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The following diagrams illustrate the method: Les cartes ou les planches trop grandes pour dtre reproduites en un seul clich6 sont fllm^es A parti: de I'angle sup6rieure gauche, de gauche A droite et de haut en bas, en prenant le nombre d'images nicessaire. Le diagramme suivant iliustre la mithode : 1 2 3 1 2 3 ♦ , ; . « : ,^ 3 THE ESSEE"TIALS OF ELEMENTARY Chemistry and Chemical Physics, FOR THE ASSISTANCE OF t ' ^ High School Students and Intermediate Candidates^ COMPILED AND COLLATED , BY - A. W. AYTOUN FINLAY, ' Soienoe Master, Brantford Collegiate Institute. .\ . First Place Medallist (1865), OF "• .^■■' ,.;,. "■ ■ THE SCIENCE AND ART DEPARTMENT * ' :. ' ■ ■■ • - • ■-^. .-. .. OP H. M. MOST HONOURABLE COMMITTEE OF PRIVY COUNCIL ON EDUCATION. TORONTO : W. WARWICK & SON, PUBLISHERS. 1880. mmm ■<:■». .-:• ; ' : < » L J'\ Entered according to the Act of the Parliament of Canada, ill the year one thousand eight hundred and eighty, by Wil- liam Warwick & Son, in the office of the Minister of Agri- culture. . .>,^ -■■•■. .! . - '.v;--^ »...■'., -J.., •►. ..-.,.,■ >- > .- , ■,-. ■.■n .w ^n V W' ' ■* \ ' I ■- . ■^ ^ V '•~ **»^itt-. ■»"•*» rsj'»tipf *^ .V DUDLEY & BmiNS, PRINTERS, COLBORNE St., TORONTO. ■V J& '•t'^' I ' PREFACE. The raison d^^tre of this little book is as follows : The compiler has, during some years, been obliged, for lack of a suitable handbook, to give to his large classes in Chemistry copious explanatory notes and definitions. This practice has at length become such a serious task that, in self-defence, he has sought re- lief by resorting to publicktion. ^ Unless a compiler be the veriest literary mechanic his work can hardly fail to bear some impress of his own distinctive method of imparting instruction, and the experience of the writer, in the past, encourages him to hope that he is contributing a not unwelcome aid to a large and increasing class of students, in the Collegiate Institutes and High Schools of Ontario. Tlie matter of the work has been evolved in its present form from a great number of notes collected at various times from many sources, but in every case from good authorities on the subject treated of. These notes have been so condensed and altered, for convenience sake, that they are to all intents ori- ginal as to shape^ but the essential matter of the authors consulted has been carefully retained. The following are the principal authorities whose works have been utilised, or collated : Ansted, Tyndall, Ganot, Gerhardt, Ure, Hoffmann, Frankland and Bloxam. Especially to tlie personal and inva1u.\b]e IV PREFACE, ^ tuition of his sometime teachers — Professors Tyndall and Frankland, and to the valuable treatises of Professor Bioxam — is the compiler indebted. In two important points the work will be found to diffj^r from most elementary handbooks, viz : — the ab- sence of illustrations, and the paucity of detailed ex- periments. As regards illustrations, the opinion of the writer is that, except in large and technical manuals, they are almost useless, and quite unneces- sary, since a teacher who knows his business can eithei illustrate his lecture by dashing off a rough sketch on the black-board, or, better still, can rig up apparatus before the student, thereby obviating the necessity for superfluous encroachments upon the space which ought to be devoted to the letter-press, as well as materially reducing the cost of the work. The same objection applies, in a less degree perhaps, to lengthy details of experiments ; such details are no doubt very proper and necessary in large manuals, but, for class work, the teacher ought to know the details thoroughly, and, in such a course of study as the present hand- book is intended to cover, it is from him that the student has a right to expect them, illustrated at . the same time, by the actual performance of all such ex- periments as the teacher's apparatus permits of. , This is the writer's own practice, with the addition that he insists on the performance of the experi- ments, under his direction, by the students themselves; as well as on verbal and written description of the experiments forming a portion of -the ordinary class work. PREFACE. It is difficult to understand what objection "can be . made to such a substitution of practical work for mere book-work, except by such teachers as those re- ferred to by Professor Bloxam, ** who have themselves never had the opportunity of learning how to conduct the simplest chemical operation." The following re- mark of the same author is so much to the point that " it may be quoted entire : " To acquire a knowledge of the rudiments of Chemistry by personal observa- tion, has, without doubt, a very beneficial effect ; but -- ,to get up a number of formulae and equations, with the sole object of gaining a certain number of marks at examination, altogether defeats the object with which Chemistry should be introduced into a system of liberal education," The introduction of tables of tests for the more important elements, acids and gases, and the addition of the Intermediate and other pro- fessional examination questions will, the compiler feels assured, be fully appreciated by students. With regard to these questions, it has not been the design to adopt a mechanical method of question and answer, but, except in special cases, simply to assist the student in finding the answers for himself, by directing him to the paragraphs where they will be found. In conclusion, *he following merits are claimed for this juvt ^'" adoiuun to the literature of technical education i''irst, — It represents the latest results of the labours of the highest authorities in chemical and physical science. Second, — It ^contains a larger amount of information on the subjects treated of than any other book of the same moderate compass and PREFACE. price; and, Third, — It has been compiled with a spec al view to meet the requirements of Ontario pro- fessional students. How far these requirements have been met, it is now left to the class interested to decide. ' • -* ^^ ■ , A. W. A. !•'. Brantford, February, 1880. i/ /• . V > INDEX. ( The numbers refer to paragraphs). Acetylene 130 Acid, definition 39 Acids, water-type theory of 46 binary theory of 46 unitary theory of 46 monobasic 46 dibasic 46 tribasic . . . • 46 Adhe*^ion " 6 Aerated bread 127 After- lamp 127,128 Agate 162 Air 113 Albumen, test for phosphoric acids 155 Alkali, definition. ... : 40 Alkalies, principal 40 Alkaline earths , 40 Allotropic 50 Alloys 35 Amalgam 35 ammonium 35 ' electrical 35 Amethyst 162 Ammonia 121 Nessler's test for 121 Ammoniacal liquor 121 Ammonium 122 Amorphous 48 Analysis 28 Anchor ice 109 Anhydrate 47 Anhydrous 47 Animals and plants, respiration of 1 14 Anthracite 125 Antichlore 147 Antiseptics 135- 147 Aqua fortis lao Aqua regia. ^ , , I40 VIII INDEX. Argentlte Arsenic te^t for I Arsenic acid Arseniettecl hydrogen Arsenious acid Assay note Atmolysis Atmosphere Atom, defi ' ion Atomic he. Atomicity Atomic theory Atomic weight r Attraction, chemical laws of Augite Barometer Base, definition Battery, galvanic Grove's Bell-metal '. Benzine Beryl ' Biboi;£ite of Soda Blacking, sulphuric acid in ^ Black-lead Bleaching powder _ Bleachiiig \yith chlorine , . chloride of lime ^ . ozone sulphurous acid Blende Blood, Day's test for Blowers, in coal mines Blue Vitriol Blue John Boilers, furring of Boiling point Bone ash Boracic acid Borax Boron Boyle's law Brass Bread, rising of aeration of 146 164 70,171 166 167 16S 61 28 68,113 21 97 29 20 24 26 27 162 67 41 100 lOI 35 132 16? i6o 149 124 141 137 141 107 . 147 146 107 128 J49 144 109 81 152 159 160 158 69 35 127 127 INDEX. Brimstone Bristol diamonds. Bromine Bronze , IJrown acid 146 ' 162 142 35 • •••.i<«..«« ••.. .t* 149 Biiiner, Bunsen's 132 Cairngorm stones 162 Calcedony 162 Calcium, carbonate 127 sulphate 149 Calico printing 136,141 Caloric. Calorific intensity, value. . . Carbolic acid Carbon 94 disulphide group of elements Carbonic acid Carbonic oxide Carnelian Carre's freezing machine. Catalysis Catseye .... Chalk Chalybeate waters . Charcoal absorption of gases by . . . c decolorising properties of deodorising properties of.. Chemical equation equivalent Chemistry, definitipn derivation of name ... organic, defined inorganic, defined .... Chili saltpetre Chlorate of potash Chloric acid Chloride of lime Chlorine Deacon's process with hydrogen bleaching action of disinfecting properties of. Weldon's process Chlorochromic acid , 96 93 ' 135 124 151 161 127 126 162 123 28 162 127 109 124 r24 124 124 32 30 14 17 15 16 IfO 138 138 141 137 137 m 37>i4i 141 137 132 \ INDEX. Chlorophyl. 114 Choke-clamp 127,128 Cinnabar < 146 Clarke's test, for hard water 109 Coal .' 125 bituminous 125 cannel 125 Coal-gas, manufacture of i ^l purification of i j i Cobalt glance 1 64 Cohesion 5 Coil, induction 1 04 Coke - 1 24 Colcothar 149 Cold, greatest artificial ...<, ^ 115 Combination by weight 4 24 by volume 25 Combustion, definition 72 Compound, chemical . • ) 9 Compound, mechanical, or niixiure 18 Condenser. . 131 Conduction of heat 90 Copper pyrites , 146 sulphide 146 Copperas, blue > . . . 149 green 149 Coprolite « , 152 Corpse lights 128 Crystals 4^,49 of the leaden chamber , 149 Crystalline 48 Davy lamp • 133 Deacon's process 137 Decomposition, definition 28 Density, defined 3^ Density of compound gases * 27 Derbyshire spar 144 Dew 113 Dialysis 28 Diamond , 1 24 Diathermancy of carbon disulphide ^ 151 Diatomic 29 jI>^ffusion of gases 105 Dimorphous 51 Disinfecting with chloride of lime 141 chlorine • • • 137 Distillation 83 fractional 83 \» INDEX. J* 114 [27,128 146 109 125 125 125 164 5 104 124 149 115 24 25 72 J9 18 90 146 146 149 149 152 128 48,49 149 48 133 137 28 • 27 144 113 28 124 29 los 51 141 137 83 83 Divalent Drummond lijr^*^ Drying gas*^ , cij,,. nt for. . . Dutch liqi _ . . . .• Dyad Ebullition , Electrolysis Electro-negative positive Element, definition Elements, now recognized. Elements, table of Elements, ancient types of. Emerald Endosmosi3 Equivalence Ethylene Evaporation Exosmosis Expansion of gases y , liquids solids Explosions in coal mines. . , Felspar Fermentation Filtration Fire-damp Flame, luminosity structure of Flint Fluoride of silicon Fluorine . . Fluorspar ^., . Fogs %f Formulae, empirical and rational calculation of Freezing mixtures Fuels, relative heating power of . Furring of kettles and boilers . . . Fusible alloy. Fusion Galena Galvanic battery , Garnet Gas, manufacture of . . . . Gasometer Gases, diffusion of characteristics of. 29 III 149 129 29 103 102 102 9 12 13 II 162 56 30 129 84 56 77 75 74 12S 162 127 59 128 132 132 162 145 144 144 113 33,65 65 88 125 109 35 86 146 100 162 131 Ids 172 xu INDEX. Germnn silver Glass, corrosion by hydrofluoric acid Glauber's salt Goaf Gold, testing with nitric acid Gramme Graphite , Green, Scheele's Grove's battery Gun-metal Gypsum Hail Halogens Haloid salts Hardness of water., permanent temporary . Hartshorn, spirit of. . Heat, nature of atomic latent ........ sources specific Heat-units , Heavy carburetted hydrogen . Heliotrope . . Hemming's jet Hepatic springs Hoar-frost . . Hydrates Hydraulic cement main Hydro-carbons Hydrochloric acid Hydrofluoric acid Hydrofluosilicic acid Hydrogen : . . . arsenietted phosphide of phosphuretted . . . . , sulphuretted peroxide Hydiogonium Hydrometer Hydrous Hydrosulphuric acid Ice, anchor 35 145 149 128 120 66 124 16s loi 35 149 113 144 144 109 109 109 121 70 97 93 71 92 94 129 162 134 109 113 47 163 131 132 139 145 161 108 167 157 157 150 no 122 9S 47 ISO 109 INDEX, Xlll 122 47 ISO Induction coil Inorganic chemistry defined. Iodide of potassium Iodine . .' Iodised starch paper Iron pyrites Isomerism I-omorphous Jaspei Joule's equivialent Kaolin Kupfernickel Lamp-black Laughing gas Law, constancy of constitution constant proportions , combining weight of compounds , Mariotte's multiple proportion.' reciprocal proportion , I^eaden chambers , . . cisterns, dangers of Light carburetted hydrogen Lignite Lime purifier water . . . , Litre Liquor ammonise Lucifer matches Luting, for iron joints Manganese, dioxide. red oxide recovery for chlorine residuum arble Mariotte's law , Marsh gas Marsh's test for arsenic Mass, defined Matches, lucifer w silent without phosphorus Matter, defmition conditions of Meerschaum Metals, defined 34 iletaphosphoric acid diethyl 104 16 143 143 107 146 55 53 162 94 162 164 1:24 128 27 27 27 69 27 27 149 109 128 131 127 66 121 153 146 106 106 137 127 69 128 170 4 153 153 I 7 162 .103 128 XIV INDEX, • V*; Metre Mispickel Mixture, defined. . Mokcular formulic. Molecule, defined . . Monad Monatomic Monovalent Muriatic acid Nascent state Negative pole Nessler's test Nickel glance Nitre Nitric acid oxide » _- peroxide pentoxide Nitrogen oxides of Nitrous acid oxide Nitro-muriatic acid , Nomenclature 36, 43, 44, 45, Non-metals 34, Nordliausen oil of vitriol Oil of vitriol../ ,. Oleic acid Olefiant gas Onyx. Opal, Organic chemistry, defined Orpiment Orthophosphoric acid Osmosis , Oxalic acid Oxycalcium light Oxidising flame Oxygen Oxygenated water Oxyhydrogen bloWpipe Ozone - Paint, blackened by sulphuretted hydrogcii Palladium, occlusion of hydrogen by Paper, action of sulphuric aciS on Parchment, vegetable , Peat 164 18 23 22 29 29 29 139 31 [02 [21 L64 [20 [20 16 18 19 12 12 17 IS 40 57 03 49 49 09 29 b2 62 15 [69 155 56 ■36 II 132 106 10 TI 10; CO [22 149 [49 ^25 INDEX. xy ^ 66 164 • 18 23 22 . 29 29 V 29 : 139 31 .„I02 121 164 120 120 . 116 . 118 . 119 112 112 .. IIS 140 \. 45. 57 34, 103 149 149 109 129 lb2 162 15 169 »55 56 136 III 132 106 no ITI 10/ ICO 122 149 149 125 *ewter '.■ . 35 *hosphoric anhydride 154 acid 15s *hosphorous anhydride 154. 'hosphonis 152 amorphous 152 *hosphuretted hydrogen 157 Mants and animals, respiration of 1 14 'lumbago 124 'ole, negative 102 positive 102 Polymorphous 5^ Porcelain clay 102 Potassium, action on water 108 Precipitation 60 Pseudomorphous 54 Pyrophosphoric acid 155 Qualitative analysis 61 Quantitative analysis 61 Quantivalence 29 Quartz/ 102 Radiation of heat 91 Radical, compound 37 salt 38 Rain 113 Rational formula 33, 65 Realgar 168 Reducing^ flame. , 132 Reinsch's test 171 Respiration of plants and animals 114, 127 Rising of breac' 127 Rock crystal 162 I Safety lamp 133 Sal-ammoniac 121 >alt, defined ,^ 42 Jaltpetre , 120 Chili 120 Jalt-radical, defined *. 38 Jand 162 Jcheele's green . \ 165 Scrubber 131 5ea-water 109 mot, small , 35 Jilica 162 Mlicates 162 [ilicic acid.,., 162 |ilico-fluoric acid , ^(.l XVJ INDEX, Silicon Snow Soap, effect of hard >\ Uer on . . . Soda, caustic Sodium, action on waier Softening hard water Soil, value of phosphorus in Solder Solidification Solution Specific gravity of gases liquids solids Specific heat Speculum metal Spirit of salt Stains of fruit or wine removed. . Stalactites Stalagmites Standard gold silver Steam Stearic acid Sublimation Sugar, effect of sulphuric acid on Sulphur flowers of. group of elements dioxide Sulph -etted hydrogen Sulphuric anhydride acid Sulphuring casks ,. . Sulphurous acid bleaching with . . Symbols Synthesis Temperature, absolute relative Tests, indicating ior acids metals .... confirming for acids Tetrad Tetratomic Tetravalent Theory, atomic Thermal unit i6i 113 109 108 108 109 152 35 87 58 98 98 98 92 35 139 147 109 109 35 35 109 109 85 149 146 146 146 147 148 149 147 147 147 32 28 80 80 63 62 64 29 29 29 20, 94 INDEX, xvii Thermometers, construction . Celsius' .... ^ Fahrenheit's Reamur's. . . De Lisle's . . Breguet's. . . Thermometer, air maximum . . . . mmimum, Tincal Triad. Triatomic Trivalent Type-metal Valency of elements Vaporization Vapour, defined ......... Vitriol chambers Vitriol, blue green white Volume, defined [Volume of gas, calculation, absolute . . . [Water [Water-type theory [Weight, atomic absolute Weldon's chlorine process. "'^ood, value of as fuel 'east 'ero, absolute relative ic, sulphate 78 78 78 78 7? 7? 7^ 7^ 78 1 6c 29 2r 29 35 29 84 82 149 149 149 149 2 99 99 109 46 24 99 '37 125 127 79 79 108 jrmediate Exam. Papers. A selection of questions from the examination papers of First- class candi- dates. . s I -\ Preliminary Definitions. I. Matter is anything which possesses weight ; what- ever, therefore, is subject to the law of gravitation is material in its nature. a. The volume of any body of matter is the space occu^jied by it. 3. The density of a body is the relative close- ness of the particles of matter of which it is composed. 4. The mass of a body is the whole q^uautity of matter contained in it. 5. Cohesion is a force acting between the particles of the same kind of matter at inappreciable distances, serving to unite and retain them in contact with each other. 7. Adhesion is a force acting at inappreciable dis- tanceSj which retains the particles of dissimilar bodies in contact with each other. 7. Matter exists in three different conditions — solid, liquid, and gaseous. Liquids and gases are in- cluded also under the name of fluids. Liquids may be practically defined as incompressible, and gases as com- pressible fluids. The solid state is characterised by such cohesion between the material particles, that they can only be separated by an effort, more or less considerable. In the liquid state, the cohtsion of the particles is so weak that they can easily move over, and about one another. In the gaseous state the cohesion of the particles is entirely overcome, and, in its stead, there is a constant tendency to separation, which causes expansion to be a marked characteristic of this condition of matter. ! II M ESSENTIALS OF CttEMISTRV 8. Every separated portion of matter is found, on examination, to be either an elementary substance, or a compound substance. 9. An element is that form of matter which can- not be reduced to a simpler form. 10. A compound is that form of matter which can be resolved into two, or more, constituent ele- ments. IT. The ancients recognized four elements, or, more correctly speaking, four types of elements : Earth, Air, Water, and Fire. With earth, were classed all solids. With air, were classed — smoke, steam, and everything of an aSriform nature ; with water, all li- quids j and with fire, — light, heat, flame; lightning and all similar phenomena. 12. There are, at present, 64 elements determined ; and these for the sake of convenience, are classified as non-metals or metalloids, and metals, there being 15 non-metals and 49 metals. No strict line of de- marcation is to be understood as existing between these two classes. ^ 13. The following table exhibits the name, with its derivation; the symbol; combining weight; atomicity; discoverer, and date of discovery, when known ; of each of the more important non-metals and metals. It is to be noted that the symbols of the elen~ents are the inital letters of the Latin names, which are often different from the vulgar names ; and when two, or more, elements have the same initial, a small letter is added to the initial, to distinguish between the ele- ments symbolized. jments, or, elements : ere classed steam, and ^ater, all li- ghtning and [etermined ; •e classified | there being line of de- g between le, with its I; atomicity; known ; of md metals. [leirents are :h are often len two, or lall letter is len the ele- C/3 SB 01 a ^:3 * 2.^ '^ r» r* » J S — * - — re 2\?' 5 » •13 re Q. re r re §5.Sgg;^-rre«5 8 «♦»» ^re -,. re I— I ^ re Co ,_ o* Da3-«0«93 — » a a-i? ;2 3. re » t-lOB HI 3^ I'p 2 <''«^ P ""^ QD 2 ? =■ c 5-B re 2,» c .. => S ! r* CO S W M ►-" , -- ^, - J (-*s ry CO f^, ^^ T^ '^ ^^ ("^ ^^ 1'*' (^1 *^ Kfi t-J rTi "^ fiS vi Kfi ,■« r^ H* i_j »aj p^ ^^ ^la ^ i A ^ >a/w2<»Ti^H'05i«>.«S§Wi4k5• a CO W :d p c tiq « "• " — P f 2. ©: ^1 cs P H re. p .^3^:3- S 00 CO o o 00 ~J l-i i-< 1-1 M H* M 1^ M l-> 00 00 -M « -^ -^ ^ •>* 00 • ••«••• 7^ t. f-* h-l )-• (/- - 1 -I (-■OO •^1 r«M r •-T«I-^ 00 00 CO 00 t;i 00 "v> «;« 00 CiSCO^ ©(-"l-OObSOWOtO ^-ll^ pC^OOC (SOOM OOO IT' 9 o 09 .^ K M o p :^ 2 o o as 3 o n O -1 H 7> H ESSENTIALS OF CHEMISTRY s I \ . vj 14. Chemistry is the science by aid of which are investigated the inherent, or acquired properties of the elementary and compound substances, which make up the solid and liquid material of the globe, and its gas- eous envelope ; and by its means the chemist is ena bled to resolve matter into its simplest constituents, 3 and to combine the simple elements with each other so as to form compounds. Chemistry is likewise an art, since it enunciates certain rules and methods for effecting the objects above enumerated. It is divided into two branches — Organic, and Inorganic Chemistry. 15. Organic Chemistry treats of those substances which are formed by the operation of Animal, or Vege- table Life ; as flesh, hair, wood, etc. I 16. Inorganic Chemistry treats of those sub- stances, which are formed without direct vital inter- vention ; as limestone, salt, blerxhing powder, etc. 17. The name Chemistry has been variously derived from — Kyamon^ an Arabic word signifying " the sub- stance, or constitution of anything"; Chymos (Gr.) "a juice"; or from Chim, or Kimy " darkness," the ancient name of Egypt ; in which country, the science proba- bly attracted attention at an early date. 18. A Mechanical Compound is one in which no union exists between the constituents, the particles simply lying side by side, without actual change in their characteristic properties. 19. A Chemical Compound is one in which two, • or more elements are united together, forming a sub- stance differing in most of its properties from those of its constituents, which have consequently lost their distin guishing characteristics. AND CHEMICAL PHYSICS, S h ') 20. For the explanation of many of the phenomena ^ of chemical action, it has been found convenient to * adopt what is called the Atomic Theory propounded ^ by Dalton, in 1803. This theory is not to be regarded, " in its entirety, as anything more than a convenient ex- position of actual facts ; and the laws, enunciated in connection with it, as regulating the combination and decomposition of substances, maintain their force, and truth, although the doctrine of a'.oms be abandoned. [According to th( Atomic Theory, all matter is built ' up of minute particits, incapable of further subdivision, which are termed atoms; and these atoms unite, among [themselves, to form molecules. The atoms of an ele- lent are all equal in weight, and similar ; but the itoms of one element are not necessarily of equal 'eight to the atoms of another element. • ■."'"* 21. An Atom is the ultimate chemical particle of in element, or is tie smallest portion which can enter • Into a chemical compound. It has been shown by Dr. *^ [rhomson, that a portion of lead, which cannot exceed the 888,000,000,000,000th of a cubic inch, is still asible; so ths.t the hypothetical atom is, by no means, [o be thought of as a tangible particle. * -. A Molecule is the ultimate physical particle ^f matter, and ' m aggregation of atoms ; being the [mallest portion of an element, or of a compound, [apable of an independent existence, or of taking part a chemical reaction. Elementary molecules are sup-"^ >osed to contain two atoms, but phosphorus, arsenic, lercury, and cadmium are notable exceptions to this hypothesis, the noiccules of the former two apparently ESSENTIALS OE CHEMISTRY containing four atoms; and the molecules of the latter two containing one atom. The atoms of the elements all occupy the same space, in the gaseous condition, and hence the proportional weights of the elements may be ascertained experimentally, when they can be volatilized. 23. The molecule of a compound must be care- fully distinguished from that of an element. Elemen- tary molecules, with certain exceptions, have been said (22) to contain two atoms, but a molecule of a com- pound may be built up of two or more atoms ; not- withstanding which it still occupies the space of one molecule or two atoms of an element in the gaseous condition, such as hydrogen. This fact may be enun- ciated as follows : — The molecule of matter, either ele- mentary or compound, occupies in the gaseous condi- tion the volume of two atoms, or one molecule of hydrogen. Thus in the examples HCl, HaO, H3N, H4C, although there are two, three, four, and five atoms com. bined,the molecule really consists of two atoms, for these formulae do not imply a mixture of H + CI, H -f H -f O, etc., but express the combination of certain elements to form compounds differing in most of their properties from those of their constituent elements, and since condensation is a common result of chemical combin- ation, it is found that the molecule H^C, actually occu- pies the volume of H -f H, and adopting, for the sake of convenience, the language of the atomic theory, the smallest conceivable portion of H4C incapable of fur- ther subdivision, mechanically, could still be broken up by chemical means into its constituent atoms of hvdrogen and car>" ' AND CHEMICAL PHYSICS. ihe latter elements :ondition, elements ey can be t be care- Elemen- been said of a com- jms; not- ce of one e gaseous f be enun- either ele- ous condi- olecule of S5N,H,C, toms coni- 5, for these : + H + o, ements to properties and since ,1 combin- lally occu- r the sake heory, the ble of fur- Da broken atoms of % 24. The Proportional weight, Combining weight, or Atomic weight of an element is found by taking, as a unit, the weight of any known volume of a certain element, in the gaseous condition, and comparing the weight of an equal volume of every other element, in the same condition and at the same temperature, and barometric pressure, with the unit adopted. Whatever the unit may be, the resulting numbers will be proportional. Thus, if a pint of hydro- gen gas be taken, and its absolute weight is found to be one grain, the weight of a pint of oxygen will be sixteen grains ; the weight of a pint of nitrogen will be fourteen grains ; and a pint of mercury in the gas- eous condition will weigh 200 grains, etc. This rela- tive proportion will evidently hold good, if any other standard of volume be adopted, as — 2l quart, a gallon, a cubic inch, a cubic foot, or a litre, that is, the abso- lute weights will differ, but not the relative weights. If now, it be agreed upon to take any volume of hydrogen, and call its weight i, this becomes the unit of Atomic, or, more correctly, of Proportional weight ; and although oxygen is in certain scales taken as the unit gas, hydrogen, being the lightest kno;vn element, is perhaps the most suitable for the purpose, and is the one commonly adopted. 25. In speaking of the combination of two or more elements it is possible to do so either with reference to the weight of the elementary atoms entering into the compound, or with reference to the number of atoms. Thus, in the compound H2O, the elements combine in the proportion of 2 atoms or volumes H, 8 ESSENTIALS OF CHEMISTRY to I atom or volume O, or by weight in the proportion of 2 of H, to 1 6 of O, the ratio between the atom of H, and the atom of O, being i : i6. Again, in the compound KClOi, by reference to the *able of Atomic weights (13) it will be seen that the above symbols represent, not merely certain elements, but definite proportional quantities of the elements by weight. Thus: — K=39-i ; Cl=35-5; 03=16x3=48; there- fore KClOs expresses a combination by weight of 39*1 + 35'5 + 48, but by atom or volume i + i + 3. 26. The force which causes different elements to unite, to form new substances, is called Chemical Attraction, and the act of union is called Chemi- cal Combination, Chemical Attraction can, at present, only be defined by stating its effects ; as the manner of its operation is not clearly understood. 2 7. Although the precise nature of the force termed chemical attraction is not known, its results are al- ways definite; and its operation may be considered as governed by certain constant and well defined laws ; they are as follow : — I. " The same substance consists invariably of the same elements." Thus pure water, no matter whence taken, always consists of hydrogen and oxygen. II. "The elements which form a chemical com- pound are always united in it, in the same proportion, by weight." Thus, in water; the proportions, by weight, of K, and O, are always 2 to 16. III. " If two elements combine in certain propor- tion with a third, they combine in the same proportion with each other." Thus iodine combines with potas- AND CHEMICAL PHYSICS. slum in the proportion, by weight, of 127 to 39*1, and chlorine combines with potassium in the proportion of 35*5 to 39"i, but iodine and chlorine likewise com- bine together, in precisely the same proportion of 127 to 35'5- I IV. " When one element combines with another in\ several proportions, the higher proportions are raulti- * pies of the first, or lowest." Thus — N2O, N2O2, NaOsj ' N2O4, N205=28 : 16, 28 : 32, 28 : 48, 28 -, 64, 28 : 80. V. "The combining proportion of a compound substance is the sum of the combining proportions of its constituents." Thus the combining proportion of water (H2O) is 2 + 16 = 183 of copper oxide (CuO) 63-5 + 16=79-5. Note. — The density of a compound gas is one-half the combining weight, since the molecular volume contains two atomic volumes, e.g.^ CO2— molecular weight=i2 + 32=44, and atomic weight=^^. 28. The separation of a compound into its constit- uents is called Chemical Decomposition. When chemical decomposition is experimentally performed, for the purpose of ascertaining the composition of a substance, the operation is termed Analysis ; when the decomposition is effected by galvanic action, the operation is called Electrolysis ; and if the separa- tion be made by a process of filtration through a mem- brane, it is termed Dialysis. Atmolysis expresses the separation of two gases from one another by rea- son of their different ratio of diffusion through a mem- brane, or porous partition. When a substance in contact with another substance causes or facilitates a 10 ESSENTIALS OF CHEMISTRY change of condit^'on of the latter, without being itself effected, it is said to act by Catalysis. When a chemical compound is artificially formed, by causing proper proportions of its constituents to unite, the operation is called Synthesis^ which is just the oppo- site of analysis. -f 29. In forming a chemical compound, the atoms of all the elements are not of equal value or valency ; thus hydrogen and chlorine combine together in the proportion of atom to atom to form HCl (hydrochloric acid gas) ; hydrogen and oxygen, in the proportion of two atoms to one atom, to form HjO (water) ; hydro- gen and nitrogen, in the proportion of three atoms to one atom, to form HjN (ammonia); hydrogen and carbon, in the proportion of four atoms to one atom, to form H4C (light carburetted hydrogen). The stu- dent will remark the somewhat peculiar circumstance that the four most important elements, H, O, N and C, are respectively monad, dyad, triad and tetrad. This atom-fixing power is called atomicity, or quan- tivalence, and the elements are arranged in groups according as they have the power to fix i, 2, 3, 4, 5, or 6 atoms of hydrogen, or of :- .1 element which com- bines with hydrogen, in the proportion of atom to atom. Thus, all the elements are either monads, monatomic, monovalent, or univalent like CI ; dyads, diatomic, or divalent like O ; triads, tri- ; atomic, or trivalent like N ; tetrads, tetratomic [ or quadrivalent like C ; pentads like Sb, or hex- ads like Crj the last two terms are, however, less commonly used, and, although employed by Frank- AND CHEMICAL PHYSICS, it ing itself When a causing lite, the ie oppo- itoms of ilency ; IX in the ochloric )rtion of ; hydro- toms to ;en and le atom, rhe stu- mstance \ and C, . This quan- groups 3, 4, 5» :h com- Ltora to onads, ike CI \ ds, tri- ; itomic j ►r hex- er, less Frank- land and other chemists of repute, are possibly super- fluous. An atom of a dyad may combine with two atoms of a monad as H2O, or with one atom of a dyad as CuO, and in like manner, an atom of a tetrad may combine with four atoms of a monad as CH4, or with two atoms of a dyad as CO2. 30. The distinction between the atom-fixing power of the element, or quantivalence, and the molecule-formmg power, or equivalence, is to be carefully noted ; the former relates to the valency of the element only, the latter relates to the proportion by weight in which the atoms replace each other, or, the chemical equivalent of an element expresses the weight which is required to replace or fix i part by weight of H in its combinations. Thus in HgO, the quantivalence of O is 2, but the equivalence equal to H2=-V'=^i ^^ H4C, valency of C=4, equivalence^ H4=^=3 ; in H3N, valency of N=3, equivalence = N lj3=Jg*-=4'66j in HCl, valency of CI =1, equivalence =: g=Ap-=35-5. 31. An element is said to be in the nascent state, at the moment in which it is liberated from a com- pound substance ; and it is found to combine with much greater energy, in this condition, than when existing in the free state, because, in the latter case, the atoms are aggregated as molecules ; while, in the former case, the atoms being for the moment free, but unable to exist in that condition, instantly seize upon atoms of other elements present, to form the readiest possible molecular combination. 12 ESS^TIALS OF CHEMISTRY I 32. Since the iijirne. of every element has a combin- ing nuniber attach^, it follows that the symbol of an element does^j»)t merely represent the name, but stands for a definite quantity of the element ; for example \ O. does riot stand for any quantity of oxygen, but for exactly 16 parts by weight of that element, when compared with an equal volume of H. Hg. stands for 200 parts of mercury. Ag. for 108 parts of silver. If more than one combining proportion of an element be present in a compound, a small numeral indicating the multiple is placed to the right of the symbol, as — NjOg, where two proportions of nitrogen are indicated as combining with five proportions of oxygen, or N=i4 x 2 = 28, 0=i6 x 5=80. N2O5 is called a chemical formula, and indicates a union be- tween the elements symbolized ; it therefore represents a molecule. If a numeral be placed to the left of a formula it multiplies the proportion of every symbol, as far as the first comma, sign of addition, or period : ^'St 3Mn02=Mn304 + O2. Here a combination of 3 equivalents of Mn=i65, with 3 x 16 x 2 of 0=96, on being decomposed gives 165 parts of Mn united to 64 parts of O. w^hile 32 parts of O are set at liberty. Such a representation as the last example is called an equation, and as the symbols on the left side of the sign of equality shew what was the orig'ual composi- tion of the body taken, and the symbols on the right side shew the result of decomposition, the equation is said to represent a chemical reaction, "'.''* In writing formulae, it is customary to place the symbol of the element present least resembling oxygen - ^ jiOn-I • . \ AND CHEMICAL PHYSICS. 13 -■^^j r-f first ; and in the case of salts, the symbol of the metal is usually written first. ^ , > . .' ^ 33. Formulae are either empirical, or rational. An empirical formula simply shews the composition of a compound, that is, shews the elements present and the relative proportion that their atoms bear to one another, without regard to their absolute number, or mode of arrangement. A rational formula, on the other hand, represents not merely the elements, but the absolute number of their atoms present ; as well as the mode in which they are combined to form the compound. Ex. Hyposulphurous acid contains in 100 parts 66-66 S and 33*34 O, these numbers di- vided by their atomic weights give their atomic pro- portions ^1^2.= 2 -08 ; -^-f ^=: 2 "oS. These quotients being equal, it may be concluded that hyposulphurous acid is composed of equal atoms of the two elements. The most simple formula would be SO, but it is evi- dent it might be S2O2, or S3O3 — as they would all agree with the results of analysis, this would then be the empirical formula. The rational formula is found by further calculation to be S2O2. 34. It has been stated that the elements are divided, for the sake of convenience, into two classes — metals and metalloids, or non-metals. Metals are de- scribed as being solid, opaque, malleable, ductile, tenacious, possessing a characteristic lustre, and capa- ble of forming a base (41), by combining with oxygen ; or a salt (42), by combination with a salt radical (38). The comparative absence of the above properties ought accordingly to characterise the non-metals, but H ESS It NT/A LS OF CHEMISTRY ill reality no such broad distinction can be drawn between the classes, which merge insensibly one into the other; while, therefore, the distinction be- tween such metalloids as O, S, P or C and metals like Fe, Ag, Au, or Pb, is sufficiently marked, it is not so when such elements as As, I, or Hg, are dealt with. In the following pages the non-metals are considered as being As, B, Br, C, CI, F, H, T, N, O, P, Se, Si, S, Te; all other elements are metals. 35. When any two metals, excluding mercury, com- bine or mix together, they form an alloy ; the mixture of a metal with mercury is called an amalgam. The principal alloys are, — aluminium-bronze, a com- pound of 90 parts copper and 10 parts aluminium ; bell metal, 78 parts copper and. 22 parts tin ; gun metal, 90*5 parts copper and 9*5 parts tin ; bronze, 80 parts copper, 4 parts zinc and 16 parts tin ; brass, 64 parts copper and 36 parts zinc ; German silver, 51 parts copper, 18*5 parts nickel and 30*5 parts zinc ; Speculum metal, (^d 6 parts copper and 33*4 parts tin : solder, 2 parts tin and i part lead ; pewter, 4 parts tin and i part lead; fusible metal, 15 parts bismuth, 8 parts lead, 4 parts tin and 3 parts cad- mium ; type metal, 4 parts lead, I part antimony and occasionally a trace of copper ; shot metal, — lead, with about 40 lbs. of arsenic to the ton ; stand- ard gold, 22 parts gold and 2 parts copper; stand- ard silver, 925 parts silver and 75 parts copper. The fusing point of alloys is generally lower than the mean of the melting points of their constituents. In preparing them, the least fusible metals should be AND CHEMICAL PHYSICS. »S melted first, and the most fusible added in small quantities at a time. Mercury unites readily with most other metals, iron and platinum being the only ones which are not speedily attacked by it. Mer- cury, however, adheres to platinum, and, when min- gled with a little of the amalgam of sodium, will even adhere to iron. An amalgam of zinc and tin — mer- cury, 6 parts, zinc, i part, and tin, i part — is used to promote the action of the electrical machine. A curious amalgam of ammonium is also known, and is referred to elsewhere (122). 36. Compounds of non-metals with each other, or with the metals, take names terminating in ide ; — as oxide, iodide, etc. Occasionally the termination uret is used with the same meaning, but rarely. It is oxygen, or the element most resembling oxygen in its mode of combination, which takes the affix — idej and the name of the metal, oc element least resem- bling oxygen, gives the specific name of the com- pound, thus — hydric ox-ide ; potassic iod ide ; fer- ric ox-ide ; lead sulph-ide ; sulphur diox-ide. 37. A radical is a group of elements which is found to enter into cheYnical combination and to behave in reactions in the same manner as an elemen- tary atom. Hence a radical has been defined as being *' The proportion in which certain elements, or groups of elements may be substituted for others, or may be transferred from one body to another in the act of double decomposition." A compound radical is a group of elements which, in the various changes and decompositions which a substance undergoec^ remains 16 ESSENTJALS OF CHEMISTRY \\\ unaffected, and acts as if it were an clement. Thus, HNO3 (nitric acid) may be considered as water in which one atom of H has been replaced by the com- pound radical NO2, thus — 1{^}0. NO3 is therefore a monad radical; again, in H2SO4 (sulphuric acid), the dyad radical SO2 has replaced two atoms of H, thus— g§2 } O2, and in H8PO4, the triad radical PO has replaced three atoms of H, thus — po } O3. 