, isomeric with dry grape-sugar 
 
 C 12 H 9 C1 3 6 + 3(KO.HO) = C 12 H 12 ]2 + 3KC1. 
 
 This substance has not been crystallised ; it forms a deliquescent amorphous 
 mass, which is easily soluble in water and alcohol, but insoluble in ether. It reduces 
 the oxides of copper and silver like grape-sugar, and when acted on by nitric acid 
 is converted into oxalic acid. Phenose has not been found capable of fermentation 
 by yeast. 
 
 335. Aniline. The chief purpose to which benzole is devoted is the 
 preparation of aniline, which is subsequently converted into the bril- 
 liant dyes now so extensively used. It has been already noticed at 
 p. 128, that when benzole is dissolved in fuming nitric acid, violent action 
 takes place, and a dark red liquid is formed, from which water precipitates 
 a heavy yellow oily liquid, smelling of bitter almonds, and known as 
 nitrolenzole, which has the composition C 12 H 5 (N0 4 ), and may be regarded 
 as derived from benzole by the substitution of an equivalent of nitric per- 
 oxide for an equivalent of hydrogen 
 
 C 12 H 6 + HO. NO. = C 12 H 5 (N0 4 ) + 2HO. 
 
 Benzole. Nitrobenzole. 
 
 When nitrobenzole is placed in contact with diluted sulphuric acid and 
 metallic zinc, the (nascent) hydrogen removes the whole of the oxygen, 
 and two equivalents of hydrogen are acquired in their stead, producing 
 C 12 H 5 NH 2 , or C ]2 H 7 N, aniline 
 
 C 12 H 5 (N0 4 ) + H 6 = C J2 H 7 N + 4HO.* 
 
 Nitrobenzole. Aniline. 
 
 That aniline has been produced may be shown by neutralising the excess 
 of sulphuric acid with potash, and adding chloride of lime (hypochlorite 
 of lime), which gives a fine purple colour with aniline. 
 
 The conversion of nitrobenzole into aniline on a large scale is more 
 conveniently effected by gently heating it in a retort, with water, iron 
 filings, and acetic acid, when the deoxidising action of the acetate of iron 
 (FeO . C 4 H 3 3 ), first produced, materially assists the change, this salt 
 being converted into a basic peracetate of iron (Fe.,0 3 . 2C 4 H 3 3 ), which is 
 left in the retort, and the aniline may be distilled over, accompanied by 
 water. At the close of the distillation, a red oil passes over, which solidi- 
 fies to a crystalline mass. This is azobenzide^ C 12 H 5 N, originally obtained 
 by distilling nitrobenzole with an alcoholic solution of potash. 
 
 (When nitrobenzole, in alcoholic solution, is reduced by zinc in the 
 presence of hydrochloric acid, the solution neutralised by carbon ate of 
 
 * The change is more intelligible when molecular formulae are employed ; thus 
 
 Molecular formula. 
 Benzole, . . 6 8 H e 
 Nitrobenzole, . 6 fi H 5 (N0 2 ) 
 Aniline, . . e e H 6 NH 2 
 
 which shows that two atoms of oxygen have been displaced by two atoms of hydrogen. 
 
456 DYES FKOM COAL-TAR. 
 
 soda and boiled with, alcohol, a crystalline compound of aniline with 
 chloride of zinc (ZnCl + C 12 H 7 N) is obtained.) 
 
 Since aniline is only slightly soluble in water, and has the sp. gr. 1 '02, 
 the larger portion of it collects at the bottom of the liquid in the receiver, 
 which is milky from the presence of minute drops of aniline in suspension. 
 By pouring the contents of the receiver into a tall vessel, the greater part 
 of the aqueous fluid may be separated, and the aniline may be purified by 
 a second distillation, when the remaining water will pass over first, the 
 boiling point of aniline being 360 F. 
 
 Aniline* presents many striking features; though, colourless when per- 
 fectly pure, it soon becomes brown if exposed to the air ; its odour is very 
 peculiar and somewhat ammoniacal, and its taste is very acrid. A drop 
 falling upon a deal table stains it intensely yellow. But the character by 
 which aniline is most easily recognised, and that which, leads to its useful 
 applications, is the production of a violet colour with solution of chloride 
 of lime, by which a very minute quantity of aniline may be detected. 
 The exact nature of the chemical change connected with the production 
 of this colour has not been determined, but it is known to be an oxidation, 
 and a great number of processes have been patented from time to time 
 for the production of crimson, purple, and violet dyes by the action of 
 various oxidising agents upon aniline. 
 
 836. Coal-tar dyes. The first dye ever manufactured from aniline on a large scale 
 was that known as mauvej or aniline purple, which is obtained by dissolving aniline 
 in diluted sulphuric acid, and adding solution of bichromate of potash, when the 
 liquid gradually becomes dark-coloured, and deposits a black precipitate, which is 
 filtered off, washed, boiled with coal-naphtha to extract a brown substance, and 
 afterwards treated with hot alcohol, which dissolves the mauve. The chemical 
 change by which the aniline has been converted into this colouring-matter cannot 
 at present be clearly traced, but the basis of the colour has been found to be a sub- 
 stance which has the composition C 27 H 12 N 2 , and has been termed mauve'ine. It 
 forms black shining crystals, resembling specular iron ore, which dissolve in alcohol, 
 forming a violet solution, and in acids, with production of the purple colour. 
 Mauveine combines with the acids to form salts ; its alcoholic solution even absorbs 
 carbonic acid gas. The hydrochlorate of mauveine, C 27 H 12 N 2 . HC1, forms prismatic 
 needles with a green metallic lustre. 
 
 Very brilliant red dyes are obtained from commercial aniline by the action of 
 bichloride (tetrachloride) of carbon, bichloride of tin, perchloride of iron, chloride 
 of copper, mercuric nitrate, corrosive sublimate, and hydrated arsenic acid. It will 
 be noticed that all these agents are capable of undergoing reduction to a lower state 
 of oxidation or chlorination, indicating that the chemical change concerned in the 
 transformation of aniline into aniline-red is one in which the aniline is acted on 
 by oxygen or chlorine. 
 
 The easiest method of illustrating the production of aniline-red, on the small 
 scale, consists in heating a few drops of aniline in a test-tube with a fragment of 
 corrosive sublimate (perchloride of mercury), which soon fuses and acts upon the 
 aniline to form an intensely red mass composed of aniline-red, calomel, and various 
 secondary products. By heating this mixture with alcohol the red dye is dissolved, 
 and a skein of silk or wool dipped into the liquid becomes dyed of a fine red, which 
 is not removed by washing. 
 
 On the large scale, Magenta (as aniline-red is commonly termed) is generally pre- 
 pared by heating aniline to about 320 F. with hydrated arsenic acid, when a dark 
 semisolid mass is obtained, which becomes hard and brittle on cooling, and exhibits 
 a green metallic reflection. This mass contains, in addition to aniline-red, several 
 secondary products of the action, and arsenious acid. On boiling it with water, a 
 splendid red solution is obtained, and a dark resinous or pitchy mass is left. If 
 
 * Aniline derives its name from anil, the Portuguese for indigo, from which it may be 
 obtained by distillation with potash. 
 f French for marsh-mallow, in allusion to the colour of the flower. 
 
MAGENTA ROS ANILINE CHRYSANILINE. 457 
 
 common salt be added to the red solution as long as it is dissolved, the bulk of the 
 colouring matter is precipitated as a resinous mass, which may be purified from 
 certain adhering matters by drying and boiling with coal naphtha. The red colour- 
 ing matter is a combination of arsenic acid with a, colourless organic base, which has 
 been called rosaniline, and has the composition C 40 H 19 N 3 . 2HO (atomic formula, 
 6 20 H 19 N 3 . H 2 0). If the red solution of arseniate of rosaniline be decomposed with 
 hydrate of lime suspended in water, a pinkish precipitate is obtained, which consists 
 of rosaniline mixed with arseniate of lime, and the solution entirely loses its red 
 colour. 
 
 By treating the precipitate with a small quantity of acetic acid, the rosaniline is 
 converted into acetate of rosaniline (C 40 H 19 N 3 , HO . C 4 H 3 3 ), forming a red solution, 
 which may be filtered off from the undissolved arseniate of lime. On evaporating 
 the solution to a small bulk, and allowing it to stand, the acetate is obtained in 
 crystals which exhibit the peculiar green metallic lustre of the wing of the rose- 
 beetle, characteristic of the salts of rosaniline. This salt is the commonest com- 
 mercial form of Magenta ; its colouring power is extraordinary, a very minute particle 
 imparting a red tint to a large volume of water. Silk and wool easily extract the 
 whole of the colouring matter from the aqueous solution, becoming dyed a fast and 
 brilliant crimson ; cotton and linen, however, have not so strong an attraction for it, 
 so that if a pattern be worked in silk upon a piece of cambric, which is then im- 
 mersed in a solution of Magenta and afterwards washed in hot water, the colour 
 will be washed out of the cambric, but the red silk pattern will be left. 
 
 If a boiling solution of the acetate of rosaniline be mixed with excess of ammonia, 
 the bulk of the rosaniline will be precipitated, but if the solution be filtered while 
 hot, it deposits colourless needles of rosaniline, which become red when exposed to 
 the air, from absorption of carbonic acid, and formation of the red carbonate of 
 rosaniline. 
 
 Water dissolves but little rosaniline ; alcohol dissolves it abundantly, forming a 
 deep red solution. Rosaniline forms two classes of salts with acids, those with one 
 equivalent of acid (monacid salts) being crimson, and those with three equivalents 
 (triacid salts) having a brown colour. Thus, if colourless rosaniline be dissolved in 
 a little dilute hydrochloric acid, a red solution is obtained, which contains the 
 rnonacid hydrochlorate of rosaniline, C 40 N 19 H 3 . HC1 ; but if an excess of hydro- 
 chloric acid be added, the red colour disappears, and a brown solution is obtained, 
 from which the triacid hydrochlorate, C 40 H 19 N 3 . 3HC1, may be crystallised in brown- 
 red needles. 
 
 For experimental illustration t)f the properties of rosaniline, the liquid obtained 
 by boiling a solution of the acetate with a slight excess of lime diffused in water, 
 and filtering while hot, is very well adapted. This solution has a yellow colour, 
 and may be preserved in a stoppered bottle without alteration. If air be breathed 
 into it through a tube, the liquid becomes red from production of carbonate of 
 rosaniline. Characters painted on paper with a brush dipped in the solution are 
 invisible at first, but gradually acquire a beautiful rose colour. 
 
 When the red solution of hydrochlorate of rosaniline is slightly acidified with 
 hydrochloric acid and placed in contact with zinc, the solution becomes colourless, 
 the rosaniline acquiring two equivalents of hydrogen, and becoming leucaniline (from 
 xtt/xo? , white) C 40 H 21 N 3 , the hydrochlorate of which (C 40 H 21 N 3 . 3HC1) forms a 
 colourless solution. Oxidising agents reconvert the leucaniline into rosaniline. It 
 has been observed that pure aniline does not yield aniline-red when heated with 
 corrosive sublimate or arsenic acid, it being necessary that it should contain aaother 
 organic base, toluidine (C 14 H 9 N), which is derived from toluole (C 14 H 8 ) in the same 
 way in which aniline is derived from benzole. Since the benzole obtained from 
 coal naphtha almost invariably contains toluole, the aniline obtained from it is very 
 seldom free from toluidine. What share the toluidine has in the production of the 
 red colour is not understood, but if the aniline be prepared with benzole derived 
 from benzoic acid, and therefore free from toluole, no red is obtained. A mixture of 
 70 parts of toluidine with 30 of aniline, is said to answer best for the preparation of 
 the red and violet colouring matters. Such a mixture would contain two equivalents 
 of toluidine (C 14 H 9 N) and one equivalent of aniline (C 12 H 7 N), or C 40 H 25 N 3 , only 
 requiring the removal of H 6 by an oxidising agent to yield rosaniline C 40 H ]9 N 3 . 
 
 Aniline-yellow or chrysaniline (from %pva-to$, golden) is found among the secondary 
 products obtained in the preparation of aniline-red. It forms a bright yellow 
 powder resembling chrome-yellow, and having the composition C 4Q H 17 N 3 . It is 
 nearly insoluble in water, but dissolves in alcohol. Chrysaniline has basic pro- 
 
458 ANILINE-BLUE HYDROCYAN-ROSAN1L1NE. 
 
 perties, and dissolves in acids, forming salts. On dissolving it in diluted hydro- 
 chloric acid, and mixing the solution with the concentrated acid, a scarlet crystalline 
 precipitate of hydrochlorate of chrysaniline (C 40 H 17 N" 3 . 2HC1) is obtained, which is 
 insoluble in strong hydrochloric acid, but very soluble in water. A characteristic 
 feature of chrysaniline is the sparing solubility of its nitrate. Even from a dilute 
 solution of the hydrochlorate, nitric acid precipitates the nitrate of chrysauiline 
 (C 40 H 17 N 3 . HO . N0 5 ) in ruby-red needles. 
 
 Aniline-blue is produced when a salt of rosaniline (the commercial acetate, for 
 example) is boiled with an excess of aniline, which converts the rosaniline 
 (C 40 H ]9 N 3 ) into triphenylic rosaniline (C 40 H 16 (C 12 H 5 ) 3 N 3 ), which may be regarded as 
 having been formed by the introduction of three equivalents of the hypothetical 
 radical phenyle (C 12 H 5 ) in place of three equivalents of hydrogen, the -latter having 
 been evolved in the form of ammonia 
 
 C 40 H 19 N 3 .HC1 + 3[(C 12 H 5 ) H 2 N] = C 40 H 16 (C 12 H 6 ) 3 N 3 . HC1 + 3NH 3 . 
 
 Hydrochlorate of Aniline. Hydrochlorate of 
 
 rosaniline. triphenylic rosaniline. 
 
 The hydrochlorate is an ordinary commercial form of aniline-blue ; it has a brown 
 colour, refuses to dissolve in water, but yields a fine blue solution in alcohol. If it 
 be dissolved in an alcoholic solution of ammonia, the addition of water causes a white 
 precipitate of tbe hydrated base, triphenylic rosaniline, C,JEL e (C 10 H K ) Q N Q . 2HO, 
 
 i-v^i * * i-i-i*... -U 16\ 12 5/3 o 
 
 which becomes bluish when washed and dried. 
 
 Just as rosaniline yields leucaniline when acted on with nascent hydrogen, so 
 triphenylic rosaniline yields triphenylic leucaniline (C 40 H 18 (0 12 H 6 ) 3 N 3 ) ; this is not 
 basic like leucaniline, but a colourless neutral substance, which is reconverted into 
 blue by oxidising agents. Compounds corresponding to triphenylic rosaniline, but 
 containing methyle, ethyle, or amyle in place of phenyle, are obtained by digesting 
 rosaniline with the iodides of these radicals, at a high temperature, in sealed tubes. 
 Thus, by the action of iodide of ethyle (0 4 H 5 I) upon rosaniline, a blue crystalline 
 body, insoluble in water but soluble in alcohol, is obtained, which is a compound of 
 ethyle with triethylic rosaniline ; C 40 H 16 (C 4 H 5 ) 3 N 3 . 
 
 C 40 H 19 N 8 + 4C 4 H 5 I = C 40 H 16 (C 4 H 5 ) 3 N 3 .C 3 H 5 I + SHI. 
 Rosaniline. Ethyl-iodate of 
 
 tri-ethyl-rosaniline. 
 
 Aniline-violet appears to be formed in a similar manner. Other compounds have 
 been obtained from aniline, presenting almost every variety of colour. A green dye 
 is prepared by the action of a mixture of hydrochloric acid and chlorate of potash 
 upon aniline, and under particular conditions a black may be obtained with the same 
 agents. Another green has been made by acting upon Magenta with aldehyde. 
 
 When a solution of acetate of rosaniline is treated with cyanide of potassium, it 
 gradually loses its red colour, and deposits a white crystalline precipitate of a base 
 which has been termed hydrocyan-rosaniline, having the formula C 42 H 20 N 4 , and con- 
 tains the elements of rosaniline and hydrocyanic acid ; but this acid cannot be 
 detected in it by the ordinary tests, leading to the belief that the new base should 
 be regarded as leucaniline (C 40 H 21 N 3 ), in which one equivalent of hydrogen is re- 
 placed by an equivalent of cyanogen '(C 40 H 20 (C 2 N) N 3 ). The hydrocyan-rosaniline 
 is almost insoluble in water, and sparingly soluble in boiling alcohol. When 
 precipitated from its salts by adding an alkali, it becomes pink on exposure to sun- 
 shine. 
 
 The present extensive application of aniline to the manufacture of these 
 dyes affords a most striking example of the direct utility of pure chemistry 
 to the arts, for only ten or a dozen years ago, the name of this substance 
 was not known to any but scientific chemists, whilst at present many 
 tons are annually consumed to supply the wants of the dyers of silk and 
 woollen goods. 
 
 337. Aniline ranks as a powerful organic base, combining readily with 
 acids to form salts which are, generally speaking, easily crystallised. Like 
 ammonia, it unites directly with the hydrated acids, without any separation 
 of water ; thus, the formula for sulphate of aniline is C 12 H 7 N . HO . S0 3 , 
 
HOMOLOGUES OF BENZOLE. 459 
 
 just as that for sulphate of ammonia is NH 3 . HO . S0 3 . With the 
 hydrogen acids, also, aniline unites like ammonia, for hydrochlorate of 
 aniline is C 12 H 7 N . HC1, and hydrochlorate of ammonia, NH 3 . HC1 ; 
 and exactly as the addition of potash to the salts of ammonia causes the 
 separation of ammoniacal gas, so when added to the salts of aniline, it 
 precipitates that base in the form of oily drops, which render the liquid 
 milky. This resemblance in disposition between aniline and ammonia 
 leads to the impression that they must be moulded after a common type, 
 and. accordingly, aniline is often represented as formed from ammonia 
 (NH 3 ) by the substitution of the compound radical phenyle (Ci 2 H 5 ) for an 
 equivalent of hydrogen, and, upon this supposition, is tQimedphenylamine, 
 
 This view of the constitution of aniline is supported by the circumstance 
 of its formation when phenic or carbolic acid is heated with ammonia in 
 a tube hermetically sealed ; for there is reason to believe that this acid, 
 mentioned above as one of the chief acid products of the destructive 
 distillation of coal, is a hydrated oxide of phenyle (C 12 H 5 )0 . HO, and 
 its action upon ammonia would then be clearly explained by the 
 equation 
 
 (C 12 H 5 )O.HO + TH 3 m 2HO + NH 2 (C 12 H 5 ) 
 
 ' Fhenicadd. 
 
 When aniline is dissolved in alcohol and acted on by nitrous acid, two equivalents 
 of it lose three equivalents of (monatomic) hydrogen, and acquire, in their stead, one 
 equivalent of (triatomic) nitrogen, depositing a yellow compound, which has been 
 called diazoamidobenzole 
 
 2C 12 H 7 N + N0 3 = C 24 H n N 3 + 3HO . 
 
 Aniline. Diazoamidobenzole. 
 
 When the nitrous acid acts upon a hot solution, a base is formed isomeric 
 with the above, and called amido-diphenylimide, which is identical with a yellow 
 colouring matter obtained by the.action of stannate of soda upon a salt of aniline. Its 
 slightly acid solutions impart an intensely yellow colour to silk or wool, which is 
 removed by heat, the base being volatile. The action of nitrous acid on aniline 
 affords an example of a general method of producing compounds in which nitrogen 
 is substituted for hydrogen. 
 
 Accompanying the aniline in coal tar, there are found three other bases, 
 viz., pyridine, picoline, and quinoline. It will be seen that picoline 
 (C 12 H 7 N) is isomeric with aniline, from which, however, it differs in a very 
 striking manner, for its salts are by no means easily crystallisable, and it 
 furnishes no violet colour with oxidising agents, such as chloride of lime. 
 Picoline occurs among the products of the distillation of bones. Quino- 
 line is also formed when some of the vegetable alkaloids are distilled 
 with hydrate of potash. 
 
 338. The other constituents of the light coal naphtha, viz., toluole, 
 xylole, and isocumole, though not so important as benzole, on account of 
 their practical applications, stand in a highly interesting relation to it and 
 to each other. 
 
 These four liquids are members of a homologous series, that is, of a series 
 the members of which differ by the same number of equivalents of the 
 same elements. Thus, toluole (C 14 H 8 ) is seen to contain C 2 H 2 more than 
 benzole (C 12 H 6 ), just as isocumole (C 19 H 12 ) contains C 2 H 2 more than xylole 
 (C, 6 H 10 ). On reference to the table at p. 450, it will be seen that the 
 boiling points of the members of this' series are raised 54 F. for each 
 
460 PHENOLE OK CARBOLIC ACID. 
 
 addition of C 2 H y Thus, xylole (C 16 H 10 ) boils at 284, or 54 higher than 
 toluole (C 14 H 8 ), which boils at 230, whilst benzole (C 12 H 6 ) boils at 54 
 below this, or 176. 
 
 The members of this group are also intimately connected with those of 
 another homologous series, known as the aromatic acids, including 
 
 Benzoic acid, . . C I4 H 6 4 
 Toluicacid, . . C 16 H 8 4 
 Cuminic acid, . . C 20 H I2 4 . 
 
 By distilling each of these acids with hydrate of baryta, the correspond- 
 ing hydrocarbon is obtained, two equivalents of carbonic acid being 
 removed by the baryta ; thus, 
 
 C 14 H 6 4 - 2CO a = C 12 H 6 - 
 
 B S IC **. 
 
 The similarity between this decomposition and that by which marsh- 
 gas (C 2 H 4 ) is derived from acetic acid (CJ3.f)^ will be at once apparent 
 (see p. 88). 
 
 Each member of this series of hydrocarbons, when acted upon by nitric 
 acid, yields a iiitro-compound corresponding in composition to nitro- 
 benzole, and this, under the influence of reducing agents (such as acetate 
 of iron, or the hydrosulphate of an alkaline sulphide) yields a base homo- 
 logous with aniline. 
 
 Thus we have the three following homologous series :- 
 
 Hydrocarbon. 
 Benzole, C 12 H 6 * 
 Toluole, C 14 H 8 
 Xylole, C 16 H 10 
 
 Nitre-compound. 
 Nitrobenzole, C 12 H 5 N0 4 
 Nitrotoluole, C 14 H 7 N0 4 
 Nitroxylole, C ]6 H 9 N0 4 
 
 Base. 
 
 Aniline, C 12 H 7 N 
 Toluidine, C 14 H 9 N 
 Xylidine, C 16 H U N 
 
 339. Carbolic or plienic acid, or phenole (C J2 H 6 2 ), derives its interest 
 chiefly from its constituting a great part of the ordinary commercial 
 kreasote (from Kpeag, flesh, and o-w<o, to preserve). It is also present in 
 cow's urine, and in that of some other animals. It is found chiefly in 
 the heavy or dead oil of coal tar (p. 452), particularly in that portion 
 which distils over between 300 and 400 F., when the oil is submitted to 
 fractional distillation, and it appears to be the carbolic acid which confers 
 upon this heavy oil its valuable antiseptic properties, leading to its em- 
 ployment for the preservation of wood from decay. 
 
 In order to extract the acid from that portion of the dead oil which distils be- 
 tween 300 and 400 F., it is shaken with a hot concentrated solution of hydrate of 
 potash and some solid hydrate of potash. A white crystalline mass is deposited, 
 which is separated from the liquid portion and treated with a little water, when a 
 solution of carbolate of potash is obtained. This is separated from a quantity of 
 oil which floats above it, and decomposed with hydrochloric acid, when the carbolic 
 acid separates as an oily layer upon the surface. This is drawn off, digested with 
 a little fused chloride of calcium to remove the water, and distilled. The distilled 
 liquid, when exposed to a low temperature, solidifies to a mass of long colourless 
 needles, which are liquefied even by the warmth of the hand (93 F.) 
 
 Carbolic acid has the peculiar taste and smell of kreasote. It dissolves 
 sparingly in water, but readily in alcohol. When a piece of deal is wetted 
 
 * An equivalent of each of these hydrocarbons, in the state of vapour, occupies 4 vols., 
 that is, four times the volume occupied by an equivalent of oxygen at the same tempera- 
 ture and pressure. 
 
PICRIC OR GARB AZOTIC ACID. 461 
 
 with solution of carbolic acid, and afterwards with hydrochloric acid, it 
 becomes blue on drying. 
 
 The genuineness of a commercial sample of carbolic acid may be tested by shak- 
 ing about a drachm of it with half a pint of warm water, which will dissolve the 
 pure acid entirely, but will leave any " dead oil " undissolved. A solution of one 
 part of caustic soda in ten parts of water should dissolve five parts of pure carbolic 
 acid. 
 
 "When carbolic acid is shaken with one-fourth of its weight of water, and exposed 
 to a temperature of 39 F., it deposits six-sided prismatic crystals of a hydrate, 
 C 12 H 6 2 . HO, which is soluble in water, alcohol, and ether, and fuses at 61 F. 
 
 The acid properties of carbolic acid are of a very feeble and doubtful character. 
 It is more properly regarded as phenylic alcohol or hydrated oxide of phenyle, 
 C 12 H 5 O.HO. 
 
 Carbolic acid is very largely used as an antiseptic agent. In medicine 
 it is found very valuable, especially for the treatment of putrid sores ; 
 and, in admixture with sulphite of lime, it forms the substance known as 
 MacDougaUs disinfectant. 
 
 340. Carbazotic acid. "When carbolic acid is boiled with fuming nitric 
 acid, the solution, on cooling, deposits beautiful yellow crystals of carba- 
 zotic or picric acid, also called trinitrophenic or nitrophenisic acid, be- 
 cause it appears to be formed from phenic acid by the substitution of 
 3N0 4 for H 3 , just as nitrobenzole is formed from benzole by the substitu- 
 tion of NO, for H. 
 
 The composition of picric acid, upon this view, would be expressed by 
 the formula HO . C 12 H 2 (N0 4 ) 3 0, the equivalent of water being capable of 
 displacement by a base, forming a picrate or carbazotate ; thus if the acid be 
 added to a solution of potash, a yellow precipitate of carbazotate of potash, 
 KO . C 12 H 2 (N0 4 ) 3 0, is obtained, which has led to the employment of this 
 acid as a test for potash. 
 
 Carbazotic acid is not easily soluble in water, but dissolves readily in 
 alcohol. Its solutions have " the property of staining the skin and other 
 organic matters yellow, which is turned to advantage by the silk-dyer. 
 The intensely bitter taste of the acid has also led to its employment for 
 the adulteration of beer, to simulate the bitter of the hop. 
 
 Carbazotic acid is a very common product of the action of nitric acid 
 upon organic substances ; indigo, silk, and many resins furnish it in con- 
 siderable quantity. It is economically obtained in a pure state by the 
 action of nitric acid upon Botany Bay gum, but considerable quantities 
 are manufactured for the dyer by treating the crude carbolic acid from 
 coal tar with nitric acid. Carbazotic acid, as might be anticipated from 
 its composition, explodes when sharply heated, its carbon and hydrogen 
 being oxidised by the nitric peroxide. 
 
 When carbazotic acid is distilled with chloride of lime, it yields a heavy 
 colourless oil having a very pungent odour of mustard, and boiling at 
 248 F.* This substance has been called chloropicrine, and has the re- 
 markable formula C 2 C1 3 (N0 4 ), which may be represented as formed upon 
 the type of marsh-gas, C 2 H 4 , in which three equivalents of the hydrogen 
 are replaced by chlorine, and the fourth by nitric peroxide. Chloro- 
 picrine is frequently met with among the products of the action of chlor- 
 inating agents upon organic substances. It is almost insoluble in water, 
 but dissolves easily in alcohol and ether. 
 
 When an alcoholic solution of chloropicrine is acted on by sodium, it 
 
 * 233 -6 (Hofmann). 
 
462 NAPHTHALINE. 
 
 yields the subcarbonate of ethyle, and when treated with cyanide of potas- 
 sium, it exchanges two equivalents of chlorine for two of cyanogen, form- 
 ing an unstable dark red semi-fluid substance, having the composition 
 C 2 ClCy 2 (N0 4 ), which may be regarded as derived from marsh-gas (C 2 H 4 ) 
 by the substitution of two equivalents of cyanogen, one equivalent of 
 chlorine, and one equivalent of nitric peroxide, for the four equivalents of 
 hydrogen. 
 
 It will be instructive to compare the composition of the most important 
 members of the phenyle series, as that group of organic compounds is 
 termed, which are derived from the hypothetical radical phenyle (C 12 H 5 ) 
 Benzole or hydride of phenyle, . H(C, 2 H 5 ) 
 
 Aniline or phenylamine, . .. NH 2 (C 12 H 5 ) 
 Phenicacid, .... HO.(C 12 H 5 )0 
 Trinitrophenic or picric acid, . HO . [C 12 H 2 (N0 4 ) 3 ]0 , 
 
 It is evident that whilst aniline may be regarded as ammonia in which 
 the hypothetical phenyle is substituted for an equivalent of hydrogen, 
 phenic acid can be represented as formed from two equivalents of water 
 by the substitution of phenyle for half the hydrogen, and benzole may be 
 represented as a molecule of hydrogen, HH, in which one of the atoms is 
 replaced by phenyle. 
 
 Some specimens of the kreasote found in commerce boil at a higher 
 temperature than carbolic acid ; this is due to the presence of kresylic 
 acid (C 14 H 8 ? ), corresponding to carbolic acid, but regarded as containing 
 the hypothetical radical kresyle (C 14 H 7 ) in place of phenyle. The analogy 
 in composition is attended with a resemblance in properties, for kresylic 
 acid has the same antiseptic property as carbolic acid, and is applicable to 
 similar purposes. When acted on by nitric acid, it yields trinitrokresylic 
 acid (HO . C U H 4 (]N"0 4 ) 3 0), just as carbolic acid gives trinitrophenic acid 
 (HO.C 12 H 2 (N0 4 ) 8 0). 
 
 341. Naphthaline. The most prominent constituent of the heavy oil 
 of coal tar is the napthaline, which is easily procured in a pure state from 
 the portions obtained at the close of the distillation, by simply pressing 
 the semisolid mass to remove any liquid hydrocarbons, and boiling with 
 alcohol, from which the naphthaline crystallises on cooling in brilliant 
 pearly flakes, which may be still further purified by the process of sub- 
 limation. 
 
 In itself naphthaline is not very interesting, being a remarkably indiffer- 
 ent substance, but it has been made the subject of several beautiful in- 
 vestigations which have thrown much light upon the action of chemical 
 agents on organic compounds in general. 
 
 The most important of these researches is that upon the action of 
 chlorine and bromine on naphthaline, which originated the now universally 
 accepted doctrine of substitution, and fully established the fact, that an 
 element may be replaced in a given compound by an equivalent quantity 
 of another element of a totally different chemical character. 
 
 Thus, by the action of chlorine upon naphthaline, the hydrogen is re- 
 moved in the form of hydrochloric acid, and there are obtained six 
 new compounds by the progressive substitution of chlorine for the 
 hydrogen, which Laurent distinguished by names indicating the number 
 of equivalents of chlorine present by means of the different vowels in the 
 last syllable, introducing a new penultimate syllable when the vowels 
 were exhausted, as will be seen in the following list : 
 
SUBSTITUTION PRODUCTS FROM NAPHTHALINE. 463 
 
 - Naphthaline, . 
 Chlonaphtase, 
 Chlonaphtese, 
 Chlonaphtise, 
 Chlonaphtose, 
 
 C 20 H 7 C1 
 
 C 20 H 4 C1 4 
 
 Chlonaphtuse, . Wanting 
 
 Chlonaphthalase, . C 20 H 2 C1 8 
 
 Chlonaphthalese, . Wanting 
 
 Chlonaphthalise, . C 20 C1 
 
 20 wi 8 
 
 It will be observed that the original naphthaline type is here preserved 
 throughout, the sum of the equivalents being always 28, and the number 
 of carbon equivalents 20. 
 
 One of the most unexpected results of Laurent's investigation was the 
 disc6very that some of these compounds may be obtained in several dis- 
 tinct forms or modifications, which are isomeric, or have the same compo- 
 sition, but exhibit very different properties. Thus, there are seven varieties 
 of chlonaphtese, all containing C 20 H 6 Cl2, and yet differing from each other 
 as much as substances not having the same composition. Two of them 
 are liquids, and the five solid forms all fuse at different temperatures, 
 ranging between 88 and 214 F. Seven different forms of chlonaphtise 
 likewise exist, and four of chlonaphtose. 
 
 To account for this, Laurent supposed it to be by no means indifferent 
 which particle of hydrogen has been removed from the compound, believing 
 each to have its assigned place and specific function. Thus it may easily 
 be conceived that the replacement of different particles of hydrogen by 
 chlorine should give the seven modifications of chlonaphtese 
 
 Naphthaline, C 20 HHHHHHHH 
 
 Chlonaphtese a, C 20 C1C1HHHHHH 
 Chlonaphtese ft C 20 HHC1C1HHHH 
 
 and so on. Other more recent investigations have given greater proba- 
 bility to this hypothesis. 
 
 Bromine, as might be anticipated, yields results similar to those with 
 chlorine; but it could not have been predicted that substitution com- 
 pounds might be obtained in which one part of the hydrogen is replaced 
 by chlorine and the other by bromine. Thus, by acting upon a chlorine 
 substitution compound with bromine, or vice versa, the following sub- 
 stances were produced :* 
 
 Chlorebronaphtise, C 20 H 5 Cl 2 Br 
 
 Chlorebronaphtose, C 20 H 4 Cl 2 Br a 
 
 Chloribronaphtose, C 20 H 4 Cl 3 Br 
 
 Bromechlonaphtuse, C 20 H 3 Br 2 Cl 3 
 
 Bromachlonaphtose, C 20 H 4 BrCl 3 
 
 It will be observed that chloribronaphtose and bromachlonaphtose have 
 the same composition, though they possess different properties, and are 
 obtained in very different ways, the former being procured by the action of 
 bromine on chlonaphtise (C 20 H 5 C1,), and the latter by the action of chlorine 
 upon bronaphtese (C 20 H 6 Br 2 ). Another confirmation is thus obtained of 
 the belief, that upon the position of the hydrogen which is replaced, 
 depends the character of the resulting compound. 
 
 Naphthaline is capable of direct union with chlorine to form two 
 chlorides of naphthaline, having the formulae C 20 H 8 C1 2 and C 20 H 8 C1 4 , 
 
 * In naming these compounds, Laiirent proceeded upon the same principle. The vowel 
 immediately after the syllable chlor- or brom-, indicating the number of equivalents of that 
 element, whilst the vowel in the last syllable shows how many equivalents of hydrogen 
 have been replaced. The name begins with chlor- when the compound has been obtained 
 by the action of bromine upon a chlorine substitution product, and vice versd. 
 
464 PKOXIMA.TE CONSTITUENTS OP WOOD. 
 
 which may obviously be regarded as composed of substitution products 
 combined with hydrochloric acid. 
 
 When acted upon by nitric acid, naphthaline furnishes three substitu- 
 tion products, in which one, two, and three equivalents of hydrogen are 
 replaced by N0 4 ; and each of these compounds, under the influence of 
 reducing agents, yields a base, just as nitrobenzole, under similar treat- 
 ment, yields aniline. 
 
 By prolonging the action of boiling nitric acid upon naphthaline 
 and evaporating the solution, crystals of naphthdlic or phthalic acid, 
 2HO . C 16 H 4 6 , are obtained, which may be rendered anhydrous by subli- 
 mation. Through this acid, naphthaline is connected with the phenyle 
 series; for when phthalic acid is heated with lime, it is resolved into 
 carbonic acid and benzole 
 
 2HO.C 16 H 4 6 + 4CaO = C 12 H 6 + 4(CaO.C0 2 ). 
 
 Phthalic acid. Benzole. 
 
 Moreover, by digesting phthalate of lime with hydrate of lime at an 
 elevated temperature for several hours, it is converted into benzoate and 
 carbonate of lime 
 
 2CaO.C 16 H 4 6 + CaO.HO = CaO.C I4 H 5 3 + 2(CaO . C0 2 ). 
 
 Phthalate of lime. Benzoate of lime. 
 
 Paranaphthaline, C 30 H 12 , which is found among the last products of the 
 distillation of coal tar, and has the same percentage composition as naph- 
 thaline, differs from that substance in being almost insoluble in alcohol, 
 and fusing only at 356 F., whilst naphthaline fuses at 174 F. 
 
 Chrysene and pyrene are obtained at the close of the distillation of coal 
 tar ; they are crystalline solids not possessing any special importance, and 
 have also been observed among the products of the destructive distillation 
 of fatty and resinous bodies. 
 
 DESTRUCTIVE DISTILLATION OF WOOD. 
 
 342. The destructive distillation of wood may be advantageously 
 studied in order to gain an insight into the effects of heat upon organic 
 substances comparatively free from nitrogen, just as that of coal may serve 
 as a general illustration of the behaviour of nitrogenised bodies under 
 similar treatment. 
 
 The principal distinction between the two cases will be found to consist 
 in the absence of basic substances from the products of the distillation of 
 non-nitrogenised bodies. 
 
 All varieties of wood (freed from sap) consist essentially of cellulose, 
 lignine, and mineral substances or ash. The cellulose (C I2 H 10 10 ) com- 
 poses the wood-cells, and is therefore the most important constituent of 
 the wood, the lignine being the material with which these cells are lined, 
 and which appears to have a great influence upon the hardness of woods, 
 being more abundant in the harder varieties, and particularly in such 
 hard appendages as nut-shells. Lignine is far more easily dissolved by 
 alkalies than cellulose, which is scarcely affected by them, but it has not 
 hitherto been found possible to isolate the lignine in a state of purity for 
 the purpose of determining its exact composition, since it is always accom- 
 panied in the wood by resinous matters, giving rise to the differences of 
 
PRODUCTS FROM WOOD. 
 
 465 
 
 colour in woods, and by a small quantity of nitrogenised matter, and of 
 ash deposited with it from the sap. 
 
 The following results of the analysis of several woods will exhibit their 
 general correspondence in composition : 
 
 Wood dried in vacuo at 284 F. 
 
 
 Beech. 
 
 Oak. 
 
 Birch. 
 
 Aspen. 
 
 Willow. 
 
 Carbon, 
 
 49-46 
 
 49.58 
 
 50-29 
 
 49-26 
 
 49-93 
 
 Hydrogen, 
 
 5-96 
 
 5-78 
 
 6-23 
 
 6-18 
 
 6-07 
 
 Oxygen, 
 
 42-36 
 
 41-38 
 
 41-02 
 
 41-74 
 
 39-38 
 
 Nitrogen, ) 
 Sulphur, J 
 
 1-22 
 
 1-23 
 
 1-43 
 
 0-96 
 
 10-95 
 
 Ash, . 
 
 1-00 
 
 2-03 
 
 1-03 
 
 1-86 
 
 3-67 
 
 
 
 
 
 
 
 
 10000 
 
 100-00 
 
 100-00 
 
 100-00 
 
 100-00 
 
 Cellulose in a nearly pure condition constitutes cotton, linen, and the 
 best kinds of (unsized) paper, since the processes to which the woody 
 fibre is subjected in the preparation of these materials, destroy and 
 separate the less resistant lignine and the matters which accompany it. 
 
 On comparing the composition of wood with that of coal, it will be 
 obvious that the large proportion of oxygen in the former must give rise 
 to a great difference in the products of destructive distillation. Accord- 
 ingly, it is found that water, carbonic oxide, carbonic acid, and acetic 
 acid, all highly oxidised bodies, are produced in large quantity, and that 
 the gaseous products of the distillation of wood burn with far less light 
 than those from coal, in consequence of the smaller proportion of the 
 heavier hydrocarbons. 
 
 The principal products of the action of heat upon wood are 
 
 Wood Tar. 
 Solids. 
 
 Paraffine, . 
 Naphthaline, 
 Cedriret, 
 Pittacal, 
 
 Pyrene, 
 
 Chrysene, 
 
 Resin, 
 
 C 24 H 8 
 
 Liquids. 
 
 
 
 
 Pyroligneous or i 
 
 
 
 
 acetic acid, . J 
 
 C 4 H 4 4 
 
 
 
 Wood naphtha, 
 
 C 2 H 4 2 
 
 ' 
 
 
 Acetate of methyle, 
 
 C 2 H 3 0. 
 
 C 4 H 3 3 
 
 
 Formiate of methyle, 
 
 C 2 H 3 0. 
 
 C 2 H0 3 
 
 
 Acetone, . 
 
 6 H 6 2 
 
 
 
 Water, 
 
 
 
 Toluole, . . C 14 1 
 
 Xylole, . . C lc : 
 
 Cymole, . . C 2(V 
 
 Kreasote, . . C 14 " 
 
 Picamar, 
 
 Kapnomor, . . C 2(y 
 
 Eupione, . . C 10 ] 
 
 Gases. 
 
 Marsh-gas, G 2 H 4 
 
 Carbonic oxide, .... CO 
 
 Carbonic acid, . . . . C0 2 
 
 Of these products, by far the most important are the pyroligneous acid, 
 the wood naphtha, and acetone. 
 
466 METHYLIC ALCOHOL. 
 
 The distillation of wood with a view to the preparation of these sub- 
 stances, is conducted in the manner described in the section on wood 
 charcoal (p. 57), when the distillate separates into two portions, the 
 heavier insoluble part constituting the wood tar, whilst the light aqueous 
 layer contains the pyroligneous acid, naphtha, and acetone. 
 
 On distilling this, the two last, boiling respectively at 150 and 133 
 F., first distil over, and then the acetic acid, which boils at 943 F. The 
 acid so obtained, however, is contaminated with tarry matters, which 
 communicate the peculiar odour of wood smoke, and adapt it especially 
 for the preservation of meat. In order to obtain pure acetic acid, this 
 crude acid is neutralised with carbonate of soda, and the acetate of soda 
 thus obtained is moderately heated to expel the foreign substances. It is 
 then further purified by solution in water and crystallisation, and is dis- 
 tilled with sulphuric acid, which converts the soda into sulphate, leaving 
 the acetic acid to distil over. 
 
 343. Wood naphtha Methylic alcohol. In order to obtain the wood 
 naphtha (or proligneous ether, or wood spirit, or pyroxylic spirit), the 
 portion which distils over below 212 F. is rectified in a still containing 
 chalk, which retains the acetic acid as acetate of lime. 
 
 The wood naphtha so obtained consists chiefly of methylic alcohol 
 (C 2 H 4 2 ), but contains also acetone, acetate of methyle, and certain oily 
 substances which impart to it a peculiar odour, and cause it to become 
 milky when mixed with water. Wood generally yields about one part of 
 naphtha to twenty of acetic acid. In order to obtain the pure methylic 
 alcohol, chloride of calcium is dissolved to saturation in the crude wood 
 spirit, when a definite crystallisable compound is formed, of 2 equivalents 
 of methylic alcohol and 1 of chloride of calcium, CaCl . 2C 2 H 4 2 . This 
 is heated in a retort, placed in a vessel of boiling water, as long as any 
 acetone and acetate of methyle pass over, the above compound not being 
 decomposed at 212 C F. An equal weight of water is then added to the 
 residue in the retort, and the distillation continued, when the methylic 
 alcohol distils over, accompanied by water, and the chloride of calcium 
 remains in the retort. The diluted methylic alcohol is digested for some 
 time with powdered quick-lime, and again distilled, when it is obtained in 
 a state of purity. 
 
 The useful applications of crude wood naphtha depend upon its burning 
 with a nearly smokeless flame in lamps (though as a source of heat only, 
 not of light), and upon its power of dissolving most resinous substances 
 employed in the preparation of varnishes, stiffening for hats, &c. 
 
 Methylic alcohol is the first member of the very important homologous 
 series of alcohols, of which ordinary alcohol or spirit of wine is the type, 
 and the consideration of which may be postponed until the chemical 
 history of that alcohol shall have been studied. The designation of 
 methylic alcohol supposes the existence in the pyroligneous spirit of a 
 compound radical methyle* (C 2 H 3 ), of which methylic alcohol is the 
 hydrated oxide = (C 2 H 3 )0 . HO. This view is by no means unsupported 
 by experimental evidence ; for if wood spirit be distilled with four parts 
 of concentrated sulphuric acid, it yields a gas, the composition of which 
 is represented by the formula C 2 H 3 0, and this may be regarded as the 
 
 * From neQv, wine; i)Xrj, wood. The termination -yle is generally bestowed upon com- ' 
 pound radicals, because OXt) is put metaphorically for matter. Thus, ethyle is meant to 
 imply the matter from which ether compounds are derived. 
 
PARAFFINE. 467 
 
 oxide of methyle. Again, if wood spirit be distilled with iodine and 
 phosphorus, the hydriodic acid formed (see p. 175) acts upon the oxide of 
 methyle, producing the compound C 2 H 3 I, iodide of methyle. When this 
 is heated in contact with zinc, iodide of zinc is produced, and a gas, 
 having the composition C 2 H 3 , which is that of the radical methyle, is 
 obtained. (This important question of compound radicals will be more 
 fully discussed hereafter.) 
 
 A sulphide, bisulphide, chloride, bromide, and cyanide of methyle, may 
 also be obtained, as well as compounds of the oxide of methyle with sul- 
 phuric, nitric, acetic, &c., acids. The methyle series is, in fact, perfectly 
 parallel with the ethyle series, the members of which are far more important, 
 and will therefore be more particularly considered hereafter. 
 
 One of the most interesting compounds derived from wood spirit is the 
 salicylate of methyle , or oil of winter green (C 2 H 3 . C 14 H 5 5 ), which is ex- 
 tracted from the flowers of the Gaultheria procumbens, Und was one of the 
 first vegetable products to be prepared artificially by the chemist. It is 
 obtained by distilling wood spirit with sulphuric acid and salicylic acid 
 (HO . C U H 5 5 ), the latter acid being formed by the action of fused hydrate 
 of potash upon the salicine (C 26 H 18 14 ) extracted from willow bark. 
 
 It will be noticed that the compound of oxide of methyle (C 2 H 3 0) 
 with formic acid (C 2 H0 3 ), or the formiate of methyle, C 2 H 3 . C 2 H0 3 , would 
 have the same composition as acetic acid, HO . C 4 H 3 3 , though they are 
 very different in constitution. An excellent illustration is here afforded 
 of the distinction between an empirical and a rational formula, the former 
 simply denoting the composition of a substance, without regard to the 
 arrangement of its components, which is always indicated by the rational 
 formula. Thus, the empirical formula of acetic acid, as well as of 
 formiate of methyle, is C 4 H 4 4 , but the rational formula of the latter is 
 C 2 H 3 . C 2 H0 3 , showing it to consist of the oxide of methyle (C 2 H 3 0), 
 combined with formic acid (C 2 H0 3 ), whilst the rational formula of acetic 
 acid, HO . C 4 H 3 3 , represents it as a compound of water with acetic 
 anhydride (C 4 H 3 3 ). Such compounds are often said to be metameric, 
 the term isomeric being usually applied to compounds having the same 
 composition, but which are not known to possess a different constitution, 
 such as oil of turpentine and many of the essential oils. 
 
 344. Paraffine (C^H,.), is a beautiful, semi-transparent, waxy substance, 
 which distils over with the last portions of the tar from wood, and may 
 be obtained in larger quantity by distilling peat, as well as from the 
 mineral known as Boghead cannel. It is also found abundantly in the 
 petroleum or mineral naphtha imported from Rangoon. 
 
 In order to extract the paraffine from wood tar, advantage is taken of 
 its great resistance to the action of most chemical agents,* for which pur- 
 pose the later portions of the distillate are moderately heated with con- 
 centrated sulphuric acid, which decomposes and chars most of the 
 substances mixed with the paraffine, and allows the latter to collect as 
 an oily layer upon the surface ; this is allowed to cool and solidify, when 
 it may be purified by pressure between blotting-paper, and solution in a 
 hot mixture of alcohol and ether, from which it is deposited, on cooling, 
 in brilliant plates. 
 
 Paraffine fuses at 110 F., and may be distilled at a higher temperature ; 
 it burns, like wax, with a very luminous flame, and is employed as a sub- 
 
 * To which it owes its name, from parum, little ; affinis, allied. 
 
 2 G2 
 
468 PETROLEUM. 
 
 stitute for wax in the manufacture of candles. It is insoluble in water, 
 and dissolves sparingly in alcohol, ether being the best solvent for it. 
 
 It will be seen from the formula above given for paraffine, that the 
 exact number of equivalents of carbon and hydrogen contained in it is 
 unknown, since it does not form definite compounds with other sub- 
 stances, and therefore its exact equivalent weight cannot be ascertained ; 
 it is known, however, to contain an equal number of equivalents of carbon 
 and hydrogen. 
 
 The substance known as paraffine oil, which is used for lubricating 
 machinery, is the less volatile portion of the hydrocarbons obtained by 
 the destructive distillation of Boghead cannel (found at Bathgate, near 
 Edinburgh). The more volatile portion of the hydrocarbons so obtained 
 is employed for illuminating purposes. 
 
 Acetone will be described hereafter. 
 
 Of the other products of the destructive distillation of wood enumerated at p. 465, 
 some have been described amongst the products obtained from coal, and the re- 
 mainder have been but little studied, and have not received any useful application. 
 
 Eupione (Oi H 12 ) is a liquid lighter than water, and boiling at 116 F. 
 
 Kapnomor is an oily liquid, which boils at 360. 
 
 Picamar is another oily liquid, heavier than water. 
 
 Cedriret is a red crystalline substance. 
 
 Pittacal is a blue solid. 
 
 Stockholm tar is collected during the carbonisation of pine wood, con- 
 taining a large quantity of resin, the tar running off through an aperture 
 at the lower part of the pit, in which the imperfect combustion of the 
 wood is carried on. It differs from ordinary tar in containing large quan- 
 tities of resin and turpentine, the latter being separated from it by distil- 
 lation, and the residue constituting the pitch of commerce. 
 
 Petroleum. There are found, in different parts of the earth, generally 
 in or near the coal-formations, several solid or liquid hydrocarbons, pro- 
 bably formed during the conversion of vegetable remains into coal, some 
 of which have received useful applications. 
 
 The Rangoon tar has already been noticed as containing a considerable 
 quantity of paraffine ; the liquid part of this tar, after distillation and 
 treatment with oil of vitriol to remove hydrocarbons of the benzole series,* 
 is the liquid in which potassium and sodium are preserved ; it is com- 
 monly called petroleum or rock-oil, and appears to be a mixture of several 
 hydrocarbons. Petroleum is also employed occasionally as a solvent for 
 caoutchouc and resinous substances. In the neighbourhood of the Cas- 
 pian sea there are several springs from which rock-oil flows, together with 
 water, from the surface of which it is skimmed and sent into commerce. 
 
 American petroleum. Within the last few years abundant supplies of 
 petroleum have been obtained from wells and springs in Pennsylvania 
 and Canada, and the demand for it to serve as an illuminating agent, and 
 for the lubrication of machinery, has created a new branch of commerce, 
 giving rise to the rapid growth of " oil cities " in the neighbourhood of the 
 wells. These rock-oils have a very peculiar unpleasant odour, and appear 
 to consist chiefly of hydrocarbons belonging to the homologous series, of 
 which marsh-gas (C 2 H 4 ) is a member. Thus, the Pennsylvanian petroleum 
 has furnished the hydrocarbons, C 8 H 10 , C ]0 H 12 , C 12 H 14 , C 14 H 16 , C I6 H 18 , C 18 H 20 . 
 In addition to these, the hydrocarbons, C 20 H 20 , C 22 H 22 , C 24 H 24 , homologous 
 with olefiant gas (C 4 H 4 ), have been obtained from it. Some of the mem- 
 
 * These hydrocarbons, when treated with oil of vitriol, form acids which are soluble in 
 water. Thus benzole is converted into sulphobenzolic acid, HO . C 12 H 5 . S 2 O 5 . 
 
OIL OF TURPENTINE. 469 
 
 bers of the benzole series appear also to be present in the Canadian 
 petroleum. 
 
 The mineral substance known as bitumen or asphaltum contains a 
 hydrocarbon, apparently isomeric with oil of turpentine, together with a 
 resinous substance, and a black matter resembling pitch, and containing 
 oxygen. It is employed for making water-proof cements and black 
 varnishes, being dissolved for this purpose in turpentine. 
 
 Bituminous shale, when distilled, furnishes products which, as far as 
 they are known, are closely allied to those obtained from wood and coal. 
 
 OIL OF TURPENTINE AND SUBSTANCES ALLIED TO IT. 
 
 345. Turpentine is the generic name given to the viscous exudation 
 obtained by incising the bark of various species of pine. Several varieties 
 of turpentine are met with in commerce, of which the two best known 
 are the common turpentine which is obtained from the Scotch fir, and 
 Venice turpentine from the larch. 
 
 These are both solutions of colophony or common rosin (C 40 H 30 4 ) in 
 the essential oil of turpentine (C 20 H 16 ), and when distilled, yield from 
 75 to 90 per cent, of rosin, which remains in the retort, and from 25 to 
 10 per cent, of the essential oil, commonly sold as spirits of turpentine. 
 
 This essence of turpentine boils at 320 F., and floats upon water (sp. 
 gr. 0'864), in which it is very sparingly soluble, its proper solvents being 
 alcohol and ether. Its great inflammability renders it useful as a fuel for 
 lamps, but the large proportion of carbon which it contains causes it to 
 burn with a smoky flame, rendering it necessary either to employ lamps 
 constructed especially to afford an extra supply of air to the flame, or to 
 mix it with a certain proportion of alcohol. Camphine is distilled from 
 the turpentine of the Boston pine. 
 
 The property of turpentine to dissolve resinous and fatty substances 
 renders it exceedingly useful "in the preparation of paints and varnishes, 
 and for the removal of such substances from fabrics. It is also an excel- 
 lent solvent for caoutchouc. 
 
 One of the most remarkable features of this essential oil is the facility with which 
 it changes into isomeric or metameric modifications, exhibiting great differences 
 in their physical and chemical properties. 
 
 When heated in a closed vessel to about 480 F. for some hours, oil of turpentine 
 is converted into two isomeric modifications differing greatly from the original oil in 
 the temperature at which they boil ; for whilst oil of turpentine distils over entirely 
 at 320 F., one of these modifications, known as isoterebentfiene, boils at 350 F., and 
 the other, metaterebenthene, at 660. 
 
 When digested, in the cold, with a small proportion of oil of vitriol, oil of tur- 
 pentine yields terebene and colophene, the former boiling at 320 F., but differing 
 from oil of turpentine in its odour, which resembles thyme, and in its want of action 
 upon polarised light. 
 
 Colophene has a far higher boiling point (600), and is much heavier than tur- 
 pentine (sp. gr. 0-940), from which it is also distinguished by its indigo-blue colour 
 when seen obliquely, though it is colourless by directly transmitted light. More- 
 over, the specific gravity of the vapour of colophene is 9-52, whilst that of turpentine 
 is 4-76, or one-half that of colophene, rendering it probable that if the composition of 
 turpentine be C 20 H 16 (= 4 vols.), that of colophene is C 40 H 32 (= 4 vols.), a relation 
 expressed by saying that colophene is polymeric with turpentine. Colophene is also 
 obtained by the distillation of colophony. 
 
 The ordinary oil of turpentine appears to be really itself a compound of two 
 isomeric hydrocarbons, for when hydrochloric acid gas is passed into it, two distinct 
 isomeric compounds are formed, both expressed by the formula, C 20 H 16 . HC1, but one 
 being a solid, and the other a liquid even at F. 
 
470 ESSENTIAL OILS. 
 
 The solid compound, which is known as artificial camphor or hydrochlorate of dadyle, 
 forms white prismatic crystals very similar to camphor, and when its vapour is 
 passed over heated quick-lime, the latter removes the hydrochloric acid, and the 
 hydrocarbon known as camphilene or dadyle (Sas, a pine-torch) is obtained, which is 
 isomeric with oil of turpentine, but boils at 273 instead of 320 F., and is without 
 any action upon polarised light. 
 
 The liquid compound formed by the action of hydrochloric acid upon oil of tur- 
 pentine is called hydrochlorate ofpeucyle\ and when distilled with quick-lime yields 
 terebilene or peucyle (vtvxv, the pine), also isomeric with oil of turpentine, but without 
 action on polarised light. 
 
 Although oil of turpentine is not miscible with water, it is capable of forming 
 three compounds with it in different proportions. When the oil is long kept in 
 contact with water, crystals are deposited which have the composition C 20 H 16 . 6HO ; 
 boiling water dissolves these, and deposits them in a prismatic form on cooling. The 
 crystals fuse at about 217 F. ; and when further heated, lose two equivalents of 
 water, yielding another crystalline hydrate, which sublimes without alteration at about 
 480 F. When exposed to air this hydrate again absorbs two equivalents of water. 
 
 By distilling the aqueous solution of either of the preceding hydrates with a 
 little sulphuric acid, a liquid hydrate smelling of hyacinths is obtained ; it contains 
 C 20 H 16 . HO, and is called terpinole. 
 
 When oil of turpentine is exposed to the air, it slowly becomes solid, 
 absorbing oxygen, and becoming converted into resinous bodies. 
 
 Common rosin or colophony* This substance is composed of two 
 isomeric acids known as sylvic and pinic. When common rosin is treated 
 with cold alcohol, the greater portion of it is dissolved; and if the 
 alcohol be evaporated, it leaves an amorphous substance, which is pinic 
 acid. The residue, left undissolved by cold alcohol, is dissolved by hot 
 alcohol, and deposited in colourless prisms, which are sylvic acid. The 
 salts of these acids have the composition MO . C^H^Og, so that the acids 
 themselves must be represented as HO.C 40 H 29 3 . The pinate and syl- 
 vate of soda obtained by dissolving rosin in solution of soda or carbonate 
 of soda, are largely used in the manufacture of yellow soap, and of the 
 size for paper-makers. By distilling common rosin with the aid of super- 
 heated steam, it is obtained nearly free from colour. 
 
 346. The turpentine series of hydrocarbons. Oil of turpentine is the 
 representative of a large class of hydrocarbons, derived like itself from 
 the vegetable kingdom, and all having a percentage composition corres- 
 ponding to the formula C 20 H ]6 . All the individuals of this group resemble 
 turpentine in their liability to suffer conversion into isomeric modifica- 
 tions, in their solidification by absorption of oxygen when exposed to 
 the air, in their combination with water to form crystalline hydrates, and 
 above all, in their tendency to form artificial camphors by combining with 
 hydrochloric acid. 
 
 The oils of bergamotte, birch, camomile, carraway, cloves, hops, juniper, 
 lemons, orange, parsley, pepper, savin, tolu, thyme, and valerian, contain 
 the same hydrocarbon C 20 H 16 , generally accompanied, in the natural oil, 
 by the product of its oxidation, bearing a relation to the hydrocarbon 
 similar to that which colophony bears to turpentine. 
 
 These essential oils are generally extracted from the flowers, fruit, 
 leaves, or seeds, by distillation with water, the portion of the plant 
 selected being suspended in the still by means of a bag or perforated 
 vessel, so that there may be no danger of its being scorched by contact 
 with the hot sides of the still, and so contaminating the distillate with 
 empyreumatic matters (e/ATrvpeuto, to scorch). The water which distils over 
 
 * Colophon, a city of Ionia. 
 
CAMPHOR. 471 
 
 always holds a little of the essential oil in solution, and it is in this way 
 that the fragrant distilled waters of the druggist are obtained. When the 
 essential oil is present in large proportion, it collects as a separate layer 
 upon the surface of the water, from which it is easily decanted. The oil 
 which is dissolved in the water may be separated from it by saturating 
 the liquid with common salt, when the oil rises to the surface, or by 
 shaking it with ether, which dissolves the oil and separates from the 
 water, the ethereal solution floating upon its surface, and leaving the oil 
 wh,en the ether is evaporated. 
 
 In cases like that of jasmine, where the delicate perfume of the flower 
 would be injured by the heat, the flowers are pressed between woollen 
 cloths saturated with oil of poppy seeds, which thus acquires a powerful 
 odour of the flower. 
 
 Bisulphide of carbon is also sometimes employed as a solvent for extract- 
 ing the essential oils. 
 
 Oil of peppermint contains a hydrocarbon called menthene (C 20 H 18 ) ; 
 essence of cedar-wood contains cedrene (C 32 H 26 ). 
 
 347. Camphors. Closely allied to the essential oils are the different 
 varieties of camphor, which appear to be formed by the oxidation of 
 hydrocarbons corresponding to the essential oils. 
 
 Common camphor (C 20 H 16 2 ) is found deposited in minute crystals in 
 the wood of the Laurus campJwra or camphor laurel, from which it is 
 obtained by chopping up the branches and distilling them with water in 
 a still, the head of which is filled with straw, upon which the camphor 
 condenses. It is purified by subliming it in large glass vessels containing 
 a little lime. 
 
 Camphor passes into vapour easily at the ordinary temperature of the 
 air, and is deposited in brilliant octahedral crystals upon the sides of the 
 bottles in which it is preserved. It fuses at 347 F. and boils at 399 F., 
 and is very inflammable, burning with a bright smoky flame. It is some- 
 times dissolved in the oil used for the lamps of magic lanterns, to increase 
 its illuminating power. Camphor is lighter than water (sp. gr. 0'996), 
 and whirls about upon its surface in a remarkable way, dissolving mean- 
 while very sparingly (1 part in 1000), alcohol and ether being its appro- 
 priate solvents. 
 
 When distilled with anhydrous phosphoric acid, camphor loses two equivalents of 
 water, and yields the hydrocarbon cymole (C 20 H 14 ) homologous with benzole. 
 
 Borneo camphor (C 20 H 18 2 ) is obtained from the exudation of the Dryobalanops 
 camphora. When this exudation is distilled, a hydrocarbon called borneene (C 20 Hj 6 ), 
 isomeric with oil of turpentine, first passes over, and afterwards the camphor, which 
 is neither so fusible nor so volatile as ordinary camphor, and emits quite a different 
 odour ; it also crystallises in prisms instead of octahedra, and may be converted 
 into ordinary camphor by the action of nitric acid, which oxidises two equivalents 
 of hydrogen 
 
 ^2o H is^2 H 2 = C 20 H 16 2 . 
 Borneo camphor. Common camphor. 
 
 The Borneo camphor appears to have been formed by the combination of borneene 
 with water, for if this hydrocarbon be distilled with solution of potash, it combines 
 with two equivalents of water, and is converted into the camphor. On the other 
 hand, when Borneo camphor is distilled with anhydrous phosphoric acid, it loses two 
 equivalents of water, and yields borneene. It is interesting to remark that this 
 hydrocarbon is also found in the essential oil of valerian. 
 
 The oil of camphor which accompanies the camphor distilled from the camphor 
 laurel, contains an equivalent of oxygen less than common camphor, its formula 
 being C 20 H 16 0. 
 
472 RESINS. 
 
 348. Balsams. The vegetable exudations known as balsams are mix- 
 tures of essential oils with resins and acids probably produced by the 
 oxidation of the oils. 
 
 Balsam of Peru contains an oily substance termed cinnameine 
 (C^HggOg), a crystalline body, styracine (C 18 H S 2 ), a crystalline volatile 
 acid, the cinnamic (C 18 H 8 4 ), and a peculiar resin. 
 
 Balsam of Tolu also contains cinnamic acid and styracine, together 
 with certain resins, which appear to have been formed by the oxidation 
 of styracine. 
 
 Storax, also a balsamic exudation, contains the same substances, accom- 
 panied by a peculiar hydrocarbon, which has been named sty role, and has 
 the composition C 16 H 8 . This liquid is characterised by a remarkable 
 change which it undergoes when heated to about 400 F., being converted 
 into a colourless solid, metastyrole, which is polymeric with styrole, into 
 which it is reconverted by distillation. 
 
 349. Resins. Colophony is the best known member of the class of 
 resins, which are generally distinguished by their resinous appearance, fusi- 
 bility, inflammability, burning with a smoky flame, insolubility in water, 
 and solubility in alcohol. 
 
 As to their chemical composition, they are all rich in carbon and hydro- 
 gen, containing generally a small proportion of oxygen, and appear to 
 have been formed, like colophony (p. 470), by the oxidation of a hydro- 
 carbon analogous to turpentine. 
 
 Most of the resins also resemble colophony in their acid characters, 
 their alcoholic solutions reddening blue litmus paper, and the resins 
 themselves being soluble in the alkalies. This is the case with sandarach 
 and guaiacum resin, the former of which contains three, and the latter 
 two, resinous acids. 
 
 Copal appears to contain several resins, some neutral and some acid, 
 and is distinguished by its difficult solubility in alcohol, in which it can 
 be dissolved only after long exposure to the vapour of the solvent ; but 
 if it be exposed to the air for some time, at a moderately high tempera- 
 ture, it absorbs oxygen, and becomes far more easily soluble. Copal is 
 readily dissolved by acetone. Animi and elemi resins are somewhat 
 similar in properties to copal. 
 
 All these resins are used in the manufacture of varnishes. 
 
 Guaiacum resin is distinguished by its tendency to become blue under 
 the influence of the more refrangible and chemically active (violet) rays 
 of the solar spectrum, as well as under that of certain oxidising agents, 
 such as chlorine and ozone. 
 
 Lac, so much used in the arts, belongs to the class of resins, being the 
 exudation of certain tropical trees punctured by an insect. In its crude, 
 natural state, encrusting the small branches, it is known as stick-lac, and 
 has a deep red colour ; when broken off the branches and boiled with 
 water containing carbonate of soda, it furnishes a red colouring matter, 
 very largely used in dyeing, leaving a resinous residue termed seed-lac, by 
 fusing which the shell-lac is obtained. This resin is very complex, con- 
 taining several distinct resinous bodies. It is largely used in the manu- 
 facture of hats, of sealing-wax, and of varnishes. The lacquer applied to 
 brass derives its name from this resin, being an alcoholic solution of shell- 
 lac, sandarach, and Venice turpentine. Indian ink is made by mixing 
 lamp-black with a solution of 100 grains of lac in 20 grains of borax and 
 4 ounces of water. 
 
SUCCINIC AND BENZOIC ACIDS. 
 
 473 
 
 Amber, a fossil resinous substance, more nearly resembles this class of 
 bodies than any other, and contains several resinous bodies. It is distin- 
 guished by its insolubility, for alcohol dissolves only about one-eighth, 
 and ether about one-tenth of it. After fusion, however, it becomes soluble 
 in alcohol, and is used in this state for the preparation of varnishes. 
 
 The distinguishing peculiarity of amber is, that it yields succinic acid, 
 2 HO . C 8 H 4 6 (sucdnum, amber), when digested with alkalies, distilled, 
 or oxidised by nitric acid ; in the latter case ordinary camphor is formed 
 at the same time. 
 
 Succinic acid is also found in some of the resins of coniferous trees, and 
 in the leaves of the wormwood. It is among the products of the action 
 of nitric acid upon most fatty and waxy substances, and is present in 
 wines and other fermented liquors, being produced during the fermenta- 
 tion of sugar. The acid is characterised by the cough-provoking vapour 
 which it emits when heated. 
 
 Varnishes are prepared by dissolving resins in alcohol, or wood spirit, 
 or acetone,* a little turpentine or some fixed oil being added to prevent 
 the resin from cracking when the solvent has evaporated. In order to 
 promote the solution of the resin, it is usually powdered before being 
 treated with the solvent, and mixed with coarsely powdered glass to pre- 
 vent it from becoming lumpy. Methylated spirit is now very generally 
 used for the preparation of varnishes; it is simply spirit of wine, to 
 which a little wood naphtha has been added, to deter persons from drink- 
 ing it, and to prevent other frauds upon the Excise. 
 
 Benzoin, or gum benzoin, as it is erroneously called, is also a veget- 
 able resinous product, and is distin- 
 guished by the presence of benzole 
 acid (HO . C 14 H 5 3 ), which may be 
 obtained from it by heating the resin 
 inan iron or earthen vessel .(fig. 270) 
 covered with a perforated sheet of 
 stout paper, over which a drum or 
 cone of paper is tied. When the heat 
 of a sand-bath is applied, benzoic acid 
 rises in vapour, and is condensed in 
 beautiful feathery crystals in the 
 paper drum. It may also be ex- 
 tracted by boiling the resin with water 
 and lime, when the benzoic acid is 
 dissolved in the form of benzoate of 
 lime (CaO. C 14 H 3 3 ), and being but sparingly soluble in water, may be 
 precipitated by adding hydrochloric acid to the filtered solution. 
 
 Benzoic acid is generally recognised by its feathery appearance and 
 peculiar agreeable odour, though this does not really belong to the acid, 
 but to a little essential oil which is not easily separated ; the vapour of 
 the acid itself is very irritating and produces coughing. It fuses when 
 moderately heated, and burns with a smoky flame. Benzoic acid dissolves 
 in about 200 parts of cold and 25 parts of boiling water. Alcohol and 
 ether dissolve it easily. 
 
 The salts of benzoic acid, or benzoates, have no practical importance, 
 but the behaviour of benzoic acid when distilled with an excess of lime 
 
 Fig. 270. 
 
 Acetone readily dissolves copal, mastic, and sandaracli. 
 
474 FORMATION OF BITTER ALMOND OIL. 
 
 or baryta has already been referred to as furnishing that important hydro- 
 carbon, benzole (see p. 460). 
 
 OIL OF BITTER ALMONDS, AND ITS DERIVATIVES. BENZOYLE SERIES. 
 
 350. Benzoic acid results from the oxidation of the essential oil of 
 bitter almonds (C 14 H 6 2 ), which slowly absorbs two equivalents of oxygen 
 from the air, and is converted into hydrated benzoic acid (C 14 H 6 4 ). 
 
 The formation of the essential oil of bitter almonds is one of the most 
 interesting processes of vegetable chemistry. 
 
 Both the bitter and the sweet almond contain a large quantity of a 
 fixed oil, which may be extracted from them by pressure, but which has 
 no particular taste or odour, and differs entirely from the essential oil of 
 bitter almonds, being, in fact, very similar to ordinary olive oil. The 
 residue or almond-cake, which is left after expressing the oil, contains, in 
 the case of the bitter almond only, a bitter principle, amounting to about 
 gJg-th of the weight of the almond, which may be extracted from the cake 
 by hot alcohol, and may be crystallised from the solution ; this substance 
 is called amygdaline, and is represented by the formula C 40 H 27 N0 22 , the 
 crystals containing, in addition, six equivalents of water. 
 
 Now, if the residue left after extracting the amygdaline with alcohol 
 be mixed with water and distilled, it does not yield any essential oil, 
 although this may be obtained in abundance from the original cake after 
 maceration in water, particularly if it be digested with .water for several 
 hours before distillation. 
 
 The sweet almond, which contains no amygdaline, does not afford any 
 essential oil when distilled with water, showing that the amygdaline is 
 really the source of the essence. Again, if boiling water be poured over 
 the bitter almond cake, no essential oil is produced, even when the mix- 
 ture is allowed to stand for some time, but if to this mixture there be 
 added an emulsion of sweet almonds prepared with cold water, the bitter 
 almond oil is at once formed, which is not the case, however, if the emul- 
 sion be prepared with boiling water. 
 
 From this it is evident that a substance exists in both sweet and bitter 
 almonds which is capable of developing the essence from the amygdaline 
 contained in the latter, but which loses its power when acted upon by hot 
 water. This may be still further proved by dissolving pure amygdaline 
 in water, and adding an emulsion of sweet almonds, when the essence is 
 at once produced. 
 
 When the emulsion of sweet almonds is filtered and mixed with alcohol, 
 a white substance resembling albumen is precipitated, which contains 
 carbon, hydrogen, nitrogen, and oxygen, and very easily putrefies when 
 exposed to the air in a moist state. If this substance, which is called 
 emulsine or synaptase (crwaTrrw, to bring into action), be dissolved in cold 
 water, and mixed with a solution of amygdaline, the oil of bitter almonds 
 is soon formed in abundance, but if the solution of emulsine be boiled, it 
 is no longer capable of developing the essence. On examining the solu- 
 tion of amygdaline in which the essential oil has been produced by the 
 action of emulsine, it is found to contain, in addition, hydrocyanic acid 
 (C 2 HN), grape-sugar (C 12 H 14 14 ), and formic acid (C 2 H 2 4 ), so that the 
 decomposition may be thus represented 
 2C 40 H 27 N0 22 = 4C 14 H 6 2 + 2C.HN- + C J2 H 14 14 + 4C 2 H 2 4 + 6HO . 
 
 Amygdaline. Bitter rfmond Hydrocyanic ^^ sugar Formic 
 
BENZOYLE SERIES. 475 
 
 The formation of the essential oil of bitter almonds must be regarded, 
 therefore, as dependent upon a species of fermentation or metamorphosis 
 of the bitter principle amygdaline, induced by contact with an albuminous 
 substance, emulsine, itself very prone to undergo decomposition when 
 exposed to air in the presence of moisture. 
 
 This essential oil may also be obtained from laurel leaves, and from the 
 kernels of most stone fruit. 
 
 When the oil of bitter almonds is distilled over, it is accompanied by 
 the hydrocyanic acid formed at the same time, and it is this which renders 
 the ordinary commercial oil so powerful a poison, for if it be purified by 
 distillation from a mixture of lime and chloride of iron (see Prussian Hue), 
 which retains the hydrocyanic acid, it becomes comparatively harmless. 
 A better process for obtaining the pure oil of bitter almonds consists in 
 shaking the crude oil with an equal volume of a strong solution of bisul- 
 phite of soda, with which it forms a white crystalline compound. If this 
 be distilled with solution of carbonate of soda, the pure oil passes over. 
 
 The poisonous properties of laurel- water, and similar preparations, are 
 also due to the presence of hydrocyanic acid. 
 
 The crude essential oil of bitter almonds also contains a crystalline substance 
 called benzoine (C 28 H 12 4 ), which is interesting as being polymeric with the essence, 
 into which it may be converted by passing its vapour through a red-hot tube. The 
 crude oil may be entirely converted into this substance by shaking it with an alco- 
 holic solution of potash. 
 
 When the pure essential oil of bitter almonds (C 14 H 6 2 ) is acted upon by dry 
 chlorine, it evolves hydrochloric acid, and becomes converted into a colourless liquid, 
 having an odour of horse-radish, and containing C I4 H 5 C10 2 , 1 equivalent of hydro- 
 gen having been removed, and its place filled by an equivalent of chlorine. If this 
 liquid be acted upon by the bromides, iodides, cyanides, or sulphides of the metals, 
 the chlorine is removed in its turn, the vacancy being filled up by bromine, iodine, 
 cyanogen or sulphur, compounds being obtained which have the formulae 
 
 C u H 5 Br0 2 
 C U H 5 I0 2 
 C 14 H 5 Cy0 2 
 C 14 H 5 S0 2 
 
 When boiled with water, this chlorine compound exchanges its chlorine for the 
 oxygen of the water, and is converted into hydrated benzoic acid 
 C 14 H 5 C10 2 + 2HO = C 14 H 5 3 . HO + HC1 . 
 
 On comparing the composition of these compounds with that of the essential oil 
 from which they are derived, our attention is called to the existence of C 14 H 5 2 in 
 all of them 
 
 Oil of bitter almonds, . (C 14 H 5 2 )H 
 Benzoic acid, . . . (C 14 H 6 2 )0 . HO 
 Chlorine compound, . (C 14 H 5 2 )C1 
 Bromine . . (C 14 H 5 2 )Br, &c. 
 
 This circumstance led many chemists to assume the existence in these com- 
 pounds of the radical benzoyle (C 14 H 5 2 ). capable of playing the part of an ele- 
 mentary substance in uniting with oxygen, chlorine, &c., and therefore resembling 
 the elements in its chemical tendencies, from which resemblance it is spoken of as a 
 quasi-element or compound radical. 
 
 If this radical be represented by Bz, the formation of the members of the benzoyle 
 series from oil of bitter almonds will be simply and easily traced. 
 Oil of bitter almonds, hydride of benzoyle, . BzH 
 Benzoic acid, hydrated oxide of benzoyle^ . BzO . HO 
 
 Chloride of benzoyle, BzCl 
 
 Bromide BzBr 
 
 Iodide Bzl 
 
 Cyanide BzCy 
 
 Sulphide BzS. 
 
4To 
 
 atty 
 It fora* 
 
 Tht'> 
 
 tad ether. The formula C U H A\ should be doubled to expreW comvtlv 
 W of thfe radical (w .4**W ^iwifc). 
 It will be noticed that the cvwp^ttd BrtX or *;** 
 i the K>Te onuuertk>n of the beitsorle series A oo 
 
 be wpNented M 1^0, (or C^H^O^.C^H^CVK iroU*d by 
 
 fsu with SOU- 
 
 B.C1 
 
 *>* ^mAy^^ has x> q jl*ffal Vu>^r. 
 . but if boded with infer, bstewly cottwiuxi into 
 feyxirated beiUMJe eidL 
 
 Whoa oU oT MttMiteMHil IliMH^plKd by hyOwOe of potesh d^sohed i 
 it jMfc ta^tiNfeliCiAlV. whk^h wUl be uwre 1 ^rtk*krtj ftOk^ 
 
 ttl. ^ IT; r 1 Vi 11 V ^ Til Hi MMlUll ill itMtfcn llaniii mi 11 1 
 
 
 BY fce*y tb% IMMJJJ W <|>M^MI^|I by*O of yteA. it 
 
 KO.HO s KO.CH r O^ 4 H,, 
 
 teted i fe*Hty tnk^ ck^elr re^mbli^ bettioicikcid, bo& U 
 
 The ww reaotts exist its ift the MM of the be>yle series for *ssmi^r the 
 rnjfciMS ift the eompo/ndb derived from oil of citMMfco^ of the Mdkei tfcmKnyl^ 
 " of cimmMMMi would be * hydride of ciwMagJe (C^^O^H* 
 
 |* by caivifciu^ s^euts it 
 
 by wi oter t^Mlr to UM! of tt 
 MM )ua bMft ^teitttA. wkfek M 
 
 by its bekMTtowt wlMft fated with 
 
 qjB^o, ^ (KO.HO) (C^H^VH > co.cc^ttOgo. 
 
 CWttfettft* ***. 
 
 The 
 
 ' : "* 
 
 1 
 
 of 
 
 
 SJLUCISI AND ITS WRRiVATiYKs Oi.rv\vsips& Oil </ ^wts or 
 
 <v\mpouuvl (C^O ) i^\uwnc with 
 ckl ; Uits cv^mpoaml is easily obfcar^l tificttlfy by 
 
 by boiling it in wafer, vwfeOTing the louring 
 
 the ^aOon V boQins with hyvlmfevl oxkle of le*d. pmlpiteting the 
 of lead by hyOio^ilphuik od, Mtd f>T*pot*ta A* .fileRd Uquki 
 the $Ucift rs**tti* out* lostd mav V oHuwd by 
 
: \U(1YI,K Hiaii 477 
 
 Hi", from illnilinl, in k.uihlul \\lnl. n. ..II. ki\m- lli. . .,III|H, ,1 ..... 
 
 SlllirilH' I ('.Hill- l\ .'llll'lo III ( H|<| \\.lkl Mlltl lli:..i|lll.|i- III .III. I. I. Ill 
 
 <li .>l\, i. Milily in ln'iliii!', \\.iln ;iinl 111 ulr.nhol. It in readily iliHliiiitftiuhftd 
 
 l'\ ill. I- 'I ..'I. Mil \\lll. ll ll ;;i\. ', \\illi nilKM'lll.rillt'll HUlpllUrid lirill, \\lii. ll 
 in. null I . ll |>li ' rim.' ulnii .i|.|,||,,| lit ll ..... in I kill- ill' UK \\ill..\\ 
 \\li.H ill lilh.l Ullll .hliil.- HIllplllINC i.i.l Mini lil< linilllil.l.K of |Hi|,m<ll, 1 1. 
 
 \ i. I.I I lli' oil ul Hpinni 
 
 Till' llllllK'M HIllV.'M-.l l.\ Nlllll'lll) \\ln n I- i!.-l \\llll II (lilllln ...in. . .1 imlil I 
 (limn I iin \. i\ 1 1'in.ii l.al'li I. 'i .ill. i III. l...ihn I. . l>. < n mill Inimil I'm n I. \\ 
 
 Hliil III :. Hi. : "I U I I. -M III l> HI 11,1 III Clllllllill "I. I I" ;.n- Ml. !,,< . III! I Ullll II . M .l:i I I MM 
 HUbHlumUM'lllllHl !%!//;. . uln.-li n ll In,-... In. I L\ II,, minim Mil. .<i.|,.ui whll'll 
 It tflvOH Will) |M 1,1, 1, ,11, 1, ,.1 ll. Ml 'I'll.' t'lmil",- I . . .. il\ . 1. 1. urn . I. I, I III. ll<|i 1 1 1 loll 
 ill' -I Ci|Uivillt'lllM l|' \Vlllor III Mlllli'ilin \Vlillll |i|iiVI(|o Ilio rlrllli III .'I lilpi u Illlltlil 
 
 <',M, .,,, | 1110 ;j U H,0 4 + ', I", ,<> |4 . 
 
 ' ML n. 'illlll ' ' '.' M" ll| ', 
 
 Klllllli Hn III \ n.i|.|.r . i . . .i|'.iN.' ,.| ,11,, lin tin , li. n ih. in,', Illlll i(, will 
 
 ' I. M ml.. I. .1 II,., I ' l.l|,, Mllj',111 I - I Hn |l|'ll(|l|, I III MM III I I ll. .1 I, 11... i,l 
 
 ii|...n a m \ ,--.ilii 1 1 IH'. M UK- Im lli! mil \\llli tin , 1 1 1 n I . . I ... n I I nl I I. ,i ,i I, n I 1 1 
 
 Li' Illlll'. Mm ll.|lllil <li-|i..:ill:i II I, ,| I .l.in... .;,'... . Ulll.ll lil I- Mil- Ullll 
 
 oil ol % l>il!or ulm.mila (O u ll rt C)J 
 
 A \,'l \ ;.|l ll> III" i Mimpl,' ,,| I Im i l.il.llll \ "I I \ |, iii. li.'lu ll lllilllll.il II" lln ill. I I Inln MI 
 nl' olio olollionl, I," am. lln i i I, >nn. I 111 llm < 1 1 r ll ii ml a i in II, .il miliriin . nmlnl' lln 
 inlln.n,, of .lil.. i nn \nl.l Mil.. (| i ll'iM'Cll I |i| i n I IK'I M r. .1 1 1 .1 i n i 1 1 .IllnlillO III |llll,(l(> 
 of llVill'oj'.oll, Mild Unit u In n I In , .u. I. Mil. ,1 \\ il h diliili ; ,, n I. MM \ \ n lil (illinr pro 
 .In. I i mill i . III. .11 in- ..i ml I" Hn In I lull I" Hn u , I ill, 1 1 mi I, il (uimilu. 
 
 \\lllrll .ill", nim tlllil .ilu, lin. I i "i|ir. 'I l\ i I \ IM al In .iln in. 
 
 Tim,-, wo liii-vn 
 
 Blioin, . . . c yil ii, M o u 
 
 '.^Jj'' | O,, 
 
 Ti i. lilurnHiiliciiii', < ' ,,. ( ,|'" <> M 
 
 t'lll .ill II . (',,',' j I), 
 
 ..i.. .ih . nlno, < ', l( ,|" 1 O 4 
 
 Timl||,,|i,;al|. 
 
 VVIli'll :ui lu'llli' l:i I'll: , I \\llli In 'I Li I' <>!' |Mi|;ii(||. I In ' I M.I .hsuinhril ill Wlllrl ll.lnl 
 
 hydrochlorid an, I I.,|,|,M|. lirunliVul iin.ll,;i ..r .///,////, ,/./,/ (llo (' U ll ft O ) urn 
 
 I ;.,!, Tin :irnl Illll) Illl O I ..... lilllilli'll In, III lln nil nl Mjijl ' I Mlllllll 
 
 | ..... , .111.1 ll U ill In , , ll III. 1 1 ; .ill, -\ In- Ill-ill In ill;i III.' lillllM I. 1. 1 1 in II I Illl I nil 
 
 nit l>. n ,.i.- ni'iil lic:ii:i In nil nl' lull, i iiliinnnlu 
 
 Oil ,.l l.ill.T iilnmmlii. <',, I !<>,, 
 
 Bonzoioaoid, . ''i, 11 /' 
 
 ;,!,,!,. , , ( ] |, IIH I,,, i, ..liliilli. il III ll m,, I 11,1. n I 
 I I curl an, I ;iml : ...lium ii|nm |.l I. 
 
 0, ll,", + 2(K) U + Na 
 
 I'll, iii.l.' 
 
 Oil <irn|>ini<it, . . . <',,!!, <>, 
 Siiliryl.r m-i,|, . . . C.JI.O,, 
 
 ui nncr hy I liinuiiiiilliin ...... 
 
 Silllrylnl,. ol 
 
 lv,.i,-||y a:: . li. I,M I h:i\i- IM , i, |r,| I,, collM.I' r Dm Lill, i llllliuml nil .. liylnilr -I 
 lirn/.nslr.-M limy li!i\- n-;-.iinli-l nil nf n|inrn uu ////// ></< J 'xnlii'i/li- (< ', , 1 1,,' >, . 1 1 ) , iiiiiiiiin 
 in- (lir rxi;:lrm-,. of Mm i;nln:il Nttlin/lfi ( < ' , , 1 1 < > , i. "I wllirli ,ili< -, In- iiri.l wuiiLI l>. 
 |,hn liyilruii'il iixiilc Wo llml HUH virw nl' lln . -,.1111111! ,1'lln . I-<HM|I< <la imp 
 
 !,,), ,| |,y || M < r 1 1, MM 1 1 I .in. , . I ha I ulim lln i.il ..I |iirn-:i i In al, il Wild . I>|..M-|. of 
 |,, M . ,, N |,' p ; , : ill, |;iiirr i. i i >l>l a I nci I W ll ir ll may lie I , ; ;.i i . I, . I a.i mm |M.;II-I| nl' lln ( \\, , 
 i;i,hc.ll.i ::.ill.-\ li II . l<l 
 
 <' M llo t M I (',,11,0.. 01 = U H,0, , U H.0 4 + IHJI. 
 
 '" 
 
478 PHLORIDZINE ESCULINE. 
 
 From a careful study of the behaviour of salicine under the action of various re- 
 ao-ents, the inference has been drawn that it is a compound of saligenine (C 14 H 8 4 ) 
 with a substance (C 12 H 10 O 10 ), which becomes converted into grape-sugar, by assimila- 
 tion of water, as soon as it is separated from the saligenine. 
 
 Salicine is occasionally employed in medicine as a febrifuge, and is a 
 common adulteration of quinine. . 
 
 Salicine is the chief member of the class of substances termed glucosides, 
 from the presence of grape-sugar (glucose) among their products of decom- 
 position. To this class belong several other substances much resembling 
 salicine, and, like it, extracted from the barks of different trees. 
 
 353. Populine (C 40 H 22 16 ) is a sweet crystalline substance obtained from the 
 bark and leaves of the aspen, and especially interesting from its close connection 
 with the benzoyle and salicyle series ; for when boiled with solution of baryta, it is 
 decomposed into benzoic acid (which unites with the baryta) and salicine 
 
 C 40 H 22 16 + BaO.HO = BaO.C l4 H 6 0, + C 26 H 18 U . 
 
 Populine. Benzoate of baryta. Salicine. 
 
 Nor is this the only connecting link, for populine yields oil of spirsea when distilled 
 with sulphuric acid and bichromate of potash, and when boiled with dilute acids it 
 furnishes benzoic acid, saliretine, and grape-sugar 
 
 C 40 H 22 16 + 4HO = HO,C 14 H 5 3 + C 14 H 6 2 + C 12 H 14 14 . 
 Populine. Benzoic acid. Saliretine. Grape-sugar. 
 
 In order to explain this production of benzoyle and salicyle compounds from popu- 
 line, it is usual to regard this substance as formed from salicine (C 26 H 18 14 ) by the 
 introduction of an equivalent of benzoyle (C 14 H 5 2 ), in the place of an equivalent 
 of hydrogen 
 
 C 40 H 2 A6 = 26 H 17 (C U H 5 2 )0 U . 
 
 Populine. Benzoyle-salicine. 
 
 Phloridzine (C 42 H 24 20 ) is extracted from the bark of the apple, pear, plum, and 
 cherry tree ; it crystallises readily, is slightly bitter, and when boiled with dilute 
 acids, yields grape-sugar and a resinous substance called phloretine (C 30 H 14 O 10 ). 
 Its most interesting property is that of forming a red compound (phloridzeine} when 
 exposed to the joint influences of air and ammonia 
 
 C 42 H 24 20 + 6 + 2NH 3 = C 42 H 30 N 2 26 . 
 
 Phloridzine. Phloridzeine. 
 
 This red compound combines with ammonia to form a purple mass with a coppery 
 lustre, which dissolves in water with a fine blue colour. The production of this 
 colouring matter from phloridzine is an excellent example of that conjoined action 
 of air and ammonia by which certain natural colouring matters, such as litmus, are 
 formed from substances which are themselves destitute of colour. 
 
 Quercitrine (C 36 H 18 20 ) is the yellow colouring matter extracted by alcohol from 
 the bark of the quercitron. It is a crystallisable substance, and is decomposed by 
 boiling with acids into grape-sugar and a yellow crystalline body called quercetine 
 
 C 36 H 18 20 + 4HO = C 24 H 8 10 + C 12 H 14 U . 
 
 Quercitrine. Quercetine. Grape-sugar. 
 
 Esculine (C 42 H 24 26 ) is extracted from the bark of the horse-chestnut by boiling 
 water. If the tannin and colouring matter be precipitated from the infusion by 
 acetate of lead, the filtered liquid treated with sulphuretted hydrogen to remove the 
 excess of lead, and the solution, after a second filtration, evaporated, the esculine is 
 obtained in colourless needles. It is remarkable for its fluorescence ; although, its 
 solution is colourless by transmitted light, it appears of a beautiful deep blue colour 
 when viewed at certain angles. This substance is also a glucoside, for when 
 boiled with dilute acids, it yields grape-sugar and a crystalline substance known as 
 esculetine. 
 
 C 42 H 24 26 + 10HO = C 18 H 6 8 + 2C 12 H 14 14 . 
 Esculine. Esculetine. Grape-sugar. 
 
 Famine also occurs in the horse-chestnut bark, but in far larger quantity in the 
 
ALLYLE SERIES. 479 
 
 bark of the ash. It is distinguished from esculine by exhibiting a green 
 fluorescence. 
 
 Saponine is a substance closely allied to the glucosides, and is found in the soap- 
 wort, the fruit of the horse-chestnut, the pimpernel, the root of the pink, and in 
 many other plants. It may be extracted by boiling alcohol, which deposits it in an 
 amorphous state on cooling. Saponine is soluble in water, and its solution is cha- 
 racterised by the readiness with which it lathers, like soap and water, although it 
 may contain a very small quantity of saponine. This property leads to the use of 
 decoctions containing it, such as those of the soap-wort, and of the soap-nut of 
 India, for the purpose of cleansing certain delicate fabrics. 
 
 ficrotoxine (C 24 H U 10 ?) is a crystalline substance, to which the poisonous pro- 
 perties of Cocculus indicus are due. It appears to have feeble acid tendencies, and 
 is extracted from an acidified solution by shaking with ether. On evaporating the 
 ethereal solution it leaves prismatic needles of an intensely bitter taste. 
 
 354. ESSENTIAL OILS CONTAINING SULPHUR ALLYLE SERIES. The essen- 
 tial oils of asafcetida, of cress, garlic, horseradish, leeks, mustard, onions, 
 and radishes, differ from those which have been already described by con- 
 taining sulphur. 
 
 Those of asafoetida, cress, garlic, leeks, onions, and radishes, are com- 
 posed essentially of the same substance, represented by the formula 
 C 6 H 5 S. The essence of mustard and that of horseradish are composed of 
 C 8 H 5 NS 2 . 
 
 The chemistry of the origin of essential oil of mustard is analogous to 
 that of essence of almonds. The oil is obtained from the seeds of the 
 black mustard after removing the fixed oil (which has no pungency what- 
 ever) by pressure ; on moistening the crushed seed with water, the pro- 
 duction of the essential oil is indicated by its peculiar odour, and it may 
 be separated from the seeds by distillation. The mustard seeds con- 
 tain a salt of potash with a peculiar acid called myronic acid* 
 (HO . C 20 H 19 NS 4 lg ), together with a substance similar to the emulsine of 
 almonds, which has been termed myrosine, and is capable of inducing the 
 decomposition of the myronic acid, and the consequent production of 
 essence of mustard, just as the emulsine of almonds developes the essential 
 oil by the decomposition of the amygdaline ; in the case of mustard, how- 
 ever, the nature of the decomposition has not been so clearly made out, 
 but is probably represented by the equation 
 
 HO.CJff 19 NS 4 18 = C 8 H 5 NS a + CJSL^i + HO + 2S0 2 . 
 
 Myronic acid. * Glucose ' 
 
 The essence of mustard has been produced artificially in a very inter- 
 esting and remarkable manner. 
 
 When glycerine (the sweet principle of the fats and fixed oils) is dis- 
 tilled with the biniodide of phosphorus, a colourless ethereal liquid js ob- 
 tained, which has the composition C 6 H 5 I, and is called iodide of allyle, 
 because when distilled with sodium, it yields iodide of sodium and a 
 volatile liquid composed of C C H 5 , and called allyle, in allusion to its pecu- 
 liar odour (allium, garlic). The formation of iodide of allyle is explained 
 by the following equation 
 
 C 6 H 8 6 + PI 2 - C 6 H 5 I + P0 3 + 3HO + I. 
 
 Glycerine. Iodide of allyle. 
 
 When iodide of allyle is distilled with sulphocyanide of potas- 
 sium, an oily liquid is obtained, identical in properties and composition 
 
 * From fjivpov, an ungiient. 
 
480 GUM-RESINS. 
 
 with oil of mustard, which must therefore be regarded as a sulphocyanide 
 of allyle, its artificial production being thus explained 
 
 C 6 H 5 I + K(C 2 NS 2 ) = C 6 H 5 .C 2 NS 2 + KI. 
 
 _ 
 
 Additional interest is created in this artificial formation of joil of mus- 
 tard when it is found to be convertible into oil of garlic, by being heated 
 with sulphide of potassium, when sulphocyanide of potassium is formed at 
 the same time, thus 
 
 C 6 H 5 .C 2 NS 2 + KS = C 6 H..S + 
 
 Essence of mustard. Essence of garlic. 
 
 Hence it is inferred that the essence of garlic is a sulphide of allyle, of 
 which essence of mustard is a sulphocyanide. 
 
 A considerable number of compounds are included in the allyle series, but are not 
 at present possessed of any practical importance. 
 
 The allylic alcohol (C 6 H 5 . HO) is interesting as the prototype of a new class of 
 alcohols, parallel with that represented by common alcohol (C 4 H 5 . HO). In order 
 to obtain it, the iodide of allyle is decomposed by oxalate of silver, when oxalate of 
 allyle is obtained 
 
 C 6 H 5 I + AgO. 0,0s = C 6 H 6 O.C 2 3 + Agl. 
 Iodide of allyle. Oxalate of allyle. 
 
 By treating oxalate of allyle with ammonia, allylic alcohol and oxamide are 
 obtained 
 
 C 6 H 5 O.C 2 3 + NH 3 = C 6 H 5 O.HO + C 2 H 2 N0 2 
 
 Oxalate of allyle. Allylic alcohol. Oxamide. 
 
 Allylene (C 6 H 4 ), the olefiant gas of the allyle series, is homologous with acetylene 
 (C 4 H 2 ), and much resembles it in its chemical relations. It has been prepared by 
 heating chlorinated propylene in a sealed tube with sodium-alcohol. The chlorin- 
 ated propylene is a product of the action of pentachloride of phosphorus upon 
 acetone 
 
 C 6 H 6 2 + PC1 S = C 6 H 5 C1 + HC1 + PC1 3 2 ; 
 Acetone. Chlorinated propylene. 
 
 C 6 H 5 C1 + C 4 H 5 Na0 2 = C 6 H 4 + NaCl + C 4 H 6 2 . 
 
 Sodium-alcohol. Allylene. Alcohol. 
 
 By its action on ammoniacal nitrate of silver, it yields argentallylene, C 6 H 3 Ag. 
 When sodium is heated in allylene, carbon and hydrogen are liberated, and sodic 
 acetylide is formed, C 6 H 4 + Na 2 = C 4 Na 2 + C 2 + H 4 , a little propylene (C 6 H 6 ) 
 is formed at the same time. 
 
 355. GUM-RESINS. The gum-resins consist of a mixture of gum with 
 resin, and occasionally with essential oil, and are distinguished by their 
 behaviour when triturated with water, which dissolves the gum and leaves 
 the oil and resin suspended, giving the liquid a milky appearance. They 
 also differ from most resins in being only partially soluble in alcohol. The 
 gum-resins exude from the plants producing them in a milky state, 
 gradually solidifying by exposure to the air. 
 
 Asafcetida contains a resin of the composition C 40 H. 26 10 , and owes its 
 powerful odour to an essential oil containing sulphur, which has been 
 already noticed. Galbanum, ammoniacum, aloes, olibanum or frankincense, 
 scammony, gamboge, myrrh, and euphorbium, also belong to the class of 
 gum-resins. 
 
 Caoutchouc (C 5 H 4 ) is so far allied to the gum-resins, that it is procured 
 from a milky exudation furnished by several tropical plants, particularly 
 by the Hcevaia guianensis and Jatroplia elastica. Incisions are made in 
 
VULCANISED INDIA-RUBBER. 481 
 
 these trees, and the milky liquid thus obtained is spread upon a clay 
 bottle-shaped mould, which is then suspended over a fire; a layer of 
 caoutchouc is thus deposited upon the mould, and its thickness is after- 
 wards increased by repeated applications of the milky liquid, the mould 
 being eventually broken out of the caoutchouc bottle thus formed. The 
 dark colour of the caoutchouc found in commerce is believed to be due 
 to the smoke from the fire over which it is dried, for pure caoutchouc is 
 white, and may be obtained in this state by dissolving in washed ether 
 and precipitating it by the addition of alcohol, in which it is insoluble. 
 The caoutchouc of commerce contains a small quantity of albumen, derived 
 from the original milky liquid, this being really a solution of albumen 
 holding in suspension about 30 per cent, of caoutchouc, which rises to the 
 surface like cream, when the juice is diluted with water and allowed to 
 stand, becoming coherent and elastic when exposed to air. It will be re- 
 membered that many of the chief uses of caoutchouc depend upon its 
 physical rather than its chemical properties, its lightness (sp. gr. 0'93) 
 and impermeability to water adapting it for the fabrication of waterproof 
 articles of clothing, of life-buoys, &c., whilst its remarkable elasticity gives 
 rise to a still greater variety of applications. 
 
 For the manufacture of waterproof cloth, caoutchouc is dissolved in 
 rectified turpentine, and the solution is spread, in a viscid state, over the 
 surfaces of two pieces of cloth of the same size, which are then laid face 
 to face and passed between rollers, the pressure of which causes perfect 
 adhesion between the two surfaces. Bisulphide of carbon, benzole, and 
 coal naphtha, pertroleum, the oils, both fixed and volatile, are also 
 capable of dissolving caoutchouc. 
 
 Marine glue is a solution of caoutchouc with a little shell-lac in coal 
 tar naphtha. 
 
 Waterproof felt is made by matting together fibres of cotton im- 
 pregnated with a solution of caoutchouc in naphtha, and passing the felt 
 between rollers. When kept for a length of time, its strength and water- 
 proof qualities are deteriorated, in consequence of the oxidation of the 
 caoutchouc, which is thus converted into a resinous substance resembling 
 shell-lac, and easily dissolved by alcohol. 
 
 The alkalies and diluted acids are without effect upon caoutchouc. 
 When gently warmed, it becomes far more soft and pliable ; it fuses at 
 about 250 F., and is converted into an oily liquid which becomes viscid 
 on cooling, but will not again solidify, and is useful for lubricating stop- 
 cocks. When further heated in air, it burns with a bright smoky flame. 
 Heated in a retort, caoutchouc is decomposed into several hydrocarbons, 
 one of which, called isoprene, boils at about 100 F., and has the com- 
 position C 10 H e , while caoutcliine has the same composition as oil of 
 turpentine, and boils at 340 F. ; they are well adapted for dissolving 
 caoutchouc. 
 
 Vulcanised caoutchouc is produced by incorporating this substance with 
 2 or 3 per cent, of sulphur, which not only increases in a remarkable 
 manner its elasticity, but prevents it from cohering under pressure, and 
 from adhering to other surfaces unless strongly heated. The vulcanised 
 caoutchouc is also insoluble in turpentine and naphtha. Ordinary vul- 
 canised caoutchouc generally contains more sulphur than is stated above, 
 which causes it to become inelastic and brittle after it has been some 
 time in use ; and for some purposes, such as the manufacture of overshoes, 
 it is found advantageous to add some carbonate of lead as well as sulphur. 
 
 2n 
 
482 GUTTA PEKCHA. 
 
 When a sheet of caoutchouc is allowed to remain for some time in fused 
 sulphur at 250 F., it absorbs 12 or 15 per cent, of that element without 
 suffering any material alteration; but if it be heated for a short time to 
 300 F., it becomes vulcanised; and when still further heated, is converted 
 into the black horny substance called vulcanite or ebonite, and used for the 
 manufacture of combs, &c. By treating the vulcanised caoutchouc with 
 sulphite of soda, the excess of sulphur above 2 or 3 per cent, may be dis- 
 solved out. 
 
 There are several processes employed for the manufacture of vulcanised 
 caoutchouc; sometimes the sulphur is simply incorporated with it by 
 mechanical means. Another process consists in immersing the caoutchouc 
 in a mixture of 100 parts of bisulphide of carbon with 2 '5 parts of chloride 
 of sulphur (S 2 C1),* or in dissolving the sulphur in oil of turpentine, which 
 is afterwards used to dissolve the caoutchouc. When the turpentine has 
 evaporated, a mixture of caoutchouc and sulphur is left, which may easily 
 be moulded into any desired form, and afterwards vulcanised by exposure 
 to high pressure steam, having a temperature of about 280 F. 
 
 The true chemical constitution of vulcanised caoutchouc is not yet 
 understood ; it has been suggested that the sulphur has been substituted 
 for a portion of the hydrogen in the original caoutchouc, but it does not 
 seem improbable that this hydrocarbon may combine directly with sulphur. 
 
 Caoutchouc is by no means rare in the vegetable world, being found in 
 the milky juices of the poppy (and thence in opium), of the lettuce, of 
 the euphorbium and asclepia families. 
 
 Gutta percha, like caoutchouc, is originally a milky juice which exudes 
 from incisions made into the wood of the Isonandra percha, a native of 
 the Eastern archipelago. This juice soon solidifies when exposed to air, 
 to a brownish mass heavier than caoutchouc (sp. gr. 0*98), and differing 
 widely from it by being tough and inelastic at the ordinary temperature, 
 becoming quite soft and plastic when heated nearly to the boiling point 
 of water. Being impervious to water, it is employed as a waterproof 
 material and for water-pipes, whilst its want of conducting power for elec- 
 tricity is turned to account in the coating of wires for the electric telegraph. 
 
 Gutta percha is dissolved by the same substances which dissolve caout- 
 chouc. Though it dissolves very slowly in ether, it is not affected by 
 diluted acids and alkalies, and is employed for the manufacture of bottles 
 in which hydrofluoric acid is kept. It liquefies at a moderately high 
 temperature, and is afterwards decomposed, yielding products similar to 
 those obtained from caoutchouc. 
 
 The gutta percha of commerce appears to contain only about 80 per 
 cent, of pure gutta percha (C 40 H 32 ), which is soluble in ether, the re- 
 mainder consisting of two resins which may be dissolved out by boiling with 
 alcohol, when a white crystalline resin ,(C 40 H 32 4 ) is deposited on cooling, 
 leaving an amorphous resin (C 40 H 32 2 ) in solution. 
 
 Pure gutta percha, exposed to air, is gradually converted into these 
 resinous bodies, unless light be excluded. 
 
 356. GUMS. Connected with the substances just described as being 
 immediate products of vegetable life, are the guyns, which, though resem- 
 bling the resins in transparency and lustre, are at once distinguished from 
 them by their solubility or softening in water, and by their insolubility in 
 alcohol. 
 
 * A mixture of sulphur and chloride of lime is said to be sometimes employed. 
 
GUM STARCH. 483 
 
 Gum arabic, which may be studied as the representative of this class, 
 is an exudation from certain species of acacia, and consists essentially of 
 arabine, which has the composition C 12 H n O u . It dissolves readily, even 
 in cold water, in large proportion, forming a viscid liquid, from which the 
 arabine is precipitated in white flakes on adding alcohol. 
 
 When arabine is boiled with diluted sulphuric acid, it is converted slowly 
 into grape-sugar (C 12 H, 4 14 ) by assimilating the elements of three equiva- 
 lents of water, a property connecting it closely with starch, which is sus- 
 ceptible of a similar conversion. 
 
 But a chemical property distinguishing the gums is their behaviour 
 with nitric acid, which furnishes mucic acid (2HO . C 12 H 8 14 ) and oxalic 
 acid (HO . C 2 3 ). The latter acid is also formed by the action of nitric 
 acid upon starch and sugar, whilst mucic acid may be obtained by a 
 similar process from sugar of milk and from manna sugar (mannite). 
 
 Gum Senegal is often used in place of gum arabic, especially by calico- 
 printers to thicken their colours. It is darker in colour than gum arabic, 
 but also consists essentially of arabine. 
 