38. A salt-radical, haloid, or halogen is a sub- stance, simple or compound, combining with H to form an acid. Thus — H + Cl (hydrochloric acid), H + CN (hydrocyanic acid). ' ' ' ' 39. An acid is a hydrogen salt, possessing the fol- lowing properties in a greater or less degree : — a sour ' taste, solubility in water, power of acting upon car- bonates with effervescence, power of neutralizing alka- lies, power of changing blue litmus paper red, and brown turmeric paper yellow. Several compoimds are commonly called acids, altliongh they do not con- tain hydrogen, and are therefore, according to modern theory, excluded from this class. Such are SO2 (sul- phurous acid), SO3 (sulphuric acid), COa (carbonic acid), SiOa (silicic acid). '-'-■-■ "■ ' , " '' ^' 40. An alkali is a compound substance, soluble inl water, exerting a destructive effect upon animal mat-l ter; neutralizes acids, turns red litmus paper blue, and yellow turmeric paper brown. The principal alkalies are potash, soda, and ammonia. The alkaline earths are the oxides of barium, strontium, calcium, and magnesium. Other metallic oxides, however, AND CHEMICAL PHYSICS, 17 ;nt. Thus, water in )y the com- is therefore iiuric acid), toms of H, ical PO has ; ■ 7,. P f,, en is a sub- gr with H to ric acid), H sing the fol- ee : — a sour g upon car- alizing alka- er red, andj compoimd do not con- g to modern ire SO2 (sul- \ (carbonic e, soluble in animal mat- paper blue, le principal The alkaline iro, calcium, :s, however, ...*:. possess alkaline properties, as those of rubidium, lith- ium, caesium, silver, thallium, lead. 41. A base is a compound substance, not an alkali, capable of neutralizing an acid, and with it forming a salt. 42. A salt is a compound substance, formed by the combination of an acid with a base ; or by a metal -in combination with a salt-radical (38). Thus, ZiiO, SO3, or ZnSOi (base ZnO + acid SO3); or NaCl (metal Na + salt-radical CI). Salts are termed neutral, acid, or alkaline, according to their taste, and their effect upon vegetable colour. 43. When one combining proportion of an element unites with one combining proportion of oxygen, the resultant is called a mon-oxide, or prot-oxide ; if there be two, three, four, or five proportions of oxy- gen to the same constant proportion of the other ele- ments, these compounds are called the di-cxide, or bin-oxide, tri-oxide, tetr-oxide and pent-oxide res- pectively ; such terms as bi-sulphide, or di-sulphide, are also in use. 44. When an element forms, with oxygen, two acids, the name of the onj containing the less oxygen takes the termination ous ; and the one containing more oxygen has the termination ic ; as H2SO3 (sul- phur ous acid), and H2SO4 (sulphur- ic acid) ; if there happen to be other acid substances formed, by the same elements, intermediate to those, whose names terminate in ous and ic, the prefixes hypo and hy- per, signifying under and over, are used, as — hypo- sulphurous, etc. Instead of hyper, the abbreviation per is generally used ir I ' i8 ESSENTIA IS OF ClIEM/STRY 45. When an acid, the name of which terminates in OUS, unites with a base to form a salt, the resuUing substance has its name terminating in ite; if the name of the acid terminates in ic, the name of the salt will terminate in ate. 46. In (37) it lias been shown that according to what is called the water-type theory, an acid such as HNO3, or H2SO4 is looked upon as composed of water and a compound radical. Thus, HN03=^o.,}o, H,S04=JS }02, H8P0,=i?^ }03, in which the radi- cals NOo, SO2; PO, have displaced respectively one, two and three atoms of H from one, two and three mole^^ules of water. This view is supported by the fact that such radicals as NO2 and SO2 actually exist in an independent state, but since, in the combination of an acid with a metal, it is the hydrogen alone that is displaced irom the acid, there is another, and, for some purposes, a more convenient theory, viz., the binary theory, according to which all acids are com- posed of hydrogen combined with a radical, simple, or compound. Thus, H combines with CI to form hy- drochloric acid ; -Ha combines with SO4 to form sul- phuric acid; and H3 combines with PO4 to form phos- phoric acid. In the case of the last examples, there is the forcible objecrion that no such radical as SO4 or PO4 is known to exist, while such radicals as SO2 P2O5, from which, by combination with water, the above named acids may be obtained, have an inde- pendent existence. This theoretical objection is evad- ed by many chemists, by the adoption of what is called the unitary formula, which recognizes acids as being AND CHEMICAL PHYSICS. 19 compound substances containing hydrogen, by the dis- placement of the whole or a portion of which, by a metal, salts are formed. According to the unitary theory the formulae of such compounds as sulphuric acid, carbonic acid, or phoi phoric acid, which, accord- ing to the binary theory, would be written H2, SC 1 ; H2, CO3 ; H3, PO4 ; are written without the comma between the H and the remaining symbols : — H2SO4 ; H2CO3 ; H3PO4 ; the compound being thus expressed as an enti^^y. Either method affords a convenient and graphic means of explaining many chemical reactions ; and the formation of salts is readily exhibited by its means. Thus — acid H | CI gives salt Ag | CI ; acid H2 I SO4 gives salt Zn | SO4 ; acid H3 | PO4 gives salt Nag I PO4. From the above it is seen that only the li is displaced by the metal, and by this displacement, more or less complete, the acid is changed into a salt. According as the acid contains one, two, or three atoms of H, it is said to be monobasic, dibasic, or tril isic, and the nrmber of atoms of H present is therefore a measure of the basicity of the acid. 47. If hydrogen be present in an acid, or a salt, the term hydride, hydrate, or hydrous is occasionally [used, but if no hydrogen be present anhydride, an- [hydrate, or anhydrous is substituted. 48. All inorganic solids exist in the form of irystals, or are crystalline, or amorphous. [Crystals possess a definite form of geometrical exac- (titude ; crystalline substances are composed of ir- tregular masses of very minute and imperfect crys- [tals, and amorphous substances possess no definite form or structure. 40 ESSENTIALS OF CHEMISTRY W\ 49. Crystals are subject to very numerous modifi- cations of shape, by the replacement of angles, or of edges, and appear accordingly to present an endless variety of form to the observer ; but careful investi- gation has shown that all these forms may be reduced to six well defined systems of crystals. In other words it is found that from one primitive form, such as a cube, a great many others may be derived, by the modification of the angular points, and bounding lines ; the connection between the modified shape and the original typical crystal being Jiowever strictly traceable. Of these typical forms there are six, viz : (i) the cube; (2) the right prism on a square base; (3) the rhomboid ; (4) the right prism on a rectangu- lar base ; (5) the oblique prism on a rhombic base ; (6) the doubly oblique prism, and these characterize the systems of crystallisation as follows : — I. The Monometric, regular, cubical, tesseral or octahedral system. . . II. The Dimetric, tetragonal, square, prismatic or pyramidal system. III. The Rhombohedral, or hexagonal system. IV. The Trimetric, prismatic, orthotype, or rhombic system. V. The Monoclinic, or oblique system. VI. The Triclinic, or anorthic system. 50. When a substance is capable, according to the conditions to which it is exposed, of becoming crys- tallized, or of assuming either the amorphous, or crystalline form, often distinguished, in each case, by different properties; it is said to be allotropic. AND CHEMICAL PHYSICS, 2t ous modifi- igles, or of an endless ful investi- be reduced In other form, such ierived, by I bounding fied shape ver strictly re six, viz : [uare base ; a rectangu- nbic base ; fharacterize tesseral or :, prismatic nal system, lotype, or . '_, ''i n. iing to the iming crys- jrphous, or :li case, by >pic. 51. A substance which crystallizes according to wo different systems, or according to two different brms of the same system possessing different angular lements, is said to be dimorphous. 52. A substance which can be obtained in several brms, either crystallized, crystalline or amorphous, is aid to be polymorphous. 53. Elements, or compound substances which can eplace each other, without altering the character of a rystal, are said to be isomorphous. 54. When a substance assumes the form of another ne, differing from it in composition, it is said to be seudomorphous. 55. Isomerism, is a term used in organic hemistry to express the remarkable circumstance that ertain compounds may be obtained in several dis- nct forms, exhibiting different properties, but possess- ing the same chemical composition. - 56. Osmosis is the passage of liquids through a orous membrane, and according to the direction of e osmose impulse, it is called endosmosis or ex- mosis. It would appear that the fluid which oistens the membrane most rapidly determines the mosis from that liquid. Osmosis and Dialysis are ^osely allied phenomena. ^. ;. . v^- 57. Some terminations of names of elements are tended to denote \ certain resemblance in proper- s of these elements, viz : on, as Carb-on, Bor-on, lie-on ; and ine, ai> Chlor-ine, Brom-ine, lod-ine, d Fluor-ine. The characteristics common to these ements will be referred to in the proper place. The I 22 ESSENTIALS OF CHEMISTRY I Mi' ii • i termination, gen does not denote any community of properties. The Latin names of all metals end in um, and with the exception of Selenium., the name of no non-metal terminates in um. 58. A body is said to be dissolved and to form a solution, when its molecules co-mingle v/ith the molecules of a liquid in such a manner as to becom.e identified mechanically with them. Should the liquid and the dissolved body be capable of mutual reaction, there will of course be chemical combination as well as mechanical mixture. 59. Filtration, is the separation of solid matter held in suspension in a liquid, by straining ihe liquid through unsized paper, or some other porous sub" stance. 60. If to a liquid solution of a substance, some other substance be added, which has such an affinity for the first substance as to cause it to combine with it and to form a third substance which is insoluble, the latter will sink to the bottom of the liquid in a more or less finely divided state, and it is then said to be precipitated. 61. The identification of the metals and acids which constitute chemical compounds, is termed qualitative analysis ; the determination of the re- lative quantities of the metals and acids present in such compounds is termed quantitative analysis. The first named operation is, in the cases of the prin- cipal metals and acids at least, comparatively easy ; while the second operation when accurately per- formed, is a difficult one, requiring the greatest care. AND CHEMICAL PHYSICS. 23 munity of lis end in the name to form a v/ith the to becom.e the liquid .1 reaction, on as well lid matter ihe liquid )rous sub- ;ome other affinity for ne with it )luble, the in a more aid to be ind acids 3 termed of the re- present in analysis. f the prin- ely easy ; ately per- itest care, % and demanding the utmost nicety in manipulation. In qualitative analysis, test liquids are prepared, which by their action upon a solution of the salt to be tested, produce, or do not produce a precipitate; and, since a precipitate is simply a new chemical com- pound formed by the union of certain ingredients of the salt and of the test-liquid, or else is an elementary substance, which has been displaced from the salt solution by the ingredients of the test-liquid, according to the result with the various tests used, and accord- ing to the colour of the precipitate obtained, an accu- rate conclusion can be arrived at, as to the identity of the metal or acid contained in the salt under investi- gation. The following tables are designed to assist students in gaining an elementary knowledge of the principles of testing, but since they are particularly intended for the purpose of reference to refresh the memory regarding practical instruction afforded in the subject, they are necessarily somewhat meagre. The two tables of " Indicating Tests for Metals " and " Indicating Tests for Acids " are borrowed from the excellent little work of Mr. J. J. Grithn, entitled " Chemical Recreations." The confirming tests have been selected from various sources according to value and accuracy of result. The student must use very small quantities of the salt, and in adding the caustic potash, he must do so, drop by drop ; observ- ing not merely when precipitation takes place, but also whether an excess of the test solution re-dis- SOlves the precipitate. Saturated solutions of the substance to be tested must be used, but dry sak is 24 ESSENTIALS OF CHEMISTRY generally to be used in the blowpipe flame. In the table of indicating tests, where there are blank spaces under the names of some of the test liquids, it is to be understood that nothing farther is to be learned of the substance under examination from the use of these particular tests, and the student may therefore at once proceed to the confirming tests. It is well to apply the indicating tests for both metal and acid, before proceeding to apply the confirming tests for either. Assay notes are to be carefully and constantly used as below. ^ ASSAY NOTB FOR METAI-S, NO. llydric Sodium carbon- ate (21NaC03)_ Ammonia (NH 1, IIO) Potassium hy- drate (HKQ) Potassium ferri- cyanide (Ks Fe. cye ) Hydric sulphide! (H2S) Metal indicated. EXAMPLES OP ASSAY NOTB FOR MBTAL, NO. 1. Hydric Sodium carbon- ate (HNaCOs ) P. Ammonia (NH4, HO) P. Potassium hy- drate (HKO) White P, soluble in excess. Potassium ferri- cyanide (K3 Fe Cye) P. Hydric sulphide H2SJ Black P. Metal indicated Lead. ASSAY NOTB FOR ACIDS, NO, Barium nitrate (Ba (NO3 ) 2) r Argentic Nitrate (Ay: NO3 ) Plumbic Nitrate (Pb (N03 ) 2) Calcium chloride (CaCl2 ) Acid Indicated ASSAY NOTES. ASSAY NOTB FOR ACIDS, NO. 1. Barium nitrate (Ba (N03 ) 2) White P. soluble in nitric acid without efferves- cence. Argentic Nitrate (Ag NO3 ) Plumbic Nitrate (Pb (N03)2} Calcium ciiloride (CaCl2 ) White P. insol- uble in water. Acid indicated Oxalic acid. AND CHEMICAL PHYSICS. 25 62 Tndicatins Freclpltants for Metals In Salts. Solutions to be Neutral. Solutions to be acid. Hydric S.ilphide (U2S) Metals . Hydric Sodium Carbonatft (HNa CO3) Hydrate of Ammonia (NII4UO) Caustic Potash. (HKO) ; i Potassium Ferric van ide (K3FeCy6) Indicatkd. 8 1 None. 1 None. 1 None. None. None. None (See 121) . 1 Potassium. 2 Sodium. 3 Ammonium. 1 .- , ' 4 Barium. 5 Strontium. 6 Calcium. White. White. White. White. White. All five are insolu- ble in excess. Brown. Blue. None. Yellow. Black. 7 Manganese. 8 Iron, protosalts 9 Magnesium. 10 Cadmium. 11 Bismuth. "^ White. White. White. White. White. White. All six are soluble in excess. Yellow-red White. None. Black, Yellow. Orange. 12 Zinc. 13 Tin, protosalts. 14 Aluminum. 15 Lead. 10 Tin, persalts. 17 Antimony. ^H Black, see Gold, No. 25. Red-brown. 10 Mercury, its protosalts. 1 Blue, if boiled. Blue, if boiled, black. •■ 19 Cobalt. 20 Copper. 1 Green. Green. Green. Yellow green None. Light blue. 21 Nickel. 22 Chronfium. 23 Iron, persalts & proti^ualts, mixed 1 ... Yellow Yellow, some- times slightly, and black. Yellow red, but none from the Perchloride. None. None. Browu. * 24 Mercury, its perralts. 25 Gcfld ■ 1 1 Br Br own. own. 1 1 26 Iron iM»rsa^t'fc 27 Silv»k MMPM 26 ESSENTIALS OF CHEMISTRY 63 Indicating Frecipitants for Acids in Salts. Barium Nitrate (Ba(N03)2) Arg'cutic Nitrate (A- NO3) J'lumbic Nitrate (Pb(N03)2) Calcium Chloride (CaCb.) Salts iNDICATBt). None. None. None. None. None. None. None. None. White. Black. Yellow. White. > / 1 Nitrates. 2 Chlorates. 3 Chlorides. 4 Iodides. 5 Arsenites. C Sulphides. White. White. White. White. White. All five solu- ble in Nitric Acid with- out efferves- cence. None. Yellow. Brown. - White, soluble in water. White, insoluble in water. 7 Fluoride-s. 8 Phosphates 9 Arseniatcs. 10 Borates. 11 Oxates. ' White. Soluble in Acids with efferves- cence. • 12 Carbonates White. Insoluble in Acids. ■ • [ ■ - ' - ' ■ 13 Sulphates. Yellow. _ 14 Chromates. < , - .', I AND CHEMICAL PHYSTCS. 27 Salts DICATKl). trates. ilorates. ilorides. dides. [•senites. dphides. uoridea. losphates. :-9eniatcs. jrates. icates. Birbonatea. Lilphates. hromates. 64. Confirming Tests for Acids. TESTS (I) NITRATES. RESULTS. Addf to solution, metallic copper and a little sulphuric acid (H2 SO4 ). Add, to solution, an equal volume of H2 SO4 ; cool ; and add solution of ferrous sulphate (FeS04 )• Add, to dry nitrate, in teat tube, hydro- chloric acid (HCl) ; and heat. Dark red fumes of nitric perox- ide. A dark ring formed at junction of t A'o layers of liquid. White fumes of HNO3 are expell- ed ; they redden litmus paper. (2) CHLORATES. Add metallic copper and sulphuric acid (H2 SO4 ). Add sulphuric acid (H2 SO4 ) and ferrous sulphate (FeS04 ). Blowpipe Jlame, on copper wire with mi- crocosmic salt (NaNH4 Iir04 ). No result. No result. Bright blue flame. (3) CHLORIDES. Argentie nitrate (AgNOs ). Add manganese di-oxide, a few drops sul- phurio acid (H2 SO4 ), and heat. White curdy prccip., insoluble In nitric acid, but soluble in am- monia. Mercuric chloride (Hg(3l2 ). Add bisulphate of potash (KHSO4 ) in test tube, and heat. Bloiopipe Jlame, on copper wire with mi- crocosmic salt (NaNH4 HPO4 ). Chlorine gas evolved. (4) IODIDES. Scarlet preoip. Violet vapours fn tube. Bright green Came. (5) ARSKNITES. Solution of sulphate 0/ copper (CuS04 ), with a little ammonia (NH3 ). Solution of nitrate of silver (AgNOs ) and a little ammonia. Blowpipe inner Jlame, with hydric sodium carbonate (NaHCOs ) on charcoal. See (170.171). Green precip. Yellow precip. Odour of garlic perceptible. (6) SULPHIDES. Heat in a test tube, with a little hydro- chloric acid (HCl). Blowpipe Jlame on charcoal. Effervescence produc ' sulph- uretted hydrogen t^olved; test-paper moistened with su- gar of lead blackened. Sulphurous acid gas evolved. (7) FLUORIDES. Heat in test-tube with bisulphate of pot- assium (KHSO4 ), Apply test-paper, prepared in solution of Brazil wood, to the mouth of heated test-tube. Hydrofluoric acid evolved, cor- rodes the inside of tube. Test-paper turns yellow. xi ti h t I 1 I 28 ESSENTIALS OF CHEMISTRY TESTS (8) PHOSPHATES, RESULTS. Solution of sulphate of maynesia (Mg SO4 ), with addition of ammonia. Solution of molybdate of ammi^tiia 2 N H4 , M0O4 ) in nitric acid (HNO3 ), with small portion of solution of phosphate, in test tube ; boil. White prccip. Yellow precip. (9) ARSENIATES. Precipitate solution, by solution of ace- tate of lead, Pb (C2 H3 0-2 )2, collect on filiier, wash and dry. Ignite on charcoal in outer flame. Solution of molybdate of ammonia (2 (N H4) M0O4) Ml nitric acid (KNO3 ), boil ed with aiseniate. See (170, 171). No crystallization. No result. (10) BORATES. Mix with sulphuric acid (H2 SO4 ), boil and cool. Wash the resultant crystals of previous test ; boil with water and test with blue litmus, and brown turmeric. Moisten with sulphuric acid, mix with al- cohol, inflame mixture. Flat shining crystals of boraclo acid formed. Blue litmus turns red; brown turmeric turns yellow. Qreen flame. (11) OXALATES. Add A few drops of sulpburic acid (H2 SO4 ), apply heat. Add to solution, solution of calcium sul- phate (CaS04 ). Effervescence ; CO2 and CO evol- ved; on applying a light the CO burns. White precip. (12) CARBONATES. Mix dry carbonate with a little water, and add a few drops of hydrochloric acid (HCl). CO2 escapes with effervescence, and, on being passed into lime- water, precipitates carbonate of lime. 03) SULPHATES. Mix dry sulphate with dry hydric carbon- ate of soda (NaHCOs ), heat in inner fla,me on charcoal ; place on bright sil- ver and add a drop of water ' in a min- ute or two, wash. Baric nitrate (Ba2N03 ). Baric chloride (BaCl2 ). Black mark on stiver White precip. White precip. .* .»■ (14) CHROMATES. Mix dry chromate with dry chloride of sodium (NaCl) and a few drops of sul- phuric acid ; heat. Dihydrie sulphide (H2 S). Effervescence ; splendid red gat evolved. Green solution. AND CHEMICAL PHYSICS, fl9 65. Qualitative analysis shews the composition of a compound by determining the presence of cer- tain elements. Quantitative analysis, on the other hand, has for its object the determination of the rela- tive quantity of each element present in a definite quantity, say, one hundred parts by weight, of thr compound analysed. From this per-centage compo- sition the empirical formula and possibly the rational formula of the compound may be arrived at, by divid- ing the relative quantities by the atomic weight of the elements present. Ex. I. A compound gas is found to be made up of 27*27 parts by weight of C and 72 73 parts by weight of O"; the atomic weight of these elements bemg known, divide the relative quantities by tne atomic weights in order to arrive at the relative number of atoms, thus — 2-^^i=2-27; ^fF^-3-=4.54. According to this, 2*27 atoms of C are united with 4*54 itoms of O. Take the lowest number 2 27 as a unit, and divide the other number 4*54 by it, thus — f:^^=2, that is, 227 : 4'54=i : 2, consequently one atom of C is com- bined with two atoms of O; the simplest formula therefore is ZO^, Ex. II. Per-centages given — 44*44 S, 55.56 O, to find the formula; ^^^ = i*39 i -^f ^ - 3'47 j therefore 139 • 347 = 1 5 2'5, there can be no fraction of an atom; therefore clearing of fractions i : 2*5 = 2 : 5 ; the for- mula is therefore — S2O5. To arrive at the rational for-" mula of a substance, its atomic weight must be found. This is obtained in the case of acids by uniting them with bases, and in the case of bases by uniting them 30 ESSENTIALS OF CHEMISTRY with acids, whose atomic weights are known ; the amount of acid and base in the salt is then determined by quantitative analysis. Thus : — hyposulphite of bary- ta contains, in loo parts, 6i*6 of baryta, and 38*4 of hyposulphurous acid, and the atomic weight of the acid is arrived at, from these numbers, by a simple proportion sum : — BaO. Acid. Equivalent of BaO. 61*6 : 38*4 : : 153 : -»r=96, atomic weight of acid. The number of atoms of each constituent of the acid is now to be determined, as follows : — Acid. S in 100 parts acid. Atomic wt. of acid. lOO : 66'66 : : 96 : ^=64=2 eq. of S. Acid. 0. 100: 34*34 !: 96 ; jf=32=2 eq. of O. The rational formula for hyposulphurous acid is ac- cordingly S2O2. 66. The metre is nearly the ten-millionth part of the quadrant of the meridian of Paris. It is equal to 39'37 English inches; it is divided into tenths, hundredths, and thousandths, called respectively deci- metres, centimetres, and millimetres. A decimetre (3 '93 Eng. inches) cubed, is equal to one litre, the principal measure of capacity, which is therefore equal to 1000 cubic centii..etres and equal to i 76 Eng. pints, or to 6 1 "02 cubic inches. A cubic centimetre of pure water at 4''C. weighed at Paris, is the fundamental measure of weight, called a gramme, equal to 15*43 Eng. grs. The millimetre (0*039 Eng. inch) is the smallest mea- sure of length, and is commonly used to express the height of the barometric column, thus — 760 mm. (— 76 cm.). The kilogramme is equal to 1000 grai umes, equal to 2*2^Eng. lbs. avoir. AND CHEMICAL PHYSICS. 3" the ■nes, 67. The Barometer is an instrument lor ascer- taining the pressure of the atmosphere ; it consists in its usual form of a glass tube of about 840 mm., or T^-^ inches in length, closed at one end, and of uniform bore. This tube being very carefully heated, a portion of the contained air is expelled and the open end is now inverted in a vessel containing mercury. As the residue of the air cools the mercury ascends, and can thus be made to fill the entire tube. When this is the case, the contained mercury is heated to a high degree so as to expel any remaining bubbles of air, and the tube is now permanently inverted in a suitable vessel, or reservoir of mercury, open to the atmosphere. Li- quids transmit pressure equally in all directions, there- fore the pressure oi the atmosphere, upon the surface of the mercuiv in the reservoir, will be similarly trans- mitted by it to the rolumn of mercury in the tube. But the surface of this column will be maintained at a certain height, for sinre there is no air in the tube, the tendency of the mercury to seek the level of the fluid in the reservoir is solely due to the weight of the column, and this tendency is exactly counteracted by the contrary pressure of the atmosphere transmitted through the fluid contents of the reservoir, which pressure will evidently be equal to the weight of a column of air of the same sectional area as that of the tube, but extending through the entire thickness of the atmospheric envelope. The weight of such a column varies slightly on account of changes of tem- perature and atmospheric disturbances, but at the level of the sea and at a temperature of 0° Cent. ESSENTIALS OF CIIEMISTRV or 32° F. a column of air is found to support, on an average, a column of mercury of equal sectional area of 760 mm., or 30 in. in height ; 760 mm., or 30 in., are said accordingly to represent the normal baro- metric pressure at the sea level. Between the upper surface of the mercurial column and the closed end of the tube there is of course a vacuum, which is tech- nically known as the Torricellian vacuum. A gradu- ated scale is applied to the barometric tube, by obser- vation of which the increase or decrease of the column of mercury may be ascertained. It is evident, that if by any means the atmosphere above the barometer become heavier, it will be able to support a longer column of mercury ; but if its weight is lessened, there will be a corresponding decrease in the quantity of mercury supported in the tube. The barometer there- fore, certain corrections for temperature, elevation and capillary attraction being applied, is a tolerably accu- rate measurer of atmospheric pressure. There are many varieties of barometer : — reservoir barometers, with or without levelling screws, by means of which the surface of the fluid in the reservoir may be brought level with the zero of the scale ; siphon barometers, which are very untrustworthy ; water barometers, rarely made on account of the tube requiring to be about 40 feet in length, the normal elevation of the column of water being 33 3 feet ; the aneroid baro- meter, which is a small clock-faced instrument con- taining a metallic box exhausted of air and hermetically sealed. This box, by its contraction or expansion due to decreased, or increased pressure of the air, moves, I an area in., )aro- pper end tech- radu- ibser- lumn hat if meter onger there :ity of ithere- bn and t AND CHEMICAL PHYSICS, 33 by the agency of an arrangement of levers and springs, an index needle which moves on a pivot, indicating on a scale which is graduated in coincidence with a stand- ard barometer, the amount of pressure to which the box is subjected. This instrument is moderately accu- rate at comparatively low elevations. 68. The pressure of the Air enveloping our globe is, at the earth's surface, capable of supporting a column of mercury of about 30 inches in height ; but since mercury is 10462 times heavier than air, the pressure of the air upon one square inch of surface must be not less than i4'6 lbs. avoir. This pressure is commonly referred to as "an atmosphere"; two, seven, or thirty-five atmospheres, thus=i46 x 2 ; 146 X7 ; i4'6 X 35 ; the product in each case representing the amount of pressure on one inch surface. 69. Mariotte's, or Boyle's law is to the following effect : — " The temperature remaining constant, the volume of a given quantity of a gas is in inverse pro- portion to the pressure which it supports. Ex. : — latm. 2^m. 20 atm. JOOatm^ jatjn. -^^.^ TS^thatm. 1vol. ivol. ^(jth^ol. roDthvol. 2 vols. 20 vols. 100 vols. roDthvol. ^""^^^^ 20 vols. 70. Heat is supposed to be due to a vibratory movement of the particles of heated bodies, which movement is transmitted to the particles of other bodies, by the medium of an eminently subtile and elastic fluid, which is called ether, and in which it is propagated after the manner of sonorous waves, or undulations in air. This adulatory theory of heat, known also as the kinetic, or dynamic theory, is the only one generally admitted at present, in oppo- sition to the material theory, formerh propoundeb. 34 ESSENTIALS OF CHEMISTRY 71. The different sources of heat are: — I. Mechanical sources, comprising friction, percussion, and compression. "^ . TI. Physical sources, as solar radiation, terrestrial htat, molecular action, changes of state, and elec- tricity. III. Chemical sources, as molecular combinations, and notably combustion. 72. Combustion is the union of substances, under the influence of the force called chemical affinity, at- tended by the evolution of light and heat ; as when antimony is brought into contact with chlorine; a paper dipped in turpentine and thrown into a jar of chlorine ; or when carbon combines with oxygen to form carbonic acid gas. Combustion is the means by which we obtain all artificial heat for the general pur* poses of life, and the form of combustion we employ is the union of carbon, contained in charcoal, coal, wood, and our various fuels, with the oxygen gas con- tained in the atmosphere. The product is in these cases always the same, viz., carbonic acid gas, accom- panied perhaps by water. By what precise means these chemical actions give rise to the production of heat we do not know, but it is believed that the mole- cules of two substances about to combine are in the condition of a raised weight and the earth, and when they rush together to combine, their kinetic energy becomes heat, as in the case of the weight referred to. 73. Since heat is a rapid reciprocal motion of the molecules of matter, it is evident that the addition to a number of molecules, possessing a certain amount J, I J ider ^, at- vheti e; a ar of en to nsby Ipur^ [i;;)loy coal, con- these xom- eans on of mole- n the when nergy ed to. f the ion to ount AND CHEMICAL PHYSICS, 15 4 4" of this motion, of more of the motion, will, by pro- ducing a greater commotion, cause the molecules to occupy a larger space. This phenomena is called expansion, and is apparent in all forms of matter, solid, liquid or gaseous. Solids expand into liquids, and liquids into gases ; gases expand most ; liquids, as liquids next (127), and solids,, as solids, least. Ex- pansion then is just the opposite of cohesion, and bodies expand in proportion as cohesion of the material particles is overcome; and contraction is merely increasing cohesion of the material particles, as the motor influence — heat approaches its zero. The linear, superficial, and cubical expansion of solids may be ascertained ; but only the cubical ex- pansion of fluids can be determined. Linear expan- sion is shown by fixing one end of a bar of the sub- stance to be experimented upon, and causing the other end to press against a lever, or system of levers, by means of which any lengthening of the bar will be in- dicated on a graduated scale by a pointer ; on heating the bar, the movement of the index is at once per- ceptible. Linear expansion is not the same for all solids, and in order to ascertain it, each must there- fore be experimented upon separately. 74. Solids for the most part, when heated uni- formly, expand uniformly in length, breadth and thick- ness ; hence the co-efficient of linear expansion being given, the co-efficients of superficial, and cubical ex- pansion can easily be ascertained. The co-efificient of linear expansion is the increase in length of a sub- stance, for one degree of temperature, whose length /" IV 36 ESSENTIALS OF CHEMISTRY at some given temperature, generally o°C. (or 32° F.), is taken as unity. Thus if the length of a brass rod at the freezing point (32° F.) be taken as 1,000,000, its length at the temperature of boiling water (212° F.) is found to be 1-001,867, and the linear co-efficient of brass for 180° F. (212°— 32°) is hence 0-001,867, and for 1° F.=o-ooi,867-^i8o°=o-ooo,oio,38. The su- perficial co-efficient of a substance is equal to twice ^*ts linear expansion, and the cubical expansion to thiee times the linear. Certain crystals do not ex- pand equally in all directions ; some contract in one direction while they expand 111 another, but the total expansion is greater than the total contraction ; others expand unequally in all directions. 75. Liquids expand more than solids for an equal increment of heat, and it is obvious that in their case cubical expansion can alone be considered, but as the containing vessel expands also, it is to be observed that there is both an absolute and an apparent ex- pansion of a liquid. This distinction may even be of the greatest importance, as in the cases of the mer- curial thermometer, and the barometer, in which the absolute expansion of the mercurial column requires to be very carefully distinguished from the apparent expansion, due to the joint expansion of the mercury and the glass tube containing it. , 76. Water is a notable exception to the general law that all bodies expand when heated, and con- tract when cooled. This law when applied to water, bismuth, certain chemical compounds and gems, is only true within certain limits. Water contracts when 1/ i^ AND CHEMICAL PHYSICS. 37 heated from o°C. (32''F.) to 4°C (39-2*' F), and above this point it expands. In other words the point of greatest density of water is 4°C. and when heated above, or cooled below that point it expands. 77. The co-efficient of expansion of gases is for an increment of i°C. •003665. That is, one volume of a gas being taken at o°C. and at the normal barometric pressure — 760 mm. and raised one degree temperature on the centigrade scale, the volume becomes vol. i'oo3665 ; at 2°C., it becomes vol. 1-007330; at3"C.,vol. I 010995; increasing in volume by '003665 vol. for every degree rise of temperature. For 100 volumes the corresponding mcrease will evi- dently be — at i°C.. 100*3665; at 2°C.. 100.7330, and at 3°, ioi'0995-TooWoo = !rH ^ hence a gas expands ^\-^ of its volume lor an increase of i°C. If now a gas has been measured off at a known temperature, and it is required \o ascertain its volume at some other temperature, the calculation is easy. Ex. I. looocbc. of a gas are measured off at 0° and the temperature is raised to 20°, what would be the volume of the gas if free to expand ? The gas would increase its original volume by 20 x ^\^ of that volume, hence 273 : 273 + 20 : : 1000 :^=io73cbc. Ex. II. 2oocbc. of a gas are measured off at 2o°C. what will be the volume if the temperature be lowered to 4°G.? Since decrease of volume due to abstraction of heat takes place, in precisely the same ratio as the increase due to increments of heat, the method of calculation will be as follows: — 273 + 20 : 273 + 4 : : 200 : A:=i9ocbc. In these calculations no attention has been paid to ^ 38 ESSEN'TIALS OF CHEMISTRY ^ the atmospheric pressure, but since the volume of gas varies inversely as the pressure to which it is sub- jected (69), this neglect will necessarily cause the re- sults of the above calculation to be erroneous. Sup- posing that in Ex. I. the barometric pressure under which the gas was measured off was 760 mm. and this pressure fell to 740 mm., the statemegt of the pro- blem would be ?Io: ?SJ • J 1000: ^=iio2cbc. In Ex. II. Suppose the pressure at the time of first measurement to be 755 mm. and at the time of second measurement to be 763 mm. the statement will then be ^S^j ^n • • 200 : ^=:i87cbc. Note : — The co-efficient of expansion of gases on Fahrenheit's scale, corresponding to -^^-^ is ^^^ 78. For the measurement of relative amounts of heat, instruments called thermometers and pyro- meters are used. The principle of construction of these instruments is simply an application 01 the laws of expansion, and of contraction. In constructing a common thermometer a narrow glass tube of several inches in length, of small and uniform bore, with a bulb blown upon one enr*., is taken. This bulb, with a small portion of the tube, is filled with either mer- cury or coloured alcohol in the following manner. The entire tube is gently heated in order to expel the contained air, and the open end is then inverted in a vessel of mercury or alcohol. As the air remaining in the tube cools, the liquid in the vessel ascends to fill up the space previously occupied by the expelled air. By carefully repeating this operation as often as may be required, the bulb is at length filled, and being AND CHEMICAL PHYSICS, heated until the liquid expands so as to fill the entire tube, the latter is now hermetically sealed, and the whole allowed to cool slowly. The contained liquid gradually contracts on cooling, leaving a vacuum between its surface and the upper end of the tube. Since mercury expands more than twenty times as much as glass for equal increments of heat, and the liquid is now freed from superficial pressure, it is very susct; ible to the slightest changes of tempera- ture, and these changes are readily observed by affix- ing the tube to a graduated scale. All thermometer makers have not adopted the same graduations, and there are consequently four distinct scales in use, viz : Fahrenheit's, Celsius*, or the Centigrade, Reaumur's and De Lisle's. The first named is used by all English speaking peoples ; the second is largely used on the continent of Europe, and by scien- tific men of all nations ; the third is used in Germany and Russia ; and the fourth is only used in Russia. Although the graduation of these scales is different, there is a coincident selection of the freezing and boiling points of water under a constant pressure as fixed points. In graduation therefore the bulb is im- mersed in a vessel containing melting ice, and the surface level of the mercury, or alcohol, is accurately marked on the tube, establishing the freezing point. In like manner the entire tube is immersed in steam arising from water boiling under a barometric pressure of 760mm., and the level of the contained fluid is again accurately marked, establishing the boiling point. Fahrenheit, under a mistaken impression, I 40 ESSENTIALS OF CHEMISTRY placed the zero of his scale 32° below the freezing point, and marked the boiling point 2 12°, or 180° above the freezing point. On the Centigrade scale the freez- ing point is zero, and the space between zero and the boiling point is divided into one hundred degrees, hence the name of the instrument. On Reaumur's scale, the freezing point is zero and the boiling point is 80°. In De Lisle's thermometer the freezing point is 150° and the boiling point is zero. Since the number of graduations on these scales between the freezing and the boiling point is respectively 180° : 100° : 80 : 150 ; an easy means is afforded of reducing one scale to another. Neglecting De Lisle's thermometer, as being of little practical importance, the relation betv/een Fahrenheit's, the Centigrade, and Reaumur's ther- mometer is evidently 9 : 5 : 4 ; hence to reduce Fah. to Cent. — subtract 32° and multiply by f ; in reducing Fah. to Reaumur — subtract 32° and multiply by |. In reducing Cent or Reaumur to Fah. multiply by f or | respectively and add 32°. To convert Cent, to Reau- mur, multiply by f , or to convert Reaumur to Cent, multiply by f. Thus, i4o°F.=::(i4o— 32)B=6o°C., or i4o°F.=(i4o— 32);^=46°R. 5o°C.=(5o x |) + 32 = i22°F. or 5o°C = 5o x |=:4o°R. 5o°R.=:(5o x |) + 32 = i44-5''F.or5o°R. = 5ox f=62-5"C. Thealcohol thermometer is used for measuring low temperatures, since this liquid has never been frozen, but as it boils at the comparatively low temperature of i73°F. it is useless at temperatures approaching the boi)ing point of water. Mercury on the other hand solidifies at — SS^F. but does not boil until raised to a tempera- \ AND CHEMICAL PHYSICS. 41 ture of about 66o'*F. A mc urial thermometer, having a small metallic needle above the liquid column, when placed in a horizontal position, shews the maximum temperature reached in any given space of time, since the ascending column pushes the needle before it, and when descending leaves it behind. An alcohol thermometer having • similar needle immersed in the liquid column, when pk.ced in a horizontal posi- tion, shows the minimum temperature reached in any given space of time, since the descending surface of the column bears the needle with it by capillary attraction, but, when it re-ascends, leaves it behind at the lowest point reached. The delicacy of the mercurial ther- mometer is increased by reducing the size of the bore, and by having the walls of the bulb as thin as pos- sible, but it must be considered as giving only approxi- mate results since there are several corrections necessary, to attain even a moderate degree of accu- racy, viz : {a) for change of zero, due to a slight contraction of the bulb and tube after graduation, probably caused by imperfect annealling of the glass, (b) for position, since a perpendicular column of mercury will tend to increase the size of the bulb and thereby cause a lower reading of the scale than would be the case in a horizontal position ; {c) for unequal expansion of the glass and the contained fluid. The air thermometer consists of a buib of consider- able size communicating with a small vessel contain- ing mercury by means of a tube of small bore. When the contained air expands, the mercur}- is partially ex- pelled from the tube ; when the air contracts, the ) 42 ESSENTIALS OF CHEMISTRY mercury rises ia the tube. Since the liquid column is exposed to the pressure of the atmosphere a correction must be applied for this, before there can be any com- parison between the air thermometer and the mer-' curial thermometer. Bre'guet's thermometer consists of three thin bands of platinum, gold and silver soldered together, so as to form a fine metallic ribbon, which is twisted into a spiral coil fixed at its upper extremity, and at the lower end attached to a copper needle free to move on a pivot over a centi- grade seale. This instrument possesses extreme sen- sibility due to the unequal expansion of the three metals composing the coil. The silver forms the in- terior face of the coil, and is most expansible; the pla- tinum forms the external face and is least expansible ; whilst the gold is intermediate in position and expan- sibility. When the temperature rises, the expansion of the silver causes the coil to unroll itself, and when the temperature falls the spiral coils itself more closely. 79. Since gases increase by ^^^rd of their volume for every increment of i^C, or ^-J^^th of their volume for every increment of i°r., and since contraction of volume takes place in exactly the same ratio on abstraction of heat, it follows that, supposing the law to hold good at very low temperatures, at — 273°C., or at — 458'^., there could be no further contraction of volume, for volume would no longer exist, neither could there be any further reduction of temperature, hence the absolute zero would have been reached. That is absolute zero is 273° below freezing point ( AND CHEMICAL PHYSICS, 43 iture, :hed. boint on the Centigrade scale ; 490° below freezing point on Fahrenheit's scale, and 218° below freezing point on Reaumur's scale. 80. Absolute temperature, is the temperature of a substance measured from the absolute zero in- stead of from the relative zero of thermometric scales. Absolute temperature will be obtain ed, therefore, by adding to the relative temperature of a substance, 458° on the Fahrenheit scale ; 2 73° on the Centigrade scale, and 218° on Reaumur's scale. 81. When sufficient heat is applied to a liquid to cause it to assume the condition of vapor, which is liberated in bubbles producing violent agitation in the liquid ; the latter is said to be in a state of ebullition, or to be at the boiling point. The boiling point fbr pure water under a pressure of 760 mm. is always ioo°C., or at a pressure of 30 inches=2i2°F. A liquid containing matter in solution boils at a higher temperature than would be required by the pure liquid. The kind of material composing the vessel in which a liquid is boiled affects the boiling point; water boiled in a glass vessel for example, under the normal pressure, has been found to boil only at a temperature of ioi°C., while in copper it boils at ioo°C. This phenomenon has been ex- plained by attributing to glass a peculiar affinity for water. It is to be carefully noted that although the boiling point of a liquid containing substances in solution, or which is boiled in a glass vessel, may be above ioo°C., yet at the normal pressure the temperature of the resulting vapor is found to A\ ESSENTIALS OF CHEMISTRY be invariably i oo^C. The boiling point of water is reduced i°F., for an ascent above the level of the sea of about every 590 feet, (i.) Every liquid boils at the moment when the tension ot its vapor equals the super incumbent pressure. (2.) The boiling point is raised directly as the pressure is increased. (3.) For a given pressure the boiling point is always the same for the same liquid, but it varies for different liquids. (4.) Whatever may be the intensity of the source of heat, from the moment when ebullition commences the temperature of the liquid remains the same. 82. The distinction between gases and va- pours is not very clear, but it is usual to consider as gases those elastic fluids which retain at the normal temperature and pressure the gaseous form of matter, while those which under these conditions assume the liquid form are called vapours. Another method ot division, classifies as gases those only which ar^ per- manent elastic fluids, under every condition of temperature and pressure to which they have hitherto been submitted, while those which, either by reduction of temperature, or by augmented pressure, have been liquified, are called non-permanent gases, or vapours. As it is possible, and from recent discoveries, even probable, that all gases may be ultimately liquified, this classification is evidently an unreliable one. 83. Distillation is an operation by which liquids are separated from substances which are held by them in solution. The solution is placed in a closed vessel called a retort, which communicates, by means of a I AND CHEMICAL PHYSICS, 45 lube-like prolongation, with another closed vessel called a receiver. The communicating tube is en- closed within a larger tube, in such a ma ..ner that it is constantly surrounded by cold water. On sufficient heat being applied to the retort, the liquid is raised to its boiling point, and rapidly evaporates ; it escapes m the state of vapour from the retort towards the re- ceiver, but in its course becomes cooled down, or condensed, by passing through the cold tube, and therefore reaches the receiver in the liquid condition. On a large scale the condensation is caused by means of a worm, or spiral coil of tubing arranged inside a suitable vessel. By this operation a volatile liquid will be separated from a less volatile liquid, or from non-volatile substances ; the less volatile liquid, or the non-volatile matter, being left behind in the retort. In the case of two liquids, whenever it is desired to separate the more volatile from the less volatile, care must of course be taken that the temperature be not raised to the boiling point of the latter. The distinctive name of " fractional distillation," is given to this separation of two liquids, which is much used in the case of hydro-carbons, between the vaporisation points of which, there is often no greater difference than a few degrees of temperature. ' 84. When liquid matter assumes the gaseous condition it is said to evaporate, but the term evaporation is usually confined to the slow production of vapour, from the surface of a liquid, while the rapid production of vapour from the whole mass of liquid is called ebullition. There is no determinate 4« ESSENTIALS OF CUE MISTILY temperature at which evaporation takes place, therein notably differing from ebullition ; but it is believed that, below a certain degree of refrigeration, all evaporation ceases — e. ^., mercury below — io°, or sulphuric acid below 30°. 85. Sublimation of solids is a process analogous; to vaporisation of liquids. Volatile solid substances are converted by heat into vapour, or are sublimed, and. on cooling, they re-assume the solid form. 86. When heat is applied to matter, expansion follows. In the case of gases this expansion appears to be unlimited ; liquids expand until they reach their boiling point, when they rapidly assume the gaseous condition; while solids, on the application of heat sufficient to evercome the cohesive force of the mole- cules followed by consequent cubical expansion of the volume, gradually liquefy, and are said to be in a state of fusion. Substances of organic origin whether direct or indirect, usually however, undergo de- composition and therefore cannot be fused. Fusion is subject to the following laws : — (i.) Every body fuses at a determinate temperature, invariable for each substance, the pressure remaining constant. (2 ) Whatever may be the source of heat, from the moment when fusion commences, the tempsrature of the substance ceases to rise and remains constant until fusion Is complete. 87. Solidification is the transition of the liquid condition of matter into the solid condition, and this transition is effected 'by lowering the temperature to a sufficient degree. In a few cases, however, such as AND CHEMICAL PHYSICS. 47 tliose of ether or alcohol, solidification has not been arrived ac, although the last named liquid is said to have been reduced by the application of a powerful freezing mixture to such a state of consistency as to be poured with difficulty from one vessel to another. The laws of solidification are as follow: — (i) Solid- ification is produced for each body at a determinate temperature which is precisely that of its fusion. (2.) P>om the moment when solidification commences until it is completed, the temperature of the liquid remains constant. . 88. The fact that bodies passing from the solid to the liquid condition absorb a quantity of heat from adjacent matter is utilized, by the formation of \\ aat are called freezing mixtures, to produce a degree of artificial cold of greater or less intensity. There should be chemical affinity between the components of the mixture, and one of them at least must be a solid. The following table exhibits some of the more common freezmg mixtures, and the resultant refrigeration : — (i) Sulphate of soda, 8 lbs. ) Hydrochloric acid, 5 lbs. ) (2) Broken ice or snow, 2 lbs. ) Sea salt i lb. / - (3) Sulphate of soda, 2 lbs. ) Nitric acid (dilute) 2 lbs. j (4) Phosphate of soda, 9 lbs. \ Nitric acid (dilute) 4 lbs. J (5) Sulphate of soda, 6 lbs. Nitrate of ammonium, 5 lbs. \ + 10° to — 26* Nitric acid (dilute) 4 lbs. + 10° to— 17' + 10° to— 18' + 10° to — 19' + 10° to— 29° 48 ESSENTIALS OF CHEMISTRY 89. Conduction of heat is the transmission of the vibratory motion, which con^ilitutes heat, from tlie source of that motion through the molecules of a body ; causing a corresponding rise in its temperature. Substances composed of compact or dense matter are generally much better conductors than those of a loose or porous nature. Metals are therefore, as a rule, better conductors than stone ; stone than wood ; wood than silk or wool. Fur, feathers, sawdust, bark of trees, and similar substances are all bad conductors. The utility of woolen or silk clothing depends largely upon this lack of conductive power, and according to some, it is chiefly due to the loose texture of the woven material, the interspaces being filled with air, which is a bad conductor ; and thus the heat of the body is not permitted to escape. Glass and brick, although of a compact consistency, are poor con- ductors, because they are not homogeneous substances, but are mechanical mixtures of substances possessing very different physical characteristics. Good con- ductors are cold to the touch, because of the rapidity with which the heat of the hand is propagated through the molecules of the body. Liquids are bad con- ductors of heat, and so probably are gases ; but in the latter case there is still much room for investiga- tion, and the conductive power of gases, is, according to Dr. Tyndall, an open question ' 90. When a liquid is heated from above, its temper- ature rises very slowly on account of the defective conductive power of liquids, and the fact that the surface liquid becoming lighter as it is heated, has no AND CHEMICAL PHYSICS, 49 )ugh I con- It in Itiga- ling (per- :tive the no tendency to make way for the heavier liquid below ; but when the source of heat is placed below the con- taining vessel, the temperature rises with greater or less rapidity. This is due to the expansion of the particles of liquid immediately in contact with the source of heat, and their consequent ascent towards the surface ; a new layer of particles being thus con- stantly brought in contact with the source of heat, until the whole mass attains a uniform temperature, which is that of ebullition. The convect^JC power of liquids may be exemplified by .ference to the Gulf-stream, and other great ocean currents. Gases, as they are more expansible than liquids,, possess accordingly greater convective power, and hence the susceptibility of the atmosphere to comparatively slight changes of temperature, arising from increased or reduced terrestrial radiation, and resulting in such phenomena as the trade-winds, land and sea breezes, and winds in general. . 91. Heated substances communicate or radiate their heat in straight lines, by propagating an un- dulatory motion through the medium — ether. Sub- stances differ much in their radiating power. Bright, polished surfaces radiate least, and rough, blackened s'-^'ices radiate best. Those substances which radiate best are also the best absorbents of heat, but it has been found that white lead has quite as great an absorbent power as lamp-black. The power of reflect- ing heat is found to be the reciprocal of the absorbent power, that is the worst absorbents are the best re- flectors. Radiation <;akes place in vacuo, as is 1,^^ so ESSENTIALS OF CHEMISTRY sufficiently proved by the fact of the solar heat reacn- ing the earth, although it traverses what is believed to be a perfect vacuum before doing so. 92. The quantity of heat which a body absorbs when its sensible temperature is raised from zero to I**, compared with that which under similar conditions an equal weight of water would absorb, is called the specific heat of the body ; or it is a measure of its capacity for heat, e.g.^ If one kilogramme of mercury at 100° be mixed with a kilogramme of water at zero, the resulting temperature of the mixture is only about 3** j that is the mercury has been cooled by 97°, but this quantity of heat lost by it has only sufficed to raise the same weight of water through 3°. The heat capacity of water then is about 32 times as great as that of mercury for an equal elevation of temperature. 93. When a solid is passing into the liquid con- dition, or when a liquid is passing into the gaseous condition, the temperature of the solid and of the liquid remains constant, throughout the duration of the pro- cess of fusion, or of vaporisation, whatever may be the intensity of the heat applied. A large amount of heat, consequently, must be absorbed during the change of state, the sole effect of which is to maintain the liquid or gaseous state respectively. This amount of heat which does not affect the thermometer, and which combines in some way with the molecules of the bodv, is called Latent Heat. This term which simplj means hidden heat, does not express the operation or destination of the absorbed he * ., which is used up in conferring potential energy upon the AND CHEMICAL PHYSICS. 51 molecules of matter. In order to liquefy ice, as much heat is consumed as would suffice to raise an equal weight of water through 79*2 5°C., or through i42.65"F. ; or what is the same thing differently ex- pressed, it would raise 79*25 times that weight of water through i^C, 79-25°C. is therefore the latent heat of water. If the water obtained by melting ice be heated until it reaches a temperature of ioo°C., water-gas is given off, and there is no further rise in the temperature of the water, until the operation of vaporisation is completed. A large amount of heat is being absorbed notwithstanding, and this is con- sumed in separating the molecules, and overcoming the atmospheric pressure. The latent heat of vapor- isation of a given weight of water is sufficient to raise an equal weight of water through 537*2°C., or 96'v°F., or 537*2 times that weight of water through i°C. The latent heat of steam is therefore 537*'C. The cooling of the atmosphere, by the falling of a shower of rain ; or, by watering streets, or floors of rooms, is explained by the evaporation of the liquid and the consequent absorption of heat from adjacent matter. In like manner when steam, which has been formed under a pressure of several atmospheres, and therefore possesses a temperature considerably above ioo°C., is permitted to escape into the air, the hand may be held in it with perfect impunity, since the pressure being now less than that to which the steam was pre- viously exposed in the boiler, the water-gas will at once expand, the super-heat will become latent or Will assume the potential condition, and the heat will '%> r •: 52 ESSENTIALS OF CHEMISTRY not sensibly affect the hand thrust into it. Super- heated steam, that is steam which has been passed through a coil of piping heated to a high temperature, also permits of the hand beingpassed through it without scalding. This is supposed to be due to the fact that superheated steam being in the condition of a pure gas is a bad conductor of heat, therein differing from ordinary steam, which is simply a vapour and a much better conductor of heat. Every gas, on expanding, if it performs work must likewise absorb heat. When a gas is liquefied, or a liquid is solidified, the pre- viously latent heat becomes sensible, and this explains the action of freezing mixtures, and of such processes as that of Carry's freezing machine. 94. A thermal unit is the amount of heat requi- site to raise i kilogramme of water through i°C., or, in other terms, it is the amount of heat requisite to raise I lb. avoir, of water through i°F. The first expression is the French unit, called the calorie. A calorie, con- verted into mechanical force, would raise a weight of I kilogramme to a height of 425 metres, and conversely the fall of I kilogramme through a space of 425 metres would produce i calorie of heat ; or the amount of heat required to raise i lb. of water through i°F. would raise a weight of i lb. through 772 ft, and the fall of I lb. through 772 ft. would produce heat enough to raise i lb. of water through i°F. This latter mea- sure of the dynamical force of heat is known as "Joules* equivalent." * 95. When two elements combine together by equi- valent weights, heat is evolved. This is known as AND CHEMICAL PHYSICS, 53 the )ugh lea- lui- as Heat of Chemical Combination, or calorific value, and its nature may be best understood by means of the following examples : — The combination of one gramme of hydrogen with its equivalent — eight grammes of oxygen would evolve as much heat as would raise 34462 grammes of water from o^C. to i°C., or 39*1 grammes of potassium combining, with 35*5 grammes ofxhlorine would evolve sufficient heat to raise 104476 grammes of water from o°C. to i"C., or, again, 23 grammes of sodium combining with 35*5 grammes of chlorine would evolve sufficient heat to raise 94847 grammes of water from o^C. to i°C. The determina- tion of the heat of chemical combination is very diffi- cult, and requires accurate experiment in each indi- vidual case. 96. Calorific value is the heating power of a substance during combustion, but calorific intensity is the actual temperature of the burning substance, and this calorific intensity is calculated from the calo- rific value. When the combustion goes on in oxygen, the following is the method of calculation : — Divide the calorific value of the relative weight of the com- bining element in the compound, by the product of the specific heat of the compound into its total rela- tive weight. » ■ 97. The atomic heat of an element is obtained by multiplying its specific heat into its atomic weight. Thus — sp. heat of copper=o*o95i, atomic weight= ^3*5) atomic heat=o'o95i x 63-5 = 60389. Sp. heat of zinc=o*o955, atomic weight =65, atomic heat = 00955 X 65= 6*2075. In like manner the atomic heats ■Hill 1 ; I ' i IP '! Ill 14 ESSENTIALS OF CHEMISTRY of iron, tin and silver are rerpectively 6*3728, 6*6316, and 6'i56o, fronv which examples it appears that there is an approximation to an identity. The divergences from the general law may be partially accouiited for by the different molecular conditions of the elements during the determination of their specific heat, and by the differences in their fusion points. The atomic heats of gases are about one-half that of solids ; thus the atomic heats of hydrogen, oxygen and nitrogen are respectively 3*4090, 3*48 and 3*41. The import- ance of this law of atomic heat is evident from a con- sideration of the assistan::e which it yields in deter- mining the atomic weight of an element the sp. heat of which has been ascertained. ' Still it is to be noted that, although its truth is distinctly indicated, it has not in all cases been clearly established. It is be- lieved that this identity of atomic heats will be found to exist likewise in chemical compounds of the same group, as in chlorides, iodides, etc. . 98. The specific gravity of a body is the ratio of its weight to an equal volume of pure water at a known temperature, say, i5*55°C. As it would often be impossible to obtain equal volumes of the sub- stances whose specific gravity it is d^'ired to ascertain, advantage is taken of the principle of Archimedes, that a body immersed in water displaces a mass of the water equal in volume to itself, and has its weight diminished by that of the equal volume of water it displaces. To determ>ne, then, the sp. gravity of a soUd heavier than water, weigh the substance in air, and then in pure water at iS'SS'^C, or 6o°F. The sp. / AND CHEMICAL PHYSICS. U air. gravity of the substance is equal to its weight in air divided by the weight in air less the weight in water. Let A be the weight in air, and W the weight in water ; then s . gr.=^^3jyy. In accurate calculations the weight of the mass of air displaced by the body when weighed in air must be taken l to account. Water is 815 times heavier than air, so that from the result of the above calculation must be subtracted the result of 'he fol- lowing one- w Ex. A piece of prismatic 815 (A— W). quartz is found to weigh in air 311 '91 grains, and in water 195*46 grains, hence sp. gr. = 3TTVT-TH-i^F= 2-678; but the weight of air displaced in the first weighing = -g-y-^(7fjPfV-^-^-T^) = '002, therefore the true specific gravity is 2*678— •oo2=:2*676. If the substance be too light to sink of itself in water, it is attached i;o a sinker, the weight of which in pure water is B. ; then sp. gr. = For the determina- A+B-(W+B). tion of the specific gravity of liquids, the following method is commonly adopted. Weigh a small cylin- • der of glass, containing mercury, first in air, then in water, and then in the liquid the specific gravity of which is to be estimated. The loss of weight in water shows the weight of a volume of water equal to the volume of the cylinder, and the loss in the liquid to be tested shows the weight of an equal volume of that liquid. Divide the latter result by the former, and the quotient is the specific gravity required. Ex. The ' glass cylinder is weighed in air, and then in water, and loses in weight 442*8 grains ; it is then carefully dried and weighed in the liquid to be tested, and it loses in 56 ESSENTIALS OF CHEMISTRY 1 ! ' weight 354*3 grains; the specific gravity therefore is iiti^o*^* ^ second and direct method of ascer- taining the specific gravity of liquids, is to take a bot- tle so fitted as, when balanced by a counterpoise, to hold exactly looo grains of pure water; if now filled with nitric acid, it weighs 151 7 grains; if filled with benzol, it weighs 0*850 grains. An instrument called the hydrometer is also used to ascertain the specific gravity of liquids. This instrument is known under various names, as — lactometer, areometer, saccharo- meter, etc., according to its special application. It usually consists of a glass bulb bearing a slender stem or spindle ; the bulb is so weighted with mercury or shot that it sinks to a certain depth in liquid and maintains the stem in an upright position. The spin- dle is graduated in such a manner that its zero marks exactly the point to which it sinks in pure water. If the instrument be placed in a liquid of greater density than pure water, the spindle will accordingly stand higher ; or if the liquid be lighter than water, the spindle will sink deeper. In practice, different spin- dles are employed, according as the liquid to be tested is heavier, or lighter than pure water. To ascertain the specific gravity of a gas, a light glass globe of known weight, and of a capacity of about 50 cubic inches is used. This globe, in a perfectly dry state, is carefully filled with dry atmospheric air, and accu- rately weighed. It is then exhausted of air and filled with the dry gas of which it is required to ascertaii^ the specific gravity, and is again weighed. These weighings, less the weight of the globe, will evidently AND CHEMICAL PHYSICS. 57 give the ratio existing between the weight of air and the gas. " If the globe employed be sufficiently large to contain, at 6o°F. and 30 inches bar., 467 cubic inches of gas, the bulk will represent one grain of hydrogen gas, and that globe will contain the quanti- ties of the elementary gases which are represented by the atomic weight of these gases. That is to say, — I vol. of hydrogen being = i grain. I vol. of oxygen will be =16 grains. I /ol. of nitrogen n =14 11 I vol. of chlorine u =35*5 »» And the quantity of a compound gas will be repre- sented by its atomic weight divided by its atomic measure. Thus, — I vol. carbonic acid gas (CO2), will be =44 -4- 2 = 22 grs. I vol. carbonic oxide gas (CO), will bc= 28-^2 = 14 grs. The same volume of atmospheric air will be 14*47 grains." — Griffin, 99. It may often be necessary for the student to ascertain the absolute weight of a certain volume of a gas, and to do this he has only to remember the following facts. The weight of one litre (equal to 61*02 cubic inches) of hydrogen, at o'C, and at 760 mm. bar., pressure, is 0*08936 grammes : and, since the combining weight of elementary gases, or the density of componnd gases, is simply an expression of their relative weight compared with that of hydrogen, to find the absolute weight of a litre of any of these gases — multiply 0*08936 by the number representing the combining weight of an elementary gas, or the density ofa compound gas. Thus : — !• ESSENTIALS OF CHEMISTS > w ii M ■'iJ i1 I litre hydrogren 01=1) weighs 0-08036 grammes. « " nitrogen (N--14) ii 14x0 08036 ii II » oxygen (0=16) ii 10 x 0-08036 u ' « II marsh gas (0Il4 ), den8ity=16-T-2=8 ii 8x0 08936 ii II 11 ammonia (NH3 X ii =17-^2=8•5 ii 85x0 08636 ti 11 II carbonic acid gas (C02 ), =444-2=22 n 22x0-08938 ii Prof. W)JIrinson's "absolute volume," which serves the same purpose, is ii*2 litres; that is, this absolute volume is simply the bulk of one gramme of hydrogen; 14 grammes of nitrogen; i6 grammes of oxygen ; 8 grammes of marsh gas ; 8*5 grammes of ammonia, or 22 grammes of carbonic acid gas ; at o^'C, and at 760 mm. bar. It is useful to remember also that, in Eng- lish measurement, 100 cubic inches of hydrogen at Sa^F. and at 30 inches bar. weigh 2*22 grains ; or, at 6o*F., and at 30 inches bar., 2*14 grains. 100. When a plate of zinc and a plate of copper are immersed in a vessel containing dilute sulphuric acid, electrical action is set up ; the zinc becomes positively electrified and the copper negatively electrified ; bu':, as the current, or transmission of elec- trical force, passes through the liquid from the zinc to the copper, the copper is technically said to be posi- tively electrified, and the zinc negatively electrified; and if the two plates be joined outside the liquid by means of a copper wire, an electrical current passes from the copper to the zinc ; hence the copper plate, by which the current leaves the cell, is called the posi- tive pole, and the zinc plate, by which the current re-enters the cell, is called the negative pole. If, now, a series of such vessels furnished with zinc and copper plates and dilute sulphuric acid be arranged together, so that the copper plate of one vessel be joined to the A^'D CHEMICAL PHYSICS. 59 jerves # solute ogen; m; 8 lia, or ,t 760 Eng. en at or, at opper >huric ;omes ively elec- - ic to Dosi- fied; d by asses )late, posi- rrent now, pper ther, ) the zinc plate of the adjoining one, by means of a copper band or wire, the arrangement is called a galvanic bat- tery, and each vessel is called a cell, or an " element." There are many varieties of galvanic batteries, one of the most valuable of which, perhaps, is Groves' battery. • 1 01. Groves* battery consists of a series of cells, each cell being constituted as follows : — (I.) A vessel of glazed earthenware, or of glass containing dilute sulphuric acid (one part acid to four parts water). (II.) A lesser vessel of porous earthenware, containing concentrated nitric acid. (HI.) A bent plate of amal- gamated zinc, which fits into the larger vessel and per- mits of the porous vessel fitting in its bend. (IV.) A plate of platinum which fits into the porous vessel. The platinum plate of one cell is fastened by means of a binding screw to the zinc plate of the adjoining cell ; there vrill thus be a free platinum, and zinc plate, the former being the positive pole, the latter the negative pole. The sulphuric acid is decomposed by the action of the zinc, hydrogen is evolved, and effects the partial decomposition c^ :he nitric acid, evolving nitric oxide, and thereby preventing the polarization of the platinum plate. This is a powerful battery, but is not constant. 102. Opposite electricities attract, and similar electricities repel each other ; hence it is that elements which appear during electrolysis at the positive pole are called electro-negative, and those which appear at the negative pole are called electro-positive. 103. Electrolysis is the resolution of a chemical compound in the liquid condition, into its constituent elements, by means of a galvanic current. Let it be I ^^m ') 60 ESSENTIALS OF CHEMISTRY I' Si fi < required, for instance, to decompose water into its constituents. A glass vessel is inserted upon a suita- ble base, usually of mahogany, through which are passed two copper wires terminating inside the vessel by small platinum plates, and terminating at the other end in small brass pillars fixed in the base and sup- plied with binding screws. This vessel is partially filled with slightly acidulated water, and two test tubes of equal size filled with acidulated water are inserted in the vessel, a test tube over each platinum plate. If, now, wires from the terminal plates of a Groves* battery, of four or five cells, be connected with the small brass pillars above referred to, the circuit will be closed, electrical action is at once set up in the acidulated water and an accumulation of gas will be observed in each of the two test tubes. Since it is the platinum plate in a cell of Groves' battery, by which the current leaves the battery, the test tube which is inverted over the small platinum plate connected with it is evidently at the positive pole, and in like manner the test tube inverted over the platinum plate which is connected with the terminal zinc plate of the battery is at the negative pole. The water connecting the poles re- quires to be acidulated, because pure water conducts the current very imperfectly. It is not to be supposed that there is any transmission of gas between the poles, but only an interchange of elementary atoms, so that while the molecules of water in immediate contact with the poles liberate atoms of the constituent gases, the intervening molecules simply exchange atoms. If the galvanic circuit be broken before either test tube . AND CHEMICAL PHYSICS. 6i ;s is full of gas, it will be found that one test tube con- tains about twice as much gas as the other. By apply- ing the proper tests it will be seen that the larger quantity consists of hydrogen and the lesser quantity of oxygen. By a variety of experiments it can be shewn that the proportion ought to be exactly two of hydrogen to one of oxygen, but oxygen being rather more soluble than hydrogen in water, the apparently contradictory result mentioned above is obtained. Since oxygen appears at the positive pole it is called an electro-negative, and hydrogen appearing at the negative pole it is called an electro-positive. When compounds of metals and non-metals are decomposed by electrolysis, the non-metals appear at tUe positive pole, and the metals at the negative pole, hence metals are classified as electro positive, and non-metals as electro-negative elements. 104. An induction coil consists of (I) a primary coil of silk-covered or insulated wire, of a few yards in length, wound round a hollow cylinder, and com- municating at one extremity with the positive electrode of a battery, and at the other with the current break ; (II) a secondary coil of very fine insulated wire of great length, wound round the primary or inducing coil, (III) a bundle of soft iron wires packed in the interior and forming the core ; (IV) the hammer, a small piece of soft iron affixed to a spring, which in its normal position is pressed down upon the anvil, and through which the current passes from the coil to the anvil, and thence returns to the negative electrode of the battery to complete the circuit ; (V) the anvil, ill J: . ! 62 ESSENTIALS OF CHEMISTRY a small piece of soft iron through which the current passes from the hammer. When the circuit is com- pleted, the current passes through the primary coil and then through the hammer and anvil, but, while the current passes, the core becomes magnetic, and the hammer is therefore attracted to its projecting end ; but so soon as the hammer leaves contact with the E-iivil the current is of course broken, the core cea::es to be magnetic, and the hammer being released is immediately brought back into contact with the anvil by means of the spring, the current again passes, is again broken and so repeated action goes on, with very great rapidity. The hammer and anvil are ac- cordingly known as the current break. Each time the current is closed or broken, an induced current is manifested in the secondary coil, from the extremities of which visible discharges are obtained. 1C5. When gases of different densities are brought in contact with one another they display a constant tendency to interminr e, and this intermixture main- tains, notwithstanding that the gases may be of very different densities, thus — hydrogen and oxygen, al- though the latter gas is sixteen times as heavy as the former, will not merely intermingle, but will, after intermixture, shew no tendency towards separation. The rate of diffusion of any gas is ascertained by means of the diffi 'on tube. This is simply a gradu- ated tube of about a foot in length, open at one end and at the other stoppered with a thin plate of plaster of Paris. If the tube be filled with a gas, and the open end inverted in mercury, the mercury will be 4ND CHEMICAL PHYSICS, 63 urrent ; com- )il and lie the id the \ end ; th the cea::,es Lsed is e anvil sses, is I, with are ac- li time •rent is pmities rought >nstant main- »f very en, al- as the after ration, led by gradu- le end plaster nd the vill be ■vya seen to begin to ascend, shewing that the gas is es- caping through the porous plaster of Paris, and that the mercury is consequently being forced up in the tube by atmospheric pressure outside the tuoe. The diffusive rate of gases is in inverse ratio to the square root of their density. Thus, the density of hydrogen being i and the density of oxygen being 16, and the square root therefore being as i to 4 ; four times as much of hydrogen would pass through the plaster of Paris, in a given time, as of oxygen. Il I 'I i 64 ESSENTIALS OF CHEMISTRY PART II. CHAPTER r. OXYGEN — OZONE. Chemistry of the Non-Metals. 106. Oxygen (0"=i6. Molecular formula O2). Discovered by Dr. Priestley, 1774; by Scheele, 1775. Examined and named by Lavoisier, 1778. A colour- less, tasteless, odourless gas ; the supporter of all ordi- nary combustion ; does not burn ; not condensible to a liquid ; sp. gravity 1*1056 ; sp. heat o'2i75 ; will not combine with fluorine under any known conditions ; combines under artificial conditions with gold, silver, platinum, chlorine, bromine and iodine; and with most of the remaining elements it combines in nature. It is the most abundantly distributed element known, making nearly 50 per cent, of the solid matter of the globe, eight-ninths by weight of water, and about one- fifth by weight of air. It is slightly soluble in water. Ob- tained — (I). By application of heat to mercuric oxide — 2HgO = Hg2 + O2. Heated mercuric oxide gives — metallic mercury and oxygen. (II). Most cheaply, in large quantity, by decomposing manganese dioxide — (MnOa) ; — 3Mn02=Mn304 + 02. Heated manganese dioxide, or black oxide of manganese gives — brown oxide of manganese and oxygen. ^III). Most readily AND CHEMICAL PHYSICS. 