 Gum tmgacanth (C I2 H 10 10 ), which exudes from the Astragalus Traga- 
 cantha, is far less transparent than gum arabic, from which it also diifers 
 by not dissolving in water, but merely swelling up to a soft gelatinous 
 mass. This variety of gum, which is also called mucilage, cerasine, or 
 bassorine, is found, together with arabine, in the gum which exudes 
 from the cherry, plum, almond, and apricot trees, and gives the mucila- 
 ginous character to the watery decoctions prepared from certain seeds, such 
 as linseed and quince-seed, and from the root of the marsh-mallow. 
 
 STARCH. 
 
 357. Starch (C 12 H 10 Ojp) differs widely from the vegetable products just 
 noticed, in being an indispensable constituent of certain parts of plants, 
 in possessing an organised structure, and playing a very important part in 
 the nutrition of the plant. 
 
 In composition, it is seen to correspond with cellulose, which has also, 
 it will be remembered, an organised structure ; but the function of cel- 
 lulose in the plant appears to be chiefly, if not entirely, a mechanical one, 
 since it forms the skeleton or framework of the plant, for which its resist- 
 ance to chemical change especially adapts it; whilst it will be seen that 
 starch suffers chemical changes in the vegetable, which may be compared 
 in some measure to the digestion of the food in the animal body. 
 
 Starch is manufactured chiefly from potatoes, wheat, and rice. 
 
 The solid portion of the potato consists chiefly of starch, as appears in 
 the following result of analysis : 
 
 Composition of the Potato. 
 Water, 75-9 
 
 Vegetable albumen, 
 
 Oily matter, 
 
 Woody fibre, 
 
 Starch, 
 
 Mineral substances, 
 
 2-3 
 0-2 
 0-4 
 20-2 
 1-0 
 
 100-0 
 
 In order to extract the starch, the potatoes are rasped to a pulp, which 
 is washed upon a sieve, imder a stream of water, as long as the latter is 
 
 2 n2 
 
484 MANUFACTURE OF STARCH. 
 
 rendered milky by the starch suspended in it, the woody fibre being left 
 behind upon the sieve. The milky liquid is allowed to settle, and the 
 clear water drawn off ; the deposited starch is then stirred up with fresh 
 water, and again allowed to subside, this process being repeated as long 
 as the water is coloured, after which the starch is mixed with a small 
 quantity of water, and passed through a fine sieve to separate mechani- 
 cally mixed impurities ; it is finally drained and dried, first, in a current 
 of air, and afterwards by a gentle heat. 
 
 Starch cannot be extracted from wheat so easily as from potatoes, 011 
 account of the much larger proportion of other solid matters from which 
 it must be separated. 
 
 Composition of Wlieat. 
 Water, 12-1 
 
 Vegetable albumen, 
 
 Oily matter, 
 
 Woody fibre, 
 
 Starch, 
 
 Dextrine and sugar, 1 
 
 Gluten, 
 
 Mineral substances, 
 
 2-0 
 
 1-1 
 
 1-6 
 
 60-8 
 
 10-5 
 
 10-5 
 
 1-6 
 
 100-0 
 
 To extract the starch, the coarsely-ground wheat is moistened with 
 water, and allowed to putrefy, as it easily does, in consequence of the alter- 
 able character of the gluten (which contains carbon, hydrogen, nitrogen, 
 oxygen, and sulphur) ; the putrefying gluten excites fermentation in the 
 sugar and part of the starch, producing acetic and lactic acids. These 
 acids are capable of dissolving the remainder of the gluten, which may 
 then be washed away by water, the subsequent processes being similar to 
 those employed in the extraction of potato starch. 
 
 A far more economical and scientific method of extracting the starch 
 consists in dissolving the gluten by means of a weak alkaline solution, 
 which leaves the starch untouched. This process is especially applied in 
 the manufacture of starch from rice, the composition of which is here 
 given : 
 
 Composition of Rice. 
 
 Water, .... 5-0 
 
 Starch, 83-0 
 
 Gluten, .... 6-0 
 
 Woody fibre, . . . 4-8 
 
 Sugar, | , 
 
 Dextrine,/' 
 
 Oily matter, ... 0-1 
 
 Mineral matters, . . 0-1 
 
 100-0 
 
 The whole rice is allowed to soak for twenty-four hours in water con- 
 taining 3^-^th of its weight of caustic soda ; it is then washed and ground 
 into flour, which is again soaked for two or three days in a fresh alkaline 
 solution ; the starch is allowed to settle, and the alkaline liquor holding 
 the gluten in solution is drawn off. To complete the purification of the 
 starch, it is stirred up with water, the heavier woody fibre allowed to sub- 
 
 * The existence of sugar in wheat is denied by PSligot. 
 
PROPERTIES OF STARCH. 
 
 485 
 
 side, and the milky liquid is run off into another vessel, where it deposits 
 the starch. 
 
 Starch is usually sent into commerce in the rough prismatic fragments 
 into which it splits during the process of drying, and is generally coloured 
 blue by the addition of a little artificial ultramarine or smalt, in order to 
 correct the yellow tint of linen. Commercial starch generally contains 
 about 18 per cent, of water. 
 
 Starch being possessed of an organised structure, might be expected to 
 vary in external characters with the source from which it was derived ; 
 and, accordingly, we find that, with the help of the microscope, it may be 
 ascertained from what plant any particular specimen of starch was pro- 
 cured, a result which could not be arrived at by a chemical examination. 
 
 Thus, powdered starch from the potato (P, fig. 271) appears under the 
 microscope in very irregular ovoid granules, marked with concentric rings, 
 and of larger size than those from most other vegetables, the long diameter 
 
 Fig. 271. 
 
 of the grains being usually about yj-j- inch. Wheat starch (W) exhibits 
 grains which are nearly circular, and are not marked with rings ; they are 
 much smaller than those of potato starch, having a diameter of about 
 T oVo f an inch- The grains of rice starch (R) are angular, and still 
 smaller, measuring only about -y-faf of an inch in diameter. A. represents 
 the starch granules of arrow-root. 
 
 Starch is quite unaffected by cold water ; but if it be heated with water 
 to a temperature above 140 F., the granules swell up, burst, and yield 
 the well-known viscid liquid used by laundresses. If this be mixed with 
 a large quantity of water, and allowed to stand, some of the imperfectly 
 burst granules subside, but the greater part of the starch remains so inti- 
 mately mixed with the water, that it is not separated by filtration through 
 paper, though it has been shown that when the rootlets of a hyacinth are 
 immersed in the diluted magma of starch, the water alone is taken up by 
 the capillary vessels, affording a strong presumption that the starch was 
 simply in a state of suspension in the water. If the boiled starchjbe eva- 
 porated to dryness, a brittle mass remains, which may again be taken up 
 without difficulty by water. 
 
 This peculiar behaviour of starch with water is closely connected with 
 its use as food. Kaw starch is digested with difficulty, and often passes 
 unaltered through the bowels, but the ease with which the starch gela- 
 tinised by heat is digested, is shown by the wholesomeness of sago, 
 tapioca, and arrowroot, which consist simply of starch, and are prepared for 
 food by heating them with water to the point at which the granules burst. 
 
 Arrow-root is the starch extracted from the root of the Maranta arun- 
 dinacea, and of some other tropical plants. 
 
 In the preparation of tapioca and sago, the starch is dried at a tem- 
 perature above 140 F., so that it loses its ordinary farinaceous appearance 
 and becomes semi-transparent. 
 
486 CONVERSION OF STARCH INTO DEXTRINE. 
 
 Sago is manufactured from the pith, of certain species of palm, natives 
 of the East Indian islands. The tree is split so as to expose the pith, 
 which is mixed with water, and the starch having been separated from 
 the woody fibre in the usual manner, is pressed through % a perforated 
 metallic plate, which moulds it into small cylinders ; these are placed in a 
 revolving vessel and broken into rough spherical grains, which are steamed 
 upon a sieve, and dried. 
 
 Tapioca is obtained from the roots of the Jatropha manihot, a native 
 of America. The roots are peeled and subjected to pressure, which 
 squeezes out a juice employed by the Indians to poison their arrows, and 
 containing a deleterious substance which has been named jatrophine. 
 When the juice is allowed to stand, it deposits starch, which is well 
 washed, pressed through a colander, and dried at 212 F. 
 
 358. Dextrine. "When starch is heated in an oven to about 400 F. 
 for an hour or two, it becomes easily soluble in cold water, yielding a 
 solution having all the properties of gum ; the starch has indeed been 
 converted into a new substance known as dextrine or British gum, which 
 is largely used by calico-printers for thickening their colours, and is sub- 
 stituted for ordinary gum in many other applications. There is a current 
 anecdote which attributes the discovery of dextrine to a conflagration at 
 a starch-factory, where the work-people, who assisted in quenching the 
 fire, observed the gummy properties of the water which had been thrown 
 over the torrefied starch. In toasting bread, a portion of the starch is 
 converted into dextrine, which is dissolved by the water in the prepara- 
 tion of toast and water. 
 
 It is very remarkable that the composition of dextrine (C I2 H 10 10 ) is 
 precisely that of starch; they are isomerw bodies, so that the difference in 
 their properties must be ascribed to a difference in the arrangement of 
 their component particles ; the name of dextrine was conferred upon this 
 gummy substance on account of the power possessed by its solution of 
 causing a right-handed rotation in a ray of polarised light. When oxidised 
 by nitric acid, dextrine, like starch, is converted into oxalic acid, a cir- 
 cumstance distinguishing it from ordinary gum, which furnishes mucic 
 acid when acted upon by nitric acid. 
 
 Dextrine is usually prepared on the large scale by moistening 10 parts 
 of starch with 3 parts of water acidulated with T J^th of nitric acid ; the 
 mixture is allowed to dry, and spread upon trays in an oven, where it is 
 heated for an hour or so to 240 F. The nitric acid thus allows the 
 starch to be converted into dextrine at a temperature which would be 
 quite inadequate to effect the transformation of starch alone. 
 
 This power of accelerating the conversion of starch into dextrine is 
 shared by all acids. Hence if starch be boiled with water, and the viscid 
 liquid so obtained be mixed with an acid, and again boiled, it gradually 
 becomes thinner, and is eventually converted into dextrine. The change 
 is very readily effected by boiling the starch solution with a few drops of 
 sulphuric acid, and the gradual conversion of the starch may be traced by 
 means of an aqueous solution of iodine. On adding this solution to a por- 
 tion of the (cold) solution of starch, it produces the usual dark blue 
 colour; but on adding it, at intervals, to portions of the acidulated and 
 boiled liquid, taken away and cooled for the purpose, the blue colour will 
 be replaced by a peculiar vinous purple tint which iodine imparts to solu- 
 tions of dextrine. 
 
GERMINATION OF SEEDS. 487 
 
 The solution of iodine is much used in proximate organic analysis as a 
 test for starch, and it is necessary to bear in mind that the blue colour is 
 bleached by alkalies (which take up the iodine) and by heat, though, in 
 the latter case, it may be restored by cooling the liquid. The blue colour 
 does not appear to be due to the formation of any definite chemical com- 
 pound with the starch, but rather to a mechanical adhesion of very finely 
 divided iodine to the particles of starch. The sensitiveness of starch to 
 the action of free iodine has given rise to its application in the preparation 
 <of paper for the prevention of forgery in bankers' cheques, &c. If paper 
 be impregnated with a mixture of iodide of potassium and starch, which 
 is perfectly white, it will acquire an intense blue colour on the application 
 of any of the bleaching agents (chlorine, hypochlorous acid, chlorides of 
 lime and soda), generally used for removing ink, as these liberate the 
 iodine, which immediately blues the starch. 
 
 If the ebullition of the dextrine in contact with the sulphuric acid be 
 continued, the solution entirely loses its property of being coloured by 
 iodine, and acquires a sweet taste, the dextrine having been converted into 
 glucose or grape-sugar (C 12 H 14 14 ) by assimilating the elements of four 
 equivalents of water* 
 
 C 12 H,,0 10 + 4HO = C 12 H 14 14 . 
 
 Dextrine. Grape-sugar. 
 
 359. Germination of seeds Malting. This tendency of starch to com- 
 bine with the elements of water and pass into grape-sugar, will be found 
 of immense importance in the chemistry of vegetation, as well as in that of 
 food. It is, indeed, the chief chemical change concerned in the develop- 
 ment of living from inanimate matter, being one of the first processes 
 involved in the germination of a seed the first step in the production of 
 vegetables, which must precede the animals whose food they compose. 
 
 The components of all" seeds are similar to those of wheat, which have 
 been enumerated above ; and if they be perfectly dried immediately after 
 their removal from the parent plant, they may be preserved for a great 
 length of time unchanged, and without losing the power of germinating under 
 favourable circumstances. The essential conditions of germination are the 
 presence of air and moisture, and a certain temperature, which varies with 
 the nature of the seed. These conditions being fulfilled, the seed absorbs 
 oxygen from the air, and evolves carbonic acid, produced by the combina- 
 tion of the oxygen with the carbon of one or more of the most alterable 
 constituents of the seed, such as the vegetable albumen or the gluten. 
 This process of oxidation is attended with evolution of heat, which serves 
 to maintain the seed at the degree of warmth most favourable to germina- 
 tion. The component particles of the albumen or gluten having been set 
 in motion by the action of the atmospheric oxygen, induce a movement or 
 chemical change in the starch with which they are in contact, causing it 
 to pass into dextrine and grape-sugar, which, unlike the starch, being 
 perfectly soluble in water, are capable of affording to the developing shoot, 
 the carbon, hydrogen, and oxygen which it requires for the increase of its 
 frame. The production of grape-sugar and of dextrine in germination is 
 
 * There is some reason to believe that the formation of grape-sugar from starch results 
 from a change similar to that by which it is obtained from salicine and other glucosides. 
 Thus 
 
 C 24 H 20 20 + 4HO = C, 2 H 10 10 + C 12 H 14 14 
 2 eqs. starch. Dextrine. Glucose.- 
 
488 PROCESS OF MALTING. 
 
 well illustrated by the sweet gummy character of the bread made from 
 sprouted wheat, and is turned to practical account in the process of malting. 
 
 During the germination of all seeds, there is formed, apparently by the 
 oxidation of one of the more alterable constituents, a peculiar substance 
 containing carbon, hydrogen, nitrogen, and oxygen, which has never yet 
 been obtained from any other source, and is characterised by its remark- 
 able property of inducing the conversion of starch into dextrine and grape- 
 sugar. 
 
 This substance has been termed diastase (Scao-racris, dissension; metaph. 
 fermentation), but has never yet been obtained in a state of sufficient 
 purity to enable its formula to be satisfactorily determined. It may be 
 extracted, however, from malt, by grinding it, and mixing it with half 
 its weight of warm water, which dissolves the diastase ; the solution 
 squeezed out of the malt is heated to about 170 F., filtered from any 
 coagulated albumen, and mixed with absolute alcohol, which precipitates 
 the diastase in white flakes. One part of diastase dissolved in water is 
 capable of inducing the conversion of 2000 parts of starch into dextrine 
 and grape-sugar, the diastase itself being exhausted in the process. A 
 temperature of about 150 F. is most favourable to the action of diastase, 
 which may be arrested entirely by raising the liquid to the boiling 
 point. 
 
 The great importance of diastase in the arts of the brewer and distiller 
 is at once apparent. In the process of malting barley, the grain is soaked 
 in water, and afterwards spread out in thin layers upon the floor of a dark 
 room (thus imitating the natural condition under which the seed germi- 
 nates), which is maintained as nearly as possible at a constant and moderate 
 temperature (between 55 and 62 F.) ; spring and autumn are, therefore, 
 more favourable to malting than summer and winter. It soon evolves 
 heat, and the grains begin to swell \ in the course of twenty-four hours 
 the germination commences, and the radicle makes its first appearance as 
 a whitish protuberance ; the grain is turned two or three times a-day, in 
 order to equalise the temperature. In about a fortnight, the radicle has 
 grown to about half an inch, by which time a sufficient quantity of dias- 
 tase has been formed. In order to prevent the germination from proceeding 
 further, the grain is killed by drying it at a temperature of 90 E. on per- 
 forated metallic plates, where it is afterwards heated to about 140 F., so 
 as to render it brittle, after which it is sifted in order to separate the 
 radicle, which is now easily broken off. This radicle is found, to contain 
 as much as th of the total quantity of the nitrogen present in the barley, 
 so that the malt dust, as the siftings are called, forms a valuable manure. 
 
 100 parts of barley generally yield about 80 parts of malt, but a part of 
 the loss is due to water present in the barley, so that 100 parts of dry 
 barley yield 90 parts of malt, and 4 parts of malt dust, the difference, viz., 
 6 parts, representing the weight of the carbon converted into carbonic acid, 
 of the hyolrogen (if any) converted into water during the germination, and 
 of soluble matters removed from the barley in steeping. Malt contains 
 about -g- J-g-th of its weight of diastase, far more than enough to ensure the 
 conversion of the whole of its starch into sugar. 
 
 The following table* illustrates the change in composition suffered by barley 
 during the process of malting, leaving the moisture out of consideration : 
 
 * Lawes ; Report on the Relative Values of Unmalted and Malted Barley as Food for 
 Stock. 1866. ' 
 
CHEMISTRY OF BREWING. 
 
 489 
 
 
 Barley. 
 
 After 
 steeping. 
 
 14 days 
 on floor. 
 
 Malt after 
 sifting. 
 
 Malt Dust. 
 
 Sugar, . 
 
 2-56 
 
 1-56 
 
 12-14 
 
 11-01 
 
 11-35 
 
 Starch v ' f " V 
 
 
 
 
 
 
 Dextrine, . . . . J 
 
 80-42 
 
 81-12 
 
 70-09 
 
 72-03 
 
 43-68 
 
 Woody fibre, . . .','. . 
 
 4-69 
 
 6-22 
 
 5-03 
 
 4-84 
 
 9-67 
 
 Albuminous matter, 
 
 9-83 
 
 9-83 
 
 10-39 
 
 9-95 
 
 26-90 
 
 Mineral matter, . . . 
 
 2-50 
 
 2-27' 
 
 2-35 
 
 2-17 
 
 8-40 
 
 
 100-00 
 
 100-00 
 
 100-00 
 
 100-00 
 
 100-00 
 
 360. Brewing. In order to prepare beer, the brewer mashes the 
 ground malt with water at about 180 F. for some hours, when the dias- 
 tase induces the conversion, into dextrine and sugar, of the greater part of 
 the starch which has not been so changed during the germination, and 
 the wort is ready to be drawn off for conversion into beer. 
 
 The undissolved portion of the malt, or brewers' grains, still contains 
 a considerable quantity of gluten, and is employed for feeding pigs. 
 
 That malt contains far more diastase than is necessary to convert its 
 starch into sugar, is shown by adding a little infusion of malt to the 
 viscid solution of starch, and maintaining it at about 150 F. for a few 
 hours, when the mixture will have become far more fluid, and will no 
 longer be coloured blue by solution of iodine. In distilleries, advantage 
 is taken of the excess of diastase in malt, by adding 3 or 4 parts of 
 unmalted grain to it, when the whole of the starch in this latter is also 
 converted into dextrine and sugar, and the labour and expense of malting 
 it are avoided. 
 
 The wort obtained by infusing malt in water contains not only grape- 
 sugar, dextrine, and diastase, but a considerable quantity of nitrogenised 
 matter formed from the gluten of the barley. Before subjecting it to 
 fermentation, it is boiled with a quantity of hops, usually amounting to 
 about ^ih of the weight of the malt employed, which is found to prevent, 
 in great measure, the tendency of the beer to become sour in consequence 
 of the conversion of the alcohol into acetic acid. 
 
 The hop contains about 10 per cent, of an aromatic yellow powder, 
 called lupuline, which appears to be the active portion, and which con- 
 tains a volatile oil of peculiar odour, together with a very bitter substance. 
 
 The hopped wort is run off into a vat, where it is allowed to deposit 
 the undissolved portion of the hops, and the clear liquor is drawn" off into 
 shallow coolers, where its temperature is lowered as rapidly as possible to 
 about 60 F., the cooling being usually hastened by cold water circulating 
 through pipes which traverse the coolers. If the wort be cooled too 
 slowly, the nitrogenised matter which it contains undergoes an alteration 
 by the action of the air, in consequence of which the beer is very liable 
 to become acid. 
 
 The wort is now transferred to the fermenting tun, where it is made to 
 ferment by the addition of yeast, usually in the proportion of T-^th of 
 its volume. 
 
 Yeast is a minute fungoid vegetable, which grows in solutions contain- 
 ing sugar together with some nitrogenised substance (e.g., a salt of 
 ammonia), and the salts (phosphates of potash, soda, lime, and magnesia), 
 
490 YEAST FERMENTATION. 
 
 f 
 
 which are essential constituents of its cells. It is only recently that the 
 conditions under which the yeast plant grows have been ascertained, and 
 the seeds or germs from which it originates have hitherto eluded detection, 
 though it may be remarked that in this respect it only resembles some of 
 the lower mosses, the vegetable character of which has never been called 
 in question. 
 
 If a little white of egg, cheese, or a piece of flesh (all of which contain 
 carbon, hydrogen, nitrogen, oxygen, and phosphates), be placed in a solu- 
 tion of sugar, and allowed to undergo decomposition, a grey scum forms 
 upon the liquid, which is seen under the microscope to consist of irregu- 
 larly oval cells, the growth of which may be watched under the microscope 
 in a little of the liquid from which they were obtained, when they will 
 be found to multiply rapidly by the production of new cells on all sides 
 of them (fig. 272). The same cells will be developed very rapidly in the 
 
 sweet wort of malt, allowed to undergo decom- 
 position between 60 and 70 F. 
 
 These cells contain a substance somewhat 
 resembling albumen, enclosed in a thin mem- 
 brane, the composition of which is similar to 
 that of cellulose. They also contain a peculiar 
 nitrogenised body resembling diastase, and 
 capable of inducing the conversion of cane- 
 sugar (C 12 H ]1 ]1 ) into grape-sugar (C 12 H U 14 ). 
 Accordingly, when yeast is added to a solution 
 of cane-sugar, the liquid is found to increase 
 in specific gravity (a solution of cane-sugar 
 having a lower density than one containing 
 Fig. 272. an equivalent quantity of grape-sugar), pre- 
 
 viously to the commencement of fermentation, 
 
 and the application of tests readily proves the presence of grape-sugar in 
 the solution. 
 
 The grape-sugar then undergoes the decomposition known as alcoholic 
 fermentation, which results in the production of alcohol, carbonic acid, 
 lactic acid, succinic acid, glycerine, and a peculiar brown soluble matter, 
 together with other substances, the true nature of which is yet undeter- 
 mined. The fermentation is attended with a considerable elevation of 
 temperature. 
 
 Taking into consideration only the alcohol and carbonic acid, which are 
 the chief products, their formation from grape-sugar may be represented 
 by the equation 
 
 C 12 H 14 14 = 2C 4 H 6 2 + 4C0 2 . + 2HO. 
 
 Grape-sugar. Alcohol. 
 
 During the fermentation, the yeast cells are gradually broken up, so 
 that a given quantity of yeast is capable of fermenting only a limited 
 quantity of sugar. On an average, a quantity of yeast containing between 
 two and three parts of solid matter is required to complete the fermenta- 
 tion of 100 parts of sugar. The solution remaining after the fermenta- 
 tion is found to contain salts of ammonia, which have been formed at 
 the expense of the nitrogen of the yeast. 
 
 If the liquid in which the yeast excites fermentation contain nitro- 
 genised matters and phosphates, the yeast plant grows, and its quantity 
 increases ; thus in the sweet wort from malt, the yeast is nourished by 
 
COMPOSITION OF BEER. 
 
 491 
 
 the altered gluten and by the phosphates, so that it increases to six or 
 eight times its original weight. 
 
 If yeast be heated to the boiling point of water, the plant is killed, as 
 might be expected, and loses its power of inducing alcoholic fermentation ; 
 but it may be dried at a low temperature, or by pressure, without losing 
 its fermenting power, and dried yeast is an article of commerce. 
 
 Yeast will not cause fermentation in a solution containing more than 
 one-fourth of its weight of sugar, and the fermentation is arrested when 
 ' the alcohol amounts to one-fifth of the weight of the liquid, so that the 
 strength of fermented liquors could never exceed 20 per cent of alcohol. 
 The fermentation is also arrested by the mineral acids, and by many of 
 the substances to which antiseptic properties are commonly attributed, 
 such as common salt, kreasote, corrosive sublimate, sulphurous acid, tur- 
 pentine, &c. 
 
 In the fermentation of beer, the yeast is carried up to the surface by the 
 effervescence due to the escape of the carbonic acid, and is eventually 
 removed, in order to be employed for the fermentation of fresh quantities 
 of wort. 
 
 When the fermentation has proceeded to the required extent, the beer 
 is stored for consumption. 
 
 It will be seen that the chief constituents of beer are the alcohol, the 
 nitrogenised matter derived from the gluten of the barley, and not con- 
 sumed in the growth of the" yeast, the unaltered sugar and dextrine, the 
 brown or yellow colouring matter formed during the fermentation, the 
 essential oil and bitter principle of the hop. 
 
 Beer also contains acetic acid (formed by the oxidation of the alcohol, 
 p. 492), free carbonic acid, which gives its sparkling character, together 
 with the lactic and succinic acids and glycerine, formed as secondary pro- 
 ducts of the fermentation, and ammoniacal salts derived from the yeast. 
 The soluble mineral substances from the barley are also present, minus 
 the phosphates abstracted by the yeast. 
 
 The proportions of the constituents of course vary greatly, as will be 
 seen from the following examples : 
 
 Percentage of 
 
 Allsopp's 
 Ale. 
 
 Bass's Ale. 
 
 Strong Ale. 
 
 Whitbread's 
 Porter. 
 
 Whitbread's 
 Stout. 
 
 Alcohol 
 
 6-00 
 
 7-00 
 
 8-65 
 
 4-20 
 
 6-00 
 
 Acetic acid, .... 
 
 0-20 
 
 0-18 
 
 0-12 
 
 0-19 
 
 0-18 
 
 Sugar and other solid ) 
 matters, . . . . / 
 
 5-00 
 
 4-80 
 
 6-60 
 
 5-40 
 
 6-38 
 
 
 
 The dark colour of porter and stout is caused by the addition of a 
 quantity of high-dried malt which has been exposed to so high a tempera- 
 ture in the kiln as to convert a portion of its sugar into a dark brown 
 soluble substance called caramel. It is said that alum and sulphate of 
 iron are also added to porter and stout to cause them to froth strongly. 
 The peculiar aroma of beer is probably duo to the presence of a minute 
 quantity of some fragrant ether, produced during the fermentation. 
 
 In some cases, when the operation of brewing has been badly con- 
 ducted, the beer becomes ropy, or undergoes the viscous fermentation. In 
 this case the sugar suffers a peculiar transformation, resulting in the pro- 
 duction of a mucilaginous substance resembling gum in its composition. 
 This change may be induced in sugar by yeast which has been boiled, or 
 
492 MANUFACTURE OF VINEGAR. 
 
 by water in which flour or rice has been steeped. White wines occa- 
 sionally become ropy from a similar cause, but red wines are not liable to 
 this change, apparently because the tannin which they contain has preci- 
 pitated in an insoluble form the ferment which induces it. During this 
 viscous fermentation a part of the sugar is often converted into mannite 
 (C 12 H 14 12 ). 
 
 361. ACETIFICATION MANUFACTURE OF VINEGAR. Beer which has 
 become sour is often said to have undergone the acetous fermentation ; but 
 this is not strictly correct, the change being more similar to decay, since 
 it is one in which the oxygen of the air directly takes part. The acidity 
 of sour beer is caused by the acetic acid (C 4 H 4 4 ) formed by the action of 
 atmospheric oxygen upon the alcohol, according to the equation 
 
 C 4 H 6 2 + 4 = C 4 H 4 4 + 2HO. 
 
 Alcohol. Acetic acid. 
 
 Pure alcohol may be exposed to the air, either alone or when mixed with 
 water, for any period, without suffering oxidation ; but when in contact 
 with certain changeable organic substances, the alcohol undergoes oxida- 
 tion, and is converted into acetic acid. It is upon this circumstance that 
 the different methods of producing vinegar are based. 
 
 The most direct application of this principle is made in the so-called 
 quick vinegar process in use in continental countries where alcohol is 
 free of duty. Alcohol of about 80 per cent, is mixed with 6 parts of 
 
 water, and with about ToSo-th part 
 of yeast, or some other alterable sub- 
 stance containing nitrogen. This mix- 
 ture is heated to about 80 F., and 
 caused to trickle slowly from pieces of 
 cord fixed in a perforated shelf over a 
 quantity of wood shavings* previously 
 soaked in vinegar, which is found 
 materially to assist the acetification, 
 and packed in a tall cask (fig. 273), 
 in which holes have been drilled in 
 order to allow the entrance of air. The 
 oxidation of the alcohol soon raises the 
 temperature to about 100 F., which 
 Fig. 273. occasions a free circulation of air 
 
 among the shavings. The mixture is 
 
 passed three or four times through the cask, and in about 36 hours the 
 conversion into vinegar is completed. The oxidation of the alcohol in 
 this process is found to be arrested by the presence of essential oils, or of 
 kreasote, and similar antiseptic substances. 
 
 The necessity of affording a full supply of atmospheric air was not 
 appreciated until Liebig had proved the existence of an intermediate stage 
 in the process, consisting in a partial oxidation of the alcohol by which 
 it became converted into aldehyde (C 4 H 4 2 ), an extremely volatile liquid 
 (boiling at 70 F.), which was lost in the form of vapour, thus greatly 
 diminishing the proportion of vinegar obtained 
 
 C 4 H 6 2 + O a = C 4 H 4 2 + 2HO. 
 
 Alcohol. Aldehyde. 
 
 * These shavings appear to favour the process by serving as points of attachment for a 
 microscopic vegetable, which encourages the oxidation of the alcohol. 
 
GLUTEN VEGETABLE FIBRINE. 493 
 
 If a sufficient quantity of atmospheric air be supplied, the production of 
 aldehyde is entirely avoided. 
 
 White wine vinegar is prepared in France from light wines by a process 
 of much longer duration. A little boiling vinegar is poured into a cask, 
 partially open at the top, together with four or five gallons of white wine 
 which has been allowed to trickle over wood shavings. In a few days, 
 during which the temperature is maintained at about 80, a fresh quantity 
 of wine is poured in, and in the course of a fortnight half the vinegar con- 
 tained in the cask is drawn off, and replaced by a fresh portion of wine. 
 In this way an occasional renewal of the air in the upper part of the cask 
 is provided for. The acetification is found to proceed more rapidly in old 
 casks than in new ones, which is attributed to the presence of a peculiar 
 conferva deposited upon the sides of the former, and styled mother of 
 vinegar. It is probably for a similar reason that the acetification is pro- 
 moted by the addition of ready-made vinegar at the commencement of the 
 process. 
 
 In this country vinegar is chiefly prepared from malt, the infusion of 
 which is allowed to undergo the alcoholic and acetous fermentation. 
 
 Vinegar contains on an average about 5 per cent, of acetic acid, together 
 with small quantities of vegetable and mineral substances, varying with 
 the source from which it was obtained. Its pleasant aroma is due to the 
 presence of some acetic ether (C 4 H 5 . C 4 H 3 3 ) formed during its manu- 
 facture. The vinegar of commerce is allowed to be mixed with YoVo-th 
 of its weight of sulphuric acid in order to prevent it from becoming 
 mouldy. 
 
 BREAD. 
 
 362. The chemistry of fermentation is intimately connected with the ordi- 
 nary process of bread-making. It will be remembered that wheaten flour 
 (p. 484) consists, essentially, of starch and gluten, with a little dextrine 
 and sugar. On mixing the flour with a little water, it yields a dough, the 
 tenacity of which is due to the gluten present in -the flour. If this dough 
 be tied up in a piece of fine muslin, and kneaded under a stream of water, 
 the starch will be suspended in the water, and will pass through the 
 muslin, whilst the gluten will remain as a very tough elastic mass, which 
 speedily putrefies if exposed to the air in a moist state, and dries up to a 
 brittle horny mass at the temperature of boiling water. 
 
 On analysis, gluten is found to contain carbon, hydrogen, nitrogen, and 
 oxygen, in proportions which may be represented by the empiricarformula 
 C.^H.^l^Oy, though it cannot be regarded as a single independent sub- 
 stance, but as a mixture of three substances very closely allied in compo- 
 sition. 
 
 When gluten is boiled with alcohol, one portion refuses to dissolve, and 
 has been named vegetable fibrine, from its resemblance to the substance 
 forming the muscles of animals. When the solution in alcohol is allowed 
 to cool, it deposits a white flocculent matter, very similar to the caseine 
 which composes the curd of milk. On adding water to the cold alcoholic 
 solution, a third substance (glutine) is separated, which much resembles 
 the albumen found so abundantly in the blood. 
 
 The presence in gluten of three substances, similar to the three principal 
 components of the animal body, leads us to form a high opinion of its 
 
494 PROCESS OF BREAD-MAKING. 
 
 value as a nutritive compound. But gluten itself, separated from the flour 
 by the process above described, would be found very difficult of digestion, 
 on account of its resistance to the solvent action of the fluids in the 
 stomach ; indeed, the dough composed of flour and water is proverbially 
 indigestible, even when baked. In order to render it fit for food, it must 
 be rendered spongy or porous, so as to expose a larger surface to the action 
 of the digesting fluids of the body ; the most direct method of effecting 
 this is the one adopted in the manufacture of the aerated bread, and con- 
 sists in mixing the flour with water which has been highly charged, under 
 pressure, with carbonic acid gas ; the mixing having been effected in a 
 strong closed iron vessel, an aperture in the lower part of this is opened, 
 when the pressure of the accumulated gas forces the dough out into the 
 air, and the gas which had been imprisoned in the dough expands, con- 
 ferring great porosity and sponginess upon the mass in its attempt to 
 escape. In another process for preparing unfermented bread, the flour is 
 mixed with a little bi-carbonate of soda, and is then made into a dough 
 with water acidulated with hydrochloric acid ; the latter decomposing 
 the bi-carbonate of soda, liberates its carbonic acid, which renders the 
 bread porous. The chloride of sodium formed at the same time remains 
 in the bread. In the preparation of cakes and pastry, the same object is 
 sometimes attained by adding carbonate of ammonia to the dough. When 
 heat is applied, in the baking, the salt is converted into vapour which 
 distends the dough. 
 
 In the common process of bread-making, however, the carbonic acid 
 destined to confer sponginess upon the dough is evolved by the fermenta- 
 tion of the sugar contained in the flour ; the latter having been kneaded 
 with the proper proportion (usually about half its weight) of water, a little 
 yeast and salt are added, and the mixture is allowed to stand at a tempera- 
 ture of about 70 F. for some hours. The dough swells or rises considerably, 
 in consequence of the escape of carbonic acid, the sugar being decomposed 
 into that gas and alcohol, as in ordinary fermentation. The spongy dough 
 is then baked in an oven, heated to about 500 F., when a portion of the 
 water and the whole of the alcohol are expelled, the carbonic acid being 
 also much expanded by the heat, and the porosity of the bread increased. 
 The granules of starch are much altered by the heat, and become far more 
 digestible. Although the temperature of the inside of the loaf does not 
 exceed 212 F. the outer portion becomes dry and hard, the hottest part 
 being even torrefied or scorched into crust. 
 
 Occasionally, instead of yeast, leaven is employed, in order to ferment 
 the sugar, leaven being dough which has been left in a warm place until 
 decomposition has commenced. 
 
 The passage of new into stale bread does not depend, as was formerly 
 supposed, upon the drying of the bread consequent upon its exposure to 
 air, but is a true molecular transformation which takes place equally well 
 in an air-tight vessel, and without any loss of weight. It is well known 
 that when a thick slice of stale bread is toasted, which dries it still 
 further, the crumb again becomes soft and spongy as in new bread ; and 
 if a stale loaf be again placed in the oven, it is entirely reconverted into 
 new bread. 
 
 Wheaten flour is particularly well fitted for the preparation of bread on 
 account of the great tenacity of its gluten. Next to wheat in this respect 
 stands rye, whilst the other cereals contain a gluten so deficient in tena- 
 city that it is impossible to convert them into good bread. 
 
PRODUCTION OF GRAPE-SUGAR FROM STARCH. 495 
 
 Even in wheaten flour the tenacity of the gluten is liable to variation, 
 and in order to obtain good bread from a flour the gluten of which is 
 inferior in this respect, it is customary to employ a minute proportion of 
 alum. This addition being considered unwholesome by some persons, it 
 would be better to substitute lime-water, which has been found by Liebig 
 to have a similar effect. Sulphate of copper improves in a very striking 
 manner the quality of the bread prepared from inferior flour, but this 
 salt is far more objectionable than alum. 
 
 THE SUGARS. 
 
 363. The conversion of starch into grape-sugar, when heated in contact 
 with diluted acids (p. 487), is taken advantage of for the preparation of 
 this variety of sugar on the large scale. For this purpose, water acidulated 
 with T ^-oth of sulphuric acid is heated to ebullition, and a hot mixture of 
 starch and water allowed to flow gradually into it, so as not to reduce its 
 temperature below the boiling point. The mixture is kept boiling for 
 half-an-hour, after which chalk is added in small portions at a time to 
 neutralise the sulphuric acid, and the sulphate of lime having been 
 allowed to subside, the clear syrup is drawn off, and evaporated to the 
 crystallising point. 
 
 The grape-sugar or glucose thus manufactured cannot be employed as a 
 substitute for the sugar extracted from the sugar-cane, on account of its 
 greatly inferior sweetening power, which is less than half that possessed 
 by cane-sugar. It is, moreover, far less soluble in water, 1 part of grape- 
 sugar requiring 1^ part of water to dissolve it, whilst cane-sugar requires 
 only i part. Grape-sugar is employed, however, for the adulteration of 
 cane-sugar ; and the very crystalline, nearly white samples of moist sugar 
 met with in the shops, arB usually largely adulterated in this way. The 
 fraud is easily detected by boiling a portion of the sample with a little 
 solution of potash, when the grape-sugar is decomposed, and colours the 
 liquid intensely brown, pure cane-sugar giving very little brown colour 
 unless boiled for a long time. A more delicate mode of detection consists 
 in adding to a solution of the sugar a few drops of solution of sulphate of 
 copper, and enough solution of potash to form an intensely blue liquid. 
 The oxide of copper is not precipitated in the presence of either of the 
 sugars ; but if the blue liquid be very gently heated, a red precipitate of 
 suboxide of copper will separate if grape-sugar be present, whilst with 
 pure cane-sugar the precipitation does not take place unless the solution 
 is boiled. 
 
 Even cellulose is transformed into dextrine and grape-sugar under the 
 influence of sulphuric acid. If linen, calico, cotton-wool, or paper be 
 dried, and gradually moistened with 1J part of concentrated sulphuric 
 acid, avoiding elevation of temperature, it is converted in the course of a 
 few hours into a gummy mass which dissolves in water, and is very 
 similar to dextrine. When the cellulose has been left in contact with 
 the acid for a day or two, it should be dissolved in a large quantity of 
 water, and boiled for 8 or 10 hours in order to effect the conversion into 
 sugar ; the acid may then be neutralised with chalk, the solution filtered 
 from the sulphate of lime, and evaporated, when it furnishes a crystalline 
 mass of grape-sugar. 
 
 Closely connected with the conversion of cellulose into dextrine by 
 
496 SUGAR OF FRUITS. 
 
 contact with strong sulphuric acid, is that very remarkable change of 
 paper into vegetable parchment. If dry white blotting-paper be drawn 
 through a cooled mixture of the strongest oil of vitriol with half its bulk 
 of water, and be then thoroughly washed in a large volume of water, it 
 becomes five times as strong as before, and has Jths of the strength of 
 ordinary animal parchment. The parchment paper, when dry, is found 
 to have suffered no alteration in weight, and analysis shows its composi- 
 tion to be unchanged. This remarkable increase in strength must, there- 
 fore, be referred to a molecular alteration. The paper is also found to 
 have become almost waterproof, and presents a somewhat translucent 
 appearance like paper which has been slightly oiled. It receives many 
 useful applications, for luggage labels which are not easily torn or re- 
 moved by rain, and as a substitute for animal membrane in tying over 
 preserves, &c. 
 
 This susceptibility of conversion into grape-sugar possessed by starch 
 and cellulose, affords a very important clue in tracing the changes which 
 take place in living vegetables. It has been already seen (p. 487) that 
 during the germination of seeds, their starch is converted into sugar, in 
 order that it may be carried in a soluble form to the extending limbs 
 of the vegetable frame ; but it would appear that in these parts, where 
 a deposition of cellulose is required, the sugar (C 12 H U 14 ) is reconverted 
 into that substance (C 12 H 10 10 ). In the ripening of the fruit, how- 
 ever, the ligneous matter and the starch seem to be again converted 
 into sugar, under the influence of the vegetable acids which unripe fruits 
 contain. 
 
 Strictly speaking, the sugar contained in ripe fruits and in new honey 
 is not grape-sugar (C 12 H 14 14 ), but a distinct variety of sugar known as 
 fruit sugar or fructose, and having the composition (C^H^O^). This 
 sugar has also been designated, in reference to its characteristic feature, 
 uncrystallisable sugar, and its production seems to constitute an inter- 
 mediate stage in the transition of starch, cellulose, and cane-sugar into 
 grape-sugar. Hence it is found that if the ebullition with diluted sul- 
 phuric acid be arrested as soon as the liquid becomes sweet, no crystals 
 can be obtained, but on further ebullition, the fructose is converted into 
 crystallisable glucose. When honey is kept for some time, the fructose 
 gradually becomes converted into a crystalline mass of glucose. The 
 same change is seen to take place in raisins, which contain granules of 
 glucose, though the fresh grapes contain only fructose. 
 
 The uncrystallisable sugar forms the chief ingredient of molasses and 
 treacle, for although the fresh juice of the sugar-cane contains no fructose, 
 the treatment to which it is subjected in the extraction of the sugar occa- 
 sions a copious formation of the uncrystallisable sugar at the expense of 
 the cane-sugar. The simple ebullition of a solution of cane-sugar for a 
 considerable period is said to convert a portion of it into fructose, and if 
 a minute quantity of any uncombined acid be present, the change takes 
 place very rapidly. 
 
 364. Extraction of cane-sugar. In the extraction of sugar from the 
 sugar-cane, the latter is cut before the period of flowering, when, as might 
 be expected, this soluble nutriment of the plant is most abundant. For 
 a similar reason, the canes are cut off close to the ground, since in the 
 higher joints of the cane much of the sugar has already been consumed 
 for their development. 
 
MANUFACTURE OF SUGAR. 497 
 
 A specimen of sugar-cane from Martinique was found to contain : 
 
 Juice, .... 90-1 
 Woody fibre, . . 9-9 
 
 100-0 
 
 So that, theoretically, 100 parts of cane should yield as much as 90 parts 
 of juice. The canes are crushed between iron cylinders, which express, 
 under the best arrangements, only 65 parts of juice from 100 of cane. It 
 has been found possible to increase the yield by steaming the canes before 
 submitting them to a final pressure. The juice thus expressed contains 
 about 18 per cent, of sugar, together with the usual components of the 
 sap of plants, such as vegetable acids, albumen, salts, &c. 
 
 In the tropical climate in which the extraction is conducted, the albu- 
 men of the juice speedily alters when exposed to the air, and excites 
 fermentation in the sugar, by which a considerable quantity would be 
 lost. If the fresh juice were heated to coagulate the albumen, the free 
 acid contained in it would change a portion of the sugar into the uncrys- 
 tallisable variety. To avoid this, the juice is mixed with $^th part of 
 slaked lime, and is then heated to 140 F. in large flat copper pans. The 
 coagulated albumen rises to the surface of the heavy syrup, and forms a 
 thick scum, which is taken off, and the clear syrup is evaporated till it is 
 strong enough to crystallise, when it is run off into shallow wooden vats, 
 and allowed to cool for 24 hours. When briskly stirred, it congeals to a 
 semi-solid mass of crystals, which are allowed to drain for three weeks in 
 casks with perforated bottoms. The raw sugar thus obtained, after dry- 
 ing in the sun, is sent into commerce, the drainings being styled molasses 
 or treacle. The weight of raw sugar seldom exceeds T V^ n f the J u i ce > 
 that is, about half the quantity which the juice is known to contain, 
 the remainder having been converted into uncrystallisable sugar during 
 the process of extraction. The loss is found to be materially dimi- 
 nished by the use of vacuum parts, in which the evaporation of the 
 syrup is conducted under diminished pressure, and therefore at a lower 
 temperature. Greater economy is also introduced into the manufacture by 
 the use of the crushed canes as fuel for the evaporating fires, and by re- 
 storing their ashes to the land as food for ensuing crops. The skimmings 
 of the clarified juice are also advantageously used as manure. 
 
 The raw sugar obtained by the process just described contains about 
 60 per cent, of pure cane-sugar, the remainder consisting of water, un- 
 crystallisable sugar, colouring matter, and various salts and other foreign 
 substances derived from the cane-juice. 
 
 In the ordinary process of sugar-refining, two or three parts of raw 
 sugar are dissolved in one part of water containing a little lime in solution, 
 and mixed with three or four parts of ground bone-black for every hundred 
 of sugar ; a small quantity of serum of bullock's blood is also generally 
 added. This mixture is heated by the passage of steam through it, 
 when the albumen of the serum is coagulated, and rises to the surface in 
 the form of a scum which entangles the floating impurities as well as the 
 bone-black, and leaves the syrup much lighter in colour, a considerable 
 part of the colouring matter having been removed by the charcoal (p. 59). 
 
 The syrup is then filtered through a thick layer of coarsely powdered 
 bone-black, and is thus rendered perfectly colourless and ready for evapora- 
 tion, which is conducted in a boiler with double sides, so that it may be 
 
 2 i 
 
498 SUGAR REFINING. 
 
 heated by steam admitted between the two, and furnished with a dome 
 from which the air may be exhausted in order to allow the evaporation to 
 be conducted at a lower temperature, as well as out of contact with the 
 atmospheric oxygen, so as to diminish as far as possible the production of 
 uncrystallisable sugar. The boiling down of the syrup, which would 
 require a temperature of 230 F. at the ordinary pressure, may thus be con- 
 ducted at 160 F. When sufficiently evaporated,* the syrup is transferred 
 to a heated vat, where it is stirred until a confused crystallisation com- 
 mences, and is then drawn off into inverted sugar-loaf moulds of iron or 
 earthenware, and allowed to crystallise during about 20 hours. The 
 crystalline mass is then allowed to drain by the withdrawal of a plug at the 
 apex of the inverted cone, and is washed with a little pure syrup to re- 
 move adhering colouring matter, after which the loaf is dried in an oven 
 and finished by turning in a lathe. 
 
 The operation of washing with syrup is often referred to as claying, 
 being sometimes effected by placing some powdered sugar upon the base 
 of each loaf, and over this a cream of pure pipe-clay, the water draining 
 from which dissolves the powdered sugar, and the syrup thus formed 
 washes the loaf. The object of the clay appears to be simply to allow 
 the water to flow gradually through the sugar. 
 
 The process of refining is sometimes shortened by washing the raw sugar 
 with strong syrup, so as to remove the bulk of the impurities at the com- 
 mencement, and a very ingenious method, known as the centrifugal process, 
 has been devised for separating the syrup from the sugar thus washed. 
 The pasty mixture of sugar and syrup is introduced into a cylinder of 
 strong close metallic gauze, which is rapidly turned upon its axis, when 
 the liquid syrup of course flies off through the apertures of the gauze, and 
 is collected by a box surrounding the cylinder. A fresh quantity of syrup 
 is then introduced, and separated in the same manner, so that the washing 
 may be rapidly carried as far as may be deemed expedient. 
 
 365. During the wars of Napoleon, when the importation of sugar into 
 France was suspended, this substance was extracted from the beet-root, 
 and this process still forms a very important branch of French industry. 
 
 The white beet only is employed, on account of the difficulty of separat- 
 ing the colouring matter existing in the juice of the red variety. The 
 juice contains about ten per cent of cane-sugar, half of which only is 
 usually obtained in the crystallised state. The process adopted for ex- 
 tracting it does not differ in principle from that applied to the juice of 
 the sugar-cane. 
 
 Cane-sugar is also extracted in the United States from the sap of the 
 sugar-maple, which is collected, usually in the spring, from deep incisions 
 through the bark, into each of which a pipe of reed or elder is inserted to 
 conduct the juice into pans placed for its reception, whence it is removed 
 before it has had time to become changed by fermentation. The juice is 
 evaporated rapidly, and the raw crystalline mass sold without further 
 refining. On an average, each tree furnishes about six pounds of sugar 
 during the season. 
 
 Sugar-candy consists simply of large rhomboidal prismatic crystals of 
 sugar deposited upon strings stretched across crystallising troughs, in which 
 a strong syrup is slowly evaporated at about 170 F. 
 
 * The state of concentration of the syrup is known by the degree of viscidity which it 
 exhibits between the finger and thumb, by the length of the thread to which it may be 
 drawn, and by the mode in which this curls after breaking. 
 
CHEMICAL PROPERTIES OF THE SUGARS. 499 
 
 Barley-sugar is prepared by evaporating the syrup beyond the crystal- 
 lising point, till it solidifies on cooling, to a vitreous mass, which is poured 
 out on a cold surface and manipulated to the requisite forms. When 
 kept for some time, the transparent barley-sugar becomes crystalline and 
 opaque. 
 
 Caramel (C 12 H 9 9 ) is a dark-brown substance produced by the action of 
 a temperature of about 400 F. upon melted sugar. It is very soluble in 
 water, and gives an intensely brown liquid, for which reason it is employed 
 for colouring sauces, gravies, brandy, wines, &c. 
 
 366. Chemical properties of the sugars. Although cane and grape-sugar appear to 
 be essentially indifferent substances, they are remarkably prone to form combina- 
 tions with many basic metallic oxides. Thus a solution of cane-sugar is capable of 
 dissolving a large quantity of lime, forming a compound (CaO . C 12 H n O u ) which is 
 much more soluble in cold than in hot water, so that on boiling the transparent 
 solution it becomes perfectly opaque, but resumes its transparency on cooling. 
 
 On boiling the hydrated oxide of lead with a solution of sugar, it is dissolved, 
 and as the solution cools, a white powder is deposited, which has the composition 
 2PbO . C 12 H 9 9 + HO, the equivalent of water being expelled at a temperature of 
 212. The composition of this compound would lead to the belief that cane- 
 sugar contains two equivalents of constitutional water, and that its formula should 
 be written C 12 H 9 9 . 2HO. By carefully heating cane-sugar, the compound, 
 C 12 H 10 10 , saccharide, has been obtained, and if this be further heated it yields 
 C 12 H 9 O 9 , caramel. When a solution containing 1 part of salt and 4 parts of sugar 
 is allowed to evaporate spontaneously, it deposits a deliquescent compound con- 
 taining NaCl. 2(C 12 H 9 9 ), 3HO. 
 
 Many metallic oxides form compounds with sugar, which are readily soluble in 
 alkaline liquids, so that the addition of sugar to solutions of the oxides of copper 
 and iron prevents the precipitation of these oxides by the alkalies. 
 
 Grape-sugar also combines with many bases. The compounds which it forms 
 with the alkalies are very unstable, and their solutions, which are at first alkaline, 
 soon become neutral in consequence of the conversion of the grape-sugar into glucic 
 acid (3HO . C 24 H 15 15 ) by the loss of the elements of water. 
 
 By saturating a solution of grape-sugar with common salt, a liquid is obtained which 
 deposits well-defined crystals, having the composition 2(C 12 H 12 12 ) . NaCl . 2HO. 
 When dried at 212 it becomes, 2(C 12 H 12 12 ) . NaCl. The true formula of grape- 
 sugar is obviously C 12 H 12 12 . 2HO, for if it be dissolved in hot strong alcohol (which 
 dissolves far more grape-sngar than cane-sugar) it crystallises on cooling, in prisms, 
 which have the formula C 12 H 12 12 . Two equivalents of water may also be expelled 
 from ordinary grape-sugar at 212 F. 
 
 The action of sulphuric acid upon cane and grape-sugar is very different ; the 
 former is carbonised and completely decomposed, whilst the latter combines with 
 the sulphuric acid to form sulphosaccharic acid, which yields soluble salts with lime 
 and baryta.* 
 
 The optical properties of solutions of the sugars are now often turned to account 
 for their identification, and even for the determination of their quantities. Grape- 
 sugar and cane-sugar both rotate the plane of polarisation of a ray froi left to 
 right, cane-sugar having rather a more powerful action, but the uncrystallisable 
 fruit-sugar rotates the plane in the opposite direction, from right to left. If a solu- 
 tion of cane-sugar, possessing the rotatory power from left to right be heated with 
 hydrochloric acid, it acquires the power of rotating the plane of polarisation from 
 right to left, in consequence of the conversion into uncrystallisable sugar. 
 
 Starch-sugar exhibits three different modes of action upon polarised light, for a 
 solution which has been kept some hours rotates the plane of polarisation only half 
 as much as the freshly made solution ; and if the sugar prepared from malt be dis- 
 solved in water, the solution has thrice the rotatory power which it possesses after 
 being kept, and its rotatory power is one-third higher than that of the freshly 
 dissolved starch-sugar. All these may be reduced at once to the lowest rotatory 
 power by heating them nearly to ebullition and allowing them to cool. 
 
 * Ethyle- glucose, a bitter, fragrant oily substance, has been obtained by acting upon 
 grape-sugar with bromide of ethyle and potash ; it may be represented by the formula 
 C 12 H 8 (C 4 H 5 ) 2 10 . 
 
 2 i2 
 
500 GUN-COTTON PYROXYLINE. 
 
 367. Mannite (C 12 H 14 12 ), the sweet principle of manna (the concrete juice of the 
 Fraxinm ornus), has already been noticed as one of the products of that peculiar kind 
 of fermentation known as the viscous, to which beet-root juice is especially liable. 
 It is also found in certain mushrooms, in sea weeds, celery, asparagus, and onions. 
 By treating manna with hot alcohol, and allowing the filtered solution to cool, the 
 mannite may be obtained in beautiful prismatic crystals, which have a sweet taste, 
 and dissolve readily in water. Mannite differs widely from cane and grape-sugar 
 in not fermenting when placed in contact with yeast ; and this circumstance, taken 
 in conjunction with its composition, which differs so much from that of other mem- 
 bers of the saccharine group, has always led to the belief that it was not properly 
 classed among these. 
 
 Recent investigations have given it a place by the side of glycerine, the sweet 
 principle of fats and oils, as will be seen hereafter. 
 
 Glycyrrhizine, the sweet principle of the liquorice root, somewhat resembles man- 
 nite, but does not crystallise. 
 
 GUN-COTTON AND SUBSTANCES ALLIED TO IT. 
 
 368. Starch, the sugars, and cellulose, when acted on by the strongest 
 nitric acid, furnish compounds which are remarkable for their explosive 
 character, and are formed by the substitution of nitric peroxide (N0 4 ) for 
 a portion of the hydrogen. By far the most important of these is 
 pyroxyline (rrvp, fire, uAov, wood), which is produced by the action of 
 nitric acid upon the different forms of woody fibre, including wood, cotton, 
 and paper. 
 
 If a piece of white unsized paper (filter-paper) be soaked for a few 
 minutes in the strongest nitric acid (sp. gr. 1'52), then washed in a large 
 volume of water and allowed to dry, it will be found to have suffered 
 little alteration in appearance or texture, but to have acquired the pro- 
 perty of burning with almost explosive violence on the application of a 
 flame or even of a moderately heated glass rod. This is due to the 
 presence, in the altered paper, of a quantity of oxygen in the form of 
 N0 4 (nitric peroxide), which serves to burn up the paper very rapidly, 
 rendering it in great measure independent of any extraneous supply of 
 oxygen. The N0 4 has been introduced into the paper in the place of an 
 equivalent quantity of hydrogen, which has been converted into water by 
 the fifth equivalent of oxygen in the nitric acid (HO . N0 5 ). 
 
 The pyroxyline so obtained, however, is always associated with a 
 quantity of unaltered paper, for the water which is formed by the oxida- 
 tion of the hydrogen, dilutes the remaining nitric acid, so that unless a 
 very large proportion of nitric acid were employed, the acid would become 
 so far weakened towards the close of the operation as to be incapable of 
 converting the last portions of paper into pyroxyline. Moreover, since 
 each fibre composing the paper is a very minute tube, often folded several 
 times, it is not possible for the nitric acid to penetrate its entire substance 
 unless the paper be soaked in it for a long time. 
 
 In order to effect a more complete conversion of the woody fibre into 
 pyroxyline, the nitric acid must be mixed with strong sulphuric acid, 
 which will combine with the water produced by the action of the nitric 
 acid upon the hydrogen of the fibre, and will thus virtually maintain the 
 nitric acid at its greatest strength throughout the operation. Cotton 
 wool, from the looseness of its texture, is more easily converted into 
 pyroxyline than paper. 
 
 The following proportions may be recommended for the preparation of gun-cotton 
 on a small scale : Dry 1000 grains of pure nitre (p. 429) at a very moderate heat, 
 
MANUFACTURE OF GUN-COTTON. 501 
 
 place it in a dry retort (fig. 274), pour upon it 10 drms. (by measure) of strong sul- 
 phuric acid, and distil until 6 drms. 
 of nitric acid have passed over 
 into the receiver. Dry some pure 
 cotton wool, and weigh out 30 grains 
 of it. Mix 2^ measured drachms of 
 the nitric acid with an equal volume 
 of strong sulphuric acid in a small 
 beaker. Allow the mixture to cool, 
 immerse the cotton wool, pressing 
 'it down with a glass rod, cover the 
 beaker with a glass plate, and set it 
 aside for fifteen minutes. Lift the 
 cotton out with a glass rod, throw it 
 into a pint of water, and wash it Fig- 274. 
 
 thoroughly in a stream of water 
 
 till it no longer tastes acid or reddens blue litmus paper. Dry the cotton by exposure 
 to air or at a very moderate heat. 
 
 Very great attention has been paid to the manufacture of gun-cotton 
 during the last few years, with the object of producing a perfectly uniform 
 product which might be employed as a substitute for gunpowder. 
 
 The following is an outline of the process now generally adopted for the 
 production of large quantities of gun-cotton : 
 
 369. Manufacture of gun-cotton. The cotton is employed in the form 
 of loose skeins of about three ounces each, which are thoroughly cleansed 
 by immersion for about 15 minutes in a boiling solution of carbonate of 
 potash, containing 1 Ib. of carbonate to 3 gallons of water (sp. gr. 1'02). 
 This alkaline liquor would dissolve greasy and resinous substances, and the 
 lignine derived from any seed entangled in the cotton, these substances 
 imparting a brown colour to the solution. In order to avoid the necessity 
 of wringing the skeins by hand, they are placed in a centrifugal machine 
 (p. 498), which is a cylnrder made of iron or copper gauze, through which 
 the liquid is whirled out by the rapid rotation of the cylinder upon an 
 axle. The skeins are then washed in running water, again whirled in the 
 centrifugal machine, dried in a warm air chamber, and transferred to stone- 
 ware jars, with air-tight lids to prevent absorption of moisture. 
 
 The proportions in which it is found most advantageous to mix the 
 nitric and sulphuric acids are 1 part of nitric acid (sp. gr. 1*52) and 3 parts 
 by weight (or 2*45 by volume), of sulphuric acid (sp. gr. 1'84). These 
 proportions of the acids are placed in separate stoneware cisterns with 
 taps, and allowed to run simultaneously, in slow streams, into another 
 stoneware cistern furnished with a tap and an iron lid, through a second 
 opening in which an iron stirrer is employed to mix the acids thoroughly. 
 The mixture is set aside for several hours to become perfectly cool. 
 
 A quantity of the mixed acids is drawn off into a deep stoneware pan 
 standing in cold water, and provided with a perforated iron shelf, upon 
 which the cotton may be drained. The prepared skeins are immersed, two 
 at a time, in the acid, and stirred about in it for two or three minutes 
 with an iron stirrer. They are then placed upon the perforated shelf, and 
 the excess of acid squeezed out of them with the stirrer. Enough acid is 
 drawn from the cistern to replace that which has been absorbed by the two 
 skeins, and two more skeins are treated in the same way. Since a consider- 
 able rise of temperature is produced by the action of the nitric acid upon 
 the cotton, it is necessary to keep the pan surrounded with cold water. 
 A large proportion of the cotton is doubtless converted into gun-cotton in 
 
502 MANUFACTURE OF GUN-COTTON. 
 
 this preliminary immersion in the mixed acids; but in order to convert 
 the remainder, it is necessary to allow the cotton to remain in contact with 
 the acid for a much longer period, so as to ensure its penetration into 
 every part of the minute twisted tubes of the fibre. The preliminary 
 immersion of each skein has the advantage of wetting every part with the 
 acid, which could not be so certainly effected if several skeins were thrown 
 at once into a jar, and of preventing the great accumulation of heat which 
 would ensue if the entire chemical action were allowed to take place upon 
 a number of skeins at the same time. The amount of heat evolved during 
 the subsequent soaking in acid is comparatively small. 
 
 The skeins are next transferred to a jar with a well-fitting cover, in which 
 they are pressed down and completely covered with the mixed acids, of 
 which from 10 to 15 times the weight of the cotton will be required, 
 according to the closeness with which the skeins are packed in the jar. 
 The jar is placed in cold water, and the cotton allowed to remain in the 
 acid for 48 hours. 
 
 The skeins are then removed, with the aid of an iron hook, to the cen- 
 trifugal machine, in which they are whirled, at first slowly, and afterwards 
 at 800 revolutions per minute, during ten minutes, when the bulk of the 
 acid is separated. In order to wash away the remainder of the acid, each 
 skein is rinsed very rapidly in a large volume of water; for if the water 
 were allowed to come slowly into contact with the mixed acids, so much 
 heat would be evolved as to decompose a portion of the pyroxyline ; the 
 washing by hand is continued in a stream of water until the cotton no 
 longer tastes acid, and the skeins are then allowed to remain suspended 
 in the stream for 48 hours. 
 
 After having been drained in the centrifugal machine, they are boiled 
 for a few minutes in a solution of 1 Ib. of carbonate of potash in 3 gallons 
 of water, to neutralise any remaining trace of acid,* again drained in the 
 centrifugal machine, and left in the stream for about a fortnight. The 
 gun-cotton is then dried by exposure to air. 
 
 Divested of merely mechanical details, the manufacture of gun-cotton is 
 seen to consist of the following essential operations : 
 
 (1.) Cleansing the cotton by boiling with carbonate of potash, and subse- 
 quent washing with water. 
 
 (2.) Immersion for two or three minutes in a mixture of strongest nitric 
 acid with three times its w r eight of strongest sulphuric acid. 
 
 (3.) Soaking for 48 hours in a fresh portion of the mixed acids. 
 
 (4.) Thorough washing with water. 
 
 (5.) Boiling with carbonate of potash. 
 . (6.) Thorough washing and drying. 
 
 In the opinion of some manufacturers, it is advantageous to impregnate 
 the finished gun-cotton with a solution of silicate of soda, to dry it, and again 
 wash it with water. It was supposed that the silicate of soda was decom- 
 posed, partly by lingering traces of acid in the cotton, partly by the action 
 of atmospheric carbonic acid, a minute quantity of silica being thus 
 deposited in the fibre, which had the effect of retarding the combustion 
 to a desirable extent, and of diminishing the tendency of the cotton to 
 absorb moisture from the air. Experiments instituted by Abel tend 
 to prove that the advantages of this silicating process are altogether 
 imaginary. 
 
 * The alkaline bath would also remove any resinous substances produced by the action 
 of the nitric acid upon the seed, &,c., accidentally left in the original cotton. 
 
COMPOSITION OF GUN-COTTON. 503 
 
 370. Chemical composition of gun-cotton. Perfectly pure gun-cotton 
 contains carbon, hydrogen, nitrogen, and oxygen, in proportions which 
 correspond to the empirical formula C 12 H 7 N :J 0. 22 . The determination of 
 its rational formula is attended with difficulty, because, being an indiffe- 
 rent substance, it does not form definite combinations with other bodies 
 of known equivalent weight, and it is of course impossible to arrive at its 
 volume in the state of vapour, which so frequently affords valuable assist- 
 ance in fixing a rational formula. Having regard to the mode of its for- 
 mation from cellulose (cotton), C J2 H 10 10 , by the action of nitric acid, 
 without evolution of gas, the most probable rational formula appears to be 
 C, 2 H 7 (N0 4 ) 3 O 10 , which represents it as trinitroceHidose, or cellulose in 
 which three equivalents of nitric peroxide have been substituted for three 
 of hydrogen. The action of nitric acid upon the cotton would then be 
 represented by the equation 
 
 C M H 10 10 + 3(HO.N0 5 ) = C 12 H 7 (N0 4 ) : Ao + 6HO.* 
 
 Cellulose. Trinitrocellulose. 
 
 According to this equation, 100 Ibs. of cotton should furnish 183 Ibs. 
 of gun-cotton ; but in practice only about 177 Ibs. are obtained, a part of 
 the deficiency being accounted for by unavoidable mechanical loss, and by 
 small quantities of foreign matters dissolved out by the acids. 
 
 That the nitrogen is really present in the gun-cotton in the form of 
 nitric peroxide (N0 4 ), as implied in the above formula, is indicated by 
 the action of potash, which dissolves the gun-cotton, and yields a solution 
 containing nitrate and nitrite of potash, exactly the products which are 
 formed by the action of potash upon nitric peroxide (p. 135). 
 
 Another reaction of gun-cotton which supports the above view of its 
 constitution, is that with hydrosulphate of potassium. If some hydrate of 
 potash be dissolved in alcohol, and the solution saturated with gaseous 
 hydrosulphuric acid, an alcoholic solution of hydrosulphate of potassium 
 (KS . HS) is obtained ; and if the gun-cotton be immersed in this solution, 
 and gently heated, it will be rapidly reconverted into ordinary cotton, and 
 nitrite of potash will be found in the solution 
 
 C 12 H 7 (N0 4 ) 3 10 + 3(KS.HS) = C 12 H 10 10 + 3(KO.N0 8 ) 4- S fl . 
 
 Trinitrocellulose. Cellulose. 
 
 This is the so-called synthetical method of determining the composition 
 of gun-cotton, for of course 183 parts of the latter should furnish 100 parts 
 of cotton. 
 
 371. Products of the explosion of gun-cotton. From what has been 
 stated with respect to the products of explosion of gunpowder (p. 423), 
 it might be expected that those furnished by gun-cotton would vary 
 according to the conditions under which the explosion takes place. 
 When a mass of the cotton is exploded in an unconfined state, the 
 explosion is comparatively slow (though appearing to the eye almost in- 
 stantaneous), since each particle is fired by the flame of that immediately 
 adjoining it, the heated gas (or flame) escaping outwards, so that some 
 time elapses before the interior of the mass is ignited. But when the 
 gun-cotton is enclosed in a strong case, so that the flame from the portion 
 first ignited is unable to escape outwards and must spread into the interior 
 of the mass, this is ignited simultaneously at a great number of points, 
 and the decomposition takes place far more rapidly ; a -given weight of 
 
 * If atomic symbols and the unitary formula for nitric acid be employed, the equation 
 would become e B H 10 5 + 3HNO 8 = e 6 H 7 (NO 2 ),O 5 + 3H 8 O. 
 
504 PRODUCTS OF EXPLOSION OF GUN-COTTON. 
 
 cotton being thus consumed in a much shorter time, a far higher tempera- 
 ture is produced, and the ultimate results of the explosion are much less 
 complex, as would be expected from the well-known simplifying effect of 
 high temperatures upon chemical compounds. 
 
 Some of the earliest experiments upon gun-cotton showed that when it 
 was fired in a loose state, nitric oxide, nitrous acid, hydrocyanic acid, &c., 
 were discoverable among the gaseous products, and gave rise to melancholy 
 forebodings of injury to miners and gunners from the inhalation of the 
 poisonous vapours. Further experience has proved that no objection can 
 be made to the use of gun-cotton on this ground, for when it is employed, 
 either in fire-arms or in blasting, it is of necessity fired in a confined 
 state, and the products are simply aqueous vapour, carbonic acid, carbonic 
 oxide, and nitrogen, with a little marsh-gas and hydrogen. 
 
 The determination of the products of explosion of confined gun-cotton 
 has been effected by Karolyi in the same manner as in the case of gun- 
 powder (see p. 424), by enclosing the cotton in a cast-iron cylinder, strong 
 enough to resist bursting until the combustion of the last portion of 
 the charge, which was suspended in an iron globe exhausted of air, 
 and exploded by the galvanic battery; the total volume of the gases 
 collected in the globe was then determined and subjected to analysis. 
 The amount of gun-cotton fired was about 150 grains. Unfortunately, 
 the formula given for the sample of gun-cotton experimented on does not 
 represent the trinitrocellulose which constitutes pure gun-cotton, being 
 C 24 H 17 N" 5 38 , instead of C^H^NgO^ (representing 2 eqs. of trinitrocellulose), 
 but the difficulty attending the exact ultimate analysis of gun-cotton is so 
 great, that there is greater probability of the analysis being incorrect than 
 of the composition of the cotton having really differed materially from 
 that of trinitrocellulose. 100 grains of gun-cotton gave a quantity of 
 aqueous vapour and gaseous products, calculated to occupy, at 60 '8 F. 
 and 29 '06 in. Bar., 325*5 cubic inches, supposing the aqueous vapour to 
 remain uncondensed at that temperature. The analysis of the gas proved 
 that 100 volumes of the products of explosion contain 
 
 Aqueous vapour, 
 Carbonic oxide (CO), 
 Carbonic acid (C0 a ), 
 Nitrogen, . 
 Hydrogen, 
 Marsh-gas (C 2 H 4 ), 
 
 25-34 vols. 
 28-95 
 20-82 
 12-67 
 
 3-16 
 
 7-24 
 
 98-18 
 
 The amount of aqueous vapour was inferred from that of the hydrogen 
 contained in the gun-cotton. 
 
 If the marsh-gas and hydrogen be left out of consideration, the follow- 
 ing equation will account for the other products of the explosion, sup- 
 posing the gun-cotton to be pure trinitrocellulose 
 
 C 12 H 7 (N0 4 ) 3 10 = 9CO + 3CO 2 + 7HO + N 3 . 
 
 According to this equation, 100 grains of gun-cotton should furnish 356 
 cubic inches of gas and vapour, instead of 325*5 as determined by experi- 
 ment, and the volumes of the products should be 
 
 Aqueous vapour, . . 28 vols. 
 
 Carbonic oxide, . . . 36 ,, 
 
 Carbonic acid, . . . 12 ,, 
 
 Nitrogen, . . . . 12 
 
EFFECTS OF GUN-COTTON AND GUNPOWDER COMPARED. 505 
 
 which do not agree with the experimental results. It is not to be ex- 
 pected, however, that one simple equation should correctly represent all 
 the products of such a decomposition (see p. 425). 
 
 It has been stated* that, practically, gun-cotton is most effective in 
 guns, when of such density that 11 Ibs. occupy a cubic foot. One cubic 
 inch would then weigh 44 '5 grains, and would evolve (calculating from 
 the result of Karolyi's experiment) a quantity of steam and gas which 
 would occupy 140'5 cubic inches at 60 F. and 30 in. Bar., supposing the 
 steam to be capable of remaining uncondensed. 
 
 It was calculated at p. 426, that one cubic inch of gunpowder, or 235 
 grains (58 Ibs. to the cubic foot), would evolve 207 cubic inches of gas 
 measured at 60 F. and 30 in. Bar. 
 
 It is much to be regretted that, up to the present time, no one has 
 succeeded in determining the heat evolved in the explosion of a given 
 weight of gun-cotton, so that it is impossible to calculate the volume which 
 the products would occupy at the instant of the explosion, and therefore 
 the mechanical effect which the expanded gases are capable of producing. 
 
 Supposing the products of explosion to be equally expanded by heat 
 at the moment of explosion, it would appear at first sight that gunpowder 
 should produce a greater mechanical effect than an equal weight of gun- 
 cotton 
 
 44-5 grs. of gun-cotton occupying 1-0 cub. in. evolve 140'5 cub. in. of gas (cooled) 
 44-5 gunpowder 0-2 207 
 
 If both charges were confined in spaces which they exactly filled, the 
 pressures exerted would be 1035 atmospheres for gunpowder, and 140'5 
 atmospheres for gun-cotton. 
 
 Experience, however, has shown that a given weight of gun-cotton pro- 
 duces three times the effect, in artillery, of an equal weight of gunpowder. 
 To account for this, it might be supposed that the heat evolved in the 
 combustion of the cotton exceeds that produced by gunpowder, so that 
 although the gas from the latter is calculated to exert a higher pressure at 
 the ordinary temperature, it is less heated and expanded at the moment 
 of explosion, and therefore exerts less pressure than the gas from gun- 
 cotton. Without any such assumption, however, the superior power of 
 gun-cotton in artillery may be explained by the more complete explosion 
 of the entire charge, and by the greater rapidity of its combustion. 
 
 It is well known that a very large proportion of the charge of gun- 
 powder is blown out of the gun unburnt, whereas, by proper management, 
 every particle of the gun-cotton may be consumed. 
 
 But the greater rapidity of the combustion of gun-cotton is probably 
 the most important reason for its greater mechanical effect, since the entire 
 volume of the gas would be evolved before the confining space was ma- 
 terially enlarged by the movement of the projectile, which would thus be 
 exposed to the maximum pressure. Indeed, this rapidity of combustion 
 (due to the nature of gun-cotton as a chemical compound, and not a 
 mechanical mixture like gunpowder) was the chief obstacle to its use in 
 artillery, since it frequently burst the gun in the earlier trials, until it 
 was discovered that, by spinning and weaving the yarn into webs of 
 various degrees of closeness, the rate of combustion could be modified as 
 that of gunpowder is by granulation ; so that whilst the loose yarn burns 
 in the open air at the rate of 1 foot per second ; when twisted into thread 
 * Report of the Gun-cotton Committee to the British Association, 1863. 
 
506 PIIOPEKTIES OF GUN-COTTON. 
 
 and woven into a web for cartridges, it burns in the open air at the rate 
 of 10 feet per second, and this rate may be varied by varying the tight-- 
 ness with which the thread is twisted. When the charge is confined in 
 a gun, however, the results are not so satisfactory, since the great pressure 
 of the gas first generated drives the flame through the mass of cotton, and 
 produces almost instantaneous ignition throughout, resulting in serious 
 damage to the bore of the gun. It has been found preferable, in making 
 cartridges for fowling-pieces, to dilute the gun-cotton by mixing it with 
 some unconverted cotton. Abel reduces the gun-cotton to a pulp similar 
 to that used by paper-makers, in which state, it may, if necessary, be 
 diluted with ordinary cotton in pulp, and may be compressed into very 
 compact, slowly burning cakes, in which it offers great advantages for 
 making up a charge. 
 
 In mining operations, such as blasting rocks, it is said that gun-cotton 
 produces the same effect as six times its weight of gunpowder ; and since, 
 in such cases, the space confining the charge is incapable of gradual en- 
 largement, the rate of combustion is not of so much importance as the 
 maximum pressure to which the gas is capable of attaining, so that this 
 result can hardly be explained unless it be supposed that the heat evolved 
 in the combustion of the cotton is really greater than that furnished by 
 gunpowder an assumption which is scarcely consistent with the fact 
 that guns are much less heated by firing a certain number of rounds with 
 gun-cotton than they would be with gunpowder. It must not be for- 
 gotten, however, that since gun-cotton leaves no solid products of explo- 
 sion, the entire amount of heat, whatever that may be, is available for 
 the expansion of the gaseous products, giving it a great advantage over 
 powder, of which the solid products have, of course, to be raised to the 
 same temperature as the gases, without contributing to increase the 
 mechanical effect by their expansion. 
 
 If the end of a strand of gun-cotton yarn be kindled at a very few 
 points of the filaments, by a spark on touch-paper, or at the end of a piece 
 of string, it will undergo a very slow smouldering combustion, as first 
 observed by Abel ; and if the experiment be made in a narrow glass tube 
 closed at one end, the carbonic oxide may be kindled at the mouth of the 
 tube, whilst the cotton is smouldering inside. 
 
 372. Properties of gun-cotton compared ivith those of gunpowder. 
 Gun-cotton is more easily exploded than gunpowder ; the latter requires 
 a temperature of at least 600 P., whilst gun-cotton may explode at 277 F., 
 and must explode at 400 F. It is very difficult to explode gunpowder 
 by percussion, even between a steel hammer and anvil ; but gun-cotton 
 invariably detonates in this way, though the explosion is confined to the 
 part under the hammer. The explosion of gun-cotton is, of course, unat- 
 tended by any smoke, a most important advantage in mines, the atmo- 
 sphere of which is sometimes rendered almost intolerable by the smoke of 
 gunpowder used in blasting. The absence of residue from the gun-cotton 
 prevents the fouling of guns, and renders it unnecessary to sponge them, 
 after each discharge, for the amount of incombustible mineral matter pre- 
 sent in the cotton is very small (from 1 to 2 per cent.), and is entirely 
 scattered by the explosion. 
 
 It has already been mentioned that the explosion of gun-cotton does 
 not impart so much heat to the metal of the gun as that of powder, the differ- 
 ence being so great that, after firing 100 rounds with gun-cotton, the gun 
 
PROPERTIES OF GUN-COTTON. 507 
 
 .was not so much heated as after 30 rounds with gunpowder. This important 
 advantage of gun-cotton has been explained by some to depend upon the 
 very high specific heat of the aqueous vapour, which forms so large a portion 
 of the products of explosion. For since the specific heat of steam is 0*48, 
 and that of carbonic oxide (which, among the products from gunpowder, 
 has the highest specific heat) is 0*25, nearly twice as much heat would 
 be consumed in raising the former to a given temperature as in raising the 
 latter ; but it is hardly necessary to account for the result in this manner, 
 when it is remembered that the charge of gun-cotton is only one-third of 
 the charge of powder, that the explosion of the former is so much more 
 rapid, leaving less time for the communication of heat to the metal, and 
 that there are no highly-heated solid products left in contact with the 
 gun. Gun-cotton may be fired upon the palm of the hand with impunity, 
 or upon a heap of gunpowder without kindling it ; although it cannot be 
 doubted that the temperature of the flame is really much higher than the 
 inflaming point of powder. That the recoil of a gun charged with gun- 
 cotton is only two-thirds of that experienced with gunpowder, is a matter 
 for the consideration of the artillerist rather than the chemist. The fact 
 that if gun-cotton be used to effect a breach in palisades, &c., it must be 
 confined in a strong case, whereas gunpowder in a bag would suffice for 
 the work of demolition, is explained by what has been stated at p. 503, 
 viz., that the flame tends outwards so rapidly from loosely-confined guii- 
 cotton, that its explosion is too gradual, and it then produces less effect 
 than powder ; but when tightly confined, the flame, unable to escape, 
 pervades the whole mass, and a nearly instantaneous explosion is the 
 result. 
 
 It is evident, from the consideration of its manufacture, that gun- 
 cotton is entirely uninjured by water, so that a store of this explosive 
 might be immersed in water in case of need, and would be still service- 
 able after drying, whereas gunpowder is, of course, rendered useless by 
 contact with water, which dissolves out the nitre. Even when exposed 
 to very damp air, gunpowder is liable to injury from the effect of moisture 
 in partially separating the nitre from the other ingredients, whilst gun- 
 cotton only requires exposure to a dryer atmosphere for a short time to 
 render it fit for use. The proportion of moisture retained by gun-cotton, 
 in the ordinary state of the atmosphere, is 2 per cent. 
 
 As an objection to the employment of gun-cotton as a substitute for gun- 
 powder, it has been asserted that the trinitrocellulose is liable to undergo 
 spontaneous decomposition, which might at any time render the contents 
 of a magazine unserviceable, or might even give rise to the evolution of a 
 sufficient amount of heat to cause an explosion. The origin of thfs objec- 
 tion is to be traced to the old process for preparing gun-cotton, in which 
 the acids were not allowed to act upon the cotton for a sufficient length of 
 time, so that the whole of the cotton was not converted into true gun- 
 cotton, but some less stable substitution products were formed at the 
 same time. Another cause of spontaneous alteration is the imperfect 
 washing of the gun-cotton, whereby minute traces of acid are left in the 
 .fibre. All recent experiments, by Abel and others, appear to have proved 
 that, considering its highly complex character, gun-cotton is a very stable 
 compound under ordinary conditions; although, when kept in a moist 
 state, it developes traces of acid products, the temperature does not rise to 
 any important extent, nor is the explosive quality of the material at all 
 injured. 
 
508 PREPARATION OF COLLODION. 
 
 373. Gun-cotton is somewhat harsher to the touch than ordinary cotton, 
 and becomes remarkably electrical when rubbed between the dry fingers. It 
 is insoluble in alcohol and ether, as well as in a mixture of these solvents, 
 though ordinary specimens generally yield a small percentage of soluble 
 matter when treated with a mixture of alcohol and ether, because they 
 contain extraneous matters, such as the other substitution products to be 
 mentioned presently. Acetic ether dissolves it, and so does a mixture 
 of ordinary ether with ammonia. Strong sulphuric acid dissolves it with- 
 out carbonisation, unless any unconverted cotton should happen to be 
 present. 
 
 374. Collodion-cotton. When cotton or paper is acted upon by a mix- 
 ture of nitric and sulphuric acids containing more water than is present 
 in that employed for the preparation of gun-cotton (p. 501), compounds 
 are formed which contain less nitric peroxide, and are much less com- 
 bustible than the trinitrocellulose, from which they are also distinguished 
 by their solubility in mixtures of alcohol and ether. 
 
 In order to render evident the relations between these compounds and 
 gun-cotton, the formula of the latter must be trebled, when we have the 
 following series of nitro-compounds produced by the mixtures of nitric acid, 
 sulphuric acid and water, to which they stand opposite 
 
 Composition of the mixed acids. 
 (1.) HO . N0 5 + 2(HO . S0 3 ) 
 (2.) HO . N0 5 + 2 (HO . S0 3 ) + 3HO 
 (3.) HO . N0 6 + 2(HO . S0 8 ) + 4HO 
 (4.) HO . N0 5 + 2 (HO . S0 3 ) + 5HO 
 
 Products of their action on cellulose. 
 
 C 86 H 21 (N0 4 ) 9 30 
 
 C 36 H 22 (N0 4 ) 8 30 
 C 8G H 23 (N0 4 ) 7 3 o 
 C 36 H 24 (N0 4 ) 6 30 
 
 As might be expected, these compounds diminish in combustibility in 
 proportion as the N0 4 contained in them diminishes. The second is that 
 employed for the preparation of photographic collodion, being dissolved 
 for that purpose in a mixture of ether and alcohol. 
 
 In order to prepare the soluble cotton for collodion, three measured ounces of ordi- 
 nary nitric acid (sp. gr. 1-429) are mixed with two ounces of water in a pint beaker. 
 Nine measured ounces of strong sulphuric acid (sp. gr. 1-839) are added to this mix- 
 ture, which is continually stirred whilst the acid is being added. A thermometer is 
 placed in the mixture, which is allowed to cool to 140 F. ; 100 grains of dry cotton 
 wool, in ten separate tufts, are immersed in the mixture for five minutes, the beaker 
 being covered with a glass plate. The acid is then poured into another beaker, the 
 cotton squeezed with a glass rod, and thrown into a large volume of water ; it is 
 finally washed in a stream of water till it i& no longer acid, and dried by exposure to 
 air. (By adding to the acid which was drained out of the cotton, three drachms 
 more sulphuric acid, and immersing another 100 grains of cotton for ten minutes, a 
 second portion of -soluble cotton may be obtained.) 
 
 Collodion balloons. These balloons may be made in the following manner : 6 
 grains of the collodion cotton, prepared according to the above directions, are dissolved 
 in a mixture of 1 drachm of alcohol (sp. gr. -835) and 2 drachms of ether (sp. gr. '725), 
 in a corked test-tube. The solution is poured into a dry Florence flask, which is 
 then turned about slowly so that every part of its surface may be covered with the 
 collodion, the excess of which is then allowed to drain back into the tube. Air is 
 then blown into the flask through a long glass tube attached to the bellows (or to the 
 blowpipe-table, fig. 116) as long as any smell of ether is perceptible. A pen-knife 
 blade is carefully inserted between the flask and the neck of the balloon, which is 
 thus detached from the glass all round ; a small piece of glass tubing is introduced 
 for an inch or two into the neck of the balloon, so that the latter may cling round 
 it. Through this tube air is drawn out by the mouth until one-half of the balloon 
 has left the side of the flask and collapsed upon the other half ; by carefully twisting 
 the tube, the whole of the balloon may be detached and drawn out through the neck 
 
CHEMICAL COMPOSITION OF WINE. 509 
 
 of the flask, when it must be quickly untwisted, distended by blowing through the 
 tube, tied with a piece of silk, and suspended in the air to dry. The average weight 
 of such balloons is two grains. 
 
 When collodion-cotton is kept for some time, especially if at all damp, 
 it undergoes decomposition, filling the bottle with red fumes, and becoming 
 converted into a gummy mass, which contains oxalic acid. 
 
 375. Xyloidine is the name given to a highly combustible substance 
 analogous to pyroxyline, which is obtained by dissolving starch in the 
 strongest nitric acid, and diluting the solution with water, when the 
 xyloidine falls as a white precipitate, which may be collected upon a 
 filter, and washed till free from acid. The composition of xyloidine is 
 C 12 H 8 (N0 4 ) 2 10 , representing starch (C 12 H 10 10 ), in which 2 equivalents of 
 nitric peroxide have been substituted for 2 equivalents of hydrogen. 
 
 Nitromannite (C 12 H 8 (N0 4 ) 6 12 ) is another explosive body of the same 
 order, obtained by adding powdered mannite (C 12 H 14 12 ), in small portions, 
 to a mixture of equal measures of the strongest nitric and sulphuric acids, 
 which immediately dissolve it, and presently solidify to a mass of minute 
 needles of nitromannite, which may be washed with a large volume of 
 water, and crystallised from boiling alcohol. Under the hammer, nitro- 
 mannite explodes with a very loud report. When heated, it fuses before 
 exploding. 
 
 WINE AM) SPIRITS. 
 
 376. Wine is essentially composed of 8 or 10 parts of alcohol, with 
 85 or 90 of water, together with minute quantities of certain fragrant 
 ethers, of colouring matter, of bitartrate of potash, and of the mineral 
 substances derived from the grape-juice. Glycerine and succinic acid 
 have also been found in wines, and appear to be constant secondary pro- 
 ducts of the alcoholic fermentation. 
 
 Those wines in which the whole of the sugar has been fermented are 
 known as dry wines \ whilst fruity wines still retain a considerable 
 quantity of sugar. 
 
 The preparation of wine differs from that of beer in the circumstance 
 that no addition of ferment is necessary, the fermentation being excited 
 by a substance present in the grape-juice. This juice contains, in addition 
 to grape-sugar, vegetable albumen, tartrate of potash, and the usual 
 mineral salts found in vegetable juices. The husks, seeds, and stalks of 
 the grape contain a considerable quantity of tannin, together with certain 
 blue, red, and yellow colouring matters. 
 
 When the expressed juice remains for a short time in contact with the 
 air, the albuminous substances contained in it enter upon a state of change, 
 exciting the vinous fermentation in the sugar, and a scum of yeast is 
 formed upon the surface. If this fermentation takes place in contact with 
 the husks of the dark grapes, the alcohol dissolves the colouring matter, 
 and a red wine results ; whilst for the production of white wines, the husks, 
 &c., are separated previously to the fermentation, and the juice is exposed 
 as little as possible to the air. 
 
 White wines are rather liable to become ropy from viscous fermentation, 
 but this is prevented by the addition of a small quantity of tannin, which 
 precipitates the peculiar ferment. The tannin for this purpose is extracted 
 from the husks and stalks of the grapes themselves. 
 
510 PROPORTION OF ALCOHOL IN WINES. 
 
 Red wines, sucli as port and claret, are often very astringent from the 
 tannin dissolved out of the husks, &c., during the fermentation. Port 
 wine, when freshly bottled, still retains in solution a considerable quantity 
 of bitartrate of potash (KO . HO . C 8 H 4 10 ), but after it has been kept 
 some time, and become more strongly alcoholic, this salt is deposited, 
 together with a quantity of the colouring matter, in the form of a crust 
 upon the side of the bottle. Thus a dark fruity port becomes tawny 
 and dry when kept for a sufficient length of time, the sugar having been 
 converted into alcohol. 
 
 When the wine contains an excess of tartaric acid, it is customary to 
 add to it some neutral tartrate of potash (2KO. C 8 H 4 10 ), which precipitates 
 the acid in the form of bitartrate. 
 
 The preparation of champagne is conducted with the greatest care. The 
 juice or must is carefully separated from the marc or husk, and is often 
 mixed with one per cent, of brandy before fermentation. After about two 
 months the wine is drawn off into another cask, and clarified with isinglass 
 dissolved in white wine, and added in the proportion of about half-an- 
 ounce to 40 gallons. This combines with the tannin to form an insoluble 
 precipitate, which carries with it any impurities floating in the wine. 
 After another interval of two months, the wine is again drawn off, and a 
 second clarification takes place, and in two months more the wine is 
 drawn off into bottles containing a small quantity of pure sugar-candy 
 dissolved in white wine. The bottles, having been securely corked and 
 wired, are laid down upon their sides for eight or ten months, during 
 which time the fermentation of the newly added sugar takes place, and the 
 carbonic acid produced dissolves in the wine, whilst a quantity of yeast is 
 separated. In order to render the wine perfectly clear, the bottle is left 
 for about three weeks in such a position that the deposit may subside into 
 the neck, against the cork, which is then unwired so that the pressure of 
 the accumulated carbonic acid may force it out together with the deposit ; 
 the bottle having been rapidly filled up with white wine, is again corked, 
 wired, covered with tin foil, and sent into the market. Pink champagne 
 is prepared from the must which is squeezed out of the marc after it has 
 ceased to run freely, and contains a little of the colouring matter of the 
 husk. The colour is also sometimes imparted by adding a little tincture 
 of litmus. 
 
 The proportion of alcohol in wines varies greatly, as will be seen from 
 the following statement of the weight of alcohol in 100 parts of the wine : 
 
 Port, . . from 15 to 17. 
 Sherry, . 14 to 16. 
 Champagne, 11'5. 
 
 Claret, . . 8 to 9. 
 Rudesheimer, 7 to 8 '5. 
 
 Sherry contains from 1 to 5 per cent, of sugar, port from 3 to 7 per 
 cent., and Tokay 17 per cent. ; in the last case, the sugar is increased by 
 adding some of the must concentrated by evaporation to the wine pre- 
 viously to bottling. 
 
 The bouquet or fragrance of wine is due to the presence of certain 
 fragrant ethers, especially of oenanthic, pelargonic, and acetic ether, formed 
 during the fermentation or during the subsequent storing of the wine. 
 
THE ALCOHOLS. 511 
 
 It is to the increased quantity of such fragrant ether that the superior 
 bouquet of many old wines is due. 
 
 377. Distilled sjtirits. The varieties of ardent spirits are obtained from 
 fermented liquids by distillation, so that they consist essentially of alcohol 
 more or less diluted with water, and flavoured either with some of the 
 volatile products of the fermentation, or with some essential oil added 
 for the purpose. 
 
 Brandy is distilled from wine, and coloured to the required extent with 
 burnt sugar (caramel). Its flavour is due chiefly to the presence of 
 oenanthic ether derived from the wine. The colour of genuine pale 
 brandy is due to its having remained so long in the cask as to have dis- 
 solved a portion of brown colouring matter from the wood, and is there- 
 fore an indication of its age. Hence arose the custom of adding caramel, 
 and sometimes infusion of tea, to impart the astringency due to the tannin 
 dissolved from the wood by old brandy. 
 
 Whisky is distilled from fermented malt, which has been dried over a 
 peat fire, to which the characteristic smoky flavour is due. 
 
 Gin is also prepared from fermented malt or other grain, and is flavoured 
 with the essential oil of juniper, derived from juniper berries, added during 
 the distillation. 
 
 Rum is distilled from fermented molasses, and appears to owe its 
 flavour to the presence of butyric ether, or of some similar compound. 
 
 Arrack is the spirit obtained from fermented rice. 
 
 Kirschwasser and maraschino are distilled from cherries and their 
 stones, which have been crushed and fermented. 
 
 Some varieties of British brandy and whisky are distilled from fer- 
 mented potatoes, or from a mixture of potatoes and grain, when there 
 distils over, together with ordinary alcohol, another spirit belonging to 
 the same class, but distinguished from alcohol by its nauseous and irritat- 
 ing odour. This substance, which is known as potato-spirit, amylic 
 alcohol, or fousel oil (C 1(/ H 12 0. 2 ) also occurs, though in very minute 
 quantity, in genuine wine-brandy. The manufacturers of spirit from grain 
 and potatoes remove a considerable part of this disagreeable and unwhole- 
 some substance by leaving the spirit for some time in contact with wood- 
 charcoal. 
 
 THE ALCOHOLS AND THEIR DERIVATIVES. 
 
 378. It has already been stated that alcohol is the type of a very im- 
 portant class of compounds closely related to each other in composition 
 and properties. 
 
 The alcohols are all composed of carbon, hydrogen, and oxygen ; the 
 members of the series represented by common alcohol always contain two 
 equivalents of oxygen, and two more equivalents of hydrogen than of 
 carbon. The number of equivalents of carbon and hydrogen is always an 
 even number, so that the general formula of an alcohol of this series may 
 be written thus, C2 W H 2ft + 202. Thus, in ordinary or vinic alcohol, 
 C 4 H 6 2 , n 2, in wood-spirit or methylic alcohol, C 2 H 4 2 , n = 1, in 
 potato-spirit or amylic alcohol, C ]0 H )2 0, 2 , n = 5. 
 
 These alcohols constitute, therefore, a truly homologous series (p. 459) 
 of which many members, however, remain to be discovered. 
 
 The following table includes the alcohols of this series which are at 
 present known : 
 
512 
 
 VINIC OR ETHYLIC CLASS OF ALCOHOLS. 
 
 Chemical Name. 
 
 Source. 
 
 Equivalent 
 Formula. 
 
 Common Name. 
 
 1. Methylic alcohol 
 2. Ethylic 
 3. Propylic 
 4. Butylic 
 5. Amylic 
 6. Caproic 
 
 7. (Enanthic { 
 
 Destructive distillation of wood 
 Vinous fermentation of sugar 
 Fermentation of grape-husks 
 Fermentation of beet-root . 
 Fermentation of potatoes . . 
 Fermentation of grape-husks 
 Distillation of castor-oil with | 
 potash . , . J 
 
 C 2 H 4 2 
 
 cXo| 
 
 C 8 H 10 2 
 C 10 H 12 2 
 
 Wood naphtha 
 Spirit of wine 
 
 Fousel oil 
 
 8. Caprylic 
 10. Rutic 
 
 Fermentation of grape-husks 
 Oil of rue 
 
 C 16 H 18 2 
 C n H 
 
 
 12. Laurie ,, 
 
 Whale oil 
 
 C H 6 
 
 
 16. Cetylic 
 
 Spermaceti . 
 
 C H 
 
 Ethal 
 
 27 Cervlic , 
 
 Chinese wax . . 
 
 C H 
 
 Cerotene 
 
 30. Melissic 
 
 
 
 Melissine 
 
 
 
 
 
 The usual gradation in properties attending the gradation in composition 
 among the members of a homologous series, is strikingly exemplified in the 
 class of alcohols. The first eight members of the group, linked together 
 as they are by an almost common origin (being derived, with one exception, 
 from the fermentation of substances nearly allied, and that exception being 
 a product of destructive distillation which may be regarded as an acceler- 
 ated fermentation), and by a regularly ascending composition, would be 
 expected to resemble each other in their properties far more closely than 
 the other members of the class. Accordingly, we find that methylic, 
 ethylic, propylic, butylic, amylic, caproic, cenanthic,* and caprylic alcohols, 
 are all liquid at the ordinary temperature, that they all possess peculiar 
 and powerful odours, and may be readily distilled unchanged. Among 
 these, however, the gradation is not to be overlooked. The two first, 
 methylic and ethylic alcohols, may be mixed with water in all proportions, 
 but the third, propylic alcohol, though freely soluble in water, is not so 
 to an unlimited extent ; whilst butylic alcohol is less soluble, and amylic 
 alcohol may be said to be sparingly soluble in water. Caproic alcohol, 
 the next member, is insoluble in water; whilst caprylic is not only insoluble, 
 but possseses an oily character, leaving a greasy stain upon paper. 
 
 In their boiling points, and the specific gravities of their vapours, a 
 similar gradation is observed. 
 
 Alcohol. 
 
 Boiling Point. 
 
 Vapour Density. 
 
 
 149-9 F. 
 
 1.12 
 
 Ethylic, 
 
 173 
 
 1-61 
 
 
 205 
 
 2-02 
 
 Butylic, 
 Amylic, 
 Caproic, 
 CEnanthic, 
 Caprylic . . 
 
 233 
 269-8 
 299-309 
 327-343 
 356 
 
 2-69 
 8-15 
 3-63 
 
 4-50 
 
 
 
 
 This alcohol is of recent discovery, and has been little examined. 
 
ALCOHOLS ALDEHYDES ETHEES. 513 
 
 One equivalent of each of these alcohols yields four volumes* of vapour ; 
 or, in other words, if a given weight of the alcohol corresponding to its 
 equivalent number be converted into vapour, that vapour will occupy four 
 times as much space as would be occupied by an equivalent of oxygen at 
 the same temperature and pressure, or twice the space occupied by an 
 equivalent of hydrogen, or of water converted into vapour under the 
 same conditions. 
 
 The higher members of the group of alcohols are solid fusible bodies 
 more nearly approaching to waxy or fatty matters in their nature, and not 
 susceptible of distillation without decomposition. Far less is known of 
 these than of the alcohols containing less carbon. 
 
 The true chemical definition of an alcohol of this series rests upon the 
 circumstance, that under the influence of oxidising agents, it first parts 
 with two equivalents of hydrogen, and is converted into an aldehyde 
 (alcohol dehydrogenated), and afterwards absorbs two equivalents of 
 oxygen, yielding an acid. Thus, it has been already shown (p. 492), that 
 vinic alcohol (C 4 H 6 2 ), when exposed to air under favourable conditions, 
 yields aldehyde, C 4 H 4 2 , which, by absorbing oxygen, is converted into 
 acetic acid, C 4 H 4 4 . 
 
 The formation of an aldehyde would, therefore, be represented by the 
 general formula 
 
 2 + 2 - C 2n H 2n 2 + 2HO, 
 
 Alcohol Aldehyde. 
 
 and that of the corresponding acid by 
 
 C 2 H 2tt+2 2 + 4 -,C 2w H 2tt 4 + 2HO. 
 
 Alcohol. Acid. 
 
 In addition to this, each of these alcohols, by the loss of the elements of 
 one equivalent of water, yields an ether, corresponding to ordinary ether 
 C 4 H 5 0, which differs from vinic alcohol, C 4 H 6 2 , by the elements of an 
 equivalent of water. 
 
 The general formula representing the derivation of an ether from an 
 alcohol of the above series is 
 
 ,. to+1 
 
 Alcohol. Ether. 
 
 Hence every alcohol has its corresponding aldehyde, acid, and ether, so 
 that there are homologous series of aldehydes, acids, and ethers, just as 
 of the alcohols from which they are derived. 
 
 The only members of the aldehyde and ether series which have received 
 a large share of attention on account of their practical importance, are 
 those derived from ordinary alcohol ; but the series of acids contains many 
 members of importance, to some of which no corresponding alcohols 
 are yet known. 
 
 The very important homologous series of acids t composed after the 
 general formula C 2n H 2n 4 , includes 
 
 * Or one molecule of each alcohol yields two volumes (H = 1 vol. ). 
 t Often spoken of as the acetic series of acids, or the fatty acid series. 
 
 2K 
 
514 
 
 ACETIC SEKIES OF ACIDS. 
 
 Acid. 
 
 Source. 
 
 Equivalent 
 Formula. 
 
 1. Formic acid, 
 2. Acetic 
 
 Red ants, nettles . . . 
 Vinegar 
 
 C H 
 
 3. Propylic ,, 
 4. Butyric ,, 
 
 Oxidation of oils .... 
 Rancid butter 
 
 v ^4 xi 4 v - / 4 
 
 CH0, 
 
 6. Valerianic acid 
 
 Valerian root 
 
 C 1ft H in O, 
 
 6. Caproic 
 7. (Enanthic 
 8. Caprylic ,, 
 
 Rancid butter .... 
 Oxidation of castor oil . . 
 Rancid butter . . 
 
 C 12 H 12 4 
 C 14 H 14 4 
 C A H ft O A 
 
 9. Pelargonic acid 
 10 Rutic or capric acid 
 
 Geranium leaves .... 
 Rancid butter . . 
 
 ^16 "16^4 
 
 11. Euodic* 
 
 Oil of rue 
 
 C 90 H 99 0. 
 
 12. Laurie 
 
 Bay berries 
 
 
 13. Cocinic 
 
 Cocoa nut oil 
 
 p 24 TT 24 O 4 
 
 14. Myristic 
 15. Benic 
 
 Nutmeg butter .... 
 Oil of ben 
 
 
 16. Palmitic 
 
 
 C, 9 EL 9 0, 
 
 17. Margaric 
 
 Olive oil? 
 
 
 18 Stearic 
 
 Tallow 
 
 C H 
 
 19. Balenic 
 20 Butic 
 
 Butter 
 
 Vy 36 ix 86 w 4 
 
 C H 
 
 21. Nardic 
 27. Cerotic 
 
 Bees' wax . 
 
 v ^40' L - L 40 vy 4 
 
 30. Melissic 
 
 
 cW 
 
 
 
 60 60 4 
 
 A very gradual transition of properties is observable in the members of 
 this extended series of acids. 
 
 The first nine members of the series are liquid, the remainder solid at com- 
 mon temperatures. Of the liquids, formic acid boils at 221 F., and the boil- 
 ing points of the other members exhibit a gradual rise up to pelargonic acid, 
 which boils at 500 F. The melting-points of the solid acids also ascend 
 from 86 F. for rutic acid (C 20 H 20 4 ) to 192 F. for melissic (C 60 H 60 4 ). 
 
 Formic and acetic acids may be mixed with water in all proportions, 
 like their corresponding alcohols, the methylic and ethylic; propylic 
 acid, though soluble to a great extent in water, resembles the correspond- 
 ing alcohol in not mixing indefinitely with water. Butyric acid behaves 
 in a similar manner. Valerianic, caproic, cenanthic, and caprylic acids are 
 sparingly soluble in water. Pelargonic and capric acids are very sparingly 
 soluble, and the remaining members of the series are very decidedly fatty 
 acids, insoluble in water, and forming soaps with the alkalies. 
 
 The members of the series of alcohols, under the action of powerful 
 dehydrating agents, are capable of parting with the elements of two 
 equivalents of water, furnishing the members of a homologous series of 
 hydrocarbons related to their corresponding alcohols, as olefiant gas or 
 ethylene (C 4 H 4 ) is related to ethylic alcohol. 
 
 The general formula for the production of the homologues of ethylene 
 (or olefines) from the alcohols may be thus expressed 
 
 CTT /~\ OTTf^ (~^ T-T 
 
 Jlo 4. nVJo *" ^XIVJ = W^J-Lfe 
 
 fragrant. 
 
OLEFINES OR OLEFIANT GAS HYDROCARBONS. 
 The known members of this series of hydrocarbons are 
 
 515 
 
 Name. 
 
 Equivalent 
 Formula. 
 
 Corresponding 
 Acid. 
 
 Corresponding 
 Alcohol 
 
 1. Methylene . 
 
 C 2 H 2 
 
 Formic 
 
 Wood-naphtha 
 
 2. Ethylene '". 
 
 C 4 H 4 
 
 Acetic 
 
 Alcohol 
 
 3. Propylene 
 
 C 6 H 6 
 
 Propylic 
 
 Propylic 
 
 4. Butylene . . 
 
 C 8 H 8 
 
 Butyric 
 
 Butylic 
 
 6. Amylene . . 
 
 C 10 H 10 
 
 Valerianic 
 
 Fousel oil 
 
 6. Caproylene . 
 
 C 12 H 12 
 
 Caproic 
 
 Caproic 
 
 7. (Enanthene . 
 
 C 14 H 14 
 
 (Enanthic 
 
 (Enanthic 
 
 8. Caprylene 
 
 C 16 H 16 
 
 Caprylic 
 
 Caprylic 
 
 9. Elaene . . 
 
 C 18 H 18 
 
 Pelargonic 
 
 
 10. Paramylene . 
 
 C 20 H 20 
 
 Rutic 
 
 Rutic 
 
 16. Cetylene 
 
 C 32 H 32 
 
 Palmitic 
 
 Ethal 
 
 27. Cerotene 
 
 C 64 H S4 
 
 C erotic 
 
 Cerotene 
 
 30. Melissene 
 
 C 60 H 60 
 
 Melissic 
 
 Melissine 
 
 Of these hydrocarbons, methylene, ethylene, and propylene are gaseous ; 
 butylene is also a gas, but easily condensed to the liquid state ; the re- 
 mainder are liquid at the ordinary temperature. 
 
 This series exhibits one of the best examples of polymerism or multiple 
 relation of composition, each member of the series being represented by a 
 formula which is a multiple by some whole number of that of the first 
 member of the series. 
 
 Since one equivalent of each of these hydrocarbons in the state of 
 vapour occupies four volumes* it must follow, if their composition be cor- 
 rectly stated, that their vapour densities exhibit a multiple relation similar 
 to that which exists between their formulae. 
 