65 3. •mula O2). ;ele, 1775- A colour- Df all ordi- lensible to ; ; will not Dnditions ; )ld, silver, with most ature. It It known, tter of the ,bout one- irater. Ob- uric oxide le gives — heaply, in dioxide — langanese —brown >st readily ■I '■>■ and conveniently, by decomposing potassium chlorate ^(KClOs) ;— KC103=KC1 -f O3. Heated potassium chlorate gives — potassium chloride and oxygen. Note: — The addition of a little manganese dioxide (which acts by catalysis) causes the oxygen to come off at a somewhat lower temperature than that at which the unmixed potassium chlorate liberates it. (IV). By electrolysis (103). (V). From the air. — First oper- ation — A porcelain tube containing sodium manganate (NagMnOi) is strongly heated and steam is passed through it, oxygen is evolved and may be collected in a jar inverted over water. The reaction is represented by the equation — 2Na2Mn04+ 2H2O (in the form of steam)=4NaH0 + Mn203 + O3. Heated sodium man- ganate and steam give caustic soda, sesquioxide of manganese and O3. Second operation. — The current of steam is now discontinued, and a current of air is allowed to pass over the contents of the porcelain tube, when sodium manganate is again formed through absorption of oxygen from the air, while the nitrogen of the air passes on and may be either collected or allowed to escape. The second reaction is— 4Na HO + MnsOs + 3(0 + N^)^: 2Na2Mn04 + 2H2O + Njo. Heated caustic soda, manganese sesquioxide, and air give sodium manganate, water, and nitrogen. The water will be driven off in the form of steam, and the operation may now be repeated. One hundred cubic inches of oxygen at 6o°F. and 30 in. bar. weigh 34-203 grs. One litre at o°C. and 760 mm. bar. weighs 1-4298 grammes, or 11 -2 11. weigh 16 grammes. Ex. I. Phosphorus enflamed in oxygen in a bell-jar i t^ ESSENTIALS OF CHEMISTRY 1 I I 1 \ \v.\ 'h I J f II ill over water, burns with great energy and brilliancy, evolving fumes of phosphorus pent-oxide (P2O6), which speedily dissolve in water, forming phosphoric acid H3PO4 ; thus :— P2O5 + 3H20= 2H3PO,. Ex. II. Charcoal at a red heat placed in a jar of oxygen, burns with brilliant scintillations, forming car- bonic acid gas (CO2). Ex. III. Sulphur enflamed in a jar of oxygen, burns with a fine violet flame, forming sulphurous acid gas (SO2), which, dissolved in water, gives the unstable hydrated acid— SO2 + ^^O^ H2SO3. Ex. IV. Zinc armed with a little burning sulphur and placed in a jar of oxygen, burns with a fine green flame, forming zinc oxide (ZnO). Ex. V. Fine iron, or steel wire in the form of a spiral coil, armed with burning sulphur and dipped into a jar of oxygen, burns with bright scintillations, forming the compound oxide — Fe304 (magnetic oxide of iron)=FeO (protoxide of iron) + Fe203 (peroxide of iron). Metals in the dry condition are rarely acted upon by oxygen, but moisture promotes combination, and rusting is a familiar instance of oxidation. 107. Ozone is oxygen in an allotropic condition, apparently consisting of three atoms united to form a molecule of two atoms. The rate of diffusion of ozone agrees with this view ; some chemists, however, con- sider that it is really a trioxide of hydrogen (H2O3). Ozone is a gaseous substance possessing a peculiar smell, whence ^^s name. Given off, in comparative abundance, when an electrical machine is worked. AND CHEMICAL PHYSICS, 67 brilliancy, Pb), which horic acid in a jar of )rming car- 'gen, burns IS acid gas le unstable ng sulphur L fine green form of a nd dipped intillations, netic oxide peroxide of icted upon ation, and condition, I to form a m of ozone vever, con- en (H2O3). a peculiar omparative is worked. Traces of it are observable in the oxygen obtained by the electrolysis of water. A series of electric sparks from a coil, passed through oxygen, changes a portion of it into ozone, and the oxygen diminishes by about one-twelfth of its volume. Ozone may be prepared by suspending a stick of phosphorus in moist air in a bell-jar, but better by partially covering with water in the bottom of a bell-jar, a freshly-scraped stick of phos- phorus. It exists to a slight extent in the free state in the atmosphere, and is supposed to exercise a benefi- cial influence by oxidising noxious matter. The com- mon test for its presence is unsized paper prepared in starch paste, in which some crystals of iodide of potas- sium (KI) are dissolved. The ozone oxidises the potas- sium, liberating the iodine, which imparts a blue colour to starch. This test cannot be depended upon, as nitrogen tri-oxide, ether, turpentine, etc., have a simi- lar power of liberating iodine by absorption of oxygen. A better test is gum guaiacum, to which ozone imparts a blue colour. Ozone bleaches indigo, corrodes vul- canized caoutchouc, oxidises silver in a finely divided condition, and generally displays powerful oxidising properties. Note. — Day's Blood Test ; the suspected stain is I first moistened with a solution of gum guaiacum in alcohol, and then with a solution of hydrogen peroxide (H2O2), in ether (ozonic ether), if the stain be a blood spot, it assumes a bright blue colour, which readily leaves an impression upon white blotting paper. This reaction is due to t' e decomposition of the H^Oa in contact with blood, the liberation of oxygen and the consequent blueing of the resin. n! I ; ii ESSENTIALS OF CHEMISTRY CHAPTER II. HYDROGEN — WATER. 1 08. Hydrogen (H^=: I. Molecular formula H*). Probably known to Paracelsus, in the i6th century; re- discovered and examined by Mr. Cavendish 1781. A colourless, tasteless, odourless gas ; a non-supporter of combustion ; burns with a nearly colourless flame, combining with oxygen to form water only ; not con- densible to a liquid ; sp. gravity 0*0693 ; sp. heat 3*409 ; not met with in the free state in nature ; com- bines directly with only six elements — oxygen, chlorine, bromine, iodine, carbon and sulphur. With the last three it combines with difficulty, and it combines with chlorine and bromine alone at ordinary temperature, and even in these cases only in the presence of light. It is soluble in water to a very slight extent. Obtained, — (I.) By the action of sodium upon water — 2Na + 2H20=2HNaO + 2H. Sodium upon wates: gives caustic soda, and hydrogen. (II.) By the action of potassium upon water — 2 K + 2 H2O = 2 H KO + 2 H. Potassium and water gire caustic potash and hydrogen. In this reaction so much heat is evolved that the gas takes fire and the flame is coloured violet, because of the sublimation of a portion of the potassium. (Ill) " By the action of dilute sulphuric acid upon zinc — Zn -t- H2S04 — ZnSO^ + H2. Dilute sulphuric acid (one part H2SO4 and six parts water) and zinc give sulphate of zinc or wjiite vitriol, and hydrogen. (IV.) By the action ot dilute sulphuric acid upon iron — Ff '-Ha - 1 AND CHEMICAL PHYSICS. 69 Drmula H*). :entury; re- dish 1 781. n-supporter rless flame, ; not con- ; ; sp. heat tare : com- ;n, chlorine, ith the last nbines with jmperature, ce of light. Obtained, ;er — 2Na + mteff gives e action of IKO + 2H. 1 hydrogen. lat the gas because of num. (Ill) n zinc — Zn d (one part sulphate of V^.) By the ~Ff -Ha S04=FeS04 + Hj. Sulphuric acid and iron give sul- phate of iron, copperas or green vitriol, and hydrogen, (V.) By electrolysis (103). (VI.) By passing steam through an iron tube containing iron filings heated to a high temperature — 4H2O + Fe3== Fe304 + Hg. Black oxide of iron is formed in the tube and hydrogen is liberated. Collected by displacement either of air or water, dried by passing over calcic chloride, quick lime, or pumice stone saturated with sulphuric acid. Burns with a livid blue flame if there be traces of arsenic present, and with a yellow flame if burnt while issuing from a jet of glass containing soda in its com- position. Its flame gives very litde light, but in- tense heat. Hydrogen is the lightest known substance being 14.47 times lighter than air, and 11 162 times lighter than water ; one hundred cubic inches at 6o°F. and 33 in bar., weigh 2 "14 grains. One litre at o°C and 760mm. bar., weighs .08936 gramme, or 11.2IL weigh one gramme. If a moderately wide tube of about 20 inches in length be held over a hydrogen flame, the combination of the hydrogen with the limited quantity of oxygen entering the tube causes a series of small detonations or explosion? of the mixed gases to succeed each other, with such r'-^idity as to produce what is called the musical flame, or the hydrogen harmonicon. The dry gas is used to fill balloons, and to produce the oxy-hydrogen flame. 109. Water (H2O combining weight =18. Density of water-gas =9.) A compound of hydrogen and oxygen in the proportion, by volume, of two of hydro- I! 70 ESSENTIALS OF CHEMISTRY ■ I ; i gen to one of ox3'gen and, by weight, of two of hy- drogen to sixteen of oxygen. By electrolysis (103) water is decomposed into its constituent elements ; and by passing a series of electric sparks by means of an induction coil, through steam generated in a flask wliich communicates by a delivery tube with a test tube inverted over water, steam is likewise decomposed; the water in the test tube will be expelled by the mixed gases collecting in it, and on a light being applied to the mouth of the test tube an explosion will follow, denoting the re-combination of the gases to form water. If hydrogen and oxygen be passed into a graduated tube, over mercury, in the proportion of two of hydrogen to one of oxygen, and the electric spa^k be passed through the mixed gases, they will immedicitely combine to form water occupying the Tc^oijth part of the space previously occupied by the gases, and the mercury will ascend, and practically fill the entire tube. Certain meials have so powerful an affinity for oxygen that they are able to decompose water at ordinary temperatures ; these are — potassium, sodium, barium, strontium, calcium. The following metals decompose water by combination with its oxy- gen, at a red heat — iron, lead, zinc, bismuth, cobalt, copper, chromium, nickel, tin, antimony, aluminium. The following do not decompose water at any known temperature — gold, platinum, silver, mercury. Chlo- rine and bromine are the only elements which com- bine with water, no other elements are even dis- solved by it to any considerable degree. It has teen shewn elsev/here, that when hydrogen is burned in AND CHEMICAL PHYSICS. 71 two of hy- lysis (103) elements ; ly means of [ in a flask villi a test icomposed; r the mixed applied to will follow, ;s to form jed into a ^portion of he electric s, they will ipying the ied by the practically o powerful decompose potassium, following th its oxy- th, cobalt, luminium. my known y. Chlo- ch corn- even dis- t has been burned in 'm air, or in oxygen, water is the sole product, and the ac- curate performance of this experiment in a modified form, is the means of determining the composition of water by weight. Hydrogen is generated in the usual way, by the action of sulph'iric acid (H2SO4) upon zinc, in a Woulfe's bottle, and the gas is passed through a series of drying tubes containing ist, a solution of caustic potash (HKO), to absorb sul- phuretted hydrogen (H2S) ; 2nd, pumice stone, satu- rated with nitrate of silver (AgNOo) to absorb arsenic and antimony. 3rd. Pumice stone saturated v/ith sul- phuric acid (H2SO4) to absorb moisture. The pure, dfy, hydrogen now passes through a tube having a [bulb enlargement at its middle point in which is placed J a known weight of cupric oxide (Cu. O.) , this bulb- ''rtube is in turn connected with a receiver of known ^;, weight, kept cool during the experiment, by a constant j'^' stream of cold water ; and this receiver is finally con- nected with a dr)'ing tube of known weight, contain- ■ ing pumice stone saturated with sulphuric acid (H2 ' . SO4) to absorb moisture. When the copper oxide is t raised to a high temperature and the dry hydrogen is , passed over it, the oxygen of the oxide at once com- buies with the hydrogen, and the water gas formed passes on to the receiver where it is almost entirely condensed to the liquid condition, and any vapour that does escape from the receiver is captured in the ^drying tube connected with it. The gain in weight of [the receiver and of the last drying tube evidently re- I presents the weight of the water formed, the loss of weight of the copper oxide bulb must represent the 72 ESSENTIALS OF CHEMISTRY ill weight of liberated oxygen only, if therefore the weight of the oxygen be* subtracted from the weight of the water formed, the remaining weight is evidently that of the hydrogen. l)y this experiment, accurately per- formed, it is ascertained that loo parts water, by weight, contain ii'ii parts hydrogen and 88*89 parts oxygen. Pure water is colourless, tasteless and odourless, but in mass it appears of a bluish colour. It is almost non-elastic and is a remarkable exception to the general laws of expansion and contraction, since it reaches its maximum density at 4°C. and when heated above, or cooled below that point it expands. At 4"* C. a litre of water weighs one kilogramme, or a gallon weighs 70007 grains. The density of ice is .92, that is 92 grammes of ice occupy thoi same volume as 100 grammes of water at 4°C. When water boils (81), it It; converted into water gas, occupying 1696 times the volume of the liquid. Water is rarely found pure in nature ; it is called hard or soft according to its re- action with soap. Soap contains two acids, stearic and oleic acids which are combined with the soda of the soap. When such soap is rubbed in water con- taining sulphates, as calcium, or magnesium su'phate, the stearate and oleate are decomposed ; soluble soda salts are formed while insoluble magnesium or calcium oleates and stearates form a curdy precipitate. Soft water, on the contrary, produces a lather with soap by simple dissolution. The following is Dr. Clarke's test for the comparative hardness of water — A known quantity of soap is dissolved in alcohol, and accord- ing to the amount of this soap decomposed by water Ij AND CHEMICAL PHYSICS. 73 the weight ght of the dently that irately per- , by weight, rts oxygen. >urless, but t is almost on to the in, since it len heated is. At 4° or a gallon is .92, that me as 100 )ils (81), it times the nd pure in to its re- ds, stearic he soda of vater con- su'phate, luble soda or calcium :ate. Soft th soap by Clarke's -A known id accord- i by water under investigation, compared with the amount de- composed by water known to contain one, two, three etc., grains of calcium carbonate dissolved in 100,000 parts water, the test is said to yield results of one, two,' three etc., degrees of hardness. The principal impu- rities of water are sulphates of soda, magnesia and lime ; carbonates of magnesia and lime, car- bonic acid ga: vegetable and animal matter. Suspended impurities are got rid of by means of filtration dissolved impurities must be got rid of by distillation. Distilled water pos- sesses an msipid taste due to the absence of dis- solved air, but It may be aerated sufficiently for drinking purposes by passing it over porous char- coal. In the process of distillation, if precautions are not taken to drive off all dissolved gases, before collecting the aqueous vai)Our in the receiver, some quantity of the more soluble of these gases will of course be re-dissolved in the distilled water, and the same will be true of volatile impurities in general. Car- bonates do not remain dissolved except in presence of free carbonic acid (C.O2), hence when water con- taining carbonates is allowed to stand for some time after being drawn, till its dissolved carbonic acid has escaped, the carbonates will be found precipitated to the bottom of the containing vessel. Water percolat- ing: through limestone rock into caverns and contain- ing abundance of carbonic acid gas, and carbonate of lime in solution, on reaching the air suffers evapora- tion to a CO. iiderable degree, and most of the carbonic acid gas escapes. The carbonate of lime is IMAGE EVALUATION TEST TARGET (MT-S) « %^ v. Ki :A 1.0 I.I ■i^lM |2.5 ■ 50 "^^ ■■■ t \iS. 112.0 IL25 i 1.4 12.2 i{|M 1.6 V ^ V ^i' s\ ^ <^>^ .^J^ o"^ ^ 74 ESSENTIALS OF CHEMISTRY consequently deposited as a solid, forming stalac- tites, or pendant columns gradually elongating by the continued trickling of the water ; while that which reaches the floor of such caverns accumulates there in an upward direction forming stalagmites. This likewise explains tTie softening of water by boiling, since the carbonic acid is expelled, and the carbonates are precipitated. Temporary hardness of water is due to the presence of salts, more or less insoluble in hot water, or in water deprived of free carbonic acid ; this hardness will accordingly almost disappear after boiling. Permanent hardness, on the other hand, is due to the presence of salts which re- main soluble even in boiling water. "Washing soda (NajCOa) destroys both temporary hardness, and per- manent hardness, due to sulphates of magnesium and calcium, by forming insoluble carbonates and soluble sulphates :— CaS04 + NaaCOg^CaCOa + NajSOi ; or, MgSO* + NaaCOs^ MgCOg + NaaSO^. The addition of quick lime to hard water serves to neutralise the free carbonic acid, which combines with the lime to form calcium carbonate (CaCOa), and thus the other carbonates present, deprived of the free carbonic acid, are precipitated. Mineral waters are called chaly- beate if they contain salts of iron ; hepatic if they contain sulphur ; effervescing if they contain car- bonic acid. The presence of carbonic acid in water, in itself, cannot be regarded as detrimental since the refreshing and thirst quenching properties of water appear to be largely due to the carbonic acid gas contained. One consequence of the precipiti^tion pf ilk AND CHEMICAL PHYSICS. 7$ carbonates and sulphates from boiling water is the furring of kettles and boilers. This furring is chiefly caused by the carbonates, but, since calcium sulphate (CaSOi), seems to require about 400 parts water for its solutiofj, and is almost insoluble at temperatures above ioo"C., as would be the case in boilers, a portion of the deposit is undoubtedly due to the pre- cipitate of the sulphate also. This furring is a serious matter, not merely because of the consequent waste of fuel which takes place in heating the mineral deposit, in addition to the metal and the water, but as lending to cause explosions. To prevent furring in kettles, it is not unusual to place a round pebble in the vessel, which by its rolling, prevents the pre- cipitate forming a solid deposit. In boilers, furring may best be prevented by the addition of sal-am- ^moniac (NK4CI), which acts as follows : — 2NH4CI + )aC03=CaCl2 + (NH4)2C03. Calcium chloride re- [mains dissolved, and ammonium carbonate escapes as fa gas. Sea water contains all the salts found in other ^vaters with a great preponderance of chloride of sodium, common salt (NaCl) ; one gallon contains about 2500 grains of saline matter, of which about 1900 are salt. It is said that clothes once wetted with sea-water never become perfectly dry again, and this is attributed to the presence of magnesium chloride, which is distinguished by a constant tendency to deliquesce in moist air. Well water is usually impure on account of decaying vegetable and animal matter in solution, which percolates through the surface soil, and by its admixture with water tends to generate I 76 ESSENTIALS OF CHEMISTRY typhoid malaria and to spread epidemic 'disease. Water containing chlorides and nitrates, or nitrites, is always more or less injurious to the human system. The tests for all the impurities mentioned in this article will be found elsewhere (62, dT^^ 64). In this con- nection the danger arising from the use of leaden cisterns is to be noted. The interior of such cisterns gradually becomes oxidised by contact with the atmos- pheric oxygen ; this oxide is insoluble in hard water containing carbonates and sulphates, but the nitrates and nitrites, generally present in soft water, cause its solution in a greater or less degree, thereby rendering the water poisonous to a corresponding extent. Many salts contain water, which is in close union with the other constituents, and is hence called water of crys- tallisation, this water may generally be expelled by heating to ioo°C. Water which is still more closely connected in chemical union with a salt, and which is not expelled at ioo°C., is called water of constitu- tion. The property of water of expanding on freezing is most important in the economy of nature, for if it followed the general law and became heavier as it became colder, large bodies of water would freeze as a mass, thereby destroying all contained animal life, and, moreover, since water is heated almost emirely by convection, and therefore from below upwards, such masses of ice could never liquefy again under present conditions. Ice is generally formed on the surface, but it is occasionally formed on rock bottoms of rivers, on account of the more rapid radiation of heat from the mineral matter forming the bed of the river than AND CHEMICAL PHYSICS. 11 le of leaden from the water of the river itself; the water will, therefore, be most cooled down in contact with the bottom, and may even form masses of ice, to which the name of anchor ice has been given. ,jf'' n <; . CHAPTER III. . . HYDROGEN PEROXIDE — OXY-HYDROGEN FLAME. no. Hydrogen peroxide, Oxygenated water (H2O2). An unstable, artificially formed compound. Appears to consist of one molecule of water in com- jbination with one atom of oxygen. A liquid pos- [sessing considerably greater consistency than water; Sp. gravity i '45 ; has a slight odour of chlorine ; [readily decomposes, on the application of heat, liber- Lting oxygen. Contact with gold, platinum or silver, rhich, it will be remembered, have no direct affinity for oxygen, causes immediate decomposition of the )eroxide without any alteration of the metal. On the >ther hand, if the peroxide be dropped upon oxides ?of the above metals, they are immediately reduced [with explosion, to the metallic state. The explanation is supposed to be that the oxygen of the oxides and the oxygen of the peroxide being in different chemical :onditions there is mutual attraction between them, fas if they were different elements. Used in medicine sand in photography. Obtained by the action of hydro- chloric acid upon baric oxide — Ba02 + 2HC1=H20, + BaClj ; to the resultant solution argentic sulphate I r' 78 ESSENTIALS OF CHEMISTRY IS added, with the precipitation of baric sulphate and argentic chloride — BaClj + Ag2S04=2AgCH- BaSO*. The clear liquid is decanted, and concentrated by exposure in the receiver of an air pump, over oil of vitriol, in order to get rid of water, which evaporates more than the peroxide; bleaches litmus. Experi- ment.— Throw a little manganese dioxide (Mn02) into a solution of hydrogen peroxide and oxygen will be evolved, as may be seen by the application of the usual test — a splinter of wood in the condition of a red coal. The manganese dioxide acts like the metals mentioned above, without undergoing any decomposi- tion itself. III. When oxygen and hydrogen are mingled to- gether, in the proportions necessary for complete com- bustion, blown through a blowpipe nozzle and ignited, the almost colourless flame produced evolves intense heat estimated as being about 83oo°C, and which is capable of fusing with ease refractory sivbstances such as platinum, steel, or gold. On account of the explo- sive character of the gaseous mixture, the oxygen and hydrogen should be kept in separate reservoirs and only brought together at the point of combination, or else the mixture should be passed through a Hem- ming*s Jet to avoid risk ,f the flame passing back to the common reservoir. The Diummond light, or liue light is produced by causing a jet of oxygen to play upon a small cylinder, or ball of close-grained, well burned lime whilst it is heated in a jet of hydrogen gas ; the heat evolved by the combination of the two gases being intense, the lime is raised to a state of AND CHEMICAL PHYSICS, 79 |brilliant incandescence, and, being infusible, it gives magnificent light, suitable for signals, or for light- louse purposes. The same precautions must be idopted as in the use of the oxy-hydrogen blowpipe, [agnesia or zirconia are occasionally substituted for |ime, and the experiment raay be varied by using the >xy-calcium light, obtained by heating the lime in the lame of a spirit or oil lamp, and playing upon it with the jet of oxygen \ or, by substituting the flame of :oal gas for that of spirit, or of hydrogen, and still ^mploy'ng the oxygen jet, the oxy coal-gas light is )btained. . ^ , ■'t5 CHAPTER lY. ^ - ;^ ^ . •i.^ NITROGEN — ATMOSPHERE, <■ ■ ./ Respiration of Plants and Animals. 112. Nitrogen (N"^=: 14. Molecular formula N*). colourless, tasteless, odourless gas ; does not burn ; loes not support combustion ; not condensible to a Iquid ; soluble in cold water to a slight extent; is in- noxious in itself, but does not support animal life, tp. gravity 0*972 ; 100 cubic inches at 6o°F. and 30 L bar., weigh 30 grains ; 3 1*2 11. at o°C. and 760 mm. ir. weigh 14 grammes. Occurs free in nature, form- ig four-fifths of the atmosphere, and enters into com- [ination in many abundantly distributed compounds. [itrogen is an important element of organic life, and ts inert nature is in striking contrast to the energetic Characteristics which it appears to confer upon the i f>ril!i m n hK 80 ESSENTIALS OF CHEMISTRY compounds into which it enters. By combination with oxygen, it forms one of the most powerful acid radicals known — Nitric pentoxide (N2O5), and with hydrogen it forms one of the most powerful of alkalies — ammonia (NH3). It combines very feebly with most other elements, and hence many of its com- pounds are very unstable and explosive. Nitrogen affords an excellent illustration of the law of multiple proportions — NjO; N2O2 ; N2O3 ; N2O4 ; N2O5. Obtained by burning phosphorus over water, in a bell jar filled with air. Phosphorus- combines with the oxygen of the air forming phosphoric pentoxide (P2O5) which is evolved in dense white fumes, speedily dissolving in the water forming phosphoric acid — P2O5 + 3 H2O = 2H3PO4, and leaving free nitrogen in the jar. ^ 1 13. The atmosphere is composed chiefly of the two gases nitrogen and oxygen mechanically mixed together, in the proportion of about 79.19 vols, of ni- trogen to 2 1 "8 1 vols, of oxygen, or, by weight, about 76*99 parts nitrogen to 23*01 parts oxygen. The other constituents are aqueous vapour, carbonic acid gas, ozone and ammonia. Since the amount of aque- ous vapour varies according to temperature, rainfall, and proximity of water, it is difficult to give anything like a definite statement as to its relative amount, but it is probably on the average about 14 vols, in 1000, or 8*7 parts by weight in 1000. The amount of car- bonic acid gas is subject to considerable variations according to the locality where the air is tested ; the average amount is about 4 vols, in 10,000, or 6 parts by weight, in 1000. In crowded buildings, or places warn AND CHEMICAL PHYSICS. '8i where diffusion of gases is more or less obstructed, the proportion often rises much higher. Ozone probably fulfils important purifying functions in the atmosphere by oxidation of noxious gases, but its relative quantity cannot be calculated. Ammonia exists in the air in variable quantity, but it is in no case very abundant, the maximum amount observed being 135 vols., and the minimum amount i vol. in 1,000,000 yols. Amrao- nia is, notwithstanding its small proportional amount, a most important agent in nature, since plants derive nearly all their nitrogen from it, and thereby perfect their fructification, supplying directly or indirectly, the means of animal nutrition. The determination of the exact relative proportions of oxygen and nitrogen in air, which it is desired to test, is arrived at as follows — A large globe, exhausted of air, and of accurately known weight, is connected with a tube containing imetallic copper, but exhausted of air, closed at either fendj by a slop-cock, and having its weight also accu- I lately determined. This tube is in turn connected [with a series of U tubes containing sulphuric acid, to [absorb ammonia and water ; and this with another [series of tubes containing potash, to remove carbonic Lcid gas. On heating the copper to a red heat and )pening the stop-cocks, atmospheric air slowly passes through the purifying tubes, getting rid of its carboi icid, ammonia and aqueous vapour, and, on reachi.' the copper, the oxygen immediately combines with it [to form copper oxide, whilst the nitrogen passes alone into the globe. The increase in weight of the globe land of the tube containing the copper will, subject to ■? r 82 ESSENTI.iLS OF CHEMISTRY sundry corrections, give the relative proportions of the oxygen and nitrogen in the air. That air is a mere mechanical mixture is shewn by the fact that an arti- ficial mixture of oxygen and nitrogen, according to the proportions given above, is found to possess nearly all the properties of ordinary air, but the gases are pre- sent neither according to their atomic weights, nor in any multiple of these weights, and when thus mixed there is no evolution of sensible heat, as would be the case if chemical union had taken place ; again if air be shaken up in a bottle containing some water a por- tion of the air will be dissolved, and if this dissolved air be expelled by means of heat it will be found that the proportions of the gases are now 187 vols, of ni- trogen to I vol. of oxygen ; this is due to the fact that oxygen is more soluble that nitrogen in water, but to exhibit this difterence the gases must have been sepa- rated, and it cannot be supposed that, if the gases had been chemically united, mere mechanical action could have disunited them. There are of course many ac- cidental impurities in the air, the products of respira- tion, combustion, putrefaction and electrical agency ; such as — nitric acid ; sulphurous acid ; carbonic ox- ide ; carbon in a finely divided state ; hydro-carbons ; material particles, in the shape of dust ; and probably germs of both animal and vegetable life. The weight of the atmosphere has been referred to elsewhere (68). Since it has weight and, being composed of gases, is compressible, it follows that the density will be un- equal throughout its mass, the lower portion, exposed to the greatest superincumbent pressure, being the AND CHEMICAL PHYSICS, ions of the is a mere liat an arti- ding to the s nearly all es are pre- jhts, nor in thus mixed ould be the again if air water a por- is dissolved found that vols, of ni- ;he fact that ater, but to been sepa- e gases had iction could ;e many ac- ; of respira- :al agency; :arbonic ox- ro-carbons ; id probably The weight iwhere (68). of gases, is will be un- on, exposed being the most dense, and this variation in density may be con- sidered as approximately slated in the following law — " At a height of seven miles the density of the atmos- phere is reduced to one-fourth the density at the sea- level, and for every increase of height by seven miles the rarity of the air is similarly quadrupled." The absolute height of the atmosphere, is an open ques- tion ; but it is probably not less than 200 miles. It is generally agreed however, that there is a limit to the atmospheric layer, beyond which there is supposed to be a vacuum in which the aerial particles are pre- vented from expanding by their own weight. In the night time the radiation of heat from the earth, so re- duces the temperature of the surface that the lower layers of air coming in contact with it are cooled and condensed, to such a degree as to be unable to retain the contained aqueous vapour, as such ; and a portion is therefore deposited upon the earth as dew ; should the temperature at the moment of deposition be at, or below, the freezing-point, hoar-frost and not dew will be formed. Fogs over rivers and lakes in summer are due to the partial condensation of the aqueous vapour, rising "rom the comparatively warm water, by contact with the colder air from the land. When a mass of air comes in contact with a colder current of air the former suffers condensation, and its contained vapour is deposited as rain ; or, if the temperature be reduced to the freezing point, the condensed vapour assumes the crystalline form and falls to the earth as snow. Hail seems to be snow which has been exposed to a peculiar whirling motion, acquiring thereby a number of coats or layers in a partially congealed state. t- 84 ESSENTIALS OF CHEMISTRY 114- Oxygen mingled with Nitrogen is in- hald by animals in the process of respiration. The nitrogen is exhaled without having undergone change, but the oxygen is absorbed by endosmosis into the venous blood of the capillaries of the lungs, and is thence conveyed throughout the system, serving not merely to purify the blood by the oxidation of cai )n- aceous matter, produced by the wasting of the body, but also assisting to build up new matter to compen- sate for that waste. This oxidation serves at the same time to maintain the requisite temperature of the blood. A certain quantity of carbonic acid is given off at each expiration, and thus the breathing of ani- mals has a constant tendency to vitiate the air, by the removal of the element essential to animal life and the substitution of a compound gas destructive to that life. It is estimated that during every twenty-four hours an average adult inhales about 360 cubic feet of air, con- taining about 76 cubic feet of oxygen, and that he exhales about 1 5 cubic feet of carbonic acid gas con- taining 8 oz. solid carbon. The air expired from the lungs of man contains about 3*5 to 4 vols, carbonic acid gas in 100 vols, of air. A demonstration of this relatively large quantity of carbonic acid evolved from the lungs as compared with the amount existing in atmospheric air may be made by passing, by means of a gas holder, a known volume, say 200 cubic inches, of air through a vessel of lime-water, and then passing an equal volume of 200 cubic inches of air from the lungs, collected by displacement of water in the gas holder, through another vessel of lime water of equal AND CHEMICAL PHYSICS, 85 en IS 111- Dii. The e change, into the ;s, and is rving not Df cai )n- the bcdy, ) compen- ; the same re of the i is given ng of ani- air, by the fe and the that life, r hours an >f air, con- id that he d gas con- i from the ». carbonic ion of this ^Ived from existing in by means bic inches, en passing r from the in the gas r of equal content to the former one. The relative amount of calcium carbonate precipitated will be a fair test of the amount of carbonic acid present in each case, but since in 200 cubic inches of air there will be, .mder ordinary circumstances, only about o*o8 cubic inch, and in the same quantity of air from the lungs between 7 and 8 cubic inches of carbonic acid gas a precipitate will practically be obtained in the latter case only. Oxygen imparts to the purplish venous blood, the bright red hue of arterial blood. Pure oxygen would act with too great energy upon the system causing in- flammation of the respiratory organs, and hence the necessity for it being diluted with nitrogen. The chlorophyl, or green colouring matter of plants has the power, in the presence of diffused sunlight, of decomposing carbonic acid, absorbing carbon to form vascular tissue, and setting oxygen at liberty, thereby performing a function the reverse of that of animals, and rendering the air, vitiated by admixture of car- bonic acid, once more fitted for the support of animal life. Plants, in a sitting room, tend accordingly to purify the air, but they are objectionable in a bedroom, since they can only decompose carbonic acid in dif- fused sunlight, whilst in the dark they appear to ab- sorb a small quantity of oxygen and to evolve carbonic acid ; and air containing as much as o*i per cent, of its volume of the latter gas is injurious to the human system, an amount equal to 0*5 per cent is positively dangerous, and 8 per cent produces suffocation. The carbonic acid gas of the atmosphere not merely sup- plies the plant, through its leaves, with carbon for its 'fi' %\ 86 ESSENTIALS OF CHEMISTRY growth, but, being washed down to the earth in rain, it acts chemically upon rocks containing alkalies, forming carbonates, and thereby assists in the disinte- gration of such rocks, supplying nutriment to the plant through its roots both in the form of carbon, and by solution of mineral matter such as phosphate of lime, which water alone would be unable to dissolve, and which the plant can only take up in the dissolved CHAPTER w'r.- [Ill i ill ill'! 1 ;i, |«, ' J if il NITROUS OXIDE^NITRIC OXIDE — NITRIC TRIOXIDE- NITRIC PEROXIDE. ,iX' - T15. Nitrous oxide, nitric monoxide or Laughing gas (N20=44. Density 4^*^=22). A colourless gas possessing a slight odour and sweetish taste ; does not burn ; suppoits combustion ; con- densible to a liquid by a pressure of about 36 atmos- pheres at O^C, has a peculiar intoxicating effect upon the human system, and is hence used in the liquid state as an anaesthetic^ sp. gravity 1.53. If nitrous oxide be shaken up with water, the latter ab- sorbs about three-fourths of its volume of the gas at the ordinary temperature ; or if phosphorus be burned ia this gas it liberates nitrogen equal in volume to the original gas ; either of these tests will serve to distin- guish nitrous oxide from oxygen. The liquid nitrous oxide solidifies at about — ioo°C.; and when the liquid is mingled with bisulphide of carbon, and evaporated m AND CHEMICAL PHYSICS. 87 th in rain, I alkalies, lie disinte- ) the plant n, and by ;e of lime, solve, and dissolved ••-"r RIOXIDE — .*jt* Dxide or = 22). A d sweetish ion ; con- 36 atmos- ting effect jed in the I-53- If latter ab- the gas at be burned Lime to the to disiifi" lid nitrous the liquid evaporated in vacuOy it produces the lowest temperature hitherto reached — i4o°C. Obtained by heating nitrate of am- monia (NH4NO3); nitrous oxide and water being li' . crated — NH4N03 = N20 + 2H2O. Since the gas is very soluble in cold water it must be collected by dis- placement of hot water. '116. Nitric oxide (NO =30 ; Density =^5^= 15). A colourless, tasteless, odourless gas ; does not bum ; supports combustion with great difficulty ; not con- densible to a liquid ; almost insoluble in water sp. gravity i '04 ; readily distinguished from all other g9,ses by the red fumes produced when brought in contact with free oxygen. It is thus, in turn, a delicate test for the presence of oxygen, even in minute quantity. The red fumes consist of nitric peroxide and nitric trioxide. Obtained by heating together, in a retort, nitric acid (HNO3) and copper turnings — 8HNO3 + 3 Cu= 2NO + 3Cu(N03)2 + 4H2O, nitric oxide is evolved and cupric nitrate and water remain in the retort. The student will note that there are generally marked traces of nitrous oxide present, in the nitric oxide prepared in this way. When charcoal is burned in nitric oxide the volume of the gas is not diminished, but it is found to contain equal volumes of carbonic acid gas and nitrogen — 2NO + C=C02 + Nj. There- Ifore one voluma of nitrogen is combined with one vol- ume of oxygen to form two volumes of nitric oxide, the formula of which must therefore be NO, and not N2O3 as formerly stated. 117. Nitric trioxide, or Anhydrous nitrous acid (NjO,). An unstable compound, of which N2O, !■ i 88 ESSENTIALS OF CHEMISTRY is the doubtful formula. A volatile blue liquid, ob- tained by mixing 4 vols, of dry nitric oxide (NO) with I vol. of dry oxygen, in a vessel surrounded by a freez- ing mixture, when condensation to the liquid state takes place ; said to exist in rain and well waters in combination with alkalies. 118. Nitric peroxide (N02=46). An orange coloured liquid, at the ordinary temperature, becom- ing deeper in colour as the temperature rises, and becoming nearly coloui less at o°C. Boils at 2i°C., forming a reddish-brown gas, which becomes darker in colour as the temperature rises, and which is capa- ble of supporting the combustion of substances which burn with energy ; oxidises many of the metals, and especially potassium, which spontaneously takes fire when introduced into it. It is supposed that fuming nitric acid owes much of its oxidising power to the presence of the peroxide in it. Nitric peroxide varies in density according to temperature ; at high temper- atures the density of the volume, as compared with hydrogen, is found to be 23, but at low temperatures the formula is supposed to be N2O4, giving a density of 46. Since at low temperatures it is a liquid, and at high temperatures a gas, the preferable molecu- lar formula is NO2. Obtained by heating plumbic nitrate — Pb (N03)2=:2N02 + PbO + O, nitric peroxide and oxygen are evolved, and plumbic oxide remains. AND CHEMICAL PHYSICS, So I liquid, ob- ; (NO) with d by a freez- liquid state II waters in An orange ure, becom- rises, and Is at 2i°C., ►mes darker lich is capa- mces which metals, and y takes fire that fuming ower to the axide varies igh temper- ipared with imperatures ig a density liquid, and e molecu- ing plumbic ric peroxide de remains. . V CHAPTER VI. - NITRIC PENTOXIDE — NITRIC ACID. 119. Nitric pentoxide, Anhydrous nitric acid (N2O5). An unstable solid, in the form of transparent, colourless crystals, which liquefy at about 3o°C. and boil at 45°C. It decomposes at a higher temperature, and it is said, when enclosed in a tube, to explode with violence. When brough*- in contact with water it dissolves, forming nitric acid (HNOs), — N205 + H20 = 2HN03. Obtained by passing a cur- rent of chlorine {_ - over argentic nitrate (AgNOs) : — 2AgN03 + Cl2=N2U5+2AgCl ; the nitric pentoxide evolved is condensed in a receiver, surrounded by a freezing mixture, and argentic chloride remains in the [retort* . 120. Nitric acid (HNO3). A colourless, trans- parent liquid, when pure and not exposed to sunlight; fuming when brought in contact with moist air, on account of the absorption of moisture by the vapour of the acid; sp. gravity of strongest acid (HNO3) ^ 'S^ ; sp. gravity of ordinary aquafortis 1*29, with only 46-6 [per cent, of HNO3 present ; sp. gravity of commer- cial nitric acid, or double aquafortis 142, with 67-6 per cent of HNO3. The strong acid solidifies at — 55°C., forming a butter-like mass ; boils at 86°C. ; stains the skin and most animal and vegetable sub- stances yellow, more especially if they contain nitro- gen. Nitric acid is a powerful oxidising pgent, and '11 90 ESSENTIALS OF CIIRMTSTRY : y\ readily attacks all common metals, with the exception of gold and platinum ; it is therefore used to distin- guish gold from the baser metals ; the usual way of doing this, by touching the surface of the substance to be tested with a glass rod, moistened with the acid, is however very inaccurate, as, if the substance be well plated with gold, the result will be the same as if it were entirely composed of gold ; a fine file ought ac- cordingly to be used to penetrate the outer surface, and the test acid may then be applied. Even the weight of the metal is no criterion, since bars of pla- tinum have been coated with gold. If a piece of red- hot charcoal be plunged in strong nitric acid, tl^e oxidation is energetic enough to support the combus- tion of the charcoal. Nitric acid is obtained (I) by heating, in a retort, equal weights of potassium nitrate, or saltpetre (KNO3) and sulphuric acid (H2SO4), — KN03 + H2S04=HN03 + HKS04, nitric acid is dis- tilled into a receiver, and pr^tassic bisulphate remains in the retort; an equal weight of sulphuric acid is used in the reaction, because a less quantity requires the application of a higher temperature, which causes sundry inconvenient results. (II.) More cheaply, on the large scale, by heating, in an iron retort lined with fire-clay, sodium nitrate, or Chili saltpetre (NaNOa), with half its weight of sulphuric acid, — 2NaN03+H2 S04= 2HN03 + Na2S04, nitric acid distils over, and sodium sulphate remains in the retort. This residuum of sodium sulphate is utilised in the manufacture of glass. \ e exception ;d to distin- isual way of e substance ith the acid, ince be well ;ame as if it le ought ac- iter surface, Even the bars of pla- piece of red- ic acid, the the combus- lined (I) by sium nitrate, acid is dis- ate remains uric acid is ity requires rhich causes cheaply, on t lined with e (NaNOs), ^aNOs+Ha s over, and is residuum lufacture of AJVD CHEMICAL PHYSICS. 91 CHAPTER VII. •. < ■1 -, -f ; [mMONIA — AMMONIUM — CARRE'S FREEZING MACHINE. 121. Ammonia (NHgrriy. Density =-V-= 8 's). colourless gas, possessing an acrid taste, and pungent lell ; burns in air with great difficulty with a livid ime, forming water and liberating nitrogen ; does )t support combustion ; readily turns red litmus paper lue, or yellow turmeric paper brown ; condenses to [liquid at a temperature of — 4o"'C., or under a pres- ire of six atmospheres at io°C.; the h'quid ammonia [lidifies at — 9o°C., or under a pressure of 20 atmos- leres at — 75°C. Ammonia dissolves freely in water, rming the liquor ammoniae or spirits of hartshorn of iggists ; at o°C., water dissolves 1050 times its vol. ;ammoniai at 59", 727 vols, and at 78°, 586 vols, le existence of ammonia in the free state and its iportant functions have been alluded to elsewhere (1^3). It is obtained experimentally by heating sal- apmoniac, or hydrochlorate of ammonia, with quick- #ie ; — 2(NH4Cl) + CaO = 2NH3 + CaCU + HjO, am- monia is evolved, and calcium chloride and water remain in the vessel employed ; another method of taining the gas is to heat a quantity of liquor am- niae in a retort, when ammonia will readily be [en off at a low temperature ; collected by upward )lacement, since its sp. gravity is only 0*590, and mnot be collected over water on account of its ubillty. The sal-ammoniac of commerce is pre- ii f'^ I- ' 92 ESSEI^TIALS OF CHEMISTRY pared from the ammoniacal liquor deposited in the preparation of coal gas ; this liquor is treated with hydrochloric acid, and the solution is evaporated, when crystals of impure sal ammoniac are formed,! these are subjected to further purification, which ter- minates in the formation of the fibrous substance isold as sal-ammoniac. The most delicate test for the pre- sence of ammonia, in solution, is that known as Ness- ler's test ; it is as follows : — saturate a solution of po- m tassic iodide (KI), with mercuric iodide (HgTj), and f add excess of caustic potash ; on this test being added ^ to a solution contaWfing ammonia a brownish yellov^ precipitate is at once formed — 2HgT2 + 3KHO -1- NH, = 3KI + 2H2O -t- NHgoI, H2O. Mercuric iodide, caus- tic potash and ammonia give potassic iodide, water, and tetra-mercurammonia iodide. So delicate is tliis 1 test that -rSuth grain of ammonia in half a pint of water gives a distinct precipitate. , ,: , 122. Ammonium, (NH4). The salts of ammonia are found to possess a great resemblance to those of potassium and sodium, and an amalgam of mercury, | potassium, and sodium, when moistened with ammo- nium chloride (NH^.Cl) swells out to eight or ninej times its original volume. This last formed amalgam- possesses a metallic brilliancy, and if its temperature | be lowered to — i8°C. it crystallizes in cakes. Hence, on account of these and other circumstances, it has been found convenient to assume the existence of a' hypothetical compound metal designated ammonium. For a somewhat similar reason Professor Graham has! suggested the existence of a metal, hydro^eniam, Thus,i v?r AND CHEMICAL PHYSICS. 93 posited in the s treated with % is evaporated, c are formed, ion, which ter- substance isold 2st for the pre- nown as Ness- jolution of po- le (HgTj), and^i St being added ownish yellov7 3KHO + NH3 ic iodide, caus- iodide, \vatej, ielicate is this half a pint of ts of ammonia ice to those of m of mercury, ;d with ammo- eight or nine 'med amalgam ts temperature :akes. Hence, stances, it has existence of a id ammonium, or Graham has geniwm. Thus, \] g ilvanic action, the metal palladium has been made absorb nearly one thousand times its volume of hy- [rogen without undergoing any change in its metallic laracter, such as would naturally be expected on its )mb' nation with a non-metal. Strong objections to le existence of this hypothetical metal are the facts lat all the hydrogen can be easily recovered on the )plication of a moderate degree of heat, and that ther substances besides palladium are known to be ipable of absorbing large quantities of gases without langs of property. The hydrogen liberated from illadium is found however to possess far more active )mbining properties than ordinary hydrogen ; uniting )ontaneously with atmospheric oxygen, and combin- |g with iodine atd chlorine in the dark. 123. When liquids assume the gaseous condition of latter, a considerable absorption of heat takes place, jhich heat is said to become latent (93). Matter, contact with the liquid during vaporisation, is conse- lently deprived of a portion of its heat, and, if self a liquid, it may even be solidified through this ^straction of heat. In M. Carre's freezing machine [vantage is taken of the vaporisation of liquid am- )nia and the ready solubility of ammonia gas in cold Iter, to produce a sufficient reduction of temperature solidify water. It has been seen (ir»i) that one )lume of water at o°C. is capable of dissolving 1050 )ls. of ammonia, but, as the temperature rises, this ssolving power is lost on account of the volatile iture of the gas. Ammonia gas is furthermore bable ot being liquefied under a pressure of about ^i 94 ESSENTIALS OF CHEMISTRY six atmospheres at io°C. Two gas tiglit upright cylin- ders, which nay be referred to as A and B, are connected by a gas-tight pipe ; cylinder A contains a strong solution of liquor ammoniae (121), and his an arrangement by which the solution may readily be heated ; cylinder B is externally of the same shape as A, but instead of its top being flat it is depressed, so as to form a deep conical vessel, open at its upper end, or base. When heat is applied to A, the am- monia is driven off from the solution and passes through the connecting pipe into B ; as the tempera- ture rises the pressure inside the vessels soon attains to six or seven atmospheres, when liquefaction of the gaseous ammonia takes place ; the hollow cone in- truding into B has meanwhile been filled with cold water, and on removing the source of heat from A, the consequent condensation of aqueous vapour, which speedily follows, reduces the pressure which is neces- sary for the continued liquefaction of the gas; evapora- tion therefore at once takes place, the liquid ammonia assumes the gaseous state, and repassing into A, is absorbed by its contained water once more, but during this evaporation so much heat is absorbed from the water in the conical vessel in B, through the metallic partition, that the water is frozen into a solid mass. ;-■ f ■ CHAFTLx< VIII CARBON — COAL. 124. Carbon (C = i2). An allotroplc substance, occurring in the crystallised, crystalline and amorphous AND CHEMICAL PHYSICS. 95 pright cylin- and B, are A contains 5i), and has vj readily be same shape iS depressed, I at its upper A, the am- i and passes the tempera- soon attains 'action of the low cone in- ed with cold heat from A, irapour, which hich is neces- gas; evapora- juid ammonia ig into A, is re, but during 3ed from the 1 the metallic solid mass. f^ )ic substance, id amorphous forms. As diamond, carbon crystallises in transparent octohedral forms of the cubical system, usually colour- less, but not necessarily so, insoluble in acids ; hard- ness TO*; sp. gravity 3*5 — 3*6; a non-conductor of electricity. As graphite, plumbago, or black-lead, carbon is crystalline, but sometimes crystal ises in six-sided plates of the rhombohedral system ; opaque ; black or dark gray ; insoluble in acids ; infusible ; hardness I'o — 20 ; sp. gravity i'8 — 2*1 ; a good con- ductor of electricity; used for the manufacture of lead-pencils ; and to coat gunpowder with a fine glaze, to exclude moisture. As charcoal, coke, and lamp- black, carbon is amorphous. Wood charcoa! is ob- ained by subjecting billets of hard wood to destructive istillation, that is, by expelling the volatile constitu- nts by the application of heat, out of contact with ir. Animal charcoal, known also as ivory black or ibone black, is obtained by beating bones in closed ^vessels, or by the calcination of blood. Coke is pre- ared by subjecting coal to destructive distillation in coke oven. Lamp-black is obtained by burning hydro-carbons, uch as turpentine, or tar, in a suppl) >f air insufficient or complete combustion. When mixed with soap and inseed-oil lamp-black forms printers' ink, or, mixed ith gum-water and compressed, it forms China-ink. If diamond be exposed to the very high tempera- ure resulting from the electric discharge between the erminals of a galvanic battery, in an atmosphere ncapable of acting chemically upon it, it swells up nd finally forms a spongy black mass resembling I .;i ' ■'I 96 ESSENTIALS OF CHEMISTRY graphite, and if a known quantity, say 12 parts by weight, of diamond, or of pure charcoal, be burned in oxygen, the same quantity of oxygen, 32 parts by weight, is required in either case for complete com- bustion, with the formation of 44 parts by weight of carbonic acid gas (CO2). The fact that diamond raised to a white heat and plunged into an atmosphere of oxygen slowly burns away, is a sufficient proof that it could not have been formed at a very high tem- perature. -^ ■ " Diamonds of a cheap description have been used with advantage as drill points in tunnelling through hard rock, as in the Mont Cenis tunnel; diamond dust is used for cutting and polishing diamond itself, other substances being too soft for the purpose ; the glazier's diamond is another exai. pie of practical use of the mineral. A genuine diamond is known by its extreme hardness, resisting the scratching power of any substance, and enabling it to scratch even the hardest steel ; by its high sp. gravity (3*53), and by its insolubility in hydrofluoric acid. The calorific value (95) of carbon is 8080, or in other words a grain of carbon combining with oxygen to form carbonic acid gas evolves heat sufficient to raise 8080 grains of water through i°C. Although carbon is an invariable constituent of organic substances, it does not, at ordi- , nary temperatures, enter fl'eely into combination with other elements ; and this explains the employment of black-lead to coat iron-work, not merely for the pur- pose of giving a polish, but especially to protect it from rust or oxidation; this is also the reason for Il / A^^D CHEMICAL PHYSICS, 97 parts by arned in parts by £te com- ^eight of nd raised iphere of roof that [ligh tera- een used r through diamond »nd itself, pose; the ctical use wn by its power of even the and by its rific value I grain of )onic acid grains of invariable )t, at ordi- ation with ovment of )r the pur- protect it eason for charring the extremity of stakes which have to be fixed in the ground ; the charcoal, on the imbedded surface retarding the oxidation, or decay of the wood. Charcoal possesses the remarkable property of con- densing large quantities of gases in its pores and on its surface. This condensation varies according to the gas; charcoal absorbing loo times its volume of ammonia ; 50 times its volume of sulphuretted hydro- gen, and 10 times its volume of oxygen. This ex- plains the deodorising and disinfectant properties of porous charcoal, for, the condensation of gases in the pores and on the surface being merely a mechani- cal and not a chemical operation, noxious gases or efBuvia from putrefying matter, being absorbed, come in contact with and are oxidised by the already con- densed oxygen derived from the atmosphere, thereby losing their offensive and injurious effects. In like manner water containing organic impurities is purified by filtration through porous charcoal. To exhi it either of the above mentioned properties satisfactorily the charcoal should have been recently heated to a red heat and then cooled under mercury. Charcoal respirators are constructed on the same principle, the inhaled air being rendered inodorous and innoxious [bypassing through powdered charcoal. The decolor- ising power of charcoal Is due to a modification of the same property, by which colouring matter in solution adheres to the surface of charcoal, when filtered through it, and it can be shown to have undergone [little chemical change, if any, by being washed from lie charcoal by the action of a weak alkali in sola- 93 ESSENTIALS OF CHEMISTRY tion. Since carbon cannot be obtained in the gaseous condition, its vapour density cannot be experimentally determined, but for reasons of analogy and theory, its atomic weight has been assumed to be 1 2. When carbon is burned in oxygen, the volume of carbonic acid produced is exactly equal to the volume of oxygen taken, so that carbonic acid contains its own volume of oxygen, j - . 125. Coal is vegetable matter, which, by exposure to considerable heat resulting from decomposition, under great superincumbent mineral pressure, has be- come carbonized to a greater or less degree. Geolo- gical research teaches and proves, that submergence of considerable tracts of land has been of frequent oc- currence ; some of these tracts have been covered with dense vegetation, the growth of many centuries ; after submergence, overlying deposits of sandstone or lime- stone have been made, and the evolution of heat caused by slow decompositioa would materially affect the whole character of the compressed vegetable mass. The gradual passage of wood into coal is exhibited in the following statement — wood consists of about 50 per cent, carbon, about 42 to 45 per cent, oxygen, the 1 rest being hydrogen and mineral matter, chiefly potash, silica, soda, lime and iron. Peat or turf contains 60 per cent, carbon, in addition to oxygen, hydrogen, nitrogen and ash. Lignite contains 50 to 70 per cent, carbon. " » Bituminous coal contains about 57 per cent. car-| bon ; about 37 6 volatile matter and 5 per cent. ash. St^am coal contains 81 to 85 per cent, carbon; n toj |! Aa^d chemical physics. 99 15 per cent, volatile matter, and about 3 per cent. ash. Anthracite contains 80 to 95 per cent, carbon, with very little ash, and still less volatile matter. Wood generally retains about 20 per cent, water, even when well dried ; one pound of green wood will evaporate about five pounds of water ; a pound of dry wood seven pounds ; and a pound of pure charcoal about fourteen pounds. One and a half cubic feet of turf weighing about 30 lbs. will evaporate about 340 lbs. water. The same volume of well dried wood, weigh- ing about 45 lbs., will evaporate 270 lbs. water. The same volume of lignite, weighing about no lbs., will evaporate 800 lbs. water. The some volume of oak charc(5al weighing about 12 lbs. will evaporate 150 lbs. water ; and the same volume of coal weighing about 100 lbs. will evaporate 1200 lbs. water. CHAPTER IX. CARBONIC OXIDE — CARBONIC DIOXIDE. 126. Carbonic oxide, or Carbon ^^^..loxide (CO = 28. Density=-2|^=i4). A colourless, tasteless gas possessing a faint odour \ does not support combus- tion ; burns with a fine blue flame, forming carbonic acid ; not condensible to a liquid ; almost insoluble in water; sp. gravity 0*967; very poisonous, one volume in 100 volumes of air, according to Leblanc, rendering the air unfit for the support of animal life This is the gas which affords the blue flame, ofteu 1'i M\ ./ 100 ESSENTIALS OF CHEMISTRY seen playing over the surface of a coal fire, or even over a fire of wood. The oxygen of the air entering the fire, at the lower part of the grate, or stove, com- bines with the heated carbon of the coal or wood, to form carbonic acid ; this passing through the fire, over red hot coals, is wholly or partially, according to the amount of oxygen entering the fire, decomposed into carbon monoxide: — C02 + C = 2CO, and this issuing at the surface of the fire and coming in con- tact with a certain amount of oxygen, takes fire and is wholly, or partially reconverted into carbonic acid. Carbonic oxide is accordingly a powerful reducing agent at a high temperature. It is obtained (i) by heating sulphuric acid with one third of its weight of oxalic acid (C2H2O4 + Aq) i—CoHgO^ + (Sulphuricacid) =CO + C02+H20; the sulphuric acid absorbs the water, and the mixed gases CO + CO2 are evolved ; by passing them through a wash bottle containing caustic potash the latter gas will be absorbed, and car- bonic oxide will be liberated ; v2) by heating sulphuric acid with one third its weight of formic acid (CH2O2) : — CH2O2 + (Sulphuric acid)=CO + H2O ; the watea: is absorbed as before by the sulphuric acid, and carbonic oxide is liberated j (3) by moderately heating sulphuric acid with one-fourth of its weight of potassium *erro- cyanide (K^FeCy^) :— K4FeC6Ne + 6H2O -t- CHaSO^^e CO -H 2K2SO4 -f- 3[(NH4)2S04] -H FeSO*. Carbonic ox- ide is evolved, and potassium sulphate, ammonium sulphate, and ferric sulphate are left m the retort. Carbonic oxide is liberated abundantly in the opera- tions of the lime kiln and brick kiln. When one AND CHEMICAL PHYSICS, loi e, or even ,ir entering tove, com- r wood, to I the fire, :cordiDg to scomposed and this ng in con- 3 fire and is Donic acid. 1 reducing led (i) by s weight of phuricacld) ibsorbs the evolved ; by ling caustic 3, and car- ig sulphuric d (CH A) •• the watea: is id carbonic ig sulphuric ssium ^erro- 6H2S04=6 arbonic ox- ammonium the retort, the opera- When one volume of carbonic acid (CO2), containing its own volume of oxygen, is passed over red hot coke, it yields two volumes of carbonic oxide (CO), hence one volume of this gas contains half its volume of oxygen. . . 127. Carbonic acid gas, or Carbon dioxide (C02=44. Density=**-=22). A colourless gas, pos- sessing a pungent odour, and sharp taste ; does not support combustion under ordinary circumstances, although such substances as potassium, sodium, or carbon, sufficiently heated and plunged into carbon dioxide, deprive it of its oxygen, wholly, or partially ; sp. gravity 1*529 ; condensible to a liquid, under a pressure of about 36 atmospheres at o°C., and this liquid has the remarkable property of expanding more for equal increments of heat than the gaseous form of carbon dioxide. Water dissolves its own bulk of the gas at ordinary temperatures. It exists in the free state in the atmosphere, and escapes from the earth, and from effervescing springs, in many locaUties ; as at the famous Grotto del Cane, near Naples ; the Seltzer Spring, and the spring at Nauheim, which is said to liberate 1,000,000 lbs. of the gas annually; it is the common product of fermentation, and hence the danger arising from incautiously entering brewery vats, too soon after the liquid has been drawn off; and, since the gas readily collects at the bottom of wells where the air is very still, workmen should not descend into such places, before testing the purity of the air, with a lighted candle. Obtained (i) by the action of dilute hydrochloric acid upon pow- 102 ESSENTIALS OF CHEMISTRY dered marble, limestone or chalk :^— CaCOs + 2HCl = C02 + CaCl2 + H20 ; carbonic acid gas is evolved, and calcium chloride and water are left in the generating vessel; in this reaction there is frequently a little arsenic present, due to the impurity of the hydrochloric acid; if therefore the carbon dioxide be required pure, the second method had better be adopted : (2) by the action of dilute sul- phuric acid upon powdered marble, limestone, or chalk :— CaCOjj + H2SO4 = CO2 + CaSO* + HjO ; car- bonic acid gas is evolved, and calcium sulphate and water remain behind. Carbonic acid gas does not support animal life, since on being inhaled into the lungs it prevents the liberation, by exosmosis, of the carbonic acid gas formed in the blood, and also the passage, by endosmosis, of oxygen to the blood, for the performance of the necessary functions of circulation. Even in limited quantity, however, it affects the con- ditions of animal life injuriously, and hence the necessity of ventilation ; for it is not merely the excess, but the presence of carbon dioxide that must be guarded against, so far as is possible. Taken into the stomach, however, it is not merely harmless but grateful, since the thirst-quenching properties of many beverages, not excepting water, seem to be largely due to the presence of this gas in solution. All effervescing liquors owe this property to the dissolved carbon dioxide, which is either generated by the action of re-agents, or is compressed into the liquid by mechanical means. Carbon dioxide is the choke- damp> or, after-damp of the coal mines, since it is AND CHEMICAL PHYSICS, X03 one of the resultants of the explosion of fire-damp (CH4). It is often referred to also as fixed air. In malting, brewing, etc., and all processes m which fermentation takos part this gas is constantly evolved. Since fermentation is simply the generation and evolution of carbonic acid gas, by a process of inci- pient putrefaction promoted by the growth of fungoid vegetation : in bread-making, this process is induced by the addition of yeast, which is a mass of minute fungi, in order to cause fermentation in the dough, or in other words to generate carbonic acid gas, for the purpose of imparting a wholesome porosity, or spongi* ness to the bread. The rising oi bread then is simply due to the evolution of carbonic acid gas as follows : — Wheaten flour consists largely of starch, gluten, dextrine and sugar ; and when flour is moistened the sugar ferments, this fermentation being much accelerated by the addition of a little yeast, and the sugar is converted into alcohol and carbonic acid gas ; — the evolved gas escapes through the dough, perforating it. and honey-combing it with little cells in all directions, thereby much increasing its bulk, or causing it to rise. When the bread is heated in the oven, the alcohol is driven off, and the contained carbonic acid gas is greatly expanded, causing an equal degree of expansion in the bread, by increasing its porosity. In making what is called aerated bread, carbonic acid gas is directly supplied, by mixing the flour with water highly charged with the gr.s under pressure ; or the same result is attained by mixing the flour with sodium bicarbonate (HNaCOa), and ill 104 ESSENTIALS OF CHEMISTRY then forming the dough by the addition of water slightly acidulated with muriatic acid (HCl), chloride of sodium (common salt) is formed, and carbonic acid gas is evolved. When the liquid carbonic acid is allowed to evaporate in the aii, it does so with such rapidity, and with absorption of so much heat^ that a portion of the liquid is solidified, having a tem.perature of about — 87°C. When this solid is mixed with ether and mercury, th€ mercury is at once frozen into - a solid mass, and intense cold is caused by the rapid evaporation of the ether and the liquetied acid. This cold is estimated to reach — ioi°C. To dis- tinguish carbonic acid gas, the following test may be employed : — dissolve a little slaked lime in distilled water, and afterwards filter off the clear solution free from all sediment ; kept carefully stop- pered up, there will be no change in the solution ; but if a portion be poured into a vessel containing carbon dioxide, a white precipitate will be at once observed, due to the formation of calcium carbonate : — CaH202 -f C02-CaC03 + H20. Carbonic acid gas can be separated from other gases, by passing the mix- ture through a solution of caustic potash, which readily absorbs carbonic acid. Blue litmus paper dipped into dry carbon dioxide is not affected, but in presence of moist air, or when the paper is wet, a true acid (H2 CO3) is apparently formed, and the paper is reddened accordingly. If the red paper be now boiled in water^* the gas is driven off by the heat, and the litmus re- gains its blue colour. The hydrate (H2CO3), if existent, is unstable, and has not been obtained in a separate AND CHEMICAL PHYSICS, 105 ^ving of water ), chloride I carbonic bonic acid with such leatj that a ^mperature . with ether rozen into ed by the letied acid. To dis- test aked lime f the clear bfully stop- lution j but ing carbon i observed, :— CaH202 ?as can be \g the mix- ich readily lipped into presence of e acid (H2 s reddened jd in water^* litmus re- if existent, a separate stale ; but its existence is probable, since the dry gas produces no acid effects without the addition of water, and does not combine even with lime, unless the latter compound be considerably heated. The compounds of carbonic acid are called carbonates, and many of these, as — carbonate of soda (NaaCOa), carbonate of potash (K2CO3), carbonate of iron (FeCOs), and car- bonate of lime, chalk, or marble (CaCOa), are of the utmost importance either in the arts, or in the econo. my of nature. Tlie composition of carbon dioxide can be shewn, by passing the dry gas over a pellet of pot- assium heated in a bulb tube, the potassium combines with the oxygen of the gas, and the carbon is deposited as a black mass ; another portion of the gas combines with the potassic oxide to form carbonate of potassium, which is deposited as a white powaer : — 3CO2 + K4- 2(K2C03) + C. ' ■ - CHAPTER X. {. .. .. ■ -■ f - - ■ ' - • - -'■ " '■ ■ MARSH JAS — -OLEFIANT GAS — ACETYLENE — COAL GAS 128. Light Carburetted Hydrogen, Methyl Hydride, Marsh Gas, or Fire-damp (CH4=i6. Density = -»^ = 8). A colourless, tasteless, scentless gas ; does not support combustion ; burns with a pale, luminous flame ; not condensible to the liquid condi- tion; sp. gravity 0-557 ; very slightly soluble in water. Obtained artificially (i) by heating sodium acetate (NaC2H302) with caustic soda (HNaO) in a copper tube, for the alkali le-acts upon glass : — NaC2H502 + ^1 H m loS ESSENTIALS OF CHEMTSTRY HNaO — CH^ + NaaCOa; marsh gas is evolved, and sodium carbonate remains in the tube; (2) by heating potassium acetate (KC2H3O2) with caustic potash (H KO) :— KQH3O2 + HKO-CH, + K2CO3. As before marsh gas is evolved, and potassium carbonate re- mains. In practice, a quantity of quick lime is always added to the mixture, to the extent of about three- tenths of the whole. Marsh gas occurs free in nature, issuing from the earlh in many localities ; it is pio- duced by the decay of vegetable matter, hence the name — marsh gas ; it is commonly found in many coal pits, into the workings of which it enters by fissures, often with a singing or hissing sound, which has given rise to the miners' term *' blowers" ; it often accumu- lates to a dangerous extent in the upper part or " goaf" of deserted workings , and it is no unusual matter, in some coal pits, for the miners' candles to be surrounded by a livid blue flame, called by the miners themselves " corpse lights," the evidence of a dangerous accumu- lation of fire-damp. When mingled with the oxygen of the air, the fire-damp, as it is called, forms a most explosive compound, and hence it is a source of the greatest danger to the coal-miner. Since one mole- cule, CH4, occupies two volumes, and 12 parts by weight of carbon require 32 parts by weight of oxygen, and 4 parts by weight of hydrogen also require 32 parts by weight of oxygen for complete combustion, and the density of CH4 being -]f=8, of which 6 parts by weight must be carbon, and 2 parts by weight must be hydrogen, it follows that one volume of marsh gas will require two volumes of oxygen weighing 16 + 16 for complete combustion. But one volume of air AND CHEMICAL PTIY61CS. tor ! Wl contains only one-fifth of a volume of oxygen, therefore it will require ten volumes of air to supply two volumes of oxygen. When, therefore, fire-damp is mixed with air in the proportion of one volume to ten volumes, the mixture will be at its most explosive point, and on coming in contact with a flame an explosion of tre- mendous force follows, exerting a pressure of no less than 14 atmospheres, or 204 lbs. on the square inch. Were it not for the presence of the liberated nitrogen, it is calculated that the pressure would be not less than 37 atmosphere's, or about 540 lbs. on the square inch. The molecule CH4 combines with the oxygen of the air to form water (2H2O) and carbonic acid gas (CO2); and the formation of the latter gas adds to the danger resultinej from the explosion, since, by its weight, it finds its way into lower levels, suffocating those who may have escaped the immediate effects of the explo- sion, hence its name of "choke-damp," or ** after- damp.'* It would evidently be impossible for the miners to work in a pit liable to such explosions, if no means of moderating the danger existed; but this means is provided by the invention of the Davy Safety Lamp (133). 129. Heavy Carburetted Hydrogen, Ethy- lene, Bi-carburetted Hydrogen, or Olefiant Gas (C2H4=28. Density=-^=i4). A colourless, tasteless gas, which acts as a dyad radical ; possesses a faint odour of ether ; does not support combustion ; burns with a bright yellow flame ; condensible to a liquid under a pressure of about 5 atmospheres at — 76°C., or under 27 atmospheres at — i6°C. ; sp. gravity ■M u io3 ESSENTIALS OF CHEMISTRY o'9784 ; insoluble in water. Derives the name defiant gas from its property of combining with its own volume of chlorine, or with bromine, to form oily liquids. The combination v;ith chlorine — (C2H4CI2) is commonly known as '* Dutch liquid." Obtained by gently heat- ing concentrated sulphuric acid with alcohol (C2H6O), in the proportion of two parts by measure of the for- mer to one of the latter : — Q^^O + (sulphuric acid)= C2H4+H2O j the sulphuric acid absorbs the elements of water, and thereby liberates the gaseous ethylene. In this experiment the re-agents must be mixed toge- ther very gradually, and the delivery tube ought to be removed from the water as soon as the gas begins to come off slowly. Three ounces by measure of alcohol will give about 500 cubic inches of the gas. It is readily decomposed at high temperature into CH4, C2 Ha, and H. One volume of olefiant gas requires for its complete combustion three volumes of oxygen, forming carbonic acid and water. ^ ' * 130. Acetylene (C2H2=26. Density =2/= 13). A colourless, tasteless gas, possessing a faint odour } does not support combustion; burns with a bright smoky flame; not condensible to a liquid; slightly soluble in water; sp. gravity 0*92. When passed into animoniacal solutions containing copper or silver, acetylene combines with these metals, forming acety- lides, which, when dry, are very explosive, on the application of heat. It inflames with explosion, jvhen brought in contact with chlorine, with the formation of hydrochloric acid, and the liberation of carbon : — C2H2 + Cl2=Ca + 2HCl On the application of heat AND CHEMICAL PHYSICS. 109 to acetylene, it gradually assumes the forms of much more complex hydrocarbons. Acetylene is a constant constituent of coal-g;is, and is a product also of incom- plete combustion. It may be obtained in small quan- tity by passing an electrical discharge between two carbon points in an atmosphere of hydrogen ; in larger quantity, it is prepared by acting upon cuprous acety- lide with hydrochloric acid ; it is said also to be formed when the vapour of Dutch liquid is passed through a red hot tube. It produces a bright red precipitate when passed into an ammoniacal solution of cuprous chloride (CU2CI2). • - - - •- ^ . . • , . 