 That this is the case will be seen by the subjoined table, which illus- 
 trates very clearly the importance of determining the specific gravity of 
 the vapour of a volatile substance as a confirmation of the results of 
 analysis : 
 
 C 4 H 4 
 
 Hydrocarbon. 
 Methylene, C 2 H 
 Ethylene, 
 Propylene,f 
 Butylene, 
 Amylene, 
 Caproylene, 
 Caprylene, 
 Elaene, 
 Paramylene, C 20 H 
 Cetylene, 
 
 C 16 H 16 
 
 C 18 H 18 
 
 Specific gravity of vapour. 
 0-490 
 0-978 
 1-498 
 1-852 
 2-386 
 2-875 
 3-90 
 4-48 
 6-061 
 8-007 
 
 It will be observed that just as the formula of cetylene (C 32 H 32 ) is a 
 
 * Or one molecule occupies two volumes (H = 1 vol.). 
 
 f* These hydrocarbons are sometimes designated by names which refer to the multiple of 
 C 2 H 2 which they contain. Thus propyleue, 3(C 2 H 2 ), is sometimes called tritylene ; buty- 
 lene, tetrylene; caproylene, hexylene; &c. 
 
 2K2 
 
516 PREPARATION OF ABSOLUTE ALCOHOL. 
 
 multiple of that of methylene (C 2 H 2 ) "by 16, so, allowing for errors of 
 experiment, the vapour density of cetylene (8*007) is 16 times that of 
 methylene (0*490). 
 
 379. ALCOHOL may be studied as the type of the class to which it 
 gives a name. 
 
 When any of the fermented or distilled liquors of commerce are sub- 
 jected to distillation, the alcohol passes over during the first part of the 
 process, mixed with a considerable quantity of water ; and if the distilla- 
 tion be continued as long as any alcohol passes over, and the whole of the 
 distilled liquid be measured or weighed, the quantity of alcohol present 
 in the original liquid subjected to distillation, may be inferred (by refer- 
 ence to a table) from the specific gravity of the aqueous spirit distilled 
 from it, since the lighter it is the more alcohol it contains, the specific 
 gravity of pure alcohol being 0*794. 
 
 The strength of the spirit of wine of commerce is ascertained by deter- 
 mining its specific gravity. That known as proof spirit has the specific 
 gravity 0*920, and is so called because it is the weakest spirit which will 
 answer to the rough proof of firing gunpowder which has been moistened 
 with it and kindled. Any spirit weaker than this leaves the powder 
 moist, and does not explode it. It is then said to be under proof ^ whilst 
 a stronger spirit is spoken of as over proof. 
 
 Proof spirit contains by weight, in 100 parts 
 
 Water, ,. , 50*76 
 Alcohol, . ;v 49*24 
 
 A spirit would be spoken of as 30 per cent., for example, over proof, 
 if 100 measures of it, when diluted with water, would yield 130 measures 
 of proof spirit. A spirit 30 per cent, below proof contains, in every 100 
 measures, 70 measures of proof spirit. By repeatedly rectifying or re- 
 distilling the weak spirit obtained from a fermented liquid, collecting the 
 first portions separately, a strong spirit may be obtained, containing 90 
 per cent, of alcohol, but mere distillation will not effect a further separa- 
 tion of the water. Weak spirit may be concentrated to a greater extent 
 than this, by leaving it enclosed in a bladder for a considerable period, 
 when the water exudes through the bladder more readily than the alcohol, 
 so that the latter accumulates in the mixture to the amount of 95 per 
 cent. 
 
 Another method of separating a great part of the water consists in add- 
 ing dry carbonate of potash to the weak spirit as long as it is dissolved, 
 when the mixture separates into two layers, the lower consisting of solu- 
 tion of carbonate of potash in water, and the upper one of spirit, contain- 
 ing 89 per cent, of alcohol. By effecting the separation by means of car- 
 bonate of potash in a graduated tube, this method is sometimes employed 
 for roughly ascertaining the proportion of alcohol in a fermented or 
 distilled liquid, the foreign matters in which prevent any safe inference 
 from the specific gravity. 
 
 The last portions of water are removed from alcohol by allowing it to 
 stand for two or three days over powdered quick-lime, and distilling, when 
 the lime retains the water in the form of hydrate of lime, and the pure or 
 absolute alcohol distils over. It must then be preserved in well stopped 
 bottles, since it readily absorbs moisture from the atmosphere. Its attrac- 
 tion for water causes it to evolve heat when mixed with that liquid, and 
 
PREPARATION OF ETHER. 517 
 
 the volume of the mixture is less than the sum of the volumes of its 
 components, showing that combination has taken place. 
 
 380. ETHER, or, as it is sometimes erroneously called, sulphuric ether 
 (C 4 H 5 0), is obtained by distilling a mixture of two measures of alcohol 
 with one measure of concentrated sulphuric acid. As soon as the mixture 
 begins to blacken, in consequence of a secondary decomposition of the 
 alcohol, the retort is allowed to cool, another half measure of alcohol is 
 added, and the mixture again distilled as long as ether is obtained. 
 
 A far better method of obtaining ether is that known as the continuous 
 process. Alcohol of sp. gr. 0'830 is mixed with an equal measure of con- 
 centrated sulphuric acid, and introduced into a retort or flask (fig. 275), 
 
 Fig. 275. Continuous etherification. 
 
 which is connected with a small cistern containing alcohol. The mixture 
 in the flask is rapidly raised to the boiling point, and alcohol is allowed to 
 pass slowly in from the reservoir through a syphon furnished with a stop- 
 cock, so as to keep the liquid in the flask at a constant level. A thermo- 
 meter should be immersed in the liquid, the temperature of which should 
 be maintained at 284 to 290 F. By this process, one measure of sul- 
 phuric acid will effect the conversion into ether of thirty measures of 
 alcohol. 
 
 The boiling point of ether being very low (94'8 F.) necessitates the 
 employment of a good condensing arrangement in this process. 
 
 The liquid which distils over contains about two-thirds of its weight 
 of ether, with about one-sixth of water, and an equal quantity of alcohol. 
 Traces of sulphurous acid are also generally present. To obtain the pure 
 ether, it is shaken with water containing a little carbonate of potash, when 
 the water dissolves the alcohol, and the potash removes the sulphurous 
 acid ; the ether being very sparingly soluble in, and much lighter than 
 water (sp. gr. 0*74), rises to the surface, holding a little water in solution. 
 This upper layer is drawn off and freed from water by distillation in a 
 water-bath, at a very low heat, over quick-lime. 
 
 The explanation of the chemistry of this process of etherification will 
 be more intelligible after some other changes to which alcohol is liable 
 have been studied. 
 
518 PREPAKATION OF ETHYLIC IODIDE. 
 
 The most striking properties of ether are its peculiar odour and its 
 great volatility ; its rapid evaporation when poured upon the hand gives 
 rise to a sensation of intense cold ; and if a little ether be evaporated by 
 blowing upon it in a watch-glass with a drop of water hanging from its 
 convexity, the water will be speedily frozen. Ether is also exceedingly 
 inflammable ; and since its vapour is very heavy (sp. gr. 2*59), and passes in 
 an unbroken stream through the air for a considerable distance, great care 
 should be taken to avoid pouring it from a bottle in the neighbourhood 
 of a flame. Its flame is far more luminous than that of alcohol, and much 
 acetylene is produced during its imperfect combustion (p. 85). 
 
 The high specific gravity, volatility, and inflammability of ether vapour admit of 
 illustration by some curious experiments : 
 
 If a small piece of sponge be saturated with ether and placed in the centre of a 
 large wooden tray, two or three inches deep, the latter will soon be entirely filled 
 with the vapour, as may be shown by applying a lighted match to one corner. A 
 jug may be warmed by rinsing a little hot water round it, and this having been 
 thrown out, a few drachms of ether may be poured into the jug, which will imme- 
 diately become filled with ether vapour, and from this several glasses may be filled 
 in succession, the presence of the ether vapour being proved by a lighted taper. 
 
 A pneumatic trough may be filled with warm water, a small test-tube filled with 
 ether inverted with its mouth under the water, and the ether quickly decanted up 
 into a gas-jar also filled with hot water, where it will be immediately converted into 
 vapour, and may be decanted through the water into other vessels, and dealt witli 
 like a permanent gas. Some cold water poured over the jar containing it at once 
 proves its condensible character. 
 
 When ether is acted upon by hydrochloric, hydrobromic, or hydriodic 
 acid, the oxygen of the ether enters into combination with the hydrogen 
 of the acid, and the chlorine, bromine, or iodine, occupies its place. 
 
 Thus, with hydrochloric acid 
 
 C 4 H 5 + HC1 = C 4 H 5 C1 + HO. 
 
 In a similar manner, hydrobromic ether, C 4 H 5 Br, and hydriodic ether, 
 C 4 H 5 I, may be formed. The best method of obtaining the two last, how- 
 ever, consists in distilling moderately strong alcohol with phosphorus, and 
 either bromine or iodine, when pltosphovinic or phoaphethylic acid and 
 hydriodic ether are formed 
 
 6C 4 H 6 2 + P + I 5 = 5C 4 H 5 I + 2HO . C 4 H 5 . P0 5 + 4HO.* 
 
 Alcohol. Phosphovinic acid. 
 
 These three ethers are colourless fragrant volatile liquids, which are 
 of the greatest value in the investigation of the constitution of complex 
 organic compounds. 
 
 This remark applies particularly to hydriodic ether (iodide of ethyle), 
 which is less volatile than the others, and therefore more easily manage- 
 able in experiments requiring a high temperature. 
 
 Iodide of ethyle, or ethylic iodide, is prepared by distilling 1400 grains of ordinary 
 alcohol (sp. gr. 0-84) with 2000 grains of iodine, and 300 grains of ordinary vitreous 
 phosphorus. The iodine and phosphorus are added alternately, in small portions, 
 
 * If alcohol be written C 4 H 5 O . HO, it will be seen that this change is precisely similar 
 to that which occurs in the preparation of hydriodic acid by the simultaneous action of 
 phosphorus and iodine upon water 
 
 6[(C 4 H 5 )O.HO] + P + I 5 = 5(C 4 H 6 )I + (C 4 H 5 )0 . 2HO . PO., + 4HO 
 6(HO.HO) + P + I 5 = 5HI + H0.2HO.PO S + 4HO . 
 
THE ALCOHOL-RADICALS. 519 
 
 to the alcohol in the retort, which is immersed in cold water to moderate the action, 
 and occasionally shaken. When the whole has been added, the retort is connected 
 with a Liebig's condenser, and heated in the water-bath, when about 2 measured 
 ounces of iodide of ethyle mixed with alcohol will pass over. This is shaken in a 
 stoppered bottle with about an equal measure of water, which dissolves the alcohol, 
 leaving the iodide of ethyle to collect at the bottom as an oily layer (sp. gr. 1-97). 
 After as much as possible of the upper aqueous layer has been removed with a 
 siphon or pipette, the iodide is poured into a small retort containing fused chloride 
 of calcium in powder to remove the water. The retort is closed with a cork, and 
 set aside for some hours, when the iodide of ethyle may be distilled off in the water- 
 bath, and condensed in a Liebig's condenser. 
 
 381. ALCOHOL-RADICALS. If ethylic iodide be poured over granulated 
 zinc contained in a stout glass tube, which is then exhausted of air, herme- 
 tically sealed, and heated for two hours in an oil-bath to 300 F., a crys- 
 stalline substance is deposited which is a compound of iodide of zinc with 
 zinc-ethyle (C 4 H 5 Zn), whilst a colourless liquid separates, consisting 
 of a mixture of three hydrocarbons, which have been liquefied by their own 
 pressure. On breaking the extremity of the tube under water, this liquid 
 rapidly escapes in the form of gas, which proves on examination to contain 
 olefiant gas (C 4 H 4 ), hydride of ethyle (C 4 H 6 ), and ethyle (C 4 H 5 ), the last 
 of which may be obtained nearly pure by collecting the last portions of 
 gas separately, since ethyle is the least volatile of these hydrocarbons. 
 
 Neglecting the secondary decompositions which give rise to the other 
 products, the formation of ethyle would be represented by the simple 
 equation: 
 
 C 4 H 5 I + Zn - Znl + C 4 H 5 . 
 
 Ethylic iodide. Ethyle. 
 
 Ethyle is a colourless gas, having a faint ethereal smell, insoluble in 
 water, and requiring a pressure of two or three atmospheres for its 
 liquefaction. The interest which attaches to it is due to its being regarded 
 by many chemists as the" radical or starting-point of the series of com- 
 pounds derived from vinic alcohol, which is thence spoken of as the 
 ethyle series, and this view of the constitution of those compounds was 
 in favour long before the compound C 4 H 5 was obtained in the separate 
 state, this being a discovery of very recent date. 
 
 Mention has already been made of the existence of another radical 
 methyle (C 2 H 3 ) obtained by a similar process, which may be regarded as 
 the starting-point of the wood-spirit series. 
 
 Butyle (C 8 H 9 ), amyle (C }0 H U ), and caproyle (C 12 H 18 ), the supposed 
 radicals of the butylic, amylic, and caproic alcohols, have also been ob- 
 tained, these being liquids with progressive boiling points. We are thus 
 in possession of several members of a homologous series of hydrocarbons, 
 which may be designated the alcohol-radicals, and represented by the 
 general formula, C 2ft H 2n + 1 . 
 
 It will be evident that the series of aldehydes (C 2n H 2n 2 ) and of acids 
 derived from the alcohols (C 2n H 2n + 2 2 ), may be regarded as the hydrated oxides of 
 other radicals (C 2n H 2n _i) which resemble the non-metallic or electro-negative bodies 
 rather than the metals, by their disposition to yield acid rather than basic substances 
 when oxidised. Thus, in the series derived from common alcohol 
 
 C 4 H 4 2 = (C 4 H 3 )O.HO. 
 
 Aldehyde. 
 
 C 4 H 4 4 = (C 4 H 3 )0 3 .HO 
 Acetic acid. 
 
520 DUPLICATE NATURE OF THE ALCOHOL-RADICALS. 
 
 We should thus have corresponding series of electro-positive and electro-negative 
 radicals 
 
 Electro-positive radicals. 
 
 1 
 
 Methyle, C 2 H 3 
 
 Ethyle, C 4 H 5 
 
 Propyle, C 6 H r 
 
 Butyle, C 8 H 9 
 
 Amyle, C 10 H n 
 &c. 
 
 Electro-negative radicals. 
 
 Forrayle, C 2 H ? 
 
 Acetyle, C 4 H 3 
 
 Propionyle, C 6 H 5 ' 
 
 Butyryle, C 8 H 7 
 
 Valeryle, C 10 H 9 
 &c. 
 
 The electro-negative radicals have not been obtained in the separate state. 
 
 382. The formulae above given for the alcohol-radicals represent each 
 equivalent* as yielding only two volumes of vapour (0=1 vol.), in which 
 respect they would form exceptions to the rule which holds good with 
 all other compounds of carbon and hydrogen, viz., that one equivalent 
 in the state of vapour occupies four volumes (p. 460). t 
 
 This anomaly would disappear if the formulae were doubled, so that 
 ethyle became C 8 H 10 , amyle C 20 H 22 , and so on. Experiment has shown 
 that these formula really must be doubled in order to express correctly 
 the constitution of the hydrocarbons ; for if a mixture of iodide of ethyle 
 and iodide of amyle (C 10 H U I, prepared from fousel oil just as iodide of 
 ethyle is from alcohol) be heated with sodium, a colourless liquid is ob- 
 tained, which is a true combination of ethyle and amyle (C 4 H 5 . C 10 H n ) 
 
 C 4 H 5 I + C 10 H U I + Na 2 = 2NaI + C 4 H 5 . C 10 H U 
 
 Ethyle-a my le. 
 
 In a similar manner, ethyle -butyle (C 4 H 5 . C 8 H 9 ), methyle-cap- 
 royle (C 2 H 3 . C 12 H 13 ), butyle-amyle (C 8 H 9 . C 10 H U ), and butyle-caproyle 
 (C 8 H 9 . C 12 H 13 ), have been obtained. 
 
 These double radicals all yield four volumes of vapour for each equivalent 
 of the compound, J showing that the ordinary formula for methyle (C 2 H 3 ), 
 which furnishes only two volumes, must be converted into that of a double 
 radical, methyle-methyle (C 2 H 3 . C 2 H 3 ), which would give four volumes of 
 vapour, and in a similar manner, ethyle would become (C 4 H 5 , C 4 H 5 ), butyle 
 (C 8 H 9 . C 8 H 9 ), and so on. 
 
 This duplicate nature of the radicals at once explains the circumstance 
 that they do not unite directly with chlorine, bromine, &c., as might have 
 been expected. Thus ethyle, with iodine, does not combine to form iodide 
 of ethyle, because the ethyle itself is an ethylide of ethyle. 
 
 Again, the formation of zinc ethyle (C 4 H 5 Zn), and of hydride of ethyle 
 (C 4 H 5 H), during the action of zinc upon iodide of ethyle, becomes intel- 
 ligible upon this view. Indeed, the first stage of this action appears to 
 consist in the formation of zinc-ethyle 
 
 C 4 H 5 I + Zn 2 = C 4 H 5 Zn + Znl. 
 
 Iodide of ethyle. Zinc-ethyle. 
 
 In the second stage, the zinc-ethyle acts upon a fresh portion of iodide 
 of ethyle, producing iodide of zinc and the double radical ethyle 
 C 4 H 5 I + C 4 ELZn = Znl + C 4 H 5 . C 4 H 5 . 
 
 Iodide of ethyle. Zinc-ethyle. Ethyle. 
 
 * Or each molecule as yielding one volume of vapour (H = 1 vol.) 
 t Or one molecule in the state of vapour occupies 2 vols. (H = 1 vol. ) 
 + Or one molecule yields two volumes of vapour (H = 1 vol.) 
 
HYDRIDES OF THE ALCOHOL- RADICALS. 521 
 
 The hydride of ethyle itself clearly corresponds to the double radical 
 ethyle, one-half of which is replaced by an equivalent of hydrogen 
 (C 4 H 5 . H), itself occupying two volumes, like the compound C 4 H 5 which 
 it has displaced. 
 
 The simultaneous formation of hydride of ethyle and of olefiant gas 
 during the action of zinc upon iodide of ethyle, might be represented by 
 the equation 
 
 2C 4 H 5 I + Zn 2 = 2ZnI + C 4 H 5 .H + C 4 H 4 . 
 
 Iodide of ethyle. Hydride of ethyle. 
 
 Hydride of ethyle is the representative of a series of homologous hydro- 
 carbons, of which the first member, the hydride of methyle (C 2 H 3 . H), is 
 identical with marsh-gas. 
 
 The following table exhibits some of the chief members of the marsh- 
 gas series of hydrocarbons (general formula C 2w H 2n+2 ), as well as the cor- 
 responding alcohol radicals,* general formula 2(C 2n H 2n + 1 ) 
 
 Radical. Hydride.f 
 
 Methyle, . . C 2 H 3 . C 2 H 8 C 2 H 3 .H=C 2 H 4 
 
 Ethyle, . . . C 4 H 5 . C 4 H 5 C 4 H 5 . H = C 4 H 6 
 
 Butyle,. . . C 8 H 9 .C 8 H 9 C 8 H 9 . H = C 8 H 10 
 
 Amyle, . . . C JO H U .C 10 H U C 10 H U .H = C 10 H 12 
 
 The three first of these hydrides are gaseous, the last a volatile liquid. 
 
 If ethyle (C 4 H 5 = E) be accepted as the radical of the alcohol series, 
 then ether (C 4 H 5 0) would become the oxide of ethyle, and alcohol 
 (C 4 H 6 2 = C 4 H 5 0. HO), the hydrated oxide of ethyle; and it will be 
 seen that upon this view a considerable number of the relations of these 
 bodies can be readily explained. 
 
 383. On referring to the action of hydrochloric acid upon ether, it will 
 be seen to resemble exactly that of the same acid upon the basic oxide of 
 a metal, consisting in an exchange between the chlorine of the acid and 
 the oxygen of the base. Chloride of ethyle may also be produced by the 
 action of hydrochloric acid upon alcohol (EO . HO), just as chloride of 
 potassium is produced by the action of that acid upon hydrate of 
 potash 
 
 EO.HO + HC1 = EC1 + 2HO. 
 
 Alcohol. Chloride of ethyle. 
 
 It would be expected that the action of other acids upon alcohol would 
 correspond to their action upon hydrate of potash, and with several acids 
 this is really the case, although it is far more difficult to break up the 
 alcohol than the hydrate of potash. 
 
 If alcohol be boiled for many hours with dry oxalic acid (HO . C 2 3 ) in 
 a flask provided with a long tube, so that the volatilised alcohol may run 
 back, it is found that, on diluting the solution with water, a heavy fra- 
 grant liquid separates, which has the composition C 4 H 5 . C 2 3 , and is 
 termed oxalic ether. 
 
 Its formation may be thus represented 
 
 EO.HO + HO.C 2 3 = EO.C 2 3 + 2HO . 
 
 Alcohol. Oxalic acid. Oxalic ether. 
 
 * See also American petroleum, p. 468. 
 
 f Each of these hydrides is isomeric with the radical immediately preceding it. Thus 
 hydride of ethyle has the same composition as methyle, and is regarded by some chemists as 
 identical with it. 
 
522 NITEOUS ETHER HYDROXYLAMINE. 
 
 It is formed far more easily in the presence of strong sulphuric acid, 
 since this developes the ether (EO) to combine with the oxalic acid. % 
 
 By treatment with hydrate of potash, the oxalic ether is decomposed, 
 yielding oxalate of potash and alcohol ; thus 
 
 EO.C 2 3 + KO.HO - KO.C 2 3 + EO.HO. 
 
 But if the oxalic ether be mixed with only half the quantity of hydrate of 
 potash required for this decomposition, there is obtained, instead of oxalate 
 of potash, a salt, crystallising in pearly scales, having the composition 
 KO. EO. 2(C 2 3 ), the formation of which is easily understood 
 
 2(EO.C 2 3 ) + KO.HO = KO.E0.2C 2 3 + EO.HO. 
 
 Oxalic ether. Oxalovinate of potash. 
 
 By decomposing this salt with hydrofluosilicic acid (see p. 181) to remove 
 the potassium in an insoluble form, a new acid is obtained, which has the 
 composition HO . EO . 2C 2 3 , and is called oxalovinic or oxo.lethylic acid. 
 It might evidently be also called the binoxalate of oxide of ethyle, since it 
 corresponds in composition to the binoxalate of potash, KO . HO . 2C 2 3 . 
 
 Most of the acids form, with oxide of ethyle, compounds corresponding 
 to oxalic ether ; thus, by distilling acetic acid with alcohol and sulphuric 
 acid, and diluting the distilled liquid with water, acetic ether (EO . C 4 H 3 3 ) 
 is separated, remarkable for its very fragrant odour, which has a share in 
 the perfume of cider, perry, vinegar, and of many wines. 
 
 The ether used in medicine under the names of sweet .spirits of nitre, 
 nitrous ether, and nitric ether, is essentially a solution of nitrous ether 
 (C 4 H 5 . N0 3 ) in alcohol, and is prepared by distilling alcohol with nitric 
 acid, when a violent and complicated reaction takes place, one portion of 
 the alcohol being converted into aldehyde, at the expense of a part of the 
 oxygen of the nitric acid 
 
 2(C 4 H 6 2 ) + HO.N0 5 = C 4 H 4 2 + C 4 H 5 O.N0 3 + 4HO. 
 
 Alcohol. Aldehyde. Nitrous ether, 
 
 Nitrous ether is a very volatile liquid, characterised by a powerful odour 
 of rennet-apples, and in the pure state decomposes spontaneously, evolving 
 nitric oxide. 
 
 True nitric ether (EO . N0 5 ) may also be obtained as a fragrant, heavy oily liquid, 
 by distilling alcohol with nitric acid, under certain precautions. It is decomposed 
 with explosion at a temperature of about 200 F. 
 
 By the action of nascent hydrogen upon nitric ether, a basic substance is produced, 
 which has been named hydroxylamine, in allusion to its remarkable formula, NH 3 2 , 
 which might be regarded as ammonia, NH 3 , in which one equivalent of hydrogen 
 is replaced by hydroxyle, H0 2 
 
 C 4 H 5 O.N0 5 + H 6 = C 4 H.O.HO + 2HO + NH 3 2 . 
 Nitric ether. Alcohol. Hydroxylamine. 
 
 In order to obtain this base, 5 parts of nitric ether are acted on by 12 parts of tin 
 and 50 parts of concentrated hydrochloric acid. When the action is over, the alcohol 
 is expelled by heat, the tin precipitated by hydrosulphuric acid, the solution evapo- 
 rated to dryness, and the residue boiled with absolute alcohol, which leaves some hydro- 
 chlorate of ammonia undissolved. The hydrochlorate of hydroxylamine (NH 3 2 . HC1) 
 crystallises in long needles from the alcoholic solution. From the sulphate of hydroxy- 
 lamine, by decomposition with baryta, a solution of the base itself may be obtained; 
 but pure hydroxylamine has not been isolated from the solution, since it has a ten- 
 dency to decompose into ammonia, water, and nitrogen 
 
 3NH 3 2 = NH 3 + N 2 + 6HO. 
 Hydroxylamine. 
 The chloric ether used for medicinal purposes is riot an ether in the true sense of 
 
SULPHOVINIC ACID. 523 
 
 the term, but a solution of chloroform (C 2 HC1 3 ) in alcohol. Chloroform will be more 
 particularly described hereafter. 
 
 Perchloric ether (C # H 5 O . C10 7 ) is only interesting from the circumstance that, 
 although an oily liquid, it explodes violently under a sudden blow. 
 
 JBoracic ether, which has the remarkable formula (3EO . B0 3 ), is formed when ter- 
 chloride of boron is decomposed by alcohol 
 
 BC1 3 + 3(EO.HO) = 3EO.B0 3 -f- 3HC1 
 
 and may also be obtained by heating anhydrous boracic acid with an excess of 
 alcohol under pressure. It is lighter than water (sp. gr. 0'88), and boils at 246 F. 
 When heated with anhydrous boracic acid, it is converted into EO . B0 3 , which is 
 decomposed by heat into 3EO . B0 3 and EO . 3B0 3 , the latter being a vitreous solid. 
 When bichloride of silicon is decomposed by alcohol, the compound 2EO . Si0 2 is 
 produced 
 
 SiCl 2 + 2(EO.HO) = 2EO.Si0 2 + 2HC1. 
 
 Silicic ether. 
 
 This silicic ether is a colourless liquid, of sp. gr. 0-93, and distilling unchanged at 
 330 F. It has an ethereal odour, and burns with a brilliant flame which deposits 
 silica. When poured upon the surface of water, it gradually decomposes, with 
 separation of gelatinous hydrated silica 
 
 2EO.Si0 2 + 2HO = 2(EO.HO) + Si0 2 . 
 
 Alcohol. 
 
 When the ether is kept in a moist atmosphere, it deposits a hard transparent mass 
 of silica, known as artificial quartz. 
 
 Two other silicic ethers have been obtained, having respectively the composition 
 EO . Si0 2 and EO . 2Si0 2 ; the former liquid, the latter viscous. 
 
 Carbonic ether (EO . C0 2 ) may be obtained by heating carbonate of silver with iodide 
 of ethyle in a sealed tube ; 
 
 AgO.C0 2 + El = EO.C0 2 + Agl. 
 
 The compound 2EO . C0 2 has been obtained by the action of sodium upon an 
 alcoholic solution of chloropicrine 
 
 C 2 C1 3 (N0 4 ) + 4(EO . HO) + Na 4 = 3NaCl + NaO . N0 3 + 2(2EO . C0 2 ) + H 4 . 
 Chloropicrine. Alcohol. Subcarbonate of 
 
 ethyle. 
 
 When carbonic acid is passed through a solution of hydrate of potash in absolute 
 alcohol, the carbovinate of potash is obtained, in crystals having the composition 
 KO.E0.2C0 2 , corresponding to bicarbonate of potash, KO.H0.2C0 2 . 
 
 By the action of syrupy phosphoric acid upon alcohol, the compound 2HO . EO . P0 5 , 
 phosphovinic acid, is formed, and by neutralising it with a base, a phosphovinate may 
 be obtained, composed after the general formula 2MO . EO . P0 5 . 
 
 A second acid is formed at the same time, having the formula HO . 2EO . P0 6 , its 
 salts being MO . 2EO . PO S . Phosphovinic acid is found abundantly in the residue 
 from the preparation of iodide of ethyle. 
 
 The true phosphoric ether (3EO . P0 5 ) is also said to have been obtained. 
 
 The true sulphuric ether (EO . S0 3 ) can only be formed by passing tha vapour of 
 anhydrous sulphuric acid into ether. It is an oily liquid, heavier than water, and 
 decomposed by heat, defiant gas and alcohol being found amongst the products, for 
 C 4 H 4 + C 4 H 6 2 = 2^ 4 H.OJ. 
 
 The fragrant liquid known as heavy oil of wine, which is formed towards the latter 
 part of the preparation of ether and of defiant gas (page 85), appears to contain 
 the sulphate of oxide of ethyle, together with some hydrocarbons of the olefiant gas 
 series. When decomposed with a solution of potash, light oil of wine rises, which 
 contains hydrocarbons of ths olefiant gas series. 
 
 384. When ether or alcohol is added to concentrated sulphuric acid, 
 much heat is evolved, in consequence of the combination of the oxide of 
 ethyle with sulphuric acid, to form sulphovinic or sulphethylic acid, 
 HO . EO . 2S0 3 or bisulphate of oxide of ethyle, corresponding in com- 
 position to the bisulphate of potash, KO . HO . 2S0 3 . If baryta be now 
 added to the solution, the uncombined sulphuric acid will be precipitated 
 
524 THEORY OF FORMATION OF ETHER. 
 
 in the form of sulphate of baryta, but the sulphovinic acid will combine 
 with the base to form the sulphovinate of baryta, which may be obtained 
 by evaporating the solution, in rhombic prisms which have the formula 
 BaO . EO . 2SO 3 . 2Aq., and are easily soluble in water. By cautiously 
 adding sulphuric acid to the solution of sulphovinate of baryta till the 
 whole of the baryta is precipitated as sulphate, and evaporating the filtered 
 liquid in vacuo, the pure sulphovinic acid is obtained as a syrupy liquid 
 liable to spontaneous decomposition, and readily decomposed when heated 
 with water, into alcohol and sulphuric acid 
 
 HO.E0.2S0 3 + 2HO = 2 (HO . SO.) + EO.HO. 
 
 Sulphovinic acid. Alcohol. 
 
 385. Vinic acids are not formed by monobasic acids. It must be noticed 
 that although the greater number of the acids are capable of forming ethers, 
 only a few of them produce vinic acids. Indeed, only those acids form 
 vinic acids which there is reason to believe are polybasic, i.e., require more 
 than one equivalent of a base for the formation of a neutral salt (p. 256). 
 Thus, sulphuric acid should probably be represented by the formula 
 2HO . S 2 6 instead of by HO . S0 3 ; when sulphate of potash would become 
 2KO . S. 2 6 , bisulphate of potash KO . HO . S^0 6 , and sulphovinic acid 
 EO . HO . S 2 6 , the tendency to form a vinic acid depending upon the 
 possibility of replacing a portion of the water of hydration in the acid by 
 oxide of ethyle. In the case of nitric acid, which is undoubtedly a mono- 
 basic acid, and does not form acid salts, no vinic acid can be produced 
 the formula of the acid being HO . N0 5 , the water of hydration must be 
 entirely or not at all replaced by the oxide of ethyle. 
 
 386. Theory of etlierification. When sulphovinic acid is decomposed 
 by heat, especially in the presence of excess of alcohol, a large proportion 
 of ether is found among the products, and this has given rise to a very 
 general opinion with chemists, that the production of sulphovinic acid is 
 an intermediate stage in the formation of ether, by the ordinary process 
 of distilling alcohol with sulphuric acid. At first sight it would appear 
 that the etherification of alcohol in this process was sufficiently explained 
 by reference to the attraction of sulphuric acid for water, and consisted in 
 a simple removal of water from the alcohol by the acid, for 
 
 C 4 H 6 2 - HO - C 4 H 5 . 
 
 Alcohol. Ether. 
 
 When it is found, however, that a continuous stream of alcohol, flowing 
 into heated sulphuric acid in a retort, is converted into ether and water, 
 which is not retained by the sulphuric acid, but distils over with the 
 ether, and that this may go on almost without limit, this explanation is 
 no longer tenable. 
 
 Accordingly, the formation of ether from alcohol by the action of sul- 
 phuric acid is generally referred to the formation of sulphovinic acid as 
 soon as the alcohol and the acid are brought in contact, and the subsequent 
 decomposition of this sulphovinic acid, in the presence of water or alcohol, 
 into hydrated sulphuric acid, water, and ether ; thus 
 
 HO.E0.2S0 3 + HO = 2(HO.S0 3 ) + EO, or 
 
 Sulphovinic acid. Ether. 
 
 HO.E0.2S0 3 + EO.HO = 2(HO.S0 3 ) + 2EO 
 
 Sulphovinic acid. Alcohol. Ether 
 
DOUBLE ETHERS. 525 
 
 The hydrated sulphuric acid thus set free would of course give rise to 
 the formation of a fresh quantity of sulphovinic acid, which would be 
 decomposed in its turn, and so on without limit. 
 
 A strong argument in favour of this view is deducible from the follow- 
 ing experiment : 
 
 When amylic alcohol (the hydrated oxide of amyle, C 10 H U . HO) is 
 mixed with concentrated sulphuric acid, it forms sulphamylic acid 
 (C 10 H U . HO . 2S0 3 ), corresponding to sulphovinic acid, and if this be 
 heated in a retort, and alcohol be allowed to flow into it, as in making 
 ether, the first portion which distils over is found to be a true double 
 ether, composed of one equivalent of ethylic, and one equivalent of amylic 
 ether (C 4 H 5 . C 10 H U 0), the production of which would be represented 
 by the equation 
 
 HO . C 10 H n O . 2S0 3 + C 4 H.O . HO = C 4 H 5 . C 10 H n O + 2(HO . S0 3 ). 
 
 Sulphamylic acid. Alcohol. Amylethylic ether. 
 
 On continuing the distillation, nothing but ordinary ethylic ether is 
 obtained. 
 
 The existence of these double ethers might have been anticipated from 
 what has been said with respect to the double radicals (p. 520), but the 
 mode of formation in the above instance certainly affords support to the 
 view, that ether results from the decomposition of sulphovinic acid by 
 alcohol in the ordinary etherifying process. 
 
 On the other hand, this theory of etherification is shaken by the cir- 
 cumstance, that if vapour of alcohol be passed into boiling sulphuric acid, 
 of sp. gr. l - 52 (boiling at 290), almost the whole of the alcohol is resolved 
 into water and ether, which distil over, so that either no sulphovinic acid 
 is formed, or it is only formed to be immediately decomposed. If the acid 
 have the sp. gr. 1*61 (boiling at 330), no ether is obtained, the alcohol 
 being resolved into olefiant gas and water. 
 
 Moreover, hydrated phosphoric acid cannot be substituted for the sul- 
 phuric acid in the preparation of ether, notwithstanding that it also forms 
 a vinic acid. 
 
 Hence, many chemists are inclined to attribute to sulphuric acid a 
 specific action by contact (catalytic action) upon alcohol, causing its resolu- 
 tion into water and ether, or olefiant gas, according to the temperature. 
 
 This view receives some confirmation from the behaviour of sulphuric 
 acid towards cellulose and certain other substances, in which it causes 
 important transformations, without itself appearing to take part in the 
 change. 
 
 In connection with this subject, it is remarkably interesting to observe, 
 that alcohol may actually be reproduced from olefiant gas and water under 
 the influence of sulphuric acid. If concentrated sulphuric acid be vio- 
 lently agitated in a vessel containing olefiant gas, the latter is absorbed, 
 and on diluting the acid with water and distilling, a quantity of alcohol 
 is obtained. 
 
 This observation of modern date is in favour of the opinion, long since 
 maintained by many chemists, that olefiant gas, and the hydrocarbons 
 homologous with it, should really be regarded as the radicals of the various 
 alcohols and their derivatives. Upon this view, ether would become the 
 hydrate of ethylene (C 4 H 4 . HO), alcohol would be the li-hydrate of ethy- 
 Zene(C 4 H 4 .2HO), &c. 
 
526 WATER-TYPE VIEW OF ALCOHOLS AND ETHERS. 
 
 387. But there are some other facts which conduct us to another opinion 
 with respect to the constitution of ether and alcohol. 
 
 "When potassium or sodium is thrown into absolute alcohol, the metal 
 is dissolved with disengagement of heat and rapid evolution of hydrogen, 
 and a crystalline compound is formed, known as potassium-alcohol (ethy- 
 late of potash) or sodium-alcohol (ethylate of soda), and containing an 
 equivalent of the metal in the place of an equivalent of hydrogen ; the 
 action of potassium upon alcohol would be thus represented 
 
 C 4 H 5 O.HO + K = C 4 H 5 O.KO + H. 
 
 Alcohol. Potassium-alcohol. 
 
 Other alcohols behave in a similar manner. No one can fail to be struck 
 with the similarity which exists between the action of potassium upon 
 alcohol and upon water, and chemists have naturally endeavoured to refer 
 both actions to a common type. This may be done without difficulty, if 
 it be borne in mind that the actual result of the decomposition of water 
 by potassium is not potash, KG, but hydrate of potash, KO . HO, which 
 may with great propriety be regarded as a double equivalent of water in 
 which half the hydrogen has been displaced by potassium, KH0 2 . 
 
 The decomposition of water by potassium would then be represented 
 by the equation 
 
 + K = + H. 
 
 = |J 
 
 Alcohol may be represented with equal fitness, as water in which half 
 the hydrogen is replaced by ethyle (C 4 H 5 ), or EH0 2 , and the action of 
 potassium upon it may be thus expressed 
 
 + H - 
 
 Potassium- 
 alcohoL 
 
 In a similar manner sodium-alcohol would be formed.* 
 
 When sodium-alcohol is heated in a sealed tube with the iodide of one 
 of the alcohol-radicals, the sodium combines with the iodine, whilst the 
 alcohol-radical enters into the place of the sodium, and a double ether is 
 formed. 
 
 Thus, if iodide of methyle (C 2 H 3 I) be decomposed by sodium-alcohol 
 
 <W + 10, - Nal * E lo 
 
 2 
 ll * ) "-'2-"'3 J 
 
 Sodium-alcohol. Methyl-ethylic 
 
 ether. 
 
 p \ 
 
 In a similar manner amyl-ethylic ether, Q -^ V 2 , would be produced. 
 
 Again, if iodide of ethyle be decomposed by sodium-alcohol, common 
 ether is obtained, and the action must in consistency be similarly ex- 
 plained 
 
 ^ T 4 
 
 2 C 4 
 
 Sodium-alcohol. Common ether. 
 
 * Thallium-alcohol, C 4 H 5 T10 2 , has also been obtained as a colourless liquid remarkable 
 for its high specific gravity (3*55) and great refractive and dispersive action upon light. 
 
MERCAPTAN. 527 
 
 From this it would appear that the formula of common ether should be 
 doubled, and this would not only be consistent with the duplication of 
 the formula of ethyle (p. 520), but would destroy an existing anomaly, 
 by making the equivalent of ether in the state of vapour to occupy four 
 volumes, whereas the formula C 4 H 5 corresponds only to two volumes of 
 vapour. 
 
 Alcohol and ether would then be constituted upon the same type, that 
 of a double equivalent of water, and would still bear to each other the 
 same relation as exists between hydrate of potash and potash ; thus 
 
 Potassium series. 
 
 Potassium, . . K 
 
 Hydrate of Potash, TT > 2 
 Potash, . . x 1 2 
 
 Ethyle series. 
 
 C 4 H 5 Ethyle. 
 
 K , r, v M , Q Mcohol 
 
 The molecular formulae are more convenient for exhibiting the relation between 
 water and alcohol, and their derivatives. Thus if a molecule (see p. 52) or two 
 atoms (or volumes) of hydrogen be taken as the type, the derivation of these com- 
 pounds from it may be easily traced. 
 
 (Atomic weights ; = 12, H = 1, = 16. 
 Atomic volumes ; = 1 vol. (?), H = 1 vol., = 1 vol.) 
 
 Molecular formulce (2 vols.) 
 
 Hydrogen, HH 
 
 Water, HH . 
 
 Hydrate of potash, KH0 
 
 Ethyle, e 2 H 6 .0 2 H 5 . 
 
 Ether, e 2 H 5 .0 2 H 5 .0 
 
 Ethylate of potash, K . 2 H 5 . 
 Alcohol, H .0 2 H 5 .0 
 
 Methyl-ethylic ether, 6H 3 . 2 H 5 . 
 Ethyl-amyle, e 2 H 6 . 5 H n 
 
 388. Compounds have been obtained corresponding to alcohol and ether, in which 
 the place of the oxygen is occupied by sulphur, and which bear the same relation to 
 hydrosulphuric acid as alcohol and ether bear to water. 
 
 TT 
 
 Hydrosulphuric acid, 
 
 %H!} S * Sulphide of potash, f} S , 
 
 O H 1 TC 1 
 
 Mercaptan, 4 H 5 I S 2 Hydrosulphate of potassium, V S 2 
 
 All these compounds are distinguished for their powerful odour of garlic. This 
 is especially the case with mercaptan, which is notoriously one of the most evil- 
 smelling chemical compounds. It is prepared by distilling solution of hydrosulphate 
 of potassium (obtained by saturating potash with hydrosulphuric acid) with sulpho- 
 vinate of potash, or better, of lime 
 
 KO . C 4 H 5 . 2S0 3 + S 2 = S 2 + 2(KO . S0 3 ) . 
 
 Sulphovinate of potash. Mercaptan. 
 
 Mercaptan is a light, very volatile and inflammable liquid, sparingly soluble in 
 water. That it is constituted after the type of hydrosulphuric acid is shown by its 
 action upon metals and their oxides. Potassium acts upon it precisely as it does 
 upon alcohol 
 
 K = < S S + H 
 
 Mcrrantan Mercaptide of potassium 
 
 Mercaptan. Qf potas8ium . mercaptan . 
 
528 CYANIDES OF ALCOHOL-RADICALS. 
 
 Its name was bestowed in allusion to its action upon the oxide of mercury, when 
 it forms a white crystalline inodorous compound, insoluble in water but soluble in 
 alcohol 
 
 4 H 5 } S 2 + H S = 4 Hg } S 2 + H0 ' 
 Mercaptan. Mercaptide of mercury. 
 
 389. Hydrocyanic ether (C 4 H 6 .C 2 N = ECy), or cyanide of ethyle, fs obtained by 
 distilling sulphovinate of potash with cyanide of potassium 
 
 KO . EO . 2S0 3 + KCy = ECy + 2(KO . S0 3 ) . 
 Sulphovinate of potash. Hydrocyanic ether. 
 
 The cyanide of ethyle is a volatile poisonous liquid, smelling strongly of garlic. 
 Its most interesting feature is, that when boiled with a solution of potash, it furnishes 
 propylate of potash, whilst ammonia is evolved 
 
 C 4 H 6 . C 2 N + KO . HO + 2HO = KO . C 6 H 6 3 + NH 3 . 
 
 Hydrocyanic ether. Propylate of potash. 
 
 In a similar manner, the cyanides of all the alcohol-radicals, when boiled with 
 solution of potash, yield the potash-salt of the acid which stands next in the 
 homologous series. Thus cyanide of methyle (C 2 H 3 . C 2 N) yields the potash-salt of 
 acetic acid belonging to the ethyle series ; cyanide of amyle (C 10 H n . C 2 N) yields 
 caproate of potash belonging to the caproyle series, and so on. This mode of decom- 
 position argues strongly that hydrogen is really the type of these radicals, for when 
 hydrocyanic acid (HC 2 N) is boiled with solution of potash, it yields the potash-salt 
 of formic acid, the lowest member of the homologous series 
 
 KO . HO + 2HO = KO . C 2 H0 3 + NH, . 
 Hydrocyanic acid. Formiate of potash. 
 
 Thus, leaving the potash out of consideration ; 
 
 H.C 2 N + 4HO = C 2 H 2 4 + NH 3 
 Cyanide of hydrogen. Formic acid. 
 
 C 2 H 3 .C 2 N + 4HO = C 4 H 4 4 + NH 3 
 
 Cyanide of methyle. Acetic acid. 
 
 C 4 H 5 .C 2 N + 4HO = C 6 H 6 4 + NH 3 . 
 
 Cyanide of ethyle. Propylic acid. 
 
 A plausible explanation of these changes may be given, if the hydrocyanic acid 
 (HC 2 N) be represented as ammonia (NH 3 ), in which two equivalents of hydrogen 
 are replaced by two equivalents of carbon (just as one equivalent of hydrogen in 
 water is replaced by one equivalent of carbon to form carbonic oxide). 
 
 N 
 
 Hydrocyanic acid. Water. Formic acid. Ammonia. 
 
 H 
 
 J 4 -t- IN { 
 Cyanide of methyle. Acetic acid. 
 
 N!H 
 
 I ^2 
 
 5:1. = 
 
 '~W + 
 
 J 2 
 
 Cyanide of ethyle. Propylic acid. 
 
 The cyanides of the alcohol radicals will be again referred to under their other 
 designation of nitrilcs. 
 
ARSENICAL ALCOHOL OR ALCARSIN. 529 
 
 KAKODYLE SERIES ORGANO-METALLIC BODIES. 
 
 390. One of the most pleasing results of the progress of investigation 
 in chemistry, is the discovery of the true position among classified com- 
 pounds which is to be assigned to some substance hitherto regarded as 
 anomalous, and as destroying by its presence the symmetry and complete- 
 ness of an otherwise perfect classification. Such was the case, until 
 within the last few years, with Jcakodyle, and the bodies derived from it. 
 Discovered long before the science of organic chemistry was prepared to 
 receive it, it taxed the ingenuity of chemists to find a place for it in their 
 arrangement of organic compounds, and always occupied an anomalous 
 and isolated position. Modern research has now brought to light a whole 
 series of compounds, which would not have been complete without kako- 
 dyle, and this hitherto incomprehensible substance has at length been 
 assigned its proper place. 
 
 When a mixture of equal weights of arsenious acid and dry acetate of 
 potash is submitted to distillation, a heavy poisonous liquid is obtained, 
 which has a most disgusting odour of garlic, and takes fire spontaneously 
 when exposed to the air. This liquid, which has long been known under the 
 names of alcarsin (arsenical alcohol), and Cadet's fuming liquor, has the 
 composition C 4 H 6 AsO, and its production may be represented (if the 
 various secondary products be neglected) by the equation 
 
 2(KO.C 4 H 3 3 ) + As0 3 = C 4 H 6 AsO + 2(KO.C0 2 ) + 2C0 2 . 
 
 Acetate of potash. Alcarsin. 
 
 If acetic acid be represented by the formula derived above (p. 528) from its 
 formation in the action of water upon cyanide of methyle, the formation of alcarsin 
 would be easily explained. Acetate of potash would then be represented by the 
 
 formula ' 2 3 p > 4 , and its action upon arsenious acid might be thus ex- 
 
 pressed 
 
 Arsenious acid. Acetate of potash. Alcarsin. 
 
 Alcarsin has the properties of a base ; it is capable of combining with 
 the oxygen acids to form crystallisable salts, and in contact with the 
 hydrogen acids it furnishes water, together with a salt of the radical of the 
 acid. Thus, with hydrochloric acid, we have 
 
 C 4 H 6 AsO + HC1 = C 4 H 6 AsCl + HO. 
 
 Alcarsin. Chloride. 
 
 The best method of obtaining this chloride consists in dissolving the alcarsin 
 in alcohol, and adding an alcoholic solution of chloride of mercury, when 
 a white crystalline solid is obtained, composed of C 4 H 6 AsO . HgCl ; and 
 on distilling this with hydrochloric acid (out of contact with air), another 
 spontaneously inflammable liquid is obtained, of insupportable odour, and 
 composed of C 4 H 6 AsCl. By distilling this chloride with zinc in an atmo- 
 sphere of carbonic acid gas, a third unbearable liquid is procured, which 
 has the formula C 4 H 6 As,' x " and has been named kakodyle, in allusion to 
 
 * This formula represents only two volumes of vapour for each equivalent. Strictly 
 speaking, therefore, it should be doubled (see p. 520.) 
 
 2L 
 
530 KAKODYLE SERIES. 
 
 its intolerable odour (KCIKOS, bad). This substance is obviously the radical 
 from which the compounds just mentioned are immediately derived; thus 
 
 Kakodyle, C 4 H 6 As = Kd 
 
 Alcarsin, or oxide of kakodyle, C 4 H 6 AsO = KdO 
 Chloride of kakodyle, C 4 H 6 AsCl = KdCl. 
 
 The remarkable properties of kakodyle leave no doubt as to its being 
 really the radical of these compounds, in the same sense in which potas- 
 sium is the radical of the oxide and chloride of that metal, for kakodyle 
 enters into direct combination with chlorine and with oxygen, its attraction 
 for the latter being so energetic as to cause its spontaneous inflammation 
 in the air. 
 
 The discovery of this radical, comporting itself in all respects like a 
 metal, was of the utmost importance in its effect upon organic chemistry, 
 affording very strong ground for belief in the existence of other quasi- 
 metallic radicals, such as ethyle, methyle, &c., which have only recently 
 been isolated. A similar service had been previously rendered to the 
 science by the discovery of the compound radical cyanogen (C 2 N) belong- 
 ing to the electro-negative class opposed to the metals, and for a long time 
 these two remained the only compound radicals which had been obtained 
 in a separate form. 
 
 When kakodyle is brought gradually in contact with oxygen, it is first 
 converted into the oxide of kakodyle (C 4 H 6 AsO), and subsequently into 
 kakodylic add (HO . C 4 H 6 As0 3 = HO . Kd0 3 ), which forms prismatic 
 crystals, unaltered by air, and destitute of poisonous character. When 
 treated with hydrochloric or hydrosulphuric acid, it yields ter chloride 
 (KdCl 3 ) and tersulphide of kakodyle (KdS s ). 
 
 The most poisonous member of this series is the cyanide of kakodyle 
 (C 4 H 6 As . C 2 N = KdCy), which is easily obtained in crystals by decompos- 
 ing cyanide of mercury in solution with oxide of kakodyle 
 HgCy + KdO = HgO + KdCy . 
 
 A very minute quantity of this substance diffused in vapour through the 
 air has the most dangerous effect upon those inhaling it. 
 
 The following are the most important members of the kakodyle series : 
 
 Kakodyle, C 4 H 6 As = Kd 
 
 Oxide of kakodyle, C 4 H 6 AsO = KdO 
 
 Sulphate of kakodyle, C 4 H 6 AsO . S0 3 = KdO . S0 8 
 Sulphide of kakodyle, C 4 H 6 AsS = KdS 
 Chloride of kakodyle, C 4 H 6 AsCl = KdOl 
 Kakodylic acid, ' HO . C 4 H 6 As0 8 = HO . Kd0 3 
 
 Kakodylate of silver, AgO . C 4 H 6 As0 3 = AgO . Kd0 8 
 Tersulphide of kakodyle, C 4 H 6 AsS 8 = KdS 8 
 Terchloride of kakodyle, C 4 H 6 AsCl 3 = KdCl 3 
 
 391. Organo-metallic compounds. The only way of referring kakodyle 
 to any known series was to regard it as an association of arsenic with two 
 equivalents of methyle (C 2 H 3 ), and this supposition necessitated the 
 existence of other compounds of a similar nature, formed, that is, by the 
 association of an inorganic element with a quasi-metallic radical. Accord- 
 ingly, within the last few years, it has been discovered that by heating 
 the iodides of methyle, ethyle, and amyle, with zinc, compounds of those 
 radicals with the metal can be obtained, and these compounds, like kako- 
 dyle, are distinguished by their remarkable attraction for oxygen. 
 
PREPARATION OF ZINC-ETHYLE. 
 
 531 
 
 Nor are arsenic and zinc the only elements with which these radicals 
 can be associated; boron, potassium,' sodium, magnesium, aluminum, 
 cadmium, tin, antimony, bismuth, lead, and mercury may be made to 
 furnish similar compounds, and the principle is now fully established that 
 the alcohol-radicals can enter into combination with metals to form com- 
 pounds which are, in some cases, capable of direct union with oxygen and 
 other electro-negative elements, for which they exhibit a greater attraction 
 than the metals themselves. 
 
 'The members of this class of organo-metallic bodies which have been 
 the subjects of some of the most important researches deserve special 
 attention. 
 
 Zinc-ethyle is prepared by the action of zinc upon iodide of ethyle 
 Zn 2 = C 4 H 5 Zn + Znl. 
 
 800 grains of bright freshly granulated and thoroughly dried zinc are placed in a 
 half-pint flask (E, fig. 276), which is connected with the carbonic acid apparatus (A), 
 
 C 4 H 5 I 
 
 Fig. 276. Preparation of zinc-ethyle. - 
 
 from which the gas is passed through strong sulphuric acid in the bottles (Band C) 
 where it is thoroughly dried. A second perforation in the cork of the flask (E) allows 
 the passage of the tube /, which passes through the two corks in the wide tube F, and 
 dips into a little mercury in D. A stream of cold water is kept running through 
 the wide tube (F), being conveyed by the caoutchouc tubes 1 1 When the whole 
 apparatus has been filled with carbonic acid, the cork of the flask (E) is removed, and 
 400 grains of iodide of ethyle (perfectly free from moisture) are introduced, the col "k 
 being then replaced. The carbonic acid is again passed for a short time, and then 
 cut off by closing the nipper-tap (T) upon a caoutchouc connector, when the gas 
 escapes through the tube(G), which dips into mercury. A gentle heat is then applied 
 by a water-bath to the flask (E) till the iodide of ethyle boils briskly, the vapour 
 being condensed in the tube/, and running back into the flask. In about five hours 
 the conversion is complete, and the iodide ceases to distil. The nipper-tap (T) is 
 again opened and a slow current of carbonic acid allowed to pass ; the position of 
 the condenser (F) is reversed (fig. 277), and the tube/ is connected, by the cork K, 
 with the short test- tube ; the longer limb of a very narrow syphon (I) of stout 
 tube passes through a second perforation in the cork (K), the shorter limb passing 
 into the very short test-tube (P), the cork of which is also furnished with the short 
 piece of moderately wide tube (L). For receiving and preserving the zinc-ethyle, a 
 number of small tubes are prepared of the form shown in fig. 278. The long narrow 
 neck (R) of one of these is passed down the short tube (L) to the bottom of P, the 
 other end (N) of the tube being connected with an apparatus for passing dry car- 
 bonic acid. The whole of the apparatus being filled with this gas, the nipper-lap is 
 
 2 L 2 
 
532 ZINC-ETHYLE ZINC-METHYLE. 
 
 closed, and the flask (E) heated on a sand-bath, so that the zinc-ethyle may distil 
 over, a slow stream of carbonic acid being constantly passed into P, the excess 
 
 Fig. 277. Collection of zinc-ethyle. 
 
 escaping through L. When enough zinc-ethyle has collected in the tube (0) a 
 blowpipe flame is applied to the narrow tube (N), which is drawn off and sealed ; 
 
 the syphon tube (I) is then gra- 
 
 -x -^ dually pushed down, so that its 
 
 **~ longer limb may be sufficiently im- 
 
 mersed in the zinc-ethyle, and the 
 nipper-tap (T, fig. 276) is opened, 
 
 Fig. 278 when the pressure of the carbonic 
 
 acid forces over a part of the zinc- 
 ethyle into the tube P. By heating the tube (M) with a spirit-lamp, so as to expel 
 part of the carbonic acid, and allowing it to cool, it will become partly filled with 
 zinc-ethyle, and may be withdrawn and quickly sealed by the blowpipe. The 
 spontaneous inflammability of the zinc-ethyle, and its easy decomposition by water, 
 render great care necessary in its preparation. If an alloy of zinc with one-fourth 
 its weight of sodium be employed, the conversion may be effected in an hour. 
 
 If any moisture were present in the materials employed, it would 
 decompose a corresponding quantity of the zinc-ethyle, yielding oxide of 
 zinc and gaseous hydride of ethyle 
 
 C 4 H,.Zn + HO - C 4 H 5 .H + ZnO . 
 
 Zinc-ethyle. Hydride of ethyle. 
 
 Zinc-ethyle is a colourless liquid of powerful odour, heavier than water 
 (sp. gr. 1'18), and boiling at 244 F. In contact with atmospheric air, 
 it takes fire spontaneously, burning with a dazzling greenish-blue flame, 
 which emits white clouds of oxide of zinc. If a piece of porcelain be 
 depressed upon the flame, a deposit of metallic zinc is formed, surrounded 
 by a ring of oxide, which is yellow while hot, and white on cooling. 
 
 When oxygen is allowed to act very gradually upon zinc-ethyle, zinc- 
 alcohol (or ethylate of zinc) is formed, corresponding to potassium and 
 sodium-alcohol (ethylates of potash and soda), which have been already 
 described 
 
 C 4 H 5 .Zn + 2 - ZnO.C 4 H 5 0. 
 
 Zinc-alcohol. 
 
 Under the gradual action of other electro-negative elements, zinc-ethyle 
 is decomposed into compounds of zinc and ethyle with the particular 
 element employed ; C 4 H 5 . Zn + I 2 = C 4 H 5 I + Znl. 
 
 Zinc-methyle (C. 2 H 3 . Zn) is prepared by the action of zinc upon the iodide 
 of methyle (C 2 H 3 I), and resembles zinc-ethyle in its general character ; it 
 isj however, far more volatile and more energetic in its reactions than 
 zinc-ethyle, and is decomposed with inflammation and explosion when 
 
AKSENIO-TKIMETHYLE ARSENIO-TKIETHYLE. 533 
 
 brought in contact with water, yielding oxide of zinc and marsh-gas 
 (hydride of methyle). 
 
 C,H 3 .Zn + HO - C 2 H 3 .H + ZnO . 
 
 Hydride of methyle. 
 
 Zinc-amyle (C 10 H U . Zn) is not so violent in its reactions ; it does not 
 inflame when exposed to air, but absorbs oxygen very rapidly. 
 
 Potassium-etliyle and sodium-etliyle (C 4 H 5 . K and C 4 H 5 . Na) have as 
 yqt been obtained only in combination with zinc-ethyle by heating this 
 liquid in a sealed tube with potassium or sodium, when metallic zinc is 
 separated, and the alkali-metal takes its place 
 
 3(C 4 H 5 .Zn) + Na = 2(C 4 H 5 . Zn), C 4 H 5 . Na + Zn . 
 
 The double compound of sodium-ethyle with zinc-ethyle is a crystalline 
 solid which decomposes water with great violence, forming soda, oxide of 
 zinc, and hydride of ethyle.* Its behaviour with carbonic acid is very 
 interesting and important. 
 
 When the crystalline compound of sodium-ethyle with zinc-ethyle is 
 introduced into a bulb-tube through which dry carbonic acid gas is passed, 
 much heat is evolved, zinc-ethyle distils off, and a white solid is left in 
 the bulb, which is found to consist of the propylate of soda, NaO . C 6 H 5 3 , 
 formed according to the equation 
 
 C 4 H 5 Na + 2C0 2 = NaO.C 6 H 5 3 . 
 
 This reaction is one of very great importance, representing the first suc- 
 cessful attempt to produce directly one of the organic acids from carbonic 
 acid, and indicating a general method for the formation of the other acids 
 of the same series. 
 
 Thus, if sodiuni-methyle be treated in the same way, it yields acetate of 
 soda 
 
 C 2 H 3 Na + 2C0 2 = NaO.C 4 H 3 3 . 
 
 By heating iodide of methyle in a sealed tube with a compound of 
 arsenic and sodium, kakodyle or arsenio-dimetJiyle is obtained 
 
 2(C 2 H 3 .I) + AsNa 2 = As(C 2 H 3 ) 2 + 2NaI 
 
 Kakodyle. 
 
 and thus kakodyle finds its place among the organo-metallic bodies, the 
 existence of which it foreshadowed. 
 
 When iodide of ethyle is treated in a similar manner, arsenio-diethyle, 
 As(C 4 H 5 ) 2 , or ethyle-kakodyle, is obtained. 
 
 392. Arsenio-trimethyle, or trimethylarsiiie, As(C 2 H 3 ) 3 , and arsenio- 
 triethyle or trietliylarsine, As(C 4 H 5 ) 3 , may be obtained either by acting 
 upon the iodides of methyle and ethyle with a compound of arsenic with 
 three equivalents of sodium 
 
 3(C 2 H 3 .I) + Asl^a, = As(C 2 H 3 ) 3 + 3NaI 
 
 or by decomposing zinc-methyle or zinc-ethyle with terchloride of 
 arsenic 
 
 3(C 4 H 5 Zn) + AsCl 3 = As(C 4 H 5 ) 3 + SZnCl. 
 
 Arsenio-triethyle has a kakodylic odour, but does not take fire when ex- 
 posed to air, although it oxidises with great rapidity. Like kakodyle, it 
 
 * Strange to say, when this compound of sodium-ethyle with zine-ethyle is heated, it 
 leaves metallic sodium and zinc. 
 
534 ALUMINUM ETHIDE TKIBORETHYLE. 
 
 is capable of producing a base by combination with oxygen, which has 
 the formula As(C 4 H 3 ) 3 O. 2 , and is called arsenic triefhoxide. Similar com- 
 pounds have been obtained in which the oxygen is replaced by chlorine, 
 iodine, and sulphur. 
 
 Other arsenical compounds of ethyle and methyle have been produced, 
 containing four equivalents of the alcohol-radical and one equivalent of 
 an electro-negative element, such as oxygen or iodine, but the oxide of 
 tetrethyl-arsonium, As(C 4 H 5 ) 4 0, and its congeners are really substances 
 belonging to the ammonium family, and they will be again alluded to else- 
 where. 
 
 Stibethyle, Sb(C 4 H 5 ) 3 , or stibiotriethyle, and stibiotrimethyle, Sb(C. 2 H 3 ).., 
 are obtained by processes similar to those which furnish the corresponding 
 compounds of arsenic, which they much resemble. 
 
 Stibethyle has a powerful odour of onions, and takes fire spontaneously 
 in air. It combines with two equivalents of oxygen, chlorine, iodine, and 
 sulphur, with great energy. So powerful is its attraction for chlorine, that 
 it displaces hydrogen from concentrated hydrochloric acid 
 
 Sb(C 4 H 5 ) 3 +.2HC1 = Sb(C 4 H 5 ) 3 .Cl 2 + H 2 . 
 
 Bichloride of Stibethyle. 
 
 The binoxide of stibethyle is a basic substance. The iodide of tetre- 
 thylstibonium, Sb(C 4 H 5 ) 4 I, belongs to the ammonium family. 
 
 Mercuric methide (Hg . C 2 H ) and ethide (Hg . C 4 H 5 ) are formed by the 
 action of zinc-methyle and zinc-ethyle upon chloride of mercury 
 
 Zn.C 4 H 5 + HgCl = ZnCl + Hg.C 4 H 5 . 
 The methyle compound is the heaviest liquid (except metallic mercury) 
 which is known ; its specific gravity is 3 '07, so that glass floats upon its 
 surface, 
 
 Aluminum ethide, Ai 2 (C 4 H 5 ) 3 , is obtained by decomposing mercuric 
 ethide with aluminum, 3HgE + A1 2 = Hg 3 + Al^. It is a colour- 
 less liquid, spontaneously inflammable, and decomposed by water. The 
 corresponding methyle compound, A1 2 (C 2 H 3 ),, solidifies a little above 32 F. 
 into a transparent crystalline mass. 
 
 Triborethyle B(C4H 5 ) 3 , corresponding in composition to boracic acid, 
 BO.,, has been obtained by the action of zinc-ethyle upon boracic ether 
 (3C 4 H 5 O.B0 3 )- 
 
 3EO.B0 3 +' 3ZnE = BE 3 + 3(ZnO.EO). 
 
 Boracic ether. Zinc-ethyle. Triborethyle. Ethylate of zinc. 
 
 It distils over as a very light (sp. gr. 0'69) colourless liquid which has 
 an irritating odour, and is insoluble in water. It inflames spontaneously 
 in air, burning with a beautiful green flame, and explodes when brought 
 in contact with pure oxygen. By gradual oxidation it is converted into 
 the compound BE 3 4 , which may be distilled in vacua without decom- 
 position. When this liquid is mixed with water it is decomposed, yield- 
 ing alcohol, and a volatile white crystalline body, BH 2 EQ 4 
 
 BE 3 4 + 4HO = BH 2 E0 4 + 2(EO.HO). 
 
 Alcohol. 
 
 This substance has an agreeable odour, and a most intensely sweet 
 taste ; it is very soluble in water, alcohol, and ether. 
 
 Boric methide) B(C 2 H 3 ),, is formed by the action of a strong ethereal 
 solution of zinc-methyle upon boracic ether 
 
 3EO.BO, -f SZiiMe = BMe 3 + SZriO.EO. 
 
 Boracic ether. Zinc-methyle. Boric methide. Ethylate of zinc. 
 
BORIC METHIDE S1LICIUM-ETHYLE. 
 
 535 
 
 Its formation in this manner proves that triborethyle is not a result of 
 the mere deoxidation of boracic ether, but is produced by the substitu- 
 tion of three equivalents of ethyle for the oxygen in the boracic acid. 
 
 Boric methide is a heavy (sp. gr. 1'93) colourless gas, having an intoler- 
 ably pungent tear-exciting odour, and capable of liquefaction under a 
 pressure of three atmospheres at 50 F. When it issues very slowly into 
 the air from a tube, it undergoes partial oxidation, and produces a lam- 
 bent blue flame, invisible in daylight, and incapable of burning the 
 fingers; but when it comes rapidly into contact with air, it burns with a 
 bright green hot flame, remarkable for the immense quantity of large 
 flakes of carbon which it disperses through the air, apparently because 
 the boracic acid produced envelopes them and prevents their combustion. 
 Boric methide combines with an equal volume of ammonia gas, producing 
 a white, volatile compound NH 3 . BMe 3 , which is deposited in fine crystals 
 from its ethereal solution, and may be sublimed without decomposition. 
 Its vapour, like that of sal-ammoniac, occupies eight volumes instead of 
 four. Water absorbs very little boric methide, but alcohol dissolves it 
 readily. Solutions of the alkalies and alkaline earths also absorb it, and 
 potash decomposes the ammonia compound, but the combinations of boric 
 methide with the alkalies do not crystallise, and are decomposed even by 
 carbonic acid. 
 
 Silicmm-ethyle, SiE 2 , results from the decomposition of bichloride of 
 silicon with zinc-ethyle ; it is not decomposed by water or by solution of 
 potash, is lighter than water, and burns with a bright flame. Silicium- 
 ethyle is especially interesting as the source of a new alcohol in which a 
 part of the carbon appears to be replaced by silicon. The formula of this 
 alcohol is said to be S^C^H^O.,, which may be represented as the (miss- 
 ing, see p. 512) alcohol C 18 H 20 2 (nonyle-alcohol), in which two equivalents 
 of carbon are replaced by two equivalents of silicon. 
 
 SUidum-methyle, Si(C 2 H,). 2 , is obtained by the action of chloride of 
 silicon upon iodide of methyle in the presence of zinc. It is a liquid 
 which burns with a luminous flame, producing white fumes of silica. 
 
 393. The following table exhibits the composition of the principal com- 
 pounds of alcohol-radicals with inorganic elements which have yet been 
 analysed, omitting some of the compound ammonias, which will be noticed 
 hereafter : 
 
 Compounds of alcohol-radicals 
 with inorganic elements. 
 
 Equivalent 
 Formula. 
 
 Inorganic 
 Type. 
 
 Sodium-ethyle, .... 
 
 NaE* 
 
 NaO 
 
 Magnesium-ethyle, 
 
 MgE 
 
 MgO 
 
 Aluminum-ethyle, 
 
 AW 
 
 A1A 
 
 Zinc-methyle, .... 
 
 ZnMe 
 
 ZnO 
 
 Zinc-ethyle, .... 
 
 ZnE 
 
 ZnO 
 
 Zinc-am yle, .... 
 
 ZnAyl 
 
 ZnO 
 
 Stan-m ethyle, .... 
 
 SnMe 
 
 SnO 
 
 Stan-ethyle, .... 
 
 SnE 
 
 SnO 
 
 Sesquiethide of tin, . 
 
 Sn 3 E, 
 
 Sn f O. 
 
 Diethiodide of tin, . . . 
 
 Sn 2 E a I 
 
 Sn 2 3 
 
 * Strictly speaking, these formulae should be doubled, for, as they stand at present, they 
 correspond only to two volumes of vapour. Thus sodium-ethyle should be NaJE- and so 
 on, excepting A1 S B Sn 2 E,, Sn 2 EJ, BiE,, SbEa, AsMe r and their derivatives. 
 
536 
 
 CONSTITUTION OF ORGANO-METALLIC RADICALS. 
 
 Compounds of alcohol-radicals 
 with inorganic elements. 
 
 Equivalent 
 Formula. 
 
 Inorganic 
 Type. 
 
 Stannic ethide, .... 
 
 SnE 2 
 
 Sn0 2 
 
 Stannic ethylomethide, 
 
 SnEMe* 
 
 Sn0 2 
 
 Stannic iodethide, 
 
 SnEI 
 
 Sn0 2 
 
 Bismuthous ethide, . 
 
 BiE 3 
 
 Bi0 3 - 
 
 Bismuthous dichlorethide, . 
 
 BiEClj 
 
 Bi0 3 
 
 Plumbic ethide, .... 
 
 PbE 2 
 
 Pb0 2 
 
 Mercuric ethide, 
 
 HgE 
 
 HgO 
 
 Mercuric methide, . . . 
 
 HgMe 
 
 HgO 
 
 Stibethyle 
 
 SbE 3 
 
 Sb0 3 
 
 Antimonic triethoxide, . V 
 
 SbE 3 2 
 
 Sb0 5 
 
 Iodide of tetrethyl-stibonium, . 
 
 SbE 4 I 
 
 Sb0 6 
 
 Kadodyle, . 
 
 AsMe 2 
 
 AsS 2 
 
 Oxide of kakodyle, . '. '*. 
 
 AsMe 2 O 
 
 As0 3 
 
 Arsenious dioxymethide, . 
 
 AsMe0 2 
 
 As0 3 
 
 Trimethyle-arsine, . 
 
 AsMe 3 
 
 As0 3 
 
 Monomethyl arsenic acid, . 
 
 AsMe0 4 
 
 As0 5 
 
 Kakodylic acid, 
 
 AsMe 2 3 
 
 AsO s 
 
 Sulphokakodylic acid, 
 
 AsMe 2 S 3 
 
 As0 5 
 
 Terchloride of kakodyle, . 
 
 AsMe 2 Cl 3 
 
 As0 5 
 
 Ethyl-kakodylic acid, . . 
 
 AsE 2 3 
 
 As0 5 
 
 Arsenic triethoxide, . 
 
 AsE 3 2 
 
 As0 5 
 
 Oxide of tetrethylarsonium, 
 
 AsE 4 
 
 As0 5 
 
 Oxide of dimethyl-diethylarsonium, 
 
 AsMe 2 E 2 
 
 As0 5 
 
 Triborethyle, .... 
 
 BE 3 
 
 B0 3 
 
 Boric methide, .... 
 
 BMe 3 
 
 B0 3 
 
 Silicium-ethyle, 
 
 SiE 2 
 
 Si0 2 
 
 Silicium-methyle, 
 
 SiMe 2 
 
 Si0 2 
 
 These compounds are evidently formed upon the types of the inorganic 
 combinations of the respective elements. Those elements which combine 
 in only one proportion with oxygen or sulphur, also combine in one pro- 
 portion with an alcohol-radical ; whilst those which form more than one 
 compound with oxygen and sulphur also generally form corresponding 
 compounds with alcohol-radicals. 
 
 Thus zinc, which combines with only one equivalent of oxygen or sul- 
 phur, also associates itself with one equivalent of methyle, ethyle, or 
 amyle. Aluminum also combines only in one proportion with the alcohol- 
 radicals, but that proportion corresponds with the composition of alumina, 
 the only oxide of aluminum. 
 
 Tin, on the other hand, forms three distinct series of compounds with 
 the alcohol-radicals, composed according to the types of the protoxide, 
 sesquioxide, and binoxide of tin, respectively. And it must be observed 
 that as long as the type is adhered to, the particular radical occupying a 
 place in the compound appears to be a matter of indifference ; thus we 
 find, in the bodies composed after the type of sesquioxide of tin (Sn 2 3 ), 
 one in which the places of the three equivalents of oxygen are occupied % 
 ethyle, and another in which only two of the places are occupied by 
 ethyle (an electro-positive or quasi-metallic or basylous radical), whilst the 
 
 * Formed by the action of zinc-methyle upon the stannic iodethide, ZnMe + SnEI = 
 SnEMe + Znl. 
 
CONSTITUTION OF THE ALKALOIDS. 637 
 
 third is filled by iodine (an electro-negative or chlorous radical). The tin- 
 compounds illustrate peculiarly well the true constitution of these com- 
 pounds, for the stan-ethyle and stan-methyle, composed upon the type of 
 stannous oxide, exhibit the same tendency which is noticed in that oxide 
 to resolve themselves into metallic tin and compounds of the Sn0 2 type ; 
 thus, when stan-ethyle is subjected to distillation 2SnE SnE 2 + Sn ; 
 just as when stannous oxide is boiled with potash, 2SnO = Sn0 2 + Sn . 
 
 Among the members of the arsenic series, we have kakodyle composed 
 after the type of realgar, AsS 2 , which has no corresponding oxide j then 
 trimethylarsine representing arsenious acid, and oxide of tetramethyl- 
 arsonium (AsMe 4 0), corresponding to arsenic acid ; and just as arsenious 
 acid is converted into arsenic acid under the influence of oxidising agents, 
 so, but much more easily, the oxide of kakodyle (AsMe. 2 G), composed 
 upon the type As0 3 , is converted into kakodylic acid (AsMe 2 3 ), repre- 
 senting the type As0 5 . The stability of kakodylic acid necessarily follows 
 from its constitution, the combining tendency of arsenic is saturated in 
 the type As0 3 , the force of chemical attraction can go no further. 
 
 The discovery of these remarkable compounds draws more closely 
 together the departments of inorganic and organic chemistry, exhibits a 
 facility of interchange among elementary and compound radicals which 
 was not before suspected, and, whilst helping to establish the doctrine of 
 compound radicals, teaches that the theory of types must be regarded as 
 one of the most important guides in research. 
 
 OEGANIC ALKALOIDS AMMONIAS. 
 
 394. The attraction which the vegetable alkaloids have always possessed 
 for the chemical inquirer is easily accounted for ; composing, as they do, so 
 very small a portion of the plants in which they are found, and yet repre- 
 senting, in many cases, the whole virtue and activity of such plants in 
 their action upon the animal body, it is very natural that their composi- 
 tion should have been very carefully studied, with a view to explain the 
 changes by which they are produced in the plants, and, if possible, to 
 imitate those changes in order to obtain these valuable remedies by arti- 
 ficial means. In this study, however, the chemist has to contend with 
 difficulties of no insignificant character ; for even in the determination of 
 the ultimate composition of these alkaloids, their high equivalent weights 
 and comparatively small proportion of hydrogen render the exact determi- 
 nation of this substance a matter of great difficulty, so that even at the 
 present time the composition of some of the less known alkaloids can 
 hardly be said to be definitely established. 
 
 The following table includes the most important of those alkaloids 
 which are extracted from plants : 
 
 Alkaloid. 
 
 Source. 
 
 Equivalent Formula. 
 
 Morphine 
 
 Opium . . 
 
 C H 1Q NO ft 
 
 Codeine 
 
 
 C H NO 
 
 Narcotine 
 Papaverine 
 
 ....... 
 
 0.H M NO U 
 
 C,,H 01 NO a 
 
 Quinine 
 Cinchonine 
 
 Cinchona bark .... 
 
 C 40 H 24 N 2 4 
 C 40 H 2 N 2 2 
 
 Quinidinc 
 
 
 C H N 
 
 
 " 
 
 
538 
 
 CONSTITUTION OF THE ALKALOIDS. 
 
 Alkaloid. 
 
 Source. 
 
 Equivalent Formula. 
 
 Caffeine 
 
 Coffee ....... \ 
 
 
 Theine 
 
 Tea . J 
 
 16 H 10 N 4 4 
 
 Theobromine 
 Strychnine 
 
 Cacao-nut 
 Nux vomica 
 
 C 14 H 8 N 4 4 
 
 a,H N o 
 
 Brucine 
 
 
 C^H^NoCL 
 
 Nicotine 
 
 Tobacco . 
 
 C in HN 
 
 Solanine 
 Atropine 
 Daturine 
 Cocaine 
 
 Potato-shoots 
 Deadly nightshade . '-! 
 Stramonium . . . . . | 
 Coca-leaves . . . .'"'.' 
 
 C 34 H 23 N0 6 
 C<, A H 01 NO fi 
 
 Hyoscyamine 
 Emetine 
 Aconitine 
 
 Henbane, 
 Ipecacuanha 
 Aconite 
 
 
 Veratriiie 
 Coniine 
 Piperine 
 
 White hellebore . . 
 Hemlock 
 Pepper . . . 
 
 ^64^62^2^16 
 
 C 16 H 15 N 
 C cH NoO C 9 ) 
 
 Capsicine 
 Sparteine 
 Curarine 
 
 Cayenne pepper .... 
 Common broom .... 
 Curara poison 
 
 C 16 H 13 N 
 C 20 H 15 N 
 
 From this table it is seen that the alkaloids invariably contain nitrogen ; 
 and though this element generally forms a comparatively small part of the 
 weight of the alkaloid, not exceeding 31 per cent, in theobromine, which 
 is the richest in nitrogen, and falling as low as 3 '2 per cent, in narcotine, 
 which is the poorest, it is from this element that chemists have always 
 started in their speculations upon the constitution of these important bodies. 
 
 The earliest view of any importance respecting the constitution of the 
 alkaloids was that of Berzelius, who, resting upon the constant presence 
 of nitrogen and hydrogen in these substances, regarded them as compounds 
 of certain neutral substances (then unknown in the separate state) with 
 ammonia, to which they owed their alkaline characters, and this opinion 
 was much strengthened when it was discovered that certain organic bases 
 (though not those actually found in plants) could be produced by the 
 direct combination of ammonia with neutral substances ; thus oil of 
 mustard (C 8 H 5 IS[S 2 ), when combined with ammonia (NIL), yields the base 
 tliiosinnamine (C S H 8 N 2 S 2 ). 
 
 To this view it was objected, that ammonia could not be detected in 
 these organic bases, and as the doctrine of the displacement of one element 
 by another, or by a quasi-element, gained ground, it was suggested that 
 the organic bases might be really constituted in the same manner as 
 ammonia itself, the place of a portion of the hydrogen being occupied by 
 a group composed of carbon and hydrogen, or of carbon, hydrogen, and 
 oxygen. This view of the constitution of the alkaloids, therefore, would 
 at once propose ammonia as the type of this large class. 
 
 In the earlier attempts to refer the organic bases to ammonia as their 
 type, it was said that just as that substance is composed of four atoms 
 (one of nitrogen and three of hydrogen), so are the organic bases, but that 
 these contain only two separate hydrogen-atoms, the place of the third 
 atom of that element being occupied by a compound which discharges the 
 functions of that third atom of hydrogen, and does not destroy the alka 
 line character of the original ammonia type. 
 
ETHYLATED AMMONIAS. 539 
 
 To apply this view to one of the least complex of the organic bases, 
 aniline (C 12 H 7 N), we might represent it as ammonia (NH 3 ), in which the 
 third atom of hydrogen had been displaced by the hypothetical compound 
 radical phenyle (C 12 H 5 ) for C 12 H 7 N NH 2 . C 12 H 5 , phenylamine. 
 
 This view of the constitution of aniline was supported by the fact, that 
 aniline may be obtained by the action of heat upon phenate of ammonia ; 
 thus 
 
 NH 3 .HO.C 12 H 5 - 2HO = NH 2 .C 12 H 5 
 
 Phenate of ammonia. Aniline. 
 
 and as the substances derived from ammoniacal salts by the loss of two 
 equivalents of water were called amides (being supposed to contain 
 amidogen, NH 2 (see p. 239), this theory was spoken of as the amide-theory 
 of the constitution of organic bases. 
 
 Later research has only extended this theory, having proved that 
 ammonia is the type of at least the greater number of organic bases, and 
 that not only one, but all three of the hydrogen-atoms, are movable, and 
 may be displaced by compound radicals, whilst even the nitrogen of the 
 type also admits of replacement by other elements of the same chemical 
 family, viz., by phosphorus, arsenic, and antimony. 
 
 A more instructive example of the elasticity of a type cannot be given. 
 
 395. Ethylated ammonias and their derivatives. When iodide of 
 ethyle (C 4 H 5 I) is heated in a sealed tube with an alcoholic solution of 
 ammonia, in the proportion of single equivalents, a crystalline compound 
 is formed, which might at first be regarded merely as a combination of 
 the two bodies employed to produce it (C 4 H 5 I . NH 3 ) ; but when this 
 substance is distilled with potash, it furnishes, instead of ammoniacal gas, 
 a vapour which condenses, under the ordinary pressure in a receiver cooled 
 by ice, to a very light colourless liquid, which boils at 6 5 '6 F., and has 
 a powerful ammoniacal odour. By analysis, this liquid is found to have 
 the composition C 4 H 7 N, being, in fact, ammonia in which one-third of the 
 hydrogen has been displaced by ethyle. That this is the true view of its 
 constitution does not admit of a doubt, since it so nearly resembles 
 ammonia in all its characters, that it might easily be mistaken for that 
 substance. The ethyl-ammonia or ethylia, or ethylamine, has not only the 
 modified odour of ammonia, but is powerfully alkaline, and combines 
 readily with acids, forming salts, many of which may be crystallised. It 
 is, as might be expected, more inflammable than ammonia. 
 
 The crystalline compound formed by the action of iodide of ethyle upon 
 ammonia is the hydriodate of ethylamine 
 
 (H (C 4 H 5 ) 
 
 C 4 HJ + N^H N\ H V.HI 
 (H { H j 
 
 the hydrogen expelled from the ammonia having taken the place of the 
 ethyle in the iodide, forming hydriodic acid, which remains in combina- 
 tion with the ethylamine. 
 
 Chloride of ethyle and bromide of ethyle, when heated with ammonia, 
 yield, respectively, the hydrochlorate and hydrobromate of ethylamine, but 
 the iodide of ethyle is preferred for this and similar experiments, as being 
 less volatile, and, therefore, more manageable in sealed tubes. 
 
540 TRIETHYLAMINE. 
 
 When the hydriodate of ethylamine is distilled with potash, it behaves 
 just as hydriodate of ammonia would do if similarly treated 
 :NH 3 .HI + KO - NH 3 + KI + HO 
 
 Hydriodate of ammonia. Ammonia. 
 
 m 2 .C 4 H 5 .HI + KO = NH 2 .C 4 H 5 + KI + HO. 
 
 Hydriodate of ethylamine. Ethylamine. 
 
 Ethylamine also combines with the oxygen-acids in the same manner 
 as ammonia 
 
 Sulphate of ammonia, . . . NH 3 , HO . S0 3 
 Sulphate of ethylamine, . . NH 2 . C 4 H 5 , HO . S0 3 . 
 If any further proof were wanted that ethylamine is really composed after the 
 type of ammonia, it would be afforded, by the circumstance, that ethylamine may be 
 prepared by distilling cyanic ether with hydrate of potash. 
 
 Cyanic ether (C 4 H 5 . CyO = C 4 H 5 . C 2 NO) is obtained by distilling sulphovi- 
 nate of potash with cyanate of potash 
 
 KO . CyO + KO . C 4 H 5 . 2S0 3 = C 4 H 5 . CyO + 2(KO . S0 3 ) . 
 Cyanate of potash. Sulphovinate of potash. Cyanic ether. 
 
 Now, cyanic ether is simply cyanic acid, in which an equivalent of ethyle occupies 
 the place of an equivalent of hydrogen 
 
 Cyanic acid, . . . HO . CyO 
 Cyanic ether, . . . EO . CyO . 
 
 When cyanic acid is distilled with hydrate of potash, it yields ammonia and 
 carbonate of potash 
 
 HO . C 2 NO + 2(KO . HO) = NH 3 + 2(KO . C0 2 ) 
 
 and since cyanic ether contains an atom of ethyle, in place of an atom of hydrogen, 
 it would be expected to furnish an ammonia in which a similar displacement had 
 been effected 
 
 EO.C 2 NO + 2(KO.HO) = NH 2 E + 2(KO.C0 2 ). 
 
 Cyanic ether. Ethylamine. 
 
 If ethylamine be again acted upon by an equivalent of iodide of ethyle, 
 a second atom of hydrogen may be displaced by ethyle, and the hydriodate 
 of diethylamine is obtained 
 
 'A) (C 4 H 5 ) 
 
 H V + C 4 H 6 I = NJC 4 H 5 V .HI 
 
 Et, iy ,a mi ,,, w;- as$* 
 
 and from this hydriodate the diethylamine is obtained by distillation with 
 potash, as a colourless and inflammable liquid, strongly ammoniacal, and 
 having a much higher boiling point than ethylamine (134 '6 F.) In its 
 chemical relations diethylamine is a decided ammonia. 
 
 In order to remove the third atom of hydrogen, it is only necessary to 
 subject diethylamine to the action of iodide of ethyle 
 C 4 H 5 C 4 H 5 
 
 C 4 H 5 I = 
 
 H ) (C 4 H 5 
 
 Diethylamine. Iodide of Hydriodate of 
 
 ethyle. Triethylamine. 
 
 When this last hydriodate is distilled with potash, the triethylamine is 
 obtained as a colourless liquid, presenting the strongest evidence of its 
 relationship to ethylamine and diethylamine as well as to ammonia. It is 
 powerfully alkaline, and boils at a higher temperature than diethylamine.* 
 
 * Just as ethylamine is obtained by the action of hydrate of potash upon cyanic ether, so 
 triethylamine is formed when ethylate of potash (potassium-alcohol) acts upon cyanic ether - 
 EO.C 2 NO + 2(KO.EO) = NE 3 + 2(KO.C0 2 ). 
 
HYDRATED OXIDE OF TETRETHYLIUM. 541 
 
 But the action of iodide of ethyle does not stop here, for if triethyla- 
 mine be again heated with it, an equivalent of that base combines with 
 an equivalent of the iodide to form the compound N(C 4 H 5 ) 3 . C 4 H 5 I, which 
 may be represented as hydriodate of triethylamine in which the place of 
 the hydrogen in the hydriodic acid is occupied by ethyle. 
 
 But it will be remembered that the hydriodate of ammonia (NH 3 . HI) 
 is sometimes regarded as the iodide of a hypothetical compound metal 
 ammonium (NH 4 ), and it would appear admissible to view the above 
 'compound as iodide of ammonium (NH 4 I), in which the four atoms of 
 hydrogen are displaced by ethyle ; it would then be called iodide of tetre- 
 tliylammonium (NE 4 I), or iodide of tetrethylium. 
 
 Unlike the preceding compounds, the iodide of tetrethylium may be 
 boiled with solution of potash without decomposition, but if a solution of 
 this substance be treated with oxide of silver, iodide of silver is formed, 
 and when the solution is filtered and evaporated in vacua over sulphuric 
 acid, it deposits needle-like crystals having the composition N(C 4 H 5 ) 4 .HO. 
 This substance, which is called the hydrated oxide of tetrethylium, is 
 exactly similar in properties to the hydrates of potash and soda ; it is 
 deliquescent, absorbs carbonic acid eagerly from the air, is exceedingly 
 alkaline and caustic, expels ammonia from its salts, forms soaps with the 
 fats, and behaves in every respect like the hydrate of a fixed alkali. Its 
 taste is very bitter as well as alkaline. 
 
 It is obviously not an ammonia, but is composed after the type of 
 hydrate of potash (KO . HO), and contains, in place of the potassium, the 
 hypothetical radical tetrethylium, N(C 4 H 5 ) 4 , or ammonium (NH 4 ) in which 
 the four atoms of hydrogen have been displaced by ethyle. 
 
 The action of oxide of silver upon the iodide of tetrethylium is now 
 intelligible 
 
 NE 4 I + AgO- + HO = NE 4 O.HO + Agl. 
 
 Iodide of Hydrated oxide of 
 
 tetrethylium. tetrethylium. 
 
 The new alkali is easily decomposed ; even at a temperature below the 
 boiling point of water, it is resolved into triethylamine, olefiant gas, and 
 water 
 
 N(C 4 H 5 ) 4 O.HO = *T(C 4 H 5 ) 3 + C 4 H 4 + 2HO, 
 
 Triethylamine. 
 
 It will be remembered that the solution of ammonia in water may be 
 regarded as containing the hydrated oxide of ammonium, for 
 
 NH 3 + 2HO - NH 4 O.HO 
 
 which latter would be the true type of the hydrated oxide of tetrethylium ; 
 but so great is the want of stability in this case, that all attempts to isolate 
 the hydrated oxide of ammonium have resulted in the production of 
 ammonia and water. 
 
 Like potash, the oxide of tetrethylium is capable of forming salts with 
 the oxygen-acids without the intervention of an equivalent of water, thus 
 
 Sulphate of potash, .. . KO.S0 3 
 Sulphate of oxide of tetrethylium, (NEJO . S0 3 . 
 
 It would naturally be expected that by the action of the iodides of other 
 alcohol-radicals upon ammonia, compounds should be obtained correspond- 
 ing to those belonging to the ethyle series ; thus we have 
 
542 AMMONIUM-BASES. 
 
 (Type; ammonia NH g ). 
 
 Methylamine* NH 2 . C 2 H 
 Ethylamine, NH 2 . C 4 H 
 Amylamine, NH 2 . 1( " 
 Dimethylamine, NH.(C 2 
 
 A 
 
 ! H 3 ) 2 
 
 Diamylamine, NH . (C 10 H n )., 
 Trimethylamine, N(C 2 H 3 ) 3 
 Triethylamine, N(C 4 H 6 ) 3 
 Triamylamine,t N(C 10 H n ) 3 
 
 Diethylarnine, NH . (C 4 H 5 ) 2 
 
 (Type ; imaginary liydrated oxide of ammonium, NH 4 . HO.) 
 
 Hydrated oxides of 
 Tetramethylium, N(C H 3 ) 4 O.HO 
 Tetrethylium, N(C 4 H 5 ) 4 . HO 
 Tetramylium, N(C 10 H n ) 4 0. HO 
 
 But even here, the elasticity of the types and the replacing power of 
 the alcohol-radicals are not exhausted. 
 
 If methylamine (NH 2 . Me) be acted upon by iodide of ethyle, the 
 hydriodate of methyl-etliylamine is formed 
 
 NH 2 .Me + El NHMeE.HI 
 
 Methylamine. Iodide of ethyle. Hydriodate of methyl-ethylamine. 
 
 and by distilling this with potash, the methyl-ethylamine, much resembling 
 the other ammonia bases, is obtained. 
 
 Again, on subjecting this base to the action of iodide of amyle, and 
 distilling the product with potash, a new ammonia base is procured, in 
 which all three equivalents of hydrogen are replaced by different radicals ; 
 this base is called methyl-ethyl-amylamine, and its composition is repre- 
 sented by the formula N(C,H 3 ) (C 4 H 5 ) (C 10 HJ = NMeEAyl. 
 
 If we had started with aniline (phenylamine, NH 2 . C 12 H 5 ) in the above 
 experiment, treatment with iodide of methyle would have furnished 
 methyl-aniline or methyl-phenylamine, NH . C 12 H 5 . C 2 H 3 ; and by treating 
 this with iodide of ethyle, we should obtain ethyl-methyl-phenylamine, 
 NC 12 H 5 . C 2 H 3 . C 4 H 5 ; the action of iodide of amyle upon this last 
 ammonia would give the iodide of methyl-ethyl-amylophenylium, and on 
 decomposing this with oxide of silver there would be obtained the 
 hydrated oxide of methyl-ethyl-amylophenyl-amnionium 
 
 N(C 3 H 3 )(C 4 H 5 )(C, H 11 )(C 12 H 5 )0 . HO 
 
 a base formed upon the hypothetical type of hydrated oxide of ammonium, 
 in which each of the four equivalents of hydrogen is replaced by a different 
 radical. 
 
 This complex substance affords an excellent example of the difference 
 between an empirical and a rational formula ; its empirical formula, 
 C 2S H 25 N0 2 , which simply shows the result of its ultimate analysis, teaches 
 nothing with respect to its constitution, which is at once clear when the 
 rational formula as above written is placed before us. 
 
 Phenylamine, NH 2 (C 12 H 5 ), is found among the products of the destructive dis- 
 tillation of rosaniline (p. 457), whilst ethyl-rosaniline (aniline-violet) yields ethyl- 
 phenylamine or ethyl-aniline, NH(C 12 H 5 )(C 4 H 5 ), and phenyl-rosaniline (aniline blue) 
 yields di-phenylamine or phenyl-aniline, NH(C 12 H 5 ) 2 . 
 
 * Methylamine, which is a gas at the ordinary temperature, is far more soluble in water 
 than any other gas ; water dissolves 1150 volumes of methylamine, the solution exactly 
 resembling that of ammonia. 
 
 t Even the hypothetical hydrocarbon cetyle (C 32 H 33 ), the radical of ethal, has been sub- 
 stituted for the nitrogen in ammonia. The base tricetylamwe, N(C 32 H 33 ) 3 , which is thus 
 formed, contains only 2 per cent, of nitrogen. 
 
INVESTIGATION OF THE CONSTITUTION OF THE ALKALOIDS. 543 
 
 Diphenylamine has also been obtained by digesting hydrochlorate of aniline with 
 free aniline at a high temperature, when hydrochlorate of diphenylamine is obtained, 
 which is decomposed by a large excess of warm water, the diphenylamine rising to 
 the surface as an oil which solidifies on cooling. The change may be expressed by 
 the following equation : 
 
 NH 2 (C 12 H 5 ).HC1 + NH 2 (C 12 H 5 ) = NH(C 12 H 6 ) 2 . HOI + NH 3 . 
 
 Ditoluylamine, NH(C U H 7 ) 2 , maybe procured in a similar way by digesting hydro- 
 chlorate of toluidine with toluidine. 
 
 Phenyl-toluylamine, NH(C l2 H 5 )(C 14 H 7 ),'is formed by the action of aniline on hydro- 
 chlorate of toluidine, or by that of toluidine on hydrochlorate of aniline. 
 
 Under the action of nitric acid, di-phenylamine gives rise to di-nitro-diphenylamino, 
 NH[C 12 H 4 (N0 4 )] 2 , in which the same type is preserved, though nitric peroxide (N0 4 ) 
 is substituted for one-fifth of the hydrogen in the phenyle. 
 
 When treated with chloride of benzoyle (C 14 H 5 2 . Cl), diphenylamine yields 
 diphenyl-benzoylamine, N(C 12 H 6 ) 2 (C 14 H 5 2 ). 
 
 It will be observed that certain of these bases derived from the alcohols 
 have the same empirical formulae as those derived from coal-tar and other 
 sources, with which, however, they are by no means identical. Thus, tolui- 
 dine (C^HgN) has the same composition as methyl-aniline (NH.C lt2 H 5 . C.,H,,) ; 
 but the former is a crystalline solid, and the latter an oily liquid. Again, 
 when iodide of ethyle acts upon toluidine, an equivalent of hydrogen is 
 displaced by ethyle, and ethylo-toluidine is obtained. The composition 
 of this base, C 14 H 8 (C 4 H 5 )N, is the same as that of methyl-ethyl-aniline, 
 N(C. 2 H 3 )(C 4 H.)(C 1 ,HJ, and as that of cumidine (C, 8 H ]3 N); but in their 
 chemical properties these bodies exhibit such a difference as would be 
 expected from the difference in their constitution. 
 
 396. Investigation of the constitution of the alkaloids. It will be evi- 
 dent that the principles developed in the experiments just described may 
 be applied in investigating the constitution of the bases extracted from 
 plants. Let it be supposed that ethylamine (C 4 H 7 IS T ) was a vegetable 
 alkali of unknown constitution ; when it was found that by the action of 
 iodide of ethyle two out of the seven atoms of hydrogen could be displaced, 
 it would te at once inferred that these two atoms occupied a very different 
 position from the other five, and that the constitution of the compound 
 would be more properly expressed by writing the formula C 4 H 5 . H.-.N. 
 On applying the same principle to the examination of the natural alkaloid, 
 coniiiie (C 16 H 13 N), it was found possible, by the action of iodide of m ethyle, 
 to remove only one atom of the hydrogen, so that the formula C 16 H 14 . H . N 
 would more correctly represent the constitution of coniine, which might be 
 then regarded as ammonia in which two atoms of the hydrogen have been 
 displaced by the group C 1H H 14 , or in which each of these atoms has been 
 displaced by the group C 8 H 7 . 
 
 If we were acquainted with an iodide of this group, we have every 
 reason to expect that its action upon ammonia would lead us to the 
 artificial formation of coniine. * 
 
 Nicotine, morphine, and codeine will not part with any of their hydro- 
 gen under the action of iodide of ethyle, and must therefore be placed 
 upon the same footing as triethylamine, N(C 4 H 5 ). j , in which all three atoms 
 
 * The group Cj,H 7 is often assumed as the radical of butyric acid (C 8 H 8 4 ), and it is at 
 least a curious coincidence, that when acted upon by nitric acid, coniine actually yields 
 butyric acid. 
 
544 POLY- AMMONIAS DIAMINES. 
 
 of hydrogen are already replaced. Upon this view they would be repre- 
 sented thus 
 
 Nicotine, N(C 10 H 7 )'" 
 
 Morphine, N(C 34 H 19 6 )'" 
 
 Codeine, ^(C 36 H 2 A)"' 
 
 The mark ('") signifying that the groups are triatomic, or have the same 
 replacing value as three atoms of hydrogen. When these bases are acted 
 upon by the iodides of alcohol-radicals, there are formed, as would be 
 expected, iodides upon the type NH 4 I, from which may be obtained fixed 
 alkalies resembling the hydrated oxide of tetrethylium. Thus we have 
 the hydrated oxides of 
 
 Methyl-morphyl-ammonium, N(C 34 H 19 6 ) /// (C 2 H 3 )0 . HO 
 Ethyl-codeyl-ammonium, N(CJS n 0^ w ^CJ3. 6 )0 . HO 
 Ethyl-nicotyl-ammonium, ^(C^H^^^C.H^O . HO 
 
 397. Poly-ammonias. In speculating upon the constitution of the 
 vegetable bases, it must not be forgotten that some of them contain two 
 equivalents of nitrogen ; this is the case, for example, with cinchonine 
 (C 40 H 24 2 2 ), quinine (C 40 H 24 N 2 4 ), and strychnine (C 42 H 22 N 2 4 ). If the 
 whole of the nitrogen in these bases be due to the ammonia type, they 
 must be composed after the type of a double atom of ammonia, N 2 H 6 . In 
 the case of strychnine, it is found that the action of iodide of ethyle fails 
 to remove any portion of the hydrogen, so that if the base be really com- 
 posed after the ammonia type, it must be represented by two atoms of 
 ammonia (N 2 H 6 ), in which the whole of the hydrogen has been displaced 
 by the group (C 42 H 22 4 ), when its formula would be N 2 (C 42 H 22 4 ) vi , the 
 replacing group in this case being hexatomic, or equivalent to six atoms 
 of hydrogen. That it is by no means necessary for each atom of hydrogen 
 to be displaced by a single group or radical, is seen in a great many organic 
 compounds; thus, in chloroform (C 2 H)Cl 3 j we have the triatomic group 
 C 2 H (commonly called formyle) occupying the position of three atoms of 
 hydrogen which would be required to combine with the three atoms of 
 chlorine ; again, in Dutch liquid, (C 4 H 4 )C1 2 , we have the diatomic group 
 C 4 H 4 (ethylene) occupying the place of two atoms of hydrogen. 
 
 If the view above explained with respect to the constitution of some of 
 the natural alkaloids be correct, it ought to be possible to form artificially 
 a base in which two or three atoms of hydrogen had been displaced by 
 means of a diatomic or triatomic radical. 
 
 398. Diamines. When olefiant gas or ethylene, C 4 H 4 , is brought in 
 contact with bromine, the compound C 4 H 4 Br 2 , corresponding to Dutch 
 liquid (C 4 H 4 C1 2 ), is obtained, and from the action of ammonia upon this 
 bibromide of ethylene, there is derived a new alkaline base, having the 
 composition N" 2 H 4 (C 4 H 4 )", or two atoms of ammonia (N" 2 H 6 ), in which the 
 diatomic ethylene replaces two atoms of hydrogen. Such bases, formed 
 upon the double ammonia type, are called diamines, whilst those which 
 correspond to a single atom of ammonia are called monamines. The base 
 above mentioned is named ethylene-diamine. The diamines, like the 
 double atom of ammonia from which they are derived, are capable of 
 combining with two equivalents of hydrochloric or any similar acid, which 
 is implied by stating that they are diacid. 
 
 When Dutch liquid (bichloride of ethylene, (C 4 H 4 )"C1 2 ) is heated to 300 F. with 
 strong ammonia in a sealed tube, an action takes place corresponding to that of a 
 
TRIAMINES OR TRIPLE AMMONIAS. 545 
 
 double atom of hydrochloric acid (H 2 01 2 ) upon a double atom of ammonia (N 2 H 6 ), 
 which would give rise to a double atom of hydrochlorate of ammonia (N 2 H 6 . H 2 C1 2 ) ; 
 in the product of the action of Dutch liquid upon ammonia (N 2 H 4 (C 4 H 4 ) 2 "C1 2 ), the 
 places of four atoms of hydrogen are occupied by two atoms of the diatomic group 
 (C 4 H 4 ). But here the correspondence ceases, for whilst the hydrochlorate of 
 ammonia, when decomposed with oxide of silver, would yield ammonia and chloride 
 of silver, the new compound, when thus treated, yields a fixed alkaline base, resem- 
 bling hydrate of potash, and having the composition N 2 H 4 (C 4 H 4 ) 2 "0 2 . 2HO, which 
 represents a double atom of the hypothetical hydrated oxide of ammonium 
 2(NH 4 .HO), in which four atoms of hydrogen have been displaced by two atoms 
 of the diatomic ethylene. The name hydrated oxide of diethylene-diammonium ex- 
 presses the composition of this substance, which is remarkable for its stability, a 
 temperature above 300 F. being required to effect its decomposition, when it 
 furnishes a volatile alkali, having the composition N" 2 H 2 (C 4 H 4 ) 2 ", and called di- 
 ethylene-diamine, being evidently formed from a double atom of ammonia, in which 
 four atoms of hydrogen are replaced by two atoms of the diatomic ethylene. Its 
 production may be explained by the equation 
 
 N 2 H 4 (C 4 H 4 ) 2 "0 2 .2HO = N 2 H 2 (C 4 H 4 )/ + 4HO . 
 
 By acting upon the new ammonia with iodide of ethyle (C 4 H 5 I), the two equiva- 
 lents of hydrogen may be displaced by ethyle, yielding diethyl-diethylene-diamine, 
 N 2 (C 4 H 5 ) 2 (C 4 H 4 ) 2 ", or a double atom of ammonia (N 2 H 6 ), in which H 2 are replaced 
 by two atoms of ethyle, and H 4 by two atoms of ethylene. 
 
 By treating phenylamine (aniline), NH 2 (C 12 H 5 ), with bichloride of ethylene 
 (Dutch liquid), the diphenyl-diethylene-diamine, N 2 (C 12 H 5 ) 2 (C 4 H 4 ) 2 ", is obtained, 
 which represents a double atom of ammonia (N 2 H 6 ), in which H 2 are replaced by 
 two atoms of phenyle, and H 4 by two atoms of ethylene. By the action of chloro- 
 form upon aniline, formyl-diphenyl-diamine, N 2 (C 2 H) /// (C 12 H 5 ) 2 H, has been obtained, 
 in which H 3 are replaced by the triatomic formyle (C 2 H), and H 2 by phenyle. 
 
 It has been seen that phenylamine is produced by the deoxidising action of ferrous 
 acetate upon nitrobenzole (C 10 H 5 . N0 4 ). When di-nitrobenzole is treated in a 
 similar way, phenylene-diamine, & 2 H 4 (C 12 H 4 y' is obtained, which is evidently derived 
 from a double atom of ammonia, in which H 2 are replaced by the diatomic group 
 phenylene (C 12 H 4 ), which bears the same relation to phenyle (C 12 H 5 ) as ethylene 
 (C 4 H 4 ) bears to ethyle (C 4 H 5 ). By treating di-nitrotoluole and di-nitrocumole witli 
 ferrous acetate, tolylene-diamine- and cumylene-diamine are obtained, which are di- 
 ammonias, in which H 2 are replaced by the diatomic radicals tolylene (C 14 H 6 )" and 
 wmylene (C 18 H 10 )". These three diamines are called the aromatic diamines, since the 
 diatomic groups phenylene, tolyleue, and cumylene are closely connected, through 
 benzole (C 12 H 6 ), toluole (C W H 8 ), and cumole (C 18 H 12 ), with the aromatic acids, benzoic 
 (C 14 H 6 4 ), toluic (0 16 H 8 4 ), and cuminic (C 20 H 12 4 ). 
 