131. Coal-gas is a mechanical mixture of a num- ber of volatile hydrocarbons, and the elementary gases hydrogen, oxygen and nitrogen. It is obtained by de- structive distillation of cannel coal in iron retorts, grouped five or six together, in a horizontal position. The gaseous matter expelled by heat passes from the retorts into a large pipe, partially filled with water, called the "hydraulic main," and from this into a piece of apparatus filled v/ith water, called the ** con- denser," in which the gas rids itself of the tar, oil and most of the ammonia with which it has hitherto been mixed ; the gas now passes into the " scrubber," con- taining fragments of wet coke, which take up a, further portion of ammonia; and thence into the *' lime-puri- fier," where the carbonic acid gas and sulphuretted hydrogen are absorbed by lime ; by now passing the gas through dilute sulphuric acid all the remaining ammonia is got rid of, and the purified coal gas is stored up over water in a reservoir called a gasometer. } rfl t - ^11 i)":! ■ M :i % :1 II no ESSENTIALS OF CHEMISTRY The essential illuminating constituents of coal-gas are marsh-gas, defiant gas, acetylene, carbonic oxide, benzole vapour and hydrogen. It is of the utmost importance that sulphuretted hydrogen should be removed from coal-gas, for, by combustion, it forms sulphuric acid, which is most injurious to hangings, pictures, furniture, books, etc. The tar and the am- moniacal water, in the hydraulic main and the con- denser, are drawn off, and may be subjected to a variety of processes, resulting in the extraction of many important curjpounds, as — sal-ammoniac and aniline. The value of the illuminating power of coal- gas is determined by the aid of an instrument called a photometer, and by comparison with a spermaceti candle burning 120 grains per hour; the gas, mean- while, burning at the rate of five cubic feet per hour. CHAPTER XI. FLAME — DAVY LAMP — KEMMING'S JET. 132. Flame is caused by oxidation, or other che- mical combination of gaseous matter, but luminous flame is commonly due to the presence of carbon in a finely divided state, and its maintenance at a white heat, by the heat evolved in the oxidation of the ac- companying gas, or gases. It has however been proved by Dr. Frankland, that luminous flames may be pro- duced by increase of pressure alone, in the case of flames that are non-luminous at the ordinary pressure AND CHEMICAL PHYSICS. Ill of the atmosphere, and when solid matter is not pre- sent, as in the cases of oxygen and hydrogen, hydro- gen and chlorine. As the ordinary materials for the production of artificial light: — tallow, wax, oil, alcohol, coal-gas, etc., are all hydro-carboiis, that is, are compounds of hydrogen and carbon united together in various proportions, there is no reason to doubt that in these cases the luminosity is chiefly, if not entirely, due to the presence of the carbonaceous par- ticles in a state of incandescence. This statement may be illustrated and proved by the two following experiments : — (i) Prepare hydrogen in a Woulfe's bottle (loS) from zinc and sulphuric acid, dry and ignite the gas, place near the bottle a lighted candle, and fix a glass tube of small calibre, so that one end dips into the luminous portion of the candle flame, and the other end just enters the hydrogen flame, the latter will be observed to become luminous through admixture with the particles of carbon drawn off from the candle flame, and which are now raised to a white heat by the heat of the oxidised hydrogen. (2) Re- move the glass tube and to the mixture in the Woulfe's botde add cautiously a few drops of benzine (CgHg), gently shake the contents of the bottle, and in a min- ute or two the hydrogen flame will be seen to become brilliantly luminous, because of the addition of the hydro-carbon. As a variation of the last experiment, the following one may be performed to exhibit the luminosity caused by the presence of solid matter : — pass hydrogen through a botde in which have been placed a few drops of chlorochromic acid (CrOaCla), I 1T3 ESSENTIALS OF CHEMISTRY the vapour of which will so charge the gas, that, on the latter being ignited, it will burn with a briUiant white light, due to the presence of chromium, which is deposited on a cold plate as sesquioxide of chro- mium. A candle flame, or that of an ordinary gas jet, is a hollow cone, as may be shown by neatly pressing down on the former a sheet of white note paper, the resulting soot stain is confined to a circular ring, and not distributed over a circular area. An ordinary flame may be considered as displaying three distinct parts or areas, viz.: — (i) An internal area of non- combustion ; (2) an intermediate area of incom- plete combustion, which is the luminous portion of the flame ; (3) an external are of complete com- bustion, in which every portion of the hydrocarbons unites freely with the oxygen of the atmosphere. The internal area is really colourless, although it usually has a bluish appearance, because it is surrounded by a thin envelope of gas in a state of incomplete com- bustion. That it contains free gas is shown by dip- ping into it one end of a tube of small calibre, and applying a light at the other end ; a minute flame will be observed, due to the uncombined gas drawn off. In the intermediate area, the hydrogen combines freely with the oxygen of the atmosphere to form water, caus- ing great heat, which serves to raise the particles of carbon to a white heat. In the external area, the oxygen is sufficiently abundant to combine, not merely with the hydrogen, but with all the carbon present, forming carbonic acid gas. When coal-oil is burning with an insufficient supply of oxygen, acetylene (C2H2) II AND CHEMICAL PHYSICS, 113 is formed, in ?ddition to water and carbonic acid, and to this is partially due the offensive smell emitted under such circumstances. In chemical operations it is gienerally necessary to have a siisokeless flame, and to obtain this, and at the same time the greatest pos- sible amount of heat, means must be adopted to cause, as nearly as possible, complete combustion of the hydro-carbons employed. For this purpose advantage is taken of the Bunsen jet, which consists of a tube of a few inches in height, and of half an inch or more in width, fixed on an iron foot, or stand ; into this tube coal-gas is conducted by means of a horizontal tube inserted at its base, and this gas rises up into the tube through a flattened nib or nozzle of about an inch in height. On either side of the base are two to four apertures for the admission of air, but which may be closed or opened at will. When open, air enters, and rising through the tube along with the gas, the latter becomes permeated with oxygen, and on being ignited at the mouth of the tube it burns with an almost colour- less flame, giving off intense heat ; when the apertures are shut a jet of gas alone ascends, and a dimly-lum- inous flaring flame, principally of incomplete combus- tion, is the result. The second and third areas of flame become of importance in blowpipe analysis, as each subserves a different function. Thus, since in the second area, or that of incomplete combustion, there is a deficiency of oxygen, if a metallic oxide be I exposed before the blowpipe to the action of this inner flame, the oxide will be deprived of its oxygen and be reduced to the metallic state ; hence this ^Ti : 1li;|" i ;i'" '! IJ4 ESSENTIALS OF CHEMISTRY intermediate area is technically known as the " inner," ,or "reducing" flame; but since, in the external area, or that of complete combustion, there is a superabund- ance of oxygen and t..e heat is intense, if metals be exposed before the blowpipe to the action of this outer flame, in most' cases the metals combine with oxygen or are oxidised, and hence this external area is technically known as the " outer," or " oxidising " flame. "^.^.ii*:: '^ .-'//-^ • . " -; ," :-}-i: ■•.■.:' 133- The explosive nature of a mixture of marsh gas and air has been referred to elsewhere (128), and the frequent occjrrence of this dangerous mixture in coal mines induced Sir Humphrey Davy to devise a safety-lamp for the use of coal miners. This lamp is simply a common oil lamp surrounded by a closed cylinder of wire-gauze, This gauze, con- taining about 600 to 800 meshes in the square inch, readily permits of air or gases passing into the lamp, but does not permit of flame passing outwards, be- cause flame requires a high temperature to exist as such, and the copper or iron, of the wire gauze, being a good conductor of heat, the temperature of the flame is reduced so rapidly by contact with it, that the flame ceases to exist as such, and cannot ignite the explosive mixture, although in almost immediate contact with it. There are probably two important sources of danger in the use of thlfe lamp — the fact that if the explosive gas be abundant, the heat of combustion in the lamp may become • so great as to cause the wire itself to take fire, when of course an explosion will follow ; or, a current of air, or sudden IP Aj;s'D CHEMICAL PHYSICS, ns movement of the miner may possibly force the flame through the gauze by mechanical force, in which case also explosion will result. The Davy lamp gives a very dim light, and hence the great objection of the miner to its use ; in practice it is only used, in most cases, to test the comparative purity of the air in coal pits before the miners descend to their labour; but* this makes no provision for the danger arising from the sudden opening of " blowers," or the sudden es- cape of the fire-damp from "goafs" (128). Experi- ments to prove that flame does not pass through wire gauze of sufficient fineness : — (i) Hold a piece of wire gauze, about 8 inches square, over a wide beaker; pour alcohol into a large iron spoon or ladle, ignite it, and then pour through the gauze into the beaker ; the alcohol will pass through, while the flame will be extinguished on the surface. (2) Take the same piece of wire gauze and depress it upon a strong jet of coal gas in a state of ignition ; the gauze will be found to depress the flame in the same manner that a solid plate would do. (3) Extinguish the jet of gas used in the last experiment, place the gauze two or three inches above the nozzle, and apply a light above the gauze ; the gas will burn above but not below the gauze, and by raising it, the flame will likewise be raised, or even entirely removed. 134. Hemming's Jet is employed in the combi- nation of hydrogen and oxygen, in using the oxy- hydrogen blowpipe, or the DrUmmond light. It consists of a heavy brass tube of a few inches in length, and about half an inch internal diameter ; into ii^^ r I. 'Ill I II6< ESSENTIALS OF CHEMISTRY tills tube is closely packed a number of fine copper or brass wires, and either end is closed with a piece of copper-wire gauze, with not less than 800 meshes to the square inch ; on one end* of the tube is screwed a head bearing a brass nozzle at right angles lo the main tube, and on the other end is screwed a termi- nal piece by which the jet may be attached to tubing conducting the mixed gases from the gas-hoider, or gas-bag. On the mixed gases issuing from the nozzle being ignited, it is almost impossible that the flame can pass back through the pipe to the gas-holder, because the wire gauze prevents the flame passing through by depriving it of the heat necessary for its existence as flame, and this deprivation is rendered still more certain by the presence of the wires in the tube, and the very narrow interstices between them. .* :- ^■; .■ •\^r^ ■, Vi CHAPTER XII. CARBOLIC ACID— OXALIC ACID. 135. Carbolic acid (CeHgOa). A compound, of doubtful acid properties ; when pure, crystallizes in long, transparent, prismatic needles ; sp. gravity i'o65 ; melts at 34°C. and boils at iSy^C. ; the crystals dis- solve in about twenty-five times their bulk of water, and are soluble in alcohol and ether; possesses a pleasant odour ; does not, either in the pure or dis- solved condition, redden litmus paper. Commercial carbolic acid is a mixture of carbolic acid, cresylic AND CHEMICAL PHYSICS, 117 acid, hydro- carbons, etc., and its unpleasant odour is due to the presence, in minute quantity, of sulphur compounds. It is a powerful antiseptic, and has been employed to preserve wood from decay. Obtain^^d from one of the oils of coal-tar, called the " heavy oil," by treatment with caustic potash ; the resultant precipitate is partially re-dissolved, yielding potassium carbolate, which is treated with hydrochloric acid, the carbolic acid separating itself and floating on the sur- face of the solution. A piece of deal moistened first with carbolic acid and afterwards with hydrochloric acid becomes blue on drying. 136. Oxalic acid (C2H2O4 + 2Aq.), only known as a hydrate ; obtained in prismatic crystals, which dis- solve readily in warm water, forming a powerful acid ; melts at about ioo°C. ; sublimes at about i6o°C. ; when heated above this point it is decomposed, form- ing carbonic acid, carbonic oxide, and water (126). Oxalic acid is very poisonous; alkalme oxalates are moderately soluble in water, but others are msoluble. Obtained by heating sawdust with one part caustic potash and two parts caustic soda ; these components are mixed into a paste, which is then maintained at a moderate temperature for some hours ; the sawdust is gradually changed into oxalic acid, which combines with the soda to form sodium oxalate, a substance almost insoluble in cold water and hence easily sepa- rated from the othar components of the heated mass ; this first formed oxalate is now boiled with hydrate of lime (CaO, H2O), and insoluble calcium oxalate and caustic soda are formed — Na2C204-» CaC), H„0 = Ca i ii8 ESSENTIALS OF CHEMISTRY C2O4+ 2(NaH0); this second oxalate is now acted upon with dilute sulphuric acid, when sulphate ot lime is precipitated and crystals of oxalic acid are obtained by evaporating the solution — {CaCaO^ + 112804=; HjCj O^ + CaSO^). Sawdust yields about one-half its weight of the acid. The alkalies employed are recovered for further use. Oxalic acid may also be obtained by heating starch with nitric acid ; — nitric trioxide is evolved, and on the solution being evaporated, crys- tals of oxalic acid are obtained. Strictly speaking, this is a vegetable acid, but it is also found in ani- mal matter under certain abnormal conditions. It is largely used in calico printing, and in cleaning lea- ther and brass. In weak solution it removes ink stains. CHAPTER XIII. •^i■ vm CHLORINE— CHLORIC ACJD. .■ .■ - v"-' 137. Chlorine (CI = ZS'S\ A greenish yellow gas possessing a suffocating odour and acrid taste ; does not burn, and does not support combustion, but cer- tain metals, such as antimony or iron in a finely divided state, take fire when dropped into a jar of chlorine with the evolution of light and heat ', con- densible to a yellow liquid of sp. gravicy 1*33 under pressure of 4 atmospheres, at i5*5^€; sp. gravity 2*47; soluble in half its volume of water, forming chlorine water ; does not occur in the free state in nature, but forms important and abundant compou-^.ds, as AND CHEMICAL PnVSTCS. 119 sodium chloride or common salt, and potassium- chloride; obtained by heating common salt (NaCI) with manganese di-oxide and sulphuric acid — 2NaCl + Mn02+ 2H2SO*=Cl:i+ Na2S04+ MnSO^ + 2H2O, chlorine is evolved and manganese sulphate, sodium sulphate and water remain. A readier method of preparing chlorine is by heating hydrochloric acid and manganese di-oxide together — Mn02 + 4HC1= Clo + MnCi2+ 2H2O, chlorine is evolved, and man- ganese chloride and water remain. Collected by downward displacement of air. Deacon's process for the preparation of chlorine, on a large scale, for the manufacture of bleaching powder, is also now adopted ; it is as follows : — Air and hydrochloric acid gas are passed over heated fiie- brick, saturated with a solution of copper sulphate, water is formed and chlorine and nitrogen are liberated— 2 HC1+ air(N4 + 0)=H20 + Cl2 — N4, the presence of' the nitrogen does not ihterfere with the utility of the chlorine. By Weidon's method the chlorine combining with the metal manganese, in the second reaction, described above, is obtained in union with calcium, and the manganese is recovered for employn^nt in the de- composition of a fresh quantity of hydrochloric acid. The manganese chloride is decomposed by the addi- tion of lime : — MnCl2 + CaO=CaCl2 + MnO, calcium chloride and manganese protoxide are formed ; and 1 by the addition of more lime and under the influence J of a strong current of air, the manganese is further oxidised forming the dioxide (MnOg). Chlorine has a great afinity for hydrogen, even decomposing water I'll 1 20 ESSENTIALS OF CHEMISTRY , I to combine with it, and thereby acting indirectly as a powerful oxidising agent, and, in consequence, as an equally powerful bleaching agent. Dry chlorine possesses no bleaching properties, but the addition of water at once causes the destruction of vegetable colours with which it comes in contact. Equal volumes of chlorine and hydrogen mixed and kept ifi the dark, will not combine, but, in the presence of diffused sunlight, slow combination takes place, and, in direct sunlight, or in the presence of the magne- sium light, there is sudden combination with explo- sion, and the formation of hydrochloric acid (HCl). Most hydrogen compounds, such as ammonia, are decomposed by chlorine, often with violence. Chlo- rine also combines spontaneously with most of the metals, and among the non-metals with — bromine, iodine, sulphur, sele/iium, phosphorus and arsenic, forming chlorides. It is largely used in a combined state for the bleaching of linen and cotton articles, but it acts injuriously upon woollen, silk and straw fabrics. • . 138. Chloric acid (HClOs). A yellowish liquid possessing a strong odour ; a powerful bleaching and oxidising agent, one drop being sufficient to ignite paper, and it oxidises even the amorphous variety of phosphorus with explosive violence. Obtained by acting upon a solution of chlorate of potash (KCiOa) with hydrofluosilicic acid ( (HF)2SiF4) : — 2KCIO3 + (HF)2SiF4=2HC103 + (KF)2SiF4, insoluble potassium silicofluoride is formed, and on separating and evapo- rating the solution at a temperature below 38°C, AND CHEMICAL PHYSICS, 121 chloric acid remains. It forms important salts called chlorates, such as barium chlorate (BaClOs), much used in the manufacture of fire-woiks to produce a. brilliant green light. " " Chlorate of potash (KClOs) is useful as a source of oxygen, in calico printing, in the manufacture of luoifer matches, fire-works and percussion caps. When reduced to a powder by itself no explosive action takes place, but if mixed and powdered with any combustible substance, such as sulphur, a violent explosion follows. Obtained by passing excess of chlorine through caustic potash: — 6(KHO + Cl6=K CIO3+ 5KCI + 3H2O ; with formation of potassium chloride and water. Crystallizes in six-sided plates, which are permanent in air, and soluble in water. ■ I > CHAPTER XIV. HYDROCHLORIC ACID. .; ,\ 139. Hydrochloric acid (HCl=36-5. Density ^i|ia.=: 18-25). ^ colourless gas possessing a suffo- cating odour, fuming on exposure to air by causing condensation of its mpisture ; sp. gravity i '24 ; does not burn ; does not support ordinary combustion, but heated potassium burns in it ; condensible to a liquid under a pressure of 40 atmospheres, at io°C. ; it is readily absorbed by water, one volume of water at 5°C. dissolving as much as 480 volumes of the gas and forming i \ volume of the solution, of sp. grav • ,1 !l All ^.r lit 123 ESSENTIALS OF CHEMISTRY 1*21, and containing 43 per cent, by weight of the gas. This solution is the strongest muriatic acid, or spirit of salt of commerce. Ordinary hydrochloric acid is usually very impure, hence its yellow colour. Liquefied hydrochloric acid has a very weak action upon metals, and only partially changes the colour of litmus, while the solution has powerful acid properties. Hydrochloric acid is most destructive to vegetation, and this effect is probably due to it= affinity for the water contained in growing plants. Obtained by the action of sulphuric acid upon common salt (NaCl) : — 2NaCl -f H2S04= 2HCi + NaaSO*. Hydrochloric acid is evolved and sodium sulphate remains as a solid. This gas is liberated from volcanoes, and is found in springs and rivers of volcanic districts ; it is also arti- ficially formed wiif^n chlorine and hydrogen are ex- posed t6 sunlight. Its composition may be shewn by passing into a tube, over mercury, a measured volume of the gas, and then passing up through the mercury a pellet of sodium ; the mercury will gradually rise and finally the gas will be found to be diminished by one-half its previous volume, through combination of the chlorine of the gas with the sodium — Na-f HC1= NaCl + H. - , . , 140. Although hydrochloric acid does not attack gold by itself, when mixed with nitric acid (HNO3) in the proportion of three parts by measure of the former to one part by measure of the latter «acid, it forms the so-called aqua regia, or nitro-muriatic acid, which is capable of dissolving both gold and plati- num, forming terchloride of gold (AuClj)i and terras chloride of platinum (PtCl^). ' > AND CHEMICAL PHYSICS. 123 141. Bleaching powder appears to be a mechan- ical mixture of two chemical compounds — calcium hypochlorite (CaClaOa) and calcium oxychloride (Ca CI2, 2CaO). It is prepared by passing chlorine gas into large vessels, or chambers, containing shelves upon which is spread slaked lime (CaO, HjO) ; — 4 (CaO, H2O) + Cl4=(CaCl202 + CaCls, 2CaO) + 4H2O. When the bleaching powder is to be used, it is mixed with water, and the calcium hypochlorite (CaClgOa) and calcium chloride (CaCl2) are dissolved, while the insoluble lime is precipitated. Into this bleaching solution, considerably diluted with water, are placed the articles of cotton or linen which are to be bleached, having previously been cleansed from greasy matter and other impurities which might interfere with the bleaching action, by being boiled in lime water and a weak solution of soda. Little or no bleaching action will be visible during this immersion, but on the fabric being removed from the bleaching solution and placed in very dilute sulphuric acid, the colours will be de- stroyed by the liberation of chlorine — (CaClaO.^ + Ca CI2) + 2H2S04= 2CaS0, + 2H2O + CI4. Calcium sul- phate and water are formed and chlorine gas is evol- ved. The chlorine decomposes water to combine with its hydrogen, thereby liberating oxygen, which in the nascent condition acts with great energy, and immediately oxidises the colouring matter and conse- quently destroys it. The partially 01 entirely bleached material is then removed from the acid or "souring** solution, and the excess of acid is neutralized by im- mersion in an alkaline solution, and abundant rinsing. f i ! 124 ESSENTIALS OF CHEMISTRY :ff'V' This process is fuvtbercdrried out in calico printing, by bleaching portions of a coloured cloth according to pattern. To do this, the cloth is stamped in pat- terns or devices with a pasle of flour, or gum, contain- ii>g an acid, such as tartaric or sulphuric acid. When the paste has become dry, the cloth is immersed in a hot weak bleaching solution, when the portions covered with the acidulated paste will be bleached, and the other portions not sensibly affected. , . The disinfecting properties of chlorine and of chloride of lime are no doubt due to much the same reaction as in bleaching ; that is, union of chlorine with the hydrogen of noxious gases, such as ammonia, sul- phuretted hydrogen and other hydrogen compounds, the products of animal or vegetable putrefaction, de- composes and therefore destroys them. To use the disinfectant most readily, the following methods may be adopted. Saturate a cloth in a strong solution of bleaching powder and hang it up in a convenient place ; the carbonic acid of the air causes a slow evolution of hypochlorous acid, which is not inferior to chlorine as a disinfectant ; or, if a more powerful effect be desirable, place some bleaching powder in a dish with half its weight of powdered alum, or with some dilute sulphuric acid poured over, when, in either case, chlorine will be rapidly given off. The application of Deacon's process to the manu- facture of bleaching powder has already been referred to (137). I AND CHEMICAL PHYSICS. 125 CHAPTER XV. ' , ... >4 BROMINE, IODINE, FLUORINE, HYDROFLUORIC ACID. > 142. Bromine (Br. -=80) a liquid of dark brownish- red colour ; very volatile, evolving deep orange col- oured fumes, even at low temperatures ; possesses a very peculiar and offensive odour to which it owes its name. It is even more objectionable than chlorine, and produces more pronounced irritation of the mu- cous membranes ; sp. gravity 2 '966 ; boils at 63°C., giving off vapour of sp. gravity 5*54. At — 25°C. bro- - mine forms a brown, crystalline, semi-metallic looking solid ; it is only slightly soluble in water, one part by weight requiring 33 times as much water for its solu- tion. Obtained from certain mineral springs, such as those of Kreuznach and Kissingen ; from the bittern, or mother-liquor of sea-water, remaining after the separation by crystallisation of chloride of sodium, and other salts ; and from the mother-liquor of the Stassfurth salt works. Since chlorine displaces bro- mine from its combination with metals, a current of chlorine is passed into the spring water, or mother- liquor containing bromine, in combination usually with sodium, potassium or magnesium; — KBr-hCl=KCl + Br., a chloride is formed and bromine is liberated in the liquid ; to the solution, ether (QHiqO) is add- ed, and this liquid, having a much greater solvent power for bromine than water possesses, abstracts it from the solution, and, being lighter than water, it forms a superficial orange coloured layer containing 126 ESSENTIALS OF CHE^fISTRY al! the bromine in solution. This surface layer is now carefully decanted off, and is mixed with caustic pot- ash ; potassium bromide and potassium bromate are formed, the colour is destroyed, and the ether rising to the surface in a pure state is removed for future use, — 6 HKO + Bre=5KBr + KBr03 + 3H20; this aqueous solution is heated to get rid of the water, and the solid residue of the bromide and bromate of potassium is heated to decompose the bromate — KBr03=KBr + 03. The bromide is now heated with manganese di-oxide and sulphuric acid — 2KBr • + MnOa +' 2H2SO4 = K2SO4 + MnSO* + Br^, potas- sium sulphate and manganese sulphate are formed, whilst bromine distils over and is condensed in a re- ceiver. In most of its chemical properties it resem- bles chlorine, but being more expensive than the lat- ter, it is of little practical importance. It has how- ever been used as a disinfectant, and in photography ; and the bromides of potassium, and ammonium are used in medicine. 143. Iodine (1=127). A c orming grayish- black brittle scales posses ' uietallic lustre; sp. gravity 4*95; volatile even ^ ordinary temperatures , giving off a faint smell resembling that of sea-air ; fuses at io7°C., and boils at lys'^C. evolving beautiful mauve coloured fumes. Sp. gravity of vapour 8716, possessing a strong odour. If a scale be placed upon the hand for a few seconds, it will be found on re- moval to have left a yellowish-brown stain. Soluble in water to a very slight degree, but dissolving freely in carbon di-sulphide, ether or alcohol ; with the last AND CHEMICAL PHYSICS, ia7 named forming the tincture of iodine of the drug shops. The best test forr the presence of iodine is the deep bkie colour it forms by its action upon starch. Thus if a compound containing iodine be added to some weak cold starch paste, and a few drops of chlo- rine be dropped into the mixture, the iodine will be liberated and combining with the starch will form a characteristic blue colour ; if excess of chlorine be added, there may be no colour visible, since there may be enough chlorine to combine, not merely with the constituents formerly united with the iodine, but with the iodine itself. By dissolving excess of iodine, in carbon di-sulphide, a solution is obtained, possessing the peculiar property of permitting all heat rays to pass freely, but intercepting all light rays, it is there- fore of the first importance in experiments relating to diathermancy. ' * -• Iodide of potassium (KI=i66) is much the most useful compound of iodine, being of frequent use in the laboratory, in medicine, and in photogra- phy. It is obtained in cubical or octahedral translu- cent crystals, by dissolving iodine in potassic hydrate, which results in the formation of potassic iodide and potassic iodate— 3T2 + 6HK0= 5KI -f KIO3 + 3H2O ; the mixture is evaporatad to dryness, and the potassic iodate is decomposed by the application of heat. 144. Fluorine (F=i9), a gaseous element, said to be of a greenish colour ; does not combine with oxygen, but its affinity for most substances with which it comes in contact is so powerful that it has not been found possible to isolate it, so as to determine its ■ J r '?| 128 ESSENTIALS OF CHEMISTRY 'I i V ■ I Mnv^• . « -- ■■ :.'■' .. <■ , ■ \:..Y .■--. " ,•• .. - '. t.< . .'•-'\ , CHAPTER XVII. -'vwUib^ SULPHUR DIOXIDE — ANHYDROUS SULPHURIC ACID. 147. Sulphurous acid, or sulphur dioxide (502)= 64. Density=-\'*^=32). A colourless gas, pos- sessmg a suffocating smell, and unpleasant taste ; does not burn ; does not support combustion ; sp. gravity 225 ; 100 cubic inches weigh 68*69 grains ; very sol- uble in water, one volume of water at o^C. absorbing 63*86 volymes, and at 2o''C., 36 volumes of the gas ; 9^ AND CHEMICAL FHYSICS. 135 condensible to a colourless liquid of sp. gravity 1.45, under a pressure of about two atmospheres, at i5°C., and this liquid solidifies into a white crystalline mass at — 79°C. Sulphur dioxide is not abundant in the free state in nature, for although a volcanic product, and generated to a large extent in large towns as a product of combustion, it is so easily oxidised, and converted into sulphuric acid, that its presence is rarely discernible ; it is the sole product of burning sulphur, but is experimentally obtained by heating sul- phuric acid with copper — 2H2SO4 + Cu=S02 + CuSO^ + 2H2O, sulphate of copper and water are formed, and sulphurous acid is evolved. It possesses rather weak acid properties, but combines with bases to form salts, called sulphites, the most important of which are — ammonium sulphite ( (NH4)2S03, H2O), calcium sul- phite (CaSO,, H2O), sodium sulphite (NagSOg, H2O), which last sulphite is extensively used as an antichlo^e to "kill the bleach" or neutralize the excess of chlo- rine, after bleaching rags for paper making : — NajSOa + CI2 + H20=Na2S04 + 2HCI. With solution of pot- ash also, sulphurous acid combines to form both a sulphite and a disulphite — SO2 + 2HKO=K2SOs + H20, and SO2 + HKO'^KHSOg. Sulphurous acid is useful as an antiseptic, for destroying the vegetable matter producing fermentation, henpe it is used for fumigating casks] it is also an excellent disinfectant, and a destroyed of mqst kinds of vermin ; it is obtained for these purposes simply by bupiing a sufficiency of sulphur with a moderate supply of air. If burning sulphur be placed iu a chimney in which the soot is I! J! 1 \\ 136 ESSENTIALS OF CHEMISTRY .m\ on fire, and the supply of air be almost cut off, the fire will speedily be extinguished. This acid is the prin- cipal bleaching agent for fabrics of silk or wool, of straw, sponge, and other animal or vegetable materials which would be injuriously affected by chlorine, or its compounds. The bleaching is performed by hanging the ihoi'^^ened articles in a chamber, where they are exposed to the sulphurous acid obtained by burning sulphur. The colouring matter does not appear in general to be destroyed by the acid, but rather to form a colourless compound with it, although one explana- tion of the bleaching action is that deoxidation of the colouring matter, or water present takes place, with the formation of sulphuric acid. That the latter ex- planation is not in all cases correct, is proved by the fact that in course of time the original colour some- times re-appears, as in the case of straw, flannel, etc., which gradually become yellow, perhaps through the change of sulphurous acid into sulphuric acid, by slow- oxidation; but in the case of woollen goods, the yellow colour is probably due to the neutralization of the acid, by the alkalies commonly used in washing materials. Fruit and wine stains can be readily removed from linen by solution of sulphurous acid. 148. Anhydrous sulphuric acid,orsulphur tri- oxide (S03=8o). S02and SOsare the only compounds of sulphur with oxygen which have been obtained in the separate state. Sulphur trioxide is a solid compound of white needle-like fibres ; its cp. gravity is i '9 ; fumes when exposed to air, through condensation of moisture, and soon deliquesces; when dropped into water it dis- AND CHEMICAL PHYSICS, 137 solves with a loud hissing sound, caused by the rapid evolution of steam ; it boils at about 5o°C. Its aque- ous solution is hydrated sulphuric acid, or oil of vitriol, probably the most important acid known, although the trioxide has in itself no acid properties, producing no change on blue litmus. It is obtained by passing oxy- gen and sulphurous acid through a tube containing heated platinum, or oxide of copper, or chromium, which appears to act by catalysis, causing the forma- tion of sulphur trioxide. It is better obtained by heat- ing disulphate of soda (Na2S207). The trioxide distils over and sodium sulphate (NaSO*)^ remains. If 32* grains of sulphur be oxidised by boiling with nitric acid, and the excess of acid expelled by heat ; the resultant sulphuric acid mixed with excess, say 300 grains, of lead oxide, and all the water expelled by heating at a high temperature, the mixture of lead oxide and lead sulphate will weigh 380 grains, shew- ing that 32 parts of sulphur have combined with oxy- gen of the nitric acid to form 80 grains of sulphuric acid. Hence the sulphuric acid contains 32 grains of sulphur and 48 grains of oxygen, corresponding to the formula SO3. . : - .• .. CHAPTER XVIII. SULPHURIC ACID. 149. Hydrated sulphuric acid (112804=98). An oily liquid \ when pure, colourless ; without any distinctive odour; powerfully corrosive of organic 138 ESSENTIALS OF CHEMISTRY \\\ 1 ; matter; cp. gravity 1*84; boils at 338*0., its vapour formlpg dense irritating fumes by combination with the moisture ef the air ; solidifies at about — 34°C., and the solid possesses the remarkable peculiarity of re- quiring a much higher temperature than that at which it solidifies to liquefy again. Obtained (i) by the dis' tillation of the sulphate of iron, (FeSO* + 7aq.). The crystals are first exposed to air, so that the sulphate may be reduced to the persulphate — 2(FeS04) + 0= Fe20, 2SO4, and after being dried are distilled at a red heat in eaiithenware retorts ; enough water always * remains in the persulphate to permit of a hydrate being formed, and it accordingly distils over as HgO, 2SO2, which may be considered as the formula of Nordhausen Oil of Vitriol, so called from the place in Saxony, where it is prepared; the peroxide of iron (FejOa), remaining in the retort, is a red powder known by the name of " colcothar," used for polishing plate glass and metals. The sp. gravity of Nordhausen oil of vitriol is i "9 ; it is chiefly used in dissolving indigo to produce the Saxon blue dye, and is a convenient source whence to obtain anhydrous sulphuric acid, for if heated in a retort, anhydrate (SO3) distils over and becomes condensed, in a receiver surrounded by a freezing mixture, while sulphuric acid (H2SO4) is left in the retort. The Nordhausen process is simple but expensive, and as enormous quantities of sulphuric acid are now used, a cheaper process is a necessity. ) (2) A series of leaden chambers of great capacity has, placed in its close proximity, a furnace of suita- ble size, which performs three functions, as (ollo^-rr AND CHEMICAL PHYSICS, 139 (a) it burns iron pyrites (FeS.^) in presence of air, thereby evolving sulphurous acid (SO2) \ (b) the cora- buslion of the sulphur heats an iron vessel, placed in the upper part of the furnace, containing sodium ni- trate (NaNOs), and dilute sulphuric acid, from which the vapour of nitric acid (HNO3) is evolved; (c) it heats a boiler, and thereby supplies steam, which is introduced in jets at different points of the leaden chambers. The air supplied to the burning sulphur of the pyrites is regulated so as to admit of the pas- sage of just about so much oxygen as will, in combi- nation with the SO2, form SO3 ; the nitric acid vapour enters the chambers along with the sulphur dioxide and air; the floor of the chambers is covered with water to a depth of about two inches. The. sulphur- ous acid acts upon the vapour of nitric acid in the presence of the steam, forming nitric oxide and hy- drated sulphuric acid, which collects in the water on the floor of the chambers : — 3SO2 + 2HNO3 + 2Fl20= 2NO + 3H2SO4. The nitric oxide (NO) again takes up oxygen from the air admitted with the sulphurous acid and becomes nitric peroxide (NO2), which, in the presence of water, oxidises more sulphurous acid, changing it into sulphuric acid — 2SO2+ 2NO2+ 2H2O = 2H2S04 + 2NO. The nitric oxide evidently act's the part of a mere carrier, or intermediary, for the transference of oxygen, and it is to be observed that there will be a constantly recurring diminution of volume, since 4 vols. SO2 and 4 vols. NO2 yield but 4 vols. NO. The nitrogen jof the atmosphere takes no part in : 1 1 W 140 ESSENTIALS OF CHEMISTRY the reactions of the leaden chambers, and to prevent its accumulation it must be got rid of. This was for- merly done by permitting of its escape, by a tall chimney at the opposite end of the chambers to that at which the various gases, or vapours, enter; but this also permitted of the escape of a considerable amount of nitric oxide, to avoid which loss, the nitro- gen is now made to pass through a leaden chamber filled with coke, over which sulphuric acid trickles ; the nitrogen escapes while the acid absorbs the nitric oxide, and being conveyed to another point, the acid is again made to trickle over coke through which the slilphurous acid and air entering the chambers must ipass, at the same time taking up the nitric oxide from the sulphuric acid. * Before the introduction of this process, it required an amount of sodium nitrate of about -rV^h of the weight of the sulphur, to convert it into sulphuric acid, while at present about g'^th suffices. The acid is allowed to collect on the floor of the chamber until its sp. gravity is about i'6, and it contains about 70 per cent, of H2SO4. It is now withdrawn, to prevent it absorbing nitric oxide; to form a stronger acid, this weak acid is heated in evaporating pans of lead to drive off a portion of the water, and it is concen- trated till the liquid has acquired a sp. gravity of 1*72, and contains about 80 per cent, of H2SO4; this is the brown acid of commerce, and is commonly used in the rougher manufacturing processes. Sinoe lead would be attacked by the acid on further con- centration, this process must' be carried out in glass AND CHEMICAL PHYSICS, 141 retorts,' or in platinum stills. The glass retorts are lieated in sand baths, but breakages are fi'equent on account of the high temperature (338°G.) at which the acid boils, and because it boils with a violent bump- ing, called ** succussion," and this adds largely to the cost of the preparation of the acid ; on the other hand, while with a platinum still the risk of fracture disappears and the distillation may be carried on with great rapidity, the first cost of the still itself is great, amounting to not less than $10,000 to $15,000, In such retorts, or stills, the acid is concentrated till it acquires a density of 1*84. Over 100,000 tons of sulphuric acid are consumed annually in Great Britain, independently of the large quantity exported. Until towards the middle of last century it was sold at about $9.50 per lb., at the present time it costs about 2}4 cents per lb. A peculiar crystalline substance of doubtful com- position, but temporarily represented by the formula 2(N0, SO3) H2O, is formed in the production of sul- phuric acid when the supply of steam is insufficient, and hence commonly known as the crystals of the leaden chamber. According to some chemists, this substance has an important effect in the* process ; while, according to others, it is an accidental formation of a useless and unprofitable nature. All ordinary metals, except gold and platinum, are acted upon by heated concentrated sulphuric acid, hence it is used to separate gold from silver or cop- per. If some lump sugar be moistened with warm water and then treated with sulphuric acid, it swells fi- I I42 ESSEJSTTIALS OF CHEMISTRY up, with evolution of heat, into a black carbonaceous mass ; this same action upon saccharine matter is taken advantage of in the manufacture of blacking, which contains treacle and sulphuric acid. All such action may be considered as due to the affinity of the acid for water, the removal of which from organic compounds tends to eliminate the carbon. If two measures of acid be added to one of water, the mix- ture cooled, and paper immersed in it and afterwards washed, the so-called vegetable parchment is obtained; the nature of the change is not known, but there is no difference in the weight of the paper. Even dilute sulphuric acid attacks cloth most injuriously, and the red stains produced should be removed by neutraliz- ing the acid with an alkali, and the spot carefully washed. Strong acid is much used in chemical oper- ations as a drying agent for gases, etc., usually by passing the gases over pumice stone saturated with the acid. The following are the principal compounds of sulphuTic acid with the metals : — Sulphate of pot- ash (K2SO4) ; sulphate of soda, or Glauber's Salt (Nag SO^-t- 10 Aq.) ; sulphate of baryta, or heavy spar (Ba SO4) ; sulphate of lime, or gypsum (CaS04 + 2 Aq.) ; sulphate of magnesia, or Epsom Salts (MgSOi + 7 Aq.); sulphate of iron, copperas, or green vitriol (FeS04 + 7 Aq.); sulphate of zinc, or white vitriol (ZnS04 + 7 Aq.) ; sulphate of lead (PbS04) ; sulphate of copper, blue vitriol or blue stone (CUSO4+ 5 Aq.). 150. Sulphuretted hydrogen, or Hydrosul- phuric acid (H2S=:34; Density=Y-=i7). A colourless gas possessing a peculiarly offensive odour AND CHEMICAL PHYSICS. 143 Lceous :ter is eking, 1 such of the rganic [f two e mix- rwards :ained; e is no dilute ,nd the utraliz- irefuUy il oper- illy by d with Dounds of pot- t (Naa )ar (Ba Aq.); 7Aq.); 5O4 + 7 ;opper, rosul- A odour )• and taste, the odour being that of rotten eggs : does not support combustion ; burns with a pale blue flame forming sulphurous acid and water — H2S + 03=802 + H2O, a little sulphuric acid (H2SO4) is also formed ; and, in an insufficient supply of air, sulphur is liberated-/ sp. gravity 1*1912 ; soluble in water at oX. to the ex-\ tent of 4*37 volumes of -he gas in one volume of water ; condensible to a colourless liquid under a pres- sure of 16 atmospheres, at i5°C. ; this liquid is solidi- fied at — 86"C. Hydrosulphuric acid is obtained by the action of dilute sulphuric acid upon iron sulphide : — FeS + H2S04=H2S + FeSO^, sulphuretted hydrogen is liberated and sulphate of iron is formed ; the gas thus prepared generally contains free hydrogen, which does not practically interfere with its action. If the pure gas be required, however, it may be prepared by heating hydrochloric acid with antimony sulphide — Sb2S3 + 6HCl=3H2S + 2SbCl3, sulphuretted hydrogen is liberated and antimony trichloride formed. The gas is quite irrespirable, and is most injurious to animal life, even when mixed with 1000 times its volume of air. Both the gas and its aqueous solution are feebly acid to blue litmus paper. It occurs free in nature, in mineral r^prings, and is liberated from volcanoes. It is a product of the decay of organic matter con- taining sulphur, and hence the compa ' Dn of its odour with that of rotten eggs, the smell of the egg being due to liberation of the gas ; when water boils over on a coal or coke fire, the same offensive odour may be noticed, due to the combination of the sulphur of the coal with the hydrogen of the water. It ; ' i If i ! i- 144 ESSENTIALS OF CHEMISTRY attacks silver, forming a black film of silver sulphide ; hence the discolouration of silver egg spoons, of silver plate exposed to the fumes of impure coal gas, or of a silver coin in contact with a lucifer match ; the tar- nish may be removed by washing the silver with strong ammonia, or with cyanide of potassium (KCN), but as the latter compound is a deadly poison, great care must be taken in its use. In the same way white lead paint is blackened by the formation of plumbic sulphide (PbS) ; and paintings, in the colours of which lead is an ingredient, are injuriously attacked by sul- phuretted hydrogen. It has been found, however, that colours so injured are gradually restored to their original hue by exposure to light ^nd air, the black sulphide becoming oxidised and changed into white sulphate of lead (PbSOi). Sulphurette i hydrogen is a useful reagent in the laboratory, as it enables the analytical chemist to arrange the metals in groups ac- cording to their behaviour with it. Thus if the gas be passed into an acid solution of arsenic, antimony, tin, gold, platinum, silver, mercury, lead, bismuth, copper or cadmium, insoluble sulphides will be precipitated ; this group may be further divided by the addition of ammonic sulphide ((NH4)2S) which dissolves the first five sulphides, but not the remaining six. Other eight metals — iron, uranium, chromium, alu- " minum, cobalt, manganese, nickel and zinc, in an alka- line solution, are precipitated by sulphuretted hydro- gen, but chromium and aluminum do not combine with the sulphur. Hydrogen disulphide (H jg) is an oily liquid, obtained by acting upon calcium disulphide i • AND CHEMICAL PHYSICS. 145 with muriatic acid — CaS2 + 2HCl=H2S2 + CaCl2, the lighter calcium chloride may be decanted off, leaving the hydrogen disulphide behind. In its properties it resembles hydrogen dioxide, possesses a peculiar smell and is a bleaching agent. li !l CHAPTER XIX. CARBON DISULPHIDE— PHOSPHORUS-LUCIFER MATCHES OXIDES OF PHOSPHOROUS — PHOSPHORIC ACID — PHOSPHOROUS ANHYDRIDE — PHOSPHORETTED \ HYDROGEN. ^ v 151. Carbon Disulphide (€82=76) a colourless, volatile liquid, possessing a disgusting odour; insoluble in water, but soluble in alcohol, ether and oils ; sp. gravity 1*26; boils at 46*5°C. and its vapour has a density of 38 ; it has never been solidified. Carbon disulphide is very inflammable, taking fire at a very low temperature, and burning with a bright, blue flame, producing carbonic and sulphurous acids (CS2 + Ofi=:C02+ 2SO2) j its vapour is injurious and ought not be inhaled ; it is said to act on the system like sulphuretted hydrogen. Obtained by passing sul- phur vapour over charcoal heated to redness. Of much importance in manufactures as a solvent for oils, fats, sulphur, phosphorus, caoutchouc, etc., and for extracting essential oils, as those of roses, jasmine, lavender, etc. It has also been employed to steep seed grain in, in jrder to kill insects without injuring 146 ESSENTIALS OF CHEMISTRY the seed. It is of notable service in experiments in diathermancy, since it is found to absorb only about 5 per cent, of the heat rays passing through it, and most of the light rays ; but an opaque solution of iodine in the disulphide has been found by Professor Tyndall to absorb all the light rays, and to permit of the passage of nearly all the heat rays. 152. Phosphorus (P=3i ; the vapour of P is 62 times as heavy as H so that its atom only occupies half a volume.) An almost colourless, wax Hke, vitreous solid, of sp. gravity 1*83, but artificially ob- tained in dodecahedral crystals of sp. gravity 2*34 ; transparent when fresh but soon becoming opaque ; melts at 44°C, but gives off faintly luminous fumes at ordinary temperature, possessing the odour of garlic ; boils at about 29o°C., out of contact with air, forming a colourless vapour ; density of vapour 4*35. Insoluble in water, but very soluble in carbon disulphide, and to a slight degree in olive oil and benzole. Very in- flammable, taking fire when heated above the melting point, or when subjected to a slight degree of friction, burning with a brilliant white light and evolving dense white ames of phosphorus pentoxide (P2O6). Even when exposed to air, at a temperature con- siderably below the melting point, it slowly oxidises forming phosphorus trioxide (P2O3). It is the only element prepared from animal matter. It is obtained from — bones of oxen, imported from Monte Video ; exhausted animal charcoal of sugar refineries; and mineral phosphate of lime. These various substances contain from 60 to 90 per cent, of their weight of AND CHEMICAL PHYSICS. 147 nts in about t, and on of fessor mit of P is cupies : like, ly ob- 2-34; )aque ; mes at garlic ; minga loluble e, and ery in- lelting iction, olving ;p.A). J con- ddises 2 only tained Hdeo ; 1; and tances rht of phosphate of lime, or from 12 to 16 per cent, of phosphorus. The powdered bone-ash, or bone earth, is acted upon by dilute sulphuric acid and heat, which causes the separation of a portion of the calcium, as insoluble calcium sulphate (CaSO^), calcium super- phosphate (H^CaPaOg) being left in solution — CagPg Os + 2H2S04=2CaS04 -h H^CaPaOs. The superphos- phate solution is filtered off and evaporated to a j syrup, which is mixed with powdered charcoal, dried in an iron vessel and then in a stone-ware retort. The carbon combines with the oxygen to form carbonic oxide (CO), the phosphorus distils over into a receiver containing water, to prevent combination with the oxy- gen of the air, and calcium phosphate remains in the retort — aH^CaPaOs + ioC= loCO + P4 + CagPaOs + 6 H2O. The phosphorus thus obtained is red and opaque, and is again melted under warm water, and squeezed through wash leather to remove mechanical impurities. It is again melted under ammonia to neutralise acid impurities; and again under acidulated bichromate of potash, to oxidise a lower oxide of " phosphorus present to the pentoxide, which dissolves out. The phosphorus is then washed, melted under water> and cast into the sticks, in which it is generally offered for sale. Phosphorus is allotropic, and under the influence of light it becomes white and opaque ; exposed to direct sunlight it becomes red ; heated to near its melting point and then suddenly cooled, it assumes a viscous condition. When heated to a temperature of about 232°C., under pressure, in an at- mosphere of carbonic acid* gas, phosphorus is con- 148 ESSENTIALS OF CHEMISTRY '•A verted into a red amorphous substance of sp. gravity 2-14, which is little affected in air, is not luminous, emits no odour, is not poisonous, inflames at 232°C., and is reconverted into ordinary phosphorus, and is in- soluble in disulphide of carbon and other solvents of ordinary phosphorus. The following, with some modifications, are the properties of ordinary and red phosphorus, as contrasted by Mr. G. Gore. Ordinary phosphorus is poisonous ; evolves a strong odour ; luminous in the dark ; melts at 44*'C. ; very transpa- rent ; almost colourless ; freely soluble, in various liquids ; vitreous ; soft, may be indented by the nail ; flexible as lead. Red phosphorus is innocuous ; nearly odourless; perfectly illuminous ; melts at 260' C. ; amorphous ; hard as common brick ; brittle as glass. At the beginning of last century phosphrous was sold in England at $1.25 per oz., at present its price is about 4 cents per oz. On account of its inflammability, phosphorus should always be cut under water, as it inflicts painful and dangerous burns. This element is capable of enter- ing into union with oxygen, chlorine, bromine, iodine, sulphur and most of the metals, even gold and plati- num ; forming phosphides and phosphurets. It has also the peculiar property, for a non-metal, of precipi- tating metals from the solution of their compounds, uniting itself with the oxygen present. For experi- mental purposes, a little red amorphous phosphorus may be prepared, by placing small fragments of com- mon phosphorus in contact with some iodine, and quickly wrapping the substances up in a piece of tin AIVD CHEMICAL PHYSICS. 149 foil, combustion will at once take place, and, if excess of phosphorus be present, a portion will be in the rmorphous condition. The principal use of red phos- phorus is in the manufacture of lucifer matches, in which it is partially replacing the ordinary form. ' Although not found in a free state in nature, )hos- phorus is abundant throughout the world in the form of phosphates, and being an essential ingredient of the food of plants, and consequently of animals, its comparative abundance in the soil of a country, is a measure of the capacity of that soil as a supporter of animal life. It is abundant in the minerals — apa- tite, coprolite and phosphorite, all of which are eagerly sought after by agriculturists, for use as valuable manures. 153. Lucifer matches are prepared by vipping small splints of wood, cut to the proper dimensions by machinery, with some easily inflammable substance, as sulphur, or wax, which serves to communicate flame to the wood. The matches, which are prepared in bundles, are then tipped with yet more combustible matter — a compound of phosphorus, chlorate of pot- ash (KCIO3), red lead (PbgOi), fine sand and glue. The chlorate of potash causes the match to ignite with '^ slight explosion ; but, if what are called silent matches are required, the chlorate is replaced by nitrate of potash (KNO3), or by nitrate of lead (Pb(N03)2). The purpose to be served by the above mentioned compounds, is simply, by their ready deoxi- dation to accelerate the combustion of the phosphorus, when it is ignited by friction. The glue sei*ves to m fj ; -1 ISO ESSENTIALS OF CHEMISTRY bind the constituents together and to the wood, and also to protect the composition from moisture : the sand or powdered glass serves to intensify the friction ; and colou. 'ng matter is also present as a rnere matter of taste. When the match is ignited, the chlorate of pot- ash gives off all its oxygen and is converted into potassic chloride (KCl) ; the lead compounds are pro- bably reduced by deoxidation to plumbic oxide (PbO); the nitrogen is evolved in the free state ; the sulphur and phosphorus combine with the oxygen of the various ingredients, as well as with the oxygen of the air, to form phosphoric pentoxide (P2O6), and sul- phurous acid (SO2) ; and a small portion of the latter compound combines with an additional atom of at- mospheric oxygen to form sulp.mric acid, which com- bines with the potassium of the nitre to form potassic sulphate (K2SO4). Safety matches differ from ordinary matches, in having the match composition partially on the match and partially on a rubber, usually affixed to the match- box. The matches are tipped with sulphur, or wax, sulphide of antimony (SbaSs), chlorate of potash (KCIO3), and powdered glass, and the rubber is coated with amorphous phosphoms mixed with pow- dered glass; sometimes the ends of the match are tipped differently, and ignition only takes place when the match is broken and the two ends rubbed together. On account of the gret value of phosphorus com- pounds as manure, attempts have been made to sub- stitute a mixture of chlorate of potash and hyposulphite pf lead for the ordinary match composition. To give i AND CHEMICAL PHYSICS. IS' some idea of the extent to which this valuable con- stituent of fertile soils is withdrawn from what may- be considered its legitimate use, it may be stated that some English firms manufacture as many as ten mil- lions of matches per day; and one Birmingham firm alone makes daily over eight miles of wick for wax vestas, while in Sweden, Norway, Prussia, and Austria, matches are annually manufactured by thousands of tons. 154. Phosphorus forms only two oxides which have been separated andexamined — phosphorus acid (P2O3), and phosphoric acid (P2O5). Phosphoric anhydride, or phosphorus pentoxide (P2O5) is readily obtained by burning phosphorus in oxygen or air» when it is evolved in dense white fumes, which con- dense to a white powder. It combines energetically with water forming the common phosphoric acid — P,05 + 3H20=2H3P04. This acid is also called Orthophosphoric acid ; if, however, the anhydrate combines with only one molecule of water M eta- phosphoric acid is formed — P2O3 + H20 = 2HP03^ if with two molecules of water Pyrophosphoric acid — (H4P2O7) is obtained. 155. Metaphosphoric acid (HPO3) is best ob- tained, by gently heating phosphorus with dilute nitric acid until the phosphorus is dissolved, and then evaporating the solution to a syrup in a platinum ves- sel— 10 HNO3+ Pa =ioNO+ 2 H2O + 6HPO3. This form is called glacial phosphoric acid, and by union with one molecule of water forms the ordinary acid — HPO3 + H20=H3P04. It forms salts called meta- 152 ESSENTIALS OF CHEMISTRY phosphates, as, when argentic nitrate (AgNOs) is added to it, a gelatinous precipitate of argentic metaphos- phate is formed— 2(AgN03) + 2HPO, 2HNO3+2 AgPO,. Pyrophosphoric acid (H4P2O7) is obtained in combination with metals, forming pyropho^i-h'-ies. When aqueous solution of metaphosphoric acid is heated for some time it loses the power of forming a precipitate with argentic nitrate, but if the solution be neutralised by the addition of ammonia, a white precipitate of argentic pyrophosphate is obtained— - (2HPO3 + H20) + 4 AgNOs + 2 NH3 = Ag,PA + (2N H3, 4HNO3). Pyrophosphoric acid has been obtained in crystals, by decomposing plumbic pyrophosphate (PbaP^Oy) with sulphuretted hydrogen, and evapo- rating the clear solution over oil of vitriol in vacuo, Orthophosphoric acid, or common phosphoric acid (H3PO4) is obtained either by the union of phos- phoric pentoxide (P2O6) with water as above, or from metaphosphates or pyrophosphates by boiling for some time in acidified liquid, or, by fusion with excess of caustic alkali, or with a carbonate.. It is called the common acid, because most of the phosphates in common use are salts of this acid. It will be ob- served by the student that these different conditions of phosphoric acid — metaphosphoric, pyrophosphoric and orthophosphoric are monobasic, dibasic or strictly speaking tetrabasic, and tribasic respectively. It is also to be observed that this variety of constitution of phosphoric acid renders it peculiarly fitted to take part in vital phenomena, and it is found accordingly AND CHEMICAL PHYSICS. 153 to be a constituent of nerve matter, etc., in the human body. Orthophosphoric and pyrophosphoric acids do not, and metaphosphoric acid does, coagulate albu- men. Orthophosphoric acid gives a yellow precipitate, m.etaphosphoric acid gives a gelatinous precipitate, and pyrophosphoric acid gives no precipitate, except- in presence of an alkali, with argentic nitratf (AgNOs). 156. Phosphorous anhydride (P2O3) is the product of the combustion of phosphorus, in a limited supply of air. Phosphorus is placed in a long glass tube and heated, air being allowed to enter only through a tube of very small bore, the phosphorus burns with a pale blue flame forming white flakes of phosphorous anhydride. This substance dissolves readily in water — P2O3 + 3H20=2H3P03 and absorbs moisture from the air, and, on being heated in a closed tube, it is decomposed into phosphoric pentoxide Und free phosphorus — 5P203=3P205 + P4. 157. Phosphuretted Hydrogen (PHs=34; Density=-3/==i7) a colourless gas, possessing the odour of putrid fish ; very poisonous; sp. gravity 1*19, burns with bright white flame, evolving dense vapour of phosphoric pentoxide. It has no acid properties, but it possesses some analogy to ammonia, although destitute of alkalme power ; it has been condensed to a liquid under high pressure. Obtained by heating hydrated phosphorous acid (H3PO3), when phosphoric acid is formed and phosphuretted hydrogen is evolved. To prepare it for experimental purposes the following method is adopted : — A retort of moderate size is nearly filled with a strong solution of caustic potasl^ I J. i. j.^ I > r ■•. I ■* ., IS4 ESSENTIALS OP CHEMISTRY im in which are placed a few pellets of phosphorus ; to prevent the spontaneous combustion of the gas in the retort a few drops of ether should be added, the solution is thea cautiously heated till it boils, and the extremity of the delivery tube may then be dipped under water. In a few minutes small bubbles of white vapour will ascend through the water, giving off a most unpleasant and characteristic odour; other bubbles will soon follow, and these will ignite spontaneously on coming in contact with the air, with a bright flash and evolution of fumes of phosphoric acid. The fumes assume a very peculiar form — that of symmetri- cal revolving rings, gradually enlarging as they ascend in the air, and apparently made up of an infinite num- ber of small rings, gyrating at right angles to the plane of the primary rings. If the gas be passed into a jar of osygen, the flash is very vivid, and the concussion will shatter any but a strong jar. To insure the com- bustion of each bubble a trace ot chlorine should be added to the oxygen. The phosphuretted hydrogen represented by the formula PHg is not spontaneously inflammable, but this property is due to the presence of another hydride, called liquid phosphide of hydro- gen (PH2). The gas prepared as above appears to be a mixture of phosphuretted hydrogen, liquid phos- phide of hydrogen, and hydrogen, the latter gas being liberated from the water by deoxidation, on account of the formation of .potassic hypophosphite (KPH2O2). A little turpentine added to a jar of the spontaneously inflammable gas deprives it of the property, and, ' on the other hand, a trace of nitrous acid imparts AND CHEMICAL PHYSICS. m the property of spontaneous inflammability. Sponta- neously inflammable phosphuretted hydrogen may be obtained also, by throwing pieces < calcium phosphide on warm water. . CHAPTER XX. BORON — BORACIC ACID — BORAX — SILICON — SILICA — HYDRAULIC CEMENT. 158. Boron (B=ii), a solid, obtained in the form of an amorphous greenish powder, by fusing five parts of boron tri-oxide (B2O3) with three parts sodium (Na), in an iron crucible. Obtained in octahedral crys- tals, by heating amorphous boron with aluminum ; sp. gravity of crystallised variety 2'68, hardness 10; not attacked by any acid, but dissolved by fused alkaline hydrates ; burns when heated in chlorine, forming boron trichloride (BCI3) ; partially burns when heated in oxygen, forming boracic acid {B2O3). Boron unites directly, at a red heat, with nitrogen. 159. Boracic acid (B2O3 anhydrate), (H3BO3 hydrate) is the only oxide of boron. Obtained chiefly from the volcanic district of Tuscany, called the Maremna, and also from various lakes in California ; a colourless, glassy substance, dissolving in water or alcohol ; sp. gravity 1.83 ; gives a fine green flame before the blowpipe ; crystallises out of its solution in pearl-coloured scales ; gives no acid result with test paper, but unites with bases, and forms borates. In Italy, boracic acid is economically obtained from the \ % m 156 ESSENTIALS OF CHEMISTRY hot springs, in which it is found, by evaporating the water in shallow leaden pans, by the agency of the steam from the springs themselves. 1 60. Borax, Biborate of soda (2NaB02,B203 + 10 Aq.) crystallises in transparent prisms, but when heated forms a white spongy mass, soluble in water ; before the blowpipe fuses to a colourless glass, and, since it acts as a flux, it is very useful i. blowpipe analysis, by forming glasses of characteristic colours, when heated with salts of various metals. Commonly used as a flux in soldering. Obtained native from Thibet and California, under the commercial name of tincal. 161. Silicon (Si=28). Does not exist in the free state, but obtained artificially in three conditions — crystallised, amorphous and graphitoidal. Crystallised silicon is in the form of brilliant octahedra, possess- ing a dark hue, and iridescent lustre ; sp. gravity 2*5 ; hard enough to scratch glass with ease. This form is obtained by fusing silicon at a temperature about that of the melting point of cast iron. Amorphous silicon is a brown powder, which burns with brilliant com- bustion in oxygen, forming silica (^^O^ ; soluble in caustic potash, and in hydrofluoric acid (HF); ob- tained by heating together* fine sand (SiOg), powdered fluorspar (CaFg), and sulphuric acid : — Si02 + 2CaF2 + 2H2S04=SiF4+ 2CaS04+ 2H2O, silicon tetra-fluoride is evolved and is passed under mercury into water ; in which it forms s'.lica (Si02), 2nd silico-fluoric acid (SiH2Fe). Mercury must be used in this operation, for, unde" water, the silica formed would stop up the AND CHEMICAL PHYSICS. 157 the the delivery pipe, and thereby cause an explosion. The acid liquor is now neutralised by the addition of caus- tic potash, forming potassic "'lica fluoride (2KF, SiF4) and this salt being dried, is heated with about its own weight of sodium, when sodium fluoride (NaF), is formed in addition to potassium fluoride (KF), and amorphous silicon is separated by washing. Graphi- toidal silicon is obtained by heating the amorphoi s silicon to a high temperature \ it is in black crystalline scales, possessing a semi-metallic lustre; this form does not burn in oxygen, nor does it dissolve in hydrofluo- ric acid, but it may be dissolved in a mixture of nitric and hydrofluoric acids j silicon differs from carbon in being fusible at a high temperature, in forming only one compound with hydrogen and that one very un- stable, and in combining directly with nitrogen at a high temperature, while nitrogen will not combine with carbon except in presence of alkalies. Silicon is capable of displacing carbon from carbonic acid (CO2). Carbon, boron, and silicon form a group, the members of which resemble each c^her in their allo- tropism, their infusibility, and by their combining with oxygen to form feeble acids. The group is allied to the metals through silicon, which in some of its salts resembles tin. 162 Silica, silicic acid, or silicic di-oxide (SIO2), is one of the most abundant mmeral constitu- ents of the globe ; it occurs pure as rock-crystal or quartz, crysiallises in six-sided prisms of the rhombo- hedr il system ; when pure colourless, but often col- cured, fcrming umethysts, cairngorm stones, Bristol II 111 158 ESSENTIALS OF CHEMISTRY diamonds, or smoky quartz ; and, in the uncrystallised form, chalcedony, carnelian, onyx, catseye, opal, helio- trope, agAte, jasper, flint, sand, etc. Silica is little affected by any acid, except hydrofluoric acid (HF), which decomposes it, forming silicon tetra-fluoride and water — SiOa + 4HF = SiF^ + 2 HjO. Notwithstanding this apparent insolubility of silica, it is found in plants, and in many natural waters, such as the Geysers of Iceland. In the crystallised state, silica ^'s infusible before the blowpipe; hardness 7; sp. gravity 2 '5-2 '8. Pure amorphous silica may be prepared by fusing a silicate, in the powdered condition, with five or six times its weight of the carbonates o. potassium and sodium in equal parts ; the glassy mass formed is dis- solved in dilute hydrochloric acid, and the mixture evaporated to dryness ; by this process the precipita- ted silica has lost its solubility and, on the dry mass being acted upon with dilute hydrochloric acid, the other constituents of the mixture are dissolved, whilst the amorphous silica remains as a gritty white pow- der. In this form silica is soluble in hot alkaline so- lutions, therein differing from the crystallised variety ; its sp. gravity is 2*3. If a very dilute solution of the glassy mnss, referred to above as being dissolved in hydrochloric acid, be placed upon a dialiser, the hy- drochloric acid, and the sodium chloride formed will be diffused out, leaving behind a pure solution of silicic acid, which, when allowed to stand for a few hours, becomes gelatinous. Silica acts as a weak acid at ordinary temperatures, and, at high tempera- tures, displaces most of the other acids from their AND CHEMICAL PHYSICS, 159 pera- iheir combinations. Since, in general, acids can only be displaced from their combinations by acids, this will explain the term acid, as applied to the dif- ferent varieties of silica — flint, sand, quartz, etc., sub- stances which appear to lack all the characteristics of a true acid. With bases, silica forms an abundant class of minerals called silicates, among the most im- portant of which are : — Steatite, or soapstone ; meer- schaum ; serpentine ; felspar ; mica ; talc ; augite ; garnet; emerald; beryl; porcelain clay; kaolin. Alka- line silicates, in combination with silicates of lead, cal- cium and other metals, form the several varieties of glass. . J 163. Hydraulic Cement is prepared by calcin- ing together calcium carbonate with clay, which is chiefly silicate of alumina. The carbonic acid ga» is expelled and the calcium unites with silicic acid, form- ing calcium silicate (CaO, Si02) and probably also aluminate of calcium. If the calcination be carefully performed and not carried too far, the resulting com- pound on being finely powdered and mixed with water is found to set rapidly, the hardening of the best kinds being complete in two or three days, when the cement is found to be unaffected by contact with water. This hardening is due to the formation, by the silicates and the aluminate, of hydrated double silicates and aluminates, upon which water has no fur- ther action. About 10 to 25 per cent, of the com- pound ought to be clay and the remainder calcium carbonate. •i> Vr;-:,..^_i.vlo i6o ESSENTIALS OF CHEMISTRY CHAPTER XXI. ARSENIC — ARSENIOUS ACID — ARSENIC ACID. 164. Arsenic (As =7 5). Thevapouf of Asis 150 times as heavy as H, so that its atom only occupies half a volume). An element sometimes considered a metal, but, since its characteristics closely connect it with phosphorus and it is incapable of forming a base with oxygen, it is probably best considered as a non- metal. Arsenic possesses a steel-gray colour, and metallic lustre ; soon tarnishes in air by oxidation ; is a conductor of electricity ; very brittle ; crystallises in rhombohedrons ; sp. gravity 5 "96 ; volatilises with- out fusion at i8o°C., giving off vapour which possesses a characteristic odour of garlic. The vapour con- denses in a compact metallic looking mass, but, if heated in air to about 71'^C., white fumes of arsenious acid (AS2O3) are given off. When arsenic is heated to a red heat it burrj^ with a livid blue flame, forming the above named acid. If powdered arsenic be drop- ped into chlorine gas, it burns, forming arsenic tri- chloride (ASCI3). Arsenic is rarely found native, but generally in union with iron, cobalt, copper, or nickel ore, or with sulphur ; sometimes, also, it is found in combination with oxygen and metals in arseniates. Obtained from arsenical pyrites (FeSj, FeAsj) by heat- *ng it in earthen cylinders, the arsenic is driven off as a vapour, which distils into iron rect.vers, in which it condenses as a bright metallic looking solid. It is also prepared from other ores containing it by roast- ^ ' AND CHEMICAL PHYSICS. i6i is 150 iupies jred a lect it abase a. non- •, and on ; is tallises :s with- ssesses r con- but, if lenious heated orming ; drop- nic tri- ve, but nickel mnd in jniates. »y heat- 1 off as hich it It is \f roast- ing on the hearth of a reverberatory furnace, in con- tact with heated air. The arsenic becomes oxidised, by the atmospheric oxygen, forming arsenic triox- ide (AS2O3), which passes off as vapour into long flues, in which it condenses to a white crystalline sub- stance. The trioxide, in a powdered condition, is then mixed with half its weight of charcoal, and heated in a crucible, which is covered by a cap which is pro- tected from the he it below by a perforated iron shield. Carbonic oxide is formed and escapes through a hole in the cap, and arsenic vapour con- denses in the cool upper portion of the vessel — AS2O3 + €3= Asj + 3CO. Arsenic is poisonous, both pure and in its compounds, but, in the pure state, the symp- toms of poisoning do not appear till a considerable time after administration, probably not until it is oxi- dised in the stomach and changed to arsenious acid. Arsenic is used to prevent smut in grain, is mixed with the alloys employed in making telescopic spec- ula, and enters into the composition of small shot. The following are the principal arsenides : — Kupfer- nickel (NiAs), Arsenical Nickel (NiAsj), Cobalt Ar- senide (C0AS2), Mispickel, or Arsenical pyrites (FeS.^, FeAsa), Cobalt Glance (C0S2, CoAsj), Red Orpiment, or Realgar (AS2S2), Nickel Glance (NiSgNiAsg), Yellow Orpiment (AS2S3). The elements nitrogen, phospho- rus and arsenic display certain analogies in their oxy- gen and hyd'-ogen compounds ; there are likewise analogies between the hydrogen compounds of arsenic and p^Hmony ; and arsenic trioxide is capable of oc- cupyi'ip; the place of antimony trioxide (Sb208)in cer- ' > ■ i . ■i - \i If I I I 1 62 ESSENTIALS OF CHEMISTRY W4 '^% I I ■ii Hi tain salts. The sulphides of arsenic and antimony have also a considerable degree of correspondence in composition, and in some of their properties. ^ 165. Asenious Acid (As203= 198). A white solid crystalline, or amorphous substance, possessing very poisonous properties. The crystalline variety, sp. gravity 2-69, is obtained when its vapour is quickly condensed, or when it separates from its solutions ; the amorphous form, sp. gravity 37, is obtained when the vapour condenses on a hot surface. Volatilises at i93*3°C., depositing brilliant octahedral crystals on a cool surface. It is not merely not soluble in water in any great degree, 20 oz. of water in the course of sev- eral hours not dissolving more than 20 grs. of arseni- ous acid, but when thrown upon water it manifests great repulsion to it, the particles collecting in little globular clusters on the surface. This comparative insolubility renders it almost tasteless and delays the developement of its poisonous properties, when it is taken into the stomach. The :^mallest quantity which has been known to prove fatal is 2*5 grs. By long boiling in water, however, it is possible to obtain a much stronger solution, viz. : about 219 grs. in 20 oz. Arsenious acid is obtained chiefly from arsenical pyrites (FeSo, FeAsj), by roasting in muffles, or ovens, through which a current of air passes, converting by ] oxidation the arsenic into arsenious acid, and the sul- phur into sulphurous acid; these acids are conveyed into chambers, from which the sulphurous acid is car- ried off, while the arsenious acid is condensed as a Arsenious acid thus prepared is powdei AND CHEMICAL PHYSICS. 163 lony :e in solid very ', sp. lickly ions ; when ses at 3 on a iter in Df sev- arseni- nifests ti little irative ys the n it is which y long ptain a 20 oz. Isenical ovens, ting by the sul- eyed is car- ^d as a lared is \ 1 Inv again sublimed in small quantities in iron vessels, and is condensed into vitreous arsenious acid, possessing a somewhat glassy appearance, but finally becoming opaque. It is usually sold in the form of a wliite powder. Arsenious acid very slightly aflfects blue lit- mus paper, it is easily dissolved in hydrochloric acid, forming terchloride of arsenic (AsCIs), and octahedral crystals of aisenious acid ; it also dissolves in alkaline solutions, forming alkaline arsenites. When a little is thrown upon a red hot-coal, the peculiar garlic odour of arsenic is perceptible. It is used to prevent putre- faction of pelts, etc., and is accordingly employed in the preservation of stuffed animal; Scheele's green, arsenite of copper (2CuO,H2^- '""' ^ '" *4 brilliant green colour used for colouring wr - ipers, calicoes, fea- thers, artificial flowers, etc. All materials, or fabrics, so coloured, are more or less poisonous, both to those who make use of them and to those who prepare them. 166. Arsenic Acid (AsgOg). A white amorphous substance, somewhat less poisonous than arsenious acid, cannot be volatilised without decomposition ; not soluble to any great degree in water ; has powerful acid properties. Obtained by oxidising arsenious acid with nitric acid — AS2O3+ 2HNO8 + 2H20=N203 + 2H8ASO4. Nitric trioxide fumes are given off, and prismatic crystals of hydrated arsenic acid remain ; when these are heated to about 26o''C., all the water is driven off, and arsenic acid remains. It is largely used ill calico printing, and in the manufacture of the aniline dye — Magenta. Its most important salt is 1 64 ESSENTIALS OF CHEMISTRY arseniate of soda (H2Na4As208+ i4Aq.), used exten- sively by calico printers, on account of its feebly alka- line properties. CHAPTER XXII. ARSENIETTED HYDROGEN — REALGAR — ORPIMENT — marsh's TEST — REINSCH'S TEST. 167. Arsenietted hydrogen (AsHg). A colour- less gas ; very poisonous ; slightly soluble in water ; burns with a livid blue flame, forming water and fumes of arsenious acid— -2ASH3 + Og— AS2O3 -f 3H2O ; but, in contact with a cold surface, as of porcelain, pure ar- senic is deposited. It posseses a sickly, garlic-like, smell ; is condensible to a liquid at — 40C. Obtained by the action of dilute sulphuric acid upon zincic arse- nide — ZngAss + 3H2S04= 2 AsHg + 3ZnS04. Arseniet- ted hydrogen is evolved and zinc sulphate remains in solution. The student will observe that the three gases —ammonia, phosphuretted hydrogen, and arseniet- ted hydrogen form a group possessing certain analo- gies and properties in common. In each there are three volumes of hydrogen ; they all possess peculiar and powerful odours ; all are decomposed by heat ; all are inflammable, ammonia least so : the first two are alkaline ; *^hey are all derived from their corres- ponding oxygen compounds (N2O3, P2O3, and As^Os) by contact with zinc and sulphuric acid. 168. Realgar, arsenic disulphide (AsaSj), found na- tive in veins ; crystallises in oblique prisms, possessing AND CHEMICAL PHYSICS. i6S exten- ' alka- :nt — . colour- water ; i fumes ) ; but, pure ar- :lic-like, btained cic arse- irseniet- nains in ee gases arseniet- n analo- lere are peculiar yj heat ; first two r ccrres- d As^Os) bund na- ossessing a red colour; sp. gravity 3*55. Obtained artificially (i) by heating arsenious acid and sulphur together — - 2As203 + S7=2As2S.2 + 3S02, sulphurous acid escapes and realgar is left: (2) by distilling arsenical pyrites with - iron pyrites — FeS2, FeAso + 2FeS2=4FeS -f AsgSj, real- gar distils over and condenses to a red solid, and iron sulphide remains. Realgar burns in air with a blue flame, forming arsenious and sui,phuroiis acids. If • thrown into melted saltpetre, it burns with a brilliant white flame, forming arseniated sulphate of potash. It . is consequently an important ingredient in signal lights, Indian fire and fire works. 169. Orpiment, arsenic tersulphide (AsoS^), found native in beds and veins ; crystallises in prisms ; colour bright yellow ; sp. gravity 3*48 ; obtained by heating arsenious acid with sulphur — 2AS2O3 + S9— 2 AS2S3 + 3SO2, sulphurous acid escapes, and yellow or- piment remains. The paint sold as King's Yellow is a mixture of orpiment and arsenious acid. Both real- gar and orpiment are poisonous. 170. In the application of what is called Marsh's test for arsenic, in cases of poisoning, the operator causes the evolution of hydrogen, in the usual way, by the action of dilute sulphuric acid upon granulated zinc. Care must be taken to ascertain the purity of the metal and the acid, as both are liable to contain traces of arsenic. The Woulfe's bottle, employed in ' the evolution of the gas, is provided with a thistle tube as usual, and a delivery tube of hard German glass bent at right angles, and terminating in a fine jet. When the escaping hydrogen is ignited, a little of the i66 ESSENTIALS OF CHEMISTRY liquid matter suspected of containing some form of arsenic is added to the solution in the bottle, through the thistle tube. If arsenic be present, the flame will now assume the livid blue colour characteristic of arsenietted hydrogen, and, on pressing down on the flame a piece of cold porcelain, a dark brown deposit possessing the metallic lustre of arsenic will gradually be formed upon it. If a spirit lamp be placed under the horizontal portion of the delivery tube, the arseni- etted hydrogen is decomposed, the livid hue disap- pears and arsenic is deposited on the sides of the tube. The arsenic deposited may be converted into arsenious acid and the usual tests applied (63 and 64). Antimonietted hydrogen (SbHs), when subjected to Marsh's test, gives very similar results to arsenietted hydrogen ; but the arsenical deposit yields octahedral crystals, and the antimony yields prismatic crystals. The antimony deposit is black, the arsenical is brown, and, Anally, antimony is soluble in ammonium bisul- phide ( (N 114)2 Sj{), which hardly affects the arsenical deposit. 171. In applying Reinsch's test for arsenic, the suspected solution is acidulated with hydrochloric acid, a piece of bright copper is introduced into it, and heat is applied. If arsenic be present, an iron- grey deposit of cupric arsenide (CU5AS2) will be formed on the surface of the copper. This deposit is care- fully scraped off, washed, dried, and heated in a bulb reduction tube, whsn minute crystals of arsenious acid (AsaOs) are deposited against the sides of the upper part of the tube. These crystals, on being dissolved m AND CHEMICAL PHYSICS, 167 in water, may be subjected to the usual tests (d^ and 64). Reinsch's test will apply equally well to arsenious acid or to arsenic acid, but in the latter case an excess of hydrochloiic acid must be added. :'^;;*,,«.;; «,. 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"a ^ • ..a a • :i S i o A 3 00 O S o B © Si © s i .2 L : S a . •^ CO • •*3 a •3 S3 © o © a o a a • -fJ to p ti) © © 0} o a o a o i 1^ 10 g ^- o 55 CO 04 CO a 1^ 0^ (72 M A' o K CO H o M o o o m g S b OB OQ o a & OQ '•■ -' < INTERMEDIATE EXAMINATION. CHEMISTRY. Questions, with answers, or references to paragraphs, where the answers may be found, , JUNE, 1876. . ' 1. How would you prepare Hydrogen ? State fully by what means you would show its most important properties. ' Ans. Par. 108. 2. Describe fully the modes of decomposing water, which you have seen. You are asked to say whether a given specimen of water is hard or soft, how will you determine the fact ? If the water is hard, describe (with reasons) all the means by which you can make it soft ' Ans. Pars. 103, 109. 