 Paraniline (G 24 H 14 N 2 ) is obtained as a secondary product in the manufacture of 
 aniline, with which it is polymeric. Its properties are very different from those of 
 aniline, for it is solid at the ordinary temperature, forming silky needles which melt 
 when heated, and boil beyond the range of the thermometer, distilling unchanged. 
 It combines with acids, forming beautiful crystalline salts, the study of which proves 
 it to be a diamine. 
 
 399. Triamines. The triamines are formed upon the type of a treble 
 atom of ammonia (N 3 H 9 ), in which the hydrogen is replaced either entirely 
 or in part by other radicals. Thus, diethylene-triamine, N 3 H 5 (C 4 H 4 ) 2 ", 
 and triethylene-triamine, N 3 H 3 (C 4 H 4 ) 3 ", are obtained by the action of bi- 
 bromide of ethylene (C 4 H 4 Br 2 ) upon ammonia. They are powerfully 
 alkaline liquids, which are capable of absorbing carbonic acid from the 
 air. The triamines are generally capable of forming three classes of salts, 
 the tnonacid, diacid, and triacid salts, containing respectively one, two, 
 and three equivalents of acid. 
 
 Di-ethylene-di-ethyl-triamine, N 3 H 3 (C 4 H 4 ) 2 ''(C 4 H 5 ) 2 , is produced by the joint 
 action of ethylamine and ammonia upon bibromide of ethylene 
 
 2[(C 4 H 4 )"Br 2 ] + 3NH 2 (C 4 H 5 ) + NH 3 = 
 N 3 H 3 (C 4 H 4 ) 2 (C 4 H 6 ) 2 . SHBr + NH 2 (C 4 H 6 ) . HBr . 
 
 2 M 
 
546 TETRAMINES OR QUADRUPLE AMMONIAS. 
 
 It forms splendidly crystallised salts, and is evidently derived from three atoms of 
 ammonia (N 8 H 9 ), by the substitution of two atoms of ethylene (C 4 H 4 ) 2 " for H 4 , 
 and two atoms of ethyle (C 4 H 5 ) 2 for H 2 . 
 
 Carbotriamine (guanidine), N 3 H 6 6 iv , is a treble atom of ammonia, in which four 
 atoms of hydrogen are replaced by one atom of tetratomic carbon (see p. 153). It 
 is formed by heating ammonia with subcarbonate (ortliocarbonate) of ethyle iu a 
 sealed tube to about 300 F. 
 
 2(2C 4 H 6 . C0 2 ) + 3NH 3 + 2HO = N 3 H 5 C 2 ".2HO + 4(C 4 H 6 O.HO). 
 
 The change is more clearly explained by representing the subcarbonate of ethyle as 
 formed upon the type of four equivalents of water (H 4 4 ) in which H 2 are replaced 
 by (C 4 H 6 ) 2 , and the remaining H 2 by C" (as in C"0 2 ). 
 
 2[ (C $P 2 }0 4 1 + 3NH 3 + 2HO = N 3 H 6 C 2 ".2HO + ( C *jSjW* 1 6 
 Subcarbonate of ethyle. Guanidine. 4 eqs. alcohol. 
 
 Guanidine may also be obtained by heating chloropicrine in a sealed tube, with 
 an alcoholic solution of ammonia, to 212 F., when the following reaction ensues 
 
 C 2 C1 8 (N0 4 ) + 3NH 3 = N 3 H 6 C 2 " . HC1 + 2HC1 + N0 3 + HO . 
 
 Chloropicrine. 
 
 It will be remembered that the subcarbonate of ethyle itself is obtained by the 
 action of sodium upon an alcoholic solution of chloropicrine (p. 523). 
 
 Melaniline, C 26 H 13 N 3 , a crystalline base, produced by the action of chloride of 
 cyanogen upon aniline, may be regarded as diphenyl-guanidine, N 3 H 3 (C 12 H 5 ) 2 C 2 ", 
 or guanidine in which two atoms of phenyle have replaced two of hydrogen. 
 
 The beautiful aniline dyes appear to be salts of certain triamines formed by the 
 replacement of the hydrogen in a treble atom of ammonia by hydrocarbon radicals. 
 
 According to Hofmann, rosaniline, the base of the aniline red produced by the 
 action of oxidising agents upon aniline containing toluidine, is possibly phenylene- 
 ditolylene-triamine, N 3 (C 12 H 4 )' / (C 14 H 6 ) 2 ' / H 3 . 2HO, the phenylene being derived from 
 the aniline, NH 2 (C 12 H 5 ), and the tolylene from the toluidine, NH 2 (C 14 H 7 ) . Ani- 
 line blue, formed by the action of aniline upon aniline red, would be phenylene- 
 ditolylene-triphenyl-triarnine, N 3 (C }2 H 4 )''(C U H 6 ) 2 "(C 12 H 5 ) 3 . 2HO, having been formed 
 from rosaniline by the substitution of three atoms of phenyle for H 3 . Aniline 
 violet, the result of the action of iodide of ethyle upon rosaniline, would be phenylene- 
 ditolylene-triethyl-triamine, N 8 (0 la H 4 )"(C 14 H 6 ),"(C 4 H 5 ), . 2HO, or rosaniline contain- 
 ing three atoms of ethyle in place of H 3 . 
 
 The trichloride of diethylem-triammonium, N 3 (C 4 H 4 ) 2 "H 8 . C1 3 , has also been ob- 
 tained. 
 
 400. Tetramines are formed upon the type of four atoms of ammonia, 
 and therefore contain four atoms of nitrogen, and are able to combine with 
 four atoms of a hydrogen acid. Thus, if bibromide of ethylene be allowed 
 to act upon ethylene-diamine in the presence of hydrobromic acid, the 
 hydrobromate of triethylene-tetramine is obtained 
 
 .(C 4 H 4 )"Br 2 + 2N 2 (C 4 H 4 )"H 4 + 2HBr = N 4 (C 4 H 4 ) 3 "H 6 . 4HBr 
 
 Ethylene-diamine. 
 
 and if this be decomposed with oxide of silver, a strongly alkaline solu- 
 tion is obtained, which contains triethylene-tetramine, N 4 (C 4 H 4 ) 3 "H 6 , or 
 a quadruple atom of ammonia (N 4 H 12 ), in which half the hydrogen is 
 replaced by three atoms of diatomic ethylene. 
 
 By acting on C 4 H 4 Br 2 with ethylamine, a salt is obtained, having the compo- 
 sition N 4 (C 4 H 4 ),"(C 4 H,) 4 H 2 . Br 4 , representing four atoms of bromide of ammonium 
 (N 4 H 16 Br 4 ) in which H 10 are replaced by 5(C 4 H 4 )", and H 4 by (C 4 H 5 ) 4 . From this 
 bromide a strongly alkaline base, the hydrated oxide of pentethylene-tetrethyl-tetr- 
 ammonium, N 4 (C 4 H 4 )/(C 4 H 5 ) 4 H 2 4 . 4HO, is obtained, which is formed upon the type 
 of four atoms of the imaginary hydrated oxide of ammonium (NH 4 0. HO). 
 
TRIETHYLPHOSPHINE. 547 
 
 The action of iodide of ethyle (C 4 H 5 I) upon this base replaces each of the remain- 
 ing atoms of hydrogen by ethyle, yielding N 4 (C 4 H 4 ) 6 "(C 4 H.) 6 H0 4 . 4HO and 
 N 4 (C 4 H 4 );'(C 4 H S ) 6 4 .4HO. 
 
 When diethylamine (NH(C 4 H 5 ) 2 ) acts on bibromide of ethylene, the bromide of 
 tri-ethylene-octethyl-tetrammonium, N 4 (C 4 H 4 ) 3 // (C 4 H 5 ) 8 H 2 . Br 4 , is obtained, which also 
 furnishes a powerfully alkaline base, N 4 (C 4 H 4 ) 3 "(C 4 H S ) 8 H 2 4 . 4HO. 
 
 401. We are not entirely dependent upon purely artificial processes 
 for the ammonia bases containing alcohol-radicals. Many processes of 
 putrefaction furnish certain of these bases which had hitherto been over- 
 looked in consequence of their resemblance to ammonia. Thus, putre- 
 fying flour yields ethylamine, trimethylamine, and amylamine ; trimethy- 
 lamine is also found in the roe of herrings, as also in putrefied urine and 
 in the chenopodium vulvaria; it may also be obtained by distilling ergot 
 of rye with potash. Methylamine, ethylamine, propylamine (NH 2 . C 6 H 7 ), 
 butylamine (NH 2 . C 8 H 9 ), or petinine, and amylamine, are found among 
 the products of the destructive distillation of bones. 
 
 402. Ammonias and ammonium bases containing phosphorus, arsenic, 
 and antimony. It might be expected that the ammonia type was not 
 susceptible of any further modifications, but it has been found that even 
 the nitrogen of that type may be represented by other elements which are 
 chemically related to it. 
 
 Antimony, arsenic, and phosphorus, it will be remembered, all form 
 compounds with three atoms of hydrogen, SbH 3 , AsH 3 , and PH 3 , which 
 may be regarded as formed upon the ammonia type. Neither of these 
 substances, however, possesses any alkaline character, the last alone being 
 capable of combining with certain acids (hydrobromic and hydriodic). 
 
 Mention has already been made of the circumstance that compounds 
 corresponding to antimonietted, arsenietted, and phosphuretted hydrogen 
 may be obtained, in which the place of the hydrogen is occupied by cer- 
 tain alcohol-radicals; but in these cases the hydrogen does not admit of 
 partial replacement, only those compounds which correspond to triethy- 
 lamine and trimethylamine having been obtained. 
 
 Triethylstibine, Sb(C 4 H 5 ) 3 , and triethylarsine, As(C 4 H 5 ) 3 , have already 
 been noticed amongst another class of bodies to which they seem properly 
 to belong, since they are not capable of forming salts corresponding to 
 those of ammonia, and appear really to be composed after the types Sb0 3 
 and As0 8 (see p. 536). 
 
 With triethylphosphine, however, the case is different ; this substance, 
 P(C 4 H 5 ) 3 , is a true ammonia, capable of forming salts with the acids, like 
 ethylamine, although exhibiting, unlike that body, a very powerful ten- 
 dency to combine directly with two equivalents of oxygen and sulphur, to 
 form compounds resembling those of the arsenic and antimony series (see 
 p. 537), and formed upon the type of phosphoric acid (P0 5 ). Thus we 
 have 
 
 Binoxide of triethylphosphine, PE 3 O 2 
 Bisulphide, . . . PE 3 S 2 
 
 and the corresponding compounds containing methyle. 
 
 Triethylphosphine is obtained by the action of terchloride of phos- 
 phorus upon zinc- ethyle, PC1 3 + 3ZnE = PE, + 3ZnCl. It is a vola- 
 tile liquid of a very peculiar powerful odour, the vapour of which, when 
 mixed with oxygen, explodes with great violence at a temperature far 
 below -212. 
 
 2 M 2 
 
548 . PLATAMMONIUM COMPOUNDS. 
 
 By acting upon triethylstibine, or stibio-triethyle, with iodide of ethyle, 
 an iodide is obtained which, when decomposed by oxide of silver, yields 
 the hydrated oxide of tetrethylstibonium (SbE 4 . HO), formed after the 
 type of hydrated oxide of ammonium (NH 4 . HO). 
 
 In a similar manner there are obtained the hydrated oxides of tetrethyl- 
 arsonium (AsE 4 . HO) and tetrethylphosphonium (PE 4 . HO), and 
 their corresponding methyle compounds. 
 
 These substances are precisely similar in properties to the hydrated 
 oxide of tetrethylium, being powerfully caustic alkalies bearing a close 
 resemblance to hydrate of potash. 
 
 A very remarkable base has also been obtained, composed after the 
 type of a double atom of the imaginary hydrated oxide of ammonium 
 (I^ 2 H 8 2 . 2HO), in which one atom of nitrogen has been replaced by 
 phosphorus, and the other by arsenic, whilst of the hydrogen, two atoms 
 are replaced by the diatomic radical ethylene (C 4 H 4 ) // , and the remainder 
 by ethyle. This base has been styled the hydrated oxide of ethylene- 
 hexethyle-diphospharsonium, and its formula is 
 
 PAs(C 4 H 4 y(C 4 H 5 ) 6 2 .2HO. 
 
 This base combines with two equivalents of acids to form salts, and 
 behaves in every respect as a double equivalent of hydrate of potash 
 would do. 
 
 By acting upon triethylphosphine with chloroform (C 2 HC1 3 ), contain- 
 ing the triatomic radical formyle (C 2 H)'", a chloride has been obtained 
 which is composed upon the type of three atoms of chloride of am- 
 monium (3NH 4 C1 = IST 3 H 12 C1 3 ), in which one-fourth of the hydrogen 
 is replaced by formyle and the rest by ethyle ; the composition of this 
 chloride is therefore (P 3 (C 2 H)'"(C 4 H 5 ) 9 C1 3 ) ; from this compound various 
 salts have been obtained containing the corresponding oxide, combined 
 with three equivalents of the acids, but the hydrated oxide itself has not 
 been obtained. 
 
 3P(C 4 H 5 ) 3 + (C S H)'"C1 3 = 
 
 Triethylphosphine. Chioroform. 
 
 403. The insight into the constitution of the bases derived from ammonia, which 
 has been acquired in the researches detailed above, has induced chemists to endea- 
 vour to apply the same principles to certain inorganic hases derived from ammonia 
 by the action of metallic salts. 
 
 Thus, by the action of (proto) chloride of platinum upon ammonia (see p. 398), 
 a compound is obtained which may be regarded as simply PtCl . NH 3 ; but when 
 this is treated with oxide of silver, the Cl is removed in the form of chloride of 
 silver, and a caustic alkaline base is separated, which has the formula PtO . NH 3 . HO, 
 or rather, viewed upon the type of hydrated oxide of ammonium, NH 8 Pt.O.HO, 
 hydrated oxide of platammonium, or hydrate of platosamine. 
 
 By employing ethylamine instead of ammonia, there would be obtained 
 NHoEPt . . HO, hydrated oxide of ethyloplatammonium. 
 
 When the compound PtCl . NH 3 (or rather NH 3 Pt . 01, chloride of platammonium) 
 is again treated with ammonia, it yields NH 3 Pt . Cl . NH 3 , and when this is decom- 
 posed with oxide of silver, another caustic alkali is obtained, having the composition 
 NH 3 Pt . . NH 3 . HO, which may be regarded as NH 2 Pt(NH 4 )0 . HO, the hydrated 
 oxide of platammon-ammonium, or hydrate of diplatosamine ; it would then become 
 a hydrated oxide of ammonium (NH 4 . HO), in which one atom of hydrogen is 
 replaced by platinum and another by ammonium. 
 
 Very remarkable and beautiful crystalline compounds have also been obtained, 
 which are formed after the type of chloride of platammonium, but contain either 
 phosphorus, antimony, or arsenic, in place of nitrogen, and ethyle in place of 
 hydrogen ; these are 
 
AMIDES. 549 
 
 Chloride of plato-triethyl-phosphonium, . . PPt(C 4 H 5 ) 8 .01 
 
 arsonium, . . AsPt(C 4 H 5 ) 3 . Cl 
 
 stibonium, . . SbPt(C 4 H 6 ) 3 . Cl 
 
 Corresponding salts have also been obtained containing gold iii the place of 
 platinum, and forming beautiful colourless crystals. 
 
 In some bases, chlorine, bromine, and even nitric peroxide (N0 4 ) have 
 been introduced in the place of hydrogen into the alcohol-radical, but in 
 all these cases the basic energy is diminished by such substitution, and in 
 some altogether destroyed. 
 
 Thus, in the aniline (phenylamine) series, we have 
 
 Chloraniline, , . . NH 2 (C 12 H 4 C1), weak base. 
 
 Dichloraniline, . . . NH 2 (C 12 H 3 C1 2 ), weaker base. 
 
 Trichloraniline, . . . NH 2 (C 12 H 2 C1 3 ), neutral. 
 
 Nitraniline, . . . NH 2 [C 12 H 4 (N0 4 )], weak base. 
 
 Dinitraniline, . . . NH 2 [C 12 H 3 (N0 4 ) 2 ], neutral. 
 
 404. Amides. When oxalate of ammonia (NH 4 . C 2 3 ) is subjected 
 to distillation, a white, crystalline sparingly soluble substance is obtained, 
 which has been named oxamide, and is represented by the formula 
 NH 2 . C 2 2 . This substance is derived from the ammonia-salt by the loss 
 of 2 equivalents of water 
 
 NH 4 O.C 2 3 - 2HO - NH 2 .C 2 2 
 
 and its close relationship to oxalate of ammonia is shown by the circum- 
 stance that it is reconverted into that salt, if heated with water in a 
 sealed tube to 436 F., or by simply boiling it with water to which a 
 little acid or alkali has been added. 
 
 Oxamide is more readily prepared by decomposing oxalic ether with 
 ammonia, when it is obtained as a white crystalline precipitate 
 
 C 4 H 5 O.C 2 3 + NH 3 = C 4 H 6 O.HO + 
 
 Oxalic ether. Alcohol. Oxamide. 
 
 If one of the compound ammonias, such as ethylamine and aniline, be 
 employed instead of ammonia, etJilyoxamide and oxanilide are produced 
 
 C 4 H 5 O.C 2 3 + NH 2 .C 4 H 5 = C 4 H 5 O.HO + NH . C 4 H 5 . C 2 2 , 
 
 Oxalic ether. Ethylamine. Ethyloxamide. 
 
 C 4 H 5 O.C 2 3 + NH 2 .C 12 H 5 = C 4 H 5 O.HO + NH . C 12 H 5 . C 2 3 . 
 
 Aniline. Oxanilide. 
 
 Oxamide is the representative of a large class of bodies, known as the 
 amides, which may be denned as substances capable of being converted, by 
 the assimilation of the elements of two equivalents of water, into the 
 ammonia-salts from which they are derived. 
 
 Some other interesting members of this class are here enumerated, 
 together with the corresponding ammonia-salts 
 
 Formamide, . . . NH 2 . C 2 H0 2 
 
 Acetamide, . . . NH 2 . C 4 H 3 2 
 
 Butyramide, . . . NH 2 . C 8 H 7 2 
 
 Benzamide, . . . NH 2 .C 14 H S 2 
 
 Formiate of ammonia, NH 4 . C a H0 8 
 Acetate, .... NH 4 O.C 4 H 3 8 
 Butyrate, .... NH 4 O.C 8 H 7 8 
 Benzoate, .... NH 4 O.C 14 H 5 8 
 
 It is evident that these amides may be regarded as derived from ammonia 
 by the substitution of a compound group for one of the three atoms of 
 hydrogen. 
 
550 NITRILES IMIDES. 
 
 When binoxalate of ammonia (NH 4 . C 2 0,, HO . C 2 3 ) is distilled, at a 
 moderate heat, a solid acid substance is left in the retort, which is known 
 as oxamic acid, NH 2 . C 2 2 , HO . C. 2 3 , and may be regarded as composed 
 of oxamide (derived from neutral oxalate of ammonia), with the extra 
 equivalent of hydrated oxalic acid. That it contains no oxalic acid as 
 such is proved by its yielding soluble crystallisable salts with lime and 
 baryta, both which yield insoluble salts with oxalic acid. 
 
 When the solution of oxamic acid in water is boiled, it is reconverted 
 into the binoxalate of ammonia 
 
 NH 2 . C A, HO . C 2 3 + 2HO = NH 4 . C 2 3 , HO . C 2 3 . 
 
 Oxamic acid. Binoxalate of ammonia. 
 
 Oxamic acid is the representative of a limited class of acids formed in a 
 similar manner.* 
 
 405. Nitriles. When oxalate of ammonia is mixed with anhydrous 
 phosphoric acid and distilled, it loses four equivalents of water, leaving 
 cyanogen, NH 4 . C 2 3 - 4HO = C 2 IS T . 
 
 In a similar manner, benzoate of ammonia yields benzonitrile 
 NH 4 O.C 14 H 5 3 - 4HO = C 14 H 5 N. 
 
 Benzoate of ammonia. Benzonitrile. 
 
 The new compound is an oil which has a powerful odour of bitter almonds, 
 and is reconverted into benzoate of ammonia by boiling with dilute acids 
 or alkalies. 
 
 The term nitrile is applied to all similar substances which are derived 
 from ammoniacal salts by the loss of four equivalents of water, and are 
 capable of reconversion into those salts. It will be remembered that 
 many of these nitriles are identical with the cyanides of the alcohol- 
 radicals. 
 
 Oxalonitrile, NC 2 = Cy, cyanogen. 
 
 Formonitrile, NC 2 H = HCy, hydrocyanic acid. 
 
 Acetonitrile, NC 4 H 3 = C 2 H 3 . C 2 N, cyanide of methyle. 
 
 Propionitrile, NC 6 H 5 = C 4 H 5 .C 2 N, ethyle. 
 
 Benzonitrile, NC 14 H 5 = C 12 H 5 . C 2 N, phenyle. 
 
 A by no means numerous class of substances, frequently spoken of as 
 the imides^ are obtained by the action of heat upon the acid ammonia 
 salts of certain bibasic acids, by the loss of four equivalents of water, thus 
 
 NH 4 O.HO.C 20 H 14 6 - 4HO = NH . C 20 H 14 4 . 
 
 Bicamphorate of ammonia. Camphorimide. 
 
 406. If the amides be regarded as immediately derived from ammonia by substi- 
 tution, their want of alkaline properties must be ascribed to the introduction of an 
 electro-negative radical in place of the hydrogen (see p. 520). 
 
 Thus, if oxalic acid be regarded as HO . (C 2 2 )0, the hydrated oxide of oxalyle, 
 then oxamide may be viewed as ammonia, in which one atom of hydrogen has been 
 
 displaced by that radical ; N 
 
 * Strictly speaking, oxalic acid being a bibasic acid, 2HO . C 4 6 , its ammonia-salt 
 should be written 2NH 4 . C 4 6 , when oxamide would become N 2 H 4 . C 4 4 , and the formula 
 of oxamic acid would be doubled, but this would in no way affect the general principles 
 stated in the text. 
 
 "I* This designation was originally employed upon the supposition that these bodies con- 
 tain the imaginary radical imidogen, NH ; and, in a similar manner, the amides were 
 supposed to contain amidogen, NH 2 . 
 
METAL- AMIDES. 551 
 
 Again, if benzoic acid arid salicylic acid, respectively, be regarded as hydrated 
 oxides of benzoyl, (C 14 H 5 2 )0 . HO, anifof salicyle, (C U H 6 4 )0 . HO, then their amides 
 would be represented 
 
 Benzamide, N I " 5 2 
 
 I "2 
 
 Salicylamide, N | U H 6 4 
 ( "2 
 
 and it should be possible to procure them from ammonia by processes similar to 
 that which furnishes ethylamine, &c. It is found that when chloride of benzoyle is 
 Heated with ammonia, benzamide is really produced 
 
 C 14 H 6 2 .C1 + 2NH 3 = NH 2 .C 14 H 5 O a + NH 4 C1 . 
 
 Chloride of benzoyle. Benzamide. 
 
 But we ought also to be able to carry the substitution farther by displacing the 
 remaining hydrogen ; accordingly, when benzamide and salicylamide are heated 
 together, ammonia is disengaged, and benzoyl-salicylainide obtained 
 
 ( CuH 5 2 ( C U H 5 4 f C 14 H 5 2 
 
 H{ H * { H = N {0 1( H A + NH S . 
 
 Benzamide. Salicylamide. Benzoyl-salicylamide. 
 
 Amides have even been obtained in which the three atoms of hydrogen in 
 ammonia are displaced by different radicals. 
 
 It is evident that the iniides might be regarded as ammonias in which two atoms 
 of hydrogen have been replaced by a diatomic radical, thus 
 
 Camphorimide, N { ( C 2oH-i 
 
 and the nitriles, as ammonias in which all the hydrogen has been replaced by a 
 triatomic radical, but experimental evidence is scarcely in favour of these views. 
 
 If the amides be really derivatives from ammonia, it would be expected that 
 similar bodies should be derived from phosphuretted hydrogen (PH 3 ). An example 
 of these is furnished by tribenzoyl-phosphide, P(C 14 H 5 2 ) 3 , which is obtained by the 
 action of chloride of benzoyle upon phosphuretted hydrogen. 
 
 PH 3 + 3(C 14 H 5 2 .C1) = P(C 14 H 5 2 ) 3 + 8HC1. 
 Chloride of benzoyle. Tribenzoyl-phosphide. 
 
 407. Metal-amides. The possibility of substituting metals for the 
 hydrogen in ammonia has only recently been fully established, though it had 
 long been known that when potassium and sodium were heated in gaseous 
 ammonia, hydrogen was evolved, and potassamide and sodamide were 
 produced 
 
 + K - NHK + H. 
 
 When potassamide is heated, ammonia is evolved, and tripotassamide 
 (NK 3 ) produced 
 
 If ammoniacal gas be passed into an ethereal solution of zinc-ethyle, 
 hydride of ethyle is evolved, and a white amorphous precipitate of 
 zincamide separates 
 
 NH 3 + C 4 H 5 .Zn = NH 2 .Zn + C 4 H 5 .H. 
 
 Zinc-ethyle. Zincamide. Hydride of ethyle. 
 
 When zincamide is brought in contact with water, it is decomposed with 
 evolution of heat, yielding hydrated oxide of zinc and ammonia 
 
 NH 2 Zn + 2HO = JSTH } + ZnO.HO. 
 The decomposing action of zinc-ethyle upon the bases derived from 
 
552 CHLOROFORM. 
 
 ammonia is parallel with that upon ammonia itself. Thus, with 
 aniline 
 
 NH 2 .C 12 H 5 + C 4 H 5 Zn = NH.Zn.C 12 H 5 + C 4 H 5 .H 
 
 Aniline. Zinc-ethyle. Zinc-phenylimide. Hydride of ethyle. 
 
 When the zinc-phenylimide is treated with water, of course aniline is re- 
 produced. 
 
 When 'diethylamine is heated with zinc-ethyle 
 
 N(C 4 H 5 ) 2 H + C 4 H 5 Zn = ^(C.H^Zn + C 4 H 5 .H. 
 
 Diethylamine. Diethylzincamine. 
 
 When zincamide is heated above 400 F., it is decomposed into ammo- 
 nia and nitride of zinc (NZn 3 ), which represents ammonia, in which the 
 three atoms of hydrogen are replaced by zinc 
 
 Zincamide. Nitride of zinc. 
 
 The nitride of zinc is a grey powder, which is unaffected by a red heat, if 
 air be excluded. If it be moistened with water, it becomes red hot, 
 being decomposed with great violence, according to the equation 
 
 NZn 3 + 6HO - NH 3 + 3(ZnO.HO). 
 
 It might be anticipated that if the amides be truly formed after the 
 ammonia-type, they should behave towards zinc-ethyle in the same manner 
 as ammonia and aniline. 
 
 By heating oxamide with zinc-ethyle, one of its atoms of hydrogen may 
 be replaced by zinc 
 
 NH 2 .C 2 2 + ZnC 4 H 5 = NH.Zn.C 2 2 + C 4 H 5 .H. 
 
 Oxamide. Zinc-oximide. 
 
 In a similar manner, acetamide (NH 2 . C 4 H 3 2 ) is converted into zinc- 
 acetimide (NHZn . C 4 H 3 2 ). These bodies are reconverted into their cor- 
 responding amides and oxide of zinc, when treated with water. 
 
 DEEIVATIVES OF THE ALCOHOLS. 
 
 408. Chloroform. Among the useful substances prepared from members 
 of the alcohol series, chloroform (CgHClg) occupies a prominent position. 
 
 It is prepared by distilling 1 part of alcohol with 6 parts of chloride 
 of lime, and 24 parts of water, until about 1J part has passed over; 
 the distilled liquid, consisting chiefly of water and chloroform, separates 
 into two layers, the heavier being chloroform (sp. gr. 1 *5). The upper 
 aqueous layer having been drawn off by a siphon, the chloroform is 
 shaken with oil of vitriol to remove certain volatile oils, which have dis- 
 tilled over with it, and as soon as it has risen to the surface of the oil of 
 vitriol, it is drawn off and rectified by distillation, until it boils regularly 
 at 142 F. 
 
 The chemical change involved in the preparation of chloroform appears 
 to consist of two distinct stages, in the first of which the alcohol is con- 
 verted into chloral by the action of the chlorine furnished by the chloride 
 of lime, C 4 H 6 2 + CJ^ = C 4 HC1 3 2 + 5HC1; the hydrochloric acid is, of 
 
 Alcohol. Chloral. 
 
 course, neutralised by the lime. In the second stage, the chloral is acted 
 upon by the hydrate of lime, which is always present in commercial 
 chloride of lime, and is converted into chloroform and formiate of lime, 
 C 4 HC1 3 2 + CaO.HO = CaO.C 2 H0 3 + CJBEG^-. 
 
 Chloral. Formiate of lime. Chloroform. 
 
PERFUME-ETHERS. 553 
 
 Chloroform is remarkable for its very fragrant odour, and for the power 
 of its vapour to produce insensibility to pain, for which purpose it is 
 often used in surgical operations. This property is not peculiar to chloro- 
 form, but is possessed in different degrees by most other liquids of power- 
 ful ethereal odour, such as ordinary ether, bisulphide of carbon, bichloride 
 (tetrachloride) of carbon, &c. Chloroform is also used for dissolving 
 caoutchouc, which it takes up more readily and abundantly than any 
 other liquid, and is employed for extracting the poisonous alkaloids (par- 
 ticularly strychnine), when mixed with organic matters. The name chlo- 
 roform has been conferred upon this substance on the supposition that it 
 contained the radical of formic acid (formyle C 2 H), and it is sometimes 
 styled the ter chloride of formyle. This belief is encouraged by its 
 behaviour with an alcoholic solution of potash, when it yields formiate of 
 potash and chloride of potassium 
 
 C 2 HC1 3 + 4(KO.HO) = KO.C 2 H0 3 + 3KC1 + 4HO. 
 
 Chloroform. Formiate of potash. 
 
 But the processes by which it may be formed would lead us to regard it 
 as a substitution-product from marsh-gas (hydride of methyle, C 2 H 3 . H). 
 If marsh-gas be diluted with an equal volume of carbonic acid, and to 1 
 volume of this mixture at least 1 J volume of chlorine be added, chloro- 
 form is slowly produced, C 2 H 4 + C1 6 = 3HC1 + CfLC\. Chloroform is 
 also formed by the action of chlorine upon chloride of methyle 
 
 C 2 H 3 C1 + C1 4 = C 2 HC1 3 + 2HC1. 
 
 Wood-spirit (hydrated oxide of methyle) may be employed instead of 
 alcohol for the preparation of chloroform. 
 
 If chloroform be distilled in a current of chlorine, it is converted into 
 bichloride of carbon, C 2 HCI 3 + CL, - C 2 C1 4 + HC1 . When chloroform 
 is heated with amalgam of potassium, acetylene (C 4 H 2 ) is disengaged, 
 which is polymeric with the hypothetical radical formyle C 2 H . 
 
 Bromoform (C 2 HBr 3 ) and lodoform (C 2 HI 3 ) have no practical interest. 
 
 Chloral (C 4 HCI 3 2 ), which has been mentioned as resulting from the 
 action of chlorine upon alcohol, may be regarded as aldehyde (C 4 H 4 2 ), in 
 which 3 atoms of hydrogen are replaced by chlorine. 
 
 The most interesting feature of chloral, which is a colourless oily liquid, 
 is its spontaneous transformation into a porcelain-like mass, which has the 
 same composition as the liquid, and may be reconverted into it by 
 distillation. 
 
 409. Perfume-ethers. Certain of the compound ethers, formed by the 
 combination of oxide of ethyle and its analogues with the acids of the 
 acetic series, are employed in perfumery and confectionery. 
 
 Thus, the butyrate of ethyle, or butyric ether (C 4 H 5 . C 8 H 7 3 ), pre- 
 pared by distilling butyrate of potash with alcohol and sulphuric acid, has 
 a decided flavour of pine apples. Acetate of amyle (C 10 H n O . C 4 H 3 3 ) has 
 a very strong resemblance in taste and smell to the jargonelle pear ; it is 
 obtained by distilling fousel oil (hydrated oxide of amyle) with acetate of 
 soda and sulphuric acid. 
 
 The valerianate of amyle, which has the flavour of apples, and is known 
 as apple-oil, is obtained by distilling fousel oil with sulphuric acid 
 and bichromate of potash, when the chromic acid of the latter oxidises one 
 
554 ALDEHYDES. 
 
 portion of the hydrated oxide of amyle (C 10 H n O . HO), converting it into 
 valerianic acid (C 10 H 9 3 . HO), which then unites with another portion 
 of oxide of amyle, forming the valerianate of amyle (C 10 H n O . C 10 H 9 3 ). 
 
 410. ALDEHYDES Vinic or acetic aldehyde. It has been already noticed 
 (p. 492) that a considerable loss of alcohol has occasionally taken place in 
 the manufacture of vinegar, in consequence of the formation of aldehyde 
 (C 4 H 4 2 ) instead of acetic acid (C 4 H 4 4 ) by a partial oxidation of the alcohol. 
 In order to prepare aldehyde in quantity, alcohol is distilled with sulphuric 
 acid and binoxide of manganese, or with sulphuric acid and bichromate of 
 potash, or it may be oxidised by chlorine in the presence of water. 
 
 Three parts of binoxide of manganese in fine powder are introduced into a retort, 
 and a mixture of 3 parts of sulphuric acid and 2 of water, which has been allowed to 
 cool, is poured upon it. 2 parts of alcohol (sp. gr. -85) are then added, the mixture 
 very gently heated, and the vapours condensed in a Liebig's condenser, or in a 
 worm (fig. 196) supplied with iced water. If bichromate of potash be employed, 3 
 parts of the salt are introduced into the retort with 2 parts of alcohol. The retort is 
 placed in cold water to moderate the action, and a mixture of 4 parts of sulphuric 
 acid with three times its volume of water is allowed to flow slowly into the retort. A 
 very gentle heat may be applied when the action has moderated. 
 
 In these processes the alcohol is oxidised according to the equation 
 C 4 H 6 0. 2 + 2 = C 4 H 4 2 + 2HO. 
 
 Alcohol. Aldehyde. 
 
 In the first process the oxygen is derived from the binoxide of manganese, 
 leaving sulphate of manganese (MnO . S0 3 ) in the retort ; in the second 
 process, the chromic acid of the bichromate furnishes the oxygen, sulphate 
 of chromium (Cr. 2 3 . 3S0 3 ) being formed. As might be expected, a portion 
 of the alcohol is oxidised to a higher degree, and converted into acetic 
 acid (C 4 H 4 4 ), so that some acetic ether comes over together with the 
 aldehyde. Another product, acetal, is also found in the distillate, which 
 has the composition C 12 H 14 4 , and may be regarded as resulting from the 
 union of 2 eqs. of ether formed by a secondary action of the sulphuric acid 
 upon the alcohol, with 1 eq. of aldehyde (2C 4 H 5 . C 4 H 4 2 ). 
 
 By redistilling the aldehyde with an equal weight of fused chloride of calcium in 
 a gently heated water-bath, it may be freed from most of the water and alcohol, which 
 are left behind in the retort, the boiling point of aldehyde being only 67'8 F. After 
 rectification, it may be separated from the acetic ether and acetal, by taking advan- 
 tage of its property of combining with ammonia to form a compound which is 
 insoluble in ether ; the rectified aldehyde is mixed with twice its volume of ether, 
 placed in a bottle surrounded by ice, and saturated with gaseous ammonia (p. 117), 
 when white needle-like crystals of aldehyde-ammonia (NH 3 . C 4 H 4 2 ) are deposited. 
 By distilling this compound with diluted sulphuric acid, and condensing the vapour 
 in a thoroughly cooled receiver, pure aldehyde is obtained, from which the last por- 
 tions of water may be removed by standing over fused chloride of calcium and a final 
 distillation. 
 
 Aldehyde may be recognised by its peculiar acrid odour, which affects 
 the eyes, as well as by its volatility and inflammability. It absorbs 
 oxygen from air even at the ordinary temperature, and is gradually con- 
 verted into acetic acid. Its attraction for oxygen enables it to reduce the 
 salts of silver to the metallic state, and a characteristic test for aldehyde 
 consists in adding a little nitrate of silver and a trace of ammonia ; on 
 heating, the silver is deposited as a mirror on the sides of the test-tube. 
 In contact with hydrate of potash, aldehyde undergoes decomposition, 
 yielding a brown substance (resin of aldehyde) and a solution of acetate 
 
ACETIC ALDEHYDE. 
 
 555 
 
 and formiate of potash, 
 may be reproduced 
 
 KO.C 4 H 3 3 
 
 By distilling a mixture of these two salts, aldehyde 
 
 KO.C 2 H0 3 = 2(KO.C0 2 ) + C 4 H 4 2 . 
 
 Acetate of potash. Formiate of potash. Aldehyde. 
 
 These reactions lend some support to the opinion, that aldehyde should 
 be represented as being framed upon the model of a molecule of hydrogen 
 (HH), in which the place of one atom of hydrogen is occupied by acetyle 
 (C 4 H 3 2 ), the hypothetical radical of acetic acid. For if formiate of potash 
 be distilled with hydrate of potash, it yields carbonate of potash and two 
 atoms of hydrogen, KO . CJH0 3 + KO.HO = 2(KO.C0 2 ) + HH; and 
 if acetate of potash be employed instead of the hydrate, aldehyde is 
 obtained instead of hydrogen 
 
 KO . C 2 HO S 
 
 KO.(C 4 H a 2 )0 = 2(KO.C0 2 ) + (C 4 H 3 2 )H. 
 
 On this view it is easy to explain the tendency of aldehyde to undergo 
 oxidation, both the radical, acetyle, and the hydrogen, acquiring oxygen, 
 and forming acetic acid, just as hydrogen is converted into water by oxi- 
 dation.* 
 
 Type. Molecule of water, HO . HO 
 Acetic acid, (C 4 H 3 2 )0 . HO 
 
 Type. Molecule of hydrogen, H . H 
 Aldehyde (hydride of ace- 
 tyle), C 4 H 3 2 . H 
 
 As might be anticipated, it is found that when vapour of aldehyde is 
 passed over heated hydrate of potash (mixed with lime) it yields acetate of 
 potash and hydrogen, C 4 H 3 2 . H + KO . HO - H . H + KO . (C 4 H 3 2 )0 . 
 
 By the action of potassium, the atom of hydrogen may be displaced from 
 the aldehyde, and the compound (C 4 H 3 2 )K obtained. 
 
 In contact with water and sodium amalgam, aldehyde combines with 
 the nascent hydrogen, and produces alcohol. Chlorine displaces three- 
 fourths of the hydrogen from aldehyde, producing chloral, C 4 C1 3 H0 2 , 
 which has been already noticed as yielding chloroform when acted on by 
 alkalies. 
 
 Perfectly pure aldehyde cannot be kept for any length of time, even in 
 sealed tubes, since it becomes converted into metaldehyde and elaldehyde, 
 which have the same composition as aldehyde, but differ widely from it 
 in properties, metaldehyde being a crystalline solid, and elaldehyde a liquid, 
 boiling at 201 F. The true formula of elaldehyde would appear to be 
 C 12 H 12 B , for the specific gravity of its vapour is 4 '52, or three times that 
 of aldehyde vapour (1-53). Metaldehyde is reconverted into aldehyde 
 when heated to 400 F. in a sealed tube. 
 
 When aldehyde is treated with a saturated solution of bisulphite of 
 soda (NaO . HO . 2S0 2 ), it forms a crystalline compound, which is soluble 
 in water, but insoluble in the saline solution, and contains the elements 
 of 1 eq. of the aldehyde and 1 eq. of the bisulphite. 
 
 If the view above referred to is correct, which represents aldehyde as 
 the hydride of acetyle (the radical of acetic acid), each of the acids belong- 
 ing to the acetic series would be expected to have a corresponding alde- 
 hyde. Accordingly, just as acetate of lime, when distilled with formiate 
 of lime, yields acetic aldehyde, so valerianic, cenanthic, and caprylic 
 
 * Aldehyde is also sometimes represented as the hydrated oxide of the hydrocarbon 
 designated acetyle at p. 520, when its formula becomes (C 4 H 3 )0 . HO. . " 
 
556 ACETONES OR KETONES. 
 
 aldehydes may be obtained by distilling the corresponding lime-salts with 
 formiate of lime. 
 
 The chief aldehydes of this series which have at present been examined 
 are 
 
 Acetic aldehyde, . . . 4 H 4 2 * 
 
 Propionic aldehyde, . . C 6 H 6 2 
 
 Butyric aldehyde, . . C 8 H 8 2 
 
 Valeric aldehyde, . . C 10 H 10 2 
 
 (Enanthic aldehyde, . . C l4 H 14 O a 
 
 Caprylic aldehyde, . . C 16 H 16 3 
 
 Rutic aldehyde, . . . C 20 H 20 O a 
 
 Euodie aldehyde, . . C 22 H 22 O a 
 
 Laurie aldehyde, . . C 24 H 24 3 
 
 The radicals corresponding to acetyle, which may be regarded as asso- 
 ciated with hydrogen in these aldehydes, have not, for the most part, been 
 isolated j a substance having the same composition as butyryle (CgH^O.,), 
 the supposed radical of butyric acid (C 8 H 8 4 ), has, however, been obtained 
 from that acid by an indirect process. 
 
 Acetic, propionic, and butyric aldehydes have been found among the 
 products of the oxidising action of a mixture of binoxide of manganese 
 and sulphuric acid upon fibrine, albumen, and caseine. 
 
 Valeric aldehyde is obtained, like acetic aldehyde, by distilling the cor- 
 responding alcohol (amyle-alcohol, C 10 H 12 2 ) with sulphuric acid and 
 bichromate of potash. 
 
 Capric (rutic), euodic, and lauric aldehydes are found in essential oil of 
 rue. The higher aldehydes of the series are not so easily oxidised as those 
 containing a lower number of carbon equivalents. 
 
 When an aldehyde is heated with one of the bases derived from 
 ammonia by the substitution of an alcohol-radical for one atom of hydro- 
 gen, the other two atoms of hydrogen of the ammonia are replaced by the 
 diatomic hydrocarbon of the aldehyde ; thus 
 
 2NH 2 C 10 H U + 2C 14 H 14 2 *= 4HO + N 2 (C 10 H n ) 2 (C 14 H 14 )/ . 
 
 Amylamine. (Enanthic aldehyde. Di-cenanthylene-di-amylamine- 
 
 This reaction has been recommended for the determination of the 
 replaceable (or typical) hydrogen in organic bases. 
 
 411. ACETONES. If the lime salts of the acids of the acetic series, 
 instead of being distilled with formiate of lime, as for the preparation of 
 the aldehydes, be distilled alone, or with quick-lime, a series of homo- 
 logous products is obtained, each of which is isomeric with the aldehyde 
 of the series next below it in the table, though totally different from that 
 aldehyde in properties. 
 
 Thus, by distilling acetate of lime with lime, the liquid acetone 
 (C 6 H 6 2 ) is obtained, which has been already noticed among the products 
 of the distillation of wood 
 
 2(CaO.C 4 H 3 3 ) = 2(CaO.C0 2 ) + C 6 H 6 2 . 
 
 Acetate of lime. Acetone. 
 
 Acetone has the same composition as propionic aldehyde. By similar 
 
 * It will be remarked that these aldehydes are isomeric with the compound ethers 
 formed by their acids ; thus, acetic aldehyde is isomeric with acetic ether, for 
 
 2C 4 H 4 2 = G 4 H fi O.C 4 H 3 3 
 but the sp. gr. of aldehyde vapour (1-63) is only half that of acetic ether vapour (3 -06). 
 
OIL OF BITTER ALMONDS AN ALDEHYDE. 557 
 
 processes the following acetones (or Jtetones, as they are frequently called) 
 have been obtained : 
 
 Acetone, :, -. . C 6 H 6 2 
 
 Propione, . . * C 10 H 10 2 
 
 Butyrone, . . . C 14 H U 2 
 
 Valerone, . . . C 18 H 18 2 
 
 These substances are allied, in some of their properties, to the aldehydes, 
 especially in forming crystalline compounds with bisulphite of soda. 
 Hence many chemists have been led to believe that they are composed, 
 like the aldehydes, after the model of a molecule of hydrogen, but that in 
 the acetones the radicals of the corresponding acids are associated, not 
 with an atom of hydrogen, but with an atom of the hydrocarbon radical 
 of the next lower alcohol. Thus, the acetone of the acetic series (C 6 H 6 2 ) 
 would be composed of the radical acetyle (C 4 H 3 2 ) associated with methyle 
 (C. 2 H 3 ), and this view of its constitution is supported by the formation 
 of acetone, when chloride of acetyle is acted upon by zinc-methyle 
 
 C 4 H 3 2 .C1 + C 2 H 3 .Zn = C 4 H 3 2 .C 2 H 3 + ZnCl. 
 
 Chloride of acetyle. Zinc-methyle. Acetone. 
 
 In a similar manner, chloracetene (resulting from the action of chloro- 
 carbonic acid on aldehyde) yields acetone when acted on by methylate of 
 soda (sodium-methyle-alcohol) 
 
 (C 4 H 3 )C1 + (C 2 H 3 )Na0 3 = NaCl + C 4 H 3 2 .C 2 H 3 . 
 
 Chloracetene. Methylate of soda. Acetone. 
 
 Further corroboration is obtained by distilling a mixture of equivalent 
 quantities of acetate and valerianate of potash, when an acetone is obtained, 
 which contains valeryle (C 10 H 9 2 ), associated with methyle (C 2 H 3 ) 
 
 KO.C 4 H 3 3 + KO.C 10 H 9 3 = 2(KO.C0 2 ) + C 10 H 9 2 . C 2 H 3 . 
 
 Acetate of potash. Valerianate of potash. 
 
 It will be remembered that when acetate of potash is distilled with 
 hydrate of potash, it yields marsh-gas by a precisely parallel reaction 
 
 KO.C 4 H 3 3 + KO.HO = 2(KO.C0 2 ) + H.C 2 H 3 . 
 
 Acetate of potash. Marsh-gas. 
 
 Acetone may also be prepared by distilling sugar with eight times its 
 weight of quick-lime, when it is accompanied by another liquid, metavetone, 
 C 6 H 5 0, which differs from acetone in being insoluble in water. When 
 this liquid is heated with bichromate of potash and sulphuric acid, it is 
 oxidised and converted into metacetonic or propionic acid, HO . C 6 H 5 3 , 
 which may also be produced by the oxidation of acetone. 
 
 412. The description above given of the properties of aldehyde will 
 have recalled those of some of the essential oils containing oxygen. Thus, 
 essential oil of bitter almonds (C 14 H 6 2 ), when exposed to air, absorbs 
 oxygen, and is converted into benzoic acid (C 14 H 6 4 ), just as aldehyde 
 (C 4 H 4 2 ) passes into acetic acid (C 4 H 4 4 ). Moreover, oil of bitter 
 almonds forms a crystalline compound with bisulphite of soda, similar to 
 that formed by aldehyde, and its conversion into this compound is some- 
 times resorted to in order to obtain the pure oil. 
 
 In constitution, also, oil of bitter almonds (hydride of benzoyle, 
 C 14 H 5 2 . H) closely resembles aldehyde (hydride of acetyle, C 4 H 3 2 . H), 
 and just as the latter may be obtained by distilling acetate of potash with 
 
558 POLYATOMIC ALCOHOLS. 
 
 formiate of potash, so benzole aldehyde (oil of bitter almonds) may be 
 obtained from benzoate of potash 
 
 KO.(C 14 H 5 2 )0 + KO.C 2 H0 3 = 2(KO . C0 2 ) + C 14 H 5 2 .H. 
 
 Benzoate of potash. Formiate of potash. Benzole aldehyde. 
 
 Oil of bitter almonds is produced, together with some aldehydes of the 
 acetic series of acids (p. 556), when certain albuminous bodies are oxi- 
 dised by sulphuric acid and binoxide of manganese. 
 
 When benzoic aldehyde is acted on by an alcoholic solution of hydrate 
 of potash, an oily liquid is obtained, which stands in the same relation to 
 benzoic aldehyde as alcohol bears to acetic aldehyde 
 
 2(C 14 H 5 2 .H) + EX). HO = KO . (C 14 H 5 2 )0 + C 14 H 8 2 . 
 
 Benzole aldehyde. Benzoate of potash. Benzoic alcohol. 
 
 The hydrochloric ether of benzoic alcohol, C 14 H 7 C1, is sometimes called 
 chloride of benzyle, the radical benzyle, C 14 H 7 , being supposed to have the 
 same relation to the benzoic series as ethyle has to the acetic series. By 
 the action of ammonia upon chloride of benzyle, benzylamine, NH 2 (C 14 H 7 ), 
 and tri-benzylamine, N(C 14 H 7 ) 3 , have been obtained ; the former is isomeric 
 with toluidine, but is by no means identical with it, for benzylamine is a 
 liquid having basic properties far more powerful than those of tolui- 
 dine, and it is very readily soluble in water, which dissolves but little of 
 the latter base. 
 
 The benzoic acetone or benzone (C 26 H 10 2 ) has been obtained by the distil- 
 lation of benzoate of lime. It is often called benzophenone, being regarded as 
 an association of benzoyle with phenyle, C 14 H 5 2 . C 12 H 5 ; for when distilled 
 with hydrate of potash, it yields benzoate of potash and benzole (hydride 
 of phenyle) 
 
 C 14 H 5 2 -C 12 H 5 + KO.HO = KO.(C 14 H 5 2 )0 + C 12 H 5 .H. 
 
 Benzophenone. Benzoate of potash. Benzole. 
 
 Oil of cinnamon (p. 476) or hydride of cinnamyle (C 18 H 7 2 . H) is the 
 aldehyde of cinnamic acid (C 1S H M 4 ) ; and essential oil of cummin contains 
 the aldehyde (C 20 H n 2 . H) of cuminic acid (C 20 H 12 4 ), and yields cuminic 
 alcohol (CjjH^Oj when treated with alcoholic solution of potash. Oil of 
 spiraea or hydride of salicyle (C 14 H 5 4 . H) is the aldehyde of salicylic acid 
 (C 14 H 6 6 ). Hydride of anisyle (C 16 H 7 4 . H), obtained by the oxidation 
 of oil of aniseed, is the aldehyde of anisic acid (C lf; H H O p ), and of anisic 
 alcohol (C 1G H 10 2 ). These aldehydes allow their associated atom of hydro- 
 gen to be displaced by chlorine more readily than the aldehydes of the 
 acetic series, to form chlorides of their respective radicals (p. 475). 
 
 GLYCOL POLYATOMIC ALCOHOLS. 
 
 413. It has been already shown (p. 526) that alcohol may be con- 
 veniently regarded as composed after the fashion of a molecule of water 
 (H 2 O) in which half the hydrogen has been displaced by ethyle (6 2 H B ) ; 
 according to this view alcohol is represented by the molecular formula 
 H(6 2 H 5 )0 ; and it is a monatomic alcohol, for it contains the monatomic 
 radical (O 2 H 5 )'. But if, following the same plan, a diatomic radical, such 
 as ethylene (C 4 H 4 )", were to displace half the hydrogen in water, the dis- 
 placement could not be effected in less than two molecules of water (H 4 O 2 ), 
 and a diatomic alcohol would result. 
 
 Glycol (C 4 H 6 4 ) is the representative of the diatomic alcohols, and may 
 be regarded as four equivalents of water, in which half the hydrogen is 
 replaced by ethylene (H (C 4 H 4 )"0 4 ). It is obtained by the action of 
 
GLYCOL. 559 
 
 biniodide of ethylene (formed by the direct union of olefiant gas with 
 iodine) upon acetate of silver 
 
 2(AgO.C 4 H 3 3 ) + (C 4 H 4 )"I 2 = 2AgI + (C 4 H 4 )"0 2 . 2C 4 H 3 3 . 
 
 Acetate of silver. * Binacetate of glycol. 
 
 The binacetate of glycol thus formed corresponds to the acetic ether 
 ((C 4 H 5 )0 . C 4 H 3 3 ) derived from common alcohol; but since glycol is 
 diatomic, it combines with two equivalents of acetic acid. When the 
 result of this action is distilled, the binacetate of glycol passes over as a 
 colourless liquid, which sinks in water, and boils at 365 F.* 
 
 Glycol can be obtained from the binacetate by digesting it with hydrate 
 of potash for some time at 360 F., and distilling, when the glycol passes 
 over, its boiling point being 387 F. It is a colourless liquid, having a 
 sweet taste, whence it derives its name (y\vKv<s, sweet). Like common 
 alcohol, it mixes with water in all proportions, and may be distilled 
 without decomposition. It also gives an inflammable vapour, and has 
 never been frozen ; but, unlike alcohol, it is heavier than water (sp. gr. 
 1*125), and does not mix with ether, though alcohol dissolves it readily. 
 
 Glycol is also capable of uniting with one equivalent of acetic acid, 
 forming the monacetate of glycol, C 4 H 4 2 . HO . C 4 H 3 3 , and a remarkable 
 compound has been obtained containing glycol in combination with 
 acetic and butyric acids ; this acetobutyrate of glycol has the composition 
 
 C 4 H 4 2 .C 4 H 3 3 .C 8 H 7 3 . 
 
 The action of hydrochloric acid upon glycol does not perfectly corres 
 pond with its action upon common alcohol, for instead of yielding a chlo- 
 ride of ethylene, it gives a compound of hydrochloric acid with oxide of 
 ethylene 
 
 H 2 (C 4 H 4 )"0 4 + HC1 = (C 4 H 4 )"0 2 .HC1 + 2HO. 
 
 Glycol. . Chlorhydrine of glycol. 
 
 By decomposing this compound with potash, the binoxide of ethylene 
 (C 4 H 4 )"0 2 is obtained, as a colourless liquid, which boils at 56 F., and is, 
 therefore, not identical with aldehyde (which boils at 68 F.), though it 
 has the same composition. It is obvious that glycol might be represented 
 as (C 4 H 4 )"0 2 . 2HO, the hydrated binoxide of ethylene, and this view is 
 favoured by the circumstance that glycol may be formed by heating the 
 binoxide of ethylene with water in a sealed tube ; but, on the other hand, 
 when glycol is treated with chloride of zinc, to dehydrate it, ordinary alde- 
 hyde (C 4 H 4 2 ), and not the ethylenic binoxide, is produced. 
 
 By the action of pentachloride of phosphorus upon glycol, the bichloride 
 of ethylene, or Dutch liquid, is obtained 
 
 H 2 (C 4 H 4 )"0 4 + 2PC1 5 - (CJE^'CL, + 2HC1 + 2PO.C13. 
 
 riv/vo Bichloride of Oxychloride of 
 
 ethylene. phosphorus. 
 
 It will be observed that this equation is the exact counterpart of that 
 which represents the action of pentachloride of phosphorus upon water, 
 substituting diatomic ethylene for monatomic hydrogen 
 
 H 2 (H 2 )"0 4 + 2PC1 5 = (H,)"C1, + 2HC1 + 2P0 2 CL 3 . 
 Sodium acts upon glycol in the same manner as upon ordinary alcohol, 
 but in consequence of the di-atomic character of glycol, the reaction 
 
 * A liquid isoraeric with binacetate of glycol, but boiling at 336 F., is obtained by heat- 
 ing aldehyde in a sealed tube with acetic anhydride. 
 
560 
 
 LACTIC SERIES OF ACIDS. 
 
 takes place in two stages, producing, successively, mono-sodium glycol 
 HNa(C 4 H 4 ) // O 4 , and di-sodium glycol, Na 2 (C 4 H 4 )"0 4 , "both, which are solid. 
 When . glycol is exposed to the action of oxygen in the presence of 
 platinum-black, or when it is cautiously oxidised with nitric acid, it be- 
 comes converted into glycolic acid, C 4 H 4 6 , which bears the same relation 
 to it as acetic acid bears to common alcohol, as will be evident from the 
 following equations :* 
 
 H(C 4 H 5 ).0 2 + 4 = H(C 4 H 3 2 ).0 2 + 2HO 
 
 AlcolioL Acetic acid. 
 
 H 2 (C 4 H 4 )".0 4 + 4 = H 2 (C 4 H 2 2 )".0 4 + 2HO 
 
 GlycoL Glycolic acid. 
 
 in which the change consists, in both cases, in the substitution of 2 for 
 H 2 in the radical of the alcohol, acetic acid being formed upon the type 
 of two equivalents of water (H 2 2 ) in which H is replaced by C 4 H 3 2 , 
 and glycolic acid upon the type of four equivalents (H 4 4 ), in which H. 
 are replaced by C 4 H 2 2 . If the oxidation with nitric acid be carried 
 farther, the remainder of the hydrogen in this last radical is replaced by 
 oxygen, and oxalic acid is produced 
 
 H 2 (C 4 H 2 2 )''.0 4 + 2 = H 2 (C 4 4 )".0 4 + 2HO, 
 
 Glycolic acid. Oxalic acid. 
 
 By the action of nascent hydrogen upon oxalic acid, the 2 in the 
 radical may be again displaced by H 2 , so that glycolic acid is reproduced. 
 
 Glycolic acid forms a syrupy liquid which resembles lactic acid, but is 
 distinguished from it by being precipitated with acetate of lead. Unlike 
 oxalic acid, glycolic is a monobasic acid, only one equivalent of its hydro- 
 gen being replaceable by a metal. Glycolic acid is found together with 
 oxalic acid among the products of the action of nitric acid upon alcohol 
 in the preparation of fulminate of mercury, which is easily accounted for 
 by the connection between alcohol and ethylene, which is best exhibited 
 by writing the formula of alcohol (C 4 H 4 ) . 2HO. 
 
 Glycolic acid is the first member of a series of homologous acids, of 
 which the most important is lactic acid, these acids standing in the same 
 relation to the glycols in which the members of the acetic series stand to 
 the alcohols. 
 
 Lactic Series of Acids. 
 
 Name. 
 
 Equivalent 
 Formula. 
 
 Source. 
 
 Glycolic acid, 
 
 C,HA 
 
 Oxidation of glycol and of alcohol. 
 
 Lactic acid, 
 
 C 6 H 6 6 
 
 Fermentation of cane and milk sugars. 
 
 Butylactic acid, . 
 
 C 8 H 8 6 
 
 Oxidation of butyl-glycol. 
 
 Valerolactic acid, 1 
 
 C 10 H 10 6 
 
 ( Decomposition of bromo-valerianic 
 ( acid with oxide of silver. 
 
 Leucic acid, 
 
 C 12 H 12 6 
 
 Action of nitric acid on leucine. 
 
 It will be observed that these acids are intermediate, with respect to 
 the number of equivalents of oxygen which they contain, between the 
 acetic and the oxalic series of acids ; thus 
 
 Acetic acid, 
 Glycolic 
 Oxalic 
 
 C 4 H 4 4 
 C 4 H 4 6 
 C 4 H. 2 ? 
 
 Propionic acid, 
 Lactic ,, 
 Malonic 
 
 C 6 H 6 4 
 C 6 H 6 6 
 C fi H 4 8 
 
 * The aldehyde of glycol, glyoxal, C 4 H 2 4 , is found among the products of the decom- 
 position of nitrous ether in contact with water. 
 
FORMATION OF LEUCIC FROM OXALIC ACID. 561 
 
 These three series of acids, therefore, present a relation to each other 
 similar to that between the three series of alcohols, represented by 
 
 Yinic alcohol, . . C 4 H.0 2 
 Glycol, . . . C 4 H0 4 
 Glycerine, . .. CX 
 
 Just as acetic and glycolic acids are formed by the oxidation of alcohol 
 and glycol, so the oxidation of glycerine by nitric acid furnishes glyceric 
 add, CsH.O,. 
 
 The transition from the oxalic series to the lactic series of acids has 
 been effected in the case of leucic acid, which has been artificially formed 
 from oxalic acid, by converting it into oxalic ether, and acting upon this 
 with zinc-ethyle, when leucic ether is obtained, from which leucic acid is 
 easily prepared. The reaction is rendered intelligible if the two acids be 
 thus formulated 
 
 Oxalic acid, . . C 4 H 8 
 Leucic . CX(C 4 H 5 ) 2 6 
 
 from which it appears that, neglecting intermediate stages, the zinc of the 
 zinc-ethyle removes two equivalents of oxygen from the oxalic acid, leav- 
 ing two equivalents of ethyle in their stead, so that leucic acid may be 
 regarded as diethoxalic acid, or oxalic acid containing two equivalents of 
 ethyle instead of two equivalents of oxygen. If oxalate of methyle be 
 substituted for oxalate of ethyle in this experiment, leucate of methyle, 
 C. 2 H H . C 12 H n 5 , is obtained, and when this is decomposed by baryta, and 
 the leucate of baryta treated with sulphuric acid, fine crystals of leucic 
 acid are obtained which are readily soluble in water, alcohol, and ether, 
 and sublime slowly at the ordinary temperature.* By the reaction be- 
 tween iodide of methyle, oxalate of methyle, and amalgamated zinc, 
 dimethoxalic acid, C^.^C^.^.fl^ has been obtained, which may be re- 
 garded as oxalic acid containing two equivalents of methyle in the place 
 of two equivalents of oxygen. Dimethoxalic acid is isomeric with buty- 
 lactic or acetonic acid (C 8 H 8 6 ) ; it crystallises in prisms resembling those 
 of oxalic acid, which may be sublimed at 122 F., and volatilise slowly 
 even at the ordinary temperature. 
 
 From the other hydrocarbons of the olefiant gas series (p. 515), glycols 
 may be prepared by processes similar to that which furnishes ethylene- 
 glycol. Thus propylene (C 6 H 6 ) yields propylene-glycol, H 2 (C fi H 6 )". 4 ; 
 butylene (C 8 H 8 ), butylene-glycol, H. 2 (C 8 H 8 )". 4 ; amylene (C 10 H 10 ), amy- 
 lene-glycol, H 2 (C 10 H 10 ) // . 4 ; it is a very remarkable circumstance that the 
 boiling points and specific gravities of these ^liquids decrease as the com- 
 plexity of the formula increases, which is quite contrary to ordinary 
 experience; thus amylene-glycol (C 10 H 12 0,) has the sp. gr. 0'987, and 
 boils at 351 F., whilst propylene-glycol (CyH^OJ has the sp. gr. 1*051, 
 and boils at 371 F. 
 
 When propylene-glycol is slowly oxidised, it is converted into lactic 
 acid, exactly as glycol is converted into glycolic acid 
 
 H 2 (C,H,,)". 4 + 4 = H 2 (C 8 H 4 0,)". 4 + 2HO. 
 
 Propylene-glycol. . Lactic acid. 
 
 The difference between the diatomic character of glycol and the mona- 
 
 * It is said that this leucic acid, though clpsely resembling that obtained from oxalic 
 ether, is riot identical with it. 
 
 2 N 
 
562 WATER-TYPE VIEW OF POLYATOMIC ALCOHOLS. 
 
 tomic character of ordinary alcohol, is strongly marked in their behaviour 
 with the organic acids, for whilst the monatomic alcohol yields (with 
 monobasic acids) only one series of compound ethers containing one equi- 
 valent of acid, the diatomic glycol yields two series containing respectively 
 one and two equivalents of acid ; thus we have monacetate of glycol 
 (C 4 H 4 )"0 2 . HO . C 4 H a 3 , and binacetate of glycol, (C 4 H 4 )':0 2 . 2C 4 H 3 3 . 
 In the last series, it is not necessary that the two equivalents should con- 
 sist of the same acid, as may be seen in the acetobutyrate of glycol, 
 (C 4 H 4 )"0 2 . C 4 H 3 3 . C 8 H 7 3 , in which the glycol is combined with acetic 
 and butyric acids. 
 
 Just as polyatomic ammonias are formed upon the type of several atoms 
 of ammonia, so polyatomic alcohols may be produced by the substitution 
 of compound radicals for hydrogen in a multiple alcohol type. Thus, by 
 heating glycol in a sealed tube with binoxide of ethylene, di-ethylene- 
 trialcohol, H 2 (G 2 H 4 ) // 2 3 , is produced, which is formed upon the type of 
 three molecules of alcohol, H 3 (6 2 H 5 ) 3 3 . In a similar manner, tri-ethy- 
 lene-tetralcohol, H 2 (6 2 H 4 )/ / O 4 , is formed upon the quadruple alcohol type 
 H 4 (0 2 H 5 ) 4 4 . 
 
 It will be seen hereafter that glycerine (C 6 H 8 6 ), the sweet principle of 
 oils and fats, is a triatomic alcohol, formed upon the type of three mole- 
 cules of water (H 6 O 3 ), in which half the hydrogen is replaced by the 
 triatomic radical, (6 3 H 5 )% glyceryle, the molecular formula of glycerine 
 being H 3 (e 3 H 5 )'"0 3 . 
 
 It is easy to convert a diatomic into a monatomic alcohol ; for example, 
 if the chlorhydrine of glycol be treated with amalgam of sodium in the 
 presence of water, it becomes converted into ordinary (monatomic) alcohol 
 
 C 4 H_C10 2 4- HO + Na 2 = C 4 H 6 2 + NaO + NaCl . 
 
 Chlorhydrine A1 , , 
 
 of glycol. AlcohoL 
 
 The relation of the alcohols to water as their primary type is here 
 exhibited 
 
 TT 1 
 
 Type, one molecule of water, H 2 3 = ^ > 2 
 
 Vinic alcohol, C 4 H 6 O a ^j. ,, 1 2 
 
 Type, two molecules of water, H 4 4 = H f ^ 4 
 Glycol, C 4 H S 4 
 
 Type, three molecules of water, H 6 6 = H 2 V 6 
 
 Hj 
 
 H 2 ) 
 Diethylene-trialcohol, C 8 H 10 6 = (C 4 H 4 )'' V 6 
 
 (cXrJ 
 
 Glycerine, C 6 H 8 6 , c jA,,, j 6 
 
 TT \ 
 
 Type, four molecules of water, H 8 8 = 2 > 8 
 
 Triethylene-tetralcohol, C 12 H 14 S - / 2 w, 8 
 
ACETATES ACETONE. 563 
 
 The compounds formed by the action of acids upon these alcohols would 
 then be represented by such formulae as the following : 
 
 Acetic ether, .... ^/S^y \ 2 
 
 W4-"-5/ J 
 
 Monacetateofglycol, . . ^^^JO 
 Binacetate of glycol, . . ^/c J H V' } 4 
 
 Acetobutyrate of glycol, (C 8 H 7 2 )' > 4 
 
 flWJ 
 
 Monacetine, .... ( 4 5 ^ 1 O e 
 Diacetine, ..... $$jffi'}* 
 
 Triacetine, ..... ^CJHJ^ } 6 
 
 ACETIC ACID THE FATTY ACID SERIES. 
 
 414. The most useful of the acids belonging to the acetic series (see 
 p. 514) is acetic acid itself, the preparation of which has been already de- 
 scribed. 
 
 Many of its salts are extensively employed in the arts. Acetate of 
 alumina (A1 2 3 . 3C 4 H 3 3 ) is used as a mordant by the dyer and calico- 
 printer. Acetate of lead or sugar of lead (PbO . C 4 H $ 3 , 3Aq.) is pre- 
 pared by dissolving litharge (PbO) in an excess of acetic acid, when the 
 solution deposits prismatic" crystals of the acetate which are easily dis- 
 solved by water and alcohol. 
 
 Goulard's extract, or tribasic acetate of lead, is prepared by dissolving 
 litharge in solution of acetate of lead ; it may be obtained in needle-like 
 crystals, which have the composition (3PbO . C 4 H 3 S , HO). 
 
 Verdigris, or basic acetate of copper (2CuO . C 4 H 3 3 , 6HO), is prepared 
 by piling up sheets of copper with layers of fermenting husks of grapes 
 (the marc of the wine-press), when the oxide of copper, formed at the ex- 
 pense of the oxygen of the air, combines with the acetic acid furnished 
 by the oxidation of the alcohol. 
 
 Acetone (C 6 H 6 2 ) is obtained by the destructive distillation of acetate 
 of lime 
 
 2(CaO . C 4 H 3 3 ) - 2(CaO.CO t ) + C 6 H,0 2 
 
 Acetate of lime. Acetone. 
 
 a decomposition which possesses some general interest since the lime-salts 
 of the other acids of the acetic series yield ketones in a similar manner 
 (see p. 556). 
 
 The acetone thus obtained is an ethereal liquid lighter than water, boil- 
 ing at 133 F., and burning with a luminous flame. It is easily miscible 
 with water, but separates when hydrate of potash is added, rising to the 
 surface. 
 
 Under the action of chlorine, acetic acid loses an atom of hydrogen, 
 taking chlorine in its place, and forming chloracetic add, HO . C 4 H.,C10 3 ;* 
 
 * Bichloracetic acid, HO . C 4 HC1 2 3 , has recently been obtained. 
 
 2 N 2 
 
564 ANHYDRIDES OF ORGANIC ACIDS. 
 
 and if the action be promoted by sun-light, trichloracetic acid may be 
 formed, HO . C 4 C1 3 3 , which may be crystallised. This latter acid has a 
 peculiar interest on account of its being concerned in the production of 
 acetic acid from inorganic materials, which was one of the first examples 
 of the actual synthesis of organic compounds. 
 
 By passing vapour of sulphur over red-hot carbon, bisulphide of carbon, 
 CS 2 , is formed. When this is boiled with a mixture of hydrochloric and 
 nitric acids, a white crystalline substance is obtained, which contains 
 CSC1 2 2 . By passing the vapour of this substance through a red-hot 
 tube it suffers decomposition, and liquid protochloride of carbon, C 4 C1 4 , is 
 found among the products 
 
 4CSCLA = C 4 C1 4 + C1 4 + 4S0 2 . 
 
 By exposing this chloride of carbon, in the presence of water, to the 
 action of chlorine encouraged by sunlight, tricliloracetic acid is obtained 
 
 C 4 C1 4 -f 4HO + C1 2 - HO.C 4 C1 3 3 + 3HC1 . 
 
 By acting upon the solution of trichloracetic acid with amalgam of potas- 
 sium, acetate of potash is formed 
 
 HO.C 4 CLA + K 6 + 4HO = KO.C 4 H :J 3 + 2(KO.HO) + 3KC1. 
 
 Trichloracetic acid. Acetate of potash. 
 
 From the acetate of potash, of course, acetic acid is readily obtained. 
 
 The synthesis of acetic acid has been effected in a simpler manner by 
 the action of chlorocarbonic acid upon marsh-gas, when hydrochloric acid 
 and acetic oxychloride are formed 
 
 C 2 H 4 + 2COC1 - (C 4 H 3 0,)C1 + HC1. 
 
 Acetic oxychloride. 
 
 When the acetic oxychloride is decomposed by water, acetic acid is pro- 
 duced 
 
 (C 4 H 4 2 )C1 + 2HO - HO.C 4 H 3 3 + HC1 . 
 
 This appears to be an example of a general method of synthesis of the 
 volatile fatty acids, starting from the marsh-gas hydrocarbons derived from 
 them ; thus, hydride of amyle, C 10 H 12 , treated in a similar manner, yields 
 caproic acid, HO . C 12 H U S . 
 
 415. Anhydrides of organic acids Acetic anhydride. The course of 
 investigation by which, of late years, much light has been thrown upon 
 the true constitution of acetic acid, and therefore of many other organic 
 acids, is of a very instructive character. The strongest acetic acid which 
 can be prepared (see p. 466) is known as glacial acetic acid, from its crys- 
 tallising in icy leaflets at about 55 F. This acid has the composition 
 C 4 H 4 4 ; but if it be neutralised with carbonate of soda, the acetate of 
 soda obtained has the formula NaO . C 4 H 3 3 , showing that the elements 
 of an equivalent of water have been removed from the acid in the act of 
 combining with the soda. This has led chemists to regard ordinary 
 acetic acid as hydrated acetic acid, a compound of water with anhydrous 
 acetic acid, C 4 H 3 0, ; but all attempts to obtain this body by the abstrac- 
 tion of water from acetic acid have failed entirely. The application of 
 the principle of substitution or displacement, however, has brought this 
 substance to light. 
 
ACETIC ANHYDRIDE. 565 
 
 When acetic acid is distilled with terchloride of phosphorus, a colourless, 
 very pungent liquid is obtained, which is commonly spoken of as acetic 
 oxychloride, C 4 H 3 2 C1, and may be regarded as the anhydrous acetic acid 
 from which one equivalent of oxygen has been removed, the vacancy 
 being filled up by an equivalent of chlorine 
 
 2[HO.(C 4 H 3 2 )0] + PC1 3 - HO + HC1 + PO, + 2[(C 4 H 3 2 )C1] . 
 
 Acetic acid. Acetic oxychloride. 
 
 ' That this acetic oxychloride (or chloride of acetyle) really bears a very 
 close relationship to acetic acid, and is, in fact, composed after the same 
 type, is shown by the action of water, which at once reproduces the acetic 
 acid, exchanging its oxygen for the chlorine of the oxychloride 
 
 (C 4 H,0 2 )C1 + 2HO = HO . (C 4 H a O,)0 + HC1 
 
 Acetic oxychloride. Acetic acid. 
 
 but the C 4 H,0 3 thus formed combines immediately with an equivalent of 
 water to form the hydrated acetic acid. The action takes place with 
 explosive violence. 
 
 If hydrate of potash be allowed to act upon the chloride of acetyle, it 
 is the potash which exchanges its oxygen for the chlorine, whilst the 
 water, as before, enters into combination with the C 4 H 3 3 
 
 (C 4 H 3 2 )C1 + KO.HO - HO.(C 4 H 3 2 )0 + KC1 . 
 
 But if acetate of potash (KO . C 4 H 3 3 ) be employed instead of hydrate 
 of potash, the potash still exchanges its oxygen for the chlorine ; but the 
 C 4 H 3 3 with which it was combined, enters into combination with the 
 C 4 H 3 :i formed during the reaction, and thus produces a double atom of 
 the radical supposed to exist in acetic acid, and commonly spoken of as 
 acetic anhydride 
 
 (G 4 H 3 o 2 )ci + Ko.c 4 H 3 o 3 - C.HA.C.HP, + KCI. 
 
 Acetic oxychloride. Acetate of potash. Acetic anhydride. 
 
 Acetic anhydride has also been obtained by heating dry acetate of lead 
 or of silver with bisulphide of carbon in a sealed tube to about 320 F. 
 for several hours, the tube being occasionally opened to relieve the pres- 
 sure of the carbonic acid evolved 
 
 2(PbO.C 4 HA) + CS 2 - 2PbS + C0 2 + 2(C 4 HX\) . 
 
 The acetic anhydride is a neutral oily liquid which may be distilled off 
 in the above experiment. Its smell recalls that of acetic acid, but affects 
 the eyes strongly. It sinks in water, but dissolves slowly, with evolution 
 of heat and formation of hydrated acetic acid.* 
 
 The most convincing proof that this anhydride is really an association 
 of two atoms (each representing two volumes of vapour (O = 1 volume)) 
 is obtained by acting upon the acetate of potash with the benzoic instead 
 of the acetic oxychloride, when a benzo-acetic anhydride is formed, con- 
 
 * If acetic anhydride be heated with an excess of binoxide of barium, it yields acetate of 
 baryta, carbonic acid, and methyle gas (p. 519). 
 
 2(C 4 H 3 3 ) + Ba0 2 = BaO . C 4 H 3 0. t + C 2 H 3 > 2C0 2 . 
 By absorbing the carbonic acid with potash, the pure methyle gas is easily obtained. 
 
506 CONSTITUTION OF ACETIC ACID. 
 
 taining benzoic anhydride (C 14 H 5 O ,) in combination with acetic anhydride 
 (C 4 HA)- 
 
 (C 14 HA)C1 + KO.C 4 HA = KC1 + C 14 HA-C 4 HA 
 
 Benzoic Acetate of Benzo-acetic 
 
 oxychloride. potash. anhydride. 
 
 and the true nature of this double anhydride is seen by its conversion into 
 a mixture of hydrated benzoic and acetic acids when left in contact with 
 water. 
 
 By methods similar to that employed for acetic acid, the anhydrides of 
 many other organic acids may be obtained, being thus removed from the 
 list of hypothetical compounds to take their places among recognised forms 
 of combination. 
 
 The mode of formation of these anhydrides, however, occasions serious 
 doubt as to the propriety of regarding the acids in their ordinary form as 
 hydrates, or compounds containing water. If acetic acid, for example, be 
 really a hydrate of the radical C 4 H 3 3 , why are we unable to remove the 
 water by the application of some dehydrating agent, instead of having 
 recourse to the above circuitous process ? The answer appears to be, that 
 the acetic anhydride is really formed by a process of substitution, and is 
 not to be regarded as pre-existent in the ordinary acetic acid. 
 
 Ordinary acetic acid may, with great advantage for explaining many 
 points in its history, be regarded as composed after the type of two 
 equivalents of water in which half the hydrogen is replaced by the com- 
 pound group C 4 H 3 2 
 
 HO.C 4 H 3 3 = C A C 
 
 The composition of the acetic oxychloride (C 4 H 3 2 C1), and of acetamide, 
 
 . C 4 H 3 2 , speaks strongly in favour of this view. 
 Acetate of potash would then be represented by the formula 
 
 , = KO.C 4 HA 
 
 being formed from acetic acid by the substitution of potassium for the 
 hydrogen ; and if we represent hydrate of potash upon the water-type, its 
 behaviour with acetic acid would be thus expressed 
 
 <WU . C 4 H 3 2 ) Q H 
 
 Hi 2 "~~ 17" i Q "*" TT 
 
 J J\. j 2 Jtl 
 
 H potash f Acetic acid. Acetate of potash. Water. 
 
 The formation of the double anhydride by the action of the acetate of 
 potash upon acetic oxychloride, would then consist simply in the substitu- 
 tion of the C 4 H 3 2 in the latter for the K in the former 
 
 c 4 H 3 o 8 .ci = 'o a + KC1 
 
 Acetate of Acetic Acetic 
 
 potash. oxychloride. anhydride. 
 
 and, upon the same principles, the formation of the benzo-acetic anhydride 
 would be thus represented 
 
 + KCI - 
 
 Acetate of Benzoic Benzo-acetic 
 
 potash. oxychloride. anhydride. 
 
FORMIC ACID. 567 
 
 Peroxides of organic radicals. Considerable support has been offered 
 to this view of the constitution of the organic acids, by the discovery of 
 certain compounds which bear the same relation to the anhydrides as 
 binoxide of hydrogen bears to water. 
 
 When binoxide of barium is acted on by hydrochloric acid, chloride 
 of barium and binoxide of hydrogen are formed 
 
 Ba0 2 + HC1 - Bad + H0 2 . 
 
 If binoxide of barium be acted on by benzoic oxychloride (chloride of 
 benzoyle), the products are chloride of barium and benzoic peroxide 
 (binoxide of benzoyle) 
 
 Ba0 2 + (C 14 H 5 2 )C1 = Bad + (C 14 H 5 2 )0 2 . 
 
 The benzoic peroxide may be obtained in fine crystals from its ethereal 
 solution, but like the binoxide of hydrogen, it is easily decomposed at 
 about 2 1 2 F. with explosive violence. By the action of alkalies, it is resolved 
 into benzoic acid and oxygen, just as binoxide of hydrogen yields water 
 and oxygen 
 
 (C 14 H 5 2 )0 2 + KO = KO.(C 14 H 5 2 )0 + O. 
 
 By acting upon acetic anhydride with binoxide of barium, the acetic per- 
 oxide (or binoxide of acetyle) is obtained 
 
 Ba0 2 + 2(C 4 H0 2 )0 = BaO . (C 4 H 3 0. 2 )0 + (C 4 H/X)0 2 . 
 
 Acetate of baryta. Acetic peroxide. 
 
 The acetic peroxide is an oily liquid, insoluble in water, and exploding 
 with great violence when heated. It has the powerful oxidising pro- 
 perties which would be expected from its chemical resemblance to binoxide 
 of hydrogen. The true relationship between these substances is best seen 
 in their atomic formulae 
 
 Water - peroxide Acetic anhydride. Acetic peroxide. 
 
 416. Formic acid (HO. C a H0 3 ) is regarded with great interest by the 
 chemist, from its occurring both in the animal and vegetable kingdoms, 
 and from the ease with which it may be artificially obtained. This acid 
 is found in the leaves of stinging-nettles, and was originally obtained by 
 distilling the red ants (formica rufa), whence it derives its name. 
 
 It has long been prepared in laboratories by the oxidation of various 
 organic substances, particularly by distilling starch with binoxide of 
 manganese and sulphuric acid. Another more modern process, 'which 
 yields it more abundantly, consists in distilling dried oxalic acid with 
 enough glycerine to cover it, in a water-bath, when it is resolved into 
 carbonic acid and formic acid 
 
 2(110. C 2 OJ = HO.C 2 H0 3 + 2C0 2 . 
 
 Oxalic acid. Formic acid. 
 
 The glycerine appears to act by producing an unstable compound with 
 the formic acid (analogous to the stearines and acetines, see p. 575), which 
 is afterwards decomposed. The solution of formic acid thus obtained con- 
 tains 75 per cent, of true hydrated formic acid. If dried oxalic acid be 
 heated in the aqueous formic acid, and the solution allowed to crystallise, 
 the oxalic acid retains the water, and when the liquid is decanted from 
 
568 FURFUROLE BUTYRIC ACID. 
 
 the crystals and distilled, pure hydrated formic acid is obtained, and may 
 be crystallised at a low temperature. 
 
 But the most remarkable method of obtaining formic acid is that in 
 which it is formed from inorganic materials. When formic acid is heated 
 with strong sulphuric acid, it is resolved into water and carbonic oxide, 
 HO.C,H0 3 = 2HO + 2CO. 
 
 It might, therefore, be expected to be reproducible by the co'mbination of 
 those two substances, and accordingly, if moistened hydrate of potash be 
 heated for some hours to 212 F. in a flask filled with carbonic oxide, the 
 gas is absorbed, and fonniate of potash produced, from which the formic 
 acid may be obtained by distillation with diluted sulphuric acid 
 
 KO.HO + 2CO = KO.C 2 H0 3 . 
 
 Formiate of potash. 
 
 This is a far simpler example of the synthesis of an organic compound 
 from inorganic materials than that of acetic acid above referred to, and 
 since the carbonic oxide may be prepared by heating carbonate of baryta 
 with metallic iron, this method of synthesis is quite independent of any 
 organic source of carbon. Ethylate of soda, NaO . C 4 H 5 0, also absorbs 
 carbonic oxide, forming ethyl-formiate of soda, NaO . C 2 (C 4 H 5 )0 3 , isomeric 
 with propionate of soda, a little of this salt being also formed. 
 
 In properties, formic acid bears a great general resemblance to acetic 
 acid, but has a more powerful action upon the skin when in the concen- 
 trated form. 
 
 Furfurole (C 10 H 4 4 ), or oil of ants, accompanies the formic acid obtained by dis- 
 tilling amylaceous matters with binoxide of manganese and sulphuric acid. It is 
 prepared in quantity by distilling bran (freed from starch and gluten by steeping 
 in a cold weak solution of potash) with half its weight of sulphuric acid (previously 
 diluted with an equal bulk of water), a current of steam being forced through the 
 mixture ; the furfurole distils over with the water, from which it may be separated 
 by fractional distillation. It is a colourless oily substance smelling of bitter almonds, 
 becoming brown when exposed to the air, and but slightly soluble in water. Strong 
 sulphuric acid dissolves it to a purple liquid, from which water precipitates it un- 
 changed. Furfurole resembles the aldehydes in its property of reducing oxide of 
 silver, and in forming a crystalline compound with bisulphite of soda. It is con- 
 vertible by oxidation into pyromucic acid (C 10 H 4 6 ), the acid obtained by distilling 
 the mucic acid derived from the oxidation of gum or milk-sugar. The systematic 
 name for furfurole, therefore, would be pyromucic aldehyde. 
 
 Just as oil of bitter almonds (benzoic aldehyde), when acted on by ammonia, is 
 converted into hydrobenzamide, so furfurole yields furfuramide 
 
 3C 14 H 6 2 + 2NH 3 = C 42 H 18 N 2 + 6HO 
 Oil of bitter almonds. Hydrobenzamide. 
 
 3C 10 H 4 4 + 2NH 8 = C 30 H 12 N 2 6 + 6HO . 
 Furfurole. Furfuramide. 
 
 And, just as hydrobenzamide, when boiled with solution of potash, yields the iso- 
 meric base amarine or benzoline (C 42 H 18 N 2 ), so furfuramide, when boiled with potash, 
 gives fur/urine (C 30 H 12 N 2 6 ), which is isomeric with it. 
 
 Butyric acid (HO . C 8 H 7 3 ) is found not only in rancid butter, but in 
 the juice of muscular flesh, and is a frequent product of fermentation. 
 Indeed, the best mode of obtaining this acid consists in exciting fermen- 
 tation in sugar by contact with cheese; the liquid soon becomes acid in 
 consequence of the formation of lactic acid (the acid of sour milk), and if 
 it be neutralised from time to time with chalk, this fermentation continues 
 until the whole is converted into a pasty crystalline mass of lactate . of 
 
SYNTHESIS OF. ACIDS OF THE ACETIC SE1UES. 569 
 
 lime (CaO . C 6 H 5 5 ). The formation of lactic acid from sugar becomes 
 intelligible on comparing the formulae 
 
 1 equivalent of cane-sugar, C 12 H U U 
 
 2 equivalents of lactic acid, C 12 H 12 12 
 
 After a time the mass becomes more fluid, at the same time evolving 
 bubbles of gas, which contain carbonic acid and hydrogen, for the lactate 
 of lime is undergoing a fermentation, by which it is converted into buty- 
 rate of lime 
 2(CaO.C 6 H 5 5 ) + HO - CaO.C 8 H 7 3 + CaO.C0 2 + 3CO a + H 4 . 
 
 Lactate of lime. Butyrate of lime. 
 
 Ey distilling the butyrate of lime with dilute hydrochloric acid, an aqueous 
 solution of butyric acid is obtained, and on saturating this with chloride 
 of calcium, the acid collects as an oily layer upon the surface. It is 
 remarkable for its powerful odour of rancid butter.* 
 
 Synthetical formation of acids of the acetic series. By a very remark- 
 able process of substitution, butyric acid has been derived from acetic 
 acid. When sodium is heated with acetic ether, it is gradually dissolved, 
 with disengagement of hydrogen, and the liquid solidifies on cooling, to a 
 crystalline mass of sodacetic ether, or acetic ether in which one atom of the 
 hydrogen has been displaced by sodium 
 
 C 4 H 5 O.C 4 H 3 3 + Na - C 4 H 5 . C 4 (H 1 Na)0 8 + H. 
 
 Acetic ether. Sodacetic ether. 
 
 By digesting the sodacetic ether with iodide of ethyl for several hours in 
 a close vessel, at 212 F., the atom of sodium is exchanged for ethyle, and 
 ethacetic ether, or butyric ether, is produced 
 
 C 4 H 5 . C 4 (H 2 Na)0 3 + C 4 H 5 I = Nal + C 4 H 5 . C 4 H 2 (C 4 H 5 )0 3 . 
 
 Sodacetic ether. Iodide of ethyl. Ethacetic or butyric ether. 
 
 From this ether the ethacetic acid, HO . C 4 H 2 (C 4 H 5 )0 3 , has been prepared 
 and found to be identical with butyric acid, HO . C 8 H 7 O rt . 
 
 The connection thus established between butyric acid and the ethyle 
 series helps to explain the production of that acid in the fermentation 
 of sugar. 
 
 But butyric ether has also been obtained by another process of substitu- 
 tion, which aifords a proof that the same substance may be correctly 
 represented by two distinct rational formulae. 
 
 The substitution of sodium for hydrogen in acetic ether may extend to 
 two atoms of hydrogen, and if the disodacetic- ether so produced be digested 
 with iodide of methyle, butyric ether is obtained 
 
 C 4 H 5 O.C 4 (HNa 2 )0 3 + 2C 2 H 3 I = 2NaI + C 4 H 5 . C 4 H(CX),0 8 . 
 
 Disodacetic ether. Iodide of methyle. Dimethacetic or butyric ether. 
 
 So that butyric acid may be regarded, according to the method by which 
 it is produced, either as ethacetic acid, formed from acetic acid by the 
 substitution of an equivalent of ethyle for one of hydrogen, or as dimeth- 
 acetic acid, resulting from the substitution of two equivalents of methyle 
 for two of hydrogen. 
 
 When disodacetic ether is acted on by iodide of ethyle, it yields dieth- 
 acetic ether 
 C 4 H 5 O . C 4 (HJSa 2 )0 3 + 2C 4 H 5 I - 2NaI + C 4 H 5 . C 4 H(C 4 H 5 ) 2 / 
 
 Disodacetic ether. Iodide of ethyle. Diethacetic ether. 
 
 * Butyric acid and some of its homologues (as valerianic and caproic) appear to be pre- 
 sent in the perspiration of the skin, and to cause the disagreeable odour of close rooms. 
 
570 VALEKIANIC ACID. 
 
 This ether has an odour resembling peppermint, and its composition is 
 the same as that of caproic ether, C 4 H 5 . C 12 H n 3 ; but the diethacetic 
 acid prepared from it, though isomeric with caproic acid (HO . C^H^O,), 
 is not identical with it. 
 
 The acid next in the series, oenanthic (HO . C 14 H 13 3 ), may be obtained 
 from the ether produced by the action of iodide of amyle upon sodacetic 
 ether 
 
 C 4 H 5 O.C 4 (H 2 Na)0 3 + C 10 H n I = Nal + C 4 H 5 . C 4 H 2 (C 10 H n )0 3 . 
 
 Sodacetic ether. ^ Amyl-acetic ether. 
 
 From this ether, the amyl-acetic acid, HO . C 4 H. 2 (C 10 H n )0 3 , which appears 
 to be identical with oenanthic acid, has been obtained. 
 
 These reactions help to explain the production of several of the alcohols 
 corresponding to the acetic series of acids, during the fermentation of grape- 
 husks (marc of the wine-press). 
 
 Among the products of the action of sodium and ethylic iodide upon acetic ether, 
 
 , which, when distilled with alkaline 
 isomeric with the acetone of propionic 
 
 is a liquid having the composition C 16 H 14 6 , which, when distilled with alkaline 
 bases, yields ethylated acetone, C 6 H 5 (C 4 H 6 )0 2 , i 
 
 C 16 H U 6 + 2(BaO.HO) = C 10 H 10 2 + C 4 H 6 2 + 2(BaO.C0 2 ). 
 
 Ethylated Alcohol 
 
 acetone. 
 
 Another liquid produced by the action of ethylic iodide upon disodacetic ether has 
 the composition C 20 H 18 6 , which furnishes diethylated acetone, C 6 H 4 (C 4 H 5 ) 2 2 , when 
 distilled with baryta water 
 
 C, H 18 0, + 2(BaO.HO) = C 14 H 14 2 + C 4 H s O a + 2(BaO.C0 2 ). 
 
 Diethylated acetone is a liquid smelling of camphor, and boiling at 280 F. It is 
 isomeric with butyrone, which boils at 290 F., and with oenanthic aldehyde or 
 oananthole, which boils at 312 F. 
 
 By treating acetic ether with sodium and methylic iodide, the corresponding 
 methylated acetones may be obtained. 
 
 Methylated acetone, C 6 H 5 (C 2 H 3 )0 2 , has the odour of chloroform, and is identical 
 with the ethyl-acetyle, C 4 H 3 2 . C 4 H 5 , obtained by the action of zinc-ethyle upon 
 chloride of acetyle. 
 
 Dimethylated acetone, C 6 H 4 (C 2 H 3 ) 2 2 , has an odour of parsley. 
 
 Vdlerianic acid (HO . C JO H 9 3 ) derives interest from the circumstance, 
 that some of its salts, particularly the valerianate of zinc, are used medi- 
 cinally. 
 
 This acid is found in valerian root, and in the berries of the guelder- 
 rose. It is one cause of the peculiar odour of decaying cheese, and of 
 whale and seal oils. 
 
 Artificially, it is best obtained by distilling fousel oil (amylic alcohol, 
 C 10 H 12 2 ) with sulphuric acid and bichromate of potash, when the oxygen 
 of the chromic acid converts part of the amylic alcohol into valerianic 
 acid 
 
 C 10 H 12 2 + 4 = C i0 H 1() 4 + 2HO. 
 
 Fousel oil. Valerianic acid. 
 
 The distilled liquid is really a mixture of valerianic acid and valeria- 
 nate of amyle (C 1(J H n O . C i0 H 9 O a ), but when treated with hydrate of 
 
CHEMISTRY OF SOAP. 571 
 
 potash the latter is decomposed, yielding fousel oil and valerianate of 
 potash 
 
 C 10 H U O.C 10 H 9 3 + KG. HO = C 10 H U O.HO + KO.C 10 H 9 3 . 
 
 Valerianate of amyle. Fousel oil. Valeriunate of potash. 
 
 By distilling the valerianate of potash with sulphuric acid, the valeri- 
 anic acid is obtained as an oily liquid of very remarkable odour, which 
 recalls that of butyric acid. 
 
 '417. The separation of the volatile acids belonging to the acetic series 
 is a problem which frequently presents itself to the chemist, and is effected 
 by a very instructive process of partial saturation, founded upon the prin- 
 ciple, that when a mixture containing two acids with different boiling 
 points is partially neutralised by an alkali and distilled, the more volatile 
 of the two acids (i.e., that having the lower boiling point) will pass over, 
 whilst the other remains in combination with the alkali. 
 
 In applying this method, for example, to a mixture of valerianic acid 
 (boiling at 347 F.) and butyric acid (boiling at 315 F.), in unknown 
 proportions, the liquid would be divided into two equal parts, one of 
 which would be exactly neutralised with potash, and then distilled to- 
 gether with the other half. If there were just enough valerianic acid to 
 combine with the potash, pure valerianate of potash would be left in the 
 retort, and the more volatile butyric acid would pass over. If there were 
 more valerianic acid than would be required to combine with the potash, 
 the excess of that acid would distil over, together with the butyric acid, 
 whilst valerianate of potash alone would be left in the retort. By distill- 
 ing this salt with sulphuric acid, the pure valerianic acid would be ob- 
 tained, and the separation of the rest of the valerianic from the butyric 
 acid would be effected by one or two repetitions of the process. 
 
 If the valerianic acid present in the mixture were not in sufficient 
 quantity to combine with the potash added, then butyrate of potash, as 
 well as valerianate, would be left in the retort, and pure butyric acid would 
 distil over. By distilling the mixture of valerianate and butyrate of 
 potash with sulphuric acid, a mixture of the two acids would be obtained 
 which would require a repetition of the process. 
 
 In any case, it will be observed that this process must yield one of the 
 acids .in a state of purity. 
 
 The same principle applies to the separation of three or more volatile 
 acids, but the process involves, of course, a greater number of distillations. 
 
 418. SOAP. The manufacture of soap affords an excellent instance of 
 a process which was in use for centuries before anything was kno*wn of 
 the principles upon which it is based, for it was not till the researches of 
 Chevreul were published in 1813 that any definite ideas were entertained 
 with respect to the composition of the various fats and oils from which 
 soaps are made. 
 
 The investigations of Chevreul are conspicuous among the labours 
 which have contributed in so striking a manner to the rapid advancement 
 of chemistry during the present century ; undertaken when the chemistry 
 of organic substances had scarcely advanced beyond the dignity of an art, 
 when the principles of classification were almost entirely empirical, and 
 hardly any research had been published which could serve as a model, 
 these researches reflect the remarkable sagacity and accuracy of their 
 author. 
 
572 ACTION OF ALKALIES ON FATS. 
 
 The sense of our obligation to this eminent chemist is further increased, 
 when we remember that the ultimate analysis of organic substances was 
 then effected by a very difficult and laborious process, whilst the doctrine 
 of combining proportions was so imperfectly understood, that it could aiford 
 but little assistance in confirming or interpreting the results of analysis. 
 
 All soaps result from the action of the alkalies upon the oils and fats. 
 
 In the manufacture of soap, potash and soda are the only alkalies em- 
 ployed, the former for soft, the latter for hard soaps. 
 
 The fatty matters employed by the soap-maker are chiefly tallow, palm 
 oil, cocoa-nut oil, and kitchen stuff, for hard soaps, and seal oil and whale 
 oil for soft soaps. 
 
 In the manufacture of hard soap, the alkali is prepared by boiling a 
 solution of carbonate of soda (soda-ash) with lime to remove the carbonic 
 acid 
 
 NaO.C0 2 + CaO.HO = CaO . C0 2 + NaO . HO 
 
 the clear solution of hydrate of soda, or soda-ley, being drawn off from 
 the insoluble carbonate of lime. 
 
 The tallow is at first boiled with a weak soda-ley, because the soap 
 which is formed is insoluble in a strong alkaline solution, and would 
 envelope and protect a quantity of undecomposed tallow ; in proportion 
 as the saponification proceeds, stronger leys are added, until the whole of 
 the grease has disappeared. In order to separate the soap which is 
 dissolved, advantage is taken of the insolubility of soap in solution of salt ; 
 a quantity of common salt being thrown into the boiler, the soap rises to 
 the surface, when the spent ley is drawn off from below, and the soap 
 transferred to iron moulds that it may harden sufficiently to be cut up 
 into bars. 
 
 In order to understand the chemistry of this process, it is necessary to 
 know that tallow is a mixture of two fatty substances, one of which, 
 stearins* (C 1U H 110 12 ), is solid, and the other, oleine (C 114 H 104 12 ), liquid, 
 the quantity of stearine being about thrice that of oleine. 
 
 When these fats are acted upon by soda, they undergo decomposition, 
 furnishing stearic and oleic acids, which combine with the soda to form 
 soap, whilst a peculiar sweet substance, termed glycerine, passes into 
 solution; the nature of the decomposition in each case will be understood 
 from the following equations : 
 
 H- 3(NaO.HO) = 3(NaO . C 36 H, 5 3 ) + C 6 H 8 6 
 
 Stearine. Stearate of soda Glycerine. 
 
 C 6 HA. (CAA), + 3(NaO.HO) = 3(NaO . CJE^O.,) + C 6 H 8 6 
 
 Oleine. Oleate of soda. Glycerine. 
 
 so that the soap obtained by boiling tallow with soda is a mixture of the 
 stearate of soda with about a third of its weight of oleate of soda, and 
 from 20 to 30 per cent, of water. 
 
 Palm oil is composed chiefly ofpdlmitine (C 102 H 98 12 ), a solid fat which 
 is resolved by boiling with soda into palmitate of soda (palm oil soap) and 
 glycerine 
 
 .^AA). t 3(NaO.HO) = 3(NaO . C. S H 31 3 ) + C C H 3 0,, . 
 
 Palmitine. Palmitate of soda. Glycerine. 
 
 In th,e fish oils, the predominant constituent is oleine, so that when 
 
 * iVe'a/o, tallow. 
 
STEARIC AND OLEIC ACIDS. 573 
 
 boiled with hydrate of potash, they yield oleate of potash (KG . C 36 H 33 3 ), 
 which composes the chief part of soft soap. 
 
 Castile soap is made from olive oil, which contains oleine and a solid fat 
 known as margarine. The latter appears to be really composed of palmi- 
 tine and stearine, so that the Castile soap is a mixture of oleate, palmitate, 
 and stearate of soda. 
 
 The peculiar appearance of mottled soap is caused by the irregular dis- 
 tribution of a compound of the fatty acid with oxide of iron, which 
 arranges itself in veins throughout the mass. If the soap contained too 
 much water, so as to render it very fluid when transferred to the moulds, 
 this iron compound would settle down to the bottom, leaving the soap 
 clear, so that the mottled appearance is often regarded as an indication 
 that the soap does not contain an undue proportion of water ; it is imi- 
 tated, however, by stirring into the pasty soap some sulphate of iron and 
 a little impure ley containing sulphide of sodium, so as to produce the 
 dark sulphide of iron by double decomposition.* 
 
 In the manufacture of yellow soap, in addition to tallow and palm oil, 
 a considerable proportion of common rosin (see p. 470) is added to the soap 
 shortly before it is finished. 
 
 Soft soap is not separated from the water by salt like hard soap, but is 
 evaporated to the required consistency. 
 
 Transparent soaps are obtained by drying hard soap, dissolving it in hot 
 spirit of wine, and pouring the strong solution into moulds after the greater 
 part of the spirit has been distilled off. 
 
 Silicated soap is a mixture of soap with silicate of soda. 
 
 Glycerine soap is prepared by heating the fat with alkali and a little 
 water to about 400 F. for two or three hours, and running the mass at 
 once into moulds. It is, of course, a mixture of soap and glycerine. 
 
 The proportion of water in soaps is very variable, some specimens contain- 
 ing between 70 and 80 per cent. The smallest proportion is about 30 per cent. 
 
 The theory of saponification, stated above, has received the strongest 
 confirmation within the last few years, by the synthetic production of the 
 fats from glycerine and the fatty acids formed in their saponification. 
 
 Preparation of the fatty acids. All the soaps, when mixed with acids, 
 undergo decomposition, their alkalies combining with the acid added, 
 whilst the fatty acids separate either in the solid form (in the case of stearic 
 and palmitic acids), or as an oily liquid (in the case of oleic acid). Thus, 
 if soap obtained by boiling tallow with soda be dissolved in hot water, 
 and mixed with an excess of tartaric acid, an oil rises to the surface which 
 concretes into a buttery mass on cooling. This mass, composed of stearic 
 and oleic acids, is submitted to pressure in order to separate the "greater 
 part of the liquid oleic acid, and the stearic acid which is left is purified 
 by crystallisation, first from alcohol, and afterwards from ether. 
 
 Stearic acid is thus obtained in transparent colourless plates which have 
 the composition HO . C 36 H 3 .O 3 ; they are, of course, insoluble in water, but 
 dissolve in hot alcohol, the solution being acid to test-papers. 
 
 All the stearates are insoluble in water except those of the alkalies, so 
 that if a solution of common soap (containing stearate of soda) be mixed 
 with a solution of lime or magnesia, a stearate of lime or magnesia is 
 separated in the insoluble form, and it will be remembered that this 
 decomposition of soap is produced by the action of hard waters (page 40). 
 
 * A soap which contains much more than 30 per cent, of water is said not to admit of 
 mottling. 
 
574 DECOMPOSITION OF FATS BY SULPHURIC ACID. 
 
 419. CANDLES. Since tallow fuses at about 100 F., and stearic acid 
 not below 159, it is evident that, independently of other considerations, 
 the latter would be better adapted for the manufacture of candles, for such 
 candles would never soften at the ordinary atmospheric temperature in 
 any climate, and would have much less tendency to gutter in consequence 
 of the excessive fusion of the fuel around the base of the wick. The 
 gases furnished by the destructive distillation of stearic acid in the wick 
 of the candle burn with a brighter name than those produced from tallow. 
 Accordingly the manufacture of stearine (or more correctly, stearic acid) 
 candles* has now become a very important and instructive branch of 
 industry. 
 
 The original method of separating the stearic acid from tallow on the 
 large scale, consisted in mixing melted tallow with lime and water, and 
 heating the mixture for some time to 212 by passing steam through it. 
 The tallow was thus converted into the insoluble stearate and oleate of 
 lime, which was drained from the solution containing the glycerine, and 
 decomposed by sulphuric acid. The mixture of stearic and oleic acids 
 thus obtained was cast into thin slabs, which were packed between pieces 
 of cocoa-nut matting, and well squeezed in a hydraulic press, which forced 
 out the oleic acid, leaving the stearic and palmitic acids in a fit state for 
 the manufacture of candles. 
 
 The separation of the solid fatty acids from tallow and other fats may 
 also be effected by the action of sulphuric acid, a process extensively 
 applied in this country to palm and cocoa-nut oils. These fats are mixed 
 in copper boilers with about one-sixth of their weight of concentrated sul- 
 phuric acid, and heated by steam to about 350 F. for some hours, when 
 part of the glycerine is converted into sulphoglyceric acid (C 6 H 8 6 . 2SO,), 
 and the remainder is decomposed by the sulphuric acid, carbonic and sul- 
 phurous acids being disengaged, whilst a dark-coloured mixture of palmitic, 
 stearic, and oleic acids is left. A part of the oleic acid becomes converted 
 in this process into elaidic acid, which has the same composition, but 
 differs from oleic acid in fusing at about 113 F., so that the amount of 
 solid acid obtained by this process is much increased. This mixture is 
 well washed from the adhering sulphuric and sulphoglyceric acids, and 
 transferred to a copper still into which a current of steam is passed, which 
 has been raised to about 600 F. by passing through hot iron pipes. 
 These fatty acids could not be distilled alone without decomposition, but 
 under the influence of a current of steam they pass over readily enough, 
 leaving a black pitchy residue in the retort, which is employed in making 
 black sealing wax and for other useful purposes. 
 
 The distilled fatty acids are broken up and pressed between cocoa-nut 
 matting to remove the oleic acid. 
 
 One great advantage of this process, which is commonly, though incor- 
 rectly, styled the saponification by sulphuric acid, is its allowing the con- 
 version of the worst kinds of refuse fat into a form fit for the manufacture 
 of candles ; thus the fat extracted from bones in the manufacture of glue, 
 and that removed from wool in the scouring process, may be turned to 
 profitable account. 
 
 It will be remarked that in this process the palmitic, stearic, and oleic 
 acids are formed from the palmitine, stearine, and oleine existing in the 
 fats, by the assimilation of the elements of water and the subsequent 
 
 * Composite candles are made of a mixture of stearic and palmitic acids. 
 
SYNTHESIS OF NEUTRAL FATS. 575 
 
 separation of glycerine, just as in the ordinary process of saponification by 
 means of alkalies. 
 
 Strictly speaking, the action appears to consist of two stages ; for when 
 concentrated sulphuric acid is allowed to act upon the natural fats in the 
 cold, it combines with each of their ingredients, forming the acids known 
 as sulphostearic, sulphopalmitic, sulpholeic, and sulphoglyceric, which are 
 soluble in water, though not (with the exception of the last) in water 
 containing sulphuric acid. 
 
 x The second stage consists in the decomposition of the sulpho-fatty acids 
 by the high temperature in contact with steam, the sulphoglyceric acid 
 having been in great measure cjecomposed into secondary products before 
 the distillation is commenced. 
 
 Within the last few years, the extraction of the solid acids from the 
 natural fats has been effected by a process known as saponification by 
 steam, which allows the glycerine also to be obtained in a pure state. It 
 is only necessary to subject the fat, in a distillatory apparatus, to the 
 action of steam, at a temperature of about 600 F., to cause both the 
 fatty acids and the glycerine to distil over ; the former may be separated 
 as usual into solid and liquid portions by pressure, whilst the glycerine, 
 which is obtained in aqueous solution below the layer of fatty acids, is 
 concentrated by evaporation and sent into commerce as a very sweet 
 colourless viscid liquid. The saponification of palmitine, for instance, by 
 steam, would be represented by the equation 
 
 C 6 H 5 8 .(C 32 H 81 3 ) 3 + 6HO = 3(HO.C 32 H 31 8 ) + C 6 H 8 6 . 
 
 Palmitine. Palmitic acid. Glycerine. 
 
 420. In the artificial formation of natural fats, this change has been 
 reversed, for by heating 3 equivalents of stearic, palmitic, or oleic acid with 
 1 equivalent of glycerine, in a sealed tube, for several hours, to about 
 500 F., 6 equivalents of water are eliminated, and stearine, palmitine, or 
 oleine is produced. 
 
 By a similar process, compounds have been formed from glycerine with 
 one and two equivalents of the fatty acids, so that we are acquainted, in 
 the stearine series, for example, with 
 
 Stearic acid. Glycerine. 
 
 Monostearine, . C 42 H 42 8 = C^H^C^ + C 6 H S 6 - 2HO 
 Bistearine, . . C 78 H 76 10 = 2(C 36 H 36 4 ) + cXo - 4HO 
 Terstearine . . C I14 H 110 12 - 3(C 36 H, 6 4 ) + C 6 H S 6 - 6HO 
 
 The last representing stearine as it exists in the natural fats. 
 
 Nor is it only with the fatty acids, properly so called, that glycerine will 
 furnish glycerides, as these bodies are termed, similar compounds having 
 been obtained with acetic and benzoic acids. 
 
 The hydrogen-acids are also capable of acting upon glycerine in a similar manner. 
 Thus, when glycerine (C 6 IL0 6 ) is acted on by hydrochloric acid, an oily liquid. 
 chlorhydrine (C C H 7 4 C1), is obtained, the glycerine having combined with 1 equiva- 
 lent of hydrochloric acid, and 2 equivalents of water having been separated. 
 
 Dichlorhydrine (C 6 H 6 2 C1 2 ) results from the union of glycerine with 2 equivalents 
 of hydrochloric acid, and separation of 4 equivalents of water; whilst, to form 
 trichlorhydrine (C 6 H 6 C1 8 ), 3 equivalents of hydrochloric acid are taken up, and 6 
 equivalents of water removed. 
 
 By the action of oxide of silver, in presence of water, the chlorhydrines may be 
 reconverted into glycerine. The examination of these chlorhydrines has pointed 
 out the method of effecting the conversion of a triatomic alcohol, (glycerine) into a 
 
576 GLYCERINE. 
 
 diatomic alcohol (glycol), for if chlorhydrine be acted on by sodium dissolved in mer- 
 cury, in the presence of water, it is converted into the glycol of propylene 
 
 C 6 H 7 4 C1 + HO + Na 2 = C 6 H 8 4 + NaO + NaOl . 
 Chlorhydrine. Propyl-glycol. 
 
 This tendency of glycerine to form compounds with the acids, the 
 formation of which is attended (like that of the ethers from alcohol) with 
 separation of the elements of water, has led chemists to look upon glyce- 
 rine as an alcohol a view which is also supported by its combining with 
 sulphuric and phosphoric acids to form sulphogly eerie (C 6 H 7 O g . HO . 280^) 
 and phosphoglyceric acids, just as alcohol forms sulphovinic and phospho- 
 vinic acids. A compound has even been obtained, which is believed to 
 stand to glycerine in a relation similar to that which ether bears to 
 alcohol ; the formula of this gly eerie ether, as it is called, is C 6 H 5 3 , differ- 
 ing from glycerine (C 6 H 8 6 ) by the elements of 3 equivalents of water. 
 
 The formation of stearine from stearic acid and glycerine would then 
 be quite analogous to that of acetic ether, for example, from acetic acid 
 and alcohol, as will be seen by comparing the two equations 
 
 HO.C 4 H } 3 + C 4 H 5 O.HO = C 4 H 5 O.C 4 H 3 3 + 2HO 
 
 Acetic acid. Alcohol Acetic ether. 
 
 (3HO.C 36 H 35 3 ) + C 9 H,0 3 .3HO - C C H 3 3 . 3C 36 H 35 3 + 6HO . 
 
 Stearic acid. **%$$? ^in, 
 
 The only difference between the two reactions is, that in the latter, 3 equi- 
 valents of acid are concerned, and 3 equivalents of water are removed 
 from the glyceric alcohol. This circumstance, taken together with some 
 other features of glycerine, has induced those chemists who consider 
 alcohol as formed upon the type of a molecule of water, to look upon 
 glycerine as derived in a similar manner from 3 molecules of water, in 
 which half the hydrogen is replaced by the triatomic radical, glyceryle 
 (O 3 H 5 )'"; thus- 
 
 Type . . . g JO Type |s|o 3 
 
 Alcohol 
 
 Ether, . ^H 5 j e Glyceric ether, 
 
 421. Glycerine is obtained on the small scale by boiling olive oil with 
 litharge and water, until the stearic, oleic, and palmitic acids are converted 
 into their lead-salts (lead plaster), which are insoluble, whilst the glyce- 
 rine, together with a little oxide of lead, pass into solution. The lead is 
 precipitated by hydrosulphuric acid, and the filtered liquid concentrated 
 by evaporation. ** 
 
 The chief uses of glycerine as an application to the skin, and a remedy 
 in cases of deafness, depend upon its oily consistency, and its want of 
 volatility, which preserves surfaces to which it is applied in a moist and 
 supple condition. 
 
 Glycerine cannot be distilled alone without decomposition, though it has 
 been seen to be capable of distillation in a current of highly heated steam. 
 When decomposed by distillation, it evolves very irritating vapours of 
 aeroleine (C H 4 2 ), which is a constant product of the destructive distilla- 
 tion of fats containing glycerine, and gives rise to the peculiar disgusting 
 odour of a smouldering tallow candle ; composite candles, being made of 
 
ACIDS OF THE ACRYLIC SERIES. 
 
 577 
 
 stearic and palmitic acids (without glycerine) do not emit this odour of 
 acroleine when blown out. 
 
 Acroleine is best obtained in the pure state by distilling glycerine 
 with anhydrous phosphoric acid, which removes 4 equivalents of water 
 (C^Og - 4HO = C tt H 4 2 ). It is a colourless liquid, distinguished by its 
 intensely irritating vapour, which affects the eyes very strongly. From a 
 chemical point of view it is interesting, as being the aldehyde of the allyle 
 series (see p. 479), and, therefore, another link connecting that series with 
 glycerine. By treatment with oxide of silver, acroleine is converted into 
 acrylic acid (C 6 H 4 4 ), bearing the same relation to acroleine (C 6 H 4 2 ) that 
 acetic acid (C 4 H 4 4 ) bears to ordinary aldehyde (C 4 H 4 2 ). The iodide of 
 allyle and allylic alcohol have been already noticed (p. 479). 
 
 The allyle series, therefore, is perfectly parallel with the ethyle series, 
 and it seems very probable that allylic alcohol is a member of a homo- 
 logou's series of alcohols having the general formula C 2n H 2n 2 , with a series 
 of acids corresponding to the acetic series, but having the general formula 
 C 2n H 2tt _ 2 4 , of which the following members are known : 
 
 Acrylic Series of Acids. 
 
 Acid. 
 
 Equivalent 
 Formula. 
 
 Source. 
 
 Acrylic . . 
 
 C 6 H 4 4 
 
 Oxidation of acroleine. 
 
 Crotonic 
 
 <W>1 
 
 Croton-seed oil. 
 
 Angelic . . 
 
 
 Angelica root. 
 
 Pyroterebic 
 
 C 12 H 10 4 
 
 Turpentine. 
 
 Damaluric . 
 
 C 14 H 12 4 
 
 Cow's urine (Sa^axo;, a calf). 
 
 Campholic . 
 
 C 20 H 18 4 
 
 Camphor. 
 
 Moringic 
 
 
 Moringa aptera (oil of ben). 
 
 Hypogeic . 
 
 } 
 
 1 Oil of ground nut. 
 
 Physetoleic 
 
 } C 32 H 30 4 
 
 1 Sperm-whale oil (Physeter macrocephalus). 
 
 Oleic . . 
 
 C 36 H 34 4 
 
 Most oils. 
 
 Doeglic . . 
 
 C 38 H 36 4 
 
 Doegling train oil. 
 
 Brassic . . 
 
 1 
 
 f Mustard seed (fixed) oil. 
 
 Erucic . . 
 
 | * 
 
 \ Colza oil (Brassica oleifera). 
 
 These acids are monobasic, their salts being formed by the substitution of 1 eq. of 
 a metal for 1 eq. of hydrogen, or of 1 eq. of a basic protoxide for 1 eq. of water. 
 
 The following table exhibits the principal members of the allyle series, together 
 with the corresponding members of the ethyle series : 
 
 Ethyle Se 
 
 ries. 
 
 Allyle Series. 
 
 Ethyle, . . , 
 
 C 4 H 5 .C 4 H 5 
 
 Allyle, 
 
 C 6 H 5 .C 6 H 5 
 
 Ether, . 
 
 C 4 H 5 O.C 4 H 6 
 
 Allylic ether, 
 
 C 6 H 6 . C 6 H 6 
 
 Alcohol, 
 
 C 4 H 5 .-HO 
 
 Allylic alcohol, . 
 
 C 6 H 6 . HO 
 
 Iodide of ethyle, . 
 
 C 4 H 5 I 
 
 Iodide of allyle, . 
 
 C 6 H 5 I 
 
 Acetic ether, 
 
 C 4 H 5 O.C 4 H 3 3 
 
 Acetate of allyle, 
 
 C 6 H 5 . C 4 H 3 8 
 
 Aldehyde, . 
 
 C 4 H 4 2 
 
 Allyle aldehyde, . 
 
 C 6 H 4 2 (acroleine) 
 
 Acetic acid, . 
 
 C 4 H 4 4 
 
 Acrylic acid, 
 
 C 6 H 4 4 
 
 Sulphide of ethyle, 
 
 C 4 H 5 S 
 
 Sulphide of allyle, 
 
 C 6 H 5 S (oil of garlic) 
 
 Triethylamine, 
 
 N(C 4 H 5 ) 3 
 
 Triallylamine, 
 
 N(C 6 H 6 ) 8 
 
 Hydrated oxide of 
 Tetrethylium, . 
 
 }N(C 4 H 6 ) 4 O.HO 
 
 Hydrated oxide of 
 Tetrallylium, . 
 
 | N(C 6 H 5 ) 4 . HO 
 
 
 
 2o 
 
578 STEARIC GLUCOSE GLUCO-TARTARIC ACID. 
 
 It has been seen (p. 479) that glycerine, when distilled with biniodide 
 of phosphorus, yields iodide of allyle (C 6 H 5 I). When this liquid is treated 
 with bromine it yields a crystallisable terbromide of allyle, C 6 H 5 Br 3 ; and 
 if this be decomposed by acetate of silver, it furnishes the glyceride known 
 as teracetine, thus 
 
 C 6 H 5 Br 3 + 3(AgO.A) = C (i H 5 3 .3A + SAgBr. 
 
 Terbromide of allyle. Acetate of silver. Teracetine. 
 
 When teracetine is submitted to the action of hydrate of baryta, glyce- 
 rine is reproduced 
 
 C 6 H 5 3 -3A + 3(BaO.HO) = C 6 H 8 6 + 3(BaO.A). 
 
 Teracetine. Glycerine. Acetate of baryta. 
 
 This affords an interesting example of the conversion of a monatomic 
 radical, allyle (C 6 H 5 )', into a triatomic radical, glyceryle (C 6 H 5 )'". 
 
 422. A very interesting chemical similarity has been pointed out 
 between glycerine and mannite (C 6 H 7 O e ). It will be remembered that 
 the former is a constant product of the alcoholic fermentation, and the 
 latter of a peculiar kind of fermentation (the viscous), to which sac- 
 charine liquids are subject. 
 
 When mannite is heated, under pressure, with the acids of the acetic 
 series, it forms compounds corresponding to those obtained when glycerine 
 is so treated. Thus, with stearic acid 
 
 C 6 H,0 6 + S(C x R. x O t ) = C U4 H 108 U + 7HO. 
 
 Mainite. Stearic acid. 
 
 But it will be observed that 7 equivalents of water are here eliminated 
 instead of 6 eqs., as in the case of glycerine. The further examination of 
 mannite explains this, for it is not that substance which is the true ana- 
 logue of glycerine, but one which is obtained by heating mannite to 400 F., 
 when it loses an equivalent of water, and is converted into mannitane 
 
 C 6 H 7 6 - HO = C 6 H 6 5 . 
 
 Mannite. Mannitane. 
 
 This mannitane or mannite-glycerine is a viscous substance, presenting 
 a very strong resemblance to glycerine, so that it is not unlikely to have 
 been mistaken for this substance in examining some of the natural fats. 
 The mannite-glycerides, or compounds formed by heating mannite with 
 the fatty acids, are scarcely to be distinguished from stearine, palmitine, 
 &c. They are saponified by alkalies in exactly the same manner. 
 
 Cane-sugar and grape-sugar are capable of forming compounds corre- 
 sponding to those obtained by the action of acids upon glycerine and 
 mannite. Thus, if grape-sugar be heated to 250 F. for several hours in 
 contact with stearic acid, it is converted into a fusible solid, insoluble in 
 water, but soluble in alcohol and ether 
 
 C 12 H 12 12 + 2(0,11,0,) - C 84 H 7B M f 6HO. 
 
 S53S5J stearic aci(L stearic glucose - 
 
 When grape-sugar is heated with tartaric acid, a similar reaction takes 
 place, but the resulting product is a new acid 
 
 C 12 H 12 12 + 2(2HO.C 8 H 4 10 ) = 2HO . C 28 H 16 28 + 6HO. 
 
 SSytoSS)! Tartaric acid. Gluco-tartaric acid. 
 
 Cane-sugar behaves in a similar manner. 
 
NITROGLYCERINE. 579 
 
 423. Nitroglycerine, or glonaine. This violently explosive substance is 
 very easily prepared by dissolving glycerine in a mixture of equal measures 
 of the strongest nitric and sulphuric acids, previously cooled, and pouring 
 the solution in a thin stream into a large volume of water, when the nitro- 
 glycerine is precipitated as a colourless heavy oil (sp. gr. 1*6). It is 
 advisable to add the glycerine to the mixed acids in very small quantities 
 at a time, and to cool the mixture in a vessel of water after each addition. 
 When the nitroglycerine has subsided, the water may be poured off, and 
 the oil shaken several times with water, so as to wash it thoroughly. 
 The formation of nitroglycerine resembles that of gun-cotton (see p. 503), 
 three equivalents of hydrogen being removed from the glycerine by the 
 oxidising action of the nitric acid, and three equivalents of nitric peroxide 
 introduced in their place 
 
 C 6 H 8 6 + 3(HO.N0 3 ) = C fi H 5 (M)J 8 6 + 6HO. 
 
 Glycerine. Nitroglycerine. 
 
 This oil is far more violent in its explosive effects than gun-cotton, 
 more nearly resembling the fulminates, though not so easily exploded. 
 If a drop of nitroglycerine be placed on an anvil, and struck sharply, it 
 explodes with a very loud report, even though not free from water ; and 
 if a piece of paper moistened with a drop of it be struck, it is blown into 
 small fragments. On the application of a flame or of a red-hot iron to 
 nitroglycerine, it burns quietly; and when heated over a lamp in the open 
 air it explodes but feebly. In a closed vessel, however, it explodes at 
 about 360 F. with great violence. For blasting rocks the nitroglycerine 
 is poured into a hole in the rock, and exploded by the concussion 
 caused by a particular kind of fuze charged with a little gunpowder. 
 It has been stated to produce the same effect in blasting as ten times its 
 weight of gunpowder, and much damage has occurred from the accidental 
 explosion of nitroglycerine "in course of transport. When nitroglycerine 
 is kept, especially if it be not thoroughly washed, it decomposes, with 
 evolution of nitrous fumes and formation of crystals of oxalic acid; and 
 it may be readily imagined that, should the accumulation of gaseous pro- 
 ducts of decomposition burst one of the bottles in a case of nitroglycerine, 
 the concussion would explode the whole quantity. 
 
 Nitroglycerine is readily soluble in ether and in wood-spirit, and some- 
 what less soluble in alcohol ; it is reprecipitated by water from these last 
 solutions. It solidifies at 40 F. A drop of nitroglycerine is said to cause 
 very violent headache, and in larger doses it appears to be decidedly 
 poisonous. 
 
 OILS AND FATS. 
 
 424. A very remarkable feature in the history of the fats is the close 
 resemblance in chemical composition and properties which exists between 
 them, whether derived from the vegetable or the animal kingdom. They 
 all contain two or more neutral substances which furnish glycerine when 
 saponified, together with some of the acids of the acetic series or or series 
 closely allied to it. 
 
 One of the most useful vegetable fatty matters is palm-oil, which is 
 extracted by boiling water from the crushed fruit of the Elais Guineensis, 
 an African palm. It is a semi-solid fat, which becomes more solid when 
 kept, since it then undergoes a species of fermentation, excited apparently 
 
 2 o 2 
 
580 
 
 SERIES OF BIBASIC FATTY ACIDS. 
 
 by an albuminous substance contained in it, in consequence of which the 
 palmitine (C 102 H 98 O 12 ) is converted into glycerine and palmitic acid. The 
 bleaching of palm-oil is effected by the action of a mixture of sulphuric 
 acid and bichromate of potash, which oxidises the yellow colouring matter. 
 
 Cocoa-nut oil is also semi-solid, and is remarkable for the number of 
 acids of the acetic series which it yields when saponified, viz., caproic, 
 caprylic, rutic, lauric, myristic, and palmitic. 
 
 These fats are chiefly used in the manufacture of soap and candles. 
 
 Salad oil, or sweet oil (olive oil), is obtained by crushing olives, and an 
 inferior kind which is used for soap is obtained by boiling the crushed 
 fruit with water. When exposed to a temperature of about 32 F. a con- 
 siderable portion of the oil solidifies ; this solid portion is generally called 
 margarine (C 108 H 104 12 ) ; it is much less soluble in alcohol than stearine, 
 though more so than palmitine. When saponified, margarine yields 
 glycerine and margaric acid (C^H^OJ. This acid appears to be really 
 composed of stearic and palmitic acids, into which it may be separated by 
 repeated crystallisation from alcohol, when the palmitic acid is left in 
 solution. The fusing-point of margaric acid is 140 F., that of stearic 
 being 159, and that of palmitic, 144, but a mixture of 10 parts of pal- 
 mitic with 1 part of stearic acid fuses at 140. 
 
 That portion of the olive oil which remains liquid below 32 con- 
 sists of oleine (C 114 H 104 12 ), and forms nearly three- fourths of its weight. 
 Oleine is not so easily saponified as the solid fats, and is resolved by 
 that process into glycerine and oleic acid (C 36 H 34 4 ), which differs from the 
 other fatty acids by remaining liquid at temperatures above 40 F., and 
 by absorbing oxygen from the air, when it is converted into a new acid 
 which is not solidified by cold. 
 
 Oleic acid is used in greasing wool for spinning, being much more 
 easily removed by alkalies than olive oil which was formerly employed. 
 Oleate of ammonia is sometimes employed as a mordant for the aniline 
 dyes on cotton. 
 
 The characteristic feature of oleic acid is its furnishing a solid crys- 
 tallised acid when submitted to destructive distillation ; this acid is called 
 sebacic acid, and is one of a series of bibasic acids, most of the other mem- 
 bers of which may be obtained from oleic acid by the action of nitric acid. 
 
 Bibasic Fatty Acid Series. 
 
 Acid. 
 
 Equivalent 
 Formula. 
 
 Source. 
 
 Oxalic 
 
 C 4 H 2 8 
 
 Oxalis acetosella (wood sorrel), &c. 
 
 Malonio 
 
 C 6 H 4 8 
 
 Oxidation of malic acid. 
 
 Succinic 
 
 C 8 H 6 8 
 
 Amber (succinum). 
 
 Lipic 
 
 C 10 H 8 8 
 
 Oxidation of oleic acid (\'nros,fat). 
 
 Adipic 
 
 C 12 H 10 8 
 
 (adeps,fat). 
 
 Pimelic 
 
 C U H 12 8 
 
 (a-T/KfXjJ, fat). 
 
 Suberic 
 
 Ci 6 H u 8 
 
 Oxidation of stearic acid, and of cork (suber). 
 
 Anchoic * . 
 Lepargylic | 
 
 } C 18 H 16 8 
 
 Oxidation of Chinese wax, and of cocoa-nut oil. 
 
 Sebacic 
 
 C 20 H 18 8 
 
 Distillation of oleic acid. 
 
 * From ayxw, to throttle, from its suffocating vapours, 
 t From XtVa/oyos, having white skin. 
 
FIXED OILS. 581 
 
 The neutral salts of the acids of this series are formed by the displace- 
 ment of two equivalents of hydrogen by a metal, or of two equivalents of 
 water by a basic protoxide. Thus, neutral succinate of potash has the 
 composition C 8 (H 4 K 2 )0 8 ,'or 2KO . C^O V 
 
 It is worthy of remark, that nine acids of the series, C 2n H 2 , l 4 (from 
 acetic to capric inclusive), are found among the products of the action of 
 nitric acid upon oleic acid. 
 
 It is well known that salad oil becomes rancid, and exhales a disagree- 
 able odour after being kept for some time. This appears to be due to a 
 fermentation similar to that noticed in the case of palm oil, originally 
 started by the action of atmospheric oxygen upon albuminous matters 
 present in the oil ; the neutral fatty matters are thus partly decomposed, 
 as in saponifi cation, their corresponding acids being liberated, and giving 
 rise (in the case of the higher members of the acetic series, such as caproic 
 and valerianic) to the disagreeable odour of rancid oil. By boiling the 
 altered oil with water, and afterwards washing it with a weak solution of 
 soda, it may be rendered sweet again. 
 
 Almond oil, extracted by a process similar to that employed for olive oil, 
 is also very similar in composition; but colza oil, obtained from the seeds 
 of the Brassica oleifera, contains only half its weight of oleine, and hence 
 solidifies more readily than the others. 
 
 Colza oil is largely used for burning in lamps, and undergoes a process 
 of purification from the mucilaginous substances, which are extracted with 
 it from the seed, and leave a bulky carbonaceous residue when subjected 
 to destructive distillation in the wick of the lamp. To remove these the 
 oil is agitated with about 2 per cent, of oil of vitriol, which carbonises 
 the mucilaginous substances, but leaves the oil untouched. When the 
 carbonaceous flocks have subsided, the oil is drawn off, washed to remove 
 the acid, and filtered through charcoal. 
 
 Linseed oil, obtained from the seeds of the flax plant, is much richer in 
 oleine than any of the foregoing, exhibiting no solidification till cooled 
 to 15 or 20 F. below the freezing point. It exhibits, however, in a far 
 higher degree, a tendency to become solid when exposed to the air, which 
 has acquired for it the name of a drying oil, and renders it of the greatest 
 use to painters. This solidification is attended with absorption of oxygen, 
 which takes place so rapidly in the case of linseed oil, that spontaneous 
 combustion has been known to take place in masses of rag or tow which 
 have been smeared with it.* 
 
 The tendency of linseed oil to solidify by exposure is much increased by 
 heating it with about 2 V^ n f litharge, or -j^th of binoxide of manganese ; 
 these oxides are technically known as dryers, and oil so treated is called 
 boiled linseed oil. The action of these metallic oxides is not well understood. 
 
 The strong drying tendency of linseed oil is supposed to be due to a 
 peculiarity in the oleine, which is said not to be ordinary oleine, but to 
 furnish a different acid, linoleic acid, when saponified. When linseed oil 
 is exposed for some time to a high temperature, it becomes viscous and 
 treacly, and is used in this state for the preparation of printing-ink. If 
 the viscous oil be boiled with dilute nitric acid, it is converted into artifi- 
 cial caoutchouc, which is used in the manufacture of surgical instruments. 
 This property appears to be connected with the drying qualities of the oil. 
 
 * During the oxidation, a volatile compound is formed which resembles acroleine in 
 smell, and colours unsized paper brown. It has been suggested that the brown colour 
 and musty smell of old books may be due to the oxidation of the oil in the printing-ink. 
 
582 FATS SPERMACETI. 
 
 Castor oil, obtained from the seeds of Ricinus communis, also yields a 
 peculiar acid when saponified, termed ridnoleic (HO . C 36 H 33 5 ), con- 
 taining two more equivalents of oxygen than oleic acid, which it much 
 resembles. The destructive distillation of castor oil yields osnanthic 
 acid (HO . C^H^Og), and oenanthole or oenanthic aldehyde (C U H 14 2 ), and 
 by distilling it with hydrate of potash, caprylic alcohol (C 16 H 18 2 ) is ob- 
 tained. As in the case of olive oil, the cold drawn castor oil, which is 
 expressed from the seeds without the aid of heat, is much less liable to 
 become rancid. Castor oil is much more soluble in alcohol than any 
 other of the fixed oils. 
 
 The various fish oils, such as seal and whale oil, also consist chiefly of 
 oleine, and appear to owe their disagreeable odour to the presence of cer- 
 tain volatile acids, such as valerianic. 
 
 Cod-liver oil appears to contain, in addition to oleine and stearine, a 
 small quantity of acetine (C 18 H 14 12 ), which yields acetic acid and glycerine 
 when saponified. Some of the constituents of bile have also been traced 
 in it, as well as minute quantities of iodine and bromine. 
 
 Butter contains about two-thirds of its weight of solid fat, which con- 
 sists in great part of margarine (see p. 580), but contains also butine, which 
 yields glycerine and butic acid (HO . C 40 H 39 3 ) when saponified. The 
 liquid portion consists chiefly of oleine. Butter also contains small quan- 
 tities of butyrine, caproine, and caprine, which yield, when saponified, 
 glycerine and butyric (HO . C 8 H 7 3 ), caproic (HO . C ]2 H n 3 ), and capric 
 (HO . C^H^Og) acids, distinguished for their disagreeable odour. 
 
 Fresh butter has very little odour, being free from these volatile acids, 
 but if kept for some time, especially if the caseine of the milk has been 
 imperfectly separated in its preparation, spontaneous resolution of these 
 fats into glycerine and the volatile disagreeable acids takes place. By 
 salting the butter this change is in great measure prevented. 
 
 The fat of the sheep and ox (suet, or when melted, tallow) consists chiefly 
 of stearine, whilst in that of the pig (lard) oleine predominates to about 
 the same extent as in butter. Margarine (or palmitine 1) is also present in 
 these fats. 
 
 Human fat contains chiefly oleine and margarine (or, if we do not admit 
 the independent existence of the latter, palmitine and stearine). 
 
 Sperm oil, which is expressed from the spermaceti found in the brain 
 of the sperm whale, owes its peculiar odour to the presence of a fat which 
 has been called phocenine, but which appears to be valerine, as it yields 
 glycerine and valerianic acid (HO . C 10 H 9 3 ) when saponified. 
 
 The beautiful solid crystalline fat, known as spermaceti or cetine, differs 
 widely from the ordinary fatty matters, for when saponified (which is not 
 easily effected), it yields no glycerine, but in its stead another alcohol 
 termed ethal (C 32 H 34 2 ), which is a white crystalline solid, capable of being 
 distilled without decomposition. 
 
 The soap prepared from spermaceti, when decomposed by an acid, yields 
 palmitic acid (HO . C 32 H 31 3 ), (formerly called ethalic acid), to which ethal 
 is the corresponding alcohol. 
 
 Palmitic acid and ethal are formed from spermaceti by the assimilation of the 
 elements of water, just as stearic acid and glycerine are formed from stearine 
 
 C 64 H 64 4 + 2HO = C 32 H 34 2 + HO . C 32 H 31 3 . 
 EthaL Palmitic acid. 
 
WAX, 
 
 583 
 
 Upon the compound radical theory, ethal would be represented as the hydrated 
 oxide of cetyle (C 32 H 33 )0 . HO, and as the alcohol of the cetyle series running parallel 
 with the ethyle series. The following characteristic members of the series have 
 been studied : 
 
 Cetyle Series. 
 Cetylene, C 32 H 32 
 Cetylic ether, C 32 H 33 . 
 Ethal, C 32 H 33 . HO 
 
 Palmitic acid, C 32 H 31 3 . HO 
 Spermaceti, C 32 H 33 . C 32 H 31 3 
 
 Ethyle Series. 
 Ethylene, C 4 H 4 
 Ether, C 4 H 5 
 
 Alcohol, C 4 H 5 . HO 
 Acetic acid, C 4 H 3 3 . HO 
 Acetic ether, C 4 H 6 . C 4 H 3 8 
 
 Chinese wax, the produce of an insect of the cochineal tribe, is analogous 
 in its chemical constitution to spermaceti. When saponified by fusion 
 with hydrate of potash, it yields cerotine or cerylic alcohol (C 54 H 65 . HO), 
 corresponding to ethal, and cerotic acid (HO . C 54 H 53 0.,), corresponding to 
 palmitic acid. Cerotic acid is also contained in ordinary bees' wax, from 
 which it may be extracted by boiling alcohol, and crystallises as the solu- 
 tion cools. It forms about two-thirds of the weight of the wax. 
 
 Bees' wax also contains about one-third of its weight of myricine 
 (C 92 H 92 4 ), a substance analogous to spermaceti, which yields, when sapo- 
 nified, palmitic acid and melissine (C 60 H 61 . HO), an alcohol corresponding 
 to ethal. The colour, odour, and tenacity of bees' wax appear to be due 
 to the presence of a greasy substance called ceroleine, which forms about 
 ^th of the wax, and has not been fully examined. The tree-wax of 
 Japan is said to be pure palmitine. 
 
 Wax is bleached for the manufacture of candles, by exposing it in thin 
 strips or ribands to the oxidising action of the atmosphere, or by boiling 
 it with nitrate of soda and sulphuric acid. Chlorine also bleaches it, but 
 displaces a portion of the hydrogen in the wax, taking its place and 
 causing the evolution of hydrochloric acid vapours when the w.ax is burnt. 
 
 The following table includes the principal fatty bodies and their corresponding 
 acids, with their fusing points : 
 
 Neutral 
 
 Fats. 
 
 Equivalent 
 Formula. 
 
 Chief 
 Source. 
 
 Fusing 
 Point. 
 
 Fatty 
 Acids. 
 
 Equivalent 
 Formula. 
 
 Fusing 
 Point. 
 
 Stearine* 
 
 C 114 H lloOi2 
 
 Tallow 
 
 125 to 157 
 
 Stearic 
 
 C 36 H 36 4 
 
 159 
 
 Palmitine 
 
 C 102 H 98 12 
 
 Palm oil 
 
 114 to 145 
 
 Palmitic 
 
 C 32 H 32 4 
 
 144 
 
 Margarine 
 
 C 108 H 1M 12 
 
 Olive oil 
 
 116 
 
 Margaric 
 
 C 34 H 34 4 
 
 140 
 
 Oleine 
 
 C,,4H 10 A S 
 
 M 
 
 Below 32 
 
 Oleic 
 
 C 3eH 31 4 
 
 40 
 
 Cetino 
 
 C 64 H 64 4 
 
 Spermaceti 
 
 120 
 
 Palmitic 
 
 C 32 H 32 4 
 
 144 
 
 Myricine 
 
 C 92 H S24 
 
 Bees' wax 
 
 162 
 
 " 
 
 
 ' 
 
 VEGETABLE ACIDS. 
 
 425. Oxalic acid. This very poisonous acid occurs pretty abundantly 
 in the vegetable kingdom, being found in the leaves of the wood sorrel as 
 binoxalate of potash (salt of sorrel, KO . HO . 2C 2 3 + 2Aq.), in the stalks 
 of rhubarb, in some sea-weeds, as oxalate of soda, and in lichens, some of 
 which contain more than half their weight of oxalate of lime. Oxalate of 
 lime has also been found in wood. In certain unhealthy conditions of the 
 
 * Stearine and palmitiue are said to present three modifications with different fusing 
 points. 
 
584 PREPARATION OF OXALIC ACID. 
 
 animal frame, oxalate of lime is produced, being either excreted in the 
 urine, or forming a calculus (mulberry calculus) in the bladder. In such 
 cases the oxalic acid appears to be formed in consequence of an imperfec- 
 tion in that oxidising process by which the carbon and hydrogen of the 
 various parts of the frame are finally converted into carbonic acid (CO.,) 
 and water (HO), the production of oxalic acid (CgHOJ representing the 
 penultimate stage of that process. 
 
 With the exception of carbonic acid, no carbon compound is more com- 
 monly met with than oxalic acid, as a product of the action of oxidising 
 agents upon organic substances, especially upon those which do not con- 
 tain nitrogen, such as sugar (C 12 H u O n ), starch (C 12 H 10 10 ), and woody 
 fibre. 
 
 Oxalic acid is largely employed in calico-printing, in cleansing leather 
 and brass, as a solvent for Prussian blue in the preparation of blue ink, 
 &c., and for taking iron-mould out of linen. It is manufactured on the 
 large scale by oxidising saw-dust with a mixture of hydrate of potash and 
 hydrate of soda; the latter would not produce oxalic acid without the 
 hydrate of potash, and this alone would be too expensive. 1 eq. of hydrate 
 of potash and 2 eqs. of hydrate of soda are mixed in solution, which should 
 have the sp. gr. 1-35, made into a thick paste with sawdust, and heated 
 upon iron plates for several hours ; hydrogen is evolved, from the decom- 
 position of the water in the alkaline hydrates, the oxygen serving to 
 convert the wood into oxalic acid, which forms more than one-fourth of 
 the' weight of the grey mass finally obtained. On treating this mass with 
 cold water, a quantity of oxalate of soda is left undissolved ; this is boiled 
 with hydrate of lime, when the oxalic acid is converted into the insoluble 
 oxalate of lime, and hydrate of soda is dissolved ; the oxalate of lime is 
 then decomposed by dilute sulphuric acid, when the sparingly soluble 
 sulphate of lime is formed, and the solution yields crystals of oxalic acid 
 (HO. C 2 3 . 2Aq.) on evaporation. The whole of the alkali originally 
 employed is recovered by evaporating the liquors to dryness, calcining to 
 destroy organic matter, and decomposing the alkaline carbonates with 
 hydrate of lime. The sawdust yields about half its weight of crystallised 
 oxalic acid. 
 
 Before the introduction of this process, oxalic acid was sold at nearly 
 twice its-present cost, being then usually obtained by the action of nitric 
 acid either upon molasses or upon starch-sugar* (p. 495) in leaden 
 vessels, which were found to remain unattacked by the acid as long as any 
 sugar remained unoxidised. 
 
 For experiment on the small scale, oxalic acid may be prepared by gently heating 
 100 grains of starch with 1 measured ounce of nitric acid (sp. gr. 1-38), when 
 abundant fumes of nitrous acid (N0 3 ) will indicate the deoxidation suffered by the 
 nitric acid. When this has abated, the solution may be transferred to a dish, and 
 slowly evaporated to about one-sixth of its bulk ; on cooling, a mass of beautiful 
 four-sided prismatic crystals of oxalic acid will be obtained. 
 
 The crystals of oxalic acid may be represented by the empirical formula 
 C 2 H 3 6 , but when they are heated to 212 F. they lose water, melting 
 first, if the heat be suddenly applied,t but efflorescing without fusion if 
 heated gradually. The dried or effloresced oxalic acid has the composi- 
 tion C 2 H0 4 , showing that 2 eqs. of water of crystallisation have been exr- 
 
 * Hence the common name, acid of sugar. 
 
 t By suddenly heating the crystals with a lamp in a test-tube, much of the acid may be 
 sublimed in long prismatic crystals. 
 
PROPERTIES OF OXALIC ACID. 585 
 
 pelled, and that the crystals would be more correctly represented by 
 C 2 H0 4 . 2 Aq. On neutralising oxalic acid with potash and soda, salts are 
 obtained which, when dried at 212 F., have the composition KO . C 2 0., 
 and NaO . C 2 3 , and if solutions of these salts be precipitated by nitrate 
 of lead or of silver, the oxalates of lead (PbO . C 2 3 ) and of silver 
 (AgO . C 2 3 ) are obtained. Hence it would appear that the composition 
 of anhydrous oxalic acid is C 2 3 , and that the acid dried at 212 F. 
 should be represented as HO . C 2 3 . All attempts, however, to procure 
 C 2 , itself have failed. If the dried acid be heated to about 320 F., it 
 sublimes in crystals, but above that temperature it is decomposed into 
 water, carbonic acid, carbonic oxide, and some formic acid (see p. 567). 
 When heated with dehydrating agents, such as sulphuric acid, it is also 
 decomposed into carbonic acid and carbonic oxide (p. 79). It would 
 appear, therefore, more consistent with the results of experiment, not to 
 insist upon the existence of the C 2 3 , but to write the dried oxalic acid 
 as C 2 H0 4 , representing its salts as being formed by the displacement of 
 the hydrogen by a metal, thus, oxalate of potassium, C 2 K0 4 , oxalate of 
 silver, C 2 Ag0 4 . But oxalic acid has the power of forming acid salts, in 
 which only a part of the hydrogen is displaced by the metal, such as 
 binoxalate of potassium, KO . HO . 2C 2 0. } , or C 4 (KH)0 8 ; it also forms two 
 compound ethers, oxalic ether or oxalate of ethyle, C 4 H 5 . C 2 0,, or 
 C 2 (C 4 H 5 )0 4 , and binoxalate of ethyle or oxalovinic acid, C 4 H 5 . HO. 2C 2 0.,, 
 or C 4 (C 4 H 5 )H0 8 ; so that it would appear to be necessary that oxalic acid 
 should be represented by the formula C 4 H 2 8 , when it would be a bibasic 
 acid, requiring 2 eqs. of a metal to form a neutral salt. It will be seen 
 that this formula has been adopted at p. 580, where oxalic acid is repre- 
 sented as the first member of the bibasic fatty acid series. 
 
 Oxalic acid is rather sparingly soluble in cold water, requiring about 
 nine times its weight ; hot water dissolves it more abundantly, and it is 
 moderately soluble in alcohol. The aqueous solution is intensely acid, 
 more nearly resembling the strong mineral acids than one of vegetable 
 origin, and is exceedingly poisonous, a property which is the more dan- 
 gerous on account of the resemblance of the crystallised oxalic acid to 
 Epsom salts (sulphate of magnesia), from which, however, it may be 
 readily distinguished by its sour taste and by the action of heat, which 
 entirely dissipates the oxalic acid, but only expels water from Epsom 
 salts. Fortunately, a considerable quantity of the acid is required to 
 cause death, in ordinary cases 100 grains or more. The chemical anti- 
 dote employed to counteract its effect is chalk suspended in water, the 
 lime of the chalk combining with the acid to form the insoluble and 
 harmless oxalate of lime (CaO . C 2 3 ). The insolubility of the oxalate of 
 lime renders the oxalic acid one of the most delicate tests for lime, which 
 may be detected, for example, in common water, by adding oxalic acid 
 and a slight excess of ammonia, when a white cloud of oxalate of lime is 
 produced. Conversely, of course, salts containing calcium (chloride of 
 calcium, for instance) may be employed to detect oxalic acid, the precipi- 
 tated oxalate of lime being distinguished from other similar precipitates by 
 its insolubility in acetic acid. 
 
 As might be expected from its composition (C 2 H0 4 ), oxalic acid is 
 easily converted into carbonic acid and water by oxidising agents ; thus, 
 if a hot solution of oxalic acid be poured upon powdered binoxide of 
 manganese, violent effervescence takes place from the rapid evolution of 
 carbonic acid., 
 
586 PREPARATION OF TARTARIC ACID. 
 
 Binoxalate of potash (KO . HO . 2C. 2 3 + 2Aq., or KHO^.H^) is 
 sold under the names of salt of sorrel and essential salt of lemons, and is 
 employed for the same purposes as oxalic acid. It is a sparingly soluble 
 salt, requiring 40 parts of cold water to dissolve it, and has occasionally 
 caused accidents by being mistaken for cream of tartar (bitartrate of 
 potash), from which it is readily distinguished by the action of heat, 
 which chars the bitartrate, but not the binoxalate, an alkaline mass con- 
 taining carbonate of potash being left in both cases. 
 
 Quadroxalate of potash (KO . 3HO . 4C 2 3 + 4Aq.,orKH 3 2e 2 4 . 2H 2 O) 
 is also sometimes sold as salts of lemon ; it is even less soluble than the 
 binoxalate. 
 
 Oxalate of ammonia (NH 3 . HO . C 2 3 + Aq., or (NH 4 ) 2 2 4 . H 2 O), so 
 much used in chemical analysis as a precipitant for lime, is obtained by 
 mixing solution of oxalic acid with a slight excess of ammonia, and eva- 
 porating the solution, from which the oxalate of ammonia crystallises, on 
 cooling, in fine prismatic needles. 
 
 The action of heat upon this salt has been described at p. 549. 
 
 Oxalate of silver (AgO . C 2 3 , or Ag 2 O 2 4 ) is obtained as a white preci- 
 pitate when nitrate of silver is added to oxalate of ammonia. It is re- 
 markable for being decomposed with a slight explosion when heated in 
 the dry state, metallic silver being left, AgO . C 2 3 = Ag + 2C0 2 . 
 
 426. Tartaric acid. The most important of the vegetable acids is tar- 
 taric acid (C 8 H 6 12 ), which occurs in many fruits, but more especially in 
 the grape, the juice of which deposits it, during fermentation, in the form 
 of bitartrate of potash, which is known in commerce as tartar or argol. 
 This salt dissolves with difficulty in cold water, but may be dissolved in 
 boiling water, from which it crystallises in prisms on cooling. When 
 thus purified, it is known as cream of tartar, and has the composition 
 KO.C 8 H 5 U , representing tartaric acid in which the elements of one 
 equivalent of water have been replaced by those of potash. The solution 
 of this salt is acid to test-papers, and if it be neutralised with potash and 
 evaporated, it yields crystals of a very soluble salt, having the composition 
 2KO . C 8 H 4 10 . This is regarded as the neutral tartrate of potash, cream 
 of tartar being a bitartrate, KO . HO . C 8 H 4 10 , inasmuch as tartaric acid 
 is a bibasic acid, requiring two equivalents of an alkali to form a neutral 
 salt. The crystallised tartaric acid is therefore regarded as 2HO . C 8 H 4 10 , 
 the two equivalents of water being replaced by an alkali in order to form 
 a neutral salt, whilst, if half the .water only be replaced, an acid salt or 
 bitartrate is produced. 
 
 In order to prepare tartaric acid, which is largely used in dyeing and 
 calico-printing, the impure bitartrate of potash is boiled with water, and 
 carbonate of lime (chalk) is added as long as it causes effervescence from 
 the escape of carbonic acid ; the result of this change is the formation of 
 tartrate of lime, which is insoluble, and tartrate of potash, which dissolves 
 in the water 
 
 2(KO . HO . CgHpJ + 2(CaO.C0 2 ) - 
 
 Bitartrate of potash. Carbonate of lime. 
 
 2KO.C 8 H 4 10 + 2CaO.C 8 H 4 10 + 2HO + 2C0 2 . 
 
 Tartrate of potash. Tartrate of lime. 
 
 Chloride of calcium is then added to the mixture, which converts the 
 whole of the tartaric acid into the insoluble tartrate of lime 
 
 2KO.C 8 H 4 10 + 2CaCl = '2KC1 + 2CaO . C S H 4 10 . 
 
TARTAR-EMETIC. 587 
 
 The tartrate of' lime is strained off, washed, and boiled with diluted sul- 
 phuric acid, when sulphate of lime remains undissolved, and tartaric acid 
 may be obtained in crystals by evaporating the filtered solution 
 
 2CaO.C 8 H 4 10 + 2(HO.S0 3 ) - 2HO.C 8 H 4 10 + 2(CaO.S0 3 ). 
 
 Tartrate of lime. Tartaric acid. 
 
 Large transparent prisms are thus obtained, which are very soluble in 
 water. When kept, the solution, unless very strong, deposits a curious 
 fungoid growth, and acetic acid is found in it. When heated to about 
 340 F., the crystals fuse without loss of weight; but on examining the 
 fused mass, it is found to be no longer tartaric acid, but a mixture of two 
 new acids. One of these, metatartaric acid, has the same formula as tar- 
 taric acid (2HO . C 8 H 4 10 ), but cannot be crystallised. Its salts are more 
 soluble in water than the tartrates, and ara converted into the latter when 
 boiled with water. The other acid, uotartoric, is also uncrystallisable, 
 but has the formula (HO, C 8 H 5 U ), being a monobasic acid, one equiva- 
 lent of the basic w r ater of the tartaric acid having been incorporated with 
 the acid itself. The isotartrate of potash (KO . C 8 H 5 O n ) has the same 
 composition as the bitartrate (KO . HO . C 8 H 4 10 ), but is far more soluble. 
 It is converted into that salt by boiling with water. 
 
 At 374 F. tartaric acid loses its basic water, and is converted into tar- 
 taric anhydride (C 8 H 4 ]0 ), which is a white insoluble substance, convertible 
 into tartaric acid by prolonged contact with water. 
 
 Tartar-emetic. One of the commonest salts of tartaric acid is tartar- 
 emetic, the double tartrate of antimony and potash, which is prepared by 
 boiling antimony with sulphuric acid, driving off the excess of acid by 
 heat, and digesting the residual teroxide of antimony with cream of tartar 
 and a little water for some hours. The changes involved in the process 
 are thus represented 
 
 Sb 2 + 3(HO.SO a ) = 2Sb0 3 + 3HO + 3S0 2 
 Sb0 3 + KO.HO.C 8 H 4 10 - KO.Sb0 3 .C 8 H 4 10 + HO. 
 
 Bitartrate of potash. Tartar-emetic. 
 
 On boiling the mixture with water, and filtering, the cooled solution 
 deposits octahedral crystals,- of the formula KO . Sb0 3 . C 8 H 4 10 . Aq. 
 
 The water of crystallisation may be expelled at 212 F. ; and if the salt be 
 heated to 400 F. it loses two additional equivalents of water, and becomes 
 KO . Sb0 3 . C 8 H 2 8 , which is reconverted into tartar-emetic when dissolved 
 in water. 
 
 When a little hydrochloric acid is added to a solution of tartar-emetic, a precipi- 
 tate of teroxide of antimony is formed, which dissolves easily in an excess of the 
 acid. If kept for a length of time in solution, tartar-emetic is decomposed, octa- 
 hedral crystals of teroxide of antimony heing deposited, and the solution ceases to 
 be precipitated by hydrochloric acid. The reaction to test-paper, which was 
 slightly acid, is now slightly alkaline. 
 
 Compounds perfectly analogous to tartar-emetic have been obtained, in 
 which the antimony is replaced by boron or by arsenic, and the potassium 
 by silver, lead, or sodium. 
 
 It will be observed that tartar-emetic, and its analogues, present an 
 anomaly in their composition, for it might be expected that the teroxide 
 of antimony (Sb0 3 ) would replace three equivalents of potash instead of 
 one. The composition of the substance KO . Sb0 3 . C 8 H 2 8 is very singular, 
 but it might be reconciled with that of crystallised tartaric acid by repre- 
 
588 RACEMIC ACID. 
 
 senting it thus, C^KSb"')*^, that is, crystallised tartaric'acid (C 8 H ti 12 ), 
 in which one equivalent of hydrogen has been replaced by potassium, and 
 three equivalents by the triatomic antimony. 
 
 The beautiful prismatic crystals known as Roctielle salt consist of a 
 double tartrate of potash and soda (KO. NaO . C 8 H 4 10 , 8Aq.), prepared 
 by neutralising cream of tartar with carbonate of soda. 
 
 Tartaric acid has been obtained artificially by the action of nitric acid 
 upon sugar of milk or gum, which supplies a link of connection between 
 this acid and the members of the sugar group which accompany it in 
 plants. 
 
 Tartaric acid is easily convertible into succinic and malic acids, as might 
 be anticipated from an inspection of their formulae 
 
 Tartaric acid, . . 2HO.C 8 H 4 10 
 Malic . . 2HO.C 8 H 4 8 
 Succinic . . 2HO.C 8 H 4 6 
 
 When tartaric acid is heated with phosphorus and iodine in the presence 
 of water (or, which amounts to the same thing, when it is heated with 
 hydriodic acid), the acid is deoxidised, and malic and succinic acids are 
 produced, thus 
 
 2HO.C 8 H 4 10 + 4HI = 2HO.C 8 H 4 6 + I 4 + 4HO . 
 
 Tartaric acid. Succinic acid. 
 
 Tartaric and malic acids are frequently associated in fruits, and succinic 
 acid is found among the products of fermentation of grape-juice. 
 
 Succinic acid may be reconverted into tartaric acid by heating it with 
 bromine and water, when it is converted into bibromosuccinic acid, 
 2HO . C 8 (H 2 Br 2 )0 6 , which furnishes tartaric acid when decomposed with 
 oxide of silver 
 
 2HO . C 8 (H 2 Br 2 )0 6 + 2AgO + 2HO = 2HO . C 8 H 4 10 + 2AgBr . 
 
 Bibromosuccinic acid. Tartaric acid. 
 
 When bromosuccinic acid, 2HO . C 8 (H o Br)0 6 , is decomposed with oxide 
 of silver, malic acid is formed 
 
 2HO . C b (H 3 Br)0 6 + 3AgO = 2AgO.C 8 H 4 8 + AgBr + HO. 
 
 Bromosuccinic acid. Malatc of silver. 
 
 427. The tartaric acid found in grapes is accompanied, particularly in those of 
 certain vintages and districts, by another acid called racemic or paratartaric acid, 
 which has the same composition as tartaric acid, but crystallises with two equivalents 
 of water (2HO . C 8 H 4 10 . 2Aq.) The crystalline forms of these acids are the same, but 
 the crystals of racemic acid effloresce, from loss of water, when exposed to the air. 
 Solution of racemic acid is precipitated by the salts of lime, which do not precipitate 
 tartaric acid unless it be previously neutralised. Moreover, although racemic acid 
 forms, with potash and oxide of antimony, a salt corresponding in composition to 
 tartar-emetic, this does not crystallise in octahedra, but in tufts of needles. 
 
 There is a marked ditference in the action of these two acids and their salts upon 
 polarised light, for solutions of racemic acid and the racemates do not alter the plane 
 of polarisation, whilst tartaric acid and the tartrates rotate it to the right. 
 
 On carefully examining the crystalline forms of the tartrates, Pasteur observed 
 that they generally presented an exception to that law of crystalline symmetry, which 
 requires that a modification existing on any edge or face of a crystal should be 
 repeated on all its other similar edges or faces, whereas in the crystals of the tartrates, 
 certain of the edges are truncated without any corresponding modification of the 
 others, and hemihedral forms are thus produced. Now, in general, it is found tKat if 
 a substance forms hemihedral crystals, their hemihedrism is of such a character 
 that they can be superposed upon each other, so that the united crystals shall exhibit 
 
CITRIC ACID. 589 
 
 a perfect symmetry upon each side of the plane of junction ; but the hemihedrism of 
 the tartrates is such, that the crystals do not exhibit this symmetry when superposed 
 upon each other, but when one is superposed upon the reflection of the other in a 
 mirror, so that instead of presenting crystals which are, as usual, partly right and 
 partly left-handed in their want of symmetry, the crystals of the tartrates are either 
 all right-handed or all left-handed hemihedral crystals. 
 
 When the action of solutions of these salts upon polarised light came to be 
 examined, it was found that the right-handed crystals always rotated the plane of 
 polarisation to the right, whilst the left-handed crystals produced a left-handed 
 rotation. 
 
 On separating the acids from these salts, they resembled each other precisely in 
 all their chemical properties, but the acid from the right-handed salts furnished 
 crystals which were hemihedral right-handedly, whilst that of the left-handed salts 
 furnished left-handed hemihedral crystals ; moreover, the solution of the right- 
 handed acid exerted a right-handed rotation upon the plane of polarisation, which 
 was turned in the opposite direction by a solution of the left-handed acid. 
 
 The former acid has been named dextro-tartaric acid, and is the usual form in 
 which this acid is met with ; the other acid has been called Isevo-tartaric acid. In 
 their chemical relations these acids are perfectly identical ; for the chemist they are 
 botli the same tartaric acid, equally well adapted for all the uses to which this acid 
 is applied. 
 
 Pasteur found that the double racemate of soda and ammonia furnished a crop of 
 crystals containing both right-handed and left-handed hemihedral forms, and on 
 separating them by hand, he found that the action of their solutions on polarised 
 light corresponded with their hemihedrism, and on isolating the acids, the right- 
 handed crystals furnished dextro-tartaric, the left-handed, Isevo-tartaric acid. 
 
 This analysis of racemic acid was soon confirmed by its synthesis. On mixing 
 concentrated solutions of equal parts of dextro-tartaric and Isevo-tartaric acids, a 
 considerable rise of temperature was observed, showing that combination had taken 
 place, and the solution which had no longer the power of rotating the plane of 
 polarisation furnished crystals of racemic acid. 
 
 This remarkable instance of chemical combination between two acids which are, 
 in their chemical properties, perfectly identical, to furnish a new acid differing from 
 both, affords, by analogy, some support to the theory of the duplex constitution of 
 many elementary and compound bodies. 
 
 428. Citric acid (C r2 H 8 14 ) occurs in lemons, oranges, and most acidu- 
 lous fruits. It is prepared from lemon-juice, which contains the acid in 
 a free state, by neutralising it with chalk, when the citrate of lime 
 (3CaO . C 12 H 5 O n ) is obtained, which is decomposed by dilute sulphuric 
 acid ; the filtered solution, when evaporated, yields prismatic crystals of 
 citric acid, which contain C 12 H 8 14 . 2Aq. They fuse at 212F., and lose 
 the two equivalents of water of crystallisation. From the formula of the 
 citrate of lime, it will be seen that citric acid is tribasic, and should be 
 written 3HO . C 12 H 5 11 ; hence, like ordinary phosphoric acid, .it forms 
 three series of salts. The citrates of soda, for example, have the com- 
 position 
 
 Na0.2HO.C 12 H 5 O u .2Aq. 
 
 2^aO.HO.C 12 H 5 O n .2Aq. 
 
 When citric acid is heated above 300 F., it is converted into aconitic 
 acid (3HO . C ]2 H 3 9 ), another vegetable acid found in the different 
 varieties of monkshood (aconitum). 
 
 Citric acid is employed in dyeing and calico-printing, as well as in 
 medicine. 
 
 By fermentation in contact with yeast, the citrate of lime is converted into 
 acetate and butyrate of lime, with evolution of carbonic acid and hydrogen. The 
 crude citrate of lime prepared in Sicily, and imported for the preparation of the acid, 
 is found sometimes to undergo this change spontaneously, so that it has been 
 
590 MALIC ACID TANNIC ACID. 
 
 recommended to neutralise the hot lemon-juice with carbonate of magnesia (which 
 is abundant in Italy), when the tribasic citrate of magnesia is precipitated in minute 
 crystals. By dissolving this precipitate in a fresh quantity of hot lemon-juice, and 
 evaporating, the bibasic citrate of magnesia is obtained in crystals, which is recom- 
 mended as the best form in which to import the acid into this country. 
 
 429. Malic acid (2HO . C 8 H 4 8 ) is a crystalline acid found, as its name 
 implies, in apples, and in many other fruits. It is present, together with 
 oxalic acid, in rhubarb. Tobacco leaves also contain it in the form of 
 bimalate of lime, CaO . HO . C 8 H 4 8 . 
 
 In order to extract the malic acid from rhubarb stalks, it is converted into malate 
 of lime, the solubility of which enables it to be separated from the insoluble 
 citrate and tartrate of lime. The juice is squeezed out of the stalks by a press, 
 nearly neutralised with slaked lime suspended in water, and chloride of calcium 
 is added. The precipitate containing tartrate, citrate, phosphate, and oxalate of 
 lime, is filtered off, and the liquid boiled down, when malate of lime (2CaO . C 8 H 4 8 ) 
 is separated. This is washed and added to hot nitric acid, diltited with ten 
 measures of water, as long as it continues to be dissolved. On cooling, bimalate 
 of lime (CaO . HO . C 8 H 4 8 ) is deposited, which is dissolved in water and decom- 
 posed by acetate of lead, when it gives a curious precipitate of malate of lead 
 (2PbO . C 8 H 4 8 . 6Aq.), which becomes crystalline on standing, and fuses in the 
 liquid below the temperature of boiling water. By suspending the malate of lead 
 in water, and decomposing it with hydrosulphuric acid, the lead is separated 
 as sulphide, and a solution of malic acid is obtained, which gives deliquescent 
 prismatic crystals of the acid when evaporated to a syrup and set aside. Malic 
 acid is decomposed by heat into two isomeric acids, the malceic and fumaric 
 2HO . C 8 H 2 6 ; the latter is found in the plant known as fumitory (Fumaria 
 officinalis). 
 
 An excellent source of malic acid is the juice of the unripe berries of 
 the mountain-ash, in which it is accompanied by a volatile oily acid of 
 pungent aromatic odour ; this has been called parasorbic acid, and has the 
 formula HO . C 12 H 7 3 . When fused with hydrate of potash, or boiled 
 with a strong mineral acid, it suffers a remarkable conversion into a 
 crystalline solid acid, having precisely the same composition, called sorbic 
 acid. 
 
 Under the influence of yeast, in the presence of water, malate of lime is 
 converted into succinate and acetate of lime 
 
 3(2HO . C 8 H 4 8 ) = 2(2HO.C b H 4 ) + HO.C 4 H 3 3 + 4C0 2 + 2HO . 
 
 Malic acid. Succinic acid. Acetic acid. 
 
 The amide of malic acid, malamide, C 8 H 8 N 2 6 (malate of ammonia, 
 2NH 4 . C 8 H 4 8 minus 4HO), has attracted some attention, because it has 
 the same composition as asparagine, a crystalline substance extracted from 
 the juice of asparagus, marsh-mallow root, and some other plants ; but it 
 is not identical with it, though asparagine, when acted on by nitrous acid, 
 yields malic acid 
 
 C 8 H 8 K 2 6 + 2N0 3 . = 2HO.C 8 H 4 8 + 2HO + N 4 . 
 
 Asparagine. Malic acid. 
 
 Asparagine is really the amide of another acid, the aspartic, into the 
 ammonia-salt of which it becomes converted when heated for some time 
 with water 
 
 C 8 H 8 N 2 6 + 2HO - NH 4 0.-C 8 H G N0 7 . 
 
 Asparagine. Aspartate of ammonia. 
 
 430. Tannic acid, or tannin (C 54 H 22 :!4 ), the astringent principle of 
 gall-nuts, from which it may be extracted by water, is characterised by 
 
TANNING. 591 
 
 two very useful properties, viz., that of yielding a "black precipitate with 
 the salts of peroxide of iron, and of forming a tough insoluble compound 
 with gelatine and gelatigenous membrane, the first being turned to account 
 in the preparation of ink, and the second in that of leather. 
 
 For the preparation of ink, three quarters of a pound of bruised nut- 
 galls are digested in a gallon of cold water, and six ounces of green 
 vitriol (sulphate of iron) are added, together with six ounces of gum, and 
 a few drops of kreasote. The mixture is set aside for two or three weeks, 
 being occasionally agitated, and the ink afterwards poured off from the 
 undissolved part of the nut-galls. 
 
 Pure sulphate of iron (FeO . S0 3 ) and tannic acid might be mixed 
 without change ; but when the mixture is exposed to the air, oxygen is 
 absorbed, converting the protoxide of iron (FeO) into sesquioxide (Fe 2 3 ), 
 which combines with the tannic acid to form a black precipitate of 
 tannate of sesquioxide of iron, the exact composition of which is not 
 known. The gum is added to render the liquid viscous, so as to prevent 
 the subsidence of the black precipitate, and the kreasote prevents the ink 
 from becoming mouldy. The brown colour of the ink in old manuscripts 
 is due to the tannic acid having been partly removed by oxidation, leaving 
 the brown peroxide of iron ; the stain of iron-mould left by ink on linen 
 after washing is due to the entire removal of the tannic acid by the alkali 
 in the soap. 
 
 Tanning. When infusion of nut-galls is added to a solution of gelatine, 
 the latter combines with the tannic acid, and a bulky precipitate is 
 obtained. If a piece of skin, which has the same composition as gelatine, 
 be placed in the infusion of nut-galls, it will absorb the whole of the 
 tannic acid, and become converted into leather, which is much tougher 
 than the raw skin, less permeable by water, and not liable to putrefaction. 
 
 The first operation in the conversion of hides into leather, after they 
 have been cleansed, consists in soaking them for three or four weeks in 
 pits containing lime and water, which saponifies the fat, and loosens the 
 hair. The same object is sometimes attained by allowing the hides to 
 enter into putrefaction, when the resulting ammonia has the same effect as 
 the lime. The loosened hair having been scraped off, the hides are soaked 
 for twelve hours in water containing T^Vtf^h of sulphuric acid, which 
 removes adhering lime, and opens the pores of the skin, so as to fit it to 
 receive the tanning liquid. 
 
 The tanning material generally employed for hides is the infusion of 
 oak-bark, which contains querci-tannic acid, very similar in properties to 
 tannic acid. The hides are soaked in an infusion of oak-bark for about 
 six weeks, being passed in succession through several pits, in which the 
 strength of the infusion is gradually increased. They are then packed in 
 another pit with alternate layers of coarsely ground oak-bark ; the pit is 
 filled with water, and left at rest for three months, when the hides are 
 transferred to another pit, and treated in the same way ; but, of course, the 
 position of the hides will be now reversed that which was uppermost, 
 and in contact with the weakest part of the tanning liquor, will now be 
 at the bottom. After the lapse of another three months the hide is gene- 
 rally found to be tanned throughout, a section appearing of a uniform 
 brown colour. It has now increased in weight from 30 to 40 per cent. 
 The chemical part of the process being now completed, the leather is sub- 
 jected to certain mechanical operations to give it the desired texture. For 
 tanning the thinner kinds of leather, such as morocco, a substance called 
 
592 GALLIC ACID. 
 
 sumach is used, which consists of the ground shoots of the Rhus Coriaria, 
 and contains a large proportion of tannic acid. 
 
 Morocco leather is made from goat and sheep skins, which are denuded 
 of hair by liming in the usual way, but the adhering lime is afterwards 
 removed by means of a bath of sour bran or flour. In order to tan the 
 skin so prepared, it is sewn up in the form of a bag, which, is filled with 
 infusion of sumach, and allowed to soak in a vat of the infusion for some 
 hours. A repetition of the process, with a stronger infusion, is necessary ; 
 but the whole operation is completed in twenty-four hours. The skins 
 are now washed and dyed, except in the case of red morocco, which is 
 dyed before tanning, by steeping it first in alum or chloride of tin, as a 
 mordant, and afterwards in infusion of cochineal. Black morocco is dyed 
 with acetate of iron, which acts upon the tannic acid. The aniline dyes 
 are now much employed for dyeing morocco. 
 
 The kid of which gloves are made is not actually tanned, but submit- 
 ted to an elaborate operation called tawing, the chief chemical features of 
 which are the removal of the excess of lime,* and opening the pores of 
 the skin by means of a sour mixture of bran and water, in which lactic 
 acid is the agent ; and the subsequent impregnation of the porous skin 
 with chloride of aluminum, by steeping it in a hot bath containing alum 
 and common salt. The skins are afterwards softened by kneading in a 
 mixture containing alum, flour, and the yolks of eggs. The putrefaction 
 of the skin is as effectually prevented by the chloride of aluminum as by 
 tanning. 
 
 Wash leather and buckskin are not tanned, but shamoyed, which con- 
 sists in sprinkling the prepared skins with oil, folding them up and 
 stocking them under heavy wooden hammers for two or three hours. 
 When the grease has been well forced in, they are exposed in a warm 
 atmosphere, to promote the drying of the oil by absorption of oxygen 
 (p. 581). These processes having been repeated the requisite number of 
 times, the excess of oil is removed by a weak alkaline bath, and the skins 
 are dried and rolled. The buff colour of wash-leather is imparted by a 
 weak infusion of sumach. 
 
 Parchment is made by stretching lamb or goat skin upon a frame, re- 
 moving the hair by lime and scraping, as usual, and afterwards rubbing 
 with pumice stone, until the proper thickness is acquired. 
 
 Tannic acid, like many other proximate constituents of vegetables 
 (see p. 476), when boiled with diluted sulphuric acid, yields grape-sugar, 
 whilst a new acid may be obtained from the solution, which is known as 
 gallic acidt 
 
 CJH.O,, + 10HO = S^HA.) + C, 2 H 14 14 . 
 
 Tannic acid. Gallic acid. Grape-sugar. 
 
 The addition of dilute sulphuric acid to the infusion of gall-nuts pro- 
 duces a precipitate composed of tannic and sulphuric acids, but this 
 dissolves when boiled with excess of sulphuric acid, suffering the above 
 change. 
 
 431. Gallic acid (3HO . C 14 H 3 7 ) is also formed by the oxidation of 
 tannic acid when exposed to the air, particularly in the presence of the 
 
 * Polysulphides of sodium and calcium are sometimes employed for removing the hair. 
 
 t It will be perceived that tannic acid is analogous in constitution to the gluco-tartaric 
 acid mentioned at p. 578, which splits into grape-sugar and tartaric acid when boiled with 
 diluted sulphuric acid, exactly as tannic acid splits into grape-sugar and gallic acid. 
 
PYROGALLINE OR PYROGALLIC ACID. 593 
 
 matters associated with it in the gall-nut, which seem to act like the 
 ferment in the quick vinegar process (p. 492). The method generally 
 practised for obtaining gallic acid consists in exposing powdered nut-galls 
 in a moist state to the action of the air for some weeks, in a warm place, 
 when oxygen is absorbed, and carbonic acid evolved, the powder becoming 
 covered with crystals of gallic acid (tannic acid does not crystallise). By 
 boiling the mass with water the gallic acid is extracted, and since, unlike 
 tannic acid, it is very sparingly soluble in cold water, the greater portion 
 crystallises out as the solution cools, in long silky needles, containing 
 C I4 H 6 1? + 2Aq. 
 
 In this process another acid is obtained in small quantity, which is 
 insoluble in water, and has been called ellagic acid (HO . C U H 2 O 7 ) ; it 
 possesses some interest, because it is found as a product of animal life in 
 certain intestinal concretions or bezoars, occurring in the antelopes of 
 Central Asia. 
 
 In most astringent substances a small quantity of gallic acid accom- 
 panies the tannic. 
 
 Gallic acid dissolves in oil of vitriol with a red colour, and when the 
 solution is poured into water, a red-brown precipitate is obtained, called 
 rafigallic acid (C 14 H 6 10 ), which is interesting from its property of dyeing 
 calico red, if previously mordanted with alum. 
 
 When powdered nut-galls are heated in an iron pan surmounted with 
 a cone of paper (see benzoic acid, p. 473) to about 420, a quantity of 
 crystals sublime into the cone, which are pyrogallic acid (C ]2 H 6 6 ), or 
 more properly, pyrogalline, for it is doubtful whether it is really an acid 
 substance. 
 
 Its formation from the tannic acid of the galls is explained by the 
 equation 
 
 C 54 H 22 34 + 2HO = 4(C I2 H 6 6 ) + 6C0 2 . 
 
 Tannic acid. Pyrogallic acid. 
 
 As its name implies, this acid may also be obtained by the action of heat 
 upon gallic acid, which suffers a similar decomposition.* 
 
 This substance is extensively prepared for use in photography, in which 
 art its great tendency to absorb oxygen is called into play, rendering it 
 capable of decomposing the salts of silver with immediate separation of 
 the metal. 
 
 The solution of pyrogallic acid soon becomes brown when exposed to 
 the air, from absorption of oxygen, and if it be mixed with an alkali, it 
 absorbs oxygen almost instantaneously, acquiring a very dark brown colour. 
 This property renders pyrogallic acid very useful in the analysis of air 
 and of other gases containing uncombined oxygen ; a portion of air con- 
 fined in a graduated tube over mercury (see fig. 7 3), is shaken with a 
 strong solution of potash to absorb carbonic acid, and the diminution 
 of volume having been noted, some solution of pyrogallic acid is intro- 
 duced ; on shaking for a few seconds, the oxygen is entirely absorbed, 
 when the volume of the nitrogen may be observed. 
 
 The salts of tannic and gallic acids are not very well known. The 
 latter appears to be a tribasic acid, so that its true formula would be 
 3HO . C J4 H 3 7 , the 3HO being replaceable by a basic oxide. 
 
 * By heating gallic acid under pressure with two or three parts of water to 410 F. for 
 half-an-hour, and evaporating the solution, it is said that the theoretical quantity of pyro- 
 gallic acid may be obtained. 
 
 2 p 
 
594 COMPOSITION OF OPIUM. 
 
 The acid character of pyrogallic acid is very feeble. 
 
 The three acids are distinguished by their action upon the salts of iron. 
 With pure protosulphate of iron (FeO . S0 3 ) neither tannic nor gallic acid 
 gives any reaction, but pyrogallic acid gives a deep indigo blue solution ; 
 whilst with persulphate (Fe 2 3 . 3S0 3 ) or perchloride (Fe 2 Cl 3 ) of iron, 
 the two former give a bluish-black precipitate, and pyrogajlic acid gives 
 a bright red solution. 
 
 The presence of tannic acid in a vegetable infusion is easily recognised 
 by the addition of perchloride of iron, but the hue which is produced is 
 not the same in all astringent substances, because they contain different 
 varieties of tannin. 
 
 All these varieties, however, differ from tannic acid properly so called, 
 in not furnishing pyrogallic acid when heated. 
 
 The astringent principle of catechu and kino, which are used by tanners, 
 is called mimotannic acid. 
 
 VEGETABLE ALKALOIDS. 
 
 432. In some plants the vegetable acids are combined with vegetable 
 alkalies or alkaloids ; thus, in opium, the morphine is combined with 
 meconic acid ; in cinchona bark, the quinine is combined with kinic acid. 
 The methods adopted for the separation of these alkaloids from the acids 
 and other substances associated with them are among the most important 
 processes of practical chemistry. 
 
 Extraction of the alkaloids from opium. Opium is the concrete milky 
 juice which exudes on incising the unripe capsules of the Papaver somni- 
 ferum, and is imported into this country from Persia, Turkey, Bengal, and 
 Egypt, in the form of round masses or cakes enveloped in leaves ; it has a 
 dark colour, a soft waxy consistence, and a peculiar characteristic odour. 
 "Different samples vary much in composition, but the following result of 
 an analysis of Smyrna opium will give an idea of the nature of this com- 
 plex drug : 
 
 100 parts of Smyrna Opium contained 
 
 Gum, 
 
 Caoutchouc, 
 Resin, 
 Oily matter, 
 Meconic acid, 
 Morphine, . 
 Narcotine, . 
 
 26-2 
 6-0 
 36 
 2-2 
 5-0 
 
 10-8 
 6-8 
 
 Narceine 6-7 
 
 Meconine, . . . 08 
 
 Codeine, .... 0-7 
 
 Colouring and other organic 1 *... 
 
 matters, 
 
 Water, .... 9-9 
 
 The medicinal value of opium appears to be due chiefly to the morphine 
 (C^H^NOu), which is present, for the most part, in the state of meconate 
 of morphine ; in order to obtain it in the separate state, the opium is cut 
 into slices and digested with water at a moderate heat for two or three 
 hours ; the liquor is then strained and evaporated, a little chalk being 
 added to neutralise the free acid. The concentrated solution, containing 
 chiefly morphine and codeine, in combination with meconic and sulphuric 
 acids, is mixed with solution of chloride of calcium, when the meconic 
 acid is precipitated in combination with lime, carrying with it a great 
 part of the colouring matter, and leaving in solution the hydrochlorates of 
 morphine and codeine, which may be obtained in crystals by evaporation. 
 
EXTRACTION OF QUININE. 595 
 
 The hydrochlorates are decolorised with animal charcoal and recrystallised. 
 On adding ammonia to the solution containing these salts, the morphine 
 only is precipitated, and may be purified by crystallisation from alcohol, 
 which deposits it in white rectangular prisms, having the formula 
 C, 4 H 19 N0 6 + 2Aq. 
 
 The solution from which the morphine has been precipitated still con- 
 tains the hydrochlorate of codeine, and on decomposing it with potash, the 
 codeine is precipitated in crystals, of the composition C 36 H. 21 N0 6 + 2Aq. 
 
 The mother-liquor from the hydrochlorates of morphine and codeine 
 contains narcotine, narceine, meconine, thebaine, and papaverine, together 
 with resin and colouring matter.* 
 
 The leading features of morphine are its sparing solubility in cold 
 water, its bitter taste and alkaline reaction, and narcotic poisonous pro- 
 perties. It is generally identified by its giving an inky blue colour with 
 perchloride of iron, and a golden yellow with nitric acid. 
 
 The hydrochlorate of morphine (C 34 H 19 NO 6 . HC1), or muriate of mor- 
 phia, is the chief form in which this alkaloid is used medicinally. 
 
 Narcotine (C 46 H 25 N0 14 + 2Aq.) possesses some interest as having been 
 the first base extracted from opium, whence it may be obtained by simply 
 treating the drug with ether, in which the morphine is insoluble. The 
 greater part of the narcotine is left in the residue after exhausting the 
 opium with water, from which it is extracted by digestion with acetic 
 acid; on neutralising the solution with ammonia, narcotine is precipi- 
 tated. It is a weak base, and has no alkaline reaction. 
 
 The meconic acid which exists in opium is a tribasic acid, having the 
 formula 3HO . C 14 HO n ; it is soluble in hot water, and crystallises on cool- 
 ing in plates which contain six equivalents of water of crystallisation. 
 It gives a blood-red colour with solution of perchloride of iron. 
 
 433. Extraction of quinine. The cinchona or Peruvian bark, so highly 
 prized for its medicinal qualities, is obtained chiefly from the districts 
 around the Andes, and is imported in three varieties, of which the yellow 
 cinchona is richest in quinine, the pale or grey bark in cinchonine, whilst 
 the red bark contains both these bases in considerable quantity. The 
 alkaloids are combined with Tdnic acid, and with a variety of tannin 
 known as quinotannic acid. 
 
 In order to extract them, the bruised bark is boiled with diluted 
 hydrochloric acid, and the filtered solution, containing the hydrochlorates 
 of quinine and cinchonine, is mixed with enough lime diffused through 
 water to render it alkaline. The quinine and cinchonine, which are very 
 sparingly soluble in cold water (requiring about 400 times their weight to 
 dissolve them), are precipitated together with some of the colouring 
 matter of the bark. 
 
 The precipitate having been collected upon a linen strainer and strongly 
 pressed, is treated with boiling alcohol, which dissolves both the alkaloids, 
 leaving any excess of lime undissolved. A part of the alcohol is then 
 recovered by distillation, and the solution containing the quinine and 
 cinchonine is neutralised with sulphuric acid, so as to convert the alkaloids 
 into sulphates, and is then decolorised with animal charcoal, and allowed 
 to crystallise. Sulphate of quinine, being much less soluble in water than 
 the sulphate of cinchonine, crystallises out first, leaving the latter in 
 solution.. 
 
 * KdaSeia, a poppy head ; vapw\. torpor ; firiKaw, a poppy. 
 
596 KINONE HYDROKINONE. 
 
 The sulphate of quinine is dissolved in water and decomposed by am- 
 monia, when the quinine is separated as a white powder, which may be 
 dissolved in alcohol and crystallised. 
 
 The liquid from which the sulphate of quinine has been deposited con- 
 tains, in addition to the sulphate of cinchonine, another base having the 
 same composition as quinine, but distinguished from it by the indisposi- 
 tion of its sulphate to crystallise. This base is termed quinidine, and is- 
 produced from quinine under the influence of an excess of acid ; it is the 
 most important constituent of the substance called quinoidine or amorphous 
 quinine, which is prepared for sale from the mother-liquors of the sulphate 
 of quinine, and forms a cheap substitute for quinine in medicine. 
 
 Quinine crystallises in small prisms, which have the composition 
 C 40 H 24 N 2 4 . 6Aq., and although sparingly soluble, even in boiling water, 
 it has an extremely bitter taste, which is also possessed by its salts. 
 
 Quinine is employed in medicine in the form of sulphate 
 
 (CJBWVHO.SO, + 7Aq.) 
 
 which requires as much as 700 parts of cold water to dissolve it, but is 
 readily dissolved in water acidulated with sulphuric acid, when it is con- 
 verted into the acid sulphate of quinine (C 40 H, 4 N 2 4 . 2(HO . SO 8 )). 
 The solution is remarkable for its action upon light, for although it is 
 perfectly colourless when held directly in front of the eye, if seen obliquely 
 it appears to have, especially at the edge, a beautiful pale blue colour. 
 This phenomenon, which is termed fluorescence, has been already referred 
 to in the case of other substances (p. 478). 
 
 Quinic or Tcinic acid. By evaporating the infusion of cinchona bark 
 from which the quinine and cinchonine have been separated by lime, 
 crystals of kinate of lime are obtained, and by decomposing these with 
 sulphuric acid, the kinic acid (2HO . C 28 H 20 20 ) passes into solution, whence 
 it may be obtained in prismatic crystals. 
 
 This acid is chiefly interesting on account of the peculiar properties of 
 some of its derivatives. When distilled with sulphuric acid and binoxide 
 of manganese, the oxygen evolved from the mixture converts the kinic 
 acid into a new substance, which condenses in beautiful yellow needles, 
 called kinone 
 
 2HO . C 28 H 20 20 + 8 = 2(C ie H 4 4 ) + 4CO., + 14HO. 
 
 Kinic acid. Kinone. 
 
 The same substance is obtained in a similar manner from one of the 
 constituents of the coffee-berry (caffeic or caffeotannic acid). By dissolv- 
 ing kinone in water containing sulphurous acid gas, and evaporating the 
 solution, colourless crystals of hydrokinone are obtained 
 
 C 12 H 4 4 + 4HO + 2S0 2 = C 12 H 6 4 + 2(HO.S0 3 ). 
 
 Kinone. Hydrokiuone. 
 
 When a solution of kinone is mixed with one of hydrokinone, beauti- 
 ful green crystals are deposited, which are known as green hydrokinone 
 (C 12 H 4 4 . C 12 H 6 4 ), and may also be obtained by the action of oxidising 
 agents, such as ferric chloride, upon hydrokinone. When kinone is acted 
 on with hydrochloric acid and chlorate of potash, it is converted into a 
 yellow crystalline body, known as perchlorokinole or chlor anile (C 12 C1 4 4 ), 
 which is also obtained in a similar way from aniline, salicirie, and isa- 
 tine. Potash dissolves it when heated, giving a purple solution. 
 
COMPOSITION OF COFFEE. 597 
 
 434. Theme or caffeine Tea Coffee. A very remarkable instance of 
 the application of chemistry to explain the use of widely different articles 
 of diet by different nations, with a view to the production of certain 
 analogous effects upon the system, is seen in the case of coffee, tea, Para- 
 guay tea, and the kola-nut (of Central Africa), which are very dissimilar 
 in their sensible properties, and afford little or no gratification to the 
 palate, owing what attractions they possess chiefly to the presence, in 
 each, of one and the same active principle or alkaloid, which has a 
 special effect upon the animal economy. This alkaloid is known as 
 caffeine or theine, and is associated in the three articles of diet men- 
 tioned above, with various substances, which give rise to their diversity 
 in flavour. 
 
 The raw coffee-berry presents, on the average, the following composi- 
 tion : 
 
 100 parts of Raw Coffee contain 
 
 Woody fibre, 84-0 
 
 Water, 12-0 
 
 Fat 12-0 
 
 Cane sugar and gum, . . . . 15-5 
 
 Legumine, or some allied substance, . 13-0 
 
 Caffeine, 1*5 
 
 Caffeic acid, 4-0 
 
 Mineral substances, . . . . 7-0 
 
 When the raw berry is treated with hot water, the infusion, which con- 
 tains the sugar and gum, the legumine, caffeine, and caffeic acid (C 14 H 8 O 7 ), 
 has none of the peculiar fragrance which distinguishes the ordinary be- 
 verage, and is due to an aromatic volatile oily substance termed caffeone, 
 formed during the roasting to which the berry is subjected before use. 
 This volatile oil, which is present in very minute quantity, is produced 
 from one of the soluble constituents of the berry (probably from the 
 caffeic acid), for if the infusion of raw coffee be evaporated to dryness, 
 the residue, when heated, acquires the characteristic odour of roasted 
 coffee. 
 
 The roasting is effected in ovens at a temperature rather below 400 F., 
 when the berry swells greatly, and loses about ^th of its weight, becoming 
 brittle, and easily ground to powder. It also becomes very much darker 
 in colour, from the conversion of the greater part of its sugar into caramel 
 (p. 499), which imparts the dark-brown colour to the infusion of coffee. 
 If the roasting be carried too far, a very disagreeable flavour is imparted to 
 the coffee by the action of heat upon the legumine and other nitrogenised 
 substances contained in the berry. 
 
 From 100 parts of the roasted coffee, boiling water extracts about 20 
 parts, consisting of caffeine, caffeic acid, caramel, legumine, a little sus- 
 pended fatty matter, fragrant volatile oil (caffeone), and salts of potash 
 (especially the phosphate). The undissolved portion of the coffee contains, 
 beside the woody fibre, a considerable quantity of nitrogenised (and nutri- 
 tious) matter, and hence the custom, in some countries, of taking this 
 residue together with the infusion. 
 
 In order to extract the caffeine from the infusion of coffee, it is mixed 
 with solution of tribasic acetate of lead, to precipitate the caffeic acid and 
 a part of the colouring matter. Through the filtered solution, sulphuretted 
 hydrogen is passed to remove the lead as sulphide, and the liquid filtered 
 
598 TEA COCOA. 
 
 from this is evaporated to a small bulk, Avhen the caffeine crystallises out 
 in white silky needles, which have a bitter taste, and the composition 
 C 16 H 1(r N" 4 4 . 2HO. Its basic properties are very feeble. 
 
 The constituents of the leaves of the tea-plant (Thea Sinemsis) exhibit a 
 general similarity to those of the coffee-berry. In the fresh leaf we find, 
 in addition to the woody fibre, a large quantity of a substance containing 
 nitrogen, similar to legumine, an astringent acid similar to tannic acid, a 
 small quantity of caffeine, and some mineral constituents. 
 
 The aroma of tea does not belong to the fresh leaf, but is produced, like 
 that of coffee, during the process of drying by heat, which developes a 
 small quantity of a peculiar volatile oil, having powerful stimulating pro- 
 perties. The freshly-dried leaf is comparatively so rich in this oil 
 that it is not deemed advisable to use it until it has been kept for some 
 time. 
 
 Green and black tea are the produce of the same plant, the difference 
 being caused by the mode of preparation. For green tea the leaves are 
 dried over a fire as soon as they are gathered, whilst those intended for 
 black tea are allowed to remain exposed to the air in heaps for several 
 hours, and are then rolled with the hands and partially dried over a fire, 
 these processes being repeated three or four times to develope the desired 
 flavour. The black colour appears to be due to the action of the air upon 
 the tannin present in the leaf. 
 
 Boiling water extracts about 30 parts of soluble matter from 100 of 
 black tea, and 36 from 100 of green tea. The principal constituents of 
 the infusion of tea are tannin, aromatic oil, of which green tea contains 
 about 0'8 and black tea 0*6 per cent., and caffeine, the proportion of 
 which, in the dried leaf, varies from 2 '2 to 4'1 per cent., being present in 
 larger quantity in green tea. 
 
 The spent leaves contain the greater part of the legumine, and a con- 
 siderable quantity of caffeine, which may be extracted by boiling them 
 with water, and treating the decoction as above recommended in the case 
 of coffee. 
 
 If tea be boiled with water, the solution precipitated with tribasic 
 acetate of lead, the filtered liquid evaporated to dryness, and the residue 
 cautiously heated, the caffeine sublimes in beautiful crystals. 
 
 Cocoa and chocolate are prepared from the cacao-nut, which is the 
 seed of Theobroma Cacao, and is characterised by the presence of more 
 than half of its weight (minus the husk) of a fatty substance known as 
 cacao-butter, and consisting of oleine and stearine, which does not become 
 rancid like the natural fats generally. The cacao-nut also contains a 
 large quantity of starch, a nitrogenised substance resembling gluten, to- 
 gether with gum, sugar, and theobromine, a feeble base very similar to 
 caffeine, but having the composition C 14 H 8 isT 4 4 . 
 
 The seeds are allowed to ferment in heaps for a short time, which im- 
 proves their flavour, dried in the sun and roasted like coffee, which de- 
 velopes the peculiar aroma of cocoa. The roasted beans having been 
 crushed and winnowed to separate the husks, are ground in warm mills, 
 in which the fatty matter melts and unites with the ground beans to a 
 paste, which is mixed with sugar and pressed into moulds. In the pre- 
 paration of chocolate, vanilla and spices are also added. 
 
 From the composition of cocoa and chocolate it is seen that when con- 
 sumed, as is usual, in the form of a paste, they would prove far more 
 nutritious than mere infusions of tea and coffee. 
 
TOBACCO. 599 
 
 Caffeine appears to be a methylated derivative from theobromine, for when it is 
 boiled with potash, methylamine is evolved, and by acting with iodide of methyle 
 (C 2 H 3 I) upon a silver-compound obtained from theobromine, C 14 (H 7 Ag)N 4 4 , the 
 silver and methyle change places, yielding Agl and caffeine, C 14 H r (C 2 H 3 )N 4 4 , or 
 methyle-theobromine. 
 
 435. The vegetable alkali strychnine (C 42 H 22 N 2 4 ), only too well known 
 for its activity as a poison, is contained in crow-fig or Nux-vomica, the 
 seed of the poison-nut tree of the East Indies, and in several other plants 
 of the same family. The strychnine appears to be combined, in the nux- 
 vomica, with lactic acid, and is accompanied by a second alkaloid, brucine 
 (C 46 H 26 N 2 8 ). In order to extract it, the bruised seeds are boiled with 
 water acidulated with hydrochloric acid, the solution is strained, and ren- 
 dered alkaline by adding hydrate of lime, which displaces the strychnine 
 and brucine from their combination with the acid, and separates them in 
 the form of a precipitate. When this is boiled with alcohol, the excess of 
 lime remains undissolved, whilst the strychnine and brucine are carried 
 into solution ; and since the former is less soluble in alcohol than the 
 latter, it is deposited, before the brucine, on evaporating the liquid, in the 
 form either of octahedral or prismatic crystals, which have an intensely 
 bitter taste. This remarkable bitterness is one of the most prominent 
 characters of strychnine; for although 7000 parts of water are required to 
 dissolve one part of this alkaloid, the solution possesses an intolerably 
 bitter flavour, even when further diluted with 100 times its weight of 
 water. Chloroform and benzole both dissolve strychnine with great ease; 
 and since these liquids refuse to mix with water, they are often employed 
 to extract the poison from a large bulk of aqueous liquid by agitating it 
 with a small quantity of one of them, which is then separated from the 
 water and evaporated, in order to obtain the strychnine in the solid form. 
 Very minute quantities may then be identified by moistening with strong 
 sulphuric acid, and adding a minute quantity of chromate of potash, when 
 the chromic acid acts upon the strychnine, giving rise to products of oxida- 
 tion, which pervade the liquid in the form of beautiful purple streaks. 
 
 Curarine, C 20 H 15 N, is a crystalline alkaloid which has been extracted 
 from the woorari or curara poison employed by the American Indians for 
 poisoning arrows. It dissolves easily in water and alcohol, but not in 
 ether. Strong sulphuric acid gives it a fine blue colour. 
 
 436. TOBACCO owes its active character chiefly to the presence of a vege- 
 table alkali which is not found in any other plant than the Nicotiana 
 tabacum, from the leaf of which the various forms of tobacco are manu- 
 factured. This alkali, nicotine (C 10 H 7 N), is distinguished from most 
 others by the absence of oxygen, and by its liquid condition at th ordi- 
 nary temperature. 
 
 In order to extract the nicotine from tobacco, the leaves are boiled with 
 water, which dissolves the alkaloid, in combination with malic and citric 
 acids. The liquid, having been strained, is evaporated to a syrup and 
 mixed with alcohol, when it separates into two layers, of which the 
 upper contains the salts of nicotine dissolved in alcohol, the lower aqueous 
 layer retaining the greater part of the extraneous vegetable matters. The 
 alcoholic layer having been drawn off, is next shaken with potash, to 
 combine with the acids, and with ether to dissolve the nicotine then set 
 free. On decanting the ethereal solution of nicotine which rises to the 
 surface, and evaporating the ether, the nicotine is left in the form of an 
 oily liquid, which is colourless when perfectly pure, but soon acquires a 
 
600 COLOURING MATTER OF PLANTS. 
 
 dark brown colour when exposed to the air. It is very readily distin- 
 guished by its very pungent, irritating odour, recalling that of tobacco, 
 and which is very perceptible at the common temperature, although the 
 boiling point of nicotine is so high as 480 F. Water, alcohol, and ether 
 dissolve nicotine with facility. The poisonous action of this alkaloid upon 
 animals is very powerful, death almost immediately following its adminis- 
 tration. The Virginia tobacco contains more nicotine than other varieties, 
 the alkaloid amounting to nearly 7 per cent, of the weight of the leaf 
 dried at 212 JF., whilst the Maryland and Havannah varieties contain 
 only 2 or 3 per cent, of nicotine. Tobacco is remarkable for the very 
 large amount of ash which it leaves when burnt, amounting to about one- 
 fifth of the weight of the dried leaf, and containing about one-third of car- 
 bonate of potash, resulting from the decomposition of the malate, citrate, 
 and nitrate of potash during the combustion. The presence of this latter 
 salt in large quantity (3 or 4 parts in 100 of the dried leaf) distinguishes 
 tobacco from most other plants, and accounts for the peculiar smouldering 
 combustion of the dried leaves. 
 
 Cigars are made directly from the tobacco leaves, which are only mois- 
 tened with a weak solution of salt in order to impart the requisite sup- 
 pleness; but snuff, after being thus moistened, is subjected, in large 
 heaps, to a fermentation extending over eighteen or twenty months, which 
 results in its becoming alkaline from the development of carbonate of 
 ammonia (by the putrefaction of the vegetable albumen in the leaf) and 
 of a minute quantity of free nicotine, which imparts the peculiar pungency 
 to this form of tobacco. The aroma of the snuff appears to be due to 
 the production of a peculiar volatile oil during the fermentation. The 
 proportion of nicotine in snuff is only about two per cent., being one-third 
 of that found in the unfermented tobacco; and a great part of this exists 
 in the snuff in combination with acetic acid, which is also a result of the 
 fermentation. It is also not improbable that a little acetic ether is pro- 
 duced, and perhaps some other acids and ethers of the acetic series (e.g., 
 butyric and valerianic), of which extremely minute quantities would give 
 rise to great differences in the aroma of the snuff. 
 
 VEGETABLE COLOURING MATTERS. 
 
 437. Notwithstanding the great variety and beauty of the tints exhi- 
 bited by plants, comparatively few yield colouring matters which are 
 sufficiently permanent to be employed in the arts, the greater number of 
 them fading rapidly as soon as the plant dies, since they are unable to 
 resist the decomposing action of light, oxygen, and moisture, unless sup- 
 ported by the vital influence in the plant, some of them even fading during 
 the life of the plant, as may be seen in some varieties of the rose, which 
 are only fully coloured in those parts which have been partly obscured. 
 
 The green colouring matter of plants has been termed chlorophyll* and 
 is a resinous substance containing carbon, hydrogen, nitrogen, and oxygen, 
 which has never yet been obtained in so pure a condition that its composi- 
 tion could be accurately determined, since it cannot be crystallised or 
 distilled, and is therefore not amenable to the usual methods by which 
 organic substances are obtained in a pure state. 
 
 When green leaves are boiled with alcohol, the latter acquires a fine 
 green colour, and, when evaporated, deposits the chlorophyll. When the 
 * XXa>/oo?, green ; <f)v\\ov, a leaf. 
 
VEGETABLE DYES. 601 
 
 alcoholic solution of chlorophyll is boiled with alcoholic solution of 
 potash, and hydrochloric acid afterwards added, a yellow precipitate (pTiyl- 
 loxanthine) is obtained, and a fine blue colouring matter (phyllocyanine) 
 remains in solution. The blue matter contains nitrogen, and both are 
 insoluble in water. The autumnal colour of leaves may possibly be due 
 to the disappearance of the phyllocyanine. On immersing green leaves in 
 chlorine they assume an autumnal tint. 
 
 The blue colouring matter contained in many flowers, such as the violet, 
 has been named cyanine. Acids change its blue colour to red, and hence 
 the blue colour is exhibited only by flowers the juice of which is neutral, 
 whilst red flowers yield an acid juice. The colouring matter of grapes 
 and of red wine appears to be identical with cyanine. 
 
 Two yellow colouring matters have been extracted from flowers, and 
 have been named xanthine and xantheine, the latter being soluble in 
 water. 
 
 Saffron is a yellow colouring matter obtained from, the flowers of the 
 Crocus sativus, which are themselves of a blue colour, but have yellow 
 anthers. When these are dried and pressed into cakes, they form the 
 saffron of commerce, which is characterised by its very remarkable and 
 somewhat agreeable odour. The yellow colouring matter is readily dis- 
 solved by water and alcohol, but its chemical composition has not been 
 determined. 
 
 Sajjlower consists of the petals of the Cartliamus tinctorius, a plant 
 cultivated in Egypt. It furnishes a red colouring matter called cartha- 
 mine (C i8 H J6 14 ), which is used in dyeing, although it fades easily when 
 exposed to light. It exhibits the characters of an acid, being dissolved 
 by alkalies and reprecipitated by acids, a circumstance which is taken 
 advantage of in extracting it from the safflower. 
 
 The orange-yellow colouring matter known as annatto is extracted from 
 the seeds of the Bixa Orellana, a native of the West Indies. The colouring 
 principle has been called Irixine, and is dissolved by alkalies, but precipi- 
 tated again by acids. Annatto is used for colouring butter and cheese. 
 
 A valuable yellow colour is obtained from the weld, or Reseda luteola, by 
 boiling the dried leaves with water. This colouring matter is termed 
 luteoline (C 40 H 14 O 6 ), and may be sublimed in yellow needles. 
 
 The woods of various trees, when boiled with water, furnish colouring 
 matters of considerable importance ; thus, the wood of Moms tinctoria, or 
 fustic, a West Indian tree, yields a crystalline yellow colour called mori- 
 tannic acid (C^H^O^), 
 
 Logwood is the wood of the Hcematoxylon Campechianum, which grows 
 at Campeachy, in the Bay of Honduras. Its most important constituent 
 is a yellow colouring matter called licematoxyline, which may be obtained 
 in needle-like crystals having the composition (C 32 H 14 O 12 , 2Aq.) It be- 
 comes intensely red in contact with alkalies and oxygen, from the formation 
 of haematein (C 32 H 12 12 ). Chromate of potash gives an intense black 
 colour with infusion of logwood, which has been used as an ink, but is not 
 permanent. 
 
 Brazil wood, which is employed in the preparation of red ink, contains 
 a colouring matter somewhat resembling that of logwood. 
 
 The well-known Turkey red colour is obtained from madder, the root 
 of the Rubia tinctorwn, imported from the south of France and the 
 Levant. This root does not contain any red colouring matter during the 
 life of the plant, but a yellow substance (rubian, C^H^OJ, from the decom- 
 
602 COLOURING MATTERS PREPARED FROM LICHENS. 
 
 position of which the madder red is obtained. There are several methods 
 in use for obtaining the red colour from madder. If the root be steeped 
 in water for some time, so that some of the nitrogenised constituents begin 
 to undergo decomposition, a peculiar fermentation is excited in the rubian, 
 resulting in its decomposition into several new bodies, the chief of which 
 are a red crystalline colouring matter, alizarine (C 14 H 5 4 . 3Aq.), and an 
 uncrystallisable sugar. The alizarine may be dissolved out either by water 
 or alcohol, and may be obtained in beautiful plates having a golden lustre. 
 
 If the madder root be boiled with water, the rubian is dissolved, and 
 when this solution is boiled with dilute sulphuric acid, the rubian under- 
 goes a decomposition similar to that mentioned above, and the alizarine, 
 being insoluble in the dilute acid, is precipitated. 
 
 Madder, which has been treated with hot sulphuric acid, so as to decom- 
 pose the rubian, is used in print-works under the name of garancine, and 
 yields a red solution containing alizarine when boiled with water. 
 
 Turmeric is the root of an East Indian plant, the Curcuma longa; its 
 colouring matter, called curcumine, is nearly insoluble in water, but dis- 
 solves in alcohol. Its yellow colour is changed to brown by alkalies, 
 which leads to its use in the laboratory as a test of alkalinity. 
 
 438. Litmus, archil, and cudbear are brilliant, though not very per- 
 manent purple and violet colours, prepared from various lichens, such as 
 Roccella tinctoria (litmus), and Lecanora tartar ea (cudbear*). 
 
 Archil and cudbear owe their colour chiefly to the presence of orceine 
 (C 14 H 7 N0 6 ), which does not exist ready formed in any of the lichens, but 
 is developed during the preparation which they undergo. 
 
 If either of the above lichens be digested for some hours with lime and 
 water,' and the filtered solution be neutralised with hydrochloric acid, a 
 white gelatinous precipitate is obtained, which dissolves in hot alcohol, 
 and is deposited in crystals on cooling. This substance m&j consist, 
 according to the particular lichen employed, of one or more acids, the chief 
 of which have been named erythric (C 32 H 16 16 ), evernic (HO . C 34 H 15 X J, 
 and lecanoric (C 32 H 14 14 ) acids. These acids are remarkable for the facility 
 with which they furnish compound ethers when boiled with alcohol. 
 
 When either of these acids is boiled with an excess of lime or baryta, it 
 is decomposed, and if the excess of base be removed by carbonic acid, the 
 filtered liquid evaporated to a syrup, and extracted with boiling alcohol, 
 the latter deposits prismatic crystals of orci?ie (C U H 8 4 . 2Aq.) The 
 formation of this body will be understood from the following equations 
 
 CJXA, + 4CaO = 4(CaO.C0 2 ) * 2(C U H 8 O 4 ) . 
 
 Ei-ythric acid. Orcine. 
 
 0^0,4 4- 2(CaO.HO) = 2(CaO . C0 2 ) + C 18 H 10 O 8 + C 14 H 8 O 4 . 
 
 Evernic acid. ^Idd?* Orcine ' 
 
 Pure oreine is a colourless substance, but when exposed to the joint action 
 of ammonia and air, it is converted into a beautiful red colouring matter, 
 orceine 
 
 C 14 H 8 4 + NH 3 + 6 - C ]4 H 7 N0 6 + 4HO . 
 
 Orcine. Orceine. 
 
 Orceine does not crystallise, and dissolves to a slight extent only in water, 
 * Said to have been named after Cuthbert, a manufacturer of the dye. 
 
BLUE AND WHITE INDIGO. 603 
 
 but readily in alcohol and in alkaline liquids, yielding, in the latter case, 
 a beautiful purple solution, which becomes red when mixed with acids, and 
 deposits red flakes of orceine. 
 
 The chemistry of the processes by which archil and cudbear are pre- 
 pared will now be easily understood. The powdered lichen is mixed with 
 urine (to furnish ammonia) and lime, and exposed to the air for some 
 weeks, when the lime decomposes the erythric and other acids, with forma- 
 tion of orcine, which then passes into orceine under the influence of the 
 ammonia and atmospheric oxygen. 
 
 The preparation of litmus from the Roccella tinctoria is similar to that 
 just described, but a mixture of carbonate of ammonia and carbonate of 
 potash is employed instead of the urine and lime. The chemical change 
 which takes place, although similar in principle, is not precisely identical 
 with the foregoing, for the principal colouring matter developed appears 
 to be a red substance called azolitmine (GjULjSQ^ which difiers from 
 orceine by its insolubility in alcohol. It dissolves in alkaline solutions 
 with a beautiful blue colour, which is immediately reddened by acids, a 
 property frequently turned to account by the chemist for detecting the 
 acid reaction. Litmus occurs in commerce in small cakes, which are made 
 up with chalk. 
 
 Erythrite (C 8 H I0 8 ) is a crystalline substance extracted from various 
 lichens and fungi, which forms combinations with the fatty acids similar 
 to those formed by glycerine. It is sometimes represented as a tetratomic 
 alcohol (p. 562), (C 8 H 6 ) iv H 4 . 8 . 
 
 439. Indigo blue (C 16 H 5 ]Sr0 2 ) is prepared from various species of Indigo- 
 fera, grown in China, India, and America. The plants are covered with 
 cold water and allowed to ferment ; as soon as a blue scum appears upon 
 the surface, a little lime is added and the mixture stirred briskly for some 
 time, when the indigo is deposited in a pulverulent form it is collected 
 on calico strainers, pressed, and cut up into cakes. 
 
 The theory of the process is not yet clearly explained ; it is certain that 
 the indigo blue does not pre-exist in the plant, but is a product of the 
 fermentation. Recent observations have shown that the indigo plants 
 probably contain a substance called indican (C 32 H 33 N(X 6 ), which stands 
 in a similar relation to indigo blue to that in which rubian stands to 
 alizarine (in the case of madder) ; it is soluble in water, and when heated 
 with an acid, splits up into indigo blue, indigo red, and a peculiar un- 
 crystallisable sugar. The indigo red may be extracted from commercial 
 indigo by boiling with alcohol, in which the indigo blue is insoluble. 
 Since indigo blue is insoluble in all ordinary solvents, it is necessary, in 
 order to use it for dyeing, to reduce it to the condition of white indigo, 
 which is soluble in alkalies. 
 
 If 2 parts of protosulphate of iron (copperas) be dissolved in 200 parts of 
 water, and well shaken in a stoppered bottle with 1 part of powdered 
 indigo and 3 of slaked lime, the indigo will disappear, and on allowing 
 the precipitate to subside, a yellow fluid will be obtained, which becomes 
 blue at the surface as soon as it is exposed to air. If this solution be 
 mixed with hydrochloric acid, out of contact with air, a flocculent precipi- 
 tate of white indigo is obtained. The composition of this substance is 
 C 16 H 6 NO 2 , and it is formed from blue indigo (C 16 H 5 NO 2 ) by the addition of 
 an atom of hydrogen derived from water, the oxygen of which has com- 
 bined with the protoxide of iron ;. _one portion of the lime combines with 
 
604 DYEING AND CALICO-FEINTING. 
 
 the sulphuric acid of the sulphate of iron, whilst another serves to dissolve 
 the white indigo, which is soluble in alkaline liquids 
 
 FeO.S0 3 + CaO.HO = FeO.HO + CaO.S0 3 . 
 2(FeO.HO) + HO + C 18 H B NO f = Fe 2 3 .2HO + C 16 H G N0 2 . 
 
 Blue indigo. White indigo. 
 
 The solution of white indigo prepared by this process is employed for 
 dyeing linen and cotton, which are immersed in the vat, and then exposed 
 to the air, the oxygen of which removes an atom of hydrogen from the white 
 indigo, and the blue indigo thus formed is precipitated upon the fibre. 
 
 Other reducing agents are sometimes substituted for the protosulphate 
 of iron. Even decaying vegetable matter effects the conversion of blue 
 into white indigo in an alkaline liquid. Thus, for some purposes, the 
 vat is prepared by fermenting a mixture of indigo, madder, carbonate 
 of potash, and lime, when the hydrogen extricated in the fermentation of 
 the vegetable matter converts the blue into white indigo, which is then 
 dissolved by the potash liberated from the carbonate by the lime. 
 
 When cloth is dyed with indigo (Saxony blue) the colour is dissolved 
 by means of sulphuric acid. Fuming sulphuric acid dissolves indigo blue 
 very readily, but oil of vitriol does not act quite so well. The solution 
 thus obtained is commonly called sulphindigotic acid, but it really contains 
 two acids, the sulphindylic (HO . C 16 H 4 NO . 2S0 3 ) and hyposulpldndigotic. 
 
 On heating indigo, it evolves purple vapours, which condense in pris- 
 matic crystals of a coppery lustre, consisting of pure indigotine or indigo 
 blue (C 16 H 5 N~0. 2 ), which may be obtained in larger quantity by digesting 
 indigo with grape-sugar, caustic soda, and weak alcohol, when a solution 
 of white indigo is obtained which deposits the crystallised indigotine on 
 exposure to air. 
 
 440. Animal colouring matters. From the animal kingdom only two 
 colouring matters of any great importance are derived, viz., cochineal and 
 lac, both which are obtained from insects of the coccus tribe. The colour- 
 ing matter of cochineal is known as carmine, and may be extracted from 
 the insects by water or alcohol. It has acid properties, and has been 
 named carminic acid (C.JH.^O^). Carmine-lake is a combination of this 
 acid with alumina, precipitated when a solution of alum and an alkaline 
 carbonate are added to one of cochineal. 
 