3. State all the forms in which Carbon is found in nature. By what experiments would you show its im- portant properties. You are given a black substance like coal, and asked to say whether it is carbon or not; how will you determine this ? Ans. Pars. 124, 125. 4. How would you obtain Carbonic Acid from chalk — represent the reaction by an equation. A current of atmospheric air passes up through a bright coal fire, state all the changes which it undergoes till it enters the atmosphere again, > , Ans. Pars. 127, 126. EXAMINATION QUESTIONS, ETC, 171 5. How is Chlorine prepared ? State the experi- ments by which you would show its properties. On what does its bleaching power depend ? You are given a piece of calico, and requested to bleach it — state fully how you would proceed. Ans. Pars. 137, 141. 6. When an ordinary friction match is lighted, what gases are given off? Describe the properties of any of them. , , Ans. Par. 153. ' 7. State what substances are represented by the following formulas, and mention any experiments in which you have seen any of them occur : MnOa, Fe304, PaOg, ZnSOi, NH4CI, CaCoj. Ans. Mn02, manganese dioxide, Pars. 106, 137. FcaO^, magnetic oxide of iron, a compound of pro- toxide of iron (FeO) and peroxide of iron (Fe203), Par. 106. P2O5 phosphoric pentoxide, Par. 112. ZnSo4 zinc sulphate or white vitriol, Par. 108. NH4 CI sal-ammoniac; Par. 121. CaCos carbonate of lime, Pars. 127, 121. DECEMBER 1876. - 1. Describe and explain some method of obtaining oxygen. How would you shew its principal proper- ties ? What quantity of oxygen is required for the complete combustion of 100 grs. of pure charcoal? Ans. Pars. 106, 127, C02= 12 + 32=44; therefore 12 : 32 : : 100 \ X* ' ' 2. Explain what is meant by the combining measure of a gas, and state what the combining measure of hydrogen, chlorine and hydrochloric acid will be if we assume that of oxygen to be i. t 172 EXAMINATION QUESTIONS, ETC. I til! I' i Ans. Pars. 24, 25, 98, 99. . 3. Describe and explain any experiments that il- lustrate the action of plants and animals upon the air. What substances are found in the air in addition to the two principal gases ? Ans. Pars. 114, 113. 4. It was anciently believed that fire, earth, air and water were elements, state the views which now prevail as to the nature of each of these things. What is now meant by the term element ? Ans. Pars. 11, 12, 9. 5. Explain a method of preparing nitric acid, and state its composition by weight. What is a nitrate ? Show how the presence of a nitrate in a liquid may be detected. Ans. Par. 120, HN03=i + 14 + 48=63. Pars. 45, 63,64. 6. Name and give the formulae of the oxides of nitrogen, sulphur and carbon. Ans. Pars. 112, 148, 126, 127. 7. Calculate the per centage of the various elements cont2!iied in nitric acid, ammonia, sulphuric acid and common salt. . . . ' . w- Ans. Par. 120, HN03=i + 14 + 48=63 j therefore 63 ; 100 : : I ; p/c of H. 63 : 100 : : 14 : p/c of N.' 63 : 100 : : 48 : p/c of O. Par. 121, NH3=t4 + 3 = 17 ; therefore 17 : 100 : : 14 : p/c of N. 17 : 100 : : 3 : p/c of H. Par. 149, H2S04=2 + 32 + 64=98 j therefore 98 : 100 1:2: p/c of H. 98 : 100 : : 32 : p/c of S. 98 : 100 : : 64 : p/c of O. Par. 137, NaCl [ EXAMIJ^ATIOISr QUESTIONS, ETC. I7i •—23 + 3S*5 = 58'5 ; therefore 58-5 : 100 : t 23 : p/c of Na, 58-5 : 100 : : 355 : p/c of CI. 8. Explain the terms acid, alkali and salt. Ans. Pars. 39, 40, 42. JULY EXAMINATIONS, 1877. SECOND CLASS TEACHERS AND INTERMEDIATE. 1. Give two methods of preparing Hydrogen. By what experiments would you show its most important properties ? ^ Ans. Par. 108. 2. How would you prepare Nitric Acid ? Describe any experiments v,'ith Nitric Acid which you have seen. Ans. Par, 120. 3. State the different forms in which Carbon occurs in nature. Port wine filtered through charcoal is de- prived of its colour ; give the reasons of this. How is charcoal used as a disinfectant ? Give the theory of its action. , Ans. Par. 124. - 4. How would you prepare Carbonic Acid from Chalk and Sulphuric Acid ? Express the reaction by an equation. Bread is raised by the liberation of Carbonic Acid. Explain. Ans. Par. 127. 5. What is meant by combustion ? Explain fully the substances formed when a candle is burned (i) in oxygen, (2) in a limited supply of air. Ans. Pars. 72, 132. li SBC 174 EXAMINATION QUESTIONS, ETC. 6. Write down the formulae and molecular weights of water, ammonia, hydrochloric acid, sulphuric acid, ferrous sulphate, phosphoric acid. "* ' Ans. Pars. 109, 121, 139, 149, 155. ^'^ 7. (i) How many grammes of oxygen are required to burn 24 grammes of carbon and 32 grammes of sulphur ? (2) How many lbs. of zinc are there in 350 lbs. of zinc sulphate ? Ans. (i) C02~i2 + 32=44; therefore 12 : 24 : : 32 : Oxygen required; and 802=32 + 32. (2) ZnS04=65-2 + 32 + 64=161-2, therefore 161*2 ; 350 : : 65*2 ; amount of zinc. 8. Describe any two experiments which you have performed yourself, and the purpose for which you performed them. Ans. This question ought sufliciently to impress the student, with the necessity of practical work in Chemistry. — (Author). 9. How would you obtain chlorine from common salt? Give the equation respecting the reaction. Describe any experiments with chlorine you may have seen. Ans. Par. 137. 'y '< t;l I :■' DFXEMBER 1877. ^ I. Describe any experiments you may have seen which prove (i) that chemical action generally pro- duces a change of state (3) that chemical action generally produces a change of temperature. Ans. Pars. 62, 63, 106, 108. EXAMINATION QUESTIONS, ETC. 175 weights ric acid, _ • - . > I' required mmes of o lbs. of 24 : : 32 re i6i'2 ou have lich you press the work in common reaction, nay have ive seen ally pro- 1 action 2. Give the principal properties of oxygen. De- scribe its preparation from potassic chlorate, repre- senting the reaction by an equation. Ans. Par. 106, 3. What quantity of oxygen by weight and also by volume can be obtained by the decomposition of 100 grains of potassium chlorate ? Ans. KC103 = 39*1 +35-5 + 48 = 122-6; therefore 122*6 : ICO : : 48 : 39'i5. 11*2 litres of oxygen weigh 16 grammes (Par. 99), therefore 16 : 39'i5 : : 11*2 : volume of oxygen in litres ; or (Par. 98), 467 cubic inches of oxygen weigh 16 grains; therefore 16 ; 39*15 : : 46*7 : volume of oxygen in cubic inches. 4. Give the symbol, atomic weight, and chief pro- perties of chlorin*^ To what are its bleaching and deodorizing properties due? Express in words the meaning of the equation — 2NaCl + MnOa + 2H3S04 =Cl2 + NajSO^ + MnSOi + 2HaO. Ans. Par. 137. 5. Give the symbol and atomic weight of sulphur. Describe any method of preparing sulphuric acid. How would you prepare crystals of sulphur. What would be their shape ? Ans. Pars. 146, 149. 6. What is the action of water upon each of the following substances ? Hydrogen, carbonic anhy- dride, ammonia, and sodium. Ans. Hydrogen has no effect upon water beyond dissolving in it to the extent of 2 volum^es hydrogen in 100 volumes water. CO2 + H20=H2C03 (carbonic acid, which changes > I 176 EXAMINATION QUESTIONS, ETC, blue litmus paper red). NHs, ammonia dissolves to the extent of 1090 volumes in one of water, forming a strongly alkaline solution. Na2 + 2H20=2HKO + Hj. Caustic soda is formed and hydrogen is liberated. 7. What weight and volume of carbonic acid gas would be produced by burning 5 grains of carbon in oxygen gas ? Ans. €02=12 + 32=44; therefore 12 : 5 : : 44 : ^ =weight of CO2 produced. Density of C02=V-= 22; therefore 11*2 litres weigh 22 grammes (Par. 99); therefore 22 \ x \ : 11-2 : volume of COj produced. 8. Give a brief account of the atmosphere, includ- ing its extent, pressure, composition and chemical re- lations. Ans. Pars. 113, 114, 68, 69. 9. Describe minutely any chemical experiment you have yourself performed. JULY 1878. 1. Give the names and atomic weights of the ele- ments represented by the following symbols : — Al, C, Ca, Cu, Fe, CI. Pb. S. P. " »' '■ Ans. Par. 13. 2. Explain what occurs in the distillation of water, and how the water is purified by the process. What ^ kind of impurities will remain in the distilled water, and how can they be detected ? -^ Ans. Pars. 109, 62, 63, 64. 3. Represent the following statement by means of an equation : — If 100 grammes of marble be mixed with EXARfIiVATI0r7 QUESTWyS, ETC, 177 solves to forming is formed acid gas :arbon in : : 44 • ^ (Par. 99) J oduced. re, includ- lemical re- riment you of the ele- Is :— Al, C, ►n of water, ess. What illed water, )y means of mixed with 73 grammes of hydrochloric acid it will yield in grammes of calcic chloride, 18 grammes of water, and 44 of carbonic anhydride. Ans. Par. 127. 4. Describe fully the preparation of O from potassic chlorate, representing the reaction by an equation. How much potassic chlorate must be taken to yield 10 lbs. of oxygen ? . Ans. Par. 106. KC103=39i +35*5 + 48=122*6 ; therefore 48 : 10 ; : 122 6 : amount of potassic chlorate. ' 5. Give the properties of hydrogen. Describe the process for obtaining hydrogen which is represented in the equation — H2SO4 + Zn = ZnSO^ + Hj. Ans. Par. 108. 6. Explain the chemical relations between chalk, quick lime and slaked lime ; also the preparation of chloride of lime, and the reactions by which that sub- stance evolves chlorine, when acted on by sulphuric acid and when exposed to the air. • Ans. Chalk is calcic carbonate (CaCOa), if this be sufficiently he .ed, it is decomposed into carbonic acid gas (CO2), and calcic oxide (CaO) commonly called quick lime ; if water be added to quick-lime the hydrated oxide — (CaO + HaO) commonly called slaked lime is formed. Par. 141. 7. What is the compostion of lucifer matches? What purpose does each ingredient serve, and what chemical action occurs when you strike a match ? Ans. Par. 153. i^' 178 EXAMINATION QUESTIONS, ETC, 8. A compound on an analysis, is found to yield tlie following percentages : — Potassium, 49.95 ; Nitro- gen, 16.45 ; Oxygen, 37.60. Calculate its formula, and give its name. ,>.-.' Ans. K = 4^»jfi^ = i-27. N = J-J^ = ri8. 0^^\i^ = 2*35; therefore i*i8 : 1*27 : 2*35 = KN02 (Potassic Nitrite). 9. State what experiments you have yourself per- formed, and describe minutely any one of them. * DECEMBER, 1878. ^ ^ . INTERMEDIATE EXAMINATIONS. • I. State the laws of combining proportions. In one ounce of each of the following gases what weight of each element would there be : — Carbon monoxide, carbon dioxide, marsh gas (CH4), oleliant gas (C2H4), acetylene (C2H2) ? ^ - What would be the volume of an ounce of carboii dioxide, if, at the same temperature and pressure, 50 cubic inches of hydrogen weigh one grain ? . ..•. Ans. (1) Par. 27. - ..^s- • (2) CO=i2 + i6; therefore one oz. contains of carbon f oz. and of oxygen ^ oz. ' '- *" * !< r': -i C02=i2 + 32; therefore one oz. contains of car- ^ bon j\ oz. and of oxygen t\ oz. CH4=i2 + 4; therefore one oz. contains of car- bon \ oz. and of hydrogen ^ oz. ; C2H4 = 24 + 4 ; therefore one oz. contains of car- bon § oz. and of hydrogen \ oz. to yield 5 ; Nilro- formula, m ' i * '■"'.' (Potassic irself per- them. * ons. gases what : — Carbon I^), olefiant of carboii pressure, 50 ? ,,- ....... contains of ains of car- lins of car- ains of car- EX A Mm A TION Q UESTIONS, E TC. 1 79 QH, = 24 + 2 ; therefore one oz. contains of car- bon 1 1 oz. and of hydrogen i^t oz. (3) If one grain of hydrogen measure 50 cubic inches, one ounce (480 grains) will measure 50 x 480 -= 24000 cubic inches ; but carbon dioxide is 22 times heavier than hydrogen (Par. 99) ; therefore volume of one ounce carbon dioxide = 24000 -r 22 = 1091 cubic { inches. l 2. Describe a method of preparing hydrogen. Write in symbols the reaction occurring. By what experiments could the most important pro- perties of hydrogen be exhibited ? Ans. Par. 108. 3. By what experiments could air be shown to be a mechanical mixture of two gases, oxygen and nitrogen? Give the names and symbols of the chief com- pounds of oxygen and nitrogen. Write in symbols the reaction that occurs in the preparation of nitric acid from nitre, and calculate the weight of commercial nitric acid (2HNO3, 3H2O) that 337 oz. of nitre are capable ol yielding, (K= 39- 0- Ans. (i) Par. 113. (2) Par. 112. (3) Par. 120. 101*1 parts by weight of nitre yield 6^ parts by weight of nitric acid, therefore loi'i : 337 : : 63 : commercial acid yieldea uy 337 oz. = 209 oz. 4. Name the allotropic forms of carbon. I In preparing carbon monoxide from oxalic acid a mixture of carbon monoxide and carbon dioxide is obtained ; how can the carbon dioxide be removed ? Ans. Pars. 124, 126. .■< i8o EXAMINATION QUESTIONS, ETC. ' 5. Describe a method of preparing and collecting chlorine. Represent the reaction by an equation. ■" What are the principal properties of chlorine ? . Ans. Par. 137. ,' '^ 6, How many gallons of oil of vitriol, sp. gravity I "85, could be obtained from in lbs. of sulphur, a gallon of water weighing 10 lbs. ? You are given two bottles, one containing sulphuric acid, the other containing nitric acid, how could you determine which held the sulphuric acid? Ans. (i) Par. 149. (2) 98 parts by weight of oil of vitriol contain 32 parts by weight of sulphur, there- fore 32 : III : : 98 : 340 lbs. and 340 lbs., according to uld you ht of oil ir, there- ccording a candle. e expres- ement ? lical inix- oxide is a rs. *8, 19. ■( ■ ygen. curs when ite. You are given three vessels, and are told that one contains Oxygen ; one, Nitrogen Monoxide ; and one, common Air ; how would you determine which ves- sel contains the Oxygen ? What volume of Oxygen will 8 ounces of Potassium Chlorate yield; a cubic foot of Hydrogen at 6o°F. and 30 ins. bar. weighing 37 grains? (K— 39*1)." Ans, (i) Par. 106. (2) Par. 106. (3) Par. 116. (4) 122*6 parts by weight potassic chlorate yield 48 parts by weight of oxygen, therefore — 122'6 : 8 : : 48 '* Z'^Z^ ^'id, (par. 98), 467 cubic inches of oxygen weigh 16 grains, therefore 16 : 3*13 : : 467 : 9*14= volume of oxygen in cubic inches. 3. How may Nitrogen, Nitric Oxide (NO), Nitrous Anhydride (N2O3), and Nitrogen Peroxide (NO2) be severally obtained from Nitric Acid or a Nitrate ? Ans. Nitrogen may be obtained by decomposing ammonia, by passing it through a red-hot tube, when nitrogen and hydrogen are liberated. Pars. 116, 117, 118. ' . 4. How could you distinguish Carbon Dioxide from Nitrogen ? The gas that sometimes collects at the bottom of deep wells is said to be Carbon Dioxide. By what experiments could you test the correctness of this state- ment? /' How could you distinguish between Marsh Gas and Hydrogen? Between Olefiant Gas and Carbon Monoxide ? Ans. (i) Pars. 112, 127. (2) Par. 127, (3) Pars. 108, 128. (4) Par. 126, 129. '' \ 182 EXAMINATION QUESTIONS, ETC, • 5. In what respect does Sulphur resemble Oxygen ? By what other means, besides burning Sulphur, can Sulphur Dioxide be prepared ? t Explain its action with solutions (i) of Potash, (2) \ of Chlorine. ' Ans. (i) Par. 146. (2) Par. 147. (3) Par. 147. I 6. How much Phosphorus is contained in 1 20 lbs. of bone ash, consisting of 88*4 per cent, of Cas (PO*);^ and 11*5 per cent, of CaCOg? (Ca = 4o). • What volume of Hydrogen is contained in one ounce of Microcosmic Salt NaNH4HP04, 4H2O ? (37 grains of hydrogen to the cubic foot ; Na = 23). Ans. (i) ICO lbs. bone-ash contain 88*4 per cent, of calcium phosphate, therefore 120 lbs. bone-ash con- tain 1 06 '08 lbs. calcium phosphate; but the combin- ing weight of calcium phosphate (Caj {^0^^=^ 120 + 62 + 128 = 310 parts by weight , therefore 310 : io6' 08 :: 62 : 21*21 =the amount of phosphorus in 120 lbs. bone-ash. (2) The combining weight of the salt — NaNH^, HPO4, 4H20 = 23 + i4-f4.-i-i +31 + 644- S + 64 = 209 parts by weight, containing 13 parts by weight of hydrogen, therefore 209 : 480 : : 13 : 298 = amount in grains of hydrogen; and 37:29-8::i728 : 1392 cubic inches, the volume of hydrogen present. i 7. What is the simplest formula that can be assigned to a substance containing Carbon, 54-5 iM^liVf^ Hydrogen, 9*2 J- per cent. ? Oxygen, 36*3 Ans. Oxygen ^i^q3.=2-27. Carbon ^y*j5.=4.24^ Hy. drogen ^^^=9-2 ; therefore 2*27 : 4*54 : 9*2 = 1 12:4 =OC2H4, that is, C^H^O (Vinic aldehyde). EXAMINATION QUESTIONS, ETC, 183 )xygen ? lur, can tash, (2) xr. 147- 120 lbs. as (PO4), ne ounce 37 grains per cent. 2-ash con- i combin- .)=I20 + 510 : io6- IS in 120 )f the salt 31 + 64 + parts by 13 : 298 •8:: 1728 n present. .t can be J muvk^i :4.54» Hy- ! = ! -.2 : 4 8. The chimney-glass increases the brightness of the flame of the common coal-oil lamp. Why does it do so? If you drive a current of air into the flame of an ordinary candle, the flame appears less bright than it did before the introduction of the air. Explain why this is the case ? ' Ans. Par. 132. See especially — " Bunsen's Jet." - ■j .-. SELECTION OF QUESTIONS FROM THE^ PAPERS OF FIRST-CLASS CANDI- DATES. Note. — Questions and answers — 34, 37, 38, have been taken from the Quarterly Magazine of the Ham- ilton Coll. Institute. ' ' ' ISt CLASS PROVINCIAL CERTIFICATES. / 1. Explain the processes by which the composition of water has been ascertained with reference to both relative weights and volumes of its constituents. Name some of the impurities of water, and state how you would detect them. j . Ans. Pars. 103, 109, 62, 6^^ 64. ; ^ // 2. Give an account of the preparation and pro- perties of sulphuric acid (oil of vitriol). State tht* action, when heated, it has with (i) potassium bi- chromate, (2) mercury, (3) potassium chlorate. What is the test for detecting it ? ■■ !■ I' 4': \. i84 EXAMINATION QUESTIONS, ETC, Ans. Par. 149. (i) KgO, 2Ci03 + 4H2S04=:K2S04 + Cr23S04 + 4H2O + O3. Bichromate of potash and sulphuric acid give — potassium sulphate, sulphate of the sesquioxide of chromium, water and oxygen. (2) Hg + H2S04=HgS04 + H2. Mercury and sulphuric acid give mercuric sulphate and hydrogen. (3) 3KCI 03 + 2H2SO^=KC104 + 2KHSO4 + 2CIO2 + H2O. Chlorate of potash and sulphuric acid give — perchlo- rate of potash, bi-sulphate of potash, chloric dioxide and water. Pars, d^^ 64. 3. What substances are manufactured from common salt ? Describe the processes employed. Ans. Pars. 137, 139. NajjCOs. 4. The density of a gaseous hydro-carbon is 15 times that of hydrogen ; the weight of the carbon is 4 times that of the hydrogen. Find the formula which represents its molecular composition. Ans. The density of a compound gas is one-half the combining weight; therefore the density being 15, the combining weight of thQ hydro-carbon is 30, and four-fifths of this, that is 24 parts by weight are carbon, and one-fifih, or 6 parts by weight is hydrogen. But the combining weight of carbon is 12, and that of hydrogen is i ; therefore the formula is evidently QHo (methyl). 5. A franc weighing 5 grains is dissolved in nitric acid, and the addition of hydrochloric acid to the solution gives a precipitate which, when washed and dried, weighs 5*97916 grains. Find the percentage of silver in the French silver coinage. €1=35*5, Ag. = iq8. EXAMINA TION QUES7 IONS, E TC. 185 )tash and ilphate of ^gen. (2) sulphuric (3) 3KCI )2 + H2O. — perchlo- ic dioxide n common bon is 15 ; carbon is nula which is one-half y being 15, is 30, and weight are 3 hydrogen. 2, and that s evidently id in nitric cid to the washed and percentage =35'5» Ag. Ans. AgN03 + HCl=Aga + HN03. Ag=io8, CI = 35'5- AgCl = 143*5. (^) 5"979i6 x 108 -f 143-5 =4.5. (b) 4*5 X 100 f 5 = 90. French silver coin- age, accordingly, contains 90 p. c. of silver. 6. Define a radical in chemistry, and explain what is meant by the quantivalence of a radical. Ans. Pars. 37, 38, 46. 7. What is Ozone ? How is it prepared, and what are the physical and chemical differences between it and oxygen ? Ans. Par. 107. 8. You have given you a tew iron nails, some pure tin foil, copper filings, and a little granulated zinc, with concentrated nitric acid, and distilled water. State what chemical changes you can produce with these materials, and express the changes by equa- tions. Ans. (i) Concentrated nitric acid does not act upon iron, and, if the iron be immersed in concen- trated acid and then in dilute acid, there will still be no reaction, unless the iron has been carefully dried after being taken from the strong acid. In this re- fractory condition, the iron is said to be in the " passive state.'* Dilute acid readily attacks iron, forming ferrous nitrate — Fe + 2HN03=Fe(N03)2 4- H2. (2) Tin is reduced to the state of an oxide by the action of nitric acid — 4HNO3 + Sn=Sn02 + 2H2 O + 4NO2. Stannic oxide, water and nitric peroxide are formed. (3) Cu3 + 8HN03=3(Cu(N03)2) + 4H2 O + 2NO. Dilute nitric acid and copper give cupric tA-S ■■ I i86 EXAMINATION QUESTIONS, ETC. nitrate, water and nitric oxide. (4) Zn + 9HN03= 4Zn(N03)2 + 3H20 + NH3. Zinc and dilute nitric acid give zinc nitrate, water and ammonia. 9. How would you obtain evidence of the presence of Ammonia, whether pure or combined, in a given solution? Ans. Par. 121. 10. We inhale air and throw off carbonic acid from our lungs. How would you show experimentally that the amount of CO2, in a given volume of air, which comes from our lungs, is .%r greater than the quantity of carbonic acid, which is found in an equal volume of the air which we inhale ? Ans. Par. 114. 11. The value of a ton of Sicilian sulphur, contain- ing 94 per cent, of S, is $25, that of a ton of iron pyrites^ FeS2, containing 46.5 per ce -t. of sulphur, is $7.10 : Ascertain which can be more profitably worked in the manufacture of sulphuric acid, having regard merely to the respective sources of sulphur. Ans. 112804=98, containing 32 parts by weight of S. (i) One ton Sicilian sulphur contains 1880 lbs. of sulphur, and this amount would permit of the forma- tion of 57575 lbs. of sulphuric acid. (2) One ton of pyrites contains 930 lbs. of sulphur, which would permit of the formation of 2848*12 lbs. of sulphuric acid. Equal quantities may now be compared, to obtain the true comparison of the cost of manufacture in each case. ., 12. A Specimen of spring water is supposed to con- EXAMmATION QUESTIONS, ETC. 187 tain sulphuretted hydrogen. How would you ascertain whether sulphuretted hydrogen is really present? Ans. Par. 150 13. By what experiment would you prove that common phosphorus, and red or amorphous phos- phorus are allotropic modifications of the element phosphorus ? Ans. By heating a little red or amorphous phos- phorus in a narrow test tube, when it will gradually be converted into vitreous or common phosphorus. ^ 14. Describe Marsh's test for arsenic, with its modi- fications and fallacies. .; ' Ans. Par. 170. 15. 100 cubic centimetres of ammonia gas are completely decomposed by a series of electric sparks, yielding 200 centimetres of mixed hydrogen and nitrogen \ an excess of oxygen is next added, when the volume of the mixed gases is found to amount to 290 cubic centimetres; the mixture is now exploded, when x/5 cubic centimetres of gas remain : Show from these data that the symbol of ammonia is NH3. Ans. The amount of oxygen added is evidently 90 cubic centimetres. After explosion only 65 cubic centimetres remain; therefore 290 — 65 = 225 cubic centimetres which have been condensed, but this amount must have gone to form water, containing 150 cubic centimetres of hydrogen and 75 cubic centi- metres of oxygen. 90 cubic centimetres of oxygen were added to the mixture ; therefore 90 — 75 = 15; the amount remaining after explosion. 65 — 1 5 = 50, which must be the amount of nitrogen. The original mix- lS8 EXAMINATION QUESTIONS, ETC, tare therefore was — 50 cubic centimetres of nitrogen and 150 cubic centimetres of hydrogen, that is 50: 150 1:1:3; therefore the formula is NH3. 16. A watch spring is burned in a closed vessel of Oxygen, state — (i) Whether the weight of the bottle and its con- tents is affected by the combustion ? (2) What is the nature of the products formed by the combustion ? . - (3) Whether the whole of the oxygen originally present filling the bottle, is still present, and if so in what form ? Ans. Par. 106. 17. Flint is said to be a compound of silex, which, although it has no acid or sour taste, is also called silicic acid ; why is it so called ? ' Ans. Par. 162. 18. Under what conditions is carbonic oxide con- verted into carbonic acid, and carbonic acid into carbonic oxide ? Explain the action of carbonic acid on plants in daytime and at night. r r Ans. Pars. 126, 114. ' 19. I pour hydrochloric acid upon some marble, iron, and lime, each placed in a separate vessel with a little water. I perform a similar experiment with sulphuric acid, and with nitric acid; describe the result produced in each case, . ;r, , -,,, v Ans. (i) 2HCI + CaC03 = CaC, + HjO + CO.. Hydrochloric acid and marble give calcium chloride, water, and carbonic acid gas. (2) 2HCI + Fe=H2 + FeCla, hydrochloric acid and iron give hydrogf^n and a EXAMINATION QUESTIONS, ETC. 1S9 )f nitrogen hat is 50 • 3- ;d vessel of xnd its con- s formed by -n originally and if so in silex, which, is also called lie oxide eon- nic acid into carbonic acid some marble, ate vessel with [periment with cribe the result H2O + CO2. Icium chloride, Cl + Fe=H2 + e hydrogen and chloride of iron. (3) 2HCl + CaO = CaCla + HaO, hydrochloric acid and lime give calcium chloride and water. (4) CaC03+ K,S04 = CaSO* + H2O + CO,, sulphuric acid and marble give calcium sulphate, water, and carbonic acid gas. (5) Fe + HaSO^^Fe SO4 + H2, sulphuric acid and iron give iron sulphate and hydrogen. (6) CaO + H2S04=CaS04 + H2O, sulphuric acid and lime give calcium sulphate and water. (7) CaCOj + 2HN03=Ca(N03)2 + CO2 + H^O, nitric acid and marble give calcic nitrate, carbonic acid gas, and water. (8) See answer to question 8. (9) CaO + 2HN03=Ca(N03)2 + H2O, nitric acid and Imie give calcium nitrate and water. 20. Give some account of the manufacture of coal gas, mentioning the useful, the useless, and the hurtful products ; and the methods of removing the last. Ans. Par. 131. - ; 21. A solution of potassium chlorate was reduced to chloride and then precipitated by an excess of silver nitrate ; 7*275 grammes of silver chloride were obtained : what was the weight ot the chlorate in the solution? . Ans. Ag=io8,Cl=35*5, AgCl=i43"5- ( "^ i43'5 • 7*275 •• : 35*5 '- i*8. K=:39-i, 01=355, 03=48, K C103=i22'6. (2) 35*5 : 1*8 : : 1226 : 6*2. The weight of potassium chlorate in solution was therefore 62 grammes. 22. A mineral water, in addition to chlorides, con- tains small quantities of iodides and bromides : how would you detect the presence of these salts in water ? Ans. Pars. 63, 64. • I ipo EXAMINATION QUESTIONS, ETC. 23. Describe the properties of carbon, which tend to show that diamond cannot have been formed at a temperature, at which pure iron melts. How would you show that carbonic acid (CO2) is a compound of _ carbon and oxygen, and that it contains (very nearly) its own volume of oxygen ? . • , Ans. Pars. 124, 127. 24. Describe how you would prove bone ash to consist chiefly of calcium phosphate. Explain the decomposition of bone-ash by diluted sulphuric acid. Explain, by means of symbols, the reaction which takes place, when a solution of sodium carbonate is added to one of phosphoric acid. Ans. Par. 152. NajCOs + H3PO4 = Na2HP04 + CO2 + H2O. Sodium carbonate and orthophosphoric acid give hydric sodium phosphate, carbonic acid, and water. 25. Describe the leading properties of arsenic, and name those elements that are usually grouped with it. What means do we possess for the detection of small quantities of arsenic ? Ans. Pars. 164, 170, 171. 26. Distinguish between atomic, equivalent, and molecular weights. Give the atomic and equivalent weights of mercury, zinc, chlorine, iodine, sulphur, iron, and copper. Write down the molecular weights of H2S, PClfi, AsHs, H2SO,. Ans. Pars. 24, 25, 30, 13. 27. Half-a-pound of pure zinc is put into a vessel containing a small quantity of water; H2SO4 is then added in quantity just sufficient to dissolve the zinc, EXAMINATION QUESTIONS, ETC, 191 and leave no free acid : name, describe briefly, and give the exact weight of all the resulting products, whether gaseous or solid, the superfluous water being . evaporated. Ans. Par. 108. . 28. Draw a diagram representing the structure of flame, and explain briefly. Of three lamps, one is burning in the ordinary way, another has the wick turned up so high as to give off a large amount of smoke, while the third is so much agitated by the wind as to be lendered almost non-luminous : de- scribe, accurately, the chemical processes going on in each of these cases. Ans. Par. 132. 29. Certain hard waters become soft after boiling, while others retain their hardness : explain the reason, naming the substances present in each case, stating how the latter class may be rendered soft, and repre- senting by equations the chemical changes that take place. Ans. Par. 109. 30. How would you prove that the burning of diamond in a jar of oxygen, and the consuming of particles of carbon in the lungs are really the same processes and produce the same redults ? ; - Ans. In either case, if the resultant gas be passed into lime water, a precipitate of the same substance — calcium carbonate (CaCOs) will be formed, shewing that the product of both operations is the same — car- bonic acid gas (CO2). r II il 19a EXAMINATION QUESTIONS, ETC. 31. The analysis of a compound leads to these numbers : — - . - Carbon 37*20 .' , Hydrogen 7*90 , ^ Chlorine 54*95 100-05 , Prove that the formula CiHgCl represents correctly the composition of the body. Ans. C 37.20 -^ 12 = 310. H7'90-f 1 = 7*90. CI. S4'95^35*5 = i'54. i*54: 3'io ^ 7'9o+i 12:5. The formula is therefore CIC2H6, or C^\JZ\. 32. A piece of bright green wall paper supposed to contain arsenic is given you : describe fully all the experiments by which you could ascertain the pre- sence of arsenic in the paper, . '■ • Ans. Pars. 170, 171. 33. The formula of water was formerly written K O, and subsequently for some years H2O2 (assuming 0=8). Discuss both these formulae, pointing out any inconsistencies you may detect in them. Give reasons for adopting the formula now in use. Ans. The formula HO expresses the union of one atomic volume of hydrogen with one of oxygen. On the other hand the formula H2O2 expresses the chem-j cal union of two atomic volumes of hydrogen with two of oxygen, but decomposition of water by electro- ' lysis (103) proves that the actual composition of, water is two atomic volumes of hydrogen to one of oxygen, giving the formula H2O, and this; is further justified, when the composition of water by weight is ascertained by synthesis (109). EXAMINATION QUESTIONS, ETC, 193 Its correctly = 7-90. CI. •.2:5. The supposed to fully all the tain the pre- rly written R P2 (assuming pointing out , them. Give 1 use. union of one f oxygen. On sses the chem-i hydrogen with Iter by electro- \ omposition of. )gen to one of thid is further ater by weight 34. A solution contains Potassic Chlorate and Po- tassic Chloride ; a precipitate of 2*87 grammes of Silver Chloride is produced when Silver Nitrate is added, and separated by filtration ; the remaining so- lution is acted on by nascent Hydrogen, when a fur- ther precipitate of 0*359 grammes of Sil 2r Chloride is produced by Silver Nitrate. Calculate tiie amount of Potassic Chloride, and Potassic Chlorate present. Ans. Argentic Nitrate precipitates only the Chlo- ride. KCl + AgNOs+AgCl. (39 + 35*5) + (108^14 + 48) = (39+14 + 48) + {io8 + 35'S.) 74*5 + 170 loi 143*5 From this equation we see that 143*5 P^^^s AgCl correspond to 35*5 of Chlorine, or to 74*5 of Potassic Chloride (KCl); therefore, 2*87 grammes of Silver Chloride, the precipitate from the solution of Chlo- ride, would, by proportion, correspond 10 i '49 gramme of (KCl) Potassic Chloride. KCIO3 + 3H2=KC1 + 3H2O. (39 + 35*S + 48) + 6= (39 + 35 -5) + 3(2 +16). 122*5 + 6 = 74*5 + 54. From this equation it is seen that every 74-5 parts of Potassic Chloride, (KCl) correspond to 122-5 parts of Potassic Chlorate, (KCIO3). Above, it is found that 143*5 of AgCl correspond to 74*5 of K CI, therefore, 143*5 P^^^s of AgCl correspond to 122*5 parts of Potassic Chlorate^ (KCIO3/; there- fore o*359 grammes of AgCl precipitated represents 0*306 grammes of Potassic Chlorate (KCIO3) in the original solution. 35. Write equations for the manufacture of Car- bonic Oxide, Nitric Oxide, Iodine, Bromine, Chlorine. 1 !! 194 EXAMINATION QUESTIONS, ETC. Ans. Pars. 126, 116, 143. 142, 137. 36. Describe the manufacture of *' Bleaching Pow- der^^ giving equations. Explain fully its bleaching power. Ans. Par. 141. 37. 560 litres of chlorine act on slacked lime what weight of " bleaching powder " is produced ? Ans. 560 litres of chlorine weigh 1,775 grammes, (11 '2 litres of chlorine weigh 35*5 grammes) 2(CaO,H20) + 4Cl=CaCl2 + CaCl202 + 2H20. 2(40+ 16 + 2+ i6) + i42=(40+7i) + (4D + 7i+32) + 2(2+ 16) 148 +142= III +143 + 36 " Bleaching powder is a mechanical mixture of all the substdnc?5S on the right side of the equation ; then 142 grammes of chlorine would produce 290 grammes of bleaching powder, and 1.775 grammes of chlorine would yield 3,625 grammes of bleaching powder. 38. 1 1 20 litres of hydric sulphide at i5°C. and 720 mm. pressure are required \ how much ferrous sul- phide will just yield this quantity ? What weight of oxygen would be required to burn ud the above gas ? Ans. 1 1 20 litres of Hydric Sulphate, at i5°C. and 720 mm. pressure, become ii2o[ jX H8» or 100578 litres at Zero C. and 760 mm. pressure. 11*2 litres of Hjdric sulphide weigh 17 grammes, therefore, 100578 litres weigh 1526-63 grammes, the weight of gas required. FeS + H2SO4 = H2S. + FeS O* (56 + 32) + (2 + 32 + 64)=(2 + 32) + (56 + 32 + 64) 88 + 98 + 34 + 152, TC. EXAMmATIOl^ QUESTIONS, ETC. >95 aching Pow- ts bleaching ^d lime what ced? 75 grammes, nes) 2O. + 32)4-2(2+16) + 36 fixture of all equation ; then 290 grammes es of chlorine 5 powder. i5X.and 720 h ferrous sul- /hat weight of le above gas ? !, at i5°C. and mm. pressure, h 17 grammes, ; grammes, the 34 parts of Hydric Sulphide require 88 parts of Ferrous Sulphide, therefore, 1526 63 grammes of Sul- phuretted Hydrogen require 3951*28 grammes of Ferrous Sulphide. Each molecule of HjS requires three atoms of Oxy- gen to completely burn it. H2S=03= H2O. + SO2 (2 + 32) + 48 = (2 + 16) -h (32 + 32) 34 + 48 = 18 64 therefore, every 34 parts of H2 S. require 48 of Oxy- gen, or 1526*63 grammes require 2155*24 grammes of Oxygen for complete combustion. 39. Define the term " Co-efficient of Expansion." If the co-efficient of expansion of atmospheric air for the centigrade scale be t^t^^, find the temperature to which 500 cubic centimetres of air (measured at i5°C.) must be raised in order that its volume may become 700 cubic centimetres, no change of pressure taking place meanwhile. Ans. Par. 74, — ^g^—^' =: 403*2 ; therefore 403*2 — 273 = i3o*2°C., = the temperature to which the gas must be raised. 40. Explain the principles on which the determina- tion of atomic weights is based. One part by weight of hydrogen is combined with three parts by weight of carbon in marsh-gas, with six parts by weight of carbon in olefiant-gas, and with twelve parts by weight of carbon in acetylene. Again, one part by weight of hydrogen is combined with eight parts by weight of oxygen in water, and eight parts by weight I 196 EXAMINATION QUESTIONS, ETC. ; t\ of oxygen are combined with three parts by weight of carbon in carbonic anhydride, and with six parts by weight of carbon in carbonic oxide. Why is the atomic weight of carbon taken as 12, instead of as 6 or as three ? Arjs. Par. 20. Marsh-gas (CH4) and carbonic acid gas (CO2) are natural products, while defiant gas (C2 PI4) and carbonic oxide (CO) can only be obtained by artificial means ; moreover, the last named gases have a tendency to pass into the form of the first named. Thus, carbonic oxide when heated in presence of oxygen, invariably passes into carbonic acid, and when olefiant gas is heated to a high temperature, it is decomposed into marsh gas, acetylene and hydro- gen, both of these gases therefore appear to be un- stable compounds. Now the composition of marsh gas (CH4) indicates that carbon is a tetrad element, and the composition of carbonic acid gas, in which one atom of carbon combines with two atoms of the dyad element oxygen, justifies this conclusion. 41. What is understood by the theory of atomicity ? What atomicity or quantivalence do you assign to nitrogen, arsenic, iron, and copper respectively, and why ? ' Ans. Pars. 29, 13. 42. What is a compound radical 1 Give examples. Select the compound radicals from among the follow- ing : KCl, H3N, H4N, H,0, KHO, SO,,, SO3. Ans. Par. 37. 43. Ten grains of air are passed at a very high temperature over an excess of carbon. What pro- . EXAMINATION QUESTIONS, ETC. 197 duct is formed, and what is the approximate weight of it? Ans. Par. 126. 44. What compounds of sulphur are there, which, in their constitution and general reactions resemble the corresponding compounds of oxygen ? How is sulphur now recovered from alkali-waste ? What are the respective formulae of iron pyrites, copper pyrites, zinc blende, realgar, galena, and cinnabar ? What are the products furnished by these several minerals when heated in presence of air ? Ans. Par. 146. 45. On testing a certain liquid you find that it reddens blue litmus-paper. What conclusion can you draw from this ? Had the liquid burned reddened litmus-paper blue, what conclusion could you have drawn ? Ans. Pars. 39, 40. 46. What chemical changes occur when an aqueous solution of potassic iodide is added to an aqueous solution of each of the following salts : — Mercuric chloride, lead nitrate, sodium sulphate, silver nitrate, and Ljodium sulphite ? Ans. 2KI + HgCl2 = Hgia + 2KCI. Potassic iodide and mercuric chloride give mercuric iodide and potassic chloride. 2KI + Pb(N03)2 = Pbia + 2KNO3. Potassic iodide and plumbic nitrate, give plumbic iodide and nitre. 2KI + Na2S04 = K9SO4 + 2NaI. Potassic iodide and sodium sulphate give potassic sulphate and sodium iodide. "'^-.■' I _ 198 EXAMINATION QUESTIONS, ETC, I 1 HI i :f Piil ;KI + AgN03=KN03 + AgT. Potassic iodide and argentic nitrate, give nitre and argentic iodide. 2KI + Na2S03=K2S03 + 2NaI. Potassic iodide and sodium sulphite give potassic sulphite and sodium iodide. 47. You are given seven test tubes, and are told that in one there is pure water, and, in the other six, there are respectively aqueous solutions of silver nitrate, copper nitrate, zinc sulphate, calcium chloride, mag- sium sulphate, and potassium nitrate. How could you determine which test tube contains the pure water, which the silver nitrate, which the copper nitrate, etc. ? Ans. Pars. 62, 63, 64. 48. Give the composition of the atmosphere in, say, I coo parts. State in full your reasons for believ- ing that the combination of the two principal gases is only a mixture, and not a chemical union. Ans. Par. 113. ' 49. "4°C. is said to be the point of maximum den- sity of water." Explain the exact meaning of this statement, and discuss the general bearing of the fact upon the economy of nature. Ans. Pars. 76, 109. 50. One litre of hydrogen at the standard pressure and temperature being '08936 grammes, what will be the weight of one litre of steam, ammonia, or carbonic acid? Ans. Par. 99. . , -,. ' ^ ^ ^ . , /. - .\. FINIS. >n4.' r nitrate, iride, mag- low could 5 the pure the copper osphere in, s for believ- ipal gases is .ximum den- ling of this ig of the fact dard pressure what will be a, or carbonic