 DYEING AND CALICO-PRINTING. 
 
 441. The object of the dyer being to fix certain colouring matters per- 
 manently in the fabric, his processes would be expected to vary with the 
 nature of the latter and of the colour to be applied to it. In order that 
 uniformity of colour and its perfect penetration into the fibre may be 
 attained, it is evident that the colouring matter must always be employed 
 in a state of solution; and it must be rendered fast, or not removable by 
 washing, by assuming an insoluble condition in the fibre. The simplest 
 form of dyeing is that in which the fibre itself forms an insoluble com- 
 pound with the colouring matter. Thus, if a skein of silk be immersed 
 in a solution of indigo in sulphuric acid, it removes the whole of the 
 colouring matter from the liquid, and may then be washed with water 
 without losing colour ; but if the same experiment be tried with cotton, 
 the indigo will not be withdrawn from the solution, and when the cotton 
 
USE OF MORDANTS. 605 
 
 has been well squeezed and rinsed with water, it will become white again. 
 It may be stated generally, that the animal fabrics (silk and wool) will 
 absorb and retain colouring matters with much greater facility than 
 vegetable fabrics (cotton and linen). In the absence of so powerful an 
 attraction between the fibre and the colouring matter, it is usual to impreg- 
 nate the fabric with a mordant or substance having an attraction for the 
 colour, and capable of forming an insoluble combination with it, so as to 
 retain it permanently attached to the fabric. Thus, if a piece of cotton 
 be 1 boiled in a solution of acetate of alumina, the alumina will be precipi- 
 tated in the fibre ; and if the cotton be then soaked in solution of 
 cochineal or of logwood, the red colouring matter will form an insoluble 
 compound (or lake) with the alumina, and the cotton will be dyed of a 
 fast red colour. 
 
 Another method of fixing the colour in the fabric consists in impregnat- 
 ing the latter with two or more liquids in succession, by the admixture 
 of which the colour may be produced in an insoluble state. If a piece of 
 any stuff be soaked in solution of perchloride of iron, and afterwards in 
 ferrocyanide of potassium, the Prussian blue which is precipitated in the 
 fibre will impart a fast blue tint. 
 
 An indispensable preliminary step to the dyeing of any fabric is the 
 removal of all natural grease or colouring matter, which is effected by 
 processes varying with the nature of the fibre, and is preceded, in the 
 cases of cotton and woollen materials which are to receive a pattern, by 
 certain operations of shaving and singeing for removing the short hairs 
 from the surface. 
 
 From linen and cotton, the extraneous matters (such as grease and resin) 
 are generally removed by weak solutions of carbonate of potash or of 
 soda, and the fabrics are afterwards bleached by treatment with chloride 
 of lime (p. 145). But since the fibres of silk and wool are much more 
 easily injured by alkalies -and by chlorine, greater care is requisite in 
 cleansing them. Silk is boiled with a solution of white soap to remove 
 the gum, as it is technically termed ; but the natural grease is extracted 
 from wool by soaking at a moderate temperature in a weak bath either of 
 soap or of ammoniacal (putrefied) urine. Both silk and wool are bleached 
 by sulphurous acid (p. 197). 
 
 Among the red dyes the most important are madder, Brazil wood, 
 cochineal, lac, and the colours derived from aniline. 
 
 In dyeing red with madder or Brazil wood, ths linen, cotton, or wool 
 is first mordanted by boiling in a solution containing alum and bitartrate 
 of potash, when it combines with a part of the alumina, and on plunging 
 the stuff into a hot infusion of madder, the colouring matter forms^an in- 
 soluble combination with that earth. 
 
 To dye Turkey-red, the stuff is also mordanted with alum, but has pre- 
 viously to undergo several processes of treatment with oil and with galls, 
 the necessity of which is satisfactorily established in practice, though it is 
 not easy to explain their action. The colour is finally brightened by 
 boiling the stuff with chloride of tin. 
 
 Woollen cloth is dyed scarlet with lac or cochineal, having been first 
 mordanted by boiling in a mixture of bichloride of tin and bitartrate of 
 potash. 
 
 The aniline colours (see p. 456) are employed for dyeing silk and wool, 
 either without any mordant or with the help of albumen. 
 
 Blues are generally dyed with indigo (p. 603), or with Prussian blue ; in 
 
606 PATTERNS IN CALICO-FEINTING. 
 
 the latter case the stuff is steeped successively in solutions of a salt of 
 peroxide of iron and of ferrocyanide of potassium. Aniline blue is also 
 much employed for silk and woollen fabrics. 
 
 The principal yellow dyes are weld, quercitron, fustic, annatto, chrys- 
 aniline, and chromate of lead. For the four first colouring matters 
 aluminous mordants are generally applied. Chromate of lead is produced 
 in the fibre of the stuff, which is soaked for that purpose, first in a solu- 
 tion of acetate or nitrate of lead, and then in chromate of potash. 
 
 Carbazotic acid (p. 461) is also sometimes employed as a yellow dye. 
 
 In dyeing blacks and browns, the stuffs are steeped first in a bath con- 
 taining some form of tannin (p. 590), such as infusion of galls, sumach or 
 catechu, and afterwards in a solution of a salt of iron, different shades 
 being produced by the addition of indigo, of sulphate of copper, &c. 
 
 442. The art of calico-printing differs from that of dyeing, in that the 
 colour is required to be applied only to certain parts of the fabric, so as 
 to produce a pattern or design either of one or of several colours. 
 
 A common method of printing a colourad pattern upon a white ground 
 consists in impressing the pattern by passing the stuff under a roller, to 
 which an appropriate mordant thickened with British gum (p. 486) is ap- 
 plied. The stuff is then dunged, i.e., drawn through a mixture of cow- 
 dung and water, which appears to act by removing the excess of the 
 mordant, and afterwards immersed in the hot dye-bath, when the colour 
 becomes permanently fixed to the mordanted device, but may be removed 
 from the rest of the stuff by washing. 
 
 If the pattern be printed with a solution of acetate of iron, and the 
 stuff immersed in a madder-bath, a lilac or black pattern will be obtained 
 according to the strength of the mordant employed. By using acetate of 
 alumina as a mordant, the madder-bath would give a red pattern. 
 
 A process which is the reverse of this is sometimes employed, the 
 pattern being impressed with a resist, that is, a substance which will pre- 
 vent the stuff from taking the colour in those parts which have been 
 impregnated. with it. For example, if a pattern be printed with thickened 
 tartaric or citric acid, and the stuff be then passed through an aluminous 
 mordant, the pattern will refuse to take up the alumina, and subse- 
 quently, the colour from the dye-bath. Or a pattern may be printed with 
 nitrate of copper, and the stuff passed through a bath of reduced indigo 
 (p. 603), when the nitrate of copper will oxidise the indigo, and by con- 
 verting it into the blue insoluble form, will prevent it from sinking into 
 the fibre on those parts to which the nitrate has been applied, whilst else- 
 where, the fibre, having become impregnated with the white indigo, 
 acquires a fast blue tint when exposed to the air. 
 
 Sometimes the stuff is uniformly dyed, and the colour discharged in 
 order to form the pattern. A white pattern is produced upon a red 
 (madder) or blue (indigo) ground by printing with a thickened acid dis- 
 charge, and passing the stuff through a weak bath of chloride of lime, 
 which removes the colour from those parts only which were impregnated 
 with the acid (p. 145). By adding nitrate of lead to the acid discharge, 
 and finally passing the stuff through solution of chromate of potash, a 
 yellow pattern (chromate of lead) may be obtained upon the madder red 
 ground. 
 
 By applying nitric acid as a discharge, a yellow pattern may be obtained 
 upon an indigo ground (p. 125). 
 
DIFFICULTIES OF ANIMAL CHEMISTRY. 607 
 
 Very brilliant designs are produced by mordanting the stuff in a solu- 
 tion of stannate of potash or soda (p. 388), and immersing it in dilute sul- 
 phuric acid, which precipitates the stannic acid in the fibre. When the 
 thickened colouring matters are printed on in patterns, and exposed to the 
 action of steam, an insoluble compound is formed between the colour and 
 the stannic acid, which usually exhibits a very fine and permanent colour. 
 
 It is evident that by combining the principles of which an outline has 
 just been given, the most varied parti-coloured patterns may be printed. 
 
 ANIMAL CHEMISTRY. 
 
 443. Our acquaintance with the chemistry of the substances composing 
 the bodies of animals is still very limited, although the attention of many 
 accomplished investigators has been directed to this branch of the science. 
 The reasons for this are to be found, firstly, in the susceptibility to change 
 exhibited by animal substances when removed from the influence of life ; 
 and secondly, in the absence, in such substances, of certain physical pro- 
 perties by which we might be enabled to separate them from other bodies 
 with which they are associated, and to verify their purity when obtained 
 in a separate state. Two of the most important of these properties are 
 volatility and the tendency to crystallise. When a substance can suffer 
 distillation without change, it will be remembered that its boiling point 
 affords a criterion of its purity; or if it be capable of crystallising, this 
 may be taken advantage of in separating it from other substances which 
 crystallise more or less easily than itself, and its purity may be ascertained 
 from the absence of crystals of any other form than that belonging to the 
 substance. But the greater number of the components of animal frames can 
 neither be crystallised nor distilled, so that many of the analyses which 
 have been made of such substances differ widely from each other, because 
 the analyst could never be sure of the perfect purity of his material ; and 
 even when concordant results have been obtained as to the percentage 
 composition of the substance, the atomic formula deduced from it has been 
 of so singular and exceptional a character as to cast very strong suspicion 
 upon the purity of the substance. 
 
 Accordingly, the chemical formulae of a great many animal substances 
 are perfectly unintelligible, conveying not the least information as to the 
 position in which the compound stands with respect to other substances, 
 or the changes which it might undergo under given circumstances. 
 
 It has been shown in the previous chapters of this work that we are 
 gradually learning to class all compound bodies under a few typical forms, 
 so that the chemical properties of any substance may in many cases be 
 predicted from its composition as indicating the type to which it belongs. 
 Take, for example, the class of alcohols (C 2B H 2n + 2O 2 ), or of volatile acids 
 (CjjnHunOJ, or of ammonias (XY 3 ), and it will be seen that even those 
 formulae which are apparently the most complex, are perfectly intelligible 
 when referred to their proper type (p. 542). But the extraordinary for- 
 mulae, for example, deduced from the ultimate analysis of 
 
 Albumen, ^yJ 
 
 Caseine, C 288 H 228 N 36 90 S 2 
 
 cannot be referred to any known type, and refuse to be classed with other 
 substances, even if a type were invented expressly for them. 
 
608 PREPARATION OF LACTIC ACID. 
 
 Animal chemistry is for the above reasons in a very backward condition, 
 as compared with vegetable and mineral chemistry, though an observation 
 of the progress of research affords us the consolation, that a steady advance 
 is being made towards a generalisation of the facts which have been dis- 
 covered, especially by analogical reasoning from those two other depart- 
 ments of the science. 
 
 MILK. The chemistry of milk is well adapted to introduce the study 
 of animal chemistry, because that liquid contains representatives of all the 
 substances which make up the animal frame; and it is on this account 
 that it occupies so high a position among articles of food. 
 
 Although, to the unaided eye, milk appears to be a perfectly homo- 
 geneous fluid, the microscope reveals the presence of innumerable globules 
 floating in a transparent liquid, which is thus rendered opaque. If milk 
 be very violently agitated for several hours, masses of an oily fat (butter, 
 p. 582) are separated from it, and leave the liquid transparent. This fat 
 was originally distributed throughout the milk in minute globules enclosed 
 in very thin membranes, which were torn by the violent agitation, and 
 the fatty globules then cohered into larger masses. 
 
 For the preparation of butter, it is usual to allow the milk to stand for 
 some hours, when a layer of cream collects upon the surface, the proportion 
 of which is very variable, but is generally about ^ th of the volume of the 
 milk. This cream contains about 5 per cent, (by weight) of fat, 3 per 
 cent, of caseine, and water. When the cream is churned, the enclosing 
 membranes of the fat globules are broken, and the fat unites into a semi- 
 solid mass of butter, from which the butter-milk containing the caseine 
 may be separated. If this be not done effectually, the caseine which is 
 left in the butter, being a nitrogenised substance, will soon begin to decom- 
 pose, and will induce a decomposition in the butter (p. 582), resulting in 
 the elimination of certain volatile acids, which impart to it a rancid and 
 offensive taste and odour. To prevent this, salt is generally added to 
 butter which has been less carefully prepared, in order to preserve the 
 caseine from decomposition. 
 
 Pure butter is essentially a mixture of margarine and oleine with smaller 
 quantities of other fats, such as butyrine, caprine, and caproine (p. 582). 
 
 Fresh milk is slightly alkaline to test-papers, but after a short time it 
 acquires an acid reaction; and if it be then heated, it coagulates from the 
 separation of the caseine. This spontaneous acidification of milk is caused 
 by the fermentation of the sugar of milk, under the influence of the caseine, 
 which results in the production of lactic acid, according to the equation 
 
 C 12 H 12 12 = 2(HO.C 6 H 5 5 ). 
 
 Sugar of milk. Lactic acid. 
 
 The caseine, being insoluble in the acid fluid, separates in the form of 
 curd. This development of lactic acid is spoken of as the lactic fermenta- 
 tion, and may be excited not only in milk sugar, but in other substances 
 analogous to it. This is taken advantage of in the preparation of lactic 
 acid, for which purpose 8 parts of cane-sugar are dissolved in 50 parts of 
 water, and 1 part of poor cheese with 3 parts of chalk are added to the 
 mixture, which is then allowed to remain for some weeks at about 80 F. 
 The lactic acid formed from the cane-sugar (C 12 H U U ), under the influence 
 of the changing caseine in the cheese, combines with the lime of the chalk, 
 disengaging the carbonic acid, and forming crystals of lactate of lime 
 (CaO . C 6 H 5 5 ). This is dissolved in boiling water, recrystallised in order 
 
CHEESE. 609 
 
 to purify it, and digested with one-third of its weight of sulphuric acid, 
 which converts the lime into sulphate, liberating the lactic acid ; by add- 
 ing alcohol, the whole of the sulphate of lime is precipitated, and the 
 lactic acid is dissolved by the alcohol, which leaves it on evaporation as a 
 colourless, syrupy, very acid liquid, which may be distilled, though with 
 some loss from decomposition, if heated out of contact with air. 
 
 By heating lactic acid to about 270 F. for a considerable length of 
 time, an equivalent of water is expelled from it, and the lactic anhydride 
 (CgJI 5 5 ) is left as a brownish glassy substance, which is reconverted into 
 the hydrated acid by boiling with water. At a temperature of 500 E. 
 lactic acid undergoes a destructive distillation, the most interesting pro- 
 duct of which is a transparent crystalline substance called lactide (C 6 H 4 O 4 ), 
 differing from lactic acid by the elements of two equivalents of water, 
 which it resumes when dissolved in that liquid, being converted into 
 hydrated lactic acid (C 6 H 6 O 6 ). -When lactic acid is heated with hydriodic 
 acid in a sealed tube, it is converted into propionic acid 
 
 HO.C 6 H 5 5 + 2HI = HO.C 6 H 5 3 + 2HO + I 2 . 
 
 Lactic acid. Propionic acid. 
 
 Lactic acid is an important constituent of the animal body, being found 
 in the juice of muscular flesh, in the gastric juice, &c. 
 
 If milk be maintained at a temperature of about 90 F., the fermenta- 
 tion induced by the caseine results in the production of alcohol and car- 
 bonic acid, for although milk-sugar is not fermented like ordinary sugar 
 by contact with yeast, it appears, under the influence of the changing 
 caseine at a favourable temperature, to be converted first into grape-sugar 
 (p. 490), and afterwards into alcohol and carbonic acid. The Tartars pre- 
 pare an intoxicating liquid, which they call koumiss, by the fermentation 
 of milk. 
 
 When an acid is added to milk, the caseine is separated in the form of 
 curd, in consequence of the neutralisation of the soda which retains it 
 dissolved in fresh milk, and this curd carries with it, mechanically, the 
 fat globules of the milk, leaving a clear yellow whey. 
 
 In the preparation of cheese, the milk is coagulated by means of rennet, 
 which is prepared from the lining membrane of a calf's stomach. This is 
 left in contact with the warm milk for some hours, until the coagulation is 
 completed. This action of rennet upon milk has not yet received any satis- 
 factory explanation. The curd is collected and pressed into cheeses, which 
 are allowed to ripen in a cool place, where they are occasionally sprinkled 
 with salt. The peculiar flavour which the cheese thus acquires is due to 
 the decomposition of the fatty matter under the influence of the caseine, 
 giving rise to the production of certain volatile acids, such as butyric, 
 valerianic, and caproic, which have very powerful and characteristic odours. 
 If this ripening be allowed to proceed very far, ammonia is developed by 
 the putrefaction of the caseine, and in some cases the ethers of the above- 
 mentioned acids are produced, at the expense probably of a little sugar of 
 milk left in the cheese, conferring the peculiar aroma perceptible in some 
 varieties of it. 
 
 The different kinds of cheese arc dependent upon the kind of milk 
 used in their preparation, the richer cheeses being, of course, obtained 
 from milk containing a large proportion of cream ; such cheese fuses at a 
 moderate heat, and makes good toasted cheese, whilst that which contains 
 little butter never fuses completely, but dries and shrivels like leather. 
 
 2 Q 
 
610 SUGAR OF MILK. 
 
 Caseine. The pure curd of milk is known as caseine, and consists 
 essentially of carbon, hydrogen, nitrogen, oxygen, and a small proportion 
 (one per cent.) of sulphur. The simplest expression of the result- of the 
 analysis of caseine, in formula, would be C 144 H 114 N 18 45 S, but the anoma- 
 lous complexity of this formula conveys a suspicion that the composition of 
 pure caseine has yet to be fixed. By whatever process it has been purified, 
 hitherto it has always been found to retain saline matters. The com- 
 plexity of its composition accounts for its liability to undergo putrefactive 
 decomposition. 
 
 Coagulated caseine is characterised by the facility with which it is dis- 
 solved by alkaline solutions, such as carbonate of soda, yielding a liquid 
 upon the surface of which, when boiled, an insoluble pellicle forms, exactly 
 similar to that which forms upon the Surface of boiled milk. Coagulated 
 caseine may also be dissolved by acetic or oxalic acid, but the addition of 
 sulphuric or hydrochloric acid reprecipitates it, these acids apparently 
 forming insoluble compounds with caseine. 
 
 If skimmed milk be carefully evaporated to dryness, and the fat extracted 
 from the residue by ether, the caseine is left in the soluble form mixed 
 with milk-sugar, and is capable of dissolving in water or in weak alcohol. 
 
 Caseine appears to possess the properties of a weak acid, since it 
 combines both with the alkalies and alkaline earths, and is even said to 
 be capable of partially neutralising the former. A mixture of cheese and 
 slaked lime is sometimes used as a cement for earthenware, the caseine 
 combining with the lime to form a hard insoluble mass. The curd of 
 milk, washed and dried, is used by calico-printers, under the name of 
 lactarine, for fixing colours. If it be dissolved in weak ammonia, mixed 
 with one of the aniline dyes, printed on calico, and steamed, the 
 ammonia is expelled, and the colour is left behind as an insoluble com- 
 pound with the caseine. 
 
 Caseine, or a substance so closely resembling it as to be easily con- 
 founded with it, is found in peas, beans, and most leguminous seeds. If 
 dried peas be crushed and digested for some time in tepid water, a turbid 
 liquid is obtained, holding starch in suspension. If this be allowed to 
 settle, the clear liquid is an impure aqueous solution of legumi?ie, or vege- 
 table caseine, which constitutes about one-fourth of the weight of the peas. 
 
 This solution is not coagulated by heat, but becomes covered with a 
 pellicle similar to that which forms upon the surface of boiled milk. It 
 is coagulated by acetic acid and by rennet, just as is the case with the 
 caseine of milk. 
 
 Sugar of milk. When whey is evaporated to a small bulk and allowed 
 to cool, it deposits hard white prismatic crystals of sugar of milk, or 
 lactine (C 12 H 12 12 ), which is much less soluble, and therefore less sweet 
 than cane-sugar. 
 
 Like this latter it may be converted into grape-sugar (C 12 H 14 14 ) by 
 taking up the elements of two equivalents of water when boiled with 
 dilute acids. Milk-sugar resembles the other sugars in its capability of 
 combining with some bases, such as the alkalies, alkaline earths, and oxide 
 of lead ; with the latter it forms two insoluble compounds, viz. 
 
 C 24 H ]9 19 , 5PbO and C 24 H 19 19 . lOPbO . 
 
 At about 300 F. the crystals of milk-sugar fuse, and part with five 
 equivalents of water, so that it does not appear improbable that its true 
 formula should be written C, 4 H, 9 19 . 5HO. 
 
BLOOD. 
 
 611 
 
 It will be seen that the characteristic constituents of milk are the 
 caseine and milk-sugar, but the proportions in which these are present 
 vary widely, not only with the animal from which the milk is obtained, 
 but with the food and condition of the animal. A general notion of their 
 relative quantities, however, may be gathered from the following table, 
 exhibiting the results of the analyses made by Boussingault : 
 
 
 Cow. 
 
 Ass. 
 
 Goat. 
 
 Woman. 
 
 Water, . . . 
 
 874 
 
 90-5 
 
 82-0 
 
 88-4 
 
 Butter, . . . 
 
 4-0 
 
 1-4 
 
 4-5 
 
 2-5 
 
 Milk-sugar, ) 
 Soluble salts, ) 
 
 60 
 
 6-4 
 
 4-5 
 
 4-8 
 
 Caseine, j 
 Insoluble salts, J 
 
 3-6 
 
 1-7 
 
 9-0 
 
 3-8 
 
 The soluble salts present in milk include the phosphates of potash and 
 soda, and the chlorides of potassium and sodium, whilst the insoluble 
 salts are the phosphates of lime, magnesia, and oxide of iron. All these 
 salts are in great request for the nourishment of the animal frame. 
 
 The milk supplied to consumers living in towns is subject to consider- 
 able adulteration ; but in most cases this is effected by simply removing 
 the cream and diluting the skimmed milk with water, a fraud which is 
 not easily detected, as might be supposed, by determining the specific 
 gravity of the milk, for since milk is heavier than water (1'032 sp. gr.), 
 and the fatty matter composing cream is lighter than water, a certain 
 quantity of cream might be removed, and water added, without altering 
 the specific gravity of the milk. 
 
 The most satisfactory method of ascertaining the quality of the milk 
 appears to consist in setting it aside for twenty-four hours in a tall narrow 
 tube (lactometer), divided into 100 equal parts, and measuring the pro- 
 portion of cream which separates, this averaging, in pure milk, from eleven 
 to thirteen divisions. By shaking milk with a little potash (to dissolve 
 the membrane which envelopes the fat globules) and ether, the butter may 
 be dissolved in the ether which rises to the surface, and if this be poured 
 off and allowed to evaporate, the weight of the butter may be ascertained. 
 1000 grains of milk should give, at least, 27 or 28 grains of butter. 
 Since, however, the milk of the same cow gives very different quantities 
 of cream at different times, it is difficult to state confidently that adultera- 
 tion has been practised. It is said that certain yellow colouring matters, 
 such as annatto and turmeric, as well as gum, starch, &c., are occasionally 
 employed to confer an appearance of richness upon impoverished milk. 
 
 444. BLOOD. The blood from which the various organs of the body 
 directly receive their nourishment is the most important, as well as the 
 most complex of the animal fluids. Its chemical examination is attended 
 with much difficulty, on account of the rapidity with which it changes 
 after removal from the body of the animal. 
 
 On examining freshly drawn blood under the microscope, it is observed 
 to present some resemblance to milk in its physical constitution, consist- 
 ing of opaque flattened globules floating in a transparent liquid ; the 
 globules, in the case of blood, having a well-marked red colour. 
 
 2 Q 2 
 
612 COMPOSITION OF BLOOD GLOBULES. 
 
 In a few minutes after the blood has been drawn, it begins to assume 
 a gelatinous appearance, and the semi-solid mass thus formed separates 
 into a red solid portion or clot, which continues to shrink for ten or 
 twelve hours, and a clear yellow liquid or serum. It might be supposed 
 that this coagulation is due to the cooling of the blood, but it is found by 
 experiment to take place even more rapidly when the temperature of the 
 blood is raised one or two degrees after it has been drawn ; and on the 
 other hand, if it be artificially cooled, its coagulation is retarded. Indeed, 
 the reason for this remarkable behaviour of the blood is not yet understood. 
 
 If the coagulum or clot of blood be cut into slices, tied In a cloth, and 
 well washed in a stream of water, the latter runs off with a bright red 
 colour, and a tough yellow filamentous substance is left upon the cloth ; 
 this substance is called fibrine, and its presence is the proximate cause of 
 the coagulation of the blood, for if the fresh blood be well whipped with 
 a bundle of twigs or glass rods, the fibrine will adhere to them in yellow 
 strings, and the defibrinated blood will no longer coagulate on standing. 
 If this blood, from which the fibrine has been extracted, be mixed with 
 a large quantity of a saline solution (for example, 8 times its bulk of a 
 saturated solution of sulphate of soda), and allowed to stand, the red 
 globules subside to the bottom of the vessel. 
 
 These globules are minute bags of red fluid, enclosed in a very thin 
 membrane or cell-wall, and if water were mixed with the defibrinated 
 blood, since its specific gravity is lower than that of the fluid in the 
 globules, it would pass through the membrane (by endosmose), and so swell 
 the latter as to break it and disperse the contents through the liquid. 
 
 The red fluid contained in these blood globules consists of an aqueous 
 solution, containing as its principal constituents a substance known as 
 globuline, which very nearly resembles albumen, and the peculiar colour- 
 ing matter of the blood, which is called hcematine. 
 
 Beside these, the globules contain a little fatty matter and certain 
 mineral constituents, especially the iron (which is associated in some 
 unknown form with the colouring matter), the chlorides of sodium and 
 potassium, and the phosphates of potash, soda, lime, and magnesia. 
 
 Though the quantities of these constituents are not invariable, even in 
 the same individual, the following numbers may be taken as representing 
 the average composition of these globules : 
 
 1000 parts of Blood Globules contain 
 
 Water, .... 688-00 Organic substances of } 
 Globuline, . . . 282-22 unknown nature, . J 
 
 Hsematine, . . . 16-75 
 Fat, .... 2-31 
 
 . The mineral substances consist of 
 
 Mineral substances,* . 8'12 
 
 Potassium, . . . 3-328 
 
 Phosphoric acid, . . 1-134 
 
 Sodium, .... 1-052 
 
 Chlorine, . . . 1-686 
 
 Oxygen, .... 0-667 
 
 Phosphate of lime, . . 0-114 
 
 Phosphate of magnesia, . 0-073 
 
 Sulphuric acid, . . 0-066 
 
 Globuline is a substance very similar in its character and composition 
 to albumen ; it is found also in large proportion in the matter composing 
 the crystalline lens of the eye. 
 
 The hcematine or Jmmatosine must be accounted the most important 
 
 * Exclusive of the iron which is associated with the luematiue. 
 
COMPOSITION OF LIQUOR SANGUINIS. 613 
 
 constituent of the blood globules, since it appears to be more intimately 
 connected than any other with the functions discharged by the blood in 
 nutrition and respiration. 
 
 In order to obtain it in the separate state, the blood globules are boiled 
 with alcohol acidulated with sulphuric acid, and the red solution mixed 
 with carbonate of ammonia, which separates the greater part of the globu- 
 line the filtered liquid is evaporated to dryness, and all soluble matters 
 are extracted by successive treatments with water, alcohol, and ether. By 
 again dissolving the brown residue in alcohol containing ammonia, filter- 
 ing, evaporating to dryness, and removing any soluble matter by water, a 
 dark brown substance is obtained, which is supposed to be pure hsematine, 
 though no longer in the soluble state in which it existed in the blood. It 
 is now dissolved only by alkalies or by acidulated alcohol. 
 
 In its chemical composition haematine is remarkable for the presence 
 of iron, associated in a very intimate manner with carbon, hydrogen, 
 nitrogen, and oxygen, so that it cannot be recognised by the ordinary 
 tests. The formula which has been assigned to it is C 44 H 22 lN" 3 6 !Fe, but it 
 is rather doubtful whether it has been analysed in a perfectly pure state. 
 
 The most important chemical property of haematine is its behaviour 
 with oxygen. It is well known that the blood issuing from an artery has 
 a much brighter red colour than that drawn from a vein, and that when 
 the latter is allowed to coagulate, the upper part of the clot, which is in 
 contact with the air, is brighter than the lower part. 
 
 When the dark red blood drawn from a vein is shaken up with air or 
 oxygen, a quantity of the latter is absorbed, and a nearly equal volume of 
 carbonic acid is disengaged, the dark red colour being at the same time 
 changed to the bright red characteristic of arterial blood. The carbonic 
 acid exists already formed in the venous blood, and is given off if the 
 blood is exposed under an exhausted receiver. The condition assumed 
 by the oxygen when absorbed by the blood is not yet clearly understood, 
 but it is generally allowed that the conversion of venous into arterial 
 blood is due to the displacement of carbonic acid by oxygen. 
 
 The liquid in which the blood globules float is an alkaline solution con- 
 taining albumen, fibrine, and saline matters in about the proportions here 
 indicated. 
 
 1000 parts of Liquor Sanguinis contain 
 
 Water, .... 902-90 Organic substances of un- 1 Q. 
 Albumen, . . . 78-84 known nature, . . / 
 
 Fibrine, .... 4-05 
 
 Organic substances of un- 
 
 known nature, 
 Mineral substances, . . 8-55 
 
 Fat, .... 1-72 
 
 The mineral substances consist of 
 
 Sodium, .... 8-341 
 
 Chlorine,. . . . 3-644 
 
 Potassium, . . . 0-323 
 
 Oxygen 0-403 
 
 Phosphoric acid, . . 0-191 
 
 Sulphuric acid, . . 0-115 
 
 Phosphate of lime, . . 0-311 
 
 Phosphate of magnesia, . 0-222 
 
 The alkaline character of this liquid appears to be due to the presence of 
 carbonate and phosphate of soda. 
 
 The albumen present in the serum of blood eauses it to coagulate to a 
 gelatinous mass when heated, this property being the distinctive feature 
 of albumen. This substance may be obtained as a transparent yellow 
 
614 COMPOSITION OF EGGS. 
 
 mass, resembling gum, and dissolving slowly in water, by evaporating 
 either serum of blood or white of egg below 120 If. ; but if the tempera- 
 ture be raised above that point, the albumen is coagulated, and cannot be 
 redissolved in water unless heated with it under pressure. 
 
 Albumen, like caseine, has never been obtained perfectly free from 
 saline matters, particularly the alkaline and earthy phosphates, and much 
 difficulty attends the exact determination of its composition. The simplest 
 formula which can be assigned to it is C 216 H 169 N 27 K8 S 2 . 
 
 It will be remembered that a substance identical with, or very closely 
 resembling, albumen, and known as vegetable albumen, is found in those 
 vegetable juices which are coagulated by heat. 
 
 Fibrine, as existing in blood, differs from all other animal substances 
 by its tendency to spontaneous coagulation. When coagulated it exhibits 
 characters very similar to those of coagulated albumen ; but when sepa- 
 rated from the freshly drawn blood by violent stirring, it forms elastic 
 strings which dry into a yellow horny mass. Fibrine is one of the most 
 important constituents of the animal frame, for all muscular flesh consists 
 of this substance. The gluten found in the seeds of the cerealia bears a 
 very close resemblance to fibriiie, and is often called vegetable fibrine. 
 
 The same formula has been often assigned to fibrine as to albumen, and 
 its complexity would explain its disposition to putrefy when removed 
 from the influence of life. It does not appear quite certain that the 
 fibrine dissolved in the blood is identical in composition with that of 
 muscular fibre. Some analyses have shown that the muscular fibrine con- 
 tains more oxygen than blood-fibrine, and this latter more than albumen, 
 affording some ground for the belief that the blood-fibrine represents the 
 transition state between the albumen of the serum and the muscular flesh 
 into which it is eventually converted. 
 
 Albumen, fibrine, and caseine have been regarded by some chemists 
 as compounds of the same primary substance (proteine) combined with 
 different proportions of sulphur and phosphorus, the proteine being 
 isolated by boiling the albuminous body with potash and precipitating the 
 solution by an acid. The composition usually assigned to this substance 
 is C 36 H 27 N 4 12 ; but since it is neither crystallisable nor capable of conver- 
 sion into vapour, there is no proof of its purity ; and the great use which 
 has been made of this substance by writers on animal chemistry is due to 
 the apparent simplicity which it confers upon the relations existing 
 between the numerous modifications of albumen, fibrine, and caseine, the 
 ultimate formula of which present so high a degree of complexity. 
 
 EGGS. The shell of the egg contains about nine-tenths of its weight of 
 carbonate of lime, associated with animal matter. The white of egg con- 
 sists of albumen (about 12 per cent.), water (about 86 per cent.), and 
 small quantities of soluble salts. It is alkaline, from the presence of a 
 little soda. Raw white of egg has no smell of sulphuretted hydrogen, 
 and does not blacken silver ; but after boiling, both these properties are 
 manifested, showing that it suffers some decomposition during coagulation. 
 
 Yolk of egg contains a modification of albumen termed vitelline, and 
 owes its colour to a yellow oil which may be extracted with ether, and 
 contains phosphoric acid. The yolk of hens' eggs has about half the 
 weight of the white, and commonly contains about half its weight of 
 water, 16 per cent, of vitelline, 30 per cent, of fat, and 1-5 per cent, of 
 saline matters. 
 
JUICE OF FLESH KREATINE. 615 
 
 445. FLESH. The fibrine composing muscular flesh contains about 
 three-fourths of its weight of water, a part of which is due to the blood 
 contained in the vessels traversing it, and another part to the juice of flesh, 
 which may be squeezed out of the chopped flesh. In this juice of flesh 
 there are certain substances which appear to play a very important part in 
 nutrition. The liquid is distinctly acid, which is remarkable when the 
 alkaline character of the blood is considered, and contains phosphoric, 
 lactic, and butyric acid, together with kreatine, inosite, and saline matters. 
 By soaking minced flesh in cold water and well squeezing it in a cloth, a 
 red fluid is obtained containing the juice of flesh mixed with a little 
 blood. When the liquid is gently heated, the albumen of the blood and 
 of the juice is coagulated in flakes stained with the colouring matter ; 
 the liquid filtered from these may be mixed with baryta water to precipi- 
 tate the phosphoric acid ; and after a second nitration, evaporated to a 
 syrupy consistence and set aside, when beautiful colourless prismatic 
 crystals are obtained, consisting of a feeble organic base called kreatine* 
 the composition of which is represented by the formula C 8 H 9 N 3 4 . 2 Aq. 
 
 The quantity of this substance obtained from the flesh of different 
 animals varies very considerably, that of fowls having been found hitherto 
 most productive, and next that of fish. 1000 parts of the flesh of fowl 
 furnished 3 '2 parts of kreatine, 1000 parts of cod, 1*71 of kreatine, and 
 1000 of beef, 0*70 parts. Human flesh is said to contain a large proportion 
 of kreatine. 
 
 When boiled with acids, kreatine loses the elements of water, and is 
 converted into a powerful base called kreatinine (C 8 H 7 ]S" 3 2 ), which is also 
 found in minute proportion, accompanied by kreatine, in the urine. 
 
 Boiled with alkalies, kreatine gains the elements of water, and furnishes 
 two organic bases, urea (also found in urine), and sar cosine (crdpg, flesh). 
 
 C 8 H 9 N 3 4 + 2HO = C 2 H 4 N 2 2 + C 6 H 7 N0 4 . 
 
 Kreatine. Urea. Sarcosina 
 
 From the concentrated flesh-extract which has deposited the kreatine, 
 there may be obtained, by careful treatment, crystals of a sweet substance 
 called inosite or sugar offlesh, and having the composition C 12 H 12 12 . 4Aq. 
 At a temperature below 212 F. it loses two equivalents of water, and has 
 then the same composition as dry grape-sugar, C 12 H 14 14 , with which, 
 however, it is certainly not identical. 
 
 Inosite has been obtained in very minute proportion from flesh, but 
 unripe beans are said to yield as much as 0*75 per cent, of this interesting 
 sugar. 
 
 The saline constituents of the juice of flesh are chiefly phosphates of 
 potash, magnesia, and lime, with a little chloride of sodium. 
 
 It is worthy of notice that potash is the predominant alkali in the 
 juice of flesh, whilst soda predominates in the blood, especially in the 
 serum. 
 
 According to Liebig, the acidity of the juice of flesh is chiefly due to 
 the acid phosphate of potash, KO . 2HO . P0 5 , whilst the alkalinity of 
 the blood is caused by the phosphate of soda, 2NaO . HO . P0 5 ; and it 
 lias been suggested that the electric currents which have been traced in 
 the muscular fibres are due to the mutual action between the acid juice of 
 flesh and the alkaline blood, separated only by thin membranes from each 
 other, and from the substance of the muscles and nerves. 
 
 * From Kpe'os, Jleah. 
 
616 GELATINE CHONDRINE. 
 
 The average composition of flesh, may be represented as follows : 
 
 Water 78 
 
 Fibrine, vessels, nerves, cells, 1 ., 
 
 &c., .... | 17 
 
 Albumen, .... 2-5 
 
 Other constituents of the \ 9 - 
 
 juice of flesh, . . J 
 
 100-0 
 
 Cooking of Meat. A knowledge of the composition of the juice of flesh 
 explains the practice adopted in boiling meat, of immersing it at once in 
 boiling water, instead of placing it in cold water, which is afterwards 
 raised to the boiling point. In the latter case, the water would soak into 
 the meat, and remove the important nutritive matter contained in the 
 juice ; whilst, in the former, the albumen in the external layer of flesh is 
 at once coagulated, and the water is prevented from penetrating to the 
 interior. In making soup, of course, the opposite method should be fol- 
 lowed, the meat being placed in cold water, the temperature of which is 
 gradually raised, so that all the juice of flesh may be extracted, and the 
 muscular fibre and vessels alone left. 
 
 The object to be attained in the preparation of beef-tea, is the extraction 
 of the whole of the soluble matters from the flesh, to effect which the 
 meat should be minced as finely as possible, soaked for a short time in an 
 equal weight of cold water, and slowly raised to the boiling point, at 
 which it is maintained for a few minutes. The liquid strained from the 
 residual fibrine contains all the constituents of the juice except the 
 albumen, which has been coagulated. 
 
 When meat is roasted, the internal portions do not generally attain a 
 sufficiently high temperature to coagulate the albumen of the juice, but 
 the outside is heated far above 212 F. ; so that the meat becomes 
 impregnated to a greater extent with the melted fat, and some of the con- 
 stituents of the juice in this part suffer a change, which gives rise to the 
 peculiar flavour of roast meat. The brown sapid substance thus pro- 
 duced has been called osmazome* but nothing is really known of its true 
 nature. 
 
 In salting meat for the purpose of preserving it, a great deal of the 
 juice of flesh oozes out, and a proportionate loss of nutritive matter is sus- 
 tained. 
 
 446. Gelatine. When portions of meat, containing cartilages (gristle) 
 or tendons, are boiled for some time with water, the liquid so obtained 
 sets to a jelly on cooling. This is due to the presence of gelatine or 
 chondrine, or both substances so nearly resembling each other, that they 
 were long confounded under the name of gelatine. The difference in their 
 origin is that gelatine is obtained by the action of water at a high tem- 
 perature on skin, membrane, and bone,t whilst chondrine is obtained in 
 the same way from the cartilages. In their properties there is very little 
 difference, the most important being that a solution of chondrine is preci- 
 pitated by acetic acid, by alum, and by acetate of lead, which do not pre- 
 cipitate gelatine. 
 
 In composition there is a considerable difference between gelatine and 
 
 * From 0070';, odour; &>/ios, soup. 
 
 t The animal matter of bone appears to be isomeric with gelatine, and is called osseinc. 
 
WOOL SILK. 617 
 
 chondrine, the latter containing considerably more oxygen and less nitro- 
 gen. The simplest formulae which have been assigned to them are 
 
 Gelatine, . . . 
 
 Chondrine, . . . 
 
 but they both contain phosphates of lime and magnesia in a very intimate 
 state of association. 
 
 The characteristic properties of gelatine are the tendency of its solution 
 to gelatinise on cooling, and the formation of an insoluble compound with 
 tannic acid. The latter is the foundation of the art of tanning (p. 591), 
 and the former is turned to account in the preparation of jelly, size, and 
 glue. A solution containing only one per cent, of gelatine will set on 
 cooling, though if it be repeatedly boiled it loses this property. 
 
 Isinglass is a very pure variety of gelatine prepared from the air bladder 
 of fishes, especially of the sturgeon. 
 
 For the manufacture of glue the refuse and parings of hides are gene- 
 rally employed, after being cleansed from the hair and blood by steeping 
 in lime water, and thoroughly exposed to the air for some days, so as to 
 convert the lime into carbonate, and prevent the injurious effect of its 
 alkaline character upon the gelatine. They are then boiled with water 
 till the solution is found to gelatinise firmly on cooling, when it is run 
 off into another vessel, where it is kept warm to allow the impurities to 
 settle down, after which it is allowed to gelatinise in shallow wooden 
 coolers. The jelly is cut up into slices, and dried upon nets hung up in 
 a free current of air. Spring and autumn are usually selected for drying 
 glue, since the summer heat would liquefy it, and frost would, of course, 
 split it, and render it unfit for the market. 
 
 Size is made in a similar manner, but finer skins are employed, and 
 the drying is omitted, the size being used in the gelatinous state. The 
 best size is made from parchment cuttings. 
 
 By the action of acids or alkalies upon gelatine, two crystalline organic 
 bases may be obtained, known by the names of glycocoll, glycocine, or 
 sugar of gelatine (C 4 H 5 N0 4 ), and leucine (C 12 H 13 N0 4 ). 
 
 It will be seen that glycocine is isomeric with nitrous ether (C 4 H 5 0. N0 8 ), 
 and leucine with the (at present unknown) nitrous ether of the caproic 
 series. Leucine has been found in bullock's lungs and in calf's liver. 
 
 A large number of animal substances very nearly resemble gelatine in 
 their composition ; among these are hair, wool, nails, horns, and hoofs. 
 
 Hair contains, in addition to carbon, hydrogen, nitrogen, and oxygen, 
 from 3 to 5 per cent, of sulphur. 
 
 Wool has sometimes to be separated from the cotton in worn-out mixed 
 fabrics. The mixture is plunged into diluted hydrochloric acid, dried at 
 220 F., and submitted to the action of a machine (devil), which removes 
 the cotton, rendered brittle by the action of the acid, in the form of dust, 
 and leaves the wool fibres -untouched. When the object is to save the 
 cotton fibre, the fabric is exposed to high-pressure steam, which has no 
 action upon cotton, but converts the wool into a brown matter easily re- 
 moved by a beating machine, and sold, for manure, as ulmate of am- 
 monia. 
 
 Silk is said to consist of three layers, the outermost consisting of gela- 
 tine, and soluble in water; the next of albumen, soluble in acetic acid on 
 boiling ; and the third of a nitrogenised substance called sericine, which is 
 
618 UKEA. 
 
 insoluble in water and acetic acid. Spider's threads appear to consist of 
 this substance. 
 
 Sponge consists of a similar material, which has been called fibroine. 
 
 447. URINE. The urine of animals is characterised by the presence of 
 certain substances which are only met with in very minute quantities, if 
 at all, in a state of health, in the other fluids of the body. " The most im- 
 portant of these are an organic base called urea, uric acid, and hippuric 
 acid. 
 
 Urea. When human urine is evaporated to about an eighth of its 
 original bulk, and mixed with an equal volume of nitric acid, a semi- 
 solid mass is formed consisting of pearly scales of nitrate of urea 
 (C 2 H 4 N 2 ? . HO . N0 3 ). If these be washed with cold water, afterwards 
 dissolved in boiling water, and treated with carbonate of baryta, the nitric 
 acid combines with the baryta, and the carbonic acid having no tendency 
 to combine with the urea, passes off, leaving the urea in solution 
 
 C 2 H 4 N 2 2 . HO. N0 5 + BaO . C0 2 = C 2 H 4 N 2 2 + BaO . NO. + HO + C0 2 . 
 
 Nitrate of urea. Urea, 
 
 After filtering from the excess of carbonate of baryta, the liquid is 
 evaporated on a water-bath, when a mixture of urea and nitrate of baryta 
 is obtained, from which the urea may be extracted by hot alcohol. On 
 evaporating the alcohol, beautiful prismatic crystals of urea are deposited. 
 These crystals, when once separated from the urine in a pure state, may 
 be preserved indefinitely even if dissolved in water; but the urea occur- 
 ring in the urine is very soon decomposed, a putrefactive decomposition 
 being excited by the mucus, a changeable substance somewhat resembling 
 albumen, which collects in feathery clouds in the urine. The change 
 which is thus induced in the urea results in its conversion into carbonate 
 of ammonia 
 
 C 2 H 4 N 2 2 + 4HO = 2(NH 4 . C0 2 ) . 
 
 Urea. Carbonate of ammonia, 
 
 It is in consequence of this change that the urine so soon exhales an 
 ammoniacal odour. In order to effect the same change in pure urea, it 
 is necessary to heat it with water under high pressure. When urea is 
 combined with hydrochloric acid, and the hydrochlorate is heated, it 
 furnishes hydrochlorate of ammonia and cyanuric acid, according to the 
 equation 
 
 3(C 2 H 4 T 2 2 .HC1) == 3(NH 3 .HC1) + 
 
 Hydrochlorate of urea. Cyanuric acid. 
 
 When cyanuric acid is distilled, it yields 3 equivalents of hydrated 
 cyanic acid (HO . C 2 jSTO), and the connexion thus established between 
 urea and the cyanogen series becomes intelligible when we see that this 
 base is isomeric with cyanate of ammonia (NH 3 . HO . C 2 lSrO). In fact, 
 by combining hydrated cyanic acid with ammonia, and evaporating the 
 solution, no cyanate of ammonia, but simply urea, is obtained. 
 
 Upon this has been founded a process for obtaining urea artificially, 
 which has attracted a great deal of attention as one of the earliest examples 
 of the production in the laboratory, of a complex substance formed in the 
 animal body. For the artificial production of urea, 56 parts of well-dried 
 ferrocyaiiide of potassium are intimately mixed with 28 parts of dried 
 binoxide of manganese, and the mixture heated to dull redness in an iron 
 
CONSTITUTION OF UREA. 619 
 
 dish, and stirred until it ceases to smoulder. The oxygen supplied by the 
 binoxide of manganese converts the potassium and part of the cyanogen 
 of the ferrocyanide into cyanate of potash, the remainder of the cyanogen 
 being burnt, and the iron converted into oxide 
 
 - 9 = 2(KO.C 1 NO) + 2C0 2 + N + FeO . 
 
 Cyanate of potash. 
 
 On treating the residue with cold water, the cyanate of potash is dis- 
 solved out, and after the insoluble portion has subsided, the liquid may 
 be poured off, and 41 parts of sulphate of ammonia dissolved in it. Sul- 
 phate of potash and cyanate of ammonia are thus formed 
 
 KO.C.NO + NH 3 .HO.S0 3 = KO.SO 3 + NH 3 .HO.C 2 NO 
 
 and if the solution be evaporated to dryness (on a water-bath) the latter 
 salt is transformed into urea, which may be separated from the sulphate 
 of potash by alcohol, which dissolves the urea only. 
 
 448. The true constitution of urea has been the subject of much discussion among 
 chemists. The circumstance that, under certain conditions, this base assimilates 
 the elements of four equivalents of water and is converted into carbonate of ammonia, 
 has led to the opinion that urea should be classed among the amides (p. 549), when 
 it would be represented as derived from two equivalents of carbonate of ammonia 
 (NH 4 O . C0 2 ) by the loss of four equivalents of water, just as oxamide is derived 
 from oxalate of ammonia 
 
 2(NH 4 O.C0 2 ) - 4HO = C 2 H 4 N 2 O a 
 
 Carbonate of ammonia. Urea. 
 
 2(NH 4 . C 2 3 ) - 4HO = 2(C 2 H 2 N0 2 ) . 
 Oxalate of ammonia. Oxamide. 
 
 The question naturally presents itself, whether the various bases formed by sub- 
 stitution from ammonia (p. 539) would furnish corresponding ureas when acted 
 upon by cyanic acid. This has been actually found to be the case; ethylamine 
 NH 2 (C 4 H 6 ), for example, acting'upon cyanic acid, yields ethyl-urea, which is isomeric 
 with the cyanate of ethylamiue, just as urea is isomeric with cyanate of ammonia. 
 
 NH 2 (C 4 H 5 )HO.C 2 NO = C 2 H 3 (C 4 H 5 )N 2 2 . 
 
 Cyanate of ethylamine. Ethyl-urea. 
 
 It is evident that if urea be derived from a double molecule of ammonia by the 
 substitution of C 2 2 for H 2 , then ethyl-urea will be derived in a similar manner 
 from a double molecule of ethylamine. 
 
 N 2 H 4 (C 4 H 5 ) 3 N 2 H 3 (C 4 H 5 )(C 2 2 )". 
 
 Ethylamine. Ethyl-urea. 
 
 In this case it will be observed that the diatomic group, C 2 2 , is substituted for one 
 atom of the hydrogen, and one atom of its representative, ethyle. 
 
 It will be remembered that the amides can be obtained by the action of ammonia 
 upon the corresponding ethers; thus oxalic ether treated with ammonia gives oxamide, 
 and the conversion may be intelligibly represented thus 
 
 (CO)-) H o (OA)") 
 
 V^4 vy 4/ I Q -t- H > N = H VN 4- S 
 
 Oxalic ether. Ammonia. Oxamide. AlcohoL 
 
 In a similar manner, carbonic ether, when heated in a sealed tube with an 
 alcoholic solution of ammonia, yields urea and alcohol 
 
 HO (0,0,)" 
 
 + H. I IT. = 
 
 i 
 
 r 
 
 Carbonic ether. Ammonia. Urea. Alcohol. 
 
620 URIC OR LITHIC ACID. 
 
 When cyanic ether (C 4 H 5 . C 2 NO) is acted on by ammonia, it yields ethyl-urea, 
 the action being precisely parallel to that of ammonia upon cyanic acid 
 
 HO.C 2 NO + NH 3 = NH 3 .HO.C 2 NO 
 
 Cyanic acid. Urea. 
 
 (C 4 H 5 )O.C 2 NO + NH 3 = NH 3 .(C 4 H 5 )O.C 2 NO. 
 
 Cyanic ether. Ethyl-urea. 
 
 Many other compound ureas of this description have been obtained, in which 
 the hydrogen is partly or entirely replaced by the alcohol-radicals. The relation 
 existing between these and their prototype, urea, will be seen in the following 
 examples : 
 
 Urea, ..... C 2 H 4 N 2 2 
 
 f C 4 H 5) 
 Ethyl-methyl-urea, . . C 2 \ C 2 H 3 I N a O, 
 
 I H 2 J 
 Tetrethyl-urea, . . . C 2 (C 4 H 5 ) 4 N 2 2 
 
 Diphenyl-urea, . . . 
 
 |^ I N 2 2 . 
 
 The supposition that urea is really constituted upon the ammonia type derives 
 some confirmation from the circumstance, that a number of substances have been 
 obtained which bear the same relation to urea as the amides do to ammonia. They 
 are, therefore, sometimes styled ureides, and sometimes compound ureas, in which a 
 negative or acid radical occupies the place of a part of the hydrogen. In illustra- 
 tion of the mode of formation of the bodies of this class, the production of benzureide 
 or benzoyl-urea may be referred to* 
 
 When ammonia acts upon chloride of benzoyle, it yields benzamide and hydro- 
 chloric acid 
 
 C 14 H 5 2 .C1 + NH 3 = C 14 H 5 2 -NH 2 + HC1. 
 
 Chloride of benzoyle. Benzamide. 
 
 If urea be substituted for the ammonia, benzureide and hydrochloric acid are 
 formed 
 
 C 14 H 5 2 .C1 + C 2 H 4 N 2 2 = C ]4 H 6 2 . C 3 H 3 N 2 2 + HC1 . 
 
 Chloride of benzoyle. Urea. Benzureide. 
 
 Both reactions become much more intelligible if urea and its derivatives be allowed 
 to be composed upon the ammonia type 
 
 NH 8 + (C 14 H 5 2 )C1 = NH 2 (C 14 H 5 2 ) + HC1 
 
 Ammonia. Chloride of benzoyle. Benzamide. 
 
 N 2 H 4 (C 2 2 )" + (C 14 H 5 2 )C1 = N 2 H 8 (C U H 5 2 ) (C 2 2 )" + HC1 . 
 Urea. Chloride of benzoyle. 
 
 By similar processes there have been obtained 
 
 Acetyl-urea, .... N 2 H/C 4 H 3 2 )(C 2 2 ) " 
 Butyryl-urea, . . . N 2 H 3 (C 8 H 7 2 ) (C 2 a )", &c. 
 
 449. Uric acid. When human urine is acidified with hydrochloric acid 
 and allowed to stand for some time, it deposits minute hard red grains, 
 consisting of uric acid (C 10 H 4 N 4 6 ) tinged with the urinary colouring 
 matter. In urine the acid is present as urate of soda and urate of ammonia, 
 which are often deposited from urine in slight derangements of the system, 
 when they are present in excess, these salts being very much more soluble 
 in warm water than in cold. Since uric acid and its salts are very common 
 ingredients of calculi, this acid is sometimes called lithic acid (XMos, 
 a stone). 
 
 As the quantity of uric acid in human urine does not exceed 1 grain 
 in 1000, recourse is had to other sources for the preparation of this acid, 
 
ALLOXAN MUREXIDE. G21 
 
 which is now extensively used for the preparation of the murexide 
 employed in calico-printing. 
 
 The excrements of the boa-constrictor and of birds, which consist almost 
 entirely of acid urate of ammonia, and guano, which has been formed 
 by the partial decomposition of the excrements of sea-birds, are excellent 
 sources of uric acid. The separation of the uric acid from acid urate 
 of ammonia is easily effected by dissolving it in solution of potash, filter- 
 ing, and adding hydrochloric acid, when the uric acid, which requires 
 lOjOOO parts of cold water to dissolve it, is precipitated as a white 
 crystalline powder. 
 
 When a solution of potash is saturated with uric acid in the cold, and 
 boiled down out of contact with air, small needle-like crystals are deposited, 
 having the composition 2KO . C 10 H 2 N 4 4 , and if this be dissolved in water, 
 and carbonic acid be passed through the solution, half the potash is re- 
 moved as carbonate, and a granular precipitate of acid urate of potash, 
 KO . HO . C 10 H. 2 N 4 4 , is deposited. Uric acid, therefore, is a bibasic acid, and 
 the formula of the acid itself (C 10 H 4 N 4 O 6 ) should be written 2HO . C 10 H 2 N 4 4 . 
 
 When uric acid is added by degrees to strong nitric acid, it dissolves with 
 effervescence and evolution of heat ; the solution, on cooling, deposits 
 octahedral crystals of a substance called alloxan (C 8 H 2 N 2 O g ), which may 
 be represented as formed by the oxidation of the uric acid according to 
 the following equation 
 
 C 10 H 4 N 4 6 + HO.N0 6 = C 8 H 2 N- 2 8 + 2C0 2 + N 2 . + NH 3 . 
 
 Uric acid. Alloxan. 
 
 Alloxan has the curious property of staining the fingers of a beautiful pink 
 colour, and its solution gives an intense purple colour with sulphate of 
 iron. 
 
 A connexion is established, by means of alloxan, between uric acid 
 and urea, which becomes important, because these two bodies, accompanied 
 by a small quantity of allox-an, are always found together in the urine. 
 Alloxan appears to be the intermediate stage in the conversion of uric 
 acid into urea by oxidation, for if a solution of alloxan be boiled with 
 peroxide of lead (Pb0 2 ) carbonic acid is evolved, and the alloxan is con- 
 verted into urea by oxidation 
 
 C 8 H 2 N 2 8 + 2HO + 4Pb0 2 = C 2 H 4 N 2 2 + 6C0 2 + 4PbO . 
 
 Alloxan. Urea. 
 
 When sulphuretted hydrogen is passed through a solution of alloxan, 
 the liquid is troubled by the separation of sulphur, and deposits prismatic 
 crystals of alloxantine (C 16 H 4 N 4 14 ), which is derived from two equivalents 
 of alloxan by the removal of two equivalents of oxygen 
 
 2C 8 H 2 N 2 8 + 2HS = C 16 H 4 ]Sr 4 O 14 + 2HO + S 2 T 
 
 Alloxan. Alloxantine. 
 
 If 4 grains of alloxantine and 7 grains of crystallised alloxan be dissolved 
 in half an ounce of hot water, and 80 grains of a cold saturated solution 
 of carbonate of ammonia added, the carbonic acid is disengaged with 
 effervescence, and the liquid assumes a brilliant purple colour, depositing 
 as it cools splendid crystals, which have a red colour by transmitted light, 
 and reflect a play of green and gold, like the wing of the sun-beetle. 
 
 This magnificent substance is known as murexide, and appears to be 
 formed according to the following equation 
 
 C 1G HA0 14 4- C S H 2 N 2 8 + 4NH 3 .. C 4 H 12 N 10 1C + GHO . 
 
 Alloxantine. Alloxan. Murexide. 
 
622 HIPPURIC ACID. 
 
 The beautiful colour of murexide has been applied in dyeing and calico- 
 printing, being prepared for that purpose from the uric acid furnished by 
 guano. 
 
 450. Hippuric acid. Another acid peculiar to the urine, and found 
 in very minute quantity in human urine, is hippuric acid (C 18 H 9 ISr0 6 ), so 
 named because it occurs in far larger quantity in the urine of horses (tWos, 
 a horse) and cows, the cow's urine yielding more than 1 per cent, of the 
 acid. It is generally prepared from cow's urine by evaporating it to about 
 an eighth of its bulk, and adding an excess of hydrochloric acid. On 
 standing, long prismatic needles of hippuric acid are deposited. It is 
 remarkable that this acid can be obtained only from the urine of stall-fed 
 cows, or of horses kept at rest, for if the animals are actively exercised, 
 the above treatment educes benzoic acid (C 14 H 6 4 ) in place of hippuric. 
 Again, only the fresh urine yields hippuric acid, for after putrefaction, 
 only benzoic acid can be obtained from it. Conversely, if benzoic acid be 
 administered to an animal, it makes its appearance as hippuric acid in 
 the urine. 
 
 The relation between these two acids becomes evident when hippuric 
 acid is boiled for some time with strong hydrochloric acid ; on cooling, 
 the solution deposits crystals of benzoic acid, and if the liquid separated 
 from these be evaporated, neutralised with ammonia and mixed with 
 alcohol, crystals of glycocoll (p. 617) are obtained 
 
 + 2HO = C 14 H 6 4 + C 4 H 5 N0 4 . 
 
 This result has been confirmed synthetically by acting upon the com- 
 pound resulting from the action of glycocoll on oxide of zinc, with chloride 
 of benzoyle (p. 475), when hippuric acid is reproduced. 
 
 C 4 (H 4 Zn)lSr0 4 + C 14 H 5 2 .C1 = ZnCl + C 18 H 9 N0 6 . 
 
 Zinc-glycocolL Chloride of benzoyle. Hippuric acid. 
 
 Hippuric acid, therefore, may be represented as benzoyle-glycocoll, 
 9A(C U H B ? )N0 4 . A very interesting illustration of the doctrine of 
 substitution is connected with these acids. By acting upon hippuric acid 
 with nitric and sulphuric acids, it is converted into nitro-hippuric acid by 
 the substitution of NO 4 for one equivalent of its hydrogen, and if this 
 acid be boiled with hydrochloric acid, it yields nitrobenzoic acid, just as 
 hippuric yields benzoic acid 
 
 . + 2HO 
 
 Nitro-hippuric acid. Nitro-benzoic acid. Glycocoll. 
 
 In contact with bases, hippuric acid forms salts of the general for- 
 
 En n uH ^ 8 ' S that the acid itself should be writ* 611 as 
 
 T i 
 
 a addition to the organic substances which have been already men- 
 
 d as occurring in the urine (urea, uric acid, mucus, hippuric acid, 
 
 ie), it always contains a large proportion of alkaline and earthy 
 
 alts, especially of chloride of sodium, phosphate and sulphate of potash, 
 
 fl phosphates of lime, magnesia, and ammonia. 
 
FOOD OF PLANTS. 623 
 
 The average composition of human urine may be thus stated 
 
 Water 956-80 
 
 Ur ea, 14-23 
 
 Uric acid, 0-37 
 
 Mucus, ] 0-16 
 
 Hippuric acid, kreatinine, colouring matter, I 
 and unknown organic matters, . J 
 
 Chloride of sodium, 7-22 
 
 Phosphoric acid, 2-12 
 
 Potash, ^.93 
 
 Sulphuric acid, 1-70 
 
 Lime, 0-21 
 
 Magnesia , Q-12 
 
 Soda 0-06 
 
 999-94 
 
 CHEMISTEY OF VEGETATION. 
 
 451. The ultimate elements of plants, that is, the substances with which 
 plants must be supplied in one form or other, to sustain their growth, 
 are carbon, hydrogen, nitrogen, oxygen, sulphur, phosphorus, chlorine, 
 silicon, potassium, sodium, calcium, magnesium, iron, manganese. 
 
 Of these, the carbon, hydrogen, nitrogen, oxygen, sulphur, and phos- 
 phorus are grouped together to form the various organic compounds 
 furnished by plants, the remaining elements being arranged generally in 
 the following forms : 
 
 Chlorides of potassium and sodium, 
 
 Sulphate of lime, 
 
 Silicates of potash and soda, 
 
 Phosphates of iron (manganese?), lime, magnesia, and ammonia, 
 
 Compounds of potash, soda, and lime, with vegetable acids. 
 
 Plants are capable of receiving food either in the form of gas through 
 the instrumentality of their leaves, or in solution by their roots. 
 
 The carbon, which is their most important constituent as regards quantity, 
 is taken up in the form of carbonic acid by both these organs of the 
 plant. This carbonic acid is derived either from the surrounding atmo- 
 sphere or from the decay of the organic matters contained in the soil 
 which surrounds the roots of the plant. 
 
 The hydrogen is derived partly from water and partly from the am- 
 monia which is carried down to the roots of the plant by rain, or is 
 evolved in the putrefaction and decay of the nitrogenised organic matters 
 of the soil. The ammonia also forms one great source of the nitrogen in 
 plants, another being the nitric or nitrous acid, which is either brought 
 down by the rain, or formed within the soil by the nitrification of tin- 
 ammonia (p. 122). As to the oxygen, it is obtained both from tj?e car- 
 bonic acid and water, which contain this element in larger proportion than 
 is ever present in any vegetable product. 
 
 The sulphur and phosphorus contained in the organic parts of the 
 plant appear to be chiefly derived from the sulphates and phosphates of 
 the soil. 
 
 The chlorine, silicon, and the metals, are derived from the mineral con- 
 stituents of the soil. 
 
 It is not difficult to imagine the course of formation of a fertile soil 
 from a primary rock (of granite, for example) under the influence of the 
 atmosphere and rain, exerted through a very long period. 
 
624 ACTION OF MANURES. 
 
 It will be remembered that granite consists essentially of quartz (silica), 
 feldspar (silicate of alumina and potash or soda), and mica (silicates of 
 alumina, iron, potash, and magnesia); in addition to these there may 
 always be found in granite minute quantities of phosphate of lime, of sul- 
 phates, of chlorides, and of manganese. 
 
 By the disintegration of such a rock under the action of air and moisture 
 (p. 286), a soil will be formed containing the various mineral substances 
 required for the food of the plant. If now, upon the thin layer of soil 
 thus formed over the face of the rock, some seeds of the lower orders of 
 plants, the lichens, for instance, be deposited, they will grow and fructify, 
 deriving their carbon, hydrogen, nitrogen, and oxygen from the air and 
 rain, and their mineral constituents from the soil. The death of these 
 lichens would add new elements of fertility to the soil, in the shape of the 
 food which they had condensed from the air, and of the saline ingredients 
 which had been converted within their organisations into forms better 
 suited to sustain the higher orders of plants. Given, then, the seeds of a 
 higher vegetation, a similar process may be supposed to take place, and at 
 length animals would be attracted to the spot by the prospect of vegetable 
 food, and by transporting to it elements which they had derived from 
 other sources, would eventually confer upon it the highest fertility. 
 The soil then coming under tillage, the crops raised upon it are consumed 
 by animals and removed to a distance, so that the mineral food contained 
 in the soil is by degrees exhausted, and unless it is restored the soil be- 
 comes barren. 
 
 To restore its fertility is the object of manuring, which consists in add- 
 ing to the soil some substance which shall itself serve directly as food for 
 the plant, or shall so modify, by chemical action, some material already 
 present in the soil, as to convert it into a state in which the plant may 
 take advantage of it. 
 
 As examples of substances which are added as direct food for plants, 
 may be enumerated 
 
 (1.) The ashes of peat, turf, coal, &c., which furnish the mineral sub- 
 stances originally obtained from the soil by the vegetables from which 
 these materials were formed. 
 
 (2.) Gypsum, or sulphate of lime, and sulphate of magnesia, which ap- 
 pear to be valuable not only as sources of sulphur, calcium, and mag- 
 nesium, but because they are capable of decomposing the carbonate of 
 ammonia, which is either brought down by rain or evolved by putrefaction 
 in the soil, and of converting it into sulphate of ammonia which is re- 
 tained in the soil, whereas the carbonate, being a volatile salt, would be 
 again exhaled into the air and lost to the plants. 
 
 (3.) Phosphate of lime, or bone-ash, which is most commonly con- 
 verted into the soluble superphosphate of lime (p. 223) by treatment with 
 sulphuric acid, before being employed as a manure. 
 
 (4.) Chloride of sodium, or common salt, serves as a source of sodium, 
 for in contact with the carbonate of lime, which is found in all fertile 
 soils, it is partly converted into carbonate of soda, which may in turn be 
 converted into silicate of soda, or any other salt of that alkali necessary 
 to the growth of the plant. 
 
 (5.) Nitrate of soda (Peruvian nitre) is held to be of great service in 
 some cases, as yielding both soda and nitrogen in a form serviceable to the 
 plant. 
 
 (6.) The silicates of potash and soda, which are especially useful to 
 
FALLOWING - ROTATION OF CROPS. 625 
 
 th C ' e rr C nto a considerable proportion of silica 
 their stems; since, although that substance is contained in abundance 
 
 **> - "urse, 
 
 flfcS r JT**S* Pknts ' P lou g hed into a >il, would obviously 
 
 furnish food for other plants by their gradual putrefaction and decay * 
 
 (.) li tones, which furnish carbonic acid and ammonia by the putrefac- 
 
 lime gelatinous matter, as well as a large supply of phosphate of 
 
 (10.) Urine, yielding much carbonate of ammonia by the decomposition 
 ol its urea and uric acid, and an abundance of the phosphates and other 
 saline matters required by the plant. 
 
 (11.) Solid excrements of various animals, containing the insoluble 
 salts (especially phosphates) of the animal's food, as well as easily putres- 
 cible organic matters yielding much ammonia and sulphuretted hydrogen. 
 
 (12.) Guano, the dung of carnivorous sea-birds, which owes its very 
 high value partly to the large proportion of urate of ammonia and other 
 nitrogenised organic substances which it contains, and partly to the pre- 
 sence of phosphates and salts of the alkalies. 
 
 (13.) Soot, which appears to act chiefly by virtue of the salts of 
 ammonia derived from the destructive distillation of the coal. 
 
 The chief substance employed for acting chemically upon the consti- 
 tuents of the soil, so as to render them more serviceable to the plant, is lime, 
 which modifies in a very important manner both the organic and mineral 
 portions of the soil. Its action upon the former consists in promoting its 
 decay, and the conversion of its elements into those forms, viz., carbonic 
 acid, water, ammonia, and nitric acid, in which they may be of service to 
 the plant. Upon the inorganic constituents of the soil lime acts by 
 assisting the decomposition of minerals, particularly of those which con- 
 tain the alkalies (such as feldspar), and thus converting them into soluble 
 forms. 
 
 In some cases fertility is restored to an apparently exhausted soil, with- 
 out the addition of manure, by allowing it to lie fallow for a time, so that, 
 under the influence of the air and moisture, such chemical changes may 
 take place in it as will again replenish it with food available for the crops. 
 It is not even necessary in all cases that the soil should be altogether re- 
 leased from cultivation ; for even though it may refuse to feed any longer 
 one particular crop, it may furmsh an excellent crop of a different 
 description, and, which is more remarkable, it may, after growing two or 
 three different crops, be found to have regained its power of nourishing 
 the very crop for which it was before exhausted. Experience of this Has 
 led to the adoption of the system of rotation of crops, by which a soil is 
 made to yield, for example, a crop of barley, and then successive crops of 
 grass, beans, turnips, and barley again. 
 
 The possibility of this rotation is partly accounted for by the difference 
 in the mineral food removed from the soil by different crops ; thus turnips 
 require much of the alkalies and lime ; wheat, much alkali and silica ; 
 barley, much lime and silica; and clover, much lime, so that the soil 
 which had been exhausted for wheat, because it no longer contained 
 enough soluble silica, might still yield sufficient alkali and lime to a crop 
 of turnips, and when the alkali was exhausted, might furnish enough lime 
 
 '- R 
 
626 GROWTH OF PLANTS. 
 
 to a crop of clover, after which, in consequence of the chemical changes 
 allowed by lapse of time in the soil, more of the original minerals com- 
 posing it might have been decomposed and rendered available for a fresh 
 wheat crop. 
 
 Another explanation of the benefit of systems of rotation may be given 
 in those cases in which the debris of the preceding crop are allowed to 
 remain on the land, Some plants, extending their roots more deeply into 
 the soil, avail themselves of mineral food which is beyond the reach of 
 plants furnished with shorter roots, and when the refuse of the former 
 plants is ploughed into the land, the surface is enriched with the food 
 collected from the sub-soil. 
 
 Our knowledge of the chemical operations taking place in the plant, 
 and resulting in the elaboration of the great variety of vegetable products, 
 is very slight indeed. "We appear to have sufficient evidence that sugar 
 and starch, for example, are constructed in the plant from carbonic acid 
 and water, that gluten results from the mutual action of the same com- 
 pounds, together with ammonia, or nitric acid, and certain sulphates and 
 phosphates, but what the intermediate steps in this conversion may be we 
 are not in a position even to hazard a guess. 
 
 All seeds contain starch, gluten, or some similar nitrogenised substance 
 (legumine, for example), together with mineral matters, these being pro- 
 vided for the nourishment of the young plant until its organs are suffi- 
 ciently developed to enable it to procure its own food from the air or from 
 the soil. 
 
 During the process of germination the seed absorbs oxygen and evolves 
 carbonic acid, and since the albuminous constituent is the most mutable 
 substance present, it is probably this which undergoes oxidation, and 
 excites the conversion of the insoluble starch into soluble sugar. At this 
 stage the seed requires, as is well known, a fair supply of water, the 
 elements of which are required for the conversion of the starch (C 12 H 10 10 ) 
 into sugar (C 12 H 12 1? ) ; water is also required to dissolve the sugar as well 
 as the altered albuminous matter and the mineral salts, in order to form the 
 sap of the embryo plant. These constituents of the sap, directed by the 
 mysterious vital energy in the seed, buildup the root, which extends itself 
 in search of nourishment down into the soil, and the leaves which dis- 
 charge a similar function with respect to the air. As soon as the leaves 
 are developed, the plant becomes able to decompose carbonic acid, water, 
 and ammonia, to provide the organic components of its sap. Some part 
 of these changes at least appears to take place in the leaves of the plant, 
 from which, during the day-time, oxygen (together with a little nitrogen) 
 is continually evolved. The leaves have been compared to the lungs of 
 animals, the functions of which they reciprocate, for whilst, in the lungs 
 of animals, an absorption of oxygen and an evolution of carbonic acid is 
 observed, in the leaves of plants, it is the carbonic acid which is absorbed 
 and oxygen is disengaged. 
 
 In the dark, plants exhale carbonic acid, but in much smaller quantitv 
 than they decompose in the light. 
 
 That oxygen must be evolved, if plants construct their carbonaceous 
 
 apounds from carbonic acid and water, is obvious on reflecting that all 
 Jompounds contain less oxygen, in proportion to their carbon and 
 nyarogen, than is contained in carbonic acid and water. 
 
 us, we may conceive the formation of all the compounds of carbon 
 
RIPENING OF FRUITS. 627 
 
 and hydrogen, or of those elements with oxygen, which are met with in 
 plants, by the concurrence, in various proportions, of carbonic acid and 
 water, and the separation of the whole or a part of their oxygen 
 
 To take an example; cellulose (C 12 H 10 10 ) would result from the coali- 
 tion of 12 eqs. of carbonic acid and 10 eqs. of water, with separation of 
 24= eqs. of oxygen. Again, malic acid, C 8 H 6 10 , would require 8 eqs of 
 carbonic acid and 6 eqs. of water, whilst 12 eqs. of oxygen would be 'set 
 
 It is equally easy to represent the formation of nitrogenised compounds 
 from carbonic acid, water, and ammonia, with separation of oxygen, for 
 the nitrogen in all such compounds is present in so small a number of 
 equivalents, relatively to the carbon and hydrogen, that the amount of 
 oxygen separated from the carbonic acid and water would always far more 
 than suffice to convert the whole of the hydrogen of the ammonia into water, 
 even if this hydrogen did not itself take part in the formation of the 
 compound. Suppose, for instance, that the formation of quinine is to be 
 accounted for 
 
 40C0 3 + 18HO + 2NH 3 C 40 H 24 N 2 O 4 + O 94 . 
 
 Quinine. 
 
 If sulphur be a constituent of the vegetable compound to be formed, 
 it is ^ conceivable that the sulphuric acid derived from the sulphates pre- 
 sent in the soil should co-operate with the carbonic acid, water, and am- 
 monia. 
 
 If the composition of gluten be correctly represented by the formula 
 ^2i6H 169 N 27 68 S 2 , the equation explaining its formation from the above con- 
 stituents of the food of the plant would be written 
 
 216C0 2 + 88HO + 27NH 3 + 2S0 3 = 
 
 The chemical tendency of vegetables, therefore, is to reduce to a lower 
 state of oxidation the substances presented in their food, whilst animals 
 exhibit a reciprocal tendency" to oxidise the materials on which they feed. 
 
 With respect to the last stage in the existence of the plant, the ripening 
 of the fruit, we know a little more concerning the chemical changes which 
 it involves. 
 
 Most fruits, in their unripe condition, contain cellulose, starch, and 
 some one or more vegetable acids, such as malic, citric, tartaric, and 
 tannic, the latter being almost invariably present, and causing the pecu- 
 liar roughness and astringency of the unripe fruit. The characteristic 
 constituent of unripe fruits, however, ispectose, a compound of carbon, 
 hydrogen, and oxygen, the composition of which has not been exactly 
 determined. Pectose is quite insoluble in water, but during the ripening 
 of the fruit it undergoes a change induced by the vegetable acids, and is 
 converted intopectine (C^H^OJ, which is capable of dissolving in water, 
 and yields a viscous solution. As the maturation proceeds, the pectine 
 itself is transformed into pectic acid (C^H^O^), and pectosic acid 
 (CjjHjjOjo), which are soluble in boiling water, yielding solutions which . 
 gelatinise on cooling. It is from the presence of these acids, therefore, 
 that many ripe fruits are so easily convertible into jellies. 
 
 Whilst the fruit remains green, its relation to the atmosphere appears 
 to be the same as that of the leaves, for it absorbs carbonic acid, and 
 evolves oxygen ; but when it fairly begins to ripen, oxygen is absorbed 
 from the air, and carbonic acid is evolved, whilst the starch and cellulose 
 
 2n2 
 
628 PRESERVATION OF WOOD. 
 
 are converted into sugar, under the influence of the vegetable acids (p. 496), 
 and the fruit becomes sweet. It has been already seen that the conver- 
 sion of starch and cellulose (C 12 H 10 10 ) into sugar (C 12 H 12 O 12 ) would simply 
 require the assimilation of the elements of water, so that the absorption of 
 oxygen and evolution of carbonic acid are probably necessary for the con- 
 version of the tannic and other acids into sugar. For example 
 
 C 54 H 22 34 + 2HO + 0^ = 2C 12 H 12 12 + 30 GO, 
 
 Tannic acid. Fruit-sugar. 
 
 3C 8 H 6 12 + 6 = C 12 H 12 12 + 6HO + 12C0 2 . 
 
 Tartaric acid. 
 
 When the sugar has reached the maximum, the ripening is completed ; 
 and if the fruit be kept longer, the oxidation takes the form of ordinary 
 decay. 
 
 The scheme of natural chemistry would not be complete unless provi- 
 sion were made for the restoration of the constituents of plants, after death, 
 to the atmosphere and soil, where they might afford food to new genera- 
 tions of plants. Accordingly, very shortly after the death of a plant, if 
 sufficient moisture be present, the changeable nitrogenised (albuminous) 
 constituents begin to putrefy, and chemical motion being thus excited, is 
 communicated to the other parts of the plant, under the form of decay, so 
 that the plant is slowly consumed by the atmospheric oxygen, its carbon 
 being reconverted into carbonic acid, its hydrogen into water, and its 
 nitrogen into ammonia, these substances being then transported in the 
 atmosphere to living plants which need them, while the mineral consti- 
 tuents of the dead plant are washed into the soil by the rain. 
 
 Moist wood is slowly converted by decay into a brown substance, which 
 has been called humus, and forms the chief part of the organic matter in 
 soils. Alkalies dissolve this substance, and on the addition of an acid 
 to the brown solution, a brown precipitate is obtained, which is said to 
 contain humic, ulmic, and geic acids, but these substances do not crystal- 
 lise, and their existence as definite acids appears to be somewhat doubt- 
 ful. Two other acids of a similar kind, crenic and apocrenic acids 
 (KPJVT), a well), have been obtained from the same source, and are also 
 found occasionally in mineral waters. 
 
 When it is desired to preserve wood from decay, it is impregnated with 
 some substance which shall form an unchangeable compound with the 
 albuminous constituents of the sap. Kreasote (p. 460) and corrosive 
 sublimate (kyanidng) are occasionally used for this purpose, the wood 
 being made to imbibe a diluted solution of the preservative, either by 
 being soaked in it or under pressure. 
 
 In Boucherie's process for preserving wood, the natural ascending force 
 ot the sap is ingeniously turned to account in drawing up the preservative 
 solution. A large incision being made around the lower part of the trunk 
 
 the growing tree, a trough of clay is built up around it, and filled with a 
 weak solution of sulphate of copper, acetate of iron, or chloride of calcium, 
 .liven after the tree has been felled, it may be made to imbibe the pre- 
 erving solution whilst in a horizontal position, by enclosing the base of 
 the trunk in an impermeable bag supplied with the liquid from a reservoir, 
 ine impregnation of the wood with such solutions not only prevents 
 growth f eCay '- rendeiS ** l6SS Hable to the attacks of ^sects and the 
 
CHEMISTRY OF DIGESTION. 629 
 
 NUTRITION OF ANIMALS. 
 
 452 Between the chemistry of vegetable and that of animal life there 
 s this fundamental distinction, that the former is eminently constructive 
 and the latter destructive. The plant, supplied with compounds of the 
 simplest kind carbonic acid, water, and ammonia constructs such com- 
 plex substances as albumen and sugar ; whilst the animal, incapable of 
 deriving sustenance from the simpler compounds, being fed with those of 
 a more complex character, converts them eventually, for the most part 
 into the very materials with which the constructive work of the plant 
 commenced. It is indeed true, that some of the substances deposited in 
 the animal frame, such as fibrine and gelatinous matter, rival in com- 
 plexity many of the products of vegetable life ; but for the elaboration 
 of these substances, the animal must receive food somewhat approach- 
 ing them in chemical composition. It is to this nearer resemblance 
 between the food of animals and the proximate constituents of their 
 frames, that we may partly ascribe the greater extent of our knowledge 
 on the subject of the nutrition of animals, which is, however, far from 
 being complete. 
 
 The ultimate elements contained in the animal body are the same as 
 those of the vegetable, but the proximate constituents are far more 
 numerous and varied. 
 
 The bones, containing the phosphates and carbonates of lime and mag- 
 nesia, together with gelatinous matter, require that the animal should be 
 supplied with food which, like bread, contains abundance of phosphates, 
 as well as the nitrogenised matter (gluten) from which the gelatinous 
 substance may be formed. In milk, the food of the young animal, we 
 have also the necessary phosphates, whilst the caseine affords the supply 
 of nitrogeneous matters. 
 
 Muscular flesh finds, in the gluten of bread and the caseine of milk, the 
 nitrogenised constituent from which its fibrine might be formed with even 
 less transformation than is required for fhe gelatinous matter of bone, 
 since the composition of fibrine, gluten, and caseine is very similar. 
 
 The albumen and fibrine of the blood have also their counterparts in 
 the gluten and caseine of bread and milk, whilst all the salts of the blood 
 may be found in either of these articles of food. 
 
 Bread and milk, therefore, may be taken as excellent representatives 
 of the food necessary for animals, and the same constituents are received 
 in their flesh diet by animals which are purely carnivorous, but in a 
 higher stage of preparation. 
 
 It is natural to suppose that those parts of the frame which contain no 
 nitrogen should be supplied by those constituents of the food which are 
 free from that element, such as the starch in bread and the sugar and fat 
 in milk. 
 
 Before the food can be turned to account for the sustenance of the body, 
 it must undergo digestion, that is, must be either dissolved or otherwise 
 reduced to such a form that it can be absorbed by the blood, which it 
 accompanies into the lungs to undergo the process of respiration, and thus 
 to become fitted to serve for the nutrition of the various organs of the 
 body, since these have to be continually repaired at the expense of the 
 constituents of the blood. 
 
030 COMPOSITION OF BILE. 
 
 The first step towards the digestion of the food is its disintegration, 
 effected by the teeth, with the aid of the saliva, by which it should be 
 reduced to a pulpy mass. The saliva is an alkaline fluid characterised by 
 the presence of a peculiar albuminous substance called ptyaline (TTTVW, to 
 spit), which easily putrefies. The action of saliva in mastication is 
 doubtless in great part a mechanical one, but it is probable that its 
 alkalinity assists the process chemically, by partly emulsifying the fatty 
 portions of the food. The liability of ptyaline to putrefaction -favours the 
 supposition that it may act in some way as a ferment in promoting the 
 digestion. 
 
 This disintegration of the food is of course materially assisted by the 
 cooking to which it has been previously subjected, the hard and fibrous 
 portions having been thereby softened. 
 
 The food now passes to the stomach, in which it remains for some time, 
 at the temperature of the body (98 K), in contact with the gastric juice, 
 the chief chemical agent in the digestive process. 
 
 The gastric juice, which is secreted by the lining membrane of the 
 stomach, is an acid liquid, containing hydrochloric and lactic acids. It is 
 characterised by the presence of a peculiar substance belonging to the 
 albuminous class of bodies, which is called pepsine (TT^TTTW, to digest), and 
 possesses the remarkable power of enabling dilute acids, by its mere 
 presence, to dissolve such substances as fibrine and coagulated albumen, 
 which would resist the action of the acid alone for a great length of 
 time. 
 
 An imitation of the gastric juice may be made by digesting the mucous 
 membrane of the stomach for some hours in warm very dilute hydrochloric 
 acid. The acid liquid thus obtained is capable of dissolving meat, curd, 
 &c., if it be maintained at the temperature of the body. The pepsine 
 prepared from the stomach of the pig and other animals is sometimes 
 administered medicinally in order to assist digestion. 
 
 The principal change which the food suffers by the action of the gastric 
 juice is the conversion of the fibrinous and albuminous constituents into 
 soluble forms ; the starch is also partly converted into dextrine and sugar, 
 but the fatty constituents are unchanged. 
 
 The food which has thus been' partially digested in the stomach is called 
 ^7 physiologists chyme, and passes thence into the commencement of the 
 intestines (the duodenum), where it is subjected to the action of two more 
 chemical agents, the bile and the pancreatic juice. 
 
 Bile consists essentially of a solution of two salts known as glycocholate 
 and taurocholate of soda. Both glycocholic and taurocholic acids are 
 resinous, and do not neutralise the alkali, so that the bile has a strong 
 alkaline character. Another characteristic feature of this secretion is the 
 large proportion of carbon which it contains. Glycocholic acid has the 
 composition HO . C 52 H 42 lSrO n , and contains therefore 67 per cent, of carbon, 
 whilst taurocholic acid, HO . C 52 H 44 13 S 2 , contains 61 per cent. The 
 names of these acids have reference to the circumstance that they furnish 
 respectively glycocoll and taurine, together with two new acids free from 
 nitrogen, when they are boiled with dilute hydrochloric acid 
 
 HO.C 52 H 42 NO U + HO = CJB^O. + C 4 H 5 N0 4 
 
 Glycoeholic acid. Choloidic acid. Glycocoll. 
 
 HO.C 62 H 44 N0 13 S 2 + 2HO . C 4 H 7 KO fi S 2 ., 
 
 Taurocholic acid. Taurine . ' Cholic acid! 
 
CHEMISTliY OF NUTRITION. G31 
 
 Taurine forms colourless crystals of great beauty, and is remarkable for 
 the large proportion (above 25 per cent.) of sulphur which it contains It 
 also presents an interesting example of a complex animal derivative 
 which may be artificially prepared in. a very simple manner. 
 
 When defiant gas is passed over anhydrous sulphuric acid, it is absorbed, 
 1 the product be dissolved in water, neutralised with ammonia and 
 evaporated, crystals of isethionate of ammonia are obtained 
 C 4 H 4 f 2S0 3 + NH 3 + 2HO NH 3 . HO . C 4 H 5 S 2 O 7 . 
 
 Isethionate of ammonia. 
 
 When this salt is moderately heated, it loses two equivalents of water 
 and leaves taurine 
 
 NH 3 .HO.C 4 H 5 S 2 7 2HO . C 4 H 7 N0 6 S a . 
 
 Isethionate of ammonia. Taurine. 
 
 Another characteristic ingredient of the bile is cholesterine* (C^H^OJ, 
 a crystalline substance somewhat resembling the fate, and often deposited 
 in large quantity in the form of biliary calculi. It has also been found 
 in peas, wheat, and some vegetable oils. 
 
 The peculiar colouring matter of the bile has never been obtained in a 
 pure state. 
 
 A peculiar substance called glycogen, or animal starch (C 12 H 10 10 ), has 
 been found in the liver, and becomes speedily converted into sugar after 
 death, by assimilating the elements of water. 
 
 The special function of the bile in the digestion of the food has not 
 been explained, but from its strongly alkaline reaction it does not appear 
 improbable that it assists in the digestion of fatty substances. 
 
 The pancreatic juice is another alkaline secretion, which differs from 
 the bile in containing a considerable quantity of albumen, and is very 
 putrescible. Its particular office in digestion appears to consist in promot- 
 ing the conversion of the starchy portions of the food into sugar (p. 496), 
 though it also has a powerful action upon the fats, causing them to form 
 an intimate mixture, or emulsion, with water, and partly saponifying them. 
 The digestion of the starch and sugar is completed by the action of the 
 intestinal fluid in the further passage of the food through the intestines, 
 so that when it arrives in the small intestines, all the soluble matters have 
 become converted into a thin milky liquid called chyle, which has next to 
 be separated mechanically from the insoluble portions, such as woody 
 fibre, &c., which are excreted from the body. 
 
 This separation is effected in the small intestines by means of two 
 distinct sets of vessels, one of which (the mesenteric veins) absorbs the 
 dissolved starchy portions of the food, and conveys them to tin- liver, 
 whence they are afterwards transferred to the right auricle of the heart. 
 The other set of vessels (lacteals) absorbs the digested fatty matters,, and 
 conveys them, through the thoracic duct, into the subclaviaii vein, and 
 thence at once into the right auricle of the heart. 
 
 From the right auricle this imperfect blood passes into the right 
 ventricle of the heart, and is there mixed with the blood returned from 
 the body by the veins, after having fulfilled its various functions in lh- 
 system. The mixture, which has the usual dark brown colour of venous 
 blood, is next forced, by the contraction of the heart, into the lungs, 
 where it is distributed through an immense number of extremely fine 
 vessels traversing the lungs, in contact with the minute tubes containing 
 * From X"^> Hie ; <niap.f"t. 
 
(332 CHEMISTRY OF NUTRITION. 
 
 the inspired air, so that the venous blood is only separated from the air 
 by very thin and moist membranes. Through these membranes the dark 
 venous blood gives up the carbonic acid with which it had become charged 
 by the oxidation of the carbon of the organs, in its passage through the 
 body, and acquires, in return, about an equal volume of oxygen, which 
 converts it into the bright crimson arterial blood. In this state it returns 
 to the left side of the heart, whence it is conveyed, by the arteries, to the 
 different organs of the body. 
 
 The chemistry of the changes effected and suffered by the blood in its 
 circulation through the body is very imperfectly understood. One of its 
 great offices is the supply of the oxygen necessary to oxidise the com- 
 ponents of the various organs, and thus to evolve the heat which maintains 
 the body at its high temperature. The results of the oxidation of these 
 organs are undoubtedly very numerous; among them we may trace 
 carbonic (C0 2 ), sulphuric (S0 3 ), phosphoric (P0 5 ), lactic (C 6 H 5 5 ), butyric 
 (C 8 H 7 3 ), and uric (C 10 H 2 N 4 OJ acids, as well as urea (C 2 H 4 N 2 2 ), and some 
 other substances. The destroyed tissues must at the same time be replaced 
 by the deposition, from the blood, of fresh particles similar to those which 
 have been oxidised. In the course of the blood through the circulation, 
 the above products of oxidation have to be removed from it the carbonic 
 acid by the lungs and skin the sulphuric, phosphoric, and uric acids, 
 and the urea, by the kidneys. 
 
 The various liquid secretions of the body, such as. the bile, the saliva, 
 the gastric juice, &c., have also to be elaborated from the blood during its 
 circulation through the arteries, after which it returns, by the veins, to 
 the heart, to have its composition restored by the matters derived from 
 the food, and to be reconverted into arterial blood in the lungs. 
 
 When it is remembered that the body is exposed to very considerable 
 variations of external heat and cold, a question occurs as to the provision 
 made for maintaining it at its uniform temperature. This is effected 
 through the agency of the fat which is deposited in all the organs of the 
 body. Since fatty substances in general are particularly rich in carbon 
 and hydrogen, their oxidation within the body would be attended with 
 the production of more heat than that of those parts of the organs which 
 contain much nitrogen and oxygen. Accordingly, when the body is 
 exposed to a low temperature, a larger quantity of its fat is consumed by 
 the oxidising action of the blood, and a corresponding increase takes 
 place in the amount of heat evolved, thus compensating for the greater 
 loss of heat suffered by the body in the cooler atmosphere. Of course, in 
 cold weather, when more oxygen is required to maintain the heat of the 
 frame, a larger quantity of that gas is inhaled at each breath on account 
 of the higher specific gravity of the air, in addition to which we have the 
 quickened respiration which always attends exposure to cold. 
 
 To supply this extra demand for carbon and hydrogen in cold weather, 
 we instinctively have recourse to such substances as fat, starch, sugar, &c., 
 which contain those elements in large proportion, and these aliments, free 
 from nitrogen, are often spoken of as the respiratory constituents of food ; 
 whilst flesh, gluten, albumen, &c, which contain nitrogen, are styled the 
 plastic elements of nutrition (TrXao-o-w, to form). 
 
 Bearing in mind that the food has a twofold office to nourish the 
 
 frame and to maintain the animal heat it will be evident that a judiciously 
 
 regulated diet will contain due proportions of those nitrogenous consti- 
 
 uents, such as albumen, fibrine, and cascine, which serve to supply the 
 
CHEMISTKY OF FOOD. 633 
 
 waste of the organs, and of such non-nitrogenised bodies as starch and 
 sugar, from which fat may be elaborated to sustain the bodily warmth. 
 
 ihe proportion which these two parts of the food should bear to each 
 other will, of course, depend upon the particular condition of existence 
 in the animal Thus, for a growing animal, a larger proportion of the 
 mtrogemsed or plastic portion of food would be required than for an 
 animal whose growth had ceased; and animals exposed to a low tempera- 
 ture would require more of the non-nitrogenised or heat-giving portions of 
 the food. 
 
 Accordingly we fin( l that a man can live upon a diet which contains 
 (as m the case of wheaten bread) five parts of non-nitrogenised (starch 
 and sugar) to one part of nitrogenised food (gluten); whilst an infant, 
 whose increasing organs require more nitrogenised material, thrives upon 
 milk, in which this amounts to one part (caseine) for every four parts of 
 the non-nitrogenised portion (milk-sugar and fat). 
 
 The inhabitants of cold climates consume, as is well known, much 
 more oil and fat than those of the temperate and hot regions. 
 
 An examination of the composition of different articles of food affords 
 us an explanation of the custom which experience has warranted, of asso- 
 ciating particular varieties of food. Thus, assuming as our standard of 
 comparison the composition of bread, which contains one of nutritive to 
 five of heat-giving matter, the propriety of associating the following kinds 
 of food will be appreciated : 
 
 
 Nutritive. 
 
 Heat-giving. 
 
 I Beef, 
 
 1 
 
 1-7 \ 
 
 \ Potatoes, 
 
 . 1 
 
 10 } 
 
 ( Ham, . 
 1 Veal, . 
 
 . 1 
 . 1 
 
 3 \ 
 01 / 
 
 f Mutton, 
 
 . 1 
 
 2-7 \ 
 
 1 Eice, . 
 
 .... 1 
 
 12-8 / 
 
 All muscular or mental exertion is attended with a corresponding 
 oxidation of the tissues of the frame, just as each movement of a steam- 
 engine may be traced to the combustion of a proportionate quantity of 
 coal under the boiler ; and hence such exertion both creates a demand 
 for food, and quickens the respiration to obtain an increased supply of 
 oxygen. 
 
 Experiment has proved that the proportion which the oxygen consumed 
 in respiration bears to the carbonic acid exhaled, depends very much upon 
 the nature of the food. Thus an animal fed upon vegetable matters, such 
 as starch and sugar (the oxygen in which exactly suffices to convert the 
 hydrogen into water), will turn nearly all the inspired oxygen to acctmnt 
 in the formation of carbonic acid, the volume of which will be nearly 
 equal to that of the oxygen which disappears at each inspiration; but wln-n 
 flesh, or particularly fat, is consumed, much more of the inspired oxygen 
 is required to convert the hydrogen of the food into water, so that tlui 
 volume of the carbonic acid is far less than that of the oxygen consumed 
 in respiration. When an animal has been kept for a length of tiiw 
 without food, the proportion between the volume of the carbonic arid 
 and that of the oxygen consumed, is the same as if the animal were being 
 fed upon a flesh diet, inasmuch as its own flesh alone is now supporting 
 its respiration. 
 
634 CHANGES AFTER DEATH. 
 
 CHANGES IN THE ANIMAL BODY AFTEE DEATH. 
 
 453. After the death of animals, just as after that of plants, their com- 
 ponent parts are reduced to the primary forms from which they were 
 derived, so that they may begin again at the foot of the ascending scale 
 of life. Very soon after life is extinct, the atmospheric oxygen begins 
 to induce a change in some of the nitrogenous constituents, and this 
 change is soon communicated to all parts of the body, which undergo 
 a putrefaction or metamorphosis, of which the ultimate results are the 
 conversion of the carbon into carbonic acid, the hydrogen into water, 
 the nitrogen into ammonia, nitrous and nitric acids, and the sulphur 
 into sulphuretted hydrogen and sulphuric acid. The mineral constituents 
 of the animal frame then mingle with the surrounding soil, and are 
 ready to take part in the nourishment of plants, which construct the 
 organic components of their frames from the carbonic acid and ammonia 
 furnished by the putrefaction of the animal, and then serve in their turn 
 as sustenance for animals whose respiration supplies the air with carbonic 
 acid, and takes in exchange the oxygen eliminated by the plant. 
 
 The functions of the two divisions of animate nature are, therefore, 
 perfectly reciprocal, and this relationship must be regarded as the founda- 
 tion of economical agriculture. 
 
 If it were possible to prevent the change of the atmosphere, it is quite 
 conceivable that a perpetual succession of plants and animals could be 
 raised upon a given farm without any importation of food, provided that 
 there was also no exportation. Or even, permitting an exportation of 
 food, the succession of plants and animals raised upon the same land 
 might be, at least, a very long one, if the solid and liquid excrements of 
 the animals, to feed whom this exportation took place, were restored to the 
 land upon which this food was raised. The explanation of this is, that 
 the solid and liquid excrements of the animal contain a very large propor- 
 tion of the mineral constituents of the soil, in the very state in which 
 they are best fitted for assimilation by the crop, and as long as the soil 
 contains the requisite supply of mineral food, the plant can derive its 
 organic constituents from the atmosphere itself. 
 
 Forasmuch, however, as the vegetable and animal food produced upon 
 a farm is generally exported to feed the dwellers in towns, whose excre- 
 ments cannot, without excessive outlay, be returned to the soil whence 
 the food was derived, it becomes necessary for the agriculturist to pur- 
 chase farm-yard manure, guano, &c., in order to prevent the exhaustion of 
 his soil. A great manufacturing country, in which the majority of the 
 inhabitants are congregated in very large numbers around a few centres 
 of industry, at a distance from the land under tillage, is thus of necessity 
 dependent for a considerable proportion of its food upon more thinly 
 populated countries where manufactures do not nourish, to which it ex- 
 ports in return the produce of the labour which it feeds. 
 
 The parts of the frames of animals differ very considerably in their 
 tendency to putrefaction. The blood and muscular flesh undergo this 
 change most readily, as being the most complex parts of the body, whilst 
 the fat remains unchanged for a much longer period, and the bones and 
 hair will also resist putrefaction for a great length of time. 
 
 The comparative stability of the fat is observed in the bodies of animals 
 which have been buried for some time in a very wet situation, when they 
 
NATURE OF PUTREFACTION. 635 
 
 are often found converted almost entirely into a mass of adipocere, con- 
 sisting of the stearic and margaric acids derived from the fat. 
 
 When an animal body is thoroughly dried, it may be preserved un- 
 changed for any length of time, and this is the simplest of the methods 
 adopted for the preservation of animal food, becoming far more efficacious 
 when combined with the use of some antiseptic substance such as salt, 
 sugar, spice, or kreasote. 
 
 The preservative effects of salt and sugar are sometimes ascribed to the 
 attraction exerted by them upon moisture, which they withdraw from the 
 flesh, whilst spices owe their antiseptic power to the essential oils, which 
 appear to have a specific action in arresting fermentative change, a cha- 
 racter which also belongs to kreasote, carbolic acid, and probably to other 
 substances which occur in the smoke of wood, well known for its efficacy 
 in curing animal matter. 
 
 A process commonly adopted for the preservation of animal and vege- 
 table food consists in heating them with a little water in tin canisters, 
 which are sealed air-tight as soon as the steam has expelled all the air, 
 and if the organic matter be perfectly fresh, this mode of preserving it is 
 found very successful, though, if putrefaction has once commenced, to ever 
 so slight an extent, it will continue even in the sealed canister, quite in- 
 dependently of the air. 
 
 Modern experiments have disclosed a great imperfection in our acquaint- 
 ance with the conditions under which putrefaction takes place, and appear 
 to indicate the presence in the atmosphere of some minute solid particles 
 which appear to be minute ova or germs, and have the power of inducing 
 the commencement of this change. It has been found that milk, for 
 example, may be kept for a very considerable period without putrefying, 
 if it be boiled in a flask, the neck of which is afterwards loosely stopped 
 with cotton wool, whilst, if the plug of cotton wool be omitted, the other 
 conditions being precisely the same, putrefaction will take place very 
 speedily. 
 
 Perfectly fresh animal matters have also been preserved for a length of 
 time in that state, in vessels containing air which has been passed through 
 red-hot tubes with the view of destroying any living germs which might 
 be present, and such substances have been found to putrefy as soon as the 
 unpurified air was allowed access to them. 
 
 The extremes of the scale of animated existence would appear to meet 
 here. The highest forms of organised matter, immediately after death, 
 serve to nourish some of the lowest orders of living germs, which help to 
 resolve the complex matter into the simpler forms of carbonic acid am 
 monia, &c., which are returned to the atmosphere, the great receptacle for 
 the four chief elements of living matter. 
 
INDEX. 
 
 The names of minerals are printed in italics. 
 
 ABEL'S experiments on gun-cotton, 506. 
 fuze- composition, 348. 
 
 Acetamide, 549. 
 
 Acetic acid, HO . C 4 H 3 3 , 514. 
 
 artificial formation, 533. 
 formed from alcohol, 492. 
 formed from citric, 589. 
 glacial, HO . C 4 H 3 3 , 564. 
 purification, 466. 
 synthesis of, 564. 
 anhydride, C 4 H 8 3 , 565. 
 ether, 522. 
 oxychloride, 565. 
 peroxide, 567. 
 Acetification, 492. 
 Acetine, 582. 
 
 Acetone, C 6 II 6 2 , 465, 556. 
 diethylated, 570. 
 dimethylated, 570. 
 ethylated, 570. 
 methylated, 570. 
 properties, 563. 
 Acetones, 556. 1 
 
 Acetonic acid, 561. 
 Acetonitrile, 550. 
 Acetyle, 519, 555. 
 
 binoxide, 567. 
 chloride, 565. 
 urea, 620. 
 Acetylene, C 4 H 2 , 83. 
 
 composition by volume, 100. 
 copper test for, 84. 
 detection in coal-gas, 102. 
 formed from olefiant gas, 87. 
 molecular formula, 83. 
 preparation from coal-gas, 83. 
 
 ether, 83. 
 properties, 84. 
 silver precipitate, 84. 
 synthesis, 83. 
 
 Acetylide of copper, preparation, 83. 
 potassium, 84. 
 sodium, 84. 
 Acid, 7. 
 
 definition, 9. 
 of sugar, 584. 
 radicals, C2*H ?n _i, 520. 
 unitary definition, 256. 
 Acids, anhydrous, 50. 
 
 acrylic series of, Qz* H2 n _ 2 04, 577. 
 aromatic, 460, 545. 
 bibasic, constitution, 255 . 
 
 Acids, dibasic, unitary definition, 256. 
 hydrated, 50. 
 monobasic, constitution, 255. 
 
 unitary definition, 256. 
 of the acetic series, 514. 
 lactic series, 560. 
 organic, constitution, 566. 
 oxalic series of, 580. 
 polybasic, 524. 
 tribasic, constitution, 256. 
 
 unitary definition, 256. 
 vegetable, 583. 
 volatile, separation, 571. 
 water- type view of, 254. 
 Acidulous waters, 45. 
 Aconitic acid, 589. 
 Aconitine, 538. 
 
 Acrylic acid, HO . C 8 H 3 3 , 577. 
 Actinic rays of light, 140. 
 Adapter, 83. 
 Adipic acid, 580. 
 Adipocere, 635. 
 Aerated bread, 494. 
 After-damp, 69. 
 Ag, silver, 361. 
 AgBr, bromide of silver, 366. 
 AgCl, chloride of silver, 365. 
 Agl, iodide of silver, 366. 
 AgO, oxide of silver, 364. 
 AgO . NO W nitrate of silver, 364. 
 Agriculture, economy of, 634. 
 AgS, sulphide of silver, 366. 
 Agate, 102. 
 Aich-metal, 342. 
 
 Air, analysis of by nitric oxide, 131. 
 by phosphorus, 17. 
 by pyrogallic acid, 593. 
 atmospheric, 16. 
 benzolised for illuminating, 97. 
 burnt in coal -gas, 95. ^ 
 
 candle test applied to, 68. 
 effect of combustion on, 67. 
 effect of electric sparks on, 123. 
 eudiometric analysis, 34. 
 exact analysis by copper, 18. 
 germs of life in, 635. 
 proportion of ammonia in, 113. 
 weight of 100 cubic inches, 14. 
 Al, aluminum, 285. 
 AL0 3 , alumina, 288. 
 Alabaster, 279. 
 
 oriental, 43. 
 Albite, 290. 
 Albumen of blood, 613. 
 
638 
 
 INDEX. 
 
 Alcarsin, 529. 
 Alcohol, C 4 H B 2 , 516. 
 absolute, 516. 
 allylic, 480. 
 amylic, C 10 H 12 2 , 511. 
 anisic, 558. 
 benzole, 558. 
 caprylic, 582. 
 cerylic, 583. 
 chemical constitution, 525. 
 
 definition, 513. 
 cuminic, 558. 
 flame, 98. 
 from milk, 609. 
 methylated, 473. 
 methylic, C 2 H 4 O 2 , 466. 
 molecular formula, 527. 
 radicals, CznRzn + w 519. 
 
 doubled formulae, 520. 
 synthesis, 525. 
 water-type view, 526. 
 Alcoholic fermentation, 490. 
 Alcohols and their derivatives, 511. 
 boiling points, 512. 
 diatomic, 558. 
 equivalent volumes, 513. 
 general properties, 512. 
 molecular formulae, 558. 
 volumes, 513. 
 monatomic, 558. 
 
 table of, 512. 
 polyatomic, 558. 
 triatomic, 562. 
 vapour-densities, 512. 
 vinic series, C2H2n + 2 2 , 514. 
 Aldehyde, acetic or vinic, C 4 H 4 2 , 554. 
 -ammonia, NH 3 , C 4 H 4 2 , 554. 
 benzoic, 557. 
 butyric, 556. 
 caprylic, 556. 
 
 chemical constitution, 555. 
 cinnamic, 558. 
 cuminic, 558. 
 euodic, 556. 
 formation in vinegar-making, 
 
 492. 
 
 lauric, 556. 
 cenanthic, 556. 
 preparation, 554. 
 properties, 554. 
 propionic, 556. 
 pyromucic, 568. 
 resin, 554. 
 rutic, 556. 
 salicylic, 558. 
 valeric, 556. 
 Aldehydes, 554. 
 
 action on amines, 556. 
 derivation from alcohols, 513. 
 Alder-wood, composition, 419. 
 Ale, composition, 491. 
 Algaroth, powder of, 381. 
 Alizarine, 602. 
 Alkali, definition, 8. 
 
 manufacture, 264. 
 metals, group of, 274. 
 works, fumes from, 148. 
 Alkaline earth metals, general review, 282. 
 
 earths, 24. 
 Alkaloids, constitution, 538. 
 
 determined, 543. 
 organic, 537. 
 
 Alkaloids, vegetable, extraction of, 594. 
 Allotropy, 188. 
 1 Alloxan, C 8 H 2 N 2 O 8 , 621. 
 i Alloxantine, C 16 H 4 N 4 14 , 621 . 
 Allyle, C 6 H,, 479. 
 iodide, 479. 
 series, 479, 577. 
 sulphide, 480. 
 sulphocyanide, 480. 
 terbromide, 578. 
 Allylene, 480. 
 Allylic alcohol, 480. 
 
 aldehyde, 577. 
 Almond cake, 474. 
 
 oil, 581. 
 Almonds, 474. 
 Aloes, 480. 
 Aludels, 367. 
 Alum, 286. 
 
 basic, 288. 
 concentrated, 286. 
 in bread, 494. 
 shale, 287. 
 uses, 287. 
 
 Alumina, A1 2 3 , 288. 
 acetate, 563. 
 
 action of fluoride of silicon on, 180. 
 atomic formula, 292. 
 hydrate, 288. 
 phosphates, 291. 
 silicates, 290. 
 sulphate, 286. 
 Aluminite, 253. 
 Aluminum, Al, 285. 
 
 action on water, 24. 
 and copper, 290. 
 bronze, 290. 
 chloride, A1 2 C1 3 , 288. 
 
 molecular formula, 292.- 
 vapour-density, 292. 
 equivalent and atomic weights, 
 
 291. 
 
 ethide, A1 2 (C 4 H S ) 3 , 534. 
 extraction, 289. 
 fluoride, 179. 
 methide, 534. 
 properties, 289. 
 silicide, 107. 
 1 Alums, 210, 287. 
 
 Amalgam for electrical machines, 369. 
 of ammonium, 119. 
 of sodium, 119. 
 
 ! Amalgamating zinc plates, 368. 
 , Amalgamation of gold ores, 403. 
 of silver ores, 362. 
 ! Amalgams, 369. 
 I Amarine, 568. 
 ! Amber, 473 
 I Amethyst, 102, 326. 
 Amides, constitution, 550. 
 formation, 549. 
 of phosphoric acid, 239. 
 Amide theory of organic bases, 539. 
 Amidide of potassium, 551. 
 Amidodiphenylimide, 459. 
 Amidogen, NH 2 , 539. 
 Ammonia, NH 3 , 113. 
 
 absorbed by charcoal, 58. 
 absorption by water, 114. 
 action of iodine on, 176. 
 -alum, 287. 
 and chlorine, 143. 
 
INDEX. 
 
 639 
 
 Ammonia, arsenite, 244. 
 
 as food for plants, 113. 
 bicarbonate, 270. 
 bihydrosulphate, 271. 
 bisulphate, 269. 
 burnt in oxygen, 117. 
 carbonate, NH 4 . C0 2 , 270. 
 combination with acids, 118. 
 combining volume, 119. 
 weight, 119. 
 common carbonate, 2NHX) . 3CO 
 
 269. 
 
 composition, 120. 
 decomposed by the spark, 118. 
 delicate test for, 373. 
 explosion with oxygen, 122. 
 formation from nitric acid, 127. 
 gas, dried, 117. 
 
 preparation, 114. 
 group of hydrogen compounds, 
 
 hydriodate, 176, 272. 
 hydrobromate, 272. 
 hydrochlorate, NH 3 .HC1, 113. 
 properties, 270. 
 hydrosulphate, NH 3 . HS, 271. 
 hyposulphite, 272. 
 identified, 114. 
 
 in waters, examination for, 373. 
 isethionate, 631. 
 liquefied, 116. 
 molecular formula, 120. 
 molybdate, 393. 
 muriate, 270. 
 Nessler's test for, 373. 
 nitrate, 311. 
 
 decomposed by heat, 130. 
 preparation, 130. 
 nitrification of, 122. 
 oxalate, NH 4 . C 2 3 , 584. 
 properties, 114. 
 proportion in air, 113. 
 salts, 269. 
 sesquicarbonate, 2NH 4 . 3C0 2 , 
 
 269. 
 solution, determination of 
 
 strength, 115. 
 
 solution, specific gravity, 115. 
 sources of, 113. 
 sulphate, NH 4 . SO,, 269. 
 urate, 621. 
 volcanic, 267. 
 Ammoniacal liquor, 449.. 
 
 extraction of ammonia 
 
 from, 113. 
 Ammoniacum, 489. 
 Ammonia-meter, 115. 
 Ammonias, complex, 537. 
 ethylated, 539. 
 
 Ammoniated chloride of silver, 116. 
 Ammonide, sulphuric, NH 3 . SO 3 , 269. 
 Ammonium, NH 4 , 269. 
 
 amalgam, 119. 
 bisulphide, 272. 
 bromide, 272. 
 chloride, 270. 
 
 properties, 270. 
 heptasulphide, 272. 
 iodide, 272. 
 oxide, NH 4 O, 269. 
 pentasulphide, 272. 
 sulphide, NH 4 S, 271. 
 
 I Ammonium sulphide, yellow, 272. 
 
 sulphocyanide prepared 217 
 theory, 118. 
 ! Amorphous, 55. 
 Amorphous phosphorus, 226 
 Amygdaline, 474, 
 Amylacetic (oenanthic) acid, 570 
 Amylamine, 542, 547. 
 Amyle, C 10 H n , 519. 
 acetate, 553. 
 valerianate, 553. 
 Amylene, 515. 
 Amylene-glycol, 561. 
 Amylethylic ether, 525. 
 Amylic alcohol, C 10 H,,0,, oil 
 Amylic iodide, 520. 
 Analysis of gaseous hydrocarbons, 99. 
 of marsh-gas, 99. 
 organic, 73. 
 
 calculation of, 74. 
 Anatase, 391. 
 Ancaster stone, 414. 
 Anchoic acid, 580. 
 Angelic acid, 577. 
 Anglesite, PbO . SO,, 359. 
 Anhydride, acetic, 565. 
 
 benzoacetic, 565. 
 benzoic, 476. 
 carbonic, 75. 
 lactic, 609. 
 nitric, 129. 
 phosphoric, 231. 
 sulphuric, 209. 
 sulphurous, 200. 
 tartaric, 587. 
 
 Anhydrides of organic acids, 564. 
 Anhydrous, 47. 
 Anhydrous acids, 50. 
 Aniline, C 12 H 7 N, 455. 
 -black, 458. 
 -blue, 458. 
 
 constitution, 546. 
 colours, 456. 
 constitution, 539. 
 -green, 458. 
 -purple, 456. 
 -red, 456. 
 
 constitution, 546. 
 salts, 458. 
 test for, 455, 
 -violet, 458. 
 
 constitution, 546. 
 -yellow, 457. 
 Animal charcoal, 59. 
 
 chemistry, 607. 
 heat, 632. 
 
 Animals, and plants, reciprocity of, 634. 
 changes after death, ' 
 destmctive functions of, 89tf 
 nutrition of, 629. 
 oxidising functions of, 627. 
 \iltimate elements of, 629. 
 Animi resin, 472. 
 Aniseed, essential oil of, 476, 658. 
 Anisic acid, 476, 558. 
 
 alcohol, 558. 
 Anisyle hydride, 476. 
 Annatto, 601. 
 Ansell's fire-damp indicate 
 Anthracite, 63. 
 
 composition, 434. 
 production of flame from, 77. 
 
640 
 
 INDEX. 
 
 Antichlore, 199, 212. 
 Anticorrosive caps, 157. 
 Antimonic acid, SbO w 379. 
 Antimonietted hydrogen, 380. 
 Antimony, Sb, 378. 
 
 action on water, 24. 
 
 amorphous, 379. 
 
 antiraoniate of teroxide, 
 Sb0 3 , Sb0 5 , 379. 
 
 butter of, 881. 
 
 chlorosulphide, 381. 
 
 compounds, atomic formulae, 
 
 crocus, 378. 
 crude, SbS 3 , 378. 
 detected, 193, 380. 
 juivalent and atomic weights, 
 
 extraction in the laboratory, 
 
 378. 
 
 glass of, 382. 
 grey ore of, SbS 3 , 378. 
 ore, red, Sb0 3 . 2SbS 3 , 382. 
 
 white, Sb0 3 , 379. 
 oxide, Sb0 3 , 379. 
 oxy chloride, 381. 
 oxysulphide, 382. 
 pentachloride, SbCl 5 , 381. 
 pentasulphide, SbS 5 , 382. 
 potassio-tartrate, 587. 
 regulus, 378. 
 sulphide identified, 381. 
 sulphides, 381. 
 terchloride, SbCl 3 , 381. 
 teroxide, Sb0 3 , 379. 
 tersulphide, 378. 
 tested for lead and iron, 382. 
 triatomic, 382. 
 uses, 379. 
 
 vermilion, 213, 382. 
 
 Antiseptic properties of carbolic acid, 461. 
 kresylic acid, 462, 
 sulphurous acid, 198. 
 Antozone, 52. 
 Ants, acid of, 567. 
 
 oil of, 568. 
 Apatite, 222. 
 Apocrenic acid, 628. 
 Apple-oil, 553. 
 
 Aq., water of crystallisation, 48. 
 Aqua fortis, 125. 
 regia, 167. 
 Arabine, 482. 
 
 Arachidic (butic) acid, 514. 
 Arbor Dianse, 369. 
 Archil, 602. 
 Argand lamp, 96. 
 Argent-acetyle, chloride of, 84. 
 
 oxide of, 84. 
 Argent-allylene, 480. 
 Argillaceous iron ores, 301. 
 Argol, 258, 586. 
 Arrack, 511. 
 
 Arragonite, CaO . C0 2 , 278. 
 Arrowroot, 485. 
 Arseniates, 246. 
 
 normal ratio of, 254. 
 Arsenic, As, 240. 
 
 bisulphide, 249. 
 combining volume, 244. 
 detection, 247. 
 extraction, 240. 
 
 Arsenic, extraction from organic matters, 248. 
 in copper, 340. 
 native, 240. 
 oxides, 242. 
 pentasulphide, 250. 
 subsulphide, 249. 
 sulphides, 249. 
 terbromide, 249. 
 terchloride, 248. 
 terfluoride, 249. 
 teriodide, 249. 
 tersulphide, 249. 
 
 identified, 250. 
 triethoxide, 534. 
 white, 242. 
 Arsenic acid, As0 5 , 245. 
 
 action of hydrosulphuric acid 
 
 on, 250. 
 Arsenical nickel, NiAs, 330. 
 
 paper-hangings, 245. 
 pyrites, 240. 
 soap, 244. 
 Arsenic-eating, 245. 
 Arsenides, 240. 
 Arsenietted hydrogen, AsH 3 , 246. 
 
 decomposed by heat, 
 
 247. 
 
 Arsenio-diethyle, 533. 
 -dimethyle, 533. 
 -sulphides, 240. 
 -triethyle, 533. 
 -trimethyle, 533. 
 Arsenious acid, As0 3 , 242. 
 
 action of ammonia on, 244. 
 chlorine on, 248. 
 hydrochloric acid 
 
 on, 248. 
 hydrosulphuric 
 acid on, 250. 
 
 behaviour with water, 243. 
 composition, 243. 
 crystalline, 243. 
 identified, 241. 
 molecular formula, 244. 
 opaque, 243. 
 smallest fatal dose, 243. 
 tribasic, 244. 
 vitreous, 242. 
 
 Arseniuretted or arsenietted hydrogen, 246. 
 As, arsenic, 240. 
 Asafoetida, 480. 
 
 essential oil of, 479. 
 Asbestos, 280. 
 
 AsH 3 , arsenietted hydrogen, 246. 
 Ashes of coal, 63. 
 As0 3 , arsenious acid, 242. 
 As0 6 , arsenic acid, 245. 
 Asparagine, 590. 
 Asparagus, 500. 
 Aspartic acid, 590. 
 Assay of gold by cupellation, 405. 
 Atacamite, 346. 
 Atmolysis, 28. 
 
 Atmosphere, composition, 16. 
 Atmospheric air, 16. 
 Atmospheric germs of putrefaction, 635. 
 Atom, definition, 52. 
 etymology, 36. 
 Atomic formula of alumina, 292. 
 
 arsenic acid, 244. 
 boracic acid, 112. 
 chloride of silicon, 165. 
 
INDEX. 
 
 641 
 
 Atomic formula of chloride of zinc, 298. 
 
 hydrate of soda, 268. 
 
 hyposulphite of soda, 213. 
 
 oxide of zinc, 298. 
 
 phosphoric acid, 231. 
 
 potash, 261. 
 
 potassic hydrate, 261. 
 
 silicic acid, 109. 
 
 soda, 268. 
 Atomic formulae of alkaline earths, 285. 
 
 antimony compounds, 
 383. 
 
 bismuth compounds, 377. 
 
 chlorides of carbon, 164. 
 iron, 324. 
 
 chromium compounds, 
 334. 
 
 copper compounds, 348. 
 
 gold compounds, 408. 
 
 lead compounds, 360. 
 
 manganese compounds, 
 090 
 
 0.40. 
 
 mercury compounds, 375- 
 oxides of chlorine, 161. 
 
 iron, 324. 
 oxides of nitrogen, 137. 
 platinum compounds. 
 
 399. 
 
 salts, 257. 
 
 silver compounds, 366. 
 sulphates, 211. 
 tin compounds, 390. 
 types of, 151. 
 Atomic heat, definition, 283. 
 
 of magnesium, 284. 
 Atomic heats, 37. 
 
 of compound bodies, 284. 
 oxygen, hydrogen, and 
 
 nitrogen, 284. 
 potassium, sodium, and 
 
 lithium, 284. 
 
 Atomicities, classification by, 251. 
 Atomicity, 151. 
 
 importance in theory, 251. 
 notation of, 251. 
 Atomic theory, 36. 
 
 unitary formulae of salts, 257. 
 weight, 36. 
 
 of sulphur, 194. 
 Atropine, 538. 
 
 Attraction, chemical, definition, 1. 
 Au, gold, 402. 
 
 AuCl 3 , terchloride of gold, 406. 
 Augite, 291. 
 Auric acid, Au0 3 , 406. 
 Autogenous soldering, 203. 
 Azobenzide,455. 
 Azolitmine, 603. 
 Azote, etymology, 113. 
 
 B, BORON, 109. 
 
 Ba, barium, 275. 
 
 BaCl, chloride of barium, 276. 
 
 Balenic acid, 514. 
 
 Balloons, 27. 
 
 made, 508. 
 Balsam of Peru, 472. 
 tolu, 472. 
 Balsams, 472. 
 Banca tin, 385. 
 BaO, baryta, 276. 
 BaO . C0 2 , carbonate of baryta, 275. 
 
 BaO. NO W nitrate of baryta, 276. 
 BaO. S0 3 , sulphate of baryta, 275. 
 Barilla, 264. 
 Bar-iron, best, 312. 
 
 composition, 314. 
 crystalline, 315. 
 fibrous, 312. 
 manufacture, 309. 
 Barium, Ba, 275. 
 
 action on water, 24. 
 binoxide, 276. 
 chloride, BaCl, 276. 
 diatomic, 285. 
 
 equivalent and atomic weights, 283. 
 sulphide, 275. 
 Barley sugar, 499. 
 Baryta, BaO, 276. 
 
 carbonate, 276. 
 
 preparation from heavy 
 
 spar, 276. 
 chlorate, 277. 
 hydrate, BaO . HO, 276. 
 hypophosphite, 234. 
 in glass, 410. 
 nitrate, BaO . N0 a , 276. 
 sulphate, 275. 
 
 decomposition, 276. 
 sulphovinate, 524. 
 Barytocalcite, 278. 
 Basalt, 291. 
 Base, definition, 10. 
 Basicity of acids determined, 257. 
 Basic oxides, 10. 
 Bassorine, 483. 
 Basylous, 250. 
 Bathgate coal, 468. 
 Bath stone, 414. 
 Baths, photographic, recovery of silver from, 
 
 365. 
 
 Battery, galvanic, 20. 
 Baume's flux, 219. 
 
 Bauxite, extraction of aluminum from, 289. 
 Baysalt, 263. 
 Beans, inosite in, 615. 
 Bear, 393. 
 Beef-tea, 616. 
 Beehive-shelf, 12. 
 Beer, composition, 491. 
 ropy, 491. 
 sparkling, 71. 
 Bees' wax, 583. 
 Bell-metal, 342, 387. 
 Bengal saltpetre, KO.NO,, 415. 
 Benic acid, 514. 
 Benzamide, 549. 
 Benzoacetic anhydride, 565. 
 Benzoicacid, HO.CuH/),, 473. 
 in cow s urine, 622. 
 alcohol, 476, 558. 
 anhydride, 476. 
 peroxide, 567. 
 Benzoin, gum, 473. 
 Benzoine, 475. 
 Benzole or benzine, C^H^, 454. 
 
 action of nitric acid on, 128. 
 chloride of, 455. 
 Benzol ine, 568. 
 Benzolised air, 97. 
 Benzone, 558. 
 Benzonitrile, 550. 
 Benzophenone, 558. 
 Benzoyle, C U H S 2 , 475. 
 
 2 8 
 
642 
 
 INDEX. 
 
 Benzoyle, binoxide, 567. 
 
 compounds, 475. 
 
 flycocoll, 622. 
 ydride, 475. 
 
 salicylamide, 551. 
 
 salicyle, 477. 
 
 series, 475. 
 Benzoyle-xirea, 620. 
 Benzureide, 620. 
 Benzylamine, 558. 
 Benzyle, chloride, 558. 
 Bergamotte, essential oil of, 470. 
 Beryl, 292. 
 
 Bessemer's process (iron), 314. 
 Bezoars, 593. 
 Bi, bismuth, 376. 
 Bibasic acids, constitution, 255. 
 Biborate of soda, 267. 
 Bibromosuccinic acid, 588. 
 Bicarbonate of lime, 41. 
 
 soda, NaO.H0.2C0 2 , 266. 
 Bicarbonates, 75. 
 Bichloracetic acid, 563. 
 Bi-equivalent elements, 152. 
 Bile, 630. 
 Bimetantimoniate of potash, 380. 
 
 soda, 380. 
 Binary formulae, 50. 
 
 theory of acids, 254. 
 salts, 254. 
 
 Binoxide of hydrogen, 50. 
 nitrogen, 130. 
 BiO 3 , bismuthic oxide, 377. 
 Birch, essential oil of, 470. 
 BiS 3 , bismuthic sulphide, 377. 
 Biscuit porcelain, 412. 
 Bismuth, Bi, 376. 
 
 action on water, 24. 
 
 equivalent and atomic weights, 
 377. 
 
 glance, 377. 
 
 impurities, 376. 
 
 nitrate, BiOj.SNOs, 377. 
 
 ochre, 377. 
 
 oxides, 377. 
 
 oxy chloride, 377. 
 
 sulphides, 377. 
 
 telluride, 222. 
 
 terchloride, BiCl 3 , 377. 
 
 triatomic, 377. 
 
 trisnitrate, 377. 
 Bismuthic acid, 377. 
 Bistearine, 575. 
 
 Bisulphate of potash, KO . HO .2S0 3 , 124. 
 Bisulphide of carbon in coal-gas, 216. 
 Bisulphites, 199. 
 Bisulphuret of carbon, 215. 
 Bitter almond oil, C,.H R 0,, 474. 
 Bittern, 168, 263. 
 Bituminous coal, 63. 
 Bixine, 601. 
 Black ash, 265. 
 
 liquor, treatment, 266. 
 Blackband, 301. 
 Black dyes, 606. 
 Blacking, vitriol in, 206. 
 Black lead, 55. 
 
 crucibles. 56. 
 vitriol, 345. 
 wash, 372. 
 Blast-furnace, 303. 
 
 chemical changes in, 304. 
 
 Blast-furnace gases, 305. 
 Blasting with gunpowder, 428. 
 Bleaching by chloride of lime, 145. 
 chlorine, 144. 
 ozone, 15. 
 
 sulphurous acid, 197. 
 powder, 145. 
 Bleach killed, 199. 
 Blende, ZnS,. 294. 
 Blistered steel, 316. 
 Block tin, 385. 
 Blood, 611. 
 
 action of oxygen on, 613. 
 aeration of, 631. 
 coagulation of, 612. 
 defibrinated, 612. 
 formation from food, 629, 631. 
 globules, 612. 
 venous and arterial, 613. 
 Bloom (iron), 310. 
 Bloomery forge, 321. 
 Blowers in coal-mines, 89. 
 Blowpipe, cupellation with, 355. 
 flame, 98. 
 oxy-hydrogen, 37. 
 reduction of metals by, 99. 
 table, 106. 
 test for lithium, 272. 
 
 potassium, 261. 
 sodium, 266. 
 Blue blaze, 299. 
 bricks, 413. 
 copperas, 344. 
 dyes, 606. 
 
 fire composition, 158. 
 flowers, colouring matter of, 601. 
 malachite, 346. 
 metal (copper), 339. 
 oxide of molybdenum, 393. 
 
 tungsten, 392. 
 pill, 368. 
 pots, 56. 
 
 Prussian, Fe 4 Fcy 3 , 436. 
 stone, 344. 
 Thenard's, 329. 
 Turnbull's, 443. 
 verditer, 345. 
 vitriol, 344. 
 
 water of copper mines, 339. 
 writing paper, 290. 
 BO, boracic acid, 109. 
 Bodies of animals, putrefaction of, 634. 
 Boghead cannel, 468. 
 Boiler fluid, arsenical, 245. 
 
 incrustations, 41. 
 Boiling meat, 616. 
 Boiling point, definition, 47. 
 Boiling points of benzole series, 459. 
 Boiling process (iron), 313. 
 Bolsover stone, 414. 
 Bone-ash, 222. 
 
 as manure, 624. 
 black, 59. 
 earth, as manure, 
 formation from food, 629. 
 Bones, ammonia furnished by, 547. 
 as manure, 625. 
 composition, 222. 
 destructive distillation, 59. 
 Boracic acid, B0 3 , 109. 
 
 atomic formula, 112. 
 crystals, 110. 
 
INDEX. 
 
 G43 
 
 Boracic acid, equivalent, 111. 
 identified, 110. 
 in glass, 410. 
 manufacture, 109. 
 tribasic, 111, 
 vitreous, 110. 
 anhydride, 112. 
 ether, 523. 
 lagunes, 109. 
 Uoradte, 282: 
 Borates, 111. 
 
 normal ratio of, 254. 
 Borax, NaO . 2B0 3 , 109, 267. 
 glass, 267. 
 identified, 267. 
 manufacture, 267. 
 refining, 267. 
 uses, 267. 
 vitrefied, 267. 
 Boric ethide, 534. 
 
 methide, 534. 
 Borneene, 471. 
 Borneo camphor, 471. 
 Borofluoric acid, 182. 
 Borofluorides, 182. 
 Boron, B, 109. 
 
 amorphous, 111. 
 atomic weight, 112. 
 chloride, BC1 3 , 166. 
 combining weight, 111. 
 crystallised, 111. 
 diamond, 111. 
 fluoride, BF 3 , 182. 
 graphitoid, 111. 
 nitride, 111. 
 terchloride, 166. 
 terfluoride, 182. 
 Botany Bay gum, 461. 
 Boucherie's process for preserving wood, 
 Bouquet of wines, 510. 
 Boyle's fuming liquor, 272. 
 Br, bromine, 168. 
 Brandy, 511. 
 Brass, 342. 
 
 for engraving, 342. 
 guns, 387. 
 preparation, 342. 
 Brassic acid, 577. 
 Braunite, Mn 2 3 , 326. 
 Brazil wood, 601. 
 Bread, 493. 
 
 aerated, 494. 
 new and stale, 494. 
 Brewing, 489. 
 Bricks, 413. 
 
 efflorescence on, 268. 
 Bright iron, 308. 
 Brimstone, 185. 
 Britannia metal, 386. 
 British brandy, 511. 
 
 gum, 486. 
 
 Br0 3 , bromic acid, 169. 
 Brochantite, 345. 
 Bromates, 169. 
 Bromic acid, 169, 
 Bromine, Br, 168. 
 
 action on potash, 168. 
 chloride of, 170. 
 etymology, 169. 
 hydrate, 169. 
 identified, 169. 
 in waters, 168. 
 
 Bromine, useful applications, 169 
 
 with hydrogen, 169. 
 Bromoform, 553. 
 Bromosuccinic acid, 588 
 Bronze, 342, 387. 
 
 annealing of, 387 
 coin, 387. 
 powder, 390. 
 Brookite, 391. 
 
 Brown acid (sulphuric), 205. 
 blaze, 299. 
 coal, 63. 
 dyes, 606. 
 haematite, 301. 
 Brucine, 538. 
 Brucite, 282. 
 Brunolic acid, 450. 
 Brunswick green, 346, 
 Bubbles, explosive, 32. 
 Buckskin, 592. 
 Bug-poison, 371. 
 Building-materials, 413. 
 
 stone, effect of air of towns on, 414. 
 
 preservation of, 414. 
 Bullets, rifle, 355. 
 
 shrapnel, 355. 
 Burner, air-gas, 96. 
 Bunsen's, 96. 
 gauze, 96. 
 hot-air, 96. 
 ring, 46. 
 rosette, 45. 
 
 Burners, smokeless, 96. 
 Burnett's disinfecting fluid, 298. 
 Burnt iron, 315. 
 Butic acid, 514, 582. 
 Butine, 582. 
 Butter, 582. 
 Butter-milk, 608. 
 
 preparation of, 608. 
 Butylactic acid, 560. 
 Butylamine, 547. 
 Butyle, C 8 H 9 , 519. 
 -amyle, 520. 
 -caproyle, 520. 
 Butylene, 515. 
 
 -glycol, 561. 
 Butylic alcohol, 512. 
 Jutyramide, 549. 
 
 "Butyric acid, HO. C f H 7 O B , 514, 668. 
 formed, from citric, 589. 
 synthesis of, 569. 
 two rational formulae of, 569. 
 ether, 553. 
 Jutyrine^ 582. 
 lutyrone, 557. 
 Jutyryle, 520, 556. 
 -urea, 620. 
 
 C, CARBON, 53. 
 
 Ca, calcium, 277. 
 
 Cacao-butter, 598. 
 
 CaCl, chloride of calcium, 280. 
 
 Cadet's fuming liquor, 529. 
 
 Cadmia, CdS. 299. 
 
 Cadmium, Cd, 299. 
 
 carbonate, 299. 
 
 diatomic, 299. 
 
 equivalent and atomic weights, 
 299. 
 
 identified, 299. 
 
 iodide, 299. 
 
644 
 
 INDEX. 
 
 Cadmium oxide, 299. 
 
 sulphide, CdS, 299. 
 vapour density, 299. 
 Csesia, 274. 
 
 carbonate, 274. 
 Csesium, 273. 
 
 equivalent weight, 275. 
 platinochloride, 397. 
 properties, 274. 
 Caen-stone, 414. 
 CaF, fluoride of calcium, 177. 
 Caffeic acid, 597. 
 Caffeine, C 16 H 10 N 4 4 , 538. 
 
 chemical constitution, 595. 
 extraction of, 597. 
 formed from theobromine, 599. 
 Caffeone, 597. 
 Cairnc/orm, stones, 102. 
 CaMng-coal, 63. 
 Calamine, ZnO . C0 2 , 294. 
 
 electric, 294. 
 Calcareous waters, 41. 
 Calcium, Ca, 277. 
 Calcium, action on water, 24. 
 bisulphide, 195, 280. 
 chloride, CaCl, 280. 
 diatomic, 285. 
 
 equivalent and atomic weights, 283. 
 fluoride, CaF, 177. 
 oxychloride, 145, 280. 
 pentasulphide, 195, 280. 
 phosphide, 236. 
 silicide, 280. 
 sulphide, 280. 
 Calc-spar, 278. 
 Calculation of formulae, 121. 
 Calico-printing, 604. 
 Calomel, Hg 2 Cl, 372. 
 
 molecular formula of, 374. 
 Calorific intensity, 431. 
 Cameos, 102. 
 
 Camomile, essential oil of, 470. 
 Camphilene, 470. 
 Camphine, 97, 469. 
 Campholic acid, 577. 
 Camphor, C M H 16 O 471. 
 artificial, 470. 
 oil of, 471. 
 Camphors, 471. 
 Camphorimide, 550. 
 Candle, chemistry of, 93. 
 Candles, 574. 
 
 composite, 574, 576. 
 Cane-sugar, C lz H. u O n , 496. 
 
 action of yeast on, 490. 
 composition, 499. 
 Cannel gas, composition, 101. 
 CaO, lime, 278. 
 
 CaO . COa, carbonate of lime, 278. 
 CaO . 0, oxalate of lime, 585. 
 CaO . SOg, sulphate of lime, 279. 
 Caoutchine, 481. 
 Caoutchouc, 480. 
 
 artificial, 581. 
 in plant juices, 482. 
 solvents for, 481. 
 Cap composition, 446. 
 Capric (rutic) acid, 514. 
 Caprine, 582. 
 Caproic acid, 514. 
 
 alcohol, 512. 
 Caproine, 582. 
 
 Caproyle, C 12 H 13 , 519. 
 Caproylene, 515. 
 Caprylene, 515. 
 Caprylic acid, 514. 
 
 alcohol, 512, 582. 
 Capsicine, 538. 
 Caramel, 499. 
 Carbazotic acid, 461. 
 Carbolic acid, C 12 H 6 2 , 460'. 
 
 antiseptic character, 635. 
 tests of purity, 461. 
 Carbon, C, 53. 
 
 and hydrogen, 82. 
 
 oxygen, 7. 
 atomicity, 152. 
 atomic weight, 82. 
 bichloride, C 2 C1 4 , 162. 
 chemical relations of, 60. 
 chlorides of, 162. 
 circulation in nature, 64. 
 determination of, 73. 
 equivalent weight, 81. 
 hypothetical vapour density, 80. 
 natural sources, 53. 
 oxides of, 63. 
 physical properties, 61. 
 sesquichloride, C 4 C1 W 162. 
 subchloride, C 4 C1 2 , 162. 
 use in metallurgy, 61. 
 Carbonate of baryta and lime, 278. 
 lime and soda, 278. 
 lime in waters, 41. 
 
 natural sources of, 65. 
 Carbonates, 75. 
 
 alkaline, 275. 
 atomic formulae, 76. 
 equivalent formulae, 76. 
 normal, 253. 
 unitary formulae, 76. 
 Carbon, bisulphide, CS 2 , 215. 
 
 composition, 218. 
 molecular formula, 218. 
 uses, 216. 
 burnt to carbonic oxide, calorific 
 
 value of, 433. 
 
 calorific intensity calculated, 431. 
 calorific value, 61, 429. 
 chlorides, composition by volume, 
 
 163. 
 
 chlorides, molecular formulae, 164. 
 group of elements. 112, 251. 
 iodide, 176. 
 
 liquid sesquichloride, C 2 CL,, 164. 
 oxychloride, C 2 2 C1 2 , 165. 
 protochloride, C 4 C1 4 , 162. 
 Carbonic acid, C0 2 , 63. 
 
 absorption by water, 70. 
 analysis of, 76. 
 combining weight, 81. 
 composition by volume, 80. 
 decomposed by carbon, 76. 
 
 potassium, 76, 
 determination of, 73. 
 equivalent volume, 80. 
 evolved by plants, 64. 
 experiments with, 66. 
 formation of propylic acid 
 
 from, 533. 
 
 formed in combustion, 63. 
 respiration, 63. 
 in air, sources of, 63. 
 in breathed air, 69. 
 
INDEX. 
 
 645 
 
 Carbonic acid, injurious effects of, 68. 
 liquefaction of, 72. 
 molecular formula, 82. 
 volume, 82. 
 weight, 82. 
 preparation, 65. 
 properties, 65. 
 salts of, 75. 
 separation from other gases, 72. 
 springs, 64. 
 synthesis of, 53. 
 Carbonic anhydride, 75. 
 
 ether, 523. 
 Carbonic oxide, CO, 76. 
 
 absorption by cuprous chlo 
 
 ride, 252. 
 action on heated metallic 
 
 oxides, 80. 
 calorific value, 433. 
 composition by volume, 80. 
 decomposition by heat, 80. 
 formation in fires, 77. 
 formed from steam, 78. 
 identified, 77. 
 
 loss of heat in furnaces pro- 
 ducing, 433. 
 
 metallurgic applications, 77. 
 molecular formula, 82. 
 volume, 82. 
 weight, 82. 
 
 poisonous properties, 78. 
 preparation from carbonic 
 
 acid, 76. 
 preparation from ferrocy- 
 
 anide of potassium, 79. 
 preparation from oxalic 
 
 acid, 78. 
 properties, 78. 
 Carbonisation, 53. 
 Carbonising fermentation, 61. 
 Carbotriamine, 546. 
 Carbovinate of potash, 523. 
 Carburetted hydrogen, 88. 
 Carmine, 604. 
 Carmine lake, 604. 
 Carminic acid, 604. 
 Carnallite, 261. 
 Carnelian, 102. 
 
 Carraway, essential oil of, 4V 0. 
 Carre's freezing apparatus, 116. 
 Carthamine, 601. 
 Cartilage, 616. 
 Case-hardening, 319. 
 Caseine, 608. 
 
 vegetable, 493, 610. 
 Cassia, essential oil, 476. 
 Cassiterite, Sn0 2 , 388. 
 Cast-iron, composition of, 307. 
 for ordnance, 309. 
 fusing point, 309. 
 grey, 308. 
 malleable, 319. 
 mottled, 308. 
 phosphorus in, 307. 
 silicon in, 108. 
 specific gravity, 309. 
 sulphur in, 307. 
 varieties of, 308. 
 white, 308. 
 Castor oil, 582. 
 
 cold-drawn, 582. 
 Cast steel, 317. 
 
 Catalan process, 320 
 Catalysis, 51, 525. 
 Catechu, 594. 
 Ca'ts eye, 102. 
 Caustic alkali, 9. 
 
 etymology of, 259. 
 lunar, AgO . NO^, 364. 
 potash, 259. 
 soda, 266. 
 Cd, cadmium, 299. 
 Cedar-wood, essential oil, 471. 
 Cedrene, 471. 
 Cedriret, 465, 468. 
 Celery, 500. 
 
 Celestine, SrO . S0 3 , 277. 
 Cellulose, C 12 H 10 10 , 464. 
 
 converted into sugar, 495. 
 solvent for, 344. 
 Cement for earthenware, 610. 
 
 Keene's and Keating's, 280. 
 Portland, 415. 
 Roman, 415. 
 Scott's, 415. 
 Cementation process, 316. 
 
 theory of, 317. 
 
 Centrifugal sugar drainer, 498. 
 Cerasine, 483. 
 Cerite, 293. 
 Cerium, Ce, 293. 
 
 oxalate, 293. 
 oxides, 293. 
 Ceroleine, 583. 
 Cerotene, 515. 
 Cerotic acid, 514, 583. 
 Cerotine, 583. 
 Ceruse, 358. 
 
 Cerylic alcohol, 512, 583. 
 Cetine, 582. 
 " ;yle, C 32 H 33 , 583. 
 series, 583. 
 Cetylene, 515. 
 2etylic alcohol, 512. 
 
 ether, 583. 
 C 2 H 3 , methyle, 466. 
 H V marsh-gas, 88. 
 2 H 4 2 , methylic alcohol, 466. 
 ~! 4 H 2 , acetylene, 83. 
 ! 4 H 3 3 , anhydrous acetic acid, 560. 
 ! 4 H 4 , olefiaut gas, 85. 
 ! 4 H 4 C1 2 , Dutch liquid, 86. 
 ! 4 H 5 , ethyle, 519. 
 D 4 H 4 0, ether, 517. 
 ~' 4 H 8 2 , alcohol, 516. 
 8 H 4 0, , tartaric acid in combination, 586. 
 C 12 H 4 , phenyle, 459. 
 J 12 H 6 , benzole, 454, 
 ) 12 H.N, aniline, 455. 
 ^XOj, benzoyle, 475. 
 20 H 8 , naphthaline, 462. 
 Chalcedony, 102. 
 Vialk, CaO.CO.,278. 
 
 decomposed by sodium, 7ti. 
 in waters, 41. 
 precipitated, 157. 
 Chalybeate waters, 45, 322. 
 Chameleon mineral, 327. 
 Champagne, 510. 
 Dharbon roux, 419. 
 'harcoal, absorption of gases by, 58. 
 action of steam on, 78. 
 alder, ronii'<iti<m, 410. 
 animal, 59. 
 
646 
 
 INDEX. 
 
 Charcoal as fuel, 61. 
 ash, 420. 
 burning, 57. 
 combustion of, 60. 
 decolorising properties, 59. 
 deodorising properties, 58. 
 examination, 420. 
 for gunpowder, 419. 
 oxidised by nitric acid, 126. 
 preparation in the laboratory, 429. 
 prepared at different temperatures, 
 
 419. 
 
 properties of, 206. 
 retort, 57. 
 suffocation, 78. 
 wood, 56. 
 
 Charring by steam, 419. 
 Cheese, 609. 
 Cheltenham water, 45. 
 Chemical equivalent, definition, 23. 
 Chemistry, definition, 1. 
 Cheques, prepared paper for, 487. 
 Chessylite, 346. 
 
 ChevreuPs investigations, 571. 
 Chili saltpetre, NaO . N0 5 , 415. 
 Chill-casting, 309. 
 Chimney, hot air, for lamps, 96. 
 use of, in lamps, 96. 
 ventilation by, 69. 
 Chimneys on fire extinguished, 197. 
 Chinese wax, 583. 
 Chlonaphthalise, C 20 C1 8 , 163. 
 Chloracetic acid, HO . C 4 H 2 C1Q 3 , 563. 
 Chloracetine, 557. 
 Chloral, C 4 HC1 3 2 , 552. 
 Chloranile, 596. 
 Chloraniline, 549. 
 Chlorate of baryta, 277. 
 
 potash, KO . C10 ? , 155. 
 
 action of heat on, 159. 
 sulphuric acid 
 
 on, 159. 
 
 and sugar inflamed, 160. 
 Chlorate of potash burnt in coal-gas, 158. 
 preparation, 155. 
 preparation of oxygen 
 
 from, 13. 
 Chlorates, 157. 
 
 normal ratio of, 254. 
 Chlorhydrine, 575. 
 
 of glycol, 559. 
 Chloric acid, C10 W 155. 
 
 hydrated, 157. 
 ether, 522. 
 peroxide, C10 4 , 159. 
 
 Chloride of aluminum and sodium, 289. 
 ammonium, NH 4 C1, 113. 
 calcium tube, 73. 
 lime, 145. 
 
 constitution of, 155. 
 spontaneous decomposi- 
 tion, 155. 
 nitrogen, 166. 
 
 preparation, 166. 
 potassiiim, solubility of, 416. 
 soda, 155. 
 sodium, 416. 
 sulphuryle, 198. 
 thionyle, 198. 
 Chlorine, Cl, 137. 
 
 action on ammonia, 143. 
 
 hydrosulphuricacid, 191. 
 
 Chlorine, action on leaves, 144. 
 
 sal-ammoniac, 167. 
 water, 142. 
 and hydrogen, 140. 
 
 exploded by sun- 
 light, 141. 
 exploded by spark^ 
 
 141. 
 
 atomicity of, 151. 
 bleaching by, 144. 
 chemical relations of, 139. 
 disinfecting properties, 145. 
 equivalent, 150. 
 etymology, 139. 
 experiments with, 139. 
 group of elements, 182, 251. 
 hydrate, 139. 
 liquefied, 139. 
 occurrence in nature, 137. 
 oxides, 153. 
 
 atomic and molecular 
 
 formulae of, 161. 
 composition by volume. 
 
 161. 
 
 general revieAv, 161. 
 oxidising action, 144. 
 peroxide, 159. 
 preparation, 138. 
 properties, 139. 
 taper in, 143. 
 water, 139. 
 Chlorite, 290. 
 Chlorites, 161. 
 Chlorobenzole, 455. 
 Chlorocarbonic acid, C^O^l^ 165. 
 
 atomic constitution, 
 
 252. 
 
 Chlorochromic acid, 333. 
 Chloroform, C 2 HC1 3 , 552. 
 Chloronitric gas, 167. 
 Chloronitrous gas, 167. 
 Chlorophosphanude, 239. 
 Chlorophyll, 600. 
 Chloropicrine, C 2 C1 3 (N0 4 ), 461. 
 Chlorosulphuric acid, 198. 
 Chlorous acid, C10 3 , 160. 
 Chocolate, 598. 
 Choke-damp, 69. 
 Cholesterine, C,JEL,0 9 , 631. 
 Cholic acid, 630. 
 Choloidic acid, 630. 
 Chondrine, 616. 
 
 Chromates, normal ratio of, 254. 
 of lead, 332. 
 of potash, 332. 
 Chrome-alum, 333. 
 
 Chrome-iron-ore, FeO . Cr 2 3 , 323, 331. 
 Chrome-yellow, PbO . Cr0 3 , 332. 
 Chromic acid, Cr0 3 , 331. 
 
 action of hydrochloric acid 
 
 on, 150. 
 Chromium, Cr, 331, 
 
 action on water, 24. 
 
 chlorides, 333. 
 
 compounds, atomic formulae, 334. 
 
 diatomic, 334. 
 
 equivalent and atomic weights, 
 
 334. 
 
 oxides, 331. 
 oxychloride, 334. 
 protoxide, 333. 
 sesquichloride, 333. 
 
INDEX. 
 
 647 
 
 Chromium sesquioxide, C^O,, 332. 
 sesquisulphide, 334. 
 sulphate, 332. 
 terrtuoride, 334. 
 Chrysaniline, 457. 
 Chrysene, 464. 
 Chrysoberyl, 292. 
 Chrysocolla, 346. 
 Churning, 608. 
 Chyle, 631. 
 Chyme, 630. 
 Cigars, 600. 
 Cinchona bark, 595. 
 Qinchonine, 537. 
 
 extraction of, 595. 
 Cinder, 62. 
 
 Cinder-fall of blast-furnace, 304. 
 Cinder-iron, 306. 
 Cinnabar, HgS, 367. 
 Cinnameine, 472. 
 Cinnamic acid, C^H^ 472. 
 Cinnamon, essential oil of, 476. 
 Cinnamyle, hydride, 476. 
 Circulation of blood, chemistry of, 631. 
 Cisterns, incrustations in, 42. 
 Citric acid, 3HO . C 12 H 5 O n , 589. 
 Cl, chlorine, 137. 
 
 Clark's process for softening water, 43. 
 Clay, 286. 
 Claying sugar, 498. 
 Clay ironstone, average yield, 305. 
 kidney form, 301. 
 Clay ironstones, 301. 
 CIO, hypochlorous acid, 154. 
 C10 3 , chlorous acid, 160. 
 C1O 4 , chloric peroxide, 159. 
 C10 5 , chloric acid, 155. 
 C10 7 , perchloric acid, 159. 
 Clot of blood, 612. 
 Cloves, essential oil of, 470. 
 C 2 N, cyanogen, 440. 
 CO, carbonic oxide, 76. 
 C0 2 , carbonic acid, 63. 
 C.,O 3 , oxalic acid in combination, 585. 
 Coal, 61. 
 
 ash of, 63. 
 
 Bathgate, 468. 
 
 bituminous, 63. 
 
 composition of, 434. 
 
 Boghead, 468. 
 
 brown, 63. 
 
 caking, 63. 
 
 cannel, 451. 
 
 combustion of, 62. 
 
 composition of, 63. 
 
 distillation of, 100, 448. 
 
 formation of, 61. 
 
 mines, fire-damp of, 88. 
 
 pit, 63. 
 
 products of combustion, 62. 
 distillation, 100. 
 
 stone, 63. 
 
 varieties of, 63. 
 
 Welsh, 63. 
 Coal-gas, 100. 
 
 composition ol, 101. 
 manufacture, 449. 
 
 effect on chemistry, 448. 
 purification, 450. 
 removal of bisulphide of carbon 
 
 from, 217. 
 Coal-naphtha, treatment of, 453. 
 
 Coal-tar, 450. 
 
 distillation of, 452. 
 dyes from, 456. 
 Coarse copper, 339. 
 Coarse-metal (copper), CuFeS 2 , 337. 
 Cobalt, Co, 329. 
 
 action on water, 24. 
 arseniate, 240. 
 bloom, 3CoO . As0 4 , 240. 
 chloride, 330. 
 
 commercial oxide, preparation, 329. 
 glance, CoAs, CoS,, 329. 
 oxides, 329. 
 phosphate, 329. 
 pyrites, Co 2 S 3 , 330. 
 separation from nickel, 329. 
 sulphides, 330. 
 Cocaine, 538. 
 Cocculus Indicus, 479. 
 Cochineal, 604. 
 Cocinic acid, 514. 
 Cocoa, 598. 
 Cocoa-nut oil, 580. 
 Codeine, 537. 
 
 constitution, 544. 
 extraction, 594. 
 Cod-liver oil, 582. 
 Coesium, 273. 
 
 separation from potassium, 397. 
 Coffee, composition, 597. 
 
 roasting, 597. 
 Coil, induction, 22. 
 Coin-bronze, 342. 
 Coke, 62. 
 
 action of steam on, 78. 
 composition, 434. 
 Colcothar, 201, 322. 
 Cold, greatest artificial, 130. 
 saturated solution, 47. 
 -shortness in iron, 315. 
 Collodion, balloons made, 508. 
 
 cotton, 508. 
 Colophene, 469. 
 Colophony, 469. 
 Coloured fires, 158. 
 Colouring-matters, animal, 604. 
 
 vegetable, 600. 
 Colu'mUte, 393. 
 Columbium, 393. 
 Colza-oil, 581. 
 Combination by volume, 37. 
 
 definition, 1. 
 
 Combined carbon in cast-iron, 307. 
 Combining proportions, 2. 
 
 weights of compounds, 9, 
 Combustibles and supporters, reciprocity of, 
 
 95. 
 
 Combustion, acetylene formed in, 83. 
 definition, 5. * 
 
 formation of carbonic adl in, 
 
 63. 
 
 -furnace, 73. 
 in air, definition, 6. 
 in confined air, 67. 
 in oxygen, 8. 
 U'Hiprnitiiiv ill'. |:51. 
 Common salt, NaCl, i'5-j. 
 Composition and constitution, 467. 
 Compound and mixture, di>tin. timi, 19, 
 
 definition, I. 
 Concrete, I!.".. 
 Condenser, Liebig'.-. 
 
648 
 
 INDEX. 
 
 Condurrite, 240. 
 
 Condy's disinfecting fluid, dJ8. 
 
 Coniine, 538. 
 
 constitution, 543. 
 Constitution of salts, 252. 
 Converting furnace, 316. 
 Converting vessel, Bessemer's, 314. 
 Cooking, 616. 
 Copal, 472. 
 Copper, Cu, 335. 
 
 acetylide, 84. 
 
 action of nitric acid on, 126. 
 
 on ammonia and air, 344. 
 on water, 24. 
 
 alloys of, 342. 
 
 amalgam, 369. 
 
 ammonio-sulphate, 345. 
 
 Anglesea, 339. 
 
 arsenite, 245. 
 
 basic acetate, 563. 
 
 carbonates, 335, 346. 
 phosphates, 346. 
 
 best selected, 337. 
 
 blistered, 338. 
 
 chlorides, 346. 
 
 cleaned, 344. 
 
 compounds, atomic formulae, 348. 
 
 detected in lead, 355. 
 
 diatomic, 348. 
 
 dry, 338. 
 
 effect of impurities on, 340. 
 phosphorus on, 340. 
 sea- water on, 341. 
 
 electric conductivity of, 340. 
 
 electrotype, 340. 
 
 emerald, 346. 
 
 equivalent and atomic weights, 348. 
 
 extraction in laboratory, 339. 
 
 fusing point, 341. 
 
 glance, Cu 2 S, 335. 
 
 hydrated oxide, 345. 
 
 hydride, 234. 
 
 Lake Superior, 340. 
 
 lead in, 339. 
 
 metallurgy of, 335. 
 
 moss, 338. 
 
 'native, 335. 
 
 nitride, 348. 
 
 ore, grey, 335. 
 red, 335. 
 variegated, 335. 
 
 ores, 335. 
 
 fusion for coarse metal, 336. 
 white metal, 336. 
 roasting, 335. 
 treatment of, for silver, 361. 
 
 overpoled, 338. 
 
 oxide, CuO, 343. 
 
 oxides, 343. 
 
 oxychloride, 341, 346. 
 
 peacock, 335. 
 
 pentasulphide, 347. 
 
 phosphide, 236, 348. 
 
 poling or toughening, 338. 
 
 precipitated, 84. 
 
 properties of, 341. 
 
 pyrites, CuFeS 2 , 335. 
 
 quadrant-oxide," 343. 
 
 refining, 33 3. 
 
 rose, 539. 
 
 sand, 335. 
 
 separated from silver, 365. 
 
 Copper silicates, 346. 
 
 smelting, composition of products 
 from, 339. 
 
 smelting, summary of, 335. 
 
 smoke, 336. 
 Spanish, 340. 
 
 subchloride, Cu 2 Cl, 346. 
 
 suboxide, Cu 2 0, 344. 
 
 subsulphide, Cu 2 S, 347. 
 
 sulphate, CuO . S0 3 , 344. 
 
 action of heat on, 210 
 in bread, 494. 
 
 sulphides, 347. 
 
 tinning, 342, 386. 
 
 tough-cake, 339. 
 
 tough-pitch, 338. 
 
 underpoled, 339. 
 
 verdigris, 342. 
 
 vessels for cooking, 341. 
 
 with aluminum, 290. 
 Copperas, FeO.S0 3 , 323. 
 
 blue, 34l. 
 Coprolite, 222, 230. 
 Coquimbite, 324. 
 Coral, 278. 
 
 Corpse-light in coal-mines, 91. 
 Corrosive sublimate, HgCl, 370. 
 
 antidote to, 371. 
 antiseptic properties, 
 
 371. 
 
 molecularformula, 374. 
 Corundum, 288. 
 Cotton, 465. 
 
 and wool, separation of, 617. 
 
 dissolved by ammonio-cupric solu- 
 tions, 344. 
 Cr, chromium, 331. 
 Crackers, detonating, 447. 
 Cream, 608. 
 
 Cream of tartar, 258, 586. 
 Creasote, 462. 
 Crenic acid, 628. 
 Cress, essential oil of, 479. 
 Cresylic acid, C U H 8 O 2 , 462. 
 Cr0 3 , chromic acid, 331. 
 Cr 2 O 3 , sesquioxide of chromium, 332. 
 Crocus of, antimony, 378. 
 Crookes' discovery of thallium, 360. 
 Cross-stone, 180. 
 Crotonic acid, 577. 
 Crow-fig, 599. 
 Crucibles, 413. 
 
 black lead, 56. 
 graphite, 56. 
 Cryolite, 266. 
 Crystalline lens, 612. 
 Crystallisation, 47. 
 
 Crystals from the leaden chambers, 202. 
 CS 2 , bisulphide of carbon, 215. 
 Cu, copper, 335. 
 CuCl, cupric chloride, 346. 
 CuoCl, cuprous chloride, 346, 
 Cudbear, 602. 
 Cumidine, 543. 
 Cuminic acid, HO . C 20 H U 3 , 476. 
 
 alcohol, 558. 
 
 Cummin, essential oil, 476. 
 Cumyle, 476. 
 
 hydride, 476. 
 Cumylene, 545. 
 
 diamine, 545. 
 CuO, oxide of copper, 343. 
 
INDEX. 
 
 649 
 
 CuO . S0 3 , sulphate of copper, 344. 
 Cupel-furnace, 353. 
 Cupellation on the large scale, 353. 
 small scale, 355. 
 Cupric acid, 344. 
 
 chloride, Cud, 346. 
 oxide, CuO, 343. 
 Cupros-acetyle, chloride, 84. 
 
 oxide, 84. 
 
 Cuprous acetylide, preparation, 83. 
 chloride, Cu 2 Cl, 346. 
 
 ammoniacal, 346. 
 solution, preparation, 84. 
 oxide, Cu 2 0, 344. 
 Curarine, 599. 
 Curcumine, 602. 
 Curd of milk, 608. 
 Curing animal matters, 635. 
 Current, electric, 20. 
 CuS, sulphide of copper, 347. 
 Cyamelide, 442. 
 Cyanic acid, hydrated, 442. 
 
 ether, 540. 
 Cyanide of phosphorus, 444. 
 
 potassium, KC 2 N, 440. 
 
 commercial, 441. 
 from blast-furnaces, 
 
 441. 
 
 Cyanides of alcohol-radicals, 528. 
 Cyanine, 601. 
 Cyanogen, C 2 N, 436. 
 
 chlorides, 443. 
 compounds, 436. 
 preparation, 440. 
 solution, metamorphosis of, 440. 
 Cyano-metallic radicals, 543. 
 Cyanuric acid, 443, 618. 
 Cy 3 Fe, ferrocyanogen, 437. 
 Cylinder-charcoal, 57, 420. 
 Cymole, C 20 H 14 , 465, 471. 
 
 DADTLE, 470. 
 
 hydroehlorate, 470. 
 Damaluric acid, 577. 
 Daturine, 538. 
 Davy-lamp, 90. 
 Dead head, 387. 
 Dead oil of coal-tar, 452. 
 Decay, 64. 
 
 Decolorising by charcoal, 59. 
 Decomposing-cell, 20. 
 Decomposition, definition, 1. 
 Definition of acid salt, 253. 
 
 alcohol, 513. 
 
 atomic heat, 283. 
 
 basic salt, 253. 
 
 normal salt, 253. 
 
 salt, 253. 
 Deflagrating collar, 10. 
 
 spoon, 7. 
 Deflagration, 88. 
 Dehydration, 50. 
 Deliquescence, 49. 
 Density, absolute, 422. 
 apparent, 422. 
 Deodorising by charcoal, 59. 
 chlorine, 146. 
 
 Dephlogisticated muriatic acid, 146. 
 Derbyshire spar, 177. 
 Desilverising lead, 352. 
 Destructive distillation, definition, 56. 
 Detonating tubes, 157. 
 
 Devitrification, 410. 
 Dextrine, C 12 H 10 10 , 486. 
 Dextrotartaric acid, 589. 
 Dhil mastic, 357. 
 Diacetine, 563. 
 Diacid diamines, 544. 
 Dialysis, 104. 
 Diamines, 544. 
 
 aromatic, 545. 
 Diamond, 53. 
 
 ash of, 55. 
 combustion of, 54. 
 dust, 55. 
 glazier's, 55. 
 Diamylamine, 542. 
 Diaspore, 288. 
 Diastase, 488. 
 Diathermanous, 216. 
 Diatomic elements, 152. 
 Diazoamido-benzole, 459. 
 Dichloraniline, 549. 
 Dichlorhydrine, 575. 
 Didymium, Di, 293. 
 Diet, regulation of, 632. 
 Diethacetic acid, 570. 
 ether, 569. 
 
 Diethoxalic acid, 561. 
 Diethylamine, NH(C 4 H 5 ) 2 , 540. 
 Diethyl-diethylene-diamine, 545. 
 Diethylene-diamine, N 2 H 2 (C 4 H 4 )2, 545. 
 
 -diammonmm, hydrate of, 545. 
 -diethyl-triamine, 545. 
 -trialcohol, 562. 
 -triamine, 545. 
 
 -triammonium, trichloride, 546. 
 Diethylzincamine, 562. 
 Diflusibility of gases, definition, 27. 
 law of, 29. 
 measurement of, 28. 
 rate of, 28. 
 Diffusion-tube, 28. 
 Digestion, 629. 
 
 Dimethacetic (butyric) ether, 569. 
 Diuiethoxalic acid, 561. 
 Dimethylamine, 542. 
 Dimorphous, 55. 
 Dinas fire-bricks, 413. 
 Dinitraniline, 549. 
 Dinitrobenzole, 128. 
 Dinitro-diphenylamine, 543. 
 Dioenanthylene-diamylamine, 556. 
 Dioptase, 346. 
 Diphenylamine, 543. 
 Diphenyl-benzoylamine, 543. 
 
 -diethylene-diamine, 545. 
 -guanidine, 546. 
 -urea, 620. 
 Diplatinamine, 399. 
 
 Diplatosamine, 398. 
 
 hydrate, 398. 
 hydrochlorate, 398. 
 sulphate, 398. 
 Direct combination, 4. 
 Discharge in calico-printing, 145, 606. 
 Disinfectant, MacDougall's, 461. 
 Disinfecting by chloride of lime, 1 1<>. 
 chlorine, 145. 
 ferric chloride, 324. 
 manganates, 327. 
 Disinfecting fluid, Burnett's, 298. 
 
 Condy's, 327. 
 Disintegration of rocks, 71. 
 
650 
 
 INDEX. 
 
 Disodacetic ether, 569. 
 Displacement, collection of gas by, 31. 
 Dissociation of pentachloride of phosphorus, 
 
 238. 
 Dissociation of sal-ammoniac, 271. 
 
 vermilion vapour, 375. 
 Distillation, 45. 
 
 definition of, 45. 
 destructive, 56. 
 dry, 56. 
 
 fractional, 452. 
 Distilled sulphur, 420. 
 
 water, 45. 
 
 Dithionic (hydrosulphuric) acid, S 2 5 , 213. 
 Ditoluylamine, 543. 
 Doeglic acid, 577. 
 Dolomite, MgO . CaO . 2C0 2 , 280. 
 Dough, 493. 
 Downcast shaft, 70. 
 Dryers, 581. 
 Drying gases, 49. 
 
 in vacuo, 207. 
 oils, 581. 
 
 over oil of vitriol, 207. 
 Ductility of copper, 341. 
 Dung as manure, 625. 
 
 -substitute, 246, 268. 
 Dutch liquid, C 4 H 4 C1 2 , 86. 
 
 action of chlorine on, 162. 
 Dutch metal in chlorine, 140. 
 Dyad elements, 152. 
 Dyeing, 604. 
 
 EARTHENWARE, 413. 
 Earths, alkaline, 24. 
 proper, 285. 
 Ebonite, 482. 
 
 Economico-furnace for lead-smelting, 351. 
 Effervescence, 71. 
 Efflorescence, 48. 
 Eggs, 614. 
 Egg shells, 65, 614. 
 Elaene, 515. 
 Elaidic acid, 574. 
 Elaldehyde, 555. 
 Elba iron ore, 302. 
 Electrical amalgam, 369. 
 Electrogilding, 406. 
 Electrolysis, definition, 21. 
 
 of hydrochloric acid, 141. 
 
 of water, 19. 
 
 Electro-negative elements, 21. 
 Electroplating, 363. 
 Electro-positive elements, 21. 
 Element, definition, 1. 
 Elements, non-metallic, general review, 250. 
 Elemi resin, 472. 
 Ellagic acid, 593. 
 Embolite, 366. 
 Emerald, 292. 
 
 of Limoges, 368. 
 Emery, 288. 
 Emetics, 587. 
 Emetine, 538. 
 Empirical formulas, 74. 
 Empirical and rational formulae, 467. 
 Empyreumatic, 470. 
 Emulsine, 474. 
 Enamel glass, 411. 
 Endosmose, 612. 
 English sulphuric acid, 201 
 Epsom salts, 281. 
 
 Equivalent, definition, 23. 
 formulae, 36. 
 
 of a base determined, 121. 
 of an acid determined, 75. 
 Equivalent volumes of the alcohol-radical*, 
 
 520. 
 
 Equivalent volumes of the ethers, 527. 
 olefines, 515. 
 Equivalents, table of, 2. 
 Erbium, 293. 
 Erucic acid, 577. 
 Erythric acid, 602. 
 Erythrite, 603. 
 Esculetine, 478. 
 Esculine, 478. 
 Essence of almonds, 474. 
 
 turpentine, 469. 
 Essential oils containing sulphur, 479. 
 
 extraction of, 470. 
 Ethal, C 32 H 34 O 2 , 582. 
 Ethalic acid, 582. 
 Ether, C 4 H 5 0, 517. 
 
 chemical constitution, 525. 
 decomposition by heat, 83. 
 molecular formula, 527. 
 water-type view, 527. 
 Etherification, continuous, 517. 
 
 theory of, 524. 
 
 Ethers, derivation from alcohols, 513. 
 double, 525. 
 doubled formulas, 527. 
 perfuming and flavouring, 553. 
 Ethylamine, NH 2 (C 4 H 5 ), 539, 547. 
 Ethylammonia or ethylia, 539. 
 Ethylaniline, 542. 
 Ethylate of potash, 526. 
 soda, 526. 
 zinc, 532. 
 
 Ethyl-codeyl-ammonzum, hydrate of, 544. 
 Ethyle, C 4 H 5 , 519. 
 Ethyle-amyle, 520. 
 -butyle, 520. 
 cyanide, 528. 
 hydride, 521. 
 hypothesis, 521. 
 iodide, 518. 
 kakodyle, 533. 
 orthocarbonate, 523. 
 subcarbonate, 523. 
 sulphide, 527. 
 Ethylene, C 4 H 4 , 85. 
 
 bibromide, 544. 
 
 binoxide, 559. 
 
 diamine, N 2 H 4 (C 4 H 4 ), 544. 
 
 hexethyl-diphosphonium, hydrate 
 
 of, 548. 
 
 hypothesis, 525. 
 Ethylformiate of soda, 568. 
 Ethylglucose, 499. 
 Ethylic alcohol, 512. 
 bromide, 518. 
 chloride, 518. 
 ether, 517. 
 iodide, 518. 
 Ethyl-methyl-phenylamiue, 542. 
 
 -urea, 620. 
 
 nicotyl-ammonium, hydrate of, 544. 
 Ethylo-platammonium, hydrate of, 548. 
 
 toluidine, 543. 
 Ethyloxamide, 549. 
 Ethyl-urea, 619. 
 Euchlorine, 160. 
 
INDEX. 
 
 651 
 
 Eudiometer, Cavendish's, 33. 
 
 etymology, 33. 
 
 siphon, 34. 
 
 Ure's, 34. 
 Eudiometric analysis of air, 34. 
 
 marsh-gas, 99. 
 Euodic acid, 514. 
 Euphorbium, 480. 
 Eupione, 465. 
 Eupyrion matches, 160. 
 Evernic acid, 602. 
 Excretion, 632. 
 
 Explosion of hydrogen and oxygen, 32. 
 Explosions in coal-mines, 89. 
 
 F, FLUORINE, 177. 
 Fagotting, 312. 
 Fallowing, 625. 
 Fast colours, 604. 
 Fats, 579. 
 
 table of, 583. 
 Fatty acid series, 514. 
 Fatty acids, preparation, 573. 
 Fey, ferrocyauogen, 437. 
 Fe, iron, 300. 
 
 Fe 2 Cl 3 , perchloride of iron, 324. 
 Fe 4 Fcy 3 , Prussian blue, 436. 
 Feldspar, 285. 
 
 potash-, 290. 
 soda-, 290. 
 
 Fennel, essential oil of, 476. 
 FeO, protoxide of iron, 322. 
 Fe 2 3 , peroxide of iron, 322. 
 Fe 3 4 , magnetic oxide of iron, 323. 
 FeO . S0 3 , protosulphate of iron, 323. 
 Fermentation, 64. 
 
 acetous, 492. 
 
 alcoholic, 490. 
 
 arrested by sulphurous acid, 
 
 &c., 198, 491. 
 production of carbonic acid 
 
 in, 64. 
 viscous, 491. 
 Ferric acid, Fe0 3 , 323. 
 chloride, 324. 
 
 molecular formula, 324. 
 vapour density, 324. 
 oxide, 322. 
 sulphate, 324. 
 Ferricum, 325. 
 
 Ferricyanogen (ferridcyanogen), Cy 6 Fe 2 , 443. 
 Ferrocyanates, 437. 
 Ferrocyanic acid, 437. 
 Ferrocyanide of potassium, K 2 Cy 3 Fe, 437. 
 
 action of sul- 
 phuric acid on, 
 
 Ferrocyanogen, Cy 3 Fe, 437. 
 Ferrosoferric oxide, 323. 
 Ferrosum, 325. 
 Ferrous oxide, 322. 
 
 sulphate, 323. 
 
 Ferruretted chyazic acid, 436. 
 FeS 2 , iron pyrites, 185. 
 Fibrine, blood-, 614. 
 
 extracted from blood, 612. 
 
 muscle-, 614. 
 
 vegetable, 493. - 
 Fibroine, 618. 
 Fibrous bar-iron, 312. 
 Filtration, 59. 
 Finerv-cinder, 2FeO. Si0 2 , 31". 
 
 Fire-bricks, 413. 
 Fire-clay, 286. 
 Fire-damp, 88. 
 
 conditions of inflammation, 89. 
 indicator, 89. 
 
 Fire, white, composition for, 249. 
 Fires, blue flame in, 77. 
 
 coloured, 158. 
 Fish oils, 572. 
 shells, 65. 
 
 Fixing photographic prints, 212. 
 Flags, Yorkshire, 413. 
 Flake-white, 377. 
 Flame, analysis of by siphon, 95. 
 blowpipe, 98. 
 cause of luminosity in, 92. 
 definition of, 8, 92. 
 effect of atmospheric pressure on, 97. 
 oxygen on, 99. 
 wire-gauze on, 90. 
 experimental study of, 93. 
 extinction by gases, 67. 
 extinguished by carbonic acid, 67. 
 
 good conductors, 90. 
 
 nature of, 92. 
 oxidising, 98. 
 reducing, 98. 
 relation of fuel to, 97. 
 separation of carbon in, 94. 
 structure of, 92. 
 supply of air to, 96. 
 Flames, simple and compound, 92. 
 
 smoky, 97. 
 
 Flask, to make a three-necked, 95. 
 Flesh, 615. 
 
 composition of, 616. 
 juice of, 615. 
 Flint, 102. 
 
 and steel, 102. 
 Flints dissolved, 268. 
 Florence flask, 14. 
 Floss-hole, 311. 
 
 Flour, proximate analysis of, 493. 
 Flowers bleached by sulphurous acid, 198. 
 Fluoboric acid, 182. 
 Fluorescence, 478, 596. 
 Fluoric acid, HF, 177. 
 Fluoride of calcium, 177. 
 
 silicon, 179. 
 Fluorides, 179. 
 Fluorine, F, 177. 
 
 attempts to isolate, 1 79. 
 calculated specific gravity of, 170. 
 Fluor-spar, CaF, 177. 
 Flux, Baume's, 419. 
 
 in iron smelting, 304, 306. 
 Food, effect of, upon respiration, J533. 
 exportation, 634. 
 plastic constituents of, 632. 
 preservation of, 635. 
 respiratory constituents of, 632. 
 Forge-iron, 309. 
 Fonnamide, 549. 
 
 Formic acid, HO . C g H0 3 , 514, 567. 
 Foi-monitrile, 550. 
 Formulae, atomic, 36. 
 
 calculation of, 74. 
 empirical and rational, 1>7. 
 equivalent, 36. 
 molecular, 51. 
 Formylamine, hydriodate of, 404. 
 
052 
 
 INDEX. 
 
 Formyl-diphenyl-diamine, 545. 
 Formyle, C 2 H, 520. 
 
 terchloride of, 552. 
 Fouling of guns, 428. 
 Foundry-iron, 309. 
 Fousel-oil, 511. 
 Fowler's solution, 245. 
 Fractional distillation, 452. 
 Frankincense, 480. 
 FranJdinite, ZnO . Fe 2 3 , 323. 
 Free-stone, 413. 
 Freezing-apparatus, 116. 
 
 in red-hot crucible, 197. 
 mixtures, 117, 130, 271. 
 of water, 46. 
 
 with bisulphide of carbon, 216. 
 French chalk, 280. 
 Friction-tubes, 157. 
 
 composition for, 157. 
 Fructose, C 12 H 12 O 12 , 496. 
 Fruits, ripening of, 627. 
 Fuel, calculation of calorific intensity, 432, 
 
 value, 430. 
 chemistry of, 429. 
 practical applications of, 431. 
 Fuels, composition of, 434. 
 
 illuminating, composition of, 97. 
 Fuller's earth, 286. 
 Fulminic acid, 445. 
 Fulminate of mercury, C 4 Hg 2 N 2 4 , 444. 
 
 action of hydrochloric 
 
 acid on, 447. 
 preparation, 444. 
 properties, 445. 
 silver, 446. 
 Fulminates, chemical constitution, 447. 
 
 double, 447. 
 Fulminating gold, 407. 
 
 platinum, 397. 
 silver, 364. 
 Fumaric acid, 590. 
 Fumigating with chlorine, 146. 
 
 sulphurous acid, 198. 
 Fuming sulphuric acid, 201. 
 Fumitory, 590. 
 Funnel-tube, 25. 
 Fur in kettles, 40. 
 Furfuramide, 568. 
 Furfurine, 568. 
 Furfurole, C 10 H 4 4 , 568. 
 Furnace, charcoal, 106. 
 
 regenerative, 434. 
 ^ reverberatory, 311. 
 Sefstrbm's, 321. 
 Furnaces, theory of, 430. 
 
 waste of heat in, 433. 
 Fused common salt, 108. 
 Fusible alloy, 299. 
 Fusing-points of fats, 583. 
 Fusion, 105. 
 Fustic, 601. 
 Fuze, Armstrong percussion, 229. 
 
 Oadolinite, 293. 
 Galbanum, 480. 
 Galena, PbS, 349. 
 Gallic acid, 593. 
 Gall-nuts, 590. 
 Galvanic battery, 20. 
 Galvanised iron, 294. 
 Gamboge, 480. 
 Gangue, 306. 
 
 Garancine, 602. 
 
 Garlic, essence, artificial production, 480 
 
 essential oil of, 479. 
 Garnet, 290. 
 Gas, air vitiated by, 69. 
 
 -burner, Bunsen's rosette, 45. 
 ring, 46. 
 smokeless, 96. 
 -carbon, 449. 
 composition of, 101. 
 -cylinder, 12. 
 -holder, 54. 
 valuation of, 96. 
 -jar, 14. 
 
 manufacture of, 449. 
 Gaseous hydrocarbons, analysis of, 99. 
 Gases, diffusion of, 19. 
 
 expansion by heat, 427. 
 in waters, 39. 
 Gastric juice, 630. 
 Gaultheria, oil of, 467. 
 Gauze burner, 96. 
 Gaylussite, 278. 
 G edge's metal, 342. 
 Geic acid, 628. 
 Gelatine, 616. 
 German silver, 330. 
 Germination, 487, 626. 
 Geysers, 103. 
 Gilding, 406. 
 
 porcelain, 412. 
 Gin, 511. 
 
 Gl, glucinum, 292. 
 Glass, 409. 
 
 bottle, 410. 
 coloured, 410. 
 composition of, 409. 
 corrosion by hydrofluoric acid, 478. 
 crown, 410. 
 decolorised, 410. 
 etched, 178. 
 flint, 410. 
 -gall, 410. 
 
 manufactxire of, 409. 
 of antimony, 382. 
 plate, 410. 
 
 plate perforated, 202. 
 -pots, 413. 
 silvered, 363. 
 window, 409. 
 Glauberite, 268. 
 Glauber's salt, 138. 
 Glaze for earthenware, 413. 
 Glazier's diamond, 55. 
 Globuline, 612. 
 Glonoine, 597. 
 Glucic acid, 499. 
 Glucina, 293. 
 
 separation from alumina, 293. 
 Glucinum, Gl, 292. 
 Glucose, C 12 H 14 O 14 , 487. 
 artificial, 495. 
 stearic, 578. 
 Glucosides, 476. 
 Gluco-tartaric acid, 578. 
 Glue, 617. 
 Gluten, 493. 
 
 varieties of, 494. 
 Glutine, 493. 
 Gly eerie acid, 561. 
 
 alcohol, 576. 
 ether, 576. 
 
INDEX. 
 
 653 
 
 Glycerides, 575. 
 Glycerine, C 6 H 8 6 , 576. 
 
 converted into glycol, 576. 
 extraction of, 575. 
 molecular formula of, 562. 
 properties, 576. 
 soap, 573. 
 triatomic, 562. 
 Glyceryle, C 6 H,, 562. 
 Glycocholic acid, 630. 
 Glycocoll (glycocine), C 4 H 5 N0 4 , 617. 
 Glycogen, 631. 
 Glycol, C 4 H 6 4 , 558. 
 
 acetobutyrate of, 562. 
 aldehyde of, 560. 
 binacetate of, 559. 
 chlorhydrine of, 559. 
 converted into alcohol, 562. 
 nionacetate of, 562. 
 Glycolic acid, HO . C 4 H 3 Oj, 560. 
 Glycols, 558. 
 Glycyrrhizine, 500. 
 Glyoxal, 560. 
 Gneiss, 291. 
 Gold, Au, 402. 
 
 and sodium, hyposulphite, 407. 
 
 assay by cupellation, 405. 
 
 coin, 404. 
 
 compounds, atomic formulae of, 408. 
 
 crucible, 406. 
 
 dissolved, 167. 
 
 equivalent and atomic weights, 408. 
 
 extracted from old silver, 404. 
 
 extraction, 403. 
 
 fulminating, 407. 
 
 identification of, 126. 
 
 in chlorine, 140. 
 
 lace cleaned, 441. 
 
 treatment of, 405. 
 leaf, 405. 
 oxides of, 406. 
 physical properties, 405. 
 protochloride, AuCl, 407. 
 refining, 404. 
 
 removal of mercury from, 368. 
 ruby, 227, 406. 
 
 separated from silver and copper, 207. 
 standard, 404. 
 
 specific gravity of, 405. 
 sulphides of, 408. 
 terchloride, AuCl 3 , 406. 
 testing, 405. 
 thread, 406. 
 triatomic, 408. 
 Goulard's extract, 563. 
 Gradational relations of elements, 182, 275, 
 
 283. 
 
 Grains, brewers', 489. 
 Granatite, 180. 
 Granite, 285. 
 
 disintegration of, 286. 
 Granitic rocks, 258. 
 Granulated zinc, 25. 
 Grape-husks, 509. 
 juice, 509. 
 sugar, Ci 2 H u 14 , 487. 
 
 composition, 499. 
 distinguished from cane- sugar, 
 
 495. 
 
 Grapes, colouring matter of, 601. 
 Graphite, 55. 
 
 ash of, 55. 
 
 Graphite crucibles, 56. 
 
 in cast-iron, 55, 307. 
 uses of, 56. 
 
 Grease removed from clothes, 454. 
 Green, arsenical, 245. 
 
 borate of chromium, 333. 
 Brunswick, 346. 
 chrome, 332. 
 colour of plants, 600. 
 fire, composition for, 158. 
 flame of baryta, 277. 
 
 boracic acid, 110. 
 copper, 346. 
 thallium, 361. 
 malachite, 346. 
 mineral, 346. 
 Kinman's, 330. 
 salt of Magnus, 398. 
 vitriol, 323. 
 Grey copper ore, 335. 
 Grey iron, 308. 
 
 nickel ore, 330. 
 powder, 368. 
 Gristle, 616. 
 Grotto del Cane, 66. 
 Grough saltpetre, 415. 
 Groups of non-metallic elements, 250. 
 Grove's battery, 20. 
 Guaiacum resin, 472. 
 Guanidine, 546. 
 Guanite, 282. 
 Guano, 621, 625. 
 Guelder rose, 570. 
 Gum Arabic, 482. 
 British, 486. 
 Senegal, 483. 
 tragacanth, 483. 
 Gum-resins, 480. 
 Gums, 482. 
 
 Gun-cotton, C la H 7 (N0 4 ),O lo , 500. 
 atomic formula, 503. 
 compared with gunpowder, 505. 
 composition, 503. 
 equation of explosion, 504. 
 in mining, 506. 
 
 Karolyi's experiments on, 504. 
 manufacture, 501. 
 
 summary of, 502. 
 objections to, 507. 
 preparation on the small scale, 
 501. 
 
 products of explosion, 503. 
 properties, 506. 
 
 pulp, Abel's, 506. 
 
 reconversion, 503. 
 
 silicated, 502. 
 
 slow combustion of, 506. 
 
 woven, Lenk's, 506." 
 Gun-metal, 342, 386. 
 Gun-paper, 500. 
 Gunpowder, 415. 
 
 calculation of force, 425. 
 
 collection of gases from, 424. 
 
 composition, variations in, 481. 
 
 dusting, 422. 
 
 effect of pressure on explosion 
 of, 428. 
 
 equation of explosion, 425. 
 
 examination of, 423. 
 
 facing, 422. 
 
 glazing, 422. 
 
 granulating or corning, 422. 
 
654 
 
 INDEX. 
 
 Gunpowder, heat of combustion, 426. 
 
 hygroscopic character, 422. 
 incorporation, 421: 
 influence of si/e of grain, 427. 
 manufacture, 421. 
 mechanical effect, 427. 
 preparation in the laboratory, 
 
 429. 
 
 pressing, 422. 
 products of explosion, 423. 
 
 slow combustion, 
 
 428. 
 
 properties, 422. 
 smoke, 428. 
 specific heat of products from, 
 
 426. 
 temperature of combustion, 
 
 427. 
 
 volume of gas from. 424. 
 white, 158. 
 Gutta percha, 482. 
 Gypsum, 279. 
 
 II, HYDROGEN, 19. 
 
 Hsemateine, 601. 
 Hsematine, 613. 
 Haematite, brown, 301. 
 
 red, Fe 2 3 , 301. 
 Hsematosine, 613. 
 Hsematoxyline. 601. 
 Hair, 617. 
 Hair-dye, 357, 365. 
 Halogen, definition of, 10. 
 Halogens, general review of, 182. 
 Haloid salts, 10, 182. 
 Hammer-slag, 312. 
 Hard metal, 386. 
 Hardness, degrees of, 43. 
 permanent, 43. 
 temporary. 43. 
 Hard water, 40. 
 Harrogate water, 45. 
 Hartshorn, spirit of, 116. 
 Hausmannitc, Mn 3 4 , is 326. 
 HBr, hydrobromic acid, 169. 
 HC1, hydrochloric acid, 147. 
 HCy, hydrocyanic acid, 438. 
 Heat and temperature, 431. 
 
 atomic, 37. 
 
 rays separated from light, 172, 216. 
 
 relation to chemical attraction. 12. 
 Heath's patent (steel), 318. 
 Heating of hayricks, 61. 
 Heat of combustion of hydrocarbons, 430 
 Heat-units, 426. 
 Heavy lead-ore, Pb0 2 , 357. 
 spar, BaO . S0 3 , 275. 
 Hemihedral crystals, 588. 
 Hemming's jet, 90. 
 Hepatic waters, 45. 
 EtF, hydrofluoric acid, 177. 
 HF. SiF 2 , hydrofluo-silicic acid, 181. 
 Hg, mercury, 367. 
 HgCl, mercuric chloride, 370. 
 Hg 2 Cl, mercurous chloride, 372. 
 HgO, mercuric oxide, 369. 
 Hg 2 0, mercurous oxide, 369. 
 HgO, N0 5 , mercuric nitrate, 370. 
 H 2 0, NO S , mercurous nitrate, 370. 
 HgS, sulphide of mercury, 367. 
 Hg 2 S, mercurous sulphide, 373 
 HI, hydriodic acid, 174. 
 
 Hippuric acid, HO,C 18 H 8 NO S , 622. 
 
 artificial formation, 622. 
 extraction from cow's urine, 
 
 622. 
 
 HO, water, 38. 
 
 HO^Jnnoxide of hydrogen, 50. 
 HO . Ascetic acid, 563. 
 3HO . Ci^ citric acid, 589. 
 Homogeneous metal, 319. 
 Homologous series, 459. 
 Honey, 496. 
 
 HO . N0 5 , hydrated nitric acid, 123. 
 HO . 0, oxalic acid, 583. 
 Hoofs, 617. 
 Hops, 489. 
 
 essential oil of, 470. 
 Hornblende, 291. 
 Horn-lead, 359. 
 
 -silver, 365. 
 Horns, 617. 
 Horse-chestnut bark, 478. 
 
 -hair inflamed by nitric acid, 128. 
 -radish, essential oil of, 479. 
 HO . S0_ 3 , hydrated sulphuric acid, 200. 
 2HO . T, tartaric acid, 586. 
 Hot blast, theory of, 432. 
 blast iron, 305. 
 saturated solution, 47. 
 HS, hydrosulphuric acid, 189. 
 Humic acid, 628. 
 Humus, 628. 
 Hyacinth, 293. 
 
 Hydrargyrum cum creta, 368. 
 Hydrated acids, 50. 
 bases, 49. 
 
 Hydrate of lime, CaO . HO, 49. 
 potash, KO . HO, 50. 
 Hydrates, 47. 
 Hydraulic cements, 414. 
 
 main, 449. 
 
 Hydrides of alcohol-radicals, 521. 
 Hydriodate of potash, 176. 
 Hydriodic acid, HI, 174. 
 
 composition by volume, 175, 
 gas, preparation, 175. 
 reducing properties, 175. 
 solution, preparation, 175. 
 ether, 518. 
 Hydroboracite, 282. 
 Hydrobromic acid, HBr, 169. 
 
 composition by volume, 
 
 ether, 518. 
 Hydrocarbons, 82. 
 
 heat of combustion of, 430. 
 turpentine-series, 470. 
 Hydrochloric acid, HC1, 160. 
 
 absorption by water, 147. 
 action of heat on, 148. 
 action on metallic oxides, 
 
 150. 
 action on metals, 149. 
 
 nitric acid, 167. 
 plants, 149. 
 analysis of, 150. 
 atomic constitution, 151 . 
 composition by volume, 
 
 decomposed by the bat- 
 tery, 131. 
 equivalent, 150. 
 
INDEX. 
 
 655 
 
 Hydrochloric acid from alkali- works, 148. 
 gas, preparation of. 147. 
 liquid, 149. 
 
 molecular formula, 151. 
 properties, 147. 
 pure, preparation of, 148. 
 synthesis of, 140. 
 valuation of, 148. 
 yellow, 148. 
 Hydrochloric ether, 518. 
 
 gas, dry, preparation, 148. 
 Hydrocyanic acid, HC 2 N, 438. 
 
 anhydrous, 439. 
 Liebig's test for, 442. 
 ether, 528. 
 
 Hydrocyan-rosaniline, 458. 
 Hydroferricyanic acid, H 3 Cy 6 Fe 2 , 443. 
 Hydroferrocyanic acid, H 2 Cy 3 Fe, 437. 
 Hydrofluoboric acid, 182. 
 Hydrofluoric acid, HF, 177. 
 
 action on metals, 178. 
 silica, 178. 
 calculated specific gravity, 
 
 179. 
 
 composition, 179. 
 gas, 178. 
 Hydrofluo-silicic acid, HF . SiF 2 , 181. 
 
 decomposed by heat. 
 
 181. 
 Hydrogen, H, 19. 
 
 and arsenic, 246. 
 carbon, 82. 
 sulphur, 190. 
 binoxide, 50. 
 calorific intensity calculated, 432. 
 
 value, 31, 430. 
 chemical properties, 30. 
 relations, 38. 
 
 determination, in gases, 35. 
 displaced by sodium, 23. 
 etymology of, 30. 
 experiments with, 27. 
 flame, 31. 
 
 identification of, 21. 
 natural sources, 19. 
 peroxide, 50. 
 persulphide, 195. 
 phosphides, 235. 
 physical properties, 26. 
 poured up through air, 27. 
 preparation with iron, 24. 
 zinc, 25. 
 selenietted, 219. 
 sulphuretted, 189. 
 Hydrokinone, 596. 
 Hydronitroprussic acid, 444. 
 Hydroselenic acid, HSe, 220. 
 Hydrosulphocarbonic acid, 217. 
 Hydrosulphocyanic acid, HCyS 2 , 442. 
 Hydrosulphuric acid, HS, 189. 
 
 action on iodine, 175. 
 metallic chlorides, 193. 
 
 oxides, 192. 
 
 solutions of metals, 193. 
 sulphurous acid, 214. 
 composition, 194. 
 disposal of, 191. 
 liquefied, 195. 
 molecular formula, 194. 
 pi'eparation, 190. 
 production in waters, 211. 
 solution of, 191. 
 
 Hydrosulphuric acid, test for, 192. 
 
 use in analysis,- 193. 
 ether, 527. 
 Hydrotelluric acid, HTe, 221. 
 Hydroxylamine, NH 3 2 , 127, 522. 
 Hyoscyamine, 538. 
 Hypobromous acid, 169. 
 Hypochlorite of lime, CaO . CIO, 145. 
 Hypochlorous acid, CIO, 154. 
 
 action on sal-ammoniac, 
 
 167. 
 
 Hypogeic acid, 577. 
 Hyponitric acid, 134. 
 Hyponitrous acid, 132. 
 Hypophosphites, 234. 
 Hypophosphorous acid, PO, 234. 
 Hyposulphates, 214. 
 Hyposulphindigotic acid, 604. 
 Hyposulphite of soda, NaO . S 2 2 , 213. 
 
 and perchloride of iron. 
 
 214. 
 decomposed by acids, 
 
 2137 
 
 decomposed by heat, 213. 
 Hyposulphites, 211. 
 
 constitution of, 213. 
 
 Hyposulphuric (dithionic) acid, S 2 O 5 , 213. 
 Hyposulphurous acid, S 2 O 2 , 211. 
 
 formed from sulphur- 
 ous acid, 213. 
 
 I, IODINE, 170. 
 
 Ice, 46. 
 
 Iceland spar, CaO . C0 2 , 278. 
 
 Illuminating gas from water, 78. 
 
 Imides, 550. 
 
 constitution of, 651. 
 Imidogen, NH, 550. 
 Incorporating mill, 421. 
 Incrustation on charcoal, 99. 
 Incrustations in boilers, 41. 
 Indian fire, 249. 
 Indican, 603. 
 Indifferent oxides, 11. 
 Indigo, action of chlorine on, 144. 
 
 blue, C 18 H 5 N0 2 , 603. 
 
 copper, CuS, 347. 
 
 reduced, 603. 
 vat, preparation, 604. 
 white, C 16 H 6 N0 2 , 603. 
 Indigotine, 604. 
 Indium, 299. 
 
 oxide, 299. 
 Induction coil, 22. 
 
 tube, Siemens', 15. 
 Ink, 591. 
 
 blue, 438. 
 from logwood, 601. 
 red, 601. 
 
 stains removed, 154. 
 vanadium, 393. 
 
 Inorganic substances, definition, 3. 
 Inosite, C 12 H 12 12 , 615. 
 Instantaneous light, 395. 
 Intensity and quantity, electric, 21. 
 Introduction, 1. 
 Intumescence, 267. 
 lodates, 174. 
 lodic acid, 10,., 173. 
 Iodide of nitrogen, 176. 
 potassium, 176. 
 
656 
 
 INDEX. 
 
 Iodide of silver, Agl, 366 
 Iodine, I, 170. 
 
 action on ammonia, 17o. 
 
 potash, 172. 
 and starch, 172. 
 bromides, 176. 
 chloride, IC1, 176. 
 etymology of, 171. 
 extraction from sea- weed, 171. 
 identified, 172. 
 oxides, 173. 
 terchloride, IC1 3 , 176. 
 test for, 172. 
 tincture of, 172. 
 Iodised starch paper, 15. 
 lodoform, 553. 
 Iridium, Ir, 401. 
 
 ammoniochloride, 401. 
 -black, 401. 
 chlorides, 402. 
 oxides, 401. 
 Iron, Fe, 300. 
 
 action of acids on, 322. 
 
 air of towns on, 294. 
 hydrochloride acid on, 149. 
 on water, 24. 
 amalgam, 369. 
 and carbon, 307. 
 and oxygen, 10. 
 
 and potassium, ferrocyanide, 438. 
 bar-, 312. 
 
 basic persulphate, 200. 
 bisulphide, 302. 
 black oxide, 323. 
 bright, 308. 
 burnt in bisulphide of carbon flame, 
 
 216. 
 
 carbonate, 397. 
 cast, 307. 
 
 chemical properties, 231. 
 chlorides, atomic formulae, 324. 
 cold short, 315. 
 cyanide, FeC 2 N, 438. 
 diatomic, 324. 
 
 equivalent and atomic weights, 324. 
 extraction in the laboratory, 321. 
 ferricyanide, 443. 
 fibre in, 315. 
 galvanised, 294. 
 glance, 302. 
 grey, 308. 
 
 group of metals, general review, 334. 
 homogeneous, 319. 
 in blood, 612. 
 in zinc, 297. 
 iodide, 176. 
 
 magnetic oxide, Fe 3 4 , 323. 
 metallurgy, 302. 
 mottled, 308. 
 -mould, 322, 591. 
 occurrence in nature, 300. 
 of antiquity, 320. 
 ores, 300. 
 
 British, composition, 301. 
 calcining or roasting, 303. 
 oxides, 322. 
 
 atomic formulae, 324. 
 passive state of, 322. 
 perchloride, Fe 2 Cl 3 , 324. 
 peroxide, Fe 2 O 3 , 322. 
 
 action of hydrosiilphuric 
 acid on, 193. 
 
 Iron persulphate, Fe 2 3 . 3S0 3 , 324. 
 
 phosphates, 324. 
 
 phosphorus in, 315. 
 
 plates cleansed, 385. 
 
 protochloride, 324. 
 
 proto-sesquioxide, 323. 
 
 proto-sulphate. 323. 
 
 uses, 323. 
 
 protoxide, FeO, 10, 322. 
 
 prussiate, 436. 
 
 pure, preparation of, 321. 
 
 purification, 309. 
 
 pyrites, FeS 2 , 185, 302. 
 
 pyrophoric, 11, 80. 
 
 red oxide, 322. 
 
 red short, 315. 
 
 refining, 310. 
 
 rust, ammonia in, 121. 
 
 rusting of, 322. 
 
 sand, 302. 
 
 scales, 312. 
 
 scurf, 413. 
 
 separation from manganese, 328. 
 
 sesquichloride, 324. 
 
 sesquiferrocyanide, 438. 
 
 sesqui-iodide, 177. 
 
 sesquioxide, 11. 
 
 sesquisulphate, 324. 
 
 smelting, English method, 303. 
 
 specular, 406. 
 
 steely, 315. 
 
 sulphate, action of heat on, 210. 
 
 nitric acid on, 131. 
 
 sulphide, preparation, 190. 
 
 sulphuret, 190. 
 
 sulphur in, 315. 
 
 tincture of, 324. 
 
 tinned, 385. 
 
 triatomic, 325. 
 
 useful properties of, 302. 
 
 variation in strength of, 315. 
 
 white, 308. 
 
 wire, composition, 313. 
 
 works of the Pyrenees, 321. 
 
 wrought or bar, composition, 313. 
 direct extraction, 320. 
 manufacture, 309. 
 Tseritie, 391. 
 Tsethionic acid, 631. 
 Isinglass, 617. 
 Isocumole, 450. 
 Isodimorphism, 379. 
 
 of antimonious oxide and 
 
 arsenious acid, 251. 
 Isomerism, 467. 
 
 explanation of, 463. 
 Isomorphism, 251. 
 Isoprene, 481. 
 Isotartaric acid, 587. 
 Isoterebenthene, 469. 
 Ivory-black, 59. 
 
 JATROPHINE, 486. 
 
 Jellies, fruit, 627. 
 
 Jelly, 617. 
 
 Jet for burning gases, 31. 
 
 Jeweller's rouge, 322. 
 
 Juice of sugar-cane, 497. 
 
 Juniper, essential oil of, 470. 
 
 K, POTASSIUM, 258. 
 
INDEX. 
 
 657 
 
 Kakodyle, C 4 H 6 As, 529. 
 
 chemical constitution of, 530. 
 
 chloride, 529. 
 
 cyanide, 530. 
 
 oxide, 529. 
 
 series, 529. 
 Kakodylic acid, 530. 
 Kaolin, 286. 
 Kapnomor, 465. 
 
 Karolyi's experiments on gunpowder, 424. 
 KC1, chloride of potassiiim, 261. 
 KC1, PtCl^ platinochloride of potassium, 397. 
 , KCy, cyanide of potassium, 440. 
 KCyS 2 , sulphocyanide of potassium, 442. 
 Kelp, 170. 
 
 Kermes mineral, 382. 
 Kernel roasting, 347. 
 Ketones, 557. 
 
 K 2 Fcy, ferrocyanide of potassium, 437. 
 K 3 Fdcy, ferricyanide of potassium, 443. 
 KI, iodide of potassium, 176. 
 Kid, 592. 
 
 King's yellow, 249. 
 Kinic acid, 596. 
 Kino, 594. 
 
 Kinone, C 12 H 4 4 , 596. 
 Kirschwasser, 511. 
 Kish, 55. 
 Klumene, 83. 
 KO, potash, 259. 
 
 KO . CIO S , chlorate of potash, 155. 
 KO . CO 2 , carbonate of potash, 258. 
 KO . Cr0 3 , chromate of potash, 332. 
 KO . 2Cr0 3 , bichromate of potash, 331. 
 KO . CyO, cyanate of potash, 442. 
 KO . HO, caustic potash, 259. 
 KO . HO . 2C0 2 , bicarbonate of potash, 261. 
 KO . HO . 2S0 3 , bisulphate of potash, 210. 
 Kola nut, 597. 
 
 KO . Mn. 2 7 , permanganate of potash, 327. 
 KO . NO.,, saltpetre or nitre, 415. 
 KO . Sb6 5 , antimoniate of potash, 380. 
 KO. SbOg.T, tartar-emetic, 587. 
 Koumiss, 609. 
 Kreasote, 460, 635. 
 Kreatine, C 8 H 9 N 3 4 , 615. 
 
 extraction from flesh, 615. 
 Kreatinine, C 8 H 7 N 3 02, 615. 
 Kresyle, 462. 
 
 Kresylic acid, 0^0*, 462. 
 Krupp's steel, 320. 
 Kryolite, 3NaF. A1 2 F 3 , 179. 
 KS, sulphide of potassium, 262. 
 Kupfernickel, Ni 2 As, 330. 
 Kyanising wood, 628. 
 
 LAC, 604. 
 
 seed, 472. 
 stick, 472. 
 Lacquer, 472. 
 Lacquering, 343. 
 Lactarine, 610. 
 Lactic acid, HO . C 8 H 5 5 , 561, 608. 
 
 converted into butyric, 569. 
 
 propionic, 609. 
 preparation, 608. 
 anhydride, C 6 H 6 4 , 609. 
 fermentation, 608. 
 series of acids, 560. 
 Lactide, 609. 
 Lactine, C u H,,0 la , 610. 
 Lactometer, 611. 
 
 Lsevotartaric acid, 589. 
 Lagunes, boracic, 109. 
 Lakes, alumina, 288. 
 Lamp, action explained, 93. 
 -black, 56. 
 without flame, 395. 
 Lanarkite, 359. 
 Lanthanium, La, 293. 
 Lapis lazuli, 291. 
 Lard, 582. 
 Laughing gas, 130. 
 Laurel water, 439, 475. 
 Laurent's doctrine of substitution, 463. 
 
 nomenclature. 463. 
 Laurie acid, 514. 
 
 alcohol, 512. 
 Laurite, 401. 
 
 Law of multiple proportions, 135. 
 Lead, Pb, 348. 
 
 acetate, PbO . C 4 H 3 3 , 563. 
 
 action of acids on, 355. 
 
 sulphuric acid on, 205* 
 on water, 24, 44. 
 
 amalgam, 369. 
 
 argentiferous, 352. 
 
 basic carbonate, 356. 
 chromate, 332. 
 
 binoxide, 357. 
 
 calcining, 351. 
 
 carbonate, native, 359. 
 
 chloride, PbCl, 359. 
 
 chlorosulphide, 360. 
 
 chromate, PbO . Cr0 3 , 332. 
 
 colic, 358. 
 
 compounds, atomic formulae, 360. 
 
 diatomic, 360. 
 
 dichromate, 332. 
 
 equivalent and atomic weights, 360. 
 
 extraction in the laboratory, 354. 
 
 fusing point of, 348. 
 
 -glazed earthenware, .412. 
 
 hard, 351. 
 
 hydrated oxide, 357. 
 
 improving process, 351. 
 
 in cider, &c., 356. 
 
 iodide, Pbl, 173, 360. 
 
 malate, 590. 
 
 metallurgic chemistry, 349. 
 
 molybdate, 393. 
 
 native, 349. 
 
 ores, 349. 
 
 oxide, use of, in glass, 410. 
 
 oxides, 356. 
 
 oxychloride, 359. 
 
 peroxide, PbO 2 , 357. 
 
 phosphate, 359. 
 
 plaster, 576. 
 
 protoxide, PbO, 356. 
 
 pyrophorus, 356. 
 
 selenide, 360. 
 
 smelting, 349. 
 
 Spanish, 351. 
 
 specific gravity, 348. 
 
 sulphate, PbO . SO,, 349, 359. 
 
 sulphides, 360. 
 
 tartrate, preparation, 356. 
 
 tribasic acetate, 563. 
 
 uses, 355. 
 
 vanadiate, 393. 
 Lead-vitriol, PbO. S0 3 , 359. 
 Leaden cisterns, danger, 44. 
 coffins, corrosion, 356. 
 
 2T 
 
658 
 
 INDEX. 
 
 Leadhillite, 359. 
 Leather, 591. 
 Leaven, 494. 
 
 Leaves, formation of, 626. 
 Lecanoric acid, 602. 
 Leeks, essential oil of, 479. 
 Legumine, 610. 
 Lemery's volcano, 189. 
 Lemons, essential oil of, 470. 
 Lepargylic acid, 580. 
 Lepidolite, 272. 
 Leucaniline, 457. 
 
 triphenylic, 458. 
 Leucic acid, HO . C 12 H n 5 , 560. 
 Leucine, C 12 H 13 N0 4 , 617. 
 Leucone, 108, 166. 
 Li, lithium, 272. 
 Libethenite, 346. 
 
 Lichens, colouring matter from, 602. 
 Liebig's condenser, 46. 
 Life, its extremes meet, 635. 
 Light, action on chloride of silver, 205. 
 
 -rays separated from heat, 172, 216. 
 Light carburetted hydrogen, 88. 
 
 oil of coal-tar, 452. 
 Lignine, 464. 
 Lignite, 63. 
 
 composition, 434. 
 Lime, CaO, 278. 
 
 action on soils, 625. 
 
 agricultural uses, 625. 
 
 bicarbonate, 41. 
 
 bimalate, 590. 
 
 burning, 278. 
 
 carbonate, CaO . C0 2 , 278. 
 in waters, 41. 
 
 fat, 279. 
 
 hydrate, CaO . HO, 278. 
 
 hypochlorite, 145. 
 
 hyposulphite, 195. 
 
 kilns, 278. 
 
 -light, 37. 
 
 lactate, 608. 
 
 overburnt, 279. 
 
 oxalate, CaO . C 2 3 , 535. 
 
 platinate, 396. 
 
 poor, 279. 
 
 purifier, 450. 
 
 -stone, CaO . C0 2 , 278. 
 
 sulphate, CaO . S0 3 , 279. 
 
 superphosphate, 223. 
 
 test for, 585. 
 
 water, 279. 
 Linen, 465. 
 Linoleic acid, 581. 
 Linseed, 483. 
 
 oil, 581. 
 
 boiled, 581. 
 Lipic acid, 580. 
 
 Liquation of argentiferous copper, 361. 
 Liquor ammonias, 113. 
 
 sanguinis, composition, 613. 
 Liquorice root, 500. 
 Litharge, PbO, 356. 
 Lithia, 272. 
 
 carbonate, 272. 
 mica, 272. 
 phosphate, 272. 
 Lithic (uric acid), 621. 
 Lithium, Li, 272. 
 
 blowpipe test for, 272. 
 equivalent weight, 275. 
 
 Litmus, 602. 
 
 commercial, 603. 
 
 paper, 5. 
 
 Loadstone, Fe 3 4 , 11, 302. 
 Loam, 286. 
 Logwood, 601. 
 
 Looking-glasses silvered, 368. 
 Lucifer matches, 157, 228. 
 
 tipped with sulphur. 225. 
 Luminosity of flames, 92. 
 Lunar caustic, 364. 
 Lupuline, 489. 
 Luteoline, 601. 
 Luting for crucibles, 295. 
 iron joints, 189. 
 
 MACDOUGALL'S disinfectant, 61. 
 
 Madder, 601. 
 
 Magenta, 456. 
 
 Magic lantern, oil for, 471. 
 
 Magnesia, MgO, 280. 
 
 ammonio-phosphate, 282. 
 arsenite, 244. 
 borate, 282. 
 calcined, 282. 
 carbonate, 281. 
 citrate, 590. 
 hydrate, 282. 
 hydraulic, 282. 
 medicinal, 281. 
 phosphate, 282. 
 silicates, 280. 
 sulphate, MgO . S0 3 , 281. 
 Magnesian limestone, 280. 
 
 for building, 414. 
 Magnesite, 280. 
 Magnesium, Mg, 280. 
 
 action on water, 24. 
 chloride, 108, 282. 
 
 extraction from sea- 
 water, 263. 
 diatomic, 285. 
 equivalent and atomic weights, 
 
 283. 
 
 extraction, 281 
 nitride, 280. 
 properties, 280. 
 silicide, 108. 
 
 Magnet-fuze composition, 348. 
 Magnetic iron ore, Fe 3 O 4 , 302. 
 Magnus' green salt, 398. 
 Malachite, 335. 
 Malseic acid. 590. 
 Malamide, 590. 
 Malic acid, 2HO. C 8 H 4 8 , 590. 
 
 converted into acetic, 590. 
 
 succinic, 590. 
 
 extracted from rhubarb, 590. 
 formed from siiccinic, 588. 
 tartaric, 588. 
 
 Malleability of copper, 341. 
 Malleable cast iron, 319. 
 Malonic acid, 580. 
 Malt dust, 488. 
 
 high dried, 491. 
 Malting, 487. 
 Manganate of potash, 326. 
 Manganese, Mn, 325. 
 
 action on water, 24. 
 alum, 326. 
 
 binoxide, action of sulplmric 
 acid on, 210. 
 
INDEX. 
 
 659 
 
 Manganese, black, 325. 
 
 carbonate, 326. 
 
 chlorides, 328. 
 
 diatomic, 328. 
 
 equivalent and atomic weights, 
 
 328. 
 
 hydrated peroxide, 325. 
 oxides, 325. 
 peroxide, 325. 
 protoxide, MiiO, 326. 
 recovery from chlorine residues, 
 
 328. 
 1 x red oxide, 325. 
 
 separation from iron, 328. 
 sesquioxide, Mn a 3 , 326. 
 spar, MnO . C0 2 , 326. 
 sulphate, MnO . S0 3 , 326. 
 test for, 326. 
 
 Manganic acid, Mn0 3 , 326. 
 Manganite, Mn 2 3 . HO, 326. 
 Manna, 500. 
 Mannitane, 578. 
 Mannite, C 6 H 7 6 , 500. 
 
 glycerides, 578. 
 glycerine, 578. 
 stearine, 578. 
 Mantle of flame, 94. 
 Manures, 624. 
 Manuring, 624. 
 Maraschino, 511. 
 Marble, 278. 
 Margaric acid, 514, 580. 
 Margarine, 573. 
 Marine glue, 481. 
 Marking-ink, 365. 
 Marl, 286. 
 Marsh-gas, C 2 H 4 , 88. 
 
 and chlorine, 144. 
 composition by volume, 100. 
 eudiometric analysis, 99. 
 identified, 88. 
 molecular formula,. 83. 
 preparation, 88. 
 series, CznHzn + z, 521. 
 Marsh-mallow, 483. 
 Marsh's test for arsenic, 247. 
 Mascagnine, NH 4 . S0 3 , 269. 
 Massicot, PbO, 356. 
 Matches, 157. 
 
 eupyrion, 160. 
 lucifer, 228. 
 safety, 228. 
 silent, 228. 
 vesta, 160. 
 
 without phosphorus, 228, 
 Matt, 337. 
 
 Matter, definition of, 1. 
 Mauve, 456. 
 Mauveine, 456. 
 Meadow-sweet, oil of, 476. 
 Meal powder, 422. 
 Meconic acid, 3HO.C U H0 1U 595. 
 Meerschaum, 280. 
 Melaniline, 546. 
 Melissene, 515. 
 Melissic acid, 514. 
 
 alcohol, 512. 
 Melissine, 583. 
 Menachanite, 391. 
 Mendipite, PbCl. 2PbO, 359. 
 Menthene, 471. 
 Mercaptan, 527. 
 
 Mercaptide of mercury, 528. 
 Merchant bar iron, 312. 
 Mercuramine, 370. 
 Mercuric ethide, Hg. C 4 H S , 534. 
 
 iodide, Hgl, 373. 
 
 methide, 534. 
 
 nitrate, HgO . N0 5 , 370. 
 
 sulphate, HgO.S0 3 , 370. 
 Mercuricum, 375. 
 Mercurosum, 375. 
 Mercurous iodide, Hg 2 I, 372. 
 
 nitrate, Hg 2 . NO 5 , 370. 
 sulphate, Hg 2 O.S0 3 , 370. 
 Mercury, Hg, 367. 
 
 action of hydrosulphuric acid on, 
 192. 
 
 ammoniated oxide, 369. 
 
 subchloride, 371. 
 
 bichloride or perchloride, 370. 
 
 black oxide, Hg 2 0, 369. 
 
 chloride, HgCl, 370. 
 
 chlorosulphide, 373. 
 
 compounds, molecular formulae. 
 375. 
 
 cyanide, HgC 2 N, 439. 
 
 diatomic, 375. 
 
 equivalent and atomic weights, 
 373. 
 
 extraction from its ores, 367. 
 
 frozen by liquid sulphurous acid, 
 
 fulminate, Hg 2 C 4 N 2 4 , 444. 
 iodide, 173. 
 metallurgy of, 367. 
 nitrate, HgO . N0 5 , 370. 
 nitric oxide of, 369. 
 nitride, 370. 
 oxides, 369. 
 
 protochloride, Hg 2 Cl, 372. 
 protonitrate, Hg 2 O.NO w 370. 
 prussiate, 436. 
 red oxide, HgO, 369. 
 stains removed from gold, 368. 
 subsulphide, 373. 
 sulphate, 370. 
 sulphide, 367. 
 uses of, 368. 
 volatility of, 368. 
 yellow oxide, HgO, 369. 
 Metacetone, 557. 
 Metacetonic (propylic) acid, 514. 
 Metal, definition, 11. 
 Metalamides, 551. 
 Metaldehyde, 555. 
 Metallic oxides, action of hydrochloric acid 
 
 on, 150. 
 
 Metallurgy of copper, 335. 
 iron, 302. 
 lead, 349. 
 tin, 383. 
 zinc, 295. 
 
 Metals, action of hydrochloric acid on, 149. 
 hydrosulphuric acid on, 
 
 192. 
 
 oxygen-acids on, 126. 
 sulphuric acid on, 207. 
 on water, 23. 
 
 burnt in sulphur vapour, 189. 
 chemistry of, 258. 
 classification of, 23. 
 iron group, gi neral review, 334. 
 noble, 24. 
 
 2x2 
 
660 
 
 INDEX. 
 
 Metals, of the alkalies, general review, 274. 
 of the alkaline earths, 282. 
 of the earths proper, 285. 
 platinum group, 402. 
 relations to oxygen, 8. 
 Metal-slag (copper), 338. 
 Metameric, 467. 
 Metantimonic acid, 380. 
 Metaphosphates, normal ratio of, 254. 
 Metaphosphoric acid, HO . P0 a , 231. 
 Metastannic acid, Sn 5 O 10 , 388. 
 Metastyrole, 472. 
 Metatartarie acid, 587. 
 Metaterebenthene, 469. 
 Meteoric iron, 300. 
 Methyl-acetyle, 557. 
 Methylamine, 542, 547. 
 Methylaniline, 542. 
 Methylated spirit, 473. 
 Methyle, C 2 H 3 , 466. 
 
 -caproyle, 520. 
 
 iodide, 467. 
 
 oxide, 466. 
 
 -phenylainine, 542. 
 
 prepared from acetic anhydride , 565. 
 
 salicylate, 467. 
 
 series, 467. 
 
 -theobromine, 599. 
 
 -valeryle, 557. 
 Methylene, 515. 
 Methylethylamine, 542. 
 Methylethylamylophenylium, hydrate of, 
 
 Methylethylaniline, 542. 
 Methylethylic ether, 526. 
 Methylmorphylammonium, hydrate of, 544. 
 Methylic acetate, 466. 
 
 alcohol, C.H.O^ 466, 512. 
 
 formiate, 467. 
 
 hydrate, 466. 
 Mg, magnesium, 280. 
 MgO, magnesia, 280. 
 MgO . S0 3 , sulphate of magnesia, 281. 
 Mica, 285, 290. 
 Microcosmic salt, 232. 
 Mild alkali, 9. 
 Milk, 608. 
 
 adulteration, 611. 
 coagulation of, 608. 
 composition of, 611. 
 Mill-cake, 422. 
 
 furnace, 312. 
 Millstone grit, 413. 
 Mimotannic acid, 594. 
 Mine iron, 306. 
 Mineral alkali, definition, 8, 
 
 green, 346. 
 
 silicates, 290. 
 
 waters, 45. 
 
 yellow, 359. 
 Mines, ventilation, 70. 
 Minium, Pb 3 4 , 357. 
 Mirbane, essence of, 128. 
 Mirrors, manufacture, 368. 
 Mispickel, FeS 2 . FeAs, 240. 
 Mixture and compound, distinction, 19. 
 Mn, manganese, 325. 
 Mn0 2 , peroxide of manganese, 325. 
 Moire metallique, 387. 
 Molasses, 496. 
 
 Molecular formula of acetylene, 83. 
 ammonia, 120. 
 
 Molecular formula of arsenietted hydrogen, 
 
 247. 
 
 arsenious acid, 244. 
 bisulphide of carbon, 
 218, 
 calomel, 374. 
 carbonic acid, 82. 
 
 oxide, 82. 
 chloride of aluminum, 
 
 292. ' 
 
 chloride of silicon, 165. 
 corrosive sublimate, 
 
 374. 
 dichloride of sulphur, 
 
 219. 
 
 ferric chloride, 52. 
 glycerine, 562. 
 hydrochloric acid, 151. 
 hydrogen, 52. 
 hydrosulphuric acid, 
 
 194. 
 
 marsh-gas, 83. 
 nitric acid, 129. 
 
 anhydride, 130. 
 oil of vitriol, 209. 
 olefiant gas, 83. 
 
 oxygen, 52. 
 phosphuretted hydro- 
 gen, 237. 
 
 stannic chloride, 390. 
 sulphurous acid, 199. 
 vermilion, 375. 
 water, 52. 
 Molecular formulae, 51. 
 
 of alcohols, 558. 
 
 chlorides of carbon, 
 
 164. 
 
 etherand alcohol, 527. 
 mercury compounds, 
 
 375. 
 
 oxides of chlorine, 161. 
 oxides of nitrogen, 
 
 137. 
 Molecular volumes of alcohol-radicals, 520. 
 
 olefines, 515. 
 weight, 52. 
 
 Molecule, definition, 52. 
 of water, 52. 
 Molecules, 51. 
 Molybdate of lead, 393. 
 Molybdena, MoS 2 , 392. 
 Molybdenum, Mo, 392. 
 
 bisulphide, 392. 
 blue oxide, 393. 
 chlorides, 393. 
 metallic, 393. 
 oxides, 393. 
 sulphides, 393. 
 
 393. 
 
 dialysed, 393. 
 ochre, 393. 
 Monacetine, 563. 
 Mona copper, 339. 
 Monad elements, 152. 
 Monamines, 539. 
 Monatomic elements, 152. 
 Monkshood, 589. 
 
 Monobasic acids, constitution of, 255. 
 Monophosphamide, 239. 
 Monostearine, 575. 
 Mordants, 605. 
 Moringic acid, 577. 
 
INDEX. 
 
 661 
 
 Moritannic, acid, 601. 
 Morocco leather, 592. 
 Morphine, C 34 H 19 N0 6 , 537. 
 
 characters of, 595. 
 
 constitution, 544. 
 
 extraction, 594. 
 
 hydrochlorate, 595. 
 Mortar for building, 414. 
 Mosaic gold, 390. 
 Mountain ash berries, 590. 
 Mucic acid, 483. 
 Mucilage, 483. 
 Mucus, 618. 
 Muffle, 355. 
 
 Mulberry calculus, 584. 
 Multiple proportions, law of, 135. 
 Mundic, FeS 2 , 302. 
 Muntz-metal, 341. 
 Murexide, 621. 
 Muriate of morphia, 595. 
 Muriatic acid, 147. 
 Muscle formed from food, 629. 
 Mushrooms, 500. 
 Muslin, uninflammable, 269, 392. 
 Mustard, essential oil of, 479. 
 
 artificial production, 479. 
 Myricine, 583. 
 Myristic acid, 514. 
 Myronic acid, 479. 
 Myrosine, 479. 
 Myrrh, 480. 
 
 N, NITROGEN, 112. 
 
 Na, sodium, 262. 
 
 NaCl, common salt, 262. 
 
 Nails, 617. 
 
 NaO, soda, 266. 
 
 NaO . 2B0 3 , borax, 109, 267. 
 
 NaO . C0 2 , carbonate of soda, 264. 
 
 NaO . HO, caustic soda, 266. 
 
 NaO . HO . 2CO.J, bicarbonate of soda, 266. 
 
 2NaO . HO . P0 5 , phosphate of soda, 232, 
 268. 
 
 NaO . N0 5 , nitrate of soda, 415. 
 
 NaO . S0 3 , sulphate of soda, 268. 
 
 NaO . S 2 2 , hyposulphite of soda, 211. 
 
 NaO . W0 3 , tungstate of soda, 392. 
 
 Naphtha, coal, 452. 
 wood, 466. 
 
 Naphthalic acid, 464. 
 
 Naphthaline, C 20 H ? , 462. 
 
 chlorides, 463. 
 
 chlorine substitution-products 
 
 from, 463. 
 
 nitro - substitution - products 
 from, 464. 
 
 Naphthalising, 95. 
 
 Naples yellow, 380. 
 
 Narcotine, 537. 
 
 extraction, 595. 
 
 Nardic acid, 514. 
 
 Negative pole, 20. 
 
 Nessler's test for ammonia, 373. 
 
 Nettles, acid of, 567. 
 
 Neutralisation, definition, 9. 
 
 Neutrality of constitution, 253. 
 
 NH 3 , ammonia, 113. 
 
 NH 4 , ammonium, 269. 
 
 NH 4 C1, chloride of ammonium or sal-am- 
 moniac, 114. 
 
 NH 4 C1, PtCl 2 , ammonio-chloride of plati- 
 num, 394. 
 
 NH 3 , HC1, sal-ammoniac, 114. 
 NH 4 O, oxide of ammonium, 269. 
 NH 4 . C0 2 , carbonate of ammonia, 270. 
 2NH 4 . 3CO.y sesquicarbonate of ammonia, 
 
 269. _ 
 
 NH 4 . O, oxalate of ammonia, 586. 
 NH 4 O . S0 3 , sulphate of ammonia, 269. 
 NH 4 S, sulphide of ammonium, 271. 
 Ni, nickel, 330. 
 Nickel, Ni, 330. 
 
 action on water, 24. 
 arsenical, NiAs, 330. 
 arsenio-sulphide, 330. 
 glance, NiAs, NiSj, 330. 
 oxides, 330. 
 sulphate, 330. 
 sulphides, 331. 
 Nicotine, C 10 H 7 N, 538. 
 
 constitution, 544. 
 extraction, 599. 
 properties, 600. 
 Nil album, 295. 
 Niobic acid, Nb0 2 , 393. 
 Niobium, Nb, 393. 
 Nipper-tap, 142. 
 Nitraniline, 549. 
 Nitrate of potash, action of heat on, 133. 
 
 solubility, 416. 
 silver prepared from standard 
 
 silver, 365. 
 soda, solubility, 416. 
 Nitrates, composition, 129. 
 
 decomposition by heat, 129. 
 formation in nature, 122. 
 normal ratio of, 254. 
 oxidising properties, 128. 
 Nitre, KO . N0 5 , 413. 
 
 action on carbon, 418. 
 artificial production, 416. 
 cubic, 280. 
 examination of, 418. 
 -heaps, 416. 
 overfused, 417. 
 properties, 418. 
 purified in the laboratory, 419. 
 refining, 417. 
 
 relation to combustion, 418. 
 Nitric acid, N0 5 , 123. 
 
 action on benzole, 128. 
 charcoal, 126. 
 hydrochloric acid, 167. 
 indigo, 125. 
 metals, 126. 
 organic substances, 127. 
 phosphorus, 126. 
 sulphurous acid, 202. 
 turpentine, 127. 
 anhydrous, 129. 
 cause of colour, 124. 
 combining weight, 128. 
 decomposed by heat, 124. 
 light, 125. 
 distillation of, 125. 
 formed from air, 123. 
 
 ammonia, 122. 
 from batteries, 134. 
 fuming, 125. 
 
 hydratcd, HO . N0 5 , 123. 
 molecular formula, 129. 
 oxidising properties, 126. 
 preparation on the large scale, 
 124. 
 
662 
 
 INDEX. 
 
 Nitric acid, preparation (Jn a small scale, 124. 
 properties, 125. 
 strongest, preparation, 125. 
 test of strength, 125. 
 unitary formula, 129. 
 anhydride, 129. 
 
 equivalent, 129. 
 ether, 522. 
 oxide, N0 2 , 130. 
 
 absorbed by sulphuric acid, 204. 
 
 behaviour with hydrogen, 132. 
 composition by volume, 136. 
 equivalent, 136. 
 identified, 130. 
 pure, preparation, 131. 
 with bisulphide of carbon, 142. 
 peroxide, N0 4 , 134. 
 
 composition by volume, 136. 
 Nitrification, theory of, 122. 
 Nitriles, 550. 
 Nitrites, 133. 
 Nitrobenzoic acid, 622. 
 Nitrobenzole, C 12 H 5 (N0 4 ), 455. 
 preparation, 128. 
 Nitrogen, N, 112. 
 
 atomicity of, 152. 
 binoxide, 130. 
 bisulphide, 218. 
 bromide, 170. 
 bulbs, 120. 
 
 chemical relations, 113. 
 chloride, 166. 
 
 preparation, 166. 
 circulation in nature, 113. 
 combining volume, 120. 
 weight, 120. 
 determination, 120. 
 etymology, 18. 
 function in air, 19. 
 group of elements, 251. 
 identification of, 19. 
 iodide, 176. 
 oxides, 123. 
 
 atomic constitution, 137. 
 general review, 135. 
 peroxide, 134. 
 preparation, 112. 
 properties, 18. 
 protoxide, 130. 
 
 Nitrogenised bodies identified, 60. 
 Nitroglycerine, 579. 
 
 use in blasting, 579. 
 Nitrohippuric acid, 622. 
 Nitromannite, 509. 
 Nitromuriatic acid, 167. 
 Nitrophenisic acid, 461. 
 Nitroprussides, 444. 
 Nitrosubstitution products, 128. 
 Nitrotoluole, 460. 
 Nitrous acid, N0 3 , 132. 
 
 action on hydrosulphuric acid, 
 
 action on organic substances, 
 
 133. 
 
 commercial, 134. , 
 
 composition by volume, 136. 
 equivalent of, 136. 
 formed from ammonia, 122. 
 oxidising and reducing power, 
 
 135. 
 ether, 522. 
 
 Nitrous oxide, NO, 130. 
 
 composition by volume, 136. 
 
 equivalent, 136. 
 
 identified, 130. 
 Nitroxylole, 460. 
 NO, nitrous oxide, 130. 
 NO 2 , nitric oxide, 130. 
 N0 3 , nitrous acid, 132. 
 N0 4 , nitric peroxide, 134. 
 N0 5 , nitric acid, 123. 
 Noble metals, 24. 
 Non-metallic elements, 1. 
 Nordhausen oil of vitriol, 200. 
 Normal ratios of salts, 254. 
 Normal salt, unitary definition, 257. 
 Normandy's still, 46. 
 Nuggets, 403. 
 Nutrition of animals, 629. 
 
 plants, 623. 
 
 plastic elements of, 632. 
 Nux-vomica, 599. 
 
 0, OXYGEN, 4. 
 
 0, oxalic acid, 583. 
 Oak bark, 591. 
 Ochres, 286. 
 CEnanthene, 515. 
 (Enanthic acid, 514, 582. 
 
 synthesis, 570. 
 alcohol, 512. 
 GEnanthole, 582. 
 
 Oil gas absorbed by sulphuric acid, 209. 
 Oil of spiraea, 476. 
 Oil of vitriol, HO.S0 3 , 200. 
 brown, 205. 
 
 decomposed by boiling, 208. 
 dehydrated by phosphoric acid, 
 
 209. 
 
 dissociation of, 209. 
 distillation of, 206. 
 manufacture, 203. 
 molecular formula, 209. 
 sulphate of lead in, 206. 
 Oil of wine, 523. 
 Oils, 579. 
 Olefiant gas, C 4 H 4 , 85. 
 
 absorbed by sulphuric acid, 
 
 209. 
 
 combination with chlorine, 86. 
 composition by volume, 100. 
 converted into alcohol, 525. 
 decomposed by chlorine, 87. 
 heat, 87. 
 the spark, 87. 
 identification of, 86. 
 molecular formula, 83. 
 preparation, 85. 
 with iodine, 176. 
 Olefines, C 2 H 2n , 514. 
 Oleic acid, HO . C 36 H 33 3 , 580. 
 
 action of nitric acid on, 581. 
 Oleine, C 114 H 104 12 , 572. 
 
 synthesis of, 575. 
 Olibanum, 480. 
 Oligist iron ore, 302. 
 Olive-oil, 573, 580. 
 Olivine, 282. 
 Onions, 500. 
 
 essential oil of, 479. 
 Onyx, 102. 
 Oolite limestone, 278. 
 Oolitic iron ore, 302. 
 
INDEX. 
 
 B63 
 
 Opal, 102. 
 
 Opium, composition, 594. 
 
 extraction of alkaloids from, 594. 
 Orange chrome, 2PbO . CrO 3 , 332. 
 Orange, essential oil of, 470. 
 Orceine, 602. 
 Orcine, 602. 
 Ore-furnace, 336. 
 Organic analysis, elementary, 73. 
 
 and inorganic substances, 435. 
 chemistry, 435. 
 matter identified, 53. 
 siibstances, definition, 3. 
 
 synthetical formation, 83. 
 Organo-metallic bodies, 529. 
 
 table of, 535. 
 Oriental alabaster, 43. 
 Orpiment, red, AsS 2 , 249. 
 
 yellow, AsS 3 , 249. 
 Orthoclase, 290. 
 
 Orthophosphates, normal ratio of, 254. 
 Orthophosphoric acid, 3HO. P0 5 , 232. 
 Osmazome, 616. 
 Osmic acid, Os0 4 , 400. 
 Osmiridiwn, 394. 
 Osmium, Os, 400. 
 
 chlorides, 401. 
 oxides, 401. 
 tetrasulphide, 403. 
 Osseine, 616. 
 Oxalates, 585. 
 Oxalethylic acid, 522. 
 Oxalic acid, HO . C,0 8 , 583. 
 analysis of, 74. 
 bibasic, 585. 
 
 chemical constitution, 585. 
 doubled formula, 585. 
 fatal dose, 585. 
 occurrence in nature, 583. 
 preparation, 584. 
 properties, 585. 
 test for, 585. 
 uses, 584. 
 ether, 521. 
 Oxalonitrile, 550. 
 Oxalovinic acid, 522. 
 Oxalyle, G) v 550. 
 Oxamic acid, 550. 
 Oxamide, NH 2 . C 2 O 2 , 549. 
 Oxanilide, 549. 
 Oxidation, definition, 5. 
 
 of tissue, products, 632. 
 Oxides, 5. 
 
 metallic, action of hydrochloric acid 
 
 on, 150. 
 li ydrosulphuric 
 acid on, 192. 
 sulphuric acid on, 
 
 209. 
 
 nomenclature of, 11. 
 Oxidising blowpipe flame, 98. 
 Oxycalcium light, 38. 
 Oxygen, O, 4. 
 
 absorption by pyrogallic acid, 593. 
 atomicity of, 152. 
 blowpipe flame, 99. 
 burnt in ammonia, 122. 
 combustion in, 6. 
 detected in mixed gases, 130. 
 determination of, in gases, 34. 
 effect on flame, 99. 
 electro-negative. 51 . 
 
 Oxygen, electro-positive, 51. 
 etymology, 8. 
 evolved from steam, 102. 
 experiments with, 6. 
 extracted from air, 12. 
 group of elements, 250. 
 identified, 12. 
 natural sources, 4. 
 preparation, 11. 
 
 from bichromate of pot- 
 ash, 210. 
 from chloride of lime, 
 
 155. 
 from sulphate of zinc, 
 
 210. 
 from sulphuric acid, 
 
 207. 
 
 properties, 4. 
 purification, 53. 
 relation to metals, 8. 
 
 non-metals, 8. 
 Oxygenated water, 50. 
 Oxygenised muriatic acid, 146. 
 Oxyhydrogen blowpipe, 37. 
 Oxymuriatic acid, 146. 
 Ozone, 14. 
 
 electrolytic, 21. 
 experiments with, 16. 
 in the atmosphere, 16. 
 nature of, 52. 
 specific gravity of, 52. 
 test for, 15. 
 Ozonisation by ether, 16. 
 
 phosphorus, 16. 
 Ozonised air, 15. 
 
 oxygen, 15. 
 Ozonising tube, 15. 
 
 P, PHOSPHORUS, 222. 
 
 Paint blackened by hydrosulphtiric acid, 192. 
 
 removed from clothes, 484. 
 Paintings, effect of light and air on, 192. 
 Palladamine, hydrochlorate, 399. 
 Palladium, Pd, 399. 
 
 carbide, 400. 
 chlorides, 400. 
 cyanide, 399. 
 nitrate, 400. 
 oxides, 400. 
 Palmitic acid, 514. 
 Palmitine, C 102 H 9S 0, 2 , 572. 
 
 synthesis of, 575. 
 Palm-oil, 572, 579. 
 
 bleaching of, 579. 
 Pancreatic juice, 631. 
 Panification, 494. 
 Papaverine, 537. 
 Paper, 465. 
 
 action of nitric acid on, 500. 
 dissolved by ammonio-eupvir solu- 
 tions, 344. 
 
 for cheques, &c., 487. 
 for photographic printing, 21 1. 
 Paracyanogen, C 6 N 3 , 440. 
 Parafline, C*H*, 465, 467. 
 extraction, 467. 
 oil, 468. 
 
 Paraguay tea, 597. 
 Paramylene, 515. 
 I'aranaphthalinc, 4('<L 
 Paraniline, 515. 
 Parasorbio acid, 5i'<>. 
 
664 
 
 INDEX. 
 
 Paratartaric'acid, 588. 
 Parchment, 592. 
 
 size, 617. 
 
 vegetable, 496. 
 Paris yellow, 359. 
 Parsley, essential oil of, 470. 
 Partial saturation, method of, 571. 
 Parting of gold by sulphuric acid, 207. 
 Passive state of metals, 322. 
 Patent yellow, 359. 
 Pattinson's process, 352. 
 Paviine, 478. 
 Paving stones, 413. 
 Pb, lead, 348. 
 PbCl, chloride of lead, 359. 
 Pbl, iodide of lead, 360. 
 PbO, protoxide of lead, 356. 
 PbO. A; acetate of lead, 563. 
 PbO . C 4 H 3 3 , acetate of lead, 563. 
 PbO . Cr0 3 , chromate of lead, 332. 
 PbO . S0 3 , sulphate of lead, 349, 359. 
 PbS, sulphide of lead, 349. 
 Pd, palladium, 399. 
 Pea, iron ore, 301. 
 Pear flavour, 553. 
 Pearlash, 258. 
 Pearl hardener, 280. 
 Pearls, 65. 
 Pearl-spar, 282. 
 Pearl white, BiCl 3 , 2Bi0 3 , 377. 
 Peas, 610. 
 Peat-bog, 62. 
 
 composition, 434. 
 Pectic acid, 627. 
 Pectine, 627. 
 Pectose, 627. 
 Pectosic acid, 627. 
 Pelargonic acid, 514. 
 Pentathionic acid, S 5 5 , 214. 
 Pentethylene-tetrethyl-tetrammonium, hy- 
 
 drated oxide of, 546. 
 Pepper, essential oil of, 470. 
 Peppermint, essential oil of, 471. 
 Pepsine, 630. 
 Perchlorates, 159. 
 Perchloric acid, C10 7 , 159. 
 
 hydrated, 159. 
 ether, 523. 
 
 Perchlorokinone, 596. 
 Perchromic acid, 333. 
 Percussion cap composition, 446 
 
 fuze, 160. 
 
 Perfume-ethers, 553. 
 Perfumes, extraction of, 471. 
 Peridase, 282. 
 Pericline, 290. 
 Periodates, 174. 
 Periodic acid, I0 7 , 174. 
 Permanent gas, 4. 
 
 ink, 365. 
 
 white, 275. 
 
 Permanganate of potash, KO . Mn 2 0~, 327. 
 Permanganates, normal ratio of, 2541 
 Permanganic acid, 327. 
 Peroxide, definition, 11. 
 Perspiration of the skin, 569. 
 Peruvian bark, 595. 
 
 , 
 
 Petiniue, 547. 
 Petrifying springs, 42. 
 Petroleum, 88, 468. 
 
 Peucyle, 470. 
 Pewter, 386. 
 Phenic acid, 460. 
 Phenole, C 12 H 6 2 , 460. 
 Phenose, 455. 
 Phenylamine, 459, 539. 
 Phenylaniline, 542. 
 Phenyle, C 12 H 5 , 459. 
 
 hydrated oxide of, 459. 
 Phenylene-diamine, 545. 
 Phenylene-ditolylene-triamine, 546. 
 Phenylene-ditolylene-triethyl-triamine, 546. 
 Phenylene - ditolylene - triphenyl - triamine, 
 
 Phenylic hydride, 462. 
 Phenyl-toluylamine, 543. 
 Philosopher's wool, 295. 
 Phlogistic theory, 146. 
 Phlogiston, 146. 
 Phloretine, 478. 
 Phloridzeine, 478. 
 Phloridzine, 478. 
 Phocenine, 582. 
 Phosgene gas, C 2 2 C1 2 , 165. 
 Phospham, 239. ' 
 Phosphamic acid, 239. 
 Phosphates, normal ratio of, 254. 
 Phosphethylic acid, 518. 
 Phosphides, 227. 
 Phosphites, 234. 
 Phosphodiamide, 239. 
 Phosphoglyceric acid, 576. 
 Phosphomolybdate of ammonia, 393. 
 Phosphorescence, 224. 
 
 prevented, 225. 
 Phosphoric acid, P0 5 , 229. 
 
 anhydrous, preparation, 
 
 atomic formula, 237. 
 
 bibasic, 232. 
 
 common, 232. 
 
 composition, 233. 
 
 di-hydrated, 231. 
 
 glacial, 230. 
 
 hydrated, preparation, 230. 
 
 molybdic test for, 393. 
 
 monobasic, 232. 
 
 monohydrated, 231. 
 
 tribasic, 232. 
 
 trihydrated, 232. 
 anhydride, 231. 
 ether, 523. 
 
 Phosphorised oil, 225. 
 Phosphorite, 222. 
 Phosphorous acid, P0 3 , 233. 
 Phosphorus, P, 222. 
 
 action of potash on, 235. 
 
 allotropic modifications, 226. 
 
 amorphous, 226. 
 
 and oxygen, 5. 
 
 black, 227. 
 
 bromides, 238. 
 
 burnt under water, 160, 235. 
 
 chemical relations, 227. 
 
 chlorides, 237. 
 
 cyanide, 444. 
 
 distilled, 226. 
 
 fuze composition, 229. 
 
 iodides, 238. 
 
 match-bottle, 225. 
 
 occurrence in nature, 222. 
 
 oxides, 229. 
 
INDEX. 
 
 665 
 
 Phosphorus, oxychloride, 237. 
 
 composition, 238. 
 pentachloride, 237. 
 
 action of am- 
 monia on, 239. 
 composition, 238. 
 poisonous properties, 227. 
 precipitation of metals by, 227. 
 preparation, 222. 
 properties, 222. 
 red, 226. 
 suboxide, 235. 
 sulphides, 238. 
 sulphochloride, 238. 
 terchloride, 237. 
 
 action of ammonia 
 
 on, 239. 
 
 composition, 238. 
 transformed by iodine, 233. 
 viscous, 227. 
 vitreous, 226. 
 Phosphotriamide, 239. 
 Phosphovinic acid, 518. 
 Phosphurets, 227. 
 
 Phosphuretted hydrogen, gaseous, PH 3 , 235. 
 analogy with am- 
 
 amonia, 236. 
 composition, 236. 
 liquid, 236. 
 molecular formula, 
 
 237. 
 
 solid, 236. 
 Photographic baths, recoverv of silver from. 
 
 365. 
 
 Photographic printing, 212. 
 Phthalic acid, 464. 
 Phyllocyanine, 601. 
 Phylloxanthine, 601. 
 Physetoleic acid, 577. 
 Picamar, 465. 
 Picoline, 450. 
 Picric acid, 461. 
 Picrotoxine, 479. 
 Pig iron, 305. 
 Pimelic acid, 580. 
 Pimple metal (copper), 339. 
 Pine apple flavour, 553. 
 Pinic acid, 470. 
 Pink salt, NH.Cl.SnCl,, 389. 
 Pins tinned, 386. 
 Pipe-clay, 286. 
 Pipeline, 538. 
 Pipette, curved, 73. 
 Pit charcoal, 420. 
 Pitch, 452, 468. 
 Pitchblende, 300. 
 Pittacal, 465, 468. 
 
 Plants and animals, reciprocity of, 634. 
 changes after death, 628. 
 chemical changes in, 626. 
 constructive power of, 627. 
 evolution of carbonic acid by, 04. 
 food of, 71, 623. 
 nutrition of, 623. 
 reducing functions of, 626. 
 ultimate elements of, 623. 
 Plaster of Paris, 273. 
 
 overburnt, 279. 
 preparation, 279. 
 
 Platammon-ammonium, hydrated oxide, 548. 
 Platammonium, hydrated oxide, 548. 
 Platina, muriate, 397. 
 
 Platinamine, 398. 
 
 Platinates, 396. 
 
 Platinised asbestos, 132. 
 
 Platinochloride of potassium, KC1 . PtClj, 
 
 Platinoid metals, general review of, 402. 
 Platinum, Pt, 394. 
 
 amalgam, 369. 
 Platinum, ammonio-chloride, NELC1 . PtCl 
 
 394. 
 
 and rhodium alloy, 400. 
 attacked by sulphuric acid, 207. 
 bichloride, PtCl., 397. 
 black, 395. 
 
 compounds, atomic formulas, 399. 
 corroded, 396. 
 
 by arsenites, 244. 
 phosphorus, 227. 
 silicon, 107. 
 crucible heated, 105. 
 equivalent and atomic weights, 
 
 399. 
 
 extraction, 394. 
 fulminating, 397. 
 ores, analysis, 402. 
 oxides, 396. 
 
 protochloride, PtCl, 398. 
 separation from iridium, 396. 
 spongy, 396. 
 
 stills for sulphuric acid, 205. 
 sulphides, 399. 
 tetratomic, 399. 
 uses of, 395. 
 Platosamine, hydrate, 398. 
 
 hydrochlorate, 398. 
 sulphate, 398. 
 
 Plato-triethyle-arsonium, chloride, 549. 
 -phosphonium, 549. 
 -stibonium, 549. 
 Plumbago, 55. 
 Plumbic acid, Pb0 2 , 358. 
 Pneumatic trough, 12. 
 P0 3 , phosphorous acid, 233. 
 P0 5 , phosphoric acid, 229. 
 Poison-nut, 599. 
 Pole, negative, 20. 
 positive, 20. 
 Pollux, 274. 
 Polyammonias, 544. 
 Polyatomic alcohols, 544. 
 Polyhalite, 281. 
 
 Polymerising by sulphuric acid, 452. 
 Polymerism, 515. 
 Populine, 478. 
 Porcelain, 411. 
 
 English, 412. 
 glazed, 412. 
 painting, 412. 
 Porous cell experiment, 29. 
 Porphyry, 290. 
 Porter, composition, 491. 
 Portland cement, 415. 
 
 stone, 414. 
 Port wine crust, 510. 
 
 effect of keeping, 510. 
 Positive pole, 20. 
 Potash-albite, 290. 
 Potash, KO, 259. 
 
 anhydrous, 260. 
 antimoniate, KO . SbO a , 380. 
 arsenite, 244. 
 atomic formula, 261. 
 
666 
 
 INDEX. 
 
 Potash, aurate, 406. 
 
 biantimoniate, 380. 
 
 bicarbonate, KO . HO . 2C0 2 , 261. 
 
 bichromate, KO . 2Cr0 3 , 331. 
 
 bimetantimoniate, 380. 
 
 binoxalate, 584. 
 
 bisulphate, KO . HO . 2S0 3 , 124, 210. 
 
 bitartrate, 259, 586. 
 
 bi-urate, 621. 
 
 bromate, 168. 
 
 bulbs, 73. 
 
 carbonate, KO . CO^ 258. 
 
 caustic, 259. 
 
 chlorate, KO . C10 5 , 157. 
 
 chromate, KO . Cr0 3 , 332. 
 
 cyanate, KO . C 2 NO, 442. 
 
 ferrate, 323. 
 
 from wool, 259. 
 
 fulminurate, 448. 
 
 fused, 259. 
 
 hydrate, KO . HO, 259. 
 
 atomic formula, 261. 
 hydriodate, 176. 
 in flesh, 615. 
 iodates, 174. 
 isocyanurate, 448. 
 manganate, 326. 
 inetantimoniate, 380. 
 metastannate, 388. 
 nitrate, 415. 
 
 solubility, 416. 
 oleate, 573. 
 osmite, 401. 
 perchlorate, 159. 
 permanganate, 327. 
 plumbate, 358. 
 prussiate, K 2 Cy 3 Fe, 437. 
 quadroxalate, 586. 
 red prussiate, 443. 
 sulphate, KO . S0 3 , 210. 
 tartrate, 2KO . C 8 H 4 10 , 586. 
 terchromate, 332. 
 test for, 48. 
 trithionate, 214. 
 urate, 621. 
 
 Potassamide, NH 2 K, 551. 
 Potassium, K, 258. 
 
 action on hvdrosulphuric acid, 
 192. 
 
 action on water, 23. 
 
 alcohol, 526. 
 
 amidide, 551. 
 
 atomic weight, 261. 
 
 binoxide, 262. 
 
 bisulphide, 262. 
 
 blowpipe test for, 261. 
 
 bromide, 168. 
 
 chloride, KC1, 261. 
 
 extraction from sea- 
 water, 263. 
 solubility, 416. 
 
 cyanide, K . C 2 N, 440. 
 pure, 441. 
 
 equivalent weight, 261. 
 
 ethyle, 533. 
 
 extraction, 260. 
 
 ferricyanide, K 3 Cy B Fe 2 , 443. 
 
 ferrocyanide, K 2 Cy 3 Fe, 437. 
 
 heated in carbonic acid, 76. 
 
 iodide, KI, 176. 
 
 mercaptan, 527. 
 
 pentasulphide, 262. 
 
 Potassium peroxide, 262. 
 
 platinochloride, KC1 . PtCl 2 , 397. 
 properties, 260. 
 silicon" uoride, 181. 
 sulpharsenite, 249. 
 sulphide, KS, 262. 
 sulphocyanide, K.CyS 2 , 442. 
 tersulphide, 262. 
 tetrasulphide, 262. 
 Potato, composition, 483. 
 spirit, 511. 
 
 starch, extraction, 483. 
 Pottery, 411. 
 Press cake, 422. 
 Preston salts, 270. 
 Promethean light, 160. 
 Proof spirit, 516. 
 Propione, 557. 
 
 Propionic (propylic) acid, 514. 
 Propionitrile, 550. 
 Propionyle, 520. 
 Propylamine, 547. 
 Propylene, 515. 
 Propylene-glycol, 561. 
 Propylic acid, HO . C 6 H A, 514. 
 Propylic acid, artificial formation, 533. 
 Propylic alcohol, 512. 
 Proteine, 614. 
 
 Proximate organic analysis, 451. 
 Prussian blue, Fe 4 Fcy 3 , 436. 
 
 constitution, 438. 
 decomposition by alkalies, 
 
 438. 
 
 native, 324. 
 preparation, 437. 
 soluble, 438. 
 Prussiate of potash, action of sulphuric 
 
 acid on, 79. 
 Prussic acid, HCy, 436. 
 
 in bitter almond oil, 479. 
 of the Pharmacopoeia, 439. 
 Psilomelane, 325. 
 Pt, platinum, 394. 
 PtCl, platinous chloride, 398. 
 PtCl 2 , bichloride of platinum, 397. 
 Ptyaline, 630. 
 
 Puddled bar, composition, 313. 
 bars, 312. 
 steel, 320. 
 
 Puddling, disadvantages of, 313. 
 dry, 313. 
 loss in, 313. 
 mechanical, 314. 
 process of, 311. 
 Pulvis fulminans, 419. 
 Pumice stone, 286. 
 Purbeck stone, 414. 
 Purple of Cassius, 407. 
 Putrefaction, 64. 
 
 ammonias furnished by, 547. 
 modern researches on, 635. 
 Putty powder, 388. 
 Pyrene, 464. 
 Pyridine, 450. 
 Pyrites arsenical, 240. 
 
 capillary, NiS, 331. 
 efflorescent, 201. 
 
 extraction of sulphur from, 185. 
 Fahlun, 219. 
 oxidation in air, 201. 
 white, 201. 
 P^yrogallic acid, 593. 
 
.INDEX. 
 
 667 
 
 Pyrogalline, 593. 
 Pyroligneous acid, C 4 H 4 4 , 465. 
 
 ether, 466. 
 Pyrolusite, Mn0 2 , 325. 
 
 preparation of oxygen from, 12. 
 Pyromucic acid, 568. 
 Pyroplioric iron, 80. 
 Pyrophorus, lead, 356. 
 Pyrophosphates, normal ratio of, 254. 
 Pyrophosphoric acid, 2HO. P0 5 , 231. 
 Pyroterebic acid, 577. 
 Pyroxylic spirit, 466. 
 >Pyroxyline, 500. 
 
 QUADREQDIVALENT ELEMENTS, 152. 
 
 Quantity and intensity, electric, 21. 
 Quartation of gold, 405. 
 Quartz, 102. 
 
 artificial, 105, 523. 
 Quercetine, 478. 
 Quercitannic acid, 591. 
 Quercitrine, 478. 
 Quercitron, 606. 
 Quick lime, CaO, 49. 
 Quicksilver, 367. 
 Quince-seed, 483. 
 Quinic acid, 596. 
 Quinidine, 537. 
 
 extraction, 596. 
 Quinine, C 40 H 24 N 2 O 4 , 537. 
 
 amorphous, 596. 
 
 extraction, 595. 
 
 sulphate, 596. 
 Quinoidine, 596. 
 Quinoline, 450. 
 Quinotannic acid, 595. 
 
 RACEMIC ACID, 588. 
 Radicals, alcohol-, 539. 
 negative, 520. 
 polyatomic, 544. 
 positive, 520. 
 
 Radishes, essential oil of, 479. 
 Railway bars, 312. 
 Rain water, 38. 
 Raisins, 496. 
 Rancid oils, 581. 
 Rangoon tar, 468. 
 Rational formulae, 74. 
 Ratios, normal, of salts, 254. 
 Realgar, AsS 2 , 249. 
 Reaumur's porcelain, 410. 
 Red copper ore, Cu 2 0, 335. 
 Red dyes, 605. 
 
 fire, composition for, 158. 
 
 flowers, colouring matter of, 601. 
 
 lead, Pb 3 4 , 357. 
 
 -ore, PbO . Cr0 3J 332. 
 
 ochre, 301. 
 
 orpiment, 249. 
 
 paints, 373. 
 
 precipitate, 369. 
 
 -shortness, 315. 
 
 silver-ore, 3AgS . AsS,, 240. 
 
 sulphide of antimony, 382. 
 Reduced, 12. 
 
 Reducing blowpipe flame, 98. 
 Reduction of metals by carbonic oxide, 80. 
 
 on charcoal, 99. 
 Refinery, 309. 
 Refining cast-iron, 309. 
 Refraction of saltpetre, 414. 
 
 Refrigerator, Carre's, 116. 
 
 Regulus, 337. 
 
 Regulus of antimony, 378. 
 
 Rennet, 609. 
 
 Resins, 472. 
 
 Resists (calico-printing), 606. 
 
 Respiration, 63. 
 
 formation of carbonic acid in, 63. 
 
 in confined air, 68. 
 Retort, 46. 
 Rhodium, Ro, 400. 
 
 oxides, 400. 
 sesquichloride, 400. 
 sodiochloride, 400. 
 sulphides, 400. 
 Rice, composition, 484. 
 Ricinoleic acid, 582, 
 Rinman's green, 330. 
 Rising of bread, 494. 
 Rivers, self-purifying power of, 39. 
 River-water, 39. 
 Ro, rhodium, 400. 
 Roasting, effect on sulphides, 194. 
 
 meat, 616. 
 
 Rochelle salt, KO . NaO . C 8 H 4 10 , 588. 
 Rock crystal, 102. 
 Rock oil, 468. 
 Rock salt, 262. 
 Rocks, disintegration, 71. 
 Roman cement, 415. 
 Rosaniline, 457. 
 
 acetate, 457. 
 
 action of cyanide of potassium on, 
 458. 
 
 triethylic, 458. 
 
 triphenylic, 458. 
 Rosette copper, 339. 
 Rosiclers, 366. 
 Rosin, 469. 
 
 soap, 470. 
 Rosolic acid, 450. 
 Rotation of crops, 625. 
 Rubian, 601. 
 Rubidia, 274. 
 Rubidium, Kb, 273. 
 
 equivalent weight, 275. 
 
 platinochloride, 397. 
 
 properties, 274. 
 
 separation from potassium, 397. 
 Ruby, 288, 332. 
 Ruby glass, 406. 
 Rue, essential oil of, 556. 
 Rufigallic acid, 593. 
 Ruhmkorff 's induction coil, 22 
 Rum, 511. 
 Rust, 2Fe 2 3 .3HO, 11, 321. 
 
 ammonia in, 121. ^ 
 
 Rusty deposit in waters, 45. 
 Ruthenic acid, 401. 
 Ruthenium, Ru, 401. 
 Rutic acid, 514, 
 
 alcohol, 512. 
 Rutile, Ti0 2 , 391. 
 Rye flour, 494. 
 
 S, SULPHITE, 183. 
 
 Saccharide, 499. 
 Saccharine matters, 495. 
 Safety-lamp, behaviour in mint's, !*1. 
 
 Davy's, 90. 
 
 precautions in using, 91. 
 
 Stephenson's, 89. 
 
668 
 
 INDEX. 
 
 Safflower, 601. 
 Saffron, 601. 
 Sago, 485. 
 Salad oil, 580. 
 Sal-alembroth, 371. 
 Sal-ammoniac, NH 4 C1, 114. 
 
 action on metallic oxides, 271. 
 composition by volume, 271. 
 vapour-density of, 271. 
 Sal gem, 262. 
 Salicine, 476. 
 
 derivatives, 476. 
 Salicyle, C U H 5 4 , 477. 
 hydride, 477.. 
 
 Salicylic acid, HO . C U H S 5 , 477. 
 Saligenine, 477. 
 Saline waters, 45. 
 Saliretine, 477. 
 Saliva, 630. 
 Sal polychrest, 211. 
 Sal-prunelle, 418. 
 Salt-cake, 264. 
 Salt as manure, 624. 
 common, 262. 
 definition, 10. 
 etymology, 252. 
 extraction, 262. 
 fused, 108. 
 
 -gardens of Marseilles, 263. 
 -glazing, 413. 
 of lemons, 586. 
 of sorrel, 584. 
 of tartar, 259. 
 preservative effect, 635. 
 table-, 263. 
 
 unitary definition, 256. 
 useful applications, 263. 
 Salting of meat, 616. 
 Saltpetre, KO.N0 5 , 415. 
 
 as manure, 624. 
 i cubical, NaO.N0 5 , 415. 
 -flour, 417, 
 impurities, 418. 
 
 prepared from nitrate of soda, 416. 
 properties, 418. 
 refining, 417. 
 
 old process, 417. 
 tests of purity, 418. 
 Salt-radical, definition, 10. 
 Salt-radicals, 182. 
 Salts, acid, 253. 
 
 atomic unitary formulae, 257. 
 basic, 253. 
 binary theory, 254. 
 constitution of, 252. 
 definition, ,253. 
 double, constitution, 255. 
 haloid, 182, 252. 
 mutual decomposition of, 416. 
 neutral, 253. 
 normal, 253. 
 normal ratios of, 254. 
 oxyacid, 252. 
 water-type theory of, 254. 
 Sal volatile, 270. 
 Sand, 102. 
 Sandarach, 472. 
 Sandstone, 413. 
 
 Craiffleith, 413. 
 Sap of plants, 626. 
 Saponification by steam, 575. 
 
 sulphuric acid, 574. 
 
 Saponification, theory of, 572. 
 
 Saponine, 479. 
 
 Sapphire, 288. 
 
 Sarcosine, C 6 H 7 N0 4 , 615. 
 
 Saturated solution, 47. 
 
 Savin, essential oil of, 470. 
 
 Saxon sulphuric acid, 200. 
 
 Saxony blue, 604. 
 
 Sb, antimony, 378. 
 
 SbCl 3 , terchloride of antimony, 381. 
 
 SbCl 5 , pentachloride of antimony, 381. 
 
 Sb0 3 , antimonic oxide, 379. 
 
 SbO 5 , autimonic acid, 379. 
 
 SbS 3 , tersulphide of antimony, 381. 
 
 Scammony, 480. 
 
 Scarlet dyes, 605. 
 
 Scheele's green, 2CuO . HO . AsO s , 245. 
 
 prussic acid, 439. 
 Scheelite, CaO . WO 3 , 392. 
 Schlippe's salt, 382. 
 Scotch pebbles, 102. 
 Scott's cement, 415. 
 Scrubber, 449. 
 Se, selenium, 219. 
 Seal-oil, 582. 
 Sea-water, 45. 
 
 extraction of salt from, 203. 
 Sea-weed, 500. 
 Sebacic acid, 580. 
 Secretion, 632. 
 Sedative salt, 109. 
 Seeds, composition, 626. 
 
 germination, 487. 
 Sefstrom's furnace, 321. 
 Sel d'or, 407. 
 Selenic acid, Se0 3 , 220. 
 Selenides, 219. 
 Selenietted hydrogen, 220. 
 Selenious acid, Se0 2 , 220. 
 Selenite, 279. 
 Selenium, Se, 219. 
 
 chlorides, 220. 
 sulphides, 220. 
 Seltzer water, 45. 
 Separating funnel, 83. 
 Sericine, 617. 
 Serpentine, 282. 
 Serum, 612. 
 Shaft, downcast, 70. 
 
 upcast, 70. 
 Shamoying 592. 
 Shear-steel, 317. 
 
 Sheep-dipping compositions, 244. 
 Shell-lac, 472. 
 Sherry, 510. 
 Shot, 355. 
 Si, silicon, 102. 
 Sicilian sulphur, 184. 
 Siemens' induction-tube, 15. 
 
 regenerative furnace, 434. 
 Sienna, 286. 
 
 SiF 2 , fluoride of silicon, 179. 
 Signal-light composition, 249. 
 Silica, Si0 2 , 102. 
 
 amorphous, 104. 
 
 crystalline, 104. 
 
 dissolved by hydrofluoric acid, 178. 
 
 gelatinous, preparation, 181. 
 
 in plants, 103. 
 
 in waters, 103. 
 
 Silicate of alumina and soda, 289. 
 soda, 103. 
 
INDEX. 
 
 669 
 
 Silicated soap, 573. 
 Silicates, 105. 
 
 normal ratio of, 254. 
 Silicic acid, SiO 2 , 102. 
 
 atomic formula, 109. 
 bibasic, 106. 
 equivalent of, 106. 
 formerly Si0 3 , 109. 
 hydrated, 104. 
 solution of, 104. 
 ether, 523. 
 
 Silicide of magnesium, 108. 
 ^Silicium, 106. 
 
 ethyle, 535. 
 methyle, 535. 
 Silicon 1 uoric acid, 181. 
 Silicon, Si, 102. 
 
 action of hydrochloric acid on, 166. 
 
 amorphous, 107. 
 
 and nitrogen, 107. 
 
 a tetratomic element, 165. 
 
 atomic weight, 109. 
 
 bisulphide, 218. 
 
 chloride, SiCl 2 , 165. 
 
 combining weight, 108. 
 
 diamond, 107. 
 
 fluoride, SiF 2 , 179. 
 
 composition byvolumej 81 . 
 importance in mineralogy, 
 
 180. 
 
 preparation, 180. 
 fused, 107. 
 graphitoid, 107. 
 hydride, 107. 
 
 hypothetical vapour-density, 165. 
 resembles carbon, 107. 
 Silicone, 108. 
 Silk, 617. 
 Silver, Ag, 361. 
 
 action of hydrochloric acid on, 149. 
 
 hydrosulphuric acid on, 192. 
 amalgam, 369. 
 arsenite, 244. 
 basic periodate, 174. 
 bromide, AgBr, 366. 
 chloride, AgCl, 365. 
 
 action of light on, 212. 
 reduction of, 365. 
 cleaned, 192. 
 coin, 363. 
 
 compounds, atomic formulae of, 366. 
 crucibles, 364. 
 detected in lead, 355. 
 equivalent and atomic weights, 366. 
 extracted from its ores, 213. 
 extraction by amalgamation, 362. 
 from copper-ores, 361. 
 
 lead, 352. 
 frosted, 363. 
 
 fulminate, Ag 2 C 4 N 2 4 , 446. 
 fusing-point, 364. 
 fulminating, 364. 
 glance, AgS, 366. 
 hyposulphite, 212. 
 in lead, 352. 
 iodide, 173. 
 metaphosphate, 231. 
 native, 361. 
 nitrate, AgO . N0 5 , 364. 
 
 preparation from standard 
 
 silver, 365. 
 nitride, 364. 
 
 Silver ore, red, 366. 
 oxalate, 586. 
 oxide, AgO, 364. 
 oxides, 364. 
 oxidised, 363. 
 periodate, 174. 
 plate, 363. 
 properties, 364. 
 pure, preparation, 363. 
 pyrophosphate, 231. 
 recovered from photographic baths, 
 
 refining, 362. 
 
 separated from copper, 365. 
 
 solder, 363. 
 
 stains removed, 364. 
 
 standard, 362. 
 
 subchloride, 366. 
 
 sulphide, AgS, 366. 
 
 native, 361. 
 tarnished, 192. 
 tree, 369. 
 triphosphate, 232. 
 Silvering brass or copper, 363. 
 dry, 363. 
 glass, 363. 
 Simple solution, 47. 
 SiO 2 , silicic acid, 102. 
 Siphon eudiometer, 34. 
 Size, 617. 
 Slag, blast-furnace, composition, 306. 
 
 iron in, 309. 
 iron-refinery, 310. 
 lead-furnace, 350. 
 metal (copper), 338. 
 ore-furnace, 337. 
 puddling-furnace, 313. 
 refinery (copper), 339. 
 roaster (copper), 338. 
 Slaked lime, CaO . HO, 278. 
 Slaking of lime, 49. 
 Slate, 286. 
 Slow portfire, 418. 
 Smalt, 329. 
 Smelling-salts, 270. 
 Smoke, cause of, 62. 
 
 consumption, 62. 
 prevention, 62. 
 Smokeless gas-burners, 96. 
 Sn, tin, 383. 
 
 SnCl, protochloride of tin, 389. 
 SnCl 2 bichloride of tin, 389. 
 SnO, protoxide of tin, 388. 
 Sn0 2 , binoxide of tin, 388. 
 Snow, 46. 
 
 SnS, protosulphide of tin, 389. 
 SnS 2 , bisulphide of tin, 390. 
 Snuff, 600. 
 
 50 2 , sulphurous acid, 196. 
 
 50 3 , sulphuric acid, 200. 
 S 2 2 , hyposulphurous acid, 211. 
 Soap, 571. 
 
 arsenical, 244. 
 Castile, 573. 
 glycerine, 573. 
 mottled, 573. 
 -nut, 479. 
 palm-oil, 572. 
 rosin in, 573. 
 silicated, 573. 
 transparent, 573. 
 -wort, 479. 
 
670 
 
 INDEX. 
 
 Soap, yellow, 573. 
 
 Soaps decomposed by acids, o/o. 
 
 Soda, NaO, 266. 
 
 acid pyrophosphate, 233. 
 action on hard waters, 43. 
 aluminate, 289. 
 arseniates, 246. 
 arsenite, 245. 
 ash, 265. 
 
 manufacture, 264. 
 atomic formula, 268. 
 basic periodate, 174. 
 biborate, 267. 
 bicarbonate, 266. 
 bimetantimoniate, 380. 
 bisulphate, 209. 
 bitungstate, 392. 
 carbonate, NaO . C0 2 , 264. 
 
 manufacture from common 
 
 salt, 264. 
 medicinal, 265. 
 caustic, NaO . HO, 266. 
 chloride, 155. 
 common phosphate, 2NaO . HO . P0 5 , 
 
 232. 
 
 crystals, 265. 
 hydrate, 266. 
 hypochlorite, 155. 
 hypophosphite, 234. 
 hyposulphite, NaO . S 2 2 , 211. 
 
 use in photography, 212. 
 in blood, 615. 
 -lime, 120. 
 -lye, 266, 572. 
 manganate, 327. 
 manufacture of, history, 264. 
 
 influence on useful 
 
 arts, 265. 
 
 metaphosphate, 233. 
 nitrate, 268, 415. 
 
 conversion into nitrate of pot- 
 ash, 416. 
 solubility, 416. 
 obtained from kryolite, 266. 
 oleate, 572. 
 palmitate, 572. 
 
 phosphate, 2NaO . HO . P0 5 , 268. 
 phosphite, 234. 
 platinate, 396. 
 pyrophosphate, 233. 
 silicate, 103, 268. 
 stannate, NaO . Sn0 2 , 388. 
 stearate, 572. 
 subphosphate, 232. 
 sulphate, NaO . SO 3 , 268. 
 
 extracted from sea- water, 263. 
 sulphite, 199. 
 sulphoxy-phosphate, 238. 
 test for, 380. 
 tetrathionate, 214. 
 tungstate, NaO . W0 3 , 385, 392. 
 urate, 621. 
 washing-, 265. 
 waste, 212. 
 -water, 71. 
 
 powders, 71. 
 Sodacetic ether, 569. 
 Sodamide, NH 2 Na, 551. 
 Sodium, Na, 262. 
 
 action on water, 23. 
 -alcohol, 526. 
 -amalgam, 119. 
 
 Sodium and oxygen, 8. 
 
 atomic weight, 268. 
 aurochloride, 407. 
 blowpipe-test for, 266. 
 chloride, 262. 
 
 commercial importance, 
 
 137. 
 
 solubility, 163, 416. 
 equivalent weight, 268. 
 -ethyle, 533. 
 extraction, 267. 
 fluoride, 179. 
 -glycol, 560. 
 
 line in the spectrum, 273. 
 nitroprusside, 444. 
 pentasulphide, 213. 
 platinochloride, 397. 
 silicofluoride, 108. 
 sulphantimoniate, 193. 
 sulpharseniate, 193. 
 sulpharsenite, 250. 
 sulphostannate, 193. 
 Soffioni, 109. 
 
 artificial, 110. 
 Softening waters, 43. 
 Soft soap, 572. 
 water, 40. 
 
 Soils, formation, 71, 623. 
 impoverished, 624. 
 iron in, 323. 
 Solanine, 538. 
 Solder, 355. 
 
 brazier's, 343. 
 coarse, 386. 
 fine, 386. 
 
 silversmith's, 363. 
 
 Soldering, use of sal-ammoniac in, 271. 
 Soluble glass, 268. 
 Solution, 47. 
 Soot, 62. 
 
 as manure, 625. 
 Sorbic acid, 590. 
 Sorrel, salt of, 584. 
 Soup, 616. 
 Sparkling wines, 71. 
 Sparteine, 538. 
 
 Spathic iron ore, FeO . C0 2 , 302. 
 Specific gravity of gases defined, 4. 
 
 influence of tempera- 
 ture on, 194. 
 liquids, defined, 46. 
 
 determined, 115. 
 solids, defined, 46. 
 Specific heat defined, 426. 
 of atoms, 37. 
 of magnesium, 284. 
 relation to equivalent weights, 
 
 283. 
 Specific heats of potassium, sodium, and 
 
 lithium, 284. 
 Spectroscope, 273. 
 Spectrum analysis, 273. 
 
 use of bisulphide of car- 
 bon in, 216. 
 
 Specular iron ore, Fe 2 O 3 , 302. 
 Speculum metal, 342, 387. 
 Speiss, 329. 
 Spelter, 296. 
 Spermaceti, 582. 
 Sperm oil, 582. 
 Spheroidal state, 197. 
 Spices, preservative effect of, 635. 
 
INDEX. 
 
 671 
 
 Spiegel-eisen, 319. 
 Spindle, MgO . A1 2 3 , 288, 3243. 
 Spirit, methylated, 473. 
 of salt, 138. 
 of wine, 516. 
 Spirits, 511. 
 
 of turpentine, 469. 
 Spirting avoided, 105. 
 Sponge, 618. 
 
 ashes of, 171. 
 Spongy platinum, 394. 
 Spontaneous combustion of phosphorus, 12. 
 Springs, petrifying, 42. 
 Spring water, 39, 71. 
 Sprouting of silver, 354. 
 Sr, strontium, 277. 
 SrO, strontia, 277. 
 
 SrO . C0 2 , carbonate of strontia, 277. 
 SrO . N0 5 , nitrate of strontia, 277. 
 SrO . S0 3 , sulphate of strontia, 277. 
 Stains of fruit removed, 197. 
 Stalactites, 42. 
 Stalagmites, 42. 
 Stannates, 388. 
 Stannic acid, Sn0 2 , 388. 
 
 dialysed, 388. 
 hydrated, 388. 
 chloride, SnCl 2 , 389. 
 
 molecular formula, 390. 
 oxide, Sn0 2 , 388. 
 sulphide, SnS 2 , 390. 
 Stannous chloride, SiiCl, 389. 
 oxide, SnO, 388. 
 sulphide, SnS, 389. 
 Star antimony, 378. 
 Starch, C 12 H 10 10 , 483. 
 
 action of water on, 485. 
 a glucoside, 487. 
 and iodine, 172. 
 blue, 291. 
 commercial, 485. 
 extraction from potatoes, 483. 
 rice, 484. 
 wheat, 484. 
 from different plants distinguished, 
 
 485. 
 
 in food, 485. 
 iodised, 487. 
 paste, preparation, 15. 
 Stassfurthite, 261, 416. 
 Staurotide or staurolite artificially formed, 
 
 180, 
 
 Steam, composition by volume, 35. 
 decomposed by carbon, 78. 
 chlorine, 142. 
 electric sparks, 22. 
 latent heat of, 432. 
 specific gravity calculated, 35. 
 Stearic acid, HO . C^B.,,0^ 514, 573. 
 Stearic glucose, 578. 
 Stearine, C 1U H 110 12 , 572. 
 candles, 574. 
 synthesis of, 575. 
 Steatite, 280. 
 Steel, 315. 
 
 annealing, 318. 
 
 Bessemer, 319. 
 
 blistered, 316. 
 
 cast, 317. 
 
 distinguished from iron, 319. 
 
 German, 320. 
 
 hardening, 318. 
 
 Steel, Krupp's, 320. 
 
 made with coal-gas, 319. 
 manufacture, 315. 
 mild, 319. 
 natural, 320. 
 nitrogen in, 319. 
 Parry's, 319. 
 puddled, 320. 
 shear, 318. 
 tempering, 318. 
 tilted, 317. 
 titanium in, 319. 
 Stereochromy, 268. 
 Sterro-metal, 342. 
 Stibethyle, Sb(C 4 H 5 ) 3 , 534. 
 Stibiotriethyle, 534, 547. 
 Stibio-trimethyle, 534. 
 Still, 45. 
 
 Stockholm tar, 468. 
 Stone, artificial, 268. 
 -coal, 63. 
 decayed, 414. 
 test of durability, 414. 
 -ware, 412. 
 Storax, 42. 
 
 Stout, composition, 491. 
 Straits tin, 385. 
 Stream-tin ore, 383. 
 Strontia, carbonate, 277. 
 
 nitrate, SrO . N0 5 , 277. 
 sulphate, 277. 
 
 Strontianite, SrO . C0 2 , 277. 
 Strontium, Sr, 277. 
 
 action on water, 24. 
 diatomic, 285. 
 
 equivalent and atomic weigh ts,283. 
 properties, 277. 
 sulphide, 277. 
 Struvite, 382. 
 
 Strychnine, C 42 H 22 N 2 4 , 538. 
 constitution, 544. 
 extraction, 599. 
 identified, 599. 
 properties of, 599. 
 Stucco, 280. 
 Styracine, 472. 
 Styrole, 472. 
 Suberic acid, 580. 
 Sublimate, corrosive, 370. 
 Sublimation, 114, 473. 
 Sublimed sulphur, 420. 
 Substitution, 23. 
 
 of chlorine for hydrogen, 144. 
 Succinic acid, 2HO. CH 4 8 , 473, 580. 
 
 conversion into tartaric, 588. 
 formed from tartaric, 588. 
 Succussion, 205. 
 
 Suet, 582. 
 
 Sugar, action of oil of vitriol on, 206. 
 adulteration, 495. 
 -candy, 495. 
 
 -cane, composition, 497. 
 extraction, 496. 
 from beet-root, 498. 
 
 linen, &c., 495. 
 -lime, 499. 
 loaf-, 498. 
 maple-, 495. 
 of flesh, 615. 
 of fruits, C 12 H 12 0, 2 , 496. 
 of gelatine, 617. 
 of manna, 500. 
 
672 
 
 INDEX. 
 
 Sugar of milk, C 12 H 12 O 12 , 608. 
 
 preservative effect of, 635. 
 raw, 497. 
 -refining, 60, 497. 
 starch-, 495. 
 uncrystallisable, 496. 
 with chloride of sodium, 499. 
 with oxide of lead, 499. 
 Sugars, 495. 
 
 chemical properties, 499. 
 optical properties, 499. 
 Sulphamylic acid, 525. 
 Sulphantimoniates, 382. 
 Sulphantimonites, 382. 
 Sulpharsenic acid, 250. 
 Sulpharsenious acid, 250. 
 Sulphate of soda and lime, 268. 
 
 crystallisation of, 48. 
 composition, 48. 
 Sulphates, 209. 
 
 acid, 210. 
 
 action of heat on, 210. 
 
 atomic formulae of, 211. 
 
 double, 210. 
 
 in common use, 211. 
 
 native, 183. 
 
 normal, 253. 
 
 reduced to sulphides, 210. 
 
 unitary formulae of, 211. 
 
 action of air on, 193. 
 
 native, 183. 
 
 precipitated by hyposulphites, 
 
 Sulphindigotic acid, 604. 
 Sulphindylic acid, 604 
 Sulphites, 199. 
 
 normal ratio of, 254. 
 Sulphobenzolic acid, 468. 
 Sulphocarbonates, 217. 
 Sulphocarbonic acid, 217. 
 Sulphocyanide of ammonium, preparation 
 
 Sulphocyanogen, CyS 2 , 442. 
 3id, 574. 
 
 Sulph 
 
 lphogl 
 lpholei 
 
 ycen 
 
 Sulpholeic acid, 575. 
 Sulphopalmitic acid, 575. 
 Sulphophosphotriamide, 239. 
 Sulphosaccharic acid, 499 
 Sulphostearic acid, 575 
 Sulphovinic acid, C 4 H 5 0. HO . 2S0 3 , 523. 
 Sulphoxyphosphoric acid, 238. 
 Sulphur, S, 183. 
 
 -acids, 193. 
 
 action of alkalies on, 189. 
 lime on, 195. 
 
 allotropic states of, 188. 
 
 amorphous or insoluble 187 
 
 and oxygen, 7. 
 
 atomic weight, 194. 
 
 -bases, 193. 
 
 chemical relations, 189. 
 
 chloride, SCI, 219. 
 
 combining volume, 194 
 
 dichloride, S 2 C1, 218. 
 
 molecular formula, 219 
 dimorphous, 188 
 distilled, 185. 
 ductile, 187. 
 electro-negative, 187. 
 electro-positive, 187. 
 
 Sulphur, examination of, 421. 
 extraction, 184. 
 
 from copper-pyrites, 
 
 186. 
 
 from iron-pyrites, 185. 
 flowers of, 185. 
 for gunpowder, 420. 
 function in gunpowder, 421. 
 group of elements, 221. 
 home sources of, 135 
 iodide, SI, 219. 
 milk of, 186. 
 
 occurrence in nature, 183. 
 octahedral, 188. 
 of coal mines, 91. 
 ores, 183. 
 oxides, 195. 
 
 oxidised and dissolved, 189. 
 by nitric acid, 126. 
 plastic, 187. 
 prismatic, 188. 
 properties, 186. 
 refining, 185. 
 roll-, 185. 
 rough, 185. 
 -salts, 193. 
 subiodide, S,J, 219. 
 sublimed, 185. 
 test for, 444. 
 uses, 186. 
 
 vapour-density, 195. 
 Sulphureous waters, 45. 
 Sulphuretted hydrogen, HS, 189 
 Sulphuric acid, S0 ? , 200. 
 
 action on bromides, 170. 
 copper, 196. 
 fats, 574. 
 fluor-spar, 177. 
 lead, 205. 
 metallic oxides, 
 
 209. 
 
 metals, 207. 
 organic matters, 
 
 206. 
 
 silver, 207. 
 anhydrous, 209. 
 
 preparation, 201. 
 attraction for water, 206. 
 bibasic, 211. 
 caution in diluting, 206. 
 combinations with water, 
 
 208. 
 
 composition, 208. 
 concentrated, 206. 
 concentration, 205. 
 decomposition by heat 207 
 diluted, turbidity of, 206 
 distillation of, 206. 
 formation, 200. 
 from the chambers, 205. 
 fuming, 200. 
 
 glacial, 208. 
 ydrated, HO. S0 3 , 200. 
 manufacture, 203. 
 
 chemical prin- 
 ciples, 201. 
 history of, 201. 
 illustrated, 
 
 202. 
 
 summary, 206. 
 Nordhausen, 200. 
 polymerising by, 452. 
 
INDEX. 
 
 673 
 
 Sulphuric acid, reduced by hydriodic acid, 
 
 175. 
 
 use in gas-analysis, 209. 
 vapour-density of, 208. 
 anhydride, 209. 
 
 decomposed by heat. 
 
 208. 
 
 ether, 517. 
 
 Sulphuring casks, 198. 
 Sulphurous acid, S0 2 , 196. 
 
 a reducing agent, 198. 
 action on hydrosulphuric 
 acid, 219. 
 
 nitric acid, 202. 
 nitric peroxide, 
 
 202. 
 
 zinc, 213. 
 composition, 199. 
 hydrated, 197. 
 liquefaction, 196. 
 molecular formula, 199. 
 properties, 196. 
 reduced by phosphorous 
 
 acid, 234. 
 separated from other gases, 
 
 358. 
 
 solubility in water, 197. 
 anhydride, 200. 
 Sulphuryle, 198. 
 Sumach, 592. 
 
 Superphosphate of lime, 223. 
 Supersaturated solution, 48. 
 Swedish iron ore, 302. 
 Sweet oil, 580. 
 Sweet spirits of nitre, 522. 
 Syenite, 291. 
 Sylvic acid, 470. 
 Symbols, 2. 
 Sympathetic ink, 49. 
 Synaptase, 474. 
 Synthesis of acetic acid, 533, 564. 
 
 acids of the acetic series, 569. 
 
 butyric acid, 569. 
 
 formic acid, 568. 
 
 guanidine, 546. 
 
 hippuric acid, 622. 
 
 leucic acid, 561. 
 
 neutral fats, 575. 
 
 organic substances, 83, 435. 
 
 propylic acid, 533. 
 
 taurine, 631. 
 
 urea, 618. 
 
 volatile fatty acids, 569. 
 
 water, 33. 
 
 T, TARTARIC ACID, 586. 
 
 Tagalite, 346. 
 
 Talc, 280. 
 
 Tallow, 572, 582. 
 
 Tank-waste, 212. 
 
 Tannic acid, 590. 
 
 Tannin, 590. 
 
 Tanning, 591. 
 
 Tantalic acid, TaO a , or Ta0 5 , 394. 
 
 Tantalite, 394. 
 
 Tantalum, Ta, 394. 
 
 Tap-cinder, composition, 313. 
 
 Tapioca, 485. 
 
 Tar-charcoal, 420. 
 
 Tar, coal, 450. 
 
 wood, 465. 
 Tan-agon, essential oil of, 476.6 
 
 Tartar, 586. 
 
 salt of, 259. 
 
 -emetic, KO . Sb0 3 . T, 587. 
 Tartaric acid, 2HO . C 8 H 4 10 , 586. 
 
 artificial formation, 588. 
 
 bibasic, 586. 
 
 conversion into malic acid, 
 
 588. 
 conversion into succinic acid, 
 
 588. 
 formed from succinic acid, 
 
 588. 
 
 anhydride, 587. 
 
 Tartrate of potash and soda, 588. 
 Taurine, C 4 H T NO 6 S 2 , 631. 
 
 artificial formation, 631. 
 Taurocholic acid, 630. 
 Tawing, 592. 
 Te, tellurium, 220. 
 Tea, composition, 597. 
 Telluretted hydrogen, 221. 
 Telluric.acid, Te0 3 , 221. 
 Telluride of bismuth, 220. 
 Telluride of potassium, 221. 
 Tellurium, Te, 220. 
 
 characterised, 221. 
 foliated, 220. 
 graphic, 220. 
 sulphides, 221. 
 Tellurous acid, Te0 2 , 221. 
 Temper spoilt, 318. 
 Tempering, colours in, 318. 
 Tenacity of copper, 341. 
 
 iron, 341. 
 Tendons, 616. 
 Tennantite, 240. 
 Terbium, 293. 
 Terebene, 469. 
 Terebilene, 470. 
 Terequivalent elements, 152. 
 Terne-plate, 386. 
 Terpinole, 470. 
 Terstearine, 575. 
 Test tube, 13. 
 Tetrad elements, 152. 
 Tetramercurammonium, oxide, 369. 
 Tetramethylium, hydrated oxide, 542. 
 Tetramines, 546. 
 
 Tetramylium, hydrated oxide, 542. 
 Tetrathionic acid, S 4 5 , 214. 
 Tetratomic elements, 152. 
 Tetrethylarsonium, hydrate, 548. 
 Tetrethylium, hydrated oxide, N(C 4 H 5 ) 4 . 
 
 HO, 541. 
 iodide, 541. 
 
 Tetrethylphosphoiiium, hydrate, -548. 
 Tetrethylstibonium, hydrate, 548. 
 Tetrethyl-urea, 620. 
 Thallium, Tl, 360. 
 
 alcohol, 526. 
 
 equivalent and atomic weights, 
 
 361. 
 
 extracted from flue-dust, 360. 
 for green fire, 361. 
 salts, 361. 
 
 Theine, C I8 H 10 N 4 4 , 538. 
 Thtnardite, 268. 
 Theobromine, C U H 8 N 4 4 , 538, 598. 
 
 converted into caffeine, 599. 
 Theory, atomic, 36. 
 
 Thermometers for very low temperatures, 
 216. 
 
 2 u 
 
674 
 
 INDEX. 
 
 Thionyle, 198. 
 
 Thiosinnamine, 538. 
 
 Thorina, 293. 
 
 Thorinum, Th, 293. 
 
 Thorite, 293. 
 
 Thyme, essential oil of, 470. 
 
 Tile copper, 338. 
 
 Tiles, 413. 
 
 Tin, Sn, 383. 
 
 action of acids on, 387. 
 
 nitric acid on, 127. 
 on hydrosulphuric acid, 192. 
 
 water, 24. 
 alloys of, 386. 
 amalgam, 368. 
 bichloride, SnCl 2 , 389. 
 binoxide, Sn0 2 , 388. 
 bisulphide, SnS,y 390. 
 boiling, 384. 
 
 compounds, atomic formulae, 390. 
 crystals, 389. 
 dropped, 385. 
 
 equivalent and atomic weights, 390. 
 extraction in the laboratory, 385. 
 foil, 385. 
 grain, 385. 
 identified, 385. 
 impurities, 387. 
 metallurgy of, 383. 
 nitromuriate, SnCl 2 , 389. 
 Tin-ore of Montebras, 394. 
 Tin-ores, mechanical treatment of, 383. 
 oxychloride, 389. 
 plate, 385. 
 properties of, 385. 
 protochloride, SnCl, 389. 
 protosulphide, SnS, 389. 
 protoxide, SnO, 388. 
 pure, preparation, 387. 
 pyrites, SnS, 389. 
 refining by liquation, 384. 
 salts, 389. 
 sesquioxide, 389. 
 stannate, 389. 
 -stone, Sn0 2 , 383. 
 tetratomic, 390. 
 tree, 389. 
 Tincal, 109. 
 
 refining of, 267. 
 Tinned iron, 385. 
 Tinning brass, 386. 
 copper, 386. 
 
 Tin-white cobalt, CoAs, 329. 
 Titanic acid, Ti0 2 , 391. 
 
 dialysed, 391. 
 
 extracted from iron-sand, 391. 
 hydrated, 391. 
 properties, 391. 
 Titanic iron, 302. 
 Titanium, Ti, 391. 
 
 bichloride, 391. 
 bisulphide, 391. 
 cyanonitride, 391. 
 metallic, 391. 
 nitride, 391. 
 protoxide, 391. 
 sesquichloride, 391. 
 sesquioxide, 391. 
 tetratomic, 392. 
 Tl, thallium, 360. 
 Toast, 486, 494. 
 Tobacco, 599. 
 
 Tokay, 510. 
 Tolu balsam, 472. 
 
 essential oil, 470. 
 Toluidine, 457, 460, 543. 
 Toluole, C 14 H 8 , 450. 
 Tolylene, 545. 
 
 diamine, 545. 
 Topaz, 179, 288. 
 Touch-paper, 418. 
 Touch-stone, 127. 
 Trap-rock, 291. 
 Treacle, 496. 
 Tree- wax of Japan, 583. 
 Triad elements, 152. 
 Triacetine, 563. 
 Triacid triamines, 545. 
 Triamines, 545. 
 Triamylamine, 542. 
 Triatomic elements, 152. 
 Tribasic phosphates, 232. 
 
 phosphoric acid, 232. 
 Tribenzoyl-phosphide, 551. 
 Tribenzylamine, 558. 
 Triborethyle, B(C 4 H 5 ) 3 , 534. 
 Tricetylamine, 542. 
 Trichloracetic acid, HO . C 4 C1 3 3 , 564. 
 Trichloraniline, 549. 
 Trichlorhydrine, 455. 
 
 of phenose, 455. 
 Triethylamine, N(C 4 H 5 ) 3 , 540. 
 Triethylarsine, As(C 4 H 5 ) 3 , 533, 547. 
 Triethylene - octethyl-tetrummonium, hydrat- 
 ed oxide, 547. 
 
 Triethylene-tetralcohol, 562. 
 Triethylene-tetramine, 546. 
 Tri-ethylene-triamine, N 3 H 3 (C 4 H 4 ) 3 , 545. 
 Triethylphosphine, P(C 4 H 5 ) 3 , 547. 
 Triethylstibine, Sb(C 4 H 5 ) 3 , 547. 
 Trimethylamine, 547. 
 Trimethylarsine, 533, 542. 
 Trinitro-ceUulose, 503. 
 Trinitrocresylic acid, 462. 
 Trinitrophenic acid, 461. 
 Triphane, 272. 
 Triple phosphate, 282. 
 Tripotassamide, NK 3 , 551. 
 Trithionic acid, S 3 5 , 214. 
 Tungsten, W, 392. 
 
 binoxide, 392. 
 
 blue oxide, 392. 
 
 chlorides, 392. 
 
 metallic, 392. 
 
 separated from tin-ores, 385. 
 
 steel, 392. 
 
 sulphides, 392. 
 
 test for, 392. 
 Tungstic acid, W0 3 , 392. 
 
 dialysed, 392. 
 
 Turbith or turpeth mineral, 37 J. 
 Turkey red, 601. 
 Turmeric, 602. 
 
 action of bbracic acid on, 110. 
 Turnbull's blue, Fe 3 Fdcy, 443. 
 Turner's yellow, 359. 
 Turpentine, C 20 H 16 , 469. 
 
 action of nitric acid on, 127. 
 hydrates, 470. 
 hydrocarbons, 470. 
 in chlorine, 143. 
 Turquoise, 291. 
 Tuyere pipes, 304. 
 Type-furniture alloy, 352. 
 
INDEX. 
 
 675 
 
 Type-metal, 355, 387. 
 Types, chemical, 151. 
 
 U, UKIC ACID, 621. 
 
 Ulmate of ammonia as manure, 617. 
 
 Ulmic acid, 628. 
 
 Ultramarine, artificial, 291. 
 
 green, 291. 
 Umber ,286. 
 
 Uniequivalent elements, 152. 
 Unitary definitions, 256. 
 % formula of nitric acid, 129. 
 
 oil of vitriol, 209. 
 phosphoric acid, 237. 
 formulae, 50. 
 
 of chlorates, 161. 
 hypochlorites, 161. 
 nitrates, 129. 
 sulphates, 211. 
 Upcast shaft, 70. 
 Uranium, U, 299. 
 
 oxides, 300. 
 Urea, C 2 H 4 N 2 2 , 618. 
 analysis of, 121. 
 artificial formation, 618. 
 chemical constitution, 619. 
 extraction from urine, 618. 
 isomeric with cyanate of ammonia, 618. 
 nitrate, 618. 
 Ureides, 620. 
 Uric acid, 2HO . C 10 H 2 N 4 4 , 621. 
 
 action of nitric acid on, 621. 
 
 bibasic, 621. 
 
 extraction from boa-excrement,621. 
 
 urine, 621. 
 Urine, 618. 
 
 as manure, 625. 
 composition, 623. 
 putrefaction of, 618. 
 
 VACUUM-PANS, 497. 
 
 Valentinite, 379. 
 
 Valerian, essential oil of, 470. 
 
 Valerianic acid, SO . C 10 H 9 3 , 514, 570. 
 
 Valerian root, 570. 
 
 Valerine, 582. 
 
 Valerolactic acid, 560. 
 
 Valerone, 557. 
 
 Valeryle, 520, 557. 
 
 Vanadic acid, -V0 3 , 393. 
 
 Vanadium, V, 393. 
 
 chlorides, 393. 
 
 ink, 393. 
 
 metallic, 393. 
 
 oxide, 393. 
 
 sulphide, 393. 
 Vapour-densities, influence of temperature 
 
 on, 194. 
 
 Vapour-densities of the olefines, 515. 
 Varnishes, 473. 
 Vegetable parchment, 208. 
 Vegetation, chemistry of, 623. 
 Venetian red, 322. 
 Venice turpentine, 469. 
 Ventilation, illustrations of, 69. 
 
 necessity for, 69. 
 Veratrine, 538. 
 Verdigris, 563. 
 Verditer, 345. 
 Vert de Guignet, 33. 
 Vermilion, HgS, 373. 
 Vesta matches, 160. 
 
 Vinegar, composition, 493. 
 
 French, 493. 
 
 malt, 493. 
 
 manufacture, 492. 
 
 mother of, 493. 
 
 sulphuric acid in, 493. 
 
 white wine, 493. 
 Vinic acids, 524. 
 Vitelline, 614. 
 Vitriol-chambers, 203. 
 
 corrosive properties of, 206. 
 Vivianite, 324. 
 Volcanic ammonia, 267. 
 Volcano, artificial, 189. * 
 
 Voltameter, 33. 
 
 Volume of gas, calculation of, 13. 
 Volumes, combining, 37. 
 
 of compound gases, 37. 
 Vulcanised caoutchouc, 481. 
 Vulcanite, 482. 
 
 W, TUNGSTEN, 392. 
 
 Wad, 325. 
 
 Walls, efflorescence on, 268. 
 
 Washing precipitates, 105. 
 
 Wash-leather, 592. 
 
 Watch-spring for burning in oxygen, 10. 
 
 action upon metals, 23. 
 analysis, 19. 
 
 atomic formula, H 2 O, 36. 
 chemical relations of, 47. 
 crystallisation of, 46. 
 decomposed by battery, 19. 
 
 heat, 21. 
 distilled, 45. 
 electrolysis of, 19. 
 from natural sources, 38. 
 -gas, 78. 
 hard, 40. 
 
 molecule, H^Oa, 52. 
 of constitution, 49. 
 of crystallisation, Aq., 48. 
 oxygenated, 50. 
 purification, 45. 
 soft, 40. 
 synthesis, 33. 
 Waterproof cloth, 481. 
 
 felt, 481. 
 Waters, ammonia detected in, 373. 
 
 mineral, 45. 
 
 Water-type theory of acids and salts, 254. 
 Watery vapour, 47. 
 Wavellite, 291. 
 Wax, bees', 583. 
 
 bleaching, 583. 
 Chinese, 583. 
 Weld, 601. 
 Welding, 315. 
 Well-water, 39. 
 Welsh coal, 63. 
 Whale-oil, 582. 
 Wheat, composition, 484. 
 
 sprouted, 488. 
 Wheaten flour, 494. 
 Whey, 609. 
 Whisky, 511. 
 White gunpowder, 158. 
 iron, 308. 
 lead, 358. 
 
 manufacture, 358. 
 ore, PbO . CO,, 349. 
 
676 
 
 INDEX. 
 
 White metal, Cu 2 S, 337. 
 
 precipitate, NH 2 Hg . HgCl, 371. 
 
 fusible, NH 2 Hg.HCl,372. 
 
 vitriol, 298. 
 
 Willow-bark, bitter principle, 476. 
 Windows, crystals on, 269. 
 Wine, 509. 
 Wines, dry, 509. 
 
 fruity, 509. 
 
 proportion of alcohol in. 510. 
 
 red, 509. 
 
 ropy, 492. 
 
 white, 509. 
 WAter-green oil, 467. 
 Wire iron, 312. 
 Witherite, BaO . C0 2 , 275. 
 Wolfram, 383, 392. 
 Wood, carbonisation of, 57. 
 
 -charcoal, 56. 
 
 combustion, 56. 
 
 composition, 464. 
 
 destructive distillation of, 56, 464. 
 
 for gunpowder-charcoal, 419. 
 
 -naphtha, C 2 H 4 2 , 466. 
 
 preservation of, 628. 
 
 -smoke, 635. 
 
 -spirit, 466. 
 
 -tar, 465. 
 Woody fibre, 465. 
 Wool, 617. 
 
 Wool and cotton, separation, 617. 
 Worm, 45. 
 Wormwood, 473. 
 Wort, 489. 
 Wrought iron, 309. 
 
 XANTHEINE, 601. 
 Xanthine, 601. 
 Xylidine, 460. 
 Xyloidine, 509. 
 Xylole, 450. 
 
 YEAST, 489. 
 
 dried, 491. 
 Yellow, chrome, 332. 
 
 dyes, 606. 
 
 fire, composition for, 286. 
 
 flowers, 601. 
 
 ochre, 301. 
 
 orpiment, 249. 
 
 Paris, 359. 
 Yttrium, Y, 293. 
 
 | Yttrotantalite, 394. 
 
 I ZAPFBE, 329. 
 Zinc, Zn, 294. 
 
 -acetimide, 552. 
 action of air on, 294. 
 
 hydrochloric acid on,' 149. 
 sulphuric acid,on, 297. 
 on water, 24. 
 -alcohol, 531. 
 -amalgam, 369. 
 amalgamated, 368. 
 -amide, NH 2 Zn, 551. 
 -amyle, 533. 
 and oxygen, 9. 
 arsenide, 246. 
 arsenite, 244. 
 boiling-point, 295. 
 carbonate, 294. 
 chloride, 298. 
 
 atomic formula, 298. 
 diatomic, 298. 
 dissolved by potash, 298. 
 distilled, 295. 
 
 equivalent and atomic weights, 298. 
 -ethyle, C 4 H 5 Zn, 531. 
 extraction, 295. 
 
 Belgian method, 296. 
 English method, 295. 
 Silesian method, 296. 
 granulated, 25. 
 hyposulphite, 213. 
 identified, 297. 
 impurities in, 297. 
 metallurgy of, 295. 
 -methyle, 532. 
 nitride, 552. 
 ores, 294. 
 oxide, ZnO, 298. 
 
 atomic formula, 298. 
 in glass, 410. 
 oximide, 552. 
 phenylimide, 552. 
 removal of lead from, 297. 
 sulphate, ZnO . S0 3 , 298. 
 
 action of heat on, 210. 
 sulphide, 294. 
 valerianate, 570. 
 -white, 298. 
 Zircon, 293. 
 Zirconia, 293. 
 Zirconium,. Zr, 293. 
 ZnS, sulphide of zinc, 294. 
 
 THE END. 
 
 XKILT, ANl> COMPANY. I'RIXTEHS. KPlXBUHfiH. 
 
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A CLASSIFIED INDEX 
 
 TO 
 
 MISSIS. ClflOTUL & SUMS' 
 
 ANATOMY, 
 
 Anatomical Remembrancer 
 Flower on Nerves . . 
 Hassall's Micros. Anatomy 
 HeaVs Anatomy of the Lungs 
 Heath's Practical Anatomy 
 Holden's Human Osteology 
 Do. on Dissections . . 
 Huxley's Comparative Anatomy 2 1 
 Jones' and Sieveking's Patho- 
 logical Anatomy . . 
 MacDougal Hirschfeld on the 
 
 Nervous System 
 Maclise's Surgical Anatomy 
 St. Bartholomew's Hosp 
 
 Catalogue 
 
 Sibson's Medical Anatomy 
 Waters' Anatomy of Lung 
 Wheeler's Anatomy for Artists 
 Wilson's Anatomy . . 
 
 CHEMISTRY. 
 
 Bernays' Notes for Students 
 
 Bloxam's Chemistry 
 
 Bowman's Practical Chemistry 
 
 Do. Medical dp. 
 Fownes' Manual of Chemistry 
 
 Do. Actonian Prize . . 
 
 Do. Qualitative Analysi 
 Fresenius' Chemical Analysis 
 Galloway's First Step 
 
 Do. Second Step .. 
 
 Do. Analysis .. .. 
 
 Do. Tables .. .. 
 Griffiths' Four Seasons . . 
 Horsley's Chem. Philosophy 
 Mulder on the Chemistry of Wine 27 
 Plattner & Muspratton Blowpipe 28 
 Speer's PathoL Chemistry 
 Button's Volumetric Analysis 
 
 CLIMATE. 
 
 Aspinall on San Remo 
 Bennet's Winter in the South of 
 
 Europe 
 
 Chambers on Italy . . 
 Dalrymple on Egypt . . 
 Francis on Change of Climate 
 
 Hall on Torquay 
 
 Haviland on Climate . . 
 
 Lee on Climate 
 
 Do. Watering Places of England 24 
 McClelland on Bengal . . 
 McNicoll on Southport . . 
 Martin on Tropical Climates 
 Moore's Diseases of India 
 Scoresby-Jackson's Climatology 31 
 Shapter on South Devon . . 
 Siordet on Mentone 
 Taylor on Pau and Pyrenees 
 
 
 DEFORMITIES, &c. 
 
 PAGE 
 
 FAGE 
 
 .. 7 
 
 Adams on Spinal Curvature . . 6 
 
 .. 16 
 
 Do. on Clubfoot 6 
 
 .. 19 
 
 2S 19 
 
 Bigg's Orthopraxy 10 
 Bishop on Deformities .. ..10 
 
 .. 20 
 
 Do. Articulate Sounds .. 10 
 
 .. 20 
 
 Brodhurst on Spine 11 
 
 .. 20 
 
 Do. on Clubfoot .. ..11 
 
 my 21 
 
 Godfrey on Spine 17 
 
 0- 
 
 Hugman on Hip Joint . . . . 21 
 
 .. 22 
 
 Salt on Lower Extremities . . 31 
 
 the 
 
 Tamplin on Spine 34 
 
 .. v 
 
 
 .. 25 
 
 
 
 tal 
 .. 31 
 
 
 .. 32 
 
 DISEASES OF WOMEN 
 
 .. 37 
 
 ts 38 
 
 AND CHILDREN, 
 
 .. 39 
 
 Ballard on Infants and Mothers 7 
 
 
 Bennet on Uterus 9 
 
 
 Bird on Children 10 
 
 
 Bryant's Surg. Diseases of Child. 1 1 
 
 
 Eyre's Practical Remarks .. 15 
 
 .. 9 
 
 Harrison on Children .. ..19 
 
 .. 10 
 
 Hood on Scarlet Fever, &c. ..21 
 
 ry 10 
 .. 10 
 
 Kiwisch (ed. by Clay) on Ovaries 13 
 Le.e's Ovarian & Uterine Diseases 24 
 
 
 Do. on Speculum 24 
 
 .' 16 
 
 Ritchie on Ovaries 30 
 
 . 16 
 
 Seymour on Ovaria 32 
 
 9 . 16 
 
 Tilt on Uterine Inflammation . 35 
 
 . 17 
 
 Do. Uterine Therapeutics . 35 
 
 . 17 
 
 Do. on Change of Life . . .35 
 
 . 17 
 
 Underwood on Children . . .36 
 
 . 17 
 
 Wells on the Ovaries 38 
 
 . 18 
 
 West on Women 38 
 
 . 21 
 
 ine27 
 
 Do. (Uvedale) on Puerp. Diseases 38 
 
 ipc28 
 .. 33 
 
 ~*~v~^ " 
 
 3 . 34 
 
 
 
 GENERATIVE ORGANS, 
 
 
 Diseases of, and SYPHILIS. 
 
 .. 7 
 
 Acton on Reproductive Organs 6 
 
 of 9 
 
 Coote on Syphilis 14 
 Grant on Bltiddcr 17 
 
 ! 12 
 . 14 
 
 Hutchinson on Inherited Syphilis 22 
 Judd on Syphilis 23 
 
 . 16 
 
 Lee on Syphilis *J4 
 
 . 19 
 . 19 
 . 24 
 
 Parker on Syphilis 27 
 Wilson on Syphilis 39 
 
 nd 24 
 
 
 .. 25 
 
 MWWltWW 
 
 .. 25 
 
 
 
 .. 26 
 
 
 .. 26 
 
 gy 31 
 
 HYGIENE. 
 
 . . S2 
 
 Armstrong on Naval Hygiene 7 
 
 .. 32 
 
 Beale's Laws of Health .. .. 8 
 
 .. 34 
 
 Do. Health and Disease .. 8 
 
 HYGIENE continued. 
 
 PACK 
 
 Carter on Training 12 
 
 Chavasse's Advice to a Mother . . 13 
 Do. Advice to a Wife .. 13 
 Dobell's Germs and Vestiges of 
 
 Disease 15 
 
 Do.* 1 Diet and Regimen ..15 
 Fife & Ur quhart on Turkish Bath 1 6 
 Gordon on Army Hygiene . . 17 
 
 Granville on Vichy 18 
 
 Hartwig on Sea Bathing . . . . 19 
 Do. Physical Education 19 
 Hufeland's Art of prolonging Life 21 
 Lee's Baths of France, Germany, 
 
 and Switzerland 24 
 
 Moore's Health in Tropics .. 26 
 
 Parkes on Hygiene 27 
 
 Parkin on Disease 28 
 
 Pearse's Notes on Health.. .. 28 
 Pickford on Hygiene .. ..28 
 
 Robertson on Diet 30 
 
 Routh on Infant Feeding . . . . 30 
 Wells' Seamen's Medicine Chest 38 
 
 Wife's Domain 38 
 
 Wilson on Healthy Skin .. ..39 
 Do. on Mineral Waters .. 39 
 Do. on Turkish Bath .. ..39 
 
 MATERIA MEDICA and 
 PHARMACY. 
 
 Bateman's Magnacopia . . . . 8 
 
 Beasley'a Formulary 9 
 
 Do. Receipt Book .. ..9 
 Do. Book of Prescriptions 9 
 Frazer's Materia Medica . . .. 16 
 Nevins' Analysis of Pharmacop. 27 
 Pereira's Selecta e Prsescriptis 28 
 Prescriber's Pharmacopoeia .. 29 
 Royle's Materia Medica . . . . 31 
 Squire's Hospital Pharmacopeias 33 
 Do. Companion to the Phar- 
 
 macopaeia 33 
 
 Steggall's First Lines for Che- 
 mists and Druggists .. .34 
 Stowe's Toxicological Chart . 34 
 
 Taylor on Poisons 35 
 
 Wat-ing's Therapeutics .. .37 
 Wittstein's Pharmacy .. ,59 
 
 MEDICINE. 
 
 Adams on Rheumatic Gout . . 
 
 Addison on Cell Therapeutics. . 
 Do. on Healthy and Dis- 
 eased Structure 
 
 Aldis's Hospital Practice . . 
 
 Anderson (Andrew) on Fever. . 
 Do. (ThosJ on Yellow Fever 
 
IV 
 
 CLASSIFIED INDEX. 
 
 MEDICINE continued. 
 
 i 
 
 1 Austin on Paralysis 
 
 Barclay on Medical Diagnosis . . 
 
 Do. on Gout 
 
 Barlow's Practice of Medicine 
 
 Basham on Dropsy 
 
 Brinton on Stomach 
 
 Do. on Intestinal Obstruction 
 
 Budd on the Liver 
 
 Do. on Stomach 
 
 Camplin on Diabetes 
 
 Chambers on the Ind gestions 
 Do. Lectures . .. 
 
 Cockle on Cancer 
 
 Davey'sGanglionicNervous Syst. 
 Day's Clinical Histories . . .. 
 
 Eyre on Stomach 
 
 Foster on the Sphygmograph . . 
 Fuller on Rheumatism . . 
 
 Gairdner on Gout 
 
 Gibb on Throat 
 
 Do. on Laryngoscope . . 
 Granville on Sudden Death . . 
 
 Griffith on the Skin 
 
 Gully's Simple Treatment 
 Habershon on the Abdomen . . 
 
 Do. on Mercury 
 Hall (Marshall) on Apncea . . 
 
 Do. Observations . . 1 
 
 Headland Action of Medicines 1 
 
 Do. Medical Handbook 1 
 
 Hooper's Physician's Vade- 
 
 Mecum 1 
 
 Inman's New Theory 
 
 Do. Myalgia 
 
 James on Laryngoscope . . 2 
 Jones (Bence) on Pathology and 
 
 Therapeutics 2 
 
 Maclachlan on Advanced Life . . 2 
 MacLeod on Acholic Diseases . . 2 
 Marcet on Chronic Alcoholism . 2 
 Macpherson on Cholera . . 2 
 Markham on Bleeding . . 2 
 Meryon on Paralysis 
 Mushet on Apoplexy . . . . 27 
 Nicholson on Yellow Fever . ! 27 
 Parkin on Cholera ... . 
 Pavy on Diabetes ... 
 Peet's Principles and Practice 
 
 of Medicine .. . . 
 Roberts on Palsy ... 
 Robertson on Gout 
 Sansom on Cholera . '.'. "31 
 Savory's Compendium 
 Semple on Cough . \' m 
 
 Seymour on Dropsy 3; 
 
 Shaw's Remembrancer .. .'.' 32 
 Shrimpton on Cholera 32 
 
 Smee on Debility . ' 32 
 
 Thomas' Practice of Physic .' 35 
 Thudichum on Gall Stones 
 Todd's Clinical Lectures . . 36 
 Tweedie on Continued Fevers 36 
 Walker on Diphtheria 
 What to Observe at the Bedside 25 
 Williams' Principles . . 
 Wright on Headaches 
 
 MICROSCOPE. 
 
 Beale on Microscope in Medicine 8 
 Carpenter on Microscope . . . . 12 
 ocnacht on do. .. 31 
 
 MISCELLANEOUS. 
 
 Acton on Prostitution K 
 
 Barclay's Medical Errors . . 
 
 MISCELLANEOUS cont d - 
 
 PACE 
 
 Barker & Edwards' Photographs 
 Bascome on Epidemics . . 
 
 Bryce on Sebastopol 11 
 
 Buckle's Hospital Statistics ..11 
 
 Cooley's Cyclopaedia 13 
 
 Gordon on China 17 
 
 Graves' Physiology and Medicine 1 7 
 Guy's Hospital Reports .. ..17 
 Harrison on Lead in Water . . 19 
 Hingeston's Topics of the Day . . 20 
 
 Howe on Epidemics 21 
 
 Lane's Hydropathy 23 
 
 Lee on Homoeop. and Hydrop. 24 
 London Hospital Reports.. ..25 
 
 Marcet on Food 25 
 
 Massy on Recruits 26 
 
 Mayne's Medical Vocabulary . . 26 
 
 Part's Case Book 
 
 Redwood's Supplement to Phar- 
 macopoeia 30 
 
 Ryan on Infanticide 31 
 
 St. George's Hospital Reports . . 31 
 Simms' Winter in Paris . . . . 32 
 
 Snow on Chloroform 33 
 
 Steggall's Medical Manual .. 34 
 Do. Gregory's Conspectus 34 
 
 Do. Celsus 
 
 Waring's Tropical Resident at 
 
 Home 37 
 
 Whitehead on Transmission .. 38 
 
 OPHTHALMOLOGY-cow^ 
 
 PAGE 
 
 . 15 
 . 20 
 21 
 
 Dixon on the Eye 
 
 Hogg on Ophthalmoscope 
 Hulke on the Ophthalmoscope 
 Jago on Entoptics . . 
 Jones' Ophthalmic Medicine 
 
 Do. Defects of Sight 
 
 Do. Eye and Ear . . 
 Macnamara on the Eye . ^ 
 
 Nunneley on the Organs of Vision 2 7 
 Solomon on Glaucoma 
 Walton on the Eye . , 
 Wells on Spectacles ., 
 
 PHYSIOLOGY. . 
 
 Carpenter's Human 12 
 
 Do. Manual 12 
 
 Heale on Vital Causes .. ..19 
 Richardson on Coagulation . . 30 
 
 Shea's Animal Physiology 32 
 
 Virchow's (ed. by Chance) Cel- 
 lular Pathology 12 
 
 PSYCHOLOGY. 
 
 NERVOUS DISORDERS 
 AND INDIGESTION. 
 
 Althaus on Epilepsy, Hysteria 7 
 Birch on Constipation .. ..10 
 
 Jarter on Hysteria 12 
 
 )owning on Neuralgia .. ..15 
 
 lunt on Heartburn 21 
 
 Jones (Handfield) on Functional 
 
 Nervous Disorders 22 
 
 ..eared on Imperfect Digestion 23 
 -ebb on Nervous Aifections . . 24 
 ;adcliffe on Epilepsy . . . . 29 
 Jeynolds on the Brain 
 
 Do. on Epilepsy . . . . 
 owe on Nervous Diseases . . 
 ieveking on Epilepsy . . 
 'urnbull on Stomach 
 
 Arlidge on the State of Lunacy 7 
 Bucknill and Tuke's Psycholo- 
 gical Medicine 12 
 
 Conolly on Asylums 13 
 
 Davey on Nature of Insanity . . 15 
 
 Dunn on Psychology 15 
 
 Hood on Criminal Lunatics . . 21 
 Millingen on Treatment of In sane26 
 Murray on Emotional Diseases 27 
 
 Noble on Mind 27 
 
 Sankey on Mental Diseases . . 31 
 Williams (J. H.) Unsoundness of 
 Mind.. .. as 
 
 OBSTETRICS. 
 
 James on Placenta Prsevia . . 
 
 Hodges on PuerperalConvulsions 2 
 
 ee.'s Clinical Midwifery .. ..24 
 
 )o. Consultations 24 
 
 eishman's Mechanism of 'Par- 
 turition 24 
 
 'retty's Aids during Labour . 29 
 
 Mestley on Gravid Uterus . 29 
 
 amsbotham's Obstetrics . . '. 29 
 
 Do. Midwifery.. . so 
 
 nclair & Johnston's Midwifery 32 
 
 mellie's Obstetric Plates . . 33 
 
 mith's Manual of Obstetrics . . 33 
 
 Wayne's Aphorisms . . 34 
 
 aller's Midwifery .. .. ^37 
 
 OPHTHALMOLOGY. 
 
 ooper on Injuries of Eye . . 13 
 Do. on Near Sight .. 13 
 
 alrymple on Eye .. .. 14 
 
 PULMONARY and CHEST 
 DISEASES, &c. 
 
 Alison on Pulmonary Consump- 
 tion ( 
 
 Barker on the Lungs . . . . 
 
 BiUing on Lungs and Heart .. 1C 
 
 Bright on the Chest . . . . " 
 
 Cotton on Consumption . . 
 
 Do. on Stethoscope .. 
 
 , Davies on Lungs and Heart 
 
 I Dobell on the Chest . . 
 
 Do. on Tuberculosis . . 
 
 Do. on Winter Cough . . 
 
 Fcnwick on Consumption . . 
 
 Fuller on Chest 
 
 Do. on Heart 
 
 Jones (Jas.) on Consumption 
 I Laennec on Auscultation . . 
 | Markham on Heart 
 
 Peacock on the Heart 
 
 Richardson on Consumption 
 
 Salter on Asthma . . 
 . Skoda on Auscultation 
 
 Thompson on Consumption 
 
 Timms on Consumption , 
 
 Turnbull on Consumption 
 
 Waters on Emphysema . 
 
 Weber on Auscultation , 
 
-30- 
 
 CLASSIFIED INDEX. 
 
 RENAL and URINARY 
 DISEASES. 
 
 PAGE 
 
 Acton on Urinary Organs . 6 
 Beale on Urine 8 
 
 SURGERY. 
 
 PAGE 
 
 Adams on Reparation of Tendons 6 
 Do. Subcutaneous Surgery 6 
 Anderson on the Skin . . . . 7 
 
 SURGERY continued. 
 
 Maclise on Fractures *|j 
 Maunder's Operative Surgery * 26 
 Nayler on Skin Diseases . . 
 Nunneley on Erysipelas .. **-(. 
 
 Bird's Urinary Deposits . 10 
 Coulson on Bladder .. .14 
 Hassall on Urine .. .19 
 Parkes on Urine .. .. .27 
 Thudichum on Urine . 35 
 Todd on Urinary Organs . . 36 
 
 SCIENCE. 
 
 Baxter on Organic Polarity . . 8 
 Beiltley's Manual of Botan-y . 9 
 Bird's Natural Philosophy . 10 
 Craig on Electric Tensior i . 14 
 Hardwich's Photograph:/ .. . 19 
 Hinds' Harmonies 20 
 Howard on the Clouds .. .21 
 Jones on Vision 23 
 
 Brodhurst on Anchylosis . . ..11 
 Bryant on Diseases of Joints .. 11 
 Do. Clinical Surgery ..11 
 Callender on Rupture . ..12 
 Chapman on Ulcers 12 
 Do. Varicose Veins . ..12 
 Clark's Outlines of Surgery . . 13 
 Collis on Cancer 13 
 Cooper (Sir A.)onTestis. ..14 
 Do. (S.) Surg. Dictionary 14 
 Coulson on Lithotomy . . . 14 
 Curling on Rectum 14 
 Do. onTestis M 
 Druitt' s Surgeon's Vade-Mecum 1 5 
 Fayrer's Clinical Surgery ..16 
 Fergusson's Surgery . . . . . . 1 6 
 Gamgee'sAmputation at Hip-joint 1 7 
 Gant's Principles of Surgery .. 17 
 Heath's Minor Surgery and 
 
 Pirrie's Surgery .. * v * Jl 
 Pirrie & Keith on Acu' f 
 Price on Excision of Y 522 OQ 
 Salt on Rupture.. ^ee-jomt 29 
 Sansom on Chloro' ** 
 Smith (Hy.) on F /,?J m rA " " J 
 Do. on Hsemr MetOt . . . . 33 
 
 'and S- ' ') Dental Anatomy 
 c auireor argery 33 
 atamr*r - 1 Skin Diseases . . . . 33 
 Sf A '* Surgical Manual ,. 34 
 T] on Amputation .. ... 35 
 T Jipson on Stricture .. ..35 
 Jo. on Prostate . . . . 35 
 Do. Lithotomy and Lithotrity 35 
 Tomes' Dental Surgery . . . . 36 
 Toynbee on Ear 36 
 Wade on Stricture .36 
 
 Do. on Body, Sense , and Mind 23 
 Mayne's Lexicon 26 
 Noad on the Induct orium . . 27 
 Pratt's Genealogy of Creation . . 29 
 Do. Eccentric <fc <" Jentric Force 29 
 Do. on Orbital ? .lotion . . . . 29 
 Do.Astronomic.- .^Investigations 29 
 Do. Oracles of -God 29 
 Rainey on She! is 29 
 Reymond's An imal Electricity 3( 
 Taylor's Medi cal Jurisprudence 3> 
 Unger's Bota nical Letters .. 3 
 Vfistises.ofCJreation .. .,36 
 
 Higginbottom on Nitrate of Sir trer2( 
 Hodgson on Prostate . . . . ' 2 C 
 Holt on Stricture ..- t> 2 1 
 James on Hernia 
 Jordan's Clinical Sur' , ery 
 Lawrence's Surgery * 23 
 Do. Ruptures.. . 2c 
 Lee on the RerJmnj, &c, . 24 
 Liston's Surgery 24 
 Logan on f^n Diseases . 24 
 MacleodX Surgical Diagnosis 25 
 Do. Surgery of the Crimea 25 
 
 Wilson on Skin Diseases . . . . 39 
 Do. Portraits of Skin Diseases 39 
 Yearsley on Deafness .. ..39 
 Do. on Throat 39 
 
 VETERINARY MEDICINE. 
 
 Blame's Veterinary Art .. ..10 
 Boureuisnon on the Cattle Plae-iiei n 
 
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